The effect of the lithium perchlorate concentration in sulfolane (in the range from 0.1M to 2.8М) on the performance of lithium-sulfur cells is studied. It is shown that the concentration of lithium ...perchlorate in sulfolane considerably affects the depth of electrochemical reduction of sulfur, the reactivity of lithium polysulfides, and the coulomb efficiency of cycling of lithium-sulfur cells. The maximum depth of electrochemical reduction of sulfur is reached at the concentration of lithium perchlorate in sulfolane of 1.0M, while the minimum depth is reached at 2.8М. The depth of electrochemical reduction of sulfur is limited by the number of free solvent molecules. An increase in the concentration of the support salt results in an increase in the coulomb efficiency of cycling of lithium-sulfur cells. At concentrations of the support salt above 2.4М, the coulomb efficiency of cycling of lithium-sulfur cells is close to 100%.
We believe that the concentration of support salts affects the species of lithium polysulfides, their association-dissociation equilibria in electrolyte solutions and the processes of solvation of lithium ions contained in lithium polysulfides and support salts, and thus determines the performance of lithium-sulfur cells.
•Concentration of LiClO4 in sulfolane affects the performance of lithium-sulfur cells.•Reactivity of Li2Sn is determined by concentration of support salts in electrolyte.•Concentration of support salts affects association-dissociation equilibria of Li2Sn.•Electrolyte solvents solvate lithium ions in both Li2Sn and support lithium salts.•Depth of S reduction is limited by amount of free molecules of electrolyte solvents.
This work is to study the reasons for the relatively low efficiency of sulphur reduction (about 75%) in lithium-sulphur batteries. The two main reasons for that are suggested to be: the relatively ...low electrochemical activity of low order lithium polysulphides and blocking of the carbon framework of the sulphur electrode by insoluble products of electrochemical reactions - sulphur and lithium sulphide. The electrochemical activity of lithium polysulphides with different composition (Li sub(2)S sub(n), n = 2-6) has been studied in 1 M solutions of CF sub(3)SO sub(3)Li in sulfolane. It is shown that lithium polysulphides including lithium disulphide are able to electrochemically reduce with efficiency close to 100%. The electrochemical activity of lithium polysulphides decreases with the order. The order of lithium polysulphides affects the value of voltage of discharge plateaus but not the efficiency of sulphur reducing in the lithium polysulphides species. The relatively low efficiency of sulphur reduction in the lithium-sulphur batteries is more likely caused by blocking of carbon particles in the sulphur electrode by insoluble products of electrochemical reactions (sulphur and lithium sulphide). This prevents the electrochemical reduction of low order lithium polysulphides and especially lithium disulphide.
We have studied the interaction of polycrystalline samples of lithium nitride with metallic lithium. We have found that upon contact, metallic lithium spontaneously dissolves into polycrystalline ...lithium nitride samples. Spontaneous penetration of metallic lithium into polycrystalline samples of lithium nitride leads to the appearance of electronic conductivity and the formation of mixed ion-electronic conductors.
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•Interaction of metallic lithium and polycrystalline lithium nitride is studied.•Metallic lithium spontaneously penetrates in a pellet of Li3N.•Penetration of lithium in Li3N leads to short circuit of the cell Li │ Li3N │ Li.•Penetration of Li in Li3N leads to the formation of mixed ion-electronic conductors.
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•Activated carbon quantitatively sorb Tc under oxidizing conditions.•Tc isn’t leached from the activated carbon during treatment by H2O, NH2OH and 6 M HCl.•Natural bentonite clay with ...activated carbon additives has high Tc sorption ability.•Clay with carbon additive is a promising material for Tc immobilization in RW sites.
Safe disposal of nuclear waste in a geologic repository will rely on natural geologic features and engineered barriers to greatly retard the movement of radionuclides from the repository. Clay minerals including bentonite are effective in retarding the migration of many radionuclides, but are ineffective for anionic radionuclides, of which pertechnetate is of particular concern owing to its relatively long half-life and the lack of natural isotopes that dilute it. Activated carbon is proposed as an additive material for reducing pertechnetate mobility in the nearfield. Activated carbon materials of different origins quantitatively sorb pertechnetate from aqueous solution under oxidizing conditions during the first day of contact, and sequential extraction showed that 73 % of this technetium is in the strongly bound fraction. X-ray photoelectron spectra (XPS) and extended X-ray absorption fine structure (EXAFS) spectra both demonstrated that no reduction of technetium occurred in the studied systems. The interaction of technetium with a composite material consisting of bentonite and activated carbon was studied at the first time. Effective technetium sorption was shown, with distribution coefficients (Kd) up to 740 cm3. g−1.
The changes in the properties of lithium–sulphur cell components (electrolyte, sulphur and lithium electrodes) during cycling are studied by AC impedance spectroscopy. It is shown that during the ...charge and discharge of lithium–sulphur cells the conductivity of the electrolyte is changed. We believe that the observed changes in the electrolyte conductivity can be explained by the formation of soluble lithium polysulphides by electrochemical reactions. The properties of the electrolyte significantly influence the rate of the electrochemical processes which occur both on the sulphur and lithium electrodes in lithium–sulphur cells.
Molecular dynamics simulation of LiClO
4
solutions in sulfolane has been performed in a wide range of concentrations from 2 × 10
2
to 7 × 10
3
mol/m
3
(7 M) using the Opslaa force field. It was found ...that the total coordination number (the sum of coordination numbers for sulfolane and perchlorate anion) of the lithium cation decreased with an increase in the lithium perchlorate concentration in solution from 5.7 to 4.5. It was shown that sulfolane solvates one lithium cation by one oxygen atom regardless of the salt concentration; but above the salt concentration 2 × 10
3
mol/m
3
(2 M) (molar ratio of sulfolane/LiClO
4
< 5), sulfolane acts as a bridging ligand between two lithium cations; the lithium perchlorate anion is coordinated with the lithium cation by one oxygen atom; only at the molar ratio sulfolane/LiClO
4
= 1 (salt concentration 7 × 10
3
mol/m
3
) the perchlorate anion acts as a bridging ligand and is coordinated with several lithium cations at once. At a concentration of 2.35 × 10
3
mol/m
3
(sulfolane/LiClO
4
= 4), the structure of the first solvation shell of the lithium cation changes; the perchlorate anion is introduced in it, filling the vacancies in the coordination sphere that appear because of the lack of free sulfolane molecules.
The effect of the force field, atomic charges of sulfolane and perchlorate anion, and scale of ionic charges on the results of molecular dynamics (MD) simulation of the physicochemical properties of ...a 1 M LiClO
4
solution in sulfolane was evaluated. The simulation was performed using the OPLS-AA, Amber (GAFF), Charmm, and Gromos force fields. The best correlation between the calculated and experimental physicochemical properties of the solution was obtained using the OPLS-AA force field, the atomic charges calculated by the B3LYP/aug-cc-pVTZ method, and with ionic charges scaled by 80% as default charges (±1.0). The coordination number of the lithium cation with respect to sulfolane was calculated: 5.3 with ionic charges scaled by 100% and 4.7 for 80%. It was shown that sulfolane is coordinated to the lithium cation by one oxygen atom of the sulfone group.
The solubility of sulfur in sulfolane and solutions of lithium salts LiBF
4
, LiClO
4
, LiPF
6
, LiSO
3
CF
3
and LiN(SO
2
CF
3
)
2
in sulfolane, which are promising electrolytes for lithium-sulfur ...batteries, was determined by UV-vis spectroscopy. It was found that the solubility of sulfur in sulfolane at 30°C is 82.0 mM, and in sulfolane solutions of lithium salts (1 M) it is 4–9 times lower. The dependence of sulfur solubility on the concentration of lithium salts is not linear: it is 32.9 and 5.8 mM for sulfolane solutions containing 0.5 and 2.35 M of LiClO
4
, respectively.
This article focuses on modeling 90Sr migration in strong nitrate solutions in aquifers used for radioactive waste disposal. This type of radioactive waste disposal is typical only for the Russian ...Federation and is a unique object of study. The calculations are based on the laboratory study of strontium sorption in nitrate solutions on sandy, loamy and clayey rocks under biotic (with natural microbial communities obtained from Seversky repository) and abiotic conditions. To obtain a strontium sorption model, first, an ion exchange model in PHREEQC software is fitted to the experimental data both manually and automatically (using MOUSE software). Since real nitrate-ion concentrations at radioactive waste injection sites can reach values of hundreds of grams per liter, strontium Kd values are predicted for high ionic strength (for which no experimental study of strontium sorption efficiency has been carried out) with PHREEQC-model. The strontium transport models accounting for sorption and the nitrate reduction processes have been developed using two numerical software packages: the GeRa 3D hydrogeological simulation code and the PHREEQC reactive transport code. Reactive transport modeling under different conditions shows a high sensitivity to dispersion. A significant effect of sorption of nitrate ion on Sr sorption is shown and a relatively small contribution of microbial processes to strontium transport is noted for liquid radioactive waste injection sites.
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•Model of ion exchange and NO3− reduction was used for Sr reactive transport modeling.•Microbial nitrate reduction can affect Sr transport in subsurface media.•Nitrate-ion cannot be considered as a neutral non-absorbable tracer.
