## 2 Method
### Data Collection and Preprocessing  
With the rapid development of green transportation and new-energy electric vehicles, the currently industrialized cathode materials for LIBs used both domestically and internationally include LiFePO4, lithium manganese (LiMn2O4), and ternary materials (Li(Ni,Co,Mn)O2). Among the metal elements comprising the cathode materials of the battery, Co is the most expensive, with limited reserves, Ni and Mn are more affordable, and Fe is the cheapest. Therefore, the LiFePO4 battery is relatively cost-effective. In addition, the LiFePO4 battery offers advantages such as high safety, long cycle life, good performance at high temperatures, and environmental friendliness. These qualities have made it widely adopted in new-energy electric vehicles [43]. Therefore, we have selected the 18,650 LiFePO4 battery for charge-discharge cycle experiments. This allowed us to gather multiple charge-discharge cycle experimental data for the LIB and accumulate a substantial database. In this study, multiple 18,650 LiFePO4 batteries with a rated capacity of 2500 mAh were employed. These experiments were carried out on a battery tester, model CT-4008T-5V6A-S1, which was connected to a computer. The battery tester was configured and monitored using the BTS Control battery testing software on the computer. Battery data was collected and counted using the BTSDA battery data collection software. The laboratory environment was maintained at a temperature of 25 \(\pm\) 2 \({}^{\circ}\)C. Each charge-discharge cycle of the battery included the following steps. 1. Secure the LIB in the device using the battery tester's upper and lower fixtures and allow it to sit undisturbed for ten minutes. 2. Connect the battery tester to the computer and use the BTS Control software to send commands to the battery tester: discharge the LIB at a constant current rate of 1 C to a cut-off voltage of 3 V and output the corresponding battery data. 3. The LIB remains idle on the battery tester for ten minutes. 4. Send commands to the battery tester through the BTS Control software: charge the LIB at a constant current rate of 1 C until it reaches the cut-off voltage of 4.2 V, then continue with constant voltage charging until the current drops to 0.1 C, and output the corresponding battery data. 5. Repeat steps 1 to 4. Collect data from multiple charge-discharge cycle experiments for the LIB. Collect the battery data output by using the BTSDA software on the computer connected to the battery tester. The data recorded in the experiment include the cycle index, charge-discharge capacity, median voltage, and charge-discharge time of the LIB. Data collection was concluded when the capacity of the 18,650 LiFePO4 battery decayed to 20% of the rated capacity, after which data processing was initiated. Data standardization is a fundamental step in data preprocessing. After obtaining a set of original data, it is common to analyze whether there are any outliers present, and if so, they need to be treated to reduce noise. For LIB charge-discharge cycle data, one can plot the curves of cycle number versus actual capacity to observe the presence of outliers. We use the 3 Sigma method to find abnormal data, and the specific implementation process is as follows. 1. Calculate the difference between the capacity values of the (\(i-1\)) th and (\(i\)+1) th cycle periods, where \(i\) is an integer greater than 1 and less than the total number of cycle periods. 2. Calculate the mean (\(\alpha\)) and standard deviation (\(\sigma\)) of these differences. 3. Identify data points whose values fall outside the range (\(\alpha-3\sigma\), \(\alpha+3\sigma\)) with a probability lower than 0.01 as outliers. 4. The average value of the data in the same category as the abnormal data in the previous cycle and the next cycle is taken as representing the data after the abnormal data processing.