Structural Stability of Single-Crystalline Ni-Rich Layered Cathode upon Delithiation
Gi-Mun Han, Ye-Sung Kim, Hoon‐Hee Ryu, Yang‐Kook Sun, Chong Seung Yoon
Abstract
Single-crystalline (SC) Li[Ni1–x–yCoxMny]O2 (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[Ni0.7Co0.15Mn0.15]O2 NCM cathode is charged to 4.3 V. However, in the charged SC-Li[Ni0.9Co0.05Mn0.05]O2 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[Ni0.9Co0.05Mn0.05]O2 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%.