## 3 Evaluation on LiB Electrodes
### Current Collector Material and Thickness  
The characteristics that determine the properties are derived from the requirements and properties for the current collector. The material is an essential feature of the current collector and can be functionalised, in particular, to optimise properties. However, the mentioned properties are also dependent on the geometry of the current collector and the arrester position. Thus, the characteristics of current collector cross section, current collector width, thickness and length are defined.  
There are also various dependencies between individual characteristics. The dependencies sometimes exist beyond the limits of the individual component. For example, the length and width of the current collector affect the coating surfaces of the electrodes. Due to the specifications for cell geometry, geometric variables of length and width of the current collector are already taken into account and are not included as a separate complexity feature. However, the thickness, the material and the position of the tab have a significant influence on the complexity and are, therefore, defined as complexity features of the current collector.  
The choice of material for the current collector, on the other hand, is primarily dependent on the active materials used. An example is the use of aluminium in combination with lithium titanate on the anode side. Furthermore, the choice of the current collector material depends on the electrolyte used. For example, pure lithium metal can be selected as the anode in combination with a solid electrolyte. The current arrester variants have different requirements with regard to handling. On the other hand, the thickness and hardness of the material also determine coating, buckling and bulging behaviour of the coated electrodes. Thinner foils are, e.g., more flexible and more vulnerable to air currents during drying and, therefore, can cause damages in the coating. In addition, strength (e.g., tensile strength) is important for web tension during the coating process. If the tensile strength of the foil is low, less web tension is possible and tear offs are more likely. In particular, thin or soft foils are particularly difficult to handle during the production of  
Figure 6: Complexity characteristic value layer thickness of the electrode \(n_{\text{SD}}\).  
electrodes and cells. In summary, the different current collector variants are evaluated on the basis of criteria energy (density), production complexity (handling) and temperature (tempering properties) (compare Table 5).  
Accordingly (with a minimum possible score of 3 and a maximum possible score of 15), the complexity values shown in Figure 7 result in individually considered current collector variants depending on the evaluation.  
This results in the relationship shown in Equation (5).  
\[K_{B,S}(n_{B,S})=-0.1\cdot n_{B,S}+1.6 \tag{5}\]  
This results in average specific complexity values at a thickness of 8-12 \(\upmu\)m. There is a tendency for hard aluminium current collectors to be less complex and thin foils to show the greatest complexity. When updating the evaluation of the considered current collectors, a simple adjustment of the specific complexity index is possible.  
\begin{table}
\begin{tabular}{l c c c} \hline \hline
**Current Collector Variant** & **Energy** & **Production Complexity** & **Temperature** \\ \hline Cu 6 \(\upmu\)m & ++ & - - & - \\ Cu 8 \(\upmu\)m & + & - & o \\ Cu 12 \(\upmu\)m & - & + & + \\ Cu 20 \(\upmu\)m & - - & ++ & ++ \\ Al 8 \(\upmu\)m hard & ++ & + & o \\ Al 12 \(\upmu\)m hard & + & ++ & + \\ Al 20 \(\upmu\)m hard & - & ++ & ++ \\ Al 8 \(\upmu\)m soft & ++ & - & o \\ Al 12 \(\upmu\)m soft & + & + & + \\ Al 20 \(\upmu\)m soft & - & ++ & ++ \\ \hline \hline \end{tabular}
\end{table}
Table 5: Evaluation of selected current collector properties.  
Figure 7: Complexity index of various current collectors.