Lithium–air (Li–air) batteries have recently received much attention due to their extremely high theoretical energy densities. The significantly larger theoretical energy density of Li–air batteries is due to the use of a pure lithium metal anode and the fact that the cathode oxidant, oxygen, is stored externally since it can be readily obtained from the surrounding air. However, before Li–air batteries can be realized as high-performance, commercially viable products there are still numerous scientific and technical challenges that must be overcome, from designing the cathode structure, to optimizing the electrolyte compositions and elucidating the complex chemical reactions that occur during charge and discharge. The scientific obstacles that are related to the performance of Li–air batteries open up an exciting opportunity for researchers from many different backgrounds to utilize their unique knowledge and skills to bridge the knowledge gaps that exist in current research projects. This review article is a summary of the most significant developments and challenges of practical Li–air batteries and the current understanding of their chemistry.
A comparison of current and developing batteries.
The energy density of the lithium–air battery with respect to the anode could reach 13,000 Wh kg−1—quite close to the 13,200 Wh kg−1 of gasoline, they note. Although researchers have made significant progress, the Li–air battery is still at an embryonic stage, with numerous scientific and technical challenges that must be overcome if the promise is to be realized. The key areas for future research are as follows:
1. Porous carbon-based air cathode. The oxygen cathode is the key component related to the performance of a Li–air battery, in which the electrons are confined inside the electrode material while the oxygen is in both the gaseous and solution phases and the lithium ions are contained in the electrolyte solution.
Design and synthesis of a novel porous carbon material with high conductivity, which would ensure sufficient pores to store discharge products, channels to diffuse oxygen and good electrolyte wettability. This would provide an adequate and suitable three-phase interface (solid–liquid–gas) for the charge/discharge process.
2. Screening bifunctional cathode catalysts with improved activity for both the ORR during discharge and the OER during charge, achieving a high round-trip efficiency.
3. Development of stable electrolytes with high O2 solubility, excellent lithium ionic conductivity, low viscosity and vapor pressure.
4. Developing a high lithium ionic conducting separator and a high throughout oxygen-breathing membranes used at the cathode to block H2O, CO2 and other air components except O2.
5. Understanding of the complex chemical reaction mechanisms that occur during charge and discharge.