45 results found
White G, Hales A, Patel Y, et al., 2022, Novel methods for measuring the thermal diffusivity and the thermal conductivity of a lithium-ion battery, Applied Thermal Engineering, Vol: 212, Pages: 118573-118573, ISSN: 1359-4311
Huang M, Kirkaldy N, Zhao Y, et al., 2022, Quantitative characterisation of the layered structure within lithium-ion batteries using ultrasonic resonance, Journal of Energy Storage, Vol: 50, Pages: 1-14, ISSN: 2352-152X
Lithium-ion batteries (LIBs) are becoming an important energy storage solution to achieve carbon neutrality, but it remains challenging to characterise their internal states for the assurance of performance, durability and safety. This work reports a simple but powerful non-destructive characterisation technique, based on the formation of ultrasonic resonance from the repetitive layers within LIBs. A physical model is developed from the ground up, to interpret the results from standard experimental ultrasonic measurement setups. As output, the method delivers a range of critical pieces of information about the inner structure of LIBs, such as the number of layers, the average thicknesses of electrodes, the image of internal layers, and the states of charge variations across individual layers. This enables the quantitative tracking of internal cell properties, potentially providing new means of quality control during production processes, and tracking the states of health and charge during operation.
Russell F, Hales A, White G, et al., 2022, A system for determining Li-ion cell cooling coefficients., HardwareX, Vol: 11
Current battery data sheets focus on battery energy and power density, neglecting thermal performance. This leads to reduced system level efficiency since cells with poor thermal performance require larger, heavier cooling systems to maintain cell temperatures in a suitable range. To address this a new metric, the Cell Cooling Coefficient (CCC), has been developed and it's use as a tool for appropriate cell selection has been demonstrated. It also allows the pack designer to calculate which cooling direction method is most suitable by comparing CCC values for tab and surface cooling. The metric is the ratio between the heat rejected from the cell and the temperature difference between the hottest and coolest point. It therefore has units W K - 1 and allows a pack designer to easily calculate the required amount of cooling power for the cell given a maximum acceptable temperature rise. In this paper we describe a system and method for the accurate determination of the CCC with the aim of facilitating wider adoption of the metric. The system is able to reliably quantify the surface and tab cooling CCC of any pouch cell.
Diaz LB, Hales A, Marzook MW, et al., 2022, Measuring Irreversible Heat Generation in Lithium-Ion Batteries: An Experimental Methodology, JOURNAL OF THE ELECTROCHEMICAL SOCIETY, Vol: 169, ISSN: 0013-4651
Roe C, Feng X, White G, et al., 2022, Immersion cooling for lithium-ion batteries – a review, Journal of Power Sources, Vol: 525, Pages: 231094-231094, ISSN: 0378-7753
Battery thermal management systems are critical for high performance electric vehicles, where the ability to remove heat and homogenise temperature distributions in single cells and packs are key considerations. Immersion cooling, which submerges the battery in a dielectric fluid, has the potential of increasing the rate of heat transfer by 10,000 times relative to passive air cooling. In 2-phase systems, this performance increase is achieved through the latent heat of evaporation of the liquid-to-gas phase transition and the resulting turbulent 2-phase fluid flow. However, 2-phase systems require additional system complexity, and single-phase direct contact immersion cooling can still offer up to 1,000 times improvements in heat transfer over air cooled systems. Fluids which have been considered include: hydrofluoroethers, mineral oils, esters and water-glycol mixtures. This review therefore presents the current state-of-the-art in immersion cooling of lithium-ion batteries, discussing the performance implications of immersion cooling but also identifying gaps in the literature which include a lack of studies considering the lifetime, fluid stability, material compatibility, understanding around sustainability and use of immersion for battery safety. Insights from this review will therefore help researchers and developers, from academia and industry, towards creating higher power, safer and more durable electric vehicles.
Li S, Kirkaldy N, Zhang C, et al., 2021, Optimal cell tab design and cooling strategy for cylindrical lithium-ion batteries, Journal of Power Sources, Vol: 492, Pages: 1-16, ISSN: 0378-7753
The ability to correctly predict the behavior of lithium ion batteries is critical for safety, performance, cost and lifetime. Particularly important for this purpose is the prediction of the internal temperature of cells, because of the positive feedback between heat generation and current distribution. In this work, a comprehensive electro-thermal model is developed for a cylindrical lithium-ion cell. The model is comprehensively parameterized and validated with experimental data for 2170 cylindrical cells (LG M50T, NMC811), including direct core temperature measurements. The validated model is used to study different cell designs and cooling approaches and their effects on the internal temperature of the cell. Increasing the number of tabs connecting the jellyroll to the base of the cylindrical-can reduces the internal thermal gradient by up to 25.41%. On its own, side cooling is more effective than base cooling at removing heat, yet both result in thermal gradients within the cell of a similar magnitude, irrespective of the number of cell tabs. The results are of immediate interest to both cell manufacturers and battery pack designers, while the modelling and parameterization framework created is an essential tool for energy storage system design.
Edge JS, O'Kane S, Prosser R, et al., 2021, Lithium ion battery degradation: what you need to know, Physical Chemistry Chemical Physics, Vol: 23, Pages: 8200-8221, ISSN: 1463-9076
The expansion of lithium-ion batteries from consumer electronics to larger-scale transport and energy storage applications has made understanding the many mechanisms responsible for battery degradation increasingly important. The literature in this complex topic has grown considerably; this perspective aims to distil current knowledge into a succinct form, as a reference and a guide to understanding battery degradation. Unlike other reviews, this work emphasises the coupling between the different mechanisms and the different physical and chemical approaches used to trigger, identify and monitor various mechanisms, as well as the various computational models that attempt to simulate these interactions. Degradation is separated into three levels: the actual mechanisms themselves, the observable consequences at cell level called modes and the operational effects such as capacity or power fade. Five principal and thirteen secondary mechanisms were found that are generally considered to be the cause of degradation during normal operation, which all give rise to five observable modes. A flowchart illustrates the different feedback loops that couple the various forms of degradation, whilst a table is presented to highlight the experimental conditions that are most likely to trigger specific degradation mechanisms. Together, they provide a powerful guide to designing experiments or models for investigating battery degradation.
Prosser R, Offer G, Patel Y, 2021, Lithium-Ion Diagnostics: The First Quantitative In-Operando Technique for Diagnosing Lithium Ion Battery Degradation Modes under Load with Realistic Thermal Boundary Conditions, JOURNAL OF THE ELECTROCHEMICAL SOCIETY, Vol: 168, ISSN: 0013-4651
Hua X, Heckel C, Modrow N, et al., 2021, The prismatic surface cell cooling coefficient: A novel cell design optimisation tool & thermal parameterization method for a 3D discretised electro-thermal equivalent-circuit model, eTransportation, Vol: 7, Pages: 1-15, ISSN: 2590-1168
Thermal management of large format prismatic lithium ion batteries is challenging due to significant heat generation rates, long thermal ‘distances’ from the core to the surfaces and subsequent thermal gradients across the cell. The cell cooling coefficient (CCC) has been previously introduced to quantify how easy or hard it is to thermally manage a cell. Here we introduce its application to prismatic cells with a 90 Ah prismatic lithium iron phosphate cell with aluminium alloy casing. Further, a parameterised and discretised three-dimensional electro-thermal equivalent circuit model is developed in a commercially available software environment. The model is thermally and electrically validated experimentally against data including drive cycle noisy load and constant current CCC square wave load, with particular attention paid to the thermal boundary conditions. A quantitative study of the trade-off between cell energy density and surface CCC, and into casing material selection has been conducted here. The CCC enables comparison between cells, and the model enables a cell manufacturer to optimise the cell design and a systems developer to optimise the pack design. We recommend this is operated together holistically. This paper offers a cost-effective, time-efficient, convenient and quantitative way to achieve better and safer battery designs for multiple applications.
Hales A, Brouillet E, Wang Z, et al., 2021, Isothermal Temperature Control for Battery Testing and Battery Model Parameterization, SAE INTERNATIONAL JOURNAL OF ELECTRIFIED VEHICLES, Vol: 10, Pages: 105-122, ISSN: 2691-3747
Hales A, Prosser R, Diaz LB, et al., 2020, The Cell Cooling Coefficient as a design tool to optimise thermal management of lithium-ion cells in battery packs, ETRANSPORTATION, Vol: 6, ISSN: 2590-1168
Bravo Diaz L, He X, Hu Z, et al., 2020, Review—meta-review of fire safety of lithium-ion batteries: industry challenges and research contributions, Journal of The Electrochemical Society, Vol: 167, Pages: 1-14, ISSN: 0013-4651
The Lithium-ion battery (LIB) is an important technology for the present and future of energy storage, transport, and consumer electronics. However, many LIB types display a tendency to ignite or release gases. Although statistically rare, LIB fires pose hazards which are significantly different to other fire hazards in terms of initiation route, rate of spread, duration, toxicity, and suppression. For the first time, this paper collects and analyses the safety challenges faced by LIB industries across sectors, and compares them to the research contributions found in all the review papers in the field. The comparison identifies knowledge gaps and opportunities going forward. Industry and research efforts agree on the importance of understanding thermal runaway at the component and cell scales, and on the importance of developing prevention technologies. But much less research attention has been given to safety at the module and pack scales, or to other fire protection layers, such as compartmentation, detection or suppression. In order to close the gaps found and accelerate the arrival of new LIB safety solutions, we recommend closer collaborations between the battery and fire safety communities, which, supported by the major industries, could drive improvements, integration and harmonization of LIB safety across sectors.
Dondelewski O, Szemberg OConnor T, Zhao Y, et al., 2020, The role of cell geometry when selecting tab or surface cooling to minimise cell degradation, eTransportation, Vol: 5, Pages: 1-12, ISSN: 2590-1168
Thermal management of lithium ion batteries is critical to maintain cells at their optimum temperature and balance performance with degradation. Previous work has shown tab cooling to be better for performance and lifetime, but only if sufficient heat removal can be achieved, which depends in part on cell geometry. In this paper, a large form-factor pouch cell is shown to suffer from faster degradation when tab-cooled although still benefitting from higher useable energy. This paper introduces the ratio of surface-to-tab cell cooling coefficient, CCCratio, as a qualitative measure to assess a cell’s suitability for tab cooling. For low CCCratio cells, tab cooling results in more useable energy and lower degradation rates than surface cooling. However, the large pouch cell used in this study has a high CCCratio, indicating that it is difficult to remove sufficient heat through tab cooling. At beginning of life, tab cooling allows access to more usable energy in the cell, but the rate of high temperature-induced degradation is greater, compared to the surface cooled cell. As a result, the useable energy from the tab cooled cell diminishes more rapidly, and after a certain cycle count, the useable energy from the surface cooled cell is superior. The optimum cooling approach will therefore be dependent on the desired lifetime of the system. This research should be of particular interest to cell and battery pack designers.
Offer G, Patel Y, Hales A, et al., 2020, Cool metric for lithium-ion batteries could spur progress, Nature, Vol: 582, Pages: 485-487, ISSN: 0028-0836
Feng X, Merla Y, Weng C, et al., 2020, A reliable approach of differentiating discrete sampled-data for battery diagnosis, ETRANSPORTATION, Vol: 3, ISSN: 2590-1168
Hales A, Marzook MW, Bravo Diaz L, et al., 2020, The surface cell cooling coefficient: a standard to define heat rejection from lithium ion battery pouch cells, Journal of The Electrochemical Society, Vol: 167, ISSN: 0013-4651
There is no universal and quantifiable standard to compare a given cell model's capability to reject heat. The consequence of this is suboptimal cell designs because cell manufacturers do not have a metric to optimise. The Cell Cooling Coefficient for pouch cell tab cooling (CCC tabs ) defines a cell's capability to reject heat from its tabs. However, surface cooling remains the thermal management approach of choice for automotive and other high-power applications. This study introduces a surface Cell Cooling Coefficient, CCC surf which is shown to be a fundamental property of a lithium-ion cell. CCC surf is found to be considerably larger than CCC tabs , and this is a trend anticipated for every pouch cell currently commercially available. However, surface cooling induces layer-to-layer nonuniformity which is strongly linked to reduced cell performance and reduced cell lifetime. Thus, the Cell Cooling Coefficient enables quantitative comparison of each cooling method. Further, a method is presented for using the Cell Cooling Coefficients to inform the optimal design of a battery pack thermal management system. In this manner, implementation of the Cell Cooling Coefficient can transform the industry, by minimising the requirement for computationally expensive modelling or time consuming experiments in the early stages of battery-pack design.
Zhao Y, Diaz LB, Patel Y, et al., 2019, How to cool lithium ion batteries: optimising cell design using a thermally coupled model, Journal of The Electrochemical Society, Vol: 166, Pages: A2849-A2859, ISSN: 0013-4651
Cooling electrical tabs of the cell instead of the lithium ion cell surfaces has shown to provide better thermal uniformity within the cell, but its ability to remove heat is limited by the heat transfer bottleneck between tab and electrode stack. A two-dimensional electro-thermal model was validated with custom made cells with different tab sizes and position and used to study how heat transfer for tab cooling could be increased. We show for the first time that the heat transfer bottleneck can be opened up with a single modification, increasing the thickness of the tabs, without affecting the electrode stack. A virtual large-capacity automotive cell (based upon the LG Chem E63 cell) was modelled to demonstrate that optimised tab cooling can be as effective in removing heat as surface cooling, while maintaining the benefit of better thermal, current and state-of-charge homogeneity. These findings will enable cell manufacturers to optimise cell design to allow wider introduction of tab cooling. This would enable the benefits of tab cooling, including higher useable capacity, higher power, and a longer lifetime to be possible in a wider range of applications.
Liu X, Ai W, Naylor Marlow M, et al., 2019, The effect of cell-to-cell variations and thermal gradients on the performance and degradation of lithium-ion battery packs, Applied Energy, Vol: 248, Pages: 489-499, ISSN: 0306-2619
The performance of lithium-ion battery packs are often extrapolated from single cell performance however uneven currents in parallel strings due to cell-to-cell variations, thermal gradients and/or cell interconnects can reduce the overall performance of a large scale lithium-ion battery pack. In this work, we investigate the performance implications caused by these factors by simulating six parallel connected batteries based on a thermally coupled single particle model with the solid electrolyte interphase growth degradation mechanism modelled. Experimentally validated simulations show that cells closest to the load points of a pack experience higher currents than cells further away due to uneven overpotentials caused by the interconnects. When a cell with a four times greater internal impedance was placed in the location with the higher currents this actually helped to equalise the cell-to-cell current distribution, however if this was placed at a location furthest from the load point this would cause a ~6% reduction in accessible energy at 1.5 C. The influence of thermal gradients can further affect this current heterogeneity leading to accelerated aging. Simulations show that in all cases, cells degrade at different rates in a pack due to the uneven currents, with this being amplified by thermal gradients. In the presented work a 5.2% increase in degradation rate, from -7.71 mWh/cycle (isothermal) to - 8.11 mWh/cycle (non-isothermal) can be observed. Therefore, the insights from this paper highlight the highly coupled nature of battery pack performance and can inform designs for higher performance and longer lasting battery packs.
Hales A, Diaz LB, Marzook MW, et al., 2019, The cell cooling coefficient: A standard to define heatrejection from lithium-ion batteries, Journal of The Electrochemical Society, Vol: 166, Pages: A2383-A2395, ISSN: 0013-4651
Lithium-ion battery development is conventionally driven by energy and power density targets, yet the performance of a lithium-ion battery pack is often restricted by its heat rejection capabilities. It is therefore common to observe elevated cell temperatures and large internal thermal gradients which, given that impedance is a function of temperature, induce large current inhomogeneities and accelerate cell-level degradation. Battery thermal performance must be better quantified to resolve this limitation, but anisotropic thermal conductivity and uneven internal heat generation rates render conventional heat rejection measures, such as the Biot number, unsuitable. The Cell Cooling Coefficient (CCC) is introduced as a new metric which quantifies the rate of heat rejection. The CCC (units W.K−1) is constant for a given cell and thermal management method and is therefore ideal for comparing the thermal performance of different cell designs and form factors. By enhancing knowledge of pack-wide heat rejection, uptake of the CCC will also reduce the risk of thermal runaway. The CCC is presented as an essential tool to inform the cell down-selection process in the initial design phases, based solely on their thermal bottlenecks. This simple methodology has the potential to revolutionise the lithium-ion battery industry.
Zhao Y, Spingler FB, Patel Y, et al., 2019, Localized swelling inhomogeneity detection in lithium ion cells using multi-dimensional laser scanning, Journal of The Electrochemical Society, Vol: 166, Pages: A27-A34, ISSN: 1945-7111
The safety, performance and lifetime of lithium-ion cells are critical for the acceptance of electric vehicles (EVs) but the detection of cell quality issues non-destructively is difficult. In this work, we demonstrate the use of a multi-dimensional laser scanning method to detect local inhomogeneities. Commercially available cells with Nickel Cobalt Manganese (NMC) cathode are cycled at various charge and discharge rates, while 2D battery displacement measurements are taken using the laser scanning system. Significant local swelling points are found on the cell during the discharge phase, the magnitude of swelling can be up to 2% of the cell thickness. The results show that the swelling can be aggravated by a combination of slow charge rate and fast discharge rate. Disassembly of the cells shows that the swelling points are matched with the location of ‘adhesive-like’ material found on the electrode surfaces. Scanning Electron Microscope (SEM) images show that the material is potentially blocking the electrodes and separators at these locations. We therefore present laser-scanning displacement as a valuable tool for defect/inhomogeneity detection.
Skamniotis C, Patel Y, Elliott M, et al., 2018, Toughening and stiffening of starch food extrudates through the addition of cellulose fibres and minerals, Food Hydrocolloids, Vol: 84, Pages: 515-528, ISSN: 0268-005X
Pet food, one of the largest type of commercial packaged foods, continuously sets new challenges, amongst them the possibility to enhance palatability via adjusting product composition. This will optimise texture perception across consumer groups of diverse chewing capabilities, as well as improve food oral breakdown efficiency with further impact on metabolic health and nutrient bioavailability in the digestive process. Our aim is to pioneer new methods of controlling texture by answering longstanding questions such as the impact of nutrients on the mechanical properties of foods. The impact of cellulose fibres and minerals on the fracture toughness and stiffness properties of starch food extrudates is investigated for the first time through employing tensile tests and two fracture toughness tests namely Essential Work of Fracture (EWF) and cutting, on four different compositions. Fibres alone are found to increase stiffness (stiffening) and toughness (toughening) whereas minerals decrease stiffness (softening) with a minor influence on toughness. Interestingly, fibres and minerals combined maximise toughening at 28% compared to pure starch, due to the synergistic effect of fibre-matrix de-bonding and fibre breakage mechanisms at the crack tip. These new results indicate that texture can be significantly altered through the addition of minerals and short fibres. Such information is critical in the design of products that need to satisfy both nutritional and textural criteria.
Zhao Y, Patel Y, Zhang T, et al., 2018, Modeling the effects of thermal gradients induced by tab and surface cooling on lithium ion cell performance, Journal of The Electrochemical Society, Vol: 165, Pages: A3169-A3178, ISSN: 0013-4651
Lithium ion batteries are increasingly important in large scale applications where thermal management is critical for safety and lifetime. Yet, the effect of different thermal boundary conditions on the performance and lifetime is still not fully understood. In this work, a two-dimensional electro-thermal model is developed to simulate cell performance and internal states under complex thermal boundary conditions. Attention was paid to model, not only the electrode stack but also the non-core components (e.g. tab weld points) and thermal boundaries, but also the experiments required to parameterize the thermal model, and the reversible heat generation. The model is comprehensively validated and the performance of tab and surface cooling strategies was evaluated across a wide range of operating conditions. Surface cooling was shown to keep the cell at a lower average temperature, but with a large thermal gradient for high C rates. Tab cooling provided much smaller thermal gradients but higher average temperatures caused by lower heat removing ability. The thermal resistance between the current collectors and tabs was found to be the most significant heat transfer bottleneck and efforts to improve this could have significant positive impacts on the performance of li-ion batteries considering the other advantages of tab cooling.
Zhang X-F, Zhao Y, Liu H-Y, et al., 2018, Degradation of thin-film lithium batteries characterised by improved potentiometric measurement of entropy change, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 20, Pages: 11378-11385, ISSN: 1463-9076
Ardani MI, Patel Y, Siddiq A, et al., 2017, Combined experimental and numerical evaluation of the differences between convective and conductive thermal control on the performance of a lithium ion cell, Energy, Vol: 144, Pages: 81-97, ISSN: 0360-5442
Testing of lithium ion batteries is necessary in order to understand their performance, to parameterise and furthermore validate models to predict their behaviour. Tests of this nature are normally conducted in thermal/climate chambers which use forced air convection to distribute heat. However, as they control air temperature, and cannot easily adapt to the changing rate of heat generated within a cell, it is very difficult to maintain constant cell temperatures. This paper describes a novel conductive thermal management system which maintains cell temperature reliably whilst also minimising thermal gradients. We show the thermal gradient effect towards cell performance is pronounced below operating temperature of 25 °C at 2-C discharge under forced air convection. The predicted internal cell temperature can be up to 4 °C hotter than the surface temperature at 5 °C ambient condition and eventually causes layers to be discharge at different current rates. The new conductive method reduces external temperature deviations of the cell to within 1.5 °C, providing much more reliable data for parameterising a thermally discretised model. This method demonstrates the errors in estimating physiochemical paramet ers; notably diffusion coefficients, can be up to four times smaller as compared to parameterisation based on convective test data.
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.
Zhao Y, Patel Y, Hunt IA, et al., 2017, Preventing lithium ion battery failure during high temperatures by externally applied compression, Journal of Energy Storage, Vol: 13, Pages: 296-303, ISSN: 2352-152X
Lithium-ion cells can unintentionally be exposed to temperatures outside manufacturers recommended limits without triggering a full thermal runaway event. The question addressed in this paper is: Are these cells still safe to use? In this study, externally applied compression has been employed to prevent lithium ion battery failure during such events. Commercially available cells with Nickel Cobalt Manganese (NCM) cathodes were exposed to temperatures at 80 °C, 90 °C and 100 °C for 10 h, and electrochemically characterised before and after heating. The electrode stack structures were also examined using x-ray computed tomography (CT), and post-mortems were conducted to examine the electrode stack structure and surface changes. The results show that compression reduces capacity loss by −0.07%, 4.95% and 13.10% respectively, measured immediately after the thermal testing. The uncompressed cells at 80 °C showed no swelling, whilst 90 °C and 100 °C showed significant swelling. The X-ray CT showed that the uncompressed cell at 100 °C suffered de-lamination at multiple locations after test, and precipitations were found on the electrode surface. The post-mortem results indicates the compressed cell at 100 °C was kept tightly packed, and the electrode surface was uniform. The conclusion is that externally applied compression reduces delamination due to gas generation during high temperature excursions.
Kamaludin MA, Patel Y, Williams JG, et al., 2017, A fracture mechanics approach to characterising the environmental stress cracking behaviour of thermoplastics, Theoretical and Applied Fracture Mechanics, Vol: 92, Pages: 373-380, ISSN: 0167-8442
Environmental stress cracking (ESC) is known to affect certain thermoplastics and occurs under simultaneous exposure to both applied stress and a hostile environment. The combination of these can cause a crack to form from a flaw in the material; upon reaching a critical size, the crack may accelerate thus causing catastrophic failure in the component. Various tests have been utilised to measure the resistance of different polymers to ESC, but these are often material- and application-specific and overlook the different stages of the failure process. In the present work, a fracture mechanics approach has been developed and applied, with a view to developing a test method that has wide applicability and provides both insight into the failure mechanisms as well as information for engineering design. Experimental results are presented for the following polymer-environment combinations: linear low-density PE in Igepal solution, HIPS in sunflower oil, and PMMA in methanol. It is shown that the representation of the results in the form of G versus crack velocity and G versus time can distinguish between materials of varying ESC resistance, identify the important regions of the failure process, and enable component life prediction.
Walus S, Offer GJ, Hunt I, et al., 2017, Volumetric expansion of Lithium-Sulfur cell during operation – Fundamental insight into applicable characteristics, Energy Storage Materials, Vol: 10, Pages: 233-245, ISSN: 2405-8297
During the operation of a Lithium-Sulfur (Li-S) cell, structural changes take place within both positive and negative electrodes. During discharge, the sulfur cathode expands as solid products (mainly Li2S or Li2S/Li2S2) are precipitated on its surface, whereas metallic Li anode contracts due to Li oxidation/stripping. The opposite processes occur during charge, where Li anode tends to expand due to lithium plating and solid precipitates from the cathode side are removed, causing its thickness to decrease. Most research literature describe these processes as they occur within single electrode cell constructions. Since a large format Li-S pouch cell is composed of multiple layers of electrodes stacked together, and antagonistic effects (i.e. expansion and shrinkage) occur simultaneously during both charge and discharge, it is important to investigate the volumetric changes of a complete cell. Herein, we report for the first time the thickness variation of a Li-S pouch cell prototype. In these studies we used a laser gauge for monitoring the cell thickness variation under operation. The effects of different voltage windows as well as discharge regimes are explored. It was found that the thickness evolution of a complete pouch cell is mostly governed by Li anodes volume changes, which mask the response of the sulfur cathodes. Interesting findings on cell swelling when cycled at slow currents and full voltage windows are presented. A correlation between capacity retention and cell thickness variation is demonstrated, which could be potentially incorporated into Battery Management System (BMS) design for Li-S batteries.
Zhang X-F, Zhao Y, Patel Y, et al., 2017, Potentiometric measurement of entropy change for lithium batteries, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, Vol: 19, Pages: 9833-9842, ISSN: 1463-9076
Chang L, Patel Y, Wang H, et al., 2016, The Partitioning of Plastic Energy in Cutting Tests, 21st European Conference on Fracture (ECF), Publisher: ELSEVIER SCIENCE BV, Pages: 309-315, ISSN: 2452-3216