QuantumScape said its new Osprey platform swaps the liquid in its cathode for a sulfide solid electrolyte, and that the cells have hit 1,000 full cycles to 80 percent capacity at just one atmosphere of pressure, Electrek reported.
That would be a big deal for the sulfide camp, which includes Toyota, Samsung SDI, BYD, and Factorial, whose cells typically need heavy clamping to work. But the white paper behind the announcement shows these are small, early lab cells, and some headline numbers come with important conditions, Electrek reported.
A ceramic separator, with the sulfide in the cathode
QuantumScape's current product is not all-solid-state. The new white paper describes the QSE platform, including the QSE-5 cell it is shipping as samples from its Eagle Line pilot production in San Jose, as a ceramic separator paired with "a relatively conventional high-nickel NMC cathode and a liquid catholyte." The solid part is the separator. The cell is built "anode-free," and lithium plates against the separator during the first charge.
Osprey keeps that separator and anode-free design and swaps the liquid in the cathode for a solid sulfide electrolyte, which makes the whole cell solid. QuantumScape has spent years arguing that sulfide electrolytes cannot work as separators, and the white paper doubles down, calling their problems "fundamental properties" of the material. The company lists four issues: sulfides react with lithium metal, they need high pressure to keep contact with the electrodes, they struggle at room temperature and below, and they cannot handle fast charging with a lithium-metal anode before dendrites form.
The pressure point is the one automakers care about most. QuantumScape illustrated it this way: 20 atmospheres on a single 10-by-24.2-centimeter cell works out to roughly 5,000 kilograms of force, about three mid-size cars, Electrek reported. Many sulfide cells in labs run at 30 to 100-plus atmospheres. QuantumScape's pitch is to keep the sulfide in the cathode, where it is good at moving lithium ions, and let the ceramic separator handle the lithium metal.
Strong cycle life, and headlines with conditions
The strongest result was cycle life. A 2-layer cell with a 50-by-65-millimeter cathode, the same area as QSE-5, ran 1,000 cycles to about 80 percent capacity. The test used full 1C charge and 1C discharge, 0 to 100 percent state of charge, 30 degrees Celsius, and 1 atmosphere. The cathode loading was 5.5 milliamp-hours per square centimeter, in line with commercial EV cells. Electrek said it could not find published data that contradicts QuantumScape's claim that no other sulfide-based cell has shown this. But the cell is small: two layers at that size come out to roughly 0.3 to 0.4 amp-hours, compared with about 5 amp-hours for a QSE-5.
Other headlines need more context. The press release's "five-minute fast charging from 10% to 80%" was achieved at 10C, in a 2-layer cell, at 80 degrees Celsius, or 176 degrees Fahrenheit. The chart itself is captioned "High temperature enables 5 min fast charge." QuantumScape did not publish a room-temperature fast-charge result. "Operational down to -20°C" came from a single-layer cell with a 21-by-21-millimeter cathode, discharged slowly at C/3. The "up to ~1,100 Wh/L" figure is a projection based on high-loading cathodes; the test backing that up used an 11-millimeter coin-size cell at 3 atmospheres, not 1, and ran for 100 cycles. For reference, QSE-5 is rated at 844 watt-hours per liter and 301 watt-hours per kilogram, Electrek reported.
The cycle-life result at 1 atmosphere is the part that stands out. The fast-charge, cold-weather, and energy-density claims are real tests, but they were run on small cells, sometimes at high temperature or higher pressure, and they are not yet a production pack.