Impact of Chelating Agent Choice on Growth Kinetics and Defect Chemistry in Sol-Gel-Synthesized Li- and Mn-Rich...

The electrochemical performance and structural stability of Li- and Mn-rich layered oxide cathodes are critically influenced by synthesis conditions, yet the roles of chelating agents and defect chemistry remains elusive. In this study, we systematically investigate Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ cathode powders synthesized via the sol-gel method using citric acid or oxalic acid as the chelating agent, each calcined at 850 and 900 °C. Despite introducing greater initial disorder, oxalic acid-derived samples, particularly the one calcined at 900 °C, demonstrate improved electrochemical stability and capacity retention. Operando XRD reveals that this material undergoes a pronounced unit cell expansion during the first cycle, a response linked largely to the mobility and homogenization of oxygen vacancies introduced during the synthesis. This structural flexibility accommodates redox-driven strain during cycling, which limits Li/TM mixing and enables over-reduction of Ni, as confirmed by operando XANES and ex situ EXAFS. These results highlight that oxygen vacancy mobility during cycling dominates the effects of the initial structural order, where different types of defects are present, and plays a decisive role in governing redox pathways and cycling stability. The selection of the precursor allows tailoring introduction of these defects without postsynthesis treatment. This study provides a comprehensive framework for designing high-performance Li- and Mn-rich layered oxide cathodes by tuning synthesis chemistry to engineer beneficial structural disorder and defect dynamics.