Introduction
As we enter a new era of electrification the question of “Where is battery tech going next?” becomes increasingly pertinent. With advancements in materials science and engineering, the future of battery technology promises enhanced performance, safety and sustainability, potentially revolutionizing fast-growing sectors, from passenger EVs and grid storage to other forms of transportation such as airplanes and ships. This article is the third of a three-part series exploring a selection of the most relevant, cutting-edge battery technologies on the horizon, their potential impacts on the lithium-ion incumbent, and the timeline for their development and commercialization.
You can find the first article in this series on solid-state batteries and the current challenges facing Li-on batteries here and the second article on sodium-ion batteries here.
What makes lithium-sulfur batteries different?
Lithium-sulfur (LiS) batteries use lithium metal (or lithium metal-based composites) as their anode and sulfur (or sulfur-based composites) as their cathode, aiming to take advantage of the high specific capacity of these two materials in the same cell. With these electrodes, LiS batteries have a theoretical gravimetric energy density of ~2,500 Wh/kg, almost 10x that of today’s best lithium-ion batteries. LiS batteries also operate on different electrochemical principles than lithium-ion batteries due to their elemental electrodes, which do not intercalate[1] lithium ions. On the anode, lithium ions are stored and released through electroplating and dissolution respectively, while on the cathode, sulfur reacts with lithium ions to ultimately form Li2S.
What challenges do lithium-sulfur batteries face?
The key challenge that has prevented LiS batteries from reaching technological maturity and entering mass production is their low cycle life (LiS manufacturer Lyten’s cycle life target is 500 C/3 cycles by 2026). [1] The low cycle life of LiS batteries is caused by several different factors, including dendrite formation on the anode, the polysulfide shuttle effect and cathode swelling. Dendrite formation is one of the key challenges for any battery using lithium metal as an electrode. Due to the cyclical dissolution and electroplating of lithium on the anode, the solid electrolyte interface (SEI) grows irregularly, leading to dendrite formation and premature cell death. The polysulfide shuttle effect occurs when lithium polysulfides formed as reaction intermediates at the cathode dissolve into the electrolyte, depleting the cathode, corroding the anode and subsequently reducing cycle life. Sulfur cathodes are also prone to significant swelling (up to 80%) when Li2S is absorbed, placing significant stress on the electrode and leading to premature electrode failure.
LiS batteries use specialized materials to mitigate these challenges. Composite cathodes and anodes are becoming more common to reduce dendrite formation, the polysulfide shuttle effect and swelling by stabilizing lithium and sulfur within composites. Other electrode modification strategies including protective electrode coatings and interlayers are also being investigated to limit chemical degradation within the battery. Electrolytes are also being carefully tuned to reduce side reactions on the cathode and anode while still allowing for rapid ion transport and reaction kinetics. However, these modifications come at the cost of energy density. Modern LiS batteries only have an energy density of ~500 Wh/kg, still ~2x that of the best lithium-ion batteries but a far cry from the theoretical limit of ~2,500 Wh/kg.
In addition to low cycle life, LiS batteries also suffer from low cathode conductivity due to the removal of metals from the cathode, furthering the need for novel cathode materials. Lastly, despite their high gravimetric energy densities, LiS batteries have not seen similar improvements to volumetric energy density (LiS manufacturer Li-S Energy reached 540 Wh/L at R&D scale in 2024), [2] which is still on par with lithium-ion batteries. While this is sufficient for commercially viability, the potential advantage of LiS batteries compared to lithium-ion batteries is reduced without the ability to save both weight and space.
Why could lithium-sulfur batteries be better than lithium-ion?
LiS batteries will have two key advantages over lithium-ion batteries if they can be successfully commercialized, higher gravimetric energy density and lower costs. Higher gravimetric energy density will help reduce the weight of all types of EVs, improving range and potentially enabling electric aircraft if energy density further improves. They are particularly well suited to replacing NMC batteries in electric vehicles, where cycle life is less critical than performance. There is also significant potential for LiS batteries to reach lower ultimate costs than lithium-ion batteries, driven by the low cost and relative abundance of sulfur compared to the metal-based cathodes of lithium-ion batteries. As costs decrease, LiS batteries may also be used in consumer electronics but are unlikely to make it to any applications where cycle life is paramount, such as stationary storage.
There is also the potential for greater supply chain security with the use of LiS batteries. Sulfur is an industrial byproduct of oil and gas refining and readily available across the world, although very long-term supply may become a challenge as the world transitions away from fossil fuels. Another supply chain benefit is the lack of established LiS supply chain, which has the potential to reduce supply chain concentration in a single geography.
Key players to know
LiS battery developments have come from startups, with almost no announcements from major players, unlike solid-state and sodium-ion batteries. Sony is the lone exception, with a 2015 announcement promising LiS battery commercialization by 2020 that went unmet, with no news from the multinational since then. [3]
Among startups, Lyten is the most advanced, offering A samples for testing and recently announcing plans to build a 10 GWh LiS cathode, anode and battery gigafactory in Nevada. [4] Although long ramp-up times are expected after Phase 1 of the facility is opened in 2027, as with all gigafactories, commercial LiS battery production in this decade would already be an achievement. Other companies to watch include Germany’s theion, which uses a crystalline sulfur cathode and Australia’s Li-S Energy, which is using boron nitride nanotubes to improve chemical stability in its batteries.
These startups are looking to avoid the failures that have plagued some older LiS startups such as Oxis Energy and Sion Power. Oxis Energy was a UK startup working on semi-solid-state LiS batteries that filed for bankruptcy in 2021, its technology was sold to Gelion, an Australian startup that is still active in LiS batteries. Sion Power was a US startup that was developing LiS batteries since the 2000s but shifted to lithium-metal batteries in 2015 after struggling to solve issues related to cycle life and volumetric energy density. [5]
Apricum’s takeaway
LiS batteries have sufficiently mitigated many of their key challenges and appear ready for commercial production within the 2020s, although their full performance potential is still a long way from realization. LiS batteries are likely to see use in applications where weight is paramount, but cycle life is not, such as drones and electric vehicles. While commercial manufacturing of any new battery technology comes with significant challenges, Apricum expects these challenges to be solved and LiS batteries to become a viable battery technology within the next ten years.
Summary
Lithium-sulfur (LiS) batteries are an upcoming battery technology that are reaching the first stages of commercial production in this decade. They are characterized by excellent gravimetric energy density, low-cost materials and low cycle lives, well suited to drone applications and to replace NMC batteries in electric vehicles. LiS batteries are also one of the few technologies without significant Chinese involvement in the supply chain. If energy density improves, they may also be a key enabler of electric aviation in the future.
How Apricum can help
Apricum is a strategy consulting and investment banking boutique exclusively focused on renewable energy and cleantech. We have exceptional experience and knowledge across the battery and energy storage value chains. Our unique blend of strategy consulting and transaction advisory helps clients with both direction and execution. Over 14 years we have delivered over 350 successful projects in 30 countries. We offer a complete spectrum of services in strategy consulting from technology assessment, market screening, value chain analysis, business model development, and due diligence to investment banking (corporate and asset M&A, debt and equity fundraising, and corporate finance). If you would like to learn more about how we can support your company in entering or expanding your activities in battery materials, please contact Partner Florian Haacke. If you would like to learn more about how we can support your company in entering or expanding your activities in energy storage, please contact Partner Florian Mayr.
Sources
[1] https://www.nasa.gov/wp-content/uploads/2024/01/05-nasa-workshop-babuganguli.pdf
[2] https://www.lis.energy/portfolio/li-s-energy-achieves-45-increase-in-volumetric-energy-density-with-new-20-layer-semi-solid-state-lithium-sulfur-battery/
[3] https://www.greencarcongress.com/2015/12/20151221-sony.html
[4] https://lyten.com/2024/10/15/lyten-announces-plans-to-build-the-worlds-first-lithium-sulfur-battery-gigafactory-in-nevada/
[5] https://sionpower.com/files/IB_Li-S2Licerion.pdf
[1] Intercalation is the reversible insertion of a molecule or ion into layered materials. In lithium-ion batteries, intercalation occurs at both the anode and cathode to store ions from the electrolyte.
