ABSTRACT
This study investigates a salt design principle for aqueous battery electrolytes by combining chaotropic ions, guanidium cations (Gdm) and bis(trifluoromethanesulfonyl)imide anions (TFSI), forming GdmTFSI. This salt's crystal structure was solved via single-crystal X-ray diffraction and characterized using Fourier-transform infrared spectroscopy. Study reveals that GdmTFSI salt disrupts the hydrogen bonding network of aqueous solutions, impacting water reactivity at electrochemical interfaces.
ABSTRACT
Ca metal anode rechargeable batteries are seen as a sustainable high-energy density and high-voltage alternative to the current Li-ion battery technology due to the low redox potential of Ca metal and abundance of Ca. Electrolytes are key enablers on the path towards next-generation battery systems. Within this work, we synthesize a new calcium tetrakis(hexafluoroisopropyloxy) aluminate salt, Ca[Al(hfip)4]2, and benchmark it versus the state-of-the-art boron analogue Ca[B(hfip)4]2. The newly developed aluminate-based electrolyte exhibits improved performance in terms of conductivity, Ca plating/stripping efficiency, and oxidative stability as well as Ca battery cell performance. A marked improvement of 0.5 V higher oxidative stability can pave the path towards high-voltage Ca batteries. A critical issue of solvent quality during salt synthesis is identified as well as solvent decomposition at the Ca metal/electrolyte interface, which leads to passivation of the Ca metal anode. However, the new aluminate salt with preferable electrochemical properties over the existing boron analogue opens up a new area for future Ca battery research based on aluminium compounds.
ABSTRACT
The crystal structure of the co-crystal of aqua-tri-fluorido-boron with two ethyl-ene carbonate (systematic name: 1,3-dioxolan-2-one) mol-ecules, BF3H2O·2OC(OCH2)2, was determined by low-temperature single-crystal X-ray diffraction. The co-crystal crystallizes in the ortho-rhom-bic space group P212121 with four formula units per unit cell. The asymmetric unit consists of an aqua-tri-fluorido-boron mol-ecule and two ethyl-ene carbonate mol-ecules, connected by O-Hâ¯O=C hydrogen bonds. This crystal structure is an inter-esting example of a superacidic BF3H2O species co-crystallized with an organic carbonate.
ABSTRACT
While less mature than the Li-ion battery, technologies based on Na, K, Mg, and Ca are attracting more and more attention from the battery community. New material (cathode, anode, or electrolyte) testing for these post-Li systems commonly involves the use of an electrochemical setup called a half-cell in which metal counter and reference electrodes are used. Here we first describe the different issues that become critical when moving away from Li with respect to the cell hardware (cell design, current collector, separator, insulator) and the nature of the counter and reference electrodes. Workarounds are given, and a versatile setup is proposed to run reliable electrochemical tests for post-Li battery materials in general, in a broad range of electrolyte compositions.
ABSTRACT
Water-in-salt and water-in-bisalt electrolytes have recently attracted much attention due to their expanded electrochemical stability windows. The concentration limit of such electrolytes is constrained by the solubility of the lithium salts employed, ca. 21 m (mol kg-1) for LiTFSI (lithium bis(trifluoromethanesulfonyl)imide). By adding a second lithium salt, the total salt concentration can be increased, but the hydrogen evolution keeps limiting the application of such systems in batteries with low potential anodes. Herein we report a water-in-bisalt electrolyte with a record salt concentration (31.4 m LiTFSI + 7.9 m Li[N(CH3)2((CH2)3SO3)((CH2)4SO3)]) in which the bulky anion completely prevents the crystallization, even at such low water contents. Although the hydrogen evolution reaction is not completely suppressed, the expanded electrochemical stability window allows for low potential reactions such as aluminum-lithium alloying. The high salt concentration favors the formation of a suitable passivation layer that can be further engineered by modifying the anion structure.
ABSTRACT
Mixing the standard battery salt LiTFSI with various Li-salts of novel pseudo-delocalized organic anions [N(CH3)2((CH2)nSO3)((CH2)mSO3)]- (MMnm11), results in super-cooled solvent-free liquid electrolytes with glass transition temperatures of ca. 50 °C. Synthesis routes and full chemical characterisation of the new pseudo-delocalized anions are presented, as well as phase and thermal stabilities. The ion conductivities and electrochemical stabilities are evaluated towards lithium and sodium battery application.
