Carbon-coated Lithium Iron Phosphate Research Articles

Preparation of C-LiFePO 4/polypyrrole lithium rechargeable cathode by consecutive potential steps electrodeposition

In this work carbon coated lithium iron phosphate (C-LiFePO 4)/polypyrrole (PPy) composite preparation has been carried out using electrochemical techniques. This composite has been deposited on a stainless steel mesh in order to use it as a cathode in a lithium-ion battery. When an oxidation potential is applied to the working electrode, the pyrrole monomer is polymerized and the C-LiFePO 4 particles are incorporated into the polymer matrix and bound to the polymer and mesh. An experimental procedure was performed in order to understand how the composite formation is carried out and what the oxidation state of the composite material is during the charge–discharge process. As the electrochemical method of synthesis has a big influence in the electrochemical properties of the polymer, the use of consecutive potential steps has been studied in order to improve the charge-storage capacity of the composite material. The influence on the final composite properties of the oxidation-deposition time and potential and the effect of the number of cycles has been analyzed. An improvement of about 20% has been achieved using short oxidation times (3 s) at 0.9 V vs. Ag/AgCl. The reasons for this improvement are discussed and analyzed using different experimental techniques.

Electrochemical properties of carbon-coated LiFePO 4 synthesized by a modified mechanical activation process

Carbon-coated lithium iron phosphate (LiFePO 4/C) composites were synthesized by conventional mechanical activation (MA) process and also by a modified MA process. Phase-pure particles were obtained of ∼100 nm size with a nano-meter thick web of carbon surrounding the particles. The composite prepared by the modified MA process shows good performance as cathode material in lithium cells at room temperature. A high performance was achieved at 0.1 C-rate with >96% utilization of the active material. A stable cycle performance even at higher C-rates was achieved with a cathode that has a total carbon content of only 12 wt%. The use of the modified MA process to synthesize LiFePO 4/C has promise to be an efficient process to decrease the total carbon content of the cathode, resulting in the enhanced energy density.

Lithium iron phosphate with high-rate capability synthesized through hydrothermal reaction in glucose solution

Carbon-coated lithium iron phosphate (LiFePO 4/C) was hydrothermally synthesized from commercial LiOH, FeSO 4 and H 3PO 4 as raw materials and glucose as carbon precursor in aqueous solution at 180 °C for 6 h followed by being fired at 750 °C for 6 h. The samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and constant current charge–discharge cycling test. The results show that the synthesized powders are in situ coated with carbon precursor produced from glucose. At ambient temperature (25 ± 2 °C), the specific discharge capacities are 154 mAh g −1 at 0.2 C and 136 mAh g −1 at 5 C rate, and the cycling capacity retention rate reaches 98% over 90 cycles. The excellent electrochemical performance can be correlated with the in situ formation of carbon precursor/carbon, thus leading to the even distribution of carbon and the enhancement of conductibility of individual grains.

Electrochemical properties of lithium iron phosphate cathode material using polymer electrolyte

Carbon-coated lithium iron phosphate (LiFePO4/C) cathode material was synthesized by mechano-chemical activation method. The performance of LiFePO4/C in lithium battery was tested with an electrospun polymer-based electrolyte. Liquid electrolyte of 1M lithium hexafluorophosphate (LiPF6) in ethylene carbonate/dimethyl carbonate (EC/DMC) (1 : 1vol) was incorporated in electrospun poly(vinylidene fluoride-co-hexafluoropropylene) (P(VdF-HFP)) microfibrous membrane to prepare the polymer electrolyte (PE). The cell based on Li|PE|Li FePO4/C exhibited an initial discharge capacity of 142 mAh g−1 at 0.1 C-rate at room temperature. Good cycling performance even under the high current density of 2 C could be obtained. Impedance spectroscopy was applied to investigate the material behavior during 0.1 C-rate charge–discharge cycling. When the fresh cell and the cell after different cycles were compared, impedance resistance was found to decrease with cycling. Impedance study indicated good cycle life for the cell when tested at room temperature.

A modified mechanical activation synthesis for carbon-coated LiFePO 4 cathode in lithium batteries

An efficient synthesis based on mechanical activation (MA) was developed for carbon-coated lithium iron phosphate (LiFePO 4/C). The conventional MA process was modified by introducing two initial steps of slurry phase blending of the ingredients and solvent removal by rotary evaporation, so as to get an intimate mixing and homogenous dispersion of conductive carbon in the sample. Phase-pure, nanometer-sized particles of the active material covered with a porous, nanometer-sized web of carbon were obtained. LiFePO 4/C exhibited remarkably good electrochemical properties when evaluated as cathodes in room temperature lithium cells. An initial discharge capacity of 166 mAh/g (corresponding to 97.6% of theoretical capacity) was achieved at 0.1 C-rate. A very stable cycle performance was also realized; good capacity retention up to 100 cycles was achieved at different current densities.

High temperature stability of batteries containing Carbon-Coated Lithium Iron Phosphate

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