Key points of the ternary lithium battery material test
The performance of the material determines the use of the material, and also determines the performance and quality of the product. For the development of lithium battery technology, the research of materials cannot be separated from the testing of materials. What test items and test points are needed for ternary lithium battery materials? Let’s take a look together.
Lithium-ion battery has developed rapidly in recent years. With its high energy density, good multiplier performance and cycle performance, it has become the main power source of electric vehicles, occupying a very important place in new energy, and also put forward a new development path for global energy and environmental problems.
Table of Contents
Nickel cobalt manganese oxide ternary lithium battery (LiNixCoyMnzO2) cathode material is one of the cathode materials with the highest energy density under development, with significant performance advantages, and is one of the most important development directions of vehicle power battery cathode materials in the future.
What is the material of ternary lithium battery?
Ternary lithium battery usually refers to lithium nickel cobalt manganese oxide (LiNixCoyMnzO2) or lithium nickel cobalt aluminate as the cathode material, nickel cobalt manganese ternary cathode material combined with the characteristics of LiNiO2, LiCoO2, LiMn2O4.
Compared with lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate and lithium nickel manganese oxide and other materials have the advantages of high energy density, good cycle stability, low cost and so on, currently has emerged in the application of new energy vehicle power battery, is considered to be one of the most promising cathode materials in the future.
Ternary lithium battery material test project
The performance of the material determines the use of the material, and also determines the performance and quality of the product. The research of materials cannot be separated from the testing of materials. What test items and testing instruments are needed for ternary lithium battery materials?
Scanning electron microscope (SEM) as a commonly used imable electron microscope, is commonly used to study the microorganization, morphology and composition of materials. It works based on the interaction between the electrons and the matter under test.
High-energy electron beam bombardment material sample surface, the sample surface will produce back scattering electrons, secondary electrons, electronic, visible fluorescence, X-ray and continuous X-ray, transmission electrons and in visible, ultraviolet, infrared light area of electromagnetic radiation, etc., through these signals, can obtain the microscopic organization, morphology, chemical composition, crystal structure and internal electric field or magnetic field information.
The scanning electron microscope delivers these detected signals to the display tube, which displays the SEM images in the screen. SEM combined with an X-ray spectrometer (EDS) can also analyze the chemical composition of the sample.
SEM diagram of ternary lithium battery material
(2) Transmission electron microscopy (TEM)
Transmission electron microscope (TEM) is a kind of electron beam as a light source, which projects the accelerated and aggregated electron beam onto a very thin sample (usually made with ultra-thin microer). The incident electrons collide with the atoms in the sample material and change direction, resulting in three-dimensional Angle scattering.
The size of the scattering Angle is correlated with the density and thickness of the sample, so the images with different light and shade can be formed. The images will be displayed on the imaging devices (such as fluorescent screen, film, and photosensitive coupling components) after amplification and focusing. Namely, the TEM images. TEM is used to analyze the size and the overall distribution of particles in the sample.
Transmission electron microscope diagram of ternary lithium battery material
Structural analysis
(1) X-ray diffraction analysis
X-ray diffraction (XRD) is commonly used to qualitatively or quantitatively analyze the crystal structure, crystal cell parameters, phase content and internal stress of materials. The idea is to bomb the metal palladium with a high-energy electron beam to produce X-rays or because it has characteristic X-rays at specific wavelengths corresponding to the elements in the palladium.
Later, characteristic X-rays are used to illuminate samples of a certain thickness from different angles, and rays of different wavelengths are generated through the diffraction process, which are collected and displayed on the collector. Finally, the analyzed data can obtain some characteristics of the samples. It is a common method used to determine the crystal structure.
X-ray diffraction analysis map of ternary lithium battery materials
(2) Infrared spectroscopy analysis
Infrared spectroscopy (FT-IR) can reflect the physical process and the characteristics of molecular structure. The infrared absorption spectrum is that the absorption peak is mainly reflected by the vibration form of each molecule and each group.
From the perspective of optical spectroscopy, the one-to-one correspondence between infrared spectrum and structure can further analyze and summarize the characteristic absorption rules of various groups by accumulating a large number of infrared spectrum data of compounds, so as to infer the structure of unknown objects with the help of infrared spectrum.
Infrared spectroscopy (FT-IR) has a very wide range, with a qualitative analysis of the functional groups on the surface of the material, and many materials are characterized by infrared spectroscopy.
Ired spectrum diagram of ternary lithium battery materials
Composition analysis
(1) X-ray photoelectron energy spectrum
X-ray photoelectron spectroscopy (XPS) working principle is that under the irradiation of the sample to be tested and X-rays, the inner electrons or valence electrons of atoms or molecules in the sample are excited and emitted, and the excited electrons are called photoelectrons.
After measuring the energy of the photoelectron, the energy spectrum of the photoelectron is obtained, and the surface atomic information of the sample is obtained. The detection method can not only provide information on the surface structure of chemical molecules and the valence states of atoms, but also provide information on the composition, content, chemical valence states and chemical bonds of elements on the surface of materials.
X-ray photoelectron energy spectrum of ternary lithium battery material
(2) X-ray energy dispersion spectrum (EDS)
X-ray Energy Dispersive Spectrometer (EDS) is used to analyze the type and content of the microcomponent elements of the material, with the use of scanning electron microscopy and transmission electron microscopy.
In the vacuum chamber, the surface of the sample is bombarded with electron beams to stimulate the material to emit characteristic X-rays. According to the wavelength of characteristic X-rays, the material elements above Be in the periodic table are qualitatively and semi-quantitatively analyzed.
The EDS map of the ternary lithium battery materials
Inductively coupled plasma emission spectrum is a method to determine the composition and content of elements in a sample based on the wavelength and intensity of the characteristic spectrum emitted by the gaseous atoms or ions in the matter to be tested.
When the valence electron in the atom is bombarded by the external energy, the excited state, and then returns to the lower energy state or the ground state, the excitation energy is released in the form of radiation to produce the spectral line.
The wavelength of each emitted spectral line depends on the difference between the two energy levels before and after the transition. The atoms of specific elements can produce a series of characteristic spectral lines of different wavelengths, which are arranged in a certain order and maintain a certain intensity ratio. The samples were analyzed qualitatively according to the spectral wavelength and quantitatively by the intensity of emitted light.
Relationship between spectral line intensity and concentration:
I is the intensity of the emission characteristic line; C is the concentration of the measured element; a is a constant, related to the sample composition, morphology and determination conditions; b is the self-absorption coefficient, in most cases in the ICP light source b 1.
Physical properties
(1) Synchronous heat analysis
Differential thermal-thermal weight analysis (TG-DSC) is also called synchronous thermal analysis, is the thermal weight analysis and differential scanning calorimetry.
In the same test using the same sample can synchronize the mass change and heat absorption related information, can be used to study the material weight ratio, weight loss temperature, decomposition residue, glass transition, phase transition, reaction temperature and heat enthalpy, determine the purity of the substance, study the compatibility of each component of the mixture, etc.
The TG-DSC plot of the ternary lithium battery material
(2) Particle analysis
Particle analysis is an analytical method used to measure the particle size. Laser particle size analyzer is usually used for testing and analysis. Its working principle is to measure the scattering spectrum of the particle group of the laser by analyzing the size and distribution of the particle size.
In the case of laser beam irradiation, the diameter of the measured particles is inversely proportional to the angle of the scattered light, and the intensity of the scattered light decreases regularly with the increase of the scattered light angle. After the laser emitted by the laser is amplified, filtered and converged to the sample area of the particle group, the particle group of different sizes will produce the scattering spectrum under the laser irradiation of the laser.
The spatial distribution and intensity of the scattering spectrum are related to the distribution and size of the measured particle group. After the scattering spectrum is received by the photodetector array, it is converted into an electrical signal, and sent to the computer after amplification and A / D conversion for data processing, that is, the information parameters such as the distribution and size of the particles to be measured are obtained.
Graph of the particle size distribution
(3) Specific surface area and pore size (BET)
The BET specific surface test is mainly used to test the specific surface area of the material. The principle is that at a certain test temperature, the amount of gas adsorbed by the solid sample is proportional to the mass of the solid sample, and has a close relationship with the gas pressure and the types of solid and gas.
In the case of certain gas type, gas pressure and temperature, the amount of adsorption gas in the solid sample depends on the distribution of the internal and external pores of the sample material, so determine the adsorption isotherm of the sample at a certain temperature:
n=f (P)T
In formula: n——The amount of gas absorbed by the sample;
P——gas pressure;
T——test temperature.
According to the formula, the specific surface area of the material can be obtained, so as to further understand the distribution information of the internal and external pores of the material.
N2 absorption curve and aperture distribution of ternary lithium battery material
(4) Conductivity
The conductivity of lithium iron phosphate battery material is usually determined by the four-probe method. The specific method is as follows: the material to be measured is made into cylindrical sheets (φ 10 mm, h 2mm) under a certain pressure, and then sintering under 800 degrees under inert atmosphere protection for 8 h.
You need to ensure that no powder is glued off when the probe contacts and does not break while moving. The electrical conductivity is calculated by the following formula:
σ=4L/πRd^2
In formula: L——The thickness of the sample;
d——Is the diameter of the sample;
R——Is the electrical resistance of the sample.
The electrochemical properties
(1) Constant current charge and discharge performance
Constant charging current and discharge test is the most important and direct method to detect the electrochemical performance of materials. Constant current charge and discharge test is commonly used to analyze the charge-to-discharge specific capacity and cycling performance of electrode materials at different rates. The specific capacity of the electrode material is calculated as follows:
Actual weight-specific capacity: C =I *T/W（m Ah/g）
In formula: M—the molecular weight of the electrode material;
I——Constant charge and discharge current (mA);
T——Time of charge and discharge (h);
W——The mass of the active material in the electrode material (the carbon layer is also considered active in the presence of carbon coating).
Diagaph of constant current charge and discharge performance of ternary lithium battery materialsStep ratio and cycle performance diagram of ternary lithium battery material
(2) Cyclic voltammetry test
Cyclic voltammetry uses a constant potential rate to scan from the start potential, change the direction of the scanning potential, sweep back to the start potential at the same rate, record the current change of the electrode, obtain the i-E curve, it can be used to judge the mass transfer thermodynamics and dynamics of the electrode electrochemical reaction, such as the reaction mechanism of the electrode, the reversibility of the electrode reaction, the electrochemical reactivity, etc.
The cyclic voltammetric curve of ternary lithium battery materials
(3) AC-level impedance test
Electrochemical Impedance Spectroscopy, the basic principle is to analyze a small and specific amplitude of the detected system, and to analyze the dynamics of the electrode process through the relationship between the corresponding response signal and the disturbance signal.
Since the alternating signal with small values basically does not interfere with the state of the detected system, the AC impedance method is used by many researchers to accurately detect the connection between the dynamic parameters of the electrode process and the electrode state.
Compared with other cyclic voltammetric tests, the AC impedance test method unique adopts the analysis method of the electrode impedance spectrum and equivalent circuit, and it is easier to obtain various parameters between the electrode interface and the dynamics of the electrode process, such as the transmission resistance of the charge interface and the diffusion coefficient of lithium ions.
The AC impedance spectrum of ternary lithium battery materials
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Key points of the ternary lithium battery material test
The performance of the material determines the use of the material, and also determines the performance and quality of the product. For the development of lithium battery technology, the research of materials cannot be separated from the testing of materials. What test items and test points are needed for ternary lithium battery materials? Let’s take a look together.
Lithium-ion battery has developed rapidly in recent years. With its high energy density, good multiplier performance and cycle performance, it has become the main power source of electric vehicles, occupying a very important place in new energy, and also put forward a new development path for global energy and environmental problems.
Nickel cobalt manganese oxide ternary lithium battery (LiNixCoyMnzO2) cathode material is one of the cathode materials with the highest energy density under development, with significant performance advantages, and is one of the most important development directions of vehicle power battery cathode materials in the future.
What is the material of ternary lithium battery?
Ternary lithium battery usually refers to lithium nickel cobalt manganese oxide (LiNixCoyMnzO2) or lithium nickel cobalt aluminate as the cathode material, nickel cobalt manganese ternary cathode material combined with the characteristics of LiNiO2, LiCoO2, LiMn2O4.
Compared with lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate and lithium nickel manganese oxide and other materials have the advantages of high energy density, good cycle stability, low cost and so on, currently has emerged in the application of new energy vehicle power battery, is considered to be one of the most promising cathode materials in the future.
Ternary lithium battery material test project
The performance of the material determines the use of the material, and also determines the performance and quality of the product. The research of materials cannot be separated from the testing of materials. What test items and testing instruments are needed for ternary lithium battery materials?
Formal representation
Structural analysis
Complexity analysis
Physical property
Electrochemical properties
Specific test method of the materials
Formal representation
(1) Scanning electron microscopy (SEM)
Scanning electron microscope (SEM) as a commonly used imable electron microscope, is commonly used to study the microorganization, morphology and composition of materials. It works based on the interaction between the electrons and the matter under test.
High-energy electron beam bombardment material sample surface, the sample surface will produce back scattering electrons, secondary electrons, electronic, visible fluorescence, X-ray and continuous X-ray, transmission electrons and in visible, ultraviolet, infrared light area of electromagnetic radiation, etc., through these signals, can obtain the microscopic organization, morphology, chemical composition, crystal structure and internal electric field or magnetic field information.
The scanning electron microscope delivers these detected signals to the display tube, which displays the SEM images in the screen. SEM combined with an X-ray spectrometer (EDS) can also analyze the chemical composition of the sample.
(2) Transmission electron microscopy (TEM)
Transmission electron microscope (TEM) is a kind of electron beam as a light source, which projects the accelerated and aggregated electron beam onto a very thin sample (usually made with ultra-thin microer). The incident electrons collide with the atoms in the sample material and change direction, resulting in three-dimensional Angle scattering.
The size of the scattering Angle is correlated with the density and thickness of the sample, so the images with different light and shade can be formed. The images will be displayed on the imaging devices (such as fluorescent screen, film, and photosensitive coupling components) after amplification and focusing. Namely, the TEM images. TEM is used to analyze the size and the overall distribution of particles in the sample.
Structural analysis
(1) X-ray diffraction analysis
X-ray diffraction (XRD) is commonly used to qualitatively or quantitatively analyze the crystal structure, crystal cell parameters, phase content and internal stress of materials. The idea is to bomb the metal palladium with a high-energy electron beam to produce X-rays or because it has characteristic X-rays at specific wavelengths corresponding to the elements in the palladium.
Later, characteristic X-rays are used to illuminate samples of a certain thickness from different angles, and rays of different wavelengths are generated through the diffraction process, which are collected and displayed on the collector. Finally, the analyzed data can obtain some characteristics of the samples. It is a common method used to determine the crystal structure.
(2) Infrared spectroscopy analysis
Infrared spectroscopy (FT-IR) can reflect the physical process and the characteristics of molecular structure. The infrared absorption spectrum is that the absorption peak is mainly reflected by the vibration form of each molecule and each group.
From the perspective of optical spectroscopy, the one-to-one correspondence between infrared spectrum and structure can further analyze and summarize the characteristic absorption rules of various groups by accumulating a large number of infrared spectrum data of compounds, so as to infer the structure of unknown objects with the help of infrared spectrum.
Infrared spectroscopy (FT-IR) has a very wide range, with a qualitative analysis of the functional groups on the surface of the material, and many materials are characterized by infrared spectroscopy.
Composition analysis
(1) X-ray photoelectron energy spectrum
X-ray photoelectron spectroscopy (XPS) working principle is that under the irradiation of the sample to be tested and X-rays, the inner electrons or valence electrons of atoms or molecules in the sample are excited and emitted, and the excited electrons are called photoelectrons.
After measuring the energy of the photoelectron, the energy spectrum of the photoelectron is obtained, and the surface atomic information of the sample is obtained. The detection method can not only provide information on the surface structure of chemical molecules and the valence states of atoms, but also provide information on the composition, content, chemical valence states and chemical bonds of elements on the surface of materials.
(2) X-ray energy dispersion spectrum (EDS)
X-ray Energy Dispersive Spectrometer (EDS) is used to analyze the type and content of the microcomponent elements of the material, with the use of scanning electron microscopy and transmission electron microscopy.
In the vacuum chamber, the surface of the sample is bombarded with electron beams to stimulate the material to emit characteristic X-rays. According to the wavelength of characteristic X-rays, the material elements above Be in the periodic table are qualitatively and semi-quantitatively analyzed.
(3) Inductively coupled plasma emission spectrum (ICP)
Inductively coupled plasma emission spectrum is a method to determine the composition and content of elements in a sample based on the wavelength and intensity of the characteristic spectrum emitted by the gaseous atoms or ions in the matter to be tested.
When the valence electron in the atom is bombarded by the external energy, the excited state, and then returns to the lower energy state or the ground state, the excitation energy is released in the form of radiation to produce the spectral line.
The wavelength of each emitted spectral line depends on the difference between the two energy levels before and after the transition. The atoms of specific elements can produce a series of characteristic spectral lines of different wavelengths, which are arranged in a certain order and maintain a certain intensity ratio. The samples were analyzed qualitatively according to the spectral wavelength and quantitatively by the intensity of emitted light.
Relationship between spectral line intensity and concentration:
I is the intensity of the emission characteristic line; C is the concentration of the measured element; a is a constant, related to the sample composition, morphology and determination conditions; b is the self-absorption coefficient, in most cases in the ICP light source b 1.
Physical properties
(1) Synchronous heat analysis
Differential thermal-thermal weight analysis (TG-DSC) is also called synchronous thermal analysis, is the thermal weight analysis and differential scanning calorimetry.
In the same test using the same sample can synchronize the mass change and heat absorption related information, can be used to study the material weight ratio, weight loss temperature, decomposition residue, glass transition, phase transition, reaction temperature and heat enthalpy, determine the purity of the substance, study the compatibility of each component of the mixture, etc.
(2) Particle analysis
Particle analysis is an analytical method used to measure the particle size. Laser particle size analyzer is usually used for testing and analysis. Its working principle is to measure the scattering spectrum of the particle group of the laser by analyzing the size and distribution of the particle size.
In the case of laser beam irradiation, the diameter of the measured particles is inversely proportional to the angle of the scattered light, and the intensity of the scattered light decreases regularly with the increase of the scattered light angle. After the laser emitted by the laser is amplified, filtered and converged to the sample area of the particle group, the particle group of different sizes will produce the scattering spectrum under the laser irradiation of the laser.
The spatial distribution and intensity of the scattering spectrum are related to the distribution and size of the measured particle group. After the scattering spectrum is received by the photodetector array, it is converted into an electrical signal, and sent to the computer after amplification and A / D conversion for data processing, that is, the information parameters such as the distribution and size of the particles to be measured are obtained.
(3) Specific surface area and pore size (BET)
The BET specific surface test is mainly used to test the specific surface area of the material. The principle is that at a certain test temperature, the amount of gas adsorbed by the solid sample is proportional to the mass of the solid sample, and has a close relationship with the gas pressure and the types of solid and gas.
In the case of certain gas type, gas pressure and temperature, the amount of adsorption gas in the solid sample depends on the distribution of the internal and external pores of the sample material, so determine the adsorption isotherm of the sample at a certain temperature:
n=f (P)T
In formula: n——The amount of gas absorbed by the sample;
P——gas pressure;
T——test temperature.
According to the formula, the specific surface area of the material can be obtained, so as to further understand the distribution information of the internal and external pores of the material.
(4) Conductivity
The conductivity of lithium iron phosphate battery material is usually determined by the four-probe method. The specific method is as follows: the material to be measured is made into cylindrical sheets (φ 10 mm, h 2mm) under a certain pressure, and then sintering under 800 degrees under inert atmosphere protection for 8 h.
You need to ensure that no powder is glued off when the probe contacts and does not break while moving. The electrical conductivity is calculated by the following formula:
σ=4L/πRd^2
In formula: L——The thickness of the sample;
d——Is the diameter of the sample;
R——Is the electrical resistance of the sample.
The electrochemical properties
(1) Constant current charge and discharge performance
Constant charging current and discharge test is the most important and direct method to detect the electrochemical performance of materials. Constant current charge and discharge test is commonly used to analyze the charge-to-discharge specific capacity and cycling performance of electrode materials at different rates. The specific capacity of the electrode material is calculated as follows:
Theoretical weight-specific capacity: C0= 26.8*1000 / M（mAh/g）
Actual weight-specific capacity: C =I *T/W（m Ah/g）
In formula: M—the molecular weight of the electrode material;
I——Constant charge and discharge current (mA);
T——Time of charge and discharge (h);
W——The mass of the active material in the electrode material (the carbon layer is also considered active in the presence of carbon coating).
(2) Cyclic voltammetry test
Cyclic voltammetry uses a constant potential rate to scan from the start potential, change the direction of the scanning potential, sweep back to the start potential at the same rate, record the current change of the electrode, obtain the i-E curve, it can be used to judge the mass transfer thermodynamics and dynamics of the electrode electrochemical reaction, such as the reaction mechanism of the electrode, the reversibility of the electrode reaction, the electrochemical reactivity, etc.
(3) AC-level impedance test
Electrochemical Impedance Spectroscopy, the basic principle is to analyze a small and specific amplitude of the detected system, and to analyze the dynamics of the electrode process through the relationship between the corresponding response signal and the disturbance signal.
Since the alternating signal with small values basically does not interfere with the state of the detected system, the AC impedance method is used by many researchers to accurately detect the connection between the dynamic parameters of the electrode process and the electrode state.
Compared with other cyclic voltammetric tests, the AC impedance test method unique adopts the analysis method of the electrode impedance spectrum and equivalent circuit, and it is easier to obtain various parameters between the electrode interface and the dynamics of the electrode process, such as the transmission resistance of the charge interface and the diffusion coefficient of lithium ions.