Ionic Liquids For Zn-Air Batteries
The Zn-air battery takes the oxygen in the air as the active material of the positive electrode and the metal as the active material of the negative electrode. The oxygen reaches the gas-solid-liquid three-phase interface through the gas diffusion electrode and generates electrical energy by electrochemical reaction with the zinc. The metal fuel consumed by Zn-air battery can be concentrated and restored by renewable energy to realize the regeneration cycle and help alleviate the problem. Zn-air battery is a new type of high energy chemical power supply with great research value and great application potential. The research and development of Zn-air battery products has become an important direction of technological development in the field of new energy vehicles. Ionic liquid is liquid phase at low temperature, which can be applied in Zn-air battery. Furthermore, with the advantages of no side reaction, high thermal stability and others, the use of ionic liquid as electrolyte in Zn-air battery system is a new green process with great research value.
- Increase discharge current density: The discharge current density is an important performance index of Zn-air battery, and the use of ionic liquid is helpful to improve the discharge current density. It has been reported that the concentration of zinc oxide dissolved in ionic liquid [MIm][TfO] can reach to high concentration, which can be applied in Zn-air batteries to achieve high current density discharge.
Figure 1. Proposed reaction mechanism of zinc oxide with the ionic liquid [MIm][TfO].
- Improve the safety of Zn-air batteries: The application of ionic liquid in Zn-air battery can reduce the danger of short circuit caused by the formation of zinc dendrite and the piercing of diaphragm, so as to improve the safety of Zn-air battery. For example, a team reported that by adding different mass fractions of EMIDCA ionic liquid to the traditional KOH electrolyte, the morphology of the zinc electrode can be controlled under the condition of rapid electrochemical reaction kinetics, which helps to form porous zinc film and prevent the growth of zinc dendrites.
Figure 2. SEM image of electrodeposited zinc. (a) 9M KOH+5wt% ZnO; (b) 9M KOH + 5wt% ZnO EMIDCA ionic liquid.
- Others: In addition to the applications mentioned above, ionic liquids have a variety of other applications in Zn-air batteries including increasing open circuit potential and energy density. For example, the results of some research groups show that the potential of Zn/Zn(II) reduction reaction in DCA- based ionic liquid is more negative than that in TFSI-based ionic liquid, and it is predicted that DCA- based ionic liquid as the electrolyte of Zn-air battery will have higher open circuit potential and energy density.
- Liu Z, Abedin S E, Endres F. Dissolution of zinc oxide in a protic ionic liquid with the 1-methylimidazolium cation and electrodeposition of zinc from ZnO/ionic liquid and ZnO/ionic liquid–water mixtures[J]. Electrochemistry Communications, 2015, 58:46-50.
- Xu M, Ivey DG, Qu W, Xie Z, Dy E. Ionic Liquids: Synthesis, Characterization and Applications (M). New York: Nova Science Publishers, Inc., 2014. 99–123.
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