Publications
180 results found
Propp K, Marinescu M, Auger DJ, et al., 2016, Multi-temperature state-dependent equivalent circuit discharge model for lithium-sulfur batteries, Journal of Power Sources, Vol: 328, Pages: 289-299, ISSN: 1873-2755
Lithium-sulfur (Li-S) batteries are described extensively in the literature, but existing computational models aimed at scientific understanding are too complex for use in applications such as battery management. Computationally simple models are vital for exploitation. This paper proposes a non-linear state-of-charge dependent Li-S equivalent circuit network (ECN) model for a Li-S cell under discharge. Li-S batteries are fundamentally different to Li-ion batteries, and require chemistry-specific models. A new Li-S model is obtained using a ‘behavioural’ interpretation of the ECN model; as Li-S exhibits a ‘steep’ open-circuit voltage (OCV) profile at high states-of-charge, identification methods are designed to take into account OCV changes during current pulses. The prediction-error minimization technique is used. The model is parameterized from laboratory experiments using a mixed-size current pulse profile at four temperatures from 10 °C to 50 °C, giving linearized ECN parameters for a range of states-of-charge, currents and temperatures. These are used to create a nonlinear polynomial-based battery model suitable for use in a battery management system. When the model is used to predict the behaviour of a validation data set representing an automotive NEDC driving cycle, the terminal voltage predictions are judged accurate with a root mean square error of 32 mV.
Wu B, Parkes MP, de Benedetti L, et al., 2016, Real-time monitoring of proton exchange membrane fuel cell stack failure, Journal of Applied Electrochemistry, Vol: 46, Pages: 1157-1162, ISSN: 1572-8838
Uneven pressure drops in a 75-cell 9.5-kWe protonexchange membrane fuel cell stack with a U-shaped flowconfiguration have been shown to cause localised flooding.Condensed water then leads to localised cell heating, resultingin reduced membrane durability. Upon purging of the anodemanifold, the resulting mechanical strain on the membranecan lead to the formation of a pin-hole/membrane crack and arapid decrease in open circuit voltage due to gas crossover.This failure has the potential to cascade to neighbouring cellsdue to the bipolar plate coupling and the current densityheterogeneities arising from the pin-hole/membrane crack.Reintroduction of hydrogen after failure results in cell voltageloss propagating from the pin-hole/membrane crack locationdue to reactant crossover from the anode to the cathode, giventhat the anode pressure is higher than the cathode pressure.Through these observations, it is recommended that purging isavoided when the onset of flooding is observed to preventirreparable damage to the stack.
Hunt I, Zhao Y, Patel Y, et al., 2016, Surface cooling causes accelerated degradation compared to tab cooling for lithium-Ion pouch cells, Journal of the Electrochemical Society, Vol: 163, Pages: A1846-A1852, ISSN: 0013-4651
One of the biggest causes of degradation in lithium-ion batteries is elevated temperature. In this study we explored the effects ofcell surface cooling and cell tab cooling, reproducing two typical cooling systems that are used in real-world battery packs. For newcells using slow-rate standardized testing, very little difference in capacity was seen. However, at higher rates, discharging the cellin just 10 minutes, surface cooling led to a loss of useable capacity of 9.2% compared to 1.2% for cell tab cooling. After cyclingthe cells for 1,000 times, surface cooling resulted in a rate of loss of useable capacity under load three times higher than cell tabcooling. We show that this is due to thermal gradients being perpendicular to the layers for surface cooling leading to higher localcurrents and faster degradation, but in-plane with the layers for tab cooling leading to more homogenous behavior. Understandinghow thermal management systems interact with the operation of batteries is therefore critical in extending their performance. Forautomotive applications where 80% capacity is considered end-of-life, using tab cooling rather than surface cooling would thereforebe equivalent to extending the lifetime of a pack by 3 times, or reducing the lifetime cost by 66%.
Sarwar W, Offer G, Gopalakrishnan K, et al., 2016, Combined Battery/Supercapacitor Hybridised Energy Storage Systems for Hybrid Electric Vehicles, 18th International Meeting on Lithium Batteries (IMLB), Publisher: The Electrochemical Society (ECS), ISSN: 0160-4619
Automakers are striving to increase electric vehicle driving range without compromising performance and simultaneously reducing charging times. However, this requires an increase of both the energy and power density of the Energy Storage System (ESS); though in battery design these two attributes are generally mutually exclusive therefore a compromise must be made. It is hypothesised that a Hybridised Energy Storage System (HESS) consisting of Supercapacitors (SC) and high energy density batteries in parallel with no DC/DC converter could result in an ESS with improved energy and power density in comparison to an ESS consisting of batteries only. To enable automotive engineers to design such systems we have created a toolset (i.e. models) that can accurately reproduce the behaviour of such a HESS, in particular, the interactions between the battery and SC. Further, the tool is valid over a range of conditions known to affect system performance such as temperature. The tools are also validated with experimental data where the individual contributions of the battery and SC can be assessed.A high-fidelity physically meaningful electrical Equivalent Circuit Model (ECM) of a supercapacitor is combined with a physical pseudo-3D thermal model. Separately, a physics-based battery model is generated and parameterised for an NCA 18650 cell. Model order reduction techniques are used to obtain an acceptable simulation time, resulting in a physics-informed electrical ECM which is subsequently coupled with a high-fidelity thermal model. Both models are individually validated across a range of operating conditions including temperature and current. The validated models are paired and the HESS model is validated over an automotive drive cycle with a particular emphasis placed upon battery current and temperature evolution. The generated toolset demonstrated that a HESS can provide superior performance to a battery only system for particular applications, however power availabilit
Offer GJ, Hunt I, Merla Y, et al., 2016, Detecting, Diagnosing and Controlling Degradation in Lithium Ion Battery Packs, ECS Meeting Abstracts, Vol: MA2016-03, Pages: 1196-1196
<jats:p> <jats:sup> </jats:sup>One of the biggest causes of degradation in lithium-ion batteries is elevated temperature. In electric vehicle, particularly hybrid vehicle applications this can be very difficult to manage, and without fundamentally redesigning the cell is the province of the battery pack engineer. Yet how battery pack design affects both cell performance and degradation has been very poorly studied in the past. The latest work of the electrochemical science & engineering group at Imperial College London on understanding how thermal gradients affect performance and degradation, and how thermal techniques can be used to detect and diagnose path dependent degradation will be presented. State-of-the-art models that can reproduce the diagnostic outputs and can be embedded in battery management systems and could therefore be used for diagnostic and even prognostic purposes in real world battery packs will also be presented. </jats:p> <jats:p>Recent work exploring the effect of cell surface cooling and cell tab cooling is shown, reproducing two typical cooling systems that are used in real-world battery packs. It is shown that cooling method alone can significantly affect useable capacity. For new cells at C/20 discharge, very little difference in capacity was seen, however, at 6C discharge surface cooling led to a loss of useable capacity of 9.2% compared to 1.2% for cell tab cooling. Furthermore, after cycling the cells for a 1,000 times at 6C discharge and 2C charge, surface cooling resulted in a degradation rate three times higher than cell tab cooling. Using incremental capacity analysis, electrochemical impedance analysis and thermal models of cells, it is shown that this is due to thermal gradients being perpendicular to the layers for surface cooling leading to higher local currents and faster degradation, but in-plane with the layers for tab cooling leading to more ho
Gopalakrishnan K, Zhang T, Offer GJ, 2016, A Fast, Efficient Discrete-Time Realization Algorithm for Reduced-Order Battery Models, ECS Meeting Abstracts, Vol: MA2016-03, Pages: 844-844
<jats:p> Research into reduced-order models (ROM) for lithium-ion batteries is motivated by need for a real-time embedded model with the accuracy of physics-based models but having computational simplicity comparable to that of equivalent-circuit models. An attractive approach to this problem was recently proposed by Lee et al [1] with a model order reduction method known as Discrete-time-Realization Algorithm (DRA). The ROM obtained in standard state-space representation could then be used to obtain the time-evolution of all the internal electrochemical quantities of the standard porous-electrode model. An unresolved issue of this reduced-order modelling approach is the high computation requirement associated with the DRA, which has to be performed multiple times to identify cell parameters at various SOC and temperatures. </jats:p> <jats:p>In this presentation, we analyse the computational bottleneck in the existing DRA and propose a significant improvement to the overall modelling procedure. Our analysis indicates the Singular Value Decomposition of a large Block-Hankel matrix of the system’s Markov parameters is a key inefficient step for the overall high computational requirement of DRA. A fast computational approach is presented that significantly reduces both the memory and the floating-point operation count by bypassing the redundant step of forming the large Block-Hankel matrix. Comparisons with the existing DRA method highlight the significant reduction in computation time and memory usage (Figure 1), as well as the accuracy improvement in key electrochemical quantities, afforded by our new method. With the aid of the improved modelling procedure, the transfer functions forming the porous electrode model is reformulated and suitably combined to arrive at a physics-informed equivalent circuit model of the Panasonic NCA 18650 BD cells used in automotive applications.</jats:p> <jats:p> <
Offer GJ, Zhang T, Marinescu M, et al., 2016, Understanding Lithium Sulfur Cells, Modelling the Mechanisms behind Voltage- and Capacity-Drop during Discharge, ECS Meeting Abstracts, Vol: MA2016-03, Pages: 775-775
<jats:p> The lithium-sulphur (Li-S) cell could provide the next step-change in battery technology with a promising practical energy density of 500-600 Wh/kg. However, a lack of understanding of the complex electrochemical, transport, and phase-change phenomena in Li-S cells is arguably holding back development. Acquiring this knowledge requires experimental characterizations in tandem with mechanistic modelling. In this presentation, we will give an overview of our work on understanding and modelling lithium sulfur cells, and include our latest work on models that capture the essential features of lithium sulfur cell performance. We will also discuss how these models are being used to increase the useable performance of lithium sulfur cells, inform cell design and materials selection, and to create reduced order models for control and system design. </jats:p> <jats:p>Existing Li-S models do not sufficiently capture the voltage- and capacity-drop mechanisms of Li-S cells during discharge. We first demonstrate that introducing a concentration dependence of the electrolyte conductivity is necessary to retrieve the experimentally documented trends in electrolyte resistance, which contributes to a major voltage-loss mechanism for high-energy density Li-S cells. We further illustrate the existence of an often overlooked potential drop mechanism – the ‘precipitation overpotential’ – which originates from the limited rate of lithium sulphide precipitation. In addition, we propose that the rate capability of high energy-density Li-S cells is mainly limited by the slow transport of ionic species, as is evident from the good agreement between experimental and model-predicted capacity loss at high discharge currents as well as a cell capacity recovery phenomenon that we report for the first time. </jats:p> <jats:p>References: </jats:p> <jats:p>Modeling the voltage loss m
Shahed Khah N, Offer GJ, Patel Y, et al., 2016, The Effects of High G Impacts on Li-Ion Batteries, ECS Meeting Abstracts, Vol: MA2016-03, Pages: 1036-1036
<jats:p> Increasing electrification of vehicles has led to a growing demand for Li-ion batteries in automotive applications. Automotive vehicles experience cyclic mechanical loads during operation, which may include; acceleration, deceleration, shock, vibration and collision. Most of these events are not severe and do not have an instantaneous effect on the battery, however it is unclear if there is a cumulative effect over time. This cumulative effect may have a significant impact on performance and safety of the battery. The collective effect of these types of mechanical events is not well characterised and there exists a gap in knowledge. This is due to the difficulty in replicating real world conditions in the laboratory. </jats:p> <jats:p>This project focusses on the study of Li-ion batteries during static testing (3-point bend) and dynamic testing (acceleration/deceleration pulses). Several 3 point bend tests were carried out where the cell was bent to up to 30 mm and the relaxation behaviour was captured by monitoring the reduction in load over time. The electrochemical impedance of the cells was also monitored during the relaxation period and then cycled between 2.7 and 4.2 V. After each cycle, EIS was performed in order to detect impedance variation. The gradual separation of the internal structure of the cells was also captured using X-ray tomography as demonstared in fig.1. This image reveals clear separation of the internal layers at the point of contact with the side rollers and this significant separation will directly impact the performance of the cell in long term. High precision coulometry was also used as another technique to predict the cycle life of the cells besides identifying any degradation mechanism due to the severe bending. For dynamic testing cells were exposed to up to 1000 g pulses, using a drop tower (10 kJ maximum energy input). Impedance, differential capacity, and capacity of the cells were analysed
Shahed Khah N, Offer GJ, Patel Y, et al., 2016, The Effects of High G Impacts on Li-Ion Batteries, ECS Meeting Abstracts, Vol: MA2016-01, Pages: 460-460
<jats:p>Increasing electrification of vehicles has led to a growing demand for Li-ion batteries in automotive applications. Automotive vehicles experience cyclic mechanical loads during operation, which may include; acceleration, deceleration, shock, vibration and collision. Most of these events are not severe and do not have an instantaneous effect on the battery, however it is unclear if there is a cumulative effect over time. This cumulative effect may have a significant impact on performance and safety of the battery. The collective effect of these types of mechanical events is not well characterised and there exists a gap in knowledge. This is due to the difficulty in replicating real world conditions in the laboratory. </jats:p> <jats:p>This project focusses on the study of Li-ion batteries during static testing (3-point bend) and dynamic testing (acceleration/deceleration pulses). Several 3 point bend tests were carried out where the cell was bent to up to 30 mm and the relaxation behaviour was captured by monitoring the reduction in load over time. The electrochemical impedance of the cells was also monitored during the relaxation period and then cycled between 2.7 and 4.2 V. After each cycle, EIS was performed in order to detect impedance variation. The gradual separation of the internal structure of the cells was also captured using X-ray tomography as demonstared in fig.1. This image reveals clear separation of the internal layers at the point of contact with the side rollers and this significant separation will directly impact the performance of the cell in long term. High precision coulometry was also used as another technique to predict the cycle life of the cells besides identifying any degradation mechanism due to the severe bending. For dynamic testing cells were exposed to up to 1000 g pulses, using a drop tower (10 kJ maximum energy input). Impedance, differential capacity, and capacity of the cells were analysed be
Wu B, Merla Y, Yufit V, et al., 2016, Novel application of differential thermal voltammetry as an in-depth state-of-health diagnosis method for lithium-ion batteries, Journal of Power Sources, Vol: 307, Pages: 308-319, ISSN: 1873-2755
Understanding and tracking battery degradation mechanisms and adapting its operation have become a necessity in order to enhance battery durability. A novel use of differential thermal voltammetry (DTV) is presented as an in-situ state-of-health (SOH) estimator for lithium-ion batteries.Accelerated ageing experiments were carried on 5Ah commercial lithium-ion polymer cells operated and stored at different temperature and loading conditions. The cells were analysed regularly with various existing in-situ diagnosis methods and the novel DTV technique to determine their SOH. The diagnosis results were used collectively to elaborate the degradation mechanisms inside the cells. The DTV spectra were decoupled into individual peaks, which each represent particular phases in the negative and positive electrode combined. The peak parameters were used to quantitatively analyse the battery SOH.A different cell of the same chemistry with unknown degradation history was then analysed to explore how the cell degraded. The DTV technique was able to diagnose the cell degradation without relying on supporting results from other methods nor previous cycling data.
Marinescu M, Zhang T, Offer G, 2016, A zero dimensional model of lithium-sulfur batteries during charge and discharge, Physical Chemistry Chemical Physics, Vol: 18, Pages: 584-593, ISSN: 1463-9076
Lithium-sulfur cells present an attractive alternative to Li-ion batteries due to their large energy density, safety, and possible low cost. Their successful commercialisation is dependent on improving their performance, but also on acquiring sufficient understanding of the underlying mechanisms to allow for the development of predictive models for operational cells. To address the latter, we present a zero dimensional model that predicts many observed features in the behaviour of a lithium-sulfur cell during charge and discharge. The model accounts for two electrochemical reactions via the Nernst formulation, power limitations through Butler-Volmer kinetics, and precipitation/dissolution of one species, including nucleation. It is shown that the precipitation/dissolution causes the flat shape of the low voltage plateau, typical of the lithium-sulfur cell discharge. During charge, it is predicted that the dissolution can act as a bottleneck, as for large enough currents smaller amounts dissolve. This results in reduced charge capacity and an earlier onset of the high plateau reaction, such that the two plateaus merge. By including these effects, the model improves on the existing zero dimensional models, while requiring considerably fewer input parameters and computational resources. The model also predicts that, due to precipitation, the customary way of experimentally measuring the open circuit voltage from a low rate discharge might not be suitable for lithium-sulfur. This model can provide the basis for mechanistic studies, identification of dominant effects in a real cell, predictions of operational behaviour under realistic loads, and control algorithms for applications.
Parkes MA, Chen T, Wu B, et al., 2015, “can” you really make a battery out of that?, Journal of Chemical Education, Vol: 93, Pages: 681-686, ISSN: 1938-1328
This classroom activity introduces students to battery electrochemistry through the construction of a simple battery made from household products. Students will use a set of simple design rules to improve the performance of the battery, and power a light emitting diode. The electrochemical performance of the batteries is characterized using potentiostatic cyclic voltammetry and chronoampometry, and suggestions for implementing this activity into a high school teaching environment are presented. Designed for United Kingdom secondary schools and exam boards, the supplementary teaching package contains problem sheets and activities appropriate for students age 14 and up.
Sarwar W, Marinescu M, Green N, et al., 2015, Electrochemical double layer capacitor electro-thermal modelling, Journal of Energy Storage, Vol: 5, Pages: 10-24, ISSN: 2352-152X
An electro-thermal model is generated to predict the internal temperature of an electrochemical double-layer capacitor (EDLC) undergoing high current charging/discharging. The model is capable of predicting the electrical and thermal behavior of a cell over a wide range of operating conditions. Spiral symmetry is used to reduce the heat generation and transfer model from 3D to a pseudo-3D, which runs faster without losing fidelity. Unlike existing models, each element in the developed model retains physical meaning and the electrical model is coupled with a high-fidelity thermal model including material geometries, thermal properties and air gaps. Unequal entropy is calculated using first principles, included in the model and compared to experimental data, and shown to be valid. More entropic heat is generated at the positive electrode than the negative in a typical EDLC, and there is little spatial variation of heat generation rate within the jelly-roll. The heat-transfer model predicts temperature variations within a cell; this study examines these variations for multiple conditions. Whilst undergoing high current charging (2 s, 400 A, 650 F cell), a temperature gradient in excess of 3.5 °C can be generated between the positive terminal and the jelly-roll. The time dependent spatial temperature distribution within a cell is explored.
Zhang T, Marinescu M, O'Neill L, et al., 2015, Modeling the voltage loss mechanisms in lithium-sulfur cells: the importance of electrolyte resistance and precipitation kinetics., Physical Chemistry Chemical Physics, Vol: 17, Pages: 22581-22586, ISSN: 1463-9084
Understanding of the complex electrochemical, transport, and phase-change phenomena in Li-S cells requires experimental characterization in tandem with mechanistic modeling. However, existing Li-S models currently contradict some key features of experimental findings, particularly the evolution of cell resistance during discharge. We demonstrate that, by introducing a concentration-dependent electrolyte conductivity, the correct trends in voltage drop due to electrolyte resistance and activation overpotentials are retrieved. In addition, we reveal the existence of an often overlooked potential drop mechanism in the low voltage-plateau which originates from the limited rate of Li2S precipitation.
Lomberg M, Boldrin P, Tariq F, et 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.
Mazur CM, Brandon, Offer, et al., 2015, Understanding the drivers of fleet emission reduction activities of the German car manufacturers, Environmental Innovation and Societal Transitions, Vol: 16, Pages: 3-21, ISSN: 2210-4224
The current mobility system, dominated by fossil fuel poweredautomobiles, is under increasing pressure due to its environmentalimpact. To address this issue there is a need for a transitionof the system towards one that is more sustainable, including theintroduction of car technologies that allow a decrease in fuel consumptionand the substitution of fossil fuels as primary energysource. Due to the stability of the current automotive industryand the dominance of the internal combustion engine technology,it is expected that the incumbent firms and their activities willplay a crucial role in the transition. Policy makers have thereforeintroduced a variety of policies to encourage the industry to providesuitable solutions.We have conducted amicro-level analysis of howthe threemain German carmanufacturers have changed their activitiesin the field of low emission vehicle technologies in response tonational/international events and policy making. Our analysis suggeststhat policy makers only have limited influence on the typeof disruptive solution that is chosen by these individual companiesand that activities related to solutions that were not familiar to theindividual car manufacturer were mainly induced by internal or external champions. Still, while the existence of regulatory policiesallowed such activities to succeed, on its own it only encouraged theindustry to work on incremental solutions based upon the knowledgealready possessed.
Duboviks V, Lomberg M, Maher RC, et al., 2015, Carbon deposition behaviour in metal-infiltrated gadolinia doped ceria electrodes for simulated biogas upgrading in solid oxide electrolysis cells, Journal of Power Sources, Vol: 293, Pages: 912-921, ISSN: 1873-2755
One of the attractive applications for reversible Solid Oxide Cells (SOCs) is to convert CO2 into CO via high temperature electrolysis, which is particularly important for biogas upgrading. To improve biogas utility, the CO2 component can be converted into fuel via electrolysis. A significant issue for SOC operation on biogas is carbon-induced catalyst deactivation. Nickel is widely used in SOC electrodes for reasons of cost and performance, but it has a low tolerance to carbon deposition. Two different modes of carbon formation on Ni-based electrodes are proposed in the present work based on ex-situ Raman measurements which are in agreement with previous studies. While copper is known to be resistant towards carbon formation, two significant issues have prevented its application in SOC electrodes – namely its relatively low melting temperature, inhibiting high temperature sintering, and low catalytic activity for hydrogen oxidation. In this study, the electrodes were prepared through a low temperature metal infiltration technique. Since the metal infiltration technique avoids high sintering temperatures, Cu–Ce0.9Gd0.1O2−δ (Cu-CGO) electrodes were fabricated and tested as an alternative to Ni-CGO electrodes. We demonstrate that the performance of Cu-CGO electrodes is equivalent to Ni-CGO electrodes, whilst carbon formation is fully suppressed when operated on biogas mixture.
Parkes MA, Refson K, d'Avezac M, et al., 2015, Chemical descriptors of yttria-stabilized zirconia at low defect concentration: an ab initio study., Journal of Physical Chemistry A, Vol: 119, Pages: 6412-6420, ISSN: 1520-5215
Yttria-stabilized zirconia (YSZ) is an important oxide ion conductor with applications in solid oxide fuel cells (SOFCs) and oxygen sensing devices. Doping the cubic phase of zirconia (c-ZrO2) with yttria (Y2O3) is isoelectronic, as two Zr(4+) ions are replaced by two Y(3+) ions, plus a charge compensating oxygen vacancy (Ovac). Typical doping concentrations include 3, 8, 10, and 12 mol %. For these concentrations, and all below 40 mol %, no phase with long-range order has been observed in either X-ray or neutron diffraction experiments. The prediction of local defect structure and the interaction between defects is therefore of great interest. This has not been possible to date as the number of possible defect topologies is very large and to perform reliable total energy calculations for all of them would be prohibitively expensive. Previous theoretical studies have only considered a selection of representative structures. In this study, a comprehensive search for low-energy defect structures using a combined classical modeling and density functional theory approach is used to identify the low-energy isolated defect structures at the dilute limit, 3.2 mol %. Through analysis of energetics computed using the best available Born-Mayer-Huggins empirical potential model, a point charge model, DFT, and a local strain energy estimated in the harmonic approximation, the main chemical and physical descriptors that correlate to the low-energy DFT structures are discussed. It is found that the empirical potential model reproduces a general trend of increasing DFT energetics across a series of locally strain relaxed structures but is unreliable both in predicting some incorrect low-energy structures and in finding some metastable structures to be unstable. A better predictor of low-energy defect structures is found to be the total electrostatic energy of a simple point charge model calculated at the unrelaxed geometries of the defects. In addition, the strain relaxation energ
Hunt IA, Patel Y, Szczygielski M, et al., 2015, Lithium Sulfur battery nail penetration test under load, Journal of Energy Storage
Finegan DP, Scheel M, Robinson JB, et al., 2015, In-operando high-speed tomography of lithium-ion batteries during thermal runaway, Nature Communications, Vol: 6, ISSN: 2041-1723
Hewa Dewage HARINI, wu BILLY, Tsoi ANTHONY, et al., 2015, A novel regenerative hydrogen cerium fuel cell for energy storage applications, Journal of Materials Chemistry A, Vol: 3, Pages: 9446-9450, ISSN: 2050-7496
A novel regenerative hydrogen cerium fuel cell is presented which has the potential to deliver both low cost and high performance. A 5 cm2 prototype is demonstrated, achieving 148 mW cm−2 when fully charged. Rate determining processes within the cell are identified.
Mazur C, Contestabile M, Offer GJ, et 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
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Wu B, Yufit V, Merla Y, et al., 2015, Differential thermal voltammetry for tracking of degradation in lithium-ion batteries, Journal of Power Sources, Vol: 273, Pages: 495-501, ISSN: 0378-7753
Monitoring of lithium-ion batteries is of critical importance in electric vehicle applications in order to manage the operational condition of the cells. Measurements on a vehicle often involve current, voltage and temperature which enable in-situ diagnostic techniques. This paper presents a novel diagnostic technique, termed differential thermal voltammetry, which is capable of monitoring the state of the battery using voltage and temperature measurements in galvanostatic operating modes. This tracks battery degradation through phase transitions, and the resulting entropic heat, occurring in the electrodes. Experiments to monitor battery degradation using the new technique are compared with a pseudo-2D cell model. Results show that the differential thermal voltammetry technique provides information comparable to that of slow rate cyclic voltammetry at shorter timescale and with load conditions easier to replicate in a vehicle.
Offer GJ, 2015, Automated vehicles and electrification of transport, ENERGY & ENVIRONMENTAL SCIENCE, Vol: 8, Pages: 26-30, ISSN: 1754-5692
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- Citations: 32
Wild M, O'Neill L, Zhang T, et al., 2015, Lithium sulfur batteries, a mechanistic review, ENERGY & ENVIRONMENTAL SCIENCE, Vol: 8, Pages: 3477-3494, ISSN: 1754-5692
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Duboviks V, Maher RC, Kishimoto M, et 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
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.
Lomberg M, Ruiz-Trejo E, Offer G, et al., 2014, Characterization of Ni-Infiltrated GDC Electrodes for Solid Oxide Cell Applications, JOURNAL OF THE ELECTROCHEMICAL SOCIETY, Vol: 161, Pages: F899-F905, ISSN: 0013-4651
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.
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