The concept of lithium metal batteries in turn raises the prospect of mobile devices and vehicles carrying more charge without adding weight, thanks to the better energy density that pure lithium metal anodes can provide. However, until they become a reality, scientists' efforts have been hampered by various unwanted chemical reactions with the electrolyte that separates the electrodes.
An electrolyte is a solution that carries lithium ions back and forth between the anode and cathode as they are charged. More specifically, the atoms in the metal alloy are easily dissolved in the electrolyte solution, and as the battery cycles, the electrodes fall off and eventually begin to crack and degrade.
Now, scientists at MIT believe they have found a viable path forward - a new electrolyte that overcomes these problems and also allows the next generation of batteries to make a significant jump in power per weight without sacrificing cycle life.
In tests, the new electrolyte proved to be highly resistant to dissolving metal atoms, which prevented the loss of mass and the cracking phenomenon that usually results. In addition, it reduces the accumulation of excess compounds on the electrode surface by more than ten times, yet still allows the lithium ions needed to charge the battery to move easily.
And it also proved to have high performance when combined with the standard cathodes used in today's lithium batteries (metal oxides made from lithium, nickel, manganese and cobalt). The researchers also point out that the way it interacts with the lithium metal cathode could really open up some exciting avenues.
This electrolyte has the chemistry to resist oxidation of high-energy nickel-rich materials, prevent particle breakage and stabilize the cathode during cycling," said Yang Shao-Horn, a professor at MIT. This electrolyte also allows stable and reversible stripping and plating of lithium metal, which is an important step toward achieving rechargeable lithium metal batteries."
"In addition, its energy density is twice that of the most advanced lithium-ion batteries. This discovery will facilitate further electrolyte research and the design of liquid electrolytes for lithium-metal batteries comparable to solid-state electrolytes." He added.
The team said the new electrolyte could be made into a lithium-metal battery capable of storing about 260 watt-hours per kilogram of lithium-ion cells, potentially up to about 420 watt-hours per kilogram. That would translate into longer ranges for electric cars and longer-lasting power on portable devices.
The researchers' next goal is to scale up production to bring down the cost of this technology. While this electrolyte is easy to produce, it does involve a rarely used precursor compound, making it expensive to obtain, though this may change as production volumes increase.
Another advantage of the technology is that it does not require a major redesign of the cell structure, which the team describes as a "temporary" replacement for the current electrolyte.
"I think if we can show the world that this is a great electrolyte for consumer electronics, the incentive to scale up further will help drive prices down," said study author Jeremiah Johnson.