Xiaoniu Guo, Shuai Guo, Shaohua Ge, Longfei Wen, Zhichao Gong, Yi Yang, Junyu Li, Ruixue Wang, Zhengkun Xie, Jiyu Zhang, Jun Luo, Jianqiang Kang, Lingfei Zhao, Jun Lu, Junhua Shao, Weihua Chen
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 cmcathode -2, 194.4 Wh kg-1, based on total cell mass) and a stable pouch cell of 4.5 V-class Na||Na2.466Fe1.724Mg0.043(SO4)3 (18.7 mg cmcathode -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.