Electrochemical Interfaces with Non-Cottrellian Current-Time Scaling in Energy Storage
Authors: Schoetz Theresa , Ghasemiahangarani Parham , Gordon Leo W. , Xu Jeffrey H. , Wang Jonah , Hawkins Brendan , Messinger Robert J. 
Published: December 2024

Researchers developing the next generation of energy storage systems are challenged to understand and analyze the different charge storage mechanisms, subsequently, use this understanding to design and control materials and devices that bridge the gap between high specific energy and power at a target cycle life. Correctly identifying and quantifying the prominent charge storage mechanism, which is either faradaic diffusion-limited, faradaic non-diffusion-limited (or pseudocapacitive), or capacitive, is of the utmost importance for understanding how the system functions and tuning material properties for specific applications. The different charge storage mechanisms are defined by a characteristic current-time scaling, that has been expressed for faradaic diffusion-limited (Cottrell relationship) and true capacitive charge storage and has been used to disentangle and determine the prominent mechanisms. However, the characteristic current-time scaling for faradaic non-diffusion-limited (or pseudocapacitive) charge storage remains unelucidated despite to date many energy storage devices, particularly those having ionic liquids, deep eutectic solvents or highly concentrated electrolytes, exhibit electrochemical interfaces with faradaic non-diffusion-limited charge storage.

This talk presents the work on a theoretical intuitive framework for pseudocapacitive charge storage taking into consideration the faradaic nature of this mechanism and deviation from the classic electrochemical interface structure, which is the root cause for pseudocapacitance1. The theory will be corroborated with experimental current-time scaling using conventional variable-rate cyclic voltammetry and variable-rate AC cyclic voltammetry at higher harmonics. The results emphasize the distinct current-time scaling of pseudocapacitive charge storage mechanism and shed light on interfacial kinetics and mass transport processes in multivalent batteries with ionic liquid or deep eutectic solvents. The insights inform electrode and electrolyte material design, e.g., for fast-charging2,3and low-temperature batteries4,5.

1 Schoetz, T., Gordon, L. W., Ivanov, S., Bund, A., Mandler, D. & Messinger, R. J. Disentangling faradaic, pseudocapacitive, and capacitive charge storage: A tutorial for the characterization of batteries, supercapacitors, and hybrid systems. Electrochimica Acta
412, 140072 (2022).

2 Xu, J. H., Schoetz, T., McManus, J. R., Subramanian, V. R., Fields, P. W. & Messinger, R. J. Tunable Pseudocapacitive Intercalation of Chloroaluminate Anions into Graphite Electrodes for Rechargeable Aluminum Batteries. Journal of The Electrochemical Society
168, 060514 (2021).

3 Leung, O. M., Gordon, L. W., Messinger, R. J., Prodromakis, T., Wharton, J. A., Ponce de León, C. & Schoetz, T. Solid Polymer Electrolytes with Enhanced Electrochemical Stability for High-Capacity Aluminum Batteries. Advanced Energy Materials
14, 2303285 (2024).

4 Hawkins, B. E., Schoetz, T., Gordon, L. W., Kt, S., Wang, J. & Messinger, R. J. Reversible Zinc Electrodeposition at −60 °C Using a Deep Eutectic Electrolyte for Low-Temperature Zinc Metal Batteries. The Journal of Physical Chemistry Letters
14, 2378-2386 (2023).

5 Schoetz, T., Xu, J. H. & Messinger, R. J. Ionic Liquid Electrolytes with Mixed Organic Cations for Low-Temperature Rechargeable Aluminum–Graphite Batteries. ACS Applied Energy Materials
6, 2845-2854 (2023).