2.2.2. Function and Functional Unit

The function of the system is the recovery of the cathode material of TBs according to the described waterjet-based recycling process. Therefore, the functional unit is defined as the recycling of one kilogram of TBs and the associated reference flow is defined as the path of the cathode material from one kilogram of TBs. The amount of cathode material depends on the battery composition. In this study, the amount corresponds to 171 g of NMC cathode material.

#### 2.2.3. System Boundaries and Cut-Off Criteria

Figure 2 shows the system boundaries which define the valid assessment space for the LCA of the waterjet-based TB recycling. This system represents a gate-to-gate constellation, because only the production of the recyclate cathode material is considered [27]. Impacts on an environmental balance can be distributed as a result of by-products recovered through a recycling process, such as metals from the battery housing and others. Those impacts are resulting from primary extractions, which could be avoided for the materials of those by-products. Therefore, credits can be distributed to this extent, which usually leads to a positive impact on the environmental balance [27]. In this LCA, by- products of the battery are not further treated or evaluated. Since no credits are to be collected for the LCIA for the resulting by-products, their further treatments are outside the system boundary. The same applies to transport and waste treatments. The remaining electrical energy from the TBs is not considered, and therefore leaves the system boundary. Thus, the system boundaries only include the environment of the battery recycling plant. The geographical boundaries of this system are defined as Germany. The time frame of the study is set to the publication date of this study. For this study, in terms of mass, energy, or environmental relevance, no cut-off criteria are set.

**Figure 2.** System boundaries of the life cycle assessment (LCA) for the waterjet-based direct traction batteries (TBs) recycling process. Processes outside of the system boundary are not included in this study.

#### 2.2.4. Method of Impact Assessment

The LCI of this ecological study is evaluated according to the CML2001 method [28]. The CML method is an impact-oriented approach that assigns the data of the LCI to the environmental impacts. This multidimensional approach aims at the direct material and

energetic allocation of all impact flows between the environment and the production system [29]. In this study, only the impact category of the GWP, measured in kg CO2 equivalents (CO2e), is discussed, and evaluated.
