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Lithification and expansion process of graphite electrode

Graphite electrode thickness changes are as follows:

graphite electrode
  • The pole piece is rolled, when it is left to stand, and the thickness will rebound .and the compaction density is greate, the greater the rebound; under the same stress, and the adhesive is the greater the elastic modulus, the smaller the bounce the pole piece is placed, and drying will also cause .and the pole piece rebounded.
  • The pole piece absorbs the electrolyte to swell, and the thickness of the pole piece increases.
  • During the charge and discharge process, and the lithium insertion causes electrode expansion caused by changes in the lattice parameters.

Graphite electrode button half-cell lithiation and pole piece expansion process are shown in Figure 1.

Graphite electrode charge-discharge electrode electrochemical expansion process
  • (1) between the f + e: When graphite is first lithiated, in the 800mV-200mV voltage interval, it is mainly the SEI film formation process, the particle rearrangement process in the pole pieces, and the 2H => 1L process. About 1.5%.

  • (2) between the d + c: In the 200mV-100mV voltage range, the 1L => 4L => 3L transition process mainly occurs, and the expansion rate of the pole piece is also about 1.5%.

  • (3) between the b: In the 100mV voltage platform, the process of 3L => 2 mainly occurs. In this process, the pole piece hardly expands.

  • (4) between the a: In the 70mV voltage platform, the process of 2 => 1 mainly occurs. In this process, the expansion rate of the pole piece is about 1.2%.

Figure 2 shows the graphite electrode lithium desorption process.

XRD pattern of graphite charge and discharge process

The evolution process of the XRD spectrum measured on-line. Can visually observe the evolution of various phases during the DE lithiation of graphite.

Figure 3 is the expansion curve of the NMC-graphite electrode full cell.

The capacity expansion rate is the second derivative.and the expansion curve obtained is two inflection, corresponding to x = 0.23 and x = 0.5, respectively. As can be seen from Table 1, these two points correspond to the 3L and 2 phases in Table 1. Between these two points, the battery hardly undergoes expansion, and the slope of the expansion curve is small, which is consistent with the expansion curve of the graphite electrode, corresponding to the 3L => 2 transition process, and its slope is much smaller than other processes. Therefore, the expansion process of a full cell mainly depends on the expansion of the graphite electrode.

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