Thermal Stability Comparison of LiFePO4/Graphite and LiMn0.6Fe0.4PO4/Graphite Pouch Cells using Accelerating Rate Calorimetry

LiMn 0.6 Fe 0.4 PO 4 has attracted attention as a promising, high-energy, and cost-effective alternative to LiFePO 4 (LFP) for lithium-ion batteries. However, its thermal stability, especially at full cell level, remains less understood compared to LFP. This study compares the cycling performance and thermal stability of LiMn 0.6 Fe 0.4 PO 4 /graphite and LFP/graphite pouch cells using a consistent electrolyte formulation: 1.2 m lithium bis(fluorosulfonyl)imide (LiFSI) in ethylene carbonate (EC):ethyl methyl carbonate (EMC):dimethyl carbonate (DMC) (25:5:70 by volume) with 2 wt% vinylene carbonate (VC). Thermal stability was evaluated with two ∼250 mAh pouch cells through accelerating rate calorimetry at elevated temperatures. After roughly 275 cycles at C/3 and 40 °C, the LFP/graphite cells retained 91% of their initial capacity, while LMFP/graphite cells retained 89%, indicating slightly better electrochemical stability for LFP cells. Exothermic reactions in LMFP cells initiated around 125 °C, compared to 140 °C for LFP, implying higher thermal vulnerability. Despite this, both cell types exhibited similar self-heating rates below 0.1 °C min −1 , demonstrating strong safety performance. Overall, although LMFP offers a higher voltage window, its thermal stability and cycling performance still slightly lag behind LFP.