Patent Description:
A secondary battery can be charged and discharged, unlike a primary battery that cannot be charged. Low-capacity secondary batteries packaged in the form of a pack including a single battery cell are used as the power source for various portable small-sized electronic devices, such as, for example, mobile phones or camcorders, and high-capacity secondary batteries having several tens to several hundreds of battery cells connected to one another are used as the power source for motor drives, such as those in hybrid vehicles.

Such a secondary battery includes an electrode assembly including a positive electrode and a negative electrode, a case accommodating the electrode assembly, and electrode terminals connected to the electrode assembly. The case is classified into a cylindrical type, a prismatic type or a pouch type according to its external shape. Among others, pouch type secondary batteries may be easily modified in various shapes and may be formed of a lightweight laminate exterior material. Prior art document <NUM> (<CIT>) discloses a lithium ion secondary battery having an irregular shape with a unitary anode and unitary cathode that are spirally wound and that provide a high energy density for an implantable biomedical device.

The above information disclosed in this Background section is only for enhancement of understanding of the background of the described technology and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.

The present invention provides a secondary battery capable of enhancing safety and test reliability.

A difference between a lateral length of the outer electrode plate and a lateral length of the inner electrode plate may range from <NUM> to <NUM>.

A difference between a longitudinal length of the outer electrode plate and a longitudinal length of the inner electrode plate may range from <NUM> to <NUM>.

A plurality of inner electrode plates are of the same size, and a plurality of second electrode plates are of the same size.

The outer electrode plate may include a first active material layer formed on only one surface thereof facing the second electrode plate.

At least one end of the outer electrode plate may be located at the same position as or further inward than one end of the inner electrode plate.

The secondary battery may further include a separator interposed between the first electrode plate and the second electrode plate, the separator extending in a perpendicular direction to a direction in which current collector tabs formed at the first electrode plate and the second electrode plate protrude, and being bent in a Z-shaped configuration.

Also provided is a secondary battery including: an electrode assembly in which a first electrode plate and a second electrode plate are alternately stacked; and a case for accommodating the electrode assembly, wherein the first electrode plate includes an outer electrode plate located at the outermost part of the electrode assembly, and an inner electrode plate located inside the electrode assembly, and at least one end of the outer electrode plate is located at the same position as or further inward than one end of the inner electrode plate.

A plurality of inner electrode plates may be of the same size, and a plurality of second electrode plates may also be of the same size.

As described above, the secondary battery according to an embodiment is capable of enhancing safety and test reliability by preventing deformation of the outer electrode plate during thermal compression such that the outer electrode plate located at the outermost part of the electrode assembly is formed to be smaller than the inner electrode plate.

Hereinafter, example embodiments of the present invention will be described in detail.

Various embodiments of the present invention may be embodied in many different forms and should not be construed as being limited to the example embodiments set forth herein. Rather, these example embodiments of the invention are provided so that this invention will be thorough and complete and will convey inventive concepts of the invention to those skilled in the art.

In addition, in the accompanying drawings, sizes or thicknesses of various components are exaggerated for brevity and clarity. In addition, it will be understood that when an element A is referred to as being "connected to" an element B, the element A can be directly connected to the element B or an intervening element C may be present and the element A and the element B are indirectly connected to each other.

As used herein, the singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprise or include" and/or "comprising or including," when used in this specification, specify the presence of stated features, numbers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, numbers, steps, operations, elements, components, and/or groups thereof.

Spatially relative terms, such as "beneath," "below," "lower," "above," "upper," and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. For example, if the device in the figures is turned over, elements described as "below" or "beneath" other elements or features would then be oriented "on" or "above" the other elements or features.

<FIG> is a perspective view of a secondary battery according to an embodiment. <FIG> is a perspective view of an electrode assembly according to an embodiment.

Referring to <FIG> and <FIG>, the secondary battery <NUM> according to an embodiment includes an electrode assembly <NUM> and a case <NUM>.

The electrode assembly <NUM> includes a first electrode plate <NUM>, a second electrode plate <NUM>, and a separator <NUM> interposed between the first electrode plate <NUM> and the second electrode plate <NUM>. The electrode assembly <NUM> may be formed by stacking a plurality of first electrode plates <NUM> and a plurality of second electrode plates <NUM>. In addition, as shown in <FIG>, the separator <NUM> may be shaped of a plate and may be bent in a Z-shaped configuration so as to be interposed between the first electrode plate <NUM> and the second electrode plate <NUM> to then be stacked. Of course, the separator <NUM> may also include a plurality of separators each disposed between the first electrode plate <NUM> and the second electrode plate <NUM>, like the plurality of first electrode plates <NUM> and the plurality of second electrode plates <NUM>. In addition, in order to prevent a short circuit between the first electrode plate <NUM> and the second electrode plate <NUM>, the separator <NUM> may be formed to be larger than the first electrode plate <NUM> and the second electrode plate <NUM>. Additionally, the plurality of first electrode plates <NUM> may be arranged to be located at the outermost part of the electrode assembly <NUM>, that is, at the topmost or bottommost parts of the stacked electrode assembly <NUM>.

Each of the first electrode plates <NUM> includes a first electrode current collector <NUM> formed of a metal foil such as an aluminum foil, a first active material layer <NUM> located on opposite surfaces of the first electrode current collector <NUM> and having a first active material coated thereon, and a first uncoated portion <NUM> not having the first active material coated thereon. The first active material may be a lithium-containing transition metal oxide represented by a metal oxide such as LiCoO<NUM>, LiNiO<NUM>, LiMnO<NUM>, LiMn<NUM>O<NUM>, or LiNi<NUM>-x-yCoxMyO<NUM>, where <NUM>≤x≤<NUM>, <NUM>≤y≤<NUM>, <NUM>≤x+y≤<NUM>, and M is a metal such as Al, Sr, Mg, or La, or a lithium chalcogenide compound. For example, the first electrode plate <NUM> may be a positive electrode plate. In addition, the first electrode plate <NUM> may include a first current collector tab <NUM> formed on the first uncoated portion <NUM>. Here, the first current collector tab <NUM> is formed by being previously cut so as to upwardly protrude when the first electrode plate <NUM> is formed, and thus is integrally formed with the first electrode current collector <NUM>. That is, the first current collector tab <NUM> may be regarded as the first uncoated portion <NUM>. The plurality of first electrode plates <NUM> are stacked such that the first current collector tabs <NUM> are superposed at the same position. In addition, the plurality of first current collector tabs <NUM> may be welded to one another, and a first electrode lead <NUM> may be attached to the welded first current collector tabs <NUM>. The first electrode lead <NUM> may protrude to the exterior side of the case <NUM>, which will later be described.

Each of the second electrode plates <NUM> includes a second electrode current collector <NUM> formed of a metal foil such as a copper or nickel foil, a second active material layer <NUM> located on opposite surfaces of the second electrode current collector <NUM> and having a second active material coated thereon, and a second uncoated portion <NUM> not having the second active material coated thereon. The second active material may be a carbonaceous material, such as crystalline carbon, amorphous carbon, a carbon composite, or carbon fiber, a lithium metal or a lithium alloy. For example, the second electrode plate <NUM> may be a negative electrode material. In addition, the second electrode plate <NUM> may include a second current collector tab <NUM> formed on the second uncoated portion <NUM>. Here, the second current collector tab <NUM> is formed by being previously cut so as to upwardly protrude when the second electrode plate <NUM> is formed, and thus is integrally formed with the second electrode current collector <NUM>. That is, the second current collector tab <NUM> may be regarded as the second uncoated portion <NUM>. The plurality of second electrode plates <NUM> are stacked such that the second current collector tabs <NUM> are superposed at the same position. In addition, the plurality of second current collector tabs <NUM> may be welded to one another, and a second electrode lead <NUM> may be attached to the welded second current collector tabs <NUM>. The second electrode lead <NUM> may protrude to the exterior side of the case <NUM>, which will later be described.

The separator <NUM>, disposed between the first electrode plate <NUM> and the second electrode plate <NUM>, prevents a short circuit therebetween and allows lithium ions to move. The separator <NUM> may include polyethylene, polypropylene, or a composite film of polyethylene and polypropylene. The separator <NUM> may extend in a perpendicular direction to a direction in which first current collector tab <NUM> and the second current collector tab <NUM> protrude, and may be bent in a Z-shaped configuration to be interposed between the first electrode plate <NUM> and the second electrode plate <NUM>.

The case <NUM> includes a lower case part <NUM> in which the electrode assembly <NUM> is accommodated, and an upper case part <NUM> coupled to the lower case <NUM>. The case <NUM> may be divided into the upper case part <NUM> and the lower case part <NUM> by bending a middle portion of an integrated rectangular pouch film. In addition, the lower case part <NUM> includes an accommodation groove <NUM> formed by a pressing process to accommodate the electrode assembly <NUM>, and a sealing part <NUM> to be sealed with the upper case part <NUM>. The sealing part <NUM> may be located at one side along which the upper case part <NUM> and the lower case part <NUM> are integrated to contact each other, and at the other three sides. The case <NUM> includes two long sides where the upper case part <NUM> and the lower case part <NUM> face each other, and two short sides disposed perpendicular to the two long sides and facing each other. Here, the first electrode lead <NUM> and the second electrode lead <NUM> of the electrode assembly <NUM> are drawn out through one of the two short side, the one facing the other short side where the upper case part <NUM> and the lower case part <NUM> are coupled to each other. Here, an insulation member (not shown) may be attached to each of the first electrode lead <NUM> and the second electrode lead <NUM> to prevent a short circuit between each of the first and second electrode leads <NUM> and <NUM> and the case <NUM>.

In addition, the electrode assembly <NUM> and an electrolyte are accommodated in the case <NUM> to then be subjected to a heat-press process, thereby completing the secondary battery <NUM>. As the result of the heat-press process, an adhesion force is created between the first electrode plate <NUM> and the separator <NUM> and between the second electrode plate <NUM> and the separator <NUM>. For example, the adhesion force created between the first electrode plate <NUM> and the separator <NUM> may range from <NUM> mN/<NUM> to <NUM> mN/<NUM>, and the adhesion force created between the second electrode plate <NUM> and the separator <NUM> may range from <NUM> mN/<NUM> to <NUM> mN/<NUM>. Here, the adhesion force created between the first electrode plate <NUM> or the second electrode plate <NUM> and the separator <NUM> may be measured using a suitable method known in the art. Examples of the method for measuring the adhesion force may include, but not limited to, the following method according to Article <NUM> of the Korean Industrial Standard KS-A-<NUM> (a test method of an adhesive tape and sheet). A separator is cut to have a width of <NUM> and a length of <NUM>, and a tape (Nitto) is adhered to one surface of the separator to obtain a specimen. The first electrode plate or the second electrode plate is compressed on the other surface of the separator by reciprocating once a compression roller having a load of <NUM> at a speed of <NUM>/min. <NUM> minutes later after the compression, the specimen is <NUM>° overturned and about <NUM> peeled off, and the separator and the tape on one surface of the separator are fixed into an upper clip of a tensile strength tester, and the first electrode plate or the second electrode plate compressed on the other surface of the separator is fixed into a lower clip and pulled at a speed of <NUM>/min to measure a pressure when the first electrode plate or the second electrode plate is peeled off from the separator.

<FIG> is a cross-sectional view of the electrode assembly according to an embodiment. <FIG> is a plan view of the electrode assembly according to an embodiment.

Referring to <FIG> and <FIG>, the first electrode plate <NUM> includes an outer electrode plate 110A located at the outermost part of the electrode assembly <NUM>, and the inner electrode plate 110B located inside the electrode assembly <NUM>. The outer electrode plate 110A is formed to be smaller than the inner electrode plate 110B. Here, the outer electrode plate 110A located at the outermost part of the electrode assembly 100a may include a first active material layer <NUM> formed on only one surface of the first electrode current collector <NUM>. That is, the first active material layer <NUM> makes contact with the separator <NUM> on the outer electrode plate 110A and is formed on a surface of the outer electrode plate facing the second electrode plate <NUM>. Additionally, a plurality of inner electrode plates 110B located further inward than the outer electrode plate 110A are formed to have the same size. In addition, the second electrode plate <NUM> is formed to be larger than the outer electrode plate 110A and may be formed to be of the same size as or be larger than the inner electrode plate 110B in size. In other words, the outer electrode plate 110A is smaller than the inner electrode plate 110B and the second electrode plate <NUM>. In addition, a plurality of second electrode plates <NUM> located further inward than the outer electrode plate 110A are also formed to have the same size.

As described above, if the outer electrode plate 110A located at the outermost part of the electrode assembly <NUM> is formed to be smaller than the inner electrode plate 110B and the second electrode plate <NUM>, the outer electrode plate 110A located at the outermost part may be prevented from being bent or deformed when the heat-press process is performed after inserting the electrode assembly <NUM> into the case <NUM>. That is, the inner electrode plate 110B and the second electrode plate <NUM>, which are located further inward than the outer electrode plate 110A, may function as supports, thereby preventing the outer electrode plate 110A located at the outermost part of the electrode assembly <NUM> from being bent or deformed during the heat-press process. Additionally, since the plurality of inner electrode plates 110B and the plurality of second electrode plates <NUM> located further inward than the outer electrode plate 110A are each of the same size, the outer electrode plate 110A may be more securely supported during the heat-press process. For example, if an outer electrode plate located at the outermost part is formed to be larger than inwardly located inner electrode plates, the outer electrode plate protruding to the exterior side of the inner electrode plates may be bent to the interior side of an electrode assembly due to a force applied during a heat-press process. Accordingly, there is a potential risk of a short circuit between the outer electrode plate and the second electrode plate, and an error may be detected in the X-ray test performed after the heat-press process. In the present invention, however, since the outer electrode plate 110A plate located at the outermost part is smaller than the inner electrode plate 110B, X-ray test reliability may be enhanced by preventing deformation of the outer electrode plate 110A.

Specifically, as shown in <FIG>, a lateral length (W1) of the outer electrode plate 110A is smaller than a lateral length (W2) of the inner electrode plate 110B (W1<W2), and the lateral length (W2) of the inner electrode plate 110B is smaller than a lateral length (W3) of the second electrode plate <NUM> (W2<W3). In addition, a longitudinal length (H1) of the outer electrode plate 110A is smaller than a longitudinal length (H2) of the inner electrode plate 110B (H1<H2), and the longitudinal length(H2) of the inner electrode plate 110B is smaller than a longitudinal length (H3) of the second electrode plate <NUM> (H2<H3). Accordingly, an area of the outer electrode plate 110A is smaller than that of the inner electrode plate 110B, and the area of the inner electrode plate 110B is smaller than that of the second electrode plate <NUM>.

In another embodiment, the lateral length (W2) of the inner electrode plate 110B may be equal to the lateral length (W3) of the second electrode plate <NUM> (W2=W3), and the longitudinal length (H2) of the inner electrode plate 110B may be equal to the longitudinal length (H3) of the second electrode plate <NUM> (H2=H3), so that the inner electrode plate 110B and the second electrode plate <NUM> may be formed to have the same area. Even in this case, the outer electrode plate 110A is formed to be smaller than the inner electrode plate 110B and the second electrode plate <NUM>.

A difference between the lateral length (W1) of the outer electrode plate 110A and the lateral length (W2) of the inner electrode plate 110B may range from <NUM> to <NUM>. Here, if the difference between the lateral length (W1) of the outer electrode plate 110A and the lateral length (W2) of the inner electrode plate 110B is less than <NUM>, an alignment process margin may be small, so that the outer electrode plate 110A may protrude more than the inner electrode plate 110B at some portions. In addition, if the difference between the lateral length (W1) of the outer electrode plate 110A and the lateral length (W2) of the inner electrode plate 110B is greater than <NUM>, the outer electrode plate 110A may be inordinately reduced in size, resulting in a reduction of capacity of the electrode assembly <NUM>.

A difference between the longitudinal length (H1) of the outer electrode plate 110A and the longitudinal length (H2) of the inner electrode plate 110B may range from <NUM> to <NUM>. Here, if the difference between the longitudinal length (H1) of the outer electrode plate 110A and the longitudinal length (H2) of the inner electrode plate 110B is less than <NUM>, an alignment process margin may be small, so that the outer electrode plate 110A may protrude more than the inner electrode plate 110B at some portions. In addition, if the difference between the longitudinal length (H1) of the outer electrode plate 110A and the longitudinal length (H2) of the inner electrode plate 110B is greater than <NUM>,, the outer electrode plate 110A may be inordinately reduced in size, resulting in a reduction of capacity of the electrode assembly <NUM>.

Claim 1:
A secondary battery comprising:
an electrode assembly in which a first electrode plate and a second electrode plate are alternately stacked; and
a case for accommodating the electrode assembly,
wherein the first electrode plate includes an outer electrode plate located at the outermost part of the electrode assembly, and an inner electrode plate located inside the electrode assembly,
wherein the inner electrode plate comprises a plurality of inner electrode plates of the same size,
wherein the second electrode plate comprises a plurality of second electrode plates of the same size, and
and the outer electrode plate is smaller than the plurality of inner electrode plates and the plurality of second electrode plates.