Search

A first composite material containing uniformly dispersed disaggregated detonation nanocrystalline diamonds (DNDs) in SiO2 aerogel matrix was prepared. The synthetic protocol included hydrolysis of tetramethyl orthosilicate (Si(OMe)4, TMOS) by hydrosol of surface carboxylated DNDs with a typical size of 4–5 nm with DMSO serving as a cosolvent and a stabilizer of DND single crystals. Composite samples containing DNDs in silica aerogel matrix in concentration 1.0, 0.1 and 0.01 % w/w were prepared at ambient temperature. HRTEM data revealed that DNDs nanocrystals were uniformly distributed in aerogel and did not form aggregates. Textural and optical composites' properties were determined. [ABSTRACT FROM AUTHOR]

Superionic sulfide solid electrolytes (SEs) are of considerable interest for application in solid‐state batteries, but suffer from limited stability. When in combination with state‐of‐the‐art cathode active materials (CAMs), severe degradation at the CAM/SE interface occurs during electrochemical cycling. To improve upon the interfacial stability, inert coatings can be applied to the CAM particles, with the goal of preventing direct contact to the SE. In this study, different methods of depositing coatings, including hexagonal boron nitride, tungsten sulfide and exfoliated ((CH3(CH2)3)4N)4Nb6O17, in the form of nanosheets onto the free surface of a Ni‐rich LiNixCoyMnzO2 (NCM) CAM are examined and compared with one another. While dry coating is shown to produce relatively uniform coatings (good surface coverage), the secondary particle morphology of the NCM makes ball milling as a mechanical deposition method less attractive. In contrast, deposition from dispersions in organic solvents yields protective coatings with a lower degree of surface coverage. The different materials are electrochemically tested in liquid‐ and solid‐electrolyte‐based lithium‐ion batteries. A stabilizing effect from nanosheet coating is only observed for the cells with lithium thiophosphate SE. [ABSTRACT FROM AUTHOR]

Silicon (Si) is anticipated to become one of the most promising anode materials for high‐energy‐density solid‐state battery (SSB) applications owing to its high theoretical specific capacity and low working potential. This work compares the electrochemical behavior of slurry‐cast electrodes in Si|Li6PS5Cl|In/InLi cells, with micron‐sized Si particles (≥99% active electrode material content) and polyacrylic acid (PAA) or polyvinylidene fluoride (PVDF) serving as active material and aqueous/nonaqueous model binder, respectively. The cycling stability of Si‐PVDF cells is found to decrease with increasing binder content (accelerated capacity fade), whereas the Si‐PAA cells show more or less the opposite trend. However, they exhibit a similar performance when using 0.5 wt% binder, with specific capacities of ≈850 mAh g−1 (for −0.51–0.11 V vs In/InLi) and high capacity retention depending on the cutoff potentials. This result suggests that PVDF can be substituted for by PAA in Si anodes for SSBs, thereby potentially decreasing cost and environmental impact. [ABSTRACT FROM AUTHOR]

Lithium-thiophosphate-based all-solid-state batteries (ASSBs) are increasingly attracting attention for high-density electrochemical energy storage. In this work, the cycling performance of single and polycrystalline forms of LiNixCoyMnzO2 (NCM, with =83% Ni content) cathode active materials in ASSB cells with an Li4Ti5O12 composite anode is explored, and the advantages and disadvantages of both morphologies are discussed. The virtual lack of grain boundaries in the quasi-single-crystalline material is found to contribute to improved stability by eliminating the tendency of Ni-rich NCM particles to crack during cycling, due to volume differences between the lithiated and delithiated phases. Although the higher crack resistance mitigates effects of chemical oxidation of the lithium thiophosphate solid electrolyte, the cells suffer from electrochemical side reactions occurring at the cathode interfaces. However, coating the single-crystal particles with a protective LiNbO3 overlayer helps to stabilize the interface between cathode active material and solid electrolyte, leading to a capacity retention of 93% after 200 cycles (with qdis? 160 mAh gNCM -1 or1.7 mAh cm-2 at C/5 rate and 45 °C). Overall, this work highlights the importance of addressing electro-chemo-mechanical phenomena in ASSB electrodes. [ABSTRACT FROM AUTHOR]

Permanent magnets based on neodymium‐iron‐boron (Nd‐Fe‐B) alloys provide the highest performance and energy density, finding usage in many high‐tech applications. Their magnetic performance relies on the intrinsic properties of the hard‐magnetic Nd2Fe14B phase combined with control over the microstructure during production. In this study, a novel magnetic hardening mechanism is described in such materials based on a solid‐state phase transformation. Using modified Nd‐Fe‐B alloys of the type Nd16Febal‐x‐y‐zCoxMoyCuzB7 for the first time it is revealed how the microstructural transformation from the metastable Nd2Fe17Bx phase to the hard‐magnetic Nd2Fe14B phase can be thermally controlled, leading to an astonishing increase in coercivity from ≈200 kAm−1 to almost 700 kAm−1. Furthermore, after thermally treating a quenched sample of Nd16Fe56Co20Mo2Cu2B7, the presence of Mo leads to the formation of fine FeMo2B2 precipitates, in the range from micrometers down to a few nanometers. These precipitates are responsible for the refinement of the Nd2Fe14B grains and so for the high coercivity. This mechanism can be incorporated into existing manufacturing processes and can prove to be applicable to novel fabrication routes for Nd‐Fe‐B magnets, such as additive manufacturing. [ABSTRACT FROM AUTHOR]

Improving the interfacial stability between cathode active material (CAM) and solid electrolyte (SE) is a vital step toward the development of high‐performance solid‐state batteries (SSBs). One of the challenges plaguing this field is an economical and scalable approach to fabricate high‐quality protective coatings on the CAM particles. A new wet‐coating strategy based on preformed nanoparticles is presented herein. Nonagglomerated nanoparticles of the coating material (≤5 nm, exemplified for ZrO2) are prepared by solvothermal synthesis, and after surface functionalization, applied to a layered Ni‐rich oxide CAM, LiNi0.85Co0.10Mn0.05O2 (NCM85), producing a uniform surface layer with a unique structure. Remarkably, when used in pelletized SSBs with argyrodite Li6PS5Cl as SE, the coated NCM85 is found to exhibit superior lithium‐storage properties (qdis ≈ 204 mAh gNCM85−1 at 0.1 C rate and 45 °C) and good rate capability. The key to the observed improvement lies in the homogeneity of coating, suppressing interfacial side reactions while simultaneously limiting gas evolution during operation. Moreover, this strategy is proven to have a similar effect in liquid electrolyte‐based Li‐ion batteries and can potentially be used for the application of other, even more favorable, nanoparticle coatings. [ABSTRACT FROM AUTHOR]

The energy density of layered oxide cathode materials increases with their Ni content, while the stability decreases and degradation becomes more severe. A common strategy to mitigate or prevent degradation is the application of protective coatings on the particle surfaces. In this article, a room‐temperature, liquid‐phase reaction of trimethylaluminum (TMA) and tetraethyl orthosilicate (TEOS) with adsorbed moisture on either LiNi0.85Co0.10Mn0.05O2 or LiNiO2, yielding a hybrid coating that shows synergetic benefits compared to coatings from TMA and TEOS individually, is reported. The surface layer is investigated in long‐term pouch full‐cell studies as well as by electron microscopy, X‐ray photoelectron spectroscopy, and differential electrochemical mass spectrometry, demonstrating that it prevents degradation primarily by a fluorine‐scavenging effect, and by reducing the extent of rock salt‐type phase formation. [ABSTRACT FROM AUTHOR]

As‐cast aluminum–magnesium alloys with 3, 5, and 10 wt% Mg are subjected to high‐pressure torsion (HPT) at room temperature: 5 GPa, five turns with rotation speed of 1 rpm. HPT leads to the strong grain refinement for both (Al) solid solution and intermetallic β‐phase. Transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and X‐ray diffraction (XRD) are used to characterize the phase transitions under heating of the HPT‐treated alloys. The decomposition of the solid solution in the ultrafine‐grained Al–10 wt% Mg alloy obtained by HPT does not follow the equilibrium diagram. The results of DSC, XRD, and TEM show that the Mg‐rich intermetallic phases appear during heating in the following sequence: GP zones → β → ε → β → γ → β. The (Al)/(Al) grain boundaries (GBs) in the fine‐grained Al–10 wt% Mg alloy after HPT and annealing up to 400 °C (i.e., in the solid solution area, far from solvus and solidus lines) contain the Mg‐rich areas. This can be the result of possible GB phase transitions with the formation of Mg‐rich GB phases. The GBs in the binary AlMg can contain the thin layers of a GB phase far away from the solvus line. [ABSTRACT FROM AUTHOR]

Herein, a study on radiation‐induced defect structures in a reactor Fe–14Cr–1W (wt%) steel with grain sizes of 5 μm and 110 nm is presented. Self‐ion irradiation of the steel in both states is conducted with a damage dose of 10 dpa. Microstructure characterization shows that the density of intragranular radiation‐induced dislocations is significantly lower in case of the nanostructured material. From the results obtained, it follows that microstructure refinement to a grain size of about 100 nm can be effectively used to approach a problem of higher defect production rate in Fe–Cr steels driven by irradiation and to produce alloys with significantly enhanced mechanical performance as well as radiation tolerance. [ABSTRACT FROM AUTHOR]

The Ti-Fe alloys are quite important among various Ti-based alloys doped with b-stabilisers. Severe plastic deformation by the high pressure torsion (HPT) leads to the strong grain refinement in Ti-Fe alloys. The high-pressure vTi-phase appears during HPTof the Ti-1 wt.% Fe alloy. However, the vTi does not appear after uniaxial compression at the same pressure, without torsion. vTi remains quenched after pressure release and disappears by heating around 140-150 °C. However, the further alloying with iron suppresses the formation of wTi-phase. As a result, wTi does not appear after HPTin the Ti-10 wt.% Fe alloy. [ABSTRACT FROM AUTHOR]

Bulk nanocrystalline ferrite with a grain size below 20 nm is stabilized thanks to grain boundary segregations of carbon atoms. This structure has been obtained through severe plastic deformation of a carbon steel containing only 0.45 wt% carbon with a bainitic microstructure. Both the mean grain size and resulting strength are similar to these obtained in pearlitic steels containing twice as much carbon and deformed in the same conditions. This indicates that very high strength can be achieved in nanocrystalline steels with much lesser carbon content. In this work, the authors using high pressure torsion demonstrated that grain size below 20 nm can be stabilized in a medium carbon C45 steel thanks to grain boundary segregations of carbon atoms. Both the mean grain size and resulting strength are similar to these obtained in pearlitic steels containing twice as much carbon and deformed in the same conditions. [ABSTRACT FROM AUTHOR]