By Kent Griffith
August 13, 2020 | Lithium-ion batteries have been enjoying center stage in the tech world for their role in our digital daily lives and the transformation from combustion to electric vehicles. A capstone moment for lithium-ion batteries was the recognition of M. Stanley Whittingham, John Goodenough, and Akira Yoshino with the 2019 Nobel Prize in Chemistry. The prize marked a lifetime of accomplishments, particularly their early work in the 1970s and 1980s. Of course, the development of lithium-ion batteries has involved uncountable scientists and engineers, for whom the International Battery Seminar has been a premier gathering that dates back to just after the discovery of the prototypical lithium cobalt oxide (LiCoO2) layered cathode (DOI: 10.1016/0025-5408(80)90012-4). As such, you can imagine the excitement as Professor Stan Whittingham virtually presented the opening plenary of the 2020 International Battery Seminar in the year of the lithium-ion battery Nobel Prize. In the midst of a global pandemic, the conference moved online for the first time in its 37-year history, but the lack of physical presence could not slow the momentum of this dedicated group. Rather than cheering in a crowded auditorium, we welcomed Whittingham into our homes and offices to hear about the history and future of the lithium-ion battery.
Professor Whittingham, still an active researcher at Binghamton University in New York state, has been around since the beginning of lithium-ion batteries. The Nobel Laureate spoke at the International Battery Seminar on “The Li Battery: From Its Origin to Enabling an Electric Economy.” He conceptualized a lithium-ion battery based on intercalation into titanium disulfide (TiS2) while working for Exxon Research and Engineering Company in the mid 1970s and brought a working cell shutting lithium between TiS2 and a lithium metal anode into the world (DOI: 10.1126/science.192.4244.1126).
As he describes it, “TiS2 gave an almost perfect cathode” owing to its metallic conductivity, layered structure, and ‘soft lattice’. The only problem: “The voltage is really too low.” Titanium disulfide incorporates lithium at about 2 V, which motivated the work of Professor Goodenough’s team to develop lithium cobalt oxide with a voltage near 4 V. Doubling the voltage provides twice the energy for every lithium ion stored. Another historical note that Whittingham mentioned was that titanium disulfide provided a training ground for young researchers at the time including Jeff Dahn, a name that will be familiar to those following Telsa as he is currently the NSERC/Tesla Canada Industrial Research Chair at Dalhousie University in Nova Scotia. Dahn received special mention both for his early ties to Whittingham’s original cathode, and the fact that he would present the next plenary in the opening session.
Moving beyond the original battery design, Whittingham touched on the plethora of cathode and anode materials put forth over the coming decades. The list of key contenders has included lithium–aluminum alloys, carbon, tin, silicon, and pure lithium at the anode and lithium cobalt oxide, lithium nickel cobalt aluminum oxide (NCA), lithium nickel manganese cobalt oxide (NMC), lithium iron phosphate (LFP), and other manganese and vanadium oxides and phosphates as cathode materials. Whittingham has focused recently on moving beyond standard cathodes by investigating multiple lithium ion storage in lithium vanadyl phosphate (Li2VOPO4) (DOI: 10.1039/C8CC02386G). The idea here is that, if two lithium ions can be cycled in and out, the energy will be higher. It was noted that vanadium is more abundant than cobalt and nickel, but questions remain surrounding its toxicity. In particular, Whittingham believes phosphates should be suitable for large-scale energy storage applications such as grid storage. There are still challenges to overcome, and Whittingham states that NMC and NCA will likely dominate for at least 5–10 years based on the rapid growth of battery manufacturing facilities in recent years and planned/under construction.
Another focal point of Whittingham’s plenary was the work of the Battery500 program, a US Department of Energy–funded initiative, of which he is a member. The long-term goal of the Battery500 program is to develop a cell that meets the 500 Wh/kg target for energy density. Achieving this lofty goal would dramatically increase the driving range of EVs and accelerate their widespread adoption. From the materials perspective, it will require success with challenging materials such as Li metal anodes and sulfur cathodes. However, some promising intermediate goals were met with the recent demonstrations of a 350 Wh/kg pouch cell based on NMC622 and a 400 Wh/kg cell based on NMC811.
Looking to the future, Whittingham posited that new manufacturing technologies are needed. As one example, lithium iron/manganese phosphate should be a very cheap cathode to produce as it relies on low-cost metals; however, it is not much less than NMC due to the high manufacturing costs that are required to produce nanoparticles and introduce carbon-coatings to aid the electronic properties. Another specific reference from Whittingham was to the need to eliminate toxic chemicals, a directive aimed at the harmful organic solvent known as NMP used in the slurry processing of most cathode materials. Alternatives do exist, such as dry processing or water-based processing, but the shift toward nickel-rich cathode materials has brought additional challenges due to its increased moisture sensitivity. Another highly desirable manufacturing advance is the production of thicker electrodes without sacrificing performance. As electrode thickness increases, the distance that lithium ions and electrons must travel increases, which usually translates to slower charging rates and lower peak power output. However, thicker electrodes minimize the amount of inactive materials such as copper and aluminum foils used as current collectors—one of the many trade-offs involved in battery manufacturing.
A way to bring down cell cost and increase the efficiency of cell production would be to eliminate the time-consuming, and therefore expensive, formation cycling. In formation cycling, cells are cycled a several times at a slow rate to create a solid–electrolyte interphase (SEI) and evolve gases that are then removed from the cell before the final sealing step. If an effective SEI could be designed, we could eliminate the formation cycling step entirely. Beyond performance, another aspect of advanced manufacturing and cell design that Whittingham emphasized is the development of cells that are built to be easily recycled. In the next decade, the number of large EV battery packs reaching end-of-life will be far greater than the quantity we have faced so far, so improved and efficient recycling methods are urgently needed. Initiatives such as the ReCell Center at Argonne National Laboratory and the ReLiB program within the Faraday Institution in the UK are aimed directly at this challenge.
A lively Q&A session followed the plenary session, with Whittingham and Dahn fielding questions across the range of battery energy storage technologies and applications. Whittingham reiterated the importance of safety for the future of batteries and came out in support of technologies such as LFP, which has been making a comeback in China and which he believes may make a resurgence in the US. Fast charging is another key parameter for the EV driving experience, but Whittingham warns that fast charging comes at the sacrifice of the lifetime of the cell with current technologies. The question of “ultimate limit of energy density” came up, and Whittingham pointed back to the Battery500 goal of reaching 500 Wh/kg. On that subject though, the audience was reminded that lithium–sulfur cells are relatively low density and thus may face size issues even if their weight targets are achieved. All of the options for 500 Wh/kg depend on safely enabling lithium metal anodes where Whittingham started 45 years ago, a main topic of the conference and certainly an open problem in the field. For a field as large and dynamic as lithium-ion batteries, Whittingham provided an impressively comprehensive and power-packed plenary full of firsts: the first International Battey Seminar since lithium-ion batteries won the Nobel Prize and the first to take place online. Hopefully we will be back together in person next year, but, regardless, the lithium-ion battery has secured its place in history and is ready to usher in the electric vehicle era.
Editor’s Note: Did you miss the 2020 International Battery Seminar? Because the event was virtual, you can still access the event including all of the recorded sessions, presentations, and materials. Register for PREMIUM POST-EVENT ON-DEMAND.