3M’s approach reduces the amount the anode expands by using amorphous silicon, rather than crystalline silicon, and pairing this with inert materials, helping to stabilize the system. 3M engineers have also developed better methods for depositing the materials onto the films that are later rolled up to form a cylindrical battery. They are now optimizing these methods for large-scale manufacturing.
The new materials reduce but do not eliminate expansion and contraction as the ions move in and out of the anode. As a result, the researchers are developing new battery designs that can absorb the changes in size. Obrovac says that these designs, along with the new electrode and electrolyte materials, should be ready for battery manufacturers to start incorporating into their products sometime next year.
Ted Miller, supervisor of advanced battery technology at Ford Motor, in Dearborn, MI, says that a move away from graphite to these kinds of anodes is, in addition to offering capacity gains, essential for coping with extremely cold conditions that they could be exposed to in vehicle applications. Under these conditions, charging a battery can cause lithium metal to build up, sometimes doing many months’ worth of damage to the battery in the course of a few minutes. Moving away from graphite will prevent the reactions that lead to lithium-metal buildup, Miller says.So far, only one alloy-based anode is being used commercially: a battery from Sony called Nexelium, which uses a tin-based anode. But this technology will start to appear more often, according to MIT materials scientist Yet-Ming Chiang. “It’s a very logical direction” for battery companies to go in, he says.