# A Strategic Pathway from Cell to Pack-Level Battery Lifetime Model Development
## 2 Aging Dataset  
Any lifetime campaign to generate a degradation dataset and understand aging behavior requires a long-term engagement of resources. Thanks to the research community that many of the aging datasets of Li-ion technology variants are publicly available [36]. However, an LTO cell database is challenging to find due to barriers such as lack of commercial availability, cost, low energy density, etc. Nonetheless, a commercial TOSHIBA SCBi(tm) 23 Ah LTO cell is utilized in the Horizon2020 GHOST project considering its safe chemistry, high specific power, long lifetime, etc. The cell has a nominal voltage of 2.3 V, high input/output power (1000 W), compact design (W116 \(\times\) D22 \(\times\) H106 mm), and a light weight (0.55 kg). The prismatic-shaped 45 cells have been used to perform a series of electrical, thermal, and lifetime tests. The campaign generates a novel battery aging dataset that facilitates the degradation understanding of the studied battery type and helps to parameterize the lifetime model. The adapted test methodology for the aging study is focused on both the degradation aspects (cycle life and calendar life). It consists of a series of cycle and calendar aging tests at given stress and/or operating conditions to understand the degradation behavior. Regular performance tests are also performed between the aging rounds to learn the non-linear degradation trend. One can find the details of the test flow in the authors' previous work that is based on similar test protocols listed in Table 1[37]. As part of an EU project, at least 2 cells per condition are studied and the average result is used for the model development. As shown in Table 1, the degradation rate of the cells' aging performance is targeted to study by 5 stress factors which are DoD, mid-SoC, temperature, charge and discharge current rates or C-Rates for cycle life and 2 stress factors which are storage temperature and SoC for calendar life, respectively. The influence of these factors is investigated separately, and their joint influence corresponds to the actual measured data. The cycling profile consists of a series of charge and discharge processes until the number of Full Equivalent Cycles (FECs) is reached. An FEC (as in Equation (1)) is calculated based on the charge ampere-hour throughput and it is considered as the cycle count to compare the degradation results. Typically, 300 FEC per round is performed on the investigated cells considering its long lifetime nature specified by the manufacturer. Regular reference performance tests such as capacity test (full DoD with 1C-rate) and hybrid pulse power characterization (HPPC) tests (varying pulses at three SoC points), etc., are performed at cycling temperature to track the degradation. The calendar storage tests are done at the specific condition with a frequency of one month before performing check-up tests. The 1C discharge capacity and the internal resistance from a 10-s 3C discharge pulse are recorded to calculate the SoH of the battery. The battery is considered dead or has reached EoL once the SoH drops below 80% [38]. \[\text{FEC}=\frac{23,000\text{ Ah}}{\text{No. of performed cycles}*\text{ charge Ah per cycle}} \tag{1}\]  
To verify the validity of the lifetime model to be developed based on the parameters acquired from the different characterization tests, an independent validation test is required to be conducted. The designed validation test can be used to compare the model output checking the accuracy of the model to a dynamic and realistic condition. The worldwide harmonized light vehicles test cycle (WLTC) has been selected to perform the validation of the model [39]. For this research work, a current load profile representing a high-power application has been derived and modified to emulate real-life driving. The Fiat 500X vehicle is used as a reference to generate the current profile and