Study of the effect of particle size

Lithium-ion batteries (LIB) have been widely used in various applications due to their advantages including no memory effect, long storage time and low self-discharge rate. Due to the need to store more energy, manufacturers have focused on developing higher energy density batteries in response to the growing demand for LIB in electrical products.

Image credit: Bettersize Instruments Ltd.

The energy density of the anode can be significantly increased by optimizing the size and shape of the graphite particles. The ideal graphite particle size is around 20 µm, which allows batteries to store more energy. In addition, the circularity of graphite has a direct impact on energy storage.

The higher the circularity of the graphite particles, the higher the tapped density. The optimal tapped density for graphite should be greater than 1 g/mL to hold more energy. Bettersize Lab used the Bettersizer S3 Plus to conduct an experiment to determine the impact of particle size and shape on the energy density of LIBs.

Optical system of the Bettersizer S3 Plus.

Figure 1. Optical system of the Bettersizer S3 Plus. Image credit: Bettersize Instruments Ltd.

Results

Particle size distribution

The Bettersizer S3 Plus was used to quantify the particle size and particle size distribution of graphite samples using only laser diffraction. Figure 2 illustrates the particle size distribution of the three samples, while Table 1 lists typical size values. The particle size gradually increases from sample A to sample C, as shown in Figure 2.

The median size values ​​of the three samples (D50) are 6.804 μm, 15.98 μm and 23.72 μm, respectively.

Particle size distribution of three graphite samples.

Figure 2. Particle size distribution of three graphite samples. Image credit: Bettersize Instruments Ltd.

Table 1. Typical particle size values ​​of graphite samples. Source: Bettersize Instruments Ltd.

To taste D10 (µm) D50 (µm) D90 (µm)
Sample A 4.264 6.804 10:49
B-sample 9.220 15.98 27.18
Sample C 11:60 a.m. 23.72 39.98

Lithium intercalation performance is affected by particle size, which is reflected in the initial reversible capacity, irreversible capacity, and cyclic performance of LIBs. According to the results, the initial irreversible capacity decreases as the particle size increases.

The reversible capacitance increases with particle size, peaking at 20 μm. Among the graphite samples from 13 to 80 μm,1 the 20 μm graphite sample shows the best energy storage performance. The D50 values ​​in sample B and sample C are close to 20 μm, indicating that they will perform better in energy storage than in sample A.

Particle shape

Using only dynamic image analysis, the Bettersizer S3 Plus can assess shape parameters. Table 2 shows the results of measuring the circularity of three graphite samples.

Three graphite samples have mean circularity (C50) values ​​of 0.862, 0.896, and 0.876, respectively. Sample B has a higher tapped density (1.01 g/mL) than the other two graphite samples.

Table 2. Circularity and packed density of graphite samples. Source: Bettersize Instruments Ltd.

To taste Circularity Tap density (g/mL)
C10 C50 C90
Sample A 0.813 0.862 0.917 0.85
B-sample 0.842 0.896 0.950 1.01
Sample C 0.774 0.876 0.924 0.95

When the anode has a high volumetric energy density, it tends to hold more energy, which is influenced by the density drawn off. An ideal tapped density for spherical graphite in the manufacture of anodes is greater than 1 g/mL.2

As the particle size increases, the tapped density also increases, because sample A has the smallest particle size and the smallest tapped density.

The tapped density can be affected not only by the particle size but also by the shape of the raw materials. According to surveys, the tapped density has a positive relationship with circularity,3 which implies that sample B (1.01 g/mL) has a higher packed density than sample C (0.95 g/mL).

Sample B sample should have the highest energy holding capacity of the three samples based on the tapped density and particle size results.

Repeatability

Repeatability is an essential parameter in particle size measurement. Figure 3 shows that the particle size distributions of the three replicates of Sample C are nearly identical.

Sample repeatability C.

Picture 3. Sample repeatability C. Image credit: Bettersize Instruments Ltd.

The repeatability of typical values ​​for Sample C is shown in Table 3. Size values ​​D10, D50 and D90 have a repeatability of 0.28%, 0.08% and 0.33%. Thanks to its high repeatability, the Bettersizer S3 Plus is extremely reliable.

Table 3. Repeatability of typical particle size values. Source: Bettersize Instruments Ltd.

Samples D10 (µm) D50 (µm) D90 (µm)
Sample C-1 11:60 a.m. 23.72 39.98
Sample C-2 11:55 a.m. 23.74 40.09
Sample C-3 11.54 23.76 40.24
Repeatability 0.28% 0.08% 0.33%

Conclusion

The energy storage capacity of the anode in LIBs is determined by the size and shape of the particles, which must be managed and evaluated within an optimal range to improve the efficiency of the manufacturing process.

Circularity and particle size of graphite should be measured using dynamic image technique and laser diffraction method, respectively, in accordance with Chinese standard GB/T 38887-2020.4

To obtain particle size and shape results separately, the conventional method requires two instruments. With laser diffraction and dynamic imaging technology combined in one instrument, the Bettersizer S3 Plus is the best choice for fabricators looking for particle size and shape results in a single measurement.

References

  1. Chen, J., Zhou, H., Chang, W. and Ci, Y. (2003). Effect of particle size on lithium intercalation performance of graphite anode. Acta Physico-Chimica Sinica, 19(03), 278-282.
  2. Yan, C., Zhang, M. and Lin, Y. (2015). Effect of graphite particle size on bulk density of valve. Non-metallic mines, 38(3).
  3. Teng, D., Li, P., Yuan, N., Lyu, J., Chen, J., Lin, L. & Chen, H. (2021). Optimization of natural graphite spheroidization process parameters. China Powder Science and Technology, 27(4).
  4. GB/T 38887-2020 – spherical graphite.

This information has been extracted, reviewed and adapted from materials provided by Bettersize Instruments Ltd.

For more information on this source, please visit Bettersize Instruments Ltd.

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