Operando Deconvolution of Solvation Desolvation Energy and Interfacial Charge Transfer
Operando deconvolution isolates ion desolvation from interfacial charge transfer, enabling electrolyte formulations that eliminate low-temperature power loss.
Donor Number
Meaning
Quantitative measurement of Lewis basicity defines the coordinating ability of solvent molecules toward a standard electron acceptor. The donor number of a solvent determines how strongly it interacts with lithium ions in an electrolyte solution. High values indicate a strong ability to solvate cations, which promotes salt dissociation but can hinder desolvation at the electrode surface.
Lewis Basicity
Calorimetric measurements of the reaction enthalpy with antimony pentachloride in an inert solvent establish this parameter. Solvents with a high donor number, such as dimethyl sulfoxide, strongly coordinate with lithium cations, forming stable solvation shells. This strong coordination lowers the energy of the solvated ion.
It also decreases the rate of desolvation during the intercalation process.
Solvent Chemistry
Electrolyte formulation relies on balancing these values to optimize both ion transport and interfacial stability. Linear carbonates possess lower values than cyclic carbonates, which affects their respective solvation behavior. Mixing solvents with complementary properties generates a solvation shell that maintains high ionic conductivity while allowing easy charge transfer.
This combination prevents the co-intercalation of solvent molecules into the anode.
Performance Tradeoff
Selecting the appropriate basicity represents a critical compromise in cell design. A high donor number improves the solubility of lithium salts and increases the concentration of free carrier ions, but it also increases the viscosity of the electrolyte. Manufacturers measure these effects to avoid high low-temperature resistance and to ensure that the solid electrolyte interphase forms correctly.
Sourcing specialists evaluate these solvent properties when purchasing raw materials for specific temperature-range requirements. Chemical suppliers provide detailed chromatography and spectroscopic reports to verify that impurities do not skew the apparent donor number, because trace water or basic contaminants will alter the electrochemical behavior and degrade the cell over extended cycling.