Fossil energy players continue to question the power of renewables to transform the global economy, but their grip on reality is loosening with each new development in clean technology. The field of large-scale energy storage is a good example. Just a few years ago, battery life was measured in hours. Now the discussion had evolved to a season-by-season scale, allowing wind and solar to respond to peak heating or cooling times of the year.
The limits of lithium-ion energy storage
Rechargeable lithium-ion batteries have long been the gold standard for energy storage. They are clearly at the forefront of the electric vehicle market, among many other applications. However, the area of power generation is tricky for conventional Li-ion technology.
Even with the latest improvements, the best Li-ion batteries for bulk energy storage only offer a few hours of power output before needing to be recharged. This suits many use cases, but not those that require power for a full day, let alone an entire season.
Cascading banks of Li-ion batteries could extend lead times, but the cost and complexity of such a system pose daunting hurdles.
The hibernating energy storage solution
Today, almost every bulk and long-term energy storage system in the United States deploys 100-year-old technology in the form of “water batteries”, i.e. the hydroelectricity pumped.
That’s about to change, if researchers at the US Department of Energy’s Pacific Northwest National Laboratory are on the right track. They have developed a long lasting hibernating battery made with an electrolyte that can be cooled from a liquid to a solid when excess renewable energy is plentiful, then thawed to release energy when needed.
According to PNNL, the freeze-thaw system can store energy for months at a time and sit idle without losing a significant amount of capacity.
So far, PNNL has tested the system on a prototype the size of a hockey puck. Over a 12-week period, the system retained 92% of its capacity, which is impressive compared to the loss of capacity that plagues conventional lithium-ion technology when idle.
The system seems quite simple, as described by the lab:
“The battery is first charged by heating it to 180 degrees Celsius, allowing ions to flow through the liquid electrolyte to create chemical energy. Then the battery is cooled to room temperature, essentially blocking the battery energy. The electrolyte becomes solid and the energy-carrying ions remain almost stationary. When energy is needed, the battery is warmed up and the energy flows.
The secret to molten salt energy storage
Free lunch doesn’t exist, the devil is in the details. You can get all of those from the team’s research paper, published in the journal Physical Sciences Cell Reports under the title, “A molten salt freeze-thaw battery for seasonal storage.”
If the molten salt angle sounds familiar, it’s the same energy storage medium deployed in some types of concentrated solar power systems.
In an interesting twist, researchers have been working on ways to increase the heat level in concentrated solar power systems without blowing the whole thing up. This requires substantial improvement in the metals and other materials that make up a CSP system. The solution goes through nickel, also in play for the PNNL hibernation battery.
PNNL points out that nickel also joins its interest in developing a relatively inexpensive energy storage technology that reduces or even eliminates the use of toxic substances.
“The…molten aluminum-nickel-salt battery is full of common materials that are abundant on Earth,” PNNL explains, noting that the anode is a solid plate of aluminum and the cathode is a plate of nickel.
“They are immersed in a sea of molten salt electrolyte which is solid at room temperature but sinks to liquid form when heated. The team added sulfur, another common and inexpensive element, to the electrolyte to improve the energy capacity of the battery”, adds the laboratory.
Longer-lasting battery for long-lasting energy storage
The team used the same earth-abundant, low-cost strategy to develop the separator that goes between the anode and the cathode. The classic approach is to deploy a high-tech ceramic, such as that used in some solid-state lithium-ion batteries. However, these are expensive and the PNNL team was concerned that a ceramic separator could break under freeze-thaw cycles.
They opted for fiberglass and the results are impressive. Before the price of nickel suddenly skyrocketed in recent months, the materials used in the new hibernation battery cost a total of only $23 per kilowatt hour, more or less.
Next steps include using iron as another money-saver, with the goal of reducing costs to around $6 per kilowatt-hour. According to PNNL, this is about 15 times less than the materials used in a typical Li-ion battery.
“The battery’s theoretical energy density is 260 watt-hours per kilogram – higher than today’s lead-acid and flux batteries,” PNNL also notes.
If you’re wondering about the new battery’s ability to withstand many charge cycles, that’s a good question. The researchers did not focus on the durability performance of conventional Li-ion batteries, as they designed a system that grid operators can deploy on a seasonal basis. If this corresponds to a maximum of 4 charge-discharge cycles per year, a system with a lifespan of only 100 cycles could depend on 30 years of operation.
As an example, the lab describes how a transportable version of its energy storage system could be trucked to a wind farm in the spring, when HVAC energy demand is relatively low. After absorbing excess clean kilowatts, the battery can be trucked to a substation and parked there until needed for peak demand periods in the summer.
The technology could also be used in corporate parks and other campuses. To learn more, see PNNL’s marketing page for the “Temperature based hibernation battery.”
If the element of trucking sounds familiar, check out the “Hydro Electric Truck” concept that sent the Clean Technica fire comment thread a while ago.
About that nickel…
Speaking of the price of nickel, energy storage innovators have turned to nickel to cut costs and avoid the use of toxic materials, but Russia’s murderous rampage through Ukraine has upended the nickel market. nickel. Some nickel trade shenanigans on the London Metals Exchange which are currently being investigated by regulators in Europe were also factored into the debacle.
Even before the price spike, nickel has become a hot topic when the US Geological Survey added nickel to its new list of critical materials, which it adopted in 2018.
The new USGS list organizes substances according to their use, unlike the familiar “mineral group” categories. This includes national security, economic activity, renewable energy development and infrastructure.
The list also points out areas of vulnerability, and nickel is one of them. In 2021, the USGS only identified an operating nickel mine in the United Statesthe Eagle Mine in Michigan, which produces nickel in concentrate for markets in Canada and elsewhere abroad.
The only other sources relate to the recovery of scrap nickel from other operations, including a Superfund site in Missouri and another site in Montana.
The heat is on to develop more nickel mining sites in the United States, but elements of environmental and social justice are also at play.
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Picture: Freeze-thaw battery for long-term energy storage by Sara Levine, PNNL.
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