Thermal Monitoring of LiFePO4 Lithium Battery System for the Use of an Electric Boat with Recharging Based on Photovoltaic Systems.

Abstract

The performance of a battery energy system and its accuracy in State of Charge (SoC) (%) estimation for electric boats and electric vehicles are significantly influenced by ambient temperature. In this study, the battery will operate at extreme temperatures within Titicaca Lake, located at an altitude of 3850 meters above sea level. Therefore, the objective is to study a battery model that considers ambient and extreme temperatures. The cell must operate at critical values with a current of 150 A, a voltage of 3.65 V, and observe thermal aging that affects the capacity due to multiple charges and discharges. The method applied to lithium iron phosphate batteries LiFePO4 involved wear testing, considering three stress factors (time, temperature, and state of charge (SoC) (%)). Capacity measurements and resistance calculations tracked short-term degradation behaviors. The Shepherd model was established to identify battery aging using a simple but accurate two-step nonlinear regression approach; also the thermal analysis of the battery cell was conducted to identify the most critical zone of the cell in terms of heat generation. For further evaluation of the proposed strategies, a computational fluid dynamics (CFD) model was built in COMSOL Multiphysics® and validated with a thermographic camera to identify the temperature in the cells. The final arrangement of the LiFePO4 battery is the 16s1p prismatic cell type (16 cells in series and one parallel), with the cell experiencing a temperature variation of approximately 1° C higher than that of the outer parts.