Crystal Chemistry and Ionic Conductivity of the NASICON-Related Phases in the Li3-xNaxV2(PO4)3 System.

In the present work, we studied crystal phases in the Li3-xNaxV2(PO4)3 system over a wide range of x prepared by four synthesis methods: mechanochemically assisted solid-state synthesis, 'soft chemistry' sol-gel approach, chemical (CIE) and electrochemical (EIE) ion exchange starting from Li3V2(PO4)3 (anti-NASICON, P21/c S.G.), and Na3V2(PO4)3 (NASICON, C2/c S.G.). EIE was studied by operando and ex situ XRD in Li3V2(PO4)3 vs Na and Na3V2(PO4)3 vs Li electrochemical cells. It was shown that both mechanochemically assisted solid-state and sol-gel synthesis methods do not result in the single-phase Na3-xLixV2(PO4)3. In contrast, CIE and EIE lead to deep substitution degrees and proceed much easier in the NASICON framework (Na3V2(PO4)3), where more than 2/3 of Na+ ions per f.u. are replaced with Li+ resulting in Na0.6Li2.4V2(PO4)3 (R3̅ S.G.), while in the anti-NASICON framework (Li3V2(PO4)3), only 1/3 of Li+ ions are replaced with Na+ resulting in Li2NaV2(PO4)3 (Pbcn S.G.), which was shown to be a metastable phase, and after high-temperature treatment, it decomposes into two NASICON-type compounds. The ionic conductivity was analyzed both theoretically and experimentally, and the results show that in the NASICON framework, the migration of both Na+ and Li+ ions is realized, while in the anti-NASICON framework, the Li+ migration is preferable. The contribution of the electronic component to total conductivity was determined.

An all solid-state Li ion battery composed of low molecular weight crystalline electrolyte.

Conduction mechanisms in solid polymer electrolytes of Li ion batteries have always been a concern due to their theoretical limitation in conductivity value. In an attempt to increase the ionic conductivity of solid state electrolytes, used in lithium ion secondary batteries (LiBs), we studied the synthesis and conductive properties of a low molecular weight cyclic organoboron crystalline electrolyte. This electrolyte was expected to show better electrochemical properties than solid polymer electrolytes. The electrolyte was doped with LiTFSI salt via two different methods viz. (1) facile grinding of the crystalline sample with lithium salt under a nitrogen atmosphere and (2) a conventional method of solvent dissolution and evaporation under vacuum. The electrochemical properties were studied under specific composition of Li salt. The presence of crystallinity in the electrolyte can be considered as an important factor behind the high ionic conductivity of an all solid electrolyte of this type. Charge-discharge properties of the cell using the electrolyte were investigated in anodic half-cell configuration.

Few-Layered MoS2/Acetylene Black Composite as an Efficient Anode Material for Lithium-Ion Batteries.

Novel MoS2/acetylene black (AB) composite was developed using a single-step hydrothermal method. A systematic characterization revealed a few-layered, ultrathin MoS2 grown on the surface of AB. The inclusion of AB was found to increase the capacity of the composite and achieve discharging capacity of 1813 mAhg-1.

Sacrificial Reducing Agent Free Photo-Generation of Platinum Nano Particle over Carbon/TiO2 for Highly Efficient Oxygen Reduction Reaction.

Electrocatalytic materials for oxygen reduction reaction, currently dominated by platinum/carbon catalyst is marred by drawbacks such as use of copious amount of Pt and use of "non-green" sacrificial reducing agent (SRA) during its synthesis. A single stroke remedy for these two problems has been achieved through an in-situ aqueous photoreduction void of even trace amounts of SRA with an enhanced activity. Reduction of PtCl62- salt to Pt nano particles on carbon substrate was achieved solely using solar spectrum as the source of energy and TiO2 as photocatalyst. Here, we demonstrate that this new procedure of photoreduction, decorates Pt over different types of conducting allotropes with the distribution and the particle size primarily depending on the conductivity of the allotrope. The Pt/C/TiO2 composite unveiled an ORR activity on par to the most efficient Pt based electrocatalyst prepared through the conventional sacrificial reducing agent aided preparation methods.

A crystalline low molecular weight cyclic organoboron compound for efficient solid state lithium ion transport.

We report the synthesis of a crystalline cyclic organoboron compound that shows an anomalous Li-ion conduction behaviour with specific composition and method of insertion of a Li salt. The enhanced ionic conductivity of crystalline boric ester/LiTFSI prepared by the grinding method should be due to the formation of regulated ion-conduction channels scaffolded by boron-anion interaction.

Platinum decorated functionalized defective acetylene black; a promising cathode material for the oxygen reduction reaction.

A novel single-pot method to exfoliate and functionalize acetylene black is proposed. The deliberate functionalization was found to enhance the intrinsic oxygen reduction efficiency along with the nucleation and growth of platinum nano-particles on the surface. The resulting material showed enormously high oxygen reduction reactivity compared to its commercial counterparts.

Boric ester-type molten salt via dehydrocoupling reaction.

Novel boric ester-type molten salt was prepared using 1-(2-hydroxyethyl)-3-methylimidazolium chloride as a key starting material. After an ion exchange reaction of 1-(2-hydroxyethyl)-3-methylimidazolium chloride with lithium (bis-(trifluoromethanesulfonyl) imide) (LiNTf2), the resulting 1-(2-hydroxyethyl)-3-methylimidazolium NTf2 was reacted with 9-borabicyclo[3.3.1]nonane (9-BBN) to give the desired boric ester-type molten salt in a moderate yield. The structure of the boric ester-type molten salt was supported by 1H-, 13C-, 11B- and 19F-NMR spectra. In the presence of two different kinds of lithium salts, the matrices showed an ionic conductivity in the range of 1.1 × 10⁻4-1.6 × 10⁻5 S cm⁻¹ at 51 °C. This was higher than other organoboron molten salts ever reported.

Lithium ion conductive behavior of TiO2 nanotube/ionic liquid matrices.

A series of TiO2 nanotube (TNT)/ionic liquid matrices were prepared, and their lithium ion conductive properties were studied. SEM images implied that ionic liquid was dispersed on the whole surface of TNT. Addition of TNT to ionic liquid (1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide (BMImTFSA)) resulted in significant increase of ionic conductivity. Furthermore, lithium transference number was also largely enhanced due to the interaction of anion with TNT. Vogel-Fulcher-Tammann parameter showed higher carrier ion number for TNT/BMImTFSA in comparison with BMImTFSA.

Electrochemical characterization of TiO2/WOx nanotubes for photocatalytic application.

TiO2/WOx nanotubes have unique photo-energy retention properties that have gathered scientific interest. Herein, we report the synthesis, morphological characterization, and the electrochemical characterization of TiO2/WOx nanotubes compared with pure TiO2 nanotubes, prepared by anodization technique. Significant structural differences were not observed in TiO2/WOx nanotubes as observed by using scanning electron microscopy and transmission electron microscopy. The charge transfer resistance of TiO2/WOx before and after photo irradiation determined by using electrochemical impedance spectroscopy proves the inherent energy retention property which was not observed in pure TiO2 nanotubes.