Sponge breakthrough could expand range of electric vehicles

Through research funded by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy, Pacific Northwest National Laboratory (PNNL) has developed a porous, sponge-like nanomaterial made of silicon that could help lithium-ion batteries run longer by giving the batteries’ electrodes the space they need to expand without breaking. This means that the lithium-ion batteries that power electric vehicles could store more energy and run longer on a single charge with the help of a silicon sponge.

Credit: PNNL

As silicon has more than 10 times the energy storage capacity of graphite, the porous material will replace the graphite traditionally used in one of the battery’s electrodes.

“Silicon has long been sought as a way to improve the performance of lithium-ion batteries, but silicon swells so much when it is charged that it can break apart, making a silicon electrode inoperable,” said Pacific Northwest National Laboratory Fellow Ji-Guang “Jason” Zhang.

 

The chemistry of lithium-ion batteries limits how much energy they can store, so to increase the battery’s energy capacity, researchers are looking at new materials such as silicon. A lithium-ion battery with a silicon electrode could last about 30 percent longer than one with a graphite electrode. An average electric vehicle could drive about 130 miles on a single charge if it used a lithium-ion battery with PNNL’s silicon electrode.

The drawback is that silicon expands as much as three times in size when it charges, creating pressure within the material that causes it to break. While scientists have attempted to make nano-sized battery components, hoping the smaller size would give the silicon enough room to expand, these efforts have fallen short on producing market-ready technologies.

Enter the sponge. The carbon-coated silicon electrode was put through a series of charges and discharges. The researchers found that while being charged, the new electrode mostly expanded into the empty spaces created by the material’s porous structure. The outside shape of the electrode only expanded by 30 percent — much less than the 300 percent usually seen in silicon electrodes — and the new electrode didn’t break down. After more than 1,000 charge-and-discharge cycles, the electrode maintained more than 80 percent of its initial energy storage capacity.

Researchers now plan to develop a larger prototype battery with their silicon sponge electrode, creating a more streamlined production process so their new electrode can be produced at a reasonable cost.

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