Lithium metal deposition in microstructures of Li Ion batteries

Kurzfassung

Lithium-metal deposition is one of the important degradation mechanisms in Lithium-ion batteries. Especially at low temperatures and high charging rates metallic lithium may be formed on the surface of the active particles of the anode due to kinetic and transport constraints, which decrease the rate of Li ion intercalation. Although partially reversible, there remains always an irreversible capacity loss under cycling, once plating is initiated. The necessary condition for plating is the drop of the local potential below the Li/Li+ Redoxpotential. This local condition cannot be read off directly from the observed overall cell voltage. It rather depends on the local current and potential distribution in the microstructure of the electrode, which is experimentally not accessible. Once the metal film is formed somewhere in the anode, the local potential distribution is changed due to the different conduction properties of the metal, even if the external operating conditions remain constant. In order to understand the influence of the microstructure on the necessary conditions for metal deposition and its subsequent influence on the potential distribution, it is necessary to model and simulate the local potential distribution in electrodes on the scale of the active particles. In the presentation, the model for simulating the plating conditions in real electrode microstructures of Li ion batteries is presented. The influence of the microstructure and operating conditions on the spatio-temporal behavior of the plating condition is studied as well as the modification of the potential distribution due to the presence of Li metal in the microstructure. Based on a new theory for Li dendrite dissolution also the contribution of this process to the irreversible capacity loss upon cycling is discussed.