Porous carbon can be tailored to great effect for electrochemical energy storage. In this study, we propose a novel structured spherical carbon with a macrohollow core and a microporous shell derived from a sustainable biomass, amylose, by a multistep pyrolysis route without chemical etching. This hierarchically porous carbon shows a particle distribution of 2–10 μm and a surface area of 672 m2 g–1. The structure is an effective host of sulfur for lithium–sulfur battery cathodes, which reduces the dissolution of polysulfides in the electrolyte and offers high electrical conductivity during discharge/charge cycling. The hierarchically porous carbon can hold 48 wt % sulfur in its porous structure. The S@C hybrid shows an initial capacity of 1490 mAh g–1 and retains a capacity of 798 mAh g–1 after 200 cycles at a discharge/charge rate of 0.1 C. A capacity of 487 mAh g–1 is obtained at a rate of 3 C. Both a one-step pyrolysis and a chemical-reagent-assisted pyrolysis are also assessed to obtain porous carbon from amylose, but the obtained carbon shows structures inferior for sulfur cathodes. The multistep pyrolysis and the resulting hierarchically porous carbon offer an effective approach to the engineering of biomass for energy storage. The micrometer-sized spherical S@C hybrid with different sizes is also favorable for high-tap density and hence the volumetric density of the batteries, opening up a wide scope for practical applications.Keywords: amylose; biomass material; electrochemical performance; lithium−ion batteries; sulfur cathode;

Lithium sulfide, Li2S, is a promising cathode material for lithium–sulfur batteries (LSBs), with a high theoretical capacity of 1166 mA h g−1. However, it suffers from low cycling stability, low-rate capability and high initial activation potential. In addition, commercially available Li2S is of high cost and of large size, over ten microns, which further exacerbate its shortcomings as a sulfur cathode. Exploring new approaches to fabricate small-sized Li2S of low cost and to achieve Li2S cathodes of high electrochemical performance is highly desired. This work reports a novel mechanochemical method for synthesizing Li2S of high purity and submicron size by ball-milling LiH with sulfur in an Ar atmosphere at room temperature. By further milling the as-synthesized Li2S with polyacrylonitrile (PAN) followed by carbonization of PAN at 1000 °C, a Li2S/C hybrid with nano-sized Li2S embedded in a mesoporous carbon matrix is achieved. The hybrid with Li2S as high as 74 wt% shows a high initial capacity of 971 mA h g−1 at 0.1C and retains a capacity of 570 mA h g−1 after 200 cycles as a cathode material for LSBs. A capacity of 610 mA h g−1 is obtained at 1C. The synthesis method of Li2S is facile, environmentally benign, and of high output and low cost. The present work opens a new route for the scalable fabrication of submicron-sized Li2S and for the development of high performance Li2S-based cathodes.

Reticulated mesoporous Fe2O3@C flakes, consisting of nanocrystalline α-Fe2O3 encased within a thin carbon skeleton, were synthesized using ferrocene as iron and carbon sources and a novel reaction agent of ammonium sulphate via a facile two-step heating route. Those flakes, which were several nanometers thick and 1–2 μm in diameter, showed high capacity, excellent cyclic stability and rate capability as an anode material for lithium-ion batteries (LIBs). An initial reversible capacity of 910 mA h g−1 at a discharge/charge current of 0.1 A g−1 was obtained, and the capacity showed a gradual increase during cycling, reaching a high capacity of 1080 mA h g−1 after 120 cycles. An in situ lithiation study by transmission electron microscopy showed that the reticulated mesopores and the ultrathin feature of the Fe2O3@C flakes can largely accommodate the mechanical stresses and volume expansion of Fe2O3 during lithiation and hence maintain their integrity and provide excellent properties. The thin carbon skeleton not only facilitates the electronic conduction, but also inhibits the aggregation of nanocrystalline Fe2O3 flakes. The facile fabrication method and the unique structure of the mesoporous Fe2O3@C flakes offer high performance for LIB anodes and great potential for other applications of Fe2O3.

•Carbon coated Fe3O4 is prepared by chemical vapor deposition from nano-Fe2O3.•High concentration of acetylene is used as the vapor for the chemical deposition.•Nano-Fe2O3 is reduced to Fe3O4 and recrystallizes to octahedra during deposition.•The composite comprises bi-morphological submicro-octahedra and nanospheres.•The carbon coated Fe3O4 anode material shows superior cycling stability.Carbon coated Fe3O4 composite (Fe3O4@C) with bi-morphological architecture has been prepared via a chemical vapor deposition at 450 °C from Fe2O3 nanoparticles by using acetylene as the deposition vapor and carbon source. The Fe2O3 are fully reduced to Fe3O4 in a 10 min of deposition, showing submicron-sized octahedral Fe3O4 particles coated partially with a thin carbon layer mainly, and a few nano-sized Fe3O4 particles coated with carbon also. The deposition period of 20 min results in a further growth of the octahedral Fe3O4 particles and a reduction of the number of the nano-sized ones, correlating to a thick and fully coated carbon layer. Impurities of iron carbides generate in the composite with further prolonging the deposition to 30 min. The Fe3O4@C composite from 20 min of deposition shows superior electrochemical property to others. An initial reversible capacity of 570 mAh g−1 is obtained and the capacity fading is less than 5% after 60 cycles. The fabrication method is facile and time-saving. Such submicron size-predominated Fe3O4@C composite is hopefully not only favorable in alleviating the agglomeration of the iron oxide during cycling, but also helpful in getting high packing density of the anode material.

Soluble inverse-vulcanized hyperbranched polymers (SIVHPs) were synthesized via thiol–ene addition of polymeric sulfur (S8) radicals to 1,3-diisopropenylbenzene (DIB). Benefiting from their branched molecular architecture, SIVHPs presented excellent solubility in polar organic solvents with an ultrahigh concentration of 400 mg mL−1. After end-capping by sequential click chemistry of thiol–ene and Menschutkin quaternization reactions, we obtained water soluble SIVHPs for the first time. The sulfur-rich SIVHPs were employed as solution processible cathode-active materials for Li–S batteries, by facile fluid infiltration into conductive frameworks of graphene-based ultralight aerogels (GUAs). The SIVHPs-based cells showed high initial specific capacities of 1247.6 mA h g−1 with 400 charge–discharge cycles. The cells also demonstrated an excellent rate capability and a considerable depression of shuttle effect with stable coulombic efficiency of around 100%. The electrochemical performance of SIVHP in Li–S batteries overwhelmed the case of neat sulfur, due to the chemical fixation of sulfur. The combination of high solubility, structure flexibility, and superior electrochemical performance opens a door for the promising application of SIVHPs.

•Improved hydrogen storage property is obtained for a combined Ca(BH4)2+LiBH4.•Particulate LaMg3 alloy is added to the system assisted with a ball milling in H2.•LaMg3 is hydrogenated to low crystalline MgH2 and amorphous La-containing hydride.•The system possesses 70% of its first hydrogen desorption capacity after 5 cycles.A combined Ca(BH4)2+LiBH4 system with improved hydrogen storage properties is obtained by the addition of a particulate LaMg3 alloy assisted with ball milling in a H2 atmosphere. It is found that LaMg3 is mostly hydrogenated to symbiotic low crystalline MgH2 and amorphous La-containing hydride of fine particles after the milling, which are homogenously embedded in the Ca(BH4)2+LiBH4 matrix. The multi-hydride system shows significant improvements in both hydrogen storage thermodynamics and kinetics. Particularly, the system with LaMg3 addition in a molar ratio of 0.3 shows an overall superior hydrogen storage property. The main dehydrogenation starts from ca. 200 °C, which is 100 °C lower than the main dehydrogenation temperature of the pristine Ca(BH4)2+LiBH4 system. Re-hydrogenation initiates at a low temperature of ca. 150 °C, and the system maintains 70% of its first hydrogen desorption capacity after 5 cycles. The mechanism of the improved hydrogen storage properties of the combined system 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.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.

A porous Ca(BH4)2-based hydride, CaB2H7, with nano-TiO2 introduced in situ, was successfully synthesized via mixing Ca(BH4)2 with Ti(OEt)4 followed by heat treatment. The effects of the porous structure and introduction of TiO2 on both the non-isothermal and isothermal hydrogen desorption–absorption properties of the porous system were systematically investigated. The results show significant improvements on both the kinetics and thermodynamics of hydrogen desorption–absorption of the porous CaB2H7–0.1TiO2 system, compared with the dense Ca(BH4)2. The desorption peak temperature is reduced by more than 50 °C and sorption capacity of ca. 5 wt% H2 is rapidly achieved below 300 °C. The porous structure was retained in the dehydrogenated products, and rapid hydrogen absorption, approximately 80% of the desorption capacity, is obtained upon heating the product, post-dehydrogenated at 300 °C for 1 h, to 350 °C at 90 bar H2. External addition of nano-TiO2 also enhances the hydrogen storage properties of Ca(BH4)2, but to a lesser extent, compared with the synergetic effect of the porous structure and the in situ formed nano-TiO2. In addition, desorption–absorption mechanisms of the porous CaB2H7–0.1TiO2 system are also proposed.

•Fe3O4/C composites are synthesized from Fe2O3/acetylene black by carbothermal reduction.•Fe3O4 particles inherit the nano-size feature of Fe2O3 and are well dispersed in the composite.•Fe3O4/C composites with sufficient carbon provide superior electrochemical performance.•The method is facile in large-scale production of anode material for lithium-ion batteries.Fe3O4/C composites are synthesized by ball milling nano-sized Fe2O3 powder with acetylene black (AB) in different ratios followed by a carbothermal reduction at 600 °C for 6 h. Structural evolution of the Fe2O3/AB mixtures during the carbothermal reduction and the electrochemical properties of the Fe3O4/C composites as anode materials for lithium-ion batteries are investigated. The results show that Fe2O3 has been fully reduced to Fe3O4 during the reduction. The Fe3O4 particles inherit the nano-size feature of Fe2O3 and are well dispersed in the composites. The composites with 60 and 70 wt.%AB additions possess a close capacity of ca. 430 mAh g−1 after 100 cycles, showing retentions of 85% and 95%, respectively. The Fe3O4/C composites converted from Fe2O3/AB mixtures show better electrochemical performance than the mixtures. The favorable electrochemical performance of the Fe3O4/C composites is mainly attributed to the homogeneous distribution of the Fe3O4 nanoparticles in the carbon matrix and the comparatively high electronic conductivity of Fe3O4. The synthesis method is suggested to be facile in large-scale production of superior anode materials for lithium-ion batteries.

Carbon coating and nano-scale particle size are two impactful factors in improving the rate capability of LiFePO4 cathode materials for lithium-ion batteries. However, both factors decrease the tap density of the materials and are possibly causing unfavorable effect on the volumetric capacity of the cathode materials and thus the batteries, which is undesirable in commercial application. In the present study, LiFePO4 materials with moderate particle size of sub-micron and trace carbon content (0.5–0.9 wt.%) are synthesized by a mechanical activation method. High-electronic conductivity iron phosphides (Fe2P/FeP) are in situ introduced into the LiFePO4 materials and the amount is modified by the calcination temperature. Electrochemical testing shows that Fe2P/FeP plays an important role in improving the high-rate capability of LiFePO4 with moderate particle size. The product calcined at 700 °C, which has a high-tap density of 1.37 g cm−3 correlating to a specific surface area approximately of 4 m2 g−1, possesses discharge capacities of 110 and 100 mAh g−1 at discharge rates of 5 C and 10 C, respectively. The introduction of Fe2P/FeP in an amount of ca. 5 wt.% rather than carbon coating and the moderate particle size of LiFePO4 are promising approaches to obtain LiFePO4 cathode material of high-rate capability without unduly compromising its volumetric capacity.Highlights► High-electronic conductivity iron phosphides (Fe2P/FeP) are in situ introduced into the LiFePO4 materials with particle size of sub-micron and trace carbon. ► The sub-micron size of the particles and trace carbon result in a high-tap density (1.37 g cm−3) for the LiFePO4 material. ► Fe2P/FeP plays an important role in improving the high-rate capability of the LiFePO4 material. ► The LiFePO4 material provides promising high-rate capability without unduly compromising its volumetric energy density.

A two-step ball-milling method has been provided to synthesize Mg(BH4)2 using NaBH4 and MgCl2 as starting materials. The method offers high yield and high purity (96%) of the compound. The as-synthesized Mg(BH4)2 is then combined with LiAlH4 by ball-milling in order to form new multi-hydride systems with high hydrogen storage properties. The structure, the dehydrogenation and the reversibility of the combined systems are studied. Analyses show that a metathesis reaction takes place between Mg(BH4)2 and LiAlH4 during milling, forming Mg(AlH4)2 and LiBH4. Mg(BH4)2 is excessive and remains in the ball-milled product when the molar ratio of Mg(BH4)2 to LiAlH4 is over 0.5. The onset dehydrogenation temperature of the combined systems is lowered to ca. 120 °C, which is much lower than that of either Mg(BH4)2 or LiAlH4. The dehydrogenation capacities of the combined systems below 300 °C are all higher than that of both Mg(BH4)2 and LiAlH4. The combined systems are reversible for hydrogen storage at moderate hydrogenation condition, and rapid hydrogenation occurred within the initial 30 min. Moreover, the remained Mg(BH4)2 in the combined systems is found also partially reversible. The mechanism of the enhancement of the hydrogen storage properties and the dehydrogenation/hydrogenation process of the combined systems were discussed.Highlights► A high yield method to synthesize Mg(BH4)2 with high purity is provided. ► Mg(BH4)2 is combined with LiAlH4 by ball-milling, forming new systems. ► The combined systems show lowered dehydrogenation temperature. ► The combined systems show partial reversibility of hydrogen storage. ► The dehydrogenation and hydrogenation process of the combined systems is studied.

A high-strength SiC composite with SiC whiskers (SiCw) as reinforcement has been fabricated by liquid silicon infiltration (LSI) using pyrolyzed rice husks (RHs) as raw material. RHs were coked and pyrolyzed subsequently at high temperature to obtain a mixture containing SiC whiskers, particles, and amorphous carbon. The pyrolyzed RHs were then milled and modeled to preforms, which were then used to fabricate biomorphic SiCw/SiC–Si composites by liquid silicon infiltration at 1,450, 1,550, and 1,600 °C, respectively. Dense composite with a density of 3.0 g cm−3 was obtained at the infiltration temperature of 1,550 °C, which possesses superior mechanical properties compared with commercial reaction-sintered SiC (RS-SiC). The Vickers hardness, flexure strength, elastic modulus, and fracture toughness of the biomorphic SiCw/SiC–Si composite were 18.8 ± 0.6 GPa, 354 ± 2 GPa, 450 ± 40 MPa, and 3.5 ± 0.3 MPa m1/2, respectively. Whereas the composites obtained at the other two infiltration temperatures contain unreacted carbon and show lower mechanical properties. The high flexure strength of the biomorphic composite infiltrated at 1,550 °C is attributed to the dense structure and the reinforcement of the SiC whiskers. In addition, the fracture mechanism of the composite is also discussed.

Multi-carbides/(Al, Si) composites were prepared by a spontaneous reactive melt infiltration technique. B4C and B4C with extra carbon (B4C/C) preforms were infiltrated with Al–Si alloys with Si contents ranging from 36 to 80 wt.%. The infiltration was conducted at temperatures 200 °C above the liquidus of the Al–Si alloys. Influence of the composition of the Al–Si alloys on the structure and the correlation of the structure and the mechanical properties of the composites have been studied. The alloys show good infiltration ability to the B4C and B4C/C preforms. The Al–Si alloys reacted with B4C, forming new carbides. Composites composed of carbides of SiC, B4C, AlB12C2, Al3B48C2 and residual Si and Al are obtained. The typical upper values of Vickers hardness and flexure strength are 17 ± 3 GPa and 328 ± 8 MPa, respectively, which are provided by the infiltration couple of B4C/Al–55 wt.% Si. The fracture mechanism of the composites has also been discussed.Highlights► Multi-carbide-based composites were fabricated by reactive melt infiltration. ► The fabrication was performed by infiltrating Al–Si alloys into B4C preforms. ► The microstructure and the mechanical properties of the composites were studied. ► The fracture mode of the composites was discussed. ► The work provides a facile method in fabricating multi-carbide-based composites.

Reticulated mesoporous Fe2O3@C flakes, consisting of nanocrystalline α-Fe2O3 encased within a thin carbon skeleton, were synthesized using ferrocene as iron and carbon sources and a novel reaction agent of ammonium sulphate via a facile two-step heating route. Those flakes, which were several nanometers thick and 1–2 μm in diameter, showed high capacity, excellent cyclic stability and rate capability as an anode material for lithium-ion batteries (LIBs). An initial reversible capacity of 910 mA h g−1 at a discharge/charge current of 0.1 A g−1 was obtained, and the capacity showed a gradual increase during cycling, reaching a high capacity of 1080 mA h g−1 after 120 cycles. An in situ lithiation study by transmission electron microscopy showed that the reticulated mesopores and the ultrathin feature of the Fe2O3@C flakes can largely accommodate the mechanical stresses and volume expansion of Fe2O3 during lithiation and hence maintain their integrity and provide excellent properties. The thin carbon skeleton not only facilitates the electronic conduction, but also inhibits the aggregation of nanocrystalline Fe2O3 flakes. The facile fabrication method and the unique structure of the mesoporous Fe2O3@C flakes offer high performance for LIB anodes and great potential for other applications of Fe2O3.

Lithium sulfide, Li2S, is a promising cathode material for lithium–sulfur batteries (LSBs), with a high theoretical capacity of 1166 mA h g−1. However, it suffers from low cycling stability, low-rate capability and high initial activation potential. In addition, commercially available Li2S is of high cost and of large size, over ten microns, which further exacerbate its shortcomings as a sulfur cathode. Exploring new approaches to fabricate small-sized Li2S of low cost and to achieve Li2S cathodes of high electrochemical performance is highly desired. This work reports a novel mechanochemical method for synthesizing Li2S of high purity and submicron size by ball-milling LiH with sulfur in an Ar atmosphere at room temperature. By further milling the as-synthesized Li2S with polyacrylonitrile (PAN) followed by carbonization of PAN at 1000 °C, a Li2S/C hybrid with nano-sized Li2S embedded in a mesoporous carbon matrix is achieved. The hybrid with Li2S as high as 74 wt% shows a high initial capacity of 971 mA h g−1 at 0.1C and retains a capacity of 570 mA h g−1 after 200 cycles as a cathode material for LSBs. A capacity of 610 mA h g−1 is obtained at 1C. The synthesis method of Li2S is facile, environmentally benign, and of high output and low cost. The present work opens a new route for the scalable fabrication of submicron-sized Li2S and for the development of high performance Li2S-based cathodes.