Improved compatibility of aqueous electrolyte with TiO2(B) toward high-voltage aqueous rechargeable Mg-ion batteries

Aqueous rechargeable Mg-ion batteries (ARMIBs) are promising for large-scale energy storage due to the aqueous electrolyte's high safety and low cost. However, the aqueous electrolyte's narrow electrochemical stability window (ESW) significantly hinders the development of ARMIBs, especially the compatibility of electrolytes with anode materials. We first report a TiO2(B) anode for ARMIBs that has high compatibility with wide potential aqueous electrolytes (ESW: ∼3.66 V), thus resulting in a low magnesiated potential (∼0.95 V vs. Mg2+/Mg), highest capacity (50 mA g−1: 247.7 mAh g−1) reported for Ti-based oxide anodes in aqueous metal-ion batteries thus far, and fast Mg2+ diffusion kinetics (∼3.49 × 10−11 cm2 s−1). When the magnesiated TiO2(B) (MgxTiO2(B)) anode is paired with V2O5, the MgxTiO2(B)||V2O5 full cell can deliver high voltage (2.5 V), high capacity (100 mA g−1: 64.4 mAh g−1, based on the total electrode mass) and high cycling stability with no capacity decay after 200 cycles at 100 mA g−1. The versatile intercalation chemistry of TiO2(B) observed here is expected to spur the development of high-voltage ARMIBs.