## 3 Results and Discussion
#### 3.1.1 Use and Cool-Down Phase I  
The highest temperature in the simulation is reached with the non-convective air (used as reference). Even though the temperature transported to the battery pack's surface is high in comparison to that of the other materials, the system is not able to transfer enough heat in the use phase (A). In combination with the very low heat capacity, this leads to a very high temperature of 86.5 \({}^{\circ}\)C in the cells at the end of discharging. This is beyond the typical specification of commercially available cells and the manufacturer's recommendations (~80 \({}^{\circ}\)C for discharging); thus, the use of this system cannot be recommended for the investigated use scenario. During cool-down phase I, the cells cool down fast (~0.5 \({}^{\circ}\)C/min, with an average cooling rate of 12-30 min), but due to the high maximum temperature, it takes until minute 133.5 to cool down to the charging start temperature, which is significantly later than that for the other investigated cooling materials.  
Heat-conductive polymer I is characterized by high thermal conductivity but a low heat capacity. With a peak temperature of 72.3 \({}^{\circ}\)C, it performs in the use phase (A) better than the reference system but worse than the other two solid materials. Even though the peak temperature is 14.2 \({}^{\circ}\)C lower than the reference state, it is only 7.7 \({}^{\circ}\)C below the recommended maximum temperature. Due to the high thermal conductivity, the subsequent cool down (B) is quick (~0.4 \({}^{\circ}\)C/min, with an average cooling rate of 12-30 min), and the charging start temperature is achieved after 98.5 min.  
Heat-conductive polymer II exhibits the lowest peak temperature (68.1 \({}^{\circ}\)C) of both materials without latent heat storage (phase change). The high heat capacity is able to take up a high amount of the thermal energy created during discharging in a short time span. Its cool down by contrast is slower compared to that of the other materials (~0.3 \({}^{\circ}\)C/min, with an average cooling rate of 12-30 min). The charging start temperature is reached after 102 min.  
The latent heat storage material is able to absorb a certain amount of thermal energy by a phase change (solid to liquid) at 39 \({}^{\circ}\)C. This significantly lowers the maximum temperature at the end of the use phase. With this and the high specific heat, it reaches at peak temperature of 63.7 \({}^{\circ}\)C only and outperforms all other materials, even though it has the lowest thermal conductivity. However, the thermal energy stored in the phase change is released during cool-down phase II and therefore prolongs the cool down to room temperature. Note that if a transition temperature of 39 \({}^{\circ}\)C is not reached in the cool-down phase and thus re-solidification does not happen, the latent heat is not available in the following second use phase. The cool-down speed is slow (~0.3 \({}^{\circ}\)C/min, with an average cooling rate of 12-30 min), but due to the low maximum temperature, the charging start temperature is reached after 81 min, which is the fastest in comparison with the other materials.