Structural Stability of Single-Crystalline Ni-Rich Layered Cathode upon Delithiation

Single-crystalline (SC) Li[Ni 1– x – y Co x Mn y ]O 2 (NCM) cathodes are an effective solution for countering the interparticle cracking of Ni-rich NCM cathodes with Ni < 80%. Transmission electron microscopy analysis indicates that no irreversible structural damage is observed when the SC-Li[Ni 0.7 Co 0.15 Mn 0.15 ]O 2 NCM cathode is charged to 4.3 V. However, in the charged SC-Li[Ni 0.9 Co 0.05 Mn 0.05 ]O 2 cathode the internal strain generated by the H2 → H3 transition is aggravated by the slow migration rate of Li ions, which produced nonuniform Li distributions and structural inhomogeneities. The charged SC-Li[Ni 0.9 Co 0.05 Mn 0.05 ]O 2 cathode experiences intraparticle cracking at a microscopic scale, and submicroscopic cracks appear at the boundaries among multiple phases present in the charged state even after the first charge. We suggest that a slow rate of Li extraction or particle size reduction would ameliorate the structural defects at the end of charging and improve the cycling stability for Ni-rich SC-layered cathodes Ni > 90%.