Enhancing sodium ion transport in batteries through a crosslinked ceramic network-coated polyethylene (PE) separator

As integral constituents of sodium ion batteries (SIBs), separator not only segregate positive and negative electrodes but also wield significant influence over electrochemical performance enhancement. Here, we present a hydroxyapatite nanowires composite separator (N-HAP@PE) by blade coating, boasting exceptional Na-ion transport capacity and high safety. The N-HAP@PE separator features a crosslinked ceramic network structure coating endowed with polar functional groups (-OH), providing excellent electrolyte wettability. Its compatibility with ester-based electrolytes promotes efficient transport of Na-ion between the cathode and anode, increasing the ion conductivity (0.215 mS cm⁻¹) and a Na-ion transference number (0.62). Importantly, the sodiophilic HAP-NWs coating enables highly reversible Na plating and stripping while inhibiting dendrite formation. Ultimately, the N-HAP@PE separator assembled with NaNi_1/3Fe_1/3Mn_1/3O₂ cathode (areal density: 13.24 mg cm⁻²) and hard carbon anode (areal density: 6.3 mg cm⁻²), exhibits excellent capacity retention (85 %) after 200 cycles at 2C. This offers a new approach for the development of high-performance and low-cost sodium-ion batteries.