Electronic Structure Modulation of MOF-Based Host–Guest Recognition Polymer Electrolytes for High-Performance All-Solid-State Sodium Metal Batteries

Abstract

Transitioning from gel to all-solid-state sodium metal batteries (ASSMBs) is essential for upgrading the energy density and safety of flexible energy storage devices. Herein, a novel host-guest recognition strategy for all-solid-state composite polymer electrolytes (CPEs) is proposed by introducing Fe-Ni bimetallic Metal-organic frameworks (MOFs) into the PEO matrix. Fe-Ni MOF with various synergetic sites serves as a ‘host’ platform for CPEs to weaken the Coulombic interaction between Na⁺ and bis(trifluoromethysulfonyl)imide (TFSI-), thereby promoting the dissociation of sodium salt. They reduce the Na⁺ migration barrier and improve high-voltage stability. The optimized CPE achieves an ionic conductivity of 1.37×10⁻⁴ S cm⁻¹ at 30 °C, and the Na+ transference number increased threefold (from 0.23 to 0.63). The corresponding Na//Na symmetric cells operate stably for 1150 h at 25 ℃, and the Na// Na3V2(PO4)3 (NVP) cells demonstrate 97.2% capacity retention after 600 cycles at 1C. Thanks to the high oxidation limit of the CPE (4.5 V), the Na3V2(PO4)2F3 (NVPF)-based ASSMBs demonstrate stable cycling over 500 cycles within the voltage range of 2.5-4.3 V. Furthermore, the all-solid-state Na metal pouch cell exhibits an high initial discharge specific capacity of 113.4 mAh/g and remains stable for 56 cycles at 0.1C. This innovative host-guest recognition polymer electrolyte offers valuable insights for enhancing rapid ion transport and contributing to the better understanding of the underlying Na⁺ kinetics mechanisms.