Additive-assisted quasi-dry process enabling freestanding sulfide electrolyte films for all-solid-state batteries

Sulfide solid-state electrolyte films that combine thinness, high ionic conductivity and large-area feasibility are needed to improve energy density and enable industrial-scale production of all-solid-state batteries. However, workable processing methods to integrate these critical features remain technically challenging. Herein, we demonstrate a quasi-dry process utilizing an organic additive (i.e., α-pinene), through which the fabricated sulfide electrolyte films successfully integrate all the aforementioned merits. α-Pinene is chemically compatible with Li_5.5PS_4.5Cl_1.5, improves film flexibility via stress dissipation, enhances ionic conductivity by promoting a more even distribution of the polytetrafluoroethylene binder, and facilitates film densification through lubrication. The resultant films with enhanced densification (porosity reduced from 12.24% to 7.78%) retain over 85% ionic conductivity of the pristine powder, exhibit an ionic conductivity of 4.79 mS/cm at 25 °C, with a thickness of 28 μm and lateral dimensions of 30 × 10 cm². The Li₄Ti₅O₁₂ | Li_5.5PS_4.5Cl_1.5 | LiNbO₃@LiNi_0.8Co_0.1Mn_0.1O₂ full cells present a capacity retention of 93% after 500 cycles at 1 C under 2 MPa. At the stack level, a 50 mAh pouch cell retains 83% capacity after 1000 cycles at 0.5 C under 2 MPa. This work proposes an additive-assisted quasi-dry process, paving a pathway for material-process optimization toward potentially scalable fabrication of all-solid-state batteries.