JP2003203636A - Conductive assistant for non-aqueous electrolyte secondary battery positive electrode and positive pole plate using the same, and non-aqueous secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-aqueous electrolyte secondary battery that is superior in charging and discharging cycle characteristics and storage characteristics by improving the positive electrode conductive assistant of the non-aqueous electrolyte secondary battery. <P>SOLUTION: As a conductive assistant for a positive electrode pole plate, expanded graphite having the DBP absorption quantity of 200 ml/100 g or more and 500 ml/100 g or less is used, thereby, the active material, the conductive assistant, and the binder are uniformly dispersed, thus adhesion is improved and uniform reaction is carried out. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a conductive agent for a positive electrode of a non-aqueous electrolyte secondary battery, a positive electrode plate and a non-aqueous electrolyte secondary battery using the same, and particularly excellent in charge / discharge cycle characteristics and storage characteristics. And a non-aqueous electrolyte secondary battery.

[0002]

2. Description of the Related Art In recent years, the performance of mobile electronic devices such as mobile phones and personal digital assistants largely depends not only on the performance of semiconductor elements and electronic circuits, but also on the performance of rechargeable secondary batteries. It is desired that the capacity of the secondary battery to be mounted be increased and that the weight and size be reduced at the same time.
As a secondary battery that meets these demands, a nickel-hydrogen storage battery having an energy density about twice that of a nickel-cadmium storage battery has been developed, and a lithium-ion battery having a higher energy density than that has been developed and has become the mainstream.

In this lithium ion battery, an electrode plate group in which a positive electrode and a negative electrode are spirally wound or laminated via a separator is housed in a battery case, a nonaqueous electrolytic solution is injected, and caulking sealing or laser sealing is performed. It is configured by The battery electrode plate used in this battery is generally rolled after applying an active material (a positive electrode active material or a negative electrode active material), a conductive agent, a binder (binder), etc. to a current collector, drying the same. It is manufactured by slitting a product into a predetermined size and shape.

More specifically, as a method for producing a battery electrode plate, a paste prepared by kneading and dispersing an active material and a binder in a solvent is applied to one side or both sides of a current collector, dried and rolled. , A method of manufacturing an electrode plate is adopted.

In order to obtain a non-aqueous electrolyte secondary battery having excellent charge / discharge cycle characteristics and storage characteristics, carbon black and graphite having a specific surface area and a DBP absorption amount defined as conductive agents constituting the positive electrode plate. The combined use method (Japanese Patent Laid-Open No. 62-213863), the method using carbon black whose particle size, DBP absorption amount and specific surface area are specified (Japanese Laid-Open Patent Publication No. 9-213309), the DBP absorption amount and the iodine adsorption amount A method using the specified carbon black (Japanese Patent Laid-Open No. 2001-110424) has been proposed.

[0006]

With these carbon blacks, it is possible to recognize improvements in the conductivity of the positive electrode plate. However, since carbon black has a structure structure, it is difficult to uniformly disperse the positive electrode active material and the binder in a paste state, and the paste is solidified during storage, resulting in solid-liquid separation or sedimentation. As a result, after coating and drying, segregation of the active material, the conductive agent, and the binder causes insufficient adhesion to the current collector and nonuniformity of the reaction. When the discharge cycle is performed, there is a problem that the active material is peeled off from the current collector and is dropped off, and the battery capacity is reduced.

Further, graphite is excellent in the conductivity in the crystal plane direction but inferior in the conductivity in the c-axis direction, so that the capacity of the positive electrode is reduced.

Therefore, a proposal of using expanded graphite as a conductive agent for the positive electrode is disclosed in JP-A-10-188993 and JP-A-2.
000-12023, etc.
The P absorption amount is not described.

[0009]

The present invention is intended to solve the above-mentioned problems and provides JIS K6 as a conductive agent for a positive electrode.
Non-aqueous electrolyte secondary battery positive electrode using expanded graphite having a DBP absorption amount of 200 ml / 100 g or more and 500 ml / 100 g or less as measured by the A method defined in 217 (Testing method for basic performance of carbon black for rubber) It is a conductive agent.

Then, a non-aqueous electrolyte solution comprising at least this positive electrode active material containing a conductive material and a lithium-containing metal oxide as a main component, a positive electrode plate made of a binder, a negative electrode plate, a separator and a non-aqueous electrolyte solution. It is the next battery.

As a conductive agent for the positive electrode, the DBP absorption amount is 20.
By using the expanded graphite in an amount of 0 ml / 100 g or more and 500 ml / 100 g or less, the expanded graphite has a shape that is difficult to be oriented by the expansion treatment, so that the dispersibility is improved during kneading and dispersion, and the inside of the electrode plate is improved. It becomes a random shape, shows uniform and high conductivity without being influenced by conductivity in the c-axis direction like graphite, and improves charge / discharge cycle characteristics and storage characteristics.

Further, since it does not have a structure structure like carbon black, aggregation with the positive electrode active material and the binder is unlikely to occur. Therefore, since the active material, the conductive agent and the binder are uniformly dispersed in the electrode plate, the adhesion with the current collector is improved, and the uniform reaction proceeds, so that the deterioration of the battery capacity is reduced. You can

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of a cylindrical lithium secondary battery according to an embodiment of the present invention.

As shown in FIG. 1, an electrode plate group in which a positive electrode plate 5 and a negative electrode plate 6 are spirally wound with a separator 7 interposed is housed in a battery case 8 having a cylindrical shape with a bottom. The negative electrode lead 9 connected to the negative electrode plate 6 is electrically connected to the case 8 via the lower insulating plate 10, and the positive electrode lead 3 connected to the positive electrode plate 5 is connected via the upper insulating plate 4 to the sealing plate 1.
Is electrically connected to the internal terminal of the battery, a nonaqueous electrolytic solution (not shown) is injected, and the sealing plate 1 and the battery case 8 are caulked and sealed by the insulating gasket 2.

The positive electrode plate 5 comprises a positive electrode active material, a binder, a conductive agent and, if necessary, a thickening agent on one or both sides of a current collector made of an aluminum foil or a foil subjected to lath processing or etching treatment. Can be prepared by coating, drying and rolling a paste prepared by kneading and dispersing in a solvent. The thickness of the positive electrode plate needs to be wound as faithfully as possible to its shape using a winding core, and is preferably 130 μm to 200 μm thick and flexible.

As the positive electrode active material, for example, a lithium-containing transition metal compound capable of accepting lithium ions as a guest is used. For example, a composite metal oxide of at least one metal selected from cobalt, manganese, nickel, chromium, iron and vanadium and lithium, L
iCoO ₂ , LiMnO ₂ , LiNiO ₂ , LiCo _x Ni
_(1-x) O ₂ (0 <x <1), LiCrO ₂ , αLiFe
O ₂ , LiVO _{2 and the} like are preferable.

The binder is not particularly limited as long as it is a material that is stable with respect to the solvent and electrolytic solution used. Specific examples thereof include polyvinylidene fluoride (PVDF), copolymer of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) (P (VDF-HFP)), polytetrafluoroethylene, styrene-butadiene rubber,
Examples thereof include isopropylene rubber, butadiene rubber, ethylene propylene diethane polymer and the like.

Examples of the thickener include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch and casein.

The conductive agent has a DBP absorption of 200 m.
Expanded graphite of 1/100 g or more and 500 ml / 100 g or less is used. Expanded graphite has a shape that does not easily orient due to the expansion treatment, so the dispersibility is improved during kneading and dispersion, and it becomes a random shape inside the electrode plate. As a result, a non-aqueous electrolyte secondary battery excellent in charge / discharge cycle characteristics and storage characteristics can be obtained because it shows uniform and high conductivity.

By the way, the absorbed amount of expanded graphite is 200 m.
When it is less than 1 / g, the conductivity is insufficient and the charge / discharge cycle characteristics are not good. Conversely, if the amount of absorption becomes too large, cracks will occur. This is because expansion proceeds excessively and the volume of the conductive agent increases, making the expanded graphite brittle, and the progress of pulverization due to agitation during paste production and shear stress during rolling. Conceivable. Considering the stabilization of the manufacturing process, the DBP absorption amount is 200 to 400.
The range of ml / 100g is more preferable.

As the solvent, a solvent capable of dissolving the binder is suitable, and in the case of an organic binder, N-methyl-2-pyrrolidone (NMP), N, N-dimethylformamide, tetrahydrofuran, dimethylacetamide. , Dimethylsulfoxide, hexamethylsulfolamide, tetramethylurea, acetone, methylethylketone, and other organic solvents are preferably used alone or mixed, and in the case of an aqueous binder, water or warm water is preferable.

The negative electrode plate 6 is prepared by applying, drying, and rolling a paste prepared by kneading and dispersing a negative electrode active material, a binder, and optionally a conductive agent in a solvent on one side or both sides of the current collector. be able to. Then, the thickness of the negative electrode plate 6 needs to be wound as faithfully as possible to its shape by using a winding core,
Similar to the positive electrode plate 5, it is preferable that the thickness is 140 μm to 210 μm and that it is flexible.

The copper or copper alloy used as the negative electrode current collector is not particularly limited, and examples thereof include rolled foil, electrolytic foil, and the like, and the shapes thereof include foil, perforated foil, expanded material, lath material and the like. It doesn't matter.

Further, the stronger the tensile strength is, the more preferable the thickness of copper is, but if the thickness is thicker, the void volume inside the battery decreases and the energy density decreases, so 20 μm or less is preferable, and the range of 8 to 15 μm is optimum.

As the negative electrode active material, for example, a material containing graphite having a graphite type crystal structure capable of absorbing and desorbing lithium ions, such as natural graphite or artificial graphite is used. In particular, it is preferable to use a carbon material having a graphite type crystal structure in which the lattice spacing (d ₀₀₂ ) of the lattice plane (002) is 3.350 to 3.400 Å.

As the binder, the solvent, and the conductive agent and plasticizer which can be added if necessary, the same ones as those for the positive electrode can be used.

The separator 7 has a thickness of 10 to 30 μm.
m is preferably a microporous polyolefin resin such as polyethylene resin or polypropylene resin.

The non-aqueous electrolytic solution comprises a non-aqueous solvent and an electrolyte, and the non-aqueous solvent contains a cyclic carbonate and a chain carbonate as main components. As the cyclic carbonate, ethylene carbonate (EC),
It is preferably at least one selected from propylene carbonate (PC) and butylene carbonate (BC). Further, as the chain carbonate,
Dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EM
It is preferably at least one selected from C) and the like.

As the electrolyte, for example, a lithium salt having a strong electron-withdrawing property is used, and for example, LiPF ₆ or LiB is used.
F ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , L
iN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , Li
C (SO ₂ CF _{3) 3} and the like. These electrolytes may be used alone or in combination of two or more. These electrolytes are preferably dissolved in the non-aqueous solvent at a concentration of 0.5 to 1.5M.

[0031]

The present invention will be described in detail below with reference to examples and comparative examples, but these do not limit the present invention in any way.

Example 1 First, as a positive electrode active material, Li was used.
50 parts by weight of CoO ₂ powder, 1.0 part by weight of expanded graphite having a DBP absorption of 400 ml / 100 g as a conductive agent,
As a binder, 0.75 part by weight of PVDF was added to NMP98.
200 parts by weight of a solution dissolved in 25 parts by weight was mixed, kneaded and dispersed to obtain a positive electrode paste.

The obtained positive electrode paste was applied onto both sides of an aluminum foil having a thickness of 20 μm using a die coater, dried, rolled, and cut to produce a positive electrode plate 5 having a thickness of 0.18 mm, and the positive electrode plate 1 of Example was prepared. did.

Example 2 A positive electrode plate 5 prepared in the same manner as in Example 1 except that expanded graphite having a DBP absorption amount of 200 ml / 100 g was used as a conductive agent was used as an example positive electrode plate 2.

Example 3 A positive electrode plate 5 produced in the same manner as in Example 1 except that expanded graphite having a DBP absorption of 500 ml / 100 g was used as a conductive agent was used as an example positive electrode plate 3.

Comparative Example 1 A positive electrode plate 5 prepared in the same manner as in Example 1 except that carbon black having a DBP absorption of 400 ml / 100 g was used as a conductive agent was used as a comparative positive electrode plate 1.

Comparative Example 2 A positive electrode plate 5 was prepared in the same manner as in Example 1 except that graphite having a DBP absorption of 400 ml / 100 g was used as a conductive agent.

Comparative Example 3 A positive electrode plate 5 prepared in the same manner as in Example 1 except that expanded graphite having a DBP absorption amount of 150 ml / 100 g was used as a conductive agent was used as a comparative positive electrode plate 3.

Comparative Example 4 A positive electrode plate 5 prepared in the same manner as in Example 1 except that expanded graphite having a DBP absorption of 600 ml / 100 g was used as a conductive agent was used as a comparative positive electrode plate 4.

The positive electrode plates 1 to 1 obtained in this way
The surface states of the positive electrode plates 3 of the example positive electrode plate 3 and the comparative positive electrode plate 1 to the comparative positive electrode plate 4 were confirmed. For confirmation of the surface state, the number of aggregates and cracks and pinholes of 1 mm or more existing on the surface of the positive electrode plate of 1000 cm ² were visually counted, and the results are shown in Table 1.

[0041]

[Table 1]

From the results shown in Table 1, when carbon black was used as the conductive agent, the dispersion was insufficient and agglomerates were generated. Further, when graphite was used as a conductive agent, it was easy to be oriented, and thus cracks were generated. Also, with respect to the expanded graphite, when the absorption amount was small, the charge-discharge cycle characteristics were poor, and conversely, when it was too large, cracks occurred. This is because expansion proceeds excessively and the volume of the conductive agent increases, making the expanded graphite brittle, and the progress of pulverization due to agitation during paste production and shear stress during rolling. Conceivable. Considering the stabilization of the manufacturing process, it was revealed that the DBP absorption amount is more preferably in the range of 200 to 400 ml / 100 g.

Next, flake graphite powder 5 was used as the negative electrode active material.
0 parts by weight, 5 parts by weight of styrene-butadiene rubber as a binder, and 23 parts by weight of a thickener prepared by dissolving 1 part by weight of carboxymethyl cellulose in 99 parts by weight of water as a thickener were kneaded and dispersed to obtain a paste for negative electrode. . The obtained negative electrode paste was applied onto both surfaces of a negative electrode current collector made of copper foil having a thickness of 12 μm using a die coater, dried, rolled, and cut to prepare a negative electrode plate 6 having a thickness of 0.20 mm.

The positive electrode plate 1 to the positive electrode plate 3 of the above-described example, the positive electrode plate 5 of the comparative example positive electrode plate 1 to the comparative example positive electrode plate 4 and the negative electrode plate 6 are spirally wound while being insulated from each other through the separator 7. The rotated electrode plate group was deep-drawn from a non-aqueous electrolyte resistant stainless steel plate, housed in the battery case 8, and the non-aqueous electrolyte solution was injected.
As the non-aqueous electrolyte, 30 vol of ethylene carbonate
%, 50% by volume of diethyl carbonate and 20% by volume of methyl propionate, LiPF ₆ was dissolved as an electrolyte in a concentration of 1 mol / liter as an electrolyte. The nonaqueous electrolytic solution is impregnated into the positive electrode active material layer and the negative electrode active material layer, and plays a role of transferring Li ions between the positive electrode plate 5 and the negative electrode plate 6 through the minute holes of the separator in the battery reaction.

Then, a sealing plate 1 is arranged above the opening of the battery case 8 and caulked and sealed with an insulating gasket 2, and a cylindrical non-aqueous liquid having a diameter of 17 mm and a height of 50 mm and a battery capacity of 780 mAh. Making an electrolyte secondary battery,
Example battery 1 to example battery 3 and comparative example battery 1 to comparative example battery 4 corresponding to example positive electrode plate 1 to example positive electrode plate 3 and comparative example positive electrode plate 1 to comparative example positive electrode plate 4, respectively.

Charge / discharge cycle characteristics and storage characteristics of these batteries were evaluated. 1 charge / discharge cycle characteristic
In the environment of 20 ° C using 0 batteries, constant current charging of 550mA (0.7CmA) was performed until the battery voltage reached 4.2V, and then the current value further attenuated to 40m.
780m after charging to A (0.05CmA)
The evaluation was performed by repeating the charge / discharge cycle under the charge / discharge conditions of discharging to a discharge end voltage of 3.0 V with a constant current of A (1 CmA). At this time, the battery capacity in the third cycle was taken as the initial capacity, and the number of cycles until the battery capacity decreased to 80% of the initial capacity was measured. Table 2 shows the results of the average value of the number of charge / discharge cycles.

The storage characteristics were 20 ° C. using 20 batteries each.
In this environment, the battery capacity was measured under the above-mentioned charge and discharge conditions, and then the battery capacity was measured again after storing the battery in a charged state for 20 days in an environment of 60 ° C. From the obtained battery capacity before and after storage, the storage recoverability was determined according to the following formula. (Storage recoverability (%) = ((capacity after storage) / (initial capacity)) × 100). Table 2 shows the result of the average value of the storage recoverability.

[0048]

[Table 2]

From the results of Table 2, the batteries of Example battery 1 to Example battery 3 were less charged than the batteries of Comparative example battery 1 to Comparative example battery 4 even if the charge / discharge cycle was repeated, and the battery capacity was less deteriorated. It was found that the discharge cycle characteristics were excellent.

In each of the batteries of the examples, as a conductive agent, the DBP absorption amount was 200 ml / 100 g or more, 500 ml / 100.
Since expanded graphite of g is used, it has a shape that is less likely to be oriented than graphite, so the dispersibility in the paste during kneading and dispersion is good, and the adhesion with the current collector is improved. It is considered that the battery capacity is less deteriorated because it exhibits uniform and high conductivity without being influenced by the conductivity in the direction.

Further, from the results of Table 2, it was revealed that the batteries of Examples were less in capacity deterioration and excellent in capacity recovery even in high temperature storage than the batteries of Comparative Examples.

[0052]

As described above, according to the present invention, since the active material, the conductive agent and the binder are uniformly dispersed, the adhesiveness with the current collector is excellent and the uniform reaction proceeds. A non-aqueous electrolyte secondary battery having excellent charge / discharge cycle characteristics and storage characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a lithium secondary battery according to an embodiment of the present invention.

[Explanation of symbols]

1 Seal plate 2 Insulation gasket 3 Positive lead 4 Upper insulating plate 5 Positive plate 6 Negative plate 7 separator 8 battery case 9 Negative electrode lead 10 Lower insulation plate

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Akira Matsuo             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. (72) Inventor Sumito Ishida             1006 Kadoma, Kadoma-shi, Osaka Matsushita Electric             Sangyo Co., Ltd. F-term (reference) 5H029 AJ04 AJ05 AK03 AL07 AM03                       AM07 BJ02 BJ14 CJ08 DJ08                       DJ16 EJ04 HJ07                 5H050 AA07 AA10 BA17 CA08 CA09                       CB08 DA02 DA10 EA09 FA05                       FA17 GA10 HA00 HA07

Claims (3)

[Claims] 1. A conductive material for a positive electrode according to JIS K621.
The DBP absorption amount measured by the A method specified in 7 (Testing method for basic performance of carbon black for rubber) is 20.
A conductive agent for a positive electrode of a non-aqueous electrolyte secondary battery, characterized by using expanded graphite of 0 ml / 100 g or more and 500 ml / 100 g or less. 2. A positive electrode plate comprising at least the conductive agent according to claim 1, a positive electrode active material containing a lithium-containing metal oxide as a main component, and a binder. 3. A non-aqueous electrolyte secondary battery comprising the positive electrode plate, the negative electrode plate, the separator and the non-aqueous electrolytic solution according to claim 2.