Abstract
Room temperature ionic liquids (RTILs) are solvent-free liquids comprised of densely packed cations and anions. The low vapor pressure and low flammability make ILs interesting for electrolytes in batteries. In this work, a new class of ionic liquids were formed for rechargeable aluminum/graphite battery electrolytes by mixing 1-methyl-1-propylpyrrolidinium chloride (Py13Cl) with various ratios of aluminum chloride (AlCl3) (AlCl3/Py13Cl molar ratio = 1.4 to 1.7). Fundamental properties of the ionic liquids, including density, viscosity, conductivity, anion concentrations and electrolyte ion percent were investigated and compared with the previously investigated 1-ethyl-3-methylimidazolium chloride (EMIC-AlCl3) ionic liquids. The results showed that the Py13Cl–AlCl3 ionic liquid exhibited lower density, higher viscosity and lower conductivity than its EMIC-AlCl3 counterpart. We devised a Raman scattering spectroscopy method probing ILs over a Si substrate, and by using the Si Raman scattering peak for normalization, we quantified speciation including AlCl4−, Al2Cl7−, and larger AlCl3 related species with the general formula (AlCl3)n in different IL electrolytes. We found that larger (AlCl3)n species existed only in the Py13Cl–AlCl3 system. We propose that the larger cationic size of Py13+ (142 Å3) versus EMI+ (118 Å3) dictated the differences in the chemical and physical properties of the two ionic liquids. Both ionic liquids were used as electrolytes for aluminum–graphite batteries, with the performances of batteries compared. The chloroaluminate anion-graphite charging capacity and cycling stability of the two batteries were similar. The Py13Cl–AlCl3 based battery showed a slightly larger overpotential than EMIC-AlCl3, leading to lower energy efficiency resulting from higher viscosity and lower conductivity. The results here provide fundamental insights into ionic liquid electrolyte design for optimal battery performance.
Highlights
In recent years, with the increased deployment of portable devices, electric vehicles and renewable energy, rechargeable batteries with high energy density, power density, safety and long cycle life at low cost become highly desired
Our group has developed rechargeable Al–graphite battery based on two types of electrolytes, an IL electrolyte made by mixing 1-ethyl-3-methylimidazolium chloride (EMIC) and AlCl3 and an quasi IL or deep-eutectic solvent (DES) by mixing urea with AlCl3.7–9 The batteries operate by reversible redox of Al at the negative Al foil electrode, and reversible carbon redox through chloroaluminate anion intercalation and deintercalation at the graphite positive electrode.[7,8,9,17,18,19]
Clear liquid could not form in Py13Cl–AlCl3 IL until AlCl3/Py13Cl molar ratio reached 1.4
Summary
With the increased deployment of portable devices, electric vehicles and renewable energy, rechargeable batteries with high energy density, power density, safety and long cycle life at low cost become highly desired. Lithium ion batteries (LIBs) have high energy density and high capacity and are regarded as one of the most promising energy. The electrolyte lies at the heart of a battery. With the advances in battery technology, the development of a safe and stable electrolyte is critically important. Room temperature ionic liquids (RTILs) are safe and sufficiently conducting, useful as battery electrolytes.[10,11,12,13,14] Various ionic liquids have been investigated for different types of batteries, including LIB and AIB.[2,15,16] Our group has developed rechargeable Al–graphite battery based on two types of electrolytes, an IL electrolyte made by mixing 1-ethyl-3-methylimidazolium chloride (EMIC) and AlCl3 and an quasi IL or deep-eutectic solvent (DES) by mixing urea with AlCl3.7–9 The batteries operate by reversible redox of Al at the negative Al foil electrode, and reversible carbon redox through chloroaluminate anion intercalation and deintercalation at the graphite positive electrode.[7,8,9,17,18,19] Still, much room exists in developing new IL electrolytes to improve Al battery, and especially, to understanding the relations
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
