Lithium–Oxygen Batteries and Related Systems: Potential, Status, and Future

Abstract

The goal of limiting global warming to 1.5 °C requires a drastic reduction in CO2 emissions across many sectors of the world economy. Batteries are vital to this endeavor, whether used in electric vehicles, to store renewable electricity, or in aviation. Present lithium-ion technologies are preparing the public for this inevitable change, but their maximum theoretical specific capacity presents a limitation. Their high cost is another concern for commercial viability. Metal−air batteries have the highest theoretical energy density of all possible secondary battery technologies and could yield step changes in energy storage, if their practical difficulties could be overcome. The scope of this review is to provide an objective, comprehensive, and authoritative assessment of the intensive work invested in nonaqueous rechargeable metal−air batteries over the past few years, which identified the key problems and guides directions to solve them. We focus primarily on the challenges and outlook for Li−O2 cells but include Na−O2, K−O2, and Mg−O2 cells for comparison. Our review highlights the interdisciplinary nature of this field that involves a combination of materials chemistry, electrochemistry, computation, microscopy, spectroscopy, and surface science. The mechanisms of O2 reduction and evolution are considered in the light of recent findings, along with developments in positive and negative electrodes, electrolytes, electrocatalysis on surfaces and in solution, and the degradative effect of singlet oxygen, which is typically formed in Li−O2 cells. CONTENTS 3.4.1. Electrolytes 3.4.2. Development of New Solvents for Li−O2 N 3.7. Novel Electrolytes and Electrodes AH 3.7.1. The Possibilities and Development of Active Metal (Li, Na) Protection AH 3.7.2. Solid-State Li−Air and Na−Air Batteries AJ 3.7.3. On the Use of Ionic Liquids and Molten Salts AL 3.7.4. On the Possible Use of Solid Li-Oxide Cathodes and the Connection to Lithiated Transition Metals AN 3.8. Studies with Consideration of Practical Metal−Air Batteries AN 3.8.1. Li Batteries with Lithium Oxygen Compound Cathodes (and Closed Systems) AN 3.8.2. Challenges of Capacity and Kinetics AO 3.8.3. On the Validity of E nergy Density Calculation of Li (Na)−Oxygen Batteries AO 3.8.4. From Oxygen to Air AP 3.8.5. Configuration of Li−Air Cells and the Balance of Plant AQ 4. Future Perspective AR 5. Conclusion AS Author Information AT Corresponding Authors AT Authors AT Author Contributions AT Notes AT Biographies AT Acknowledgments AV Abbreviations Used AV References AV G Figure 28. Representative methods for protecting Li metal in Li−O2 batteries. (A) Gel or solid electrolyte. Reproduced with permission from ref 256.

Persistent and reversible solid iodine electrodeposition in nanoporous carbons

“…Processes in the positive electrode of a hybrid NaI supercapacitor are comparable to those in common conversion-type battery electrodes, such as Li-S or Li-O 2 battery cathodes, where solid Li 2 S or Li 2 O 2 precipitate from solution species 46 , 47 . During charging and discharging, the solid active material is deposited within the nanopore network of a carbon cathode.…”

Selected future tasks in electrochemical research related to advanced power sources

“…However, as reflected by comprehensive review articles that were published recently, these systems are still in basic research stage, as they suffer from too many problems of component compatibility in the highly reactive environment that non-aqueous oxygen electrochemistry induces. [8] In summary, combining Li metal anode with sulphur in rechargeable batteries is a great challenge and may provide power sources of the highest energy density. Developing concepts of solid-state batteries will enable to use more effectively Li metal anodes in rechargeable batteries, thus, opening horizons for new families of very high energy density batteries.…”

Challenges and Strategy on Parasitic Reaction for High‐Performance Nonaqueous Lithium–Oxygen Batteries

“…The mechanism of reverse OER, accompanied with the oxidation of Li 2 O 2 to Li + and O 2 in charge process, is still in debate due to its complexity than ORR. [17,18] On account of the fact that insulating solid Li 2 O 2 with a wide bandgap (4-5 eV) leads to sluggish reaction kinetics, which further causes large discharge/charge overpotential, poor rate capability, and bad cycle life. [9,19] Much effort has been made to investigate cathode structure, [20,21] electrocatalyst optimization, [22,23] and working mechanism [24,25] over the last few years, focusing on adjusting the growth route, morphology, and structure of Li 2 O 2 to accelerate the reaction kinetics.…”