JP3057499B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a chargeable / dischargeable nonaqueous electrolyte secondary battery used as a power source for various electronic devices, and particularly to a nonaqueous electrolyte having excellent charge / discharge cycle characteristics. The present invention relates to a liquid secondary battery.

[Summary of the Invention]

The present invention provides a non-aqueous electrolyte secondary battery having a negative electrode material composed mainly of a carbonaceous material and a positive electrode material composed of a material mainly composed of a lithium-manganese composite oxide. It is intended to improve.

[Conventional technology]

A so-called non-aqueous electrolyte battery using lithium as a negative electrode active material and an organic electrolyte as an electrolyte has advantages such as low self-discharge, high nominal voltage, and extremely excellent storage stability. . A typical example is a so-called lithium-manganese dioxide battery using manganese dioxide as a positive electrode active material. A battery having a long-term reliability of 10 years has been developed and widely used as a power source for electronic watches and memory backup.

By the way, most of the non-aqueous electrolyte batteries conventionally used are primary batteries, but in recent years, with the spread of portable devices such as video cameras and small audio devices, secondary batteries can be used conveniently and economically for a long time. Demand for secondary batteries is increasing.

Application of the above-described lithium-manganese dioxide battery to a secondary battery is also being studied. In this case, a discharge reaction proceeds by lithium ion being a negative electrode active material being ionized and doped into manganese dioxide being a positive electrode active material,
The reverse reaction, ie, undoping, causes the charging reaction to proceed. However, such a secondary battery has a drawback that as the number of charge / discharge cycles increases, lithium ions doped in manganese dioxide gradually become less undoped and the discharge capacity decreases.

In view of this, the present applicant has previously proposed in Japanese Patent Application No. 63-187563 a non-aqueous electrolyte secondary battery using a lithium-manganese composite oxide having excellent charge / discharge efficiency as a positive electrode active material.

[Problems to be solved by the invention]

By the way, when the above-mentioned lithium-manganese composite oxide is used as a positive electrode active material, part of lithium of the above-mentioned lithium-manganese composite oxide is discharged and deposited on the negative electrode during charging. The charge / discharge cycle characteristics of such a non-aqueous electrolyte secondary battery are largely governed by the charge performance of a negative electrode containing lithium as an active material. However, conventionally, this is not always sufficient. There was a problem that the lithium deposited on the separator penetrated the separator and caused an internal short circuit.

Therefore, an object of the present invention is to provide a non-aqueous electrolyte secondary battery having excellent charge / discharge cycle characteristics.

[Problems to be solved by the invention]

The present inventors believe that the charge performance of the negative electrode, which governs the charge-discharge cycle characteristics, depends on the selection of the negative electrode material,
As a result of examining a wide range of substances, the present inventors have found that a carbon material is particularly suitable as a negative electrode active material in a wound type secondary battery, and have completed the present invention.

That is, a non-aqueous electrolyte secondary battery according to the present invention includes a negative electrode, which has a negative electrode material, a positive electrode material, and a non-aqueous electrolyte, and is formed by molding the negative electrode material on both sides of a belt-shaped current collector; In a non-aqueous electrolyte secondary battery obtained by winding a positive electrode formed on both sides of a belt-shaped current collector with a separator, the negative electrode material is a negative electrode material mainly composed of a carbon material. , The positive electrode material is LiMn ₂ O ₄ or Li _x Mn ^(m) O _{(x + m) / 2} (however,
X in the formula is a number selected to satisfy the condition of 0.5 ≦ x ≦ 0.7, m is a manganese valence analysis value, and 3.80 ≦ m ≦
3.90, 4.03 ≦ m + ≦ x ≦ 4.55. ) Is a positive electrode material.

First, typical examples of the carbonaceous material that is the main component of the negative electrode material include a pitch-based material, a fired carbide of an organic polymer material, and a fired carbide of an organic low-molecular compound.

Examples of the pitch-based material include pitch obtained by pyrolysis of petroleum and coal such as petroleum pitch, asphalt pitch, coal tar pitch, crude oil cracking pitch, and petroleum sludge pitch, and pitch-based calcined carbide such as needle coke. Alternatively, the pitch may be formed by thermal decomposition of an organic polymer material or an organic low-molecular compound described later.

The organic polymer material used as a raw material of the calcined carbide is an acrylic resin, a polyacrylonitrile resin, a vinyl acetate resin, a polyvinyl alcohol resin, a polyvinyl acetal resin, an ABS resin, a polyamide resin, a polyimide resin, a polyamide imide resin, a vinyl halide resin. It can be arbitrarily selected from a wide range of materials such as resin, polyvinylidene chloride resin, polyacetylene, cellulose resin, polyphenylene resin, and furan resin. In particular, furan resins are suitable, and various furan resins such as furfural phenol resin, body, furfuryl alcohol dimethylol urea resin, furfuryl alcohol resin, furfuryl alcohol formaldehyde resin, and furfural ketone resin can be used.

Further, examples of the organic low molecular weight compound serving as a raw material of the calcined carbide include naphthalene, phenanthrene, anthracene, triphenylene, pyrene, chrysene, naphthacene,
Fused polycyclic hydrocarbons such as picene, perylene, pentaphene, pentacene and derivatives thereof, indole, isoindole, quinoline, isoquinoline, quinoxaline,
Phthalazine, carbazole, acridine, phenazine,
Examples include condensed heterocyclic hydrocarbons such as phenanthridine and derivatives thereof.

On the other hand, as the lithium-manganese composite oxide as a main component of the positive electrode material, a compound whose composition is represented by a simple integer ratio such as LiMn ₂ O ₄ or Li _x Mn ^(m) O _{(x + m) / 2}
A compound represented by the following formula is used. In the latter case, x is a number selected so as to satisfy the condition of 0.5 ≦ x ≦ 0.7. Further, m is a manganese valence analysis value, and satisfies the following conditions.

3.80 ≦ m ≦ 3.90 4.30 ≦ m + x ≦ 4.55 The compound represented by the above formula Li _x Mn ^(m) O _{(x + m) / 2} has a manganese valence analysis value m of LiMn ₂ O ₄ (m = 3.5)
Is different from

As the non-aqueous electrolyte, an electrolyte obtained by dissolving a lithium salt as an electrolyte in an organic solvent is used.

The organic solvent is not particularly limited, but for example, propylene carbonate, ethylene carbonate,
1,2-dimethoxyethane, 1,2-diethoxyethane, γ-
Butyrolactone, tetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, methylsulfolane, acetonitrile,
Organic solvents such as propionitrile can be used alone or as a mixture of two or more.

Examples of the lithium salt dissolved as an electrolyte in the organic solvent include LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , and LiB (C ₆ H ₅ ) ₄ , L
Conventionally known materials such as iCl, LiBr, CH ₃ SO ₃ Li, and CF ₃ SO ₃ Li can be used. Among them, LiClO ₄ and LiBF ₄ are particularly preferred.

[Action]

In the non-aqueous electrolyte secondary battery of the present invention, at the time of charging, part of lithium ions is released from LiMn ₂ O ₄ or Li _x Mn ^(m) O _{(x + m) / 2} , which is the positive electrode active material, and this is the main component of the negative electrode. Is doped into the carbonaceous material. Therefore, unlike the case where dendrite is deposited on the surface of the negative electrode material, there is no possibility of causing an internal short circuit. During discharge, lithium ions are quickly undoped from the carbonaceous material. Therefore, even after repeated charge / discharge cycles, deterioration of the battery capacity can be suppressed to a very low level.

〔Example〕

Hereinafter, preferred embodiments of the present invention will be described based on experimental results.

ExampleThis example is a propylene carbonate obtained by dissolving pitch coke as a carbonaceous material as a main component of a negative electrode material, LiMn ₂ O ₄ as a lithium-manganese composite oxide as a main component of a positive electrode material, and LiPF ₆ as a nonaqueous electrolyte. This is an example in which a cylindrical battery is configured using a mixed solvent of / 1,2-dimethoxyethane.

The negative electrode was prepared as follows. First, 90 parts by weight of pulverized pitch coke was added with 10 parts by weight of polyvinylidene fluoride as a binder to form a negative electrode material, and then the negative electrode material was dispersed in N-methylpyrrolidone to prepare a slurry. Further, the slurry was uniformly applied to both sides of a strip-shaped copper foil serving as a negative electrode current collector, dried, and then compression-molded by a roller press to form a strip-shaped negative electrode.

On the other hand, the positive electrode was prepared as follows. First, a mixture of 1 mol of manganese dioxide and 0.25 mol of lithium carbonate was calcined at 800 ° C. for 5 hours in air to prepare LiMn ₂ O ₄ . Next, 86 parts by weight of LiMn ₂ O ₄ were mixed with 10 parts by weight of graphite as a conductive agent and 4 parts by weight of polyvinylidene fluoride as a binder to prepare a positive electrode material. Further, a slurry was prepared by dispersing the positive electrode material in N-methylpyrrolidone,
This was uniformly coated on both sides of a strip-shaped aluminum foil serving as a positive electrode current collector, dried, and then compression-molded by a roller press to form a strip-shaped positive electrode.

Subsequently, a cylindrical battery as shown in FIG. 1 was prepared by the following procedure using the above-mentioned negative electrode and positive electrode. First, the negative electrode (1) and the positive electrode (2) were wound up in a roll via a porous polypropylene separator (3) to form a wound body. Next, an insulating plate (4) was inserted into the bottom of a nickel-plated iron battery can (5), and the wound body was stored. Next, in order to collect the current of the negative electrode (1), one end of a nickel negative electrode lead (7) was pressed and the other end was welded to the battery can (5). Next, in order to collect the power of the positive electrode (2), one end of an aluminum positive electrode lead (6) was attached to the positive electrode (2) by ultrasonic welding, and the other end was welded to the lid (7). . The battery can (5)
Into which a mixed solvent of propylene carbonate / 1,2-dimethoxyethane in which LiPF ₆ is dissolved at a concentration of 1 mol / is injected as a non-aqueous electrolyte, and the insulating plate (4) is again charged and The battery can (5) and the lid (7) were caulked via a gasket (6) and sealed. As described above, the diameter 1
A cylindrical battery A having a size of 3.8 mm and a height of 42 mm was prepared.

As a comparison with the above-mentioned cylindrical battery A, the present inventors further compared in the following Comparative Examples 1 to 5 cylindrical batteries B to cylindrical batteries each having a negative electrode composed of various metal foils instead of carbonaceous materials. Battery F was prepared.

Comparative Example 1 A cylindrical battery B was prepared in the same manner as in Example, except that a band-shaped copper foil serving as a negative electrode current collector was laminated with a band-shaped lithium foil as a negative electrode.

Comparative Example 2 A cylindrical battery C was prepared in the same manner as in Example, except that a strip-shaped copper foil was used as a negative electrode.

Comparative Example 3 A cylindrical battery D was prepared in the same manner as in Example, except that a strip-shaped aluminum foil was used as a negative electrode.

Comparative Example 4 A cylindrical battery E was prepared in the same manner as in Example, except that a strip-shaped nickel foil was used as a negative electrode.

Comparative Example 5 A cylindrical battery F was prepared in the same manner as in Example, except that a strip-shaped lead foil was used as a negative electrode.

A charge / discharge cycle test was performed on the cylindrical batteries A to F produced in the above Examples and Comparative Examples. In one cycle, the charging current is 220mA and the upper limit voltage is
It combines 3.5-hour constant-current charging with 4 V and constant-resistance discharging with a 14 Ω load connected and a final voltage of 2.9 V. The results are shown in FIG. In the figure, the vertical axis indicates the discharge capacity (m
Ah), the horizontal axis represents the number of cycles (times), and curves A to E represent the charge / discharge cycle characteristics of the cylindrical batteries A to E, respectively. From this figure, it can be seen that the battery capacity of each of the cylindrical batteries B to F produced in each comparative example is reduced to about 1/10 of the initial value at the time when the charge / discharge cycle test is performed 20 to 50 cycles. On the other hand, the cylindrical battery A according to the example has an initial value of 8 even after 200 cycles.
It is clear that the battery capacity is maintained at 0% or more and the cycle life is extremely excellent.

〔The invention's effect〕

As is clear from the above description, in the nonaqueous electrolyte secondary battery of the present invention, the lithium ions released from the positive electrode active material at the time of filling do not precipitate in the form of dendrites on the surface of the negative electrode. There is no risk of short circuit. In addition, since the above-mentioned lithium ion shows a rapid doping or undoping behavior with respect to the negative electrode material according to charge / discharge, the non-aqueous electrolyte secondary battery which has very little deterioration in battery capacity due to charge / discharge cycles and has excellent long-term reliability. Can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a configuration example of a cylindrical battery according to one embodiment of the present invention. FIG. 2 is a characteristic diagram showing charge / discharge cycle characteristics of the cylindrical batteries according to the example and the comparative example. DESCRIPTION OF SYMBOLS 1 ... Negative electrode 2 ... Positive electrode 3 ... Separator 5 ... Battery can

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-114065 (JP, A) JP-A-63-174059 (JP, A) JP-A-1-173574 (JP, A) JP-A-63-164 187569 (JP, A) JP-A-62-122066 (JP, A) JP-A-58-220362 (JP, A) JP-B-58-34414 (JP, B2) US Patent 4507371 (US, A) Tsutomu Kotsuki, "Research on Manganese Dioxide for Lithium Nonaqueous Solvent Batteries", Research Report of Asahi Glass Industrial Technology Promotion Association, issued on January 30, 1989, Vol. 53, p. 107-112 (58) Field surveyed (Int. Cl. ⁷ , DB name) H01M 10/40 H01M 4/58 JICST file (JOIS) WPI / L (QUESTEL)

Claims (1)

(57) [Claims] 1. A negative electrode comprising a negative electrode material, a positive electrode material and a non-aqueous electrolyte, wherein the negative electrode material is formed on both sides of a strip-shaped current collector, and the positive electrode material is formed on both sides of a strip-shaped current collector. A non-aqueous electrolyte secondary battery obtained by winding a positive electrode formed through a separator, wherein the negative electrode material is a negative electrode material mainly composed of a carbon material, and the positive electrode material is LiMn ₂ O ₄ Or Li _x Mn ^(m) O _{(x + m) / 2}
(Where x in the formula is a number selected so as to satisfy the condition of 0.5 ≦ x ≦ 0.7, m is a manganese valence analysis value, and 3.
80 ≦ m ≦ 3.90, 4.03 ≦ m + x ≦ 4.55. A non-aqueous electrolyte secondary battery comprising a positive electrode material mainly comprising: