Cracking the problem of cracking cathodes: Polycrystalline cathode materials that contain a combination of nickel, manganese, and cobalt have been used for advanced lithium batteries. These materials fracture at high voltage, which increases surface area and leads to more side reactions and shorter cycle life. Using single-crystalline samples as model materials, Bi et al. observed changes in nickel-rich cathodes to study the fracture behavior under well-characterized conditions. As the material is charged and lithium is removed, specific planes glide over one another and microcracks are observed. However, this process is reversed on discharge, removing all traces of the microcracking. The authors developed a diffusion-induced stress model to understand the origin of the planar gliding and propose ways to stabilize these nickel-rich cathodes in working batteries. Science , this issue p. 1313