Degradation Mechanisms at the Li10GeP2S12/LiCoO2 Cathode Interface in an All-Solid-State Lithium-Ion Battery

All-solid-state batteries (ASSBs) show great potential for providing high power and energy densities with enhanced battery safety. While new solid electrolytes (SEs) have been developed with high enough ionic conductivities, SSBs with long operational life are still rarely reported. Therefore, on the way to high-performance and long-life ASSBs, a better understanding of the complex degradation mechanisms, occurring at the electrode/electrolyte interfaces is pivotal. While the lithium metal/solid electrolyte interface is receiving considerable attention due to the quest for high energy density, the interface between the active material and solid electrolyte particles within the composite cathode is arguably the most difficult to solve and study. In this work, multiple characterization methods are combined to better understand the processes that occur at the LiCoO₂ cathode and the Li₁₀GeP₂S₁₂ solid electrolyte interface. Indium and Li₄Ti₅O₁₂ are used as anode materials to avoid the instability problems associated with Li-metal anodes. Capacity fading and increased impedances are observed during long-term cycling. Postmortem analysis with scanning transmission electron microscopy, electron energy loss spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy show that electrochemically driven mechanical failure and degradation at the cathode/solid electrolyte interface contribute to the increase in internal resistance and the resulting capacity fading. These results suggest that the development of electrochemically more stable SEs and the engineering of cathode/SE interfaces are crucial for achieving reliable SSB performance.

Applying Capacitive Energy Storage for In Situ Manipulation of Magnetization in Ordered Mesoporous Perovskite-Type LSMO Thin Films

Mesostructured nonsilicate materials, particularly mixed-metal oxides, are receiving much attention in recent years because of their potential for numerous applications. Via the polymer-templating method, perovskite-type lanthanum strontium manganese oxide (La_1-xSr_xMnO₃, LSMO, with x ≈ 0.15 to 0.30) with a continuous 3D cubic network of 23 nm pores is prepared in thin-film form for the first time. Characterization results from grazing incidence X-ray scattering, X-ray photoelectron spectroscopy, Rutherford backscattering spectrometry, and electron microscopy and tomography show that the dip-coated sol-gel-derived films are of high quality in terms of both composition and morphology and that they are stable to over 700 °C. Magnetic and magnetotransport measurements demonstrate that the material with the highest strontium concentration is ferromagnetic at room temperature and exhibits metallic resistivity behavior below 270 K. Besides, it behaves differently from epitaxial layers (e.g., enhanced low-field magnetoresistance effect). It is also shown that carriers (electrons and holes) can be induced into the polymer-templated mesostructured LSMO films via capacitive double-layer charging. This kind of electrostatic doping utilizing ionic liquid gating causes large relative changes in magnetic susceptibility at room temperature and is a viable technique to tune the magnetic phase diagram in situ.

Interfacial Processes and Influence of Composite Cathode Microstructure Controlling the Performance of All-Solid-State Lithium Batteries

All-solid-state lithium-ion batteries have the potential to become an important class of next-generation electrochemical energy storage devices. However, for achieving competitive performance, a better understanding of the interfacial processes at the electrodes is necessary for optimized electrode compositions to be developed. In this work, the interfacial processes between the solid electrolyte (Li₁₀GeP₂S₁₂) and the electrode materials (In/InLi and Li_xCoO₂) are monitored using impedance spectroscopy and galvanostatic cycling, showing a large resistance contribution and kinetic hindrance at the metal anode. The effect of different fractions of the solid electrolyte in the composite cathodes on the rate performance is tested. The results demonstrate the necessity of a carefully designed composite microstructure depending on the desired applications of an all-solid-state battery. While a relatively low mass fraction of solid electrolyte is sufficient for high energy density, a higher fraction of solid electrolyte is required for high power density.

Phase formation and stability in TiO x and ZrO x thin films: Extremely sub-stoichiometric functional oxides for electrical and TCO applications

Most functional materials are thermodynamic equilibrium phases representing minima in the thermodynamic phase space. However, it is expected that many metastable phases with highly interesting properties also exist. Here, we report on a systematic approach to prepare thin-films of such non-equilibrium phases based on the gas phase deposition methods sputtering and pulsed laser deposition (PLD). Our synthetic strategy is to deposit a “precursor phase” which is amorphous or already a crystalline non-equilibrium phase. Subsequent heat treatment leads to the nucleation of crystalline phases which again may be metastable or stable compounds. In the present paper we focus on the binary systems Ti–O and Zr–O, both systems being widely applied and technologically relevant. Highly oxygen-deficient titanium oxide (TiO1.6) and zirconium oxide (ZrO) films prepared by pulsed laser deposition at room temperature are optically absorbing and possess electronic conductivities in the range of 10 S/cm. Both materials are metastable in respect to both composition and structure. For TiO1.6 we find an amorphous matrix with embedded grains of cubic titanium monoxide (γ-TiO) directly after deposition. Upon annealing nanocrystalline grains of metallic Ti are formed in the amorphous matrix due to an internal solid-state disproportionation whereas the electrical conductivity of the films increases and comes close to metal-like conductivity (1000 S/cm) at about 450 °C. Congruently, room temperature deposited ZrO films with an average composition of Zr:O= 1:1 contain small ZrO nanocrystals within an amorphous matrix. Heat treatment again leads to an internal disproportionation reaction whereas small crystals of Zr2O and ZrO2 precipitate at temperatures as low as 75 °C. Increasing the temperature then results in the crystallization of metastable tetragonal ZrO2 at about 400 °C. Sputter deposition allows a subtler control of the oxygen partial pressure. Slightly non-stoichiometric TiO2−x films form a degenerate semiconductor with room temperature conductivities as high as 170 S/cm. Moreover, controlling both, the doping level and the vacancy concentration of these films allows to control the phase formation and the transition temperature between the rutile and anatase TiO2 polymorphs. Niobium doping of sputter deposited TiO2 can lead to films with very high electrical conductivities while maintaining a high optical transmittance demonstrating the potential of the material as an alternative transparent conducting oxide (TCO) with extraordinary properties.

Interfacial Reactivity Benchmarking of the Sodium Ion Conductors Na3PS4 and Sodium β-Alumina for Protected Sodium Metal Anodes and Sodium All-Solid-State Batteries

The interfacial stability of solid electrolytes at the electrodes is crucial for an application of all-solid-state batteries and protected electrodes. For instance, undesired reactions between sodium metal electrodes and the solid electrolyte form charge transfer hindering interphases. Due to the resulting large interfacial resistance, the charge transfer kinetics are altered and the overvoltage increases, making the interfacial stability of electrolytes the limiting factor in these systems. Driven by the promising ionic conductivities of Na₃PS₄, here we explore the stability and viability of Na₃PS₄ as a solid electrolyte against metallic Na and compare it to that of Na-β″-Al₂O₃ (sodium β-alumina). As expected, Na-β″-Al₂O₃ is stable against sodium, whereas Na₃PS₄ decomposes with an increasing overall resistance, making Na-β″-Al₂O₃ the electrolyte of choice for protected sodium anodes and all-solid-state batteries.

Temperature-induced transformation of electrochemically formed hydrous RuO2 layers over Ru(0001) model electrodes

Hydrous RuO2 reveals excellent performance both as a supercapacitor and as a heterogeneous oxidation catalyst. Molecular understanding of these processes needs, however, a model system with preferably low structural and morphological complexity. This goal is partly accomplished here by using single crystalline Ru(0001) as a template on which hydrous RuO2 is electrochemically formed. The hydrous RuO2 layers on Ru(0001) and their temperature induced transformation under ultra high vacuum (UHV) conditions are comprehensively characterized by scanning electron microscopy and X-ray photoemission spectroscopy. The hydrous RuO2 layer grows with an intricate morphology governed by the presence of step bunching regions of the Ru(0001) surface. Upon annealing to 200 °C in UHV the hydrous RuO2 layer transforms mostly into flat metallic Ru islands and occasionally into (100) and (111) oriented RuO2 particles aligned along the high symmetry direction of Ru(0001).

Hierarchical Carbon with High Nitrogen Doping Level: A Versatile Anode and Cathode Host Material for Long-Life Lithium-Ion and Lithium-Sulfur Batteries

Nitrogen-rich carbon with both a turbostratic microstructure and meso/macroporosity was prepared by hard templating through pyrolysis of a tricyanomethanide-based ionic liquid in the voids of a silica monolith template. This multifunctional carbon not only is a promising anode candidate for long-life lithium-ion batteries but also shows favorable properties as anode and cathode host material owing to a high nitrogen content (>8% after carbonization at 900 °C). To demonstrate the latter, the hierarchical carbon was melt-infiltrated with sulfur as well as coated by atomic layer deposition (ALD) of anatase TiO2, both of which led to high-quality nanocomposites. TiO2 ALD increased the specific capacity of the carbon while maintaining high Coulombic efficiency and cycle life: the composite exhibited stable performance in lithium half-cells, with excellent recovery of low rate capacities after thousands of cycles at 5C. Lithium-sulfur batteries using the sulfur/carbon composite also showed good cyclability, with reversible capacities of ∼700 mA·h·g(-1) at C/5 and without obvious decay over several hundred cycles. The present results demonstrate that nitrogen-rich carbon with an interconnected multimodal pore structure is very versatile and can be used as both active and inactive electrode material in high-performance lithium-based batteries.

Correlation of electrochromic properties and oxidation states in nanocrystalline tungsten trioxide

In nanocrystalline tungsten trioxide, the main coloration change can be attributed to the formation of W⁴⁺.

Quantification of calcium content in bone by using ToF-SIMS--a first approach

The determination of the spatially resolved calcium distribution and concentration in bone is essential for the assessment of bone quality. It enables the diagnosis and elucidation of bone diseases, the course of bone remodelling and the assessment of bone quality at interfaces to implants. With time-of-flight secondary ion mass spectrometry (ToF-SIMS) the calcium distribution in bone cross sections is mapped semi-quantitatively with a lateral resolution of up to 1 μm. As standards for the calibration of the ToF-SIMS data calcium hydroxyapatite collagen scaffolds with different compositions were synthesized. The standards were characterised by loss of ignition, x-ray diffractometry (XRD) and x-ray photoelectron spectroscopy (XPS). The secondary ion count rate for calcium and the calcium content of the standards show a linear dependence. The obtained calibration curve is used for the quantification of the calcium content in the bone of rats. The calcium concentration within an animal model for osteoporosis induction is monitored. Exemplarily the calcium content of the bones was quantified by XPS for validation of the results. Furthermore a calcium mass image is compared with an XPS image to demonstrate the better lateral resolution of ToF-SIMS which advances the locally resolved quantification of the calcium content.