JP2001076723A - Polymer lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polymer lithium secondary battery capable of enhancing the filling density of a negative electrode and a keeping long charge/discharge cycle life. SOLUTION: A negative electrode 2 contains graphite base meso-phase pitch carbon particles capable of storing.releasing lithium ions, having the 50% particle diameter D50 of 10-30 μm and a specific surface area of 0.5-2.5 m2/g and a graphite base granular carbon material capable of storing/releasing lithium ions, having the 50% particle diameter D50 of 2.0-25 μm and a specific surface area of 0.5-20.0 m2/g.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a polymer lithium secondary battery having an improved negative electrode.

[0002]

2. Description of the Related Art In recent years, with the development of electronic equipment, there has been a demand for the development of a non-aqueous electrolyte secondary battery that is small, lightweight, has a high energy density, and can be repeatedly charged and discharged. Such a secondary battery includes a negative electrode using lithium or a lithium alloy as an active material, a positive electrode containing an oxide, sulfide, or selenide such as molybdenum, vanadium, titanium, or niobium as an active material, and a nonaqueous electrolyte. There is known a lithium secondary battery including:

In recent years, a negative electrode containing a carbonaceous material that absorbs and releases lithium ions, such as coke, graphite, carbon fiber, a resin fired body, and pyrolytic gas phase carbon, has been used as a negative electrode. The development and commercialization of lithium ion secondary batteries using lithium and lithium manganese oxide-containing batteries are being actively pursued.

Incidentally, polymer lithium secondary batteries have been developed for the purpose of further reducing the weight and size of the secondary batteries. This polymer lithium secondary battery has a positive electrode,
A power generation element is mainly provided by integrating a negative electrode and an electrolyte layer disposed between the positive electrode and the negative electrode. The positive electrode, the negative electrode, and the electrolyte layer include a non-aqueous electrolyte and a polymer having a function of holding the electrolyte, respectively.
This polymer plays a role of integrating the positive electrode, the negative electrode, and the electrolyte layer in addition to holding the non-aqueous electrolyte as described above. Specifically, a copolymer of vinylidene fluoride (VdF) -hexafluoropropylene (HFP) is used as the polymer.

The negative electrode of this polymer lithium secondary battery is as follows:
It has a structure in which a negative electrode layer containing a material that absorbs and releases lithium ions, a nonaqueous electrolyte, and a polymer having a function of holding the nonaqueous electrolyte is stacked on a current collector. As the material for storing and releasing lithium ions, a carbon material for storing and releasing lithium ions is used. By using a carbon material that occludes and releases lithium ions for the negative electrode of a polymer lithium secondary battery, the precipitation of lithium dendrite is suppressed, and the negative electrode characteristics are improved.
The safety and charge / discharge cycle life of the secondary battery are improved. As the carbon material that stores and releases lithium ions, for example, carbon fibers such as mesophase-based carbon fibers or carbon particles such as mesophase-based carbon particles are used.

[0006]

However, in the case of a negative electrode containing carbon fibers or carbon particles as a material for inserting and extracting lithium ions, it is necessary to use them alone to increase the packing density in order to improve the capacity. The structure of the material may be damaged, the flexibility of the electrode may be reduced, or a sufficient packing density may not be obtained. The carbon fibers or carbon particles contained in the negative electrode expand and contract when lithium ions are inserted into and desorbed from the carbon layer in accordance with the charge / discharge reaction. Therefore, when the flexibility of the negative electrode decreases, the expansion and contraction of the carbon particles (carbon fibers) are repeated as the charge / discharge cycle progresses, so that the fine structure in the negative electrode layer gradually collapses, and as a result, There is a problem that the charge / discharge cycle life of the secondary battery is shortened. Further, when one kind of carbon particles is used as a material for inserting and extracting lithium ions to improve the packing density of the negative electrode, there is a problem that the flexibility of the negative electrode is reduced.

An object of the present invention is to provide a polymer lithium secondary battery having a high capacity and maintaining an excellent charge / discharge cycle life.

[0008]

The polymer lithium secondary battery according to the present invention stores and releases lithium ions, and
0% particle size D ₅₀ is 10 to 30 μm, and specific surface area is 0.
It absorbs and releases graphite-based mesophase pitch carbon particles of 5 to 2.5 m ² / g and carbon black and / or lithium ions, and has a 50% particle size D ₅₀ of 2.0 to 25 μm.
And a graphite-based granular carbon material having a specific surface area of 0.5 to 20.0 m ² / g.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an example of a polymer lithium secondary battery according to the present invention will be described with reference to FIG.

That is, a polymer lithium secondary battery is:
A power generation element is mainly provided by integrating a positive electrode 1, a negative electrode 2, and an electrolyte layer 3 disposed between the positive electrode 1 and the negative electrode 2. The positive electrode 1 has a structure in which a positive electrode layer 5 is supported on both surfaces of a current collector 4. On the other hand, the negative electrode 2
Has a structure in which a negative electrode layer 7 is supported on both surfaces of a current collector 6. The strip-shaped positive electrode terminal 8 is obtained by extending the current collector 4 of each of the positive electrodes 1 in a strip shape. On the other hand, the strip-shaped negative electrode terminal 9 is
The current collector 6 of the negative electrode 2 is extended in a belt shape. The positive electrode lead 10 is connected to the two positive terminals 8. A negative lead (not shown) is connected to the negative terminal 9. The power generating element having such a configuration is sealed in a state in which the positive electrode lead 10 and the negative electrode lead extend from the exterior material 11 in an exterior material 11 made of a film material having a barrier function against moisture, air, and the like. Have been.

As the positive electrode, the negative electrode and the electrolyte layer of the polymer lithium secondary battery, for example, those described below can be used.

1) Positive Electrode The positive electrode has a structure in which a positive electrode layer containing a positive electrode active material, a non-aqueous electrolyte, and a polymer having a function of holding the non-aqueous electrolyte is supported on a current collector.

Examples of the positive electrode active material include various oxides (eg, lithium-manganese composite oxide such as LiMn ₂ O ₄ , manganese dioxide, lithium-containing nickel oxide such as LiNiO _2, and lithium-containing cobalt oxide such as LiCoO _2). Oxide, lithium-containing nickel-cobalt oxide, lithium-containing amorphous vanadium pentoxide and the like, and chalcogen compounds (for example, titanium disulfide and molybdenum disulfide). Among them, it is preferable to use a lithium manganese composite oxide, a lithium-containing cobalt oxide, and a lithium-containing nickel oxide.

The non-aqueous electrolyte is prepared by dissolving an electrolyte in a non-aqueous solvent.

Examples of the non-aqueous solvent include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and dimethyl carbonate (D
MC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), γ-butyrolactone (γ-
BL), sulfolane, acetonitrile, 1,2-dimethoxyethane, 1,3-dimethoxypropane, dimethyl ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran and the like. The non-aqueous solvents may be used alone or as a mixture of two or more.

Examples of the electrolyte include lithium perchlorate (LiClO ₄ ) and lithium hexafluorophosphate (L
iPF _6), boric tetrafluoride lithium (LiBF _4), lithium hexafluoroarsenate (LiAsF _6), lithium salts such as lithium trifluoromethane sulfonate (LiCF ₃ SO ₃₎ may be mentioned.

The amount of the electrolyte dissolved in the non-aqueous solvent is desirably 0.2 mol / l to 2 mol / l.

It is desirable that the polymer having a function of holding the non-aqueous electrolyte further has a binding function. Examples of the polymer having a function of retaining a non-aqueous electrolyte and a binding function include, for example, polyethylene oxide derivatives,
Examples thereof include a polypropylene oxide derivative, a polymer containing the derivative, and a copolymer of vinylidene fluoride (VdF) and hexafluoropropylene (HFP). Among them, a VdF-HFP copolymer is preferable.

The positive electrode may include a conductive material from the viewpoint of improving conductivity. Examples of the conductive material include artificial graphite, carbon black (eg, acetylene black), nickel powder, and the like.

As the current collector, for example, those having a porous structure such as an aluminum mesh, an aluminum expanded metal or an aluminum punched metal, or a metal foil such as an aluminum foil can be used. . When a metal foil is used as the current collector, it is preferable that the positive electrode layer be supported on only one surface of the current collector. Further, in FIG. 1 described above, the current collector and the positive electrode terminal are formed of the same material, but may be formed of different materials.

The positive electrode lead can be formed, for example, from an aluminum foil.

2) Negative Electrode This negative electrode has a structure in which a negative electrode layer containing a negative electrode active material, a non-aqueous electrolyte, and a polymer having a function of holding the electrolyte is supported on a current collector.

The negative electrode active material absorbs lithium ions.
-Release, 50% particle size D₅₀Is 10 to 30 μm and the ratio is
Surface area 0.5-2.5m^Two/ G graphite mesophe
Fine pitch carbon particles, carbon black and / or
Occludes and releases lithium ions, 50% particle size D₅₀Is 2.
0 to 25 μm and specific surface area of 0.5 to 20.0 m ^Two
/ G of a graphite-based granular carbon material.

(1) Graphite-based mesophase pitch carbon particles The graphite-based mesophase pitch carbon particles have a temperature of 2800 ° C. to 3000 ° C. under normal pressure or reduced pressure in an inert gas atmosphere such as argon gas or nitrogen gas. By firing the mesophase pitch. Since such carbon particles have a high amount of inserting and extracting lithium ions, the capacity of the negative electrode can be further improved.

The is due to the following reason is to define the 50% particle diameter D ₅₀ of the graphite-based mesophase pitch carbon particles in the range. When the 50% particle size D ₅₀ exceeds 30 μm, it becomes difficult to improve the active material filling density of the negative electrode. When the 50% particle size D ₅₀ is smaller than 10 μm, the smaller the 50% particle size D ₅₀ is, the easier it is to improve the packing density. A side reaction easily occurs between them, and a sufficient charge / discharge cycle life cannot be obtained. A more preferred range of the 50% particle size D ₅₀ is 20 to 25 m.

The specific surface area of the graphite-based mesophase pitch carbon particles is defined in the above range for the following reason. When the specific surface area is less than 0.5 m ² / g, it becomes difficult to reduce the amount of occlusion and release of lithium ions, and it is difficult to increase the viscosity of the paste used in the negative electrode preparation step described below to an optimum value for coating and film formation. Therefore, a negative electrode having a uniform thickness cannot be obtained. On the other hand, the specific surface area is 2.5 m ² /
When the amount exceeds g, a side reaction occurs on the surface of the negative electrode, causing a significant decrease in discharge capacity due to self-discharge, or it becomes difficult to uniformly disperse the carbon particles in the paste, and the coatability is poor. An uneven distribution of carbon particles occurs.
A more preferable value of the specific surface area is 0.7 to 1.8 m ² / g.
It is. The specific surface area is measured by the BET method.

(2) Graphite-based granular carbon material The graphite-based granular carbon material is obtained, for example, by firing an organic polymer compound (eg, phenol resin, polyacrylonitrile, cellulose, etc.), coke, mesophase, etc. It can be formed from what is obtained by firing pitch, artificial graphite, natural graphite, or the like. Above all, it is preferable to be formed from what is obtained by firing mesophase pitch or coke at a temperature of 2800 ° C. to 3000 ° C. under normal pressure or reduced pressure in an inert gas atmosphere such as argon gas or nitrogen gas. If a graphite-based granular carbon material having a specific particle size and specific surface area made of such a material is used, the flexibility of the negative electrode can be further increased, so that the charge / discharge cycle life can be further improved.

50% particle diameter D of the graphite-based granular carbon material₅₀
Is specified in the above range for the following reasons.
is there. 50% particle size D₅₀Exceeds 25 μm, the negative electrode
It becomes difficult to improve the material packing density. 50% particle size
D₅₀Although the smaller is easier to improve the packing density,
50% particle size D₅₀Is less than 2.0 μm, the non-aqueous electrolyte
Reaction area with the non-aqueous electrolyte
Response may be more likely to occur.
There is a possibility that the life of the device may not be obtained. 50% particle size D ₅₀Upper limit
A more preferable value is 20 μm. On the other hand, 50%
Particle size D₅₀Is more preferably 3.0 μm.
You.

The specific surface area of the graphite-based granular carbon material is defined in the above range for the following reason.
The negative electrode is prepared by forming a paste containing the negative electrode active material and the polymer into a sheet and laminating the same on a current collector, or applying a paste containing the negative electrode active material and the polymer to the current collector. Is done. If the specific surface area of the graphite-based granular carbon material is larger than 20 m ² / g, it will be difficult to uniformly disperse it in the paste, the coatability will be poor, and the distribution in the negative electrode will be uneven. For this reason, the negative electrode characteristics are degraded, which adversely affects the battery characteristics. The lower limit of the specific surface area is set to 0.5 m ² / g. This is because the occlusion / release amount of lithium ions is reduced, or it is difficult to increase the viscosity of the negative electrode paste to an optimum value for coating and film formation, so that a negative electrode having a uniform thickness cannot be obtained. . A more preferable upper limit of the specific surface area is 16.0 m.
² / g. Further, a more preferable value of the lower limit of the specific surface area is 0.7 m ² / g. The specific surface area is BE
It is measured by the T method.

The shape of the graphite-based granular carbon material is a true sphere,
It can be almost spherical or scaly.

(3) Carbon Black As the carbon black, there is no particular limitation on the production method and production method, and for example, acetylene black, Ketjen black, furnace black and the like can be used. Further, several types of carbon blacks may be mixed and used.

It is preferable that the above-mentioned graphite-based granular carbon material and / or carbon black is mixed in an amount of 2 to 20 parts by weight based on 100 parts by weight of the graphite-based mesophase pitch carbon particles. This is due to the following reasons. If the mixing ratio exceeds 20 parts by weight, a high active material packing density may not be obtained. On the other hand, if the mixing ratio is less than 2 parts by weight, the effect of mixing is difficult to appear, the filling efficiency of the negative electrode active material is poor, and a long life may not be obtained due to a decrease in the flexibility of the negative electrode. A more preferable range of the mixing ratio is 4 to 15 parts by weight.

As the non-aqueous electrolyte and the polymer having a function of holding the non-aqueous electrolyte, the same ones as those described for the positive electrode described above are used.

As the current collector, for example, a collector having a porous structure such as a copper mesh, a copper expanded metal or a copper punched metal, or a metal foil such as a copper foil can be used. When a metal foil is used as the current collector, it is desirable that the negative electrode layer be supported on only one surface of the current collector. Further, in FIG. 1 described above, the current collector and the negative electrode terminal are formed from the same material, but may be formed from different materials.

3) Electrolyte Layer The electrolyte layer is a sheet containing a non-aqueous electrolyte and a polymer having a function of holding the electrolyte.

As the non-aqueous electrolyte and the polymer having a function of holding the non-aqueous electrolyte, the same polymers as those described for the positive electrode described above are used.

The electrolyte layer may contain an inorganic filler such as silicon oxide powder from the viewpoint of further improving the strength.

The polymer lithium secondary battery according to the present invention can be manufactured, for example, by the method described below. First, a positive electrode, a negative electrode and an electrolyte layer not impregnated with a non-aqueous electrolyte are prepared by the method described below.

The positive electrode not impregnated with the non-aqueous electrolyte is mixed, for example, with an active material, a polymer having a function of holding the non-aqueous electrolyte, a conductive material, and a plasticizer in an organic solvent such as acetone.
The paste is prepared by preparing a paste and forming a film to form a positive electrode sheet, and bonding the obtained positive electrode sheet to a current collector by, for example, thermocompression bonding. Alternatively, the positive electrode may be manufactured by applying the paste to a current collector.

For the negative electrode not impregnated with the non-aqueous electrolyte, for example, an active material, a polymer having a function of holding the non-aqueous electrolyte, and a plasticizer are mixed in an organic solvent such as acetone, and a paste is prepared. Then, a negative electrode sheet is prepared, and the obtained negative electrode sheet is bonded to a current collector by, for example, thermocompression bonding. Further, the negative electrode may be manufactured by applying the paste to a current collector.

The electrolyte layer not impregnated with the non-aqueous electrolyte is, for example,
Inorganic filler, a polymer having a function of holding a non-aqueous electrolyte and a plasticizer are mixed in an organic solvent such as acetone,
It is produced by preparing a paste and forming a film.

The plasticizer has a function of retaining the non-aqueous electrolyte, has excellent compatibility with the polymer having the swelling ratio in the above-mentioned specific range, and can improve the flexibility of the positive and negative electrodes and the electrolyte layer. It is preferable that the polymer has four properties that it can promote the melting of the polymer during thermocompression bonding and can be easily removed. Examples of the plasticizer include dibutyl phthalate (DBP), dimethyl phthalate (DMP), and ethyl phthalyl ethyl glycolate (EP).
EG) and the like. As the plasticizer, one or more selected from the above types can be used.

Subsequently, an electrolyte layer not impregnated with the non-aqueous electrolyte is disposed between the positive electrode not impregnated with the non-aqueous electrolyte and the negative electrode not impregnated with the non-aqueous electrolyte, thereby producing a laminate. The obtained laminate is integrated by thermocompression bonding. Then, after removing the plasticizer from the laminate by, for example, solvent extraction, impregnated with a non-aqueous electrolyte,
For example, the polymer lithium secondary battery according to the present invention can be obtained by sealing with an exterior material made of a film material having a barrier function against moisture and air.

As described in detail above, the polymer lithium secondary battery according to the present invention absorbs and releases lithium ions,
A graphite-based mesophase pitch carbon particle having a 50% particle diameter D ₅₀ of 10 to 30 μm and a specific surface area of 0.5 to 2.5 m ² / g, and absorbing and releasing carbon black and / or lithium ions; % particle diameter D ₅₀ of 2.0 to 25
and a graphite-based granular carbon material having a specific surface area of 0.5 to 20.0 m ² / g. In such a negative electrode, a gap between carbon particles can be filled with a granular carbon material or carbon black having a different shape or specific surface area, so that the active material filling density can be improved while ensuring flexibility. Therefore, according to the negative electrode, it is possible to suppress a side reaction between the carbon material and the non-aqueous electrolyte while having a high active material filling density, and to insert and release lithium ions with the progress of the charge and discharge cycle. Is repeated, it is possible to suppress the gradual collapse of the fine structure in the negative electrode layer, so that a high capacity and long life polymer lithium secondary battery can be realized.

Further, when forming the negative electrode active material from the graphite-based granular carbon material and / or carbon black and the graphite-based mesophase pitch carbon particles, the graphite-based granular carbon material and / or carbon black is mixed with the graphite-based granular carbon material and / or carbon black. 2 to 100 parts by weight of mesophase pitch carbon particles
By mixing 20 parts by weight, the charge / discharge cycle life of the polymer lithium secondary battery can be further improved.

[0046]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments according to the present invention will be described below in detail with reference to the drawings.

Example 1 <Preparation of Positive Electrode Not Impregnated with Nonaqueous Electrolyte> 56% by weight of a lithium manganese composite oxide represented by a composition formula of LiMn ₂ O ₄ as an active material, and 5% by weight of carbon black And vinylidene fluoride-hexafluoropropylene (VdF
A paste was prepared by mixing 17% by weight of a copolymer powder of -HFP) and 22% by weight of dibutyl phthalate (DBP) in acetone. The obtained paste is applied on a polyethylene terephthalate film (PET film),
Sheeted. The obtained positive electrode sheet was disposed on both sides of an aluminum expanded metal, and hot roll pressing was performed to produce a non-aqueous electrolyte-unimpregnated positive electrode. The expanded metal made of aluminum has a belt-like extension as a positive electrode terminal.

<Preparation of Negative Electrode Impregnated with Nonaqueous Electrolyte> Mesophase pitch carbon particles were pulverized and then heat-treated at 2800 ° C. to obtain a 50% particle diameter D ₅₀ of 22 μm and a BE
Graphite-based mesophase pitch carbon particles having a specific surface area of 1.2 m ² / g by T method were obtained. 0.5 part by weight of acetylene black was added to 100 parts by weight of the obtained graphite-based mesophase pitch carbon particles, and 58% by weight of this mixed powder was added.
, VdF-HFP copolymer powder 17% by weight, DB
P25% by weight was mixed in acetone to prepare a paste. The obtained paste is applied on a PET film,
Sheeted. The obtained negative electrode sheet was disposed on both sides of a copper expanded metal, and subjected to hot roll pressing to produce a non-aqueous electrolyte-unimpregnated negative electrode. The copper expanded metal has a strip-shaped extension as a negative electrode terminal.

<Preparation of Electrolyte Layer>
3 parts by weight and 22.2% of VdF-HFP copolymer powder
Parts by weight and 44.5 parts by weight of DBP were mixed in acetone to form a paste. The obtained paste was applied on a PET film, formed into a sheet, and cut to form an electrolyte layer not impregnated with a non-aqueous electrolyte.

<Preparation of Nonaqueous Electrolyte> LiPF ₆ as an electrolyte was mixed with ethylene carbonate (EC) and dimethyl carbonate (DMC) in a nonaqueous solvent in a volume ratio of 2: 1 at a concentration of 1 mol / mol. 1 to prepare a non-aqueous electrolyte.

<Assembly of Battery> The obtained non-aqueous electrolyte impregnated positive electrode, negative electrode and electrolyte layer were laminated in the order of (positive electrode / electrolyte layer / negative electrode / electrolyte layer / positive electrode) and heated and pressed by a heated rigid roll. Then, a laminate was produced. Such a laminate was immersed in methanol and left with stirring with a magnetic stirrer to perform solvent extraction. This operation was repeated until the concentration of DBP in methanol became 20 ppm or less, thereby removing DBP from the laminate.

A positive electrode lead made of strip-shaped aluminum foil was connected to the positive electrode terminal of the positive electrode. Further, a negative electrode lead made of a strip-shaped copper foil was connected to the negative electrode terminal of the negative electrode.

Next, the laminate was immersed in the non-aqueous electrolyte. Laminate film (exterior material) consisting of thermoplastic resin layer / aluminum foil / resin layer
Then, the positive and negative electrode leads were coated so as to extend from the film, and the openings were heat-sealed to produce the polymer lithium secondary battery having the structure shown in FIG. 1 described above.

Example 2 A negative electrode not impregnated with a non-aqueous electrolyte was prepared as described above except that the mixing ratio of acetylene black was 4.0 parts by weight with respect to 100 parts by weight of graphite-based mesophase pitch carbon particles. A polymer lithium secondary battery was manufactured in the same manner as in Example 1.

Example 3 In the preparation of a negative electrode not impregnated with a non-aqueous electrolyte, the mixing ratio of acetylene black was adjusted to 10.0 with respect to 100 parts by weight of graphite-based mesophase pitch carbon particles.
A polymer lithium secondary battery was manufactured in the same manner as in Example 1 except that the amount was changed to parts by weight.

Example 4 In the preparation of a negative electrode not impregnated with a non-aqueous electrolyte, the mixing ratio of acetylene black was adjusted to 20.0 parts by weight per 100 parts by weight of graphite-based mesophase pitch carbon particles.
A polymer lithium secondary battery was manufactured in the same manner as in Example 1 except that the amount was changed to parts by weight.

Example 5 In the preparation of a negative electrode not impregnated with a non-aqueous electrolyte, the mixing ratio of acetylene black was 25.0 with respect to 100 parts by weight of graphite-based mesophase pitch carbon particles.
A polymer lithium secondary battery was manufactured in the same manner as in Example 1 except that the amount was changed to parts by weight.

Example 6 In the preparation of a negative electrode not impregnated with a non-aqueous electrolyte, a 50% particle size D ₅₀ was 4.0 μm instead of acetylene black, and the specific surface area by the BET method was 16.
Except for using flaky artificial graphite of 0 m ² / g,
A polymer lithium secondary battery was manufactured in the same manner as in Example 1 described above.

Example 7 A negative electrode not impregnated with a non-aqueous electrolyte was prepared except that the compounding ratio of flaky artificial graphite was 4.0 parts by weight per 100 parts by weight of graphite-based mesophase pitch carbon particles. A polymer lithium secondary battery was manufactured in the same manner as in Example 6 described above.

Example 8 In the preparation of a negative electrode not impregnated with a non-aqueous electrolyte, the mixing ratio of flaky artificial graphite was changed to 10.0 parts by weight with respect to 100 parts by weight of graphite-based mesophase pitch carbon particles. A polymer lithium secondary battery was manufactured in the same manner as in Example 6 described above.

Example 9 A negative electrode not impregnated with a non-aqueous electrolyte was prepared except that the blending ratio of flaky artificial graphite was 20.0 parts by weight per 100 parts by weight of graphite-based mesophase pitch carbon particles. A polymer lithium secondary battery was manufactured in the same manner as in Example 6 described above.

Example 10 A negative electrode not impregnated with a non-aqueous electrolyte was prepared except that the blending ratio of flaky artificial graphite was 25.0 parts by weight with respect to 100 parts by weight of graphite-based mesophase pitch carbon particles. A polymer lithium secondary battery was manufactured in the same manner as in Example 6 described above.

Example 11 A polymer lithium secondary battery was manufactured in the same manner as in Example 1 except that a negative electrode not impregnated with a nonaqueous electrolyte described below was used.

The same acetylene black as described in Example 1 was used for 100 parts by weight of the same graphite-based mesophase pitch carbon particles as described in Example 1 above.
0 parts by weight and 7.0 parts by weight of flaky artificial graphite similar to that described in Example 6 described above were added.
Wt% and VdF-HFP copolymer powder 17 wt%
And 25% by weight of DBP were mixed in acetone to prepare a paste. The obtained paste was applied on a PET film to form a sheet. The obtained negative electrode sheet was disposed on both sides of a copper expanded metal, and subjected to hot roll pressing to produce a non-aqueous electrolyte-unimpregnated negative electrode. In addition,
The copper expanded metal has a strip-shaped extension as a negative electrode terminal.

Comparative Example A polymer lithium secondary battery was manufactured in the same manner as in Example 1 except that a negative electrode not impregnated with a nonaqueous electrolyte described below was used.

The same graphite-based mesophase pitch carbon particles as described in Example 1 were used at 58% by weight and VdF
A paste was prepared by mixing 17% by weight of -HFP copolymer powder and 25% by weight of DBP in acetone. The obtained paste was applied on a PET film to form a sheet. The obtained negative electrode sheet was disposed on both sides of a copper expanded metal, and subjected to hot roll pressing to produce a non-aqueous electrolyte-unimpregnated negative electrode. The copper expanded metal has a strip-shaped extension as a negative electrode terminal.

With respect to the obtained secondary batteries of Examples 1 to 11 and Comparative Example, constant-current constant-voltage charging was performed at 0.5 C at a charge end voltage of 4.2 V, and at 0.5 C, the discharge end voltage was reduced. A charge / discharge cycle for performing a constant current discharge of 2.8 V is performed for 300 cycles, the discharge capacity at the first cycle and the 300th cycle is measured, and a capacity retention ratio at the 300th cycle with respect to the first cycle is calculated. It is shown in FIG.

[0068]

[Table 1]

As is clear from Table 1, the 50% particle size D ₅₀
Is 10 to 30 μm, and the specific surface area is 0.5 to 2.5 m
² / g of graphite-based mesophase pitch carbon particles and carbon black and / or lithium ions, having a 50% particle size D ₅₀ of 2.0 to 25 μm and a specific surface area of 0.5 to 20. It can be seen that the secondary batteries of Examples 1 to 11 including the negative electrode containing the graphite-based granular carbon material of 0 m ² / g have a high initial capacity and can improve the capacity retention after 300 cycles.

On the other hand, in the secondary battery of the comparative example provided with the negative electrode using only the graphite-based mesophase pitch carbon particles satisfying the above-mentioned specific conditions as the active material, the initial capacity and the capacity retention rate after 300 cycles were different from those of the embodiment. It turns out that it is inferior compared with the secondary batteries of Nos. 1-11.

In the above-described embodiment, a polymer lithium secondary battery having a unit cell having a five-layer structure in which a positive electrode, an electrolyte layer, a negative electrode, an electrolyte layer, and a positive electrode are stacked in this order has been described. Is not limited to such a five-layer structure. For example, a positive electrode, a negative electrode, and an electrolyte layer may be used one by one to form a three-layer structure.

[0072]

As described above, according to the present invention, it is possible to provide a high-capacity, long-life polymer lithium secondary battery having a negative electrode efficiently filled with an active material.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a polymer lithium secondary battery according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Positive electrode, 2 ... Negative electrode, 3 ... Electrolyte layer, 4 ... Positive electrode collector, 5 ... Positive electrode layer, 6 ... Negative electrode current collector, 7 ... Negative electrode layer, 11 ... Exterior film.

Continued on the front page F-term (reference) 5H003 AA02 AA04 BB01 BC01 BC06 BD02 BD05 5H014 AA01 EE08 HH01 HH06 5H029 AJ03 AJ05 AK03 AK05 AL06 AL08 AM03 AM04 AM05 AM07 AM16 BJ04 DJ17 EJ12 HJ05 HJ07

Claims (1)

[Claims] 1. 50% absorbing and releasing lithium ions
In the particle diameter D ₅₀ of 10 to 30 [mu] m, and a specific surface area of 0.5
It absorbs and releases graphite-based mesophase pitch carbon particles of 2.5 m ² / g and carbon black and / or lithium ions, and has a 50% particle size D ₅₀ of 2.0 to 25 μm,
And a graphite-based granular carbon material having a specific surface area of 0.5 to 20.0 m ² / g.