Areas of Expertise (7)
Industry Strategy Automotive
Battery Systems Engineering
Chalmers University of Technology: M.Sc., Technology Management 2008
University of Cambridge: M.A., Engineering 1993
Selected Media Appearances (3)
Behind the scenes of Britain's battery revolution
Fortunately, Britain has bodies like the WMG enterprise and the government-academia-industry Faraday Foundation, a 10-year co-operative set up last year and in which Greenwood is also heavily involved, to pick up the baton. Faraday is backed initially by £237 million from the government and is already investigating highly promising solid-state and lithium anode battery technology. Studies are looking at how batteries degrade in use, boosting computer modelling as an aid to battery development and improving recycling techniques. Participants are determined to avoid what happened with nickel-metal hydride battery technology, which was discovered in Oxford but sold in difficult economic times to a Japanese developer that made billions...
End of life automotive batteries
Future of Technology Series online
‘We can’t just look at recycling current batteries from our electric vehicles, we need to design future batteries with recycling and the environment in mind’ – Prof. Dave Greenwood
Meet Coventry’s battery boffin taking on Tesla
The Times online
Unfortunately for Greenwood, all 2.5m of the phones sold around the world have been recalled by the South Korean technology giant, making it nigh on impossible to buy them. “They’re like hen’s teeth,” he complained as he paced across a glass and steel walkway at Warwick University.
Selected Articles (6)
Current “state‐of‐the‐art” monitoring and control techniques for lithium‐ion cells rely on full‐cell potential measurement and occasional surface temperature measurements. However, Li‐ion cells are complex multi‐layer devices and as such these techniques have poor resolution, limiting applicability. In this work we develop hybrid thermo‐electrochemical sensing arrays placed within the cell. The arrays are integrated into A5 pouch cells during manufacture and are used to create thermal maps in parallel with anode and cathode electrochemical data. The sensor array can be adapted to a range of cell formats and chemistries and installed into commercial or other industrially relevant cells, incorporating enhanced thermal and electrochemical diagnostic capability into a standard cell build.
The number of electric vehicle (EV) batteries reaching end-of-service is set to increase from thousands to tens of thousands per annum by 2025. These end-of-service batteries typically retain significant capacity and power delivery capability, and their re-use in so-called ‘second-life’applications has been proposed as a means to extend the battery value chain, offset a portion of their up-front cost and minimise waste by deferring recycling. Accurate grading of used battery assets is essential in order to assign them an appropriate valuation in the second-life market. These grading activities account for the majority of the cost incurred in repurposing batteries at present, due largely to the time required for testing, which typically employs DC techniques taking up to several hours to perform a capacity measurement.
This paper presents experimental investigations into the wear performance of non-reinforced POM (Polyoxymethylene) and 28% GFR POM (glass fibre reinforced POM) gear pairs; polymer running against polymer is a little studied but important system. All the gears were manufactured locally by injection moulding. The injection mould design and manufacturing process are briefly described and progress in the control of injection moulding processes for polymer and fibre reinforced polymer gears is discussed. A specifically designed polymer composite gear test rig was used for this research. Performance differences for the POM and GFR POM gears are observed, notably their loading capacity and failure modes. Both POM and GFR POM gear pairs, showed a clear wear transition torque for a given running speed. Above the transition torque the wear rate accelerated rapidly causing thermal failure, while below the transition torque the gears had a very low specific wear rate. Significant performance enhancements were seen for the GFR POM gears, with an increase of around 50% in load carrying capacity when compared to the non-reinforced POM gears. The wear mechanisms are briefly discussed, noting that most data available for polymer gear design is not representative of these polymer against polymer pairings.
This work investigates the capacitive capabilities of Li-ion pouch and cylindrical cells in respect to the provision of Frequency Response services and a potential for reduction in battery ageing effects. This is achieved using Electrochemical Impedance Spectroscopy (EIS) and a novel method of identifying and defining the threshold frequency between pseudo-capacitive and diffusion processes of the cell. It is found that this threshold frequency is independent of current intensity up to 1 C, showing that even at high power, pseudo-capacitance has significant impact. However, a severe dependency upon relative cell surface area and State of Charge (SoC) is identified. Symmetrical charge-discharge pulses of up to 10 s utilise primarily cell capacitance. Literature indicates, that this level of utilisation reduces the electrochemical ageing impact significantly. This article displays a method to identify and isolate these processes for any given cell and to allow enhancement of conventional ageing modelling.
Cooling the surface of large format batteries with solid conductive plates, or fins, has an inherent advantage of reducing the number of liquid seals relative to some mini-channel cold plate designs, as liquid is not passed through the numerous individual plates directly. This may reduce the overall pack leakage risk which is of utmost importance due to safety concerns associated with the possibility of a cell short circuit and thermal runaway event. However, fin cooling comes at a cost of an increased thermal resistance which can lead to higher cell temperatures and a poorer temperature uniformity under aggressive heat generation conditions. In this paper, a novel graphite-based fin material with an in-plane thermal conductivity 5 times greater than aluminium with the same weight is presented for advanced battery cooling. The thermal performance of the fin is benchmarked against conventional copper and aluminium fins in an experimental programme cycling real 53 Ah pouch cells. The results from the extensive experimental testing indicate that the new fin can reduce both the peak measured temperature and surface temperature gradient by up to 8 °C and 5 °C respectively, when compared to aluminium fins under an aggressive electric vehicle duty-cycle.
Lithium-ion-based secondary battery packs are emerging as an alternative power source and are being increasingly used in electric vehicles, hybrid or plug-in hybrid electric vehicles. Typically, a standard automotive battery pack consists of hundreds, even thousands, of individual cells which are connected in series and/or parallel to deliver the required power and capacity. There is an increasing need for manufacturing of battery packs to meet the demand reflecting the uptake of these vehicles. This triggers the need for suitable joining methods which will provide mechanical strength on a par with electrical and thermal characteristics. This work focuses on characterisation of shear strength of battery tab-to-tab joints for both similar and dissimilar materials by using combinations of aluminium (Al) and nickel-coated copper (Cu[Ni]) tabs. The joining techniques with application for battery tab interconnects are ultrasonic metal welding, resistance spot welding and pulsed TIG spot welding. Lap shear and T-peel tests are performed to evaluate the joint strength. In general, lap shear strength is four to seven times higher than the T-peel strength obtained from all three joining methods. In addition, an indicator is developed in this paper based on lap shear-to-T-peel strength reduction ratio which provides additional information on joint strength characteristics, and subsequently, it can be used as a threshold by quality engineers for an indication on selection of joining methods having an acceptable strength reduction ratio.