Engineering ion migration and interface chemistry via covalent organic framework-enhanced polymer electrolytes for fast-charging sodium solid-state batteries.

Abstract

Solid-state sodium batteries offer a promising route toward safe and cost-effective energy storage, yet their practical implementation remains limited by the difficulty of coupling fast ion transport with stable electrode-electrolyte interfaces, especially under fast-charging and long-cycling conditions. Here we report a covalent organic framework/poly(sodium acrylate-co-fluorinated ethylene) (COF/PNSE) composite electrolyte developed through synergistic structural and chemical regulation. The aligned nanoporous COF provides continuous Na⁺ transport pathways while mechanically reinforcing the PNSE matrix, delivering an ionic conductivity of 1.2 mS cm^-1 at 30 °C. This integrated electrolyte enables robust Na metal compatibility, as demonstrated by symmetric Na cells operating for 6,750 h with low polarization of 85 mV and a critical current density of 1.9 mA cm^-2. Na | |Na_2/3Ni_1/3Mn_2/3O₂ batteries deliver 82.5 mAh g^-1 at 1 A g^-1 and retain 77.2% capacity after 1,000 cycles at 100 mA g^-1, while maintaining 92.7% retention at 4.2 V over 180 cycles and 83.5% retention at 1 A g^-1 over 2,000 cycles. Ah-level pouch cells further retain 87.3% capacity after 488 cycles at 1 A. Mechanistic analyses reveal that the COF framework guides uniform Na deposition and promotes dual-gradient NaF/Na₂O-rich interphases, suppressing dendrite growth and stabilizing both electrodes. These findings inform future composite electrolyte design for solid-state sodium batteries.