Ceramic synthesis of disordered lithium rich oxyfluoride materials

Disordered lithium-rich transition metal oxyfluorides with a general formula Li$_{1+x}$MO$_{2}$F$_{x}$ (M being a transition metal) are gaining more attention due to their high specific capacity which can be delivered from the facecentered cubic (fcc) structure. The most common synthesis procedure involves use of mechanosynthesis. In this work, ceramic synthesis of lithium rich iron oxyfluoride and lithium rich titanium oxyfluoride are reported. Two ceramic synthesis routes are developed each leading to the different level of doping with Li and F and different levels of cationic disorder in the structure. Three different Li$_{1+x}$MO$_{2}$F$_{x}$ samples (x ¼ 0.25, 0.3 and 1) are compared with a sample prepared by mechanochemical synthesis and non-doped LiFeO2 with fcc structure. The obtained lithium rich iron oxyfluoride are characterized by use of M€ossbauer spectroscopy, X-ray absorption spectroscopy, NMR and TEM. Successful incorporation of Li and F have been confirmed and specific capacity that can be obtained from the samples is in the correlation with the level of disorder introduced with doping, nevertheless oxidation state of iron in all samples is very similar. Conclusions obtained from lithium rich iron oxyfluoride are validated by lithium rich titanium oxyfluoride

Reversible lithium insertion into Na2Ti6O13 structure

Pure Na2Ti6O13 phase was successfully prepared from partially washed (Na,H)TiO nanotubes and used as an insertion material for lithium ions. Results show that the structure can accommodate upto 3 mol of lithium per 1 mol of Na2Ti6O13. Accommodation of 0.5 mol of lithium per one titanium atom corresponds to the partial reduction of Ti4+ to Ti3+ and occurs several 100s of millivolts lower than typically encountered for titanium in an octahedral oxygen environment such as Li4Ti5O12. Lithium insertion into this phase was evaluated using especially in situ X-ray. Lithium insertion into Na2Ti6O13 phase includes three domains corresponding to two solid–solutions and a biphasic transition in the potential range between 1.5 V and 1.0 V vs. lithium. The process is very reversible so that after re-oxidation the structure is completely preserved. Capacity fading observed during the cycling is explained by parasitic reactions attributed to a catalytic effect of the exposed bare surface on the electrolyte degradation. Keywords: Na2Ti6O13, Titanium oxide, Anode, Lithium insertion, Li-ion batterie

Preparation, Characterization and Properties of Pt-Cu Co-reduced and Pt-on-Cu Skin Type Bimetallic Carbon-Supported (Vulcan XC72) Electrocatalysts

Pt/Cu salt co-reduction and, subsequent reduction of Cu(acac)2 and PtCl2 allows to generate either alloyed Pt-Cu or skin type Pt-on-Cu carbon-supported (20 wt%, Pt:Cu = 50:50 a/o on Vulcan XC72) electrocatalysts. An examination by TEM revealed that the co-reduced Pt-Cu catalyst have well dispersed bimetallic nanoparticles (av. particle size 3.6 nm). The skin type Pt-on-Cu catalyst shows tiny Pt clusters (1-2 nm) decorating the surface of larger Cu particles (6-8 nm). XRD pattern of the co-reduced Pt-Cu catalyst shows weak and broad diffraction peaks consistent with a predominantly alloyed composition (plus a few Pt crystallites). Pattern of the skin type Pt-on-Cu/C catalyst reveals larger nanoparticles and points to the formation of (surface) alloy. SEM/EDAX showed a uniform metal distribution present in both Pt-Cu systems. XPS measurements indicated that in both cases only Pto is present. In co-reduced alloy catalyst a higher amount of Cu2+ was present at the nanoparticle surface (Cuo/ Cu2+ = 0.6), while on the surface of the skin type Pt-on-Cu system Cuo and Cu2+ exist in equal amounts (Cuo/ Cu2+ = 1.0). Both types of Cu containing catalysts have higher mass specific activity in hydrogen oxidation reaction (HOR) than the industrial benchmark Pt/C catalyst. The electrocatalytic properties depend on morphological structure subtleties