Research for military and space applications is at the cutting edge and frequently spun-off into commercial applications. So when the US space agency NASA supports the development of advanced energy storage technologies for its own use it is worthy of notice.
NASA’s recent solicitation covered two areas: ‘High specific energy system level concepts’, focusing on cell chemistry and system level battery technologies, such as packaging and cell integration; and ‘Very high specific energy devices’, focusing on energy storage technologies that can go beyond the current theoretical limits of lithium batteries while maintaining the cycle life and safety characteristics demanded of energy storage systems used in space applications.
For these NASA has selected four projects, one focusing on silicon anode-based cells for high specific energy systems, and three focusing on lithium-sulphur (Li-S) batteries.
Silicon anode technology
Of the four projects, the silicon anode development was the only award to a non-university applicant, going to the innovative Silicon Valley startup Amprius.
Silicon anode technology is expected to lead to the next generation lithium-ion batteries, with increased capacity and longevity. Silicon has more than 10 times the storage capacity of the graphite traditionally used in Li-ion batteries (in the second electrode, the other being the lithium).
Despite the infancy of the technology, Amprius is reported already to be shipping silicon anode Li-ion batteries with a capacity around 20% more than traditional batteries to some smartphone manufacturers. Amprius was also the recipient in January of $30 million in funding to further develop and commercialize its technology.
The British company Nexeon is another working in this area and has a patented technology available for licencing. In July the US Department of Energy’s Pacific Northwest National Laboratory (PNNL) also announced a breakthrough. The challenge with the technology is that when charged the silicon swells making it liable to break apart and become inoperable. PNNL has developed a porous sponge-like silicon material, which undergoes much less expansion, as when the silicon expands it fills the spongy holes. This technology will now be developed into a larger battery prototype, along with a streamlining of the production process to reduce the cost.
Li-S technology is another technology that has the potential to offer a significantly greater energy density, up to 10 times, that of traditional Li-ion batteries. Sulphur is also very low cost.
Again, the US DOE at its Oak Ridge National Laboratory (ORNL) has been behind a breakthrough in the development of this technology. The main challenge is that the liquid electrolyte that joins the two electrodes essentially destroys the sulphur cathode, limiting its lifetime. Last year ORNL announced the development of both a new sulphur-rich cathode as well as a solid electrolyte, which combined with a lithium anode to provide about four times the energy density of traditional Li-ion technology. As an added bonus, the all solid battery improves safety due to the absence of the flammable liquid electrolyte.
At the time, the ORNL team indicated that while the technology was in the demonstration stage, a patent was pending and it could potentially move quickly into commercial applications.
One of the NASA projects (at the University of Maryland) will be developing highly stable garnet solid electrolytes. The others are at California Institute of Technology and Indiana University.
Applications for electric vehicles
It is not necessary to go into space to appreciate the benefits these new technologies promise, including longer discharge times, increased lifetimes, greater safety, and reduced costs.
Among the many devices these batteries would power, arguably one of the most important beneficiaries could be electric vehicles, with the increased range they would gain and improving their attractiveness to drivers.