Binders with cationic semi-interpenetrating networks for sodium-ion batteries under extreme conditions

Sodium-ion batteries (SIBs) represent a promising solution for energy storage applications. However, the current performance of SIBs remains suboptimal, particularly under demanding operating conditions, where challenges such as electrode degradation and detachment significantly undermine battery functionality. To overcome these challenges, a multifunctional binder incorporating a cationic semi-interpenetrating polymer network (C-SIPN) structure has been developed, to overcome the limitations of conventional PVDF binders. The C-SIPN binder incorporates a substantial number of polar functional and cationic groups, which markedly enhance the ionic conductivity. This modification also effectively improves the mechanical properties of the electrodes. Na₃V₂(PO₄)₃ (NVP) half-cells employing the C-SIPN binder exhibit superior cycling stability and rate performance at both room and low temperatures. Specifically, the capacity retention at a 10C rate after 5000 cycles at 25 °C reaches 95.9 %. Remarkably, even after 10,000 cycles, the capacity retention remains as high as 94.2 %. Under low-temperature conditions of −20 °C, the discharge capacity at a 1C rate retains 85.6 % of the value measured at 25 °C. Furthermore, kinetic analysis reveals that the C-SIPN binder significantly enhances the diffusion of Na⁺ ions within the SIBs. Additionally, X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses of the cycled electrodes show that the C-SIPN binder preserves the structural integrity of the NVP cathode and effectively mitigates electrode degradation during prolonged cycling, thereby enhancing the overall cycling stability of the batteries. Furthermore, the applicability of the C-SIPN binder was extended to Na_0.66Mn_0.55Ni_0.4Co_0.05O₂ (NMNC)) cathode materials and NVP//hard carbon full cells, in which it demonstrated outstanding electrochemical performance. These results underscore the binder's broad versatility and potential for practical implementation in various SIBs systems. © 2025 Elsevier B.V.