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Here we report the formation of three distinct Sn-based active materials for Li-ion battery anodes, formed from the same metal–organic material (MOM) precursor sql-1-Cu-SNIFSIX. The materials were ...

Li-ion batteries (LIBs) have become critical components in the manufacture of electric vehicles (EVs) as they offer the best all-round performance compared to competing battery chemistries. However, LIB performance at low temperature (LT) extremes of EV operation (typically −40 to 0 °C) suffers from a reduced output and diminished cycle life. LT cycling increases cell impedance, diminishing Li ion diffusion through the cell, exacerbating electrode polarisation, and hindering interfacial Li+ desolvation. Herein, we present a comprehensive review of (i) the factors that influence LT Li-ion performance, (ii) outline the shortcomings of the current state-of-the-art and (iii) discuss recent findings in the field, focusing on alternative anode materials with particular emphasis on high-capacity, fast charging alternatives to the archetypal carbon (graphite) anode. Different approaches to improve LT LIB performance are outlined in an in-depth analysis of recent improvements from the anode perspective. These include electrolyte-driven enhancements, the resurgence of Li metal batteries, the impact of conductive coatings, elemental doping and nanocomposite formation, substitution of intercalating anodes with high-capacity Li alloying and Li conversion materials, and fast redox pseudocapacitance.

peer-reviewed The full text of this article will not be available until the embargo expires on the 13/10/2021 Transition metal dichalcogenides (TMDs) are increasingly of interest in the field of lithium ion batteries due to their unique structure. However, previous preparation methods have mainly focused on their growth from substrates or by exfoliation of the bulk materials. Considering colloidal synthesis has many advantages including precision control of morphology and crystal phases, there is significant scope for exploring this avenue for active material formation. Therefore, in this work, we explore the applicability of colloidal TMDs using WSe2 nanocrystals for Li ion battery anodes. By employing colloidal hotinjection protocol, we first synthesize 2D nanosheets in 2H and 1T’ crystal phases. After detailed structural and surface characterization, we investigate the performance of these nanosheets as anode materials. We find that 2H nanosheets outperformed 1T’ nanosheets exhibiting a higher specific capacity of 498 mAh g-1 with an overall capacity retention of 83.28%. Furthermore, to explore the role of morphology on battery performance 3D interconnected nanoflowers in 2H crystal phase were also investigated as an anode material. A noteworthy specific capacity of 982 mAh g-1 after 100 cycles was exhibited by these nanoflowers. The anode materials are characterized prior to cycling and after 1, 25, and 100 charge/discharge cycles, by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), to track the effects of cycling on the material.

peer-reviewed CuZnSe2 (CZSe) is an important ternary semiconductor comprised of earth-abundant elements with a suitable bandgap for visible light absorption and structural/stoichiometric versatility that make it a promising candidate for photovoltaic applications. Here we report the controlled synthesis of the compound copper chalcogenide in nanocrystal form using a colloidal hot injection approach. Furthermore, we demonstrate control over the crystal phase to occur as either wurtzite (WZ) or zinc blende (ZB) as a function of the presence and absence of phosphine-based ligands. A major emission peak was observed at ∼1.7 eV using low-temperature photoluminescence (PL), ranging from 30 to 200 K. Additionally, we demonstrate the ability to extend this synthetic protocol to form a polytype structure comprised of a ZB core with a WZ shell.

Herein, we report the formation of core@shell nanowires (NWs) comprised of crystalline germanium NW cores with amorphous silicon shells (Ge@aSi) and their performance as a high capacity Li-ion battery anode material. The Ge NWs were synthesized directly from the current collector in a solvent vapor growth (SVG) system and used as hosts for the deposition of the Si shells via a plasma-enhanced chemical vapor deposition (PECVD) process utilizing an expanding thermal plasma (ETP) source. The secondary deposition allows for the preparation of Ge@aSi core@shell structures with tunable Ge/Si ratios (2:1 and 1:1) and superior gravimetric and areal capacities, relative to pure Ge. The binder-free anodes exhibited discharge capacities of up to 2066 mAh/g and retained capacities of 1455 mAh/g after 150 cycles (for the 1:1 ratio). The 2:1 ratio showed a minimal ∼5% fade in capacity between the 20th and 150th cycles. Ex situ microscopy revealed a complete restructuring of the active material to an interconnected Si

Calcium carbonate and carbonate-hydroxyapatite are known to form inorganic components of crystals and calcareous concretions found in many non-skeletal tissues and structures including the pineal gland. We used advanced surface analyses techniques such as polarization microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), microfocus X-ray diffraction (XRD), transmission electron microscopy with selected area electron diffraction (TEM-SAED) to investigate samples extracted from rat pineal gland after irradiation with visible light for 12 h. Single-crystal X-ray diffraction showed that the concretions were largely amorphous with the presence of some nanocrystalline phases. High resolution TEM-SAED revealed the presence of iron oxide in the form of hematite. Spectroscopy data especially Raman spectroscopy revealed a mixed nature of these concretions, which corresponded reasonably with XPS, TEM and XRD. Overall the study confirms the presence of a mixed phase of calcium carbonates including calcite, aragonite and vaterite. We note that aragonite is not a common occurrence in vertebrates and recommend further investigation to rule out any link to pathology.

peer-reviewed Silicon nanowires (Si NWs) are a promising anode material for lithiumion batteries (LIBs) due to their high specific capacity. Achieving adequate mass loadings for binder-free Si NWs is restricted by low surface area, mechanically unstable and poorly conductive current collectors (CCs), as well as complicated/expensive fabrication routes. Herein, a tunable mass loading and dense Si NW growth on a conductive, flexible, fire-resistant, and mechanically robust interwoven stainless-steel fiber cloth (SSFC) using a simple glassware setup is reported. The SSFC CC facilitates dense growth of Si NWs where its open structure allows a buffer space for expansion/ contraction during Li-cycling. The Si NWs@SSFC anode displays a stable performance for 500 cycles with an average Coulombic efficiency of >99.5%. Galvanostatic cycling of the Si NWs@SSFC anode with a mass loading of 1.32 mg cm−2 achieves a stable areal capacity of ≈2 mAh cm−2 at 0.2 C after 200 cycles. Si NWs@SSFC anodes with different mass loadings are characterized before and after cycling by scanning and transmission electron micros-copy to examine the effects of Li-cycling on the morphology. Notably, this approach allows the large-scale fabrication of robust and flexible binder-free Si NWs@SSFC architectures, making it viable for practical applications in high energy density LIBs.

The electrochemical performance of Ge, an alloying anode in the form of directly grown nanowires (NWs), in Li-ion full cells (vs LiCoO2) was analyzed over a wide temperature range (−40 to 40 °C). LiCoO2||Ge cells in a standard electrolyte exhibited specific capacities 30× and 50× those of LiCoO2||C cells at −20 and −40 °C, respectively. We further show that propylene carbonate addition further improved the low-temperature performance of LiCoO2||Ge cells, achieving a specific capacity of 1091 mA h g–1 after 400 cycles when charged/discharged at −20 °C. At 40 °C, an additive mixture of ethyl methyl carbonate and lithium bis(oxalato)borate stabilized the capacity fade from 0.22 to 0.07% cycle–1. Similar electrolyte additives in LiCoO2||C cells did not allow for any gains in performance. Interestingly, the capacity retention of LiCoO2||Ge improved at low temperatures due to delayed amorphization of crystalline NWs, suppressing complete lithiation and high-order Li15Ge4 phase formation. The results show that alloying anodes in suitably configured electrolytes can deliver high performance at the extremes of temperature ranges where electric vehicles operate, conditions that are currently not viable for commercial batteries without energy-inefficient temperature regulation.

peer-reviewed The full text of this article will not be available in ULIR until the embargo expires on the 10/07/2021 Addition of electrolyte additives (ethylene or vinylene carbonate) is shown to dramatically improve the cycling stability and capacity retention (1600 mAhg-1) of Si nanowires (NWs) in a safe ionic liquid (IL) electrolyte (0.1LiTFSI-0.6PYR13FSI-0.3PYR13TFSI) . We show using post-mortem SEM and TEM, a distinct difference in morphologies of the active material after cycling in the presence or absence of the additives. The difference in performance is shown by post-mortem XPS analysis to arise from a notable increase in irreversible silicate formation in the absence of the carbonate additives. The composition of the solid electrolyte interphase (SEI) formed at the active material surface was further analysed using XPS as a function of the IL components revealing that the SEI was primarily made up of N, F and S containing compounds from the degradation of the TFSI and FSI anions.

A solution based synthesis of well-ordered Cu-rich silicide nanoarchitectures, consisting of a pair of layered cups and stems (ρ-Cu15Si4) is demonstrated. The as-grown ρ-Cu15Si4typically exhibits distinct interconnected 1D stems, consisting of a stack of nanorods (∼300 nm in length), terminated with concave hexagonal 3D cups that evolve through a self-regulated layer-by-layer growth mechanism. Discrete-time ex situ experimental observations reveal that the ρ-Cu15Si4evolution is driven by interatomic diffusion, initially triggering the formation of binary-phase silicide islands (spheres) followed by the formation of hexagonal discs, stem growth, and lateral elongation in exactly opposite directions. It is further shown that electrochemically pregrown Cu-crystals can facilitate the direct growth of ρ-Cu15Si4in high yield with enhanced substrate coverage.

peer-reviewed The full text of this article will not be available in ULIR until the embargo expires on the 23/07/2021 Silicon nanowires (Si NWs) have been identified as an excellent candidate material for the replacement of graphite in anodes, allowing for a significant boost in the capacity of lithium‐ion batteries (LIBs). Herein, high‐density Si NWs are grown on a novel 3D interconnected network of binary‐phase Cu‐silicide nanofoam (3D CuxSiy NF) substrate. The nanofoam facilitates the uniform distribution of well‐segregated and small‐sized catalyst seeds, leading to high‐density/single‐phase Si NW growth with an areal‐loading in excess of 1.0 mg cm−2 and a stable areal capacity of ≈2.0 mAh cm−2 after 550 cycles. The use of the 3D CuxSiy NF as a substrate is further extended for Al, Bi, Cu, In, Mn, Ni, Sb, Sn, and Zn mediated Si NW growth, demonstrating the general applicability of the anode architecture.

peer-reviewed Here we report an interesting observation on anode materials for lithium ion batteries that undergo combined conversion and alloying lithiation processes during cycling (CAMs). These materials are generating interest as low cost and high capacity alternatives to graphite. We find that common testing protocols (CTPs) are unsuitable for assessment of CAMs due to their distinct multi‐step lithiation characteristics. CTPs involve reporting total gravimetric capacity in a half‐cell configuration alone (opposite Li foil), without individual analysis of each process; energy density and the problems associated with wide discharge voltages are not addressed. Through isolating the individual lithiation processes of a model system (Cu2ZnSnS4), we determine that the conversion processes are highly unstable, whereas the alloying processes exhibit remarkable capacity retention. We demonstrate that inclusion of the conversion processes in cycling actually reduced full cell energy density when compared with alloying alone. This indicates that CTPs may well underestimate the stability of CAMs. It is apparent that the true advantage of CAMs lies in the synergistic combination of the capacity of the alloying portion, and the stability provided by the uncycling Li2S buffer material. Finally, we prescribe a set of testing protocols for a meaningful assessment of new CAMs.

peer-reviewed The full text of this article will not be available in ULIR until the embargo expires on the 31/10/2020 Herein, copper silicide (Cu15Si4) nanowires (NWs) grown in high densities from a metallic Cu substrate are utilized as nanostructured hosts for amorphous silicon (aSi) deposition. The conductive Cu15Si4 NW scaffolds offer an increased surface area, versus planar substrates, and enable the preparation of high capacity Li-ion anodes consisting of a nanostructured active material. The formation method involves a two-step process where Cu15Si4 nanowires are synthesized from a Cu substrate via a solvent vapor growth (SVG) approach followed by the plasma enhanced chemical vapor deposition (PECVD) of aSi. These binder-free anodes are investigated in half-cell (versus Li-foil) and full-cell (versus LCO) configurations with discharge capacities greater than 2000 mAh/g retained after 200 cycles (half-cell) and reversible capacities of 1870 mAh/g exhibited after 100 cycles (full-cell). Noteworthy rate capability is also attained where capacities of up to 1367 mAh/g and 1520 mAh/g are exhibited at 5C in half-cell and full-cell configurations respectively, highlighting the active material’s promise for fast charging and high power applications. The anode material is characterized prior to cycling and after 1, 25 and 100 charge/discharge cycles, by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), to track the effects of cycling on the material. ACCEPTED peer-reviewed

peer-reviewed Herein, textured Cu foil is presented as an attractive current collector substrate for directly grown Ge nanowire (NW) anodes. Compared to planar stainless steel (SS) current collectors, textured Cu led to an increase in achievable mass loading, removal of the requirement for a catalyst deposition step, improved adhesion of the active material and dramatically enhanced capacity retention. When SS and textured Cu foil based anodes with similar areal loadings (∼1.4 mA h cm−2) were compared, the capacity after 250 cycles for textured Cu was 2.7 times higher than the SS anode, illustrating the key role of the current collector.

peer-reviewed Herein, the electrochemical performance of directly grown Ge nanowire anodes in full-cell Li-ion configurations (using lithium cobalt oxide cathodes) are examined. The impacts of voltage window, anode/cathode balancing and anode preconditioning are assessed. The cells had a useable upper cutoff of 3.9 V, with a higher voltage cutoff of 4.2 V shown by SEM analysis to lead to Li plating on the anode surface. The rate performance of Ge NW anodes was shown to be boosted within full-cells compared to half-cells, meaning that existing studies may underestimate the rate performance of alloying mode anode materials if they are only based on half-cell investigations. The capacity retention of the full-cells is lower compared to equivalent half-cells due to progressive consumption of cyclable Li. This phenomenon is demonstrated using a parallel anode and cathode delithiation approach that could be extended to other full-cell systems. The findings stress the importance of testing promising anode materials within full-cell configurations, to identify specific capacity fade mechanisms that are not relevant to half-cells and aid the development of higher energy density storage systems.

peer-reviewed Development of cost effective and increasingly efficient sustainable materials for energy storage devices, such Li ion batteries, is of crucial future importance. Herein, the preparation of carbon nanofibers from biopolymer blends of lignin (by-product from the paper and pulp industry), with polylactic acid (PLA) and a thermoplastic elastomeric polyurethane (TPU) are described. Scanning electron microscopy (SEM) analysis shows the evolving microstructural morphology after each processing step, (electrospinning, stabilization and carbonization). Importantly, it is possible to tailor nanofiber porosity utilising miscibility/immiscibility rules between lignin and the polymer additive (PLA/TPU). PLA blends (immiscible) generate porous structures while miscible lignin/TPU blends are solid when carbonised. Electrodes produced from 50 % of PLA blends have capacity values of 611 mAhg-1 after 500 charge/discharge cycles; the highest reported to date for sustainable electrodes for Li-ion batteries. Thus, this work will promote the development of lignocelluose waste materials as high performace energy storage materials

peer-reviewed A scalable and cost-effective process is used to electroplate metallic Zn seeds on stainless steel substrates. Si and Ge nanowires (NWs) are subsequently grown by placing the electroplated substrates in the solution phase of a refluxing organic solvent at temperatures >430 °C and injecting the respective liquid precursors. The native oxide layer formed on reactive metals such as Zn can obstruct NW growth and is removed in situ by injecting the reducing agent LiBH4. The findings show that the use of Zn as a catalyst produces defect-rich Si NWs that can be extended to the synthesis of Si–Ge axial heterostructure NWs with an atomically abrupt Si–Ge interface. As an anode material, the as grown Zn seeded Si NWs yield an initial discharge capacity of 1772 mAh g−1 and a high capacity retention of 85% after 100 cycles with the active participation of both Si and Zn during cycling. Notably, the Zn seeds actively participate in the Li-cycling activities by incorporating into the Si NWs body via a Li-assisted welding process, resulting in restructuring the NWs into a highly porous network structure that maintains a stable cycling performance.

New techniques to directly grow metal oxide nanowire networks without the need for initial nanoparticle seed deposition or postsynthesis nanowire casting will bridge the gap between bottom-up formation and top-down processing for many electronic, photonic, energy storage, and conversion technologies. Whether etched top-down, or grown from catalyst nanoparticles bottom-up, nanowire growth relies on heterogeneous material seeds. Converting surface oxide films, ubiquitous in the microelectronics industry, to nanowires and nanowire networks by the incorporation of extra species through interdiffusion can provide an alternative deposition method. It is shown that solution-processed thin films of oxides can be converted and recrystallized into nanowires and networks of nanowires by solid-state interdiffusion of ionic species from a mechanically contacted donor substrate. NaVO3 nanowire networks on smooth Si/SiO2 and granular fluorine-doped tin oxide surfaces can be formed by low-temperature annealing of a Na diffusion species-containing donor glass to a solution-processed V2 O5 thin film, where recrystallization drives nanowire growth according to the crystal habit of the new oxide phase. This technique illustrates a new method for the direct formation of complex metal oxide nanowires on technologically relevant substrates, from smooth semiconductors, to transparent conducting materials and interdigitated device structures.

peer-reviewed Here we report the first detailed investigation into the selenization mechanism of thin films of wurtzite copper zinc tin sulfide (CZTS) nanorods (NRs), giving particular emphasis to the role of the long-chain organic ligands surrounding each NR. During selenization, the NRs undergo a selenium-mediated phase change from wurtzite to kesterite, concurrent with the replacement of sulfur with selenium in the lattice and in-situ grain growth, along with the recrystallization of larger copper zinc tin selenide (CZTSe) kesterite grains on top of the existing film. By utilizing a facile ligand removal technique, we demonstrate that the formation of a large grain overlayer is achievable without the presence of ligands. In addition, we demonstrate an elegant ligand-exchange based method for controlling the thickness of the fine grain layer. This report emphasizes the key role played by ligands in determining the structural evolution of CZTS nanocrystal films during selenization, necessitating the identification of optimal ligand chemistries and processing conditions for desirable grain growth.

peer-reviewed Highly aligned copper zinc tin sulfide nanorods electrophoretically deposited directly on the current collector are tested for suitability as Li-ion battery anodes in both half-cell (HC) and full-cell (FC) configurations. This facile fabrication process offers several advantages for high-performance nanostructured battery electrodes, notably the formation of a dense, conductive carbon and binder-free film maximizing active material content. High initial capacities of 1611 and 1369 mA h g–1 are achieved for the HC and FC, respectively. The capacity trends and degradation mechanisms for this combined alloying and conversion material are analyzed in detail using differential capacity plots and electrochemical impedance spectroscopy, and it is determined that an evolution in the electrode resistance (instead of typical material pulverization/delamination) is the major driver of an initial capacity fade followed by a dramatic capacity recovery. Differences in capacity retention trends between HCs and FCs are highlighted, emphasizing the importance of extended testing in commercial style setups for complete material evaluation.

peer-reviewed Herein, we report a novel approach to form axial heterostructure nanowires composed of linearly distinct Ni silicide (Ni2Si) and Si segments via a one-pot solution synthesis method. Initially, Si nanowires are grown using Au seeds deposited on a Ni substrate with the Si delivery in the solution phase using a liquid phenylsilane precursor. Ni silicide then forms axially along the wires through progressive Ni diffusion from the growth substrate, with a distinct transition between the silicide and pure Si segments. The interfacial abruptness and chemical composition of the heterostructure nanowires was analysed through transmission electron microscopy, electron diffraction, energy dispersive X-ray spectroscopy, aberration corrected scanning transmission electron microscopy and atomically resolved electron energy loss spectroscopy. The method represents a versatile approach for the formation of complex axial NW heterostructures and could be extended to other metal silicide or analogous metal germanide systems.

In this report we examine the influence of electrode binder and electrolyte solvent on the electrochemical response of carbon based Li-O2 battery cathodes. Much higher discharge capacities were noted for cathodes discharged in DMSO compared to TEGDME. The increased capacities were related to the large spherical discharge products formed in DMSO. Characteristic toroids which have been noted in TEGDME electrolytes previously were not observed due to the low water content of the electrolyte. Linear voltage sweeps were used to investigate ORR in both of the solvents for each of the binder systems (PVDF, PVP, PEO and PTFE) and related to the Li2O2 formed on the cathode surfaces. Galvanostatic tests were also conducted in air as a comparison with the pure O2 environment typically used for Li-O2 battery testing. Interestingly, tests for the two electrolytes showed opposite trends in terms of discharge capacity values with capacities increased in TEGDME (compared to those seen in O2) and decreased in DMSO. The report highlights the key roles of electrolyte and cathode composition in determining the stability of Li-O2 batteries and highlights the importance of identifying more stable electrolyte/cathode pairings.

This review outlines the developments and recent progress in metal-assisted chemical etching of silicon, summarizing a variety of fundamental and innovative processes and etching methods that form a wide range of nanoscale silicon structures. The use of silicon as an anode for Li-ion batteries is also reviewed, where factors such as film thickness, doping, alloying, and their response to reversible lithiation processes are summarized and discussed with respect to battery cell performance. Recent advances in improving the performance of silicon-based anodes in Li-ion batteries are also discussed. The use of a variety of nanostructured silicon structures formed by many different methods as Li-ion battery anodes is outlined, focusing in particular on the influence of mass loading, core-shell structure, conductive additives, and other parameters. The influence of porosity, dopant type, and doping level on the electrochemical response and cell performance of the silicon anodes are detailed based on recent findings. Perspectives on the future of silicon and related materials, and their compositional and structural modifications for energy storage via several electrochemical mechanisms, are also provided.

The electrochemical behaviour of MnO2 nanorod and Super P carbon based Li-O2 battery cathodes in water-containing sulfolane and anhydrous DMSO electrolytes are shown to be linked to specific discharge product formation. During discharge, large layered spherical agglomerates of LiOH were characteristically formed on the MnO2 cathodes while smaller, toroidal, spherical Li2O2 particles and films were formed on the Super P cathodes. In an anhydrous DMSO based electrolyte the LiOH structures were also found on cathodes discharged in the anhydrous electrolyte, suggesting that MnO2 initiates electrochemical decomposition of the DMSO electrolyte to form LiOH via H2O reactions with Li2O2. The LiOH crystals are uniquely formed on MnO2, and segregated to this phase even in mixed oxide-carbon cathodes. In contrast, no Li2O2 toroids were noted on Super P cathodes discharged in the DMSO based electrolytes. Instead, the morphology varied from smaller sheets (at high discharge current) to much larger agglomerates (at low discharge currents). In mixed carbon-MnO2 nanorod cathodes, the use of PVDF initiates H2O formation that affects discharge products and an overall mechanism governing phase formation at MnO2 in sulfolane and anhydrous DMSO with and without PVDF binder is presented. This work highlights the importance of careful consideration of electrolyte-cathode material-discharge product interactions in the search for more stable Li-O2 systems.

Transparent thin films can now be site-selectively patterned and positioned on surface using mask-defined electrodeposition of one oxide and overcoating with a different solution-processed oxide, followed by thermal annealing. Annealing allows an interdiffusion process to create a new oxide that is entirely transparent. A primary electrodeposited oxide can be patterned and the secondary oxide coated over the entire substrate to form high color contrast coplanar thin film tertiary oxide. The authors also detail the phase formation and chemical state of the oxide and how the nature of the electrodeposited layer and the overlayer influence the optical clearing of the patterned oxide film.

Widespread issues with the fundamental operation and stability of Li-O2 cells impact cycle life and efficiency. While the community continues to research ways of mitigating side reactions and improving stability to realize Li-O2 battery prospects, we show that limiting the depth-of-discharge while unbalancing discharge/charge rate symmetry can extend Li-O2 battery cycle life by ensuring efficient reversible Li2O2 formation, markedly improving cell efficiency. Systematic variation of the discharge/charge currents shows that clogging from discharging the Li-O2 cell at high current (250 μA) can be somewhat negated by recharging with a lower applied current (50 μA), with a marked improvement in cycle life achievable. Our measurements determined that specific reduction of the depth of discharge in decrements from equivalent capacities of 1000 mAhg−1 to 50 mAhg−1 under symmetric discharge/charge currents of 50 μA strongly affect the cumulative discharge capacity of each cell. A maximum cumulative discharge capacity occurs at ∼10 % depth of discharge (500 mAhg−1) and the cumulative discharge capacity of 39,500 mAhg−1 is significantly greater than that of cells operated at higher and lower depths of discharge. The results emphasize the importance of appropriate discharge/charge rate and depth of discharge selection for other cathode/electrolyte combinations for directly improving the cycle life performance of Li-O2 batteries.

Solid-state sensor nanostructured materials (SnO2, ZnO and CeO2) have been prepared by pyrolysis of macromolecular complexes: PSP-co-4-PVP x (SnCl2)n, PSP-co-4-PVP x (ZnCl2)n and PSP-co-4-PVP x (Ce(NO3)3)n in several molar ratios under air at 800 degrees C. The as-prepared nanostructured SnO2 exhibits morphologies and particle sizes which are dependent upon the molar ratio of the SnCl2:PSP-co-4-PVP. When a larger weight fraction of the inorganic salt in the precursor mixture is used (1:10 > 1:5 > 1.1) larger crystalline crystals are found for each oxide. For ZnO and CeO2 agglomerates of morphologies from the respective hexagonal and cubic structures were observed with typical sizes of 30-50 nm in both cases for a precursor mixture ratio of 1:1.

The Li+ insertion and extraction characteristics at n-type and p-type Si(100) electrodes with different carrier density and doping type are investigated by cyclic voltammetry and constant current measurements. The insertion and extraction potentials are demonstrated to vary with cycling and the occurrence of an activation effect is shown in n-type electrodes where the charge capacity and voltammetric currents are found to be much higher than p-type electrodes. A rate-dependent redox process influenced by the surface region electronic density, which influences the magnitude of cyclic voltammetry current is found at Si(100) surface regions during Li insertion and extraction. At p-type Si(100) surface regions, a thin, uniform film forms at lower currents, while also showing a consistently high (>70%) Coulombic efficiency for Li extraction. The p-type Si(100) surface region does not undergo crack formation after deintercalation and the amorphization was demonstrated using transmission electron microscopy (TEM). X-ray photoelectron spectroscopy (XPS) and Raman scattering demonstrate that highly doped n-type Si(100) retains Li as a silicide and converts to an amorphous phase as a two-step phase conversion process. The findings show the succinct dependence of Li insertion and extraction processes for uniformly doped Si(100) single crystals and how the doping type and its effect on the semiconductor-solution interface dominate Li insertion and extraction, composition, crystallinity changes and charge capacity.

peer-reviewed Here we report the formation of high-performance and high-capacity lithium-ion battery anodes from high-density germanium nanowire arrays grown directly from the current collector. The anodes retain capacities of similar to 900 mAh/g after 1100 cycles with excellent rate performance characteristics, even at very high discharge rates of 20-100C. We show by an ex situ high-resolution transmission electron microscopy and high-resolution scanning electron microscopy study that this performance can be attributed to the complete restructuring of the nanowires that occurs within the first 100 cycles to form a continuous porous network that is mechanically robust. Once formed, this restructured anode retains a remarkably stable capacity with a drop of only 0.01% per cycle thereafter. As this approach encompasses a low energy processing method where all the material is electrochemically active and binder free, the extended cycle life and rate performance characteristics demonstrated makes these anodes highly attractive for the most demanding lithium-ion applications such as long-range battery electric vehicles. ACCEPTED peer-reviewed

We investigate the impact of using a carbon based gas diffusion layer (GDL) as the current collector for Li-O2 batteries. It is shown that the GDL actively participates in ORR during discharge conditions and, if its mass is not accounted for, can lead to inflated discharge capacity figures compared to inert cathode supports. SEM and XRD analyses show that Li2O2 discharge products form on cathodes composed of as-received GDL in a similar manner to that observed for carbon on stainless steel (SS) current collectors (at applied currents of 100 μA cm−2 or less). The relative activity of the GDL, carbon on GDL and carbon-on-stainless steel current collectors from voltammetric measurements confirmed ORR and OER processes to be similar at all carbon-based surfaces. When heated above 300◦C, degradation of the binder in the GDL and associated loss of carbon from the substrate surface leads to reduced discharge times compared to the pristine GDL substrates. The data highlight the importance of the contribution to ORR/OER in carbon-based active current collector substrates when determining gravimetric capacities of Li-O2 batteries. © 2014 The Electrochemical Society. [DOI: 10.1149/2.0021414jes] All rights reserved.

Porous semiconductors structured top-down by electrochemical means, and from bottom-up growth of arrays and arrangements of nanoscale structures, are shown to be amenable to a range of useful thermal, optical, electrical and electrochemical properties. This paper summarises recent investigations of the electrochemical, electrical, optical, thermal and structural properties of porous semiconductors such as Si, In2O3, SnO2 and ITO, and dispersions, arrays and arrangements of nanoscale structures of each of these materials. We summarize the property-inspired application of such structurally engineered arrangements and morphologies of these materials for antireflection coatings, broadband absorbers, transparent contacts to LEDs that improve transmission, electrical contact and external quantum efficiency. Additionally the possibility of thermoelectric performance through structure-mediated variation in thermal resistance and phonon scattering without a p-n junction is shown through phonon engineering in roughened nanowires. Lastly, we show that bulk crystals and nanowires of p- and n-type doped Si are promising for use as anodes in Li-ion batteries.

Silicon and germanium nanowires are grown in high density directly from a tin layer evaporated on stainless steel. The nanowires are formed in low cost glassware apparatus using the vapor phase of a high boiling point organic solvent as the growth medium. HRTEM, DFSTEM, EELS, and EDX analysis show the NWs are single crystalline with predominant ⟨111⟩ growth directions. Investigation of the seed/nanowire interface shows that in the case of Si an amorphous carbon interlayer occurs that can be removed by modifying the growth conditions. Electrochemical data shows that both the tin metal catalyst and the semiconductor nanowire reversibly cycle with lithium when the interface between the crystalline phases of the metal and semiconductor is abrupt. The dually active nanowire arrays were shown to exhibit capacities greater than 1000 mAh g–1 after 50 charge/discharge cycles.

We report a method for solvent-less growth of single crystalline hematite Fe2O3 nanoparticles from metal-containing polymeric macromolecular complexes, and demonstrate their efficient photocatalytic degradation of persistent cationic dye pollutants under visible light. Macromolecular complexes such as chitosan·(FeCl2)y, chitosan·(FeCl3)y, PS-co-4-PVP·(FeCl2)y and PS-co-4-PVP·(FeCl3)y with controlled polymer : metal molar ratios of 1 : 1 and 5 : 1 were prepared by single reaction of the respective polymers and iron chloride salts in CH2Cl2. The stable insoluble compounds were characterized by elemental analysis, infra-red spectroscopy, EPR and diffuse reflectance spectroscopy, and confirm Fe salts with degrees of coordination of ∼60–70%. Pyrolysis of these macromolecular precursors under air and at 800 °C forms networked Fe2O3 nanoparticles, whose volumetric density, size and shape is controlled by the metal content and the nature of the macromolecular complex (chitosan or PS-co-4-PVP). For both polymers, the 1 : 1 molar ratio precursor produces nanoparticles ranging from 10–200 nm with a moderate superparamagnetic behavior and optical bandgap marginally larger than bulk Fe2O3. A matrix-incubated formation mechanism involving the carbonization of the organic matter, forming voids within the macromolecular complex wherein the Fe centres coalesce, oxidize and crystallize into nanoparticles is also proposed. The hematite Fe2O3 nanoparticle materials demonstrate very efficient photocatalytic degradation of persistent water pollutants such as the cationic dye methylene blue. The nanoparticulate material obtained from chitosan·(FeCl2)y 1 : 1 under the simulated sunlight (full visible spectrum) irradiation provides high rate degradation of MB by 73% in 60 min and >94% after 150 min, measured at 655 nm.

Herein, we describe the growth of Si nanowires (NWs) in the vapor phase of an organic solvent medium on various substrates (Si, glass, and stainless steel) upon which an indium layer was evaporated. Variation of the reaction time allowed NW length and density to be controlled. The NWs grew via a predominantly root-seeded mechanism with discrete In catalyst seeds formed from the evaporated layer. The NWs and substrates were characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), scanning transmission electron microscopy (STEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray photoelectron spectroscopy (XPS). The suitability of the indium seeded wires as anode components in Li batteries was probed using cyclic voltammetric (CV) measurements. The route represents a versatile, glassware-based method for the formation of Si NWs directly on a variety of substrates.

peer-reviewed The quaternary copper chalcogenide, Cu2ZnSnS4, is an important emerging material for the development of low cost and sustainable solar cells. Here we report a facile solution synthesis of stoichiometric Cu2ZnSnS4 in size controlled nano-rod form (11 ×35 nm). The monodisperse nanorods have a band gap of 1.43 eV and can be assembled into perpendicularly aligned arrays by controlled evaporation from solution.

Herein, we describe the growth of highly dense germanium nanowire mats directly on copper foil by a self-induced, solid seeded protocol. The existence of Cu3Ge tips on each of the nanowires indicat...

Here we show the impact of preferred growth directions and defects in the formation of complex Ge nanowire (NW) structures grown by a simple organic medium based synthesis. Various types of NWs are examined including: straight defect free NWs; periodically bent NWs with precise angles between the NW segments; NWs with mutually exclusive lateral or longitudinal faults; and more complex “wormlike” structures. We show that choice of solvent and reaction temperature can be used to tune the morphology of the NWs formed. The various types of NWs were probed in depth using transmission electron microscopy (TEM), scanning electron microscopy (SEM), selected area electron diffraction (SAED), and dark field TEM (DFTEM).

High performance thin film lithium batteries using structurally stable electrodeposited V2O5 inverse opal (IO) networks as cathodes provide high capacity and outstanding cycling capability and also were demonstrated on transparent conducting oxide current collectors. The superior electrochemical performance of the inverse opal structures was evaluated through galvanostatic and potentiodynamic cycling, and the IO thin film battery offers increased capacity retention compared to micron-scale bulk particles from improved mechanical stability and electrical contact to stainless steel or transparent conducting current collectors from bottom-up electrodeposition growth. Li(+) is inserted into planar and IO structures at different potentials, and correlated to a preferential exposure of insertion sites of the IO network to the electrolyte. Additionally, potentiodynamic testing quantified the portion of the capacity stored as surface bound capacitive charge. Raman scattering and XRD characterization showed how the IO allows swelling into the pore volume rather than away from the current collector. V2O5 IO coin cells offer high initial capacities, but capacity fading can occur with limited electrolyte. Finally, we demonstrate that a V2O5 IO thin film battery prepared on a transparent conducting current collector with excess electrolyte exhibits high capacities (∼200 mAh g(-1)) and outstanding capacity retention and rate capability.

Producción Científica, Porous GaN based LEDs produced by corrosion etching techniques demonstrated enhanced light extraction efficiency in the past. However, these fabrication techniques require further postgrown processing steps, which increase the price of the final system. In this paper, we review the process followed towards the fabrication of fully porous GaN p-n junctions directly during the growth step, using a sequential chemical vapor deposition (CVD) process to produce the different layers that form the p-n junction., Junta de Castilla y León (programa de apoyo a proyectos de investigación – Ref. VA302U13)

peer-reviewed Here we describe a relatively facile synthetic protocol for the formation of Si-Ge and Si-Ge-Si1-xGex axial nanowire heterostructures. The wires are grown directly on substrates with an evaporated catalytic layer placed in the vapour zone of a high boiling point solvent with the silicon and germanium precursors injected as liquids sequentially. We show that these heterostructures can be formed using either indium or tin as the catalyst seeds which form in situ during the thermal anneal. There is a direct correlation between growth time and segment length allowing good control over the wire composition. The formation of axial heterostructures of Si-Ge-Si1-xGex nanowires using a triple injection is further discussed with the alloyed Si1-xGex third component formed due to residual Ge precursor and its greater reactivity in comparison to silicon. It was found that the degree of tapering at each hetero-interface varied with both the catalyst type and composition of the NW. The report shows the versatility of the solvent vapour growth system for the formation of complex Si-Ge NW heterostructures. ACCEPTED peer-reviewed

High quality 2D and 3D inverse opals and hollow sphere arrays of vanadium oxide are grown on conductive substrates from colloidal polymer sphere templates formed by electrophoretic deposition or surfactant-assisted dip-coating. Inverse opals (IOs) are formed using variants of solution drop-casting, N2-gun assisted infiltration and high-rate (200 mm min−1) iterative dip-coating methods. Through Raman scattering, transmission electron microscopy and optical diffraction, we show how the oxide phase, crystallinity and structure are inter-related and controlled. Opal template removal steps are demonstrated to determine the morphology, crystallinity and phase of the resulting 2D and 3D IO structures. The ability to form high quality 2D IOs is also demonstrated using UV Ozone removal of PMMA spheres. Rapid hydrolysis of the alkoxide precursor allows the formation of 2D arrays of crystalline hollow spheres of V2O5 by utilizing over-filling during iterative dip-coating. The methods and crystallinity control allow 2D and 3D hierarchically structured templates and inverse opal vanadium oxides directly on conductive surfaces. This can be extended to a wide range of other functional porous materials for energy storage and batteries, electrocatalysis, sensing, solar cell materials and diffractive optical coatings.

A rapid synthetic protocol for the formation of high-performance Ge nanowire-based Li-ion battery anodes is reported. The nanowires are formed in high density by the solvent-free liquid deposition of a Ge precursor directly onto a heated stainless steel substrate under inert conditions. The novel growth system exploits the in situ formation of discrete Cu3Ge catalyst seeds from 1 nm thermally evaporated Cu layers. As the nanowires were grown from a suitable current collector, the electrodes could be used directly without binders in lithium-ion half cells. Electrochemical testing showed remarkable capacity retention with 866 mAh/g achieved after 1900 charge/discharge cycles and a Coulombic efficiency of 99.7%. The nanowire-based anodes also showed high-rate stability with discharge capacities of 800 mAh/g when cycled at a rate of 10C.

This report investigates the influence of electrolyte selection and the addition of Pd nanoparticle catalysts on the morphology of discharge products for Li-O2 battery cathodes. Super P carbon cathodes (on stainless steel current collectors) were subjected to single discharges at various applied currents (50 µA, 100 µA, 250 µA) using either a sulfolane/LiTFSI or TEGDME/LITFSI electrolyte. The morphologies of the discharge product were noted to be different for each electrolyte while there was also a clear variation with respect to applied current. Finally, the impact of adding 25% (by weight) Pd nanoparticle catalysts to the cathodes was investigated. The results obtained show clearly that the nature of discharge products for Li-O2 battery cathodes are strongly dependent on applied current, electrolyte choice and the addition of a catalyst material.

This review outlines the developments in the structure, composition, size, and shape control of many important and emerging Li-ion battery materials on many length scales, and details very recent investigations on how the assembly and programmable order in energy storage materials have not only influenced and dramatically improved the performance of some Li-ion batteries, but offered new routes toward improved power densities. This review also describes and discusses material aspects of hybrid and multiphasic materials including silicon, germanium, a wide range of metal oxides, alloys and crystal structures, carbons and other important materials. Methods including engineered porosity that offer the energy density of Li-ion batteries and the power density of pseudocapacitors are also highlighted. Recent developments in the analytical methods, electrochemical response, and the structure, composition, size, shape and defined assembly of active materials for a wide range of Li-ion cathodes and anodes are compared and assessed with respect to cell performance. Perspectives on the future development of energy storage materials based on structure as well as chemistry are also outlined.

The growth of Si/Ge axial heterostructure nanowires in high yield using a versatile wet chemical approach is reported. Heterostructure growth is achieved using the vapor zone of a high boiling point solvent as a reaction medium with an evaporated tin layer as the catalyst. The low solubility of Si and Ge within the Sn catalyst allows the formation of extremely abrupt heterojunctions of the order of just 1–2 atomic planes between the Si and Ge nanowire segments. The compositional abruptness was confirmed using aberration corrected scanning transmission electron microscopy and atomic level electron energy loss spectroscopy. Additional analysis focused on the role of crystallographic defects in determining interfacial abruptness and the preferential incorporation of metal catalyst atoms near twin defects in the nanowires.

peer-reviewed By using Si(100) with different dopant type (n(++)-type (As) or p-type (B)), we show how metal-assisted chemically etched (MACE) nanowires (NWs) can form with rough outer surfaces around a solid NW core for p-type NWs, and a unique, defined mesoporous structure for highly doped n-type NWs. We used high resolution electron microscopy techniques to define the characteristic roughening and mesoporous structure within the NWs and how such structures can form due to a judicious choice of carrier concentration and dopant type. The n-type NWs have a mesoporosity that is defined by equidistant pores in all directions, and the inter-pore distance is correlated to the effective depletion region width at the reduction potential of the catalyst at the silicon surface in a HF electrolyte. Clumping in n-type MACE Si NWs is also shown to be characteristic of mesoporous NWs when etched as high density NW layers, due to low rigidity (high porosity). Electrical transport investigations show that the etched nanowires exhibit tunable conductance changes, where the largest resistance increase is found for highly mesoporous n-type Si NWs, in spite of their very high electronic carrier concentration. This understanding can be adapted to any low-dimensional semiconducting system capable of selective etching through electroless, and possibly electrochemical, means. The process points to a method of multiscale nanostructuring NWs, from surface roughening of NWs with controllable lengths to defined mesoporosity formation, and may be applicable to applications where high surface area, electrical connectivity, tunable surface structure, and internal porosity are required. (C) 2013 AIP Publishing LLC. PUBLISHED peer-reviewed

Porous GaN layers are grown on silicon from gold or platinum catalyst seed layers, and self-catalyzed on epitaxial GaN films on sapphire. Using a Mg-based precursor, we demonstrate p-type doping of the porous GaN. Electrical measurements for p-type GaN on Si show Ohmic and Schottky behavior from gold and platinum seeded GaN, respectively. Ohmicity is attributed to the formation of a Ga2Au intermetallic. Porous p-type GaN was also achieved on epitaxial n-GaN on sapphire, and transport measurements confirm a p-n junction commensurate with a doping density of similar to 10(18) cm(-3). Photoluminescence and cathodoluminescence confirm emission from Mg-acceptors in porous p-type GaN. (C) 2013 AIP Publishing LLC.