Technical Field
[ 1 ] The present invention relates to a battery safety device adapted to form an
electrical circuit and convert a charged state of the battery to a discharged state when
compressed by a predetermined pressure or higher. Also, the present invention relates
to a battery having the safety device.
Background Art
[2] As recent electronic appliances rapidly become wireless and portable, a non-
aqueous electrolyte secondary battery having large capacity and high energy density
has been developed as their driving power source. However, such a non-aqueous
electrolyte secondary battery is exposed to danger in that, when a strong external
pressure or an external impact caused by a nail or nipper is applied, the interior of the
cell is damaged and the cell may ignite or explode.
[3] In particular, since the positive electrode active material is sensitive to voltage, the
reactivity between the positive electrode and the electrolyte increases aS the battery is
charged and the voltage rises. The surface of the positive electrode then decomposes
and oxidation reaction occurs to the electrolyte. This increases the danger of fire or
explosion.
[4] Such a safety problem becomes more important as the battery, specifically the non-
aqueous electrolyte secondary battery (for example, lithium secondary battery), has
larger capacity and higher energy density.
Disclosure
[5] The present invention is directed to that substantially obviates one or more
problems due to limitations and disadvantages of the related art.
[6] It is an object of the present invention to provide a method for lowering the
charged state of a cell before it is damaged by an external impact caused by a pressure,
a nail or a nipper by positioning a safety device inside or outside the cell so that the
battery is safe from the external impact

[7] To achieve this object and other advantages in accordance with the purpose of the
invention, as embodied and broadly described herein, there is provided a battery comprising
an electrode assembly and a safety device on and positioned outside of the electrode
assembly, wherein the safety device is adapted to form an electrical circuit when a
predetermined pressure or higher is applied to both of the electrode assembly and the safety
device and convert state of charge of the electrode assembly to a discharged state, wherein
the safety device has a first metal plate, a PSCF (pressure-sensitive conducting film), and a
second metal plate, which are in contact with each other, and wherein the safety device is
adapted to discharge the electrode assembly within 60 seconds when a predetermined
pressure or higher is applied to the safety device and the first and second metal plates are
directly electrically connected in parallel to positive and negative electrodes, respectively.
[8] According to another aspect of the present invention, there is provided a safety
device for a battery, comprising a first metal plate, a pressure-sensitive conducting film
and a second metal plate, which are adapted to form an electrical circuit when compressed
by a predetermined pressure or higher and convert the charged state of the battery to the
discharged state, wherein the first metal plate, the pressure-sensitive conducting film, and
the second metal plate are adapted to discharged the battery within 60 seconds when a
predetermined pressure or higher is applied to the first metal plate, the pressure-sensitive
conducting film, and the second metal plate, and the first and second metal plates are to be
directly electrically connected in parallel to positive electrode and negative electrode of the
battery, respectively, and the safety device is on and positioned outside of the electrode
assembly.
[9] According to still another aspect of the present invention, there is provided a method
for adjusting the safety of a battery by converting the charged state of the battery to the
discharged state, before the battery is damaged by a pressure, through an electrical circuit
formed on a safety device by means of the pressure, wherein the safety device has a first
metal plate, a pressure-sensitive conducting film, and a second metal plate which are
sequentially laminated and are in contact with each other, and wherein the safety device is
adapted to discharged the battery within 60 seconds when a predetermined pressure or
higher is applied to both of the battery and safety device, and the first and second metal

plates are directly electrically connected in parallel to positive electrode and negative
electrode of the battery, respectively, and the safety device is on and positioned outside of
the battery.
[11] Additional advantages, objects, and features of the invention will be set forth in
part in the description which follows and in part will become apparent to those having
ordinary skill in the art upon examination of the following or may be learned by
practicing the invention. The objectives and other advantages of the invention may be
realized and attained by the structure particularly pointed out in the written description
and claims hereof as well as the appended drawings.
Description of Drawings
[12] The accompanying drawings, which are included to provide a further un-
derstanding of the invention and are incorporated in and constitute a part of this ap-
plication, illustrate embodiment(s) of the invention and together with the description
serve to explain the principle of the invention. In the drawings:
[13] FIG. 1 is a diagrammatic view showing the operating principle of an ACF safety
device according to the present invention;

[14] FIG. 2 is a diagrammatic view showing a pouch-type battery having an ACF safety
device electrically connected thereto according to the present invention;
[15] FIG. 3 is a diagrammatic view showing a metal can-type battery having an ACF
safety device electrically connected thereto according to the present invention;
[16] FIG. 4 is a graph showing the result of local crush experiment of a battery man-
ufactured in Example 1;
[17] FIG. 5 is a graph showing the result of local crush experiment of a battery man-
ufactured in Example 2;
[18] FIG. 6 is a graph showing the result of local crush experiment of a battery man-
ufactured in Example 3; and
[19] FIG. 7 is a graph showing the result of local crush experiment of a battery man-
ufactured in Comparative example 1.

Mode for Invention
[20] Reference will now be made in detail to the preferred embodiment of the present
invention, examples of which are illustrated in the accompanying drawings.
[21] Hereinafter, according to the present invention will be explained with reference to
the accompanying drawings.
[22] The present invention is characterized in that in order to lower the charged state of
a cell by sensing the application of an external impact caused by a pressure, a nail, or a
nipper or an external pressure to a battery, a battery is provided with a safety device
adapted to exhibit electrical conductivity in the case of an external impact or external
compression.
[23] As a non-limiting example of a safety device for exhibiting electrical conductivity
in the case of an external impact or external compression, the present invention
provides a safety device having a PSCF interposed between two metal plates (for
example, collectors) through which current can flow and adapted to conduct current,
when a predetermined pressure or higher occurs, in the direction of the pressure (refer
to FIG. 1).
[24] As a non-limiting example of the PSCF, an ACF (anisotropic conductive film) is
provided.
[25] The ACF refers to an adhesive film including an insulating adhesive having a
thickness of 15-35um and electrically conductive balls composed of fine electrically
conductive particles having a diameter of 3-15µm dispersed therein. The idea of the
present invention is not limited by the thickness of the adhesive film and the diameter
of the electrically conductive particles constituting the ACF. The electrically
conductive particles include carbon fibers, metal (Ni, solder), and metal.
(Ni/Au)-coated plastic balls. This is just an illustration of the embodiments of the
present invention and is not a general term for the PSCF. It is obvious t:> those skilled
in the art that any PSCF can be applied to the principle of the present invention.
[26] The adhesive material includes thermoplastic material (styrene butadiene rubber,
polyvinyl butylene), thermosetting material (epoxy resin, polyurethane, acrylic resin),
and a mixture of thermoplastic material and thermosetting material.
[27] The metal plate used in the present invention may be made of any metal having
electrical conductivity, such as aluminum metal, copper metal, and nickel metal.
[28] The metal plate preferably has excellent thermal conductivity so that, in a normal
or special situation, heat can be dispersed from inside the battery to the thermally
conductive metal plate via a terminal.
[29] The operation of a battery having a safety device adapted to exhibit electrical con-
ductivity when a predetermined pressure or higher is applied in the case of an external,
impact or external compression according to the present invention will aow be

described with reference to the drawings.
[30] The safety device according to the present invention includes a first metal plate, a
second metal plate, and a PSCF interposed between both metal plates and adapted to
exhibit electrical conductivity when a predetermined pressure or higher is applied. An
example of the safety device, as shown in FIG. 1, includes collectors acting as the
metal plates and an ACF acting as the PSCF.
[31 ] The ACF acts as a nonconductor through which no current is applied to flow
during a normal state and, when a predetermined pressure or higher occurs, conducts
current in the direction of the pressure.
[32] As shown in FIG. 1, the first metal plate (collector) of both metal plates positioned
on both surfaces of the ACF is electrically connected to the positive electrode of the
battery and the second metal plate (collector) to the negative electrode thereof.
[33] In the battery having the inventive safety device connected thereto, both metal
plates are electrically insulated from each other by the ACF, as long as no external
pressure is applied to them, and no current flows between them. The battery then
functions normally and maintains the charged state.
[34] When a pressure caused by an external impact and the like is applied to the battery
having the inventive safety device connected thereto, both metal plates are electrically
connected to each other. This is because the ACF exhibits electrical conductivity when
the pressure reaches a predetermined level. The battery is then discharged and the
internal voltage of the battery drops abruptly. In the discharged state, the battery does
not ignite nor explode even when an impact caused by an external pressure, a nail, or a
nipper is applied thereto. As such, the present invention can improve the safety of the
battery by lowering the charged state of the cell before it explodes, when a pre-
determined pressure or higher is applied to the metal plates due to an external impact
cause by a pressure, a nail, or a nipper.
[35] The inventive safety device is preferably positioned perpendicularly to a direction
in which most pressure is applied to the battery in the case of an external impact or
external compression.
[36] The inventive safety device may be positioned inside or outside the cell, but is
preferably positioned outside.
[37] When positioned outside the battery, the inventive safety device may be used while
being exposed or while being enclosed by a polymer layer having electrical insulation
property.
[38] Meanwhile, examples of connection of the safety device according to the present
invention to a battery are illustrated FIG. 2.
[39] FIG. 2 shows a pouch-type battery having the inventive safety device connected
thereto.

[40] In general, a pouch-type battery is of a lamination type and includes at least one
positive electrode plate and at least one negative electrode plate which are laminated
alternately. The lamination-type battery has positive and negative electrode leads for
connecting the positive and negative electrode plates to the exterior of he battery, re-
spectively. The leads are connected to a power source on the exterior of the battery
sheath.
[41] The inventive safety device including the first and second metal plates and the
ACF interposed between them are laminated together with the outermost positive
electrode plate and/or the outermost negative electrode plate. The first metal plate is
electrically connected to a part of the positive electrode plate, to the positive electrode
lead, or to the positive electrode terminal and the second metal plate is electrically
connected to a part of the negative electrode plate, to the negative electrode lead, or to
the negative electrode terminal.
[42] The inventive safety device may be laminated directly adjacent to the electrode
plate, but is preferably laminated on the exterior of the battery sheath and only
electrically connected to the positive and negative electrodes.
[43] FIG. 3 shows a can-type battery having the inventive safety device connected
thereto.

[44] In general, a can-type battery has an electrode assembly including positive and
negative electrode plates and a separator placed in a container including a can and a
cap. The container acts as an electrode terminal (positive electrode terminal in FIG. 3)
and an electrode terminal having the opposite polarity (negative electrode terminal in
FIG. 3) protrudes from the container while being insulated.
[45] The container of the can-type battery can act as the first metal plate of the inventive

safety device. Therefore, the second metal plate of the inventive safety device is
positioned parallel to at least one surface of the container with the ACF interposed
between them and a part of the second metal plate is electrically connected to the
electrode terminal having the opposite polarity.
[46] The inventive safety device may be used for any type of battery, including a
primary battery and a secondary battery, as long as it has been charged. As a non-
limiting example, the inventive safety device may be used for a lithium secondary
battery including a) a positive electrode capable of lithium ion intercalution/dein-
tercalation, b) a negative electrode capable of lithium ion intercalation/deintercalation,
c) a porous separator, and d) a non-aqueous electrolyte including lithium salt and
electrolyte compound.
[47] The non-aqueous electrolyte includes cyclic carbonate and/or linear carbonate. The
cyclic carbonate may be, for example, ethylene carbonate (EC), propylene carbonate
(PC), gamma-butyrolactone (GBL). The linear carbonate is, for example, preferably at

least one selected from the group consisting of diethyl carbonate (DEC), dimethyl
carbonate (DMC), ethylmethyl carbonate (EMC), and methyl propyl carbonate (MPC).
[48] The lithium salt included in the non-aqueous electrolyte is preferably selected from
the group consisting of LiClO4 , LiCF3 SO3 , LiPF , LiBF , LiAsF , and LiN(CF3 SO2 )2 .
[49] As the negative electrode active material, carbon, lithium metal or alloy is
preferably used. In addition, metal oxide capable of lithium ion intercalation/dein-
tercalation and having a potential for lithium of less than 2V, such as TiO2 or SnO 2,

may also be used.
[50] The positive electrode active material is preferably a lithium-containing transition
metal oxide and, for example, is preferably at least one selected from the group
consisting of LiCoO2 , LINiO2 , LiMn2 O4 , LiMnO2 , and LiNi Cox O2 (0