Li diffusion efficiency reflects the kinetics of Li intercalation/de-intercalation in solid electrode materials and determines the rate performances of Li ion batteries. Traditional techniques including the electrochemical impedance spectroscopy, potential intermittent titration technique, potential relaxation technique, galvanostatic intermittent titration technique, and cyclic voltammetry, could lead to significant disagreement on Li chemical diffusion coefficients due to the limited reliability of the parameters required for calculating Li diffusion coefficients. Based on the Nernst-Einstein equation, a double-battery system is proposed for the direct measurement of chemical diffusion coefficients of Li in solid electrodes. With the double-battery system, Li diffusion coefficients in the intercalation/deintercalation of graphite electrodes featured with phase-transition and double-phase regions, are measured efficiently, with consistent values in the range of 10(-10)-10(-9) cm(2)/s. The direct measurement then allows for the evaluation of the diffusion barrier associated with Li intercalation/de-intercalation in the electrodes. (C) 2019 Elsevier Ltd. All rights reserved.