| LiCoO2 has been widely used as a cathode material in commercial lithium ion battery production at present. Due to the high cost and its own disadvantages of LiCoO2, many efforts have been made to replace it. Layered structure LiNi1/3Co1/3Mn1/3O2 composite compound has been considered as a promising candidate of new-generation cathode materials for rechargeable lithium ion batteries due to its higher capacity, longer cycle life, lower cost and no harm to environment. The research development of lithium ion battery was summarized in this paper. Based on this, a co-precipitation method was applied to obtain a new type of cathode material LiNi1/3Co1/3Mn1/3O2, and the synthesis technological condition and parameters were investigated systematically and optimized. And then the electrochemical characteristics, ICP-OES, XRD and SEM of the prepared LiNi1/3Co1/3Mn1/3O2 samples were investigated, and TiO2 modified LiNi1/3Co1/3Mn1/3O2 was prepared and characterized.Thermodynamic analysis of the Me2+ (Me = Ni, Co, Mn) - NH3 - OH- - H2O co-precipitation system was carried out. The thermodynamic analysis results show that the optimal pH value and ammonia concentration range for the precursor synthesis are 10.5～11 and 0.1～0.5 mol·L-1, respectively. The effects of several factors such as precipitating agent, pH value and ammonia concentration on precursors were investigated. On this basis, the optimal synthesis technological parameters were obtained, i. e. , NaOH + NH3·H2O as precipitating agent, controlling pH value of the solution as 10.5～11, the ammonia concentration as 0.24 mol·L-1. Considering of Mn(OH)2 being easily oxydated during the synthesis process, small amount of hydrazine hydrate was added in the precursor co-precipitation process. Hydrazine hydrate can inhibit effectively the oxidation reaction of manganese and the enhance operation reproducibility of preparation process and the electrochemical performance of LiNi1/3Co1/3Mn1/3O2 material with the optimal amout 0.48 mol·L-1 for hydrazine hydrate.The effects of different calcination temperature, calcination time and ratio of Li (LiOH·H2O) / Me (Me = Ni1/3Co1/3Mn1/3) on the structure and performance of the synthesized layered cathode material were investigated. On this basis, the optimal synthesis conditions were obtained, i. e., precursor was calcined at 500℃for 4 h, and then LiOH·H2O and precursors were mixed with 1.05 / 1 of Li / Me, the mixed materials were calcined at 500℃for 5 h and then calcined at 950℃for 12 h. Based on the above optimal conditions, the initial discharge capacities are 193.2 mAh·g-1 and 174.8 mAh·g-1, respectively, with a density of 0.1 C and 1 C at the potential range of 2.5～4.6 V, and the capacity retention maintains 94.16 % after 30 charge discharge cycles at the density of 1C. Cycle voltammetry test shows that one pair of redox peaks was corresponding to the redox process of Ni2+ / Ni4+ couple.In order to improve the cycle performance of layered LiNi1/3Co1/3Mn1/3O2, surface modification was carried out using TiO2 as coating agent. The results show that small TiO2 modification did not change the layered structure and tap density of LiNi1/3Co1/3Mn1/3O2, and the optimal coating amout was 2.0 %. And its capacity retains 95.74 % after cycling 30 times at the density of 1 C in the potential range of 2.5～4.6 V. |
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