Vacancies-Induced Delocalized States Cobalt Phosphide for Binder-Free Anode Toward Stable and High-Rate Sodium-Ion Batteries.

Metal phosphides with easy synthesis, controllable morphology, and high capacity are considered as potential anodes for sodium-ion batteries (SIBs). However, the inherent shortcomings of metal phosphating materials, such as conductivity, kinetics, volume strain, etc are not satisfactory, which hinders their large-scale application. Here, a CoP@carbon nanofibers-composite containing rich Co─N─C heterointerface and phosphorus vacancies grown on carbon cloth (CoP_1-x@MEC) is synthesized as SIB anode to accomplish extraordinary capacity and ultra-long cycle life. The hybrid composite nanoreactor effectively impregnates defective CoP as active reaction center while offering Co─N─C layer to buffer the volume expansion during charge-discharge process. These vast active interfaces, favored electrolyte infiltration, and a well-structured ion-electron transport network synergistically improve Na⁺ storage and electrode kinetics. By virtue of these superiorities, CoP_1-x@MEC binder-free anode delivers superb SIBs performance including a high areal capacity (2.47 mAh cm^-2@0.2 mA cm^-2), high rate capability (0.443 mAh cm^-2@6 mA cm^-2), and long cycling stability (300 cycles without decay), thus holding great promise for inexpensive binder-free anode-based SIBs for practical applications.