JP2002216843A - Manufacturing method of lithium polymer cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a lithium polymer cell with excellent reliability, small variation of a thickness during the storage for long time at high temperature, and high discharge capacity keeping ratio. SOLUTION: A copolymer of Vinylidene fluoride-hexafluoropyrene P(VDF-HFP) is used as a polymer retaining nonaqueous electrolyte liquid, and a mixed solvent, containing at least one kind of solvent with boiling point of not less than 120 deg.C, is used as a solvent of the electrolyte. A uniform and fine gel is formed by keeping it in the state of reduced pressure of less than 15 Pa, at the temperature of 90 deg.C-100 deg.C, for 30 minutes-one hour, and by further keeping it for 30 minutes-3 hours while keeping above temperature, under normal pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a lithium polymer battery, and more particularly, it is possible to suppress swelling and capacity deterioration of a battery, particularly during high-temperature long-term storage, by producing an optimum gel. The present invention relates to a method for manufacturing a lithium polymer battery.

[0002]

2. Description of the Related Art In recent years, with the development of electronic equipment, there has been a demand for the development of a secondary battery that is small, lightweight, has a high energy density, and can be repeatedly charged and discharged. As such a secondary battery, a lithium battery including a negative electrode using lithium metal or a lithium alloy as an active material, and a positive electrode using an oxide, sulfide, or selenide such as molybdenum, vanadium, titanium, or niobium as an active material is used. Secondary batteries are known. However, a secondary battery provided with a negative electrode using lithium metal or a lithium alloy as an active material, lithium dendrites precipitate on the negative electrode when charging and discharging are repeated,
There is a problem that the charge / discharge cycle life is short.

[0003] For this reason, the negative electrode, for example coke, graphite, carbon fiber, resin fired body, a lithium ion, such as pyrolytic vapor carbon using a carbonaceous material for absorbing and releasing, electrolytes such as LiPF ₆ A lithium secondary battery using a non-aqueous electrolyte in which is dissolved in a solvent such as ethylene carbonate or propylene carbonate has been proposed. In the lithium secondary battery, the deterioration of the negative electrode characteristics due to dendrite deposition can be improved, so that the charge and discharge cycle life and safety can be improved.

On the other hand, since solidification of the electrolyte provides a battery free from liquid leakage, it has been regarded as the ultimate battery. However, it has a problem that the ionic conductivity is several orders of magnitude lower than that of the solution type. However, it did not lead to the emergence of a versatile battery.

However, when the polymer is gelled together with an organic solvent-based electrolyte, the ionic conductivity becomes 10 ⁻³ S / cm.
As a result, polymer electrolytes with high ionic conductivity can be obtained, and by using this as a battery separator, batteries with good characteristics can be obtained. Became.

US Pat. No. 5,296,318 discloses a chargeable / dischargeable lithium intercalation battery having a hybrid polymer electrolyte provided with flexibility by using a polymer for a binder for a positive electrode, a negative electrode, and a separator, that is, lithium. A polymer battery is disclosed.

The positive electrode is made of, for example, an active material composed of a lithium-cobalt composite oxide, a polymer composed of a copolymer P (VDF-HFP) of vinylidene fluoride and hexafluoropyrene, and a plasticizer such as DBP (dibutyl phthalate). A positive electrode paste containing: is applied to an aluminum current collector,
After being dried and rolled, it is cut into predetermined dimensions to produce a positive electrode.

The negative electrode is, for example, an active material composed of a carbonaceous material such as graphite capable of inserting and extracting lithium ions, and a polymer composed of a copolymer P (VDF-HFP) of vinylidene fluoride-hexafluoropyrene. And DBP
A negative electrode paste containing a plasticizer such as (dibutyl phthalate) is applied to a copper current collector, dried and rolled, and then cut into predetermined dimensions to produce a negative electrode.

Next, a polymer separator made of P (VDF-HFP) not impregnated with an electrolytic solution is interposed between the positive electrode and the negative electrode, and is laminated by heating and pressing with a heated rigid roll. Next, the plasticizer contained in the laminated film is extracted using an organic solvent such as xylene, and dried under reduced pressure. The power generation element thus obtained is housed in a bag-shaped outer case (hereinafter referred to as an outer case) made of a laminated sheet in which an aluminum foil is disposed between resin films and the whole is laminated and integrated, In this method, a non-aqueous electrolyte is injected, and a heating process is performed to gel the polymer and the separator in the positive electrode plate and the negative electrode plate, thereby retaining the non-aqueous electrolyte.

As a method for gelling, Japanese Patent Laid-Open No.
Japanese Patent Application Laid-Open No. 2000-12076 discloses a method of gelling at a temperature of 90 ° C. to 120 ° C. by using a non-aqueous electrolyte containing propylene carbonate as an electrolyte solvent and using polyvinylidene fluoride as a polymer. Discloses a method of gelling at a temperature of 60 ° C. to 90 ° C. with an open circuit voltage of 3.6 V or less.

[0011]

However, under such gelling conditions, it is difficult to uniformly penetrate the non-aqueous electrolyte throughout the battery, and the non-aqueous electrolyte which does not gel remains. Therefore, for example, when the battery is stored at a high temperature of 90 ° C. for a long period of time, the solvent or the electrolyte in the non-gelled electrolyte solution easily undergoes a decomposition reaction to generate gas, thereby causing the battery to swell. It turned out that there was. Furthermore, due to the uneven gel structure,
It was also found that the structure was destroyed during high-temperature storage, making it difficult to maintain the capacity of the battery.

Therefore, in the present invention, a copolymer P (VDF-H) of vinylidene fluoride-hexafluoropyrene) is used.
To provide a method for producing a lithium polymer battery having excellent high-temperature long-term storage characteristics by using FP) to simultaneously make the electrolyte uniformly penetrate into the entire battery and to gel the electrolyte to form a denser gel structure. Aim.

[0013]

In order to achieve the above object, the present invention provides a power generation element in which a positive electrode plate and a negative electrode plate are insulated from each other through a separator in the outer case,
A step of holding the non-aqueous electrolyte in the power generation element and sealing the positive electrode lead and the negative electrode lead to which one ends of the positive electrode plate and the negative electrode plate are connected, respectively, in a state where the positive electrode lead and the negative electrode lead are drawn out from the sealing portion of the outer case. A first charging step in which a charging process is performed until a predetermined battery voltage is generated to complete the initial gas generation;
A first aging step of storing for 30 minutes to 1 hour in an environment of ° C., then returning to normal pressure while maintaining the above temperature, and storing for another 30 minutes to 3 hours. A second charging step for generating gas and stabilizing the battery characteristics, a second aging step for storing the charged state in an environment of about 60 ° C. to 70 ° C., and a part of the outer case is opened and accumulated inside. This is a method for manufacturing a lithium polymer battery in which the above-described steps are performed in the order of the step of discharging gas and the step of resealing the outer case.

The polymer holding the non-aqueous electrolyte inside the positive electrode and the negative electrode is vinylidene fluoride-hexafluoropyrene P
Using a copolymer of (VDF-HFP) and a mixed solvent containing at least one solvent having a boiling point of 120 ° C. or higher as an electrolyte solution solvent composition, a pressure of 90 ° C. to 100 ° C. under a vacuum reduced pressure of 15 Pa or less is used. It is stored for 30 minutes to 3 hours under the environment to completely remove the gas remaining in the power generation element from the power generation element, and then returns to normal pressure to further remove the gas for 3 hours under the environment.
By storing and gelling from 0 minutes to 1 hour, a uniform and dense gel is formed over the entire battery, and it is possible to suppress lithium battery swelling and capacity deterioration especially during long-term storage at high temperatures, and to achieve a highly reliable lithium polymer battery. Become.

The vacuum pressure is preferably 15 Pa or less. If it exceeds 15 Pa, it is difficult to completely remove the gas from the electrode plate, and a clear effect of the vacuum pressure is not recognized.

The vacuum decompression time is preferably in the range of 30 minutes to 3 hours. If it is less than 30 minutes, the effect of completely removing the gas in the power generating element is small. It is not preferable because decomposition of the electrolyte therein occurs.

[0017]

Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1 and 2 are a top view and a sectional view, respectively, of a lithium polymer battery according to the manufacturing method of the present invention. The positive electrode 1 is formed by applying a paste obtained by kneading and dispersing a positive electrode active material, a polymer as a conductive agent and a binder and an electrolyte retainer in an organic solvent, to both sides of an aluminum foil current collector 1a, drying and rolling, This is a positive electrode active material layer 1b.

A polymer separator 3 made of the above-mentioned film is disposed between the two positive electrodes, and a carbonaceous material and the polymer as a binder and an electrolyte retainer are placed between the separators 3 with an organic solvent. There is a negative electrode 2 in which a paste kneaded and dispersed in is coated on both sides of a copper foil current collector 2a, dried and rolled to form a negative electrode active material layer 2b, and the whole is laminated as shown in FIG. Power generation element 4 is configured.

Reference numeral 1c denotes a lead mounting portion provided on the current collector of the positive electrode, to which a positive electrode lead 5 is welded.
2c is a lead attachment portion provided on the current collector of the negative electrode,
The negative electrode lead 6 is welded here. Reference numeral 7 denotes an outer case made of a laminated film in which a metal foil is used as an intermediate layer, a resin film is laminated on the inner side, and a resin film is laminated and integrated on the outer side. In the power generation element 4 housed inside the outer case 7, the positive electrode lead 5 and the negative electrode lead 6 are drawn out of the outer case 7, and the leading ends are input / output terminals 8,9. Reference numerals 10 and 11 denote insulating protective films provided at intermediate portions of the leads 5 and 6, which are used to seal the openings of the outer case 7 by heat sealing or the like.
This ensures electrical insulation and airtightness. The outer case 7 is formed by cutting the laminate film into a strip shape, folding the laminate film at the center T in the length direction thereof, and heat-sealing the upper and lower sides P1 and P2 in advance, and has an opening. 1 remaining
The power generating element 4 is inserted from the side P3, and a predetermined amount of the non-aqueous electrolyte is injected.

The non-aqueous electrolyte used here is prepared by dissolving an electrolyte such as LiPF ₆ or LiBF ₄ in a mixed solvent containing at least one solvent having a high boiling point of 120 ° C. or higher. Examples of the solvent having a high boiling point of 120 ° C. or higher include ethyl carbonate (EC), propylene carbonate (PC), and butylene carbonate (B
C), diethyl carbonate (DEC) and the like can be used. The high-boiling point solvent and the low-boiling point solvent are mixed to make the viscosity appropriate so that the electrolyte can be uniformly spread over the entire electrode plate and the stability of the electrolytic solution can be ensured. The volume ratio is preferably 50% or more. If the ratio of the high boiling point solvent is less than 50% by volume, the composition will be undesirably volatilized in a vacuum depressurized state in a first aging step described later, causing a change in the electrolyte composition.

The remaining one side P3 of the opening
The part is heat-sealed and sealed.

Next, the first charging step is a step of performing a charging process until a predetermined battery voltage is generated to complete the initial gas generation. The predetermined battery voltage in this step needs to be 3.7 V or more.

This is because if there is a battery voltage of 3.7 V or more, a decrease in the battery voltage in a high-temperature environment in a first aging step, which will be described later, that is, a deterioration in capacity is minimized.

The first aging step is performed at 90 ° C. under a reduced pressure of 15 Pa or less at the predetermined battery voltage.
Aging was performed in an environment of 100 ° C. for 30 minutes to 3 hours to remove the polymer in the positive electrode plate and the negative electrode plate in the power generating element and the residual gas in the separator, and then returned to normal pressure while maintaining the same temperature. This is a step of generating gas from the power generation element at the same time as gelation.

The second charging step is a step of charging only the required amount of electricity, generating gas from the power generating element, and stabilizing the battery characteristics. The charging process is performed at 95% to 1% of the battery capacity.
A range of 05% is preferred.

In the second aging step, the battery is stored in an environment of about 60 ° C. to 70 ° C. in this charged state, and further gas is generated from the power generating element, the gas is completely discharged, and the battery characteristics are stabilized. It is a process. If the temperature is lower than 60 ° C., the discharge of gas is insufficient, and if the temperature is higher than 70 ° C., the battery characteristics deteriorate, which is not preferable. The aging time is preferably in a range of 50 hours to 72 hours in an environment of 60 ° C, and is preferably in a range of 40 hours to 55 hours in an environment of 70 ° C.

Next, there is provided a method for manufacturing a lithium polymer battery, comprising the steps of: opening a part of an outer case, discharging gas accumulated inside, and sealing the outer case again.

[0029]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples.

The positive electrode 1 is composed of 100 parts by weight of a positive electrode active material containing lithium cobalt oxide as a main component, 5 parts by weight of acetylene black as a conductive agent, and vinylidene fluoride (VDF) which is a polymer as a binder and an electrolyte retainer. P (VDF-) with hexafluoropropylene (HFP)
HFP) 8 parts by weight of a plasticizer and 10 parts by weight of DBP (dibutyl phthalate) are kneaded and dispersed in an organic solvent composed of NMP (N-methyl-2-pyrrolidone). After coating, drying and rolling on both surfaces of the current collector 1a, the current collector 1a is cut into a predetermined size to form a positive electrode active material layer 1b. A polymer separator 3 made of the P (VDF-HFP) film is disposed between the two positive electrode active material layers, and 100 parts by weight of carbon powder and the binder and The polymer P (VDF-
HFP) powder and 30 parts by weight of a plasticizer, DBP (dibutyl phthalate), are kneaded and dispersed in an organic solvent mixture of acetone and cyclohexanone, and are coated on both sides of a lath-processed copper foil current collector 2a. After being deposited, dried, and rolled, there is a negative electrode 2 having a predetermined size and a negative electrode active material layer 2b formed thereon. The entirety of the negative electrode 2 is laminated and integrated as shown in FIG. Next, DBP as a plasticizer contained in the power generating element is extracted using an organic solvent such as xylene, and dried under reduced pressure at a temperature of 100 ° C.

Reference numeral 1c denotes a lead mounting portion provided on the current collector of the positive electrode, to which an aluminum positive electrode lead 5 is welded. Reference numeral 2c denotes a lead mounting portion provided on the current collector of the negative electrode, to which a negative electrode lead 6 made of copper foil is welded.

The power generation element 4 thus manufactured has an outer case 7 made of an aluminum laminate film having an aluminum foil as an intermediate layer, a polypropylene film on the inner side, and a polyethylene terephthalate film and a nylon film on the outer side. The lead 5 of the positive electrode and the lead 6 of the negative electrode are housed inside, and are drawn out of the exterior case 7.
It is.

Next, LiPF ₆ was dissolved at a concentration of 1.0 mol in a mixed solvent of propylene carbonate (PC) having a boiling point of 242 ° C. and dimethyl carbonate (DMC) having a boiling point of 90 ° C. at a volume ratio of 7: 3. After the injection using the non-aqueous electrolyte, the heat-welded portion P3 was heat-sealed and sealed.

Reference numerals 10 and 11 denote insulating protective films provided at intermediate portions of the leads 5 and 6, which are used to electrically insulate and airtighten the leads 5 and 6 when the opening of the outer case 7 is sealed by heat sealing or the like. Is to ensure.

In the first charging step, a charging process was performed until a battery voltage of 3.75 V was generated, thereby completing the initial gas generation.

In the first aging step, aging is carried out at a temperature of 95 ° C. for 1 hour at a battery voltage of 3.75 V at a pressure of 15 Pa, 5 Pa, and 2 Pa using a vacuum decompression device. The pressure was returned to normal pressure, and the system was further stored for 1 hour, and the polymer in the positive electrode plate and the negative electrode plate in the power generating element and the separator were gelled, and at the same time, gas was generated from the power generating element.

In the second charging step, the battery was charged with 100% of the battery capacity, and gas was generated from the power generating element and the battery characteristics were stabilized.

In the second aging step, the battery is kept in this charged state in an environment of about 60 ° C. for 65 hours, and further gas is generated from the power generating element, and the gas is completely discharged.
Stabilized battery characteristics.

In a dry atmosphere, a part of the outer case was opened and pressed with a load of 0.4 MPa for 1 second to discharge gas accumulated inside. Then, the outer case was closed again and the battery capacity was 1000 mAh. A lithium polymer battery was obtained.

Comparative Example A lithium polymer battery having a battery capacity of 1000 mAh was obtained in the same manner as in Example 1 except that in the first aging step, aging was performed only at normal pressure.

(Geling Pressure Condition and Change in Battery Thickness During Storage at High Temperature) Each of the batteries obtained in the Examples and Comparative Examples was charged with 4.2 V at a charging current of 0.2 CmA (200 mA).
After the battery was charged until the temperature reached, the battery was stored at a high temperature of 90 ° C., and the battery thickness was measured. Table 1 shows the results of measuring the battery thickness at a temperature of 90 ° C. under a load of 0.2 MPa using a micrometer in order to measure accurately.
The numbers in the table represent the amount of change from the battery thickness before storage as m.
Shown in m units.

[0042]

[Table 1]

From Table 1, it can be seen that the change in the thickness of the battery prepared under a reduced pressure of 15 Pa or less at the time of the first aging is about 1/100 since the battery does not swell as compared with the battery prepared under normal pressure. The value is significantly reduced to 10, indicating that the entire battery can be formed of a uniform and dense gel by aging under reduced pressure in a vacuum.

(Geling Pressure Conditions and Capacity Retention after Long-Term Storage at High Temperature) Each of the batteries obtained in Examples and Comparative Examples was
After charging to 4.2 V with a charging current of 0.2 CmA (200 mA), the battery was stored at a high temperature of 90 ° C.
The discharge capacity was measured. The battery after storage was charged at 0.2 CmA (2
Table 2 shows the results of the discharge capacity retention ratio when the battery was charged to 4.2 V at a charging current of 00 mA) and then discharged to 3.0 V at a current value of 0.2 CmA (200 mA).
The numbers in the table indicate the percentage of the discharge capacity when the initial discharge capacity is 100%.

[0045]

[Table 2]

From Table 2, it can be seen that the retention rate of the discharge capacity after high-temperature storage of the battery prepared under a reduced pressure condition of 15 Pa or less during the first aging is higher than that of the battery prepared under normal pressure. ing. From this, it was found that the gel produced in a vacuum depressurized state did not cause structural destruction even during high-temperature storage, and maintained a high capacity retention rate.

[0047]

As described above, according to the method for producing a lithium polymer of the present invention, vinylidene fluoride-hexafluoropyrene P (VDF-HFP) is added to the polymer holding the nonaqueous electrolyte inside the positive electrode and the negative electrode. Using a polymer, and using a mixed electrolyte composition containing at least one solvent having a boiling point of 120 ° C. or more as a solvent composition of the electrolyte, 30 minutes in an environment of 90 ° C. to 100 ° C. under a vacuum reduced pressure of 15 Pa or less. Storage for about 1 hour, then return to normal pressure while maintaining the above temperature, and further store for 30 minutes to 3 hours to gel, so that the change in battery thickness is small even during long-term storage at high temperature and high discharge capacity is maintained. It is possible to provide a highly reliable lithium polymer battery having a high efficiency.

[Brief description of the drawings]

FIG. 1 is a top view of a battery according to an embodiment of the present invention.

FIG. 2 is a sectional view of the battery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode 1a Positive electrode collector 1b Positive electrode active material layer 1c Positive electrode lead attaching part 2 Negative electrode 2a Negative electrode collector 2b Negative electrode active material layer 2c Negative electrode lead attaching part 3 Separator 4 Power generating element 5 Positive electrode lead 6 Negative electrode lead 7 Outer case 8 Positive electrode Output terminal 9 Negative electrode output terminal 10 Positive electrode lead insulating protective film 11 Negative electrode lead insulating protective film P1 Outer case heat welded part P2 Outer case heat welded part P3 Outer case heat welded part T Outer case bent part

 ────────────────────────────────────────────────── ─── Continued on the front page F term (reference) 5H029 AJ03 AJ04 AJ05 AJ11 AK03 AL07 AM03 AM05 AM07 AM16 BJ04 BJ12 CJ02 CJ05 CJ12 CJ16 CJ28 DJ02 EJ01 EJ14 HJ00 HJ14 HJ15 HJ18

Claims (4)

[Claims] 1. A power generating element in which a positive electrode plate and a negative electrode plate are insulated via a separator in a bag-shaped outer case made of a laminated sheet in which a metal foil is disposed between resin films and the whole is laminated and integrated. While the non-aqueous electrolyte is held in the power generating element, and the positive electrode lead and the negative electrode lead to which one ends of the positive electrode plate and the negative electrode plate are connected are drawn out from the sealing portion of the outer case. A first charging step of performing a charging process until a predetermined battery voltage is generated to finish initial gas generation;
30 minutes to 1 in an environment of 90 ° C to 100 ° C under vacuum and reduced pressure
A first aging step of storing for a period of time, then returning to normal pressure while maintaining the temperature, and further storing for 30 minutes to 3 hours;
A second charging step of charging only the required amount of electricity, generating gas from the power generating element and stabilizing the battery characteristics, a second aging step of storing the charged state in an environment of about 60 ° C to 70 ° C, exterior A method for manufacturing a lithium polymer battery, in which the above steps are performed in the order of a step of opening a part of the case to discharge gas accumulated inside and a step of resealing the outer case. 2. The method for manufacturing a lithium polymer battery according to claim 1, wherein the predetermined battery voltage is 3.7 V or more. 3. The method according to claim 1, wherein the power generation element includes a polymer comprising a copolymer P (VDF-HFP) of vinylidene fluoride-hexafluoropyrene and a solvent having a boiling point of 120 ° C. or higher as a solvent composition of the non-aqueous electrolyte. The method for producing a lithium polymer battery according to claim 1, wherein the mixed solvent contains at least one kind of solvent. 4. The method for producing a lithium polymer battery according to claim 1, wherein the reduced pressure in vacuum is 15 Pa or less.