KIST-IAE Joint Research Team Develops a 2D Catalyst That Breaks Performance Barriers in Lithium-Air Batteries

As the EV and energy storage systems market (primarily for solar installations) experience rapid growth, their major limitation has been the energy density cap of current lithium-ion technologies. The challenge in this industry has always been to increase the battery energy density to be able to store more charge in the same battery weight. Researchers have been working on different solutions, such as developing more energy dense silicon anodes, and one other angle that has shown great promise is the lithium-air battery design. Theoretically, this battery can provide 10X the energy density of current lithium-ion batteries, which means it could be at par or store more power than silicon anode lithium-ion batteries. However, these batteries have proven difficult to commercialize because they have limited active catalytic sites that promote oxygen reaction when charging and discharging. This results in slow reactions and short lifespans. But a joint team of researchers from the Center for Extreme Materials Research at KIST (Korea Institute of Science and Technology) and the Advanced Materials Processing Center at IAE (Institute for Advanced Engineering) has cracked this code.

The Challenge

2D materials (most notably transition metal dichalcogenides or TMDCs) have proven effective as electrocatalysts in lithium-air batteries due to their highly flexible surface reactivity and electronic structures. Among these TDMCs, those in the 1 T′ phase, such as 1 T′ tungsten diselenide (1 T′-WSe2), have the ideal structural platform that combines high electrical conductivity with large basal plane active site tunability and effective charge transport. However, these TDMCs still have a critical limitation, which is low catalytic activity, especially when dealing with charge-neutral reactants, such as oxygen. Remember, lithium-air batteries use lithium oxidation and oxygen reduction to generate electricity, so the low catalytic activity hampers oxygen reduction.

This inertness is attributed to the full chalcogen-coordination nature in the basal plane, and most of the previous research has been focused on introducing under-coordinated edge sites that have suitable electronic states to support oxygen reduction. However, these edge sites represent only a small fraction of the total surface area of the 2D basal plane, resulting in sluggish oxygen reduction and oxygen evolution reactions. This limits the performance and practical applications of lithium-air batteries.

Solutions Developed Over The Years

To try to activate the entire 2D basal plane, researchers have tried several strategies to structurally tune the 2D TDMC basal plane, which include:

• Surface decoration with nanoparticles and adatoms

• Chemical exfoliation

• Point defect engineering

• Phase transformation

However, these techniques are still not effective because none maintains high electrical conductivity, which is essential for efficient charge transfer in such electrocatalytic systems. Metallic phases in the TDMC are the only way to ensure quick electron transport across the entire 2D plane for efficient oxygen reduction and evolution. But these metal phases must maintain their structural integrity during vacancy formation, as well as prolonged oxygen reduction and evolution cycles, which makes substitutional metal doping suitable for providing atomic-scale vacancy engineering.

Substitutional Metal Doping Strategy Used by the KIST-IAE Joint Research Team

This research team used the  strategy of substituting platinum metal atoms into the layered structure of the 2D tungsten diselenide basal plane, which formed atomic-level vacancies where selenium atoms were intentionally missing from the surface. This lack of selenium atoms forms a strong reaction site across the entire plane that absorbs and activates oxygen molecules strongly, resulting in stronger oxygen reduction and evolution reactions. This breakthrough maximizes the usage of the 2D TDMC plane in the lithium-air battery, making it a fully active site without affecting conductivity.

Research Findings

The lithium-air battery this team prototyped had its 2D tungsten diselenide basal plane made more active using targeted substitutional platinum doping. It demonstrated a stable lifespan exceeding 550 cycles when exposed to rapid charge-discharge conditions at the 1C rate (1 hour charging and discharging cycles), as well as superior stability and durability compared to other lithium air batteries in the market that have higher cost commercial catalysts, such as ruthenium oxide and platinum on carbon (Pt/C), when subjected to different charge-discharge conditions ranging from 0.1C to 3C. These results showed potential and a move towards the right direction when it comes to developing the next generation of lithium-air batteries that deliver high charge densities with minimal performance degradation even when subjected to high-speed charging conditions.

Practical Applications of This Lithium-Air 2D Catalyst Discovery Breakthrough

By overcoming the structural and performance limitations of the 2D materials used to make the electrocatalysts in lithium-air batteries for oxygen reduction and evolution reactions, these power storage solutions become viable in EVs, particularly because they hold more charge, meaning car owners will enjoy electric mobility more without anxiety range. Electric trucks can also become more viable because these energy dense batteries will hold enough charge to haul heavy cargo and containers for long distances before stopping over for recharging. Speaking of recharging, the fully highly reactive surface for oxygen evolution supports fast charging, so these energy dense batteries can be filled faster, provided charging stations contain superchargers.

Energy Storage Solutions (ESS) will also benefit from this research because solar batteries for domestic or commercial use will come closer to providing 24-hour electricity owing to their energy dense nature.

Besides lithium-air batteries, this breakthrough is expected to contribute to performance enhancement and cost reduction in other energy applications that require high-performance oxygen reduction and evolution catalysts, such as hydrogen fuel cells and water electrolysis.

Dr. Sohee Jeong from KIST acknowledged that this research is significant because it provides an atomic level control technique that utilizes the previously untapped basal plane in the electrocatalytic reaction while maintaining the structural advantages and integrity of the 2D materials. Dr. Gwang-Hee Lee from IAE further added that this materials research has rapidly cracked the fast charge-discharge performance, which was a major challenge in lithium-air batteries.

This South Korean research team from the two institutions invited participation from the Lawrence Livermore National Laboratory (LLNL) in the United States to enhance the study’s global competitiveness and credibility.