关键词: 钠离子电池, 水系电解液, 乙酸铵, 盐包水

Abstract:

Low-cost and high-safety aqueous sodium-ion batteries have received widespread attention in the field of large-scale energy storage, but the narrow electrochemical stability window (1.23 V) of water limits the energy density of aqueous sodium-ion batteries. The “water-in-salt” strategy which uses the interaction between cations and water molecules in the solution can inhibit water decomposition and broaden the electrochemical stability window of water. In this work, two types of low-cost salts, namely, ammonium acetate (NH₄CH₃COOH) and sodium acetate (NaCH₃COOH), were used to configure a mixed aqueous electrolyte for aqueous sodium-ion batteries. The solution consisted of 25 mol·L ^-1 NH₄CH₃COOH and 5 mol·L^-1 NaCH₃COOH, used as an aqueous electrolyte, exhibited a wide electrochemical stability window of 3.9 V and high ionic conductivity of 28.2 mS·cm^-1. The composite of layered manganese dioxide and multi-wall carbon nanotubes (MnO₂/CNTs) was used as a positive electrode material, while the carbon-coated NaTi₂(PO₄)₃ with NASICON structure was used as a negative electrode material. Both of these electrode materials had excellent electrochemical performances in the aqueous electrolyte. A full cell achieved an average working voltage of about 1.3 V and a discharge capacity of 74.1 mAh·g^-1 at a current density of 0.1 A·g^-1. This aqueous sodium-ion battery displayed excellent cycling stability with negligible capacity losses (0.062% per cycle) for 500 cycles. The safe and environmentally friendly aqueous acetate electrolyte, with a wide electrochemical stability window, showed the potential to be matched with positive materials having higher potential and negative materials having lower potential for further improving the voltage of aqueous sodium-ion batteries and promoting the development of aqueous batteries for large-scale energy storage technology.

Key words: sodium ion battery, aqueous electrolyte, ammonium acetate, water-in-salt