Role of solvent-anion charge transfer in oxidative degradation of battery electrolytes

• Published in: Nature communications 2019-07, Vol.10 (1), p.3360-10, Article 3360
• Main Authors: Fadel, Eric R., Faglioni, Francesco, Samsonidze, Georgy, Molinari, Nicola, Merinov, Boris V., Goddard III, William A., Grossman, Jeffrey C., Mailoa, Jonathan P., Kozinsky, Boris
• Format: Article
• Language: English
• Subjects: 119/118; 639/301/1034/1035; 639/301/1034/1037; 639/4077/4079/891; 639/638/440; 639/638/563/606; Anions; Batteries; Charge transfer; Computer applications; Coupling (molecular); Decomposition; Degradation; Electrochemistry; Electrolytes; Humanities and Social Sciences; Ionization; Ionization potentials; Lithium; Lithium-ion batteries; multidisciplinary; Nonaqueous electrolytes; Organic chemistry; Oxidation; Prediction models; Quantum chemistry; Rechargeable batteries; Science; Science (multidisciplinary); Solvents; Voltage stability
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-019-11317-3

Electrochemical stability windows of electrolytes largely determine the limitations of operating regimes of lithium-ion batteries, but the degradation mechanisms are difficult to characterize and poorly understood. Using computational quantum chemistry to investigate the oxidative decomposition that govern voltage stability of multi-component organic electrolytes, we find that electrolyte decomposition is a process involving the solvent and the salt anion and requires explicit treatment of their coupling. We find that the ionization potential of the solvent-anion system is often lower than that of the isolated solvent or the anion. This mutual weakening effect is explained by the formation of the anion-solvent charge-transfer complex, which we study for 16 anion-solvent combinations. This understanding of the oxidation mechanism allows the formulation of a simple predictive model that explains experimentally observed trends in the onset voltages of degradation of electrolytes near the cathode. This model opens opportunities for rapid rational design of stable electrolytes for high-energy batteries. Based on computations, the authors show that voltage stability of battery electrolytes is determined not by a single component but by formation of charge transfer complexes between salt anions and solvent molecules. A physical model is proposed and validated on several common electrolyte compositions.