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1.
ACS Omega ; 4(5): 8312-8317, 2019 May 31.
Artigo em Inglês | MEDLINE | ID: mdl-31459918

RESUMO

In the present work, we report, for the first time, a novel one-step approach to prepare highly graphitized carbon (HGC) material by selectively etching calcium from calcium carbide (CaC2) using a sulfur-based thermo-chemical etching technique. Comprehensive analysis using X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, and N2 adsorption-desorption isotherms reveals a highly graphitized mesoporous structure for the CaC2-derived carbon with a specific surface area of 159.5 m2 g-1. Microscopic analysis displays micron-scale mesoporous frameworks (4-20 µm) with a distinct layered structure along with agglomerates of highly graphitized nanosheets (about 10 nm in thickness and 1-10 µm lateral size). The as-prepared HGC is investigated for the role of an anode material for lithium- and sodium-ion batteries. We found that HGC exhibits good lithium storage performance in the 0.01-1.5 V range (reversible capacity of 272.4 mA h g-1 at 50 mA g-1 after 100 cycles and 214.2 mA h g-1 at 500 mA g-1 after 500 cycles), whereas, when sodium is considered, we observed a drop in the overall electrochemical performance owing to the high graphitization degree. More importantly, the present study provides a perspective approach to fabricate HGC via a simple, cost-effective, and efficient synthetic route using CaC2 and sulfur as reactants.

2.
ACS Appl Mater Interfaces ; 10(29): 24910-24919, 2018 Jul 25.
Artigo em Inglês | MEDLINE | ID: mdl-29965723

RESUMO

The low electrical conductivity and ordinary lithium-ion transfer capability of Li4Ti5O12 restrict its application to some degree. In this work, dual-phase Li4Ti5O12-TiO2 (LTOT) was modified by composite zirconates of Li2ZrO3, Li6Zr2O7 (LZO) to boost the rate capabilities and cyclability. When the homogeneous mixture of LiNO3, Zr(NO3)4·5H2O and LTOT was roasted at 700 °C for 5 h, the obtained composite achieved a superior reversible capacity of 183.2 mAh g-1 to the pure Li4Ti5O12 after cycling at 100 mA g-1 for 100 times due to the existence of a scrap of TiO2. Meanwhile, when the composite was cycled by consecutively doubling the current density between 100 and 1600 mA g-1, the corresponding reversible capacities are 183.2, 179.1, 176.5, 173.3, and 169.3 mAh g-1, signifying the prominent rate capabilities. Even undergoing 1400 charge/discharge cycles at 500 mA g-1, a reversible capacity of 144.7 mAh g-1 was still attained, denoting splendid cyclability. From a series of comparative experiments and systematic characterizations, the formation of LZO meliorated both the Li+ migration kinetics and electrical conductivity on account of the concomitant superficial Zr4+ doping, responsible for the comprehensive elevation of the electrochemical performance.

3.
ACS Appl Mater Interfaces ; 9(50): 43603-43613, 2017 Dec 20.
Artigo em Inglês | MEDLINE | ID: mdl-29172428

RESUMO

Poor ionic and electronic conductivities are the key issues to affect the electrochemical performance of Li2ZnTi3O8 (LZTO). In view of the water solubility, low melting point, good electrical conductivity, and wettability to LZTO, Na2MoO4 (NMO) was first selected to modify LZTO via simply mixing LZTO in NMO water solution followed by calcining the dried mixture at 750 °C for 5 h. The electrochemical performance of LZTO could be enhanced by adjusting the content of NMO, and the modified LZTO with 2 wt % NMO exhibited the most excellent rate capabilities (achieving lithiation capacities of 225.1, 207.2, 187.1, and 161.3 mAh g-1 at 200, 400, 800, and 1600 mA g-1, respectively) as well as outstanding long-term cycling stability (delivering a lithiation capacity of 229.0 mAh g-1 for 400 cycles at 500 mA g-1). Structure and composition characterizations together with electrochemical impedance spectra analysis demonstrate that the molten NMO at the sintering temperature of 750 °C is beneficial to diffuse into the LZTO lattices near the surface of LZTO particles to yield uniform modification layer, simultaneously ameliorating the electronic and ionic conductivities of LZTO, and thus is responsible for the enhanced electrochemical performance of LZTO. First-principles calculations further verify the substitution of Mo6+ for Zn2+ to realize doping in LZTO. The work provides a new route for designing uniform surface modification at low temperature, and the modification by NMO could be extended to other electrode materials to enhance the electrochemical performance.

4.
ACS Appl Mater Interfaces ; 9(2): 1426-1436, 2017 Jan 18.
Artigo em Inglês | MEDLINE | ID: mdl-28001350

RESUMO

Ionic conductor of Li2SiO3 (LSO) was used as an effective modifier to fabricate surface-modified Li4Ti5O12 (LTO) via simply mixing followed by sintering at 750 °C in air. The electrochemical performance of LTO was enhanced by merely adjusting the mass ratio of LTO/LSO, and the LTO/LSO composite with 0.51 wt % LSO exhibited outstanding rate capabilities (achieving reversible capacities of 163.8, 157.6, 153.1, 147.0, and 137.9 mAh g-1 at 100, 200, 400, 800, and 1600 mA g-1, respectively) and remarkable long-term cycling stability (120.2 mAh g-1 after 2700 cycles with a capacity fading rate of only 0.0074% per cycle even at 500 mA g-1). Combining structural characterization with electrochemical analysis, the LSO coating coupled with the slight doping effect adjacent to the LTO surface contributes to the enhancement of both electronic and ionic conductivities of LTO.

5.
ACS Appl Mater Interfaces ; 7(9): 5107-15, 2015 Mar 11.
Artigo em Inglês | MEDLINE | ID: mdl-25706088

RESUMO

Sulfur-containing carbon nanofibers with the graphene layers approximately vertical to the fiber axis were prepared by a simple reaction between thiophene and sulfur at 550 °C in stainless steel autoclaves without using any templates. The formation mechanism was discussed briefly, and the potential application as anode material for lithium-ion batteries was tentatively investigated. The carbon nanofibers exhibit a stable reversible capacity of 676.8 mAh/g after cycling 50 times at 0.1 C, as well as the capacities of 623.5, 463.2, and 365.8 mAh/g at 0.1, 0.5, and 1.0 C, respectively. The excellent electrochemical performance could be attributed to the effect of sulfur. On one hand, sulfur could improve the reversible capacity of carbon materials due to its high theoretical capacity; on the other hand, sulfur could promote the formation of the unique carbon nanofibers with the graphene layers perpendicular to the axis direction, favorable to shortening the Li-ion diffusion path.

6.
ACS Appl Mater Interfaces ; 5(19): 9470-7, 2013 Oct 09.
Artigo em Inglês | MEDLINE | ID: mdl-24007324

RESUMO

Fe-Mn-O composite oxides with various Fe/Mn molar ratios were prepared by a simple coprecipitation method followed by calcining at 600 °C, and carbon-coated oxides were obtained by pyrolyzing pyrrole at 550 °C. The cycling and rate performance of the oxides as anode materials are greatly associated with the Fe/Mn molar ratio. The carbon-coated oxides with a molar ratio of 2:1 exhibit a stable reversible capacity of 651.8 mA h g(-1) at a current density of 100 mA g(-1) after 90 cycles, and the capacities of 567.7, 501.3, 390.7, and 203.8 mA h g(-1) at varied densities of 200, 400, 800, and 1600 mA g(-1), respectively. The electrochemical performance is superior to that of single Fe3O4 or MnO prepared under the same conditions. The enhanced performance could be ascribed to the smaller particle size of Fe-Mn-O than the individuals, the mutual segregation of heterogeneous oxides of Fe3O4 and MnO during delithiation, and heterogeneous elements of Fe and Mn during lithiation.

7.
ACS Appl Mater Interfaces ; 5(10): 4209-15, 2013 May 22.
Artigo em Inglês | MEDLINE | ID: mdl-23627302

RESUMO

FeWO4 (FWO) nanocrystals were prepared at 180 °C by a simple hydrothermal method, and carbon-coated FWO (FWO/C) was obtained at 550 °C using pyrrole as a carbon source. The FWO/C obtained from the product hydrothermally treated for 5 h exhibits reversible capacities of 771.6, 743.8, 670.6, 532.6, 342.2, and 184.0 mAh g(-1) at the current densities of 100, 200, 400, 800, 1600, and 3200 mA g(-1), respectively, whereas that from the product treated for 0.5 h achieves a reversible capacity of 205.9 mAh g(-1) after cycling 200 times at a current density of 800 mA g(-1). The excellent electrochemical performance of the FWO/C results from the combination of the nanocrystals with good electron transport performance and the nitrogen-doped carbon coating.

8.
J Colloid Interface Sci ; 329(1): 48-53, 2009 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-18922543

RESUMO

High molecular weight powdery polyacrylonitrile (PAN) polymers were prepared by aqueous suspension polymerization employing itaconic acid (IA) as comonomer and alpha,alpha(')-azobisisobutyronitrile (AIBN) as initiator at 60 degrees C. PAN polymers obtained with different monomer ratios were characterized by EA, DSC, FTIR and XRD. It is investigated that the oxygen element content in PAN polymers increased with the increase of required IA amounts in the feed and heat-treatment temperatures. DSC curves of PAN copolymers exhibited the triplet character, owing to the exothermic cyclization and oxidative reactions during heat-treatment process. Introduction of IA in the feed relaxed exothermic reactions of PAN polymers under air atmosphere. Structure and crystallinity changes were affected by required IA amounts in the feed and enhancement of heat-treatment temperatures. The characteristic functional groups (including C[triple bond]N, C=O, CH(2)) presented in FTIR spectra of PAN polymers indicated copolymerization reaction of AN and IA. Existence of some organic groups (C-O, C=C and/or C=N) indicated formation of ladderlike structure during heat-treatment process. PAN homopolymer had the better crystallinity (mainly peak intensity and peak area around 2theta = 17 degrees) than most RT-PAN copolymers. When heat-treatment temperature is around 210 degrees C, peak intensity, peak area, L(c) and CI of HT-PAN polymers corresponding to samples 1# and 2# got maxima, while crystallinity became weak at higher heat-treatment temperatures.

9.
Inorg Chem ; 43(12): 3558-60, 2004 Jun 14.
Artigo em Inglês | MEDLINE | ID: mdl-15180407

RESUMO

TiN nanocrystals were successfully prepared through the direct reaction between TiCl(4) and NaNH(2) induced at 300 degrees C. The yield based on Ti is approximately 80%. X-ray powder diffraction indicated that the product was cubic TiN with a lattice constant of a = 4.243 A. Transmission electron microscopy revealed that nanocrystalline TiN with a diameter of 10 nm or so and extremely long straight rods were synthesized. The possible formation mechanism was also proposed.

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