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

ABSTRACT: 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.

SUBMITTER: Paolella A

PROVIDER: S-EPMC4264480 | biostudies-literature | 2014 Dec

REPOSITORIES: biostudies-literature

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

Paolella Andrea A Bertoni Giovanni G Marras Sergio S Dilena Enrico E Colombo Massimo M Prato Mirko M Riedinger Andreas A Povia Mauro M Ansaldo Alberto A Zaghib Karim K Manna Liberato L George Chandramohan C

Nano letters 20141118 12

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 synthesi ...[more]

PMID: 25372361

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Project description:A new synthetic method to grow O-deficient rutile TiO2(s) nanorods (NRs) and nanowires (NWs) by a vapor-solid reaction growth method is developed. TiCl4(g) was employed to react with commercially supplied CaTiO3(s) (size 2-4 ?m) at 973 K under atmospheric pressure to generate TiO2(s) NRs (diameters 80-120 nm, lengths 1-4 ?m). The reaction employing TiCl4(g) and CaO(s) at 973 K also generated CaTiO3(s) (size 4-13 ?m) as the intermediate which reacted further with TiCl4(g) to produce NWs (diameters 80-120 nm, lengths 4-15 ?m). This is the first report of 1D rutile TiO2(s) nanostructure with such a high aspect ratio. Both of the NRs and the NWs, with compositions TiO1.81 and TiO1.65, respectively, were single crystals grown in the [001] direction. Their morphology was affected by the reaction temperature, the concentration of TiCl4(g), and the particle size of CaTiO3(s). The NRs and the NWs were investigated as anode materials for Li+-ion batteries. At constant current rates 1, 2, and 5 C (1 C = 170 mA g-1) for 100 cycles, the cycling (1.0-3.0 V) performance data of the NRs were 146, 123, and 104 mA h g-1, respectively. On the other hand, the cycling performance data of the NWs were 120, 80, and 52 mA h g-1, respectively. This is attributed to the high Li+ ion diffusion rate (D Li+ ) of the NRs (29.52 × 10-15 cm2 s-1), which exceeds that of the NWs (8.61 × 10-15 cm2 s-1). Although the [001] growth direction of the NR crystals would provide the fastest channels for the diffusion of Li+ ions and enhance the battery capacity, the extremely long channels in the NWs could hamper the diffusion of the Li+ ions. The O-deficiency in the structure would increase the conductivity of the electrode material and improve the stable cycling stability of the batteries also. The long-term cycling test at 2 C for the battery constructed from the NRs retained 121 mA h g-1 after 200 cycles and 99.2 mA h g-1 after 800 cycles. The device has an excellent long-term cycling stability with a loss of only 0.04% per cycle.

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

Publications

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

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