Understanding conversion mechanism of NiO anodic materials for Li-ion battery using in situ X-ray absorption near edge structure spectroscopy

•A direct conversion between NiO and Ni is confirmed by in situ XANES technique.•The capacity and reversibility of NiO anode is highly affected by the particle size.•Micro-NiO exhibits a low capacity with absence of phase transformation.•Nano-NiO exhibits reversible phase transformation between NiO and Ni metal.•The isolated Ni particles can lose conductivity by a polymer layer or Li2O matrix.

Nano-scaled NiO particles (nano-NiO) are prepared by a ligand stabilization method and compared with micron-sized NiO particles (micro-NiO) as anodic material of Li-ion battery. The structural and physical properties are characterized by N2 physisorption, transmission electron microscopy, and X-ray diffraction. The nano-NiO shows uniform spheres with an average particle size of 9 nm with high and stable discharge capacity of 637 mAh g−1, while the micro-NiO forms irregularly shaped particles with an average particle size of 750 nm with low capacity of 431 mAh g−1 at 0.5C. In situ X-ray absorption near edge structure (XANES) analysis reveals that the capacity and reversibility of the NiO anode is highly affected by the particle size of the NiO. The micro-NiO exhibits a low capacity with absence of phase transformation upon the discharge/charge cycles. In contrast, the nano-NiO exhibits a high capacity with reversible phase transformation between NiO and Ni metal upon the cycle test.

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