With the aid of chronopotentiometry, voltammetry, and potentiostatic closure, the electrochemical characteristics of lithium intercalation to polyacrylonitrile carbon fiber was determined, namely, the capacitance, kinetic currents, lithium diffusion coefficient, autocharge currents. The study was made at 298 К in 1 M solutions of LiClOr in some mixed organic solvents (propylene carbonate – dimethoxyethane 7:3, propylene carbonate – diethyl carbonate 3:1). Heteroatom introduction is shown to significantly raise the specific capacitance in comparison with the corresponding non-doped carbon fiber at a high reversibility by current (98-100%). The polarization characteristics of kinetic current is of the linear nature up to 0.300 V, which is evidence of a noticeable influence of the passivating film's ionic conduction properties on the lithium intercalation kinetics. The dopants (boron, cadmium) reduce the polarization resistance significantly in comparison with the corresponding non-doped carbon fiber. The diffusion coefficients of lithium in the boron- and boron-cadmium-doped carbon fiber is equal to (1,2·10^-11-3,7·10^-11 and (0,9·10^-11-2,2·10^-11 cm²/s, respectively.