JP2000113877A - Lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery having the high capacity, excellent in charging and discharging cycle characteristics, and having the small quantity metal used by making a negative electrode of a mixed system of a conductive auxiliary material of carbon grains having metal for making alloy with lithium and graphite capable of being intercalated and de-intercalated, and making the grain diameter of carbon grains having metallic particles smaller than the grain diameter of graphite. SOLUTION: A negative electrode is preferably a mixed system of a conductive auxiliary material of carbon grains having metal for forming alloy with lithium and amorphous carbon, and metal in the conductive auxiliary material is selected from Al, Sb, B, Ba, Bi, Cd, Ca, Ga, In, Ir, Pd, Pb, Hg, Si, Ag, Sr, Te, Ti and Sn. It is desirable that the specific surface area of the carbon grain is in the range of 1 to 1000 m2/g and that the grain diameter of metallic particles is 500 nm or less. Therefore, the service capacity is increased, electric conductivity is improved, the output density is increased, cycle characteristics are improved, and heat radiation property is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery, and more particularly, to a negative electrode for a lithium secondary battery having a large discharge capacity and a high power density and excellent cycle characteristics. In particular, a mixture of graphite particles capable of intercalating and de-intercalating Li ions using carbon particles carrying a metal that forms an alloy at an atomic ratio of 7 or less with respect to 1 lithium atom, and amorphous carbon. The present invention relates to an improvement in a battery using the current collector as a negative electrode.

[0002]

2. Description of the Related Art Conventionally, (Li) metal and alloys such as Li--Al and Li--Pb have been used as a negative electrode of a lithium secondary battery. Have shortcomings, short cycle life and low energy density. Recently, research on using a carbon material for a negative electrode has been actively conducted to solve these problems. This type of negative electrode is disclosed, for example, in Japanese Patent Laid-Open No. 5-29907
No. 3, JP-A-2-121258.

The structure disclosed in Japanese Patent Application Laid-Open No. H5-299073 is a method in which the surface of highly crystalline carbon particles forming a core is coated with a film containing a metal element of Group VIII, and carbon is further coated thereon. The composite is used as an electrode material, whereby the carbon material having a surface turbulent layer structure assists the intercalation of lithium, and the charge / discharge capacity and the charge / discharge rate are remarkably improved due to the large surface area of the electrode.

On the other hand, in Japanese Patent Application Laid-Open No. 2-121258, H / C <0.15, interplanar spacing> 0.337 n in hexagonal system
By using a mixture of a carbon material having a crystallite size Lc <15 nm in the m and C axis directions and a metal alloyable with Li, the charge / discharge cycle life is long and the charge / discharge characteristics at a large current are good. And

However, in each case, the difficulty in synthesizing the negative electrode carbon material and the theoretical capacity of carbon have not been drawn out.
The power density was not yet sufficient. Further, there is a problem that metal-supported carbon is expensive depending on the price of the metal.

[0006]

As described above, when a carbon material and a composite material are used as a negative electrode, there are problems in that the theoretical capacity of carbon cannot be obtained, that the electrode is difficult to manufacture, and that the cost is low.

An object of the present invention is to use a carbon particle carrying fine particles of a metal which can be alloyed with lithium for a negative electrode as a conductive additive, thereby achieving high capacity, excellent charge / discharge cycle characteristics, and a small amount of metal used. An object of the present invention is to provide a lithium secondary battery.

[0008]

The present inventors have conducted various studies to solve the above-mentioned problems, and as a result, have completed the present invention based on the following findings.

FIG. 5 shows the measurement results of the cycle characteristics B1 'and A1' of the conventional negative electrode and the improved negative electrode of the present invention. The carbon used was natural graphite that had been subjected to a high-purification treatment, and had a particle size of about 11 μm. A solution in which polyvinylidene fluoride (hereinafter abbreviated as PVDF) is dissolved in N-methylpyrrolidone (hereinafter abbreviated as NMP) is used as a binder so that the carbon and PVDF have a weight ratio of 90:10. The paste thus obtained was applied to a 20 μm-thick copper foil as a current collector.

An improved negative electrode was prepared according to the following procedure. 9.0 g of highly purified natural graphite (particle size 11 μm) is suspended in 450 ml of water containing 25 ml of ethyl alcohol. This was heated to about 60 ° C., and with strong stirring.
Dissolve 73 g of silver nitrate (AgNO ₃ ). 0.5% by weight of sodium tetrahydroborate (NaB
H4) Drop the aqueous solution with a micro tube pump,
Complete the reduction reaction over time. After that, filtration
It was washed with water and vacuum dried at 300 ° C. for 6 hours.

According to the chemical analysis, the amount of the obtained powder A was 9.9% by weight with respect to 10.0% by weight of the charged composition. In addition, A
When the state of g was examined, only diffraction lines of silver in a metallic state were detected. Next, when the dispersion state of Ag was observed by an energy dispersive electron probe microanalysis, the Ag particles were distributed on the front surface of the graphite particles and were slightly concentrated on the end surfaces of the graphite particles. Further, when the size of the Ag particles was observed with a transmission electron microscope, several 100 nm
The following particles were almost uniformly dispersed. This carbon material was applied to a Cu foil in the same manner as described above.

After air-drying, both were vacuum-dried at 80 ° C. for 2 hours, molded at a pressure of 0.5 ton / cm ₂ , and further vacuum-dried at 120 ° C. for 3 hours to obtain negative electrodes.
Combining one of these negative electrodes with a lithium metal counter electrode with a polyethylene microporous membrane serving as a separator in between,
A test cell using 1 M LiPF ₆ / ethylene carbonate-dimethyl carbonate (hereinafter abbreviated as EC-DMC) as an electrolyte and lithium metal as a reference electrode was assembled. For the conventional negative electrode and the improved negative electrode,
Using this test cell, a cycle test was performed at a charge / discharge rate of 120 mA per gram of carbon and a charge / discharge potential width of 0.01 to 1.0 V.

As is clear from FIG. 5, when the conventional negative electrode is used, the discharge capacity decreases every cycle, and after about 500 cycles, the discharge capacity decreases to about 6 times the initial capacity.
It dropped to 0%. On the other hand, when the improved negative electrode 2 is used,
The initial discharge capacity is about 30 mAh / cm ₃ larger than that of the carbon-only negative electrode due to the addition of the alloying capacity of Ag and Li, and the life reduction rate is 4.5 even after 500 cycles.
(%), The effect of the improved negative electrode was very small. This improvement in cycle characteristics is considered to be because the metal-carrying carbon negative electrode was able to suppress a decrease in the current collection effect between carbon particles due to electrode swelling due to volume changes due to repeated charge and discharge.

From the above results, increasing the current collecting performance of the negative electrode mixture layer is an important factor for improving the discharge capacity and the cycle characteristics. By supporting fine metal particles on carbon, the It has been found that an alloying capacity can be used, and a function of improving electrical conductivity and thermal conductivity by interposing a metal between carbon particles can be expected.

The gist of the present invention will be described. That is, the first invention is a lithium secondary battery including a pair of positive and negative electrodes, a separator interposed between the positive and negative electrodes, and an electrolytic solution for immersing the positive and negative electrodes and the separator.
The negative electrode is a lithium secondary battery, wherein carbon particles supporting a metal that forms an alloy at an atomic ratio of 1 or less to 1 lithium atom are conductive assistants.

According to a second aspect of the present invention, a pair of a positive electrode and a negative electrode,
In a lithium secondary battery including a separator interposed between the positive and negative electrodes and an electrolyte for immersing the positive and negative electrodes and the separator, the negative electrode carries a metal that forms an alloy at an atomic ratio of 7 or less with respect to 1 lithium atom. A lithium secondary battery characterized in that it is a mixed system of a carbon particle conductive aid and graphite capable of intercalating and deintercalating Li ions.

According to a third aspect of the present invention, the negative electrode is a mixed system of a carbon particle conductive additive supporting a metal forming an alloy at an atomic ratio of 7 or less to 1 lithium atom and amorphous carbon. Lithium secondary battery.

According to a fourth aspect of the present invention, the metal supported on the conductive additive is Al, Sb, B, Ba, Bi, Cd, Ca, Ga, I
n, Ir, Pd, Pb, Hg, Si, Ag, Sr, T
A lithium secondary battery comprising at least one of e, Tl and Sn.

According to a fifth aspect of the present invention, the carbon particles have a specific surface area of 1 to 1000 m ₂ / g and the supported metal particles have a particle size of 5 to 5 m ₂ / g.
A lithium secondary battery having a thickness of not more than 00 nm.

According to a sixth aspect of the present invention, there is provided a negative electrode comprising a carbon particle conductive auxiliary material supporting a metal forming an alloy at an atomic ratio of 7 or less to 1 lithium atom and graphite capable of intercalating and deintercalating Li ions. The current collector is held in a mixed system with the particles, and the graphite particles have a plane spacing (d002) of 0.3354 to 0.3369 nm by an X-ray diffraction method.
A lithium secondary battery having a crystal size (Lc) in the C-axis direction of 30 nm or more and a specific surface area of 0.1 to 30 m ₂ / g.

According to a seventh aspect of the present invention, there is provided a negative electrode comprising a current collector comprising a mixture of a carbon particle conductive auxiliary material supporting a metal forming an alloy at an atomic ratio of 7 or less to 1 lithium atom and amorphous carbon particles. Wherein the amorphous carbon particles have a plane distance (d002) of 0.337 nm or more determined by an X-ray diffraction method.

According to an eighth aspect of the present invention, there is provided a unit cell comprising a combination of a negative electrode, a positive electrode and an electrolyte, wherein the positive electrode material is LiXO ₂ or LXO _2.
A lithium secondary battery comprising iX ₂ O ₄ (X is one or a plurality of transition metals such as Co, Ni, and Mn), and the composition ratio of Li is excessive relative to the stoichiometric composition.

According to a ninth aspect, in the lithium secondary battery, the electrolyte layer is a copolymer electrolyte such as polyvinylidene fluoride and hexafluoropropylene.

According to a tenth aspect of the present invention, there is provided a lithium secondary battery in which a separator is interposed between a positive electrode and a negative electrode, and the positive and negative electrodes and the separator are immersed in an electrolyte solution. It is composed of graphite capable of intercalating and deintercalating ions and carbon particles having metal particles forming an alloy with Li, wherein the amount of metal particles in this mixed layer is at least 1% by weight (%). Lithium secondary battery.

11. The lithium secondary battery according to claim 10, wherein the amount of metal particles forming an alloy with Li in the mixed layer is 1 to 5% by weight (%).

A twelfth aspect of the present invention is the lithium secondary battery according to claim 10, wherein said carbon particles carrying metal particles have a particle size smaller than that of graphite.

The carbon supporting the metal as the conductive additive according to the present invention includes amorphous carbon having a high specific surface area, and graphite capable of intercalating and deintercalating Li ions includes highly crystalline carbon particles, For example, it is obtained by heat-treating a graphitizable material obtained from natural graphite, petroleum coke or coal pitch coke at a high temperature of 2500 ° C. or higher. The average particle size of the amorphous carbon and graphite is preferably 50 μm or less, and more preferably 0.1 to 20 μm. The shape may be spherical, massive, scaly, fibrous, or a crushed product thereof.

Next, as the supported metal, Al, Sb, B,
Ba, Bi, Cd, Ca, Ga, In, Ir, Pd, P
At least one of b, Hg, Si, Ag, Sr, Te, Tl and Sn is selected, but an element satisfying the following conditions is preferable.

(1) an alloy composition having a high lithium content,
(2) Relatively small atomic weight and relatively high density (3) Easy reduction, (4) Low oxidation-reduction potential of lithium alloy (5) Less disposal problem, (6) Relatively inexpensive .

The metal can be supported by vapor deposition, sputtering, wet reduction, electrochemical reduction, plating,
And a method such as a gas-phase reducing gas treatment method, but an optimal supporting method may be applied according to the type of metal used. The amount of metal carried is 10 to 50 wt (%), preferably 10 to 50 wt (%).
３０30 wt (%) is optimal. In addition, the particle size of the supported metal is as small as possible when considering the precipitation and dissolution rate of the lithium alloy during charge and discharge, and the fine particles are longer in consideration of the collapse of the metal particles due to the change in volume during alloying. It is expected to be advantageous for extending the life, and a condition satisfying these conditions is desirably 500 nm or less.

A negative electrode is prepared using the metal-supported carbon particles obtained above and graphite capable of intercalating and deintercalating Li ions. In this case, a binder is used. The binder is not particularly limited as long as it does not react with an electrolytic solution such as EPDM (ethylene propylene terpolymer), PVDF, and polytetrafluoroethylene. The amount of the binder is 1 to 30 w per carbon.
t (%), preferably 5 to 15 wt (%) is suitable. As the negative electrode shape using the aforementioned mixture, a sheet shape,
It is possible to adapt to the shape of the battery by filling it into a film or a foamed metal on a film or a metal foil. The thickness of the mixture layer is preferably in the range of 10 to 200 μm.

The negative electrode thus obtained can be combined with a commonly used positive electrode, separator and electrolyte to form an optimal lithium secondary battery. As the active material used for the positive electrode, a general formula LiXO ₂ or LiXO ₂
A composite oxide represented by X ₂ O ₄ (X is one or more of transition metals such as Co, Ni and Mn), for example, LiCoO
₂ , LiNiO ₂ , LiMnO ₂ , Li (Ni1-xCo
x) O _2, with respect to stoichiometric composition of the composite oxide containing lithium, such as LiMn ₂ O ₄ and LiMn ₂ O ₄ compounds may Li is used an excess of things, carbon black or carbon of which the conductive agent A mixture of the binder and the binder is applied to a current collector such as an Al foil to form a positive electrode.

As the separator, a porous film of polypropylene, polyethylene or polyolefin is used. As the electrolyte, propylene carbonate (P
C), ethylene carbonate (EC), 1,2- {methoxyethane (DME),} methyl carbonate (DM
Two or more kinds of mixed solvents such as C), diethyl carbonate (DEC), and methyl ethyl carbonate (MEC) are used. LiPF ₆ , LiBF ₄ ,
LiClO _{4 and the} like, and those dissolved in the above solvents are used. Further, a polymer electrolyte having the functions of a separator, an electrolytic solution and an electrolyte may be used.

In the lithium secondary battery having the above-described structure, the carbon negative electrode is made of a carbon particle conductive auxiliary material carrying a metal forming an alloy at an atomic ratio of 7 or less to 1 lithium atom and Li
By improving the ion into a mixed system of graphite and amorphous carbon capable of intercalating and deintercalating, (1) increase in discharge capacity, (2) electric conductivity, (3) power density, (4) Cycle characteristics, (5) improvement of heat dissipation in the assembled battery, (6) high-speed charge and discharge, and (7) reduction of the amount of supported metal became possible.

[0035]

(Example 1) 8.0 g of acetylene black (specific surface area: 70 m ² / g) was added to 20 vol.
(%) Of ethyl alcohol in 1800 ml of water. This was heated to about 50 ° C. and stirred vigorously.
Dissolve 15 g of silver nitrate (AgNO ₃ ). To this, 2.0% by weight of sodium tetrahydroborate (N
aBH ₄ ) An aqueous solution is dropped with a micro tube pump,
Complete the reduction reaction over 4 hours.

Thereafter, the mixture was filtered, washed with water, and vacuum dried at 150 ° C. for 6 hours. According to the chemical analysis, the amount of the powder A obtained was 1% with respect to 20.0 (%) weight of the charged composition.
The loading amount was 9.8% by weight (%), which was a good value. Further, when the presence state of Ag was examined by X-ray diffraction, only the diffraction line of silver in a metallic state was detected.

Next, when the dispersion state of Ag was observed by an energy dispersive electron probe microanalysis, the Ag particles were distributed on the front surface of acetylene black. Further, when the size of the Ag particles was observed with a transmission electron microscope, particles having a size of 500 nm or less were almost uniformly dispersed.

Example 2 8.0 g of carbon black (specific surface area: 600 m ² / g) is suspended in 1800 ml of water containing 20 vol (%) of ethyl alcohol.
This is heated to about 50 ° C., and 3.15 g of silver nitrate (AgNO ₃ ) is dissolved with vigorous stirring. 2.0% (%) sodium tetrahydroborate (NaBH ₄ )
The aqueous solution is dropped by a microtube pump, and the reduction reaction is completed over 4 hours.

Thereafter, the mixture was filtered, washed with water, and vacuum dried at 150 ° C. for 6 hours. According to the chemical analysis, the amount of the obtained powder B supported was 1% with respect to 20.0 (%) weight of the charged composition.
The loading amount was 9.8% by weight (%), which was a good value. Further, when the presence state of Ag was examined by X-ray diffraction, only the diffraction line of silver in a metallic state was detected. Next, when the dispersion state of Ag was observed by an energy dispersive electron probe microanalysis, the Ag particles were distributed in front of the graphite particles. Further, when the size of the Ag particles was observed with a transmission electron microscope, particles having a size of 500 nm or less were almost uniformly dispersed.

(Example 3) The powder A obtained in the first embodiment has a plane distance (d002) of 0.3 according to the X-ray diffraction method.
At 36 nm, the crystal size (Lc) in the C-axis direction is 100
The graphite having a specific surface area of 3.2 m ² / g was mixed at a weight ratio of (1: 9).
Using a methylpyrrolidone solution, applying a paste in which the mixed powder and PVDF were in a weight ratio of 90:10 to a 20-μm-thick copper foil as a current collector, air-dried, and then dried at 80 ° C. for 3 hours;
After vacuum drying for 0.5 hour and molding at a pressure of 0.5 ton / cm ² , vacuum drying was further performed at 120 ° C. for 2 hours to obtain a negative electrode.
These negative electrodes were combined with a lithium metal counter electrode with a polyethylene film interposed therebetween, and 1 MliPF ₆ / EC-
A test cell using lithium metal for the DMC and the reference electrode was assembled. The charge / discharge current density is 0.3 to 4.0 mA / cm
^2. The upper and lower limit potentials of charge and discharge are 1.0V and 0.0V, respectively.
1V.

The results are shown in FIG. 6 in comparison with the graphite negative electrode and the graphite negative electrode according to the present invention. In FIG. 6, the horizontal axis is the discharge current density, and the vertical axis is the discharge capacity retention ratio (%).
It is represented by As is clear from the figure, the current density is 1 m.
No difference is observed between the negative electrode of the present invention and the prior art negative electrode up to A / cm ^2, but the capacity of the discharge characteristic B1 of the prior art using the graphite only negative electrode is remarkably reduced from around 1 mA / cm ^2. On the other hand, it can be seen that there is little decrease in the discharge capacity retention ratio of the discharge characteristic A1 using the negative electrode composed of the carbon material carrying Ag of the present invention and graphite. Ag in the negative electrode of the present invention
The amount is 2 wt (%) based on the mass of the active part. Incidentally, powder B obtained in the second embodiment was subjected to the same test as powder A, and almost the same results were obtained.

(Example 4) Obtained in the first embodiment.
Powder A and a plane distance (d002) by X-ray diffraction method of 0.3
At 36 nm, the crystal size (Lc) in the C-axis direction is 100
nm and specific surface area is 3.2m^Two/ G of graphite in weight ratio
Mix at (5:95) and (15:85) and bind to this
Using an N-methylpyrrolidone solution of PVDF as an agent,
The mixed powder and PVDF should be in a weight ratio of 90:10.
The paste is applied to a 20 μm thick copper foil as a current collector.
Cloth, air dried, vacuum dried at 80 ° C for 3 hours, 0.5 ton
/ Cm ^TwoAfter molding under pressure of
It was air-dried to obtain a negative electrode.

When a test similar to that of Example 3 was performed using these negative electrodes, values almost the same as those in FIG. 6 were shown. By the way, the amount of Ag used is 1wt in the case of (5:95)
(%) And (15:85) correspond to 3 wt (%).

(Example 5) The powder A obtained in the above-mentioned mode 1 had a plane distance (d002) of 0.382 as determined by X-ray diffraction.
of amorphous carbon having a specific surface area of 4.5 m ² / g in a weight ratio of (1: 9),
Using N-methylpyrrolidone solution of DF, mixed powder and P
A paste in which VDF is adjusted to a weight ratio of 90:10 is applied to a 20 μm-thick copper foil as a current collector, air-dried, and then dried.
After vacuum drying at 0 ° C. for 3 hours and molding at a pressure of 2.0 ton / cm ² , vacuum drying was further performed at 120 ° C. for 2 hours to obtain a negative electrode.

These negative electrodes were combined with a lithium metal counter electrode with a polyethylene film interposed therebetween, and 1 M LiP
F ₆ / PC-DMC, was assembled test cell using lithium metal reference electrode. The charge / discharge current density is 0.3 to 4.
0 mA / cm ² , the upper and lower limit electric potentials of charge and discharge were 1.
5V and 0.005V. Charging was performed by the CCCV method for 4 hours. For comparison, a similar test was performed for a negative electrode containing only amorphous carbon. As a result, as in Example 3, 2
While the capacity of the negative electrode made of only amorphous carbon is remarkably reduced from around mA / cm ² , the A
It was confirmed that the negative electrode in which the g-supported carbon material and the amorphous carbon were mixed had a small decrease in the discharge capacity retention ratio.

Example 6 8.0 g of acetylene black (specific surface area: 70 m ² / g) is suspended in 1800 ml of water containing 20 vol (%) of ethyl alcohol.
This was heated to about 50 ° C., and 3.8 g Sn
The _{Cl22H 2 O 2mlCH 3 COOH + 200mlC} 2
Adding a solution dissolved in H ₅ OH. 2.0% (%) sodium tetrahydroborate (NaBH)
4) The aqueous solution is dropped with a microtube pump, and the reduction reaction is completed over 4 hours.

Thereafter, the mixture was filtered, washed with water, and vacuum dried at 150 ° C. for 6 hours. The obtained powder C was subjected to a reduction treatment at 400 ° C. for 5 hours in a stream of 1% H ₂ / He. The powder C was subjected to chemical analysis and found to be 19.7% by weight (%) with respect to 20.0% by weight of the charged composition.
When the existence state of Sn was examined by X-ray diffraction, a trace amount of diffraction lines based on Sn and SnO ₂ in a metallic state were detected. Next, when the dispersion state of Sn was observed by an energy dispersive electron probe microanalysis,
The particles were distributed in front of the acetylene black. Further, when the size of the Sn particles was observed with a transmission electron microscope, particles having a size of 500 nm or less were almost uniformly dispersed.

(Example 7) The powder C obtained in the above-mentioned embodiment 6 had a plane distance (d002) of 0.3 according to the X-ray diffraction method.
At 36 nm, the crystal size (Lc) in the C-axis direction is 100
The graphite having a specific surface area of 3.2 m ² / g was mixed at a weight ratio of (1: 9).
Using a methylpyrrolidone solution, applying a paste in which the mixed powder and PVDF were in a weight ratio of 90:10 to a 20-μm-thick copper foil as a current collector, air-dried, and then dried at 80 ° C. for 3 hours;
After vacuum drying for 0.5 hour and molding at a pressure of 0.5 ton / cm ² , vacuum drying was further performed at 120 ° C. for 2 hours to obtain a negative electrode.
The same test as in Example 3 was performed using these negative electrodes.
As a result, the discharge capacity retention ratio at a current density of ² mA / cm ² was 95 (%).

(Example 8) The powder C obtained in the above-mentioned embodiment 6 had a plane distance (d002) of 0.3 according to the X-ray diffraction method.
Amorphous carbon having a specific surface area of 82 nm and a specific surface area of 4.5 m ² / g was mixed at a weight ratio of (1: 9), and an N-methylpyrrolidone solution of PVDF was used as a binder. A paste in which PVDF was adjusted to a weight ratio of 90:10 was applied to a copper foil having a thickness of 20 μm as a current collector, air-dried, and then vacuum-dried at 80 ° C. for 3 hours to obtain 2.0 ton / cm ^2.
, And vacuum dried at 120 ° C for 2 hours to obtain a negative electrode.

These negative electrodes were combined with a lithium metal counter electrode with a polyethylene film interposed therebetween, and 1 M LiP
F ₆ / PC-DMC, was assembled test cell using lithium metal reference electrode. The charge / discharge current density is 0.3 to 4.
0 mA / cm ² , the upper and lower limit electric potentials of charge and discharge were 1.
5V and 0.005V. Charging was performed by the CCCV method for 4 hours. The negative electrode obtained by mixing the Sn-supporting carbon material and amorphous carbon according to the present invention had a discharge capacity retention of 93 (%) at a current density of ² mA / cm ² .

(Embodiment 9) In this embodiment, the first embodiment will be described.
The configuration of the battery obtained by combining the negative electrode, the positive electrode, and the electrolyte obtained in the above will be described.

A mixture slurry of LiCoO ₂ as a positive electrode active material, artificial graphite as a conductive agent, and polyvinylidene fluoride as a binder in a weight ratio of 87: 9: 4 was applied on both sides of an Al foil as a current collector. After drying and rolling, a positive electrode was prepared.

As an electrolytic solution, ethylene carbonate (E
C) and dimethyl carbonate (DMC) in a volume ratio of 1:
1M / l of LiPF ₆ as an electrolyte in the solvent mixed in 2
To obtain an electrolyte solution.

An AA battery using a negative electrode, the above-described positive electrode and an electrolytic solution will be described with reference to FIG.

In FIG. 1, a positive electrode 6 and a negative electrode 7 and a separator 8 of a polyethylene porous film for separating these two electrodes, a negative electrode can 9, a positive electrode lead 10, a negative electrode lead 11, a positive external terminal 12, a sealing gasket 13, an insulating plate 14 and the like.

The positive electrode 6 and the negative electrode 7 are spirally wound via the separator 8 and housed in the negative electrode can 9. The positive electrode 6 is connected to a positive electrode external terminal 12 via a positive electrode lead 10. The negative electrode 7 is connected to a negative electrode can 9 via a negative electrode lead 11 so that electric energy can be extracted to the outside. A sealing gasket 13 is insulated and sealed between the positive electrode external terminal 12 and the negative electrode can 9. The insulating plate 14 corresponding to the bottom surface of the negative electrode can 9 comprises the negative electrode can 9, the separator 8 and the positive electrode 6.
Is insulated between The button-type battery shown in FIG.
Since the main components of the battery are the same, in the button-type battery, the same components as those of the battery of FIG.

The structure of the negative electrode 7 will be described with reference to FIGS. A mixed layer 7B is coated on a conductive member such as a Cu foil 7A. The mixed layer 7B intercalates Li ions,
It is composed of a layer in which graphite 7G that can be deintercalated and carbon fine particles 7C carrying Ag7D (hereinafter referred to as a conductive additive) carrying an alloy with Li are mixed with a binder 7E. Binder 7E is graphite 7G, Ag7
D, a binder for binding the carbon particles 7C.

The mixing ratio of graphite 7G and the conductive additive will be described with reference to FIG. FIG. 4 shows that when Ag is 1% (%), graphite 7G is 95% (%) and the conductive additive is 5% (%), and 20% (5%) of 5% (1%) is 1%. (%) Of Ag. When Ag is 5% by weight (%), graphite 7G is 75% by weight (%) and the conductive additive is 25% by weight, and 20% (25%) of 25% by weight is 5% by weight (%). ) Ag.

For this reason, as is apparent from the discharge capacity retention ratio characteristics shown in FIG. 4, in the conventional characteristic B containing no Ag, when the weight becomes 5% (%) or less, the discharge capacity retention ratio drops sharply and the battery is used as a battery. Can not.

However, if the characteristic A of the present invention contains Ag in the range of 1% by weight (%) to 5% by weight (%),
The characteristic A of the discharge capacity maintenance ratio can be maintained at 90 (%), but when Ag becomes 1% by weight or less, the discharge capacity maintenance ratio sharply decreases and the battery cannot be used. Further, even if Ag contains 5% by weight or more, the discharge capacity retention ratio does not change. Therefore, it is most economical to contain 1% by weight to 5% by weight. The effect of can be achieved. If the Ag content is 15% by weight (%) or more, the cost will be high and the cost will not be increased.

When the particle size of the carbon particles 7C carrying Ag7D (conductive auxiliary material) is smaller than that of graphite 7G, the conductive auxiliary material easily penetrates between graphite 7G and graphite 7G. As the packing density (%) is increased, the contact points between the particles are increased, and the current path is increased. As a result, for example, as shown in FIG. Even if the discharge current density mA / cm ² exceeds 1, a large current can flow without abrupt reduction.

FIG. 5 shows the number of charge / discharge cycles (times) and discharge capacity (mAh / mAh) of the lithium secondary battery of the present invention.
FIG. ³ is a characteristic diagram showing a relationship with cm ³ ). In the present invention, the above-described negative electrode was used as the negative electrode of the present invention and the conventional lithium secondary battery. In the conventional example, a mixture of graphite and carbon was used. The test conditions in FIG. 5 were as follows: charge / discharge rate: 1 C, charge end voltage: 4.2 V, discharge end voltage: 2.5 V.

As a result, even if the number of cycles increases, the characteristic A1 of the lithium secondary battery of the present invention does not decrease even if the number of cycles increases, as compared with the conventional characteristic B1. And 300 cycles, stable performance can be obtained, whereas in the conventional characteristic B1, as the number of cycles increases, the discharge capacity decreases significantly and the performance becomes unstable. For this reason, if a lithium secondary battery using the negative electrode of the present invention is used, a stable sound can be obtained for a long period of time without frequently replacing the lithium secondary battery, as compared with a conventional lithium secondary battery. Now you can enjoy the lights.

FIG. 6 is a graph showing the relationship between the discharge capacity maintenance ratio (%) and the discharge current density (mA / cm ² ). The discharge characteristic A1 of the present invention can flow a large current without drastically decreasing even if the discharge current density (mA / cm ² ) increases as compared with the conventional discharge characteristic B1, and is the same as FIG. In addition, the above-described effects can be achieved.

[0065]

As described above, the negative electrode obtained by the present invention, that is, a conductive auxiliary material in which carbon particles carry fine particles of a metal which forms an alloy at an atomic ratio of 7 or less with respect to 1 atom of lithium and graphite or non-conductive material When mixed with crystalline carbon and used for the negative electrode, by interposing a metal between carbon particles, (1) electric conductivity is improved, and the speed of charge / discharge reaction is improved.
(2) Since the discharge capacity increases, the output density of the battery naturally increases. (3) The cycle characteristics are improved in association with (1), and the heat dissipation of the assembled battery can be improved. (4) The amount of supported metal used can be reduced.

[Brief description of the drawings]

FIG. 1 is a side sectional view of a lithium secondary battery shown as an example of the present invention.

FIG. 2 is a cross-sectional view of a button-type lithium secondary battery shown as another embodiment of the present invention.

FIGS. 3A and 3B are a side sectional view of the negative electrode in FIG. 1 and a configuration diagram of a mixed layer used in FIG.

FIG. 4 is a characteristic diagram showing the relationship between the amount of Ag used for the negative electrode of FIG. 1 and the discharge capacity.

FIG. 5 is a characteristic diagram showing the relationship between the discharge capacity and the number of cycles in FIG.

FIG. 6 is a characteristic diagram showing a relationship between a discharge capacity and a discharge current in FIG.

[Explanation of symbols]

6 positive electrode, 7 negative electrode, 7A Cu foil, 7B mixed layer, 7
C: Ag, 7D: carbon particles, 7G: graphite, 8: separator, 9: negative electrode can.

[Procedure amendment]

[Submission date] July 30, 1999 (July 7, 1999)
0)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

And 1. A positive electrode and a negative electrode, a separator interposed between the positive and negative electrodes, a lithium secondary battery comprising a positive and negative electrodes and electrolyte separators immersion, the load,
Lithium conductive additive of arm and alloys metal carrying carbon particles to form the intercalate, brat in deintercalating
Is a mixed system with graphite and metal particles
A lithium secondary battery , wherein the particle size of elementary particles is smaller than the particle size of graphite .

Wherein said load according to claim 1, characterized in that a mixed system of conductive agent and the amorphous carbon in the carbon particles carrying a metal which forms a lithium and alloys Lithium secondary battery.

3. The metal according to claim 1, wherein the metal carried on the conductive auxiliary material is Al, Sb, B, Ba, Cd, Ca, G
a, In, Ir, Pd, Pb, Hg, Si, Ag, S
A lithium secondary battery using at least one of r, Te, Tl, and Sn.

The specific surface area of claim 4, wherein said carbon particles are 1 to 1000
m ² / g, and the particle size of the supported metal carbon particles is 500 nm.
The lithium secondary battery according to claim 1, wherein:

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0015

[Correction method] Deleted

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction contents]

The gist of the present invention will be described below. That is,
1 of the invention includes a positive electrode and a negative electrode, a separator interposed between the positive and negative electrodes, a lithium secondary battery comprising a positive and negative electrodes and electrolyte separators immersion, the load is re <br/> Chiu arm and covering Conductive auxiliary material of carbon particles carrying metal that forms gold and black that can be intercalated and deintercalated
Carbon particles mixed with lead and carrying metal particles
A lithium secondary battery , wherein the particle size of the particles is smaller than the particle size of graphite .

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction contents]

[0017] The load of the second invention, according to claim 1, characterized in that a mixed system of conductive agent and the amorphous carbon in the carbon particles carrying a metal which forms a lithium and alloys 4. The lithium secondary battery according to 1.

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction contents]

According to a third aspect of the present invention, in the first or second aspect,
The metal supported on the conductive auxiliary material is Al, Sb, B, Ba, C
d, Ca, Ga, In, Ir, Pd, Pb, Hg, S
A lithium secondary battery using at least one of i, Ag, Sr, Te, Tl and Sn.

[Procedure amendment 6]

[Document name to be amended] Statement

[Correction target item name] 0019

[Correction method] Change

[Correction contents]

A fourth aspect of the present invention is the lithium secondary battery according to claim 1 or 2, wherein the specific surface area of the carbon particles is 1 to 1000 m ² / g, and the particle size of the supported metal carbon particles is 500 nm or less. Next battery.

[Procedure amendment 7]

[Document name to be amended] Statement

[Correction target item name] 0020

[Correction method] Deleted

[Procedure amendment 8]

[Document name to be amended] Statement

[Correction target item name] 0021

[Correction method] Deleted

[Procedure amendment 9]

[Document name to be amended] Statement

[Correction target item name] 0022

[Correction method] Deleted

[Procedure amendment 10]

[Document name to be amended] Statement

[Correction target item name] 0023

[Correction method] Deleted

[Procedure amendment 11]

[Document name to be amended] Statement

[Correction target item name] 0024

[Correction method] Deleted

[Procedure amendment 12]

[Document name to be amended] Statement

[Correction target item name] 0025

[Correction method] Deleted

[Procedure amendment 13]

[Document name to be amended] Statement

[Correction target item name] 0026

[Correction method] Deleted

[Procedure amendment 14]

[Document name to be amended] Statement

[Correction target item name] 0032

[Correction method] Change

[Correction contents]

By combining the load thus obtained with a commonly used positive electrode, separator and electrolyte, an optimum lithium secondary battery can be obtained. The active substance used for the positive electrode is represented by the general formula LiXO ₂
Or a composite oxide represented by LiX ₂ O ₄ (X is one or more of transition metals such as Co, Ni and Mn), for example, L
iCoO ₂ , LiNiO ₂ , LiMnO ₂ (Ni1-xC
ox) O ₂ , LiMn ₂ O ₄ Lithium-containing composite oxides, and LiMn ₂ O ₄ compounds may contain an excess of Li relative to the stoichiometric composition of the compound. A mixture of carbon and a binder is applied to a current collector such as an Al foil to form a positive electrode. here,
The stoichiometric composition is, for example, when the element Mn is used, Li
The stoichiometric composition of the contained Mn spinel compound is Li ₁
Mn ₂ O ₄ and deviates from the stoichiometric composition
_Means Li ₁ + Mn 2 _{—xO 4 —Y} composition .

[Procedure amendment 15]

[Document name to be amended] Statement

[Correction target item name] 0034

[Correction method] Change

[Correction contents]

The above configuration Te placed <br/> in the lithium secondary battery according to, conductive additive and Li ion intercalated carbon particles carrying a metal which forms a lithium and alloys carbon load, de By improving to a mixed system of graphite and amorphous carbon which can be intercalated, (1) increase of discharge capacity,
(2) improvement in electrical conductivity, (3) increase in power density,
(4) Improvement of cycle characteristics, (5) Improvement of heat dissipation in the assembled battery, (6) High-speed discharge, and (7) Reduction of supporting metal.

[Procedure amendment 16]

[Document name to be amended] Statement

[Correction target item name] 0059

[Correction method] Change

[Correction contents]

[0059] Therefore, when equal to or less than conventional characteristics 1 B in 5 weight not including Ag as is clear from the discharge capacity maintenance rate characteristics of FIG. 4 (%), as a battery discharge capacity retention ratio rapidly decreases I can not use it.

[Procedure amendment 17]

[Document name to be amended] Statement

[Correction target item name] 0062

[Correction method] Change

[Correction contents]

FIG. 5 shows the number of charge / discharge cycles (times) and discharge capacity (mAh / mAh) of the lithium secondary battery of the present invention.
FIG. ³ is a characteristic diagram showing a relationship with cm ³ ). The negative electrode of the present invention and the conventional lithium secondary battery use the load described above in the present invention, but the conventional example uses a mixture of graphite and carbon. Charge / discharge speed: 1C, charge as test conditions in FIG.
The end voltage was set to 4.2 V, and the discharge end voltage was set to 2.5 V.

[Procedure amendment 18]

[Document name to be amended] Statement

[Correction target item name] 0065

[Correction method] Change

[Correction contents]

[0065]

Load obtained by the present invention as described above, according to the present invention, i.e., a conductive additive that carrying the fine particles of the metal forming the lithium and alloy carbon particles and graphite and amorphous carbon mixture Then, when used for a load, by interposing a metal between carbon particles, (1) the electric conductivity is improved, and the speed of the charge / discharge reaction is improved. (2) Since the discharge capacity increases, the output density of the battery naturally increases. (3) The cycle characteristics are improved in association with (1), and the heat dissipation of the assembled battery can be improved. (4) Reduce the amount of supported metal used. ────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] December 20, 1999 (1999.12.
20)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

And 1. A positive electrode and a negative electrode, a separator interposed between the positive electrode and the negative electrode, a lithium secondary battery comprising an electrolytic solution for <br/> immersed the positive electrode and the negative electrode and the separator, the negative electrode the conductive auxiliary material and the intercalated carbon particles carrying a metal which forms an alloy with lithium, as well as a mixed system of graphite as possible out deintercalated, particle size of the carbon particles carrying metallic particles A lithium secondary battery having a particle size smaller than that of graphite.

Wherein said negative electrode, the lithium secondary according to claim 1, characterized in that a mixed system of conductive agent and the amorphous carbon in the carbon particles carrying a metal which forms an alloy with lithium Next battery.

3. The method according to claim 1, wherein the metal carried on the conductive additive is Al, Sb, B, Ba, Bi , Cd, C
a, Ga, In, Ir, Pd, Pb, Hg, Si, A
A lithium secondary battery using at least one of g, Sr, Te, Tl and Sn.

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction contents]

The gist of the present invention will be described below. That is, the first invention includes a positive electrode and a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte immersing the positive electrode and the negative electrode and the separator, the negative electrode is alloyed with lithium conductive additive to intercalate metal supported carbon particles, as well as a mixed system of graphite as possible out deintercalating, the particle size of the carbon particles carrying metal particles are smaller than the particle size of the graphite Characteristic lithium secondary battery.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction contents]

[0017] The negative electrode of the second invention, according to claim 1, characterized in that a mixed system of conductive agent and the amorphous carbon in the carbon particles carrying a metal which forms an alloy with lithium Lithium secondary battery.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction contents]

According to a third aspect of the present invention, in the first or second aspect,
The metals supported on the conductive additive are Al, Sb, B, Ba, B
i , Cd, Ca, Ga, In, Ir, Pd, Pb, H
A lithium secondary battery using at least one of g, Si, Ag, Sr, Te, Tl and Sn.

[Procedure amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0032

[Correction method] Change

[Correction contents]

The negative electrode thus obtained is usually a positive electrode used, by combining a separator and an electrolyte, can be optimized lithium secondary battery.
As the active material used for the positive electrode, a general formula LiXO ₂ or L
a composite oxide represented by iX ₂ O ₄ (X is one or a plurality of transition metals such as Co, Ni and Mn), for example, LiCo
O ₂ , LiNiO ₂ , LiMnO ₂ , Li (Ni _1-x C
_{o x) O 2, LiMn 2} O 4 , etc. composite oxide containing lithium, and to a stoichiometric composition of Li ₁ Mn ₂ O ₄ compound may Li is used an excess of things, a conductive agent thereto A mixture of carbon black or carbon and a binder is applied to a current collector such as an Al foil to form a positive electrode. here,
The stoichiometric composition is, for example, when the element Mn is used, Li
The stoichiometric composition of the contained Mn spinel compound is Li ₁
Mn ₂ O ₄ , deviating from the stoichiometric composition refers to the Li _{1 -x} Mn _{2 -x} O ₄ composition.

[Procedure amendment 6]

[Document name to be amended] Statement

[Correction target item name] 0034

[Correction method] Change

[Correction contents]

[0034] In the lithium secondary battery structured as above, conductive agent and Li ion intercalated carbon particles carrying a metal which forms an alloy with lithium carbon anode, graphite may deintercalating and non By improving the mixed system with crystalline carbon, (1) increase in discharge capacity, (2) increase in electric conductivity, (3) increase in output density,
(4) Improvement of cycle characteristics, (5) Improvement of heat dissipation of the assembled battery, (6) High-speed charge / discharge, and (7) Reduction of the amount of supported metal became possible.

[Procedure amendment 7]

[Document name to be amended] Statement

[Correction target item name] 0062

[Correction method] Change

[Correction contents]

FIG. 5 shows the number of charge / discharge cycles (times) and discharge capacity (mAh / mAh) of the lithium secondary battery of the present invention.
FIG. ³ is a characteristic diagram showing a relationship with cm ³ ). In the present invention, the above-described negative electrode was used as the negative electrode of the present invention and the conventional lithium secondary battery. In the conventional example, a mixture of graphite and carbon was used. The test conditions in FIG. 5 were as follows: charge / discharge rate: 1 C, charge end voltage: 4.2 V, discharge end voltage: 2.5 V.

[Procedure amendment 8]

[Document name to be amended] Statement

[Correction target item name] 0065

[Correction method] Change

[Correction contents]

[0065]

As described above, the negative voltage obtained by the present invention is obtained.
If the electrode , that is, a graphite and amorphous carbon are mixed with a conductive auxiliary material carrying fine particles of a metal that forms an alloy with lithium on carbon particles and used as a negative electrode , by interposing a metal between carbon particles, (1) The electric conductivity is improved, and the speed of the charge / discharge reaction is improved. (2) Since the discharge capacity increases, the output density of the battery naturally increases. (3) The cycle characteristics are improved in association with (1), and the heat dissipation of the assembled battery can be improved. (4) Kill <br/> the supported metal usage in reduction.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Junya Kaneda 7-1-1, Omikacho, Hitachi City, Ibaraki Prefecture Inside the Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Ren Muranaka 7, Omikacho, Hitachi City, Ibaraki No. 1-1 F-term in Hitachi Research Laboratory, Hitachi Ltd. (Reference) 5H029 AK03 AL07 AL12 AL19 AM04 AM05 BJ02 BJ03 BJ14 DJ16 DJ18 EJ04 HJ01 HJ02 HJ05 HJ07 HJ13

Claims (12)

[Claims] 1. A lithium secondary battery comprising a positive electrode and a negative electrode, a separator interposed between the positive and negative electrodes, and an electrolyte for immersing the positive and negative electrodes and the separator, wherein the negative electrode has a lithium atom of 7 or less per 1 lithium atom. A lithium secondary battery, wherein carbon particles supporting a metal forming an alloy in an atomic ratio are conductive additives. 2. A lithium secondary battery comprising a positive electrode and a negative electrode, a separator interposed between the positive and negative electrodes, and an electrolyte for immersing the positive and negative electrodes and the separator, wherein the negative electrode has a lithium atom of 7 or less per 1 lithium atom. A lithium secondary battery characterized in that it is a mixed system of a conductive additive of carbon particles carrying a metal forming an alloy in an atomic ratio and graphite capable of intercalating and deintercalating Li ions. 3. The negative electrode according to claim 1, wherein the negative electrode is a mixed system of a carbon particle conductive assistant supporting a metal forming an alloy at an atomic ratio of 7 or less to 1 lithium atom and amorphous carbon. Item 3. The lithium secondary battery according to Item 1 or 2. 4. The method according to claim 1, wherein the metal supported on the conductive additive is Al, Sb, B, Ba, Bi, Cd, C
a, Ga, In, Ir, Pd, Pb, Hg, Si, A
A lithium secondary battery using at least one of g, Sr, Te, Tl and Sn. 5. The carbon particles have a specific surface area of 1 to 1000.
The lithium secondary battery according to claim 1, wherein m ² / g, and the particle size of the supported metal particles is 500 nm or less. 6. The graphite particles have a plane distance (d002) of 0.3354 to 0.3369 nm as determined by X-ray diffraction.
In lithium secondary battery according to claim 2, wherein the size of the C-axis direction of crystal (Lc) is at 30nm or more and a specific surface area of 0.1~30m ² / g. 7. The current collector comprises a negative electrode, wherein a current collector contains a mixed system of carbon particle conductive aids supporting a metal forming an alloy at an atomic ratio of 7 or less to lithium atoms and amorphous carbon particles. The lithium secondary battery according to claim 1, wherein the amorphous carbon particles have a plane distance (d002) of 0.337 nm or more determined by an X-ray diffraction method. 8. The unit cell according to claim 1, wherein the cathode material is LiXO ₂ or LiX ₂ O ₄ (X is Co, Ni, M
n or one or more kinds of transition metals), and LiMn
A lithium secondary battery wherein the composition ratio of ₂ O ₄ is such that Li is excessive relative to the stoichiometric composition. 9. The lithium secondary battery according to claim 8, wherein the electrolyte layer is a copolymer electrolyte such as polyvinylidene fluoride and hexafluoropropylene. 10. A lithium secondary battery in which a separator is interposed between a positive electrode and a negative electrode, and the positive and negative electrodes and the separator are immersed in an electrolytic solution, wherein the negative electrode covers a conductive material with a mixed layer, and intercalates Li ions. And carbon particles having metal particles forming an alloy with Li. The amount of metal particles in this mixed layer is 1% by weight or more (%). Next battery. 11. The lithium secondary battery according to claim 10, wherein the amount of metal particles forming an alloy with Li in the mixed layer is 1 to 5% by weight (%). 12. The lithium secondary battery according to claim 10, wherein the particle size of the carbon particles carrying the metal particles is smaller than that of graphite.