Turning Over a New Leaf in Energy Storage

Batteries have never been more efficient or had greater energy density than they do today. Technological advancements in recent years have been driven by our need to power an increasing number of Internet of Things devices spread around the globe, and ever more electric vehicles that are hitting the streets. The demand for high-capacity, long-lasting batteries continues to surge, prompting intense research and development efforts aimed at further enhancing battery performance, lifespan, and safety.

This demand may be driving some crucial technological advancements, but it is also a reminder that the number of batteries being used to power our devices is rising sharply. Unfortunately, today’s batteries are generally made with toxic materials and have limited lifespans. As they age and get replaced, many of these batteries are discarded, greatly contributing to the growing problem of electronic waste accumulation and the resulting environmental consequences.

For reasons such as these, it is growing increasingly clear that incremental improvements in battery technology are not sufficient to both meet our needs and protect the environment. Entirely different ways of thinking about powering our devices are urgently needed. Researchers at Tohoku University in Japan have put forward a novel idea that may serve to power many of our gadgets in an environmentally-friendly manner one day.

The team recognized that the respiratory system in plants, in which plants harvest energy from the Sun to make sugar from water in the ground and carbon dioxide from the air, is analogous to the charging and discharging cycle in batteries. Yet, plant respiratory systems are highly efficient and do not negatively impact the environment.

This observation led the researchers to design a new type of battery that is inspired by plants. The battery is paper-based and relies on interactions between magnesium and air, with activation by water, to produce an electrical current. It does not contain any toxic materials, exhibits high levels of performance, and has a minimal impact on the environment, even after it is disposed of.

The battery is composed of a thin magnesium foil, which serves as its anode, that is adhered to a piece of paper. On the other side of the paper is a catalyst that acts as the cathode, in conjunction with a gas diffusion layer. The paper is partially submerged in water, which it draws in through capillary action, to activate the battery. The batteries can be “recharged” by replacing the magnesium foil after it has been exhausted.

When connected to an open circuit, the battery was found to be capable of generating 1.8 volts of electricity. Furthermore, a 1.0 volt current density of 100 milliamps per square centimeter, and a maximum output of 103 milliwatts per square centimeter was observed. Given the energy efficiency of modern electronics, this is enough power for the operation of many sensors and microcontrollers.

To demonstrate the potential of their technology, the researchers developed a number of wearable devices that were powered by the paper battery. In one demonstration, a pulse oximeter, which measures blood oxygen levels and pulse, was successfully powered by the battery. In another demonstration, operation of a GPS logger was also shown to be feasible. The versatility and sustainability of this system may make it a viable option for powering many of our electronic devices in the future.