Low‐Oxidized Siloxene Nanosheets with High Capacity, Capacity Retention, and Rate Capability in Lithium‐Based Batteries

Abstract

The mechanical degradation experienced by Si electrodes during Li (de)alloying reactions can potentially be mitigated by using Si‐based materials with layered 2D geometries. Such materials are expected to exhibit favorable mechanical properties and be capable of buffering the volume change associated with (de)lithitation. In this work, 2D siloxene nanosheets are synthesized using a facile topotactic reaction followed by ultrasonication as an exfoliation step. Detailed structural and chemical characterization via electron microscopy, X‐ray photoelectron spectroscopy (XPS), and Raman spectroscopy is conducted, revealing a low‐oxidized siloxene nanosheet material with only 15% surface Si‐oxide. The obtained siloxene nanosheets are tested as Li‐ion negative electrodes in lithium‐based electrochemical cells. The cells exhibit high rate capability with a capacity of 935 mAh g–1 at 3200 mA g–1 and ≈99.5% coulombic efficiency. The inclusion of fluoroethylene carbonate (FEC) in the electrolyte improves capacity retention over 200 cycles from 13% to 77% at 1000 mA g–1. This behavior is attributed to the FEC decomposition forming a solid electrolyte interphase (SEI) with higher ion conductivity and robust LiF/LixPOyFz content, as characterized via XPS Raman spectroscopy.

Two-Dimensional Siloxene Nanosheets: Impact of Morphology and Purity on Electrochemistry

“…The XRD pattern of CaSi 2 is shown with peaks for FeSi 2 and bulk Si impurities present. Two trigonal CaSi 2 phases crystallizing in the R̅ 3 m space group in the CaSi 2 material (70 wt % of 6R as Materials Project identifier mp-2699 and 7 wt % of 3R as Materials Project identifier mp-2700). The two impurities, cubic Si Fd 3 ̅m (Crystallography Open Database entry #9011998) and tetragonal FeSi 2 phase crystallizing in P 4/ mmm (Crystallography Open Database entry #9014404) contributed 16 and 7 wt % based on Rietveld refinement (Figure S1), respectively.…”

“…Siloxene nanosheets were synthesized by a method adapted from previous work. 17 Briefly, CaSi 2 (Nanoshell, 99.9%, 40−60 μm) was added to concentrated HCl at 0 °C. The mixture was stirred vigorously under inert gas.…”

“…Rietveld refinements were performed with GSAS-II software. 17,32 Two trigonal CaSi 2 phases crystallizing in the R̅ 3m space group were used to fit the CaSi 2 starting material (Materials Project identifiers mp-2699 and mp-2700, respectively). 33,34 Cubic Si crystallizing in Fd3̅ m and tetragonal FeSi 2 crystallizing in P4/mmm (Crystallography Open Database entries #9011998 and #9014404, respectively) 35,36 were present as impurities in the CaSi 2 precursor.…”

“…Powder XRD patterns were collected using a Rigaku Miniflex 600 diffractometer with Cu Kα radiation (λ = 1.5406 Å) and Bragg–Brentano geometry. Rietveld refinements were performed with GSAS-II software. , Two trigonal CaSi 2 phases crystallizing in the R̅ 3 m space group were used to fit the CaSi 2 starting material (Materials Project identifiers mp-2699 and mp-2700, respectively). , Cubic Si crystallizing in Fd 3 ̅m and tetragonal FeSi 2 crystallizing in P 4/ mmm (Crystallography Open Database entries #9011998 and #9014404, respectively) , were present as impurities in the CaSi 2 precursor. The synthesized siloxene was fit using trigonal Si 6 H 6 O 3 with P 3 space group (Crystallography Open Database entry #1536253)…”

Boosting the Temperature Adaptability of Lithium Metal Batteries via a Moisture/Acid‐Purified, Ion‐Diffusion Accelerated Separator

“…[19] Alternatively, the ether-based solvents ((1,3-dioxolane, ethylene glycol dimethylether) or the film-forming additives (fluoroethylene carbonate, vinylene carbonate, and lithium difluorooxalato borate) were directly adopted in the electrolyte to in situ form the favorable passivation components. [20][21][22] Upon the high-voltage cycling or at the low temperature conditions, however, the low oxidation resistance of ethers or insufficient dynamics of the derived species (LiF, poly(vinylene carbonate)) also lead to the enhanced interfacial charge transfer resistance, which inevitably jeopardized the power output of the cell. [23,24] Moreover, the "lithiophilic" seeds (e.g., Ag, Au, and Zn) were also used to induce the preferential Li + influx toward the specific location and mitigate the nucleation barrier.…”