Degradation Model Considering Electrolyte Dry-out Factor of Lithium Ion Battery and Lifetime Prediction of Combined Battery System for Automotive Application

We developed a combined battery system using a “capacity-type” battery and a “power-type” battery for low-cost electric vehicles, which can prolong the battery life. In order to estimate the effect of the proposed combined battery system, an accurate degradation model of lithium ion batteries is needed. It is known that the main degradation factor of lithium ion batteries is the side reaction, which is the reason for the solid electrolyte interface. Usually, this degradation process of lithium ion batteries follows a square root of time law. However, in the case of some lithium ion batteries, this rule cannot be applied due to the fact that they degrade suddenly. We developed a degradation model for lithium ion batteries considering this sudden degradation, including the dissipation phenomena of the conduction path due to electrolyte dry-out. We simulated the life-extension effect of the combined battery system by using the developed degradation model and found that the “capacity-type” battery lifetime in the case of the combined battery system can be 1.65 times longer than that of the original “capacity-type only” battery system.