[Complete Battery Mastery]⑮ The 'Anode Material King' Lithium Metal Commercialization Is Near

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On December 7th last year, LG Energy Solution and Professor Hee-Tak Kim's joint research team at KAIST announced research results on lithium metal batteries capable of 900 km on a single charge and over 400 recharge cycles. This is about 50% higher than the current driving range of lithium-ion batteries (approximately 600 km). A few days later, on December 13th, SES AI, headquartered in Boston, USA, announced that it had started supplying lithium metal battery B samples to its clients.

Lithium metal batteries, along with solid-state batteries and lithium-sulfur batteries, are attracting attention as next-generation batteries, but there are still significant challenges to overcome, such as fire risks and short lifespans. However, recent successive advancements in research results have led to evaluations that commercialization is within sight.

Theoretical Capacity 10 Times That of Graphite, Dendrites Remain a Challenge

Lithium metal batteries generally refer to batteries using lithium metal as the anode. Since Sony first commercialized lithium-ion batteries in 1991, secondary battery technology has focused mainly on cathode materials. After decades of research on cathode materials reached its limits, researchers' attention has shifted to anode materials.

Silicon anode materials, introduced earlier, are one such example. Silicon anodes are commercialized by mixing only about 5% with conventional graphite due to swelling phenomena. Overcoming swelling is the main challenge for silicon anodes. (Refer to Complete Battery Mastery Episode 11)

Lithium metal is a future secondary battery technology that attracts even more attention than silicon anodes. Among researchers, it is called the "final boss" or the "Holy Grail" of anode materials.

The theoretical capacity of graphite used in lithium-ion batteries is 372 milliampere-hours per gram (mAh/g), whereas lithium metal's theoretical capacity is 3860 mAh/g, more than 10 times higher. Lithium has a low potential of -3.040 V relative to the standard hydrogen electrode (SHE) and a low density of 0.534 g/cm³, making it a promising future anode material.

Lithium metal anodes are made by coating copper foil with lithium metal foil tens of nanometers thick. Lithium metal itself is lightweight and much thinner than graphite, allowing for significant reductions in battery size and volume compared to conventional graphite or silicon anodes. This can improve energy density, enabling electric vehicles to travel longer distances with the same battery size. Due to its light weight, lithium metal batteries are also expected to be used in drones (unmanned aerial vehicles).

Development process of lithium-ion battery anode materials. Image source: MIT News

Lithium metal is actively researched not only for commercialized lithium-ion batteries but also as an anode material for next-generation secondary batteries such as solid-state and lithium-sulfur batteries. For example, lithium-sulfur batteries use sulfur as the cathode material and lithium metal as the anode. If lithium metal is applied to the anode while keeping the cathode material of conventional lithium-ion batteries and using solid electrolytes, it becomes a solid-state battery. Of course, achieving this at a commercial level is a separate challenge.

The biggest barrier lithium metal batteries must overcome is dendrites. Dendrites refer to the formation of tree-branch-like crystals when lithium ions migrating to the anode during charging form these structures.

When graphite is used as the anode, lithium ions migrating to the anode are stably inserted into the layered structure of graphite, so dendrites rarely form. In contrast, in lithium metal batteries, lithium ions migrating to the anode immediately undergo a reduction reaction with lithium metal and easily deposit on the anode surface. If the deposited lithium continues to grow and pierces the separator to reach the cathode, a short circuit occurs, causing the battery to explode.

Dendrites also affect battery lifespan. In lithium-ion batteries, during charge and discharge, a solid electrolyte interface (SEI) layer forms between the anode and electrolyte. The SEI layer acts as a pathway for stable lithium ion movement and prevents corrosion of lithium by blocking contact with the electrolyte. However, if lithium deposits unevenly and concentrates in one area, the SEI layer is damaged, reducing charge-discharge efficiency. Continued lithium deposition depletes lithium and significantly decreases battery capacity.

There have been several attempts to commercialize lithium metal batteries, but all failed due to unresolved dendrite issues. Nobel laureate Professor Stanley Whittingham first developed a battery in the 1970s using titanium disulfide (TiS2) as the cathode and lithium metal as the anode, but it did not lead to commercialization.

Before lithium-ion batteries appeared, in 1988, Canadian company Moli Energy commercialized a lithium metal battery using molybdenum disulfide (MoS2) as the cathode in collaboration with Professor Jeff Dahn of Dalhousie University. However, this battery had to be massively recalled due to fires, and the company went into bankruptcy. Dendrites were identified as the cause of the fires. (Refer to Complete Battery Mastery Episode 3)

French Bollor? electric bus equipped with a lithium metal polymer battery

In 2021, RATP, the public transportation operator in Paris, France, introduced Bluebus from the Bollor? Group. This bus was equipped with a lithium metal polymer (LMP) battery developed by Blue Solutions, a subsidiary of Bollor? Group. However, after two fires occurred in 2022, RATP suspended operation of 149 buses equipped with this battery. Since this battery uses a polymer (solid polymer) electrolyte instead of liquid, it is sometimes classified as a solid-state battery.

To suppress dendrite formation in lithium metal, researchers are trying various approaches, such as coating the lithium metal surface, optimizing electrolyte components, and introducing additives. As a result, meaningful outcomes are being announced one after another.

SK and Hyundai Invested US SES AI "Commercialization by 2025"

SES AI is considered the closest to commercializing lithium metal batteries. On December 13th, at the Battery World event, the company announced a joint development agreement (JDA) with a major automaker to mass-produce lithium metal battery B samples. SES AI had previously signed JDAs for A samples with global automakers including General Motors (GM) in the USA, Honda in Japan, and Hyundai Motor Company, and among them, it signed a priority B sample contract with one.

SES AI explains on its website that "by the time the B sample is completed, risks related to module and pack technology are considered fully eliminated, and there are no disruptive risks in the supply chain and manufacturing process." After passing through C and D sample stages, the battery can be installed in electric vehicles.

Considering that B sample testing takes 1-2 years and C and D sample testing another 1-2 years, commercialization could be possible within about two years. In fact, the company has set a goal to commercialize lithium metal batteries around 2025. SES AI also plans to apply lithium metal batteries to urban air mobility (UAM).

Chi Chao Hu, founder of SES AI, is introducing lithium metal batteries at the Battery World event held in November 2021. Photo by SES AI

SES AI, headquartered in Boston, USA, was founded in 2012 by Dr. Qichao Hu, an MIT alumnus. Initially named Solid Energy Systems, the company later changed its name to SES AI. As the name suggests, the company initially developed solid-state batteries but later shifted focus to lithium metal batteries, seeing higher commercialization potential. In an interview with Fortune Korea (August 2023 issue), founder Qichao Hu said, "Solid-state is still too far away," and described "hybrid lithium metal as the end game."

The company first showcased a lithium metal battery prototype in 2016, attracting global automakers' attention. It also has close ties with South Korea. SK invested twice in 2018 and 2021, acquiring a 12.7% stake. Hyundai Motor Company also invested $100 million. SES AI was listed on NASDAQ in February 2022 and has factories in Shanghai, China, and Chungju, South Korea. The Chungju factory is interpreted as targeting domestic customers.

SES AI uses deep learning technology to develop battery materials, which is why "AI" is part of its name. The company explained that it suppressed lithium formation by applying high-concentration solvent-in-salt electrolytes, protective coatings, and composite lithium metals. In 2021, SES AI unveiled a lithium metal battery weighing 0.982 kg with a capacity of 107 ampere-hours (Ah). The gravimetric energy density was 417 Wh/kg, and volumetric energy density was 935 Wh/L.

Domestic Achievements Emerging

LG Energy Solution and Professor Hee-Tak Kim's team at KAIST jointly developed lithium metal battery technology that achieves an energy density of over 400 Wh/g, enabling 900 km driving on a single charge and over 400 recharge cycles. The joint research team explained that they solved technical challenges by applying a previously unreported borate-pyran-based liquid electrolyte for lithium metal batteries for the first time worldwide.

Part of the paper published on November 23 in Nature Energy by LG Energy Solution and Professor Hee-Tak Kim's team at KAIST.

The borate-pyran electrolyte redesigns the SEI formed on the lithium metal anode surface into a dense structure, blocking corrosion reactions between the electrolyte and lithium. The research team explained that this technology simultaneously solves dendrite and corrosion problems, improving charge-discharge efficiency. The research results were published online on November 23 in the world-renowned journal Nature Energy.

On November 28, Lotte Chemical announced that it had developed the country's first polymer-based solid electrolyte separator coating material manufacturing technology to solve the instability of lithium metal anodes and completed domestic patent applications. This technology focuses on coating functional materials that improve lithium ion flowability on the separator of lithium metal batteries to suppress dendrite formation. The company explained that this technology preserved over 90% capacity after 500 recharge cycles.

In 2021, Lotte Chemical invested in the US startup SOELECT, which develops lithium metal anodes, and signed a JDA. Through about two years of joint research, they developed and applied related technologies. The two companies are considering building a gigawatt-scale (GWh) lithium metal anode production facility worth about $200 million in the US by 2025.

MIT News, Doubling battery power of consumer electronics, 2016.8.16
KIC News Volume 21, No. 6, 2018, Trends in Next-Generation Lithium Metal Anode Protective Film Technology
Electrek, SES shares plans for world’s largest lithium-metal facility to build 107 amp-hour EV batteries. 2021.11.3
electrive, Paris public transport operator orders 109 electric buses by Bluebus, 2021.1.9
InsideEV, Paris Suspends 149 Bollor? Electric Buses After Two Fires, 2022.5.2
Fortune Korea, “Battery technology competition has entered the endgame,” 2023.8.4
Nature Energy, Borate-pyran lean electrolyte-based Li-metal batteries with minimal Li corrosion, 2023.11.23
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SES AI Website