Improvement of the electrochemical performance of a nickel rich LiNi0.5Co0.2Mn0.3O2 cathode material by reduced graphene oxide/SiO2 nanoparticle double-layer coating

摘要

Due to its high discharge capacity, low cost, and good safety, LiNi0.5Co0.2Mn0.3O2 (NCM 523) is regarded as a promising cathode material for the next-generation of lithium-ion batteries. However, poor cycling stability and rate capability are the main disadvantages of the NCM 523 cathode material. In this work, SiO2 single layer-coated and reduced graphene oxide (outer)/SiO2 (inner) double layer-coated NCM 523 have been prepared by a facile wet chemical method. Field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) analysis, transmission electron microscopy (TEM), Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy results confirm that NCM 523 particles were successfully coated with SiO2 and reduced graphene oxide (RGO)/SiO2 nano-metric layers. It has been found that although the SiO2 layer improves the structural stability of NCM 523 particles, it decreases the discharge capacity and rate capability due a reduction in the reactive area of Li+ transfer. The RGO/SiO2-coated NCM 523 sample shows excellent cycling stability with a retention of 88.5% compared to 57.8% for pristine NCM 523 after 100 cycles at 0.1C. Moreover, the double layer-coated sample exhibits superior rate capability at large current densities with 73.4 and 59.3% retention at 2C and 5C, compared to 50.5 and 30.6% of pristine NCM 523 respectively. Improving the structural stability with an inner SiO2 layer and increasing the Li+ diffusion and electron conductivity with an outer RGO layer are the main reasons for the significant improvement in the electrochemical properties of the RGO/SiO2-coated NCM 523 cathode.