Polyquaternium mediated dual regulation of polyanionic cathodes achieving electron-ion synergistic interfaces for low-temperature sodium-ion storage

Sodium-ion batteries (SIBs) are promising for large-scale energy storage due to the abundance and low cost of sodium resources. However, the sluggish kinetics and unstable interface at low temperatures hinder its practical applications. Here, we propose a dual-regulation strategy utilizing polyquaternium-10 (PQ-10) to construct an electron-ion synergistic interface. PQ-10 regulates precursor nucleation through electrostatic interactions and simultaneously serves as a nitrogen-containing carbon source during in situ carbonization. The dual regulation enables uniform particle formation and a continuous nitrogen-doped carbon coating, improving interfacial stability and charge transport. The nitrogen-doped carbon layer reduces interfacial impedance, enhances reaction kinetics, and reconfigures interfacial electronic structure, stabilizing the Na₃V_1.925Mg_0.075(PO₄)₃ (NVMP)/carbon interface, promoting Na⁺extraction/insertion, and accelerating electron/ion transport. At −20 °C, the NVMP/C-N@CNT-2 cathode delivers a high specific capacity (103.3 mAh g⁻¹at 0.1 C, 95.9% of room-temperature capacity), exceptional rate capability (67.5 mAh g⁻¹at 30 C), and ultra-stable cycling stability (approximately 100% retention after 5000 cycles at 10 C). This work delivers new insights into interfacial design principles enabling enhanced low-temperature performance.