Capacity-Fading Model of Lithium-Ion Battery Applicable to Multicell Storage Systems

Abstract

This paper proposes a capacity-fading model of a lithium-ion (Li-ion) battery. The model includes two capacity fade mechanisms, i.e., loss of lithium and increased cell resistance. It is based on a conventional model consisting of a voltage source and three internal resistances. The voltage source is a function of the amount of lithium in the positive electrode. The shape of voltage curve is affected by the discharging current. Its effect is larger than that of internal resistances, and is included in the model. Some parameters vary with the cumulative charge involved in the cycling. A closed form of the capacity is derived. The model reproduces variation in voltage curve due to the capacity fading. The model is applied to a pack of four parallel-connected batteries. It is degraded as a single battery, but some unevenness exists among batteries. The model accurately expresses their behaviors.