Journal ClubShu Jinbo2012.11.27

Direct Synthesis of Self-Assembled Ferrite/Carbon Hybrid

Nanosheets for High Performance Lithium-Ion Battery Anodes

Journal of the American Chemical Society Received: June 8, 2012

Department of Nano Science and Technology, Graduate School of Convergence Science and Technology, Seoul National University, South Korea

• Rapidly growing demand for energy storage devices for portable electronic devices and electric vehicles will require high perform-ance rechargeable batteries.

• Although LIBs have been widely used in a variety of applications, many issues including their energy density, durability, and economic effciency are still being intensively studied for further improvement.

• Transition-metal oxides are promising high-energy-density materials with their high theoretical capacity ( 1000mAhg∼ −1), which consid-erably exceeds that of commercial graphitic anodes (372 mAh g−1).

• 1.INTORDUCTION

• However,low electrical conductivity and poor durability have impeded their use as LIB electrode materials.

• Solutions:Nanostructure and carbon coating

Herein, we present a single-step method for the direct preparation of self-assembled ferrite/carbon hybrid nanosheets, and their applicati

ons to high performance lithium-ion battery anodes.

• 2.EXPERIMENTAL SECTION

Experiment process

• 2.EXPERIMENTAL SECTION

Preparation of 16 nm Iron-Oxide/Carbon Hybrid Nanosheets.

In a typical synthesis, 0.36 g of iron(III) chloride hexahydrate was dissolved in 1.0 mL of DI water and then mixed with 1.22 g of sodium oleate.

The resulting mixture was aged at 85°C for 3 h, and then was mixed with 10 g of sodium sulfate powder.

The mixture was heated to 600 °C at the heating rate of 10 °C min−1 under N2 atmosphere and then kept at that temperature for 3 h.

Afterbeing cooled, the product was washed with DI water and dried at 100°C for 6 h.

The 30 nm Iron-Oxide/Carbon Nanosheets was achieved at the same condition except a heating rate of 5°Cmin-1

• 2.EXPERIMENTAL SECTION

Preparation of 3-D Nanocomposites

The procedure was the same as the preparation of ferrite/carbon hybrid nanosheets described above except that sodium sulfate powder was not added.

Preparation of 10 nm Manganese-Ferrite/Carbon Nanosheets.

0.087 g of manganese(II) chloride tetrahydrate and 0.24 g of iron(III) chloride hexahydrate were dissolved in 1.0 mL of DI water. And the following process was the same as above.

(a) FESEM image and (b) TEM image of 30 nm ironoxide/carbon nanosheets

(c) FESEM image, and (d) TEM image of 10 nm manganese-ferrite/carbon nanosheets

systhesis strategies

First, the surface of thermally stable salt particles was used as the template for the 2-D nanostructure.

Second, metal-oleate complex was used as the precursor of both ferrite and carbon.

“wrap-bake-peel process”

WRAP an aqueous solution of metal chloride and sodium oleate were mixed together, whereupon sodium sulfate was added and then ground mechanically until it became a fine powder. During this process, in situ formed metal-oleate complex was uniformly coated on the surface of sodium sulfate particles.

BAKE This mixture was heated at 600 °C under inert atmosphere to form 2-D ferrite/carbon hybrid nanosheet structures.

PEEL the hybrid nanosheets were separated by dissolving sodium sulfate particles in deionized (DI) water.

an in situ synthesis of nanoparticles embedded in a porous carbon matrix through a miniemulsion polymeriza-on process

a thermal treatment method, called as “wrap-bake-peel process,”

Thermal dynamics and optimization on solid-state reaction for synthesis of Li2MnSiO4 materials

Journal of Power Sources211 (2012) 97-102

School of Chemistry and Materials Science, Shanxi Normal University, Linfen 041004, China

• In the present study, to further understand solid-state reaction during preparing Li2MnSiO4, the synthetic process was analyzed by thermogravimetry-differential scanning calorimetry (TG-DSC) and Fourier transform infrared spectroscopy (FTIR).

• Based on the thermal dynamic results, an optimized step-sintering method was proposed to prepare Li2MnSiO4

• 1.Introduction

• Lithium transition metal orthosilicates (Li2MSiO4, M=Fe2+, Mn2

+, Co2+, Ni2+), have been attracting much attention as promising new storage cathodes.

• Among these silicate family materials, Li2MnSiO4 is considered to have a more potential market value than other counterparts.

There are the hightheoretical capacities over 300 mAhg-1 if the transition metal

ions can be oxidized and reduce reversibly from Mn2+ to Mn4+

Li2MnSiO4 shows appropriate lithium extraction voltage, which can be more suitable for the current organic electrolytes.

The resources to prepare Li2MnSiO4 material are plentiful and clean

• 1.Introduction

• 2.Experimental

stoichiometric amount of SiO2, LiCH3COO and Mn(CH3COO)2 were ground to fine powder together

the stoichiometric precursors were first heated to 200 and stayed fo℃r 2 h. Then, after milling and compacting, the obtained mixture was again transferred into vacuum tube furnace and successively calcinated at 400 for 3 h, 500 for 2 h, 700 for 10 h.℃ ℃ ℃

3.1 TG-DTG

• 3. Results and discussion

• In the present study, the TG-DSC and FTIR experiments infer that the main reaction of Li2MnSiO4 should be completed before 450℃

• 3. Results and discussion

3.2. FTIR at different temperatures

• 3. Results and discussion

3.3. SEM

• The samples show irregularly-shaped aggregates composed of nanometer-sized primary particles(10-100 nm).

3.4. XRD

• It can be seen that the positions of main peaks are almost similar for the both samples.

• A few MnO impurities can be detected in both cases, in agreement with other reports

• 3. Results and discussion

3.5 electrochemical performance

• 3. Results and discussion

• It can be seen that the initial charge capacities are 146.5 mAhg-1for LMS cell and 201.8 mAhg-1 for O-LMS cell, corresponding to the exaction of 0.88 and 1.21 Li per unit formula respectively.

• 4. Conclusions

• main reaction of Li2MnSiO4 should be completed before 450℃

• Capacities of 146.5 mAhg-1for LMS cell and 201.8 mAhg-1 for O-LMS cell are achieved, corresponding to the exaction of 0.88 and 1.21 Li per unit formula respectively.

LiNi0.5Mn1.5O4 Hollow Structures as High-Performance Cathodes for

Lithium-Ion Batteries

Angewandte ChemieReceived: October 4, 2011

School of Chemical and Biomedical EngineeringNanyang Technological University

• To meet the requirements of these applications of LIBs, further improvements in terms of energy and power densities, safety, and lifetime are required.

• When compared to pristine LiMn2O4, Ni-doped LiNi0.5Mn1.5O4 shows significantly improved cycling performance and increased energy density

• Herein, we present a morphology-controlled synthesis of LiNi0.5Mn1.5O4 hollow microspheres and microcubes with nanosized subunits by an impregnation method followed by a simple solidstate reaction

• 1.INTORDUCTION

• 2.Experimental

• In step 1, the MnCO3 microspheres and microcubes are converted into MnO2 bythermal decomposition at 400 .℃

2MnCO3 +O2 MnO2 +2CO2.

• In step 2, LiOH·H2O and Ni(NO3)2·6H2O are introduced into the mesopores of the MnO2 microspheres/microcubes by a simple impregnation method

• The reactions involved in step 3 are multi-step and rather complicat-ed, including a ground step and a calcination process.

3.1. XRD

• Both patterns can be assigned to well-crystallized cubic spinel LiNi0.5Mn

1.5O4 , with minor residues that can be attributed to LixNi1-xO2.

• 3. Results and discussion

• 3. Results and discussion

3.2. SEM

nanocubes are formed with additional NH4SO4

3.4 electrochemical performance

• 3. Results and discussion

• As the current density increases from 1 to 2, 5, 10, and 20C, the discharge capacity decreases slightly from 118 to 117, 115, 111.5, and 104 mAhg-1, respectively

• 4. Conclusions

• uniform LiNi0.5Mn1.5O4 hollow microspheres/microcubes with nanosized building blocks have been synthesized by a facile impregnation approach.

• the nanosized/submicrometer-sized building blocks provide short distances for Li+ diffusion and large electrode–electrolyte contact area or high Li+ flux across the interface,

• the structural strain and volume change associated with the repeated Li+ insertion/extraction processes could be buffered by the porosity in the wall and interior void space, thus improving the cycling stability.

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