Room-Temperature Flexible Quasi-Solid-State Rechargeable Na-O2 Batteries.

Abstract

Rechargeable Na–O2 batteries have been regarded as promising energy storage devices because of their high energy density, ultralow overpotential, and abundant resources. Unfortunately, conventional Na–O2 batteries with a liquid electrolyte often suffer from severe dendrite growth, electrolyte leakage, and potential H2O contamination toward the Na metal anode. Here, we report a quasi-solid-state polymer electrolyte (QPE) composed of poly(vinylidene fluoride–co-hexafluoropropylene)–4% SiO2–NaClO4–tetraethylene glycol dimethyl ether for rechargeable Na–O2 batteries with high performance. Density functional theory calculations reveal that the fluorocarbon chains of QPE are beneficial for Na+ transfer, resulting in a high ionic conductivity of 1.0 mS cm–1. Finite element method simulations show that the unique nanopore structure and high dielectric constant of QPE can induce a uniform distribution of the electric field during charge/discharge processes, thus achieving a homogeneous deposition of Na without dendrites. Moreover, the nonthrough nanopore structure and hydrophobic behavior resulting from fluorocarbon chains of QPE could effectively protect Na anode from H2O erosion. Therefore, the fabricated quasi-solid-state Na–O2 batteries exhibit an average Coulombic efficiency of up to 97% and negligible voltage decay during 80 cycles at a discharge capacity of 1000 mAh g–1. As a proof of concept, flexible pouch-type Na–O2 batteries were assembled, displaying stable electrochemical performance for ∼400 h after being bent from 0 to 360°. This work demonstrates the application of the quasi-solid-state electrolyte for high-performance flexible Na–O2 batteries.