Gao Liu Develops Cheap Battery Booster

Gao Liu's polymer boosts battery storage capacity 30% without new manufacturing methods.

Gao Liu has developed a way to boost the storage capacity of batteries by at least 30 percent without changing their current manufacturing methods. The breakthrough can be used to improve the range of electric cars and the capacity of cell phone batteries without increasing their cost.

The super elastic, highly conductive polymer developed and patented by Liu’s team at Lawrence Berkeley National Laboratory can bind into stable electrodes materials like silicon and tin that have much higher charge-storage capacities than currently used materials but had been deemed too volatile until now.

The storage capacity of lithium-ion batteries (LiB) depend to a large extent on the amount of lithium ions that can be stored by the anode, the negative electrode. Current LiBs use graphite, but materials like silicon can store 10 times more lithium than graphite.

“Graphite soaks up lithium like a sponge, holding its shape, but silicon is more like a balloon,” explains Liu. Silicon swells and shrinks by a factor of three or four times with each charge and discharge. “After a few rounds of charge and discharge, pretty soon the silicon particles are not in touch with each other.” That results in loss of conductivity and capacity.

Past efforts at creating a binder for silicon anodes had failed because researchers tried to use polymers that lose conductivity in conditions found in battery anodes, Liu decided. With the help of theoretical chemists Liu found a polymer with the right electrical properties, then modified it to be much stickier. An important aspect of this binder is that Liu could use conventional battery anode-production process to create silicon anodes, ensuring that it won’t add to battery production costs.

So far Liu has tested the silicon anode over 650 charging cycles and found that they maintain a storage capacity of 1,400 milliamp hours per gram, nearly five times the 300 ma-h/gm of conventional anodes. A bonus is that Liu’s anode is also more stable. Full batteries that use the silicon anode store about 30 percent more total energy than a commercial lithium-ion battery of the same weight. That represents a huge efficiency leap over the 5% annual efficiency increase that battery researchers have been able to achieve to date. In fact, Liu’s binder has produced an efficiency advance that’s nearly on par with that achieved using pure silicon nanowires like those made by Amprius, founded by Stanford materials professor Yi Cui. The nanowires don’t require binders but require entirely new and more expensive manufacturing processes.

Liu has found that his binder works equally well to make anodes with tin and other efficient but volatile materials.

Liu’s team is now working with 3M anode researchers who had been scaling up production of silicon-based battery materials that don’t expand as much during charging. Liu is also discussing ways to commercialize his breakthrough with other companies.