JPH113698A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery, which has high capacity and excellent cycle characteristic, at a low cost by using the positive electrode active material of the mixture of three kinds of lithium nickel compound oxide, lithium cobalt compound oxide and lithium manganese compound oxide. SOLUTION: Lithium nickel compound oxide is desirably included in the mixture of three kinds of material at 25 wt.% or more on a point of safety. Total content of lithium nickel compound oxide and lithium cobalt compound oxide is desirably set at 20 wt.% or more so as to improve the large current discharging capacity. In the case where the mean grain diameter of the lithium manganese compound oxide is expressed with (dm), and mean grain diameter close to the (dm) among each mean grain diameter of the lithium manganese compound oxide and the lithium cobalt compound oxide is expressed with (dnc), a desirable difference between (dm) and (dnc) is 0.5 μm or more. Fine charge is performed and quantity of the binder is reduced by giving a difference of grain diameter. With this structure, a positive electrode with a good balance of capacity, cycle characteristic and cost can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lithium ion secondary battery provided with a positive electrode using a lithium compound as an active material.

[0002]

2. Description of the Related Art Lithium-ion batteries using an intercalation compound in which lithium ions are occluded in a host material such as carbon (here, a host material is a material that can occlude and release lithium ions) are used as a negative electrode material. It has high energy density, is lightweight, and has high safety because it does not use lithium metal. Therefore, it is expected to be widely used as a power source for small portable electronic devices such as portable radio telephones, portable personal computers, and portable video cameras.

A lithium ion battery has a negative electrode plate in which a negative electrode mixture containing the above host material is held on a negative electrode current collector, and a reversible lithium ion such as a lithium cobalt composite oxide or a lithium nickel composite oxide. A positive electrode plate that holds a positive electrode mixture containing a positive electrode active material that undergoes an electrochemical reaction on a positive electrode current collector, and holds an electrolyte and intervenes between a negative electrode plate and a positive electrode plate to prevent a short circuit between both electrodes. And a separator. The electrolyte is usually made of an aprotic organic solvent in which a lithium salt such as LiClO ₄ or LiPF ₆ is dissolved, but may be a solid electrolyte. However, when the electrolyte is solid, the separator is not essential.

[0004]

As the positive electrode active material,
In addition to the above-described lithium cobalt composite oxide and lithium nickel composite oxide, a lithium manganese composite oxide is also known. Among them, lithium cobalt composite oxide is
A high discharge capacity can be obtained with a stable discharge voltage, and electron conductivity is exhibited by discharge (LiCoO _{2 has} a conductivity of 10 ^-2 S / cm). Demonstrates, but is expensive. The lithium-nickel composite oxide has the largest discharge capacity, but is inferior in large current performance because the voltage drops with discharge.

In this regard, lithium manganese composite oxides
Inexpensive, hard to break down even at high temperatures, and safe. Therefore, it is advantageous for a battery requiring a capacity of 10 Ah or more, such as an electric vehicle. However, lithium manganese composite oxide is
Electron conductivity is 2 more than that of lithium cobalt composite oxide
Since it is lower than an order of magnitude, carbon or the like as a conductive additive must be added in an amount of 5% or more (usually 10%), and as a result, the energy density is low. It has disadvantages such as a small discharge capacity, particularly a small discharge capacity at a large current, and a large deterioration in cycle characteristics due to an increase in resistance due to collapse of a conductive matrix due to expansion and contraction during charging and discharging. And so on.

Accordingly, an object of the present invention is to provide a low-cost, high-capacity, positive-electrode active material having excellent cycle characteristics based on a lithium-manganese composite oxide by mixing and using three types of composite oxides. Is to provide.

[0007]

In order to achieve the above object, a lithium ion secondary battery according to the present invention is characterized in that the positive electrode active material comprises a lithium nickel composite oxide, a lithium cobalt composite oxide, and a lithium manganese composite oxide. It is characterized by comprising a mixture of three types.

By virtue of these features, the high capacity and electron conductivity of the lithium-cobalt composite oxide, the high capacity of the lithium-nickel composite oxide, the low price of the lithium-manganese composite oxide, and the reduction of the amount of the conductive additive are exhibited. In addition, it is possible to obtain a positive electrode that is balanced in all aspects of capacity, cycle, and price.

If the content of the lithium manganese composite oxide in the three-component mixture is less than 25% by weight, the safety of the lithium manganese composite oxide is hardly exhibited in an actual battery, so that the content is preferably 25% by weight or more. The total content of the lithium nickel composite oxide and the lithium cobalt composite oxide is preferably 20% by weight or more. This is because, when it is more than this, the large current discharge capacity becomes particularly high.

Further, when the average particle diameter of the lithium manganese composite oxide is dm and the average particle diameter closer to dm among the average particle diameters of the lithium nickel composite oxide and the lithium cobalt composite oxide is dnc, The difference from dnc is 0.
It is preferable that the thickness be 5 μm or more. This is because by providing a difference in the particle size, the particles can be packed most closely, and as a result, the binder can be reduced.

[0011]

【Example】

[Example 1] This is an example of the beaker test of the present invention. Commercially available LiMn ₂ O _{4 having} an average particle size of 1 μm;
5 μm of commercially available LiCoO ₂ and 0.7 μm of commercially available LiNiO ₂ were mixed in the proportions shown in Table 1, and 91 parts by weight of the mixture were mixed with 6 parts by weight of polyvinylidene fluoride as a binder and acetylene black 3 as a conductive agent. Parts by weight
After appropriately adding methyl-2-pyrrolidone to prepare a paste, the mixture was applied to both sides of a 20-μm-thick aluminum foil, dried and pressed to produce a positive electrode plate.

The positive electrode plate and the negative electrode plate made of Li metal were immersed in an electrolytic solution comprising a mixed solution of ethylene carbonate: diethyl carbonate = 1: 1 (volume ratio) containing 1 mol / l of LiClO ₄ .

After the positive electrode plate is charged at a constant current of 1 mA to a cutoff voltage of 4.1 V, 1 mA (discharge rate 0.2 C), 5 mA
The battery was discharged to a final voltage of 3.0 V at a constant current of (1C) or 10 mA (2C). The discharge capacity at that time is also shown in Table 1 and plotted in FIG. In FIG. 1, the vertical axis represents the discharge capacity, and the horizontal axis represents LiCoO ₂ and LiNiO ₂ in the mixture.
Shows the total weight ratio. In Table 1, Ni column, Co column,
The (Ni + Co) column and the Mn column are LiNiO ₂ and L, respectively.
iCoO ₂ , (LiNiO ₂ + LiCoO ₂ ) and LiM
It shows the weight ratio of n ₂ O ₄ .

[0014]

[Table 1] As seen in FIG. 1, the discharge capacity was increased when the total content of LiCoO ₂ and LiNiO ₂ was 40% by weight or more.
In particular, when the LiCoO ₂ content is 20% by weight or more, the discharge rate 2
The high rate discharge characteristics of C were good.

[Embodiment 2] This is an embodiment of an actual battery of the present invention. The positive electrode plate used in Example 1 was used. The negative electrode plate 4 is made of graphite (graphite) as a host material on both surfaces of a current collector made of a copper foil having a thickness of 20 μm.
86 parts and 14 parts of polyvinylidene fluoride as a binder were mixed, and a mixture prepared in the form of a paste was applied, dried, and pressed to produce.

The separator is a microporous polyethylene membrane. The electrolyte was ethylene carbonate: diethyl carbonate = 1: 1 containing 1 mol / l of LiPF _6.
(Volume ratio).

The dimensions of each battery element are such that the positive electrode plate has a thickness of 2
00 μm, width 175 mm, separator 35 μm thick
m, width 200 mm, negative plate 150 μm thick, width 18
The length was 0 mm, and they were superposed in order and wound around the polyethylene core in an elliptical shape around the core, and then stored in a battery case. The battery case has a cylindrical shape with a diameter of 66 mm and a height of 220 mm, and is made of stainless steel 304. A hole for injecting an electrolyte is provided at the top of the lid of the battery case, and a safety valve is provided at the bottom. When a nail was penetrated from the side of the battery, the safety valve operated with a battery having a LiMn ₂ O ₄ content of 20% by weight or less in the positive electrode active material. Those above 30% by weight did not work.

[0018]

According to the present invention, a battery which is inexpensive, safe and has a high discharge capacity can be obtained.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the total content of LiCoO ₂ and LiNiO ₂ and the discharge capacity.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takao Fukunaga 1st institution, Nishino-sho, Ino Babacho, Kichijo-in, Minami-ku, Kyoto, Kyoto (72) Inventor Minoru Mizutani Minoru Mizutani, Kichijo-in, Minami-ku, Kyoto, Kyoto No. 1 Ino Baba-cho, Nosho, Japan Battery Co., Ltd.

Claims (5)

[Claims] 1. A lithium ion battery provided with a positive electrode using a lithium compound as an active material, wherein the active material comprises a mixture of three kinds of lithium nickel composite oxide, lithium cobalt composite oxide and lithium manganese composite oxide. Characteristic lithium ion secondary battery. 2. The lithium ion secondary battery according to claim 1, wherein the content of the lithium manganese composite oxide in the three-component mixture is 25% or more. 3. The total content of lithium nickel composite oxide and lithium cobalt composite oxide in the three-component mixture is 20.
The lithium ion secondary battery according to claim 1, which is not less than% by weight. 4. The lithium ion secondary battery according to claim 3, wherein the content of the lithium-cobalt composite oxide in the three-component mixture is 10% by weight or more. 5. When the average particle diameter of the lithium manganese composite oxide is dm, and the average particle diameter of the lithium nickel composite oxide and the lithium cobalt composite oxide which is closer to dm is dnc. Is 0.5 μm.
The lithium ion secondary battery according to claim 1, which is at least m.