The Study of the Binder Poly(acrylic acid) and Its Role in Concomitant Solid–Electrolyte Interphase Formation on Si Anodes

Abstract

We use neutron reflectometry to study how the polymeric binder, poly(acrylic acid) (PAA), affects the in situ formation and chemical composition of the solid−electrolyte interphase (SEI) formation on a silicon anode at various states of charge. The reflectivity is correlated with electrochemical quartz crystal microbalance to better understand the viscoelastic effects of the polymer during cycling. The use of model thin films allows for a well-controlled interface between the amorphous Si surface and the PAA layer. If the PAA perfectly coats the Si surface and standard processing conditions are used, the binder will prevent the lithiation of the anode. The PAA suppresses the growth of a new layer formed at early states of discharge (open circuit voltage to 0.8 V vs Li/Li + ), protecting the surface of the anode. At 0.15 V, the SEI layer underneath the PAA changes in chemical composition as indicated by an increase in the scattering length density and thickness as the layer incorporates components from the electrolyte, most likely the salt. At lithiated and delithiated states, the SEI layer changes in chemical composition and grows in thickness with delithiation and shrinks during lithiation.

Lithium Difluorophosphate as an Effective Additive for Improving the Initial Coulombic Efficiency of a Silicon Anode

“…It can be seen from the curve that the leakage current without additives is significantly higher than that of the electrolyte with 2 wt.% LiDFP. And it indicates that the reduction potential of the electrolyte is close to the lithium potential [35]. The 2 wt.% LiDFP additives can increase the stability and decrease the reduction resistance of the electrolyte.…”

“…For XPS F1s spectra in Figures c and 5d, two distinct characteristic peaks are shown in the sites of 685.08 eV and 687.15 eV, which is attributed to the surface groups of P−F and Li−F. And, the P−F group mainly reflects the response peaks of LiPF 6 and LiDFP in the electrolyte . Whereas the Li−F group is attributed to the decomposition reaction of the above lithium salts at the reduction potential.…”

“…For XPS F1s spectra in Figures 5c and 5d, two distinct characteristic peaks are shown in the sites of 685.08 eV and 687.15 eV, which is attributed to the surface groups of PÀ F and LiÀ F. And, the PÀ F group mainly reflects the response peaks of LiPF 6 and LiDFP in the electrolyte. [35] Whereas the LiÀ F group is attributed to the decomposition reaction of the above lithium salts at the reduction potential. After adding the additives, the increasing of LiÀ F intensity indicates that the adding of LiDFP induced the formation of LiÀ F. [36] And the LiÀ F is often not easy to form without additive, so its content is very low in electrolyte samples when the components of the esterified lithium and lithium carbonate are significantly reduced.…”

Advances of polymer binders for silicon‐based anodes in high energy density lithium‐ion batteries

“…Later, Komaba et al demonstrated that SiO anode with PAA binder showed the best performances compared to that of PVDF, PVA or CMC binders (Figure 5B). 74 Many studies have demonstrated that PAA could react with the surface hydroxyl group on Si to form covalent bonds (Figure 5C) 75‐77 and PAA is helpful to form a concomitant SEI layer on the surface of Si particles 78,79 . In addition, the binding ability of PAA can also be regulated or optimized though neutralization by NaOH or LiOH, and controlling its M w (Figure 5C).…”

Challenges and Recent Progress on Silicon‐Based Anode Materials for Next‐Generation Lithium‐Ion Batteries

“…With the development of high‐performance LIBs, the role of binder gradually become main influence factor. [ 51 ] Up to now, apart from polyvinylidene difluoride (PVdF) and carboxymethyl cellulose/styrene butadiene rubber (CMC/SBR), various new polymer binders have been reported, including binding actions of volume change alleviation, [ 52 ] dispersing function, [ 53 ] SEI contribution, [ 54,55 ] electronic conduction, [ 56 ] and ionic conduction [11b,57] …”