Prediction of Large Format High Power Cell Performance Using NTG Model

Abstract

Accurate prediction of cell performance using electrochemical parameters has always been a challenge in terms of computational complexity and collection of parameters for individual cell components (such as cathode, anode and electrolyte). In construction of a completely physics based model, the parameterisation is tedious and extremely time consuming. In order to save time and maintain accuracy, an alternate mathematical model which demands less experimental inputs especially from full cell alone is of interest in this study. In addition, the model which offers scope to manipulate the geometrical features such as tab positions and cell dimensions to further optimise the cell performance at minimal computational time is desirable. NTG model is a semi empirical model which predicts the transient behaviour of lithium ion batteries. In this study, two significant full cell parameters namely effective conductance and open circuit voltage are determined for a high power cell by stepped pulse experiments over a wide range of operating temperatures between -25°C and 50°C. Other parameters such as cell thermal conductivity, specific heat capacity and density are also determined. Additional heat balance equations are incorporated to simulate the thermal behaviour of cell. The model is constructed using partial differentiation equations in COMSOL and solved across a representative 3D geometry. Interestingly, the electrochemical performance curves and the cell surface temperature from simulations are quite close to that of experiments. The feasibility of potential, current density and temperature distribution in three dimensions in this model give better insights into the underlying battery physics. Although the diffusion of lithium ions is overlooked in this model for simplicity, the model offers the advantage of faster simulations for high power cells where the electrode loading is lesser.