Electrolyte effects and stability of Zn/Li dual-ion batteries with water-in-salt electrolytes

Aqueous zinc-ion batteries have emerged as promising candidates for safe and cost-effective energy storage, yet their performance remains constrained by electrode stability and electrolyte composition. In this study, we investigate the electrochemical behavior of various electrode materials utilizing water-in-salt dual-ion electrolytes. Our findings highlight the critical influence of substrate materials on electrochemical stability, with titanium exhibiting superior anodic stability compared to, e.g., aluminum. Furthermore, we demonstrate the feasibility of LiFePO 4 as a positive electrode, revealing a redox potential of 1.17 V vs. Zn 2+ /Zn in chloride-based electrolyte, which shifts positively with increasing lithium concentration. The observed potential variation with electrolyte composition underscores the need for optimized formulations to enhance the battery performance. Additionally, while LiMnPO 4 offers a higher theoretical voltage, its cycling stability remains limited, suggesting that material modifications are necessary. Finally, we highlight the overlooked impact of electrolyte impurities on battery performance, emphasizing the importance of high-purity electrolyte components. These insights contribute to the development of more stable and efficient Zn-ion batteries, paving the way for their practical deployment in energy storage applications. • Electrode stability in WiSE depends on the substrate material; Ti is the best. • LiFePO 4 has superior charge capacity and cycling stability in WiSE. • The formal potential of LiFePO 4 shifts positively with Li + concentration. • LiMnPO 4 provides higher voltage, but needs activation and is unstable at cycling. • Trace Mn 2+ impurities in WiSE mimic the electrochemistry of LiMnPO 4 .