Electrochemical Impedance Spectroscopy Analysis - Research on Lithium Ion Batteries

A lithium ion battery, that is, a secondary battery using a compound capable of reversibly intercalating and deintercalating lithium ions as a positive electrode and a negative electrode:

When charging, lithium ions in the positive electrode are extracted from the positive electrode active material and embedded in the negative electrode active material;

At the time of discharge, lithium ions are extracted from the negative electrode active material and embedded in the positive electrode active material. Therefore, the charge and discharge capacity, cycle stability, charge and discharge rate, and high and low temperature charge and discharge performance of lithium ion batteries are all related to the elution and embedding of lithium ions in the electrode active material, the diffusion in the electrolyte, and the passage of lithium ions. The processes of the solid electrolyte interface (SEI) membrane on the surface of the anode active material particles are closely related.

Studying the relevant kinetic parameters of the above process is of great significance for understanding the comprehensive electrochemical performance of the corresponding lithium ion battery.

As an important method study the electrochemical interface process. Electrochemical impedance spectroscopy (EIS) is widely used to study the insertion and extraction of lithium ions in the oxidation of carbon materials and transition metals.

The so-called EIS is an AC test method for obtaining feedback of corresponding electric signals in the frequency domain by applying a sinusoidal AC signal with certain amplitude and a different frequency to the electrochemical system. The typical Li+ battery EIS spectrum will be analyzed in combination with the specific physical and chemical processes during charging and discharging.

During lithium-ion battery charging, the process of lithium ion elution and embedding in the chimeric electrode includes the following five steps, as shown in Figure 2 (Barsoukov et al. proposed a modification process):

Step 1: electron transport to the surface of the active material and transport between the active material particles, and transport of lithium ions in the electrolyte;

Step 2: diffusion of lithium ions through the SEI film on the surface of the active material particles;

Step 3: charge transfer process (or reaction bonding process) of electrons and lithium ions at a conductive junction;

Step 4: a diffusion process of lithium ions in the solid particles inside the active material particles;

Step 5: Lithium ions accumulate in the active material, consume and thereby cause a change in the crystal structure of the active material particles or the formation of a new phase (this portion of the common EIS map is not tested due to test frequency limitations).

Using an electrochemical workstation, an AC impedance scan was performed between 10 kHz and 50 μHz to obtain an EIS map as shown in Fig. 3. The map was specifically disassembled and analyzed, as shown in Table 1.

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