FB2-SiSuFest - Evaluation von Siliziumanoden in sulfidischen Festkörperbatterien

Abstract

In the SiSuFest project, the Cl-rich argyrodite Li5.5PS4.5Cl1.5 was synthesized and provided to the project partners by UoM along with commercial argyrodite solid-electrolytes (AP 1.2). In AP 2, SiNx anode composites were optimized for eventual use in full cells. The optimization process was first focused on the mass ratio of SiNx to solid electrolyte and conductive additives, then on the nitrogen content and particle size of the SiNx active material (AP 2.2). Electrochemical cycling and in vivo pressure measurements combined to suggest the best SiNx-anodes could be made from SiNx with intermediate nitrogen contents and an average particle size of approximately 100 nm. This combination enables relatively high capacity retention and low volume expansion, without sacrificing too much capacity as compared to Si-anodes. Full cells were made from the optimized SiNx-anodes and NMC-cathodes, and a set of electrochemical cycling conditions were tested to investigate the stability of these cells (AP 2.4). The results indicated a bottleneck arising from Li-ion transport, but further investigation and optimization is needed to pinpoint which materials are most at fault and to identify the limits of solid-state batteries with SiNx anodes. Impedance evolution of SiNx composites was studied with (time-resolved) electrochemical impedance spectroscopy (AP 3.3), which revealed three distinct processes related to the lithiation of SiNx. The exact nature of these processes is still unknown, and will likely require additional advanced characterization to elucidate.