Electrochemical Impedance Spectroscopy for Electrode Process Evaluation: Lithium Titanium Phosphate in Concentrated Aqueous Electrolyte

Aqueous electrolytes in the form of highly concentrated solutions stand as a viable alternative to the organic counterpart as battery electrolytes thanks to the low flammability, toxicity, cost and large availability, while keeping good potential windows. In this work, a half-cell constituted of lithium titanium phosphate in a binary aqueous solution of sodium acetate (7 mol kg(-1)) and potassium acetate (20 mol kg(-1)) as a promising anode for sodium-ion batteries is characterized with constant current, static and dynamic electrochemical impedance spectroscopy to reveal its thermodynamic and kinetic properties. The experiments permit to withdraw some information on the thermodynamics (activation energy of processes) and kinetics (processes' parameters evolution) of the system. Physical information was extracted from impedance spectra with mathematical regression of a porous electrode intercalation model available in literature using an innovative procedure of batch-fitting of a complete set of spectra at once. The advantage and shortcoming on using impedance in battery-development is discussed.