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All-solid-state batteries are intensively investigated, although their performance is not yet satisfactory for large-scale applications. In this context, the combination of Li 10 GeP 2 S 12 solid electrolyte and LiNi 1-x-y Co x Mn y O 2 positive electrode active materials is considered promising despite the yet unsatisfactory battery performance induced by the thermodynamically unstable electrode|electrolyte interface. Here, we report electrochemical and spectrometric studies to monitor the interface evolution during cycling and understand the reactivity and degradation kinetics. We found that the Wagner-type model for diffusion-controlled reactions describes the degradation kinetics very well, suggesting that electronic transport limits the growth of the degradation layer formed at the electrode|electrolyte interface. Furthermore, we demonstrate that the rate of interfacial degradation increases with the state of charge and the presence of two oxidation mechanisms at medium (3.7 V vs . Li + /Li < E  < 4.2 V vs . Li + /Li) and high ( E  ≥ 4.2 V vs . Li + /Li) potentials. A high state of charge (>80%) triggers the structural instability and oxygen release at the positive electrode and leads to more severe degradation. Fundamental investigations at the electrode/electrolyte interface are essential for developing high-energy batteries. Here, the authors investigate the degradation mechanisms at the LGPS/NCM622 interface providing a quantitative model to interpret the interfacial resistance growth.

Solid-state batteries have recently attracted great interest as potentially safe and stable high-energy storage systems. However, key issues remain unsolved, hindering full-scale commercialization.

All-solid-state Li batteries (ASSBs) employing inorganic solid electrolytes offer improved safety and are exciting candidates for next-generation energy storage. Herein, we report a family of lithium mixed-metal chlorospinels, Li 2 In x Sc 0.666− x Cl 4 (0 ≤  x  ≤ 0.666), with high ionic conductivity (up to 2.0 mS cm −1 ) owing to a highly disordered Li-ion distribution, and low electronic conductivity (4.7 × 10 −10  S cm −1 ), which are implemented for high-performance ASSBs. Owing to the excellent interfacial stability of the SE against uncoated high-voltage cathode materials, ASSBs utilizing LiCoO 2 or LiNi 0.85 Co 0.1 Mn 0.05 O 2 exhibit superior rate capability and long-term cycling (up to 4.8 V versus Li + /Li) compared to state-of-the-art ASSBs. In particular, the ASSB with LiNi 0.85 Co 0.1 Mn 0.05 O 2 exhibits a long life of >3,000 cycles with 80% capacity retention at room temperature. High cathode loadings are also demonstrated in ASSBs with stable capacity retention of >4 mAh cm −2 (~190 mAh g −1 ). Intensive research is underway to develop solid-state electrolytes for rechargeable batteries. Here the authors report a family of mixed-metal halospinel electrolytes that exhibits promising properties for high-performance solid-state batteries.

Lithium-metal batteries with a solid electrolyte separator are promising for advanced battery applications, however, most electrolytes show parasitic side reactions at the low potential of lithium metal. Therefore, it is essential to understand how much (and how fast) charge is consumed in these parasitic reactions. In this study, a new electrochemical method is presented for the characterization of electrolyte side reactions occurring on active metal electrode surfaces. The viability of this new method is demonstrated in a so-called anode-free stainless steel ∣ Li 6 PS 5 Cl ∣ Li cell. The method also holds promise for investigating dendritic lithium growth (and dead lithium formation), as well as for analyzing various electrolytes and current collectors. The experimental setup allows easy electrode removal for post-mortem analysis, and the SEI’s heterogeneous/layered microstructure is revealed through complementary analytical techniques. We expect this method to become a valuable tool in the future for solid-state lithium metal batteries and potentially other cell chemistries. In lithium-metal batteries, it is vital to quantify electrolyte side reactions occurring at the metal anode surface. Here, the authors introduce an electrochemical technique, using a series of small-step lithium deposition followed by open circuit voltage analysis, to accurately measure these reactions.

Increasing the specific energy, energy density, specific power, energy efficiency and energy retention of electrochemical storage devices are major incentives for the development of all-solid-state batteries. However, a general evaluation of all-solid-state battery performance is often difficult to derive from published reports, mostly due to the interdependence of performance measures, but also due to the lack of a basic reference system. Here, we present all-solid-state batteries reduced to the bare minimum of compounds, containing only a lithium metal anode, β-Li 3 PS 4 solid electrolyte and Li(Ni 0.6 Co 0.2 Mn 0.2 )O 2 cathode active material. We use this minimalistic system to benchmark the performance of all-solid-state batteries. In a Ragone-type graph, we compare literature data for thiophosphate-, oxide-, phosphate- and polymer-based all-solid-state batteries with our minimalistic cell. Using fundamental equations for key performance parameters, we identify research targets towards high energy, high power and practical all-solid-state batteries. Considering the interdependence of performance measures and the lack of a basic reference system for all-solid-state batteries, Jürgen Janek and co-workers analyse literature performance data for major types of all-solid-state batteries and benchmark them against minimalistic reference cells.

The growth of lithium dendrites in inorganic solid electrolytes is an essential drawback that hinders the development of reliable all-solid-state lithium metal batteries. Generally, ex situ post mortem measurements of battery components show the presence of lithium dendrites at the grain boundaries of the solid electrolyte. However, the role of grain boundaries in the nucleation and dendritic growth of metallic lithium is not yet fully understood. Here, to shed light on these crucial aspects, we report the use of operando Kelvin probe force microscopy measurements to map locally time-dependent electric potential changes in the Li 6.25 Al 0.25 La 3 Zr 2 O 12 garnet-type solid electrolyte. We find that the Galvani potential drops at grain boundaries near the lithium metal electrode during plating as a response to the preferential accumulation of electrons. Time-resolved electrostatic force microscopy measurements and quantitative analyses of lithium metal formed at the grain boundaries under electron beam irradiation support this finding. Based on these results, we propose a mechanistic model to explain the preferential growth of lithium dendrites at grain boundaries and their penetration in inorganic solid electrolytes. Lithium metal penetration into solid-state electrolytes is a major drawback for developing all-solid-state batteries. Here, authors, via operando force microscopy, demonstrate that the trapping of electrons in garnet-type solid-state electrolyte grain boundaries is the origin of cell failure.

All-solid-state lithium batteries have attracted widespread attention for next-generation energy storage, potentially providing enhanced safety and cycling stability. The performance of such batteries relies on solid electrolyte materials; hence many structures/phases are being investigated with increasing compositional complexity. Among the various solid electrolytes, lithium halides show promising ionic conductivity and cathode compatibility, however, there are no effective guidelines when moving toward complex compositions that go beyond ab -initio modeling. Here, we show that ionic potential, the ratio of charge number and ion radius, can effectively capture the key interactions within halide materials, making it possible to guide the design of the representative crystal structures. This is demonstrated by the preparation of a family of complex layered halides that combine an enhanced conductivity with a favorable isometric morphology, induced by the high configurational entropy. This work provides insights into the characteristics of complex halide phases and presents a methodology for designing solid materials. The pursuit of all-solid-state batteries has motivated advancements in materials design. Here, the authors present a methodology demonstrating that ionic potential effectively captures crucial interactions within halide materials, guiding the design of the new materials with enhanced performance.

The operation of combined mass spectrometry and electrochemistry setups has recently become a powerful approach for the in situ analysis of gas evolution in batteries. It allows for real-time insights and mechanistic understanding into different processes, including battery formation, operation, degradation, and behavior under stress conditions. Important information is gained on the safety and stability window as well as on the effect of protecting strategies, such as surface coatings, dopings, and electrolyte additives. This review primarily aims at summarizing recent findings on the gassing behavior in different kinds of liquid- and solid-electrolyte-based batteries, with emphasis placed on novel cathode-active materials and isotope labeling experiments, to highlight the relevance of in situ gas analysis for elucidation of reaction mechanisms. Various instrumental and experimental approaches are presented to encourage and inspire both novices and experienced scientists in the field. Graphical abstract

The discharging and charging of batteries require ion transfer across phase boundaries. In conventional lithium-ion batteries, Li + ions have to cross the liquid electrolyte and only need to pass the electrode interfaces. Future high-energy batteries may need to work as hybrids, and so serially combine a liquid electrolyte and a solid electrolyte to suppress unwanted redox shuttles. This adds new interfaces that might significantly decrease the cycling-rate capability. Here we show that the interface between a typical fast-ion-conducting solid electrolyte and a conventional liquid electrolyte is chemically unstable and forms a resistive solid-liquid electrolyte interphase (SLEI). Insights into the kinetics of this new type of interphase are obtained by impedance studies of a two-chamber cell. The chemistry of the SLEI, its growth with time and the influence of water impurities are examined by state-of-the-art surface analysis and depth profiling. Li + -selective solid electrolytes may enable next-generation battery systems, such as Li–S and Li–O 2 . Now, in an exemplar system, it is shown that a resistive interphase forms at the interface between solid and liquid electrolytes, termed the solid-liquid electrolyte interphase (SLEI). An in situ study of this undesirable effect is supported by state-of-the-art surface analysis.