Final Report Summary - LISF (Mechanics of Energy Storage Materials: Swelling and Fracturing in Lithium ion Batteries electrodes during Charging/Discharging Cycles.)
Among the various possible choices, the most suitable energy storage carriers are electrochemical batteries, namely portable devices capable to deliver the stored chemical energy as electrical energy with high conversion efficiency and without any gaseous emission. Lithium-ion batteries (LiBs) currently have the highest energy storage density of any rechargeable battery technology and the power sources of choice for consumer market. However, the present LiBs, although commercial realities, are not yet at such a technological level to meet the requirements of two main applications that show great potential for LiBs: Electric Vehicles and Smart Grid technology.
The EU report “Research Priorities for Renewable Energy technology by 2020 and Beyond” envisages milestones towards the establishment of a common strategy for the development of Europe’s electricity networks. The first was set in April 2006 when the paper “Vision and Strategy for Europe’s Electricity Networks of the Future” was published. In this Vision, future electricity markets and networks must provide all consumers with a highly reliable, flexible, accessible and cost-effective power supply, fully exploiting the use of both large centralized generators and smaller distributed power sources across Europe. This new concept of electricity networks, known as the ‘SmartGrids’ vision, requires research to make storage options economic in the medium to long term. The EU report “Knowledge for Growth, Prospects for science, technology and innovation” of December 2009, at page 66: “It is generally agreed in scientifically and technically informed circles that European energy supply will require the development and eventual global deployment of a range of technologies in the field of Electric Vehicles [...] that either have still to reach the prototype stage, or if they have done so, remain far from widespread commercial feasibility.”. Today there is a clear gap between European and U.S.A./Asian energy storage manufacturers in regards of LiBs. As for the manufacturing, Europe currently has a very small market share. However, this market is predicted to grow very rapidly to 12 times its current size by 2018. The European battery industry will not survive amidst the determined U.S.A./Asian competition unless action is taken.
This research proposal was strictly inherent to the Parts I and II of the Horizon 2020 program. It targets bottom up fundamental scientific results (Part I) related to the methodologies to deal with the micro-mechanics of irreversible processes and with nanotechnologies and innovative, advanced materials (Part II).
In contrast to attempting to tailor a single electrode material for LiBs, nano-structured materials, composites, and architectures can provide an optimum way of crafting desired characteristics. Appealing classes of materials are Li metal alloys, e.g. silicon (Li-Si), and tin (Li-Sn), due to their specific capacity which largely exceeds that of conventional anode based on graphite. The potentialities of these materials have been known for some time, but their exploitation has been until recently prevented by serious mechanical issues associated with the large volume expansion-contraction changes experienced during the lithium alloying-de-alloying electrochemical process, that in turn induced cracks and eventually, pulverization of the electrode, finally leading it to die in just few cycles.
Theoretical and computational modeling provides the ability to predict, tailor and shape LiBs features. Material modeling, multi-scale and multi-physics processes taking place during charge/discharge were the focus of the present project. Moving from the state of art of the field, the modeling of multi-physics processes at the micro-scale as well as at the macro-scale has been significantly improved through tailoring of the computational homogenization (CH) technique.
A CH scheme for LiBs has been achieved in the present project by using a multiscale strategy with a complex multi-particle representative volume element (RVE). The following major advances have been achieved: i) electroneutrality has been taken in to account in its correct nature of “assumption” rather than being a fundamental law; ii) Maxwell's equations have been rigorously considered in a quasi-static sense; iii) the scale separation has been investigated and properly accounted for, with special emphasis of the time scale separation that was never investigated before; iv) the steady-state mass and charge transport assumption at the microscale was removed and the scale transitions are elaborated for a time dependent formulation; v) the Hill-Mandel scale transition equation has been extended and applied accordingly. The new formulation of the governing equations for a two-scale analysis of Li-ion battery cells has been summarized in several papers submitted for publication in major international scientific journals.
Indeed the present project was permeated by multidisciplinary research. Complementarity of skills led to involve in the project the group of Catalysis & Energy (CE) at the TU/e, Department of Chemical Engineering and Chemistry, exploiting the potential of converging knowledges and technologies. Constitutive assumptions, computational procedures and results based on the new formulation have been the subject of further publications and of on going research and that has being developed and finalized in cooperation with CE.
A rigorous analysis of general principles of non-equilibrium thermodynamics have been performed moving from the rate at which power is expended on a material region, in terms of mechanical contribution as well as of the power due to mass transport and to electromagnetic interactions. Two study-cases have been numerically simulated. The former concerns a one-dimensional application to ionic transport in Li-ion batteries electrolyte. The outcomes published in the literature have been perfectly recovered but by modeling Maxwell's law explicitly no theoretical contradictions, common in other approaches, arise.
The proposed framework has been further applied to a two-dimensional problem, to investigate the micro structural behavior of a multi phases separator. Boundary conditions descend from a multi scale theoretical formulation for batteries. A strong influence of the geometry at the microscale is observed from the outcomes, in particular at the interface between fluid electrolyte and the separator membrane, suggesting that microscopic investigations might be crucial for a deep understanding of the overall battery behavior and of the failure mechanisms.
This last numerical evidence strengthens the conceptual framework of the present proposal, namely that electrochemical and mechanical performance of Li batteries strongly depends on the interaction between macro and micro-scale phenomena, in particular within the electrodes.
This vision may influence significantly the design of next generation of LiBs. The latter have the potential to usher in a wireless revolution, particularly the much desired use for Electric Vehicles and Smart Grid technology, key players in the achievement of the 20/20/20 New EU Strategic Energy Policy in terms of sustainable energy usage. The methodology and the multi-disciplinary framework achieved insofar in the present project may relieve the gap between European and U.S.A./Asian research and manufacturing of Li-ion knowledge, research, and technology thus increasing competitiveness and scientific excellence of the European academia and research. The partners aim at strengthening their actual cooperation towards a Network of Excellence with the potential to become a team for a Cooperation Action within the Horizon 2020 framework and to establish trans-European research and innovation networks that pool industrial and research resources together so to ensure long term EU leadership on low carbon technologies.
Whilst the research itself provided a mean to achieve the EU ambitions, it provided also an important educational tool for the training of the highly skilled workforce who will design and implement the new energy systems of the future. Graduate and post graduate student have been engaged in the present project. They found this research training to be an excellent grounding for a career in this rapidly growing field.
The EU report “Research Priorities for Renewable Energy technology by 2020 and Beyond” envisages milestones towards the establishment of a common strategy for the development of Europe’s electricity networks. The first was set in April 2006 when the paper “Vision and Strategy for Europe’s Electricity Networks of the Future” was published. In this Vision, future electricity markets and networks must provide all consumers with a highly reliable, flexible, accessible and cost-effective power supply, fully exploiting the use of both large centralized generators and smaller distributed power sources across Europe. This new concept of electricity networks, known as the ‘SmartGrids’ vision, requires research to make storage options economic in the medium to long term. The EU report “Knowledge for Growth, Prospects for science, technology and innovation” of December 2009, at page 66: “It is generally agreed in scientifically and technically informed circles that European energy supply will require the development and eventual global deployment of a range of technologies in the field of Electric Vehicles [...] that either have still to reach the prototype stage, or if they have done so, remain far from widespread commercial feasibility.”. Today there is a clear gap between European and U.S.A./Asian energy storage manufacturers in regards of LiBs. As for the manufacturing, Europe currently has a very small market share. However, this market is predicted to grow very rapidly to 12 times its current size by 2018. The European battery industry will not survive amidst the determined U.S.A./Asian competition unless action is taken.
This research proposal was strictly inherent to the Parts I and II of the Horizon 2020 program. It targets bottom up fundamental scientific results (Part I) related to the methodologies to deal with the micro-mechanics of irreversible processes and with nanotechnologies and innovative, advanced materials (Part II).
In contrast to attempting to tailor a single electrode material for LiBs, nano-structured materials, composites, and architectures can provide an optimum way of crafting desired characteristics. Appealing classes of materials are Li metal alloys, e.g. silicon (Li-Si), and tin (Li-Sn), due to their specific capacity which largely exceeds that of conventional anode based on graphite. The potentialities of these materials have been known for some time, but their exploitation has been until recently prevented by serious mechanical issues associated with the large volume expansion-contraction changes experienced during the lithium alloying-de-alloying electrochemical process, that in turn induced cracks and eventually, pulverization of the electrode, finally leading it to die in just few cycles.
Theoretical and computational modeling provides the ability to predict, tailor and shape LiBs features. Material modeling, multi-scale and multi-physics processes taking place during charge/discharge were the focus of the present project. Moving from the state of art of the field, the modeling of multi-physics processes at the micro-scale as well as at the macro-scale has been significantly improved through tailoring of the computational homogenization (CH) technique.
A CH scheme for LiBs has been achieved in the present project by using a multiscale strategy with a complex multi-particle representative volume element (RVE). The following major advances have been achieved: i) electroneutrality has been taken in to account in its correct nature of “assumption” rather than being a fundamental law; ii) Maxwell's equations have been rigorously considered in a quasi-static sense; iii) the scale separation has been investigated and properly accounted for, with special emphasis of the time scale separation that was never investigated before; iv) the steady-state mass and charge transport assumption at the microscale was removed and the scale transitions are elaborated for a time dependent formulation; v) the Hill-Mandel scale transition equation has been extended and applied accordingly. The new formulation of the governing equations for a two-scale analysis of Li-ion battery cells has been summarized in several papers submitted for publication in major international scientific journals.
Indeed the present project was permeated by multidisciplinary research. Complementarity of skills led to involve in the project the group of Catalysis & Energy (CE) at the TU/e, Department of Chemical Engineering and Chemistry, exploiting the potential of converging knowledges and technologies. Constitutive assumptions, computational procedures and results based on the new formulation have been the subject of further publications and of on going research and that has being developed and finalized in cooperation with CE.
A rigorous analysis of general principles of non-equilibrium thermodynamics have been performed moving from the rate at which power is expended on a material region, in terms of mechanical contribution as well as of the power due to mass transport and to electromagnetic interactions. Two study-cases have been numerically simulated. The former concerns a one-dimensional application to ionic transport in Li-ion batteries electrolyte. The outcomes published in the literature have been perfectly recovered but by modeling Maxwell's law explicitly no theoretical contradictions, common in other approaches, arise.
The proposed framework has been further applied to a two-dimensional problem, to investigate the micro structural behavior of a multi phases separator. Boundary conditions descend from a multi scale theoretical formulation for batteries. A strong influence of the geometry at the microscale is observed from the outcomes, in particular at the interface between fluid electrolyte and the separator membrane, suggesting that microscopic investigations might be crucial for a deep understanding of the overall battery behavior and of the failure mechanisms.
This last numerical evidence strengthens the conceptual framework of the present proposal, namely that electrochemical and mechanical performance of Li batteries strongly depends on the interaction between macro and micro-scale phenomena, in particular within the electrodes.
This vision may influence significantly the design of next generation of LiBs. The latter have the potential to usher in a wireless revolution, particularly the much desired use for Electric Vehicles and Smart Grid technology, key players in the achievement of the 20/20/20 New EU Strategic Energy Policy in terms of sustainable energy usage. The methodology and the multi-disciplinary framework achieved insofar in the present project may relieve the gap between European and U.S.A./Asian research and manufacturing of Li-ion knowledge, research, and technology thus increasing competitiveness and scientific excellence of the European academia and research. The partners aim at strengthening their actual cooperation towards a Network of Excellence with the potential to become a team for a Cooperation Action within the Horizon 2020 framework and to establish trans-European research and innovation networks that pool industrial and research resources together so to ensure long term EU leadership on low carbon technologies.
Whilst the research itself provided a mean to achieve the EU ambitions, it provided also an important educational tool for the training of the highly skilled workforce who will design and implement the new energy systems of the future. Graduate and post graduate student have been engaged in the present project. They found this research training to be an excellent grounding for a career in this rapidly growing field.
