Tailored surface structure of LiFePO4/C nanofibers by phosphidation and their electrochemical superiority for lithium rechargeable batteries

Reduced Graphene Oxide Coating LiFePO4 Composite Cathodes for Advanced Lithium-Ion Battery Applications

Recently, the application of LiFePO4 (LFP) batteries in electric vehicles has attracted extensive attention from researchers. This work presents a composite of LFP particles trapped in reduced graphene oxide (rGO) nanosheets obtained through the high-temperature reduction strategy. The obtained LiFePO4/rGO composites indicate spherical morphology and uniform particles. As to the structure mode of the composite, LFP distributes in the interlayer structure of rGO, and the rGO evenly covers the surface of the particles. The LFP/rGO cathodes demonstrate a reversible specific capacity of 165 mA h g-1 and high coulombic efficiency at 0.2 C, excellent rate capacity (up to 10 C), outstanding long-term cycling stability (98%) after 1000 cycles at 5 C. The combined high electron conductivity of the layered rGO coating and uniform LFP particles contribute to the remarkable electrochemical performance of the LFP/rGO composite. The unique LFP/rGO cathode provides a potential application in high-power lithium-ion batteries.

Etched colloidal LiFePO4 nanoplatelets toward high-rate capable Li-ion battery electrodes

LiFePO4 has been intensively investigated as a cathode material in Li-ion batteries, as it can in principle enable the development of high power electrodes. LiFePO4, on the other hand, is inherently "plagued" by poor electronic and ionic conductivity. While the problems with low electron conductivity are partially solved by carbon coating and further by doping or by downsizing the active particles to nanoscale dimensions, poor ionic conductivity is still an issue. To develop colloidally synthesized LiFePO4 nanocrystals (NCs) optimized for high rate applications, we propose here a surface treatment of the NCs. The particles as delivered from the synthesis have a surface passivated with long chain organic surfactants, and therefore can be dispersed only in aprotic solvents such as chloroform or toluene. Glucose that is commonly used as carbon source for carbon-coating procedure is not soluble in these solvents, but it can be dissolved in water. In order to make the NCs hydrophilic, we treated them with lithium hexafluorophosphate (LiPF6), which removes the surfactant ligand shell while preserving the structural and morphological properties of the NCs. Only a roughening of the edges of NCs was observed due to a partial etching of their surface. Electrodes prepared from these platelet NCs (after carbon coating) delivered a capacity of ∼ 155 mAh/g, ∼ 135 mAh/g, and ∼ 125 mAh/g, at 1 C, 5 C, and 10 C, respectively, with significant capacity retention and remarkable rate capability. For example, at 61 C (10.3 A/g), a capacity of ∼ 70 mAh/g was obtained, and at 122 C (20.7 A/g), the capacity was ∼ 30 mAh/g. The rate capability and the ease of scalability in the preparation of these surface-treated nanoplatelets make them highly suitable as electrodes in Li-ion batteries.

Morphology-controlled synthesis of self-assembled LiFePO4/C/RGO for high-performance Li-ion batteries

Novel architectured LiFePO4 (LFP) that consisted of ordered LFP nanocubes was prepared through a facile hydrothermal method using polyethylene glycol (PEG) as a surfactant. The micro/nanostructured LFP with various morphologies ranging from cube cluster to rugby-like structure was synthesized via controlling the pH values of the precursor. A reasonable assembly process elucidating the formation of the hierarchical structure is also provided based on the experimental results. After a combination of carbon (C) coating and reduced graphene oxide (RGO) wrapping, the obtained LFP/C/RGO composites exhibit enhanced electrochemical performance compared to that of blank LFP synthesized under the same condition. Among as-synthesized cube-cluster-like, dumbbell-like, rod-like, and rugby-like composites, the rugby-like LFP/C/RGO reveal the best electrochemical properties with the discharge specific capacity of ∼150 mA h g(-1) after 100 cycles and a high reversible specific capacity of 152 mA h g(-1) at 0.1 C. The prepared LFP/C/RGO composite can be a promising cathode material for high energy, low cost, and environmentally friendly lithium-ion batteries.