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Layered Delafossite-type Lix(M1M2M3M4M5…Mn)O2 materials, a new class of high-entropy oxides, were synthesized by nebulized spray pyrolysis and subsequent high-temperature annealing. Various metal species (M = Ni, Co, Mn, Al, Fe, Zn, Cr, Ti, Zr, Cu) could be incorporated into this structure type, and in most cases, single-phase oxides were obtained. Delafossite structures are well known and the related materials are used in different fields of application, especially in electrochemical energy storage (e.g., LiNixCoyMnzO2 [NCM]). The transfer of the high-entropy concept to this type of materials and the successful structural replication enabled the preparation of novel compounds with unprecedented properties. Here, we report on the characterization of a series of Delafossite-type high-entropy oxides by means of TEM, SEM, XPS, ICP-OES, Mössbauer spectroscopy, XRD including Rietveld refinement analysis, SAED and STEM mapping and discuss about the role of entropy stabilization. Our experimental data indicate the formation of uniform solid-solution structures with some Li/M mixing.

High‐entropy materials have drawn much attention as battery materials due to their distinctive properties. Lithiated high‐entropy oxide (Li0.33(MgCoNiCuZn)0.67O, LiHEO) exhibits both high lithium‐ion and electronic conductivity, making it a potential coating material for layered Ni‐rich oxide cathodes (Li1+x(Ni1−y−zCoyMnz)1−xO2, NCM or NMC) in conventional Li‐ion battery cells; however, high‐temperature synthesis limits its application. Therefore, a photonic curing strategy is used for synthesizing LiHEO and the non‐lithiated form (denoted as high‐entropy oxide [HEO]), and nanoscale coatings are successfully produced on LiNi0.85Co0.1Mn0.05O2 (NCM851005) particles. To one's knowledge, this is the first report on particle coating with high‐entropy materials using photonic curing. NCM851005 with LiHEO‐modified surface shows good cycling stability, with a capacity retention of 97% at 1 C rate after 200 cycles. The improvement in electrochemical performance is attributed to the conformal coating that prevents structural changes caused by the reaction between cathode material and liquid electrolyte. Compared to bare NCM851005, the coated material shows a significantly reduced tendency for intergranular cracking, successfully preventing electrolyte penetration and suppressing side reactions. Overall, photonic curing presents a novel cost‐ and energy‐efficient synthesis and coating procedure that paves the way for surface modification of any heat‐sensitive material for a wide range of applications. [ABSTRACT FROM AUTHOR]

The synthesis of LiNiO2 (LNO) typically involves oxidizing Ni(II) to Ni(III), thus leading to NiLi point-defect formation. Here, materials containing Ni(IV) in the form of overlithiated Li1+xNi1−xO2 (0 ≤ x ≤ 1/3) are converted into LNO. This method produces low defect-density samples at high temperatures, offering an attractive route toward coarse-grained particles that are naturally coated by the byproduct Li2O. In thiophosphate-based solid-state batteries, this kind of self-coating effect shows a direct correlation between residual lithium content and cycling performance. [ABSTRACT FROM AUTHOR]

Ni‐rich LiNixCoyMnzO2 cathode materials offer high practical capacities and good rate capability, but are notorious for being unstable at high state of charge. Here, a series of such layered oxides with nickel contents ranging from 88 to 100 mol% is fabricated by sodium‐to‐lithium ion exchange, yielding materials devoid of NiLi•${\mathrm{Ni}}_{{\mathrm{Li}}}^ \bullet $ substitutional defects. Examining the initial charge/discharge cycle reveals effects that are specifically caused by transition‐metal substitution, which would otherwise be obscured by changes in lithium‐site defect concentration. Lowering the nickel content helps to stabilize the high‐voltage regime, while simultaneously negatively affecting lithium diffusion. Operando X‐ray diffraction indicates mitigation of volume variation during cycling and transition toward solid‐solution behavior with sufficiently high cobalt and manganese contents, thus providing an explanation for the increased stability. The interplay between transition‐metal substitution, kinetic hindrance, and solid‐solution behavior may be a result of local inhomogeneities due to lithium‐vacancy pinning, which is further elucidated through density functional theory calculations. Overall, this work sheds new light on the effects of manganese and cobalt incorporation into the transition‐metal layer and their conjunction with NiLi•${\mathrm{Ni}}_{{\mathrm{Li}}}^ \bullet $ defects. [ABSTRACT FROM AUTHOR]

Sodium-ion batteries offer an attractive alternative to lithium-based chemistries due to the lower cost and abundance of sodium compared to lithium. Using solid electrolytes instead of liquid ones in such batteries may help improve safety and energy density, but they need to combine easy processing with high stability toward the electrodes. Herein, we describe a new class of solid electrolytes that are accessible by room-temperature, aqueous synthesis. The materials exhibit a garnet-type zinc hexacyanoferrate framework with large diffusion channels for alkaline ions. Specifically, they show superionic behavior and allow for facile processing into pellets. We compare the structure, stability, and transport properties of lithium-, sodium-, and potassium-containing zinc hexacyanoferrates and find that Na2Zn3[Fe(CN)6]2 achieves the highest ionic conductivity of up to 0.21 mS/cm at room temperature. In addition, the electrochemical performance and stability of the latter solid electrolyte are examined in solid-state sodium-ion batteries. [ABSTRACT FROM AUTHOR]

In recent years, the concept of entropy stabilization of crystal structures in oxide systems has led to an increased research activity in the field of "high entropy oxides". These compounds comprise the incorporation of multiple metal cations into single-phase crystal structures and interactions among the various metal cations leading to interesting novel and unexpected properties. Here, we report on the reversible lithium storage properties of the high entropy oxides, the underlying mechanisms governing these properties, and the influence of entropy stabilization on the electrochemical behavior. It is found that the stabilization effect of entropy brings significant benefits for the storage capacity retention of high entropy oxides and greatly improves the cycling stability. Additionally, it is observed that the electrochemical behavior of the high entropy oxides depends on each of the metal cations present, thus providing the opportunity to tailor the electrochemical properties by simply changing the elemental composition.

The development of improved solid electrolytes (SEs) plays a crucial role in the advancement of bulk‐type solid‐state battery (SSB) technologies. In recent years, multicomponent or high‐entropy SEs are gaining increased attention for their advantageous charge‐transport and (electro)chemical properties. However, a comprehensive understanding of how configurational entropy affects ionic conductivity is largely lacking. Herein we investigate a series of multication‐substituted lithium argyrodites with the general formula Li6+x[M1aM2bM3cM4d]S5I, with M being P, Si, Ge, and Sb. Structure‐property relationships related to ion mobility are probed using a combination of diffraction techniques, solid‐state nuclear magnetic resonance spectroscopy, and charge‐transport measurements. We present, to the best of our knowledge, the first experimental evidence of a direct correlation between occupational disorder in the cationic host lattice and lithium transport. By controlling the configurational entropy through compositional design, high bulk ionic conductivities up to 18 mS cm−1 at room temperature are achieved for optimized lithium argyrodites. Our results indicate the possibility of improving ionic conductivity in ceramic ion conductors via entropy engineering, overcoming compositional limitations for the design of advanced electrolytes and opening up new avenues in the field. [ABSTRACT FROM AUTHOR]

Ceramic ion conductors play a pivotal role as electrolytes in solid‐state batteries (SSBs). Aside from the ionic conductivity, their (electro)chemical stability has a profound effect on the performance. Lithium thiophosphates represent a widely used class of superionic materials, yet they suffer from limited stability and are known to undergo interfacial degradation upon battery cycling. Knowledge of composition‐dependent properties is essential to improving upon the stability of thiophosphate solid electrolytes (SEs). In recent years, compositionally complex (multicomponent) and high‐entropy lithium argyrodite SEs have been reported, having room‐temperature ionic conductivities of σion>10 mS cm−1. In this work, various multi‐cationic and ‐anionic substituted argyrodite SEs are electrochemically tested via cyclic voltammetry and impedance spectroscopy, as well as under operating conditions in SSB cells with layered Ni‐rich oxide cathode and indium‐lithium anode. Cation substitution is found to negatively affect the electrochemical stability, while anion substitution (introducing Cl−/Br− and increasing halide content) has a beneficial effect on the cyclability, especially at high current rates. [ABSTRACT FROM AUTHOR]

Lithium‐excess cation‐disordered rocksalt materials are a promising class of transition metal‐based cathodes that exhibit high specific capacity and energy density. The exceptional performance is achieved through participation of anionic redox in addition to cationic redox reactions in the electrochemistry. However, anionic redox reactions accompanied by oxygen evolution, accelerated electrolyte breakdown, and structural evolution lead to voltage hysteresis and low initial Coulombic efficiency. Herein, an Al2O3 layer with varying thickness has been coated onto a high‐entropy disordered rocksalt oxyfluoride cathode through atomic layer deposition to enhance battery performance. The results indicate that the utilization of a uniform Al2O3 coating improves the capacity retention and rate capability of the cathode, with the performance being strongly dependent on the layer thickness. Further investigation into cathode–electrolyte interfacial reactions reveals that the thin protecting Al2O3 coating can reduce the decomposition of electrolyte on the cathode surface but cannot prevent bulk phase degradation during prolonged cycling. These findings highlight the need for optimized coating design on the disordered rocksalt cathode to improve battery performance. [ABSTRACT FROM AUTHOR]

The ability to accommodate multiple principal cations within a single crystallographic structure makes high entropy oxides (HEOs) ideal systems for exploring new composition–property relationships. In this work, the high-entropy design strategy is extended to strained single-crystal HEO-manganite (HEO-Mn) thin films. Phase-pure orthorhombic films of (Gd0.2La0.2Nd0.2Sm0.2Sr0.2)MnO3 were deposited on three different single-crystal substrates: SrTiO3 (STO) (100), NdGaO3 (110), and LaAlO3 (LAO) (100), each inducing different degrees of epitaxial strain. Fully coherent growth of the thin films is observed in all cases, despite the high degree of lattice mismatch between HEO-Mn and LAO. Magnetometry measurements reveal distinct differences in the magnetic properties between epitaxially strained HEO-Mn thin films and their bulk crystalline HEO counterparts. In particular, the bulk polycrystalline HEO-Mn shows two magnetic transitions as opposed to a single one observed in epitaxial thin films. Moreover, the HEO-Mn film deposited on LAO exhibits a significant reduction in the Curie temperature, which is attributed to the strong variation of the in-plane lattice parameter along the thickness of the film and the resulting changes in the Mn–O–Mn bond geometry. Thus, this preliminary study demonstrates the potential of combining high entropy design with strain engineering to tailor the structure and functionality of perovskite manganites. [ABSTRACT FROM AUTHOR]

Single crystal (SC) layered lithium metal oxides (LiNixCoyMnzO2, referred to as NCMs or NMCs) represent a new material design with unique benefits compared to their polycrystalline counterparts. However, preparation of SC-NCMs remains challenging, with methods such as molten salt synthesis being largely dependent on recipe-by-recipe reporting and no overarching conception of how to prepare desirable materials. For a model NCM, LiNiO2 (LNO), we use experimental design methodology to identify how the factors of salt selection, salt mixtures, and molar salt ratio affect the critical features of grain size, crystal defect content (), and particle size distribution. Herein, we identify that NaCl and KCl are salts which can be used to control particle size at relatively low defect content, while sulfate-containing salts are deleterious to quality LNO. The results of this work set out to provide a more comprehensive understanding of how others could prepare well-ordered SC-NCMs of specific particle size. [ABSTRACT FROM AUTHOR]

This paper reports the cross-plane thermal conductivity of highly-ordered amorphous and crystalline templated mesoporous titania thin films measured by the 3ω method from 30 to 320 K. Both sol-gel and nanocrystal-based films were synthesized by evaporation-induced self-assembly, with average porosity of 30% and 35%, respectively. The pore diameter ranged from 14 to 25 nm. The size of crystalline domains in polycrystalline mesoporous films was 12 to 13 nm while the nanocrystals in the nanocrystal-based film were 9 nm in diameter. At high temperatures, the thermal conductivity of amorphous dense and mesoporous films showed similar trends with respect to temperature. This was attributed to the fact that the presence of pores had a purely geometrical effect by reducing the cross-sectional area through which heat can diffuse. By contrast, the thermal conductivity of polycrystalline dense and mesoporous films behave differently with temperature due to phonon scattering by pores and crystalline nanosize domains. In addition, at low temperatures, the presence of pores caused the thermal conductivity of mesoporous films to be less temperature dependent than their dense counterparts. Despite its crystallinity, the thermal conductivity of the nanocrystal-based film was about 40% less than that of the polycrystalline mesoporous films. This was mainly attributed to its larger porosity, smaller crystal size, and strong phonon scattering at the poorly interconnected nanocrystal boundaries. These results suggest various ways to control the thermal conductivity of mesoporous materials for various applications.

This paper reports the cross-plane thermal conductivity of amorphous and crystalline mesoporous titania thin films synthesized by evaporation-induced self-assembly. Both sol-gel and nanocrystal-based mesoporous films were investigated, with average porosities of 30% and 35%, respectively. The pore diameter ranged from 7 to 30 nm and film thickness from 60 to 370nm while the average wall thickness varied from 3 to 50 nm. The crystalline domain sizes in sol-gel films varied from 12 to 13 nm while the nanocrystal-based films consisted of monodisperse nanocrystals 9 nm in diameter. The cross-plane thermal conductivity was measured at room temperature using the 3w method. The average thermal conductivity of the amorphous sol-gel mesoporous titania films was 0.37 ± 0.05 W/m.K. It did not show strong dependence on pore diameter, wall thickness, and film thickness for sol-gel amorphous mesoporous titania thinfilms. This result can be attributed to the fact that heat is carried, in the amorphous matrix, by localized non-propagating vibrational modes. The thermal conductivity of crystalline sol-gelmesoporous titania thin films was significantly larger at 1.06 ± 0.04 W/m.K and depended on the organic template used to make the films. The thermal conductivity of nanocrystal-based thin films was 0.48 ± 0.05 W/m.K and significantly lower than that of the crystalline sol-gel mesoporous thin films. This was due to the fact that the nanocrystals were not as well interconnected as the crystalline domains in the crystalline sol-gel films. These results suggest that both connectivity and size of the nanocrys-tals or the crystalline domains can provide control over thermal conductivity in addition to porosity.