The Solid Electrolyte Interphase (SEI) is a thin layer that forms on the surface of the anode (and to some extent the cathode) in lithium-ion batteries during the first few charge/discharge cycles (especially the first charge). It results from the electrolyte reacting with the electrode at the electrochemical interface. The SEI prevents continuous electrolyte decomposition, effectively “passivating” the electrode. A good SEI is stable and stays intact during cycling, allowing lithium ions to pass but preventing further parasitic reactions. The SEI is crucial because a stable SEI leads to long battery life and good efficiency.
NOVONIX pays considerable attention to SEI formation and stability. Through coulombic efficiency measurements, they gauge how much lithium is consumed in SEI formation (first cycle inefficiency largely goes into SEI). If they try a new electrolyte additive, they’ll look for improvements like higher first-cycle efficiency and better sustained efficiency, indicating a more robust SEI. NOVONIX can use methods like impedance spectroscopy to monitor SEI resistance growth. NOVONIX’s experience would, for example, guide a client on formation cycling (the initial slow charging cycles to form the SEI) – proper formation is key to battery life. NOVONIX’s knowledge and diagnostic tools help tailor the SEI via electrolyte chemistry and formation processes, aiming for an SEI that maximizes battery performance and longevity.
