JP2000149993A - Film-like lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent internal short-circuit between a positive electrode and a negative electrode. SOLUTION: This secondary battery B1 has structure wherein a power generating element A with a polymer solid electrolyte film 3 sandwiched between a positive electrode collecting plate 1A with a positive mixture layer 1B carried and a negative electrode collecting plate 2A brought into close contact with a foil 2B of metal Li or lithium alloy is sealed using two sheets of armoring materials 4, 4 arranged in both faces of the generating element A, and at least, a peripheral edge part 3A of the polymer solid electrolyte film 3 is sealed in such a condition as sandwiched between peripheral edge parts 4A, 4A of the two materials 4, 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film-shaped Li secondary battery using metal Li or a Li alloy as a negative electrode active material, and more particularly, to a battery based on a dendrite that grows in the course of repeated charging and discharging. The present invention relates to a film-shaped Li secondary battery in which internal short-circuit is prevented and the safety and cycle life characteristics of the battery are improved.

[0002]

2. Description of the Related Art In recent years, as various electronic devices such as mobile phones and video cameras have become smaller and lighter,
With respect to these drive power supplies, demands for further downsizing and weight reduction are increasing in addition to improvement of battery characteristics such as higher energy density. In addition, there is a strong demand for miniaturization of secondary batteries, and in particular, a demand for a reduction in thickness has been remarkable.

For example, in the case of a Li-ion secondary battery using a non-aqueous electrolyte, a prismatic battery has been developed in order to respond to a demand for thinning, and a rectangular battery having a thickness of about 7 mm has already been mounted on a real machine. ing. In this prismatic battery, a power generating element having a separator interposed between a positive electrode and a negative electrode is housed together with a non-aqueous electrolyte in a metal prismatic container manufactured by deep drawing, and an opening of the prismatic container. The part has a sealed structure.

However, in the case of this prismatic battery, the external dimensions are uniquely determined by the external dimensions of the metal rectangular container used, so that the degree of freedom in the form of the battery cannot be obtained, and the battery cannot be obtained. Since the can is manufactured by deep drawing, there is a limit in reducing the thickness. For this reason, a film-type secondary battery having a small overall thickness and some flexibility by using a polymer solid electrolyte film as the electrolyte has been developed. In particular, Li secondary batteries using metallic Li or Li alloy foil as the negative electrode, a porous carbon material and the like as the negative electrode,
In addition, since the energy density is higher than that of a Li-ion secondary battery using a non-aqueous electrolyte, extremely vigorous development research is being advanced.

FIG. 4 is an exploded perspective view showing an example of a film-shaped Li secondary battery using a metallic Li or Li alloy foil as a negative electrode. In this battery, a positive electrode 1 on which a positive electrode active material layer 1B is supported on one surface of a positive electrode current collector plate 1A from which a positive electrode terminal 1a is drawn, and a negative electrode current collector plate 2A from which a negative electrode terminal 2a is drawn. Between the negative electrode 2 and the metal Li or Li alloy foil 2B adhered to the
Power generation element A with film 3 of polymer solid electrolyte sandwiched
Is configured. The external dimensions of these three members are substantially the same, or the external dimensions of the polymer solid electrolyte film 3 are slightly larger than those of the former two.

[0006] On both surfaces of the power generating element A, two exterior members 4 and 4 having outer dimensions larger than those of the positive electrode 1 and the negative electrode 2 are provided.
Are arranged, and the outer peripheral parts 4A, 4A of the respective exterior materials 4, 4 are arranged.
Are heat-sealed in a frame shape, for example, so that the power generating element A is sealed. Here, the positive electrode 1 is manufactured, for example, as follows. First, the active material L
A powder of a material such as iCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , a binder such as polyvinylidene fluoride or styrene rubber, and a conductive material such as carbon black are mixed at a predetermined ratio. The mixture is, for example, N-methyl-2-
A positive electrode mixture paste is prepared by kneading using a non-aqueous solvent such as pyrrolidone. Then, the paste is applied to one surface of a positive electrode current collector plate 1A made of, for example, aluminum foil having a positive electrode terminal 1a, and after being dried, the whole is subjected to a rolling treatment. On one surface of the positive electrode current collector plate 1A, a dried product of the paste is applied. A positive electrode 1 carrying a certain positive electrode active material layer 1B is manufactured.

In the case of the negative electrode 2, a metal Li or Li alloy foil 2B having a predetermined thickness is prepared, and the foil 2B is overlaid on one surface of a negative electrode current collector 2A made of, for example, a SUS net. It can be manufactured by bringing the foil into close contact with a net. Further, as the polymer solid electrolyte film 3, a so-called gel electrolyte obtained by swelling a film-shaped polymer matrix with a predetermined electrolyte is usually used. Examples of such a gel electrolyte include those having an acrylonitrile copolymer as a polymer matrix disclosed in JP-A-7-37419 and polyacrylonitrile disclosed in JP-A-8-264205. Examples of the polymer matrix include a polymer matrix. Further, polyethylene oxide or polypropylene oxide contains a Li salt, and Li
Electrolytes that form ionic complexes are also used.

[0008] In addition, as the exterior materials 4, 4, as shown in FIG.
A laminate film having a layer structure as shown in FIG. That is, a film made of a polymer such as polyethylene terephthalate is laminated on both surfaces of the aluminum foil 4a, or the above polymer is coated to form polymer thin layers 4b, 4b. On the thin layer 4b, a layer 4c of a hot melt material such as an ethylene-vinyl acetate copolymer, an ethylene-acrylate copolymer, or a polypropylene copolymer is formed.

In manufacturing the battery, the power generation element A is sandwiched between the hot melt material layers 4c, 4c of the two laminated films 4, 4, and the periphery of the laminated film protruding outside the power generation element A Only the part 4A is heat-pressed. As a result, the plan view of FIG. 6 and the VII-VII of FIG.
As shown in FIG. 7 which is a cross-sectional view along the line, only the peripheral portion 4A of the laminate film has an airtight sealing structure sealed with a hot melt material, and the power generation element A is sealed inside, A film-shaped Li secondary battery in which the positive electrode terminal 1a and the negative electrode terminal 2a protrude on one side is obtained. That is, in the case of the battery shown in FIG. 7, the power generating element A is housed in a closed space formed by heat-sealing only the outer edges of the outer packaging materials 4 and 4 in a frame shape.

The exterior materials 4 and 4 are not limited to the two laminated films shown in FIG. 4, and the layer structure is such that the laminated film shown in FIG. Alternatively, a bag having a predetermined shape may be manufactured, the power generation element A may be inserted therein, and then the opening of the bag may be heated and pressed to form a sealed structure. Since each element of the battery is formed of a thin leaf, the thickness of the battery is significantly thinner than that of a rectangular battery using a rectangular container for accommodating an electrolytic solution, and at the same time, the battery is provided with some flexibility. Therefore, there is an advantage that the degree of freedom of the space is increased when mounting on various electronic devices.

[0011]

By the way, the biggest problem for practical use of a film-shaped Li secondary battery using a metal Li or Li alloy foil as a negative electrode is as follows. That is, when charge and discharge are repeated, Li dendrite grows on the negative electrode side, and it becomes powdery and peels off from the negative electrode. For example, in the case of the battery having the structure shown in FIGS. In some cases, the battery may move to the positive electrode side through the gap C between the power generation element A and the battery and cause an internal short circuit of the battery.

When such a problem occurs, not only does the charge / discharge cycle life characteristic of the battery significantly decrease, but also heat generation due to an internal short-circuit and further fire may occur. The present invention solves the above-mentioned problems in a film-shaped Li secondary battery using a metal Li or Li alloy foil as a negative electrode and using a polymer solid electrolyte film as an electrolyte, preventing an internal short circuit, and providing a charge / discharge cycle. An object is to provide a film-shaped Li secondary battery having excellent life characteristics.

[0013]

In order to achieve the above object, the present invention provides a negative electrode in which a positive electrode current collector plate supporting a positive electrode mixture layer and a metal Li or Li alloy foil are adhered to each other. In a film-shaped Li secondary battery having a structure in which a power generation element in which a film of a polymer solid electrolyte is sandwiched between a current collector plate and two external packaging materials arranged on both surfaces of the power generation element are sealed. A film-shaped Li secondary battery is provided, wherein at least a peripheral portion of the polymer solid electrolyte film is sealed in a state sandwiched between peripheral portions of the two package members.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a sectional structure of an example B1 of the battery of the present invention. The battery B1 can be manufactured by overlapping each element as shown in the exploded perspective view of FIG. In this case, as the polymer solid electrolyte film 3, a film whose outer dimensions are larger than the outer dimensions of the positive electrode 1 and the negative electrode 2 and smaller than the outer dimensions of the outer packaging materials 4 and 4 is used.

Therefore, when the respective elements are overlapped, the peripheral portion 3A of the polymer solid electrolyte film 3 is sandwiched between the peripheral portions 4A of the two outer packaging materials 4, 4.
When the peripheral edges 4A of the two exterior materials 4 and 4 are heat-sealed, for example, the entire sealing structure is formed with the peripheral edge 3A of the polymer solid electrolyte film 3 sandwiched therebetween. Is done.

Therefore, in the case of this battery B1, the space between the power generation element A and the peripheral portion 4A of the outer package 4 is vertically separated by the peripheral portion 3A of the polymer solid electrolyte film 3, and FIG. No gap C is formed as in the case of the conventional battery shown in FIG. Therefore, even if dendrite grows on the negative electrode 2 side in the course of repeated charging and discharging and becomes a powder and peels off, the powder does not move to the positive electrode 1 side. That is, since the path causing the internal short circuit is cut off, no internal short circuit occurs.

The width of the sealing structure is preferably such that the width W1 at the peripheral portion 4A of the exterior material is about 1 cm from the viewpoint of securing the whole airtightness. FIG. 2 shows another example B2 of the battery of the present invention. In the case of the battery B2, the portion to be sealed with the two exterior materials 4 and 4 is the peripheral portion 3A of the polymer solid electrolyte film 3 as in the case of the battery B1.
However, the periphery of the power generating element A is also sealed.

Also in this case, since the path of the dendrite generated on the negative electrode side to the positive electrode side is cut off, no internal short circuit occurs in the battery. Also in this battery, the width W2 of the sealing structure may be about 1 cm. In the case where the sealing structure is formed by applying the heat fusion, it means that conditions are employed so as not to deteriorate the characteristics of the positive electrode, the negative electrode, and the polymer solid electrolyte film in both the battery B1 and the battery B2. Not even. For example, an appropriate temperature and an appropriate heating time should be employed.

Regarding the temperature, for example, by measuring the calorific value of the polymer solid electrolyte sheet and the positive and negative electrodes in advance, the upper limit temperature at which they are not deteriorated is confirmed, and the temperature at which the exterior material exhibits appropriate fusion strength is determined. What is necessary is to grasp | ascertain as a lower limit temperature, and just to employ | adopt the temperature between these upper limit temperature and lower limit temperature, and to perform heat fusion. In the above description, the sealing is performed by applying heat fusion, but the sealing is not limited to the application of heat fusion, and fusion using ultrasonic waves can be applied. .

[0020]

EXAMPLES (1) Production of Battery LiCoO ₂ powder having an average particle size of 5 μm, TB4300 (trade name, carbon black manufactured by Tokai Carbon Co., Ltd.), and polyvinylidene fluoride powder were mixed in a weight ratio of 87: 8: 5. The mixture was mixed, N-methyl-2-pyrrolidone was added thereto, and the mixture was stirred to prepare a paste of the positive electrode mixture.

This paste was applied to one side of a 50 μm-thick aluminum foil by a doctor blade method, dried at a temperature of 200 ° C. for 30 minutes, and further roll-rolled to a thickness of 1 μm.
A 50 μm positive electrode plate was manufactured. And cut this,
The outer dimensions of the part excluding the positive terminal are 15mm long and 15mm wide
Was manufactured as the positive electrode 1. On the other hand, vertical 15mm, horizontal 15mm,
A metal Li foil having a thickness of 300 μm was prepared, and the metal Li foil was pressure-bonded to one surface of a SUS304 net having the same outer dimensions as the metal Li foil and a thickness of 50 μm under an Ar atmosphere having a dew point of −60 ° C. or less. Thus, a negative electrode 2 was manufactured.

Further, using Nipol 1571 (trade name, acrylonitrile butadiene copolymer: NBR manufactured by Zeon Corporation), the film was further dried by a casting method to form a film having a length of 17 mm, a width of 17 mm and a thickness of about 150 μm. did. Then, in an Ar atmosphere having a dew point of −60 ° C. or less,
The above-mentioned film was immersed for 6 hours in a non-aqueous solution in which 1 mol of lithium perchlorate was dissolved per liter of a mixed solvent of ethylene carbonate and dimethyl carbonate (volume ratio 1: 2), taken out, and the adhered liquid on the surface was wiped off. Swollen, about 29mm long, 29mm wide, about 2mm thick
A polymer solid electrolyte film 3 having a thickness of 50 μm was produced. The ionic conductivity of the obtained polymer solid electrolyte film 3 was 2 × 1 according to the impedance method.
It was 0 ^-3 s / cm.

Next, in an Ar atmosphere having a dew point of −60 ° C. or less, the positive electrode 1, the polymer solid electrolyte film 3 and the negative electrode 2 are superposed to form a power generating element A. Two laminated films 4 and 4 having an outer dimension of 39 mm were arranged. The laminated film used was such that a 5 μm-thick PET film was laminated on both sides of a 40 μm-thick aluminum foil, and one surface of one PET film was Admer VE.
A layer having a thickness of 50 μm made of 300 (trade name, hot melt agent manufactured by Mitsui Petrochemical Industry Co., Ltd.) is formed.

Then, the peripheral edges of the laminated films 4 and 4 were heat-sealed at 170 ° C. for 3 seconds in a frame shape having a width of 10 mm. A portion about 5 mm from the edge of the peripheral edge 3A of the polymer solid electrolyte film 3 is sandwiched between the peripheral edges 4A, 4A of the laminate film with a thickness of about 0.4 mm to form a sealing structure. Battery B1 indicated by No. 1 was obtained. This is referred to as Example 1.

A battery was manufactured in the same manner as in Example 1 except that the peripheral edges 4A, 4A of the laminated films 4, 4 were heat-sealed with a width of about 15 mm at the time of heat-sealing. In this battery, the periphery 3A of the polymer solid electrolyte film is, of course, about 3 mm from the end of the periphery of the power generation element A.
The mm portion was also sandwiched between the peripheral edges 4A of the laminate film with a thickness of about 0.9 mm to form a sealing structure, resulting in the battery B2 shown in FIG. This is Example 2.

On the other hand, a battery was assembled in the same manner as the battery B1 of Example, except that the outer dimensions of the polymer solid electrolyte film were 17 mm in length and 17 mm in width. In the case of this battery, the peripheral edges 4A, 4A
The periphery of the polymer solid electrolyte film is not sandwiched between A. This is a comparative example.

(2) Battery Characteristics These batteries were placed in a constant temperature bath at 25 ° C. for 2.25 m.
A charge / discharge cycle test was performed at a constant current of A and a battery voltage of 3 to 4.3 V. For Example 1 and Comparative Example, the capacity per unit weight of the positive electrode active material after each cycle (unit:
mAh / g) is shown in FIG.

As is apparent from FIG. 3, in the case of Example 1, the charge / discharge behavior up to 40 cycles is normal, and even after the completion of 40 cycles, the capacity shows a value of about 95% of the initial capacity. I have. However, in the case of the comparative example, the capacity is remarkably reduced from the 10th cycle, and is only about 10% of the initial capacity at the end of the 20th cycle. Also,
Also in the case of Example 2, the charge / discharge behavior up to 40 cycles was normal, and the capacity at the end of 40 cycles was about 9% of the initial capacity.
It showed a value of 4%.

[0029]

As is apparent from the above description, the film-shaped Li secondary battery of the present invention has a state in which at least the peripheral portion of the polymer solid electrolyte film is sandwiched between the peripheral portions of the exterior material. The movement path of the dendrite between the positive electrode and the negative electrode is shut off, thereby preventing a short circuit inside the battery. As a result, the film-like Li secondary battery of the present invention has excellent cycle life characteristics and improved safety.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a sectional structure of a film-shaped Li secondary battery B1 of the present invention.

FIG. 2 is a sectional view showing a sectional structure of another film-shaped Li secondary battery B2 of the present invention.

FIG. 3 is a graph showing battery characteristics.

FIG. 4 is an exploded perspective view showing a conventional film-shaped Li secondary battery.

FIG. 5 is a sectional view showing a sectional structure of a laminate film.

FIG. 6 is a plan view showing a conventional film-shaped Li secondary battery.

FIG. 7 is a sectional view taken along line VII-VII in FIG.

[Explanation of symbols]

 Reference Signs List A Power generating element 1 Positive electrode 1a Positive electrode terminal 1A Positive electrode current collector 1B Positive electrode active material layer 2 Negative electrode 2a Negative electrode terminal 2A Negative electrode current collector 2B Metal Li or Li alloy foil 3 Polymer solid electrolyte film 3A Peripheral portion of film 3 4 Exterior Material (laminated film) 4A Peripheral edge of exterior material 4 4a Aluminum foil 4b Polymer thin layer 4c Hot melt material

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H011 AA13 BB04 CC10 DD14 JJ25 5H029 AJ05 AJ12 AK03 AL12 AM02 AM03 AM07 AM16 BJ04 CJ05 DJ02 DJ03 DJ07 HJ12

Claims (2)

[Claims] 1. A power generation system in which a polymer solid electrolyte film is sandwiched between a positive electrode current collector carrying a positive electrode mixture layer and a negative electrode current collector having a metal Li or Li alloy foil adhered thereto. The elements are arranged on two sides of the power generating element.
In a film-shaped Li secondary battery having a structure sealed by using two exterior materials, at least a peripheral portion of the polymer solid electrolyte film is sealed while being sandwiched between the peripheral portions of the two exterior materials. A film-shaped Li secondary battery. 2. The film-shaped Li secondary battery according to claim 1, wherein the sealing is performed by heat fusion.