Realizing four-electron conversion chemistry for all-solid-state Li||I2 batteries at room temperature

Abstract Rechargeable Li||I 2 batteries based on liquid organic electrolytes suffer from pronounced polyiodides shuttling and safety concerns, which can be potentially tackled by the use of solid-state electrolytes. However, current all-solid-state Li||I 2 batteries only demonstrate limited capacity based on a two-electron I − /I 2 polyiodides chemistry at elevated temperatures, preventing them from rivaling state-of-the-art lithium-ion batteries. Herein, we report a fast, stable and high-capacity four-electron solid-conversion I − /I 2 /I + chemistry in all-solid-state Li||I 2 batteries at room temperature. Through the strategic use of a highly conductive, chlorine-rich solid electrolyte Li 4.2 InCl 7.2 as the catholyte, we effectively activate the I 2 /I + redox couple. This activation is achieved through a robust I-Cl interhalogen interaction between I 2 and the catholyte, facilitated by an interface-mediated heterogeneous oxidation mechanism. Moreover, apart from serving as Li-ion conduction pathway, the Li 4.2 InCl 7.2 catholyte is demonstrated to show a reversible redox behavior and contribute to the electrode capacity without compromising its conductivity. Based on the I − /I 2 /I + four-electron chemistry, the as-designed all-solid-state Li||I 2 batteries deliver a high specific capacity of 449 mAh g -1 at 44 mA g -1 based on I 2 mass and an impressive cycling stability over 600 cycles with a capacity retention of 91% at 440 mA g -1 and at 25 °C.