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Charge and discharge profiles
Machine-accessible metadata file describing the reported data: https://doi /10.6084/m9 gshare.14495604
The battery module can be decomposed into cells and used components according to UL 1974. The used components of the battery systems, such as the battery enclosure, battery management system (BMS), thermal management systems, and other auxiliary systems, should not be considered for repurposing if they have already been used longer than the calendar expiration date specified by the original manufacturer. The cells preparing for repurposing will undergo the performance test for sorting. UL 1974 suggests that the following test procedures shall be conducted by the repurposed manufacturer as part of the routine analysis of the incoming battery assembly:
Incoming open circuit voltage (OCV) measurements (Sec. 19.2 of UL 1974)
Incoming high voltage isolation check (Sec. 19.3 of UL 1974)
Capacity check (Sec. 19.4 of UL 1974)
Internal resistance check (Sec. 19.5 of UL 1974)
Discharge/charge cycle test (Sec. 19.7 of UL 1974)
Self-discharge (Sec. 19.8 of UL 1974)
The charge and discharge profile measurement according to Sec. 19 of UL 1974 is divided into two primary procedures. The first procedure with detailed steps containing Secs. 19.2 and 19.4 of UL 1974 are listed in Table 1. The second procedure with detailed steps containing Secs. 19.5, 19.7, and 19.8 of UL 1974 are listed in Table 2. The key parameters in the procedures are described as follows.
In this work, the voltage ranging from 2.5 to 3.5 V is adopted for safe working of the repurposed LFP battery cells (i.e., Vcut = 2.5 V and Vthres = 3.5 V), which is narrower than the safe working voltage range of new LFP battery cells (2–3.65 V). The voltage range can be adjusted according to the manufacturer''s design. In addition, the designed test procedures based on UL 1974 can be used for other types of Li-ion repurposed batteries.
It should be noted that not all battery cells are appropriate for repurposing. Before module disassembly, the OCV check is suggested for an effective judgement. For the modules with OCVs in the normal working range, their cells possess the potential for repurposing. For the modules with OCVs outside the normal working range, their cells should be recycled directly, saving the cost and time of the measurement.
Direct current internal resistance (DCIR) of batteries indicates the resistance of current flowing through the battery. The value of DCIR is not fixed and varies depending on multiple factors, such as battery materials, type and concentration of electrolyte, temperature, as well as depth of discharge. The variation of DCIR has a great influence on battery discharge performance, especially for high power batteries. In general, the better the battery, the lower the internal resistance. Therefore, most battery manufacturers identify DCIR as a primary indicator for evaluating battery quality.
Many techniques are applied to measure the DCIR of batteries, such as the tests conducted according to the IEC 61951-1 standard79, IEC 61960-3 standard80, and ISO 12405-4 standard81. In UL 1974, the two-tier DC load method is adopted, offering an alternative method by applying two sequential discharge loads of different currents and time durations. The battery first discharges at a lower constant current I1 for t1 seconds, dropping to a voltage V1, and then discharges at a higher constant current I2 for t2 seconds, dropping to a voltage V2 (as shown in Fig. 2). The DCIR, RDC, is obtained by the Ohm''s law as
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