JP3329161B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nonaqueous electrolyte secondary battery, and more particularly to an improvement in battery characteristics by improving a binder used for a positive electrode thereof.

[0002]

2. Description of the Related Art In recent years, portable and cordless electronic devices have been rapidly developed, and secondary batteries having a small size, light weight and high energy density are mainly used as power sources for these devices. Among them, non-aqueous electrolyte secondary batteries, especially lithium secondary batteries, are regarded as promising as batteries having high voltage and high energy density.

In order to withstand these heavy loads, it is desirable to increase the surface area of the electrode and increase the contact area with the counter electrode. That is, as a battery structure, a spiral structure in which positive and negative electrode active materials are applied together with a conductive material and a binder on a thin metal foil current collector and wound through a separator is advantageous.

A positive electrode using this lithium composite oxide is kneaded with a binder dissolved in an organic solvent and a conductive material,
It is prepared by coating and drying on a current collector and then bonding it by rolling or the like. As a binder, polyvinylidene fluoride (Japanese Patent Application Laid-Open No. 4-24959) or a polyimide resin (Japanese Patent Application Laid-Open No. 57-210568) is used. ) Has been proposed.

[0005] However, polyvinylidene fluoride is
Although it has excellent adhesion to metal oxides, it is suitable for integrating positive electrode active materials, but adhesion to a collector metal such as copper or aluminum is not so good. For this reason, batteries using polyvinylidene fluoride as a binder for the positive electrode made of a compound capable of inserting and extracting lithium,
As the charge / discharge cycle is repeated, the adhesion between the current collector and the electrode layer deteriorates, and there is a problem that the life of the battery is shortened due to a decrease in the discharge capacity.

[0006] Polyimide resin is excellent in adhesion to a current collector metal such as copper and aluminum.
Low conductivity to current collector metal. Therefore, a battery using a polyimide resin as a binder for a positive electrode made of a compound capable of inserting and extracting lithium has a high internal resistance of the battery. There's a problem.

[0007]

SUMMARY OF THE INVENTION The present invention provides a non-aqueous electrolyte secondary battery which prevents the positive electrode active material from peeling off from the current collector metal and has a small capacity reduction due to repeated charge / discharge cycles. is there.

[0008]

In order to solve the above-mentioned problems, the present invention relates to a negative electrode comprising lithium, a lithium alloy, or a compound capable of inserting and extracting lithium, and a compound comprising a compound capable of reversibly charging and discharging lithium. And a mixture of polyvinylidene fluoride and an organic compound having an imide group is used as a binder that is a component of the positive electrode. The positive electrode according to the present invention uses a mixture of polyvinylidene fluoride and an organic compound having an imide group dissolved in an organic solvent as a binder, kneads it with a conductive material, coats it on a current collector, dries it, and bonds it by rolling or the like Is created.

The organic compound having an imide group includes
Compounds 1 to 29 represented by [Chemical Formula 1] have excellent adhesion to the current collector metal.

[0010]

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[0011]

BEST MODE FOR CARRYING OUT THE INVENTION In the battery of the present invention, polyvinylidene fluoride and an organic compound having an imide group are used as a binder, and the adhesion between the positive electrode active materials is polyvinylidene fluoride, the positive electrode active material and the current collector metal. Is realized by an organic compound having an imide group. For this reason, the conventional problem that the adhesion between the current collector and the electrode layer is deteriorated while the charge / discharge cycle is repeated and the discharge capacity is reduced, thereby shortening the life of the battery can be solved.

When the content ratio of the organic compound having an imide group to the positive electrode active material is too large, although the binding property with the current collector metal is improved, the conductivity with respect to the current collector metal is lowered. Is not preferable. Therefore, the content ratio of the organic compound having an imide group to the positive electrode active material is more preferably 0.05 to 0.25 parts by weight.

[0013]

【Example】

Embodiment 1 Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a longitudinal sectional view of the cylindrical battery used in this example. In the figure, reference numeral 1 denotes a battery case formed by processing a stainless steel plate having resistance to organic electrolyte, 2 denotes a sealing plate provided with a safety valve, and 3 denotes an insulating packing. Reference numeral 4 denotes an electrode group, in which a positive electrode and a negative electrode are spirally wound a plurality of times via a separator and housed in the case 1. A positive electrode lead 5 is drawn from the positive electrode and connected to the sealing plate 2, and a negative electrode lead 6 is drawn from the negative electrode and connected to the bottom of the battery case 1. Reference numeral 7 denotes an insulating ring provided on the upper and lower portions of the electrode plate group 4, respectively.

The positive electrode is made of LiNi _0.9 Co _0.1 as an active material.
The O ₂ was used. 4 parts by weight of acetylene black is mixed with 10 parts by weight of the positive electrode active material, and 4 parts by weight of polyvinylidene fluoride and 0.1 parts by weight of compounds 1 to 29 represented by Chemical Formula 1 (each corresponding to batteries 1 to 29). Dissolved N-
A methylpyrrolidone solution was added as a binder and kneaded to form a paste. Next, this paste was applied on both sides of an aluminum foil, dried, and then rolled to obtain a positive electrode plate having a thickness of 0.14 mm, a width of 37 mm, and a length of 250 mm.

As the negative electrode, a mesophase small sphere graphitized (hereinafter referred to as mesophase graphite) was used. 100 parts by weight of the mesophase graphite was mixed with 3 parts by weight of styrene / butadiene rubber as a binder, and an aqueous carboxymethyl cellulose solution was added and kneaded to form a paste. This paste was applied to both sides of a copper foil, dried, and rolled to obtain a negative electrode plate having a thickness of 0.21 mm, a width of 39 mm, and a length of 280 mm.

A lead made of aluminum is attached to the positive electrode plate, and a lead made of nickel is attached to the negative electrode plate, and spirally wound through a polyethylene separator having a thickness of 0.025 mm, a width of 45 mm, and a length of 740 mm. Diameter 1
It was delivered to a 4.0 mm, 50 mm high battery case.

As the electrolytic solution, a solution prepared by dissolving 1 mol / l lithium hexafluorophosphate as an electrolytic solution in a solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 20:80 was injected. Then, the battery was sealed to obtain a completed battery.

Example 2 An N-methylpyrrolidone solution obtained by dissolving 4 parts by weight of polyvinylidene fluoride and 0.2 part by weight of the compound 1 represented by the chemical formula 1 with respect to 100 parts by weight of the positive electrode active material was used as a binder. In addition, a positive electrode plate and a battery were formed in the same manner as in Example 1 to obtain a battery 30.

Example 3 An N-methylpyrrolidone solution obtained by dissolving 4 parts by weight of polyvinylidene fluoride and 1.0 part by weight of compound 1 represented by the formula (1) to 100 parts by weight of a positive electrode active material was bound. A positive electrode plate and a battery were formed in the same manner as in Example 1 in addition to the agent, and a battery 31 was obtained.

Comparative Example 1 N was obtained by dissolving only 4 parts by weight of polyvinylidene fluoride with respect to 100 parts by weight of the positive electrode active material.
Example 1-methylpyrrolidone solution was added as binder
A positive electrode plate and a battery were formed in the same manner as described above.

Comparative Example 2 An N-methylpyrrolidone solution in which only 4 parts by weight of the compound 1 represented by the chemical formula 1 was dissolved with respect to 100 parts by weight of the positive electrode active material was added as a binder.
The positive electrode plate and the battery were formed in the same manner as in Example 1, and the battery 33
And

These batteries were subjected to a high load discharge test and a charge / discharge cycle test under the following conditions. Charging is 4.2
The battery was charged at a constant voltage of 2 V for 2 hours, and a constant current charge of 420 mA was set until the battery voltage reached 4.2 V. A constant current discharge was performed at 1220 mA in the high load discharge test and 610 mA in the cycle test, and the discharge end voltage was set to 3.0 V. Such charge / discharge was performed in an environment of 20 ° C. In the cycle test, the discharge capacity at the fifth cycle was set as the initial capacity, and the value of the number of cycles was read when the discharge capacity deteriorated to 300 mAh as the end of cycle life. The results are shown in Tables 1 and 2.

[0023]

[Table 1]

[0024]

[Table 2]

According to Tables 1 and 2, the initial capacity of the battery when constant current discharge is performed at 610 mA is represented by the chemical formula 1 for a battery (battery 32) having only polyvinylidene fluoride as a binder and for polyvinylidene fluoride. It can be seen that there is almost no change in the batteries to which Compounds 1 to 29 are added (Batteries 1 to 31).
However, the capacity of the battery (Battery 33) containing only an organic compound containing an imide group as the binder was particularly small. This is because the organic compound containing an imide group has excellent adhesion to the current collector metal, but has no conductivity to the current collector metal, so that the internal resistance of the battery increases.

When a constant current discharge was carried out at a high load of 1220 mA, a battery was prepared by adding 0.1 to 0.2 parts by weight of a compound 1-29 represented by the chemical formula 1 to polyvinylidene fluoride as a binder. In the batteries 1 to 30), the capacity was not so much reduced as compared with the battery (battery 32) using only polyvinylidene fluoride as the binder, but the compound 1 represented by the chemical formula 1 was added to the polyvinylidene fluoride as 1. The capacity of the battery (Battery 31) added with 0 parts by weight and the battery (Battery 33) containing only the organic compound containing an imide group as the binder were significantly reduced. this is,
This is because, since the organic compound having an imide group itself has no conductivity, when the content ratio of the organic compound having an imide group in the binder increases, the conductivity to the current collector metal decreases.

The battery (batteries 1 to 31) obtained by adding the compounds 1 to 29 represented by the chemical formula 1 to polyvinylidene fluoride compared to the battery (battery 32) containing only polyvinylidene fluoride as the binder has a longer life. The number of late cycles has improved significantly. This is because the excellent adhesion of the BMI to the current collector metal in the binder prevents the positive electrode active material from peeling off from the current collector metal due to the repetition of the charge / discharge cycle. This is because a decrease in capacity is reduced. The number of cycles also increased with an increase in the amount of the organic compound containing an imide group in the binder, but no significant difference was found between the respective numbers of cycles. This is because even with a small amount of BMI in the binder, the adhesion to the current collector metal is sufficiently maintained. Although the number of cycles at the end of life of a battery (battery 33) containing only an organic compound containing an imide group as the binder is not so large, this is because the initial capacity is small, so that the discharge capacity is only quickly deteriorated to 300 mAh. .

From the above, it can be seen that the present invention provides a method for collecting active materials involved in a charge / discharge cycle by using an appropriate amount of an organic compound having an imide group together with polyvinylidene fluoride as a binder for a positive electrode of a nonaqueous electrolyte secondary battery. Separation from the conductor metal can be prevented, whereby the cycle characteristics of the battery can be improved.

In the above embodiment, LiNi _0.9 Co _0.1 O ₂ was used as the positive electrode active material, but the active material was represented by the general formula Li _x NiO ₂ , Li _x CoO ₂ , Li _x Mn ₂ O ₄ (0
≦ x ≦ 1.2) lithium composite oxide represented by, or the general formula _{Li x N (1-y)} M y O 2 (0 ≦ x ≦ 1.2,0 ≦
y ≦ 0.5, N and M are Ni, Ti, V, Cr, Mn, F
e, 2 of metal elements such as Co, Cu, Zn, Al and B
The same effect can be obtained by using a positive electrode material such as a lithium composite oxide represented by the following formula (1).

In the above embodiment, the evaluation was performed using a cylindrical battery. However, similar results can be obtained even when the battery shape is different, such as a square battery.

Further, in the above embodiments, a carbonaceous material was used for the negative electrode. However, since the effect of the present invention acts on the positive electrode plate, lithium, a lithium alloy, a compound capable of inserting and extracting lithium, and the like can be used. Similar effects can be obtained.

In the above embodiment, lithium hexafluorophosphate was used as the electrolyte. However, other lithium-containing salts such as lithium perchlorate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, hexafluorofluoride, etc. Similar effects were obtained with lithium arsenate and the like.

In the above embodiment, a mixed solvent of ethylene carbonate and ethyl methyl carbonate was used. However, other non-aqueous solvents, for example, cyclic esters such as propylene carbonate, cyclic ethers such as tetrahydrofuran, and chain-like solvents such as dimethoxyethane. Similar effects were obtained by using a non-aqueous solvent such as a chain ester such as ether or methyl propionate, or a multi-component mixed solvent thereof.

[0034]

As described above, by using an appropriate amount of an organic compound having an imide group together with polyvinylidene fluoride as a binder for the positive electrode according to the present invention, peeling of the active material from the current collector metal accompanying the charge / discharge cycle can be prevented. Can be prevented,
A non-aqueous electrolyte secondary battery having excellent cycle characteristics can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view of a cylindrical battery according to an example of the present invention and a comparative example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Battery case 2 Sealing plate 3 Insulation packing 4 Electrode group 5 Positive electrode lead 6 Negative electrode lead 7 Insulation ring

Continuation of the front page (56) References JP-A-6-275279 (JP, A) JP-A-7-122303 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4 / 02-4/04 H01M 4/62

Claims (2)

(57) [Claims] 1. A binder comprising a negative electrode made of lithium, a lithium alloy, or a compound capable of inserting and extracting lithium, and a positive electrode made of a compound capable of reversibly charging and discharging lithium. Non-aqueous electrolyte secondary battery characterized by using a mixture of polyvinylidene fluoride and an organic compound having an imide group. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the content ratio of the organic compound having an imide group to the positive electrode active material is 0.05 to 0.25 parts by weight.