Lithium ion batteries are widely used in our daily lives due to their advantages such as cleanliness, high energy density, and good cycling performance. Especially in recent years, with the rapid development of new energy vehicles and energy storage power stations, the amount of lithium-ion batteries used is beyond imagination. A new energy vehicle integrates thousands of batteries, up to several hundred kilograms, and the huge amount of batteries are concentrated together, making safety issues particularly important. In recent years, lithium battery electric vehicles, automobiles, and energy storage power stations have all experienced combustion and explosion accidents. Therefore, research on the quality and safety of lithium batteries has been increasingly valued, and higher requirements have been put forward for the quality inspection technology of lithium batteries, including positive and negative electrode materials, separators, copper foil, aluminum foil, and even outer packaging materials.

Oubotong Group has long been engaged in micro analysis work in the fields of light and electron microscopy. Through communication with our customers, we have found that their micro analysis currently has problems such as low efficiency, significant subjective human factors, and non standardization. Therefore, we have established Huihong Technology Company to use intelligent software to achieve automation and standardization of micro analysis.

1、 Lithium ion battery material microscopic intelligent analysis system (LIBMAS)

Lithium ion battery refers to a general term for batteries with lithium ion embedded compounds as electrode materials, which mainly rely on the movement of lithium ions between the positive and negative electrodes to work. Due to defects in the material processing, lithium batteries still have a certain probability of failure during use or storage^[1]For example, during the charging and discharging process, porous electrodes undergo volume expansion and contraction, causing particles to gradually crack. These cracks initiate and propagate along the original defects, leading to mechanical fracture of the material and disintegration of the electrode structure, resulting in electrode material pulverization. The failure of these materials seriously reduces the performance of lithium batteries, affecting their reliability and safety in use.

Figure 1: Huihong Lithium ion Battery Microscopic Intelligent Analysis System

In response to various failure issues that arise during the use of lithium batteries, Huihong Intelligent Technology has tailored exclusive software for customers to meet all their needs. Advanced AI technology and image processing technology are used to quickly and accurately analyze lithium battery materials, including single crystal aggregation recognition, cracking ball recognition, secondary ball particle distribution uniformity judgment, cross-sectional pore statistics, and diaphragm pore statistics.

1) Identification:

Usually, the co precipitation method is used to prepare ternary positive electrode materials^[2]Agglomeration and stacking of nanoscale primary particles into spherical secondary particles, but this stacking structure is prone to crack formation, leading to battery performance degradation.

Figure 2: Software intelligently distinguishes between cracked balls and regular balls

By using Huihong LIBMAS, the proportion of cracked balls can be quickly calculated and the crack information of cracked balls can be obtained, thereby improving the process conditions, as shown in Figure 2.
The interior of the positive electrode particles is usually a polycrystalline structure formed by secondary spherical particles. When we set aside the secondary spherical particles, we found that there were a large number of cracks in the particle cross-section after cyclic charging and discharging, as shown in Figure 3. Use LIBMAS to identify cross-sectional pores and quickly obtain cross-sectional pore results.

Figure 3: Identification of secondary spherical cross-section pores

2) Aggregate particle identification:

The positive electrode ternary particles usually need to be sintered under high temperature pure oxygen, and the sintered ternary products generally have a typical agglomerate morphology, consisting of primary particles with a particle size of several hundred nanometers and secondary spherical particles between a few to ten micrometers. In the past, manual statistical analysis was used, which required manual measurement one by one after SEM imaging, resulting in a large workload and human measurement errors; By using Huihong Intelligent Analysis Software, one can operate with just one click, simplify the process, and quickly obtain standardized statistical results in a short period of time, as shown in Figure 4.

Figure 4: Identification of secondary spherical particles formed by primary particle aggregation

The particle size of electrode materials affects the capacity, rate performance, and cycling performance of batteries^[3]Small sized particles can shorten the solid-state diffusion path of lithium ions, while internal porous particles can provide more channels for lithium ion migration. However, a particle size that is too small can lead to low Coulombic efficiency and packing density, affecting the overall capacity of the battery. The Huihong LIBMAS can efficiently identify the particle size (length, width, circumference, area, etc.) and distribution, as shown in Figure 5.

Figure 5: Software automatically distinguishes agglomerated particles and agglomerated particle cross-sections

3) Single crystal particle identification:

Compared to individual nanoparticles, aggregated particles have advantages such as smaller specific surface area, better particle flowability, higher compaction density, and better electrode slurry processability. However, during the repeated charging and discharging process of the aggregates, the electrodes constantly expand and contract, and the internal particles are easily broken. Compared to polycrystalline positive electrode materials that are prone to particle crushing, many studies have shown that^[4,5]We have started to explore the properties of single crystal ternary cathode materials based on the crystal structure itself. The results show that single crystal ternary materials have better mechanical strength, which suppresses particle breakage and also has better thermal stability in high-temperature cycling. Research such as this requires accurate identification of single crystal particles and their internal distribution. Huihong Technology LIBMAS can automatically identify single crystal particles with clear contours in agglomerated particles, and measure and count their diameters, as shown in Figure 6.

Figure 6: Identification of Single Crystal Particles

4) Size secondary ball recognition:

In addition, Huihong LIBMAS can accurately identify all large secondary spherical particles and small particles on the image, and calculate the uniformity of the distribution of large and small particles based on their area. As shown in Figure 7.

Figure 7: Identification and Statistics of Uniformity of Particle Distribution of Small and Medium Sized Balls

5) Diaphragm porosity statistics:

As an important component of lithium batteries, lithium battery separators are polymer functional materials with nanoscale microporous structures. Their main function is to prevent short circuits caused by contact between the two poles and to allow electrolyte ions to pass through. Related research confirms^[6]The more uniform the pore size distribution of the separator, the better the electrical performance of the battery.

The distribution of pore size is mainly observed using scanning electron microscopy (SEM), but relying solely on visual observation images results in certain errors and low efficiency in characterizing porosity. Therefore, in order to obtain the porosity of materials more accurately and visually, it is necessary to combine image processing software with SEM to meet the requirements of membrane pore distribution and quantitative analysis.

Figure 8: Identification of Diaphragm Pores and Porosity Statistics

Huihong LIBMAS can quickly obtain the porosity information of the separator, detect the porosity, pore diameter, and fiber diameter of the separator, and perform statistical analysis, thereby vividly describing the structural details of the separator surface and improving the accuracy of lithium battery separator porosity evaluation, as shown in Figure 9.

2、 Lithium ion battery foreign matter analysis system (LIBIAS)

At present, the industry mainly classifies metal and magnetic foreign substances in lithium battery cathode materials into the following three aspects: metal and non-metal large particles, magnetic foreign substances, and Cu/Zn elemental substances^[7]The ways in which foreign objects are introduced include the introduction of raw materials and the production process. In order to effectively control the content of non-metallic/metallic/magnetic foreign objects in the positive and negative electrode materials of lithium-ion batteries, professional equipment and software are generally used to perform morphology and composition statistics on the foreign object particles in the raw materials after initial screening. In the past, the industry used methods such as light mirrors or manual measurement. However, these traditional detection methods often have some shortcomings in the accuracy, comprehensiveness, and consistency of data results, which poses significant challenges to accurate detection. At present, the main problems faced in the detection of foreign particles in lithium battery materials are: 1) wide source and difficult traceability of foreign objects, 2) large amount of data and time-consuming and laborious, 3) easy agglomeration of particles and high difficulty in identification.

Figure 1: Images of the same particle under an optical microscope (left) and an electron microscope (right), as well as EDS spectrum identification, show that the main component of the particle is Fe

Figure 2: Distribution of all particles on the filter membrane under electron microscopy image

Figure 3: Particle aggregation phenomenon on the filter membrane

In response to the shortcomings of traditional software, Huihong Technology Company, a subsidiary of Europol Group, has developed the "Lithium ion Battery Foreign Object Analysis System" (LIBIAS). This is a fully automatic cleanliness analysis system that integrates accurate, efficient, and easy to operate functions, which can achieve high-definition BSE image acquisition and shooting, image processing, element quantitative testing, and other functions. Including: 1) easy-to-use testing program, 2) open standard library editing system, 3) one click generation of corresponding report charts.

Figure 4: Pie chart of particle type proportion (left), ternary statistical phase diagram (right)

Huihong Intelligent Technology is a service provider specializing in micro intelligent image analysis application solutions in the industrial field. With the vision of "adhering to originality and leading industrial analysis with information technology", we can provide users with intelligent microscopic analysis solutions for lithium batteries in all scenarios. The "Lithium ion Battery Material Microscopic Intelligent Analysis System (LIBMAS)" and "Lithium ion Battery Foreign Matter Analysis System (LIBIAS)" developed by Huihong Intelligent Technology combine high-resolution scanning electron microscopy with intelligent analysis software to solve the full range of lithium ion battery related analysis from lithium battery raw materials to positive and negative electrode plates, separators, and lithium battery cleanliness, helping researchers develop lithium battery products with superior performance.

References:

[1] Wang Qi-Yu, Wang Shuo, Zhou Ge, Zhang Jie-Nan, Zheng Jie-Yun, Yu Xi-Qian, Li Hong. Progress on the failure analysis of lithium battery. Acta Phys. Sin. , 2018, 67(12): 128501. doi: 10.7498/aps.67.20180757.

[2] https://doi.org/10.1016/j.powtec.2009.12.002

[3] Yang Shaobin, Liang Zheng Principles and Applications of Lithium ion Battery Manufacturing Process [M]

[4] https://www.science.org/doi/abs/10.1126/science.abc3167.

[5] Xiao Jianwei, Liu Liangbin, Fu Zewei, etc Single crystal LiNi_xCo_yMn_1-x-yO₂Research progress on ternary positive electrode materials [J]. Battery Industry, 2017, 21 (2): 51-54

[6] Mao Jiyong, Xu Hanliang. The Effect of Diaphragm Porosity on Battery Performance in Lithium ion Batteries [J]. Guangzhou Chemical Industry, 2018, 46 (14): 78-80

[7] Hui Sheng, Zhan Yongli, Li Jiang Research on Process Control of Metal and Magnetic Foreign Matter in Lithium Battery Positive Electrode Materials [J]. World Nonferrous Metals, 2021 (17): 166-168