3d orbital electron tunning and crystal engineering enables high-capacity vanadium oxide for aqueous ammonium ion batteries

Vanadium pentoxide (V2O5) has shown great potential as the electrode for aqueous ammonium ion batteries (AAIBs) owing to its good electrochemical reversibility and high theoretical capacity. However, the electrochemical performance of V2O5 is seriously limited by the weak NH4+ adsorption capability and insufficient active sites of vanadium oxide originated from the unsuitable 3d orbital electron state. Herein, the strategy of a 3d orbital electron tunning and crystal engineering is used to increase the ammonium ion storage capacity of V2O5 electrode. The experimental results show that the modified 3d orbital state of V4+ (t2g1) can effectively increase the active sites of V2O5. Therefore, the as-prepared N-VO exhibits a high specific capacity of 249.3 mA h g−1 at 1.0 A g−1 and 69.5 mA h g−1 at 10.0 A g−1, superior to other reported anode material for AAIBs. Noticeably, the prepared resultant quasi-solid-state ammonium ion battery can display considerable cycling stability with capacity retention of 87.9% after a long cycle life of 10 000 cycles at 1 A g−1 and impressive mechanical flexibility with no capacity decay after cycling at different bending angles.