The Synthsis And Modification Of Ternary Layered LiNi_1-x-yCo_xM_yO₂ Cathode Material

Single LiNiO₂ and LiCoO₂ layered cathode materials have many shortcomings,muiti-element compound layered cathode materials can integrate the advantages of these at the same time,so this kind of materials are regarded as the most promising material to supersede commercialized LiCoO₂.In this study, the spherical precursor of Ni_0.8Co_0.15Al_0.05（OH）₂ and Ni_0.6Co_0.2Mn_0.2（OH）₂ were synthesized from liquid-phase co-precipitation method respectively. LiNi_0.8Co_0.15Al_0.05O₂ and LiNi_0.6Co_0.2Mn_0.2O₂ powders synthesized from co-precipitated spherical metal hydroxide by the high temperature solid method. In this paper, we seek for the optimal the process conditions of high temperature sintering stage and LiNi_0.6Co_0.2Mn_0.2O₂ material was modified by surface coating AlPO4 to improve its high temperature cycle performance. Moreover, a variety of analytical methods such as TG-DTA、XRD、SEM、EDS、CV、EIS、Land were used to make a systematic study on the structure, morphology and electrochemical properties of the cathode materials.（1） The experimental results show that the precursor Ni_0.8Co_0.15Al_0.05（OH）₂ possess regular crystal structure, uniformly distributed and easy dispersibility of the particles.The filamentous primary particle accumulated to grow the spherical secondary particles.TG-DTA analysis of the mixture of the precursor and LiOH·H2O indicated that it was appropriate to adopt the two-stage sintering condition. The optimum experimental conditions were achieved as follows: 500oC5 h and 720oC20 h, in oxygen atmosphere,the oxygen flow rate of 300mL/min lithium molar ratio n（Li）/（Ni+Col+Al）=1.08. For the desired sample, the highest discharge capacity of the material was 199.5mAh/g and90.3% of the capacity was maintained after 80 cycles. Cycle voltammrtry tests confirmed the good reversibility and stronger cycle stability of the material. Its electrochemical performance under the condition of 0.2C-2C rate was relatively good,but at the high rate of 5C, the capacity of the material degraded quickly to only about70mAh/g.（2） The precursor Ni_0.6Co_0.2Mn_0.2（OH）₂ had spherical morphology and the transition metal content by EDS test with the qualitative analysis close to the theoretical value.Li Ni_0.6Co_0.2Mn_0.2O₂ powders were synthesized from co-precipitated spherical metal hydroxide by the high temperature solid method. The material, synthesized by theoptimum conditions, the initial discharge capacity was 159.3mAh/g, and remained139.1mAh/g after 50 cycles at 0.5C in the voltage of range of 2.7⁴.3V,room temperature. However, the Li Ni_0.6Co_0.2Mn_0.2O₂ material had the initial discharge capacity of 172.1mAh/g and was inferior to 38% capacity retention of the samples in the charge-discharge test under 55 ℃. The effects of the coated AlPO4 on the elevated temperature properties of LiNi_0.6Co_0.2Mn_0.2O₂ was investigated. The results showed that the right amount of Al PO4-coated could improve the high temperature cycle stability.The 2.wt% AlPO₄-coating material showed excellent high temperature cycle stability,the initial discharge capacity was 165.9mAh/g and 50 cycles under 55℃ capacity retention rate is 75.4%.