A team of scientists in Japan has developed a new method of making all-solid-state batteries that could reduce the cost of mass production of this alternative to lithium-ion batteries.
The method, developed by a research group at the Tokyo Institute of Technology, would allow battery materials to be exposed to air during manufacturing, reducing the need for expensive equipment — a step toward making these batteries mainstream in electric vehicles.
All-solid-state batteries are considered safer than lithium-ion batteries because they do not use flammable organic solvents, and they can have greater energy density.
But they tend to have shorter life spans because their electrodes expand and contract, disrupting the connection to the solid conductive material.
And the sulfide compounds seen as a potential electrolyte for all-solid-state automotive batteries react readily with water. This makes them unstable when exposed to air, so they have to be handled in a vacuum.
The Japan Science and Technology Agency estimates that the facilities needed to make all-solid-state batteries cost 10 to 20 times as much as those for current lithium-ion batteries.
A research group at the Tokyo Institute of Technology, led by assistant professor Shintaro Yasui, sought to develop a solid electrolyte that could be applied as a coating with no need for special equipment.
The electrolyte is composed mainly of a compound of lithium, boron and oxygen that is ground in a special process and mixed with water and nonvolatile, nonflammable lithium salts to form a slurry.
One current collector is coated with the cathode material and the electrolyte in layers. The same process is done separately for the anode, and both are naturally air-dried. The electrolyte penetrates into the area around the electrode materials, ensuring close contact between the layers.
The components were stacked and sealed with a film, and the battery’s performance was measured at room temperature under pressures of up to 30 megapascals.
The battery’s ionic conductivity, a measure of its performance, was 5.9 millisiemens per centimeter, a relatively high figure among electrolytes for all-solid-state batteries.
It can withstand about 300 charging cycles, and Yasui said “we have our sights on as many as 1,000 cycles.”
But the battery has the potential to break down at about 140 degrees Celsius, giving it a relatively low temperature resistance. The battery has been used at about 2.4 volts, and whether it can be used at higher voltages remains to be seen.
A number of automakers are aiming to put all-solid-state batteries on the road in the latter half of this decade.
“We want to bring it to point of commercialization within about 10 years,” Yasui said.
