JP2002208432A - Manufacturing method of a nonaqueous electrolyte secondary cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a non aqueous electrolyte secondary cell with improved life characteristics. SOLUTION: For the manufacturing method of a non aqueous electrolyte secondary cell, melamine and/or derivative of melamine is added.

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 used, for example, as a power source for portable equipment or a power source for driving electric vehicles.

[0002]

2. Description of the Related Art In recent years, portable information devices such as laptop computers and word processors, AV devices such as camera-integrated VTRs and liquid crystal televisions, mobile communication devices such as mobile phones, and batteries as power sources for electric vehicles have become increasingly important. Devices requiring high current and large output have been developed in various ways, and batteries with higher energy density have been demanded. In order to meet the demand, non-aqueous electrolyte secondary batteries have been proposed and have been put to practical use.

[0003] However, these batteries are not yet satisfactory, and further longer life and lower cost are required.

In response to such demands, for example, resources,
From the viewpoint of cost, utilization of lithium manganate as a positive electrode active material is expected to be promising.

[0005]

In addition to the above requirements for non-aqueous electrolyte secondary batteries, lithium manganate, which is expected to be used, has a long life if used in non-aqueous electrolyte secondary batteries. There is a problem that it becomes shorter.

Accordingly, an object of the present invention is to improve the life characteristics of a non-aqueous electrolyte secondary battery and to manufacture a non-aqueous electrolyte secondary battery using lithium manganate to improve the life characteristics of the non-aqueous electrolyte secondary battery. The aim is to provide a method.

[0007]

Means for Solving the Problems A method for manufacturing a nonaqueous electrolyte secondary battery according to the present invention, which solves the above-mentioned problems, includes a step of adding melamine and / or a melamine derivative.

The melamine and / or melamine derivative may be added, for example, after injecting the electrolyte into the battery container, or may be added to the electrolyte, or the battery may be constituted by using the one previously supported on a separator. May be. Alternatively, a battery may be manufactured by using one that has been added to the electrolytic solution in advance. It is particularly preferable to add it to the electrolytic solution.

According to the present invention, a non-aqueous electrolyte secondary battery having improved life characteristics can be manufactured.

In the above nonaqueous electrolyte secondary battery, a composite oxide composed of lithium and a transition metal, such as lithium cobalt oxide, lithium manganate, and lithium nickel oxide, and an interlayer compound containing lithium are used as the positive electrode active material. Can be.

Preferably, when lithium manganate, especially spinel-type lithium manganate, is used,
By adding melamine and / or melamine derivatives, it is possible to obtain a non-aqueous electrolyte secondary battery having excellent high-temperature characteristics and improved life characteristics, in particular, by suppressing a decrease in battery capacity due to charge and discharge at high temperatures.

[0012] It is not clear at present that the use of the spinel-type lithium manganate as the positive electrode active material improves the battery characteristics. And / or an interaction between the melamine derivative and a film is formed. For example, the decrease in capacity at high temperature is considered to be caused by the elution of manganese. It is considered that this film is formed to suppress the elution of manganese from the surface of the spinel-type lithium manganate particles.

When using spinel-type lithium manganate containing an aluminum element as the positive electrode active material, the addition of melamine and / or a melamine derivative has a remarkable effect on the improvement of the battery life characteristics.

When the melamine and / or melamine derivative is added to the electrolyte in the non-aqueous electrolyte secondary battery, it is preferable that the melamine and / or melamine derivative be added so that the content in the electrolyte is less than 7% by weight.

The content of the additive contained in the electrolytic solution changes with the passage of time and the charge / discharge reaction. For example, immediately after battery production and after repeated use of the battery, the content of the same battery is different. However, if the amount contained in the electrolytic solution is too large, the discharge capacity may be reduced, or additives that do not contribute to the improvement of the life characteristics may be present, which may be uneconomical or impair the electrolytic solution characteristics. Or a factor. For this reason, the content of the additive is preferably not more than a certain amount, and is preferably less than 7% by weight. The content is the weight of the additive in the total weight of the electrolyte including the melamine and the like to be added,
When a plurality of additives are contained, the total weight of the plurality of additives is preferably less than 7% by weight. In addition, since the content varies depending on the use condition, less than 7% by weight means
It means that it is less than this value in any use state. Also, if the amount is too small, the effect of improving the life characteristics is not sufficiently exhibited, so it is preferable to add 0.03% by weight or more.

The specific surface area of the lithium manganate is preferably 0.1 to 2.0 m ² / g.

If the specific surface area of lithium manganate is too large, the life characteristics, especially at high temperatures, will be poor, and if it is too small, the discharge capacity will be small. For example, if the specific surface area is less than 0.1 m ² / g, there is a problem that the reaction area between the active material and the electrolytic solution is too small, the current density becomes excessively large, the capacity decreases, and the voltage decreases.
When the specific surface area exceeds 2 m ² / g, there is a problem that the reaction area with the electrolytic solution increases and the charge / discharge characteristics deteriorate. For this reason, it is necessary to use lithium manganate having a specific surface area in a predetermined range according to the battery configuration. When an electrolytic solution to which an additive such as the above melamine is added is used, preferably 0.1 to 2. range of 0 m ² / g, more preferably better to use what is in a range of 0.2~0.6m ² / g, it is possible to elicit life characteristics improving effect by the additive. In particular, when the amount of the additive is less than 7% by weight, the use of a material having a surface area within this range can more effectively improve the life characteristics and reduce the capacity. It will not be triggered.

The average particle size of the lithium manganate is preferably 10 μm to 15 μm.

By setting the particle size in such a range,
In addition to the above effects, it is possible to manufacture a battery having a high energy density and a good yield during manufacturing. further,
The content of 7% by weight or less, and 0.1 to 2.0 m ² / g.
By having both of the specific surface area and the specific surface area, the effect of improving the life characteristics becomes remarkable.

The tap density of the lithium manganate is preferably 1.8 g / cc to 2.0 g / cc.

By setting the tap density in such a range, it is possible to manufacture a battery having a high energy density in addition to the above effects.

The above-mentioned electrolyte preferably contains a mixed solvent of ethylene carbonate and a low-viscosity solvent.

By using such a solvent, the effect of improving the life characteristics due to the interaction between the lithium manganate and the electrolyte containing the additive is easily exerted.

Furthermore, it is preferable that the above-mentioned electrolyte contains lithium hexafluorophosphate.

By using such an electrolyte, it is possible to manufacture a battery having excellent safety and excellent discharge characteristics, and it is possible to reliably exert the above-described effect of improving the deterioration characteristics.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with specific examples.

The non-aqueous electrolyte secondary battery according to the present invention is manufactured using a positive electrode having spinel lithium manganate as an active material, a negative electrode, and a non-aqueous electrolyte containing melamine.

In general, lithium manganate which can be used as the active material of the positive electrode has a layered structure and a spinel structure, and the latter spinel type lithium manganate is preferably used. Examples of the spinel-type lithium manganate include LiMn ₂ O ₄ ,
LiMn _1.9 Fe _0.1 O ₂ , Li in which part of manganese is replaced by iron, magnesium, chromium, aluminum, etc.
Mn _1.9 Mg _0.1 O ₂ , LiMn _1.9 Cr _0.1
O _2, LiMn _1.9 Al _0.1 O ₂ or the like can be used. Note that lithium nickel oxide may be mixed with other active materials, for example, lithium nickel oxide is mixed with lithium nickel oxide by 20% by weight.

Particularly, spinel-type lithium manganate
Is, for example, Li_XMn_YAl _ZO₄(Where X,
Y and Z are 1 ≦ X ≦ 1.2, X + Y = 3, 0 ≦ Z ≦ 0.
1 and Y + Z = 2 are satisfied. )
Can be used. This is a manga of such composition
Lithium acid salt is particularly excellent in stability, such as melamine
Especially in combination with the electrolyte containing the compound
This is because a long-life battery can be realized.

It is to be noted that whether or not it is spinel type lithium manganate can be confirmed by, for example, X-ray diffraction measurement.
This can be confirmed by observing 2θ peaks around 5 °, 36 °, 38 °, 44 °, 48 °, and 58 °.

For the positive electrode, for example, a positive electrode mixture obtained by adding a conductive agent, a binder, a solvent, and the like to such lithium manganate powder is applied to the surface of the current collector, dried, and pressed. It is produced by doing. At this time, in the present invention, the amount of the conductive agent is preferably 2 to 5% by weight, and the amount of the binder is preferably 6 to 10% by weight. In the present invention, acetylene black is particularly preferred as the conductive agent, and the energy density can be increased.

Examples of the negative electrode active material include lithium alloys such as lithium metal and lithium-aluminum alloy, graphite, pyrolytic carbon, cokes, organic polymer compound fired bodies, carbonaceous materials such as carbon fiber and activated carbon, and polyacetylene. And a polymer such as polypyrrole, and a negative electrode is manufactured using these. At this time, in the present invention, the amount of the binder is 6
The content is preferably set to 10 to 10% by weight.

As the electrolyte, a non-aqueous electrolyte obtained by dissolving an electrolyte such as a lithium salt in an organic solvent can be used.
As the organic solvent, for example, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, dipropyl carbonate, methyl formate, ethyl formate, propyl formate, formate compound, propionate compound, dimethoxyethane, Diethoxyethane, diethoxypropane, dioxolane, ether compounds such as dioxane, γ-butyrolactone, cyclic esters such as δ-hexyllactone, sulfolane, organic sulfur compounds such as dimethylsulfolane and the like can be used,
These can be used alone or in combination of two or more.

As the electrolyte, for example, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium hexafluoroantimonate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium trifluoroacetate and the like are used. be able to.

In particular, in the case of the present invention, it is preferable that the above-mentioned electrolytic solution contains a mixed solvent of ethylene carbonate and a low-viscosity solvent, and it is more preferable to use lithium hexafluorophosphate as the electrolyte. Lithium hexafluorophosphate (chemical formula: LiPF ₆ ) has advantages of high conductivity and excellent safety. As the low-viscosity solvent, a so-called low-viscosity solvent may be used, but at a solvent temperature of 21 ° C., a solvent having a viscosity of 1.5 Cst (a value obtained by measuring with a Canofenske viscometer) or less is used. Preferably, for example, diethyl carbonate, dimethyl carbonate, ethyl methyl ketone, diethylene glycol and the like are used.

In the non-aqueous electrolyte secondary battery according to the present invention, for example, such a positive electrode and a negative electrode are housed in a battery container in a state where they face each other with a separator or the like interposed therebetween, and the electrolytic solution is placed in this container. Although it is produced by injecting, in order to make melamine contained in the electrolytic solution, for example, melamine is previously supported on a separator or the like, or an electrolytic solution to which melamine is added may be used. it can.

The content of additives such as melanin in the electrolytic solution changes depending on the use condition of the battery, and becomes the largest immediately after the battery is produced. However, the content immediately after the battery is produced should be less than 7% by weight. Preferably, the content is less than 7% by weight regardless of the use condition of the battery.

In order to adjust the content in the electrolytic solution as described above, it is preferable to use an electrolytic solution to which melamine is added. In this case, the amount of the additive is 0.03% by weight. % Or more and less than 7% by weight is particularly preferable. If the amount is less than 0.03% by weight, the formed film is not sufficient. If the amount is more than 7% by weight, the thickness of the film is sufficient. This is because it is considered impossible to obtain.

Further, when the content is less than 7% by weight, the specific surface area of the lithium manganate particles is 0.1 to 10%.
It is preferable to be 2.0 m ² / g, further, in addition to this, the average particle diameter of the lithium manganate particles, 10 [mu]
m to 15 μm.

Further, in order to increase the energy density of the battery and maintain a good life, the tap density of lithium manganate is preferably 1.8 g / cc to 2.0 g / cc.

[0041]

EXAMPLES The present invention will be described below with reference to examples.

In this example, lithium manganate (Li _1.125 Mn _1.875 O ₄ ) was used as the positive electrode active material, natural graphite was used as the negative electrode, polyvinylidene fluoride resin was used as a binder for the positive electrode and the negative electrode, and as an additive to the electrolyte solution. Melamine is applied to a cylindrical lithium ion secondary battery.

FIG. 1 shows a structural diagram.

In FIG. 1, an electrode group in which a positive electrode (1) and a negative electrode (2) are spirally wound via a separator (3) is formed of a nickel-plated iron bottomed cylinder having an inner diameter of 15.3 mm. Battery case (4). here,
Since the battery case is made of iron, the battery case corresponds to the negative electrode side. (5) is a center pin for winding the positive electrode (1) and the negative electrode (2) through the separator (3) and is made of aluminum having an outer diameter of 3 mm and a length of 26 mm. As the separator (3), a polyethylene microporous film having a thickness of 25 μm was used.

The positive electrode (1) is made of aluminum having a thickness of 20 μm.
Li on both sides of the foil_1.125Mn _1.875O₄Grain
Child (specific surface area 0.4m²/ G, average particle size 12 μm,
Binder density of 1.9 g / cc)
90 weight layers of acetylene black as a conductive agent
%: 6% by weight: 4% by weight (solid content ratio)
After mixing into a paste, coating, drying and rolling, the length is 470
mm and a width of 24 mm were used. Note that Li
_1.125Mn_1.875O₄Particles of X-ray diffraction measurement
As a result, it was confirmed that it was spinel-type lithium manganate.
I accepted.

For the negative electrode (2), natural graphite and polyvinylidene fluoride as a binder were added on both sides of a copper foil having a thickness of 14 μm.
0% by weight: 10% by weight (solid content ratio), mixed in paste form, applied, dried and rolled, then 490 mm in length and 2 in width
The one cut to 6 mm was used. (6) is a lid, which is caulked and sealed in the battery case (4) via a gasket (7). The inner surface of the lid (6) has a positive electrode (1)
The positive electrode lead (8) connected to is welded.

The electrolyte contains 1 mol / l of LiPF ₆ in ethylene carbonate (EC): diethyl carbonate (D
A mixture obtained by adding melamine to a mixture of EC) = 1: 1 (volume ratio) at a ratio shown in Table 1 was used.

As described above, the outer diameter is 15.9 mm and the height is 33
mm cylindrical batteries A to H were assembled.

As a comparative example, a cylindrical lithium ion secondary battery was assembled under the same conditions as in the example except that melamine was not added. This battery is referred to as battery Z.

A life test was performed on these batteries A to Z.

As a test method, a temperature of 45 ° C., a charging current of 1
A, charging was performed at a constant current and a constant voltage of a charging upper limit voltage of 4.1 V for 3 hours, and discharging was performed at a current of 1 A to 2.75 V, and a change in discharge capacity was examined.

The test quantity is 5 pieces each.

[0053]

[Table 1]

Table 2 shows the initial discharge capacity, the discharge capacity after 500 cycles, and the capacity retention.

[0055]

[Table 2]

From the test results, it is understood that the battery using the melamine of the present invention has excellent life characteristics. When the amount is 0.03% by weight or more, the effect is recognized. However, when the amount is 7% by weight, the dielectric constant of the electrolyte decreases, and the battery capacity decreases. Preferably, the content is 0.1% by weight or more and 1.0% by weight or less.

Note that Li _1.1 Mn _1.805 Al
_{When the 0.095} O ₄ particles were used as the positive electrode active material, the same results as described above were obtained.

[0058]

According to the present invention, a non-aqueous electrolyte secondary battery having improved life characteristics can be provided.

[Brief description of the drawings]

FIG. 1, showing an embodiment of the present invention, is a structural diagram of a cylindrical lithium ion secondary battery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 Battery case 5 Center pin 6 Lid 7 Gasket 8 Positive electrode lead 9 Negative electrode lead 10 PTC element 11 Safety valve 12 Insulator 1 13 Insulator 2

Claims (4)

[Claims] 1. A method for producing a non-aqueous electrolyte secondary battery, comprising a step of adding melamine and / or a melamine derivative. 2. The non-aqueous electrolyte secondary battery has an electrolyte,
The method for producing a non-aqueous electrolyte secondary battery according to claim 1, wherein the step of adding the melamine and / or the melamine derivative is a step of adding the melamine to the electrolytic solution. 3. The method for producing a non-aqueous electrolyte secondary battery according to claim 2, wherein the electrolytic solution contains a mixed solvent of ethylene cardnate and a low-viscosity solvent. 4. The method for producing a non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material of the non-aqueous electrolyte secondary battery is a spinel type lithium manganate. .