Synthesis and electrochemical investigation of garnet-polymer composite electrolytes for solid state batteries

Solid state lithium batteries are considered an alternative to currently available lithium ion batteries. The development of a suitable electrolyte is essential for commercialisation of bulk-type solid state batteries. This thesis is concerned with the synthesis of a solid state electrolyte as a composite of ceramic Li7La3Zr2O12 (LLZO) and a polymer electrolyte based on poly(ethylene oxide) (PEO). First, the synthesis of Al substituted LLZO by means of co-precipitation is described. The obtained powder is characterised with regard to its structural, chemical and electrochemical properties. In the second part, free-standing and flexible composite membranes (containing up to 40 vol% LLZO in polymer electrolyte (PEO20LiClO4) matrix) are manufactured by tape casting. In the third part, the LLZO/PEO20LiClO4 interface is identified as obstructive to continuous Li ion conduction. A model system is developed and investigated by means of impedance spectroscopy

Serpentine (Floating) Ice Channels and their Interaction with Riverbed Permafrost in the Lena River Delta, Russia

Arctic deltas and their river channels are characterized by three components of the cryosphere: snow, river ice, and permafrost, making them especially sensitive to ongoing climate change. Thinning river ice and rising river water temperatures may affect the thermal state of permafrost beneath the riverbed, with consequences for delta hydrology, erosion, and sediment transport. In this study, we use optical and radar remote sensing to map ice frozen to the riverbed (bedfast ice) vs. ice, resting on top of the unfrozen water layer (floating or so-called serpentine ice) within the Arctic’s largest delta, the Lena River Delta. The optical data is used to differentiate elevated floating ice from bedfast ice, which is flooded ice during the spring melt, while radar data is used to differentiate floating from bedfast ice during the winter months. We use numerical modeling and geophysical field surveys to investigate the temperature field and sediment properties beneath the riverbed. Our results show that the serpentine ice identified with both types of remote sensing spatially coincides with the location of thawed riverbed sediment observed with in situ geoelectrical measurements and as simulated with the thermal model. Besides insight into sub-river thermal properties, our study shows the potential of remote sensing for identifying river channels with active sub-ice flow during winter vs. channels, presumably disconnected for winter water flow. Furthermore, our results provide viable information for the summer navigation for shallow-draught vessels

Organic carbon in subsea permafrost: a globally significant but inert carbon pool Frederieke Miesner

Subsea permafrost underlays 2.4 million km2 of the Arctic Shelf, an area equaling ~18% of the terrestrial permafrost region. Most of it was inundated at some point after the last glacial maximum and is in an advanced state of warming. How much organic carbon (OC) accumulated, how this carbon pool was affected by permafrost presence and degradation over time, how much carbon still remains today and how much of it may be mobilized are major unknowns in the global carbon cycle. Recent estimates of OC decomposition from thawing submarine permafrost were as high as 8 Tg OC per year in methane alone. Here, we combine a numerical model of sedimentation and permafrost evolution with simplified carbon turnover to estimate accumulation and microbial decomposition of organic matter on the pan-Arctic shelf over the past four glacial cycles (450 kyr). Organic carbon decomposition is modeled with a reactivity continuum model using inversely determined parameters from incubation experiments and liquid water content within the permafrost as the limiting factor rather than temperature alone. We find that Arctic shelf permafrost is a long-term carbon sink storing 2822 (1518 - 4982) Pg OC, two to four times the amount stored in lowland permafrost. Although subsea permafrost is currently thawing, prior microbial decomposition and organic matter aging would limit decomposition rates to less than 48 Tg OC per year even if all frozen sediment deposited in the past 450 kyr thawed immediately. Since actual thaw rates are orders of magnitude lower, true emissions due to subsea permafrost thaw are also orders of magnitude lower than this. The OC pool in shelf permafrost is therefore largely immobilized. Compared to the organic matter in thawing permafrost large emissions are more likely derived from older and deeper sources as shelf’s frozen lid, the permafrost, becomes more permeable

Submarine Permafrost as a Long-term Late Quaternary Carbon Sink

Organic carbon (OC) stored in Arctic continental shelf sediment is a climate-sensitive but poorly quantified component of the global carbon cycle. The current interglacial period means that most shelf permafrost, along with its OC, is currently warmer than -2 °C, and therefore susceptible to small additional warming in the near future. Estimating how much OC is potentially stored in subsea permafrost is thus key to a quantitative understanding of potential impacts of permafrost thaw on carbon mobilization in a warming Arctic. We developed a process-based model of permafrost distribution and organic matter (OM) sedimentation and decomposition to estimate the contribution of submarine permafrost to Arctic shelf organic carbon stocks. Driven by Earth System Model forcing, our model calculates 1D heat flow below the earth surface, ice caps and sea bed, and uses a reactivity continuum model of OM decomposition. We restrict our modeling to sediment that was buried within the last four glacial cycles (450 kyr), and therefore neglect OC stocks deeper than about 100 m, including any gas hydrates. Restricting OM decomposition to the liquid habitat for microbial activity in the sediment, we estimated that permafrost below the Arctic Shelf stores at least as much OC as the terrestrial counterpart at pre-industrial time, and probably in the range of twice to three times as much OC. We compared the effect of varying the OC sedimentation rates and OC reactivity. Higher reactivity in marine sediments combined with lower ice contents to increase the rate of OM decomposition, relative to sediment deposited in terrestrial settings. As a result, permafrost in our model preserved a greater proportion of marine OM from decomposition while having little effect (< 5%) on the amount of recalcitrant terrestrial OC. These differences in sedimentation rate and reactivity influence the distribution of OC preservation on the Arctic shelf. Our modeling shows that subsea permafrost is a relevant OC stock and that more research is needed to understand microbial OM decomposition in cold but not necessarily frozen sediments. Given that deeper deposits and gas hydrates are not included, we provide conservative estimates of Arctic shelf OC stocks and suggest that the shelves have acted as long-term carbon sinks over multiple glacial--interglacial cycles

Synthese und elektrochemische Charakterisierung von Granat-Polymer Komposit-Elektrolyten für Festkörperbatterien

Solid state lithium batteries are considered an alternative to currently available lithium ion batteries. The development of a suitable electrolyte is essential for commercialisation of bulk-type solid state batteries. This thesis is concerned with the synthesis of a solid state electrolyte as a composite of ceramic Li7La3Zr2O12 (LLZO) and a polymer electrolyte based on poly(ethylene oxide) (PEO). First, the synthesis of Al substituted LLZO by means of co-precipitation is described. The obtained powder is characterised with regard to its structural, chemical and electrochemical properties. In the second part, free-standing and flexible composite membranes (containing up to 40 vol% LLZO in polymer electrolyte (PEO20LiClO4) matrix) are manufactured by tape casting. In the third part, the LLZO/PEO20LiClO4 interface is identified as obstructive to continuous Li ion conduction. A model system is developed and investigated by means of impedance spectroscopy

Influence of Screw Design and Process Parameters on the Product Quality of PEO:LiTFSI Solid Electrolytes Using Solvent-Free Melt Extrusion

All-solid-state battery (ASSB) technology is a new energy system that reduces the safety concerns and improves the battery performance of conventional lithium-ion batteries (LIB). The increasing demand for such new energy systems makes the transition from laboratory scale production of ASSB components to larger scale essential. Therefore, this study investigates the dry extrusion of poly(ethylene oxide):lithium bis (trifluoromethylsulfonyl)imide (PEO:LiTFSI) all-solid-state electrolytes at a ratio of 20:1 (EO:Li). We investigated the influence of different extruder setups on the product quality. For this purpose, different screw designs consisting of conveying, kneading and mixing elements are evaluated. To do so, a completely dry and solvent-free production of PEO:LiTFSI electrolytes using a co-rotating, intermeshing, twin-screw extruder under an inert condition was successfully carried out. The experiments showed that the screw design consisting of kneading elements gives the best results in terms of process stability and homogeneous mixing of the electrolyte components. Electrochemical impedance spectroscopy was used to determine the lithium-ion conductivity. All electrolytes produced had an ionic conductivity (σionic) of (1.1–1.8) × 10−4 S cm−1 at 80 °C

Influence of Solid Fraction on Particle Size during Wet-Chemical Synthesis of β-Li₃PS₄ in Tetrahydrofuran

For all-solid-state batteries, the particle size distribution of the solid electrolyte is a critical factor. Small particles are preferred to obtain a high active mass loading of cathode active material and a small porosity in composite cathodes. In this work, the influence of the solid fraction in the wet-chemical synthesis of β-Li3PS4 in tetrahydrofuran (THF) is investigated. The solid fraction is varied between 50 and 200 mg/mL, and the obtained samples are evaluated using X-ray diffraction, SEM and electrochemical impedance measurements. The sizes of the resulting particles show a significant dependency on the solid fraction, while a good ionic conductivity is maintained. For the highest concentration, the particle sizes do not exceed 10 µm, but for the lowest concentration, particles up to ~73 µm can be found. The ionic conductivities at room temperature are determined to be 0.63 ± 0.01 × 10−4 S/cm and 0.78 ± 0.01 × 10−4 S/cm for the highest and lowest concentrations, respectively. These findings lead to an improvement towards the production of tailored sulfide solid electrolytes

Time resolved impedance spectroscopy analysis of lithium phosphorous oxynitride - LiPON layers under mechanical stress

In this paper we present investigations on the morphological and electrochemical changes of lithium phosphorous oxynitride (LiPON) under mechanically bent conditions. Therefore, two types of electrochemical cells with LiPON thin films were prepared by physical vapor deposition. First, symmetrical cells with two blocking electrodes (Cu/LiPON/Cu) were fabricated. Second, to simulate a more application-related scenario cells with one blocking and one non-blocking electrode (Cu/LiPON/Li/Cu) were analyzed. In order to investigate mechanical distortion induced transport property changes in LiPON layers the cells were deposited on a flexible polyimide substrate. Morphology of the as-prepared samples and deviations from the initial state after applying external stress by bending the cells over different radii were investigated by Focused Ion Beam- Scanning Electron Microscopy (FIB-SEM) cross-section and surface images. Mechanical stress induced changes in the impedance were eva luated by time-resolved electrochemical impedance spectroscopy (EIS). Due to the formation of a stable, ion-conducting solid electrolyte interphase (SEI), cells with lithium show decreased impedance values. Furthermore, applying mechanical stress to the cells results in a further reduction of the electrolyte resistance. These results are supported by finite element analysis (FEA) simulations

An energy conserving method for simulating heat transfer in permafrost with hybrid modeling

Rapid climate change has lead to widespread warming of land surface temperatures throughout the Arctic, thereby accelerating the thawing of perennially frozen, carbon-rich soil, most commonly referred to as permafrost. Subsurface modeling of heat and water transport plays a key role in understanding how past, present, and future changes in the climate affect the rate and extent of permafrost thaw. We propose a novel hybrid modeling approach for solving by reparameterizing it as a universal partial differential equation, where the inverse enthalpy operator is represented by a universal approximator. Such a method would alleviate one of the major numerical difficulties in the simulation of two-phase heat transport and would allow for efficient and flexible modeling of permafrost at large time scales