The potentiostatic intermittent titration technique (PITT) is an electroanalytical method that has been widely used to study diffusion of solutes (such as lithium) in electrode materials. Here, we extend the conventional PITT method to account for finite interfacial reaction kinetics and derive analytic equations for electric current under PITT operations. Using the modified PITT, the lithium diffusion coefficient in host materials and the interfacial reaction kinetics can be determined simultaneously. We demonstrate this modified PITT by an example of lithium diffusion in graphite (mesocarbon microbeads, MCMB) and show the improvements of the modified PITT theory over the conventional PITT for investigating the kinetics of electrodes comprising spherical particles.