The familiar button battery is the workhorse of small electronics. While it is likely to continue to power our existing watches and calculators for a little while yet, it has become the limiting factor for many key design points of these devices. Like a shipping container in a world of instant messaging, it has no future. One company, Imprint Energy, has assembled a total assault package which might sound the death knell – a rechargeable, flexible, customisable, and printable battery that is cheaper, safer and more powerful.
The key technology developed by Imprint Energy is a polymer electrolyte that allows zinc-based batteries to be recharged. It prevents the formation of fingers which typically bridge across typical liquid electrolytes over time and make charging impossible. The flexible and customisable zinc anode, electrolyte, and metal oxide cathode of the battery are printed in the form of electrochemical inks. The printing process is similar to old fashioned silk-screening where material is deposited in a pattern by squeezing it through a mesh over a template. While this screen printing is different from what we tend to think of nowadays as 3D printing, the use of inkjets and other technologies are driving new convergent, hybrid techniques.
The implication of this for product designers is that instead of building the device around the power source, not only can the power source be built around the device, it can be the device. Screen printing is also being used to fabricate electronic components that will address the need for cheap and disposable electronics.
Norway-based Thin Film Electronics has created prototype all-printed devices that include temperature sensors, memory, logic, and a battery from Imprint Energy. Smart stickers for time-sensitive food or medicines could be printed that might store details of its temperature, chemical exposure, freshness, and history of shock during handling. A target price of 20 pence would open up a lot of applications where previously a simple temperature sensor and a few bits of storage might currently run to £20.
The machinery to print different kinds of electronic components from just a few materials still needs to evolve to where it can become a flexible and affordable all-in-one platform. As a raw material, zinc has already proved itself to be extremely versatile. It has neither the danger nor cost of lithium and has built an expansive resume of interesting devices that it can be fashioned into.
For example, zinc nanowires with diameters of only 40nm can be made with different properties depending on whether they are crystalline or non-crystalline. They can also be made to exhibit piezoeletric behaviour and can be woven into clothing for sensing or providing higher voltages for other applications. Zinc aerographite, 5,000 times less dense than water, can be fabricated by vapour depositing carbon layers onto zinc backbones to provide a light conductive matrix similar in structure to aerogel.
At the present time, Imprint Energy is claiming that its battery has an energy density at least as good as lithium-polymer batteries, and that’s likely to improve. This may even give the higher-energy-density zinc-air battery technology pause for concern, considering its other advantages.
Hearing aids, for example, put a premium on high power capacity and tolerate the high self-discharge rates and non-rechargeability of zinc-air batteries. These batteries are typically activated only when needed by removing a sealing strip that lets air enter the cell, but thereafter have a maximum lifetime of just a few weeks. A battery which eliminates these issues and at the same time opens up new approaches to hearing aid design would be welcome.
It may not be possible for one battery technology to address every power need effectively, but Imprint Energy appears to be taking aim at several of them. Once its technology begins to catch on, we might say goodbye to the button battery.