Electron-conductive binder for silicon negative electrode enabling low-pressure all-solid-state batteries

While solid electrolyte-excluded Si electrodes can form in situ lithiated monolithic structures with minimal side reactions, their poor performance at low operating pressures remains a formidable challenge for all-solid-state batteries. Herein, we propose an electrically conductive binder-poly(3,4-ethylenedioxythiophene):poly((styrene sulfonic acid)_x-co-(maleic acid)_y) (PEDOT:P(SS_x-co-MA_y))-that is scalable, fluorine-free, and water-processable. This binder offers sufficient e^--conductivity to eliminate carbon additives, while ensuring strong adhesion and electrochemical stability in contrast to conventional liquid electrolyte systems. Ex situ measurements reveal disrupted e-connectivity during delithiation at 5 MPa, resolved by employing PEDOT:P(SS_x-co-MA_y). The improved electrochemical performance of Si electrodes comprising PEDOT:P(SS_x-co-MA_y), compared with those using conventional polyvinylidene fluoride, is validated in (Li-In) | Li₆PS₅Cl | Si half cells and Si | Li₆PS₅Cl | LiNi_0.70Co_0.15Mn_0.15O₂ full cells at 30 °C and 5 MPa, achieving 134 mAh g^-1 at 0.5 C with 86% capacity retention after 100 cycles. Finally, 233 mAh pouch-type Si || LiNi_0.83Co_0.12Mn_0.05O₂ ASSBs are demonstrated, highlighting the potential of PEDOT:P(SS_x-co-MA_y) as a practical binder platform for high-energy ASSBs.