Crystal Facet Engineering of BiOCl Fillers in Solid Polymer Electrolytes

Solid polymer electrolytes (SPEs) have attracted much attention due to their high flexibility and good interfacial contact with electrodes. Incorporating appropriate inorganic fillers into the polymer matrix is a normal and effective method to improve its performance. Despite extensive research on novel fillers, the role of filler crystal facets in SPEs remains unexplored. In this work, BiOCl nanosheets with exposed {001} and {010} facets (BOC-001 and BOC-010) are selectively applied as fillers to form composite solid polymer electrolytes (CSPE-BOC). Both calculations and experimental measurements reveal that filler of BOC-010 promote the dissociation of LiTFSI more effectively and facilitate faster Li⁺ migration on its surface, compared to BOC-001. As a result, CSPE-10BOC-010 exhibits an enhanced Li⁺ ionic conductivity (0.83 mS cm^-1 at 60 °C) and Li⁺ transference number (0.38). The Li symmetric cells with the CSPE-BOC-010 exhibit an ultra-long lifespan, with more than 2,000 hours of stable cycling at 0.2 mA cm^-2. The Li/CSPE-10BOC-010/LFP battery also has an excellent cycling performance at 60 °C, retaining140 mA h g^-1 at 1 C after 390 cycles. This work deepens the understanding of the crystal plane characteristics of fillers in SPEs and offers a novel, promising strategy to enhance SPE performance.