Influence Of Composition Change Of Ternary Layered Materials On Interface Failure With Sulfide Electrolyte

With the increasing demand of electric cars and electronic products,the high energy density of Li-ion batteries is becoming more and more concerned.Solid-state lithium batteries with non-flammable solid electrolytes,are considered to be one of the most promising energy storage devices.In recent years,solid electrolyte has been closely monitored for its high ionic conductivity.Since first proposed in 1999,the layered ternary cathode material LiNi_xCo_yMn_1-x-yO₂（NCM）has received widespread attention due to its excellent performance.However,it is believed that the deterioration of the interface between the NCM cathode material and the sulfide solid electrolyte is the main reason that restricts the electrochemical performance of all solid-state batteries.At present,most researches focus on the modification of cathode materials and interface.There is still a lack of systematic research on the influence of NCM cathode materials with different compositions on interface problems.Based on the above introduction,this work starts from the composition of NCM and combines the LiNiO₂-LiCoO₂-LiMnO₂ ternary phase diagram.Co-precipitation method and high-temperature solid-phase method are used to prepare cathode materials to eliminate the influence of the particle size and morphology of the material on the overall experiment.Firstly,in order to control the valence state of the transition metal elements to be consistent,Niand Co series materials LiNi_xCo_1-xO₂ without Mn were synthesized.The electrochemical performance of each material was compared and combined with the impedance spectrum of the solid-state battery.If Ni³⁺rises,the specific capacity of the battery will increase,and will also lead to a decrease in cycle performance.The impedance change at the interface is more obvious,and the cathode/electrolyte interface deteriorates more seriously.Furthermore,in order to study the influence of Ni²⁺on the deterioration of the interface,a series of LiCo_x(Ni_0.5Mn_0.5)_1-xO₂materials with the same content of Niand Mn was designed and synthesized.Similarly,comparing the electrochemical performance and the impedance spectra of solid-state batteries,it is found that the increasing Ni²⁺content in the positive cathode material will also have a negative impact on the interface stability.