In the search for lithium-ion batteries with ever-higher charge capacity, researchers have found that replacing the typical graphite anodes with ones made of silicon could boost the batteries’ charge capacity, in principle, by a factor of 10. But with each charge-discharge cycle, the silicon swells and shrinks substantially, cracking the anode and quickly ending the battery’s life. Stanford University’s Chao Wang, Zhenan Bao, Yi Cui, and coworkers show that the cracking problem can be controlled by coating the anode with a stretchable self-healing polymer (Nat. Chem. 2013, DOI: 10.1038/nchem.1802). The team fashioned anodes from low-cost millimeter-sized silicon particles and coated them with a randomly branched hydrogen-bonding polymer. Analyses show that the polymer remains pliable and stretchable at room temperature, and its molecular chains readily reorient at fracture sites. As such, the polymer quickly repairs microsized cracks in the anode and maintains electrical contact among the silicon particles. The team reports that unlike earlier silicon-based Li-ion batteries, which barely survived 10 charge-discharge cycles, the new test batteries retained their charge capacities through 100 cycles.