High-voltage Zn/LiMn0.8Fe0.2PO4 aqueous rechargeable battery by virtue of “water-in-salt” electrolyte

• First demonstration of a high-voltage (≥ 1.8 V) aqueous Zn/LiMn0.8Fe0.2PO4 battery
• A “water-in-salt” solution with wide potential window is used as the electrolyte.
• Designed aqueous battery shows a high energy density of 183 Wh/kg.
• The activity of LiMn0.8Fe0.2PO4 depends on the pH value of the electrolyte.

A LiMn0.8Fe0.2PO4 cathode and a Zn anode, for the first time, are combined in a full cell possessing a high operating voltage exceeding 1.8 V. By virtue of a water-in-salt electrolyte containing lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) and ZnSO4, two reversible reactions of Li+ extraction/insertion (cathode) and Zn dissolution/deposition (anode) can be realized in the aqueous system. Such novel battery delivers an energy density of 183 Wh/kg based on the total mass of the active electrode materials. The high reversibility of the system enables sustaining more than 150 cycles (0.3 C) without obvious capacity fading. Moreover, it is demonstrated that the electrochemical characteristics of the LiMn0.8Fe0.2PO4 is critically dependent on the pH value of the electrolyte.

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