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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