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.
Marcus-Hush Theory
Meaning
Electron transfer model establishes the relationship between activation energy and the reorganization energy of reactants during redox processes at electrode surfaces. When applied to battery systems, Marcus-Hush theory describes how the solvation shell reorganizes as a lithium ion transfers between the liquid electrolyte and the solid host. The framework models the nonlinear dependence of reaction rate on overpotential, deviating from classical Butler-Volmer behavior at high driving forces.
Kinetic Framework
The mathematical foundation of this approach utilizes a quadratic energy-potential relationship to calculate the activation barrier of charge-transfer reactions. In this model, the reorganization energy reflects the structural changes in the active ion and its coordination shell. A higher reorganization energy increases the activation barrier, which slows down the reaction.
This analysis helps researchers identify why certain solvent-salt combinations exhibit sluggish charge-transfer kinetics.
Interfacial Application
Measurements of exchange current density at different anode and cathode surfaces validate the predictions of this theoretical framework. The model accounts for the electronic density of states in the electrode, explaining differences in transfer rates between metallic lithium and intercalating compounds. Solvation structures that require significant rearrangement to release the cation yield lower transfer rates.
This structural dependency highlights the need for electrolytes with low desolvation barriers.
Design Consequence
Sourcing and formulation engineers use these thermodynamic calculations to design electrolytes that minimize reorganization energy, ensuring rapid charge transfer. Lowering the activation barrier at the interface improves the fast-charging capabilities of the battery. Suppliers modify solvent compositions to reduce the change in coordination volume during the transition state.
This material optimization ensures that the cells achieve high power density while preventing lithium plating during rapid charge cycles.