Study On The Effect Of Cathode Modification On The Performances Of High Voltage Lithium Manganate/Lithium Titanate Battery

With the advantages of high energy density,long cycle life,low price and easy portability,lithium-ion batteries are widely used in electric vehicles,portable devices and military aerospace.Lithium-ion battery consists of several parts:cathode material,anode material,diaphragm and electrolyte.Among them,the performance of cathode material is one of the factors that directly affect the performance of the battery,so the in-depth research on cathode material can promote the development of lithium-ion batteries.The spinel material Li Ni_0.5Mn_1.5O₄（LNMO）has an advantage of high energy density due to its Ni²⁺/Ni⁴⁺redox coupling that produces a high operating voltage of about 4.7 V（vs.Li/Li⁺）,making it one of the most attractive cathode materials for Li-ion batteries.Spinel Li₄Ti₅O₁₂ is a"zero-strain"insertion semiconductor material that has become a highly sought-after anode material for power Li-ion batteries due to its excellent cycling performance and stable structure.In this paper,a high-voltage lithium manganate Li Ni_0.5Mn_1.5O₄ cathode material with a spinel structure is selected as the research object,which is modified by solid electrolyte surface coating and metal aluminum ion doping,and the cathode is matched with lithium titanate as the cathode to investigate the effect of cathode modification on the electrochemical performance of the whole battery.The specific research contents and results are as follows:1.High-voltage lithium manganate Li Ni_0.5Mn_1.5O₄（LNMO）materials coated with a solid electrolyte Li_1.3Al_0.3Ti_1.7（PO₄）₃（LATP）were prepared by the sol-gel method.The Li Ni_0.5Mn_1.5O₄ materials coated with Li_1.3Al_0.3Ti_1.7（PO₄）₃ were characterized by scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,X-ray diffraction（XRD）,charge-discharge analysis and electrochemical impedance（EIS）analysis.The experimental results show that the crystallinity of the cathode material is good after LATP coating,which can enhance the thermal stability of the material.The first charge/discharge test at 0.2 C magnification showed that the LNMO/LATP2sample coated with 2 wt%Li_1.3Al_0.3Ti_1.7（PO₄）₃ had the highest platform capacity.After50 charge/discharge cycles under constant current charge/discharge conditions with a current of 0.5 C,it was found that the highest capacity retention and the best LNMO/LTO full cell cycling performance were achieved when the LATP cladding was2 wt%;the material with 2 wt%cladding had the best multiplicative performance.The analysis of the median discharge voltage after 50 cycles of constant current charge/discharge at 0.5 C showed that the sample with 2 wt%of coating had the highest median voltage retention and the slowest voltage decay.The results of AC impedance analysis（EIS）showed that the materials with 1 wt%and 2 wt%of LATP coating had lower Rct values than the original materials,and the LATP coating promoted the charge transfer of Li⁺,which could improve the interfacial stability and reduce the interfacial charge transfer resistance.2.The effect of metal-Al ion doping on high-voltage Li Ni_0.5Mn_1.5O₄ materials was investigated.The Al-doped high-voltage Li Ni_0.5Mn_1.5-xAl_xO₄ materials were prepared by organic matter-assisted combustion method.The experimental samples were characterized by scanning electron microscopy,transmission electron microscopy,X-ray diffraction,and electrochemical impedance analysis.The experimental results showed that the Al elements were uniformly doped into the Li Ni_0.5Mn_1.5O₄ material.The cell shrinkage of the sample after Al doping indicates that the Al element has entered the material lattice and achieved the bulk phase doping.The first charge/discharge test at 0.2 C magnification showed that the appropriate amount of Al doping could inhibit the occurrence of Mn³⁺/Mn⁴⁺electrochemical reaction and Mn³⁺production,and improve the stability of the structure.After 50 charge/discharge cycles at a constant current of 0.5 C,the sample with a doping amount of x=0.1 showed a capacity retention of 70%and the LNMO/LTO full cell exhibited the most excellent cycling performance.The doped and undoped five materials were tested at 0.2 C～10 C for charge/discharge,and it was found that the doped material with x=0.05 had the best multiplicative performance;the Al-doped cathode material could reduce the loss of energy density of the full cell.50 cycles of charge/discharge at 0.5 C constant current showed that the median discharge voltage could be effectively maintained by the appropriate amount of Al element doping.The results of AC impedance analysis（EIS）show that the Rct values of materials with doping amounts of x=0.1,x=0.15 and x=0.20are abnormally large,probably due to excessive Al doping,which aggravates the side reactions of the electrolyte inside the cell causing difficulties in Li-ion movement.