Effect of Carbon-Coating on Internal Resistance and Performance of Lithium Iron Phosphate Batteries

In this paper, the LiFePO4 material was modified by carbon coating using polyvinyl alcohol (PVA) and Ketjen black as the composite carbon sources. Firstly, the structure, electron and ion transport properties of LiFePO4 and carbon-coated LiFePO4 were calculated by first-principles and density functional theory. The calculation results show that after carbon coating, the coating system will change from semiconductor properties to conductor properties, and its electronic conductivity will be significantly improved. Then, different proportions of Ketjen black and PVA (polyvinyl alcohol) were mixed to prepare a composite carbon source, which was then coated with carbon on the surface of the LiFePO4 cathode material. The prepared LiFePO4/C samples were characterized by XRD, SEM, physical properties and electrochemical properties. The 14500 cylindrical steel shell battery was prepared by using lithium iron phosphate materials coated with different carbon sources. By testing the internal resistance, rate performance and cycle performance of the battery, the effect of carbon coating on the internal resistance of the battery and the electrochemical performance of the full battery was studied and analyzed. The experimental results show that when Ketjen Black:PVA = 2:1, the synthesized LiFePO4/C cathode material exhibits the best rate performance and cycle stability. The compaction density of the pole piece is reduced, the internal resistance of the battery is reduced, and the electrochemical performance of the battery is improved.