S. V. Savilov

Array of nanosheets render ultrafast and high-capacity Na-ion storage by tunable pseudocapacitance

Sodium-ion batteries are a potentially low-cost and safe alternative to the prevailing lithium-ion battery technology. However, it is a great challenge to achieve fast charging and high power density for most sodium-ion electrodes because of the sluggish sodiation kinetics. Here we demonstrate a high-capacity and high-rate sodium-ion anode based on ultrathin layered tin(II) sulfide nanostructures, in which a maximized extrinsic pseudocapacitance contribution is identified and verified by kinetics analysis. The graphene foam supported tin(II) sulfide nanoarray anode delivers a high reversible capacity of ∼1,100 mAh g−1 at 30 mA g−1 and ∼420 mAh g−1 at 30 A g−1, which even outperforms its lithium-ion storage performance. The surface-dominated redox reaction rendered by our tailored ultrathin tin(II) sulfide nanostructures may also work in other layered materials for high-performance sodium-ion storage.

Graphene wrapped ordered LiNi0.5Mn1.5O4 nanorods as promising cathode material for lithium-ion batteries.

LiNi0.5Mn1.5O4 nanorods wrapped with graphene nanosheets have been prepared and investigated as high energy and high power cathode material for lithium-ion batteries. The structural characterization by X-ray diffraction, Raman spectroscopy, and Fourier transform infrared spectroscopy indicates the LiNi0.5Mn1.5O4 nanorods prepared from β-MnO2 nanowires have ordered spinel structure with P4332 space group. The morphological characterization by scanning electron microscopy and transmission electron microscopy reveals that the LiNi0.5Mn1.5O4 nanorods of 100–200 nm in diameter are well dispersed and wrapped in the graphene nanosheets for the composite. Benefiting from the highly conductive matrix provided by graphene nanosheets and one-dimensional nanostructure of the ordered spinel, the composite electrode exhibits superior rate capability and cycling stability. As a result, the LiNi0.5Mn1.5O4-graphene composite electrode delivers reversible capacities of 127.6 and 80.8 mAh g−1 at 0.1 and 10 C, respectively, and shows 94% capacity retention after 200 cycles at 1 C, greatly outperforming the bare LiNi0.5Mn1.5O4 nanorod cathode. The outstanding performance of the LiNi0.5Mn1.5O4-graphene composite makes it promising as cathode material for developing high energy and high power lithium-ion batteries.

Black mesoporous Li4Ti5O12−δ nanowall arrays with improved rate performance as advanced 3D anodes for microbatteries

Binder-free and self-standing lithium titanate nanoarrays could be promising 3D anodes for lithium-ion microbatteries. The intrinsic poor electrical conductivity of Li4Ti5O12, however, spoils its rate performance and restrains its application in commercial batteries. In this work, black mesoporous Li4Ti5O12−δ nanowall arrays with oxygen vacancies are synthesized by a facile hydrothermal method with post heat treatment in an Ar atmosphere. The heat treatment in an inert atmosphere is effective for generating oxygen vacancies by forming Ti3+ ions in Li4Ti5O12−δ nanowall arrays, thus greatly enhancing the electron transfer in the spinel structure. Consequently, the black mesoporous Li4Ti5O12−δ nanowall arrays exhibit greatly improved electrode kinetics and rate performance compared to the stoichiometrical Li4Ti5O12 and Li4Ti5O12/TiO2 dual phase nanowall arrays. In specific, the black mesoporous Li4Ti5O12−δ nanowall arrays can deliver a large specific capacity of about 115 mA h g−1 at 20C as well as excellent cycling stability, making them promising as 3D anodes for advanced lithium-ion microbatteries.

Double stabilization of nanocrystalline silicon: a bonus from solvent

Double stabilization of the silicon nanocrystals was observed for the first time by 29Si and 13C MAS NMR spectroscopy. The role of solvent, 1,2-dimethoxyethane (glyme), in formation and stabilization of silicon nanocrystals as well as mechanism of modification of the surface of silicon nanocrystals by nitrogen-heterocyclic carbene (NHC) was studied in this research. It was shown that silicon nanocrystals were stabilized by the products of cleavage of the C–O bonds in ethers and similar compounds. The fact of stabilization of silicon nanoparticles with NHC ligands in glyme was experimentally detected. It was demonstrated that MAS NMR spectroscopy is rather informative for study of the surface of silicon nanoparticles but it needs very pure samples.Graphical Abstract

A hybrid polymer/oxide/ionic-liquid solid electrolyte for Na-metal batteries

The development of solid electrolytes with superior electrical and electrochemical performances for the room-temperature operation of sodium (Na)-based batteries is at the infant stage and still remains a challenge. Herein, we, for the first time, report hybrid solid electrolytes consisting of PEO20–NaClO4–5% SiO2–x% Emim FSI (x = 50, 70) designed for solid-state Na-metal batteries. The hybrid design yields a solid electrolyte featuring a high room-temperature ionic conductivity of 1.3 × 10−3 S cm−1, suitable mechanical property, a wide voltage stability window of 4.2 V and a high Na+ transference number of 0.61. A prototypical Na-metal battery using this hybrid solid electrolyte demonstrates promising long-term cycling performances at room temperature and at an elevated temperature of 60 °C for 100 cycles. The finding implies that the hybrid solid electrolyte is promising for Na-metal batteries operating at room temperature.

Carboxylated and decarboxylated nanotubes studied by X-ray photoelectron spectroscopy

Carbon nanotubes (CNTs) of the conic and cylindrical structure were studied by X-ray photoelectron spectroscopy in the initial state and after carboxylation and decarboxylation reactions. The O=C—O and C—O groups were revealed on the surface of the chemically modified samples. It was found that both the carboxylated and decarboxylated cylindrical CNTs contain a smaller amount of oxygen than the corresponding conic CNTs apparently due to differences in their structures.

New subvalent bismuth telluroiodides incorporating Bi2 layers : the crystal and electronic structure of Bi2TeI

Two new subvalent bismuth telluroiodides, Bi2TeI and Bi4TeI1.25, were prepared by the gas-phase synthesis. The compositions of these phases were determined by energy-dispersive X-ray spectroscopy. X-ray diffraction study of melt grown Bi2TeI single crystals demonstrated that the compound crystallizes in the monoclinic system (space group C/2m) with the unit cell parameters a = 7.586(1) Å, b = 4.380(1) Å, c = 17.741(3) Å, β = 98.20°. The layered crystal structure of Bi2TeI consists of weakly bonded two dimensional blocks with a stoichiometry of the title compound. The blocks are stacked along the c axis. Each block consists of eight atomic layers alternating in the Te-Bi-I-Bi-Bi-I-Bi-Te order and includes a double layer of bismuth atoms. Based on the results of ab initio quantum-chemical calculations, the title compound is expected to possess a pronounced anisotropy of conductivity.

Carbon nanotube directed three-dimensional porous Li2FeSiO4 composite for lithium batteries

Lithium iron silicate (Li2FeSiO4) is capable of affording a much higher capacity than conventional cathodes, and thus, it shows great promise for high-energy battery applications. However, its capacity has often been adversely affected by poor reaction activity due to the extremely low electronic and ionic conductivity of silicates. Here, we for the first time report on a rational engineering strategy towards a highly active Li2FeSiO4 by designing a carbon nanotube (CNT) directed three-dimensional (3D) porous Li2FeSiO4 composite. As the CNT framework enables rapid electron transport, and the rich pores allow efficient electrolyte penetration, this unique 3D Li2FeSiO4-CNT composite exhibits a high capacity of 214 mAh·g−1 and retains 96% of this value over 40 cycles, thus, outstripping many previously reported Li2FeSiO4-based materials. Kinetic analysis reveals a high Li+ diffusivity due to coupling of the migration of electrons and ions. This research highlights the potential for engineering 3D porous structure to construct highly efficient electrodes for battery applications.

MULTIWALLED CARBON NANOTUBES AND NANOFIBERS: SIMILARITIES AND DIFFERENCES FROM STRUCTURAL, ELECTRONIC AND CHEMICAL CONCEPTS; CHEMICAL MODIFICATION FOR NEW MATERIALS DESIGN

Present work points out the differences between possible tubular carbon structures: nanotubes and nanofibers, as well as describes ways of their modification for utilization for new materials design. For material characterization, XRD, XPS, Raman spectroscopy, thermal analysis, HRTEM and SEM, pore size distribution, EELS, elemental analysis and adiabatic bomb calorimetry were used. Heats of formation for nanotubes and nanofibers and their dependence on carboxylation extent as well as properties of the modified materials are also discussed. The perspectives of applications of modified carbon nanotubes in catalysis and polymers chemistry are given.

Synthesis and electrocatalytic activity of platinum nanoparticle/carbon nanotube composites

Pt/CNT nanocomposite materials with an average platinum particle size of 3–5 nm and platinum content of 13–28 wt % have been prepared by reducing chloroplatinic acid, H2PtCl6, in the presence of conical carbon nanotubes. The effect of synthesis conditions on the average platinum particle size, total platinum content, and surface composition of the nanocomposites has been studied using X-ray photoelectron spectroscopy, IR spectroscopy, electron microscopy, X-ray diffraction, and thermogravimetry. The materials have been tested as catalysts for hydrogen oxidation and oxygen reduction. Their performance has been assessed by cyclic and steady-state voltammetric techniques. The structure and composition effects on the electrocatalytic properties of the nanocomposites are discussed.