Nascent SEI-Surface Films on Single Crystalline Silicon Investigated by Scanning Electrochemical Microscopy

Abstract

Silicon is a promising high-capacity host material for negative electrodes in lithium-ion batteries with low potential for the lithiation/delithiation reaction that is outside the stability window of organic carbonate electrolytes. Thus, the use of such electrodes critically depends on the formation of a protective solid electrolyte interphase (SEI) from the decomposition products of electrolyte components. Due to the large volume change upon charging, exposure of the electrode material to the electrolyte must be expected, and facile reformation of SEI is a scope for improving the stabilities of such electrodes. Here, we report the formation of incipient SEI layers on monocrystalline silicon by in situ imaging of their passivating properties using scanning electrochemical microscopy after potentiodynamic charging to different final potentials. The images show a local initiation of the SEI growth at potentials of around 1.0 V vs Li/Li+ in 1 M LiClO4 in propylene carbonate.

Surface Properties of Battery Materials Elucidated Using Scanning Electrochemical Microscopy: The Case of Type I Silicon Clathrate

“…Most importantly, the feedback remains positive throughout the rest of the cathodic scan and in the initial stages of the anodic scan, which indicates that the surface maintains its increased activity for the redox mediator regeneration. This could be either due to an electrically conducting character or due to pinholes as a result of an inhomogeneous SEI formation . In both cases it suggests that no effective SEI layer, which would be characterized by structural intactness and passivating properties, is formed on the ball‐milled sample (AM‐2) during the cathodic scan of the cycle.…”

“…This could be either due to an electrically conducting character or due to pinholes as a result of an inhomogeneous SEI formation. [9] In both cases it suggests that no effective SEI layer, which would be characterized by structural intactness and passivating properties, is formed on the ball-milled sample (AM-2) during the cathodic scan of the cycle. At potentials more negative than 0.08 V vs. Li/Li + , a continuous decrease in tip current was observed, which is indicative of the development of a more passivating character on the surface of the electrode.…”

“…Furthermore, it would help to better design optimized electrolyte formulations for these novel materials. Scanning electrochemical microscopy (SECM) has been previously used to investigate the surface reactivity of LIB materials, which in case of anode materials can be directly related to the electrical properties of the SEI . Operando SECM in feedback mode using redox mediators has been previously employed to investigate SEI formation on graphite and amorphous silicon anode films during lithiation.…”

“…Scanning electrochemical microscopy (SECM) has been previously used to investigate the surface reactivity of LIB materials, which in case of anode materials can be directly related to the electrical properties of the SEI. [9,10] Operando SECM in feedback mode using redox mediators has been previously employed to investigate SEI formation on graphite and amorphous silicon anode films during lithiation. The effect of mechanical stress on the stability of the SEI on graphite and the influence of silicon volume changes on the formation of cracks in the SEI were investigated.…”

Solid Electrolyte Interphase Evolution on Lithium Metal Electrodes Followed by Scanning Electrochemical Microscopy Under Realistic Battery Cycling Current Densities

“…[10,11] Recently, we introduced a setup in which SECM images are recorded after intermittent potentiodynamic charging steps by which incipient steps of SEI formation on Si electrodes were uncovered. [12] The current densities had to remain far below those of lithiation-delithiation cycles in real batteries. Herein, we report new experiments at Li metal electrodes, in which we combine realistic current densities for the electrochemical dissolution and deposition of Li with SECM images of the local SEI properties.…”