Direct Prelithiation of Silicon-Based Composite Electrodes via Island-like Thermal Evaporation
A.R. de L. Musgrove, Katie L. Browning, Robert L. Sacci, Andrew M. Ullman, Harry M. Meyer, Kyle Musgrove, Joseph Quinn, S. Möller, Martin Finsterbusch, Gabriel M. Veith
Abstract
Irreversible losses of Li during solid electrolyte interface (SEI) conditioning in batteries are a key contributor to the lower specific capacities observed in silicon-containing Li-ion batteries. Herein, thermal evaporation of between 1 and 20 μm of Li onto Si-based composite anodes has been investigated as a prelithiation method to compensate for such losses. Additionally, to account for mechanical strain caused by Li–Si alloying and electrode expansion during the deposition, a stainless-steel mesh is applied to the electrodes before prelithiation to form “island-like” deposition on the electrode surface. The open circuit potential was also found to decrease as a function of increased Li evaporation, consistent with the potentials of electrochemically prepared Li x Si alloys. Prelithiating to compensate for irreversible Li losses to SEI formation resulted in full cells with a 15.8% increase in initial Coulombic efficiency and a 47.8% reduction in irreversible capacity loss after SEI formation cycling. Subsequent C/3 cycling showed up to a 62.9% increase in the specific capacity in prelithiated cells. X-ray photoelectron spectroscopy (XPS) revealed differences in the SEI composition that was formed by electrochemical cycling and reactively formed in prelithiated cells upon exposure to the Gen2 + 3% FEC electrolyte. The reactively formed SEI from the spontaneous reaction with lithiated silicon was carbonate-rich, while the electrochemical SEI formation showed significantly more LiPF x species, which could play a role in overall cycling performance.