Nanostructure of lithium peroxide enhances lithium-oxygen battery performance
The lithium-oxygen battery is one of the most promising means of energy storage with the essential precondition of high theoretical energy density applied for the electric vehicle. However, the insulating lithium peroxide formed during discharge is oxidized slowly. This formation causes the appearance of large overpotential. The KAIST team led by Byun has sought to enhance the rate and efficiency of next-generation lithium peroxide batteries. The research group demonstrated that one-dimensional and amorphous nanostructure types can be oxidized at a markedly fast rate, which has resulted in an improved “round-trip” efficiency of ~80% for the lithium-oxygen battery.
A high worldwide demand for next-generation energy storage in applications for electric vehicles (EVs) has been driving rapid growth of battery research. In particular, as the current battery technologies (e.g. <0.2 kWh kg–1cell for lithium-ion batteries) have far lower capabilities than the required target performance (0.5 kWh kg–1cell by 2030 (2010 NEDO EV roadmap)), new electrochemical arrays rendering higher-energy-density batteries should be implemented. In this context, lithium-oxygen (Li–O2) batteries hold promise on account of their possessing more than 3–5 times higher energy density than that found for the lithium-ion battery. However, developmental progress of the Li–O2 battery has been slow due to the appearance of serious problems such as low round-trip efficiency.
Recently, the Byon group (Department of Chemistry) and the Jung group (EEWS) at KAIST have demanstrated high round-trip efficiency of ~80% for Li–O2 batteries by forming one-dimensional nanostructures of amorphous Li2O2. During discharge, this unique shape of Li2O2 is formed along to the mesoporous carbon channels in CMK-3 electrode where two-electron-transfer-based O2 reduction reaction occurs. The subsequent charge process reveals facile O2 evolution and profound efficacy in suppressing the rise of oxidation potential from the nanostructural Li2O2, demonstrating far faster oxidation in comparison with that found for the typical bulk Li2O2.
This result is attributed to the large surface area of Li2O2 in which the equilibrium (2Li+ + O2 + 2e– ⇄ Li2O2) occurring with the Li+-containing electrolyte solution provides the highly abundant and facile mobility of Li+ and charge carriers. Therefore, the Li2O2 nanostructure has unprecedented high electrical and ionic conductivity, which can promote the oxidation rate even with high current densities. Accompanying DFT calculations also reveal that disordered geometric arrangements of the surface atoms in the amorphous structure lead to weaker binding of the key reaction intermediate (lithium superoxide), yielding smaller overpotential compared to the crystalline surface. This study suggests a strategy to enhance the oxidation rate of insulating Li2O2 by exploiting size, shape and structure.
Including website for more information
* lab webpage : https://www.emdl.kaist.ac.kr/