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A new approach to high-energy rechargeable calcium batteries

A novel electrolyte may just be the solution to room-temperature rechargeable calcium (Ca) batteries. EU-funded researchers explain how.

ENERGY

Scientific advances

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It looks like Ca is not only good for your bones, it may also be good for the planet. According to scientists, it could be a key component in their efforts to meet the world’s rising energy demands while also reducing emissions. How? Through its potentially promising role in the development of efficient and cost-effective energy storage technologies. The market for electric vehicles and grid electric storage is growing rapidly, which in turn is increasing the need for reliable and energy-efficient rechargeable batteries. However, the current rechargeable lithium-ion batteries (LIBs) may not be as safe, cost-efficient and sustainable as we would like. Scientists are therefore searching for promising alternatives, one of which is a battery system based on a multivalent metal such as Ca. Ca batteries could be the high-energy, low-cost solution we are looking for, but there’s an obstacle in their development: they lack the practical electrolytes needed for efficient Ca deposition. Researchers supported by the EU-funded E-MAGIC project have made a discovery that could overcome this obstacle. In their paper published in the journal ‘Energy & Environmental Science’, the scientists reported a novel borate-based electrolyte – calcium tetrakis(hexafluoroisopropyloxy)borate, or Ca[B(hfip)4]2 – that exhibited reversible Ca deposition at room temperature as well as high oxidative and ionic stability. Their finding could pave the way for high-energy room-temperature rechargeable Ca batteries.

The promise of Ca batteries

The paper discusses the feasibility of creating a new class of Ca electrolytes that are based on Ca compounds with weakly coordinating anions. According to the authors, “[t]he straightforward synthetic method for formulating new Ca salts by incorporation of various fluorinated alkoxyborates anions will serve as a useful tool for further optimization of the electrolyte properties. The Ca[B(hfip)4]2 electrolytes exhibit state-of-the-art electrochemical properties in terms of high oxidative stability, high ionic conductivity and good capability of long-term reversible Ca cycling.” The development of battery technologies based on multivalent metals like Ca may be a promising option for improving energy densities while also slashing cost. Multivalent ions could double or triple the battery capacity compared to monovalent LIBs or sodium-ion batteries. Additionally, unlike lithium or sodium, multivalent metallic anodes have the potential to significantly increase the energy densities of batteries. The above properties aren’t the only reason why Ca batteries can be considered an attractive alternative for post-LIB technologies. A rising concern stemming from the rapid growth of the battery market revolves around the medium- and long-term availability of certain raw materials – cobalt, nickel and lithium – that are used in commercial LIBs. Ca, on the other hand, is the fifth most abundant element in the Earth’s crust. Moreover, it’s equally distributed geographically and is also safe and nontoxic. Alongside Ca, scientists are also looking to magnesium (Mg), another promising multivalent metal in the drive to develop better rechargeable batteries. This metal is the focus of E-MAGIC (European Magnesium Interactive Battery Community) that aims to develop an innovative approach for new-generation, high-energy–density and environmentally friendly rechargeable Mg batteries. The project also intends to reinforce an Mg-based battery community that will establish an active scientific relationship with the rest of the world. For more information, please see: E-MAGIC project website

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