A step-channel gel polymer electrolyte for solid-state sodium batteries

Gel polymer electrolytes (GPEs) paired with abundant sodium (Na) and high-voltage polyanionic cathode, offer improved energy density and superior safety, positioning them as scalable alternatives for resource-limited lithium batteries. However, such technologies are plagued by critical interfacial engineering challenges: existing GPEs fail to sustain (electro)-chemical stability and mechanical close contact at high-loading cathodes and highly reactive anodes. Here, we report a rationally engineered GPE featuring biphasic polymer, creating step channels and polymer-solvent dipole adsorption to address the key issues. It enables volume-constrained bidirectional transport of infilling linear ether and cyclic carbonate solvents and endows the polymer with differential mechanical viscoelasticity for high-loading cathodes and ductile Na anodes. Therefore, a high-energy-density full cell of Na||Na₃V₂(PO₄)₃ (34.1 mg cm_cathode ^-2, 194.4 Wh kg^-1, based on total cell mass) and a stable pouch cell of 4.5 V-class Na||Na_2.466Fe_1.724Mg_0.043(SO₄)₃ (18.7 mg cm_cathode ^-2, ∼100% after 100 cycles) were demonstrated, with safety validation included. The design principles were established for this new chemical engineering pathway towards practical solid-state batteries.