For smart devices or clothing to be considered truly wearable, all components should be thin, compact, soft and stretchable to conform with human skin and integrate seamlessly into everyday life without making a product uncomfortable. The power source is a key component in wearable devices and smart clothing. While batteries are the most common power supply used today, they are currently limited in regard to size and weight. The majority of commercially available batteries are still considered bulky and heavy, and usually the battery must be removed before the clothing is washed, which compromises wearability.

Smart wearables are often treated as fad items, where the device is no longer worn after a couple of months after purchase due to difficulties related to integrating them to daily routine. Therefore, smart devices are more likely to enhance a user’s life for longer time periods if the wearable is designed to cut down barriers to engagement, such as needing to regularly charge the battery of the device. This would help to increase the demand for wearables to incorporate flexible, stretchable and thin devices that can provide sustainable, autonomous power, and do not require replacing, removing or charging of the built-in power supply.

The most advanced flexible batteries available on the market incorporate lithium-ion, vacuum-deposited lithium, or zinc batteries. There are advantages and disadvantages to each - lithium-ion batteries can be manufactured at a low cost, but they are bulky and cannot provide the high power required for some smart wearable applications. Extremely thin lithium batteries are available; however, they are costly, and provide an even smaller energy capacity than lithium-ion batteries. Zinc batteries are extremely low cost and provide a larger energy capacity than lithium-ion. However, zinc batteries are only suitable for low power devices. Therefore, the limitations associated with these materials have had a direct impact on the flexibility and shape of batteries for wearable devices that are currently available on the market [1].

Additionally, lithium-ion, lithium and zinc batteries incorporate carbon collectors and electrodes which help reduce the weight of the battery, however, these materials also commonly limit the electrical conductivity and therefore electrical power that can be achieved. Additionally, if these parts were replaced with metal, the amount of electrical power the battery can provide is increased. However, corrosion due to the chemical reactions within the battery is increased as well, reducing the life span of the battery and limiting the battery’s power output [1].

The research suggests that one way to address this challenge could be incorporation of graphene in energy storage. Graphene is a single-atom-thick sheet of hexagonally arranged, bonded carbon atoms. It has been named a ‘wonder material’ due to its long list of remarkable intrinsic properties including very high tensile strength, excellent thermal and electrical conductivity, as well as high flexibility, elasticity and lightweight, which can lead to unexpected advances. Graphene at room temperature has the highest electrical current density which is one million times that of copper and the highest intrinsic electronic mobility (of charge carriers) equal to 2-2.5*10⁵ cm² V^-1 s^-1, which is 100 times that of silicon. With this in mind, graphene has the potential to be the fastest and most efficient conductor and can be used as a superconductor which can carry electricity with 100% efficiency [2]. See here.

In addition to graphene’s electrical properties, this material is also thought to be a good replacement for activated carbon in batteries and supercapacitors. This is due to graphene’s high surface area that has been found to be even higher than activated carbon. Therefore, by incorporating graphene in energy storage, an increased electrostatic charge storage can be increased [3].

The research suggests that by replacing the other carbon materials or metals that are usually incorporated inside the battery, with graphene, it is possible to achieve a thinner and more flexible and higher energy battery with increased power storage. In this innovation profile, WTiN reports on a method to produce a textile material discovered by researchers from RMIT University in Melbourne, Australia [4]. The team has demonstrated how to produce a flexible and stretchable graphene supercapacitor that can be fabricated in only three minutes.

Additionally, WTiN discusses a soon to be commercially available technology named the Flexibat. This is a graphene-based battery from the company Zinergy UK that is the outcome of a collaborative research project funded by Innovate UK.