QuantumScape Corporation, a Volkswagen Group-backed developer of next-generation solid-state lithium-metal batteries for use in electric vehicles (EVs), released performance data demonstrating that its technology addresses fundamental issues holding back widespread adoption of high-energy density solid-state batteries, including charge time (current density), cycle life, safety, and operating temperature.

A commercially viable solid-state lithium-metal battery is an advancement that the battery industry has pursued for decades, as it holds the promise of a step function increase in energy density over conventional lithium-ion batteries, enabling electric vehicles with a driving range comparable to combustion engine-based vehicles. QuantumScape’s solid-state battery is designed to enable up to 80% longer range compared to today’s lithium-ion batteries.

Previous attempts to create a solid-state separator capable of working with lithium metal at high rates of power generally required compromising other aspects of the cell (cycle life, operating temperature, safety, cathode loading, or excess lithium in the anode). QuantumScape’s newly-released results, based on testing of single-layer battery cells, show its solid-state separators are capable of working at very high rates of power, enabling a 15-minute charge to 80% capacity, faster than either conventional battery or alternative solid-state approaches are capable of delivering.

QuantumScape single-layer solid-state pouch cell.

In addition, the data shows QuantumScape battery technology is capable of lasting hundreds of thousands of miles, and is designed to operate at a wide range of temperatures, including results that show operation at -30 degrees Celsius.

The tested cells were large-area single-layer pouch cells in the target commercial form factor with zero excess lithium on the anode and thick cathodes (>3mAh/cm²), running at rates of one-hour charge and discharge (1C charge and 1C discharge) at 30 degrees Celsius. These tests demonstrated robust performance of these single layer pouch cells even at these high rates, resulting in retained capacity of greater than 80% after 800 cycles (demonstrating high columbic efficiency of greater than 99.97%).

QuantumScape ceramic solid-state separator.

The hardest part about making a working solid-state battery is the need to simultaneously meet the requirements of high energy density (1,000 Wh/L), fast charge (i.e., high current density), long cycle life (greater than 800 cycles), and wide temperature-range operation. This data shows QuantumScape’s cells meet all of these requirements, something that has never before been reported. If QuantumScape can get this technology into mass production, it holds the potential to transform the industry.

—Dr. Stan Whittingham, co-inventor of the lithium-ion battery and winner of the 2019 Nobel prize in chemistry

These results blow away what was previously thought to be possible in a solid-state battery. Supporting high enough current density to enable fast charge without forming dendrites has long been a holy grail of the industry. This data shows the capability to charge to 80% capacity in 15 minutes, corresponding to an astonishingly high rate of lithium deposition of up to a micron per minute.

—Venkat Viswanathan, battery expert and professor of materials science at Carnegie-Mellon University

QuantumScape’s team of scientists have worked over the past decade to create the next generation of battery technology: solid-state batteries with lithium-metal anodes. With processes and materials protected by over 200 patents and applications, QuantumScape’s proprietary solid-state separator replaces the organic separator used in conventional cells, enabling the elimination of the carbon or carbon/silicon anode and the realization of an “anode-less” architecture, with zero excess lithium.

In such an architecture, an anode of pure metallic lithium is formed in situ when the finished cell is charged, rather than when the cell is produced. Unlike conventional lithium-ion batteries or some other solid-state designs, this architecture delivers high energy density while enabling lower material costs and simplified manufacturing.

Beyond its ability to function at high rates of power while delivering high energy density, other key characteristics of QuantumScape’s solid-state lithium-metal battery technology include:

• Zero excess lithium: In addition to eliminating the carbon or carbon/silicon anode, QuantumScape’s solid-state design further increases energy density because it uses no excess lithium on the anode. Some previous attempts at solid-state batteries used a lithium foil or other deposited-lithium anode, which reduces energy density.

• Long life: Because it eliminates the side reaction between the liquid electrolyte and the carbon in the anode of conventional lithium-ion cells, QuantumScape’s battery technology is designed to last hundreds of thousands of miles of driving. Alternative solid-state approaches with a lithium metal anode typically have not demonstrated the ability to work reliably at close to room temperatures (30 degrees Celsius) with zero excess lithium at high current densities (>3mAh/cm²) for more than a few hundred cycles, and result in a short-circuit or capacity loss before the life target is met. By contrast, today’s test results show that QuantumScape’s battery technology is capable of running for over 800 cycles with greater than 80% capacity retention.

• Low-temperature operation: QuantumScape’s solid-state separator is designed to operate at a wide range of temperatures, and it has been tested to -30 degrees Celsius, temperatures that render some other solid-state designs inoperable.

• Safety: QuantumScape’s solid-state separator is noncombustible and isolates the anode from the cathode even at very high temperatures—much higher than conventional organic separators used in lithium-ion batteries.

Volkswagen has made a corporate funding commitment of $300+ million to date with QuantumScape to promote the joint development of solid-state battery technology. The two established a joint venture in 2018 to prepare for the mass production of solid-state batteries for Volkswagen.