Secondary battery and electrode plate therefor

A secondary battery includes a first electrode plate, a second electrode plate, a separator interposed therebetween, and at least one insulation member. The first electrode plate has a first electrode collector having at least one surface on which a first electrode active material is coated to form a coating portion, a first electrode uncoated portion formed on at least one end of the first electrode collector, and a first protrusion formed on at least one end of the electrode coating portion. The second electrode plate includes a similar second electrode collector, a second electrode coating portion, a second electrode uncoated portion, and a second protrusion. The separator insulates the first electrode plate from the second electrode plate. The at least one insulation member is formed on and covers the first protrusion, the second protrusion, or both such that an electrolyte is flowable through the at least one insulation member.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean patent application No. 10-2004-0086903 filed in the Korean Intellectual Property Office on Oct. 28, 2004, the entire disclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a secondary battery and an electrode plate, and more particularly to a secondary battery having an insulation member installed on an electrode plate of the secondary battery in order to prevent a short circuit between electrodes.

BACKGROUND OF RELATED ART

Recently, electric/electronic appliances having compact sizes with light weight, such as cellular phones, notebook computers and camcorders, have been actively developed and produced. Such electric/electronic appliances are equipped with battery packs so that users can use the electric/electronic appliances in various places even if electric power sources are not separately provided for the electric/electronic appliances. A battery pack includes at least one battery capable of outputting an operational voltage at a predetermined level in order to operate the electric/electronic appliances for a predetermined period of time.

Secondary batteries, which are rechargeable batteries fabricated in small sizes with high capacity, are currently employed in the secondary battery packs due to their economical advantages. Secondary batteries are extensively used as power sources for portable electronic appliances, such as camcorders, portable computers, and portable phones. For instance, Ni-MH batteries, Li-ion batteries and Li-ion polymer batteries have been developed as power sources for the portable electronic appliances.

In particular, lithium secondary batteries have an operational voltage of more than 3.6V, which is three times higher than that of Ni—Cd batteries or Ni-MH batteries used as power sources for the portable electronic appliances. In addition, lithium ion secondary batteries have high energy density per unit weight, so lithium ion secondary batteries are extensively used in advanced electronic technology fields.

A Li-ion secondary battery includes a bear cell, which is fabricated by accommodating an electrode assembly including a positive electrode plate, a negative electrode plate and a separator in a can made from aluminum or an aluminum alloy together with an electrolyte and sealing the can with a cap assembly.

In a typical polymer secondary battery, in which an electrode plate or a separator is made from polymer, the separator acts as the electrolyte or is impregnated with an electrolyte component, so the electrolyte is not leaked or leakage of the electrolyte is significantly reduced. Thus, a pouch can be used instead of the can.

In a typical Li-ion secondary battery, an electrode plate is formed by coating slurry (also referred to as a material forming an electrode coating portion) including electrode active materials (lithium oxides for a positive electrode (cathode) and carbon materials for a negative electrode (anode)) onto an electrode collector made from metal foil.

The slurry can be formed by mixing a solvent with a plasticizer, an electrode active material and a binder. In addition, a negative electrode collector is mainly made from copper and a positive electrode collector is mainly made from aluminum. The binder includes PVDF (Poly Vinylidene Fluoride) or SBR (Styrene Butadiene Rubber), and the solvent includes acetone or NMP (N-Methyl Pyrrolidone). It is also possible to use water as the solvent.

The electrode assembly includes a positive electrode plate, a separator, and a negative electrode plate, which are strips sequentially stacked and rolled in the form of a jelly roll, or spiral.

A slit die is formed on at least one surface of the electrode collector forming the positive electrode plate or the negative electrode plate. Slurry is fed into the slit die formed on the surface of the electrode collector, so that an electrode coating portion is formed on the surface of the electrode collector.

The slurry fed into the slit die of the electrode collector is a fluid including a solvent and a binder. The solvent is volatilized through a dry process so that the slurry is bonded to the electrode collector with sufficient bonding strength by means of the binder.

The electrode active material is coated on the electrode collector corresponding to a length of an electrode while forming an uncoated portion between the electrode coating portions in order to allow an electrode tab to be welded to the uncoated portion. Accordingly, the electrode collector includes the electrode coating portions and the uncoated portion.

However, although it may vary depending on slurry coating apparatuses, the slurry may be conglomerated on a coating start portion and a coating end portion of the electrode collector, so the coating start portion and the coating end portion of the electrode collector may slightly protrude as compared with other coating portions. Such protruding portions are formed at both ends of the electrode coating portions of the positive electrode plate and the negative electrode plate.

For this reason, pressure is concentrated on the protruding sections when winding the electrode assembly or external impact is applied to the electrode assembly, so the separator used for insulating the positive electrode plate from the negative electrode plate may be damaged. If a short circuit is generated between the positive electrode plate and the negative electrode plate due to the damage of the separator, not only is a yield rate of the secondary batteries reduced, but also an accident may occur.

In order to solve the above problems, an insulation layer is conventionally formed on the protruding sections of the electrode coating portions coated on at least one surface of the positive electrode plate or the negative electrode plate, thereby preventing the positive electrode plate from making contact with the negative electrode plate and preventing the separator from being damaged due to the protruding sections.

However, in this case, the insulation layer may cover a part of the electrode coating portion, so the reaction area of the electrode coating portion is reduced. Accordingly, capacity of the secondary battery is reduced proportionally to the reduction of the reaction area of the electrode coating portion.

That is, since the capacity of the secondary battery is proportional to the reaction area of the electrode coating portion of the positive electrode and the negative electrode, if the reaction area of the electrode coating portion is reduced due to the insulation layer, the capacity of the secondary battery is also reduced.

SUMMARY OF THE INVENTION

Accordingly, embodiments of the present invention may solve one or more of the above-mentioned problems occurring in the prior art, and are directed to providing a secondary battery capable of preventing battery capacity from being reduced while forming an insulation layer on protrusions formed on both ends of an electrode coating portion of an electrode assembly in order to prevent a short circuit between electrode plates.

In one embodiment, a secondary battery has a first electrode plate including a first electrode collector, the electrode collector having at least one surface on which a first electrode active material is coated to form a first electrode coating portion. A first electrode uncoated portion is formed on at least one end of the first electrode collector, and a first protrusion is formed on an end of the first electrode coating portion. A second electrode plate includes a second electrode collector, the second electrode having at least one surface on which a second electrode active material is coated to form a second electrode coating portion. A second electrode uncoated portion is formed on at least one end of the second electrode collector, and a second protrusion is formed on an end of the second electrode coating portion. A separator is interposed between the first and second electrode plates to insulate the first electrode plate from the second electrode plate. At least one insulation member is formed on and covers the first protrusion, the second protrusion, or both, such that an electrolyte is flowable through the at least one insulation member.

According to an exemplary embodiment of the present invention, the at least one insulation member is formed on an entire surface of the first electrode plate, the second electrode plate, or both. In one embodiment, the at least one insulation member is formed on two ends of the first electrode coating portion, the second electrode coating portion, or both. The insulation member may have a width in a range of about 10 to 20 mm.

The at least one insulation member, in one embodiment, includes a base substrate and an adhesive layer coated on at least one surface of the base substrate. The base substrate is made from a porous material having a heat-deflection temperature above 150° C. and a porosity above 1%. The base substrate is made from one material selected from the group consisting of porous polyethylene (PE), porous polyphenylene (PP), porous polyurethane, porous silicon dioxide, polyphenylene sulfide, and polyphenylacetylene.

The base substrate includes a heat-activated tape, which is made from PE or PP. The heat-activated tape can be a non-adhesive heat-activated tape, on which an adhesive layer is not formed.

The base substrate may have a thickness of less than 20 μm.

The adhesive layer may include an adhesive material, which does not react with the electrolyte. The adhesive layer includes a hot melt material, which is one selected from the group consisting of a rubber-based hot melt material, a silicon-based hot melt material, and an acrylic-based hot melt material.

The adhesive layer may be coated on the base substrate in a pattern having openings at a predetermined interval from each other. The adhesive layer may be coated on the base substrate in a stripe pattern or a lattice pattern, and may have a thickness of less than 10 μm.

The at least one insulation member may also have a mesh structure or be formed with a plurality of perforation holes. An area of the perforation holes may be within a range of about 30 to 90% with respect to a total area of the insulation member bonded to a surface of the first electrode coating portion, the second electrode coating portion, or both. At least five perforation holes may be formed in the insulation member bonded to the surface of the first electrode coating portion, the second electrode coating portion, or both.

The adhesive layer may have a thickness of less than 50 μm.

In another embodiment, an electrode plate includes an electrode collector, the electrode collector having at least one surface on which an electrode active material is coated to form an electrode coating portion. An electrode uncoated portion is formed on at least one end of the electrode collector, and a protrusion is formed on an end of the electrode coating portion. An insulation member is formed on and covers the protrusion, such that an electrolyte is flowable through the insulation member.

DETAILED DESCRIPTION

Hereinafter, examples of embodiments of the present invention will be described with reference to the accompanying drawings. In the following description and drawings, the same reference numerals are used to designate the same or similar components, so repetition of the description on the same or similar components will be omitted.

Referring toFIGS. 1 to 7, the secondary battery100of the present invention includes a case110, a jelly roll type electrode assembly200within the case110, and a cap assembly300coupled to an upper portion of the case110.

The case110is made from a metallic member having a rectangular box shape, one side of which is opened. The case110may act as a terminal.

The electrode assembly200includes a first electrode plate210provided with a first electrode tap215, a second electrode plate220provided with a second electrode tap225, and a separator230interposed between the first and second electrode plates210and220. The first and second electrode plates210and220and the separator230are rolled in the form of a jelly roll, thereby forming the electrode assembly200.

The cap assembly300has a planar cap plate310having a size and a shape corresponding to those of an opening section of the case110. The cap plate310is formed at a center portion thereof with a terminal hole311and an electrolyte injection hole312is formed at one side of the cap plate310in order to inject an electrolyte into the case110. A plug315is inserted into the electrolyte injection hole312, thereby sealing the electrolyte injection hole312.

An electrode terminal320(for example, a negative electrode terminal) is inserted into the terminal hole311. A gasket330having a tube shape is installed around the electrode terminal320in order to electrically insulate the electrode terminal320from the cap plate310.

An insulation plate340is disposed below the cap plate310and a terminal plate350is disposed below the insulation plate340.

The first electrode tap215extending from the first electrode plate210is welded to a lower portion of the cap plate310and the second electrode tap225extending from the second electrode plate220is welded to a lower portion of the electrode plate320.

An insulation case360is installed at an upper surface of the electrode assembly200in order to electrically insulate the electrode assembly200from the cap assembly300while covering an upper end portion of the electrode assembly200. The insulation case360has an electrolyte hole362positioned corresponding to the electrolyte injection hole312of the cap plate310in such a manner that the electrolyte can be injected into the case110.

FIG. 2is a view illustrating the electrode assembly according to one embodiment of the present invention, andFIGS. 3 and 4are sectional views illustrating an electrode collector of the secondary battery according to one embodiment of the present invention. Referring toFIGS. 2 to 4, the electrode assembly200includes the first electrode plate210, the second electrode plate220and the separator230, which are in the form of strips. At this time, the first and second electrode plates210and220may have a positive polarity or a negative polarity. In the following description, the first electrode plate210will be referred to as a positive electrode plate and the second electrode plate220will be referred to as a negative electrode plate.

The positive electrode plate210includes a positive electrode collector211made from a metallic thin film having superior conductivity, such as aluminum foil, and a positive electrode coating portion213coated on both surfaces of the positive electrode collector211. Chalcogenide compounds, such as LiCoO2, LiMn2O4, LiNiO2, LiNi1-x, CoxO2(0<x<1), or LiMn2O2, can be used as positive electrode active materials. However, the present invention is not limited as to the above positive electrode active materials.

Positive uncoated portions217, in which the positive electrode coating portion213is not formed, is formed at both end portions of the positive electrode plate210. A positive electrode tap215is electrically connected to one of the positive uncoated portions217.

The negative electrode plate220includes a negative electrode collector221made from a metallic thin film having superior conductivity, such as copper foil or nickel foil, and a negative electrode coating portion223coated on both surfaces of the negative electrode collector221. Carbon-based materials, Si, Sn, tin oxides, composite tin alloys, transition metal oxides, lithium metal nitrides or lithium metal oxides can be used as negative electrode active materials. However, the present invention is not limited as to the above negative electrode active materials.

A negative uncoated portion227, in which the negative electrode coating portion223is not formed, is formed at both end portions of the negative electrode plate220, respectively. A negative electrode tap225is electrically connected to one of the negative uncoated portions227.

In addition, the positive and negative electrode plates210and220include insulation members240, respectively. The insulation members240cover protrusions a, a′ on end portions of the positive and negative electrode coating portions213,223.

That is, the insulation members240surround the protrusions a, a′ which are formed on uneven parts of the end portions of the positive and negative electrode coating portions213and223provided on one surface of the positive and negative electrode collectors211and221of the positive and negative electrode plates210and220. In one embodiment, the insulation members240cover entire surfaces of the positive and negative electrode plates210and220or at least one of both ends of the protrusions a, a′ of the positive and negative electrode coating portions213and223.

In one embodiment, the insulation member240has a width (d) of about 15 mm. If the insulation member240has a width (d) exceeding a range of between 10 to 20 mm, the movement of the electrolyte may be interrupted. In addition, if the insulation member240has a width (d) below a range of between 10 to 20 mm, the insulation members240may be separated from the positive and negative electrode collectors211and221due to external force applied thereto by the electrolyte being moved.

As shown inFIG. 5a, the insulation member240aincludes a base substrate241and an adhesive layer243acoated on at least one surface of the base substrate241. The internal temperature of the base substrate241may rise up to about 150° C. if the secondary battery is overcharged. Accordingly, in one embodiment, the base substrate241is formed by using materials having a heat-deflection temperature above 150° C.

The base substrate241may be made from a porous material in such a manner that the electrolyte can pass through the base substrate241.

The porous material has a porosity above 1% for allowing the electrolyte to easily pass through the porous material. In one embodiment, the porous material is one selected from the group consisting of polyphenylene sulfide (PPS), porous polyphenylene (PP), porous polyethylene (PE), porous polyurethane, porous silicon dioxide, and polyphenylacetylene (PPA). However, the present invention is not limited as to the above porous materials.

A heat-activated tape made from PP or PE can be used for the base substrate241. In addition, the heat-activated tape may be a non-adhesive heat-activated tape, in which an adhesive layer is not formed. The heat-activated tape can be laminated on the positive and negative electrode plates210and220(FIGS. 1-5a) even if weak heat is applied thereto. In one embodiment, the base substrate241has a thickness (H) less than 20 μm in order to minimize a thickness of the insulation member240a.

The adhesive layer243aincludes an adhesive material, which does not react with the electrolyte. The adhesive material includes a hot melt material extracted from a glue gun. The hot melt material is one selected from the group consisting of a rubber-based hot melt material, a silicon-based hot melt material, and an acrylic-based hot melt material. However, the present invention is not limited as to the above hot melt materials.

Since the hot melt material is extracted from the glue gun, it is easy to align the adhesive layer243aon the base substrate241. In addition, the hot melt material, such as 100% thermoplastic resin, is coated on the base substrate241in a liquid phase under a high temperature and is solidified within a short period of time, so that the hot melt material is securely bonded to the base substrate241.

As shown inFIGS. 5ato5c, the adhesive layers243a-243cof the insulation members240a-240care coated on the base substrates241while forming predetermined paths therebetween in order to allow the electrolyte to flow through the paths. The adhesive layers may be formed on the base substrate241in a stripe pattern. That is, the adhesive layers can be formed lengthwise along the base substrate241(see,243ainFIG. 5a) or widthwise along the base substrate (see,243binFIG. 5b). In addition, the adhesive layers can be formed in a lattice pattern (see,243cinFIG. 5c). Although a hexahedral lattice pattern is shown inFIG. 5c, the present invention is not limited thereto.

In one embodiment, a minimum amount of adhesive material is coated on the base substrate241such that a thickness (h) of the adhesive layer is less than 10 μm in order to minimize a volume of the electrode assembly.

The insulation member240dshown inFIG. 6has a plurality of perforation holes245formed in the base substrate241ain order to allow the electrolyte to pass through the base substrate241a. In addition, it is also possible to fabricate the base substrate241bof the insulation layer240ewith a mesh structure (see,FIG. 7). In these cases, the electrolyte can easily pass through the insulation member240eeven if the insulation member240eis made from an ion non-permeable material.

AlthoughFIG. 6illustrates that the perforation holes245are spaced at a predetermined interval from each other, the present invention does not limit the alignment of the perforation holes245. For instance, the perforation holes245can be aligned while being offset from each other. In one embodiment, at least five perforation holes245are formed in the base substrate241din such a manner that an area of the perforation holes245is within a range of about 30 to 90% with respect to a total area of the base substrate241a bonded to upper surfaces of the positive and negative electrode coating portions213and223(FIGS. 1-4,6).

In this embodiment, the insulation member240dhas a thickness less than 50 μm in order to minimize a volume of the electrode assembly200.

As mentioned above, according to embodiments described above, the insulation member used for covering the protrusions of the secondary battery is made from a porous material. In addition, the size of the insulation member and distribution of the adhesive layers are minimized in such a manner that the volume of the electrode assembly can be minimized while facilitating the movement of the electrolyte. Accordingly, the short circuit between the electrodes can be prevented, thereby preventing the separator from being damaged.