Superionic composite electrolytes with continuously perpendicular-aligned pathways for pressure-less all-solid-state lithium batteries

Solid electrolytes are promising candidates for safe, high-energy battery systems. Composite solid electrolytes, in particular, hold the potential to combine high ionic conductivity with stable electrode interfaces. However, a fundamental trade-off often exists between ion conduction and mechanical properties. Here we present a composite solid electrolyte design that decouples ion conduction from mechanical flexibility, achieving a high ionic conductivity of 10.2 mS cm^-1 at 25 °C while maintaining close mechanical contact with the electrode. The composite architecture consists of alternating layers of perpendicularly aligned (PA) Li_0.3Cd_0.85PS₃ nanosheets, to establish continuous superionic conduction pathways, and Li-containing polyethylene oxide (PEO) layers, to ensure flexibility and interfacial compatibility. At 25 °C, this PA-Li_0.3Cd_0.85PS₃/PEO electrolyte enables Li||LiNi_0.8Co_0.1Mn_0.1O₂ coin cells (stack pressure during assembly <0.5 MPa) to retain 92% discharge capacity after 600 cycles at 0.2 mA cm^-2, with an average cycling Coulombic efficiency of 99.9%, and also facilitates practical use of pressure-less (stack pressure <0.1 MPa) Li||LiFePO₄ pouch cells. This composite design strategy is further validated by substituting Cd with Mn in the inorganic sulfide nanosheets to produce a PA-Li_0.46Mn_0.77PS₃/PEO electrolyte, exhibiting an ionic conductivity of 6.1 mS cm^-1 at 25 °C and good mechanical flexibility.