A Raman spectroscopic evaluation of numerous crystalline solvates with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI or LiN(SO2CF3)2) has been conducted over a wide temperature range. Four new crystalline solvate structures-(PHEN)3:LiTFSI, (2,9-DMPHEN)2:LiTFSI, (G3)1:LiTFSI and (2,6-DMPy)1/2:LiTFSI with phenanthroline, 2,9-dimethyl[1,10]phenanthroline, triglyme, and 2,6-dimethylpyridine, respectively-have been determined to aid in this study. The spectroscopic data have been correlated with varying modes of TFSI(-)···Li(+) cation coordination within the solvate structures to create an electrolyte characterization tool to facilitate the Raman band deconvolution assignments for the determination of ionic association interactions within electrolytes containing LiTFSI. It is found, however, that significant difficulties may be encountered when identifying the distributions of specific forms of TFSI(-) anion coordination present in liquid electrolyte mixtures due to the wide range of TFSI(-)···Li(+) cation interactions possible and the overlap of the corresponding spectroscopic data signatures.
Atomic layer deposition (ALD) is a viable means to add corrosion protection to copper metal. Ultrathin films of AlO, TiO, ZnO, HfO, and ZrO were deposited on copper metal using ALD, and their corrosion protection properties were measured using electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry (LSV). Analysis of ∼50 nm thick films of each metal oxide demonstrated low electrochemical porosity and provided enhanced corrosion protection from aqueous NaCl solution. The surface pretreatment and roughness was found to affect the extent of the corrosion protection. Films of AlO or HfO provided the highest level of initial corrosion protection, but films of HfO exhibited the best coating quality after extended exposure. This is the first reported instance of using ultrathin films of HfO or ZrO produced with ALD for corrosion protection, and both are promising materials for corrosion protection.
Atomic layer deposition (ALD) of vanadium oxide is a viable means to add pseudocapacitive layers to porous carbon electrodes. Two commercial activated carbon materials with different surface areas and pore structures were acid treated and coated by V2O5 ALD using vanadium triisopropoxide and water at 150 °C. The V2O5 ALD process was characterized at various temperatures to confirm saturated ALD growth conditions. Capacitance and electrochemical impedance analysis of subsequently constructed electrochemical capacitors (ECs) showed improved charge storage for the ALD coated electrodes, but the extent of improvement depended on initial pore structure. The ALD of V2O5 onto mesoporous carbon increased the capacitance by up to 46% after 75 ALD cycles and obtained a maximum pseudocapacitance of 540 F/g(V2O5) after 25 ALD cycles, while maintaining low electrical resistance, high columbic efficiency, and a high cycle life. However, adding V2O5 ALD to microporous carbons with pore diameters of <11 Å showed far less improvement, likely due to “blocking off” of the micropores and reducing the accessible surface area. Results show that ALD is a viable means to construct high-performance supercapacitors from activated carbon which is the basis for commercial products, and a clear understanding of carbon electrode pore structure, layer conformality, and layer thickness are necessary to fully optimize performance.
Molecular dynamics (MD) simulations of acetonitrile (AN) mixtures with LiBF 4 , LiCF 3 SO 3 and LiCF 3 CO 2 provide extensive details about the molecular-and mesoscale-level solution interactions and thus explanations as to why these electrolytes have very different thermal phase behavior and electrochemical/physicochemical properties. The simulation results are in full accord with a previous experimental study of these (AN) n -LiX electrolytes. This computational study reveals how the structure of the anions strongly influences the ionic association tendency of the ions, the manner in which the aggregate solvates assemble in solution and the length of time in which the anions remain coordinated to the Li + cations in the solvates which result in dramatic variations in the transport properties of the electrolytes. Understanding the origin of the widely varying transport properties (e.g., viscosity, ionic conductivity and diffusion coefficients) of battery electrolytes remains a key challenge. The present work continues a detailed study into the solution structure of electrolytes-ion solvation and ionic association interactions-to provide mechanistic explanations for electrolyte properties. Previous manuscripts have examined in detail acetonitrile electrolytes with numerous lithium salts: (AN) n -LiX. [1][2][3][4][5][6] Electrolytes with the most strongly associated anions studied (i.e., CF 3 SO 3 − and CF 3 CO 2 − ), in which anion. . . Li + cation coordination (i.e., ionic association interactions) is a prominent feature of solvate formation, were found to have a much lower ionic conductivity than electrolytes with more weakly coordinating anions (e.g., PF 6 − and ClO 4 − ). 3 This is as one might expect once the ionic association tendency of the salts is well understood, but the details of why the conductivity values are low are missing.Two particularly notable points from the previous studies are that:(1) The average solvation numbers, obtained from a Raman spectroscopic analysis, for the (AN) n -LiCF 3 CO 2 solutions were found to be almost constant near a value of 1 (i.e., one AN molecule per Li + cation) over a wide concentration range, even for very dilute solutions. It remains unclear, however, as to why such electrolytes have such a low degree of solvation and why highly concentrated (>5 M) liquid electrolytes-perhaps contrary to expectations-can be prepared with LiCF 3 CO 2 with this being the case.(2) Experimental measurements of the solution structure and transport properties of (AN) n -LiCF 3 SO 3 mixtures were unobtainable due to the rapid crystallization of a solid solvate phase (i.e., (AN) 1 :LiCF 3 SO 3 ) from the electrolytes. 1 Liquid electrolytes with this salt can, however, be readily studied using molecular dynamics (MD) simulations to better understand how and why solution interactions differ for differing anions.The present work therefore delves deeper into the molecular-and mesoscale-level interactions using MD simulations applied to the characterization of (AN) n -LiCF 3 SO 3 and -LiCF ...
This work highlights the intrinsic capabilities and limitations of coating microporous materials using atomic layer deposition (ALD).
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