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

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 SCLi[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 SClayered cathodes Ni > 90%.

Automated summary

Single-crystalline NCM cathodes are effective in countering interparticle cracking, but high nickel content SC cathodes may experience internal strain and microscopic cracking during the charging process.