@misc{LangnerSieberAcker, author = {Langner, Thomas and Sieber, Tim and Acker, J{\"o}rg}, title = {Studies on the deposition of copper in lithium-ion batteries during the deep discharge process}, series = {Scientific Reports}, journal = {Scientific Reports}, number = {11}, issn = {2045-2322}, doi = {10.1038/s41598-021-85575-x}, abstract = {End-of-life lithium-ion batteries represent an important secondary raw material source for nickel, cobalt, manganese and lithium compounds in order to obtain starting materials for the production of new cathode material. Each process step in recycling must be performed in such a way contamination products on the cathode material are avoided or reduced. This paper is dedicated to the first step of each recycling process, the deep discharge of lithium-ion batteries, as a prerequisite for the safe opening and disassembling. If pouch cells with different states of charge are connected in series and deep-discharged together, copper deposition occurs preferably in the cell with the lower charge capacity. The current forced through the cell with a low charge capacity leads, after lithium depletion in the anode and the collapse of the solid-electrolyte-interphase (SEI) to a polarity reversal in which the copper collector of the anode is dissolved and copper is deposited on the cathode surface. Based on measurements of the temperature, voltage drop and copper concentration in the electrolyte at the cell with the originally lower charge capacity, the point of dissolution and incipient deposition of copper could be identified and a model of the processes during deep discharge could be developed.}, language = {en} } @misc{SchoenekerlAcker, author = {Sch{\"o}nekerl, Stefan and Acker, J{\"o}rg}, title = {The Role of the Molecular Hydrogen Formation in the Process of Metal Ion Reduction on Multi-crystalline Silicon in a Hydrofluoric Acid Matrix}, series = {Nanomaterials}, volume = {11}, journal = {Nanomaterials}, number = {4}, issn = {2079-4991}, doi = {10.3390/nano11040982}, abstract = {Metal deposition on silicon in hydrofluoric acid (HF) solutions is a well-established process for the surface patterning of silicon. The reactions behind this process, especially the formation or the absence of molecular hydrogen (H2) are controversially discussed in the literature. In this study, several batch experiments with Ag+, Cu2+, AuCl4- and PtCl62- in HF matrix and multi-crystalline silicon were performed. The stoichiometric amounts of the metal depositions, the silicon dissolution and the molecular hydrogen formation were determined analytically. Based on these data and theoretical considerations of the valence transfer, four reasons for the formation of H2 could be identified. Firstly, H2 is generated in a consecutive reaction after a monovalent hole transfer (h+) to a Si-Si bond. Secondly, H2 is produced as a result of a monovalent hole transfer to the Si-H bonds. Thirdly, H2 occurs if Si-Si back bonds of the hydrogen-terminated silicon are attacked by Cu2+ reduction resulting in the intermediate species HSiF3, which is further degraded to H2 and SiF62-. The fourth H2-forming reaction is the reduction of oxonium ions (H3O+) on the silver/, copper/ and gold/silicon contacts via monovalent hole transfer to silicon. In the case of (cumulative) even-numbered valence transfers to silicon, no H2 is produced. The formation of H2 also fails to appear if the equilibrium potential of the 2H3O+/H2 half-cell does not reach the energetic level of the valence bands of the bulk or hydrogen-terminated silicon. Non-hydrogen-forming reactions in silver, copper and gold deposition always occur with at least one H2-forming process. The PtCl62- reduction to Pt proceeds exclusively via even-numbered valence transfers to silicon. This also applies to the reaction of H3O+ at the platinum/silicon contact. Consequently, no H2 is formed during platinum deposition.}, language = {en} } @misc{HeroldAcker, author = {Herold, Steven and Acker, J{\"o}rg}, title = {Strain enhanced chemical oxidation of silicon wafer}, series = {Materials Science in Semiconductor Processing}, volume = {135}, journal = {Materials Science in Semiconductor Processing}, issn = {1369-8001}, doi = {10.1016/j.mssp.2021.106105}, pages = {6}, abstract = {The effect of strain through mechanical processing on the formation of silicon dioxide, one of the most important chemical reactions for the fabrication of semiconductors, biosensors or photovoltaics, has not yet been studied in detail. In this study, we use the surface modification of silicon by alkylsilanes and Raman microscopy techniques to visualise where different oxidants react preferentially on mechanically processed surfaces. We found that HNO3, H2O2 as well as H2SiF6 only oxidise tensile strained silicon areas and do not oxidise unstrained silicon even after long reaction times. Furthermore, a comparison between H2O2 and HNO3 in the presence of HF was also carried out and it was shown that H2O2/HF only etches away tensile strained areas, whereas HNO3/HF initially attacks the tensile strained areas but also forms NOx species. These NOx species then lead to a strain unselective, geometry-based etching mechanism. These results lead to new possibilities in strain lithography,high-precision etching, as well as in the structuring of biosensors and localisation of surface modifications.}, language = {en} } @misc{RietigGrafeAcker, author = {Rietig, Anja and Grafe, Hans-Joachim and Acker, J{\"o}rg}, title = {New insights into boron species in acidic digestion solutions of boron-doped silicon}, series = {Journal of Analytical Atomic Spectrometry}, volume = {36}, journal = {Journal of Analytical Atomic Spectrometry}, number = {11}, issn = {1364-5544}, pages = {2492 -- 2500}, abstract = {The exact and precise determination of the boron concentration in silicon is still a challenge. A systematic investigation dealing with the digestions of 60 silicon samples with HF-HNO3 and subsequent boron determination by ICP-OES revealed that the concentration found could be up to 60\% lower than the actual boron concentration depending on the composition of the sample solution. As the original boron-silicon compound that was identified was colloidally precipitated in the presence of an excess of hydrofluoric acid and then partially retained by filtration or by the sample introduction system, systematic lower boron concentrations were determined. In acidic, HF-free digestion solutions, this compound existed in a soluble form parallel to the borate in B(OH)4-. In an excess of hydrofluoric acid, the compound was converted into the colloidal form and, in parallel, B(OH)4- was converted to tetrafluoroborate, BF4-. For the composition of the colloidal compound, a molar ratio of boron to silicon of 1 : 4 could be determined. 11B-ss-NMR analysis revealed a tetrahedral geometry compound with a central boron atom surrounded by four silicon atoms. It is assumed that a soluble form with four -Si(OH)3 groups was present in the hydrofluoric acid-free solutions, while an insoluble form with four -SiF3 groups was present in HF-containing solution.}, language = {en} } @misc{RietigLangnerAcker, author = {Rietig, Anja and Langner, Thomas and Acker, J{\"o}rg}, title = {Comprehensive stoichiometric studies on the reaction of silicon in HF/HNO3 and HF/HNO3/H2SiF6 mixtures}, series = {Physical chemistry, chemical physics}, volume = {24}, journal = {Physical chemistry, chemical physics}, number = {5}, issn = {1463-9076}, doi = {10.1039/d1cp05418j}, pages = {3094 -- 3108}, language = {en} } @misc{RietigGrafeAcker, author = {Rietig, Anja and Grafe, Hans-Joachim and Acker, J{\"o}rg}, title = {Understanding the Reasons for Erroneous Determinations of Boron in Silicon following Wet Chemical Digestion in HF/HNO3}, series = {Proceedings of the Silicon for the Chemical \& Solar Industry XVI}, journal = {Proceedings of the Silicon for the Chemical \& Solar Industry XVI}, isbn = {978-82-692919-0-2}, doi = {10.2139/ssrn.4123058}, pages = {14}, language = {de} } @incollection{RietigAcker, author = {Rietig, Anja and Acker, J{\"o}rg}, title = {Ressourcensicherung durch Recycling von Sekund{\"a}rrohstoffen}, series = {Systemwissen f{\"u}r die vernetzte Energie- und Mobilit{\"a}tswende}, booktitle = {Systemwissen f{\"u}r die vernetzte Energie- und Mobilit{\"a}tswende}, edition = {2. Auflage}, publisher = {Vereinigung f{\"u}r Betriebliche Bildungsforschung e.V.}, address = {Berlin}, isbn = {978-3-9816861-8-0}, pages = {141 -- 152}, language = {de} } @misc{ErnstUebelBrendleretal., author = {Ernst, Owen C. and Uebel, David and Brendler, Roman and Kraushaar, Konstantin and Steudel, Max and Acker, J{\"o}rg and Kroke, Edwin}, title = {Silicon-28-Tetrafluoride as an educt of Isotope-Engineered Silicon Compounds and Bulk Materials for Quantum Systems}, series = {Molecules}, volume = {29}, journal = {Molecules}, number = {17}, publisher = {MDPI AG}, issn = {1420-3049}, doi = {10.3390/molecules29174222}, pages = {31}, abstract = {This review provides a summary of the existing literature on a crucial raw material for the production of isotopically pure semiconductors, which are essential for the development of second-generation quantum systems. Silicon-28-tetrafluoride (28SiF4) is used as an educt for several isotope-engineered chemicals, such as silane-28 (28SiH4) and silicon-28-trichloride (28SiHCl3), which are needed in the pursuit of various quantum technologies. We are exploring the entire chain from the synthesis of 28SiF4 to quantum applications. This includes the chemical properties of SiF4, isotopic enrichment, conversion to silanes, conversion to bulk 28Si and thin films, the physical properties of 28Si (spin neutrality, thermal conductivity, optical properties), and the applications in quantum computing, photonics, and quantum sensing techniques.}, language = {en} } @misc{DommaschkSieberAcker, author = {Dommaschk, Maria and Sieber, Tim and Acker, J{\"o}rg}, title = {Lithium-ion batteries: direct solid sampling for characterisation of black mass recyclates using graphite furnace atomic absorption spectrometry}, series = {Journal of Analytical Atomic Spectrometry}, volume = {39}, journal = {Journal of Analytical Atomic Spectrometry}, number = {10}, publisher = {Royal Society of Chemistry (RSC)}, issn = {0267-9477}, doi = {10.1039/D4JA00207E}, pages = {2522 -- 2531}, abstract = {A straightforward, efficient and robust method was developed in this study to analyse the metal content of complex recyclates from cathode coatings (LiNixMnyCo1-x-yO2) recovered from spent lithium-ion batteries.}, language = {en} } @misc{LangnerSieberRietigetal., author = {Langner, Thomas and Sieber, Tim and Rietig, Anja and Merk, Virginia and Pfeiffer, Lutz and Acker, J{\"o}rg}, title = {A Phenomenological and Quantitative View on the Degradation of Positive Electrodes from Spent Lithium-ion Batteries in Humid Atmosphere}, series = {Scientific Reports}, volume = {13}, journal = {Scientific Reports}, issn = {2045-2322}, doi = {10.1038/s41598-023-32688-0}, abstract = {The present study deals with the phenomenological observation of the corrosion of the positive electrode foil of lithium-ion batteries containing LiNi0.6Co0.2Mn0.2O2 (NMC) as cathode material. Due to the presence of moisture, localized water accumulation is formed on the NMC surface. The water absorbed by the electrolyte reacts with the NMC under Li+/H+ exchange and the resulting pH increase leads to dissolution of the carrier foil and characteristic salt-like blooms on the NMC surface. With the increase in the relative area occupied by the holes in the aluminum foil per time, a sufficiently suitable parameter was found with which to quantitatively determine the extent of corrosion. The degree of degradation depends on time and ambient humidity. It was shown that functional recycling with the water jet method is no longer applicable for degraded foils, since the mechanical stability of the foils decreases as corrosion progresses. Lithium, aluminum, sulfur and oxygen were detected in the blooms using SEM-EDX and Laser-Induced-Breakdown-Spectroscopy (LIBS). The underlying NMC layer was found to contain mainly aluminum and significantly lower lithium content than the non-degraded material. SEM and Raman microscopy analyses also showed that the active material is also locally degraded and therefore no longer suitable for functional recycling.}, language = {en} } @misc{RietigLangnerAcker, author = {Rietig, Anja and Langner, Thomas and Acker, J{\"o}rg}, title = {About determining reliable etching rates and the role of temperature in kinetic experiments on acidic wet chemical etching of silicon}, series = {Physical Chemistry Chemical Physics}, volume = {25}, journal = {Physical Chemistry Chemical Physics}, number = {16}, issn = {1463-9084}, doi = {10.1039/D2CP05837E}, pages = {11387 -- 11397}, language = {en} } @misc{RietigAcker, author = {Rietig, Anja and Acker, J{\"o}rg}, title = {Kinetic studies on acidic wet chemical etching of silicon in binary and ternary mixtures of HF, HNO3 and H2SiF6}, series = {Physical Chemistry Chemical Physics}, volume = {25}, journal = {Physical Chemistry Chemical Physics}, number = {38}, issn = {1463-9084}, doi = {10.1039/d3cp03188h}, pages = {26245 -- 26257}, language = {en} }