Scientists continue to explore advanced battery technologies that could help us harness the full potential of renewable energy, working to address the intermittent nature of solar and wind power. A team from the Pacific Northwest National Laboratory (PNNL) has developed a new design that meets some important requirements in this area, demonstrating a type of “hibernating” battery that can retain its energy for months.
The type of energy storage technology this research focuses on is known as a molten salt battery. These batteries have been around for over 50 years in various forms and are considered a grid-scale storage solution for renewable energy due to their low cost and use of common materials.
These devices use molten salt as the electrolyte, which is the solution that carries electrical charge between the battery’s two electrodes, the cathode and the anode. By keeping the electrolyte at a high temperature, the salt is kept in a molten state and flows like a liquid, but at room temperature it becomes solid. The PNNL team exploited these attributes to produce what is described as a temperature-based hibernation battery.
The device consists of an aluminum anode and a nickel cathode, which are immersed in a sulfur-doped molten salt electrolyte to increase their capacity. The battery is charged by heating it to 180°C, which causes ions to flow through the liquid electrolyte to generate chemical energy. As the battery cools to room temperature, the electrolyte solidifies and the ions freeze, retaining energy until the battery is warmed to circulate again.
For this reason, the scientists also call the device a “freeze-thaw battery”, and although the prototype is only the size of a hockey puck, they are optimistic about its scalability potential. .
Its theoretical density is 260 Wh per kilogram, higher than current lead-acid and flux batteries, and its energy is stored at a material cost of around $23 per kWh, which the team hopes to reduce to around $6 per kWh by incorporating iron into the design. In testing, the battery retained 92% capacity for 12 weeks.
It’s a bit like growing food in the garden in the spring, putting the leftovers in a container in the freezer, and thawing them for dinner in the winter.
Minyuan “Miller” Li.
The PNNL team opted for an alternative to the ceramic separator used in typical molten salt batteries, opting instead for fiberglass, which they say is cheaper and more durable.
Over time, scientists hope the technology could offer a form of seasonal energy storage, harvesting energy at one time of year for use at another. And because the battery can sit idle while retaining most of its stored energy, it would only need to be charged and discharged a few times a year.
You can start to imagine something like a big battery on a 12m semi-trailer parked at a wind farm. The battery is charged in the spring, then the truck is driven down the road to a substation where the battery is available when needed during the summer heat.
Vince Sprinkles.
More information: www.sciencedirect.com (English text).
Via www.pnnl.gov