QuantumScape, a solid-state Li-ion battery start-up founded by former Stanford university researchers, plans to go public on the New York Stock Exchange, after merging with Kensington Capital Acquisition Corp, a special purpose acquisition company (SPAC). The merged company will be valued at about US$3.3Bn.
QuantumScape’s anode-free solid-state battery technology uses a solid ceramic electrolyte and eliminates anode materials. QuantumScape states that the energy density of its solid-state battery exceeds 400 Wh/kg, an 80% increase compared with the best commercialised Li-ion battery in 2020.
VW is the largest shareholder of QuantumScape. In June 2020, VW announced plans to invest another US$200M in QuantumScape, aimed at advancing the development and commercialisation of solid-state batteries technology.
With the potential to double energy density, solid-state batteries have created very high expectations on the road to eliminating EV driver range anxiety. However, problems concerning material selection for battery components, as well as technology scale-ups, make for a more challenging road than many expect.
A step-change to significantly increase energy density in the cell comes from the use of electrodes with higher energy density. Lithium metal is considered the best candidate for an anode thanks to its lowest redox potential and highest theoretical capacity amongst all possible anode materials. In practice, however, repeated plating and stripping of lithium results in an electrode of “mossy” surface, with needles (including dendrites) and porosity generating undesired side reactions leading to cell failure.
Anode-free cell configuration has great potential to improve the performance of lithium metal anodes. “Anode-free” does not mean a Li-ion battery works without an anode but, rather, the absence of a host to receive the lithium plated on the anode current collector. An anode-free cell is normally assembled in the discharge state (like conventional Li-ion batteries with a graphite anode). During first charging, the anode forms in-situ on the collector foil as Li-ions are deposited as lithium metal. This, therefore, enables the maximum possible energy density to be achieved from a given cathode system. It also saves the cost of using, tape casting, and manufacturing Li-ion batteries with anode materials, simplifying the cell structure.
Despite these advantages, Roskill believes several key problems must be tackled to successfully scale up the technology. A major challenge is how to handle the large volume change of the cell that accompanies depositing and stripping of lithium metal. Additionally, QuantumScape’s solid-state battery uses a solid ceramic electrolyte; manufacturing oxide electrolyte with high conductivity in a cost-competitive way is equally important. Overcoming the discontinuous contact between solid materials is also still a challenge in solid-state battery development.
Despite the significant advances of QuantumScape’s technology, Roskill believes that solid-state batteries will not take over commercially until 2030, at least for high-volume automotive uses, given the lengthy testing and qualification phases that accompany new technology in such safety-critical applications.
Roskill’s Lithium-ion batteries: Outlook to 2029, 4th Edition report was published in May 2020. Click here to download the brochure for the report, or to access further information.