A New Nickel/cobalt Borate as High‐Performance Anode Material for Sodium‐Ion Batteries

Abstract Sodium‐ion batteries (SIBs) are widely considered a promising option for large‐scale energy storage, but their energy density is limited by the low specific capacity anode material. Herein, we synthesize a compound, namely Co 2 Ni(BO 3 ) 2 (denoted as CNBO), which is firstly served as an anode material in SIBs. The in‐situ X‐ray diffraction (XRD) and ex‐situ X‐ray photoelectron spectroscopy (XPS) are conducted to elucidate the Na‐ion storage mechanism, which involves a conversion reaction with a theoretical specific capacity of 546 mAh g −1 . As anode material for SIBs, CNBO exhibits a high initial reversible specific capacity of 544.2 mAh g −1 and maintains good cycling performance (319.2 mAh g −1 for 80 cycles at 0.2 A g −1 ) with remarkable rate capabilities (235.3 mAh g −1 at 2 A g −1 ). Furthermore, a sodium‐ion full cell using CNBO as the anode and Na 3 V 2 (PO 4 ) 3 as the cathode (CNBO||NVP) can attain a maximum energy density of 146 Wh kg −1 with excellent cycle stability and rate capabilities. This work presents the possibilities for developing metal borate‐based materials for efficient sodium‐ion storage.