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

Abstract

The impact of the binding, solution structure, and solution dynamics of poly­(vinylidene fluoride) (PVDF) with silicon on its performance as compared to traditional graphite and Li1.05Ni0.33Mn0.33Co0.33O2 (NMC) electrode materials was explored. Through refractive index (RI) measurements, the concentration of the binder adsorbed on the surface of electrode materials during electrode processing was determined to be less than half of the potentially available material resulting in excessive free binder in solution. Using ultrasmall-angle neutron scattering (USANS) and small-angle neutron scattering (SANS), it was found that PVDF forms a conformal coating over the entirety of the silicon particle. This is in direct contrast to graphite–PVDF and NMC–PVDF slurries, where PVDF only covers part of the graphite surface, and the PVDF chains make a network-like graphite–PVDF structure. Conversely, a thick layer of PVDF covers NMC particles, but the coating is porous, allowing for ion and electronic transport. The homogeneous coating of silicon breaks up percolation pathways, resulting in poor cycling performance of silicon materials as widely reported. These results indicate that the Si–PVDF interactions could be modified from a binder to a dispersant.

Advances in Polymer Binder Materials for Lithium-Ion Battery Electrodes and Separators

“…Figure 1 illustrates several structural formulas and graphical representations of various types of traditional polymer binders used in LIBs. PVDF is frequently chosen as the preferred binder for graphite anodes and Li1.05Ni0.33Mn0.33Co0.33O2(NCM)-based electrodes due to its electrochemical stability and flexibility, allowing for mechanical compression and decompression during the charging and discharging cycles [9]. The reactivity of PVDF with lithiated graphite and metallic lithium has raised significant concerns regarding the thermal runaway of LIBs under abusive conditions.…”

“…Zhang et al conducted DSC investigations on positively charged anodes and reported that an exothermic reaction, commencing at approximately 230 °C and reaching its maximum at around 300 °C, was likely attributed to the interaction between the PVDF binder and metallic lithium [10]. During the 1980s, PTFE (polytetrafluoroethylene) resin found extensive use as a binding agent for both anode components within PVDF is frequently chosen as the preferred binder for graphite anodes and Li 1.05 Ni 0.33 Mn 0.33 Co 0.33 O 2 (NCM)-based electrodes due to its electrochemical stability and flexibility, allowing for mechanical compression and decompression during the charging and discharging cycles [9]. The reactivity of PVDF with lithiated graphite and metallic lithium has raised significant concerns regarding the thermal runaway of LIBs under abusive conditions.…”

Advances in Polymer Binder Materials for Lithium-Ion Battery Electrodes and Separators

“…PVDF is frequently chosen as the preferred binder for graphite anodes and Li1.05Ni0.33Mn0.33Co0.33O2(NCM)-based electrodes due to its electrochemical stability and flexibility, allowing for mechanical compression and decompression during the charging and discharging cycles [8]. The reactivity of PVDF with lithiated graphite and metallic lithium has raised significant concerns regarding the thermal runaway of LIBs under abusive conditions.…”

N-Type Polyoxadiazole Conductive Polymer Binders Derived High-Performance Silicon Anodes Enabled by Crosslinking Metal Cations

“…Traditional binders such as polyvinylidene difluoride, carboxymethyl cellulose, , poly­(acrylic acid) (PAA), and polysaccharides , have been widely tested for Si anodes. However, these binders cannot intrinsically prevent the capacity decay caused by the crushing of Si particles, which become electronically inactive once they lose contact with conductive materials during cycling.…”