The H₃PO₄/H₂SO₄/HNO₃ chemical functionalization optimized performances of functionalized carbon fibers via preventing fibers from over-oxidation

A series of functionalization methods was used to functionalize carbon fibers. These functionalization methods were all simple. In addition, these methods exhibit excellent carboxyl functionalization effects. Besides, except for H₃PO₄/H₂SO₄/HNO₃ chemical oxidation method, these functionalization methods are all popular methods. The demands for multifunctional structural electrode materials are high. Hence, the functionalization needs to preserve the tensile strength and electrochemical properties while increasing the concentration of acidic groups on the surface of carbon fibers. As proven, the H₃PO₄/H₂SO₄/HNO₃ chemical oxidation method is the most promising functionalization method compared with any other methods. This method preserved the tensile strength of carbon fibers and moderately increased capacity, displayed positive effect on electrochemical kinetics, decreased the charge-transfer impedance, and ensured the stability and reversibility of capacity. Because of its preserved properties and the functionalized surface, this kind of functionalized carbon fibers is more suitable for using as the anode of multifunctional structural lithium-Ion batteries. The appearance of H₃PO₄ hindered the formation of defects on turbostratic structure of carbon fibers. The modification on the surface of electrode material could also affect the electrochemical properties of carbon fibers.