JP4368119B2 - Method for producing non-aqueous electrolyte secondary battery - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement in a non-aqueous electrolyte secondary battery intended to improve charge / discharge cycle characteristics.
[0002]
[Prior art]
In recent years, mobile information terminals such as mobile phones, notebook personal computers, and PDAs have been rapidly reduced in size and weight, and batteries as drive power sources are required to have higher capacities. A non-aqueous electrolyte secondary battery represented by a lithium ion secondary battery has a high energy density and a high capacity, and is therefore widely used as a driving power source for the mobile information terminal as described above.
[0003]
Such a non-aqueous electrolyte secondary battery normally uses a positive electrode including a lithium-containing transition metal composite oxide and a negative electrode including a carbon material that absorbs and releases lithium ions. In this battery, lithium does not exist in a metallic state, and lithium ions only move between the positive and negative electrodes. Therefore, precipitation of dendritic lithium is suppressed, and the battery is excellent in safety.
[0004]
Specific examples of the lithium-containing transition metal composite oxide include lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), and lithium manganate (LiMn ₂ O ₄ ).
Here, although batteries using lithium cobaltate or lithium nickelate can provide excellent discharge characteristics, the thermal stability of lithium cobaltate or lithium nickelate itself is low, so safety in the event of battery abnormalities such as heat generation There is a problem that is not enough. On the other hand, in batteries using lithium manganate, lithium manganate is excellent in thermal stability, so the safety during battery abnormalities is improved, but lithium manganate has lower discharge characteristics than lithium cobaltate etc. There is a problem that sufficient battery characteristics cannot be obtained. In order to solve this problem, lithium cobaltate or lithium nickelate and lithium manganate are mixed to form a positive electrode active material.
[0005]
However, since it is difficult to mix lithium cobaltate or lithium nickelate and lithium manganate in a uniformly dispersed state, there are local portions with poor dispersion. And the problem that the cycle characteristics deteriorate because the adhesion between the active materials decreases due to the expansion and contraction of the active material particles due to the insertion / extraction of lithium ions in the portion, and the crystal structure of the active material is likely to collapse. have.
[0006]
By the way, as a technique for obtaining a battery having excellent positive electrode performance in which electrochemical reactions are performed with high density and high efficiency, mother particles having a large particle size and child particles having a smaller particle size than the mother particles are mixed, There is a technique of using integrated composite particles as a positive electrode active material (see, for example, Patent Document 1).
[0007]
[Patent Document 1]
Japanese Patent Laid-Open No. 10-162825 (pages 2 to 4)
[0008]
According to this technique, the number of junctions between the active material particles can be reduced, and the amount of the binder used can be reduced, so that a battery excellent in conductivity and active material filling rate can be obtained. Is done. However, according to the above technique, the electrical conductivity in the composite particles due to contact between the particles is not sufficient, and overcharge is likely to occur in the particles (mother particles) near the center of the composite particles during the charge / discharge reaction. Since the crystal structure of the active material is easily destroyed by this overvoltage, there is a problem that the cycle characteristics are deteriorated.
[0009]
[Problems to be solved by the invention]
The present invention has been made in view of the above circumstances, and combines the excellent discharge characteristics of lithium cobaltate and lithium nickelate with the excellent thermal stability of lithium manganate, and improves the charge / discharge cycle characteristics. An object of the present invention is to provide a method for producing a nonaqueous electrolyte secondary battery .
[0010]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides a first step in which a cobalt compound and / or a nickel compound and a manganese compound are mixed and pulverized to primary particles, the primary particles are granulated, and a primary particle mixture. The second step of forming an aggregate, the primary particle mixture aggregate, and a lithium compound are mixed and sintered, primary particles composed of lithium cobaltate and / or lithium nickelate, and primary particles composed of lithium manganate. And a third step of forming positive electrode active material secondary particles sintered in a state of being in contact with each other, and a method for producing a non-aqueous electrolyte secondary battery.
[0011]
By using the above method, it is easy to make a nonaqueous electrolyte secondary battery including positive electrode active material secondary particles in which primary particles of lithium cobaltate and / or lithium nickelate and lithium manganate are in contact with each other and sintered. Can be manufactured.
[0012]
According to the above configuration, the primary particles of lithium cobaltate and / or lithium nickelate and lithium manganate are in contact with each other and sintered to form secondary particles of the positive electrode active material. Since the adhesion between the particles is extremely high, the conductivity is excellent. Therefore, since no overvoltage is generated in the secondary particles during the charge / discharge reaction, a battery having excellent charge / discharge cycle characteristics can be obtained.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described based on examples. In addition, this invention is not limited to the following Example, In the range which does not change the summary, it can change suitably and can implement.
[0018]
( Reference Example 1)
First, an overall image of the battery according to Reference Example 1 will be described with reference to FIGS. 1 is a front view of a non-aqueous electrolyte secondary battery according to an embodiment of the present invention, FIG. 2 is a cross-sectional view taken along line AA in FIG. 1, and FIG. 3 is a laminate outer package used for the non-aqueous electrolyte secondary battery. FIG. 4 is a perspective view of an electrode body used in a nonaqueous electrolyte secondary battery.
[0019]
As shown in FIG. 2, the nonaqueous electrolyte secondary battery of the present invention has an electrode body 1, and this electrode body 1 is disposed in a storage space 2. As shown in FIG. 1, the storage space 2 is formed by sealing the upper and lower ends and the center portion of the laminate outer package 3 with sealing portions 4a, 4b, and 4c, respectively. The storage space 2 contains a gel polymer electrolyte containing a nonaqueous solvent, an electrolyte salt, and a polymer. As shown in FIG. 4, the electrode body 1 is formed by winding a positive electrode 5, a negative electrode 6, and a separator (not shown in FIG. 4) separating these two electrodes into a flat spiral shape. Produced.
[0020]
Further, the positive electrode 5 is connected to a positive electrode lead 7 made of aluminum, and the negative electrode 6 is connected to a negative electrode lead 8 made of copper, so that chemical energy generated inside the battery can be taken out as electric energy to the outside. .
[0021]
In addition, as shown in FIG. 3, the specific structure of the laminate outer package 3 is such that adhesive layers 12 and 12 (thickness: 5 μm) made of modified polypropylene are formed on both sides of the aluminum layer 11 (thickness: 30 μm), respectively. In this structure, resin layers 13 and 13 (thickness: 30 μm) made of polypropylene are bonded to each other.
[0022]
Next, a battery manufacturing method will be described.
[0023]
<Preparation of positive electrode active material secondary particles>
Lithium cobaltate (LiCoO ₂ ) and spinel-type lithium manganate (LiMn ₂ O ₄ ) are mixed at a mass ratio of 1: 1, dispersed in water, wet ball milled, and each of lithium cobaltate and lithium manganate. Primary particle mixture. Subsequently, this mixture was granulated by spray drying to obtain primary particle aggregates. Thereafter, the aggregate was sintered in air at 900 ° C. to form positive electrode active material secondary particles.
[0024]
<Preparation of positive electrode>
90 parts by mass of the active material positive electrode active material secondary particles prepared above, 5 parts by mass of a conductive agent made of acetylene black, 5 parts by mass of a binder made of polyvinylidene fluoride (PVdF), and N-methyl-2 -Pyrrolidone (NMP) was mixed to obtain an active material slurry.
[0025]
The active material slurry was uniformly applied to both surfaces of a positive electrode core body made of an aluminum foil having a thickness of 20 μm by a doctor blade, and then passed through a heated drier to be dried. The solvent was removed. Next, this electrode plate was rolled by a roll press so that the thickness was 0.17 mm, and a positive electrode was produced.
[0026]
<Preparation of negative electrode>
A negative electrode active material made of graphite (d = 0.336 nm), a binder made of polyvinylidene fluoride (PVdF), and N-methyl-2-pyrrolidone (NMP) were mixed to obtain an active material slurry. This active material slurry was uniformly applied to both sides of a copper foil (thickness 20 μm) as a negative electrode core with a doctor blade, and then passed through a dryer to dry, thereby providing an organic solvent necessary for slurry preparation. Was removed. Subsequently, this electrode plate was rolled with a roll press so that the thickness was 0.14 mm, thereby producing a negative electrode.
[0027]
<Preparation of pregel solution>
In a mixed solvent obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) at a mass ratio of 3: 7, LiPF ₆ and LiN (C ₂ F ₅ SO ₂ ) ₂ as an electrolyte salt at a molar ratio of 5:95. The mixed electrolyte salt was dissolved to a total of 1 M (mol / liter) to prepare an electrolyte solution. 10 parts by mass of polyethylene glycol diacrylate was added to 90 parts by mass of this electrolytic solution to obtain a pregel solution.
[0028]
<Creation of electrode body>
After attaching the positive electrode lead 7 or the negative electrode lead 8 to the positive electrode and the negative electrode produced as described above, both electrodes are sandwiched by a separator made of a polyethylene microporous film (thickness: 0.025 mm), and each electrode plate Overlapping was performed with the center line in the width direction matched. Then, it wound with the winder and taped the outermost periphery, and produced the flat spiral electrode body 1.
[0029]
After preparing a sheet-like laminate material having a five-layer structure of resin layer (polypropylene) / adhesive layer / aluminum alloy layer / adhesive layer / resin layer (polypropylene), the resin in the vicinity of the ends of the aluminum laminate material The layers were overlapped and the overlapped portion was welded to form the sealing portion 4c. Next, the electrode body 1 was inserted into the storage space 2 of the cylindrical aluminum laminate material. At this time, the electrode body 1 was arranged so that both leads 7 and 8 protruded from one opening of the cylindrical aluminum laminate material. Thereafter, the resin layer inside the aluminum laminate material in the opening from which both electrode tabs protruded was welded and sealed to form the sealing portion 4a. At this time, welding was performed using a high frequency induction welding apparatus.
[0030]
After injecting the pregel solution from the other opening, the opening is heated and welded in the same manner to form a sealing portion 4b, and the pregel solution is polymerized by heating to form the non-aqueous solution according to Reference Example 1. An electrolyte secondary battery was produced.
[0031]
(Example 2)
A battery was produced in the same manner as in Reference Example 1 except that the production method of the positive electrode active material secondary particles was changed to the method shown below.
[0032]
<Preparation of Positive Electrode Active Material Secondary Particles According to Example 2>
Cobalt oxide (Co ₃ O ₄ ) and manganese oxide (MnO ₂ ) are mixed at a mass ratio of 1: 1 in terms of LiCoO ₂ : LiMn ₂ O ₄ , dispersed in water, wet ball milled, It was set as the primary particle mixture of each manganese oxide. Subsequently, this mixture was granulated by spray drying to obtain primary particle aggregates. Thereafter, the agglomerate and the lithium compound were mixed and subjected to two-stage sintering at 700 ° C. for 5 hours and 900 ° C. for 5 hours in the air to obtain positive electrode active material secondary particles.
[0033]
(Comparative Example 1)
A battery was fabricated in the same manner as in Reference Example 1 except that the positive electrode active material primary particle aggregate of Reference Example 1 was used as it was without sintering.
[0034]
(Comparative Example 2)
A battery was fabricated in the same manner as in Reference Example 1 except that lithium cobalt oxide and lithium manganate mixed at a mass ratio of 1: 1 without being pulverized were used as the positive electrode active material.
[0035]
A cycle characteristic test was performed on the batteries of Reference Example 1, Example 2, and Comparative Examples 1 and 2 prepared above. The conditions of the cycle characteristic test were as follows, and the cycle capacity retention rate was determined by the following equation. In addition, the nominal capacity | capacitance of all the produced batteries was 500 mAh.
[0036]
Charging to 4.2V at a constant current of 1.1It (500mA) and then charging for a total of 3 hours at a constant voltage of 4.2V.
2. Pause for 10 minutes.
3. Discharge to 2.75 V at 1 It (500 mA).
4. Pause for 10 minutes. Then return to 1.
[0037]
Cycle capacity retention rate (%) = 100 × discharge capacity at the nth cycle / discharge capacity at the first cycle
The results of the cycle characteristic test are shown in Table 1 below, and the graph is shown in FIG.
[0039]
[Table 1]
[0040]
From Table 1 and FIG. 5, the cycle capacity retention rate at the 800th cycle was 83.5 to 84% in Reference Example 1 and Example 2 , while 76.5 to 79.5% in Comparative Examples 1 and 2 and 4%. It can be seen that the cycle capacity retention ratio at the 1000th cycle or more in% is lower than that in Reference Example 1 and Example 8 by 81.5 to 82%, and in Comparative Examples 1 and 2 by 70 to 75% and 6.5% or more. .
[0041]
This is considered as follows. In Comparative Example 2 in which lithium cobaltate and lithium manganate were mixed at a mass ratio of 1: 1 without being pulverized as the positive electrode active material, both of the dispersions in the mixture of lithium cobaltate and lithium manganate were used. The condition is not uniform. Therefore, the influence of expansion / contraction of the active material accompanying charging / discharging appears remarkably in the locally dispersed portion in the positive electrode plate where the dispersion is poor. As a result, the adhesiveness between the active materials is lowered, the crystal structure of the active material is easily broken, and the cycle characteristics are considered to be lowered.
[0042]
On the other hand, in Comparative Example 1, an active material in which lithium cobaltate and lithium manganate are mixed and pulverized and then granulated to form primary particle aggregates is used. For this reason, unlike the comparative example 2, since the dispersion state of lithium cobaltate and lithium manganate is good, the adhesiveness between the active materials does not decrease due to the expansion and contraction of the active materials accompanying charge and discharge. However, since electrical conduction in the aggregate is due to contact between the primary particles, the electrical conductivity in the aggregate is low, and an overvoltage is generated in the primary particles existing near the center of the aggregate. It is considered that the crystal structure easily collapses due to this overvoltage, resulting in cycle deterioration.
[0043]
Unlike Comparative Examples 1 and 2 described above, in Reference Example 1 and Example 2 , primary particles are sintered and integrated secondary particles are used as the positive electrode active material. The adhesion between particles is high and the conductivity is high. Therefore, it is considered that a battery having high cycle characteristics was obtained because no overvoltage was generated in the secondary particles and the crystal structure did not collapse.
[0044]
Moreover, when the positive electrode active material after a cycle test was taken out and XRD diffraction was performed, the increase in the half-value width, which is a signal of the degree of crystal collapse, was found to be Comparative Example 2> Comparative Example 1> Reference Example 1 = Example 2 It was confirmed in the order of. This result supports the above consideration.
[0045]
[Other matters]
In the above examples, the positive electrode active material obtained by mixing lithium cobaltate and lithium manganate and sintering was used. However, when lithium nickelate was used instead of lithium cobaltate, lithium cobaltate was used. The same effect as when used is obtained. Moreover, the same effect is acquired even if it uses the positive electrode active material which mixed three types, lithium cobaltate, lithium nickelate, and lithium manganate.
The same effect can be obtained when these lithium cobaltate, lithium nickelate, and lithium manganate contain different metal elements in the crystal lattice.
[0046]
In the present invention, the mixing ratio of lithium cobaltate and lithium manganate is not limited to 1: 1 by mass ratio. However, as a preferable mixing ratio, the mixing ratio of “lithium cobaltate + lithium nickelate” and “lithium manganate” is in the range of 8: 2 to 2: 8 in terms of molar ratio.
[0047]
Moreover, in the said Example, although the battery using a laminated exterior body was produced, it can apply to batteries of various shapes, such as a cylindrical type, a coin type | mold, and a square type. It can also be implemented in a non-aqueous electrolyte secondary battery that does not use a gel polymer.
[0048]
Moreover, although the slurry was apply | coated with the doctor blade in the said Example, you may use a die-coater. Further, an active material paste can be used instead of the active material slurry, and the coating can be performed by a roller coating method or the like. Moreover, it can produce similarly even if it uses an aluminum mesh instead of an aluminum foil.
[0049]
In addition, as the non-aqueous electrolyte used in the electrolytic solution, a high dielectric constant solvent having high lithium salt solubility such as ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, 1, 2-dimethoxyethane, tetrahydrofuran, anisole, 1,4-dioxane, 4-methyl-2-pentanone, cyclohexanone, acetonitrile, propionitrile, dimethylformamide, sulfolane, methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate And low viscosity solvents such as ethyl propionate can be used alone or in admixture of two or more.
[0050]
In addition to graphite, carbon black, coke, glassy carbon, carbon fiber, or a fired body thereof can be used as the negative electrode material.
[0051]
As the electrolyte salt, LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiClO ₄ , LiPF ₆ , LiBF _4, etc. may be used alone or in combination of two or more. Can do. In addition, the amount dissolved in the nonaqueous solvent in the previous period is preferably 0.5 to 2.0 mol / liter.
[0052]
【The invention's effect】
As described above, according to the present invention, it is possible to realize a battery that draws only the advantages of both lithium cobaltate and lithium manganate and has excellent charge / discharge cycle characteristics.
[Brief description of the drawings]
FIG. 1 is a front view of a nonaqueous electrolyte secondary battery according to the present invention.
FIG. 2 is a cross-sectional view taken along line AA in FIG.
FIG. 3 is a cross-sectional view of a laminate outer package used in the nonaqueous electrolyte secondary battery according to the present invention.
FIG. 4 is a perspective view of an electrode body used in the nonaqueous electrolyte secondary battery according to the present invention.
FIG. 5 is a graph showing the relationship between the number of cycles and the capacity retention rate in Examples and Comparative Examples.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Electrode body 2 Storage space 3 Aluminum laminate exterior body 4a, 4b, 4c Sealing part 5 Positive electrode 6 Negative electrode 7 Positive electrode lead 8 Negative electrode lead

Claims (1)

A first step of mixing a cobalt compound and / or a nickel compound and a manganese compound and pulverizing them to primary particles;
A second step of granulating the primary particles to form a primary particle mixture aggregate;
The primary particle mixture aggregate and the lithium compound were mixed and sintered, and the primary particles composed of lithium cobaltate and / or lithium nickelate and the primary particles composed of lithium manganate were sintered in contact with each other. A third step of forming positive active material secondary particles;
The manufacturing method of the nonaqueous electrolyte secondary battery characterized by the above-mentioned.