## 3 Methodology  
The cells used in the experiment (Table 1) were Efest (Shenzhen, China) IMR18650 LMO cells with a nominal capacity of 3100 mAh [17], HETE ELECTRONICS GROUP (Shenzhen, China) HTCF18650 LFP cells with a nominal capacity of 1600 mAh [18], Samsung SDI (Cheonan-si, Republic of Korea) INR18650-29E lithium NMC oxide cells with a nominal capacity of 2900 mAh [19] and LTO Battery Co. (Shenzhen, China) LTO18650 LTO cells with a nominal capacity of 1300 mAh [20]. A nickel stripe of 45 mm \(\times\) 10 mm \(\times\) 0.15 mm was welded on both sides of the cell poles. A WIKA CTR-2000--precision thermometer from WIKA company (Klingenbergam Main, Germany) was used for temperature measurement and calibration inside the calorimeter [21]. Two of these thermometers were used with two PT-100 probes i.e., temperature sensors. The CTP5000-250 [22] reference thermometer from WIKA company consists of components such as a Resistance Temperature Detector (RTD), lead wire, sheath, and  
Figure 2: The structure of a calorimeter is formed by a vacuum flask containing the lithium–ion cell inside a liquid with a thermometer and a calorifier [7]. a connection. Both devices were supported by LabView software (v2.13.16) and had an RS232 interface. The CTR-2000 thermometer has an accuracy of 0.01 \({}^{\circ}\)K.  
The HI190M magnetic stirrer from Hanna Instruments company (Woonsocket, RI, USA) [23] was used to ensure an even temperature distribution inside the calorimeter flask. The stirrer bar inside the calorimeter rotated at 250 rotations per minute (rpm). The stainless-steel 0.5 L flask of Dewar GSS/DSS 500 model from KGW Isotherm company (Karlsruhe, Germany) was used for the experiment. The plug to cover the flask was made of polyurethane for good thermal isolation [24]. They formed a thermal insulator to obtain a quasi-adiabatic calorimeter. The reason for such insulation was to ensure that negligible heat energy could escape from the calorimeter. Moreover, to support the experiment for low temperatures, the calorimeter liquid was a mixture of 50% water and 50% glycol with a freezing point around \(-33\)\({}^{\circ}\)C. This ensured that the water inside the calorimeter did not freeze at 0 \({}^{\circ}\)C and \(-10\)\({}^{\circ}\)C testing temperatures. In total, 300 mL of liquid were used per calorimeter. Four flasks were procured for the experiments. A calibration heater was used to calculate the heat capacity of the setup. The calibration heater acted as a heating resistor. One axially wired resistor with a ceramic housing from Hi Tech Resistors HTR (Nagpur, India) was used for the experiments for each flask. The model has a resistance value of 6.8 \(\Omega\) with a maximum load capacity of 11 W [25]. It was found that these resistors heat up the temperature of the calorimeter liquid by approx. 1.1 \({}^{\circ}\)C with a voltage supply of 5 V.  
The BTS4000-5V6A model from Neware company (Shenzhen, China) was used for the pre-cycling of the cells to generate the current profile for the measurement cycle and as the power supply for the calibration heater. For each channel, it uses a four-wire measurement. The tester contained a control unit and several racks with eight channels each so that cells can pre-cycle quickly, with an aim to measure four cells at the same time [26]. To accelerate the temperature equalization, the calorimeter liquid was brought to the required test temperature using the F32 thermostat from JULABO (Seelbach, Germany) thermostat before it was filled into the calorimeter [27]. By using a VTS 4150-5 model of VOTSCH (Balingen, Germany) climate chamber, it was possible to generate a stable ambient temperature for the calorimeter during the experiment [28]. The measurements, with the help of a calorimeter and magnetic stirrer, occurred in the climate chamber, while the temperature-measuring devices and the battery tester were located outside. The flask was placed on the magnetic stirrer with the stirring bar inside.