Modulating local electronic structure enhances superior electrochemical activity in Li-rich oxide cathodes

Li2MnO3 is the parent compound of Li-rich Mn-based cathode materials for high energy density Li-ion batteries. The existence of oxygen vacancies yields anomalous capacity and can significantly increase the electrochemical activity of Li2MnO3, attracting considerable interest. However, the mechanism behind oxygen vacancies in Li2MnO3 is still under debate, due to the challenges in directly observing O and following relevant changes upon electrochemical cycling. Herein, to address the poor electrochemical activity of Li2MnO3 and further reveal its reaction mechanism, a mechanical thermal activation engineering strategy was used to synthesize Li2MnO3 with different contents of oxygen vacancies. The electronic structure can be effectively modulated by introducing different contents of oxygen vacancies in the local atomic coordination around Mn and O, which induces the distortion of the interfacial structure with a higher lattice d-spacing and effectively stimulates the electrochemical activity. By combining in situ XRD, ex situ XPS and ex situ Raman to investigate the evolution of Mn and O in Li2MnO3 during cycling. It is found that the Mn-O hybridization shows strong correlations with the oxygen redox behaviors, and high electrochemical activity and excellent cycling stability cannot coexist. Thus, the electrochemical activity and stability of Li2MnO3 are affected synchronously by lattice vacancies and local coordination configuration. This work provides valuable insights into the origin of electrochemical activity in Li2MnO3, which may inspire the design of high energy density cathode materials.

Automated summary

Li2MnO3 is the parent compound of Li-rich Mn-based cathode materials and has attracted considerable interest due to its high electrochemical activity caused by the existence of oxygen vacancies. The mechanism behind the oxygen vacancies in Li2MnO3 is still under debate. In this study, Li2MnO3 with different oxygen vacancy contents was synthesized using a mechanical thermal activation engineering strategy to investigate its electrochemical activity. It was found that the introduction of oxygen vacancies effectively modulates the electronic structure, inducing distortion of the interfacial structure and stimulating the electrochemical activity. The evolution of Mn and O in Li2MnO3 during cycling showed that the Mn-O hybridization is strongly correlated with the oxygen redox behaviors, and high electrochemical activity and cycling stability cannot coexist. This work provides valuable insights into the origin of electrochemical activity in Li2MnO3 for the design of high energy density cathode materials.