Jaewon Jin

Nanoparticulate Iron Oxide Tubes from Microporous Organic Nanotubes as Stable Anode Materials for Lithium Ion Batteries

During the last several decades, diverse porous materials have been prepared for a wide range of applications, such as adsorbents, gas storage materials, and solid supports for catalytic materials. These materials can be classified into three groups according to their components: inorganic materials, metal–organic composites, and purely organic systems. Among these porous materials, organic porous materials have recently attracted special attention because of their low densities and robustness. The accumulated organic synthetic methods can also be easily applied for the designed synthesis of organic porous materials with tailored functionalites. Thus, in a short period, diverse microporous organic networks have been prepared through diverse C C bond-forming reactions. In the synthesis of porous organic networks, the rigid building blocks are chosen so that the connection of these building blocks through covalent bonds induces the intrinsic porosity of the materials. Related studies have focused on the inner porosity and the resultant high surface area of materials. However, porous organic systems with well-defined outer shapes are rare. In particular, the template-free synthesis of hollow organic materials is quite rare. It is noteworthy that in the synthesis of secondary target inorganic materials using porous materials, the organic templates can be easily removed by combustion in air. In these cases, the outer shapes of materials along with their inner porosity are very critical for obtaining well-defined materials. Moreover, inorganic materials with a particulate surface could be obtained from the microporosity of organic network. Recently, Cooper and others have shown that Sonogashira coupling between alkynes and arylhalides is a very efficient method for the preparation of microporous organic materials. The resultant materials themselves showed promising gas-adsorption capacities. It can be expected that more diverse functional sites can be introduced into materials by designing the organic building blocks. During our trials for introduction of viologen groups into microporous organic materials, we observed the unexpected formation of microporous organic nanotubes. Herein, we present the preparation of microporous organic nanotubes and the template synthesis of iron oxide nanotubes with particulate walls and their application as anode materials for high-performance lithium ion batteries. Figure 1a shows the synthesis of microporous organic nanotubes (MONTs). For preparation of the MONT, two building blocks, N,N’-di(4-iodophenyl)-4,4’-bipyridinium dichloride (2 equiv) and tetra(4-ethynylphenyl)methane (1 equiv) were dissolved in a 3:2:2 mixture of toluene, methanol, and triethylamine. After adding catalytic amount of bis(triphenylphosphine)palladium dichloride and copper iodide, the reaction mixture was heated at 90 8C for 72 h to form precipitates. After cooling to room temperature, the solid was retrieved by centrifugation and washed with excess dimethyl sulfoxide, methanol, dichloromethane, and diethyl ether. The resultant materials were dried under a vacuum for a day. The obtained precipitates were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). As shown in typical SEM images(Figure 1b), the obtained materials have a 1D character with mild ending-parts. Interestingly, a careful investigation of the materials by TEM revealed the hollow inner space and dark-contrasted walls (Figure 1c–e; Supporting Information, Figure S1). The average diameter and thickness of the wall of MONT were (92 19) nm and (31 4) nm, respectively. Brunauer– Emmett–Teller (BET) analysis showed the microporous character of materials with type I N2 isotherm at 77 K, 765.0 mg 1 surface area, and 1.01 cmg 1 pore volume (P/P0=0.995; Figure 2a). Powder X-ray diffraction (PXRD) studies revealed the amorphous character of MONT that has been observed previously (Supporting Information, Figure S2). Thermogravimetric analysis (TGA) of the materials showed that they are stable up to 205 8C and then slowly decomposed at a higher temperature (Figure 2b). Solidstate C NMR spectroscopy showed signals at d= 62 ppm, d= 90 ppm, and d= 120–160 ppm for benzyl, alkyne, and aryl groups, respectively (Figure 2c). Elemental analysis of mate[*] N. Kang, Dr. J. H. Park, J. Choi, J. Jin, J. Chun, Dr. I. G. Jung, Prof. S. U. Son Department of Chemistry and Department of Energy Science Sungkyunkwan University, Suwon 440-746 (Korea) E-mail: sson@skku.edu

Fe3O4 nanosphere@microporous organic networks: enhanced anode performances in lithium ion batteries through carbonization

Very thin microporous organic networks were formed on the surface of Fe3O4 nanospheres by Sonogashira coupling of tetra(4-ethynylphenyl)methane and 1,4-diiodobenzene. The thickness was controlled by screening the number of building blocks. Through carbonization, Fe3O4@C composites were prepared. The Fe3O4@C composites with 4-6 nm carbon thickness showed promising reversible discharge capacities of up to 807 mA h g(-1) and enhanced electrochemical stability.

Columnar assembly and successive heating of colloidal 2D nanomaterials on graphene as an efficient strategy for new anode materials in lithium ion batteries: the case of In2S3 nanoplates

This study shows that heat-treatment of colloidal inorganic nanoplates with columnar assembly under argon is a good strategy for development of anode materials. The heating of colloidal In2S3 nanoplates under argon resulted in the formation of film-like materials through interconnection of plates in a side by side manner. When the columnarly assembled colloidal In2S3 plates were heated at 400 °C under argon for 2 hours on graphene, more efficient anode materials with smaller diameters were obtained. Interestingly, the heat-treated columnarly assembled In2S3 plates on graphene had a layered structure, which was attributed to the possible existence of carbon materials between plates formed by the heat-treatment of surfactants under argon. The resultant graphene–In2S3 composites showed enhanced discharge capacities, up to 716–837 mA h g−1, as well as excellent stabilities. In addition, the materials showed promising coulombic efficiencies and rate performances. We believe that, based on the strategy in this work, diverse graphene–inorganic nanomaterial composites with a layered structure can be prepared and applied as new anode materials in lithium ion batteries.

A chemical bottom-up and successive top-down approach for nanoporous SnO2 hollows from Ni3Sn2 nanoalloys: high surface area photocatalysts and anode materials for lithium ion batteries

This work shows that a chemical bottom-up and successive top-down approach is a good synthetic strategy for nanoporous hollow materials. The heating of 3 eq. nickel chloride and 2 eq. tin chloride at 280 °C in the presence of oleylamine resulted in the formation of intermetallic Ni3Sn2 alloy materials. According to mechanistic studies, zerovalent nickel formed by the reduction of precursor induced the reduction of the tin precursor to form Ni3Sn2 alloys. The Ni3Sn2 nanoparticles were characterized by SEM, TEM, PXRD and EDS. When the Ni3Sn2 nanoparticles were treated with 1% nitric acid for 48 hours, the nickel component was completely etched. The resultant materials were nanoporous SnO2 hollow materials, which were characterized by TEM, PXRD and XPS. Due to the nanoparticulate characteristics of shells, BET analysis on the SnO2 hollows showed nanoporosity and a high surface area of 101 m2 g−1. The hollow SnO2 materials with nanoparticulate shells showed excellent photocatalytic activities in the decomposition of Rhodamine B. Moreover, they showed promising electrochemical performances with a discharge capacity of 560 mA h g−1 after 30 cycles and stabilities as anode materials in lithium ion batteries. The preparation of a multi-component alloy and the selective etching strategy can be further expanded to other intermetallic alloy systems for the development of functional materials.

Cationically Substituted Bi0.7Fe0.3OCl Nanosheets as Li Ion Battery Anodes

Cation substitution of Bi3+ with Fe3+ in BiOCl leads to the formation of ionically layered Bi0.7Fe0.3OCl nanosheets. The synthesis follows a hydrolysis route using bismuth(III) nitrate and iron(III) chloride, followed by postannealing at 500 °C. Room temperature electrical conductivity improves from 6.11 × 10-8 S/m for BiOCl to 6.80 × 10-7 S/m for Bi0.7Fe0.3OCl. Correspondingly, the activation energy for electrical conduction reduces from 862 meV for pure BiOCl to 310 meV for Bi0.7Fe0.3OCl. These data suggest improved charge mobility in Bi0.7Fe0.3OCl nanosheets. Density functional theory calculations confirm this behavior by predicting a high density of states near the Fermi level for Bi0.7Fe0.3OCl. The improvement in electrical conductivity is exploited in the electrochemical performance of Bi0.7Fe0.3OCl nanosheets. The insertion capacity of Li+ ions shows an increase of 2.5×, from 215 mAh·.g-1 for undoped BiOCl to 542 mAh·g-1 for Bi0.7Fe0.3OCl after 50 cycles at a current density of 50 mA·g-1. Thus, the direct substitution of Bi3+ sites with Fe3+ in BiOCl results in nanosheets of an ionically layered ternary semiconductor compound which is attractive for Li ion battery anode applications.