Based on the resistive-reactant concept, a simple mathematical model for lithium intercalation/deintercalation in a lithium iron phosphate electrode is developed. Demonstrative experiments are provided to shed light on the resistive-reactant feature of this electrode. Without embedding any special feature of the two-phase process, the model consists of regular concentration-dependent lithium diffusion inside four groups of active-material particles that have different connectivities to the conductive matrix of the electrode. Model-experiment comparisons reveal the effectiveness of the resistive-reactant concept for a quantitative description of the charge/discharge as well as the path dependence observed in lithium iron phosphate electrodes. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3515902] All rights reserved.