Synthesis and Electrochemical Properties of Rhombohedral LiFePO4/C Microcrystals Via a Hydrothermal Route for Lithium Ion Batteries (original) (raw)
Related papers
Solid State Ionics, 2014
This paper describes the preparation, characterization and electrochemical study of various iron and lithium iron phosphates. The pristine iron phosphate samples obtained were amorphous materials with various textural properties, in terms of average pore size, pore order and specific surface area. Some solids were mesoporous, featuring high surface area, narrow pore size distribution and high pore volume. Lithium iron phosphates were obtained by chemical lithiation of these iron phosphates, using LiI dissolved in acetonitrile. These materials were amorphous and electrochemically inactive against lithium. Following heating at 550°C, the materials crystallized and showed disparate electrochemical performance in lithium half-cells. This can be ascribed not only to the presence in the samples of impurities of different nature (and inherent to the synthesis method), but also to different textural and morphological properties. In fact, the best electrochemical performance was that of crystallized LiFePO 4 obtained from the mesoporous iron phosphate and consisting of rounded nanoparticles with high surface area and adequate porosity. As a result, a better electrolyte impregnation in the porous structures is highly expected. Furthermore, enhancement of the lithium ion diffusion inside the network is observed. This justifies the potential use of carbon-free mesoporous precursors of LiFePO 4 . However, introduction of a conductive carbon coating onto the phosphate particles and/or removal of the impurities prove necessary for good capacity retention upon cycling.
A controllable synthesis of flower-like lithium iron phosphate LiFePO4 (LFP) was obtained via a two-stage heating during hydrothermal process. In the first stage, the temperature was held at 105 °C (LFP1), 120 °C (LFP2), 150 °C (LFP3) and 190 °C (LFP4) for 5 h. In the final stage, the temperature was held constant at 400 °C under H2/N2 atmosphere for 4 h. To increase the electrochemical reversibility and electronic conductivity, LFP is treated with polyethylene glycol (PEG) as the templating agent and carbon sources for the as-prepared materials. This is to obtain a modified LFP cathode with optimum electrical contact between the electroactive materials and the carbon-filled electrode matrix which is found to be effective in terms of raising the electrochemical performance of the Li-ion batteries. Results show that as the first-stage temperature increased, the corresponding electrochemical performance of the resulting sample has been increased up to a temperature of 150 °C. Galvanos...
2011
CITATIONS 3 READS 69 4 authors, including: Some of the authors of this publication are also working on these related projects: Synthesis and studies on controlled porosity composite thin layers and systems for energy storage and conversion applications View project Research Cooperation Project: Synthesis and studies on controlled porosity composite thin layers and systems for energy storage and conversion applications (2014-2017) View project
Hydrothermal synthesis of high surface LiFePO4 powders as cathode for Li-ion cells
Journal of Power Sources, 2006
An easy, quick and low cost hydrothermal synthesis was developed to prepare high surface area phospho-olivine LiFePO 4 powders to be used as cathode material for Li-ion batteries. The samples were prepared in double distilled water starting from commercial LiOH, FeSO 4 , H 3 PO 4 and using solutions with different concentrations of a surfactant compound (CTAB), in order to increase the specific surface areas, obtaining powders with very small grain size. The structural, morphological and electrochemical properties were investigated by means of X-ray powder diffraction (XRPD), ICP-AES, BET method, scanning electron microscopy (SEM) and constant current charge-discharge cycling. The electrochemical performances of LiFePO 4 prepared in this manner showed to be positively affected by the presence of CTAB during synthesis, showing capacities near the theoretical value, only slightly affected by the discharge regime (from C/20 to 10C).
A study on LiFePO 4 and its doped derivatives as cathode materials for lithium-ion batteries
Journal of Power Sources, 2006
LiFePO 4 , doped LiM x Fe 1−x PO 4 , and Li 1−x M x FePO 4 compounds have been prepared via a sol-gel synthesis method. The physical properties of the as-prepared lithium iron phosphates were characterised by X-ray diffraction, X-ray absorption near-edge spectroscopy (XANES), and magnetic susceptibility. The electrochemical properties lithium iron phosphates were tested by a variety of electrochemical techniques. Lithium iron phosphate electrodes demonstrated a stable discharge capacity of 160-165 mAh g −1 , almost approaching the theoretical capacity. The good electronic conductivity and nanocrystalline could contribute to the unique performance of lithium iron phosphate electrodes. Lithium iron phosphates have a significant potential to be used as a new cathode materials in Li-ion batteries.
Journal of Physics and Chemistry of Solids, 2010
The electrochemical performance of carbon-coated nanocrystalline LiFePO 4 prepared by a freeze-drying method is examined. This method is based on the thermal decomposition of homogeneous phosphateformate precursors. Structural and morphological characterization of LiFePO 4 is carried out by powder XRD, BET measurements, SEM and XPS analyses. The electrochemical behaviour is tested in model lithium cells using galvanostatic mode. By changing the solution concentration, the freeze-drying method allows preparing LiFePO 4 with mean particle sizes between 60 and 100 nm and different particle size distributions. The content of carbon appearing mainly on the particle surface depends on both the solution concentration and the annealing temperature. The effect of particle size distribution on the voltage profile of LiFePO 4 is also demonstrated. The specific capacity is mainly determined by the amount of carbon deposited on the particle surfaces.
Rsc Advances, 2013
Three dimensional hierarchical flower-like lithium iron phosphate (LiFePO 4) mesocrystals were successfully synthesized via a solvothermal approach with the utilization of a mixture of water/ethylene glycol/ dimethylacetamide (H 2 O/EG/DMAC) as co-solvent. No other surfactant or template agent was used and beautiful micro-sized LiFePO 4 mesoporous structures with a special rose-like morphology were obtained. The hierarchical LiFePO 4 mesocrystals were assembled by well crystallized nano-sized LiFePO 4 thin plates with a thickness around 100 nm. The characteristics and electrochemical dynamics as well as performance of the obtained hierarchical flower-like LiFePO 4 mesocrystals were carefully investigated. The flower-like hierarchical LiFePO 4 mesocrystals showed a high initial lithium intercalation capability of 147 mA h g 21 at a current density of 17 mA g 21 (0.1 C), which should be attributed to the high specific surface area resulting from the mesoporous superstructure and well crystallized LiFePO 4 nano-plate composition units. Polyvinylpyrrolidone (PVP) was introduced during the solvothermal synthesis as an in situ carbon coating source. The obtained flower-like C-coated LiFePO 4 mesocrystals exhibited even better initial lithium intercalation capability of 161 mA h g 21 at 0.1 C and showed improved lithium storage performance at high rates as well as good cyclic stability.
Pure lithium iron phosphate (LiFePO 4 ) and carbon-coated LiFePO 4 (C-LiFePO 4 ) cathode materials were synthesized for Li-ion batteries. Structural and electrochemical properties of these materials were compared. X-ray diffraction revealed orthorhombic olivine structure. Micro-Raman scattering analysis indicates amorphous carbon, and TEM micrographs show carbon coating on LiFePO 4 particles. Ex situ Raman spectrum of C-LiFePO 4 at various stages of charging and discharging showed reversibility upon electrochemical cycling. The cyclic voltammograms of LiFePO 4 and C-LiFePO 4 showed only a pair of peaks corresponding to the anodic and cathodic reactions. The first discharge capacities were 63, 43, and 13 mAh/g for C/5, C/3, and C/2, respectively for LiFePO 4 where as in case of C-LiFePO 4 that were 163, 144, 118, and 70 mAh/g for C/5, C/3, C/2, and 1C, respectively. The capacity retention of pure LiFePO 4 was 69% after 25 cycles where as that of C-LiFePO 4 was around 97% after 50 cycles. These results indicate that the capacity and the rate capability improved significantly upon carbon coating.
Electrochemical Performance of Sol-Gel Synthesized LiFePO[sub 4] in Lithium Batteries
Journal of The Electrochemical Society, 2004
LiFePO 4 , Li 0.98 Mg 0.01 FePO 4 , and Li 0.96 Ti 0.01 FePO 4 were synthesized via a sol-gel method using a variety of processing conditions. For comparison, LiFePO 4 was also synthesized from iron acetate by a solid-state method. The electrochemical performance of these materials in lithium cells was evaluated and correlated to LiFePO 4 powder morphology and residual carbon structure, as determined by Raman microprobe spectroscopy. For materials with mean agglomerate sizes below 20 m, an association between structure and crystallinity of the residual carbon and improved utilization was observed. Addition of small amounts of organic compounds or polymers during processing results in carbon coatings with higher graphitization ratios and better electronic properties on the LiFePO 4 samples and improves cell performance in some cases, even though total carbon contents remain low ͑Ͻ2%͒. In contrast, no performance enhancement was seen for samples doped with Mg or Ti. These results suggest that it should be possible to design high-power LiFePO 4 electrodes without unduly compromising energy density by optimizing the carbon coating on the particles.