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Conversion-alloying-type compounds offer many new possibilities as anode materials for Li-ion cells, but also show some drawbacks related to their intrinsic characteristics. To overcome those limitations, the consecutive steps of electrochemical processes occurring in the selected Zn2SnO4 inverse spinel are studied in detail i.e. by operando X-ray diffraction, ex situ X-ray absorption spectroscopy, and transmission electron microscopy. Decomposition of the spinel phase upon the 1st lithiation proceeds with the precipitation of Li2O and metallic particles, which further form LiZn and LixSn. A multicomponent matrix is created, which allows for reversible lithium storage. After dealloying upon the 1st delithiation, a Li6ZnO4/Li4ZnO3-type phase is formed in the conversion reaction, indicating reactivity between ZnO and Li2O. Initially, α-Sn is likely precipitated, which is transformed into β-Sn during the 2nd cycle, indicating aggregation. Understanding the electrochemical reaction mechanism allowed identifying essential issues, important for the practical application of the Zn2SnO4 anode: too high reaction voltage vs. Li+/Li with large hysteresis during the conversion reaction; metallic particle aggregation; large volume changes during deep (de-)alloying; mechanical problems on prolonged cycling. While the full-range capacity of the developed anodes reaches 920 mA h g−1 after 10 cycles at a current of 50 mA g−1 and over 460 mA h g−1 at 1000 mA g−1, their operation range has to be limited in order to overcome the listed problems. This can be achieved by the controlled electrochemical prelithiation of Zn2SnO4 anodes before assembling full-cells. For the first time, excellent cycling stability is reached for micrometer-sized solid-state-synthesized Zn2SnO4, working in full Li-ion cells. [ABSTRACT FROM AUTHOR]

Among the for the first time reported Cr-containing high entropy La1−xSrx(Co,Cr,Fe,Mn,Ni)O3−δ (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) perovskite-type oxides, the selected Sr-doped La0.7Sr0.3(Co,Cr,Fe,Mn,Ni)O3−δ material is documented to possess attractive properties as a candidate air electrode material for Solid Oxide Fuel Cells (SOFCs). Nanosized powders of the considered oxides are obtained using a modified Pechini sol–gel method. In the formed solid solution with a simple perovskite structure the strontium solubility limit is found to be at least x = 0.3. Room temperature (RT) structural data indicate the presence of rhombohedral structural distortion (R3¯c symmetry) in the materials. High-temperature structural studies for the selected La0.7Sr0.3(Co,Cr,Fe,Mn,Ni)O3−δ indicate the occurrence of a phase transition to an aristotype Pm3¯m structure at ca. 800 °C. The linear thermal expansion coefficient in the RT-1000 °C range is found to be moderate, 16.0(3) × 10−6 K−1. The results of impedance spectroscopy measurements support the semiconducting-type behavior of the electrical conductivity for all single-phase materials, in a temperature range of RT-1000 °C. The maximum recorded conductivity for the La0.7Sr0.3(Co,Cr,Fe,Mn,Ni)O3−δ composition exceeds 16 S cm−1 in the 900–1000 °C range, being suitable for application. Furthermore, chemical stability toward the La0.8Sr0.2Ga0.8Mg0.2O3−δ (LSGM) electrolyte is proven. Considering the presence of chromium, typically deleterious to the performance, the measured value of the total cathodic polarization resistance for the La0.7Sr0.3(Co,Cr,Fe,Mn,Ni)O3−δ-based electrode, being 0.126 Ω cm−2 at 900 °C, seems to be very attractive. The results obtained for a button-type fuel cell indicate power densities at a level of 550 mW cm−2 at 900 °C. Therefore, it can be considered that the high entropy-based approach enables to propose alternative SOFC air electrode materials, with otherwise inaccessible chemical compositions. [ABSTRACT FROM AUTHOR]

Phase composition, crystal structure, and selected physicochemical properties of the high entropy Ln(Co,Cr,Fe,Mn,Ni)O3−δ (Ln = La, Pr, Gd, Nd, Sm) perovskites, as well as the possibility of Sr doping in Ln1−xSrx(Co,Cr,Fe,Mn,Ni)O3−δ series, are reported is this work. With the use of the Pechini method, all undoped compositions are successfully synthesized. The samples exhibit distorted, orthorhombic or rhombohedral crystal structure, and a linear correlation is observed between the ionic radius of Ln and the value of the quasi-cubic perovskite lattice constant. The oxides show moderate thermal expansion, with a lack of visible contribution from the chemical expansion effect. Temperature-dependent values of the total electrical conductivity are reported, and the observed behavior appears distinctive from that of non-high entropy transition metal-based perovskites, beyond the expectations based on the rule-of-mixtures. In terms of formation of solid solutions in Sr-doped Ln1−xSrx(Co,Cr,Fe,Mn,Ni)O3−δ materials, the results indicate a strong influence of the Ln radius, and while for La-based series the Sr solubility limit is at the level of xmax = 0.3, for the smaller Pr it is equal to just 0.1. In the case of Nd-, Sm- and Gd-based materials, even for the xSr = 0.1, the formation of secondary phases is observed on the SEM + EDS images. [ABSTRACT FROM AUTHOR]

Benefits emerging from applying high-entropy ceramics in Li-ion technology are already well-documented in a growing number of papers. However, an intriguing question may be formulated: how can the multicomponent solid solution-type material ensure stable electrochemical performance? Utilizing an example of nonequimolar Sn-based Sn 0.8 (Co 0.2 Mg 0.2 Mn 0.2 Ni 0.2 Zn 0.2 ) 2.2 O 4 high-entropy spinel oxide, we provide a comprehensive model explaining the observed very good cyclability. The material exhibits a high specific capacity above 600 mAh g -1 under a specific current of 50 mA g -1 and excellent capacity retention near 100% after 500 cycles under 200 mA g -1 . The stability originates from the conversion-alloying reversible reactivity of the amorphous matrix, which forms during the first lithiation from the initial high-entropy structure, and preserves the high level of cation disorder at the atomic scale. In the altered Li-storage mechanism in relation to the simple oxides, the unwanted aggregated metallic grains are not exsolved from the anode and therefore do not form highly lithiated phases characterized by large volumetric changes. Also, the electrochemical activity of Mg from the oxide matrix can be clearly observed. Because the studied compound was prepared by a conventional solid-state route, implementation of the presented approach is facile and appears usable for any oxide anode material containing a high-entropy mixture of elements.