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  • Journal article
    Pang M-C, Hao Y, Marinescu M, Wang H, Chen M, Offer GJet al., 2019,

    Experimental and numerical analysis to identify the performance limiting mechanisms in solid-state lithium cells under pulse operating conditions.

    , Physical Chemistry Chemical Physics, Vol: 21, Pages: 22740-22755, ISSN: 1463-9076

    Solid-state lithium batteries could reduce the safety concern due to thermal runaway while improving the gravimetric and volumetric energy density beyond the existing practical limits of lithium-ion batteries. The successful commercialisation of solid-state lithium batteries depends on understanding and addressing the bottlenecks limiting the cell performance under realistic operational conditions such as dynamic current profiles of different pulse amplitudes. This study focuses on experimental analysis and continuum modelling of cell behaviour under pulse operating conditions, with most model parameters estimated from experimental measurements. By using a combined impedance and distribution of relaxation times analysis, we show that charge transfer at both interfaces occurs between the microseconds and milliseconds timescale. We also demonstrate that a simplified set of governing equations, rather than the conventional Poisson-Nernst-Planck equations, are sufficient to reproduce the experimentally observed behaviour during pulse discharge, pulse charging and dynamic pulse. Our simulation results suggest that solid diffusion in bulk LiCoO2 is the performance limiting mechanism under pulse operating conditions, with increasing voltage loss for lower states of charge. If bulk electrode forms the positive electrode, improvement in the ionic conductivity of the solid electrolyte beyond 10-4 S cm-1 yields marginal overall performance gains due to this solid diffusion limitation. Instead of further increasing the electrode thickness or improving the ionic conductivity on their own, we propose a holistic model-based approach to cell design, in order to achieve optimum performance for known operating conditions.

  • Journal article
    Mazur C, Contestabile M, Offer GJ, Brandon NPet al., 2015,

    Assessing and comparing German and UK transition policies for electric mobility

    , ENVIRONMENTAL INNOVATION AND SOCIETAL TRANSITIONS, Vol: 14, Pages: 84-100, ISSN: 2210-4224
  • Journal article
    Duboviks V, Maher RC, Kishimoto M, Cohen LF, Brandon NP, Offer GJet al., 2014,

    A Raman spectroscopic study of the carbon deposition mechanism on Ni/CGO electrodes during CO/CO2 electrolysis

    , PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 16, Pages: 13063-13068, ISSN: 1463-9076
  • Journal article
    Howey DA, Mitcheson PD, Yufit V, Offer GJ, Brandon NPet al., 2014,

    Online Measurement of Battery Impedance Using Motor Controller Excitation

    , IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY, Vol: 63, Pages: 2557-2566, ISSN: 0018-9545
  • Journal article
    Tariq F, Yufit V, Eastwood DS, Merla Y, Biton M, Wu B, Chen Z, Freedman K, Offer GJ, Peled E, Lee PD, Golodnitsky D, Brandon NPet al., 2014,

    In-Operando X-ray Tomography Study of Lithiation Induced Delamination of Si Based Anodes for Lithium-Ion Batteries

    , Electrochemistry Letters, Vol: 3

    Silicon-Lithium based rechargeable batteries offer high gravimetric capacity. However cycle life and electrode microstructure failure mechanisms remain poorly understood. Here we present an X-ray tomography method to investigate in-operando lithiation induced stress cracking leading to the delamination of a composite Si based electrode. Simultaneous voltage measurements show increased cell resistance correlating with severe delamination and microstructural changes. 3D analysis revealed 44.1% loss of the initial electrode-current collector area after 1 hour of operation at 2.4 mA/cm2 and a 21.2% increase in new anode surface area. The work represents a new basis for future investigation of Si based anodes.

  • Journal article
    Wu B, Parkes MP, Yufit V, De Benedetti L, Veismann S, Wirsching C, Vesper F, Martinez-Botas RF, Marquis AJ, Offer GJ, Brandon NPet al., 2014,

    Design and testing of a 9.5 kWe proton exchange membrane fuel cell-supercapacitor passive hybrid system

    , International Journal of Hydrogen Energy

    The design and test of a 9.5 kWe proton exchange membrane fuel cell passively coupled with a 33 × 1500 F supercapacitor pack is presented. Experimental results showed that the system reduced dynamic loads on the fuel cell without the need for additional DC/DC converters. Fuel efficiency gains of approximately 5% were achieved by passive hybridisation in addition to addressing two main operational degradation mechanisms: no-load idling and rapid load cycling.Electrochemical Impedance Spectroscopy measurements indicated that the supercapacitor capacitance dropped with decreasing cell voltage and suggested that operation below 1.3 V is not recommended. Knee-frequency measurements suggested little benefit was gained in using passive systems with load cycles that have frequency components above 0.19 Hz. Analysis of system sizing suggested using the minimum number of supercapacitors to match the open circuit voltage of the fuel cell to maximise load buffering.

  • Journal article
    Wu B, Yufit V, Marinescu M, Offer GJ, Martinez-Botas RF, Brandon NPet al., 2013,

    Coupled thermal–electrochemical modelling of uneven heat generation in lithium-ion battery packs

    , Journal of Power Sources, Vol: 243, Pages: 544-554, ISSN: 0378-7753

    Abstract In battery packs with cells in parallel, the inter-cell connection resistances can cause unequal loads due to non-uniform interconnect overpotentials and consequentially lead to non-uniform heating. This article explores how load imbalances are generated in automotive applications, by describing a battery pack with finite interconnect resistances. Each cell inside the pack is represented by a pseudo 2D electrochemical model coupled with a lumped thermal model. Increasing the number of cells in parallel results in a linear increase in load non-uniformity, whilst increasing the ratio of interconnect to battery impedance results in a logarithmic increase in load non-uniformity, with cells closest to the load points experiencing the largest currents. Therefore, interconnect resistances of the order of mΩ can have a significant detrimental impact. Under steady state discharge the cell impedance changes until the loads balance. This process, however, can take hundreds of seconds and therefore may never happen under dynamic load cycles. Cycling within a narrow state-of-charge range and pulse loading are shown to be the most detrimental situations. Upon load removal, re-balancing can occur causing further heating. Simulation of a 12P7S pack under a real world load cycle shows that these effects could cause localised thermal runaway.

  • Journal article
    Maher RC, Duboviks V, Offer GJ, Kishimoto M, Brandon NP, Cohen LFet al., 2013,

    Raman Spectroscopy of Solid Oxide Fuel Cells: Technique Overview and Application to Carbon Deposition Analysis

    , FUEL CELLS, Vol: 13, Pages: 455-469, ISSN: 1615-6846
  • Journal article
    Marinescu M, Wu B, Von Srbik M, Yufit V, Offer GJet al., 2013,

    The effect of thermal gradients on the performance of battery packs in automotive applications

    , IET Conference Publications, Vol: 2013

    Thermal gradients arising inside a battery pack for automotive applications are calculated for 200 A discharge via a multiparticle thermal-electrochemical coupled high fidelity model for a 12P7S 4.8 Ah cell pack. The effect of such gradients at the cell level are studied in a first approximation under a corresponding discharge at 15 A, by discretising the cell into units at fixed temperatures throughout the discharge. The immediate time evolution of load distribution through the various parts of the cell shows a complex behaviour, dependent on parameters such as temperatures, state of charge and load characteristics.

  • Journal article
    Wu B, Yufit V, Campbell J, Offer GJ, Martinez-Botas RF, Brandon NPet al., 2013,

    Simulated and experimental validation of a fuel cell-supercapacitor passive hybrid system for electric vehicles

    , IET Conference Publications, Vol: 2013

    The concept of a fuel cell-supercapacitor hybrid system involves the direct coupling of the two devices to achieve the same benefits of hybridisation but without the need for costly DCDC converters. Using an experimentally validated steady state fuel cell model and a transmission line based supercapacitor model, it has been shown that the passive hybridisation allows for efficiency gains of approximately 16% compared to a pure fuel cell system. Under load, the supercapacitors meets the peak power requirement due to their lower impedance giving the FC time to ramp up. Under no load conditions, the fuel cell gradually charges the supercapacitors back to the steady state thermodynamic equilibrium potential. A fast fourier transform analysis of the respective loads under an automotive drive cycle showed that the supercapacitors act as a low pass filter, reducing the magnitude of load oscillations from the fuel cell. This therefore addresses two of the main modes of fuel cell degradation in automotive applications: rapid power cycling and no load idling.

  • Journal article
    Troxler Y, Wu B, Marinescu M, Yufit V, Patel Y, Marquis AJ, Brandon NP, Offer GJet al., 2013,

    The effect of thermal gradients on the performance of lithium ion batteries

    , Journal of Power Sources, Pages: accepted-accepted, ISSN: 0378-7753

    Abstract An experimental apparatus is described, in which Peltier elements are used for thermal control of lithium-ion cells under isothermal and non-isothermal conditions, i.e. to induce and maintain thermal gradients. Lithium-ion battery packs for automotive applications consist of hundreds of cells, and depending on the pack architecture, individual cells may experience non-uniform thermal boundary conditions. This paper presents the first study of the impact of artificially induced thermal gradients on cell performance. The charge transfer resistance of a 4.8 Ah is verified to have a strong temperature dependence following the Arrhenius law. Thermal cycling of the cell, combined with slow rate cyclic voltammetry, allows to rapidly identify phase transitions in electrodes, due to the thermal effect of entropy changes. A cell with a temperature gradient maintained across is found to have a lower impedance than one held at the theoretical average temperature. This feature is attributed to details of the inner structure of the cell, and to the non-linear temperature dependence of the charge transfer resistance.

  • Conference paper
    von Srbik MT, Martinez-Botas R, 2012,

    Vehicle Optimisation for Regenerative Brake Energy Maximisation

    , IMechE Sustainable Vehicles Technologies Conference

    Regenerative braking is an effective method to increase the driving range of Hybrid Electric Vehicles (HEV) and to reduce overall vehicle fuel consumption. This paper presents the potential savings due to regenerative braking and the resulting driving range extension. A Cooperative Regenerative Braking Strategy (CRBS) Matlab/Simulink environment has been developed. The regenerative energy and efficiency are evaluated for given driving cycle time-trace and vehicle component configuration in a flexible simulation platform architecture containing reduced-order component models.The paper focuses on vehicle configuration comparison and quantification including economic considerations. A sensitivity study yielded the isolated dependency of regeneration efficiency performance on several parameters, in decreasing order of impact: electric machine efficiency, drive type, power train configuration, brake torque application, shifting strategy, air resistance and vehicle mass. The resulting significance to improvements of the overall vehicle includes the likelihood of advances in the respective technologies.Optimum configurations for specific vehicle types and driving scenarios have been devised and potential savings due to CRBS implementation quantified; pointing towards the great significance of vehicle configuration optimisation for a particular application rather than the broadest customer base possible.Future projections in terms of Carbon Dioxide emission reduction due to regenerative braking and component optimisation (up to 40%) were made. The likelihood of technology advances and acceleration of innovation market diffusion following consumption trends were taken into account.Barriers to quick market implementation were explored, including initial capital investment, consumer reluctance to change, and marketing difficulties. Future development challenges in the Hybrid vehicle industry are discussed.

  • Report
    Contestabile M, Offer GJ, North R, 2012,

    Electric Vehicles: A Synthesis of the Current Literature with a Focus on Economic and Environmental Viability

    , Publisher: LCAworks
  • Journal article
    Brightman E, Maher R, Offer GJ, Duboviks V, Heck C, Cohen LF, Brandon NPet al., 2012,

    Designing a miniaturised heated stage for in situ optical measurements of solid oxide fuel cell electrode surfaces, and probing the oxidation of solid oxide fuel cell anodes using in situ Raman spectroscopy

    , REVIEW OF SCIENTIFIC INSTRUMENTS, Vol: 83, ISSN: 0034-6748
  • Journal article
    Offer GJ, Yufit V, Howey DA, Wu B, Brandon NPet al., 2012,

    Module design and fault diagnosis in electric vehicle batteries

    , Journal of Power Sources

    Systems integration issues, such as electrical and thermal design and management of full battery packs–often containing hundreds of cells–have been rarely explored in the academic literature. In this paper we discuss the design and construction of a 9 kWh battery pack for a motorsports application. The pack contained 504 lithium cells arranged into 2 sidepods, each containing 3 modules, with each module in a 12P7S configuration. This paper focuses particularly on testing the full battery pack and diagnosing subsequent problems related to cells being connected in parallel. We demonstrate how a full vehicle test can be used to identify malfunctioning strings of cells for further investigation. After individual cell testing it was concluded that a single high inter-cell contact resistance was causing currents to flow unevenly within the pack, leading to cells being unequally worked. This is supported by a Matlab/Simulink model of one battery module, including contact resistances. Over time the unequal current flowing through cells can lead to significant differences in cells’ state of charge and open circuit voltages, large currents flowing between cells even when the load is disconnected, cells discharging and aging more quickly than others, and jeopardise capacity and lifetime of the pack.

  • Conference paper
    Wu B, Offer GJ, Yufit V, Howey DA, Brandon NPet al., 2012,

    Fault analysis in battery module design for electric and hybrid vehicles

    , Power Electronics, Machines and Drive
  • Journal article
    Wu B, Matian M, Offer GJ, 2012,

    Hydrogen PEMFC system for automotive applications

    , International Journal of Low Carbon Technologies

    A balance of plant (BOP) system for a 9.5-kWe Nedstack P9.5-75 low-temperature proton exchange membrane fuel cell (FC) stack was tested up to a power of 2 kWe. The system has been designed to act as a range extender for a series hybrid electric vehicle driven under urban duty cycles. Vehicle simulations have estimated that an average gross power requirement of 4 kWe is needed from the FC, whilst simulations of the FC stack and BOP components have allowed for characterisation of transient behaviour and performance degradation.

  • Journal article
    Marinescu M, Urbakh M, Kornyshev AA, 2012,

    Voltage-dependent capacitance of metallic nanoparticles at a liquid/liquid interface

    , PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 14, Pages: 1371-1380, ISSN: 1463-9076
  • Journal article
    Kornyshev AA, Marinescu M, Paget J, Urbakh Met al., 2012,

    Reflection of light by metal nanoparticles at electrodes

    , PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 14, Pages: 1850-1859, ISSN: 1463-9076
  • Journal article
    Marinescu M, Kornyshev AA, Flatte ME, 2012,

    Electrical control of Faraday rotation at a liquid/liquid interface

    , Applied Physics Letters
  • Journal article
    Contestabile M, Offer GJ, Slade R, Jaeger F, Thoennes Met al., 2011,

    Battery electric vehicles, hydrogen fuel cells and biofuels. Which will be the winner?

    , Energy and Environmental Science, Vol: 10, Pages: 3754-3772
  • Journal article
    Offer GJ, Contestabile M, Howey DA, Clague R, Brandon NPet al., 2011,

    Techno-economic and behavioural analysis of battery electric, hydrogen fuel cell and hybrid vehicles in a future sustainable road transport system in the UK

    , Energy Policy, Vol: 39, Pages: 1939-1950, ISSN: 0301-4215
  • Journal article
    Marinescu M, Urbakh M, Barnea T, Kucernak AR, Kornyshev AAet al., 2010,

    Electrowetting Dynamics Facilitated by Pulsing

    , JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 114, Pages: 22558-22565, ISSN: 1932-7447
  • Journal article
    Kornyshev AA, Kucernak AR, Marinescu M, Monroe CW, Sleightholme AES, Urbakh Met al., 2010,

    Ultra-Low-Voltage Electrowetting

    , JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 114, Pages: 14885-14890, ISSN: 1932-7447
  • Report
    DECC, 2010,

    2050 Pathways Analysis. Department Energy and Climate Change

    , 2050 Pathways Analysis, URN 10D/764

    The analysis in the 2050 Pathways work presents a framework through which to consider some of the choices and trade-offs which we will have to make over the next forty years. It is system-wide, covering all parts of the economy and all greenhouse gas emissions released in the UK. It shows that it is possible for us to meet the 80% emissions reduction target in a range of ways, and allows people to explore the combinations of effort which meet the emissions target while matching energy supply and demand.

  • Journal article
    Offer GJ, Howey DA, Contestabile M, Clague R, Brandon NPet al., 2010,

    Comparative analysis of battery electric, hydrogen fuel cell and hybrid vehicles in a future sustainable road transport system

    , Energy Policy, Vol: 38, Pages: 24-29

    This paper compares battery electric vehicles (BEV) to hydrogen fuel cell electric vehicles (FCEV) and hydrogen fuel cell plug-in hybrid vehicles (FCHEV). Qualitative comparisons of technologies and infrastructural requirements, and quantitative comparisons of the lifecycle cost of the powertrain over 100,000 mile are undertaken, accounting for capital and fuel costs. A common vehicle platform is assumed. The 2030 scenario is discussed and compared to a conventional gasoline-fuelled internal combustion engine (ICE) powertrain. A comprehensive sensitivity analysis shows that in 2030 FCEVs could achieve lifecycle cost parity with conventional gasoline vehicles. However, both the BEV and FCHEV have significantly lower lifecycle costs. In the 2030 scenario, powertrain lifecycle costs of FCEVs range from $7360 to $22,580, whereas those for BEVs range from $6460 to $11,420 and FCHEVs, from $4310 to $12,540. All vehicle platforms exhibit significant cost sensitivity to powertrain capital cost. The BEV and FCHEV are relatively insensitive to electricity costs but the FCHEV and FCV are sensitive to hydrogen cost. The BEV and FCHEV are reasonably similar in lifecycle cost and one may offer an advantage over the other depending on driving patterns. A key conclusion is that the best path for future development of FCEVs is the FCHEV.

  • Journal article
    Brett DJL, Kucernak AR, Aguiar P, Atkins SC, Brandon NP, Clague R, Cohen LF, Hinds G, Kalyvas C, Offer GJ, Ladewig B, Maher R, Marquis A, Shearing P, Vasileiadis N, Vesovic Vet al., 2010,

    What happens inside a fuel cell? Developing an experimental functional map of fuel cell performance

    , ChemPhysChem, Vol: 11, Pages: 2714-2731
  • Journal article
    Cordner M, Matian M, Offer GJ, Hanten T, al Eet al., 2010,

    Designing, building, testing and racing a low-cost fuel cell range extender for a motorsport application

    , Journal of Power Sources
  • Journal article
    Offer GJ, Brandon NP, 2009,

    The effect of current density and temperature on the degradation of nickel cermet electrodes by carbon monoxide in solid oxide fuel cells

    , CHEMICAL ENGINEERING SCIENCE, Vol: 64, Pages: 2291-2300, ISSN: 0009-2509
  • Journal article
    Offer GJ, Mermelstein J, Brightman E, Brandon NPet al., 2009,

    Thermodynamics and Kinetics of the Interaction of Carbon and Sulfur with Solid Oxide fuel Cell Anodes

    , JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Vol: 92, Pages: 763-780, ISSN: 0002-7820

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Dr Ian Campbell

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