Degradation Phenomena in Silicon/Graphite Electrodes with Varying Silicon Content

Abstract

The degradation phenomena of Silicon/Graphite electrodes and the effect of FEC as electrolyte additive was investigated through galvanostatic cycling, XPS analyses and SEM cross section analyses. To understand the direct influence of silicon on the electrode degradation, the silicon amount was varied between 0%-30%. By evaluating the cycling performance and the accumulated capacity loss of the different Si/Gr electrodes (cycled with and without 10 vol-% of FEC), we see that the capacity decay can be distinguished into two phenomena, where one is independent of the Si/Gr ration while the other one depends on the Si content. As expected, adding FEC improves the cell performance and minimizes the capacity decay. Combing our XPS data and SEM cross section analyses on cycled electrodes, this improvement stems from a thin and flexible SEI including poly(vinyl carbonate) that helps maintaining the overall electrode integrity as we observe less electrode fractures and less pronounced thickness increase. Si/Gr electrodes with 10 and 20% Si content showed very similar accumulated irreversible capacity losses over 100 cycles indicating that with 10 % FEC as electrolyte additive, also higher Si contents could be feasible for future high energy density anodes.

From Additive to Cosolvent: How Fluoroethylene Carbonate Concentrations Influence Solid–Electrolyte Interphase Properties and Electrochemical Performance of Si/Gr Anodes

“…The re-emergence of the Li x SiO y species could be due to cracks in the electrode coating, resulting from the low FEC content in the electrolyte after 100 cycles. This was seen in a previous work, in which cracks in the electrode coating could be observed in cross-sectional SEM micrographs after cycling in the absence of FEC . As seen in the analysis of the C 1s spectra, the SEI is predominantly made of EC and DMC decomposition products, which may lead to a less flexible SEI .…”

“…Regarding C–F and Si–F environments, the literature is divided. While XPS measurements indicate C–F and Si–F species, − they could not be detected via ss-NMR. , Along with its influence on SEI properties, FEC appears to affect the interaction between the SEI and the electrode . Its presence seems to promote the formation of organosiloxane (i.e., −Si–C−) species and thereby influences the adhesion of the organic SEI to silicon surfaces .…”

Potential and Limitations of Research Battery Cell Types for Electrochemical Data Acquisition

“…In these systems, complete consumption of FEC is marked by a distinct drop in capacity retention [27,36,37] . However, from a material testing perspective, excess electrolyte volumes “turn off” some of the undesired side reactions described above and therefore allow the investigation of other degradation phenomena [38,39] . Lastly, insufficient drying of cell components (electrodes, separators or coin cell parts) or high moisture levels within the electrolyte can lead to electrolyte and electrolyte salt decomposition reactions (e. g., electrolytes containing LiPF 6 as conducting salt), resulting in aging effects.…”

Charge Dynamics Induced by Lithiation Heterogeneity in Silicon‐Graphite Composite Anodes

“…[6,[8][9][10][11][12][13] Currently, it is expected that high energy density electrodes will rely on composite systems, based on the combination of "robust" graphite and high-capacity Si, with the possible addition of stabilizing phase or dual-phase materials. [14][15][16][17][18][19][20][21] However, gaining knowledge on charging and capacity fading mechanisms remains a challenge to unlock large-scale applications of these materials.…”