The main methods and contents of battery material testing

Electrochemical testing of battery materials

Electrochemical testing is one of the main methods to evaluate the performance of battery materials. Electrochemical testing typically includes cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge/discharge tests.

Cyclic voltammetry

Cyclic voltammetry is a very useful electrochemical research method that can be used to study the properties, mechanisms, and kinetic parameters of electrode reactions. It can also be used for the quantitative determination of reactant concentrations, the coverage of adsorbates on electrode surfaces, the electrode's active area, as well as kinetic parameters such as electrode reaction rate constants, exchange current densities, and transfer coefficients.

(1) Determination of electrode reversibility: The voltage scanning process in cyclic voltammetry includes both cathodic and anodic directions. Therefore, from the obtained cyclic voltammogram, the peak heights and symmetry of the oxidation and reduction waves can be used to determine the reversibility of electroactive species reacting on the electrode surface. If the reaction is reversible, the curve is symmetric about the baseline; if the reaction is irreversible, the curve is asymmetric.

(2) Determination of electrode reaction mechanisms: Cyclic voltammetry can also study electrode adsorption phenomena, electrochemical reaction products, electrochemical-chemical coupled reactions, etc., which is very useful for studying the oxidation-reduction mechanisms of organic substances, organometallic compounds, and biomaterials.

Figure 1: Electrochemical test curves

Electrochemical Impedance Spectroscopy

The EIS impedance method is a method of measuring the impedance during an electrochemical reaction. EIS measures the electrical impedance of the electrode material by applying small electrical signals at different frequencies. By analyzing the electrical impedance of the electrode material, the electrochemical reaction kinetics, diffusion coefficient, and interface reaction between the electrode material and the electrolyte can be obtained.

Figure 2:Applications of Electrochemistry in Energy

Galvanostatic charge/discharge tests

The constant current charge and discharge test is one of the standard tests to evaluate the performance of a battery. In this test, the battery is charged and discharged by applying a constant current to evaluate the battery's performance indicators such as capacity and cycle life.

Figure 3:Examples of Galvanostatic Intermittent Titration Technique (GITT)

Chemical analysis of battery materials

Atomic Absorption Spectroscopy (AAS)

Atomic absorption spectroscopy is a method for determining the content of metal elements in battery materials, by analyzing the chemical composition of battery materials, including copper, nickel, lithium, cobalt and other metal elements, to determine their content. Atomic absorption spectroscopy uses the principle that atoms absorb a specific wavelength of light in a beam of light of a specific wavelength, and determines the amount of an element by measuring the intensity of the light being absorbed in a sample.

Figure 4: Schematic diagram of Atomic Absorption Spectroscopy

X-ray diffraction (XRD)

X-ray diffraction is a method for determining the crystal structure of battery materials, which is suitable for analyzing the crystal structure and crystallographic parameters of materials, such as lattice constant, crystal morphology, etc. Battery materials are often composed of multiple crystalline phases, and XRD allows for quick and accurate determination of crystal structure and composition.

Figure 5: Experimental Examples of XRD

Infrared Spectroscopy (IR)

Infrared spectroscopy is a method for the determination of organic compounds in battery materials and can be used to analyze samples such as organic solvents, polymers, gases, etc. In infrared spectroscopy, the absorption spectrum of an organic compound consists of infrared rays of specific wavelengths, and the chemical structure of the sample is determined by measuring the amount of absorption at these wavelengths.

Thermogravimetric Analysis (TGA)

Thermogravimetric analysis is a method for determining the thermal stability and thermogravimetric weight of battery materials, which can be used to analyze the purity and thermal properties of materials. In TGA, the sample is heated at a constant rate of warming, the change in the weight of the sample is proportional to the change in temperature, and the thermal properties of the material can be determined by analyzing the relationship between the mass of the sample and the temperature.

Figure 6: Comparison of TGA Test Results at Atmospheric and Low Pressure

Nuclear Magnetic Resonance (NMR)

NMR is a method for determining the molecular structure and chemical properties of battery materials and can be used to analyze the composition, purity, and structure of materials. In NMR, the sample is exposed to a strong magnetic field, and the chemical structure and composition of the sample are determined by detecting the nuclear spin in the sample.

Figure 7: Experimental Examples of Nuclear Magnetic Resonance Spectroscopy

Mass Spectrometry (MS)

Mass spectrometry analysis of battery materials can be used to determine the molecular weight, molecular structure and chemical composition of various chemical substances in the material, and mass spectrometry analysis can be subdivided into gas chromatography mass spectrometry (GC-MS), liquid chromatography mass spectrometry (LC-MS), time-flight mass spectrometry (TOF-MS), ion degradation mass spectrometry (CID-MS), etc.

Figure 8: liquid-phase product analysis using online