JPH0963583A - Lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary battery with high capacity suitable for the power sources of various types of portable electronic apparatus by solving the problem for obtaining high capacity which cannot obtain in a lithium secondary battery using a lithium manganese composite oxide as a positive active material. SOLUTION: A lithium secondary battery has a negative electrode 5 capable of absorbing/releasing lithium, a nonaqueous electrolyte, and a positive electrode using a lithium-containing oxide as an active material. The positive active material has peaks around 19 deg., 22 deg., 32 deg., 37 deg., 42 deg., 44.5 deg., 53 deg., 56.5 deg., and 66 deg. of 2θ in the X-ray diffraction pattern using Cuk αray, and has a ratio of the peak strength around 56.5 deg. and the maximum peak strength around 37 deg. of 0.05 to less than 0.4.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a lithium secondary battery, and more particularly to a lithium secondary battery having an improved positive electrode.

[0002]

2. Description of the Related Art For example, portable equipment such as a portable telephone, cordless equipment such as a cordless telephone, audio-visual equipment such as a video camera, office equipment such as a word processor, home electric appliances with a built-in memory, an electric vehicle, or a solar battery. Lithium, which can be used for a long time and economically, is desired as a main power supply for a combined clock and a power supply for memory backup. In this type of lithium secondary battery, titanium disulfide, vanadium pentoxide, manganese oxide, etc. are used as a positive electrode active material, and among them, manganese oxide, which is abundant in resources and inexpensive, is drawing attention. .

By the way, in the case of manganese oxide, manganese dioxide, which is composed (formed) of only manganese and oxygen, has poor reversibility during charge and discharge and poor charge and discharge characteristics.
For example, it has been proposed to use it in the state of a lithium manganese composite oxide in which a lithium salt is introduced into manganese oxide, such as LiMn ₂ O ₄ (for example, US Pat. No. 4,50).
No. 7,371). The lithium manganese composite oxide of this kind, in addition to the _{LiMn 2 O 4, Li 2 Mn} 4 O 9, Li
Compounds of spinel structure such as ₄ Mn ₅ O ₁₂ [eg Ma
t.Res.Bull., 25, p 657 (1990)], and also Li ₂ Mn O ₃
Manganese dioxide containing (JP-A-63-114064)
Etc. are known.

Furthermore, recently, in the X-ray diffraction pattern by Cuk α-ray, 2θ is 19 °, 21 ° and 33 °, respectively.
Has peaks near °, 37 °, 42 °, 53 ° and 66 °,
And the intensity ratio between the peak around 21 ° and the peak around 19 ° is
A lithium manganese composite oxide having a value of 1: 0.7 to 1: 1.2 has been proposed as a positive electrode active material (Japanese Patent Application Laid-Open No. 5-17.
4821 publication).

[0005]

However, in the case of spinel type, the lithium manganese composite oxide is limited in the position of lithium (Li) that can be occupied in the spinel structure, and the effective potential range that can be used for charge and discharge is limited. Has the drawback of being small. In the case of manganese dioxide containing Li ₂ Mn O _3, since Li ₂ Mn O ₃ is not involved in charging and discharging, there is a problem that the battery capacity decreases.

As a result of intensive studies on the above-mentioned defects and problems, the present inventors have found that 2θ is 19 °, 22 °, 32 °, 37 °, and 2θ in the X-ray diffraction pattern by Cuk α-ray, respectively.
Lithium-containing material having peaks near 42 °, 44.5 °, 53 °, 56.5 ° and 66 °, and having a ratio between the peak intensity near 56.5 ° and the maximum peak intensity near 37 ° of 0.05 to less than 0.4 It has been found that when an oxide is used as a positive electrode active material, it functions as a high-capacity lithium secondary battery.

The present invention has been made on the basis of the above findings, and solves the problem of high capacity, which cannot be achieved by a conventional lithium secondary battery using a lithium manganese composite oxide as a positive electrode active material, and has various problems. An object of the present invention is to provide a high-capacity lithium secondary battery suitable for a power source of the portable electronic device.

[0008]

The invention according to claim 1 is a lithium secondary battery comprising a negative electrode which occludes and releases lithium ions, a non-aqueous electrolyte, and a positive electrode which uses a lithium-containing oxide as an active material. In the X-ray diffraction pattern by Cuk α ray, 2θ is 19 ° and 22 °, respectively.
°, 32 °, 37 °, 42 °, 44.5 °, 53 °, 56.5 ° and 66
It has a peak near ° and a peak intensity near 56.5 °.
The lithium secondary battery is characterized by having a ratio with a maximum peak intensity around 37 ° of 0.05 to less than 0.4.

According to a second aspect of the present invention, in the lithium secondary battery according to the first aspect, the positive electrode active material is produced by heat-treating a mixture of electrolytic manganese dioxide and lithium hydroxide or lithium hydroxide monohydrate. It is characterized by being.

The positive electrode active material has a BET specific surface area of 20 to 50 neutralized with a lithium salt and ammonia or caustic soda.
It is obtained by reacting m ² / g of electrolytic manganese dioxide at a temperature of 250 to 420 ° C. (preferably 340 to 400 ° C.) for about 10 to 30 hours. Here, examples of the lithium salt include lithium hydroxide (LiOH), lithium carbonate (Li ₂ CO ₃ ), and hydrated salts thereof. In addition, the use of electrolytic manganese dioxide having a BET specific surface area of 20 to 50 m ² / g is because when the BET specific surface area is smaller than 20 m ² / g, the reaction with the lithium salt does not proceed to the inside and the unreacted portion Is left, the discharge capacity tends to be small. Conversely, B
When the ET specific surface area is larger than 50 m ² / g, the reactivity with the lithium salt is good but bulky, so that the filling amount of the active material is reduced and the discharge capacity is reduced.

Further, in the reaction between the lithium salt and electrolytic manganese dioxide, it is preferable to select the composition ratio (mol ratio) of the lithium salt and manganese dioxide in the range of 1: 3 to 1: 7. That is, if the composition ratio of manganese dioxide to the lithium salt is smaller than the above range, the remaining amount of the lithium salt increases and the battery capacity decreases, and if the composition ratio of manganese dioxide to the lithium salt becomes larger than the above range. However, the amount of unreacted γ-β-phase manganese dioxide increases and the battery capacity decreases.

In the present invention, the positive electrode is the positive electrode active material,
Mix the conductive material and the adhesive material and press-mold, or suspend the positive electrode active material, the conductive material and the adhesive material in an appropriate solvent, apply the suspension to the current collector, and dry to form a thin plate. It can be produced by Here, examples of the conductive material include acetylene black, carbon black, graphite, and the like, and examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), ethylene-propylene-. Diene copolymer (EPDM), styrene-butadiene rubber (SBR), etc. can be used. Then, the mixing ratio of the positive electrode active material, the conductive material and the binder is preferably in the range of 80 to 95 mass% of the positive electrode active material, 3 to 20 mass% of the conductive material, and 2 to 7 mass% of the binder. . As the current collector, for example, aluminum foil, stainless steel foil, nickel foil, titanium foil or the like can be used.

In the present invention, as the separator that electrically insulates between the positive electrode and the negative electrode, for example, a synthetic resin non-woven fabric, a polyethylene porous film, or a polypropylene porous film can be used.

In the present invention, the storage of lithium ions
Examples of the negative electrode to be released include lithium metal, lithium-containing aluminum, alloys such as indium, gallium, tin, and magnesium, or carbonaceous materials. Here, as the carbonaceous material, for example, various cokes, mesophase type carbons, pyrolytic carbons, graphites,
Examples include fired bodies of organic polymers.

In the present invention, the electrolyte that forms one component of the non-aqueous electrolyte is, for example, lithium perchlorate (LiClO).
₄ ), lithium hexafluorophosphate (LiPF ₆ ), lithium borofluoride (LiBF ₄ ), lithium trifluorometasulfonate (LiCF ₃ SO ₃ ), and other lithium salts. Of these, LiPF ₆ and LiBF ₄ are more preferable in consideration of safety and battery performance. On the other hand, examples of the solvent for the electrolyte include cyclic carbonates such as ethylene carbonate, propylene carbonate and butylene carbonate, chain carbonates such as ethylmethyl carbonate, dimethyl carbonate and dimethyl carbonate, and esters such as γ-butyrolactone and γ-valerolactone. , 1,2-
Examples thereof include one or a mixture of two or more ethers such as dimethoxyethane, dimethoxyethane, dimethoxypropane, 1,3-dioxolane, tetrahydrofuran, 4-methyl-1,3-dioxolane, and 2-methyltetrahydrofuran.

In the non-aqueous electrolyte secondary battery according to the present invention, 2θ is 19 °, 22 °, 32 °, 37 °, 42 °, 4 in the X-ray diffraction pattern by Cuk α ray as the positive electrode active material.
Has peaks near 4.5 °, 53 °, 56.5 ° and 66 °,
Further, a lithium-containing oxide having a ratio of the peak intensity near 56.5 ° to the maximum peak intensity near 37 ° of 0.05 to less than 0.4 is used. And, such a positive electrode active material,
Since it works effectively such that a wide effective potential range that can be used for charging and discharging can be taken, not only can the capacity of the battery be increased, but also such an excellent function can be retained and exhibited for a long period of time.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.

Example 1 100 g of electrolytic manganese dioxide having an average particle size of 10 μm and a BET specific surface area of 30 m ² / g was preliminarily coarsely pulverized with lithium hydroxide to obtain Li / Mn.
An amount corresponding to 1/4 in mol ratio was added, and the mixture was mixed in an automatic mortar for 1 hour. The mixture was placed in a 115 mm × 115 mm × 60 mm quartz glass boat and heated at 110 ° C. for 2 hours to remove water.

The mixture from which the water was removed was placed in an automatic mortar.
After re-mixing for an hour, the quartz glassy boat was placed in the boat almost evenly and then in an electric furnace at 20 ° C. in the atmosphere at 380 ° C.
A heat treatment was carried out for a period of time to prepare a positive electrode active material. This positive electrode active material has a Cuk α-ray X-ray diffraction pattern,
θ is 19 °, 22 °, 32 °, 37 °, 42 °, 44.5 respectively
Has peaks near °, 53 °, 56.5 ° and 66 °, and
The peak intensity near 56.5 ° was 0.15 compared to the maximum peak intensity near 37 °. Note that FIG. 1 is a characteristic diagram showing the X-ray diffraction pattern.

To 90 parts by weight of the above positive electrode active material, 10 parts by weight of graphite (conductive material) was added and mixed in an automatic mortar for 10 minutes, and then 3 parts by weight of Teflon powder was added to the mixture for about 10 minutes until sufficient fiberization was achieved. Mixing continued. Next, the mixed powder was thoroughly crushed in a blender and then sieved to remove coarse particles. About 0.4 g of the positive electrode active material-based mixed powder thus obtained was weighed and compression-molded to a diameter of 15.5 mm and a thickness of 0.8 mm to prepare a pellet-shaped positive electrode active material.

Next, the negative electrode (diameter 1
6.0mm, 1.0mm thick Li metal foil), current collector (nickel foil), separator (combination of polypropylene porous film and polypropylene non-woven fabric), electrolytic solution (ethylene carbonate / diethyl carbonate containing 1 mol of LiClO ₄ ). (Volume ratio 1: 1)), the outer can and the cap were assembled to fabricate a coin-type lithium secondary battery whose main part is shown in cross section in FIG. In FIG.
1 is an outer can, 2 is a positive electrode current collector, 3 is a positive electrode active material, 4
Is a separator, 5 is a negative electrode, 6 is a negative electrode current collector, and 7 is a cap, and the opening 7 of the outer can 1 has a cap 7
The opening end edge portion of (1) is liquid-tightly caulked and sealed via an insulating ceiling 8.

The button-type lithium secondary battery cell having the above structure was discharged at 20 ° C. and 250 μA to 2.0 V (first discharge), then charged at 250 μA to 3.4 V, and further discharged at 250 μA to 2.0 V. Then, the discharge specific capacity of the positive electrode was measured (second discharge). As a result, the specific capacity of the second discharge was 195 mAh / g.

Examples 2, 3 and 4 In the case of Example 1, 100 g of electrolytic manganese dioxide having an average particle size of 10 μm and a BET specific surface area of 30 m ² / g was preliminarily coarsely pulverized with lithium hydroxide to obtain a Li / Mn mol ratio. Instead of adding an amount corresponding to 1/4, an amount equivalent to 1/3 in Li / Mn mol ratio (Example 2), an amount equivalent to 1/5 in Li / Mn mol ratio (Example 3),
Alternatively, a positive electrode active material was prepared under the same conditions as in Example 1 except that the Li / Mn mol ratio was 1/7 (Example 4). In addition, these positive electrode active materials have 2θ of 19 ° and 22 ° respectively in the X-ray diffraction pattern by Cuk α-ray.
°, 32 °, 37 °, 42 °, 44.5 °, 53 °, 56.5 ° and 66
The peak intensity around 56.5 ° has a peak in the vicinity of 37 °, and the peak intensity around 56.5 ° is 0.06 in the case of Example 2, 0.25 in the case of Example 3, and 0.37 in the case of Example 4. It was a value. It is to be noted that FIG.
It is a characteristic view showing an X-ray diffraction pattern in the case of, and the same X-ray diffraction pattern is shown in the cases of Examples 3 and 4.

Further, a positive electrode was formed by using each of the positive electrode active materials, a button-type lithium secondary battery similar to that in the case of Example 1 was manufactured, and characteristic evaluation was performed in the same manner as in Example 1. As a result, the results shown in Table 1 were obtained.

[0025] Examples 5, 6, 7 and 8 In the case of Examples 1 to 4, the average particle size is 25 μm, BE
A positive electrode active material was prepared under the same conditions as in Example 1 except that electrolytic manganese dioxide having a T specific surface area of 30 m ² / g was used.

In the X-ray diffraction pattern of Cuk α-ray, these positive electrode active materials have 2θ of 19 °,
22 °, 32 °, 37 °, 42 °, 44.5 °, 53 °, 56.5 ° and
In the case of Example 5, the peak intensity near 56.5 ° is 0.18 in comparison with the maximum peak intensity around 37 °.
Of Example 6, the value of 0.06 in the case of Example 6, the value of 0.24 in the case of Example 7, and the value of 0.35 in the case of Example 8. Also in the case of these positive electrode active materials, the X-ray diffraction patterns were as shown in FIGS. 1 and 3, respectively.

Further, a positive electrode was prepared using each of the positive electrode active materials, and button-type lithium secondary batteries similar to those in Example 1 were manufactured, and the characteristics were evaluated in the same manner as in Example 1. As a result, the results shown in Table 2 were obtained.

[0028] Examples 9, 10, 11, 12 In the case of Examples 1 to 4, average particle diameter 40 μm, BE
A positive electrode active material was prepared under the same conditions as in Example 1 except that electrolytic manganese dioxide having a T specific surface area of 30 m ² / g was used.

In the X-ray diffraction pattern by Cuk α-ray, these positive electrode active materials have 2θ of 19 °,
22 °, 32 °, 37 °, 42 °, 44.5 °, 53 °, 56.5 ° and
In the case of Example 9, the peak intensity near 56.5 ° is 0.20 compared with the maximum peak intensity around 37 °.
Of Example 10, the value of 0.07 in Example 10, the value of 0.26 in Example 11, and the value of 0.37 in Example 12.

Further, a positive electrode was prepared by using each of the positive electrode active materials, and button-type lithium secondary batteries similar to those in Example 1 were manufactured, and the characteristics were evaluated in the same manner as in Example 1. As a result, the results shown in Table 3 were obtained.

As a comparative example, 100 g of electrolytic manganese dioxide having an average particle size of 10 μm and a BET specific surface area of 30 m ² / g was added with lithium nitrate which had been roughly crushed in advance in an amount corresponding to 1/4 in Li / Mn mol ratio. A positive electrode active material was prepared under the same conditions as in Example 1.

These positive electrode active materials are shown in FIG. 4 in the X-ray diffraction pattern by Cuk α-ray.
θ is 19 °, 22 °, 32 °, 37 °, 42 °, 44.5 °,
It had peaks near 53 ° and 66 ° and no peak near 56.5 °. Therefore, the peak intensity around 56.5 ° was 0 compared to the maximum peak intensity around 37 °. Then, a positive electrode was prepared using this positive electrode active material, button-type lithium secondary batteries similar to those in Example 1 were respectively manufactured, and the results of characteristic evaluation performed in the same manner as in Example 1 were shown. It is also shown in Table 3.

[0033] Although the example of the configuration of the button type lithium secondary battery has been described above, the present invention is not limited to the above examples, and various modifications can be made without departing from the spirit of the invention. For example, the form / structure of the lithium secondary battery may be cylindrical.

[0034]

As can be seen from the description of the above embodiment,
According to the present invention, in terms of resources and costs, manganese oxide, which is expected and attracting attention as a positive electrode active material, is put into practical use, and it is possible to provide a compact and high-capacity lithium secondary battery. In other words, the utilization efficiency and capacity reduction, which had been problematic in the case of spinel structure-type lithium manganese composite oxides or manganese dioxide containing Li ₂ MnO ₃ , which have been tried and studied as positive electrode active materials, have been solved. Thus, a long-life, high-capacity lithium secondary battery will be provided.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing an X-ray diffraction pattern by Cuk α-ray of a positive electrode active material according to a first example.

FIG. 2 is a sectional view showing a configuration example of a main part of a button type lithium secondary battery according to the present invention.

FIG. 3 is a characteristic diagram showing an example of an X-ray diffraction pattern by Cuk α ray of the positive electrode active material according to the second example.

FIG. 4 is a characteristic diagram showing an example of an X-ray diffraction pattern of a conventional positive electrode active material by Cuk α ray.

[Explanation of symbols]

 1 ... outer can 2 positive electrode current collector 3 positive electrode active material 4 separator 5 negative electrode 6 negative electrode current collector 7 cap 8 insulation Ceiling

Continued Front Page (72) Inventor Kazuo Ansai 3-4-10 Minami-Shinagawa, Shinagawa-ku, Tokyo Inside Toshiba Battery Co., Ltd.

Claims (2)

[Claims] 1. A lithium secondary battery comprising a negative electrode which absorbs and releases lithium ions, a non-aqueous electrolyte, and a positive electrode which uses a lithium-containing oxide as an active material, wherein the positive electrode active material is Cuk α-ray. In the X-ray diffraction pattern by, 2θ is 19 °, 22 °, 32 °, 37 °, 42 °,
Has peaks near 44.5 °, 53 °, 56.5 ° and 66 °,
A lithium secondary battery having a ratio of a peak intensity near 56.5 ° to a maximum peak intensity near 37 ° of 0.05 to less than 0.4. 2. The lithium secondary according to claim 1, wherein the positive electrode active material is prepared by heat-treating a mixture of electrolytic manganese dioxide and lithium hydroxide or lithium hydroxide monohydrate. battery.