Patent ID: 12206119

MODE FOR CARRYING OUT THE INVENTION

Advantages and features of the present invention, and implementation methods thereof will be clarified through following embodiments described with reference to the accompanying drawings. The present invention may, however be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art. Further, the present invention is only defined by scopes of claims. Like reference numerals refer to like elements throughout.

Unless terms used in the present invention are defined differently, all terms (including technical and scientific terms) used herein have the same meaning as generally understood by those skilled in the art. Also, unless defined clearly and apparently in the description, the terms as defined in a commonly used dictionary are not ideally or excessively construed as having formal meaning.

In the following description, the technical terms are used only for explaining a specific exemplary embodiment while not limiting the present invention. In this specification, the terms of a singular form may include plural forms unless specifically mentioned. The meaning of “comprises” and/or “including” does not exclude other components besides a mentioned component.

Hereinafter, preferred embodiments will be described in detail with reference to the accompanying drawings.

FIG.1is an assembled view of a pouch type secondary battery1according to an embodiment of the present invention.

As illustrated inFIG.1, a pouch type secondary battery1according to an embodiment of the present invention includes a pouch type battery case13and an electrode assembly10accommodated in the battery case13.

The electrode assembly10may be a stacked structure including two electrodes such as a cathode and an anode and a separator interposed between the electrodes to insulate the electrodes from each other or disposed at a left or right side of one electrode. The stacked structure may have various shapes without being limited in shape. For example, the cathode and the anode, each of which has a predetermined standard, may be stacked with the separator therebetween, or the stacked structure may be wound in the form of a jelly roll. Each of the two electrodes has a structure in which active material slurry is applied to a metal foil or a mesh-shaped collector including aluminum and copper. The slurry may be usually formed by agitating a granular active material, an auxiliary conductor, a binder, and a plasticizer with a solvent added. The solvent may be removed in the subsequent process.

As illustrated inFIG.1, the electrode assembly10includes the electrode tabs11. The electrode tab11is connected to each of a cathode and an anode of the electrode assembly10to protrude to the outside of the electrode assembly10, thereby providing a path, through which electrons are moved, between the inside and outside of the electrode assembly10. A collector of the electrode assembly10is constituted by a portion coated with an electrode active material and a distal end, on which the electrode active material is not applied, i.e., a non-coating portion. Also, each of the electrode tabs11may be formed by cutting the non-coating portion or by connecting a separate conductive member to the non-coating portion through ultrasonic welding. As illustrated inFIG.1, the electrode tabs11may protrude from one side of the electrode assembly10in the same direction, but the present invention is not limited thereto. For example, the electrode tabs11may protrude in directions different from each other.

In the electrode assembly10, the electrode lead12is connected to the electrode tab11through spot welding. Also, a portion of the electrode lead12is surrounded by an insulation part14. The insulation part14may be disposed to be limited within a sealing part, at which an upper pouch131and a lower pouch132are thermally fused, so as to be bonded to the battery case13. Also, electricity generated from the electrode assembly10may be prevented from flowing to the battery case13through the electrode lead12, and the sealing of the battery case13may be maintained. Thus, the insulation part14may be made of a nonconductor having non-conductivity, which is not electrically conductive. In general, although an insulation tape which is easily attached to the electrode lead12and has a relatively thin thickness is mainly used as the insulation part14, the present invention is not limited thereto. For example, various members may be used as the insulation part14as long as the members are capable of insulating the electrode lead12.

The electrode lead12may extend in the same direction or extend in directions different from each other according to the formation positions of the cathode tab111and the anode tab112. The cathode lead121and the anode lead122may be made of materials different from each other. That is, the cathode lead121may be made of the same material as the cathode plate, i.e., an aluminum (Al) material, and the anode lead122may be made of the same material as the anode plate, i.e., a copper (Cu) material or a copper material coated with nickel (Ni). Also, a portion of the electrode lead12, which protrudes to the outside of the battery case13, may be provided as a terminal part and electrically connected to an external terminal.

The battery case13is a pouch made of a flexible material. Also, the battery case13accommodates the electrode assembly10so that a portion of the electrode lead12, i.e., the terminal part is exposed and then is sealed. As illustrated inFIG.1, the battery case13includes the upper pouch131and the lower pouch132. An accommodation space1331in which a cup part133is formed to accommodate the electrode assembly10may be provided in the lower pouch132, and upper pouch131may cover an upper side of the accommodation space1331so that the electrode assembly10is not separated to the outside of the battery case13. Although the cup part133is formed in only the lower pouch132inFIG.1, the present invention is not limited thereto. For example, the cup part133may be variously formed, for example, formed in the upper pouch. As illustrated inFIG.1, one side of the upper pouch131and one side of the lower pouch132may be connected to each other. However, the present invention is not limited thereto. For example, the upper pouch131and the lower pouch may be separately manufactured to be separated from each other.

When the electrode lead12is connected to the electrode tab11of the electrode assembly10, and the insulation part14is provided on a portion of the electrode lead12, the electrode assembly10may be accommodated in the accommodation space provided in the cup part133of the lower pouch132, and the upper pouch131may cover an upper portion of the accommodation space. Also, the electrolyte is injected, and the sealing part provided on an edge of each of the upper pouch131and the lower pouch132is sealed. The electrolyte may move lithium ions generated by electrochemical reaction of the electrode during charging and discharging of the secondary battery1. The electrolyte may include a non-aqueous organic electrolyte that is a mixture of a lithium salt and a high-purity organic solvent or a polymer using a polymer electrolyte. The pouch type secondary battery1may be manufactured through the above-described method.

FIG.2is an enlarged cross-sectional view of the pouch type secondary battery1according to an embodiment of the present invention, andFIG.3is an enlarged cross-sectional view illustrating a state in which the pouch type secondary battery1increases in thickness according to an embodiment of the present invention.

As described above, when an over-voltage occurs at a low temperature, a charging current density increases, and thus lithium ions of the cathode are not rapidly accommodated in an anode active material coating layer. As a result, the lithium ions are accumulated on the surface of the anode and are precipitated as metallic lithium. This is called lithium plating.

When the lithium plating occurs on the anode, the electrode assembly10increases in thickness as illustrated inFIG.3. Accordingly, the pouch type secondary battery1may increase in total thickness to deteriorate assembly quality of the secondary battery1and reduce energy efficiency to volume.

FIG.4is a cross-sectional view of a pouch film134according to an embodiment of the present invention.

According to an embodiment of the present invention, the pouch for the secondary battery may include a heat dissipation layer1344made of ceramic containing lambda trititanium pentoxide, and when a pressure is applied, heat may be released to the outside to increase in temperature, thereby preventing the lithium plating from occurring even if the over-voltage occurs at the low temperature.

For this, the pouch for the secondary battery according to an embodiment of the present invention includes a surface protection layer1342made of a first polymer and formed on the outermost layer; a sealant layer1343made of a second polymer and formed on the innermost layer; a gas barrier layer1341made of a metal and stacked between the surface protection layer1342and the sealant layer1343; and a heat dissipation layer1344made of ceramic, stacked between the surface protection layer1342and the sealant layer1343, and releasing heat to the outside when a specific pressure is applied thereto. Also, the ceramic may be lambda trititanium pentoxide and be converted into beta trititanium pentoxide when a pressure greater than 60 MPa is applied.

The pouch that is the battery case13of the pouch type secondary battery1according to an embodiment of the present invention may be manufactured by drawing the pouch film134. That is, the pouch film134is elongated by using a punch or the like to form a cup part133, thereby manufacturing the pouch13. According to an embodiment of the present invention, as illustrated inFIG.4, the pouch film134includes the gas barrier layer1341, the surface protection layer1342, and the sealant layer1343.

The gas barrier layer1341may secure mechanical strength of the pouch13, block introduction and discharge of a gas or moisture outside the secondary battery1, and prevent an electrolyte from leaking. In general, the gas barrier layer1341is made of a metal, and the metal may include aluminum. Aluminum may secure the mechanical strength having a predetermined level or more, but be light in weight. Thus, aluminum may secure complement and heat dissipation for electrochemical properties due to the electrode assembly10and the electrolyte. However, the present invention is not limited thereto. For example, the gas barrier layer1341may be made of various materials. For example, the gas barrier layer1341may be made of one material or a mixture of two or more materials selected from the group consisting of Fe, Cr, Mn, Ni and Al. Here, the gas barrier layer1341is made of a material containing iron, the mechanical strength may be improved. When the gas barrier layer1351is made of a material containing aluminum, flexibility may be improved. Thus, the material forming the gas barrier layer1351may be used in consideration of the characteristics of the gas barrier layer1351.

If the gas barrier layer1341is made of aluminum, the gas barrier layer1341may have a thickness of about 30 μm to about 80 μm. If the gas barrier layer1341has a thickness less than 30 μm, the gas barrier layer1341is excessively thin to cause deterioration in moldability and generate a large number of pinholes, thereby deteriorating battery quality. On the contrary, if the gas battier layer has a thickness greater than 80 μm, the total thickness of the pouch is thick to increase in volume of the secondary battery and deteriorate in energy density. More preferably, the gas barrier layer1341may have a thickness of 30 μm to 50 μm.

The surface protection layer1342is made of the first polymer and disposed at the outermost layer to protect the secondary battery1against external friction and collision and also electrically insulates the electrode assembly10from the outside. Here, the outermost layer represents a layer disposed at the last when oriented in a direction opposite to the direction in which the electrode assembly10is disposed with respect to the gas barrier layer1341. The first polymer forming the surface protection layer1342may include at least one or more materials selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate (PET), polyvinyl chloride, acrylic polymer, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylene benzobisoxazole, polyarylate, teflon, and glass fiber. Particularly, a polymer such as a nylon resin or polyethylene terephthalate (PET) having mainly abrasion resistance and heat resistance is used.

The surface protection layer1342may have a thickness of 12 μm to 25 μm if made of PET. If the surface protection layer1342has a thickness less than 2 μm, external insulation may be deteriorated, and adhesion with the gas barrier layer1341may be deteriorated. On the contrary, if the surface protection layer1342has a thickness greater than 25 μm, the total thickness of the pouch is thick to increase in volume of the secondary battery and deteriorate in energy density. More preferably, the surface protection layer1342may have a thickness of 20 to 25 μm.

The surface protection layer1342may have a single layer structure made of any one material or may be provided in plurality. That is, the surface protection layer1342may have a composite layer structure which is constituted by layers respectively made of two or more materials. In this case, the plurality of surface protection layers1342may include a first surface protection layer made of polyethylene terephthalate (PET) and formed at the outermost layer and a second surface protection layer made of nylon and stacked inside the first surface protection layer.

The sealant layer1343is made of the second polymer and disposed at the innermost layer to directly contact the electrode assembly10. Here, the innermost layer represents a layer disposed at the last when oriented in a direction opposite to the direction in which the electrode assembly10is disposed with respect to the gas barrier layer1341. In the pouch, when the pouch film134having a stacked structure as described above is drawn using a punch, a portion of the pouch film134is elongated to form a cup part133including an accommodation space1331having a bag shape. Also, when the electrode assembly10is accommodated in the accommodation space1331, the electrolyte is injected. Thereafter, when the upper pouch131and the lower pouch132may contact each other, and thermal compression is applied to the sealing part, the sealant layers1343may be bonded to each other to seal the pouch. Here, since the sealant layer1343directly contacts the electrode assembly10, the sealant layer1343may have to have insulating properties. Also, since the sealant layer1343contacts the electrolyte, the sealant layer1343may have to have corrosion resistance. Also, since the inside of the battery case13is completely sealed to prevent materials from moving between the inside and outside of the battery case13, high sealability has to be realized. That is, the sealing part on which the sealant layers1343are bonded to each other has to have superior thermal bonding strength. In general, the second polymer forming the sealant layer1343may include at least one or more materials selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymer, polyacrylonitrile, polyimide, polyamide, cellulose, aramid, nylon, polyester, polyparaphenylene benzobisoxazole, polyarylate, teflon, and glass fiber. Particularly, a polyolefin-based resin such as polypropylene (PP) or polyethylene (PE) may be used for the sealant layer1343. Polypropylene (PP) is excellent in mechanical properties such as tensile strength, rigidity, surface hardness, abrasion resistance, and heat resistance and chemical properties such as corrosion resistance and thus is mainly used for manufacturing the sealant layer1343. Furthermore, the sealant layer1343may be made of a casted polypropylene, an acid modified polypropylene, or a polypropylene-butylene-ethylene terpolymer. Here, the acid-treated polypropylene may be maleic anhydride polypropylene (MAH PP).

The sealant layer1343may have a thickness of 30 μm to 100 μm if the sealant layer1343is made of polypropylene (PP). If the sealant layer1343has a thickness less than 30 μm, the sealant layer1343may be deteriorated in durability such as internal breakage during the sealing. On the contrary, if the sealant layer1343has a thickness greater than 100 μm, the total thickness of the pouch is thick to increase in volume of the secondary battery and deteriorate in energy density. More preferably, the sealant layer1343may have a thickness of 50 μm to 80 μm.

The sealant layer1343may have a single layer structure made of any one material or may be provided in plurality. That is, the surface protection layer1342may have a composite layer structure which is constituted by layers respectively made of two or more materials. In this case, the plurality of sealant layers1343may include a first sealant layer made of acid modified polypropylene (PPa) and formed at the innermost layer and a second sealant layer made of cast polypropylene (CPP) and stacked outside the first sealant layer.

According to one embodiment of the present invention, the pouch film134further includes a heat dissipation layer1344made of ceramic, stacked between the surface protection layer1342and the sealant layer1343, and releasing heat when a specific pressure is applied.

The heat dissipation layer1344is made of ceramic, which absorbs heat and then is converted into another material when a specific pressure is applied to release the absorbed heat to the outside. Here, the ceramic may be lambda titanium pentoxide (λ-Ti3O5).

The heat dissipation layer1344may be stacked inside the gas barrier layer1341as illustrated inFIG.4. Particularly, it is preferable that one surface of the heat dissipation layer1344is stacked in direct contact with the gas barrier layer1342. As a result, the heat dissipation layer1344is disposed between the electrode assembly10and the gas barrier layer1341. Thus, when the electrode assembly10increases in thickness, the pressure may be effectively applied to the heat dissipation layer1344by the gas barrier layer1341made of the metal.

FIG.5is a conceptual view of lambda trititanium pentoxide and beta trititanium pentoxide.

As illustrated inFIG.5, lambda titanium pentoxide (λ-Ti3O5) may be constituted by only titanium atoms (Ti) and oxygen atoms (O) and may absorb heat of about 230 kJ/L. Also, in a state in which lambda titanium pentoxide absorbs heat and is stored, when a pressure greater than about 60 MPa is applied, lambda titanium pentoxide is converted into beta-titanium pentoxide (β-Ti3O5). Here, lambda titanium pentoxide and betatritium pentoxide are different from each other only in the physical bonding structure of the atoms but have constituent materials that are not chemically different from each other.

Lambda titanium pentoxide is pressurized and converted into beta-titanium pentoxide to release the stored heat having about 230 kJ/L to the outside. As a result, the ambient temperature may increase.

As described above, when the over-voltage occurs at a low temperature, the charging current density may increase, and the lithium plating occurs on the anode to increase in thickness of the electrode assembly. Accordingly, there are problems that the pouch type secondary battery increases in total thickness, assembly quality of the secondary battery is deteriorated, and energy efficiency to volume is reduced.

However, according to an embodiment of the present invention, the pouch for the secondary battery may include the heat dissipation layer1344made of ceramic containing lambda trititanium pentoxide, and when a pressure is applied, heat may be released to the outside to increase in temperature, thereby preventing the lithium plating from occurring even if the over-voltage occurs at the low temperature.

Beta-titanium pentoxide which releases heat is converted into lambda titanium pentoxide by absorbing surrounding heat again. Therefore, the heat dissipation layer1344may continuously repeat the above process.

FIG.6is a cross-sectional view of a pouch film134aaccording to another embodiment of the present invention.

In the pouch film134according to an embodiment of the present invention, the gas barrier layer1341has the single layer structure, and the heat dissipation layer1344is stacked inside the gas barrier layer1341.

However, in the pouch film134aaccording to another embodiment of the present invention, as illustrated inFIG.6, a plurality of gas barrier layers1341aand1341bmay be provided. That is, the pouch film134amay have a composite layer structure which is constituted by layers respectively made of two or more materials. Even in this case, the plurality of gas barrier layers1341aand1341bmay be made of the same kind of metal. That is, the gas barrier layer1341may be made of one material or a mixture of two or more materials selected from the group consisting of Fe, Cr, Mn, Ni and Al.

The heat dissipation layer1344may be stacked between the plurality of gas barrier layers1341aand1341bas illustrated inFIG.6. Particularly, it is preferable that both surfaces of the heat dissipation layer1344are stacked in direct contact with the gas barrier layers1341aand1341b. As a result, when the electrode assembly10increases in thickness, a pressure may be more effectively applied to the heat dissipation layer1344by the gas barrier layers1341aand1341bmade of metal.

FIG.7is a cross-sectional view illustrating a state in which a surface protection layer1342and a sealant layer1343of the pouch film134ahave a composite film structure according to another embodiment of the present invention.

Even according to another embodiment of the present invention, the surface protection layer1342may have a single layer structure made of any one material or may be provided in plurality. That is, the pouch film134amay have a composite layer structure which is constituted by layers respectively made of two or more materials. In this case, the plurality of surface protection layers1342may include a first surface protection layer1342amade of polyethylene terephthalate (PET) and formed at the outermost layer and a second surface protection layer1342bmade of nylon and stacked inside the first surface protection layer.

The sealant layer1343may have a single layer structure made of any one material or may be provided in plurality. That is, the pouch film134amay have a composite layer structure which is constituted by layers respectively made of two or more materials. In this case, the plurality of sealant layers1343may include a first sealant layer1343amade of acid modified polypropylene (PPa) and formed at the innermost layer and a second sealant layer1343bmade of cast polypropylene (CPP) and stacked outside the first sealant layer.

Those with ordinary skill in the technical field of the present invention pertains will be understood that the present invention can be carried out in other specific forms without changing the technical idea or essential features. Therefore, the above-disclosed embodiments are to be considered illustrative and not restrictive. Accordingly, the scope of the present invention is defined by the appended claims rather than the foregoing description and the exemplary embodiments described therein. Various modifications made within the meaning of an equivalent of the claims of the invention and within the claims are to be regarded to be in the scope of the present invention.