Publications
71 results found
Toleuova A, Maskell WC, Yufit V, et al., 2015, Mechanistic Studies of Liquid Metal Anode SOFCs I. Oxidation of Hydrogen in Chemical - Electrochemical Mode, JOURNAL OF THE ELECTROCHEMICAL SOCIETY, Vol: 162, Pages: F988-F999, ISSN: 0013-4651
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- Citations: 6
Tariq F, Kishimoto M, Yufit V, et al., 2014, 3D imaging and quantification of interfaces in SOFC anodes, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, Vol: 34, Pages: 3755-3761, ISSN: 0955-2219
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- Citations: 23
Howey DA, Yufit V, Mitcheson PD, et al., 2014, Impedance measurement for advanced battery management systems
We present a fast, low-cost approach to measure battery impedance 'on-line' in a vehicle across a range of frequencies (1-2000 Hz). Impedance measurement has promise for improving battery management since it is a very effective non-invasive method of diagnosing the internal state of an electrochemical cell. It is useful for estimating temperature, ageing, state of charge (SOC) and for fault detection. The aim of this paper is firstly to explore the usefulness of impedance for estimating SOC, focusing on lithium-ion iron phosphate (LFP) and nickel manganese cobalt oxide (NMC) cells, and secondly to demonstrate the performance of a low cost impedance measurement system that uses an existing motor drive similar to that of an electric vehicle to excite the battery current. We find that measurements made with this system are accurate to within a few per cent of results from an expensive, bulky commercial system. For SOC estimation in NMC cells, the charge transfer resistance and SEI layer resistance vary significantly with SOC. In LFP cells the parameter variation is much less obvious, although the double layer capacitance of the full pack may be a useful indicator of SOC.
Howey DA, Mitcheson PD, Yufit V, et 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.
Tariq F, Yufit V, Eastwood DS, et 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.
Wu B, Parkes MP, Yufit V, et 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.
Chakrabarti MH, Brandon NP, Hajimolana SA, et al., 2014, Application of carbon materials in redox flow batteries, JOURNAL OF POWER SOURCES, Vol: 253, Pages: 150-166, ISSN: 0378-7753
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- Citations: 238
Eastwood DS, Yufit V, Gelb J, et al., 2014, Lithiation- Induced Dilation Mapping in a Lithium- Ion Battery Electrode by 3D X- Ray Microscopy and Digital Volume Correlation, ADVANCED ENERGY MATERIALS, Vol: 4, ISSN: 1614-6832
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- Citations: 84
Tariq F, Yufit V, Kishimoto M, et al., 2014, Three-dimensional high resolution X-ray imaging and quantification of lithium ion battery mesocarbon microbead anodes, JOURNAL OF POWER SOURCES, Vol: 248, Pages: 1014-1020, ISSN: 0378-7753
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- Citations: 65
Tariq F, Yufit V, Kishimoto M, et al., 2014, Advanced 3D Imaging and Analysis of SOFC Electrodes, Symposium on Solid State Ionic Devices 10 held during the 226th Meeting of the Electrochemical-Society, Publisher: ELECTROCHEMICAL SOC INC, Pages: 81-86, ISSN: 1938-5862
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- Citations: 2
Wu B, Yufit V, Marinescu M, et 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.
Chakrabarti MH, Brandon NP, Mjalli FS, et al., 2013, Cyclic Voltammetry of Metallic Acetylacetonate Salts in Quaternary Ammonium and Phosphonium Based Deep Eutectic Solvents, JOURNAL OF SOLUTION CHEMISTRY, Vol: 42, Pages: 2329-2341, ISSN: 0095-9782
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- Citations: 19
Ristic M, Gryska Y, McGinley JVM, et al., 2013, Supercapacitor Energy Storage for Magnetic Resonance Imaging Systems, IEEE Transactions on Industrial Electronics, Vol: PP, ISSN: 0278-0046
Magnetic Resonance Imaging (MRI) involves very short pulses of very high current. Substantial savings in the high cost of MRI installations may be realised by employing suitable electrical energy storage, for which supercapacitors are strong candidates in view of high specific power and long cycle life. A key question is whether the well-known capacitance degradation with increased frequency is compatible with the complex and highly variable duty cycles of various MRI sequences. Compatibility of the supercapacitor voltage range with the MRI system must also be considered. We present a detailed analysis of power duty profiles in MRI, using actual imaging sequences, that has not been reported previously. We also propose and validate a simplified supercapacitor model that can accurately simulate its performance in the MRI system, involving pulses several orders of magnitude shorter than those considered previously. Results of equivalent experiments involving Lithium-Ion Iron Phosphate (LiFePO4) batteries are also reported. Finally, we present a detailed analysis of the overall energy storage performance in a realistic neurological examination. The study is based on a specific system of our own design and we fully disclose its relevant parameters, so that the results would be of direct practical value to the wider community, including developers of MRI.
Chakrabarti MH, Low CTJ, Brandon NP, et al., 2013, Progress in the electrochemical modification of graphene-based materials and their applications, Electrochimica Acta, Vol: 107, Pages: 425-440, ISSN: 0013-4686
Graphene is a 2D allotrope of carbon with exciting properties such as extremely high electronic conductivity and superior mechanical strength. It has considerable potential for applications in fields such as bio-sensors, electrochemical energy storage and electronics. In most cases, graphene has been functionalized and modified with other materials to prepare composites. This work reviews the electrochemical modification of graphene. Commencing with a brief history, a summary of several different means of modifying graphene to effect diverse applications is provided. This is followed by a discussion on different composite materials that have been prepared with reduced graphene oxide prior to moving onto a detailed consideration of six different methods of electrochemically modifying graphene to prepare composite materials. These methods involve cathodic reduction of graphene oxide, electrophoretic deposition, electro-deposition techniques, electrospinning, electrochemical doping and electrochemical polymerization. Finally a consideration on the applications of electrochemically modified graphene composite materials in various fields is presented prior to discussing some prospects in enhancing the electrochemical process to realize excellent and economic composite materials in bulk.
Somalu MR, Yufit V, Brandon NP, 2013, The effect of solids loading on the screen-printing and properties of nickel/scandia-stabilized-zirconia anodes for solid oxide fuel cells, INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, Vol: 38, Pages: 9500-9510, ISSN: 0360-3199
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- Citations: 33
Chakrabarti MH, Brandon NP, Hashim MA, et al., 2013, Cyclic Voltammetry of Iron (III) Acetylacetonate in Quaternary Ammonium and Phosphonium Based Deep Eutectic Solvents, INTERNATIONAL JOURNAL OF ELECTROCHEMICAL SCIENCE, Vol: 8, Pages: 9652-9676, ISSN: 1452-3981
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- Citations: 20
Somalu MR, Yufit V, Shapiro IP, et al., 2013, The impact of ink rheology on the properties of screen-printed solid oxide fuel cell anodes, INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, Vol: 38, Pages: 6789-6801, ISSN: 0360-3199
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- Citations: 27
Marinescu M, Wu B, Von Srbik M, et 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.
Wu B, Yufit V, Campbell J, et 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.
Troxler Y, Wu B, Marinescu M, et 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.
Yufit V, Hale B, Matian M, et al., 2013, Development of a Regenerative Hydrogen-Vanadium Fuel Cell for Energy Storage Applications, JOURNAL OF THE ELECTROCHEMICAL SOCIETY, Vol: 160, Pages: A856-A861, ISSN: 0013-4651
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- Citations: 38
Somalu MR, Muchtar A, Baboli MG, et al., 2013, Understanding the Relationship between Ink Rheology and Film Properties for Screen-Printed Nickel/Scandia-Stabilized-Zirconia Anodes, 13th International Symposium on Solid Oxide Fuel Cells (SOFC-XIII), Publisher: ELECTROCHEMICAL SOC INC, Pages: 1321-1330, ISSN: 1938-5862
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- Citations: 9
Toleuova A, Yufit V, Simons SJR, et al., 2013, A Rotating Electrolyte Disc (RED) for Operation in Liquid Metal Anode SOFCs, Conference on High Temperature Experimental Techniques and Measurements at the 224th Electrochemical-Society Meeting (ECS), Publisher: ELECTROCHEMICAL SOC INC, Pages: 65-70, ISSN: 1938-5862
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- Citations: 1
Touleva A, Yufit V, Simons S, et al., 2013, A review of liquid metal anode solid oxide fuel cells, Journal of Electrochemical Science and Engineering
Offer GJ, Yufit V, Howey DA, et 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.
Wu B, Offer GJ, Yufit V, et al., 2012, Fault analysis in battery module design for electric and hybrid vehicles, Power Electronics, Machines and Drive
Yufit V, Shearing P, Hamilton RW, et al., 2011, Investigation of lithium-ion polymer battery cell failure using X-ray computed tomography, ELECTROCHEMISTRY COMMUNICATIONS, Vol: 13, Pages: 608-610, ISSN: 1388-2481
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- Citations: 89
Somalu MR, Yufit V, Cumming D, et al., 2011, Fabrication and characterization of Ni/ScSZ cermet anodes for IT-SOFCs, INTERNATIONAL JOURNAL OF HYDROGEN ENERGY, Vol: 36, Pages: 5557-5566, ISSN: 0360-3199
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- Citations: 65
Yufit V, Brandon NP, 2011, Development and application of an actively controlled hybrid proton exchange membrane fuel cell-Lithium-ion battery laboratory test-bed based on off-the-shelf components, JOURNAL OF POWER SOURCES, Vol: 196, Pages: 801-807, ISSN: 0378-7753
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- Citations: 9
Somalu MR, Brandon NP, Yufit V, 2011, A Study of the Rheological Properties of NiO/ScSZ Screen-Printing Inks and Their Application to SOFC Anodes, 12th International Symposium on Solid Oxide Fuel Cells (SOFC), Publisher: ELECTROCHEMICAL SOC INC, Pages: 1483-1500, ISSN: 1938-5862
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- Citations: 5
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