Anionic/cationic grafted silica modified separator boosting efficient Li-ion transport

The utilisation of lithium metal electrodes in high-energy-density rechargeable batteries is impeded by two crucial obstacles: the low mobility and thermal stability of polyolefin separators. Aiming at the structural defects of traditional polyolefin separators, this study proposes a surface functionalization modification strategy based on anionic or cationic surface modified silica nanoparticles. The surface grafting reaction induced by the silane coupling agent has been demonstrated to be an effective method for the construction of sulfonic acid (-SO 3 H) and amino (−NH 2 ) functional groups on the surface of silica nanoparticles. The resultant functionalised nanoparticles (SiO 2 -SO 3 H/SiO 2 -NH 2 ) have been shown to possess ion selectivity. Furthermore, based on the self-polymerization characteristics of dopamine, a uniform polydopamine (PDA) interface layer was constructed on the surface of polypropylene (PP) separator to improve the hydrophilic properties of polyolefin separator. Subsequently, the functionalized ionic silica particles were loaded on the surface of PDA modified PP separator by impregnation method, and the effects of different functional groups on the performance of separator and battery were systematically studied. The results showed that the wettability and flame retardancy of PP separator grafted with -SO 3 H group surpassed those of the pristine PP separator and -NH 2 group modified system. Notably, the -SO 3 H modified separator exhibits exceptional electrolyte absorption (>200 %) and a remarkably low contact angle (12.6°), while concurrently attaining a lithium ion transference number (t Li + ) of up to 0.77. In the LiFePO 4 ||Li battery system, the separator can output a discharge specific capacity of 161 mAh g −1 at 1C rate, which is 12.3 % higher than that of the unmodified PP separator (142.5 mAh g −1 @ 1C, LiFePO 4 ||Li). In addition, the battery assembled by the sulfonic acid-modified separator has a content retention rate of >95 % after 300 cycles, showing excellent rate performance and cycle stability. This synergistic strategy based on interfacial anion and cation functionalization and nanoparticle composite modification provides an innovative technical path for the development of lithium battery separators with high lithium ion migration and thermal safety.