JPH1196987A - Degassing method during initial charge of lithium secondary battery and its degassing structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To release a gas generated during initial charge without strictly controlling humidity by injecting an electrolytic solution from an injection mouth provided at the bottom most end of a recessed part formed at a battery can toward inside of the can, mounting a metallic ball to close the injection mouth being fell in the recessed part of the injection mouth by its own weight, performing initial charge, and then fixing the metallic ball by means of resistance welding after completing initial charge. SOLUTION: This is composed of a pan bottom shape recessed part 3 formed roundly at a can lid 1a, an injection port 5 formed concentrically opened at the most bottom end of the recessed part 3, and a metallic ball 4 contained in the recessed part. A sliding surface material 11 that is non-soluble to an electrolytic solution is injected between a periphery of the injection port 5 and the metallic ball 4 so as to return the electrolytic solution that adheres inside of the recessed part 3 to inside a battery can. When an inside pressure becomes to be high by a generated gas during initial charge, the metallic ball 4 rises by the gas to release the gas outside the battery can. After completing the initial charge, the metallic ball 4 is resistance welded between the recessed part 3 to seal. Thereby, an initial charge can be easily performed in a normal working room.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a degassing method for discharging gas generated at the time of initial charging of a lithium secondary battery to the outside and a degassing structure thereof.

[0002]

_2. Description of the Related Art In general, a lithium secondary battery uses, as a positive electrode active material, a lithium-containing oxide of a transition metal, that is, LiMO ₂ having a layered structure or LiM ₂ O ₄ having a spinel structure (where M is a transition metal, for example, cobalt,
Manganese or nickel iron), and a carbon material is used as a negative electrode material, and charge and discharge are performed by a reversible reaction between the positive electrode and the negative electrode, in which one absorbs lithium ions released by the other. .

[0003] In such a lithium secondary battery, there is a problem that gas is generated inside at the time of the first charge and the internal pressure rises.

Conventionally, the following measures have been taken to solve this problem. (1) Due to the structure of the lithium secondary battery, a thick can is used for the battery can in order to have sufficient mechanical strength to withstand an increase in internal pressure during initial charging. (2) At the time of manufacturing a lithium secondary battery, the battery can is opened to perform initial charging. That is, due to the structure, the battery can is left in a state in which gas escapes, and the initial charging is performed while the inside of the battery is open to the outside, and the gas is simultaneously vented. After degassing, the battery can is completely sealed.

[0005]

However, the method (1) of using a thick can has a problem that the internal volume of the battery can is reduced and the battery capacity of the lithium secondary battery is reduced.

On the other hand, the method (2) has an advantage that the battery can is made thinner because the battery can is sealed after degassing first. However, the conventional degassing method in which the inside of the lithium secondary battery is opened and the first charge is performed has the following problems. (A) Since the inside of the battery is opened to the outside at the time of initial charging, the electrolytic solution evaporates, and the battery characteristics deteriorate. (B) In addition, the electrolyte component adheres to the sealing portion, resulting in poor sealing. In order to improve the reliability of the sealing, a step of wiping the electrolyte component attached to the sealing portion is required. (C) Further, strict humidity control during charging is required. That is, during charging, it is necessary to ensure a dry environment with a relative humidity of 1 to 2%, but it is difficult to achieve such an environment with a normal air conditioner. For this reason, it is necessary to prepare a special drying room.

[0007] The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide a lithium secondary battery that does not require strict humidity control during charging, and that is not required during initial charging. It is an object of the present invention to provide a method of degassing at the time of initial charging and a degassing structure thereof, which can release gas and do not cause poor sealing or deterioration of battery characteristics.

[0008]

In order to achieve the above object, according to the present invention, a method and a structure for degassing a lithium secondary battery at the time of initial charging are configured as follows.

In other words, in the method for degassing at the time of the first charge according to the first aspect, the note provided at the lowermost end in the concave portion formed in the battery can of the lithium secondary battery by being depressed toward the inside of the can. After injecting the electrolytic solution from the liquid port, a metal sphere that drops into the liquid injection port by its own weight and closes the liquid injection port is loaded into the concave portion, and an electrolytic solution is inserted into a gap between the liquid injection port and the metal ball. An insoluble oil is injected into the liquid, and initial charging is performed in this state, the metal ball is floated by the pressure of gas generated inside the can at the time of charging to discharge the gas, and the gas is discharged. After completion of the injection, the metal ball closing the liquid inlet is fixed by resistance welding and sealed.

Further, in the gas venting structure at the time of the first charge according to the second aspect, the electrolyte injection port provided in the battery can of the lithium secondary battery is formed in a circular shape at the lowermost end of the concave portion recessed toward the inside of the can. In the concave portion, a metal ball that drops into the liquid inlet by its own weight and closes the liquid inlet and closes it, and floats by the gas pressure generated inside the can at the time of initial charging to open the liquid inlet is loaded, An oil insoluble in the electrolytic solution is injected into the gap between the periphery of the liquid port and the metal ball.

According to the degassing method and the degassing structure at the time of the first charge having the above configuration, before the first charge, the metal sphere in the concave portion closes the liquid inlet at the bottom center. But,
When gas is generated during the initial charge and the internal pressure is increased, the gas pushes up the metal spheres to float and the gas is released from between the oily substances. At this time, the released gas pushes the oily substance and the outside air outward, so that the oily substance and the outside air do not enter the battery can during the initial charge. At the same time as the internal pressure decreases, the metal sphere drops and the injection port is closed.

That is, the metal sphere and the oily substance act as a check valve. For this reason, it is not necessary to prepare a special drying room in which the relative humidity is 1 to 2% as in the related art.
The first charge can be performed in a work room using a normal air conditioner. Therefore, humidity management during charging becomes extremely easy.

[0013] Further, since a film is formed of an oily substance on the surface of the metal ball or in the gap between the metal ball and the liquid inlet, the gas is generated at the time of the first charge, so that the film is formed at the liquid inlet in the battery can. Even if the droplets of the electrolyte component fly toward, the droplets adhere to the film of the oily substance, fall, and are collected in the battery can.
For this reason, unlike the conventional case, the dried electrolyte component does not remain in the form of a white powder in the sealing portion after the completion of the initial charging, and a step of wiping the electrolyte component attached to the sealing portion is not required. Therefore, the reliability of the sealing portion is improved.

Furthermore, if the metal ball is sealed by resistance welding after the initial charge is performed, the check is made during the initial charge of the metal ball. Not only can it function as a valve, but it can also act as a contact for the welding electrode, thus simplifying the manufacturing process. In addition, since the electrolyte does not adhere around the inlet, no trouble occurs.

Further, for example, the recess is formed in a pot-like shape with a circular recess, and the liquid inlet is provided concentrically at the center of the bottom wall. The inner peripheral side bottom wall is curved downward and curled, the inner diameter of the peripheral wall of the concave portion is set to less than twice the diameter of the metal ball, and the inner peripheral side of the liquid injection port peripheral edge. If the distance from the starting point of the downward bending of the bottom wall to the peripheral wall surface of the concave portion is set to be equal to or less than the radius of the metal sphere, the metal sphere is lifted and moved to the outermost periphery in the concave portion by the pressure in the can, and Even when the metal ball is in contact with the wall surface, the center (center of gravity) of the metal sphere faces the injection port and is always located above it, so if the gas in the can is released and its pressure decreases, It can be automatically dropped by its own weight toward the injection port to close it, and the bottom of the pot bottom Jo was capable allowed to dwell held.

[0016]

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

FIG. 1 is an exploded perspective view schematically showing the entire structure of a flat rectangular lithium ion secondary battery employing a gas vent structure according to the present invention, and FIG. 2 is a longitudinal sectional view showing the gas vent structure. FIG. 3 is a plan view showing the gas vent structure. As shown in FIG. 1, an oblong prismatic lithium ion secondary battery includes an electrode body 12 in which a positive electrode plate and a negative electrode plate are spirally wound non-circularly with a separator interposed therebetween, and a battery can housing the electrode body. 1 and a can lid 1a for sealing the upper opening of the battery can 1, and the gas vent structure according to the present invention is applied to the electrolyte injection portion 2 provided on the can lid 1a. .

The pouring section 2 has a pot-shaped concave portion 3 formed in a circular shape on the can lid 1a, and a pouring port 5 formed concentrically at the center of the bottom wall 3a, which is the lowermost portion of the concave portion 3. And a metal ball 4 placed in the recess 3. here,
The diameter D1 of the recess 3 is not more than twice the diameter M of the metal ball 4 (D1
≦ 2M), and the depth H is set to be equal to or larger than the radius M / 2 of the metal sphere 4 (H ≧ M / 2). The diameter D2 of the liquid inlet 5 opened at the center of the bottom wall 3a is smaller than the diameter M of the metal ball 4. The central bottom wall 6 at the periphery of the liquid injection port 5 is rounded with a radius R1 and is curved downward so as to be curled. A metal ball 4 closes the liquid injection port 5 in the recess 3. Can be closed. Also,
The width (distance) W from the bending start point 7 to the peripheral wall 3b of the pot bottom-shaped recess 3 is set to be equal to or less than the radius M / 2 of the metal sphere (W ≦ M / 2).

That is, the inner diameter D1 and the depth H of the recess 3
The diameter D2 of the injection port 5, the diameter M of the metal ball 4, and the peripheral wall 3
The mutual dimensional relationship of the width W from b to the bending start point 7 is
The metal ball 4 always drops by its own weight into the liquid inlet 5 in the recess 3, and closes the liquid inlet 5. In other words, the inner shape of the concave portion 3 is such that the metal ball 4 is automatically moved by its own weight to the liquid inlet 5
It is shaped so that it falls down and stably closes it. Specifically, the metal sphere 4 in the concave portion 3 normally closes the liquid inlet 5 formed in the center of the bottom portion, but as shown in FIG. Even when the metal ball 4 moves to the outermost part in the radial direction of the metal ball 3 and is in contact with the peripheral wall 3 b, the center (center of gravity) 8 of the metal ball 4 moves downward to the peripheral part 6 of the liquid inlet 5. Are formed on the inner side of the bending start point 7 and on the liquid inlet 5 side. The outer peripheral edge 9 of the concave portion 3 bordering the battery can surface is rounded with a radius R2, and the radius R3 extends from the bottom wall 3a of the concave portion 3 to the peripheral wall 3a.
Rounded.

Further, in the gap between the metal ball 4 and the periphery of the injection port 5 in the recess 3, the electrolyte component adhering in the recess is slid and returned into the battery can 1. A lubricating substance 11 consisting of an insoluble oil is injected. Specifically, this smooth material 11 is made of polybutene (molecular weight: about 300).
Consists of Although this polybutene does not cause any trouble even if it enters into the battery can 1, the concave portion 3 is formed in the shape of a pot bottom as described above so that the polybutene can be stored here. Is provided. In addition, this polybutene has high viscosity and exhibits syrup-like fluidity.

The metal sphere 4 of the liquid injection section 2 configured as described above
The smooth surface substance 11 is provided in the recess 3 after the electrolyte is injected from the injection port 5. That is, after the injection, the metal spheres 4 are first loaded into the concave portions 3, and the smooth surface substance 11 is further injected in a state where the metal spheres 4 fall into the injection port 5 and block the injection port 5. Thereafter, the lithium-ion secondary battery is initially charged.

The function of the liquid injection section 2 during the initial charging is as follows. That is, at the beginning of the initial charging, as shown in FIG. 4 (a), the injection port 5 is closed by the metal ball 4, and the outer periphery is surrounded by the smooth surface material 11 made of an oily substance and sealed. I have. When gas is generated during the initial charging and the internal pressure in the battery can 1 increases, the metal sphere 4 is pushed up by the gas and floats up, as shown in FIG. Released outside the can. When the internal pressure decreases, the metal ball 4 simultaneously lowers, and the liquid inlet 5 is closed. That is, the metal ball 4 functions as a check valve. In the meantime, since the smooth surface substance 11 composed of an oily substance is pushed to the outer periphery by the released gas, it does not flow into the battery can 1,
There is no outside air.

During the above-mentioned initial charge, droplets of the electrolytic solution components splash toward the liquid inlet 5 and the vicinity thereof inside the battery can 1. In the gap between the can and the mouth 5, a film of the smooth surface substance 11 made of an oily substance is formed, so that the electrolytic solution component adheres to the smooth surface substance 11. That is, due to the action of the smooth surface material 11, the electrolyte component slides down on the smooth surface material 11 and is returned into the battery can 1. For this reason, unlike the related art, the electrolyte component does not remain attached to the sealing portion and does not remain as a dry white powder, and the reliability of the sealing portion is improved.

After the initial charging, as shown in FIG. 5, the battery can 1 is placed on the counter electrode 13 for resistance welding, and the electrode 14 of the resistance welding machine is placed in the recess 3 of the liquid injection section 2. The metal ball 4 is pressed against a certain metal ball 4 and sealed between the metal ball 4 and the battery can 1 by resistance welding. The metal ball 4 is pushed and the edge 6 of the injection port 5
At the time of contact, that is, at the time of contact between metals, resistance welding is automatically started. At this time, the oily substance 11 does not hinder the welding, and the trouble due to the adhesion of the electrolyte can be avoided.

<Example> LiCoO ₂ as a positive electrode active material
, 91 parts by weight of graphite, 4 parts by weight of graphite as a conductive agent, and 5 parts by weight of PVDF as a binder. An appropriate amount of N-methylpyrrolidinone was added and mixed well to obtain a paint. Separately, 90 parts by weight of graphite and 10 parts by weight of PVDF were mixed, and an appropriate amount of N-methylpyrrolidinone was added similarly to the positive electrode and mixed well to obtain a paint.

Subsequently, 20 μm Al was used as a positive electrode current collector.
Using foil and 10 μm Cu as the negative electrode current collector, first apply on one side, and after drying, apply the same on the other side,
Drying was performed. The electrode coated on both sides was roll-rolled, and the rolled positive electrode was 220 μm and the negative electrode was 130 μm.

Subsequently, for the positive electrode, a width of 31 mm and a length of 33
0 mm, the negative electrode was cut into a width of 33 mm and a length of 380 mm, and a 100 μm-thick strip lead plate 15 was formed at the end of the positive electrode.
And a strip-shaped lead plate 16 having a thickness of 50 μm was welded to the negative electrode portion.

The electrode prepared above was combined with a thickness of 25 μm and a width of 35
An electrode body 12 (FIG. 3) having a width of 29 mm × a height of 35 mm and a thickness of 7 mm and a cross section of an ellipse was prepared using a microporous membrane made of polypropylene having a thickness of 7 mm as a separator.

An insulating sheet is disposed above and below the electrode body, and the electrode body 12 is accommodated in the battery can 1.
6 is welded to the vicinity of the opening of the can, and one end of the positive electrode lead plate 15 is welded to one end of the inside of the positive electrode terminal 17 formed on the lid, and the opening of the can 1 is formed by the can lid 1a. After closing, the periphery was joined by laser welding and integrated to produce a 30 mm × 40 mm × 8 mm flat rectangular lithium ion secondary battery (700 mAh).

The can lid 1a is formed with a liquid injection section 2 having the above-described gas vent structure according to the present invention.
Then, a sufficient amount of electrolyte was injected from the injection port 5 of the above, and then the metal ball 4 was loaded into the concave portion 3 of the injection section 2. This metal ball 4
Used stainless steel balls (diameter M = 3 mm). The concave portion 3 of the liquid injection section 2 has a depth H = about 2 mm and an inner diameter D1 = φ
The diameter of the injection port 5 was 4.5 mm, and the diameter D2 of the injection port 5 was 1.8 mm. In addition, polybutene (molecular weight: about 300) was injected into the gap between the metal sphere 4 and the recess 3 as a smooth surface substance 11 composed of an oily substance.

Next, initial charging was performed. This first charge is 7
It went to 4.1V at 0 mA. About 3 from the start of the first charge
Gas generation continued for a period of time, but did not occur thereafter.

Thereafter, the liquid injection section 2 was sealed with a resistance welding machine. As shown in FIG. 5, the battery can 1 is placed on the mating electrode 13 of resistance welding, and the electrode 14 of the resistance welding machine is pressed against the metal ball 4 of the liquid injection section 2 so that the metal ball 4 and the battery can 1 was sealed by resistance welding.

On the other hand, for a flat rectangular battery of the same standard,
A lithium-ion secondary battery that was initially charged after the battery can 1 was sealed after the liquid injection part was closed, and after the initial charge was performed with the liquid injection part opened and degassing performed, As a comparative example, a prototype was made with a lithium-ion battery sealed by closing. For gas vented in the open state,
The electrolyte components were wiped off well and spot welding was performed.
The initial charge was also performed at 70 mA to 4.1 V.

A cycle test was further performed on these three types of prismatic batteries. The results of this cycle test are shown in the graph of FIG. In FIG. 6, a represents the case of the prismatic battery according to the present invention, b represents the case of the prismatic battery degassed in the open state, and c represents the prismatic battery initially charged without degassing in the closed state. Each case is shown.

As is clear from FIG. 6, when the capacity of the first cycle in the prismatic battery a of the present invention is 100,
The capacity of the prismatic battery b that has been vented in the open state is nearly 10% lower than that. This is considered to be due to the intrusion of moisture and a change in the composition of the electrolytic solution as a result of degassing in the open state. Further, in the case of the prismatic battery c which was not degassed in a sealed state, gas was accumulated inside and a swelling of about 1 mm occurred. In addition, there was a change in capacity during the charging cycle, which is considered to be caused by instability of electrode contact.

As described above, the prismatic lithium secondary battery of the present invention was able to release gas efficiently, and the battery characteristics were good because the sealing was not required and the electrolyte component wiping step was unnecessary.

[0037]

As described in detail above, the following excellent effects can be obtained according to the degassing method and the degassing structure at the time of the initial charge in the lithium secondary battery according to the present invention.

(1) Before the first charge, the injection port is sealed with a metal sphere in the concave portion and an oily substance. If gas is generated during the initial charge and the internal pressure becomes high, the metal sphere is used with the gas. The gas sphere and the oily substance can function as a check valve that automatically lifts up and releases gas through the space between the oily substances, releases gas through the space between the oily substances, and automatically closes the injection port with the weight of the metal sphere when the internal pressure drops. Therefore, it is not necessary to prepare a special drying room with a relative humidity of 1 to 2% unlike the conventional case, and the initial charging can be easily performed in a work room using a normal air conditioner. This makes it extremely easy to control humidity during charging.

(2) Since a film is formed of an oily substance on the surface of the metal sphere or in the gap between the metal sphere and the liquid injection port, the liquid injection port in the battery can is caused by gas generation at the time of the first charge. Even if the droplets of the electrolyte component come in, the droplets adhere to the film of the oily substance, fall down, and are collected in the battery can. The electrolyte component does not remain in the form of white powder, and a step of wiping the electrolyte component attached to the sealing portion is not required. Therefore,
The reliability of the sealing portion is improved.

(3) If the metal ball is fixed to the battery can by resistance welding after the initial charge and the injection port is sealed, the metal ball only functions as a check valve during the initial charge. Instead, it can function as a contact of the welding electrode, and the manufacturing process can be simplified.

(4) The recess is formed in the shape of a circular pot bottom, and the liquid inlet is provided concentrically at the center of the bottom wall, and the inner peripheral side bottom wall of the liquid inlet peripheral edge is downward. And the inside diameter of the peripheral wall of the concave portion is set to be less than twice the diameter of the metal sphere, and the inner peripheral side bottom wall of the peripheral edge of the liquid inlet starts bending downward. If the distance from the point to the peripheral wall surface of the concave portion is set to be equal to or less than the radius of the metal sphere, the metal sphere is floated and moved to the outermost periphery in the concave portion by the pressure in the can, and is brought into contact with the peripheral wall surface. Even so, the center (center of gravity) of the metal ball faces the injection port and is always located above the injection port. Therefore, when the gas in the can is released and the pressure is reduced, the injection port is automatically adjusted by its own weight. Can be depressed so as to block it, and keep the oil stagnant at the bottom of the pot It can be.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an assembled state of a lithium secondary battery provided with a degassing structure for adopting a degassing method at the time of initial charging according to the present invention.

FIG. 2 is a cross-sectional view showing a configuration of a liquid injection section formed in the lithium secondary battery of FIG.

FIG. 3 is a plan view showing a configuration of a liquid injection section formed in the lithium secondary battery of FIG.

FIGS. 4A and 4B show the action of a metal ball in the liquid injection section, where FIG. 4A is a view when the metal ball is in a closed state, and FIG.
FIG. 4 is a view showing a state in which gas escapes from between the metal ball and the metal ball.

FIG. 5 is a view showing a method of resistance welding of metal spheres when manufacturing the lithium secondary battery of FIG. 1;

FIG. 6 is a graph showing charge cycle characteristics of a lithium secondary battery manufactured by employing the method of degassing during initial charging according to the present invention;
5 is a graph showing a comparison between the charge cycle characteristics of a battery manufactured by a conventional degassing method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Battery can 2 Injection part 3 Concave part 3a Bottom wall 3b Perimeter wall 4 Metal ball 5 Injection port 6 Inner peripheral part of bottom wall 7 Curve start point 8 Center of metal sphere 11 Smooth substance 12 Winding body 13 Counter electrode 13 Electrode of resistance welding machine 17 Positive electrode terminal D1 Inner diameter of concave part D2 Diameter of injection port H Depth of concave part M Diameter of metal sphere W Width (distance) from starting point of bending to peripheral wall of concave part

Continued on the front page (72) Inventor Yoshiro Harada 5-36-11 Shimbashi, Minato-ku, Tokyo Inside Fuji Electric Chemical Co., Ltd.

Claims (4)

[Claims] An electrolyte is injected into a battery can of a lithium secondary battery from a liquid inlet provided at a lowermost end of a recess formed by being recessed toward the inside of the can, and then into the recess. A metal ball which drops into the liquid inlet by its own weight and closes the liquid inlet is loaded, and an insoluble oily substance with respect to the electrolyte is injected into a gap between the liquid inlet and the metal ball. In this state, the first charge is performed, and the metal sphere is floated by the pressure of the gas generated inside the can at the time of the charge to discharge the gas and discharge the gas at the time of the first charge in the lithium secondary battery. Method. 2. A liquid inlet for an electrolytic solution provided in a battery can of a lithium secondary battery is formed in a circular shape at the lowermost end of a concave portion recessed toward the inside of the can, and the liquid is injected into the concave by its own weight. A metal sphere that drops into the mouth and closes it and floats with the gas pressure generated inside the can at the time of the first charge to open the injection port is loaded, and a gap between the circumference of the injection port and the metal ball is A degassing structure for a lithium secondary battery, wherein an oily substance insoluble in an electrolyte is injected. 3. The lithium secondary battery according to claim 1, wherein, after the completion of the initial charge, the metal ball that has closed the liquid inlet is fixed by resistance welding and sealed. Degassing method. 4. The recess is formed in a pot bottom shape with a circular recess, and the liquid inlet is provided concentrically at the center of the bottom wall.
The inner peripheral bottom wall of the liquid inlet peripheral edge is curved downward and curled, and the inner diameter of the peripheral wall of the concave portion is set to be less than twice the diameter of the metal ball, and 3. The lithium secondary battery according to claim 2, wherein a distance from a starting point of downward bending of the inner peripheral side bottom wall of the liquid port peripheral edge to a peripheral wall surface of the concave portion is set to be equal to or less than a radius of the metal sphere. Outgassing structure at the time of the first charge in the secondary battery.