EIS test of EINHEL Li battery

Experiment setup

Experiment setup

Instrument: CS350M potentiostat/galvanosatat

Technique: Potentiostatic EIS

Parameters: frequency range: 100k Hz ~0.01Hz, 10 points/decade, AC Amplitude: 5 mV, DC potential: 0 V vs. OCP.

We used 2-electrode mode for Eis test of the battery cell. The green WE and white SENSE alligators were connected together to the positive electrode, the yellow RE and red CE alligators connected together to the negative electrode. As the voltage was high for the EINHEL Li battery module, we disassembled it and took 2 single battery cells(3.85V) for EIS test.

Fig. 1 EIS test parameter setting interface

 Single Li-ion cell
 We disassemble the battery module, and take two single cells to do the EIS test. The results are shown in Fig. 2.

Fig 2. EIS of the single cell

 In Figure 2, The red and black curve represents the impedance spectrum of the two battery cells, respectively. There is a typical capacitance arc in high-frequency region. The oblique line in the low-frequency region may be related to the diffusion of lithium ions. Therefore, Warburg impedance is used.

Fig 3. equivalent circuit of the single cell

 Fitting results using the equivalent circuits mentioned above

There are performance differences between the two lithium-ion battery cells. Cell #1 exhibits a lower internal resistance (Rs) and a higher double-layer capacitance (Cdl) of 2.374 F, indicating that its electrode active material has a larger effective surface area(ECSA) compared to Cell #2, resulting in greater charge storage capacity. This observation is further supported by the charge transfer resistance (Rct), where Cell #1 shows a smaller Rct than Cell #2. These results suggest that Cell #1 is in a better condition than Cell #2.

 As reported in the literature, the quality of lithium-ion cells can be evaluated based on Rs and Rct values - the smaller these parameters, the better the cell performance.