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A sodium bis(fluorosulfonyl)imide (NaFSI)‐based multifunctional electrolyte is developed by partially replacing NaPF6 salt in the electrolyte to improve the wide temperature range working capability of NaNi1/3Fe1/3Mn1/3O2/hard carbon (NNFM111/HC) sodium‐ion batteries (SIBs). The capacity retention of the SIBs with NaFSI‐NaPF6 dual salt electrolyte increases from 47.2 % to 75.5 % after 250 cycles at 25 °C, and from 51.0 % to 82.3 % after 80 cycles at 45 °C, and the 1 C discharge capacity retention at the low temperature of −20 °C also increases 26.8 %. In the single salt system, NaPF6 effectively passivate the aluminum foil and NaFSI passivate the electrode/electrolyte interface. The synergistic effect of NaPF6 and NaFSI greatly improves the battery performance in a wide temperature range. This NaFSI‐based dual salt electrolyte also effectively overcomes the flaws when the SIBs using NaFSI or NaPF6 independently, and makes it more suitable for SIBs, indicating promising prospects in the commercial application of NNFM111/HC SIBs. [ABSTRACT FROM AUTHOR]

Polyethylene oxide (PEO)‐based polymer electrolytes with good flexibility and viscoelasticity, low interfacial resistance, and fabricating cost have caught worldwide attention, but their practical application is still hampered by the instability at high voltages and the low ionic conductivity (10−8 to 10−6 S cm−1). Herein, we rationally designed defects‐abundant Ga2O3 nanobricks as multifunctional fillers and constructed a PEO‐based organic‐inorganic electrolyte for lithium metal batteries. Due to the abundant O‐defects feature of Ga2O3 filler, this PEO‐based composite electrolyte not only broadens electrochemical stability window (over 5.3 V versus Li/Li+) but also in situ forms a Li–Ga alloy and solid electrolyte interphase (SEI) film during the cycling process causing a rapid diffusion of Li+ ions. The as‐prepared electrolyte has good interface compatibility with Li metal (without short‐circuiting over 500 h at 0.2 mA cm−2) and possesses superior high ionic conductivity. The assembled all‐solid‐state LiFePO4//Li cells attained an excellent cycling performance of 146 mAh g−1 over 100 cycles at 0.5 C. The XPS analysis reveals that Ga2O3 nanobricks can form in situ a Li−Ga alloy layer at the polymer/anode interface. This work shed a light on designing high ionic conductivity lithium alloys in the composite electrolyte, which can improve the electrochemical properties of PEO‐based polymer electrolytes. [ABSTRACT FROM AUTHOR]