PVDF-HFP@Nafion-based quasisolid polymer electrolyte for high migration number in working rechargeable Na-O2 batteries.

Rechargeable sodium-oxygen (Na-O₂) battery is deemed as a promising high-energy storage device due to the abundant sodium resources and high theoretical energy density (1,108 Wh kg^-1). A series of quasisolid electrolytes are constantly being designed to restrain the dendrites growth, the volatile and leaking risks of liquid electrolytes due to the open system of Na-O₂ batteries. However, the ticklish problem about low operating current density for quasisolid electrolytes still hasn't been conquered. Herein, we report a rechargeable Na-O₂ battery with polyvinylidene fluoride-hexafluoropropylene recombination Nafion (PVDF-HFP@Nafion) based quasisolid polymer electrolyte (QPE) and MXene-based Na anode with gradient sodiophilic structure (M-GSS/Na). QPE displays good flame resistance, locking liquid and hydrophobic properties. The introduction of Nafion can lead to a high Na⁺ migration number (t_Na⁺ = 0.68) by blocking the motion of anion and promote the formation of NaF-rich solid electrolyte interphase, resulting in excellent cycling stability at relatively high current density under quasisolid environment. In the meantime, the M-GSS/Na anode exhibits excellent dendrite inhibition ability and cycling stability. Therefore, with the synergistic effect of QPE and M-GSS/Na, constructed Na-O₂ batteries run more stably and exhibit a low potential gap (0.166 V) after an initial 80 cycles at 1,000 mA g^-1 and 1,000 mAh g^-1. This work provides the reference basis for building quasisolid state Na-O₂ batteries with long-term cycling stability.