JPH01279578A - Non-aqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To make the effective electrode area larger and improve the energy density by exposing a copper foil surface at the outermost peripheral portion of a negative electrode material. CONSTITUTION:A baked organic substance forming a negative electrode material is applied to both sides of a copper foil 5, but at a particular part of the copper foil 5, corresponding to the outermost peripheral portion thereof when it is used as a winding member, said substance is applied to only one side of the copper foil 5. Therefore, at this part 5a, the copper foil is exposed. Accordingly, the negative electrode active material in the outermost peripheral portion of the winding member, which is not contributing to the discharge capacity, is removed and effective utilization of the interior volume of the battery can be enabled. Thus, the number of turns of the winding member and the effective electrode area are increased and a higher energy density can be achieved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a non-aqueous electrolyte secondary battery used as a power source for driving various electrical devices.

[Summary of the invention]

The present invention provides a so-called jelly roll type nonaqueous electrolyte secondary battery in which a wound body consisting of a negative electrode material, a positive electrode material, and a separator is housed in a battery can, in which a copper foil surface of the outermost portion of the negative electrode material is provided. By exposing this, the effective electrode area can be increased, and a battery with high energy density and long discharge duration can be obtained.

[Conventional technology]

Conventionally, nickel-cadmium storage batteries, lead-acid batteries, silver oxide-zinc storage batteries, and the like, which use an aqueous electrolyte, have been known as high-output secondary batteries. These aqueous electrolyte secondary batteries are high-output batteries with low internal resistance and can withstand large currents, but the electrolyte easily decomposes above a certain voltage, so they generally have low voltage and low energy density. There are disadvantages such as low

On the other hand, non-aqueous electrolyte secondary batteries have excellent features such as being able to increase electromotive force and having high energy density. As electrode materials for such non-aqueous electrolyte secondary batteries, electrode active materials that utilize intercalation or doping phenomena of layered compounds, which are essentially different reaction types from aqueous storage batteries, are attracting attention.

These new electrode active materials are expected to have extremely excellent charge/discharge cyclability because they do not cause complex chemical reactions during electrochemical reactions during charging and discharging.For example, electrode active materials that utilize doping phenomena are When an organic fired body is used as the material, it is said that excellent performance is exhibited when such an organic fired body is used. In particular, when such a fired organic material is used as a negative electrode active material, it is excellent in cycle life characteristics, self-discharge characteristics, and current efficiency during charging and discharging.

[Problem to be solved by the invention]

However, even in non-aqueous electrolyte secondary batteries that use organic calcined bodies as negative electrode active materials, higher energy density and
It has been pointed out that a long discharge duration is necessary. In principle, this requirement can be met by increasing the electrode area. However, in a jelly roll type non-aqueous electrolyte secondary battery, the effective volume within the battery can is limited, so it is difficult to increase the output of the battery by increasing the electrode area.

The present invention was proposed in view of the above circumstances, and an object of the present invention is to provide a non-aqueous electrolyte secondary battery with a larger effective electrode area and higher energy density.

[Means for Solving the Problems] The inventors of the present invention have conducted various studies to achieve the above-mentioned objectives, and as a result, have come to the following knowledge.

That is, in general, in a non-aqueous electrolyte secondary battery, M4 foil is used for the negative electrode current collector, aluminum foil or the like is used for the positive electrode current collector, and both the negative electrode current collector and the positive electrode current collector are coated on both sides of the current collector. An active material is deposited on the electrode to form a negative electrode material and a positive electrode material, respectively. A wound body in which the negative electrode material and the positive electrode material are spirally laminated and wound with a separator in between is housed in a battery can with the negative electrode positioned at the outermost periphery. At this time, in the outermost portion, only the active material on one side of the current collector of the negative electrode faces the positive electrode through the separator, and therefore, the reaction occurs on only one side of the negative electrode. In other words, since the opposite side of the negative electrode faces the battery can, active material that does not contribute to discharge capacity is placed inside the battery can, making it impossible to achieve higher energy density.In other words,
It is thought that if the active material that does not contribute to the discharge capacity is eliminated, the volume of the battery can can be used effectively.

The present invention was completed based on such knowledge, and a negative electrode material made of a fired organic material coated on both sides of copper foil is wound together with a positive electrode material through a separator, and is placed inside a battery can. The nonaqueous electrolyte secondary battery is housed in a non-aqueous electrolyte secondary battery, and is characterized in that the outermost peripheral portion of the negative electrode material has a copper foil surface exposed.

The negative electrode of the nonaqueous electrolyte secondary battery according to the present invention is a current collector! Li ff! It is made by applying an organic fired material, which is a negative electrode active material, to both sides of i.

The current collector is required to have high conductivity, high mechanical strength, and not be alloyed with the lithium ions to be doped, and copper foil is suitable.

For example, A2, Mg, Zn, etc. may become alloyed and may not function as a current collector. Alternatively, nickel, stainless steel, etc. have low conductivity and must be made somewhat thick, which is disadvantageous in terms of battery capacity.

In addition, when copper foil is used for the current collector, its thickness is 7 to 30
It is preferable to use μ intestine. If the thickness of the copper foil is less than 7μ, it is difficult to use due to mechanical strength problems;
If it exceeds -, the battery energy density decreases.

The fired organic material applied to the current collector is obtained, for example, by thermal decomposition or firing carbonization of various organic compounds. An example of such an organic fired material is vapor grown carbon fiber. The vapor-grown carbon fiber is a carbon material obtained by vapor-phase thermal decomposition of carbon compounds such as benzene, methane, and carbon oxide in the presence of a transition metal catalyst, etc., and can be obtained by a known method similar to this. Generally, it is obtained in the form of fibers, that is, carbon fibers, by such a method, but it may be used as it is in the form of fibers, or it may be used in the form of pulverized powder. Another example is pitch-based carbon fiber. - Examples include petroleum pitch, asphalt pitch,
Pitch obtained by thermal decomposition of petroleum and coal such as coal tar pitch, crude oil cracking pinch, and petroleum sludge pitch, pitch obtained by thermal decomposition of high molecular weight polymers, and pitch obtained by thermal decomposition of organic low molecular compounds such as tetrabenzophenazine. Examples include the pitch that is used. Specific examples of such pitch-based calcined carbides include needle coke and the like. Still another example is a calcined carbide of a polymer containing acrylonitrile as a main component.

These fired organic substances are applied to both sides of the copper foil, but especially to the part corresponding to the outermost periphery of the copper foil when it is made into a rolled body, one side of the copper foil (inner part) is coated. Apply only. Therefore, the copper foil will be exposed in this part. It is desirable that the copper foil be exposed for one circumference of the outermost circumference, but it is not necessarily necessary to expose the copper foil for one circumference.
Some effect can be expected.

On the other hand, for the positive electrode, a known positive electrode active material mainly containing lithium is used, such as LiMnzO4, lithium cobalt composite oxide, and the like.

The electrolyte is not particularly limited, but includes, for example, propylene carbonate, ethylene carbonate,
1,2-dimethoxyethane, 1,2-jethoxyethane, T-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3 dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, methylsulfolane, acetonitrile, pro- A single solvent such as pionitrile or a mixed solvent of two or more can be used.

Any conventionally known electrolyte can be used,
LiCl0. , LiAsF6, LiPF6, LiBF4
, LiB(CillsL, LiCl, LiBr, C
One or two of ToSOsLi, CFx5OsLi, etc.
A mixture of more than one species can be used.

Further, the separator may be made of any conventionally known insulating material, such as polypropylene, polytetrafluoroethylene, polyethylene, polyacetal, etc.

[Effect]

According to the non-aqueous electrolyte secondary battery of the present invention, by exposing the copper foil surface of the outermost part of the negative electrode material, the negative electrode active material in the outermost part of the wound body that does not contribute to the discharge capacity is removed. This makes it possible to effectively utilize the internal volume of the battery can. As a result, compared to a wound body using a negative electrode material made by coating the entire surface of both sides of copper foil with an organic fired body, the number of windings of the wound body can be increased, the effective electric scratching area can be increased, and the energy consumption can be increased. Density can be increased.

〔Example〕

Hereinafter, specific examples of the non-aqueous electrolyte secondary battery to which the present invention is applied are as follows.
An i-embodiment will be described with reference to the drawings.

This example uses a so-called jelly-roll type non-container in which a negative electrode material made of a fired organic material coated on both sides of copper foil is wound together with a positive electrode material through a separator and housed in a battery can. It is suitable for water electrolyte secondary batteries.

To create the above-mentioned non-aqueous electrolyte secondary battery, first, 91 parts by weight of lithium cobalt composite oxide is added as a positive electrode active material.
A positive electrode paste was prepared by mixing 6 parts by weight of graphite as a conductive agent, 3 parts by weight of polyvinylidene fluoride as a binder, and wet-mixing N-methyl-2-pyrrolidone as a dispersant.

This positive electrode paste was uniformly applied to both sides of an aluminum foil having a thickness of 20 μm as a positive electrode current collector, and dried, and then a positive electrode sheet having a thickness of 180 μm was produced using a roll press. However, an exposed end portion of the positive electrode current collector was provided at the positive electrode mounting portion at the end of the positive electrode sheet, the positive electrode paste not being coated on both surfaces. The width of the positive electrode sheet prepared above is 43Ml.
11. It was cut into a length of 290 m+*, and an aluminum foil positive electrode lead (2) was connected to the exposed end portion of the positive electrode current collector by ultrasonic welding to produce a positive electrode (1).

Next, as a negative electrode active material, 90 parts by weight of carbon was mixed with 10 parts by weight of polyvinylidene fluoride, and N-methyl-2-pyrrolidone was wet-mixed as a dispersant to prepare a negative electrode paste. This negative electrode pace l
−(4), (4) is a negative electrode current collector with a thickness of 10 μm
#i4 foil (5) was uniformly coated on both sides and dried to prepare a negative electrode sheet. However, a copper foil surface exposed portion (5a) corresponding to the area of the outermost peripheral portion of the wound body was provided at the negative electrode lead attachment portion at the end of the negative electrode sheet. The negative electrode sheet produced above was cut to a width of 43 m+ and a length of 285 mm, and a negative electrode lead (6) made of a nickel material was connected to the exposed copper foil surface portion (5a) of the negative electrode current collector by ultrasonic welding. , and was used as a negative electrode (3).

The electrode produced by the above method was wound with a winder through a polypropylene separator (7) having a thickness of 25 μm to form a wound body. Here, the copper foil surface exposed portion (5a
) was positioned at the outermost periphery of the wound body. A bottom insulating plate (8) was attached to the wound body, which was housed in a nickel-plated battery can (10), and the negative electrode lead (6) was spot welded to the bottom of the battery can. The battery can (10) corresponds to a negative electrode can.

Next, the 'r! 1. After inserting the upper insulating plate (9) into the rolled body inside the can (10) and inserting the Gaskera l-(11), the positive electrode lead (2) and the aluminum safety valve (12) are ultrasonically welded. Then, the battery can (1O) was impregnated with a non-aqueous electrolyte, and a lid (13) was placed on the safety valve (12). The safety valve (1) is ultrasonically welded to the positive electrode lead (2).
2) will be in contact with each other. Therefore, the lid (13)
is the positive electrode can of the battery.

As described above, a jelly roll type non-aqueous electrolyte secondary battery having an outer diameter of 14+u+ and a height of 50 fi 1 g was assembled.

Comparative Example Battery B was prepared as a comparative example of the reference example (Example Battery A). Comparative Example Battery B was prepared using a jelly roll type non-aqueous electrolyte solution in the same manner as in the previous example, except that a negative electrode material in which the negative electrode active material was evenly coated on the surface of the outermost copper foil was used. It was manufactured as a secondary battery. In Comparative Example Battery B, the negative electrode active material was evenly applied to the outermost steel foil surface of the negative electrode material, so the negative electrode had a width of 4311 mm and a length of 275 mm, and the positive electrode had a width of 43 mm and a length of 280 mm. Ta.

After battery assembly for both Example Battery A and Comparative Example Battery B,
Discharge was performed at a constant current of 55+*A until the final voltage reached 2.5V. Table 1 shows the discharge duration until the above conditions are met for Example Battery A and Comparative Example Battery B, and the Example Battery A.
and shows the energy density of Comparative Example Battery B.

(See the margins below) Table 1 From Table 1, it can be seen that, compared to Comparative Example Battery B, Example Battery A showed an increase in discharge duration of 24 minutes, and an increase in energy density of 20 WH/f.

〔Effect of the invention〕

As is clear from the above description, in the non-aqueous electrolyte secondary battery of the present invention, the outermost copper foil surface of the negative electrode material is exposed, so the electrode thickness at the outermost peripheral part of the negative electrode material can be reduced. Therefore, the volume inside the battery can can be used effectively. Therefore, according to the present invention, it is possible to increase the number of windings of the wound body and increase the effective electrode area, and to provide a nonaqueous electrolyte secondary battery that has a high energy density and a long discharge duration. is possible.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing a negative electrode of a non-aqueous electrolyte secondary battery according to the present invention, and FIG. 2 is a sectional view thereof. FIG. 3 is a cross-sectional view showing the wound body housed in the battery can with the outermost periphery opened. FIG. 4 is a partially exploded external perspective view of a configuration example of a cylindrical non-aqueous electrolyte secondary battery. 1... Kingship 3... Negative electrode 4... Negative electrode paste 5... Copper foil 5a... Copper foil surface exposed portion 7... Separator 10... ...Battery can Figure 1 Figure 2! Figure 3

Claims (1)

[Scope of Claims] A nonaqueous electrolyte secondary battery in which a negative electrode material made of a fired organic material coated on both sides of a steel foil is wound together with a positive electrode material via a separator and housed in a battery can. , A non-aqueous electrolyte secondary battery characterized in that a copper foil surface is exposed at the outermost periphery of the negative electrode material.