Solvent-free dry cyclized polyacrylonitrile-coated LiNi0.87Co0.13O2 cathode for improving the electrochemical performance of Li-ion batteries

A Ni-rich LiNi0.87Co0.13O2 cathode was modified through dry surface-coating with cyclized-polyacrylonitrile (c-PAN). The c-PAN coating was obtained by heat treatment of polyacrylonitrile (PAN), used as a coating material for improving the electrochemical performance of the cathode. The cyclized PAN structure was confirmed by Raman spectroscopy, with the appearance of two carbon sp2 peaks in the range of 1200–1800 cm−1. Electrochemical tests showed that over 80% of the first discharge capacity was retained for the 2 wt% c-PAN coated electrode, whereas the capacity retention of the uncoated electrode was only about 77% after 100 cycles at a rate of 0.5C. At a high rate of 5C, the coated sample delivered a discharge capacity of 180.7 mAh g−1 in the 5th cycle and retained a discharge capacity of 212.6 mAh g−1 at 0.1C in the rate performance test, which is higher than the values of 165.2 and 198.6 mAh g−1 for the uncoated sample at 5C and 0.1C, respectively. These improvements could be attributed to the c-PAN coating layer, which limited the side reaction between the electrode and electrolyte, resulting in a higher Li-ion diffusion coefficient and a slower increase in the charge transfer resistance.