Advanced Na[Ni0.25Fe0.5Mn0.25]O2/C-Fe3O4 sodium-ion batteries using EMS electrolyte for energy storage.

While much research effort has been devoted to the development of advanced lithium-ion batteries for renewal energy storage applications, the sodium-ion battery is also of considerable interest because sodium is one of the most abundant elements in the Earth's crust. In this work, we report a sodium-ion battery based on a carbon-coated Fe3O4 anode, Na[Ni0.25Fe0.5Mn0.25]O2 layered cathode, and NaClO4 in fluoroethylene carbonate and ethyl methanesulfonate electrolyte. This unique battery system combines an intercalation cathode and a conversion anode, resulting in high capacity, high rate capability, thermal stability, and much improved cycle life. This performance suggests that our sodium-ion system is potentially promising power sources for promoting the substantial use of low-cost energy storage systems in the near future.

Anatase titania nanorods as an intercalation anode material for rechargeable sodium batteries.

For the first time, we report the electrochemical activity of anatase TiO2 nanorods in a Na cell. The anatase TiO2 nanorods were synthesized by a hydrothermal method, and their surfaces were coated by carbon to improve the electric conductivity through carbonization of pitch at 700 °C for 2 h in Ar flow. The resulting structure does not change before and after the carbon coating, as confirmed by X-ray diffraction (XRD). Transmission electron microscopic images confirm the presence of a carbon coating on the anatase TiO2 nanorods. In cell tests, anodes of bare and carbon-coated anatase TiO2 nanorods exhibit stable cycling performance and attain a capacity of about 172 and 193 mAh g(-1) on the first charge, respectively, in the voltage range of 3-0 V. With the help of the conductive carbon layers, the carbon-coated anatase TiO2 delivers more capacity at high rates, 104 mAh g(-1) at the 10 C-rate (3.3 A g(-1)), 82 mAh g(-1) at the 30 C-rate (10 A g(-1)), and 53 mAh g(-1) at the 100 C-rate (33 A g(-1)). By contrast, the anode of bare anatase TiO2 nanorods delivers only about 38 mAh g(-1) at the 10 C-rate (3.3 A g(-1)). The excellent cyclability and high-rate capability are the result of a Na(+) insertion and extraction reaction into the host structure coupled with Ti(4+/3+) redox reaction, as revealed by X-ray absorption spectroscopy.

Influence of temperature on lithium-oxygen battery behavior.

In this Letter we report an electrochemical and morphological study of the response of lithium-oxygen cells cycled at various temperatures, that is, ranging from -10 to 70 °C. The results show that the electrochemical process of the cells is thermally influenced in an opposite way, that is, by a rate decrease, due to a reduced diffusion of the lithium ions from the electrolyte to the electrode interface, at low temperature and a rate enhancement, due to the decreased electrolyte viscosity and consequent increased oxygen mobility, at high temperature. In addition, we show that the temperature also influences the crystallinity of lithium peroxide, namely of the product formed during cell discharge.

Structure of solid-supported lipid membrane probed by noble metal nanoparticle deposition.

Direct deposition of a noble metal layer onto a solid-supported membrane was proposed as an indirect microscopy tool to visually observe different lipid phases that may develop in the lipid membrane. The method relied on the different permeability of the lipid membrane towards the incident atoms during deposition. Liquid state or structural defects such as phase boundaries, step ledges in a multi-lamellar stack, and pores permitted the metal atoms to penetrate and nucleate inside the membrane whereas rigid gel state was relatively impermeable to the incident atoms, thus enabling visualization of liquid phase or structural defects inside the gel state. Based on the proposed method, we demonstrated the phase states resulting from thermotropic transitions of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), dioleoylphosphatidylethanolamine (DOPE)/DPPC mixture, and 1,2-dioleoyl-3-trimethylammonium propane (DOTAP). Although the proposed method does not allow in-situ observation of equilibrium states, the method should be an excellent complementary tool for visualizing the lipid phases as the method can resolve fine structural details (up to tens of nanometer scale) as seen in the DPPC membrane while providing macroscopic images (up to several micrometers).

Nanostructured high-energy cathode materials for advanced lithium batteries.

Nickel-rich layered lithium transition-metal oxides, LiNi(1-x)M(x)O(2) (M = transition metal), have been under intense investigation as high-energy cathode materials for rechargeable lithium batteries because of their high specific capacity and relatively low cost. However, the commercial deployment of nickel-rich oxides has been severely hindered by their intrinsic poor thermal stability at the fully charged state and insufficient cycle life, especially at elevated temperatures. Here, we report a nickel-rich lithium transition-metal oxide with a very high capacity (215 mA h g(-1)), where the nickel concentration decreases linearly whereas the manganese concentration increases linearly from the centre to the outer layer of each particle. Using this nano-functional full-gradient approach, we are able to harness the high energy density of the nickel-rich core and the high thermal stability and long life of the manganese-rich outer layers. Moreover, the micrometre-size secondary particles of this cathode material are composed of aligned needle-like nanosize primary particles, resulting in a high rate capability. The experimental results suggest that this nano-functional full-gradient cathode material is promising for applications that require high energy, long calendar life and excellent abuse tolerance such as electric vehicles.

Deposition of metal nanoparticles on phospholipid multilayer membranes modified by gramicidin.

A planar dipalmitoyl phosphatidylcholine (DPPC) multilayer phospholipid membrane was structurally modified by introducing a transmembrane protein, gramicidin (up to 25 mol %), to study its effect on the metal nanoparticles deposited on the membrane. Without gramicidin, when 3-nm-thick Ag, Sn, Al, and Au were deposited, the nanoparticles hardly nucleated on the DPPC membrane in rigid gel state (except for Au); however, the gramicidin addition dramatically enhanced the DPPC membrane surface's affinity for metal atoms so that a dense array of metal (Ag, Sn, and Au) or metal-oxide (Al-oxide) nanoparticles was produced on the membrane surface. The particle sizes ranged from 3 to 15 nm depending on the metal and gramicidin concentration, whereas the particle density was strongly dictated by the gramicidin concentration. The proposed method provides a convenient, generally applicable synthesis route for preparing different metal or metal-oxide nanoparticles on a relatively robust biocompatible membrane.

Optical and structural properties of Ag:Ta2O5 nanocomposites.

In this paper, we investigated the optical and structural properties of the Ag:Ta2O5 nanocomposites. The nanocomposite films were prepared by magnetron co-sputtering of Ta2O5 with Ag chips. The transmission electron microscopy images clearly revealed that Ag nanoparticles were successfully produced by post-thermal annealing of the deposited films. The reflection spectra exhibited the surface plasmon resonance behavior. The photoluminescence (PL) spectra indicated that the Ag:Ta2O5 nanocomposites exhibited larger PL intensity than pure Ag or pure Ta2O5. The PL enhancement is thought to be due to the surface plasmon resonance of Ag nanoparticles. From the spatial intensity distributions that were obtained by solving Maxwell equations using the three-dimensional, finite-difference time-domain method, we found that there was strong confinement of optical field near the Ag nanoparticle. This optical confinement effect makes it possible to exhibit the enhanced PL.

Coalescence and polygonization of Au nanoparticles embedded in liquid-crystalline lipid membrane.

Coarsening behavior of Au nanoparticles (AuNPs) embedded in a liquid crystalline lipid (1,2-dioleoyl-3-trimethylammonium-propane, DOTAP) membrane was investigated by heat treating the AuNP-embedded DOTAP membrane at 80 degrees C with 15% and 80% relative humidity (RH). The coarsening rate was (D) to approximately t0.6 regardless of the humidity; however, the spatial distribution and the coarsening mechanism differed depending on the humidity. In addition, extended treatment at 15% RH resulted in formation of large polygonized AuNPs from the lipid segregation.

A transmission electron microscopy study of the electrochemical process of lithium-oxygen cells.

The electrochemical reaction of a lithium-oxygen cell using a tetraethylene glycol dimethyl ether-lithium triflate, TEGDME-LiCF(3)SO(3) electrolyte, is investigated by a detailed transmission electron microscopy analysis. The results confirm the reversibility of the process by showing the formation-dissolution of lithium peroxide, Li(2)O(2), upon repeating cell charge and discharge cycles.

Turning on Lithium-Sulfur Full Batteries at -10 °C.

Lithium-sulfur (Li-S) batteries using Li2S and Li-free anodes have emerged as a potential high-energy and safe battery technology. Although the operation of Li-S full batteries based on Li2S has been demonstrated at room temperature, their effective use at a subzero temperature has not been realized due to the low electrochemical utilization of Li2S. Here, ammonium nitrate (NH4NO3) is introduced as a functional additive that allows Li-S full batteries to operate at -10 °C. The polar N-H bonds in the additive alter the activation pathway of Li2S by inducing the dissolution of the Li2S surface. Then, Li2S with an amorphized surface layer undergoes the modified activation process, which consists of the disproportionation and direct conversion reaction, through which Li2S is efficiently converted into S8. The Li-S full battery using NH4NO3 delivers a reversible capacity and cycling stability over 400 cycles at -10 °C.

Surface plasmon resonance tuning of silver nanoparticle array produced by nanosphere lithography through ion etching and thermal annealing.

It was demonstrated that size of the Ag nanoparticles array fabricated by nanosphere lithography (NSL) can be changed as needed by reactive ion etching (RIE) of the self-assembled polystyrene (PS) nanosphere template and post-annealing of the Ag particle array. A macroscopic 2D array of ordered Ag nanoparticles stretching over an area greater than 1 cm2 was achieved using a modified nanosphere lithography method. The wavelength corresponding to the extinction maximum of the surface plasmon resonance (SPR) from the Ag nanoparticle array was systematically tuned by RIE of the PS template. Additional tuning of SPR was achieved by post-annealing the Ag nanoparticles which induced shape-changes in the Ag nanoparticles. We demonstrated that SPR can be tuned over the entire visible spectrum by RIE of the PS mask and thermal annealing, which can be potentially used to display localized SPR spectrum (hence, different color) throughout the visible range.

Reversible size-tuning of self-assembled silver nanoparticles in phospholipid membranes via humidity control.

A monolayer of 5-nm-sized Ag nanoparticles embedded in a liquid-crystalline lipid membrane undergoes a reversible morphological change during hydration and dehydration of the lipid membrane. High mobility of the encapsulating lipid molecules, chemically bound to the Ag atoms, induces redistribution of metal particles to produce significant and optically detectable changes in nanoparticle morphology. The morphological change occurs on a time scale that enables the Ag-nanoparticle-embedded membrane to be used as a convenient visual sensor for moisture and other organic solvents, as well as for biosensing by virtue of the biocompatibility of the lipid molecules. The mechanism demonstrated here can also be extended to construct guided nanostructures based on self-assembled nanoparticles.

The catalytic effect of Pt nanoparticles supported on silicon oxide nanowire.

3.5 nm sized Pt nanocatalysts supported on silicon oxide nanowires (SiO(X)NWs) were fabricated by decorating the SiO(X)NWs with Pt nanoparticles using a simple physical deposition system without any surface pretreatment. High curvature of the nanowire surface together with the weak metal-substrate interaction helped to maintain discrete particle morphology with spherical shapes during deposition. Catalytic efficiency of the SiO(X)NWs coated with Pt nanoparticles was demonstrated through reduction of methylene blue in the presence of sodium borohydride. It was demonstrated that the highly curved nanowire surface allowed the Pt nanoparticles to be loaded with increased particle density, providing a larger surface area for the catalytic reaction. It was also shown that a simple heat treatment in vacuum improves the effectiveness of the Pt nanoparticles as a catalyst without loss of catalytic activity when used repeatedly. We expect that this metal nanoparticle-decorated nanowire can be easily extended to other heterogeneous reactions and can also be used as a template for building three-dimensional hierarchical nanostructures.

Degradation Mechanism of Highly Ni-Rich Li[NixCoyMn1-x-y]O2 Cathodes with x > 0.9.

A series of Ni-rich Li[NixCo(1-x)/2Mn(1-x)/2]O2 (x = 0.9, 0.92, 0.94, 0.96, 0.98, and 1.0) (NCM) cathodes are prepared to study their capacity fading behaviors. The intrinsic trade-off between the capacity gain and compromised cycling stability is observed for layered cathodes with x ≥ 0.9. The initial specific capacities of LiNiO2 and Li[Ni0.9Co0.05Mn0.05]O2 are 245 mAh g-1 (91% of the theoretical capacity) and 230 mAh g-1, and their corresponding capacity retentions are 72.5% and 88.4%. However, the capacity retention characteristic deteriorates at an increasingly faster rate for x > 0.95, in contrast with the nearly linear increase of specific capacity. The fast capacity fading stems from the chemical attack of the cathode by the electrolyte infiltrated through the microcracks, resulting from the mechanical instability inflicted by the anisotropic internal strain caused by the H2 ⇆ H3 phase transition. Thus, the capacity fading of the NCM cathodes for x > 0.9 critically depends on the extent of the H2 → H3 phase transition. Retardation or protraction of the H2 ⇆ H3 phase transition by engineering the microstructure should improve the cycle life of these highly Ni-enriched NCM cathodes.

Capacity Degradation Mechanism and Cycling Stability Enhancement of AlF3-Coated Nanorod Gradient Na[Ni0.65Co0.08Mn0.27]O2 Cathode for Sodium-Ion Batteries.

O3-type Na[Ni xCo yMn z]O2 materials are attractive cathodes for sodium-ion batteries because of their full cell fabrication practicality, high energy density, and relatively easy technology transfer arising from their similarity to Li[Ni xCo yMn z]O2 materials, yet their performance viability with Ni-rich composition ( x ≥ 0.6) is still doubtful. More importantly, their capacity degradation mechanism remains to be established. In this paper, we introduce an O3-type Ni-rich AlF3-coated nanorod gradient Na[Ni0.65Co0.08Mn0.27]O2 cathode with enhanced electrochemical performance in both half-cells and full cells. AlF3-coated nanorod gradient Na[Ni0.65Co0.08Mn0.27]O2 particles were synthesized through a combination of dry ball-mill coating and columnar composition gradient design and deliver a discharge capacity of 168 mAh g-1 with 90% capacity retention in half cells (50 cycles) and 132 mAh g-1 with 90% capacity retention in full cells (200 cycles) at 75 mA g-1 (0.5C, 1.5-4.1 V). Through analysis of the cycled electrodes, the capacity-degradation mechanism was unraveled in O3-type Ni-rich Na[Ni xCo yMn z]O2 from a structural perspective with emphasis on high-resolution transmission electron microscopy, providing valuable information on improving O3-type Na[Ni xCo yMn z]O2 cathode performance.

Interface morphology effect on the spin mixing conductance of Pt/Fe3O4 bilayers.

Non-magnetic (NM) metals with strong spin-orbit coupling have been recently explored as a probe of interface magnetism on ferromagnetic insulators (FMI) by means of the spin Hall magnetoresistance (SMR) effect. In NM/FMI heterostructures, increasing the spin mixing conductance (SMC) at the interface comes as an important step towards devices with maximized SMR. Here we report on the study of SMR in Pt/Fe3O4 bilayers at cryogenic temperature, and identify a strong dependence of the determined real part of the complex SMC on the interface roughness. We tune the roughness of the Pt/Fe3O4 interface by controlling the growth conditions of the Fe3O4 films, namely by varying the thickness, growth technique, and post-annealing processes. Field-dependent and angular-dependent magnetoresistance measurements sustain the clear observation of SMR. The determined real part of the complex SMC of the Pt/Fe3O4 bilayers ranges from 4.96 × 1014 Ω-1 m-2 to 7.16 × 1014 Ω-1 m-2 and increases with the roughness of the Fe3O4 underlayer. We demonstrate experimentally that the interface morphology, acting as an effective interlayer potential, leads to an enhancement of the spin mixing conductance.

Area-selective growth of amorphous carbon nanofibers via catalytic decomposition of polyimide thin film.

A dense layer of amorphous carbon nanofibers was fabricated by pyrolyzing a thin film of polyimide using a monolayer of gold nanoparticles as a catalyst.

Characterization of Sputter-Deposited LiCoO2 Thin Film Grown on NASICON-type Electrolyte for Application in All-Solid-State Rechargeable Lithium Battery.

All-solid-state Li-rechargeable batteries using a 500 nm-thick LiCoO2 (LCO) film deposited on two NASICON-type solid electrolyte substrates, LICGC (OHARA Inc.) and Li1.3Al0.3Ti1.7(PO4)3 (LATP), are constructed. The postdeposition annealing temperature prior to the cell assembly is critical to produce a stable sharp LCO/electrolyte interface and to develop a strong crystallographic texture in the LCO film, conducive to migration of Li ions. Although the cells deliver a limited discharge capacity, the cells cycled stably for 50 cycles. The analysis of the LCO/electrolyte interfaces after cycling demonstrates that the sharp interface, once formed by proper thermal annealing, will remain stable without any evidence for contamination and with minimal intermixing of the constituent elements during cycling. Hence, although ionic conductivity of the NASICON-type solid electrolyte is lower than that of the sulfide electrolytes, the NACSICON-type electrolytes will maintain a stable interface in contact with a LCO cathode, which should be beneficial to improving the capacity retention as well as the rate capability of the all-solid state cell.

Novel core-shell-structured Li[(Ni0.8Co0.2)0.8(Ni0.5Mn0.5)0.2]O2 via coprecipitation as positive electrode material for lithium secondary batteries.

We have successfully synthesized a spherical core-shell structure based on Li[(Ni0.8Co0.2)0.8(Ni0.5Mn0.5)0.2]O2 via a coprecipitation route. According to the careful examination by scanning electron microscopy (SEM), transmission electron microscopy energy-dispersive spectroscopy (TEM-EDS), and X-ray diffraction (XRD), it was found that the core-shell particle consisted of Li[Ni0.8Co0.2]O2 as the core and Li[Ni0.5Mn0.5]O2 as the shell, of which the thickness was estimated to be 1 to approximately 1.5 microm. Both the core and shell were dense as confirmed by SEM. Though the core-shell-structured Li[(Ni0.8Co0.2)0.8(Ni0.5Mn0.5)0.2]O2 delivered a slightly reduced initial discharge capacity, the capacity retention and thermal stability were significantly improved relative to those of the Li[Ni0.8Co0.2]O2 electrode without the Li[Ni0.5Mn0.5]O2 shell. The carbon/Li[Ni0.8Co0.2]O2 pouch cell underwent an explosive ignition during the nail penetration test, whereas the carbon/Li[(Ni0.8Co0.2)0.8(Ni0.5Mn0.5)0.2]O2 cell remained stable, demonstrating the superior thermal stability of the core-shell electrode. As a new positive electrode material, the core-shell-structured Li[(Ni0.8Co0.2)0.8(Ni0.5Mn0.5)0.2]O2 is a significant breakthrough in the development of high-capacity lithium secondary batteries.

Critical Role of pH Evolution of Electrolyte in the Reaction Mechanism for Rechargeable Zinc Batteries.

The reaction mechanism of α-MnO2 having 2×2 tunnel structure with zinc ions in a zinc rechargeable battery, employing an aqueous zinc sulfate electrolyte, was investigated by in situ monitoring structural changes and water chemistry alterations during the reaction. Contrary to the conventional belief that zinc ions intercalate into the tunnels of α-MnO2 , we reveal that they actually precipitate in the form of layered zinc hydroxide sulfate (Zn4 (OH)6 (SO4 )⋅5 H2 O) on the α-MnO2 surface. This precipitation occurs because unstable trivalent manganese disproportionates and is dissolved in the electrolyte during the discharge process, resulting in a gradual increase in the pH value of the electrolyte. This causes zinc hydroxide sulfate to crystallize from the electrolyte on the electrode surface. During the charge process, the pH value of the electrolyte decreases due to recombination of manganese on the cathode, leading to dissolution of zinc hydroxide sulfate back into the electrolyte. An analogous phenomenon is also observed in todorokite, a manganese dioxide polymorph with 3×3 tunnel structure that is an indication for the critical role of pH changes of the electrolyte in the reaction mechanism of this battery system.