WO2004097971A1

WO2004097971A1 - Stacked lithium secondary battery and its fabrication

Info

Publication number: WO2004097971A1
Application number: PCT/KR2004/000961
Authority: WO
Inventors: Whanjin Roh
Original assignee: Enerland Co. Ltd.
Priority date: 2003-04-25
Filing date: 2004-04-26
Publication date: 2004-11-11

Abstract

There is provided a method for fabricating a stacked lithium secondary battery in which a plurality of cathode plates and a plurality of anode plates, each of which are separated by a separator, are alternatively facing each other. The method comprises a) providing a pre-stacked body comprised of a first separator, a plurality of first electrode plates adhered onto upper surface of the first separator in a neighboring manner, a second separator located on the first electrode plates, and a plurality of second electrode plates adhered onto upper surface of the second separator in a neighboring manner; b) successively folding the pre-stacked body in a fixed one direction along folding lines formed between the electrode plates to obtain a stacked body; and c) housing the obtained stacked body within a pouch, followed by injection of an electrolyte solution and packaging. The method simplifies the folding process by a fixed one-directional folding rather than a zig-zag folding, and reduces the scale of a facility required for the adhesion process by minimizing the length occupied by the electrode plates. Further, the separator can be tightly fastened such that the charge/discharge characteristics and cycle life of the battery can be enhanced, compared to a zig-zag folding.

Description

STACKED LITHIUM SECONDARY BATTERY

AND ITS FABRICATION

TECHNICAL FIELD OF THE INVENTION The present invention relates to a lithium secondary battery and its fabrication, more specifically to a stacked lithium secondary battery in which a plurality of cathode plates and a plurality of anode plates, each of which are separated by a separator, are alternatively facing each other and its fabrication.

BACKGROUND OF THE INVENTION

A battery is a device to convert chemical energy of chemicals into electrical energy through electrochemical reaction, and is classified into two categories: a primary battery and a secondary battery. Among the rechargeable secondary battery, lithium secondary battery is the most important one, because it has the highest voltage and the largest energy density among existing batteries.

One of the conventional methods for fabricating the lithium secondary battery is described in Fig. 8. The lithium secondary battery according to the method is fabricated by successively depositing a grid-type anode current collector (11), a matrix-film type anode (12), a matrix-film type separator (13), a matrix-film type cathode (14) and a grid-type cathode current collector (15), followed by laminating the members to integrate them, and folding the laminated members in a zig-zag fashion. More detailed explanation can be obtained from US 5,460,904. The lithium secondary battery fabricated by the method ("integrated lithium secondary battery") comprises both the anode and the cathode in an integral form, and it suffers from the disadvantage that damage to the electrodes sometimes occurs in the folding process. In order to avoid the above disadvantages, KR 309,604 and 336,396 disclose examples in which a plurality of anode plates and a plurality of cathode plates are used. Fig. 9 is a cross sectional view showing an arrangement of a plurality of anode plates and cathode plates on a separator, in accordance with the KR 309,604. The method disclosed in KR 309,604 and 336,396 comprises adhering a plurality of anode plates (22) to one surface of the separator (21) with a predetermined interval (a distance inside which at least one electrode plate can be inserted), adhering a plurality of cathode plates (23) to the other surface of the separator (21) with a predetermined interval (a gap inside which at least one electrode plate can be inserted), and folding the separator in a zig-zag fashion to obtain a lithium secondary battery having a stacked structure in which each of the anode plates (22) and each of the cathode plates (23) are alternatively stacked. Unexplained reference numeral (24) is an adhesive layer. The stacked lithium secondary battery avoids the disadvantage of the above mentioned integrated lithium secondary battery; this method can prevent the damage to the electrode caused by a folding process. However, they are also suffered from the disadvantages that the folding process is complicated, and that it is difficult to tightly fasten the separator because folding of the separator is performed in zig-zag fashion. The gap formed between the electrodes and the separator and caused by loose fastening of the separator deteriorates cycle life of an electrochemical cell and charge/discharge characteristics. Particularly, as the surface area of the electrode is larger, the probability of the gap formation is higher, which makes it difficult to fabricate a cell having uniform electrical property. Further, as the electrode plates are adhered in a manner such that an interval within which at least one cathode or anode plate is inserted, the length of the separator to which the electrode plates are adhered is longer, which requires a larger facility and a larger working space. KR published Patent No. 2002-93781 by our present inventor disclose a method for fabricating a lithium secondary battery, comprising arranging both of the anode plates and the cathode plates onto one surface of the separator in a predetermined order, and then folding the separator in a fixed one direction rather than in a zig-zag fashion. The method avoids the disadvantages caused by the zig-zag folding, and provides an additional advantage that adhesion of the electrode plates are performed in one direction to facilitate the adhesion of the electrode plates. However, the method suffers from a possible electrical short by neighboring arrangement of the cathode plate and the anode plate. In addition, the method suffers from a requirement of a larger facility and a larger working space caused by larger length of the separator to which the electrode plates are adhered.

For these reasons, new stacked lithium secondary battery and its fabrication which solve the disadvantages caused by the zig-zag folding (difficulty of the folding process and reduced cycle life of the battery) and which prevent the possible electrical short are being demanded.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method for fabricating a stacked lithium secondary battery in which folding is performed in a fixed one-direction rather than in a zig-zag fashion to enhance the charge/discharge characteristics of the cell and a possible electrical short is prevented.

Another object of the present invention is to provide a method for fabricating a stacked lithium secondary battery in which the length occupied by electrode plates is minimized such that only small-scaled facility is required for adhesion of the electrode plates.

Other object of the present invention is to provide a method for fabricating a stacked lithium secondary battery in which an adhesion process of electrode plates can be simplified. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a drawing showing a pre-stacked body in accordance with the present invention, in which Fig. 1(A) and Fig. 1(B) are a cross-sectional view and a top view thereof, respectively.

Fig. 2 is a drawing showing a preferred embodiment of the present invention to obtain the pre-stacked body, in which Fig. 2(A) and Fig. 2(B) are a cross-sectional view and a top view thereof, respectively.

Fig. 3 is a drawing illustrating the process for fabricating the pre-stacked body using the arrangement of Fig. 2, in which Fig. 3(A) and Fig. 3(B) are respectively a cross-sectional view and a top view showing the arrangement of the electrode plates after folding the portion to which no anode plate is attached, and Fig. 3(C) and Fig. 3(D) are respectively a cross-sectional view and a top view showing the arrangement of the electrode plates after an accompanying attachment of the cathode plates has been carried out. Fig. 4 is a drawing showing another preferred embodiment of the present invention to obtain the pre-stacked body.

Fig. 5 is a perspective view of an electrode plate having a tap obtained by coating both surfaces of a current collector with a solution containing an electrode active material, and cutting the coated current collector in a suitable size. Fig. 6A and 6B show the stacked bodies obtained from the successive folding of the pre-stacked bodies in a fixed one-direction.

Fig. 7 is a characteristic graph showing cycle life of the battery of Example 2. Fig. 8 is a drawing showing a conventional method for fabricating an integrated lithium secondary battery. Fig. 9 is a cross-sectional view showing an arrangement of a plurality of anode plates and cathode plates onto a separator, in accordance with a prior art of KR 309,604.

DETAILED DESCRIPTION OF THE INVENTION

The method according to the present invention comprises: a) providing a pre-stacked body comprised of a first separator, a plurality of first electrode plates adhered onto upper surface of the first separator in a neighboring manner, a second separator located on the first electrode plates, and a plurality of second electrode plates adhered onto upper surface of the second separator in a neighboring manner; b) successively folding the pre-stacked body in a fixed one direction along folding lines formed between the electrode plates to obtain a stacked body; and c) housing the obtained stacked body within a pouch, followed by injection of an electrolyte solution and packaging.

Fig. 1 is a drawing showing a pre-stacked body in accordance with the present invention, in which Fig. 1(A) and Fig. 1(B) are a cross-sectional view and a top view thereof, respectively. As shown in Fig. 1(A) and Fig. 1(B), according to the method of the present invention, a plurality of first electrode plates (100a) and second electrode plates (100b) (hereinafter, totally "100") are adhered onto a first separator (200') and a second separator (200") (hereinafter, totally "200"), respectively. Herein, the electrode plates (100) adhered onto the separator (200) are arranged in a neighboring manner. As used herein, the term "neighboring" should not be understood that there is physical contact between two adjoining plates, but it means that the two adjoining plates can be overlapped each other when one of the two plates is fold along a folding line (300) formed between the two adjoining plates. Besides neighboring arrangement, the electrode plates (100) should be arranged onto the separator (200) to satisfy the requirements that taps (103a) of the first electrode plates (100a) should overlap one another and taps (103b) of the second electrode plates (103b) should be overlap one another, when successively folded along the folding lines (300). The overlapped taps (103a, 103b) are each independently connected to suitable lead lines (for example, nickel and aluminum lead lines, respectively) by an ultrasonic welding. Preferably, in Fig. 1, the first electrode plates (100a) are anode plates, and the second electrode plates (100b) are cathode plates.

In the pre-stacked body, the first separator (200') and the second separator (200") can exist in a separate form. The separate form of the first separator (200') and the second separator (200") can be obtained from independent attachment of a plurality of the anode plates (100a) and a plurality of the cathode plates (100b) to separated separators (200' and 200"). Such a form can simplify the adhesion process of the electrode plates (100). For example, according to the electrode plate's arrangement of KR 309,604, which is shown in Fig. 9, a plurality of anode plates (22) are adhered on one surface of the separator (21) with a predetermined interval, and then, the separator (21) is turned over to attach a plurality of cathode plates (23) to the other surface of the separator (21). Herein, the turning-over process should be accurately performed. If not so, the cathode plates (23) might be attached in a wrong position, thereby resulting in quality deterioration. Further, inadequate attachment of the cathode plates (23) spoils the anode plates (22) as well as the cathode plates (23), which causes economic loss. Therefore, independent attachment of the anode plates (100a) and the cathode plates (100b) to the separated separators (200' and 200") avoids such a problem.

Alternatively, in the pre-stacked body, the first separator (200') and the second separator (200") can exist in a connected form. Herein, the first separator (200') and the second separator (200") exist as one sheet. Such a form can be obtained by adhering a plurality of anode plates (100a) to a portion of one surface of a separator (200) in a neighboring manner as shown in Fig. 2(A) or Fig. 2(B), covering the anode plates (100a) with the separator (200) by folding along a folding line (300) the portion to which no electrode plate is adhered (please refer to Fig. 3(A) and Fig. 3(B) which respectively shows a cross-sectional view and a top view of the folded structure along a folding line (300)), and then adhering a plurality of cathode plates (100b) onto the separator (200) in a neighboring manner and in the same direction with the adhesion direction of the anode plates (100a) (please refer to Fig. 3(C) and 3(D) ). Another embodiment in which the first separator (200') and the second separator (200") exist in a connected form is shown in Fig. 4. As shown in Fig. 4, a plurality of anode plates (100a) are attached to an upper side of a first row (200') of a separator (200) in a neighboring manner and a plurality of cathode plates (100b) are attached to a lower side of a second row (200') of a separator (200) in a neighboring manner. Thereafter, the first row (200') and the second row (200") of the separator (200) are folded along a central line A- A' to give the pre-stacked body of Fig. 1.

The stacked body according to the present invention can exist in a form in which unit members (10a and 10b, totally "10") are successively deposited, which is shown in Fig. 1(C).

Adhesion of the electrode plates (100) to the separator (200) is performed by a well known method of the art. For example, a binder can be coated onto the separator (200) to which the electrode plates (100) will be fixed, or it can be coated onto the electrode plates (100) which will be adhered to the separator (200). As a binder to be used, an ion conductive polymer material selected from the group consisting of polypropylene oxide, polyurethane, polymethylmethacrylate, polybutylmethacrylate, polycyanoacrylate, polyethylene acrylic acid, polyacrylonitrile, polyvinylidene fluoride, polyhexapropylene fluoride, polyethylene oxide, or mixture thereof can be mentioned. The ion conductive polymer material is dissolved into a suitable solvent, and then coated on the separator (200) or the electrode plates (100). As a solvent to be used, dimethyl carbonate, acetonitrile, tetrahydrofurane, acetone and methyl ethyl ketone can be mentioned.

Fig. 5 is a perspective view showing a preferred embodiment of the electrode plate (100) in accordance with the present invention. As shown in Fig. 5, the electrode plate (100) is prepared by coating both surfaces of a current collector (101) with a solution containing an electrode active material to form a coating layer (102) of the electrode active material, followed by cutting the coated current collector (101) in a suitable size. On condition that the electrode plate (100) has a tap, the electrode plate (100) can be cut into, for example, a rectangular or circular shape. The shape of the electrode plate (100) can be changed depending on the desired form of the final electrochemical cell. That is, the electrode plate (100) having a desired shape can be mass-manufactured by adjusting the template of a cutter or a puncher in a suitable shape. The electrode active material (a cathode active material and an anode active material) coated on the surface of the current collector (101) is not particularly limited. The material that has been used as an electrode active material in the filed of a lithium secondary battery can be widely used. Preferred cathode and anode active materials are exemplified in US Patent Nos. 5,837,015, 5,635,151 and 5,501,548. Specifically, a lithium transition metal oxide capable of intercalation/deintercalation of lithium ion, such as LiCoO₂, LiMn₂O₄, LiNiO₂ or LiMnO₂, can be mentioned as a cathode active material. As an anode active material, a material capable of intercalation/deintercalation of lithium ion, such as lithium metal, lithium alloy, carbon and graphite, can be mentioned. Preferably, the anode active material is carbon or graphite. The cathode active material has a high electrochemical potential during intercalation/deintercalation reaction, while the anode active material has a low electrochemical potential. The cathode or anode material is dispersed into a suitable solvent, coated onto the surface of the current collector (101), and cut into a desired size to form a cathode or anode plate, respectively. The electrode active material may be coated on one surface of the current collector. Preferably, it is coated on both surfaces of the current collector (101), as shown in Fig. 5. Double-sided coating provides an increased discharge capacity per unit volume. With regard to preferred examples of the current collector (101), please refer to US Patent Nos. 5,837,015, 5,635,151 and 5,501,548, which are incorporated herein by reference. According to the specific embodiment of the present invention, an aluminum thin plate and a copper thin plate were used as a cathode and anode current collector (101), respectively. Meanwhile, the electrode active material is, in general, coated on the surface of the current collector (101) in combination with a current conductive material that increases conductivity of the electrochemical cell and a binder that adheres both the electrode active material and the current conductive material to the current collector (101). The choice of the current conductive material and the binder would be readily accomplished in reference to the electrode active material that is well known to a person of ordinary skill in the art to which the present invention pertains. If necessary, other additives (for example, an antioxidant, a flame retardant, and so on) can be optionally used.

The number of the anode plates (100a) or the cathode plates (100b) can be suitably selected, regarding the anode active material to be used, the cathode active material to be used, the electrolyte to be used, and the desired discharge capacity of the battery. Generally, the number of the anode plates (100a) used is more than that of the cathode plates (100b) by 1. When the number of the anode plate (100a) is more than 100, the folding process may be complicated. Therefore, the anode plates are used in a range of 2-100. Preferably, 3-50, more preferably, 3-20, most preferably 4-15 anode plates are used.

Fig. 6 is a cross-sectional view showing stacked bodies obtained from successive folding of the pre-stacked body shown in Fig. 1(A) or 1(B) in a fixed one-direction. As shown in Fig. 6, the staked bodies comprises a plurality of the anode plates (100a) and the cathode plates (100b) which are facing each other and separated by the separator (200). The anode plates (100a) and the cathode plates (100b) are completely separated by the separator (200) so that the danger of an electrical short is completely removed. At this time, the separator (200) is successively folded in a fixed one direction along the folding lines (300), yielding a configuration in which separated double-layered films are successively folded in a fixed one- direction from an inner side to an outer side. Specifically, the separator (200) does not have a configuration in which a single-layered film is successively folded in a fixed one-direction from an inner side to an outer side (so called "spiral shape") which was generally shown in the conventional stacked battery, but has the configuration in which separated double-layered films are successively folded in a fixed one-direction from an inner side to an outer side, and into spaces formed between the double-layered films, the anode plates (100a) and the cathode plates (100b) are alternatively positioned. The configuration of the separator (200) according to the

present invention has

because the double-layered films are successively folded in a

fixed one-direction from an inner side to an outer side. In a meanwhile, in the pre-staked body shown in Fig. 3(C) or 3(D), the separator (200) is successively folded along folding lines (300) after the portion to which no electrode plate is attached has been folded such that it has a configuration in which a connected double-layered film is successively folded from an inner

side to an outer side. In this case, the separator (200) has a configuration of

because a connected double-layered film is successively folded from an inner side to an outer side. In this configuration, the separator (200) prevents a direct electrical contact of the anode plates (100a) with the cathode plates (100b) and provides pores for ion passage. Preferred examples are porous polyolefin films such as a polyethylene film or a polypropylene film, porous polyvinylidene fluoride films, porous hexapropylene fluoride films and porous polyethylene oxide films, but are not limited thereto. The polyethylene film is being widely used as a separator (200) in the art. The separator (200) may be comprised of two or more porous films.

Generally, a final battery is produced by housing the stacked body into a pouch of the package, followed by injection of the electrolyte solution and heat sealing of the package under vacuum. At this time, iron or aluminum is in general used as a packaging material. As an electrolyte, liquid electrolyte, gel polymer electrolyte or solid polymer electrolyte can be used. According to the preferred embodiment of the present invention, a liquid electrolyte solution, prepared by dissolving lithium salts such as LiCF₃SO₃, Li(CF₃SO₂)₂, LiPF₆, LiBF₄, LiClO₄ or LiN(SO₂C₂F₅)₂ into a polar organic solvent such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate, was used.

The steps of the method according to the present invention can be continuously performed to produce a lithium secondary battery in a large scale. For example, the adhesion process of the electrode plates and the folding process can be continuously performed after a rolled separator has been rolled out in a suitable speed. In doing so, the electrode plates are neighboring each other, which decrease both the space required for the adhesion of the plates and the scale of the facility required for the adhesion of the plates. In addition, the adhesion processes of the electrode plates (specifically, the adhesion of anode plates and the adhesion of the cathode plates) are performed in the same direction such that a turning-over process of the separator after either the anode plates or the cathode plates has been adhered to the separator can be omitted. Further, the separator onto which the electrode plates are arranged is folded in a fixed one-direction rather than in a zig-zag fashion such that tight fastening of the separator can be accomplished. And, the total number of the folding is reduced as much as 1/2, compared with the conventional methods, which enhances the performance of the process. From the method according to the present invention, a stacked lithium secondary battery comprising a plurality of anode plates and a plurality of cathode plates which are separated by a separator and facing each other is obtained. More specifically, the stacked lithium secondary battery comprises a plurality of anode plates, a plurality of cathode plates, a separator separating the anode plates and the cathode plates, and an electrolyte, wherein the separator has a configuration in which a double-layered film is successively folded in a fixed one-direction from an inner side to an outer side, the anode plates and the cathode plates are facing each other and alternatively arranged into empty spaces formed between the double-layered film, taps of the anode plates and taps of the cathode plates are each independently overlapping one another, and the electrolyte are charged between the anode plates and the separator and between the cathode plates and the separator. The stacked lithium secondary battery avoids the danger of an electrical short caused by an undesired contact of the cathode plate with the anode plate. Further, because the stacked lithium secondary battery is obtained from a fixed one-directional folding, charge/discharge characteristics are enhanced. Specifically, compared to the lithium secondary battery obtained from a zig-zag folding disclosed in KR 309,604 and 336,396, the lithium secondary battery obtained from a fixed one-directional folding enables to tightly fasten the separator, to enhance charge/discharge characteristics, and to extend the cycle life of the battery.

In the following, the present invention will be more fully described referring to specific

Examples. However, it should be understood that the Examples are suggested only for illustration and should not be construed to limit the scope of the present invention. Numerous modifications could be made without departing from the scope and the spirit of the invention.

Examples Example 1: Preparation of an electrode plate

A cathode plate sheet was prepared by the conventional process: a mixture of 100 g of LiCoO₂ powder as a cathode active material, 5g of carbon black as a current conductive material and 5g of polyvinylidene fluoride as a binder was homogeneously mixed, and then 100ml of N- methylpyrrolidone was added to the mixture. The obtained solution was coated onto both sides of a aluminum foil having a thickness of 15 μ which serves as a cathode current collector, dried and then pressed with a roll presser. The thickness of the cathode plate sheet was 150 μm.

Likewise, an anode plate sheet was prepared: lOOg of graphite powder and lOg of polyvinylidene fluoride as a binder was homogeneously mixed, and then 100ml of N- methylpyrrolidone was added to the mixture. The obtained solution was coated onto both sides of a copper foil having a thickness of 15

which serves as an anode current collector, dried and then pressed with a roll presser. The thickness of the cathode plate sheet was 150 μm.

The cathode and anode plate sheets were cut with a puncher such that the cathode and anode plates as shown in Fig. 5 in which each of the cathode and anode plates with dimensions of 3 cm x 4 cm has a tap having dimensions of 0.5 cm x 0.5 cm were obtained. The cathode plates and the anode plates obtained were stored into a cassette.

Example 2: Fabrication of a battery from a double-layered pre-stacked body. A polymer solution was prepared by mixing acetonitrile (available from Aldrich) and polyethylene oxide (available from Aldrich, average molecular weight 1,000,000) at a ratio of 100:3 by weight.

The rolled porous polyethylene sheet (Tecklon ^M manufactured by ENTEK, thickness:

25 μni) which serves as a separator was rolled out in a doublet, and onto one surface of each polyethylene sheet, the polymer solution was coated with a liquid constant delivery apparatus in a thickness of 2 μm. Thereafter, the cathode plates and the anode plates from the cassette were delivered to one side of each of the double-layered separators onto which the polymer solution was coated and arranged in an order as shown in Fig. 1. The double layered films were overlapped and then successively folded along the folding lines, thereby forming a stacked body as shown in Fig. 6A in which a plurality of the anode plates and the cathode plates, each of which are separated by a separator, are facing each other. The projected taps of the cathode plates and the anode plates were led out by nickel and aluminum leads and welded in parallel with an ultrasonic wave, respectively. The stacked body was housed within an aluminum laminating sheet having a pouch to house the stacked body, and an electrolyte solution prepared by dissolving 1.2 mol of LiPF₆ into 3 ml of a mixed solvent of ethylene carbonate and ethylmethyl carbonate (1 : 1 , by volume) was injected into the pouch. Heat-sealing under vacuum produced a stacked lithium secondary battery having a thickness of 38 mm, width of 35 mm and length of 62 mm.

Example 3: Fabrication of a battery using the arrangement shown in Fig. 2. The rolled porous polyethylene sheet (Tecklon™ manufactured by ENTEK, thickness:

25 μm) which serves as a separator was rolled out, and onto a portion of one surface of the polyethylene sheet, the polymer solution was coated with a liquid constant delivery apparatus in a thickness of 2 μm. Thereafter, the anode plates from the cassette were delivered to the portion of one side of the separator onto which the polymer solution was coated and attached in an order as shown in Fig 2. After the portion to which no anode plate is attached had been folded, the polymer solution was coated onto the folded portion with the liquid constant delivery apparatus and the cathode plates from the cassette were attached in the same direction with that of the anode plates. Successive folding in a fixed one-direction gave a stacked body shown in Fig. 6B in which a plurality of the anode plates and the cathode plates separated by a separator are facing each other. The projected taps of the cathode plates and the anode plates were led out by nickel and aluminum leads and welded in parallel with an ultrasonic wave, respectively. The stacked body was housed within an aluminum laminating sheet having a pouch to house the stacked body, and the electrolyte solution prepared by dissolving 1.2 mol of LiPF₆ into 3 ml of a mixed solvent of ethylene carbonate and ethylmethyl carbonate (1 :1, by volume) was injected into the pouch. Heat-sealing under vacuum produced a stacked lithium secondary battery having a thickness of 38 mm, width of 35 mm and length of 62 mm.

Example 4: Fabrication of a battery from a double-rowed pre-stacked body.

The rolled porous polyethylene sheet (Tecklon™ manufactured by ENTEK, thickness: 25 μm) which has a double-rowed structure and serves as a separator was rolled out and onto upper side of a first row, the polymer solution was coated with a liquid constant delivery apparatus in a thickness of 2 μm. Thereafter, the anode plates from the cassette were delivered and attached to the upper side of the separator onto which the polymer solution was coated. After the portion to which no anode plate is attached had been folded along the central line(A- A'), the polymer solution was coated onto the folded portion with the liquid constant delivery apparatus and the cathode plates from the cassette were attached in the same direction with that of the anode plates. Successive folding with a fixed one-direction gave a stacked body shown in Fig. 6A in which a plurality of the anode plates and the cathode plates separated by a separator are facing each other. The projected taps of the cathode plates and the anode plates were led out by nickel and aluminum leads and welded in parallel with an ultrasonic wave, respectively. The stacked body was housed within an aluminum laminating sheet having a pouch to house the stacked body, and the electrolyte solution prepared by dissolving 1.2 mol of LiPF₆ into 3 ml of a mixed solvent of ethylene carbonate and ethylmethyl carbonate (1 :1 , by volume) was injected into the pouch. Heat-sealing under vacuum produced a stacked lithium secondary battery having a thickness of 38 mm, width of 35 mm and length of 62 mm. Comparative Example 1

A plurality of anode plates was adhered onto one side of a separator in which an interval (3.3 cm) was formed between the two anode plates. Thereafter, the separator was turned over and then a plurality of cathode plates was attached onto the opposite side of the separator such that the arrangement shown in Fig. 9 was obtained. Folding was performed in a zig-zag fashion to give a stacked body. The projected taps of the cathode plates and the anode plates were led out by nickel and aluminum leads and welded in parallel with an ultrasonic wave, respectively. The stacked body was housed within an aluminum laminating sheet having a pouch to house the stacked body, and the electrolyte solution prepared by dissolving 1.2 mol of LiPF₆ into 3 ml of a mixed solvent of ethylene carbonate and ethylmethyl carbonate (1 :1, by volume) was injected into the pouch. Heat-sealing under vacuum produced a stacked lithium secondary battery having a thickness of 38 mm, width of 35 mm and length of 62 mm.

Table 1 summarizes the results of the Examples and Comparative Example 1. Table 1

Test 1 : Test of Cycle life of batteries Cycle life of the battery of Example 2 was tested and compared with that of Comparative Example 1. The results thereof are shown in Fig 7. As shown in Fig. 7, the lithium secondary battery of the present invention retained 92% or more discharge capacity after more than 150 cycles, while the battery of Comparative Example 1 had a discharge capacity of less than 88% and the tendency of reduction was increasingly high. The batteries of Examples 3 and 4 gave almost the same results with that of Example 2.

As described above, the method according to the present invention gave the following benefits: firstly, there is no danger of an electrical short caused by an undesired contact of a cathode plate with an anode plate, because the cathode and anode plates are definitively separated by a separator. And, because folding is performed in a fixed one-direction rather than in a zig-zag fashion, the disadvantages caused by a zig-zag folding can be avoid, for example inconvenience of the process, difficulty for tight fastening of a separator which results a gap between the electrode plate and a separator and reduces the cycle life of the battery. Besides the above advantages, the method reduces the scale of an facility required for adhering electrode plates and enables to efficiently utilize a working space, because the anode plates as well as the cathode plates are neighboring one another such that the portion to which the electrode plates are adhered can be reduced as much as 1/2, compared with KR 309,604, KR 336,396 and KR published patent 2002-93781. Further, the number of folding is reduced as much as 1/2, compared with KR 309,604, KR 336,396 and KR published patent 2002-93781, which increases the efficiency of the process. In addition, the lithium secondary battery fabricated by the method according to the present invention has highly enhanced charge/discharge characteristics because of stable interface by tight fastening of the separator sandwiched between the anode plate and the cathode plate during successive folding. And, the battery has no danger of an electrical short due to a complete separation between an anode plate and a cathode plate by a separator.

Claims

1. A method for fabricating a stacked lithium secondary battery, comprising: a) providing a pre- stacked body comprised of a first separator, a plurality of first electrode plates adhered onto upper surface of the first separator in a neighboring manner, a second separator located on the first electrode plates, and a plurality of second electrode plates adhered onto upper surface of the second separator in a neighboring manner; b) successively folding the pre-stacked body in a fixed one direction along folding lines formed between the electrode plates to obtain a stacked body; and c) housing the obtained stacked body within a pouch, followed by injection of an electrolyte solution and packaging.

2. The method according to claim 1, wherein the first separator and the second separator are separated such that the two separators exist in an independent form.

3. The method according to claim 1, wherein the first separator and the second separator are connected each other.

4. The method according to claim 1, wherein the pre-stacked body is obtained by attaching a plurality of the anode plates to a portion of one surface of the separator in a neighboring manner, covering the anode plates with the separator by folding the portion to which no electrode plate is attached along a folding line, and attaching a plurality of the cathode plates onto the separator in a neighboring manner and in the same direction with the adhesion direction of the anode plates.

5. The method according to claim 1, wherein the pre-stacked body is obtained by attaching a plurality of the anode plates to an upper side of a first row of the separator in a neighboring manner, and a plurality of the cathode plates to a lower side of a second row of the separator in a neighboring manner, and folding the separator along a central line formed between the first row and the second row of the separator.

6. The method according to claim 1, wherein the pre-stacked body comprises multiple unit members deposited in a successive manner in which each unit member has a first separator, a plurality of first electrode plates adhered onto upper surface of the first separator in a neighboring manner, a second separator located on the first electrode plates, and a plurality of second electrode plates adhered onto upper surface of the second separator in a neighboring manner.

7. The method according to claim 1, wherein each of the first electrode plate and the second plate is obtained by coating an electrode active material onto both sides of a current collector.

8. The method according to claim 7, wherein the first electrode plate is an anode plate and the anode active material is selected from metallic lithium, lithium alloy, carbon and graphite, the second electrode plate is a cathode plate and the cathode active material is a lithium transition metal oxide, the separator is a porous film selected from the group consisting of a polyethylene film, a polypropylene film, a polyvinylidene fluoride film, a hexapropylene fluoride film, a polyethylene oxide film and a mixture thereof, and the electrolyte is selected from liquid electrolyte, gel polymer electrolyte and solid polymer electrolyte.

9. A stacked lithium secondary battery, comprising a plurality of anode plates, a plurality of cathode plates, a separator separating the anode plates and the cathode plates, and an electrolyte, wherein the separator has a configuration in which a double-layered film is successively folded in a fixed one-direction from an inner side to an outer side, the anode plates and the cathode plates are facing each other and alternatively arranged into empty spaces formed between the double-layered film, taps of the anode plates and taps of the cathode plates are each independently overlapping one another, and the electrolyte are charged between the anode plates and the separator and between the cathode plates and the separator.