Stretchable battery research and development

Stretchable battery currently under research and development is expected to solve the above problems. The team of Professor Kong Desheng of Nanjing University and Associate Researcher Bai Chong proposed an electrode based on a microscopic wrinkle structure and a method that can realize a stretchable battery.

What is a stretchable battery?

Stretchable battery is one of the building blocks of wearable electronics. It is not just an energy storage device, but an intersecting system involving mechanics, electricity, and electrochemistry.

Lithium-ion battery (LIB), as one of the best rechargeable batteries, has the characteristics of high energy density, long life, and low self-discharge rate.

It consists of positive and negative electrodes, current collectors, separators, electrolytes, and sealing materials. To make a stretchable battery, all of these components must function reliably under mechanical deformation.

Although stretchability can be achieved by prestraining or blending with large amounts of elastomers that do not participate in energy storage, this leads to deterioration of energy density and rate performance.

Furthermore, most approaches only make certain specific components stretchable, rather than the entire full cell. Therefore, the stretchable battery has a resistance and a long length.

Stretchable battery representative – zinc ion rechargeable battery

Aqueous zinc-ion rechargeable batteries mainly include the following highlights:

First, this stretchable battery realizes the macroscopic stretching deformation of the battery itself by means of the reversible extension of the microscopic fold structure of the electrode, effectively avoiding the large deformation of the battery in three-dimensional space, so as to facilitate a close fit with the skin;

Second, this stretchable battery is based on a non-burning water-based gel electrolyte, which can avoid the internal short circuit of the battery generated by stretching deformation, hence minimizing the risk of fire caused by thermal runaway and enhancing the battery system’s safety.

Third, the research group proposed a method to prepare stretchable metal thin film current collectors. Compared with the previous ones, the tensile deformation range of the current collector and the structural stability during the deformation process have been significantly improved.

Fourth, based on the optimized control of the wrinkled electrodes, the fabricated stretchable battery has a very compact structure with a thickness of only 1 mm.

Stretchable battery is expected to drive other functional electronic devices when worn on the skin, thereby getting rid of the shackles of an external power supply and realizing the portable wearable of the entire electronic device system.

Detailed explanation of stretchable battery technology

Wrinkle structure
By adopting the method of “pre-stretching-transfer-laminating”, the conductive film can be combined with the stretched elastic matrix. After releasing the tensile strain, the wrinkled structure can be obtained.

This is a very effective method for fabricating stretchable current collectors and electrodes. It should be noted that the microscopic morphology of wrinkles is closely related to the thickness, elastic modulus and tensile strain of the current collector material itself.

Elastic film
Use a layer of 1 µm thick elastic film as the supporting substrate to support the metal thin film.

On the one hand, this significantly improves the operability of the metal film during transfer and lamination; on the other hand, this layer of elastic film can effectively improve the structural integrity of the metal film.

In order to reduce the damage of mechanical strain to the metal film, a high-conductivity stretchable current collector that can be stretched repeatedly 1000 times in a wide range is finally prepared.

This means that it is expected to prepare a stretchable positive/negative electrode by loading the positive/negative electrode material of the battery on the surface of this current collector.

Stretchable electrodes
The loading of electrode materials not only affects the microscopic folds and skin-fitting wearability of electrodes, but also correlates with the energy storage performance of batteries.

When the loading of electrode active materials is too high, it will lead to a sharp increase in the surface roughness of wrinkled electrodes, as well as the attenuation of mechanical durability, and will produce macroscopic wrinkles or even curls, which will hinder the assembly of batteries.

Focusing on the balance between microscopic wrinkle morphology, electrode mechanical durability and battery energy storage performance, they optimized the loading of metal zinc anode material and manganese dioxide cathode material to prepare a stretchable electrode , which has the advantages of low roughness and excellent mechanical durability.

Using the classic “sandwich” structure, a stretchable battery can be obtained by assembling a stretchable positive electrode, a gel electrolyte, and a stretchable negative electrode.

The future direction of stretchable battery

In this study, the research group used an elastic film to support the metal thin film current collector, which improved the microstructural stability of the current collector while improving the tensile deformation capacity of the current collector.

As a multi-layer composite film system composed of metal film, elastic film and elastic matrix, the role played by the elastic film in it is also worthy of further study.

However, the elastic modulus, thickness and interfacial bonding energy of the elastic film and other parameters affect the fluctuation degree of the microscopic wrinkle structure and the structural stability, which need to be further analyzed.

In addition, they also prepared stretchable gold and silver current collectors. How to use this strategy to prepare stretchable current collectors that are cheap and have good electrochemical stability is another issue worth thinking about.

Summary

In conclusion, stretchable batteries have great potential to revolutionize the field of wearable technology. However, the development of stretchable batteries is still at an early stage, and many challenges need to be overcome, such as improving the energy density and durability of batteries.

Overall, stretchable battery offers a promising battery solution to the limitations of conventional batteries in wearable technologies. With continued research and development, stretchable battery has the potential to revolutionize the field and bring new possibilities to wearable devices.