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

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. <i>Operando</i> 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 <i>operando</i> XANES and <i>ex situ</i> 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.