JP2002216847A - Lithium ion polymer secondary cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a discharging capacity big, by surely preventing short circuit inside, and to improve cycle property of the discharging capacity. SOLUTION: The lithium ion polymer secondary cell has an electrode body 20 composed by laminating a positive electrode sheet 11 and a negative electrode sheet 14 interposing a polymer electrolyte layer 17 lying between a positive electrode activator 13 of the positive electrode sheet having the positive electrode activator formed on a positive electrode current collector foil 12, and a negative electrode activator 16 of the negative electrode sheet having the negative electrode activator formed on a negative electrode current collector foil 15. The cell is characterized by the form of the belt-shaped electrode body which is formed by folding once or more than twice, and by forming a notched part on the positive electrode current collector foil of the positive electrode sheet, and/or the negative electrode current collector foil of the negative electrode sheet, located at the outside of the folded part of the electrode body, or by forming a notched part on the positive electrode sheet and/or the negative electrode sheet, so as not to electrically cutting them off from each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium ion polymer secondary battery comprising an electrode body in which a positive electrode sheet and a negative electrode sheet are laminated with a polymer electrolyte layer interposed.

[0002]

2. Description of the Related Art With the spread of portable devices such as video cameras and notebook personal computers in recent years, demand for thin batteries has increased. As this thin battery, a lithium ion polymer secondary battery formed by laminating a positive electrode sheet and a negative electrode sheet is known. This positive electrode sheet is made by forming an active material on the surface of the positive electrode current collector foil,
The negative electrode sheet is made by forming an active material on the surface of the negative electrode current collector foil. A polymer electrolyte layer is interposed between the active material of the positive electrode sheet and the active material of the negative electrode sheet. In this battery, a positive electrode terminal and a negative electrode terminal for taking out a potential difference in each active material as a current are provided on the positive electrode current collector foil and the negative electrode current collector foil, and the stacked body is sealed in a package. Thereby, a lithium ion polymer secondary battery is formed. In this lithium ion polymer secondary battery, desired electricity can be obtained by using the positive electrode terminal and the negative electrode terminal drawn out of the package as terminals of the battery.

[0003]

However, in order to increase the discharge capacity of this lithium ion polymer secondary battery, it is necessary to increase the areas of the positive electrode sheet and the negative electrode sheet. Simply enlarging the area of the positive electrode sheet and the negative electrode sheet results in a battery having a relatively large area, though thin, and has a problem that its handling becomes difficult. In order to solve this problem, it is conceivable to fold the enlarged positive and negative electrode sheets into desired sizes. However, when the positive electrode sheet and the negative electrode sheet are folded in a stacked state, the positive electrode sheet or the negative electrode sheet in the fold portion is bent, and the sheet in the portion is separated from the electrolyte layer, and the effective surface area of the interface between the electrode and the electrolyte is reduced. As a result, there is a problem that the discharge capacity decreases and resistance is generated inside the battery to deteriorate the cycle characteristics of the discharge capacity. Also,
When the deflection is relatively large, there is also a problem that a so-called internal short circuit occurs in which the positive electrode sheet and the negative electrode sheet directly contact each other. An object of the present invention is to provide a lithium ion polymer secondary battery capable of reliably preventing internal short-circuit, increasing discharge capacity, and improving cycle characteristics of discharge capacity.

[0004]

According to the first aspect of the present invention,
As shown in FIG. 1, a positive electrode active material 13 of a positive electrode sheet 11 in which a positive electrode active material 13 is formed on a surface of a positive electrode current collector foil 12 is provided.
A positive electrode sheet 11 and a negative electrode sheet 14 are laminated with a polymer electrolyte layer 17 interposed therebetween, and a negative electrode active material 16 of a negative electrode sheet 14 having a negative electrode active material 16 formed on the surface of a negative electrode current collector foil 15. This is an improvement of the lithium ion polymer secondary battery including the electrode assembly 20. The characteristic configuration is that the electrode body 20 is formed in a band shape and is folded one or more times, and the cathode current collector of the cathode sheet 11 located outside the fold of the folded electrode body 20. Foil 12 or negative electrode sheet 1
A cut is provided in one or both of the negative electrode current collector foils 15 of No. 4. In the invention according to the first aspect, since the strip-shaped electrode body 20 is folded, the size is not increased even if the discharge capacity is increased. The positive electrode current collector foil 12 of the positive electrode sheet 11 or the negative electrode current collector foil 15 of the negative electrode sheet 14 located outside the fold of the folded electrode body 20
Cuts are provided in either one or both, so that the positive electrode sheet 11 or the negative electrode sheet 1
4 is prevented from being bent, a decrease in discharge capacity caused by the bending is suppressed, and an internal short circuit is prevented.
Further, since the polymer electrolyte layer 17 is formed between the positive electrode active material 13 of the strip-shaped positive electrode sheet 11 and the negative electrode active material 16 of the negative electrode sheet 14, the polymer electrolyte layer 17 is sandwiched between the polymer electrolyte layers 17 by a folded structure. The active materials in the positive electrode sheet 11 and the negative electrode sheet 14 share the same electrolyte, so that the internal impedance between the active materials is uniform, and the cycle characteristics are improved.

As shown in FIG. 3, the invention according to claim 2 comprises a positive electrode active material 13 of a positive electrode sheet 11 in which a positive electrode active material 13 is formed on the surface of a positive electrode current collector foil 12, and a negative electrode current collector foil. Negative electrode sheet 1 having negative electrode active material 16 formed on the surface of 15
4 is a lithium ion polymer secondary battery comprising an electrode body 20 in which a positive electrode sheet 11 and a negative electrode sheet 14 are laminated with a polymer electrolyte layer 17 interposed between the negative electrode active material 16 and the negative electrode active material 16. The characteristic configuration is such that the electrode body 20 is formed in a band shape and is folded one or more times, and the positive electrode sheet 11 located outside the fold of the folded electrode body 20 is formed.
Alternatively, one or both of the negative electrode sheets 14 are provided with cuts so as not to be electrically interrupted. In the invention according to claim 2, the positive electrode sheet 11 or the negative electrode sheet 1 located outside the fold of the folded electrode body 20
4 is provided with a notch so as not to be electrically interrupted, so that the positive electrode sheet 11 or the negative electrode sheet
And prevents a decrease in discharge capacity due to the bending and prevents an internal short circuit.

The invention according to claim 3 is the invention according to claim 1 or 2, wherein, as shown in FIG. 4, the polymer electrolyte layer 17 is formed of a positive electrode active material or a negative electrode active material 16 of a positive electrode sheet or a negative electrode sheet 14. Is a lithium ion polymer secondary battery that covers at least one side of either or both of the above. According to the third aspect of the invention, the contact area between the active material and the polymer electrolyte layer 17 increases, the area of the active material as an electrode increases, and the internal impedance decreases. Also,
The edge of the active material that is relatively easy to dry is placed on the polymer electrolyte layer 1
7, the polymer electrolyte layer 17 prevents drying in that portion, suppresses an increase in internal resistance, and further improves the cycle characteristics of the discharge capacity and the high-rate charge / discharge characteristics.

The invention according to claim 4 is the invention according to claims 1 to 3
As shown in FIG. 2, one side edge 15 of a strip-shaped positive electrode current collector foil or negative electrode current collector foil 15 is provided.
a protrudes from one side edge 12a of the plurality of negative electrode current collector foils or positive electrode current collector foils 12 and the other side edge 12b of the plurality of negative electrode current collector foils or the positive electrode current collector foil 12 has a band-like positive electrode current collector. A positive electrode terminal 23 is provided, which is stacked so as to protrude from the other side edge 15b of the body foil or the negative electrode current collector foil 15 and interconnects the plurality of protrusions 12c of the positive electrode current collector foil. Is a lithium ion polymer secondary battery provided with a negative electrode terminal 21 for interconnecting the plurality of protrusions 15c. In a general lithium ion polymer secondary battery, a positive electrode terminal and a negative electrode terminal for extracting a potential difference of each active material as a current are provided at one position of a positive electrode and a negative electrode current collector foil. Then, the terminals 21, 23
Can be easily provided, and the fabrication of the lithium ion polymer secondary battery is relatively easy. Furthermore, since a plurality of protrusions are connected to each other, low resistance is provided inside the long strip-shaped electrode,
A uniform current can flow, and charging / discharging with a large current becomes possible.

[0008]

Next, a first embodiment of the present invention will be described in detail with reference to the drawings. As shown in FIG. 1, a lithium ion polymer secondary battery 10 has a positive electrode sheet 11
An electrode body 20 is formed by interposing a polymer electrolyte layer 17 between the cathode sheet 11 and the anode sheet 14 and laminating the cathode sheet 11 and the anode sheet 14. The positive electrode sheet 11 is a positive electrode current collector foil 1
The negative electrode sheet 14 is formed on the surface of the negative electrode current collector foil 15 by forming the positive electrode active material 13 on the surface of the negative electrode active material 1.
6 is formed. In addition, the polymer electrolyte layer 1
7 is interposed between the positive electrode active material 13 formed on the positive electrode current collector foil 12 and the negative electrode active material 16 formed on the surface of the negative electrode current collector foil 15. The lithium ion polymer secondary battery 10 uses a band-shaped electrode body 20 to increase the discharge capacity, and the band-shaped electrode body 20 is folded one or more times. The folded electrode body 20 is provided with a cut in one or both of the positive electrode current collector foil 12 and the negative electrode current collector foil 15 located outside the fold. In addition,
The negative electrode current collector foil 15 in this embodiment is a Cu foil, and a carbon-based active material is used as the negative electrode active material 16.
The positive electrode current collector foil 12 is an Al foil, and the positive electrode active material 1
For example, LiCoO ₂ is used for 3.

As shown in FIGS. 4 (a) and 4 (b), a specific procedure for forming the negative electrode active material 16 on the surface of the negative electrode current collector foil 15 is as follows. The negative electrode active material slurry is applied to the upper surface of the strip-shaped negative electrode current collector foil 15 by a doctor blade method and dried. Here, the doctor blade method is one of the methods of forming ceramics into a sheet, and the thickness of the slip carried on a carrier such as a carrier film or an endless belt is determined by a knife edge called a doctor blade and a carrier. This is a method of precisely controlling the thickness of the sheet by adjusting the distance between the sheets. A coating method using a comma roll or a roll instead of the doctor blade method is also possible. On the other hand, the negative electrode active material 16 is the surface except for the other side portion 15b, and the negative electrode current collector foil 15 in the drawing is used.
The polymer electrolyte layer 17 is formed by applying and drying an electrolyte slurry on the upper surface of the negative electrode active material 16. The polymer electrolyte layer 17 is formed so as to have an area covering the negative electrode active material 16. Specifically, as shown in FIG. 4C, an electrolyte slurry is applied so as to cover the negative electrode active material 16, and then dried to form an area covering the negative electrode active material 16.

The procedure for producing the positive electrode sheet 11 is the same as the procedure for producing the negative electrode sheet 14 described above. Specifically, a positive electrode active material slurry prepared by dispersing and mixing the positive electrode active material in a solvent is applied by a doctor blade method and dried to form the positive electrode active material 1 on the upper surface of the positive electrode current collector foil 12.
Form 3 The positive electrode active material 13 is formed except for one side of the positive electrode current collector foil 12, and the polymer electrolyte layer 17 is formed to have an area covering the positive electrode active material 13. The polymer electrolyte layer 17 is formed so as to cover the positive electrode active material 13 by applying an electrolyte slurry so as to cover the positive electrode active material 13 and then drying the slurry.

Next, as shown in FIG. 5, a polymer electrolyte layer 17 is interposed between the positive electrode sheet 11 and the negative electrode sheet 1.
4 are stacked. This lamination is performed by thermocompression bonding. That is, the positive electrode sheet 11 is disposed on the negative electrode sheet 14, and is passed through a pair of rollers 19, 19 heated to a predetermined temperature and rotating in opposite directions, as shown by solid arrows in FIG. With the layer 17 interposed, the positive electrode sheet 11 and the negative electrode sheet 14 are thermocompression bonded. The positive electrode sheet 11 is disposed on the negative electrode sheet 14 in such a manner that one side edge 15a of the strip-shaped negative electrode current collector foil 15 has a band-shaped positive electrode current collector foil 1.
2 and is arranged so that the other side edge 12b of the strip-shaped positive electrode current collector foil 12 projects from the other side edge 15b of the strip-shaped negative electrode current collector foil 15. The strip-shaped electrode body 20 is formed by this thermocompression bonding.

[0012] Next, as shown in FIG.
A cut is made in each of the portions located outside the fold when 0 is folded. The electrode body 20 is placed on a moving body such as a carrier belt, and is moved while holding the electrode body 20 horizontally by rollers provided above and below, and is positioned outside the fold when the electrode body 20 is folded. A notch is formed by applying a blade to the portion from above and below. The cuts are made by applying a blade to a thickness corresponding to the positive and negative electrode current collector foils.

As shown in FIG. 7, the folding of the electrode body 20 is performed by alternately folding portions provided with cuts at a predetermined pitch corresponding to the interval between the folds. When folded in this way, one side edge 15 of the plurality of negative electrode current collector foils 15
a protrudes from one side edge 12a of the plurality of positive electrode current collector foils 12, and the other side edge 12b of the plurality of positive electrode current collector foils 12 protrudes from the other side edge 15b of the plurality of negative electrode current collector foils 15. It is laminated in a state where it is done.

On the other hand, as shown in FIGS. 2 and 7, a plurality of projections 15c of the negative electrode current collector foil 15 projecting from one end 12a of the plurality of positive electrode current collector foils 12 are connected to each other. One end of the negative electrode terminal 21 to be connected is provided by a stopper 22, and a plurality of protruding portions 12 c of the positive electrode current collector foil 12 protruding from the other end edges 15 b of the plurality of negative electrode current collector foils 15 are provided. One end of a positive electrode terminal 23 connected to each other is provided by a stopper 22.

As shown in FIGS. 1 and 2, the band-shaped electrode body 20 folded in this manner is sealed with a package sheet 24. Package sheet 2 in this embodiment
Reference numeral 4 denotes an aluminum foil on which polypropylene is laminated, which is sealed by sandwiching the band-shaped electrode body 20 folded between the pair of package sheets 24 by thermocompression bonding around the package sheet 24 in a vacuum atmosphere. The periphery of the pair of package sheets 24 is thermocompression-bonded so that the other end of the positive electrode terminal 23 and the other end of the negative electrode terminal 21 are exposed outside the package sheet 24, respectively. The secondary battery 10 includes the positive and negative electrode terminals 2 drawn from the package sheet 24.
By using the other ends of the terminals 1 and 23 as terminals of a battery, desired electricity can be obtained.

The lithium ion polymer secondary battery 10 thus configured has a band-shaped electrode body 2 having an enlarged area.
Since the 0 is folded, the discharge capacity can be increased while maintaining a relatively small and thin state. In addition, since a cut is provided in one or both of the positive electrode current collector foil 12 and the negative electrode current collector foil 15 located outside the fold of the folded electrode body 20,
Even if the fold is bent by folding, the positive electrode current collector foil 12 or the negative electrode current collector foil 15 is cut from the cut provided outside the fold.
Is separated, so that a problem that the sheet is separated from the electrolyte layer due to bending can be prevented. In addition, the polymer electrolyte layer 1
7 is the positive electrode active material 13 and the negative electrode sheet 1 of the positive electrode sheet 11
Since each of the negative electrode active materials 16 has an area for covering the negative electrode active material 4, the effective electrode area increases and the internal resistance can be further reduced. Further, the polymer electrolyte layer 17 covering the end of the active material which is easy to dry suppresses an increase in internal resistance generated at the end, thereby improving the cycle characteristics of the discharge capacity and the high rate charge / discharge characteristics.

A second embodiment of the present invention will be described with reference to FIG. 2, the same reference numerals as those in FIG. 1 denote the same components. This embodiment differs from the first embodiment in the following points. That is, a cut is provided in one or both of the positive electrode sheet 11 and the negative electrode sheet 14 located outside the fold of the folded electrode body 20 so as not to be electrically interrupted. The configuration other than the above is the same as that of the first embodiment. Compared with the first embodiment, in the second embodiment, one or both of the positive electrode sheet 11 and the negative electrode sheet 14 located outside the fold of the folded electrode body 20 are electrically connected. By making a cut in a part of the outside so as not to block the positive electrode current collector foil 12
Alternatively, since a cut is made in one or both of the negative electrode current collector foils 15, the same effect as in the first embodiment is obtained, and further, one or both of the positive electrode active material 13 and the negative electrode active material 16 are provided. Since a cut is made in a part of the outside so as not to be electrically interrupted, the active material can be effectively used, thereby further improving the capacity.

[0018]

As described above, according to the present invention, the band-shaped electrode body having an increased area is folded in order to increase the discharge capacity, so that the discharge capacity can be increased in a relatively small and thin state. it can. In addition, since a cut is provided in one or both of the positive electrode current collector foil and the negative electrode current collector foil located outside the fold of the folded electrode body, a fold portion generated by folding. In this case, it is possible to prevent a problem that the positive electrode sheet or the negative electrode sheet peels off from the electrolyte layer due to stretching or bending. Further, since the polymer electrolyte layer is formed between the positive electrode active material of the belt-shaped positive electrode sheet and the negative electrode active material of the negative electrode sheet, the positive electrode sheet and the negative electrode sheet sandwiched between the polymer electrolyte layers by a folded structure are formed. Since the active materials in (1) and (2) share the same electrolyte, the internal impedance between the active materials becomes uniform, and the cycle characteristics can be improved.

If the polymer electrolyte layer has an area for covering the active material, the effective electrode area increases to further reduce the internal resistance, and the polymer electrolyte layer to be coated reduces the drying at the end of the active material. To prevent the internal resistance from increasing with time. As a result, the cycle characteristics of the discharge capacity and the high rate charge / discharge characteristics can be improved.

Further, if a positive electrode terminal is provided so as to connect a plurality of protrusions of the positive electrode sheet to each other and a negative electrode terminal is provided so as to connect a plurality of protrusions of the negative electrode sheet to each other, the The operation of providing a positive electrode terminal and a negative electrode terminal for extracting a potential difference as a current is simplified, and a so-called low-cost, high-capacity lithium ion polymer secondary battery can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view taken along line AA of FIG. 2 showing a secondary battery of the present invention.

FIG. 2 is a cross-sectional view of the secondary battery taken along line BB of FIG. 1;

FIG. 3 is a sectional view taken along line AA of FIG. 2 showing another secondary battery of the present invention.

FIG. 4 is a view showing a manufacturing process of the positive electrode sheet.

FIG. 5 is a perspective view showing a state in which a positive electrode sheet is thermocompression-bonded to the negative electrode sheet.

FIG. 6 is a view showing a step of making a cut in the electrode body.

FIG. 7 is an exploded perspective view showing the configuration of the secondary battery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Lithium ion polymer secondary battery 11 Positive electrode sheet 12 Positive electrode current collector foil 12a One side edge 12b The other side edge 12c Projection 13 Positive electrode active material 14 Negative sheet 15 Negative electrode current collector foil 15a One side edge 15b The other side Side edge 15c Projection 16 Negative electrode active material 17 Polymer electrolyte layer 20 Electrode body 21 Negative terminal 23 Positive terminal

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tadashi Kobayashi 1-297 Kitabukurocho, Omiya City, Saitama Prefecture Inside Mitsubishi Materials Research Institute (72) Inventor Akihiro Higami 1-297 Kitabukurocho, Omiya City, Saitama Mitsubishi Materials (72) Inventor Sawako Takeuchi 1-297 Kitabukuro-cho, Omiya-shi, Saitama F-term in Mitsubishi Materials Research Institute (reference) 5H017 AA03 AS02 BB14 CC01 EE01 EE05 HH04 HH05 5H022 AA09 CC03 CC12 CC15 CC16 CC23 EE01 EE04 5H029 AJ02 AJ03 AJ05 AJ06 AJ14 AK03 AL06 AM01 AM16 BJ04 BJ15 CJ03 CJ04 CJ06 DJ01 DJ07 EJ01 HJ07 HJ12 5H050 AA02 AA07 AA08 AA19 BA18 CA08 CB07 DA07 DA08 FA06 FA18 GA03 GA04 GA08

Claims (4)

[Claims] A positive electrode active material (1) is provided on the surface of a positive electrode current collector foil (12).
3) the positive electrode active material of the positive electrode sheet (11) formed (13)
And a polymer electrolyte layer (17) interposed between the negative electrode active material (16) of the negative electrode sheet (14) in which the negative electrode active material (16) is formed on the surface of the negative electrode current collector foil (15). In a lithium ion polymer secondary battery comprising an electrode body (20) in which the positive electrode sheet (11) and the negative electrode sheet (14) are laminated, the electrode body (20) is in a strip shape and is at least once or twice. The positive electrode current collector foil (12) of the positive electrode sheet (11) or the negative electrode current collector of the negative electrode sheet (14), which is formed by folding and located outside the fold of the folded electrode body (20) A lithium ion polymer secondary battery characterized in that one or both of the foils (15) are provided with cuts. 2. A positive electrode active material (1) is provided on the surface of a positive electrode current collector foil (12).
3) the positive electrode active material of the positive electrode sheet (11) formed (13)
And a polymer electrolyte layer (17) interposed between the negative electrode active material (16) of the negative electrode sheet (14) in which the negative electrode active material (16) is formed on the surface of the negative electrode current collector foil (15). In a lithium ion polymer secondary battery comprising an electrode body (20) in which the positive electrode sheet (11) and the negative electrode sheet (14) are laminated, the electrode body (20) is in a strip shape and is at least once or twice. The positive electrode sheet (11) and the negative electrode sheet (14) located outside the fold of the folded electrode body (20) are formed so as not to be electrically interrupted. A lithium ion polymer secondary battery, characterized in that a notch is provided in the lithium ion polymer secondary battery. 3. The method according to claim 1, wherein the polymer electrolyte layer (17) is a positive electrode sheet (11).
Alternatively, the positive electrode active material (13) or the negative electrode active material (1
3. The lithium ion polymer secondary battery according to claim 1, wherein at least one side of either or both of the above 6) is coated. 4. A strip-shaped positive electrode current collector foil or a negative electrode current collector foil (1
5) one side edge (15a) projects from one side edge (12a) of a plurality of negative electrode current collector foils or positive electrode current collector foils (12), and the plurality of negative electrode current collector foils or positive electrode current collectors The other side edge (12b) of the foil (12) protrudes from the other side edge (15b) of the strip-shaped positive electrode current collector foil or the negative electrode current collector foil (15) and is laminated, and the positive electrode current collector foil A positive electrode terminal (23) for connecting the plurality of protrusions (12c) to each other is provided, and a negative electrode terminal (21) for connecting the plurality of protrusions (15c) of the negative electrode current collector foil (15) to each other is provided. The lithium ion polymer secondary battery according to any one of claims 1 to 3, which is provided.