Konjac glucomannan biopolymer as a multifunctional binder to build a solid permeable interface on Na₃V₂(PO₄)₃/C cathodes for high-performance sodium ion batteries

The cathode materials for sodium ion batteries (SIBs) are intrinsically unstable due to their oxidation by electrolyte solution at high voltage; thus, developing novel solid permeable interfaces as passivation layers is critical to avoid these side oxidation reactions and increase the cycling durability of SIBs. Nevertheless, the abuse of passivation layers can hinder the Na⁺transfer and further impact the rate capability. Herein, we demonstrated an effective approach that utilized konjac glucomannan (KGM) biopolymer as a multifunctional binder to build stable solid permeable interface films to achieve high-performance for Na₃V₂(PO₄)₃/C (NVP) cathodes. Compared with polyvinylidene difluoride (PVDF), the strong adhesion and solid permeable interface films of KGM protect the integrity of the electrodes. The unique conductive network and rich polar functional groups enable KGM to enhance the transfer of electrons and Na⁺ions at the interfaces. Thanks to the multiple functions of KGM offering adhesion strength, a conductive network and a solid permeable interface, the NVP cathode exhibited a reversible capacity of 108.0 mA h g⁻¹at 0.5C (1C = 117 mA g⁻¹). At a high rate of 50C, NVP profited from KGM to show a good capacity of 63.1 mA h g⁻¹and a high durability of 10 000 cycles with a small fading rate of 0.00259% per cycle. Hard carbon‖NVP full batteries, using KGM as the cathode binder, possessed a high specific energy of 137.7 W h kg⁻¹, indicating the potential applications of KGM as an environmentally friendly binder for achieving high-rate capacity and long-term cycling durability of SIBs.