Improved Rate Capability of Li-Rich Cathode Materials by Building a Li+-Conductive LixBPO4+x/2 Nanolayer from Residual Li2CO3 on the Surface

Lithium- and manganese-rich layered oxides face great challenges for practical applications, including gradual voltage decay upon normal charge/discharge cycling and the relatively low volumetric energy density. This series of materials generally suffer from a great reduction in reversible capacity with an increase of the current density and the loading density of the electrode, which can be attributed to the low Li+ conductivity of the material, as previously reported. Herein, BPO4 is proposed to encapsulate Li-1.16(Ni0.25Mn0.75)(0.84)O-2 (LNMO) particles and is expected to form a Li-doped LixBPO(4+x/2) (LBP) layer as a lithiumion conductor on the particle surface to facilitate the transportation of Li+ across the solid-liquid interface. The results confirm that the LBP layer was formed, providing a lithium-ion diffusion path and suppressing the undesired interfacial reactions. A LNMO sample coated with 1.6 mol% LBP (LBP@LNMO) demonstrated excellent rate capability, retaining 90.2, 80.2, 61.2, and 43.5% at 1, 2, 5, and 10 C rates of the capacity at the 0.5 C rate. Moreover, the modified material is clearly relieved from voltage fading and offers improved cycling stability at 55 degrees C, which mainly contributes to a decrease in the polarization and an increase in the interfacial stability under the protection of the LBP layer. It implies that the dual functional coating is an effective route to promote the lithium-transport kinetics.