Bond Length as a Unified Descriptor for Stable Iodine Battery

Dissolution of active materials in the electrolyte and their subsequent shuttling are common challenges for realizing stable electrodes in rechargeable batteries. These issues become particularly pronounced in cathodes with high solubility, including high-energy iodine electrodes. The interaction strength of iodine with the host electrode and electrolyte is critical for determining electrochemical stability, yet there is a lack of an appropriate parameter to quantify it. Our findings reveal that, as a weak Lewis acid, iodine's interaction strength is highly influenced by the nucleophilicity of surrounding ligands. We propose the I-I bond length, which can be conveniently probed through Raman tests, as a unified descriptor to predict the iodine electrode stability. The asset of this descriptor is demonstrated in (i) rational design of complex electrodes to enhance the binding strength between iodine and host and (ii) efficient screening of electrolyte solvents to minimize the shuttle. The collective effects enable stable cycling of Li-I₂ batteries under the challenging current rate of 0.1 C for over 4000 h. Overall, the unified descriptor provides a powerful means to expedite electrode and electrolyte design for overcoming active material dissolution challenges.