Battery Materials

Lithium-ion batteries present special analytical challenges in the quest to improve quality, safety, and lifespan of products developed in this fast-growing battery chemistry. The basic structure of Lithium-ion batteries (LIB) consists of as many as 10 different thin films that are synthesized to form at least that many solid−solid interfaces. These interfaces are thin layers of cathode materials, insulating barriers, anode materials, metal current collectors, and electrolyte - in the form of powders, sheets, and fluids. All these varied components require assessment before and after assembly and after repeated charge/discharge operations.

Another challenge in developing LiB materials is that they can react with and degrade upon exposure to air. JEOL has developed an air-isolated workflow solution to prevent exposure to atmosphere during imaging and analysis, from sample preparation to introduction into the electron microscope. The JEOL air-isolated transfer vessel is compatible with the JEOL SEM, TEM, EPMA, Auger, Broad Ion Beam Cross Section Polisher, and FIB-SEM.

Examining cross sections in the SEM provides essential information about the crystal structure, layer or film thicknesses, existence of voids or cracks and other properties that might impact battery materials performance and reliability. To create pristine, artifact-free cross sections without crumbling, smearing, or distorting the sample, JEOL has the ideal solution in its Cross Section Polisher, a broad ion beam milling system with LN2 cooling. Air-sensitive samples can be loaded into the JEOL CP using the air-isolation transfer vessel.

Focused Ion Beam sample preparation with the JEOL dual beam FIB-SEM allows for site-specific observation and milling prior to air-isolated transfer to the TEM. The JEOL FIB-SEM offers the cutting edge in preparing samples for the Transmission Electron Microscope.

Scanning Electron Microscopes (SEM) support the development of new LIB technologies with morphological observation at the micrometer to nanometer scale, as well as the chemical analysis needed to create high-performance coatings and powders. Ultra-low voltage imaging combined with signal filtering in the SEM allows direct imaging and analysis of battery constituents (anode and cathode) with nanometer resolution. Additionally, one of the important aspects of the analysis is the ability to probe chemistry of the constituents at nm scale.

JEOL Field Emission SEMs perform microanalysis with energy dispersive spectroscopy (EDS) at extremely low voltages to pinpoint localized makeup of the specimens and, in particular, low atomic number materials such as carbon and fluorine. The Gather-X Windowless EDS has higher sensitivity and low-energy X-Ray detection for lithium. The JEOL Soft X-ray spectrometer (SXES) delivers high spectral resolution (0.3eV) which allows for the Nitrogen Kα and Titanium Lℓ line to be resolved with a separation of only 1.78eV. It has ultra-low energy, low-concentration sensitivity with the capability to detect Li even at low single digit weight percent concentration.

Transmission Electron Microscopes (TEM) provide unique details about battery materials down to the atomic scale. Scanning/Transmission Electron Microscopes (S/TEM) provide site-specific data are sensitive to chemical species, electronic structure, oxide state, and intercalculation in LiB materials. Using S/TEM one can directly image pure Lithium and pure Oxygen columns in a pristine state, characterize the material before it undergoes cycling or baseline characterization, and also characterize cycled materials.

To prevent electron beam damage of these sensitive battery materials, JEOL S/TEM imaging techniques such as Optimum Bright Field (OBF) STEM imaging and Electrostatic Dose Modulation are used. The use of novel detectors and detection methods, real-time dose control, and chemical spectroscopy enhance the efficiency and applicability of STEM characterization to battery materials.