Do you know about SBR adhesives?

Foreword: SBR for lithium batteries is a styrene-butadiene latex, an aqueous binder. It is formed by emulsion polymerization and copolymerization of styrene (Styrene) and butadiene (butadiene) monomers with water as a medium and emulsifier initiator. The state is an aqueous emulsion with a solid content of about 50%.

What is SBR?

SBR for lithium batteries is a styrene-butadiene latex and an aqueous binder. It is formed by emulsion polymerization and copolymerization of styrene (Styrene) and butadiene (Butadiene) monomers with water as a medium, adding an emulsifier initiator, etc. The state is a solid content of about 50% water emulsion.

SBR latex particle unit is a core-shell structure, the shell is a cross-linked structure of copolymer molecular chains, and the shell is a hydrophilic polar group and surfactant, so the oily styrene and butadiene polymer can exist stably in water

SBR is a substance that coexists with hydrophilicity and lipophilicity.

- Aqueous groups combine with foil surface groups to form bonding force, which is beneficial to dispersibility and slurry stability

- The oily segment is combined with the negative electrode graphite to form a bonding force, so as to achieve the effect of bonding

Some important parameters of SBR

Particle size: With the same addition amount, the small particle size determines that the contact point between the binder and the active material increases, so it can have higher bonding force. The consistency of particle size distribution is also the criterion for judging the quality of SBR.

Crosslinking degree: divided into high crosslinking and low crosslinking degree SBR, high crosslinking degree, slow film formation, strong cohesion, low elongation, and low crosslinking is just the opposite.

Tg temperature: The glass transition temperature of SBR is the temperature at which it changes from a high elastic state to a glassy state. High Tg indicates that the material is relatively resistant to low temperature. For lithium batteries, an appropriately low Tg temperature will help the low temperature performance of the battery. Of course, this single factor is not an absolute factor. Synthetic monomers S-styrene and B-butadiene are called S-hard monomer and B-soft monomer, respectively. The Tg temperature of SBR is 100 ° C and -50 ° C, and the Tg temperature of SBR is adjusted by controlling the different proportions of the two.

Liquid absorption performance: including liquid absorption capacity and liquid absorption expansion performance, a good SBR must have a good balance of liquid absorption performance and smaller expansion performance.

Elongation: This is related to the elasticity of SBR. After elongation like a spring, it can return to the initial state. Now Si anode materials have higher requirements for this.

Film formation process: divided into stable state and unstable state, as shown below