‘Salty' freeze-thaw battery a step toward long term seasonal storage capacity
A prototype ‘freeze-thaw’ battery that traps energy as it transitions from liquid to solid could lead to grid-scale storage of renewable energy, developers have said.
Scientists from Pacific Northwest national laboratories are launching an innovative energy storage system that can store ice-free energy for up to months without losing storage space.
They are considered an important development towards battery storage. The researchers explain that the battery's initial charge is done by heating it to 180° C, which enables the flow and formation of ions from the electrolytic ions through the liquid. The resulting cooling at room temperature locks down battery energy.
Long-duration battery freezes renewable energy for later use
The development will enable the grid to store renewable energy at grid scale. The battery was designed to store energy for months without losing much capacity by the DOE Pacific Northwest National Laboratory.
The prototype was about the shape of a hockey puck but researchers say it could become useful for storing renewable energy in times when demand was high.
How does it work?
The short simple answer:
The new “freeze-thaw battery” consists of an aluminum anode and nickel cathode, both immersed in a sea of molten-salt electrolyte that is solid at room temperature but flows like a liquid when heated.
The team added sulfur – another common, low-cost element – to the electrolyte to enhance the battery‘s energy capacity.
"The heat to melt the salt for operations would ideally be coming from renewables, in particular excess generation... However, if renewables are unavailable, the system can operate on other energy sources, such as waste heat, additional battery systems, or fossil fuels to jump start.”
The short nerdy answer:
In a paper published in the journal Cell Reports Physical Science, the researchers explain that the battery is first charged by heating it up to 180 degrees Celsius or 356 degrees Fahrenheit, allowing ions to flow through the liquid electrolyte to create chemical energy.
Then, the battery is cooled to room temperature, essentially locking in the battery’s energy. It then becomes solid and the ions that shuttle energy stay nearly still. When the energy is needed, the battery is reheated and the energy flows.
In their paper, the PNNL’s team also points out that batteries designed for seasonal storage would likely charge and discharge just once or twice a year.
Unlike batteries designed to power electric cars, laptops or other consumer devices, they don’t need to last hundreds or thousands of cycles.
The long answer:
The freeze-thaw phenomenon is possible because the battery’s electrolyte is molten salt—a molecular cousin of ordinary table salt. The material is liquid at higher temperatures but solid at room temperature.
The freeze-thaw concept dodges the issue of batteries self-discharging when they sit idle. Or in other words not holding a charge.
A fast discharge rate, like that of batteries in most cars or laptops, would hamper a grid battery designed to store energy for months. Notably, the PNNL freeze-thaw battery has retained 92% of its capacity over 12 weeks.
In other words, the energy doesn’t degrade much; it’s preserved, just like food in a freezer. It won't last forever but it certainly beats moldy cheese.
“It’s a lot like growing food in your garden in the spring, putting the extra in a container in your freezer, and then thawing it out for dinner in the winter,” said first author Minyuan “Miller” Li.
The Nerdy Advantage
One of the biggest advantages of the battery is the composition of the separator placed between the anode and the cathode.
Most higher-temperature molten-salt batteries require a ceramic separator, which can be more expensive to make and susceptible to breakage during the freeze-thaw cycle.
The freeze-thaw battery’s chemistry, however, allows for the use of simple fiberglass. This cuts costs and makes the battery sturdier when undergoing freeze-thaw cycles.
How much will it cost?
According to the research group, the battery’s energy is stored at a materials cost of about $23 per kilowatt-hour, measured before a recent jump in the cost of nickel.
The team is exploring the use of iron, which is less expensive, in hopes of bringing the materials cost down to around $6 per kilowatt-hour, roughly 15 times less than the materials cost of today’s lithium-ion batteries.
How will it work practically?
“You can start to envision something like a large battery on a 40-foot tractor-trailer parked at a wind farm,” said co-author Vince Sprenkle, senior strategic advisor at PNNL. “The battery is charged in the spring, and then the truck is driven down the road to a substation where the battery is available if needed during the summer heat.”
Speculation (The fun part)
Apparently this idea isn't new; the battery's theoretical energy density, storage capacity, and its use with the electric grid according to one hacker news comment said.
"Storing heat in rock is very natural. It's how geothermal works, after all... The other thing one can do is store cold. This is useful not only for cooling, but for increasing the efficiency of storage of work, since one can generate heat and cold via a heat pump, then reverse that cycle to recover the work. An efficiency of 65% or so may be reasonably achievable with the high temperature in the temperature range of ordinary steel." According to user pfdiets.
There is also speculation online such as Reddit user DevoidHT who said "Sometimes, these technologies just aren’t scalable of feasible being mass produced. Just because these technologies don’t mature doesn’t mean they’re being silenced, R&D is expensive and not everyone is willing to invest in it."
Another speculator from the same website suggested it may be hurtful to give too much coverage of the topic when the end user wont see it for a couple more years. "This has happened with all sorts of technology. It always gets hyped up when it is still small scale and preliminary. People see these headlines and expect to see the new tech immediately when really it is years away or worse it never scales effectively. The bummer is that hyping some of this stuff too early can hurt or slow the development long term."
Conclusion
New batteries designed for long duration grid battery's theoretical energy density may be a long way from application but the science is now there to support a new age of efficiency and progress towards a more sustainable and healthier world.