In situ Synchrotron XRD of Silicon Nanowires on 3D Carbon Substrates for Li-Ion- and Li-S-Batteries

TONY JAUMANN; EIKE AHRENS; JUAN BALACH; ANDREAS KRAUSE; WALTER M. WEBER; SUSANNE DÖRFLER; MARKUS PIWKO; HOLGER ALTHUES; LARS GIEBELER

Encuentro; 20th Topical Meeting of the International Society of Electrochemistry; 2017

Silicon is one of the most promising negative electrode materials for Lithium-Ion- and post Lithium-Ion batteries and is already partially implemented in commercialized Lithium-Ion batteries (LIB). It is well known that the use of silicon nanostructures enhances the reversibility significantly compared to bulk silicon since the volume change is going along without significant fracture of individual particles. Furthermore, silicon nanowires (Si-NW) turned out to be a highly efficient design due to their unique properties of continues electrical contact to the current collector and the superior stress compensation.In this work, Si-NW deposited on free standing gas-diffusion-layers (GDL) were implemented in various rechargeable lithium-batteries systems and studied by in situ synchrotron XRD combined with post mortem XPS. The Si-NW@GDL offer reversible areal capacities of up to 8 mAh/cm2 at a total anode mass of just 9 mg/cm2 making it an attractive candidate as high-performance anode. Pre-lithiated Si-NW were successfully employed in high-energy Li-S batteries with highly extended lifetime compared to conventional Li-S batteries.[1]Nevertheless, we still find considerable degradation of Si-NW, particular in dependency of the chosen electrolyte system such as ethers for Li-S batteries or carbonates for LIB. In order to understand these degradation phenomena, we carried out in situ synchrotron XRD measurements to identify structural changes and post mortem XPS analyses to obtain a better understanding of the surficial mechanisms. Galvanostatic cell tests were conducted under test conditions typically used in real systems while recording diffraction patterns on modified coin cells at synchrotron facilities near Barcelona (ALBA) and in Hamburg (DESY). Our in-house developed cell set-up allows to record high-quality patterns of eight cells within the hutch of the beamline ensuring the production of reproducible high-quality data.[2] We investigated conventional carbonate- (LP30) and ether-based electrolyte systems with and w/o additives such as FEC/VC. Among various findings, we observed that at moderate C-rates ranging from C/5 to C/15 the silicon is not fully utilized. New phases were observed evolving over the period of cycling which depend on the carbonate- or ether-based electrolyte system. Furthermore, we could for the first time analyze a Si-Li-S (SLS) full-cell by in situ synchrotron XRD. Finally, our findings are compared to our previous work about silicon nanoparticles within porous carbon scaffolds.[3][4] We found similar characteristics unique for the ether- or carbonate-based electrolyte system. We believe that this study provides valuable insights in tailoring nanostructured silicon anodes for LIB and post LIB.