JP2000012030A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve cycle life characteristics at high temperatures by causing a positive electrode having a spinel-type lithium manganate (LiMn2O4) as a main constituent to contain a specific amount of lithium cobaltate (LiCoO2). SOLUTION: An amount added to lithium cobaltate to be contained in a positive electrode is set 1 to 20 wt.% of a spinel-type lithium manganate. The spinle-type lithium manganate and the lithium cobaltate used as positive- electrode active materials can be manufactured by weighting a lithium salt material, a manganase salt material or a cobalt salt material, respectively according to a desired composition, sufficiently mixing them together, and heating/firing them at temperatures within a range of 600 deg.C to 1,100 deg.C in the air. A spinel-type lithium manganate, LiMn2O4 (M is a metallic element), having a different kinds of element added thereto or a lithium-rich spinel-type lithium manganate, Li(1+x)Mn2O4 (x is the amount of excess lithium) may be used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery containing spinel-type lithium manganate as a main component as a positive electrode active material, and relates to cycle life characteristics and safety.

[0002]

2. Description of the Related Art In recent years, with the spread of portable devices such as video cameras, mobile phones, and notebook personal computers, secondary batteries having a small size, light weight and high energy density have been demanded. In various secondary batteries, lithium ion secondary batteries using a carbonaceous material as a negative electrode active material and lithium cobalt oxide as a positive electrode active material have been widely put into practical use. However, this battery has a disadvantage that the cost of the battery increases due to the scarcity of cobalt resources.

[0003] From the viewpoint of resource amount and cost, utilization of spinel-type lithium manganate as a positive electrode active material is being studied. In addition, spinel-type lithium manganate has attracted attention as a positive electrode active material suitable for a large-sized non-aqueous electrolyte secondary battery because it has better thermal stability than lithium cobaltate. However, when a battery was trial-produced using the above-mentioned spinel-type lithium manganate as a positive electrode active material and subjected to a cycle life test at each temperature of 50 ° C., a problem that the life was short was recognized.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to improve the cycle life characteristics at high temperatures in a non-aqueous electrolyte secondary battery mainly composed of spinel-type lithium manganate as a positive electrode active material. .

[0005]

According to a first aspect of the present invention, there is provided a positive electrode comprising spinel-type lithium manganate as a main component, a negative electrode capable of inserting and extracting lithium by charge and discharge, and a non-electrode. In a non-aqueous electrolyte secondary battery comprising an aqueous electrolyte, the positive electrode contains lithium cobaltate, and in the second invention, the addition amount of the lithium cobaltate to the spinel-type lithium manganate is 1 to 3. 20% by weight.

[0006]

DETAILED DESCRIPTION OF THE INVENTION The spinel-type lithium manganate and lithium cobaltate used as the positive electrode active material for the non-aqueous electrolyte secondary battery of the present invention include lithium, manganese, and cobalt nitrates, oxides, and sulfates. It can be produced using a salt, a hydroxide, a halide or the like as a raw material.
For example, it can be manufactured by weighing a lithium salt raw material, a manganese salt raw material, or a cobalt salt raw material in accordance with a desired composition, mixing them sufficiently, and baking them in air in a temperature range of 600 ° C. to 1100 ° C. At this time, spinel-type lithium manganate LiMn ₂ MO ₄ (M
May be a metal element), lithium-rich spinel-type lithium manganate Li (1 + x) Mn ₂ O ₄ (x is an excess amount of lithium) or lithium-rich spinel-type lithium manganate Li (1 + x) Mn ₂ MO ₄ of different element addition type .

The negative electrode active material capable of inserting and extracting lithium includes, for example, carbons such as cokes, amorphous carbons, graphites, fired pyrocarbon organic polymer compounds, carbon fibers, and activated carbon. The material may be a polymer such as polyacetylene. Further, a lithium alloy such as a lithium aluminum alloy can also be used.

As the non-aqueous electrolyte, an electrolyte obtained by dissolving a lithium salt electrolyte in a conventionally known non-aqueous electrolyte solvent can be used. That is, as the solvent for the non-aqueous electrolyte, propylene carbonate, ethylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyl lactone, sulfolane, 1,2-dimethoxyethane, 1,2 At least one of aprotic organic solvents such as diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolane, acetonitrile, methyl acetate, methyl butyrate, phosphoric acid triester;
A solvent in which at least one species is mixed, and a lithium salt soluble in the solvent, for example, LiClO ₄ , LiBF ₄ , LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃
CO ₂ , LiAsF ₆ , LiSbF _{6 and the} like can be used. In particular, propylene carbonate, ethylene carbonate, cyclic carbonates such as vinylene carbonate and dimethyl carbonate, chain carbonates such as diethyl carbonate 1
The solvent mixture or more, the non-aqueous electrolyte preferably includes LiBF4 and / or LiPF _6.

As the separator, an insulating thin film having a high ion permeability and a predetermined mechanical strength is used, and a thin film of polyethylene or polypropylene is preferable. Other configurations of the non-aqueous electrolyte secondary battery, for example, a battery can and an upper lid, can be the same as the conventional non-aqueous electrolyte secondary battery. Also, the shape of the battery is not particularly specified, and various shapes such as a cylindrical shape and a square shape can be adopted. Hereinafter, embodiments of the present invention will be described.

[0010] 1. 1. Positive Electrode FIG. 1 is a sectional view of a cylindrical nonaqueous electrolyte secondary battery embodying the present invention. Reference numeral 1 denotes a positive electrode current collector, which is an aluminum foil having a thickness of 20 μm. The plane size is 55 mm × 510 mm. 2 is a positive electrode active material layer. As the positive electrode active material, a lithium manganese composite oxide having an average particle diameter of 10 μm, a carbon powder having an average particle diameter of 3 μm as a conductive additive, and polyvinylidene fluoride (hereinafter abbreviated as PVdF) as a binder,
Mix at 90: 5: 5 wt% respectively. In the present invention, as described later, lithium cobaltate was added to this mixture. There, N-methyl-2-pyrrolidone is charged and mixed to prepare a slurry. This slurry was applied to both sides of an aluminum foil having a thickness of 20 μm, and after drying the solvent, it was rolled with a roller press to produce a positive electrode mixture electrode, which was cut into a width of 54 mm and a length of 450 mm. Thus, a short positive electrode was produced.

2. Negative electrode As the negative electrode active material, a binder of an amorphous carbon material having an average particle diameter of 20 μm and polyvinylidene fluoride (PVdF) was used.
The mixture was mixed at 10% by weight, and N-methyl-2-pyrrolidone was added and mixed to prepare a slurry-like solution. This mixed solution was applied to both sides of a copper foil 3 having a thickness of 10 μm as a current collector, the solvent was dried, and then rolled with a roller press.
A negative electrode mixture electrode was prepared, and then 56 mm wide and 5 mm long.
It was cut into 60 mm to produce a strip-shaped negative electrode.

3. Battery The positive electrode and the negative electrode produced by the above-described method are 40 μm thick,
It is wound through a separator 5 made of a microporous polyethylene film having a width of 58 mm to form a spiral wound group.
The wound group is inserted into the battery can 6, and a nickel tab terminal previously welded to the copper foil of the negative electrode current collector 3 is welded to the bottom of the battery can. Next, 1 m of LiPF ₆ was added to a solution in which ethylene carbonate and dimethyl carbonate were mixed at a volume ratio of 1: 2.
5 ml of the electrolytic solution dissolved at a concentration of ol / l was injected into the battery container. The electrolyte is propylene carbonate in volume ratio:
LiPF _{6 in} a mixed solvent of dimethyl carbonate = 3: 7 at 1M /
l Dissolved. Next, an aluminum tab terminal previously welded to the aluminum foil of the positive electrode current collector 1 is welded to the lid, and the lid is disposed on the upper portion of the battery can via the insulating gasket 9, and this portion is caulked and sealed. , Diameter 18m
m, a cylindrical battery having a height of 65 mm was produced. Reference numeral 9 denotes an electrically insulating gasket. Here, in the positive electrode cap 7, a current interrupting mechanism that operates in response to an increase in battery internal pressure and a valve mechanism that opens in response to a pressure higher than the pressure at which the current interrupting mechanism operates are incorporated. In the present embodiment, the operating pressure of the current interrupting mechanism was 8 kgf / cm ² , and the operating pressure of the valve mechanism was 20 kgf / cm ² . Thus, the battery of the example is completed.

4. Initial charge / discharge test After the produced battery was left at 25 ° C. for 24 hours, an initial charge / discharge test was performed. That is, after charging for 4 hours at a charging voltage of 4.2 V (however, a limiting current of 320 mA), discharging was performed for 10 cycles to a discharging end voltage of 2.5 V with a discharging current of 1 A.

5. Cycle Test A part of the battery subjected to the initial charge / discharge test was charged at a charge current of 1 A at 50 ° C., a charge end voltage of 4.2 V for 5 hours, and a discharge current of 1 A.
, A charge / discharge cycle test was performed under the condition of a discharge end voltage of 2.5 V. Disassemble the battery after 100 cycles charge and discharge,
The amount of manganese eluted into the electrolyte and the manganese content in the negative electrode mixture were measured.

6. High-temperature heating test After 200 cycles of the above-described cycle test, a high-temperature heating test was performed. In this high-temperature heating test, the battery was fixed in a constant temperature bath in a charged state, and heated at a heating rate of 5 ° C./min for 15 minutes.
Heat to 0 ° C. Thereafter, the temperature of 150 ° C.
After holding for a minute, the presence or absence of rupture or ignition of the battery was measured.

[0016]

EXAMPLES (Examples 1 to 9, Comparative Example 1) As shown in Table 1, the mixing weight ratio of lithium cobalt oxide to spinel type lithium manganate was 0, 1, 5, 10,
Each battery was trial-produced under the other manufacturing conditions described above, with 20, 30, 40, 50, 60, and 70% by weight.

FIG. 2 shows the cycle life characteristics of these batteries. In the battery of Comparative Example 1, the discharge capacity sharply decreased from the point of time exceeding 100 cycles. On the other hand, in the battery mixed with lithium cobaltate, it was found that the discharge capacity was small and the cycle life characteristic at 50 ° C. was improved when lithium cobaltate exceeded 1% by weight. The reason for this is that the addition of lithium cobalt
It is considered that the conductivity is improved.

Table 1 shows the batteries of Examples 1 to 9 and Comparative Example 1 which were subjected to a high-temperature heating test for 10 batteries each, and the number of batteries which burst or ignited was shown. The mixing ratio of lithium cobaltate is 20% by weight
Above, the battery was found to rupture and ignite.

From the above results, the mixing ratio of lithium cobaltate to spinel-type lithium manganate was from 1 to 20.
By setting the weight%, a battery having high safety and excellent cycle life characteristics can be obtained. In addition, a part of the manganese element of the spinel-type lithium manganate is replaced with another element such as cobalt, nickel, aluminum, iron, magnesium, and strontium, and part of the cobalt element of the lithium cobalt oxide is nickel, manganese, Similar effects were obtained with compounds substituted with elements such as magnesium, aluminum, iron, and magnesium.

[0020]

[Table 1]

[0021]

The use of a mixture of spinel-type lithium manganate and lithium cobaltate as the active material of the positive electrode provides a non-aqueous electrolyte secondary battery having excellent cycle life characteristics at 50 ° C. and high-temperature heating characteristics. it can.

[Brief description of the drawings]

FIG. 1 is a sectional view of a cylindrical nonaqueous electrolyte secondary battery embodying the present invention.

FIG. 2 shows cycle life characteristics of each battery.

[Explanation of symbols]

1 is a positive electrode current collector, 2 is a positive electrode active material layer, 3 is a negative electrode current collector,
4 is a negative electrode active material layer, 5 is a separator, 6 is a battery can, 7 is a positive electrode cap, 8 is a positive electrode lead, and 9 is a gasket.

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Claims (2)

[Claims] A spinel type lithium manganate (LiMn)
_In a non-aqueous electrolyte secondary battery comprising a positive electrode mainly composed of ₂ O ₄ ), a negative electrode capable of occluding and releasing lithium by charging and discharging, and a non-aqueous electrolyte, the positive electrode includes lithium cobalt oxide (LiCoO ₂ ). A non-aqueous electrolyte secondary battery comprising: 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the amount of the lithium cobaltate added to the spinel-type lithium manganate is 1 to 20% by weight.