Research On Interface Modification And Performance Of Sulfide Based Solid State Lithium Batteries

All-solid-state lithium batteries(ASSLB)are considered to be promising nextgeneration battery technologies due to their high safety,higher energy density and power density.However,the low Li+ ionic conductivity of the solid-state electrolytes(SSEs)and the poor internal interface within the ASSLBs greatly limit its electrochemical performance.Therefore,the search for SSEs with high Li+ ionic conductivity and optimization of the internal interface within the ASSLBs are the key ways to improve the electrochemical performance of ASSLBs.The SSEs applied to the ASSLBs are mainly classified into polymer-based SSEs,inorganic oxide-based SSEs,and inorganic sulfide-based SSEs.Recently,SSEs have been greatly developed.Among them,sulfide-based SSEs have the highest ionic conductivity,and their Li+ ionic conductivities are as high as 10-3-10-2 S cm-1,which quite even exceed the Li+ ionic conductivity of the traditional liquid organic electrolyte.Moreover,the pellets of sulfide-based SSEs with a very small grain boundary impendance can be obtained by a simple mechanical cold pressing method,which greatly simplifies the fabircation process of the inorganic ASSLBs.However,the problems of poor internal interface contact and interface side reaction of the sulfide-base ASSLBs are still challenging.Aiming to solve the above-mentioned problems,the main research contents of this project are listed below.The method of in-situ synthesis of the composite electrode by a liquid-phase method is designed to optimize the internal interface contacts between active materials and SSEs.Here,we choose Li7P3S11 glass-ceramic electrolyte as research object,which has the advantage of low heat treatment temperature.The raw materials of Li2 S and P2S5 are uniformly mixed with the active material Li4Ti5O12 in the200# mineral spirit,then the solvent is volatilized,and the vacuum heat treatment is performed at 260?.Li7P3S11 glass-ceramic SSE was in-situ coated onto the surface of Li4Ti5O12 particles,and the composite electrode material with close interface was obtained(denoted as LTO@LPS).Then,the differences in performance of the composite electrode prepared by in-situ liquid phase method and ordinary ball milling method were investigated.The results show that the composite electrode material synthesized by in-situ liquid phase method greatly enhances the rate and cycle performances.The LTO@LPS cells was conducted under 1 C at 80?,and it can deliver a discharge specific capacity of 110 m Ah g-1 after 300 cycles,with a capacity retention of over 90%.The effect of incorporating a small amount of sulfide solid electrolytes-compatible solvated ionic liquid [Li(Triglyme)]+[TFSI]-(denoted as Li G3)into the ASSLBs on the battery's electrochemical active interface was investigated.Firstly,the physicochemical properties of Li G3 and the compatibility between Li G3 and sulfidebased SSEs were investigated.Then,Li G3 was added to full-fill the voids within the composite electrode,which can further enrich Li+ ionic conduction path and increase electrochemical active interfaes within the composite electrode.It can simultaneously stabilize the composite electrode structure,thereby improving the cycle stability and capacity characteristics of the ASSLBs.The results show that the ASSLBs with 5wt% Li G3 addition and Li4Ti5O12 as active material can deliver 160 m Ah g-1 at 0.25 C after 1500 cycles,with a high capacity retention over 92% and 75 m A h g-1 under 2.5 C high rate for 2000 cycles,showing excellent cycle stability and structural stability of the ASSLBs.In order to achieve higher energy density of solid-state batteries,the interface construction method and interface reaction mechanism in the solid-state lithiumsulfur system were systematically studied.Firstly,a compact and dense composite electrode is fabricated by a two-step mechanical milling method followed by 5 wt% Li G3 addition,and its cycle stability and electrode reaction process were further investigated.The results show that in the quasi-solid-state lithium-sulfur battery,Li G3 not only plays the role of wetting the internal interface within the composite electrode,but also changes the electrode reaction process of the active sulfur,which from a solid-phase reaction turns to solid-liquid dual-phase reaction.On the other hand,the sulfide-based SSEs guaranteed Li+ transport for the solid-phase reaction in the discharge process of the quasi-solid lithium-sulfur battery,and the combination of the two ensures the excellent electrochemical performance of the quasi-solid lithium-sulfur battery.With 5wt% Li G3 addition,the quasi-solid lithium-sulfur batteries deliver a discharge specific capacity of more than 1000 m Ah g-1 after 100 cycles at 0.1 C,and the capacity retention is 98.2%.