To improve the cycle performance, z Li 2 TiO 3 @LiNi 0.5 Mn 0.5 O 2 ( z = 0, 1, 3 and 5 mol%) (“@” means “was coated on the surface of”) cathode materials have been successfully prepared via a syn-lithiation strategy. The high-resolution transmission electron microscope (HRTEM) structural analysis results show that Li 2 TiO 3 is evenly coated on the surface of LiNi 0.5 Mn 0.5 O 2 , with the thickness of the coating layer of approximately 10 nm. The electrochemical characterizations of the synthesized z Li 2 TiO 3 @LiNi 0.5 Mn 0.5 O 2 suggest that 1 mol% Li 2 TiO 3 @LiNi 0.5 Mn 0.5 O 2 electrode shows the best electrochemical performance, including the highest capacity and best cycle stability and rate performance. The capacity retention at 25 °C is improved by approximately 23% by the 1 mol% Li 2 TiO 3 coating. The improved cycling performance of LiNi 0.5 Mn 0.5 O 2 arises from the presence of the Li 2 TiO 3 surface layer, which suppresses the direct contact between the active materials and the electrolytes, enhances the lithium ion diffusion through the electrode/electrolyte interface, expands the BET area, stabilizes the structure and prevents the pulverization of the active materials during repeated charging/discharging. The XPS results showed that Li 2 TiO 3 coating layer could inhibit electrolyte decomposition, and the decomposition of electrolyte on the surface of coating electrode is different from that of LiNi 0.5 Mn 0.5 O 2 electrode.
Layered cathode materials for lithium-ion batteries have been extensively investigated; however, comparatively scant attention has been paid to Mn-rich layered cathode materials. Herein, LiNi 0.5 Mn 0.5 O 2 cathode materials are doped to investigate the effect of doping elements on the electrochemical properties of Mn-rich layered cathodes. XRD (X-ray diffraction), XPS (X-ray photoelectron spectroscopy), and SQUID (superconducting quantum interference device) results reveal that Mo doping affects the electrochemical properties of the cathode materials by changing the valence state of transition metal ions. Due to the Mo 6+ ions doping, a large proportion of Mn 3+ ions present in LiNi 0.5 Mn 0.5 O 2 were converted to Mn 4+ ions, which alleviated the Jahn-Teller effect and reduced the elongated Mn-O octahedra, thus increasing the Li layer spacing and facilitating Li + diffusion. Therefore, 1 % Mo-doped cathode exhibits a significantly improved Li-ion diffusion coefficient and superior rate performance with a specific discharge capacity of 103 mAh·g −1 at 5C. Meanwhile, the cathode materials significantly improve cycling performance due to the reduction in the amount of Mn 3+ . The current study provides guidelines for the modification of Mn-rich layered cathodes in the future.
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