Composite Electroforming As Novel and Innovative Synthesis Method of Additive-Free Cathodes for Li-S Batteries

Abstract

The increasing requirements for high power and energy storage systems have led to the implementation of a considerable number of electrode materials. Several crucial parameters such as energy, power density, rate capability and cyclability can be significantly influenced by modifying, in addition to the active materials chemistry, the manufacturing process of the electrode in the metal matrix. The novel electrodes for Li-S batteries proposed in the present work are intended to make a significant contribution to overcoming the concept-related disadvantages of the state-of-the-art conventional coating processes. Their basic development and suitability were investigated by our research group in various projects [1-4].The recently self-developed composite electroforming [5] is a very promising electrodes production process. It is significantly improving the existing conventional coating technology in terms of reduced technological steps, low costs and better electrochemical performance. The aforementioned manufacturing process consists on electroforming the metal matrix, which operates as a current collector foil, in a one-step process. Simultaneously, the active material is incorporated into the metal matrix by means of composite plating [6]. In contrast to the state-of-the-art approach using non-conducting binders such as PVDF and non-binding conductive agents such as carbon black, conductivity and mechanical stability can be synergistically optimized.In the present work, composite electroformed foils, composed of Ni matrix and sulfur loaded on Al alloy carrier particles AlSi10Mg, are used as cathodes for Li-S batteries. The synthesis procedure consists on the selective etching of the Al particles which are used as dispersoids in the composite electroforming process. BET results proved that after etching, the specific area is remarkably increased. Afterwards, the etched Al alloy particles are cemented with cobalt nanocrystallites, as these act as ideal electrocatalysts for the sulfur half cell [7].In a way to optimize the composite electroformed cathodes, which should ideally consist of a dense monolayer of sulfur loaded carrier particles without Ni overgrowth, several parameters can be evaluated. In the present work, parameters such as particle concentration in the electrolyte, current density, nickel concentration, pH value, temperature and convection are kept constant. Only the current and thus the corresponding time to achieve the desired composite thickness are varied. Moreover, the experimental conditions were extended to the application of pulse and pulse reverse plating.Therefore, in order to evaluate the parameter-structure relationships and to assess the efficacy of the presented approach, a broad range of morphological testing by SEM of all the composite electroformed cathodes was carried out. Furthermore, the electrochemical behavior of the novel cathodes that were galvanostatically cycled at slow and moderate rates was investigated and will be presented.[1] C. Erhardt, Ş. Sörgel, S. Meinhard, T. Sörgel, J. Power Sources, 296 (2015) 70-77.[2] T. Sörgel, ZVO report, 1 (2019) 46.[3] S. Meinhard, O. Kesten, K. Jäger, I. Hägele, T. Sörgel, Galvanotechnik, 8 (2020) 1164-1169.[4] A. K. Jäger, S. Meinhard, O. Kesten, I. Hägele, T. Sörgel, WoMag, 4 (2020) 25-26.[5] T. Sörgel, S. Meinhard, Ş. Sörgel, Film Composite Material, EP 3114721 B1, 2015.[6] T. Sörgel, J. Meyer, WOMag, 9 (2013) 24–33.[7] Ş. Sörgel, O. Kesten, A. Wengel, T. Sörgel, Energy Storage Mater. 2018, 10, 223-232.