Imperial College London

Dr Laura Bravo Diaz

Faculty of EngineeringDepartment of Mechanical Engineering

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409City and Guilds BuildingSouth Kensington Campus

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Publications

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14 results found

Kallitsis E, Lander L, Edge J, Bravo Diaz L, Brown A, Kelsall G, Offer G, Korre Aet al., 2022, Safe and sustainable lithium-ion batteries, Safe and Sustainable Lithium-ion Batteries, Publisher: Imperial College London - Energy Futures Lab

The transition to clean energy and electric mobility is driving unprecedented demand for lithium-ion batteries (LIBs). This paper investigates the safety and sustainability of LIBs, exploring ways of reducing their impact on the environment and ensuring they do not pose a danger to health of workers or users.

Report

Diaz LB, Hales A, Marzook MW, Patel Y, Offer Get al., 2022, Measuring Irreversible Heat Generation in Lithium-Ion Batteries: An Experimental Methodology, JOURNAL OF THE ELECTROCHEMICAL SOCIETY, Vol: 169, ISSN: 0013-4651

Journal article

Hales A, Prosser R, Bravo Diaz L, White G, Patel Y, Offer GJ, Marzook WWJet al., 2021, The Cell Cooling Coefficient As a Design Tool to Optimize Thermal Management of Lithium-Ion Cells in Battery Packs, ECS Meeting Abstracts, Vol: MA2021-02, Pages: 422-422

Journal article

Edge JS, O'Kane S, Prosser R, Kirkaldy ND, Patel AN, Hales A, Ghosh A, Ai W, Chen J, Yang J, Li S, Pang M-C, Bravo Diaz L, Tomaszewska A, Marzook MW, Radhakrishnan KN, Wang H, Patel Y, Wu B, Offer GJet 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.

Journal article

Hales A, Prosser R, Diaz LB, White G, Patel Y, Offer Get 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

Journal article

Bravo Diaz L, He X, Hu Z, Restuccia F, Marinescu M, Barreras JV, Patel Y, Offer G, Rein Get 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.

Journal article

Offer G, Patel Y, Hales A, Bravo Diaz L, Marzook Met al., 2020, Cool metric for lithium-ion batteries could spur progress, Nature, Vol: 582, Pages: 485-487, ISSN: 0028-0836

Journal article

Hales A, Marzook MW, Bravo Diaz L, Patel Y, Offer Get 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.

Journal article

Zhao Y, Diaz LB, Patel Y, Zhang T, Offer GJet 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.

Journal article

Hales A, Diaz LB, Marzook MW, Zhao Y, Patel Y, Offer Get 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.

Journal article

Bravo Diaz L, Hales A, Zhao Y, Marzook MW, Patel Y, Offer GJet al., 2019, Cell Heat Generation and Dissipation: From Experimentation to Application for Cell Design., ECS Meeting Abstracts, Vol: MA2019-04, Pages: 185-185

<jats:p> Lithium ion batteries (LIBs) are increasingly important in ensuring sustainable mobility and reliable energy supply, storing and managing energy from renewable sources [1]. Temperature is a critical factor in LIBs performance optimisation where large temperature deviations within the cell could lead to accelerated degradation and in extreme cases, thermal runaway. Thermal management has therefore become the focus of intensive research in an attempt to improve battery performance and lifespan [2-5]. Despite the growing research interest in this area, cell heat generation and heat dissipation pathways are not usually considered when designing a cell. This typically leads to cells with thermal bottlenecks prone to internal thermal gradients. With the goal of improving performance and lifetime, a two-dimensional electro-thermal model has been developed to simulate cell performance and internal states under complex thermal boundary conditions [6]. This model can be used to assess different cooling strategies and parameters such us tab position and dimensions can be optimised from the thermal performance perspective for a particular cell chemistry and geometry. </jats:p> <jats:p>In this study, a novel experimental procedure is employed to evaluate cell heat generation and dissipation for various operation conditions. The two-dimensional electro-thermal model was employed to assess the internal temperature distribution during the measurements and to verify the heat dissipation patterns observed during the experiments. As a result, a new metric, the Cell Cooling Coefficient (CCC) is proposed to evaluate the thermal pathways of a cell cooled via its tabs. <jats:list list-type="simple"> <jats:list-item> <jats:p>International Energy Agency. Tracking Clean Energy Progress 2017. 1–82 (2017). doi:10.1787/energy_tech-2014-en</jats:p> <

Journal article

Diaz LB, Hanlon JM, Bielewski M, Milewska A, Gregory DHet al., 2018, Ammonia Borane Based Nanocomposites as Solid-State Hydrogen Stores for Portable Power Applications, ENERGY TECHNOLOGY, Vol: 6, Pages: 583-594, ISSN: 2194-4288

Journal article

Balducci G, Diaz LB, Gregory DH, 2017, Recent progress in the synthesis of nanostructured magnesium hydroxide, CRYSTENGCOMM, Vol: 19, Pages: 6067-6084, ISSN: 1466-8033

Journal article

Hanlon JM, Diaz LB, Balducci G, Stobbs BA, Bielewski M, Chung P, MacLaren I, Gregory DHet al., 2015, Rapid surfactant-free synthesis of Mg(OH)(2) nanoplates and pseudomorphic dehydration to MgO, CRYSTENGCOMM, Vol: 17, Pages: 5672-5679, ISSN: 1466-8033

Journal article

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