SECONDARY BATTERY EMPLOYING BATTERY CASE OF
HIGH STRENGTH
FIELD OF THE INVENTION
The present invention relates to a secondary battery with a high-strength
battery case. More specifically, the present invention relates to a secondary battery
utilizing a high-strength battery case capable of significantly reducing the risk of
invasion, ignition or explosion as compared to conventional batteries, even when the
battery is exposed to external physical impact or is pressed by sharp objects.
BACKGROUND OF THE INVENTION
Generally, a lithium ion polymer battery 1, also called "a pouch cell", as shown
in FIGS. 1 and 2, is made up of a case body 2 including an internal space 2a having a
predetermined size formed therein; a cover 3 rotatably connected to the case body 2; an
electrode assembly 4 composed of a cathode plate 4a, an anode plate 4b and a separator
sheet 4c and being placed on a receiving part 2a of the case body 2; connection parts
extending outward hi the length direction from the ends of the cathode plate 4a and
anode plate 4b of the electrode assembly 4; and a cathode terminal 6 and an anode
terminal 7 connected to the corresponding connection parts 5.
Extension portions 2b having predetermined "widths for heat sealing "are"formed
horizontally and outward on the upper edges of the electrode assembly-receiving part
of the case body 2. In addition, non-conductive terminal tapes 8 are attached to the
central parts of the cathode terminal 6 and anode terminal 7 connected to the
corresponding connection parts 5, in order to prevent short-circuiting between a heat
sealer (not shown) and the electrode terminals 6 and 7 when the extension portions 2b
of the case body 2 and edges 3a of the cover 3 are heat sealed via the heat sealer, and at
the same time, in order to increase scalability between respective terminals 6 and 7 and
sealing parts 2b and 3a.
Therefore, the battery is prepared by placing an electrode assembly 4
composed of the cathode plate 4a, the anode plate 4b and the separator sheet 4c in the
receiving part 2a of the case body 2, injecting a predetermined amount of an electrolyte
into the receiving part 2a, and sealing the extension portions 2b of the case body 2 and
the edges 3 a of the cover 3 using the heat sealer (not shown) such that the electrode is
not leaked out, under the condition in which the cover 3 is close to the case body 2.
Herein, the connection parts 5 of the electrode assembly 4 are connected to the
corresponding electrode terminals 6 and 7 having terminal tapes 8 attached to the
central parts thereof, and some portions of these electrode terminals 6 and 7 and
terminal tapes 8 protrude outside of the case body 2 and cover 3.
Meanwhile, the case body 2 and cover 3 are, respectively, made up of an outer
coating layer 9a formed of an oriented nylon (ONy) film, a barrier layer 9b formed of
aluminum (Al) and an inner sealant layer 9c formed of a cast polypropylene film (CPP),
and the edge of the inner sealant layer 9c is coated with a hot melt layer (not shown),
thus enabling the extension portions 2b of the case body 2 and the edges 3a of the cover
3 to be closely fixed therebetween, via heat and pressure of the heat sealer.
However, the conventional case body and cover made up of the outer coating
layer of ONy, the barrier layer of aluminum (Al) and the inner sealant layer of CPP
have suffered from problems such as invasion, ignition or explosion due to
susceptibility to damage thereof when the battery made up of such a case body and
cover is exposed to physical impact or is pressed by sharp objects.
SUMMARY OF THE INVENTION
Therefore, the present invention has been made in view of the above
problems, and it is an object of the present invention to provide a secondary battery
utilizing a high-strength battery case capable of significantly reducing the probability
of invasion, ignition or explosion as compared to conventional batteries, even when
the battery is exposed to external physical impact or is pressed by sharp objects.
In accordance with an aspect of the present invention, the above and other
objects can be accomplished by the provision of a secondary battery having an
electrode assembly installed hi a battery case made up of a laminated sheet composed
of an outer coating layer of a polymer film, a barrier layer of a metal foil and an inner
sealant layer of a polyolefin material, wherein the metal foil of the barrier layer is
formed of an aluminum alloy, the outer coating layer is formed of polyethylene
naphthalate (PEN) and/or the outer surface of the outer coating layer is provided with a
polyethylene terephthalate (PET) layer, and wherein the battery case has a nail
penetration resistance force of more than 6.5 kgf.
Therefore, the secondary battery in accordance with the present invention is
characterized by high strength in a manner that the barrier layer of the metal foil is
' constructed to" improve the strength of the battery case in addition to blocking
functions such as the prevention of entrance or leakage of materials exhibited by
conventional arts as a main function, and the outer coating layer or the outer surface
thereof further includes an additional resin layer.
The nail penetration resistance force means the penetration force measured
according to the Puncture Test FTMS 101C Method. In this connection, conventional
laminated sheet-type battery cases have nail penetration resistance force of about 5.0
kgf, while the battery case in accordance with the present invention has a nail
penetration resistance force of at least 6.5 kgf, preferably 6.5 to 10.0 kgf and more
preferably 7.0 to 8.5 kgf. It can be said that a nail penetration resistance force within the
above range will ensure battery safety is secured against the probability of damage to
the battery by a variety of nail-like members when the battery is used.
The barrier layer contributing to increased strength of the battery case has a
thickness of 20 to 150 pm. Where the thickness of the barrier layer is too thin, it is
difficult to obtain desired material-blocking and strength-improving effects. In contrast,
where the thickness of the barrier layer is too thick, this undesirably leads to lowered
processability and an increased thickness of the sheet.
The aluminum alloy constituting the barrier layer exhibits a difference in
strength thereof depending upon the species of the alloy ingredients, and includes, but is
not limited to, aluminum alloy Nos. 8079, 1N30, 8021, 3003, 3004, 3005, 3104 and
3105, for example. These aluminum alloys may be used alone or any combination
thereof. Table 1 below discloses the species of the alloy ingredients and contents
thereof. The balance except for "Others" is the content of aluminum.
(Table Removed) Among the above-mentioned aluminum alloys, 8079, 1N30, 8021 and 3004
may in particular be preferably employed as the metal foil of the barrier layer.
The polymer film of the outer coating layer preferably has a thickness of 5 to
40 urn. Where the film thickness is too thin, it is difficult to obtain predetermined
strength. In contrast, where the film thickness is too thick, this undesirably leads to an
increased thickness of the sheet. As described hereinbefore, the polymer film of the
outer coating layer hi the present invention may be optionally formed of PEN, or
otherwise may be preferably formed of an oriented nylon film.
When a PET layer is optionally added to the outer surface of the outer coating
layer, the PET layer preferably has a thickness of 5 to 30 pni. Where the film thickness
is too thin, it is difficult to achieve strength improving effects via addition of the PET
layer. Conversely, where the film thickness is too thick, the thickness of the sheet is
-undesirably increased.
Even though use of the PEN film as the outer coating layer and addition of the
PET layer to the outer surface of the outer coating layer are optional, the abovementioned
desired nail penetration resistance force should be obtained via the
application of at least one of these layers. In addition, co-application of the PEN film
and PET layer can further improve the strength of the battery case.
The electrode assembly is not particularly limited and thus may also be a jellyroll
type or stacked type. In addition, there is no particular limit to the construction of
the electrode assembly so long as it can be installed in the battery case in accordance
with the present invention. For example, lithium ion batteries, lithium ion polymer
batteries and lithium polymer batteries can be employed.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects, features and other advantages of the present
invention will be more clearly understood from the following detailed description
taken in conjunction with the accompanying drawings, in which:
FIG. 1 schematically shows an exploded perspective view and a partially
enlarged cross-sectional view of a pouch type of a lithium ion polymer battery in
accordance with a conventional art;
FIG. 2 schematically shows a perspective view of a battery of FIG. 1 in an
assembled state; and
FIG. 3 schematically shows an exploded perspective view and a partially
enlarged cross-sectional view of a pouch type of a lithium ion polymer battery in
—accordance with one embodiment of the present invention."
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Hereinafter, the present invention will be described in more detail with
reference to the accompanying drawings.
FIG. 3 schematically shows an exploded perspective view of a secondary
battery utilizing a battery case made up of a high-strength laminated sheet hi
accordance with the present invention.
Referring to FIG. 3, a battery 1 in accordance with the present invention,
similar to the battery in FIG. 1, takes a structure in which an electrode assembly 4 is
installed hi a battery case made up of a case body 2 having a receiving part 2a formed
therein and a cover 3 rotatably and integrally formed on one end of the case body 2.
The case body 2 and cover 3 form a battery case 9 of a laminated sheet
composed of an outer coating layer 9a of a polymer film, a barrier layer 9b of a metal
foil and an inner sealant layer 9c of a polyolefin material, wherein the outer surface of
the outer coating layer 9a is provided with a PET layer 9d having excellent tensile
strength, impact strength and durability.
A polymer film of the outer coating layer 9a is formed of an oriented nylon
film ONylS or ONy25. Herein, the number suffixed to the right of ONy represents a
thickness. The outer coating layer 9a may be formed of PEN having excellent tensile
strength, impact strength and durability.
The metal foil of the barrier layer 9b is formed of an aluminum alloy No. 8079,
1N30,8021 or 3004.
The inner sealant layer 9c is formed of a cast polypropylene fihn (GPP) and nas
a thickness of 30 to 150 (Jin.
The laminated sheet constituting the battery case in the battery of the present
invention can be fabricated in various manners.
For example, the laminated sheet can be prepared by sequentially stacking
films and metal foils constituting the respective layers followed by bonding
therebetween. Bonding can be carried out via dry lamination or extrusion lamination.
Dry lamination is a method involving applying an adhesive between two materials,
drying and bonding two materials at a temperature and pressure higher than room
temperature and atmospheric pressure using a heating roll. In addition, extrusion
lamination is a method involving applying an adhesive between two materials and
bonding two materials at room temperature under predetermined pressure using a
pressing roll.
EXAMPLES
Now, the present invention will be described in more detail with reference to
the following examples. These examples are provided only for illustrating the present
15 invention and should not be construed as limiting the scope and spirit of the present
invention.
[Examples 1 through 4 and Comparative Example 1]
Laminated sheets were prepared according to composition formula given in
Table 2 below. Utilizing the thus-prepared laminated sheets, pouch types of battery
cases having a structure as shown in FIG. 3 were prepared via dry lamination.
(Table Removed)Note: The number suffixed to the right of PET, ONy, PEN, Al and CPP represents a
thickness.
A stacked type of an electrode assembly, as shown hi FIG. 3, was mounted on
the respective battery cases, and the resulting structures were impregnated with an
electrolyte. Then, a case body and a cover were heat sealed therebetween, thereby
preparing pouch types of battery cells.
Nail penetration resistance forces of the thus-prepared battery cells were
measured using a battery penetration experimental apparatus (UTM tester) under FTMS
101C conditions. The results thus obtained are given in Table 3 below. Nail penetration
resistance force on the above apparatus was expressed as force measured when a naillike
member has penetrated through the battery case by pushing the member on the
(Table Removed)As can be seen from Table 3, it was confirmed that a conventional battery
(Comparative Example 1) is penetrated by the nail-like member at force of 5.0 kgf,
while all batteries of the present invention (Examples 1 through 4) exhibit a penetration
force of more than 6.5 kgf. Therefore, it can be seen that batteries of the present
invention are not easily penetrated by impact of various nail-like members that can be
considered during the use of batteries and thus are capable of securing battery safety.
Further, it was confirmed that batteries of Examples 1 and 2, hi which a PET layer was
added to the outer surface of the outer coating layer, particularly exhibit excellent
mechanical strength.
INDUSTRIAL APPLICABILITY
As apparent from the above description, a battery in accordance with the
present invention achieves high mechanical strength via provision of a barrier layer of
an aluminum (Al) alloy and a PEN outer coating layer and/or an additional PET layer.
Therefore, it is possible to prepare a battery having further improved safety due to the
ability to significantly reduce the probability of invasion, ignition or explosion as
compared to conventional batteries, even when the battery is exposed to external
physical impact or is pressed by sharp objects.
Although the preferred embodiments of the present invention have been
disclosed for illustrative purposes, those skilled in the art will appreciate that various
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modifications, additions and substitutions are possible, without departing from the
scope and spirit of the invention as disclosed in the accompanying claims.

WHAT IS CLAIMED IS;
1. A secondary battery having an electrode assembly installed in a battery case
made up of a laminated sheet composed of an outer coating layer of a polymer film, a
barrier layer of a metal foil and an inner sealant layer of a polyolefin material, wherein
the metal foil of the barrier layer is formed of an aluminum alloy, the outer coating layer
is formed of polyethylene naphthalate (PEN) and/or the outer surface of the outer
coating layer is provided with a polyethylene terephthalate (PET) layer, and wherein the
battery has a nail penetration resistance force of more than 6.5 kgf.
2. The battery according to claim 1, wherein the nail penetration resistance force
is in the range of 6.5 to 10.0 kgf.
3. The battery according to claim 1, wherein the barrier layer has a thickness of
20 to 150 urn.
4. The battery according to claim 1, wherein the aluminum alloy is selected from
the group consisting of aluminum alloy Nos. 8079, 1N30, 8021, 3003, 3004, 3005,
3104, 3105 and any combination thereof.
5. The battery according to claim 4, wherein the aluminum alloy is selected from
the group consisting of aluminum alloy Nos. 8079, 1N30, 8021, 3004 and any
combination thereof.
6. The battery according to claim 1, wherein the outer coaling layer has a
thickness of 5 to 40 urn.
7. The battery according to claim 1, wherein the polymer film of the outer
coating layer is formed of polyethylene naphthalate (PEN), or otherwise is formed of
an oriented nylon film.
8. The battery according to claim 1, wherein the PET layer has a thickness of 5
to 30 um when the PET layer is optionally added to the outer surface of the outer
coating layer.