Researchers at Nanyang Technological University, Singapore (NTU Singapore) have developed a thin and flexible paper battery that could one day become an environmentally sustainable option for powering flexible and wearable electronic systems.
The NTU Singapore-developed zinc batteries are made up of electrodes (through which the electrical current leaves or enters the battery) screen-printed onto both sides of a piece of cellulose paper that has been reinforced with hydrogel.
Once the battery has been expended, it can be buried in soil, where it breaks down completely within a month.
In a proof-of-concept experiment described in the scientific journal Advanced Science, the NTU team demonstrated how a 4cm x 4cm square printed paper battery could power a small electric fan for at least 45 minutes. Bending or twisting the battery did not interrupt the power supply.
In another experiment using a 4cm x 4cm battery to power an LED, the scientists showed that despite cutting away parts of the paper battery, the LED remained lit, indicating that cutting does not affect the functionality of the battery.
The scientists think their printed battery could be integrated into flexible electronics such as foldable smartphones that are already on the market, or biomedical sensors for health monitoring.
Professor Fan Hongjin from the NTU School of Physical and Mathematical Sciences and the study’s co-lead author, said: “Traditional batteries come in a variety of models and sizes, and choosing the right type for your device could be a cumbersome process. Through our study, we showed a simpler, cheaper way of manufacturing batteries, by developing a single large piece of battery that can be cut to desired shapes and sizes without loss of efficiency. These features make our paper batteries ideal for integration in the sorts of flexible electronics that are gradually being developed.”
Assistant Professor Lee Seok Woo from the NTU School of Electrical and Electronic Engineering and the study’s co-lead author, said: “We believe the paper battery we have developed could potentially help with the electronic waste problem, given that our printed paper battery is non-toxic and does not require aluminum or plastic casings to encapsulate the battery components. Avoiding the packaging layers also enables our battery to store a higher amount of energy, and thus power, within a smaller system.”
With hydrogel and cellulose are naturally broken down by bacteria, fungi, and other microorganisms, the battery can simply be buried in soil at the end of its life span where it breaks down in a matter of weeks, making it a fully biodegradable product.
To demonstrate the paper battery’s biodegradability, the NTU scientists buried it in the soil of a rooftop garden on the NTU campus. The hydrogel-reinforced cellulose paper started fracturing after two weeks and degraded completely within a month.
Prof Fan said: “When decomposition happens, the electrode materials are released into the environment. The nickel or manganese used in the cathodes will remain in their oxide or hydroxide forms, which are close to the form of natural minerals. The zinc found in the anode will be naturally oxidized to form a non-toxic hydroxide. This points to the battery’s potential as a more sustainable alternative to current batteries.”
The NTU team hopes to demonstrate the complete integration of the printed paper battery into other printed electronics, electronic skins, as well as energy storage systems deployed in the environment.