Graphite|LiFePO4 lithium-ion battery working at the heat engine coolant temperature

•Possibility of Li-ion cell operation in the cooling system of a car heat engine (90 °C) was demonstrated.•Electrodes were characterized by EIS, SEM and charging/discharging tests.•Impedance of the system decreased with increased temperature.•The system showed high capacity at increased temperature.•The electrolyte was characterized by low vapor pressure and decreased ignition point.

Electrochemical properties of the graphite anode and the LiFePO4 cathode, working together with the 1 M LiPF6 in TMS (sulpholane) at 90 °C have been studied. The general aim of the investigation was to demonstrate a potential application for a Li-ion cell working in the cooling system of a car heat engine (90 °C). Electrodes were characterized with the use of electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) as well as galvanostatic charging/discharging tests. SEM images of both electrodes after charging/discharging processes were covered with a film (electrochemical SEI formation). The charge transfer resistance at 90 °C, Rct, of the C6Li|Li+ anode and the LiFePO4 cathode was 24 Ω and 110 Ω, respectively. Reversible capacity of the LiC6 anode after 10–20 cycles, at a low current rate was close to the theoretical value of 370 mAh g−1 however an increasing current rate decreased to ca. 200 mAh g−1 (for 1C). The reversibility of the process was close to 95%. The capacity of the LiFePO4 cathode was ca. 150 mAh g−1, almost independent of the current rate and close to the theoretical value of 170 mAh g−1.