JP3743774B2 - Non-aqueous electrolyte battery - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a nonaqueous electrolyte battery such as a lithium secondary battery.
[0002]
[Prior art]
Nonaqueous electrolyte batteries were initially commercialized as primary batteries for watches and cameras. Since then, research has progressed on positive electrodes such as metal oxides and metal composite oxides such as lithium cobaltate, and negative electrodes such as carbon and graphite holding lithium ions, and high energy density non-aqueous electrolyte secondary batteries using them. Batteries have been developed and are recently widely used for portable electronic devices such as portable video cameras, portable personal computers, and portable radio telephones.
[0003]
In order to obtain a high energy battery, it is necessary to use a material having a high voltage and a large capacity per unit weight as an active material of the battery. As such a negative electrode material, an alkaline metal such as lithium is used for the negative electrode. Or an alloy thereof, or carbon holding lithium ions is used. Since these negative electrode materials react directly with water, an aqueous electrolyte solution cannot be used, and an electrolytic solution in which a lithium salt or the like is dissolved in an organic solvent, that is, a nonaqueous electrolytic solution is used.
[0004]
[Problems to be solved by the invention]
Non-aqueous electrolyte secondary batteries usually have a high discharge voltage, a large capacity, a good cycle life, no gas generation in the battery reaction, and a sealed structure for essentially eliminating moisture. . In nonaqueous electrolyte secondary batteries, it is necessary to apply a certain amount of pressure to the electrodes inside the battery to stabilize the reaction, so iron has mainly been used as the material for the battery case.
[0005]
However, since the density of iron is as high as 7.87 g / cm ^3, the ratio of the weight of the battery case to the total weight of the battery generally reached about 30 percent, depending on the size of the battery. . In this case, no matter how much high-energy material is used for the battery active material, the advantage is lost.
[0006]
Therefore, it is conceivable to increase the energy density per weight of the battery by using a material having a density as low as possible, such as a polymer compound, for the battery case of the non-aqueous electrolyte secondary battery. The specific gravity of the polymer compound is about 1.4 polyvinyl chloride, about 0.95 polyethylene, about 0.90 polypropylene and about 1.05 polystyrene, which is considerably smaller than that of metal.
[0007]
However, since the strength of the polymer material is inferior to that of metals such as iron, it is not very suitable when the battery is used alone, but when it is used as an assembled battery combining a plurality of batteries. In general, since a plurality of batteries are used in a different case, the battery can be used even if the battery case does not have the strength of iron.
[0008]
However, when a polymer material is used for the battery case, another problem arises. That is, the polymer material has a property of allowing water to pass well. The moisture permeability of the polymer material (unit: g · cm × 10 ¹² / cm ² · sec · cmHg) is high density polyethylene = 5.1, cast polypropylene = 4.8, polystyrene = 96, polyvinyl chloride = 110. Since the value is quite large except for fluororesin, such as polytrifluoroethylene chloride = 0.25, water enters the battery through the case during long-term storage and the battery deteriorates. There was a problem that it would end up.
[0009]
Some fluororesins have a moisture permeability of 0.023 (the unit is the same as above) and do not allow much water to pass through, and it is conceivable that the battery case is made of only the fluororesin. Since the specific gravity is about 2, it is not suitable as a case of a high energy density battery.
[0010]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides a battery case of a non-aqueous electrolyte battery comprising a polymer layer of a compound in which all hydrogen of ethylene is substituted with fluorine and chlorine, and a solid material disposed on both sides thereof. It attaches with the layer which becomes .
[0011]
DETAILED DESCRIPTION OF THE INVENTION
The present invention can be applied to all primary batteries and secondary batteries using a non-aqueous electrolyte, and is particularly effective for a battery used as a power source for various portable devices requiring high energy density. The nonaqueous electrolyte battery according to the present invention uses a battery case composed of at least three layers, and uses a polymer of a compound in which all hydrogen of ethylene is substituted with fluorine and chlorine for an intermediate layer. This prevents moisture from entering the battery.
[0012]
A polymer of a compound in which all hydrogen of ethylene is substituted with fluorine and chlorine is a substance generally known as “fluorine oil”, and a polymer of a compound in which all four hydrogens are substituted with fluorine, or three It is a generic term for polymers of ethylene trifluoride chloride substituted with fluorine and one substituted with chlorine, and takes various forms from liquid to wax at room temperature depending on the average molecular weight.
[0013]
When fluorine oil is used for the intermediate layer of the battery case, the fluorine oil may be liquid. Therefore, the fluorine oil layer must be sandwiched from both sides, so at least three layers are required. You can use more than one layer.
[0014]
Here, the case where the simplest battery case has three layers will be described. Of the three layers constituting the battery case, the inner layer of the battery case is the first layer, the intermediate layer is the second layer, and the outer layer of the battery case is the third layer. In order to obtain a high energy density battery, it is desirable that the specific gravity (density) of all the materials constituting the battery is as small as possible. Therefore, the first layer, the second layer, and the third layer are all low in density. It is necessary to select from materials.
[0015]
The first and third layers must use solid materials to maintain their shape, and the first layer is in direct contact with the electrolyte, so it reacts with it depending on the electrolyte used It is necessary to select a material that does not, and in any case, a polymer material is preferable.
[0016]
The present invention uses a polymer of a compound in which all hydrogen of ethylene is substituted with fluorine and chlorine, that is, fluorine oil, in the second layer. Among fluorine oils, those with a low average molecular weight are substances that have unique properties as liquid organic compounds, but as the number of chlorine substitutions increases, the properties of fluorine change little by little. Of the substituents, at least one is preferably fluorine, and most preferably trichloroethylene chloride in which three are substituted with fluorine and one is substituted with chlorine.
[0017]
In order to obtain a high energy density battery, it is necessary to make the battery case as light as possible. To that end, the thickness of the battery case should be reduced. For this reason, as the fluorine oil used in the second layer, either liquid or solid can be used, but liquid is preferred from the viewpoint that it is easy to form a thin layer. That is, the viscosity at 25 ° C. of fluorine oil varies depending on the average molecular weight. When the average molecular weight is 500, the viscosity is about 20 to 50 centipoise, and when the average molecular weight is 700, the viscosity is about 500 to 900 centipoise and the average molecular weight is In the case of 1100, it becomes grease-like. The fluorine oil used for the second layer of the battery case of the present invention can be used with any of these viscosities, or one kind may be used, or two or more kinds may be used in combination.
[0018]
Furthermore, since the specific gravity of fluorine oil is usually about 1.9 to 2.0, it is preferable to reduce the weight by reducing the thickness of the fluorine oil layer as much as possible. In addition, the first layer and the third layer do not necessarily need to be composed of a single material, and may be composed of a plurality of layers in which layers composed of two or more materials are laminated.
[0019]
In addition, as an electrolyte of a high energy density non-aqueous electrolyte battery, a wide potential window, high ionic conductivity, a wide use temperature range, a system that is stable with respect to an electrode material and an active material is desirable. Further, ethylene carbonate (EC) is preferable as the high dielectric constant solvent, and dimethyl carbonate (DMC) and diethyl carbonate (DEC) are preferable as the low viscosity solvent. The mixing ratio of these solvents is EC: DMC: DEC = 2: 2 by volume ratio. A solution in which LiPF ₆ as a salt having excellent potential stability and safety is dissolved in this mixed solvent is used.
[0020]
In addition to the above, various organic solvents such as propylene carbonate, 1,2-dimethoxyethane, 1,2-butylene carbonate can be used as the solvent for the electrolyte, and LiClO ₄ can be used as the electrolyte salt in addition to LiPF _6. Lithium salts such as LiBF ₄ , LiAsF ₆ , and LiCF ₃ SO ₃ can also be used, but are not limited thereto.
[0021]
Furthermore, the positive electrode active material is preferably a composite oxide of lithium and cobalt / nickel / manganese / iron, or a composite oxide having two or more selected from lithium and cobalt / nickel / manganese / iron. Active materials include metallic lithium and lithium alloys, or carbon materials that occlude lithium ions, such as low-temperature fired low crystalline carbon to highly crystalline carbon such as natural graphite, and mixtures of shapes, types, and multiple types. However, it is of course not limited to these.
[0022]
【Example】
The structure of the nonaqueous electrolyte battery according to the present invention will be described in detail with reference to a preferred embodiment.
[0023]
[Example 1]
In order to compare the non-aqueous electrolyte secondary battery according to the present invention with the conventional non-aqueous electrolyte secondary battery, the following three non-aqueous electrolyte secondary batteries were produced and their characteristics were determined. For the three batteries produced, all the same electrodes and electrolytes were used except that the battery cases were different as follows.
[0024]
Battery A (battery of the present invention): A three-layer case is used for the battery case.
Battery B (conventional battery): Iron is used as a battery case material.
Battery C (comparative battery): Polypropylene is used as the battery case material.
[0025]
FIG. 1 shows a cross-sectional structure of a non-aqueous electrolyte secondary battery A according to the present invention. The battery 1 includes a positive electrode plate 2, a negative electrode plate 3, a separator 4 and an electrolyte (not shown) in a battery case 5. This is a stored prismatic lithium secondary battery.
[0026]
The positive electrode plate 2 has a weight ratio of 90 parts of LiCoO ₂ as an active material, 4 parts of acetylene black as a conductive additive, 6 parts of polyvinylidene fluoride as a binder, and N-methyl-2-pyrrolidone 100 as a solvent. The parts were mixed to form a paste, which was coated, dried and rolled on both sides of an aluminum foil having a thickness of 20 μm, and cut to a width of 30 mm.
[0027]
The negative electrode plate 3 was prepared by mixing 88 parts of carbon powder, 12 parts of polyvinylidene fluoride as a binder, and 150 parts of N-methyl-2-pyrrolidone as a solvent into a paste, and a copper foil having a thickness of 18 μm. It was prepared by coating, drying and rolling on both sides of the film and cutting it to a width of 30 mm.
[0028]
The separator 4 is made of a polyethylene microporous film having a thickness of 25 μm and a width of 32 mm, and the electrolytic solution is absorbed therein. As the electrolytic solution, a mixed solution of ethylene carbonate: dimethyl carbonate: diethyl carbonate = 2: 2: 1 (volume ratio) containing 1 mol / l of LiPF ₆ was used.
[0029]
The battery case 5 has a thickness of 0.42 mm and an inner dimension of 33 × 47 × mm. The material of the first layer 6 and the third layer 8 is a polypropylene plate having a thickness of 0.2 mm. Between the layer 6 and the third layer 8, a second layer 7 made of ethylene trifluoride chloride (a liquid form at room temperature) having a thickness of 0.02 mm and an average molecular weight of about 500 is attached.
[0030]
The positive electrode plate 2, the separator 4 and the negative electrode plate 3 are sequentially stacked and wound in an oval shape around a polyethylene core 9, and then electrically connected to the positive electrode lead wire 10 or the negative electrode lead wire 11. Connected and stored in battery case 5.
[0031]
The negative electrode lead wire 11 is made of nickel, and one end thereof is resistance-welded in advance to an eccentric position of a rectangular plate-like lid 12 made of iron and having a through hole in the center. A cylindrical positive electrode terminal 13 is airtightly fixed to the through-hole of the lid 12 with a low melting point glass 14, and a part of the positive electrode lead wire 10 made of SUS317J1 is resistance-welded to the positive electrode terminal 13.
[0032]
Then, the positive electrode plate 2 and the negative electrode plate 3 are separated from each other at the end of the spiral electrode group, the end of the positive electrode plate 2 is connected to the other end of the positive electrode lead wire 10, and the end of the negative electrode plate 3 is connected to the negative electrode lead wire 11. It is resistance welded to the other end. The connection end of the positive electrode plate 2 and the connection end of the negative electrode plate 3 are insulated by a polypropylene cover 15. In addition, the positive electrode plate 2 and the positive electrode lead wire 10 are connected by the staking method.
[0033]
The battery was sealed by pushing the lid 12 into the battery case 5. The case of the conventional battery B is obtained by nickel plating with a thickness of 2 μm on the surface of an iron main body having a thickness of 0.3 mm and an inner size of 33 × 47 × 7 mm. The case of the battery C as a comparative example was made of polypropylene having a thickness of 0.45 mm and an inner size of 33 × 47 × mm.
[0034]
Comparing the weights of the battery cases, the weights of the battery A and the battery C using a polymer material for the battery case are about one-eighth of the weight of the battery B using iron for the battery case. It was. When these three batteries were charged and discharged for 5 cycles under the following conditions immediately after production, there was no difference in discharge voltage or capacity.
[0035]
Ambient temperature: 25 ° C
Charging: [200mA constant current, up to 4.1V] + [4.1V constant voltage, 5 hours]
Discharge: 400mA constant current, final voltage 3.0V
[0036]
Then, after standing at room temperature for 6 months, charging and discharging were performed under the same conditions. The discharge characteristics of the battery A and the battery B were almost the same as those immediately after the production, but the discharge of the battery C using polypropylene as the battery case The capacity was reduced to about 70 percent immediately after fabrication.
[0037]
[Example 2]
As the material of the second layer of the battery case, the second layer 7 made of ethylene trifluoride chloride (grease-like at room temperature) having an average molecular weight of about 1100 is used. A non-aqueous electrolyte secondary battery which is the same as the battery A described above was produced. The discharge characteristics of this battery were almost the same immediately after fabrication and after storage for 6 months.
[0038]
[Example 3]
As the material for the second layer of the battery case, the second layer 7 made of ethylene trifluoride chloride (hard wax shape at room temperature) having an average molecular weight of about 1300 is used. All other points are described in Example 1. A non-aqueous electrolyte secondary battery that was the same as the battery A was prepared. The discharge characteristics of this battery were almost the same immediately after fabrication and after storage for 6 months.
[0039]
【The invention's effect】
The non-aqueous electrolyte secondary battery according to the present invention includes a polymer of a compound in which all of hydrogen in ethylene is substituted with fluorine or chlorine, a so-called fluorine oil layer, in the battery case. When water permeates through this layer, fluorine oil does not absorb water, and thus does not allow water to pass through. Water is blocked by the fluorine oil layer and does not enter the battery. Therefore, instead of using a metal with a high density such as iron for the battery case, a material with a low density, such as various polymer materials, can be used. Thus, a high energy density battery is obtained by significantly reducing the weight of the battery case. Furthermore, since the nonaqueous electrolyte secondary battery according to the present invention includes a layer made of a solid material disposed on both sides of the polymer layer in the battery case, the shape of the polymer layer is maintained. The
[0040]
In addition, when only one type of fluoro oil is used, when it is a liquid at room temperature, two or more types may be mixed, or two or more types of wax and liquid may be used in combination. There is no change in sex.
[0041]
Further, the battery case according to the present invention is effective not only in the case of the airtight lid structure using the low melting point glass described in the embodiment, but also in the case of a structure with a safety valve attached, for example. This is effective not only for water electrolyte secondary batteries but also for nonaqueous electrolyte primary batteries.
[Brief description of the drawings]
FIG. 1 is a diagram showing a cross-sectional structure of a nonaqueous electrolyte secondary battery A according to the present invention.
DESCRIPTION OF SYMBOLS 1 Battery 2 Positive electrode plate 3 Negative electrode plate 4 Separator 5 Battery case 6 First layer of battery case 7 Second layer of battery case 8 Third layer of battery case 12 Lid

Claims (1)

A non-aqueous electrolyte battery comprising: a battery case comprising a polymer layer of a compound in which all hydrogen of ethylene is substituted with fluorine and chlorine; and a layer made of a solid material disposed on both sides thereof. .

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