Secondary battery

1. A secondary battery, comprising an electrode assembly, a positive terminal, a negative terminal, a top cover plate, a conductive plate and a contact plate, wherein

the electrode assembly comprises a positive electrode plate, a negative electrode plate and a separator between the positive electrode plate and the negative electrode plate, the positive electrode plate is electrically connected with the positive terminal, and the negative electrode plate is electrically connected with the negative terminal,

the negative terminal comprises a terminal body and an extending portion connected with the terminal body,

the contact plate is attached to the negative terminal, the contact plate comprises a deformable portion and a protruding head, the deformable portion is formed as a sheet structure, the protruding head is connected with the deformable portion and protrudes in a direction toward the top cover plate, an outer edge of the deformable portion is connected with the extending portion,

the top cover plate is insulated from the negative terminal and is electrically connected with the positive terminal, the conductive plate is electrically connected with the top cover plate,

the contact plate is configured to deform to contact the conductive plate via the protruding head when an internal pressure of the secondary battery exceeds a reference pressure, so as to form an electrical connection path passing through the positive electrode plate, the positive terminal, the top cover plate, the conductive plate, the contact plate, the negative terminal and the negative electrode plate, and

a resistivity of the conductive plate is greater than or equal to a resistivity of the contact plate, and is less than a resistivity of the top cover plate.

2. The secondary battery according to claim 1 , wherein a mounting groove is defined at a side surface of the top cover plate facing toward the electrode assembly, and the conductive plate is embedded into the mounting groove and is fixedly connected with the top cover plate.

3. The secondary battery according to claim 1 , wherein the top cover plate is provided with a first through-hole, the conductive plate is embedded into the first through-hole and is fixedly connected with an inner wall of the first through-hole.

4. The secondary battery according to claim 1 , wherein the top cover plate is provided with a second through-hole, the conductive plate comprises a first plate, a second plate and a middle portion between the first plate and the second plate, the middle portion is embedded into the second through-hole, and the first plate and/or the second plate is fixedly connected with the top cover plate.

5. The secondary battery according to claim 1 , further comprising a case, wherein the top cover plate covers the case to form a first chamber and a second chamber, the first chamber is configured to package the electrode assembly, the second chamber is configured to provide deforming space for the contact plate, and

the first chamber is spaced from the second chamber by the contact plate.

6. The secondary battery according to claim 5 , wherein the extending portion is provided with an opening, and the contact plate seals the opening, so as to separate the first chamber from the second chamber.

7. The secondary battery according to claim 6 , wherein the extending portion, the contact plate and the conductive plate are made of copper, and the top cover plate is made of aluminum.

8. The secondary battery according to claim 6 , further comprising a sealing member, wherein the sealing member is arranged between the top cover plate and the extending portion; the sealing member comprises a first sealing surface and a second sealing surface, the first sealing surface is contacted with the top cover plate, and the second sealing surface is contacted with the extending portion or the contact plate, the first sealing surface and the second sealing surface are arranged opposite to each other along a height direction of the secondary battery.

9. The secondary battery according to claim 1 , further comprising a fusing member, wherein the fusing member is connected in series into the electrical connection path passing through the positive electrode plate, the positive terminal, the top cover plate, the conductive plate, the contact plate, the negative terminal and the negative electrode plate;

a cross-sectional area of the fusing member is smaller than cross-sectional areas of other portions in the electrical connection path;

the fusing member is connected in series between the positive electrode plate and the positive terminal.

10. The secondary battery according to claim 6 , further comprising a sealing member, wherein the sealing member is arranged between the top cover plate and the contact plate; the sealing member comprises a first sealing surface and a second sealing surface, the first sealing surface is contacted with the top cover plate, and the second sealing surface is contacted with the extending portion or the contact plate, the first sealing surface and the second sealing surface are arranged opposite to each other along a height direction of the secondary battery.

11. The secondary battery according to claim 1 , further comprising a fusing member, wherein the fusing member is connected in series into the electrical connection path passing through the positive electrode plate, the positive terminal, the top cover plate, the conductive plate, the contact plate, the negative terminal and the negative electrode plate;

a cross-sectional area of the fusing member is smaller than cross-sectional areas of other portions in the electrical connection path;

the fusing member is connected in series between the negative electrode plate and the negative terminal.