Evaluation of Electrochemical Parameters for Cycle Aging LiCoO2 lithium-Ion Batteries by Quantifying the Incremental Capacity Curve

Abstract

One of the difficulties encountered in the electrochemical theory for modeling the response of aged lithium ion batteries involves finding the evolution of the associated parameters, such as electrode volume fraction and initial lithium ion concentration in electrode at each cycle. This paper proposes an approach, called the first order compatibility method, to determining the values of these parameters and their cycle evolution. We notice that the lowest point of the first valley in the incremental capacity curve, which presents the first order information about the capacity-voltage relation of a battery in the discharge process, regularly moves to new positions as the cycle number increases. These movements are quantified by performing aging experiments on cycled LiCoO2 cells, and are then linked to the database established by the electrochemical simulations with varying the two selected electrochemical parameters, namely the initial lithium ion concentration in negative electrode and the volume fraction of negative electrode. This approach helps to optimally determine the evolution of the two parameters, which reveals that the former one decreases with increasing cycle number when the cell is cycled at small C rate, and however at high rate the latter one dominates the aging process.