## 1 Introduction  
Ramping up the usage of lithium-ion batteries (LIBs) on a global scale, mainly in the automotive context, requires, besides cell ageing, a broad understanding of both the electrical and the thermal behaviour. Ideal thermal management, especially for large-scale battery systems, is crucial for the maximum possible power and energy supply the system can contribute at a particular state. This optimisation must be done to improve the acceptance of electric vehicles by minimising the required battery cells due to higher power and energy availability without decreasing the driving range.  
Thermal characterisation is divided into two general approaches. The first uses external excitation to obtain both the heat capacity (e.g., calorimetric tests [1, 2, 3]) and the thermal conductivity (e.g., one-sided heat pulses using a calefaction plate [4, 5, 6] or a flashlight [7, 8]). Often these methods require extended auxiliary testing equipment. The other approach uses internal thermal excitation of heat created by the current in the cell. These tests require only standard laboratory equipment and are faster and easier to integrate into battery characterisation procedures.  
In this paper, the focus lies on the usage of the latter. Here, the literature introduces and discusses multiple different approaches. The procedures often follow well-known electrical characterisation methods, for instance, pulse response triggered by a direct current as in the hybrid pulse power characterisation [9] or using a sinusoidal current as in electrochemical impedance spectroscopy [10, 11].  
These testing principles are adjusted to observe the thermal response of the cell [12; 13]. Thermal characterisation tests need a longer overall testing time due to the longer time constants, and obtaining an appropriate temperature response often requires high currents, which leads to necessary adaptations in the testing schemes. The state of charge (SOC) plays an essential role in the thermal behaviour of a battery cell. While the parameters of the cell remain nearly constant, as shown in this paper following the literature [14; 15; 16], the heating of the battery itself differs due to the so-called reversible heat term. Therefore, pulsing the excitation current at a relatively high frequency is often required to maintain a quasi-stationary SOC for obtaining the thermal parameters [17; 18; 19]. This paper uses thermal impedance spectroscopy (TIS) as an easy-to-implement approach to calculate the battery cell's heat capacity and thermal conductivity for large-area cells. TIS was first introduced by [12] using an external heating coil to investigate the temperature response of the cell and afterwards adapted by other researchers using internal heating [20; 21] to obtain the cell's parameters. The investigations mostly correspond to smaller cell formats, for example cylindrical [21; 22] or small pouch cells [20; 23]. This paper firstly investigates and compares two same-sized large-area cells with different cell configurations and capacities, as further described in Section 2.2. Utilising a polystyrene arrangement around the significant cell surfaces in this paper shows that the TIS can be used for automotive-sized cells accordingly while also displaying the cell behaviour in the complete operational range. The results can benefit the implementation of a thermal management system in automotive applications by showing considerable differences in the system behaviour at usage.