Bulk Doping And Surface Modification Of High-voltage Spinel LiNi_0.5Mn_1.5O₄ Cathode Material

With the rapid development of new energy electric vehicles,higher requirements are being placed on the cost and energy density of lithium-ion batteries.Spinel type LiNi_0.5Mn_1.5O₄（abbreviated as LNMO）has attracted much attention due to its high energy density（650 Wh/kg）,working voltage（4.7 V）,low cost,and other advantages.However,the structure of LNMO is unstable during high voltage cycling,and serious side reactions between its surface and the electrolyte limit its further development.In this work,doping and coating modification strategies are adopted to optimize LNMO positive electrode and improve its electrochemical performance.The specific research contents are as follows:（1）Nd³⁺is selected to modify LNMO by bulk doping,and Nd³⁺is added in the process of sol gel synthesis of LNMO.Using the rivet effect of rare earth elements and the strong binding energy of Nd³⁺–O^2-bond,the structural stability of LNMO is improved,the content of Mn³⁺is reduced,and the dissolution of Mn is inhibited.The results show that the capacity retention rate of LNMO doped with 0.01 stoichiometric ratio after 300 cycles at 1 C is 96.5%,while the unmodified sample is only 52.7%.（2）PrF₃ nanocoatings are constructed by wet chemistry to stabilize the surface of LNMO electrodes to solve such problems.The electrochemical test results show that the Pr F₃ nanocoating can effectively improve the electrochemical performance of LNMO electrode,especially at high temperature.The LNMO sample with 1wt%Pr F₃coating has a discharge specific capacity of 110.3 m Ah g^-1 after 100 cycles at 55℃and0.2 C,with a capacity retention rate of 91.4%.However,the capacity of the uncoated sample decays to 0 after 91 cycles.The post cycle electrode test shows that Pr F₃nanocoating can serve as an artificial CEI film to suppress the side reaction between LNMO and electrolyte.（3）Mg_0.5Ti₂（PO₄）₃（MTP）precursor with LNMO precursor,and generate a uniform MTP coating layer in situ on the surface of LNMO through one calcination.The process of co crystallization and calcination can limit the secondary growth of LNMO particles,shorten the diffusion path of Li⁺,and realize co-doping of Mg²⁺and Ti⁴⁺to improve the structural stability of LNMO,achieving the effect of triple optimization.The capacity retention rate of LNMO with a 1%molar ratio of MTP coating after 500 cycles at 1 C is 81.7%,while the unmodified sample is only 39.3%.