TECHNICAL FIELD
The present application claims priority to Korean Patent Application No. 10-2020-
0140614 filed on October 27, 2020 in the Republic of Korea, the disclosures of which are
incorporated herein by reference.
The present disclosure relates to a secondary battery and a cap assembly used
10 therefor, and more particularly, to a secondary battery having increased safety in case of
ignition or explosion, and a cap assembly used therefor.
BACKGROUND ART
Recently, as portable devices such as smartphones and laptop computers,
15 transportation means such as electric vehicles, electric kickboards, and electric twowheeled vehicles, and devices such as energy storage systems (ESS) are widely used, the
interest in secondary batteries serving as a core part for supplying power is growing.
In particular, since secondary batteries can be used repeatedly for a long period of
time by being charged and discharged, the secondary batteries have been widely used in
20 various fields in recent years. The secondary batteries may include several types of
batteries. Among them, a lithium secondary battery has a great capacity compared to
nickel-cadmium batteries or nickel-hydrogen batteries and is more spotlighted due to its
high energy density per unit weight, so it is utilized more and more.
3
The lithium secondary battery generally uses lithium oxide and carbonaceous
material as a positive electrode active material and a negative electrode active material,
respectively. The lithium secondary battery includes an electrode assembly in which a
positive electrode plate and an negative electrode plate respectively coated with the
5 positive electrode active material and the negative electrode active material are disposed
with a separator interposed between them, and an exterior material which seals and
receives the electrode assembly together with an electrolyte.
Meanwhile, depending on the shape of the battery case, a lithium secondary battery
may be classified into a can-type secondary battery where the electrode assembly is
10 included in a battery can made of a metal material and a pouch-type battery where the
electrode assembly is included in a pouch of an aluminum laminate. In addition,
depending on the shape of the metal can, the can-type secondary battery may be further
classified into a cylindrical battery and a rectangular battery. The exterior material of the
rectangular or cylindrical secondary battery includes a battery can and a cap assembly
15 hermetically coupled to an open end of the battery can.
FIG. 1 is a sectional view showing a cap assembly 10 of a conventional cylindrical
secondary battery.
Referring to FIG. 1, the cylindrical secondary battery generally includes a
cylindrical battery can 20, a jelly-roll type electrode assembly 30 received in the battery
20 can 20, a cap assembly 10 coupled to the upper portion of the battery can 20, a beading
portion 40 provided at the front end of the battery can 20 for mounting the cap assembly 10,
and a crimping portion 50 for sealing the battery.
The electrode assembly 30 is wound into a jelly-roll shape in a state where a
4
separator is interposed between a positive electrode and a negative electrode. A positive
electrode lead 31 is attached to the positive electrode and connected to the cap assembly 10,
and a negative electrode lead (not shown) is attached to the negative electrode and
connected to the lower end of the battery can 20.
5 The cap assembly 10 includes a top cap 11 forming a positive electrode terminal, a
safety vent 12 for interrupting a current and/or for exhausting gas when the pressure in the
battery increases, an insulation member 13 for electrically separating the safety vent 12
except for a specific portion from a current interrupt member 14, and a current interrupt
member 14 connected to a positive electrode lead 31 connected to the positive electrode,
10 which are laminated in the above order. In addition, the cap assembly 10 is mounted to
the beading portion 40 of the battery can 20 in a state of being mounted to a gasket 15.
Therefore, in a normal operating condition, the positive electrode of the electrode assembly
30 is electrically connected to the top cap 11 via the positive electrode lead 31, the current
interrupt member 14, and the safety vent 12.
15 In such a cap assembly, when ignition or the like occurs at the electrode assembly
30, the pressure inside the battery can 20 increases. In addition, the pressure increase
deforms the safety vent 12 so that the gas inside the battery can 20 is discharged to the
outside. However, during the gas discharge process, the active material of the electrode
assembly 30 may be discharged to the outside of the battery can 20 in a heated state. The
20 high-temperature active material discharged in this way may be adhered in the form of a
fallout to other components around the secondary battery, for example other secondary
batteries, to heat the secondary batteries.

WHAT IS CLAIMED IS:
1. A cap assembly for a secondary battery, which is coupled to an open end of
a battery can, the cap assembly comprising:
5 a top cap disposed on an uppermost portion of the cap assembly in a protrusive
form to form a positive electrode terminal;
a safety vent disposed below the top cap to deform a shape when an internal
pressure of the battery can increases;
a gasket configured to surround edges of the top cap and the safety vent; and
10 a screen member interposed between the top cap and the safety vent and having an
edge surrounded by the gasket, the screen member being at least partially configured in a
mesh form.
2. The cap assembly for a secondary battery according to claim 1, further
15 comprising:
a current interrupt member having an upper portion connected to a lower end of
the safety vent and a lower portion connected to an electrode assembly and configured to
interrupt electric connection between the electrode assembly and the top cap when the
safety vent deforms.
20
3. The cap assembly for a secondary battery according to claim 1,
wherein the screen member is formed in a dome shape such that at least a central
portion thereof protrudes upward.
31
4. The cap assembly for a secondary battery according to claim 1,
wherein the screen member includes a protrusion formed to protrude upward or
downward.
5
5. The cap assembly for a secondary battery according to claim 1,
wherein the screen member includes a plurality of unit screens stacked on each
other in a vertical direction.
10 6. The cap assembly for a secondary battery according to claim 5,
wherein the plurality of unit screens are configured to have different mesh forms
from each other.
7. The cap assembly for a secondary battery according to claim 5,
15 wherein an upper screen among the plurality of unit screens is formed in a dome
shape such that at least a central portion is convex upward, and a lower screen among the
plurality of unit screens is formed in a dome shape such that at least a central portion is
convex downward.
20 8. The cap assembly for a secondary battery according to claim 7,
wherein the lower screen is configured such that a convex shape thereof is
reversed from a downward direction to an upward direction by the deformation of the
safety vent.
32
9. The cap assembly for a secondary battery according to claim 8,
wherein the lower screen is configured such that at least some of holes formed
therein are located at different positions from holes formed in the upper screen in a
5 horizontal direction when the convex shape is reversed.
10. A secondary battery, comprising the cap assembly for a secondary battery
according to any one of claims 1 to 9.
10 11. A battery pack, comprising at least one secondary battery according to
claim 10.