Researchers from around the world are looking for the successor to the lithium-ion battery for electric cars, power tools, and electronics—one that will store more energy with less size and weight, charge more quickly, and have improved safety.
All battery chemistries come with tradeoffs. The challenge for researchers is to figure out how to mitigate the negatives while preserving the benefits of different chemistries.
Honda is the latest automaker investing in what it sees as the next big breakthrough in battery technology—not more advanced lithium-ion, such as solid-state lithium-ion cells—but entirely different battery chemistry.
Along with researchers at CalTech and NASA's Jet Propulsion Lab in California, Honda published a report on new fluoride-ion batteries it is developing, in the journal Science.
Fluoride-ion batteries have long been a viable chemistry except for one thing: To get ions to flow through their solid electrolyte, they had to operate at more than 300 degrees Fahrenheit. Running that hot in a car or especially a mobile device could have disastrous implications.
Honda says that by using a stable liquid fluoride electrolyte made of tetraalkylammonium fluoride salts dissolved in an organic, fluorinated ether solvent, it can produce a cell that conducts electricity at room temperature to provide power and to recharge. The cathode is a nano-structure made of copper, lanthanum, and fluorine that resists the kind of dendrite growth that can lead to premature failure and even thermal runaway in a lithium-ion cell.
The researchers say that the cell can operate over a wide range of voltages.
Honda says that the cells don't pose a safety risk from overheating and believes that they can reach energy densities up to 10 times higher than the theoretical limits of lithium-ion batteries. Higher energy densities could allow automakers to build cars with 300 miles of range or more with smaller, lighter, and cheaper battery packs.
Another advantage, the automaker says, is that the batteries rely on easier materials to obtain than lithium and cobalt, which would do less environmental damage in mining and refining them.
Japanese automakers, in particular, (with the notable exception of Nissan) have been skeptical of using lithium-ion technology and have focused instead on fuel cells. Several executives and engineers at Japanese automakers have said that they are waiting for the next big breakthrough in batteries beyond lithium-ion before beginning the transition to electric cars.
Rechargeable fluoride-ion batteries could be one such breakthrough.