Electronic enthusiasts provide you with ultra-comprehensive
characterization techniques and classic application examples of lithium battery
materials. In the development process of lithium-ion batteries, we hope to
obtain a large amount of useful information to help us conduct data analysis on
materials and devices to understand their various aspects. aspects of
performance. At present, the commonly used research methods for lithium-ion
battery materials and devices mainly include characterization methods and
electrochemical measurements.
In the development process of lithium-ion batteries, we hope to obtain a
large amount of useful information to help us analyze data on materials and
devices to understand their various aspects of performance. At present, the
commonly used research methods for lithium-ion battery materials and devices
mainly include characterization methods and electrochemical measurements.
The electrochemical test is mainly divided into three parts: (1) charge and
discharge test, which mainly looks at the battery's charge and discharge
performance and rate; (2) cyclic voltammetry, which mainly looks at the
battery's charge and discharge reversibility, peak current, and peak value. bit;
(3) EIS AC impedance, looking at the resistance and polarization of the battery,
etc.
The following is a brief introduction to the characterization methods used
in comprehensive research on lithium batteries, which are roughly divided into
eight parts: composition characterization, morphology characterization, crystal
structure characterization, material functional group characterization,
observation of material ion transport, and material micromechanics Properties,
material surface work functions and other experimental techniques.
1. Ingredient characterization
(1) Inductively coupled plasma (ICp)
Used to analyze the constituent elements of matter and the content of
various elements. ICp-AES can well meet the needs of routine analysis of
primary, secondary and trace elements in laboratories. Compared with ICp-AES,
ICp-MS is a newly developed technology in recent years. The instrument is more
expensive and the detection limit is lower. Mainly used for trace/ultra-trace
analysis.
When Aurbac et al. studied the interface problem between the cathode
material and the electrolyte, they used ICp to study the solubility of LiCOO2
and LiFepO4 in the electrolyte. By changing parameters such as temperature and
the type of lithium salt in the electrolyte, ICp is used to measure the changes
in the Co and Fe content in the electrolyte when the parameters are changed,
thereby finding the key to reducing the dissolution of the cathode material in
the electrolyte. It is worth noting that if the element content is high (for
example, higher than 20%), the error will be large when using ICp detection, and
other methods should be used in this case.
(2) Secondary ion mass spectrometry (SIMS)
The sample composition is characterized by emitting hot electrons to ionize
argon or oxygen plasma to bombard the surface of the sample, and detect the
charged ions or ion clusters overflowing from the sample surface. It can image
the isotope distribution and characterize the sample composition; detect the
longitudinal distribution of the sample composition.
Ota et al. used TOFSIMS technology to study the components of the SEI film
formed on the surfaces of the graphite negative electrode and LiCOO2 positive
electrode after vinyl sulfite was added as an additive to the standard
electrolyte. Castle et al. used SIMS to detect the distribution of Li+ from the
electrode surface to the interior of V2O5 after lithium insertion to study the
diffusion process of Li+ in V2O5.
(3) X-ray photon spectrum (XpS)
It was gradually developed and improved in the 1950s and 1960s by Professor
KaiSiegbahn and his group from the Institute of Physics of Uppsala University in
Sweden. X-ray photoelectron spectroscopy can not only measure the constituent
elements on the surface, but also provide information on the chemical state of
each element. It has high energy resolution, a certain spatial resolution
(currently at the micron scale), and a time resolution (minute level). .
It is used to measure the constituent elements of the surface and give
information on the chemical state of each element.
Hu Yongsheng et al. used XPS to study the composition of SEI generated by
VEC on the graphite surface under high voltage. It is mainly composed of C, O,
and Li. Combined with FTIR, it was found that the main component is alkoxy
lithium salt.
(4) Electron energy loss spectrum (EELS)
By utilizing the energy lost by inelastic scattering such as electron
excitation and ionization on the surface of the material caused by incident
electrons, the composition of the element can be obtained by analyzing the
location of the energy loss. EELS has a better resolution effect on light
elements than EDX. The energy resolution is 1 to 2 orders of magnitude higher.
Due to the transmission electron microscope technology, the spatial resolution
can also reach the order of 10*10m. It can also be used for Test the film
thickness and have a certain time resolution. By fitting the EELS spectrum with
density functional function (DFT), we can further obtain accurate information on
the valence states and even electronic states of elements.
AI. Sharab et al. used STEMEELS combined technology to study the chemical
element distribution, structural distribution and valence state distribution of
iron fluoride and carbon nanocomposites under different charge and discharge
states when studying nanocomposite electrode materials of iron fluoride and
carbon.
(5) Scanning transmission X-ray microscopy (STXM)
New spectroscopy microscopy technology based on the third generation
synchrotron radiation light source, high-power laboratory X-ray source, and
X-ray focusing technology. Using the principle of transmission X-ray absorption
imaging, STXM can achieve three-dimensional imaging with high spatial resolution
of tens of nanometers, while also providing certain chemical information. STXM
can achieve non-destructive three-dimensional imaging, which can provide key
information for understanding complex electrode materials, solid electrolyte
materials, separator materials, electrodes and batteries, and these technologies
can realize in-situ testing functions.
Sun et al. studied that carbon-coated Li4TI5O12 has better rate performance
and cycle performance than before without coating. The author used STXMXANES and
high-resolution TEM to determine that the amorphous carbon layer was uniformly
coated on the surface of LTO particles, with a coating thickness of
approximately 5nm. Among them, the author obtained the C, TI, and O distribution
of a single LTO particle through STXM, in which C is coated on the particle
surface.
(6) X-ray absorption near-edge spectrum (XANES)
It is a technology for calibrating elements and their valence states. The
same element in the same valence state in different compounds has high
absorption of X-rays of specific energy, which we call near-edge absorption
spectrum. In the field of lithium batteries, XAS is mainly used for charge
transfer research, such as the price change problem of transition metals in
cathode materials.
Kobayashi et al. used XANES to study LiNi0.80Co0.15Al0.05O2 cathode
material. XANES detected Li2Co3 and other additional cubic phase impurities on
the particle surface.
(7) X-ray fluorescence spectrometry (XRF)
A method that uses primary X-ray photons or other microscopic ions to
excite atoms in the substance to be measured, causing them to produce
fluorescence (secondary X-rays) to analyze material components and study
chemical states. According to different excitation, dispersion and detection
methods, it is divided into X-ray spectroscopy (wavelength dispersion) and X-ray
energy spectroscopy (energy dispersion). According to different dispersion
modes, X-ray fluorescence analyzers are divided into X-ray fluorescence
spectrometers (wavelength dispersion) and X-ray fluorescence spectrometers
(energy dispersion). XRF is widely used in the industry to analyze the main
components and impurity elements of lithium-ion battery materials. The detection
limit for some elements can reach the order of 10-9.
2. Morphological characterization
(1) Scanning electron microscope (SEM)
Collect secondary electron information on the surface of the sample to
reflect the surface morphology and roughness of the sample. SEM with EDS
accessories can further analyze element types, distribution and
semi-quantitative analysis of element content. Although the resolution of SEM is
much smaller than that of TEM, it is still the most basic tool for
characterizing the particle size and surface morphology of battery
materials.
Based on the use of sealed transfer boxes to transfer samples, Li Wenjun et
al. redesigned the sample holder for scanning electron microscopy of metallic
lithium electrodes, and studied the formation process of surface pores and
dendrites during the intercalation and extraction of Li from metallic lithium
electrodes.
(2) Transmission electron microscope (TEM)
The morphology and characteristics of the surface and interface of
materials are often introduced in the literature on surface coating and surface
SEI. TEM can also be equipped with energy spectrum accessories to analyze the
type and distribution of elements. Compared with SEM, TEM can observe smaller
particles, and high-resolution transmission electron microscopy can observe the
crystal lattice. The function of in-situ TEM is more powerful. In-situ cells are
assembled in the TEM electron microscope cavity, and at the same time, with the
help of TEM's high Resolution characteristics, real-time measurement and
analysis of the morphology and structural evolution of battery materials during
cycling
Huang Jianyu et al. used an in-situ sample rod to conduct in-situ
characterization of the morphology and structural evolution of SnO2 during the
process of inserting and desorbing lithium in ionic liquids. Subsequently, they
improved the device for the TEM in-situ battery experiment and used lithium
oxide naturally produced on metal Li as the electrolyte to replace the
originally used ionic liquid, which improved the stability of the experiment and
better protected the electron microscope cavity. body.
Extended reading: Academic dry stuff│The role of in-situ transmission
electron microscopy in the study of gas-liquid phase chemical reactions of
materials
(3) Atomic force microscope (AFM)
The observation of nanoscale flat surfaces is often used in the
characterization of carbon materials.
3. Crystal structure characterization
(1) X-ray diffraction technology (XRD)
Through XRD, the crystal structure, crystallinity, stress, crystal
orientation, superstructure and other information of the material can be
obtained. It can also reflect the average crystal structure properties of the
bulk material and the average unit cell structure parameter changes. After
fitting, the atomic occupancy can be obtained information
Thurston et al. applied in-situ XRD technology to lithium-ion batteries for
the first time. By using hard X-rays from synchrotron radiation sources to
detect bulk electrode materials in in-situ battery devices, the results of
lattice expansion and contraction, phase changes, and multiphase formation can
be intuitively observed.
(2) Extended X-ray absorption fine spectroscopy (EXAFS)
A technology that reflects the differences and changes in the local
structure of the material by absorbing some incident photons of specific energy
through the interaction between X-rays and the sample's electrons. It has
certain energy and time resolution capabilities and mainly obtains the radial
distribution, bond length, and Information such as degree of order and
coordination number; a strong light source from a synchrotron radiation source
is usually required to implement EXAFS experiments.
Jung et al. used EXAFS analysis to study the electrochemical properties of
carbon nanofibers embedded with SnOx/CuOx. They showed that the carbon
nanofibers embedded with SnOx/CuOx have a disordered structure, forming a
special distribution of SnOx particles, resulting in electrochemical Chemical
properties have been improved.
(3) Neutron diffraction (ND)
When there are larger atoms in the lithium-ion battery material, it will be
difficult for X-rays to accurately detect the lithium ion occupation. Neutrons
are sensitive to lithium in lithium-ion battery materials, so neutron
diffraction plays an important role in the research of lithium-ion battery
materials.
Arbi et al. determined the Li+ occupancy in the lithium-ion battery solid
electrolyte material LATp through neutron diffraction.
(4) Nuclear Magnetic Resonance (NMR)
NMR has high energy resolution and spatial resolution, and can detect
chemical information in materials and image them, detect dendrite reactions,
measure lithium ion self-diffusion coefficients, and study phase transition
reactions inside particles.
Gray et al. have conducted a large amount of research work on NMR in
lithium-ion battery cathode materials. It shows that rich chemical information
and local charge order and disorder information can be obtained from the NMR
spectrum of the cathode material, and paramagnetic or metallic materials can be
detected, and the weak changes in the electronic structure caused by doping can
also be detected to reflect Element chemical state information. In addition,
combined with isotope tracing, side reactions in the battery can also be
studied.
(5) Spherical aberration correction scanning transmission electron
microscope (STEM)
Purpose: Used to observe the arrangement of atoms, atomic-level real-space
imaging, and clearly see the crystal lattice and atomic occupancy; has high
requirements on samples; can realize in-situ experiments
Oshima et al. used a spherical aberration-corrected scanning transmission
microscope (ABF-STEM) with annular brightfield imaging to observe the atomic
arrangement of Li, V, and O in Li2VO4 in real space.
(6)Raman
In the early days, Raman spectroscopy was used to study the crystal
structure of LiCOO2. There are two Raman active modes in LiCOO2, the peak of CoO
stretching vibration Alg and the peak of OCoO bending vibration Eg. It is also
often used to characterize the degree of graphitization of carbon materials in
lithium-ion batteries.
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