Enabling improved electrochemical properties by uniform sodium doping for Li-rich Mn-based Li1.2Mn0.54Ni0.13Co0.13O2 layered oxide

As one of the most promising cathode materials, Li-rich Mn-based-layered oxides (LRMOs) are highly expected to be applied in high-energy lithium-ion batteries (LIBs), but they always suffer from inferior cyclability and severe voltage decay during long-term cycling. To stabilize the crystalline structure and improve the electrochemical performance, here different proportions of Na+ ions were doped into the typical Li rich Li1.2Mn0.54Ni0.13Co0.13O2 oxide to replace partial Li sites through a synchronous solid-phase sintering reaction. The comparison of XRD patterns and Raman spectroscopy indicates that all the as-fabricated materials integrate hexagonal alpha-NaFeO2 LiMO2 (R (3) over bar m) phase and monoclinic Li2MnO3 (C2/m) phase in their composition and show little difference in local structure. SEM and TEM images further verify that the assembled particles are well-crystallized, and the primary grain size gradually decreases with the increase of Na dopant. Importantly, the cathodes with Na incorporation exhibit higher capacity retention (80.82% after 200 cycles at 1 C), better rate capability (124.0 mAh g(-1) at 5 C rate), and lower voltage fading as compared with the bare one. Based on a series of physicochemical characterization, these favorable improvements can be mainly ascribed to the mitigatory polarization, suppressed internal impedance, better reversibility, and Li+ ions diffusion dynamics of the modified electrodes. Thus, we envision that this simple Na doping technique can be extended to optimize the electrochemical properties of other layer-structured battery materials.