Detection of the knee point in lithium-ion battery

The dataset used in our study consists of 60 commercial lithium-ion batteries cycled under various operating conditions. These high-power NCA/Gr-Si cylindrical cells, manufactured by Samsung SDI (INR 18650-30Q), were cycled using vertical cylindrical fixtures on a battery cycler (CRC 05-10, Wonik PNE, South Korea) in a temperature-controlled chamber. The cells have a nominal capacity of 3 Ah and a nominal voltage of 3.6V. The voltage-cutoffs (2.5 V and 4.2 V, corresponding to 0%−100% SOC) adopted in this work were based on the manufacturer’s manual.

1st cycle aging test (SOH100→SOH80) under various operating conditions
The cells were cycled under nine different operating conditions. The operating conditions were differentiated based on chamber temperature, (dis)charging cut-off voltages, and charging rates, while the discharge was identically conducted at 1C constant current (CC). The chambers were set to four different temperatures: 10 °C, 25 °C, 45 °C, and 60 °C. Within each temperature, the tests were further subdivided based on charging C-rate into low C-rate (0.5C and 1C) and high C-rate (3C) conditions. For 45 °C and 60 °C conditions, further subdivisions with regard to charging rate were not conducted. At every 50 to 100 cycles, including BOL and EOL, every cell was subjected to the reference performance test (RPT) to measure SOH and kinetic properties (1C capacity and DCIR). The cycles lasted until the SOH reached SOH80. Especially, additional 1/30C (dis)charging cycles were conducted at EOL.

Second cycle life test (SOH80→SOH60) after the EOL
all the 60 cells were subjected to an additional cycling test with an identical cycling protocol (0.5C CC with CV of 0.25C cut-off for charge and 0.5C CC for discharge, 2.5 V−4.2 V) at 25°C, and the capacity of 0.2C−0.2C cycle was checked every 50 cycles. The cycles lasted until the SOH reached SOH60.