Preparation And Modification Of Li-rich Mn-based Solid Solution By Solid-Phase Method

Li_1.2Ni_0.13Co_0.13Mn_0.54O₂,Li-rich Mn-based cathode material with high specific capacity has attracted widespread attention due to the redox of anions.However,unstable oxygen in the surface structure of materials can be generated and released through oxidation reactions,accompanied by the structural collapse of material,exhibiting a series of problems such as rapid voltage decay,poor rate performance,and poor cycle stability.These are key issues that hinder the commercialization of Li-rich Mn-based cathode materials.The traditional bulk doping method can reduce the ability of oxygen anions to participate in redox reactions,resulting in a decrease in the actual capacity of Li-rich Mn-based cathode materials.Therefore,this article studyed doping F element on the surface of Li-rich Mn-based cathode materials in order to improve the binding force between oxygen and transition metals,inhibit the release of oxygen while maintaining the ability of oxygen anions to participate in redox reactions.The main contents are as follows:（1）The layered Li-rich Mn-based cathode material LNCM was prepared by solid-phase sintering method,which is simple in preparation process and suitable for large-scale production.The effects of synthesis conditions such as calcination temperature,reaction time,and reaction materials on the structure,morphology,and properties of LNCM were studied.The structural stability and cycle stability of LNCM were improved by controlling factors such as the grain size and the degree of Li/Ni mixing.Electrochemical performance studies have shown that the Li-rich Mn-based cathode material synthesized from metal oxides at a reaction time of 10 hours and a calcination temperature of 900℃has good electrochemical performance.Finally,the first discharge specific capacity of LNCM is 264.7 m Ah·g^-1,the initial coulomb efficiency（ICE）is77.9%,and the capacity retention rate for 100 cycles at a current density of 1 C is 66.8%.（2）A modified material Li_1.2Ni_0.13Co_0.13Mn_0.54O₂-_xF_x doped with fluorine in bulk phase was synthesized by solid-state sintering method to improve LNCM structural stability.The analysis of material structure and electrochemical performance shows that element F can be doped into the lattice of Li-rich Mn-based materials without changing the layered structure,while improving the covalence of the transition metal oxygen bond.Therefore,it can effectively inhibit the irreversible loss of lattice oxygen and stracture phase transtion.When the doping amount of F element is 5 mol%,the bulk doped synthesis Li_1.2Ni_0.13Co_0.13Mn_0.54O_1.95F_0.05 has good electrochemical performance,with a first discharge specific capacity of 204.0 m Ah·g^-1,the ICE of 61.4%,and a capacity retention rate of 73.1%for 100 cycles at 1 C.（3）On the basis of this study,the surface doped modified material Li_1.2Ni_0.13Co_0.13Mn_0.54O₂-_xF_x was synthesized by using a simple solution method.Studies on the structure and electrochemical properties indicate that the doping of F element into the lattice of the surface structure of the material,improve the stability of the surface structure while retaining the ability of oxygen anions within the particles to participate in redox reactions.When the doping amount of F element is 5 mol%,the surface doped synthesis Li_1.2Ni_0.13Co_0.13Mn_0.54O_1.95F_0.05 has good electrochemical performance,with a first discharge specific capacity of 210.3 m Ah·g^-1,the ICE is 74.8%,and a capacity retention rate of 93.5%for 100 cycles at 1 C.