JPH04328277A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To improve the charge/discharge cycle characteristic of a nonaqueous electrolyte secondary battery using lithium compound oxide as the positive electrode active material. CONSTITUTION:In a nonaqueous electrolyte secondary battery using LixMO2 (M represents at least one kind of transition metals, and desirably at least one kind of Co and Ni, and 0.05<=(x)<=1.10) as a positive electrode and using a carbon material, which can dope and dedope lithium, as the negative electrode active material, ratio of the carbon (CO3<2->) included in LixMO2 as the positive electrode active material is set 0.41weight% or less.

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 camera-integrated VTRs, cellular phones, and laptop computers have appeared, and there is a strong desire to develop secondary batteries with high energy density as power sources for these devices. Traditionally, secondary batteries such as lead batteries and Ni-Cd batteries have been popular as batteries for these portable power sources, but these batteries are difficult to reduce in weight and still pose problems such as environmental protection. ing.

Under these circumstances, there are great expectations for non-aqueous electrolyte secondary batteries as non-polluting batteries and batteries with high energy density. In this non-aqueous electrolyte secondary battery, in order to obtain a battery with higher energy density, for example, in JP-A-63-59507, a lithium composite oxide Lix MY O2 (M is C) is used as a positive electrode active material.
A non-aqueous electrolyte secondary battery has been proposed using a non-aqueous electrolyte (representing Ni or Ni). Since this battery exhibits a high charge/discharge voltage, it has the advantage of providing high energy density.

By the way, among the performances required of a secondary battery that can replace conventional lead batteries and Ni--Cd batteries are low-temperature load characteristics and high-temperature life characteristics. In particular, portable devices such as camera-integrated VTRs, cellular phones, and laptop computers may be left unattended or charged inside a car, and cycle life at high temperatures is an important aspect of battery performance. be positioned.

[0005] Therefore, when evaluating the battery characteristics of a non-aqueous electrolyte secondary battery that uses LixMO2 as a positive electrode active material and a carbon material as a negative electrode active material, the cycle life is found to be short even at 100% depth of discharge as long as it is used at room temperature. It has been confirmed that it has a long life of about 1200 cycles. Furthermore, it has been confirmed that it can maintain a capacity of 70% or more of normal temperature even at low temperatures (at least -20°C), and has performance that can replace conventional lead batteries and Ni-Cd batteries.

[0006]

[Problems to be Solved by the Invention] However, this battery has the disadvantage that repeated charging and discharging cycles at high temperatures cause a significant drop in capacity, and when charging and discharging cycles are performed in an atmosphere of 45°C, the battery capacity decreases to about 1/10 or less of that at room temperature. It will reach the end of its lifespan. The present invention has been proposed in view of the above-mentioned conventional circumstances, and aims to improve the charge/discharge cycle life of non-aqueous electrolyte secondary batteries in which a lithium composite oxide is used as a positive electrode and a carbon material is used as a negative electrode when used at high temperatures. The purpose is to

[0007]

[Means for Solving the Problems] In order to achieve the above object, the inventors of the present invention have conducted various studies and have determined that the carbonate content (Co32-) contained in the positive electrode active material should be reduced to 0.4
It has been found that if the content is 1% by weight or less, capacity loss can be suppressed even when used at high temperatures. The present invention was completed based on such knowledge, and Lix MO2 (However, M
is at least one transition metal, preferably Co or N
represents at least one type of i, 0.05≦X≦1.10
It is. ) and a lithium-doped cathode active material.
It comprises a negative electrode active material made of a dedoped carbon material and a non-aqueous electrolyte, and is characterized in that the carbonate content contained in the positive electrode active material is 0.41% by weight or less.

[0008] In the present invention, a carbon material is used as the negative electrode active material, but any carbon material that can be doped and dedoped with lithium may be used, such as pyrolytic carbons, cokes (pitch coke), etc. , needle coke, petroleum coke, etc.), graphites, glass carbons, fired bodies of organic polymer compounds (phenol resins, furan resins, etc. are fired and carbonized at appropriate temperatures), carbon fibers, activated carbon, etc. be able to.

[0009] In addition, as an electrolyte, LiClO4,
LiAS F6, LiPF6, LiBF4, Li
B(C6H5)4, LiCl, LiBr, CH2
Materials such as SO3 Li and CF3 SO3 Li can be used. As an organic solvent, propylene carbonate,
enhylene carbonate, 1,2-dimethoxyethane,
1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,
A single solvent or a mixture of two or more of 3-dioxolane, sulfolane, acetonitrile, diethyl carbonate, dipropyl carbonate, and the like can be used.

0010

[Effect] Although the details regarding the effect of carbonate in the positive electrode active material on capacity reduction due to high-temperature cycles are unknown,
As charge and discharge cycles are repeated at high temperatures, carbonic acid from the positive electrode active material dissolves into the electrolyte, and during charging, the lithium doped into the carbon material that is the negative electrode active material turns into inert lithium, resulting in a decrease in capacity. This is considered to be the cause of the decline.

[0011] In the present invention, the carbonic acid content is 0.41
Since the content is set to be less than % by weight, a decrease in capacity due to the carbonic acid content is suppressed, and charge/discharge cycle performance, especially at high temperatures, is improved.

0012

Embodiments Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings.

Example 1 The non-aqueous electrolyte secondary battery produced in this example is shown in FIG.
It is a cylindrical spiral battery as shown in the figure. First of all,
LiNiY Co1-Y O2 (Y
=0.6) LiNi0.6 Co0.4
O2 was synthesized. Lithium carbonate and cobalt carbonate were mixed in a ratio of 0.5 mol, 0.6 mol, and 0.4 mol, respectively, and calcined in air at 900° C. for 7 hours, followed by pulverization in an automatic mortar. This process of firing → pulverization was repeated four more times, and the LiNi0
．． 6 Co0.4 O2 was obtained.

The obtained LiNi0.6 Co0.4 O
The carbonic acid content in 2 was determined by decomposing the sample with sulfuric acid, introducing the generated Co2 into a barium chloride and sodium hydroxide solution to absorb it, and titrating it with a standard hydrochloric acid solution. As a result, the carbonate content was 0.32% by weight. A positive electrode mixture was prepared by mixing 91 parts by weight of the LiNi0.6 Co0.4 O2 obtained in this way, 6 parts by weight of graphite as a conductive agent, and 3 parts by weight of polyvinylidene fluoride as a binder. -Methyl-2-pyrrolidone to form a slurry.

Next, as the positive electrode current collector 10, a thickness of 20 μm was prepared.
The above slurry of the positive electrode was uniformly applied to both sides of a belt-shaped aluminum foil, and after drying, compression molding was performed using a roll press machine to produce a belt-shaped positive electrode 2. As the negative electrode active material, petroleum pitch is used as the starting material, and 10 to 20% of functional groups containing oxygen are added to it.
After introduction (so-called oxygen crosslinking), 1 in an inert gas stream.
By firing at 000°C, a non-graphitic carbon material with properties close to glassy carbon was obtained. As a result of X-ray diffraction measurement of this material, the interplanar spacing of the (002) plane was 3.76 Å, and the true specific gravity was 1.58. The carbon material obtained in this way was
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 with a thickness of 10 μm is prepared as the negative electrode current collector 9, and the above-mentioned negative electrode slurry is uniformly applied to both sides of the copper foil, and after drying, compression molding is performed using a roll press machine to form a strip-shaped negative electrode. 1 was produced. The separator 3 has a thickness of 25
Using microporous polypropylene film, the negative electrode 1
, the positive electrode 2 and the separator 3 were spirally wound to produce an electrode element as shown in FIG. The electrode element thus obtained was housed in a nickel-plated iron can 5. Insulating plates 4 are arranged on both the upper and lower surfaces of the spiral electrode element, an aluminum positive electrode lead 12 is led out from the positive electrode current collector 10 and attached to the battery lid 7, and a nickel negative electrode lead 11 is led out from the negative electrode current collector 9 to form a battery. Welded to can 5.

Next, an electrolytic solution containing 1 mol/l of LiPF6 dissolved in a mixed solvent of 50% by volume of propylene carbonate and 50% by volume of 1,2-dimethoxyethane was poured into the battery can. The battery can 5 and the battery lid 7 are caulked and sealed via an insulating gasket 6 coated with asphalt.
A cylindrical spiral battery with a diameter of 20 mm and a height of 50 mm was produced.

Example 2 Similarly to 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 heated at 900° C. for 7 hours in air. The mixture was fired in an automatic mortar and then ground in an automatic mortar. Next, put 4 kg of this material into a container containing 20 liters of pure water and stir for 30 minutes.
After that, filtration was performed using a glass filter, and LiNi0
．． 6 Co0.4 O2 was obtained. Obtained LiNi0
．． The carbonic acid content contained in 6 Co0.4 O2 was measured and found to be 0.41% by weight. A cylindrical spiral battery was produced in the same manner as in Example 1, except that this was used as the positive electrode active material.

Example 3 LiNi0.6 Co0.4 was prepared using the same method as in Example 2.
O2 was synthesized, and water washing and filtration were repeated five times. The carbonate content of the obtained LiNi0.6 Co0.4 O2 was 0.16% by weight. A cylindrical spiral battery was produced in the same manner as in Example 1, except that this was used as the positive electrode active material.

Example 4 The active material was synthesized as follows. Lithium carbonate, nickel carbonate, and cobalt carbonate were mixed at a ratio of 0.425 mol to 0.4 mol of 0.6 mol, fired in air at 900°C for 7 hours, and then crushed in an automatic mortar to obtain Li0. 85Ni
0.6 Co0.4 O2 was obtained. The obtained Li0.
The carbonic acid content of 85Ni0.6 Co0.4 O2 is 0.
It was 0.068% by weight. A cylindrical spiral battery was produced in the same manner as in Example 1, except that this was used as the positive electrode active material.

Comparative 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, in the same manner as in Example 1, and the mixture was heated at 900° C. in air for 7 hours. LiNi0.6 Co0.4 O2
I got it. Obtained LiNi0.6 Co0.4 O2
The carbonate content was measured and found to be 1.65% by weight. Example 1 except that this was used as the positive electrode active material
A cylindrical spiral battery was fabricated in the same manner as above.

Comparative Example 2 Lithium carbonate, nickel carbonate, and cobalt carbonate were mixed in a molar ratio of 0.5 mole to 0.6 mole to 0.4 mole, respectively, in the same manner as in Example 1, and the mixture was heated at 900° C. in air for 7 hours. LiNi0.6 Co0.4 is fired and then crushed in an automatic mortar.
Obtained O2. Obtained LiNi0.6 Co0.4
The carbonate content of O2 was 3.78% by weight. A cylindrical spiral battery was produced in the same manner as in Example 1, except that this was used as the positive electrode active material.

[0023] Above-mentioned Examples 1, 2, 3, 4 and Comparative Example 1
, 2, in an atmosphere of 60°C, at a charging voltage of 4.
It was set at 1V (maximum) and charged at a constant current of 1A for 3 hours. The discharge was performed at a final voltage of 2.7 in the same 60°C atmosphere.
A constant resistance discharge of 6.2Ω was performed to 5V. Figure 2 shows the discharge capacity in each cycle. As shown in FIG. 2, the battery of Comparative Example 2 with a high carbonate content in the positive electrode active material had a large capacity drop with cycling, with a capacity of 201 at the 100th cycle.
It has decreased from wh/l to 74 wh/l (37%). In addition, even in the battery of Comparative Example 1 with a relatively high carbonate content, the capacity at the 100th cycle was 5% compared to the initial capacity.
It has fallen to 6%.

On the other hand, in the batteries of Examples 1, 2, 3, and 4, where the carbon dioxide content in the positive electrode active material is low, the capacity decrease with cycling is small, and the capacity at the 100th cycle is smaller than the initial capacity. The values ranged from 76% to 89%. In this way, batteries with a high carbonate content in the positive electrode active material experience a large capacity drop when repeated charge/discharge cycles at high temperatures, whereas batteries with a carbonate content of 0.41% by weight or less It can be seen that this makes it possible to reduce the decrease in capacity due to cycles at high temperatures, and the effect is significant.

Example 5 LiCoO2 was synthesized as a positive electrode active material. Lithium carbonate and cobalt carbonate were mixed at a ratio of 0.5 mole each, fired in air at 900°C for 7 hours, and then ground in an automatic mortar to obtain LiCoO2. Obtained LiC
The carbonate content of oO2 was measured and found to be 0.01% by weight. Example 1 except that this was used as the positive electrode active material
A cylindrical spiral battery was fabricated in the same manner as above.

Comparative Example 3 As in Example 5, lithium carbonate and cobalt carbonate were each added to zero.
．． The Li
CoO2 was obtained. The carbonate content of the obtained LiCoO2 was measured and found to be 2.97% by weight. A cylindrical spiral battery was produced in the same manner as in Example 1, except that this was used as the positive electrode active material. The batteries of Example 5 and Comparative Example 3 were charged at a constant current of 1 A for 3 hours in an atmosphere of 60° C. with a charging voltage set at 4.1 V (maximum).

Discharge was carried out at a constant resistance of 6.2Ω to a final voltage of 2.75V in the same atmosphere at 60° C., and the discharge capacity at each cycle is shown in FIG. LiNi0.6C
o0.4 Similarly to the case of O2, in the case of LiCoO2, Comparative Example 2 with a high carbonate content in the positive electrode active material
The capacity of these batteries decreases significantly with charge/discharge cycles. On the other hand, the battery of Example 5, which contained less carbonate, showed a small decrease in capacity, and the capacity at the 100th cycle was 82% of the initial capacity.

In this way, the positive electrode active material is LiCoO2
Even in this case, it was confirmed that by reducing the carbonate content to 0.41% by weight or less, it was possible to reduce the decrease in capacity due to high-temperature cycles, and this effect was significant. From the above examples, it can be seen that Lix MO2 contained in the positive electrode active material represented by The carbonic acid content (Co32-) produced is 0.
．． It was confirmed that by setting the content to 41% by weight or less, the charge/discharge cycle performance could be significantly improved at high temperatures.

Note that the present invention is not only applicable to the cylindrical spiral type secondary battery shown in the embodiments, but also to various types of batteries such as button-shaped, coin-shaped, and square-shaped batteries. It is.

[0030]

Effects of the Invention As is clear from the above description, in the present invention, in a nonaqueous electrolyte secondary battery in which a lithium composite oxide is used as a positive electrode and a carbon material is used as a negative electrode, the carbonate content in the positive electrode active material can be reduced to 0. Since the content is .41% by weight, it is possible to reduce the decrease in capacity due to charge/discharge cycles at high temperatures.

[0031] This makes it possible to provide a secondary battery with high energy density and excellent charge/discharge cycle performance, which has great industrial value.

[Brief explanation of drawings]

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

FIG. 2 is a characteristic diagram showing the difference in charge/discharge cycle characteristics depending on the carbonate content contained in LiNi0.6 Co0.4 O2.

FIG. 3 is a characteristic diagram showing the difference in charge/discharge cycle characteristics depending on the carbonate content contained in LiCoO2.

[Explanation of symbols]

1...Negative electrode 2...Positive electrode 3...Separator

Claims (1)

[Claims] Claim 1: Lix MO2 (where M represents at least one transition metal, 0.05≦X≦1.10
It is. ) and a lithium-doped cathode active material.
A non-aqueous electrolyte 2 comprising a negative electrode active material made of a dedoped carbon material and a non-aqueous electrolyte, characterized in that the carbon content contained in the positive electrode active material is 0.41% by weight or less. Next battery.