JPH11233148A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress collecting resistance in a low level even in the case of a long electrode, and to provide high output. SOLUTION: At least either of the number of leads 12a, 12b, 12c connected to a negative electrode 3 or the number of leads 13a, 13b connected to a positive electrode 6 satisfies the conditional expression Xa>=[(1.72×10<4> ×La)/(Wa×ta]<1/2> (where La represents a length of the negative electrode, Wa reresents a width of the negative electrode, and ta represents a thickness of a negative electrode collector. The number corresponding to an integer out of the Xa is the number of the leads in the negative electrode), or the conditional expression Xc>=[(2.75×10<-4> ⊗Lc)/(Wc×tc)]<1/2> (where Lc represents a length of the positive electrode, Wc represents a width of the positive electrode, and tc pepresents a thickness of a positive electrode collector. The number corresponding to an integer out of the Xc is the number of the leads in the positive electrode).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a non-aqueous electrolyte secondary battery suitable as a power source used at a high output density such as a power source for a hybrid electric vehicle.

[0002]

2. Description of the Related Art As an alternative to an aqueous secondary battery such as a nickel cadmium battery, a non-aqueous electrolyte secondary battery has been developed because of its high energy density and light weight.

This non-aqueous electrolyte secondary battery is a battery using a negative electrode and a positive electrode capable of doping and undoping lithium, and a non-aqueous electrolyte in which an electrolyte salt is dissolved in a non-aqueous solvent. As a material for the negative electrode, for example, a carbon material or the like is used, and as a material for the positive electrode, for example, a lithium transition metal composite oxide such as LiCoO ₂ is used.

There are various types of non-aqueous electrolyte secondary batteries such as a coin type and a cylindrical type, and the shape of the electrode is selected according to the type of the battery. For example, in the case of a cylindrical nonaqueous electrolyte secondary battery, a strip-shaped negative electrode in which a negative electrode mixture layer is formed on both sides or one side of a negative electrode current collector, and a positive electrode on both sides or one side of a positive electrode current collector A wound electrode body is used in which a band-shaped positive electrode on which a mixture layer is formed is laminated via a separator, and the laminate is wound. Here, the negative electrode current collector,
A negative electrode lead and a positive electrode lead are respectively attached to the positive electrode current collector at one location, and current is taken out through these leads.

[0005] The capacity and output density of a battery differ depending on the shape of the electrode. For example, when the thickness of the electrode mixture layer is increased, the amount of active material charged in the battery increases, and the battery capacity increases. However, when the thickness of the electrode mixture layer is increased, the length of the electrode that can be accommodated in the battery becomes shorter, so that the reaction surface area becomes smaller and the output density becomes smaller.

Here, in the conventional cylindrical nonaqueous electrolyte secondary battery, the thickness of the positive electrode mixture layer on one side is 80 to 90 μm.
And it is relatively thick. This is because non-aqueous electrolyte secondary batteries are mainly used as power supplies for portable devices. As a power source used in a portable device, it is important to use the battery for a long time, that is, to have a large discharge capacity.

On the other hand, recently, attention has been paid to the lightness of the non-aqueous electrolyte secondary battery, and the non-aqueous electrolyte secondary battery has been used as a power source for a hybrid electric vehicle or an engine start. Are being considered. The power source used in these devices is often capable of discharging and charging both in a short time of about several seconds and with high power, and it is important that the power density is larger than the capacity. Therefore, in this case, it is necessary to reduce the thickness of the electrode mixture layer and increase the length of the electrode housed in the battery so as to increase the reaction surface area.

[0008]

However, in the above-mentioned wound electrode body, if the length of the electrode is directly increased, there arises a problem that the electric resistance in the current collector increases and the output decreases. Would. As a method of reducing the electric resistance of the current collector, it is conceivable to increase the thickness of the current collector. Inconveniences such as an increase are caused.

Accordingly, the present invention has been proposed in view of such a conventional situation, and has as its object to provide a non-aqueous electrolyte secondary battery in which current collecting resistance is suppressed low and high output is obtained. And

[0010]

In order to achieve the above-mentioned object, a nonaqueous electrolyte secondary battery of the present invention comprises a negative electrode mixture layer formed on a strip-shaped negative electrode current collector made of Cu. It has a negative electrode and a positive electrode in which a positive electrode mixture layer is formed on a strip-shaped positive electrode current collector made of Al, and leads are connected in parallel in the longitudinal direction of the negative electrode and the positive electrode. , Or at least one of the following conditions:

Xa ≧ [(1.72 × 10 ⁻⁴ × La) / (Wa × ta)] ^1/2 Equation 1 (where La is the length (cm) of the negative electrode, and Wa is the width of the negative electrode) (Cm) and ta are the thickness (cm) of the negative electrode current collector, and the number corresponding to an integer in Xa is the number of negative electrode leads.) Xc ≧ [(2.75 × 10 ⁻⁴ × Lc) / (Wc × tc)] ^1/2 Equation 2 (where Lc is the length (cm) of the positive electrode, Wc is the width (cm) of the positive electrode, and tc is the thickness of the positive electrode current collector ( In addition, the number corresponding to an integer in Xc is the number of leads of the positive electrode.) In the nonaqueous electrolyte secondary battery, the number of leads connected to the negative electrode and the positive electrode is expressed by Equation 1 or Equation 2. If it is determined according to the dimensions of the negative electrode and the positive electrode and the thickness of the current collector so as to satisfy the condition, the current-collecting resistance can be suppressed low, and a high output can be obtained.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described.

FIG. 1 shows an example of the non-aqueous electrolyte secondary battery according to the present invention.

As shown in FIG. 1, this non-aqueous electrolyte secondary battery has a negative electrode 3 in which a negative electrode mixture layer 2 is formed on both surfaces of a negative electrode current collector 1 and a positive electrode current collector 4 having both surfaces. The positive electrode 6 formed with the positive electrode mixture layer 5 is wound through a microporous membrane separator 7 made of polypropylene, polyethylene, or the like, and the battery can is placed in a state where the insulator 8 is placed above and below the wound body. 9.

A battery cover 10 is attached to the battery can 9 by caulking through a sealing gasket 11,
Each of them is electrically connected to a negative electrode or a positive electrode via a negative electrode lead 12 and a positive electrode lead 13, and is configured to function as a negative electrode or a positive electrode of a battery.

However, in this battery, a current interrupting thin plate is provided as a safety device, and the positive electrode lead 13 is welded to the current interrupting thin plate 14 and attached thereto. The electrical connection with 10 is achieved.

In the battery having such a configuration,
When the pressure inside the battery rises, the thin plate
Is pushed up and deformed. Then, the positive electrode lead 13 is cut leaving a portion welded to the current interrupting thin plate 14, and the current is interrupted.

FIG. 2 is a development view of the negative electrode 3 and the positive electrode 6. As described above, the negative electrode 3 and the positive electrode 6 have negative electrode leads 12a, 12b, 12
c, the positive electrode leads 13a and 13b are connected respectively. At the connection portions of the negative electrode leads 12a, 12b, 12c and the positive electrode leads 13a, 13b, a current collector is exposed without forming a mixture layer, and the exposed current collectors are connected to the negative electrode leads 12a, 12b. , 12c, positive electrode lead 13a, 1
3b is directly welded.

In this non-aqueous electrolyte secondary battery, in particular, the negative electrode leads 12a, 12b, and 12c are connected in parallel in the longitudinal direction of the negative electrode in a number corresponding to an integer of Xa represented by the formula 1, Xa ≧ [(1.72 × 10 ⁻⁴ × La) / (Wa × ta)] ^1/2 Formula 1 (where, La is the length (cm) of the negative electrode, Wa is the width (cm) of the negative electrode, ta Is the thickness (cm) of the negative electrode current collector.) Further, the positive electrode leads 13a and 13b have X
The number corresponding to the integer of c is connected in parallel in the longitudinal direction of the positive electrode.

Xc ≧ [(2.75 × 10 ⁻⁴ × Lc) / (Wc × tc)] ^1/2 Equation 2 (where Lc is the length (cm) of the positive electrode, and Wc is the width of the positive electrode (Cm) and tc are the thickness (cm) of the positive electrode current collector.) As described above, the number of the negative electrode leads 12a, 12b, 12c, and the positive electrode leads 13a, 13a,
When 13b is connected, the current collecting resistance is reduced to 5 mΩ or less even when the electrode length is increased, and a large output can be obtained while improving the current density. The effect can be obtained even if any one of the connection conditions of the negative electrode leads 12a, 12b, 12c and the positive electrode leads 13a, 13b is satisfied, but the effect is more improved if both conditions are satisfied. high.

Here, it is a necessary condition for the battery used in a hybrid vehicle that uses gasoline and electricity as a power source to make the current collecting resistance 5 mΩ or less.

That is, it is desirable that the battery used in the hybrid vehicle be as small as possible and have a high output. Here, in general, in the case of a small car, 20 k
An output of about W is required. Also, the required voltage is determined by the operating voltage of the motor, and considering this, current efficiency, safety, etc., the number of series cells is about 100 cells. Therefore, a battery used for a vehicle needs an output of about 200 W per cell.

On the other hand, the open-circuit voltage of the battery is about 3.8 V. In this case, in order to obtain an output of 200 W, the internal resistance must be 16 mΩ or less.

Here, the internal resistance of the battery is defined as the reaction resistance related to the battery reaction, the resistance derived from the electrolyte or the separator,
It is divided into current collecting resistors, of which the reaction resistance is about 7-8m
Ω, the resistance derived from the electrolytic solution and the separator is about 4 mΩ, and the current collecting resistance must be about 5 mΩ or less in order to keep the internal resistance of the battery at 16 mΩ or less without changing them. Thus, a battery used in a hybrid vehicle needs to have a current collecting resistance of 5 mΩ or less.

The negative leads 12a, 12b and 12c and the positive leads 13a and 13b are connected in a predetermined number as described above. In this case, the connection positions thereof are also important. For example, the number of leads of the negative electrode is increased by one from the number of leads of the positive electrode, and as shown in FIG.
a, 12b, and 12c are connected at equal intervals, and two of them are connected to the electrode ends 3a and 3b. On the other hand, the positive electrode lead 13
a and 13b may be connected to positions corresponding to the middle points Ca and Cb between the negative electrode leads. In this case, the midpoint Cc between the adjacent positive electrodes 13a and 13b and the positive electrode lead 1
Distance from 3a or 13b, and electrode end 6a or 6
b and the distance between the positive electrode lead 13a and 13b are equal.

Here, the case where three negative electrode leads and two positive electrode leads are connected is taken as an example, but the same applies to other numbers of leads as long as the above conditions are satisfied.

In the present invention, the negative electrode lead 12 and the positive electrode lead 13 are connected to the negative electrode 3 and the positive electrode 6, respectively, under such conditions. Any of the known materials can be used.

First, the negative electrode mixture layer contains a negative electrode material capable of doping and undoping lithium ions and a binder.

As the negative electrode material, for example, a carbonaceous material or the like is used. As the carbonaceous material, pyrolytic carbons, cokes (pitch coke, needle coke,
Petroleum coke, etc.), graphites, glassy carbons, carbons using an organic polymer as a precursor (such as those obtained by firing a furan resin or the like at an appropriate temperature), carbon fibers, activated carbon, and the like.

As the binder for holding the negative electrode material on the positive electrode current collector and the positive electrode current collector, those commonly used can be used. For example, a fluorine-based resin such as polyvinylidene fluoride is used as the binder, and a copper foil or the like is used as the current collector.

The positive electrode mixture layer contains a positive electrode material capable of doping and undoping lithium ions, a conductive agent and a binder.

As the positive electrode material, for example, Li _x MO ₂ (where M is one or more transition metals, preferably Mn, Co,
At least one of Ni and Fe. Also, 0.05 ≦
x ≦ 1.10) is used.

As a conductive agent for imparting conductivity to the positive electrode, a binder for holding the positive electrode material on the positive electrode current collector, and a positive electrode current collector, those commonly used can be used.

For example, graphite and carbon black are used as the conductive agent, fluorine resin such as polyvinylidene fluoride as the binder, and aluminum foil as the positive electrode current collector.

In this battery, a non-aqueous electrolyte obtained by dissolving an electrolyte salt in a non-aqueous solvent is used.

Examples of the non-aqueous solvent include cyclic carbonates such as propylene carbonate, ethylene carbonate and butylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, dipropyl carbonate and ethyl methyl carbonate; ether compounds such as dimethoxyethane and tetrahydrofuran; -Cyclic esters such as butyrolactone, sulfolane and the like are used alone or in combination.

As the electrolyte salt, LiPF ₆ , LiPF
Lithium salts such as BF ₄ , LiCF ₃ SO ₃ , LiClO ₄ and LiAsF ₆ are used.

[0038]

EXAMPLES Examples of the present invention will be described based on experimental results.

Experimental Example 1 Example 1 In Example 1, the length La of the negative electrode was 485.5 cm, the width Wa of the negative electrode was 7.65 cm, and the thickness ta of the negative electrode current collector was ta:
0.0015 cm, three negative electrode leads were attached to the negative electrode, the positive electrode length Lc: 470.0 cm, and the positive electrode width Wc:
7.25 cm, thickness tc of positive electrode current collector: 0.0020 c
m is an example of a non-aqueous electrolyte secondary battery in which two positive electrodes are attached to the positive electrode.

This non-aqueous electrolyte secondary battery was manufactured as follows.

First, the negative electrode was manufactured as follows.

A carbon material was synthesized by calcining the petroleum pitch in an inert gas stream, and the carbon material was pulverized to obtain a carbon material powder having an average particle diameter of 20 μm.

A negative electrode mixture is prepared by mixing 90 parts by weight of the carbon material powder and 10 parts by weight of vinylidene fluoride resin as a binder, and the negative electrode mixture is dispersed in N-methylpyrrolidone. A negative electrode mixture slurry was obtained. next,
This negative electrode mixture slurry was applied to both surfaces of a negative electrode current collector made of a copper foil having a thickness of 0.0015 cm except for a lead welding portion. Then, the negative electrode current collector was compressed from both sides with a roll to produce a negative electrode original plate, which was 7.65 cm wide.
It was cut to a length of 485.0 cm. Here, [(1.72
× 10 ^-4 × La) / (Wa × ta)] ^1/2 is 2.70. As shown in FIG. 2, the negative electrode lead was welded to the negative electrode at three midpoints between both ends. The negative electrode lead is made of Cu having a width of 13 mm and a thickness of 0.1 mm.
It is a lead made of.

The positive electrode was manufactured as follows.

LiCoO ₂ powder 95 having an average particle size of 10 μm
By weight, 1.5 parts by weight of graphite serving as a conductive agent, 0.5 parts by weight of carbon black, and 3 parts by weight of vinylidene fluoride resin serving as a binder were mixed to prepare a positive electrode mixture. The positive electrode mixture slurry was obtained by dispersing the positive electrode mixture in N-methylpyrrolidone. Then, this positive electrode mixture slurry was applied to both surfaces of a positive electrode current collector made of an aluminum foil having a thickness of 0.0020 cm except for a welded portion of a lead. Then, the positive electrode current collector was compressed from both sides with a roll to produce a positive electrode original plate, and was 7.25 cm in width.
It was cut to a length of 470.0 cm. Here, [(2.75
× 10 ^-4 × Lc) / (Wc × tc)] ^1/2 is 2.99. As shown in FIG. 2, two positive electrodes are provided on the positive electrode such that the distance between the center between the two positive electrode leads and the positive electrode and the distance between the electrode end and the positive electrode on the electrode end side are equal. The lead was welded. The positive electrode lead has a width of 15 m.
m, an Al lead having a thickness of 0.2 mm.

The negative electrode, the positive electrode, and the separator thus manufactured are stacked in the order of negative electrode, separator, positive electrode, and separator, and a polypropylene inner core (outer diameter: 7 mm; The electrode element was manufactured by winding up to a length of 81 mm). The separator has a width of 80.
It is a polypropylene microporous sheet having a length of 5 mm and a length of 5100 mm, and two separators are arranged between the electrodes.

Incidentally, a polyimide tape was applied to the positive electrode portion opposite to the portion of the negative electrode where the negative electrode mixture was not applied (lead welded portion) so that the movement of ions between the electrodes was eliminated. Further, the negative electrode lead and the positive electrode lead were respectively derived from different end faces of the electrode element.

Next, insulators were arranged above and below the manufactured electrode element, and this was inserted into a nickel-plated iron cylindrical can. Then, the negative electrode lead was welded to the bottom of the can, and the positive electrode lead was welded to the current blocking thin plate.

Subsequently, LiBF ₄ was added to a mixed solvent of propylene carbonate and diethyl carbonate in a cylindrical can.
Was dissolved at a concentration of 1.5 mol / liter. Then, the top cover was placed on the open side of the cylindrical can, and caulked via a gasket for insulating sealing, and sealed to produce a cylindrical nonaqueous electrolyte secondary battery (diameter 40 mm, height 90 mm).

Comparative Example 1 As shown in FIG.
And the number of the positive electrode leads 17 to be welded to the positive electrode 16 was one, the negative electrode lead 15 was welded to the end of the negative electrode 14, and the positive electrode lead 17 was welded to the opposite end of the positive electrode 16. Except for the above, a non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1.

COMPARATIVE EXAMPLE 2 As shown in FIG.
The number of a and 19b is two, the number of positive leads 21 to be welded to the positive electrode 20 is one, the negative leads 19a and 19b are welded to both ends of the negative electrode 18, and the positive lead 21 is connected to the positive electrode 20.
A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the non-aqueous electrolyte secondary battery was welded to the center of the battery.

The output characteristics and the internal resistance of the battery manufactured as described above were analyzed. Table 1 shows the results.

[0053]

[Table 1]

As shown in Table 1, the battery of Example 1 in which the number of the negative electrode leads satisfies the predetermined condition has a lower current collecting resistance and a lower internal resistance than the batteries of Comparative Examples 1 and 2. It is kept small and a large output density is obtained.

Thus, setting the number of leads in accordance with the length and width of the electrode and the thickness of the current collector is effective in lowering the internal resistance of the battery and obtaining a large output density. I understood.

Further, a non-aqueous secondary battery was manufactured in the same manner as in Example 1 except that the number of both the negative electrode lead and the positive electrode lead was three. The positive electrode lead was attached to the positive electrode in the same manner as the negative electrode lead. When the current-collecting resistance of this non-aqueous electrolytic secondary battery was measured, it was reduced by about 1 (mΩ) from that of Example 1 to about 2 (mΩ). It was confirmed that, when satisfying the predetermined condition, it was possible to further suppress the current collecting resistance.

[Experimental Example 2] Next, the number of positive electrode leads was set to 1
A non-aqueous electrolytic secondary battery was fabricated in the same manner as in Example 1 except that the battery was fixed to a book and the number of negative electrode leads was changed, and the current collection resistance, total resistance, and battery capacity ratio of these batteries were examined.

FIG. 5 shows the results. In FIG. 5, the horizontal axis indicates the number of leads, and the vertical axis indicates the resistance and the battery capacity ratio. In FIG. 5, ○ indicates current collecting resistance, □ indicates total resistance, and △ indicates battery capacity ratio. However, the battery capacity ratio is a ratio when the battery capacity of a battery having one negative electrode lead is set to 1.

As can be seen from the results shown in FIG. 5, as the number of leads increases, the current collecting resistance decreases. However, as the number of leads increases, the battery capacity decreases. This is because the portion of the battery that does not contribute to the battery reaction increases. The total resistance increases and decreases according to these correlations. The total resistance takes the minimum value when the number of leads is three, and does not change much when the number of leads is more than three. However, when the number of leads is further increased, the total resistance increases due to an increase in reaction resistance and the like.

That is, from these results, it was confirmed that the effect of lowering the current collecting resistance was increased as the number of leads was increased. Further, it was confirmed that it is preferable that the number of leads be in a range where the total resistance does not increase.

In this case, the investigation was conducted by changing the number of the negative electrode leads. However, the same result was obtained when the investigation was conducted by changing the number of the positive electrode leads. If the number of both is increased, the effect of lowering the current collection resistance becomes more remarkable.

[0062]

As is clear from the above description, in the nonaqueous electrolyte secondary battery of the present invention, since the number of leads connected to the positive electrode or the negative electrode is regulated, the internal resistance is suppressed to a small value and the high output Can be obtained. Therefore, the mass of the battery required to obtain the same output is smaller than that of the conventional battery. In addition, since the internal resistance is low, the energy efficiency of charging and discharging is extremely high, and since the generation of Joule heat due to charging and discharging is small, the heat radiation processing becomes easy. In addition, it is possible to prevent an increase in battery mass and a decrease in capacity due to an unreasonable increase in the number of leads.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing an example of a non-aqueous electrolyte secondary battery to which the present invention is applied.

FIG. 2 is a plan view showing a state in which three negative electrode leads are attached to a negative electrode, and two positive electrode leads are attached to a positive electrode.

FIG. 3 is a plan view showing a state in which one negative electrode lead is attached to a negative electrode and one positive electrode lead is attached to a positive electrode.

FIG. 4 is a plan view showing a state where two negative electrode leads are attached to a negative electrode and one positive electrode lead is attached to a positive electrode.

FIG. 5 is a characteristic diagram showing a relationship between the number of leads, a resistance, and a battery capacity ratio.

[Explanation of symbols]

3 negative electrode, 6 positive electrode, 12a, 12b, 12c negative electrode lead, 13a, 13b positive electrode lead

Claims (4)

[Claims] 1. A negative electrode in which a negative electrode mixture layer is formed on a strip-shaped negative electrode current collector made of Cu, and a positive electrode in which a positive electrode mixture layer is formed on a strip-shaped positive electrode current collector made of Al. And a lead is connected in parallel in the longitudinal direction of the negative electrode and the positive electrode, and the number of these leads satisfies at least one of the conditions of Formula 1 or Formula 2. battery. Xa ≧ [(1.72 × 10 ⁻⁴ × La) / (Wa × ta)] ^1/2 Formula 1 (where La is the length of the negative electrode (cm), Wa is the width of the negative electrode (cm)) , Ta are the thickness (cm) of the negative electrode current collector, and the number corresponding to an integer in Xa is the number of the negative electrode leads.) Xc ≧ [(2.75 × 10 ⁻⁴ × Lc) / (Wc × tc)] ^1/2 Formula 2 (where, Lc is the length (cm) of the positive electrode, Wc is the width (cm) of the positive electrode, and tc is the thickness (cm) of the positive electrode current collector. In addition, the number corresponding to an integer in Xc is the number of positive electrode leads.) 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode mixture contains a carbon material. 3. The positive electrode mixture layer is made of Li _x MO ₂ (where M is one of Co, Ni, Mn, Cr, Fe, V, and Al).
More than types, and 1.1 ≧ x ≧ 0.4. 2. The non-aqueous electrolyte secondary battery according to claim 1, further comprising a lithium transition metal composite oxide represented by the formula (1). 4. Three or more negative leads are connected to the negative electrode at equal intervals, two of which are connected to the negative electrode end, two or more positive leads are connected to the positive electrode, and between adjacent positive leads. The non-aqueous electrolyte secondary battery according to claim 1, wherein a distance between a center point of the positive electrode lead and a distance between a positive electrode end and a positive electrode lead on the positive electrode end side is equalized.