Stabilizing sodium vanadate hydrate via TMP-added concentrated bisalt electrolytes for high-performance aqueous zinc metal batteries

Sodium vanadate hydrate (NaV$_3$O$_8$·1.5H$_2$O, NVO) is a promising layered cathode material that offers a high theoretical capacity while delivering exceptional fast-charging performance. However, the long-term cycling performance of NVO at moderate current densities (0.25C to 2C) for practical application is hampered by significant vanadium dissolution, and structural degradation induced by Na$^+$-pillar loss. Herein, a concentrated bisalt electrolyte based on a water-trimethyl phosphate (TMP) mixture is designed to simultaneously suppress vanadium dissolution and Na$^+$ interlayer leakage of NVO. The proposed electrolyte consists of 1 m ZnAc$_2$ and 5 m NaAc in an 80:20 (v/v) H$_2$O/TMP mixture. The failure of NVO cathodes is attributed to vanadium dissolution (induced by active water attack and local pH fluctuations) as well as Na$^+$-pillar loss, as identified through various characterization techniques such as X-ray diffraction and electron microscopy. This failure mechanism can be effectively mitigated by the high abundance of Na$^+$, hydrophilic acetate anions, and TMP molecules in the electrolyte. These components collectively suppress water activity, restrict anodic OH$^−$ crossover and proton co-insertion into NVO via hydrogen bond modulation and Zn$^{2+}$ solvation structure regulation, and meanwhile preserve the intact nanostructure of NVO cathode. ... mehrThis approach enables Zn||NVO full cells to achieve exceptional cycling stability (∼1.6 mAh cm$^{−2}$ for 240 cycles at 0.1 A g$^{−1}$), underscoring its practical potential.