JP2003151635A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery with high safety and high discharging characteristics by facilitating the diffusion of gas generated inside and the supply of a nonaqueous electrolyte to between electrode plates. SOLUTION: This square nonaqueous electrolyte battery 1 has a power generating element prepared by spirally winding or stacking a positive plate 3 formed by laminating a positive active material layer on a current collector, a negative plate 4 formed by laminating a negative active material layer on a current collector, and a separator 5, and is constituted by pouring the nonaqueous electrolyte in the power generating element, and a heat resistant gas diffusion layer 20 is installed between the positive plate 3 or the negative plate 4 and the separator 5.

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 lithium ion battery, a thin active material layer is formed on a thin plate-shaped current collector for both the positive electrode and the negative electrode in order to improve the characteristics during high-rate discharge, and a spiral or flat plate is formed together with a separator. It has a structure in which it is housed in a battery container as a power generation element having a laminated shape.

Due to this electrode structure, in the injection of liquid in the production of a lithium ion battery, the air entrapped inside the power generating element when the power generating elements are stacked is not replaced by the electrolytic solution but remains as bubbles, The capacity characteristics of the battery may be adversely affected. In addition, when charging and discharging, some of the solvent may be decomposed to generate gas, but in the power generation element with such a laminated shape, the internal gas accumulates without being released to the outside of the power generation element. It becomes a bubble. Therefore, the active material in contact with the bubbles is not used, which similarly causes a decrease in capacity. In particular, in a large-sized battery such as an electric vehicle that is being actively developed at present, the battery size becomes large, and these phenomena become remarkable. In order to solve a phenomenon such as defective injection of an electrolytic solution, for example, Japanese Unexamined Patent Application Publication No.
In the invention disclosed in the 1-23612 publication, an attempt is made to improve the supply of the electrolytic solution and the diffusion of the gas by providing a groove on the surface of the positive electrode active material, but this was insufficient.

Further, a lithium ion battery is used as a separator which is a thermoplastic resin film such as polyethylene provided with a large number of minute holes. This is because when the temperature inside the battery provided with the separator rises due to a short circuit inside or outside the battery, the separator is softened or melted, and the minute holes provided in the separator are closed, and the lithium ions in the electrolytic solution The purpose is to stop the movement and cut off the current. However, even after the minute holes of the separator are closed and the current is cut off, it takes a certain amount of time for the heat generated in the power generation element to be transferred to the separator, so that the temperature of the separator may continue to rise. In such a case, since the separator is thermoplastic, there is a possibility that the separator melts to open a large hole and the bipolar plates are short-circuited.

[0005]

The present invention has been completed based on the above circumstances, and is excellent in safety, and is capable of diffusing gas generated inside the power generation element and preventing non-existence between the electrode plates. It is an object of the present invention to provide a non-aqueous electrolyte secondary battery that facilitates the supply of water electrolyte and has excellent discharge characteristics.

[0006]

According to the invention of claim 1, a positive electrode plate comprising a current collector and a positive electrode active material layer laminated thereon,
A negative electrode plate formed by stacking a negative electrode active material layer on a current collector, and a power generation element formed by spirally winding or stacking a separator made of a microporous film of a thermoplastic resin, the power generation element being non-aqueous. A non-aqueous electrolyte secondary battery constructed by injecting an electrolytic solution is characterized in that a heat resistant gas diffusion layer is provided between a positive electrode plate or a negative electrode plate and a separator.

In the invention of claim 1, the gas diffusion layer is provided between the positive electrode or the negative electrode and the separator. This allows
The gas diffusion layer serves as a path for the electrolyte to enter from the outside of the power generating element to the inside during the injection of the manufacturing process, and at the same time, serves as a path through which the air existing inside the power generating element is discharged to the outside, and bubbles inside the power generating element It can be prevented from occurring. Further, since the gas diffusion layer serves as a path through which the gas generated in the positive electrode or the negative electrode during charging / discharging diffuses to the outside of the power generating element, it is possible to prevent bubbles from being generated inside the power generating element during charging / discharging. As a result, the proportion of the positive electrode or negative electrode active material that can be used increases, so that the capacity characteristics of the lithium ion battery are improved.

Further, even if a short circuit occurs inside or outside the battery and the temperature of the battery rises to melt the separator, the gas diffusion layer is heat resistant and does not melt at the same temperature as the thermoplastic resin. Prevents short circuits and excels in safety.

The invention of claim 2 is characterized in that the gas diffusion layer is composed of a non-woven fabric made of glass fibers or high melting point polymer fibers. Since the nonwoven fabric has continuous voids, the voids facilitate the movement of gas or electrolyte. Further, even if the separator is melted by heat, the glass fiber of the non-woven fabric or the fiber of the high melting point polymer prevents a short circuit between the electrode plates.

The invention of claim 3 is characterized in that the gas diffusion layer is a high-melting-point polymer film having a large number of liquid passage holes formed of circular holes. This liquid passage hole enables the movement of ions between the electrode plates and can effectively prevent a short circuit between the electrodes when the separator is melted.

The invention of claim 4 is characterized in that the high melting point polymer fiber or the high melting point polymer film is subjected to a surface modification treatment for enhancing the wettability with an electrolytic solution. Accordingly, it is possible to prevent bubbles from being generated on the surface of the high melting point polymer fiber or the high melting point polymer film when the electrolytic solution is injected during manufacturing.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic cross-sectional view of a prismatic non-aqueous electrolyte secondary battery 1 according to an embodiment of the present invention. The prismatic non-aqueous electrolyte secondary battery 1 comprises a spirally-wound electrode group 2 as a power generating element and a non-aqueous electrolyte solution (not shown) containing an electrolyte salt, which is housed in a battery case 6.

As shown in FIG. 1, the spiral electrode group 2 has a gas diffusion layer 20 disposed between a positive electrode plate 3 and a negative electrode plate 4 together with a separator 5 and is integrally molded by a roll press or the like and wound. It has a different structure. Alternatively, the spirally wound electrode group 2 can be manufactured by winding the respective elements without integrating them. In FIG. 1, the position of the gas diffusion layer 20 in the spiral electrode group 2 is arranged on the positive electrode plate 3 side with respect to the separator 5, but it may be on the negative electrode plate 4 side. Also,
The gas diffusion layer 20 may be sandwiched between two layers of the separator 5, or the separator 5 may be sandwiched between two layers of the gas diffusion layer 20.

The gas diffusion layer 20 may be in the form of a non-woven fabric formed using the fibrous heat-resistant material shown in FIG. 2 or in the form of a mesh shown in FIGS. Further, as shown in FIG. 5, glass fibers or heat-resistant resin fibers are arranged so as to extend in a direction perpendicular to the longitudinal directions of the positive electrode plate 3 and the negative electrode plate 4, and are arranged in the longitudinal direction of the positive electrode plate 3 and the negative electrode plate 4. The fibers can be arranged at intervals so that they do not overlap. The distance between the fibers for facilitating gas escape is 1 mm to
It is preferable to arrange them at intervals of 5 mm. In addition, as shown in FIG. 6, the liquid-permeable holes 25 are formed in the heat-resistant resin-molded film.
Can be provided. The liquid passage hole 25 can be opened by an electron beam, a laser beam, or a mechanical method.

Examples of the heat-resistant resin which can be in the form of fibers or films include the following. Aromatic polyimide (hereinafter sometimes referred to simply as polyimide), polyamideimide, aromatic polyamide (hereinafter sometimes referred to as aramid), polycarbonate, polyacetal, polysulfone, polyphenyl sulfide, polyether ether ketone, aromatic polyester, poly Examples include ether sulfone and polyether imide. In particular, polyimide, polyamide-imide and aramid are preferable in that they can withstand deformation due to heat.

The fiber material is not particularly limited as long as it is a heat resistant fiber. Therefore, in addition to the fibers made of the above heat-resistant resin, glass fibers, alumina fibers, alumina-silica fibers, ceramic fibers, zirconia fibers, rock wool, Tyranno fibers, silicon carbide fibers, potassium titanate fibers, alumina whiskers, boric acid. Inorganic fibers such as aluminum whiskers can be exemplified. In particular, glass fiber is desirable because of its ease of handling and its price.

The surface modification treatment of the polymer fiber or polymer film includes radical treatment. For example,
When UV irradiation is performed in the presence of oxygen, the surface is oxidized by ozone or the like generated at that time, and a carboxylic acid group, a carbonyl group, a hydroxyl group, an amino group or the like can be generated. Therefore, the affinity of the polymer surface for the solvent, that is, the wettability of the polymer surface is improved. In addition to ultraviolet irradiation, surface modification can be performed by gamma ray irradiation or corona discharge.

A battery lid 7 provided with a safety valve 8 is attached to the battery case 6 by laser welding, the positive electrode terminal 10 is connected to the positive electrode plate 3 via a positive electrode lead 11, and the negative electrode plate 4 is connected to the battery case 6. It is electrically connected by contact with the inner wall of the.

The positive electrode plate 3 is provided with a positive electrode active material layer composed of a positive electrode mixture containing a substance that absorbs and releases lithium ions on both sides of a positive electrode current collector made of, for example, aluminum, nickel, or stainless. It has a different structure.

The positive electrode plate 3 is manufactured as follows, for example. A positive electrode active material is mixed with a conductive agent such as graphite or carbon black and a binder such as polyvinylidene fluoride to prepare a positive electrode mixture. Then, this positive electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to prepare a paste. This is applied to both surfaces of the positive electrode current collector, dried, and then compressed and smoothed by a roll press or the like to manufacture the positive electrode plate 3.

The positive electrode active material is not particularly limited, and for example, a compound capable of inserting and extracting lithium can be used,
For example, LiCoO ₂ , LiNiO ₂ , LiMn
₂ O ₄ , Li ₂ Mn ₂ O ₄ , MnO ₂ , FeO ₂ , V ₂
Such as O ₅ , V ₆ O ₁₃ , TiO ₂ , TiS _2, etc.,
Formula LixMO ₂ or LiyM ₂ O _4, (provided that, M
Can be a transition metal, a complex oxide represented by 0 ≦ x ≦ 1, 0 ≦ y ≦ 2), an oxide having tunnel holes, or a metal chalcogenide having a layered structure.

It is also possible to use an inorganic compound in which a part of the transition metal M is substituted with another element. Further, an organic compound such as a conductive polymer such as polyaniline can be used. In addition, regardless of whether it is an inorganic compound or an organic compound, the above various active materials can be mixed and used.

The negative electrode plate 4 has a structure in which a negative electrode current collector made of copper, nickel, or stainless is provided on both surfaces with a negative electrode active material layer made of a negative electrode mixture containing a substance that absorbs and releases lithium ions. ing. Note that the negative electrode active material layer may be provided not only on both surfaces but also on one surface.

The negative electrode plate 4 is manufactured, for example, as follows. The negative electrode active material is mixed with a binder such as polyvinylidene fluoride to prepare a negative electrode mixture. Then, this negative electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to obtain a slurry. This is applied on both sides of the negative electrode current collector, dried, and then compressed and smoothed by a roll press or the like to manufacture the negative electrode plate 4.

The negative electrode active material is not particularly limited, and examples thereof include known cokes, glassy carbons, graphites, non-graphitizable carbons, pyrolytic carbons, carbonaceous materials such as carbon fibers, and metals. Lithium, lithium alloy, polyacene, or tin oxide glass, lithium / titanium composite oxide, iron oxide, ruthenium oxide, molybdenum oxide, tungsten oxide, titanium oxide, tin oxide, metal oxide such as tin oxide, etc. Alternatively, two or more kinds may be mixed and used, but it is particularly preferable to use a carbonaceous material because of its high safety.

As the non-aqueous electrolyte of the present invention, a non-aqueous electrolytic solution can be used. As the non-aqueous electrolyte, for example, a mixed solvent of ethylene carbonate and methyl ethyl carbonate or a mixed solvent of ethylene carbonate and dimethyl carbonate can be used. In the mixed solvent, propylene carbonate, butylene carbonate, vinylene carbonate, trifluoropropylene carbonate, γ-butyrolactone, 2-methyl-γ-butyl lactone, acetyl-γ-butyrolactone, γ-valerolactone, sulfolane, 1,2-dimethoxy. Ethane, 1,2-diethoxyethane, tetrahydrofuran,
2-methyltetrahydrofuran, 3-methyl-1,3-
Dioxolane, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, dimethyl carbonate,
Diethyl carbonate, methyl ethyl carbonate, dipropyl carbonate, methyl propyl carbonate,
You may use ethyl isopropyl carbonate, dibutyl carbonate, etc. individually or in mixture of 2 or more types.

The electrolyte salt as a solute of the non-aqueous electrolyte is not particularly limited, and for example, LiClO ₄ , LiAsF ₆ , Li
PF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiCF ₃ C
F ₂ SO ₃ , LiCF ₃ CF ₂ CF ₂ SO ₃ , LiN
_{(CF 3 SO 2) 2,} LiN (C 2 F 5 SO 2) 2 and the like may be used alone or as a mixture of two or more. Among them, LiPF ₆ is preferably used as the electrolyte salt.

As the separator 5, a synthetic resin microporous film can be preferably used. Among them, polyethylene and polypropylene microporous film, or polyolefin microporous film such as a composite microporous film, thickness, film strength,
It is preferably used in terms of film resistance and the like.

[0029]

EXAMPLES Examples of the present invention will be shown below, but the present invention is not limited thereto. <Example 1> A prismatic non-aqueous electrolyte secondary battery 1 shown in Fig. 1 was produced. First, the production of the negative electrode plate 4 will be described. 90 parts by weight of graphite as a negative electrode active material and 10 parts by weight of polyvinylidene fluoride (hereinafter abbreviated as PVdF) as a binder are mixed, and N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP) is appropriately added and dispersed. , A paste was prepared. Width 80mm, length 2480mm, thickness 15μ
m of the copper negative electrode current collector was uniformly applied to both surfaces and dried. Then, the negative electrode current collector coated with the paste was passed through a hot press roller, and further vacuum dried at 150 ° C. to evaporate NMP to prepare a negative electrode plate 4. The obtained negative electrode had a thickness of 185 μm and a porosity of 30 to 50%. The porosity was calculated from the true density of the substance forming the active material layer and the thickness of the obtained active material layer.

Next, the production of the positive electrode plate 3 will be described. 92 parts by weight of LiCoO _{2 as a} positive electrode active material, 3 parts by weight of acetylene black as a conductive material, and 5 parts by weight of PVdF as a binder were mixed, and NMP was appropriately added and dispersed to prepare a paste. Width 78 mm, length 2340 mm, thickness 2
This paste was applied to a 0 μm positive electrode current collector, and the negative electrode plate 4
A positive electrode plate 3 was produced in the same manner as in. The obtained positive electrode plate 3 had a thickness of 176 μm and a porosity of 30 to 40%.

As the gas diffusion layer 20, a glass fiber nonwoven fabric 21 as shown in FIG. 2 was used. The diameter of the glass fiber is 1 μm, and the sheet thickness of the glass fiber nonwoven fabric 21 is 5
was μm.

The separator 5 has a width of 86 mm and a length of 2
A microporous polyethylene film having a thickness of 893 mm and a thickness of 16 to 25 μm was used. The air permeability of this separator 5 is 50.
It was 0 sec / 100 cc, and the porosity was 46%.
The thickness of the separator 5 was changed according to the thickness of the glass fiber nonwoven fabric 21 so that the electrode plate spacing was 25 μm.

As the non-aqueous electrolyte, ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed in a volume ratio of 30:70, and LiPF ₆ was added to this solution in an amount of 1.2.
Mol / liter dissolved therein was used.

As shown in FIG. 2, the negative electrode plate 4, the separator 5, the glass fiber non-woven fabric 21, the positive electrode plate 3, the glass fiber non-woven fabric 21 and the separator 5 are laminated in this order by using the above-mentioned components and roll-pressed to be integrated. Turned into The integrated electrode group was wound to produce a spiral electrode group 2. A rectangular nonaqueous electrolyte secondary battery 1 having a rated capacity of 10 Ah, a width of 60 mm, a height of 100 mm and a thickness of 22 mm was produced using the spiral electrode group 2.

Comparative Example 1 A prismatic non-aqueous electrolyte secondary battery 1 was produced in which only the separator 5 was sandwiched between the positive electrode plate 3 and the negative electrode plate 4 and the gas diffusion layer 20 was not provided. The other components are the same as those in the first embodiment.

Example 2 A prismatic non-aqueous electrolyte secondary battery 1 was produced by using the gas diffusion layer 20 made of the mesh glass fiber 22 as shown in FIG. A cross section of the reticulated glass fiber 22 is shown in FIG. The reticulated glass fiber 22 is reduced in total thickness by calendering, and intersecting fibers are fused. One side A of the openings of the mesh is 20 μm,
The fiber diameter was 5 μm. The other components are the same as those in the first embodiment.

<Embodiment 3> As shown in FIG. 5, glass fibers 23 are extended on the separator 5 at right angles to its longitudinal direction.
Spacing (B) that does not overlap the separator 5 in the longitudinal direction
A prismatic non-aqueous electrolyte secondary battery 1 was produced using the gas diffusion layer 20 arranged in. The glass fiber 23 had a diameter of 5 μm and a length of 90 mm. Each glass fiber 23
Was placed on the separator 5 and roll-pressed to integrate the positive electrode plate 3, the negative electrode plate 4, and the separator 5 into a sheet. The sheet is wound to form a spiral electrode group 2,
A prismatic non-aqueous electrolyte secondary battery 1 was produced. The other components are the same as those in the first embodiment.

Example 4 As the gas diffusion layer 20, a non-woven fabric 21 of polyimide fiber was used to fabricate a prismatic non-aqueous electrolyte secondary battery 1. This polyimide fiber is a polymer of pyromellitic dianhydride and 4,4′-diaminodiphenyl ether in a fibrous form. Further, the surface of the polyimide fiber was surface-modified to improve its wettability with an organic solvent. The modification was performed by radical treatment. The diameter of the polyimide fiber was 1 μm, and the sheet thickness of the nonwoven fabric 21 was 5 μm. The other components are the same as those in the first embodiment.

Example 5 As shown in FIG. 6, a prismatic nonaqueous electrolyte secondary battery 1 using a polyimide film 24 having a liquid passage hole 25 and a surface modified as a gas diffusion layer 20 was produced. The polyimide film 24 is a film formed from the resin used in the polyimide fiber used in Example 4. The porosity of the polyimide film 24 is 30 to
60%, and the liquid passage holes 25 were circular with a diameter of 20 μm. The thickness of the film was 10 μm. The other components are the same as those in the first embodiment. The porosity of the polyimide film 24 was calculated by the ratio of the area of the liquid passage holes 25 to the area of the entire gas diffusion layer.

<Measurement> (Charge / Discharge Cycle Test and Rate Test) Regarding the prismatic non-aqueous electrolyte secondary battery 1 produced above, in a room temperature atmosphere,
It was charged up to 4.2 V at a constant current of 0.5 C and discharged up to 2.75 V at a constant current of 2 C. After carrying out 200 cycles of charging and discharging with the above-mentioned charging and discharging as one cycle,
The battery was charged to 4.2 V at a constant current of 0.5 C, and the discharge capacity up to a final voltage of 2.75 V was measured at a constant current of 0.5 C. In addition, even with a constant current of 5 C, the final voltage is 2.75.
The discharge capacity up to V was measured.

(Oven Test) The prismatic non-aqueous electrolyte secondary battery 1 produced above was charged to 4.2 V at room temperature and a constant current of 0.5 C. After charging, install the battery in the oven and raise the temperature to 180 ° C at a rate of 5 ° C / min.
Hold for minutes. From the start of temperature increase to the end of holding at 180 ° C. for 90 minutes, the change in AC resistance at 1 kHz was measured, and the presence or absence of an internal short circuit was observed.

<Results> The results of the above cycle test, rate test and oven test of the prismatic non-aqueous electrolyte secondary batteries 1 of Examples 1 to 5 and Comparative Example 1 are shown together with the properties of the gas diffusion layer 20. Shown in 1.

[0043]

[Table 1]

The influence of the presence or absence of the gas diffusion layer 20 on the battery characteristics will be examined. In Table 1, the gas diffusion layer 20
Comparing Comparative Example 1 not including the gas diffusion layer with Examples 1 to 5 including the gas diffusion layer 20, the discharge capacity at a discharge current 5C after 200 cycles of Comparative Example 1 without the gas diffusion layer 20 is 8 Ah. On the other hand, in Examples 1 to 5 including the gas diffusion layer, the discharge capacity was 8.5 to 9.0.
It became Ah, and it was found that the discharge capacity at the time of high rate discharge after 200 cycles was improved.

This is because by providing the gas diffusion layer 20 between the separator 5 and the positive electrode plate 3, it is possible to easily supply the electrolyte solution and discharge the gas at the time of initial injection, and to diffuse the gas at the time of charging and discharging. It is considered that this is because the active material in the spiral electrode group 2 can be effectively used.

Further, in Comparative Example 1 not including the gas diffusion layer 20, an internal short circuit occurred in the oven test, whereas in Examples 1 to 5 in which the gas diffusion layer 20 was provided, an internal short circuit occurred. It did not occur. Therefore,
It has been found that by providing the gas diffusion layer 20, it is possible to prevent a short circuit of the electrode in a high temperature state.

This is because the internal temperature of the battery exceeds the melting temperature of the microporous polyethylene which is the separator 5.
Even if is melted, the gas diffusion layer 20 made of glass fiber or high melting point polymer retains the shape of the melted separator 5, or the gas diffusion layer 20 itself serves as a spacer to form the positive electrode plate 3 and the negative electrode plate 4. This is to maintain insulation between them.

[0048]

According to the non-aqueous electrolyte secondary battery of the present invention, it is possible to provide a non-aqueous electrolyte secondary battery which is excellent in safety and discharge characteristics.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a prismatic nonaqueous electrolyte secondary battery according to an embodiment of the present invention.

FIG. 2 is an exploded perspective view of a power generation element

FIG. 3 is an exploded perspective view of a power generation element

FIG. 4 is a sectional view of a gas diffusion layer.

FIG. 5 is an exploded perspective view of a power generation element

FIG. 6 is an exploded perspective view of a power generation element.

[Explanation of symbols]

1. Rectangular non-aqueous electrolyte secondary battery 3 ... Positive electrode plate 4 ... Negative electrode plate 5 ... Separator 20 ... Gas diffusion layer

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Claims (4)

[Claims] 1. A positive electrode plate formed by stacking a positive electrode active material layer on a current collector, a negative electrode plate formed by stacking a negative electrode active material layer on a current collector, and a separator formed of a microporous film of a thermoplastic resin. In a non-aqueous electrolyte secondary battery comprising a power generation element that is wound or laminated in a spiral shape, and a non-aqueous electrolyte is injected into the power generation element, the positive electrode plate or the negative electrode plate and the separator. A non-aqueous electrolyte secondary battery comprising a heat-resistant gas diffusion layer provided between and. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the gas diffusion layer is made of a non-woven fabric made of glass fiber or high melting point polymer fiber. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the gas diffusion layer is made of a high-melting-point polymer film having a large number of liquid passage holes formed of circular holes. 4. The high-melting-point polymer fiber or the high-melting-point polymer film is subjected to a surface modification treatment for enhancing the wettability with respect to the electrolytic solution. The non-aqueous electrolyte secondary battery according to item 3.