Dead batteries are bummer to all of us, but it can mean life or death on the battlefield. You can always carry lots of extra batteries, but that is extra weight, too. It would be preferable to have better batteries. There have been vast improvements in recent years, but when your technology is enabling Soldiers, you need better than good. That’s why the US Army is engineering ahead of the curve.
As described in an Army News Release, chemical engineers there are developing a high-voltage, corrosion-resistant, Li-based battery. By modifying the battery chemistry, the team has been able to increase the voltage as well as the stability.
Cynthia Lundgren, a chemist and Chief of the Electrochemistry Branch of the Power and Energy Division in the Sensors and Electron Devices Directorate, describes it this way, “If we could raise the voltage of a single cell - energy density is a direct function of the voltage - we could make the battery lighter," she said. "The problem is, as you go up in voltage, the electrode becomes much more energetic, and so it reacts with the electrolyte."
Longevity is important in battery design. Batteries rely on an electrochemical cell to generate power, and part of that process involves the corrosion of an anode due to the electrode potential. Ideally this process is reversible in rechargeable batteries, but as you probably know, even rechargeable batteries die over time.
The problem is that the process is not perfectly reversible, and the anode tends to degrade with repeated use. The researchers are working on an iron-doped lithium cobalt phosphate cathode (LiCoPO4), developed by Army chemist, Jan Allen. Though capable of achieving high voltages (4.9V), the battery degrades rapidly through reaction of the electrolyte with the electrodes.
By adding a corrosion inhibitor to the electrolyte, the battery could be made stable and maintain the higher voltage. The inhibitor, tris (hexafluoroisopropyl) phosphate (HFiPP), is something that could be easily incorporated into the manufacturing of the batteries. The team is in the process now of scaling up from their button cells to larger, “pouch” cells. The work could mean better performance and reliability. A classic win-win scenario.
Images: US Army