Thermal Behavior Test and Simulation of Fresh and Aged Lfp/Lto Rechargeable Cells

Abstract

The thermal behavior of fresh and aged LiFePO4/Li4Ti5O12 (LFP/LTO) 26650 cells at 30% and 100% state of charge (SOC) was studied by Accelerating Rate Calorimetry (ARC). No thermal runaway was observed from the ARC tests on the LFP/LTO cells. The heat generation of each reaction during the thermal heating including LFP/electrolyte, LTO/electrolyte, and electrolyte decomposition was analyzed using Differential Scanning Calorimetry (DSC). Thermal parameters were extracted from DSC test results and used in the ARC simulation to analyze the contribution of heat generation of each component. Major contribution of the heat generation at 100% SOC is the reaction between LTO and electrolyte at around 200oC. Reactions between LFP and electrolyte occurs at a high temperature close to the electrolyte decomposition at temperature above 250oC. At 30% SOC, the heat generation amount from both electrodes are similar. Aged cell electrodes showed benign thermal behavior comparing to the fresh cell electrodes. In spite of the observation of solid electrolyte interface (SEI) decomposition on the DSC of LTO/electrolyte, no corresponding heat generation was captured in the ARC test of full cell, which indicates the difference on SEI formation in full cell and half-cell contains LTO. Overall the LFP/LTO shows minimal self-heating under ARC conditions and exhibits beneficial safety features.