JPH0684516A - Nonaqueous electrolyte secondary cell - Google Patents

Abstract

PURPOSE:To improve collecting efficiency and the safety of a cell by coating the surface of graphite as negative electrode material with an amorphous coke layer. CONSTITUTION:A nonaqueous electrolyte secondary cell is composed of a positive electrode mainly made of a lithium-containing composite oxide, nonaqueous electrolyte, and a negative electrode. In the negative electrode, the surface of graphite, whose d002 value of a lattice plane, (002) plane, spacing by X-ray diffraction is 3.354A or more and the dimension of a crystal in a C axis is 200Angstrom or more, is coated by an amorphous cake layer, or the coke layer, whose d002 value of the lattice plane, (002) plane, spacing by the X-ray diffraction is 3.43Angstrom or more and the dimension of the crystal in the C axis is 200Angstrom or less. Thereby, it is possible to improve collecting efficiency, and suppress the increase of cell internal pressure accompanying gas generation resulting from electrolyte decomposition, and the like during the process of full charging, and the like.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary battery using a non-aqueous electrolyte solution, and more particularly to a negative electrode material thereof.

[0002]

2. Description of the Related Art Conventionally, metallic lithium has been widely used as a negative electrode active material in lithium secondary batteries. However, when metallic lithium alone is used as the negative electrode active material,
When discharged as lithium ions during discharge, the surface of the negative electrode becomes uneven, and during charging, lithium is intensively electrodeposited on the convex portions of the surface and grows in dendritic form, resulting in dendritic growth. Since lithium contacts the positive electrode to cause an internal short circuit or lithium deposits on the surface of the negative electrode in a moss-like manner and falls off, there is a problem that the life due to charge / discharge cycles is extremely short.

Therefore, it has been proposed to use a lithium alloy such as lithium-aluminum as the negative electrode. By using this lithium alloy, it is possible to suppress the generation of lithium in a dendritic or mossy form on the surface of the negative electrode, and prevent the finely divided negative electrode active material from falling off from the negative electrode due to repeated internal short circuits and repeated charging and discharging. The charge / discharge cycle characteristics can be improved.

However, since a lithium alloy such as a lithium-aluminum alloy is very hard, it is difficult to bend or wind the lithium alloy to form an electrode, and it is limited to a flat type. There is a problem that it can be used only with a shaped battery.

Therefore, in order to solve the above-mentioned problems, JP-A-57-208079 and JP-A-63-2 are used.
In 4555, graphite is proposed as a negative electrode material which is excellent in flexibility and in which mossy lithium is not likely to be electrodeposited due to repeated charge / discharge cycles.

However, when graphite is used as the negative electrode material, there is some difficulty in the adhesion to the interface of the conductive core, which is presumed to be due to the self-lubricating property of graphite, and the current collection efficiency decreases.

Further, in the battery using graphite as the negative electrode material, there is a problem that the battery is not sufficiently stable at high temperature when the battery is fully charged, that is, in a state where it is doped with lithium ions. was there.

[0008]

DISCLOSURE OF THE INVENTION The present invention solves the above problems, improves the current collection efficiency, and raises the internal pressure of the battery due to gas generation due to decomposition of the electrolytic solution at the time of full charge and the like. To improve the safety of the battery.

[0009]

A non-aqueous electrolyte secondary battery of the present invention comprises a positive electrode mainly composed of a lithium-containing composite oxide,
In a non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte and a negative electrode, the negative electrode has a d ₀₀₂ value of a lattice spacing of (002) planes by X-ray diffraction of 3.354 Å or more and a C-axial direction. Amorphous coke layer or lattice plane by X-ray diffraction (002) on the surface of graphite with crystallite size of 200Å or more
It is covered with a coke layer having a surface spacing d ₀₀₂ value of 3.43 Å or more and a crystallite size in the C-axis direction of 200 Å or less.

The amorphous coke layer or the lattice spacing of the lattice plane (002) by X-ray diffraction has a d ₀₀₂ value of 3.43 Å or more and a crystallite size in the C-axis direction of 200.
Å The coke layer below is formed by firing coal tar pitch in a reducing atmosphere.

[0011]

In the non-aqueous electrolyte secondary battery according to the present invention, a mixture of graphite and coal tar pitch is used as a negative electrode material, and the surface of the graphite is coated with an amorphous coke layer or a coke layer to form a negative electrode material. Since the bondability with the core can be improved, the current collection efficiency increases,
The battery characteristics are improved.

[0012]

【Example】

[Example 1] As a negative electrode material, coal tar pitch was mixed with natural graphite at a weight ratio of 7: 3 to obtain 16
After heat-mixing at 0 ° C. for 1 hour, pressure was applied to form pellets. Then, the formed pellets are put into a magnetic crucible. Furthermore, by newly inserting natural graphite into this magnetic crucible, the molded pellets were shielded from the outside air, and argon gas was mixed into the magnetic crucible to make an argon atmosphere. And 250 at a temperature rising rate of 100 ° C./h
After heating up to ℃ and firing for 4 hours, heating rate is 10 again.
Repetition of increasing the temperature by 50 ° C. at 0 ° C./h and firing at 300 ° C. for 4 hours was repeated up to 800 ° C. to obtain a sample in which an amorphous coke layer was uniformly formed on the graphite surface. This sample was pulverized into a powder having an average particle size of 5 to 25 μm, and polyvinylidene fluoride (PVdF) previously dissolved in N-methyl-2-pyrrolidone as a binder was added so as to have a solid content of 15 parts by weight. , Into a slurry. This slurry was applied on both surfaces of a copper foil having a thickness of 18 μm, dried, and then rolled by a roller press machine to produce a negative electrode a ₁ .

Example 2 As a negative electrode material, natural graphite was used.
On the other hand, coal tar pitch was mixed at a weight ratio of 7: 3.
Combine, heat mix at 160 ° C for 1 hour, pressurize and mix.
It was molded into a cot shape. The molded pellets are then magnetized.
Put in a sex crucible. Furthermore, in this magnetic crucible, a new
Pellets formed by inserting natural graphite into
Insulate from the outside air and mix argon gas into the magnetic crucible.
The atmosphere of argon. And the temperature rising rate is 50 ° C /
The temperature was raised to 250 ° C. at h, baked for 8 hours, and then heated again.
Raise 50 ° C at a temperature rate of 100 ° C / h and raise at 300 ° C for 8 hours
Repeated firing up to 800 ° C
Of the lattice plane (002) plane by X-ray diffraction on the plane
₀₀₂The value is 3.45Å or more, and the crystallite size in the C-axis direction is
A sample with a coke layer of less than 200Å was obtained.
It was This sample is crushed to obtain powder having an average particle size of 5 to 25 μm.
Finally, the same as Example 1 except that it was used as a negative electrode material.
Negative electrode a₂Was produced.

Comparative Example 1 As a negative electrode material, the average particle size is 5 to 25 μm, the d ₀₀₂ value of the lattice plane (002) plane in X-ray diffraction is 3.35Å, and the size of the crystallite in the C-axis direction is 2.
290 Å natural graphite powder, the same average particle diameter, and the d ₀₀₂ value of the lattice plane (002) plane in X-ray diffraction of 3.46 to
3.48Å, the crystallite size in the C-axis direction is 15 to 25Å
PV which was dry-mixed with coke of 10% at an addition rate of 10% and previously dissolved in N-methyl-2-pyrrolidone as a binder
dF was added so as to have a solid content of 15 parts by weight to obtain a slurry. This slurry is applied on both sides of a copper foil having a thickness of 18 μm, dried, and then rolled by a roller press machine,
A negative electrode x ₁ was produced.

[Comparative Example 2] A negative electrode x ₂ was produced in the same manner as in Comparative Example 1 except that the addition rate of coke was 20%.

[Comparative Example 3] A negative electrode x ₃ was prepared in the same manner as in Comparative Example 1 except that the addition rate of coke was 30%.

[Comparative Example 4] A negative electrode x ₄ was produced in the same manner as in Comparative Example 1 except that the addition rate of coke was 40%.

[Comparative Example 5] A negative electrode x ₅ was produced in the same manner as in Comparative Example 1 except that the addition rate of coke was 50%.

[Comparative Example 6] A negative electrode x ₆ was produced in the same manner as in Comparative Example 1 except that the addition ratio of coke was 60%.

[Comparative Example 7] A negative electrode x ₇ was produced in the same manner as in Comparative Example 1 except that the addition rate of coke was 70%.

Comparative Example 8 As a negative electrode material, the average particle size was 5 to 25 μm, the d ₀₀₂ value of the lattice plane (002) plane in X-ray diffraction was 3.35Å, and the size of the crystallite in the C-axis direction was 2.
A negative electrode x ₈ was produced in the same manner as in Comparative Example 1 except that 290 Å natural graphite was used.

[Comparative Example 9] As a negative electrode material, the average particle diameter was 5 to 25 µm, the d ₀₀₂ value of the lattice plane (002) plane in X-ray diffraction was 3.46 to 3.48Å, and the size of the crystallite in the C-axis direction. A negative electrode x ₉ was produced in the same manner as in Comparative Example 1 except that petroleum coke having a size of 15 to 25 Å was used.

[Experiment 1] The results of the peel strength test and the charge / discharge characteristics of each negative electrode are shown in Table 1 and FIGS.

[0024]

[Table 1]

The charge and discharge characteristics are as follows: negative electrode a ₁ , a ₂ , x
₄ , x ₈ , and x ₉ , respectively, metal lithium was used for the counter electrode and the reference electrode, and the electrolyte solution was 1 mol / dm ³ ,
LiPF ₆ , EC / DMC and 1 mol / dm ³ , LiP
A beaker cell was assembled and measured using two types of F ₆ and PC / DMC. When an EC-based electrolyte is used in FIG.
FIG. 2 shows charge / discharge characteristics when a PC-based electrolytic solution is used.

As can be seen from Table 1, in the negative electrodes a ₁ and a ₂ , a bonding property of negative electrode x ₉ or more was obtained. Negative electrode x ₈ using only graphite as an active material showed the smallest peel strength and could be peeled off even with a slight force, so careful attention was required.

Next, as can be seen from FIGS. 1 and 2, EC
In the system electrolyte solution, the negative electrode x ₈ exhibits ideal charge / discharge characteristics, but in the PC system electrolyte solution, the potential does not drop from around 1.0 V, indicating that the battery cannot be charged.

On the other hand, the negative electrodes a ₁ and a ₂ show sufficient charge / discharge characteristics in both EC type and PC type electrolytic solution systems.

The negative electrodes a ₁ and a ₂ also have a very high bonding property, and have a very high discharge capacity in both EC-based and PC-based electrolytic solutions.

This is because the amorphous carbon layer or coke layer, which is the second component, was uniformly formed on the graphite surfaces of the negative electrodes a ₁ and a ₂ , and the decomposition of the electrolytic solution, which is a side reaction, was suppressed. It is considered that the capacity was high and the initial charge / discharge efficiency was high. Further, when fully charged with the EC-based electrolytic solution, no gas generation was observed even by heating in the PC-based electrolytic solution, whereas gas generation was observed with the negative electrode x ₈ .

As a result, in the negative electrodes a ₁ and a ₂ , it is possible to prevent the decomposition of the electrolytic solution at the time of high temperature due to full charge to generate a gas, and therefore, when the negative electrode is incorporated in a battery, the battery generated by the gas generation is prevented. An increase in internal pressure can be suppressed.

Example 3 Commercially available cobalt trioxide (C)
o ₃ O ₄ ) and lithium carbonate were mixed sufficiently so that the atomic ratio was 1: 1 and then calcined in air at 600 ° C. for 6 hours, pulverized and mixed, and further calcined at 850 ° C. for 12 hours to obtain lithium cobalt. A composite oxide LiCoO ₂ was synthesized and used as a positive electrode active material.

After taking 85 parts by weight of the above-mentioned positive electrode active material, 8 parts by weight of artificial graphite powder and 2 parts by weight of carbon black were thoroughly mixed, and then P dissolved in N-methyl-2-pyrrolidone was used.
VdF was added as a solid content to 5 parts by weight to obtain a slurry.

This positive electrode slurry has a length of 355 mm and a width of 4
Both sides are coated on 0 mm thick aluminum foil with a thickness of 20 μm, dried, rolled by a roller press machine, nickel lead spot welding is applied to the ends, and vacuum dried at 110 ° C. for 3 hours to obtain a positive electrode plate. Was produced.

A nickel lead was spot-welded to the end of the negative electrode a ₁ and vacuum dried at 110 ° C. for 3 hours to produce a negative electrode plate.

The positive electrode plate and the negative electrode plate were wound around a porous polypropylene separator having a thickness of 25 μm to form a spiral electrode body. The spirally wound electrode body was placed in a nickel-plated iron outer can, and after the electrolytic solution was injected, the outer can was sealed with a sealing body through a gasket to prepare a cylindrical battery A ₁ of the invention.

The electrolyte used was LiPF ₆ dissolved in a mixed solution of ethylene carbonate and dimethyl carbonate so as to have a concentration of 1 mol / dm ³ .

[0038] Except for making a negative electrode plate with Example 4 anode a _2, in the same manner as in Example 3, the present invention cell A ₂
Was produced.

Comparative Example 10 A comparative battery X ₁ was prepared in the same manner as in Example 3 except that the negative electrode plate was prepared using the negative electrode x _4.
Was produced.

Comparative Example 11 Comparative battery X ₂ was prepared in the same manner as in Example 3 except that the negative electrode plate was prepared using negative electrode x _8.
Was produced.

Comparative Example 12 Comparative battery X ₃ was prepared in the same manner as in Example 3 except that the negative electrode plate was prepared using negative electrode x _9.
Was produced.

[Experiment 2] Next, the discharge capacity of each battery was measured. The condition at this time is 200 mA at room temperature.
The battery is charged until the battery voltage reaches 4.1 V with the charging current of 1 and then discharged until the battery voltage reaches 2.75 V with the discharging current of 200 mA. The result is shown in FIG.
Further, FIG. 4 shows cycle characteristics obtained by repeating the series of charging and discharging.

From FIGS. 3 and 4, the batteries A ₁ and A _{2 of the} present invention are shown.
Has a discharge capacity of 500 mA or more, which is equivalent to that of the comparative battery X ₂ . Here, the battery capacity of the comparative battery X ₃ is much lower than that of the batteries A ₁ and A ₂ of the invention. Furthermore, in the cycle characteristics, the comparative battery X ₁ ~
The discharge capacity of X ₃ decreased as the number of cycles increased, but the batteries A ₁ and A ₂ of the present invention did not decrease much from the initial discharge capacity even if the number of cycles increased. I understand.

This is considered to be related to the peel strength (bondability) of the negative electrode. By not only simply mixing graphite and coke as a negative electrode material like Comparative Battery X ₁ , but also by coating the surface of graphite with amorphous coke or coke as in the batteries A ₁ and A ₂ of the present invention, The negative electrode material and the core can be bonded very well, and the peel strength can be improved.

That is, the high peeling strength means that the core and the negative electrode material are not peeled off even after repeated charging and discharging.
It is considered that the discharge capacity does not decrease because there is no defective current collection due to discharge.

Further, according to the discharge characteristics of FIG. 3, in the battery of the present invention, the battery voltage gradually decreases at the end of discharge, so that it is possible to easily detect the remaining capacity, which was difficult for the comparative battery X _2. It became so.

[0047]

EFFECT OF THE INVENTION As a negative electrode material, a graphite surface having a d ₀₀₂ value of the lattice spacing (002) plane of 3.354 Å or more by X-ray diffraction and a crystallite size in the C-axis direction of 200 Å or more, by d _{00 2} values of spacing of lattice plane (002) plane by an amorphous coke layer or X-ray diffraction is the size of the C-axis direction of crystallites more 3.43Å were coated with the following coke 200 Å, a high voltage A non-aqueous electrolyte secondary battery having a high capacity and a high bonding property between the negative electrode material and the core can provide a non-aqueous electrolyte secondary battery excellent in current collection efficiency and the like.

[Brief description of drawings]

FIG. 1 is a diagram showing charge / discharge characteristics in an EC-based electrolytic solution.

FIG. 2 is a diagram showing charge / discharge characteristics in a PC-based electrolytic solution.

FIG. 3 is a diagram showing discharge characteristics of a battery of the present invention and a comparative battery.

FIG. 4 is a diagram showing cycle characteristics of the battery of the present invention and a comparative battery.

[Explanation of symbols]

a ₁ , a ₂ ... Negative electrode x _{1 to} x ₉ ... Negative electrode A ₁ , A ₂ ... Inventive battery X _{1 to} X ₃ ... Comparative battery

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] May 10, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction content]

[0009]

A non-aqueous electrolyte secondary battery of the present invention comprises a positive electrode mainly composed of a lithium-containing composite oxide,
In a non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte and a negative electrode, the negative electrode has a d ₀₀₂ value of a lattice spacing of (002) planes by X-ray diffraction of 3.354 Å or more and a C-axial direction. the size of the crystallite surface of the above graphite 200 Å, Amorufu
Carbon layer or lattice plane by X-ray diffraction (002)
It is covered with a coke layer having a surface spacing d ₀₀₂ value of 3.43 Å or more and a crystallite size in the C-axis direction of 200 Å or less.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction content]

Also, the d ₀₀₂ value of the interplanar spacing between the amorphous carbon layer or the lattice plane (002) plane by X-ray diffraction is 3.43 Å or more and the size of the crystallite in the C-axis direction is 200
Å The coke layer below is formed by firing coal tar pitch in a reducing atmosphere.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0011

[Correction method] Change

[Correction content]

[0011]

In the non-aqueous electrolyte secondary battery according to the present invention, a mixture of graphite and coal tar pitch is used as a negative electrode material, and the surface of graphite is coated with an amorphous carbon layer or a coke layer to form a negative electrode. Since the bondability between the material and the core can be improved, the current collection efficiency increases,
The battery characteristics are improved.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction content]

[0012]

Example 1 As a negative electrode material, coal tar pitch was mixed with natural graphite at a weight ratio of 7: 3 to prepare 16
After heat-mixing at 0 ° C. for 1 hour, pressure was applied to form pellets. Then, the formed pellets are put into a magnetic crucible. Furthermore, by newly inserting natural graphite into this magnetic crucible, the molded pellets were shielded from the outside air, and argon gas was mixed into the magnetic crucible to make an argon atmosphere. And 250 at a temperature rising rate of 100 ° C./h
After heating up to ℃ and firing for 4 hours, heating rate is 10 again.
0 ° C. / h repeatedly that firing 50 ° C. heated for 4 hours at 300 ° C. at a go to 800 ° C., Cupid graphite surface
A sample in which the fas carbon layer was uniformly formed was obtained. This sample was pulverized into a powder having an average particle size of 5 to 25 μm, and polyvinylidene fluoride (PVdF) previously dissolved in N-methyl-2-pyrrolidone was added as a binder so that the solid content was 15 parts by weight. , Into a slurry. This slurry was applied on both surfaces of a copper foil having a thickness of 18 μm, dried, and then rolled by a roller press machine to produce a negative electrode a ₁ .

[Procedure correction 6]

[Document name to be amended] Statement

[Correction target item name] 0044

[Correction method] Change

[Correction content]

This is considered to be related to the peel strength (bondability) of the negative electrode. By not only simply mixing graphite and coke as a negative electrode material like Comparative Battery X ₁ , but also by coating the surface of graphite with amorphous carbon or coke as in the batteries A ₁ and A ₂ of the present invention, The negative electrode material and the core can be bonded very well, and the peel strength can be improved.

[Procedure Amendment 7]

[Document name to be amended] Statement

[Correction target item name] 0047

[Correction method] Change

[Correction content]

[0047]

EFFECT OF THE INVENTION As a negative electrode material, a graphite surface having a d ₀₀₂ value of the lattice spacing (002) plane of 3.354 Å or more by X-ray diffraction and a crystallite size in the C-axis direction of 200 Å or more, The amorphous carbon layer or the lattice spacing (002) plane by X-ray diffraction having a d _{00 2} value of 3.43 Å or more and a crystallite size in the C-axis direction of 200 Å or less is coated with coke. A non-aqueous electrolyte secondary battery having a high voltage and a high capacity, and having a high bonding property between the negative electrode material and the core can provide a non-aqueous electrolyte secondary battery excellent in current collection efficiency and the like.

Claims (2)

[Claims] 1. A non-aqueous electrolyte secondary battery comprising a positive electrode containing a lithium-containing composite oxide as a main component, a non-aqueous electrolyte, and a negative electrode, wherein the negative electrode has a lattice plane (00) by X-ray diffraction.
2) The surface of graphite having a d ₀₀₂ value of the surface spacing of 3.354 Å or more and a crystallite size in the C-axis direction of 200 Å or more is used as an amorphous coke layer or a lattice plane (0
02) A non-aqueous electrolyte secondary battery characterized by being coated with a coke layer having a d ₀₀₂ value of the interplanar spacing of 3.43 Å or more and a crystallite size in the C-axis direction of 200 Å or less. 2. The amorphous coke layer or the lattice spacing (002) plane obtained by X-ray diffraction has a d ₀₀₂ value of 3.43 Å or more and a crystallite size in the C-axis direction of 200 Å.
The non-aqueous electrolyte secondary battery according to claim 1, wherein the following coke layer is formed by firing coal tar pitch in a reducing atmosphere.