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  • Journal article
    Nguyen T-T, Demortière A, Fleutot B, Delobel B, Delacourt C, Cooper Set al., 2020,

    The electrode tortuosity factor: why the conventional tortuosity factor is not well suited for quantifying transport in porous Li-ion battery electrodes and what to use instead

    , npj Computational Materials, Vol: 6, ISSN: 2057-3960

    The tortuosity factor of porous battery electrodes is an important parameter used to correlate electrode microstructure with performance through numerical modeling. Therefore, having an appropriate method for the accurate determination of tortuosity factors is critical. This paper presents a numerical approach, based on simulations performed on microstructural image data, which enables a comparison between two common experimental methods. Several key issues with the conventional “flow through” type tortuosity factor are highlighted, when used to characterise electrodes. As a result, a new concept called the “electrode tortuosity factor” is introduced, which captures the transport processes relevant to porous electrodes better than the “flow through” type tortuosity factor. The simulation results from this work demonstrate the importance of non-percolating (“dead-end”) pores in the performance of real electrodes. This is an important result for optimizing electrode design that should be considered by electrochemical modelers. This simulation tool is provided as an open-source MATLAB application and is freely available online as part of the TauFactor platform.

  • Journal article
    Gayon-Lombardo A, Lukas M, Brandon N, Cooper Set al., 2020,

    Pores for thought: generative adversarial networks for stochastic reconstruction of 3D multi-phase electrode microstructures with periodic boundaries

    , npj Computational Materials, Vol: 6, ISSN: 2057-3960

    The generation of multiphase porous electrode microstructures is a critical step in the optimisation of electrochemical energy storage devices. This work implements a deep convolutional generative adversarial network (DC-GAN) for generating realistic n-phase microstructural data. The same network architecture is successfully applied to two very different three-phase microstructures: A lithium-ion battery cathode and a solid oxide fuel cell anode. A comparison between the real and synthetic data is performed in terms of the morphological properties (volume fraction, specific surface area, triple-phase boundary) and transport properties (relative diffusivity), as well as the two-point correlation function. The results show excellent agreement between datasets and they are also visually indistinguishable. By modifying the input to the generator, we show that it is possible to generate microstructure with periodic boundaries in all three directions. This has the potential to significantly reduce the simulated volume required to be considered “representative” and therefore massively reduce the computational cost of the electrochemical simulations necessary to predict the performance of a particular microstructure during optimisation.

  • Journal article
    Nguyen T-T, Demortiere A, Fleutot B, Delobel B, Cooper SJ, Delacourt Cet al., 2020,

    Resolving the Discrepancy in Tortuosity Determination for Battery Porous Electrodes Via a Numerical Approach

    , ECS Meeting Abstracts, Vol: MA2020-01, Pages: 2724-2724
  • 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
    Boldrin P, Brandon NP, 2019,

    Progress and outlook for solid oxide fuel cells for transportation applications

    , Nature Catalysis, Vol: 2, Pages: 571-577, ISSN: 2520-1158

    With their high temperatures and brittle ceramic components, solid oxide fuel cells (SOFCs) might not seem the obvious fit for a power source for transportation applications. However, over recent years, advances in materials and cell design have begun to mitigate these issues, leading to the advantages of SOFCs such as fuel flexibility and high efficiency being exploited in vehicles. Here, we review these advances, look at the vehicles that SOFCs have already been used in, discuss the areas that need improvement for full commercial breakthrough and the ways in which catalysis can assist with these. In particular, we identify lifetime and degradation, fuel flexibility, efficiency and power density as key aspects for SOFCs’ improvement. Expertise from the catalysis landscape, ranging from surface science and computational materials design, to improvements in reforming catalysts and reformer design, are instrumental to this goal.

  • Journal article
    Chen J, Ouyang M, Boldrin P, Liu X, Darr J, Atkinson A, Brandon NPet al., 2019,

    Fabrication and Characterisation of Nanoscale Ni-CGO Electrode from Nano-Composite Powders

    , ECS Transactions, Vol: 91, Pages: 1799-1805, ISSN: 1938-6737
  • Journal article
    Ouyang M, Bertei A, Cooper SJ, Wu Y, Liu X, Boldrin P, Kishimoto M, Wu B, Brandon NPet al., 2019,

    Design of fibre Ni/CGO anode and model interpretation

    , ECS Transactions, Vol: 91, Pages: 1721-1739, ISSN: 1938-6737

    A new structure of Ni/gadolinium-doped ceria (CGO) is prepared by a highly tuneable and facile combination of electrospinning and tape-casting method. The structure consists of a network made by continuous Ni fibres and filled in with CGO matrices. When used as the anode of solid oxide fuel cell (SOFC), though it has a lower triple phase boundary (TPB) density, it exhibits better performance compared with impregnated and cermet Ni/CGO with higher nickel loading. An algorithm is developed to determine the ceria-pore double phase boundary (DPB) density with different distance from nickel phase. Using the results, the relative electrochemical reaction rate on DPB and TPB of three different electrodes are calculated and proves that fibre-matrices structure has the morphology advantage of efficiently making use of all ceria-pore DPB. The relative contribution of DPB and TPB in anode reaction of SOFC is quantified in the first time and the importance of DPB is further stressed. This work provides new inspirations in material design of SOFC/SOEC and develops a novel strategy to evaluate the performance of electrodes quantitatively.

  • Conference paper
    Stevenson GR, Boldrin P, Brandon NP, 2019,

    Liquid-based synthesis of nickel- And lanthanum- co-doped strontium titanates for use as anodes in all-ceramic solid oxide fuel cell anodes

    , Pages: 1761-1770, ISSN: 1938-6737

    Nickel- lanthanum- co-doped compositions of strontium titanate have been synthesized and characterized by a scaleable liquid-based synthesis that may offer an alternative to conventional solid-state synthesis. La Sr Ti Ni O is synthesized from soluble precursors followed by calcination in air. The materials can be made phase pure at temperatures as low as 1250°C, as highlighted by X-ray diffraction, and nickel exsolves in hydrogen in the same way as solid-state-synthesized materials. The particle size can be varied by calcination temperature and ball milling between 2 µm and 20 µm. The material is then measured electrochemically by electrochemical impedance spectroscopy and 4-point DC conductivity. A reduction in particle size from 20 µm to 9 µm results in a large improvement in impedance response measured. 0.52 0.28 0.94 0.06 3

  • Journal article
    Daemi SR, Tan C, Volkenandt T, Cooper SJ, Palacios-Padros A, Cookson J, Brett DJL, Shearing PRet al., 2018,

    Visualizing the carbon binder phase of battery electrodes in three dimensions

    , ACS Applied Energy Materials, Vol: 1, Pages: 3702-3710, ISSN: 2574-0962

    This study presents a technique to directly characterize the carbon and binder domain (CBD) in lithium-ion (Li-ion) battery electrodes in three dimensions and use it to determine the effective transport properties of a LiNi0.33Mn0.33Co0.33O2 (NMC) electrode. X-ray nanocomputed tomography (nano-CT) is used to image an electrode composed solely of carbon and binder, whereas focused ion beam–scanning electron microscopy is used to analyze cross-sections of a NMC electrode to gain morphological information regarding the electrode and CBD porosity. Combining the information gathered from these techniques reduces the uncertainty inherent in segmenting the nano-CT CBD data set and enables effective diffusivity of its porous network to be determined. X-ray microcomputed tomography (micro-CT) is then used to collect a NMC data set that is subsequently segmented into three phases, comprised of active material, pore, and CBD. The effective diffusivity calculated for the nano-CT data set is incorporated for the CBD present in the micro-CT data set to estimate the ensemble tortuosity factor for the NMC electrode. The tortuosity factor greatly increases when compared to the same data set segmented without considering the CBD. The porous network of the NMC electrode is studied with a continuous pore size distribution approach that highlights median radii of 180 nm and 1 μm for the CBD and NMC pores, respectively, and with a pore throat size distribution calculation that highlights median equivalent radii of 350 and 700 nm.

  • Journal article
    Niania M, Podor R, Britton TB, Li C, Cooper SJ, Svetkov N, Skinner S, Kilner Jet al., 2018,

    In situ study of strontium segregation in La<inf>0.6</inf>Sr<inf>0.4</inf>Co<inf>0.2</inf>Fe<inf>0.8</inf>O<inf>3- δ</inf>in ambient atmospheres using high-temperature environmental scanning electron microscopy

    , Journal of Materials Chemistry A, Vol: 6, Pages: 14120-14135, ISSN: 2050-7496

    Samples of the solid oxide fuel cell cathode material La0.6Sr0.4Co0.2Fe0.8O3-δ(LSCF) were annealed using High-Temperature Environmental Scanning Electron Microscopy (HT-ESEM) from room temperature to 1000 °C in atmospheres of pure oxygen, pure water and ambient lab air. Image series of each heat treatment were taken where microstructural changes were observed and compared between samples. Strontium segregation rate was found to be significantly increased in the presence of pure water as compared to pure O2and ambient air. Electron backscattered diffraction (EBSD) was performed in order to assess the effect of crystal orientation on particle formation and surface sensitive chemical analysis techniques were used to determine the chemical changes at the grain surface as a result of the different heat treatments. It was shown that crystal orientation affected the nature and growth rate of strontium-based particles, however, due to the pseudo-symmetry of La0.6Sr0.4Co0.2Fe0.8O3-δ, precise crystal orientation relationships could not be determined. The chemical composition of the grain surface was found to be approximately equal under each atmosphere.

  • Journal article
    Téllez Lozano H, Druce J, Cooper SJ, Kilner JAet al., 2017,

    Double perovskite cathodes for proton-conducting ceramic fuel cells: are they triple mixed ionic electronic conductors?

    , Science and Technology of Advanced Materials, Vol: 18, Pages: 977-986, ISSN: 1468-6996

    Published by National Institute for Materials Science in partnership with Taylor & Francis. 18 O and 2 H diffusion has been investigated at a temperature of 300 °C in the double perovskite material PrBaCo 2 O 5+δ (PBCO) in flowing air containing 200 mbar of 2 H 2 16 O. Secondary ion mass spectrometry (SIMS) depth profiling of exchanged ceramics has shown PBCO still retains significant oxygen diffusivity (~1.3 × 10 −11 cm 2 s −1 ) at this temperature and that the presence of water ( 2 H 2 16 O), gives rise to an enhancement of the surface exchange rate over that in pure oxygen by a factor of ~3. The 2 H distribution, as inferred from the 2 H 2 16 O − SIMS signal, shows an apparent depth profile which could be interpreted as 2 H diffusion. However, examination of the 3-D distribution of the signal shows it to be nonhomogeneous and probably related to the presence of hydrated layers in the interior walls of pores and is not due to proton diffusion. This suggests that PBCO acts mainly as an oxygen ion mixed conductor when used in PCFC devices, although the presence of a small amount of protonic conductivity cannot be discounted in these materials.

  • Conference paper
    Ouyang M, Boldrin P, Brandon NP, 2017,

    Methane Pulse Study on Nickel Impregnated Gadolinium Doped Ceria

    , 15th International Symposium on Solid Oxide Fuel Cells (SOFC), Publisher: ELECTROCHEMICAL SOC INC, Pages: 1353-1366, ISSN: 1938-5862
  • Book chapter
    Cooper SJ, brandon NP, 2017,

    Solid Oxide Fuel Cell Lifetime and Reliability

    , Solid Oxide Fuel Cell Lifetime and Reliability Critical Challenges in Fuel Cells, Editors: Ruiz-Trejo, BOLDRIN, Publisher: Academic Press, Pages: 1-15, ISBN: 9780128097243

    For its holistic approach, this book can be used both as an introduction to these issues and a reference resource for all involved in research and application of solid oxide fuel cells, especially those developing understanding in ...

  • Book chapter
    Cassidy M, Neagu D, Savaniu C, Boldrin Pet al., 2017,

    New Materials for Improved Durability and Robustness in Solid Oxide Fuel Cell

    , Solid Oxide Fuel Cell Lifetime and Reliability: Critical Challenges in Fuel Cells, Pages: 193-216, ISBN: 9780081011027

    This chapter provides an overview of the considerations that must be made regarding new materials development for improved durability and robustness in solid oxide fuel cells (SOFCs). A number of recent development concepts are outlined for the core cell materials of anode, electrolyte, and cathode, in particular new catalytic approaches such as catalyst impregnation and exsolution on the anode to improve redox and fuel flexibility and reduced temperature cathodes. Some of the challenges of scaling up into larger stacks are also discussed. Here the interactions of cell materials with stack materials, in particular the interconnect, are summarized, such as chromium poisoning and cell to interconnect electrical contact, both of which feature prominently in SOFC stack lifetime issues. Barriers to new materials development are outlined along with the potential for accelerated testing.

  • Book
    Brandon NP, Ruiz-Trejo E, Boldrin P, 2017,

    Solid Oxide Fuel Cell Lifetime and Reliability: Critical Challenges in Fuel Cells

    , ISBN: 9780081011027

    Solid Oxide Fuel Cell Lifetime and Reliability: Critical Challenges in Fuel Cells presents in one volume the most recent research that aims at solving key issues for the deployment of SOFC at a commercial scale and for a wider range of applications. To achieve that, authors from different regions and backgrounds address topics such as electrolytes, contaminants, redox cycling, gas-tight seals, and electrode microstructure. Lifetime issues for particular elements of the fuel cells, like cathodes, interconnects, and fuel processors, are covered as well as new materials. They also examine the balance of SOFC plants, correlations between structure and electrochemical performance, methods for analysis of performance and degradation assessment, and computational and statistical approaches to quantify degradation. For its holistic approach, this book can be used both as an introduction to these issues and a reference resource for all involved in research and application of solid oxide fuel cells, especially those developing understanding in industrial applications of the lifetime issues. This includes researchers in academia and industrial R&D, graduate students and professionals in energy engineering, electrochemistry, and materials sciences for energy applications. It might also be of particular interest to analysts who are looking into integrating SOFCs into energy systems. Brings together in a single volume leading research and expert thinking around the broad topic of SOFC lifetime and durability. Explores issues that affect solid oxide fuel cells elements, materials, and systems with a holistic approach. Provides a practical reference for overcoming some of the common failure mechanisms of SOFCs. Features coverage of integrating SOFCs into energy systems.

  • Conference paper
    Millan M, Lorente E, Boldrin P, Brandon Net al., 2016,

    Integration of gasification and fuel cells: Interaction between the anode and contaminants in the syngas

    Fouling due to carbon deposition on the fuel cell anode reduces the performance of the cell. • The addition of steam above S/C of 1 was found to reduce carbon deposition from tars but not fully suppress coke formation. • A combination of high S/C=ratio and current density may effectively inhibit carbon formation, maintaining cell performance. • Benzene and toluene represent a "worst-case scenario" as tar models and light fractions are more likely to produce carbon deposits.

  • Conference paper
    Lomberg M, Boldrin P, Tariq F, Offer G, Wu B, Brandon NPet al., 2015,

    Additive manufacturing for solid oxide cell electrode fabrication

    , ECS Conference on Electrochemical Energy Conversion & Storage with SOFC-XIV, Publisher: Electrochemical Society, Pages: 2119-2127, ISSN: 1938-6737

    Additive manufacturing can potentially offer a highly-defined electrode microstructure, as well as fast and reproducible electrode fabrication. Selective laser sintering is an additive manufacturing technique in which three-dimensional structures are created by bonding subsequent layers of powder using a laser. Although selective laser sintering can be applied to a wide range of materials, including metals and ceramics, the scientific and technical aspects of the manufacturing parameters and their impact on microstructural evolution during the process are not well understood. In the present study, a novel approach for electrode fabrication using selective laser sintering was evaluated by conducting a proof of concept study. A Ni-patterned fuel electrode was laser sintered on an yttria-stabilized zirconia substrate. The optimization process of laser parameters (laser sintering rate and laser power) and the electrochemical results of a full cell with a laser sintered electrode are presented. The challenges and prospects of using selective laser sintering for solid oxide cell fabrication are discussed.

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

    Assessing and comparing German and UK transition policies for electric mobility

  • 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

    This paper presents a fast cost-effective technique for the measurement of battery impedance online in an application such as an electric or hybrid vehicle. Impedance measurements on lithium-ion batteries between 1 Hz and 2 kHz give information about the electrochemical reactions within a cell, which relates to the state of charge (SOC), internal temperature, and state of health (SOH). We concentrate on the development of a measurement system for impedance that, for the first time, uses an excitation current generated by a motor controller. Using simple electronics to amplify and filter the voltage and current, we demonstrate accurate impedance measurements obtained with both multisine and noise excitation signals, achieving RMS magnitude measurement uncertainties between 1.9% and 5.8%, in comparison to a high-accuracy laboratory impedance analyzer. Achieving this requires calibration of the measurement circuits, including measurement of the inductance of the current sense resistor. A statistical correlation approach is used to extract the impedance information from the measured voltage and current signals in the presence of noise, allowing a wide range of excitation signals to be used. Finally, we also discuss the implementation challenges of an SOC estimation system based on impedance.

  • 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, Vol: 39, Pages: 7885-7896, ISSN: 0360-3199

    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
  • Conference paper
    Ruiz-Trejo E, Boldrin P, Lubin A, Tariq F, Brandon N, Fearn S, Chater R, Atkinson A, Tighe C, Darr Jet al., 2013,

    Silver-ceria composites for oxygen separation from air

    , 224th Electrochemical society meeting
  • 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

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