WO2007034799A1

WO2007034799A1 - Flat organic electrolyte battery

Info

Publication number: WO2007034799A1
Application number: PCT/JP2006/318566
Authority: WO
Inventors: Shinji Fujii; Susumu Yamanaka; Toshihiko Ikehata
Original assignee: Matsushita Electric Industrial Co., Ltd.
Priority date: 2005-09-21
Filing date: 2006-09-20
Publication date: 2007-03-29

Abstract

Disclosed is a flat organic electrolyte battery capable of stably discharging in an extremely low temperature environment without deteriorating characteristics of conventional graphite fluoride lithium batteries. Specifically disclosed is a flat organic electrolyte battery comprising a negative electrode, a positive electrode, an organic electrolyte solution, a separator, a top plate, a positive electrode case and a gasket. The negative electrode contains either metal lithium or a lithium alloy as a negative electrode active material. The positive electrode contains 100 parts by weight of graphite fluoride as a positive electrode active material and 15-30 parts by weight of a conductive agent. The separator is interposed between the negative electrode and the positive electrode. The top plate is in contact with the negative electrode and also serves as a negative electrode terminal. The positive electrode case is in contact with the positive electrode and also serves as a positive electrode terminal. The gasket is interposed between the positive electrode case and the top plate.

Description

Specification

Flat organic electrolyte battery

Technical field

The present invention relates to a flat organic electrolyte battery using lithium metal or lithium alloy as a negative electrode active material and graphite fluoride as a positive electrode active material.

Background art

In general, an organic electrolyte battery has a high energy density, is excellent in reliability such as storability and leakage resistance, and can be reduced in size and weight. For this reason, demand is increasing year by year as a main power source for various electronic devices and as a memory backup power source. In a typical primary battery of this type, lithium metal is used for the negative electrode, manganese dioxide, graphite fluoride, titanium chloride, silver chromate, etc. are used for the positive electrode. Also, typical secondary batteries use lithium metal and lithium occluding / releasing alloys for the negative electrode, carbon metal oxides, polyacene, and materials that form intercalation compounds with lithium ions for the positive electrode. . Examples of such positive electrode active materials include metal oxides such as niobium pentoxide, vanadium pentoxide, and manganese dioxide, composite oxides of lithium and metal oxides, titanium disulfide, molybdenum disulfide, and the like. Examples thereof include conductive polymers such as polyaline and polyacene. The main shape of the battery is a cylindrical shape or a flat shape.

[0003] Among them, a flat-type lithium graphite fluoride battery has excellent long-term storage characteristics of 10 years or more at room temperature, and is therefore widely used as a power source for memory backup. However, recently there has been a demand for use in severe temperature environments such as automobiles and industrial equipment, and electrical characteristics have also changed from conventional weak current discharges such as memory backups to high current discharge pulse applications. And then.

In order to satisfy such a requirement, for example, US Pat. No. 5246795, Japanese Patent Laid-Open No. 8-31 429, and Japanese Patent Laid-Open No. 2002-170575 disclose a battery constituent material in a flat lithium graphite fluoride battery. A method for improving the high-temperature storage characteristics has been proposed.

[0005] However, the conventional lithium graphite fluoride battery has the following problems in discharging in a low temperature environment. Discharge of fluorinated graphite lithium battery from metallic lithium as negative electrode The process proceeds when the dissolved lithium ions are inserted between the fluorinated graphite layers as the positive electrode. At that time, lithium ions are inserted between the fluorinated graphite layers in a solvated state with the electrolytic solution. Therefore, the positive electrode using fluorinated graphite increases in volume (expands) as the discharge progresses. In particular, the expansion rate tends to increase as the discharge load increases and the temperature decreases. This is presumed to be because the spread of the interlayer is different from the conventional one because lithium ions rapidly enter the fluorinated graphite layer. At this time, the volume expansion of the pellet-shaped positive electrode proceeds both in the diameter direction and in the thickness direction. When expanded in the diametrical direction, depending on the balance between the outer diameter of the positive electrode and the inner diameter of the gasket, the positive electrode expanded in the diametrical direction may come into contact with the inner wall of the gasket, and the positive electrode may be pushed by the gasket and the positive electrode may crack. In this case, the internal resistance of the battery increases, and the battery voltage may decrease during discharge.

[0006] In order to solve such a problem, a method is conceivable in which the diameter of the pellet-shaped positive electrode that is pressure-molded into a cylindrical shape is extremely small with respect to the inner wall of the gasket. This prevents the positive electrode from contacting the inner wall of the gasket. However, if the diameter of the positive electrode is made extremely small, the area facing the negative electrode also decreases at the same time, which may cause deterioration of the characteristics of the graphite lithium fluoride battery itself, such as the closed circuit voltage (CCV) characteristic. There is.

[0007] In addition to the positive electrode active material, the positive electrode of the flat organic electrolyte battery is mainly composed of a conductive agent that plays a role of increasing conductivity and a binder that keeps the positive electrode in a pellet form. It is blended as Therefore, it is conceivable to increase the amount of the binder as a method for improving the deterioration of the battery characteristics accompanying the expansion of the positive electrode in a low temperature environment. Examples of the binder include tetrafluorinated styrene resin (PTFE) and styrene butadiene rubber (SBR). It is considered that the strength of the positive electrode can be increased by increasing the binder content, and the volume expansion of the positive electrode pellet during discharge in a low temperature environment of a fluorinated graphite lithium battery can be suppressed. It is done.

[0008] On the other hand, the discharge reaction proceeds by inserting lithium ions dissolved in negative electrode force between fluorinated graphite layers in the positive electrode. For this reason, when the amount of the binder not involved in the discharge reaction is increased, the insertion of lithium ions between the fluorinated graphite layers may be inhibited. Therefore, an excessive increase in the binder may also cause deterioration of battery characteristics.

Disclosure of the invention [0009] The present invention is a flat organic electrolyte battery that can be stably discharged in a discharge under an extremely low temperature environment without reducing the characteristics of the graphite fluoride lithium battery. The flat organic electrolyte battery of the present invention includes a negative electrode, a positive electrode, an organic electrolyte, a separator, a sealing plate, a positive electrode case, and a gasket. The negative electrode uses metallic lithium or lithium alloy as the negative electrode active material. The positive electrode includes 100 parts by weight of graphite fluoride as a positive electrode active material and 15 parts by weight or more and 30 parts by weight or less of a conductive agent. The separator is interposed between the negative electrode and the positive electrode. The sealing plate contacts the negative electrode and also serves as the negative electrode terminal. The positive electrode case contacts the positive electrode and doubles as the positive electrode terminal. The gasket is interposed between the positive electrode case and the sealing plate. According to the configuration of the present invention, the direct current resistance of the positive electrode itself is reduced by adding a conductive agent added to supplement the conductivity of the positive electrode active material, such as graphite and acetylene black, in excess of the conventional amount. As a result, insertion of lithium ions into the fluorinated graphite proceeds more smoothly, so that excessive expansion of the positive electrode during discharge in a low temperature environment is suppressed. Therefore, the discharge characteristics under a low temperature environment are improved as compared with the conventional fluorinated graphite lithium battery.

Brief Description of Drawings

FIG. 1 is a cross-sectional view of a flat organic electrolyte battery according to an embodiment of the present invention.

Explanation of symbols

[0011] 1 Positive electrode case

2 Sealing plate

3 Positive electrode

4 Negative electrode

5 Senator

6 Gasket

6A inner wall

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a cross-sectional view of a flat organic electrolyte battery according to an embodiment of the present invention. The battery includes a positive electrode 3 disposed in a positive electrode case 1 having an upper opening, a negative electrode 4 disposed via a separator 5 that holds an organic electrolyte, and a sealing plate 2. After the sealing plate 2 is combined with the positive electrode case 1 through the grease gasket 6 having a cross-sectional shape and a force, The opening of the pole case 1 is force-sealed inside to form a sealing portion. Positive electrode case 1 contacts positive electrode 3 to serve as a positive electrode terminal, and sealing plate 2 contacts negative electrode 4 to serve as a negative electrode terminal.

The positive electrode 3 includes fluorinated graphite as a positive electrode active material, and the negative electrode 4 includes metallic lithium or a lithium alloy as a negative electrode active material. In particular, the positive electrode 3 contains 15 to 30 parts by weight of a conductive agent with respect to 100 parts by weight of fluorinated graphite. By using such a positive electrode 3, excessive volume expansion of the positive electrode 3 during discharge in a low temperature environment is suppressed, and discharge characteristics in an extremely low temperature environment are improved.

[0014] Fluorinated graphite, which is a positive electrode active material, is produced by reacting a carbon material such as coatus or graphite with fluorine gas at a temperature of about 250 to 650 ° C. Depending on the fluorination treatment, (C F) (where x = 0.5-1), (C F) or a mixture thereof is formed. There is no particular limitation on the shape and particle size of the fluorinated graphite in combination with the organic electrolyte, but it is preferable to use needle coatas as a starting material and fluorinated at 400 ° C. Yes. Further, when the positive electrode 3 is constituted, a conductive agent or a binder is mixed with fluorinated graphite to form a positive electrode mixture. The positive electrode mixture is pressure-molded into a cylindrical shape, and then dried to form a pellet-shaped positive electrode. 3 is produced.

[0015] As the conductive agent, it is preferable to use natural graphite, artificial graphite, acetylene black, furnace black or the like alone or a mixture thereof. As a result, the conductivity in the positive electrode 3, the moldability of the positive electrode 3, and the strength durability are obtained. As the binder, styrene-butadiene rubber, fluorine-based resin and the like are mainly used.

Conventionally, a conductive agent has been added to assist the conductivity by covering the active material surface with a conductive agent when the conductivity of the active material itself is low. For this reason, increasing the amount of conductive agent added will improve the battery characteristics such as CCV characteristics. Even if it is added excessively, the characteristics will not improve. On the other hand, in a lithium fluoride graphite battery, the addition of a conductive agent suppresses the volume expansion of the positive electrode 3 associated with the discharge as well as imparting conductivity. Therefore, the larger the amount of conductive agent added, the more the volume expansion of the positive electrode 3 is suppressed until the end of discharge, and the battery characteristics are improved.

[0017] Note that, when a large amount of conductive agent is added with a constant amount of active material, the thickness of the positive electrode 3 increases. To do. Therefore, the positive electrode case 1 and the sealing plate 2 may be deformed by the pressing force at the time of sealing. Such deformation lowers the sealability of the caulking portion, and deteriorates the leakage resistance and storage characteristics. Further, as described later, when a large amount of a conductive agent is added, the formability of the positive electrode 3 is lowered. Therefore, the addition amount of the conductive agent is desirably in the range of 15 parts by weight or more and 30 parts by weight or less with respect to 100 parts by weight of graphite fluoride as the positive electrode active material.

For the negative electrode 4, one or more of lithium alloys such as metallic lithium, Li—Al, Li Sn, Li—NiSi, and Li—Pb are used.

[0019] The organic electrolytic solution is prepared by dissolving a solute in an organic solvent. Examples of organic solvents include polar solvents such as propylene carbonate, butylene carbonate, ethylene carbonate, snorephoran, and _butyl lactone, and low-viscosity solvents such as 1,2-dimethoxyethane, dimethyl carbonate, diethyl carbonate, and ethylmethyl carbonate. One or more can be used. In order to use in a high temperature environment, it is preferable to use y-ptyllactone alone. Solutes include lithium borofluoride, lithium phosphorus hexafluoride, lithium trifluoromethanesulfonate, and LiN (CF SO), LiN (C

3 2 2

F SO), LiN (CF SO) (C F SO), or the like can be used. Of these, Hough

2 5 2 2 3 2 4 9 2

Lithium fluoride is preferable because it has good storage characteristics at high temperatures and can exhibit stable discharge characteristics when dissolved in an organic solvent at a concentration of 0.5 to 1.5 molZl.

[0020] The gasket 6 is annular in order to insulate the positive electrode case 1 also serving as the positive electrode terminal and the sealing plate 2 also serving as the negative electrode terminal, and its cross section has an L shape. The gasket 6 preferably has a rib-like inner wall portion 6A in the battery inner space, and the inner wall portion 6A has a structure facing a power generating element constituted by the positive electrode 3 and the negative electrode 4. The gasket 6 has the inner wall 6A to prevent the positive electrode 3 and the sealing plate 2 from coming into contact with each other and short-circuiting when the positive electrode 3 expands in the diameter direction or the positive electrode 3 is displaced from the center. Is done.

[0021] In configuring other batteries, known materials can be used for the separator, the positive electrode case, the sealing plate, and the like.

Hereinafter, as more specific examples, batteries A to F are manufactured, and the effects of the present embodiment will be described using these batteries. First, battery A will be described.

[0023] The positive electrode 3 is produced as follows. First, a conductive agent for 100 parts by weight of graphite Add 15 parts by weight of acetylene black, and 10 parts by weight of styrene butadiene rubber as a binder, and mix to prepare a positive electrode mixture. This positive electrode mixture is filled in a cylindrical mold having a diameter of 17. Omm, press-molded, and dried at 100 ° C for 24 hours.

[0024] The negative electrode 4 is formed by punching a metal lithium hoop-like material having a thickness of 1. Omm into a circle. The negative electrode 4 is pressed against the inner surface of the central portion of the sealing plate 2 by pressure. The separator 5 is made of a polypropylene (PP) non-woven fabric punched into a larger diameter than the positive electrode 3 and the negative electrode 4. In addition, a solution prepared by dissolving lithium borofluoride in lmol / 1 at γ-petit rataton is used as the organic electrolyte.

[0025] This battery is manufactured by the following procedure. First, the positive electrode 3 and the separator 5 are arranged inside the positive electrode case 1, and 1. Og of organic electrolyte is injected. Next, the sealing plate 2 having the negative electrode 4 bonded to the inner surface of the central portion is inserted into the positive electrode case 1. At this time, the power generation element in which the positive electrode 3 and the negative electrode 4 are disposed to face each other via the separator 5 is accommodated in the inner space of the battery container surrounded by the sealing plate 2 and the positive electrode case 1 insulated by the gasket 6. Thereafter, the peripheral edge of the positive electrode case 1 is deformed inward by a caulking jig, and is folded back along the peripheral edge of the sealing plate 2 together with the gasket 6. As a result, the peripheral portion of the sealing plate 2 is also tightened with the vertical force through the gasket 6. An inwardly folded portion is formed in the positive electrode case 1, and has a cross-sectional shape as shown in FIG. 1, with a diameter of 24.5 mm and a thickness of 5. Omm battery is obtained. The gasket 6 is made of polyphenylene sulfide (PPS) having a cross-sectional shape of force, and the inner wall 6A of the gasket 6 in contact with the power generation element has an inner diameter of 20. Omm.

[0026] For batteries B, C, and D, batteries are fabricated under the same conditions as battery A, except that the blending ratio of acetylene black, which is a conductive agent, is 20 parts by weight, 25 parts by weight, and 30 parts by weight, respectively. On the other hand, batteries E and F are produced under the same conditions as battery A except that the mixing ratio of acetylene black is 5 parts by weight and 10 parts by weight, respectively.

[0027] In batteries A to F, the amount of active material of positive electrode 3 is adjusted so that the theoretical capacity of the battery is regulated by positive electrode 3 to be 550 mAh. In addition, the pellet thickness is varied so that the density of the positive electrode 3 is also equal, and the thickness of the negative electrode 4 is adjusted to produce a battery.

[0028] When the amount of the conductive agent exceeds 30 parts by weight, the positive electrode 3 cracks during pressure molding.

It is difficult to perform pressure molding with such a conductive agent amount. [0029] The battery produced as described above was evaluated by performing the following tests. First, 10 batteries from battery A to battery F were each connected with a resistance of 30 kΩ and discharged under an environment of 20 ° C. The battery was discharged to a final voltage of 2. OV and the discharge capacity was measured. In addition, each battery was disassembled after discharging to 50% of the theoretical capacity of 550 mAh, and the diameter of each positive electrode 3 was measured. (Table 1) shows the average value of the discharge capacity of each battery and the average value of the positive electrode 3 diameter.

[0030] [Table 1]

[0031] As is apparent from the results of (Table 1), the smaller the amount of acetylene black as the conductive agent, the smaller the obtained discharge capacity. In particular, battery E has a capacity of about 70% of the theoretical capacity of 550 mAh, and no power is obtained. On the other hand, the capacity of the conductive agent is not less than 15 parts by weight with respect to 100 parts by weight of graphite fluoride.

[0032] The cause of the decrease in discharge capacity due to the difference in the amount of the conductive agent is considered as follows. The positive electrode 3 expands in volume as the discharge proceeds. Such volume expansion is more pronounced when discharging under severe conditions such as large current discharge or discharge in a low temperature environment than during discharge under weak current or discharge at room temperature or high temperature. It is. From these conditions, it is considered that lithium ions are inserted between layers of fluorinated graphite in different states during discharge under severe conditions, and the layers are greatly expanded. Therefore, the positive electrode 3 comes into contact with the gasket 6 during the discharge, and the positive electrode 3 is cracked and broken. As a result, the organic electrolyte solution withered rapidly, and the internal resistance of the battery increased, which is presumed to decrease the discharge capacity. Increasing the amount of the conductive agent reduces the DC resistance of the positive electrode 3 and facilitates the insertion of lithium ions into the fluorinated graphite. As a result, the positive electrode 3 is discharged in a low temperature environment. Excessive expansion is suppressed. For this reason, it is considered that the spread between the fluorinated graphite layers due to discharge in a low temperature environment is reduced, and a discharge capacity close to the theoretical capacity can be obtained.

[0033] In addition, it is obvious from (Table 1) that the expansion of the positive electrode 3 is suppressed even when discharging is performed with the same load by increasing the amount of the conductive agent. This also suggests that the cause of the difference in the discharge capacity due to the difference in the amount of the conductive agent as estimated above is due to the volume expansion of the positive electrode pellet.

[0034] Next, a battery was fabricated under the same conditions as Battery A except that acetylene black, which is a conductive agent, was changed to natural graphite, and the same evaluation was performed. In this case, the same result was obtained. Obtained. In other words, the result was that the discharge capacity at low temperature was close to the theoretical capacity in the range of 15 parts by weight to 30 parts by weight with respect to 100 parts by weight of the graphite conductive graphite. Similar results were obtained when the conductive agent was changed to artificial graphite or furnace black.

[0035] In addition to PPS, polyethylene naphthalate, polyethylene terephthalate, or PP may be used as the material of the gasket 6. In addition to PP, the separator 5 may be made of non-woven cloth or microporous film of polyethylene (PE), polyphenylene sulfide (PPS), or polyethylene terephthalate (PET).

Industrial applicability

[0036] According to the present invention, the low-temperature discharge characteristics of a graphite fluoride lithium battery can be improved.

For this reason, it will lead to the expansion of the use of graphite fluoride lithium batteries to applications other than the backup of the use of the catalyst, and thus the industrial utility value is extremely large.

Claims

The scope of the claims

[1] a negative electrode having a negative electrode active material of at least one of metallic lithium and a lithium alloy;

A positive electrode comprising 100 parts by weight of fluorinated graphite as a positive electrode active material and 15 to 30 parts by weight of a conductive agent;

An organic electrolyte,

A separator interposed between the negative electrode and the positive electrode;

A sealing plate that contacts the negative electrode and also serves as a negative electrode terminal;

A positive electrode case that contacts the positive electrode and also serves as a positive electrode terminal;

A flat organic electrolyte battery comprising a gasket interposed between the positive electrode case and the sealing plate.

2. The flat organic electrolyte battery according to claim 1, wherein the conductive agent includes at least one of natural graphite, artificial graphite, acetylene black, and furnace black.