Here,
as with previous work, atomic layer deposition (ALD) has been used
to deposit Al2O3 on positive electrode active
materials, LiCoO2, to create a protective barrier layer,
suppress the high potential phase transition, and thus reduce the
subsequent Co dissolution. However, in this study it was found that
it also resulted in the reduction of the charge transfer resistance
at the positive electrode–electrolyte interface, thus enhancing
the performance of the battery. Energy-dispersive X-ray spectroscopy,
in conjunction with transmission electron microscopy, shows that a
discrete Al2O3 shell was not formed under the
selected growth conditions and that the Al diffused into the bulk
LiCoO2. The resulting active oxide material, which was
significantly thicker than the nominally ALD growth rate would predict,
is proposed to be of the form LiCoO2:Al with amorphous
and crystalline regions depending on the Al content. The cells consisting
of the modified electrodes were found to have good cycling stability
and discharge capacities of ∼110 mA h g–1 (0.12 mA h cm–2) and ∼35 mA h g–1 (0.04 mA h cm–2) at 50 and 100 C, respectively.
Metal organic decomposition (MOD) using octylic acid salts was applied to synthesize a BaTiO3–LiCoO2 (BT–LC) composite powder. The Ba and Ti octylates were utilized as metal precursors, in an attempt to synthesize homogeneous BT nanoparticles on the LC matrix. The BT–LC composite, having a phase-separated composite structure without any impurity phase, was successfully obtained by optimizing the MOD procedure. The composite prepared using octylate precursors exhibited a sharper distribution and better dispersibility of decorated BT particles. Additionally, the average particle size of the decorated BTs using metal octylate was reduced to 23.3 nm, compared to 44.4 nm from conventional processes using Ba acetate as well as Ti alkoxide as precursors. The composite cathode displayed better cell performance than its conventional counterpart; the discharge capacity of the metal octylate-derived specimen was 55.6 mAh/g at a 50C rate, corresponding to 173% of the capacity of the conventional specimen (32.2 mAh/g). The notable improvement in high rate capability obtained in this study, compared with the conventional route, was attributed to the higher density of the triple junction formed by the BT–LC–electrolyte interface.
Cobalt blue is one of the most chemically and thermally stable blue pigments. However, cobalt is scarce and expensive. To minimize the use of cobalt and reduce production costs and toxicity, cobalt blue core‐shell pigments were synthesized by a solid‐state method, which is cheaper than a liquid‐phase reaction. Small cobalt hydroxide particles and large α‐alumina particles, in various ratios, were used as the starting materials. The dry mixed powders were calcined at 1200°C for 2 hours. Elemental mappings of the surfaces and cross sections of the synthesized particles showed that the cobalt blue had a core‐shell structure. X‐ray diffraction patterns showed that the synthesized cobalt blue consisted of an α‐alumina core and a cobalt aluminate shell. The color tone of the synthesized cobalt blue was evaluated from the lightness (L*) and chroma (C*) values. The color tone of the cobalt blue synthesized in this study was almost same as those of commercially available samples although the cobalt molar fraction was lower than the stoichiometric ratio (Co/(Co + Al) = 0.33, Co/Al = 0.5) which was calculated from the chemical reaction formula.
Heat treatment of metal–organic frameworks (MOFs) has provided a wide variety of functional carbons coordinated with metal compounds. In this study, two kinds of zinc‐based MOF (ZMOF), C16H10O4Zn (ZMOF1) and C8H4O4Zn (ZMOF2), were prepared. ZMOF1 and ZMOF2 were carbonized at 1000 °C, forming CZMOF1 and CZMOF2, respectively. The specific surface area (SBET) of CZMOF2 was ~2700 m2 g−1, much higher than that of CZMOF1 (~1300 m2 g−1). A supercapacitor electrode based on CZMOF2 achieved specific capacitances of 360, 278, and 221 F g−1 at 50, 250, and 1000 mA g−1 in an aqueous electrolyte (H2SO4), respectively, the highest values reported to date for ZMOF‐derived electrodes under identical conditions. The practical applicability of the CZMOF‐based supercapacitor was verified in non‐aqueous electrolytes. The initial capacitance retention was 78% after 100 000 charge/discharge cycles at 10 A g−1. Crucially, the high capacitance of CZMOF2 arises from pore generation during carbonization. Below 1000 °C, pore generation is dominated by the Zn/C ratio of ZMOFs, as carbon atoms reduce the zinc oxides formed during carbonization. Above 1000 °C, a high O/C ratio becomes essential for pore generation because the oxygen functional groups are pyrolyzed. These findings will provide insightful information for other metal‐based MOF‐derived multifunctional carbons.
Drastic enhancement in the high‐rate capability of lithium‐ion batteries to the level of supercapacitors while maintaining high energy density is required for next‐generation power sources. Incorporating dielectric BaTiO3 (BTO)‐based nanocubes (NCs) into the active materials–electrolyte interface provides an ultrafast charge transfer pathway via the dielectric layer. The highly dispersed NC‐decorated LiCoO2 (LCO) treated at the optimized temperature of 600 °C displays significantly enhanced high‐rate capability; the cell maintains 56.7 mAh g‐1 at 50C (1C = 160 mA g‐1), which compares with null capacity at the same rate for bare LCO. Comparing the NCs with conventional sol‐gel‐derived nanoparticles, the capacity retention at 10C (vs 0.1C) steadily increases with increasing active materials–dielectric–electrolyte triple‐phase interface (TPI) in the NC‐decorated case, whereas the capacity retention decreases markedly at similar TPI density in the sol‐gel case. In the sol‐gel case, the amount of Li ions accumulating at the TPI greatly exceeds the maximum amount of Li ions involved in electron exchange through the redox reaction within the charge/discharge time. In the NC case, most Li ions at the TPI participate effectively in the redox reaction, which results in fast charge transfer since the TPI sites are abundantly supplied with Li ions.
Der elektrische Widerstand von 4 Ni‐Co‐Legierungen (5, l0, 25 und 40 At.‐% Co) in H, oder D2 wird unter stationären Bedingungen bei 25°C und Drücken bis zu 28 kbar gemessen.
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