Study On Lithium Ion Transport In Cathodes And Cathodes/electrolyte Interface Of All Solid State Lithium Ion Batteries

All-solid-state lithium-ion batteries（ASSLIBs）are considered as one of the best options for the next generation of energy storage devices due to their high safety,high energy density,wide operating temperature range,and stable cycling performance.However,interface issues are crucial factors affecting the performance of ASSLIBs,and the poor mechanical stability,chemical stability,and electrochemical stability of interfaces limit the ion transport performance,which prevents ASSLIBs from achieving their expected energy density and cycling capability.Previous research on ASSLIBs interface ion transport mostly focused on the interface morphology,structure,and composition,elucidating the effects of these changes on battery performance.However,it is difficult to directly obtain the influence of these changes on interface ion transport from morphology,structure,and composition information.Therefore,it is great significance to directly observe interface ion transport in experiments to understand the structure-performance relationship of interfaces in ASSLIBs and provide guidance for improving the performance and optimizing the structure of ASSLIBs.This study investigates the dynamic evolution of charge distribution within the cathode particles and at the cathode/electrolyte interface in all-solid-state lithium-ion batteries using in-situ electron microscopy combined with differential phase contrast imaging technique.The research achieves a visual representation of the relationship between interface structure and ion transport.The findings of this paper contribute to the enrichment of ion conduction theory at the interfaces of solid-state lithium batteries.Additionally,the research provides guidance for establishing new methods for interface modification,ultimately offering direct experimental evidence for the development of high-performance solid-state lithium-ion batteries.The main research contents are as follows:（1）We studied the lithium-ion transport behavior in ASSLIBs with the lithium-rich layered oxide（LLO）cathode/sulfide electrolyte using spherical aberration corrected transmission electron microscopy and in situ DPC-STEM.The in situ DPC-STEM technique directly observed the structure of the LLO cathode at the atomic level.The difference in lithium ion transport performance caused by the nanoscale phase separation of Li TMO₂ and Li₂Mn O₃ in the LLO cathode was observed by using DPC-STEM.The net charge density distribution of the cathode and cathode/electrolyte interface in the LLO cathode was obtained by DPC-STEM,demonstrating the accumulation of lithium ions in the LLO cathode and cathode/solid electrolyte interface,elucidating the influence of the LLO cathode structure on ion transport performance,and providing new insights into the limited activation of the Li₂Mn O₃ phase in ASSLIBs.（2）We studied the all-solid lithium ion battery with layered oxide high nickel cathode（NCM811）/sulfide electrolyte.The interfacial structure of NCM811 coated with Li_xZr_y（PO₄）₃/sulfide electrolyte,the polycrystalline grain boundary structure of NCM811 and the evolution of these two interfacial structures during charging and discharging were investigated by using condenser spherical correction electron microscopy.The results show that Li_xZr_y（PO₄）₃ forms a nanocrystalline-amorphous lithium ion conduction network on the surface of NCM811 secondary particles.Nanocrystalline-amorphous structure can effectively relief the stress concentration and harmful surface phase transformation caused by volume change during the charging and discharging process,and improve the cyclic performance.The net charge density distribution on positive electrode grain boundary and positive electrode/electrolyte was studied by in-situ DPC-STEM.The results show that the presence of Li_xZr_y（PO₄）₃coating significantly reduces the accumulation of lithium ions at the positive/electrolyte interface and the positive secondary particle boundary.Meanwhile,the comparison of dynamic charge accumulation between grain boundary and interface shows that the positive/solid electrolyte interface has a greater hindrance to lithium ion transport,which also provides direct experimental evidence for interface design.