Nickel-cobalt layered double hydroxide cathode materials with excellent cycle stability for nickel-metal hydride batteries

Nickel-cobalt layered double hydroxides (Ni-Co LDHs) with different Ni/Co molar ratios (3:1, 4:1 and 5:1) are synthesized by a simple and effective one-step solvothermal method and then are used as cathode materials for nickel-metal hydride (Ni-MH) batteries. In comparison with the Ni(OH)₂, the Ni-Co LDHs electrodes display higher discharge capacity and excellent cycling stability, especially the electrode with a Ni/Co molar ratio of 4:1 (NC 2). The NC 2 electrode obtains a maximum discharge capacity of 356.2 mAh/g at the discharge rate of 200 mA/g, and delivers a high capacity retention of 99.1% after 200 cycles. The results of microstructure characterization reveal that the Ni-Co LDHs exhibit a unique three-dimensional flower-like morphology and the enlarged interlayer spacing, which can promote ion transmission and charge transfer. In addition, the excellent structural stability of the Ni-Co LDHs and Co-Co LDHs in the KOH alkaline electrolyte and the synergies between them may also be essential for the improvement of electrochemical performances. The present work provides valuable information to explore a promising cathode material for the advanced nickel-metal hydride batteries.