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 LiFePO4 as a positive electrode, revealing a redox potential of 1.17 V vs. Zn2+/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 LiMnPO4 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.