RESUMEN
The bad electrochemical performance circumscribes the application of commercial TiO2 (c-TiO2) anodes in Li-ion batteries. Carbon coating could ameliorate the electronic conductivity of TiO2, but the ionic conductivity is still inferior. Herein, a co-modification method was proposed by combining the solid electrolyte of lithium magnesium silicate (LMS) with pitch-derived carbon to concurrently meliorate the electronic and ionic conductivities of c-TiO2. The homogeneous mixtures were heated at 750 °C, and the co-modified product with suitable amounts of LMS and carbon demonstrates cycling capacities of 256.8, 220.4, 195.9, 176.4, and 152.0 mA h g-1 with multiplying current density from 100 to 1600 mA g-1. Even after 1000 cycles at 500 mA g-1, the maintained reversible capacity was 244.8 mA h g-1. The superior rate performance and cyclability correlate closely with the uniform thin N-doped carbon layers on the surface of c-TiO2 particles to favor the electrical conduction, and with the ion channels in LMS as well as the cation exchangeability of LMS to facilitate the Li+ transfer between the electrolyte, carbon layers, and TiO2 particles. The marginal amount of fluoride in LMS also contributes to the excellent cycling stability of the co-modified c-TiO2.
RESUMEN
The poor cyclability and rate property of commercial TiO2 (c-TiO2) hinder its utilization in lithium-ion batteries (LIBs). Coating carbon is one of the ways to ameliorate the electrochemical performance. However, how to effectively form a uniform thin carbon coating is still a challenge. On the basis of the strong interaction of the TiO2 surface with carboxyl groups, herein a new tactic to achieve uniform and thin carbon layers on the c-TiO2 particles was proposed. When mixing c-TiO2 with citric acid containing carboxyl groups in deionized water, the high-affinity adsorption of TiO2 for carboxyl groups resulted in self-assembled carboxylate monolayers on the surface of TiO2 which evolved into a uniform few-layered amorphous carbon coating during carbonizing at 750 °C. The product derived from the mixture of c-TiO2 and citric acid with a mass ratio of 1 : 0.3 exhibits the optimal performance, revealing a high specific capacity (256.6 mA h g-1 after 50 cycles at 0.1 A g-1) and outstanding cycling stability (retaining a capacity of 160.0 mA h g-1 after 1000 cycles at 0.5 A g-1). The greatly enhanced capacity and cyclability correlate with the uniform few-layered carbon coating which not only ameliorates the electronic conductivity of c-TiO2 but also avoids the reduction in ionic conductivity caused by thick carbon layers and redundant carbon.
RESUMEN
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.
RESUMEN
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.
RESUMEN
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.
RESUMEN
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.
RESUMEN
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.
RESUMEN
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.
RESUMEN
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.