The Lithium-ion battery is everywhere,in smart phones,laptops,an array of other consumer electronics, and the newest electric cars. Good as they are, they could be much better, especially when it comes to lowering the cost and extending the range of electric cars. To do that, batteries need to store a lot more energy.

The anode is a critical component for storing energy in lithium-ion batteries. A team of scientists at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) has designed a new kind of anode that can absorb eight times the lithium of current designs, and has maintained its greatly increased energy capacity after over a year of testing and many hundreds of charge-discharge cycles.

The secret is a tailored polymer that conducts electricity and binds closely to lithium-storing silicon particles, even as they expand to more than three times their volume during charging and then shrink again during discharge. The new anodes are made from low-cost materials, compatible with standard lithium battery manufacturing technologies. The research team reports its findings in Advanced Materials, now available online.

High-capacity expansion

“High-capacity lithium-ion anode materials have always confronted the challenge of volume change-swelling-when electrodes absorb lithium,” says Gao Liu of Berkeley Lab’s Environmental Energy Technologies Division (EETD), a member of the BATT program (Batteries for Advanced Transportation Technologies) managed by the Lab and supported by DOE’s Office of Vehicle Technologies.

Says Liu, “Most of today’s lithium battery pack has anodes made of graphite, which is electrically conducting and expands only modestly when housing the ions between its graphene layers. Silicon can store 10 times more-it has by far the highest capacity among lithium-ion storage materials-but it swells to more than three times its volume when fully charged.”

This kind of swelling quickly breaks the electrical contacts in the anode, so researchers have concentrated on finding other ways to use silicon while maintaining anode conductivity. Many approaches have been proposed; some are prohibitively costly.

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