Effect Of Surface Modification Of LiCoO₂ Cathode On The LiCoO₂-solid Electrolyte Interface In All-solid-state Batteries

In the sulfide lithium-ion all-solid-state battery（ASSLB）system,the interface problem between the sulfide solid electrolyte and the layered oxide cathode is a key issue in the performance degradation of the solid-state battery.The residual base on the surface of the cathode material has a certain influence on the stability of the interface;in addition,the surface coating of the cathode material is also an effective and mature solution to improve the performance of the cathode material,however,the coating phase will change with the change of temperature and other feeding conditions,thus affecting the performance of the cathode material and the stability of the interface.Based on the above considerations,this paper investigates the type of residual bases on the surface of LCO and the effect of surface residual base replacement on the cathode performance and interfacial stability using LiCoO₂（LCO）as the original material.In addition,the phase and properties of LCO surface coating with Nb-containing compounds and the effect on the interface are investigated in detail.Firstly,we found the presence of residual alkali on the surface of LCO,and then we regulated the residual alkali on the surface of LCO by calcination with LiOH·H₂O after washing,so that the composition of residual alkali on the surface of LCO was converted from Li₂CO₃ to Li₂O.The performance of the LCO@Li₂O-2 cathode was significantly improved,with a capacity retention of 95.4%after 150 weeks of cycling at 0.5C and a capacity of 103.2 m Ah g^-1 at 2C.The stability of the interface and side reactions were investigated by chemical and electrochemical impedance tests and X-ray photoelectron spectroscopy（XPS）of the electrode after cycling.The results show that the original Li₂CO₃ on the LCO surface leads to a decrease in the stability of the LCO/solid-state electrolyte（SSE）interface;while the Li₂O regulating layer constructed using surface residual base regulating method significantly improves the interfacial stability and suppresses the interfacial side reactions.In addition,it was also found that by changing the coating conditions during the coating of Nb-containing compounds,different phases of the coating layer can be constructed on the surface of LCO through a long-time investigation.By increasing the amount of coating,the coating layers with different phases were constructed under different metal Li input and different heat treatment temperatures,and the types of coating phases were investigated using X-ray powder diffraction.Single-phase coatings of Co₃O₄,Nb₂O₅,LiNbO₃ and Li₃NbO₄ could be constructed under certain conditions,and the coatings were characterized by X-ray photoelectron spectroscopy and field emission swept electron microscopy.The effect of different coatings on the interface during cycling was also investigated using electrochemical impedance test,GITT test,X-ray photoelectron diffraction,and Raman spectroscopy,and the degradation of the interface and the anode side after cycling was analyzed by characterizing the cathode pole piece after cycling using field emission swept surface electron microscopy and ultra-high resolution transmission electron microscopy.It was found that LiNbO₃ and Li₃NbO₄ can play a significant role in the enhancement of the interfacial stability,with LiNbO₃ showing a more obvious advantage by virtue of its excellent ionic and electronic conductivity,while Co₃O₄,Nb₂O₅ has a negative impact on the interfacial performance...