JP2005149861A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery capable of restraining evaporation of solvent components of nonaqueous electrolyte at injection operation and securing low-temperature performance. <P>SOLUTION: A lithium ion secondary battery 1 has an inner lid 6 on which, a liquid injection port for injecting nonaqueous electrolyte having a diameter almost the same as that of a battery can 3 is arranged above an electrode group housed in the battery can 3. The liquid injection port is sealed with a liquid tap 9 in free detachment. The inner lid 6 is made of electric insulating resin with a melting point of 130°C, and melts down at abnormalities of the battery. A battery lid 7 is fixed in caulking to the battery can 3 over the inner lid 6. During an injection operation of the nonaqueous electrolyte, it is injected from the liquid injection port, and the liquid injection port is kept sealed with the liquid tap 9 while the nonaqueous electrolyte permeates. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly, to a non-aqueous electrolyte secondary battery having a structure capable of suppressing volatilization of a non-aqueous electrolyte solvent component during a non-aqueous electrolyte pouring operation.

  Lithium ion secondary batteries have a higher energy density than lead batteries and nickel metal hydride batteries, and are therefore used in various applications. This battery system is sometimes called a non-aqueous electrolyte secondary battery because a non-aqueous electrolyte solution that is stable against oxidative decomposition is used in order to ensure a high voltage.

Non-aqueous electrolytes are required to have a high dielectric constant in order to ensure high-rate discharge characteristics and a sufficiently low viscosity characteristic even at low temperatures in order to ensure performance when used at low temperatures. For this reason, the composition of the nonaqueous electrolytic solution includes a mixed solvent of a solvent having a high dielectric constant (generally relatively high viscosity) and a low viscosity solvent, and lithium such as lithium hexafluorophosphate (LiPF ₆ ) as a solute. What dissolved the salt is generally used.

  In order to ensure the low temperature performance of such a non-aqueous electrolyte secondary battery, a technique for modifying the non-aqueous electrolyte itself (see, for example, Patent Document 1) and a technique for filling the voids in the battery with a gas such as methane gas (For example, refer to Patent Document 2).

  When injecting a non-aqueous electrolyte into a non-aqueous electrolyte secondary battery, the non-aqueous electrolyte does not like moisture, and thus is often injected in a dry environment such as a dry room or a glove box.

Japanese Patent Application No. 2001-217006 Japanese Patent Application No. 11-224690

  However, when a non-aqueous electrolyte is poured into a battery in a dry environment, the non-aqueous electrolyte, especially the low-viscosity component in the mixed solvent, volatilizes due to its vapor pressure, and the non-aqueous electrolyte remains in its original mixing ratio. In some cases, it cannot be present in the secondary battery. In particular, this problem becomes apparent when the sealing portion of the nonaqueous electrolyte secondary battery has a structure in which an injection stopper that can be opened and closed for each injection cannot be attached, such as a caulking structure.

  That is, in the non-aqueous electrolyte injection operation, since the penetration of the non-aqueous electrolyte into the separator and the active material is slow, the calculation is based on the electrode group itself and the void volume created by the electrode group, the current collector, and the battery can. In order to inject the predetermined amount of the electrolytic solution, even if the nonaqueous electrolytic solution is filled in the battery can for the first time, the nonaqueous electrolytic solution cannot be injected up to the predetermined amount at that time. For this reason, it is necessary to repeat the work of injecting the non-aqueous electrolyte several times after injecting the non-aqueous electrolyte first, standing for a while, waiting for the penetration of the non-aqueous electrolyte, and then injecting the non-aqueous electrolyte. Accordingly, the low viscosity component of the non-aqueous electrolyte solution volatilizes during the liquid injection operation, resulting in adverse effects such as a decrease in low-temperature performance of the non-aqueous electrolyte secondary battery.

  An object of the present invention is to provide a non-aqueous electrolyte secondary battery that can suppress the volatilization of a non-aqueous electrolyte solvent component at the time of liquid injection work and can ensure low-temperature performance.

  In order to solve the above problems, the present invention is a non-aqueous electrolyte secondary battery having an outer diameter that is substantially the same as the inner diameter of the container and can be sealed above the electrode group accommodated in the container. An inner lid in which an opening for injecting the non-aqueous electrolyte is formed is disposed, and a sealing lid for the container is fixed above the inner lid.

  In the present invention, an inner lid having an outer diameter substantially the same as the inner diameter of the container and having an opening for injecting a non-aqueous electrolyte is disposed above the electrode group accommodated in the container. Therefore, during the non-aqueous electrolyte injection operation, the opening is opened and injected, and the non-aqueous electrolyte solvent is sealed by sealing the opening while the non-aqueous electrolyte is infiltrated. Since volatilization is suppressed, the low temperature performance of the nonaqueous electrolyte secondary battery can be ensured.

  In the present invention, the opening may be sealed with a removable liquid stopper. Also, if the inner lid is made of an electrically insulating material having a melting point of 150 ° C. or lower, the inner lid melts when the battery is abnormal such as during overcharge, so a large amount of gas generated by decomposition of the non-aqueous electrolyte is It can be opened to the outside through the sealing lid. Furthermore, in order to ensure airtightness in the battery, the sealing lid may be caulked and fixed to the container via a gasket. Further, if the peripheral edge portion of the inner lid is positioned below the caulking fixing portion, it is possible to secure an accommodation space for the lead wire led out to the external terminal of the sealing lid. Furthermore, the inner lid has a current collecting member disposed above the electrode group and disposed on one side of the inner lid, and a lead wire having one end fixed to the other side of the inner lid and the other end led to the sealing lid A conductive member that connects the two may be embedded.

  According to the present invention, the inner lid having an outer diameter substantially the same as the inner diameter of the container and having an opening for injecting a non-aqueous electrolyte, which is substantially the same as the inner diameter of the container, is formed above the electrode group accommodated in the container. Therefore, during the non-aqueous electrolyte pouring operation, the opening is opened and injected, and the non-aqueous electrolyte is sealed while the non-aqueous electrolyte is infiltrated. Since the volatilization of the solvent is suppressed, an effect that the low temperature performance of the non-aqueous electrolyte secondary battery can be secured can be obtained.

  Hereinafter, an embodiment in which the present invention is applied to a cylindrical lithium ion secondary battery will be described with reference to the drawings.

  As shown in FIG. 1, the lithium ion secondary battery 1 of the present embodiment includes a strip-shaped positive electrode and a negative electrode having separators in a cylindrical cylindrical bottomed battery can 3 centered on a hollow FRP shaft core 4. The electrode group 2 wound through is accommodated. The electrode group 2 is infiltrated with a non-aqueous electrolyte described later.

  A metal ring-shaped current collecting member 5 is disposed above the electrode group 2. The current collecting member 5 has a large diameter enlarged portion on the upper side and a small diameter reduced portion on the lower side. The reduced diameter portion is inserted into the shaft core 4 and is fixed to the shaft core 4 to ensure rotation prevention. A tab derived from the electrode group 2 and described later is ultrasonically welded to the outer periphery of the enlarged diameter portion of the current collecting member 5.

  Above the current collecting member 5, an inner lid 6 made of an electrically insulating resin having a reverse hat shape and a melting point of 150 ° C. or less is disposed. The top portion of the reverse hat of the inner lid 6 is in surface contact with the upper surface and inner peripheral surface of the enlarged diameter portion of the current collecting member 5, and the inner lid 6 is supported by the current collecting member 5. The reverse hat flange part (peripheral part) of the inner lid 6 has substantially the same outer shape as the inner diameter of the battery can 3, and the outer peripheral end face is arranged in contact with the battery can 3. In the present embodiment, medium density polyethylene (melting point: 130 ° C.) is used as the material of the inner lid 6.

  In the center of the top of the reverse hat of the inner lid 6, a liquid injection port (through hole) is formed as an opening for injecting a circular non-aqueous electrolyte described later. The liquid injection port is arranged on the upper side of the inner lid 6 and sealed with a removable liquid stopper 9. The liquid injection port is provided with a female screw, and the liquid stopper 9 is provided with a male screw.

  Further, one end of a current collecting lead 8 having the other end connected (fixed) to the battery lid 7 is fixed at a position avoiding the liquid injection port at the top of the reverse hat of the inner lid 6. For the current collecting lead 8, for example, a ribbon type in which about 10 aluminum thin plates are laminated can be used in order to secure a cross-sectional area allowing a large current. The current collecting lead 8 can be deformed, and is bent in a substantially S shape as shown in the state of the finished product and is accommodated in the reverse hat portion of the inner lid 6.

  A conductive material such as aluminum or aluminum alloy is vapor-deposited on the reverse hat top of the inner lid 6 and the outer periphery in surface contact with the current collecting member 5. The inner lid 6 is embedded with an aluminum conductive member for electrically connecting the conductive material and one end of the current collecting lead 8 described above. Therefore, the tab derived from the electrode group 2 is electrically connected to the inner lid 6 through the current collecting member 5, the vapor-deposited conductive material and conductive material of the inner lid 6, and the current collecting lead 8. Note that one end of the current collecting lead 8 is ultrasonically welded to a conductive member embedded in the inner lid 6.

  Above the inner lid 6, a battery lid 7 having a built-in safety valve and having an external terminal is disposed. The periphery of the battery lid 7 is caulked and fixed to the battery can 3 via a gasket (not shown). The caulking fixing portion is located above the reverse hat flange portion of the inner lid 6. Therefore, the reverse hat flange portion of the inner lid 6 is in contact with the outer peripheral portion of the battery lid 7 and is pressed by the battery lid 7 from above to prevent rotation.

  Next, a manufacturing procedure of the lithium ion secondary battery 1 of the present embodiment will be described.

  85 parts by weight of a positive electrode active material made of lithium manganese composite oxide powder, 9 parts by weight of graphite-based carbon material as a conductive additive, and polyvinylidene fluoride so that the solid content of polyvinylidene fluoride is 6 parts by weight as a binder A 12% solution of / n-methylpyrrolidone was mixed, stirred with a despa / planetary mixer for 1 hour, and uniformly coated and dried on an aluminum foil (positive electrode current collector) with a coating machine equipped with a comma coater and a drying furnace. This was rolled and molded so that the density of the positive electrode mixture had a predetermined value, and then cut into predetermined dimensions and shapes to obtain a positive electrode. The positive electrode current collector was notched at predetermined intervals, and the remaining rectangular notch was used as a tab.

  Amorphous carbon is used for the negative electrode active material, 88 parts by weight of the amorphous carbon, 5 parts by weight of vapor-grown carbon fiber as the conductive auxiliary agent, and 7 parts by weight of the solid polyvinylidene fluoride as the binder. In this way, a 12% solution of polyvinylidene fluoride / n-methylpyrrolidone was mixed and stirred for 1 hour with a desper / planetary mixer. Uniform coating and drying. This was rolled and cut in the same manner as the positive electrode to obtain a negative electrode. The negative electrode current collector was notched at predetermined intervals, and the remaining rectangular notch was used as a tab.

  The positive electrode and the negative electrode are arranged so that the positive and negative electrode tabs are opposite to each other in the vertical direction, and are wound by interposing the polyethylene microporous film as a separator around the shaft core 4 between the positive and negative electrodes. 2 was produced.

  The diameter-reduced portions of the positive and negative current collecting members 5 (the negative electrode side is not shown, the same applies hereinafter) are inserted and fixed in the shaft core 4, and the positive and negative electrode tabs positioned above and below the electrode group 2 are attached to the current collecting members 5. Ultrasonic welding. Next, a conductive member in which the reverse hat top portion of the inner lid 6 is pressed until it makes surface contact with the current collecting member 5, and the other end of the current collecting lead 8 connected to the battery lid 7 is embedded in the current collecting member 5. Was ultrasonically welded. At this stage, the liquid stopper 9 is not attached to the liquid inlet, and the battery lid 7 is not crimped and fixed to the battery can 3, so that the current collecting lead 8 is expanded almost linearly. ing.

A non-aqueous electrolytic solution in which a lithium salt such as lithium hexafluorophosphate (LiPF ₆ ) was dissolved in an organic solvent in which ethyl carbonate, dimethyl carbonate, and diethyl carbonate were mixed at a predetermined ratio was added to this. The liquid was poured from the liquid inlet, and immediately after the liquid injection, the liquid inlet 9 was sealed with the liquid stopper 9. After this injection, in order to wait for the penetration of the non-aqueous electrolyte into the electrode group 2 (separator, positive and negative electrode active material mixture), the solution was replenished after 1 hour and then replenished after another 6 hours. The liquid was poured up to. The liquid stopper 9 was removed when the replacement was performed, and the liquid inlet was immediately sealed with the liquid stopper 9 after the replacement.

  After the injection of the non-aqueous electrolyte is completed, the current collecting lead 8 is bent into a substantially S shape and accommodated in the reverse hat portion of the inner lid 6, and the battery lid 7 is fixed by caulking at the upper opening of the battery can 3. Thus, the lithium ion secondary battery 1 was completed.

  Next, the operation and the like of the lithium ion secondary battery 1 of the example manufactured according to the present embodiment (hereinafter referred to as the battery of the example) will be described. For comparison, the battery of the comparative example in which the liquid is injected without attaching the inner lid 6 to the battery of the embodiment is also shown.

  The battery of the example has an inner lid 6, and since the hermetic seal in the battery 1 is maintained by closing the liquid stopper 9 while waiting for infiltration, the low-viscosity solvent component in the non-aqueous electrolyte solvent, etc. Without volatilizing, the non-aqueous electrolyte can be present in the battery 1 with the desired composition. On the other hand, in the comparative battery having no inner lid, part of the non-aqueous electrolyte component tends to evaporate during this waiting time, and the melting point of the whole solvent is lowered thereby, and part of the solution is crystallized. Sometimes.

  FIG. 2 shows capacities during high rate discharge at −15 ° C. of the example and the comparative example. The vertical axis shows the percentage of the battery when the discharge capacity at 25 ° C. and 0.5 C discharge is 100. In all discharge rates, the battery of the example showed a higher discharge capacity than the battery of the comparative example not having the inner lid 6. Therefore, the battery of the example can secure the original performance of the non-aqueous electrolyte by preventing volatilization during the pouring operation of the highly volatile low-viscosity solvent in the non-aqueous electrolyte using the inner lid 6. found.

  In addition, since the inner lid 6 of the battery of the embodiment shields the portion in which the electrode group 2 is housed from the outside, heat is generated when the battery is abnormal such as overcharge, and the like due to decomposition of the non-aqueous electrolyte. When a large amount of gas is generated, a mechanism for releasing the internal pressure is required. In the battery of the embodiment, the inner lid 6 is made of a resin having a melting point of 150 ° C. or lower, so that the inner lid 6 itself melts due to heat generated when an abnormality occurs and does not hinder the release of gas inside. doing. Table 1 below shows the results of comparing the maximum temperature with the phenomenon when the 2C overcharge test was performed with the comparative example battery and the example battery with the same structure except for the presence of the inner lid 6. There was no difference between the phenomenon and the maximum temperature, and no decrease in safety due to the presence of the inner lid 6 was observed. Therefore, it was found that the battery of the example having the inner lid 6 has no problem in terms of safety.

  In addition, since the conductive member is embedded in the battery of the example, it is electrically connected from the electrode group 2 to the external terminal of the battery lid 7 in the normal time (when the battery is not abnormal) as in the comparative example battery. And the inner lid 6 does not become an obstacle in electrical connection.

  In the above-described embodiment, the inner lid 6 is illustrated as having an inverted hat shape, but it is needless to say that the present invention is not limited to such a shape. Moreover, although the thing using a current collection ring was illustrated in the said embodiment, this invention is applicable also to the type of battery which does not use a current collection ring. Further, in the above embodiment, the screw tap type is illustrated as the liquid stopper 9, but a press-fitting type made of resin may be used. Moreover, although the example which vapor-deposited the electroconductive material in the inner cover 6 and embedded the electroconductive member was shown in the said embodiment, you may make it make a metal material the part which contacts the current collection member of an inner cover. Further, in the above embodiment, medium density polyethylene is exemplified as the material of the inner lid 6, but the present invention is not limited to this, and various electrical insulating materials having a melting point of 150 ° C. or less can be used. it can.

  The present invention is a non-aqueous electrolyte secondary battery that can suppress the volatilization of the non-aqueous electrolyte solvent component during injection work and can ensure low-temperature performance, thus contributing to the manufacture and sale of non-aqueous electrolyte secondary batteries. And has industrial applicability.

It is sectional drawing of the lithium ion secondary battery of embodiment which can apply this invention. It is a characteristic diagram which shows the relationship between the discharge rate and discharge capacity ratio of the battery of an Example and a comparative example.

Explanation of symbols

1 Lithium ion secondary battery (non-aqueous electrolyte secondary battery)
2 Electrode group 3 Battery can (container)
5 Current collecting member 6 Inner lid 7 Battery lid (sealing lid)
8 Current collector lead (lead wire)
9 Liquid stopper

Claims (6)

  An inner lid having an outer diameter substantially the same as the inner diameter of the container and having an opening for injecting a non-aqueous electrolyte is disposed above the electrode group housed in the container. The non-aqueous electrolyte secondary battery is characterized in that a sealing lid for the container is fixed above the container.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the opening is sealed with a removable liquid stopper.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the inner lid is made of an electrically insulating material having a melting point of 150 ° C. or less.   4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the sealing lid is fixed by caulking to the container via a gasket. 5.   The non-aqueous electrolyte secondary battery according to claim 4, wherein a peripheral edge portion of the inner lid is positioned below the caulking fixing portion.   The inner lid has a current collector disposed above the electrode group and disposed on one side of the inner lid, one end fixed to the other side of the inner lid, and the other end led out to the sealing lid. The nonaqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein a conductive member connecting the lead wire is embedded.