Synthesis Of Lithium-ion Battery Cathode Material LiNi_0.6Co_0.2Mn_0.2O₂ By Solid State Method And Magnesium Ion Doping Modification

LiNi_0.6Co_0.2Mn_0.2O₂ combines the advantages of high stability,easy preparation,high capacity and low cost of ternary cathode materials and is a promising cathode material for lithium ion batteries.For such materials,the coprecipitation precursor method is generally used at present,but the precursor method requires high control accuracy,long process and large waste liquid,which makes it difficult to effectively reduce its manufacturing cost.In this paper,the electrochemical performance of LiNi_0.6Co_0.2Mn_0.2O₂ cathode material synthesized by traditional solid-state method is improved by selecting suitable manganese sources,improving the mixing method,optimizing the Li excess ratios and improving the sintering system,and the effects of Mg ions doping on its electrochemical performance is discussed.The details are as follows:The effects of three different Mn sources of MnO₂,Mn₃O₄ and Mn?CH₃COO?₂·4H₂O on the physical and electrochemical performances of LiNi_0.6Co_0.2Mn_0.2O₂ cathode material synthesized by the solid-state method are studied.XRD,XPS and SEM test results show that compared with MnO₂ and Mn₃O₄,the product with Mn?CH₃COO?₂·4H₂O has a higher crystallinity,a lower degree of cation mixing,and the particles morphology mainly reveals polyhedral single crystal with diameters of about 0.2–0.5?m,which has a narrower of distribution and a better of dispersion.Electrochemical test results show that the product synthesized with Mn?CH₃COO?₂·4H₂O as manganese source has a high electrochemical reversibility and a low electrochemical impedance,and delivery a specific discharge capacity of 163.8 mAh·g^-1 at 0.1C,which is greater than 148.1 mAh·g^-1 and 160.5 mAh·g^-1 of MnO₂and of Mn₃O₄,respectively;the capacity retention rate of is 98.2%higher than 88.9%of MnO₂and 96.0%of Mn₃O₄ after 100 cycles at 0.5C rate.The lithium ion diffusion coefficient is 6.58×10^-9 cm²·s^-1,which is about 1.4 times than that of the product prepared with other tow manganese source.In order to explore the suitable process conditions for the preparation of LiNi_0.6Co_0.2Mn_0.2O₂ cathode material by solid-state method with manganese acetate,the effects of the three key parameters on the physical and electrochemical performance of the product were investigated,including Li excess ratios,calcination temperature and calcination time.The experimental results show that proper increase of Li excess ratios,calcination temperature or calcination time can help to improve the crystal structure order,particle dispersibility and electrochemical performance of the product.The product obtained by sintering 875?for 21 h with an excess Li ratio of 10%has a high order of crystal structure,and the particle is regular polyhedron with a size of about 0.5–1.0?m and good dispersion.It displays an initial discharge specific capacity of 177.8 mAh·g^-1 with a coulombic efficiency of 88.7%at 0.1C,a capacity retention rate of 95.7%after 100 cycles at 0.5CThe effect of Mg²⁺doping on the physical and chemical properties of Li[Ni_0.6Co_0.2Mn_0.2]_1-xMg_x O₂?x=0,0.01,0.03,0.05?is investigated.The experimental results show that the proper amount of Mg²⁺can effectively improve the order of the crystal structure of LiNi_0.6Co_0.2Mn_0.2O₂.The 3%Mg²⁺doped sample has a good cycle stability,and the capacity retention rate is 94.9% after 100 cycles at 0.5C at 25?,which close to 95.3%of the substrate,but the capacity retention rate reach up to 95.5%at 55?,which higher than 86.9%of th substrate.The 1%Mn²⁺doped sample has a good rate performance,and the specific discharge capacity at 2C is85.7%of that at 0.1C,which higher than 78.6%of the substrate,and its lithium ion diffusion coefficient is about 2.44×10^-9 cm² s^-1,which is 1.7 times that of the substrate.