Start-Up Charging Strategy for a Large-Format NMCA/Graphite Pouch Cell from Subzero Temperature Using an Electrochemical, Thermal, and Mechanical Life Model

Abstract

Start-up strategy of battery pack in vehicular applications is crucial to secure the performance of the battery system, particularly at subzero temperatures. In this paper, a new strategy for cold start-up is proposed using an electrochemical, thermal, and mechanical life model. Especially, the conventional mechanical model that requires complex multi-dimensional lithium-ion concentration is simplified to reduce the computational cost. The developed model is experimentally validated with voltage responses at −10 °C under various current profiles, which predicts capacity fade by chemical and mechanical degradation. Further analysis is performed using the model, which provides the detailed mechanisms of the degradation. Finally, a new charging algorithm targeting the start-up strategy at subzero temperature is developed. The proposed profile consists of discharge pulses applied at the start to stimulate the increase of the battery temperature and then charging current that optimally minimizes the capacity fade and charging speed. The pulse parameters and charging current profile are optimized using Genetic algorithm and nonlinear model predictive control, respectively. The algorithm is implemented in a battery-in-the-loop system and compared with CC/CV charging methods from a subzero temperature. The results of the new method have shown improved charging efficiency and cycle life.