JP2012178237A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery which is excellent in safety while achieving high capacity or high energy density by structuring an electrode group in which the diffusion of short-circuit currents or heat is turned to be beneficial to safety.SOLUTION: This nonaqueous electrolyte secondary battery A includes: a negative pole 10: a positive pole 20; a separator 30 for isolating those negative pole and positive pole; and nonaqueous electrolyte. Then, at least a part of the outermost peripheral section of the negative pole 10 is formed with an unapplied section to which any negative pole active material is not applied, and from which a negative pole core body is exposed, and a negative pole collector tab 10a is welded to the outside of roll of the unapplied section, and the unapplied section is bent to the inside of roll so as to be positioned at the back side of the welding surface of the negative collector tab 10a with the negative pole core body, and the negative pole core bodies are arranged so as to be overlapped with each other so that an overlapped section 11a of the negative pole core bodies can be formed.

Description

  The present invention includes a negative electrode in which a negative electrode active material is applied to a negative electrode core, a positive electrode in which a positive electrode active material is applied to a positive electrode core, a separator that separates the negative electrode and the positive electrode, and a nonaqueous electrolyte. The present invention relates to a non-aqueous electrolyte secondary battery.

  In recent years, non-aqueous electrolyte secondary batteries have been required to have higher safety as their use as various power sources expands. Here, when the capacity is increased or the energy density is increased, if this type of non-aqueous electrolyte secondary battery generates abnormal heat for some reason, the instantaneous explosion energy becomes large, causing explosion or It has become difficult to suppress phenomena such as ignition. Against this background, in applications of non-aqueous electrolyte secondary batteries such as personal computers (PCs), electric tools, and electric motorcycles, safety due to impact from the outside of the non-aqueous electrolyte secondary battery is regarded as important. It came to be.

  In this case, there are a nail penetration test (penetration test) and an impact test in the safety test of the nonaqueous electrolyte secondary battery. Here, the nail penetration test is a test in which a sharp elongated metal rod (nail) is penetrated from a side surface of a fully charged nonaqueous electrolyte secondary battery at a certain speed to forcibly short-circuit. The impact test is a test in which a “weight” having a predetermined mass is dropped vertically from right above the nonaqueous electrolyte secondary battery to give an impact force to the nonaqueous electrolyte secondary battery. In any of these tests, as a matter of course, it is desirable that abnormalities such as rupture and ignition do not occur.

  Therefore, this kind of non-aqueous electrolyte secondary battery can be used even if an abnormal situation occurs, such as when the battery is crushed, overcharged, pierced by a nail, or abnormally heated from the outside. A non-aqueous electrolyte secondary battery that can ensure safety by suppressing the rapid temperature rise is proposed in, for example, Patent Document 1 (Japanese Patent Laid-Open No. Hei 8-153542). In the nonaqueous electrolyte secondary battery proposed in Patent Document 1, when an abnormal situation occurs, metals having sufficiently small electrical resistance are short-circuited. Specifically, a positive electrode equipotential exposed metal portion that does not have a positive electrode active material layer at the end of the positive electrode and a negative electrode equipotential exposed metal portion that does not have a negative electrode active material layer at the end of the negative electrode are provided. I have to.

JP-A-8-153542

  However, when performing a nail penetration test, safety may differ depending on where the nail is inserted in the nonaqueous electrolyte secondary battery. For this reason, even if it employ | adopted the electrode group structure which was proposed by the patent document 1 mentioned above, the problem that safety | security cannot be ensured enough occurred. For example, when there is a negative electrode current collecting tab at a position where the nail is pierced, it is usually considered that the nail penetrates the electrode group as it is and is short-circuited when there is no hard object in the place where the nail penetrates. However, when there is a negative electrode current collecting tab at a location where the nail penetrates, the negative electrode current collecting tab is crushed because the nail cannot penetrate the negative electrode current collecting tab. For this reason, a safety | security difference will come out by which position of a nonaqueous electrolyte secondary battery pierces a nail.

  In addition, there may be a difference in safety depending on whether the nail penetrates the electrode group slowly or at a stroke. In this case, when the nail penetrates the electrode group at once, the short-circuit area is increased and the short-circuit current is increased, so that the short-circuited nonaqueous electrolyte secondary battery is quickly discharged. For this reason, since the battery capacity has already decreased at the time when the short-circuited part reaches a high temperature, it is considered that the battery is unlikely to burst or ignite. On the other hand, the shorter the speed at which the nail is pierced into the electrode group, the smaller the short circuit, so the short circuit current is small. Thereby, even when the short-circuited part reaches a high temperature, the battery capacity is sufficiently maintained, and the battery tends to rupture or ignite, resulting in a decrease in safety.

  In addition, when the nail hits the negative electrode current collecting tab, the nail pushes the negative electrode current collecting tab without penetrating the negative electrode current collecting tab. At this time, it is considered that the edge of the negative electrode current collecting tab breaks the negative electrode core or the separator and contacts the positive electrode to cause a short circuit. Also in this case, the short circuit current is small due to the minute short circuit. As a result, when the short-circuited part reaches a high temperature, the battery capacity is sufficiently maintained, which may lead to battery rupture or ignition.

Furthermore, even in the impact test, when the “weight” having a predetermined mass is dropped, if the negative current collector tab is at the position where the “weight” falls, the negative current collector tab is tilted or deformed. It is expected to bite into the electrode group. For this reason, a minute short circuit easily occurs, and as a result, there arises a problem that the battery is ruptured or ignited.
Therefore, the present invention has been made to solve the above problems, and even if a short circuit occurs in the battery, the electrode group is such that the short circuit current and heat diffusion are in a direction advantageous to safety. This structure is intended to provide a non-aqueous electrolyte secondary battery that is excellent in safety while at the same time achieving high capacity and high energy density of the battery.

  The nonaqueous electrolyte secondary battery of the present invention includes a negative electrode in which a negative electrode active material is applied to a negative electrode core, a positive electrode in which a positive electrode active material is applied to a positive electrode core, a separator that separates the negative electrode and the positive electrode, A non-aqueous electrolyte. In order to solve the above problem, the positive electrode and the negative electrode are spirally wound with a separator interposed therebetween, and the negative electrode active material is not applied to a part of the outermost peripheral portion of the negative electrode, and the negative electrode core is exposed. And the negative electrode current collecting tab is welded to the outer side of the negative electrode core of the uncoated part, and the negative electrode core of the uncoated part is connected to the negative electrode core of the negative electrode current collecting tab. It is folded back inside the winding so as to be located on the back side of the welding surface, and is arranged so that the negative electrode cores of the uncoated part are overlapped to form an overlapping part of the negative electrode cores. To do.

  Here, the negative electrode core in the non-coated portion of the negative electrode active material formed on the outermost peripheral portion of the negative electrode is folded back inside the winding so as to be located on the back side of the welding surface of the negative electrode current collecting tab with the negative electrode core. In addition, when the overlapped part of the negative electrode core in the uncoated part is formed, even if the nail is inserted into the negative electrode current collecting tab, the battery does not rupture or ignite, which is excellent in safety. In addition, a non-aqueous electrolyte secondary battery could be obtained. The cause is not clear, but the negative electrode core of the non-coated portion of the negative electrode active material is folded back inside the winding so that the negative electrode current collector tab is located on the back side of the welding surface with the negative electrode core, and the uncoated portion It is considered that the short-circuit current and the thermal diffusion when the short-circuit occurs in the overlapped portion are changed in a direction advantageous for safety.

  In this case, the overlapping portion of the negative electrode cores in the uncoated portion is folded back to the inner side so as to be located on the back side of the welding surface with the negative electrode core of the negative electrode current collecting tab, and the negative electrode cores are doubled. After being arranged so as to overlap with each other, it is further folded back to the inside of the winding so that the negative electrode cores are arranged so as to overlap with each other, and when a short circuit occurs at the overlapping portion, It can be said that the thermal diffusion is further preferred by changing in a direction that is more advantageous for safety.

  In the present invention, even when a nail is inserted into the negative electrode current collecting tab, the battery does not rupture or ignite, so that the battery has a high capacity and a high energy density, while ensuring safety. An excellent nonaqueous electrolyte secondary battery can be provided.

It is sectional drawing which shows typically the principal part of the outermost periphery side of the cross section of the nonaqueous electrolyte secondary battery of Example 1 of this invention. It is sectional drawing which shows typically the principal part of the outermost periphery side of the cross section of the nonaqueous electrolyte secondary battery of Example 2 of this invention. It is sectional drawing which shows typically the principal part of the outermost periphery side of the cross section of the nonaqueous electrolyte secondary battery of the comparative example 1 of this invention.

1. Negative Electrode The negative electrode 10 is composed of a negative electrode core (in this case, a copper foil having a thickness of 8 μm) 11 and a negative electrode mixture layer 12 formed on both surfaces of the negative electrode core 11. In this case, the negative electrode mixture layer 12 is composed of 97 parts by mass of a negative electrode active material made of natural graphite (in this case, having an average particle diameter of 20 μm), and polyvinylidene fluoride (PVdF) as a binder. Is composed of 3 parts by mass.

  And such a negative electrode 10 was produced as follows. First, 97 parts by mass of a negative electrode active material made of natural graphite and 3 parts by mass of polyvinylidene fluoride (PVdF) as a binder were mixed and then mixed with an N-methylpyrrolidone (NMP) solution. Thus, a negative electrode slurry was prepared. The obtained negative electrode slurry was applied to both surfaces of a negative electrode core (for example, a copper foil having a thickness of 8 μm) by a doctor blade method and dried to form a negative electrode mixture layer 12 on the negative electrode core 11. After that, it is rolled using a compression roller and cut into predetermined dimensions (in this case, the length of the short side is 59 mm and the length of the long side is 650 mm) and the negative electrode current collecting tab The negative electrode 10 was produced by forming 10a.

2. Positive electrode The positive electrode 20 includes a positive electrode core body (in this case, an aluminum foil having a thickness of 15 μm) 21 and a positive electrode mixture layer 22 formed on both surfaces of the positive electrode core body 21. In this case, the positive electrode mixture layer 22 is composed of 94 parts by mass of a positive electrode active material made of lithium-cobalt composite oxide (LiCoO ₂ ), 3 parts by mass of carbon powder as a conductive agent, and polyvinylidene as a binder. Fluoride (PVdF) consists of 3 parts by mass.

And such a positive electrode 20 was produced as follows. That is, first, 94 parts by mass of a positive electrode active material made of a predetermined amount of lithium-cobalt composite oxide (LiCoO ₂ ), 3 parts by mass of carbon powder as a conductive agent, and polyvinylidene fluoride powder as a binder. After mixing to 3 parts by mass, this was mixed with an N-methylpyrrolidone (NMP) solution to prepare a positive electrode slurry.

  The obtained positive electrode slurry is applied to both surfaces of a positive electrode core (in this case, an aluminum foil having a thickness of 15 μm) 21 by a doctor blade method and dried to form a positive electrode mixture layer 22 on the positive electrode core 21. Formed. After that, it is rolled using a compression roller and cut into predetermined dimensions (in this case, the length of the short side is 56 mm and the length of the long side is 620 mm) and the positive electrode current collecting tab (Not shown) was formed, and the positive electrode 20 was produced.

3. The spiral electrode group Next, the negative electrode 10 and the positive electrode 20 produced as described above were overlapped with a separator 30 made of a polyethylene microporous film interposed therebetween, and then wound in a spiral shape by a winder, The spiral electrode group a of Example 1, the spiral electrode group b of Example 2, and the spiral electrode group x of Comparative Example 1 were produced.

  In this case, in the spiral electrode group a of Example 1, as shown in FIG. 1, only the negative electrode core 11 without the negative electrode mixture layer 12 (uncoated portion) is present on the outermost peripheral portion of the negative electrode 10. It is in a certain state. And the negative electrode current collection tab 10a is welded to the winding outer side of the negative electrode core 11 of this uncoated part. Further, the negative core 11 in the uncoated portion is folded back inside the winding so as to be located on the back side of the welding surface of the negative current collecting tab 10a, so that the negative cores 11 in the uncoated portion are double stacked. And an overlapped portion 11a of an uncoated portion is formed.

  Further, in the spiral electrode group b of Example 2, as shown in FIG. 2, as in the spiral electrode group a of Example 1, the negative electrode without the negative electrode mixture layer 12 in the outermost peripheral portion of the negative electrode 10. There is a state in which only the core body 11 (uncoated part) is present, and the negative electrode current collecting tab 10a is welded to the outer side of the negative electrode core body 11 in the uncoated part. And the negative electrode core 11 of the uncoated part is folded back inside the winding so that it is located on the back side of the welding surface of the negative electrode current collecting tab 10a, and the negative electrode cores 11 of the uncoated part overlap each other. After the arrangement, the non-coated portion 11b is formed by folding back to the inside of the winding so that the uncoated portions of the negative electrode cores 11 are arranged in a triple layer.

  Furthermore, in the spiral electrode group x of Comparative Example 1, as shown in FIG. 3, the negative electrode without the negative electrode mixture layer 12 at the outermost peripheral portion of the negative electrode 10, as in the spiral electrode group a of Example 1. There is a state in which only the core body 11 (uncoated part) is present, and the negative electrode current collecting tab 10a is welded to the outer side of the negative electrode core body 11 in the uncoated part. In this case, the negative electrode core 11 of the uncoated part is left as it is without being folded back to the inner side.

4). Nonaqueous electrolyte secondary battery Next, an iron outer can (in this case, having a diameter of 18 mm and a height of 650 mm) 40 was prepared. Thereafter, the spiral electrode group (a, b, x) produced as described above is inserted into the outer can 40 and a positive current collecting tab (not shown) is attached to the outer can (bottom terminal). And the negative electrode current collecting tab 10a was welded to the bottom (negative electrode terminal) of a sealing body (not shown). Next, lithium hexafluorophosphate (LiPF ₆ ) as an electrolyte salt was added to a mixed solvent in which ethylene carbonate (EC) and methyl ethyl carbonate (MEC) were mixed so that the volume ratio was 3: 7 (25 ° C.). A nonaqueous electrolyte in which was dissolved to 1.2 mol / liter was injected. Then, the opening part of the armored can 40 was sealed with the sealing body, and the nonaqueous electrolyte secondary batteries A, B, and X each having a design capacity of 3000 mAh were produced.

  Here, a non-aqueous electrolyte secondary battery using the spiral electrode group a of Example 1 was designated as battery A. Similarly, a non-aqueous electrolyte secondary battery using the spiral electrode group b of Example 2 was designated as battery B, and a non-aqueous electrolyte secondary battery using the spiral electrode group x of Comparative Example 1 was designated as battery X.

5. Non-aqueous electrolyte secondary battery test (1) Nail penetration test Next, each battery (A, B, X) produced as described above was charged at a constant current of 1500 mA at room temperature (about 25 ° C). 4. Charged to reach 40V. Further, the battery was charged at a constant voltage of 4.40 V until the current value reached 60 mA. Thereafter, each battery (A, B, X) was placed horizontally with the position where the negative electrode current collecting tab 10a is located directly above. Next, a SUS nail having a diameter of 3.0 mm is vertically dropped at a constant speed in accordance with the position of the negative electrode current collecting tab 10a, and each battery (A, B, X) is forcibly short-circuited, A nail penetration test was conducted to visually confirm whether or not an abnormal state such as rupture or ignition occurred in the battery. In this case, the nail drop speed was set to 100 mm / sec and 50 mm / sec each for two cells, and if the battery did not rupture or ignite, it was determined OK and the battery When rupture or ignition occurred, it was determined as NG, and the number of them was determined, and the results shown in Table 1 below were obtained.

(2) Impact test Each battery (A, B, X) produced as described above was charged at room temperature (about 25 ° C) with a constant current of 1500 mA until the battery voltage reached 4.40V. Further, the battery was charged at a constant voltage of 4.40 V until the current value reached 60 mA. After that, after each battery (A, B, X) is placed horizontally, a SUS cylindrical rod having a diameter of 16 mm is crossed perpendicularly to each battery (A, B, X). And fixed. Next, an impact test was performed in which a SUS weight having a mass of 9.8 kg was freely dropped vertically from a position having a height of 60 cm to give an impact to the battery. In this case, two cells are performed, and if the battery does not rupture or ignite, it is determined to be OK, and if the battery ruptures or ignites, it is determined to be NG. The result was as shown.

  As is clear from the results of Table 1 above, regarding the nail penetration test, the overlap of the negative electrode core 11 on the back surface where the negative electrode current collecting tab 10a is welded at the uncoated portion of the negative electrode 10 as in the battery X When there is no alignment, it can be seen that the nail penetration test is NG regardless of the drop speed of the nail. This is because when the nail hits the negative electrode current collecting tab 10a, the nail pushes the negative electrode current collecting tab 10a without penetrating the negative electrode current collecting tab 10a, and the edge of the negative electrode current collecting tab 10a becomes the negative electrode core. 11 or the separator 30 is contacted with the positive electrode 20 to cause a short circuit. In this case, the short-circuit current is small due to the minute short-circuit, and the battery capacity is sufficiently maintained even when the short-circuit portion reaches a high temperature. This is considered to have caused the battery to burst or ignite.

  On the other hand, when there is an overlapping portion (double overlapping portion) 11a of the core body 11 on the back surface where the negative electrode current collecting tab 10a in the uncoated portion at the winding end portion of the negative electrode 10 is welded as in the battery A, It can be seen that the nail penetration test is OK when the nail drop speed is fast (100 mm / sec). This is because when the nail hits the negative electrode current collecting tab 10a, the nail pushes the negative electrode current collecting tab 10a without penetrating the negative electrode current collecting tab 10a, and the edge of the negative electrode current collecting tab 10a becomes the negative electrode core. It is considered that when the electrode 11 and the separator 30 are broken to come into contact with the positive electrode 20, the discharge is quickly performed by the overlapping portion (double overlapping portion) 11 a of the negative electrode core 11.

  As a result of the smooth diffusion of short circuit current and heat when a short circuit occurs in the overlapping part (double overlapping part) 11a of the negative electrode core 11, the battery is already at the time when the short circuit point has reached a high temperature. Since the capacity is reduced, it is considered that the battery is less likely to burst or ignite, and the safety is improved. When the nail drop speed is slow (50 mm / sec), the nail penetration test is NG. However, when the nail drop speed is slow (50 mm / sec), a short circuit occurs due to a short circuit. This is considered to be smaller. Thereby, even when the short-circuited part reaches a high temperature, the battery capacity is sufficiently maintained, and it is considered that the battery has ruptured or ignited.

  Furthermore, as in the case of battery B, when there is an overlapping portion (triple overlapping portion) 11b of the negative electrode core 11 on the back surface where the negative electrode current collecting tab 10a is welded at the uncoated portion of the winding end portion of the negative electrode 10, It can be seen that the nail penetration test is OK whether the nail drop speed is slow or fast. This is because when the nail hits the negative electrode current collecting tab 10a, the nail pushes the negative electrode current collecting tab 10a without penetrating the negative electrode current collecting tab 10a, and the edge of the negative electrode current collecting tab 10a becomes the negative electrode core. It is considered that when the electrode 11 is broken and contacted with the positive electrode 20, the discharge is rapidly performed by the overlapping portion (triple overlapping portion) 11 b of the negative electrode core 11. Thereby, as a result of smooth diffusion of short-circuit current and heat when a short circuit occurs in the overlapping part (triple overlapping part) 11b of the negative electrode core 11, the battery capacity has already been reached when the short-circuited part reaches a high temperature. Therefore, it is considered that the battery is less likely to rupture or ignite, improving safety.

  As for the impact test, when there is no overlap of the negative electrode core 11 on the back surface where the negative electrode current collecting tab 10a is welded at the uncoated portion at the winding end portion of the negative electrode 10 as in the battery X, the impact test is performed. Whereas it is NG, like the batteries A and B, the overlapping portion of the negative electrode core 11 on the back surface where the negative electrode current collecting tab 10a is welded in the uncoated portion of the winding end portion of the negative electrode 10 ( It can be seen that the impact test is OK when there is a double overlap portion) 11a and an overlap portion (triple overlap portion) 11b of the negative electrode core 11.

  This is because when there is an overlap portion (double overlap portion) 11a of the negative electrode core body 11a and an overlap portion (triple overlap portion) 11b of the negative electrode core body 11 on the back surface where the negative electrode current collecting tab 10a is welded, As a result of smooth diffusion of short-circuit current and heat when a short circuit occurs in the overlapping part (double overlapping part) 11a and the overlapping part (triple overlapping part) 11b, the short-circuited part reaches a high temperature. Since the battery capacity has already decreased, it is considered that the battery is less likely to rupture or ignite and the safety is improved.

In the above-described embodiment, an example in which natural graphite is used as the negative electrode active material has been described. However, in addition to natural graphite, a carbon-based material capable of occluding and releasing lithium ions, such as carbon black, coke, and glass. Known carbon or carbon fiber may be used. Further, the lithium as a positive electrode active material - cobalt composite oxide has been described example using (LiCoO _2), lithium - not limited to cobalt composite oxide (LiCoO _2), also using other lithium-containing composite oxide Good.

A, B: non-aqueous electrolyte secondary battery, 10: negative electrode, 10a: negative electrode current collecting tab, 11: negative electrode core, 11a: overlapping portion (double overlapping portion) of negative electrode core, 11b: negative electrode core Overlapping part (triple overlapping part), 12 ... negative electrode mixture layer, 20 ... positive electrode, 21 ... positive electrode core, 22 ... positive electrode mixture layer, 30 ... separator, 40 ... outer can

Claims (2)

A nonaqueous electrolyte comprising: a negative electrode having a negative electrode core coated with a negative electrode active material; a positive electrode having a positive electrode core coated with a positive electrode active material; a separator separating the negative electrode and the positive electrode; and a nonaqueous electrolyte. A secondary battery,
The positive electrode and the negative electrode are spirally wound with a separator in between,
The negative electrode active material is not applied to a part of the outermost peripheral part of the negative electrode, and an uncoated part where the negative electrode core is exposed is formed,
A negative electrode current collector tab is welded to the outer side of the negative electrode core of the uncoated part,
The negative core of the uncoated part is folded back to the inner side so as to be positioned on the back side of the welding surface of the negative current collecting tab with the negative core, so that the negative cores of the uncoated part overlap each other. The non-aqueous electrolyte secondary battery is characterized in that an overlapping portion of the negative electrode core is formed.   The overlapping portion of the negative electrode core is folded back to the inside of the winding so as to be positioned on the back side of the welding surface of the negative electrode current collecting tab with the negative electrode core, and the negative electrode cores are disposed so as to overlap each other. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte secondary battery is formed so as to be further folded back to the inner side of the winding and arranged so that the negative electrode cores overlap in triplicate.

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