Amorphous-Si@SiOx/C composites with amorphous Si particles as core and coated with a double layer of SiOx and carbon are prepared by ball-milling crystal micron-sized silicon powders and ...carbonization of the citric acid intruded in the ball-milled Si. Different ratios of Si to citric acid are used in order to optimize the electrochemical performance. It is found that SiOx exists naturally at the surfaces of raw Si particles and its content increases to ca. 24 wt.% after ball-milling. With an optimized Si to citric acid weight ratio of 1/2.5, corresponding to 8.4 wt.% C in the composite, a thin carbon layer is coated on the surfaces of a-Si@SiOx particles, moreover, floc-like carbon also forms and connects the carbon coated a-Si@SiOx particles. The composite provides a capacity of 1450 mA h g−1 after 100 cycles at a current density of 100 mA g1, and a capacity of 1230 mA h g−1 after 100 cycles at 500 mA g1 as anode material for lithium-ion batteries. Effects of ball-milling and the addition of citric acid on the microstructure and electrochemical properties of the composites are revealed and the mechanism of the improvement in electrochemical properties is discussed.
•Amorphous Si (a-Si) powder with SiOx surface layer introduced is prepared by ball-milling.•Carbon coating and floc-like carbon are introduced in situ in the a-Si@SiOx particles.•The a-Si@SiOx/C composite with 8 wt.% C provides superior electrochemical performance.•The method is facile in large-scale production of Si-based anode material for LIBs.
The superior catalytic effects derived from a 2D Ti3C2 (MXene), synthesized by the exfoliation of Ti3AlC2 powders, towards the hydrogen storage reaction of MgH2 were demonstrated. The 5 wt% ...Ti3C2-containing MgH2 releases 6.2 wt% H2 within 1 min at 300 °C and absorbs 6.1 wt% H2 within 30 s at 150 °C, exhibiting excellent dehydrogenation/hydrogenation kinetics.
•Progress in lithium alloys and metal oxides as anode materials for lithium-ion batteries is reviewed.•Electrochemical characteristics and lithium storage mechanisms of lithium alloys and metal ...oxides are summarized.•Strategies for improving electrochemical lithium storage properties of lithium alloys and metal oxides are discussed.•Challenges in developing lithium alloys and metal oxides as commercial anodes for lithium-ion batteries are pointed out.
Lithium alloys and metal oxides have been widely recognized as the next-generation anode materials for lithium-ion batteries with high energy density and high power density. A variety of lithium alloys and metal oxides have been explored as alternatives to the commercial carbonaceous anodes. The electrochemical characteristics of silicon, tin, tin oxide, iron oxides, cobalt oxides, copper oxides, and so on are systematically summarized. In this review, it is not the scope to retrace the overall studies, but rather to highlight the electrochemical performances, the lithium storage mechanism and the strategies in improving the electrochemical properties of lithium alloys and metal oxides. The challenges and new directions in developing lithium alloys and metal oxides as commercial anodes for the next-generation lithium-ion batteries are also discussed.
The design of metal oxide catalysts predominantly focuses on the composition or geometry engineering to enable optimized reactivity on the surface. Despite the numerous reports investigating the ...surface chemisorption of organic molecules on metal oxides, insights into how adsorption of organic modifiers can be exploited to optimize the catalytic properties of metal oxides are lacking. Herein, we describe the use of enolic acetylacetones to modify the surface Lewis acid properties of manganese oxide catalysts. The acetylacetone modification is stable under the reaction conditions and strongly influences the redox-acid cooperative catalysis of manganese oxides. This enables a rational control of the oxidation selectivity of structurally diverse arylmethyl amines to become switchable from nitriles to imines.
Critical limitations in applying MgH
2
as a hydrogen-storage medium include the high H
2
desorption temperature and slow reaction kinetics. In this study, we synthesized hierarchical porous TiNb
2
O
...7
spheres in micrometer scale built with 20–50 nm nanospheres, which showed stable activity to catalyze hydrogen storage in MgH
2
as precursors. The addition of 7 wt.% TiNb
2
O
7
in MgH
2
reduced the dehydrogenation onset temperature from 300 to 177 °C. At 250 °C, approximately 5.5 wt.% H
2
was rapidly released in 10 min. Hydrogen uptake was detected even at room temperature under 50 bar hydrogen; 4.5 wt.% H
2
was absorbed in 3 min at 150 °C, exhibiting a superior low-temperature hydrogenation performance. Moreover, nearly constant capacity was observed from the second cycle onward, demonstrating stable cyclability. During the ball milling and initial de/hydrogenation process, the high-valent Ti and Nb of TiNb
2
O
7
were reduced to the lower-valent species or even zero-valent metal, which
in situ
created multivalent multielement catalytic surroundings. A strong synergistic effect was obtained for hybrid oxides of Nb and Ti by density functional theory (DFT) calculations, which largely weakens the Mg-H bonding and results in a large reduction in kinetic barriers for hydrogen storage reactions of MgH
2
. Our findings may guide the further design and development of high-performance complex catalysts for the reversible hydrogen storage of hydrides.
•Mesohollow and microporous carbon fibers were prepared via electrospinning and carbonization.•Sulfur (S) incorporated into the porous fibers by thermal heating in 60wt.%, forming composite.•S fills ...fully in the micropores and partially in the mesohollows of the carbon fibers.•The composite shows high capacity and capacity retention as cathode material for Li–S batteries.•Mesohollow and microporous structure is effective in improving the property of S cathode.
Mesohollow and microporous carbon nanofibers (MhMpCFs) were prepared by a coaxial electrospinning with polyacrylonitrile (PAN) and polymethylmethacrylate (PMMA) as outer and inner spinning solutions followed by a carbonization. The carbon fibers were thermal treated with sublimed sulfur to form S/MhMpCFs composite, which was used as cathode material for lithium–sulfur batteries. Electrochemical study shows that the S/MhMpCFs cathode material provides a maximum capacity of 815mAh/g after several cycles of activation, and the capacity retains 715mAh/g after 70cycles, corresponding to a retention of 88%. The electrochemical property of the S/MhMpCFs composite is much superior than the S-incorporated solid carbon fibers prepared from electrospinning of single PAN. The mechanism of the enhanced electrochemical property of the S/MhMpCFs composite is discussed.
▶ State-of-the-art of new R-Mg-Ni-based hydrogen storage electrode alloys is reviewed. ▶ Electrode performances of the R-Mg-Ni-based alloys depend strongly on the stoichiometric ratio, alloy ...components and microstructure. ▶ Optimized alloy compositions contain mainly metallic elements of La, Mg, Ni, Co, Mn and Al. ▶ Pulverization of particles and oxidation/corrosion of active components are responsible for the fast capacity degradation. ▶ Low-Co or Co-free R-Mg-Ni-based electrode alloys should be developed.
This review is devoted to new rare earth–Mg–Ni-based (R–Mg–Ni-based) hydrogen storage alloys that have been developed over the last decade as the most promising next generation negative electrode materials for high energy and high power Ni/MH batteries. Preparation techniques, structural characteristics, gas–solid reactions and electrochemical performances of this system alloy are systematically summarized and discussed. The improvement in electrochemical properties and their degradation mechanisms are covered in detail. Optimized alloy compositions with high discharge capacities, good electrochemical kinetics and reasonable cycle lives are described as well. For their practical applications in Ni/MH batteries, however, it is essential to develop an industrial-scale homogeneous preparation technique, and a low-cost R–Mg–Ni-based electrode alloy (low-Co or Co-free) with high discharge capacity, long cycle life and good kinetics.
Conduction with fast Li ion conductivity at room temperature is a major challenge for the development of all solid-state Li-ion batteries. Herein, we demonstrate a novel room-temperature ultrafast ...Li-ion conductor, lithium borohydride ammonia borane complexes ((LiBH4) x ·AB). The incorporation of AB into the LiBH4 structure intrinsically increases the cell volume and decreases the volume density of Li ion, which substantially facilitates the Li-ion conduction. The LiBH4·AB complex delivers up to 4.04 × 10–4 S cm–1 of ion conductivity at 25 °C with nearly negligible electron conductivity. The Li-ion transference number is higher than 0.999 at 40 °C. The room-temperature Li-ion conductivity obtained is largely superior to other LiBH4-based solid-state electrolytes reported previously under identical conditions. Moreover, the ultrafast Li-ion conduction remains stable upon heating and cooling cycling (18–55 °C). Ab initio molecular dynamics simulations display a kind of 1D Li diffusion channel along the b direction in the LiBH4·AB structure, which offers a much lower activation energy barrier (0.12 eV), consequently enabling superior Li-ion conductivity at room temperature.
Herein, we demonstrate the successful preparation of a novel complex transition metal oxide (TiVO3.5) by oxidizing a solid-solution MXene (Ti0.5V0.5)3C2 at 300 °C and its high activity as a catalyst ...precursor in the hydrogen storage reaction of MgH2. The prepared TiVO3.5 inherits the layered morphology of its MXene precursor, but the layer surface becomes very coarse because of the presence of numerous nanoparticles. Adding a minor amount of TiVO3.5 remarkably reduces the dehydrogenation and hydrogenation temperatures of MgH2 and enhances the reaction kinetics. The 10 wt% TiVO3.5-containing sample exhibits optimal hydrogen storage properties, as it desorbs approximately 5.0 wt% H2 in 10 min at 250 °C and re-absorbs 3.9 wt% H2 in 5 s at 100 °C and under 50 bar of hydrogen pressure. The apparent activation energy is calculated to be approximately 62.4 kJ/mol for the MgH2-10 wt% TiVO3.5 sample, representing a 59% reduction in comparison with pristine MgH2 (153.8 kJ/mol), which reasonably explains the remarkably reduced dehydrogenation operating temperature. Metallic Ti and V are detected after ball milling with MgH2; they are uniformly dispersed on the MgH2 matrix and act as actual catalytic species for the improvement of the hydrogen storage properties of MgH2.
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•A complex oxide TiVO3.5 is synthesized for catalyzing hydrogen release from MgH2.•The Ti3+ and V4+ in TiVO3.5 are reduced to the zero-valence state after milling.•The MgH2-10 wt% TiVO3.5 sample exhibits improved hydrogen storage properties.•The presence of TiVO3.5 reduces the dehydrogenation onset temperature by 70 °C.•The dehydrogenated MgH2-10 wt% TiVO3.5 sample absorbs 3.9 wt% H2 in 5 s at 100 °C.
Poor reversibility and high desorption temperature restricts the practical use of lithium borohydride (LiBH4) as an advanced hydrogen store. Herein, a LiBH4 composite confined in unique ...double‐layered carbon nanobowls prepared by a facile melt infiltration process is demonstrated, thanks to powerful capillary effect under 100 bar of H2 pressure. The gradual formation of double‐layered carbon nanobowls is witnessed by transmission electron microscopy (TEM) observation. Benefiting from the nanoconfinement effect and catalytic function of carbon, this composite releases hydrogen from 225 °C and peaks at 353 °C, with a hydrogen release amount up to 10.9 wt%. The peak temperature of dehydriding is lowered by 112 °C compared with bulk LiBH4. More importantly, the composite readily desorbs and absorbs ≈8.5 wt% of H2 at 300 °C and 100 bar H2, showing a significant reversibility of hydrogen storage. Such a high reversible capacity has not ever been observed under the identical conditions. The usable volumetric energy density reaches as high as 82.4 g L−1 with considerable dehydriding kinetics. The findings provide insights in the design and development of nanosized complex hydrides for on‐board applications.
A double‐layered carbon nanobowl‐confined LiBH4 composite is prepared by a facile melt infiltration process. The composite readily desorbs and absorbs ≈8.5 wt% of H2 at 300 °C and 100 bar of hydrogen pressure. The practical volumetric energy density reaches as high as 82.4 g L−1 with considerable dehydriding kinetics after cold pressing to form a pellet.
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