水系钠离子电池因其低成本和高安全性有望在大规模储能领域得到广泛应用,但稀水溶液的电化学稳定窗口窄（1.23 V）,限制了钠离子电池的能量密度。“water-in-salt”盐包水策略可有效扩宽水的电化学稳定窗口。本文中通过使用高浓度的乙酸铵（CH₃COONH₄,25 mol·L^-1）与乙酸钠（CH₃COONa,5 mol·L^-1）,将水的电化学稳定窗口扩宽至3.9 V。该高浓度水溶液与MnO₂/CNTs正极和NaTi₂(PO₄)₃/C负极组装的全电池平均工作电压为1.3 V,容量可以达到74.1 mAh·g^-1。

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.