Summary of the activities and impact of the research exchange that took place during 2018-2019.
Describe the area of focus for your researcher exchange?
The area of focus in this exchange programme is understanding the interplay between the electrochemical performance and microstructure in energy storage materials via multi-length scale image-based modelling technique, which will provide more insights into the design of next-generation battery electrode towards the improved energy/power performance and phase change materials (PCM) for high efficient energy storage and thermal management of the battery.
In a bid to reverse the global warming and cutdown fossil fuel consumption, substantial effort has been made to facilitate the revolution of electric vehicles, the market penetration of which is highly dependent on the accessible driving range, cost and safety. These are closely linked to the microstructure of the electrodes. Unravelling the fundamental science and underlying physical processes of the interplay between local/global performance and microstructural parameters have a significant impact on advanced electrode design, engineering and manufacturing. Moreover, the fast development of PCM in the last years provide a new alternative in battery thermal management system due to its high energy efficiency, low cost and sustainability.
Thus, this research exchange programme will be an important part of the Faraday Battery Challenge, aiming to use correlative imaging, advanced material characterisation and 3D image-based modelling to understand the fundamental science and predict performance of energy storage materials. The knowledge of the mass transport and electrochemical performance will be translated to improvements of microstructure design and optimisation at the cell level and eventually the system level.
How did the work you carried out during your exchange fit the MANIFEST research programme?
During this visit, we conducted large amount of electrode preparation, assembling and electrochemical test to measure the fundamental but critical metrics used for battery modelling, such as OCV, solid-state diffusivity and charge transfer resistance. It is of great importance to build the battery model based on the kinetic parameters directly measured from the as-prepared material instead of references to improve the reliability of the prediction of electrochemical state variables such as state-of-lithiation, heterogeneous charge transfer density etc. This is critical in unravelling the dependence of global material performance on the local microstructure and is highly consistent with Task 2.1 and 2.2 in WP2 of MANIFEST programme.
I also discussed with Dr. Zhiwei Ge and Mr. Yanqi Zhao in Prof. Ding’s group regarding the data analysis of the thermal chemical material and PCM obtained from the X-ray computed tomography and develop image-based model to track the microstructural evolution after thermal cycles, proposing new geometry for the application of PCM embedded foam copper to the battery thermal management. This is well aligned with another target of the MANIFEST research programme - to investigate an effective way to integrate the energy storage device into the energy system.
We also discussed the possibility to leverage the multi-scale imaging suite located in Electrochemical Innovation Lab in UCL to aid the materials modelling from sub-micron to centimetre length scale to examine the scalability of the current microstructure design.
How did you benefit from taking part in the MANIFEST exchange programme?
As a modeller, personally I learnt a great number of experimental skills, from battery fabrication ans Swagelok cell assembling, to the operation of three electrodes electrochemical test, Potentiostatic Intermittent Titration Test (PITT) and Galvanostatic Intermittent Titration Test (GITT) and Electrochemical Impedance Spectroscopy (EIS), by which I can find out the essential modelling parameters that cannot be extracted from X-ray tomography data. These experiments provide me with new insights into linking the battery modelling with the experiment and what in turn can inform the experiment design for the examination and improved understanding of the battery degradation mechanism.
I also have had a better understanding of a wide range of different energy storage materials, their principles and applications, which substantially broadens my vision about the energy conversion and also, enlightened me how I can apply my expertise in 3D microstructural characterisation and modelling to help the material design and optimisation in more comprehensive instances.
In a long term, I have made contacts with the talented researchers in Prof. Ding and Prof. Kendrick’s group and understood their projects. This undoubtedly will create potential collaboration possibilities and further academic activities between University of Birmingham and University College London.
What were the main outputs of the researcher exchange?
The first outcome of this exchange programme is that a 3D microstructure-resolved physics-based battery model for material design and performance prediction is developed, based on the obtained kinetic parameter from the lab. With the experiment data, the faithfulness of the original model is considerably enhanced. The heterogenous intercalation in Li-ion battery as a function of different discharge C-rate, the electrolyte concentration distribution and the Li-ion flux spatial distribution thus can be quantified and visualised (see figure). This highlights the importance of microstructure control in manufacturing. For example, it is found that the particle size, shape, pore size and porosity in the vicinity of the separator are dominant in determining the rate capability of the battery charge and discharge. A comparison of different perspective microstructure for next-generation battery electrode will also be undertaken. This will be discussed extensively in the paper to be published.
What plans do you have for further collaborations with your host institution?
There will be very profound and planned collaborations in the near future. For instance, the effect of electrode calendaring and the resultant porosity, electrode thickness on the battery performance will be examined systematically by linking X-ray CT 3D microstructure and image-based modelling to the electrochemical test to verify the state-of-the-art processing parameters so as to rationalise the manufacturing. Battery degradation as a function of cycle times and fast-charge/discharge will also be investigated by the performance and microstructure correlation.
Comprehensive microstructure characterisation on PCM embedded copper foams of distinct feature size will be undertaken, followed by thermal simulation based on X-ray tomography data to verify the efficacy of different designs and the application of PCM on battery thermal control. Microstructural evolution of thermal chemical energy storage material from the fresh to reacted states will be tracked, quantified and modelled to highlight the relationship between the material thermal resistance and cycle time.