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In order to become commercially viable, sodium-ion batteries need to deliver long cycle life with good capacity and energy density while still ensuring safety. Electrolyte plays a key role forming solid electrolyte interphase (SEI) layers at low potential, which affects the thermal stability and cycle life of the anode materials under consideration. In this study, an ether-based non-flammable electrolyte, 1 M NaBF4 in tetraglyme, is tested for sodium storage using a non-carbonaceous anode material Na2Ti3O7/C, and the results are compared with those obtained with the popularly used carbonate-based electrolyte, 1 M NaClO4 in ethylene carbonate (EC) and propylene carbonate (PC) (v/v = 1:1). The Na2Ti3O7/C versus Na cells using 1 M NaBF4 in tetraglyme show a much higher first cycle Coulombic efficiency (73%) than those using 1 M NaClO4 in EC/PC (33%). Thermal stability studies using differential scanning calorimetry (DSC) conclusively show that Na2Ti3O7/C electrodes cycled with 1 M NaBF4 in tetraglyme are more thermally stable than the one cycled with 1 M NaClO4 in EC/PC. Further investigations on the formation of SEI layers were performed using attenuated total reflection-Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, electrochemical impedance spectroscopy, and DSC studies. These studies unambiguously demonstrate that the SEI formed on Na2Ti3O7/C using 1 M NaBF4 in tetraglyme is not only less resistive but also more stable than the SEI formed using 1 M NaClO4 in EC/PC.

Here, we present a comprehensive study of choice of electrolyte, anode and cathode to develop commercially viable non-flammable sodium-ion battery. We report hard carbon (HC) vs. Na using ether-based non-flammable electrolyte (1 ​M NaBF4 in tetraglyme) and compare storage performance, thermal stability and SEI formation with those obtained using carbonate-based electrolyte (1 ​M NaClO4 in EC:PC = 1:1 v/v). The results shows that 1 ​M NaBF4 in tetraglyme works as a better electrolyte than carbonate-based electrolyte for HC anode. We present and compare storage performances of pristine and aliovalent-doped Na3V2(PO4)3 (NVP) vs. Na. Doped-NVP outperforms pristine cathode in terms of specific capacity and rate capability. 18650-type non-flammable sodium-ion cells fabricated using modified NVP vs. HC exhibits energy density of 60 ​Wh kg−1. When discharged at a high rate close to 5C, the cell successfully retains 83% of its storage capacity obtained at low rate. When cycled at C/5, doped NVP vs. HC 18650 ​cell retains 90% of its initial capacity after 200 cycles.

P3-Na0.9Fe0.5Mn0.5O2 is reported as a new P-type cathode material for Na-ion batteries. The P3 structure can accommodate 0.9 mole of Na-ions leading to a high discharge capacity of 155 mA h g−1 and does not require sacrificial salts for full-cell operation. Operando X-ray diffraction and ex situ X-ray absorption studies are also reported.

A novel, water-stable and high energy density cathode material Na0.9Cu0.12Ni0.10Fe0.30Mn0.43Ti0.05O2 (NCNFMT) is reported here along with a thorough understanding of structural events during battery operation. Systematic substitutions are carried out, which lead to increase in specific energy densities of this family of cathodes from 274.6 W h kgcathode−1 (NCFM – Na0.9Cu0.22Fe0.30Mn0.48O2) to 304.2 W h kgcathode−1 (NCFMT – Na0.9Cu0.22Fe0.30Mn0.43Ti0.05O2) and finally to 350.7 W h kgcathode−1 (NCNFMT – Na0.9Cu0.12Ni0.10Fe0.30Mn0.43Ti0.05O2). Operando X-ray diffraction reveals phase transformations and ex situ EXAFS shows the evolution of local environments around transition metals during charge/discharge. Monoclinic distortions in the NCFM material during O3–P3 phase transformations are suppressed by Ti4+ substitution leading to improvements in the cycling performance of NCFMT. Cu–O octahedral sites exhibit huge Jahn–Teller distortion: Ni2+ substitution in place of Cu2+ not only leads to more ordered Ni–O, but it also helps extract more Na ions from the O3 cathode structure, thus boosting the capacity while also showing good cycling stability due to the highly reversible bond-length and local environmental changes as revealed by EXAFS analyses. X-ray photoelectron spectroscopy shows a titanium-rich surface for NCFMT and NCNFMT which helps improve water-stability. The capacity retention after 200 cycles at 0.2C is 84%, 96% and 90% for NCFM, NCFMT and NCNFMT respectively. The delivered storage capacities of NCFM, NCFMT and NCNFMT are 21 mA h g−1, 47 mA h g−1 and 60 mA h g−1 respectively at 3C. 18650 type Na-ion batteries using the NCNFMT cathode material against a hard carbon anode are also reported to demonstrate potential scalability of the NCNFMT cathode and efficacy of a 1 M NaBF4 tetraglyme electrolyte system for the first time. 18650 cells deliver a specific energy density of 62 W h kgtotal_18650_weight−1 with 90% energy efficiency, thus being suitable for large scale energy storage applications.

International audience; Sodium rich iron hexacyanoferrates were prepared by coprecipitation, hydrothermal route, and under reflux, with or without dehydration. They were obtained with different structures described in cubic, orthorhombic or rhombohedral symmetry, with variable compositions in sodium, water and cationic vacancies, and with a variety of morphologies. This series of sodium rich Prussian Blue Analogs allowed to address the relationship between synthesis conditions, composition, structure, morphology and electrochemical properties in Na-ion batteries. A new orthorhombic phase with the Na 1.8 Fe 2 (CN) 6 •0.7H 2 O composition synthesized by an hydrothermal route at 140°C is reported for the first time, whereas a phase of Na 2 Fe 2 (CN) 6 •2H 2 O composition obtained under reflux, previously described with a monoclinic structure, shows in fact a rhombohedral structure.

We report the synthesis, characterization, and performance evaluation of tungsten (W) incorporated vanadium oxide (VO2) nanocomposite cathode material for improved lithium storage performance. VO2 nanorods, 100–200 nm in diameter and 1–3 μm in length are synthesized using a hydrothermal method. W incorporation at different weight percent results in the VO2 morphology shifting from rods to a sheet type structure. The lithium storage performance of VO2 has improved remarkably by increasing the loading of W to an optimal level, which influence the intercalation/ deintercalation of lithium ions into the expanded lattices of VO2. The maximum specific capacity observed for the optimal VO2/W4 composite was 381 mAh/g at a current density of 0.1 C. Cyclic voltammetry measurements showed the presence of an electroactive V3+/V4+ redox couple, leading to lower peak separation and voltage polarization differences. Superior charge storage performance was observed with the VO2/W4 composite as compared to the VO2 based devices.

NASICON-structured Li1+xZr2-xLax(PO4)3 (x = 0–0.2) solid electrolytes are prepared by sol-gel method. The influence of substitution of La3+ for Zr4+ on the ionic conductivity, morphology, and structure of the parent compound LiZr2(PO4)3 (LZP) is investigated. Rietveld refinement of powder x-ray diffraction data reveals that the La3+ substitution stabilizes the LZP in the highly conducting rhombohedral R 3 ¯ c phase at room temperature. La3+ substituted LZP display enhanced ionic conductivity, showing the highest ionic conductivity of 0.72 × 10−4 S/cm at room temperature for the composition Li1.1Zr1.9La0.1(PO4)3. The improvement in conductivity of LZP with another aliovalent substituent, Mg2+, whose ionic radii is similar to Zr4+ (0.72 A) is also investigated. Further, the activation energy decreases from 0.53 eV for the parent LZP to 0.42 eV for x = 0.1 La3+ substituted LZP. Lithium-ion transference number obtained by direct current polarization for Li1.1Zr1.9La0.1(PO4)3 is 0.99, confirming the high ionic conducting nature of the solid electrolyte. Cyclic voltammetry recorded for Li1.1Zr1.9La0.1(PO4)3 shows electrochemical stability window up to ∼4.0 V vs. Li. In particular, La3+ substituted NASICON-type LZP (x = 0.1) exhibits good chemical and structural stability after exposing to air, water, Li metal, acidic and basic solutions.

In this article, we report a high-performing fluorophosphate-based cathode material for sodium-ion battery, namely NaVPO4F, synthesised by a facile one-step soft template method. We compared physical and electrochemical properties between the NaVPO4F materials synthesised using V2O3 and V2O5 as starting precursors. FESEM images show that the samples consist of particles of size in the range 200–800 nm. The synthesised NaVPO4F using V2O5 cycled vs. sodium metal at 0.1 C is able to deliver a high discharge capacity of 133 mAh g−1, with a flat discharge plateau at 3.33 V. At a moderate current rate of 1 C, it still manages to achieve a reversible discharge capacity of 121 mAh g−1, and retains 82% of its initial capacity after 2500 cycles. Notably, this electrode material exhibits impressive long-term cyclability at high rates, where it is able to retain 81 and 77% of respective initial discharge capacities even after 10,000 cycles at 10 and 20 C. This durable performance of NaVPO4F using V2O5 precursor is attributed to the good electrode surface integrity owing to negligible volume changes as confirmed by FESEM experiment.

Viability of room-temperature rechargeable in-situ sodium plated batteries (INPBs) with bare Cu current collector foil as anode is reported which operated by sodium plating-stripping on Cu foil during each charge-discharge cycle, respectively. Using 1M NaBF4 in tetraglyme electrolyte, an Na2Fe2(CN)6//Cu INPB delivered 336Wh/kg specific energy density with 76% retention in 100cycles. Keywords: In-situ sodium plating, Anode-free, Current collector anode, Non-dendritic, NaBF4 in tetraglyme, Na2Fe2(CN)6

The individual physico-chemical processes in lithium-ion batteries namely solid-state diffusion and charge transfer polarization are difficult to be tracked by impedance spectroscopy due to simultaneous contributions from cathode and anode. A deeper understanding of various polarization processes in lithium-ion batteries is important to enhance storage performance and cycle life. In this context, the polarization processes occurring in cylindrical 18650 cells comprising different cathodes against graphite anode (LiNi 0.2 Mn 0.2 Co 0.6 O 2 vs. graphite; LiNi 0.6 Mn 0.2 Co 0.2 O 2 vs. graphite; LiNi 0.8 Co 0.15 Al 0.05 O 2 vs. graphite and LiFePO 4 vs. graphite) are investigated by deconvolution of impedance spectra across various states of charge. Further, cathodes and anodes are extracted from the investigated 18650-type cells and tested in half-cells against Li-metal as well as in symmetric cell configurations to understand the contribution of cathode and anode to the full cells of various battery chemistries studied. Except for the LiFePO 4 vs. graphite cell, the polarization resistance in graphite of other cells are found to be higher than those of the investigated cathodes, proving that the polarization in lithium-ion battery is largely influenced by the graphitic anode. Furthermore, the charge transfer polarization resistance encountered by the cathodes investigated in this work is found to be a strong function of the states of charge.

In this article, we propose key design criteria to synthesis carbon coated α-Li3V2(PO4)3 positive electrode material for high power lithium batteries. A facile and scalable one-pot soft template method is adopted to synthesize α-Li3V2(PO4)3/C (LVP/C), which exhibits unique morphology of micron-size mesoporous secondary particles comprising interconnected primary nanoparticles showing good storage and rate performances with long cycle life. This cathode material displays high discharge capacities of 178, 90 and 59 mAh.g−1 at 0.1C, 30C and 80C, respectively. The mesoporous LVP/C with a 3D lithium diffusion network exhibits better rate performance (90 mAh.g−1 at 30C) as compared to the known phosphate, silicate or oxide cathode materials for lithium-ion batteries (LIBs). In addition, LVP/C electrode material retains 80% (at 1C) and 100% (at 20C) of its initial capacity after 1,000 cycles. The phase transitions during delitiation/litiation are discussed at different cutoff voltages, corresponding to the number of moles of lithium involved in the redox reactions. The reversibility of electrochemical extraction/insertion processes are confirmed using operando XRD measurements. Observed storage performances can be attributed not only to high crystallinity of LVP/C calcined at 800°C for 6 h; also to the unique mesoporous architecture of this carbon coated cathode material forming high packing density during the soft template synthesis. Obtained dense packed mesoporous architecture of LVP/C allows favourable (i) electrolyte wettability for lithium-incorporation from the electrolyte and (ii) long electronic wiring by the well-connected carbon coating towards the current collector.

We report the synthesis of low and high temperature polymorphs of Li 2 MnSiO 4 and dependence of lithium storage performance on such polymorphs. Two polymorphs namely, Pmn 2 1 (low temperature/orthorhombic polymorph) and P 2 1 / n (high temperature/monoclinic polymorph) are isolated by controlling the calcination temperature. Among them the electrochemical performance of Pmn 2 1 is found to be better than P 2 1 / n . Orthorhombic polymorph ( Pmn 2 1 ) of carbon coated Li 2 MnSiO 4 exhibits an impressive discharge capacity of 262 mAh g −1 at 0.1C and rate performance up to 5C; in contrast P 2 1 / n delivers only a discharge capacity of 164 mAh g −1 at 0.1C at room temperature. Notably, the capacity of Pmn 2 1 phase is almost 1.5–2 times higher than P 2 1 / n phase at all current rates. Capacity retention of 90% is reported for orthorhombic polymorph until 30 cycles at 0.1C. Further the voltage profiles and polarization of orthorhombic phase are much better than the monoclinic phase. Such perceivable differences in the rate performances and voltage profiles is argued to be due to variations in the activation energy barrier and hopping distance of lithium-ion in the crystal structures. Besides the role of polymorphism, we also show here that the structural stability during cycling is critical in retaining high storage performance.

A new sodium storage pathway is unveiled for the anode Na2Ti3O7 which involves the newly discovered intermediate phase of Na3 − xTi3O7. Details about this Na2Ti3O7 ⇋ Na3 − xTi3O7 sodium storage pathway and how it relates to the conventional Na2Ti3O7 ⇋ Na4Ti3O7 pathway are mentioned. This Na2Ti3O7 ⇋ Na3 − xTi3O7 pathway has the lowest redox voltage of 0.2 V vs Na/Na+ ever reported for any non-carbon based sodium-ion battery anode along with moderately high capacity approaching 89 mAh/g, negligible polarization, excellent rate performance (up to 80 C, or 45 s response) and good cycle life till 1500 cycles. These results indicate this pathway's potential as an anode for sodium-ion batteries meant for diverse applications. Keywords: Na2Ti3O7, Na3 − xTi3O7, Lowest voltage anode, Voltage step, Sodium-ion battery

Deployment of micro-grids using renewable energy (solar and wind power) requires large-scale electrical energy storage (EES) systems. Currently, lithium-ion batteries (LIBs) are leading candidates for EES. High power density LIBs addressing intermittency of renewables use expensive lithium titanate as anode. Besides, lithium is a scarce resource. Sodium, on the other hand, is the sixth most abundant element on the Earth’s crust. Sodium-ion batteries (NIBs) operating at ambient temperature are expected to be durable, safe and inexpensive. Regardless of the relatively lower energy density of NIBs, they can effectively be employed in micro-grid applications, where the weight and footprint requirement are not severe. We present here recently developed non-flammable sodium-ion conducting glyme based electrolyte displaying excellent storage performance of low voltage anodes as well as high voltage cathodes for sodium-ion cells. Employing this liquid electrolyte, non-flammable sodium-ion cells (18650-type) have been fabricated using rhombohedral Prussian Blue analogoue1 or sodium vanadium phosphate as cathode and hard carbon as anode with energy density in the range 40 – 60 Wh/kg (kg refers to the total 18650 full cell weight) and impressive 4C rate performance. This ultra-safe commercial type sodium-ion cells have relatively higher energy density than the reported aqueous (non-flammable) commercial NIBs. We further present thermal (DSC analyses) and safety parameters (heat losses and internal resistance evaluations) of the above 18650 cells which help in developing thermal management systems for NIB packs for possible micro-grids (100-500 kWh) to address the intermittency of renewable energy.

We report here the potential competency of MnCO3 versus MnO2 for supercapacitor applications. MnCO3 was synthesized by a hydrothermal method using KMnO4 as a manganese source and either sugar or pyrrole as carbon source. MnCO3 synthesized using sugar and pyrrole as carbon source is referred hereafter as MnCO3(s) and MnCO3(p), respectively. The synthesized products were characterized by powder X-ray diffraction, scanning electron microscopic and transmission electron microscopic studies. Microscopic studies revealed that MnO2 possesses micro-flower-like morphology constructed by self-assembled nano-petals. While the morphology of MnCO3(s) is sub-micron size particles of different shape, the morphology of MnCO3(p) is crystalline particles of 10–20 nm dia. The capacitive characteristics of MnO2, MnCO3(s) and MnCO3(p) were evaluated in aqueous 0.1 M Mg(ClO4)2 electrolyte between 0 and 1 V using cyclic voltammetry and galvanostatic charge/discharge cycling. Specific capacitance (SC) values of 216 and 296 F g−1 obtained for MnCO3(s) and MnCO3(p) are 35 and 85 % higher than SC value of 160 F g−1 obtained for MnO2, respectively. Besides better capacitive storage characteristics, MnCO3(s) and MnCO3(p) have also exhibited better rate capability and cycle life than MnO2.

Two new organic dyes based on trifluorenylamine donor and cyanoacrylic acid acceptor have been synthesized and characterized by optical and electrochemical measurements and density functional theory calculations. It is found that the trifluorenylamine donor is beneficial to red-shift the absorption and to lower the oxidation potential when compared to the triphenylamine donor. The variations in the photovoltaic performance of the dyes are corroborated by the dye loading data, incident photon to current conversion efficiency and the interfacial kinetic parameters estimated from the intensity modulated photovoltage/photocurrent spectral measurements. A dye with fluorene and bithiophene segments in the π-linker exhibited device efficiency up to 5.8%. The enhanced power conversion efficiency exhibited by this dye when compared to its analogue containing diphenylaminofluorne donor is attributed to its superior anti-aggregation ability and the comparatively prolonged electron lifetime.

Nanostructured pure Na2FePO4F was synthesised by a soft template method, followed by high-energy ball milling (HEBM) process and post-heat treatment. Physical and electrochemical properties of this sample were compared with as-prepared (pristine) sample. FESEM images recorded on the ball milled samples showed that the particles were of spherical morphology, with particle size centred around 100 nm. BET analysis illustrated a correlation between the surface area of the material with the electrochemical performance. Rietveld refinement of XRD patterns of the pristine and the HEBM samples together with the obtained reliability factor values demonstrated lower percentage of antisite disorder in HEBM sample. Compared to the pristine sample, which delivered an initial discharge capacity of only 87 mA h g−1, the HEBM sample showed an impressive storage capacity of 116 mA h g−1 at 0.1 C. Furthermore, at 1 C after 200 cycles, the ball milled sample displayed stable cyclability, retaining almost 80% of its initial discharge capacity, with an average coulombic efficiency of 99.4%. The improved sodium storage performance as compared to the pristine sample is discussed in terms of the reduced antisite disorder and associated sodium ion diffusion.

Palladium nanoparticles decorated graphene (Gra/Pd nanocomposite) was synthesized by simultaneous chemical reduction of graphene oxide and palladium salt in a single step. The negatively charged graphene oxide (GO) facilitates uniform distribution of Pd 2+ ions onto its surface. The subsequent reduction by hydrazine hydrate provides well dispersed Pd nanoparticles decorated graphene. Different amount of Pd nanoparticles on graphene was synthesized by changing the volume to weight ratio of GO to PdCl 2 . X-ray diffraction studies showed FCC lattice of Pd with predominant (1 1 1) plane. SEM and TEM studies revealed that thin graphene nanosheets are decorated by Pd nanoparticles. Raman spectroscopic studies revealed the presence of graphene nanosheets. The electro-catalytic activity of Gra/Pd nanocomposites toward methanol and ethanol oxidation in alkaline medium was evaluated by cyclic voltammetric studies. 1:1 Gra/Pd nanocomposite exhibited good electro-catalytic activity and efficient electron transfer. The kinetics of electron transfer was studied using chronoamperometry. Improved electro-catalytic activity of 1:1 Gra/Pd nanocomposite toward alcohol oxidation makes it as a potential anode for the alcohol fuel cells.

An architecture featuring carbon coated, interconnected nano-grains constructed with mesopores is developed for LiMnPO 4 cathode material. This architecture facilitates enhanced lithium ionic and electronic transports; favours improved lithium storage performance. Mesoporous LiMnPO 4 /C electrode delivers discharge capacity of 140 mAh g −1 at 0.05 C using galvanostatic cycling mode. This best electrochemical response of LiMnPO 4 /C at constant current mode is complemented by diffusion studies using cyclic voltammetry and impedance spectroscopy. Further, the interdependence of lithium storage performance on carbon content, milling time (2, 4, 6 and 10 h), grain size and porous characteristics (surface area, pore size and pore volume) is also discussed. Finally, the feasibility of LiMnPO 4 /C cathode is evaluated against Li 4 Ti 5 O 12 /C anode in a full cell.

Sodium storage in α-MoO3 anode material is reported here for the first time. Upon cycling in the voltage window 0.04–3.0 V, MoO3 anode delivers first cycle sodiation and desodiation capacities of 771 and 410 mAh g−1. The average sodiation and desodiation potentials of the stable cycles lie below 1.0 V with attractive voltage profiles. MoO3 anode also shows favorable rate performance and long cycle life over 500 cycles. Keywords: Sodium-ion battery, Anode material, Conversion reaction, High rate performance, Long term cyclability, Full cell testing

Sodium ion batteries are attractive for the rapidly emerging large-scale energy storage market for intermittent renewable resources. Currently a viable cathode material does not exist for practical non-aqueous sodium ion battery applications. Here we disclose a high performance, durable electrode material based on the 3D NASICON framework. Porous Na3V2(PO4)3/C was synthesized using a novel solution-based approach. This material, as a cathode, is capable of delivering an energy storage capacity of ∼400 mWh/g vs. sodium metal. Furthermore, at high current rates (10, 20 and 40 C), it displayed remarkable capacity retention. Equally impressive is the long term cycle life. Nearly 50% of the initial capacity was retained after 30,000 charge/discharge cycles at 40 C (4.7 A/g). Notably, coulombic efficiency was 99.68% (average) over the course of cycling. To the best of our knowledge, the combination of high energy density, high power density and ultra long cycle life demonstrated here has never been reported before for sodium ion batteries. We believe our findings will have profound implications for developing large-scale energy storage systems for renewable energy sources.

Metal oxide semiconductors are promising interfacial materials for organic photovoltaics (OPVs) because of their electrical properties and solution processability. In this article, we report the fabrication of poly(3-hexylthiophene):[6,6]-phenyl-C61 butyric acid methyl ester (P3HT:PCBM) OPV devices incorporating solution-based NiO interfacial layers that show promising enhancements of the device photocurrent and stability. We discuss the impact of parasitic shunt and series resistances on device performance as well as the ambient degradation of these devices, studied with intensity modulated photocurrent spectroscopy (IMPS). The results showed that charge extraction was predominantly affected by degradation via decrease in carrier mobility and increased trapping/recombination, revealing the physical mechanism behind the degradation observed. 2012 Elsevier Ltd. All rights reserved.

A critical component in bulk-heterojunction (BHJ) organic photovoltaics (OPVs) is the charge-selective interfacial layer, which plays a vital role in achieving high device performance and stability. Here, we present the performance of molybdenum oxide (MoOx) hole selective interfacial layers for BHJ OPVs based on poly(3-hexylthiophene) (P3HT) donor and [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) acceptor, prepared by a facile, low-temperature solution process. The results showed that the MoOx films enhanced device efficiency and stability in comparison to reference devices containing the conventional poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) interfacial layer. Furthermore, a high fill factor (∼69%) close to the theoretical maximum value predicted for the P3HT:PCBM BHJ system was achieved. Despite their hole selective nature, ultraviolet photoemission spectroscopy (UPS) revealed that the MoOx films were n-type. This hole selective behavior can be explained by invoking band b...

The present work demonstrates the usefulness of nickel oxide as a hole transporting material in solid state dye-sensitized solar cells (SSDSSCs). We report on the photovoltaic performances of sensitized TiO2/NiO heterojunctions, and demonstrate that the TiO2 film thickness and morphology, as well as NiO film thickness, have significant effects on the photovoltaic behaviour of TiO2/NiO SSDSSC. Under 1 sun AM1.5G simulated illumination, the SSDSSCs demonstrated best photovoltaic performance with a short circuit photocurrent density, open circuit voltage, fill factor and efficiency of 0.91 mA cm−2, 780 mV, 40% and 0.3%, respectively. This study draws attention to the feasibility of enhancing the photovoltaic performance in SSDSSC devices through development of appropriately designed sensitized TiO2/NiO heterojunctions.

The morphology of electrode materials is addressed as a key factor controlling rapid lithium storage in anisotropic systems such as LiFePO4. In view of this, we have synthesized nanoplates of LiFePO4 with a uniform coating of a 5 nm thick amorphous carbon layer by the solvothermal method and investigated their electrochemical storage behavior. The obtained nanoplates are well characterized by XRPD, SEM, HRTEM and XPS techniques. The thickness along the b-axis is found to be 30–40 nm; such a morphology favors short diffusion lengths for Li+ ions, while the external conductive carbon coating provides connectivity for facile electron diffusion, resulting in high rate performances. Increase in the size of the nanoplates results in poor lithium storage performance. The storage performance of nanoplates is compared with that of mesoporous nanoparticles of LiFePO4 with non-uniform carbon coating. This paper thus describes the advantages of thinner nanoplates for high rate storage performances of battery electrode materials.

The present work is devoted to a systematic investigation of ionic and electronic conductivity as well as chemical Li-diffusivity in single crystalline LiFePO 4 as a function of crystallographic orientation over an extended temperature range. Besides chemical analysis of the elemental ratio of the crystal, we also determined the Fe occupancy on the lithium lattice positions by single crystal X-ray diffraction and synchrotron X-ray radiation followed by Rietveld refinement. AC impedance as well as improved DC polarization/depolarization measurements have been carried out using electronically as well as ionically blocking cells. The activation energies obtained for electronic and ionic conductivities are in the range of 0.55–0.59 eV and of 0.62–0.74 eV, respectively, depending on the orientations. The ionic conductivity is much smaller than the electronic conductivity along all three axes and the electronic conductivity, ionic conductivity and chemical diffusivity of Li ion are found to be effectively two-dimensional (i.e., isotropic in the b–c plane).

Nanoporous materials have attracted great technological interest during the past two decades, essentially due to their wide range of applications: they are used as catalysts, molecular sieves, separators and gas sensors as well as for electronic and electrochemical devices. Most syntheses of nanoporous materials reported so far have focused on template-assisted bottom-up processes, including soft templating (chelating agents, surfactants, block copolymers and so on) and hard templating (porous alumina, carbon nanotubes and nanoporous materials) methods. Here, we exploit a mechanism implicitly occurring in lithium batteries at deep discharge to develop it into a room-temperature template-free method of wide applicability in the synthesis of not only transition metals but also metal oxides with large surface area and pronounced nanoporosity associated with unprecedented properties. The power of this top-down method is demonstrated by the synthesis of nanoporous Pt and RuO2, both exhibiting superior performance: the Pt prepared shows outstanding properties when used as an electrocatalyst for methanol oxidation, and the RuO2, when used as a supercapacitor electrode material, exhibits a distinctly better performance than that previously reported for non-hydrated RuO2 (refs 19,20).

In this paper, we report that Li can be stored in RuO2 with an unusually high coulombic efficiency. The process involves three electrochemical steps: i) formation of a Ru/Li2O nanocomposite, ii) formation of a Li-containing surface film, and iii) interfac

Nanocrystalline tin oxide (SnO2) material with different grain sizes was synthesized by using a chemical precipitation method. This material was characterized by using the X-ray diffraction and transmission electron microscopy. The electrical properties of compressed nanocrystalline SnO2 were studied by using impedance spectroscopy. AC conductivity data for SnO2 material having grain sizes between 9 and 34 nm were analyzed using a power law. The exponent n is found to be 0.5 for bulk (34 nm) and unity for material with grain size below 18 nm. The results show a universal behavior for very low average grain sizes and the non-universal behavior for larger grain sizes even at room temperature.

Electrical conductivity and dielectric measurements have been performed for nanocrystalline NiFe2O4 spinel for four different average grain sizes, ranging from 8 to 97 nm. The activation energy for the grain and grain boundary conduction and its variation with grain size have been reported in this paper. The conduction mechanism is found to be due to the hopping of both electrons and holes. The high-temperature conductivity shows a change of slope at about 500 K for grain sizes of 8 and 12 nm and this is attributed to the hole hopping in tetrahedral sites of NiFe2O4. Since the activation energy for the dielectric relaxation is found to be almost equal to that of the dc conductivity, the mechanism of electrical conduction must be the same as that of the dielectric polarization. The real part e' of the dielectric constant and the dielectric loss tanδ for the 8 and 12 nm grain size samples are about two orders of magnitude smaller than those of the bulk NiFe2O4. The anomalous frequency dependence of e' has been explained on the basis of hopping of both electrons and holes. The electrical modulus analysis shows the non-Debye nature of the nanocrystalline nickel ferrite.

A combined experimental and computational study of disodium pyridine-2,5-dicarboxylate (Na2PDC) is presented exploring the possibility of using it as a potential anode for organic sodium-ion batteries. This electrode material can reversibly insert/release two Na cations per formula unit, resulting in high reversible capacity of 270 mA h g−1 (236 mA h g−1 after accounting for the contribution from Super P carbon) with excellent cyclability 225 mA h g−1, with retention of 83% capacity after 100 cycles, and good rate performance with reversible capacity of 138 mA h g−1 at a 5 C rate. The performance of disodium pyridine dicarboxylate is therefore found to be superior to that of the related and well investigated disodium terephthalate. The material shows two voltage plateaus at about 0.6 V up to Na2+1PDC and then 0.4 V up to full sodiation, Na2+2PDC. The first plateau is attributed to the coordination of inserted Na to nitrogen atoms with bond formation, i.e., a different mechanism from the terephthalate analog. The subsequent plateau is due to coordination to the carboxylic groups.

Organic solar cells based on poly(3-hexylthiophene) and [6,6]-phenyl-C61-butyric acid methyl ester were fabricated with electrodeposited TiOx electron extraction layers 5-180 nm thick. Electrodeposition under ambient conditions is an attractive, facile and viable approach to prepare metal oxide interfacial layers. The TiOx films obtained displayed a linear relationship between thickness and deposition time when fabricated under ambient conditions using an aqueous air stable peroxotitanium precursor. The precursor solution was prepared from titanium isopropoxide using a chelate process, which allowed water to be used as solvent due to considerably decreased sensitivity of the precursor solution towards hydrolysis. Highly conformal TiOx films, typically observed with vacuum deposition techniques, were obtained on the indium tin oxide substrate upon electrogeneration of OH(-) ions using H2O2 additive. Conversely, significantly rougher films with spherical growths were obtained using NO3(-) additives. Low temperature annealing at 200 °C in air was found to greatly improve purity and O stoichiometry of the TiOx films, enabling efficient devices incorporating the electrodeposited TiOx to be made. Using MoOx as the hole extraction layer, the maximum power conversion efficiency obtained was 3.8% (Voc = 610 mV; Jsc = 10.6 mA/cm(2); FF = 59%) under simulated 100 mW/cm(2) (AM1.5G) solar irradiation, whereas an efficiency of 3.4% was achieved with fully solution processed interfacial layers comprising the electrodeposited TiOx films and a surfactant-modified PEDOT:PSS hole extraction layer.

Dielectric constant ( e ′) and dielectric loss tangent (tan δ ) of gadolinium substituted Ni–Zn ferrites have been investigated in the high frequency range 1–15 MHz by an HP 4192A impedance analyser controlled by a PC. The values of complex dielectric constant ( e ″) have been computed from e and tan δ . Plot of e ′ and tan δ vs. frequency show a normal dielectric behaviour of spinel ferrites. A qualitative explanation is given for the composition and frequency dependence of dielectric constant and dielectric loss tangent.

Physical properties such as dielectric, specific heat, thermal expansion, and mechanical hardness have been measured for sodium p-nitrophenolate dihydrate single crystals. The dielectric measurements were made both as a function of frequency (in the range 15 kHz–10 MHz) and temperature (in the range 30–80 °C). For the range of frequencies measured the values were found to vary between 4.03 and 3.69 for e11, 8.11 and 7.05 for e22, and 5.71 and 5.36 for e33 at room temperature, and piezoelectric resonances were observed at certain frequencies. The dielectric measurements made as a function of temperature did not exhibit any anomaly in the temperature range measured. The specific heat studies carried out for this compound showed ≈30% increase in Cp with the temperature in the measured range. The thermal expansion measured as a function of temperature in the range 30–80 °C exhibited linear behavior and the average thermal expansion coefficients were found to be α1=7.48×10−5 K−1, α2=4.30×10−6 K−1, and α3=1.99×...

We describe briefly the experimental facilities developed for the measurement of thermal conductivity of solids in the temperature range 10K–300K. Different techniques have been used for the determination of thermal conductivity, depending on the relaxation time of the system under investigation. Measurements on stainless steel 304, using steady state and non-steady state methods are presented. Values of thermal conductivity obtained by both these methods agree to each other and are consistent with those reported earlier.

Size reduction in nanocrystals leads to a variety of unexpected exciting phenomena due to enhanced surface-to-volume ratio and reduced length for the transport [1, 2]. Here, we consider the effects of nano-size on the kinetics and thermodynamics and study its bearing on the lithium storage performance in insertion and conversion based Li storage mechanism. Firstly, we investigate the storage performance of nanocrystalline LiMnPO4 by insertion reaction. Ball milling of LiMnPO4 synthesized by soft-template method with carbonaceous materials helps to reduce the grain size as well as formation of a thin layer of carbon coating. Nanostructuring by ball milling process promotes high surface area of the active electrode material for improved electrolyte wetting, short transport length for Li diffusion while the carbon coatings facilitates electronic wiring all of which contribute to the enhanced storage performance. Additionally, we show that combining nanostructuring with divalent cation doping further improves the storage performance of the system which make them potential high voltage cathodes for real applications. Secondly, we discuss the size effect on thermodynamics during the conversion reaction, considering Fe2O3 as an example. The process of Li storage by conversion induces drastic size reduction, leading to stabilization of metastable phase of g-Fe2O3. We show here that apart from kinetics, thermodynamics at nanosize also limit the rate of conversion reaction. Finally, we show that Fe2O3 can be a potential anode material for practical applications as they demonstrate a high degree of reversibility ~ 90% and excellent high rate performance.© (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

ac Conductivity measurements are carried out across the metal to insulator transition in NiAl0.7Cr0.7Fe0.6O4. The low frequency data is analyzed using Summerfield scaling theory for hopping conductivity. The exponent of the scaling behavior has significantly different values in the conducting and insulating regimes. The hopping frequency and the zero frequency conductivity are found to increase with temperature, slowly in the metallic regime and rapidly in the insulating regime.

The dielectric parameters of 50-μm-thick polyimide samples irradiated in air with 1 MeV electrons and in BF3 solution with Co-60 gamma rays were studied. The dielectric constant of polyimide was found to decrease with increasing electron fluence and dose of gamma rays. At an electron fluence of ∼1015 e/cm2, the dielectric constant decreased from its virgin value of 3.15 to 2.4, measured at a frequency of ∼7 MHz. Furthermore, by irradiating polyimide samples in BF3 solution with gamma rays, boron and fluorine diffused into each polyimide sample from both sides. In these polyimide samples, the dielectric constant decreased further to ∼2.1 (7 MHz). In a plot of dielectric loss, e″, vs log (f ), two peaks were observed over a frequency range 100 Hz–7 MHz, in virgin as well as in the electron- and gamma-ray-irradiated polyimide samples. The dielectric loss increased with increasing electron fluence or dose of gamma rays. The refractive index (632.8 nm) of polyimide decreased from the virgin value of 1.74 to 1....

The Energy crisis happens to be one of the greatest challenges we are facing today. In this view, much effort has been made in developing new, cost effective, environmentally friendly energy conversion and storage devices. The performance of such devices is fundamentally related to material properties. Hence, innovative materials engineering is important in solving the energy crisis problem. One such innovation in materials engineering is porous materials for energy storage. Porous electrode materials for lithium-ion batteries (LIBs) offer a high degree of electrolyte-electrode wettability, thus enhancing the electrochemical activity within the material. Among the porous materials, mesoporous materials draw special attention, owing to shorter diffusion lengths for Li + and electronic movement. Nanostructured mesoporous materials also offer better packing density compared to their nanostructured counterparts such as nanopowders, nanowires, nanotubes etc., thus opening a window for developing electrode materials with high volumetric energy densities. This would directly translate into a scenario of building batteries which are much lighter than today's commercial LIBs. In this article, the authors present a simple, soft template approach for preparing both cathode and anode materials with high packing density for LIBs. The impact of porosity on the electrochemical storage performance is highlighted.

Nanostructured materials have triggered a great excitement in recent times due to both fundamental interest as well as technological impact relevant for lithium ion batteries (LIBs). Size reduction in nanocrystals leads to a variety of unexpected exciting phenomena due to enhanced surface-to-volume ratio and reduced transport length. We will consider a few examples of nanostructured electrode materials in the context of lithium batteries for achieving high storage and high rate performances. 1. LiFeP0 4 nanoplates synthesized using solvothermal method could store Li-ions comparable to its theoretical capacity at C/10, while at 30C, they exhibit storage capacity up to 45 mAh/g. Size reduction (~30 nm) at the b-axis favors the fast Li-ion diffusion. In addition to this, uniform ~5 nm carbon coating throughout the plates provides excellent electronically conducting path for electrons. This nano architecture enables fast insertion/extraction of both Li-ions as well as electrons. 2. Mesporous-TiO 2 with high surface area (135m 2 /g) synthesized using soft-template method exhibits high volumetric density compared to commercial nanopowder (P25), with excellent Li-storage behavior. C16 meso-TiO 2 synthesized from CTAB exhibits reversible storage capacity of 288mAh/g at 0.2C and 109 mAh/g at 30C. 3. Zero strain Li 4 Ti 5 O 12 anode material has been synthesized using several wet chemical routes; the best condition has been optimized to achieve storage capability close to theoretical limit of 175mAh/g at C/10. At 10C, we could retain lithium storage up to 88 mAh/g. 4. We report our recent results on α-Fe 2 O 3 and γ-Fe 2 O 3 using conversion reaction, providing insight for a better storage capability in γ-phase than the α-phase at 2C resulting solely from the nanocrystallinity.

In view of increasing scientific and technological interest in nanomaterials, it is important to examine whether or, more exactly, to what extent the thermodynamic parameters change with size. Electrochemical e.m.f. measurements which provide a direct and elegant access to these thermodynamic data have been used in this study to investigate the excess contributions of anatase due to nano-size. The e.m.f. measurements are carried out (250-450 degrees C) on different particle sizes (1.2 microm-5 nm) using the cell: Au, O(2), Na(2)Ti(6)O(13), TiO(2) (anatase) |Na-beta'' alumina |TiO(2) (rutile), Na(2)Ti(6)O(13), O(2), Au. The e.m.f. observed is closely related to the difference of the Gibbs energies of formation (Delta(f)G degrees) of the titania crystals on both sides. Such cell voltage measurements with various sizes of anatase (1200, 100, 15, and 5 nm) as working electrodes enable us to calculate the excess enthalpy and entropy due to surface contributions and to provide refined data for the macroscopic anatase. No electrochemical Ostwald ripening or chemical Ostwald ripening was observed in the case of anatase nanoparticles up to 500 degrees C.

International audience; Nanocrystalline RuO2 was electrochemically lithiated using a 6Li-enriched negative electrode, and selected samples at various states of lithiation-delithiation were characterized ex situ by 6Li magic-angle spinning nuclear magnetic resonance (6Li MAS NMR). In the first plateau (up to one Li per RuO2), a signal with considerable shift and loss of intensity is observed, showing a strongly paramagnetic character for the LiRuO2 phase. A signal due to solid electrolyte interphase (SEI) appears at 0 ppm on this first plateau, but significantly grows only on the subsequent conversion plateau (from 1 to 4 Li/RuO2). Li2O is detected only at the very end of the latter plateau. On further lithiation (4 to 5.5 Li/RuO2), the magnitude of the Li2O signal remains constant, and a new signal at 4 ppm appears, that we can assign to interfacial Li hypothesized earlier in this system. Upon subsequent delithiation, NMR shows that the interfacial Li first disappears, then Li2O also disappears, and the reconstructed Li-RuO2 phase is clearly different from the one formed during the initial lithiation of RuO2. Besides, the SEI signal slightly changes but does not decrease in magnitude upon delithiation. NMR results are in satisfactory agreement with the characteristic features of the proposed “job-sharing” mechanism.