Porous material for secondary batteries, method for manufacturing the same, and secondary battery

Abstract

This invention provides a porous material for secondary batteries containing a sulfonic acid group-containing polymer that can be manufactured with high reactivity and safety, as well as a method for manufacturing the same. [Solution] The porous material for secondary batteries of the present disclosure contains a sulfonic acid group-containing polymer, and the sulfonic acid group-containing polymer is a reaction product of a hydroxyl group-containing polymer and an inorganic sulfate. The method for producing the porous material for secondary batteries of the present disclosure comprises the steps of (S1) preparing a porous material containing the hydroxyl group-containing polymer, and (S2) immersing the porous material in an aqueous solution containing an inorganic sulfate, removing the porous material from the aqueous solution containing an inorganic sulfate, and heating the porous material.

Description

Technical Field

[0001] The present disclosure relates to a porous body for a secondary battery, a method for manufacturing the same, and a secondary battery.

Background Art

[0002] Conventionally, as separators for alkaline secondary batteries such as nickel-hydrogen secondary batteries and nickel-cadmium secondary batteries, polyolefin non-woven fabrics such as polypropylene non-woven fabrics have been widely used from the viewpoints of alkali resistance and self-discharge suppression. In particular, polyolefin non-woven fabrics treated with an acid having a sulfate group or the like are suitable. Patent Document 1 discloses a separator for an alkaline secondary battery made of a polyolefin porous body treated with an acid having a sulfate group or SO3 gas (Claim 1). Examples of the acid having a sulfate group include fuming sulfuric acid, concentrated sulfuric acid, and sulfuric anhydride (Claim 2). When a polyolefin is treated with an acid having a sulfate group or SO3 gas, a sulfonic acid group is introduced into the polyolefin. By this sulfonation oxidation, the polyolefin porous body becomes hydrophilic to the electrolyte, the holding power of the electrolyte is improved, and the charge-discharge characteristics of the battery including the same can be improved.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the method described in Patent Document 1, since the reactivity of the sulfonation oxidation treatment for polyolefin is not high, it is necessary to use strong treatment agents such as fuming sulfuric acid, concentrated sulfuric acid, sulfuric anhydride, and SO3 gas, and the safety is not very high.

[0005] This disclosure is made in view of the above circumstances and aims to provide a porous material for secondary batteries that contains a sulfonic acid group-containing polymer and can be manufactured with good reactivity and high safety, as well as a method for manufacturing the same. [Means for solving the problem]

[0006] This disclosure provides the following porous material for secondary batteries, a method for manufacturing the same, and a secondary battery. The porous material for secondary batteries of this disclosure is Contains a polymer containing sulfonic acid groups, The aforementioned sulfonic acid group-containing polymer is a reaction product of a hydroxyl group-containing polymer and an inorganic sulfate.

[0007] The hydroxyl group-containing polymer can be one or more selected from the group consisting of polyvinyl alcohol, ethylene vinyl alcohol copolymer, and polyvinyl acetal. The inorganic sulfate can be one or more selected from the group consisting of ammonium sulfate, aluminum ammonium sulfate, and sodium sulfite.

[0008] The method for manufacturing a porous body for secondary batteries described herein is: Step (S1) of preparing a porous body containing the hydroxyl group-containing polymer, The process includes the steps of immersing the porous body in an aqueous solution containing an inorganic sulfate, removing the porous body from the aqueous solution containing an inorganic sulfate, and heating the porous body (S2).

[0009] The secondary battery of this disclosure includes a negative electrode, a positive electrode, a separator made of the porous material for secondary batteries of this disclosure described above, and an electrolyte.

[0010] The technology disclosed herein involves reacting a porous material containing a hydroxyl group-containing polymer with an inorganic sulfate, thereby enabling the production of porous materials for secondary batteries with high reactivity and safety. [Effects of the Invention]

[0011] According to the present disclosure, there can be provided a porous body for a secondary battery containing a sulfonic acid group-containing polymer and capable of being produced with good reactivity and high safety, and a method for producing the same.

Brief Description of the Drawings

[0012] [Figure 1] It is a flowchart of a method for producing a porous body for a secondary battery of the present disclosure. [Figure 2] It is an overall view schematically showing a configuration example of a secondary battery of the present disclosure. [Figure 3] It is a partial cross-sectional view of the secondary battery in FIG. 2. [Figure 4] It is an example of measurement of an XPS spectrum.

Embodiments for Carrying Out the Invention

[0013] [Porous Body for Secondary Battery] The porous body for a secondary battery of the present disclosure contains a sulfonic acid group-containing polymer. The sulfonic acid group-containing polymer contained in the porous body for a secondary battery of the present disclosure is a reaction product of a hydroxyl group-containing polymer and an inorganic sulfate.

[0014] [Method for Producing Porous Body for Secondary Battery] As shown by the flowchart in FIG. 1, the method for producing a porous body for a secondary battery of the present disclosure includes a step (S1) of preparing a porous body containing a hydroxyl group-containing polymer, and a step (S2) of immersing the porous body in an aqueous solution containing an inorganic sulfate, taking out the porous body from the aqueous solution containing the inorganic sulfate, and heating the porous body.

[0015] (Step (S1)) In step (S1), a porous body containing a hydroxyl group-containing polymer is prepared. The form of the porous body is not particularly limited, and examples thereof include fibrous fabrics such as woven fabrics and non-woven fabrics; porous films, etc. Among them, fibrous fabrics such as woven fabrics and non-woven fabrics are preferable, and non-woven fabrics are particularly preferable. Examples of the porous body containing a hydroxyl group-containing polymer include a porous body composed of a hydroxyl group-containing polymer; and a composite porous body in which a hydroxyl group-containing polymer is present on the surface of a porous body not containing a hydroxyl group-containing polymer. Examples of the composite porous body include a porous body obtained by immersing a porous body not containing a hydroxyl group-containing polymer in a solution containing a hydroxyl group-containing polymer to attach the hydroxyl group-containing polymer to the porous body not containing a hydroxyl group-containing polymer.

[0016] The hydroxyl group-containing polymer is not particularly limited, and one or more selected from the group consisting of polyvinyl alcohol, ethylene vinyl alcohol copolymer (EVOH), and polyvinyl acetal are preferable. Polyvinyl acetal is a resin produced by acetalization of a polyvinyl alcohol-based resin such as polyvinyl alcohol and ethylene vinyl alcohol copolymer (EVOH), and examples thereof include vinylon and polyvinyl butyral.

[0017] (Step (S2)) In step (S2), the porous body containing a hydroxyl group-containing polymer prepared in step (S1) is immersed in an aqueous solution containing an inorganic sulfate. The inorganic sulfate is not particularly limited, and an inorganic salt having water solubility and capable of desorbing a sulfonic acid group by heating is preferable. The inorganic salt may be a simple salt or a double salt. One or more selected from the group consisting of ammonium sulfate (NH4(SO4)4), ammonium aluminum sulfate (AlNH4(SO4)2), and sodium sulfite (Na2SO3) are preferable. The concentration of the aqueous solution containing an inorganic sulfate is not particularly limited, and is preferably a saturated concentration or a concentration close thereto.

[0018] Next, the porous body is taken out from the aqueous solution containing an inorganic sulfate, and the porous body is heated (also referred to as heat treatment). The heat treatment is preferably performed in an inert atmosphere. Examples of the inert atmosphere include an inert gas atmosphere such as nitrogen gas and argon gas. If necessary, drying may be performed at a temperature lower than the heat treatment temperature before the heat treatment. The heat treatment temperature and drying temperature are not particularly limited and can be appropriately designed depending on the type of inorganic sulfate. The heat treatment temperature should be any temperature at which the sulfone oxidation reaction occurs, preferably 60°C or higher and less than 160°C. The heat treatment temperature is more preferably 60°C to 155°C. The lower limit is even more preferably 70°C, particularly preferably 80°C, and most preferably 90°C. The upper limit is even more preferably 150°C, even more preferably 140°C, particularly preferably 130°C, and most preferably 120°C. When drying is performed before heat treatment, the drying temperature should be lower than the heat treatment temperature, preferably between 40°C and 90°C. The drying temperature is more preferably 40°C to 85°C. The lower limit is particularly preferably 50°C, and most preferably 60°C. The upper limit is particularly preferably 80°C. Drying can be done by natural drying, reduced pressure drying, or reduced pressure drying.

[0019] By reacting one or more hydroxyl groups (-OH) contained in a hydroxyl group-containing polymer with an inorganic sulfate at an appropriate temperature, the hydroxyl group-containing polymer is sulfonated, and a sulfonic acid group (-SO3H) is introduced. As an example, the presumed reaction equation between a hydroxyl group-containing polymer and ammonium aluminum sulfate (AlNH4(SO4)2) is shown below. [ka]

[0020] Process (S2) may be performed multiple times. When process (S2) is performed multiple times, the type of inorganic sulfate may or may not be changed.

[0021] (Process (S3)) The porous body obtained after step (S2) may be washed and dried as needed. There are no particular restrictions on the cleaning method, but washing with water is preferred. As described above, the method for manufacturing a porous body for secondary batteries according to this disclosure is used to manufacture the battery.

[0022] The technology disclosed herein allows for the simple, highly reactive, and safe production of porous materials for secondary batteries containing sulfonic acid group-containing polymers without the use of strong treatment agents such as fuming sulfuric acid, concentrated sulfuric acid, and sulfuric anhydride containing sulfate ions, or SO3 gas, or special treatment equipment. Porous materials for secondary batteries having sulfonic acid groups exhibit high hydrophilicity, electrolyte-hydrophilicity, and excellent electrolyte retention. Secondary batteries using these porous materials as separators exhibit excellent charge-discharge characteristics and effectively suppress self-discharge. A porous material for secondary batteries, in which sulfonic acid groups are introduced into a porous body made of a hydroxyl group-containing polymer, is particularly preferable because the entire porous body is hydrophilic, the sulfonic acid groups are well bound to the porous body and difficult to detach, and it has excellent chemical stability.

[0023] As described above, this disclosure provides a porous material for secondary batteries that contains a sulfonic acid group-containing polymer and can be manufactured with good reactivity and high safety, as well as a method for manufacturing the same.

[0024] [Secondary battery] The secondary battery of this disclosure includes a negative electrode, a positive electrode, a separator made of the porous material for secondary batteries of this disclosure described above, and an electrolyte. Figures 2 and 3 schematically show examples of secondary battery configurations. Figure 2 is an overall view, and Figure 3 is a partial cross-sectional view. Both are schematic diagrams. The secondary battery 1 shown in Figure 2 contains an electrode stack 20 and an electrolyte (not shown in Figure 3) inside a battery container 11. The electrode stack 20 is made up of a negative electrode 21, a separator 22, and a positive electrode 23 stacked on top of each other. Known materials can be used as the negative electrode, positive electrode, and electrolyte. The secondary battery of this disclosure is preferably an aqueous secondary battery, and more preferably an alkaline secondary battery such as a nickel-metal hydride secondary battery or a nickel-cadmium secondary battery.

[0025] [Application] Applications of the secondary battery of this disclosure include power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs), gasoline-powered vehicles, and diesel-powered vehicles, and it is particularly suitable for power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and battery electric vehicles (BEVs). Other applications of the secondary battery of this disclosure include powering vehicles other than cars (e.g., railways, ships, and aircraft); and powering electrical products such as information processing devices. [Examples]

[0026] Examples and comparative examples of the present invention will be described below. [Example E1] A nickel-plated steel sheet was prepared as the negative electrode current collector. 95 parts by mass of LaNi5 alloy (hydrogen storage alloy), 1 part by mass of carboxymethylcellulose, 5 parts by mass of a dispersion solution (50% by mass) of styrene-butadiene copolymer (SBR), and 1 part by mass of crystalline carbon powder were mixed. Pure water was added to the resulting mixture and mixed for 15 minutes using a "rotation / revolution mixer" manufactured by Sinky Co., Ltd. to obtain a slurry-like anode mixture. The obtained negative electrode mixture was applied to the surface of the negative electrode current collector, with a basis weight of 100 mg / cm² after drying. 2 The coating was applied in this manner. The resulting coating layer was dried at 80°C for 2 hours, and a negative electrode active material layer was formed by pressurizing it with a linear pressure of 1 ton using a roll press manufactured by Tester Giken Co., Ltd. A 120 μm thick stainless steel foil was joined to the end of the resulting laminate using a resistance welding machine to obtain the negative electrode.

[0027] The positive electrode was fabricated using the same method as the negative electrode. A positive electrode active material layer containing nickel hydroxide was formed on the surface of a nickel porous material (Sumitomo Electric Industries' "Ni Cellmet®"), which served as the positive electrode current collector. A 120 μm thick stainless steel foil was bonded to the end of the resulting laminate to obtain the positive electrode.

[0028] The porous material is made of polyvinyl acetal (acetal of polyvinyl alcohol, vinylon), a hydroxyl group-containing polymer, with a thickness of 120 μm and a basis weight of 36 g / m². 2 I prepared a nonwoven fabric. This nonwoven fabric was immersed for 10 minutes in a saturated aqueous solution of ammonium aluminum sulfate (AlNH4(SO4)2), which is an inorganic sulfate-containing aqueous solution. The nonwoven fabric was removed from the inorganic sulfate-containing aqueous solution, dried at 60°C while suspended, heat-treated in a heating furnace at 115°C for 2 hours under an inert atmosphere, and then allowed to cool naturally. The nonwoven fabric was cooled to room temperature (20-25°C), washed three times with water, and dried at 60°C for 30 minutes to obtain sulfonated nonwoven fabric (sulfonated polyvinyl acetal nonwoven fabric).

[0029] The obtained sulfonated nonwoven fabric was used as a separator. The obtained sulfonated nonwoven fabric was placed between the negative electrode and the positive electrode to obtain an electrode laminate. The resulting electrode stack was placed in a battery container, an appropriate amount of 6M potassium hydroxide aqueous solution was added dropwise to the container as an electrolyte, the container was sealed, and left to stand for a certain period of time to produce a secondary battery (single cell).

[0030] [Example E2] The same nonwoven fabric used in Example E1 was prepared. Similar to Example E1, the nonwoven fabric was immersed in a saturated aqueous solution of ammonium aluminum sulfate (AlNH4(SO4)2), which is an inorganic sulfate-containing aqueous solution. The nonwoven fabric was then removed from the inorganic sulfate-containing aqueous solution, dried, heat-treated, and washed with water. Furthermore, the nonwoven fabric after the above treatment was immersed in a saturated aqueous solution of sodium sulfite (Na2SO3), dried at 60°C while suspended, heat-treated in a constant-temperature oven at 90°C for 2 hours, and allowed to cool naturally. The nonwoven fabric, cooled to room temperature (20-25°C), was washed three times with water and dried at 60°C for 30 minutes to obtain sulfonated nonwoven fabric (sulfonated polyvinyl acetal nonwoven fabric). The obtained sulfone-oxidized nonwoven fabric was used as a separator to produce a secondary battery (single cell) in the same manner as in Example E1.

[0031] [Example E3] A polyolefin nonwoven fabric (polypropylene nonwoven fabric) was prepared as a porous material. This nonwoven fabric was immersed in an aqueous solution of ethylene vinyl alcohol copolymer (EVOH) (3% by mass), and the nonwoven fabric removed from the EVOH aqueous solution was dried to obtain an EVOH-modified polyolefin nonwoven fabric. Similar to Example E1, the obtained EVOH-modified polyolefin nonwoven fabric was immersed in a saturated aqueous solution of ammonium aluminum sulfate (AlNH4(SO4)2), which is an inorganic sulfate-containing aqueous solution. The nonwoven fabric was then removed from the inorganic sulfate-containing aqueous solution, dried, heat-treated, and washed with water to obtain a sulfonated nonwoven fabric (sulfonated EVOH-modified polyolefin nonwoven fabric). The obtained sulfone-oxidized nonwoven fabric was used as a separator to produce a secondary battery (single cell) in the same manner as in Example E1.

[0032] [Comparative Example EC1] As a porous material, a sulfonated nonwoven fabric (sulfonated polyolefin nonwoven fabric, commercially available) was prepared by sulfonating a polyolefin nonwoven fabric (polypropylene nonwoven fabric) with hot concentrated sulfuric acid (conc. H2SO4). Using this sulfone-oxidized nonwoven fabric as a separator, a secondary battery (single cell) was fabricated in the same manner as in Example E1.

[0033] [Comparative Example EC2] As the porous material, the same nonwoven fabric prepared in Example E1 was used. Without performing sulfone oxidation treatment on this nonwoven fabric, the untreated nonwoven fabric (untreated polyvinyl acetal nonwoven fabric) was used as a separator, and a secondary battery (single cell) was manufactured in the same manner as in Example E1.

[0034] [Comparative Example EC3] As the porous material, we prepared commercially available polyolefin nonwoven fabric (polypropylene nonwoven fabric) (untreated polyolefin nonwoven fabric) that had not undergone sulfone oxidation treatment.

[0035] [Summary of results] X-ray photoelectron spectroscopy (XPS) analysis was performed on the surface of the sulfone-oxidized nonwoven fabrics used as separators in Examples E1, E3, and Comparative Example EC1, and the untreated polyolefin nonwoven fabric used as a separator in Comparative Example EC3. The obtained XPS spectra (S2p spectra) are shown in Figure 4. In comparative example EC3, the untreated polyolefin nonwoven fabric used as a separator did not show a peak derived from -SO2- around 169 eV in the XPS spectrum. In the sulfonated nonwoven fabrics used as separators in Examples E1, E3, and Comparative Example EC1, a peak originating from -SO2- was observed around 169 eV in the XPS spectrum. No peaks were found that could not be identified, indicating the absence of free sulfonic acid groups. It was confirmed that the sulfonic acid groups were present in a form bonded to the polymer contained in the nonwoven fabric.

[0036] Table 1 shows the S element concentration [atomic%] determined from the peak intensity of the -SO2- derived peak (around 169 eV) in the nonwoven fabrics used as separators in Examples E1 and E3, and Comparative Examples EC1 and EC3.

[0037] [Table 1]

[0038] In the sulfonated nonwoven fabrics obtained in Examples E1 and E3, it was confirmed that the amount of sulfonic acid groups was equivalent to or close to that of the sulfonated nonwoven fabric obtained in Comparative Example EC1.

[0039] The following tests were performed on the secondary batteries (single cells) obtained in Examples E1 to E3 and Comparative Examples EC1 and EC2. After activating the secondary battery by performing 5 charge-discharge cycles under a charge-discharge rate of 0.2C, the battery was placed in a constant temperature chamber at 45°C and a self-discharge test was conducted. The voltage was measured at the start of the self-discharge test, and after 50 hours, 100 hours, and 150 hours. The evaluation results are shown in Table 2.

[0040] [Table 2]

[0041] In comparative example EC2, which used untreated polyvinyl acetal nonwoven fabric as a separator, the secondary battery exhibited unstable performance during cycle charging and discharging before the self-discharge test, and the self-discharge test results were also poor. In self-discharge tests, the secondary batteries obtained in Examples E1 to E3 exhibited voltage changes similar to those of the secondary battery obtained in Comparative Example EC1, confirming that they possess battery characteristics equivalent to those of the secondary battery obtained in Comparative Example EC1. In Examples E1 to E3, porous materials for secondary batteries containing sulfonic acid group-containing polymers were successfully manufactured with high reactivity and safety without the use of strong treatment agents such as hot concentrated sulfuric acid.

[0042] The present invention is not limited to the embodiments described above, and design modifications can be made as appropriate without departing from the spirit of the invention. [Explanation of symbols]

[0043] 1 Secondary battery 11 Battery container 20 Electrode Stack 21 Negative electrode 22 Separators 23 Positive electrode

Claims

1. Contains a polymer containing sulfonic acid groups, The aforementioned sulfonic acid group-containing polymer is a porous material for secondary batteries, which is a reaction product of a hydroxyl group-containing polymer and an inorganic sulfate.

2. The porous body for a secondary battery according to claim 1, wherein the hydroxyl group-containing polymer is one or more selected from the group consisting of polyvinyl alcohol, ethylene vinyl alcohol copolymer, and polyvinyl acetal.

3. The porous body for secondary batteries according to claim 1 or 2, wherein the inorganic sulfate is one or more selected from the group consisting of ammonium sulfate, aluminum ammonium sulfate, and sodium sulfite.

4. Step (S1) of preparing a porous body containing the hydroxyl group-containing polymer, A method for producing a porous body for a secondary battery according to claim 1 or 2, comprising the steps of immersing the porous body in an aqueous solution containing an inorganic sulfate, removing the porous body from the aqueous solution containing an inorganic sulfate, and heating the porous body (S2).

5. A secondary battery comprising a negative electrode, a positive electrode, a separator made of a porous material for secondary batteries as described in claim 1 or 2, and an electrolyte.

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