Lithium-ion batteries have succeeded in powering small portable electric devices due to their high energy density. However, it is still debatable whether mineral resources can meet the increasing demand associated with the growth of Li-ion into large scale energy storage systems. As a result, potassium- and sodium-ion batteries are considered alternative energy storage options because of the natural abundance of K and Na resources. Potassium’s standard redox potential is lower than that of Na and is even below Lithium’s potential in non-aqueous electrolytes (i. e. propylene carbonate (PC) and ethylene carbonate/diethyl carbonate electrolyte (EC/DEC)).^1-3It is therefore likely that K ion batteries can deliver a high cell voltage as compared to Na and Li systems.

Only few cathode compounds are reported to date for K ion batteries. In this early stage, it is important to design cathode materials that can maintain their crystal structures during de/intercalation of large K ions. We develop a new cathode material for K ion batteries and investigate K storage mechanism in this new cathode compound by in-situdiffraction characterization combined with electrochemical measurements. Lastly, we further demonstrate the practical feasibility of K ion batteries by constructing full cells. We consider that this work can suggest a guideline to open up new research opportunities in the development of K ion batteries.

References

1. Eftekhari, A., Jian, Z. & Ji, X. Potassium Secondary Batteries. ACS Appl. Mater. Sci., (2016).

2. Marcus, Y. Thermodynamic functions of transfer of single ions from water to non-aqueous and mixed solvents: Part 3 - Standard potentials of selected electrodes. Pure and Applied Chemistry 57, 1129, (1985).

3. Komaba, S., Hasegawa, T., Dahbi, M. & Kubota, K. Potassium intercalation into graphite to realize high-voltage/high-power potassium-ion batteries and potassium-ion capacitors. Electrochem. Commun. 60, 172-175, (2015).