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The formation of lithium‐ion batteries is a time‐consuming and important process during manufacturing. During the formation, surface layers on the electrodes are formed that affect the cell performance. State‐of‐the‐art formation procedures consist of several slow current cycles as it is believed to guarantee good surface layer properties while preventing degradation processes. Herein, five different formation strategies with process times between 52.79 and 1.68 h for coin cells with a lithium reference electrode are assessed. The fastest method is based on a fast charging approach that prevents lithium‐plating. Based on a real‐time negative electrode voltage control to a threshold of 20 mV, lithium‐plating is successfully prevented while ensuring a fast formation process. The formation is finished after just one cycle and results to similar cell and electrode resistance, impedance, and capacity retention compared to the other strategies. The fast charging formation approach leads to the lowest degradation when storing the cells at 80% state of charge and 60 °C for 28 days. The results conclude that the fast charging formation method with real‐time control of the negative electrode voltage is a beneficial method as it leads to faster process times while ensuring durable cell properties. [ABSTRACT FROM AUTHOR]

In order to make electric transportation more accessible, the cost of lithium‐ion batteries must decrease. One way to achieve this is by increasing the production rates, especially in the time‐consuming steps of electrolyte filling and cell formation. Within this work, lithium‐ion pouch and hardcase cells are filled with electrolyte and the formation is started at varying wetting degrees. Data from the formation, stabilization, and life cycle testing are analyzed to determine the effect of an incomplete wetting degree on the cell quality. Additionally, postmortem analysis is performed to help understand the mechanisms induced when a cell with incomplete wetting is subjected to a current. The pouch cells demonstrate a linear capacity fade, regardless of the wetting degree, but feature strong lithium plating which becomes visible during postmortem analysis. In contrast, the hardcase cells display a clear correlation between the cell quality and the wetting degree in both the life cycle test and the postmortem analysis. It is shown that a wetting degree of 98% is required before starting the formation to avoid lithium plating in the cell. [ABSTRACT FROM AUTHOR]

The solid–electrolyte interphase (SEI) in lithium‐ion batteries is mainly built during cell formation. The SEI significantly influences safety, aging, and performance. Due to the manifold influential factors, it is time‐consuming to systematically optimize the cell formation. Herein, a novel procedure to characterize the SEI growth during the first cycle of formation with low experimental effort is introduced. Coin cells in a three‐electrode setup are tested under pseudo‐open‐circuit conditions. By evaluating the differential voltage, the capacity loss due to SEI formation during the first cycle is estimated. The identification of the SEI growth curve is carried out using various methods, which are compared in detail. The approach is exemplary applied to compare different electrolytes. It is shown that the approach can be used to parameterize SEI growth models. An analysis of these models indicates that the SEI growth can be explained by a combination of two growth mechanisms, that is, interstitial diffusion and electron tunneling, while the latter is dominant in the beginning of the formation. Further, based on the results it is suggested that the transition between these mechanisms is influenced by the electrolyte. [ABSTRACT FROM AUTHOR]

The results of the thermal-electric simulations of the coated conductors with systematic variation of the buffer layers are explained. These simulations find a large number of applications in the filed of electric power.

According to the relevant IEC standards vacuum circuit-breakers have to meet various needs, e.g. the interruption capability, making operations, and dielectric strength. Besides the interruption of short-circuit currents, switching of capacitive currents causes high stress of the circuit-breaker. Switching of capacitor banks, overhead lines, or cables leads to very small currents in comparison with short circuit currents. After current interruption the circuit-breaker must withstand twice the peak value of the system voltage. Furthermore, restrikes can lead to voltage multiplication. This conjunction of relatively small breaking currents with high voltage stress must be considered in detail. This work introduces a test arrangement for combined tests of making operation, current interruption, and dielectric stress of a vacuum gap under capacitive switching condition. A test vessel permits investigations of various contact materials and designs. It is connected to a synthetic test circuit which provides the appropriate test currents and capacitive voltage. During the test sequence the contacts are stressed by inrush-currents up to 4.5 kA peak, followed by a breaking operation at 500 A peak and a subsequent capacitive voltage up to 50 kV peak. Both the appearance of pre-ignitions at contact closing and the behavior under capacitive voltage stress after breaking are indications of the contact surface conditions. Index Terms--Capacitive switching, inrush-current, pre-arcing, restrike, welding force, vacuum circuit-breaker.