The Role of Silicon in Silicon-Graphite Composite Electrodes Regarding Specific Capacity, Cycle Stability, and Expansion

Abstract

Silicon-based electrodes are promising candidates to enable the next generation of Lithium-ion batteries with high energy densities on the cell level beyond 350 Wh kg−1 [1, 2]. Nevertheless, the commercialization of silicon-based electrodes is still hindered due to the large volume expansion during cycling of up to 300% [3]. This volume expansion upon repeated (de-)lithiation of silicon particles worsens the electrode integrity by causing isolation of active material components [4-6]. Continuous electrolyte decomposition at the silicon/electrolyte interface, caused by the repeated volume expansion and contraction, results in a gradual loss of active lithium [7].While X-ray diffraction (XRD) as well as theoretical methods provide atomic scale information, dilatometry is an appropriate tool for the in-situ investigation of the volumetric work of battery composite electrodes on the macroscopic level. Therefore, the technique itself as well as the obtained data have a high potential for their industrial implementation [8].In this work, the expansion of a single-side-coated silicon-based anode is investigated with a commercial, high-precision dilatometer, which detects the thickness change perpendicular to the surface of the coating on the electrode level during cycling against a lithium metal counter electrode. The measured samples consist of 95 wt.% active material (0 - 20 wt.% of silicon in combination with 95 - 75 wt.% of graphite, respectively) and 5 wt.% of non-active components.The investigated samples in this work differ in their silicon and graphite content. Moreover, the samples were also investigated electrochemically via conventional coin cells. The comparable electrochemical behavior of the electrodes in both experiment methods is proof of the plausibility of the dilatometry results. Increasing the silicon content led to higher specific capacities of the SiG electrodes. The relative capacity loss and the thickness change increased linearly with the silicon content as well. Based on the characteristic thickness change for the SiGs, we concluded that silicon predominantly lithiated before graphite, and delithiated after graphite.The used non-commercial electrodes were designed and produced within the scope of the project “HighSafeII”, funded by the German Federal Ministry of Education and Research (BMBF) under grant number 03XP0306B. Literature [1] D. Andre, S.-J. Kim, P. Lamp, S. F. Lux, F. Maglia, O. Paschos, and B. Stiaszny, “Future generations of cathode materials: an automotive industry perspective”, J. Mater. Chem. A, 3 (13), 6709 (2015).[2] O. Gröger, H. A. Gasteiger, and J.-P. Suchsland, “Review—Electromobility: Batteries or Fuel Cells?”, J. Electrochem. Soc., 162 (14), A2605 (2015).[3] D. Ma, Z. Cao, and A. Hu, “Si-Based Anode Materials for Li-Ion Batteries: A Mini Review” Nano-Micro Lett, 6(4), 347 (2014).[4] M. N. Obrovac, L. Christensen, D. B. Le, and J. R. Dahn, “Alloy Design for Lithium-Ion Battery Anodes”, J. Electrochem. Soc., 154 (9), A849 (2007).[5] D. S. M. Iaboni and M. N. Obrovac, “Li15Si4 Formation in Silicon Thin Film Negative Electrodes”, J. Electrochem. Soc., 163 (2), 255 (2016).[6] M. N. Obrovac and V. L. Chevrier, “Alloy Negative Electrodes for Li-Ion Batteries”, Chem. Rev., 114, 11444 (2014).[7] R. Petibon, V. Chevrier, C. P. Aiken, D. S. Hall, S. Hyatt, R. Shunmugasundaram, and J. R. Dahn, “Studies of the Capacity Fade Mechanisms of LiCoO2/Si-Alloy: Graphite Cells”, J. Electrochem. Soc., 163 (7), 1146 (2016).[8] Daniel Sauerteig, Svetlozar Ivanov, Holger Reinshagen, Andreas Bund, „Reversible and irreversible dilation of lithium-ion battery electrodes investigated by in-situ dilatometry“, J. Power Sources, 342, 939-946 (2017).