Periodic Reporting for period 2 - HIDDEN (HINDERING DENDRITE GROWTH IN LITHIUM METAL BATTERIES)
Reporting period: 2022-03-01 to 2024-02-29
The HIDDEN project has focused on extending the lifetime of Lithium-Metal (Li°) Batteries (LMBs) by preventing dendrite growth. Dendrites are metallic strands that are formed at the lithium/electrolyte interface during charging and discharging, unless protective layers or self-healing methods are used. They will eventually lead to a short circuit in the battery, which is both a performance and safety issue. It is important to find a solution to prevent dendrite growth, as LMBs are a key-enabling technology for batteries with high energy density. Such batteries would enable wider electrification of transportation and offer longer driving range.
In the lifespan of the HIDDEN project, the consortium has focused both on developing and testing the self-healing materials and upscaling the processes simultaneously. In addition, methods to detect the possible degradation and trigger the self-healing methods have been developed. Fascinating results have been achieved over the course of the project’s duration. Following many exciting research activities and synergistic collaborations with other research groups within the Battery 2030+ framework, the final project results are now available.
Two self-healing methods have been explored in the HIDDEN project framework regarding battery technologies. These are Thermotropic Ionic Liquid Crystal (TILC) electrolytes and piezoelectric separators. The self-healing capacity of the TILC electrolyte was demonstrated in symmetric Li°│ TILC │ Li° cells, showing that it is even possible to bring a short-circuited cell back to life with the self-healing protocol developed in HIDDEN. On the other hand, the piezoelectric separators showed at best a 65 % increase in lifetime when compared to a reference Li-metal cell with a standard separator and a liquid electrolyte. The self-healing separator was shown to work both in coin and pouch cells, and the processing of the separator was eventually upscaled into pilot level.
In the lifespan of the HIDDEN project, the consortium has focused both on developing and testing the self-healing materials and upscaling the processes simultaneously. In addition, methods to detect the possible degradation and trigger the self-healing methods have been developed. Fascinating results have been achieved over the course of the project’s duration. Following many exciting research activities and synergistic collaborations with other research groups within the Battery 2030+ framework, the final project results are now available.
Two self-healing methods have been explored in the HIDDEN project framework regarding battery technologies. These are Thermotropic Ionic Liquid Crystal (TILC) electrolytes and piezoelectric separators. The self-healing capacity of the TILC electrolyte was demonstrated in symmetric Li°│ TILC │ Li° cells, showing that it is even possible to bring a short-circuited cell back to life with the self-healing protocol developed in HIDDEN. On the other hand, the piezoelectric separators showed at best a 65 % increase in lifetime when compared to a reference Li-metal cell with a standard separator and a liquid electrolyte. The self-healing separator was shown to work both in coin and pouch cells, and the processing of the separator was eventually upscaled into pilot level.
In significant achievements towards LMBs striving toward enabling a higher energy density technology, new generation of dynamically self-assembling/healing electrolytes (TILCs) and piezoelectric separators were developed. The self-healing methods of HIDDEN were analysed also with life cycle assessment (LCA) methods.
The HIDDEN project upscaled the synthesis of the TILC material to a level of hundreds of grams and demonstrated its potential to prevent dendrite growth both by modelling and by experimental results. The related research strategies implemented within symmetric Li°│TILC│ Li° coin cells proved to mitigate the nucleation and growth of Li° dendrites. TILCs allow both preventive and curative self-healing solutions. This is possible through the dynamic control of the Li-ion flow by the self-assembled electrolyte, and at the Li°/TILC interfaces by the application of a temperature-regulated self-healing protocol, respectively. In addition to materials and processing methods, a cell level heating element was developed for controlling the self-healing. The consortium also developed algorithms and protocols to trigger the heating scheme at the required timing.
Piezoelectric separators developed during HIDDEN synergistically provide a complementary preventive solution leveraging their role in mitigating the nucleating and growth of Li° dendrites through regulating the ion flux by a local electric field generated by Li° dendrites, leading to an efficient countermeasure. For the preparation of piezoelectric separator, a Non-solvent Induced Phase Separation (NIPS) process was used, taking advantage of the polymer’s difference in solubility in two different solvents to trigger a phase separation from liquid to solid. Then, PVDF-TrFE was investigated as a potential material to mitigate Li° dendrite growth. In the framework of the HIDDEN project, the process was scaled up to a Roll-to-Roll (R2R) pilot line. Finally, the produced membranes were compared in full battery configurations, demonstrating the potential of piezoelectric polymers in mitigating the capacity fade in lithium metal cells. This demonstration emphasises the promising application of such materials to be used for achieving the goal of the HIDDEN project.
The HIDDEN project successfully created 10 Key Exploitable Results, namely:
1. Library of new Thermotropic Ionic Liquid Crystals (TILCs)
2. Deep learning solution for electrolyte property assessment and design (structure & molecular architecture to properties solver)
3. Piezoelectric separator
4. Characterization and detection of dendrite growth
5. Laser cutting of Li° negative electrode
6. Quality assurance measurement devices within the assembly process
7. Heating element
8. Coating process for the TILC electrolyte & proof-of-concept demonstration of self-healing
9. Optimized assembly process
10. Battery Management System (algorithms, software, hardware)
These results were widely disseminated via online channels (HIDDEN website, social media) as well as in other dissemination means, such as newsletter and scientific publications and conference participations. Partners will exploit the project results in diverse ways: non-commercial exploitation includes using the knowledge in further research, as well as educational activities while commercial exploitation plans concern licensing agreements with industrial players, provision of technology consulting towards industrial players as well as direct use of the technology by the industrial partners.
The HIDDEN project upscaled the synthesis of the TILC material to a level of hundreds of grams and demonstrated its potential to prevent dendrite growth both by modelling and by experimental results. The related research strategies implemented within symmetric Li°│TILC│ Li° coin cells proved to mitigate the nucleation and growth of Li° dendrites. TILCs allow both preventive and curative self-healing solutions. This is possible through the dynamic control of the Li-ion flow by the self-assembled electrolyte, and at the Li°/TILC interfaces by the application of a temperature-regulated self-healing protocol, respectively. In addition to materials and processing methods, a cell level heating element was developed for controlling the self-healing. The consortium also developed algorithms and protocols to trigger the heating scheme at the required timing.
Piezoelectric separators developed during HIDDEN synergistically provide a complementary preventive solution leveraging their role in mitigating the nucleating and growth of Li° dendrites through regulating the ion flux by a local electric field generated by Li° dendrites, leading to an efficient countermeasure. For the preparation of piezoelectric separator, a Non-solvent Induced Phase Separation (NIPS) process was used, taking advantage of the polymer’s difference in solubility in two different solvents to trigger a phase separation from liquid to solid. Then, PVDF-TrFE was investigated as a potential material to mitigate Li° dendrite growth. In the framework of the HIDDEN project, the process was scaled up to a Roll-to-Roll (R2R) pilot line. Finally, the produced membranes were compared in full battery configurations, demonstrating the potential of piezoelectric polymers in mitigating the capacity fade in lithium metal cells. This demonstration emphasises the promising application of such materials to be used for achieving the goal of the HIDDEN project.
The HIDDEN project successfully created 10 Key Exploitable Results, namely:
1. Library of new Thermotropic Ionic Liquid Crystals (TILCs)
2. Deep learning solution for electrolyte property assessment and design (structure & molecular architecture to properties solver)
3. Piezoelectric separator
4. Characterization and detection of dendrite growth
5. Laser cutting of Li° negative electrode
6. Quality assurance measurement devices within the assembly process
7. Heating element
8. Coating process for the TILC electrolyte & proof-of-concept demonstration of self-healing
9. Optimized assembly process
10. Battery Management System (algorithms, software, hardware)
These results were widely disseminated via online channels (HIDDEN website, social media) as well as in other dissemination means, such as newsletter and scientific publications and conference participations. Partners will exploit the project results in diverse ways: non-commercial exploitation includes using the knowledge in further research, as well as educational activities while commercial exploitation plans concern licensing agreements with industrial players, provision of technology consulting towards industrial players as well as direct use of the technology by the industrial partners.
The HIDDEN project has shown that a shorted cell can be recovered to its original level of performance by the developed self-healing methods, using the TILC electrolytes and a specially designed temperature protocol. To the best of our knowledge, this kind of self-healing effect has never been shown till date. Even though it was demonstrated for a symmetric Li°│ TILC │ Li° cell, and not in a full cell configuration, it shows the potential of the developed methodology.
Regarding the piezoelectric separator, the HIDDEN consortium showed that the PVDF-TrFE material can be used as a separator to increase the lifetime of LMBs by 65%, and that it is possible to upscale the processing of the separator up to the pilot level. This is a significant improvement towards future impact, as it indicates that it was already possible to transfer the idea from lab to pilot scale, and eventually to industrial scale after further process optimization.
The developed algorithms to detect the growth of dendrites and to trigger the self-healing protocol also go beyond the state-of-the-art and hold a chemistry-neutral dimension. Indeed, they will be useful for future battery developers beyond LMBs, as the methods are suitable for following the degradation in a wide range of battery chemistries.
Also, the environmental aspects were analysed. Based on the LCA performed in HIDDEN, PVDF separators have a slightly lower environmental impact than polypropylene (PP) separators from a material perspective. The TILC electrolyte has a higher impact, but as the TILC synthesis (used as a basis for the LCA calculation) was still performed at a relatively small scale, upscaling to industrial level should help to reduce the environmental impact.
Regarding the piezoelectric separator, the HIDDEN consortium showed that the PVDF-TrFE material can be used as a separator to increase the lifetime of LMBs by 65%, and that it is possible to upscale the processing of the separator up to the pilot level. This is a significant improvement towards future impact, as it indicates that it was already possible to transfer the idea from lab to pilot scale, and eventually to industrial scale after further process optimization.
The developed algorithms to detect the growth of dendrites and to trigger the self-healing protocol also go beyond the state-of-the-art and hold a chemistry-neutral dimension. Indeed, they will be useful for future battery developers beyond LMBs, as the methods are suitable for following the degradation in a wide range of battery chemistries.
Also, the environmental aspects were analysed. Based on the LCA performed in HIDDEN, PVDF separators have a slightly lower environmental impact than polypropylene (PP) separators from a material perspective. The TILC electrolyte has a higher impact, but as the TILC synthesis (used as a basis for the LCA calculation) was still performed at a relatively small scale, upscaling to industrial level should help to reduce the environmental impact.