Lithium-ionFull Cell Manufacturing Process Training--Adhesive Section

1.The function and selection requirements of adhesives

1.1.The function of adhesives

 

Cathode and anode slurries:

Provide viscosity to ensure that particles in the slurry do not easily settle and maintain slurry stability

Provide viscosity for good fluidity

Provide viscosity to facilitate effective dispersion of materials

 

Cathode and anode electrodes：

Provide adhesive force to ensure good contact between active materials, conductive carbon, and current collectors.

Provide adhesive force to ensure good contact between particles.

The rolling process is resistant to deformation and breakage.

 

Pouch Cell :

Good adhesion to metal foils and will not peel off the metal foils due to the use of electrolyte, charging, and discharging.

Good electrochemical stability within a wide voltage range.

High melting point and a low swelling rate. Even under high temperatures, the combined structure of the adhesive and the active material needs to remain stable. Adhesives usually undergo swelling, and if the swelling exceeds a certain degree, it will affect the conductivity between the active material and the current collector, leading to capacity fade of the battery. Therefore, it is necessary to control its swelling rate.

Excellent ion transport properties and electronic conductivity.

 

2.Common classifications and introductions

2.1.Common classifications of  adhesives

 

2.1.1.Commonly Used adhesives:
PVDF— Commercially Used Cathode adhesive
CMC,SBR—Commercially Used Anode  adhesive
PTFE—Adhesive for Supercapacitors

 

2.1.2.New adhesives
PAA—High-Strength Silicon Anode  adhesive
PAN—Improved Rate Capability and Low-Temperature Performance
PMMA—Experimental Type
PAI—Experimental Type
PI—Experimental Type
PVA(Polyvinyl Alcohol) —Experimental Type
Sodium Alginate - Experimental Type

 

2.2.PVDF

 

PVDF is a polymer material with a high dielectric constant. It exhibits excellent chemical         stability, temperature characteristics, mechanical properties, and processability, which         positively contribute to enhancing bonding performance. PVDF is widely used in lithium-ion         batteries as an adhesive for both positive and negative electrodes. The PVDF monomer         consists of two hydrogen atoms and two fluorine atoms (—CH2—CF2). The electrons of the         hydrogen atoms tend to be biased towards other atoms, making them donors. The covalent         bond electron cloud is biased towards the fluorine atoms, thus fluorine atoms are referred         to as acceptors. Among the crystalline forms of PVDF, the α-form is the most stable, while         the remaining part is amorphous. The amorphous region serves as a good matrix for polar         molecules, allowing lithium ions to penetrate through the swollen thin layer of PVDF.

 

2.3.CMC

 

CMC can effectively increase the viscosity of the slurry,improve its fluidity, and enhance         the coating appearance.