JP2001357874A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery of high reliability capable of suppressing voltage drop and excellent in the lifetime characteristic. SOLUTION: In a nonaqueous electrolyte, leveling agent is contained to suppress concentrated precipitation of metal ions in an electrode plat. Examples of such a leveling agent are 1,5-naphthalene-sodium disulfonate, 1,3,6-naphthalene- sodium trisulfonate, saccharin, aldehyde, gelatin, 2 butyne-1,4diol, quinaldine, pyridium compound, ethylene-cyane hydrine, azo dye, potassium thiocyanate, and potassium pyrophosphate.

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 in which a positive electrode capable of releasing and storing lithium ions by charging and discharging and a negative electrode capable of storing and releasing lithium ions by charging and discharging are infiltrated into a non-aqueous electrolyte. It relates to improvement of life characteristics and reliability of a water electrolyte secondary battery.

[0002]

2. Description of the Related Art Non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries are mainly used for portable devices such as VTR cameras, notebook computers, and mobile phones, taking advantage of their high energy density. ing. Particularly in recent years, lithium ion secondary batteries using a material capable of inserting and extracting lithium ions, such as a carbon material, for the negative electrode have become widespread. Usually, the internal structure of a lithium ion secondary battery is a wound type. That is, a positive electrode and a negative electrode obtained by applying an active material to a metal foil are wound with a separator interposed therebetween, and the wound body (wound group) is housed in a cylindrical battery can serving as a container, and a nonaqueous electrolyte is poured. After the solution, the cap is put on and sealed.

When assembling a battery, a carbon material used as a negative electrode active material is in a state where lithium ions have been completely released, that is, in a discharged state. Therefore, normally, the positive electrode also has a discharged active material, for example, lithium cobalt oxide (Li).
CoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ), or the like is used.
Since such a positive electrode active material does not have sufficient electron conductivity, in the positive electrode of a lithium ion secondary battery, the positive electrode active material generally has a low cost and stable inside the battery such as graphite or carbon black as a conductive agent. A conductive powder is contained, a binder (binder) is further added, and the mixture is used.
Then, the function as a battery is given to the lithium ion secondary battery by initial charging after assembly.

[0004] Non-aqueous electrolyte secondary batteries have the advantages of high capacity and high output. For this reason, recently, it has been used as a power source for an electric vehicle or a hybrid electric vehicle using both an internal combustion engine and an electric motor (hereinafter, both are referred to as electric vehicles). When a non-aqueous electrolyte secondary battery is used as a power source for an electric vehicle, a plurality of non-aqueous electrolyte secondary batteries are used as a battery module by electrically connecting them in series to secure a high voltage. The voltage and the like of each of the non-aqueous electrolyte secondary batteries connected to are controlled by a control circuit in the battery module.

[0005]

However, among the non-aqueous electrolyte secondary batteries constituting the battery module, even one of the non-aqueous electrolyte secondary batteries has battery characteristics such as voltage and capacity that are different from those of other non-aqueous electrolyte secondary batteries. If the battery characteristics are deteriorated due to a difference or a change over time, the non-aqueous electrolyte secondary battery having the abnormal characteristics becomes a load of another non-aqueous electrolyte secondary battery, and deteriorates the characteristics of the entire battery module. In particular, if the self-discharge is different, there is a problem in that the voltage drop of each non-aqueous electrolyte secondary battery varies, and the characteristics and life of the entire battery module become extremely short. Also, if the variation in the voltage drop of each non-aqueous electrolyte secondary battery is too large, the control circuit cannot control and adjust the voltage of the non-aqueous electrolyte secondary battery. Runs out of control and causes a decrease in the reliability of the battery module.

An object of the present invention is to provide a highly reliable non-aqueous electrolyte secondary battery capable of suppressing voltage drop, having excellent life characteristics, and having high reliability.

[0007]

In order to achieve the above-mentioned object, the present invention provides a positive electrode capable of releasing and occluding lithium ions by charging and discharging, and a negative electrode capable of occluding and releasing lithium ions by charging and discharging. In a non-aqueous electrolyte secondary battery impregnated with a non-aqueous electrolyte, the non-aqueous electrolyte contains a leveling agent that suppresses concentrated precipitation of metal ions at the positive electrode and / or the negative electrode. Features.

In the present invention, the voltage drop is caused by the fact that metal ions in the battery concentrate on the electrode plate during charge / discharge and cause a minute short circuit (self-discharge) between the positive and negative electrodes.
Paying attention to the fact that voltage variation occurs between non-aqueous electrolyte secondary batteries, and including a leveling agent in the non-aqueous electrolyte that suppresses the concentrated precipitation of metal ions at the positive electrode and / or the negative electrode. Thus, concentrated precipitation of metal ions on the electrode plate is suppressed. According to the present invention, the concentration of metal ions on the electrode plate can be suppressed by the inclusion of the leveling agent, so that a voltage drop due to a minute short circuit can be suppressed and the deterioration of the electrode plate can be suppressed. Therefore, a highly reliable non-aqueous electrolyte secondary battery having excellent life characteristics can be obtained.

In this case, the leveling agent is preferably a substance having a polyether group or an organic sulfone group, or a phosphorus compound or a sulfur compound.
Sodium 5-naphthalene-disulfonate, 1,3,6
Naphthalene-sodium trisulfonate, saccharin,
More preferably, it is at least one selected from the group consisting of aldehyde, gelatin, 2-butyne-1,4 diol, quinaldine, pyridium compound, ethylene cyanohydrin, azo dye, potassium thiocyanate and potassium pyrophosphate.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a sealed cylindrical lithium ion secondary battery for an electric vehicle will be described below with reference to the drawings.

<Preparation of Positive Electrode> 80% by weight of lithium manganate (LiMn ₂ O ₄ ) powder (hereinafter referred to as wt.) As a positive electrode active material capable of releasing and occluding lithium ions by charging and discharging.
Expressed as%. ), 15 wt% of carbon powder having a different bulk density as a conductive agent, and 5 wt% of polyvinylidene fluoride (PVDF) as a binder, and N-methyl-
It is dissolved in 2-pyrrolidone (hereinafter referred to as NMP) and kneaded to obtain a slurry. The obtained slurry is applied to both sides of an aluminum foil (positive electrode current collector) using a comma roll,
After drying, a positive electrode active material layer is formed.

As shown in FIG. 2 (A), when a slurry is applied by a comma roll, the length required for the positive electrode is applied continuously so that the application position coincides with the front and back surfaces, and the positive electrode active material is applied. In order to prevent the layer 2 from being cut, slitting is performed while leaving one side of the aluminum foil 1 (the portion where the positive electrode tab terminal 8 is formed) at 30 mm and leaving the opposite side of the aluminum foil 1 at 3 mm. Next, as shown in FIG. 2 (B), one side of the aluminum foil 1 left by 30 mm is cut out by rectangular punching to form a positive electrode tab terminal 8. Then, the positive electrode is heated to 80 ° C to 12 ° C.
In a roll press having a roll heated to 0 ° C,
A band-shaped hoop is produced by compressing the powder under a press pressure (linear pressure) of 200 to 500 kg / cm until the bulk density of the positive electrode active material layer 2 becomes 2.6 g / cm ³ .

<Preparation of Negative Electrode> Amorphous carbon powder was used as a negative electrode active material capable of inserting and extracting lithium ions by charging and discharging. NMP was added to a mixture of 90 wt% of carbon powder and 10 wt% of PVDF, and kneaded. To get a slurry. Using a comma roll, the obtained slurry is continuously coated on both surfaces of the copper foil 3 (negative electrode current collector) with the length required for the negative electrode using a comma roll so that the coating position is the same on the front and back surfaces. To form a negative electrode active material layer 4.

As shown in FIG. 2A, one side of the copper foil 3 (the portion where the negative electrode tab terminal 9 is formed) is 3 so that the negative electrode active material layer 4 is not cut during slurry coating using a comma roll.
The slit is left leaving 3 mm on the opposite side of the copper foil 3, leaving 0 mm. Next, as shown in FIG. 2B, one side of the copper foil 3 left by 30 mm is cut out by rectangular punching to form a negative electrode tab terminal 9. Then, the negative electrode is heated to 80 ° C to 120 °.
C. Using a roll press having a roll heated to C, the belt-shaped hoop is compressed at a pressing pressure (linear pressure) of 200 to 500 kg / cm until the bulk density of the negative electrode active material layer 4 becomes 1.0 g / cm ^3. Make it.

<Assembly of Battery> The obtained band-shaped positive and negative electrode hoops are arranged so that the positive electrode tab terminal 8 and the negative electrode tab terminal 9 are on the opposite sides in the vertical direction, and the band-shaped lithium ion can pass therethrough. It piles up through a separator and winds. At this time, the ends of the positive and negative hoops except for the positive electrode tab terminal 8 and the negative electrode tab terminal 9 do not protrude from the outer dimensions of the separator in the length and width directions so that the positive and negative electrodes do not contact. Wind up. The required length of the electrode plate is wound, and the positive and negative electrode hoops are cut to form a wound group. In addition, a polyethylene microporous sheet can be used for the separator.

As shown in FIG. 1, the positive electrode tab terminal 8 and the negative electrode tab terminal 9 located above and below the winding group are welded to the positive electrode current collecting ring 11 and the negative electrode current collecting ring 12 which are annular conductors, respectively. The current collecting ring 11 is welded to the battery lid 7 having an internal safety valve and serving as an external terminal, and the negative electrode current collecting ring 12 is welded to the cylindrical bottomed battery can 6 serving as an external terminal via conductor leads. Next, a non-aqueous electrolyte containing a leveling agent (hereinafter, referred to as a leveling agent-containing electrolyte) is supplied to the battery can 6.
After that, the opening of the battery can 6 is sealed with a battery lid 7 via a gasket 10 to thereby form the lithium ion secondary battery 2.
Assemble 0. Then, by performing initial charging at a predetermined voltage and current, the lithium ion secondary battery 20 is given a function as a battery.

<Preparation of Electrolyte Solution> In the above-described electrolyte solution containing a leveling agent, a lithium salt is used as an electrolyte, and concentration of metal ions on an electrode plate is suppressed in a nonaqueous electrolyte solution obtained by dissolving the lithium salt in an organic solvent. Add a trace amount of a leveling agent (for example, 0.00
1 mol) is used (added). Here, the leveling agent is to prevent the metal to be plated in electrolytic plating from being locally concentrated and precipitated.
A substance which is mixed and dispersed in an electrolytic solution in order to smooth a plating surface by uniformly dispersing and depositing, and is also called a smoothing agent, a brightener, a leveler, a smoothing agent, and a brightener. As a leveling agent (hereinafter, referred to as a leveling agent) that suppresses concentrated precipitation of metal ions on the electrode plate, for example, a substance having a polyether group or an organic sulfone group, or a phosphorus compound or a sulfur compound can be used. .

[0018]

EXAMPLE Next, according to the above embodiment, lithium hexafluorophosphate (LiPF ₆ ) was added to a mixed solution obtained by mixing ethylene carbonate (EC) and dimethyl carbonate (DMC) at a volume ratio of 1: 2. Various leveling agents were added to the non-aqueous electrolyte dissolved in 1 mol / liter in an amount of 0.001.
A lithium ion secondary battery of an example manufactured using a leveling agent-containing electrolyte solution added in a molar amount will be described. Note that a lithium ion secondary battery of a comparative example manufactured for comparison is also described. However, in the batteries of the respective examples, in order to promote the concentrated precipitation of metal ions on the electrode plates, the positive electrode active material layer 2 was intentionally made to contain 7 ppm of copper powder of about 10 to 15 μm, and thus the above-described procedure was carried out. It is different from the lithium ion battery 20 in the form.

Example 1 As shown in Table 1 below, in the battery of Example 1, 0.1% of sodium 1,5-naphthalene-disulfonate was added to the above-mentioned nonaqueous electrolyte as a leveling agent.
001 mol of the leveling agent-containing electrolyte was injected to assemble the battery. The metal impurity content in the non-aqueous electrolyte before injecting the leveling agent was adjusted to 1 ppm or less.

[0020]

[Table 1]

(Embodiment 2) As shown in Table 1, Embodiment 2
In the battery of Example 1, except that an electrolyte containing a leveling agent to which 1,3,6 naphthalene-sodium trisulfonate was added instead of the sodium 1,5-naphthalene-disulfonate of Example 1 was injected. Assembled in the same manner as the battery.

(Embodiment 3) As shown in Table 1, Embodiment 3
The battery of Example 1 was assembled in the same manner as the battery of Example 1 except that an electrolyte containing a leveling agent to which saccharin was added instead of the sodium 1,5-naphthalene-disulfonate of Example 1 was injected.

(Embodiment 4) As shown in Table 1, Embodiment 4
The battery of Example 1 was assembled in the same manner as the battery of Example 1 except that an electrolyte containing a leveling agent to which aldehyde was added instead of sodium 1,5-naphthalene-disulfonate of Example 1 was injected.

(Embodiment 5) As shown in Table 1, Embodiment 5
The battery of Example 1 was assembled in the same manner as the battery of Example 1, except that an electrolyte containing a leveling agent to which gelatin was added instead of sodium 1,5-naphthalene-disulfonate of Example 1 was injected.

(Embodiment 6) As shown in Table 1, Embodiment 6
The battery of Example 1 was the same as the battery of Example 1 except that an electrolyte containing a leveling agent to which 2-butyne-1,4 diol was added instead of the sodium 1,5-naphthalene-disulfonate of Example 1 was injected. Assembled.

(Embodiment 7) As shown in Table 1, the embodiment 7
The battery of Example 1 was assembled in the same manner as the battery of Example 1 except that an electrolyte containing a leveling agent to which quinaldine was added instead of sodium 1,5-naphthalene-disulfonate of Example 1 was injected.

Example 8 As shown in Table 1, Example 8
The battery of Example 1 was assembled in the same manner as the battery of Example 1, except that an electrolyte containing a leveling agent to which a pyridium compound was added instead of sodium 1,5-naphthalene-disulfonate of Example 1 was injected.

(Example 9) As shown in Table 1, Example 9
The battery of Example 1 was assembled in the same manner as the battery of Example 1, except that an electrolyte solution containing a leveling agent to which ethylene cyanohydrin was added instead of sodium 1,5-naphthalene-disulfonate of Example 1 was injected.

Example 10 As shown in Table 1, in the battery of Example 10, an electrolyte containing a leveling agent to which an azo dye was added instead of the sodium 1,5-naphthalene-disulfonate of Example 1 was injected. A battery was assembled in the same manner as in the battery of Example 1 except that the battery was drained.

(Example 11) As shown in Table 1, in the battery of Example 11, an electrolyte containing a leveling agent containing potassium thiocyanate instead of sodium 1,5-naphthalene-disulfonate of Example 1 was used. A battery was assembled in the same manner as the battery of Example 1 except that the liquid was injected.

Example 12 As shown in Table 1, in the battery of Example 12, a leveling agent-containing electrolytic solution obtained by adding potassium pyrophosphate in place of sodium 1,5-naphthalene-disulfonate of Example 1 was used. Example 1 except that the liquid was injected.
The battery was assembled in the same manner as the battery.

Comparative Example As shown in Table 1, the battery of the comparative example was assembled in the same manner as the battery of Example 1 except that no leveling agent was added to the non-aqueous electrolyte.

<Initial charge and test> Next, for each of the batteries of Examples and Comparative Examples assembled as described above, initial charge was performed under the following conditions, and a voltage drop rate measurement test for measuring the voltage drop rate was performed. did.

1. Initial charge / discharge conditions (1) Charging: constant voltage charging 4.1 V, limiting current 2000 m
A, 4h, 25 ° C (2) Discharge: constant current discharge 3000 mA, end voltage 2.7
V, 25 ° C (3) Charging: constant voltage charging 4.1V, limiting current 4000m
A, 3 h, 25 ° C (4) Discharge: constant current discharge 4000 mA, cutoff voltage 2.7
V, 25 ° C (5) Charging: constant voltage charging 3.7V, limiting current 4000m
A, 3h, 25 ° C

2. Voltage drop rate measurement test Each battery was left after the first charge, and the voltage dropped between the second and third weeks of the battery was divided by 7 to calculate the voltage drop rate per day (mV / day).

Table 2 below shows the test results of the voltage drop rate measurement test.

[0037]

[Table 2]

As shown in Table 2, the voltage drop rate of the battery of the embodiment in which the leveling agent was added to the non-aqueous electrolyte was at most 4%.
mV / day, which is 15 mV / day of the battery of the comparative example.
The voltage drop is significantly smaller than that of This is because the addition of the leveling agent to the non-aqueous electrolyte causes the copper to dendrite on the electrode plate and does not precipitate in a concentrated manner, thereby suppressing a minute short circuit.

As described above, in the lithium ion secondary battery according to the present embodiment, the concentration of metal ions on the electrode plate is suppressed, so that the voltage drop due to a minute short circuit can be suppressed. The battery in which the minute short circuit is suppressed has a small voltage drop with the passage of time, and therefore has a long life and can ensure reliability. Such a lithium ion secondary battery has a small voltage drop and a small variation between batteries, and thus is suitable for a battery constituting a battery module.

In the above embodiment, an example was shown in which LiPF ₆ was used as the electrolyte of the non-aqueous electrolyte.
₄ , LiAsF ₆ , LiBF ₄ , LiB (C
_{6 H 5) 4, CH 3} SO 3 Li, can be used CF 3 _SO 3 Li and the like, and mixtures thereof, and in a volume ratio of ethylene carbonate and dimethyl carbonate as an organic solvent 1: mixture in a ratio of 2 Examples in which the mixed solution was used were shown, but in addition to these, propylene carbonate, diethyl carbonate, 1,2-dimethoxyethane, 1,2
-Diethoxyethane, γ-butyrolactone, tetrahydrofuran, 1,3-dioxolan, 4-methyl-1,3
-Dioxolane, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile and the like or a mixed solvent of two or more thereof can be used, and the mixing ratio is not limited.

In the above embodiment, a plurality of leveling agents have been exemplified. However, other leveling agents which suppress the concentrated precipitation of metal ions on the electrode plate, and materials having a leveling action, may be used as the leveling agent. it can.

Furthermore, in this embodiment, an example was shown in which lithium manganate was used as the positive electrode active material and graphitic carbon was used as the negative electrode active material. However, lithium-cobalt composite oxide or lithium-nickel composite oxide was used as the positive electrode active material. Natural graphite, artificial graphite materials, carbon materials such as coke and the like may be used as the material and the negative electrode active material, and the particle shape thereof is also particularly limited, such as flaky, spherical, fibrous, and massive shapes. Not something. Note that lithium manganate having a spinel crystal structure has a feature of being superior in thermal stability to lithium cobaltate and lithium nickelate. Therefore, large-sized lithium manganate for power storage and electric vehicles is used. It is preferable to use lithium manganate as a positive electrode active material for an ion secondary battery.

[0043]

As described above, according to the present invention,
The concentration of metal ions on the electrode plate can be suppressed by the inclusion of the leveling agent, so that a voltage drop due to a minute short circuit can be suppressed, and the deterioration of the electrode plate can be suppressed. The effect that an excellent and highly reliable non-aqueous electrolyte secondary battery can be obtained can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a plan view showing a belt-shaped hoop of a positive electrode and a negative electrode of the embodiment, (A) showing a state after slurry coating,
(B) shows a state after the tab terminals are formed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode collector 2 Positive electrode active material layer 3 Negative electrode collector 4 Negative electrode active material layer 5 Separator 6 Battery can 7 Battery lid 8 Positive tab terminal 9 Negative tab terminal 10 Gasket 11 Positive current collecting ring 12 Negative current collecting ring 20 Lithium Ion secondary battery

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Tomohiro Iguchi 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 F term in Shin-Kobe Electric Co., Ltd. (reference) 5H029 AJ05 AK03 AL08 AM03 AM05 AM07 BJ02 BJ14 DJ08 DJ09 EJ03 EJ11

Claims (3)

[Claims] 1. A non-aqueous electrolyte secondary battery in which a positive electrode capable of releasing and occluding lithium ions by charging and discharging and a negative electrode capable of occluding and releasing lithium ions by charging and discharging are impregnated in the non-aqueous electrolyte. In a battery, a non-aqueous electrolyte secondary battery is characterized in that the non-aqueous electrolyte contains a leveling agent that suppresses concentrated precipitation of metal ions at the positive electrode and / or the negative electrode. 2. The method according to claim 1, wherein the leveling agent is a substance having a polyether group or an organic sulfone group, or a phosphorus compound or a sulfur compound.
3. The non-aqueous electrolyte secondary battery according to 1. 3. The leveling agent comprises sodium 1,5-naphthalene-disulfonate, 1,3,6 naphthalene-
Sodium trisulfonate, saccharin, aldehyde,
Gelatin, 2-butyne-1,4 diol, quinaldine, pyridium compound, ethylene cyanohydrin, azo dye,
The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte secondary battery is at least one of a group consisting of potassium thiocyanate and potassium pyrophosphate.