One of the enabling technologies of our 21st-century lifestyle is the lithium–ion battery. These energy packs make possible mobile phones and electric cars, laptops and health-care devices, robots and remotely operated sensors, and much more. Perhaps unsurprisingly, earlier this year their developers were awarded the Nobel Prize for chemistry.
But materials scientists desperately need better batteries for the Internet of Things, for the next generation of personal devices, and much more. Better batteries will also be called on to play a major role in storing the energy from renewable, but inconstant, sources such as the wind and the sun.
Battery performance is the result of numerous different factors. Energy density is crucial; so is the ability to hold charge without it leaking away. Then there is rechargeability—not just once but thousands or tens of thousands of times—and, of course, safety.
Electrochemists know only too well how delicate this balancing act is. Consequently, battery makers are cautious about trying new approaches, lest one aspect of performance drop. So enhancements are usually incremental and tiny. Where are the big improvements we need likely to come from?
Today we get an answer of sorts: batteries of the future will be made via 3D printing, say Vladimir Egorov at the University of Cork in Ireland and a few colleagues. These folks have surveyed the various new printing techniques for batteries and suggest that this will make possible a new generation of smaller, more capable devices.
First some background. 3D printing is the general term for a variety of techniques that allow three-dimensional objects to be constructed by adding material layer by layer. It can be a way to make prototype designs for testing—not to mention exotic food items, replacement body parts, and even entire buildings. Using many printing machines in parallel allows the mass production of items such as car and aircraft parts and shoes. And when a new design is available, it can be printed quickly, with minimal reconfiguration of a factory space.
Materials scientists have also begun to experiment with ways to print electronic circuits using polymer inks and a silver polymer for traces, so soldering is no longer needed. In this way, circuit boards can take on more or less any shape and even form part of a device’s structure.
However, a significant limitation is the need to incorporate conventional batteries, which come in specific sizes and shapes.
The ability to print 3D batteries will change that. “If they can be printed to seamlessly integrate into the product design, for aesthetic as well and comfort or functional reasons, the bulkier and fixed form factor standard battery need not be accommodated at product design stage,” say Egorov and co.
This is easier said than done. The electroactive materials used in batteries are inherently reactive, and structures such as anodes and cathodes are physically complex. They must often be ordered like crystals, and sometimes porous like molecular sponges. Always, they must be chemically well characterized.
It is challenging to create versions of these materials that are suitable for 3D printing, whether by the extrusion of a solid or a liquid or by the polymerization of liquid. Once printed, these materials must maintain their electrical interconnections, tightly control any chemical reactions that take place between components, and ensure that the batteries can charge and discharge over many cycles.
Most important of all, batteries must be safe. All batteries have to pass strict safety standards before they can be used in homes, in vehicles, on airplanes, and so on. Batteries that leak can cause expensive damage. But the most serious risk is fire. It may be that the testing criteria will have to change to allow for new designs that constantly change.
And even if all these challenges can be overcome, another question looms. Will 3D batteries be any more capable than existing designs?
Egorov and co provide a comprehensive overview of the materials, methods, and challenges facing the battery industry in printing the power packs of the future. But the reviewers miss an important element of future battery design where 3D printing could have an important role to play.
One of the biggest and most important challenges for the battery industry is in making their products recyclable. Today’s batteries are specifically designed so that they cannot easily be taken apart, so reusing the valuable materials they contain is almost impossible.
That does not sit well for a technology that will have to play a central role in society’s transition from fossil fuels to renewable energy.
So change is much needed. The current thinking is that batteries must be designed from the start with recycling in mind, and that this will require an entirely new mind-set from battery designers. The flexibility that 3D printing allows has the potential to kick-start and accelerate this much-needed revolution.
While Egerov and co ignore this issue (the term “recycling” does not appear in their paper), the rest of the battery industry cannot afford to.
