Study On Synthesis,modification And Application Of Chlorine-rich Lithium Argyrodite Electrolyte

All-solid-state battery（ASSB）with high safety and high energy density has become one of the hottest topics of battery research field in recent years.As the key material of ASSB,the comprehensive performance of solid electrolyte has a direct impact on the practical process of high-performance ASSB.Chlorine-rich lithium argyrodite electrolyte Li_5.5PS_4.5Cl_1.5 is one kind of sulfide solid electrolyte with great practical prospect due to the ultra-high room temperature ionic conductivity and the relatively low raw material cost.However,the study of this electrolyte is not deep enough at present,there are many problems need to be solved urgently.The preparation of Li_5.5PS_4.5Cl_1.5 in large quantity is difficult,the air stability and electrochemical stability of the electrolyte are poor,the electrolyte/electrode interface stability and the improvement mechanism are not clear.Aiming at the above problems,this paper first studies the synthesis and modification of Li_5.5PS_4.5Cl_1.5 electrolyte from the perspectives of optimizing the synthesis route and oxygen doping,and then reveals the effects of different factors on the Li_5.5PS_4.5Cl_1.5electrolyte/cathode interface stability and the electrochemical performances of ASSB from the perspectives of crystallinity and particle size of electrolyte and cathode coating.The main research contents are as follows:1.Facile synthesize Li_5.5PS_4.5Cl_1.5 electrolyte with high room temperature ionic conductivity(9.03×10^-3 S cm^-1)by optimizing the sintering temperature and duration.The ASSBs use composite cathode(Li Ni_0.6Co_0.2Mn_0.2O₂)without carbon are constructed,achieving ultra-long cycle life（10000 cycles and 200 cycles,respectively）and superior capacity retention at a high rate under room temperature and-20℃.2.Li_5.5PS_4.5Cl_1.5 electrolyte is modified by oxygen-doping.The as-prepared Li_5.5PS_4.425O_0.075Cl_1.5 exhibits high air stability,superior stability with high-voltage（4.5 V）cathode and Li-metal anode,and maintains high room temperature ionic conductivity(7.15×10^-3 S cm^-1).3.The effects of crystallinity of the Li_5.5PS_4.5Cl_1.5 electrolyte on the physicochemical properties and solid interfaces in ASSBs are explored.The Li-ion transfer is faster at crystalline Li_5.5PS_4.5Cl_1.5/cathode interface,enabling higher capacity and superior rate performance of constructing ASSBs.However,the glass-ceramic Li_5.5PS_4.5Cl_1.5/cathode interface is more stable,and the glass-ceramic Li_5.5PS_4.5Cl_1.5 electrolyte exhibits better mechanical stability.4.The effects of particle size distribution of Li_5.5PS_4.5Cl_1.5 in cathode composite and electrolyte layer on solid interfaces are studied.The small-size Li_5.5PS_4.5Cl_1.5 can improve the contact area of electrolyte/cathode interface,which is suitable for using in composite cathode to promote the capacity of active material;the large-size Li_5.5PS_4.5Cl_1.5 with fewer grain boundaries is suitable to be used as solid electrolyte layer to improve the rate performance of ASSB.Nevertheless,the structure of the small-size Li_5.5PS_4.5Cl_1.5electrolyte is more stable at high temperature,and it is suitable to be used as solid electrolyte layer at 60℃.5.The Li Nb O₃-coating strategy is taken to improve the Li_5.5PS_4.5Cl_1.5/Li Ni_0.7Co_0.1Mn_0.2O₂ interface stability.The effect mechanisms of coating layer on the electrochemical performance of ASSBs at different rates and a wide temperature range（-20℃,room temperature,and 60℃）are revealed.At a lower temperatures（-20℃）,the coating layer promotes the interfacial Li-ion dynamics dramatically,resulting in a significant increase in the specific capacity of the ASSB.While at higher temperatures（room temperature and 60℃）,the key role of the coating layer is to alleviate the change of cathode volume and the electrolyte/cathode interface side reactions,ensuring the long-term cycle stability of ASSBs.This thesis systematically studied the synthesis and modification of Li_5.5PS_4.5Cl_1.5electrolyte and the interface improvement strategies of the Li_5.5PS_4.5Cl_1.5-based ASSBs.The results of this thesis are of great significance to accelerate the practical process of Li_5.5PS_4.5Cl_1.5 electrolyte in the field of ASSBs.