The rechargeable lithium metal battery has been plagued by short life expectancy and occasional fires. To combat these problems, a new coating significantly extends the battery’s life. To deal with the combustion issue, the coating greatly limits the tiny needlelike structures — or dendrites — that pierce the separator between the battery’s positive and negative sides. In addition to ruining the battery, dendrites can create a short circuit within the battery’s flammable liquid. Lithium-ion batteries occasionally have the same problem but dendrites have been a non-starter for lithium metal rechargeable batteries to date. Dendrites also have prevented lithium metal batteries from being used in what may be the next generation of electric vehicles.
Lithium metal batteries can hold at least a third more power per pound as lithium-ion batteries and are significantly lighter because they use lightweight lithium for the positively charged end rather than heavier graphite. If they were more reliable, these batteries could improve portable electronics, from note-book computers to cellphones, but the real advantage would be for electric cars, whose batteries spend about a fourth of their energy carrying themselves around.
The coating was tested on the positively charged end — the anode — of a standard lithium metal battery, which is where dendrites typically form. The specially coated anodes were combined with other commercially available components to create a fully operational battery. After 160 cycles, the lithium metal cells still delivered 85 percent of the power that they did in the first cycle. Regular lithium metal cells deliver about 30 percent after that many cycles, rendering them nearly useless even if they don’t explode.
The new coating prevents dendrites from forming by creating a network of molecules that deliver charged lithium ions to the electrode uniformly. It prevents unwanted chemical reactions typical for these batteries and also reduces a chemical buildup on the anode, which quickly devastates the battery’s ability to deliver power.
Use in electric vehicles is the ultimate goal; however, commercialization would likely start with consumer electronics to demonstrate the battery’s safety.