Research On Modification Of Lithium-rich Layered Material Li_1.5Mn_0.7Co_0.15Ni_0.15O_2.5

Lithium-ion batteries are a major research hotspot in the current energy field and have broad application prospects.Lithium-ion battery is mainly composed of cathode material,anode material,separator and electrolyte.Among them,the cathode material is one of the key factors to determine the performance of lithium ion batteries,so the study of cathode materials is of great significance for lithium ion batteries.Lithium-rich layered materials have become the most widely studied cathode materials due to their high specific capacity,low cost and low pollution.At the same time,there are some problems such as low initial coulomb efficiency,fast voltage decay and poor rate performance.In order to improve these shortcomings,this paper takes the layered lithium-rich material Li_1.5Mn_0.7Co_0.15Ni_0.15O_2.5 as the research object,and uses the rare earth element La doping and coating on the surface of solid electrolyte to modify it.The specific research contents and results are as follows:1.The effect of rare earth element La doping on lithium-rich layered materialLi_1.5Mn_0.7Co_0.15Ni_0.15O_2.5wasstudied.La-doped Li_1.5Mn_0.7Co_0.15Ni_0.15O_2.5 samples were prepared by solid-state sintering method,and the doping amounts are 0 wt%,0.1 wt%,0.2 wt%and 0.3 wt%.The x-ray diffraction（XRD）experiment shows that the La-doped samples still maintain layered structure,and no impurity phase is observed.Li_1.5Mn_0.7Co_0.15Ni_0.15O_2.5 is composed of Li₂Mn O₃ phase and Li Ni_1/3Co_1/3Mn_1/3O₂ phase.The charge-discharge tests in the range of 2.0-4.5V show that the first discharge specific capacity and the first coulombic efficiency of the samples doped with 0.1 wt%and 0.2 wt%La are significantly better than those of the original samples.The initial specific discharge capacity increases from 236.2 m Ah/g to 251.5 m Ah/g and 254.9 m Ah/g.The first coulombic efficiency after doping increases from 77.95%to 82.56%and83.78%,respectively.The initial specific discharge capacity of the sample doped 0.3wt%La is only 230.2m Ah/g,the initial coulombic efficiency is65.33%,and the electrochemical performance is poor.The above results fully show that a small amount of La doping has a good effect on lithium-rich manganese-based materials.The voltage attenuation can also be alleviated by doping La.After 50 cycles,the voltage of the undoped sample decreases by0.254 V,while that of the sample with 0.1 wt%doping amount decreases by0.2326 V.The mitigation of voltage attenuation can effectively avoid the transformation of layered structure to spinel structure during the cycle.2.Lithium-rich layered material Li_1.5Mn_0.7Co_0.15Ni_0.15O_2.5 coated with solid electrolyte Li_1.4Al_0.4Ti_1.6（PO₄）₃（LATP）is prepared by sol-gel method,and the coating amount is 0 wt%,0.5 wt%,1 wt%,1.5 wt%and 2 wt%.The Lithium-rich layered material Li_1.5Mn_0.7Co_0.15Ni_0.15O_2.5was characterized by scanning electron microscopy,ansmission electron microscopy,X-ray diffraction,charge-discharge analysis,thermal analysis and electrochemical impedance spectroscopy.The experimental results show that LATP coating improves the cycle stability of the material.After 200 cycles at 0.6 C rate,the cycle retention rate of the uncoated sample is 72.7%,and the cycle stability of the sample with 1 wt%coating amount is the best to reach 85%.After multiple cycles,LATP coating effectively inhibits energy attenuation.LATP can improve the rate performance of the material.The sample with 1 wt%coating amount has the best rate performance,and the specific discharge capacity can still maintain 71.5 m Ah/g at 10 C rate,while the discharge specific capacity of the sample without coating is 60.1 m Ah/g.LATP coating alleviates the side reaction between the material surface and the electrolyte.As a solid electrolyte,it promotes the transmission of Li⁺and reduces the charge transfer impedance of the material.DSC was used to test the thermal stability of the samples before and after coating in fully charged state.DSC results show that LATP coating can improve the thermal stability of the materials.This work shows that coating LATP by sol-gel method can effectively improve the electrochemical performance of lithium-rich layered material.