Toxic solvent-free low-temperature fabrication and electrochemical performance of LiTa2PO8 ceramic matrix–based composite solid electrolytes containing polyvinylidene fluoride

Most studies of Composite solid electrolytes (CSEs) are composed of a polymer matrix and ceramic fillers. Polymer matrix–based CSEs are prepared by dissolving a polymer and lithium (Li) salt in a toxic organic solvent; then, a ceramic filler is added, and the toxic solvent is evaporated. These electrolytes contain 80%–90% polymer; however, they still have low thermal and electrochemical stability and unsatisfactory suppression of Li dendrite growth compared to inorganic ceramic electrolytes (ICEs). Ceramic matrix–based CSEs have high electrochemical and thermal stability, and good interfacial contact with electrodes. In this study, ceramic matrix–based CSEs were fabricated at a low temperature using a nontoxic solvent via the cold sintering process (CSP). Then, polyvinylidene fluoride (PVDF) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) were introduced on the LiTa2PO8 (LTPO) particle interface. In addition, the effect of the ratio of LTPO–PVDF and PVDF–LiTFSI at the LTPO particle interface on the microstructure and electrochemical properties of composite pellets was investigated. LTPO–PVDF pellets exhibited a relative density of 82%–86%, and high adhesion between LTPO particles was observed due to the formation of PVDF–LiTFSI amorphous layer on the particle interface. The LTPO–PVDF composite pellets exhibited a high total ionic conductivity of 4.59 × 10−4 S/cm at room temperature (RT), negligible electronic conductivity of 3.89 × 10−8 S/cm, low activation energy of 0.259 eV, and sufficient electrochemical stability. Coin cells with LiMn0.6Fe0.4PO4 (LMFP) cathode exhibited a high initial discharge capacity of ∼145 mAh/g and capacity retention of approximately 85% after 50 cycles at RT. These results prove that the CSP is an ideal fabrication method for CSEs than the conventional methods that use toxic solvents and that introducing an amorphous layer at the particle interface in ceramic matrix–based CSEs improves their ionic conductivity.