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(SSx-co-MAy))—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(SSx-co-MAy). The improved electrochemical performance of Si electrodes comprising PEDOT:P(SSx-co-MAy), compared with those using conventional polyvinylidene fluoride, is validated in (Li-In) | Li6PS5Cl | Si half cells and Si | Li6PS5Cl | LiNi0.70Co0.15Mn0.15O2 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 || LiNi0.83Co0.12Mn0.05O2 ASSBs are demonstrated, highlighting the potential of PEDOT:P(SSx-co-MAy) as a practical binder platform for high-energy ASSBs. Silicon negative electrode in all-solid-state batteries can lose electrical contact at low stack pressure, reducing performance. Here, the authors introduce a conductive, water-processable polymer binder that preserves contact and supports stable operation at low stack pressure.