Cap assembly for secondary battery, secondary battery and battery module

A cap assembly for a secondary battery, comprising a cap plate, a first electrode terminal, a sealing member, a fixing member and a connecting member, wherein:

• the cap plate has an electrode lead-out hole;
• the first electrode terminal comprises a first terminal board and a second terminal board connected with the first terminal board, wherein the first terminal board is located at a side of the second terminal board away from the cap plate, the second terminal board completely covers the electrode lead-out hole, and the material of the first terminal board and the material of the second terminal board have different base metals;
• the sealing member surrounds the electrode lead-out hole and is disposed between the cap plate and the first electrode terminal to seal the electrode lead-out hole;
• wherein the cap plate is made of a metal material, the connecting member is made of a metal material, the fixing member is a hard plastic member, the fixing member is directly fixed to the connecting member, the connecting member is in direct contact with the cap plate so that the connecting member is fixed to the cap plate, the fixing member is directly fixed to the cap plate by the connecting member, and an outer peripheral surface of the first electrode terminal is at least partially surrounded by the fixing member to fix the first electrode terminal to the fixing member, and wherein the first electrode terminal is completely located outside a shell of the secondary battery.