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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