Lithium–Air Batteries: Air-Electrochemistry and Anode Stabilization

Abstract

Conspectus It is a permanent issue for modern society to develop high-energy-density, low-cost, and safe batteries to promote technological innovation and revolutionize the human lifestyle. However, the current popular Li-ion batteries are approaching their ceiling in energy density, and thus other battery systems with more power need to be proposed and studied to guide this revolution. Lithium–air batteries are among the candidates for next-generation batteries because of their high energy density (3500 Wh/kg). The past 20 years have witnessed rapid developments of lithium–air batteries in electrochemistry and material engineering with scientists’ collaboration from all over the world. Despite these advances, the investigation on Li–air batteries is still in its infancy, and many bottleneck problems, including fundamental and application difficulties, are waiting to be resolved. For the electrolyte, it is prone to be attacked by intermediates (LiO2, O2 –, 1O2, O2 2–) and decomposed at high voltage, accompanying side reactions that will induce cathode passivation. For the lithium anode, it can be corroded severely by H2O and the side products, thus protection methods are urgently needed. As an integrated system, the realization of high-performance Li–air batteries requires the three components to be optimized simultaneously. In this Account, we are going to summarize our progress for optimizing Li–air batteries in the past decade, including air-electrochemistry and anode optimization. Air-electrochemistry involves the interactions among electrolytes, cathodes, and air, which is a complex issue to understand. The search for stable electrolytes is first introduced because at the early age of its development, the use of incompatible Li-ion battery electrolytes leads to some misunderstandings and troubles in the advances of Li–air batteries. After finding suitable electrolytes for Li–air batteries, the fundamental research in the reaction mechanism starts to boom, and the performance has achieved great improvement. Then, air electrode engineering is introduced to give a general design principle. Examples of carbon-based cathodes and all-metal cathodes are discussed. In addition, to understand the influence of air components on Li–air batteries, the electro-activity of N2 has been tested and the role of CO2 in Li–O2/CO2 has been refreshed. Following this, the strategies for anode optimization, including constructing artificial films, introducing hydrophobic polymer electrolytes, adding electrolyte additives, and designing alloy anodes, have been discussed. Finally, we advocate researchers in this field to conduct cell level optimizations and consider their application scenarios to promote the commercialization of Li–air batteries in the near future.

PTFE Enhances Discharge Performance of Carbon Cathodes in Potassium‐Oxygen Batteries**

“…In brief, an outer‐sphere SET enables fast kinetics of oxygen reduction reaction (ORR) and is highly reversible. Further, even simple carbon cathode materials show low cycling overpotential (≈50 mV), whereas LOB with precious metal catalysts typically exhibit substantial overpotential from 0.7 V to 1.5 V [1,12] . The catalytic activity of graphitic carbon is indicated to outperform metal catalysts such as gold or platinum in KOB [7] .…”

A nitroaromatic cathode with an ultrahigh energy density based on six-electron reaction per nitro group for lithium batteries

“…They store energy via insertion/extraction of Li ions, which highly depends on the crystal structure and limits their capacities and energy densities (<300 mAh⋅g −1 with energy density of <1,000 Wh⋅kg −1 ). Some new battery systems with conversion reaction cathodes, such as Li-S (2,600 Wh⋅kg −1 ) and Li-O 2 (3,450 Wh⋅kg −1 ) batteries ( 13 – 19 ), have been extensively investigated due to their high theoretical energy densities. However, they suffer from serious dissolution, interfacial stability, and/or side reaction issues, and the practical energy densities are much lower than their theoretical values.…”

Aprotic lithium air batteries with oxygen-selective membranes

“…From the above discussion and from the literature [120][121][122], it can be suggested that utilization of LAB in electric vehicles is the best possible alternate of the gasoline-based transportation due to its high specific capacity. But their operation is limited due to their side reactions with moisture and carbon dioxide present in the atmosphere [123][124][125]. The presence of moisture in the battery is more dangerous than CO 2.…”