Synthesis and electrochemical analysis of vapor-deposited carbon-coated LiFePO4

Solvothermal synthesis of monodisperse LiFePO4 micro hollow spheres as high performance cathode material for lithium ion batteries

A microspherical, hollow LiFePO4 (LFP) cathode material with polycrystal structure was simply synthesized by a solvothermal method using spherical Li3PO4 as the self-sacrificed template and FeCl2·4H2O as the Fe(2+) source. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show that the LFP micro hollow spheres have a quite uniform size of ~1 μm consisting of aggregated nanoparticles. The influences of solvent and Fe(2+) source on the phase and morphology of the final product were chiefly investigated, and a direct ion exchange reaction between spherical Li3PO4 templates and Fe(2+) ions was firstly proposed on the basis of the X-ray powder diffraction (XRD) transformation of the products. The LFP nanoparticles in the micro hollow spheres could finely coat a uniform carbon layer ~3.5 nm by a glucose solution impregnating-drying-sintering process. The electrochemical measurements show that the carbon coated LFP materials could exhibit high charge-discharge capacities of 158, 144, 125, 101, and even 72 mAh g(-1) at 0.1, 1, 5, 20, and 50 C, respectively. It could also maintain 80% of the initial discharge capacity after cycling for 2000 times at 20 C.

Hierarchical LiFePO4/C microspheres with high tap density assembled by nanosheets as cathode materials for high-performance Li-ion batteries

In this paper, LiFePO(4)/C microspheres consisting of closely packed nanosheets have been synthesized via a simple solvothermal method and a subsequent carbon coating procedure. In order to clarify the microstructure of the product, the as-prepared composite has been characterized by various techniques, such as powder x-ray diffraction, scanning electron microscopy, energy dispersive spectrum, Raman spectroscopy and high-resolution transmission microscopy. Results show that the LiFePO(4)/C microspheres are uniform with a particle size of 8-10 μm. The microspheres are composed of densely compacted nanosheets with a thickness of 20-30 nm. The gaps between the nanosheets are estimated to be 10-50 nm; a carbon layer with a thickness of ~4 nm is coated on the surface of the LiFePO(4) spheres. The tap density of the LiFePO(4)/C composite reaches up to 1.5 g cm(-3). As cathode material for Li-ion batteries, the composite exhibits a high capacity: 155 mAh g(-1), 144 mAh g(-1), 129 mAh g(-1), and 104 mAh g(-1) at 0.1 C, 1 C, 5 C and 10 C, respectively. Furthermore, the material also shows good cycling stability at both low and high current rates. The unique nanostructure of the material promises its excellent electrochemical properties as a cathode material for lithium batteries.

LiFePO(4) nanocrystals: liquid-phase reduction synthesis and their electrochemical performance

Nanosized LiFePO4 is a kind of promising material for high performance lithium ion batteries; however, the synthesis of nanosized LiFePO4 still has some challenges in forming an orthorhombic phase in atmospheric liquid phase and protecting the LFP nanoparticles from aggregation, etc. In this work, LiFePO4 nanocrystals were synthesized through a high-temperature (350 °C) liquid-phase reduction method. The size and morphology of nanocrystals can be readily controlled by tuning the ratio of solvents, and the size-dependent behavior of lithium storage performance is also observed. After a carbon-coating surface treatment, rhombic-shaped LiFePO4 nanocrystals display excellent lithium storage properties with high reversible capacities and good cycle life (141.0 mAh g(-1) at 0.5 C after 50 cycles etc.). This method can be extended to prepare LiMnPO4 nanorods by substituting iron source with manganese salt.

Molecular Wiring of Insulators: Charging and Discharging Electrode Materials for High-Energy Lithium-Ion Batteries by Molecular Charge Transport Layers

Self-assembled monolayers (SAMs) of redox-active molecules on mesoscopic substrates exhibit two-dimensional conductivity if their surface coverage exceeds the percolation threshold. Here, we show for the first time that such molecular charge transport layers can be employed to electrochemically address insulating battery materials. The widely used olivine-structured LiFePO4 was derivatized with a monolayer of 4-[bis(4-methoxyphenyl)amino]benzylphosphonic acid (BMABP) in this study. Fast cross-surface hole percolation was coupled to interfacial charge injection, affording charging and discharging of the cathode material. These findings offer the prospect to greatly reduce the amount of conductive carbon additives necessary to electrochemically address present metal phosphate cathode materials, opening up the possibility for a much improved energy storage density. When compared at equal loading, the rate capability is also enhanced with respect to conventional carbon-based conductive additives.