Utilization of Redox-active liquid electrolytes for Highly Reversible Na metal plating-stripping in the Seawater Battery Anode system

Abstract

As the demand for renewable energy generation continues to rise, the requirement for large-scale energy storage systems (ESS) capable of efficiently storing and managing energy has become increasingly critical. However, lithium-ion batteries, which are dominating the ESS sector in the current secondary battery market, are persistently challenged by concerns over thermal stability, raising significant fire safety issues. Additionally, their reliance on rare and scarce materials has led to escalating raw material costs and heightened concerns regarding domestic supply constraints. To address these limitations, seawater batteries (SWBs) have been developed, which utilize sodium resources instead of the scarce lithium. SWBs employ seawater as the cathode material, the most abundant resource on Earth, thereby replacing the costly cathode materials used in LIBs and enhancing energy density to its theoretical value, 3051 Wh L-1. These characteristics position SWBs as a promising next-generation battery technology. Despite these advantages, the fixed volume of the anode compartment in SWBs, due to the inflexible NASICON material, necessitates maximizing energy density within limited space. Sodium metal, with its low reduction potential and high volumetric capacity, is an optimal choice for achieving high energy density. However, sodium metal’s high reactivity leads to undesirable side reactions with conventional electrolytes, posing significant challenges. To address these issues, this study introduces a novel liquid electrolyte specifically tailored for the SWB architecture.

1. Introduction of Redox-active Electrolytes for Increasing Na metal Coulombic Efficiency. The practical deployment of seawater batteries has been constrained by the insufficient chemical and electrochemical stability of their anode components. To address this limitation, a novel stability-enhanced strategy was introduced, utilizing a sodium-biphenyl-dimethoxyethane solution as a redox-active functional anolyte. This innovative anolyte demonstrates exceptional electrochemical stability and outstanding cycling performance compared to traditional electrolyte systems.

2. Optimization of Electrolytes for Mitigating NASICON Cracks by Na metal Under certain conditions, such as high current densities or extended distances between the solid electrolyte and the current collector, redox-active electrolytes may exhibit reduced cycling performance due to issues related to sodium metal deposition on the surface of the solid electrolyte. In this study, we investigated the underlying mechanisms of sodium metal deposition on solid electrolyte surfaces when utilizing redox-active electrolytes with electronic conductivity. Through comprehensive electrochemical analysis, we identified key factors influencing sodium metal deposition, including electronic conductivity, the distance between components, and current density. By changing the concentration and electronic conductivity of the electrolytes, we established optimized operating parameters to minimize solid electrolyte cracking and maintain stable cycling performance. Furthermore, we propose the use of additives as a future direction to address dendrite growth originating from the current collector, an issue not fully resolved by the current approach.