Final Report Summary - MATFLEXEND (MATerials for FLEXible ENergy harvesting Devices)
Executive Summary:
The MATFLEXEND project is a collaboration focusing on the development of novel, durable materials to facilitate effective energy harvesting and micro batteries. Technological developments include flexible electrical conductors and dielectrics for capacitive harvesters as well as rechargeable microbatteries, which have applications in the growing wearable electronics sector. One of the most important considerations for those attempting to find cost-effective means of facilitating wearable technology is how to harvest energy in a practical, reliable and cheap way. While this has historically proved extremely difficult – not least because reliability and cost have often been mutually exclusive properties – MATFLEXEND is advancing the development of flexible and durable materials that boast very real potential to transform energy harvesting.
MATFLEXEND (MATerials for FLEXible ENergy harvesting Devices) is a three-year project composed of a consortium of 10 partners from several European countries. Led by the Fraunhofer Institute for Reliability and Microintegration IZM (Fraunhofer IZM). The project features three most important work packages: materials development; fabrication and printing technology; and device development. Thus both, basic materials development and functional demonstrators are included in the project.
One of the key concepts of MATFLEXEND has been micro energy harvesting, something that enables two key features: wireless and service-free operation. These features ensure that sensor networks require no cabling, no change of battery, and can operate autonomously for many years. Additionally, such technology advances the field of wearable electronics as improved energy harvesting relieves each user of the burden associated with managing batteries – whether that is repeatedly charging them or replacing them. However, in the case of medical devices, either worn or implanted, changing the batteries is often practically impossible. MATFLEXEND is developing technology that can convert mechanical energy into electricity at low frequencies and low forces.
Three of the most impactful developments of the project are high-k dielectrics; flexible electrical conductors; and micro battery prototypes. High-k dielectrics were developed by researchers at Imperial College London and increase the energy density of capacitive harvesters. Ultimately, this enables electrical energy to be generated from mechanical motion. As the capacity of the harvester is changed through a deformation of the flexible electrode, charges are supplied and released at different voltage levels. The flexible electrical conductors were co-developed with researchers based at the University of Vienna and Imperial. Flexible composite conductors based on an open porous PolyHIPE polymer doped with conducting particles were developed for this purpose. Conductivity was improved more than two orders of magnitude over existing state-of-the-art technology.
The development of flexible rechargeable batteries is of equal importance, as they are essential for the buffering and smoothing of the harvested energy. Two battery configurations have been tested: the conventional configuration with stacked electrodes and a coplanar electrode arrangement that offers advantages in processing and mechanical flexibility. The fabrication of these different battery configurations has been simplified by novel printable electrolytes and separators that were developed as part of the project.
Project Context and Objectives:
The MATFLEXEND project is a collaboration focusing on the development of novel, durable materials to facilitate effective energy harvesting and micro batteries. Technological developments include flexible electrical conductors and dielectrics for capacitive harvesters as well as rechargeable microbatteries, which have applications in the growing wearable electronics sector. One of the most important considerations for those attempting to find cost-effective means of facilitating wearable technology is how to harvest energy in a practical, reliable and cheap way. While this has historically proved extremely difficult – not least because reliability and cost have often been mutually exclusive properties – MATFLEXEND is advancing the development of flexible and durable materials that boast very real potential to transform energy harvesting.
MATFLEXEND (MATerials for FLEXible ENergy harvesting Devices) is a three-year project composed of a consortium of 10 partners from several European countries. Led by the Fraunhofer Institute for Reliability and Microintegration IZM (Fraunhofer IZM). The project features three most important work packages: materials development; fabrication and printing technology; and device development. Thus both, basic materials development and functional demonstrators are included in the project.
One of the key concepts of MATFLEXEND has been micro energy harvesting, something that enables two key features: wireless and service-free operation. These features ensure that sensor networks require no cabling, no change of battery, and can operate autonomously for many years. Additionally, such technology advances the field of wearable electronics as improved energy harvesting relieves each user of the burden associated with managing batteries – whether that is repeatedly charging them or replacing them. However, in the case of medical devices, either worn or implanted, changing the batteries is often practically impossible. MATFLEXEND is developing technology that can convert mechanical energy into electricity at low frequencies and low forces.
Three of the most impactful developments of the project are high-k dielectrics; flexible electrical conductors; and micro battery prototypes. High-k dielectrics were developed by researchers at Imperial College London and increase the energy density of capacitive harvesters. Ultimately, this enables electrical energy to be generated from mechanical motion. As the capacity of the harvester is changed through a deformation of the flexible electrode, charges are supplied and released at different voltage levels. The flexible electrical conductors were co-developed with researchers based at the University of Vienna and Imperial. Flexible composite conductors based on an open porous PolyHIPE polymer doped with conducting particles were developed for this purpose. Conductivity was improved more than two orders of magnitude over existing state-of-the-art technology.
The development of flexible rechargeable batteries is of equal importance, as they are essential for the buffering and smoothing of the harvested energy. Two battery configurations have been tested: the conventional configuration with stacked electrodes and a coplanar electrode arrangement that offers advantages in processing and mechanical flexibility. The fabrication of these different battery configurations has been simplified by novel printable electrolytes and separators that were developed as part of the project.
While Fraunhofer IZM coordinates MATFLEXEND, the project involves nine other partners:
Imperial College London develops thermal and photochemically curable nanoparticle composites and conducts research into processability and printability of high-k dielectrics.
The University of Vienna develops and provides PolyHIPE electrolytes and elastomers for converter spring elements.
Eurecat studies harvester and system durability, and conducts research that seeks to integrate harvesters and micro batteries into garments.
SMARTEX proposes a range of commercially realistic applications in technical textiles, and will disseminate the concept of the project into a fashion ecosystem.
LAAS-CNRS develops an electrophoretic deposition process for flexible-battery electrode materials.
VARTA Microbatteries assesses the compatibility of the most promising PolyHIPE electrolytes. In addition, this team conducts tests such as processing and printing technology with novel materials.
ANITRA Technologies lead the communication and dissemination of the project’s findings. They set up dedicated workshops including audiences from research and industry.
PARDAM s.r.o. develop and optimise materials for Li-ion batteries and supplies nanoparticles for Imperial College London to prepare high-k dielectric composites.
COMCARD creates the specification of and materials for the smart card demonstrators. They also test a variety of materials to optimise the converter efficiency.
Project Results:
1.1 Dielectric
SBTO provided by PARDAM and commercial BTO nanoparticles were successfully functionalised with poly(methylmethacrylate) and scaled up to 20g. The functionalised materials were incorporated into epoxy, the functionalisation improved the wetting properties and individualization of the nanoparticles/fibres within the epoxy, in turn improving dielectric properties (up to 92 has been achieved). The inks (~40 ml each) were sent to EURECAT for printing. The inks were stable and successfully printed at EURECAT and yielded homogeneous, mechanically robust thin (5 - 10 μm) layers which can be used for harvesters (IZM and Imperial are currently using these films to build the harvesters). The dielectric breakdown strength of the SBTO-f epoxy nanocomposites of previous films ca. 100 V μm-1. The dielectric properties of the EURECAT films are currently being measured. Conductive fillers (SWNTs, carbon nanohorns (CNHs), carbon nanoonions (CNOs) have been negatively charged in Na/naphthalene DMAc solution and the individualised species have been reacted with a solution of DMAc/PVDF. The stable mixtures of carbon nanomaterial (CNM) in PVDF are drop cast and dried to make flexible dielectrics. Draft publications are also being prepared for the SBTO dielectrics and the insulated conductors.
1.2 Conductive elastomers
The final polyHIPEs based conducting elastomer has been fabricated using a polyacrylate based polyHIPE impregnated with negatively charged SWNTs. Previous polyHIPE can only be deposited onto thin Al foil but with further improvement in the SWNTs adhesion layer, it is now possible to deposit the polyHIPE onto a Cu foil which gives a much higher mechanical robustness to the electrode. The surface roughness of the polyHIPE has been reduced by first depositing a thin layer of negatively charged SWNTs onto the SWNTs impregnated polyHIPE, then finish with a thin negatively charged graphene coating. Various surface patterns have been investigated for the final conducting elastomer prototype in order to reduce the adhesion between elastomer and dielectric under compression. A screen printed polyHIPE with a zig-zag cross section pattern is the best specimen, has the lowest surface roughness and do not adhere to the dielectric. A spring element polyHIPE (UNIVIE) was also printed onto a screen printed polyHIPE surface but a rough surface was formed after the impregnation process and did not proceed further. Imperial is now combining the conducting elastomer with the dielectric to make a demonstration harvester device. A draft manuscript for the SWNTs impregnated polyHIPE has been prepared and Imperial Innovation is currently doing a business feasibility case for the polyHIPE idea. The work may be patented if there is a good business potential and the draft manuscript will be circulated among the partners once the decision on patent is made.
1.3 electrolytes
Many characterizations of RT-IL based Li+-electrolytes suitable for use as internal phase for high internal phase emulsion templates, which can be processed by printing into macroporous polymer microbattery separators have been performed. Furthermore, it was attempted to successfully assemble and characterize working full cell Li+-batteries. The temperature dependent dynamic viscosities of various 0.5M Li+-salt solutions (LiBF4, LiClO4, LiAsF6, LiN(SO2CF3)2 and LiPF6) in [EMIM][BF4] were measured. The dynamic viscosities of Li-salt containing [EMIM][BF4] increased when they contained a dissolved Li salt, but decrease with increasing temperature obeying a VTF behaviour. Temperature dependent Li+-transfer numbers determined by PSGE-NMR revealed rather low values between 0.014 and 0.016 at room temperature, caused by the low Li+ concentration in [EMIM][BF4]. Also further investigations on the thermal behaviour of the in situ RT-IL Li+-electrolyte filled poly(LMA-co-DDDMA)HIPE separators were carried out in order to determine cause of the increasing the MacMullin numbers with increasing temperature. DSC measurements revealed no significant influence on the RT-IL Li+-electrolytes thermal behaviour by the separator. Furthermore conductivity measurements from cyclic heating up and cooling down revealed the process was reversible. Therefore, this effect might be caused by the increasing degree of freedom of the long alkaline side chains of the repeat units with increasing temperature. Finally new LTO-1.0M LiBF4 in [EMIM][BF4]-in-(LMA-co-DDDMA)-NMC full cell configurations were built up now showing more promising performance due to availability of better balanced electrode materials.
1.4 Nanofibers
Force spinning was developed as a cost efficient method to produce nano fibers for battery electrodes (LTO anode) and high-k dielectrics (BTO, SPTO), The problem of precipitation of spinning solution of SBTO during repeated preparation was solved. The milling process was optimized to provide the required particle size (4-7 µm) for next printing steps.
Several tests on optimization of the calcination process of TiO2 nanofibers have been performed to evaluate potential of this technology for calcination of inorganic nanofibers. Test on prototype machine showed small decrease of polymer matrix from precursor fibers comparing to the results reached at laboratory level. TiO2 was used for comparison with laboratory tests to evaluate the possibility for up scaling.
SiO2 nanofibers were produced and successfully tested at IZM for application of this new material for printable battery separator. This new material is unique mainly from the production and economic point of view as precursor is 1000times cheaper than TEOS and production yield is 50% higher that TEOS (current production technology).
2. Demonstrators
-Batteries
Rechargeable micro batteries which are thin, in part bendable and can be adapted to the form factor of the application are required for several wearable and miniaturized electronic products. A special segmented battery packaging concept has been developed which uses pre-patterned current collector foils as battery housing, laminate battery assembly, simultaneous microfluidic electrolyte filling of all battery segments and final sealing on substrate level. The size and shape of the battery can be easily changed by only altering the lithography masks. The battery thickness is in the range between 0.3 and 1 mm resulting in an area capacity between ca. 1 and 5 mAh/cm2. While commercial electrode materials and electrolyte (1M LiPF6, EC:DEC) for lithium ion batteries were used in most cases, novel nitridated Li4Ti5O12 (LTO) electrode fibers and self-made separator composites with materials provided by the partner PARDAM were tested and developed at Fraunhofer IZM. All fabrication steps and materials were optimized towards the foil type segmented micro battery:
- The performance of LTO anode fibers were tested against commercial powders.
- Electrode and separator pastes were optimized for stencil print and dispensing including water based binder.
- Electrodes (LTO anode and LiNi1/3Co1/3Mn1/3O2 (NMC) cathode) and ceramic separator printing processes required for the segmented electrode shape were developed.
- Battery assembly and final sealing was developed including low water permeation rate lamination between top and bottom package, electrolyte filling with help of a microfluidic adapter.
Half and full cell tests and cycling with increasing C-rate are used to study the influence of material and packaging parameters on the electrochemical performance. 6x8 mm2 prototypes of 0.7 mAh were fabricated with high reproducibility. They work stable until a current of 2C and showed stable cycle life.
- Harvester
Polymer based capacitive harvester were demonstrated which can later be fabricated with help of roll-to-roll and low cost printing methods. In contrast to electrostatic MEMS based parallel plate transducers or dielectric elastomer systems here, the capacitance is varied as function of the mechanical load by changing of the top electrode area with help of an electrically conducting composite elastomer. In case of the composite elastomer electrode the maximum capacitance in compressed state does not only depend on the thickness and permitivity of the dielectric but first of all on the quality of the interface and the micro structure of the conducting phase in the composite electrode at the interface which was investigated by FEM Maxwell simulation.
An equivalent circuit model is used to study the influnce of the leakage current inside the dielectric and the bulk resistivity of the elastomer electrode.
First experiments with the novel printed dielectrics in contact with elastomer electrodes have been performed to prove the harvesting principle at low frequencies. The maximum capacity was between 0.4 and 0.8 nF/cm2. FEM simulations and experimental results clearly indicate that the specific capacity is not limited by the dielectric material but due to the elastomer electrode. No more than ca. 1 nF/cm2 can be practically achieved with the used conducting elastomer. A capacity of 650 pF/cm² was achieved with screen printed dielectrics fabricated at IMPERIAL and printed at EURECAT. Charges between 25 and 70 nAs per cm2 have been transferred per cycle at 100 V/200 V. At an actuation frequency of ca.1 Hz this corresponds to 0.5 ... 1.5 µW/cm2.
UniVien optimized harvester variants for low and higher force applications. More than 100.000 cycles were tested without degradation.
Another aspect concerns the adaption of an electronic circuit interface which will allow the charge of a battery with the capacitive harvester. An electronic module was developed that allows the online measurement of the harvested energy.
Potential Impact:
Rechargeable batteries as temporary energy storages and energy harvesters will find many applications in the future. They are basic hardware components for energy autarkic micros systems which are required for internet of things, industry automation (industry 4.0) smart environments, health care and medical devices, consumer applications like sportswear and intelligent homes. Some special small scale application will be in the research area like tracking of small animals in the wild.
In particular several special results and activities the MATFLEXEND were identified to have great impact and exploitation potential by the partners:
– P1 Energy converters, small secondary batteries and general harvesting.
– P2 High-k polymer dielectrics, disperse SWCNTs "nanotubides", highly "conductive & compliant" elastomers
– P3 PolyHIPEs, RTIL-in-polyHIPEs, patterning
– P4 Smart Shoes, Gait Analysis, Decorative applications + textiles
– P5 Insoles, Smart-shoe SDK electronics
– P6 Electrophoretic deposition + (patterned) EPD
– P7 COTS button cells for wearables, printing flexible batteries
– P8 Anitra – workshops, nomenclatures, tools for Desk Research, ontologies
– P9 Nanofibers for battery electrode or release materials. Forcespinning + enhancements
– P10 Smart Cards
Dissemination activities:
Partner P7 VARTA attended trade fairs including LOPEC-C, IDTech, with an own booth including MATFLEXEND visuals and promoting power to Wearables + toher appplications.
At IDTechEx in Berlin, April 2015 and 2016. P1 Fraunhofer had its own booth, and substantial amounts of visitors´ traffic. P8 was present as well, doing networking with e.g. Fraunhofer ISC (presssure-sensors-sock by), small battery exhibitor ILIKA, a Southampton battery spinout, Gore, a provider of high-tech fabrics. P8 was also invited to an NCP NMBP contacts-seminar in Mainz, May 12th, 2016, participating in interviews and discussing energy harvesting with PTZ Jülich.
Finally, P8 was invited to present some thoughts about EU Dissemination on May 24, 2016, it including some most interesting & relevant reports on the EU´s Open Data initiatives.
Other such information to be found in the "News" page of the project Website.
P1 and P8 gave a 2 pp. interview to IMPACT, a openly distributed magazine reporting on EU research. This is to be published on paper and in November 2016.
The article in particular stresses the importance of Open Access - for smaller Partners - in order to find competing developments, partnering and marketing opportunities. An author´s copy is uploaded to, and open-access-available from the MATFLEXEND public Website in the "News" section. It has also been distributed as part of the 390+ mailshot for the Workshop.
In June 26th, 2015, P8 Anitra gave a short presentation on Exploitation approaches to the Dresden Cluster worskhop, in addition to the IZM technical presentation reported in the Table above.
Magazines database - an update: building a focused magazines database
In the Dissemination report, P8 had offered some trivial hints about how to google more specifically, essentially by building a mindmap of keywords. As for finding suitable magazines, it became clear from discussions that Partners wanted to select their own magazines, so as an experiment. P8 combined proposed keywords from 7.2.5 a) below, with the keyword "journal", yielding a table, extracts of which are shown in the second periodic report.
Partner EURECAT developed an idea for outdoor use of printable, textile photovoltaics in an energy harvesting system. A small draft proposal outline MOSENHAR "MOSaic ENergy HARvester) has been developed off-project and circulated, to partners and to SMEs.
The new idea would combine small solar cells and batteries into planar mini-energy harvesters as part of a mosaic of rigid elements, which could be plane or 3-dimensional.
We have been in touch a number of times with the Open Innovation Systems Group at DG CONECT (Dr. Bror Salmelin) raising a series of issues about using Cognitive Computing in Energy Harvesting in particular, in the EU in general, and in assisting better Dissemination by the EU, prior to launching a Call.
It later resulted in a preliminary proposal outline (ENHARONT ENergy HARvester ONTology) which has been researched outside MATFLEXEND but might be a follow-up project. It is discussed here as a part of Dissemination, since it might be relevant to the "Energy Harvesting Cluster".
This will be considered on a strictly pragmatic basis, i.e.: can it be practically useful? The US Army, Airbus, and some materials scientists in the US and Japan seem to think so.
Prospects include DFKI, Univ. Manchester, Univ. Southampton, Hahn-Schickhard Gesellschaft, DFKI Deutsches Forschungszentrum für Künstliche Intelligenz; with IZM acting as a domain expert. Support by industry (Nicomatic?) and perhaps Bundeswehr will be critical.
In Addition P8 found references to an earlier idea by P1 IZM, namely to affix small energy harvesters to animals, small birds and even larger insects. This seems of interest for at least two reasons: the bird-watchers - especially the Swiss Vogelwarte Sempach, CH - together with FH Bern, have devised lightweight (1 gram > weight (?!)) geolocation devices for migratory birds, essentially adding GPS logging to the traditionally-used rings of old. Extraordinary ingenuity has resulted in such light packages logging a year´s worth of GPS data - sampling location once per week, and using a primary battery. More ambitious and publicly-announced work has started at the Max-Planck-Institute in Radolfzell, DE, which literally hired a rocket scientist to develop ultra-small transponders that could send a data salvo to the International Space Station, again with few-gram hardware. Besides being able to follow birds in real time, one can here address birds that do not necessarily return to their starting point; and perhaps even more impactfully, larger insects such as bees and agricultural pests, which cannot easily be caught again for readout. So this sytem in spite of its small market may have huge impact on agriculture.
In other activity IZM and Anitra found a group in Barcelona (Dr. C. Flox and Prof. Morante, IREC) using electrospun nanofibers to enhance electrode performance in a V2O5 redox-flow battery; broadly similar to some work that P1 IZM has conducted with P9 PARDAM for LiOn batteries. Now PARDAM has expertise in both electrospinning and force-spinning (the latter, safer and cheaper) and so, contact with PARDAM and IREC has been set up, with both parties due to meet at NANOTECH 2016, end-September, in Valencia. Georg Schmid Energy Systems, a subsidiary of Georg Schmid (www.schmid-group.com) are in contact with IREC and also with Imperial / Materials.
In an earlier exercise with UNIVIE had considered alternative uses of their RTIL-polyHIPE separators in electrochemical sensor applications (the PAPFIL workshop, conducted off-project), as well as using them asdsorb/desorb media (adsorb-in-situ / desorb-in-Gas-Chromatograph/MS) for volatile organic compounds.
In exploitation desk research, we then found some publications about pharma release to a skin, from an RTIL vehicle and contacted Univ. Bath (Prof. Guy + Dr. Delgado) as well as Univ. Nottingham (Prof. Croft) plus another worker at Univ. New Lisboa (Prof. Marrucho) to discuss possible use of the UNIVIE RTIL-imbibed elastomers in a smart bandage. Contact with P3 UNIVIE was subsequently established, with a view to discuss a future project re. topical (= 2-D patterned) administration of certain medication to a wound, or to diseased fingernails - where such "transdermal" pharma release is notoriously difficult. We also found that electro-spun nanofiber felts by P9 PARDAM might offer an alternative path to continuous topical release from a bandage. A post-project workshop is planned to deal with these issues, and to finding a call.
Work done by P2 Imperial on conductive elastomers is seems in practical applications, such as conformable electronic shielding and will be published after resolving IPR issues; high-k dielectrics trivially allow more compact capacitors terms (as in e.g. more compact rectifiers), and we expect more examples from Solvay. From the Dissemination point of view, our contribution has been to establish (and much later re-establish) contact with Solvay. Solvay will present its own progress in high-k dielectrics at the Vienna workshop, with opportunities to discuss more collaboration.
Nano-tubide work reported in the first workshop and project review might be relevant to supercapacitor work, which could widely apply to energy storage.
List of Websites:
5. www.matflexend.eu
contact:
Dr. Robert Hahn Fraunhofer IZM
Gustav-Meyer-Allee 25, 13355 Berlin, Germany
0049 30 46403611, robert.hahn@izm.fraunhofer.de
The MATFLEXEND project is a collaboration focusing on the development of novel, durable materials to facilitate effective energy harvesting and micro batteries. Technological developments include flexible electrical conductors and dielectrics for capacitive harvesters as well as rechargeable microbatteries, which have applications in the growing wearable electronics sector. One of the most important considerations for those attempting to find cost-effective means of facilitating wearable technology is how to harvest energy in a practical, reliable and cheap way. While this has historically proved extremely difficult – not least because reliability and cost have often been mutually exclusive properties – MATFLEXEND is advancing the development of flexible and durable materials that boast very real potential to transform energy harvesting.
MATFLEXEND (MATerials for FLEXible ENergy harvesting Devices) is a three-year project composed of a consortium of 10 partners from several European countries. Led by the Fraunhofer Institute for Reliability and Microintegration IZM (Fraunhofer IZM). The project features three most important work packages: materials development; fabrication and printing technology; and device development. Thus both, basic materials development and functional demonstrators are included in the project.
One of the key concepts of MATFLEXEND has been micro energy harvesting, something that enables two key features: wireless and service-free operation. These features ensure that sensor networks require no cabling, no change of battery, and can operate autonomously for many years. Additionally, such technology advances the field of wearable electronics as improved energy harvesting relieves each user of the burden associated with managing batteries – whether that is repeatedly charging them or replacing them. However, in the case of medical devices, either worn or implanted, changing the batteries is often practically impossible. MATFLEXEND is developing technology that can convert mechanical energy into electricity at low frequencies and low forces.
Three of the most impactful developments of the project are high-k dielectrics; flexible electrical conductors; and micro battery prototypes. High-k dielectrics were developed by researchers at Imperial College London and increase the energy density of capacitive harvesters. Ultimately, this enables electrical energy to be generated from mechanical motion. As the capacity of the harvester is changed through a deformation of the flexible electrode, charges are supplied and released at different voltage levels. The flexible electrical conductors were co-developed with researchers based at the University of Vienna and Imperial. Flexible composite conductors based on an open porous PolyHIPE polymer doped with conducting particles were developed for this purpose. Conductivity was improved more than two orders of magnitude over existing state-of-the-art technology.
The development of flexible rechargeable batteries is of equal importance, as they are essential for the buffering and smoothing of the harvested energy. Two battery configurations have been tested: the conventional configuration with stacked electrodes and a coplanar electrode arrangement that offers advantages in processing and mechanical flexibility. The fabrication of these different battery configurations has been simplified by novel printable electrolytes and separators that were developed as part of the project.
Project Context and Objectives:
The MATFLEXEND project is a collaboration focusing on the development of novel, durable materials to facilitate effective energy harvesting and micro batteries. Technological developments include flexible electrical conductors and dielectrics for capacitive harvesters as well as rechargeable microbatteries, which have applications in the growing wearable electronics sector. One of the most important considerations for those attempting to find cost-effective means of facilitating wearable technology is how to harvest energy in a practical, reliable and cheap way. While this has historically proved extremely difficult – not least because reliability and cost have often been mutually exclusive properties – MATFLEXEND is advancing the development of flexible and durable materials that boast very real potential to transform energy harvesting.
MATFLEXEND (MATerials for FLEXible ENergy harvesting Devices) is a three-year project composed of a consortium of 10 partners from several European countries. Led by the Fraunhofer Institute for Reliability and Microintegration IZM (Fraunhofer IZM). The project features three most important work packages: materials development; fabrication and printing technology; and device development. Thus both, basic materials development and functional demonstrators are included in the project.
One of the key concepts of MATFLEXEND has been micro energy harvesting, something that enables two key features: wireless and service-free operation. These features ensure that sensor networks require no cabling, no change of battery, and can operate autonomously for many years. Additionally, such technology advances the field of wearable electronics as improved energy harvesting relieves each user of the burden associated with managing batteries – whether that is repeatedly charging them or replacing them. However, in the case of medical devices, either worn or implanted, changing the batteries is often practically impossible. MATFLEXEND is developing technology that can convert mechanical energy into electricity at low frequencies and low forces.
Three of the most impactful developments of the project are high-k dielectrics; flexible electrical conductors; and micro battery prototypes. High-k dielectrics were developed by researchers at Imperial College London and increase the energy density of capacitive harvesters. Ultimately, this enables electrical energy to be generated from mechanical motion. As the capacity of the harvester is changed through a deformation of the flexible electrode, charges are supplied and released at different voltage levels. The flexible electrical conductors were co-developed with researchers based at the University of Vienna and Imperial. Flexible composite conductors based on an open porous PolyHIPE polymer doped with conducting particles were developed for this purpose. Conductivity was improved more than two orders of magnitude over existing state-of-the-art technology.
The development of flexible rechargeable batteries is of equal importance, as they are essential for the buffering and smoothing of the harvested energy. Two battery configurations have been tested: the conventional configuration with stacked electrodes and a coplanar electrode arrangement that offers advantages in processing and mechanical flexibility. The fabrication of these different battery configurations has been simplified by novel printable electrolytes and separators that were developed as part of the project.
While Fraunhofer IZM coordinates MATFLEXEND, the project involves nine other partners:
Imperial College London develops thermal and photochemically curable nanoparticle composites and conducts research into processability and printability of high-k dielectrics.
The University of Vienna develops and provides PolyHIPE electrolytes and elastomers for converter spring elements.
Eurecat studies harvester and system durability, and conducts research that seeks to integrate harvesters and micro batteries into garments.
SMARTEX proposes a range of commercially realistic applications in technical textiles, and will disseminate the concept of the project into a fashion ecosystem.
LAAS-CNRS develops an electrophoretic deposition process for flexible-battery electrode materials.
VARTA Microbatteries assesses the compatibility of the most promising PolyHIPE electrolytes. In addition, this team conducts tests such as processing and printing technology with novel materials.
ANITRA Technologies lead the communication and dissemination of the project’s findings. They set up dedicated workshops including audiences from research and industry.
PARDAM s.r.o. develop and optimise materials for Li-ion batteries and supplies nanoparticles for Imperial College London to prepare high-k dielectric composites.
COMCARD creates the specification of and materials for the smart card demonstrators. They also test a variety of materials to optimise the converter efficiency.
Project Results:
1.1 Dielectric
SBTO provided by PARDAM and commercial BTO nanoparticles were successfully functionalised with poly(methylmethacrylate) and scaled up to 20g. The functionalised materials were incorporated into epoxy, the functionalisation improved the wetting properties and individualization of the nanoparticles/fibres within the epoxy, in turn improving dielectric properties (up to 92 has been achieved). The inks (~40 ml each) were sent to EURECAT for printing. The inks were stable and successfully printed at EURECAT and yielded homogeneous, mechanically robust thin (5 - 10 μm) layers which can be used for harvesters (IZM and Imperial are currently using these films to build the harvesters). The dielectric breakdown strength of the SBTO-f epoxy nanocomposites of previous films ca. 100 V μm-1. The dielectric properties of the EURECAT films are currently being measured. Conductive fillers (SWNTs, carbon nanohorns (CNHs), carbon nanoonions (CNOs) have been negatively charged in Na/naphthalene DMAc solution and the individualised species have been reacted with a solution of DMAc/PVDF. The stable mixtures of carbon nanomaterial (CNM) in PVDF are drop cast and dried to make flexible dielectrics. Draft publications are also being prepared for the SBTO dielectrics and the insulated conductors.
1.2 Conductive elastomers
The final polyHIPEs based conducting elastomer has been fabricated using a polyacrylate based polyHIPE impregnated with negatively charged SWNTs. Previous polyHIPE can only be deposited onto thin Al foil but with further improvement in the SWNTs adhesion layer, it is now possible to deposit the polyHIPE onto a Cu foil which gives a much higher mechanical robustness to the electrode. The surface roughness of the polyHIPE has been reduced by first depositing a thin layer of negatively charged SWNTs onto the SWNTs impregnated polyHIPE, then finish with a thin negatively charged graphene coating. Various surface patterns have been investigated for the final conducting elastomer prototype in order to reduce the adhesion between elastomer and dielectric under compression. A screen printed polyHIPE with a zig-zag cross section pattern is the best specimen, has the lowest surface roughness and do not adhere to the dielectric. A spring element polyHIPE (UNIVIE) was also printed onto a screen printed polyHIPE surface but a rough surface was formed after the impregnation process and did not proceed further. Imperial is now combining the conducting elastomer with the dielectric to make a demonstration harvester device. A draft manuscript for the SWNTs impregnated polyHIPE has been prepared and Imperial Innovation is currently doing a business feasibility case for the polyHIPE idea. The work may be patented if there is a good business potential and the draft manuscript will be circulated among the partners once the decision on patent is made.
1.3 electrolytes
Many characterizations of RT-IL based Li+-electrolytes suitable for use as internal phase for high internal phase emulsion templates, which can be processed by printing into macroporous polymer microbattery separators have been performed. Furthermore, it was attempted to successfully assemble and characterize working full cell Li+-batteries. The temperature dependent dynamic viscosities of various 0.5M Li+-salt solutions (LiBF4, LiClO4, LiAsF6, LiN(SO2CF3)2 and LiPF6) in [EMIM][BF4] were measured. The dynamic viscosities of Li-salt containing [EMIM][BF4] increased when they contained a dissolved Li salt, but decrease with increasing temperature obeying a VTF behaviour. Temperature dependent Li+-transfer numbers determined by PSGE-NMR revealed rather low values between 0.014 and 0.016 at room temperature, caused by the low Li+ concentration in [EMIM][BF4]. Also further investigations on the thermal behaviour of the in situ RT-IL Li+-electrolyte filled poly(LMA-co-DDDMA)HIPE separators were carried out in order to determine cause of the increasing the MacMullin numbers with increasing temperature. DSC measurements revealed no significant influence on the RT-IL Li+-electrolytes thermal behaviour by the separator. Furthermore conductivity measurements from cyclic heating up and cooling down revealed the process was reversible. Therefore, this effect might be caused by the increasing degree of freedom of the long alkaline side chains of the repeat units with increasing temperature. Finally new LTO-1.0M LiBF4 in [EMIM][BF4]-in-(LMA-co-DDDMA)-NMC full cell configurations were built up now showing more promising performance due to availability of better balanced electrode materials.
1.4 Nanofibers
Force spinning was developed as a cost efficient method to produce nano fibers for battery electrodes (LTO anode) and high-k dielectrics (BTO, SPTO), The problem of precipitation of spinning solution of SBTO during repeated preparation was solved. The milling process was optimized to provide the required particle size (4-7 µm) for next printing steps.
Several tests on optimization of the calcination process of TiO2 nanofibers have been performed to evaluate potential of this technology for calcination of inorganic nanofibers. Test on prototype machine showed small decrease of polymer matrix from precursor fibers comparing to the results reached at laboratory level. TiO2 was used for comparison with laboratory tests to evaluate the possibility for up scaling.
SiO2 nanofibers were produced and successfully tested at IZM for application of this new material for printable battery separator. This new material is unique mainly from the production and economic point of view as precursor is 1000times cheaper than TEOS and production yield is 50% higher that TEOS (current production technology).
2. Demonstrators
-Batteries
Rechargeable micro batteries which are thin, in part bendable and can be adapted to the form factor of the application are required for several wearable and miniaturized electronic products. A special segmented battery packaging concept has been developed which uses pre-patterned current collector foils as battery housing, laminate battery assembly, simultaneous microfluidic electrolyte filling of all battery segments and final sealing on substrate level. The size and shape of the battery can be easily changed by only altering the lithography masks. The battery thickness is in the range between 0.3 and 1 mm resulting in an area capacity between ca. 1 and 5 mAh/cm2. While commercial electrode materials and electrolyte (1M LiPF6, EC:DEC) for lithium ion batteries were used in most cases, novel nitridated Li4Ti5O12 (LTO) electrode fibers and self-made separator composites with materials provided by the partner PARDAM were tested and developed at Fraunhofer IZM. All fabrication steps and materials were optimized towards the foil type segmented micro battery:
- The performance of LTO anode fibers were tested against commercial powders.
- Electrode and separator pastes were optimized for stencil print and dispensing including water based binder.
- Electrodes (LTO anode and LiNi1/3Co1/3Mn1/3O2 (NMC) cathode) and ceramic separator printing processes required for the segmented electrode shape were developed.
- Battery assembly and final sealing was developed including low water permeation rate lamination between top and bottom package, electrolyte filling with help of a microfluidic adapter.
Half and full cell tests and cycling with increasing C-rate are used to study the influence of material and packaging parameters on the electrochemical performance. 6x8 mm2 prototypes of 0.7 mAh were fabricated with high reproducibility. They work stable until a current of 2C and showed stable cycle life.
- Harvester
Polymer based capacitive harvester were demonstrated which can later be fabricated with help of roll-to-roll and low cost printing methods. In contrast to electrostatic MEMS based parallel plate transducers or dielectric elastomer systems here, the capacitance is varied as function of the mechanical load by changing of the top electrode area with help of an electrically conducting composite elastomer. In case of the composite elastomer electrode the maximum capacitance in compressed state does not only depend on the thickness and permitivity of the dielectric but first of all on the quality of the interface and the micro structure of the conducting phase in the composite electrode at the interface which was investigated by FEM Maxwell simulation.
An equivalent circuit model is used to study the influnce of the leakage current inside the dielectric and the bulk resistivity of the elastomer electrode.
First experiments with the novel printed dielectrics in contact with elastomer electrodes have been performed to prove the harvesting principle at low frequencies. The maximum capacity was between 0.4 and 0.8 nF/cm2. FEM simulations and experimental results clearly indicate that the specific capacity is not limited by the dielectric material but due to the elastomer electrode. No more than ca. 1 nF/cm2 can be practically achieved with the used conducting elastomer. A capacity of 650 pF/cm² was achieved with screen printed dielectrics fabricated at IMPERIAL and printed at EURECAT. Charges between 25 and 70 nAs per cm2 have been transferred per cycle at 100 V/200 V. At an actuation frequency of ca.1 Hz this corresponds to 0.5 ... 1.5 µW/cm2.
UniVien optimized harvester variants for low and higher force applications. More than 100.000 cycles were tested without degradation.
Another aspect concerns the adaption of an electronic circuit interface which will allow the charge of a battery with the capacitive harvester. An electronic module was developed that allows the online measurement of the harvested energy.
Potential Impact:
Rechargeable batteries as temporary energy storages and energy harvesters will find many applications in the future. They are basic hardware components for energy autarkic micros systems which are required for internet of things, industry automation (industry 4.0) smart environments, health care and medical devices, consumer applications like sportswear and intelligent homes. Some special small scale application will be in the research area like tracking of small animals in the wild.
In particular several special results and activities the MATFLEXEND were identified to have great impact and exploitation potential by the partners:
– P1 Energy converters, small secondary batteries and general harvesting.
– P2 High-k polymer dielectrics, disperse SWCNTs "nanotubides", highly "conductive & compliant" elastomers
– P3 PolyHIPEs, RTIL-in-polyHIPEs, patterning
– P4 Smart Shoes, Gait Analysis, Decorative applications + textiles
– P5 Insoles, Smart-shoe SDK electronics
– P6 Electrophoretic deposition + (patterned) EPD
– P7 COTS button cells for wearables, printing flexible batteries
– P8 Anitra – workshops, nomenclatures, tools for Desk Research, ontologies
– P9 Nanofibers for battery electrode or release materials. Forcespinning + enhancements
– P10 Smart Cards
Dissemination activities:
Partner P7 VARTA attended trade fairs including LOPEC-C, IDTech, with an own booth including MATFLEXEND visuals and promoting power to Wearables + toher appplications.
At IDTechEx in Berlin, April 2015 and 2016. P1 Fraunhofer had its own booth, and substantial amounts of visitors´ traffic. P8 was present as well, doing networking with e.g. Fraunhofer ISC (presssure-sensors-sock by), small battery exhibitor ILIKA, a Southampton battery spinout, Gore, a provider of high-tech fabrics. P8 was also invited to an NCP NMBP contacts-seminar in Mainz, May 12th, 2016, participating in interviews and discussing energy harvesting with PTZ Jülich.
Finally, P8 was invited to present some thoughts about EU Dissemination on May 24, 2016, it including some most interesting & relevant reports on the EU´s Open Data initiatives.
Other such information to be found in the "News" page of the project Website.
P1 and P8 gave a 2 pp. interview to IMPACT, a openly distributed magazine reporting on EU research. This is to be published on paper and in November 2016.
The article in particular stresses the importance of Open Access - for smaller Partners - in order to find competing developments, partnering and marketing opportunities. An author´s copy is uploaded to, and open-access-available from the MATFLEXEND public Website in the "News" section. It has also been distributed as part of the 390+ mailshot for the Workshop.
In June 26th, 2015, P8 Anitra gave a short presentation on Exploitation approaches to the Dresden Cluster worskhop, in addition to the IZM technical presentation reported in the Table above.
Magazines database - an update: building a focused magazines database
In the Dissemination report, P8 had offered some trivial hints about how to google more specifically, essentially by building a mindmap of keywords. As for finding suitable magazines, it became clear from discussions that Partners wanted to select their own magazines, so as an experiment. P8 combined proposed keywords from 7.2.5 a) below, with the keyword "journal", yielding a table, extracts of which are shown in the second periodic report.
Partner EURECAT developed an idea for outdoor use of printable, textile photovoltaics in an energy harvesting system. A small draft proposal outline MOSENHAR "MOSaic ENergy HARvester) has been developed off-project and circulated, to partners and to SMEs.
The new idea would combine small solar cells and batteries into planar mini-energy harvesters as part of a mosaic of rigid elements, which could be plane or 3-dimensional.
We have been in touch a number of times with the Open Innovation Systems Group at DG CONECT (Dr. Bror Salmelin) raising a series of issues about using Cognitive Computing in Energy Harvesting in particular, in the EU in general, and in assisting better Dissemination by the EU, prior to launching a Call.
It later resulted in a preliminary proposal outline (ENHARONT ENergy HARvester ONTology) which has been researched outside MATFLEXEND but might be a follow-up project. It is discussed here as a part of Dissemination, since it might be relevant to the "Energy Harvesting Cluster".
This will be considered on a strictly pragmatic basis, i.e.: can it be practically useful? The US Army, Airbus, and some materials scientists in the US and Japan seem to think so.
Prospects include DFKI, Univ. Manchester, Univ. Southampton, Hahn-Schickhard Gesellschaft, DFKI Deutsches Forschungszentrum für Künstliche Intelligenz; with IZM acting as a domain expert. Support by industry (Nicomatic?) and perhaps Bundeswehr will be critical.
In Addition P8 found references to an earlier idea by P1 IZM, namely to affix small energy harvesters to animals, small birds and even larger insects. This seems of interest for at least two reasons: the bird-watchers - especially the Swiss Vogelwarte Sempach, CH - together with FH Bern, have devised lightweight (1 gram > weight (?!)) geolocation devices for migratory birds, essentially adding GPS logging to the traditionally-used rings of old. Extraordinary ingenuity has resulted in such light packages logging a year´s worth of GPS data - sampling location once per week, and using a primary battery. More ambitious and publicly-announced work has started at the Max-Planck-Institute in Radolfzell, DE, which literally hired a rocket scientist to develop ultra-small transponders that could send a data salvo to the International Space Station, again with few-gram hardware. Besides being able to follow birds in real time, one can here address birds that do not necessarily return to their starting point; and perhaps even more impactfully, larger insects such as bees and agricultural pests, which cannot easily be caught again for readout. So this sytem in spite of its small market may have huge impact on agriculture.
In other activity IZM and Anitra found a group in Barcelona (Dr. C. Flox and Prof. Morante, IREC) using electrospun nanofibers to enhance electrode performance in a V2O5 redox-flow battery; broadly similar to some work that P1 IZM has conducted with P9 PARDAM for LiOn batteries. Now PARDAM has expertise in both electrospinning and force-spinning (the latter, safer and cheaper) and so, contact with PARDAM and IREC has been set up, with both parties due to meet at NANOTECH 2016, end-September, in Valencia. Georg Schmid Energy Systems, a subsidiary of Georg Schmid (www.schmid-group.com) are in contact with IREC and also with Imperial / Materials.
In an earlier exercise with UNIVIE had considered alternative uses of their RTIL-polyHIPE separators in electrochemical sensor applications (the PAPFIL workshop, conducted off-project), as well as using them asdsorb/desorb media (adsorb-in-situ / desorb-in-Gas-Chromatograph/MS) for volatile organic compounds.
In exploitation desk research, we then found some publications about pharma release to a skin, from an RTIL vehicle and contacted Univ. Bath (Prof. Guy + Dr. Delgado) as well as Univ. Nottingham (Prof. Croft) plus another worker at Univ. New Lisboa (Prof. Marrucho) to discuss possible use of the UNIVIE RTIL-imbibed elastomers in a smart bandage. Contact with P3 UNIVIE was subsequently established, with a view to discuss a future project re. topical (= 2-D patterned) administration of certain medication to a wound, or to diseased fingernails - where such "transdermal" pharma release is notoriously difficult. We also found that electro-spun nanofiber felts by P9 PARDAM might offer an alternative path to continuous topical release from a bandage. A post-project workshop is planned to deal with these issues, and to finding a call.
Work done by P2 Imperial on conductive elastomers is seems in practical applications, such as conformable electronic shielding and will be published after resolving IPR issues; high-k dielectrics trivially allow more compact capacitors terms (as in e.g. more compact rectifiers), and we expect more examples from Solvay. From the Dissemination point of view, our contribution has been to establish (and much later re-establish) contact with Solvay. Solvay will present its own progress in high-k dielectrics at the Vienna workshop, with opportunities to discuss more collaboration.
Nano-tubide work reported in the first workshop and project review might be relevant to supercapacitor work, which could widely apply to energy storage.
List of Websites:
5. www.matflexend.eu
contact:
Dr. Robert Hahn Fraunhofer IZM
Gustav-Meyer-Allee 25, 13355 Berlin, Germany
0049 30 46403611, robert.hahn@izm.fraunhofer.de
