In a recent paper published in Cell Reports Physical Science, they demonstrated how freezing and thawing a molten salt solution creates a rechargeable battery that can store energy. Contact online >>
In a recent paper published in Cell Reports Physical Science, they demonstrated how freezing and thawing a molten salt solution creates a rechargeable battery that can store energy...
Molten-salt batteries are a class of battery that uses molten salts as an electrolyte and offers both a high energy density and a high power density. Traditional non-rechargeable thermal batteries can be stored in their solid state at room temperature for long periods of time before being activated by heating.
Li et al. construct a rechargeable battery with earth-abundant elements that can be frozen to preserve the stored electric energy, like preserving food in a freezer. With heat, the energy can be effectively recovered even months later, potentially opening new possibilities toward seasonal energy storage and renewable energy integration.
In this review, the general principles of molten salts and recent research progresses on molten salt-based battery materials are surveyed. Molten-salt synthesis of electrode materials, including sintering and electrolysis, are emerging as competitive substitutes for conventional synthesis techniques.
Rechargeable Molten Salt Battery Freezes Energy in Place for Long-Term Storage
Close-up of the freeze-thaw battery developed by the Pacific Northwest National Laboratory team.
Andrea Starr/Pacific Northwest National Laboratory
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Anna Blaustein is a science journalist. She has a bachelor''s degree in biology from Bowdoin College and a master''s degree in science writing from the Massachusetts Institute of Technology.
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During spring in the Pacific Northwest, meltwater from thawing snow rushes down rivers and the wind often blows hard. These forces spin the region''s many power turbines and generate a bounty of electricity at a time of mild temperatures and relatively low energy demand. But much of this seasonal surplus electricity—which could power air conditioners come summer—is lost because batteries cannot store it long enough.
Molten-salt batteries are a class of battery that uses molten salts as an electrolyte and offers both a high energy density and a high power density. Traditional non-rechargeable thermal batteries can be stored in their solid state at room temperature for long periods of time before being activated by heating. Rechargeable liquid-metal batteries are used for industrial power backup, special electric vehicles[citation needed]and for grid energy storage, to balance out intermittent renewable power sources such as solar panels and wind turbines.
In 2023, the use of molten salts as electrolytes for high-energy rechargeable lithium metal batteries was demonstrated.[1][2]
Since the mid-1960s much development work has been undertaken on rechargeable batteries using sodium (Na) for the negative electrodes. Sodium is attractive because of its high reduction potential of −2.71 volts, low weight, relative abundance, and low cost. In order to construct practical batteries, the sodium must be in liquid form. The melting point of sodium is 98 °C (208 °F). This means that sodium-based batteries operate at temperatures between 245 and 350 °C (470 and 660 °F).[6] Research has investigated metal combinations with operating temperatures at 200 °C (390 °F) and room temperature.[7]
The sodium–sulfur battery (NaS battery), along with the related lithium–sulfur battery employs cheap and abundant electrode materials. It was the first alkali-metal commercial battery. It used liquid sulfur for the positive electrode and a ceramic tube of beta-alumina solid electrolyte (BASE). Insulator corrosion was a problem because they gradually became conductive, and the self-discharge rate increased.
Because of their high specific power, NaS batteries have been proposed for space applications.[8][9] An NaS battery for space use was successfully tested on the Space Shuttle mission STS-87 in 1997,[10] but the batteries have not been used operationally in space. NaS batteries have been proposed for use in the high-temperature environment of Venus.[10]
A consortium formed by Tokyo Electric Power Co. (TEPCO) and NGK Insulators Ltd. declared their interest in researching the NaS battery in 1983, and became the primary drivers behind the development of this type ever since. TEPCO chose the NaS battery because its component elements (sodium, sulfur and ceramics) are abundant in Japan. The first large-scale field testing took place at TEPCO''s Tsunashima substation between 1993 and 1996, using 3 × 2 MW, 6.6 kV battery banks. Based on the findings from this trial, improved battery modules were developed and were made commercially available in 2000. The commercial NaS battery bank offers:
A lower-temperature[11] variant of molten-salt batteries was the development of the ZEBRA (originally, "Zeolite Battery Research Africa"; later, the "Zero Emissions Batteries Research Activity") battery in 1985, originally developed for electric vehicle applications.[12][13] The battery uses NaNiCl2 with Na+-beta-alumina ceramic electrolyte.[14]
When not in use, Na-NiCl2 batteries are typically kept molten and ready for use because if allowed to solidify they typically take twelve hours to reheat and charge.[25] This reheating time varies depending on the battery-pack temperature, and power available for reheating. After shutdown a fully charged battery pack loses enough energy to cool and solidify in five-to-seven days depending on the amount of insulation.[citation needed]
Sodium metal chloride batteries are very safe; a thermal runaway can be activated only by piercing the battery and also, in this unlikely event, no fire or explosion will be generated. For this reason and also for the possibility to be installed outdoor without cooling systems, make the sodium metal chloride batteries very suitable for the industrial and commercial energy storage installations.
In 2014 researchers identified a liquid sodium–cesium alloy that operates at 50 °C (122 °F) and produced 420 milliampere-hours per gram. The new material was able to fully coat, or "wet," the electrolyte. After 100 charge/discharge cycles, a test battery maintained about 97% of its initial storage capacity. The lower operating temperature allowed the use of a less-expensive polymer external casing instead of steel, offsetting some of the increased cost of cesium.[28]
Innovenergy in Meiringen, Switzerland has further optimised this technology with the use of domestically sourced raw materials, except for the nickel powder component. Despite the reduced capacity compared with lithium-ion batteries, the ZEBRA technology is applicable for stationary energy storage from solar power. In 2022, the company operated a 540 kWh storage facility for solar cells on the roof of a shopping center, and currently produces over a million battery units per year from sustainable, non-toxic materials (table salt).[29]
Professor Donald Sadoway at the Massachusetts Institute of Technology has pioneered the research of liquid-metal rechargeable batteries, using both magnesium–antimony and more recently lead–antimony. The electrode and electrolyte layers are heated until they are liquid and self-segregate due to density and immiscibility. Such batteries may have longer lifetimes than conventional batteries, as the electrodes go through a cycle of creation and destruction during the charge–discharge cycle, which makes them immune to the degradation that afflicts conventional battery electrodes.[30]
The technology was proposed in 2009 based on magnesium and antimony separated by a molten salt.[31][32][33] Magnesium was chosen as the negative electrode for its low cost and low solubility in the molten-salt electrolyte. Antimony was selected as the positive electrode due to its low cost and higher anticipated discharge voltage.
In 2011, the researchers demonstrated a cell with a lithium anode and a lead–antimony cathode, which had higher ionic conductivity and lower melting points (350–430 °C).[30] The drawback of the Li chemistry is higher cost. A Li/LiF + LiCl + LiI/Pb-Sb cell with about 0.9 V open-circuit potential operating at 450 °C had electroactive material costs of US$100/kWh and US$100/kW and a projected 25-year lifetime. Its discharge power at 1.1 A/cm2 is only 44% (and 88% at 0.14 A/cm2).
A recent innovation is the PbBi alloy which enables lower melting point lithium-based battery. It uses a molten salt electrolyte based on LiCl-LiI and operates at 410 °C.[36]
Ionic liquids have been shown to have prowess for use in rechargeable batteries. The electrolyte is pure molten salt with no added solvent, which is accomplished by using a salt having a room temperature liquid phase. This causes a highly viscous solution, and is typically made with structurally large salts with malleable lattice structures.[37]
Thermal batteries use an electrolyte that is solid and inactive at ambient temperatures. They can be stored indefinitely (over 50 years) yet provide full power in an instant when required. Once activated, they provide a burst of high power for a short period (a few tens of seconds to 60 minutes or more), with output ranging from watts to kilowatts. The high power is due to the high ionic conductivity of the molten salt (resulting in a low internal resistance), which is three orders of magnitude (or more) greater than that of the sulfuric acid in a lead–acid car battery.
One design uses a fuze strip (containing barium chromate and powdered zirconium metal in a ceramic paper) along the edge of the heat pellets to initiate the electrochemical reaction. The fuze strip is typically fired by an electrical igniter or squib which is activated with an electric current.
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