JP2001185139A - Positive electrode material for secondary battery using nonaqueous electrolyte and manufacturing method therefor and lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary battery having lithium manganate as a positive electrode material having high-temperature characteristics superior to conventional lithium secondary batteries. SOLUTION: The positive electrode material for the secondary battery using a nonaqueous electrolyte and obtained by mixing lithium manganate with at least one metallic acetate selected from nickel, cobalt, iron, and tin, of 0.1-5 mol% for the manganese and by applying heat treatment to the resulting mixture is used as a material for the positive electrode 2 of the lithium secondary battery. The high-temperature characteristics of the lithium manganate formed by adding the metal and by using the acetate are enhanced compared with those of conventional lithium secondary batteries using other additives.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive electrode material for a non-aqueous electrolyte secondary battery which can be used for a lithium secondary battery and the like, a method for producing the same, and a lithium secondary battery using the positive electrode material for the non-aqueous electrolyte secondary battery. More specifically, a positive electrode material for a non-aqueous electrolyte secondary battery, in which the elution of manganese is suppressed and the high-temperature characteristics of the battery such as high-temperature storage characteristics and high-temperature cycle characteristics are improved, a method for producing the same, and a method for producing the non-aqueous electrolyte secondary battery The present invention relates to a lithium secondary battery using a positive electrode material.

[0002]

2. Description of the Related Art With the rapid progress of portable and cordless personal computers and telephones in recent years, the demand for secondary batteries (storage batteries) as power sources for driving them has been increasing. Among them, lithium secondary batteries are particularly expected because they have the smallest size and high energy density. Lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiN
iO ₂ ), lithium manganate (LiMn ₂ O ₄ ) and the like are used. These composite oxides have 4
Since the battery has a potential of V or higher, the battery can have high energy density.

[0003] Of the above composite oxides, lithium cobaltate and lithium nickelate have a theoretical capacity of 280 mAh /
g of lithium manganate, whereas the theoretical capacity of lithium manganate is as small as 148 mAh / g, but the raw material manganese oxide is abundant and inexpensive. This has the advantage that the stability of the target is not lost. However, this lithium manganate has a drawback that manganese is easily eluted at high temperatures, and battery performance at high temperatures such as high-temperature storage properties and high-temperature cycle characteristics is inferior. In order to eliminate such disadvantages, boron (for example, JP-A-4-237970 and JP-A-8-195200) is used as an additive substance.
Attempts have been made to improve the high temperature characteristics of the positive electrode material by producing the positive electrode material by a wet method using aluminum, chromium, iron, nickel, cobalt, calcium, magnesium and the like (Japanese Patent Laid-Open No. 11-240721). I have. In the latter method, a positive electrode material is manufactured using a metal carbonate, nitrate or an organometallic complex. However, the high-temperature characteristics of the positive electrode material thus obtained are not sufficiently satisfactory.

[0004]

SUMMARY OF THE INVENTION In order to improve the high temperature properties of this lithium manganate, the present applicant has developed zinc,
A dry manufacturing method of a positive electrode material for a lithium secondary battery in which at least one metal selected from iron, nickel and tin is added in the form of an oxide or a hydroxide has been proposed. The positive electrode material manufactured by the method according to the prior application shows improvement in high-temperature characteristics as compared with the conventional positive electrode material for lithium secondary batteries, but is still insufficient and has a particularly high high-temperature storage capacity retention ratio (manganese elution). Further improvement in prevention efficiency) is desired.
The present inventors have reached the present invention as a result of studying the addition form of the additional metal and the heat treatment temperature.

[0005]

The present invention relates to lithium manganate and at least one metal selected from the group consisting of nickel, cobalt, iron and tin in an amount of 0.1 to 5 mol% based on manganese in the lithium manganate. The acetate salt of
Preferably, a method for producing a positive electrode material for a non-aqueous electrolyte secondary battery, comprising heat-treating at 400 to 700 ° C. to fix the nickel and / or cobalt, and using nickel and / or cobalt as a metal. Is desirable. The positive electrode material for a non-aqueous electrolyte secondary battery manufactured in this manner is suitably used in a lithium secondary battery.

Hereinafter, the present invention will be described in detail. The present invention
By specifying the type (quantity of salt) and amount of the additive compound for improving the performance of lithium manganate and, if necessary, the heat treatment temperature, a non-aqueous electrolyte secondary battery with unprecedented high temperature battery characteristics A positive electrode material for a battery and a lithium secondary battery using the material can be provided. As the lithium manganate which is a raw material of the positive electrode material for a non-aqueous electrolyte secondary battery of the present invention, a conventional compound may be used as it is. For example, lithium carbonate (LiCO ₃ ), lithium nitrate (LiNO ₃ ), lithium hydroxide (LiOH), etc., which are lithium raw materials, are replaced with manganese dioxide (MnO ₂ ), which is a manganese raw material.
Lithium manganate can be obtained by heat treatment with manganese trioxide (Mn ₂ O ₃ ), manganese oxyhydroxide (MnOOH), or the like.

[0007] Manganese dioxide is desirable as a manganese raw material, because manganese dioxide is used as a positive electrode material for lithium primary batteries, and lithium is easily incorporated into the structure, and the tap density of electrolytic manganese dioxide is easily increased. . When manganese dioxide is used as the manganese raw material and lithium hydroxide is used as the lithium raw material, when calcination is performed in a rotary kiln, the adhesion to the furnace core tube becomes too large, and the operability is reduced. Lithium manganate is generally not preferred because of low battery performance. The most desirable combination of manganese and lithium is manganese dioxide and lithium carbonate. These manganese and lithium raw materials are desirably pulverized before or after mixing both raw materials in order to obtain a larger contact area.

The weighed and mixed raw materials are used as they are or after granulation. Granulation may be a wet method or a dry method, such as extrusion granulation, tumbling granulation, fluidized granulation, mixed granulation, spray drying granulation, pressure molding granulation, or flake granulation using a roll. It can be carried out. The mixed raw material of manganese and lithium thus obtained is put into a firing furnace and fired at, for example, 600 to 1000 ° C. to obtain lithium manganate. Although a single-phase lithium manganate can be obtained even at a temperature of about 600 ° C., since the growth rate of grains is low at a low firing temperature, it is usually 750 ° C., preferably 850 ° C.
Firing at a temperature of at least ℃ is desirable.

A furnace used for the firing includes a rotary kiln and a stationary furnace.
Lithium manganate is obtained by baking for at least an hour, preferably for 5 to 20 hours. Of the multiple types of lithium manganate, spinel-type lithium manganate is frequently used because it has a potential of 4V class. In the present invention, 0.1 to 5 mol% of an acetate of at least one metal selected from nickel, cobalt, iron and tin with respect to manganese of lithium manganate is added as an additive compound. In general, if it is less than 0.1 mol%, the high-temperature preservability becomes small, and if it exceeds 5 mol%, the initial discharge capacity decreases. As an additive compound, nickel acetate or cobalt acetate is desirable, but a corresponding effect can be obtained with iron or tin acetate. Then a mixture of lithium manganate and metal acetate
The heat treatment is performed at a temperature of 400 to 700 ° C. Heat treatment outside of this temperature range tends to somewhat reduce the high temperature storage stability of the resulting positive electrode material, but it is not fatal,
The heat treatment may be performed at a temperature lower than 700 ° C. or higher than 700 ° C.
The heat treatment time is suitably 0.5 to 10 hours.

[0010] The positive electrode material for a non-aqueous electrolyte secondary battery thus produced is mixed with a conductive agent and a binder and molded to form a positive electrode material. As the material on the negative electrode side, a material capable of inserting and extracting lithium such as lithium itself and carbon is preferably used. As the non-aqueous electrolyte, one obtained by dissolving a lithium compound such as lithium hexafluoride (LiPF ₆ ) in a mixed solvent such as ethylene carbonate-dimethyl carbonate is preferably used, but is not limited thereto. Those dissolved in an organic solvent such as sulfolane can also be used.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a lithium secondary battery using a positive electrode material for a non-aqueous electrolyte secondary battery of the present invention will be described with reference to the drawings. FIG. 1 is a longitudinal sectional view of a coin-type lithium secondary battery using the positive electrode material for a non-aqueous electrolyte secondary battery of the present invention.

A positive electrode material for a non-aqueous electrolyte secondary battery, which is adjusted using an acetate such as cobalt or nickel, is provided on the upper inner surface of a stainless steel case 1 having a dish-like shape and having resistance to organic electrolyte. A positive electrode 2 mixed and formed with a conductive agent and a binder is installed via a current collector (not shown), and the peripheral edge is bent downward on the upper surface of the positive electrode 2, and the bent front end is formed of the case 1. The partition plate 3 that contacts the inner surface is in contact. The upper portion of the peripheral edge of the case 1 is further bent inward to form a space in the peripheral portion of the case 1, and the space is filled with a fixing resin 4, and the inner surface thereof is the outer surface of the downward bent portion of the partition plate 3. Is in contact with This fixing resin 4
A peripheral portion of a lid 5 having a plurality of steps formed in the peripheral portion is inserted and fixed therein, and powdered carbon or the like is electrically conductive or bound between the lower surface of the lid 5 and the partition plate 3. A negative electrode 6 solidified with an agent is provided via a current collector (not shown).

Using the case 1 and the lid 5 of the lithium secondary battery having such a configuration as a positive electrode terminal and a negative electrode terminal, respectively, the battery is charged when energized, and a resistor is connected between both terminals after charging to function as a battery. I do. At this time, since a material having good high-temperature characteristics is used as the positive electrode material, even in the case of a secondary battery such as an electronic device used at a relatively high temperature, deterioration of the battery characteristics is suppressed to a minimum.

Next, examples of the positive electrode material for a non-aqueous electrolyte secondary battery of the present invention and a method for producing the same will be described, but the examples do not limit the present invention.

Example 1 To 1 kg of electrolytic manganese dioxide, 230 g of lithium carbonate was added and mixed, and then placed in a box furnace maintained at 800 ° C. and calcined for 20 hours to obtain a spinel-type lithium manganate. An aqueous cobalt acetate solution prepared by dissolving 1.38 g (0.1 mol% based on manganese) of cobalt acetate tetrahydrate as an additive compound in 100 ml of water was used to obtain 500 g of spinel-type lithium manganate obtained as described above. Was dropped. The cobalt acetate was adhered to the surface of lithium manganate using a high-speed mixer while dropping, and then dried at 80 ° C. for 12 hours to remove water. Further, heat treatment was performed at 500 ° C. for 2 hours to obtain a positive electrode material for a non-aqueous electrolyte secondary battery.

90 parts by weight of the obtained positive electrode material, 7 parts by weight of acetylene black as a conductive agent, and 3 parts by weight of polytetrafluoroethylene as a binder were sufficiently mixed at room temperature to prepare a positive electrode mixture. The positive electrode mixture is used as a positive electrode material and metallic lithium is used as a negative electrode material. Both are connected via a stainless steel current collector to a case and a lid, both of which are made of stainless steel, and are impregnated with an electrolyte. Separate each other with a porous polypropylene partition plate, diameter 20 mm, height 1.6
The lithium secondary battery shown in FIG. As an electrolytic solution, the solvent was equal volume mixture of ethylene carbonate and 1,3-dimethoxyethane, it was used after lithium hexafluorophosphate dissolved 1 mol / liter.

After measuring the initial capacity of the thus-prepared lithium secondary battery, a charge / discharge test was performed as follows. The current density was 0.5 mA / dm ² , the temperature was fixed at 20 ° C., and the voltage was charged / discharged in a range of 4.3 V to 3 V. The batteries were charged to 4.3 V and stored for 3 days in an environment of 80 ° C., and the storage characteristics of the batteries were measured using the discharge capacity of these batteries as the capacity retention rate after high-temperature storage. Table 1 shows the added compounds and the amounts thereof, the heat treatment temperature for fixing the metal, the initial capacity, and the capacity retention rate after high-temperature storage.

Example 2 The amount of cobalt acetate tetrahydrate was 6.89 g (based on manganese).
A lithium secondary battery was manufactured under the same conditions as in Example 1 except that the amount was 0.5 mol%), and the initial capacity and the capacity retention after high-temperature storage were evaluated under the same conditions. The results are shown in Table 1.

Example 3 A lithium secondary battery was manufactured under the same conditions as in Example 1 except that the amount of cobalt acetate tetrahydrate was changed to 27.6 g (2 mol% based on manganese). The capacity and the capacity retention rate after high-temperature storage were evaluated. The results are shown in Table 1.

Example 4 The amount of cobalt acetate tetrahydrate was 6.89 g (based on manganese).
0.5 mol%), and repeated 10 times of treatment and drying of the cobalt acetate solution with a high-speed mixer, to produce a lithium secondary battery under the same conditions as in Example 1. After storage, the capacity retention was evaluated. The results are shown in Table 1.

[0021]

[Table 1]

Example 5 Nickel acetate tetrahydrate instead of cobalt acetate tetrahydrate
A lithium secondary battery was manufactured under the same conditions as in Example 2 except that 6.88 g (0.5 mol% based on manganese) was used, and the initial capacity and the capacity retention after high-temperature storage were evaluated under the same conditions. The results are shown in Table 1.

Examples 6 and 7 The heat treatment temperature for fixing cobalt was 400 ° C. (Example 6) or
A lithium secondary battery was manufactured under the same conditions as in Example 2 except that the temperature was changed to 700 ° C. (Example 7), and the initial capacity and the capacity retention after high-temperature storage were evaluated under the same conditions. The results are shown in Table 1.

Examples 8 and 9 The heat treatment temperature for fixing cobalt was 350 ° C. (Example 8)
A lithium secondary battery was manufactured under the same conditions as in Example 2 except that the temperature was changed to 800 ° C. (Example 9), and the initial capacity and the capacity retention after high-temperature storage were evaluated under the same conditions. The results are shown in Table 1.

Comparative Example 1 A lithium secondary battery was manufactured under the same conditions as in Example 1 except that cobalt acetate tetrahydrate was not dissolved, and the initial capacity and the capacity retention after storage at high temperature were evaluated under the same conditions. . The results are shown in Table 1.

Comparative Example 2 A lithium secondary battery was prepared under the same conditions as in Example 4 except that the treatment and drying in a high-speed mixer were repeated 20 times, and the initial capacity and the capacity retention after high-temperature storage were measured under the same conditions. evaluated. The results are shown in Table 1.

Comparative Example 3 5.8 g of cobalt oxide instead of cobalt acetate tetrahydrate
A lithium secondary battery was fabricated under the same conditions as in Example 1 except that (about 1 mol% based on manganese) was used, and the initial capacity and the capacity retention after high-temperature storage were evaluated under the same conditions.
The results are shown in Table 1.

Comparative Example 4 A lithium secondary battery was produced under the same conditions as in Comparative Example 3 except that 5.8 g of nickel oxide (about 1 mol% based on manganese) was used instead of cobalt oxide, and the initial conditions were the same. The capacity and the capacity retention rate after high-temperature storage were evaluated. The results are shown in Table 1.

Comparative Example 5 A lithium secondary battery was manufactured under the same conditions as in Comparative Example 3 except that 14.2 g of cobalt nitrate (about 1 mol% based on manganese) was used instead of cobalt oxide. The capacity and the capacity retention rate after high-temperature storage were evaluated. The results are shown in Table 1.

The following can be understood from the experimental results of Examples 1 to 9 and Comparative Examples 1 to 5. Comparative Example 1 without the additive compound,
Comparing Examples 1 to 5 in which the additive compound is present and the heat treatment temperatures are the same, it can be seen that there is no significant difference in the initial capacity, but a remarkable difference is observed in the capacity retention after high-temperature storage. In other words, in comparison with the 65% of Comparative Example 1, the maximum is 92% (Example 3) and the minimum is 86% in the example.
(Examples 1 and 5) showed an improvement of 20% or more.

When the addition amount and the heat treatment temperature are the same and the added compound is changed from cobalt acetate (Example 2) to nickel acetate (Example 5), the initial capacity is increased from 112 mAh / g.
Reduced to 110 mAh / g and the capacity retention rate after storage at high temperatures from 89% to 8
Although reduced to 6%, the addition of nickel showed a significant improvement in the capacity retention after storage at high temperatures. Even when the heat treatment temperature changes from 500 ° C. to 400 ° C. (Example 6) or 700 ° C. (Example 7), the initial capacity is almost the same, and the capacity retention rates after high-temperature storage are 85% (Example 6) and 88%, respectively. % (Example 7). Further heat treatment temperature 350
The initial capacity is almost the same even if the temperature changes further to 800 ° C and 800 ° C, and the capacity retention rate after storage at high temperature is 72% (Example 8).
And 78% (Example 9), which was higher than that of Comparative Example 1.

However, when the addition amount is excessively high as 10 mol% (Comparative Example 2), the capacity retention rate after storage at high temperature is maintained at a relatively high level of 78%, but the initial capacity is 98% mAh / g. It was greatly reduced compared to the case without the compound. When the added compound was replaced with an oxide instead of acetate (Comparative Examples 3 and 4), the capacity retention after storage at high temperature was reduced as compared with the case of equivalent acetate. Furthermore, when the added compound was replaced with nitrate instead of acetate (Comparative Example 5), the capacity retention after storage at high temperature was reduced as compared with the case of equivalent acetate.

[0033]

The present invention relates to lithium manganate and 0.1 to 5 mol% of an acetate of at least one metal selected from nickel, cobalt, iron and tin based on manganese in the lithium manganate. A method for producing a positive electrode material for a non-aqueous electrolyte secondary battery, comprising mixing and heat-treating at 400 to 700 ° C. to fix the nickel and / or cobalt. The positive electrode material for a non-aqueous electrolyte secondary battery manufactured by the method (claim 3) and a lithium secondary battery having the positive electrode material for a non-aqueous electrolyte secondary battery according to claim 3 as a positive electrode material ( Claim 4).

When a metal acetate is added as an additive compound, the high-temperature characteristics, particularly the capacity retention after high-temperature storage, are greatly improved as compared with conventional cathode materials to which boron or metal nitrate is added, and manganese during charge and discharge is improved. Elution is suppressed. Therefore, when such a positive electrode material is used as a lithium secondary battery in an electronic device or the like, when the device is used at a high temperature, the performance of the electronic device, which tends to deteriorate, can be efficiently protected. These effects in the present invention are remarkable when the metal acetate used is cobalt acetate or nickel acetate (claim 2).

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view illustrating a lithium secondary battery having a cathode material for a non-aqueous electrolyte secondary battery of the present invention as a cathode material.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Case 2 Positive electrode 3 Partition board 4 Resin for fixing 5 Lid 6 Negative electrode

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5H003 AA01 AA04 BA01 BA03 BB05 BC06 BD01 BD03 5H014 AA02 BB01 BB06 EE10 HH01 HH08 5H029 AJ02 AJ05 AK03 AL06 AL12 AM03 AM05 AM07 BJ03 CJ02 CJ08 HJ01 HJ14

Claims (4)

[Claims] 1. Lithium manganate and at least one selected from nickel, cobalt, iron and tin in an amount of 0.1 to 5 mol% based on manganese in the lithium manganate.
A method for producing a positive electrode material for a non-aqueous electrolyte secondary battery, comprising mixing acetates of various kinds of metals and performing a heat treatment at 400 to 700 ° C. to fix the nickel and / or cobalt. 2. The method according to claim 1, wherein the metal is nickel and / or cobalt. 3. Lithium manganate and at least one selected from nickel, cobalt, iron and tin in an amount of 0.1 to 5 mol% based on manganese in the lithium manganate.
A positive electrode material for a non-aqueous electrolyte secondary battery, comprising mixing an acetate of a kind of metal, performing heat treatment, and fixing the nickel and / or cobalt. 4. Lithium manganate and at least one selected from nickel, cobalt, iron and tin in an amount of 0.1 to 5 mol% based on manganese in the lithium manganate.
A lithium secondary battery comprising, as a cathode material, a cathode material for a non-aqueous electrolyte secondary battery in which an acetate of a metal is mixed, heat-treated, and the nickel and / or cobalt is immobilized.