Ultrathin conformal polycyclosiloxane films to improve silicon cycling stability

Abstract

Electrochemical reduction of lithium ion battery electrolyte on Si anodes was mitigated by synthesizing nanoscale, conformal polymer films as artificial solid electrolyte interface (SEI) layers. Initiated chemical vapor deposition (iCVD) was used to deposit poly(1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane) (pV4D4) onto silicon thin film electrodes. pV4D4 films (25 nm) on Si electrodes improved initial coulombic efficiency by 12.9% and capacity retention over 100 cycles by 64.9% relative to untreated electrodes. pV4D4 coatings improved rate capabilities, enabling higher lithiation capacity at all current densities. Impedance spectroscopy showed that SEI resistance grew from 50 to 191 ohms in untreated Si and only 34 to 90 ohms in pV4D4-coated Si over 30 cycles. Post-cycling Fourier transform infrared and x-ray photoelectron spectroscopy showed that pV4D4 moderated electrolyte reduction and altered SEI composition, with LiF formation being favored. This work will guide further development of polymeric artificial SEIs to mitigate electrolyte reduction and enhance capacity retention in Si electrodes.

Nanoscale control by chemically vapour-deposited polymers

“…92,93 For lithium ion batteries, a solid electrode interface (SEI) consisting of a conformal, 25 nm thick iCVD organosiloxane, improved the initial coulombic efficiency and capacity retention upon repeated cycling of silicon anodes. 94 The ultrathin and conformal nature of iCVD copolymers from HEMA and a crosslinking monomer are desired for solid-state polymer electrolytes for 3D microbatteries 95 and for stabilizing electroactive polymers 96 Device Fabrication…”

Chemically vapor deposited polymer nanolayers for rapid and controlled permeation of molecules and ions

“…As solid electrode interface layers (SEI), conformal iCVD poly(V4D4) films on silicon anodes improved the initial coulombic efficiency, as well as the capacity retention upon repeated cycling. 90 For application in 3D batteries, ultrathin and conformal solid polymer electrolytes are desired. 91 Using the V4D4 monomer resulted in exceptionally smooth and conformal films, even at thicknesses of ~10 nm (Fig.…”

Humidity‐Initiated Gas Sensors for Volatile Organic Compounds Sensing

“…Second, fully crosslinked polymers (NP4 and H0) have a relatively high GA detection limit of ≈55 ppb. Since GA has a much larger diameter (0.9 nm) than both the mesh size of H0 (<0.5 nm) [ 35 ] and the ring diameter of NP4 (0.4 nm), [ 33 ] we propose that these relatively high detection limits are the result of size exclusion; GA cannot absorb appreciably within these fully crosslinked polymers and so, the response of these Type II sensors is limited to that of other sorption processes. Finally, polar (P1) and hydrogen bonding (H60, H90, and H100) polymers with mesh size above GA size‐exclusion have very low solubility for GA (χ > 2) and yet have low GA detection limit (<20 ppb).…”

“…For the polar surface modification, P1, we use the homopolymer of the monomer, cyanoethyl acrylate. [28] For the four non-polar surface modifications, NP1 to NP4, we use the homopolymer of the monomer butyl acrylate, [29] cyclohexyl methacrylate, [30] benzyl methacrylate, [31] or 1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane, [32,33] respectively. The hydrogen bonding polymers are hydrogels formed from the iCVD copolymerization of hydroxyethyl methacrylate (HEMA) with the crosslinking monomer ethylene glycol diacrylate (EGDA), [34][35][36] where H100 represents a homopolymer of HEMA (100 mol% HEMA) and H0 represents a homopolymer of EGDA (0 mol% HEMA).…”