Expandable microbead, preparation thereof, electrode plate and secondary battery comprising expandable microbead

A method for preparing an expandable microbead, comprising:

• step (1):
• preparing a prepolymerization solution of a melamine resin from formaldehyde and melamine, wherein optionally, the prepolymerization solution comprises formaldehyde, melamine, a solvent, and a prepolymer of formaldehyde and melamine, and more optionally, a solid content of the prepolymerization solution is 3-30%, optionally 10-25%;
• step (2):
• preparing an emulsion from a foamable azo compound, wherein optionally, the foamable azo compound includes azodicarbonamide, azobisisobutyronitrile, and/or diisopropyl azodicarboxylate, and more optionally, a solid content of the emulsion is 2-20%, optionally 5-10%;
• and
• step (3):
• preparing the expandable microbead from the prepolymerization solution in the step (1) and the emulsion in the step (2).

An electrode plate, comprising a current collector and a safe conductive coating, wherein the safe conductive coating is coated on a part or whole of the current collector, the safe conductive coating comprises a conductive agent, an expandable microbead, a binder, and optionally a dispersant, wherein the expandable microbead has a core-shell structure, the shell comprises or consists of a melamine resin, and the core comprises a foamable azo compound;

• optionally, the shell has a thickness of 0.05-0.5 μm, optionally 0.1-0.2 μm;
• optionally, the foamable azo compound includes azodicarbonamide, azobisisobutyronitrile, and/or diisopropyl azodicarboxylate;
• optionally, the expandable microbead has an initial foaming temperature of 80° C.-200° C., and an optimal initial foaming temperature of 100° C.-150° C.;
• and
• optionally, the expandable microbead has a Dv50 of 0.2-10 μm, optionally 0.5-5 μm, and more optionally, the expandable microbead has a Dv50 of less than or equal to a thickness of the safe conductive coating.