Monika Michalska

Novel graphene oxide/manganese oxide nanocomposites

A new synthesis method of obtaining nanocomposites, consisting of manganese oxides nanoparticles embedded in carbonaceous matrix, is reported. The method is based on thermal processing of precursor consisting of lithium and manganese salts mixed with citric and acetic acids. The nanocomposite morphology, composition and structure can be tuned by selecting specific thermal processing routes (e.g. pressure, temperature, time, etc.). For instance, foam or microspheres morphology can be obtained by heating the precursor in a vacuum at moderately low temperatures (ca. 300–400 °C). Similarly, depending on the ambient pressure during heating above the recrystallization temperature (ca. 400–450 °C), the forming nanocomposite will consist of either MnO or LiMn2O4 nanoparticles, i.e. materials which are of importance for lithium-ion batteries as anodes and cathodes, respectively. Finally, the structure of the carbonaceous matrix can be tuned primarily by controlling the annealing temperature. For instance, annealing in the temperature range of about 600–800 °C can lead to the formation of graphene-related structures, such as modified graphene oxide. We used this method to produce example nanocomposites, performed their detailed characterization and proposed a mechanism to explain their formation.

STEM study of Li4Ti5O12 anode material modified with Ag nanoparticles

Comprehensive scanning transmission electron microscopy (STEM) analysis of Li4Ti5O12 (LTO) powder modified by deposited Ag nanoparticles was performed. Nanocomposite powders with Ag content of 1 wt.%, 4 wt.%, 10 wt.% were fabricated in a chemical process from suspensions of Ag and LTO. Apart from the STEM results, the presence of pure silver on the surface of the ceramic powder was confirmed by XRD and XPS analyses. The silver particles deposited on the LTO particles were characterized using the EDS mapping technique. The quantified results of the EDS mapping showed a relatively homogenous distribution of silver nanoparticles on the powder surface for every metal content. The mean diameter of the nanoparticles deposited on the LTO powder was about 4 nm in all cases. An increase in the Ag content during chemical surface modification did not cause changes in the microstructure. Focusing on an analysis of the metallic nanoparticles on the ceramic powder, electron tomography was used as an investigative technique. A very precise analysis of three‐dimensional nanostructures is desirable for a comprehensive analysis of complex materials. The quantified analysis of the Ag nanoparticles visualized using electron tomography confirmed the results of the size measurements taken from the two‐dimensional EDS maps.

Electrochemical properties of lithium–titanium oxide, modified with Ag–Cu particles, as a negative electrode for lithium-ion batteries

Composites of Li4Ti5O12 with Ag–Cu particles were successfully synthesized by solid-state reaction followed by thermal decomposition of the metal substrates. The presence of metallic particles was confirmed by X-ray diffraction, scanning transmission electron microscopy and X-ray photoelectron spectroscopy. Galvanostatic charge–discharge tests showed improved specific capacity and capacity retention of Li4Ti5O12/Ag–Cu composites at a 10C current rate, while cyclic voltammetry and electrochemical impedance spectroscopy revealed changes in Li+ ion chemical diffusion coefficient values and charge-transfer resistance with increasing amount of Ag–Cu in prepared powders. The synthesis and structural, morphological and electrochemical evaluation of Li4Ti5O12/Ag–Cu powders, carried out in this work, were also presented here for the first time.

Graphene oxide-assisted synthesis of LiMn2O4 nanopowder

Abstract The article reports sol-gel synthesis of nanosized spinel-type lithium manganese oxide LiMn2O4 (LMO) carried out in the presence of graphene oxide (GO) and its electrochemical lithium insertion ability. The synthesis was performed in an aqueous environment with lithium acetate and manganese acetate used as precursors and citric acid as a chelating agent. The material was characterized by X-ray diffraction, SEM microscopy, Raman spectroscopy and cyclic voltammetry. The calcination step totally eliminated graphene from the final product, nevertheless its presence during the synthesis was found to affect the resulting LiMn2O4 morphology by markedly reducing the size of grains. Moreover, potentials of electrochemical lithium insertion/deinsertion reactions have been shifted, as observed in the cyclic voltammetry measurements. Along with the diminished grain size the voltammetric curves of the graphene oxide-modified material exhibit higher oxidation and lower reduction peak currents. The study demonstrates that GO mediation/assistance during the sol-gel synthesis fosters more nanostructured powder and changes the electrochemical characteristics of the product

Analysis of the surface decoration of TiO2 grains using silver nanoparticles obtained by ultrasonochemical synthesis towards organic photovoltaics

In this article, we present a wet ultrasonochemical synthesis of nanocrystalline TiO2 powders in the anatase form in ethanol solution and their surface decoration using uniformly dispersed Ag metallic nanoparticles of about 4 nm at concentration of n = 0.5 to 2.5 wt% and those of 10–20 nm larger at a higher concentration than 1 wt%. The structure of the prepared composites was characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM), Raman and X-ray photoelectron spectroscopy (XPS). Optical properties were determined using UV-vis spectroscopy. Six polymer solar cells with modification by an TiO2/n-Ag hole transporting layer were manufactured and studied under AM 1.5G-simulated solar illumination (100 mW cm−2). The best performance was obtained for a device with the ITO/(PEDOT:PSS):1.5%Ag in TiO2/P3HT:PCBM/Al architectures. Under these conditions, a PCE of 2.07% with open circuit voltage Voc = 0.612 V, short circuit current density Jsc = 5.94 mA cm−2, and fill factor FF = 0.57 was achieved. Additionally, devices were tested by electrochemical impedance spectroscopy under illumination and a well-fitted equivalent circuit was proposed. Finally, our idea of the linkage of TiO2/n-Ag with PEDOT:PSS and P3HT in the constructed devices taking into account the amount of Ag in TiO2 was proposed.

Formation of Fe and Ni substituted LiMn2-XMXO4 nanopowders and their crystal and electronic structure and magnetic properties

Abstract The Pechini sol-gel method was applied to obtain LiMn2–xTxO4 (T = Ni, Fe; x = 0.1 to 0.5) nanopowders. Crystal and electronic structures, chemical composition and magnetic properties of the materials were characterized by X-ray diffraction, XPS, SEM/EDX microscopy, prompt gamma-ray activation analysis (PGAA), Mössbauer spectroscopy and magnetic susceptibility, respectively. XRD measurements showed that the LiMn2–xNixO4 were single phase for x = 0.1 and 0.2. Three samples with higher Ni content contained some addition of a second phase. Analysis of the oxidation state of the dopants by XPS revealed ionic Ni2+ and Fe3+. Mössbauer spectroscopy also confirmed 3+ oxidation state of iron and its location in octahedral sites, which excluded the inverse spinel configuration. XPS examinations showed that Mn3+ ions dominated in the iron substituted series whereas the Mn4+ was dominant in the nickel series.