Lithium-ion battery electrodes bound together by a new highly conductive material have a much greater storage capacity—a development that could eventually increase the range of electric cars and the life of smart-phone batteries without increasing their cost. Unlike many high-capacity electrodes developed over the last few years, these can be made using the equipment already found in today’s battery factories.
The key is a stretchy, highly conductive polymer binder that can be used to hold together silicon, tin, and other materials that can store a lot of energy but that are ordinarily unstable. Researchers at the Lawrence Berkeley National Laboratory painstakingly engineered this new polymer binder and used it to make a silicon anode for a rechargeable lithium-ion battery with a storage capacity 30 percent greater than those on the market today. It’s also more stable over time than previously developed electrodes.
When a lithium-ion battery is charged, lithium ions are taken up by one of the electrodes, called the anode. The more lithium the anode can hold, the more energy the battery can store. Silicon is one of the most promising anode materials: it can store 10 times more lithium than graphite, which is used to make the anodes in the lithium-ion batteries on the market today
The Berkeley group’s anodes have been tested in over 650 charging cycles. They maintain a storage capacity of 1,400 milliamp hours per gram—much greater than the 300 or so stored by conventional anodes. Full batteries incorporating the anodes store about 30 percent more total energy than a commercial lithium-ion battery. Typically, battery capacity increases by about 5 percent a year, Liu notes. He says they’ve tested the binder in other battery anodes, including those made of tin, that have similar potential and problems, and that it should work for any such materials.
The storage capacity of these batteries is nearly as good as those made from pure silicon nanowires with no binders, says Yi Cui, professor of materials science and engineering at Stanford and one of the founders of Amprius