Study On Preparation And Modification Of LiNi_0.8Co_0.15Al_0.05O₂

The main factors affecting the energy density of batteries are cathode materials.LiNi_0.8Co_0.15Al_0.05O₂ has a high capacity and low cost.It is quite suitable for single cell battery cathode.However,its stability and rate performance are poor.Existing preparation methods are difficult to meet the market demand.In order to improve the cycle stability and rate performance of LiNi_0.8Co_0.15Al_0.05O₂ cathode material,Ni_0.8Co_0.15Al_0.05?OH?_2.05 was synthesized by co-precipitation using AlO₂^-as Al³⁺source.First,Ni_0.8Co_0.15Al_0.05?OH?_2.05 was preheated and oxidized,then lithium was mixed and sintered to obtain cathode material.The transformation of structure,morphology and electrochemical properties of the cathode materials under preheating oxidation treatment,micro changes in sintering temperature and lithium ratio was investigated.To improve the cycle and rate of LiNi_0.8Co_0.15Al_0.05O₂material,La³⁺\Na⁺\conductive graphite was added.The mechanism of electrochemical performance change was characterized by XRD,SEM,XPS,EIS and charge-discharge tests.After heat treatment,OH^-in Ni_0.8Co_0.15Al_0.05?OH?_2.05 precursors was removed and transition metal ions were oxidized.LiNi_0.8Co_0.15Al_0.05O₂ cathode was synthesized by adding lithium source and sintering.The higher heat treatment temperature,the higher the crystallinity of transition metal oxides and the more uniform the size distribution of cathode particles.The heat treatment temperature was set up at 650°C,and the obtained cathode material has the highest content of Ni³⁺.The positive electrode material has the lowest cation mixing and the best crystal order.A slight fluctuation within 750-820 ^oC caused noticeable differences in electrical properties.Optimum sintering temperature was 780 ^oC,the specific capacity at 0.5 C,2.75-4.2 V cycles is 184.65 mAh g^-1,the stable rate of 100 cycles is 84.62%,and the specific capacity of 5 C rate was 130.01 mAh g^-1.Cathode materials added with La³⁺and Na⁺were prepared by co-precipitation method and doping method.The structure,morphology and electrochemical properties of the materials were analyzed.The stability of 0.5 C was increased by20.3%,the cyclical stability of 1 C ratio was increased by 23.15%,and the specific capacity of 5 C ratio was increased by 19.90 mAh g^-1.When Na⁺content is 0.05,the performance is the best.Initial specific capacity was 206.67 mAh g^-1,cycle capacity was 193.00 mAh g^-1 at 0.5 C.After 100 cycles,cycle stability increases from 72.83%to 83.50%.Porous cathode materials were obtained by sintering conductive graphite wrapped by precursor precipitation in water.Adding amount of 2wt%endows cathode materials with the best stability and rate performance.Initial specific capacity at 0.5 C cycle was 189.78 mAh g^-1.After 100 cycles retention rates of 76.96%were increased to 88.56%,the specific capacity at 5 C cycles was increased from 122.20 mAh g^-1 to 145.30mAh g^-1.