By Kent Griffith
August 31, 2022 | Stakeholders from the solid-state battery community met in Chicago or joined online for the Solid-State Battery Summit in early August. Analysts, start-ups, material manufacturers, government agencies, national laboratories, academic scientists, and automakers discussed the status, prospects, and challenges for solid-state batteries. On the one hand, it is an extremely dynamic field with an almost continuous stream of reported progress. On the other hand, solid-state cells compete against a moving target of ever-improving conventional lithium-ion batteries and the timeline or ability to achieve widespread commercialization of solid-state technology is highly uncertain.
Halle Cheeseman, currently a program director at ARPA-E, opened the meeting on the 40th anniversary of his first day working in the battery industry. ARPA-E (Advanced Research Projects Agency–Energy), a division of the US Department of Energy, solicits high-risk, high-reward proposals that could revolutionize energy generation, storage, and use but that are too early for private investment. Some of the best-known battery start-ups have come out of projects funded by ARPA-E (Figure 1).
Over the years, ARPA-E programs have set increasingly aggressive targets for battery cost and performance, most recently targeting $75/kWh and 5- and 15-minute charging (for >200 and >400 Wh/kg batteries, respectively).
Cheeseman is well-versed in the wider battery industry and forecasted a challenging road ahead for solid-state batteries. Among his predictions, Cheeseman predicted that, “Solid-state batteries may be inevitable, but it will take a long time for them to be in mainstream EVs,” and “Solid state batteries will not require less BMS, thermal management, etc.” The latter point relates to the fact that solid electrolyte properties are quite sensitive to temperature, even if their thermal stability is higher than liquid electrolytes, and that dendrites will have to be carefully avoided when lithium metal anodes are in use, though the use of lithium metal is not a given with solid electrolytes. Of dendrites, Cheeseman said, “Blocking dendrites is foolish compared to preventing them from occurring.” He went on to caution that if the main impact of a solid electrolyte is indeed to enable lithium metal anodes and increase the energy density, then increases in vehicle range efficiency (miles traveled per kWh of battery) and advances in silicon anode technology may circumvent the motivation to adopt solid-state technology. Whenever solid-state batteries are ready for mass production, they will be competing against the incumbent technology at that time, and lithium-ion batteries with liquid electrolytes continue to improve in energy density, charge rate, and cost.
Ines Miller, P3 Group, noted that Tesla’s new 4680 cell format will set a clear benchmark for next-generation cell cost and performance metrics. A challenge for solid-state batteries is that neither lithium metal production nor oxide or sulfide solid electrolyte manufacturing are mature. Not only does this mean changes to gigafactory tooling, these processes are expected to require more expensive processing steps and/or environments than those found on conventional cell lines. According to Miller, since it is unlikely that solid-state batteries will be cost-competitive in the near future, there needs to be a differentiator to justify the added expense and effort.
In his presentation, Michael Sanders, Avicenne Energy, suggested that reliable cost estimates for solid-state batteries may not be possible at this time because there are no suppliers for some of the key materials. This issue has caused aspiring solid-state battery companies such as Solid Power to bring solid electrolyte and precursor manufacturing in-house. Avicenne is waiting to forecast the 2025–2030 solid-state battery market in more detail until later this year or next when more data is available from the pilot plants that have come online in 2022. The short-term outlook for solid-state battery capacity will continue to be dominated by small (non EV) cells with Blue Solutions remaining as the only large EV application.
Blue Solutions, the industry leader in solid-state battery production was represented at the Solid-State Battery Summit by Adrian Tylim. Blue Solutions commercialized their first electric car in 2011 with a 30-kWh solid-state pack based on a polymer solid electrolyte and a lithium metal anode. The car had a 250 km range. In 2015, they released an electric bus with a set of eight 30-kWh solid-state batteries and a range of 150 km. Blue Solutions is now looking to move beyond LFP cathodes toward nickel-rich oxides and to lower their battery operating temperature to 25–40°C. They are still focused on lithium metal anodes with polymer, gel, or polymer/ceramic electrolytes. Tylim said that they are not considering silicon anodes or sulfide or oxide electrolytes at this time. Their experience in producing lithium foil thinner than 20 µm and 160 mm in width is relatively unique in the industry and could represent a licensing opportunity. 2022 has been a challenging year, though, as the company has been set back by several EV fires, which highlight the point that moving to solid-state batteries is no guarantee of enhanced safety.
Alex Bates, Sandia National Laboratory, has been working to quantify the safety of solid-state batteries. In his presentation in Chicago, Bates considered three scenarios: a liquid-free all-solid-state battery with a lithium metal anode; a battery with a solid electrolyte separator and a lithium metal anode but with some liquid electrolyte in the cathode; and a conventional lithium-ion battery with a polymeric separator saturated with liquid electrolyte and a graphite anode. Assuming an NMC111 cathode, garnet oxide solid electrolyte (lithium lanthanum zirconium oxide, LLZO), and conventional liquid electrolyte (LiPF6 salt in carbonate solvent), Bates highlighted that short-circuited solid-state batteries may actually release more heat than conventional lithium-ion batteries owing to the energy density of lithium metal. Of course, a non-flammable ceramic oxide electrolyte is better than a flammable liquid but the oxidation reaction of lithium is more exothermic than the combustion of the carbonate solvent. If some liquid is used in a type of ‘hybrid solid-state’ battery then the heat release would be even worse. On the other hand, the temperature for thermal runaway of a conventional LIB is around 200 °C while a solid-state battery, even with a fraction of liquid electrolyte in the cathode, is pushed to 350 °C, which is a significant safety enhancement. For those interested in basic safety calculations for various battery configurations, Bates created an editable spreadsheet that is available with the team’s recent publication “Are solid-state batteries safer than lithium-ion batteries?”
Will solid-state batteries be a commercial success? Will they deliver higher energy density, lower cost, enhanced safety? Everything is on the table for solid-state batteries, but nothing is guaranteed.