JP5846056B2 - Separator manufacturing method - Google Patents

Description

The present invention relates to a process for the production of separators.

  Power storage devices such as secondary batteries and capacitors are widely used as power sources because they can be recharged and can be used repeatedly. In a secondary battery, an electrode assembly in which a sheet-like positive electrode and a negative electrode are laminated or wound so as to form a layer with a sheet-like separator interposed is housed in a case. Further, when a secondary battery is used as a power source for a traveling motor as in an electric vehicle or a hybrid vehicle, a large current charge, a large current discharge and a large capacity are required. Charging / discharging with a large current is accompanied by large heat generation inside the battery.

  Conventionally, as a separator, a microporous film using a general-purpose polymer such as polypropylene (PP) or polyethylene (PE) has been mainly used. However, PP and PE have a low melting point, and the durability tends to decrease due to large heat generation inside the battery due to charging / discharging with a large current. Also, the microporous film made of PP or PE may be damaged by short-circuit reaction heat that occurs instantaneously when an internal short circuit occurs, and such damage promotes abnormal overheating of the battery.

  Therefore, in a lithium secondary battery, in order to suppress abnormal overheating and internal short circuit that occurs mainly during production, a nonwoven fabric made of a thermoplastic resin having a meltdown temperature of 150 ° C. or more as a separator and an inorganic filler (alumina filler) In addition, it has been proposed to use a porous film made of a binder. The nonwoven fabric is made of resin fibers selected from polypropylene, polyamide, polyimide, and polyethylene terephthalate. The content of the alumina filler in the porous film is preferably 50% by mass to 99% by mass, and more preferably 90% by mass to 99% by mass (see Patent Document 1).

  As a filter suitable for a separator of a lithium secondary battery, an aluminum oxide film having a plurality of minute through holes has been proposed (see Patent Document 2). In this filter manufacturing method, an aluminum oxide film having a plurality of bottomed micropores formed on one side is prepared. Then, as shown in FIG. 5A, after the gelatin 42 is filled in the opening portion side of the micropore 41 of the aluminum oxide film 40, the whole is immersed in a dilute sodium hydroxide aqueous solution (etching solution) at a low temperature. Then, the aluminum oxide film 40 on the closed surface 43 side that is not covered with the gelatin 42 is etched. As a result, as shown in FIG. 5B, the closed surface 43 side of the aluminum oxide film 40 is etched, the bottom of the microhole 41 is removed, and the microhole 41 penetrates. However, gelatin 42 is not etched with the etchant. Next, when the gelatin 42 is dissolved and removed, a filter 45 in which a large number of through holes 44 are formed in the aluminum oxide film 40 is formed as shown in FIG.

JP 2006-505100 Gazette JP 2000-299095 A

  In the configuration of Patent Document 1, the heat resistance is higher than that of a separator made of microporous film using PP or PE, but the heat resistance is low because a resin is used in part. On the other hand, since the filter of Patent Document 2 is entirely made of an inorganic material, heat resistance can be secured when used as a separator. However, in the filter of Patent Document 2, a large number of through holes 44 formed in the aluminum oxide film 40 are formed so as to extend in parallel with the thickness direction of the aluminum oxide film 40. Therefore, when used as a separator of a lithium ion secondary battery, there is a possibility that needle-like deposits of lithium called dendrites that are generated by repeated charge and discharge pass through the through-hole 44 and the positive electrode and the negative electrode are short-circuited. .

The present invention has been made in view of the above problems, and its purpose is excellent in heat resistance unlike a resin separator, and when used as a separator of a lithium ion secondary battery, lithium needle deposits there is to provide a method for producing separators which can prevent the short circuit through the separator occurs.

In order to achieve the above object, the invention according to claim 1 is a method for manufacturing a separator used in a state of being interposed between a sheet-like positive electrode and a sheet-like negative electrode of a power storage device, and made of aluminum. A porous treatment step for performing a porous treatment for immersing the sheet in a chemical solution in which a polymer having a functional group capable of dissolving aluminum is dissolved to form pores having a pore diameter of 2 to 200 nm in the aluminum; and And an electrical insulation treatment step of performing electrical insulation treatment on the tempered aluminum sheet.

In the present invention, in the porosification treatment step, the porosification treatment is performed by immersing the aluminum sheet in a chemical solution. In the chemical solution, a polymer having a functional group that dissolves aluminum is dissolved, and part of the aluminum sheet is selectively dissolved by the action of the polymer, and openings are present on both sides of the aluminum sheet. A plurality of holes that are three-dimensionally connected in a state extending in a random direction are formed. In the electrical insulation treatment process, electrical insulation treatment is performed on the porous aluminum sheet. The electrical insulation treatment is a treatment for converting aluminum into an electrically insulative metal compound, and the aluminum sheet is transformed into, for example, an oxide, nitride, or fluoride sheet so that the electrically insulative sheet is formed. become.
Further, if the pore diameter is less than 2 nm, it is difficult for ions to pass through the separator, and if the pore diameter is greater than 200 nm, the strength of the separator becomes weak. However, in this invention, since the pore diameter is 2 to 200 nm, ions can pass smoothly and the strength necessary for the separator can be ensured.

The invention according to claim 2 is the invention according to claim 1 , wherein the chemical solution is a solution in which an amine polymer is dissolved in an aqueous solvent as the polymer. Here, the “amine polymer” means a polymer having a primary amine or a secondary amine in the side chain or main chain, and includes, for example, polyethyleneimine. Further, the “aqueous solvent” means a mixed solution of water and other liquid having a water ratio of 50% or more, or a liquid having 100% water. In the present invention, aluminum is dissolved by the action of the amino group of the amine polymer dissolved in the aqueous solvent. The position of the amino group in the solution is not uniform, and there are high and low portions, so that a plurality of holes are formed that are three-dimensionally connected to aluminum in a state that extends in a random direction rather than linearly. it is conceivable that.

The invention according to claim 3 is the invention according to claim 2 , wherein the concentration of the amine-based polymer in the solution is 1 to 50% by mass. When the concentration of the amine polymer is within this range, a separator having the desired pore diameter and pore distribution state can be easily produced.

The invention according to claim 4 is the invention according to claim 2 or 3 , wherein the amine-based polymer is polyethyleneimine. An aqueous solution of polyethyleneimine is used as the chemical solution. Polyethyleneimine is easily available and easy to handle because the chemical solution is an aqueous solution.

The invention according to claim 5 is the invention according to any one of claims 1 to 4 , wherein the electrical insulation treatment is an oxidation treatment. By the oxidation treatment, aluminum is easily changed into electrically insulating aluminum oxide (alumina). As the oxidation treatment method, treatment in an acid or gas atmosphere is preferable. In particular, heat treatment in the presence of oxygen is preferable because it is simple.

According to the invention described in 請 Motomeko 1 to claim 5, it is possible to provide a manufacturing method of the separator.

The partially broken schematic perspective view of a secondary battery. The disassembled perspective view which shows typically the positive electrode, negative electrode, and separator which comprise an electrode assembly. The figure which shows the SEM image which looked at the porous film obtained in the Example from the thickness direction. The figure which shows the SEM image which looked at the film | membrane obtained by the comparative example from the thickness direction. FIG. 5A shows a conventional manufacturing method, FIG. 5A is a cross-sectional view showing a state in which micropores in an aluminum film having bottomed micropores are filled with gelatin, FIG. 5B is a cross-sectional view showing a state after etching, and FIG. ) Is a cross-sectional view of the obtained filter.

Hereinafter, an embodiment in which the present invention is embodied in a secondary battery as a power storage device will be described with reference to FIGS.
As shown in FIG. 1, a secondary battery 10 as a power storage device includes a stacked electrode assembly 12 housed in a case 11 constituted by a case body 11 a and a lid body 11 b. In addition, although not illustrated in the case 11, the electrolyte solution is also accommodated. The secondary battery 10 is embodied as a lithium ion secondary battery.

  As shown in FIG. 2, the electrode assembly 12 includes a plurality of sheet-like positive electrodes 13 and a plurality of sheet-like negative electrodes 14 alternately with a sheet-like separator 15 interposed between the positive electrode 13 and the negative electrode 14. It is laminated and configured. The positive electrode 13 and the negative electrode 14 are formed in a rectangular shape with active material layers 13a and 14a each having an active material applied to a metal foil, and the active material non-applied portion 13b in which the active material layers 13a and 13a are not formed. Tab portions 13c and 14c are formed so as to protrude from 14b. That is, in the electrode assembly 12, a sheet-like positive electrode 13 and a sheet-like negative electrode 14 having active material layers 13a and 14a formed on at least one surface thereof, and a sheet-like separator 15 are interposed therebetween. It has the laminated structure laminated | stacked in the state.

  As shown in FIG. 1, the laminated group 16p in which the tab portion 13c is laminated is welded to the positive electrode conductive member 17, and the laminated group 16n in which the tab portion 14c is laminated is welded to the negative electrode conductive member 18. . A positive terminal 19 and a negative terminal 20 are fixed to the lid 11b. The electrode assembly 12 is electrically connected to the positive electrode terminal 19 via the positive electrode conductive member 17 and is electrically connected to the negative electrode terminal 20 via the negative electrode conductive member 18. In addition, each conductive member 17 and 18 is being fixed to the lower surface (inner surface) of the cover body 11b in the state insulated from the case 11 (case main body 11a and the cover body 11b).

Next, the separator 15 will be described in detail.
The separator 15 is formed in a sheet shape with a metal compound having electrical insulation, and has a plurality of holes 15a (illustrated in FIG. 2) having a hole diameter of 1000 nm or less and three-dimensionally connected to each other in random directions. It consists of an open-type continuous porous body having. Of the plurality of holes 15a, the holes 15a having openings on both sides of the separator 15 are opened to the outside. That is, the separator 15 has openings on both sides and does not have a large number of holes 15a without branching. The separator 15 has an arbitrary direction such as a thickness direction, a width direction, or an oblique direction with respect to the thickness direction. The plurality of holes 15a are in communication with each other along the way. Note that the hole diameter means that the hole 15a has a circular cross-sectional shape perpendicular to the direction in which the hole 15a extends, and does not mean the diameter of the hole 15a. It means that converted to the diameter of a circle with the same area.

  In this embodiment, the separator 15 uses an aluminum compound as a metal compound, and the metal compound is a metal oxide. The metal compound has a thickness of 2 to 30 nm, preferably 4 to 20 nm, and is linearly connected in a three-dimensional manner extending in a random direction. Further, the hole 15a of the metal compound, that is, the separator 15, has a hole diameter of 2 to 200 nm, preferably 4 to 100 nm. The separator 15 has a thickness of 2 to 15 μm, preferably 5 to 10 μm. The galley air permeability of the separator 15 is preferably 1 to 1000 (sec / 100 ml).

Next, a method for manufacturing the separator 15 will be described.
The separator manufacturing method includes a porous treatment step in which an aluminum sheet is immersed in a chemical solution to perform a porous treatment, and an electrical insulation treatment step in which an electrical insulation treatment is performed on the porous aluminum sheet. With.

  In the porous treatment process, the porous sheet is formed by immersing the aluminum sheet in a chemical solution. In the chemical solution, a polymer having a functional group that dissolves aluminum is dissolved. As the chemical solution, for example, a solution in which an amine polymer is dissolved in an aqueous solvent is used. Examples of the amine polymer include polyethyleneimine, and the aqueous solvent means a mixed solution of water and other liquid or a liquid of 100% water with a water ratio of 50% or more. Here, the other liquid is not particularly limited, but is preferably a solvent compatible with water, and particularly preferably alcohol.

  In the porous treatment step, the aluminum sheet is immersed in a chemical solution and subjected to an etching action, and has a plurality of holes having a hole diameter of 1000 nm or less and three-dimensionally connected to each other in a random direction. Among these holes, the holes having openings on both sides of the separator are open-type continuous porous bodies that are open to the outside. This is because the chemical solution is not a solution in which a low molecule is dissolved, but a solution in which a polymer having a functional group that dissolves aluminum is dissolved, so that the functional group that dissolves aluminum exists uniformly in the solution. Instead, it exists locally according to the spread of the polymer. As a result, a part of the aluminum sheet is selectively melted, and openings are formed on both sides of the aluminum sheet, and a plurality of holes 15a are formed which are three-dimensionally connected in a state extending in a random direction. It is thought that it is done.

  In the electrical insulation treatment process, electrical insulation treatment is performed on the porous aluminum sheet. The electrical insulation treatment is a treatment for converting aluminum into an electrically insulating metal compound, and the aluminum sheet is changed to, for example, an oxide, nitride, or fluoride sheet, and the electrically insulating sheet. become.

  As the electrical insulation treatment, an oxidation treatment is preferable. By the oxidation treatment, aluminum is easily changed into electrically insulating aluminum oxide (alumina). As the oxidation treatment method, treatment in an acid or gas atmosphere is preferable, and heat treatment in the presence of oxygen is particularly preferable because it is simple.

  An aluminum foil having a thickness of 15 μm was immersed in an aqueous solution of polyethyleneimine (concentration 5 mass%) for 10 hours. Then, it processed at 200 degreeC for 1 hour in the air, and obtained the alumina porous membrane. The amount of organic substances present in the resulting alumina porous membrane was examined and found to be 0.1% or less. That is, even if the amine polymer used for the porous treatment remains in the holes 15a, the amount thereof is small and there is no problem.

  FIG. 3 shows an SEM image (scanning electron microscope image) of the obtained porous alumina membrane as viewed from the thickness direction. This porous film consisted of an opening of about 40 nm and a net made of a linear body having a thickness of about 10 nm.

Comparative example

  An aluminum foil having a thickness of 15 μm was immersed in an aqueous solution of lithium hydroxide (concentration: 10% by mass) for 10 hours. Then, it processed at 200 degreeC for 1 hour in the air. FIG. 4 shows an SEM image of the obtained alumina film as seen from the thickness direction. FIG. 4 is a magnification of about 3 times that of FIG. In FIG. 4, there are no nets or holes. That is, it can be seen that the pore structure cannot be formed only by immersing the aluminum foil in an alkaline solution having aluminum dissolving power.

Next, the operation of the secondary battery 10 configured as described above will be described.
Although the secondary battery 10 is used alone, it is generally used as an assembled battery in which a plurality of secondary batteries 10 are connected in series or in parallel. The secondary battery 10 is used for various applications. For example, the secondary battery 10 is mounted on a vehicle and used as a power source for a traveling motor or a power source for other electrical devices.

  When the secondary battery 10 is used as a power source for a traveling motor like an electric vehicle or a hybrid vehicle, large current charging, large current discharging, and large capacity are required. Charging / discharging with a large current is accompanied by large heat generation inside the battery. When the separator 15 is made of resin, the heat resistance is low, and the durability is likely to decrease due to large heat generation inside the battery due to charging / discharging with a large current. However, since the separator 15 is formed of a porous metal compound, it can sufficiently withstand the heat generated by charging / discharging with a large current. Further, in the case where the secondary battery 10 is a lithium ion secondary battery, abnormal overheating and internal short circuit that occurs mainly during production can be suppressed.

  Furthermore, in the case of a lithium ion secondary battery, even if the separator 15 is made of ceramics having excellent heat resistance, the shape of the hole allowing the passage of ions linearly extends in the thickness direction of the separator as in Patent Document 2, There is a possibility that needle-like precipitates of lithium called dendrites that are generated by repeated charge and discharge penetrate through the holes and short-circuit the positive electrode and the negative electrode. However, in the separator 15 of this embodiment, the holes 15a extend in a state in which the holes 15a are randomly bent in an arbitrary direction such as a thickness direction, a width direction, or an oblique direction with respect to the thickness direction, and a plurality of holes 15a is the structure which is mutually connected on the way. Therefore, a short circuit between the positive electrode and the negative electrode due to dendrite is prevented.

According to this embodiment, the following effects can be obtained.
(1) The separator 15 is formed in a sheet shape with a metal compound having electrical insulation, and has a plurality of holes 15a having a hole diameter of 1000 nm or less and three-dimensionally connected to each other in a random direction. Of the plurality of holes 15a, the holes 15a having openings on both sides of the separator 15 are opened to the outside. Therefore, the separator 15 is excellent in heat resistance, and when used in a power storage device such as a secondary battery or a capacitor, durability against heat generation of the power storage device due to charging / discharging with a large current is improved. Moreover, since the holes 15a are three-dimensionally connected in a state extending in a random direction, when used in a lithium ion secondary battery, lithium needle-like precipitates called dendrites that are generated by repeated charge and discharge, Unlike the separator of Patent Document 2, it is possible to prevent the separator 15 from penetrating.

  (2) The metal compound constituting the separator 15 is an aluminum compound. Aluminum is used for various purposes as a general-purpose metal, and sheet-like materials such as aluminum foil are also readily available. In addition, compared with the case where other metals are used, the porous processing and the electrical insulation processing are facilitated.

  (3) The metal compound constituting the separator 15 is a metal oxide. The metal is not limited to an oxide, and even a nitride or halide becomes an electrical insulator. However, when the metal compound is a metal oxide, it can be obtained by a simple metal treatment.

  (4) The pore size of the open-type continuous porous body constituting the separator 15 is 2 to 200 nm. If the pore diameter is less than 2 nm, it is difficult for ions to pass through the separator, and if the pore diameter is larger than 200 nm, the strength of the separator is weakened. However, since the pore diameter is 2 to 200 nm, ions can pass smoothly and the strength necessary for the separator 15 can be ensured.

  (5) The metal compound constituting the separator 15 is formed by connecting three-dimensionally linear materials having a thickness of 2 to 30 nm extending in random directions. Therefore, the separator 15 has the necessary strength and can secure good handling properties (ease of handling).

  (6) The separator 15 has a thickness of 2 to 15 μm. When the thickness is less than 2 μm, the strength is weakened and the handling property and the electrical insulating property are deteriorated. If the thickness is 2 to 15 μm, the required strength and handling properties can be ensured. If the thickness is greater than 15 μm, the separator 15 is combined with the sheet-like positive electrode 13 and the sheet-like negative electrode 14 to have an electrode assembly 12 having a laminated structure. Is formed, the volume occupied by the separator 15 only increases, and there is no particular advantage. Since the separator 15 has a thickness of 2 to 15 μm, it can be made thinner than a conventional separator, the volume of the electrode assembly 12 can be reduced, and the volume energy density of the secondary battery 10 can be increased. . In addition, if the film thickness is small, the amount of electrolyte required is small, which contributes to cost reduction.

  (7) In the secondary battery 10 (power storage device), the sheet-like positive electrode 13 and the sheet-like negative electrode 14 in which the active material layers 13a and 14a are formed on at least one surface are in the form of a sheet An electrode assembly 12 having a laminated structure laminated with a separator 15 interposed is provided. The separator 15 includes any one of the separators (1) to (6). Therefore, the secondary battery 10 has the effect which the separator 15 in any one of (1)-(6) has.

  (8) A separator manufacturing method includes a porous processing step in which an aluminum sheet is immersed in a chemical solution in which a polymer having a functional group that dissolves aluminum is dissolved to perform the porous processing. And an electrical insulation treatment step for performing electrical insulation treatment on the aluminum sheet. Unlike the case where a low molecular weight solution that dissolves aluminum is used in the porosification treatment process, a part of the aluminum sheet is selectively dissolved, the openings are present on both sides of the aluminum sheet, and randomly. A plurality of holes 15a that are three-dimensionally connected in a state extending in various directions are formed. The porous aluminum sheet is subjected to an electrical insulation process in the electrical insulation process. Therefore, it is possible to easily manufacture the separator 15 having a plurality of holes 15a that are three-dimensionally connected in a state of having openings on both sides of the separator 15 and extending in a random direction.

  (9) The chemical solution is a solution in which an amine polymer is dissolved in an aqueous solvent. Therefore, aluminum is dissolved by the action of the amino group of the amine-based polymer dissolved in the aqueous solvent, and a plurality of holes 15a that are three-dimensionally connected to the aluminum in a state of extending in a random direction instead of linear form are formed. .

  (10) Polyethyleneimine is used as the amine polymer, and an aqueous solution of polyethyleneimine is used as the chemical solution. Polyethyleneimine is easily available and easy to handle because the chemical solution is an aqueous solution.

  (11) The concentration of the amine polymer in the solution is 1 to 50% by mass. When the concentration of the amine polymer is within this range, the separator 15 having the desired pore diameter, distribution state, etc., of the pores 15a can be easily manufactured.

(12) The electrical insulation process is an oxidation process. By the oxidation treatment, aluminum is easily changed into electrically insulating aluminum oxide (alumina).
(13) Since the heat treatment method in the presence of oxygen is employed as the oxidation treatment method, the oxidation treatment can be easily performed.

The embodiment is not limited to the above, and may be embodied as follows, for example.
The present invention is not limited to the stacked electrode assembly 12 and may be applied to a strip-shaped separator that constitutes a wound electrode assembly.

  ○ The pore diameter is not limited to the range of 2 to 200 nm, but may be 1000 nm or less. However, if the hole diameter is larger than 200 nm, the strength of the separator is weakened, so that it is necessary to increase the thickness, and it becomes difficult to apply to a wound electrode assembly. Therefore, the range of 2 to 200 nm is preferable.

  The chemical solution used for the porous treatment method in which the aluminum foil is immersed is not limited to a polyethyleneimine aqueous solution, but may be a solution in which a polymer having a functional group that dissolves aluminum is dissolved in an aqueous solvent. For example, an aqueous solution of an amine polymer other than polyethyleneimine may be used. Moreover, what melt | dissolved the amine polymer other than polyethyleneimine and polyethyleneimine in the liquid mixture of water and another solvent, for example, alcohol, may be used. However, the amount of water is 50% or more.

  ○ The porous treatment method is not limited to the chemical immersion method, and an electrolytic method may be employed. The electrolytic method is anodization treatment of aluminum foil. A large number of holes are formed by putting an aluminum foil in an electrolytic solution and passing weak direct current, alternating current, or alternating direct current using the aluminum foil as an anode. Usually, as described in Patent Document 2, a straight hole with one end closed is formed, but a bent hole may also be formed by changing electrolysis conditions such as placing a polymer electrolyte in the electrolyte. It seems possible. In addition, in the case of the chemical solution immersion method, an electrical insulation treatment is necessary after the porous treatment, but in the anodization treatment, since the aluminum is oxidized, the electrical insulation treatment is performed in parallel. Therefore, it is not necessary to perform an electrical insulation treatment after the anodizing treatment. However, it is necessary to perform a process of penetrating the hole to make the hole.

  O The method of electrical insulation treatment is not limited to oxidation, and for example, fluoride may be formed by fluorination treatment. As the fluorination treatment, there are a method of performing a heat treatment in fluorine gas and a method of reacting with hydrogen fluoride.

  (Circle) the metal used for the separator 15 is not restricted to aluminum, For example, you may use aluminum alloy, stainless steel, copper, etc. However, aluminum and aluminum alloys have a smaller specific gravity than stainless steel and copper, are preferable in terms of weight reduction, and are easily made porous.

The secondary battery 10 is not limited to a lithium ion secondary battery, and may be another secondary battery such as a nickel hydrogen secondary battery or a nickel cadmium secondary battery.
The power storage device is not limited to the secondary battery 10 and may be a capacitor such as an electric double layer capacitor or a lithium ion capacitor.

  DESCRIPTION OF SYMBOLS 10 ... Secondary battery as an electrical storage device, 12 ... Electrode assembly, 13 ... Sheet-like positive electrode, 14 ... Sheet-like negative electrode, 13a, 14a ... Active material layer, 15 ... Separator, 15a ... Hole.

Claims (5)

A method of manufacturing a separator used in a state of being interposed between a sheet-like positive electrode and a sheet-like negative electrode of a power storage device,
A porous treatment step of performing a porous treatment for immersing the aluminum sheet in a chemical solution in which a polymer having a functional group capable of dissolving aluminum is dissolved to form pores having a pore diameter of 2 to 200 nm in the aluminum ;
A separator manufacturing method comprising: an electrical insulation treatment step of performing electrical insulation treatment on the porous aluminum sheet. The method for producing a separator according to claim 1 , wherein the chemical solution is a solution in which an amine-based polymer is dissolved in an aqueous solvent as the polymer. The method for producing a separator according to claim 2 , wherein the concentration of the amine polymer in the solution is 1 to 50 mass%. Method for producing a separator according to claim 2 or claim 3 wherein the amine polymer is polyethylene imine. Method for producing a separator according to any one of the electrically insulating treatment claims 1 to 4 is an oxidation process.