Hierarchical Ni2P nanosheets anchored on three-dimensional graphene as self-supported anode materials towards long-life sodium-ion batteries

Transition metal phosphides have reached tremendous inspiration as electrode materials for sodium-ion batteries (SIBS) due to high specific capacity and low discharge potential. However, the pulverization of electrode structure during cycling is still a key factor that restricts the further development of SIBS. Herein, unique hierarchical Ni2P nanosheets/three-dimensional graphene (3DG) composite with stable structure is successfully prepared. The effects of pH on the morphology and properties of the as-prepared Ni2P are studied. When pH value is 4, the hierarchical Ni2P/3DG interdigitated networks remain higher specific capacity (313.5 mA h g(-1) at 100 mA g(-1) for 100 cycles) and better rate properties (155.4 mA h g(-1) at 1 A g(-1) after 1000 cycles). Moreover, full cells consisting of Ni2P/3DG anode and Na3V2(PO4)(3) cathode are assembled and characterized. The enhanced sodium storage can be attributed to the unique structure and high conductivity of 3DG. The hierarchical structure can effectively buffer volume expansion, prevent structure pulverization and keep intimate contact between Ni2P and electrolyte. Besides, 3DG provides fast and continuous long-distance electron transportation. These results demonstrate the hierarchical Ni2P/3DG nanocomposite electrode can be a potential choice for sodium ion storage. (C) 2019 Published by Elsevier B.V.