A major battery breakthrough could allow electric vehicles to drive longer and more safely on a single charge. Better batteries for the grid could store more energy, enabling the deployment of more wind and solar power.
"There's a global competition for these kinds of concepts," said Paul Albertus, ARPA-E program director at the Department of Energy. The program focuses on early-stage energy research that could have a significant impact on energy.
Last month, Albertus and his ARPA-E colleague Sue Babinec published an article in the journal Nature Energy, which reviewed the current state of research on lithium metal batteries and the challenges to the future.
As its name suggests, a lithium metal battery uses lithium metal in the negative electrode portion of the battery, which allows ions to travel back and forth between the negative and positive electrodes of the electrolyte during charging and discharging.
Graphite is commonly used as the negative electrode in today's lithium-ion batteries. However, by replacing graphite with metallic lithium, the battery can store more energy.
According to a Nature article, lithium metal electrodes can increase the energy of lithium batteries by 35% and the energy density by 50%. This could allow a battery to supply 350 or 400 watt-hours per kilogram or 1,000 watt-hours per liter of electrical energy.
Current lithium battery packs have an energy of approximately 150 watt-hours per kilogram and an energy density of approximately 250 watt-hours per liter.
The U.S. Department of Energy aims to find energy storage options for electric vehicle battery packs at 235 watt-hours per kilowatt and 500 watt-hours per liter.
In recent years, the ARPA-E program has launched an energy storage initiative called IONICS to provide funding for early-stage research in areas such as lithium metal electrodes. Lithium metal electrode projects utilizing ARPA-E funding include 24m, Ion Materials Entities, PolyPlus Battery Corporation, and Iowa State University.
Albertus and Babinec write that research combining lithium metal electrodes with the use of solid materials (rather than liquids) to create battery electrolytes could one day become the next generation of lithium batteries. Solid electrolytes would make batteries less flammable and safer to use.
However, technological breakthroughs in batteries are not easy to achieve. Since the 1960s, scientists around the world have been researching lithium metal electrodes, with similar studies being conducted by large battery companies, government laboratories, and startups.
The Renault-Nissan-Mitsubishi Alliance announced a strategic investment in Ionic Materials last week, hoping to develop next-generation electric vehicle batteries. Solid-state batteries are considered the holy grail for electric vehicles due to their high energy density and better heat dissipation. Companies like Toyota and Fisker are also exploring the potential of solid-state batteries.
Some small lithium metal batteries are used in niche applications such as the medical industry, but no one has yet been able to scale up batteries to the point where they can power cars or store energy for solar power plants.
In their Nature article, the authors highlight key considerations for battery researchers when undertaking these types of projects. They also point out methods to prevent errors and eliminate so-called "dendritic formations," or whisker-like lithium crystals that can grow inside the battery and cause problems.
In particular, Albertus and Babinec discovered that, using suitable low-cost components, lithium metal electrode batteries could achieve a cost of $100 per kilowatt-hour. Maintaining low cost (below that of lithium batteries) will be key to the successful market launch of new batteries.
Albertus says that unlike some widely adopted battery technologies, such as using silicon as the anode in lithium batteries, lithium metal batteries may still be a decade away.
