Performance Investigation Of Solid-state Lithium Battery Based On Li₇P₃S₁₁ Sulfide Electrolyte

Lithium-ion battery（LIBs）,as an efficient energy storage device,has been widely used in every aspect in our life.Developing the solid electrolyte materials to replace the traditional organic electrolyte and separator is considered to be an effective way to solve the safety and low energy density of lithium-ion batteries.Among these solid electrolyte materials,sulfides stand out because of its super high conductivity.However,there are still some problems when sulfide electrolyte was applied to all-solid-state battery.For cathode materials,the layered oxide cathode with high voltage do not match with sulfide electrolyte due to the space charge layer effect,which will make it difficult to obtain stable cycle performance.For forming electrolyte membrane and assembling battery,the thickness of sulfide electrolyte film obtained by conventional cold pressing is lager（>400μm）,which results the battery assembly difficulty and lower energy density.In order to solve the above problems,we designed a transition metal sulfide cathode to match Li₇P₃S₁₁ electrolyte,the all-solid-state battery show good electrochemical performance.And developed a rolling process to prepare thin sulfide composite electrolyte.The details are as follows:1.The Li₇P₃S₁₁ with ion conductivity of 0.285 m S cm^-1 was synthesised by liquid phase method.A carbon nanotube coated cobalt disulfide material（Co S₂@CNT）was prepared by in-situ carbonization and vulcanization,which have high electronic conductivity and volume expansion tolerance,matched it with Li₇P₃S₁₁ electrolyte to assemble all-solid-state battery.The CV and GITT tests showed that the introduction of CNT enhanced the reaction kinetics,the diffusion coefficient of lithium ions increases from 7.24×10^-10cm²s^-1to12.13×10^-10cm²s^-1.The first capacity of all-solid-state battery can reach 822 m A h g^-1 at 30℃with the current density of 0.1A g^-1,and the capacity retention rate is 71%after 50 cycles.The SEM of cathode/electrolyte interface after 50 cycles display there are no cracks and pores,which verified the cathode we designed match well with electrolyte.2.For solving the problem that the thickness of sulfide electrolyte prepared by cold pressing caused by low energy density,a solvent-free rolling process was designed to compound the Li₇P₃S₁₁ synthesised by liquid phase method and polytetrafluoroethylene（PTFE）powder,the thickness of electrolyte membrane was reduced to less than 100μm after cold pressing at 600 MPa.After adjust and optimize the ratio of sulfide to PTFE,100Li₇P₃S₁₁-2.5PTFE was found to own the highest ionic conductivity(4.6×10^-5 S cm^-1,25℃).The test results of symmetrical battery show that it maintained a stable cycle of 400 h when the composite electrolyte was matched with lithium-indium alloy,however,a short circuit occurred in 12 h with lithium metal.The first capacity of S/100Li₇P₃S₁₁-2.5PTFE/Li-In button-type battery can reach 785.3 m A h g^-1 at 60℃with the current density of 0.05C rate,and the capacity retention rate is 65.7%after 40 cycles.Meanwhile,it exhibits outstanding rate performance,the discharge capability can reach 399.2 m A h g^-1 at 0.2C.