Publications
58 results found
Pang M-C, Hao Y, Wang H, et al., 2019, What is the rate-limiting mechanism in solid-state lithium cells at different pulse operating conditions?, 236th ECS Meeting
Pang M-C, Hao Y, Wang H, et al., 2019, Experimental Parameterisation of the Continuum Models for Solid-state Lithium Batteries, 3rd Annual Oxford ECS Student Chapter Symposium
Campbell I, Gopalakrishnan K, Marinescu M, et al., 2019, Optimising lithium-ion cell design for plug-in hybrid and battery electric vehicles, Journal of Energy Storage, Vol: 22, Pages: 228-238, ISSN: 2352-152X
Increased driving range and enhanced fast charging capabilities are two immediate goals of transport electrification. However, these are of competing nature, leading to increased energy and power demand respectively from the on-board battery pack. By fine-tuning the number of layers versus active electrode material of a lithium ion pouch cell, tailored designs targeting either of these goals can be obtained. Achieving this trade-off through iterative empirical testing of layer choices is expensive and often produces sub-optimal designs. This paper presents a model-based methodology for determining the optimal number of layers, maximising usable energy whilst satisfying specific acceleration and fast charging targets. The proposed methodology accounts for the critical need to avoid lithium plating during fast charging and searches for the optimal layer configuration considering a range of thermal conditions. A numerical implementation of a cell model using a hybrid finite volume-spectral scheme is presented, wherein the model equations are suitably reformulated to directly accept power inputs, facilitating rapid and accurate searching of the layer design space. Electrode materials exhibiting high solid phase diffusion rates are highlighted as being equally as important for extended range as the development of new materials with higher inherent capacity. The proposed methodology is demonstrated for the common module design of a battery pack in a plug-in hybrid vehicle, thereby illustrating how the cost of derivative vehicle models can be reduced. To facilitate model based layer optimisation, the open-source toolbox, BOLD (Battery Optimal Layer Design) is provided.
Campbell ID, Marzook M, Marinescu M, et al., 2019, How observable Is lithium plating? Differential voltage analysis to identify and quantify lithium plating following fast charging of cold lithium-Ion batteries, Journal of The Electrochemical Society, Vol: 166, Pages: A725-A739, ISSN: 0013-4651
Fast charging of batteries is currently limited, particularly at low temperatures, due to difficulties in understanding lithium plating. Accurate, online quantification of lithium plating increases safety, enables charging at speeds closer to the electrochemical limit and accelerates charge profile development. This work uses different cell cooling strategies to expose how voltage plateaus arising from cell self-heating and concentration gradients during fast charging can falsely indicate plating, contrary to prevalent current assumptions. A solution is provided using Differential Voltage (DV) analysis, which confirms that lithium stripping is observable. However, scanning electron microscopy and energy-dispersive X-ray analysis are used to demonstrate the inability of the plateau technique to detect plating under certain conditions. The work highlights error in conventional plating quantification that leads to the dangerous underestimation of plated amounts. A novel method of using voltage plateau end-point gradients is proposed to extend the sensitivity of the technique, enabling measurement of lower levels of lithium stripping and plating. The results are especially relevant to automotive OEMs and engineers wishing to expand their online and offline tools for fast charging algorithm development, charge management and state-of-health diagnostics.
Pang M-C, Hao Y, Wang H, et al., 2019, Electrochemical Modelling of Relaxation Behaviour in Solid-state Lithium Batteries: From Measurements to Application Design, Materials for Clean Energy Conference
Hua X, Zhang T, Offer GJ, et al., 2019, Towards online tracking of the shuttle effect in lithium sulfur batteries using differential thermal voltammetry, Journal of Energy Storage, Vol: 21, Pages: 765-772
© 2019 Lithium sulfur (Li-S) batteries are an important next generation high energy density battery technology. However, the phenomenon known as the polysulfide shuttle causes accelerated degradation, reduced Coulombic efficiency and increased heat generation, particularly towards the end of charge. The real-time detection of the onset of shuttle during charge would improve the safety and increase cycle life of Li-S batteries in real applications. In this study, we demonstrate that the Differential Thermal Voltammetry (DTV) technique can be used for tracking shuttle during Li-S charging. By combining voltage and temperature measurements, DTV is shown to be sensitive to the magnitude of shuttle. We demonstrate significant differences in the DTV curves for Li-S cells charged at different currents and temperatures. Quantitative interpretations of the experimental DTV curves are performed through a thermally-coupled zero-dimensional Li-S model. The DTV technique, together with the model, is a promising tool for real-time detection of shuttle in applications, to inform control algorithms for deciding the end of charging, thus preventing excessive degradation and charge inefficiency.
Zhang T, Marinescu M, Offer GJ, 2019, Lithium-sulfur model development, Lithium-Sulfur Batteries, Pages: 229-247, ISBN: 9781119297864
Physics-based Li-S models provide a useful tool for understanding the complex physics and electrochemistry of Li-S cells such as polysulfide dissolution and shuttle. By elucidating the limiting processes and degradation mechanisms at cell level, Li-S models inform the rational design and optimization of Li-S cell components for achieving higher energy density and longer cycle life. Physics-based Li-S models also provide a mathematical framework for deriving reduced-order battery models necessary for the development of Li-S battery control and management systems. A battery management system with accurate Li-S models for state-of-charge (SoC) and state-of-health (SoH) estimations is essential for achieving high energy utilization and low degradation rate of Li-S batteries in applications. This chapter reviews models from zero-dimensional models to multi-scale models and the information they can provide.
Marinescu M, O'Neill L, Zhang T, et al., 2018, Irreversible vs reversible capacity fade of lithium-sulfur batteries during cycling: the effects of precipitation and shuttle, Journal of The Electrochemical Society, Vol: 165, Pages: A6107-A6118, ISSN: 1945-7111
Lithium-sulfur batteries could deliver significantly higher gravimetric energy density and lower cost than Li-ion batteries. Their mass adoption, however, depends on many factors, not least on attaining a predictive understanding of the mechanisms that determine their performance under realistic operational conditions, such as partial charge/discharge cycles. This work addresses a lack of such understanding by studying experimentally and theoretically the response to partial cycling. A lithium-sulfur model is used to analyze the mechanisms dictating the experimentally observed response to partial cycling. The zero-dimensional electrochemical model tracks the time evolution of sulfur species, accounting for two electrochemical reactions, one precipitation/dissolution reaction with nucleation, and shuttle, allowing direct access to the true cell state of charge. The experimentally observed voltage drift is predicted by the model as a result of the interplay between shuttle and the dissolution bottleneck. Other features are shown to be caused by capacity fade. We propose a model of irreversible sulfur loss associated with shuttle, such as caused by reactions on the anode. We find a reversible and an irreversible contribution to the observed capacity fade, and verify experimentally that the reversible component, caused by the dissolution bottleneck, can be recovered through slow charging. This model can be the basis for cycling parameters optimization, or for identifying degradation mechanisms relevant in applications. The model code is released as Supplementary material B.
Hunt I, Zhang T, Patel Y, et al., 2017, The effect of current inhomogeneity on the performance and degradation of Li-S batteries, Journal of the Electrochemical Society, Vol: 165, Pages: A6073-A6080, ISSN: 0013-4651
The effect of thermal gradients on the performance and cycle life of Li-S batteries is studied using bespoke single-layer Li-S cells, with isothermal boundary conditions maintained by Peltier elements. A temperature difference is shown to cause significant current imbalance between parallel connected single-layer cells, causing the hotter cell to provide more charge and discharge capacities during cycling. During charge, significant shuttle is induced in the hotter Li-S cell, causing accelerated degradation of it. A bespoke multi-tab cell in which the inner layers are electrically connected to different tabs versus the outer layers, is used to demonstrate that noticeable current inhomogeneity occurs during the operation of practical multilayer Li-S pouch cells, which is expected to affect their performance and degradation. The observed thermal and current inhomogeneity should have a direct consequence on battery pack and thermal management system design for real world Li-S battery packs.
Cleaver T, Kovacik P, Marinescu M, et al., 2017, Perspective—commercializing lithium sulfur batteries: Are we doing the right research?, Journal of The Electrochemical Society, Vol: 165, Pages: A6029-A6033, ISSN: 0013-4651
A picture of the challenges faced by the lithium-sulfur technology and the activities pursued by the research community to solve them is synthesized based on 1992 scientific articles. It is shown that, against its own advice of adopting a balanced approach to development, the community has instead focused work on the cathode. To help direct future work, key areas of neglected research are highlighted, including cell operation studies, modelling, anode, electrolyte and production methods, as well as development goals for real world target applications such as high altitude unmanned aerial vehicles.
Zhang T, Marinescu M, Walus S, et al., 2017, What Limits the Rate Capability of Li-S Batteries during Discharge: Charge Transfer or Mass Transfer?, Journal of the Electrochemical Society, Vol: 165, Pages: A6001-A6004, ISSN: 0013-4651
Li-S batteries exhibit poor rate capability under lean electrolyte conditions required for achieving high practical energy densities. In this contribution, we argue that the rate capability of commercially-viable Li-S batteries is mainly limited by mass transfer rather than charge transfer during discharge. We first present experimental evidence showing that the charge-transfer resistance of Li-S batteries and hence the cathode surface covered by Li2S are proportional to the state-of-charge (SoC) and not to the current, directly contradicting previous theories. We further demonstrate that the observed Li-S behaviors for different discharge rates are qualitatively captured by a zero-dimensional Li-S model with transport-limited reaction currents. This is the first Li-S model to also reproduce the characteristic overshoot in voltage at the beginning of charge, suggesting its cause is the increase in charge transfer resistance brought by Li2S precipitation.
Zhang T, Marinescu M, Walus S, et al., 2016, Modelling transport-limited discharge capacity of lithium-sulfur cells, Electrochimica Acta, Vol: 219, Pages: 502-508, ISSN: 0013-4686
Lithium-sulfur (Li-S) battery could bring a step-change in battery technology with a potential specific energy density of 500 - 600 Wh/kg. A key challenge for further improving the specific energy-density of Li-S cells is to understand the mechanisms behind reduced sulfur utilisation at low electrolyte loadings and high discharge currents. While several Li-S models have been developed to explore the discharge mechanisms of Li-S cells, they so far fail to capture the discharge profiles at high currents. In this study, we propose that the slow ionic transport in concentrated electrolyte is limiting the rate capability of Li-S cells. This transport-limitation mechanism is demonstrated through a one-dimensional Li-S model which qualitatively captures the discharge capacities of a sulfolane-based Li-S cell at different currents. Furthermore, our model predicts that a discharged Li-S cell is able regain some capacity with a short period of relaxation. This capacity recovery phenomenon is validated experimentally for different discharge currents and relaxation durations. The transport-limited discharge behavior of Li-S cells highlights the importance of optimizing the electrolyte loading and electrolyte transport property in Li-S cells.
von Srbik M-T, Marinescu M, Martinez-Botas RF, et al., 2016, A physically meaningful equivalent circuit network model of a lithium-ion battery accounting for local electrochemical and thermal behaviour, variable double layer capacitance and degradation, Journal of Power Sources, Vol: 325, Pages: 171-184, ISSN: 0378-7753
A novel electrical circuit analogy is proposed modellingelectrochemical systems under realistic automotive operation conditions. The model is developed for a lithium ion battery and is based on a pseudo 2D electrochemical model. Although cast in the framework familiar to application engineers, the model is essentially an electrochemical battery model: all variables have a direct physical interpretation and there is direct access to all states of the cell via the model variables (concentrations, potentials) for monitoring and control systems design. This is the first Equivalent Circuit Network-type model that tracks directly the evolution of species inside the cell. It accounts for complex electrochemical phenomena that are usually omitted in online battery performance predictors such as variable double layer capacitance, the full current-overpotential relation and overpotentials due to mass transport limitations. The coupled electrochemical and thermal model accounts for capacity fade via a loss in active species and for power fade via an increase in resistive solid electrolyte passivation layers at both electrodes. The model's capability to simulate cell behaviour under dynamic events is validated against test procedures, such as standard battery testing load cycles for current rates up to 20 C, as well as realistic automotive drive cycle loads.
Sarwar W, Engstrom T, Marinescu M, et al., 2016, Experimental analysis of Hybridised Energy Storage Systems for automotive applications, Journal of Power Sources, Vol: 324, Pages: 388-401, ISSN: 0378-7753
The requirements of the Energy Storage System (ESS) for an electrified vehicle portfolio consisting of a range of vehicles from micro Hybrid Electric Vehicle (mHEV) to a Battery Electric Vehicle (BEV) vary considerably. To reduce development cost of an electrified powertrain portfolio, a modular system would ideally be scaled across each vehicle; however, the conflicting requirements of a mHEV and BEV prevent this. This study investigates whether it is possible to combine supercapacitors suitable for an mHEV with high-energy batteries suitable for use in a BEV to create a Hybridised Energy Storage System (HESS) suitable for use in a HEV. A passive HESS is found to be capable of meeting the electrical demands of a HEV drive cycle; the operating principles of HESSs are discussed and factors limiting system performance are explored. The performance of the HESS is found to be significantly less temperature dependent than battery-only systems, however the heat generated suggests a requirement for thermal management. As the HESS degrades (at a similar rate to a specialised high-power-battery), battery resistance rises faster than supercapacitor resistance; as a result, the supercapacitor provides a greater current contribution, therefore the energy throughput, temperature rise and degradation of the batteries is reduced.
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.
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.
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.
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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- Citations: 811
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.
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.
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.
Sumislawska M, Burnham KJ, Marinescu MM, et al., 2013, Reduction of high fidelity lithium-ion battery model via data-driven system identification, Hybrid and Electric Vehicles Conference 2013 (HEVC 2013), Publisher: Institution of Engineering and Technology
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
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- Citations: 11
Marinescu M, Kornyshev AA, Flatte ME, 2012, Electrical control of Faraday rotation at a liquid/liquid interface, Applied Physics Letters
Kornyshev AA, Marinescu M, Paget J, et al., 2012, Reflection of light by metal nanoparticles at electrodes, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 14, Pages: 1850-1859, ISSN: 1463-9076
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- Citations: 27
Marinescu M, Urbakh M, Barnea T, et al., 2010, Electrowetting Dynamics Facilitated by Pulsing, JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 114, Pages: 22558-22565, ISSN: 1932-7447
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- Citations: 20
Kornyshev AA, Kucernak AR, Marinescu M, et al., 2010, Ultra-Low-Voltage Electrowetting, JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 114, Pages: 14885-14890, ISSN: 1932-7447
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- Citations: 44
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