Supercapacitors are electrochemical devices which have exceptional power densities and lifetimes, however their energy density is limited. Within the ESE group research has focused on development new carbon based materials for supercapacitors to improve their energy whilst maintaining the power density, application of pseudocapacitive materials, asymmetric electrode designs, understanding their internal thermal properties, modelling of their performance and their hybridisation with other devices.

Projects

Modelling of lithium-ion capacitors

Innovate UK logo
 
Lead researchers: Dr Ganesh Madabattula
PI’s: Dr Billy Wu, Dr Monica Marinescu and Dr Gregory Offer
 
Funding: 
  • Innovate UK, Advanced Lithium-Ion Capacitors and Electrodes (ALICE)-102655

The project aims to develop advanced lithium-ion capacitors based on lithium titanium oxide (LTO) and activated carbon as electrode materials to provide optimum energy density and power density with long cycle life for energy storage applications. Imperial provided physics-based modelling insights to the collaborators in the project to develop optimised cells. In this project, rate capability, the role of capacity ratio of electrodes, and pre-lithiation of LTO on cell performance and capacity fade were studied. The diagnostic techniques for capacity fade in the capacitors were developed. Newman’s porous electrode theory-based P2D models were simulated in COMSOL Multiphysics for the analysis.

Collaborators:
  • Johnson Matthey
  • Cummins Inc
  • University of Oxford
  • WMG-Warwick University
  • Delta Motorsport Ltd
Publications:
  1. Madabattula G, Wu B, Marinescu M, Offer G, 2020, Degradation diagnostics for Li4Ti5O12-based lithium-ion capacitors: Insights from a physics-based model, Journal of the Electrochemical Society, Vol: 167(4), Page: 043503.
  2. Madabattula G, Wu B, Marinescu M, Offer G, 2019, How to design lithium-ion capacitors: modelling, mass ratio of electrodes and pre-lithiation, Journal of The Electrochemical Society, Vol: 167, Page: 013527.
  3. Madabattula G, Wu B, Marinescu M, Offer G, 2019, 1D Electrochemical Model for Lithium Ion Capacitors in Comsol.

Multiscale modelling of high energy density supercapacitors

Innovate UK logo 
Lead researchers: Dr Tribeni Roy and Dr Mohammad Amin Samieian
PI’s: Dr Huizhi Wang, Dr Yatish Patel, Dr Monica Marinescu and Dr Gregory Offer
 
Funding: 
  • InnovateUK WIZer Batteries, collaborative R&D with Williams Advanced Engineering, CodePlay Software Ltd., ZapGO Ltd. & Silver Power Systems Ltd.

‌‌‌Research into supercapacitors has recently gained prominence owing to the development of high potential window electrolytes (ionic liquids/non-aqueous electrolytes) and a range of electrode materials with controlled porosity. Supercapacitors are viewed as an add-on to lithium-ion batteries in electric vehicles to enhance the overall power density, enable fast charging and longer cycle life. 

all figs
Figure 1. Single layer cell during MD simulations (solved using LAMMPS Constant Potential Method). Figure 2. Challenges in modelling due to processes occurring at multiple length scales in high energy density supercapacitors. Figure 3. Density distribution of electrode atom charges at fixed potential difference between the electrodes (MD). Figure 4. Charge density profiles of ionic liquid near the negative electrode with respect to variable packing fraction (solved using Modified Poisson-Nernst-Planck). Figure 5. (a) Schematic for cell expansion measurement test; and (b) Testing of high energy density supercapacitors under controlled environment

However, the behaviour of the recently developed electrolytes for enhancing energy density via formation of (crowded) double layer is not fully understood. Also, the random pore size distribution on the electrode is a limiting factor owing to reduced capacitance despite using high potential electrolytes.

We are developing multiscale models (coupled DFT-MD-FEA) to understand the behaviour of these electrolytes in terms of double-layer formation, diffusion in the electrode pores and thereby predict the optimal pore size distribution on the electrode to enhance the energy density while maintaining reasonably high-power density.

Experimental facilities include Electrochemical Impedance Spectroscopy (EIS), Cyclic Voltammetry (CV), Power cycling, Degradation tests, and Cell expansion measurement tests.

Collaborators:
Publications:
  1. To be updated.

Our paper featured as a cover page in Advanced Science

Cover Advance Science Supercaps
 
Our paper on a freeze aligned ionogel supercapacitor electrolytes was featured as a cover page in Advanced Science
 
Liu X, Taiwo OO, Yin C, Ouyang M, Chowdhury R, Wang B, 2019, Supercapacitors: Aligned Ionogel Electrolytes for High-Temperature Supercapacitors, Advanced Science, Vol: 6, Pages: 1801337
 

This work reports a self‐initiated cryopolymerization method to prepare nanocomposite ionogels with hierarchical aligned pores for use in high temperature supercapacitors. Diffusion simulations based on X‐ray tomographic 3D reconstructed images are used to explain the origins of the observed electrochemical enhancements in the aligned ionogels, which highlight the potential for structured materials in energy storage devices.