Polyvinylidene fluoride binder(PVDF) is currently the most commonly used oil binder in the lithium ion battery industry. It is a non-polar chain polymer binder. It is characterized by strong oxidation resistance, good thermal stability and easy dispersion. N-methylpyrrolidone (NMP) is required as a solvent. This solvent has a high volatilization temperature, has a certain environmental pollution, and is expensive.
Obvious deficiencies include:
1） Young’s modulus is relatively high, between 1-4GPa, the flexibility of the pole piece is not good enough;
2） When PVDF absorbs water, the molecular weight decreases and the viscosity becomes poor, so the humidity requirement for the environment is relatively high;
3） For ion and electronic insulation, there is a certain degree of swelling in the electrolyte. It reacts exothermically with lithium metal and LixC6 at higher temperatures, which is detrimental to the safety of the battery.
Conventional PVDF, the main mechanism of action is van der Waals force, that is, the intermolecular force acts as a bonding force, and some modified PVDF, the mechanism of action has two parts, one part is the van der Waals force brought by high molecular weight. On the other hand, it is due to the chemical bond between the foil and the foil.
Current synthetic methods include suspension polymerization and emulsion polymerization.
For different cathode materials, PVDF synthesized by different methods can be applied, and also combined with the corresponding homogenization process, in order to achieve a good effect.