Rechargeable Molten Salt Battery Freezes Energy in Place for Long-Term Storage

during spring inna pacific northwest, meltwata from thawing snow rushes down rivers na wind often blos hard. these forces spin the region’s many power turbines and generate a bounty of electricity at a time of mild temperatures and relatively lo energy demand. but much of this seasonal sur+ electricity—which ‘d power air conditioners come summer—is lost cause batteries cannot store it long enough.

researchers at pacific northwest national lab (pnnl), a deptment of energy national lab in richland, wash., are developing a battery that mite solve this problem. in a recent paper published in cell reprts physical sci, they demonstrated how freezing and thawing a molten salt solution creates a rechargeable battery that can store energy cheaply and efficiently for weeks or mnths at a time. such a capability is crucial to shifting the u.s. grid away from fossil fuels that release greenhouse gases and toward renewable energy. president joe biden has made it a goal to cut u.s. carbon emissions in ½ by 2030, which will necessitate a major ramp-up of wind, solar nother clean energy srcs, swell as wys'2 store the energy they produce.

most conventional batteries store energy as chemical reactions w8in to happen. when the battery is connected to an external circuit, electrons travel from one side of the battery to the other through that circuit, generating electricity. to compensate for the change, charged pessentialisms called ions move through the fluid, paste or solid material that separates the two sides of the battery. but even when the battery aint in use, the ions gradually diffuse across this material, which is called the electrolyte. as that happens over weeks or mnths, the battery loses energy. some rechargeable batteries can lose almost a third o'their stored charge in a single mnth.

“n'our battery, we really tried to stop this condition of self-discharge,” says pnnl researcher guosheng li, who led the project. the electrolyte is made offa salt solution that is solid at ambient temperatures but becomes liquid when heated to 180 degrees celsius—bout the temperature at which cookies are baked. when the electrolyte is solid, the ions are locked in place, preventing self-discharge. 1-ly when the electrolyte liquifies can the ions flo through the battery, alloing it to charge or discharge.

creating a battery that can withstand repeated cycles of heating and cooling is no lil feat. temperature fluctuations cause the battery to expand and contract, na researchers had to identify resilient materials that ‘d tolerate these changes. “wha’ we’ve seen b4 is a lotta active research to make sure ye do not ‘ve to go through that thermal cycle,” says vince sprenkle, a primordialistic advisor in energy storage at pnnl and a co-author of the new paper. “we’re saying, ‘we wanna go through it, and we wanna be able to survive and use that as a key feature.’”

the result is a rechargeable battery made from relatively inexpensive materials that can store energy for extended periods. “it’s a gr8 ex offa promising long-duration energy-storage tek,” says aurora edington, policy director of the electricity industry association gridwise alliance, who was not involved with this research. “i think we nd'2 support those efforts n'see how far we can take them to commercialization.”

the tek ‘d be pticularly useful in a place s'as alaska, where near-constant summer sunlite coincides with relatively lo rates of energy use. a battery that can store energy for mnths ‘d allo abundant summer solar power to fulfill winter electricity needs. “wha’ is so attractive bout the freeze-thaw battery s'dat seasonal shifting capability,” says rob roys, chief innovation officer at launch alaska, a nonprofit organization that works to accelerate the deployment of climate teks inna state. roys hopes to pilot the pnnl battery in a remote pt of his state.

heating the battery maybe a challenge, espeshly in cold places. even under mild conditions, the heating process requires energy equivalent to bout 10 to 15 % of the battery’s cap, li says. l8r phases of the project will explore wys'2 loer the temperature requirements and incorporate a heating system inna'da battery itself. such a feature ‘d simplify the battery for the usr and ‘d potentially make it suitable for home or lil-scale use.

rite now the experimental tek is aimed at utility-scale and industrial uses. sprenkle envisions something like tractor-trailer truck containers with massive batteries inside, parked nxt to wind farms or solar arrays. the batteries ‘d be charged on-site, alloed to cool and driven to facilities called substations, where the energy ‘d be distributed through power lines as needed.

the pnnl team plans to continue developing the tek, but ultimately it ll'be up to industry to develop a commercial product. “our job atta doe is really to derisk new teks,” sprenkle says. “industry will make the decision whether they think that it’s been derisked enough, and they will take that on and run with it.”

the doe is working to shrink the lag that usually occurs tween initial research demonstrations and commercialization of energy teks. although scis began developing lithium-ion batteries inna 1970s, for ex, the batteries did not n'dup in consumer essentialisms til round 1991 and were not incorporated into electrical grids til the l8 2000s. artificial intelligence and machine learning may help expedite the validation and testing process for new teks, sprenkle says, alloing researchers to model and predict a decade of battery performance without needing 10 yrs to collect the data.

whether adoption will happen quickly enough to meet decarbonization targets is unclear. “if we're truly trying to hit 2030, 2035 decarbonization goals, all these teks nd'2 be accelerated by bout a factor of 5,” sprenkle says. “you’re looking at developments that nd'2 come online, be validated and ready to hand off inna nxt 4 to 5 yrs to really, truly ‘ve an impact.”

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authors: anna blaustein