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.
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.
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.
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.
The pulsed method of measuring impedance is described. The cell is galvanostatically stimulated by a bipolar current signal of square shape. The cell response is registered by sampling U+i, U−i with ...selected period Δt. The impedance spectra are calculated by direct Fourier transform. The internal resistance of the lithium sulphur cell is characteristically minimum in the calculated impedance diagrams in the frequency range of 0.035–5 Hz. It is shown that the lithium sulphur cells have maximum internal resistance at the transient between high and low voltage plateaus of charge and discharge curves. The internal resistance increases significantly during the initial stages of cycling because of the formation of passivation layers at the electrodes. It was found that the internal resistance of the lithium sulphur cell in the same charge state is governed by the way in which it is achieved. This is explained by differences in molar volumes of products generated in the sulphur electrode by electrochemical reaction during charging and discharging.
•The pulsed method as a way to determine the internal resistance of batteries.•The internal resistance of Li–S cells depends on the depth of charge and discharge.•The polarization direction of lithium sulphur cell governs the internal resistance.
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.
The article deals with the problem of existence of generalized solutions to linear differential equation with a generalized coefficient
Q
which coincides with a given rational function
q
on the ...complement to the set of poles of
q
. To introduce a generalized solution, we consider approximations of the coefficient
Q
by a family of smooth functions. Then, the generalized solution is the limit of the solutions to approximating equations. A principal difference from the classical theory here is that even such simplest equations with singular coefficient
Q
may not have the solution. The main result is the description of those
Q
from the class considered for whom a generalized solution does exist.
The effect of temperature (40, 50, 60, and 70°C) on the composition of solvate complexes of lithium perchlorate with sulfolane was studied by the method of automated vacuum gravimetry during ...isothermal evaporation of the solvent. It is found that the composition of the solvate complexes of lithium perchlorate with sulfolane is determined by the temperature of their formation. Raising the temperature lowers the number of sulfolane molecules in the solvate complex. A tetrasolvate of lithium perchlorate with sulfolane forms at 40°C, and disolvates form at 50, 60, and 70°C. The composition of solvate complexes of lithium perchlorate with sulfolane is also confirmed via thermogravimetry. It is assumed that the differences between the compositions of the solvate complexes in the lithium perchlorate–sulfolane system at different temperatures are due to differences in their structure.
