JP2000090915A - Lithium manganate and organic electrolyte secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance storage characteristics and cycle life characteristic of an organic electrolyte secondary battery having a positive electrode containing lithium manganate as the main composition. SOLUTION: Lithium manganate capable of electrochemically inserting and releasing lithium by charge and discharge is used. At least one element selected from among the group comprising In, Sb, Sn, W, Mo, Ti, Au, Pt, Pd, Rh, and Pb, an oxide of these elements, or at least one element of them or the oxide of these elements and Ag or an oxide of Ag are immobilized on the surfaces of particles of lithium manganate to prepare a positive active material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to lithium manganate and an organic electrolyte secondary battery using the same.

[0002]

2. Description of the Related Art Organic electrolyte secondary batteries typified by lithium secondary batteries are mainly used in portable devices such as VTR cameras, notebook computers and mobile phones, taking advantage of their high energy density. . Particularly in recent years, lithium ion secondary batteries using a carbon material capable of occluding and releasing lithium for a negative electrode have become widespread. The internal structure of this battery is usually wound as shown below. That is,
An active material is applied to a metal foil to form a positive electrode and a negative electrode, wound through a separator, the wound material is stored in a cylindrical can serving as a container, and after pouring the electrolyte, the cap is removed. We attach and seal.

The carbon material used as the negative electrode active material is in a state where lithium is released, that is, in a discharged state when the battery is assembled. Therefore, the positive electrode is also in a discharged active material, for example, lithium cobalt oxide (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganate (LiMn).
₂ O ₄ ) is used. Then, the battery can function as a battery by initial charging, and a lithium ion secondary battery is manufactured. However, since the above-mentioned positive electrode active material does not have sufficient electron conductivity, it is used for the positive electrode as a mixture obtained by mixing a conductive powder and a binder, which are inexpensive and stable in a battery, such as graphite or carbon black, as a conductive agent. Is done.

Among the above-mentioned positive electrode active materials, a lithium secondary battery using lithium manganate having a spinel structure in the crystal structure has a higher safety by heating than a battery using lithium cobalt oxide or lithium nickel oxide. Are better. Therefore, batteries using lithium manganate as the active material for the positive electrode have attracted attention as high-safety batteries that are suitable for large-sized lithium secondary batteries for power storage, electric vehicles, and the like. In addition, lithium manganate having a spinel structure in the crystal structure causes the crystal to repeatedly expand and contract due to insertion and desorption of lithium during the charge / discharge reaction. Then, when charge and discharge are repeated, the structure of the positive electrode active material layer is collapsed, so that the electron conductivity is reduced and the charge and discharge cycle life is shortened. Furthermore, when lithium manganate is used as the positive electrode active material, Mn is contained in the organic electrolyte.
Dissolves, causing a decrease in the charge / discharge cycle life characteristics of the battery and a decrease in the storage characteristics.

As a means for improving the charge / discharge cycle, a method of fixing Ag or an oxide of Ag on the surface of lithium manganate is studied in Japanese Patent Application No. 10-249503. However, there are problems that Ag is expensive and the effect of adding Ag alone is not sufficient.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to improve the cycle life characteristics and storage characteristics of an organic electrolyte secondary battery using lithium manganate.

[0007]

According to a first aspect of the present invention, there is provided a lithium manganate capable of electrochemically inserting and desorbing lithium by charge and discharge.
In, Sb, Sn, W, Mo, Ti, Au, Pt, P
At least one element selected from the group consisting of d, Rh, and Pb or an oxide of these elements is fixed on the surface of the lithium manganate particles. In the second invention, Ag or an oxide of Ag and the above In, Sb, Sn, W, Mo, Ti, Au, Pt, P
At least one element selected from the group consisting of d, Rh, and Pb, or an oxide of these elements is immobilized on the surface of the lithium manganate particles. A third invention is characterized in that the mole percentage of the element with respect to lithium manganate is 0.5 to 10%. According to a fourth aspect of the present invention, there is provided a lithium manganate capable of electrochemically inserting and desorbing lithium by charging and discharging, wherein In, Sb, Sn, W, Mo, Ti, Au, P
At least one element selected from the group consisting of t, Pd, Rh, and Pb or an oxide of those elements is fixed on the surface of the lithium manganate particles, and lithium manganate is used for the positive electrode. Features. In the fifth invention, Ag or an oxide of Ag and the In, Sb,
Sn, W, Mo, Ti, Au, Pt, Pd, Rh, Pb
At least one element selected from the group consisting of, or an oxide of those elements, is fixed to the surface of the lithium manganate particles, wherein lithium manganate is used for the positive electrode. It is characterized by. The sixth invention is characterized in that lithium manganate in which the mole percentage of the element relative to lithium manganate is 0.5 to 10% is used for the positive electrode.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Lithium manganate Lithium manganate used for the positive electrode active material was prepared as follows. A 1M aqueous solution of manganese sulfate is dissolved in a 0.5M aqueous solution of sulfuric acid and kept at 93 ± 2 ° C., graphite is used as a counter electrode (cathode), and titanium (Ti) is used as a working electrode (anode).
Using a plate, manganese dioxide was precipitated on the working electrode by subjecting the working electrode to electrolytic oxidation at a current density of 1 A / dm ² . The manganese dioxide was peeled off from the working electrode, washed thoroughly with water, dried and then crushed in an automatic mortar for 30 minutes.
An electrolytic manganese dioxide powder (EMD) was obtained. Then EM
D and lithium carbonate, a commercially available high-purity reagent, were weighed so that the stoichiometric ratio of lithium manganate in the metal element composition ratio was obtained, mixed until uniform, filled in an alumina plate, and placed in an air stream at 600 ° C. Preliminary firing was carried out at a temperature of 10 ° C. for 10 hours. After cooling this powder to room temperature, it was pulverized in an automatic mortar to disaggregate the secondary particles. This powder was filled into an alumina dish in the same manner as in the pre-baking, and the powder was placed in an air stream at 750 ° C. for 12 hours.
Main firing was carried out for a period of time. After cooling to room temperature, the mixture was pulverized in an automatic mortar and sieved to remove particles having a particle size of 70 μm or more. The obtained lithium manganate was LiP by ICP analysis.
It was confirmed to be Mn ₂ O _4, and it was confirmed that the composition had a substantially desired composition ratio.

[0009] 2. 1. Positive Electrode FIG. 1 is a sectional view of a cylindrical lithium 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 50 mm × 450 mm. Reference numeral 2 denotes a positive electrode active material layer, which is composed of a positive electrode active material lithium manganate having a specific metal immobilized on the particle surface, graphite as a conductive additive, and polyvinylidene fluoride (PVDF) as a binder. Positive electrode active material layer 2
Is described in detail below. Lithium manganate (average particle size about 20 μm), graphite (average particle size about 0.5 μm)
m), PVDF is sufficiently mixed at a weight ratio of 80:10:10, and an appropriate amount of NMP as a dispersion solvent is added thereto, and the mixture is sufficiently kneaded and dispersed to form a slurry. This slurry is applied to both surfaces of the positive electrode current collector 1 by roll-to-roll transfer, dried, and then pressed. The thickness of the positive electrode is 21
3 ± 3 μm.

[0010] 3. The negative electrode 3 is a negative electrode current collector and is a copper foil having a thickness of 10 μm. The plane size is 50 mm × 490 mm. The negative electrode active material for absorbing and releasing lithium ions is composed of amorphous carbon (trade name: CARBOTRON P, manufactured by Kureha Chemical Industry Co., Ltd.) and polyvinylidene fluoride (PVDF) as a binder. A detailed method for forming the negative electrode active material layer 4 will be described. Carbotron P and PVDF are mixed at a weight ratio of 90:10, and an appropriate amount of NMP serving as a dispersion solvent is added thereto, sufficiently kneaded and dispersed to form a slurry. The kneaded material is applied to the negative electrode current collector 3 by roll-to-roll transfer, dried, and then pressed. The thickness of the negative electrode is 132 ± 3 μm, and the density of the negative electrode active material layer is about 1.0 g / cm ³ .

4. Battery 5 is a separator, which is a 25 μm-thick microporous polyethylene film. It is wound so that the separator 5 is arranged between the positive electrode and the negative electrode, and inserted into the negative electrode can 6. Then, the tab terminal which has been welded to the negative electrode current collector in advance is welded to the negative electrode can 6. The positive electrode tab terminal 8 is welded to the positive electrode current collector 1 in advance, and then welded to the positive electrode cap 7. Next, 5 ml of the electrolytic solution is injected into the negative electrode can 6. The electrolyte solution includes propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and vinylene carbonate (V) in a volume ratio of 30: 50: 15: 5.
In the mixed solvent of C), LiPF ₆ is dissolved at 1 M / l. The positive electrode cap 7 is placed on the upper part of the negative electrode can, and the upper part of the negative electrode can is caulked via the insulating gasket 9 to seal the battery. Here, in the positive electrode cap 7,
A current interrupt mechanism (pressure switch) that operates in response to an increase in battery internal pressure and a valve mechanism that operates at a higher pressure than the current interrupt mechanism are incorporated. In this embodiment, the operating pressure is 9 k
gf / cm ² current interrupting mechanism and operating pressure 20 kgf / c
An m ² valve mechanism was used.

5. Charge / discharge cycle life test The prepared battery was subjected to a charge / discharge cycle test under the following conditions.
The capacity retention rate was calculated from the ratio of the discharge capacity after 100 cycles to the initial discharge capacity.

Charging conditions: constant voltage charging (4.2 V), limiting current 320 mA, 8 h, 50 ° C., discharging conditions: constant current discharging (1 A), final voltage 2.8 V, 5
At 0 ° C., a pause of 10 minutes was provided between charging and discharging.

6. Storage test After the prepared battery was charged and discharged under the following conditions to check the initial discharge capacity, the battery was stored again at 50 ° C for one month while being charged again, and the capacity retention ratio after storage was measured. Charging conditions: constant voltage charging (4.2 V), limited current 320 mA, 8 h, 2
5 ° C., discharge conditions: constant current discharge (1 A), final voltage 2.5
V, 25 ° C., and a pause time of 10 minutes between charging and discharging.

[0015]

EXAMPLE Lithium manganate having a metal and metal oxide immobilized on its surface can be obtained by the following means.
That is, a mixed fired product of electrolytic manganese dioxide and lithium carbonate is dispersed in a nitrate aqueous solution of a predetermined metal, and is evaporated and evaporated.
The dried product is dispersed in an aqueous solution of an alkali metal salt of a predetermined metal chloride or oxide, neutralized, separated, and dried, and then heat-treated at a predetermined temperature in an air stream to obtain a surface. Lithium manganate in which a metal or metal oxide is immobilized.

(Example 1) The above-mentioned lithium manganate was dispersed in an aqueous solution of indium nitrate (In (NO ₃ ) ₃ ) · 3H ₂ O, a special grade reagent on the market, and aqueous ammonia was added dropwise while vigorously stirring this solution. To precipitate indium hydroxide on the surface of the lithium manganate, followed by filtration, washing with water,
The powder dried at 120 ° C. for about 24 hours was placed in an alumina baking dish and heat-treated at about 600 ° C. in an air stream. The concentration and amount of the aqueous solution of indium nitrate were adjusted to be 5% by mol as In with respect to lithium manganate. Thus, lithium manganate having indium oxide immobilized on the surface was obtained. The cylindrical lithium secondary battery described above was manufactured using this powder.

Example 2 The above-described lithium manganate was dispersed in cold water, and an aqueous solution of a commercially available special-grade reagent, antimony trichloride, was injected with vigorous stirring to precipitate antimony oxychloride on the surface of the lithium manganate. The mixture is then decanted and washed several times with warm water. The powder is placed in an evaporating dish while being moistened, an aqueous solution of a commercially available special-grade reagent, sodium carbonate, is added until the mixture becomes strongly alkaline, and the mixture is heated with stirring on a water bath. The obtained powder is filtered, washed with water,
C. for about 24 hours to obtain lithium manganate having antimony trioxide immobilized on the surface. The concentration and amount of the aqueous solution of antimony trichloride are based on
b was adjusted to be 5% by mole percent. It was confirmed by ICP analysis that Sb was approximately 5% by mol% with respect to lithium manganate. The cylindrical lithium secondary battery described above was manufactured using this powder.

(Example 3) Tin chloride was added to an aqueous solution of sodium stannate (Na ₂ SnO ₃ .3H ₂ O), a commercially available special-grade reagent, by adding α
5% by mole relative to sodium stannate was added, and the lithium manganate was dispersed therein, and neutralized with an acid while stirring. The obtained powder is filtered, washed with water,
C. for about 24 hours to obtain lithium manganate having tin oxide immobilized on the surface. The concentration and amount of the aqueous solution of α-sodium stannate and tin chloride are based on Sn with respect to lithium manganate.
Was adjusted to be 5% in terms of mole percent. I
CP analysis confirmed that Sn was approximately 5% by mole of lithium manganate. The cylindrical lithium secondary battery described above was manufactured using this powder.

Example 4 The above-mentioned lithium manganate was dispersed in an aqueous solution of an alkali metal salt of tungstic acid, a commercially available special-grade reagent, and neutralized with an acid while stirring. The obtained powder was filtered, washed with water, and dried at 120 ° C. for about 24 hours to obtain lithium manganate having tungsten oxide immobilized on the surface. The concentration and amount of the aqueous solution of tungstate is 5% by mole as W with respect to lithium manganate.
%. It was confirmed by ICP analysis that W was approximately 5% by mol% with respect to lithium manganate. The cylindrical lithium secondary battery described above was manufactured using this powder.

Example 5 The above-mentioned lithium manganate was dispersed in an aqueous solution of an alkali metal salt of molybdic acid, a commercially available special-grade reagent, and neutralized with an acid while stirring. The obtained powder was filtered, washed with water, and dried at 120 ° C. for about 24 hours to obtain lithium manganate having molybdenum oxide immobilized on the surface. The concentration and amount of the aqueous solution of molybdate were adjusted to be 5% by mol as Mo with respect to lithium manganate. Mo was found to be lithium manganate by ICP analysis. It was confirmed that the molar percentage was 5%. The cylindrical lithium secondary battery described above was manufactured using this powder.

Example 6 Gold (Au) was deposited on the surface of the above-mentioned lithium manganate. Using an ion sputter (E-1020 type) manufactured by Hitachi, Ltd., a current value of 10 to 20 m
A, gold (Au) was deposited on the surface of the above-mentioned lithium manganate by operating at a pressure of 0.1 to 0.01 Torr or less for about 1 minute. Note that, in order to deposit Au as uniformly as possible on the surface of the lithium manganate, an operation of once taking out the lithium manganate powder, stirring, and then depositing again was repeated. The above-described cylindrical lithium secondary battery was manufactured using lithium manganate having 0.5% by mole of gold immobilized on the surface thus obtained as a positive electrode active material.

(Embodiment 7) There is a method of plating palladium (Pd) on the surface of the above-mentioned lithium manganate.
Electroplating is preferably performed using the plating tank shown in FIG. FIG. 2 is a sectional view of a cylindrical plating tank. Reference numeral 51 denotes a glass container having a cylindrical Pt with both bottom surfaces opened inside.
Is disposed as a counter electrode 52, and a glass filter or unglazed bottomed cylinder is further provided inside the separator 5.
3 and the inside of the container 51 is filled with the electrolytic solution 54. Lithium manganate 55 is packed inside separator 53, and a flat plate made of Pt is inserted as cathode 56 therein, and rotated at 10 to 30 rpm while energizing. The electrolyte is an aqueous solution of Pd (NH ₃ ) ₄ (NO ₂ ) ₂ of 10 to 25 g / l, the temperature is 40 to 60 ° C., and the current density is 0.5 to ^{2 A} / dm ^{2 in} terms of the specific surface area of lithium manganate. Turn on electricity. The amount of Pd to be plated can be controlled by the amount of energized electricity (energized time). When the plating operation is completed, the Pd-plated lithium manganate is filtered, washed with water, at 120 ° C. for 24 hours.
Dry to a degree. The cylindrical lithium secondary battery described above was manufactured using the thus obtained lithium manganate having 0.5% by mole of palladium immobilized on the surface as a positive electrode active material.

Example 8 The above-mentioned lithium manganate was dispersed in an aqueous solution of commercially available special-grade reagents, sodium α-stannate (Na ₂ SnO ₃ .3H ₂ O) and antimony trichloride, and neutralized with an acid while stirring. . The obtained powder is filtered, washed with water, 1
After drying at 20 ° C. for about 24 hours, lithium manganate having tin oxide immobilized on the surface was obtained. The ratio of α-sodium stannate and antimony chloride was Sn: Sb = 98: 2 in atomic ratio. α
The concentration and amount of the aqueous solution of sodium stannate and the aqueous solution of antimony trichloride were adjusted so that the total amount of Sn and Sb was 5% by mole based on lithium manganate.
ICP analysis confirmed that the total amount of Sn and Sb was approximately 5% by mol% with respect to lithium manganate. The cylindrical lithium secondary battery described above was manufactured using this powder.

Example 9 A commercially available special-grade reagent, silver nitrate (Ag
The aforementioned lithium manganate was dispersed in a mixed aqueous solution of NO ₃ ) and antimony trichloride, and neutralized with an acid while stirring. Ag and antimony have an atomic ratio of Ag: Sb = 10: 9.
0 was set. The resulting powder was filtered, washed with water,
After drying for about h, lithium manganate having Ag and antimony immobilized on the surface was obtained. The concentration and amount of the silver nitrate (AgNO ₃ ) aqueous solution and the antimony trichloride aqueous solution were adjusted so that the total amount of Ag and Sb with respect to lithium manganate was 5% in mole percent. Ag by ICP analysis
And Sb were confirmed to be almost 5% in mole percent relative to lithium manganate. The cylindrical lithium secondary battery described above was manufactured using this powder.

(Comparative Example 1) A cylindrical lithium secondary battery was manufactured using lithium manganate in which a metal element or an oxide of a metal element was not fixed on the surface described above as a positive electrode active material.

Table 1 shows the capacity retention rate after storage and the capacity retention rate during the 100-cycle charge / discharge test with respect to the initial discharge capacity using the batteries of Examples 1 to 9 and Comparative Example 1. As is clear from Table 1, in the battery of Comparative Example 1, the capacity during the charge / discharge cycle was significantly deteriorated.
In the battery No. 9, deterioration in capacity was suppressed. When lithium manganate having a metal element or its oxide immobilized on the surface is used for the positive electrode, dissolution of the Mn component in the organic electrolyte is suppressed regardless of the state of storage or charge / discharge. Conceivable. Example 8 shows an example in which a cylindrical lithium secondary battery was manufactured using lithium manganate in which Sn and Sb were immobilized on the surface of lithium manganate as a positive electrode active material. However, instead of Sb, In was used instead of Sb. A similar effect was observed. Also, from Example 9, Ag and S
When both of b were added, better properties were exhibited. And Ag and In, Sb, Sn, W, Mo, Ti, A
Good characteristics were also exhibited when lithium manganate to which at least one element selected from the group consisting of u, Pt, Pd, Rh, and Pb or an oxide of those elements was added was used.

[0027]

[Table 1]

(Examples 10 to 14) The amount of Sn was 0.2, 0.
It adjusted so that it might be set to 5, 1, 10, and 15%, and used the lithium manganate which surface immobilized Sn by the method of (Example 3) as a positive electrode active material. In addition, Sn to be immobilized
Was adjusted by the concentration and amount of the aqueous solution of silver nitrate.

Table 2 shows the capacity retention ratio after storage of the batteries of Examples 1 and 10 to 14 and the capacity retention ratio at the 100th cycle. When the amount of Sn is less than 0.5 mol%, the capacity retention ratio is greatly deteriorated. On the other hand, when the amount of Sn increases, deterioration of capacity maintenance is suppressed, but when the molar percentage exceeds 10% and becomes 15 mol%, the initial discharge capacity is significantly reduced. When the amount of Sn is large, the initial discharge capacity decreases because the active material surface is covered with Sn, so that insertion and desorption of lithium into and from the active material do not proceed smoothly, and the internal amount due to charge transfer and diffusion is reduced. This is probably because the resistance increased.

In this embodiment, the case where Sn is used as the element to be fixed on the surface has been described. However, In, Sb, W, Mo,
Similar effects were obtained by using at least one element selected from the group consisting of Ti, Au, Pt, Pd, Rh, and Pb or an oxide of these elements. When both of these elements and Ag were added, similar good characteristics were exhibited.

[0031]

[Table 2]

The method of immobilizing a metal or metal oxide on the surface of lithium manganate is not limited to the above embodiment, but may be other methods such as a method of forming a chemical precipitate, a plating method, and a CVD method. There are a sputtering method, a mechanofusion method, a thermal decomposition method, and the like, and the same effect as the present invention was shown.

[0033]

The active material for a positive electrode according to the present invention is lithium manganate capable of electrochemically inserting and desorbing lithium by charging and discharging, and has Sb, Sn, W, Au, P on its surface.
At least one element selected from the group consisting of t, In, Ti, Pd, Pb, Mo, and Rh, and Ag or an oxide thereof are fixed. The organic electrolyte lithium secondary battery using lithium manganate for the positive electrode has an extremely large effect in that capacity deterioration can be suppressed during high-temperature storage or charge / discharge cycles.

[Brief description of the drawings]

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

FIG. 2 is a sectional view of a cylindrical plating tank.

[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 negative electrode can, 7 is a positive electrode cap, 8 is a positive electrode tab terminal, and 9 is a gasket.

 ──────────────────────────────────────────────────続 き Continuing on the front page F term (reference) 4G048 AA02 AA04 AC06 AD03 5H003 AA03 AA04 BA01 BA02 BA03 BA07 BB02 BB04 BB05 BB14 BC01 BC05 BC06 BD03 5H014 AA02 BB01 BB03 BB06 BB08 BB11 CC01 EE05 HH01 A0505 A03AM03 AM05 AM06 AM07 BJ02 BJ14 CJ02 CJ08 CJ12 CJ13 CJ14 HJ01

Claims (6)

[Claims] 1. A lithium manganate capable of electrochemically inserting and desorbing lithium by charging and discharging, comprising In, Sb,
Sn, W, Mo, Ti, Au, Pt, Pd, Rh, Pb
Lithium manganate, wherein at least one element selected from the group consisting of or an oxide of these elements is fixed on the surface of the lithium manganate particles. 2. The method according to claim 1, wherein Ag or an oxide of Ag and said In, S
b, Sn, W, Mo, Ti, Au, Pt, Pd, Rh,
The lithium manganate according to claim 1, wherein at least one element selected from the group consisting of Pb, or an oxide of these elements, is fixed on the surface of the lithium manganate particles. . 3. The lithium manganate according to claim 1, wherein the mole percentage of the element to lithium manganate is 0.5 to 10%. 4. A lithium manganate capable of electrochemically inserting and desorbing lithium by charging and discharging, comprising In, Sb,
Sn, W, Mo, Ti, Au, Pt, Pd, Rh, Pb
Organic electrolysis characterized in that at least one element selected from the group consisting of, or an oxide of those elements, is fixed to the surface of the lithium manganate particles, and lithium manganate is used for the positive electrode. Liquid secondary battery. 5. The method according to claim 1, wherein Ag or an oxide of Ag and said In, S
b, Sn, W, Mo, Ti, Au, Pt, Pd, Rh,
Lithium manganate characterized in that at least one element selected from the group consisting of Pb, or an oxide of those elements, is fixed to the surface of the lithium manganate particles, and the lithium manganate is used for the positive electrode. The organic electrolyte secondary battery according to claim 4, wherein: 6. The organic electrolyte secondary battery according to claim 4, wherein the molar percentage of the element relative to lithium manganate is 0.5 to 10%.