Abstract
Rechargeable Na–air batteries (NABs) based on abundant Na resources are generating great interest due to their high energy density and low cost. However, Na anode corrosion in ambient air and the growth of abnormal dendrites lead to insufficient cycle performance and safety hazards. Effectively protecting the Na anode from corrosion and inducing the uniform Na plating and stripping are therefore of vital importance for practical application. We herein report a NAB with in situ formed gel electrolyte and Na anode with trace residual Li. The gel electrolyte is obtained within cells through cross-linking Li ethylenediamine at the anode surface with tetraethylene glycol dimethyl ether (G4) from the liquid electrolyte. The gel can effectively prevent H2O and O2 crossover, thus delaying Na anode corrosion and electrolyte decomposition. Na dendrite growth was suppressed by the electrostatic shield effect of Li+ from the modified Li layer. Benefiting from these improvements, the NAB achieves a robust cycle performance over 2000 h in opened ambient air, which is superior to previous results. Gelation of the electrolyte prevents liquid leakage during battery bending, facilitating greater cell flexibility, which could lead to the development of NABs suitable for wearable electronic devices in ambient air.
Highlights
Current metal−O2 battery technologies with ultrahigh theoretical energy densities have difficulty satisfying the practical application demands for a long cycle life and working in ambient conditions.[1−6] This is despite the significant progress in the development of highly efficient cathode catalysts, oxidation-resistant electrolytes, and stable alkali metal anodes.[7−12] The Na−air batteries (NABs) are receiving immense attention owing to their inherent cost benefit and extremely low charge overpotential when compared with that of Li−air batteries.[3,13−15] In the typical discharge process of
A Na-based gel electrolyte was achieved by an in situ method within assembled NABs toward their operation in ambient air
Surface Li served as a sacrificial layer that reacted with EDA to form a LiEDA layer, and cross-linked with
Summary
Current metal−O2 battery technologies with ultrahigh theoretical energy densities have difficulty satisfying the practical application demands for a long cycle life and working in ambient conditions.[1−6] This is despite the significant progress in the development of highly efficient cathode catalysts, oxidation-resistant electrolytes, and stable alkali metal anodes.[7−12] The Na−air batteries (NABs) are receiving immense attention owing to their inherent cost benefit and extremely low charge overpotential when compared with that of Li−air batteries.[3,13−15] In the typical discharge process of NABs, oxygen is reduced at the cathode and is combined with Na+ which comes from the anode to form Na2O2/NaO2, which is a reversible process occurring during the following charging process.[3,16−19] The reported discharge/charge process finishes in a pure oxygen or a gaseous environment without moisture or CO2 contaminants. The Na anode corrosion and the decomposition of the electrolyte are the first and foremost issues with NABs.[20−22] In ambient air, the crossover of H2O and CO2 from the cathode to the Na anode inevitably leads to Na anode corrosion and the formation of a NaOH/Na2CO3 passivation layer on the anode, which causes severe electrode polarization and premature cell death. O2− in the reduced state can transport to the Na anode, resulting in anode corrosion and lower Coulombic efficiency.[13,23,24] electrolyte volatilization and decomposition by the metallic Na anode deteriorates the cycle performance.[13,25−27] Functional separators and protective layers have been adopted to Received: November 20, 2020 Published: January 18, 2021
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