Li 3 PO 4 ‐Coated LiNi 0.5 Mn 1.5 O 4 : A Stable High‐Voltage Cathode Material for Lithium‐Ion Batteries

LiNi 0.5 Mn 1.5 O 4 is regarded as a promising cathode material to increase the energy density of lithium‐ion batteries due to the high discharge voltage (ca. 4.7 V). However, the interface between the LiNi 0.5 Mn 1.5 O 4 cathode and the electrolyte is a great concern because of the decomposition of the electrolyte on the cathode surface at high operational potentials. To build a stable and functional protecting layer of Li 3 PO 4 on LiNi 0.5 Mn 1.5 O 4 to avoid direct contact between the active materials and the electrolyte is the emphasis of this study. Li 3 PO 4 ‐coated LiNi 0.5 Mn 1.5 O 4 is prepared by a solid‐state reaction and noncoated LiNi 0.5 Mn 1.5 O 4 is prepared by the same method as a control. The materials are fully characterized by XRD, FT‐IR, and high‐resolution TEM. TEM shows that the Li 3 PO 4 layer (<6 nm) is successfully coated on the LiNi 0.5 Mn 1.5 O 4 primary particles. XRD and FT‐IR reveal that the synthesized Li 3 PO 4 ‐coated LiNi 0.5 Mn 1.5 O 4 has a cubic spinel structure with a space group of Fd $\bar 3$ m , whereas noncoated LiNi 0.5 Mn 1.5 O 4 shows a cubic spinel structure with a space group of P 4 3 32. The electrochemical performance of the prepared materials is characterized in half and full cells. Li 3 PO 4 ‐coated LiNi 0.5 Mn 1.5 O 4 shows dramatically enhanced cycling performance compared with noncoated LiNi 0.5 Mn 1.5 O 4 .