Synthesis and electrochemical properties of Li-excess Li1+x[Ni0.5Co0.2Mn0.3]O2 cathode materials using ammonia-free chelating agent

•Ni0.5Co0.2Mn0.3(OH)2 was prepared via co-precipitation using oxalic acid as chelating agent.•The reaction mechanism for the preparation of precursor was also studied.•Effect of excess Li on the physical and electrochemical properties of the oxides was investigated.•Among the samples, Li1.1(Ni0.5Co0.2Mn0.3)O2 exhibits excellent electrochemical properties.•Such enhanced electrochemical performances are related to the improved physical properties.

Hydroxide precursor Ni0.5Co0.2Mn0.3(OH)2 with average particle size of about 9.88 μm was prepared via co-precipitation method using oxalic acid as an ammonia-free chelating agent. Well-ordered layer-structured LiNi0.5Co0.2Mn0.3O2 was synthesized with controlling the Li/(Ni + Co + Mn) molar ratio by calcining the uniform metal hydroxide with Li2CO3 at 850 °C. The effect of excessive Li on the structural and electrochemical properties of the final compounds Li1+x(Ni0.5Co0.2Mn0.3)O2 (0 ⩽ x ⩽ 0.2) was deeply investigated. Excessive Li is favorable to suppress the degree of cation mixing and improve the hexagonal ordering, indicated by the improved value of I(1 0 3)/I(1 0 4) and the decreased value of (I(0 0 6) + I(1 0 2))/I(1 0 1). Higher discharge capacity, as well as better cyclability and rate capability, was achieved for the Li-excess Li1+x(Ni0.5Co0.2Mn0.3)O2 compounds, especially the sample of Li1.1(Ni0.5Co0.2Mn0.3)O2, compared with that of Li(Ni0.5Co0.2Mn0.3)O2. It is believed that such enhanced electrochemical performances are related to the improved physical and structural properties of the Li-excess samples.

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