Rezan Demir-Cakan

Superior Storage Performance of a Si@SiOx/C Nanocomposite as Anode Material for Lithium-Ion Batteries

Rechargeable lithium-ion batteries are essential to portable electronic devices. Owing to the rapid development of such equipment there is an increasing demand for lithium-ion batteries with high energy density and long cycle life. For high energy density, the electrode materials in the lithium-ion batteries must possess high specific storage capacity and coulombic efficiency. Graphite and LiCoO2 are normally used and have high coulombic efficiencies (typically >90%) but rather low capacities (372 and 145 mAhg, respectively).[1–5] Various anode materials with improved storage capacity and thermal stability have been proposed for lithium-ion batteries in the last decade. Among these, silicon has attracted great interest as a candidate to replace commercial graphite materials owing to its numerous appealing features: it has the highest theoretical capacity (Li4.4Sio4200 mAhg) of all known materials, and is abundant, inexpensive, and safer than graphite (it shows a slightly higher voltage plateau than that of graphite as shown in Figure S1, and lithiated silicon is more stable in typical electrolytes than lithiated graphite[6]).

Cathode composites for Li-S batteries via the use of oxygenated porous architectures.

Li-S rechargeable batteries are attractive for electric transportation because of their low cost, environmentally friendliness, and superior energy density. However, the Li-S system has yet to conquer the marketplace, owing to its drawbacks, namely, soluble polysulfide formation. To tackle this issue, we present here a strategy based on the use of a mesoporous chromium trimesate metal-organic framework (MOF) named MIL-100(Cr) as host material for sulfur impregnation. Electrodes containing sulfur impregnated within the pores of the MOF were found to show a marked increase in the capacity retention of Li-S cathodes. Complementary transmission electron microscopy and X-ray photoelectron spectroscopy measurements demonstrated the reversible capture and release of the polysulfides by the pores of MOF during cycling and evidenced a weak binding between the polysulphides and the oxygenated framework. Such an approach was generalized to other mesoporous oxide structures, such as mesoporous silica, for instance SBA-15, having the same positive effect as the MOF on the capacity retention of Li-S cells. Besides pore sizes, the surface activity of the mesoporous additives, as observed for the MOF, appears to also have a pronounced effect on enhancing the cycle performance. Increased knowledge about the interface between polysulfide species and oxide surfaces could lead to novel approaches in the design and fabrication of long cycle life S electrodes.

Li–S batteries: simple approaches for superior performance

Although promising improvements have been made in the field of Li–S rechargeable batteries, they are still far from reaching the market place due to several drawbacks. To combat the solubility of polysulphides, confinement approaches aiming to trap sulphur within the cathode side have been pursued, but success has been limited. Herein, we drastically deviate from this approach and use a liquid cathode obtained either by dissolving polysulphides within the electrolyte or by placing sulphur powders in contact with the Li negative electrode. Such approaches are shown to result in greater performance than confinement approaches. Such a strategy eliminates the detrimental Li2S formation inside a porous carbon matrix and moreover leads to the formation of a protective SEI layer at the Li electrode, as deduced by impedance spectroscopy and XPS, which seems beneficial to the cell cycling performance.

3-D Coordination Polymers Based on the Tetrathiafulvalenetetracarboxylate (TTF-TC) Derivative: Synthesis, Characterization, and Oxidation Issues

The reactivity of the redox-active tetracarboxylic acid derived from the tetrathiafulvalene (TTF-TC)H(4) with alkaline cations (K, Rb, Cs) is reported. The exploration of various experimental parameters (temperature, pH) led to the formation of four crystalline three-dimensional coordination polymers formulated M(2)(TTF-TC)H(2) (M = K, Rb, Cs), denoted MIL-132(K), MIL-133(isostructural K, Rb), and MIL-134(Cs). Thermogravimetric analysis and thermodiffraction show that all of the solids are thermally stable up to 150-200 degrees C in the air. In order to exploit the possibility of oxidation of the organic linker in TTF-based compounds, they were employed as positive electrodes in a classical lithium cell. A highly reversible cyclability was achieved at high current density (10 C) with a reasonable performance (approximately 50 mAh g(-1)). Finally, combined electro-(sub)hydrothermal synthesis was used to prepare a fifth 3-D coordination polymer formulated K(TTF-TC)H(2) (denoted MIL-135(K)), this time not based on the neutral TTF-TC linker but its radical, oxidized form TTF-TC(+*). This solid is less thermally stable than its neutral counterparts but exhibits a semiconducting behavior, with a conductivity at room temperature of about 1 mS cm(-1).

Porous Carbohydrate-Based Materials via Hard Templating

Among various techniques, the hydrothermal carbonization (HTC) of biomass (either isolated carbohydrates or crude plants) is a promising candidate for the synthesis of novel carbon-based materials with a wide variety of potential applications. In this Minireview, we discuss various synthetic routes towards such porous carbon-based materials or composites through the HTC process, using the nanocasting procedure. We focus on the synthesis of carbon materials with different pore systems and morphologies directed by the presence of various nanostructured inorganic sacrificial templates. This method allows tailoring of the final structure via the tools of colloid and polymer science, leading to selectable material morphology for a wide range of applications.

Modification of the hydrogen storage properties of Li3N by confinement into mesoporous carbons

This study presents an innovative synthetic route to Li3N@carbon composites for the purpose of use as hydrogen storage materials. The synthesis method is provided by wet impregnation of mesoporous carbons (graphitic or non-graphitic) using lithium azide solutions, followed by a thermal treatment allowing the transformation of lithium azide into lithium nitride, the latter being formed into the porosity of the carbon hosts. It has been shown by X-ray diffraction that the high-pressure β-phase of Li3N can be stabilized within the carbon matrix. The resulting Li3N@carbon composites have desirable hydrogen storage properties with fast hydrogen absorption/desorption kinetics at 200 °C (much faster than those measured for non-confined Li3N) as well as a completely reversible hydrogen storage process: a 20 wt% Li3N-loaded composite leads to a reversible hydrogen storage capacity of 1.8 wt% (e.g. about 9 wt% per mass of Li3N).

An aqueous electrolyte rechargeable Li-ion/polysulfide battery

In spite of great research efforts on Li–S batteries in aprotic organic electrolytes, there have been very few studies showing the potential application of this system in aqueous electrolyte. Herein, we explore this option and report on a cheaper and safer new aqueous system coupling a well-known cathode material in Li-ion batteries (i.e. LiMn2O4) with a dissolved polysulfide anode. In comparison with classical Li–S batteries containing aprotic organic solvents, the aqueous electrolyte offers a stable cycling profile over 100 cycles with faster C-regime.

Use of ion-selective polymer membranes for an aqueous electrolyte rechargeable Li-ion–polysulphide battery

Aqueous electrolyte Li-ion–polysulphide batteries offer great promise due to the use of low-cost and abundant raw materials. Following up on our previous studies in which we explored a totally new practical battery chemistry coupling a well-known cathode material in Li-ion batteries (i.e. LiMn2O4) with a dissolved polysulphide anode, herein we aim to further develop the system by replacing the ceramic membrane with an ion-selective polymer membrane, allowing cost-effective and higher energy density options. After tuning the osmotic movements inside the membrane, dissolved polysulphide leakage from one compartment to another is successfully eliminated. With the additional use of porous silica serving as an absorbent for sulphur-based gaseous products, a 1.5 V average voltage together with a stable cycling profile over 200 cycles at high current density regimes are easily achieved.

In-situ wrapping of tin oxide nanoparticles by bacterial cellulose derived carbon nanofibers and its application as freestanding interlayer in lithium sulfide based lithium-sulfur batteries

Lithium-Sulfur (Li-S) batteries are mostly known for their high energy density and cost-effectiveness. However, their intrinsic problems hinder their implementation into the marketplace. The most pronounced problems are the parasitic reactions which occur between lithium polysulfides species and lithium metal anode, the volume expansion of sulfur (80%) at the end of discharge and the safety issues which are linked with the use of lithium metal. Herein this work, two approaches are applied to prevent these effects; one approach is the use of Li2S as cathode material, instead of starting from sulfur powder, both to circumvent the volume expansion of sulfur taking place during discharge and to enable lithium-free anodes cell assembling (i.e. Si-Li2S or Sn-Li2S cell configurations). Second approach deals with the lithium anode protection by SnO2 containing freestanding pyrolyzed bacterial cellulose interlayers located between anode and cathode electrodes. Since bacterial celluloses are formed in the presence of SnO2 nanoparticles, the resulting structure enables intimate contact between carbon and SnO2 nanoparticles. By employing Li2S cathode and freestanding interlayer concurrently, 468 mAh g-1 discharge capacity is obtained at C/10 current density over 100 cycles.