Synthesis Of High Performance And Low Cost Li_6-xPS_5-xCl_1+x Electrolytes

With the advantages of high energy density,wide electrochemical window,high safety and environmental friendliness,all-solid-state lithium batteries（ASSLBs）are regarded as one of the most promising electrochemical energy storage devices.Solid-state electrolytes（SEs）have crucial impacts on the performance of ASSLBs.The Li₆PS₅Cl argyrodite electrolyte has the high ionic conductivity at room temperature and is suitable for the application of ASSLBs.However,for sulfide electrolytes,many problems still need to be solved,including their narrow electrochemical window,poor air stability and interface compatibility against oxide-based cathodes.This thesis starts with the lithium vacancy design in the electrolyte crystal structure and increase the densification to improve the ionic conductivity and electrochemical stability of the electrolyte.The main research contents are as follows:1.In this work,a method was used to prepare Li_6-xPS_5-xCl_1+x（x=0,0.1,0.2,0.3,0.4,0.5 and 0.6）by modestly increasing the LiCl content and decreasing the Li₂S content to design the lithium vacancies in the electrolyte.Specifically,the ionic conductivities of Li_6-xPS_5-xCl_1+xcomponents with different lithium vacancy ratios were investigated.Besides,the cost of sulfide electrolytes can be reduced as the decreased usage amount of high-priced Li₂S.In particular,Li_5.6PS_4.6Cl_1.4has an ionic conductivity of up to 8.2×10^-3S/cm at room temperature and shows excellent cycling performance(a discharge capacity of 142 m Ah g^-1was maintained after 400 cycles at1C,with a capacity retention of 100%)and superior initial coulombic efficiency（86.1%at 0.2C）in ASSLB assembled with Li-In anode and NCM811 cathode.In addition,the chemical stability between the SSE and the cathode was measured and the best chemical stability was found between Li_5.6PS_4.6Cl_1.4and the cathode material.2.Subsequently,S-Li_5.6PS_4.6Cl_1.4also demonstrated excellent electrochemical performance which synthesised with self-made Li₂S to further reduce the cost and verify the generality of this sulfide electrolyte preparation strategy.The electrochemical performances of NCM811//S-Li_5.6PS_4.6Cl_1.4//Li-In ASSLB were tested with a high initial coulombic efficiency of 83.2%at 0.2C.And after 400 cycles at 1C,the discharge capacity remains at 126.2 m Ah g^-1with a capacity retention of 88.2%.Due to the higher purity of commercial Li₂S,the capacity retention of S-Li_5.6PS_4.6Cl_1.4is not as well as C-Li_5.6PS_4.6Cl_1.4,but also shows excellent electrochemical performances.In addition,the activation energy of lithium ion diffusion can be measured using temperature-dependent ionic conductivity analysis,with activation energies of 0.222 and 0.217 e V for S-Li_5.6PS_4.6Cl_1.4and C-Li_5.6PS_4.6Cl_1.4,respectively,are essentially at the same level.The lower activation energy indicates that the lithium ions have a faster migration rate in the electrolyte.On this basis,the density of S-Li_5.6PS_4.6Cl_1.4electrolyte sheet was further increased by hot pressing.As a result of the hot pressing process,the pores between the electrolyte particles are eliminated and the particles are in closer contact with each other,while a flat surface electrolyte sheet is formed,promoting uniform charge distribution on the electrolyte surface.After densification,the ionic conductivity of the electrolyte was improved and it also exhibited excellent electrochemical performances in ASSLBs.