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We report in the context of lithium-rich antiperovskite cathode materials outstanding electrochemical properties of (Li2Fe)SeO, which for the first time was synthesized via direct ball-milling. The unique structured material displays an electrochemical cycling performance of 250 mA h g−1 at 0.1C when used as a cathode in lithium-ion batteries. Comprehensive electrochemical analysis combined with detailed transmission electron microscopy studies reveal that, above 2.5 V, the multi electron storage mechanism involves conversion of (Li2Fe)SeO to Fe1−xSex. Our results furthermore demonstrate the general relevance of our findings to the whole class of antiperovskite cathode materials and present a route to strongly enhance their cell performance by avoiding the degradation path deciphered by our studies. [ABSTRACT FROM AUTHOR]

The development of electrode materials with multielectron redox functionality is imperative for next-generation Li-ion batteries with a high gravimetric capacity. Within this context, a Li-rich (Li2Fe)SO antiperovskite cathode is a promising candidate exhibiting such multielectron cationic and anionic redox features, resulting in a reversible extraction/insertion of about 1.2 Li+ per formula unit. However, it suffers from poor structural and cycling stabilities which hinder its practical application. Herein, we systematically investigate the effect of anionic substitution of S with Se on the structural, thermal and electrochemical properties of the (Li2Fe)SO cathode. With increasing the Se content, higher thermal stability and lower sensitivity to moist air were obtained. Multi-stage cationic and anionic redox processes characterized the electrochemical activity of all the prepared (Li2Fe)S1−xSexO solid solutions. The cationic redox process was shifted to higher potentials while the anionic redox process was shifted to lower potentials upon the increase of the Se content. Among the various synthesized compositions, (Li2Fe)S0.7Se0.3O exhibited the best electrochemical performance with a high discharge capacity of ∼245 mA h g−1 and an outstanding cycling stability at 0.1C current rate as well as nearly 100% capacity recovery after rate capability tests of 50 cycles. To deeply characterize (Li2Fe)S0.7Se0.3O, various ex situ and in situ techniques were applied. In contrast to (Li2Fe)SO, the substituted (Li2Fe)S0.7Se0.3O material remains crystalline without the evolution of secondary phases or superstructures after the first charge/discharge cycle highlighting its enhanced structural stability. Similar to (Li2Fe)SO, both the cation (Fe) and anions (S/Se) from (Li2Fe)S0.7Se0.3O participate in the redox process. [ABSTRACT FROM AUTHOR]

Heteroanionic materials show promising potential as 2D semiconductors due to their tunable band gaps, making them excellent candidates for photocatalytic water splitting applications. We conducted detailed theoretical and experimental analysis of two selected materials by synthesizing crystals through chemical vapor transport and investigating the impact of anion variation on crystal structure and properties. Using powder X-ray diffraction and convergent beam electron diffraction, we elucidated the non-centrosymmetric space groups of these compounds. Thermochemical studies revealed the influence of the crystal structure on the decomposition points of both compounds. Theoretical investigations predict that both materials are indirect bandgap semiconductors, which is confirmed by electron energy loss spectroscopy and photoluminescence studies.

Solid solutions of 2D transition metal trihalides are rapidly growing in interest for the search for new 2D materials with novel properties at nanoscale dimensions. In this regard, we present a synthesis method for the Cr 1- x Ru x Cl 3 solid solution and describe the behaviour of the unit cell parameters over the whole composition range, which in general follows Vegard's law in the range of a = 5.958(6) CrCl 3 … 5.9731(5) RuCl 3 Å, b = 10.3328(20) CrCl 3 … 10.34606(21) RuCl 3 Å, c = 6.110(5) CrCl 3 … 6.0385(5) RuCl 3 Å and β = 108.522(15) CrCl 3 … 108.8314(14) RuCl 3 °. The synthesized solid solution powder was subsequently used to deposit micro- and nanosheets directly on a substrate by applying chemical vapour transport in a temperature gradient of 575 °C → 525 °C for 2 h and 650 °C → 600 °C for 0.5 h as a bottom-up approach without the need for an external transport agent. The observed chromium chloride enrichment of the deposited crystals is predicted by thermodynamic simulation. The results allow for a nanostructure synthesis of this solid solution with a predictable composition down to about 30 nm in height and lateral size of several μm. When applying a quick consecutive delamination step, it is possible to obtain few- and monolayer structures, which could be used for further studies of downscaling effects for the CrCl 3 -RuCl 3 solid solution. X-ray photoelectron spectroscopy, transmission electron microscopy and Raman spectroscopy were used to confirm the purity and quality of the synthesized crystals.

A series of solid solutions (Li 2 Fe 1-y Mn y )SO with a cubic antiperovskite structure was successfully synthesized. The composition (Li 2 Fe 0.5 Mn 0.5 )SO was intensively studied as a cathode in Li-ion batteries showing a reversible specific capacity of 120 mA h g -1 and almost a 100% Coulombic efficiency after 50 cycles at 0.1C meaning extraction/insertion of 1 Li per formula unit during 10 h. Operando X-ray absorption spectroscopy confirmed the redox activity of both Fe 2+ and Mn 2+ cations during battery charge and discharge, while operando synchrotron X-ray diffraction studies revealed a reversible formation of a second isostructural phase upon Li-removal and insertion at least for the first several cycles. In comparison to (Li 2 Fe)SO, the presence of Mn stabilizes the crystal structure of (Li 2 Fe 0.5 Mn 0.5 )SO during battery operation, although post mortem TEM studies confirmed a gradual amorphization after 50 cycles. A lower specific capacity of (Li 2 Fe 0.5 Mn 0.5 )SO in comparison to (Li 2 Fe)SO is probably caused by slower kinetics, especially in the two-phase region, as confirmed by Li-diffusion coefficient measurements.