Unraveling (electro)-chemical stability and interfacial reactions of Li 10 SnP 2 S 12 in all-solid-state Li batteries

Abstract(#br)Li 10 SnP 2 S 12 (LSPS) with high ionic conductivity and moderate price is a promising solid electrolyte for all-solid-state batteries. However, the instability of LSPS and LSPS/electrodes interfaces would cause poor cycle performance issues in the LSPS-based all-solid-state batteries, which have not been well understood. Herein, we address and unravel the decomposition products of LSPS and their Li + transfer characteristics, especially on the surface of LSPS/electrodes by using solid-state nuclear magnetic resonance (ss NMR) spectroscopy coupled with X-ray photoelectron spectroscopy (XPS). The results reveal that the high mechanical energy during ball-milling process leads to the decomposition of LSPS into Li 4 SnS 4 and Li 3 PS 4 . During charge/discharge cycling, specific capacity fading of batteries originates from the formation of new interfacial layer at LSPS/Acetylene black cathode and LSPS/Li metal anode interfaces. Furthermore, our results demonstrate that the rough and porous morphology of the interface formed after cycling, rather than the decomposition products, is the critical factor which results in the increases of the interfacial resistance at LSPS/Li interface and serious formation of Li dendrite. Our results highlight the significant roles of (electro)chemical and interfacial stability of sulfide solid electrolyte in the development of all-solid-state batteries

Understanding the failure process of sulfide-based all-solid-state lithium batteries via operando nuclear magnetic resonance spectroscopy

All-solid-state lithium batteries performance is affected by the solid electrolyte interphase (SEI) and electrically disconnected (“dead”) Li metal. Here, via operando NMR measurements, the authors quantify the Li metal in the SEI and “dead” regions using various inorganic solid-state electrolytes

Gas induced formation of inactive Li in rechargeable lithium metal batteries

The formation of electrochemically inactive, or “dead”, lithium limits the reversibility of lithium metal batteries. Here the authors elucidate the (electro)chemical roles of ethylene gas produced from electrolyte decomposition on the formation of inactive lithium

Size-Dependent Chemomechanical Failure of Sulfide Solid Electrolyte Particles during Electrochemical Reaction with Lithium

The very high ionic conductivity of Li10GeP2S12 (LGPS) solid electrolyte (SE) makes it a promising candidate SE for solid-state batteries in electrical vehicles. However, chemo-mechanical failure, whose mechanism remains unclear, has plagued its widespread applications. Here, we report in situ imaging lithiation-induced failure of LGPS SE. We revealed a strong size effect in the chemomechanical failure of LGPS particles: namely, when the particle size is greater than 3 mu m, fracture/pulverization occurred; when the particle size is between 1 and 3 mu m, microcracks emerged; when the particle size is less than 1 mu m, no chemomechanical failure was observed. This strong size effect is interpreted by the interplay between elastic energy storage and dissipation. Our finding has important implications for the design of high-performance LGPS SE, for example, by reducing the particle size to less than 1 mu m the chemomechanical failure of LGPS SE can be mitigated

The stability of P2-layered sodium transition metal oxides in ambient atmospheres

Air-stability is a critical challenge faced by layered sodium transition metal oxide cathodes. Here, the authors depict a general and in-depth model of the structural/chemical evolution of P2-type layered oxides in air and propose an evaluation rule for the air-stability of layered sodium cathodes

Quantifying Degradation Parameters of Single-Crystalline Ni-Rich Cathodes in Lithium-Ion Batteries

Single-crystal LiNixCoyMnzO2 (SC-NCM, x+y+z=1) cathodes are renowned for their high structural stability and reduced accumulation of adverse side products during long-term cycling. While advances have been made using SC-NCM cathode materials, careful studies of cathode degradation mechanisms are scarce. Herein, we employed quasi single-crystalline LiNi0.65Co0.15Mn0.20O2 (SC-NCM65) to test the relationship between cycling performance and material degradation for different charge cutoff potentials. The Li/SC-NCM65 cells showed >77 % capacity retention below 4.6 V vs. Li+/Li after 400 cycles and revealed a significant decay to 56 % for 4.7 V cutoff. We demonstrate that the SC-NCM65 degradation is due to accumulation of rock-salt (NiO) species at the particle surface rather than intragranular cracking or side reactions with the electrolyte. The NiO-type layer formation is also responsible for the strongly increased impedance and transition-metal dissolution. Notably, the capacity loss is found to have a linear relationship with the thickness of the rock-salt surface layer. Density functional theory and COMSOL Multiphysics modeling analysis further indicate that the charge-transfer kinetics is decisive, as the lower lithium diffusivity of the NiO phase hinders charge transport from the surface to the bulk

Engineering Na+-layer spacings to stabilize Mnbased layered cathodes for sodium-ion batteries

钠离子电池（NIBs）具有原料储量丰富、成本低廉等优势，更有望应用于大规模储能器件，如静态储能基站和智能电网等。层状过渡金属氧化物（LiTmO2和NaxTmO2）材料目前仍然是锂离子电池（LIBs）和NIBs的主要正极材料，其晶体结构由碱金属(Li+/Na+)层和过渡金属(TmO2)层的有序堆叠组成。然而，LiTmO2和NaxTmO2材料在充放电过程中，Li+/Na+的嵌入和脱出会引起结构相变，导致电极材料容量快速衰退。杨勇课题组提出了一种简单而有效的水介导改性策略，即在Na0.67MnO2材料的Na+层中插入水分子，再通过高温脱水获得页岩状钠氧化物。该策略有效地扩大了P2型Na0.67MnO2的Na+层间距，并将颗粒转变为页岩状形态。课题组在钠离子电池层状氧化物正极材料构效关系的研究中取得重要进展。该研究工作得到美国国家强磁场实验室傅日强教授、厦门大学王鸣生教授（共同通讯）以及吴顺情教授的支持和帮助。论文第一作者为化学化工学院2017级博士研究生左文华（已毕业）。Layered transition metal oxides are the most important cathode materials for Li/Na/K ion batteries. Suppressing undesirable phase transformations during charge-discharge processes is a critical and fundamental challenge towards the rational design of high-performance layered oxide cathodes. Here we report a shale-like NaxMnO2 (S-NMO) electrode that is derived from a simple but effective water-mediated strategy. This strategy expands the Na+ layer spacings of P2-type Na0.67MnO2 and transforms the particles into accordion-like morphology. Therefore, the S-NMO electrode exhibits improved Na+ mobility and near-zerostrain property during charge-discharge processes, which leads to outstanding rate capability (100 mAh g−1 at the operation time of 6 min) and cycling stability (>3000 cycles). In addition, the water-mediated strategy is feasible to other layered sodium oxides and the obtained S-NMO electrode has an excellent tolerance to humidity. This work demonstrates that engineering the spacings of alkali-metal layer is an effective strategy to stabilize the structure of layered transition metal oxides.This work was financially supported by the National Key Research and Development Program of China (grant nos 2018YFB0905400, 2016YFB0901502), National Natural Science Foundation of China (grant nos 21761132030, 21935009, U1932201), the Fundamental Research Funds for the Central Universities (grant no. 20720200075), and the “Double-First Class” Foundation of Materials and Intelligent Manufacturing Discipline of Xiamen University. The authors thank Dr. Dong Su for the kind help and insightful discussions. W.Z. acknowledges the research fellowship from the Alexander von Humboldt Foundation. G.F.O. acknowledges the financial support from Spanish ministry of science and innovation (project nº MAT2017-84002-C2-1-R). R.F. acknowledges the support from the National High Magnetic Field Laboratory which is supported by NSF Cooperative Agreement DMR-1644779 and the State of Florida. The authors gratefully acknowledge the valuable beamtime from beamline BL14B1 of the SSRF.研究工作得到了国家自然科学基金（21761132030、21935009、 U1932201）和国家重点研发计划（2016YFB0901502）的资助