EV battery costs have declined significantly over the past ten years, from more than $1,000 per kilowatt-hour (kWh) to less than $200/kWh. Increasing cell energy is one way to decrease cost even further, as a higher specific energy value will result in fewer materials needed for the same total battery energy. However, it is difficult to increase the energy density beyond that of today’s cells, which are approximately 220 Wh/kg using graphite anodes.
Li-metal anodes deliver almost 10 times the storage capacity of graphite anodes, thus enabling much higher cell energies. However, Li-metal anodes suffer from poor cycle life (typically 10 cycles or less, compared to the 1000 cycle EV battery requirement).
Announced in 2016, the Battery500 consortium, led by the US Department of Energy (DOE) Pacific Northwest National Laboratory (PNNL), is working to to develop next-generation Li-metal anode cells delivering up to 500 Wh/kg. (Earlier post.)
In the first two years of this program, the Consortium made significant progress developing novel cell materials and integrating these materials in industry relevant pouch cells. At the beginning of the program, a Li-metal pouch cell delivered 300 Wh/kg but only cycled approximately 10 times.
Currently, the team has increased that energy density to 350 Wh/kg and extended the cycle life to more than 350 cycles. Specifically, they developed new electrolytes with enhanced stability against Li-metal, optimized the use of thick cathodes against a thin lithium foil, and applied cell-stack pressure to extend cycling life.
Stable Cycling of 350 Wh/kg Li/NMC622 Pouch Cell. Source: DOE.
Recent research on even thicker cathodes and more stable electrolytes shows a path to a 500 Wh/kg cell. Current focuses include increasing rate capability and extending cycle life.
The Battery500 team is composed of world-class scientists and engineers from four National Laboratories and five universities. Notably, two of the researchers on the team, Professor Stanley Whittingham of Binghamton University and Professor John Goodenough of the University of Texas at Austin, received the 2019 Nobel Prize in Chemistry for their work in Li-ion batteries.