Billy's research is broadly broken down into 2 main themes: energy and manufacturing.
Within energy, his research activities are at the interface between fundamental science and engineering application of electrochemical energy storage and conversion devices. Active topics include: lithium-ion batteries, metal-air batteries, supercapacitors, fuel cells and redox flow batteries.
Within manufacturing, most of his work focuses on additive manufacturing, specifically direct metal laser sintering, but with interests in advanced manufacturing techniques such as electrospinning, electrophoretic deposition and electrochemical deposition.
Check out our group website: Electrochemical Science and Engineering which is in partnership with Professor Nigel Brandon, Professor Ricardo Martinez-Botas, Dr. Vladimir Yufit and Dr. Gregory Offer.
A list of all of Billy's papers can be found on his Google scholar page.
Lithium-ion batteries are the technology of choice for consumer electronics, electric vehicles and grid scale energy storage. However, limitations with lifetime and energy density hinder their more widespread use. My research areas include:
- New battery chemistries
- Battery characterisation (Electrochemical impedance spectroscopy, x-ray tomography, cycling)
- Novel diagnostic techniques for condition monitoring
- Physics based modelling and model led control systems
- Grid scale energy storage
- Pack level design and understanding the influence of real world operating conditions
Condition monitoring of lithium-ion batteries is essential for ensuring long lifetimes. There are a number of techniques currently available however to be truly applicable the technique needs to capture the appropriate information, be easy to implement and be low cost. Our group has been developing a technique known as Differential Thermal Voltammetry (DTV) which monitors the change in voltage and temperature to infer the states of the individual positive and negative electrodes via their entropy profiles. Using this technique, battery lifetime can be prolonged by adaptively derating the battery. The below plot shows how DTV can be used to differentiate two different cells with similar remaining capacity but very different histories.
DTV experiments the data processing was done by Yuri Merla.
Environmental impact of hybrid and electric vehicles. Billy Wu and Gregory Offer. Environmental Impacts of Road Vehicles: Past, Present and Future. Royal Society of Chemistry. 2017
Extending battery life: A low-cost practical diagnostic technique for lithium-ion batteries. Yu Merla, Billy Wu, Vladimir Yufit, Nigel Brandon, Ricardo Martinez-Botas and Gregory Offer. Journal of Power Sources. 2016
Novel application of differential thermal voltammetry as an in-depth state-of-health diagnosis method for lithium-ion batteries. Yu Merla, Billy Wu, Vladimir Yufit, Nigel Brandon, Ricardo Martinez-Botas and Gregory Offer. Journal of Power Sources. 2016
An integrated approach for the analysis and control of grid connected energy storage systems. Charalampos Patsios, Billy Wu, Efstratios Chatzinikolaou, Daniel Rogers, Neal Wade, Nigel Brandon and Phil Taylor. Journal of Energy Storage. 2016
Differential thermal voltammetry for tracking of degradation in lithium-ion batteries. Billy Wu, Vladimir Yufit, Yu Merla, Ricardo Martinez-Botas, Nigel Brandon and Gregory Offer. Journal of Power Sources. 2014
In-Operando X-ray Tomography Study of Lithiation Induced Delamination of Si Based Anodes for Lithium-Ion Batteries. Farid Tariq, Vladimir Yufit, David S. Eastwood, Yu Merla, Moshiel Biton, Billy Wu, Zhangwei Chen, Kathrin Freedman, Gregory Offer, Emanuel Peled, Peter D. Lee, Diana Golodnitsky, and Nigel Brandon. ECS Electrochemistry Letters. 2014
Coupled thermal-electrochemical modelling of uneven heat generation in lithium-ion battery packs. Billy Wu, Vladimir Yufit, Monica Marinescu, Gregory J. Offer, Ricardo F. Martinez-Botas, Nigel P. Brandon. Journal of Power Sources. 2013
The effect of thermal gradients on the performance of lithium-ion batteries. Yannic Troxler, Billy Wu, Monica Marinescu, Vladimir Yufit, Yatish Patel, Andrew J. Marquis, Nigel P. Brandon and Gregory J. Offer. Journal of Power Sources. 2013
Module design and fault analysis in electric vehicle batteries. Gregory J. Offer, Vladimir Yufit, David A. Howey, Billy Wu and Nigel P. Brandon. Journal of Power Sources. 2012
Electrochemical Double Layer Capacitors, or Supercapacitors, are another type of energy storage device that is being considered as a powertrain component in electric vehicles. These are characterised by their high power rate capabilities but the drawback is their limited energy density. My research activities include:
- Modelling of supercapacitors
- Pseudocapacitors based on hybrid electrodes of mixed metal oxides and conducting polymers
- Ionogel based electrolytes
In order to improve the energy density of supercapacitors, psuedocapacitive materials are being investigated. These include transition metal oxides and conducting polymers. Metal oxides traditionally have larger specific capacities than conducting polymers, however have lower electrical conductivities limiting their power rate. By blending both conductive polymers with metal oxides, composite electrodes can be created with superior power rate capabilities. The below SEM image shows the cactus-like structure of manganese oxide which was formed electrochemically, alongside nanoparticles of doped conductive polymers (PEDOT:PSS) which were formed through electrophoretic deposition.
Electrode created by Xinhua Liu and imaged by Mengzheng Ouyang.
3D-Printed Structural Pseudocapacitors. Xinhua Liu, Rhodri Jervis, Robert Maher, Ignacio Villar-Garcia, Max Naylor-Marlow, Paul Shearing, Mengzheng Ouyang, Lesley Cohen, Nigel Brandon and Billy Wu. Advanced Materials Technologies. 2016
Tough ionogel-in-mask hybrid gel electrolytes in supercapacitors with durable pressure and thermal tolerances. Xinhua Liu, Billy Wu, Nigel Brandon and Qigang Wang. Energy Technology. 2016
Low temperature Proton Exchange Membrane Fuel Cells (PEMFCs) are the current fuel cell technology of choice in automotive applications. Current challenges limiting their widespread uptake include: limited lifetime, high cost and performance issues. My research activities in the PEMFC space include:
- Novel system and stack designs
- Design tools for PEMFC systems
- Diagnostic and characterisation techniques
As part of the Racing Green programme at Imperial, which is an undergraduate teaching project aimed at developing fuel cell, battery and hybrid electric vehicles, I help to supervise the fuel cell research and development division of Racing Green with Dr. Greg Offer and Dr. Fred Marquis.
Check out when we took the FC power generator to BBC television studios and appeared on BBC Breakfast News and Blue Peter and when we appeared in the Hybrid and Electric Vehicles magaine.
Check out a demonstration of the zero-emission FC generator at the H2Supergen BBQ as well as video of the rig in action below.
One of the fundamental problems with proton exchange membrane fuel cell (PEMFC) stacks is that if a single cell fails the whole stack fails due to the fact that all cells are connected in series. To mitigate this, our group has developed a novel type of fuel cell stack architecture called the segmented fuel cell stack, where current collectors are incorporated every 2-4 cells. Across these current collectors supercapacitors and/or batteries can be added to passively hybridise the stack. In this configuration there are multiple current paths allowing weaker cells to be less stressed. This approach has been shown to improve efficiency and reliability of fuel cell stacks.
The image below shows a prototype system developed by Max Naylor-Marlow, Alex Lama-Noujaim, Chris Caulcrick and Luan van Pletsen.
A systematic study on the use of short circuiting for the improvement of proton exchange membrane fuel cell performance. Gaurav Gupta, Billy Wu, Simon Mylius and Gregory Offer. International Journal of Hydrogen Energy. 2016.
Real-time monitoring of proton exchange membrane fuel cell stack failure. Billy Wu, Michael A. Parkes, Luca de Benedetti, Andrew J. Marquis, Gregory J. Offer and Nigel P. Brandon. Journal of Applied Electrochemistry. 2016
Design and testing of a 9.5 kWe proton exchange membrane fuel cell-supercapacitor passive hybrid system. Billy Wu, Michael A. Parkes, Vladimir Yufit, Luca De Benedetti, Sven Veismann, Christian Wirsching, Felix Vesper, Ricardo F. Martinez-Botas, Andrew J. Marquis, Gregory J. Offer and Nigel P. Brandon. International Journal of Hydrogen Energy. 2014
Hydrogen PEMFC system for automotive applications. Billy Wu, Mardit Matian and Gregory J. Offer. International Journal of Low Carbon Technologies. 2011
Redox flow batteries
Redox flow cells are electrochemical devices ideally suited for large scale grid energy storage applications. They store and release energy by changing the oxidation state of electrolyte which is pumped into an electrochemical cell, simialr to a fuel cell. They have advantages in that they can decouple power and energy which means that they can be sized more easily appropreiately than battery technologies.
The all vanadium redox flow battery is the most commercially mature flow cell technology, however the all liquid system suffers from low cell voltage and electrolyte cross-over effects. To mitigate these effects our group has been working on the development of a hydrogen-cerium flow battery. This liquid gas system allows the electrolyte crossover to be collected and recycled and the cerium, as a replacement for vanadium exhibits a higher operating voltage thus reducing the required number of cells in a stack to achieve a particular stack voltage.
The image below shows the test set-up developed by Anthony Tsoi and Dr. Harini Hewa Dewage.
The current and future prospects for vanadium flow batteries in China. Mianyan Huang, Eric Finlayson, Hanmin Liu, Jim Stover, Xiaofeng Xie, Billy Wu. The International Flow Battery Forum. 2017
A novel regenerative hydrogen cerium fuel cell for energy storage applciations. Harini Hewa Dewage, Billy Wu, Anthony Tsoi, Vladimir Yufit, Gregory Offer and Nigel Brandon. Journal of Materials Chemistry A. 2015
Additive manufacturing, which is more commonly known as 3D printing, allows for the creation of complex geometries not possible with traditional subtractive techniques. His research activities in additive manufacturing include:
- Direct metal laser sintering
- Fused deposition modelling
- Printed sensors
- Novel forms of additive manufacturing
- Design for additive manufacturing
- Metrology and characterisation
Impellers for automotive turbochargers are essential for improving fuel economy of internal combustion engines. These are typically made via multi-axis CNC milling machines with significant lead times. By using direct metal laser sintering, the mass of the impeller can be reduced improving the transient response of the component. In addition, complex geometric features can be added such as internal cooling channels which allows higher temperature operation. The below example which was made using direct metal laser sintering shows how lattice elements can be added to an impeller design.
Impeller designed by Dr. Aaron Costall and Professor Ricardo Martinez-Botas. Lattice added and printed by Max Naylor-Marlow.
A low cost desktop electrochemical metal 3D printer. Xiaolong Chen, Xinhua Liu, Peter Childs, Nigel Brandon, Billy Wu. Advanced Materials Technologies. 2017.
3D printed structural psuedocapacitors. Xinhua Liu, Rhodri Jervis, Robert C Maher, Ignacio J Villar‐Garcia, Max Naylor‐Marlow, Paul R Shearing, Mengzheng Ouyang, Lesley Cohen, Nigel P Brandon, Billy Wu. Advanced Materials Technologies. 2016
Electrical conductivity and porosity in stainless steel 316L scaffolds for electrochemical devices fabricated using selective laser sintering. Khairul Ibrahim, Billy Wu and Nigel Brandon. Materials and Design. 2016
The current landscape for additive manufacturing research. Jing Li, Connor Myant and Billy Wu. 2016.
Beyond the hype: 3D printing grows up. Billy Wu, Jing Li and Connor Myant. 2016.
Additive manufacturing for solid oxide cell fabrication. Marina Lomberg, Paul Boldrin, Farid Tariq, Gregory Offer, Billy Wu and Nigel Brandon. ECS Conference on Electrochemical Energy Conversion & Storage with SOFC-XIV
One of the key challenges for building better electrochemical devices and enabling functional materials is developing new manufacturing techniques. Our group develop new manufacturing techniques to enable better material design. Our research interests include:
- Electrospinning of nanofibres
- Electrophoretic deposition
- Electrochemical deposition
Nanofibres have a range of ideal properties and one low cost method of manufacturing them is via a process known as electrospinning. The image below shows electrospun nanofibres of PVA with carbon nanotubes. Credit Xinhua Liu.
- Max Naylor-Marlow - Energy storage for aerial robotics (Co-supervised with Dr. Mirko Kovac)
- Yu Merla - Lithium-ion batteries (Co-supervised with Dr. Gregory Offer)
- Khairul Ibrahim - Additive manufacturing (Co-supervised with Professor Nigel Brandon)
- Xiaolong Chen - Additive manufacturing (Co-supervised with Professor Peter Childs)
- Khairul Fikri - Additive manufacturing (Co-supervised with Dr. Connor Myant)
- Ashkan Kavei - Proton Exchange Membraner Fuel Cells (Co-supervised with Professor Nigel Brandon, Dr. Gregory Offer and Dr. Vladimir Yufit)
- Dr. Xinhua Liu - Novel battery materials and grid scale energy storage
- Dr. Gan Lu - Design and optimisation of fuel cell powertrains (Co-supervised with Dr. Gregory Offer)
- Dr. Gaurav Gupta - Post-doc - Proton exchange membrane fuel cells (Co-supervised with Dr. Gregory Offer)
- Dr. ChiYoung Choi - Post-doc - Proton exchange membrane fuel cells (Co-supervised with Dr. Gregory Offer)
- Dr. Jing Li - Post-doc - Additive Manufacturing Network manager (Co-supervised with Dr. Connor Myant)
- Doug Anderson - 4th year mecheng student - 3D printed lugs for carbon fibre space frames (Co-supervised with Dr. Dan Plant)
- Oisin Shaw, Anisha Kanabar, Thomas Yard, Rob Garside and Claudia Jackman-White - 3rd year mecheng students - Fuel cell powertrain (Co-supervised with Dr. Fred Marquis)
- Joint UK-India Clean Energy Centre (JUICE) - EPSRC funded centre between the UK and India for the integration of renewable energy
- ALICE (Advanced Lithium-Ion Capacitor Electrodes) - Innovate UK funded project on scale up of lithium-ion capacitor technology
- ZEBRA (Zero Emission Buses by Range Extension with fuel cells) - Innovate UK funded project on integration of hydrogen fuel cells into buses
- Imperial Additive Manufacturing Network - Imperial College funded network fund to bring together researchers working in additive manufacturing
- ICAH TechElevator - Imperial College funded grant for showcasing EPSRC funded research at Imperial
- Materials and process development for low cost 1-10kW UK fuel cell stack manufacturing - Innovate UK funded project to develop fuel cell manufacturing capability in the UK
- Lithium-ion battery modelling for power network optimisation and whole system analysis - EPSRC funded project to develop lithium-ion battery models for grid optimisation purposes.