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  1. Journal Club Shu Jinbo 2012.11.27

  2. Direct Synthesis of Self-Assembled Ferrite/Carbon Hybrid Nanosheets for High Performance Lithium-Ion Battery Anodes Journal of the AmericanChemical Society Received: June 8, 2012 Department of Nano Science and Technology, Graduate School of Convergence Science and Technology, Seoul National University, South Korea

  3. 1.INTORDUCTION • Rapidly growing demand for energy storage devices forportable electronic devices and electric vehicles will requirehigh perform-ance rechargeable batteries. • Although LIBs have been widely usedin a variety ofapplications, many issues including their energydensity, durability, and economic effciency are still beingintensively studied for further improvement. • Transition-metal oxides are promising high-energy-density materials with their high theoretical capacity (∼1000mAhg−1), whichconsid-erably exceeds that of commercialgraphitic anodes (372 mAh g−1).

  4. However,low electricalconductivity and poor durability have impeded their use as LIBelectrode 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.

  5. 2.EXPERIMENTAL SECTION Experiment process

  6. 2.EXPERIMENTAL SECTION Preparation of 16 nm Iron-Oxide/Carbon Hybrid Nanosheets. In a typical synthesis, 0.36 g of iron(III) chloride hexahydratewas dissolved in 1.0 mL of DIwater and then mixed with 1.22 g of sodium oleate. The resulting mixture was aged at 85°C for 3 h, and then wasmixed with 10 g of sodium sulfate powder. The mixture was heated to 600 °C at the heating rate of 10 °C min−1under 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.

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

  8. 2.EXPERIMENTAL SECTION Preparation of 3-D Nanocomposites The procedure was thesame as the preparation of ferrite/carbon hybrid nanosheets describedabove except that sodium sulfate powder was not added. Preparation of 10 nm Manganese-Ferrite/Carbon Nanosheets. 0.087 g of manganese(II) chloridetetrahydrate and 0.24 g ofiron(III) chloride hexahydrate were dissolved in 1.0 mL of DI water. And the following process was the same as above.

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

  10. (c) FESEM image, and (d) TEM image of10 nm manganese-ferrite/carbon nanosheets

  11. systhesis strategies First, the surface of thermally stable saltparticles was used as the template for the 2-D nanostructure. Second, metal-oleate complex was used as the precursor ofboth ferriteand carbon.

  12. “wrap-bake-peel process” WRAP an aqueous solution of metal chloride andsodium oleate were mixed together, whereupon sodium sulfatewas added and then ground mechanically until it became a finepowder. During this process, in situ formed metal-oleatecomplex was uniformly coated on the surface of sodium sulfateparticles. BAKEThis mixture was heated at 600 °C under inertatmosphere to form 2-D ferrite/carbon hybrid nanosheetstructures. PEELthe hybrid nanosheets were separated bydissolving sodium sulfateparticles in deionized (DI) water.

  13.  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,”

  14. Thermal dynamics and optimization on solid-state reaction for synthesisof Li2MnSiO4 materials Journal of Power Sources 211 (2012) 97-102 School of Chemistry and Materials Science, Shanxi Normal University, Linfen 041004, China

  15. 1.Introduction • In thepresent study, to further understand solid-state reaction duringpreparing Li2MnSiO4, the synthetic process was analyzed bythermogravimetry-differential scanning calorimetry (TG-DSC)and Fourier transform infrared spectroscopy (FTIR). • Based on thethermal dynamic results, an optimized step-sintering method wasproposed to prepare Li2MnSiO4

  16. 1.Introduction • Lithium transition metal orthosilicates(Li2MSiO4,M=Fe2+,Mn2+,Co2+,Ni2+), havebeen attractingmuch attention as promising newstorage cathodes. • Among these silicate family materials, Li2MnSiO4 is considered tohave 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

  17. 2.Experimental stoichiometricamount of SiO2,LiCH3COOandMn(CH3COO)2were ground to fine powder together thestoichiometric precursorswere first heated to 200℃and stayed for2 h. Then, after milling and compacting, the obtained mixture wasagain transferred into vacuum tube furnace and successively calcinated at 400 ℃ for 3 h, 500 ℃ for 2 h, 700℃ for 10 h.

  18. 3. Results and discussion 3.1 TG-DTG • In the present study, the TG-DSC and FTIR experiments inferthat the main reaction ofLi2MnSiO4 should be completed before450℃

  19. 3. Results and discussion 3.2. FTIR at different temperatures

  20. 3. Results and discussion 3.3. SEM • The samples show irregularly-shapedaggregates composed ofnanometer-sized primary particles(10-100 nm).

  21. 3. Results and discussion 3.4. XRD • It can be seen that the positions of main peaks are almostsimilar for the both samples. • A few MnO impurities can be detected in bothcases, in agreement with other reports

  22. 3. Results and discussion 3.5 electrochemical performance • It can be seenthat the initial charge capacities are 146.5 mAhg-1for LMS cell and201.8 mAhg-1 for O-LMS cell, corresponding to the exaction of 0.88and 1.21 Liper unit formula respectively.

  23. 4. Conclusions • main reaction of Li2MnSiO4 should be completed before450℃ • Capacities of 146.5 mAhg-1for LMS cell and201.8 mAhg-1 for O-LMS cell are achieved, corresponding to the exaction of 0.88and 1.21 Liper unit formula respectively.

  24. LiNi0.5Mn1.5O4 Hollow Structures as High-Performance Cathodes for Lithium-Ion Batteries AngewandteChemie Received: October 4, 2011 School of Chemical and Biomedical Engineering Nanyang Technological University

  25. 1.INTORDUCTION • To meet the requirements of these applications of LIBs, further improvements in terms of energy and powerdensities, safety, and lifetime are required. • When comparedto pristine LiMn2O4, Ni-doped LiNi0.5Mn1.5O4 shows significantly improved cycling performance and increased energydensity • Herein, we present a morphology-controlled synthesis ofLiNi0.5Mn1.5O4 hollow microspheres and microcubes withnanosized subunits by an impregnation method followed by a simple solidstate reaction

  26. 2.Experimental

  27. In step 1, the MnCO3microspheres and microcubes are converted into MnO2 bythermal decomposition at 400℃. 2MnCO3 +O2MnO2 +2CO2. • In step 2,LiOH·H2O and Ni(NO3)2·6H2O are introduced into themesopores of the MnO2 microspheres/microcubes by asimple impregnation method • The reactions involved instep 3 are multi-step and rather complicat-ed, including a ground step and a calcination process.

  28. 3. Results and discussion 3.1. XRD • Both patterns can be assigned towell-crystallized cubic spinel LiNi0.5Mn1.5O4 , with minor residues that can be attributed to LixNi1-xO2.

  29. 3. Results and discussion 3.2. SEM nanocubes are formed with additional NH4SO4

  30. 3. Results and discussion 3.4 electrochemical performance • As the currentdensity increases from 1 to 2, 5, 10, and 20C, the dischargecapacity decreases slightly from 118 to 117, 115, 111.5, and104 mAhg-1, respectively

  31. 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 distancesfor Li+ diffusion and large electrode–electrolyte contact areaor high Li+ flux across the interface, • the structural strain and volume changeassociated with the repeated Li+ insertion/extraction processes could be buffered by the porosity in the wall andinterior void space, thus improving the cycling stability.