JP2007095534A - Method of manufacturing nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve a positive electrode plate for nonaqueous electrolyte secondary battery which has high capacitance (highly filled) and high electron conductivity, and is strong by solving the problem that high efficient charging/discharging characteristics and cycle characteristics decrease when a conductive agent and a binder are reduced for high capacity of battery, in the case of manufacturing the positive electrode plate by a conventional method. <P>SOLUTION: In the nonaqueous electrolyte secondary battery, particularly in a manufacturing method of the positive plate, when kneading, to uniform the dispersion of the conductive agent and the binder, a positive electrode active material where DBP absorbed amount is below 20 ml/100 g is used. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a non-aqueous electrolyte secondary battery, and particularly relates to a method for producing a positive electrode plate using a positive electrode active material suitable as a raw material.

  The shape of the lithium ion secondary battery includes a cylindrical shape and a rectangular shape. In both cases, the positive electrode and the negative electrode are inserted through a separator, the wound electrode group is inserted into a battery can, and an organic electrolyte is injected and sealed. It has a structure.

As the positive electrode active material, lithium cobalt composite oxide (LiCoO ₂ , LiCo _1-xy Mg _x Al _y O ₂ ), lithium nickel composite oxide (LiNiO ₂ , LiNi _1-x Co _x O ₂ , LiNi _1-xy Co _{x Al y O 2, LiNi 1} -xy Co x Mn y O 2), lithium manganese composite oxide _{(LiMn 2 O 4, LiMn 2} -x Cr x O 4, LiMn 2-x Al x O 4, LiMn 2- _x Ni _x O ₄ ), lithium-titanium composite oxide (Li ₄ Ti ₅ O ₁₂ ), or a mixture of several combinations of the positive electrode active materials is used. As the negative electrode active material, lithium ions such as coke and graphite are used. Carbon materials that can be adsorbed and desorbed are used.

  These positive electrode active materials or negative electrode active materials include, for example, polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE) as a binder and, if necessary, a conductive agent such as acetylene black or graphite and a solvent. , Agitated and mixed, and the paste is applied to a metal foil such as aluminum or copper, dried, rolled, cut into a predetermined size and formed into a sheet, and the lithium ion secondary battery electrode To do.

  As a means for achieving a higher capacity of the lithium ion secondary battery, a method of reducing the content of a conductive agent and a binder that do not contribute to the battery reaction and filling the battery with more active material is effective. .

  However, considering the increase in the density of the positive electrode, the decrease in the conductive agent reduces the electron conductivity between the particles and deteriorates the discharge characteristics under heavy load conditions. Further, the binding force between the particles becomes weak due to the decrease in the binder. When charging / discharging is repeated in such a state, the contact between the positive electrode active material and the conductive agent is deteriorated due to expansion and contraction of the crystal lattice, leading to a decrease in battery capacity.

  For this reason, for example, Patent Document 1 proposes a method of optimizing the particle diameter of the positive electrode active material, and Patent Document 2 proposes a method of adding a different element to the positive electrode active material and dissolving it.

As described above, it has been difficult for the conventionally proposed methods to satisfy the high-efficiency discharge characteristics and the cycle characteristics while achieving an increase in battery capacity.
Japanese Patent Laid-Open No. 5-151988 JP 63-121258 A

  However, in the method of optimizing the particle diameter of the positive electrode active material as in Patent Document 1, although the cycle characteristics are improved, the high-efficiency discharge characteristics tend to be lowered. In order to improve the high-efficiency charge / discharge characteristics, it is necessary to reduce the particle diameter, thereby impairing the filling property of the positive electrode active material, and there is a concern about a decrease in battery capacity.

  Further, in the method of adding a different element to the positive electrode active material as in Patent Document 2 and solid-dissolving it, it is possible to suppress the expansion and contraction of the crystallite accompanying charge / discharge, but the discharge characteristics of the positive electrode active material are impaired. Therefore, there is a problem that the capacity of the battery is reduced.

  The present invention solves the above-mentioned problems, and by improving the manufacturing method of the positive electrode, it achieves high battery capacity while exhibiting high-efficiency charge / discharge characteristics and good cycle characteristics. An object is to provide a nonaqueous electrolyte secondary battery.

As a result of intensive studies to achieve the above object, the present inventor has an average particle diameter of 5 to 20 μm, a specific surface area of 0.2 to 2.0 m ² / g, and a DBP absorption of less than 20 ml / 100 g. By using a certain lithium-containing composite oxide as the positive electrode active material, carbon black as a conductive agent and a binder in the paste are uniformly dispersed during kneading, resulting in high electronic conductivity and extreme polarity. It was found that it has plate retention.

  At this time, it is preferable that the conductive agent is 0.5 to 5.0% by weight with respect to 100% by weight of the positive electrode active material, and the binder is 1.0 to 10.0% by weight.

  According to the present invention, by using a positive electrode active material having a small DBP absorption amount and appropriate physical properties, it is possible to produce a positive electrode plate for a non-aqueous electrolyte secondary battery with high electron conductivity and strength. Therefore, even with a small amount of a conductive agent and a binder, a high capacity (high filling) of the battery is realized while maintaining excellent high-efficiency charge / discharge characteristics and cycle life characteristics.

  First, the particle form and aggregate structure of the positive electrode active material of the present invention will be described. The positive electrode active material is composed of at least one of lithium cobalt composite oxide, lithium nickel composite oxide, lithium manganese composite oxide, and lithium titanium composite oxide. As the particle form and aggregate structure of these positive electrode active materials, spherical or sphere-like aggregates (secondary particles) in which fine spherical or flake shaped basic particles (primary particles) are closely connected are exhibited. Furthermore, the aggregates (secondary particles) are irregularly stacked to form a larger aggregated structure (tertiary particles).

  When a positive electrode active material having such a structure is kneaded by adding a conductive agent, a binder, and a dispersion medium, a portion and particles where the conductive agent, the binder, and the dispersion material exist between the positive electrode active material particles It is divided into the part that penetrates the inner hole.

  When the paste is applied to an aluminum foil and dried to produce a positive electrode plate, the conductive agent and the binder form a network between the particles of the positive electrode active material, and have electronic conductivity and binding properties.

  However, since the conductive agent and the binder encapsulated in the particles are in a functionally deactivated state, in order to improve battery characteristics, the aggregated structure (tertiary particles) and the aggregate (secondary) Particle) should be saved.

  Powder physical properties are also greatly involved in battery characteristics. If the particle size is minimized, the filling capacity of the positive electrode active material is lowered, and it is necessary to increase the conductive agent and the binder for maintaining the electron conductivity and the binding property, which may impair the battery capacity. There is. On the other hand, when the particle size is increased, if the ionic conductivity is deteriorated or the specific surface area is remarkably reduced, the effective reaction area with the electrolytic solution is reduced, and good high-efficiency charge / discharge characteristics cannot be obtained.

  From the above viewpoint, it is important to control both the powder physical properties and the aggregation structure of the positive electrode active material in order to improve battery characteristics.

    In order to control the powder physical properties of the positive electrode active material, it is necessary to change the basic structure and characteristics depending on the manufacturing conditions of the positive electrode active material, that is, the type and composition of raw materials, and the firing conditions.

  For example, when the heat treatment temperature at the time of synthesizing the positive electrode active material is increased, crystallization is promoted and sintering proceeds, cracks inside the particles disappear, and increase in the particle size and density of the positive electrode active material are promoted.

However, if the heat treatment temperature is increased too much, decomposition of the positive electrode active material and oxygen release occur, the crystal structure collapses, and the charge / discharge capacity decreases, so it is necessary to adjust to an appropriate heat treatment temperature. Also,
If the specific surface area of the positive electrode active material is significantly reduced, the effective reaction area with the electrolytic solution is reduced, and good high-efficiency charge / discharge characteristics cannot be obtained.

  The aggregate of the positive electrode active material can be controlled by mechanical pulverization and classification.

  In order to indicate the size of the aggregate structure of the positive electrode active material, DBP (dibutyl phthalate) absorption defined in JIS K-6217-4 “Carbon black for rubber—Basic characteristics—Part 4: Determination of DBP absorption” The quantity A method (mechanical method) was applied.

  It is expressed as an absorption amount based on the amount of oil that finely packs the aggregated particles of the positive electrode active material and replaces the voids. Here, an absorption meter is used, and the liquid absorption per 100 g obtained from 70% of the maximum torque when DBP (dibutyl phthalate) is added to carbon black is defined as the DBP absorption.

As a result of repeated studies by the present inventor, it is necessary to adjust the average particle diameter of the positive electrode active material in a range of 5 to ²⁰ μm and a specific surface area of 0.2 to 2.0 m ² / g.

  Further, when the DBP absorption amount of the positive electrode active material is less than 20 ml / 100 g at the time of kneading, the conductive agent and the binder are sufficiently diffused by the dispersion medium, and the high-efficiency discharge characteristics and cycle characteristics are improved.

  As the conductive agent, carbon black such as acetylene black or graphite is used, and the addition amount is preferably 0.5 to 5.0% by weight, more preferably 1.0 to 4.4% with respect to 100% by weight of the positive electrode active material. 0% by weight. If the amount of carbon black added is too small, the conductive performance may not be exhibited. On the other hand, if the amount is too large, most of the dispersion medium is absorbed by the carbon black, the fluidity is lost, and the handling property may be extremely difficult.

The dispersion medium is mainly determined by the water resistance of the positive electrode active material. For example, since lithium cobaltate (LiCoO ₂₎ has high water resistance, it can be used with either an organic solvent or water. Lithium nickelate (LiNiO ₂ ) mainly uses an organic solvent such as N-methyl-2-pyrrolidone (NMP) because lithium elutes from the inside of the crystal when touched with water and the crystal structure is destroyed.

  When water is used as the dispersion medium, it is preferable to use a dispersant. This dispersant improves the wettability between the positive electrode active material and carbon black, which is a conductive agent, and water, facilitates dispersion, increases the viscosity of the system, and maintains the paste storage stability. It is what you have.

Examples of the dispersant include cellulose polymers such as carboxymethyl cellulose (CMC) and hydroxyethyl cellulose, acrylic polymers such as sodium polyacrylate, and the like, either alone or in combination of two. Can be used. Of these, cellulosic polymers are preferred.

  As the binder, polyvinylidene fluoride or modified acrylic rubber is used if an organic solvent is used as the dispersion medium, and polytetrafluoroethylene (PTFE) is used if water is used.

The addition amount is preferably 1.0 to 10.0% by weight, more preferably 2.0 to 5.0% by weight, based on 100% by weight of the positive electrode active material. If the amount is less than 1.0% by weight, the binding force is weak, and if it exceeds 10.0% by weight, the movement of Li ions is inhibited, and the performance as a battery is deteriorated. The paste thus obtained is used as a current collector. The desired positive electrode can be produced by coating on an aluminum foil and performing processes such as rolling and cutting.

  Next, an embodiment in which the positive electrode of the present invention is used for a nonaqueous electrolyte secondary battery will be described with reference to the drawings.

In FIG. 1, a positive electrode plate 5 and a negative electrode plate 6 which are positive electrodes of the present invention are spirally wound through a separator 7 made of a polyethylene microporous film to form an electrode plate group 4. The electrode plate group 4 is housed in a battery case 1 in which an organic electrolyte resistant stainless steel plate is processed. Thereafter, a non-aqueous electrolyte solution prepared by dissolving LiPF _{6 in} a mixed solvent of ethylene carbonate and ethyl methyl carbonate at a volume ratio of 1: 1 to a concentration of 1.5 mol / liter is injected into the electrode plate group 4, and the safety valve The battery is sealed through the gasket 3 by the sealing plate 2 provided with the above. A positive electrode lead 5 a is drawn from the positive electrode plate 5 and connected to the sealing plate 2, and a negative electrode lead 6 a is drawn from the negative electrode plate 6 and connected to the bottom of the battery case 1. Insulating rings 8 are provided on the upper and lower portions of the electrode plate group 4, respectively.

  The negative electrode plate 6 was prepared by mixing 95% by weight of artificial graphite powder with 5% by weight of styrene butadiene rubber as a binder, and suspending these in an aqueous carboxymethyl cellulose (CMC) solution to form a paste. It is applied to both sides of a 15 μm thick copper foil, dried and rolled. In addition to artificial graphite, carbon materials such as natural graphite and non-graphitizable carbon, metal oxides such as SiSnO, metal nitrides, silicides, Sn alloys and the like can be used as long as they can occlude and release lithium ions.

  Examples of the present invention will be described in detail below. The present invention is not limited to these examples.

The composition formula LiNi _0.33 Co _0.33 Mn _0.33 O ₂ was used as the positive electrode active material.
As a manufacturing method, Li ₂ CO ₃ and Ni _0.33 Mn _0.33 Co _0.33 (OH) ₂ having an average particle diameter of 2 μm, 5 μm, 10 μm, and 20 μm are _{mixed in} a molar ratio of lithium to metal (total amount of nickel, manganese, and cobalt). Each was mixed to 1: 1, calcined in an air atmosphere at a firing temperature of 600 ° C. for 5 hours, and then fired in an air atmosphere at a firing temperature of 800 ° C., 900 ° C., 1000 ° C., and 1050 ° C. for 10 hours each. As a result, a composite was obtained.

  The resulting composite was pulverized by changing the shear force and compressive force applied to the aggregates with a supermass colloider manufactured by Masuko Sangyo Co., Ltd. or a PJM jet mill manufactured by Nippon Pneumatic Industry Co., Ltd. The materials were classified under various conditions using an MDS-1 airflow classifier manufactured by Nippon Pneumatic Co., Ltd., and used as positive electrode active materials 1 to 15 used in this example.

  Table 1 shows the DBP absorption amount, average particle diameter, and specific surface area of the positive electrode active materials 1 to 15.

Example 1
A positive electrode plate and a battery were prepared using the positive electrode active material 1. That is, 1% by weight of acetylene black as a conductive agent and 2% by weight of polyvinylidene fluoride (PVDF) resin as a binder are weighed with respect to 100% by weight of the positive electrode active material, and a predetermined amount of N-2-methylpyrrolidone ( NMP) and mixed with stirring to obtain a positive electrode paste. And the aluminum foil of thickness 20 micrometers was made into the electrical power collector, the said positive electrode paste was apply | coated on both surfaces, it dried and rolled using the rolling roller, it cut | judged to the predetermined dimension, and it was set as the positive electrode plate.

  Using this positive electrode plate, a cylindrical nonaqueous electrolyte secondary battery having a diameter of 18 mm, a height of 65 mm, and a nominal capacity of 2000 mAh was produced by the method described above. This manufactured battery is referred to as battery 1.

(Examples 2 to 5)
A battery was produced under the same conditions as in Example 1 except that the positive electrode active materials 2 to 5 were used. The produced batteries are designated as batteries 2-5.

(Example 6)
A positive electrode active material 4 was used, PVDF was 5 wt% as a binder, and other materials and production procedures were the same as in Example 1 to produce a nonaqueous electrolyte secondary battery. This produced battery is designated as battery 6.

(Example 7)
A non-aqueous electrolyte secondary battery was produced using the positive electrode active material 4, the addition amount of acetylene black as a conductive agent being 4 wt%, and other materials and production procedures similar to those in Example 1. This produced battery is designated as battery 7.

(Example 8)
A positive electrode plate and a battery were prepared using the positive electrode active material 4. That is, 1% by weight of acetylene black as a conductive agent and 2% by weight of polytetrafluoroethylene (PTFE) resin as a binder are weighed with respect to 100% by weight of the positive electrode active material, and these are added to a carboxymethylcellulose (CMC) aqueous solution. Suspended to form a paste, this paste is made of aluminum foil with a thickness of 20 μm as a current collector, the positive electrode paste is applied to both sides of the paste, dried and then rolled using a rolling roller, and cut into a predetermined size. A positive electrode plate was obtained.

  Using this positive electrode plate, a cylindrical nonaqueous electrolyte secondary battery having a diameter of 18 mm, a height of 65 mm, and a nominal capacity of 2000 mAh was produced by the method described above. This produced battery is designated as battery 8.

(Comparative Examples 1-10)
In Example 1, a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except for the positive electrode active materials 6 to 15. The fabricated batteries are referred to as comparative batteries 1-10.

(Comparative Example 11)
A positive electrode active material 4 was used, PVDF was 11 wt% as a binder, and other materials and production procedures were the same as in Example 1 to produce a nonaqueous electrolyte secondary battery. This manufactured battery is referred to as a comparative battery 11.

(Comparative Example 12)
A positive electrode active material 4 was used, the addition amount of acetylene black as a conductive agent was 0.1% by weight, and other materials and production procedures were the same as in Example 1 to produce a nonaqueous electrolyte secondary battery. This manufactured battery is referred to as a comparative battery 12.

  These batteries were charged in 5 hours with a charging voltage set to 4.2 V after an aging period of 24 hours had elapsed for the purpose of stabilizing the inside of the battery. Subsequently, the battery was discharged at a constant current of 400 mA (0.2 CmA) to 3.0 V, and for further stabilization, 10 charging and discharging cycles of 4.2 V charging and 3.0 V discharging were performed.

  Next, after charging for 3 hours at a charging voltage of 4.2 V, discharging was performed to 3.0 V at a constant current of 400 mA. The discharge capacity obtained at this time is 0.2 CmA capacity. Next, after charging under the above conditions, the battery was discharged to 3.0 V at a constant current of 4000 mA. The discharge capacity obtained at this time is defined as 2 CmA capacity.

  The maintenance rate with respect to 0.2 CmA capacity of 2 CmA was defined as high efficiency discharge characteristics.

Further, after charging under the above conditions, the battery was discharged to 3.0 V at a constant current of 2000 mA.
The discharge capacity obtained at this time is defined as 1 CmA (1st) capacity.

  Under these conditions, charge / discharge is repeated for 300 cycles, and the discharge capacity at the 300th cycle is set to 1 CmA (300th) capacity.

  The maintenance ratio of 1 CmA (300th) capacity to 1 CmA (1st) capacity was defined as cycle life characteristics.

  Next, evaluation results of battery characteristics are shown in Table 2.

  By comparing the battery characteristics of the batteries 1 to 5, the comparative battery 6, and the comparative batteries 11 to 15, a high-efficiency storage characteristic that is excellent even with a small amount of a conductive agent and a binder by using a positive electrode active material having a low DBP absorption amount. And cycle life characteristics.

  This suggests that the positive electrode active material having a lower DBP absorption amount improves the dispersibility of the conductive agent and the binder and forms a functional network during the production of the positive electrode plate.

  However, it was found that even when a positive electrode active material having a low DBP absorption amount was used from the comparative batteries 7 to 10, the battery characteristics were adversely affected if the physical properties were out of the proper range.

  Moreover, it turned out that there exists an appropriate range also in the addition amount of a electrically conductive agent or a binder from the comparison with the batteries 6-7 and the comparative batteries 11-12.

  From the evaluation results of the battery 8, it was found that the present invention functions effectively even when water is used as the solvent.

In recent years, electronic devices have become increasingly portable and cordless, and there is a strong demand for secondary batteries that are small, light, and have high energy density as power sources for driving these devices. From such a viewpoint, the nonaqueous electrolyte secondary battery is highly expected as a battery having a high voltage and a high energy density. Therefore, the non-aqueous electrolyte secondary battery of the present invention is useful as a power source for portable devices and the like because it has both high capacity and cycle characteristics.

Vertical section of the battery used in this example

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Battery case 2 Sealing plate 3 Gasket 4 Electrode plate group 5 Positive electrode plate 6 Negative electrode plate 5a Positive electrode lead 6a Negative electrode lead 7 Separator 8 Insulation ring

Claims (2)

A method for producing a non-aqueous electrolyte secondary battery using a lithium-containing composite oxide as a positive electrode active material, wherein the positive electrode active material, carbon black as a conductive agent, a binder and a dispersion medium are added and kneaded. In the method for producing a non-aqueous electrolyte secondary battery including at least a positive electrode plate creating step in which a viscous solution is prepared, the viscous solution is applied to the surface of a current collector, and dried.
The lithium-containing composite oxide has an average particle diameter of 5 to 20 μm, a specific surface area of 0.2 to 2.0 m ² / g, and JIS K-6217-4 “carbon black for rubber—basic characteristics—fourth. Part: How to determine the DBP absorption amount "Using an absorption meter conforming to the DBP (dibutyl phthalate) absorption amount A method defined in" Method of determining the reagent liquid with a constant speed burette, The change is measured and recorded by a torque detector, and the liquid absorption amount is less than 20 ml / 100 g when the addition amount of the reagent liquid corresponding to the torque at 70% of the generated maximum torque is taken as the liquid absorption amount. A method for producing a water electrolyte secondary battery. 2. The conductive agent is 0.5 to 5.0% by weight with respect to 100% by weight of the positive electrode active material, and the binder is 1.0 to 10.0% by weight. The manufacturing method of the nonaqueous electrolyte secondary battery of description.