9 research outputs found
Experimentelle Nachbildung von internen KurzschlĂŒssen in Lithium-Ionen-Pouchzellen mittels prĂ€ziser Nadelpenetration
Die Lithium-Ionen-Zelle ist ein weit verbreiteter elektrischer Energiespeicher und Bestandteil
vielfÀltiger technischer Produkte. Die bekannte Sicherheitsproblematik dieser
Speichertechnologie stellt hĂ€ufig gröĂere Herausforderungen fĂŒr den praktischen Einsatz dar.
Das Verlassen der Betriebsgrenzen, die Einwirkung mechanischer KrÀfte oder interne
Produktionsfehler können aufgrund der hohen Energiedichte und der Verwendung
reaktionsfreudiger Materialien zu einem âThermischen Durchgehenâ der Zelle fĂŒhren. Der
interne Kurzschluss, also der zellinterne elektrisch leitende Kontakt beider Elektroden stellt
hierbei einen besonders relevanten und gefÀhrlichen Fehlerfall dar. Genau dieser Fehlerfall ist
derzeit jedoch noch nicht vollstĂ€ndig verstanden. Ein wesentlicher Grund hierfĂŒr ist die
fehlende Möglichkeit einen realitÀtsnahen internen Kurzschluss zuverlÀssig nachbilden zu
können. Die derzeit hÀufig angewandte Nagelpenetration, als Bestandteil vieler Normen, bildet
viele Fehlerursachen des internen Kurzschlusses, insbesondere die Dendritenbildung und die
Partikelkontamination, aufgrund geringer LokalitÀt nicht realistisch nach. Sie liefert somit nur
unzureichende Erkenntnisse zur Charakteristik eines solchen internen Kurzschlusses.
In dieser Arbeit wird eine neue Methode zur realitÀtsnahen Nachbildung von internen
KurzschlĂŒssen in Pouchzellen entwickelt und an mehr als 30 Zellen erfolgreich angewendet.
HierfĂŒr wird als Nadelpenetration eine dĂŒnne Nadel (KanĂŒle) prĂ€zise und mit einer geringen
Vorschubgeschwindigkeit (1 ”m/s) von auĂen in die Zelle eingestochen. Die Minimierung von
Ă€uĂeren StörgröĂen (z.B. eine konstante Zelltemperatur) ermöglicht es, die auftretenden
Streuungen auf den internen Kurzschluss selbst zurĂŒckzufĂŒhren und so eine fundierte
Fehlerbewertung abzuleiten.
Aus der umfangreichen Zustandscharakterisierung leitet sich bisher fehlendes Wissen zur
Entstehung, Entwicklung und möglichen Detektion des internen Kurzschlusses ab, welche fĂŒr
die praktische Anwendung hohe Relevanz besitzen und dabei helfen, das ausgehende Risiko
eines internen Kurzschlusses zu minimieren.
Die Ergebnisse zeigen, dass es in vielen FĂ€llen zu einem dynamischen Prozess der
Fehlerentwicklung kommt, welcher sich insbesondere durch wiederholte kurzzeitige
Spannungsabsenkung mit darauffolgender schneller Spannungserholung (Relaxation)
charakterisiert. Dieser dynamische Zustand kann zum spontanen âThermischen Durchgehenâ
der Zelle fĂŒhren. Oftmals bildet sich jedoch nach einigen Minuten ein konstanter hochohmiger
interner Kurzschluss aus, welcher die Zelle zunÀchst unauffÀllig aussehen lÀsst. Besonders
kritisch ist hierbei, dass fĂŒr den weiteren Betrieb eine GefĂ€hrdung durch eine irreversible
StrukturbeschÀdigung gegeben ist, die sich allerdings durch keine zerstörungsfreie
elektrochemische Messmethode zuverlÀssig nachweisen lÀsst. Hieraus leitet sich als neue
Erkenntnis die Notwendigkeit ab, den internen Kurzschluss sofort bei der ersten Entstehung
durch eine genaue, hinreichend schnelle Spannungserfassung frĂŒhzeitig zu erkennen und
daraufhin MaĂnahmen zur GefĂ€hrdungsminimierung einzuleiten.The lithium-ion cell is a widely used electrical energy storage and a key component of many technical
products. However, the well-known safety issues associated with this storage technology often pose
major challenges for practical use. Running the cell out of operating limits, the effect of mechanical
forces or internal production defects can lead to a "thermal runaway" of the cell due to the high
energy density in combination with the use of reactive materials. The internal short circuit, which
means the electrically conductive contact between the two electrodes inside the cell, is a particularly
relevant and dangerous failure mode. Exactly this type of failure is currently not yet fully understood.
One of the main reasons for this is the missing possibility to reliably reproduce a close to reality
internal short circuit. Nail penetration, which is currently often used in many standards, does not
realistically replicate many of the causes of internal short-circuits, particularly dendrite formation
and particle contamination, due to its limited locality. Therefore, this method only provides
insufficient information on the characteristics of such an internal short circuit.
In this work, a new method for the realistic replication of internal short circuits in pouch cells is
developed and successfully applied to more than 30 cells. For this method, a thin needle (cannula) is
precisely penetrated into the cell from the outside with a low speed (1 ”m/s). The minimisation of
external disturbance (e.g. a constant cell temperature) makes it possible to attribute the occurring
scattering to the internal short circuit itself and thus derive a well-founded failure evaluation.
Comprehensive state characterisation has provided the missing knowledge on the triggering,
development and possible detection of the internal short circuit, which is highly relevant for practical
applications in order to minimise the outgoing risk of an internal short circuit.
The results show that in many cases a dynamic process of fault development occurs, which is
characterised in particular by repeated short-term voltage drops followed by rapid voltage recovery
(relaxation). This dynamic state can lead to spontaneous "thermal runaway" of the cell. However, a
constant high-resistance internal short circuit often develops after a few minutes, which initially
makes the cell look inconspicuous. In this case, it is particularly critical that further operation is risky
due to irreversible structural damage, which cannot be reliably detected by any non-destructive
electrochemical measurement method. The new insight derived from this is the need to detect the
internal short circuit immediately when it first occurs by precise, sufficiently fast voltage detection
and then initiate actions to minimise the danger
Phage Therapy and Photodynamic Therapy: Low Environmental Impact Approaches to Inactivate Microorganisms in Fish Farming Plants
Owing to the increasing importance of aquaculture to compensate for the progressive worldwide reduction of natural fish and to the fact that several fish farming plants often suffer from heavy financial losses due to the development of infections caused by microbial pathogens, including multidrug resistant bacteria, more environmentally-friendly strategies to control fish infections are urgently needed to make the aquaculture industry more sustainable. The aim of this review is to briefly present the typical fish farming diseases and their threats and discuss the present state of chemotherapy to inactivate microorganisms in fish farming plants as well as to examine the new environmentally friendly approaches to control fish infection namely phage therapy and photodynamic antimicrobial therapy
Diversity of Somatic Coliphages in Coastal Regions with Different Levels of Anthropogenic Activity in SĂŁo Paulo State, Brazil âż
Bacteriophages are the most abundant and genetically diverse viruses on Earth, with complex ecology in both quantitative and qualitative terms. Somatic coliphages (SC) have been reported to be good indicators of fecal pollution in seawater. This study focused on determining the concentration of SC and their diversity by electron microscopy of seawater, plankton, and bivalve samples collected at three coastal regions in SĂŁo Paulo, Brazil. The SC counts varied from <1 to 3.4 Ă 103 PFU/100 ml in seawater (73 samples tested), from <1 to 4.7 Ă 102 PFU/g in plankton (46 samples tested), and from <1 to 2.2 Ă 101 PFU/g in bivalves (11 samples tested). In seawater samples, a relationship between the thermotolerant coliforms and Escherichia coli and SC was observed at the three regions (P = 0.0001) according to the anthropogenic activities present at each region. However, SC were found in plankton samples from three regions: Baixada Santista (17/20), Canal de SĂŁo SebastiĂŁo (6/14), and Ubatuba (3/12). In seawater samples collected from Baixada Santista, four morphotypes were observed: A1 (4.5%), B1 (50%), C1 (36.4%), and D1 (9.1%). One coliphage, Siphoviridae type T1, had the longest tail: between 939 and 995 nm. In plankton samples, Siphoviridae (65.8%), Podoviridae (15.8%), Microviridae (15.8%), and Myoviridae (2.6%) were found. In bivalves, only the morphotype B1 was observed. These SC were associated with enteric hosts: enterobacteria, E. coli, Proteus, Salmonella, and Yersinia. Baixada Santista is an area containing a high level of fecal pollution compared to those in the Canal de SĂŁo SebastiĂŁo and Ubatuba. This is the first report of coliphage diversity in seawater, plankton, and bivalve samples collected from SĂŁo Paulo coastal regions. A better characterization of SC diversity in coastal environments will help with the management and evaluation of the microbiological risks for recreation, seafood cultivation, and consumption