JP2011113770A - Lithium battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium secondary battery with a large capacity and a high power, applicable for next generation clean energy vehicles such as a fuel cell vehicle, a plug-in hybrid vehicle or the like. <P>SOLUTION: The lithium secondary battery includes a cathode capable of storing and releasing lithium, an anode capable of storing and releasing lithium, a nonaqueous electrolyte solution containing lithium salt, and a separator interposed between the cathode and the anode. The separator has a structure with a porous layer containing ceramic powder and a binder at least one side of a porous polymer resin film. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a lithium battery.

  Storage batteries as power sources for next-generation clean energy vehicles such as electric vehicles, hybrid vehicles, plug-in hybrid vehicles, and fuel cell vehicles from the perspective of reducing environmental impacts such as reducing carbon dioxide emissions and reducing energy dependence on oil Expectations are increasing.

  Development of a lightweight and compact lithium secondary battery, which is the most suitable storage battery for the above-mentioned automobile power supply, is actively performed. Among the above-mentioned environmentally-friendly vehicles, the practical application of plug-in hybrid vehicles that combine the advantages of electric vehicles and hybrid vehicles is particularly expected from the viewpoint of reducing environmental impact. Lithium batteries are characterized by large capacity and high output. However, plug-in hybrid vehicles require driving using only the electric energy stored in the batteries. It is essential to ensure reliability and reliability.

  Under such a background, various techniques relating to improvement of battery reliability and safety by improving battery materials such as a positive electrode material, a negative electrode material, and an electrolytic solution have been disclosed. In terms of battery materials, there has been proposed a technique for improving the thermal stability of the positive electrode material and ensuring the safety of the battery.

  For example, Patent Documents 1 and 2 disclose a technique for a positive electrode material for the purpose of improving the thermal stability of the positive electrode material.

  Patent Document 1 discloses that in a complex oxide mainly composed of Li and Ni having a layered crystal structure, a part of Ni is a different proportion of different elements such as Al, B, Y, Ce, Ti, Sn, and the like. A positive electrode active material substituted with an element such as Co or Mn is disclosed.

  Patent Document 2 discloses a positive electrode active material mainly composed of lithium nickel cobalt composite oxide and containing lithium niobate.

JP 2000-315502 A JP 2003-77460 A

  In order to improve the safety of a storage battery that is repeatedly used (such as starting a plug-in hybrid vehicle) that discharges a large current instantaneously, there is a limit to improving the positive electrode material alone. In such a storage battery suitable for a large capacity and high power use condition, it is necessary to improve safety by adding improvements to the separator.

  An object of the present invention is to provide a lithium secondary battery that can be applied to a next-generation clean energy vehicle such as a plug-in hybrid and has a large capacity, high output, and excellent safety.

  The lithium secondary battery of the present invention includes a positive electrode that occludes and releases lithium, a negative electrode that occludes and releases lithium, a non-aqueous electrolyte containing a lithium salt, and a separator sandwiched between the positive electrode and the negative electrode. The separator has a structure in which a porous layer containing a ceramic powder and a binder is provided on at least one side of a porous polymer resin film.

  According to the present invention, it is possible to provide a lithium secondary battery having high safety and high capacity and high output suitable for a next-generation clean energy vehicle.

  In addition, according to the present invention, lithium secondary batteries can be widely provided in the industrial battery field where large capacity and high output are required.

1 is a longitudinal sectional view showing a cylindrical lithium secondary battery according to an embodiment of the present invention. FIG. 2 is a partial enlarged cross-sectional view showing an internal structure of the lithium secondary battery in FIG. 1.

  As a result of diligent research to solve the above problems, a positive electrode active material having a high nickel content, and a separator having a structure in which a porous layer of ceramic powder is provided on a porous polymer resin film are used to solve the above problems. The present inventors have found that a lithium secondary battery with high reliability and safety applicable to next-generation clean energy vehicles such as plug-in hybrids can be provided.

  Hereinafter, a lithium secondary battery according to an embodiment of the present invention will be described.

  This embodiment is basically configured as follows.

  The lithium secondary battery is a lithium secondary battery having a large battery capacity and high output, a positive electrode that occludes and releases lithium, a negative electrode that occludes and releases lithium, and a non-aqueous electrolyte containing a lithium salt And a separator sandwiched between a positive electrode and a negative electrode. The separator has a structure in which a porous layer containing a ceramic powder and a binder is provided on at least one surface of a porous polymer resin film.

  The lithium secondary battery has a battery capacity of 10 Ah or more and an output of 800 W or more.

  A plug-in hybrid vehicle requires a large current instantaneously at the time of starting or the like, and is required to travel a long distance without being charged. For this reason, said battery capacity and output are calculated | required as a battery specification.

In the lithium secondary battery, the positive electrode has a positive electrode active material containing a lithium transition metal composite oxide, and the nickel content of the metal contained in the lithium transition metal composite oxide, excluding lithium, is 50 mol%. That's it. Here, the lithium transition metal composite oxide is a metal represented by Li _a M _b O _c (M is one or more kinds of transition metals, and a, b, and c represent the ratio of the number of atoms). It is an oxide.

  By setting the nickel content to 50 mol% or more, it is possible to increase the capacity of the battery, but improvement of the separator is an important technique for ensuring the safety of the battery.

  In the lithium secondary battery, the ceramic powder is an oxide containing at least one element selected from the group consisting of aluminum, magnesium, and silicon.

  The particle size of the ceramic powder is desirably 0.1 to 1 μm, and more desirably 0.2 to 1 μm. When the particle size is smaller than 0.1 μm, the pores of the porous polymer resin film constituting the separator are likely to be clogged. In addition, when the particle size is larger than 1 μm, the porous layer formed of the ceramic powder and the binder becomes thick, which not only increases the internal resistance of the battery but also makes it difficult to produce a compact battery. It becomes.

  Moreover, since the oxide of the ceramic powder does not participate in the charge / discharge reaction of the battery, safety can be improved without impairing the reliability of the battery.

  A lithium battery suitable for a next-generation clean energy vehicle such as a plug-in hybrid is required to have a high capacity as well as a high output. As the battery capacity increases, it becomes more difficult to ensure the safety of the battery.

  The safety of lithium secondary batteries has been studied from various aspects such as battery constituent materials and battery structures.

  Regarding battery constituent materials, a positive electrode material excellent in thermal stability and a separator that prevents a short circuit between the positive electrode and the negative electrode are required.

  In general, the positive electrode material tends to generate heat due to a decrease in thermal stability in an overcharged state. This tendency is stronger in large-capacity positive electrode materials with a high nickel content.

  Therefore, in order to apply such a large-capacity positive electrode material to a battery, it is important to improve the heat resistance of the separator. That is, in the case of abnormality such as overcharge, even if the positive electrode material generates heat, if the separator has high heat resistance and the separator does not easily shrink, the short circuit between the positive electrode and the negative electrode can be avoided.

  However, when the heat resistance of the separator is low, the function of preventing the short circuit, which is an important role of the separator, is impaired due to thermal contraction, the positive electrode and the negative electrode are short-circuited, and heat generation is accelerated. As a result, in the worst case, a situation such as ignition and damage to the battery can is caused.

  A separator of a porous polymer resin film made of polyethylene, polypropylene, or the like that is generally used has a low heat-resistant temperature as low as a few tens of degrees Celsius, so there is a concern that it may be easily short-circuited due to heat generated during an abnormality.

  As a result of intensive studies from the above viewpoint, a positive electrode active material containing a lithium transition metal composite oxide having a nickel content of 50 mol% or more excluding lithium, a ceramic powder, and a binder It was revealed that a lithium secondary battery applicable to a next-generation clean energy vehicle having high capacity, high output, and high safety can be provided by using a separator having a porous layer on the surface.

  The porous polymer resin film used in the present invention is not particularly limited as long as it can be used as a separator for a lithium secondary battery.

  A ceramic powder coating slurry is prepared by adding a binder and a solvent to ceramic powder containing aluminum, magnesium or silicon oxide, and this slurry is applied to a porous polymer resin film with a coating machine. The porous layer can be formed.

  The binder may be a known binder such as polyvinylidene fluoride or fluororubber, and is not particularly limited as long as it does not adversely affect the lithium secondary battery.

  The solvent is preferably an organic solvent such as N-methyl-2-pyrrolidone.

  The thickness of the porous layer is not particularly limited, but there is no problem as long as the air permeability of the porous polymer resin film serving as the base film is not impaired. From the workability of application, etc., several μm to several tens of μm is preferable. In addition, when a coating machine suitable for double-sided coating is used from the standpoint of productivity, a porous ceramic layer is formed on both sides of the porous polymer resin film. There is no problem with the effect.

  The positive electrode used in the lithium secondary battery of the present invention is formed by applying a positive electrode mixture slurry obtained by adding a solvent to a positive electrode active material, a conductive agent and a binder to both surfaces of an aluminum foil, followed by drying and pressing. .

  The positive electrode active material is made of a lithium transition metal composite oxide, and the nickel content in the metal excluding lithium in the positive electrode active material is preferably 50 mol% or more. A part of the transition metal may be substituted with a metal element such as Mg or Al.

  The conductive agent may be a known conductive agent, for example, a carbon-based conductive agent such as graphite, acetylene black, carbon black, carbon fiber, and is not particularly limited.

  As the binder, known binders such as polyvinylidene fluoride and fluororubber may be used, and are not particularly limited. A preferred binder in the present invention is, for example, polyvinylidene fluoride.

  Further, as the solvent, various known solvents can be appropriately selected and used. For example, an organic solvent such as N-methyl-2-pyrrolidone is preferably used.

  The mixing ratio of the positive electrode active material, the conductive agent, and the binder in the positive electrode mixture is not particularly limited. For example, when the positive electrode active material is 1, the weight ratio is 1: 0.05 to 0.20: 0.02. To 0.10 (including 1: 0.05: 0.02 and 1: 0.20: 0.10) are preferred.

  The negative electrode used in the lithium secondary battery of the present invention is formed by applying a negative electrode mixture slurry obtained by adding a solvent to a negative electrode active material and a binder to both surfaces of a copper foil, and then drying and pressing.

  As the negative electrode active material, a carbon-based material such as graphite or amorphous carbon is preferable.

  As a binder, the thing similar to the said positive electrode is used, for example, and it does not specifically limit. Preferred in the present invention is, for example, polyvinylidene fluoride.

  As the solvent, for example, an organic solvent such as N-methyl-2-pyrrolidone is preferable. The mixing ratio of the negative electrode active material and the binder in the negative electrode mixture is not particularly limited. For example, when the negative electrode active material is 1, the weight ratio is 1: 0.05 to 0.20.

As the non-aqueous electrolyte used in the lithium secondary battery of the present invention, a known one may be used and is not particularly limited. Examples of non-aqueous solvents include propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, tetrahydrofuran, 1,2-diethoxyethane, and the like. One or more lithium salts selected from, for example, LiPF ₆ , LiBF ₄ , LiClO _{4, and the} like can be dissolved in one or more of these solvents to prepare a non-aqueous electrolyte.

  The shape of the lithium secondary battery includes a wound type and a stacked type, but is not particularly limited. If the lithium secondary battery of this invention is a cylindrical type, it can be manufactured as follows, for example.

  A positive electrode slurry is obtained by adding a conductive agent such as graphite and a binder such as polyvinylidene fluoride dissolved in a solvent such as N-methyl-2-pyrrolidone to the positive electrode active material in the above weight ratio and kneading.

  Next, this slurry is apply | coated to both surfaces of the aluminum metal foil of a collector. Then, it dries and presses and produces a positive electrode.

  Next, polyvinylidene fluoride or the like dissolved in N-methyl-2-pyrrolidone or the like is added to the negative electrode active material as a binder in the above weight ratio and kneaded to obtain a negative electrode slurry.

Next, after apply | coating this slurry to both surfaces of the copper foil of an electrical power collector, it dries and presses and produces a negative electrode. A lithium salt such as LiPF ₆ is dissolved in a non-aqueous solvent such as ethylene carbonate to produce a non-aqueous electrolyte.

  A porous polymer resin membrane separator provided with a ceramic porous layer is sandwiched between the obtained positive electrode and negative electrode, wound, and then inserted into a battery can molded with stainless steel or aluminum. To do. And after connecting the lead piece of an electrode and a battery can, a nonaqueous electrolyte solution is inject | poured and a battery can is sealed, A lithium secondary battery is obtained.

  FIG. 1 shows an example of a cylindrical lithium secondary battery according to the present invention.

  In this figure, the lithium secondary battery includes a positive electrode 1 including an aluminum foil as a current collector 101, and a positive electrode mixture layer 111 formed by applying the positive electrode mixture on both surfaces of the current collector 101, and a current collector. A negative electrode 2 including a negative electrode mixture layer 112 formed by applying the negative electrode mixture on both surfaces of the copper foil 102 and the current collector 102, and a separator 3 disposed between the positive electrode 1 and the negative electrode 2, The positive electrode current collecting lead piece 5 connecting the positive electrode 1 and the positive electrode current collecting lead portion 7, the negative electrode current collecting lead piece 6 connecting the negative electrode 2 and the negative electrode current collecting lead portion 8, and the negative electrode current collecting lead portion 8 A battery can 4 connected to the bottom surface, a battery lid 9 fixed by caulking to the opening end of the battery can 4 via a gasket 12, a positive electrode terminal portion 11 in contact with the back surface of the battery lid 9, and a positive electrode terminal portion 11 and a release valve 10 sandwiched between 11

  The positive electrode 1 and the negative electrode 2 are wound through a separator 3 and disposed inside the battery can 4 as an electrode group. A space formed by the battery can 4 and the battery lid 9 is filled with an electrolytic solution (not shown).

  FIG. 2 is a partially enlarged cross-sectional view showing the internal structure of the lithium secondary battery of FIG.

  In this figure, a porous layer 121 is provided on the surface of the separator 3 facing the positive electrode 1.

  The porous layer 121 is not limited to this figure, and may be provided on the surface of the separator 3 facing the negative electrode 2. Needless to say, it may be provided on both sides of the separator 3.

  Applications of the lithium secondary battery of the present invention include application to the environment-friendly automobile field such as the next-generation clean energy automobile as described above, and application to a power source such as an electric tool that requires high load characteristics and high output. And application to mobile devices.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but these examples do not limit the scope of the present invention.

In this example, LiNi _0.7 Mn _0.15 Co _0.15 O ₂ was used as the positive electrode active material. The positive electrode active material, the conductive agent graphite, and the binder polyvinylidene fluoride were kneaded for 30 minutes at a weight ratio of 85: 10: 5 using a kneader to obtain a positive electrode mixture.

  Thereafter, the positive electrode mixture was applied to both surfaces of a 30 μm thick aluminum foil as a current collector.

  On the other hand, a graphite material was used as the negative electrode active material, and polyvinylidene fluoride was used as the binder. Then, the negative electrode active material and the binder were kneaded at a weight ratio of 90:10.

  The obtained negative electrode mixture was applied to both surfaces of a copper foil having a thickness of 20 μm.

  Each of the produced positive and negative electrodes was roll-formed with a press machine and then vacuum-dried at 150 ° C. for 5 hours.

  Next, ceramic powder of aluminum oxide and polyvinylidene fluoride as a binder were kneaded at a weight ratio of 95: 5 for 30 minutes to obtain a slurry for coating ceramic powder. This was applied to one side of a porous polymer resin film (thickness 20 μm) formed of polyethylene (PE) to produce a separator provided with a porous layer of ceramic powder (thickness 5 μm). The produced separator was vacuum dried at 60 ° C., and then the positive electrode 1 and the negative electrode 2 were wound through the separator 3, and the obtained wound group was inserted into the battery can 4.

  In the present example, the porous layer of the separator was disposed so as to face the positive electrode side. The obtained negative electrode current collecting lead piece 6 was collected on the nickel negative electrode current collecting lead portion 8 and ultrasonically welded, and the current collecting lead portion was welded to the bottom of the can (FIG. 1).

  On the other hand, the positive electrode current collecting lead piece 5 was ultrasonically welded to the aluminum positive electrode current collecting lead portion 7 and then the aluminum positive electrode current collecting lead portion 7 was resistance welded to the battery lid 9.

Then, after injecting an electrolytic solution (the solute is LiPF ₆ and the solvent is a mixture obtained by mixing EC (ethylene carbonate) and MEC (methyl ethyl carbonate) in a volume ratio of 1: 2), the battery The battery lid 9 was sealed with caulking of the can 4 to obtain a cylindrical battery. Note that a gasket 12 was inserted between the upper end of the battery can 4 and the battery lid 9 for both insulation and sealing.

  A battery was produced using the same positive electrode, negative electrode, and separator provided with a ceramic porous layer as in Example 1. In this example, the ceramic porous layer was disposed so as to face the negative electrode side.

  A battery was produced using the same positive electrode and negative electrode as in Example 1. In this example, as the separator, the same polyethylene (PE) porous polymer resin film (thickness 20 μm) as that used in Example 1 was provided with a ceramic porous layer of aluminum oxide on both sides. It was. The thickness of the ceramic porous layer on one side was 4 μm.

  A battery was fabricated in the same manner as in Example 1, using the same positive electrode and negative electrode as in Example 1. In this example, a ceramic porous layer of magnesium oxide was provided on one side of a porous polymer resin film (thickness 25 μm) having three layers of polypropylene (PP) / polyethylene (PE) / polypropylene (PP) as a separator. A thing was used. The thickness of the porous layer was 6 μm.

In this example, LiNi _0.55 Mn _0.3 Co _0.25 O ₂ was used for the positive electrode, and the same negative electrode as in Example 1 was used. Further, as in Example 1, a battery was produced in the same manner as in Example 1 using a separator provided with a ceramic porous layer.

(Comparative Example 1)
A battery was produced using the same positive electrode and negative electrode as in Example 1. In this comparative example, a polyethylene (PE) porous polymer resin film (thickness 20 μm) without a ceramic porous layer was used as a separator.

(Comparative Example 2)
A battery was produced using the same positive electrode and negative electrode as in Example 1. In this comparative example, a porous polymer resin film (thickness 25 μm) having three layers of polypropylene (PP) / polyethylene (PE) / polypropylene (PP) without a ceramic porous layer was used as a separator.

  The produced battery was subjected to a capacity test, an output test, and a safety test.

  The battery was charged and discharged at a charge end voltage of 4.2 V, a discharge end voltage of 3.0 V, and a charge / discharge rate of 1 C (1 hour rate), and the capacities of the batteries prepared in Examples 1 to 5 and Comparative Examples 1 and 2 were measured.

The output was measured by 50% SOC. In this measurement, the battery was discharged at a current of 10 A, 50 A, or 100 A for 11 seconds, the voltage at the 10th second at each current value was measured, and obtained from the current-voltage characteristics. That is, the output (P _O ) is expressed by the equation P _O = I using the current value (I _D ) obtained by extrapolating the discharge end voltage (V _D ) and the current-voltage characteristic line of the battery to the discharge end voltage. It was determined from the _D × _{V D.}

  Further, the safety of the battery was evaluated by a temperature rise test of a rechargeable battery charged with a constant current and a constant voltage of 4.2 V under the conditions of 1 C and 2 hours after the end of charging. The temperature of the rechargeable battery was raised to 150 ° C. at 5 ° C./min, and the change in the battery voltage after holding for 1 hour was examined. Here, 1C is a 1 hour rate charge / discharge current value (unit is A).

  Table 1 shows the results of the capacity test and the output test.

  All the batteries that were tested showed a capacity of 10 Ah or more, a large capacity of 800 W or more, and a high output.

  Table 2 shows the temperature rise test results.

  In the batteries of Examples 1 to 5 using the separator provided with the ceramic porous layer, it was confirmed that the battery voltage was less lowered, the short-circuit when abnormal heat generation occurred in the battery was suppressed, and the safety was high. . On the other hand, in the batteries of Comparative Examples 1 and 2, since the separator had low heat resistance, the battery voltage was greatly reduced due to a short circuit, and smoke was also observed, making it difficult to ensure the safety of the battery.

  1: positive electrode, 2: negative electrode, 3: separator, 4: battery can, 5: positive electrode current collecting lead piece, 6: negative electrode current collecting lead piece, 7: positive electrode current collecting lead part, 8: negative electrode current collecting lead part, 9 : Battery cover, 10: Open valve, 11: Positive terminal, 12: Gasket.

Claims (4)

  A lithium secondary battery comprising a positive electrode that occludes and releases lithium, a negative electrode that occludes and releases lithium, a non-aqueous electrolyte containing a lithium salt, and a separator sandwiched between the positive electrode and the negative electrode. The separator has a structure in which a porous layer containing a ceramic powder and a binder is provided on at least one surface of a porous polymer resin film.   The lithium secondary battery according to claim 1, wherein the battery capacity is 10 Ah or more and the output is 800 W or more.   The positive electrode has a positive electrode active material containing a lithium transition metal composite oxide, and the nickel content of the metal contained in the lithium transition metal composite oxide, excluding lithium, is 50 mol% or more. The lithium secondary battery according to claim 1 or 2.   The lithium secondary battery according to any one of claims 1 to 3, wherein the ceramic powder is an oxide containing at least one element selected from the group consisting of aluminum, magnesium, and silicon. .

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