JP2002203550A - Lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary battery having a high safety although it has a high capacity and a high output. SOLUTION: The cylindrical lithium-ion battery 20 has a built in winding group 6 and a nonaqueous electrolytic solution in a battery container 7. As for the winding group 6, a positive electrode in which lithium manganate having average diameter not less than 2 μm of the primary particle is used as a positive electrode active substance and a negative electrode in which amorphous carbon is used as a negative electrode active substance are wound via a separator. A battery cap 6 has a rupture valve 11 to cleave at a prescribed pressure. Mn-O bonding strength rises according to the primary particle average diameter that has been grown.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery, and more particularly, to a battery container having an internal pressure release mechanism for releasing internal pressure at a predetermined pressure, a positive electrode and a negative electrode active material using lithium manganate as a positive electrode active material. The present invention relates to a lithium secondary battery having a built-in electrode group formed by winding a negative electrode using amorphous carbon through a separator, and a non-aqueous electrolyte that infiltrates the electrode group.

[0002]

2. Description of the Related Art In the field of rechargeable secondary batteries, aqueous batteries such as lead batteries, nickel-cadmium batteries, and nickel-hydrogen batteries have hitherto been the mainstream. However, as electric devices have become smaller and lighter, attention has been focused on lithium secondary batteries having a high energy density, and research, development, and commercialization have been rapidly advanced. Lithium secondary batteries for consumer use have become widespread.

[0003] On the other hand, electric vehicles (EV) and hybrid electric vehicles (HEV) in which a part of the drive is assisted by electric motors have been developed by various automobile manufacturers due to the problem of global warming and depleted fuel, and their power sources have increased capacity. High-output secondary batteries have been required. As a power source meeting such a demand, a non-aqueous solution type lithium secondary battery having a high voltage has attracted attention.

A carbon material is generally used as a negative electrode material of a lithium secondary battery. This carbon material is made of natural graphite, scale,
An amorphous carbon material obtained by firing a graphite material such as artificial graphite in a lump or a mesophase pitch graphite and a furan resin such as furfuryl alcohol is used.

[0005] In addition, lithium transition metal oxides are generally used for the positive electrode material. Among them, lithium cobalt oxide is widely used in view of the balance of capacity and cycle characteristics. Therefore, lithium manganate is promising as a positive electrode material for batteries for electric vehicles and hybrid electric vehicles, and its development is proceeding.

[0006]

However, in the case of lithium secondary batteries, safety tends to be emphasized as the capacity and output of the batteries are increased. Particularly, power sources for electric vehicles and hybrid electric vehicles are used. High capacity as used,
When a high-power secondary battery is used, it is charged and discharged at a high current, so it is electrically connected to the internal pressure of the battery in the event of an abnormality, as is generally used in small consumer lithium secondary batteries. It is difficult to provide a working current interrupt mechanism in the battery structure.

[0007] In an electric vehicle or a hybrid electric vehicle that is driven by a person, at the time of overcharging when the charge / discharge control system breaks down, at the time of a battery crash that may encounter an accidental collision, Ensuring the safety of the battery itself at the time of piercing or external short circuit is a minimum and very important battery characteristic. Battery safety here means that the behavior of the battery when the battery is exposed to abnormal conditions does not harm the human body, but also minimizes damage to the vehicle. I do.

The present invention has been made in view of the above circumstances, and has as its object to provide a lithium secondary battery having a high capacity and a high output, yet having extremely high safety.

[0009]

In order to solve the above-mentioned problems, the present invention provides a battery container having an internal pressure releasing mechanism for releasing an internal pressure at a predetermined pressure, comprising a positive electrode and a negative electrode using lithium manganate as a positive electrode active material. An electrode group in which a negative electrode using amorphous carbon as an active material is wound via a separator, and a non-aqueous electrolyte infiltrating the electrode group, in a lithium secondary battery incorporating the lithium manganate, The average particle diameter of the primary particles is 2 μm or more.

According to the present invention, in order to secure a high capacity, high output lithium secondary battery, a positive electrode using lithium manganate as a positive electrode active material, a negative electrode using amorphous carbon as a negative electrode active material, Is used. In a high-capacity, high-output lithium secondary battery, a large current charge or a large current discharge state is maintained when an overcharged state occurs, and a sudden reaction occurs in the battery container due to a chemical reaction between the nonaqueous electrolyte and the active material. In addition, a large amount of gas is generated, and the internal pressure of the battery container is increased. Generally, a lithium secondary battery has an internal pressure reduction mechanism that releases internal pressure at a predetermined pressure in the battery container in order to prevent an increase in internal pressure in the battery container, but the average primary particle diameter is 2 μm or more. By using lithium manganate grown on a positive electrode active material, Mn of lithium manganate can be increased by growing the primary particle diameter.
Since the -O bonding force is increased, the elution reaction of Mn from the lithium manganate into the nonaqueous electrolyte during overcharging can be suppressed, and the temperature rises when a battery abnormality such as overcharging continues. Even when an internal short circuit occurs, thermal runaway due to the decomposition reaction of lithium manganate can be prevented, and the battery can be safely disabled. Therefore, according to the present invention, it is possible to realize a lithium secondary battery having high safety while being high in capacity and high in output.

In this case, if lithium manganate having a spinel crystal structure is used as the positive electrode active material, the spinel crystal structure has high thermal stability, so that the safety of the lithium secondary battery can be further improved. If lithium manganate having a Li / Mn composition ratio in the range of 0.55 or more and 0.60 or less is used, the Mn elution reaction can be compared with the stoichiometric composition (Li / Mn = 0.5). Not only occurs at a higher potential, but also suppresses the progress and expansion of the Mn elution reaction in the event of a battery abnormality, making subsequent thermal runaway reactions less likely to occur and further enhancing safety in the event of a battery abnormality. be able to. Such lithium manganate has a chemical formula of Li _{1 + x} Mn _2-x O ₄
Or one obtained by substituting a part of manganese in the chemical formula with another metal element can be suitably used.

[0012]

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

(Positive Electrode) As a positive electrode active material, lithium manganate (Li _{1 + x} Mn _2-x O ₄ or Li _{1 + x} Mn ₂₋ ) having an average primary particle diameter (hereinafter, referred to as an average primary particle diameter) of 2 μm or more. _{x-y Al} y _{O 4)} powder and a scaly graphite as a conductive material, polyvinylidene fluoride and (PVDF), the weight ratio as a binder 85: 10 were mixed with 5,
A slurry in which N-methylpyrrolidone (NMP) as a dispersion solvent was added and kneaded was applied to both surfaces of a 20-μm-thick aluminum foil. Thereafter, the positive electrode having a thickness of 90 μm was obtained by drying, pressing and cutting.

Lithium manganate has a spinel crystal structure and a composition ratio of Li to Mn (hereinafter, Li / M
It is called n ratio. ) Of 0.55 to 0.60 were used. Lithium manganate can be synthesized by mixing and baking an appropriate lithium salt and manganese oxide. However, by controlling the charging ratio of the lithium salt and manganese oxide, a desired Li / Mn ratio is obtained. Can be. In addition, the used lithium manganate was photographed at random in several places with an electron microscope, the primary particle diameter was measured from the photographed electron micrograph, the number average was calculated, and the primary particle average diameter was confirmed. Was used.

(Negative electrode) To 90 parts by mass of amorphous carbon powder as a negative electrode active material, 10 parts by mass of polyvinylidene fluoride as a binder were added to the negative electrode active material, and NMP as a dispersion solvent was added thereto and kneaded. The slurry thus obtained was applied to both sides of a rolled copper foil having a thickness of 10 μm. Thereafter, drying, pressing and cutting were performed to obtain a negative electrode having a thickness of 70 μm.

(Preparation of Battery) As shown in FIG. 1, the prepared positive and negative electrodes were wound together with a polyethylene separator having a thickness of 40 μm so that these two electrode plates did not come into direct contact with each other to prepare a winding group 6. At the center of the winding, a hollow cylindrical shaft core 1 made of polypropylene was used. At this time, the positive electrode lead piece 2 and the negative electrode lead piece 3 were located on both end faces on the opposite side of the winding group 6, respectively.

After deforming the positive electrode lead piece 2 and assembling and contacting the whole near the flange peripheral surface integrally projecting from the periphery of the positive electrode current collecting ring 4, the positive electrode lead piece 2 and the flange peripheral surface are brought into contact with each other. The positive electrode lead piece 2 was connected to the flange peripheral surface by ultrasonic welding. On the other hand, the connection operation between the negative electrode current collector ring 5 and the negative electrode lead piece 3 was also performed in the same manner as the connection operation between the positive electrode current collector ring 4 and the positive electrode lead piece 2. Thereafter, an insulating coating was applied to the entire periphery of the flange of the positive electrode current collecting ring 4, and the wound group 6 was inserted into a nickel-plated steel battery container 7.

A negative electrode lead plate 8 for electrical conduction is welded to the negative electrode current collector ring 5 in advance. After the winding group 6 is inserted into the battery container 7, the bottom of the battery container 7
And was welded. On the other hand, a positive electrode lead 9 formed by overlapping a plurality of aluminum ribbons in advance is welded to the positive electrode current collecting ring 4, and the other end of the positive electrode lead 9 is sealed with a battery for closing the battery container 7. It was welded to the lower surface of the lid 10. The battery lid 10 is composed of a lid case, a lid cap, a valve retainer for maintaining airtightness, and a cleavage valve 11 as a thin plate made of an aluminum alloy as an internal pressure reducing mechanism. It is assembled by caulking the periphery. The cleavage pressure of the cleavage valve 11 is about 9 × 10 ⁵ Pa
Set to.

A predetermined amount of a non-aqueous electrolyte capable of infiltrating the entire winding group 6 is poured into the battery container 7, and then the battery cover 7 is covered with the battery cover 10 so that the positive electrode lead 9 is folded. A cylindrical lithium ion secondary battery 2 having a capacity of 4.0 Ah, which is caulked and sealed via an EPDM resin gasket.
0 was completed.

The non-aqueous electrolyte contains a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC) and diethyl carbonate (DEC) at a volume ratio of 1: 1: 1 into a mixed solution of phosphoric acid hexafluoride. Lithium (LiP
F ₆₎ was used after dissolving 1 mole / liter.

[0021]

Next, an example of the cylindrical lithium ion battery 20 manufactured according to this embodiment will be described. A battery of a comparative example produced for comparison is also described.

Example 1 As shown in Table 1 below, in Example 1, lithium manganate (Li _1.06) having a Li / Mn ratio of 0.55 and an average primary particle diameter of 2 μm was used as the positive electrode active material.
A battery was prepared using the Mn _1.94 O ₄₎ powder.

[0023]

[Table 1]

(Examples 2 and 3) As shown in Table 1,
In Examples 2 and 3, the average primary particle diameter of the positive electrode active material was
2.5 μm and 3.0 μm lithium manganate, respectively
(Li_1.06Mn _1.94O₄) Except using powder
Produced a battery in the same manner as in Example 1.

Examples 4 and 5 As shown in Table 1, in Example 4, lithium manganate (Li _1.14 Mn _1.86 O ₄ ) having a Li / Mn ratio of 0.60 was used as the positive electrode active material. In Example 5, lithium manganate (Li _1.03 Mn _1.87 Al _0.1 O ₄ ) having a Li / Mn ratio of 0.55 and partially replacing Mn with Al was used as the positive electrode active material using powder. A battery was produced in the same manner as in Example 1, except that was used.

(Comparative Examples 1 and 2) As shown in Table 1, in Comparative Examples 1 and 2, the positive electrode active material had a Li / Mn ratio of 0.55 and an average primary particle diameter of 0.5 μm. ,
1.0 μm lithium manganate (Li _1.06 Mn
_A battery was fabricated in the same manner as in Example 1, except that _1.94 O ₄ ) powder was used.

(Comparative Examples 3 and 4) As shown in Table 1, in Comparative Examples 3 and 4, lithium manganate having an average primary particle diameter of 1.0 μm was used as the positive electrode active material. In Comparative Example 3, lithium / manganate (L / Mn ratio: 0.60)
i _1.14 Mn _1.86 O ₄ ) powder, and in Comparative Example 4, lithium / manganate (Li _1.03 Mn _1.87 ) having a Li / Mn ratio of 0.55 and part of Mn substituted with Al. A
l _0.1 O ₄ ) A battery was fabricated in the same manner as in Example 1 except that powder was used.

<Test / Evaluation> Next, with respect to the batteries of the examples and comparative examples manufactured as described above, abnormal phenomena occur in the appearance of the batteries at an hourly rate (1 C) from the fully charged state after the initial stabilization operation. An overcharge test was performed in which the battery was charged at a constant current up to that time. At that time, an abnormal appearance phenomenon was observed, and the maximum temperature reached on the surface of the battery container 7 was measured. Table 2 below shows the test results of the overcharge test.

[0029]

[Table 2]

As shown in Table 2, the average primary particle diameter was 2 μm.
m or more, the batteries of Examples 1 to 3 using lithium manganate having a Li / Mn ratio of 0.55 have a maximum temperature of 130 ° C. or less on the battery surface at the time of occurrence of the phenomenon. All of them are batteries with excellent safety with only slight generation of white smoke. However, the average primary particle diameter is 1
μm or less, the batteries of Comparative Examples 1-2 using lithium manganate having a Li / Mn ratio of 0.55 reached a maximum temperature of 385-425 ° C. on the battery surface when the phenomenon occurred,
The contents were vigorously squirted from the cleavage valve 11 together with white smoke.

The average primary particle diameter is 2 μm, and L
In the battery of Example 4 using lithium manganate having an i / Mn ratio of 0.60, the maximum temperature of the battery surface at the time of occurrence of the phenomenon was 120 ° C., and the phenomenon was only slight white smoke. While the battery is excellent in safety, the battery of Comparative Example 3 using lithium manganate having an average primary particle diameter of 1 μm and a Li / Mn ratio of 0.60 has the highest temperature on the battery surface. Reached 390 ° C. and violently emitted white smoke accompanied by the contents.

Further, Li / Mn ratio = 0.5
5, even when lithium manganate in which part of Mn was substituted with Al was used, the average primary particle diameter was 2.0 μm.
The battery of Example 5 has a maximum temperature of 130 ° C. at the surface of the battery when the phenomenon occurs, and the phenomenon is a slight white smoke. In the battery of Comparative Example 4 having an average particle diameter of 1 μm, the highest temperature reached on the battery surface reached 430 ° C., and white smoke accompanied by the contents was jetted violently.

From the above results, in the batteries of Examples 1 to 5 using lithium manganate having a primary particle average diameter of 2 μm or more as the positive electrode active material, the maximum temperature of the battery at the time of overcharge can be kept low. It was found that the battery could be produced with a mild phenomenon and excellent in safety.

In this embodiment, the chemical formula Li _{1 + x}
Although lithium manganate represented by Mn _2-x O ₄ or lithium manganate in which a part of manganese in the chemical formula is substituted by Al has been exemplified, the present invention is not limited to lithium manganate having the above-described chemical formula. It is also applicable to the case where lithium manganate represented by another chemical formula in which a sufficient amount of lithium is inserted in advance is used, and Mn is replaced with a metal element such as Mg, Cr, Fe, or Ni instead of Al. It is also applicable when lithium manganate partially substituted or doped is used.

In this embodiment, a cylindrical battery is described as an example. However, the present invention is not limited to the shape of the battery, and is applicable to a square battery and other polygon batteries.
Furthermore, as a structure to which the present invention can be applied, a battery other than the above-described battery container (can) having a structure in which a battery lid is sealed by caulking may be used. An example of such a structure is a battery in which the positive and negative external terminals penetrate the battery cover and the positive and negative external terminals press against each other via the shaft core in the battery container.

Further, in this embodiment, EC, DEC, D
Although a non-aqueous electrolyte in which LiPF ₆ is dissolved in a mixed solution of MC is exemplified, a general lithium salt may be used as an electrolyte, and a non-aqueous electrolyte in which this is dissolved in an organic solvent may be used. The present invention is not particularly limited to the lithium salt and the organic solvent used. For example, as the electrolyte, LiCl
O 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. Further, as the organic solvent, 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, propionitonyl, etc. or a mixed solvent of two or more of these may be used, and the mixing ratio is also limited. It is not something to be done.

[0037]

As described above, according to the present invention,
The use of lithium manganate having an average primary particle diameter of 2 μm or more as the positive electrode active material increases the Mn-O binding force of lithium manganate due to the growth of the primary particle diameter. In addition to suppressing the elution reaction of Mn from the lithium oxide into the non-aqueous electrolyte, even when an internal short circuit occurs due to a temperature rise at the time of a battery abnormality such as continuous overcharging, lithium manganate can be prevented. Can prevent thermal runaway due to decomposition reaction of the battery and make the battery unusable safely, so it is possible to realize a highly safe lithium secondary battery with high capacity and high output. it can.

[Brief description of the drawings]

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

[Explanation of symbols]

 Reference Signs List 6 Winding group (electrode group) 7 Battery container 10 Battery cover (part of battery container) 11 Cleavage valve (internal pressure reduction mechanism) 20 Cylindrical lithium ion battery (lithium secondary battery)

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Yuichi Takatsuka 2-87-7 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 AJ02 AJ03 AJ12 AK03 AL08 AM03 AM05 AM07 BJ02 BJ14 DJ17 DJ18 HJ02 HJ05 5H050 AA02 AA08 AA15 BA17 CA09 CB09 FA19 FA20 HA02 HA05

Claims (3)

[Claims] 1. A battery container having an internal pressure release mechanism for releasing an internal pressure at a predetermined pressure, a positive electrode using lithium manganate as a positive electrode active material and a negative electrode using amorphous carbon as a negative electrode active material via a separator. And a non-aqueous electrolyte infiltrating the electrode group, wherein the average particle diameter of the primary particles of the lithium manganate is 2 μm or more. Rechargeable lithium battery. 2. The lithium secondary battery according to claim 1, wherein the lithium manganate has a spinel crystal structure, and has a Li / Mn composition ratio of 0.55 or more and 0.60 or less. battery. 3. The lithium manganate has a chemical formula Li
_{1 + x}Mn_2-xO ₄Or represented by the formula
That some of the metal has been replaced or doped with other metal elements
The lithium according to claim 1 or 2, characterized in that:
Rechargeable battery.