Pressure Dependence of Solid Electrolyte Ionic Conductivity: A Particle Dynamics Study.

The search for safe, reliable, and compact high-capacity energy storage devices has led to increased interest in all-solid-state battery research. The use of solid electrolytes provides enhanced safety and durability due to their reduced flammability and increased mechanical strength compared to organic liquid electrolytes. Still, the use of solid electrolytes remains challenging. A significant issue is their generally low Li-ion conductivity, which depends on the lattice diffusion of Li ions through the solid phase, as well as on the limited contact area between the electrolyte particles. While the lattice diffusion can be addressed through the chemistry of the solid electrolyte material, the contact area is a mechanical and structural problem of packing and compression of the electrolyte particles depending on their size and shape. This work studies the effect of pressurization on the electrolyte conductivity exploring cases of low as well as high grain boundary (GB) conductivity, compared to the bulk conductivity. Scaling dependence, σ ∼ Pη, of the conductivity σ with pressure P is revealed. For an idealized electrolyte represented as spheres in hexagonal closely packed configuration, η = 2/3 and η = 1/3 have been theoretically calculated for the two cases of low and high GB conductivity, respectively. For randomly packed spheres, the equivalent exponent values were numerically estimated to be approximately 3/4 and 1/2, respectively, which are higher than the closed packed values due to the additional decrease of porosity with the increase in pressure. As demonstrated in the study, experimental measurement of η can indicate which type of bulk or GB conductivity is dominant in a particular electrolyte powder and could be used in addition to electrochemical impedance spectroscopy measurements.

Li-Ion Permeability of Holey Graphene in Solid State Batteries: A Particle Dynamics Study.

Lithium (Li)-ion permeability of holey graphene (hG) for use as an electrically conducting scaffold in solid-state battery electrodes is explored through the means of a particle dynamics simulation model. While carbon materials do not typically exhibit Li-ion conductivity, the unique structural motif of hG, which consists of two-dimensional nanosheets with arrays of through-thickness holes, may present an opportunity for Li-ion conductors (i.e., solid electrolyte (SE) particles) to make contacts through the holes. In our model, the SE is presented as a system of hard elastic spheres conductive to Li-ions. The SE spheres are in contact with each other through compression between two plane current collectors. One hG layer is inserted between the current collectors and parallel to them. Randomly distributed circular holes in the hG allow for contact between the SE particles on both sides of the hG layer. By solving the Li-ion conducting network formed between the electrodes through the contact points of all the particles, the overall conductivity of the system was calculated as a function of SE particle size and the size and number of the hG holes (i.e., hG porosity). A critical ratio of around 4 between the SE particle size and the pore size was found. Below this critical value, the hG layer becomes practically transparent for Li-ions. This study helps to guide the design of highly efficient solid-state electrode composition and architectures using hG as a unique electrically conducting scaffold.

Spectroscopic and Theoretical Insights into Surprisingly Effective Sm(III) Extraction from Alkaline Aqueous Media by o-Phenylenediamine-Derived Sulfonamides.

Alkaline high-level waste (HLW) generated as a result of years of nuclear weapons production has complicated composition and requires comprehensive treatment methods, which would allow concentrating its most radiotoxic components in a small volume for geological disposal. We have investigated six alkyl-substituted o-phenylenediamine-derived sulfonamides for extraction and consecutive stripping of Sm(III) from alkaline aqueous media. Up to 81% of Sm(III) recovery at pH 13.0-13.5 was achieved by disulfonamide (dsa) or dsa/Et3N in CH2Cl2, measured after contact with organic phases and subsequent stripping with 0.1 M HNO3. The use of Et3N dramatically enhances Sm(III) extraction at lower pH ranges (10.5-11.5) but decreases extraction at pH 13.0-13.5, while control experiments with Et3N and no dsa showed no extraction. Analysis of the extraction equilibria gave a 1:1 sulfonamide-Sm(III) complexation ratio, with the extracted species also presumed to contain coordinated H2O or OH-, as also shown by DFT calculations. Titration experiments of sulfonamides with Sm(III) in CH3CN were consistent with a 1:1 complexation ratio of dsa-6 to Sm(III) with a K11 = 6.6 × 107 M-1 derived from nonlinear regression analysis of the 1:1 binding isotherm. Theoretical DFT calculations determined the structures of possible species formed during extraction and the thermodynamics of extraction processes based on several initial [Sm(OH)y(NO3)z(H2O)x]3-y-z species and 1:1 Sm(III)/dsa-32- complexes formed in the organic phase, in which dsa complexes to Sm(III) in its bis-deprotonated form (denoted below as dsa-32-). Organization of close ion pairs of type {Na[Sm(dsa-32-)(OH)2]·2H2O} was shown to be thermodynamically favorable for extraction from alkaline aqueous media with pH = 13.0-13.5. Theoretical calculations also demonstrated thermodynamically favorable coordination to Am(III).