Robustly immobilized Ni2P nanoparticles in porous carbon networks promotes high-performance sodium-ion storage

Transition metal phosphides are promising anode materials for next-generation rechargeable sodium-ion batteries due to the high theoretical capacities. However, the inherent low conductivity and large volume expansion of transition metal phosphides during the repeated sodiation/desodiation process critically hinder their practical applications. Herein, we immobilize Ni₂P nanoparticles robustly in porous carbon sheet networks via the pyrolysis and in-situ phosphatization of poly(acrylic acid)-Ni(NO₃)₂ gel. The resulted porous network structure, high conductivity, robust chemical combination and space confinement effect of the Ni₂P-carbon composite offer the electrode not only rigid structural stability for volume expansion over long-term cycling, but also large specific capacity and fast Na⁺/electrons transfer kinetics. As a consequence, the composite delivers a large initial discharge capacity (932 mAh g⁻¹ at 50 mA g⁻¹), a high rate capability (77 mAh g⁻¹ at 3500 mA g⁻¹), as well as a significantly enhanced long cycle-life (146 mAh g⁻¹ after 1500 cycles at 500 mA g⁻¹). The excellent Na-storage performance makes the synthesized Ni₂P-carbon composite a sound anode material for advanced rechargeable SIBs.