Study On Preparation And Modification Of Layered Lithium-Rich Manganese-Based Lithium-Ion Battery Cathode Materials

In recent years,lithium-ion batteries have been widely used in light portable electronic products as energy storage devices with the most application and development prospects,and have gradually penetrated into the automotive and aerospace industries.Therefore,it is imperative to develop cathode materials for lithium ion batteries with high energy density,safety and environmental protection.Li-rich Mn-based materials have received extensive attention due to their high specific discharge capacity（>250 mAh/g）、wide voltage window range and environmentally friendly.Which is expected to become the next generation of new Li-ion battery cathode material.However,Li-rich Mn-based materials also have some defects such as layered structure easily transfer and poor cycle stability,which hinders the apply of this material.In this paper,Li[Li_0.17Ni_0.25Mn_0.58]O₂ and Co-doped Li[Li_0.17Ni_0.25Mn_0.58]O₂ were prepared by spray-heat drying method.There are comprehensively studied and analyzed about the materials before and after doping on the structure,morphology and electrochemical properties.The result is that the XRD diffraction patterns of the materials before and after doping are basically the same,but the doping is beneficial to reduce the degree of cation mixing of the materials.The doped material has a particle diameter between 200-300 nm and undergoes secondary agglomeration to form a rough morphology.The initial discharge specific capacity of Li[Li_0.17Ni_0.25-XMn_0.58Co_0.04]O₂ increased from 242.6 mAh/g to 265.6mAh/g when X=0.04;Capacity retention rate 80.2%increased to 90.8%after 50 cycles of charge and discharge cycles,at the current density of 0.1 C.Three process conditions that have great influence on the performance of synthetic Li[Li_0.17Ni_0.25-XMn_0.58Co_0.04]O₂,Lithium ratio、Sintering temperature and sintering time was discussed.There was no significant change in the morphology of the sample when the lithium source was 5%excess.The discharge specific capacity of the first cycle was increased from265.6 mAh/g to 271.4 mAh/g and from 244.2 mAh/g to 250.1 mAh/g after 50 cycles.The sample prepared at 850°C has the best layering property and the smallest cation mixing.Which first discharge specific capacity is 273.5 mAh/g and the first cycle Coulomb efficiency is 83.99%.Capacity retention rate of 92.55%after 50 cycles at 0.1 C.Sintering time affects cell size,The material has good cell volume and electrochemical performance when the sintering time is 10 h after Jade software fitting analysis and calculation of Scherrer formula.Furthermore,in-situ composite of liquid polyacrylonitrile（LPAN）for Li[Li_0.17Ni_0.25-X.25-X Mn_0.58Co_0.04]O₂（named as LNMC@LPAN）,the surface of Li-rich Mn-based materials was formed a Nano-scale coating that effectively resist the corrosion of electrolyte and inhibit the transformation of layered to spinel structure in condition of Jahn-Teller eff ect.The material has a smoother morphology,higher conductivity,and reduced specific surface area after compounding.The cycle performance in the electrochemical propert ies of the material is greatly improved:the capacity retention ratios of the Li-rich Mn-based materials with a composite LPAN ratio of 10%,20%,and 30%after 50 cycles of charge and discharge at 0.1 C were 94.89%,95.43%,and 96.35%,and 90.98%、97.79%、98.35%at 1 C,respectively.