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QuantumScape is currently one of the most talked about companies in the field of batteries for electric vehicles. This is because of its $680M November 2020 IPO and recent announcements the company made concerning the development of a of solid-state lithium metal battery cell that has higher energy density, charges faster, lasts longer, and is safer than existing EV batteries. These claims have been supported by a recent $100M investment from Volkswagen that was apparently based on successful testing of the battery cell. Additionally, manufacturing plans have been announced to build a one GWh pilot line facility, maybe in Germany, to complement a new pre-pilot line planned for San Jose, CA.
Previously, QuantumScape had not completely described the battery’s architecture, but some of the elements were known, as was recently discussed in a Wired magazine article. The battery is apparently an “anode-free” lithium metal battery with a nickel manganese cobalt oxide (NMC) cathode with a solid ceramic electrolyte (also called a separator). A big question was the nature of the separator. The separator is the component that has hindered the commercial development of lithium metal batteries because it must be safe, stable, highly conductive to lithium ions but not electrons, and mechanically strong enough to prevent penetration by lithium dendrites growing on the anode. Finding the right material has not been easy.
Looking at QuantumScape’s patent portfolio yields some hints about the nature of the separator/solid-state electrolyte (SSE). Specifically, about 32% of QuantumScape’s published patent applications (32/99 applications) over the past eight years have dealt with “garnet-type” ceramic materials. QuantumScape’s next most active patent areas during this period concern catholytes containing lithium-silicon-lead-scandium compounds (4% of published applications) and catholytes containing lithium-phosphorus-sulfur-iodine (3% of published applications). Therefore, a reasonable guess based on patent filing activity is that QuantumScape’s separator is a garnet-type material.
Even stronger evidence comes from QuantumScape’s recent patent application US 2021/0167417 A1, published on June 3, 2021 (originally published on December 12, 2019 as WO 2019/236904 A1). This application states that it has solved many of the problems associated with solid-state batteries and describes a battery cell comprised of a cathode active layer, a sulfide catholyte, a buffer (i.e., a barrier, not a pH moderator), a binding layer, a lithium-stuffed garnet separator, and optionally, an anode. This description sounds like the battery cell that QuantumScape has been talking about in its limited public announcements because of the emphasis on the cathode, catholyte and separator. The anode in the ‘417 application is described as lithium metal, but not much else is said about it. There is no mention of an “anode-free” design (i.e., where all of the lithium metal is in the cathode during manufacturing, or before the cell is charged), but nothing in the ‘417 application rules this out.
The ‘417 application contains several examples for constructing a solid-state battery cell that illustrate the specific materials used. In all four examples where a solid-state positive electrode layer is described, LZO coated NCA is used as the cathode active material, although the application states that LZO coated NMC can also be used. (NMC is lithium-manganese-cobalt-oxide; NCA is lithium nickel-cobalt-aluminum oxide; and LZO is lanthanum zirconium oxide).
The sulfide catholyte and buffer comprise different layers of LSTPS (LSTPS is LiSiSnPS of varying atomic amounts). A representative a binding layer comprises a lithium borohydride material having the composition 3LiBH4·2LiCl·3LiNH2, and the binding layer is positioned between the buffer layer and the separator. The separator comprises a material (lithium stuffed garnet) such as LiLaZrO·Al2O3 (more specifically, LixLayZrzOt·qAl2O3, where x, y, z, and t are the subscripts for the corresponding elements). The anode is a lithium metal film evaporated onto the side of the separator not in contact with the binding layer.
In conclusion, it appears that the patent application US 2021/0167417 describes the architecture of QuantumScape’s new prototype solid-state lithium metal battery. Like many patent applications, the ‘417 application describes hundreds or thousands of possible combinations of materials for the invention. This makes it difficult to identify a specific preferred version of the battery. Also, a version of this patent application was originally filed on June 6, 2019, with a priority date of June 6, 2018, so the subject matter is only current as of these dates. Nevertheless, the ‘417 application contains a lot of information about QuantumScape’s battery development, and it seems likely that this application describes the prototype battery QuantumScape has been alluding to in public statements. A copy of the ‘417 application is available here.
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