Application Of Li-Rich Layered Oxides In All-Solid-State Batteries And The Interface Between Cathode And Electrolyte

It is a trend to develop all-solid-state lithium batteries with high safety and high specific energy,and the key to make all solid-state lithium batteries with high specific energy is to select the anode and cathode materials with high specific capacity.In recent years,lithium rich manganese base oxide(LRMO)is expected to become one of the candidate materials for the next generation of cathode materials for lithium-ion batteries due to its ultra-high specific capacity(>250 mAh g-1),low cost and high safety.However,there are few researches on the application of lithium rich manganese base oxide in solid-state lithium-ion batteries.In addition,whether based on sulfide electrolyte or halide electrolyte,all solid-state lithium batteries always show large interface impedance in the current research,which seriously affects its practical application.Therefore,it is very important to study the interface characteristics of cathode/electrolyte in solid-state batteries This project first verified the electrochemical performance of lithium rich manganese base oxide materials matching with sulfide electrolyte and halide solid electrolyte,and initially explored the feasibility of lithium rich manganese base oxide materials used in all solid-state lithium batteries.Then,through exploring the interface reaction mechanism between lithium rich manganese base oxide materials and solid electrolyte,and according to the experimental results,the interface reaction characteristics of cathode/electrolyte were obtained in order to improve the electrochemical performance of lithium rich manganese base oxide materials in halide based solid-state batteries,the interface modification method is proposed to realize the application of lithium rich manganese base oxide materials in solid-state batteries.The purpose of this project is to realize the practical application of lithium rich manganese base oxide materials in all-solid-state batteries,and to explore the electrochemical performance of lithium rich manganese base oxide materials when matching with Li3InCl6(LIC)halide electrolyte The mechanism of interface reaction between lithium rich manganese base oxide materials and halide electrolytes was studied by spectroscope,and the corresponding modification measures were put forward according to the characteristics of interface reaction.The main content of this project is divided into the following two parts:In the first part of the project,the bare lithium rich manganese base oxide materials are directly applied to all-solid-state lithium batteries to explore the electrochemical performance of lithium rich manganese base oxide materials with halide electrolyte Li3InCl6.Then,the chemical and electrochemical stability of these two materials are verified by a series of comprehensive analysis and testing methods.The main conclusions are described as follows:When the lithium rich manganese base oxide materials are matched with LIC halide electrolyte,the initial charge capacity can reach 312 mAh g-1,which is comparable to the level of traditional liquid battery,but its initial discharge capacity is relatively low,which is only 183 mAh g-1.Moreover,this solid-state battery cannot cycle stably,and the discharge capacity decreases rapidly.After 20 cycles,the discharge capacity of the battery has already dropped to 50 mAh g-1 Therefore,there concluded two main problems in this solid-state battery:the low initial cycle discharge capacity and poor cycle stability.However,the initial discharge capacity of this all-solid-state battery is still higher than that of other solid-state battery in the past few years,which indicates that the solid-state battery with lithium rich manganese base oxide materials and LIC halide electrolyte matching dose has great research value.After that,we explore the mechanism of the interface reaction through EIS and XPS,and find that the LIC electrolyte can be oxidized and decomposed under high voltage to form In2O3;on the other hand,the lattice oxygen O2-of LRMO will be transformed into O" with high oxidation activity under high voltage,which intensified the oxidation and decomposition reaction of LIC electrolyte.Then,the oxygen releases in LRMO would also lead the transition metal to migrate to the lithium layer,which causes the layered phase of the LRMO transferred into rock-salt phase,which also decreases the capacity of the battery rapidly.According to the conclusion of the first part,in the second part of this project,an inert LiNbO3(LNO)interface transition layer is introduced between the LRMO cathode materials and LIC electrolyte.The modified materials are assembled in all-solid-state battery and then checked the electrochemical performance.The mechanism of interface transition layer is preliminarily explored by the same test methods as the first part.The main conclusions are described as follows:the first coulomb efficiency of all the cathode materials with LNO-coated materials are improved,and the initial discharge capacity of the LRMO materials with 1.5wt%LNO coating layer can reach 221 mAh g-1,which is much higher than that of other research based on transition metal oxide cathode materials in all-solid-state batteries.Moreover,the initial coulombic efficiency of this cathode materials increases from 58.79%to 73.21%.By means of EIS and XPS,we conclude that the LNO interface layer can buffer the LRMO and LIC electrolyte due to the low electronic conductivity of LiNbO3,which reduces the excessive chemical potential from the LRMO materials,and further suppresses the oxidize decomposition of the O-to the LIC electrolyte under high voltage;However,the problem of lattice oxygen release in LRMO materials still exists.The transition metal migrate to lithium layer is also serious in the lithium rich manganese base oxide materials,which makes the layered structure of the material change into rock salt phase,and this phenomenon decreases the capacity of the battery.In conclusion,this paper has a certain pioneering significance in exploring the application of lithium rich manganese base oxide in all-solid-state lithium batteries.According to the interface reaction mechanism between the lithium rich manganese base oxide materials and LIC solid electrolyte,the corresponded LNO interface modification method is proposed,and some unique results are obtained.This will be of guiding significance for the research and experimental scheme of all-solid-state battery in the system with lithium rich manganese base oxide in the future.