Preparation And Properties Of Cathode/electrolyte Interface Modification For LLZO-basedsolid State Batteries

At present,the use of liquid organic electrolytes in commercial lithium-ion secondary batteries has potential safety hazards of flammability and explosion.The use of solid electrolytes instead of organic electrolytes can greatly improve the safety of lithium batteries.The garnet-type Li₇La₃Zr₂O₁₂?LLZO?electrolyte,as an inorganic electrolyte,has the advantages of high ionic conductivity,good mechanical propertiesand wide electrochemical window.However,the high interface impedance caused by its poor physical contact with the electrodes severely affects the capacity and cycle life of the battery and hinders the application and development of LLZO electrolytes.In order to solve the problem of the interface between the cathode and the electrolyte,in this paper,polypyrrole is coated on the surface of the Li[Ni_0.5Mn_0.3Co_0.2]O₂?NCM?cathode active material.Under the condition of ensuring the normal transmission of Li⁺,the cathode and the electrolyte are prevented.The occurrence of side reactions and the diffusion of elements.Subsequently,the interface treatment process is optimized,the contact between the cathode and the electrolyte is improved by preparing a co-sintered electrolyte,and Li₃PO₄ is introduced to further improve the cycle performance of the battery.First,the Li_6.35La₃Zr_1.8Ta_0.2Al_0.15O₁₂ electrolyte with a density of about 90% was prepared by the solid-phase reaction method,and the ion conductivity at room temperature can reach 6×10^-4 S cm^-1.After that,polypyrrole was coated on the surface of NCM cathode particles by chemical oxidation to obtain a composite cathode material?NCM@PPy?.Compared with the full battery assembled without PPy modified NCM cathode material,when the PPy content is 4.7 wt%,the all-solid-state lithium battery assembled with NCM@PPy composite cathode material has a lower interface resistance.At the same time,the specific discharge capacity of the battery in the first lap at 0.05 C is 136.7 m Ah/g,which is 32% higher than that of the battery without PPy coating.Next,we explored the preparation process of co-sintered electrolyte.When the co-sintering temperature is 700? and the wt ratio of positive electrode active material to electrolyte powder is 5:5,the prepared co-sintered electrolyte has the best performance.The discharge capacity of the assembled battery at the first lap at 0.05 C is144.1 m Ah/g.Compared with the battery assembled by the traditional process,the specific discharge capacity of the battery increase by 38%,and the interface resistance decrease significantly.After that,Li₃PO₄ is introduced into the co-sintering process,and the assembled all-solid-state battery has a specific discharge capacity of 138.3 m Ah/g at0.05 C for the first cycle.After 10 cycles,the specific discharge capacity is still 81.2m Ah/g,which is the same as that of the battery without Li₃PO₄.The specific capacity retention rate is increased by 10%.The experimental results show that the addition of Li₃PO₄ can enhance the physical bond between the cathode particles and the electrolyte,and further improve the cycle performance of the all-solid-state lithium battery.