Structural and Chemical Characterization of Li-Ion Batteries

Lithium ion batteries have improved rapidly in the last 10 years to become the main power source in portable electronics, telecommunications, and large capacity applications such as in electric vehicles (EV). Ongoing improvements in characterization techniques must also meet industry, regulatory and consumer needs as battery manufacturers and end-users demand higher battery efficiencies, lower cost, and most importantly, safety. At Evans Analytical Group (EAG, Inc.), we provide a suite of techniques suitable for both the structural and chemical analysis of Li-ion batteries. Both scanning and transmission electron microscopy (SEM and TEM) are used to provide the thickness and microstructure of the various layers in the battery. Ion milling techniques are used to preserve the integrity of the sample to assure an accurate representation of the original state of the battery materials. This is essential in order to properly understand process development or battery failures. TEM combined with X-Ray Diffraction (XRD) can also be used to analyze the phase transformations associated with the diffusion of Li-ions. Additionally, the thickness of the thin SEI layer caused by electrode-electrolyte interfacial reactions can only be visualized by TEM. Degradation mechanisms of the battery materials can be analyzed with surface analysis techniques such as X-ray photoelectron spectroscopy (XPS) to detect chemical state information and gas chromatography (GCMS) techniques to detect volatile components that can lead to swelling of the battery. These techniques along with Raman and infrared spectroscopy (FTIR), and Glow Discharge Mass Spectrometry (GDMS) can detect the organic and inorganic species present in the battery, including any impurities that may be present. GDMS is commonly used for purity certification of cathode materials such as LiCoO 2 , LiFePO 4 , and LiCoMnNiO x . Inductively coupled optical emission techniques (ICP-OES) can be used to determine the Li/metal ratio to within a 1% uncertainty, which is essential for tuning the cycling stability of Li-ion batteries. In this presentation we will demonstrate the multi-disciplinary approach of using these various techniques and the importance of proper sample preparation for accurate analyses of Li-ion batteries. This approach enhances the value of the information obtained and can accelerate product development.