Preparation And Electrochemical Properties Of NaCl Type High Entropy Oxide Anode Material

High entropy ceramics are a new type of ceramic material that has emerged in recent years.They are generally composed of five or more main components in equal or nearly equal molar ratios,and have a single crystal structure.Due to the unique phase composition and microstructure of this material,it has enormous exploration space in basic and applied research.In numerous studies on high entropy ceramics,rock salt type high entropy ceramics have received widespread attention from scholars both at home and abroad due to their simple structure and good electrochemical performance.On the basis of summarizing previous research,this article focuses on the systematic study of rock salt type（MgCoNiCuZn）O high entropy ceramic materials from two aspects:preparation methods and improving electrochemical performance.The specific research content and results obtained are as follows:（1）The influence of precipitation method preparation process on the microstructure and electrochemical performance of（MgCoNiCuZn）O high entropy ceramic powder was systematically studied,and the optimal process conditions for preparing（MgCoNiCuZn）O powder by this method were obtained.Research has shown that the lithium storage mechanism in the electrochemical reaction process of（MgCoNiCuZn）O is the mechanism of de intercalation lithium,and the five components have different roles in the electrode reaction process.Among them,Mg and Zn elements are the skeleton elements for constructing stable rock salt structures;The Jahn Teller synergistic effect of Cu,Ni,and Co elements is an important guarantee for achieving the lithium removal mechanism.Through this synergistic effect,Li⁺can be smoothly removed to the tetrahedral gap position.Ni and Co elements are key to the electrochemical performance of powders,and electron transfer is achieved through the valence state changes of the two elements.（2）The influence of hydrothermal preparation process on the microstructure and electrochemical performance of（MgCoNiCuZn）O high entropy ceramic powder was systematically studied,and the optimal process conditions for preparing（MgCoNiCuZn）O powder by this method were obtained.In the research,it was found for the first time that the high entropy carbonate solid solution（Mg Ni Co Cu Zn）CO₃（HECO₃s）phase was formed in the precursor obtained by hydrothermal method,and the higher the crystallinity of HECO₃s phase,the better the（MgCoNiCuZn）O crystal formed after high-temperature calcination,and the smaller the particle size,which greatly increased the contact area between the electrode and electrolyte;At the same time,the formation of HECO₃s precursor is conducive to the uniform distribution of the five metal elements in the structure,improving the active site of the reaction.Through the synergistic action of Co²⁺/Co³⁺and Jahn Teller of Ni²⁺/Ni³⁺,the crystal structure is stabilized,and the reversibility of the electrode is improved.（3）Rare earth oxide coated（MgCoNiCuZn）O powder was synthesized by hydrothermal method.The influence of different rare earth oxide coatings on the microstructure and electrochemical performance of（MgCoNiCuZn）O powder was discussed.The research results indicate that the degree of improvement in electrochemical performance of the products obtained by coating different rare earth oxides varies,in the order of Y<Yb<Ho<La<Er<Ce.The coating of rare earth oxides on the surface of（MgCoNiCuZn）O can form a uniform SEI layer on the negative electrode surface,which can withstand volume changes during cycling,stabilize the structure,and inhibit the growth of Li dendrites.（4）（MgCoNiCuZn）O powder with Fe element substituted M（M=Cu,Zn）was synthesized using hydrothermal method.The effects of different substitution amount on the microstructure and electrochemical performance of（MgCoNiCuZn）O were discussed.The research results indicate that when Fe replaces Zn,Fe enters the high entropy rock salt structure,participates in electrode reactions,and cooperates with Cu²⁺to provide more channels for the removal and insertion of Li⁺,resulting in improved electrochemical performance.The discharge capacity is631.5 F/g at 0.1 A/g,and the capacity retention rate can still reach 89%after 500 cycles.（5）（MgCoNiCuZn）O powder with Mn element substituted M（M=Cu,Zn）was synthesized using hydrothermal method.The effects of different substitution amount on the microstructure and electrochemical performance of（MgCoNiCuZn）O were discussed.After replacing M（M=Cu,Zn）with Mn,Mn forms Mn Co₂O₄ spinel phase with Co,and the content of Mn Co₂O₄ increases with the increase of substitution amount.It combines with high entropy ceramic powders to form a composite electrode,which combines the advantages of high entropy ceramic powders and Mn Co₂O₄,and significantly improves its electrochemical performance.The discharge capacity is 945.6 F/g at 0.1 A/g,and the capacity retention rate can still reach 93%after 500 cycles.