This work is an overview of various equivalent circuits (ECs) containing various degrees of detail. The ECs are evaluated in terms of model accuracy and parameterization time for the systematic assignment of an equivalent circuit to application fields. For this purpose, impedance spectra were measured using electrochemical impedance spectroscopy at different states of charge, health and temperatures. Then the parameters of the EC were extracted using the least‐squares method and the Levenberg–Marquardt algorithm. After comparing the simulated to the measured impedance spectrum, a review and assignment of equivalent circuits for potential applications is given. Simple equivalent circuits with a series resistor and a maximum of two resistance–capacitance (RC) elements are ideal for simulations with lower dynamics. Equivalent circuits with up to five RC elements or even a constant‐phase element (CPE) are promising for simulating highly dynamic processes. By using RCPE elements the impedance spectrum can be modeled with the highest accuracy, which is why this type of model should be used for diagnostic purposes.

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In lithium-ion battery production, the formation of the solid electrolyte interphase (SEI) is one of the longest process steps. [1] The formation process needs to be better understood and significantly shortened to produce cheaper batteries. [2] The electrolyte reduction during the first charging forms the SEI at the negative electrodes. [3,4] Besides that, a SEI is also formed at the positive electrode (PE-SEI) during the first cycles. [5,6] Especially, the SEI has a substantial impact on the battery's performance and aging by limiting further reductive decomposition of the electrolyte. [7] The SEI material compositions and electrochemical properties have been reviewed extensively. [7][8][9][10] State-of-the-art formation procedures in the industry last up to multiple days [1] and consist of several charge and discharge cycles. [11] Long periods at high state of charges (SOCs) increase the reduction rate at the negative electrode (NE) and the oxidation rate at the positive electrode (PE) that lead to the formation of the SEI and PE-SEI, respectively. [12] Higher SOCs lead to lower NE potentials which exponentially increase the SEI growth rate whereas increased C-rates have a linear relation. [13] Similar results for accelerated SEI growth at low NE potentials were simulated by a model based on differential voltage analysis. [14] Formation strategies with multiple subcycles at high SOCs are recommended in the literature as it was found to guarantee stable surface layer properties that resulted in good cell performance while ensuring shorter formation times, e.g., 21, [15] 14, [1] and 13 h. [16] Increased ambient temperatures and external pressure enabled a formation time about 3 h. [17] Variable fast charging current rates based on an electrode equivalent circuit model even resulted in a formation time below 1 h without negative impacts on cell performance compared to longer reference formations. [18] However, comparing formation times between different cell configurations is complicated, as different materials (e.g., electrolyte or active material) or properties (e.g., coating thickness or porosity) influence the maximum applicable current. [19] Charging currents that lead to negative NE potentials may form lithium-plating on the NE's surface [20][21][22] as lithium ions react to metallic lithium depositions instead of intercalating into the NE. [23,24] In general, lithium-plating is an undesired sidereaction which comes along with capacity loss and may result in an internal short circuit due to dendrite formation. [25][26][27] Just a part of the plated lithium is reversible and reacts back to lithium ions during discharging, which is called lithiumstripping. [28] Irreversible lithium-plating can be proved by cell disassembly and optical investigation of the NE. Therefore, it is recommended to discharge the cell to 0% SOC followed by a

Fast charging of lithium-ion batteries is often related to accelerated cell degradation due to lithium-plating on the negative electrode. In this contribution, an advanced electrode equivalent circuit model is used in order to simulate fast-charging strategies without lithium-plating. A novel parameterization approach based on 3-electrode cell measurements is developed, which enables precise simulation fidelity. An optimized fast-charging strategy without evoking lithium-plating was simulated that lasted about 29 min for a 0–80% state of charge. This variable current strategy was compared in experiments to a conventional constant-current–constant-voltage fast-charging strategy that lasted 20 min. The experiments showed that the optimized strategy prevented lithium-plating and led to a 2% capacity fade every 100 fast-charging cycles. In contrast, the conventional strategy led to lithium-plating, about 20% capacity fade after 100 fast-charging cycles and the fast-charging duration extended from 20 min to over 30 min due to increased cell resistances. The duration of the optimized fast charging was constant at 29 min, even after 300 cycles. The developed methods are suitable to be applied for any given lithium-ion battery configuration in order to determine the maximum fast-charging capability while ensuring safe and durable cycling conditions.