Li₁₅Si₄Formation in Silicon Thin Film Negative Electrodes

Abstract

The conditions for Li15Si4 formation in Si thin film negative electrodes was studied during charge and discharge cycling in lithium cells. It was found that Li15Si4 formation can be suppressed during cycling of Si thin films by stress induced from the presence of the substrate. Furthermore, Li15Si4 formation was found to be coincidental with capacity fade and delamination of the Si film from the current collector. These results deepen the understanding of the cycling of Si thin films. Moreover, they have profound implications for Si alloy negative electrodes for Li-ion batteries, as the presence of Li15Si4 during cycling can be used as a sensitive indicator for weakly bound Si regions.

The Electrochemistry of Amorphous Si-B Thin Film Electrodes in Li Cells

“…[25][26] No plateau related to Li 15 Si 4 is present during these initial cycles, which is consistent with Si films where Li 15 Si 4 formation can be suppressed by the stress between the Si film and the substrate. 27 With increasing B concentration, both sloping plateaus shorten gradually so that the reversible capacity of Si 1-x B x electrode decreases. Nevertheless, Si 1-x B x electrodes with more than 80 at% B content still show obvious lithium storage capability.…”

“…A weakly bonded Si active phase has been shown to result in Li 15 Si 4 formation and fade during cycling in thin films. 27 We will explore the longer-term cycling implications of this potentially weak interaction in a later publication using Si-B made by mechanical milling.…”

Lithiation Behavior of Silicon Nanowire Anodes for Lithium‐Ion Batteries: Impact of Functionalization and Porosity

“…[22] Another possiblee xplanation is ab uffering effect of the porous shell that hinders the volume expansion of the SiNW to some extent.L i 15 Si 4 cannoto ccur when the lithiation induced stresses suppress the electrochemical potential. [33] The porous shell prevents the expansion of the SiNW and the induced stress lowers the formation potential of Li 15 Si 4 .…”

Differentiating the Degradation Phenomena in Silicon-Graphite Electrodes for Lithium-Ion Batteries

“…1,2 In contrast to conventional intercalation anode materials, such as graphite (LiC 6 , 372 mAh g −1 , 890 Ah L −1 ), the specific capacity of silicon alloy electrodes is significantly higher (Li 15 Si 4 , 3579 mAh g −1 , 2194 Ah L −1 ). 3 Nonetheless, commercialization of silicon-based electrodes is still hampered because of two major challenges: 4 (i) Large volume expansions up to 280% upon repeated (de-)lithiation of silicon particles deteriorate the electrode integrity, thus causing isolation of active material.…”

“…While these conditions would also be satisfied by a lithium metal electrode, the third reason is (iii) to minimize side reactions of the electrolyte at the positive electrode (here: LiFePO 4 ), which would alter the electrolyte (and FEC) decomposition and thus influence its quantification. As electrolyte we use 1 M LiPF 6 in EC:EMC (LP57) with 5 wt% of the widely used fluoroethylene carbonate (FEC) as additive, which is known to significantly improve the cycling stability of the silicon-graphite electrode. 32 We also added a comparably large amount of electrolyte to the coin cells (130 μL or 84 μL cm −2 ; ∼15 times larger compared to large-scale cells), because it allows for a more precise quantification of the FEC consumption via 19 F-NMR.…”