Squeezing More Energy Out of Batteries
A new printing process could increase battery capacity by over 10 percent.
Xerox’s Palo Alto Research Center (PARC) has developed a new printing technology that promises to pack more energy into batteries for electric vehicles. By printing a striped pattern of energy storage materials and highly conductive materials, researchers at PARC are making electrodes that are much thicker than those in conventional batteries. These could increase battery storage capacity by 10 to 30 percent while costing little more to manufacture, says Scott Elrod, director of the Hardware Systems Laboratory at PARC. The technology could also apply to metal-air batteries that could store far more energy than anything on the market today.
The biggest challenge for electric vehicles remains bringing down the size and cost of their batteries. For them to compete with conventional vehicles, some experts estimate, battery costs must come down by about 75 percent. And if the batteries could store more energy, automakers could use fewer of them, thus saving money.
In conventional lithium-ion-battery manufacturing, electrode materials are applied in the form of slurry to metal foils. The thickness of the electrode is limited by the rate at which lithium ions can diffuse out of the material to reach an electrolyte. In PARC’s new approach, the electrode material, together with a highly conductive material (the company isn’t specifying what), will be forced through a flat print nozzle. The nozzle will align the materials and draw them in alternating stripes, each potentially as thin as a human hair.
The conductive material would give the lithium ions more paths along which to travel, allowing the electrode to be thicker while maintaining its ability to deliver bursts of power quickly, and without impairing the battery’s ability to store energy. About half of a conventional lithium-ion battery is made up of materials that store no energy. Every layer of electrode material requires a separator of metal foil and polymer film. With thicker electrodes, fewer layers would be required, increasing the battery’s energy density.
The work is still at an early stage, but the basic printing concept has been proved with a method PARC developed for printing thin silver lines on solar cells; these are being commercialized by a major solar manufacturer, Elrod says. The PARC researchers have so far only run simulations to determine the potential energy increases in batteries.
A number of hurdles will need to be overcome in developing the technology. For example, the conductive materials must be compatible with the electrode material and with the electrolytes in the cell, to ensure long battery life. The viscosity of the electrode paste and curing methods used will need to be optimized to ensure that print heads don’t clog and the materials don’t crack.
Eventually, the method could be adapted for metal-air batteries, in which the electrode material would be in contact with the air. The researchers would print electrode materials together with a hydrophobic air-transport material such as Teflon.