JP2003288879A - Nonaqueous electrolytic solution secondary cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolytic solution secondary cell using a separator of which, physical property value is restricted to a specific value, not generating fall off of electrode activator, having excellent cycle property and charge preservation property. <P>SOLUTION: The nonaqueous electrolyte secondary cell has a separator between a positive electrode and a negative electrode, of which, an average hole diameter measured by mercury injection method has substantially two peaks, those average hole diameters range between 0.05 μm-0.7 μm, the average hole diameter on the surface is 0.3 μm or less, and bubble point value is 0.29-0.68 MPa. By the above, the nonaqueous electrolyte secondary cell with improved cycle property and charge preservation property is obtained. <P>COPYRIGHT: (C)2004,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] TECHNICAL FIELD The present invention relates to a positive electrode, a negative electrode,
A separator that separates these positive and negative electrodes and a non-aqueous electrolytic
Non-aqueous electrolyte secondary battery with
The present invention relates to a non-aqueous electrolyte secondary battery having excellent storage characteristics. [0002] 2. Description of the Related Art In recent years, small video cameras, mobile phones,
Used as a power source for portable electronic and communication devices such as laptop computers.
Small, lightweight and high capacity non-aqueous electrolyte secondary batteries
Is now available. Such non-aqueous electrolyte secondary battery
Uses graphite that can absorb and release lithium ions
Lithium-containing cobalt oxide (LiC
oO _Two), Lithium-containing manganese oxide (LiMn)
_TwoO_Four) And other lithium-containing transition metal oxides
And dissolve lithium salt as a solute in an organic solvent
The battery is configured using the electrolyte solution. [0003] This type of non-aqueous electrolyte secondary battery has been used for a long time.
When charging and discharging are repeated, the decomposition reaction of the electrolytic solution occurs.
This causes clogging of the separator and battery
It is known to cause a decrease in performance. by the way,
The decomposition reaction of the electrolyte mainly occurs at the interface between the electrode and the separator
The reaction product causes clogging (clogging) of the separator.
Cause. In recent non-aqueous electrolyte secondary batteries, batteries
Graphite powder highly reactive with the anode material to increase the capacity of
And increase the bulk density of the active material.
You. Therefore, the clogging of the separator due to the generation of electrolyte decomposition products
There is a growing need for separators that are less likely to cause balling.
Have been. [0004] SUMMARY OF THE INVENTION Generally, a separator
Larger holes are more difficult to clog, so large holes
There is a tendency that a separator having a diameter is required. But
If the pore size of the separator is too large, removal of the electrode active material may occur.
Positive due to dendritic precipitates and dendrites of lithium
Problems such as a short circuit between the electrode and the negative electrode are likely to occur. Special
In addition, the fine particles of the electrode active material and
Dendrite generated on the negative electrode surface due to current concentration is
To enter the separator and form an internal short-circuit bridge.
This causes a problem of impairing the electrical insulation. [0005] In addition, it is necessary to increase the pore size of the separator.
The required strength cannot be obtained, and workability during battery assembly
Has also been reduced. In this way, the separation
Large hole diameter that is difficult to clog
And short circuit caused by electrode active material and dendrite penetration
It realizes a hole structure that is compatible with
Maintaining strength is quite difficult. Also,
If the pore size is large enough to prevent clogging, the cell
The parator has many places in contact with the electrolyte. others
When stored in a charged state,
This causes a problem that the charge storage characteristics deteriorate
Was. Accordingly, the present invention has been made to solve the above problems.
This was done for the purpose of
Use a parator to remove electrode active material and dendride
No short circuit, excellent cycle characteristics, and charging
A non-aqueous electrolyte secondary battery with excellent storage characteristics can be provided.
It is intended to be used. [0007] Means for Solving the Problems To achieve such an object
Therefore, the nonaqueous electrolyte secondary battery of the present invention
The average pore size measured has more than two peaks.
And their average pore size is 0.05μ
m to 0.7 μm, and the average pore diameter on the surface is
When the bubble point value is 0.39 μm or less, the bubble point value is 0.29 to 0.1 μm.
Equipped with a separator of 68 MPa between the positive electrode and the negative electrode
I am trying to. [0008] Here, the average pore measured by the mercury intrusion method
When a separator having a diameter of less than 0.05 μm is used, the electrolytic solution
Clogging due to the generation of decomposition products
The cycle characteristics are significantly reduced. In addition, the mercury intrusion method
Separator with an average pore size of greater than 0.7 μm
If used, the electrode active material may fall off or lithium dendrite
Short circuit is likely to occur and the required strength can be maintained.
And the workability during battery assembly is significantly reduced
You. Therefore, the average pore size measured by the mercury intrusion method is
Separators in the range of 0.05 μm to 0.7 μm
Must be used. The average pore diameter on the surface is 0.3 μm or less.
, It is in contact with the positive and negative electrodes even when stored in a charged state
There are fewer places in the separator that come into contact with the electrolyte
Therefore, it is possible to suppress the occurrence of decomposition reaction of the electrolytic solution due to side reactions.
I will be able to. As a result, the electrolyte solution in the separator
It is in a trapped form and holds a sufficient amount of electrolyte
As a result, the charge storage characteristics are improved. This is accompanied by the generation of decomposition products of the electrolytic solution.
To prevent clogging, the inside of the separator must be
A constant average pore size is required. Meanwhile, the positive and negative electrodes
Reduces the number of places where the
To achieve a confined configuration, the surface of the separator must be
It is clear that it is necessary to achieve a constant average pore size.
Call From these facts, the interior and surface of the separator
Having an average pore size of substantially two or more peaks.
It turns out that it is necessary to use a lator. The average pore measured by the mercury intrusion method
Bubble point value of separator with diameter of 0.3μm or less
Generally shows 0.98 MPa or more in many cases. Only
However, as described above, the average pore diameter is substantially two or more.
Having an average pore diameter of 0.05 μm to
Within the range of 0.7 μm and mean pores on the surface
Controlled so that the diameter is 0.3μm or less
The bubble point value of the separator
At 8 MPa, it is clear that the charge storage characteristics are improved.
Or it becomes. In this case, the material of the separator is not particularly limited.
However, if it is a polyethylene separator,
Has substantially two or more peaks in the average pore size,
Average pore size is in the range of 0.05 μm to 0.7 μm.
And the average pore size on the surface is 0.3 μm or less,
Control the int value to 0.29 to 0.68 MPa
This is preferable because it can be easily performed. The positive electrode active material
As long as it can be used in non-aqueous electrolyte batteries
However, lithium-containing transition metal oxides, especially lithium
Containing cobalt oxide (LiCoO_Two)
This is preferable because the effect of suppressing side reactions during electric storage can be exhibited. As the negative electrode active material, a non-aqueous electrolyte
Anything that can be used in a pond may be used, especially graphite.
If it is, it is possible to demonstrate the effect of suppressing side reactions during
Good. The electrolyte is also used in non-aqueous electrolyte batteries.
Anything can be used as long as it can be used.
Charging with a mixed solvent of steal and chain carbonate
This is preferable because the effect of suppressing side reactions during storage can be exhibited. [0014] Next, an embodiment of the present invention will be described.
This will be described below. FIG. 1 shows a non-aqueous electrolyte secondary battery according to the present invention.
Image schematically showing the cross section of the separator used for the battery
FIG. 1. Production of separator Plasticizer (eg, liquid paraffin)
Was added to an extruder and melt-kneaded. About
Through the coat hanger die onto the cooling roll.
To obtain a polymer gel sheet with a predetermined thickness.
Was. After stretching the obtained polymer gel sheet, a plasticizer
20μm thick microporous polyethylene membrane
Was prepared and used as the separator 10. Made in this way
The separator 10 has a cross-section as schematically shown in FIG.
In the vicinity of the surface (part A in FIG. 1), micropores 1 having a small average pore diameter
2 are formed, and an average hole is formed at the center of the cross section (portion B in FIG. 1).
The fine holes 11 having a large diameter are formed. [0015] Here, the stretching conditions and the conditions for extracting the plasticizer are controlled.
Have the physical properties shown in Table 1 below
Separators a, b, c, d, e, f, g, h, i
Made. In Table 1, in the mercury intrusion method, parts A and
The average pore size (μm) of parts B and B was determined by porosimetry (manufactured by Shimadzu Corporation).
Median diameter based on volume
(Μm), and the average pore size in part A is
Formed near the surface of the cross section of the radiator 10 (portion A in FIG. 1).
Represents the average pore diameter (μm) of the micropores 12, and the average pore in the B part.
The diameter is formed at the center (section B in FIG. 1) of the cross section of the separator 10.
The average pore diameter (μm) of the formed fine pores 11 is shown. The average pore size (μm) on the surface is determined by the scanning type.
Photograph of the surface of the separator with an electron microscope (SEM)
Shows the measured value of the average pore diameter of the substantial surface.
You. In addition, the bubble point (MPa)
Place the separator in (ethanol) and gradually increase the gas pressure
Pressure at the first bubble generation from the separator
Values (measured according to ASTM E-128-61)
Value. [0017] [Table 1] 2. Preparation of positive electrode Lithium-containing Kovar dioxide heat-treated at 800 ° C
(LiCoO_Two) As the positive electrode active material
Lithium-containing cobalt dioxide (LiCo as active material)
O_Two) 85% by mass and carbon powder 10 as a conductive agent
% By mass and polyvinylidene fluoride (PV
dF) 5% by mass. After this, the mixture
-Methyl-2-pyrrolidone (NMP)
The mixture was kneaded to prepare a positive electrode active material slurry. Then this positive
Positive electrode current collector made of aluminum foil with pole active material slurry
After rolling by doctor blade method on both sides of
Was rolled so as to have a thickness of 140 μm. Then 1
After vacuum drying at a temperature of 30 ° C., cut into predetermined dimensions,
A positive electrode having a positive electrode mixture layer on the surface of the positive electrode current collector was prepared.
Was. 3. Fabrication of negative electrode Using natural graphite having an average particle size of 10 μm as a negative electrode active material,
A binder was added to 95% by mass of natural graphite as the negative electrode active material.
5% by mass of polyvinylidene fluoride (PVdF)
Mixed. Thereafter, the mixture was added to N-methyl-2-pyro
Add lidon (NMP), mix and knead to mix negative active material
A rally was made. Next, this negative electrode active material slurry is
Doctor blade method on both sides of negative electrode current collector made of copper foil
After coating more, so that the thickness after rolling is 130μm
Rolled. Then, it was vacuum dried at a temperature of 130 ° C.
After that, cut to a predetermined size, the negative electrode mixture on the surface of the negative electrode current collector
A negative electrode having a layer was prepared. 4. Fabrication of non-aqueous electrolyte secondary battery Then, the microporous polypropylene made as described above
Each of the separators a, b, c, d, e, f, g,
h, i, using the positive
After laminating the electrode and the negative electrode, these are spirally formed.
Each was wound to form a columnar spiral electrode group. Then
These columnar spiral electrode groups are pressurized to flatten spiral electrodes.
Groups. Then, these are each made of metal square exterior
After inserting into the can, attach the lid to the opening of the
Sealed tightly. Next, ethylene carbonate (EC: hereinafter)
Below, simply called EC) and ethyl methyl carbonate (E
MC: hereinafter simply referred to as EMC) in a volume ratio of 40: 6.
0 in a mixed solvent mixed to be 0₆1.
0 mol / liter was dissolved to prepare a non-aqueous electrolyte. this
After that, the non-aqueous electrolyte prepared as described above from the inlet of the lid
Was injected. After this, the inlet is sealed and the non-aqueous electrolyte secondary
Batteries A to I were produced, respectively. Here, the separator a
To i were used as batteries A to I, respectively. The battery
In F, a short circuit occurred when fabricating the spiral electrode group
Therefore, the battery could not be manufactured, but here
Is a battery F for convenience. The solvent for the electrolytic solution is EC or EC.
In addition to EMC, propylene carbonate (PC),
Tylene carbonate (BC), dimethyl carbonate
(DMC), sulfolane (SL), vinylene carbonate
(VC), diethyl carbonate (DEC), tetra
Hydrofuran (THF), 1,2-diethoxyethane
(DEE), 1,2-dimethoxyethane (DME),
Toximethoxyethane (EME), γ-butyrolactone
Or a mixed solvent of two or more of these.
You may use it selectively. Solutes dissolved in this solvent
As LiPF ₆Besides, LiBF_Four, LiCF_Three
SO_Three, LiAsF₆, LiN (CF_ThreeSO_Two)_Two, LiN
(C_TwoF_FiveSO_Two)_Two, LiC (CF_ThreeSO_Two)_Three, LiCF_Three
(CF_Two)_ThreeSO _ThreeEtc. may be used. 5. Battery test (1) Cycle characteristics test At room temperature (about 25
° C) and 1It (It is the design capacity (mA) / 1h (hour
The battery voltage is 4.2 at the charging current of the numerical value represented by
Constant current charging until the voltage reaches V, and the current value at a constant voltage of 4.2 V
Until it reached 20 mA. After this, 1I
t until the battery voltage reaches 2.75V.
Charge / discharge cycle to 200 cycles
The discharge capacity at the 200th cycle
(MAh) was determined. Next, the discharge capacity of the first cycle
And the discharge capacity at the 200th cycle (%), that is,
The residual capacity ratio (%) after 200 cycles is defined as the cycle characteristic.
The results shown in Table 2 below were obtained. (2) Charging storage characteristic test Further, using each of the batteries A to I, the room temperature (about 25
° C), the battery voltage reaches 4.2 V with a charging current of 1 It.
Constant current charging until the current value reaches 20 at a constant voltage of 4.2V.
The battery was charged at a constant voltage until the current reached mA. Then, at 60 ° C, 2
After storing for 0 days, at a discharge current of 1 It, the battery voltage becomes
Discharge until reaching 2.75V, discharge after storage
Measure the capacity and charge the remaining capacity (%) before storage.
When it is obtained as the existing characteristic, the result shown in Table 2 below is obtained.
became. [0025] [Table 2]As is clear from the results in Table 2 above, the batteries
A, B, C, and D have cycle characteristics and charge storage characteristics.
It turns out that it is excellent. From this, the mercury intrusion method
Average pore diameter (average pore diameters A and B) measured by
Use a separator in the range of 5 μm to 0.7 μm
And non-aqueous electrolysis with excellent cycle characteristics and charge storage characteristics
Quality batteries can be obtained. In addition, the separator surface
When the average pore size is 0.3 μm or less, the charge storage characteristics are improved.
You can see that it goes up. In addition, the bubble point is 0.2
Cycle characteristics and charging in the range of 9 to 0.68 MPa
Excellent storage characteristics. The bubble point is 0.2
Less than 9MPa or more than 0.68MPa
And cycle characteristics are good, but storage characteristics deteriorate
You can see that. [0027] As described above, the average pore diameter is substantially 2
With one or more peaks and an average pore size of 0.05
μm to 0.7 μm and the surface
Control so that the average pore size is 0.3 μm or less.
The bubble point value of the separator prepared in
When the pressure is 0.68 MPa, the cycle characteristics are improved.
In particular, a non-aqueous electrolyte secondary battery with improved charge storage characteristics was obtained.
It can be said that it became clear. In the embodiment described above, the correct
Lithium-containing cobalt dioxide (LiCo
O_Two) And non-aqueous water using natural graphite as the negative electrode active material
An example of applying the separator of the present invention to an electrolyte secondary battery
However, the present invention is not limited to this.
Can be selected and used. For example, as a negative electrode active material
Can absorb and desorb lithium ions in addition to natural graphite
Carbon-based materials such as carbon black and coke
, Glassy carbon, carbon fiber, or a fired body of these
May be used. As the positive electrode active material, LiCoO is used._TwoLess than
In addition, Lichi can accept lithium ions as guests
Transition metal compounds such as LiNiO_Two, Li
Co_XNi_(1-X)O_Two, LiCrO_Two, LiVO_Two, LiM
nO_Two, ΑLiFeO_Two, LiTiO_Two, LiScO_Two, L
iYO_Two, LiMn_TwoO_FourEtc. may be used.
In particular, LiNiO_Two, LiCo_XNi_(1-X)O_TwoUsed alone
Or a mixture of two or more of these
It is suitable.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an image diagram schematically showing a cross section of a separator used for a non-aqueous electrolyte secondary battery of the present invention. DESCRIPTION OF SYMBOLS 10 ... Separator, 11 ... Micropore having a large average pore diameter formed at the center of the cross section, 12 ... Micropore having a small average pore diameter formed near the surface of the cross section

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Claims (1)

Claims: 1. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a separator for separating the positive electrode and the negative electrode, and a non-aqueous electrolyte, wherein the separator has a mercury intrusion. The average pore size measured by the method has substantially two or more peaks, all of which are in the range of 0.05 μm to 0.7 μm, and the average pore size of the separator surface is 0.3 μm or less. , Wherein the bubble point value is 0.29 to 0.68 MPa.