Boosting Aqueous Zn-Ion Battery Performances with Mg-Vanadate Positive and Cu-Metal Organic Framework Negative Electrodes in Inorganic Gel Electrolyte

Abstract

Aqueous Zn-ion batteries (AZIBs) are attractive, cost-effective, safe, and environmentally friendly energy storage solutions for stationary solar energy applications; offering a balanced combination of energy, power, and durability. A key challenge for AZIBs is the slow diffusion kinetics of divalent Zn²⁺ ions within the host lattices. To address this, Mg_xV₂O₅ (MgVO) as the positive and Cu-BTC metal organic framework (Cu-BTC MOF) (BTC: benzene-1,3,5-tricarboxylic acid) as the negative electrodes are designed, both of which support Zn²⁺ ion intercalation/deintercalation. The incorporation of Mg²⁺ into the V₂O₅ layer improves Zn²⁺ ion diffusion and enhances electrode stability, mitigating common issues such as layer-collapse. The Cu-BTC framework, with its open structure, facilitates efficient Zn²⁺ intercalation, significantly improving energy and power characteristics. A MgVO//Cu-BTC full cell, utilizing a ZnSO₄-silica gel electrolyte, delivers a high energy-density of 305 Wh kg⁻¹ (@ 394 W kg⁻¹) and a notable power-density of 1773 W kg⁻¹ (@ 87 Wh kg⁻¹), with stable cycling performance (≈86% capacity retention) over 200 cycles at 600 mAh g⁻¹. Additionally, the successful demonstration of a 4.5 V AZIB prototype powering a 3 V light-emitting-diode setup under solar charging shows its practical potential. With superior performance, safety, and cost-effectiveness, this AZIB offers great promise for large-scale solar energy storage.