The Preparation And Perfromance Of Li_1.256Ni_0.198Co_0.082Mn_0.689O_2.25 Cathode Materials For Lithium-ion Batteries

With the rapid development of science and technology,lithium-ion batteries have been used in various devices,including electric cars,hybrid cars and mobile electronic devices.Li-rich manganese-based layered oxide cathode material has attracted much attention in recent years due to its high electrochemical capacity,low cost and environmental friendliness.However,Li-rich manganese-based layered oxide cathode materials also has disadvantages such as poor rate performance and poor cycle performance.In this paper,Li1.256Ni0.198Co0.082Mn0.689O2.25(LLMO)cathode material was successfully prepared by co-precipitation method.At the same time,the prepared LLMO cathode material was surface modified.In this paper,the effect of reaction temperature,pH value,Li/M value and calcining condition on the electrochemical performance of the prepared materials were studied.The optimal preparation conditions were obtained through research and analysis.For the problem of poor rate performance,the LLMO cathode material was treated with different concentrations of(NH4)2S2O8 solution in this paper.The rate performance of the LLMO after treatment was improved.Through analysis and comparison of XRD and electrochemical performance,it is found that 40wt%is the optimal concentration of(NH4)2S2O8 solution,and the treated sample reveals discharge capacity of 274,232,216 and 174 mAh·g-1at current densities of 0.1C,1C,2C and 5C,respectively.In contrast,LLMO sample reveals discharge capacities of 245,209,176 and 125 mAh·g-1 at current densities of 0.1C,1C,2C and 5C,respectively.Herein,we further propose a methode to improve the rate performance and cycle performance of LLMO cathode material at the same time by constructing a spinel/Al2O3 double-shelled structure.In our work,the Al(NO3)3·9H2O was used to modified LLMO cathode material,and the spinel/Al2O3 double-shelled structure was successfully constructed after that.Through analysis and comparison of XRD,TEM,XPS and electrochemical properties,it is found that 500 ? is the best calcination temperature.The rate performance and cycle performance of sample Al-500 are significantly improved.The sample Al-500 has an initial discharge capacity of 282 mAh·g-1 at 0.1C rate,an initial discharge capacity of 240 mAh·g-1 at 1C rate,and a retention rate of 95%after 50 cycles.In addition,the sample Al-500 shows a discharge capacity of 189 mAh·g-1 at 5C rate.In contrast,the sample LLMO has an initial discharge capacity of 252 mAh·g-1 at 0.1 C rate,an initial discharge capacity of 203 mAh·g-1 at 1C rate,and a retention rate of 86%after 50 cycles.The sample LLMO shows a discharge capacity of 123 mAh·g-1 at 5C rate.Through analysis and comparison,it is proved that the spinel/Al2O3 double-shelled structure can simultaneously improve the cycle performance and rate performance of LLMO materials.