70 / 2021-06-07 18:22:49

AN ULTRATHIN, FLEXIBLE, AND HIGHLY ION CONDUCTIVE COMPOSITE SOLID-STATE ELECTROLYTE WITH VERTICALLY ALIGNED LLZO CERAMIC FRAMEWORK DERIVED FROM ANISOTROPIC CELLULOSE FILM

Cellulose microfiber,Biobased template,Aligned Li7La3Zr2O12 (LLZO) ceramic framework,Composite solid electrolyte,All Solid-state lithium-ion battery

All Solid-state lithium-ion batteries (ASSLIBs) with solid-state electrolytes (SSEs) have been attractive due to urgently safe needs. Widespread studies have focused on composite SSEs (CSEs) with great ionic conductivity of ceramic electrolytes and excellent mechanical properties of polymer electrolytes that can potentially blocking lithium dendrite penetration, enabling the application of metallic lithium anodes to achieve high energy density. To achieve electrochemical performance comparable to liquid electrolyte-based batteries, ultrathin and lightweight CSEs with interconnected and low-tortuosity structures of ceramic electrolyte are desired. Especially, vertically aligned ceramic electrolytes in the polymer matrix represent an ideal structure with straight ion pathways for maximizing ionic conductivity of CSEs. Here, we report an ultrathin, flexible, and highly ion conductive CSE with vertically aligned Li₇La₃Zr₂O₁₂ (LLZO) ceramic framework templated from anisotropic cellulose film. Firstly, the anisotropic cellulose film with oriented fiber arrangement is shaped by pre-stretching double cross-linked cellulose gel, which is produced by dissolving and regenerating microfibrillated cellulose (MFC) via a urea-alkali solution. The cellulose films are stacked to a certain thickness on the premise of keeping the fibers direction consistent, and an ultrathin layer is cut along the vertical direction of cellulose fibers as biobased template. Then LLZO ceramic framework is formed by calcining the above oriented template with adsorbed percussor at elevated temperature, resulting in vertically aligned, low tortuous, and ultrathin architecture which is consistent with the morphology of the sacrificial template. After filled with polyethylene oxide/lithium bis(trifluoromethanesulfonyl)imide (PEO/LiTFSI) electrolyte, multiscale aligned and highly ion conductive CSEs are successfully prepared. The vertically aligned LLZO ceramic provide continuous channels for fast ionic transport, while the PEO matrix renders CSEs strong and flexible, resulting in both a high ionic conductivity (2.13×10^-4 S·cm^-1 at 25°C) and good mechanical flexibility. The dual low tortuosity of CSEs reduces not only the internal resistance, but also the interface resistance of the ceramic/polymer electrolyte and the electrolyte/electrode due to the high specific surface area, effectively suppressing lithium dendrites. ASSLIBs fabricated with as-prepared ultrathin and multiscale aligned CSEs show good cycling stability (high capacity retention of 93.3% after 200 cycles at 0.5 C rate) at 25°C and withstand abuse tests such as bending, cutting and nail penetration. This study demonstrates a successful application of anisotropic cellulose film as template and a new direction for developing low-tortuosity, fast ion conducting electrolyte for ASSLIBs with high energy densities.