JPH1012274A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase a discharge capacity of a battery by limiting halide lithium solubility of an organic solvent used in an electrolyte, in a nonaqueous electrolyte secondary battery having a positive electrode and a negative electrode with graphite serving as a main constitutional material. SOLUTION: In a secondary battery having a positive electrode, negative electrode with graphic (Lc value is 150Å or more and d value is 3.38Å or less) serving as a main constitutional material and a nonaqueous electrolyte, halide lithium solubility of an organic solvent used in an electrolyte is set to 16mg/l or less. As a solute containing halogen, LiPF6 , LiBF4 , LiClO4 , LiCF3 SO3 , LiAsF6 , LiN(CF3 SO2 )2 , LiCF3 (CF2 )3 , etc., can be used. As a solvent, ethylene carbonate, propylene carbonate, cyclopentane, etc., are used. By using this electrolyte, a characteristic of high capacity of a graphite negative electrode can be displayed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery comprising a chargeable / dischargeable positive electrode, a negative electrode mainly composed of graphite, and a non-aqueous electrolyte containing a solute containing halogen. It is about.

[0002]

2. Description of the Related Art A non-aqueous electrolyte secondary battery represented by a lithium ion battery using a carbon material as a main constituent material of a negative electrode has attracted attention in terms of high energy density, safety, and the like. Since lithium ion batteries using graphite for the negative electrode have high performance, active research has been made.

[0003] As the graphite used for the negative electrode, those having high crystallinity can be said to be desirable from the viewpoint that the capacity can be increased. On the other hand, as the organic solvent constituting the non-aqueous electrolyte, propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and the like are used, and are preferable because they have high stability in the battery. It can be called an organic solvent.

However, when a non-aqueous electrolyte secondary battery is assembled using these organic solvents and a negative electrode containing graphite as a main constituent material, the charge / discharge efficiency of the graphite negative electrode decreases, and the characteristics of the graphite negative electrode deteriorate. It cannot be fully demonstrated. When a graphite negative electrode was used, it was necessary to evaluate the battery characteristics after actually assembling a test battery in order to know the electrochemical behavior of the nonaqueous electrolyte.

[0005]

The present invention comprises a negative electrode mainly composed of graphite (Lc value is 150 ° or more and d value is 3.38 ° or less), a halogen-containing solute and an organic solvent. It is intended to increase the discharge capacity of a non-aqueous electrolyte battery having a non-aqueous electrolyte.

Further, the present invention relates to a method of manufacturing a non-aqueous electrolyte secondary battery for predicting and determining an electrolyte for obtaining a battery having a large discharge capacity. Then, in this kind of secondary battery, a non-aqueous electrolyte comprising an organic solvent optimal for charge and discharge is proposed.

[0007]

SUMMARY OF THE INVENTION The present invention provides a positive electrode, graphite
(Lc value is 150 ° or more, and d value is 3.38 ° or less) Non-aqueous electrolyte secondary battery having a negative electrode having a main constituent material and a non-aqueous electrolyte solution containing a solute and an organic solvent containing halogen Wherein the solubility of lithium halide in the organic solvent used for the electrolyte is 16 mg / liter or less.

Here, the lithium halide is lithium fluoride, and the halogen-containing solute uses a compound containing fluorine. The lithium halide is lithium chloride and contains the halogen. The solute is configured to use a compound containing chlorine.

Further, the present invention provides a positive electrode and graphite (Lc value of 1).
50 ° or more, and the d value is 3.38 ° or less) in a method for producing a nonaqueous electrolyte secondary battery including a negative electrode having a main constituent material and a nonaqueous electrolyte including a solute containing a halogen and an organic solvent. The organic solvent is determined to have a solubility of lithium halide of 16 mg / liter or less, and is used for a non-aqueous electrolyte secondary battery.

Here, it is determined that the solubility of lithium fluoride in the organic solvent is 16 mg / liter or less, or the solubility of lithium chloride is 16 mg / liter or less, and the present invention is applied. Is done.

The halogen-containing solutes in this type of non-aqueous electrolyte secondary battery include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiCF
_{3 SO 3, LiA S F 6} , LiN (CF 3 SO 2) 2, LiCF 3 (CF 2) can be used ₃ SO ₃ or the like.

As the positive electrode of this type of nonaqueous electrolyte secondary battery, a metal oxide containing at least one of manganese, cobalt, nickel, vanadium, and niobium can be used.

Specific examples of the solvent include ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, cyclopentanone, sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, and 3-methyl-1,3-methyl. Oxazolidine-2-one, γ
-Butyrolactone, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, butyl methyl carbonate, ethyl propyl carbonate, butyl ethyl carbonate, dipropyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3 -
Simple substances, such as dioxolane, methyl acetate, and ethyl acetate, and two- and three- or more-component mixtures are listed.

By the way, with respect to the graphite negative electrode, electrochemical characteristics and analysis of the graphite negative electrode were performed using a mixed solvent of ethylene carbonate (EC) and propylene carbonate (PC). When EC and PC are mixed at a specific ratio, the secondary battery can be charged and discharged. As a result, charging and discharging became possible at a specific mixing ratio of EC and PC. When the graphite surface was analyzed by X-ray photoelectron spectroscopy, a thin film of lithium halide was coated on the graphite surface. Was dissolved in the non-aqueous electrolyte. Then, when the solubility of lithium halide in a chargeable / dischargeable mixed solvent was measured, it was found that the solubility was 16 mg / liter or less in all cases. Therefore, it is desirable to suppress the solubility of the lithium halide coating.

This is because, when the solubility of lithium halide in the electrolyte exceeds this value, the lithium halide coated on the graphite surface dissolves, exposing the active sites of the graphite, decomposing the electrolyte, and decomposing the graphite. This is because it is considered that crystal collapse occurs.

As described above, by forming the non-aqueous electrolyte using an organic solvent having a solubility of lithium halide of 16 mg / liter or less, the graphite anode can exhibit the characteristic of high capacity. This is the first realization of a high capacity non-aqueous electrolyte secondary battery.

Further, based on this principle, it is possible to determine an organic solvent that can be used for a non-aqueous electrolyte secondary battery.
That is, an organic solvent is prepared, and a halogen-containing solute to be used as a solute in a secondary battery is dissolved. Then, the solubility of lithium halide in the organic solvent in which the solute is dissolved is measured. If the measured value is less than 16 mg / liter, it is determined that the battery is applicable to a secondary battery, and a battery is manufactured. On the other hand, if the measured value exceeds 16 mg / liter, it is determined that it is not applicable. As a result, the battery characteristics can be predicted based on the properties of the electrolytic solution without assembling the battery, and unnecessary work and man-hours for assembling a battery with poor characteristics can be omitted.

The graphite used for the negative electrode in the present invention is defined as having a crystallite size Lc value of 150 ° or more in the C-axis direction and a d value of 3.38 ° or less on the lattice plane (002) plane. Means carbon material.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, Experiments 1 to 3 and Examples 1 to 3 for explaining the present invention will be described in detail. <Experiment 1> In order to understand the significance of the present invention, a three-electrode cell was assembled in a specific electrolytic solution, and the electrolytic solution was evaluated. (Preparation of Negative Electrode) Dispersion of graphite powder (Lc value> 1000 °, d value 3.35 °, average particle diameter 20 μm) and styrene-butadiene rubber (SBR) (solid content: 48%), which are main constituent materials of the negative electrode Was dispersed in water, and carboxymethyl cellulose (CMC) as a thickener was added to prepare a slurry. The weight composition ratio of the negative electrode after drying was graphite powder:
It is prepared so that SBR: CMC = 100: 3: 2. This slurry was applied to both surfaces of a copper foil as a negative electrode current collector by a doctor blade method, and then dried at 110 ° C for 2 hours.
It was air-dried to produce a negative electrode in which an active material layer (carbon material layer) having a thickness of 50 μm was formed on both surfaces of the copper foil. (Non-aqueous electrolyte and separator) As non-aqueous electrolytes, ethylene carbonate (EC) and propylene carbonate (P
95: 5, 80:20, 60:40, 40:60, 3
Each nonaqueous electrolyte in which LiPF ₆ was dissolved at 1 mol / liter in each mixed solvent of 0:70 was prepared. Then, a cell is assembled using each of such non-aqueous electrolytes, and a cell J1 is formed.
A, J1B, J1C, J1D, and J1E.

As the separator, a polypropylene microporous membrane was used. (Preparation of triode cell, charge / discharge conditions) To measure the negative electrode capacity, a lithium metal was used as a counter electrode, a microporous polyethylene separator was placed between the negative electrode and the graphite, and then spirally wound. To form an electrode group. This is housed in a three-electrode test cell into which an electrolyte is injected together with the lithium metal of the reference electrode, and a charge / discharge test is performed.

The charge and discharge conditions are as follows: at 25 ° C., a current density of 0.
The battery was charged to a final potential of 0 V vs. Li / Li + at 1 mA / cm ² , and discharged to a final potential of 1 V vs. Li / Li + at a current density of 0.1 mA / cm ² .

The solubility of lithium halide was measured as follows. That is, 1 g of lithium halide dried in a vacuum atmosphere at 200 ° C. was added to 100 ml of an organic solvent to which no electrolyte was added, and the mixture was sufficiently stirred and allowed to settle for 1 day. Quantified by flame photometry. In Experiment 1, lithium fluoride (LiF) was used as the lithium halide.

<Comparative Example> LiPF ₆ was used as a non-aqueous electrolytic solution in a mixed solvent of ethylene carbonate (EC) and propylene carbonate (PC) at a volume ratio of 20:80, 10:90 and 0: 100.
Was dissolved in 1 mol / liter to prepare each non-aqueous electrolyte.
Then, the cells were assembled using each non-aqueous electrolyte, and were set as cells H1A, H1B, and H1C, respectively.

The cells J1A to J1 according to the present invention described above.
E. The amount of lithium halide (LiF) dissolved and the discharge capacity were examined using cells H1A to H1C for comparison. Table 1 shows the results. In this table, the composition ratio of the organic solvent and the cell name are also shown.

[0025]

[Table 1]

As shown in Table 1 above, cells J1A to J1
Since the dissolution amount of lithium halide (LiF) of E is 16 mg / liter or less, the discharge capacity is 340 mAh / g or more, which shows excellent characteristics as compared with the cells H1A to H1C. <Experiment 2> In this experiment 3, ethylene carbonate (EC), propylene carbonate (PC),
Diethyl carbonate (DEC), dimethyl carbonate
(DMC) was used as an organic solvent. That is, the volume ratio of EC: PC: DEC: DMC is 47.5: 2.5: 25: 25, 40: 10: 25: 25, 30: 20: 25: 25, 20: 3.
0:25:25, 15: 35: 25: 25, 10: 40: 25: 25 in each mixed solvent,
Each non-aqueous electrolyte in which lithium hexafluorophosphate (LiPF ₆ ) was dissolved at 1 mol / liter was prepared. Then, a cell is assembled using each non-aqueous electrolyte, and cells J2A, J2B, J
2C, J2D, J2E, and J2F. In addition, a polypropylene microporous membrane was used as the separator.

The other experimental conditions are the same as those described in Experiment 1 above.
According to.

<Comparative Example> EC: PC:
Each non-aqueous electrolyte solution was prepared by dissolving LiPF ₆ at 1 mol / liter in each mixed solvent of DEC: DMC at a volume ratio of 5: 45: 25: 25 and 0: 50: 25: 25. Then, the cells were assembled using each non-aqueous electrolyte solution to obtain cells H2A and H2B, respectively.

The cells J2A to J2 according to the present invention described above.
F, the amount of lithium halide (LiF) dissolved and the discharge capacity were examined using cells H2A and H2B for comparison. Table 2 shows the results. In Table 2, the composition ratio of the organic solvent and the cell name are also shown.

[0030]

[Table 2]

As shown in Table 3 above, cells J2A to J2
Since the dissolution amount of lithium halide (LiF) of F is 16 mg / liter or less, the discharge capacity is 340 mAh / g or more, which is superior to the cells H2A and H2B. <Experiment 3> In Experiment 3, the case where ethylene carbonate (EC) and propylene carbonate (PC) were used as the organic solvent as the non-aqueous electrolyte was examined. That is, the volume ratio of EC to PC is 95: 5, 80:20, 60: 4.
Lithium perchlorate (LiClO ₄ ) in each mixed solvent of 0, 50:50
Was dissolved in 1 mol / liter to prepare each non-aqueous electrolyte.
Then, cells were assembled using each non-aqueous electrolytic solution, and the cells were respectively set to cells J3A, J3B, J3C, and J3D.

The other experimental conditions are the same as those described in the above Experiment 1.
According to.

<Comparative Example> EC and PC were used as non-aqueous electrolytes.
Each non-aqueous electrolyte solution was prepared by dissolving LiClO ₄ at 1 mol / liter in a mixed solvent having a volume ratio of 40:60, 20:80, and 0: 100. Then, cells were assembled using each non-aqueous electrolyte, and cells H3A, H3B, and H3C were formed, respectively.

The cells J3A to J3 according to the present invention described above.
D. The amount of lithium halide (LiCl) dissolved and the discharge capacity were examined using cells H3A to H3C for comparison. Table 3 shows the results. In Table 3, the composition ratio of the organic solvent and the cell name are also shown.

[0035]

[Table 3]

As shown in Table 3 above, cells J3A to J3
Since the dissolution amount of lithium halide (LiCl) of D is 16 mg / liter or less, the discharge capacity is 350 mAh / g or more, which shows excellent characteristics as compared with the cells H3A to H3C. <Example 1> As an organic solvent, ethylene carbonate was used.
(EC) and propylene carbonate (PC) were prepared, and a mixed organic solvent having a volume ratio of 60:40 was prepared. Here, lithium halide, lithium hexafluorophosphate (L
iPF ₆ ) was added and its solubility was measured at room temperature. This solubility was 14.5 mg / liter. Based on this value, it is determined that the value is smaller than the determination value of 16 mg / liter, and it is determined that the battery is used for a non-aqueous electrolyte secondary battery.

To this mixed organic solvent, 1 mol / liter of lithium hexafluorophosphate (LiPF ₆ ) as a solute was added to prepare a non-aqueous electrolyte.

As an electrode, a negative electrode mainly composed of graphite
(See Experiment 1 above), a positive electrode containing cobalt oxide described below as a main constituent material was prepared, and a spiral electrode body was produced together with a polypropylene separator.

The preparation of the positive electrode was performed as follows. That is, a cobalt oxide compound (LiCoO ₂ ) powder having an average particle size of 5 μm as a positive electrode active material and artificial graphite powder as a conductive agent were
The mixture was mixed at a weight ratio of 9: 1 to prepare a positive electrode mixture. This positive electrode mixture and a binder solution obtained by dissolving 5% by weight of polyvinylidene fluoride in N-methyl-2-pyrrolidone (NMP)
A slurry was prepared by kneading at a solid content weight ratio of 95: 5.
This slurry was applied to both surfaces of an aluminum foil as a positive electrode current collector with a thickness of 50 μm on each surface by a doctor blade method. After forming the positive electrode active material layer in this manner, 150
Vacuum dried at ℃ for 2 hours to obtain positive electrode.

This electrode body was inserted into a battery can, and after the above-mentioned non-aqueous electrolyte was injected, it was sealed with a sealing body provided with a safety valve mechanism. The discharge capacity of the battery of the present invention having the AA size thus obtained was 550 mAh.

The discharge capacity was measured by charging the battery immediately after assembly at 25 ° C. at a current value of 1 C up to 4.1 V, and then discharging the battery at a current value of 1 C up to 2.75 V. Is actually measured. Example 2 As an organic solvent, ethylene carbonate was used.
(EC), propylene carbonate (PC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) were prepared, and the volume ratio of EC: PC: DEC: DMC was 40: 10: 2.
A mixed organic solvent of 5:25 was prepared. Here, lithium halide, lithium hexafluorophosphate (LiPF ₆ ) was added, and its solubility was measured at room temperature. This solubility is 13.5
mg / liter. Based on this value, it is determined that the value is smaller than the determination value of 16 mg / liter, and it is determined that the battery is used for a non-aqueous electrolyte secondary battery.

To this mixed organic solvent, 1 mol / liter of lithium hexafluorophosphate (LiPF ₆ ) as a solute was added to prepare a non-aqueous electrolyte.

As an electrode, a negative electrode mainly composed of graphite
(See Experiment 1 above), a positive electrode containing cobalt oxide described later as a main constituent material was prepared, and a spiral electrode body was produced together with a polypropylene separator.

The preparation of the positive electrode was performed as follows. That is, a cobalt oxide compound (LiCoO ₂ ) powder having an average particle size of 5 μm as a positive electrode active material and artificial graphite powder as a conductive agent were
The mixture was mixed at a weight ratio of 9: 1 to prepare a positive electrode mixture. This positive electrode mixture and a binder solution obtained by dissolving 5% by weight of polyvinylidene fluoride in N-methyl-2-pyrrolidone (NMP)
A slurry was prepared by kneading at a solid content weight ratio of 95: 5.
This slurry was applied to both surfaces of an aluminum foil as a positive electrode current collector with a thickness of 50 μm on each surface by a doctor blade method. After forming the positive electrode active material layer in this manner, 150
Vacuum dried at ℃ for 2 hours to obtain positive electrode.

This electrode body was inserted into a battery can, and after the above-mentioned non-aqueous electrolyte was injected, it was sealed with a sealing body provided with a safety valve mechanism. The discharge capacity of the battery of the present invention having the AA size thus obtained was 560 mAh. The measurement of the discharge capacity was performed in the same manner as in Example 1. Example 3 As an organic solvent, ethylene carbonate was used.
(EC) and propylene carbonate (PC) were prepared, and a mixed organic solvent having a volume ratio of 80:20 was prepared. Here, lithium halide, lithium perchlorate (LiClO
₄ ) was added and its solubility was measured at room temperature. This solubility was 12.8 mg / liter. From this value, the judgment value 16
It is judged to be smaller than mg / liter, and it is decided to use it for a non-aqueous electrolyte secondary battery.

To this mixed organic solvent, 1 mol / liter of lithium perchlorate (LiClO ₄ ) as a solute was added to prepare a non-aqueous electrolyte.

As the electrode, a negative electrode mainly composed of graphite
In the same manner as in Example 1, a positive electrode containing a cobalt acid compound as a main constituent material was prepared, and a spiral electrode body was produced together with a polypropylene separator.

This electrode body was inserted into a battery can, and after the above-mentioned non-aqueous electrolyte was injected, it was sealed with a sealing body provided with a safety valve mechanism. The volume ratio of the mixture was determined by the determination of the non-aqueous electrolyte, and this was used for mass production.
The battery of the present invention having the AA size thus obtained had a discharge capacity of 540 mAh, and an excellent discharge capacity was obtained. The measurement of the discharge capacity was performed in the same manner as in Example 1.

[0049]

As described above, according to the nonaqueous electrolyte secondary battery of the present invention, a battery having a large discharge capacity can be provided.

Further, according to the method of manufacturing a non-aqueous electrolyte secondary battery of the present invention, a solvent suitable for a battery having a large discharge capacity can be predicted and determined without assembling the battery.
Its industrial value is extremely large.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Koji Nishio 2-5-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd.

Claims (6)

[Claims] 1. A cathode and graphite (Lc value is 150 ° or more, and
a non-aqueous electrolyte secondary battery having a negative electrode having a d value of 3.38 ° or less) as a main constituent material, and a non-aqueous electrolyte comprising a solute containing a halogen and an organic solvent, A nonaqueous electrolyte secondary battery characterized in that the solubility of lithium halide in the obtained organic solvent is 16 mg / liter or less. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the lithium halide is lithium fluoride, and the solute containing halogen is a compound containing fluorine. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein said lithium halide is lithium chloride, and said halogen-containing solute is a compound containing chlorine. 4. A cathode and graphite (Lc value is 150 ° or more, and
(d value is 3.38Å or less) as a main constituent material, a non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte comprising a solute containing a halogen and an organic solvent, a method for producing a non-aqueous electrolyte secondary battery, A method for producing a non-aqueous electrolyte secondary battery, comprising determining that the solvent has a solubility of lithium halide of 16 mg / liter or less and using the solvent for a non-aqueous electrolyte secondary battery. 5. A cathode and graphite (Lc value is 150 ° or more, and
a d value of 3.38 ° or less), and a non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte comprising a negative electrode having a main component of a solute containing fluorine and an organic solvent, A method for producing a non-aqueous electrolyte secondary battery, comprising determining that the solvent has a solubility of lithium fluoride of 16 mg / liter or less and using the solvent for a non-aqueous electrolyte secondary battery. 6. A cathode and graphite (Lc value is 150 ° or more, and
d value is 3.38Å or less), a non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte comprising a negative electrode having a main component of a solute containing chlorine and an organic solvent, A method for producing a non-aqueous electrolyte secondary battery, comprising determining that a solvent has a solubility of lithium chloride of 16 mg / liter or less and using the solvent for a non-aqueous electrolyte secondary battery.