JP3200867B2 - Non-aqueous electrolyte secondary battery - Google Patents

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 using a lithium composite oxide as a positive electrode active material.

[0002]

2. Description of the Related Art In recent years, new portable devices such as a camera-integrated VTR, a cellular phone, and a laptop personal computer have appeared, and development of a secondary battery having a high energy density as a power source for these devices has been strongly desired. Conventionally, secondary batteries, such as lead batteries and Ni-Cd batteries, have been widely used as portable power sources. However, these batteries are difficult to reduce in weight and leave problems such as environmental protection. ing.

[0003] Under these circumstances, great expectations are placed on non-aqueous electrolyte secondary batteries as non-polluting batteries and batteries having a high energy density. In this non-aqueous electrolyte secondary battery, in order to obtain a more high energy density batteries, for example, in JP-63-59507 Publication, lithium composite oxide as the positive electrode active material Li _x M _Y O ₂ (M is Co or Non-aqueous electrolyte secondary batteries using Ni) have been proposed. This battery has an advantage that a high energy density can be obtained because it exhibits a high charge / discharge voltage.

[0004] Among the performances required as secondary batteries that can be substituted for conventional lead batteries and Ni-Cd batteries, there are low-temperature load characteristics and high-temperature life characteristics. In particular, portable equipment such as a camera-integrated VTR, cellular phone, and laptop personal computer may be left in a car room or charged, and high cycle life at high temperatures is one of the important battery performances. Is positioned.

Therefore, Li _x MO ₂ is used as a positive electrode active material,
When battery characteristics of a nonaqueous electrolyte secondary battery using a carbon material as a negative electrode active material are evaluated, a long cycle life of about 1200 cycles is confirmed even at a discharge depth of 100% as long as the battery is used at room temperature. Further, even at a low temperature (at least −20 ° C.), it is possible to maintain a capacity of 70% or more of a normal temperature, and it has been confirmed that the battery has a performance that can replace conventional lead batteries and Ni—Cd batteries.

[0006]

However, this battery has a drawback that when the charge / discharge cycle is repeated at a high temperature, the capacity is significantly reduced. When the charge / discharge cycle is performed in an atmosphere of 45 ° C., the battery has a drawback of about 1/10 or less of the normal temperature. It will be the life.
Therefore, the present invention has been proposed in view of such conventional circumstances, and aims to improve the charge / discharge cycle life of a nonaqueous electrolyte secondary battery using a lithium composite oxide as a positive electrode and a carbon material as a negative electrode at a high temperature. The purpose is to aim.

In order to achieve the above object, the present inventors have made various studies and found that the content of carbonic acid ( CO ₃ ^2- ) contained in the positive electrode active material was reduced to 0.41% by weight or less. Then, it was found that the capacity reduction can be suppressed even when used at a high temperature. The present invention has been completed on the basis of such findings, and Li _X MO ₂ (where M represents at least one transition metal, preferably at least one of Co or Ni, and 0.05 ≦ X ≦ 1. 10). A positive electrode formed by applying a positive electrode active material comprising a positive electrode and a negative electrode active material comprising a carbonaceous material capable of doping and undoping lithium is applied to both surfaces of the current collector. in the negative electrode and the nonaqueous electrolyte and the non-aqueous electrolyte secondary battery provided with a that is, is characterized in that carbon content contained in the positive electrode active material is not higher 0.41 wt% or less.

In the present invention, a carbon material is used as the negative electrode active material, and any carbon material may be used as long as it can be doped with lithium and dedoped, and pyrolytic carbons, cokes (pitch coke) , Needle coke, petroleum coke, etc.), graphites, glass carbons, fired products of organic high molecular compounds (fired and carbonized phenol resin, furan resin, etc. at an appropriate temperature), carbon fibers, activated carbon, etc. be able to.

The electrolyte may be LiClO ₄ , L
_{iA S F 6, LiPF 6,} LiBF 4, LiB (C 6 H
₅ ) ₄ , LiCl, LiBr, CH ₂ SO ₃ Li, CF
Material such as ₃ SO ₃ Li, it can be used. Examples of the organic solvent include propylene carbonate, enylene carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran,
A single solvent such as methyltetrahydrofuran, 1,3-dioxolan, sulfolane, acetonitrile, diethyl carbonate, dipropyl carbonate, or a mixture of two or more solvents can be used.

[0010]

[Action] Although the details of the action of carbonic acid in the positive electrode active material on the capacity decrease due to the cycle at high temperature are unknown,
As the charge / discharge cycle is repeated at high temperature, carbonic acid dissolves in the electrolyte from the positive electrode active material, and during charging, the lithium doped in the carbon material, which is the negative electrode active material, becomes inactive lithium. It is thought to cause a decline.

In the present invention, the carbon content is 0.41
Since the content is not more than% by weight, the decrease in capacity due to the carbonic acid content is suppressed, and the charge / discharge cycle performance at high temperatures is particularly improved.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described below in detail with reference to the drawings.

Embodiment 1 A non-aqueous electrolyte secondary battery prepared in this embodiment is shown in FIG.
This is a cylindrical spiral type battery as shown in FIG. First, as a positive electrode active material, LiNi _Y Co _1- YO ₂ (Y = 0.6)
The synthesis of LiNi _0.6 Co _0.4 O ₂ represented by Lithium carbonate and cobalt carbonate were mixed at a ratio of 0.5 mol: 0.6 mol: 0.4 mol, respectively, and calcined in air at 900 ° C. for 7 hours, and then ground in an automatic mortar.
This operation of baking → pulverization was further repeated four times to obtain LiNi.
_0.6 Co _0.4 O ₂ was obtained.

The carbonate contained in the obtained LiNi _0.6 Co _0.4 O ₂ is obtained by decomposing a sample with sulfuric acid and producing Co ₂
Was introduced into a barium chloride and sodium hydroxide solution to be absorbed and titrated with a hydrochloric acid standard solution. As a result, the carbonic acid content was 0.32% by weight. LiN thus obtained
91 parts by weight of i _0.6 Co _0.4 O ₂ , 6 parts by weight of graphite as a conductive agent, and 3 parts by weight of polyvinylidene fluoride as a binder were mixed to prepare a positive electrode mixture, and N-methyl-2-pyrrolidone was added thereto. It was dispersed to form a slurry.

Next, as the positive electrode current collector 10, a thickness of 20 μm
The slurry of the above-mentioned positive electrode was uniformly applied to both sides of the strip-shaped aluminum foil, dried, and then compression-molded with a roll press to produce a strip-shaped positive electrode 2. Petroleum pitch is used as a starting material as a negative electrode active material, and oxygen-containing functional groups are added in an amount of 10 to 20%.
After introduction (so-called oxygen cross-linking), 1
Calcination was performed at 000 ° C. to obtain a non-graphitic carbon material having properties similar to glassy carbon. X-ray diffraction measurement of this material showed that the (002) plane spacing was 3.76 ° and the true specific gravity was 1.58. The carbon material obtained in this way is 90
Parts by weight and 10 parts by weight of polyvinylidene fluoride as a binder were mixed to prepare a negative electrode mixture, which was dispersed in N-methyl-2-pyrrolidone to form a slurry.

Next, a strip-shaped copper foil having a thickness of 10 μm is prepared as the negative electrode current collector 9, the slurry of the negative electrode is uniformly applied to both surfaces thereof, dried, and compression-molded by a roll press to form a strip-shaped negative electrode. 1 was produced. The thickness of the separator 3 is 25
The negative electrode 1, the positive electrode 2, and the separator 3 were spirally wound using a microporous polypropylene film having a thickness of μm, thereby producing an electrode element as shown in FIG. The electrode element thus obtained was stored in a nickel-plated iron can 5.
The insulating plate 4 is arranged on both upper and lower surfaces of the spiral electrode element, the aluminum positive electrode lead 12 is led out from the positive electrode current collector 10, and the nickel negative electrode lead 11 is led out from the negative electrode current collector 9. Welded to can 5.

Next, into the battery can, an electrolyte obtained by dissolving 1 mol / l of LiPF ₆ in a mixed solvent of 50% by volume of propylene carbonate and 50% by volume of 1,2-dimethoxyethane was injected. Insulating gasket 6 coated with asphalt
Then, the battery can 5 and the battery lid 7 were caulked and sealed to form a cylindrical spiral-shaped battery having a diameter of 20 mm and a height of 50 mm.

Example 2 In the same manner as in Example 1, lithium carbonate, nickel carbonate and cobalt carbonate were mixed at a ratio of 0.5 mol: 0.6 mol: 0.4 mol, respectively, and the mixture was heated at 900 ° C. for 7 hours in air. And then crushed in an automatic mortar. Next, 4 kg of this material was placed in a container containing 20 liters of pure water and stirred for 30 minutes.
After that, filtration with a glass filter is performed, and LiNi
_0.6 Co _0.4 O ₂ was obtained. The resulting LiNi _0.6 Co
As a result of measuring the carbon content contained in _0.4 O ₂ , it was 0.41% by weight. Other than using this as a positive electrode active material,
In the same manner as in Example 1, the same cylindrical spiral battery was manufactured.

Example 3 LiNi _0.6 Co _0.4 O ₂ was synthesized in the same manner as in Example 2, and washing and filtration with water were repeated five times. The carbon content of the obtained LiNi _0.6 Co _0.4 O ₂ was 0.16% by weight. Other than using this as a positive electrode active material,
A cylindrical spiral battery was manufactured in the same manner as in Example 1.

Example 4 Synthesis of an active material was carried out as follows. Lithium carbonate and nickel carbonate and cobalt carbonate were mixed in 0.425 mol versus 0.6 mol body 0.4 mole ratio, 900 ° C., and calcined at 7 hours in air, subjected to subsequent ground in an automatic mortar Li _0.85 Ni _0.6
Co _0.4 O ₂ was obtained. The obtained Li _0.85 Ni _0.6 Co
The carbon content of _0.4 O ₂ was 0.068% by weight. Except that this was used as a positive electrode active material, a cylindrical spiral battery was manufactured in the same manner as in Example 1.

[0021] Comparative Example 1 were mixed in Example 1 and the same for each 0.5 mole-for-0.6 mol versus 0.4 mole lithium carbonate and nickel carbonate and cobalt carbonate as a ratio, 900 ° C., 7 hours in air , And then pulverized in an automatic mortar, and this operation of baking → pulverization was further repeated twice to obtain LiNi _0.6 Co _0.4 O ₂ . As a result of measuring the carbon content contained in the obtained LiNi _0.6 Co _0.4 O ₂ , it was 1.65% by weight. Except that this was used as a positive electrode active material, the same cylindrical spiral-type battery was produced in the same manner as in Example 1.

COMPARATIVE EXAMPLE 2 As in Example 1, lithium carbonate, nickel carbonate and cobalt carbonate were mixed in a molar ratio of 0.5 mol: 0.6 mol: 0.4 mol, respectively, and the mixture was heated at 900 ° C. for 7 hours in air. It was calcined and then pulverized with an automatic mortar to obtain LiNi _0.6 Co _0.4 O ₂ . The carbonate content of the obtained LiNi _0.6 Co _0.4 O ₂ is
3.78% by weight. Except that this was used as a positive electrode active material, a cylindrical spiral battery was manufactured in the same manner as in Example 1.

The batteries of Examples 1, 2, 3, 4 and Comparative Examples 1 and 2 were set at a charging voltage of 4.1 V (maximum) in an atmosphere of 60 ° C. and at a constant current of 1 A for 3 hours. Charged. For the discharge, a constant resistance discharge of 6.2Ω was performed in the same atmosphere at 60 ° C. until the final voltage was 2.75V. FIG. 2 shows the discharge capacity in each cycle. As shown in FIG. 2, in the battery of Comparative Example 2 having a large amount of carbonate contained in the positive electrode active material, the capacity was significantly reduced due to the cycle, and the capacity at the 100th cycle was reduced from 201 wh / l to 74 wh / l (37%). Has been done. Comparative Example 1 having relatively high carbon content
In the battery of the above, the capacity at the 100th cycle is reduced to 56% of the initial capacity.

On the other hand, in the batteries of Examples 1, 2, 3, and 4 in which the amount of carbonic acid contained in the positive electrode active material is small, the capacity decrease due to the cycle is small, and the capacity at the 100th cycle is smaller than the initial capacity. It showed a value of 76% to 89%. As described above, the battery containing a large amount of carbonic acid in the positive electrode active material causes a large capacity decrease when the charge / discharge cycle is repeated at a high temperature, whereas the battery containing a large amount of carbonic acid is suppressed to 0.41% by weight or less. Can reduce the capacity decrease due to the high-temperature cycle, and the effect is large.

Example 5 LiCoO ₂ was synthesized as a positive electrode active material. Lithium carbonate and cobalt carbonate are each mixed at a ratio of 0.5 mol,
It was baked in air at 900 ° C. for 7 hours, and then pulverized in an automatic mortar to obtain LiCoO ₂ . LiCoO obtained
As a result of measuring the carbon content of ₂ , it was 0.01% by weight. A cylindrical spiral battery was manufactured in the same manner as in Example 1 except that this was used as a positive electrode active material.

COMPARATIVE EXAMPLE 3 As in Example 5, lithium carbonate and cobalt carbonate were mixed at a ratio of 0.55 mol to 1.0 mol, respectively.
Baked in air for hours, then crushed in an automatic mortar
iCoO ₂ was obtained. The carbon content of the obtained LiCoO ₂ was measured and found to be 2.97% by weight. Except that this was used as a positive electrode active material, a cylindrical spiral battery was manufactured in the same manner as in Example 1. Example 5 and Comparative Example 3
Was charged at 4.1 V (maximum) in an atmosphere of 60 ° C., and charged at a constant current of 1 A for 3 hours.

For the discharge, a constant resistance discharge of 6.2 Ω was performed in an atmosphere at 60 ° C. to a final voltage of 2.75 V, and the discharge capacity in each cycle is shown in FIG. LiNi _0.6 Co
_{As in} the case of _0.4 O _{2, in} the case of LiCoO ₂ , the battery of Comparative Example 2 having a large amount of carbonic acid contained in the positive electrode active material has a large capacity decrease accompanying the charge / discharge cycle. On the other hand, in the battery of Example 5 having a small content of carbonate, the capacity decrease was small, and the capacity at the 100th cycle was 82% of the initial capacity.
The value of was shown.

As described above, even when the positive electrode active material is LiCoO ₂ , by lowering the content of carbon dioxide to 0.41% by weight or less, it is possible to reduce the capacity decrease due to the cycle at a high temperature. Was confirmed to be large. From the above examples, the positive electrode active material represented by Li _X MO ₂ (where M represents a transition metal, preferably at least one of Co and Ni and 0.05 ≦ X ≦ 1.10.) Carbonic acid ( CO ₃ ^2- ) contained in
It was confirmed that by setting the content to not more than% by weight, the charge / discharge cycle performance at a high temperature can be remarkably improved.

The present invention can be applied not only to the cylindrical spiral type secondary battery shown in the embodiment but also to various types of batteries such as a button type, a coin type and a square type. It is.

[0030]

As is apparent from the above description, in the present invention, in a nonaqueous electrolyte secondary battery using a lithium composite oxide as a positive electrode and a carbon material as a negative electrode, the carbon content in the positive electrode active material is reduced to 0. Since the content is set to 0.41% by weight, it is possible to reduce a decrease in capacity due to a charge / discharge cycle at a high temperature.

As a result, a secondary battery having a high energy density and excellent charge / discharge cycle performance can be provided, and its industrial value is great.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing a configuration example of a spiral type nonaqueous electrolyte secondary battery.

FIG. 2 is a characteristic diagram showing a difference in charge / discharge cycle characteristics depending on carbonic acid contained in LiNi _0.6 Co _0.4 O ₂ .

FIG. 3 is a characteristic diagram showing a difference in charge / discharge cycle characteristics due to carbonic acid contained in LiCoO ₂ .

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Negative electrode 2 ... Positive electrode 3 ... Separator

Continuation of the front page (56) References JP-A-6-342657 (JP, A) JP-A-3-64860 (JP, A) JP-A-63-121260 (JP, A) JP-A-2-56871 (JP) JP-A-1-279578 (JP, A) JP-A-3-49155 (JP, A) JP-A-3-84872 (JP, A) JP-A-2-66856 (JP, A) 2-79566 (JP, U) Hikaru 2-150760 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 10/40 H01M 4/02-4/04 H01M 4 / 58

Claims (5)

(57) [Claims] 1. A positive electrode active material comprising Li _X MO ₂ (where M represents at least one transition metal and 0.05 ≦ X ≦ 1.10.) Is applied to both surfaces of a current collector and molded.
A negative electrode active material made of a carbonaceous material capable of doping and undoping lithium is applied to both surfaces of the current collector and molded.
The negative electrode and non-aqueous non-aqueous electrolyte secondary battery comprising an electrolyte
In the above, the carbon content contained in the positive electrode active material is 0.41% by weight.
A nonaqueous electrolyte secondary battery characterized by the following. 2. The method according to claim 1, wherein the positive electrode and the negative electrode are connected via a separator.
It is characterized by comprising a spirally wound electrode element that is wound
The non-aqueous electrolyte battery according to claim 1, wherein 3. The method according to claim 2, wherein the current collector is made of a metal foil.
The non-aqueous electrolyte secondary battery according to claim 2. 4. The method according to claim 1, wherein the positive electrode has a carbonic acid content of 0.01% by weight or less.
2. The non-aqueous electrolyte according to claim 1, further comprising:
Rechargeable battery. 5. The method according to claim 1, wherein the negative electrode has an oxygen functional group on a petroleum pitch.
It is a carbonaceous material obtained by firing after introduction.
The non-aqueous electrolyte secondary battery according to claim 1.