Preparation And Modification Of Lithium Rich-Manganese-Based Cathode Materials Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ With Stacked Structure

Lithium-rich manganese-based cathode material xLi₂MnO₃·?1-x?LiMO₂?M=Ni,Co,Mn??LRMO?has the advantages of high theoretical energy density,wide charge-discharge potential window?2.0-4.8V?,high safety and low price.It is an ideal choice for current cathode materials for high energy density power batteries.However,large irreversible capacity loss for the first time,poor cycle stability and low rate performance have greatly limited its application in high-performance lithium-ion batteries and all solid-state batteries.In view of the above problems,this thesis systematically studied the preparation of stacking structure lithium-rich manganese-based cathode materials and their microstructure,phase composition and electrochemical properties.Based on the above research,the Li₃VO₄/LiVO₃fast ion conductors heterostructure coated surface modification on the electrochemical performance of lithium-rich manganese-based cathode materials.Concluded as follow:?1?Compared with the effects of different precipitants NH₄HCO₃,NaHCO₃ and Na₂CO₃ on the composition,crystal structure and electrochemical properties of lithium-rich manganese-based cathode materials.It was found that the lithium-rich manganese-based cathode material prepared by using NH₄HCO₃ as a precipitant,complexing agent and pH adjuster has obvious stacking structure,and the materials prepared by using NaHCO₃ and Na₂CO₃ as precipitants have no stacking structure.The electrochemical performance comparison found the material with stacking structure has a specific discharge capacity of 261mAh/g at a current density of 0.1 C?C=250 mAh/g?,and the capacity retention rate is 91%after 100 cycles.No-stacking material has a specific discharge capacity of 184 mAh/g and the capacity retention of 78%after 100 cycles,indicating that the stacking structure present in the material can significantly increase the discharge specific capacity and cycle stability of the lithium-rich manganese-based positive electrode material.?2?The effects of pH value,NH₄HCO₃ concentration and calcination temperature,holding time and calcination atmosphere on the crystal structure,morphology and electrochemical properties of lithium-rich manganese-based cathode materials were systematically investigated.It was found that the positive electrode material prepared under the optimal process?pH=7.0,NH₄HCO₃ concentration is 1 mol/L,calcination temperature is850°C,holding time is 12 h,calcination atmosphere is dry air?has the best electrochemical performance.At a current density of 0.5 C,the specific discharge capacity was still 210 mAh/g after 150 cycles,and the capacity retention rate was 90.2%.At a current density of 5 C,the specific capacity is about 162 mAh/g.After 100 cycles,the specific capacity is about 145mAh/g and the capacity retention rate is 90%.?3?The lithium-rich manganese-based cathode material has poor rate performance due to its inherent low ion and electron conductivity.In this paper,a layer of Li₃VO₄/LiVO₃ fast ion conductor protective layer is coated on the surface of the lithium-rich manganese-based cathode material,which effectively reduces the side reaction at the electrolyte interface,and the high ion conductivity of the coating layer is conducive to the transmission of Li⁺,it also inhibits the release of O in Li₂MnO₃ and stabilizes the structure of the material,thereby significantly improving the first coulombic efficiency,rate performance and cycle stability of the lithium-rich manganese-based cathode material of the stack structure.It was found that the sample with a coating amount of 2wt%effectively improved the first coulombic efficiency,rate performance and cycle stability,and its performance index was far superior to that of the uncoated sample.At the current density of 0.1 C,the first Coulomb efficiency was increased from uncoated 66%to 72.5%and after 100 cycles at 2 C current density,the discharge specific capacity was 215 mAh/g and the capacity retention rate was 95%.The specific capacity of the discharge at a current density of 5 C is 181 mAh/g,the specific capacity after100 cycles is 165 mAh/g and capacity retention is 91%.