Fig. 1: Schematic representations of liquid Li||I₂ batteries and LIC7.2-based ASS Li||I₂ batteries.

Typical liquid Li||I₂ batteries show a theoretical capacity of 211 mAh g⁻¹ based on two-electron I⁻/I₃⁻/I₂ polyiodides chemistry. The use of liquid electrolytes which dissolve polyiodides leads to severe shuttle effect and thus a low coulombic efficiency, as well as the potential safety concern. In the proposed ASS Li||I₂ batteries, a fast and reversible four-electron solid-phase conversion chemistry is achieved by the design of I₂/LIC7.2 composite electrode with a stable chlorine-rich environment, which is capable of activating the I₂/I⁺ redox couple. A doubled theoretical capacity of 422 mAh g⁻¹ and high specific energy of ~1302 Wh kg⁻¹ based on the active I₂ mass (434 Wh kg⁻¹ based on the total mass of I₂ and LIC7.2) are demonstrated for the ASS Li||I₂ batteries. The use of LIC7.2 electrolytes perfectly eliminates the polyiodides shuttle problem and improves the safety. The crystalline LIC6 is used as the solid electrolyte layer due to its high ionic conductivity, and a layer of Li₁₀GeP₂S₁₂ (LGPS) is adopted between LIC6 and Li–In electrode to prevent the reduction of LIC6.