Investigation of Li3PO4 Coating and Nb5+ Doping Effect on the Crystal Structure and Electrochemical Properties of Ni-Rich LiNi0.85Co0.05Mn0.10O2 Cathode

To overcome the poor rate capacity and weak cycling performance of Ni-rich cathode materials, the Li3PO4 coating and Nb5+ doping modified LiNi0.85Co0.05Mn0.10O2 series samples were prepared by using the co-precipitation and the sol-gel methods in this work. And the X-ray diffraction, transmission electron microscopy, field emission scanning electron microscopy, energy dispersive spectroscopy, X-ray photoelectron spectroscopy and electrochemical characterization were performed to comprehensively assess the effect of Li3PO4 coating and Nb5+ doping on the morphology, structure and electrochemical properties of LiNi0.85Co0.05Mn0.10O2. The results showed that the Li3PO4 nanoparticles were covered on the surface of cathode with success and the Nb5+ ions were inserted into the crystal structure with uniformity. In comparison with the bare LiNi0.85Co0.05Mn0.10O2, the cathodes after Li3PO4 coating and Nb5+ doping demonstrated the better electrochemical properties in terms of rate capability, cycling performance and thermal stability. The 2 wt% Li3PO4 coated Li(Ni0.85Co0.05Mn0.10)0.99Nb0.01O2 delivered the capacity retention of 92.0% at 25 °C and 90.8% at 45 °C after 300 cycles at 1C rate respectively, much larger than those (83.5% and 80.1%) of the bare one. These results indicated the Li3PO4 coating and Nb5+ doping co-modification could satisfy the performance requirement of maintaining the cycling stability for Ni-rich cathodes.