A look inside lithium-air batteries, a technology with the power to revolutionize the fight against climate change

Electrifying vehicles is an important step in curtailing greenhouse gas emissions and averting the worst consequences of climate change. However, electric vehicle (EV) technology has a long way to go towards meeting the needs of all consumers. Most importantly, the current generation of EVs cannot travel far enough on a single charge to give many drivers peace of mind. For EVs to really take off, we need better batteries. Batteries with a higher specific energy—the amount of energy they can deliver per unit of battery weight. Additionally, these batteries need to have a high cycling life, meaning that they can be charged and discharged many times without performance degradation. One promising candidate is the newly developed lithium-air battery, which boasts a theoretical specific energy several times higher than any existing battery.

A recent review paper published in the journal Applied Energy by Tan et al. at the Hong Kong University of Science and Technology summarizes progress researchers have made so far on lithium-air batteries. By analyzing many studies on different aspects of battery design, the authors paint a holistic picture of the field and identify several challenges that must be explored further to advance lithium air battery technology. This article focuses on challenges related to two important components of the battery: the electrolyte and the air electrode.

The electrolyte is a mixture of chemicals that sits in the middle of the battery and plays an essential role in the chemical reactions that make the battery work. The electrolyte can be liquid or solid, and it usually consists of some salt of lithium dissolved in a solvent. The main challenge researchers face right now is the “stability” of the electrolyte mix—its ability to remain unchanged after many cycles of discharging and recharging. Researchers have so far taken two main approaches to this problem. First, they experiment with what salt and solvent, combined in what amounts, will produce the best electrolyte. Finding the right electrolyte mix involves trial and error, testing different chemical ingredients and ratios to find the best “recipe.” Second, some researchers have used “functional additives”—chemicals that “soak up” undesirable byproducts and stop them from accumulating in the battery. So far, using functional additives in batteries has been shown to markedly improve performance, and may prove key to making longer-lasting lithium-air batteries.

Equally important to building an effective lithium-air battery is a well-designed air electrode. The air electrode is the site of key reactions that make the battery work, and distinguishes the lithium-air battery from previous battery models. In a lithium-air battery, oxygen from ambient air replaces heavy metal oxides used in earlier batteries. This substitution enables the batteries to be lighter, leading to a much higher specific energy. The secret to making a better air electrode seems to lie in its physical structure. Since the air electrode’s job is to allow air to flow freely into the system, it has to be porous, like a sponge. However, solids that build up over the course of many reaction cycles can plug these pores and compromise performance. Just like a water filter begins to work more slowly as it accumulates a layer of gunk, buildup on the air electrode prevents air from traveling easily into the battery. Researchers are tackling this problem by making changes to the structure of the electrode at a very small scale. Using principles from nanotechnology, researchers can tweak the size and configuration of channels through the material in order to find a structure less susceptible to clogging. A less cloggable air electrode means a more efficient, longer-lasting lithium-air battery.

Based on all the challenges of lithium-air batteries outlined in this review paper, it might seem like this technology is too far-off to get excited about. However, the sheer number of researchers working on this problem, and the innovative solutions they have proposed, should inspire optimism. Any new technology comes with hurdles, but through diligent effort and sound science, these hurdles can be cleared more quickly than we might imagine. If the research continues on this trajectory, lithium-air batteries may bring us a step closer to the revolution we need in our energy landscape.