A mathematical model is developed to study the effect of acid attack on the Solid Electrolyte interphase (SEI layer) on the capacity fading in a lithium ion battery under conditions of storage. The model assumes that the solvent reaction at the electrode/SEI interphase is the rate limiting step in the formation of the SEI layer. The SEI layer is assumed to dissolve due to the attack of the hydrofluoric acid species (HF) at the SEI/electrolyte interphase. The model assumes that the net loss of lithium ions in the film formation reaction is proportional to the capacity fading in the battery. Model results are compared with experimental data and are found to compare well with experimental data. (C) 2016 The Electrochemical Society. All rights reserved.