Electrochemistry & Energy Devices

Whether it’s a battery or supercapacitor, an energy device must overcome transport and electrochemical barriers, inherent in their materials design, to deliver suitable power and energy density demand. During my undergraduate studies, I had the opportunity to fabricate, test, and mathematically model these devices.

All works on electrochemical capacitors were done under the supervision of Prof. Ramakrishnan Rajagopalan. All works on solid electrolytes were done under the supervision of Prof. Michael T. Lanagan, with close mentorship of Dr. Seth Berbano. Additional supervision was also done under Regis Cleary and Prof. Dinesh Agrawal.

Experimental Studies and Modeling of Electrochemical Capacitors

We developed a methodology, coined Frequency Domain Admittance Method (FDAM) for analyzing electrochemical capacitors  [1,2] . The method utilizes linear impedance data, which is rich in microscopic and macroscopic information, to predict energy and power density of a capacitor.

An illustration of the methodology. Given the physical model, one can fit its linearized form to impedance data and subsequently predict other electrochemical experiments, e.g. constant-current discharge.

FDAM was first tested to electrical double layer capacitors (EDLCs)  [1] fabricated by Danhao Ma as well as commercial ones with great success. Afterwards, we tested our methodology to \(\mathrm{MnO}_2\) and poly-pyrrole psuedocapacitors  [2] that I fabricated with similar success.

A demonstration of our methodology, which fitted the impedance data of an EDLC, made from active carbon material, (Right) and subsequently predicting its discharge behavior (Left).

The code supplementing this work is available as a Python Library on GitHub (PyFDAM). Paper on EDLCs and pseudocapacitors can be found in Ref.  [1] and  [2], respectively. Both works contribute to my thesis (Link).

Experimental Studies and Modeling of Composite Solid Electrolytes

The idea of the percolation model. The electrostatics of a composite electrolyte is modeled by the Poisson equation. Effective medium approximation can be applied when the equation is discretized, giving rise to percolation-type networks and physics.

We fabricated lithium-borate-silica composite electrolytes and characterized their impedance characteristics and microstructure  [3]. Motivated by the broad frequency response of these materials, we developed a percolation model  [4] for a multi-component solid electrolyte based on the effective medium approximation, which can explain both DC and AC conductivity of various composites.

Paper for the experiments and modeling can be found in Ref.  [3] and  [4] . Both works contribute to my thesis (PDF).

References

[1]
Hasyim, M. R., D. Ma, R. Rajagopalan, and C. Randall, Prediction of charge-discharge and impedance characteristics of electric double-layer capacitors using porous electrode theory, Journal of the Electrochemical Society 164, A2899 (2017).
[2]
Hasyim, M. R. and R. Rajagopalan, Prediction of discharge performances of pseudocapacitors using their impedance characteristics, Journal of the Electrochemical Society 167, 013536 (2020).
[3]
Hasyim, M. R., S. S. Berbano, R. M. Cleary, M. T. Lanagan, and D. K. Agrawal, Impedance spectroscopy modeling of lithium borate with silica: A dispersed ionic conductor system, Ceramics International 43, 6796 (2017).
[4]
Hasyim, M. R. and M. T. Lanagan, A new percolation model for composite solid electrolytes and dispersed ionic conductors, Modelling and Simulation in Materials Science and Engineering 26, 025011 (2018).