Despite its high energy density that can determine the driving range of battery-powered automobiles and drones, a lithium-oxygen battery has the disadvantage of a slow and irreversible charging process. One of the critical reasons for this is the insulating characteristic of lithium peroxide (Li2O2), which is formed through the electrochemical reaction between oxygen gas and lithium ion during discharge. The shape and structure controls allow Li2O2 to enhance ionic and electronic conductivity and also to decompose facilely during the charging process, for which studies have been conducted by the KAIST research team.

Research focusing on development of a new battery

For the discharging and charging process, Li2O2 is formed and decomposes, respectively, in the positive electrode of a lithium-oxygen battery. Typically, the electron and Li+ ion move very slowly in the bulk Li2O2, and the resulting sluggish decomposition during the charging process also exacerbates severe side reactions in the battery. The research team of Professor Hye Ryung Byon developed a way to design one-dimensional nanostructured, thin and non-crystalline Li2O2 that exhibited a superior decomposition rate. The shape of Li2O2 was controlled from a mesoporous carbon electrode, and the Li2O2 was formed from the confined mesopore during the discharging process.

Key technology to improve reversibility and recharge speed

The control of the shape and structure of Li2O2 is the key technology to improve the reversibility and charging speed of a lithium-oxygen battery. The research team of Professor Byon demonstrated facile decomposition appearing from the low volume and high surface area of Li2O2 by using electrochemical atomic force microscopy. Based on this knowledge, the research team developed a thin and one-dimensional nanostructure of Li2O2 as the lithium-oxygen electrochemical reaction was induced in the framework of a mesoporous carbon electrode. The one-dimensional shape of Li2O2 mimics the hexagonal channel of mesopores in the carbon electrode. In addition, the non-crystalline structure of Li2O2 also contributed to increasing ionic and electronic conductivity. The resulting Li2O2 decomposed even with an increasing charging rate over 2000 mA/gcarbon electrode, in contrast with large overpotential appearing in typical bulk Li2O2 caused by its sluggish decomposition.
The present study for the design of Li2O2 shape and structure showed the possibility of improving the performance of a lithium-oxygen battery. The knowledge to surmount the low conductivity of a discharging product has a broad application for next-generation batteries in particular and can be applied to a lithium-sulfur battery that also includes a similar challenge of insulating sulfur. This work can also contribute to commercializing lithium-oxygen battery technology in the future by providing key insights into lithium-oxygen electrochemistry.

Prof. Hye Ryung Byon
2018 KI Annual Report