milerssliu/battery-device-data-qa huggingface dataset:
For the emerging potassium-ion energy storage technology, the major challenge is seeking suitable electrode materials with a robust structure and fast kinetics for the reversible insertion/desertion of potassium ions. Here, a pseudocapacitive core–shell heterostructure of titanium oxide/carbon confined into N, P, and S co-doped carbon (TiO2/C@NPSC) is obtained by pyrolyzing a metal–organic framework (MOF) precursor of MIL-125 (Ti) modified by poly(cyclotriphosphazene-co-4,4′-sulfonyldiphenol) polymer. The distinctive structure of TiO2/C@NPSC can effectively buffer the volume variation of TiO2 nano-grains during the charge/discharge process, increase the electron/charge transfer, provide abundant active sites, and boost the pseudocapacitive-dominated K+-storage. Consequently, the TiO2/C@NPSC anode displays superior cyclability and fast kinetics behavior. Upon integrating it with a high capacitance activated carbon cathode derived from another MOF precursor, the as-built potassium-ion hybrid capacitor achieves a high-energy density of 114 W h kg−1 and a power output of 21 kW kg−1. Moreover, in a wide working potential window of 0–4.2 V, the device also maintains over 91.6% of its initial capacity after 10000 cycles, showing a superior cycle stability. Our results are conducive to understanding the importance of anode-engineering for designing advanced PIHCs.

Question: What's the anode?
Answer: TiO2/C@NPSC
The ATR-IR spectra (Fig. 2 for TiO2 based photoanode and Fig. S3† for NiO based photocathode) show that the intensity of the azido stretching bands has completely disappeared after heating, while that of the alkyne is visible meaning that there are some unreacted alkyne groups in the film. On the other hand, the stretching bands of the ester groups of the crosslinking agent 3 and that of the lactam of the DPP 1 or 2 (both around 1700 cm−1) are still clearly visible, proving that these moieties are present on the surface of the film. This result is consistent with the presence of four alkyne groups in 3 relative to only two azides on the dyes 1 or 2. The ATR-IR spectrum of the DPP 2 grafted on the electrode was not modified after heating in the crosslinking conditions (15 min at 140 °C in orthodichlorobenzene) in absence of the cross-linker 3 (Fig. S4†). This indicates that the azido groups are stable in these conditions and do not degrade upon heating at 140 °C for 15 min.

Question: What's the cathode?
Answer: NiO
For the former, metal Ni and Cu are the common conductivity improvers and can be introduced into the sulfur cathode through a straightforward addition and/or interfusion. For example, Manthiram's group presented a pie-like electrode that consists of nickel foam as a “filling” and an outer carbon shell as a “crust” for facilitating the utilization of sulfur cathodes. Copper powder was introduced into the sulfur cathode by Jia et al. through partially replacing the sulfur contained active material with Cu during the manufacture procedure of the working electrode. Very similarly, Guo and coworkers recently reported the preparation of a CNT/graphene–S–Al3Ni2 cathode with a 3D network structure using 10 wt% Al3Ni2 powder to displace the CNT/graphene–S active material, where the Al in the Al3Ni2 provides an efficient channel for fast electron and ion transfer in the three dimensions, especially along the vertical direction of the cathode. Furthermore, Zheng et al. demonstrated a copper-stabilized sulfur–microporous carbon composite synthesized by uniformly dispersing 10% highly electronically conductive Cu nanoparticles into microporous carbon (MC), followed by wet-impregnation of S. To obtain highly dispersed Cu, commercial MC with a high surface area is first selected as the matrix and carrier. An ultrasonic-assisted multiple wetness impregnation and synchro-dry method is then applied to load 50% Cu(NO3)2 ethanol alcohol solution in MC and evaporate the solvent. This process is repeated until a certain amount of Cu(NO3)2 is added to MC. Finally, Cu nanoparticles anchored in the MC are gained by the reduction of the dry precursor at 200 °C for 1 h under an argon mixed with 5% hydrogen environment. Interestingly, the Cu content in MC can be easily adjusted by controlling the amount of Cu(NO3)2 addition via impregnation times.

Question: What's the cathode?
Answer: CNT/graphene–S–Al3Ni2
For the former, metal Ni and Cu are the common conductivity improvers and can be introduced into the sulfur cathode through a straightforward addition and/or interfusion. For example, Manthiram's group presented a pie-like electrode that consists of nickel foam as a “filling” and an outer carbon shell as a “crust” for facilitating the utilization of sulfur cathodes. Copper powder was introduced into the sulfur cathode by Jia et al. through partially replacing the sulfur contained active material with Cu during the manufacture procedure of the working electrode. Very similarly, Guo and coworkers recently reported the preparation of a CNT/graphene–S–Al3Ni2 cathode with a 3D network structure using 10 wt% Al3Ni2 powder to displace the CNT/graphene–S active material, where the Al in the Al3Ni2 provides an efficient channel for fast electron and ion transfer in the three dimensions, especially along the vertical direction of the cathode. Furthermore, Zheng et al. demonstrated a copper-stabilized sulfur–microporous carbon composite synthesized by uniformly dispersing 10% highly electronically conductive Cu nanoparticles into microporous carbon (MC), followed by wet-impregnation of S. To obtain highly dispersed Cu, commercial MC with a high surface area is first selected as the matrix and carrier. An ultrasonic-assisted multiple wetness impregnation and synchro-dry method is then applied to load 50% Cu(NO3)2 ethanol alcohol solution in MC and evaporate the solvent. This process is repeated until a certain amount of Cu(NO3)2 is added to MC. Finally, Cu nanoparticles anchored in the MC are gained by the reduction of the dry precursor at 200 °C for 1 h under an argon mixed with 5% hydrogen environment. Interestingly, the Cu content in MC can be easily adjusted by controlling the amount of Cu(NO3)2 addition via impregnation times.

Question: What's the cathode?
Answer: sulfur
At a volumetric current density of 268 mA cm−3, the volumetric capacity of ∼215 mA h cm−3 of LixMnO2/nanomesh is much larger than the capacity of many 3D core–shell cathodes at similar vol. current densities, such as MnO2-coated carbon nanotubes (∼53 mA h cm−3), LiCoO2-coated carbon fiber mats (∼70 mA h cm−3), LiCoO2-coated aluminium nanowires (∼140 mA h cm−3) or V2O5-coated CNT/PAN sheets (∼155 mA h cm−3). At a vol. current density of ∼270 mA cm−3, the volumetric capacity of the nanomesh cathodes is only significantly inferior to that of LiCoO2-coated carbon foam (∼370 mA h cm−3) and Li2MnSiO4 doubly-loaded on graphene inverse opals (∼520 mA h cm−3) – both electrodes having a very high volume fraction of the active materials of 57% and 90%, respectively. Furthermore, also at high current densities above 1000 mA cm−3, the nanomesh cathode retains superior volumetric capacity to most of the electrodes, being only inferior to the two aforementioned electrodes and the V2O5-coated graphene inverse opals with a highly regular structure and larger pores. At high currents densities, however, the comparison may be additionally affected by the varying thicknesses of the electrodes (Table S3†), since thinner electrodes (such as ours) typically show better high-rate performance.

Question: What's the cathode?
Answer: LixMnO2/nanomesh
Up to now, owing to the tremendous work done by different research groups, there have been several new types of electrolysers proposed for decoupled H2/O2 generation through the utilization of redox mediators, and a list of these new electrolysers has been provided in Table S1 in the ESI.† For example, a new PEM electrolyser is proposed with polyoxometalates (POMs) used as the redox relay, and the H2/O2 generation can be decoupled both in time and in space (Scheme 1b). Such a design requires three electrodes (OER electrode, carbon electrode for reduction of the soluble POM redox mediator, and Pt catalyst for spontaneous hydrogen evolution), one soluble redox mediator (POMs), one membrane (Nafion membrane) and two cells, which potentially increases the cost for the electrolysers. A solid redox mediator, such as Ni(OH)2, has also been successfully used as the relay for decoupled water splitting (Scheme 1c). This kind of design needs no separator between the cathode and the anode; however, an auxiliary relay electrode has been used and the whole cell is still a three-component system, and the overall cost for the electrolyser may not be effectively reduced. Also, among all these designs, since the HER and OER are decoupled in time, there is always an electrode (either the HER or the OER electrode) in an idle state when the cell is in operation. For decoupled water splitting in time, the integration of the HER and OER in one electrode can effectively reduce the cost and space for the electrolyser, which is more practical for scale-up applications; however, a rational design toward this direction has not been proposed.

Question: What's the cathode?
Up to now, owing to the tremendous work done by different research groups, there have been several new types of electrolysers proposed for decoupled H2/O2 generation through the utilization of redox mediators, and a list of these new electrolysers has been provided in Table S1 in the ESI.† For example, a new PEM electrolyser is proposed with polyoxometalates (POMs) used as the redox relay, and the H2/O2 generation can be decoupled both in time and in space (Scheme 1b). Such a design requires three electrodes (OER electrode, carbon electrode for reduction of the soluble POM redox mediator, and Pt catalyst for spontaneous hydrogen evolution), one soluble redox mediator (POMs), one membrane (Nafion membrane) and two cells, which potentially increases the cost for the electrolysers. A solid redox mediator, such as Ni(OH)2, has also been successfully used as the relay for decoupled water splitting (Scheme 1c). This kind of design needs no separator between the cathode and the anode; however, an auxiliary relay electrode has been used and the whole cell is still a three-component system, and the overall cost for the electrolyser may not be effectively reduced. Also, among all these designs, since the HER and OER are decoupled in time, there is always an electrode (either the HER or the OER electrode) in an idle state when the cell is in operation. For decoupled water splitting in time, the integration of the HER and OER in one electrode can effectively reduce the cost and space for the electrolyser, which is more practical for scale-up applications; however, a rational design toward this direction has not been proposed.

Question: What's the anode?
Commercial sublimated sulfur (S) was mixed with AB (C) in a mass ratio of 8:2, and the mixture (C/S) was fully ground and heat-treated at 155 °C for 6 h in an argon atmosphere. Then, the as-obtained composite was mixed with AB and PVDF (8:1:1 by weight), followed by dispersing in NMP solvent and stirred for 12 h. Next, the slurry was uniformly cast onto an Al foil substrate and dried in a vacuum for 12 h at 60 °C. Afterwards, the coated-Al foil was cut into 12 mm wafers with a sulfur loading of ∼2.0 mg cm−2. Moreover, a cathode wafer with a high sulfur loading of ∼5.6 mg cm−2 was also prepared in the same procedure by controlling the thickness of the coating. The as-prepared C/S disc, above separators (BFO/GO/AB@PP, GO/AB@PP, and PP) and lithium plate (diameter of 15.6 mm, thickness of 250 µm) were applied to assemble a 2025-type button battery, in which the electrolyte was 1 M LiTFSI in DOL/DME (v/v = 1:1) with 1 wt% LiNO3. The electrolyte/sulfur (E/S) ratio was fixed as 12:1 (µL mg−1). The battery was charged and discharged on a Neware battery test station (5V20 mA). The cyclic voltammetry (CV) curves were operated in a voltage window between 1.7 and 2.8 V with a scanning rate of 0.1 mV s−1. The electrochemical impedance spectroscopy (EIS) plots were obtained in the frequency range from 0.1 to 100 kHz with an amplitude of 5 mV. Both CV and EIS were carried out on an electrochemical workstation (Shanghai, Chenhua, CHI660D).

Question: What's the cathode?
Answer: sulfur
Numerous studies reported core–shell 3D-nanostructured Li-ion electrodes with active components such as Si, Sn, TiO2, Nb2O5, Co3O4 or iron oxides, mostly applicable as negative electrodes (anodes). On the other hand, nanostructured 3D positive electrodes (cathodes) based on active materials with a desirable high redox potential vs. Li+/Li (e.g. lithiated manganese oxides, V2O5 or LiCoO2 have been reported in comparatively fewer publications. For such cathodes, a big difficulty lies in inherent oxidation of the 3D current collector during the synthesis of high voltage cathode materials – the latter typically requiring temperatures above 700 °C. By lowering the synthesis temperature to 300 °C, Zhang et al. and Pikul et al. successfully demonstrated both core–shell cathodes and full 3D Li-ion microbatteries which employed lithiated manganese oxides coated on inverse nickel opal current collectors. Impressively, the devices were operational at C-rates above 1000 (where the rate of 1C corresponds to the current required for 1 hour of a complete charge or discharge). The same group also demonstrated other high-performance 3D cathodes, such as a carbon foam coated with dense LiCoO2 or inverted opals doubly-filled with V2O5 and Li2MnSiO4. Currently, however, the electrode design based on regular inverse opal current collectors is difficult to envision for large scale battery manufacturing, as the fabrication of these current collectors is time consuming (e.g. >24 h for a 20 μm-thick structure), involves difficult to handle colloidal templates and is limited to small surfaces (∼1 cm2). Importantly, the application of a current collector with yet a higher volumetric surface area may allow further reducing the thickness of the active material and gaining access to its full theoretical capacity.

Question: What's the cathode?
Answer: a carbon foam coated with dense LiCoO2
Numerous studies reported core–shell 3D-nanostructured Li-ion electrodes with active components such as Si, Sn, TiO2, Nb2O5, Co3O4 or iron oxides, mostly applicable as negative electrodes (anodes). On the other hand, nanostructured 3D positive electrodes (cathodes) based on active materials with a desirable high redox potential vs. Li+/Li (e.g. lithiated manganese oxides, V2O5 or LiCoO2 have been reported in comparatively fewer publications. For such cathodes, a big difficulty lies in inherent oxidation of the 3D current collector during the synthesis of high voltage cathode materials – the latter typically requiring temperatures above 700 °C. By lowering the synthesis temperature to 300 °C, Zhang et al. and Pikul et al. successfully demonstrated both core–shell cathodes and full 3D Li-ion microbatteries which employed lithiated manganese oxides coated on inverse nickel opal current collectors. Impressively, the devices were operational at C-rates above 1000 (where the rate of 1C corresponds to the current required for 1 hour of a complete charge or discharge). The same group also demonstrated other high-performance 3D cathodes, such as a carbon foam coated with dense LiCoO2 or inverted opals doubly-filled with V2O5 and Li2MnSiO4. Currently, however, the electrode design based on regular inverse opal current collectors is difficult to envision for large scale battery manufacturing, as the fabrication of these current collectors is time consuming (e.g. >24 h for a 20 μm-thick structure), involves difficult to handle colloidal templates and is limited to small surfaces (∼1 cm2). Importantly, the application of a current collector with yet a higher volumetric surface area may allow further reducing the thickness of the active material and gaining access to its full theoretical capacity.

Question: What's the cathode?
Answer: inverted opals doubly-filled with V2O5 and Li2MnSiO4
In summary, we report a highly effective approach to prevent Li dendrite formation by an in situ formed self-repairing alloy layer (LixGa). During lithiation, evenly distributed Ga nanoparticles serve as lithiophilic sites to induce a homogeneous Li nucleation. Stress generated during Li plating can also be eliminated by the soft Ga nanoparticles. During the delithiation, metallic liquid Ga partially recovered from the dealloying process by timely filling the small gaps, which effectively avoided the generation of microcracks. A long-term cycling life of over 1800 h and 1400 h was obtained for the alloy-protected Li anodes at the high current densities of 2 mA cm−2 and 5 mA cm−2, respectively. Even increasing the current density and deposition capacity to 15 mA cm−2 and 15 mA h cm−2, respectively, the alloy-protected Li anodes still showed a stable cycling performance. Functionalized full cells coupled with LiFePO4 cathodes are finally cycled up to 600 cycles at 3C rate with the discharge capacity maintained at 128 mA h g−1. This simple and facile modification method is expected to realize the high-rate and long-life cycling of the Li metal anode and paves the way for the industrialization of Li metal batteries.

Question: What's the cathode?
Answer: LiFePO4
The rate performance of the nanomesh cathode was tested at C-rates between 1.2 and 24C (corresponding to the volumetric currents of 269 mA cm−3 and 5387 mA cm−3, respectively). For each C-rate, five discharge–charge cycles were recorded, starting from the fully charged state. Therefore, we distinguish the “initial” discharge capacities (recorded after fully charging the cathode at 4.0 V for 1 hour) from the “continuous” discharge capacities recorded in the four consecutive cycles, which also depend on the charging kinetics at each C-rate. The discharge–charge profiles recorded in the first discharge–charge cycle at each C-rate are presented in Fig. 5c. The profiles have a similar shape at all the C-rates, showing that the higher currents did not affect the mechanism of Li storage in the cathode. The initial discharge capacity at 6C was 70% of the initial discharge capacity at 1.2C. When the cathode was discharged from the fully charged state at high rates of 18C and 24C (the current required for a theoretical full discharge in ∼3 min and 2.5 min, respectively), the initial capacity was still 50% and 45% of the initial capacity at 1.2C, demonstrating good rate performance of the cathode. The rate performance is, however, much inferior to that of LixMnO2-coated inverse Ni opals synthesisedby Zhang et al. (∼55% of 1.1C capacity at 743C). This is to be expected, as the mean pore size in the LixMnO2/nanomesh is about 40 nm which is significantly smaller than that in the LixMnO2/Ni opals (pore size of a few hundred nanometers). The small pore size lowers the diffusion rate of Li+ in the electrolyte within the electrode, which gradually becomes the rate-limiting factor during fast cycling of nanoporous electrodes. The differences in relative capacities of the nanomesh cathode are also amplified by the increased loss of active capacity after high rate cycling and prolonged charging at 4 V, as the initial discharge capacity at 1.2C in the 31st cycle was 73% of the initial discharge capacity at 1.2C in the first cycle (Fig. 5d).

Question: What's the cathode?
Answer: nanomesh
In summary, we report novel free-standing DBHF nanofibers as a highly efficient and high-performance cathode for hybrid Zn batteries. Their unique structure with a fiber-in-tube hierarchical configuration, defect-rich crystals, carbon based network and hollow spherical basic units facilitates fast electron/ion transport and ORR/OER reaction kinetics. Benefitting from the advantages of the DBHF structure and the self-supporting character, the fabricated flexible hybrid Zn battery with the DBHF cathode achieves high operating voltage, high rate capability, high energy/power density and good adaptability under different working conditions. Furthermore, its outstanding stability and high efficiency are demonstrated by five-thousand high-rate cycling. More impressively, the excellent air charging capability makes it an outstanding power source for uninterrupted power supply while altering the working environment. Therefore, this work not only provides a novel strategy to synergistically improve the efficiency and performance of hybrid Zn batteries with both Zn-ion and Zn–air modes, but also opens a new avenue to fabricate high-performance flexible batteries for different electronics under various working conditions.

Question: What's the cathode?
Answer: DBHF nanofibers
In summary, we report novel free-standing DBHF nanofibers as a highly efficient and high-performance cathode for hybrid Zn batteries. Their unique structure with a fiber-in-tube hierarchical configuration, defect-rich crystals, carbon based network and hollow spherical basic units facilitates fast electron/ion transport and ORR/OER reaction kinetics. Benefitting from the advantages of the DBHF structure and the self-supporting character, the fabricated flexible hybrid Zn battery with the DBHF cathode achieves high operating voltage, high rate capability, high energy/power density and good adaptability under different working conditions. Furthermore, its outstanding stability and high efficiency are demonstrated by five-thousand high-rate cycling. More impressively, the excellent air charging capability makes it an outstanding power source for uninterrupted power supply while altering the working environment. Therefore, this work not only provides a novel strategy to synergistically improve the efficiency and performance of hybrid Zn batteries with both Zn-ion and Zn–air modes, but also opens a new avenue to fabricate high-performance flexible batteries for different electronics under various working conditions.

Question: What's the cathode?
Answer: DBHF
With the new development of electronic products and electric vehicles, state-of-the-art lithium-ion batteries are facing a grand challenge in meeting the rapidly expanding energy demand due to their inherently limited theoretical energy density. Lithium–sulfur (Li–S) batteries, on the other hand, shown to have five times higher theoretical specific capacity and energy density, have demonstrated tremendous potential for next-generation energy storage equipment applications. In addition, the environmental benignity and economic benefits of elemental sulfur further buttress its large-scale commercial manufacture. Despite these merits, the application of Li–S batteries is still hindered by some intractable challenges: firstly, the poor resistivity of elemental sulfur will reduce the utilization of raw materials and the reaction kinetics; secondly, the excessive volume expansion (∼80%) during charging/discharging may result in inevitable evolution of structures and strain; and thirdly, lithium polysulfides (LiPSs) dissolved from the cathode can penetrate the separator and deposit on the anode surface, leading to the “shuttle effect” and anode corrosion. These issues have been the bottlenecks in the development of high-performance Li–S batteries.

Question: What's the cathode?
Answer:  lithium polysulfides (LiPSs)