| Because of its high specific energy,good cycle performance,low cost,environmental benignity and etc.,the ternary NCA material is currently one of the the most potential cathode materials for lithium-ion battery.However,the harsh synthesis conditions and poor thermal stability restrict its application and development in the field of power batteries.In this paper,the preparation of NCA material and its electrochemical performance were studied with the aim of exploring a promising industrial production method.Ni0.8Co0.15Al0.05(OH)2 precursor was prepared by co-precipitation controlled crystallization method,and then,LiNi0.8Co0.15Al0.05O2 cathode material was prepared by solid state sintering method.The morphologies,structure and electrochemical properties of the precursors and NCA cathode materials were characterized by means of SEM,XRD,cyclic charge-discharge test and cyclic voltammetry,and the effects of processing methods and parameters on the structure and properties of the materials were investigated.Firstly,the precursor of NCA was prepared by using ammonia and sodium salicylate as complexing agents.The effects of different organic complexing agents,pH value and complexing agent concentration on the particle size,morphology,structure and electrochemical properties of NCA precursor were investigated.By analyzing the thermodynamic of the co-precipitation system,the optimum pH range and ammonia range concentration were determined to be pH = 10.0 ~ 11.5 and c(NH3)= 0.1 ~ 0.3mol / L,respectively,for the co-precipitation reaction.Under the conditions of sodium salicylate as complexing agent,sodium salicylate concentration of 0.05mol/L and the pH value of 10.5,the precursors had a ?-Ni(OH)2 type structure and its D50 equaled 8.53 ?m.The first specific discharge capacity of the NCA materials which were prepared from those precursors was164mAh/g at 0.2C rate.After 100 cycles,the specific discharge capacity was 131.5 mAh/g and the capacity retention rate was 80.2%,which exhibited good electrochemical performance.Secondly,the NCA materials were prepared by solid state sintering method,and the effects of sintering temperature,sintering time and lithium ratio on the structure and properties of the NCA materials were analyzed.The TG-DSC analysis of the mixed powdersof Ni0.8Co0.15Al0.05(OH)2 and Li OH·H2O was investigated.The results showed that the heat preservation temperature should be controlled in the range of 500?~ 600 ?,and the sintering temperature should be controlled at 700?~ 800?.When the lithium ratio was 1.05,the NCA materials prepared by sintering at 700?for 12 h had the best electrochemical performance.The first discharge specific capacity was 180.4 mAh /g,the first Coulomb efficiency was 87.3%,the capacity retention rate was 80.7% after 100 cycles,and the first discharge specific capacity can reach 155.7mAh / g at 1C rate.Finally,the NCA materials were prepared by sodium aluminate process(process III).The effects of pH value on morphology,structure of the precursors and electrochemical properties of the NCA materials were analyzed,and were compared with ammonia as complexing agent(process I),and ammonia and sodium salicylate as complexing agent(process ?).The NCA materials which were prepared at pH=10.0 had the best electrochemical properties.The first discharge specific capacity was 197.1mAh/g,and the first Coulomb efficiency was 88.7%.After 100 cycles,the capacity retention rate was 90.4%.The results of cyclic voltammetry indicated that the redox potential of the electrode reaction was 0.060 V,i.e.,the reversibility of electrode reaction was good.Comparing with other processes,it can be found that the process of sodium aluminate could not only solve the problem of uneven precipitation of Al3+ in process?,but also avoid the problem of anion residue of the complexing agents in process ?,which was a promising method for industrial application. |
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