Preparation And Modification Of LiNi_0.8Co_0.1Mn_0.1O₂ Materials For Lithium Ion Battery

The vigorous development of new energy electric vehicles and energy storage industries has driven the demand for lithium-ion batteries to skyrocket.In the lithium-ion battery market,especially for automotive lithium-ion batteries,ternary nickel-cobalt-manganese batteries have the advantages of both cost and energy density so that they occupy a large part of market share.Retired automotive ternary batteries can also be explored for large-scale energy storage.Increasing the proportion of nickel content in the ternary battery can achieve higher energy density.However,the increasing in the proportion of nickel content increases the difficulty of the synthesis of the positive electrode material,and it is easier to mix cations at high temperature,which reduces the active lithium content in the lithium layer.In addition,the increasing of the nickel content and the decreasing of the stable manganese content also reduces the cycle stability of the battery.The side reaction between the positive electrode and the electrolyte is more serious.In addition,the lattice oxygen on the surface of the ternary material is more likely to be lost under high temperature and high voltage,resulting in the transformation of the layered structure,the dissolution of transition metals and the increasing of gas in the battery,which are more likely to cause spontaneous combustion accidents of electric vehicles,and are also not conducive to the echelon utilization of retired ternary batteries.Solving these problems of ternary materials and releasing the new energy consumption potential is a major challenge for researchers.In this paper,using metal acetate as the reactant and citric acid as the complexing agent,the Li Ni_0.8Co_0.1Mn_0.1O₂material was prepared by the sol-gel method combined with the high temperature sintering process under oxygen atmosphere.The sintering temperature and time were changed respectively to study the influence of this two factors on the morphology,phase and electrochemical performance of the prepared material for optimizing the most suitable sintering process parameters.It is found that when the sintering time is 15 h and the sintering temperature is 750°C,the obtained material has a moderate particle size,and the primary particles are tightly agglomerated,belonging to theα-Na Fe O2 configuration.Electrochemical tests show that it has the highest 0.1 C first discharge specific capacity of 152.0 m Ah/g,but the cycle stability is poor,the capacity retention rate of 50 cycles at 1 C is only about 79.54%.In order to improve the cycle stability of the ternary material,this paper firstly prepared the amorphous Si O₂ coated ternary material by hydrolysis of tetraethyl silicate.The results show that the coating will not significantly change the degree of cation mixing and the layering structure of the ternary material.The first discharge specific capacity at0.1 C before and after coating is about 150 m Ah/g.After 100 cycles of 1 C at 3.0 V-4.5V,the capacity retention rate of the Si O₂coated material is about 91.52%,which is much higher than that of the uncoated material.The Si O₂ coating slows down the side reactions between the ternary material and the electrolyte,alleviates the phase change of H2-H3,and significantly improves the cycle stability of the ternary material.In this paper,a boron-doped ternary material was also prepared by the high temperature treatment of the powder derived from the xerogel pre-sintering with boric acid.The results show that the doping suppresses the cation mixing of the ternary material during the synthesis process,and the more excellent layered structure is obtained.The first discharge specific capacity of the doped material at 0.1 C is as high as 170.3 m Ah/g,the capacity retention rate of150 cycles at 1 C under the voltage of 3.0 V-4.5 V is 89.4%,and the capacity retention rate of 150 cycles of the undoped material is only 57.82%.Doping suppresses the unstable H2-H3 phase transformation of the ternary material during charging reduces the electrochemical reaction resistance,as well as promoting the diffusion of lithium ions,and improving the electrochemical performance of the ternary material.