Building a High-Potential Silver-Sulfur Redox Reaction Based on the Hard-Soft Acid-Base Theory

Sulfur holds immense promise for battery applications owing to its abundant availability, low cost, and high capacity. Currently, sulfur is commonly combined with alkali or alkaline earth metals in metal-sulfur batteries. However, these batteries universally face challenges in cycling stability due to the inevitable issue of polysulfide dissolution and shuttling. Additionally, the inferior stability of metal sulfide discharge compounds results in low S⁰/S^2- redox potentials (<-0.41 V vs SHE). Herein, we leverage the principle of the hard-soft acid-base theory to introduce a novel silver-sulfur (Ag-S) battery system, which operates on the reaction between the soft acid of Ag⁺ and the soft base of S^2-. Due to their high reaction affinity, the discharge compound of silver sulfide (Ag₂S) is intrinsically insoluble and fundamentally stable. This not only resolves the polysulfide dissolution issue but also leads to a predominantly high S⁰/S^2- redox potential (+1.0 V vs. SHE). We thus exploit the Ag-S reaction for a primary zinc battery application, which exhibits a high capacity of ∼620 mAh g^-1 and a high voltage of ∼1.45 V. This work offers valuable insights into the application of classic chemistry theories in the development of innovative energy storage devices.