RESUMEN
Developing electrochemical high-energy storage systems is of crucial importance toward a green and sustainable energy supply. A promising candidate is fluoride-ion batteries (FIBs), which can deliver a much higher volumetric energy density than lithium-ion batteries. However, typical metal fluoride cathodes with conversion-type reactions cause a low-rate capability. Recently, layered perovskite oxides and oxyfluorides, such as LaSrMnO4 and Sr3Fe2O5F2, have been reported to exhibit relatively high rate performance and cycle stability compared to typical metal fluoride cathodes with conversion-type reactions, but their discharge capacities (â¼118 mA h/g) are lower than those of typical cathodes used in lithium-ion batteries. Here, we show that double-layered perovskite oxyfluoride La1.2Sr1.8Mn2O7-δF2 exhibits (de) intercalation of two fluoride ions to rock-salt slabs and further (de) intercalation of excess fluoride ions to the perovskite layer, leading to a reversible capacity of 200 mA h/g. The additional fluoride-ion intercalation leads to the formation of O-O bond in the structure for charge compensation (i.e., anion redox). These results highlight the layered perovskite oxyfluorides as a new class of active materials for the construction of high-performance FIBs.
RESUMEN
Understanding the fast Li ionic conductors of oxygen-substituted thiophosphates is useful for developing all-solid-state batteries because these compounds possess a high electrochemical stability and thus may be applied as solid electrolytes. In this study, we synthesized the Li9+δP3+δ'S12-kOk series of solid solution phases with the same structure as the Li10GeP2S12 superionic conductor and characterized their crystallinity, solid solution range, and chemical stabilities. Two methods (mechanochemical and melt quenching) were used for sample synthesis. Mechanochemical synthesis was used to obtain samples within a wide range of sulfur/oxygen substitution degrees, and the solid solution range was determined to be 0 < k ≤ 3.6 based on their lattice parameter variation. Meanwhile, the melt-quenched Li9P3S9O3 phase exhibited a high degree of crystallinity up to its particle surface and was thus selected for neutron crystal structure analysis, which revealed the oxygen distribution related to the solubility limit. The highly crystalline melt-quenched Li9P3S9O3 showed better stability in the air atmosphere compared to the mechanochemically synthesized counterpart with a low crystallinity, implying that sample crystallinity is an important parameter in evaluating the air stability of thiophosphates. The promising electrochemical properties of the solid solution series were demonstrated by the stable charge-discharge cycling of an all-solid-state lithium metal cell using the Li9+δP3+δ'S12-kOk electrolyte with k = 0.9 and a conductivity of >1 × 10-3 S cm-1 at 300 K.
RESUMEN
Developing high-performance solid electrolytes that are operable at room temperature is one of the toughest challenges related to all-solid-state fluoride-ion batteries (FIBs). In this study, tetragonal ß-Pb0.78Sn1.22F4, a promising solid electrolyte material for mild-temperature applications, was modified through annealing under various atmospheres using thin-film models. The annealed samples exhibited preferential growth and enhanced ionic conductivities. The rate-determining factor for electrode/electrolyte interface reactions in all-solid-state FIBs was also investigated by comparing ß-Pb0.78Sn1.22F4 with representative fluoride-ion- and lithium-ion-conductive materials, namely, LaF3, CeF3, and Li7La3Zr2O12. The overall rate constant of the interfacial reaction, k0, which included both mass and charge transfers, was determined using chronoamperometric measurements and Allen-Hickling simulations. Arrhenius-type correlations between k0 and temperature indicated that activation energies calculated from k0 and ionic conductivities (σion) were highly consistent. The results indicated that the mass transfer (electrolyte-side fluoride-ion conduction) should be the rate-determining process at the electrode/electrolyte interface. ß-Pb0.78Sn1.22F4, with a large σion value, had a larger k0 value than Li7La3Zr2O12. Therefore, it is hoped that the development of high-conductivity solid electrolytes can lead to all-solid-state FIBs with superior rate capabilities similar to those of all-solid-state Li-ion batteries.
RESUMEN
Polycrystalline samples of Ln(18)Li(8)Rh(5-x)Fe(x)O(39) (Ln = La, Nd; 0.5 < or = x < or = 5) have been synthesized by a solid-state method and studied by a combination of dc and ac magnetometry, neutron diffraction, and Mossbauer spectroscopy. All compositions adopt a cubic structure (space group Pm3n, a(0) approximately 12 A) based on intersecting 111 chains made up of alternating octahedral and trigonal-prismatic coordination sites. These chains occupy channels within a Ln-O framework. At low values of x, iron preferentially occupies the smaller (2a) of the two distinct octahedral sites as low-spin Fe(IV). The Rh(III) on the larger (8e) octahedral site is replaced by high-spin Fe(III). Nd-containing compositions having x > 1 show spin-glass-like behavior below approximately 5 K. La-containing compositions having x > 1 show evidence of a magnetic transition at approximately 8 K, but the nature of the transition is unclear. This contrasting behavior demonstrates that, although the structural chemistry of the two systems is essentially the same, the magnetic character of the Ln cations plays an important role in determining the properties of these compounds.
