JP2000331681A - Positive electrode for lithium secondary battery and lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary battery of an excellent cycle characteristic even though high-density energy. SOLUTION: A positive electrode plate 1 is manufactured using a porous sintered body made from a complex oxide of lithium and a transition metal. For the lithium-transition metal complex oxide, one or more lithium-transition metal complex oxides having a basic structure expressed with chemical formula of LiMO2 (M is one or more transition metals selected from among nickel, cobalt, and manganese) or LiMn2O4 are mixed and used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a positive electrode plate for a lithium secondary battery and a lithium secondary battery using the same.

[0002]

2. Description of the Related Art In recent years, remarkable progress in electronic technology has realized a reduction in size and weight of electronic devices one after another. Along with this, there is an increasing demand for batteries that are power sources to be further reduced in size, weight, and energy density.

Conventionally, batteries for general use include lead batteries,
Aqueous batteries such as nickel cadmium batteries were the mainstream. However, although these aqueous batteries are excellent in cycle characteristics, they cannot be said to be sufficiently satisfactory in terms of battery weight and energy density.

Accordingly, recently, non-aqueous electrolyte batteries having a high battery voltage and a high energy density have begun to be used. A typical non-aqueous electrolyte battery is a lithium secondary battery using a material capable of reversible intercalation of lithium ions as an electrode material.

[0005] Comparing the approximate energy densities of various small rechargeable batteries used in portable equipment power supplies,
20-40 Wh / kg, 50-100 Wh /
1, 30-60 Wh / k for nickel cadmium battery
g, 100 to 160 Wh / l, 4 for nickel-metal hydride battery
5 to 65 Wh / kg, 160 to 200 Wh / l, whereas the lithium secondary battery has a capacity of 60 to 125 Wh / kg, 1
It is said to be 90 to 310 Wh / l.

[0006]

The lithium secondary battery has such an excellent energy density.
Although it is expected to be used as a power supply for portable equipment that consumes relatively large power, further improvement of cycle characteristics is one important issue.

A positive electrode plate used for a lithium secondary battery is
A positive electrode active material powder such as LiCoO2 is applied to a metal foil as a current collector using a doctor blade or the like, or a metal foil is thickly attached to a metal mesh. However, in lithium secondary batteries using these cathode plates, since the contact between the cathode active material particles is maintained by compression or adhesion via a binder or the like, the active material particles accompanying the charge / discharge cycle are Due to the expansion and contraction of the particles, the contact between the particles is loosened and the conductivity between the particles is gradually reduced, so that the discharge capacity is reduced.

The present invention has been made to solve such a problem, and an object of the present invention is to provide a lithium secondary battery having high energy density and excellent cycle characteristics. .

[0009]

Means for Solving the Problems In order to achieve the above-mentioned object, the inventors of the present invention have conducted intensive studies and have found that by using a porous body obtained by sintering a lithium / transition metal composite oxide as a positive electrode, The inventors have found that a lithium secondary battery having excellent cycle characteristics can be obtained, and have completed the present invention. That is, the first invention of the present application is a positive electrode plate for a lithium secondary battery, comprising a porous sintered body of a lithium / transition metal composite oxide.

[0010] Preferably, the porous sintered body is
Formula LiMO ₂ (M is one or more transition metals selected from nickel, cobalt, and manganese) or Formula L
It is preferable that at least one lithium-transition metal composite oxide having a basic structure represented by iMn ₂ O ₄ is mixed.

Further, a lithium secondary battery of the present invention is characterized by comprising the above-mentioned positive electrode plate of the present invention.

By using the positive electrode plate of the present invention as described above, the cycle characteristics of the lithium secondary battery are greatly improved. The reason why the cycle characteristics are remarkably improved by employing the structure of the present invention is not necessarily completely elucidated by the present inventors, but is presumed as follows. In other words, by using a porous sintered body obtained by sintering a lithium / transition metal composite oxide for the positive electrode, the particles are sintered even due to the expansion and contraction of the active material particles accompanying the charge / discharge cycle. It is considered that the conductivity between the particles was maintained without loosening the contact between the particles, thereby suppressing the decrease in the discharge capacity.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in more detail with reference to embodiments.

The positive electrode plate according to the present invention has a chemical formula L
iMO ₂ (M is one or more transition metals selected from nickel, cobalt and manganese) or a chemical formula LiMn ₂ O
After applying a lithium-transition metal composite oxide powder having a basic structure represented by ₄ on the surface of a current collector made of stainless steel, aluminum, titanium, or the like, sintering at a high temperature of 400 ° C. or more, It can be manufactured by sintering a green sheet in which powder is formed into a sheet shape by a doctor blade method or the like at a high temperature of 400 ° C. or more, and then joining metals by a plasma spraying method or the like to form a current collector.

The lithium secondary battery according to the present invention has a positive electrode,
Combination of negative electrode and separator with non-aqueous electrolyte, positive electrode, combination of negative electrode and separator with organic or inorganic solid electrolyte and non-aqueous electrolyte, positive electrode, negative electrode and combination of organic or inorganic solid electrolyte and non-aqueous electrolyte The battery can be manufactured by a combination, and the battery can have various shapes such as a cylinder, a square, a coin, a button, and a paper.

In this case, as the negative electrode active material constituting the negative electrode, metallic lithium, lithium alloy or cokes,
Glassy carbons, graphites, non-graphitizable carbons,
Carbonaceous materials such as pyrolytic carbons and carbon fibers, or host substances such as polyacene that occlude and release lithium ions can be used alone or in combination of two or more.
In particular, among these, it is desirable to use a carbonaceous material from the viewpoint of high safety. When using a non-aqueous electrolyte, the solvent is ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, trifluoropropylene carbonate, γ-butyrolactone, 2-methyl-γ-butyrolactone, acetyl-γ-
Butyrolactone, γ-valerolactone, sulfolane, 1,2
-Dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyl-
1,3-dioxolane, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl isopropyl carbonate, dibutyl carbonate, etc., alone or in combination These can be used in combination. As the electrolyte salt as a solute of the non-aqueous electrolyte, LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiCF ₃ C
F ₂ SO ₃ , LiCF ₃ CF ₂ CF ₂ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂
Etc. can be used. Among the electrolyte salts, Li
Preferably, PF ₆ is used. Further, a solid ion-conductive polymer electrolyte may be used instead of or in addition to the electrolyte salt. Of course, a plurality of types may be used.
In this case, the configuration of the nonaqueous electrolyte secondary battery includes a positive electrode,
A combination of a negative electrode and a separator with an organic or inorganic solid electrolyte and a non-aqueous electrolyte (a solvent or a solvent and an electrolyte salt), or an organic or inorganic solid electrolyte membrane and a non-aqueous electrolyte (a solvent or Solvent and electrolyte salt).

When the polymer electrolyte membrane is made of polyethylene oxide, polyacrylonitrile, polyethylene glycol, or a modified product thereof, it is lightweight and flexible, which is advantageous when used as a wound electrode plate. Further, as the electrolyte, other than the polymer electrolyte, an inorganic solid electrolyte or a mixed material of an organic polymer electrolyte and an inorganic solid electrolyte can be used. When the organic or inorganic solid electrolyte has ion conductivity, LiPF ₆
It is not necessary to use an electrolyte salt such as

[0018]

(Example 1) LiCoO having an average particle diameter of 5 μm
₍₂₎ Water, methyl cellulose and carbon black are kneaded with the powder to form a slurry. Next, the slurry was
It was applied to one side of a 0 μm SUS316 stainless steel foil, dried, and then sintered at 700 ° C. in an argon gas atmosphere. The sintered substrate thus manufactured had a porosity of 35%. Cut this substrate into φ20mm
And The negative electrode mixture was prepared as a slurry by mixing 90 parts by weight of a carbon material capable of inserting and extracting lithium ions and 10 parts by weight of polyvinylidene fluoride, adding N-methyl-2-pyrrolidone as needed, and dispersing the mixture. Make this slurry 50μ thick
After coating and drying on a copper current collector having a diameter of 21 m, compression molding was performed by a roll press, and then cut into a disk shape having a diameter of 21 mm to produce a negative electrode 2. A coin-type battery as shown in FIG. 1 was prepared using the positive electrode and the negative electrode thus prepared. FIG. 1 is a schematic cross-sectional configuration diagram showing the structure of the battery of this example. In the figure, 1 is a positive electrode, 2 is a negative electrode, 3 is a separator made of a microporous polyethylene membrane, 4 is an electrolyte, and ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are used as the electrolyte 4 in a volume ratio of 1: 1. LiPF ₆ as a Li salt in a solvent mixed in a ratio of 1.
A solution dissolved at 0 mol / l was used. In the drawing, reference numeral 5 denotes a stainless steel case that also serves as a positive electrode terminal, 6 denotes an upper lid that also serves as a negative electrode terminal, and 7 denotes a packing.

Comparative Example 1 LiCoO ₂ as an active material, acetylene black as a conductive material, and polyvinylidene fluoride as a binder were mixed, N-methyl-2-pyrrolidone was appropriately added and dispersed, and a slurry was obtained. Prepare and slurry this 20μm thick
Was uniformly coated and dried on an aluminum current collector, and then compression-molded by a roll press and then cut into a diameter of 20 mm to produce a positive electrode 1. Using this positive electrode, a coin-type battery of a comparative example was produced in the same manner as in Example 1 except for this.

[Test] The batteries of Example 1 and Comparative Example 1 were subjected to a life test. The test was repeated at 25 ° C at 25 ° C for 2 hours at a constant current / constant voltage charge of 4.1 mA at a current of 2 mA, followed by a constant current discharge of 1 mA. This was performed by determining the ratio of the discharge capacity after the cycle.

The results of the life test are shown in Table 1 below.

[0022]

[Table 1] Table 1 shows that in the example battery using the positive electrode plate made of a porous sintered body of lithium / transition metal composite oxide, a comparative example using a conventional coated positive electrode plate in which active material particles were not sintered was used. It can be seen that the capacity retention ratio is higher and the cycle characteristics are improved as compared with the battery.

[0023]

According to the present invention, a lithium secondary battery having a high capacity and excellent cycle characteristics can be manufactured.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing the structure of an example battery.

[Explanation of symbols]

 1 Positive electrode 2 Negative electrode 3 Separator 4 Electrolyte 5 Case 6 Top lid

Claims (3)

[Claims] 1. A positive electrode plate for a lithium secondary battery, comprising a porous sintered body of lithium / transition metal composite oxide. 2. The method according to claim 1, wherein the porous sintered body has a chemical formula of LiMO.
₂ (M is one or more transition metals selected from nickel, cobalt and manganese) or one or more lithium-transition metal composite oxides having a basic structure represented by the chemical formula LiMn ₂ O ₄ are mixed. The positive electrode plate for a lithium secondary battery according to claim 1, wherein: 3. A lithium secondary battery comprising the positive electrode plate according to claim 1 or 2.