Nanoscale Zirconium-Abundant Surface Layers on Lithium- and Manganese-Rich Layered Oxides for High-Rate Lithium-Ion Batteries.

Battery performance, such as the rate capability and cycle stability of lithium transition metal oxides, is strongly correlated with the surface properties of active particles. For lithium-rich layered oxides, transition metal segregation in the initial state and migration upon cycling leads to a significant structural rearrangement, which eventually degrades the electrode performance. Here, we show that a fine-tuning of surface chemistry on the particular crystal facet can facilitate ionic diffusion and thus improve the rate capability dramatically, delivering a specific capacity of ∼110 mAh g-1 at 30C. This high rate performance is realized by creating a nanoscale zirconium-abundant rock-salt-like surface phase epitaxially grown on the layered bulk. This surface layer is spontaneously formed on the Li+-diffusive crystallographic facets during the synthesis and is also durable upon electrochemical cycling. As a result, Li-ions can move rapidly through this nanoscale surface layer over hundreds of cycles. This study provides a promising new strategy for designing and preparing a high-performance lithium-rich layered oxide cathode material.

Reversible crystalline-amorphous phase transformation in Si nanosheets with lithi-/delithiation.

Silicon (Si) has a large theoretical capacity of 4200 mAhg-1 and has great potential as a high-performance anode material for Li ion batteries (LIBs). Meanwhile, nanostructures can exploit the potential of Si and, accordingly, many zero-dimensional (0D) and one-dimensional (1D) Si nanostructures have been studied. Herein, we report on two-dimensional (2D) Si nanostructures, Si nanosheets (SiNSs), as anodes for LIBs. These 2D Si nanostructures, with a thickness as low 5 nm and widths of several micrometers, show reversible crystalline-amorphous phase transformations with the lithi-/delithiation by the dimensionality of morphology and large surface area. The reversible crystalline-amorphous phase transformation provides a structural stability of Li+ insertions and makes SiNSs promising candidates for reliable high-performance LIBs anode materials.

Controlling the intercalation chemistry to design high-performance dual-salt hybrid rechargeable batteries.

We have conducted extensive theoretical and experimental investigations to unravel the origin of the electrochemical properties of hybrid Mg(2+)/Li(+) rechargeable batteries at the atomistic and macroscopic levels. By revealing the thermodynamics of Mg(2+) and Li(+) co-insertion into the Mo6S8 cathode host using density functional theory calculations, we show that there is a threshold Li(+) activity for the pristine Mo6S8 cathode to prefer lithiation instead of magnesiation. By precisely controlling the insertion chemistry using a dual-salt electrolyte, we have enabled ultrafast discharge of our battery by achieving 93.6% capacity retention at 20 C and 87.5% at 30 C, respectively, at room temperature.

Influence of vanadium doping on the electrochemical performance of nickel oxide in supercapacitors.

In this study, V-doped NiO materials were prepared by simple coprecipitation and thermal decomposition, and the effect of the vanadium content on the morphology, structural properties, electrochemical behavior, and cycling stability of NiO upon oxidation and reduction was analyzed for supercapacitor applications. The results show an improvement in the capacitive characteristics of the V-doped NiO, including increases in the specific capacitance after the addition of just 1.0, 2.0, and 4.0 at% V. All VxNi1-xO electrodes (x = 0.01, 0.02, 0.04) exhibited higher specific capacitances of 371.2, 365.7, and 386.2 F g(-1) than that of pure NiO (303.2 F g(-1)) at a current density of 2 A g(-1) after 500 cycles, respectively. The V0.01Ni0.99O electrode showed good capacitance retention of 73.5% at a current density of 2 A g(-1) for more than 500 cycles in a cycling test. Importantly, the rate capability of the V0.01Ni0.99O electrode was maintained at about 84.7% as discharge current density was increased from 0.5 A g(-1) to 4 A g(-1).

Enhancement of photoconversion efficiency of ZnO nanorod-based dye-sensitized solar cells in presence of ZrO2 thin energy barrier.

In order to enhance the power conversion efficiency of ZnO nanorods-based dye-sensitized solar cells (DSSCs), ZrO2 thin energy barriers were formed on ZnO nanorods using a sol-gel method. In DSSCs, the short-circuit current was substantially increased, and the dark current was significantly reduced in the presence of the ZrO2 layer. Due to suppressed recombination in the presence of the ZrO2 layer, 81.3% increment of power conversion efficiency is achieved compared to those without ZrO2 layer.

Enhanced photocurrent generation of binary self-assembled monolayers of di-(3-aminopropyl)-viologen and methylviologen on indium tin oxide.

The binary self-assembled monolayers (SAMs) of di-(3-aminopropyl)-viologen (DAPV) and methylviologen (MV) molecules on indium tin oxide (ITO) were prepared by dipping the DAPV SAMs/ITO substrates into MV solution. The DAPV-MV SAM films were characterized by UV-vis. absorption spectroscopy, Rutherford backscattering spectroscopy, and cyclic voltammetry. Optical band gap, lowest unoccupied molecular orbital, and highest occupied molecular orbital of DAPV-MV SAMs were measured to be 1.6, -4.3, and -5.9 eV, respectively. We found that although DAPV SAMs have a quantum yield of 0.11%, the binary SAM films have a good quantum yield of 2.30%, which was 20 times higher than that of DAPV SAMs on ITO. This result may be due to the higher adsorption property of the binary SAMs for the light in visible range compared to that of DAPV SAMs. From this study, we demonstrated that the photocurrent generation systems with a high quantum yield can be obtained by the functional binary SAMs.

Photoelectrochemical polymerization of thiophene on self-assembled RuL2(NCS)2/di(3-aminopropyl)viologen on indium thin oxide.

Polythiophene layers were formed on self-assembled monolayers (SAMs)/indium tin oxide (ITO) using photoelectrochemical polymerization. The SAMs on ITO was prepared using Ru(4,4'-dicarboxylic acid-2,2'-bipyridine)2(NCS)2 and di(3-aminopropyl)viologen. The photoelectrochemically polymerized polythiophene layers on SAMs/ITO were characterized using UV-vis. absorption spectroscopy, atomic force microscopy, scanning electron microscopy, and cyclic voltammetry. The polymer layers have thickness of 360 nm, a dense surface morphology, optical gap of 2.38 eV, highest occupied molecular orbital of -5.2 eV and lowest unoccupied molecular orbital of -2.82 eV. In photoelectrochemical cells, the polythiophene on SAMs/ITO electrode showed a photocurrent of 5 microA/cm2.

Enhanced photocurrent in the RuL2(NCS)2/ di-(3-aminopropyl)-viologen/Au nanoparticles/ITO system: use of Au nanoparticles for retardation of the back electron transfer reaction.

This paper reports the use of Au nanoparticles (NPs) as electron transfer bridge layers to improve the photocurrent of viologen/Ru complex-based photoelectrochemical cells. The Ru complex/ viologen/Au NPs on electrodes were prepared using self-assembled monolayers. The cell system showed an excellent photocurrent of 25 nA/cm2 under the 1.5 air mass condition (I = 100 mW/cm2), which is five times greater than Au NPs due to the reduced recombination reaction.

Reduced recombination and photodegradation processes of photoelectrochemical cell-based on CdSe nanofibers in the presence of PEDOT:PSS layers.

This paper reports the use of poly(3,4-ethylenedioxythiophen):poly(styrene sulfonate) (PEDOT: PSS) as a protective layer to reduce the photodegradation and recombination processes of CdSe nanofiber films. Due to reduced photodegradation and recombination processes of photoelectrochemical cell-based CdSe nanofiber films, the power conversion efficiency of CdSe nanofibers films was 1.81% in the presence of PEDOT:PSS layers under the 1.5 air mass condition (I = 80 mW/cm2), which is an 82.8% increase compared to films without PEDOT:PSS layers. Furthermore, the CdSe film was highly stable under illumination in the presence of PEDOT:PSS layers.

Modification of ion permeability utilizing pH-dependent selective swelling of polyelectrolyte multilayer films.

The selective swelling behavior of polyelectrolyte multilayer (PEM) films prepared by layer-by-layer (L-b-L) assembly influences the ion-permeability in contrast to surface charge density of the films. The cation terminated polyethylene amine (PEI) and anion terminated polyacrylic acid (PAA) were dissolved in DI water, and the pH was adjusted to 10 and 4, respectively, exemplifies thick denser film with good layering structure. The layered polyelectrolyte films has selective swelling behavior at pH 4 (PEI) or pH 10 (PAA), influences the permeability of both Ru(NH3)6(2+) and Fe(CN)6(3-) rather than surface charge character or film charge density. The swollen top most layer shows "on" character, whereas, shrunken top most layer shows "off" character for the ion-permeability. Such "on-off" character can be used for the pH-dependent switches based on surface morphology.

Exceptionally Reversible Li-/Na-Ion Storage and Ultrastable Solid-Electrolyte Interphase in Layered GeP5 Anode.

In this study, we synthesize two layered and amorphous structures of germanium phosphide (GeP5) and compare their electrochemical performances to better understand the role of layered, crystalline structures and their ability to control large volume expansions. We compare the results obtained with those of previous, conventional viewpoints addressing the effectiveness of amorphous phases in traditional anodes (Si, Ge, and Sn) to hinder electrode pulverization. By means of both comprehensive experimental characterizations and density functional theory calculations, we demonstrate that layered, crystalline GeP5 in a hybrid structure with multiwalled carbon nanotubes exhibits exceptionally good transport of electrons and electrolyte ions and tolerance to extensive volume changes and provides abundant reaction sites relative to an amorphous structure, resulting in a superior solid-electrolyte interphase layer and unprecedented initial Coulombic efficiencies in both Li-ion and Na-ion batteries. Moreover, the hybrid delivers excellent rate-capability (symmetric and asymmetric) performance and remarkable reversible discharge capacities, even at high current rates, realizing ultradurable cycles in both applications. The findings of this investigation are expected to offer insights into the design and application of layered materials in various devices.

Heterojunction of hydrophobic poly(1,4-phenylenevinylene) and hydrophilic PEDOT:PSS on hydrophilic CdS nanoparticles.

Heterojunction of hydrophobic poly(1,4-phenylenevinylene) (PPV) on hydrophilic CdS nanoparticles was successfully prepared by the multi-layering of poly(p-xylene tetrahydrothiophenium chloride) (pre-PPV: precursor of PPV polymer) and poly(3,4-ethylenedioxythiophene)/poly(styrene sulfonate) (PEDOT:PSS) in an aqueous solution followed by a thermal treatment. CdS nanoparticles thin films were prepared on tin-doped indium oxide (ITO) by a chemical-bath-deposition method. The CdS surface was hydrophilic with low water contact angle of 15 degrees. Positively charged and water-soluble pre-PPV was used to form multilayers with PEDOT:PSS by a layer-by-layer deposition method. Pre-PPV is easily converted to conjugated PPV polymer by a thermal treatment. The CdS nanoparticles-(PPV/PEDOT:PSS) multilayer films constitute efficient acceptor-sensitizer dyad systems, which generate a photocurrent of 2,660 nA/cm2 under the air mass (AM) 1.5 conditions (I=100 mW/cm2) for sample with 4.5 bilayers.

Enhanced performance of sulfur-infiltrated bimodal mesoporous carbon foam by chemical solution deposition as cathode materials for lithium sulfur batteries.

The porous carbon matrix is widely recognized to be a promising sulfur reservoir to improve the cycle life by suppressing the polysulfide dissolution in lithium sulfur batteries (LSB). Herein, we synthesized mesocellular carbon foam (MSUF-C) with bimodal mesopore (4 and 30 nm) and large pore volume (1.72 cm2/g) using MSUF silica as a template and employed it as both the sulfur reservoir and the conductive agent in the sulfur cathode. Sulfur was uniformly infiltrated into MSUF-C pores by a chemical solution deposition method (MSUF-C/S CSD) and the amount of sulfur loading was achieved as high as 73% thanks to the large pore volume with the CSD approach. MSUF-C/S CSD showed a high capacity (889 mAh/g after 100 cycles at 0.2 C), an improved rate capability (879 mAh/g at 1C and 420 mAh/g at 2C), and a good capacity retention with a fade rate of 0.16% per cycle over 100 cycles.

Lithium intercalation mechanism into FeF3·0.5H2O as a highly stable composite cathode material.

The growing demand for lithium-ion batteries (LIBs) requires investigation of high-performance electrode materials with the advantages of being environmentally friendly and cost-effective. In this study, a nanocomposite of open-pyrochlore-structured FeF3·0.5H2O and reduced graphene oxide (RGO) is synthesized for use as a high-performance cathode in LIBs, where RGO provides high electrical conductivity to the composite material. The morphology of the composite shows that FeF3·0.5H2O spheres are embedded into RGO layers and high-resolution TEM image shows that those spheres are composed of primary nanoparticles with a size of ~5 nm. The cycling performance indicates that the composite electrode delivers an initial high discharge capacity of 223 mAh g-1 at 0.05 C, a rate capability up to a high C-rate of 10 C (47 mAh g-1) and stable cycle performance at 0.05 C (145 mAh g-1 after 100 cycles) and 0.2 C (93 mAh g-1 after 100 cycles) while maintaining high electrochemical reversibility. Furthermore, the responsible electrochemical reaction is investigated using in-situ XRD and synchrotron-based X-ray absorption spectroscopy (XAS), and the XRD results show that FeF3·0.5H2O transitions to an amorphous-like phase through a lithiation process. However, a reversible oxidation change of Fe3+ ↔ Fe2+ is identified by the XAS results.

Investigation of the Na Intercalation Mechanism into Nanosized V2O5/C Composite Cathode Material for Na-Ion Batteries.

There is a significant interest to develop high-performance and cost-effective electrode materials for next-generation sodium ion batteries. Herein, we report a facile synthesis method for nanosized V2O5/C composite cathodes and their electrochemical performance as well as energy storage mechanism. The composite exhibits a discharge capacity of 255 mAh g(-1) at a current density of 0.05 C, which surpasses that of previously reported layered oxide materials. Furthermore, the electrode shows good rate capability; discharge capacity of 160 mAh g(-1) at a current density of 1 C. The reaction mechanism of V2O5 upon sodium insertion/extraction is investigated using ex situ X-ray diffraction (XRD) and synchrotron based near edge X-ray absorption fine structure (NEXAFS) spectroscopy. Ex situ XRD result of the fully discharged state reveals the appearance of NaV2O5 as a major phase with minor Na2V2O5 phase. Upon insertion of sodium into the array of parallel ladders of V2O5, it was confirmed that lattice parameter of c is increased by 9.09%, corresponding to the increase in the unit-cell volume of 9.2%. NEXAFS results suggest that the charge compensation during de/sodiation process accompanied by the reversible changes in the oxidation state of vanadium (V(4+) ↔ V(5+)).

Polythiophene-Wrapped Olivine NaFePO4 as a Cathode for Na-Ion Batteries.

The surface of olivine NaFePO4 was modified with polythiophene (PTh) to develop a high-performance cathode material for use in Na-ion batteries. The Rietveld refinement results of the prepared material reveal that PTh-coated NaFePO4 belongs to a space group of Pnma with lattice parameters of a = 10.40656 Å, b = 6.22821 Å, and c = 4.94971 Å. Uncoated NaFePO4 delivers a discharge capacity of 108 mAh g(-1) at a current density of 10 mA g(-1) within a voltage range of 2.2-4.0 V. Conversely, the PTh-coated NaFePO4 electrode exhibits significantly improved electrochemical performance, where it exhibits a discharge capacity of 142 mAh g(-1) and a stable cycle life over 100 cycles, with a capacity retention of 94%. The NaFePO4/PTh electrode also exhibits satisfactory performance at high current densities, and reversible capacities of 70 mAh g(-1) at 150 mA g(-1) and 42 mAh g(-1) at 300 mA g(-1) are obtained compared with negligible capacities without coating. The related electrochemical reaction mechanism has been investigated using in situ X-ray absorption spectroscopy (XAS), which revealed a systematic change of Fe valence and reversible contraction/expansion of Fe-O octahedra upon desodiation/sodiation. The ex situ X-ray diffraction (XRD) results suggest that the deintercalation in NaFePO4/PTh electrodes proceeds through a stable intermediate phase and the lattice parameters show a reversible contraction/expansion of unit cell during cycling.

Layered-Layered-Spinel Cathode Materials Prepared by a High-Energy Ball-Milling Process for Lithium-ion Batteries.

In this work, we report the electrochemical properties of 0.5Li2MnO3·0.25LiNi0.5Co0.2Mn0.3O2·0.25LiNi0.5Mn1.5O4 and 0.333Li2MnO3·0.333LiNi0.5Co0.2Mn0.3O2·0.333LiNi0.5Mn1.5O4 layered-layered-spinel (L*LS) cathode materials prepared by a high-energy ball-milling process. Our L*LS cathode materials can deliver a large and stable capacity of ∼200 mAh g(-1) at high voltages up to 4.9 V, and do not show the anomalous capacity increase upon cycling observed in previously reported three-component cathode materials synthesized with different routes. Furthermore, we have performed synchrotron-based in situ X-ray diffraction measurements and found that there are no significant structural distortions during charge/discharge runs. Lastly, we carry out (opt-type) van der Waals-corrected density functional theory (DFT) calculations to explain the enhanced cycle characteristics and reduced phase transformations in our ball-milled L*LS cathode materials. Our simple synthesis method brings a new perspective on the use of the high-power L*LS cathodes in practical devices.

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.

Elucidating the intercalation mechanism of zinc ions into α-MnO2 for rechargeable zinc batteries.

The intercalation mechanism of zinc ions into 2 × 2 tunnels of an α-MnO2 cathode for rechargeable zinc batteries was revealed. It involves a series of single and two-phase reaction steps and produces buserite, a layered compound with an interlayer spacing of 11 Å as a discharge product.

Continuous determination of biochemical oxygen demand using microbial fuel cell type biosensor.

A mediator-less microbial fuel cell (MFC) was used as a biochemical oxygen demand (BOD) sensor in an amperometric mode for real-time wastewater monitoring. At a hydraulic retention time of 1.05 h, BOD values of up to 100 mg/l were measured based on a linear relationship, while higher BOD values were measured using a lower feeding rate. About 60 min was required to reach a new steady-state current after the MFCs had been fed with different strength artificial wastewaters (Aws). The current generated from the MFCs fed with AW with a BOD of 100 mg/l was compared to determine the repeatability, and the difference was less than 10%. When the MFC was starved, the original current value was regained with a varying recovery time depending on the length of the starvation. During starvation, the MFC generated a background level current, probably due to an endogenous metabolism.