Lithium Ion Battery Material Testing Technology Summary

Scanning Electron Microscope (SEM)

Since the observation scale of battery materials is in the sub-micron, i.e., hundreds of nanometers to a few micrometers range, ordinary optical microscopes are unable to meet the needs of observation, while higher magnification electron microscopes are often used to observe battery materials.

Scanning electron microscope (SEM) is a more modern cell biology research tool invented in 1965, which mainly utilizes secondary electron signal imaging to observe the surface morphology of samples, i.e., scanning the samples with a very narrow beam of electrons, and generating a variety of effects through the interactions of the electron beam with the samples, which are mainly the secondary electron emission of the samples. Jinjian Lab has advanced testing equipment and a professional technical team to ensure the accuracy and reliability of the test. The team consists of national talent project inductees and senior management and technical experts in the industry, who have rich working experience in scanning electron microscope (SEM) test. Scanning electron microscope can observe the particle size and uniformity of lithium materials, as well as the special morphology of nanomaterials themselves, and even by observing the deformation of the material in the cycling process we can judge its corresponding cycle retention ability is good or bad. As shown in Fig. 1b, titanium dioxide fibers have a special mesh structure that can provide good electrochemical performance.

Figure 1: (a) Schematic structure of SEM%28SEM%29; (b) Picture obtained from SEM test (nanowires of TiO2)

1. SEM scanning electron microscope principle

As shown in Figure 1a, SEM is the use of electron beam bombardment of the surface of the sample, causing the emission of secondary electrons and other signals, mainly using SE and amplify and transfer the information carried by SE, point-by-point imaging in a time sequence, imaging on the picture tube.

2. The characteristics of the scanning electron microscope

(1) image of a strong sense of three-dimensionality, can observe a certain thickness of the sample

(2) sample preparation is simple, can observe the larger samples

(3) high resolution, 30 - 40

(4) Continuously variable magnification, from 4x - 150,000

(5) Can be equipped with accessories for quantitative and qualitative analysis of micro-regions.

3. Observation object

Powder, granule, block material can be tested, no special treatment is needed except keeping dry before testing. Mainly used to observe the surface morphology of the sample, the structure of the cut surface, the structure of the inner surface of the lumen and so on. It can intuitively respond to the special structure and distribution of the particle size of the material.

TEM Transmission Electron Microscope

Figure 2: (a) Structural schematic of TEM transmission electron microscopy; (b) TEM test photo (Co3O4 nanosheets)

1. Principle: mainly use the incident electron beam through the sample, produce carry sample cross-section inside the electronic signal, and by multi-stage magnetic lens amplification imaging in the fluorescent plate, the whole image at the same time set up.

2. Features:

(1) Ultra-thin sample, hobtained by1000

(2) Two-dimensional planar image, poor stereoscopic sensation

(3) High resolution, better than 2

(4) Complicated sample preparation

3. Object of observation

Nanoscale materials dispersed in solution, need to drop on the copper mesh before use, prepared in advance and keep dry. Mainly observe the internal ultrastructure of the sample, HRTEM high-resolution transmission electron microscope can observe the corresponding lattice and crystal surface of the material. As shown in Fig. 2b, observing the two-dimensional planar structure has a better effect, relative to the SEM's poor stereoscopic sense, but it can have a higher resolution to observe the finer parts, and the special HRTEM can even observe the material's crystal surface and lattice and other information.

Crystal Structure Testing of Materials

X-ray diffraction (XRD) is a scientific tool for probing the internal structure of a material by analyzing its diffraction pattern of X-rays. The technique can reveal key information about a material's composition, crystal structure, and the arrangement of atoms or molecules. As a primary means of physical phase and crystal structure analysis, XRD plays an important role in a variety of fields, including materials science, chemistry, and geology.

When X-rays are irradiated onto a substance, unique diffraction patterns are produced depending on the composition and structure of the substance. These patterns reflect characteristics such as the crystalline form of the substance, the way in which the molecules are bonded, the molecular configuration and conformation, etc. The advantage of XRD is that it is a non-destructive method that does not cause any damage to the sample, and at the same time, it is characterized by a high measurement accuracy and rapid analysis.

In addition, XRD's ability to provide detailed information about the integrity of crystals makes it an indispensable analytical tool in modern scientific research and industrial production. With the advancement of technology, the application of XRD continues to expand, providing an efficient and accurate solution for structural and compositional analysis of materials.

Figure 3: (a) XRD spectra of lithium materials; (b) schematic structure of X-ray diffractometer

1. XRD principle

When X-ray diffraction is projected into a crystal as an electromagnetic wave, it is scattered by the atoms in the crystal, and the scattered waves are as if they were emitted from the center of the atoms, and the scattered waves emitted from the center of each atom are similar to the source spherical waves. Since the atoms are periodically arranged in the crystal, there is a fixed phase relationship between these scattered spherical waves, which causes the spherical waves to reinforce each other in some scattering directions and cancel each other out in some directions, resulting in diffraction. The arrangement of atoms within each crystal is unique, and thus the corresponding diffraction pattern is unique, similar to a human fingerprint, and thus can be analyzed physically. The distribution pattern of diffraction lines in the diffraction pattern is determined by the size, shape and orientation of the crystal cell. The intensity of the diffraction lines is determined by the type of atoms and their position in the crystal cell. Through the Bragg's equation: 2dsinθ=nλ, we can obtain the characteristic signals of different materials by using X-rays excited by a fixed target at a special θ angle position, i.e., the characteristic peaks labeled on the PDF card.

2. XRD test characteristics

XRD diffractometer has wide applicability, usually used to measure powder, single crystal or polycrystalline and other bulk materials, and has the advantages of fast detection, simple operation, easy data processing, etc., is a standard standard “conscience product”. Not only can be used to detect lithium materials, most of the crystalline materials can be used XRD test its specific crystal type. Figure 3a shows the XRD spectrum of Co3O4, a Li-ion material, with the crystallographic information of the material labeled according to the corresponding PDF card. The black color of this figure corresponds to the block material crystallization peaks are narrow and highly pronounced, indicating that its crystallinity is very good.

3. Test object and sample preparation requirements

Powder samples or block samples with flat surface. Powder samples are required to be ground well, the sample surface should be paved to reduce the impact of stress on the measurement sample.

Cyclic Voltammetry and Cyclic Charge-Discharge for Electrochemical Performance

In the field of electrochemistry, the testing of lithium battery materials is crucial, with cyclic voltammetry (CV testing) playing a central role. This method alternates reduction and oxidation reactions at the electrode by precisely controlling the electrode potential, which is scanned in a triangular waveform. By monitoring the current versus potential, a current-potential curve can be plotted, which in turn analyzes the reversibility of the electrode reaction, the behavior of intermediates, adsorption at phase boundaries, the formation of new phases, and the characteristics of coupled chemical reactions.

The CV test not only measures the kinetic parameters of the electrode reaction, but also reveals the control steps and mechanisms of the reaction. It is a preferred method in the exploration of electrochemical systems, and has been called the “spectrum of electrochemistry” because of its ability to provide a wealth of qualitative information. In addition, the variety of electrode materials available for the CV test, including mercury, platinum, gold, glassy carbon, carbon fiber microelectrodes, and chemically modified electrodes, increases its applicability in different research scenarios.

Although the application of CV test in quantitative analysis is limited, its value in qualitative analysis cannot be underestimated, providing researchers with a powerful tool to deeply understand the nature of electrode reactions.