JP2005222757A - Finishing charge/discharge gas exhaustion method of lithium-ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charge/discharge gas exhaustion method preventing moisture and oxygen in the atmosphere from infiltrating into a battery and without fear of electrolyte solution scattering in a battery case. <P>SOLUTION: The finishing charge/discharge gas exhaustion method of a lithium-ion secondary battery consists of a process of injecting electrolyte solution into the battery before injection provided with an injection inlet, a process of mounting an external restoring gas exhaust valve on the injection inlet, a process of carrying out the finishing charge and discharge, and a process of sealing the injection inlet, where the process of the finishing charge and discharge includes a process of carrying out gas exhaustion until an inner pressure of the battery exceeding a given value gets down to a given inner pressure. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for discharging a gas generated during finish charge / discharge of a lithium ion secondary battery.

  Lithium ion secondary batteries have various features such as high energy density, high battery voltage and low self-discharge compared to conventional secondary batteries such as nickel metal hydride batteries and lead acid batteries. It is widely used for small electronic devices.

  In lithium-ion secondary batteries, battery performance deteriorates when electrodes or electrolytes come into contact with moisture or oxygen in the air.To prevent performance deterioration, the battery is sealed with caulking, laser welding, etc. It is common to have a sealed structure that cuts off the contact. However, when gas is generated inside the battery due to overcharge or short circuit, the internal pressure of the battery may increase significantly due to the sealed type. In order to avoid such a phenomenon, the lithium ion secondary battery is usually provided with a safety valve for releasing the internal pressure such as a metal thin film having a carved or etched groove.

By the way, in a lithium ion secondary battery, it is common to perform charging / discharging before shipment for the reason of stabilizing a voltage, and it becomes possible to stabilize a voltage by performing this charging / discharging. This charging / discharging is called finish charging / discharging, but gas may be generated by a side reaction caused by the electrolyte during finishing charging / discharging. In such a case, it is difficult to provide a vent hole separately from the safety valve, and once a non-returnable safety valve such as a metal thin film safety valve with an engraved or etched groove is activated, it cannot be sealed again. Therefore, before the upper lid is caulked or welded to the outer can, there is a need to set up a charging process to charge the battery for the first time, and then to perform multiple steps such as a sealing process to seal the battery can. It was.
JP 2000-353547 A JP-A-11-250887

  By the way, the lithium ion secondary battery, due to the nature of its power generation element, gas is generated in the battery can during finish charge / discharge, the gas is accumulated and the internal pressure rises, and the battery can be deformed by the internal pressure. In particular, it is known that prismatic lithium ion secondary batteries are particularly susceptible to deformation. Therefore, when manufacturing a square lithium ion secondary battery, a degassing process is performed during the initial charging process before the upper lid is joined to the outer can by caulking or welding, and then the battery can is removed. A sealing step for sealing is performed. When such a process is performed, the battery performance may be deteriorated because the electrode, the electrolyte, and the like are in contact with moisture and oxygen in the air for a long time.

  In addition, the electrolyte solution may scatter as the gas is discharged. If the electrolyte solution scatters on the outer can and the upper lid, there is a risk of causing a sealing failure. Accordingly, it is necessary to provide a cleaning process for wiping off the electrolytic solution scattered on the outer can and the like, and this process is a factor for reducing the manufacturing efficiency of the battery.

In Patent Document 1, charging / discharging is performed in a state where a temporary sealing plug made of rubber is attached, and the tip of a hollow needle communicating with a container such as a syringe is pierced from above the temporary sealing plug after charging / discharging. After removing the temporary sealing plug, the gas vent hole is sealed. However, if this method is used, the gas cannot be discharged during charging / discharging, which may deform the battery case. .

  Patent Document 2 describes that a relief valve is provided on the outer wall of the battery case that opens and discharges when the internal pressure of the battery case reaches a set pressure or higher. However, this structure increases the cost and the battery structure. There is a complicated problem. Furthermore, when a malfunction of the relief valve occurs, the outside air may come into contact with the electrolytic solution, which may cause performance deterioration.

  In order to solve the above problems, the present invention is a method for finishing charge / discharge gas discharge of a lithium ion secondary battery, the step of injecting an electrolyte into a battery before injection provided with an injection port, The process of attaching an external return type gas discharge valve to the mouth, the process of finishing charge / discharge, the process of removing the return type gas discharge valve from the liquid inlet after finish charge / discharge, and the process of sealing the liquid inlet And the step of performing the finish charge / discharge includes a step of discharging gas until the internal pressure of the battery exceeds a predetermined pressure until it becomes a predetermined internal pressure or less.

  According to the gas discharge method of the present invention, the battery can be manufactured without allowing outside air to enter the battery, and the battery structure can be simplified by allowing the resettable gas discharge valve to be attached to and detached from the liquid injection port. I can do it. Further, since the electrolytic solution does not scatter on the battery can, a cleaning process for wiping off the attached electrolytic solution is not necessary, and the production efficiency can be greatly improved.

  The present invention uses a return-type gas discharge valve that opens at a predetermined operating pressure against a slow increase in internal pressure and discharges gas to the outside of the battery, and closes when the difference from the external pressure becomes small. This return-type gas discharge valve uses a liquid injection port and can be detached, and after the first charge, the liquid injection port is sealed to make a sealed lithium ion secondary battery. By using a detachable return-type gas discharge valve, the upper lid and the outer can can be fully sealed before finishing charging, and contact with the outside air can be minimized.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  As shown in FIG. 1, an outer can 3 whose cross-sectional shape is formed into an oval shape is housed with an electrode body wound with a positive electrode, a negative electrode, and a separator, and the upper lid 4 is sealed by laser welding. The electrolytic solution is filled from the provided injection port 6 to complete the battery. At this time, portions other than the liquid injection port 6 are in a sealed state.

  2A to 2E, description will be made from the installation to the removal of the resettable gas discharge valve in the present invention. A return-type gas discharge valve is inserted into the liquid injection port 6 used in the liquid injection process in the battery filled with the electrolytic solution in the liquid injection process (FIG. 2A). At this time, if there is a gap on the surface where the valve case receiver 8 and the liquid injection port 6 of the resettable gas discharge valve 2 come into contact with each other, the electrolyte leaks from the gap. In order to prevent this, a rubber lining 11 is applied. Since the rubber lining 11 is in contact with the electrolytic solution, an ethylene-propylene copolymer (EPDM) having a high electrolytic resistance is used (FIG. 2 (e)).

  The lithium ion secondary battery 1 equipped with the resettable gas discharge valve 2 is subjected to finish charging / discharging while discharging the generated gas (FIG. 2B).

  The battery that has been subjected to the final charge / discharge is completed by removing the return-type gas discharge valve 2 from the injection port 6 (FIG. (C)) and sealing the battery by joining the injection plug 12 to the injection port 6. (Figure (d)).

  Next, the internal configuration of the resettable gas discharge valve 2 will be described with reference to FIG. A compressed spring 9 is disposed in the inner space of the valve case 7. The spring 9 extends downward in the valve case 7, and its lower end presses the elastic body 10 that closes the opening of the valve case receiver 8. ing. The elastic body 10 is in close contact with the opening edge of the valve case receiver 8 opening. The valve case 7, the valve case receiver 8 and the spring 9 used at this time are preferably made of a stainless steel material that does not corrode by the electrolyte, and the elastic body 10 is made of rubber such as EPDM or engineering plastic. A material such as is preferable.

  When the internal pressure rises at a slow rate due to gas generation when finishing charging is performed, the resettable gas discharge valve 2 of the present embodiment moves the elastic body 10 upward by the gas pressure in the battery can. The push-up spring 9 is compressed and opened, and the gas is discharged. As shown in FIG. 3, the gas discharge path passes through the gas introduction port 13, the gap between the elastic body 10 and the inner surface of the valve case 7, the spring 9, and the gas is discharged from the gas discharge port 14 to the outside. Discharge. When the pressure difference between the gas pressure inside the battery can and the outside air is reduced by discharging the gas, the spring 9 extends again and the opening of the valve case receiver 8 is closed by the elastic body 10. Thereby, the lithium ion secondary battery 1 can reproduce a sealed state. The operating pressure of the return-type gas discharge valve, that is, the compressive force capable of bringing the spring rubber plate into close contact with the opening of the valve case receiver 8 prevents deterioration of the battery performance and reduces the pressure in the battery can. It is set so that the gas can be discharged to the outside even when a significant increase in internal pressure occurs.

  In the actual manufacturing process, when the finish charging / discharging is finished, the resettable gas discharge valve 2 is removed and the liquid injection port 6 is sealed. Further, the removed return type gas discharge valve 2 can be used for finishing charge / discharge of the next lithium ion secondary battery after cleaning.

  Hereinafter, components of the lithium ion secondary battery will be described.

  The positive electrode is configured by providing a positive electrode mixture layer such as a positive electrode active material, a conductive material, and a binder on an aluminum foil as a current collector. First, a positive electrode active material, a conductive material, a binder, and a solvent are kneaded for the purpose of adjusting viscosity to produce a positive electrode mixture paste, and the positive electrode mixture paste is applied to an aluminum foil current collector and dried. . Thereafter, the sheet is processed into a predetermined size by pressing and slitting as necessary to produce a sheet-like positive electrode.

Lithium metal composite oxides such as LiCoO ₂ , LiNiO ₂ , Li ₂ MnO ₄ are used for the positive electrode active material, but a part of the above Co, Ni or Mn is further substituted with Co, Mn, Al, etc. Other element substitution types such as those substituted with Li can also be used, and these positive electrode active materials can be used as long as they are active materials capable of occluding and releasing lithium and capable of charge / discharge reactions. It is not limited to the above.

  The conductive material is for increasing electrical conductivity in order to efficiently perform the charge / discharge reaction of the positive electrode mixture. For example, carbon such as acetylene black (AB), ketjen black (KB), or graphite. Materials can be used alone or in combination.

  In addition, the binder has a bonding function between the mixture and an adhesion function between the mixture and the core material. For example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), or the like is used. When water is used as a solvent, a water-soluble dispersion of PTFE is particularly used. As the thickener, for example, a water-soluble polymer such as carboxymethyl cellulose (CMC) can be used.

In addition, a mixture paste is prepared by kneading these materials, and the mixture mixture ratio can be arbitrarily adjusted according to the suitability of the battery.

  On the other hand, the negative electrode is composed of a negative electrode active material and a negative electrode mixture layer such as a binder on a copper foil as a current collector, and a mixture paste is prepared in the same manner as the positive electrode. Then, it is processed into a predetermined size by pressing and slitting as necessary to obtain a sheet-like negative electrode.

  As the negative electrode active material, a material capable of inserting and extracting lithium ions is used. For example, a carbon material such as natural graphite, artificial graphite, or coke can be used. Although metallic lithium can be used, there are problems such as poor charge / discharge efficiency. As the binder, PVdF, styrene butadiene rubber (SBR) or the like is used, and an organic solvent such as N-methyl-2-pyrrolidone (NMP) or water is used as a solvent for dispersing these active materials and the binder. Can do.

  The separator has a function of insulating between the positive electrode and the negative electrode and further holding an electrolyte solution. The separator is made of a thin microporous film such as polyethylene (PE), polypropylene (PP), or a laminate thereof. However, the present invention is not limited to these as long as the necessary functions can be obtained.

The electrolytic solution is obtained by dissolving a lithium salt in an organic solvent. Examples of the organic solvent include cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), A single or mixed system of a chain carbonate such as ethyl methyl carbonate (EMC) is used. As the lithium salt, LiPF ₆ , LiBF ₄ , LiClO ₄ or the like can be used.

  Then, an electrode body in which the positive electrode and the negative electrode are wound through a separator is prepared, and a current collector terminal is connected to the positive electrode current collector and the negative electrode current collector, and is inserted into the outer can 3. The lithium ion secondary battery is manufactured by pouring and sealing.

The configuration of the lithium ion secondary battery used in this example will be described. The positive electrode uses LiNi _0.7 Co _0.2 Al _0.1 O _{2 as the} active material, AB as the conductive material, PTFE water-soluble dispersion liquid as the binder, and CMC as the thickener, and the mixture ratio is 88: 9: 2: 1. % Positive electrode paste is prepared by kneading. Water is used as a solvent used during kneading. This positive electrode paste is applied on an aluminum foil serving as a current collector and dried. Thereafter, the sheet is processed into a predetermined size by pressing and slitting as necessary to produce a sheet-like positive electrode.

  The negative electrode is prepared by kneading a negative electrode paste with a mixture ratio of 96: 3: 1 using artificial graphite as the active material, SBR water-soluble dispersion as the binder, and CMC as the thickener. Water is used as a solvent used during kneading. This negative electrode paste is applied onto a copper foil serving as a current collector and dried. After that, the sheet is processed into a predetermined size by pressing and slitting as necessary.

  The separator has a function of insulating between the positive electrode and the negative electrode and further holding the electrolytic solution. In this example, a separator composed of three layers of PP, PE, and PP was used.

The electrolytic solution is obtained by dissolving a lithium salt in an organic solvent, and a solvent having a mixing ratio of EC, EMC, and DMC in a 3: 3: 4 ratio is used as the organic solvent. LiPF ₆ was used as the lithium salt.

As described above, a step of winding an electrode body through a positive electrode, a negative electrode, and a separator, a step of bonding a positive electrode current collector and a negative electrode current collector to a current collector terminal, and an electrolyte The lithium ion secondary battery was produced by the step of sealing, the step of sealing by joining the outer can 3 and the upper lid 4 together.

According to the present embodiment, the operating pressure of the resettable gas discharge valve 2 is set to 0.5 kgf / cm ^2, and the elastic body 10 in the resettable gas discharge valve is a rubber plate made of EPDM. This return-type gas vent valve was attached to the liquid injection port of the battery after the liquid injection process, and finish charge / discharge was performed. At this time, the change in the internal pressure of the battery and the deformation of the outer can 3 are measured with a caliper. In addition, when measuring the outer can 3 with a caliper, it is performed at the center of the outer can 3.

  Here, the condition of finish charge / discharge will be described. The process of injecting the electrolyte solution and charging the battery in a sealed state to 4.1 V at 0.25 C and discharging to 3 V at 1 C, charging to 4.1 V at 1 C and discharging to 1 C Finish charging / discharging is performed by the process of charging up to 3V at 1C and the process of charging up to 3.7V at 1C.

In the battery of the example, when the internal pressure of the battery rises and reaches the operating pressure of the resettable gas discharge valve 2, the gas generated inside the battery is discharged, and the internal pressure of the battery does not change to 0.5 kgf / cm ² or more. In addition, since the internal pressure of the battery was set to 0.5 kgf / cm ² , the outer can 3 was not deformed. On the other hand, as a comparative example, a battery having the same electrode plate configuration and structural component configuration as that of the example was manufactured. In the example, the return-type gas vent valve 2 was attached to the liquid injection port portion, whereas in the comparative example, the battery was sealed using a rubber plug, and finish charge / discharge equivalent to the example was performed. The internal pressure change inside the battery and the thickness of the central part of the outer can 3 were measured.

  In the battery of the comparative example, as the internal pressure rises, the outer can 3 is deformed, and when the internal pressure inside the battery rises further, the rubber plug is removed, and the electrolyte is scattered outside together with the gas accumulated in the battery. As a result. In addition, since the weight of the electrolytic solution is reduced due to the cleaning process of wiping off dirt on the outer can due to the scattering of the electrolytic solution and the scattering of the electrolytic solution, an electrolytic solution supplementing process is necessary.

  From the above results, the battery of the embodiment having the resettable gas discharge valve 2 can discharge the gas to the outside of the battery in response to the increase in internal pressure due to the generation of the finish charge / discharge gas, and deformation of the outer can 3 is also seen. In addition, since the electrolytic solution was not scattered, the cleaning process and the electrolytic solution supplementing process are not required, so that the battery manufacturing efficiency can be improved.

  The resettable gas discharge valve 2 of the lithium ion secondary battery according to the present invention can perform the initial charge without deforming the battery can by discharging the gas generated during the initial charge. And since an electrode body and electrolyte solution are not made to contact oxygen and moisture in air, battery performance is not deteriorated. Further, since the electrolytic solution does not scatter, the cleaning step of wiping off the electrolytic solution can be omitted, and the production efficiency can be increased, which is useful.

The perspective view of the lithium ion battery in embodiment of this invention (A) Diagram of the battery of this embodiment when the return-type gas exhaust valve is mounted (b) Diagram of the battery of this embodiment at the time of final charge / discharge (c) Diagram after finish charge / discharge of the battery of this embodiment ( d) Drawing after sealing the battery of this embodiment (e) Cross-sectional view of the battery of this embodiment when the return type gas discharge valve is mounted Cross-sectional view of the resettable gas discharge valve of this example A perspective view of a conventional lithium ion secondary battery

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Lithium ion secondary battery 2 Resettable gas discharge valve 3 Exterior can 4 Top cover 5 Safety valve 6 Injection port 7 Valve case 8 Valve case receptacle 9 Spring 10 Elastic body 11 Rubber lining 12 Injection plug 13 Gas introduction port 14 Gas discharge port

Claims (2)

A method for finishing charge / discharge gas discharge of a lithium ion secondary battery, comprising a step of injecting an electrolyte into a pre-injection battery provided with an injection port, and an external resettable gas discharge valve at the injection port. A step of performing the finishing charge / discharge, including a step of mounting, a step of performing finish charging / discharging, a step of removing the returnable gas discharge valve from the injection port after finishing charging / discharging, and a step of sealing the injection port A method of discharging and discharging a finish charge / discharge gas of a lithium ion secondary battery comprising a step of discharging gas until the internal pressure of the battery exceeds a predetermined pressure when the internal pressure of the battery exceeds a predetermined pressure. The finishing charge / discharge gas discharging method of a lithium ion secondary battery according to claim 1, wherein an injection port in which an end portion of the injection port protrudes from a sealing plate is used.

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