Falko M. Schappacher

Low Cost, Environmentally Benign Binders for Lithium-Ion Batteries

The stringent environmental requirements regarding the mobility energy usage are forcing most automakers to develop hybrid electric vehicles, which allows for a more efficient and thus less polluting use of fossil combustibles. A vast deployment of such vehicles involves producing and recycling of batteries on the thousand tons per year scale. Present Li-ion technologies involve the use of fluorinated binders, which are costly, and the use of environmentally unfriendly volatile organic compounds for the processing, which are difficult to recycle. In this paper, it is shown that the fluorinated binders can be replaced with greener and cost-effective polymers derived from cellulose. .

Structural and magnetic phase transitions in the ternary iron arsenides SrFe2As2 and EuFe2As2

The structural and magnetic phase transitions of the ternary iron arsenides SrFe2As2 and EuFe2As2 were studied by temperature-dependent x-ray powder diffraction and 57Fe M?ssbauer spectroscopy. Both compounds crystallize in the tetragonal ThCr2Si2-type structure at room temperature and exhibit displacive structural transitions at 203?K (SrFe2As2) and 190?K (EuFe2As2), respectively, to orthorhombic lattice symmetry in agreement with the group?subgroup relationship between I4/mmm and Fmmm (?-SrRh2As2-type). 57Fe M?ssbauer spectroscopy experiments with SrFe2As2 show full hyperfine field splitting below the phase transition temperature (8.91(1)?T at 4.2?K). Order parameters were extracted from detailed measurements of the lattice parameters and fitted to a simple power law. We find a relation between the critical exponents and the transition temperatures for AFe2As2 compounds, which shows that the transition of BaFe2As2 is indeed more continuous than the transition of SrFe2As2, but it remains second order even in the latter case.

Trapping of Tin(II) and Lead(II) Homologues of Carbon Monoxide by a Benzannulated Lutidine-Bridged Bisstannylene

The reaction of the benzannulated bisstannylene ligand 2 with Sn O or Pb O generated in situ gave the pincer complexes 3 and 4. Both complexes have been characterized by X-ray diffraction and multinuclear NMR spectroscopy. A divalent state has been found by Mössbauer spectroscopy for the tin atoms in complexes 3 and 4.

Competition of magnetism and superconductivity in underdoped (Ba1- xKx)Fe2As2

Polycrystalline samples of underdoped (Ba1- xKx)Fe2As2 (x≤0.4) were synthesized and studied by x-ray powder diffraction, magnetic susceptibility, specific heat and 57Fe-Mosbauer spectroscopy. The structural phase transition from tetragonal to orthorhombic lattice symmetry shifts towards lower temperatures, becomes less pronounced at x=0.1–0.2 and is no longer present at x=0.3. Bulk superconductivity is observed in all samples except (Ba0.9K0.1)Fe2As2 by resistivity and magnetic susceptibility measurements. Specific heat data show a broad spin-density-wave (SDW) phase transition in (Ba0.9K0.1)Fe2As2, which is hardly discernible in (Ba0.8K0.2)Fe2As2. No SDW anomaly is found in the specific heat of optimally doped (Ba0.6K0.4)Fe2As2, where C changes by 0.1 J K− 1 at Tc=37.3 K. 57Fe-Mosbauer spectra show full magnetic hyperfine field splitting, indicative of antiferromagnetic (AF) ordering at 4.2 K in samples with x=0–0.2, but zero magnetic hyperfine field in samples with x=0.3. The spectra of (Ba0.9K0.1)Fe2As2 and (Ba0.8K0.2)Fe2As2 in the phase transition regions are temperature-dependent superpositions of magnetic and non-magnetic components, caused by inhomogeneous potassium distribution. Our results suggest the co-existence of AF ordering and superconductivity without mesoscopic phase separation in the underdoped region and show unambiguously homogeneous superconducting phases close to optimal doping. This is in contrast to recently reported results about single-crystal (Ba1- xKx)Fe2As2.

O3-type Na[Fe1/3Ni1/3Ti1/3]O2 cathode material for rechargeable sodium ion batteries

A Na[Fe1/3Ni1/3Ti1/3]O2 cathode material for sodium-ion batteries has been synthesized by a solid-state reaction method. The obtained Na[Fe1/3Ni1/3Ti1/3]O2 shows an O3-type structure, and delivers a discharge capacity of 117 mA h g−1 at a current density of 10 mA g−1 in a range of 1.5–4.0 V at 20 °C. Furthermore, the Na[Fe1/3Ni1/3Ti1/3]O2 cathode material shows good rate capability and cycling stability. The working and structural transition mechanisms of the Na[Fe1/3Ni1/3Ti1/3]O2 material are examined by ex situ X-ray absorption spectroscopy (XAS) and in situ X-ray diffraction (XRD) methods. The valence state of Fe ions in the Na[Fe1/3Ni1/3Ti1/3]O2 material is estimated to be 2.67+. The main redox couple is Ni2+/Ni4+, but the Fe2+/Fe3+ contributes a little as well at voltages below 2.0 V. The original O3 phase transforms to a P3 phase during sodium extraction with good reversibility, but a slightly irreversible change of lattice parameters may lead to capacity decay during long-term cycling. Moreover, the gas evolution during the first charge/discharge process is analyzed by using an operando mass spectrometry technique. The obvious release of CO2 gas at the end of the charge process may be the other origin of the capacity decay. Nevertheless, the absence of O2 evolution indicates an improved safety of the Na/Na[Fe1/3Ni1/3Ti1/3]O2 cell.

Homoleptic Diphosphacyclobutadiene Complexes [M(η4-P2C2R2)2]x− (M=Fe, Co; x=0, 1)

The preparation and comprehensive characterization of a series of homoleptic sandwich complexes containing diphosphacyclobutadiene ligands are reported. Compounds [K([18]crown-6)(thf)(2)][Fe(η(4)-P(2)C(2)tBu(2))(2)] (K1), [K([18]crown-6)(thf)(2)][Co(η(4)-P(2)C(2)tBu(2))(2)] (K2), and [K([18]crown-6)(thf)(2)][Co(η(4)-P(2)C(2)Ad(2))(2)] (K3, Ad = adamantyl) were obtained from reactions of [K([18]crown-6)(thf)(2)][M(η(4)-C(14)H(10))(2)] (M = Fe, Co) with tBuC[triple bond]P (1, 2), or with AdC[triple bond]P (3). Neutral sandwiches [M(η(4)-P(2)C(2)tBu(2))(2)] (4: M = Fe 5: M = Co) were obtained by oxidizing 1 and 2 with [Cp(2)Fe]PF(6). Cyclic voltammetry and spectro-electrochemistry indicate that the two [M(η(4)-P(2)C(2)tBu(2))(2)](-)/[M(η(4)-P(2)C(2)tBu(2))(2)] moieties can be reversibly interconverted by one electron oxidation and reduction, respectively. Complexes 1-5 were characterized by multinuclear NMR, EPR (1 and 5), UV/Vis, and Mössbauer spectroscopies (1 and 4), mass spectrometry (4 and 5), and microanalysis (1-3). The molecular structures of 1-5 were determined by using X-ray crystallography. Essentially D(2d)-symmetric structures were found for all five complexes, which show the two 1,3-diphosphacyclobutadiene rings in a staggered orientation. Density functional theory calculations revealed the importance of covalent metal-ligand π bonding in 1-5. Possible oxidation state assignments for the metal ions are discussed.

Structure and properties of Eu2Pt3Sn5

Abstract The new stannide Eu2Pt3Sn5 was synthesized by induction melting of the elements in a sealed tantalum tube in a water-cooled silica sample chamber. The structure was refined on the basis of single crystal X-ray diffractometer data: Y2Rh3Sn5 type, Cmc21, a = 453.30(9), b = 2662.9(8), c = 731.8(2) pm, wR2 = 0.0472, 1493 F2 values and 62 variables). The platinum and tin atoms build up a complex three-dimensional [Pt3Sn5] network with a broad range of Pt—Sn (264–293 pm) and Sn—Sn (308–373 pm) distances. The two crystallographically independent europium sites occupy large voids of coordination numbers 20 (Eu1) and 18 (Eu2) within the [Pt3Sn5] network. Eu2Pt3Sn5 shows Curie-Weiss behaviour in the temperature range 50–305 K with an experimental magnetic moment of 7.82(1) μB per Eu atom indicating purely divalent europium. Cp measurements show a broad anomaly with two maxima at 4.9(2) and 6.1(2) K. 151Eu Mössbauer spectra revealed both crystallographically independent europium sites to be divalent. At 4.2 K two rather different sizes of magnetic hyperfine field splittings are observed due to separate ordering of the two sites. The 119Sn Mössbauer spectrum shows complex superposition of the five signals in the paramagnetic range.

Analytical Methods for Investigation of Lithium-Ion Battery Ageing

One of the major issues battery research must address is the lifetime of a cell. This can be reduced by physical and chemical ageing processes that occur inside the cell and are influenced by both the operating strategy and the surrounding conditions (e.g. temperature). To understand battery ageing, it is necessary to analyze the materials used in a cell at the microscopic level and correlate the results with electrical measurement data. This chapter describes a strategy for performing an ageing experiment by using a combination of analytical methods.

Investigation of nano-sized Cu(II)O as a high capacity conversion material for Li-metal cells and lithium-ion full cells

In this study, self-prepared nanostructured CuO electrodes show no capacity decay for 40 cycles at 0.1C in Li metal cells. The reaction mechanisms of the CuO electrodes are investigated. With the help of in situ EIS, in situ XRD, TEM, XAS, SQUID, IC and GC-MS, it is found that the as-prepared CuO electrode undergoes significant phase and composition changes during the initial lithiation, with the transformation of CuO to nano-crystalline Cu. During the 1st delithiation, Cu is inhomogeneously oxidized, which yields a mixture of Cu2O, Cu2−xO and Cu. The incomplete conversion reaction during the 1st cycle is accompanied by the formation and partial decomposition of the solid electrolyte interphase (SEI) as the side reactions. Nevertheless, from the 1st to the 5th delithiation, the oxidation state of Cu approaches +2. After an additional formation step, the transformation to Cu and back to Cu2−xO remains stable during the subsequent long-term cycling with no electrolyte decomposition products detected. The LiNi1/3Mn1/3Co1/3O2 (NMC-111)/CuO full cells show high capacities (655.8 ± 0.6, 618.6 ± 0.9 and 290 ± 2 mA h g−1 at 0.1, 1 and 10C, respectively), within the voltage range of 0.7–4.0 V at 20 °C and a high capacity retention (85% after 200 cycles at 1C).

Investigating the lithium ion battery electrolyte additive tris (2,2,2-trifluoroethyl) phosphite by gas chromatography with a flame ionization detector (GC-FID)

The quantification of lithium ion battery electrolyte additives provides challenges in terms of methods and instrumentation. In this work, the detectability of the flame retardant additive tris(2,2,2-trifluoroethyl) phosphite (TTFPi) differs unusually when added to a standard electrolyte (1 M LiPF6 in ethylene carbonate (EC) : dimethyl carbonate (DMC) 1 : 1 wt%) using gas chromatography with a flame ionization detector (GC-FID). In this work, nuclear magnetic resonance (NMR), ion trap time of flight mass spectrometry (IT-TOF™ MS) and gas chromatography-mass spectrometry (GC-MS) are used to investigate a pure TTFPi solution and a standard battery electrolyte with TTFPi as an additive with regard to parasitic TTFPi consuming reactions and different TTFPi concentrations, respectively. NMR and IT-TOF™ MS measurements confirm the chemical stability of the TTFPi/standard electrolyte mixture and concentration dependent GC-MS and GC-FID experiments indicate a premature FID saturation limit for TTFPi in presence of standard electrolyte. The findings explain the counterintuitive absence of TTFPi for higher concentrations and provide important information for future sample preparation.