@misc{AckerLangnerMeineletal., author = {Acker, J{\"o}rg and Langner, Thomas and Meinel, Birgit and Sieber, Tim}, title = {Saw Damage as an Etch Mask for the Acidic Texturization of Multicrystalline Silicon Wafers}, series = {Materials Science in Semiconductor Processing}, volume = {74}, journal = {Materials Science in Semiconductor Processing}, issn = {1369-8001}, doi = {10.1016/j.mssp.2017.09.039}, pages = {238 -- 248}, abstract = {The surface of multicrystalline silicon solar cells are etched by mixtures of HF, HNO3 and H2SiF6 in order to remove saw damage caused by wafer slicing, as well as to create a water surface topography that provides a low reflectance for incident light, otherwise known as the texture. Topographically analyzing wafer surfaces before and after etching has revealed that the saw damage controls the texturized wafer surface's final topography.The first key factor is the dimension and magnitude of the plastic stress field introduced by indenting SiC grains into the wafer surface during the wafering process. The second key factor is that lattice-stressed silicon is etched at a higher rate than unstressed bulk silicon. At the wire entrance, side sharp and large SiC grains create the deepest indention pits, and therefore the deepest of the water surface stress fields. The lattice-disturbed silicon inside these pits is etched at a higher rate compared to the pit's side walls, which are uniformly attacked across the wafer area. Consequentially, existing pits deepen, and these areas generate the wafer's lowest reflectivity. At the wire exit side, a higher number of smaller and rounder SiC particles indent the surface and create more numerous and shallower indention pits compared to the wire entrance side. The resulting stress field is less deep, so less silicon is removed from inside of these pits during etching compared to the wire entrance side. This yields to a wafer surface region consisting of shallowly etched pits and higher reflectance. It is concluded that the saw damage acts like an etch mask in the texturization of multicrystalline silicon wafers.}, language = {en} } @misc{SieberDuckeRietigetal., author = {Sieber, Tim and Ducke, Jana and Rietig, Anja and Langner, Thomas and Acker, J{\"o}rg}, title = {Recovery of Li(Ni0.33Mn0.33Co0.33)O2 from Lithium-Ion Battery Cathodes: Aspects of Degradation}, series = {Nanomaterials}, volume = {9}, journal = {Nanomaterials}, number = {2}, issn = {2079-4991}, doi = {10.3390/nano9020246}, pages = {246 -- 259}, abstract = {Nickel-manganese-cobalt oxides, with LiNi0.33Mn0.33Co0.33O2 (NMC) as the most prominent compound, are state-of-the-art cathode materials for lithium-ion batteries in electric vehicles. The growing market for electro mobility has led to a growing global demand for Li, Co, Ni, and Mn, making spent lithium-ion batteries a valuable secondary resource. Going forward, energy- and resource-inefficient pyrometallurgical and hydrometallurgical recycling strategies must be avoided. We presented an approach to recover NMC particles from spent lithium-ion battery cathodes while preserving their chemical and morphological properties, with a minimal use of chemicals. The key task was the separation of the cathode coating layer consisting of NMC, an organic binder, and carbon black, from the Al substrate foil. This can be performed in water under strong agitation to support the slow detachment process. However, the contact of the NMC cathode with water leads to a release of Li+ ions and a fast increase in the pH. Unwanted side reactions may occur as the Al substrate foil starts to dissolve and Al(OH)3 precipitates on the NMC. These side reactions are avoided using pH-adjusted solutions with sufficiently high buffer capacities to separate the coating layer from the Al substrate, without precipitations and without degradation of the NMC particles.}, language = {en} } @misc{SieberRietigDuckeetal., author = {Sieber, Tim and Rietig, Anja and Ducke, Jana and Acker, J{\"o}rg}, title = {Direkte Feststoffanalyse von Hauptkomponenten in Kathodenmaterialien von Lithiumbatterien mittels HRCS-GF-AAS}, series = {Colloquium Analytische Atomspektroskopie - CANAS 2019, Book of Abstracts}, volume = {2019}, journal = {Colloquium Analytische Atomspektroskopie - CANAS 2019, Book of Abstracts}, editor = {Vogt, Carla}, edition = {1. Auflage}, publisher = {TU Bergakademie Freiberg}, address = {Freiberg}, pages = {S1/4}, abstract = {Zur Bestimmung der metallischen Hauptkomponenten in Lithium-Batterie-Kathodenmaterialien ist der nasschemische Aufschluss mit anschließender ICP-OES-Analyse oft das Mittel der Wahl. Da dieses Verfahren jedoch recht zeitaufwendig ist und den Einsatz starker S{\"a}uren erfordert, wurde eine Methode zur direkten Feststoffanalyse mittels HRCS-GF-AAS (high resolution continuum source graphit furnace atom absorption spectrometry) nach dem STPF-Konzept (stabilized temperature platform furnace) entwickelt. Die hohen Analytkonzentrationen erfordern dabei die Messung auf den vergleichsweise wenig intensiven Linien Li = 323,2657 nm, Ni = 294,3912 nm, Mn = 321,6945 nm und Co= 243,5823 nm. Zus{\"a}tzlich wird das Probenmaterial einer Feststoffverd{\"u}nnung mit matrixverwandten Komponenten unterzogen. Die Verd{\"u}nnung senkt zum einen die Konzentration und die Gefahr der Verschleppung der Analyten und beg{\"u}nstigt zum anderen die Freigabe des Analyten aus der Probenmatrix. Durch Aufnahme von Extinktions-Zeit-Verl{\"a}ufen im Temperaturbereich von 200 - 2600 °C konnten die Freisetzungstemperaturen f{\"u}r jeden Analyten bestimmt werden. Nach anschließenden Optimierungen der Pyrolyse- und Atomisierungstemperaturen wurde mithilfe der Einzeloxide f{\"u}r jeden Analyten die Linearit{\"a}t des Messsignals gepr{\"u}ft und der Arbeitsbereich festgelegt. Durch Vermessung von variierenden Oxidmischungen und Mischoxiden, sowie Zusatz m{\"o}glicher weiterer Interferenten, wie dem Bindermaterial PVDF wurden Spezifit{\"a}t, Selektivit{\"a}t und Robustheit der Methode {\"u}berpr{\"u}ft. Abschließend erfolgte anhand realer Proben (Recyclinggut aus Lithium-Batterie-Kathoden) ein Vergleich zwischen den Ergebnissen der direkten Feststoffanalyse mittels HRCS-GF-AAS und dem bereits etablierten Verfahren der ICP-OES Analyse nach nasschemischem Aufschluss. Nach umfangreicher Methodenentwicklung kann ein Verfahren der direkten Feststoffanalyse von Recylinggut aus Kathodenmaterialien von Lithium-Ionen-Batterien mittels HRCS-GF-AAS bereitgestellt werden, das eine schnelle und pr{\"a}zise Analyse der Hauptkomponenten Li, Ni, Mn und Co erlaubt.}, language = {de} } @inproceedings{LangnerSieberAcker, author = {Langner, Thomas and Sieber, Tim and Acker, J{\"o}rg}, title = {Lattice strain controls the etching of solar wafer surfaces}, series = {9th European Silicon Days, 9-12 September 2018, Saarbr{\"u}cken, Germany, Book of abstracts}, booktitle = {9th European Silicon Days, 9-12 September 2018, Saarbr{\"u}cken, Germany, Book of abstracts}, editor = {Scheschkewitz, David and Kickelbick, Guido}, publisher = {Universit{\"a}t des Saarlandes}, address = {Saarbr{\"u}cken}, pages = {S. 201}, abstract = {Multi-wire sawing using an abrasive SiC slurry or diamond wires constitutes the main slicing techniques for multi- and monocrystalline silicon crystals in photovoltaics. The massive mechanical load during the sawing process creates a wafer surface layer characterized by lattice defects, pits, fractures, rifts, cracks, amorphous Si and even some high-pressure Si modifications, otherwise known as saw damage.[1] This highly defect-rich surface causes the rapid recombination of electron-hole pairs, requiring that it be removed by etching in order to manufacture solar cells and to generate a surface morphology having a low reflectivity which directly affects the solar cell's efficiency. However, etching of the saw damage features of a heterogeneous and laterally unevenly distributed etch attack and a significantly higher etch rate compared to the underlying bulk silicon.[2,3] The present study is focused on the question of how mechanically introduced lattice strain in single-crystalline silicon alters the chemical reactivity of the silicon atoms affected by the strain field on a microscopic length scale. The magnitude and local distribution of lattice strain were extracted from confocal Raman microscopy measurements according to Ref. 4. One of the parameters used to describe the reactivity of silicon is the local etch rate, which was derived from the local removal before and after etching by confocal microscopy. Wet-chemical etching was performed with HF-HNO3-H2SiF6 acid mixtures of different concentrations. It was found, that the reactivity of silicon increased linearly with the magnitude of lattice strain. In particular, an increase in tensile strain led to a higher increase in reactivity compared to the increase observed with growing compressive strain. The second decisive parameter is the reactivity of the etch mixture. Diluted acid mixtures with a low reactivity attack only the highest strained Si, whereas more concentrated and therefore more reactive acid mixtures are able to attack even slightly strained Si. Side effects, such as the behavior of amorphous or nanocrystalline Si and the generation of highly reactive intermediary species while etching, are discussed.}, language = {en} } @inproceedings{SieberDuckeAcker, author = {Sieber, Tim and Ducke, Jana and Acker, J{\"o}rg}, title = {Degradation of Li(Ni₀.₃₃MnCo₀.₃₃)O₂ in the recycling of lithium battery cathodes}, series = {6th Dresden Nanoanalysis Symposium - Abstract Booklet}, booktitle = {6th Dresden Nanoanalysis Symposium - Abstract Booklet}, editor = {Zschech, Ehrenfried}, publisher = {Fraunhofer IKTS Dresden}, address = {Dresden}, pages = {S. 52}, abstract = {The compound Li(Ni₀.₃₃Mn₀.₃₃Co₀.₃₃)O₂(NMC) is the state-of-the-art lithium-ion battery cathode material. Due to the increasing demand NMC is of crucial economically importance for the worldwide emerging market of electromobility. Recycling of end-of-life lithium-ion batteries to recover NMC, in particular of batteries from automotive vehicles, is one future strategy to save costs and to become more independent from the supply of the essential elements Co and Mn. Several concepts for NMC recycling from lithium-ion batteries are based on wet-chemical process steps, in particular, to separate the NMC containing cathode layer from the underlying metal foil. However, NMC is very sensitive against the attack by water and reagents that are added to promote the separation process. The present study deals with the wet-chemical recycling of NMC using aqueous reagent solutions in a under varying process conditions. The recovered NMC samples are characterized in order to study the ongoing degradation at the surface of the NMC particles. In particular, two major degradation pathways are identified: (i) a preferential loss of lithium and nickel and (ii) the formation of passivation layers due to unwanted side reactions. DRIFT measurements are performed to study the NMC surface species after the recovery processes. SEM/EDX mappings are used to detect changes in the chemical composition in the surface region of the chemically treated NMC particles. Finally, a detailed study of the changes in the chemical state at the NMC particle surface is done by Raman microscopy by means of the deconvolution of the recorded spectra into their A1G component (representing the metal-oxide phonons) and into the Eg component (representing the oxide-metal-oxide phonons). As result of this study, the consequences of different wet-chemical process conditions on the quality of the recovered NMC material are discussed.}, 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{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{KlepelUtgenanntVormelchertetal., author = {Klepel, Olaf and Utgenannt, Stephan and Vormelchert, Carolin and K{\"o}nig, Mark and Meißner, Andr{\´e} and Hansen, Felix and B{\"o}lte, Jens-Henning Ingo Holger and Sieber, Tim and Heinemann, Robert and Bron, Michael and Rokicinska, Anna and Jarczewski, Sebastian and Kustrowski, Piotr}, title = {Redox catalysts based on amorphous porous carbons}, series = {Microporous Mesoporous Materials}, volume = {323}, journal = {Microporous Mesoporous Materials}, issn = {1387-1811}, doi = {10.1016/j.micromeso.2021.111257}, pages = {12}, language = {en} } @misc{AckerSieberLangneretal., author = {Acker, J{\"o}rg and Sieber, Tim and Langner, Thomas and Herold, Steven}, title = {The impact of lattice strain on the reactivity of silicon}, series = {Silicon for the Chemical and Solar Industry XIV}, journal = {Silicon for the Chemical and Solar Industry XIV}, editor = {Andresen, Birger and Nygaard, Lars and Rong, Harry and Tangstad, Merete and Tveit, Halvard and Page, Ingrid Gamst}, publisher = {The Norwegian University of Science and Technology}, address = {Trondheim}, pages = {11 -- 20}, abstract = {The present study is focused on the question of how lattice strain mechanically introduced into silicon alters the chemical reactivity of the silicon atoms that are affected by the strain field on a microscopic length scale. The magnitude and local distribution of lattice strain are extracted from confocal Raman microscopy measurements. The reactivity of Si is expressed by the etch rate of Si after treatment with HF-HNO3-H2SiF6 mixtures. Then, the local etch rate is calculated from the local etch depth as determined by confocal microscopy. It has been found that tensile strain leads to the highest enhancement of the etch rate, followed by a compressive strain increase in the etch rate.}, language = {en} } @misc{MeissnerSieberAcker, author = {Meißner, Andr{\´e} and Sieber, Tim and Acker, J{\"o}rg}, title = {Lattice strain and phase transformations in silicon introduced by the precipitation of Cu3Si}, series = {Silicon for the Chemical and Solar Industry XV}, journal = {Silicon for the Chemical and Solar Industry XV}, editor = {Andresen, Birger and Rong, Harry and Tangstad, Merete and Tveit, Halvard and Page, Ingrid}, publisher = {The Norwegian University of Science and Technology}, address = {Trondheim}, isbn = {978-82-997357-9-7}, pages = {47 -- 56}, abstract = {The reaction of Si with CuCl was studied by a combination of Raman microscopy, confocal microscopy and SEM-EDX. Two reaction pathways were observed to proceed at the same time. The first one is a solid state reaction between Si and Cu or CuCl that leads to a massive nucleation of Cu3Si exactly at the interfacial contacts between CuCl and Si. This study shows how the presence of the Cu3Si phase can be clearly identified and distinguished from areas simply covered with copper by means of Raman microscopic measurements. The second reaction pathway identified proceeds via a short-range gas phase transport of CuCl at low temperatures. The immediate reaction of the transported CuCl to the Si surface causes the massive spread of Cu in the close neighborhood around the CuCl source particles, however, without a nucleation of Cu3Si. The nucleation of Cu3Si precipitates and the short-range transport of CuCl have a tremendous impact on the underlying Si matrix. Tensile- and compressive-strained Si are generated in the immediate vicinity of the precipitates and at their interface to the surrounding silicon. Indications of high-pressure modifications of Si were found. Those areas of the Si surface which are affected by the short-range transport of CuCl and covered with low concentrations of copper exhibit a significant tensile strain. As recently shown, tensile and compressive strain in Si have a significant impact on the reactivity of Si. It might be assumed that Cu3Si-induced lattice strain in Si affects the reactivity of Si in the Direct Reactions in a similar matter.}, language = {en} } @misc{AckerSieberDuckeetal., author = {Acker, J{\"o}rg and Sieber, Tim and Ducke, Jana and Langner, Thomas and Rietig, Anja}, title = {Degradation effects on Li(Ni0.33Mn0.33Co0.33)O2 in the recovery of lithium battery cathodes}, series = {Advanced Lithium Batteries for Automobile Applications - ABAA 12, Book of Abstracts}, journal = {Advanced Lithium Batteries for Automobile Applications - ABAA 12, Book of Abstracts}, edition = {1. Auflage}, publisher = {Zentrum f{\"u}r Sonnenenergie- und Wasserstoff-Forschung Baden-W{\"u}rttemberg}, address = {Ulm}, pages = {28}, abstract = {The compound Li(Ni0.33Mn0.33Co0.33)O2 (NMC) is the state-of-the-art lithium-ion battery cathode material. Due to the increasing demand NMC is of crucial economically importance for the worldwide emerging market of electromobility. Recycling of end-of-life lithium-ion batteries to recover NMC, in particular of batteries from automotive vehicles, is one future strategy to save costs and to become more independent from the supply of the essential elements Co and Mn. Several concepts for NMC recycling from lithium-ion batteries are based on wet-chemical process steps, in particular, to separate the NMC containing cathode layer from the underlying metal foil. However, NMC is very sensitive against the attack by water and reagents that are added to promote the separation process. The present study deals with the wet-chemical recycling of NMC using aqueous reagent solutions in a under varying process conditions. The recovered NMC samples are characterized in order to study the ongoing degradation at the surface of the NMC particles. In particular, two major degradation pathways are identified: (i) a preferential loss of lithium and nickel and (ii) the formation of passivation layers due to unwanted side reactions. DRIFT measurements are performed to study the NMC surface species after the recovery processes. SEM/EDX mappings are used to detect changes in the chemical composition in the surface region of the chemically treated NMC particles. Finally, a detailed study of the changes in the chemical state at the NMC particle surface is done by Raman microscopy by means of the deconvolution of the recorded spectra into their A1G component (representing the metal-oxide phonons) and into the Eg component (representing the oxide-metal-oxide phonons). As result of this study, the consequences of different wet-chemical process conditions on the quality of the recovered NMC material are discussed.}, language = {en} } @misc{LangnerSieberAcker, author = {Langner, Thomas and Sieber, Tim and Acker, J{\"o}rg}, title = {Etching Shapes the Topography of Silicon Wafers: Lattice-Strain Enhanced Chemical Reactivity of Silicon for Efficient Solar Cells}, series = {ACS Applied Nano Materials}, volume = {1}, journal = {ACS Applied Nano Materials}, number = {8}, doi = {10.1021/acsanm.8b00906}, pages = {4135 -- 4144}, abstract = {Multiwire sawing of silicon (Si) bricks is the state-of-the-art technology to produce multicrystalline Si solar wafers. The massive indentation of the abrasive Si carbide or diamond particles used leads to a heavily mechanically damaged layer on the wafer surface. Etching the surface layer using typical HF-HNO3-H2SiF6 acid mixtures reveals an unevenly distributed etch attack with etch rates several times higher than known for bulk Si etching. The present study follows the hypothesis that lattice strain, introduced by the sawing process, leads to an increase of the etch rate and determines the topography of the etched wafer, the so-called texture. Scratches were introduced into single crystalline Si surfaces in model experiments, and the magnitude and local distribution of lattice strain were extracted from confocal Raman microscopy measurements. The essential parameter used to describe the local reactivity of Si is the local etch rate, which was derived by confocal microscopy from the local height before and after etching. It was found that the reactivity of Si increases linearly with the magnitude of lattice strain. An increase in tensile strain raises the reactivity of Si significantly higher than an increase of compressive strain. The second decisive parameter is the reactivity of the etch mixture that correlates with the total concentration of the acid mixtures. Diluted acid mixtures with a low reactivity attack only the highest strained Si, whereas more concentrated and, therefore, more reactive acid mixtures can attack even slightly strained Si. Side effects, such as the behavior of amorphous or nanocrystalline Si and the generation of highly reactive intermediary species while etching, are discussed. The presence of unevenly distributed lattice strain of different magnitude and the resulting unevenly distributed reactivity of Si explain the features of a heterogeneous etch attack observed and the resulting topography of the etched wafer surface.}, language = {en} }