Towards storable and durable Zn-MnO2 batteries with hydrous tetraglyme electrolyte

Aqueous rechargeable zinc-based batteries have attracted increasing interest and been considered potential alternatives for state-of-the-art lithium-ion batteries because of the low cost and high safety. Many cathode materials have been gradually developed and demonstrated excellent electrochemical performances. However, the complex electrochemistry, inevitable hydrogen release, and zinc corrosion severely hinder the practical application. The most concerned Zn-MnO2 batteries still suffer from the Mn dissolution and formation of byproducts. By adding organic solvents to inhibit the activity of water molecules, the hydrous organic electrolytes provide a sound solution for eliminating the unfavorable factors. Here we report a tetraethylene glycol dimethyl ether-based hydrous organic electrolyte consisting of LiClO4·3H2O and Zn(ClO4)2·6H2O, and a birnessite-type MnO2 cathode material for Zn-MnO2 batteries. The Li+/Zn2+ ions co-(de)insertion mechanism is ascertained by the structural and morphological analyses. The electrostatic interaction between inserted ions and crystal structure is reduced effectively by employment of monovalent Li+ ions, which ensures structural stability of cathode materials. Hydrous tetraglyme electrolyte inhibits the activity of water molecules and thus avoids the formation of byproduct Zn4ClO4(OH)7. Meanwhile, highly stable Zn plating/stripping for over 1500 h, an average coulombic efficiency of >99% in long-term cycling, and ultralong storage life (the cells can work well after stored over 1 year) are simultaneously realized in the novel electrolyte. Benefitting from these aspects, the Zn-MnO2 batteries manifest high specific capacity of 132 mA h g−1, an operating voltage of 1.25 V, and a capacity retention of >98% after 1000 cycles at a current density of 200 mA g−1.