Understanding the solid electrolyte interphase (SEI) in lithium-ion batteries could help to improve their power and lifetime. Formed through electrolyte side reactions, the SEI coats the battery’s graphite anode. An ideal SEI will inhibit its own further growth once the battery is in operation and ensure that only lithium ions and not their damaging solvation shells intercalate into the graphite. It also hinders electrolyte decomposition.
To improve the understanding of SEI formation, Harry E. Hoster, Lancaster University, UK, ALISTORE European Research Institute, Amiens, France, The Faraday Institution Quad One, Didcot, UK, and colleagues have characterized SEIs formed at different constant potentials on the chemically inactive basal plane of highly oriented pyrolytic graphite (HOPG).
The team used X‐ray photoemission spectroscopy (XPS), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) using ferrocene as an electrochemical probe to study the formation process. They found that the previously described two‐step process of SEI formation starts at about 700 mV with the formation of an organic compact layer, which is then itself reduced to a much thicker, carbonate-containing, inorganic compact layer once potentials drop.
The researchers conclude that by controlling the chemical and physical properties of the high‐potential SEI, one can significantly influence the respective properties of the final low‐potential SEI and thus influence the lifetime and conductivity properties of SEIs in commercial cells. Transforming SEI formation from a current control towards a potential control regime may yield better results in a shorter time, which is good news for this slowest and most expensive step in the fabrication of lithium-ion cells.
- Formation of the Solid Electrolyte Interphase at Constant Potentials: a Model Study on Highly Oriented Pyrolytic Graphite,
Byron K. Antonopoulos, Filippo Maglia, Felix Schmidt-Stein, Jan P. Schmidt, Harry E. Hoster,
Batteries & Supercaps 2018.