Toyota working on all-solid-state batteries as mid-term advanced battery solution; prototype cell with 400 Wh/L
Toyota Motor, like many automakers and suppliers, is pursuing the development of Li-air batteries as a very high energy density technology that would enable battery-powered vehicles with a much greater range. In an invited presentation at the 17th International Meeting on Lithium Batteries (IMLB 2014) in Como, Italy, Dr. Hideki Iba from Toyota’s Battery Research Division and Dr. Chihiro Yada from Toyota Motor Europe’s Advanced Technology group noted that Li-air batteries—assuming the attendant issues are resolved—may not be commercialized until FY 2030.
Concurrent with its work on Li-air, Toyota is also pursuing the development of all-solid-state batteries, and has already developed prototype cells with an energy density of 400 Wh/L. These, the Toyota researchers noted (again, assuming development challenges are overcome), could be commercialized by FY 2020 and see subsequent substantial improvement by FY 2025. (Earlier post.)
|Toyota has already built a prototype electric kick-board powered by a Toyota all-solid-state battery to confirm the research and demonstrate the major potential of the technology. Source: Yada and Brasse (2014). Click to enlarge.|
As reported in a paper in ATZelektronik worldwide, the high energy densities and power ratings of the all-solid state technology offer great potential. With proven discharge rates of 50C, even a deployment to electric motorsports with subsequent technology transfer seems within reach, the authors of that paper noted.
Solid-state lithium-ion batteries, with higher volumetric energy densities than currently available lithium-ion batteries, offer other advantages as well:
Improved packaging efficiency, as the cell design can allow in-series stacking and bi-polar structures. High energy densities can be achieved by reducing the dead space between single cells.
Improved safety. There is no risk of leakage of a liquid electrolyte, and the inflammable and inorganic solid electrolytes have high thermal stability.
Long cycle life.
However, all-solid-state Li-ion batteries have suffered from limited power densities until recently. One of the critical reasons for the limited power density was due to the large lithium-ion transfer resistance at the interface between cathode and solid electrolyte, Yada and Brasse note in their overview paper in ATZ. Thus, one of the major efforts in solid-state development has been boosting the power density (as well as the ever-present quest to increase energy density).
Accordingly, researchers are working in three main areas:
Developing better lithium-ion conducting solid electrolytes. These solid electrolytes are oxide-based, sulfide-based, nitride-based, etc. Sulfide-based provide relatively high ionic conductivities; for instance Li10GeP2S12 (LGPS) shows ionic conductivity as high as 1.2 × 10-2 S/cm—comparable to those of organic liquid electrolytes.
Researchers at Max Planck Institute for Solid State Research in Germany recently reported the development of two new ultrafast solid Li electrolytes which are based exclusively on abundant elements. Both compounds—Li10SnP2S12 and Li11Si2PS12 feature extremely high Li-ion diffusivities, with the Si-based material even surpassing the present record holder LGPS. (Earlier post.)
Designing improved electrode/electrolyte interfaces to reduce interfacial resistance. The interfacial modification will become increasingly important in all-solid-state batteries as well as in other next-generation batteries, Yada and Brasse note.
In a separate paper presented at IMLB 2014, Dr. Yada and colleagues from Helmholtz Institute Ulm and the German Aerospace Centre (DLR) report on their development of a new, mathematically rigorous model for a Li solid electrolyte to gain knowledge about the space charge regions at the boundaries between active particles and the electrolyte.
Improving Li-ion conductivity in active materials. Ideally, a battery with high energy density has a thin electrolyte layer and thick electrodes densely packed with active material. To meet the requirements of next-generation batteries, researchers must improve the conductivity of electrode active materials.
All-solid-state lithium-ion battery has been considered as innovative new generation batteries despite their long history. However, there remain many issues to be solved and their practical application seems limited at the present stage. Needless to say, electrode/electrolyte interfaces are very important sites to start and carry out the electrochemical reaction. Using the latest technology including advanced analyses, nano-structural adjustments of the interfaces will become a clue and breakthrough to resolve many issues of innovative new generation batteries.—Yada and Brasse (2014)
Hideki Iba and Chihiro Yada (2014) “Invited Presentation: Innovative Batteries for Sustainable Mobility,” 17th International Meeting on Lithium Batteries (IMLB 2014)
Stefanie Braun, Arnulf Latz, and Chihiro Yada (2014) “A Thermodynamically Consistent Model for Electric Double Layers in Li All-Solid-State Batteries,” 17th International Meeting on Lithium Batteries (IMLB 2014), MA2014-04
Chihiro Yada, Claudia Brasse (2014) “Better batteries with Solid-state instead of liquid-based electrolytes,” ATZelektronik worldwide Volume 9, Issue 3, pp 10-15 doi: 10.1365/s38314-014-0244-8
Noriaki Kamaya, Kenji Homma, Yuichiro Yamakawa, Masaaki Hirayama, Ryoji Kanno, Masao Yonemura, Takashi Kamiyama, Yuki Kato, Shigenori Hama, Koji Kawamoto and Akio Mitsui (2011) “A lithium superionic conductor,” Nat Mat. 10, 682–686 doi: 10.1038/nmat3066