Detailed analysis of the microstructural changes during lithiation of a full-concentration-gradient (FCG) cathode with an average composition of Li[Ni_0.75Co_0.10Mn_0.15]O₂ was performed starting from its hydroxide precursor, FCG [Ni_0.75Co_0.10Mn_0.15](OH)₂ prior to lithiation. Transmission electron microscopy (TEM) revealed that a unique rod-shaped primary particle morphology and radial crystallographic texture were present in the pre-lithiation stage. In addition, TEM detected a two-phase structure consisting of MnOOH and Ni(OH)₂, and crystallographic twins of MnOOH on the Mn-rich precursor surface. The formation of numerous twins, driven by the lattice mismatch between MnOOH and Ni(OH)₂, resulted in crenellated surfaces. Furthermore, the twins persisted in the lithiated cathode; however, their density decreased with increasing lithiation temperature. Cation disordering, which influences cathode performance, was observed to continuously decrease with increasing lithiation temperature with a minimum observed at 790 °C. Consequently, lithiation at 790 °C (for 10 h) produced optimal discharge capacity and cycling stability. Above 790 °C, an increase in cation disordering and excessive coarsening of the primary particles led to the deterioration of electrochemical properties. It is conjectured that the twins in the FCG cathode precursor promoted the optimal primary particle morphology by retarding the random coalescence of primary particles during lithiation, effectively preserving both the morphology and crystallographic texture of the precursor. Furthermore, the effects of the precursor microstructure and subsequent final primary particle morphology on the optimal lithiation schedule and cation disordering were determined.

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