Effective SEI Formation via Phosphazene‐Based Electrolyte Additives for Stabilizing Silicon‐Based Lithium‐Ion Batteries

Abstract

Silicon, as potential next‐generation anode material for high‐energy lithium‐ion batteries (LIBs), suffers from substantial volume changes during (dis)charging, resulting in continuous breakage and (re‐)formation of the solid electrolyte interphase (SEI), as well as from consumption of electrolyte and active lithium, which negatively impacts long‐term performance and prevents silicon‐rich anodes from practical application. In this work, fluorinated phosphazene compounds are investigated as electrolyte additives concerning their SEI‐forming ability for boosting the performance of silicon oxide (SiOx)‐based LIB cells. In detail, the electrochemical performance of NCM523 || SiOx/C pouch cells is studied, in combination with analyses regarding gas evolution properties, post‐mortem morphological changes of the anode electrode and the SEI, as well as possible electrolyte degradation. Introducing the dual‐additive approach in state‐of‐the‐art electrolytes leads to synergistic effects between fluoroethylene carbonate and hexafluorocyclotriphosphazene‐derivatives (HFPN), as well as enhanced electrochemical performance. The formation of a more effective SEI and increased electrolyte stabilization improves lifetime and results in an overall lower cell impedance. Furthermore, gas chromatography‐mass spectrometry measurements of the aged electrolyte with HFPN‐derivatives as an additive compound show suppressed ethylene carbonate and ethyl methyl carbonate decomposition, as well as reduced trans‐esterification and oligomerization products in the aged electrolyte.

Ethylene Carbonate-Free Electrolytes Based on Ethyl Methyl Carbonate for High-Voltage LiCoO2/Si-Graphite Lithium-Ion Batteries

“…The peak intensities of the C–O bond in the O 1s spectrum and Li x PF y /Li x PO y F z in the F 1s spectrum increase noticeably. The peak of SiO 2 in the Si 2p spectrum and two peaks at 400.0 and 398.3 eV in the N 1s spectrum corresponding to the C–N and CN bonds from PFPN are observed . These variations suggest that PFPN is involved in the formation of SEI.…”

“…The peak of SiO 2 in the Si 2p spectrum and two peaks at 400.0 and 398.3 eV in the N 1s spectrum corresponding to the C−N and C�N bonds from PFPN are observed. 41 These variations suggest that PFPN is involved in are illustrated in Figure S5a. After introducing 15 wt % PFPN into the LiPF 6 -EMC electrolyte, the value of conductivity decreases from 4.67 to 3.69 mS cm −1 .…”

“…These results confirm the formation of the CEI film on the cathode. For the LiPF 6 -EMC + 15 wt % PFPN electrolyte (Figure c), the peaks representing the phosphazene ring are not found in the N 1s spectrum, and two peaks attributed to C–N (400.0 eV) and CN (398.3 eV) bonds are identified. ,, The peak intensities of Li x PF y and Li x PO y F z change in the P 2p spectrum. These results suggest that the phosphazene ring of PFPN is completely broken and involved in CEI film formation.…”

Multifunctional Additive Ethoxy(pentafluoro)cyclotriphosphazene Enables Safe Carbonate Electrolyte for SiOx‐Graphite/NMC811 Batteries

“…The authors would like to acknowledge the work of the University of Münster, Germany, their collaboration partner in the SeNSE project, who independently conducted similar experiments and came to similar conclusions. [47] The authors thank Solvionic for providing the carbonate electrolyte and Marcel Held from Empa for providing expertise and equipment for the pouch cell experiments. Open Access funding provided by ETH-Bereich Forschungsanstalten.…”

Solid Electrolyte Interface Film-Forming and Surface-Stabilizing Bifunctional 1,2-Bis((trimethylsilyl)oxy) Benzene as Novel Electrolyte Additive for Silicon-Based Lithium-Ion Batteries

“…The structure–function relationship of electrolyte additives leads to diverse functions exhibited by additive molecules with different structures. Film-forming additives are capable of constructing an excellent SEI film, rendering them suitable for employment in Si-based anodes. − For instance, the Si–O group is a characteristic structure with film-forming ability. Zhang et al proposed a new electrolyte additive, 3-isocyanatopropyltriethoxysilane (IPTS).…”