Matter

Doped LiNiO2 has recently become one of the most promising cathode materials for its high specific energy, long cycle life, and reduced cobalt content. Despite this, the degradation mechanism of LiNiO2 and its derivatives still remains elusive. Here, by combining in situ electron microscopy and first-principles calculations, we elucidate the atomic-level chemomechanical degradation pathway of LiNiO2-derived cathodes. We uncover that the O1 phase formed at high voltages acts as a preferential site for rock-salt transformation via a two-step pathway involving cation mixing and shear along (003) planes. Moreover, electron tomography reveals that planar cracks nucleated simultaneously from particle interior and surface propagate along the [100] direction on (003) planes, accompanied by concurrent structural degradation in a discrete manner. Our results provide an in-depth understanding of the degradation mechanism of LiNiO2-derived cathodes, pointing out the concept that suppressing the O1 phase and oxygen loss is key to stabilizing LiNiO2 for developing next-generation high-energy cathode materials. U.S. Department of Energy (DOE) Office of Energy Efficiency and Renewable EnergyUnited States Department of Energy (DOE) [DE-EE0008444]; H.L.X.'s startup fund; U.S. DOE Office of Science Facility, at Brookhaven National LaboratoryUnited States Department of Energy (DOE) [DE-SC0012704]; DOE Office of Science by Argonne National LaboratoryUnited States Department of Energy (DOE) [DE-AC02-06CH11357]; Early Career Research Program, Materials Science and Engineering Divisions, Office of Basic Energy Sciences of the U.S. DOEUnited States Department of Energy (DOE) [DE-SC0021204]; National Science Foundation through the UC Irvine Materials Research Science and Engineering Center [DMR-2011967] Published version Thismaterial is based upon work supported by the U.S. Department of Energy (DOE) Office of Energy Efficiency and Renewable Energy under the award number DEEE0008444. R.Z.'s and C.H.'s work done for this study was funded by H.L.X.'s startup funding. We thank Dr. Jianli Cheng for illuminating discussions. This research used resources of the Center for Functional Nanomaterials, which is a U.S. DOE Office of Science Facility, at Brookhaven National Laboratory under contract no. DE-SC0012704. This research used resources of the Advanced Photon Source, a U.S. DOE Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under contract no. DE-AC02-06CH11357. This research made use of the AtomSegNet software42 developed and maintained under the Early Career Research Program, Materials Science and Engineering Divisions, Office of Basic Energy Sciences of the U.S. DOE, under award no. DE-SC0021204. This work used the facilities and instrumentation at the UC Irvine Materials Research Institute (IMRI), which is supported in part by the National Science Foundation through the UC Irvine Materials Research Science and Engineering Center (DMR-2011967).