JP2003346765A - Compound sheet and non-aqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator that can improve output characteristics of a battery while preventing short circuit between the electrodes in the non- aqueous electrolyte secondary battery. <P>SOLUTION: In the non-aqueous electrolyte secondary battery which comprises a positive electrode 20 and a negative electrode 30 as well as a non-aqueous electrolyte, the separator 40 that is provided between the positive electrode 20 and the negative electrode 30 is made a compound sheet having glass fiber unwoven cloth 42 on both sides of a fine porous membrane 41. With this structure, the glass fiber unwoven cloth 42 which can hold much amount of the electrolyte when the battery is assembled contacts the positive electrode 20 and the negative electrode 30, thereby, the output characteristics of the non- aqueous electrolyte secondary battery is improved. <P>COPYRIGHT: (C)2004,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte secondary battery.

[0002]

2. Description of the Related Art In a non-aqueous electrolyte secondary battery such as a lithium ion battery, a microporous film made of a thermoplastic resin having a shutdown function is used as a separator in order to improve safety. However, this non-aqueous electrolyte secondary battery has a problem that the separator thermally shrinks due to a rise in battery temperature, and as a result, the positive electrode and the negative electrode are short-circuited. Japanese Patent Application Laid-Open No. 9-161775 discloses a non-aqueous electrolyte secondary battery using a composite separator in which a microporous film such as polypropylene is provided on both sides of a glass fiber cloth. In this non-aqueous electrolyte secondary battery, even if the battery temperature rises significantly and the microporous membrane thermally contracts, the glass fiber cloth does not contract, so that short circuit due to heat can be prevented.

[0003]

However, the non-aqueous electrolyte secondary battery of this structure has a problem that the output characteristics are insufficient. The present invention has been completed on the basis of the above-described circumstances, and a composite sheet for a non-aqueous electrolyte secondary battery separator capable of providing a non-aqueous electrolyte secondary battery having good output characteristics while improving safety. And a non-aqueous electrolyte secondary battery using the composite sheet.

[0004]

According to a first aspect of the present invention, there is provided a composite sheet used as a separator of a non-aqueous electrolyte secondary battery, wherein the composite sheet is made of a thermoplastic resin. A glass fiber layer is provided on both sides of the porous membrane.

The invention according to claim 2 is the composite sheet according to claim 1, wherein the sum of the thickness of the microporous film of the thermoplastic resin and the thickness of the glass fiber layer is 50 μm or less. And

According to a third aspect of the present invention, there is provided a non-aqueous electrolyte secondary battery between a positive electrode plate and a negative electrode plate.
A separator comprising the above-described composite sheet is provided, and the non-aqueous electrolyte contains a compound having a surfactant effect.

[0007]

According to the first aspect of the present invention, the composite sheet for separator has a glass fiber layer disposed on both surfaces of a microporous thermoplastic resin film. When the composite sheet is used as a separator to form a power generating element together with the positive and negative electrode plates, the glass fiber layer comes into contact with the electrode plate. Since the glass fiber layer has larger pores and a higher porosity than the microporous thermoplastic resin film, the proportion of the electrolyte retained in the glass fiber layer is maintained in the microporous thermoplastic resin film. Larger than the ratio of the electrolyte solution to be used. For this reason, the nonaqueous electrolyte secondary battery using this composite sheet can be in contact with more electrolyte on the surface of the electrode plate than in the case where the electrode plate is in contact with the microporous thermoplastic resin film. Thereby, more lithium ions can be exchanged between the electrolyte contained in the glass fiber layer and the electrode plate, and the output characteristics of the nonaqueous electrolyte secondary battery are improved.

Further, the microporous thermoplastic resin film provided in the composite sheet has a shutdown function of stopping the movement of lithium ions by closing the microporous film at a certain temperature or higher. In addition, since the glass fiber layer having a high heat resistance is provided, short-circuiting of the electrodes can be prevented even at a temperature at which the thermoplastic resin melts. Therefore, a non-aqueous electrolyte secondary battery using this composite sheet can achieve both safety and output characteristics.

According to the second aspect of the present invention, the thickness of the entire composite sheet is set to 50 μm or less. As a result, the volume of the non-aqueous electrolyte secondary battery can be made compact, so that the output density of the non-aqueous electrolyte secondary battery can be further improved.

According to the third aspect of the present invention, the non-aqueous electrolyte of the non-aqueous electrolyte secondary battery contains a compound having a surface active effect. For this reason, the wettability of the electrolyte with respect to the glass fibers is improved, so that the electrolyte retention of the separator is further improved, and the output characteristics of the nonaqueous electrolyte secondary battery are further improved.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS <First Embodiment> A first embodiment of a composite sheet according to the present invention and a nonaqueous electrolyte secondary battery using the same will be described with reference to FIGS. I will explain it. In the non-aqueous electrolyte secondary battery of the present invention, a substantially rectangular parallelepiped power generating element 10 is housed in a rectangular container formed of a metal (not shown) together with a non-aqueous electrolyte (not shown). The power generating element 10 is configured by laminating a flat negative electrode plate 30 and a flat positive electrode plate 20 via a separator 40 made of a composite sheet as shown in FIG.

FIG. 2 is a sectional view of the power generating element 10. The positive electrode plate 20 is made of a positive electrode current collector 2 made of a metal foil such as aluminum.
A positive electrode mixture layer 22 is formed on both surfaces of the positive electrode material 1 with a substance that absorbs and releases lithium ions as a constituent element. on the other hand,
The negative electrode plate 30 includes a negative electrode current collector 31 made of a metal foil such as copper.
A negative electrode mixture layer 32 composed of a material that absorbs and releases lithium ions as a constituent element is formed on both surfaces of the negative electrode mixture layer. Positive electrode plate 2
The positive electrode lead terminal 23 and the negative electrode lead terminal 33 made of metal pieces such as nickel are welded to one end of the negative electrode plate 30 and the negative electrode plate 30, respectively. The separator 40 is made of a composite sheet, and the separator 40 is formed slightly larger than the positive electrode plate 20 and the negative electrode plate 30.

Next, the composite sheet will be described in detail.
The composite sheet is configured by providing a glass fiber nonwoven fabric 42 as a glass fiber layer on both surfaces of a microporous film 41 made of a thermoplastic resin. The thickness of the composite sheet, that is, the sum of the thickness of the microporous membrane 41 and the thickness of the glass fiber nonwoven fabric 42 is preferably 50 μm or less. Thereby, the power generation element 1
This is because 0 is compact and the output density is improved. Here, the thickness of the glass fiber nonwoven fabric 42 refers to the two glass fiber nonwoven fabrics 42 provided on both sides of the microporous membrane 41.
Means the sum of both thicknesses, not just one. Further, the ratio of the thickness of the glass fiber nonwoven fabric 42 to the total thickness of the composite sheet is preferably as large as possible. However, in the current state of the art, both the microporous film made of thermoplastic resin and the glass fiber nonwoven fabric have a thickness of less than 10 μm. Thick ones are difficult to manufacture. Therefore, when the total thickness of the composite sheet is 50 μm, the ratio of the thickness of the glass fiber nonwoven fabric 42 is 40 to 80%. By setting the ratio of the thickness of the glass fiber to the total thickness of the composite sheet in the above range, it is possible to achieve both the shutdown characteristics of the microporous membrane 41 and the retention characteristics of the electrolyte of the glass fiber nonwoven fabric 42. Become.

As the microporous film 41, a microporous film 41 of polyethylene, polypropylene, polyethylene oxide or the like can be used. The porosity of the microporous film 41 is preferably 30% or more and 60% or less, and more preferably 35% or more and 55% or less, from the balance between the electrolyte retention characteristics and the shutdown characteristics. Among them, the microporous film 41 having a porosity of 40% or more and 50% or less is particularly preferable. The microporous film 41 has a porosity of 30.
% Or more, the electrolyte retention characteristics are good and the porosity is 6%.
This is because the strength is sufficient for a separator at 0% or less.

Here, the porosity of the microporous film 41 can be obtained from the following equation. Porosity (%) = (pore volume / volume of microporous membrane) × 100 The volume of the microporous membrane 41 can be obtained from its size and thickness, and the pore volume of the microporous membrane is Can be determined by subtracting the dry weight from the water-containing weight.

The glass fiber layer is not limited to a non-woven fabric,
For example, it may be a cloth. The average diameter of the glass fibers constituting the glass fiber layer is preferably 5 μm or less, more preferably 2 μm or less. The reason is that if the average diameter of the glass fibers is larger than 5 μm, gas is likely to remain inside the glass fiber layer even when the electrolyte is injected. And the average diameter of the glass fiber is 2 μm
In the following cases, the permeation of the electrolytic solution is rapidly performed by the capillary phenomenon and no gas remains, so that the output characteristics are further improved. The maximum length of the glass fiber is 50
μm or less, more preferably 30 μm or less. By setting the maximum length of the glass fiber to 50 μm or less, the surface of the glass fiber nonwoven fabric becomes flat, and the output characteristics are further improved. The maximum length is an arbitrary 200 μm × 200 μm of glass fiber with a scanning electron microscope.
Are observed at five places, and the maximum length of the glass fiber contained therein is shown. The average diameter of the glass fibers can also be measured by observing the glass fibers with a scanning electron microscope.

The porosity of the glass fiber layer is preferably at least 40%, more preferably at least 55%. Among them, 70% or more is particularly preferable. When the porosity of the glass fiber layer is 40% or more, the amount of the nonaqueous electrolyte held in the composite sheet is sufficient, and sufficient output characteristics can be obtained. Incidentally, the calculation of the porosity of the glass fiber layer,
It can be calculated in the same manner as the porosity of the microporous film 41.

The raw material of the glass fiber used for the glass fiber layer is not particularly limited. For example, a soft glass, a potash glass, a hard glass, a tungsten glass, a super hard glass, an E glass, a quartz glass, and the like which are usually used can be used. In particular, E glass (SiO ₂ : 53.5, Al ₂ O ₃ : 15.0 wt% (wt%), CaO: 17.5 wt%, MgO: 4.5 wt%, B having excellent chemical resistance and insulation resistance)
₂ O ₃ : 8.5 wt%).

The composite sheet is manufactured, for example, by laminating a glass fiber nonwoven fabric 42 on both sides of a microporous membrane 41.

As the non-aqueous electrolyte of the present invention, either a non-aqueous electrolyte or a solid electrolyte can be used. As the solid electrolyte, a known solid electrolyte can be used, and for example, an inorganic solid electrolyte and a polymer solid electrolyte can be used.

As the non-aqueous electrolyte, a known one can be used. For example, a solution in which a lithium salt such as lithium hexafluorophosphate (LiPF ₆ ) is dissolved in a non-aqueous solvent such as a cyclic carbonate such as ethylene carbonate (EC) or a chain carbonate such as diethyl carbonate (DEC). No.

It is preferable to add a compound having a surface active effect to the non-aqueous electrolyte. As the compound having surface activity, a fluorinated alkyl ester, polyethylene glycol dimethyl ether, and γ-butyrolactone are preferable from the viewpoint of stability against a redox atmosphere inside the battery.

Polyethylene glycol dimethyl ether is CH ₃ —O— (CH ₂ —CH ₂ —O—) _n —CH ₃
The molecular weight is preferably 200 or more and 5000 or less, more preferably 200 or more and 3500 or less from the viewpoint of solubility in a non-aqueous electrolyte and surface active effects. Among them, 200 to 900 is particularly preferable.

The proportion of polyethylene glycol dimethyl ether added to the non-aqueous electrolyte is 0.5 wt% or more and 7 w
t% or less is preferable, and 1 wt% or more and 5 wt% or less are more preferable. Among them, particularly, 2 wt% or more and 4 wt% or less are preferable. This is because if the proportion of polyethylene glycol dimethyl ether added is 0.5 wt% or more, the wettability of the glass fiber nonwoven fabric 42 is improved by the surface active effect, and the output characteristics are further improved. On the other hand, if the proportion exceeds 7 wt%, the viscosity of the non-aqueous solvent increases, which hinders the movement of lithium ions.

The fluorinated alkyl ester is not particularly limited as long as it has a fluorine-substituted alkyl chain and an ester bond, but CF ₃ (CF ₂ ) ₉ COOC ₂ H ₅ is preferred. The ratio of the fluorinated alkyl ester to the non-aqueous electrolyte is 0.01 wt% or more for the same reason as the polyethylene glycol dimethyl ether.
wt% or less, more preferably 0.1 wt% or more and 4 w
t% or less is preferable. Among them, 0.5 wt% or more and 2 wt% or less are particularly preferable.

The ratio of adding γ-butyrolactone to the non-aqueous electrolyte is the same as that for polyethylene glycol dimethyl ether.
1 wt% or more and 10 wt% or less are preferable, and 3 w
The content is preferably at least t% and at most 8 wt%. Among them, especially 5w
It is preferably at least t% and at most 7 wt%.

Hereinafter, effects of the present invention will be described. Here, the positive electrode plate 20 and the negative electrode plate 30 are stacked with a separator 40 interposed therebetween, and the positive electrode mixture layer 22 is formed on the surface of the positive electrode plate 20.
The negative electrode mixture layer 32 is provided on the surface of the negative electrode plate 30. Therefore, the positive electrode mixture layer 22 and the negative electrode mixture layer 32 come into contact with the glass fiber nonwoven fabric 42 provided on both surfaces of the separator 40. Glass fiber non-woven fabric 42
Is larger in the space portion, that is, the porosity than the microporous membrane 41, so that the ratio of the nonaqueous electrolyte held in the glass fiber nonwoven fabric 42 is larger than the ratio of the nonaqueous electrolyte held in the microporous membrane 41. growing. Therefore, since the amount of the nonaqueous electrolyte contacting the positive electrode mixture layer 22 and the negative electrode mixture layer 32 increases,
The non-aqueous electrolyte secondary battery using this composite sheet has a positive electrode mixture layer 22 and a negative electrode mixture layer 32 in comparison with a case where the positive electrode mixture layer 22 and the negative electrode mixture layer 32 are in contact with the microporous film 41. It can be in contact with more electrolytes. As a result, more lithium ions can be exchanged between the nonaqueous electrolyte contained in the glass fiber nonwoven fabric 42 and the positive electrode mixture layer 22 and the negative electrode mixture layer 32, so that the output of the nonaqueous electrolyte secondary battery can be improved. The characteristics are improved.

When the battery is used for a long period of time, the non-aqueous electrolyte is decomposed and reduced as the battery is charged and discharged, and the liquid on the surfaces of the positive electrode mixture layer 22 and the negative electrode mixture layer 32 may be dried. . Even in such a case, if the composite sheet according to the present invention is used as the separator 40, the non-aqueous electrolytic solution that contacts the positive electrode mixture layer 22 and the negative electrode mixture layer 32 because the separator 40 has a high electrolyte retention rate. The volume of liquid is maintained. Thereby, the life of the nonaqueous electrolyte secondary battery is improved.

Further, when the charge / discharge of the non-aqueous electrolyte secondary battery is repeated, the non-aqueous electrolyte may be decomposed to generate fine particles of decomposition products. In the present invention, the glass fiber layer is made of glass fiber in the form of a nonwoven fabric or a cloth. The opening between the fibers of the glass fiber nonwoven fabric 42, that is, the diameter of the hole is generally 2 to 20 μm, and the diameter of the hole of the microporous membrane 41 is larger than 0.01 to 1 μm. I have. Therefore, decomposition products are less likely to be clogged in the openings of the glass fiber nonwoven fabric 42 than in the pores of the microporous membrane 41. In addition, the fine particles of the decomposition products are trapped by the glass fiber nonwoven fabric 42 and are less likely to reach the microporous membrane 41 provided between the glass fiber nonwoven fabrics 42. This makes it difficult for the decomposition products of the non-aqueous electrolyte solution to clog the microporosity of the microporous film 41. Therefore, the movement of lithium ions is not easily hindered by the microporous film 41, so that the capacity of the non-aqueous electrolyte secondary battery is not easily reduced even when charging and discharging are repeated, and the non-aqueous electrolyte The life of the secondary battery is improved.

<Second Embodiment> Next, a second embodiment will be described. The same components as those in the first embodiment are denoted by the same reference numerals, and description thereof will be omitted. FIG. 3 is an exploded perspective view showing the power generating element 10 of the nonaqueous electrolyte secondary battery according to the second embodiment. The non-aqueous electrolyte secondary battery of the present embodiment has a first
The present embodiment differs from the embodiment in that the positive electrode plate 20 is accommodated in a bag-shaped separator 50 formed in a bag shape, and the power generating element 10 is configured by stacking the positive electrode plate 20 and the negative electrode plate 30.

The bag-shaped separator 50 is obtained by bending a composite sheet having the same configuration as that of the first embodiment into a U-shape, then opening one end and partially welding both sides as indicated by reference numeral 51. Is formed. Then, the bag-shaped separator 50 is covered on the positive electrode plate 20 in the direction of arrow A from the opposite end of the positive electrode plate 20 where the positive electrode lead terminal 23 is provided as shown in FIG. B),
(C)). The non-aqueous electrolyte secondary battery according to the present embodiment,
Since the positive electrode plate 20 is covered by the bag-shaped separator 50,
The short circuit is reliably prevented, and the safety of the battery is further improved.

<Other Embodiments> In the first embodiment and the second embodiment, the non-aqueous electrolyte secondary battery including the stack type power generating element 10 in which the flat electrode plates are stacked with the separator 40 interposed therebetween has been described. The shape of the power generation element 10 is not limited to this. As the shape of the power generating element 10, for example, a power generating element of any shape, such as a wound type having a circular cross-section, an elliptical shape, and a non-circular shape, or a type in which a sheet-shaped electrode plate is folded via a separator and laminated. 10 can be used.

[0033]

The present invention will now be described by way of examples, which should not be construed as limiting the invention. 1. Production of Battery <Example 1> (Preparation of Composite Sheet) A composite sheet having a three-layer structure to be used as the separator 40 was produced by laminating a glass fiber nonwoven fabric 42 on both sides of a polyethylene microporous film 41 and then winding it. (In Table 1, "GPG" is described in the configuration of the composite sheet.)

[0034]

[Table 1]

The structure of the separator 40 is a glass fiber nonwoven fabric 42 / a microporous film 41 / glass fiber nonwoven fabric 42. The thickness of the glass fiber nonwoven fabric 42 was 10 μm, and the thickness of the microporous film 41 was 20 μm. Therefore, the entire thickness of the separator 40 as a composite sheet is 40 μm,
The ratio of the thickness of the glass fiber nonwoven fabric 42 is 50%.

As the glass fiber non-woven fabric 42, a non-woven glass fiber made of E glass having an average diameter of 1 μm and a maximum length of 50 μm and having a porosity of 70% was used.
The microporous film 41 was made of a polyethylene microporous film having a porosity of 43% and an average pore diameter of 0.3 μm.

The average diameter and the maximum length of the glass fiber were measured by observing the glass fiber with a scanning electron microscope. The average diameter of the glass fiber is any 20 μm
Observation of 5 places of × 20 μm, 10 of each,
The diameters of a total of 50 glass fibers were measured, and the average value was determined. The maximum length is the same as in the method described above.

(Preparation of Positive Electrode Plate) The positive electrode plate 20 has a thickness of 20 mm.
90% by weight of LiCoO ₂ as a positive electrode active material, 4% by weight of acetylene black as a conductive agent, and 6% by weight of polyvinylidene fluoride (PVDF) as a binder on both sides of a positive electrode current collector 21 made of a μm aluminum foil. The mixed positive electrode mixture paste was applied, pressed, and dried to form the positive electrode mixture layer 22 to be manufactured. The thickness of the entire positive electrode plate 20 was 177 μm.

(Preparation of Negative Electrode Plate) The negative electrode plate 30 has a thickness of 14
92% by weight of graphite as a negative electrode active material and PVDF as a binder on both surfaces of a negative electrode current collector 31 made of a copper foil of μm.
A negative electrode mixture in which 8% by weight was mixed was applied, and was manufactured in the same manner as the positive electrode plate 20. The size and thickness of the negative electrode plate 30 were the same as those of the positive electrode plate 20.

(Preparation of Non-Aqueous Electrolyte) A non-aqueous electrolyte was prepared by mixing ethylene carbonate (EC) and diethyl carbonate (D
EC) and LiPF ₆ in a solvent mixed at a volume ratio of 1: 1.
Was dissolved at 1 mol / l.

(Preparation of Battery) Forty positive plates 20, 41 negative plates 30, and a composite sheet of separator 40 of 8 sheets
The power generating element 10 was manufactured by laminating 0 sheets. This power generation element 1
No. 0 was stored in an aluminum prismatic battery container to produce a non-aqueous electrolyte secondary battery. The non-aqueous electrolyte is the positive electrode plate 20,
The negative electrode plate 30 and the separator 40 were sufficiently wetted, and an amount of excess electrolyte not existing outside the power generation element 10 was injected under vacuum.
The battery had a capacity of about 10 Ah and a weight of about 3 kg.

<Comparative Example 1> A non-aqueous electrolyte secondary battery different from Example 1 only in the structure of the separator 40 was manufactured. In this comparative example, the outer layer and the inner layer of the separator 40 of the first embodiment are stacked in reverse. That is,
A composite sheet having a three-layer structure in which a microporous membrane 41 was laminated on both sides of a glass fiber nonwoven fabric 42 was used as the separator 40 (in Table 1, the composite sheet was described as “PGP”). The thickness of each of the microporous films 41 was 10 μm, and the thickness of the glass fiber nonwoven fabric 42 was 20 μm. Therefore,
The total thickness of the composite sheet is 40 μm, and the ratio of the thickness of the glass fiber nonwoven fabric 42 to that is 50%.

<Comparative Example 2> A non-aqueous electrolyte secondary battery different from Example 1 only in the structure of the separator 40 was manufactured. In the present comparative example, the separator 40 was a composite sheet having a two-layer structure in which a glass fiber nonwoven fabric 42 and a microporous film 41 were laminated (in Table 1, the composite sheet was described as “GP”). The thickness of the composite sheet was 40 μm, and the thickness of the glass fiber nonwoven fabric 42 was 20 μm. Therefore, the ratio of the thickness of the glass fiber nonwoven fabric 42 to the total thickness of the composite sheet is 50%.

<Comparative Example 3> A non-aqueous electrolyte secondary battery different from Example 1 only in the structure of the separator 40 was manufactured. In this comparative example, only the microporous film 41 was used as the separator 40 ("P" is described in the configuration of the composite sheet in Table 1). The thickness of the microporous film 41 is 40
μm.

<Example 2> A non-aqueous electrolyte secondary battery different from Example 1 only in the ratio of the total thickness of the composite sheet and the thickness of the glass fiber nonwoven fabric 42 was produced. The thickness of the microporous membrane 41 is 30 μm, and the total thickness of the composite sheet is 5 μm.
It was set to 0 μm. Therefore, the ratio of the thickness of the glass fiber nonwoven fabric 42 to the total thickness of the composite sheet is 40%.

Example 3 A non-aqueous electrolyte secondary battery different from Example 1 only in the total thickness of the composite sheet and the ratio of the thickness of the glass fiber nonwoven fabric 42 was produced. The thickness of each of the glass fiber nonwoven fabrics 42 was 15 μm, and the total thickness of the composite sheet was 50 μm. Therefore, the ratio of the thickness of the glass fiber nonwoven fabric 42 to the total thickness of the composite sheet is 60%.
%.

Example 4 A non-aqueous electrolyte secondary battery different from Example 1 only in the ratio of the total thickness of the composite sheet and the thickness of the glass fiber nonwoven fabric 42 was produced. When the thickness of the glass fiber nonwoven fabric 42 is 20 μm and the thickness of the microporous membrane 41 is 10 μm, the total thickness of the composite sheet is 50 μm.
And Therefore, the ratio of the thickness of the glass fiber nonwoven fabric 42 to the total thickness of the composite sheet is 80%.

Example 5 A non-aqueous electrolyte secondary battery different from Example 1 only in the total thickness of the composite sheet was manufactured. The thickness of the glass fiber nonwoven fabric 42 was 15 μm, the thickness of the microporous membrane 41 was 30 μm, and the total thickness of the composite sheet was 60 μm. Therefore, the ratio of the thickness of the glass fiber nonwoven fabric 42 to the total thickness of the composite sheet is 50%.

Example 6 A non-aqueous electrolyte secondary battery different from Example 1 only in the total thickness of the composite sheet and the ratio of the thickness of the glass fiber nonwoven fabric 42 was produced. The thickness of the glass fiber nonwoven fabric 42 and the microporous film 41 was 20 μm, and the total thickness of the composite sheet was 60 μm. Therefore,
The ratio of the thickness of the glass fiber nonwoven fabric 42 to the total thickness of the composite sheet is 67%.

<Examples 7 to 9> Non-aqueous electrolyte secondary batteries differing from Example 1 only in the glass fibers constituting the glass fiber nonwoven fabric 42 were manufactured. In Examples 7 to 9, a glass fiber nonwoven fabric 42 made of glass fibers having the average diameter and the maximum length shown in Table 1 was used.

Example 10 A non-aqueous electrolyte secondary battery according to the second embodiment of the present invention was manufactured. The non-aqueous electrolyte secondary battery in this example had the same configuration as that of Example 1 except that the composite sheet of Example 1 was used as a bag-shaped separator 50.

<Examples 11 to 15> Non-aqueous electrolyte secondary batteries were different from Example 1 only in the composition of the non-aqueous electrolyte. Polyethylene glycol dimethyl ether (molecular weight = 900), which is a compound having a surface active effect, was added to the nonaqueous electrolyte at a ratio as shown in Table 2. In addition,
In each example, the concentration of the electrolyte salt LiPF ₆ is 1 mol / l.

[Table 2]

Examples 16 to 20 Non-aqueous electrolyte secondary batteries were different from Example 1 only in the composition of the non-aqueous electrolyte. A fluorinated alkyl ester (CF ₃ (CF ₂ ) ₉ COOC ₂ H ₅ ) which is a compound having a surface active effect was added to the non-aqueous electrolyte at a ratio as shown in Table 2. In each example, the concentration of the electrolyte salt LiPF ₆ was 1 mol / l.

<Examples 21 to 25> Example 1 and non-aqueous
A non-aqueous electrolyte secondary battery that differs only in the composition of the electrolyte was manufactured.
Was. Γ-butyrolact, a compound having a surfactant effect
Tons added to the non-aqueous electrolyte at the ratio shown in Table 2.
did. In each example, the electrolyte salt LiP
F ₆Is 1 mol / l.

2. Test (Output Characteristics Test) The batteries of Examples 1 to 25 and Comparative Examples 1 to 3 were charged at a constant current up to 4.2 V at 2 A and then charged at 4.2 V at a constant voltage. The charging time was 5 hours from the start of constant current charging. afterwards,
Perform constant current discharge, discharge depth 75%, 50% and 25%
The output power at the time of was measured, and the output density was calculated. The depth of discharge is 0% at the end of charging (4.2 V, 0 Ah).
100% at the end of discharge (2.75 V, 10 Ah)
And The output power at the discharge depths of 75%, 50% and 25% is 2.75 at a constant current of 500 mA.
When discharging to V, the fifth hour (discharge depth 25%),
The voltage was measured at the 10th hour (50% depth of discharge) and at the 15th hour (75% depth of discharge). In addition, all 20 ℃
A charge / discharge test was performed in an atmosphere of the following temperature.

3. Results (Study of Separator Configuration) Table 1 and FIG. 4 show the measurement results of the output characteristic tests of the nonaqueous electrolyte secondary batteries in Example 1 and Comparative Examples 1 to 3 in which the configuration of the composite sheet as the separator 40 was different. . The composite sheet in the battery of Example 1 has a three-layer structure in which the glass fiber nonwoven fabric 42 is provided on both sides of the microporous membrane 41. The glass fiber nonwoven fabric 42 is not provided on one side. As shown in Table 1 and FIG.
%, 50%, and 75%, the output density of the battery in Example 1 is highest.

Here, in the non-aqueous electrolyte secondary battery of Example 1, the microporous film 41 was formed on both the positive electrode plate 20 and the negative electrode plate 30.
Instead, they are in contact with the glass fiber nonwoven fabric 42. Since the glass fiber nonwoven fabric 42 has a higher porosity than the microporous membrane 41, it can contain more nonaqueous electrolyte. If the amount of the non-aqueous electrolyte contacting the positive electrode plate 20 and the negative electrode plate 30 is large, the amount of the non-aqueous electrolyte between the non-aqueous electrolyte and the positive electrode active material provided on the positive electrode plate 20 and the negative electrode active material provided on the negative electrode plate 30 is increased. The movement of lithium ions is facilitated. Thereby, it is considered that the battery of Example 1 has an improved output density as compared with the batteries of Comparative Examples 1 to 3 in which at least one of the positive electrode plate 20 and the negative electrode plate 30 is in contact with the microporous film 41. Can be

The batteries of Examples 2 to 25 having the same composite sheet structure as that of Example 1 had the output densities shown in Table 1.
As shown in Table 2 and Table 2, at 25% and 50% discharge depth, the output densities of the batteries of Comparative Examples 1 to 3 having different configurations of the composite sheet were higher.

(Study on the Ratio of the Thickness of the Glass Fiber Layer to the Total Thickness of the Composite Sheet) In Examples 1 to 4 where the ratio of the thickness of the glass fiber nonwoven fabric 42 to the total thickness of the composite sheet as the separator 40 is different. The output densities of the non-aqueous electrolyte secondary batteries are compared. As shown in Table 1, at all discharge depths, the ratio of the thickness of the glass fiber nonwoven fabric 42 to the total thickness of the composite sheet is 40% to 40%.
The output densities of the batteries in Examples 2 to 4, which are 80%, are almost the same as the output density of the batteries in Example 1.

(Examination of Total Thickness of Composite Sheet) Examples 1 to 3 in which the total thickness of the composite sheet as the separator 40 is different
The output density of the battery in No. 6 is compared. As shown in Table 1, at all discharge depths, Examples 1 to 5 in which the total thickness of the composite sheet was 50 μm or less.
It can be seen that the output density of the battery in Example 4 is larger than the output density of the batteries in Examples 5 and 6 in which the total thickness of the composite sheet is 60 μm.

(Study of Diameter and Maximum Length of Glass Fiber) Regarding the nonaqueous electrolyte secondary batteries of Examples 1 and 7 to 9 in which the average diameter and the maximum length of the glass fibers constituting the glass fiber nonwoven fabric 42 are different. Compare power density. Examples 1, 7
In this example, the average diameter of the glass fiber is 2 μm or less, and at the same time, the maximum length of the glass fiber is 50 μm or less. As shown in Table 1, the batteries in Examples 1 and 7 were Example 8 in which the average diameter of the glass fiber was 3 μm and Example 9 in which the maximum length of the glass fiber was 70 μm.
The output density is improved at all discharge depths compared to the battery of the above.

(Study of Bag-like Separator) The output densities of the batteries in Examples 10 and 1 using the bag-like separator 50 according to the second embodiment are compared.
As shown in Table 1, the output density of the battery in Example 10 is equal to the output density of the battery in Example 1 at all discharge depths.

(Study on Addition of Compound Having Surfactant Effect) Examples 1 and 11 and 2 in which additives are added to a non-aqueous electrolyte
The output density of the battery in No. 5 is compared.

Particularly, in a battery to which polyethylene glycol dimethyl ether (molecular weight = 900) is added,
More than 0.5 wt% (Example 12), 7 wt%
(Embodiment 14) In the following, the output density is further improved as compared with the embodiment 1.

Further, CF ₃ (CF ₂ ) ₉ COOC ₂ H ₅
In the battery to which is added, the addition amount is 0.01 wt%.
(Example 17) Not less than 5 wt% (Example 19) and
The output density is further improved compared to the first embodiment.

In the battery to which γ-butyrolactone was added, the addition amount was 1 wt% (Example 22) or more.
At 0 wt% or less (Example 24), the output density is further improved as compared with Example 1.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a power generating element of a nonaqueous electrolyte secondary battery according to a first embodiment of the present invention.

FIG. 2 is a sectional view taken along line II-II in FIG.

FIG. 3 is an exploded perspective view showing a power generating element of a nonaqueous electrolyte secondary battery according to a second embodiment of the present invention.

FIG. 4 is a graph showing the relationship between the depth of discharge and the output density of the nonaqueous electrolyte secondary battery according to the first embodiment of the present invention.

[Explanation of symbols]

20 ... Positive electrode plate 30 ... negative electrode plate 40 ... Separator 41 ... Glass fiber non-woven fabric 42 ... Microporous membrane

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Claims (3)

[Claims] 1. A composite sheet used as a separator of a non-aqueous electrolyte secondary battery, wherein a glass fiber layer is provided on both sides of a microporous thermoplastic resin film. 2. The composite sheet according to claim 1, wherein the sum of the thickness of the microporous thermoplastic resin film and the thickness of the glass fiber layer is 50 μm or less. 3. A separator comprising a composite sheet according to claim 1 between a positive electrode plate and a negative electrode plate, and the non-aqueous electrolyte contains a compound having a surface active effect. Non-aqueous electrolyte secondary battery.