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A novel catalyst support constructed from poly (diallydimethylammonium chloride) functionalized graphene (PDDA-GN) and H3PMo12O40 (PMO12) was prepared by layer by layer (LBL) electrostatic assembly and were used for electro-deposition of Pd particles in situ. The Pd/{PDDA-GNs/PMo12}n composite films were characterized by Raman, XPS, EDS, XRD, AFM and TEM. The composite films presented good electrocatalytic activity, better electrochemical stability and improved tolerance of CO in cyclic voltammetry, chronoamperometry and CO-stripping voltammetry tests. Especially, the catalytic activity of the as prepared composite toward formic acid electro-oxidation is 4.1 times of the commercial Pd/C catalyst. It indicates that PDDA-GNs preserve superior electric conductivity of graphene sheets in the composite films, and the introduction of electroactive PMo12 into the composite films contributes to convert intermediate species CO into CO2. The synergistic effects of PDDA-GNs and PMo12 remarkably enhance the electrocatalytic activity and stability of nano-Pd regarding formic acid oxidation. [ABSTRACT FROM AUTHOR]

Lithium-rich, layered composites of xLi2MnO3 ⋅ (1-x)Li(Ni1/3Mn1/3Co1/3)O2were synthesized via spray pyrolysis to identify the chemistry yielding optimal electrochemical performance for materials produced by this method. The x values selected for optimization were x = 0.3, 0.5, 0.7, equivalent to Li1.14Mn0.46Ni0.2Co0.2O2, Li1.2Mn0.54Ni0.13Co0.13O2 and Li1.26Mn0.6Ni0.07Co0.07O2, respectively. The materials were annealed at 850°C or 900°C for 2 hours, and then tested in coin cells. Li1.2Mn0.54Ni0.13Co0.13O2annealed at 900°C displayed the best electrochemical performance with excellent capacity retention, displaying a reversible capacity of 236 mAhg-1after 100 cycles when cycled between 2.0-4.8 V at C/10 rate, where 1C = 280 mAg-1. The cycling profiles display voltage fade, presumably due to a layered-spinel phase transformation. The synthesis method leads to high purity and excellent uniformity at the nanoscale, and the materials have less voltage fade compared to similar materials produced by co-precipitation. Voltage fade is more pronounced when the upper cut-off voltage is 4.8 V, as opposed to 4.6 V. A decrease in the Li2MnO3 content of the material reduces voltage fade, such that x = 0.3 (or Li1.14Mn0.46Ni0.2Co0.2O2) shows the best structural stability over cycling. [ABSTRACT FROM AUTHOR]

Lithium-rich, layered composites of xLi2MnO3•(1-x)LiNi1/3Mn1/3Co1/3O2 have been extensively studied for PHEVs and EVs. To ensure complete lithiation, most synthesismethods require the addition of excess lithium compared to the stoichiometric composition. In this study lithium enriched, layered composites of Li1.2Mn0.54Ni0.13Co0.13O2 were synthesized in a spray pyrolysis process. Spray pyrolysis allows for excellent control of composition and in this work the lithium content was systematically varied between 3.3 wt% excess and 3.3 wt% deficient compared to Li1.2Mn0.54Ni0.13Co0.13O2. The as-synthesized powders were annealed at 900°C for 2, 5 and 20 hours. Results indicate that as the annealing time is increased the surface areas is reduced from 9 to ~2 m² g-1. No new phases form during the annealing process although changes in the relative intensity of the (018) and (110) peaks imply a reorganization between the transition metal and lithium layers. An excess Li of 3.3 wt% is sufficient to counter these structural rearrangements and maintain discharge capacities close to 200 mAh g-1 after 100 cycles at C/3. Samples with a smaller surface area do not lead to improved capacity retention. The results also suggest that the Li2MnO3 structural component has a key role in the voltage fade for these materials. [ABSTRACT FROM AUTHOR]

The cathode material Li1.5Ni0.25Mn0.75O2.5 was synthesized through a solid-state reaction. In-situ high energy X-ray diffraction, STEM and electrochemical characterizations confirmed the composite nature of the material. We mainly found that the layered components belonging to the R...m and C2/m like-phases formed stepwise following the thermal decomposition and reaction of Li2CO3. Solid diffusion at high-temperature with extended calcination times cannot change the composite nature. [ABSTRACT FROM AUTHOR]

Spinel-layered (S-L) cathode blends of LiNi0.5Mn1.5O4-δ and Li1.5Ni0.25Mn0.75O2.5 were prepared by physical mixing during electrode fabrication. The incorporation of the spinel component in the blends (S:L ratio = 1:1) has led to the following advantages: 1) the initial-cycle efficiency, which is usually lower than 80% for the layered component, increased to 90% as the extra capacity of the spinel below 3.0 V could be utilized in the blends; 2) the rate capability of the cells was improved and reached a maximum for the blend; 3) the cycling behavior of the cells was comparable to that of the pure layered component, but superior to that of the pure spinel component cycled between 2.0 and 4.8 V. The study revealed that the introduction of the spinel component in the blends could mitigate some of the weaknesses of the layered component, and vice versa. [ABSTRACT FROM AUTHOR]