Multifunctional fluorine–nitrogen modified carbon quantum dots for enhanced solid polymer electrolytes toward solid-state lithium batteries

Abstract

Solid polymer electrolytes (SPEs) are pivotal for developing all-solid-state lithium batteries due to their enhanced safety, but their practical application is hindered by low ionic conductivity. Herein, fluorine–nitrogen-modified carbon quantum dots (FNCDs) are designed and prepared as a multifunctional filler to overcome this limitation. The FNCDs provide abundant sites for Li⁺ transport and immobilize anions (TFSI⁻), promoting Li salt dissociation. Moreover, the fluorinated surface ensures excellent compatibility with the fluorinated polymer matrix (PVDF-HFP), facilitating favorable interfacial Li⁺ hopping channels. Consequently, the FNCD-incorporated SPE (FNCDs-SPE) film achieves a high ionic conductivity of 9.59 × 10⁻⁴ S cm⁻¹ and a Li⁺ transference number of 0.77. It also exhibits enhanced mechanical strength (3.53 MPa) and elasticity (249.2% elongation). When paired with LiFePO₄, LiCoO₂, or NCM811 cathodes, the corresponding solid-state cells demonstrate exceptional cycling stability. This work highlights the great potential of zero-dimensional fluorinated carbon materials in developing high-performance SPEs.