Paul A. Connor

Novel tin oxide-based anodes for Li-ion batteries

Abstract Three new possible Li-ion battery negative electrode materials, ZnO, ZnO:SnO 2 ball-milled mixture and Zn 2 SnO 4 , were prepared, and tested electrochemically. These new materials have smaller capacities than SnO 2 , but still show reversible capacities around 500 mA h g −1 . The charge and discharge profiles of all the materials are similar, with potentials close to that of the Li + /Li(m) couple. A large loss of capacity between the initial and the later cycles, is observed similar to the tin oxides, due to the required reduction of the tin and zinc ions to the bulk metal. These materials do show some promise as Li-ion battery anodes due to their large reversible lithium capacity at low potentials.

Novel tin oxide spinel-based anodes for Li-ion batteries

In this study, a series of inverse spinel M2SnO4 (M=Mg, Mn, Co) oxides were produced and tested to probe the effect the oxide matrix has on the electrochemical performance of tin oxides. Generally, these new oxides show similar behaviour to SnO2 with the formation of a more complicated mixed metal oxide matrix affecting the potentials of tin reduction and lithium insertion. A reasonable correlation is observed between the potential of the initial reduction of the spinel oxide to metallic tin and the enthalpy of formation of the metal oxide (MO). Amongst the spinels, Mn2SnO4 exhibits the best reversibility and Mg2SnO4 the worst.

Combined X-ray study of lithium (tin) cobalt oxide matrix negative electrodes for Li-ion batteries

The lithium insertion behaviours of the oxides Co3O4 and Co2SnO4 were studied using a range of electrochemical, spectroscopic and diffraction techniques. Co K-edge EXAFS studies on the Co3O4 oxide showed that the reversible lithium insertion is coupled with changes in cobalt oxidation state. On lithium insertion, Co3O4 is reduced to yield Co(II) and yields only metallic cobalt species on complete reduction. On lithium removal an oxide of Co is formed, which from coulometry should be CoO, however, EXAFS indicates the short range structure is quite different to that of the rocksalt CoO. The long range structure of the matrix is amorphous according to XRD. The EXAFS and XRD data also revealed that both the metallic and oxide phases were disordered, having low co-ordination numbers and large shell spacings, and that there was an initial reduction to CoO before full reduction to metallic Co. The electrochemical behaviour of Co2SnO4 cells was more reminiscent of that of SnO2 than that of Co3O4, but did exhibit significant differences due to the presence of cobalt. EXAFS on Co2SnO4 cells revealed that Co is reduced to metallic cobalt on the initial discharge, but that it does not convert back to an oxide on cycling even though the electrochemical treatment was the same as for Co3O4. Together the EXAFS and Mossbauer data show that the Co and Sn are reduced concurrently, and that some of the Sn remains in the oxidised form. In summary, we have a surprising result in that the presence of the tin dramatically changes the redox behaviour of the cobalt. In a matrix derived from a cobalt oxide spinel, cobalt undergoes redox cycling, whereas in a matrix derived from a cobalt tin oxide spinel, the cobalt does not cycle whilst the tin does.

Synthesis and lithium-storage properties of MnO/reduced graphene oxide composites derived from graphene oxide plus the transformation of Mn(vi) to Mn(ii) by the reducing power of graphene oxide

In this report, a novel method is proposed to prepare MnO/reduced graphene oxide (rGO) composites via calcining the precursors (i.e. δ-MnO2/graphene oxide composites) at 500 °C in Ar using no external reducing gas, in which graphene oxide (GO) successfully serves as a reductant by releasing CO during its thermolysis for the first time. By controlling the initial ratios of GO to KMnO4, differently composed precursors can be obtained via the redox reaction between GO and KMnO4, then leading to the formation of composites with different MnO/rGO ratios and dispersion of MnO on the rGO surface (denoted as MGC1 and MGC2). When applied as an active material in lithium ion batteries, MGC1 shows excellent cycling performance and capacity retention. Under 100 and 200 mA g−1, MGC1 could deliver reversible capacities as high as 900 and 750 mA h g−1, respectively, after more than 100 cycles. Considering the simple operation and low energy consumption in the whole material synthesis processes, the present strategy is feasible and effective for practical application. Even more importantly, the reductibility of graphene oxide upon thermolysis is utilized for the first time, which is meaningful for its extension in synthesis of functional nanomaterials.

Doped tin oxides as potential lithium ion battery negative electrodes

Recently some work has shown that tin oxide compounds can be promising anode materials in rechargeable lithium batteries. These materials show a higher capacity compared to the graphite that is used commercially. The present studies are focused on zinc doped tin oxides as anode materials, especially on the effect of ball-milling on the anode capacity. Different ratios of ZnO and SnO2 with different times of ball-milling have been used as active materials. The inverse spinel, Zn2SnO4 has been prepared by both hand-grinding and ball-milling, followed by sintering and has also been investigated as an active material. Individual ball-milling of the oxides was observed to increase capacity, co-milling was fairly neutral and ball-milling before solid state reaction was observed to have a detrimental effect.

Solid Oxide Fuels Cells: Facts and Figures

Although fuel cells have been known for over 150 years, research on solid oxide fuel cells (SOFCs) based on an oxide ion conducting electrolyte only accelerated in the last 30 years. This chapter, after a brief history of SOFCs, reviews the materials for different cell components (electrolyte and the two electrodes) and cell stacks (seals and interconnects); novel materials and their structures have been investigated and developed to improve electrochemical performance. Different SOFC designs and their relative advantages and disadvantages are then discussed. Finally, various applications of SOFC power systems and the status of their demonstration and commercialization are reviewed.

How amorphous are the tin alloys in li-inserted tin oxides?

Several different metal oxides based anode systems are compared to give insight into their cycling behaviour. The simple electrochemical model for these systems does not usefully predict the ability for a battery to cycle. Pb and Zn oxides cycle less well than Sn oxides, and show more initial crystallinity. SnF2 and PbF2 cycle less well than SnO and PbO. Cubic SnP2O7 cycles better than the layered polymorph. The nature and structure of the supporting matrix is therefore important in the ability of the tin oxides to cycle. Any material with observable crystallinity in first cycle, will not cycle well.

Highly efficient, coking-resistant SOFCs for energy conversion using biogas fuels

Solid oxide fuel cells (SOFCs) afford an opportunity for the direct electrochemical conversion of biogas with high efficiency; however, direct utilisation of biogas in nickel-based SOFCs is a challenge as it is subject to carbon deposition. A biogas composition representative of a real operating system of 36% CH4, 36% CO2, 20% H2O, 4% H2 and 4% CO used here was derived from an anode recirculation method. A BaZr0.1Ce0.7Y0.1Yb0.1O3−δ (BCZYYb) infiltrated Ni-YSZ anode was investigated for biogas conversion. The infiltration of BCZYYb significantly promoted the electrochemical reactions and the cells exhibited high power output at the operational temperatures of 850, 800 and 750 °C. At 800 °C, supplied with a 20 ml min−1 biogas, the cell with a BCZYYb-Ni-YSZ anode, generated 1.69 A cm−2 at 0.8 V with an optimal amount of 0.6 wt% BCZYYb, whereas only 0.65 A cm−2 was produced with a non-infiltrated Ni-YSZ in the same conditions. At 750 °C, a maximum power density of 1.43 W cm−2 was achieved on a cell with a BCZYYb-Ni-YSZ anode, a 3 μm dense YSZ film electrolyte, a Gd0.1Ce0.9O2 (GDC) buffer layer and a La0.6Sr0.4Co0.2Fe0.8O3–Gd0.1Ce0.9O2 (LSCF-GDC) composite cathode. The cell remained stable, while operating at 0.8 V for 50 hours with a current density of 1.25 A cm−2. A well-designed cell structure and selected components made it possible to obtain excellent performance at good fuel utilisation. The analysis of gases in open-circuit conditions or under various current loads suggested that the prevalent reaction was reforming of methane without coking. This study demonstrates that the BCZYYb-Ni-YSZ is a promising electrode for carbon-containing fuel.

Oxide ion conductivity in the hexagonal perovskite derivative Ba3MoNbO8.5

Oxide ion conductors are important materials with a range of technological applications and are currently used as electrolytes for solid oxide fuel cells and solid oxide electrolyzer cells. Here we report the crystal structure and electrical properties of the hexagonal perovskite derivative Ba3MoNbO8.5. Ba3MoNbO8.5 crystallizes in a hybrid of the 9R hexagonal perovskite and palmierite structures. This is a new and so far unique crystal structure that contains a disordered distribution of (Mo/Nb)O6 octahedra and (Mo/Nb)O4 tetrahedra. Ba3MoNbO8.5 shows a wide stability range and exhibits predominantly oxide ion conduction over a pO2 range from 10-20 to 1 atm with a bulk conductivity of 2.2 × 10-3 S cm-1 at 600 °C. The high level of conductivity in a new structure family suggests that further study of hexagonal perovskite derivatives containing mixed tetrahedral and octahedral geometry could open up new horizons in the design of oxygen conducting electrolytes.

Development and performance of MgFeCrO4 – based electrodes for solid oxide fuel cells

Composite anodes for solid oxide fuel cells (SOFC) developed on yttria stabilised zirconia (YSZ) porous supports by infiltration of electrode materials has been successfully applied for various anode and cathode compositions, resulting in high performance SOFC devices. The focus of this study is the performance of the chromium-rich spinel (MgFeCrO4) as an electrode support material when used alone or impregnated. The composite anodes were prepared by aqueous infiltration of nitrate salts to produce (La0.75Sr0.25)0.97Cr0.5Mn0.5O3−δ, Ce0.9Gd0.1O2−δ, CeO2 or Pd into a MgFeCrO4 scaffold with 45% porosity and studied by electrochemical impedance spectroscopy in symmetrical cell configuration. The performance was evaluated in humidified 5% H2/Ar in order to quantify their stability and performance up to 850 °C with respect to the MgFeCrO4 porous substrate. It was found that all the impregnated phases adhere very well to the spinel and considerably enhance performance and stability to a level required for SOFC applications. MgFeCrO4/LSCM/CGO and MgFeCrO4/LSCM/CGO/Pd showed the most substantial improvement in comparison to the scaffold’s performance, with ASR values of 1.74 Ω cm2 and 0.91 Ω cm2, respectively.