The effect of surfactants and protective interlayers (commercial carbon paper and homemade mixed-conduction composites) on the electrochemical performance of sulfur batteries has been studied. Modification of cell configuration by the insertion of Toraycarbon paper between the cathode and separator improved the utilization of the active material and increased the initial discharge capacity from 800 to 1400 mAh/gS. The latter is about 84% of the theoretical value. The use of a few-micron-thick PEO-PVP-XC72 or SWCNT-PVP interlayer composites, cast on the cathode or separator, resulted in a similar positive effect on the initial sulfur utilization. The cells that were assembled in the discharge state and contained carbon interlayers exhibited a faradaic efficiency (FE) of above 99%, while the FE of the cells with the unprotected cathode is 95-96%. High faradaic efficiencies confirm the functionality of protective interlayers, which minimizes the polysulfide shuttle. Analysis of the impedance spectra of the conventional and modified cells shows that the SEI resistance decreases by about 50% and the apparent thickness of the SEI becomes smaller in the interlayer-protected cells. The cells with ultrathin composite layers hold the 30% capacity gain induced by the barrier for at least 400 cycles. The first publication on the soluble lithium polysulfides (PS) -cell is by Abraham et al. 1 The first carbon-loaded-sulfur primary and secondary batteries were presented by Peled in 1983 2 and 1989, 3 respectively. Both batteries consisted of sulfur embedded in a porous carbon matrix. As the development of lithium-ion technology began in the early 1990 s, fewer efforts were made on the Li-S system. However, since the 2000 s and especially in recent years, Li-S technology has regained scientific interest as the post lithium-ion battery. A high theoretical specific energy of 2600 Wh/kg and 2200 Wh/L, combined with inexpensive and safe raw materials, classifies the lithium/sulfur battery as a leading candidate to replace the common lithium-ion battery in many applications. Although considered a promising battery, the lithium/sulfur battery suffers from three main drawbacks, which include 80% volume expansion of the cathode during discharge, the insulating nature of the sulfur species and the solubility of sulfur and of lithium polysulfides in the electrolyte. The insulating nature of the active material requires the use of nanosize sulfur species and the addition of relatively large amounts of conductive materials, such as black carbons, which lowers both the gravimetric and the volumetric energy density of the battery. The expansion/extraction of the cathode may lead to cracks in its structure, thus reducing the durability of the cell as a result of the loss of electrical contact between the particles of the active cathode material, and between the cathode and current collector. The solubility of polysulfides leads to the loss of active cathode material followed by the irreversible capacity loss. During charging, long polysu...

The effect of compositional disorder generated by partial isomorphic substitution of cobalt by ferroactive highly charged cations Nb/Ta(v) on the phase transition “perovskite–brownmillerite”, crystal structure and microstructure of low- and high-temperature phases SrCo0.8−xFe0.2MxO3−δ (M = Nb, Ta; 0 ≤ x ≤ 0.1) was studied for ferroelastic MIEC oxide SrCo0.8Fe0.2O2.5.

A group-theoretical analysis was carried out to determine the possible orientation states of domains formed as a result of the 'perovskitebrownmillerite' phase transition in SrCo 0.8 Fe 0.2 O 2.5 oxide with mixed ionelectron conductivity (MIEC). The results of the theoretical analysis agree with the experimental data obtained in the study of the SrCo 0.8 Fe 0.2 O 2.5 microstructure by means of transmission electron microscopy. Brownmillerite SrCo 0.8 Fe 0.2 O 2.5 (BM) has a lamellar texture composed of 90 twins 60-260 nm in size; the h010i BM and h101i BM directions are linked through twinning in accordance with the predictions of the group-theoretical analysis. The presence of twins and their switching under mechanical load provide evidence that the perovskite-brownmillerite phase transition in SrCo 0.8 Fe 0.2 O 2.5 is ferroelastic. Comparative analysis of the phenomena observed for ferroelectrics and MIEC oxides indicates their similarity based on the common nature of ferroelectricity and ferroelasticity, and allows us to suppose that nonstoichiometric SrCo 0.8 Fe 0.2 O 3À with compositional disorder may be considered (in terms of its microstructural features) a 'relaxor ferroelastic'.

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