JP2001319658A - Non-aqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-aqueous secondary battery, in which a load characteristic and a cycle characteristic are improved without reducing a battery capacity to have a high capacity, superior load characteristic, and superior cycle characteristic. SOLUTION: A positive active material with a mean particle size within a range from 5 to 20 μm is used and an expansive graphite is used as an electrically conductive material to configure a non-aqueous secondary battery. As the electrically conductive material, using the expansive graphite in combination with at least one of the kinds of the other electrically conductive materials is preferable. As the electrically conductive material other than the expansive graphite, the electrically conductive materials of graphite type such as a artificial graphite and a natural graphite, and the electrically conductive materials of carbon black type such as an acetylene black and Ketchen black are preferable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous secondary battery, and more particularly, to a non-aqueous secondary battery having a high capacity and excellent load characteristics and cycle characteristics.

[0002]

2. Description of the Related Art Non-aqueous secondary batteries, such as lithium-ion batteries using a metal oxide for the positive electrode and a carbon-based material for the negative electrode, are in high demand due to their high voltage and high energy density. Increasingly.

At present, the above-mentioned lithium ion batteries include:
As a negative electrode active material, a carbon-based material such as graphite, which can take lithium ions into a matrix and can be repeatedly inserted / desorbed, or a metal oxide capable of inserting Li, is used.
A combination with a positive electrode active material composed of a lithium-containing metal oxide such as iCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ has been put to practical use.

When the above-mentioned lithium-containing metal oxide is used as a positive electrode active material of a lithium-ion battery, the lithium-containing metal oxide itself has low conductivity. .

[0005] Carbon black-based materials such as acetylene black and Ketjen black are generally used as the conductive material. This carbon black-based conductive substance has excellent conductivity and excellent liquid absorption, but is generally an inactive material in the potential region of the positive electrode where charging and discharging are performed. The addition to the mixture lowers the positive electrode capacity. That is, when the conductive material is added to the positive electrode mixture in a certain amount or more to impart good conductivity to the positive electrode and maintain good charge / discharge cycle characteristics, the positive electrode active material in the positive electrode mixture is accordingly added. However, there is a problem that the capacity ratio of the positive electrode is reduced due to a decrease in the volume ratio of the positive electrode, and the capacity of the battery cannot be increased.

[0006] On the other hand, when expanded graphite is used as the conductive material, its unique shape keeps good contact with the positive electrode active material, so that it is better than when acetylene black or Ketjen black is used. Although a positive electrode with better conductivity can be obtained, the positive electrode mixture containing expanded graphite is less likely to be molded under pressure than the positive electrode mixture containing acetylene black or Ketjen black. As a result, even if the content of the conductive substance is small, a large capacity loss occurs.

[0007]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, improves load characteristics and cycle characteristics without lowering the capacity, and achieves a high capacity, load characteristics and An object is to provide a nonaqueous secondary battery having excellent cycle characteristics.

[0008]

The present inventors have conducted intensive studies to solve the above-mentioned problems. As a result, the positive electrode mixture containing expanded graphite as a conductive material is compressed according to the particle diameter of the positive electrode active material. It has been found that the easiness of molding is greatly different, the packing density of the positive electrode active material is different, and that the load characteristics and the cycle characteristics are easily affected by the particle size of the positive electrode active material. Was completed.

That is, the present invention uses a positive electrode active material having an average particle diameter in the range of 5 to 20 μm,
It is characterized by using expanded graphite as a conductive substance, thereby improving load characteristics and cycle characteristics without lowering the capacity of a non-aqueous secondary battery, and achieving high capacity, load characteristics and cycle characteristics. An excellent non-aqueous secondary battery is provided.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a positive electrode active material having an average particle diameter in the range of 5 to 20 μm is used. This is because the mixture is easily subjected to compression molding and the packing density of the positive electrode active material can be improved. By setting the average particle diameter of the positive electrode active material to 20 μm or less, load characteristics and cycle characteristics can be improved. Thus, the average particle diameter of the positive electrode active material is set to 5 to
The reason why the filling density of the positive electrode active material is improved by setting the thickness to 20 μm or the load characteristics or cycle characteristics are improved is not always clear at present, but the voids in the positive electrode mixture layer are reduced. Is considered to be related. The average particle diameter of the positive electrode active material is 5 as described above.
It is necessary that the average particle diameter of the positive electrode active material is 10 to 20 μm, preferably 15 to 20 μm.
20 μm is more preferred. In the present invention, the average particle diameter is a particle diameter when a value integrated from 0 μm becomes 50% in a particle size distribution diagram. For example, using a particle size analyzer, scattering of the particles by laser light is performed. It can be easily calculated by measuring the diameter.

The positive electrode active material is not particularly limited as long as it satisfies the condition that the average particle diameter is in the range of 5 to 20 μm. For example, LiCoO ₂ , LiNiO _2
2 , lithium-containing metal oxides such as LiMn ₂ O ₄ ,
Sulfur-based compounds such as organic sulfur can be used.

The expanded graphite used in the present invention includes:
Those having an average particle diameter of 1 to 25 μm are preferred. That is, by setting the average particle size of the expanded graphite to 1 μm or more, the binding state between the positive electrode mixture and the positive electrode current collector can be improved, and by setting the average particle size to 25 μm or less, The dispersed state of the expanded graphite in the positive electrode mixture can be improved.

The content of the expanded graphite in the positive electrode mixture is preferably 2 to 10% by weight. That is, by setting the content of the expanded graphite in the positive electrode mixture to 2% by weight or more, the conductivity of the positive electrode mixture is improved. A decrease in the content of the substance can be suppressed, and a decrease in the capacity can be suppressed.

In the positive electrode mixture, in addition to the expanded graphite,
By containing at least one conductive material other than expanded graphite, the conductivity can be further improved, and the load characteristics and cycle characteristics can be further improved. As the conductive substance other than the expanded graphite, for example, a graphite-based material such as artificial graphite or natural graphite, or a carbon black-based material such as acetylene black or Ketjen black can be used.

For the positive electrode, for example, expanded graphite and, if necessary, at least one conductive material other than expanded graphite are added to the positive electrode active material, and a binder such as polyvinylidene fluoride is appropriately added. Into a paste with a solvent (the binder may be dissolved in the solvent in advance and then mixed with the positive electrode active material, etc.), and the obtained positive electrode mixture-containing paste is mixed with a positive electrode comprising metal foil or the like. The positive electrode mixture layer is formed by applying to a conductor and drying to form a positive electrode mixture layer and, if necessary, press forming to increase the packing density of the positive electrode active material. However, the method for manufacturing the positive electrode is not limited to the above-described example, and another method may be used. Further, the packing density of the positive electrode mixture in the positive electrode is 2.90 g / cm ³ or more, particularly 3.25 g / cm ^3.
It is preferably at least m ³ . By doing so, it is possible to suppress a decrease in the adhesiveness between the positive electrode mixtures based on the bulkiness of the expanded graphite, secure an excellent electron conduction mechanism, and improve the load characteristics.

As the negative electrode active material, for example, natural graphite,
One or more of carbon-based materials such as pyrolytic carbons, cokes, glassy carbons, fired organic polymer compounds, mesocarbon microbeads, carbon fibers, and activated carbon are used. Further, alloys such as Si, Sn, and In, or compounds such as oxides and nitrides that can be charged and discharged at a low voltage close to Li can also be used as the negative electrode active material.

The negative electrode is prepared, for example, by adding a binder to the above-mentioned negative electrode active material, mixing the mixture, and forming a paste using a solvent (the binder may be mixed with the negative electrode active material after the solvent is dissolved in advance). The obtained negative electrode mixture-containing paste is applied to a negative electrode current collector, dried to form a negative electrode mixture layer, and optionally molded by pressing to increase the packing density of the negative electrode active material. You. However, the method for manufacturing the negative electrode is not limited to the above-described example, and another method may be used.

Examples of the binder used for producing the positive electrode and the negative electrode include polyvinylidene fluoride, polytetrafluoroethylene, ethylene propylene diene rubber, fluoro rubber, styrene butadiene rubber, cellulose resin, and polyacrylic acid. Can be used alone or as a mixture of two or more. Further, as the positive electrode current collector and the negative electrode current collector, for example, foils such as aluminum, copper, nickel, and stainless steel, expanded metal, punched metal, and a net can be used. A foil is preferred, and a copper foil is particularly preferred as the negative electrode current collector.

As the electrolyte, any of a liquid electrolyte, a gel electrolyte, and a solid electrolyte can be used. In the present invention, a liquid electrolyte called an electrolyte is usually used. The electrolytic solution is prepared by dissolving an electrolyte salt in a non-aqueous solvent containing an organic solvent as a main component. Examples of the solvent include chains such as dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and methyl propionate. Organic solvents having a linear COO-bond, chain phosphate triesters such as trimethyl phosphate,
1,2-dimethoxyethane, 1,3-dioxolan, tetrahydrofuran, 2-methyl-tetrahydrofuran,
Diethyl ether or the like can be used. In addition, an amine imide organic solvent and a sulfur organic solvent such as sulfolane can also be used. Further, in forming the gel electrolyte, a polymer such as polyethylene oxide or polymethyl methacrylate may be included.

Esters are often used as other solvent components. As the ester, an ester having a high dielectric constant (dielectric constant of 30 or more) is preferable, and specific examples thereof include ethylene carbonate, propylene carbonate, butylene carbonate, gamma-butyrolactone, and the like. Sulfur esters can also be used. Further, an ester having a cyclic structure is preferable, and a cyclic carbonate such as ethylene carbonate is particularly preferable.

When preparing the electrolytic solution, dissolve in the above solvent.
As the electrolyte salt to be used, for example, LiClO_Four, Li
PF₆, LiBF_Four, LiAsF₆, LiSbF₆, L
iCF_ThreeSO_Three, LiC_FourF₉SO_Three, LiCF_ThreeCO
_Two, Li_TwoC_TwoF_Four(SO_Three)_Two, LiN (Rf₁SO
_Two) (Rf_TwoSO_Two) [Where Rf₁, Rf_TwoIs full
A substituent containing an oloalkyl group], LiN (Rf_Three
OSO_Two) (Rf_FourOSO_Two) [Where Rf_Three, Rf
_FourIs a fluoroalkyl group], LiC_nF _{2n + 1}SO
_Three(N ≧ 2), LiC (Rf_FiveSO_Two)_Three, LiN (R
f₆OSO_Two) _Two[Where Rf_Five, Rf₆Is fluoro
Alkyl group], polymer type imide lithium salt
And the like are used alone or in combination of two or more. this
When they are incorporated into the coating on the positive electrode surface,
Conductivity can be imparted, especially LiPF₆Is its effect
It is preferable because the fruits are large. Of electrolyte salt in electrolyte
The concentration is not particularly limited.
l / l or more, particularly preferably 1.2 mol / l or more.
And 1.7 mol / l or less, especially 1.5 mol
/ L or less.

As the separator, for example, a microporous film made of polyethylene, polypropylene, or a copolymer of ethylene and propylene is used.

The battery is formed, for example, by subjecting an electrode laminate having a spiral structure such as a spiral electrode body produced by spirally winding a separator between the positive electrode and the negative electrode as described above to nickel plating. It is manufactured through a process of inserting into a given battery case made of iron or stainless steel and sealing. In addition, the battery is generally provided with an explosion-proof mechanism for discharging the gas generated inside the battery to the outside at the stage when the gas has risen to a certain pressure to prevent the battery from bursting under high pressure. However, the form of the battery is not limited to the above-described cylindrical one, and may be any of a button shape, a coin shape, and a flat shape.

Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to only those examples.

Example 1 First, 1.4 m of LiPF ₆ was added to a mixed solvent of ethylene carbonate and methyl ethyl carbonate at a volume ratio of 1: 3.
ol / l was added and mixed to prepare an organic solvent-based electrolyte solution.

In preparing the positive electrode, 4.5 parts by weight of expanded graphite having an average particle diameter of 15 μm was added to 91.5 parts by weight of LiCoO ₂ having an average particle diameter of 7 μm, and the mixture was mixed. A part of polyvinylidene fluoride was dispersed in a solution of polyvinylidene fluoride dissolved in N-methyl-2-pyrrolidone to prepare a paste containing the positive electrode mixture. This positive electrode mixture paste is coated with a thickness of 20
After coating on both sides of a positive electrode current collector made of a μm aluminum foil and drying to form a positive electrode mixture layer, it is pressed and molded by a roller press, cut into a predetermined size, and welded to the lead body. Then, a belt-shaped positive electrode was manufactured.

Separately, 92 parts by weight of the mesocarbon microbeads are dispersed in a polyvinylidene fluoride-containing solution in which 8 parts by weight of polyvinylidene fluoride is dissolved in N-methyl-2-pyrrolidone in advance, and a negative electrode mixture is prepared. A containing paste was prepared. The paste containing the negative electrode mixture is applied to both surfaces of a negative electrode current collector made of a strip-shaped copper foil having a thickness of 10 μm (provided that the prepared negative electrode is spirally wound around the positive electrode via a separator to form a spiral electrode body). The negative electrode mixture-containing paste was not applied to the portion on the outer surface of the outermost peripheral portion that did not face the positive electrode when dried), dried to form the negative electrode mixture layer, and then pressed by a roller press. After cutting to a predetermined size, the lead body was welded to produce a strip-shaped negative electrode.

Next, the above-mentioned strip-shaped positive electrode was coated with a thickness of 25 μm.
The separator is made of a microporous polyethylene film, and is overlapped with the above-mentioned band-shaped negative electrode, spirally wound into a spiral electrode body, and then inserted together with an insulating plate into a cylindrical battery case having an outer diameter of 18 mm and a bottom. After welding the lead of the negative electrode to the bottom of the battery case, grooving is performed, the above electrolyte is injected into the battery case, the opening in the battery case is sealed according to a conventional method, and the battery is precharged. Go to
A cylindrical non-aqueous secondary battery having the structure shown in FIG. 1 was produced.

Here, the battery shown in FIG. 1 will be described. 1 is the positive electrode and 2 is the negative electrode. However, FIG. 1 does not show the current collectors used for producing the positive electrode 1 and the negative electrode 2 in order to avoid complication.
The positive electrode 1 and the negative electrode 2 are spirally wound with a separator 3 interposed therebetween, and are housed in a battery case 5 together with the electrolytic solution 4 as an electrode laminate having a spirally wound structure.

The battery case 5 is made of stainless steel, and an insulating plate 6 made of polypropylene is disposed at the bottom of the battery case 5 before the electrode laminate is inserted. The sealing plate 7 is made of aluminum and is in the shape of a disk. A thin portion 7a is provided at the center of the sealing plate 7 and serves as a pressure inlet 7b around the thin portion 7a for applying the internal pressure of the battery to the explosion-proof valve 9. Holes are provided. The projection 9a of the explosion-proof valve 9 is welded to the upper surface of the thin portion 7a to form a welded portion 11. In addition, the thin portion 7a provided on the sealing plate 7 and the protruding portion 9a of the explosion-proof valve 9 and the like are shown only in a cut surface so that the drawing can be easily understood, and the outline behind the cut surface is Illustration is omitted. Also, the welded portion 11 of the thin portion 7a of the sealing plate 7 and the protruding portion 9a of the explosion-proof valve 9 is shown in an exaggerated state in order to facilitate understanding on the drawing.

The terminal plate 8 is made of rolled steel, has a nickel-plated surface, and has a cap-like shape with a peripheral edge formed in a flange shape. The terminal plate 8 is provided with a gas outlet 8a. . The explosion-proof valve 9 is made of aluminum and has a disk shape.
In the center thereof, a protruding portion 9a having a tip portion is provided on the power generation element side (the lower side in FIG. 1), and a thin portion 9b is provided, and the lower surface of the protruding portion 9a is closed as described above. It is welded to the upper surface of the thin portion 7a of the plate 7 to form a welded portion 11. The insulating packing 10 is made of polypropylene and has an annular shape. The insulating packing 10 is disposed above the peripheral edge of the sealing plate 7, and the explosion-proof valve 9 is disposed thereon. The gap between the two is sealed so that the electrolyte does not leak from between the two. The annular gasket 12 is made of polypropylene, and the lead body 13 is made of aluminum. The sealing plate 7 and the positive electrode 1 are connected to each other. An insulator 14 is disposed on the electrode laminate, and the negative electrode 2 and the bottom of the battery case 5 are connected. Are connected by a lead body 15 made of nickel.

In this battery, the thin portion 7 of the sealing plate 7
a and the projecting portion 9a of the explosion-proof valve 9 come into contact at the welded portion 11,
Since the peripheral portion of the explosion-proof valve 9 and the peripheral portion of the terminal plate 8 are in contact with each other, and the positive electrode 1 and the sealing plate 7 are connected by the lead 13 on the positive electrode side, in a normal state, the positive electrode 1 and the terminal plate 8 Means a lead body 13, a sealing plate 7, an explosion-proof valve 9, and their welded parts 1
1 provides an electrical connection and functions normally as an electrical circuit.

When an abnormal situation occurs in the battery, such as when the battery is exposed to a high temperature, and gas is generated inside the battery and the internal pressure of the battery rises, the central pressure of the explosion-proof valve 9 is increased due to the rise in the internal pressure. It deforms in the direction of the internal pressure (upward direction in FIG. 1), and accordingly, the thin portion 7a integrated at the welded portion 11 is subjected to shearing force to break the thin portion 7a.
Alternatively, after the welding portion 11 between the projecting portion 9a of the explosion-proof valve 9 and the thin portion 7a of the sealing plate 7 is peeled off, the thin portion 9b provided on the explosion-proof valve 9 is torn, and gas is discharged from the terminal plate 8. The battery is designed to be discharged from the outlet 8a to the outside of the battery to prevent the battery from bursting.

[0034] LiCoO ₂ 91.5 parts by weight Example 2 The average particle diameter of 7 [mu] m, an average expanded graphite having a particle diameter of 15 [mu] m 4 parts by weight of carbon black 0.5 parts by weight of 4 parts by weight of further polyvinylidene fluoride A cylindrical non-aqueous secondary battery was manufactured in the same manner as in Example 1 except for adding.

Example 3 21.5 parts by weight of expanded graphite having an average particle diameter of 15 μm and 2 parts by weight of artificial graphite were added to 91.5 parts by weight of LiCoO _{2 having an} average particle diameter of 7 μm.
A cylindrical nonaqueous secondary battery was produced in the same manner as in Example 1, except that 0.5 parts by weight of carbon black, 0.5 parts by weight of carbon black, and 4 parts by weight of polyvinylidene fluoride were further added.

Example 4 A cylindrical non-aqueous secondary battery was manufactured in the same manner as in Example 1 except that LiCoO ₂ having an average particle diameter of 15 μm was used.

Comparative Example 1 The procedure of Example 1 was repeated, except that 4.5 parts by weight of artificial graphite and 4 parts by weight of polyvinylidene fluoride were added to 91.5 parts by weight of LiCoO _{2 having an} average particle diameter of 7 μm. Thus, a cylindrical non-aqueous secondary battery was manufactured.

Comparative Example 2 A cylindrical non-aqueous secondary battery was manufactured in the same manner as in Example 1, except that LiCoO ₂ having an average particle diameter of 25 μm was used.

Comparative Example 3 An attempt was made to produce a cylindrical nonaqueous secondary battery in the same manner as in Example 1 except that LiCoO ₂ having an average particle diameter of 3 μm was used. Was significantly reduced and the positive electrode became too thick, so that the spiral electrode body using the same could not be inserted into the battery case.

Here, the above Examples 1 to 4 and Comparative Example 1
3 shows the average particle diameter of LiCoO ₂ (positive electrode active material) and the content of the conductive substance in the positive electrode mixture of the nonaqueous secondary batteries of Nos. 1 to 3. The content of LiCoO ₂ of the positive electrode active material in the positive electrode mixture was 91.5% by weight in Examples 1-4 and Comparative Examples 1-3.
And the content of polyvinylidene fluoride as a binder in the positive electrode mixture was 4 in Examples 1-4 and Comparative Examples 1-3.
0% by weight. Table 1 also shows the packing densities of the positive electrode mixtures of Examples 1 to 4 and Comparative Examples 1 to 3.

[0041]

[Table 1]

Next, the cylindrical non-aqueous secondary batteries of Examples 1 to 4 and Comparative Examples 1 and 2 were charged and discharged under the following conditions. That is, the current is 1600 mAh (1 C) and the voltage is 3.
The battery was charged with a constant current from 0 V to 4.2 V, and after reaching 4.2 V, was held at a constant voltage of 4.2 V for 2 hours. The discharge was also performed at 1 C to 3.0 V. After repeating this charge / discharge twice, the discharge capacity was measured when the current was changed to 0.2 C, 1 C, and 2 C and discharged to 3.0 V. Table 2 shows the discharge capacity of 0.2 C (discharge capacity at a current of 0.2 C) of each battery and the capacity ratio of 2 C / 0.2 C as a percentage [(2 C
(Discharge capacity at 0.2 C / discharge capacity at 0.2 C) × 100]. Further, a current of 1600 mAh (1 C)
And charging and discharging of 300 cycles were repeatedly performed under the conditions of a voltage of 3.0 to 4.2 V. At this time, the percentage of the value obtained by dividing the discharge capacity at the time of 300 cycles by the discharge capacity obtained at the second cycle [(discharge capacity at the time of 300 cycles / discharge capacity at the second cycle) × 100] is 300 cycles Table 2 shows the capacity retention ratio at the time.

[0043]

[Table 2]

As is clear from the results shown in Table 2, the batteries of Examples 1 to 4 had a discharge capacity of 0.2 C in Comparative Examples 1 to 2.
The capacity was not reduced, and the capacity retention rate after 2 cycles of 2C / 0.2C indicating load characteristics and 300 cycles indicating cycle characteristics was high. From these results, it is understood that the batteries of Examples 1 to 4 of the present invention have improved load characteristics and cycle characteristics without causing a decrease in capacity.

In addition, comparing the batteries of Examples 1 to 3 using LiCoO ₂ (positive electrode active material) having the same average particle size, the batteries of Example 1 using only expanded graphite as the conductive material showed a higher value. The batteries of Examples 2 and 3, in which expanded graphite and other conductive materials were used in combination as the conductive materials, had better load characteristics and cycle characteristics.

[0046]

As described above, according to the present invention, load characteristics and cycle characteristics are improved without causing a decrease in capacity, and a non-aqueous secondary battery having high capacity and excellent load characteristics and cycle characteristics is provided. Could be provided.
In addition, by using expanded graphite as the conductive material and at least one other conductive material composed of a graphite-based material, a carbon black-based material, and the like, load characteristics and cycle characteristics can be further improved. Was.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view schematically showing one example of a non-aqueous secondary battery of the present invention.

[Description of Signs] 1 Positive electrode 2 Negative electrode 3 Separator

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Toshihiro Koyama 1-88 Ushitora 1-chome, Ibaraki-shi, Osaka Inside Hitachi Maxell Co., Ltd. (72) Futsuji Kita 1-1-88 Ushitora 1-chome, Ibaraki-shi, Osaka F-term in Hitachi Maxell, Ltd. (reference) 5H029 AJ03 AJ05 AK03 AL08 AM03 AM04 AM05 AM07 BJ02 DJ08 DJ16 EJ04 HJ05 5H050 AA07 AA08 BA17 CA08 CB09 DA02 DA10 EA09 EA24 FA17 HA05

Claims (2)

[Claims] An average particle diameter of the positive electrode active material is 5 to 20 μm.
A non-aqueous secondary battery characterized by using expanded graphite as a conductive substance. 2. The non-aqueous secondary battery according to claim 1, wherein the non-aqueous secondary battery contains at least one kind of conductive material in addition to the expanded graphite.