Anion-Tailored EDL Induced Triple-Layer SEI on High-Capacity Anodes Enabling Fast-Charging and Durable Sodium-Storage

High-capacity electrodes face a great challenge of cycling stability due to particle fragmentation induced conductive network failure and accompanied by sustained electrolyte decomposition for repeatedly build solid electrolyte interphase (SEI). Herein, Se-solubility induced Se_x ^2- as self-adjustment electrolyte additive to regulate electric double layer (EDL) for constructing novel triple-layer SEI (inner layer: Se; mediate layer: inorganic; outer layer: organic) on high-capacity FeS₂ anode as an example for achieving stable and fast sodium storage. In detail, Se_x ^2- in situ generated at 1.30 V (vs. Na⁺/Na) and was preferentially adsorbed onto EDL of anode, then converted to Se⁰ as inner layer of SEI. In addition, the Se_x ^2- causes anion-enhanced Na⁺ solvation structure could produce more inorganic (Se⁰, NaF) and less organic SEI components. The unique triple-layer SEI with layer-by-layer dense structure alleviate the excessive electrolyte consumption with less gas evolution. As a result, the anode delivered long-lifespan at 10 A g^-1 (383.7 mAh g^-1, 6000 cycles, 93.1 %, 5 min/cycle). The Se-induced triple-layer SEI could be also be formed on high-capacity SnS₂ anode. This work provides a novel SEI model by anion-tailored EDL towards stable sodium-storage of high-capacity anode for fast-charging.