Positive electrode paste is a mixture of conductive agent, binder, and solvent. It is prepared by kneading and mixing together. Depending on the positive electrode active material, the paste viscosity varies. Generally, the paste viscosity is less than R. Using the rheometer, the paste viscosity was measured. The conductive agent is a granular carbon aggregate, coal tar pitch, or a mixture of these. In traditional Soderberg electrode paste, the paste softens as it heats.
The paste viscosity can be reduced by adding a copolymer. Copolymer is a polymer that is added in the kneading or mixing stage of positive electrode paste. A copolymer with low molecular weight has a better paste viscosity reduction effect. However, adding large amounts of copolymer has less impact on the paste viscosity. As an example, one green Soderberg paste with a carbonization temperature of 338 K (65 degC) and another green paste with a carbonization temperature of 90 degC both have softening points of 338 K (65 degC).
Adding a copolymer with high molecular weight does not affect the peel strength of positive electrode composite. However, it can have an impact on the adhesive adhesion between the positive electrode paste and the aluminum foil. Moreover, the higher the amount of copolymer, the greater the difficulty of obtaining the paste viscosity reduction effect.
The present invention has been developed to improve the peel strength of positive electrode composite by using a combination of a monomer and a structural unit. Specifically, the structural unit consists of hydrogen atoms, which reduces the adhesive adhesion between the positive electrode active material and the binder. This helps in preventing the formation of fibers between the fluorine-based binders. These atoms also enhance the dispersibility of the positive electrode active material.
In addition, the copolymer of the present invention can be added at any stage of the kneading or preparing process. Therefore, the copolymer can be added even when the components are still in powder form. Furthermore, the paste viscosity reduction rate can be calculated for the copolymer addition. The following tables provide the viscosity and viscosity reduction rates for the positive electrode paste.
As the paste becomes fluid, the thermal conductivity of the paste begins to decrease. However, this decrease does not affect the thermal conductivity of the paste in the range of 600 degC to 873 K. On the other hand, the thermal conductivity of the paste increases dramatically as the paste approaches its maximum temperature. In comparison, the thermal conductivity of the green paste does not increase in this range.
Compared with the green pastes, the pre-baked electrode material has a higher thermal conductivity. Specifically, the pre-baked electrode material has an order of magnitude higher thermal conductivity than the green paste. When the temperature of the paste reaches 750 K, the paste's thermal conductivity is almost linear. However, when the temperature of the paste reaches 800 degC, the paste's thermal conductivity is more than four times that of the green paste.
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