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.
Highlights
Rechargeable lithium-ion batteries (LIBs) are widely used in daily applications such as cordless-home-appliances and electric vehicles because of their high specific energy, light weight, and long cycle-life [1]
The present study aims to reveal the role of Poly(vinylidene fluoride) (PVDF) in microstructure and rheological properties of cathode slurries consisting of Li(Ni1/3 Mn1/3 Co1/3 )O2 (NCM) [29,30] as an active material, carbon black (CB) as a conductive agent, PVDF as a polymeric binder, and NMP as a solvent
G0 in Figure 1B is independent of the addition of PVDF, with G” increase at high ω, which indicates that the addition of PVDF mainly increases matrix viscosity with a limited influence on the solid-like character of the CB network
Summary
Rechargeable lithium-ion batteries (LIBs) are widely used in daily applications such as cordless-home-appliances and electric vehicles because of their high specific energy, light weight, and long cycle-life [1]. A typical electrode fabrication starts with preparation of battery slurry by mixing active materials, conductive agents, polymeric binders, and solvents. The dried electrodes are calendared to improve electrical conductivity and further dried to remove the residual solvent and moisture before making the cells [2]. Many commercial LIBs use Poly (vinylidene fluoride) (PVDF) as a binder in the cathode because of its excellent electrochemical stability, good wettability with electrolyte and acceptable binding ability between active materials and current collectors [3]. (vinylidene fluoride) (PVDF) is a linear type synthetic semi-crystalline homopolymer with the repeat unit (CH2CF2). PVDF is well soluble in aprotic solvent such as Dimethylformamide (DMF), Dimethyl sulfoxide (DMSO) and N-Methyl-2-pyrrolidone (NMP), among which NMP is mainly utilized in commercial cathode LIBs
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