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.Keywords: anode material; first-principles; Li2ZnTi3O8; modification; Na2MoO4;

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.Keywords: anode material; first-principles; Li2ZnTi3O8; modification; Na2MoO4;

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.Keywords: anode materials; ionic conductor; Li2SiO3; Li4Ti5O12; surface modification;

•Mn3O4/Ni(OH)2 composites were simply synthesized by a hydrothermal method.•Mn-doped Ni(OH)2 and Ni-doped Mn3O4 enhance the conductivity of the composite.•The Mn3O4/Ni(OH)2 supercapacitor (SC) electrode exhibits excellent cyclability.•The Mn3O4/Ni(OH)2//active carbon reveals superior energy and power density.Mn3O4/Ni(OH)2 nanocomposites are simply synthesized by a hydrothermal reaction between MnCl2.4H2O, NiCl2.6H2O and NaOH at 200 °C. Compared with the individual Ni(OH)2 and Mn3O4 prepared under the same conditions, the Mn3O4/Ni(OH)2 composite hydrothermally treated for 5 h achieves excellent specific capacitance (707 F g−1 at 1 A g−1 in 1 M KOH electrolyte) and remarkable long-term cycling stability (retaining a capacitance retention of 89% after 2000 cycles at 2 A g−1). Meanwhile, the asymmetric supercapacitor constructed by the Mn3O4/Ni(OH)2 composite and active carbon delivers an energy density of 17.8 W h kg−1 at a power density of 162 W kg−1. The outstanding performance is attributable to the synergistic compositing effect of Mn3O4 and Ni(OH)2, yielding not only the mutual doping of Mn3+ in Ni(OH)2 and Ni2+ in Mn3O4 to improve the electronic conductivity of the Mn3O4/Ni(OH)2 composite but also the suitable mesoporous structure for electrolyte transfer. Thus the Mn3O4/Ni(OH)2 composites will be alternative candidates as practical electrode materials for pseudocapacitors.Download high-res image (123KB)Download full-size image

•N-doped carbon-coated TiN (TiN/C) was fabricated using pyrrole as carbon source.•The TiN/C supercapacitor retains 92% of the initial capacitance after 5000 cycles.•The carbon coating raises the anti-oxidation yet remains the activity of TiN.•Asymmetric TiN/C//MnO2 supercapacitor reveals high energy and power density.TiN used as supercapacitor (SC) electrode in aqueous electrolyte is prone to suffering from oxidation, leading to poor electrical conductivity and electrochemical activity. In this work, TiN nanoparticles were synthesized at 530 °C by the reaction between Ti powder and NH4Cl in stainless steel autoclaves, which further reacted with pyrrole at 550 °C to yield N-doped carbon-coated TiN (TiN/C) with mesopores. TiN/C as electrode material for SC exhibits excellent electrochemical performance in 1 M KOH electrolyte, achieving a specific capacitance of 102.6 F g−1 at a current density of 1 A g−1 and retaining a specific capacitance of 94.4 F g−1 after 5000 cycles (corresponding to capacitance retention of 92%). In particular, the TiN/C with a low operation voltage window and superior long-term cycling stability is a promising negative electrode for asymmetric SCs. The SC constructed by TiN/C and MnO2 reveals a high energy density of 17.2 Wh kg−1 as well as excellent cycling stability in 1 M KOH electrolyte. The protective amorphous carbon coated on the TiN nanoparticles significantly improves the anti-oxidizability of TiN yet preserves the electrochemical activity via the loose carbon structure. Therefore, the TiN/C nanocomposite with low cost is promising and applicable in SCs.Download high-res image (240KB)Download full-size image

•Li4Ti5O12 (LTO) composited with tetragonal Li2ZrO3 was simply fabricated.•Li4Ti5O12 composited with Li2ZrO3 exhibits excellent cycle and rate performance.•Li2ZrO3 and superficial Zr4+ doping enhance the conductivities of LTO.Li4Ti5O12 (LTO) is inherently a poor ionic and electronic conductor, and the modification methods available could solely meliorate either ionic or electronic conductivity. In order to simultaneously improve both the ionic and electronic conductivities, LTO was composited with Li2ZrO3 accompanying with superficial Zr4+ doping by the simple reaction between Zr(NO3)4·5H2O and LiNO3 on the LTO surface. From the comparative experiments, the as-modified LTO with a Li2ZrO3/LTO mass ratio of 0.009 and sintered at 750 °C exhibits the most excellent rate performance (achieving capacities of 155.3, 149.6, 145.4, 139.6, 130.2 and 153.2 mAh g−1 at 100, 200, 400, 800, 1600 and 100 mA g−1, respectively) and long-term cyclability (retaining a capacity of 102 mAh g−1 after the 2000th cycle at 500 mA g−1). By the detailed structural characterization and electrochemical impedance spectra analysis, the formation of the tetragonal Li2ZrO3 with good ionic conductivity and the superficial Zr4+ doping with improved electronic conductivity is responsible for the markedly enhanced cycling and rate performance of LTO.Download high-res image (538KB)Download full-size image

Nitrogen-doped TiO2 nanoparticles coated with N-doped carbon are prepared by simply hydrolyzing tetrabutyl titanate to obtain TiO2 nanoparticles followed by heating the mixture of nanoparticles and urea at 550 °C for 5 h. The combination of simultaneously N-doping with coating carbon results in the enhancement in electronic and ionic conductivities, thus the modified TiO2 exhibits outstanding reversible capacities of 227.7, 204.0, 186.4, 160.6, 113.1 mAh g−1 corresponding to current densities of 100, 200, 400, 800 and 1600 mA g−1. In particular, the modified TiO2 could deliver an excellent long-term cycling capacity of 106.4 mAh g−1 even cycled 2500 times at a high density of 500 mA g−1 with an average capacity loss of only 0.016% per cycle. The modified TiO2 fabricated by this simple and economical method could serve as the anode material for lithium-ion batteries with high power-density.

The composite oxides of TiO2 and SnO2 (Ti–Sn–O) were fabricated by a simple precipitation method, followed by sintering at 400 °C and coating with N-doped carbon at 550 °C using pyridine as the carbon source. The carbon-coated composite with a Ti/Sn molar ratio of 1.7:0.3 used as anode materials for lithium ion batteries could deliver a reversible capacity of 629 mA h g−1 after cycling 300 times at a current density of 100 mA g−1, and a capacity of 289 mA h g−1 when cycling 300 times at 500 mA g−1. The outstanding cycling performance and high-rate performance result from the uniform N-doped carbon coating around the mutually dispersed TiO2 and SnO2 nanoparticles.

Al2O3-modified Ti–Mn–O nanocomposite with nitrogen-doped carbon coating is fabricated using metal chlorides as precursors and acrylonitrile as carbon source. The composite acting as anode material for lithium-ion batteries exhibits a reversible capacity of 420.7 mA h g−1 after cycling 100 times at a current density of 100 mA g−1 and excellent rate capabilities. The enhanced electrochemical performance results from synergistic compositing effect of TiO2 and MnO/MnTiO3 with a small amount of Al2O3, combining the high capacities of MnO/MnTiO3, the structural stability of TiO2 with the dispersion effect and buffer function of Al2O3.

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.Keywords: anode material; carbon nanofiber; electrochemical performance; rate capability

Manganese silicate was simply fabricated by the reaction between Na2SiO3·9H2O and MnCl2·4H2O. The carbon-coated manganese silicate acting as anode material for lithium storage exhibits outstanding rate performance and high-rate cycling stability. Combining detailed characterizations with electrochemical measurements revealed that the uniform carbon coating around the manganese silicate nanoparticles as conductive material and the formation of lithium silicate as solid electrolyte are responsible for the excellent performance. The carbon-coated manganese silicate could meet the requirement for fast charging/discharging Li-ion batteries.

Cu-modified Li4Ti5O12 (LTO) with various Cu-doping contents was prepared via simple hydrolysis of tetrabutyl titanate in the water solution of LiOH · H2O and Cu(NO3)2 · 3H2O, followed by sintering the dried mixture at 600 °C for 5 h. By virtue of the slightly increased lattice constant, refined grains with relatively large surface area, improved electronic and ionic conductivities, the modified products exhibit excellent long-term cycling stability at a high current rate of 10 C and outstanding rate performance at 0.1–40 C. Particularly, the product with a Cu-doping content of 0.08 demonstrates prominent long-term cycling performance up to 2500 cycles at 10 C and superior capacity retention even at 10–40 C. The Cu-modified LTO could be used as efficient anode materials for long-life and high-rate lithium ion batteries.

TiO2/C nanocomposites were fabricated by simple hydrolysis of tetrabutyl titanate to yield TiO2 nanoparticles followed by carbonizing the mixture of glucose and TiO2 at 600 °C. By merely varying the weight ratio of glucose:TiO2, the electrochemical performance of the composites could be optimized significantly. At a ratio of 0.8, the composite exhibits a high reversible capacity of 283.7 mA h g−1 after cycling 100 times at a current density of 100 mA g−1, as well as the capacities of 245.1, 213.6, 179.9 and 136.6 mA h g−1 at the corresponding densities of 200, 400, 800 and 1600 mA g−1. After cycling 1000 times at 500 mA g−1, a capacity of 122.8 mA h g−1 was retained for the composite with a ratio of 0.8, and even a capacity of 149.1 mA h g−1 for the composite with a ratio of 0.7. The enhanced performance is ascribed to the carbon-coated TiO2 nanoparticles uniformly embedding in the carbon matrix with appropriate carbon content.

TiO2/Li4Ti5O12 composites with different Li:Ti molar ratios were fabricated by simply hydrolyzing tetrabutyl titanate in a water solution of LiNO3 and calcining the dried mixture at 600 °C, and the carbon-coated composites were prepared at 600 °C employing glucose as a carbon precursor. Compared to the carbon-coated TiO2 and Li4Ti5O12 prepared under the similar conditions, the carbon-coated TiO2/Li4Ti5O12 composite with Li:Ti = 4:8 exhibits a stable capacity of 227.2 mA h g−1 when cycled 100 times at a current density of 100 mA g−1, and when cycled at 200, 400, 800 and 1600 mA g−1, the corresponding capacities are 206.1, 183.0, 152.4 and 119.4 mA h g−1 with the coulombic efficiency close to 100%. The composite also reveals outstanding long-term cycling stability at 500 mA g−1 with a reversible capacity of 177.6 mA h g−1 after 850 cycles. The enhanced electrochemical performance is ascribed to the synergistic effect of the two phases of TiO2 and Li4Ti5O12 with the carbon coating.