Journal Club Shu Jinbo

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 applications 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 N 2 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 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 Li 2 MnSiO 4 materials Journal of Power Sources 211 (2012) School of Chemistry and Materials Science, Shanxi Normal University, Linfen , China

In the present study, to further understand solid-state reaction during preparing Li 2 MnSiO 4, 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 Li 2 MnSiO 4 1.Introduction

Lithium transition metal orthosilicates (Li 2 MSiO 4, M=Fe 2+, Mn 2+, Co 2+, Ni 2+ ), have been attracting much attention as promising new storage cathodes. Among these silicate family materials, Li 2 MnSiO 4 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 Mn 2+ to Mn 4+  Li 2 MnSiO 4 shows appropriate lithium extraction voltage, which can be more suitable for the current organic electrolytes.  The resources to prepare Li 2 MnSiO 4 material are plentiful and clean 1.Introduction

2.Experimental stoichiometric amount of SiO 2, LiCH 3 COO and Mn(CH 3 COO) 2 were ground to fine powder together the stoichiometric precursors were first heated to 200 ℃ and stayed for 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 Li 2 MnSiO 4 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( 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 mAhg -1 for LMS cell and 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 Li 2 MnSiO 4 should be completed before 450 ℃ Capacities of mAhg-1for LMS cell and mAhg-1 for O-LMS cell are achieved, corresponding to the exaction of 0.88 and 1.21 Li per unit formula respectively.

LiNi 0.5 Mn 1.5 O 4 Hollow Structures as High- Performance Cathodes for Lithium-Ion Batteries Angewandte Chemie Received: October 4, 2011 School of Chemical and Biomedical Engineering Nanyang 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 LiMn 2 O 4, Ni-doped LiNi 0.5 Mn 1.5 O 4 shows significantly improved cycling performance and increased energy density Herein, we present a morphology-controlled synthesis of LiNi 0.5 Mn 1.5 O 4 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 MnCO 3 microspheres and microcubes are converted into MnO 2 bythermal decomposition at 400 ℃. 2MnCO 3 +O 2 MnO 2 +2CO 2. In step 2, LiOH·H 2 O and Ni(NO 3 ) 2 ·6H 2 O are introduced into the mesopores of the MnO 2 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 LiNi 0.5 Mn 1.5 O 4, with minor residues that can be attributed to Li x Ni 1-x O Results and discussion

3.2. SEM nanocubes are formed with additional NH 4 SO 4

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 LiNi 0.5 Mn 1.5 O 4 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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