Titanium Substitution to Advance the Prospect of NaMnO$_2$ Cathodes for Practical Application in Sodium-Ion Batteries

O3-type layered oxides stand out among various Na-ion battery cathodes due to their unparalleled theoretical specific capacities. As a representative of low-cost, Mn-based cathode materials, $α$-NaMnO$_2$ (NMO) has attracted great attention. However, its practical application is hindered by poor reversibility. Compared to other O3 or O′3-type layered oxides, such as NaNiO2, NMO undergoes multiple phase transitions, with the final O1 phase negatively affecting cycling performance. In this study, precipitated Mn$_3$O$_4$ was employed, to our knowledge for the first time, as a precursor in the synthesis of NMO, and the cathode material was systematically optimized through incremental improvement via titanium substitution. NaMn$_{0.9}$Ti$_{0.1}$O$_2$ was found to exhibit enhanced stability, with the capacity retention increasing from 42 to 70% after 50 cycles at C/10, along with superior rate capability over NMO. This is due in part to titanium’s role in facilitating primary particle (grain) growth and suppressing O1 phase formation, thereby preserving structural integrity and mitigating degradation caused by volume variations and irreversible oxygen redox during battery operation. This work not only provides valuable insights into the development of next-generation NMO cathodes but also advances their potential for practical applications.