(Invited) Electrochemo-Mechanical Effects for All-Solid-State Li Batteries Employing Sulfide Inorganic Solid Electrolytes

All-solid-state Li or Li-ion batteries (ASLBs) have been emerged as a promising alternative battery to address the safety concerns and the limited energy densities for conventional lithium-ion batteries (LIBs). Particularly, deformable sulfide solid electrolyte (SE) materials are able to be integrated with electrode active materials into bulk-type ASLBs by simple cold-pressing process. Moreover, Li+ conductivities of several sulfide SEs are in the order of 10-2 S cm-1. Unfortunately, performances of the resulting ASLBs operating at room temperature were below par, which has been attributed to the narrow electrochemical stability windows of sulfide SE materials and the poor chemical compatibility between sulfide SEs and electrode active materials. Development of interfacial engineering (e.g., protective coatings such as LiNbO3 and Li3-xB1-xCxO3) could show significantly improved performances. Recently, it has been shown that the changes in volumetric strains upon repeated charge-discharge cycles could cause ionic contact loss in the composite electrodes and result in capacity fading for ASLBs. This is in contrast to conventional LIB electrodes where liquid electrolytes keep ionic contacts by simple wetting. However, previous works on such “electrochemo-mechancial” effects on the performance of ASLBs are scarce. In this presentation, we report on our recent findings on the overlooked but dominant electrochemo-mechanical effects for Ni-rich layered cathode materials for ASLBs. While the conventional Li[Ni,Co,Mn]O2 (NCM) having randomly oriented grains suffers from severe disintegration of secondary particles even at the initial cycle, full-concentration gradient NCM (FCG-NCM) retains its mechanical integrity after 100 cycles. Accordingly, their cycling stability shows huge differences, manifesting the importance of microstructural electro-chemomechanics for NCM in all-solid-state batteries. Furthermore, high resolution operando electrochemical pressiometry developed for NCM/graphite ASLBs reveals meaningful information which is complementary to the electrochemical data. Detailed discussion will be presented. References [1] K. H. Park, Q. Bai, D. H. Kim, D. Y. Oh, Y. Zhu, Y. Mo, Y. S. Jung, Adv. Energy Mater. 2018, 8, 1800035.