Hydrothermal Preparation And Electrochemical Properties Of LiNi_0.8Co_0.1Mn_0.1O₂ Cathode Materials

With the increasingly prominent environmental problems and rapid development of electric vehicles,lithium-ion batteries are increasingly being used.The requirements for high performance lithium-ion batteries are gradually increasing.The reversible capacity and cycle stability of cathode materials have become the key factors restricting the development of lithium ion batteries.Therefore,improving the performance of lithium ion battery cathode materials is the main task of current researchers.Ni-rich layered oxides cathode material has great potential for development due to its high theoretical capacity(280mAh g^-1).However,the cation mixing problem leads to poor cycle performance.In this paper,the effects of hydrothermal temperature,calcination temperature,heating rate,calcination atmosphere and sodium ion doping amount on the physical and chemical properties of Ni-rich layered oxides cathode material were systematically studied.LiNi_0.8Co_0.1Mn_0.1O₂ cathode material was prepared by hydrothermal method and the effects of hydrothermal temperature and calcination temperature on the structure and morphology were studied.The result shows that the cathode material prepared by the hydrothermal temperature between 180°C and 240°C can achieve a well-crystallinity structure,while the hydrothermal temperature below 180°C causes incomplete precipitation of Ni²⁺and poor crystallinity.Excessively high and low calcination temperature have an adverse effect on the crystallinity of the material and the formation of the layered structure.The optimum calcination temperature is 850°C,at which the cation mixing degree of the material is also the lowest.Therefore,the electrochemical performance for the material prepared at 850°C is greatly improved compared with materials prepared at other temperatures.The main reason for the presence of cations in the LiNi_0.8Co_0.1Mn_0.1O₂ material is that Ni²⁺and Li⁺radii are similar,but the Ni³⁺radius and Li⁺radius are quite different.Studies have shown that the oxidation reaction can be more sufficient by reducing the heating rate in the calcination process or changing the calcination atmosphere to oxygen,which is beneficial to the oxidation of Ni²⁺into Ni³⁺,thus effectively reducing the cation mixing degree in the material.So,electrochemical properties of the material have also been significantly improved.The LiNi_0.8Co_0.1Mn_0.1O₂ material prepared by the hydrothermal temperature 220°C,calcination temperature 850°C,calcination rate3°C/min,and calcination atmosphere of oxygen exhibits the best electrochemical performance,with initial discharge capacity is as high as 144 mAh g^-1,the capacity retention rate still 81.9%after 50 cycles.The average discharge capacity circulating at 2C current density was still 57.1mAh g^-1.Na-doped LiNi_0.8Co_0.1Mn_0.1O₂ cathode material was prepared by molten-salt method.The effect of Na⁺doping amount on electrochemical properties of materials was investigated.Studies show that Na⁺doping further reduces the cation mixing degree in the material and supports the crystal structure by entering the lithium layer.Therefore,the discharge capacity and cycle stability of the material are significantly improved.The material with Na⁺doping amount of 0.5%has the highest discharge capacity with initial discharge capacity is 172.8mAh g^-1,and the material with Na⁺doping amount of 1%has the best cyclic stability with the capacity retention rate is 92.2%after 30 cycles at 0.1C rate.