JP2001043898A - Manufacture of nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery capable of maintaining its battery performance by controlling an increase in internal resistance during the use of the battery. SOLUTION: A battery body is made by hermetically sealing a positive electrode and a negative electrode, layered with a separator interposed between them, together with a nonaqueous electrolyte, then initial charging is performed, and next, low-temperature preservation treatment is performed for preserving the battery body at low temperatures. The negative electrode is made up of a carbon material capable of doping and dedoping lithium ions or lithium or a lithium alloy. During the low-temperature preservation treatment of the battery body, the battery body is kept at a temperature lower than 15 deg.C, preferably at a temperature of 10 deg.C or less. The lower limit of the keeping temperature is set within a range not causing the nonaqueous electrolyte to freeze. This densifies films formed on the positive electrode and negative electrode after the initial charging, and suppresses the further growth of the films to inhibit internal resistance from increasing with time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a non-aqueous electrolyte secondary battery, and more particularly to a method for doping lithium ion.
The present invention relates to a method for manufacturing a non-aqueous electrolyte secondary battery having a negative electrode formed using a carbon material capable of being undoped, lithium or a lithium alloy.

[0002]

2. Description of the Related Art In recent years, with the spread of portable electronic devices such as video cameras and the like, non-aqueous electrolytic cells having a high battery voltage, a high energy density, a small self-discharge, and excellent cycle characteristics have been used for these power supplies. Demand for liquid secondary batteries is expected. Such a non-aqueous electrolyte secondary battery is formed by sealing a positive electrode and a negative electrode together with a non-aqueous electrolyte in a state of being stacked with a separator interposed therebetween. Among such non-aqueous electrolyte secondary batteries, in particular, non-aqueous electrolytes using a negative electrode composed of a carbon material capable of doping and undoping lithium ions and a positive electrode composed of a lithium composite oxide Liquid secondary batteries have excellent cycle characteristics, and also have excellent low-temperature characteristics, load characteristics, and rapid charging characteristics, and have been put to practical use as power sources for portable electronic devices.

On the other hand, the seriousness of global environmental pollution has increased, and electric vehicles (EVs) such as electric vehicles and hybrid vehicles have been developed.
The interest in non-aqueous electrolyte secondary batteries is also expected for these power sources. Such an E
Non-aqueous electrolyte secondary batteries for V are required to have higher energy density and higher load characteristics than conventional consumer batteries. By reducing the internal resistance by making the electrodes thinner and larger in area, High load charge / discharge is possible.

[0004]

However, in a non-aqueous electrolyte secondary battery, the charge / discharge cycle is repeated, or the internal resistance increases due to long-term storage, so that the discharge efficiency decreases with the use of the battery. Battery capacity decreases. In particular, in the non-aqueous electrolyte secondary battery capable of high-load charge / discharge described above, since the electrode area is large, even if the internal resistance is slightly increased due to charge / discharge cycles and aging, the resistance of the battery as a battery is reduced. The rate of increase is large, and the battery performance is significantly reduced.

Accordingly, an object of the present invention is to provide a method for manufacturing a non-aqueous electrolyte secondary battery in which an increase in internal resistance due to use of a battery can be suppressed and battery performance can be maintained.

[0006]

In order to achieve the above object, a method of manufacturing a non-aqueous electrolyte secondary battery according to the present invention comprises a non-aqueous electrolyte with a positive electrode and a negative electrode laminated with a separator interposed therebetween. After the first charging is performed, a low-temperature preservation processing step of maintaining the battery main body at a low temperature is performed. The negative electrode is formed using a carbon material capable of doping / dedoping lithium ions, lithium, or a lithium alloy. In the low-temperature preservation treatment step, the battery body is kept at a temperature of less than 15 ° C, preferably at a temperature of 10 ° C or less. The lower limit of the holding temperature is set in a range where the non-aqueous electrolyte does not solidify.

In such a manufacturing method, the rate of increase in the internal resistance of the battery is suppressed by keeping the battery body after the initial charge at a low temperature. FIG. 1 shows the relationship between the storage temperature after the initial charge and the rate of increase in the internal resistance. The rate of increase in internal resistance is the rate of increase in internal resistance after performing a high-temperature storage test on the nonaqueous electrolyte secondary battery with respect to the internal resistance of the nonaqueous electrolyte secondary battery immediately after storage processing. Is a value calculated as The internal resistance is a value calculated as ΔE / ΔI based on each voltage E measured when a different current I flows through the nonaqueous electrolyte secondary battery. As is apparent from this figure, the storage processing temperature is lower than 15 ° C. as compared with the internal resistance increase rate when the storage processing temperature is 15 ° C. or higher.
In particular, it can be seen that the rate of increase of the internal resistance is kept low at a low temperature of 10 ° C. or less.

In general, the internal resistance of a non-aqueous electrolyte secondary battery increases due to charge / discharge cycles and storage at high temperatures.
Possible causes include an increase in the contact resistance of the dielectric, active material, and conductive auxiliary constituting the electrode, deterioration of the non-aqueous electrolyte, and an increase in the internal resistance due to film growth on the electrode surface. In the manufacturing method of the present invention, the film formed on the electrode surface after the initial charge is made dense by performing the low-temperature preservation treatment on the electrode body after the initial charge, and as a result, the insulating property of the film itself is increased. Then, during the subsequent storage at high temperature,
It is considered that the growth of the film was suppressed. In particular, a non-aqueous electrolyte secondary battery having a negative electrode composed of a carbon material or lithium or a lithium alloy (a so-called lithium secondary battery or lithium ion secondary battery) has a low oxidation-reduction potential and a non-aqueous electrolyte. The reaction product of the solvent and the lithium ions in the non-aqueous electrolyte is likely to be formed as a film on the electrode surface. Therefore, by suppressing the growth of the film, the rise of the internal resistance over time can be suppressed. .

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 2 is a schematic cross-sectional view showing an example of the non-aqueous electrolyte secondary battery obtained by the production method of the present invention. The non-aqueous electrolyte secondary battery shown in this figure includes a positive electrode 1, a negative electrode 2, and a non-aqueous electrolyte obtained by dissolving an electrolyte in a non-aqueous solvent. The battery element is formed by being spirally wound. The negative electrode is configured using a carbon material capable of doping / dedoping lithium ions, lithium or a lithium alloy. This battery element was housed in a cylindrical battery can 5 with insulating plates 4 arranged on the upper and lower sides, and a negative electrode lead 6 derived from the negative electrode 2 was welded to the bottom of the can, and was derived from the positive electrode 1. The positive electrode lead 7 is welded to a safety valve 8 that shuts off current according to the internal pressure of the battery. The battery can 5 is sealed by a battery lid 10 welded via a gasket 9, and the positive electrode lead 7 is connected to the battery lid 10 via a safety valve 8.

A positive electrode active material containing a sufficient amount of lithium (Li) is suitably used for the positive electrode 1 of the nonaqueous electrolyte secondary battery having such a configuration. As such a positive electrode active material, for example, a general formula LixMO ₂ (where M is Co, N
i represents at least one of i, Mn, Fe, Al, V, and Ti, and x is a positive number), and a composite metal oxide composed of lithium and another metal can be used.

On the other hand, the anode 2 is made of a carbon material capable of doping and undoping lithium ions, lithium or a lithium alloy. As the carbon material, a graphitizable carbon material, a non-graphitizable carbon material (hard carbon), a graphite material, or the like can be used.

As the non-aqueous electrolyte, for example, an electrolyte obtained by using a lithium salt as an electrolyte and dissolving it in a non-aqueous solvent is used. Here, the non-aqueous solvent is not particularly limited, but propylene carbonate, ethylene carbonate, 1-2 dimethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran,
1,3-dioxolan, sulfolane, acetonitrile,
Organic solvents such as diethyl carbonate and dipropyl carbonate are used alone or in combination of two or more.
As the electrolyte, LiPF ₆ , LiClO ₄ , LiAs
F ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , LiCl,
LiBr, CH ₃ SO ₃ Li or the like is used.

Next, a specific embodiment of the present invention will be described. The present invention is not limited to the embodiments described below.

(Example) First, a positive electrode 1 was produced as follows. Lithium manganese spinel oxide (LiMn
₂ O ₄ ) 86 parts by weight of powder, graphite powder 1 as a conductive additive
0 parts by weight and 4 parts by weight of polyvinylidene fluoride as a binder were mixed, and this mixture was dispersed in N-methyl-2-pyrrolidone to prepare a positive electrode active material slurry.

[0015] Next, the thickness of about 20 manufactured by rolling.
This positive electrode active material slurry was uniformly applied to both surfaces of a positive electrode current collector made of a μm aluminum foil, dried, and pressed to form a belt-shaped positive electrode 1. The thickness of the mixture of the positive electrode 1 after the molding was about 80 μm.

Further, the negative electrode 2 was manufactured as follows.
90 parts by weight of hard carbon powder and 10 parts by weight of polyvinylidene fluoride as a binder were mixed, and this mixture was dispersed in N-methyl-2-pyrrolidone to prepare a negative electrode active material slurry.

Next, a thickness of about 15 mm manufactured by rolling.
This negative electrode active material slurry was uniformly applied to both surfaces of a negative electrode current collector made of a copper foil having a thickness of μm, dried, and pressed to form a strip-shaped negative electrode 2. The thickness of the mixture of the negative electrode 2 after the molding was about 60 μm.

Further, a non-aqueous electrolyte was prepared as follows. LiPF ₆ was added to a mixed solvent obtained by mixing propylene carbonate and diethyl carbonate at a volume ratio of 1: 1.
Was dissolved at a rate of 0.9 mol / liter to prepare a non-aqueous electrolyte.

The positive electrode 1 and the negative electrode 2 formed as described above, and the separator 3 made of polyethylene are laminated in the order of the negative electrode 2, the separator 3, the positive electrode 1, and the separator 3, and wound in a cylindrical shape. An element was formed.

Thereafter, with the insulating plate 4 disposed above and below the electrode element, the insulating plate 4 is mounted on a cylindrical battery can 5 having an outer diameter of 40 mm.
The negative electrode lead 6 led out of the negative electrode 2 was welded to the bottom of the battery can 5, and the positive electrode lead 7 led out of the positive electrode 1 was welded to the safety valve 8. Next, after injecting the non-aqueous electrolyte prepared as described above into the battery can 5, the battery lid 10 is attached and sealed by caulking the gasket 9 into the opening of the battery can 5, whereby Outer diameter 40
A cylindrical battery body 11 having a height of 100 mm and a height of 100 mm was formed.

Next, the battery body 11 was initially charged. The condition of the initial charge was 4.2 V, 1.5 A for 6 hours.

Thereafter, a low-temperature preservation process for maintaining the battery body 11 at a low temperature was performed. The processing conditions at this time are preservation processing temperatures of −20 ° C., −10 ° C., 0 ° C., and 10 ° C.,
Preservation treatment was performed for two weeks at each temperature, thereby producing four types of nonaqueous electrolyte secondary batteries that were subjected to low-temperature preservation treatment at each temperature.

(Comparative Example) Two kinds of non-aqueous electrolytes were prepared in the same manner as in the example except that the storage processing at each of 15 ° C. and 25 ° C. was performed instead of the low-temperature storage processing in the example. A secondary battery was manufactured.

(Measurement of Battery Characteristics) Regarding the non-aqueous electrolyte secondary battery of the embodiment and the non-aqueous electrolyte secondary battery of the comparative example manufactured as described above, a high temperature stored in a thermostat at 60 ° C. for 10 days A storage test was performed, and the internal resistance before and after the storage test was measured to calculate the rate of increase. The internal resistance was a value of ΔE / ΔI calculated from each voltage E measured when each current I of 10 A and 30 A was passed through the nonaqueous electrolyte secondary battery. FIG.
2 shows the relationship between the storage temperature at the time of the storage processing and the calculated increase rate of the internal resistance. As is clear from this figure, there is a critical point where the rate of increase of the internal resistance sharply changes in the region where the storage temperature is 10 ° C. to 15 ° C., and the non-aqueous electrolyte secondary battery of the comparative example having a temperature of 15 ° C. or more. It was confirmed that the increase rate of the internal resistance in the nonaqueous electrolyte secondary battery of the example in which the storage temperature was less than 15 ° C. (10 ° C. or less) was suppressed lower than the increase rate of the internal resistance in Example 1. Was.

This is because the film formed on the electrode surface after the first charge (consisting of the reaction product of the solvent of the non-aqueous electrolyte and the lithium ions in the non-aqueous electrolyte) forms the electrode body 1 after the first charge.
It is presumed that the film No. 1 was densified by the low-temperature preservation treatment, and as a result, the film itself was increased in insulating property, so that the film growth was suppressed during the subsequent storage at a high temperature. Therefore, it is considered that the increase in internal resistance over time due to high-temperature storage is suppressed, and the increase in internal resistance due to charge / discharge cycles is also suppressed.

[0026]

As described above, according to the method of manufacturing a non-aqueous electrolyte secondary battery of the present invention, the battery body is first charged and then subjected to a low-temperature preservation treatment, thereby achieving a high-temperature preservation and a charge / discharge cycle. It is possible to suppress the rise in internal resistance to a low level. For this reason, a non-aqueous electrolyte secondary battery can be obtained in which the battery capacity can be maintained while the discharge efficiency is kept from decreasing over time, and the battery performance can be maintained during use of the battery.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a storage temperature and a rate of increase in internal resistance during a storage process.

FIG. 2 is a schematic sectional view of a non-aqueous electrolyte secondary battery obtained by the production method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Positive electrode, 2 ... Negative electrode, 3 ... Separator, 11 ... Battery body

Claims (2)

[Claims] 1. A non-aqueous electrolyte together with a non-aqueous electrolyte in which a positive electrode and a negative electrode made of a carbon material capable of doping / dedoping lithium ions, lithium or a lithium alloy are laminated via a separator. A step of producing a sealed battery body; a step of initially charging the battery body; and a low-temperature preservation step of maintaining the battery body at a low temperature. Manufacturing method of secondary battery. 2. The method for producing a non-aqueous electrolyte secondary battery according to claim 1, wherein in the low-temperature preservation treatment step, the battery body is held at a temperature of less than 15 ° C. A method for manufacturing a secondary battery.