Role of PVDF in Rheology and Microstructure of NCM Cathode Slurries for Lithium-Ion Battery

Abstract

A binder plays a critical role in dispersion of coating liquids and the quality of coating. Poly(vinylidene fluoride) (PVDF) is widely used as a binder in cathode slurries; however, its role as a binder is still under debate. In this paper, we study the role of PVDF on the rheology of cathode battery slurries consisting of Li(Ni1/3Mn1/3Co1/3)O2 (NCM), carbon black (CB) and N-methyl-2-pyrrolidone (NMP). Rheology and microstructure of cathode slurries are systemically investigated with three model suspensions: CB/PVDF/NMP, NCM/PVDF/NMP and NCM/CB/PVDF/NMP. To highlight the role of PVDF in cathode slurries, we prepare the same model suspensions by replacing PVDF with PVP, and we compare the role of PVDF to PVP in the suspension rheology. We find that PVDF adsorbs neither onto NCM nor CB surface, which can be attributed to its poor affinity to NCM and CB. Rheological measurements suggest that PVDF mainly increases matrix viscosity in the suspension without affecting the microstructure formed by CB and NCM particles. In contrast to PVDF, PVP stabilizes the structure of CB and NCM in the model suspensions, as it is adsorbed on the CB surface. This study will provide a useful insight to fundamentally understand the rheology of cathode slurries.

Single Lithium Ion Conducting “Binderlyte” for High‐Performing Lithium Metal Batteries

“…[ 17–21 ] PVdF and its derivatives have been one of the most commonly used binder materials in commercial LIBs due to their outstanding electrochemical stability, excellent binding properties, and good wettability with the electrolyte. [ 22,23 ] However, its electrically/ionically insulating nature and the use of the toxic organic solvent, N ‐methyl‐2‐pyrrolidone (NMP), for this kind of electrode fabrication suggests an active search of more conductive and environmentally friendly polymeric materials. [ 24,25 ] In recent years, several kinds of alternative polymeric materials have been investigated for high‐voltage cathodes, [ 26–30 ] such as lithium polyacrylate (LiPAA), [ 29 ] poly (acrylic acid) (PAA)‐based amphiphilic bottlebrush polymers (BBPs), [ 30 ] and so on.…”

Significant Agglomeration of Conductive Materials and the Dispersion State Change of the Ni-Rich NMC-Based Cathode Slurry during Storage

“…In the previous study, we confirmed that the PVDF binder in the NMP-based cathode slurry plays a major role in increasing the matrix viscosity without significantly affecting the interaction between the cathode active materials and the conductive particles. 16 Therefore, the surface properties of the active material and the conductive particles are very important in the cathode slurry in forming the microstructure. However, the cathode active material and the conductive particle show quite different surface properties.…”

“…The dispersion state and the storage stability of the manufactured electrode slurry are very important as they directly affect the subsequent electrode process as well as the electrochemical performance of the batteries. Therefore, research studies on dispersion stability have been actively conducted. − …”

Evolution of Internal Stress in Heterogeneous Electrode Composite during the Drying Process

“…In an isotropic medium, the Stokes-Einstein equation D Binder = kT/3πµd can be developed to predict the effective diffusion coefficient, where µ is the viscosity of slurries, kT is thermal energy, and d is the effective diameter of BC. Consider the relation of the viscosity between CMC [41], SA [42], and PVDF [43] at a zero-shear state, we estimate that the diffusion coefficient of BC in the CMC-SBR slurry and SA slurry is 3D PVDF and 10D PVDF . Based on the tensile experimental data of SA and CMC-SBR [36], the enthalpy of vaporization of water 2257 kJ/kg [38], we compared the binder distribution and shear modulus of dried electrode films composed of PVDF, CMC-SBR, and SA, respectively, as seen in Figure 4.…”