Scientists from the Swiss Federal Institute of Technology Zurich (ETH) have now presented the prototype of a so-called thin-film battery in the specialist magazine Advanced Materials . The flexible energy storage can be bent, stretched and twisted without being damaged. The supply of electricity is also maintained throughout the deformation.
In the future, the new battery could be installed in smartphones, implants and clothing. However, optimizations are still necessary before industrial use.
Smartphones and notebooks with flexible screens , technology integrated in clothing and other innovations in the electronics industry will need new energy sources for power supply. Currently lithium ion batteries are used almost exclusively, but they are heavy and inflexible, which makes their use in future technologies in their current form significantly more difficult.
New electrolyte makes batteries flexible:
The multi-layer structure of the battery is comparable to conventional lithium-ion batteries, but for the first time only flexible components are used. Markus Niederberger, professor of multifunctional materials, explains that “as consistently as never before, only flexible components have been used to produce a lithium- ion battery .” The biggest innovation of the new battery is the electrolyte, through which the lithium Ions must move when charging and discharging. It was developed at the ETH by doctoral student Xi Chen.
The anode and cathode consist of an electrically conductive carbon , which is encased in a flexible plastic shell . The inside of this plastic cover is flocked with a layer of the tiniest silver , which overlap one another and thus maintains contact even when the plastic is deformed. The battery can still conduct electricity when it is bent or twisted. If the silver flakes lose their contact due to excessive deformation, electricity can continue to flow through the carbon-containing plastic.
More environmentally friendly materials than conventional batteries:
As Niederberger explains, the new water-based electrolyte gel is “more environmentally friendly than previous electrolyte liquids from today’s batteries, which are toxic and flammable.” The electrolyte gel developed by Xi, on the other hand, only uses lithium salt, which is dissolved in water in a high concentration . It enables the lithium ions to migrate between the cathode and anode and, at the same time, prevents the water from being electrochemically decomposed when the battery is charged and discharged.
Consistently flexible components used
The sandwich-like structure of the new battery is based on commercial batteries. For the first time, however, the researchers used only flexible components to keep the battery as a whole flexible and stretchable. “No one has ever used flexible components to manufacture a lithium-ion battery as consistently as we have,” says Niederberger.
The two current collectors for the anode and the cathode are made of a stretchable plastic that contains electrically conductive carbon. This is also the outer shell.
The researchers applied a thin layer of tiny silver flakes to the inside of the plastic. Due to the roof tile-like arrangement of the silver flakes, they do not lose contact with each other even when the plastic is stretched a lot. This guarantees the conductivity of the current collector even when it is stretched a lot. If the silver flakes nevertheless lose contact with one another, the electrical current flows – albeit weaker – through the carbon-containing plastic.
Using a soft battery gel, researchers at ETH Zurich have been able to develop a battery that can be twisted, stretched and even folded. It should be the basis for future electricity storage in foldable smartphones and clothing.
Firm and inflexible:
All batteries and accumulators are currently firm and inflexible. Damage can lead to fire, which is particularly dangerous for electric cars after an accident because they require large battery packs.
Common batteries also lead to problems when using them in clothing and electronic devices, which should best be flexible. Swiss researchers have now achieved a breakthrough, the core of the newly developed battery is filled with soft hydrogel electrolyte.
However, team leader Markus Niederberger, professor of multifunctional materials at ETH Zurich, emphasizes that commercialization of the battery is not yet an option. According to Niederberger, the loading of electrode material has to be increased beforehand.
The further development of the battery has already started, even if it is no longer carried out by the inventor of the electrolyte gel. Chen returned home after completing his doctoral thesis, where he worked as a consultant in the battery industry.
This means that the thin-film battery can even be bent, twisted and stretched without the power supply being cut off. The battery structure itself is even similar to that in common accumulators, but for the first time all the parts used are flexible, which is what characterizes the prototype. The hydrogel electrolyte was developed by ETH PhD student Xi Chen.
Optimization of the battery necessary:
Before the battery can also be used industrially, further optimizations are necessary. The five existing prototypes were glued and are therefore very likely not to be sealed in the long term. Xi, the prototype developer, has now returned to China , where he works in the battery industry. Further development is now being carried out by a new doctoral student whose main goal is to significantly increase the load of electrode material.
Markus Niederberger, professor of multifunctional materials at ETH Zurich, and his team are now solving this problem. The researchers have developed a prototype of a flexible thin-film battery. This can be bent, stretched or even twisted without the power supply being cut off.
The heart of this new battery is the electrolyte, i.e. the part of a battery through which the lithium ions have to move when the battery is discharged or charged. The electrolyte was developed by ETH doctoral student Xi Chen, first author of a study that has just been published in the journal “Advanced Materials”.
The electronics industry is increasingly relying on computers or smartphones with foldable or rollable screens. Portable mini devices or sensors are used in smart clothes to monitor body functions, for example. However, all of these devices require an energy source, and usually this is a lithium ion battery. Only: such batteries are heavy and rigid and therefore in principle unsuitable for applications in flexible electronic devices or textiles.