Assembled NiS nanoneedles anode for Na-ion batteries: Enhanced the performance by organic hyperbranched polymer electrode additives

Abstract Conversion-type materials provide abundant options for Na-ion battery anodes, but the inferior cycleability and low first-cycle coulombic efficiency block their application in full Na-ion batteries. Herein, hierarchical structures of ultra-thin NiS nanoneedles are prepared and investigated as anodes for Na-ion batteries. A new organic polymer is applied to regulate ultra-thin nanoneedle structure (~10 nm), facilitating solid-state Na+ diffusion and enhancing the rate capability. Significantly, the organic hyperbranched polymer acts as an additive uniformly distributed in the material, offering an elastic framework to prevent nanoparticle aggregation and thus improving the cycleability. The NiS electrode delivers a high capacity of 590 mA h g−1 at 100 mA g−1, and the coulombic efficiency is 93% at the first cycle. The NiS electrode also exhibits an excellent rate performance with 320 mA h g−1 capacity at 20 A g−1, as well as a remarkable cycleability with 90.2% capacity maintained after 1000 cycles. Moreover, the NiS anode shows a good compatibility with Na3V2(PO4)3/C cathode in the full Na-ion cells. The present work introduces a feasible conversion-type NiS anode for Na-ion batteries, and highlights a facile and efficient strategy for the performance improvement of conversion-type anode with such an organic hyperbranched polymer electrode additive.