NCA Ternary Cathode Material Testing

NCA ternary material inspection mainly conducts scientific testing and analysis on the chemical composition and stoichiometric ratio, crystal structure and phase purity, particle morphology and particle size distribution, specific surface area and tap density, lithium content and residual alkali content, and metal foreign matters and magnetic substances, objectively assessing the product quality grade and issuing a detailed test report, providing a basis for manufacturers' quality control and downstream users' product acceptance.

Testing Items

Chemical composition and stoichiometric ratio: The core testing item, aiming to precisely determine the contents of the three elements nickel (Ni), cobalt (Co) and aluminium (Al) in the material and their molar ratios (such as NCM811 and NCA90). Through the analysis of the accuracy and consistency of the stoichiometric ratios, the batch stability of the material is evaluated, ensuring that it meets the theoretical basis of the designed electrochemical properties.

Crystal structure and phase purity: Using the means such as the X-ray diffraction (XRD), whether the material forms the complete layered α-NaFeO2 structure (R-3m space group) is analysed, and whether the impurity phases (such as the Li2CO3, LiOH, NiO and rock salt phases) exist is detected. The order degree of the structure directly affects the smoothness of the lithium ion diffusion channels.

Particle morphology and particle size distribution: Through the scanning electron microscopy (SEM) and laser particle size analysers, the sphericity and surface smoothness of the secondary particles and the sizes of the primary particles are observed. At the same time, the particle size distribution parameters such as the D10, D50 and D90 are precisely measured, which directly affects the coating uniformity and compaction density of the electrode sheets.

Specific surface area and tap density: The specific surface area of the material is determined with the specific surface area analysers (BET method). The excessively high specific surface area will intensify the side reactions with the electrolytes. The tap density reflects the packing properties of the material particles and is the important physical indicator of evaluating the energy density potential.

Lithium content and residual alkali content: The total lithium content is precisely determined, ensuring the sufficient lithium sources. At the same time, the residual alkali contents on the material surfaces, mainly the Li2CO3 and LiOH, are quantitatively analysed. These residues will consume the electrolytes and generate the gases, and are the key factors causing the battery swelling and cycle performance deterioration.

Metal foreign matters and magnetic substances: The methods such as the magnetic substance testers and ICP-MS are adopted to strictly control the contents of the magnetic and non-magnetic metal foreign matters such as the iron (Fe), zinc (Zn) and copper (Cu) in the material, to prevent the micro short circuits inside the battery and the serious safety hazards.

Testing Scope

Raw material testing: Covering the chemical compositions, morphologies, particle sizes and impurity contents of the precursors (such as the nickel-cobalt-aluminium hydroxides or carbonates); as well as the purity, main contents and impurity elements (such as Na, K, Ca and Mg) of the lithium sources (such as the lithium carbonate and lithium hydroxide).

Process sample testing: At the key process nodes such as the high-temperature solid-phase sintering, crushing, classification, coating, washing and drying, the samples are taken for the semi-finished product testing, monitoring the crystal structure development, element distribution uniformity and impurity change trends of the intermediate products, realizing the closed-loop process control.

Finished product ex-factory testing: The full-item inspection is carried out on the final commercial NCA ternary material, ensuring that all the technical indicators (such as the chemical compositions, physical properties and electrochemical properties) meet the product specification sheets and customer agreement requirements. It is the final basis of the quality release.

Reverse analysis of the battery electrode sheets and cells: The positive electrode sheets are disassembled from the failed or cycled batteries, the NCA materials in them are recovered and tested, and the changes of the structures, morphologies and surface chemical states before and after the cycling are analysed, providing the direct evidence for the failure mechanism analysis and material improvement.

Competitive product benchmarking analysis: Through the comprehensive testing and analysis of the NCA materials sold in the market or provided by the other suppliers in the same industry, the technical characteristics in the composition design, micro-structures and property parameters are obtained, providing the references for the research and development and positioning of the own products.

Application-end adaptability testing: According to the specific application scenarios of the downstream battery customers (such as the high-energy-density electric vehicles and high-end consumer electronics), the adaptability and potential risks of the NCA material in the different electrolyte systems, different charge-discharge regimes and different temperatures are evaluated.

Testing Methods

Inductively coupled plasma optical emission spectrometry/mass spectrometry (ICP-OES/MS): This is the standard method of determining the contents of the main elements (Ni, Co, Al and Li) and trace impurity elements (such as Fe, Cu, Zn, Ca and Mg) in the NCA material. It has the characteristics of the high sensitivity, good accuracy and simultaneous analysis of the multiple elements, and is the cornerstone of the chemical composition analysis.

X-ray diffraction analysis method (XRD): The core technology of the qualitative and quantitative phase analysis. Through the Rietveld refinement, the key structural information such as the lattice parameters, unit cell volumes and cation mixing degrees (the proportion of Ni occupying the Li sites) can be precisely obtained.

Scanning/transmission electron microscopy method (SEM/TEM): The SEM is used to observe the overall morphologies, surface states and cross-section structures of the secondary particles; the TEM and high-resolution TEM (HRTEM) are used to observe the lattice fringes, grain boundary structures of the primary particles, as well as the thicknesses and uniformity of the surface coating/modification layers.

Laser diffraction particle size analysis method: The wet or dry dispersion is adopted, and the particle size distribution of the particle groups is measured by using the Mie scattering principle. This method is fast and has the good repeatability, and is the important online or offline testing means of controlling the product batch consistency.

Potentiometric titration method: Specially used to quantitatively determine the residual alkali contents (Li2CO3 and LiOH) on the NCA material surfaces. By precisely controlling the titration endpoint pH values, the contents of the two different alkaline substances can be distinguished and calculated, guiding the optimization of the washing processes.

Thermogravimetric-differential scanning calorimetry method (TG-DSC): Under the programmed temperature control, the mass changes and thermal effects of the material in the air or inert atmospheres are measured. Used to analyse the thermal stability, decomposition temperatures, residual alkali contents (calculated through the CO2 and H2O release amounts) and phase transition processes of the material.

Testing Standards

Domestic Standards:

1. GB/T 20252, Lithium cobalt oxide (cathode material product standard, providing the reference for the similar lithium-ion battery cathode materials)

International Standards:

1. ISO 9277, Determination of the specific surface area of solids by gas adsorption — BET method

2. ISO 13320, Particle size analysis — Laser diffraction methods

Note: The applicable standard can be selected according to the product use and customer trade requirements; standards agreed in the contract take precedence over general standards.

Testing Instruments and Equipment

Inductively coupled plasma optical emission spectrometer/mass spectrometer: As the core equipment of the element analysis, the plasma source temperatures are as high as 6000-10000 K, which can efficiently atomize and ionize the samples. Equipped with the auto samplers and high-resolution dispersion systems, it ensures the precision and efficiency of the trace element detection.

X-ray diffractometer: Usually equipped with the Cu target Kα radiation sources, high-speed detectors (such as the LynxEye) and high-temperature attachments. The modern XRD equipment combined with the refinement software can not only carry out the routine phase analysis, but also deeply analyse the micro defects and stress states of the crystal structures.

High-resolution field emission scanning electron microscope: Equipped with the energy dispersive spectrometers (EDS) and electron backscatter diffraction (EBSD). The FESEM provides the surface morphology images with the high detection efficiency, the EDS is used for the micro-area element composition surface distribution or line scanning analysis, and the EBSD can analyse the crystal orientations.

Specific surface area and porosity analyser: Based on the static volumetric method or dynamic flow method, through the nitrogen adsorption-desorption isotherms, the specific surface area is calculated with the BET model and the pore size distribution is analysed with the BJH model, comprehensively evaluating the surface characteristics of the material.

Automatic potentiometric titrator: Equipped with the precision pH electrodes and automatic liquid addition units, through the preset titration methods (such as setting the different endpoint pH values), the automation and standardization of the residual alkali testing are realized, greatly reducing the manual operation errors and improving the repeatability of the testing results.

Coin cell testing system and electrochemical workstation: Used for the basic electrochemical property evaluation of the material. The NCA material is made into the research electrodes and assembled into the coin half cells, the charge-discharge cycling and rate testing are carried out through the testing systems such as the Land or Arbin, and the dynamic analysis such as the CV and EIS is carried out with the electrochemical workstations.