Synthesis of Novel Lithium Salts Containing Pentafluorophenylamido-based Anions and Investigation of their Thermal and Electrochemical Properties

Abstract Three novel lithium salts, lithium bis(pentafluorophenyl)amide LiN(Pfp)2, lithium pentafluorphenyl(trifluormethylsulfonyl)imide LiN(Pfp)(Tf) and lithium pentafluorphenyl(nonafluorbutylsulfonyl)imide LiN(Pfp)(Nf) were synthesized and characterized with respect to their thermal and electrochemical properties. LiN(Pfp)2 decomposes at 108 ºC, whereas Li-N(Pfp)(Tf) and Li-N(Pfp)(Nf) show a much higher thermal stability of 307 ºC and 316 ºC, respectively. The ionic conductivity at 100 ºC measured by means of impedance spectroscopy decreases in the order LiN(Pfp)(Tf) &gt; LiN(Tf)2 &gt; LiN(Pfp)(Nf). Both, the activation energy and entropy for ion conduction in the new salts are lower than in LiN(Tf)2 (LiTFSI), most likely due to the lower symmetry of the new anions. The electrochemical stability and ionic conductivity of LiN(Pfp)(Tf) and LiN(Pfp)(Nf) solutions (0.1 mol/l) in ethylene carbonate/dimethyl carbonate (1:3 w/w) are slightly lower than those of the LiTFSI solution, but still sufficient for application in lithium ion batteries. The high thermal stability of the novel salts and their stability towards hydrolysis makes them attractive candidates for overcoming the drawbacks of LiPF6-based electrolytes at elevated temperatures.</jats:p

Reducing dielectric loss in Na0.5Bi0.5TiO3 based high temperature capacitor material

The demand for capacitors exhibiting low sensitivity towards temperature changes and high power peaks has increased significantly. Recently, Na0.5Bi0.5TiO3 (NBT) based ceramics became excellent candidates for such extreme temperature capacitors. The dielectric loss of these materials is, however, difficult to control because of the complex defect chemistry of NBT based ceramics. Therefore, it is the limiting factor for high temperature applications. In this work, we present a strategy to increase the upper temperature limit for low dielectric loss. The addition of BiAlO3 to Na0.5Bi0.5TiO3-BaTiO3-CaZrO3 reduces the loss and sensitivity towards Bi evaporation during synthesis. For unmodified samples, the relative permittivity (εr = 581, at 1 kHz) varies less than 15 %, while the dielectric loss stays below 0.02 between -68 and 368 °C. With the addition of BiAlO3, the temperature range of low loss extends from -68 to 391 °C at even higher permittivity (εr = 628, at 1 kHz)

Domain wall-grain boundary interactions in polycrystalline Pb(Zr0.7Ti0.3)O3 piezoceramics

Interactions between grain boundaries and domain walls were extensively studied in ferroelectric films and bicrystals. This knowledge, however, has not been transferred to polycrystalline ceramics, in which the grain size represents a powerful tool to tailor the electromechanical and dielectric response. Here, we relate changes in dielectric and electromechanical properties of a bulk polycrystalline Pb(Zr0.7Ti0.3)O3 to domain wall interactions with grain boundaries. Samples with grain sizes in the range of 3.9–10.4 μm were prepared and their microstructure, crystal structure, and dielectric/electromechanical properties were investigated. A decreasing grain size was accompanied by a reduction in large-signal electromechanical properties and an increase in small-signal relative permittivity. High-energy diffraction analysis revealed increasing microstrains upon decreasing the grain size, while piezoresponse force microscopy indicated an increased local coercive voltage near grain boundaries. The changes in properties were thus related to strained material volume close to the grain boundaries exhibiting reduced domain wall dynamics

Influence of the annealing conditions on temperature-dependent ferroelastic behavior of LSCF

The macroscopic ferroelastic behavior of polycrystalline (La 0.6 Sr 0.4)0.95Co0.2Fe0.8O3−d and its dependence on an- nealing conditions was investigated over a temperature range from − 150°C to 150°C. A temperature- and defect concentration-dependent variation of the ferroelastic behavior was attributed to internal stresses, oxygen defi- ciency, and a corresponding change of the crystal structure. In particular, there was an observed decrease in remanent strain and the formation of a closed ferroelastic hysteresis loop at temperatures below approximately 0 °C for samples annealed in air, which was suppressed through the reduction in oxygen vacancies by annealing the samples in oxygen. The macroscopic mechanical behavior as a function of annealing conditions is discussed with respect to the crystal structure and oxygen deficiency determined by means of x-ray and neutron diffraction

Dramatic impact of the TiO2 polymorph on the electrical properties of ‘stoichiometric’ Na0.5Bi0.5TiO3 ceramics prepared by solid-state reaction

Bulk conductivity (σb) values of nominally stoichiometric Na0.5Bi0.5TiO3 (NBT) prepared by solid-state reaction collated from literature show random variation between 10−6 to 10−3 S cm−1 (at 600 °C). This makes it challenging to obtain reliable and reproducible performances of NBT-based devices, especially as the underlying reason(s) for this variance are not fully understood. Here we report the dramatic impact of the TiO2 reagent, in particular, the polymorphic form of TiO2 on the electrical conductivity and conduction mechanism of NBT. Based on our solid-state processing route, NBT ceramics prepared by rutile TiO2 are ionically conductive, and those prepared by anatase TiO2 are insulating. The dramatic difference in electrical properties of NBT prepared using rutile and anatase TiO2 is related to the NBT formation process: the intermediate phase Bi12TiO20 is more stable during formation of NBT in the case of anatase TiO2, which reduces the volatility of Bi2O3 during solid-state reaction. These results give plausible explanations for the large variation of σb reported in the literature and highlight the importance of selecting an appropriate TiO2 reagent when targeting controllable σb in NBT-based ceramics. For ion-conducting applications (such as in intermediate-temperature solid oxide fuel cells, IT-SOFCs), rutile TiO2 should be used, and for dielectric applications (such as in multilayer ceramic capacitors, MLCC) anatase TiO2 should be used