Quantifying Interfacial Impedance in Commercial High Voltage Cathodes
Quantifying high-voltage cathode interfacial impedance via DRT spectroscopy isolates charge-transfer growth to establish batch quality rejection limits.
Parasitic Solvent Oxidation
Meaning
Side reactions quantify chemical breakdown of organic carbonate solvents at high-voltage cathode surfaces during charging and high-temperature storage. Formulations designed for high-energy cells quantify parasitic solvent oxidation to evaluate long-term coulombic efficiency and gas generation rates. The boundary of this reaction process covers non-faradaic decomposition at the cathode interface, stopping where reversible intercalation redox chemistry occurs.
Decomposition Mechanism
High-voltage cathode surfaces remove electrons from solvent molecules when operational potentials exceed electrochemical stability windows. Transition metal cations accelerate parasitic solvent oxidation by acting as catalytic sites for oxidative cleavage of cyclic and linear carbonates. The reaction products form thick resistive surface films that increase cell impedance and deplete active liquid electrolyte volume over extended storage periods.
Proton transfer reactions further degrade surrounding salt species, generating hydrofluoric acid.
Gas Generation
Oxidative decomposition releases volatile gaseous products including carbon dioxide and carbon monoxide inside sealed pouch or prismatic cells. Pressure accumulation resulting from parasitic solvent oxidation causes pouch swelling and potential venting in unvented enclosures. Gas generation rates increase exponentially with elevated operational temperatures.
Electrolyte Degradation
Consuming active solvent components increases electrolyte viscosity and reduces ionic conductivity within porous separator membranes. Adding functional film-forming additives suppresses parasitic solvent oxidation by passivating high-voltage cathode surfaces. Cell manufacturers select fluorinated solvents to extend chemical stability limits above four point five volts.