A Janus binder with electrophilic and nucleophilic dual centers for Ah-level four-electron aqueous Zn-I2 batteries

Four-electron aqueous Zn–I₂ batteries (4e AZIBs) are extremely attractive for grid-scale energy storage owing to their high theoretical energy density. However, stabilizing 4e (I⁻/I₂/I⁺) redox conversion under practical I₂ loading remains challenging owing to the thermodynamic instability of I⁺ species and mechanical degradation of the electrode. To address these issues, herein, we propose the use of polyhexamethylene guanidine hydrochloride (PHMG), a multifunctional binder possessing electrophilic and nucleophilic centers. Nucleophilic –NH– groups in PHMG form stable electron-transfer complexes with I⁺, suppressing its hydrolysis in aqueous electrolyte. Meanwhile, electrophilic –CNH₂⁺ groups strongly anchor I₃⁻ species, mitigating the comproportionation reaction between I₃⁻ and I⁺. Systematic theoretical simulations and spectral characterizations reveal the stabilization of I⁺ via selective chemisorption by the Janus binder. Furthermore, quantitative nanomechanical techniques demonstrate that the PHMG binder exhibits excellent mechanical properties, effectively withstanding changes in the electrode structure. Consequently, a cathode with an ultrahigh I₂ loading of 32.73 mg cm⁻² delivers an areal capacity of 9.65 mAh cm⁻². More specifically, a 4e Zn–I₂ pouch cell delivering a capacity of 0.76 Ah is achieved, highlighting its practical application potential. This study presents a new route for constructing 4e AZIBs, especially under high I₂ loading.