MIT Ups Energy Storage With “World’s Longest” Flexible Fiber Li-ion Battery
Advances in e-textile research have led researchers to weave Li-ion batteries into fibers. Such development promises to offer scalable power solutions to smart and flexible electronic devices.
The advent of smart, foldable, and flexible battery-powered electronics has made researchers heighten and push forward more innovations in fiber-based energy storage systems. Thanks to the miniaturized structure of fibers, batteries could be woven into them to power smart clothes, gloves, and other wearables.
Close-up view of a fiber battery embedded in textile. Image [modified] used courtesy of Khudiyev et al
Fiber is a good candidate for fabricating flexible and washable power electronics systems. Thus, recent research in flexible electronics by researchers at the Massachusetts Institute of Technology (MIT) has paved the way for developing a Li-ion (lithium-ion) battery fiber.
This new development promises to improve the energy storage capabilities in foldable battery-powered electronics.
Current Collectors in Flexible Batteries
Before diving into MIT's latest battery research, let's talk about current collectors in flexible batteries.
A typical foldable battery constitutes current collectors, electrolytes, and separators. These current collectors typically make use of both anode and cathode (generally, aluminium and copper, respectively) current collectors to transfer free electrons from active materials.
In the fabrication of flexible batteries, trade-offs between mechanical stress, porosity, and conductivity need to be considered when employing these two current collectors as they are prone to mechanical failure and pose hazards in the flexible electronic device.
Carbonaceous materials such as carbon nanotubes and carbon cloth are also employed in making current collectors.
Current collectors made from these materials can be characterized by high flexibility, lightweight, and conductivity, making them suitable for flexible battery applications.
An LED and the fiber battery solution can be woven on a single fabric. Image used courtesy of Khudiyev et al
In the novel flexible fiber battery, the MIT researchers employed lithium-iron-phosphate (LFP) as the cathode current collector and lithium titanate (LTO) as the anode current collector.
In addition, the researchers adopted carbon black material to boost electrical conductivity.
Flexible Batteries Meet Solid-state Electrolytes
Another component to consider of flexible batteries is the electrolytes, namely liquid versus solid.
Liquid electrolytes are majorly used in flexible Li-ion batteries and help ensure rapid ion mobility, facile percolation, and a stable solid-electrolyte interphase property.
However, solid electrolytes are better substituted in flexible batteries applications. Solid electrolytes give negligible electrolyte leakage compared to liquid electrolytes. At the same time, they possess a high Young's modulus which inhibits lithium dendrites.
The electrolyte used in the fabrication of the novel flexible fiber battery is a solid-state polymer electrolyte and made up of polyvinylidene fluoride (PVDF) mixed in 1 M lithium bis trifluoromethanesulfonimide (LiTFSI) in EC:PC solution.
The researchers meticulously chose the required ratio of the polymer, solvent, and other active materials to achieve mechanical integrity at low temperatures.
Also, in the fabrication process, the viscosity of the electrode and electrolyte gels became thermally drawable at a temperature of 200° C.
Drawable Fibers Accelerate 1D, 2D, and 3D Power Electronics
Overall, MIT's novel Li-ion fiber battery, which is 140 meters long, claims to be the first-ever produced flexible fiber battery via a perform-to-fiber thermal drawing approach.
The capacity discharge of the flexible Li-ion battery amounts up to 123 mAh with a discharge energy of 217 mWh.
The electrical circuit of a fiber battery-powered system for Li-Fi communication. Image used courtesy of Khudiyev et al
The thermal drawing approach allows designers to weave the flexible battery and LEDs in a single fiber for 1D power source applications.
Furthermore, the fiber battery is compatible with traditional yarns, making it useful in 2D fabric electronics via machine weaving.
Additionally, designers could also adopt the novel battery in 3D printing to create solid objects.
Future Endeavours in Flexible Fiber Battery
While researches and experiments are still being conducted to push forward innovation in the e-textile industry, the source of power for washable and foldable electronics devices still requires much attention to meet standards and safety requirements for consumers.
The flexible smart energy storage solution still requires more research to choose the appropriate components that meet mechanical integrity and electrochemical compatibility in the active materials used for fabrication.
On top of this, it is essential to look into how the flexible power solution could be cost-effective and mass-produced as proof-of-concept tests are yet to be accepted in large-scale applications.
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