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For electrochromic applications, the device shows rapid, self-powered color switching and multicolor display (color switching from light yellow to transparent, light red, dark green, dark blue and black, corresponding to the combination of the different states of the two films). As an energy storage device, the as-assembled device provides three different open-circuit potentials with an overall areal capacity of up to 933 mA h m−2. Meanwhile, the utilization of the mixed Al/Li-ion electrolyte and the addition of PEDOT:PSS into the inorganic materials greatly promote the cycle stability of the cathode films. Such a new design of the EES device with multicolor display, large charge capacity and high cycle stability can be promising for future color switching/energy storage applications, which may also provide new insights into the design of multifunctional devices.

What's the electrolyte?

mixed Al/Li-ion

Polylactic acid (PLA) is a type of bio-based, renewable, and biodegradable material made by starch raw materials from renewable plant resources. The physical properties of small molecules of poly(ethylene glycol) (PEG)–PLA were analyzed with FAMD simulations with the COMPASS forcefield, and the mechanical properties of large-chain PLC were studied using CGMD with the MARTINI force field. Recent research focused on designing PLA composites through MD simulations to improve the inherently weak mechanical properties of PLA. For example, MD simulations of the microstructures of PLA–o-carboxymethyl chitosan (CMC) composites showed that introducing CMC enhanced the stiffness of PLA, and the analysis of the interfacial properties of PLA–graphene composites yielded a scheme to design nanocomposites with high strength and toughness. Other than characterizing the molecular phenomena of polymers, the swelling behavior of cross-linked hydrogels in poor solvents were also studied using a CG model, where counterions were considered explicitly. Similar swelling conformations were found for charged cross-linked hydrogels as single polyelectrolyte chains. Furthermore, the effects of various experimentally-controlled parameters were systematically investigated to provide insight into the rational design of hydrogels with desired conformations and properties.

What's the electrolyte?

Currently, metal or metal compounds have been widely investigated as electrode materials for SCs owing to their high theoretical specific capacity. Nevertheless, the inferior electronic conductivity, poor ion-diffusion and instability (metal) of such materials still hinder their practical applications. Massive research studies have indicated that coupling with a high electronic conductivity carbon matrix is a fascinating method to address the above problems. Electrospun 1D CNFs possess high mechanical strength, excellent electronic conductivity, and a high surface area, making them a promising substrate/host for metal or metal compounds. Furthermore, CNFs within CNF-based composites offer a number of advantages: (i) the ability to effectively inhibit the agglomeration of active materials, (ii) substantial enhancement of the electrochemically active surface area, (iii) the ability to maintain the integrity of the composite electrode, (iv) more effective electrolyte permeation and ion/electron transport and (v) an enlarged voltage window. As show in Table 2, the metal compounds showed enhanced cycling performance and rate capability when hybridized with highly compatible CNFs as electrode materials in SCs. Herein, based on diverse extensively studied active materials (i.e. metals, metal oxides, metal sulfides, metal nitrides, metal phosphides, metal carbides, other nanocarbons, metal hydroxides, MOFs, and conducting polymers), different types of CNF-based composites are divided and discussed.

What's the electrolyte?

A pre-lithiated MCMB anode (Fig. S9†) is utilized to match the LLOs cathode for assembling full cells. Since the matched capacity ratio of the anode/cathode is about 1.1 in the full cells, the specific capacity is evaluated based on the weight of the LLO cathode, while the energy density is calculated based on all the components of the full cell. The electrochemical performance of MCMB|LLO full cells is shown in Fig. 5. The full cells show specific capacities of 270 and 256 mA h g−1 at the cut-offs of 4.7 V and 4.5 V with initial coulombic efficiencies of 81.2% and 84.5%, respectively. As exhibited in Fig. 5(b–f), the full cells exhibit a rapid decay of discharge capacity with a capacity retention of only 61.2% after 100 cycles at 0.5C at the cut-off of 4.7 V. By contrast, the full cells show a much enhanced cycling stability with a capacity retention of 84.5% at the cut-off of 4.4 V after the same cycling period. Also, the full cells cycled at 4.4 V show low electrochemical polarization (Fig. S10†), corresponding to the stable discharge voltage as shown in Fig. 5(f). All the components of a typical pouch full cell are shown in Fig. S11,† and the mass fraction of the cathode in a LIB full cell reaches ∼35%. High energy densities of ∼320 and 305 W h kg−1 are achieved for the MCMB|LLO full cells at the cut-offs of 4.7 and 4.4 V, respectively. If a high-capacity Si/C anode is utilized, the energy density of the full cells can be further enhanced. Improved cycling stability of energy density is also confirmed for the full cells cycled at the cut-off of 4.4 V (Fig. 5(f)). The rate capabilities of the MCMB|LLO full cells at the cut-offs of 4.7 V and 4.4 V are illustrated in Fig. 5(d and e) and S12.† The full cells cycled at the cut-off of 4.4 V deliver reversible capacities of 204.6, 186.1, 152.0, and 125.2 mA h g−1 at the high rates of 1C, 2C, 5C and 10C, respectively, which are much higher than those of cells cycled at the cut-off of 4.7 V. Similar to half cells, the full cells exhibit improved electrochemical performance at the low cut-off of 4.4 V. The performance of MCMB|LLO full cells can be further improved by optimizing the electrolyte, capacity ratio of the anode/cathode, prelithiation and full cell design in future studies.

What's the cathode?

LLOs

A pre-lithiated MCMB anode (Fig. S9†) is utilized to match the LLOs cathode for assembling full cells. Since the matched capacity ratio of the anode/cathode is about 1.1 in the full cells, the specific capacity is evaluated based on the weight of the LLO cathode, while the energy density is calculated based on all the components of the full cell. The electrochemical performance of MCMB|LLO full cells is shown in Fig. 5. The full cells show specific capacities of 270 and 256 mA h g−1 at the cut-offs of 4.7 V and 4.5 V with initial coulombic efficiencies of 81.2% and 84.5%, respectively. As exhibited in Fig. 5(b–f), the full cells exhibit a rapid decay of discharge capacity with a capacity retention of only 61.2% after 100 cycles at 0.5C at the cut-off of 4.7 V. By contrast, the full cells show a much enhanced cycling stability with a capacity retention of 84.5% at the cut-off of 4.4 V after the same cycling period. Also, the full cells cycled at 4.4 V show low electrochemical polarization (Fig. S10†), corresponding to the stable discharge voltage as shown in Fig. 5(f). All the components of a typical pouch full cell are shown in Fig. S11,† and the mass fraction of the cathode in a LIB full cell reaches ∼35%. High energy densities of ∼320 and 305 W h kg−1 are achieved for the MCMB|LLO full cells at the cut-offs of 4.7 and 4.4 V, respectively. If a high-capacity Si/C anode is utilized, the energy density of the full cells can be further enhanced. Improved cycling stability of energy density is also confirmed for the full cells cycled at the cut-off of 4.4 V (Fig. 5(f)). The rate capabilities of the MCMB|LLO full cells at the cut-offs of 4.7 V and 4.4 V are illustrated in Fig. 5(d and e) and S12.† The full cells cycled at the cut-off of 4.4 V deliver reversible capacities of 204.6, 186.1, 152.0, and 125.2 mA h g−1 at the high rates of 1C, 2C, 5C and 10C, respectively, which are much higher than those of cells cycled at the cut-off of 4.7 V. Similar to half cells, the full cells exhibit improved electrochemical performance at the low cut-off of 4.4 V. The performance of MCMB|LLO full cells can be further improved by optimizing the electrolyte, capacity ratio of the anode/cathode, prelithiation and full cell design in future studies.

What's the anode?

MCMB

A pre-lithiated MCMB anode (Fig. S9†) is utilized to match the LLOs cathode for assembling full cells. Since the matched capacity ratio of the anode/cathode is about 1.1 in the full cells, the specific capacity is evaluated based on the weight of the LLO cathode, while the energy density is calculated based on all the components of the full cell. The electrochemical performance of MCMB|LLO full cells is shown in Fig. 5. The full cells show specific capacities of 270 and 256 mA h g−1 at the cut-offs of 4.7 V and 4.5 V with initial coulombic efficiencies of 81.2% and 84.5%, respectively. As exhibited in Fig. 5(b–f), the full cells exhibit a rapid decay of discharge capacity with a capacity retention of only 61.2% after 100 cycles at 0.5C at the cut-off of 4.7 V. By contrast, the full cells show a much enhanced cycling stability with a capacity retention of 84.5% at the cut-off of 4.4 V after the same cycling period. Also, the full cells cycled at 4.4 V show low electrochemical polarization (Fig. S10†), corresponding to the stable discharge voltage as shown in Fig. 5(f). All the components of a typical pouch full cell are shown in Fig. S11,† and the mass fraction of the cathode in a LIB full cell reaches ∼35%. High energy densities of ∼320 and 305 W h kg−1 are achieved for the MCMB|LLO full cells at the cut-offs of 4.7 and 4.4 V, respectively. If a high-capacity Si/C anode is utilized, the energy density of the full cells can be further enhanced. Improved cycling stability of energy density is also confirmed for the full cells cycled at the cut-off of 4.4 V (Fig. 5(f)). The rate capabilities of the MCMB|LLO full cells at the cut-offs of 4.7 V and 4.4 V are illustrated in Fig. 5(d and e) and S12.† The full cells cycled at the cut-off of 4.4 V deliver reversible capacities of 204.6, 186.1, 152.0, and 125.2 mA h g−1 at the high rates of 1C, 2C, 5C and 10C, respectively, which are much higher than those of cells cycled at the cut-off of 4.7 V. Similar to half cells, the full cells exhibit improved electrochemical performance at the low cut-off of 4.4 V. The performance of MCMB|LLO full cells can be further improved by optimizing the electrolyte, capacity ratio of the anode/cathode, prelithiation and full cell design in future studies.

What's the anode?

Si/C

The anchoring and catalytic effect of the MoS2 NDs could be more clearly evaluated by cycling batteries at high current densities, which requires a stronger regulation of LPS diffusion and higher redox reaction kinetics at the electrode/electrolyte interfaces. Here, the MoS2 ND/porous carbon/Li2S6 electrodes exhibited discharge capacities of 1156, 1071, 993, 955, 919, and 883 mA h g−1 at 0.1, 0.2, 0.5, 1, 2, and 4C, respectively (Fig. 6c). Accordingly, the capacity retention from 0.1 to 2C was determined to be 79.5% for MoS2 ND/porous carbon/Li2S6. Under the same measurement conditions, the capacity retentions for porous carbon/Li2S6 and MoS2 sheet/porous carbon/Li2S6 were only 1.2% and 22.7%, respectively (Fig. S12, ESI†). Statistical analyses of the discharge/charge voltage profiles (Fig. S12, ESI†) revealed that MoS2 ND/porous carbon/Li2S6 retained the largest amount of polysulfides and the highest conversion efficiency with increasing current densities among the three electrodes. It is worth noting that the highly conductive porous carbon film also contributed to the excellent performance of MoS2 ND/porous carbon/Li2S6 by offering a physical barrier and electron conductive pathway to the polysulfides.

What's the electrolyte?

As illustrated in Fig. 2a, the TDAC possesses a 2π electron aromatic system that can readily undergo a single electron redox reaction to generate the corresponding TDAC radical dication. Fig. 2b presents the redox potential and solubility of TDAC salt in comparison with those of the state-of-the-art high-potential shuttle molecules. Ideally, the redox potential (protection potential) should be ∼0.2–0.3 V above the upper cut-off voltage of LIBs (normally at 4.3 V). A lower or higher potential outside the range would have the risk of escalated self-discharge during normal operation or an irreversible decomposition of battery components during overcharging. Additionally, a high solubility is desirable since it determines the maximum shuttling current. In these regards, TDAC outperforms all other shuttle candidates with the adequate redox potential of 4.55 V (vs. Li+/Li) and the highest solubility of 0.5 M (Fig. S2†). The electrolyte viscosity before and after the TDAC addition was also investigated. The concentration of 0.2 M was found to be the optimal amount. The viscosity of 0.2 M TDAC electrolyte is 2.72 mPa compared with 2.43 mPa of baseline electrolyte. The electro-kinetics of the TDAC was next investigated by cyclic voltammetry (CV) analysis as shown in Fig. 2c. Even with a high scan rate of 200 mV s−1, TDAC still exhibited a pair of well-defined redox peaks, implying a fast mass transport process within the bulk electrolyte. As shown in Fig. 2d, the diffusion coefficient of TDAC is determined to be 6 × 10−6 cm−2 s−1, which is very comparable with that of other reported shuttles. As displayed in Fig. 2e, after 1000 CV scans, the potential gap between the anodic and cathodic peaks becomes only 60 mV wider, and there is no obvious deterioration of the peak current intensity. Such excellent electrochemical stability has rarely been reported among other 4V-class shuttles. The inset photograph in Fig. 2e presents a shiny Li surface with no bubble generation after storing in TDAC-containing electrolyte solution for six months, indicating a high chemical inertness of the TDAC toward Li metal.

What's the electrolyte?

0.2 M TDAC

As illustrated in Fig. 2a, the TDAC possesses a 2π electron aromatic system that can readily undergo a single electron redox reaction to generate the corresponding TDAC radical dication. Fig. 2b presents the redox potential and solubility of TDAC salt in comparison with those of the state-of-the-art high-potential shuttle molecules. Ideally, the redox potential (protection potential) should be ∼0.2–0.3 V above the upper cut-off voltage of LIBs (normally at 4.3 V). A lower or higher potential outside the range would have the risk of escalated self-discharge during normal operation or an irreversible decomposition of battery components during overcharging. Additionally, a high solubility is desirable since it determines the maximum shuttling current. In these regards, TDAC outperforms all other shuttle candidates with the adequate redox potential of 4.55 V (vs. Li+/Li) and the highest solubility of 0.5 M (Fig. S2†). The electrolyte viscosity before and after the TDAC addition was also investigated. The concentration of 0.2 M was found to be the optimal amount. The viscosity of 0.2 M TDAC electrolyte is 2.72 mPa compared with 2.43 mPa of baseline electrolyte. The electro-kinetics of the TDAC was next investigated by cyclic voltammetry (CV) analysis as shown in Fig. 2c. Even with a high scan rate of 200 mV s−1, TDAC still exhibited a pair of well-defined redox peaks, implying a fast mass transport process within the bulk electrolyte. As shown in Fig. 2d, the diffusion coefficient of TDAC is determined to be 6 × 10−6 cm−2 s−1, which is very comparable with that of other reported shuttles. As displayed in Fig. 2e, after 1000 CV scans, the potential gap between the anodic and cathodic peaks becomes only 60 mV wider, and there is no obvious deterioration of the peak current intensity. Such excellent electrochemical stability has rarely been reported among other 4V-class shuttles. The inset photograph in Fig. 2e presents a shiny Li surface with no bubble generation after storing in TDAC-containing electrolyte solution for six months, indicating a high chemical inertness of the TDAC toward Li metal.

What's the electrolyte?

TDAC-containing

Electrochemical impedance spectroscopy (EIS) measurements were performed by Pt sputtering on both sides of the solid electrolyte pellets, and electrochemical characterization was done using SUS electrodes. Biologic VSP-300 models were electrochemically tested at a frequency range of 7 MHz to 100 MHz at 10 mV. Ionic conductivity was calculated using the following expression: where σ is the ionic conductivity (S cm−1), l is the thickness of the sample (cm), A is the measurement area (cm), and R is total resistance (Ω).

What's the electrolyte?

Fluorination can be used as a strategy to suppress the anionic redox activity, which leads to irreversible oxygen gas formation. It has also been found that the fluorination increases accessible capacity when sufficiently high concentration of fluorine is added. In spite of high fluorine content, there have been some experimental observations which indicate the anionic redox activities of oxyfluorides such as Li2Mn2/3Nb1/3O2F, Li2Mn1/2Ti1/2O2F and Li2MnO2F when they are charged up to 4.5 V or above. In this work, we focus on Li2VO2F material as a comprehensive electrochemical study showed promising results such as good initial capacity and rate capability. However, it suffers from poor cycling performance due, in part, to degradation processes occurring at the electrode–electrolyte interface during extended cycling. We report a comprehensive computational and experimental investigation on the evolution of the anionic redox process in Li2VO2F under typical cycling conditions. The computational simulations suggest that the oxygen species evolve subsequently to peroxide and to superoxide when the cell is charged up to 4.1 V, a potential lower than the commonly used upper limit of 4.5 V to 4.8 V. The formation of superoxide is confirmed using electron paramagnetic resonance spectroscopy. The superoxide remains to be present in the material upon discharge, which suggests that the superoxide formation is not entirely reversible and can contribute to the capacity fading of the material upon cycling.

What's the electrolyte?

Fig. 6a shows the transfer characteristics of OECTs fabricated with PBTTT with the two different electrolytes. Without DBSA the ON current of the device is ∼−35 μA at a gate bias of −0.8 V and the ON/OFF ratio is ∼102 with an OFF current ∼10−1 μA. This is of relatively poor performance, but when DBSA is added to the gating electrolyte it has a huge effect on the ON current which increases to −3.1 mA with no change in the ON/OFF ratio. The transconductance, gm increases from 0.05 mS (no DBSA) to 3.9 mS (with DBSA). Again, there is a significant decrease in the operation voltage with a drop in the VON value from 0.35 V to 0.12 V (ΔVON = 0.23 V) (Fig. S1 for IDS1/2 plots, ESI†). Adding DBSA also has a strong and positive effect on the transient gate bias pulse characteristics (Fig. 6b) as well as the output characteristics of PBTTT (Fig. 6c and d): IDS increases ∼25 times from ∼−140 μA without DBSA to ∼−3.3 mA with DBSA.

What's the electrolyte?

To meet the ever-increasing energy storage demand in electric vehicles and stationary storage systems, a substantial increase in the energy densities of the current Li-ion batteries (LIBs) is essential. This motivates researchers to develop alternate chemistries superior to those based on conventional LiFePO4 and LiCoO2 cathode materials. In this regard, Li–S batteries stand out among their peers because of their high energy capacity. Li–S batteries operate via a conversion based reduction reaction of sulfur (S) with Li (16Li+ + S8 + 16e− ↔ 8Li2S), leading to an exceptionally high theoretical energy density of ∼2500 W h kg−1—five times more than that of conventional LIBs (387 W h kg−1 for LiCoO2/graphite batteries). Additionally, the abundant availability and environment friendly nature of S makes it an attractive cathode material. Despite enormous potential, the practical application of Li–S batteries with liquid electrolyte systems is hindered by issues such as large volumetric changes of S and Li2S (∼80%), and the insulating nature of S and Li2Sx. The reduction of S to Li2S during the discharge cycle follows a multistep reduction reaction process, including the formation of highly soluble long-chain polysulfides (Li2Sn, 4 ≤ n ≤ 8), which are produced as intermediates of this process. Such polysulfides shuttle towards the Li anode which leads to chemical short-circuits and an unstable SEI formation on the Li anode. These polysulfides dry out the liquid electrolyte during long-term cycling which severely affects the performance of the cell. The situation is further complicated by the high loading of S on the cathode (>70% S loading, >3 mgsulfur cm−2) during cycling, which intensifies polysulfide dissolution and volume changes, and enforces structural and morphological variations. Overall, such characteristics of the Li–S system result in self-discharge phenomena, poor capacity retention and low coulombic efficiency. On the other hand, the instability of Li anodes with organic liquid electrolytes is also well-known. Li forms mossy or needle like dendritic structures upon cycling which can potentially pierce the conventional polypropylene separators, resulting in internal short circuits of the cells. To solve these problems, various strategies have been explored for both the S and the Li electrodes. For example, synthesizing S composites with carbonaceous materials and/or surface coating the cathodes with conducting polymers have helped in trapping polysulfides. Tuning the properties of organic electrolytes using different additives has been beneficial too. On the Li side, efforts include ex situ coating of Li with polymer- and carbon-based materials or formation of artificial solid–electrolyte interface (SEI) layers to protect the Li electrode from reacting with the organic liquid electrolyte.

What's the cathode?

LiFePO4

To meet the ever-increasing energy storage demand in electric vehicles and stationary storage systems, a substantial increase in the energy densities of the current Li-ion batteries (LIBs) is essential. This motivates researchers to develop alternate chemistries superior to those based on conventional LiFePO4 and LiCoO2 cathode materials. In this regard, Li–S batteries stand out among their peers because of their high energy capacity. Li–S batteries operate via a conversion based reduction reaction of sulfur (S) with Li (16Li+ + S8 + 16e− ↔ 8Li2S), leading to an exceptionally high theoretical energy density of ∼2500 W h kg−1—five times more than that of conventional LIBs (387 W h kg−1 for LiCoO2/graphite batteries). Additionally, the abundant availability and environment friendly nature of S makes it an attractive cathode material. Despite enormous potential, the practical application of Li–S batteries with liquid electrolyte systems is hindered by issues such as large volumetric changes of S and Li2S (∼80%), and the insulating nature of S and Li2Sx. The reduction of S to Li2S during the discharge cycle follows a multistep reduction reaction process, including the formation of highly soluble long-chain polysulfides (Li2Sn, 4 ≤ n ≤ 8), which are produced as intermediates of this process. Such polysulfides shuttle towards the Li anode which leads to chemical short-circuits and an unstable SEI formation on the Li anode. These polysulfides dry out the liquid electrolyte during long-term cycling which severely affects the performance of the cell. The situation is further complicated by the high loading of S on the cathode (>70% S loading, >3 mgsulfur cm−2) during cycling, which intensifies polysulfide dissolution and volume changes, and enforces structural and morphological variations. Overall, such characteristics of the Li–S system result in self-discharge phenomena, poor capacity retention and low coulombic efficiency. On the other hand, the instability of Li anodes with organic liquid electrolytes is also well-known. Li forms mossy or needle like dendritic structures upon cycling which can potentially pierce the conventional polypropylene separators, resulting in internal short circuits of the cells. To solve these problems, various strategies have been explored for both the S and the Li electrodes. For example, synthesizing S composites with carbonaceous materials and/or surface coating the cathodes with conducting polymers have helped in trapping polysulfides. Tuning the properties of organic electrolytes using different additives has been beneficial too. On the Li side, efforts include ex situ coating of Li with polymer- and carbon-based materials or formation of artificial solid–electrolyte interface (SEI) layers to protect the Li electrode from reacting with the organic liquid electrolyte.

What's the anode?

Li

To meet the ever-increasing energy storage demand in electric vehicles and stationary storage systems, a substantial increase in the energy densities of the current Li-ion batteries (LIBs) is essential. This motivates researchers to develop alternate chemistries superior to those based on conventional LiFePO4 and LiCoO2 cathode materials. In this regard, Li–S batteries stand out among their peers because of their high energy capacity. Li–S batteries operate via a conversion based reduction reaction of sulfur (S) with Li (16Li+ + S8 + 16e− ↔ 8Li2S), leading to an exceptionally high theoretical energy density of ∼2500 W h kg−1—five times more than that of conventional LIBs (387 W h kg−1 for LiCoO2/graphite batteries). Additionally, the abundant availability and environment friendly nature of S makes it an attractive cathode material. Despite enormous potential, the practical application of Li–S batteries with liquid electrolyte systems is hindered by issues such as large volumetric changes of S and Li2S (∼80%), and the insulating nature of S and Li2Sx. The reduction of S to Li2S during the discharge cycle follows a multistep reduction reaction process, including the formation of highly soluble long-chain polysulfides (Li2Sn, 4 ≤ n ≤ 8), which are produced as intermediates of this process. Such polysulfides shuttle towards the Li anode which leads to chemical short-circuits and an unstable SEI formation on the Li anode. These polysulfides dry out the liquid electrolyte during long-term cycling which severely affects the performance of the cell. The situation is further complicated by the high loading of S on the cathode (>70% S loading, >3 mgsulfur cm−2) during cycling, which intensifies polysulfide dissolution and volume changes, and enforces structural and morphological variations. Overall, such characteristics of the Li–S system result in self-discharge phenomena, poor capacity retention and low coulombic efficiency. On the other hand, the instability of Li anodes with organic liquid electrolytes is also well-known. Li forms mossy or needle like dendritic structures upon cycling which can potentially pierce the conventional polypropylene separators, resulting in internal short circuits of the cells. To solve these problems, various strategies have been explored for both the S and the Li electrodes. For example, synthesizing S composites with carbonaceous materials and/or surface coating the cathodes with conducting polymers have helped in trapping polysulfides. Tuning the properties of organic electrolytes using different additives has been beneficial too. On the Li side, efforts include ex situ coating of Li with polymer- and carbon-based materials or formation of artificial solid–electrolyte interface (SEI) layers to protect the Li electrode from reacting with the organic liquid electrolyte.

What's the electrolyte?

To meet the ever-increasing energy storage demand in electric vehicles and stationary storage systems, a substantial increase in the energy densities of the current Li-ion batteries (LIBs) is essential. This motivates researchers to develop alternate chemistries superior to those based on conventional LiFePO4 and LiCoO2 cathode materials. In this regard, Li–S batteries stand out among their peers because of their high energy capacity. Li–S batteries operate via a conversion based reduction reaction of sulfur (S) with Li (16Li+ + S8 + 16e− ↔ 8Li2S), leading to an exceptionally high theoretical energy density of ∼2500 W h kg−1—five times more than that of conventional LIBs (387 W h kg−1 for LiCoO2/graphite batteries). Additionally, the abundant availability and environment friendly nature of S makes it an attractive cathode material. Despite enormous potential, the practical application of Li–S batteries with liquid electrolyte systems is hindered by issues such as large volumetric changes of S and Li2S (∼80%), and the insulating nature of S and Li2Sx. The reduction of S to Li2S during the discharge cycle follows a multistep reduction reaction process, including the formation of highly soluble long-chain polysulfides (Li2Sn, 4 ≤ n ≤ 8), which are produced as intermediates of this process. Such polysulfides shuttle towards the Li anode which leads to chemical short-circuits and an unstable SEI formation on the Li anode. These polysulfides dry out the liquid electrolyte during long-term cycling which severely affects the performance of the cell. The situation is further complicated by the high loading of S on the cathode (>70% S loading, >3 mgsulfur cm−2) during cycling, which intensifies polysulfide dissolution and volume changes, and enforces structural and morphological variations. Overall, such characteristics of the Li–S system result in self-discharge phenomena, poor capacity retention and low coulombic efficiency. On the other hand, the instability of Li anodes with organic liquid electrolytes is also well-known. Li forms mossy or needle like dendritic structures upon cycling which can potentially pierce the conventional polypropylene separators, resulting in internal short circuits of the cells. To solve these problems, various strategies have been explored for both the S and the Li electrodes. For example, synthesizing S composites with carbonaceous materials and/or surface coating the cathodes with conducting polymers have helped in trapping polysulfides. Tuning the properties of organic electrolytes using different additives has been beneficial too. On the Li side, efforts include ex situ coating of Li with polymer- and carbon-based materials or formation of artificial solid–electrolyte interface (SEI) layers to protect the Li electrode from reacting with the organic liquid electrolyte.

What's the cathode?

LiCoO2

To meet the ever-increasing energy storage demand in electric vehicles and stationary storage systems, a substantial increase in the energy densities of the current Li-ion batteries (LIBs) is essential. This motivates researchers to develop alternate chemistries superior to those based on conventional LiFePO4 and LiCoO2 cathode materials. In this regard, Li–S batteries stand out among their peers because of their high energy capacity. Li–S batteries operate via a conversion based reduction reaction of sulfur (S) with Li (16Li+ + S8 + 16e− ↔ 8Li2S), leading to an exceptionally high theoretical energy density of ∼2500 W h kg−1—five times more than that of conventional LIBs (387 W h kg−1 for LiCoO2/graphite batteries). Additionally, the abundant availability and environment friendly nature of S makes it an attractive cathode material. Despite enormous potential, the practical application of Li–S batteries with liquid electrolyte systems is hindered by issues such as large volumetric changes of S and Li2S (∼80%), and the insulating nature of S and Li2Sx. The reduction of S to Li2S during the discharge cycle follows a multistep reduction reaction process, including the formation of highly soluble long-chain polysulfides (Li2Sn, 4 ≤ n ≤ 8), which are produced as intermediates of this process. Such polysulfides shuttle towards the Li anode which leads to chemical short-circuits and an unstable SEI formation on the Li anode. These polysulfides dry out the liquid electrolyte during long-term cycling which severely affects the performance of the cell. The situation is further complicated by the high loading of S on the cathode (>70% S loading, >3 mgsulfur cm−2) during cycling, which intensifies polysulfide dissolution and volume changes, and enforces structural and morphological variations. Overall, such characteristics of the Li–S system result in self-discharge phenomena, poor capacity retention and low coulombic efficiency. On the other hand, the instability of Li anodes with organic liquid electrolytes is also well-known. Li forms mossy or needle like dendritic structures upon cycling which can potentially pierce the conventional polypropylene separators, resulting in internal short circuits of the cells. To solve these problems, various strategies have been explored for both the S and the Li electrodes. For example, synthesizing S composites with carbonaceous materials and/or surface coating the cathodes with conducting polymers have helped in trapping polysulfides. Tuning the properties of organic electrolytes using different additives has been beneficial too. On the Li side, efforts include ex situ coating of Li with polymer- and carbon-based materials or formation of artificial solid–electrolyte interface (SEI) layers to protect the Li electrode from reacting with the organic liquid electrolyte.

What's the anode?

Li

Via this NMR study we identify and quantify some of the key SEI parameters – namely the lithium ion transport and the rate of healing – that are important in controlling the nature of lithium metal deposition. Future studies with a much wider range of additives and electrolytes are in progress to use this methodology to help design an optimal SEI layer on lithium metal that achieves uniform plating and stripping at commercially relevant current densities (>0.5 mA cm−2) with high coulombic efficiencies.

What's the electrolyte?

Current batteries (especially lithium batteries) have been suffering from a bottleneck in safety issues. For example, these batteries are prone to arouse fires or explosions at extreme temperatures or under external forces, giving rise to significant risks in people's daily lives. Fortunately, the quasi-solid-state COG@MnO2//COG@Zn battery developed in this study exhibits fascinating performance in terms of safety. Firstly, we examined its charge–discharge performance at 60 mA cm−3 in a wide temperature range, and the results are shown in Fig. 4d. At room temperature (25 °C), the battery displays a capacity of 10.3 mA h cm−3. When the temperature is decreased to −20 °C, the capacity of the battery decreases to 6.9 mA h cm−3. Moreover, when the temperature is raised up to 100 °C, the battery can still work normally with a capacity of 13.5 mA h cm−3. Overall, the capacity of the battery increases gradually and reaches the peak at 80 °C as the temperature increases from −20 to 100 °C (Fig. 4e). These results indicate that the ion transport through the gel electrolyte is influenced remarkably by the temperature, and the battery can be safely operated in a wide temperature range. Moreover, to evaluate its safety under a variety of extreme conditions, a series of destructive tests were performed on the quasi-solid-state battery. Surprisingly, the battery is still able to power an electronic temperature humidity meter normally even after being damaged under a variety of extreme conditions, such as puncturing, bending, hammering, cutting and cropping (Fig. 4f and Movies S1–S6†), suggesting its superb safety in daily use.

What's the electrolyte?

In situ GIWAXS was used to probe the crystallinity and crystallographic texture of the initial SEI layer formed on copper in 100 ppm added HF electrolyte. The initial SEI, formed by galvanostatically bringing the potential down to 0 V vs. Li/Li+ by cycling at 0.5 mA cm−2, was found to contain crystalline LiF particles as evidenced by the small broad peak at 2.71 Å−1 in the inset of Fig. 8a, corresponding to the (111) crystallographic plane. These LiF crystallites exhibit (111) texturing as shown by the peaks at ±70.5° in the I(χ) analysis (Fig. 8b and S5†), which is reasonable given the face centered cubic rock salt structure of LiF. Scherrer analysis of the LiF (111) peak width from the I(q) data indicates a crystallite size on the order of ∼5 nm, slightly larger than the SEI thickness calculated from both charged passed and XPS depth profiling, suggesting LiF does not form a continuous film. The other SEI components are either amorphous or too thin to characterize with GIWAXS. No crystallographic texture is evident in the SEI formed on copper from an electrolyte without added HF (Fig. S4†). The texturing may only occur in electrolyte with added HF because LiF is formed at higher potential vs. Li/Li+ due to selective HF reduction, and LiF is the only solid product of this reaction. Therefore, the reduction process does not have to compete for reactants (lithium ions, fluorine atoms, electrons) or physical space on the copper surface, resulting in more facile LiF deposition homogenously distributed across the working electrode. In the case without HF, multiple reduction processes (e.g. PF6−, solvent) which yield multiple solid products (e.g. LiF, Li2O, Li2CO3, organic species) all occur simultaneously at the applied scan rates, resulting in more random LiF formation.

What's the electrolyte?

HF

To further improve the purity of as-obtained H2 gas, a stir-bar was also added inside the electrolyser, and after the ORR continued for ∼50 min with magnetic stirring at a cell voltage of 0.55 V, the residual O2 gas attached in the corners or dissolved in the electrolytes can effectively be removed; there was no obvious O2 residual peak detected from the GC. Also, the residual O2 gas can simply be removed by degassing the system with a vacuum pump. However, extra energy is required for such a process.

What's the electrolyte?

Directing the morphology of lithium metal deposits during electrodeposition is crucial to the development of safe, high energy density batteries with long cycle life. Towards this end, mechanistic insight is imperative to understand the impact of electrolyte components and cycling conditions on lithium morphologies. In this work, we used a standard carbonate-based electrolyte while systematically adding water (0–250 ppm, corresponding to 0–500 ppm HF) in Li‖Cu cells to study the links between electrolyte composition, initial solid electrolyte interphase (SEI) formation, and morphology of electroplated lithium metal using electrochemical characterization, X-ray scattering, X-ray photoelectron spectroscopy, and electron microscopy. Under conditions in which the electrolyte contains several hundred ppm added HF and applied constant currents on the order of 0.5 mA cm−2, this system yields electrodeposited lithium metal with a highly monodispersed columnar morphology. Systematic experimental investigation of the HF reduction process, nature of the initial SEI, and the structure of the electrodeposited lithium metal enable insights to be drawn concerning the underlying mechanisms of columnar lithium formation. This morphology arises from an SEI layer comprising crystalline LiF deposits on the copper current collector surface, formed through selective reduction of HF at high potential, embedded in an amorphous matrix of solvent reduction products. This interphase structure contains fast lithium-ion diffusion pathways which lead to a high nucleation density and uniform growth of lithium metal deposits. The mechanism proposed herein will help to inform future electrolyte additive design and formation cycling protocols for lithium metal batteries.

What's the electrolyte?

carbonate-based

The electrochemical test of the Li–CO2 battery was performed by using a 2025 type coin cell with a hole (diameter of 1 cm) on the cathode side. As for the cathode preparation, SiC/RGO and polyvinylidene fluoride (PVDF) were blended in N,N-dimethylformamide with a mass ratio of 9:1 to obtain a slurry. The slurry was uniformly deposited on a circular carbon paper with a diameter of 1 cm, and then dried in a vacuum oven at 80 °C. The loading mass of the active material was about 0.5 mg for each pellet. Li foil was used as the anode, and a glass fiber was employed as the separator. 1 M LiTFSI dissolved in TEGDME was used as the electrolyte. The battery was assembled in an argon-filled glove box, and then installed into a self-made sealed quartz bottle. The chamber was repeatedly flushed with pure CO2 prior to the measurements to ensure that the gas in the bottle was pure CO2. Each measurement was performed after a 2 h open circuit potential step to ensure equilibrium in the cell. The electrochemical measurements were carried out using a LAND cycler (CT2001A) and an electrochemical workstation (CHI660D, Shanghai Chenhua). A 500 W Xe-lamp was used as the light source for the tests involving light assistance.

What's the cathode?

SiC/RGO and polyvinylidene fluoride (PVDF)

The electrochemical test of the Li–CO2 battery was performed by using a 2025 type coin cell with a hole (diameter of 1 cm) on the cathode side. As for the cathode preparation, SiC/RGO and polyvinylidene fluoride (PVDF) were blended in N,N-dimethylformamide with a mass ratio of 9:1 to obtain a slurry. The slurry was uniformly deposited on a circular carbon paper with a diameter of 1 cm, and then dried in a vacuum oven at 80 °C. The loading mass of the active material was about 0.5 mg for each pellet. Li foil was used as the anode, and a glass fiber was employed as the separator. 1 M LiTFSI dissolved in TEGDME was used as the electrolyte. The battery was assembled in an argon-filled glove box, and then installed into a self-made sealed quartz bottle. The chamber was repeatedly flushed with pure CO2 prior to the measurements to ensure that the gas in the bottle was pure CO2. Each measurement was performed after a 2 h open circuit potential step to ensure equilibrium in the cell. The electrochemical measurements were carried out using a LAND cycler (CT2001A) and an electrochemical workstation (CHI660D, Shanghai Chenhua). A 500 W Xe-lamp was used as the light source for the tests involving light assistance.

What's the anode?

Li foil

The electrochemical test of the Li–CO2 battery was performed by using a 2025 type coin cell with a hole (diameter of 1 cm) on the cathode side. As for the cathode preparation, SiC/RGO and polyvinylidene fluoride (PVDF) were blended in N,N-dimethylformamide with a mass ratio of 9:1 to obtain a slurry. The slurry was uniformly deposited on a circular carbon paper with a diameter of 1 cm, and then dried in a vacuum oven at 80 °C. The loading mass of the active material was about 0.5 mg for each pellet. Li foil was used as the anode, and a glass fiber was employed as the separator. 1 M LiTFSI dissolved in TEGDME was used as the electrolyte. The battery was assembled in an argon-filled glove box, and then installed into a self-made sealed quartz bottle. The chamber was repeatedly flushed with pure CO2 prior to the measurements to ensure that the gas in the bottle was pure CO2. Each measurement was performed after a 2 h open circuit potential step to ensure equilibrium in the cell. The electrochemical measurements were carried out using a LAND cycler (CT2001A) and an electrochemical workstation (CHI660D, Shanghai Chenhua). A 500 W Xe-lamp was used as the light source for the tests involving light assistance.

What's the electrolyte?

1 M LiTFSI dissolved in TEGDME

Inspired by the superior properties of the DBHF fiber cathode, solid-state hybrid batteries were fabricated. As displayed in Fig. 7a and b, a sandwich-type hybrid Zn battery is fabricated based on the DBHF cathode, Zn nanosheets@carbon cloth anode and the gel electrolyte membrane (details in ESI S-4†). Firstly, the stability and flexibility of the fabricated solid state hybrid battery were investigated. As detected in Fig. 7e, good stability in various states, from flat to high degree of bending (Fig. 7g) was achieved during cycling at 2 mA cm−2. The charge/discharge profiles of the last cycle at each bending test (Fig. 7h) indicate the two sets of well-retained voltages corresponding to the redox reaction and ORR/OER processes with negligible shape change at different bending degrees. Therefore, the results demonstrate the good stability and excellent flexibility of the prepared hybrid battery. Next, the high-rate performance of the fabricated hybrid battery was investigated at a series of current densities from 2 to 10 mA cm−2. Good cycling stabilities were achieved at different current densities (Fig. 7f). The charge voltage gradually increases and the discharge voltage decreases with increased current densities. Even at a high current density of 10 mA cm−2, the two sets of charge/discharge voltages are well retained (Fig. 7i), demonstrating its superior high rate capability. Moreover, the flexible hybrid cell exhibits high stability and high efficiency during long-term cycling at the high current density of 6 mA cm−2 (Fig. 7j). After five thousand cycles, the flexible hybrid Zn battery achieves well-defined two-set charge/discharge profiles (Fig. 7k), which demonstrate its high stability and high efficiency. Combining the above results, the solid-state hybrid battery exhibits good stability, superior high rate capability and good flexibility in an air environment, where the Zn-ion battery and Zn–air battery work simultaneously.

What's the cathode?

DBHF fiber

Inspired by the superior properties of the DBHF fiber cathode, solid-state hybrid batteries were fabricated. As displayed in Fig. 7a and b, a sandwich-type hybrid Zn battery is fabricated based on the DBHF cathode, Zn nanosheets@carbon cloth anode and the gel electrolyte membrane (details in ESI S-4†). Firstly, the stability and flexibility of the fabricated solid state hybrid battery were investigated. As detected in Fig. 7e, good stability in various states, from flat to high degree of bending (Fig. 7g) was achieved during cycling at 2 mA cm−2. The charge/discharge profiles of the last cycle at each bending test (Fig. 7h) indicate the two sets of well-retained voltages corresponding to the redox reaction and ORR/OER processes with negligible shape change at different bending degrees. Therefore, the results demonstrate the good stability and excellent flexibility of the prepared hybrid battery. Next, the high-rate performance of the fabricated hybrid battery was investigated at a series of current densities from 2 to 10 mA cm−2. Good cycling stabilities were achieved at different current densities (Fig. 7f). The charge voltage gradually increases and the discharge voltage decreases with increased current densities. Even at a high current density of 10 mA cm−2, the two sets of charge/discharge voltages are well retained (Fig. 7i), demonstrating its superior high rate capability. Moreover, the flexible hybrid cell exhibits high stability and high efficiency during long-term cycling at the high current density of 6 mA cm−2 (Fig. 7j). After five thousand cycles, the flexible hybrid Zn battery achieves well-defined two-set charge/discharge profiles (Fig. 7k), which demonstrate its high stability and high efficiency. Combining the above results, the solid-state hybrid battery exhibits good stability, superior high rate capability and good flexibility in an air environment, where the Zn-ion battery and Zn–air battery work simultaneously.

What's the anode?

Zn nanosheets@carbon

Inspired by the superior properties of the DBHF fiber cathode, solid-state hybrid batteries were fabricated. As displayed in Fig. 7a and b, a sandwich-type hybrid Zn battery is fabricated based on the DBHF cathode, Zn nanosheets@carbon cloth anode and the gel electrolyte membrane (details in ESI S-4†). Firstly, the stability and flexibility of the fabricated solid state hybrid battery were investigated. As detected in Fig. 7e, good stability in various states, from flat to high degree of bending (Fig. 7g) was achieved during cycling at 2 mA cm−2. The charge/discharge profiles of the last cycle at each bending test (Fig. 7h) indicate the two sets of well-retained voltages corresponding to the redox reaction and ORR/OER processes with negligible shape change at different bending degrees. Therefore, the results demonstrate the good stability and excellent flexibility of the prepared hybrid battery. Next, the high-rate performance of the fabricated hybrid battery was investigated at a series of current densities from 2 to 10 mA cm−2. Good cycling stabilities were achieved at different current densities (Fig. 7f). The charge voltage gradually increases and the discharge voltage decreases with increased current densities. Even at a high current density of 10 mA cm−2, the two sets of charge/discharge voltages are well retained (Fig. 7i), demonstrating its superior high rate capability. Moreover, the flexible hybrid cell exhibits high stability and high efficiency during long-term cycling at the high current density of 6 mA cm−2 (Fig. 7j). After five thousand cycles, the flexible hybrid Zn battery achieves well-defined two-set charge/discharge profiles (Fig. 7k), which demonstrate its high stability and high efficiency. Combining the above results, the solid-state hybrid battery exhibits good stability, superior high rate capability and good flexibility in an air environment, where the Zn-ion battery and Zn–air battery work simultaneously.

What's the electrolyte?

Inspired by the superior properties of the DBHF fiber cathode, solid-state hybrid batteries were fabricated. As displayed in Fig. 7a and b, a sandwich-type hybrid Zn battery is fabricated based on the DBHF cathode, Zn nanosheets@carbon cloth anode and the gel electrolyte membrane (details in ESI S-4†). Firstly, the stability and flexibility of the fabricated solid state hybrid battery were investigated. As detected in Fig. 7e, good stability in various states, from flat to high degree of bending (Fig. 7g) was achieved during cycling at 2 mA cm−2. The charge/discharge profiles of the last cycle at each bending test (Fig. 7h) indicate the two sets of well-retained voltages corresponding to the redox reaction and ORR/OER processes with negligible shape change at different bending degrees. Therefore, the results demonstrate the good stability and excellent flexibility of the prepared hybrid battery. Next, the high-rate performance of the fabricated hybrid battery was investigated at a series of current densities from 2 to 10 mA cm−2. Good cycling stabilities were achieved at different current densities (Fig. 7f). The charge voltage gradually increases and the discharge voltage decreases with increased current densities. Even at a high current density of 10 mA cm−2, the two sets of charge/discharge voltages are well retained (Fig. 7i), demonstrating its superior high rate capability. Moreover, the flexible hybrid cell exhibits high stability and high efficiency during long-term cycling at the high current density of 6 mA cm−2 (Fig. 7j). After five thousand cycles, the flexible hybrid Zn battery achieves well-defined two-set charge/discharge profiles (Fig. 7k), which demonstrate its high stability and high efficiency. Combining the above results, the solid-state hybrid battery exhibits good stability, superior high rate capability and good flexibility in an air environment, where the Zn-ion battery and Zn–air battery work simultaneously.

What's the cathode?

DBHF

To test the differences in Li deposition between the two electrolytes further, in situ NMR measurements using pulsed currents were carried out. When applying a pulsed current, short pulses for a period TON are applied, which is followed by a rest period TOFF where no current is passed (schematic, Fig. S5†). During the rest period, TOFF, two main processes occur:

What's the electrolyte?

Nanostructuring of electrodes is a known method for increasing the power density of lithium-ion (Li-ion) batteries. This can happen because of the much shorter characteristic diffusion times of ions and electrons in nanometer-thick active materials compared to the typical micron-sized active particles. Nanostructured active materials also exhibit a higher contact area with the electrode components supplying ions (the electrolyte) and electrons (the current collector and conductive additives) to the active redox sites. As a result, the time required for fully charging and discharging the electrodes can be shortened from hours to as little as a few seconds.

What's the electrolyte?

Aiming to achieve higher energy batteries, researchers have started to revisit the LiNiO2 chemistry with hopes that knowledge obtained from NMC and NCA studies could be applied to LiNiO2 and resolve the issues that were identified decades ago. Furthermore, eliminating the use of cobalt can circumvent the issues surrounding Co such as high toxicity, high cost, and child labor abuse in mining. At the material level, the most popular strategy is the bulk cationic doping to enhance the electrochemical reversibility. With doping strategies, Co-free Ni-rich layered cathode materials are expected to deliver comparable battery performance to NMCs and NCAs. In addition, many studies have been performed on modulating the electrolyte composition to improve the electrode–electrolyte interphase for stabilizing the battery performance. The surface of LiNiO2-based materials is much more reactive than NMC and NCA materials owing to the extreme Ni3+/Ni4+ redox couple. Thus, revealing the origins of surface changes can better inform the advanced design of promising LiNiO2-based materials. At present, most studies rely on ex situ characterization methods to understand the surface degradation of cathode materials, for example, transition electron microscopy (TEM) based techniques for atomic scale structural and chemical analysis, as well as surface sensitive X-ray spectroscopy for ensemble-averaged measurements to probe surface chemical information. The surface sensitive probing techniques typically have low penetrating depths, which makes it difficult to study surface chemistry under practical battery operating environments. Noticeably, the chemical and structural information on the particle surface may be influenced by a range of experimental conditions, including but not limited to, human exhalation, sample storage, and sample preparation during material surface analysis. This can skew observations found in characterization analysis, surface doping, and electrochemical protocol. Therefore, to characterize the surface of LiNiO2 properly, one must understand how the experimental conditions influence overall surface and interfacial chemistries.

What's the cathode?

Co-free Ni-rich

Aiming to achieve higher energy batteries, researchers have started to revisit the LiNiO2 chemistry with hopes that knowledge obtained from NMC and NCA studies could be applied to LiNiO2 and resolve the issues that were identified decades ago. Furthermore, eliminating the use of cobalt can circumvent the issues surrounding Co such as high toxicity, high cost, and child labor abuse in mining. At the material level, the most popular strategy is the bulk cationic doping to enhance the electrochemical reversibility. With doping strategies, Co-free Ni-rich layered cathode materials are expected to deliver comparable battery performance to NMCs and NCAs. In addition, many studies have been performed on modulating the electrolyte composition to improve the electrode–electrolyte interphase for stabilizing the battery performance. The surface of LiNiO2-based materials is much more reactive than NMC and NCA materials owing to the extreme Ni3+/Ni4+ redox couple. Thus, revealing the origins of surface changes can better inform the advanced design of promising LiNiO2-based materials. At present, most studies rely on ex situ characterization methods to understand the surface degradation of cathode materials, for example, transition electron microscopy (TEM) based techniques for atomic scale structural and chemical analysis, as well as surface sensitive X-ray spectroscopy for ensemble-averaged measurements to probe surface chemical information. The surface sensitive probing techniques typically have low penetrating depths, which makes it difficult to study surface chemistry under practical battery operating environments. Noticeably, the chemical and structural information on the particle surface may be influenced by a range of experimental conditions, including but not limited to, human exhalation, sample storage, and sample preparation during material surface analysis. This can skew observations found in characterization analysis, surface doping, and electrochemical protocol. Therefore, to characterize the surface of LiNiO2 properly, one must understand how the experimental conditions influence overall surface and interfacial chemistries.

What's the electrolyte?

The critical property of anode materials is coulombic efficiency. CE at the first cycle is particularly significant since it usually leads to the highest capacity losses due to SEI formation and other irreversible reduction processes. As shown in Chart 5e, a relatively high 1st cycle CE (>60%) is observed for carboxylates, carbonyls 10 and 21, as well as for P30, P31, and P32. For other materials, as well as for some inorganic benchmarks (carbons with a high surface area, phosphorous, FeS2), the CE is even lower. It should be noted that the CE depends not only on the material but also on the electrolyte composition. The tuning of the electrolyte is rarely reported. Some studies indicate that using ether-based electrolytes, such as KPF6 in DME, improves the CE. More attention should be paid to the electrolyte optimization, particularly for the materials that showed low CE with the carbonate-based solutions.

What's the anode?

The critical property of anode materials is coulombic efficiency. CE at the first cycle is particularly significant since it usually leads to the highest capacity losses due to SEI formation and other irreversible reduction processes. As shown in Chart 5e, a relatively high 1st cycle CE (>60%) is observed for carboxylates, carbonyls 10 and 21, as well as for P30, P31, and P32. For other materials, as well as for some inorganic benchmarks (carbons with a high surface area, phosphorous, FeS2), the CE is even lower. It should be noted that the CE depends not only on the material but also on the electrolyte composition. The tuning of the electrolyte is rarely reported. Some studies indicate that using ether-based electrolytes, such as KPF6 in DME, improves the CE. More attention should be paid to the electrolyte optimization, particularly for the materials that showed low CE with the carbonate-based solutions.

What's the electrolyte?

KPF6 in DME

• Enhancing affinity toward LiPSs promotes surface conversion to decrease the total amount of soluble LiPSs in the electrolyte, thereby ensuring shuttle suppression and high capacity. Metal sulfides with a high surface area, well-designed porosity, enhanced surface polar (functional or defective surface), desired surface selectivity (exposed crystal faces), and tailored crystalline form are a high-priority target.

What's the electrolyte?

In this study, three types of electrolytes were prepared for investigation: 1.0 M LiPF6 in ethylene carbonate/diethyl carbonate (EC/DEC, 1:1 v/v, marked as LPE-EC), 1.0 M LiPF6 in propylene carbonate/diethyl carbonate (PC/DEC, 1:1 v/v, marked as LPE-PC), and 1.0 M LiPF6 in PC/DEC (1:1 v/v, with 0.005 M LiBOB, marked as LPE-PC–LiBOB). All the electrolytes were prepared in an argon-filled glove box.

What's the electrolyte?

1.0 M LiPF6 in ethylene carbonate/diethyl carbonate

In this study, three types of electrolytes were prepared for investigation: 1.0 M LiPF6 in ethylene carbonate/diethyl carbonate (EC/DEC, 1:1 v/v, marked as LPE-EC), 1.0 M LiPF6 in propylene carbonate/diethyl carbonate (PC/DEC, 1:1 v/v, marked as LPE-PC), and 1.0 M LiPF6 in PC/DEC (1:1 v/v, with 0.005 M LiBOB, marked as LPE-PC–LiBOB). All the electrolytes were prepared in an argon-filled glove box.

What's the electrolyte?

1.0 M LiPF6 in ethylene carbonate/diethyl carbonate (EC/DEC, 1:1 v/v, marked as LPE-EC), 1.0 M LiPF6 in propylene carbonate/diethyl carbonate (PC/DEC, 1:1 v/v, marked as LPE-PC), and 1.0 M LiPF6 in PC/DEC (1:1 v/v, with 0.005 M LiBOB, marked as LPE-PC–LiBOB)

Moreover, cycling stability is a very important parameter of the electrochromic films in practical applications. We have measured the CV curves for more than 200 cycles from −0.6 to 0.9 V. In each cycle, the reversible process of coloring and bleaching can be observed in the annealed WO3−x film. Fig. 4d shows the CV curves for the first, 50th, 100th, 150th and 200th cycle. The CV curves in the first 50 cycles show slight promotion, and remain almost stable without any degradation even after 200 cycles. Such a high cycling stability may originate from the solid nanostructure of the annealed WO3−x film and the prevention of the harmful side reaction at the WO3−x film/electrolyte interface.

What's the electrolyte?

For dual-ion batteries, increasing Qm is also principally possible by, for example, increasing the concentration of redox-active nitrogen atoms in aromatic amines. For such optimized materials, where most of the active units are involved, it is expected that the operation potentials will get higher at least for conjugated structures because polymers with a high positive charge at the backbone are harder to oxidize. It will therefore be important to develop electrolytes for potassium batteries, which are tolerant to high voltages, or to elaborate protective coatings at the cathode surface. Certain progress in the development of high-voltage potassium battery electrolytes has already been achieved.

What's the cathode?

For dual-ion batteries, increasing Qm is also principally possible by, for example, increasing the concentration of redox-active nitrogen atoms in aromatic amines. For such optimized materials, where most of the active units are involved, it is expected that the operation potentials will get higher at least for conjugated structures because polymers with a high positive charge at the backbone are harder to oxidize. It will therefore be important to develop electrolytes for potassium batteries, which are tolerant to high voltages, or to elaborate protective coatings at the cathode surface. Certain progress in the development of high-voltage potassium battery electrolytes has already been achieved.

What's the electrolyte?

To address the challenges facing Li–S batteries, considerable efforts have been made to develop sulfur-based cathode composite materials, modify separators, protect Li anodes, and use conductive interlayers and/or novel electrolyte additives (Fig. 1b). These approaches have all yielded certain encouraging results. However, the above strategies often have variable effects on the performance of Li–S batteries, owing to the specificity and interdependency of the S8–Li2Sn–Li2S (solid–liquid–solid) multistage transformation. For example, the conductive interlayer introduced between the separator and cathode suppresses the migration of LiPSs, which also offers additional electron pathways that cover the top surface of the cathode. This performance enhances the use of active materials and reduces random deposition of Li2S on the surface of the Li anode, thereby restraining dendrite formation and improving the anode stability to a certain degree.

What's the cathode?

sulfur-based

To address the challenges facing Li–S batteries, considerable efforts have been made to develop sulfur-based cathode composite materials, modify separators, protect Li anodes, and use conductive interlayers and/or novel electrolyte additives (Fig. 1b). These approaches have all yielded certain encouraging results. However, the above strategies often have variable effects on the performance of Li–S batteries, owing to the specificity and interdependency of the S8–Li2Sn–Li2S (solid–liquid–solid) multistage transformation. For example, the conductive interlayer introduced between the separator and cathode suppresses the migration of LiPSs, which also offers additional electron pathways that cover the top surface of the cathode. This performance enhances the use of active materials and reduces random deposition of Li2S on the surface of the Li anode, thereby restraining dendrite formation and improving the anode stability to a certain degree.

What's the anode?

Li

To address the challenges facing Li–S batteries, considerable efforts have been made to develop sulfur-based cathode composite materials, modify separators, protect Li anodes, and use conductive interlayers and/or novel electrolyte additives (Fig. 1b). These approaches have all yielded certain encouraging results. However, the above strategies often have variable effects on the performance of Li–S batteries, owing to the specificity and interdependency of the S8–Li2Sn–Li2S (solid–liquid–solid) multistage transformation. For example, the conductive interlayer introduced between the separator and cathode suppresses the migration of LiPSs, which also offers additional electron pathways that cover the top surface of the cathode. This performance enhances the use of active materials and reduces random deposition of Li2S on the surface of the Li anode, thereby restraining dendrite formation and improving the anode stability to a certain degree.

What's the electrolyte?

To address the challenges facing Li–S batteries, considerable efforts have been made to develop sulfur-based cathode composite materials, modify separators, protect Li anodes, and use conductive interlayers and/or novel electrolyte additives (Fig. 1b). These approaches have all yielded certain encouraging results. However, the above strategies often have variable effects on the performance of Li–S batteries, owing to the specificity and interdependency of the S8–Li2Sn–Li2S (solid–liquid–solid) multistage transformation. For example, the conductive interlayer introduced between the separator and cathode suppresses the migration of LiPSs, which also offers additional electron pathways that cover the top surface of the cathode. This performance enhances the use of active materials and reduces random deposition of Li2S on the surface of the Li anode, thereby restraining dendrite formation and improving the anode stability to a certain degree.

What's the anode?

Li

In summary, it's proposed that stacking few-layer Nb2CTx with Ti3C2Tx nanosheets into composite structures is a simple and effective approach to improve the electrochemical performance of Nb2CTx-based films for supercapacitors. The intercalated Ti3C2Tx nanosheets between Nb2CTx layers effectively increase the interlayer spacing of Nb2CTx layers and impede the self-restacking of Nb2CTx nanosheets, which are favorable for electrolyte ions to rapidly diffuse and transport in the hybrid electrodes. The optimized Ti3C2Tx/Nb2CTx films possess enhanced capacitive performance and rate performance. A gravimetric capacitance of 370 F g−1 can be delivered at 2 mV s−1 and 56.1% capacitance retention at a high scan rate of 200 mV s−1. The energy density of the assembled all-solid-state supercapacitors can reach 5.5 mW h g−1 at a power density of 141.4 mW g−1, and 1.1 mW h g−1 at a high power density of 2350.0 mW g−1. The all-solid-state supercapacitors presented good flexibility and long cycling life. The all-solid-state supercapacitor was also integrated with a flex sensor to fabricate a self-powered device, where the all-solid-state supercapacitor served as a stable power source unit to drive the flex sensor. The route to fabricate Ti3C2Tx/Nb2CTx hybrid films is also applicable for other M2CTx MXenes, for example, Ti2CTx and V2CTx, improving the application potential of MXenes in flexible supercapacitors and integrated electronic devices.

What's the electrolyte?

Nowadays, carbon nanomaterials are considered as the most important supercapacitor electrode materials. But it's still a great challenge to design rational structures of carbon materials at both nano and micro scales to endow carbon electrode materials with outstanding electrochemical performance. Herein, a well-designed compressible and elastic N-doped porous carbon nanofiber aerogel (N-PCNFA) with hierarchical cellular structures in both the PAN/ZIF-8-based carbon nanofibers and the 3D carbon monolith was prepared by a simple method. A large specific surface area was obtained for the construction of abundant pore structures and a robust architecture was built by the introduction of mechanically reinforced structures, which would endow the N-PCNFA electrode material with a vast surface area for ion adsorption/desorption, plenty of short channels for electrolyte diffusion and stable frameworks during the charge/discharge process. N heteroatoms were also incorporated into the carbon material as active sites for faradaic redox reactions. Thus, the N-PCNFA electrodes exhibited superior electrochemical performance, with a high specific capacitance of 279 F g−1 at 0.5 A g−1, consisting of pseudocapacitance (∼46%) and electrochemical double-layer capacitance (∼54%), remarkable rate performance of 59% at 20 A g−1 and excellent long-term durability. Moreover, the simple and general strategy for construction of compressible and elastic porous carbon nanofiber aerogels with delicate microstructures is also applicable to other advanced functional materials for a wide range of applications.

What's the electrolyte?

The mechanism of the one-cell, two-electrode decoupled water splitting using Ni(OH)2 as the relay is shown in Fig. 1a. For the H2 evolution step, H2O is reduced on the GEE and the Ni(OH)2 electrode is oxidized to NiOOH simultaneously. By reversing the current polarity, O2 is produced on the GEE by an anodic oxidation of OH−; meanwhile the NiOOH electrode is reduced to Ni(OH)2. The cyclic voltammogram (CV) curve of the Ni(OH)2 electrode tested at a scan rate of 1 mV s−1 using Ag/AgCl as the reference electrode is shown in Fig. 1b. One pair of redox peaks located at 0.423 V/0.238 V (vs. Ag/AgCl) can be indexed to the reversible Ni(OH)2/NiOOH processes, which is consistent with the potential of the Ni(OH)2 electrode in the HER and OER processes. In operation, the one-cell, two-electrode design requires a cell voltage of 0.17 V for the OER step and 1.52 V for the HER step (Fig. 1c). The different operating voltages of the cell for HER and OER steps are caused by the redox potential of the RE (NiOOH/Ni(OH)2), which is much closer to the potential for the OER than the HER. As shown in Fig. 1d, at a cell current of 100 mA, the two-step water splitting process can be reversibly cycled for 24 rounds in 8 hours without noticeable decay. The duration for each OER and HER step was 10 min and the duration can be extended up to 3.5 h before the RE was fully consumed (Fig. S6†). Interestingly, in each gas evolution cycle, after the OER step, there is always a potential drop in the following HER step (inset in Fig. 1d). Meanwhile the HER process does not show this kind of peak. Since the ORR requires lower potential than the HER, after the OER step, there is residual O2 trapped on the GEE or dissolved in the electrolyte, and the ORR occurs to consume this O2, which temporarily reduces the cell voltage.

What's the electrolyte?

In summary, we developed a formation method of a Li protective artificial SEI layer to form a LiF and polymeric composite protection layer directly on lithium metal foil using the electrochemical reaction between the Li and the sacrificial PTFE film by using roll-pressing. The roll-press process is facile, cost-effective, eco-friendly and a mass and large-area scalable process. The composite protection layer composed of a LiF-rich layer and polyene/unsaturated fluoropolymer rich layer could significantly improve the electrochemical properties of LMBs. The LiF@Po protection layer provides a stable interface between the Li metal and the electrolyte, enabling improved Li plating/stripping behavior and ultra-long cycling stability in both the Li‖Li symmetric cell and Li‖LCO/Li‖NCM full cells. In particular, the full cell with the NCM-811 cathode and LiF@Po–Li anode exhibits reasonable electrochemical performance even with transition metal dissolution. The material design strategies presented here could provide important avenues for forming an artificial SEI layer in various applications not only in Li metal systems but also in other metal systems including sodium and potassium.

What's the cathode?

NCM-811

In summary, we developed a formation method of a Li protective artificial SEI layer to form a LiF and polymeric composite protection layer directly on lithium metal foil using the electrochemical reaction between the Li and the sacrificial PTFE film by using roll-pressing. The roll-press process is facile, cost-effective, eco-friendly and a mass and large-area scalable process. The composite protection layer composed of a LiF-rich layer and polyene/unsaturated fluoropolymer rich layer could significantly improve the electrochemical properties of LMBs. The LiF@Po protection layer provides a stable interface between the Li metal and the electrolyte, enabling improved Li plating/stripping behavior and ultra-long cycling stability in both the Li‖Li symmetric cell and Li‖LCO/Li‖NCM full cells. In particular, the full cell with the NCM-811 cathode and LiF@Po–Li anode exhibits reasonable electrochemical performance even with transition metal dissolution. The material design strategies presented here could provide important avenues for forming an artificial SEI layer in various applications not only in Li metal systems but also in other metal systems including sodium and potassium.

What's the anode?

LiF@Po–Li

In summary, we developed a formation method of a Li protective artificial SEI layer to form a LiF and polymeric composite protection layer directly on lithium metal foil using the electrochemical reaction between the Li and the sacrificial PTFE film by using roll-pressing. The roll-press process is facile, cost-effective, eco-friendly and a mass and large-area scalable process. The composite protection layer composed of a LiF-rich layer and polyene/unsaturated fluoropolymer rich layer could significantly improve the electrochemical properties of LMBs. The LiF@Po protection layer provides a stable interface between the Li metal and the electrolyte, enabling improved Li plating/stripping behavior and ultra-long cycling stability in both the Li‖Li symmetric cell and Li‖LCO/Li‖NCM full cells. In particular, the full cell with the NCM-811 cathode and LiF@Po–Li anode exhibits reasonable electrochemical performance even with transition metal dissolution. The material design strategies presented here could provide important avenues for forming an artificial SEI layer in various applications not only in Li metal systems but also in other metal systems including sodium and potassium.

What's the electrolyte?

To evaluate the performances of 2D GeP nanosheet-based photodetectors at an exact wavelength, selected wavelengths of lights (350, 365, 380, 400, 475, 550 and 650 nm) were employed (Fig. 4) in 0.1, 0.5 and 1 M KOH electrolytes. It is clear to see that the photocurrent density values are greatly smaller than the values under simulated light because of inferior light irradiation. The photocurrent density and photoresponsivity show a similar trend to the results in a simulated light state. Notably, it is also shown that such 2D GeP nanosheet-based photodetectors exhibit a higher sensitivity at a short wavelength range, especially at 350, 365 and 380 nm (Fig. 4c, f and i) and the highest photoresponsivity is 187.5 μA W−1 at 380 nm wavelength, 0.6 V applied bias potential and in 0.5 M KOH electrolyte. The above photo-response results at different wavelengths are in strong agreement with the UV-Vis absorption spectrum in Fig. 1g. Such results demonstrate great potential for high-performance UV-Vis photodetector application.

What's the electrolyte?

0.1, 0.5 and 1 M KOH

To evaluate the performances of 2D GeP nanosheet-based photodetectors at an exact wavelength, selected wavelengths of lights (350, 365, 380, 400, 475, 550 and 650 nm) were employed (Fig. 4) in 0.1, 0.5 and 1 M KOH electrolytes. It is clear to see that the photocurrent density values are greatly smaller than the values under simulated light because of inferior light irradiation. The photocurrent density and photoresponsivity show a similar trend to the results in a simulated light state. Notably, it is also shown that such 2D GeP nanosheet-based photodetectors exhibit a higher sensitivity at a short wavelength range, especially at 350, 365 and 380 nm (Fig. 4c, f and i) and the highest photoresponsivity is 187.5 μA W−1 at 380 nm wavelength, 0.6 V applied bias potential and in 0.5 M KOH electrolyte. The above photo-response results at different wavelengths are in strong agreement with the UV-Vis absorption spectrum in Fig. 1g. Such results demonstrate great potential for high-performance UV-Vis photodetector application.

What's the electrolyte?

0.5 M KOH

The detailed preparation processes of positive electrodes can be found in previous work. The mass loading of active material was ∼3.0 mg cm−2 for positive electrodes. In 2032-type half cells, lithium foil was used as the anode. Pre-lithiated MCMB was utilized as the negative electrode in full cells. The electrolyte was 1 M LiPF6 dissolved in mixed solvents of DMC and EC (7:3 by volume). Galvanostatic charge–discharge was conducted using a LAND tester (CT-2001A). All electrochemical testing was performed at room temperature (25 °C).

What's the anode?

lithium foil

The detailed preparation processes of positive electrodes can be found in previous work. The mass loading of active material was ∼3.0 mg cm−2 for positive electrodes. In 2032-type half cells, lithium foil was used as the anode. Pre-lithiated MCMB was utilized as the negative electrode in full cells. The electrolyte was 1 M LiPF6 dissolved in mixed solvents of DMC and EC (7:3 by volume). Galvanostatic charge–discharge was conducted using a LAND tester (CT-2001A). All electrochemical testing was performed at room temperature (25 °C).

What's the electrolyte?

1 M LiPF6

The stretchability was also tested through stretching the developed spring ssZIBs. First, a spring solid-state battery was prepared by sealing the cathode, anode, and CNF–PAM hydrogel electrolyte in a spring-type plastic tube. As shown in Fig. 3i, a digital clock was powered by the developed blue spring solid-state battery. As shown by the figure in Fig. 3j and k and the video provided in ESI III and IV,† the spring solid-state battery still worked well under repeated tension and contraction. This demonstrates the robust stability, high stretchability and flexibility of our ssZIBs.

What's the cathode?

The stretchability was also tested through stretching the developed spring ssZIBs. First, a spring solid-state battery was prepared by sealing the cathode, anode, and CNF–PAM hydrogel electrolyte in a spring-type plastic tube. As shown in Fig. 3i, a digital clock was powered by the developed blue spring solid-state battery. As shown by the figure in Fig. 3j and k and the video provided in ESI III and IV,† the spring solid-state battery still worked well under repeated tension and contraction. This demonstrates the robust stability, high stretchability and flexibility of our ssZIBs.

What's the anode?

The stretchability was also tested through stretching the developed spring ssZIBs. First, a spring solid-state battery was prepared by sealing the cathode, anode, and CNF–PAM hydrogel electrolyte in a spring-type plastic tube. As shown in Fig. 3i, a digital clock was powered by the developed blue spring solid-state battery. As shown by the figure in Fig. 3j and k and the video provided in ESI III and IV,† the spring solid-state battery still worked well under repeated tension and contraction. This demonstrates the robust stability, high stretchability and flexibility of our ssZIBs.

What's the electrolyte?

CNF–PAM hydrogel

Flexible lithium-ion batteries have attracted extensive attentions in electronics. However, their practical applications are primarily limited by low open-circuit voltage and energy density. Herein, we report a novel surface/interface modification strategy to obtain electrolyte-phobic carbon nanotube film as the flexible current collector for foldable lithium-ion batteries. The as-assembled battery exhibits a high open-circuit voltage of 4.04 V and energy density of ~293 Wh kg-1 with excellent flexibility and stable cycle performance. The outstanding performance is ascribed to the electrolyte-phobic surface/interfacial layer of carbon nanotube film, which restrains the intercalation of lithium ions into carbon-based current collector. This work not only demonstrates a practical solution to appreciably revamp the voltage and energy density of flexible lithium-ion batteries, but more importantly, offers valuable insights in modifying the surface/interface chemistry of carbon-based current collectors for high-performance energy storage devices.

What's the electrolyte?

The slurry for the electrocatalytic study was prepared by dispersing 10 mg active material and 5 mg Super P carbon in 250 μL isopropyl alcohol and 750 μL distilled water. After sonicating the solution for 15 minutes, 5 μL Nafion binder was added followed by further sonication for 30 minutes. Then, 5 μL of the slurry was drop-casted on a glassy carbon rotating ring disc electrode (RRDE). The electrocatalytic study was carried out at room temperature using a CH instrument (CHI700E) bipotentiostat using 0.1 M KOH as the electrolyte.

What's the electrolyte?

0.1 M KOH

For the first time, DBHF nanofibers are constructed as flexible cathodes for HZBs. The formation mechanism of the DBHF structure is probed and the relationships between the synthetic conditions and the structures of the products are carefully investigated. Moreover, the HZBs are fabricated based on the DBHF cathode, Zn nanosheet@carbon cloth anode and a polymer electrolyte. Benefitting from the unique structure, the hybrid battery achieves high energy/power density and long-term cycling stability. Moreover, the high flexibility and “air-charging” capability make it a good uninterrupted power source for flexible electronics in different environments (Fig. 1h and i).

What's the cathode?

DBHF nanofibers

For the first time, DBHF nanofibers are constructed as flexible cathodes for HZBs. The formation mechanism of the DBHF structure is probed and the relationships between the synthetic conditions and the structures of the products are carefully investigated. Moreover, the HZBs are fabricated based on the DBHF cathode, Zn nanosheet@carbon cloth anode and a polymer electrolyte. Benefitting from the unique structure, the hybrid battery achieves high energy/power density and long-term cycling stability. Moreover, the high flexibility and “air-charging” capability make it a good uninterrupted power source for flexible electronics in different environments (Fig. 1h and i).

What's the anode?

Zn nanosheet@carbon

For the first time, DBHF nanofibers are constructed as flexible cathodes for HZBs. The formation mechanism of the DBHF structure is probed and the relationships between the synthetic conditions and the structures of the products are carefully investigated. Moreover, the HZBs are fabricated based on the DBHF cathode, Zn nanosheet@carbon cloth anode and a polymer electrolyte. Benefitting from the unique structure, the hybrid battery achieves high energy/power density and long-term cycling stability. Moreover, the high flexibility and “air-charging” capability make it a good uninterrupted power source for flexible electronics in different environments (Fig. 1h and i).

What's the electrolyte?

For the first time, DBHF nanofibers are constructed as flexible cathodes for HZBs. The formation mechanism of the DBHF structure is probed and the relationships between the synthetic conditions and the structures of the products are carefully investigated. Moreover, the HZBs are fabricated based on the DBHF cathode, Zn nanosheet@carbon cloth anode and a polymer electrolyte. Benefitting from the unique structure, the hybrid battery achieves high energy/power density and long-term cycling stability. Moreover, the high flexibility and “air-charging” capability make it a good uninterrupted power source for flexible electronics in different environments (Fig. 1h and i).

What's the cathode?

DBHF

To gain more insight into the morphological changes on the electrodes, as well as the causes of mNMR < mechem, we performed spectral fittings to determine how the relative fractions of the peaks assigned to Li microstructures vs. “bulk metal” change upon plating. The spectra were deconvoluted by using two peaks around 245–252.5 ppm (“bulk metal”) and one peak at around 257.5–262.5 ppm corresponding to the microstructural peak (see an example in Fig. 2f and more detailed explanation in the ESI†). We note that previous work has shown both experimentally and with simulations that dendrites and structures growing away from the Li metal surface give rise to larger shift around 270 ppm compared to microstructures close to the surface. In the current study, the in situ PEEK capsule cell applies constant pressure within the cell and more compact structures form, leading to a narrower range of shifts. The observed shifts of the microstructure peaks (Fig. S1†) are thus similar for both electrolytes although the microstructures have very distinct morphologies as seen in the SEM figures (Fig. 2b).

What's the electrolyte?

For small molecules, making composites with conductive fillers is one of the main strategies to enhance the rate capability. Decreasing the particle size, e.g., via ball-milling, is apparently another effective approach. Conjugated polymers should have better electron conductivity and potentially perform better than non-conductive small molecules. However, the performance of reported conjugated structures was generally moderate. We suppose that this is partly because non-optimal carbonate-based electrolytes were used with these materials.

What's the electrolyte?

carbonate-based

The ITO-coated glass samples were cleaned with acetone, ethanol, and isopropanol, sequentially. The vacant assemblies were prepared by using two ITO-coated glass samples with and without WO3 layers, respectively, which were stacked with a 60 μm-thick Surlyn adhesive film. Then, two electrolyte inlets were drilled into the ITO-coated glass side without the WO3 layer. The prepared electrolyte was injected into the vacant assemblies, and the inlets were closed. All the working areas were of 2.34 cm2 (1.3 cm × 1.8 cm). Finally, the filled assemblies were subjected to UV irradiation at a wavelength of 360 nm for periods of 0, 5, 10, and 20 min.

What's the electrolyte?

EIS experiments. The electrolyte 65 mM Na[FeIII-racEDDHA], 0.7 M Na2SO4, 155 mM borate pH 9, was reduced at the negative electrode to reach 50% SoC (determined by photometry), using the same setup outlined in the charge–discharge cycling experiments. Potassium ferro/ferricyanide at 50% SoC was directly prepared with 32.5 mM K3[FeIII(CN)6], 32.5 mM K4[FeII(CN)6], 0.7 M Na2SO4, 1 mM borate, pH 9. Three-electrode configuration with two CRLEs used as working and counter electrode and a reference electrode (Ag/AgCl 3 M KCl) were connected to a BioLogic VSP potentiostat. The impedance spectra were recorded from 3 × 104 Hz to 5 × 10−2 Hz. An AC amplitude of 100 mV was applied on top of a DC potential matching the open cell potential at 50% SoC. All electrodes used had a similar roving length (72 mm) and weight (0.23 g).

What's the electrolyte?

65 mM Na[FeIII-racEDDHA], 0.7 M Na2SO4, 155 mM borate pH 9

While selecting the optimal potential range for oxocarbon derivatives, it is important to know that poorly reversible transformations can occur, especially at high potentials. For example, it is known that oxidation products of rhodizonates dissolve in the electrolytes, causing a rapid capacity decay. For this reason, only four-electron reduction is considered suitable for the practical operation of rhodizonates.

What's the electrolyte?

To assemble the ssZIBs, the polymer electrolyte was synthesized via polymerization of PAM combined with CNFs. Specifically, 1.33 g of CNFs (1.5 wt% water suspension, University of Maine, Orono, ME, USA) were first dispersed in 20 mL of 1 M Zn(CF3SO3)2 solution with extensive high-speed stirring. After that, 50 mg of ammonium persulfate, 3 g of acrylamide (AM) monomers and 50 mg of N,N′-methylenebisacrylamide (BIS) were added to the suspension. After being stirred at 25 °C for 2 h, the mixture was cast onto a glass Petri dish. Then, the formed membrane was put in an oven and heated at 60 °C for half an hour. During this heating treatment, acrylamide was grafted onto the CNF surface through free radical polymerization. Finally, after being cooled to room temperature, a crosslinked CNF–PAM film was obtained. The prepared polymeric film shows high flexibility, and can be applied as a solid-state separator directly.

What's the electrolyte?

Solid-state Zn–air battery with a sandwich structure was assembled by replacing the zinc sheet and liquid electrolyte with a zinc foil (purity 99.9 wt%) and the as-fabricated PAM sheet, respectively.

What's the electrolyte?

Among ceramic electrolytes, the garnet-structured oxide Li7La3Zr2O12 (LLZO) has attracted attention as a core material of next-generation batteries (post-LIBs) because it exhibits excellent chemical/electrochemical stability against Li metals and has large electrochemical stability window. In particular, LLZO offers significant advantages in inhibiting Li dendrite formation because it is a single-ion conductor (transference number ∼1), has a high shear modulus (∼60 GPa) and stable interface with Li metals. Despite these intrinsic advantages, LLZO still has the problem of short circuit formation caused by Li propagation through LLZO particularly under high current densities. The penetration of Li through the polycrystalline LLZO electrolyte has been recently interpreted in terms of wettability of Li metals on LLZO, mechanical failure induced by stresses during Li plating that caused flaws on the LLZO surface, high electronic conductivity and a high interfacial resistance as well as non-uniform current distribution by lithium carbonate (Li2CO3) formed on the LLZO surface by the reaction between water vapor, carbon dioxide and LLZO in ambient air. Li propagation is known to occur via preferential plating at the grain boundaries (GBs), and the interface property of Li metal and LLZO plays a critical role in Li penetration when a high current density is applied to the interfaces. Because of the impurities or defects that predominantly exist on the GBs, different energy states for reduction at GBs might lead to non-uniform distribution of Li plating and preferential propagation of Li ions through the GBs. However, the mechanism of Li dendrite formation is unclear and remains controversial. Here, we investigated the mechanism of Li dendrite formation for the crystalline Ta-doped LLZO (Li6.5La3Zr1.5Ta0.5O12, LLZTO) by examining their energy band structures and defect states using various analytical techniques including reflection electron energy loss spectroscopy (REELS), scanning photoelectron microscopy (SPEM), and nanoscale charge-based deep level transient spectroscopy (Nano Q-DLTS). The measurement results revealed that the metallic Li plating along the GBs originates from the plentiful defect states in the GBs, implying that the formation of Li dendrites can be avoided if a thin layer with a wide bandgap is coated on LLZTO grains. Based on these analytical measurements, we adopted the laser annealing of LLZTO as a bandgap engineering method to suppress the Li dendrite formation by forming a surface structure of amorphous LLZTO and Li2O2 with wide bandgaps, which can block the electron injection into the grain boundaries. In addition, our electrochemical measurement results for the laser-treated LLZTO demonstrated that the stability and cycling performance were significantly improved. This study sheds light on the importance of electronic structure, in particular, defect states in developing ceramic solid electrolytes for Li metal batteries and the practicality of surface modification by laser treatment.

What's the electrolyte?

Li7La3Zr2O12 (LLZO)

Among ceramic electrolytes, the garnet-structured oxide Li7La3Zr2O12 (LLZO) has attracted attention as a core material of next-generation batteries (post-LIBs) because it exhibits excellent chemical/electrochemical stability against Li metals and has large electrochemical stability window. In particular, LLZO offers significant advantages in inhibiting Li dendrite formation because it is a single-ion conductor (transference number ∼1), has a high shear modulus (∼60 GPa) and stable interface with Li metals. Despite these intrinsic advantages, LLZO still has the problem of short circuit formation caused by Li propagation through LLZO particularly under high current densities. The penetration of Li through the polycrystalline LLZO electrolyte has been recently interpreted in terms of wettability of Li metals on LLZO, mechanical failure induced by stresses during Li plating that caused flaws on the LLZO surface, high electronic conductivity and a high interfacial resistance as well as non-uniform current distribution by lithium carbonate (Li2CO3) formed on the LLZO surface by the reaction between water vapor, carbon dioxide and LLZO in ambient air. Li propagation is known to occur via preferential plating at the grain boundaries (GBs), and the interface property of Li metal and LLZO plays a critical role in Li penetration when a high current density is applied to the interfaces. Because of the impurities or defects that predominantly exist on the GBs, different energy states for reduction at GBs might lead to non-uniform distribution of Li plating and preferential propagation of Li ions through the GBs. However, the mechanism of Li dendrite formation is unclear and remains controversial. Here, we investigated the mechanism of Li dendrite formation for the crystalline Ta-doped LLZO (Li6.5La3Zr1.5Ta0.5O12, LLZTO) by examining their energy band structures and defect states using various analytical techniques including reflection electron energy loss spectroscopy (REELS), scanning photoelectron microscopy (SPEM), and nanoscale charge-based deep level transient spectroscopy (Nano Q-DLTS). The measurement results revealed that the metallic Li plating along the GBs originates from the plentiful defect states in the GBs, implying that the formation of Li dendrites can be avoided if a thin layer with a wide bandgap is coated on LLZTO grains. Based on these analytical measurements, we adopted the laser annealing of LLZTO as a bandgap engineering method to suppress the Li dendrite formation by forming a surface structure of amorphous LLZTO and Li2O2 with wide bandgaps, which can block the electron injection into the grain boundaries. In addition, our electrochemical measurement results for the laser-treated LLZTO demonstrated that the stability and cycling performance were significantly improved. This study sheds light on the importance of electronic structure, in particular, defect states in developing ceramic solid electrolytes for Li metal batteries and the practicality of surface modification by laser treatment.

What's the electrolyte?

LLZO

The as-prepared polymer SP, Super P carbon and poly(vinylidene fluoride) (PVDF) binder with a mass ratio of 6/3/1 were added to a flask, and then dispersed in 1-methyl-2-pyrrolidinone (NMP) after being vigorously stirred for 10 h. The obtained slurry was coated on Cu foil, followed by drying at 100 °C in vacuo. The Cu foil was punched with a diameter of 14 mm as the anode electrode and the mass of SP was about 1.8 mg. A CR2032 coin-type cell was assembled in a glove box with SP as the working electrode, Celgard2400 polypropylene as the separator, lithium foil as the counter and reference electrode, and the prepared electrolyte consisted of a mixture of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) (DMC/EMC/EC = 5/2/3 v/v/v). The galvanostatic charge–discharge (GCD) and rate properties were determined by using a LAND battery test system at room temperature. After being pre-cycled at 0.2 C (20 mA h g−1) for three cycles, the battery was then tested at 1 C (100 mA h g−1) for 200 cycles. The cyclic voltammograms (CV) ranging from 0.01 V to 3 V were recorded with a CHI600E electrochemical working station with a scan rate of 0.1 mV s−1.

What's the anode?

Cu foil

The as-prepared polymer SP, Super P carbon and poly(vinylidene fluoride) (PVDF) binder with a mass ratio of 6/3/1 were added to a flask, and then dispersed in 1-methyl-2-pyrrolidinone (NMP) after being vigorously stirred for 10 h. The obtained slurry was coated on Cu foil, followed by drying at 100 °C in vacuo. The Cu foil was punched with a diameter of 14 mm as the anode electrode and the mass of SP was about 1.8 mg. A CR2032 coin-type cell was assembled in a glove box with SP as the working electrode, Celgard2400 polypropylene as the separator, lithium foil as the counter and reference electrode, and the prepared electrolyte consisted of a mixture of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) (DMC/EMC/EC = 5/2/3 v/v/v). The galvanostatic charge–discharge (GCD) and rate properties were determined by using a LAND battery test system at room temperature. After being pre-cycled at 0.2 C (20 mA h g−1) for three cycles, the battery was then tested at 1 C (100 mA h g−1) for 200 cycles. The cyclic voltammograms (CV) ranging from 0.01 V to 3 V were recorded with a CHI600E electrochemical working station with a scan rate of 0.1 mV s−1.

What's the electrolyte?

a mixture of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) (DMC/EMC/EC = 5/2/3 v/v/v)

The specific capacitances of the as-prepared ASSPs at different scan rates are presented in Fig. 3(d). The maximum specific capacitance of Bi/CNTs is 68.7 F cm−3 calculated from CV curves, which is larger than the values of the ASSPs based on 2D Bi (specific capacitance of 36.8 F cm−3) and CNTs (specific capacitance of 29.4 F cm−3). More importantly, the specific capacitance of the as-assembled Bi/CNT ASSP still maintains 33.0 F cm−3 with 48% capacitance retention when the scan rate is increased 20-fold from 5 to 100 mV s−1, superior to 43% capacitance retention of 2D Bi, demonstrating its good rate capability. The high specific capacitance and good rate capability of the as-prepared Bi/CNT SCs are mainly attributed to the excellent electronic conductivity of the exfoliated Bi NSs and CNTs, which can provide an effective charge transport pathway during the charge/discharge process. Meanwhile, the buckled layer structure of the Bi NSs offers abundant active sites with the full surface exposed and enable fast access of electrolyte ions.

What's the electrolyte?

Electrospun nanomaterials are very promising electrode materials for SCs in terms of outstanding electronic conductivity and electrolyte accessibility, rich and uniform porosity, and excellent structural stability. In this review, we extensively discussed the recent advances in electrospun nanomaterial electrodes for SCs. Firstly, pore engineering (i.e. activation, blend polymer electrospinning, addition of metal salts, and template method) and heteroatom doping as two major approaches to improve the electrochemical performance of electrospun CNFs were reviewed. Furthermore, due to their superb mechanical strength, high electronic conductivity, good compatibility and lightweight characteristics, CNFs acting as the attractive host/substrate for diverse electroactive materials such as metal oxides, metal phosphides, and metal–organic frameworks were summarized with critical insights. Finally, electrospun carbon-free materials represented by metal oxides in different compositions (spinel-type oxides, perovskites, metal oxide–metal oxide composites, etc.) and architectures (porous, hollow, core–shell, etc.) were also discussed. Despite increasingly successful examples demonstrating the great potential of electrospun nanomaterial electrodes, there are still challenges and opportunities in this field which have not been fully explored:

What's the electrolyte?

The photovoltaic performances of the crosslinked cells are higher than the non-crosslinked ones for both TiO2 and NiO based DSSCs, whatever the redox mediator used in the electrolyte. For TiO2 based DSSCs, this mostly results from a larger short circuit photocurrent density (Jsc) with the crosslinked dyes. On the other hand, the crosslinked NiO based p-DSSCs display much higher Voc with both redox mediators. However, on NiO based p-DSSCs the iodine based electrolyte gives lower Jsc after crosslinking. Jsc is controlled by the light harvesting efficiency (LHE), the charge injection quantum yield, the charge recombination reactions and by the charge collection efficiency. LHE is certainly not the cause of the lower Jsc, because the absorbance has not changed after crosslinking. Likewise, the hole injection efficiency is most certainly not affected by the crosslinking, because the current density is not diminished after crosslinking with the cobalt electrolyte. If an enhancement of the charge recombination reactions was the cause of the lower Jsc, first the Voc would be decreased as well, which is the reverse and second it would occur with the cobalt electrolyte, which is not the case either. Logically, we can therefore interpret the lower Jsc as a consequence of the lower efficiency of the dye regeneration step, which directly reduces the charge collection efficiency. It was previously reported by Xu and co-workers, that electron deficient triazoles similar to those involved in this study can make anion–π interaction with iodide. This hypothesis is supported by observing that the 1H NMR chemical shift of triazole of the reference compound benzyl-1,2,3-triazole-4-carboxylic acid methyl ester 15 was down-field shifted upon addition of Bu4NI in the NMR tube (Fig. S24†). As a result, after crosslinking the concentration of iodide is certainly raised in the vicinity of the DPP 2 and might therefore hinder the approach of triiodide and consequently limit the charge regeneration efficiency of the reduced DPP after hole injection. In both devices, the increase of the Voc after crosslinking is most probably due to lower interfacial charge recombination coming from lower access of the redox mediator to the surface semiconductor. Indeed, inspection of the current/voltage characteristics of the solar cell recorded in the dark demonstrate that current of the crosslinked solar cells is significantly lower than the non-crosslinked ones (Fig. S20–S23†). Interfacial charge recombination between the redox mediator and the hole in NiO is known to be a major source of energy loss in p-DSSCs, therefore it is not unexpected that the reduction of this process impacts more importantly NiO based solar cells than TiO2 DSSCs.

What's the electrolyte?

iodine

The study of the voltage traces follows the methodology introduced in previous studies, to observe the characteristic peaking behaviour that originates from pitting of the stripping electrode. Previous reports have assigned the typical voltage profile to specific deposition and pitting processes: when plating Li, there is initially a large overpotential associated with the nucleation of Li deposits, which then decreases rapidly towards a local minimum due to an increased surface area for deposition. When switching polarity after the first deposition, the microstructures formed previously in the first half cycle are oxidised and removed from the stripping electrode. When all of the microstructures have been dissolved completely (or been detached from the electrode surface forming ‘dead Li’) the overpotential increases rapidly. A peak is seen as the overpotential drops again, labelled “pitting” in Fig. 4a, as this behaviour has been assigned to the onset of bulk metal dissolution or pitting of the Li metal surface and an increase in surface area. When comparing different electrolytes, a more pronounced peaking behaviour has been associated with substantial impedance differences and spatial variations in the SEI layers that lead to non-uniform stripping and the formation of dead Li.

What's the electrolyte?

In addition to such capabilities, integration of CMOS fabrication with silicon micromachining allowed for the incorporation of on-chip circuitry, such as signal amplifiers, multiplexers to reduce output channel count, or application-specific integrated circuits (ASIC). Furthermore, the monolithic integration of on-chip circuitry and electrodes reduced the parasitic capacitance between the circuits. Silicon dioxide films were often used to cover electrodes to reduce artifacts induced at the electrode–electrolyte interface.

What's the electrolyte?

In order to enhance the capacity and rate performance of the electrodes, Fan et al. used 2,6-AQDS 1b in combination with carbon nanotubes (CNTs) and a DME-based electrolyte. Reversible Qm was up to 174 mA h g−1, higher than the theoretical value. It was partially attributed to the contribution from CNTs (23 mA h g−1). The authors assembled a full cell, which had pre-potassiated graphite as an anode. The cell had a Qm of up to 87 mA h g−1 (per mass of AQDS) with an average discharge voltage of 1.1 V. At 500 mA g−1, the capacity retention of the full cell was 33% after 2500 cycles.

What's the anode?

graphite

In order to enhance the capacity and rate performance of the electrodes, Fan et al. used 2,6-AQDS 1b in combination with carbon nanotubes (CNTs) and a DME-based electrolyte. Reversible Qm was up to 174 mA h g−1, higher than the theoretical value. It was partially attributed to the contribution from CNTs (23 mA h g−1). The authors assembled a full cell, which had pre-potassiated graphite as an anode. The cell had a Qm of up to 87 mA h g−1 (per mass of AQDS) with an average discharge voltage of 1.1 V. At 500 mA g−1, the capacity retention of the full cell was 33% after 2500 cycles.

What's the electrolyte?

DME-based

The preparation of N-doped carbon nanofibers decorated with Mo2C quantum dots (Mo2C@NCF) is illustrated in Scheme 1. Mo2C@NCF was first fabricated via an electrospinning technology followed by a high-temperature annealing process. Afterwards, facile glow discharge plasma (GPD) was employed on the surface of Mo2C@NCF. Fig. 1a shows the XRD patterns of as-prepared Mo2C@NCF and GDP-Mo2C@NCF. The diffraction peaks of both Mo2C@NC and GDP-Mo2C@NC are in good agreement with that of hexagonal Mo2C (JCPDS 35-0787) without any impurity peaks, suggesting the high purity of Mo2C. After high energy glow plasma treatment, all the characteristic peaks become stronger. As shown in the SEM and TEM images (Fig. 1b and c), Mo2C@NCF displays a fibrillar structure with a smooth surface and an average diameter of ∼100 nm, and the one-dimensional orientation benefits fast transport of electrons/ions. The HRTEM images show the distribution of Mo2C quantum dots with an average diameter of 3–4 nm encapsulated in the carbon fiber though there are no lattice fringes (Fig. 1d and e). Different from that of Mo2C@NCF, the surface of GDP-Mo2C@NCF is etched using the high energy particles during the plasma process, leading to a rough appearance and exposure of Mo2C quantum dots (Fig. 1f and g). This morphological change offers a large electrode–electrolyte contact area to ensure high availability of catalytically active sites. The HRTEM images clearly demonstrate the presence of Mo2C quantum dots, and an observed lattice fringe spacing of 0.24 nm corresponding to the (101) plane of Mo2C (Fig. 1h and i). The EDX mapping images confirm the uniform distribution of C, N and Mo elements on the carbon fiber (Fig. 1j).

What's the electrolyte?

Herein, a Li/LiV2(PO4)3 primary battery (Fig. 1a) with a long shelf life is proposed, which exhibits impressive electrochemical performances under high power densities and low-temperature conditions. It has been found that the corrosion of the Al current collector triggered by the organic radical cations generated from the electrochemical oxidation of EC at high potentials; and the detrimental reaction between LiV2(PO4)3 and electrolyte lead to the self-discharge of Li/LiV2(PO4)3 primary batteries. When EC was replaced by PC, the corrosion of the Al foil was alleviated. LiBOB was found to be conducive to increase the shelf life of the Li/LiV2(PO4)3 primary batteries as it formed a protective film on the surface of the cathode, which effectively alleviated the side reaction between LiV2(PO4)3 and the electrolyte. Most importantly, the Li/LiV2(PO4)3 primary batteries exhibited excellent performances at high charge/discharge rates (up to 50C) and even at temperatures as low as −40 °C.

What's the cathode?

Herein, a Li/LiV2(PO4)3 primary battery (Fig. 1a) with a long shelf life is proposed, which exhibits impressive electrochemical performances under high power densities and low-temperature conditions. It has been found that the corrosion of the Al current collector triggered by the organic radical cations generated from the electrochemical oxidation of EC at high potentials; and the detrimental reaction between LiV2(PO4)3 and electrolyte lead to the self-discharge of Li/LiV2(PO4)3 primary batteries. When EC was replaced by PC, the corrosion of the Al foil was alleviated. LiBOB was found to be conducive to increase the shelf life of the Li/LiV2(PO4)3 primary batteries as it formed a protective film on the surface of the cathode, which effectively alleviated the side reaction between LiV2(PO4)3 and the electrolyte. Most importantly, the Li/LiV2(PO4)3 primary batteries exhibited excellent performances at high charge/discharge rates (up to 50C) and even at temperatures as low as −40 °C.

What's the electrolyte?

To compare different time scales, both relatively long and short pulse lengths were initially chosen, with TON = TOFF of either 1 s or 5 ms. The electrochemistry for pulse plating at 1 mA cm−2 and TON, TOFF = 1 s in LP30 electrolyte is shown in Fig. 5 (see Fig. S26 and S27† for additional pulse plating data for other electrolyte formulations); this corresponds to a duty cycle of θduty = TON/(TON + TOFF) = 0.5 and an average current density of 0.5 mA cm−2. Thus, the data can be readily compared to the constant current experiments at 0.5 mA cm−2.

What's the electrolyte?

LP30

Fig. 2a shows the 7Li in situ NMR spectra continuously acquired during a 0.5 mA cm−2 constant current experiment. The resonance from Li metal depends on the orientation of the Li metal anode strip with respect to the static magnetic field, B0, due to Li metal's temperature independent paramagnetism (TIP). Aligning the cell perpendicular to the B0 field results in a 7Li resonance at around 245 ppm for the pristine Li metal (Fig. 2a) and all in situ cells presented in this work were aligned in this fashion. When depositing Li in both LP30 and LP30 + FEC, a new peak around 260 ppm emerges that continues to grow as a current of 0.5 mA cm−2 is passed (Fig. 2a). This new resonance is indicative of mossy structures growing near to the Li metal surface. Whisker-like morphologies are observed in the SEM micrographs as the major morphology after plating for 3.5 mA h cm−2 in LP30 electrolyte, whereas dense, thick buds (diameter of surface features ∼5–10 μm) are observed for LP30 + FEC (Fig. 2b).

What's the electrolyte?

LP30

The electrocatalytic application of HEA NPs in the selective CO2 reduction reaction (CO2RR) has also been reported recently. For example, Nellaiappan et al. reported quinary fcc-AuPtAgPdCu NPs as an efficient CO2RR electrocatalyst toward CH4 and C2H4 in the low overpotential region. The five elements in the quinary HEA NPs were homogeneously distributed, whose chemical environments adopt metallic characteristics determined by XPS analysis except for Cu; a small amount of Cu2+ content was observed. The quinary fcc-AuPtAgPdCu NPs obtained superior selectivity toward the CO2RR in the low overpotential region, that is, FEmethane = 38.2% and FEethylene = 29.5% at −0.9 VAg/AgCl (−0.3 VRHE) in a CO2-saturated 0.5 M K2SO4 electrolyte (FE: faradaic efficiency). Based on their DFT calculation, the excellent electrocatalytic activity toward the CO2RR has mainly originated from redox-active Cu content in AuPtAgPdCu, while other elements provide an additional synergy in the CO2RR. Also, the long-term stability of the catalyst was verified by a chronoamperometry test for 5 h in a CO2-saturated 0.5 M K2SO4 electrolyte.

What's the electrolyte?

0.5 M K2SO4

The electrocatalytic application of HEA NPs in the selective CO2 reduction reaction (CO2RR) has also been reported recently. For example, Nellaiappan et al. reported quinary fcc-AuPtAgPdCu NPs as an efficient CO2RR electrocatalyst toward CH4 and C2H4 in the low overpotential region. The five elements in the quinary HEA NPs were homogeneously distributed, whose chemical environments adopt metallic characteristics determined by XPS analysis except for Cu; a small amount of Cu2+ content was observed. The quinary fcc-AuPtAgPdCu NPs obtained superior selectivity toward the CO2RR in the low overpotential region, that is, FEmethane = 38.2% and FEethylene = 29.5% at −0.9 VAg/AgCl (−0.3 VRHE) in a CO2-saturated 0.5 M K2SO4 electrolyte (FE: faradaic efficiency). Based on their DFT calculation, the excellent electrocatalytic activity toward the CO2RR has mainly originated from redox-active Cu content in AuPtAgPdCu, while other elements provide an additional synergy in the CO2RR. Also, the long-term stability of the catalyst was verified by a chronoamperometry test for 5 h in a CO2-saturated 0.5 M K2SO4 electrolyte.

What's the electrolyte?

CO2-saturated 0.5 M K2SO4

The concentration of 7Li electrolyte as a function of time is, ce7(t) = [Li+]fe7(t) with the initial condition for the fraction of 7Li in the electrolyte, fe7(0) = 0.92 (the natural abundance of 7Li). Since the diffusion coefficient in lithium metal, Dm, is more than four orders of magnitude smaller than the diffusion Li+ coefficient in the electrolyte (Table 1), the diffusion of Li+ throughout the electrolyte is considered instantaneous.

What's the electrolyte?

The Li3V2(PO4)3 (LVP) electrode slurry was prepared by mixing LVP, carbon black (Super P), and polyvinylidene fluoride (PVDF) in a weight ratio of 8:1:1 in N-methyl pyrrolidone (NMP); this slurry was coated on the Al foil followed by drying at 120 °C for 24 h. Then, the electrodes were cut into disks with a diameter of 14.0 mm and used for coin cell assembly. The mass loading of the LVP electrodes was 2.3–2.6 mg cm−2. The primary batteries (CR2016, coin-type cell) were assembled using the Li3V2(PO4)3 cathode, Celgard 2325 separator, electrolytes, and Li metal anode in an argon-filled glove box.

What's the cathode?

Li3V2(PO4)3

The Li3V2(PO4)3 (LVP) electrode slurry was prepared by mixing LVP, carbon black (Super P), and polyvinylidene fluoride (PVDF) in a weight ratio of 8:1:1 in N-methyl pyrrolidone (NMP); this slurry was coated on the Al foil followed by drying at 120 °C for 24 h. Then, the electrodes were cut into disks with a diameter of 14.0 mm and used for coin cell assembly. The mass loading of the LVP electrodes was 2.3–2.6 mg cm−2. The primary batteries (CR2016, coin-type cell) were assembled using the Li3V2(PO4)3 cathode, Celgard 2325 separator, electrolytes, and Li metal anode in an argon-filled glove box.

What's the anode?

Li metal

The Li3V2(PO4)3 (LVP) electrode slurry was prepared by mixing LVP, carbon black (Super P), and polyvinylidene fluoride (PVDF) in a weight ratio of 8:1:1 in N-methyl pyrrolidone (NMP); this slurry was coated on the Al foil followed by drying at 120 °C for 24 h. Then, the electrodes were cut into disks with a diameter of 14.0 mm and used for coin cell assembly. The mass loading of the LVP electrodes was 2.3–2.6 mg cm−2. The primary batteries (CR2016, coin-type cell) were assembled using the Li3V2(PO4)3 cathode, Celgard 2325 separator, electrolytes, and Li metal anode in an argon-filled glove box.

What's the electrolyte?

Fig. 4c shows the electrochemical impendence spectra of the full cell in the Na–H2O–urea–DMF electrolyte before cycling, after the first cycle and after 100 cycles. The Rs value of the battery in the Na–H2O–urea–DMF electrolyte, connected to the intercept on the real impedance axis at a high frequency in the EIS spectra, is relatively small and equal for the pristine state and after cycling, which suggests good ion diffusion in the electrolyte and good stability of the electrode materials before and after cycling. The Rct value represented the charge transfer resistance increase after the first cycle and after 100 cycles, indicating that a passivation layer may be formed on the NTP anode, which could be a significant factor in the improvement of the cycling performance of the NVP/NTP full cell. Moreover, the XRD patterns (Fig. S16†) and SEM images (Fig. S17†) of NVP/C and NTP/C before and after 500 cycles were recorded, respectively. The results indicate that the Na–H2O–urea–DMF electrolyte is conducive to achieving excellent stability of the NVP cathode. In addition, a NiHCF//NTP full cell displays 80% capacity retention after 2000 cycles at 2C rate (Fig. 4d).

What's the cathode?

NVP

Fig. 4c shows the electrochemical impendence spectra of the full cell in the Na–H2O–urea–DMF electrolyte before cycling, after the first cycle and after 100 cycles. The Rs value of the battery in the Na–H2O–urea–DMF electrolyte, connected to the intercept on the real impedance axis at a high frequency in the EIS spectra, is relatively small and equal for the pristine state and after cycling, which suggests good ion diffusion in the electrolyte and good stability of the electrode materials before and after cycling. The Rct value represented the charge transfer resistance increase after the first cycle and after 100 cycles, indicating that a passivation layer may be formed on the NTP anode, which could be a significant factor in the improvement of the cycling performance of the NVP/NTP full cell. Moreover, the XRD patterns (Fig. S16†) and SEM images (Fig. S17†) of NVP/C and NTP/C before and after 500 cycles were recorded, respectively. The results indicate that the Na–H2O–urea–DMF electrolyte is conducive to achieving excellent stability of the NVP cathode. In addition, a NiHCF//NTP full cell displays 80% capacity retention after 2000 cycles at 2C rate (Fig. 4d).

What's the anode?

NTP

Fig. 4c shows the electrochemical impendence spectra of the full cell in the Na–H2O–urea–DMF electrolyte before cycling, after the first cycle and after 100 cycles. The Rs value of the battery in the Na–H2O–urea–DMF electrolyte, connected to the intercept on the real impedance axis at a high frequency in the EIS spectra, is relatively small and equal for the pristine state and after cycling, which suggests good ion diffusion in the electrolyte and good stability of the electrode materials before and after cycling. The Rct value represented the charge transfer resistance increase after the first cycle and after 100 cycles, indicating that a passivation layer may be formed on the NTP anode, which could be a significant factor in the improvement of the cycling performance of the NVP/NTP full cell. Moreover, the XRD patterns (Fig. S16†) and SEM images (Fig. S17†) of NVP/C and NTP/C before and after 500 cycles were recorded, respectively. The results indicate that the Na–H2O–urea–DMF electrolyte is conducive to achieving excellent stability of the NVP cathode. In addition, a NiHCF//NTP full cell displays 80% capacity retention after 2000 cycles at 2C rate (Fig. 4d).

What's the electrolyte?

Na–H2O–urea–DMF

Fig. 4c shows the electrochemical impendence spectra of the full cell in the Na–H2O–urea–DMF electrolyte before cycling, after the first cycle and after 100 cycles. The Rs value of the battery in the Na–H2O–urea–DMF electrolyte, connected to the intercept on the real impedance axis at a high frequency in the EIS spectra, is relatively small and equal for the pristine state and after cycling, which suggests good ion diffusion in the electrolyte and good stability of the electrode materials before and after cycling. The Rct value represented the charge transfer resistance increase after the first cycle and after 100 cycles, indicating that a passivation layer may be formed on the NTP anode, which could be a significant factor in the improvement of the cycling performance of the NVP/NTP full cell. Moreover, the XRD patterns (Fig. S16†) and SEM images (Fig. S17†) of NVP/C and NTP/C before and after 500 cycles were recorded, respectively. The results indicate that the Na–H2O–urea–DMF electrolyte is conducive to achieving excellent stability of the NVP cathode. In addition, a NiHCF//NTP full cell displays 80% capacity retention after 2000 cycles at 2C rate (Fig. 4d).

What's the electrolyte?

Na–H2O–urea–DMF

Herein, we report a new finding that 3Mg/Mg2Sn alloy can be a promising solution to the aforementioned issues in Sn-based alloy-type MIB anodes. It is shown that 3Mg/Mg2Sn, which is composed of ternary phases (crystalline Mg-rich (c-Mg), amorphous Mg-rich (a-Mg), and intermetallic Mg2Sn phases), reversibly magnesiates/de-magnesiates a significant amount of Mg2+ ions in a non-Grignard and Lewis acid-free electrolyte even under high rates of C/D. In Table 1, the unprecedented electrochemical performance of 3Mg/Mg2Sn is compared with that of other popular alloy-type anodes. The origin of high capacities and excellent rate-capabilities is also discussed in the context of structural features. Finally, we describe the compatibility of 3Mg/Mg2Sn with versatile conventional electrolytes and the optimality of using 3Mg/Mg2Sn with Mg2+-trapping cathodes (e.g., Mo6S8).

What's the cathode?

Mo6S8

Herein, we report a new finding that 3Mg/Mg2Sn alloy can be a promising solution to the aforementioned issues in Sn-based alloy-type MIB anodes. It is shown that 3Mg/Mg2Sn, which is composed of ternary phases (crystalline Mg-rich (c-Mg), amorphous Mg-rich (a-Mg), and intermetallic Mg2Sn phases), reversibly magnesiates/de-magnesiates a significant amount of Mg2+ ions in a non-Grignard and Lewis acid-free electrolyte even under high rates of C/D. In Table 1, the unprecedented electrochemical performance of 3Mg/Mg2Sn is compared with that of other popular alloy-type anodes. The origin of high capacities and excellent rate-capabilities is also discussed in the context of structural features. Finally, we describe the compatibility of 3Mg/Mg2Sn with versatile conventional electrolytes and the optimality of using 3Mg/Mg2Sn with Mg2+-trapping cathodes (e.g., Mo6S8).

What's the anode?

Sn-based alloy-type MIB

Herein, we report a new finding that 3Mg/Mg2Sn alloy can be a promising solution to the aforementioned issues in Sn-based alloy-type MIB anodes. It is shown that 3Mg/Mg2Sn, which is composed of ternary phases (crystalline Mg-rich (c-Mg), amorphous Mg-rich (a-Mg), and intermetallic Mg2Sn phases), reversibly magnesiates/de-magnesiates a significant amount of Mg2+ ions in a non-Grignard and Lewis acid-free electrolyte even under high rates of C/D. In Table 1, the unprecedented electrochemical performance of 3Mg/Mg2Sn is compared with that of other popular alloy-type anodes. The origin of high capacities and excellent rate-capabilities is also discussed in the context of structural features. Finally, we describe the compatibility of 3Mg/Mg2Sn with versatile conventional electrolytes and the optimality of using 3Mg/Mg2Sn with Mg2+-trapping cathodes (e.g., Mo6S8).

What's the electrolyte?

non-Grignard and Lewis acid-free