Hailei Zhao

MoS2 Nanosheets Vertically Grown on Graphene Sheets for Lithium-Ion Battery Anodes

A designed nanostructure with MoS2 nanosheets (NSs) perpendicularly grown on graphene sheets (MoS2/G) is achieved by a facile and scalable hydrothermal method, which involves adsorption of Mo7O24(6-) on a graphene oxide (GO) surface, due to the electrostatic attraction, followed by in situ growth of MoS2. These results give an explicit proof that the presence of oxygen-containing groups and pH of the solution are crucial factors enabling formation of a lamellar structure with MoS2 NSs uniformly decorated on graphene sheets. The direct coupling of edge Mo of MoS2 with the oxygen from functional groups on GO (C-O-Mo bond) is proposed. The interfacial interaction of the C-O-Mo bonds can enhance electron transport rate and structural stability of the MoS2/G electrode, which is beneficial for the improvement of rate performance and long cycle life. The graphene sheets improve the electrical conductivity of the composite and, at the same time, act not only as a substrate to disperse active MoS2 NSs homogeneously but also as a buffer to accommodate the volume changes during cycling. As an anode material for lithium-ion batteries, the manufactured MoS2/G electrode manifests a stable cycling performance (1077 mAh g(-1) at 100 mA g(-1) after 150 cycles), excellent rate capability, and a long cycle life (907 mAh g(-1) at 1000 mA g(-1) after 400 cycles).

High-Performance Anode Material Sr2FeMo0.65Ni0.35O6−δ with In Situ Exsolved Nanoparticle Catalyst

A metallic nanoparticle-decorated ceramic anode was prepared by in situ reduction of the perovskite Sr2FeMo0.65Ni0.35O6-δ (SFMNi) in H2 at 850 °C. The reduction converts the pure perovksite phase into mixed phases containing the Ruddlesden-Popper structure Sr3FeMoO7-δ, perovskite Sr(FeMo)O3-δ, and the FeNi3 bimetallic alloy nanoparticle catalyst. The electrochemical performance of the SFMNi ceramic anode is greatly enhanced by the in situ exsolved Fe-Ni alloy nanoparticle catalysts that are homogeneously distributed on the ceramic backbone surface. The maximum power densities of the La0.8Sr0.2Ga0.8Mg0.2O3-δ electrolyte supported a single cell with SFMNi as the anode reached 590, 793, and 960 mW cm(-2) in wet H2 at 750, 800, and 850 °C, respectively. The Sr2FeMo0.65Ni0.35O6-δ anode also shows excellent structural stability and good coking resistance in wet CH4. The prepared SFMNi material is a promising high-performance anode for solid oxide fuel cells.

Carbyne polysulfide as a novel cathode material for lithium/sulfur batteries

A novel organic sulfide named carbyne polysulfide was prepared by co-heating carbyne analogue and elemental sulfur. The carbyne analogue was obtained by dehydrochlorination of polyvinylidene chloride. By means of several characterization methods, it was proved that the carbyne polysulfide has a unique and stable structure of a conducting sp2 hybrid carbon skeleton connected to energy-storing sulfur side chains. And in terms of morphology, it has a well-developed porous structure with an uneven pore size. The elements C and S in the organic sulfide are approximately 43.4 wt% and 54.1 wt% respectively. As a cathode material for lithium/sulfur batteries, the carbyne polysulfide displays a high reversible capacity of 960 mA h gsulfur−1 after 200 cycles at 0.1 C (168 mA gsulfur−1) current rate in carbonic ester electrolyte. It also exhibits a reversible capacity as high as 705 mAh gsulfur−1 when cycled at 1 C (1680 mA gsulfur−1) current rate. This organic sulfide exhibits great potential as a promising cathode material for high performance rechargeable lithium/sulfur batteries.

Investigation of In-doped BaFeO3−δ perovskite-type oxygen permeable membranes

Cobalt-free BaFe1−xInxO3−δ perovskites, with Fe partially substituted by indium at the B-site, were synthesized by a conventional solid state reaction and systematically characterized in terms of their phase composition, crystal structure, thermal reducibility, oxygen permeability, as well as structural stability in order to evaluate their application as oxygen permeation membranes. Introduction of more than 10 at.% of In into BaFe1−xInxO3−δ causes the formation of a single phase material with a cubic perovskite structure, which exhibits no phase transition during the cooling process. The thermal reducibility and thermal expansion coefficient are effectively reduced by indium doping, owing to the less changes of concentration of the oxygen vacancies in these compounds. However, the In occupying B-site breaks the B–O–B double exchange mechanism, and thus results in a gradual decrease of the electrical conductivity upon doping. Rietveld refinement and first principles calculation were performed to get an insight into the In influence on the lattice structure, oxygen migration energy and electron conduction behaviour of BaFe1−xInxO3−δ. When using He/Air as sweep/feed gas, the BaFe0.9In0.1O3−δ dense membrane with 1.0 mm thickness features a high oxygen permeation flux of 1.11 mL cm−2 min−1 at 950 °C. The observed good performance is attributed to the relatively high concentration of oxygen vacancies and low energy barrier for oxygen ion migration. It is also found that for membranes thinner than 0.8 mm, the oxygen flux is no longer limited by the bulk diffusion, while the oxygen surface exchange process becomes the dominant factor.

A new lithium secondary battery system: the sulfur/lithium-ion battery

A new lithium secondary battery system, the sulfur/lithium-ion battery, has been constructed by employing a lithium/Sn–C composite anode, a carbyne polysulfide cathode, and a carbonic ester electrolyte. Compared with a lithium/sulfur battery, the use of a lithium/Sn–C composite anode ensures the high safety of the new battery. Meanwhile, the novel battery possesses high-energy characteristics. It delivers a reversible capacity of 500 mA h g−1 after 50 cycles at a current density of 200 mA g−1, which ensures a stable specific energy of 410 W h kg−1. As all of the materials required for the new battery are readily available and low-cost, and the techniques are simple, this new battery has a strong potential for use in industry. Furthermore, there is considerable room for improvement of the energy density of the sulfur/lithium-ion battery, and the new battery is one of the most promising candidates for the next generation of high-performance rechargeable batteries.

Evaluation of La0.3Sr0.7Ti1−xCoxO3 as a potential cathode material for solid oxide fuel cells

Perovskites La0.3Sr0.7Ti1−xCoxO3 (LSTCs, x = 0.3–0.6) are systematically evaluated as potential cathode materials for solid oxide fuel cells. The effects of Co substitution for Ti on structural characteristics, thermal expansion coefficients (TECs), electrical conductivity, and electrochemical performance are investigated. All of the synthesized LSTCs exhibit a cubic structure. With Rietveld refinement on the high-temperature X-ray diffraction data, the TECs of LSTCs are calculated to be 20–26 × 10−6 K−1. LSTC shows good thermal cycling stability and is chemically compatible with the LSGM electrolyte below 1250 °C. The substitution of Co for Ti increases significantly the electrical conductivity of LSTC. The role of doping on the conduction behavior is discussed based on defect chemistry theory and first principles calculation. The electrochemical performances of LSTC are remarkably improved with Co substitution. The area specific resistance of sample La0.3Sr0.7Ti0.4Co0.6O3 on the La0.8Sr0.2Ga0.8Mg0.2O3−δ (LSGM) electrolyte in symmetrical cells is 0.0145, 0.0233, 0.0409, 0.0930 Ω cm2 at 850, 800, 750 and 700 °C, respectively, and the maximum power density of the LSGM electrolyte (400 μm)-supported single cell with the Ni–GDC anode, LDC buffer layer and LSTC cathode reaches 464.5, 648, and 775 mW cm−2 at 850 °C for x = 0.3, 0.45, and 0.6, respectively. All these results suggest that LSTC are promising candidate cathode materials for SOFCs.

A novel cobalt-free cathode material for proton-conducting solid oxide fuel cells

Developing a tailored cathode is of great importance for the improvement of proton-conducting solid oxide fuel cell (SOFC-H) performance. In this work, a novel cobalt-free cathode BaCe0.40Sm0.20Fe0.40O3−δ was designed for use in a SOFC-H. It was composed of homogeneously distributed BaCe1−x(Sm/Fe)xO3−δ and BaFe1−y(Sm/Ce)yO3−δ, which were synthesized by a simple in situ method, eliminating the separate synthesis and the mechanical mixing processes for the conventional composite materials. The BaCe0.40Sm0.20Fe0.40O3−δ cathode exhibited protonic, oxygen-ionic, and electronic conduction simultaneously in wet air, expanding the triple phase boundaries to the whole cathode. The symmetrical cell tests with BaCe0.40Sm0.20Fe0.40O3−δ as electrodes showed that the diffusion of O−ad and reduction of O−TPB were the rate limiting steps in wet air. The power density of the anode-supported single cell with Ni–BaCe0.80Sm0.20O3−δ (580 μm) anode, BaCe0.80Sm0.20O3−δ (70 μm) electrolyte and BaCe0.40Sm0.20Fe0.40O3−δ (53 μm) cathode was 194.0, 169.2, and 137.1 mW cm−2 at 750, 710, and 650 °C, respectively. These results are encouraging considering the cobalt-free nature and rather low electrical conductivity of the cathode material. The BaCe0.40Sm0.20Fe0.40O3−δ material demonstrated excellent catalytic activity towards the reactions on the cathode. Accordingly, the BaCe0.40Sm0.20Fe0.40O3−δ material can be a promising cathode for SOFC-H.

27Al and 29Si MAS–NMR studies of structural changes in hybrid aluminosilicate gels

Abstract Aluminosilicate gels with stoichiometric and nonstoichiometric compositions were synthesized by means of colloidal sol-gel method and their mullitization behavior was studied by X-ray diffraction (XRD), 27Al and 29Si magic angle spinning nuclear magnetic resonance (MAS–NMR) experiments. Particular attention was given to the structural changes of matrix accompanying the formation of mullite. The various coordinated Al occupancies were clarified by simulating the 27Al MAS–NMR spectra with Gaussian lines. The results demonstrate that the so-synthesized aluminosilicate gel is a hybrid gel containing a mixture of a single-phase gel and a diphasic gel. The mullitization of so-formed hybrid gel exhibits a consecutive one-step conversion process, but not a two-step process, much similar to that of a true diphasic mullite gel. The mullite formation from hybrid aluminosilicate gel mainly depends on the nature of dominant matrix part, but not on the nature of minor matrix part in gel. During the formation process of mullite, amorphous Si-rich phase appears as a transitional phase. The effects of gel composition and heating rate on the phase transformation behavior of hybrid aluminosilicate gel were also discussed here.

Microcrystalline SnSb Alloy Powder as Lithium Storage Material for Rechargeable Lithium-Ion Batteries

Spherical SnSb alloy powders with an average particle size of about 10 μm were prepared from Sn and Sb oxides by carbothermal reduction. The synthesized SnSb alloy shows low initial capacity loss (ca. 150 mAh/g) and high reversible capacity (around 800 mAh/g). The capacity fade of the SnSb alloy during the charge/discharge process comes mainly from the Sb component rather than Sn component. Microsized SnSb alloy exhibits a much better cycling performance when cycled at 40°C than that at ambient temperature (ca. 30°C), while it tends to be worse when cycled at 55 °C. The rate capability of SnSb alloy was also investigated.

Design and synthesis of a 3-D hierarchical molybdenum dioxide/nickel/carbon structured composite with superior cycling performance for lithium ion batteries

Molybdenum dioxide is an attractive material for anodes of lithium ion batteries due to its high theoretical capacity, more than twice that of graphite. However, slow electrode reaction kinetics and structural degradation caused by large volume changes and phase separation during cycling hinder its practical application. To solve these problems, we design and fabricate a novel, 3-D hierarchical MoO2/Ni/C architecture by a combination of a hydrothermal method with chemical vapor deposition. The nickel nanoparticles are in situ formed and disperse uniformly with flower-like MoO2 particles, which are coated by thin carbon layers. The Ni particles act as a catalyst during the carbon coating process to promote the in situ growth of graphene in the carbon layer. Together, MoO2 and nickel nanoparticles, as well as amorphous carbon and graphene sheets build a 3-D hierarchical robust MoO2/Ni/C structure with a good electronically conductive network and lots of void space. Such a 3-D hierarchical structure combines multiple advantageous features, including an enhanced 3-D electronically conductive network, plenty of tunnels for electrolyte solution penetration, void space for volume change accommodation, and more surface areas for the electrode reaction. The manufactured MoO2/Ni/C composite exhibits a high reversible capacity, and excellent rate capability of 576 and 463 mA h g−1 at current densities of 100 and 1000 mA g−1, respectively. The excellent cycling performance is recorded with a capacity of 445 mA h g−1 maintained at 1000 mA g−1 after 800 cycles. The proposed synthesis process is simple and the design concept can be broadly applied, providing a novel, general approach towards manufacturing of metal oxide/metal/carbon (graphene) composites for high energy density storage or other electrochemical uses.