A Biodegradable Gel Polymer Electrolyte Based on Polydopamine-Modified Tough Polyurethane Enabling High-Rate Sodium Batteries

A biodegradable gel polymer electrolyte based on biodegradable polyurethane (PU) coated polydopamine (PDA) was synthesized through a low-cost and simple phase inversion method for developing high-performance sodium batteries. The PU polymer substrate possesses satisfactory tensile strength and brilliant elasticity benefited from a rigid–flexible bifunctional structure, which can resist the deformation and penetration induced by the sodium dendrite. In the meantime, the ion transference number of the gel polymer electrolyte can reach up to 0.70 due to dissociation of sodium salts by polar groups on PDA@PU. Moreover, the PDA coating layer can provide higher surface energy and conjugate effect on the liquid electrolyte to construct an unblocked sodium ion transfer channel, avoid leakage risk of liquid electrolyte, and reduce side reactions at the interface. Benefiting from the synergistic effect of the PU substrate and the PDA coating layer, the gel polymer electrolyte enabled sodium battery with Na3V2(PO4)3 (NVP) cathode shows a capacity retention as high as 84% after 1000 cycles at 2 C. This work demonstrates that the synthesized gel polymer electrolyte has a surprising prospect for practical application to guarantee the high toughness and fast ion conduction simultaneously required at relatively high charge–discharge rate.