Metal oxides represent a set of promising materials for use as electrodes within lithium ion batteries, but unfortunately, these tend to suffer from limitations associated with poor ionic and electron conductivity as well as low cycling performance. Hence, to achieve the goal of creating economical, relatively less toxic, thermally stable, and simultaneously high-energy-density electrode materials, we have put forth a number of targeted strategies, aimed at rationally improving upon electrochemical performance. Specifically, in this Perspective, we discuss the precise roles and effects of controllably varying not only (i) morphology but also (ii) chemistry as a means of advancing, ameliorating, and fundamentally tuning the development and evolution of Fe3O4, Li4Ti5O12, TiO2, and LiV3O8 as viable and ubiquitous energy storage materials.

This report describes the first detailed electrochemical examination of a series of copper birnessite samples under lithium-based battery conditions, allowing a structure/function analysis of the electrochemistry and related material properties. To obtain the series of copper birnessite samples, a novel synthetic approach for the preparation of copper birnessite, CuxMnOy·nH2O is reported. The copper content (x) in CuxMnOy·nH2O, 0.28 ≥ x ≥ 0.20, was inversely proportional to crystallite size, which ranged from 12 to 19 nm. The electrochemistry under lithium-based battery conditions showed that the higher copper content (x = 0.28) and small crystallite size (∼12 nm) sample delivered ∼194 mAh/g, about 20% higher capacity than the low copper content (x = 0.22) and larger crystallite size (∼19 nm) material. In addition, CuxMnOy·nH2O displays quasi-reversible electrochemistry in magnesium based electrolytes, indicating that copper birnessite could be a candidate for future application in magnesium-ion batteries.

Titanium oxide is a ubiquitous and commonly used material in the environment. Herein, we have systematically probed the use of various hydrothermally derived titania (TiO2) architectures including zero-dimensional (0D) nanoparticles, one-dimensional (1D) nanowires, and three-dimensional (3D) urchin-like motifs as anode materials for lithium-ion batteries. The structure and morphology of these nanomaterials were characterized using electron microscopy. The surface areas of these materials were quantitatively analyzed through Brunauer–Emmett–Teller (BET) adsorption measurements and were found to be relatively similar for both 1D and 3D samples with a slightly higher surface area associated with the 0D nanoparticles. Hence, to normalize for the surface area effect, readily available 0D commercial nanoparticles (Degussa P25), which possessed a similar surface area to that of as-prepared 1D and 3D materials, were also analyzed. Electrochemical analysis revealed a superior performance of hydrothermally derived 3D urchin-like motifs as compared with both as-prepared 0D and 1D samples as well as commercial Degussa P25. Our studies suggest the greater overall importance of morphology as opposed to surface area in dictating the efficiency of the Li ion diffusion process. Specifically, the 3D urchins yielded consistent rate capabilities, delivering 214, 167, 120, 99, and 52 mAh/g under corresponding discharge rates of 0.1, 1, 10, 20, and 50 C, respectively. Moreover, these 3D motifs gave rise to a stable cycling performance, exhibiting a capacity retention of ∼90% in cycles 1–100 under a discharge rate of 1 C. Furthermore, the rate capability and cycling performance of our 3D hierarchical motifs were (i) comparable to those of anatase TiO2/TiO2-(B) hybrid structures even with little if any electrochemically promising bronze (B) phase herein and (ii) clearly enhanced as compared with previous results using similar anatase 3D microspheres.

A research project for senior undergraduates of chemistry has been developed to introduce syntheses of a series of monodispersed semiconductor PbS quantum dots (QDs) and their characterization methodologies. In this paper, we report the preparation of monodispersed semiconductor PbS QDs with sizes smaller than the exciton Bohr radius using a simple, one-step process, and the characterization of the QDs using a range of instruments, including Fourier-transform infrared spectroscopy, transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and energy-dispersive X-ray spectroscopy. Our synthesis approach involves dissolving powdered sulfur (as the S precursor) in 1-tetradecene and adding PbCl 2 as the Pb precursor to the suspension as well as oleylamine as a capping ligand. The PbS QD project represents, we believe, an almost ideal opportunity to provide exposure of undergraduate students to nanotechnology research via syntheses and characterization of semiconductor nanoparticles.A dvances in nanotechnology in the past 20 years have resulted in enormous interest in introducing nanomaterials and associated technologies into the undergraduate curriculum, especially in chemistry. 1−6 As examples, Pavel et al. 2 have reported experiments involving a scattering species, rhodamine 6G (R6G), adsorbed onto silver nanoparticles (AgNPs), with the purpose of quantitatively measuring the surface-enhanced Raman scattering (SERS) phenomenon for the system; this study also incorporated absorbance and emission measurements. Reid et al. 3 developed a laboratory experiment involving semiconductor ZnO quantum dots (QDs) focusing on band gap 3 and absorbance characterization. Also, Lisensky et al. 6 discussed a laboratory experiment involving absorbance and emission characterization of semiconductor CdSe QDs. However, most of the reported studies involve theoretical issues that are somewhat sophisticated for undergraduate chemical education purposes. In this article, we present our recently developed research project of semiconductor QD synthesis and characterization to help to promote and improve college-level education focusing on undergraduate research. We also demonstrate that an undergraduate research project can be conveniently utilized as a laboratory experiment for curriculum development purposes.The main reason we selected lead sulfide QDs to introduce nanoscience research to our undergraduates is that lead sulfide QDs can be conveniently synthesized under mild temperature in a simple, one-step noninjection process. Our approach significantly reduce burn risks to undergraduates that may occur when high-temperature syntheses are undertaken. In addition, undergraduates can gain some basic knowledge related to semiconductor QDs and their applications.Semiconductor lead chalcogenide (PbS, PbSe, PbTe) QD materials show strong quantum confinement effects due to their relative large exciton Bohr radii and dielectric constants. 7,8 The quantum confinement phenomenon 3 associated with lead chalcogenide QDs can be easily obs...

Fe 3 O 4 nanoparticles (NPs) with an average size of 8-10 nm and a loading ratio of 50 wt% have been successfully attached onto the external surfaces of multi-walled carbon nanotubes (MWNTs) by means of three different preparative approaches, namely a sonication method, a covalent attachment protocol, as well as a non-covalent π-π interaction strategy. Specifically, the Fe 3 O 4 NPs associated with the sonication method lie directly on the outer surfaces of the MWNTs. Particles covalently attached onto the MWNTs formed amide chemical bonds through the mediation of the amorphous (3-aminopropyl) triethoxysilane (APTES) linker. Finally, particles were anchored non-covalently onto the underlying conjugated MWNTs via an aromatic 4-mercaptobenzoic acid (4-MBA) linker. Both structural and electrochemical characterization protocols have been used to systematically correlate the electrode performance with the corresponding attachment strategies. Fe 3 O 4 -MWNT composites generated by the π-π interaction strategy delivered 813, 768, 729, 796, 630, 580, 522, and 762 mAh/g under rates of 200, 400, 800, 100, 1200, 1600, 2000, and 100 mA/g, with 72% retention between cycles 2 and 80, demonstrating both higher capacity and better cycling stability as compared with analogues derived from the physical sonication as well as covalent attachment strategies. This finding may be attributed to the enhanced charge and ion transport coupled with retention of physical contact with the underlying MWNTs after a large volume change during cycling. Our collective results suggest that the non-covalent π-π attachment modality is a more effective preparative strategy for enhancing the performance of MWNT-Fe 3 O 4 composite electrodes after a full discharge process. Lithium ion battery (LIB) applications have experienced significant growth over the past two decades. Today LIBs are widely used and denote the battery of choice for a wide range of applications spanning from portable electronics to electric vehicles.1-5 Although LIBs have shown impressive commercial success, an understanding of the intrinsic functioning of LIB electrodes and of their constituent component materials still represents a subject of significant research. In recent years, the use of energy storage devices has expanded into new areas, including with uninterrupted power sources (UPS), stationary storage batteries (SSBs), and the automotive market, the latter of which encompasses both electric vehicles and hybrid electric vehicles. Hence, the development of LIBs based upon the use of lower cost and more earth abundant materials embodies a highly desirable objective.As an electroactive material, the inverse spinel structure of magnetite (Fe 3 O 4 ) epitomizes a particularly promising candidate for an anode material in LIB, due to its (i) significantly larger reversible capacity (i.e. 926 mAh g −1 , when reacting with eight lithium equivalents), (ii) plentiful earth abundance, and (iii) relative non-toxicity.

Birnessite type layered manganese dioxides (δ-MnO2) have attracted considerable attention in recent years as 2D intercalation cathodes for rechargeable Li+, Na+, and Mg2+ batteries due to fast ion diffusion through their negatively charged δ-MnO2 sheets separated by interlayer cations and a stable Mn3+/4+ redox couple. Here we report the preparation and electrochemistry of zero and divalent copper co-intercalated birnessite type manganese dioxide (Cu00.03Cu2+0.21Na0.12MnO2·0.9H2O). The copper intercalated birnessite materials were fully characterized utilizing powder X-ray diffraction (XRD), inductively coupled plasma optical emission spectroscopy (ICP-OES), transmission electron microscopy (TEM). The mixed valent nature of intercalated Cu0 and Cu2+ was confirmed by X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS). Electrochemical evaluation results show that zero valent copper intercalated birnessite exhibits higher discharge capability, improved cyclability, and lower impedance compared to the Cu2+ only intercalated (Cu0.26MnO2·1.0H2O) and Cu free Na birnessite (Na0.40MnO2·1.0H2O) materials. Remarkably, zero valent copper birnessite shows almost no fade after 10 cycles at 0.1 mV/s. Electrochemical impedance spectroscopy results suggest that charge transfer resistivity of Cu0 modified samples was much lower than that of Cu2+ and Cu free birnessite, indicating that the presence of a small amount of Cu0 improves the conductivity of birnessite and results in better electrochemical cyclability, rate capability, and lower impedance.

In this report, we describe the electrochemistry of hybrid dual silver vanadium phosphorus oxide/carbon fluoride (Ag 2 VO 2 PO 4 /CF x ) cathodes with various weight ratios. Through modification of the Ag 2 VO 2 PO 4 /CF x ratio, we can control the gravimetric and volumetric capacity, as well as mitigate the voltage drop during high current pulses. The increase in impedance caused by irreversible LiF formation in CF x was reduced by the silver reduction-displacement during electrochemical discharge of the Ag 2 VO 2 PO 4 . Moreover, the addition of graphite was shown to reduce initial voltage delay. When Ag 2 VO 2 PO 4 dominates the electrode mass (i.e. 75/25 Ag 2 VO 2 PO 4 /CF x ) in the hybrid cathode, pulse testing shows less voltage drop and delay, but at the expense of capacity and energy density. As the amount of CF x in the composite increases (i.e. Ag 2 VO 2 PO 4 /CF x ratio of to 50/50 or 25/75), charge capacity and energy density increases, but at the expense of larger voltage drops and delays early in the discharge process. Thus, controlling the Ag 2 VO 2 PO 4 /CF x ratio can be used to tune the electrochemical properties of the dual cathode, allowing for optimization of capacity and power depending on the application.

The combination of ex situ X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) measurements on 2D layered copper birnessite cathode materials for lithium ion battery applications provides detailed insight into both bulk-crystalline and localized atomic structural changes resulting from electrochemically driven lithium insertion and de-insertion. Copper birnessite electrodes that had been galvanostatically discharged and charged were measured with XRD to determine the accompanying long-range crystalline structure changes, while Mn and Cu K-edge XAS measurements provided a detailed view of the Mn and Cu oxidation state changes along with variations of the local neighboring atom environments around the Mn and Cu centers. While not detectable with XRD spectra, through XAS measurements it was determined that the copper ions (Cu(2+)) are reduced to form amorphous nano-sized Cu metal, and can be oxidized back to Cu(2+). The reversible nature of the interconversion provides a rationale to the enhanced discharge capacity of copper birnessite relative to the analogous copper-free birnessite materials. The manganese oxide octahedra comprising the 2D layers in the original copper birnessite crystal structure disperse during lithium insertion, and revert back close to their original orientation after lithium de-insertion. During electrochemical oxidation or reduction the layered birnessite structure does not collapse, even though significant local disordering around Mn and Cu centers is directly observed.