JP2001332246A - Nonaqueous-electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous-electrolyte secondary battery that can improve pulse charge-discharge cycle characteristics. SOLUTION: As an anode active substance, lithium manganate is used, and the bulk density of lithium manganate is to be 0.8-1.2 g/cm3. The thickness of the one side of an anode active substance mixture layer 12 from an aluminum foil 11 is to be 30-70 μm, and mixture density of the anode active substance mixture is to be 2.2-3.0 g/cm3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a non-aqueous electrolyte secondary battery in which a positive electrode active material mixture containing lithium manganate as an active material is applied to a positive electrode current collector. .

[0002]

2. Description of the Related Art Conventionally, in the field of rechargeable secondary batteries, aqueous batteries such as lead batteries, nickel-cadmium batteries, and nickel-hydrogen batteries have been the mainstream. However, due to global warming and exhausted fuel, electric vehicles (E
V) and hybrid vehicles that support a part of the drive with an electric motor are attracting attention.
Higher capacity and higher output secondary batteries have been required. As a power source meeting such a demand, a non-aqueous solution type lithium secondary battery having a high voltage has attracted attention.

In general, a carbon material is used as a negative electrode material of a lithium secondary battery. As the carbon material, an artificial carbon material such as artificial graphite such as natural graphite, flake, or lump, a graphite material such as mesophase pitch graphite, or a furan resin such as furfuryl alcohol is used. .
Graphite-based materials are characterized by low irreversible capacity, flat voltage characteristics and high capacity, but have the problem of poor cycle characteristics. An amorphous carbon material obtained by firing a synthetic resin has the characteristic that it has a capacity greater than the theoretical capacity value of graphite and has excellent cycle characteristics, but has the disadvantage that it has a large irreversible capacity and it is difficult to increase the capacity in batteries. There is.

On the other hand, a lithium transition metal oxide is used as a positive electrode material, and among them, lithium cobalt oxide is used because of its balance in capacity and cycle characteristics. However, there is a problem that the amount of resources of cobalt as a raw material is small and the cost is high. Lithium nickelate is also being studied from the viewpoint of increasing capacity, but there is a problem in safety at the time of overcharging or destruction. For this reason, lithium manganate, which is rich in resources and excellent in safety, is considered promising as a material for secondary batteries for electric vehicles and hybrid vehicles, and is being developed.

[0005]

However, batteries for electric vehicles and hybrid vehicles, especially batteries for hybrid vehicles, do not need to have high capacity.
There is a demand for high output performance for instantaneously operating a motor that assists the power of the engine and high input characteristics for regenerating energy when the vehicle stops. That is, it is necessary for the lithium secondary battery to have good short-time charge / discharge cycle characteristics with a large current value. Such a method of use is not found in conventional consumer lithium secondary batteries.

[0006] In view of the above-mentioned proposal, an object of the present invention is to provide a non-aqueous electrolyte secondary battery capable of improving pulse charge / discharge cycle characteristics.

[0007]

In order to solve the above problems, the present invention relates to a nonaqueous electrolyte secondary battery in which a positive electrode active material mixture containing lithium manganate as an active material is applied to a positive electrode current collector. The bulk density of the lithium manganate is 0.8
１．２1.2 g / cm ³ , the thickness of one side of the positive electrode active material mixture layer from the positive electrode current collector is 30 to 70 μm,
In addition, the mixture density of the cathode active material mixture is 2.2 to 3.0.
g / cm ³ . In the present invention, the bulk density of lithium manganate, the thickness of one surface of the positive electrode active material mixture layer from the positive electrode current collector, and the range of the mixture density of the positive electrode active material mixture can be limited to suppress a decrease in output due to a pulse cycle. As a result, the pulse charge / discharge cycle characteristics of the nonaqueous electrolyte secondary battery can be improved. In this case, the bulk density of lithium manganate was set to 1.0 g / cm ³
As described above, the thickness of one side of the positive electrode active material mixture layer is preferably 50 μm or less, and the mixture density is preferably 2.5 g / cm ³ or more.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a lithium secondary battery to which the present invention is applied will be described with reference to the drawings.

(Positive electrode) Bulk density 0.8 to 1.2 g / cm
³ lithium manganate (LiMn ₂ O ₄ ) powder 90 parts by weight, flaky graphite powder 5 parts by weight as a conductive agent and polyvinylidene fluoride (PVDF) 5 parts by weight as a binder were added, and a dispersion solvent was added thereto. Was added and kneaded to prepare a mixture slurry. As shown in FIG. 1A, this mixture slurry was applied to both surfaces of an aluminum foil 11 as a positive electrode current collector having a thickness of 20 μm. Thereafter, by drying and pressing, the thickness of one side of the positive electrode active material mixture layer 12 from the aluminum foil 11 (hereinafter, referred to as the mixture layer thickness) is 30 to 70 μm, and the mixture density is 2.2 to 3. .
The positive electrode 1 was adjusted to 0 g / cm ³ and cut to obtain a positive electrode 1 having a width of 60 mm and a length of 4000 mm.

(Negative Electrode) To 90 parts by weight of amorphous carbon powder, 10 parts by weight of polyvinylidene fluoride as a binder are added, and N-methylpyrrolidone as a dispersion solvent is added thereto and kneaded to prepare a mixture slurry. did. As shown in FIG. 1 (B), this mixture slurry was rolled into a rolled copper foil 21 having a thickness of 10 μm.
, And then dried and pressed to reduce the thickness of one side of the negative electrode active material mixture layer 22 from the rolled copper foil 21 to 70
μm and cut to 65 mm in width and 450 in length
A negative electrode 2 of 0 mm was obtained.

(Preparation of Battery) The positive electrode 1 and the negative electrode 2 prepared as described above were wound through a polyethylene separator having a thickness of 40 μm and through which lithium ions can pass to prepare an electrode group. This electrode group is φ40mm, height 80mm
And connected to an external terminal, and then 1 mol / liter of lithium hexafluorophosphate (LiPF ₆ ) is dissolved in a mixed organic solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC). The obtained electrolytic solution was injected to produce a lithium secondary battery.

[0012]

Next, lithium ion batteries of examples and comparative examples manufactured according to the above-described embodiment will be described. In the following examples and comparative examples, the fabrication of the negative electrode and the battery is the same as that of the above embodiment, and only a part of the positive electrode is different. Therefore, only different points from the positive electrode of the embodiment will be described.

Comparative Example 1 In Comparative Example 1, as shown in Table 1 below, lithium manganate powder having a bulk density of 0.7 g / cm ³ was used, the mixture layer thickness was 50 μm, and the mixture density was A lithium secondary battery was produced using a positive electrode having a density of 2.5 g / cm ³ .

[0014]

[Table 1]

(Example 1) In Example 1, as shown in Table 1, except that lithium manganate powder having a bulk density of 0.8 g / cm ³ was used, a lithium secondary battery was produced in the same manner as in Comparative Example 1. A battery was manufactured.

(Example 2) In Example 2, as shown in Table 1, except that lithium manganate powder having a bulk density of 1.0 g / cm ³ was used, a lithium secondary battery was prepared in the same manner as in Comparative Example 1. A battery was manufactured.

Example 3 In Example 3, as shown in Table 1, except that lithium manganate powder having a bulk density of 1.2 g / cm ³ was used, a lithium secondary battery was manufactured in the same manner as in Comparative Example 1. A battery was manufactured.

Comparative Example 2 In Comparative Example 2, as shown in Table 1, except that lithium manganate powder having a bulk density of 1.4 g / cm ³ was used, a lithium secondary battery was prepared in the same manner as in Comparative Example 1. A battery was manufactured.

Comparative Example 3 In Comparative Example 3, as shown in Table 1, a lithium manganate powder having a bulk density of 1.0 g / cm ³ was used, and the thickness of the mixture layer was changed to 15 μm. A lithium secondary battery was produced in the same manner as in Example 1.

Example 4 In Example 4, as shown in Table 1, a lithium secondary battery was produced in the same manner as in Example 2 except that the thickness of the mixture layer was 30 μm.

Example 5 In Example 5, as shown in Table 1, a lithium secondary battery was manufactured in the same manner as in Example 2, except that the thickness of the mixture layer was 70 μm.

Comparative Example 4 In Comparative Example 4, as shown in Table 1, a lithium secondary battery was produced in the same manner as in Example 2 except that the thickness of the mixture layer was 90 μm.

Comparative Example 5 In Comparative Example 5, as shown in Table 1, a lithium secondary battery was produced in the same manner as in Example 2 except that the mixture density was 2.0 g / cm ³ . .

Example 6 In Example 6, as shown in Table 1, a lithium secondary battery was produced in the same manner as in Example 2, except that the mixture density was 2.2 g / cm ³ . .

Example 7 In Example 6, as shown in Table 1, a lithium secondary battery was produced in the same manner as in Example 2 except that the mixture density was 3.0 g / cm ³ . .

Comparative Example 6 In Comparative Example 6, as shown in Table 1, a lithium secondary battery was produced in the same manner as in Example 2 except that the mixture density was 3.5 g / cm ³ . .

(Test) Next, a pulse cycle test was performed on each of the batteries of the example and the comparative example, and the output was measured.

<Pulse Cycle Test> A high load current of about 50 A was supplied for about 5 seconds in both the charging direction and the discharging direction, and the test was continuously repeated for about 30 seconds per cycle including a pause. At 500,000 cycles, the output of each battery was measured.
The pulse cycle test was performed in an atmosphere at 50 ± 3 ° C.

<Measurement of Output> The battery was charged under a constant voltage control of 4.0 V, and was charged at a predetermined current of 10 A, 50 A, and 100 A.
Discharge was performed for 0 seconds, and the voltage at 10 seconds was recorded. The output ((W): Ia × 2.5) was defined as the output of the battery from the current value (Ia) at which a straight line plotting the voltage against the current value reached 2.5 V.

Table 2 shows the results of the pulse cycle test for each battery. Table 2 shows a pulse cycle of 5 for each battery.
The output at the time when the operation was performed 100,000 times is represented by an output ratio with the battery of Comparative Example 1 being 100.

[0031]

[Table 2]

(Evaluation) As shown in Tables 1 and 2, the bulk density of lithium manganate was 0.8 to 1.2 g / cm ^3.
In the batteries of Examples 1 to 3, the deterioration by the pulse cycle test was small. On the other hand, as in the battery of Comparative Example 1, if the bulk density is 0.7 g / cm ³ and 0.8 g / cm ³ less than, when performing a pulse cycle test, the lithium manganate powder particles in the positive electrode are entangled Since a large current is concentrated only on a portion having good conductivity, deterioration proceeds, and as a result, output is reduced. Conversely, the bulk density was 1.4 g / cm ³ and 1.2 g / c as in the battery of Comparative Example 2.
larger than m ^3, coarse particles are mixed, the reaction in the interior of the lithium manganate powder is not involved, degradation due to the pulse cycle test is large, resulting in an output reduction.

Further, when the thickness of the mixture layer is 30 μm to 70 μm as in the batteries of Examples 4 and 5, deterioration by the pulse cycle test is small. On the other hand, when the thickness of the mixture layer is smaller than 15 μm and 30 μm as in the battery of Comparative Example 3, the amount of lithium manganate that reacts per area decreases,
Since the load of lithium manganate increases with respect to a large current, deterioration occurs in the pulse cycle test, and the output decreases. Conversely, when the thickness of the mixture layer is larger than 90 μm and 70 μm as in the battery of Comparative Example 4, the distance from the aluminum foil is too large, and the reaction speed is reduced.
Output drops.

Further, as in the batteries of Examples 6 and 7,
2.2 to 3.0 g / cm³Then, pulse cycling
Less deterioration due to test. On the other hand, the battery of Comparative Example 5
2.0g / cm³And 2.2 g / cm³Yo
Lower, the conductivity in the positive electrode active material mixture layer decreases
Therefore, current concentrates only on the part where
The part deteriorates due to the cycle test, and the whole positive electrode
Causes a decrease in output. On the other hand, like the battery of Comparative Example 6,
The agent layer density is 3.5 g / cm³And 3.0 g / cm ³Higher
In this case, the amount of retained electrolyte is too small,
The response is hindered and the output is reduced.

Among the batteries of the examples, lithium manganate has a bulk density of 1.0 to 1.2 g / cm ³ , a mixture layer thickness of ³⁰ to 50 μm, and a mixture density of 2.5 to 3.0.
The batteries of Examples 2, 3, 4, and 7 in the range of g / cm ³ exhibited preferable pulse charge / discharge cycle characteristics.

As described above, in the lithium secondary battery of this embodiment, the bulk density of lithium manganate on the positive electrode side is 0.8 to 1.2 g / cm ³ , and the thickness of the mixture layer is 30 to 70 μm.
m, and the mixture density was 2.2 to 3.0 g / cm ³ ,
The pulse charge / discharge cycle characteristics can be improved.

In the present embodiment, the positive electrode compounding ratio has been described as being constant for the sake of simplicity, but the same effect can be obtained even if the positive electrode compounding ratio is changed within the range of ± 20%.
Further, in the present embodiment, the types of the conductive agent, the binder, the salt and the solvent of the electrolytic solution have been exemplified, but the present invention is not limited thereto, and various conductive agents, binders, and electrolytic solutions may be used. Can be.

Further, in this embodiment, an example was described in which amorphous carbon was used as the active material of the negative electrode. However, graphite or another material into which lithium ions can be inserted and desorbed may be used. . And in the present embodiment, the lithium secondary battery using a cylindrical can as a battery container is exemplified, but the present invention is not affected by the outer diameter of the battery can or the shape of the winding group,
The present invention is also applicable to rectangular, triangular and other polygonal lithium secondary batteries.

[0039]

As described above, according to the present invention,
Since the bulk density of lithium manganate, the thickness of one side of the positive electrode active material mixture layer from the positive electrode current collector, and the range of the mixture density of the positive electrode active material mixture were limited, it was possible to suppress output reduction due to pulse cycles. In addition, it is possible to obtain an effect that the pulse charge / discharge cycle characteristics of the nonaqueous electrolyte secondary battery can be improved.

[Brief description of the drawings]

FIG. 1A is a cross-sectional view in the thickness direction of a positive electrode,
(B) is a sectional view in the thickness direction of the negative electrode.

[Explanation of symbols]

 Reference Signs List 1 positive electrode 11 aluminum foil (positive electrode current collector) 12 positive electrode active material mixture layer 2 negative electrode

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Koji Higashimoto 2-8-7 Nihonbashi Honcho, Chuo-ku, Tokyo Inside Shin-Kobe Electric Machinery Co., Ltd. (72) Kensuke Hironaka 2-87 Nihonbashi Honcho, Chuo-ku, Tokyo No. Shin Kobe Electric Co., Ltd. F term (reference) 5H029 AJ02 AJ05 AK03 AL06 AM03 AM05 AM07 BJ02 BJ14 HJ04 HJ08 HJ09 5H050 AA02 AA07 BA17 CA09 CB07 FA05 HA04 HA08 HA09

Claims (2)

[Claims] 1. A non-aqueous electrolyte secondary battery in which a positive electrode active material mixture containing lithium manganate as an active material is coated on a positive electrode current collector, wherein the lithium manganate has a bulk density of 0.8.
１．２1.2 g / cm ³ , the thickness of one side of the positive electrode active material mixture layer from the positive electrode current collector is 30 to 70 μm,
In addition, the mixture density of the cathode active material mixture is 2.2 to 3.0.
g / cm ³ , a non-aqueous electrolyte secondary battery. 2. The bulk density of the lithium manganate is 1.0 g / cm ³ or more, the thickness of one side of the positive electrode active material mixture layer is 50 μm or less, and the mixture density is 2.5 g. / Cm ³ or more.
3. The non-aqueous electrolyte secondary battery according to 1.