bluuebunny/crossref_metadata_2025 huggingface dataset:
12V Amorphous LLTO Solid Electrolyte
Authors: Wang Yan , Zheng Zhangfeng , Liu Zi-Kui , Fang Huazhi
Published: February 2020

All solid-state rechargeable lithium battery with a solid electrolyte is recognized as one of alternative technologies for rechargeable power source, because of likely higher energy density and improved safety. High performance solid electrolyte is the bottleneck of developing solid state lithium ion batteries. In our research, amorphous lithium lanthanum titanate (LLTO) powders were prepared by a sol-gel method with an all alkoxide based route. Results showed that unlike its crystalline counterpart which turns into an electronic conductor in direct contact with lithium metal, amorphous LLTO remains to be an electronic insulator and hence is compatible with lithium metal although it also undergoes lithium insertion and the consequent reduction of Ti4+ to Ti3+. This striking difference between crystalline and amorphous LLTO could be ascribed to the atomic configuration difference, ordered versus disordered. The electronic states of a disordered system could be localized. Our results on electrochemical measurements indicated that amorphous LLTO is stable up to 12V, which can potentially be used with high voltage cathode materials.
Formation of Mono/Bi-Layer Iron Phosphate 2D-Sheets and Generation of LiFePO4 Nano-Crystals in Charge/Discharge Process for High Performance Li-Ion Batteries
Authors: Liu Tongchao , Feng Yancong , Amine Khalil , Pan Feng
Published: February 2020

Since graphene was reported by Geim and Novoselov et al.in 2004, two-dimensional (2D) layered materials (sheets) have rapidly risen to be one of the hottest topics in material science due to their attractive properties for various applications. Here we prepared mono/bi-layer iron phosphate two-dimensional (2D) materials with 0.74 nm/1.52 nm thickness by means of a simple chemically induced precipitation method and post-processing. The mechanism of growth of the atomically thin 2D-sheet crystals was investigated by experimental measurements and theoretical calculations. The crystalline 2D sheets were easily oxidized to the amorphous phase in air, and LiFePO4 nano-crystals self-nucleated from amorphous 2D sheets in the charge/discharge process. The 2D sheets show excellent performance properties as cathode materials: high initial discharge capacity of 185 mAh g-1 at 0.1 C, stable cycling (98% capacity retention over 400 cycles), and high rate capability (107 mAh g-1 at 20 C) for Li-ion storage. A model for self-nucleation of the LiFePO4nano-crystals involving double-center diffusion is discussed.

Figure 1
Enhanced High Rate Performance of a NaTi2(PO4)3/Reduced Graphene Oxide Composite Electrode Via Pyro Synthesis for Sodium Ion Batteries
Authors: Song Jinju , Park Sohyun , Gim Jihyeon , Kim Sungjin , Jo Jeonggeun , Mathew Vinod , Kim Seokhun , Kim Jaekook
Published: February 2020

The present study reports on a highly rate capable NASICON-structured NaTi2(PO4)3/ reduced graphene oxide (NTP/rGO) composite electrode synthesized by polyol-assisted pyro synthesis for Na-ion batteries (NIBs). X-ray diffraction (XRD) studies confirmed the presence of a rombohedral NaTi2(PO4)3  phase in the composite while Raman spectroscopy studies helped to identify the existence of rGO in the composite. Electron microscopy studies established that NaTi2(PO4)3  nanoparticles of average sizes ranging between 20 and 30 nm were uniformly distributed and embedded on the GO sheets. When tested for sodium storage properties, the obtained NTP/rGO composite electrode registered high rate capacities (95 mAh g-1 at 9.2 C and 78 mAh g-1 at 36.8 C) when compared to that of the NTP/C electrode (~1 mAh g-1 at 9.2 and 36.8 C). The enhanced performance of the composite electrode can be attributed to the nano-sized NaTi2(PO4)3 particles with shorter diffusion path lengths embedded on the rGO sheets with enhanced electrolyte/electrode contact areas that ultimately leads to an improvement in the electrical conductivity at high current densities. Ex-situ XANES studies confirmed reversible Na-ion intercalation/de-intercalation into/from NTP/rGO. The study thus demonstrates that the NaTi2(PO4)3/rGO nanocomposite electrode is a promising candidate for the development of high power/energy density anodes for NIBs.
NaxCo1-YTiyO2 : A New Cathode Material for High Energy Density Sodium Ion Batteries
Authors: Sabi Noha , Doubaji Siham , Solhy Abderrahim , Larzek Mohamed , Hashimoto Kazuki , Komaba Shinichi , Saadoune Ismael
Published: February 2020

Abstract:

Energy storage has become a key issue concerning our welfare in daily life; the increasing claim for powering systems has conducted energy storage to become a figuring topic.

In this regard, lithium-ion battery technology has attracted a respectful interest thanks to its suitable and attractive properties as a powerful source for high voltage applications such as cellular phones, digital cameras and hybrid electric vehicles.

Unfortunately, the little abundance of this alkali metal in the earth’s crust, its evil extraction impact on the environment, restricted its use in lithium ion batteries. In this context, sodium has drawn a wide attention thanks to its abundant resources and low cost. Sodium has a larger ionic radius (1,02 Å) and higher redox potential (-2,71 V vs SHE) of Na+/Na compared to  Li and  operates in a similar fashion. 

In the last decades, NaxCoO2was studied as an electrode material and exhibits promising performances. Nevertheless, it presents nine potential steps during the intercalation/de-intercalation process which could be considered a drawback of this electrode material.

Indeed, we investigated the NaxCo1-yTiyO2 solid solution with the aim to obtain better performances with reduced cost. P2-Na2/3Co1/2Ti1/2O2 selected phase was synthesized by solid-state method. This material offers a specific capacity of 100 mAh/g in the [2-4.2V] potential window. A good capacity retention of the Na// Na2/3Co1/2Ti1/2O2 cell was recorded with a coulombic efficiency approaching 99%. An ex-situ XRD study on the NaxCo1/2Ti1/2O2 sample evidenced that the P2-type structure is preserved until the end of the charge process where a structural transformation occurs leading to structurally faulted oxidized phase.

Key words: Na-ion batteries, NaxCo1-yTiyO2, Energy storage, Ex-situ study.

Acknowledgments:

The financial assistance  of the office Chérifien des Phosphates in the Moroccan Kingdom (OCP group): The authors are hereby acknowledged. Ms N. SABI is grateful to Mohammed VI Polytechnic University for the scholarship. 

References:

Yabuuchi, N., Kubota, K., Dahbi, M., Komaba,S. (2014), Research Development on Sodium-Ion Batteries,Chem. Rev., 23, 11636-11682.

Kubota, K., Komaba,S. (2015), Practical Issue and Future Perspective for Na-Ion Batteries, Electrochemical Society., 14, 2538-2550.  

Clément, J., Bruce, G., Grey, P.(2015),Manganese-Based P2-Type Transition Metal Oxides as Sodium-Ion Cathode Materials, Electrochemical Society., 14, 162, 2589-2604.

Figure 1
Efficiency and Long-Term Cycling Study of Carbon Anode Materials in Sodium-Ion Batteries
Authors: Bommier Clement , Ji Xiulei , Surta Wesley , Jian Zelang , Li Zhifei , Dolgos Michelle
Published: February 2020

Recently, there has been much discussion about Na-ion batteries (NIBs) emerging as one ideal technology for grid-level energy storage.  Large-scale usage of NIBs can be sustainable as the raw materials involved in making such batteries are cheap, plentiful and non-toxic.  Thus far, they have demonstrated very promising electrochemical performances in prototype experiments.

Despite the aforementioned benefits, there still remain technical issues associated with the electrode materials, which is currently hindering their development as a fully-functional commercial battery.  One of these pressing problems is the efficiency and cyclability of the anode material: an ideal material must possess both a high 1st cycle coulombic efficiency and a stable long-term cycling life—as both of these are crucial to the performance of the battery.  However, most candidate materials currently proposed in the literature do not meet such criteria.

Herein, we study self-standing cellulose-derived carbon as a model carbon, where we attempt to understand factors affecting coulombic efficiency and long-term cycling.  This material displays one of the highest reported coulombic efficiencies for carbon-based anodes in the literature, with values averaging near 90% for the first cycle with a deep-sodiation in a half-cell.  On the other hand, the carbon material also displays extremely poor rate and long-term cycling performances, which leads us to an in-depth investigation of the fading mechanism of carbon materials used as NIB anodes.

Through the course of our investigation on the fading mechanism, we are able to uncover some structural-property relationships to understand the capacity loss during long-term cycling.  This was elucidated through the use of traditional characterization methods such as XRD, Raman spectroscopy and XPS measurements along with more advanced TEM characterization, using sample “lift-outs” to probe the structural effects of long-term cycling on the carbon material.  These claims are also further supported through electrochemical data including diffusivity tests, CV and EIS measurements.  Using the information learned on the efficiency/long-term decay mechanism, we were able to devise ‘proof-of-concept’ solutions to increase long-term cycling of carbon anode materials utilized in NIBs.
A High-Power Symmetric Na-Ion Pseudocapacitor
Authors: Jian Zelang , Raju Vadivukarasi , Li Zhifei , Xing Zhenyu , Hu Yong-Sheng , Ji Xiulei
Published: February 2020

Electrochemical batteries and capacitors are important devices for electrical energy storage with wide applications from portable electronics to transportation, and to grid.  However, rechargeable batteries are typically limited in poor power density, while supercapacitors deliver low energy density.  One “Holy Grail” of energy storage is to have an energy density up to the level of Li-ion batteries and a power density and cycling life identical to supercapacitors.  Here we design a novel symmetric Na-ion pseudocapacitor with a power density exceeding 5.4 kW/kg at 11.7 A/g, a cycling life retention of 64.5% after 10,000 cycles at 1.17 A/g, and an energy density of 26 Wh/kg at 0.585 A/g.  Such a device operates on oxidation-reduction reactions occurring on both electrodes with an identical active material, viz., Na3V2(PO4)3 encapsulated inside nanoporous carbon.  This device, in a full-cell scale utilizing highly reversible, high-rate, cost-effective Na-ion intercalational pseudocapacitance, can bridge the performance gap between batteries and supercapacitors.  The characteristics of the device and the potentially low-cost production make it attractive for hybrid electric vehicles and low maintenance energy storage system.
Advanced Polymer Binder for Silicon Anodes Based High Energy Density Lithium Ion Battery
Authors: Zou Feng , Zhu Yu
Published: February 2020

The state-of-the-art lithium ion batteries (LIBs) do not have sufficient specific energy for emerging applications such as electrical vehicles. One route to increase the energy density of LIBs is the use of a silicon-based anode. Unlike conventional graphite anodes, which only have capacity of one lithium ion per six carbon atoms (372 mA-h/g), silicon-based anodes have a theoretical capacity of 4.4 lithium ions per silicon atom (4,200 mA-h/g). These results indicate that the Si anode offers great promising for achieving high specific energy LIBs. However, silicon-based anodes have yet to achieve widespread adoption or commercialization due to the large volume change that occurs upon lithiation/delithiation, resulting in severe electrode pulverization and degradation. In this work, novel polymer binder materials mitigating the volume expansion of the Si particles were developed. These binder materials were applied in half-cell and the batteries exhibited excellent cyclability. The battery exhibited area capacity over 1.5 mAh/cm2 and negligible degradation in the first 100 cycles. The first cycle coulombic efficiency is over 80%.

Figure 1 LIBs with commercial binder and UA binder. UA binder provides better cyclability at higher mass loading.

Figure 1
Effects of Electrolyte/Sulfur Ratio on Li2S Electrodeposition Kinetics in Li-S Batteries
Authors: Fan Frank , Chiang Yet-Ming
Published: February 2020

Li2S electrodeposition poses a number of challenges due to slow redox kinetics, the formation of electronically disconnected material, and the fact that Li2S is an electronic insulator. This process is also responsible for the majority of the capacity in a Li-S battery, so it is therefore important to understand and improve its kinetics. Recently we have demonstrated that Li2S electrodeposition occurs by a surface-limited 2-D island nucleation and growth process.1

Here, the kinetics of Li2S deposition on carbon from polysulfide solutions of various concentrations (in DOL:DME 1:1) were characterized potentiostatically. In general, higher polysulfide concentrations were found to result in significantly slower electrodeposition. High polysulfide concentrations can be expected in Li-S batteries with low electrolyte/sulfur (E/S) ratios, as large amounts of electrolyte tend to dilute the polysulfide. We galvanostatically cycled Li-S cells with different E/S ratios and found that a low E/S ratio does indeed result in significantly higher polarization, especially at the beginning of the Li2S precipitation plateau when nucleation of Li2S occurs.

This has significant implications for the design of sulfur cathodes, as low E/S ratios are essential for high energy density Li-S batteries.2 It is therefore necessary to improve electrodeposition kinetics at high polysulfide concentrations. Some strategies for doing so include redox mediators, as well as the use of alternative conducting substrates such as conducting oxides with higher affinities for Li2S.

 Figure: (a) Potentiostatic current vs. time curves for Li2S deposition from various concentrations (in molarity of sulfur) of polysulfide at 2.05V vs. Li/Li+. Wider peaks at higher concentrations indicate slower nucleation and growth. (b) Galvanostatic cycling of sulfur-carbon composite cathodes vs. Li at C/8 at various E/S ratios. 

References

1. F. Y. Fan, W. C. Carter, and Y.-M. Chiang, Adv. Mater., 27, 5203–5209 (2015) http://doi.wiley.com/10.1002/adma.201501559.

2. D. Eroglu, K. R. Zavadil, and K. G. Gallagher, J. Electrochem. Soc., 162, A982–A990 (2015).

Figure 1
Rechargeable Nonaqueous Aluminum Sulfur Battery
Authors: Gao Tao , Noked Malachi , Xu Kang , Wang Chunsheng
Published: February 2020

Rechargeable aluminum batteries attracted growing attentions in recent years as one candidate beyond lithium ion battery system. This is due to the great potential of aluminum metal anode owing to its high capacity (2.98 Ah/g and 8.05 Ah/cc), its negative electrochemical potential (-1.67 V vs. NHE), and its highest abundancy among metals in earth crust. Moreover, aluminum has significantly lower reactivity towards moisture and air compared to Li, Na and Mg. Reversible Al deposition/stripping in room temperature is extremely challenging due to the tendency of Al to form real passivation on its surface with both poor ionic and electronic conductivity. Nevertheless, use of aluminum anode was shown to be possible by in ionic liquid based electrolyte (RTIL-AlCl3) with up to 100% coulombic efficiency for aluminum deposition/stripping.

As a high capacity cathode material (1,675 mAh/g), sulfur has attracted intense interest in Li/S, Mg/S and Na/S systems. A rechargeable Al/S battery is also of great interest because the full cell capacity could achieve 1072 mAh/g-(total electrode mass) and voltage could achieve ~1.25 V, estimated from the Gibbs formation energy of Aluminum sulfide( -724 kJ/mol). The gravimetric energy density is hence 1340 Wh/kg, over three times of a commercial LiCoO2/graphite cell and close to that of a Li2S/silicon cell. The high energy density and low cost of both Al and S makes Al/S system a very promising battery chemistry for large scale applications like electric vehicle and grid storage.  Motivated by the potential, Cohn et al. recently demonstrated a proof-of-concept non-aqueous Al/S battery. Though demonstrating close to theoretical capacity with operating voltage of 1.2 V, the reported Al/S cell cannot be recharged, resulting in the loss of all capacity within three cycles. Up to now, there was no demonstration of reversible Al/S battery, probably due to the inability to recharge AlSx.

In this work, we demonstrate a reversible Al/S cell with specific cathode capacity of ~1200 mAh/gs for over 20 cycles. Kinetics analysis point out the system is limited by slow diffusion of Al containing anion due to the high viscosity of the ionic liquid electrolyte. Raising temperature is proved to be an effective approach to mitigate the kinetic limitation thus decrease the hysteresis during charge and discharge. Spectroscopic and microscopic observations explore the mechanism of sulfur redox in the RTIL-AlCl3 electrolyte and enabled us to monitor the interfacial processes on both the cathode and anode. We believe that the new scientific insights obtained in this work will demonstrate inspiring progress on the way to realize a rechargeable Al/S battery.
Lightweight Polyanion Frameworks for Li- and Mg-Ion Batteries
Authors: Glass Hugh F J , Dutton Siân E , Grey Clare P.
Published: February 2020

Mg-ion batteries are a promising “beyond Li-ion” technology as they offer high theoretical capacities, use cheap and abundant materials, and Mg metal can be used as the anode.1 However, the search for high voltage cathodes has been hindered by electrolyte incompatibility and sluggish kinetics which can impede intercalation and charging rates.2

MgMB2O5 (M = Mn, Fe, Co) are shown to be high voltage, high capacity cathode materials for both Li- and Mg-ion batteries. The open structure facilitates ion diffusion while the light weight polyanion framework increases capacity and voltage. The materials are produced from metal oxalate and boric acid starting materials via a solid state synthesis process. The Mg:M ratio can be altered to manipulate capacity and ordering of the cations.

Mg can be fully removed from MgMnB2O5 giving a capacity of up to 300 mAhg-1 while maintaining the structure. Removal of Mg is confirmed by refinement of powder neutron diffraction data. In a full Mg-ion cell a reversible discharge capacity of ~100 mAhg-1 has been achieved. However, due to the incompatibility of the cell with available electrolytes this is accompanied by irreversible side reactions on charge. Some promising resolutions to the electrolyte problem are discussed. Mg can also be removed from the structure when M = Co or Fe, with the change in transition metal leading to a change in operating voltage. The results presented show that this class of material is a promising candidate for a high capacity, high voltage Mg-ion cathode material.

In a Li-ion battery 1.5 Li can be intercalated into the manganese based material after Mg has been removed, giving a specific capacity of up to 250 mAhg-1 above 1.5 V. The capacity is retained over hundreds of cycles with little drop off observed even at rates of 5C. Ex-situ XRD shows a doubling of the unit cell when the material is cycled, suggesting charge ordering is occurring. Neutron diffraction refinements show a change in volume of ~2%, associated with insertion or removal of Li ions.

References:

1: H.D. Yoo, I. Shterenberg, Y. Gofer, G. Gershinsky, N. Pour and D. Aurbach, Energy Environ. Sci., 2013,6, 2265-2279 DOI: 10.1039/C3EE40871J

2: C. Bucur, T. Gregory, A. Oliver, J. Muldoon, J. Phys. Chem. Lett., 2015, 6 (18), pp 3578–3591 DOI: 10.1021/acs.jpclett.5b01219
Synergistic Suppression of Polysulfide Diffusion By Functional 2D Carbon Coating for Advanced Lithium-Sulfur Batteries
Authors: Jeong Yo Chan , Yang Seung Jae , Kim Jae Ho , Park Jisoo , Kim Yern Seung , Park Chong Rae
Published: February 2020

Lithium-sulfur batteries have been significantly studied owing to a high theoretical specific capacity of 1672 mAh g-1. However, the fast capacity fading issue which mainly stems from both polysulfide dissolution into the bulk electrolyte followed by notorious ‘shuttle reaction’ and insulating nature of sulfur are hindering commercialization of lithium-sulfur batteries. Different types of porous materials were investigated to encapsulate the soluble polysulfide species into the pore by physically and/or chemically adsorption, thus the polysulfide species are able to stay in the cathode side. In addition, electrolyte additives such as lithium nitrate and separator coating with various materials were also attempted. Among them, separator coating strategies seemed to be very effective in inhibiting polysulfide diffusion when the effect is evaluated on the basis of the areal unit scale. Furthermore it can be easily scaled up. For example, roll-to-roll process can be utilized in fabricating polysulfide-trapping material-coated separators.

In the aspect of separator oriented strategy, diverse carbon materials such as carbon black [1], carbon nanotubes [2], reduced graphene oxides [3], and microporous carbons [4] were investigated as a polysulfide trapping layer. These attempts were based on the attractive interaction to anchor the polysulfide species in the cathode side. We realized that repulsive force might be also effective in restricting polysulfide species in the cathode side during the electrochemical reactions as illustrated in Figure 1.

Here, we report a facile and effective way to suppress the polysulfide diffusion by introducing a repulsion interaction rather than an attractive interaction on the cathode side of separator. Fluorine functionalized graphene layers were examined as a potential candidate for repulsing polysulfide species from the separator. In addition to the chemically repulsive interaction, 2D shapes of fluorinated graphene layers enhance the effect of polysulfide blocking layers by increasing the diffusion length through the separator. The synergistic effect of chemical and physical nature of the functionalized carbon material led to the improved electrochemical performance. To understand the improved performance, RAMAN, XPS, SEM, AFM and EIS characterizations were conducted.

[1] Adv. Funct. Mater. 2014, 24, 5299

[2] J. Phys. Chem. Lett. 2014, 5, 1978

[3] J. Power Sources 2013, 242, 65

[4] Adv. Mater. 2014, 26, 7352

Figure 1
Ti4O7-Filled Nitrogen-Doped Carbon/Ti4O7 Double-Layer Spheres As Sulfur Host for Advanced Lithium Sulfur Batteries
Authors: Xu Hui , Yang Yuebin , Su Jingyang , Chen Guohua
Published: February 2020

Holding the largest market share, Li-ion batteries have been optimized for the post two decades, although their capacity is limited by the energy density of intercalation materials to ~300 mA h g-1. New chemistries are being sought as the next-generation energy storage device with higher energy density and reduced cost. Lithium-sulfur batteries, with their environmental benignity, competitive cost and high theoretical energy density (~2600 Wh kg-1), were intensively investigated in recent years as a promising candidate to replace the current lithium ion batteries. In this study, nitrogen-doped hollow carbon spheres (NC) with conducting Magnéli-phase Ti4O7 as the filling agent were designed delicately by employing one-step approach to reduce TiO2 and carbonize polydopamine on pre-synthesized SiO2 spheres as the sacrificial template, followed by the infiltration of sulfur at 155oC. The properties and performance of the composite (NC/Ti4O7/S) were examined and evaluated as the cathode material for lithium sulfur (Li-S) batteries. It was demonstrated that the sulfur particles could be well contained in the NC/Ti4O7 shells with the sulfur content being ~70%, while the particle size and thickness of the carbon shell can be easily tuned by controlling the reactant concentration and reaction time. The assembled battery exhibited an initial capacity of ~938 mAh g-1 at 0.5 C with a high retention rate of 94.8% after 100 cycles, which corresponds to a capacity decay of 0.052% per cycle. The NC/Ti4O7/S composite provides a promising cathode material for future lithium sulfur batteries.

Figure 1
Understanding Divalent Cation Intercalation into a Spinel-Type Mn2O4 Host Framework
Authors: Nolis Gene M , Adil Abdullah , Yoo Hyun Deog , Phillips Patrick J , Bayliss Ryan D , Klie Robert F , Cabana Jordi
Published: February 2020

Li-ion batteries dominate the mobile device market due their high energy density; and their application is being extended to the automotive and grid storage industries. However, charge storage limitations limit the applicability of classic Li-ion technologies into these new markets, thus triggering interest in new energy storage concepts. Multivalent ion intercalation is an attractive alternative because, while conceptually similar to Li-ion, they store more charge per intercalated species and observe less dramatic structural rearrangement in the host. Recently, reversible electrochemical Mg intercalation into spinel-type Mn2O4 has been reported, where Mg2+ ions occupy vacant tetrahedral sites [1]. First principles calculations by Lui et al. argue that other multivalent ions (i.e. Ca2+, Zn2+, Al3+, Y3+) may be intercalated into spinel host framework to yield high voltage cathode materials for multivalent batteries [2].

In this work, cubic phase Mn2O4 was prepared electrochemically by delithiating commercially available spinel-type LiMn2O4 in a non-aqueous environment. Following, Mn2O4electrodes were reduced in concentrated aqueous solutions of Ca-, Mg- and Zn nitrate to -0.4 V/SCE. As-prepared electrodes were characterized using powder x-ray diffraction. As shown in the figure, the cubic structure is preserved upon delithiation and significant structural changes occurred upon reduction; indicating the formation of a tetragonal spinel (likely tetrahedral site occupation) in addition to the parent cubic phase.  X-ray absorption spectroscopy and atomic resolution microscopic methods will also be used to help understand the structural changes as these divalent cations are intercalated into a spinel host framework.

References:

Kim, C., et al., Adv. Mater. 2015, 27, 3377

Miao, L., et al.,
Energy Environ. Sci. 2015, 8, 964

Figure 1
Degradation Mechanisms of Magnesium Metal Anodes in a (CF3SO2)2N- (TFSI)-Based Mg-Ion Electrolyte
Authors: Yoo Hyun Deog , Han Sang-Don , Nolis Gene M , Bayliss Ryan D , Burrell Anthony K. , Cabana Jordi
Published: February 2020

Efficiently using anodes based on the deposition of light metals would be a breakthrough that would produce leaps in energy density of rechargeable batteries. Magnesium is one of such metal electrodes that are not susceptible to dendrite formation. This unique property stems from (1) the thermodynamic stability in Grignard-based electrolytes and (2) the inherent preference to form three-dimensional deposits. However, the use of Grignard-based electrolytes results in severe chemical reactions between the nucleophilic electrolytes and electrophilic cathodes such as oxide materials. Accordingly, a lot of effort has been paid to find non-nucleophilic electrolyte solutions that deposit and dissolve Mg metal reversibly.

Among non-nucleophilic anions, bis(trifluoromethylsulfonyl)imide (CF3SO2)2N–, TFSI) anion has shown exceptional stability on Mg metal anode. And the ethereal solution of the magnesium salt (MgTFSI2) has shown quite reversible Mg metal deposition and dissolution with coulombic efficiency of ~90% and reasonable voltage stability window of about 3 V. The most important difference from the Grignard-based electrolytes is that the TFSI-based electrolyte solution is non-nucleophilic and possibly compatible with oxide cathodes, which can increase the voltage and energy density of Mg rechargeable batteries.

Herein, we report the mechanisms of degradation in the Mg metal anode and electrolyte after hundreds of cycles at high current density of 2 mA/cm2. Although the Mg metal anode operated without a significant problem at current densities lower than 0.1 mA/cm2, degradation was evident after long-term cycling at high current density. Overall, the Mg metal became mechanically brittle, with microscopy showing extremely porous structures (Fig. 1a). In addition, large hemispherical deposits up to several hundred micrometers were scattered or aggregated at the Mg surface (Fig. 1b). In turn, the color of the electrolyte turned to dark brown upon cycling, indicating a change in the chemical structure of the solvent. The macroscopic consequence was the short circuiting of the cells after several cycles at a high current density. These results suggest that the lemma of dendrite-free metal deposition is possible when the system meets several conditions such as absolute chemical stability of the metal in the electrolyte, adequate level of current density and charge density, and other engineering factors such as organic or inorganic additives that complexes with the metal ion and lead to more uniform metal deposition. Those understandings will serve as step stones to get to non-nucleophilic electrolytes, in which metal anodes operate without dendrite formation.

Figure 1
Replacement of Carbon with TiO2 Electrodes By Tuning Electronic Conductivity and Porosity for Stable Li-O2 Batteries
Authors: Nam Seunghoon , Kang Joonhyeon , Kim Chunjoong , Hyun Seungmin , Park Byungwoo
Published: February 2020

Although carbon is ubiquitously used as the basis of the cathode, its use in Li-O2 battery is still problematic in that carbon decomposes on charge above 3 V vs. Li/Li+, and leads to electrolyte decomposition on both discharge and charge, rendering it unsuitable for aprotic Li-O2 cells.  Meanwhile, a pioneering work from Bruce et al., [1] suggested that carbon be replaced with TiC which promoted reversible formation of Li2O2.  By the way, it is open to debate that the stability of TiC originates from the TiO2 at the surface, and TiO2 itself can be an air cathode, provided that the electrical conductivity is guaranteed.  For this reason, porous TiO2 [2] with some deliberate oxygen vacancies [3] was synthesized so that the electrode exhibited large surface area with moderate electronic and ionic conductivity.  The porous black electrode showed a stable cycle-life performance, and the polarization during the decomposition of Li2O2 is greatly improved.  Therefore, it is expected that the electronic conductivity- and porosity-tuned TiO2 can be a suitable substrate for Li-O2 chemistry.  Finally, the origin of high stability of this porous black TiO2 as an air cathode is also investigated.

[1] M. M. Ottakam Thotiyl, S. A. Freunberger, Z. Peng, Y. Chen, Z. Liu, and P.G.Bruce, Nat. Mater. 12, 1050 (2013).

[2] J.-H. Shin, J.-H. Kang, W.-M. Jin, J. H. Park, Y.-S. Cho, and J. H. Moon, Langmuir, 27, 85 (2011).

[3] X. Chen, L. Liu, and F. Huang, Chem. Soc. Rev. 44, 1861 (2015).
Highly Stable Carbon-Free Ag/Co3O4 Cathodes for Li-Air Batteries with Aqueous Alkaline Electrolyte: Electrochemical and Structural Investigations
Authors: Wittmaier Dennis , Wagner Norbert , Friedrich K. Andreas
Published: February 2020

The operation of a secondary lithium-air battery requires to run the battery in oxygen reduction reaction (ORR) as well as in oxygen evolution reaction (OER). OER represents the charge reaction and requires a sufficient catalyst for oxygen evolution. Currently carbon materials are widely used in cathodes of aqueous alkaline lithium-air batteries due to their high electronic conductivity, stability, relatively low costs and catalytic activity towards oxygen reduction reaction (ORR) [1, 2]. However, carbon-based cathode materials are non-stable in the potential range of OER as they start to corrode at potentials higher than open circuit voltage (OCV) [3, 4]. Corrosion leads to high degradation corresponding to successive capacity loss and ultimately destruction of the cathode. To improve long-term stability and reduce side reactions such as H2 and CO2 evolution carbon-free bifunctional cathodes for aqueous alkaline lithium-air batteries are of need [5, 6]. In this poster we present cathodes with a combination of Ag and Co3O4. Those were prepared with a dry-processed and solvent-free preparation method [7, 8]. Electrocatalytic activity regarding both ORR and OER was investigated by cyclic voltammetry (CV) for up to 300 cycles in half-cells. In addition structural and surface characteristics were investigated by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). These combined measurements give new insights in the materials’ oxidation states and the stability of Ag oxides in Ag/Co3O4 cathodes throughout a complete battery cycle [9]. Cathodes with the combination of Ag and Co3O4 show high activity for both reactions ORR and OER and a significant improvement in performance compared to both pure Ag and pure Co3O4 cathodes. Long-term tests show superior stability of the bimetal cathodes [6].

[1] H. Ohkuma, I. Uechi, M. Matsui, Y. Takeda, O. Yamamoto, N. Imanishi, J. Power Sources 245 (2014) 947.

[2] H. Arai, S. Müller, O. Haas, J. Electrochem. Soc. 147 (2000) 3584.

[3] P. N. Ross, M. Sattler, J. Electrochem. Soc. 135 (1988) 1464.

[4] P. N. Ross, H. Sokol, J. Electrochem. Soc. 131 (1984) 1742.

[5] D. Wittmaier, T. Danner, N. Wagner, K. A. Friedrich, J. App. Electrochem. 43 (2013) 73.

[6] D. Wittmaier, N. Wagner, K. A. Friedrich, H.A. Amin, H. Baltruschat, J. Power Sources 265 (2014) 299.

[7] D. Wittmaier, N. Wagner, H.A. Amin, H. Baltruschat, Patent App. PCT/EP2015/053586.

[8] D. Wittmaier, N. Wagner, H.A. Amin, H. Baltruschat, Patent App. DE 102014102304 A1.

[9] D. Wittmaier, Natalia A. Canas, I. Biswas, K. A. Friedrich, Adv. Energy Mater. 2015, doi: 10.1002/aenm.201500763.
Dynamic Modeling of the Reaction Mechanisms in a Li/O2 Battery Cell
Authors: Grübl Daniel , Mayur Manik , Bessler Wolfgang G.
Published: February 2020

Extensive research efforts on metal-air batteries are being carried out due to their high theoretical energy density. Specifically, the lithium-oxygen (Li/O2) based batteries have drawn attention of the researchers as a promising alternative to Li-ion batteries for long range electric vehicles. However, this system suffers from high overpotentials during charge, indicating asymmetrical charge/discharge reaction mechanisms. High charge overpotentials lower the energy efficiency and can increase potential-driven side reactions (e.g., electrolyte decomposition). Furthermore, the discharge product forms as a new solid phase in the cathode by a nucleation and growth process, which is in general different from lithium-ion battery technologies. Thus, a detailed understanding of the reaction mechanism is crucial for enhancing battery performance and durability.

Our approach towards understanding the charge/discharge reaction mechanism is by development and exploitation of a continuum model of a lithium-oxygen cell [1]. The one-dimensional computational domain consists of a gas reservoir filled with oxygen, a porous carbon cathode flooded with an organic electrolyte, a porous separator, and a lithium metal anode. We present a multi-step reaction mechanism of the electrochemistry in the cathode, consisting of O2 dissolution, O2 reduction, LiO2 precipitation, LiO2 disproportionation during discharge (Figure 1, left), as well as Li2O2 electrostripping during charge. In particular, the mechanism is asymmetric with respect to discharge and charge. The model is parameterized by experimental Swagelok cells [2] and galvanostatic cycling simulations are compared to experimental data. Furthermore, possible reasons for the high charge overpotential are analyzed, options to reduce the charge overpotential (e.g. redox mediator) are discussed, and a charge reaction mechanism including a surface-mediated Li2O2 dissolution is proposed (Figure 1, right). 

[1] D. Grübl, B. J. Bergner, J. Janek and W. G. Bessler, “Dynamic Modeling of the Reaction Mechanism in a Li/O2Cell: Influence of a Redox Mediator,” ECS Transactions 69(19), 11-21 (2015).

[2] B. J. Bergner, A. Schürmann, K. Peppler, A. Garsuch, and J. Janek, “TEMPO: A Mobile Catalyst for Rechargeable Li-O2 Batteries,” J. Am. Chem. Soc. 136, 15054–15064 (2014).

Figure 1
Solvation Structure of Zinc-Based Electrolytes from X-Ray Absorption Spectroscopy
Authors: Kim Soojeong , Han Sang-Don , Balasubramanian Mahalingam , Fister Timothy T
Published: February 2020

Multivalent (e.g., Mg2+, Ca2+ and Zn2+) metal cells using a nonaqeous electrolyte are potential candidates for post-lithium-ion batteries. However, the development of multivalent electrolytes is challenging due to its poor compatibility with both the metal anode and higher voltage cathode chemistries, leading to poor coulombic efficiency, formation of passivation layer on the metal anode, etc. Defining the connection between the electrochemical properties of a multivalent electrolyte system with its molecular scale structure is a crucial step for developing these new chemistries. Here we use X-ray absorption fine structure (XAFS) spectroscopy to determine the solvation structure of zinc-based electrolytes with varying solvent species and concentrations. To explore the role of ion-pairing, the results are compared to first principle simulations of the electrolyte and electrochemical data.
Novel Cathode Materials for Rechargeable Magnesium Ion Batteries
Authors: Wang Lu , Vullum-Bruer Fride
Published: February 2020

Over the past few years, considerable effort has been devoted to the development of new energy storage devices with high power and energy density to substitute Lithium-based batteries, because the predicted high demand associated with many large-scale applications has generated serious concerns regarding the safety and sustainability of metallic Li.[1] In particular, Mg ion battery (MIB) has been regarded as the most promising candidate because of its ‘green’ character, high natural abundance in the Earth’s crust (13.9% as compared to 7*10-4 % for Li), and chemical stability.[2] In comparison with Li, Mg is inherently much safer due to its stability in air and lack of dendritic formation during electrochemical cycling.[3] Also, compared to Li, Mg has a theoretical volumetric capacity of 3833 mAh cm-3, nearly twice that of Li (2061 mAh cm-3), indicating that MIB has a good potential for reaching a high volumetric energy density.[4,5] However, it is still in high demand to find the electrode materials that unites with metallic Mg and fulfil requirements such as high specific capacity, power density, rate performance and good cyclability.[2,6,7]

Here, we report several novel cathode materials, Mn3O4 nanoparticles, Mn3O4/graphene nanocomposite, Fe3O4 nanoparticles and microwave exfoliated graphite oxide (MEGO). The studies of Mg-battery performances were carried out in a standard coin cell which the synthesized materials as cathode, magnesium ribbon as anode, glass fibre as separator and (PhMgCl)2-AlCl3/THF as electrolyte. The electrochemical performance was evaluated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge techniques.

References:

[1] L. G. Lu, X. B. Han, J. Q. Li, J. F. Hua and M. G. Ouyang, J. Power Sources, 2013, 226, 272.

[2] E. Levi, Y .Gofer and D. Aurbach, Chem. Mater., 2010, 22, 860.

[3] J. O. Besenhard and M. Winter, ChemPhysChem, 2002, 3, 155.

[4] M. Matsui, J. Power Sources, 2011, 196, 7048.

[5] C. Ling, D. Banerjee and M. Matsui, Electrochim. Acta, 2012, 76, 270.

[6] H. D. Yoo, I. Shterenberg, Y. Gofer, G. Gershinsky, N. Pour and D. Aurbach, Energy Environ. Sci., 2013, 6, 2265.

[7] I. Shterenberg, M. Salama, Y. Gofer, E. Levi and D. Aurbach, MRS Bull., 2014, 39, 453.
Impact of the Water Content in Glyme-Based Electrolyte to Rechargeable Magnesium-Organic Battery
Authors: Senoh Hiroshi , Shimizu Ryo , Uchida Makoto , Sano Hikaru , Sakaebe Hikari , Yao Masaru , Takeichi Nobuhiko , Kiyobayashi Tetsu
Published: February 2020

Rechargeable magnesium battery can be a candidate of the next-generation batteries because magnesium has a higher volumetric capacity, is more abundant in terms of the resources, and is less reactive in air than lithium. We previously found that a redox-active organic compound, 2,5-di­methoxy-1,4-benzo­quinone (DMBQ), has the potential to serve as the positive electrode material for the Mg system1. Recently, we have investigated two kinds of electrolytes, sulfone-based and glyme-based electrolytes2-3, for the rechargeable magnesium-organic batteries. In the case of monoglyme-based electrolyte, the discharge voltage of the Mg-DMBQ cell significantly increases, not decreases, after a few cycles, for which, we found, a decrease in the overpotential for the Mg dissolution upon cycling is responsible3. However, what caused the decrease in the overpotential on the Mg negative electrode is not clear. In the present study, we report the impact of the water content in the monoglyme-based electrolyte to the rechargeable Mg-organic battery.

     Magnesium bis(trifluoromethane sulfonyl)amide (Mg(TFSA)2) and monoglyme were purchased from Kishida Chemical and used without further purification. The electrolyte was prepared by dissolving 0.5 mol L-1 of Mg(TFSA)2 in monoglyme. The water content of the as-prepared electrolyte was 40 ppm. Two other electrolyte solutions were prepared in which pure water was deliberately added to 100 and 1000 ppm. The electrochemical cells were set up and tested based on our previous study3.

     The specific conductivities of water-added 0.5 mol L-1 Mg(TFSA)2/monoglyme did not shift from that of the as-prepared. The discharge and charge curves of the cells in the electrolytes at various water contents showed that in all three cases the first discharge curve has two potential plateaus below 0.7 V. In the case of the water-added electrolytes, the discharge voltage during the second cycle significantly increased, while in the as-prepared electrolyte the discharge voltage remained below 0.7 V even after several cycles. The drastic dissolution of Mg from the surface of the negative electrode was observed by SEM only in the water-added electrolytes. A certain amount of water plays an important role in preparing the surface of the electrode to let Mg dissolve in the electrolyte.

1. H. Sano et al., Chem. Lett., 41, 1594 (2012).

2. H. Senoh et al., J. Electrochem. Soc., 161, A1 (2014).

3. H. Senoh et al., ECS Transactions, in press.
Metal Hybrid Supercapacitors Based on a Rocking-Chair Mechanism
Authors: Yoo Hyun Deog , Han Sang-Don , Bayliss Ryan D , Gewirth Andrew A , Burrell Anthony K. , Cabana Jordi
Published: February 2020

Supercapacitors can provide high rate capability and long-term cycleability, thanks to their simple mechanism based on the adsorption and desorption of ions on the surface of electrodes. It is possible to charge or discharge supercapacitor cells in a minute for 10,000 cycles without notable degradation. Based on the high power characteristics, supercapacitors can augment the batteries or fuel cells for electric vehicles or heavy equipment. So far, most of supercapacitors have symmetric configuration with activated carbon electrodes as the positive and negative electrodes (Fig. 1a). And they follow a Daniell-type mechanism, where the electrolyte is depleted of and replenished with ions upon charging and discharging, respectively (Fig. 1b). In this mechanism, electrolyte serves as an ionic reservoir, from which cations and anions are separated to negative and positive electrodes, respectively. As a result, sufficient volume of electrolyte is indispensable for the operation of supercapacitors. This leads to a limitation in energy density and an increase in the internal resistance as the starvation of the concentration of salts in the electrolyte decreases during operation.

Herein, we introduce a hybrid supercapacitor that follows a ‘rocking-chair’ mechanism for the first time. This hybrid supercapacitor is composed of metal anodes and activated carbon as the negative and positive electrodes, respectively (Fig. 1c). Metal (M, e.g. Mg or Zn) ions are replenished at the negative electrode while they are adsorbed into the pores of the positive electrode upon the discharging of the cell (Fig. 1d). On the other hand, metal ions are released from the positive electrode while metal is deposited on the negative electrode upon the charging of the cell. As a result, only a minimum amount of electrolyte is needed to operate the cell since the electrolyte serves exclusively as a medium of metal ion transport. The use of metal electrodes can increase the energy density of the cell significantly by virtue of the large volumetric capacity. Therefore, ‘rocking-chair’ metal hybrid supercapacitors can double the energy density of a supercapacitor, and the internal resistance can be kept constant during the operation of the cell. The electrochemical results show highly reversible reactions at the positive and negative electrodes thanks to newly-developed Mg-ion and Zn-ion electrolytes. Charge-discharge cycles at rates up to 5 mA/cm2 were possible, whereas cycling tests showed 64% retention of the capacity after 400 cycles. Detailed studies of the mechanisms of degradation and evidences of the ‘rocking-chair’-type mechanism will be presented.

Figure 1
Lithiated Polyacrylic Acid Binder to Enhance the High Rate and Pulse Charge Performances in Graphite Anodes
Authors: Chiu Kuo-Feng , Leu Hoang-Jyh , Su Shih-Hsuan , Wu Rong-Zong
Published: February 2020

Polyacrylic acid (PAA) was used as water-soluble binder for graphite anodes of lithium ion batteries, and was further lithiated by titration using LiOH aqueous (Li-PAA). PAA and Li-PAA films with different degree of lithiation were controlled by adjusting the pH value during titration. Graphite anodes with conventional polyvinylidene fluoride (PVDF) binder were also fabricated for comparison. The graphite anodes with PAA binder exhibit a low capacity of 25 mAh/g at high current rate of 2 C, whereas the electrode with PVDF binder exhibits a higher capacity of 75 mAh/g. However, graphite anodes with the Li-PAA binder show greatly improved high-rate capability, with a 2 C capacity (> 225 mAh/g) three times higher than the conventional anodes. These results can be attributed to the increase of Li+ ion concentrations in the vicinity of the active materials, which reduces the charge transfer resistance at the interface of electrode/electrolyte, as measured by electrochemical impedance spectroscopy. In addition, to test the durability of pulse current charge in the conditions of green grids, all samples were operated with 50 pulses of 5 C currents during a 0.2 C charge process to simulate the conditions of green energy grid. It was found that the graphite anodes with Li-PAA of higher Li+ ion concentrations exhibit higher durability under pulse current charge, compared with the conventional anodes. However, too high a Li+ ion concentration weakens the binding strength, and therefore a high stability Li-PAA/graphite anode requires optimized Li+ ion concentration. The results indicate that Li-PAA is an appropriate binder for anodes in green energy grid application.