Molecular ‘pulleys’ help boost battery performance
In lithium batteries with a silicon anode, researchers have applied a sophisticated method using molecular "pulleys" that aid in the expansion and contraction of the anode during cycling. The technique yields a performance in silicon anode-based lithium batteries that is similar to commercialized lithium-ion batteries with other types of anodes. In the search for ways to improve lithium batteries, one particularly appealing option is to use silicon anodes, which would enable batteries to achieve high volumetric and energy densities sufficient for electric vehicles. However, the dramatic volume changes silicon undergoes during charging causes the battery components to fail. Here, Sunghun Choi and colleagues included an anchored polymer containing rings along its backbone, known as polyrotaxane (PR), to the binder material used to hold together the particles in a silicon anode. The PR has unusual mechanical properties that arise from the sliding movement of the backbone through the rings. The PR acts as a pulley system that relieves stress on the anode, allowing it to expand and contract more easily. This technique allowed the researchers to create a silicon anode with the same areal capacities within the range of current commercial lithium-ion batteries. Furthermore, the full-cell showed decent cyclability, such as 98% retention of the original capacity after hundreds of cycles. Jaegeon Ryu and Soojin Park discuss this advance in a related Perspective.
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