Recently, Dr. Zhang Ning reported the application of nonstoichiometric ZnMn2O4/carbon composite as a new Zn-insertion cathode material in aqueous Zn(CF3SO3)2 electrolyte. This innovation improved the efficiency, safety and stability of the Zn-ion battery greatly. Related research has been published in Journal of the American Chemical Society. Zhang Ning is the first author and the instructor Cheng Fangyi is the corresponding author. The results are now patented.

    While lithium-ion batteries (LIBs) have gained huge success to power portable electronics, there are growing concerns over their cost, safety, environmental impact, and resource limitation. Meanwhile, the use of aqueous Zn-ion battery (ZIB) offers advantages including better safety, greener and less rigorous manufacturing conditions, higher ionic conductivity, low flammability and allowing multivalent charge transport carriers. Zhang Ning therefore did research on Zn-ion battery.

    To improve the electrochemical performance of rechargeable aqueous ZIB, Zhang found that ZnMn2O4 was a plausible candidate cathode material. He comparatively investigated the electrochemical properties of different zinc salts in aqueous solutions and this new cathode exhibited high specific capacity, long-term cyclability and superior rate capability. The obtained material bearing abundant cation vacancies exhibits a reversible specific capacity of 150 mAh/g at 50 mA/g and unprecedented capacity retention of 94% after 500 cycles. In addition to cathode materials, the search of comparable electrolytes also plays a pivotal importance in developing ZIBs. Due to the high ionic conductivity and electrochemical stability, Zn(CF3SO3)2 was applied in the organic gel polymer electrolyte for solid-state Zn batteries. Zhang also demonstrated that higher salt concentration could reduce the water activity and water-induced side reactions, leading to improved cycle stability of electrode in aqueous solutions.

    The use of zinc-ion battery can not only greatly enhance the battery performance, safety and stability, but also reduce costs. The current market price of zinc is about 2 US dollars per kilogram, while the price of lithium is about 300 US dollars per kilogram; from the point of view of the annual output, zinc is much easier to obtain, and thus more appropriate for mass production.

    Zhang conceded that this cathode suffered from low energy density. Its energy density was only about half of the lithium-ion battery cathode material’s, so it is more suitable for large-scale energy storage system, but not suitable for mobile phones and other portable electronic devices. He will focus on this issue in the future.