Development of an energy-dense and high-power Li-Cl₂ battery using reversible interhalogen bonds

Anionic redox reactions would achieve a higher capacity than typical transition-metal-oxide cathodes, offering low-cost chemistry for advanced lithium-ion batteries. Li-Cl₂ chemistry using anionic redox reactions of Cl^0/−1 shows superior operation voltage (∼3.8 V) and capacity (756 mAh g⁻¹). However, a redox-active and reversible chlorine cathode has not been developed in organic electrolyte-based lithium-ion batteries. Chlorine ions bonded by ionic bonding hardly dissolve in organic electrolytes, imposing a thermodynamic barrier for redox reactions. Meanwhile, chlorine gas is easily formed during oxidation. Herein, we report an interhalogen compound, iodine trichloride (ICl₃), as the cathode to address these two issues. In situ and ex situ spectroscopy data and calculations reveal that reduced Cl⁻ ions are partially dissolved in the electrolyte, and oxidized Cl⁰ is anchored by forming interhalogen bonds. A reversible Li-Cl₂ delivers a specific capacity of 302 mAh g⁻¹ at 425 mA g⁻¹ and a 73.8% capacity retention at 1,250 mA g⁻¹.