Publikationen

Calendar and cycle ageing affects the performance of the lithium-ion batteries from the moment they are manufactured. An important process that occurs as a part of the ageing is corrosion of the current collectors, especially prominent in the case of the aluminium substrate for the positive electrode. Generally, aluminium resists corrosion due to the formation of a non-permeable film of native aluminium oxide. Nevertheless, at certain electrochemical conditions corrosion affects the interface of the current collector. As a consequence of corrosion, the cathode materials lose electrical and mechanical contact with the current collector, leading to capacity and power fading. Therefore, a deeper understanding of this process and effective corrosion inhibition are necessary to prevent the deterioration of the battery performance. This review provides an updated critical overview of the mechanisms of aluminium corrosion, methodologies for analysing this phenomenon, and approaches for its effective mitigation. As the influence of multiple factors on the corrosion process has a central impact, the review discusses how they specifically affect the undergoing processes. Therefore, appropriate examples of important factors like electrolyte composition, thermal conditions and electrochemical parameters are presented to explain the specific mechanism of aluminium corrosion. Since corrosion inhibition is an important technological issue with a tremendous economic impact the review summarises how to achieve this by adjusting the electrochemical system and enhancing the knowledge on the safe operation of the positive electrode.

In the improved second-order equivalent circuit model (ECM) presented in this paper, the battery responses to operational (voltage and current) and non-operational (ambient temperature) parameters were taken into account to reach high accuracy to improve the estimation of state of charge (SOC) and state of health (SOH) of lithium–ion batteries (LIBs) of electric vehicles (EVs). Based on this model, the exponential-function fitting method is adopted to identify the battery parameters according to the test data collected from the experimental platform. The performance of the model is verified by comparing the experimental and simulated voltage under hybrid pulse power characterization (HPPC) test profile.

The effects of automotive-related lithium-ion module design, i.e. module stiffness and initial compression during module assembly on cell aging, swelling and pressure evolution are still largely unknown. This paper presents the results of a long-term aging study of 12 large-format automotive graphite/NMC 622 pouch cells, cycled for different module stiffnesses and initial compressions using design of experiments. Statistical analysis of mechanical and aging data revealed significant nonlinear (interaction) effects of both factors on pressure evolution, capacity loss and increase in internal resistance of the cells. Pressure dependent cell aging is observed over 1000 cycles, which was related to loss of active material at the cathode from differential voltage analysis. Post-mortem analysis confirmed a cathode active material loss via half- and full-cell measurements of harvested electrodes. Cross-section SEM micrographs revealed increasing NMC-particle cracking with higher pressure. Based on this, a fatigue-based aging model was developed to describe the capacity loss due to pressure dependent particle cracking. The presented approach enables both improved modeling of pressure dependent aging and lifetime optimized module design

Binder-free Ni/NiO microwire hybrid network with a nanostructured surface is synthesized by employing a facile and low-cost method, involving one-pot synthesis of Ni microwires, followed by their partial oxidation in air atmosphere. A combination of imaging, diffraction, thermodynamic and electrochemical methods has been applied to reveal the impact of the synthesis conditions on the energy storage performance of the Ni/NiO microwire networks. The thermal conditions for the synthesis have been optimized by means of thermogravimetric (TGA/DSC) analysis, where an appropriate temperature (T = 400 ˚C) for obtaining a low-defect NiO phase has been determined. The performed electrochemical characterisation of the materials has shown that setting a low temperature for the synthesis enables high reversible capacity and better cycling stability of the binder-free materials. When the Ni/NiO network structures are deposited by a conventional slurry-based technology, involving polymer binder and conductive additive, the high capacity and cycling stability of the anodes are preserved, independent of the temperature conditions of synthesis. Electrochemical impedance spectroscopy is applied to support the interpretation of our results.

In this work, an electrochemically formed porous Cu current collector (p-Cu) is utilized for the development of a high-performance binder-free silicon anode. Two electrolyte compositions based on sulfolane (SL) and [BMP][TFSI] ionic liquid (IL) are implemented for silicon deposition. The electrochemical experiments confirm the advantages of applying the p-Cu structure in terms of specific capacity, rate capability, and long-term cycling, where the best electrochemical properties have been observed for the Si deposited from SL electrolyte. The Si-based p-Cu anodes formed in SL display stable 2500 mAh g^-1 reversible capacity during the first 250 cycles and promising capacity retention. Compared to this result, the cycling performance of the same type of material deposited on flat Cu foil (f-Cu) showed significantly reduced capacity (1400 mAh g^-1) and inferior cycling performance. The positive effect can be attributed to the improved mechanical stability of the active material and accelerated ionic transport in the porous structure of the anode. The improved functional properties of the electrochemically deposited Si from SL electrolyte in p-Cu samples compared to those obtained in IL can be ascribed to differences in the chemical composition. While the layers deposited in SL electrolyte involve Si domains incorporated in a matrix containing C and O that offer high mechanical stability, the Si material obtained in IL is additionally influenced by N and F chemical species, resulting from active IL decomposition. These differences in the chemical surrounding of the Si domains are the primary reason for the inferior electrochemical performance of the material deposited from [BMP][TFSI] electrolyte. XPS analysis shows that the initial composition of the as deposited layers, containing a considerable amount of elemental Si, is changed after lithiation and that the electrochemical activity of the anode is governed by switching between the intermediate redox states of Si, where the carbon-oxygen matrix is also involved.