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Extremely Stable Sodium Metal Batteries Enabled by Localized High-Concentration Electrolytes

2018; American Chemical Society; Volume: 3; Issue: 2 Linguagem: Inglês

10.1021/acsenergylett.7b01213

2380-8195

Jianming Zheng, Shuru Chen, Wengao Zhao, Junhua Song, Mark Engelhard, Ji‐Guang Zhang,

Advanced battery technologies research

Sodium (Na) metal is a promising anode for Na-ion batteries. However, the high reactivity of Na metal with electrolytes and the low Na metal cycling efficiency have limited its practical application in rechargeable Na metal batteries. High-concentration electrolytes (HCE, ≥4 M) consisting of sodium bis(fluorosulfonyl)imide (NaFSI) and ether solvent could ensure the stable cycling of Na metal with high Coulombic efficiency but at the cost of high viscosity, poor wettability, and high salt cost. Here, we report that the salt concentration could be significantly reduced (≤1.5 M) by a hydrofluoroether as an “inert” diluent, which maintains the solvation structures of HCE, thereby forming a localized high-concentration electrolyte (LHCE). A LHCE [2.1 M NaFSI/1,2-dimethoxyethane (DME)–bis(2,2,2-trifluoroethyl) ether (BTFE) (solvent molar ratio 1:2)] enables dendrite-free Na deposition with a high Coulombic efficiency of >99%, fast charging (20C), and stable cycling (90.8% retention after 40 000 cycles) of Na∥Na3V2(PO4)3 batteries.