Effects of HF on the Lithiation Behavior of the Silicon Anode in LiPF₆ Organic Electrolyte Solution

Abstract

As one of the major impurities in the organic electrolyte, HF can react with the alkali components in the solid electrolyte interphase (SEI), such as lithium alkoxide and lithium carbonate, to form more LiF-rich SEI. Here, the effects of HF on the lithiation behavior of the single crystal Si(111) anode were studied using scanning electron microscopy, soft X-ray emission spectroscopy, and windowless energy-dispersive X-ray spectroscopy. When the Li−Si alloy is formed in 1.0 M LiPF 6 in the propylene carbonate solvent, it has a layered structure that contained the first layer of crystalline Li 15 Si 4 (c-Li 15 Si 4 ) alloy pyramids, the second layer of amorphous Li 13 Si 4 (a-Li 13 Si 4 ) alloy, and a third layer of Li-diffused Li x Si alloy. When the more concentrated HF is in the electrolyte solution, less amount of the c-Li 15 Si 4 alloy is formed in the first layer. It suggests that the Si lithiation can form only amorphous Li x Si alloy relative to the components in the electrolytes. The study also explains why only amorphous Li x Si alloy formation was observed in some previous studies.

Metaphosphate-Bridged Interface Boosts High-Performance Lithium Storage

“…It is reported that LiF plays an important role in stabilizing the SEI and is beneficial to cycle stability . It is also generally known that LiF has negligible solubility in most electrolytes and could suppress electrolyte decomposition . Therefore, the introduction of the PO 3 group leads to an SEI film with a higher LiF content, which is closely related to its superior cycling stability.…”

(3-Aminopropyl)triethoxysilane as an Electrolyte Additive for Enhancing the Thermal Stability of Silicon Anode in Lithium-Ion Batteries

“…It is widely believed that HF will attack the SEI on the anode surface and initiate further reaction between the active material and the electrolyte. 39,40 On the other hand, PF 5 and POF 3 will catalyze the ring-opening polymerization of EC or the decomposition of DEC, further generating more heat. 41 The addition of APTES reduces the effect of HF and POF 3 and their subsequent reactions.…”