JP2011071052A - Lithium-ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve safety of a flat lithium-ion secondary battery. <P>SOLUTION: A shaft core 10 is equipped with first and second conductor members 11 and 12, and a heat-contractable insulator 13 that is interposed between the conductor members to insulate the conductor members. Respective conductor members are respectively connected to a negative electrode plate and a positive electrode plate, and at a time of abnormal heat generation of the battery, the insulator is heat-contracted and both conductor members become contacted. By this, the negative electrode plate and the positive electrode plate are short-circuited via the shaft core, so that potential difference between the negative electrode plate and the positive electrode plate is eliminated, and the heat generation stops. When the abnormal heat generation occurs, by the heat contraction of the insulating material, a contact face is formed between the conductor members so that both become contactable, while at the time of high temperature, plasticity is elevated in the insulator, and furthermore, is fused. At this time, by tightening force of the separator, conductor members become approachable, and a gap is narrowed so that the conductor members are brought into contact. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a lithium ion secondary battery in which an electrode group in which a positive electrode and a negative electrode are wound around an axis through a separator is accommodated in a flat battery container.

Since lithium ion secondary batteries have a higher energy density than other secondary batteries, they are now mainly used in portable devices such as digital cameras, notebook computers and mobile phones.
In recent years, research and development of large-sized lithium ion secondary batteries for the purpose of electric vehicles and power storage have been actively conducted in order to cope with environmental problems. In particular, in the automobile industry, the development of electric vehicles using a motor as a power source and hybrid electric vehicles using both an internal combustion engine and a motor are underway, some of which have already been put into practical use. Yes.

  When a lithium ion secondary battery is used as a power source for an electric vehicle, a high voltage is secured by connecting a plurality of lithium ion secondary batteries having a predetermined capacity in series. However, when the lithium ion secondary battery falls into an overcharged state, the electrolyte contained therein is vaporized and the battery pressure is increased and the safety is lowered.To avoid this, the lithium ion secondary battery is It is used as a power supply system together with a voltage controller that controls battery voltage during charging.

  However, when a large lithium ion secondary battery is used as a power source for an electric vehicle, the battery is in an abnormal state due to an overcharge when the voltage controller fails or an external short circuit due to a crash due to an accidental collision. As a matter of course, the behavior when it falls into a vehicle does not damage the human body, and minimizing damage to the automobile has become an important issue.

  Lithium ion secondary batteries for electric vehicle power supplies are charged with large currents and discharged with large currents, so the internal pressure of the battery is generally used in small consumer lithium ion secondary batteries. It is technically difficult to provide a current interruption mechanism that operates in accordance with the rise inside the battery container.

  In addition, so-called PTC elements that detect heat and increase resistance, such as those used in lithium-ion secondary batteries for small consumers, especially mobile phones, are electric vehicles that require high output and high input. In the case of a lithium ion secondary battery for use, it is not suitable because it becomes a resistor in normal times. For this reason, there is an increasing demand for structural safety, that is, mechanical safety for the lithium ion secondary battery itself.

  Therefore, in the flat lithium ion secondary battery described in Patent Document 1, a safety mechanism is provided on the outer periphery of an electrode group in which a positive electrode and a negative electrode are wound around a shaft through a separator, and safety measures are taken when abnormal heat is generated. ing. In this safety mechanism, an electrode pair composed of copper foil and aluminum foil is provided on the outer periphery of the electrode group via a separator having a melting point lower than that of the electrode group separator. It melts faster than the separators of the group and short-circuits to block current from flowing inside the electrodes, thereby improving safety.

JP2003-243037

  However, the flat lithium ion secondary battery of Patent Document 1 has a disadvantageous volume energy density because a safety mechanism is disposed on the outer periphery of the electrode group.

(1) A lithium ion secondary battery according to the invention of claim 1 includes a positive electrode plate, a negative electrode plate, and a separator interposed between the positive electrode plate and the negative electrode plate to insulate the positive electrode plate and the negative electrode plate. An electrode group configured by winding a sheet layer around an axial core; and a battery container in which the electrode group is housed and having an external positive electrode terminal and an external negative electrode terminal. The axial core includes a first conductor member and A second conductor member and an insulating material interposed between the first and second conductor members to insulate the first and second conductor members, wherein the first conductor member is connected to the negative electrode plate. The second conductor member is connected to the positive electrode plate.
(2) The invention according to claim 2 is the lithium ion secondary battery according to claim 1, wherein the insulating material is made of a heat-shrinkable material, and the first conductor member depends on a shrinkage amount when the temperature reaches a reference temperature or higher. And the second conductor member are in contact with each other.
(3) The invention of claim 3 is the lithium ion secondary battery according to claim 1, wherein the insulating material is made of a heat-meltable material and melts when the temperature reaches a reference temperature or higher. The second conductor member is in contact with the second conductor member.
(4) The invention of claim 4 is the lithium ion secondary battery according to claim 1, wherein the shaft core is wound one or more times in advance by the separator, and the separator is made of a heat-shrinkable resin. It is characterized by that.
(5) A fifth aspect of the present invention is the lithium ion secondary battery according to the fourth aspect, wherein the separator has a thermal shrinkage rate of 2 at 120 degrees Celsius in the winding circumferential direction (MD direction) of the electrode group. % Or more.
(6) A sixth aspect of the present invention is the lithium ion secondary battery according to any one of the first to fifth aspects, wherein the insulating material has a thickness of 200 μm to 500 μm.
(7) The invention of claim 7 is the lithium ion secondary battery according to any one of claims 1 to 6, wherein the insulating material has a heat shrinkage rate of 120% or more at 120 degrees Celsius. To do.
(8) The invention of claim 8 is the lithium ion secondary battery according to any one of claims 1 to 7, wherein the insulating material is formed of polyethylene.
(9) The invention according to claim 9 is the lithium ion secondary battery according to any one of claims 1 to 8, wherein the shaft core is formed of flat first and second conductor members, The insulating material is characterized in that the first and second conductor members are bonded to the side surfaces facing each other.
(10) The invention of claim 10 is the lithium ion secondary battery according to any one of claims 1 to 9, wherein the negative external terminal is connected to the first conductor member of the shaft core, and the positive external terminal is It is connected to the second conductor member of the shaft core.
(11) The invention according to claim 11 is the lithium ion secondary battery according to any one of claims 1 to 9, wherein the first conductor member is a negative electrode current collector of the negative electrode plate, and the second conductor member is a positive electrode. The positive current collector is connected to the positive current collector of the plate, the positive current collector is connected to the positive external terminal via the positive connection plate, and the negative current collector 60 is connected to the negative external terminal via the negative connection plate It is characterized by.
(12) The invention of claim 12 is the lithium ion secondary battery according to any one of claims 1 to 11, wherein the electrode group wound in a flat shape is stored in a flat battery container. Features.

According to the present invention, since the axial core of the electrode group is formed by the first and second conductor members insulated from each other, it is possible to provide a lithium ion secondary battery with improved safety without disadvantageous volume energy density. .

The perspective view of the electrode group in embodiment of the flat lithium ion secondary battery by this invention. The front view of the electrode plate of the positive electrode of FIG. 1, or a negative electrode. The perspective view of the axial center of FIG. The table | surface which compares the structure of the electrode group in Examples 1-20 with the comparative example 1 (Table 1). The table | surface which compares the performance of Examples 1-20 and the comparative example 1 (Table 2). The graph which shows the result of the overcharge test regarding the insulating material heat shrinkage rate of Examples 1-5. The graph which shows the overcharge test result regarding Example 1 and 6-10 about the insulating material thickness. The graph which shows the overcharge test result regarding the separator preceding winding number of Examples 1, 11 and 12. The graph which shows the overcharge test result regarding Example 1 and 13-16 about an insulating-material thermal contraction rate. The graph which shows the overcharge test result regarding the material of an insulating material of Example 1, 17-20. The perspective view which shows the modification of an axial center. The perspective view which shows the other modification of an axial center.

Embodiments in which the present invention is applied to a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a flat lithium ion secondary battery mounted on an electric vehicle will be described.
[Embodiment]

  A flat lithium ion secondary battery according to an embodiment is configured such that an electrode bag 20 as a power generation element shown in FIG. 1 is covered with an insulating bag (not shown) and accommodated in a flat battery can (not shown). The As illustrated in FIG. 1, the electrode group 20 is obtained by winding a sheet layer in which a negative electrode plate 30, a separator 80, and a positive electrode plate 40 are sequentially laminated around a shaft core 10 in a flat shape.

  As shown in FIGS. 1 and 2, the positive electrode plate 40 is configured by applying a positive electrode mixture 41 to a copper plate, and the negative electrode plate 30 is configured by applying a negative electrode mixture 31 to an aluminum plate. In the positive electrode plate 40, a current collector 70 to which the positive electrode mixture 41 is not applied is formed at one end in the winding width direction (TD direction) of the electrode group 20. In the negative electrode plate 30, a current collector 60 to which the negative electrode mixture 31 is not applied is formed at the other end of the electrode group 20 in the TD direction.

  As shown in FIG. 1, the positive electrode plate 40 and the negative electrode plate 30 are arranged so that the current collectors 60 and 70 formed respectively on the positive electrode plate 40 and the negative electrode plate 30 protrude to the opposite side of the electrode group 20 in the TD direction. The separator plate 80 is interposed between the positive electrode plate 40 and the negative electrode plate 30 so that the positive electrode plate 40 and the negative electrode plate 30 are insulated from each other. Laminated. The positive electrode plate 40, the negative electrode plate 30, and the sheet layer of the separator 80 thus laminated were wound around the shaft core 10 to obtain the electrode group 20. In addition, the separator 80 may be wound around the shaft core one or more times in advance, or the number of preceding winding turns may be zero.

  As shown in FIG. 3, the shaft core 10 includes a substantially L-shaped first conductor plate (copper plate) 11 mainly made of copper and a substantially L-shaped second conductor plate mainly made of aluminum. (Aluminum plate) 12 and a heat-shrinkable insulating material 13 interposed between the conductor plates 11 and 12 to insulate the conductor plates 11 and 12. The first conductor plate 11 and the second conductor plate 12 are thin plate members having a plate thickness of about 1.5 mm, for example. The insulating material 13 has a shape corresponding to a bent space formed when the substantially L-shaped conductor plates 11 and 12 are opposed to each other in opposite directions. An acrylic resin adhesive is applied to the contact surface of the insulating material 13 with the conductive plates 11 and 12, and the conductive plates 11 and 12 are bonded to each other through the insulating material 13. As a result, a plate-like shaft core 10 having a three-layer structure in which insulation between the conductor plates 11 and 12 was ensured was obtained.

  The first conductor plate 11 is connected to the current collector 60 of the negative electrode plate 30, and the second conductor plate 12 is connected to the current collector 70 of the positive electrode plate 40. The positive electrode current collector 70 at one end of the electrode group 20 is connected by ultrasonic welding to the end of the second conductor plate (aluminum plate) 12 of the shaft core 10, and the negative electrode current collector at the other end of the electrode group 20 is connected. The portion 60 is connected to the end of the first conductor plate (copper plate) 11 of the shaft core 10 by ultrasonic welding.

  Furthermore, a positive electrode connection plate is connected to the positive electrode current collector 70 by ultrasonic welding, a positive electrode connection plate is connected to a positive electrode external terminal (not shown) of the lithium ion secondary battery, The negative electrode connection plate is connected by ultrasonic welding, and the negative electrode connection plate is connected to a negative electrode external terminal (not shown) of the lithium ion secondary battery. Therefore, the positive external terminal is connected to the second conductor plate 12 constituting the shaft core 10, and the negative external terminal is connected to the first conductor plate 11 constituting the shaft core 10. In other words, the positive external terminal and the negative external terminal are insulated by the heat-shrinkable insulating material 13 of the shaft core 10.

  The electrode group 20 to which the external terminals are connected in this way is housed in an insulating bag (not shown), which is inserted into a flat aluminum can outer battery container (not shown), and the lid and the battery container are attached. Join by laser welding. The external terminals of the positive electrode and the negative electrode are arranged at a predetermined distance on one surface of an aluminum lid (not shown) while ensuring insulation from the lid, and protrude above the battery lid.

  The aluminum lid is provided with a liquid injection port (not shown) for injecting an electrolytic solution. After pouring a predetermined amount of non-aqueous electrolyte from the pouring port, it is sealed with a pouring port lid. As the electrolytic solution, for example, lithium hexafluorophosphate is 1 mol / L in a mixed solution of ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) in a volume ratio of 1: 1: 1. Use those dissolved in

According to the lithium ion secondary battery of the embodiment configured as described above, the following operational effects can be obtained.
(1) When the electrode group 20 generates heat and exceeds the reference temperature, and the heat-shrinkable insulating material 13 contracts, the conductor plates 11 and 12 come into contact with each other. As a result, the positive external terminal and the negative external terminal are conducted, and the current flowing between the negative electrode plate 30 and the positive electrode plate 40 of the electrode group 20 is interrupted. Therefore, the heat generation phenomenon of the electrode group 20 is eliminated.
The insulating material may be selected so that the first and second conductor plates 11 and 12 come into contact with each other by melting the insulating material 13.

(2) It is not necessary to provide a heat generating safety mechanism on the outer periphery of the electrode group 20, and a safety mechanism is provided on the originally required shaft core. Therefore, it is possible to provide a flat lithium ion secondary battery that is easy to manufacture and has improved safety without reducing the volume energy density as compared with the conventional example of Patent Document 1.

  Next, examples of the flat lithium ion secondary battery according to the present invention will be described. In addition, it describes together about the battery of the comparative example 1 produced for the comparison.

In the lithium ion secondary batteries of Examples 1 to 20, the negative electrode plate 30 and the positive electrode plate 40 are the same, and are manufactured as follows.
The negative electrode plate 30 was produced as follows. 10 parts by weight of polyvinylidene fluoride (hereinafter referred to as PVDF) is added as a binder to 100 parts by weight of amorphous carbon powder as the negative electrode active material, and N-methylpyrrolidone (hereinafter referred to as NMP) as a dispersion solvent. A negative electrode mixture 31 was added and kneaded. This negative electrode mixture 31 was applied on both sides of a 10 μm thick copper foil (copper plate) leaving the solid current collecting portions 60. Thereafter, drying, pressing, and cutting were performed to obtain a negative electrode plate 30 having a thickness of 70 μm, which does not include a copper foil.

The positive electrode plate 40 was produced as follows. To 100 parts by weight of lithium manganate (chemical formula LiMnO ₂ ) as a positive electrode active material, 10 parts by weight of flaky graphite as a conductive material and 10 parts by weight of PVDF as a binder are added, and as a dispersion solvent A positive electrode mixture 41 in which NMP was added and kneaded was produced. The positive electrode mixture 41 was applied to both surfaces of an aluminum foil (aluminum plate) having a thickness of 20 μm, leaving a solid current collecting portion 70. Thereafter, drying, pressing, and cutting were performed to obtain a positive electrode plate 40 having a thickness of 90 μm in the thickness of the positive electrode active material coating portion that does not include an aluminum foil.

Next, lithium ion secondary batteries of Examples 1 to 20 manufactured by variously modifying the shaft core 10 will be described.
[Example 1]
As shown in FIG. 4 (Table 1), the insulating material 13 in the shaft core 10 was formed of polyethylene having a thickness of 300 μm and a thermal shrinkage rate of 120% at 120 degrees Celsius. The separator 80 had a thermal shrinkage rate of 4% in the MD direction at 120 degrees Celsius, and the number of leading windings was two.

[Examples 2 to 5]
As shown in FIG. 4 (Table 1), the insulating materials 13 of Examples 2 to 5 are all 300 μm in thickness, and the thermal shrinkage rate at 120 degrees Celsius is 29% in Example 2 and 38 in Example 3. %, 62% in Example 4, and 72% in Example 5. The preceding number of winding times and other conditions are the same as in the first embodiment. In Example 1, the heat shrinkage rate at 120 degrees Celsius is 50%.

[Examples 6 to 10]
As shown in FIG. 4 (Table 1), the insulating material 13 of Examples 6 to 10 has a heat shrinkage rate of 50% at 120 degrees Celsius, and the thickness is 100 μm in Example 6, 200 μm in Example 7, Example 8 was changed to 400 μm, Example 9 was changed to 500 μm, and Example 10 was changed to 600 μm. The preceding number of winding times and other conditions are the same as in the first embodiment. In Example 1, the thickness of the insulating material 13 was 300 μm.

[Examples 11 and 12]
As shown in FIG. 4 (Table 1), the insulating material 13 of Example 1 was used, and the number of leading windings was changed to 0 in Example 11 and 1 in Example 12. In addition, although the number of preceding winding turns of Example 1 is 2 rounds, other conditions are the same as that of Example 1.

[Examples 13 to 16]
As shown in FIG. 4 (Table 1), using the insulating material 13 of Example 1, the thermal contraction rate in the MD direction at 120 degrees Celsius of the separator 80 is 1% in Example 13 and 2% in Example 14. , 6% in Example 15 and 8% in Example 16. The other conditions are the same as in Example 1. In Example 1, the separator 80 has a thermal shrinkage rate of 4% in the MD direction at 120 degrees Celsius.

[Examples 17 to 20]
As shown in FIG. 4 (Table 1), the insulating material 13 is made of polypropylene (hereinafter, PP) in Example 17, polyethylene terephthalate (hereinafter, PET) in Example 18, and polyphenylene sulfide (hereinafter, PET) in Example 19. , PPS), and a resin made of a copolymer of tetrafluoroethylene and perfluoroalkoxyethylene (hereinafter referred to as PFA) in Example 20. The other conditions are the same as in Example 1. The insulating material 13 of Example 1 is polyethylene.

[Comparative Example 1]
As shown in FIG. 4 (Table 1), the shaft core 10 was formed by a single plate made of polypropylene having a thickness of 1.5 mm, instead of the configuration of FIG. As a result, the effect of short-circuiting the conductor plates 11 and 12 due to the thermal contraction of the insulating material 13 does not occur. The other conditions are the same as in Example 1.
[Test and evaluation results]

  For each of the lithium ion secondary batteries of Examples 1 to 20 and Comparative Example 1 described above, an overcharge test in which charging is performed until an abnormal phenomenon occurs in the battery at a current value of 3 hours rate (3CA) is performed. The highest temperature reached on the container surface was measured.

FIG. 5 is an evaluation list of Examples 1 to 20 and Comparative Example 1. The overall evaluation in FIG. 5 (Table 2) is as follows.
(1) When the maximum temperature reached within the number of tests (n = 5) is less than 150 degrees Celsius, the variation in the maximum temperature reached is less than 10 degrees Celsius, and the defect rate is 0%, “◎” ( Excellent).
(2) If the maximum temperature reached less than 150 degrees Celsius within the number of tests or the variation in maximum temperature reached less than 10 degrees Celsius and the defect rate is 0%, It was evaluated as “good”.

(3) “△” (problem) means that the highest temperature achieved within the number of tests is 150 degrees Celsius or higher, the variation in maximum temperature reached is 10 degrees Celsius, and the defect rate is 0% or higher. evaluated.
(4) When the maximum temperature reached within the number of tests exceeded the measurement limit of 400 degrees Celsius and a large amount of smoke was emitted, it was evaluated as “x” (bad).

  When the above-described overcharge test was performed, as shown in FIG. 5 (Table 2), the lithium ion secondary battery of Comparative Example 1 in which the shaft core was formed by a single plate made of polypropylene violently ejected smoke. The maximum temperature exceeded 400 degrees Celsius.

  On the other hand, in the batteries of Examples 1 to 20 using the shaft core 10 in which the first and second conductor plates 11 and 12 are configured with the insulating material 13 interposed as shown in FIG. The insulating material 13 in the core 10 is thermally contracted, and the first conductor plate 11 and the second conductor plate 12 are contacted and short-circuited. As a result, current flows from the positive electrode external terminal → the positive electrode connection plate → the second conductor plate 12 → the first conductor plate 11 → the negative electrode connection plate → the negative electrode external terminal, and the current flowing from the positive electrode plate 40 to the negative electrode plate 30 is cut off. Is done. As a result, the heat generation stopped, the maximum temperature reached 190 degrees Celsius or less, the amount of smoke generation was small, and it was found that the safety was high.

6 to 10 are graphs showing the results of the overcharge test in each example.
As shown in the graph of FIG. 6, in the lithium ion secondary batteries of Examples 2 and 3 having a thermal shrinkage rate of less than 50%, the maximum reached temperatures were 183 degrees Celsius and 150 degrees Celsius, respectively. On the other hand, Examples 1, 4, and 5 having thermal shrinkage of 50% or more have low maximum temperatures of 119 degrees Celsius, 113 degrees Celsius, and 108 degrees Celsius, respectively.

  Further, the lithium ion secondary batteries of Examples 2 and 3 had variations in the maximum temperature reached of 15.4% and 11.8%, whereas the lithium ion secondary batteries of Examples 1, 4 and 5 Then, the variation is as small as 3.7% to 4.1%.

  This is because the lithium ion secondary batteries of Examples 2 and 3 were slow in contact with the conductor plates 11 and 12 due to the low thermal contraction rate of the insulating material 13, or were not sufficiently contracted. That is, by using the insulating material made of a material having a somewhat high thermal contraction rate for the shaft core 10, the insulating material 13 contracts during heat generation, and the first and second conductor plates 11 and 12 come into contact with each other in a short time to increase the temperature. It can be seen that this can be suppressed.

As shown in the graph of FIG. 7, the lithium ion secondary battery of Example 10 having a thick insulating material 13 of 600 μm is compared with the lithium ion secondary batteries of Examples 1 and 6 to 9 having a thickness of 500 μm or less. The maximum temperature reached is high, and the variation is large.
This is because the contact between the conductor plates 11 and 12 is delayed in the lithium ion secondary battery of Example 10 because the insulating material 13 is thick. That is, by designing in consideration of the heat shrinkability of the insulating material 13, the first and second conductor plates 11 and 12 are brought into contact with each other in a short time due to the heat shrinkage of the insulating material 13 during heat generation. It can be seen that the rise can be suppressed.

  The lithium ion secondary battery of Example 6 having a thin insulating material 13 of 100 μm was high in safety but had a high defect rate of 52%. This is because the insulating material 13 was too thin and the insulating layer was damaged during the assembly, resulting in a short circuit.

As shown in the graph of FIG. 8, in the lithium ion secondary battery of Example 11 in which the number of leading windings was 0, the maximum temperature reached was as high as 175 degrees Celsius and the variation was as large as 12.7%.
On the other hand, the lithium ion secondary batteries of Examples 12 and 13 in which the number of leading windings is 1 turn (4 separators in total) and 2 turns (8 separators in total) are the maximum attained temperatures of 132 degrees Celsius and 144 degrees Celsius, respectively. The variation was 4.7% and 10.2%, and the maximum temperature reached was low and the variation was small as compared with the lithium ion secondary battery of Example 11.

  This is because, due to the heat shrinkability of the separator 80 in the MD direction at 120 degrees Celsius, the previously wound portions fasten the conductor plates 11 and 12, and the conductor plates 11 and 12 are brought into close contact with each other when the insulating material 13 is thermally shrunk. This is due to the realization of contact. That is, by winding a separator made of a material having a somewhat high heat shrinkage rate around the shaft core 10 or more around the shaft core 10, the separator 80 is shrunk during heat generation. Thus, it can be seen that the first and second conductor plates 11 and 12 can come into contact with each other to suppress the temperature rise.

As shown in the graph of FIG. 9, in the lithium ion secondary battery of Example 11 in which the thermal shrinkage rate of the separator 80 at 120 degrees Celsius is 1%, the maximum temperature reached 175 degrees Celsius is high, and the variation is 12.7%. large.
On the other hand, in the lithium ion secondary batteries of Examples 1 and 14 to 16 in which the thermal contraction rate of the separator is 2% or more, the maximum temperature reached is as low as 119 to 125 degrees Celsius, and the variation is as small as 2.0 to 4.7%. .

  The higher the thermal contraction rate of the separator 80, the greater the tightening force with respect to the conductor plates 11 and 12, and when the insulating material 13 contracts during heat generation, the conductor plates 11 and 12 are brought into close contact with each other, thereby ensuring the maximum temperature. It can be suppressed to.

  As shown in the graph of FIG. 10, the materials of the insulating material 13 of the lithium ion secondary batteries of Examples 1 and 17 to 20 were changed to PE, PP, PET, PPS, and PFA, respectively, and the maximum temperature reached was compared. However, the lithium ion secondary battery of Example 1 using the PE insulating material 13 was as low as 119 degrees Celsius, and the lithium ion secondary batteries of Examples 17 to 20 were as high as 153 degrees Celsius to 195 degrees Celsius.

  This is because the melting point of PE is lower than the melting points of PP, PET, PPS, and PFA, and heat shrinkage occurs first, and the conductor plates 11 and 12 are short-circuited first. That is, by designing in consideration of the melting temperature of the insulating material 13, the first and second conductor plates 11 and 12 are brought into contact with each other in a short time due to the melting of the insulating material 13 during heat generation. It turns out that it can suppress.

From the above test results, the lithium ion secondary batteries of Examples 1, 4 to 9, and 12 to 20 have the following effects.
(1) In the lithium ion secondary batteries of Examples 1 to 20, the insulating plate made of PE having a heat shrinkage rate of not less than 50% at 120 degrees Celsius and a thickness of 200 to 500 μm between the conductor plates 11 and 12. A separator 80 having a shaft core 10 having a three-layer structure in which a material 13 is arranged and having a heat shrinkage rate of 2% or more in the MD direction at 120 degrees Celsius is wound around the shaft core 10 with a preceding winding number of turns of 1 or more. It is turning. It was found that the safety was greatly improved as compared with the lithium ion secondary battery of Comparative Example 1, and the maximum temperature reached in overcharging could be reliably lowered, and there was no defect in the manufacturing process.

Embodiments 1 to 20 described above can be modified as follows.
(1) In this embodiment, stoichiometric lithium manganate (LiMn ₂ O ₄ ) is exemplified as the positive electrode active material. The lithium ion secondary battery according to the present invention includes a lithium manganese composite oxide in which another lithium manganate having a spinel crystal structure (for example, Li ₁ + xMn ₂ -xO ₄ ) or a part of lithium manganate is substituted or doped with a metal element. objects _{(e.g., Li1 + xMyMn 2 -x-yO} 4, M is Co, Ni, Fe, Cu, Al, Cr, Mg, Zn, V, Ga, B, at least one of F) cobalt having a or layered crystal structure Lithium oxide, lithium titanate, or a lithium-metal composite oxide obtained by substituting or doping a part thereof with a metal element may be used.

(2) In the present embodiment, amorphous carbon is exemplified as the negative electrode active material. However, the present invention is not limited to this. Natural graphite capable of removing and inserting lithium ions, various artificial graphite materials, coke, etc. The carbonaceous material or the like may be used, and the particle shape is not particularly limited to a scaly shape, a spherical shape, a fibrous shape, a massive shape, or the like.

(3) In this embodiment mode shows an example of using LiPF ₆ as an electrolyte, it is not limited thereto, for _{example, LiClO 4, LiAsF 6, LiBF} 4, LiB (C 6 H 5) 4 CH ₃ SO ₃ Li, CF ₃ SOLi, or a mixture thereof can be used. Moreover, in this embodiment, although the example which used the mixed solvent of EC and DMC was shown as the solvent of nonaqueous electrolyte solution, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, 1, 2- dimethoxyethane, , 2-diethoxyethane, γ-butyllactone, tetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, methyl sulfolane, acetonitrile, propionitrile, propionitrile, etc. A mixed solvent of seeds or more may be used, and the mixing ratio is not limited.

(4) In the present embodiment, an example in which PVDF is used as the binder is shown, but polytetrafluoroethylene (PTFE), polyethylene, polystyrene, polybutadiene, butyl rubber, nitrile rubber, styrene / butadiene rubber, polysulfide rubber Polymers such as nitrocellulose, cyanoethyl cellulose, various latexes, acrylonitrile, vinyl fluoride, vinylidene fluoride, propylene fluoride, chloroprene fluoride, and acrylic resins, and mixtures thereof can be used.

(5) In this embodiment, the aluminum plate 12 and the copper plate 11 are used for the shaft core. However, the present invention is not limited to this. For example, the battery potential of each electrode such as an aluminum alloy plate, a copper alloy plate, or a nickel plate is used. There is no particular limitation as long as it has electrical conductivity without being corroded by.

(6) The shaft core 10 is not limited to the configuration shown in FIG. Any material may be used as long as it is a material that deforms due to heat generated by the electrode group 20 and allows the conductor plates 11 and 12 to contact, such as a material that contracts or melts the insulating layer 13 due to heat.

(7) The structure and mechanism of the shaft core 10 are not limited to the embodiment, and any configuration can be adopted. For example, as shown in FIG. 11, a space for applying the adhesive can be secured by a configuration in which the conductor plates 11 and 12 are formed with protrusions 13P on the surfaces facing each other with a gap therebetween.

(8) The arrangement of the insulating material between the first and second conductor plates 11 and 12 which are metal positive electrode core electrodes is replaced with a method in which the end faces are opposed to each other as in the embodiment. You may make it oppose through an insulating material. An example of such an axis is shown in FIG. In this configuration, the conductor plates 11 and 12 are provided with an L-shaped step in the thickness direction and are joined via an insulating material 13 in the thickness direction. Various other configurations can be employed for the shaft core.

(9) As the insulating material, a material that becomes a gel by heat generation may be used. In this case, it is preferable to form grooves or recesses into which the gel escapes on the opposing surfaces of the metal terminals facing each other with an insulating material interposed therebetween.

(10) Instead of the plate-shaped shaft core, a shaft core made of a conductive rod-shaped or shaft-shaped conductive member may be used. In this case, both ends in the longitudinal direction may be connected to the positive electrode current collector 70 and the negative electrode current collector 60, respectively, and the members constituting the both ends may be insulated in various forms.

(11) A separator that insulates the negative electrode plate 30 and the positive electrode plate 40 is wound around the shaft core 10 in advance, but a separator made of an insulating and heat-shrinkable resin different from this separator is used as the shaft core. 10 may be wound.

(12) The shaft core may be constituted by a positive electrode core electrode and a negative electrode core electrode which are insulated with an insulating material that does not shrink by heat or an insulating material that does not gelate. That is, a shaft core in which the positive electrode core electrode and the negative electrode core electrode are not short-circuited during heat generation may be used. This is intended to improve the cooling performance by the metal shaft core. Therefore, although the effect with respect to the safety measure by heat_generation | fever is low compared with Examples 1-20, a certain amount of cooling effect can be anticipated.

10 shaft core 11 first conductor plate (copper plate)
12 Second conductor plate (aluminum plate) 13 Insulating material 20 Electrode group 30 Negative electrode plate 31 Negative electrode mixture layer 40 Positive electrode plate 41 Positive electrode mixture layer 60 Negative electrode current collector 70 Positive electrode current collector 80 Separator

Claims (12)

An electrode group comprising a positive electrode plate, a negative electrode plate, and a sheet layer that is interposed between the positive electrode plate and the negative electrode plate and laminated with a separator that insulates the positive electrode plate from the negative electrode plate, and is wound around an axis. When,
The electrode group is housed, and comprises a battery container having an external positive terminal and an external negative terminal,
The shaft core includes a first conductor member, a second conductor member, and an insulating material interposed between the first and second conductor members to insulate the first and second conductor members;
The lithium ion secondary battery, wherein the first conductor member is connected to the negative electrode plate, and the second conductor member is connected to the positive electrode plate. In the lithium ion secondary battery according to claim 1,
The insulating material is made of a heat-shrinkable material, and the first conductor member and the second conductor member are brought into contact with each other by the amount of shrinkage when the temperature exceeds a reference temperature. . In the lithium ion secondary battery according to claim 1,
The lithium ion secondary battery is characterized in that the insulating material is made from a heat-meltable material, and the first conductor member and the second conductor member are brought into contact with each other by melting when the temperature reaches a reference temperature or higher. In the lithium ion secondary battery according to claim 1,
The lithium ion secondary battery is characterized in that the shaft core is wound one or more times in advance by the separator, and the separator is made of a heat-shrinkable resin. The lithium ion secondary battery according to claim 4,
The separator is a lithium ion secondary battery, wherein a thermal shrinkage rate at 120 degrees Celsius is 2% or more in a winding circumferential direction (MD direction) of the electrode group. The lithium ion secondary battery according to any one of claims 1 to 5,
The lithium ion secondary battery, wherein the insulating material has a thickness of 200 μm to 500 μm. The lithium ion secondary battery according to any one of claims 1 to 6,
The lithium ion secondary battery, wherein the insulating material has a thermal shrinkage rate of 120% or more at 120 degrees Celsius. The lithium ion secondary battery according to any one of claims 1 to 7,
The lithium ion secondary battery, wherein the insulating material is made of polyethylene. The lithium ion secondary battery according to any one of claims 1 to 8,
The shaft core is formed of flat first and second conductor members, and the insulating material is bonded to side surfaces of the first and second conductor members facing each other. Secondary battery. The lithium ion secondary battery according to any one of claims 1 to 9,
A lithium ion secondary battery, wherein a negative electrode external terminal is connected to the first conductor member of the shaft core, and a positive electrode external terminal is connected to the second conductor member of the shaft core. The lithium ion secondary battery according to any one of claims 1 to 9,
The first conductor member is connected to the negative electrode current collector of the negative electrode plate, the second conductor member is connected to the positive electrode current collector of the positive electrode plate, and the positive electrode current collector is connected to the positive electrode external terminal via the positive electrode connection plate. The current collector 60 is connected to a negative electrode external terminal through a negative electrode connecting plate, and is a lithium ion secondary battery characterized by the above. The lithium ion secondary battery according to any one of claims 1 to 11,
A lithium ion secondary battery, wherein an electrode group wound in a flat shape is stored in a flat battery container.

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