In-Situ Li-Ion Pouch Cell Diagnostics Utilising Plasmonic Based Optical Fibre Sensors

As the drive to improve the cost, performance characteristics and safety of lithium-ion batteries increases with adoption, one area where significant value could be added is that of battery diagnostics. This paper documents an investigation into the use of plasmonic-based optical fibre sensors, inserted internally into 1.4 Ah lithium-ion pouch cells, as a real time and in-situ diagnostic technique. The successful implementation of the fibres inside pouch cells is detailed and promising correlation with battery state is reported, while having negligible impact on cell performance in terms of capacity and columbic efficiency. The testing carried out includes standard cycling and galvanostatic intermittent titration technique (GITT) tests, and the use of a reference electrode to correlate with the anode and cathode readings separately. Further observations are made around the sensor and analyte interaction mechanisms, robustness of sensors and suggested further developments. These finding show that a plasmonic-based optical fibre sensor may have potential as an opto-electrochemical diagnostic technique for lithium-ion batteries, offering an unprecedented view into internal cell phenomena

In-Situ Li-Ion Pouch Cell Diagnostics Utilising Plasmonic Based Optical Fibre Sensors

As the drive to improve the cost, performance characteristics and safety of lithium-ion batteries increases with adoption, one area where significant value could be added is that of battery diagnostics. This paper documents an investigation into the use of plasmonic-based optical fibre sensors, inserted internally into 1.4 Ah lithium-ion pouch cells, as a real time and in-situ diagnostic technique. The successful implementation of the fibres inside pouch cells is detailed and promising correlation with battery state is reported, while having negligible impact on cell performance in terms of capacity and columbic efficiency. The testing carried out includes standard cycling and galvanostatic intermittent titration technique (GITT) tests, and the use of a reference electrode to correlate with the anode and cathode readings separately. Further observations are made around the sensor and analyte interaction mechanisms, robustness of sensors and suggested further developments. These finding show that a plasmonic-based optical fibre sensor may have potential as an opto-electrochemical diagnostic technique for lithium-ion batteries, offering an unprecedented view into internal cell phenomena

Electrochemical-thermal Analysis of High Capacity Li-ion Pouch Cell for Automotive Applications

Latest regulatory trends implemented in order to limit emissions combined with research advances in alternative fuels have paved the road toward vehicle electrification. Major original equipment manufacturers (\acrshort{OEM}s) have already marketed electric vehicles in large scale but apart from business strategies and policies, the real engineering problems must be addressed. Lithium-ion batteries are a promising technology for energy storage; however, their low energy density and complex electro-chemical nature, compared to fossil fuels, presents additional challenges. Their complex nature and strong temperature dependence during operation must be studied with additional accuracy, capable to predict their behavior. In this research, a pseudo two dimensional (\acrshort{P2D}) electro-chemical model, coupled with a 3D thermal energy balance for a recent high capacity \acrshort{NMC} pouch cell for automotive applications is developed. The electrochemical model with its temperature dependent parameters is validated at different temperatures and various discharge C-rates to accurately replicate the battery cell operational conditions. The sources of heat are distinguished and characterized via advanced electrochemical-modelling approach, in various battery operations and different thermal boundary conditions. For example, it was determined that the temperature rise during discharge at high C-rates, under natural convection, could result in thermal runaway, if managed incorrectly. Ohmic heat generation of current collectors and cell tabs is investigated and included. Hence, the thermal analysis provides insights on the current and voltage profiles causing the minimum thermal stress on the cell and the location of heat generation spatially and temporally during the battery discharge. Different modelling approximation of the cell are studied starting from the cell fundamental unit. This provides effective design considerations for the battery thermal management system (\acrshort{BTMS}) to enhance performance, cycle life and safety of future electrified vehicle energy storage systems

In-situ X-ray tomographic imaging study of gas and structural evolution in a commercial Li-ion pouch cell

Gas generation within Li-ion batteries (LIB) can lead to an increase in resistance, thereby, reducing their cycle lifetime. The chance of catastrophic failure via internal gas evolution may increase as a function of cell size and capacity. However, in-situ studies of gas evolution at the cell level are very limited due to limited number of techniques that can effectively probe this. Hence, for the first time, we employed high-energy X-ray tomography to non-destructively observe the structural evolution (gas and electrodes) as a function of cycle numbers for a 400 mAh commercial Li-ion pouch cell. Gas agglomeration led to cell deformation in different areas were observed in 4D (3D + time), the subsequent quantification including the volume fraction, surface area and thickness showed a heterogeneous gas distribution, revealing the degradation mechanism involving the coalescence of gas. This study demonstrates a feasible case of the use of lab-based X-ray to investigate the cell degradation and monitor state of health (SOH) by tracking the thickness in-situ, providing practical guidance for designing safer pouch cells

Li-Ion Pouch Cell Designs; Are They Ready for Space Applications?

No abstract availabl

Li-Ion Pouch Cell Designs; Performance and Issues for Crewed Vehicle Applications

The purpose of this work: Are there any performance show stoppers for spinning them into spacecraft applications? (1) Are the seals compatible with extended vacuum operations? (2) How uniformly and cleanly are they made? (3) How durable are they

monitoring of li ion cells with distributed fibre optic sensors

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Redes de sensores de fibra ótica para monitorização in situ de baterias de ião de lítio

In this work, fiber optic sensor networks were developed to be integrated in commercially available lithium-ion batteries (cylindrical and prismatic) and pre-fabricated batteries in a laboratory environment (pouch cells), with the objective of monitoring in situ, operando and in real time, the internal and external variations of temperature and strain, under different environmental conditions and different charge and discharge rates. To this end, and in order to show the improved performance of fiber optic sensors in relation to the electronic ones, typically used in this type of application, their response time and resolution were compared. An improvement of 28% of the response time and a better resolution are attained with fiber optic sensors. Monitorization studies of the temperature and strain variations using fiber Bragg gratings (FBGs) in the cylindrical configuration have been made, as well as temperature and bi-directional strain variations in the prismatic configuration, under normal or abusive operating conditions, using the FBG method strain free. When the batteries were subjected to abusive operating conditions, it was evident that greater temperature and strain variations occur, being promoted by the rapid transport of lithium ions between the positive and negative electrodes. Due to the thermal expansion of the materials that compose the battery, its internal structure is an important parameter to consider and that can influence its behavior in terms of expansion and contraction. In order to monitor the thermal performance of lithium-ion prismatic batteries in different environmental conditions, studies were performed in which the battery operated at different discharge rates over different conditions of temperature and relative humidity, in order to simulate the performance of the battery in three distinct climates: cold, temperate, and dry. From these studies, the poor performance of this type of batteries in the cold climate, and consequent lower thermal performance was verified. A network of 37 FBG sensors has also been used to monitor the interfaces of a pack of 3 lithium polymer batteries connected in series. It was possible to perform a spatial and temporal thermal mapping under different discharge rates, and to identify areas that are more susceptible to the appearance of hot spots and that are capable of endanger its normal functioning. Hotter zones were detected near the current collectors, due to the higher density of lithium ions in this region. For the first time, the simultaneous discrimination of internal temperature and strain variations in lithium-ion batteries in the pouch cell configuration was carried out, through the incorporation of hybrid sensors, which combine the operational characteristics of the Fabry-Perot and FBG sensors. The evolution of the strain and temperature signals was followed by the proposed sensors and the largest strain variations were detected at the beginning of the discharge process, in the bottom position of the pouch cell. With the work developed in this Thesis, it is concluded that the integration of optical fiber sensors into lithium-ion batteries contributes to a better internal and external knowledge of the thermal performance and volume variations under different operating conditions. This might improve the safety conditions and optimize the design of the next generation of lithium-ion batteries.No presente trabalho, desenvolveram-se redes de sensores em fibra ótica para integrar em baterias comerciais de ião de lítio (cilíndricas e prismáticas) e em baterias pré-fabricadas em ambiente de laboratório (pouch cells), com o objetivo de monitorizar in situ, em funcionamento e em tempo real variações internas e externas de temperatura e deformação, sob diferentes condições ambientais e diferentes taxas de carga e descarga. Para tal, e de maneira a mostrar o melhor desempenho dos sensores de fibra ótica em relação aos eletrónicos tipicamente usados neste tipo de aplicação, os seus tempos de resposta e resolução foram comparados, obtendo-se uma melhoria de 28% do tempo de resposta e uma resolução superior com os sensores em fibra ótica. Foram feitos estudos da monitorização de variações de temperatura e deformação através de redes de Bragg em fibra (FBG) na configuração cilíndrica e variações de temperatura e deformação bidirecional na configuração prismática, aquando do seu funcionamento em condições normais e abusivas, através do método FBG strain-free. Quando as baterias foram submetidas a condições operacionais abusivas, ficou evidente que ocorrem maiores variações de temperatura e de deformação, sendo promovidas pelo rápido transporte dos iões de lítio entre os elétrodos positivo e negativo. Devido à expansão térmica dos materiais que compõem a bateria, a sua estrutura interna é um importante parâmetro a ter em consideração e que pode influenciar o seu comportamento em termos de expansão e contração. A fim de monitorizar o desempenho térmico de baterias prismáticas de ião de lítio em diferentes condições ambientais, realizaram-se estudos nos quais a bateria operou sob diferentes taxas de descarga em diferentes condições de temperatura e humidade relativa, por forma a simular o desempenho da bateria em três climas distintos: frio, temperado e seco. Destes estudos, constatou-se o fraco desempenho deste tipo de baterias no clima frio, e consequente inferior desempenho térmico. Uma rede de 37 sensores FBG foi ainda usada para monitorizar as interfaces de um pack de 3 baterias poliméricas de lítio, conectadas em série. Foi possível realizar um mapa térmico espacio-temporal para diferentes taxas de descarga, e identificar as zonas mais suscetíveis ao aparecimento de pontos quentes e capazes de colocar em risco o seu normal funcionamento. As zonas mais quentes foram detetadas próximas dos coletores de corrente, devido à superior densidade dos iões de lítio nesta região. Pela primeira vez, foi realizada a discriminação simultânea de variações internas de temperatura e deformação em baterias de ião lítio na configuração pouch cell, através da incorporação de sensores híbridos, que combinam as características operacionais dos sensores Fabry-Perot e FBG. A evolução da deformação e temperatura foi seguida pelos sensores propostos e as maiores variações de deformação foram detetadas no início do processo de descarga, na posição inferior da pouch cell. Com o trabalho desenvolvido nesta Tese, conclui-se que a integração de sensores em fibra ótica em baterias de ião de lítio contribui para um melhor conhecimento, interno e externo, do desempenho térmico e de variações de volume sob diferentes condições de funcionamento. Assim, poder-se-á melhorar as condições de segurança e otimizar o design da próxima geração de baterias de ião de lítio.Programa Doutoral em Engenharia Físic

Piezoresistive Free‐standing Microfiber Strain Sensor for High‐resolution Battery Thickness Monitoring

Highly sensitive microfiber strain sensors are promising for the detection of mechanical deformations in applications where limited space is available. In particular for in situ battery thickness monitoring where high resolution and low detection limit are key requirements. Herein, the realization of a highly sensitive strain sensor for in situ lithium-ion (Li-ion) battery thickness monitoring is presented. The compliant fiber-shaped sensor is fabricated by an upscalable wet-spinning method employing a composite of microspherical core-shell conductive particles embedded in an elastomer. The electrical resistance of the sensor changes under applied strain, exhibiting a high strain sensitivity and extremely low strain detection limit of 0.00005 with high durability of 10 000 cycles. To demonstrate the accuracy and ease of applicability of this sensor, the real-time thickness change of a Li-ion battery pouch cell is monitored during the charge and discharge cycles. This work introduces a promising approach with the least material complexity for soft microfiber strain gauges

Internal and External Temperature Monitoring of a Li-Ion Battery with Fiber Bragg Grating Sensors

The integration of fiber Bragg grating (FBG) sensors in lithium-ion cells for in-situ and in-operando temperature monitoring is presented herein. The measuring of internal and external temperature variations was performed through four FBG sensors during galvanostatic cycling at C-rates ranging from 1C to 8C. The FBG sensors were placed both outside and inside the cell, located in the center of the electrochemically active area and at the tab-electrode connection. The internal sensors recorded temperature variations of 4.0 ± 0.1°C at 5C and 4.7 ± 0.1° C at 8C at the center of the active area, and 3.9 ± 0.1° C at 5C and 4.0 ± 0.1° C at 8C at the tab-electrode connection, respectively. This study is intended to contribute to detection of a temperature gradient in real time inside a cell, which can determine possible damage in the battery performance when it operates under normal and abnormal operating conditions, as well as to demonstrate the technical feasibility of the integration of in-operando microsensors inside Li-ion cells