Kinetics of the Reversible Insertion of Cations in Positive Electrode Materials Under Dynamic Conditions

Abstract

The need for cost-effective energy storage systems to integrate more renewable energy has increased over the years, as we strive to reduce carbon emissions arising from the use of fossil fuels. Aqueous rechargeable batteries (ARBs) have been reported as promising energy storage system for stationary applications due to their cost-effectiveness, safety, high round trip efficiency and environmental friendliness. To optimize ARBs for enhanced electrochemical performance and to model the power-energy relation of ARBs under different working conditions, a deep understanding of the kinetics of reversible insertion process in-operando is required. To achieve this, dynamic impedance spectroscopy (DEIS) acquired using dynamic multi-frequency analysis (DMFA) was used to investigate the kinetics of the reversible insertion process in various electrode materials under working conditions.

To extract quantitative and qualitative mechanistic information that are physical correlated to the system been investigated, a model for the impedance response of (de)insertion of cations in cathode materials was developed. Using nickel hexacyanoferrate (NiHCF) films, which are unstable in their oxidized form, the advantages of using DMFA in kinetic investigation of unstable electrochemical systems was illustrated. The rate determining step of the reversible insertion process of univalent cations in NiHCF nanoparticles, a promising electrode material for ARBs was observed to depend on the state of charge. Quantitative kinetic information such as transfer coefficients and activation energies, which are useful in modelling the reversible insertion process was also extracted for the reversible insertion process of univalent cations (Na+ and K+) in NiHCF nanoparticles. The effect of film thickness on the kinetics of the reversible insertion of lithium in lithium-manganese oxide films made by multi-layer pulse laser deposition was also investigated in this work. The result indicates that processes such as (de)solvation process were independent on film thickness, while interfacial and bulk properties (charge transfer and mass transport) depended on the film thickness.