Electrodeposited Layered Sodium Vanadyl Phosphate (Na_xVOPO₄·nH₂O) as Cathode Material for Aqueous Rechargeable Zinc Metal Batteries

Abstract

Aqueous rechargeable zinc metal batteries (ARZMBs) present a safer and cost-effective solution for energy storage in stationary applications. However, a major challenge is the lack of suitable cathode materials simultaneously exhibiting high operating voltage and long cycling stability. Herein, we report the polyanionic sodium-intercalated layered vanadyl phosphate [Na x VOPO 4 •nH 2 O (NVP)] as a suitable high-voltage and stable cathode for ARZMBs. This work employs a simpler electrochemical route (electrodeposition) for the synthesis of NVP over functionalized carbon fiber substrates and its application as a binder-free cathode in ARZMBs. The electrodeposited NVP possesses a morphology of vertically aligned well-separated nanosheet bundles resembling a flower. When used as the ARZMB cathode, the NVP electrode delivers a specific discharge capacity of 100 mA h g −1 at 0.033 A g −1 and high cycling stability (98% retention of the initial capacity over 1100 cycles at 0.333 A g −1 ) in a mild aqueous electrolyte with moderate zinc salt concentration. The observed electrochemical performance of NVP is credited to the synergistic effect of unique nanoflower morphology, the pillaring effect offered by the intercalated Na, and the intimate contact of the active material with the carbon fiber network. These factors are favorable for enhancing the transport of the electrolyte ions and electrons and maintaining the structural stability of the electrode during long-term cycling. The NVP electrode could also deliver appreciable performance (a discharge capacity of 73 mA h g −1 and a current density of 0.033 A g −1 ) in quasi-solidstate ARZMB cells employing PVA/Zn(CF 3 SO 3 ) 2 gel electrolyte.

Hetero‐Solvation‐Diluted Strongly‐Coordinated Zn2+‐Cosolvent Pairs Downshifting Zn Electrode Potential for High‐Voltage Hybrid Batteries

“…Compared with other metal‐based or intercalation‐type battery systems, the full cells also show comparable advantages in terms of energy/power densities, specifically, 153.0 Wh kg −1 /0.9 kWh kg −1 based on cathode materials (Figure S30b, Supporting Information). [ 58–64 ] Moreover, when operated at a current density of 0.2 A g −1 over 735 cycles, an average specific capacity of 96.3 mA h g −1 is achieved, corresponding to an average capacity decay of 0.67‰ per cycle (Figure 5d). Such a result signifies a decent cyclability of full cells with hybrid MACC electrolytes.…”

“…(Figure S30a, Supporting Information). [58][59][60][61][62][63][64] Figure 5c shows the rate capability of full cells with hybrid electrolytes at 0.2, 0.3, 0.4, and 0.5 A g −1 , respectively. In the corresponding GCD profiles, the voltage plateaus at different current densities are wellmaintained (Figure S31a, Supporting Information).…”

Dielectric–Metallic Double-Gradient Composition Design for Stable Zn Metal Anodes

“…Some 3D conductive frameworks like CNT and porous carbon were also employed to lower the local electric field and avoid concentration polarization. − However, the nucleated Zn on such surfaces cannot be further protected since the direct exposure to the electrolyte will still thermodynamically trigger HER. The other type of coating layer is composed of electronic insulating but zincophilic materials, such as polymers with abundant 3D ionic channels − and metal oxide/nitride compounds, , where the Zn plating occurs underneath the coating layer. Thus, the HER can be hindered because of reduced electron transfer to the electrolyte. , Some inorganic dielectric materials like Kaolin, ZrO 2 , Si 3 N 4 , and CeO 2 can induce Maxwell–Wagner polarization.…”