Composite solid electrolyte with Li⁺ conducting 3D porous garnet-type framework for all-solid-state lithium batteries

A PEO-based composite solid electrolyte (CSE) reinforced by a three-dimensional (3D) porous garnet-type framework is reported. This 3D garnet framework is prepared by a template method using a nanocellulose fiber membrane as a template. The richly branched Al-doped garnet (LLZAO) framework provides more continuous Li-ion transport paths and physically prevents the lithium dendrite from unrestricted growth as well. Meanwhile, the PEO matrix not only makes the framework flexible, but also provides a “soft contact” between the electrode and electrolyte. The as-designed PEO-LLZAO composite electrolyte presents an enhanced ionic conductivity of up to 1.33 × 10⁻⁴ S cm⁻¹ at 25 °C, an improved electrochemical stability window of about 5.3 V and an impressive Li⁺ transference number (0.49). A lithium battery with LiFePO₄ and Li metal as cathode and this membrane as both electrolyte and separator was assembled, exhibiting an initial discharge capacity of 150.3 mA h g⁻¹ at a current density of 0.1C, with a capacity retention of 87.3% after 270 cycles at 60 °C. Furthermore, the CSE was sandwiched between the Li-metal and LiCoO₂ to fabricate a high-voltage solid-state battery, which delivers a good cycle life at the rate of 0.1C (60 °C). Therefore, the PEO-3D-garnet composite electrolyte is a good choice for application in solid-state lithium batteries.