Electrochemical Deposition of Li metal in a 3D Carbon Matrix for the Fabrication and Characterization of Li Metal Anodes

Kurzfassung

Abstract Lithium metal anodes (LMA) are a key element of future battery systems. They enable maximization of energy density due to extremely high theoretical specific capacity (3860 mAh.g-1), low density (0.59 g.cm-3), and lowest negative electrochemical potential (- 3.040 V compared to a standard hydrogen electrode). However, the use of metallic lithium as a negative electrode presents some challenges. Lithium tends to form dendrites during operation, which can lead to irreversible lithium depletion and negatively impact battery energy density and safety. Due to the high reactivity of the metal, decomposition products of the electrolyte can also passivate the surface and lead to cell behavior instability. The volume change during the deposition and growth of the metallic lithium leads to the deterioration of the electrochemical and mechanical stability of the battery. Moreover, the reversibility of the deposition process determines the Coulomb efficiency (CE) of the fabricated LMA and thus the electrochemical performance of the battery cell. Therefore, the further development of LMA that enables dendrite-free reversible Li deposition represents a major advance for the practical use of metallic lithium as anode in battery technology. In this context, this master thesis focuses on the electrochemical deposition of Li in 3D carbon frameworks of different structure. Using a 3D carbon hosts to introduce lithium can reduce the local current density and volume change due to the increased specific surface area. A homogeneous, reduced current density distribution can reduce dendrite formation, enabling improved electrochemical performance. Since the carbon framework can also have a positive effect on SEI formation, various electrolytes were tested for deposition in addition to different 3D carbon hosts. The experiments were carried out at different current densities from 0.2 till 4 C and a constant surface capacitance of 2.5 mAh.cm-². In addition to the detailed description of the electrochemical behavior, impedance spectroscopy was used to clarify the degradation behavior and the morphology of the Li-3D carbon anodes was characterized by cryo-SEM. Short circuits were identified as a major cause of cell failure. The most stable substrate/electrolyte system was elicited and the electrolyte/3D electrode and lithium/3D electrode interfaces were optimized. The results of this first systematic study based on commercial carbon substrates provide a solid basis for the development of future 3D carbons and lithium electrochemical deposition parameters.