Role of Low Molecular Weight Polymers on the Dynamics of Silicon Anodes During Casting

Abstract

This work probes the slurry architecture of a high silicon content electrode slurry with and without low molecular weight polymeric dispersants as a function of shear rate to mimic electrode casting conditions for poly(acrylic acid) (PAA) and lithium neutralized poly(acrylic acid) (LiPAA) based electrodes. Rheology coupled ultra‐small angle neutron scattering (rheo‐USANS) was used to examine the aggregation and agglomeration behavior of each slurry as well as the overall shape of the aggregates. The addition of dispersant has opposing effects on slurries made with PAA or LiPAA binder. With a dispersant, there are fewer aggregates and agglomerates in the PAA based silicon slurries, while LiPAA based silicon slurries become orders of magnitude more aggregated and agglomerated at all shear rates. The reorganization of the PAA and LiPAA binder in the presence of dispersant leads to a more homogeneous slurry and a more heterogeneous slurry, respectively. This reorganization ripples through to the cast electrode architecture and is reflected in the electrochemical cycling of these electrodes.

Understanding the Solution Dynamics and Binding of a PVDF Binder with Silicon, Graphite, and NMC Materials and the Influence on Cycling Performance

“…Both the Si and Gr slurries have fewer agglomerates as the shear rate is increased from 30 to 200 Hz (Figures and ). This is a typical behavior of colloids in a viscoelastic (i.e., polymer) solution as the shear force breaks agglomerate structures and the PVDF chains align in the direction of shear. − This behavior has been observed previously with Si slurries made with poly­(acrylic acid). − ,, However, at 200 Hz, the NMC slurry has an increase in the number and size of agglomerates by 4 orders of magnitude when compared to 30 Hz. This is likely because PVDF forms a thick layer on NMC particles, as mentioned previously, that can encapsulate multiple NMC particles and remain porous. , …”

“…At 30 Hz, the Si slurry is the most agglomerated. This behavior has also been observed in Si slurries with polyimide and poly­(acrylic acid) binders as is likely due to increased polymer–polymer entanglements induced by low shear forces. − However, both the Gr and NMC slurries have a decrease in the number of agglomerates by at least a factor of 2 at the equivalent shear rate. Since both Si and Gr use A-PVDF as the binder, this difference is most likely due to the differences in adsorption of PVDF on the different active materials and polymer–polymer interactions reflected by the adsorption isotherms.…”

“…38−40 This behavior has been observed previously with Si slurries made with poly(acrylic acid). [35][36][37]41,42 However, at 200 Hz, the NMC slurry has an increase in the number and size of agglomerates by 4 orders of magnitude when compared to 30 Hz. This is likely because PVDF forms a thick layer on NMC particles, as mentioned previously, that can encapsulate multiple NMC particles and remain porous.…”

Precisely Prelithiated Polyacrylic Acid Binder Improving Electrochemical Performance of Micron‐Sized Silicon Anodes for Lithium‐Ion Batteries

“…[34][35] Herein, we propose a straightforward and eco-friendly technique to synthesize a precisely-prelithiated polyacrylic acid binder (LiPAA). Different from previous reports of controlling the degree of prelithiation through pH value, [36][37] this work uses controlling the feed ratio of LiOH and PAA for precise control. Silicon microparticles, due to their robust adhesion, superior elasticity, and electrochemical stability, serve as the anode material to improve initial Coulombic efficiency (ICE) and reduce costs.…”

Poly(acrylic acid) locally enriched in slurry enhances the electrochemical performance of the SiOx lithium-ion battery anode

“…Therefore, the contour size of the PAA random coil in water is enlarged compared to the one in a poor solvent. [31][32][33] As a result, the local density of the acrylic acid functional group is decreased. Thus, the bonding interactions of PAA with the SiO x particles and copper current collector are compromised.…”