JP2001210382A - Cylindrical lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cylindrical lithium secondary battery of a high power output density which is superior in input and output characteristics. SOLUTION: Winding group W that has an opposing length A of 3420 mm between a positive electrode and negative electrode is fabricated, and a cylindrical lithium secondary battery 20 is assembled. The diameter of the winding group is 38 mm (the value of opposing length A between electrodes/group diameter B of electrode groups W) is 90. If this value becomes smaller than 90, the current density per unit area is elevated, and because facing area of electrode becomes small, current density per area rises, and battery resistance increases, and if this value becomes greater than 110, the load charge one of the active substance becomes greater because the amount of active substance per unit area decreases, and this results in the reduction of output.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cylindrical lithium secondary battery, and more particularly, to a positive electrode having a positive electrode mixture containing a positive electrode active material applied to both surfaces of a positive electrode current collector, and a negative electrode current collector. A cylindrical shape including a negative electrode coated with a negative electrode mixture containing a negative electrode active material into and out of which lithium ions can be inserted and removed by charging and discharging, and a winding group obtained by winding the negative electrode through a separator through which the lithium ions can pass. It relates to a lithium secondary battery.

[0002]

2. Description of the Related Art At present, small lithium ion secondary batteries for consumer use are widely used as typical batteries among cylindrical secondary batteries. This lithium ion secondary battery is mainly used as a power source for portable devices such as a VTR camera, a notebook computer, and a mobile phone, taking advantage of its high energy density.

On the other hand, in recent years, environmental problems have become increasingly important, and the development of low-emission vehicles has been promoted in the automobile industry and some of them have been put into practical use. Such low-emission vehicles include an exhaust gas-free electric vehicle (EV) having a battery as a sole power source, and a hybrid electric vehicle (HE) having both an internal combustion engine and a battery.
V).

[0004] Batteries serving as power supplies for EVs and HEVs include:
High energy density and high output characteristics are required.
In a power supply for EV use, there has been a need for an unprecedented battery characteristic that the high input / output repetition characteristic in a short time is good. As a battery suitable for these EV and HEV applications, a lithium ion battery has attracted attention.

[0005]

However, simply increasing the size of a conventional small-sized battery for consumer use requires only HEV.
Cannot satisfy the input / output characteristics required by
In addition, during a pulse cycle due to a large current, current concentration occurs on one active material particle where the current easily flows, and this is repeated, thereby inactivating the active material itself due to structural destruction and deteriorating input / output characteristics. Was causing.

In view of the above problems, an object of the present invention is to provide a cylindrical lithium secondary battery having a high output density and excellent input / output characteristics.

[0007]

Means for Solving the Problems To solve the above problems, the present invention relates to a positive electrode in which a positive electrode mixture containing a positive electrode active material is coated on both surfaces of a positive electrode current collector, and a negative electrode current collector. A cylindrical lithium including a negative electrode coated with a negative electrode mixture containing a negative electrode active material into which lithium ions can be inserted and removed by charge and discharge, and a winding group obtained by winding the negative electrode through a separator through which the lithium ions can pass. In the secondary battery, a ratio of a facing length of the cathode and the anode to a group diameter of the wound group is 90 or more and 110 or less.

In order to obtain high input / output characteristics, by increasing the ratio of the electrode length to the group diameter of the wound group having a fixed volume, the area where the positive electrode and the negative electrode face each other is increased. And the battery resistance can be reduced. At this time, in order to increase the electrode area, it is necessary to reduce the active material application amount per unit area.
However, when the electrode area is excessively increased, the amount of the active material applied is reduced. Therefore, even if the current density per unit area is the same, the current load applied to each active material is increased, and the reaction resistance of the electrode is increased. Therefore, in the present invention, the ratio of the facing length of the positive electrode and the negative electrode to the group diameter of the wound group is set to 90 or more and 110 or less to optimize the electrode length with respect to the group diameter of the electrode group, thereby achieving high input / output. This was a cylindrical lithium secondary battery. Such a battery can ensure a power density of 3.2 kW / dm ³ or more, and can have a high power density.

[0009]

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

<Preparation of Electrode Plate> As shown in FIG. 1, a cylindrical lithium ion battery 20 of the present embodiment comprises a positive electrode current collector W
1, a strip-shaped positive electrode having both surfaces coated with a positive electrode mixture W2, and a strip-shaped negative electrode having both surfaces of a negative electrode current collector W3 coated with a negative electrode mixture W4, with a cross-section spiral interposed therebetween through a band-shaped separator W5. A winding group W is provided.

The positive electrode current collector W1 is an aluminum foil having a thickness of 20 μm. The positive electrode mixture W2 has an average particle size of about 15 μm.
Lithium manganate (LiMn ₂
O ₄ ), graphite (average particle size of about 3 μm) and amorphous carbon (average particle size of about 50
nm) and the binder polyvinylidene fluoride (PVD)
F) as a constituent material.

To prepare the positive electrode mixture W2, lithium manganate, a carbon material (graphite and amorphous carbon) and P
VDF and VDF are mixed at a predetermined mixing ratio, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) serving as a dispersion solvent is added thereto.
Knead and disperse thoroughly to form a slurry. The kneaded material is applied to both surfaces of the positive electrode current collector W1 by a roll-to-roll transfer (roll-to-roll transfer) so as to have a substantially uniform and uniform thickness, dried, and then pressed. The mixture is compressed until the agent density becomes about 2.5 g / cm ³ to obtain a mixture layer of the positive electrode mixture W2. By controlling the coating amount of the positive electrode mixture W2, the thickness of the mixture layer was controlled to a predetermined length.

On the other hand, the negative electrode current collector W3 is a copper foil having a thickness of 10 μm. The negative electrode mixture W4 is composed of amorphous carbon as a negative electrode active material capable of inserting and removing lithium ions with lithium ions as an electrode reactive species, and PVDF as a binder.
And is a constituent material.

To prepare the negative electrode mixture W4, amorphous carbon and PVDF are mixed at a weight ratio of 90:10, and an appropriate amount of NMP serving as a dispersion solvent is added thereto, and the mixture is thoroughly kneaded. Disperse and slurry. This kneaded material is applied to both surfaces of the negative electrode current collector W3 by roll-to-roll transfer so as to have a substantially uniform and the same thickness, dried, and then pressed to have a mixture density of about 1.0 g / g. It compresses until it becomes cm < ³ >, and obtains the mixture layer of negative electrode mixture W4. The thickness of the mixture layer was controlled by controlling the coating amount of the negative electrode mixture W4, and a negative electrode having a predetermined length was obtained. In this embodiment, Carbotron P (average particle size: 10 μm) manufactured by Kureha Chemical Industry Co., Ltd. was used as the amorphous carbon.

<Preparation of Battery> The battery was wound so that a separator W5 made of a microporous polyethylene film having a thickness of 40 μm and capable of passing lithium ions was disposed between the positive electrode and the negative electrode around the winding core 17. A winding group W was prepared. The facing length of the positive electrode and the negative electrode of the winding group W is 342
0 mm to 4180 mm, and the group diameter of the wound group W is 38
mm. Therefore, assuming that the electrode (positive electrode and negative electrode) facing length is A and the group diameter of the electrode group W is B, in the present embodiment,
The value of (electrode opposing length A) / (group diameter B of electrode group W) (X value to be described later) is 90 to 110.

A positive current collecting ring 10 and a negative current collecting ring 11 were arranged at both ends of the wound group W, and each current collector was welded to the periphery of the current collecting ring. The positive current collecting ring 10 and the negative current collecting ring 11 are fixed to the end of the core 17 via the positive current collecting ring support 8 and the negative current collecting ring support 9, respectively. The winding group W with a current collecting ring is coated with an insulating coating 15 of, for example, polyimide or the like, and inserted into the battery can 16 so that the negative electrode current collecting ring 11 side is the can bottom side. The previously welded negative electrode lead plate 14 is welded to the battery can 16. At this time, the negative electrode current collecting ring spacer 7 for fixing the winding group W is disposed between the negative electrode current collecting ring 11 and the battery can 16. In addition, the positive electrode current collecting ring 10
A positive electrode lead plate B13 is previously welded to the upper surface.

On the other hand, an upper lid composed of an upper lid cap 1, an upper lid case 2, a safety valve 3, and a valve retainer 4 is separately manufactured.
The positive electrode lead plate A12 is attached to the upper lid case 2 by welding.

A winding group W is provided on the upper edge of the positive electrode current collection ring 10.
The positive electrode current collecting ring spacer 6 for fixing is disposed. The free ends of the positive electrode lead plate A12 and the positive electrode lead plate B13 are welded to each other to connect the upper lid and the winding group W with the current collecting ring. In this state, an electrolytic solution obtained by dissolving 0.8 mol / liter of lithium hexafluorophosphate (LiPF ₆ ) as a solute in a mixed solution of 40% by volume of ethylene carbonate (EC) and 60% by volume of dimethyl carbonate was used as an electrolyte. About 50 ml is poured into the battery can 16. After that, the upper lid is placed above the battery can 16 via the insulating gasket 5 and caulked, whereby the cylindrical lithium secondary battery 20 is assembled.

(Example) Next, according to the present embodiment, the group diameter B of the wound group W is fixed at 38 mm and the facing length A of the electrodes (positive electrode and negative electrode) is variously changed. The battery will be described in detail. Note that a battery of a comparative example manufactured for comparison with the battery of the example is also described.

<Example 1> As shown in Table 1 below, in Example 1, a winding group W having an electrode opposing length A of 3420 mm was prepared, and a cylindrical lithium secondary battery 20 (hereinafter referred to as Example 1). 1
Battery. ) Assembled. For the sake of convenience, the value of (electrode facing length A) / (electrode group W diameter B) is now expressed as X
In this case, the X value in this embodiment is 90.

[0021]

[Table 1]

<Examples 2 to 4> As shown in Table 1, in Example 2, the opposing length A of the electrode was 3,800 mm, in Example 3, the opposing length A of the electrode was 3,990 mm, and in Example 4, the opposing length of the electrode was 3,990 mm. Winding groups W each having a length A of 4180 mm were prepared, and the cylindrical lithium secondary batteries 20 (hereinafter referred to as Example 2) were prepared.
4 batteries. ) Assembled. The X values of the batteries of Examples 2 to 4 are 100, 105, and 110, respectively.

<Comparative Examples 1 and 2> As shown in Table 1, in Comparative Example 1, the winding group W having the electrode facing length A of 3230 mm, and in Comparative Example 2 having the electrode facing length A of 4560 mm, respectively. Then, a cylindrical lithium secondary battery (hereinafter, referred to as batteries of Comparative Examples 1 and 2) was assembled. The X values of the batteries of Comparative Examples 1 and 2 are 85 and 115, respectively.

(Test) Next, the following output density measurement test was carried out for each of the batteries of the example and the comparative example.

<Contents of power density measurement test>
4.2V at the current value (1C) that can be discharged in time
Under constant voltage control, the battery was charged for 3 hours, and the battery was fully charged. The fully charged battery was discharged at current values of 10 A, 30 A, and 90 A for 5 seconds, respectively, and the battery voltage at 5 seconds was measured. A straight line plotting the voltage against the current value is 2.
From the current value (Ia) reaching 7 V, the output ((W) = Ia)
× 2.7). The measurement was performed in an atmosphere of 25 ± 2 ° C. The output density is a value obtained by dividing the obtained output by the weight of the battery.

(Test Results and Evaluation) Table 2 below shows the output density (kW / dm ³ ) of each battery when the X value was variously changed.
The calculation results of are shown below.

[0027]

[Table 2]

As shown in Table 2, the batteries of Examples 1 to 4 in which the X value was 90 to 110 were 3.2 kW / dm.
A power density of ³ or more could be obtained. In contrast, X
With the batteries of Comparative Examples 1 and 2 having values outside the range of 90 to 110, a large output density cannot be obtained. Therefore, in order to obtain a cylindrical lithium secondary battery having a high output density with excellent input / output characteristics, the X value, that is, the value of (electrode facing length A) / (electrode group W group diameter B) should be 90 to 90%. It turns out that it needs to be in the range of 110.

The reason why the output density of the batteries of Comparative Examples 1 and 2 is small is that when the X value is smaller than 90, the facing area of the electrodes is reduced, so that the current density per area is increased and the battery resistance is reduced. When the value X increases to more than 110, the current density per unit area decreases, but the amount of active material per unit area decreases. Therefore, the load on each active material increases, and the output decreases. By inviting.

In this embodiment, the wound group W having a group diameter of 38 mm has been exemplified. However, the group diameter is not limited to 38 mm.
The facing length of the electrodes is not limited to the illustrated length, and the X value described above may be in the range of 90 to 110.

In this embodiment, lithium manganate is exemplified as the positive electrode active material. However, any transition metal oxide such as Co, Ni, Mo, V, Fe, Nb, into which lithium ions can be inserted and desorbed, can be used. It may be a composite oxide containing Mn. Further, a material in which the position of lithium or metal ion in the crystal is replaced or doped with an element such as Mg, Cr, or Fe may be used.

Further, in this embodiment, P is used as the binder.
VDF is exemplified, but as a binder other than the exemplified,
Teflon, polyethylene, polystyrene, polybutadiene, butyl rubber, nitrile rubber, styrene / butadiene rubber, polysulfide rubber, nitrocellulose, cyanoethylcellulose, various latexes, acrylonitrile, vinyl fluoride, vinylidene fluoride, propylene fluoride, chloroprene fluoride, etc. A polymer and a mixture thereof may be used.

Further, in this embodiment, amorphous carbon is used as the negative electrode active material, but graphite or other material into which lithium ions can be inserted and desorbed may be used.

[0034]

As described above, according to the present invention,
The ratio of the facing length of the positive electrode and the negative electrode to the group diameter of the wound group is 9
Since it is 0 or more and 110 or less, a cylindrical lithium secondary battery having high output density and excellent in input / output characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a cylindrical lithium secondary battery according to an embodiment to which the present invention can be applied.

[Explanation of symbols]

Reference Signs List 20 cylindrical lithium ion battery (non-aqueous electrolyte secondary battery) W Winding group W1 Positive electrode current collector W2 Positive electrode mixture W3 Negative electrode current collector W4 Negative electrode mixture W5 Separator

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Katsunori Suzuki 2-8-7 Nihonbashi Honcho, Chuo-ku, Tokyo Inside Shin-Kobe Electric Machinery Co., Ltd. (72) Kensuke Hironaka 2-87 Nihonbashi Honcho 2-chome, Chuo-ku, Tokyo F-term (reference) in Shin-Kobe Electric Co., Ltd. 5H029 AJ01 AK03 AL06 AL07 AM03 AM05 AM07 BJ02 BJ14 CJ22 DJ04 DJ07 HJ03 HJ16

Claims (2)

[Claims] 1. A positive electrode in which a positive electrode mixture containing a positive electrode active material is applied to both surfaces of a positive electrode current collector, and a negative electrode active material into which lithium ions can be inserted and removed by charging and discharging on both surfaces of a negative electrode current collector. A negative electrode coated with a negative electrode mixture, and a cylindrical lithium secondary battery including a winding group wound through a separator through which the lithium ions can pass, wherein the positive electrode and the negative electrode with respect to the group diameter of the winding group Wherein the ratio of the opposing lengths is 90 or more and 110 or less. 2. The cylindrical lithium secondary battery according to claim 1, wherein the power density is 3.2 kW / dm ³ or more.