Synthesis and characterization of integrated layered nanocomposites for lithium ion batteries

The series of Li[NixMxLi1/3-xMn2/3-x]O2 cathodes, where M is cobalt or chromium with a wide compositional range x from 0 to 0.33, were prepared by hydroxide coprecipitation method with subsequent quenching. The sample structures were investigated using X-ray diffraction results which were indexed completely on the basis of a trigonal structure of space group R3m¯ with monoclinic C2/m phase as expected. The morphologies and electrochemical properties of the samples obtained were compared as the value of x and substituted transition metal. The particle sizes of cobalt-substituted Li[NixCoxLi1/3-xMn2/3-x]O2 samples are much smaller than those of the Li[NixCrxLi1/3-xMn2/3-x]O2 system. The electrode containing Li[NixCoxLi1/3-xMn2/3-x]O2 with x = 0.10 delivered a discharge capacity of above 200 mAh/g after 10 cycles due to the activation of Li2MnO3

Effects of Self-Catalyzed Polyaniline Coating on the Electrochemical Performance of 0.4Li(2)MnO(3) center dot 0.6LiMn(0.33)Ni(0.33)Co(0.33)O(2) Electrodes

Self-catalyzed polyaniline (PANI)-coating on the surface of 0.4Li(2)MnO(3) center dot 0.6LiMn(0.33)Ni(0.33)Co(0.33)O(2) powders was prepared by chemical oxidative polymerization with the aid of the Mn4+ ions of the pristine material as oxidants. Discharge capacity of the PANI-coated electrode was 98 mAhg(-1) at 2.4 C-rate, while the uncoated sample showed 68 mAhg(-1). Discharge capacity was retained at 94% by the 40th cycle, while that of uncoated electrode was retained at 85%. The improvement of electrochemical performances is attributed to the PANI-coating that acts as a protective layer and suppresses the formation of solid electrolyte interphase layer by retarding the rate of electrolyte decomposition. (C) 2014 The Electrochemical Society. All rights reservedclos

Nanorod-assembled spinel Li1 05Mn1 O-95(4) rods with a central tunnel along the rod-axis for high rate capability of rechargeable lithium-ion batteries

Nanorod-assembled spinel Li1 05Mn1 95O4 rods with a central tunnel along the rod-axis were synthesized using highly crystalline beta-MnO2 rods as self-templates The synthesized spinel Li1 05Mn1 95O4 is an assembly of several single crystal-like nanorods with an average diameter and length of 100 and 400 nm respectively which was determined by microstructural Rietveld refinement using the synchrotron powder XRD data Galvanostatic battery testing showed that central-tunneled and nanorod-assembled Li1 05Mn1 95O4 rods have a high charge storage capacity at high current densities in comparison with those of the simnel rods without a tunnel structure and commercial powders Moreover a capacity retention value of 81% was observed at the end of 100 cycles at a current of 250 mAh g(-1

Effect of Electrolytes on the Cathode-Electrolyte Interfacial Stability of Fe-Based Layered Cathodes for Sodium-Ion Batteries

Iron (Fe)-based layered oxide cathodes that employ Fe3+/Fe4+ redox reaction present a family of attractive cathode materials for sodium-ion batteries as iron is abundant, low-cost, and environmentally benign. However, their electrochemical performance is not yet satisfactory and requires further improvement. In this study, we investigate the effect of electrolytes on the electrochemical performance of alpha-NaFeO2, a prototypical model of Fe-based layered cathodes. First, we established the critical impact of the poor cathode-electrolyte interfacial stability on cell performances. Systematic electrochemical tests and material characterizations further revealed the degradation mechanism in which the highly reactive Fe4+ state in the charged Na1-xFeO2 electrodes promotes severe electrolyte decomposition and subsequent growth of a thick interface layer that leads to impedance rise and performance degradation. In addition, the superior performance of NaPF6 over NaClO4 and the beneficial effect of the FEC additive are reported

LT-LiMn0.5Ni0.5O2: A Unique Co-Free Cathode for High Energy Li-Ion Cells

A new Li-ion battery cathode, ‘LT-LiMn0.5Ni0.5O2’, where LT refers to its relatively low synthesis temperature (400 oC), has been identified. Electrochemical data indicate that Li/LT-LiMn0.5Ni0.5O2 cells operate between 5.0 and 2.5 V with good cycling stability, yielding a cathode capacity of 225 mAh/g. The electrochemical reactions occur in two distinct steps centered at ~3.75 V and ~4.7 V during charge, and at ~4.6 V and ~3.5 V during discharge. High-angle, annular-dark-field (HAADF) scanning-transmission electron microscopy (STEM) provide evidence that LT-LiMn0.5Ni0.5O2 consists of a unique, partially-disordered LiMn0.5Ni0.5O2 structure with predominant lithiated-spinel- and layered-like character. Structural analysis of LT-LiMn0.5Ni0.5O2 with synchrotron X-ray diffraction data shows, surprisingly, that lithiated-spinel and layered models with approximately 16% (~1/6) disorder between the lithium and manganese/nickel ions, yield an identical fit to the data, complicating the determination of the exact nature and level of disorder in each structural model. We believe that this is the first report of a Mn-stabilized, lithium-nickel-oxide spinel-related structure in which the redox reactions occur almost entirely on the nickel ions, with the likelihood that oxygen redox also contributes to some capacity above 4.7 V

SYNTHESIS OF HIGHLY CRYSTALLINE OLIVINE-TYPE LiFePO4 NANOPARTICLES BY SOLUTION-BASED REACTIONS

LiFePO4 nanocrystals were synthesized in various polyol media without any further post-heat treatment. The LiFePO4 samples synthesized using three different polyol media namely, diethylene glycol (DEG), triethylene glycol (TEG), and tetraethylene glycol (TTEG), exhibited plate and rod-shaped structures with average sizes of 50–500 nm. The X-ray diffraction (XRD) patterns were indexed on the basis of an olivine structure (space group: Pnma). The samples prepared in DEG, TEG, and TTEG polyol media showed reversible capacities of 123, 155, and 166 mAh/g, respectively, at current density of 0.1 mA/cm2 with no capacity fading and exhibited excellent capacity retention up to the 50th cycle. In particular, the samples showed excellent performances at high rates of 30 and 60 C with high capacity retention. It is assumed that the nanometer size materials (~50 nm) possessing a highly crystalline nature may generate improved performance at high rate current densities.Lithium ion battery, LiFePO4, nanocrystal, cathode, polyol