JP2015050084A - Nonaqueous electrolyte secondary battery, and method for manufacturing nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery which enables the suppression of the reduction in capacity and the occurrence of battery expansion while achieving a low environmental load and a low cost as to a nonaqueous electrolyte secondary battery.SOLUTION: A nonaqueous electrolyte secondary battery comprises a positive electrode and a nonaqueous electrolyte. The positive electrode includes an aqueous binding agent as a binding agent. The nonaqueous electrolyte includes, as a sulfur-containing compound, at least one compound selected from a sulfate ester compound and a sultone compound. The content of the sulfur-containing compound to the mass of the nonaqueous electrolyte is 4.0 mass% or less.

Description

  The present invention relates to a non-aqueous electrolyte secondary battery including a positive electrode and a non-aqueous electrolyte, and a method for manufacturing the non-aqueous electrolyte secondary battery.

  In recent years, with the miniaturization and high performance of electronic devices such as mobile phones and portable audio devices, development of high performance batteries has been actively promoted, and there is a great demand for secondary batteries that can be used repeatedly by charging. It is growing. In particular, nonaqueous electrolyte secondary batteries such as lithium ion secondary batteries that exhibit high energy density and high operating voltage have attracted attention and are widely used.

  In such a non-aqueous electrolyte secondary battery, each electrode includes an active material supported on a current collector made of a conductive material as a main component. The positive electrode includes a positive electrode active material supported on the positive electrode current collector, and the negative electrode includes a negative electrode active material supported on the negative electrode current collector. And in order to bind a positive electrode active material and a negative electrode active material, the binder is used in each electrode. As such a binder, conventionally, a solvent-based binder represented by a fluorine-based polymer such as polyvinylidene fluoride (PDVF) has been often used.

  In a nonaqueous electrolyte secondary battery, for example, as described in Japanese Patent Application Laid-Open No. 2008-16414 (Patent Document 1), vinylene carbonate is often added to a nonaqueous electrolyte in order to suppress a decrease in capacity. (See paragraph 0080). Vinylene carbonate is susceptible to oxidative decomposition, and part of the side reaction product generated thereby forms a negative electrode film, which can contribute to improving battery characteristics by suppressing capacity reduction and battery swelling. (See paragraph 0073).

JP 2008-16414 A

  When a solvent-based binder is used, it is generally used by dissolving in an organic solvent such as N-methylpyrrolidone when preparing a paste with an active material. For this reason, if it is going to reduce the load given to an environment, for example, it will be necessary to collect | recover organic solvents as much as possible and reduce discharge | emission amount. As a result, the initial cost for capital investment and the operational cost for operation and management of the equipment are enormous.

  Under these circumstances, in recent years, there is an increasing need for the use of an aqueous binder (a binder that can use an aqueous solvent) for the purpose of reducing the environmental burden and reducing the cost. However, according to the study by the present inventors, when an aqueous binder is used for the positive electrode plate, the capacity is reduced even if vinylene carbonate is added to the nonaqueous electrolyte, unlike the case of using a solvent-based binder. It has been found that battery swelling may occur.

  Therefore, it is desired to suppress the occurrence of capacity reduction and battery swelling while achieving a low environmental load and cost reduction in a non-aqueous electrolyte secondary battery.

  A characteristic configuration of the nonaqueous electrolyte secondary battery according to the present invention includes a positive electrode and a nonaqueous electrolyte, and includes an aqueous binder as the binder of the positive electrode, and the nonaqueous electrolyte includes a compound containing sulfur (hereinafter, The sulfur-containing compound).

  That is, the nonaqueous electrolyte secondary battery according to the present invention combines the use of an aqueous binder as a binder for binding the positive electrode active material and the addition of a sulfur-containing compound to the nonaqueous electrolyte. It has the characteristics in the point. According to this characteristic configuration, even when an aqueous binder is used as the binder for the positive electrode, by adding a sulfur-containing compound to the non-aqueous electrolyte, the capacity reduction observed with other additives, etc. It can contribute to the improvement of battery characteristics by suppressing battery swelling.

  As the sulfur-containing compound, any of a sulfur-containing organic compound and a sulfur-containing inorganic compound can be used. The sulfur-containing compound preferably contains at least one selected from a sulfate ester compound and a sultone compound.

  If the amount of the sulfur-containing compound added to the non-aqueous electrolyte exceeds 4.0% by mass, side reactions due to the excess sulfur-containing compound increase, which may cause a reduction in capacity and battery swelling. In view of this point, as one aspect, it is preferable that the content of the sulfur-containing compound with respect to the mass of the non-aqueous electrolyte is 4.0% by mass or less.

Sectional drawing which shows the whole structure of a nonaqueous electrolyte secondary battery Schematic diagram showing schematic configuration of non-aqueous electrolyte secondary battery

  An embodiment of a nonaqueous electrolyte secondary battery according to the present invention will be described with reference to the drawings. In the present embodiment, an example will be described in which the present invention is applied to a lithium ion secondary battery in which lithium ions contained in the nonaqueous electrolyte play a role of electrical conduction. In this embodiment, an example in which the present invention is applied to a rectangular lithium ion secondary battery will be described. In the following description, the description of the action mechanism includes estimation, and the scope of the present invention is not limited by the correctness.

  As shown in FIG. 1, the non-aqueous electrolyte secondary battery 1 includes a power generation element 3, a non-aqueous electrolyte (not shown), and a container 5 that houses them. The power generation element 3 is an element that functions as a core of power generation and charging, and includes a positive electrode 10, a negative electrode 20, and a separator 30. In the present embodiment, the power generation element 3 is configured by winding the positive electrode 10 and the negative electrode 20 via the separator 30. In FIG. 2, only a part of the wound power generation element 3 is extracted and schematically shown.

  As shown in FIG. 2, the positive electrode 10 includes a positive electrode current collector 11 and a positive electrode mixture layer 12 formed on the positive electrode current collector 11. The positive electrode mixture layer 12 is a mixture layer containing a positive electrode active material, a conductive auxiliary agent, and a binder. The positive electrode mixture layer 12 can be formed, for example, by applying a paste (positive electrode paste) mixed using an appropriate solvent according to the properties of the binder to the positive electrode current collector 11 and drying it. At that time, the thickness and porosity may be adjusted by a roll press or the like.

  The positive electrode current collector 11 is configured using a conductive material. The positive electrode current collector 11 can be formed using a metal material such as aluminum, copper, nickel, stainless steel, titanium, and tantalum. As the shape, various shapes such as a sheet (foil or thin film), a plate, a columnar body, a coil, a foamed body, a porous body, and an expanded lattice can be adopted.

The positive electrode active material is a material that absorbs and releases lithium ions. As such a positive electrode active material, a lithium transition metal composite oxide capable of inserting and extracting lithium ions can be used. Examples of the lithium transition metal composite oxide include lithium / cobalt composite oxides such as LiCoO ₂ ; lithium / nickel composite oxides such as LiNiO ₂ ; and lithium / nickel composite oxides such as LiMnO ₂ , LiMn ₂ O ₄ , and Li ₂ MnO _3. Examples include manganese composite oxides. Moreover, you may use what substituted some of these transition metal atoms with the other transition metal and light metal. Alternatively, an olivine type compound capable of inserting and extracting lithium ions can be used. Examples of the olivine type compound include olivine type lithium phosphate compounds such as LiFePO ₄ .

  The conductive assistant is a material added for the purpose of improving the conductivity in the positive electrode mixture layer 12. As such a conductive assistant, various conductive materials can be used. For example, carbon materials such as acetylene black, carbon black and graphite; conductive fibers such as metal fibers; metal powders such as copper, nickel, aluminum and silver; conductive whiskers such as zinc oxide and potassium titanate; and Examples include conductive metal oxides such as titanium oxide.

  The binder (positive electrode binder) is a material added for the purpose of binding the positive electrode active material. Further, the binder also serves to bind the positive electrode active material, the conductive additive, and the positive electrode current collector 11. As such a binder, generally, a solvent-based binder in which an organic solvent is used when mixing with a positive electrode active material and a conductive additive to form a paste, and an aqueous solvent (typically, water ) Can be used. In the present invention, an aqueous binder is used as the positive electrode binder.

  As the aqueous binder added to the positive electrode mixture layer 12, it is preferable to use at least one selected from a rubber-like polymer and a resin-based polymer that can be dissolved or dispersed in an aqueous solvent. Here, the aqueous solvent represents water or a mixed solvent mainly composed of water. Examples of the solvent other than water constituting the mixed solvent include organic solvents (such as lower alcohols and lower ketones) that can be uniformly mixed with water.

  Examples of the rubber-like polymer that can be dissolved or dispersed in an aqueous solvent include styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), methyl methacrylate-butadiene rubber (MBR), and the like. These can be used as a binder preferably in a state dispersed in water. That is, examples of usable aqueous binders include an aqueous dispersion of styrene-butadiene rubber (SBR), an aqueous dispersion of acrylonitrile-butadiene rubber (NBR), an aqueous dispersion of methyl methacrylate-butadiene rubber (MBR), and the like. Is mentioned.

  Examples of the resin polymer that can be dissolved or dispersed in the aqueous solvent include acrylic resins, olefin resins, and fluorine resins. Examples of the acrylic resin include acrylic acid esters and methacrylic acid esters. Examples of the olefin resin include polypropylene (PP) and polyethylene (PE). Examples of the fluorine-based resin include polytetrafluoroethylene (PTFE). These can be used as a binder preferably in a state dispersed in water. That is, examples of usable aqueous binders include acrylic ester aqueous dispersions, methacrylic ester aqueous dispersions, polypropylene (PP) aqueous dispersions, polyethylene (PE) aqueous dispersions, and polytetrafluoro. Examples thereof include an aqueous dispersion of ethylene (PTFE).

  As the aqueous binder for the positive electrode, a copolymer containing two or more of the aforementioned components as monomers can also be used. Such copolymers include ethylene-propylene copolymer, ethylene-methacrylic acid copolymer, ethylene-acrylic acid copolymer, propylene-butene copolymer, acrylonitrile-styrene copolymer, methyl methacrylate-butadiene. -A styrene copolymer etc. can be illustrated. These can be used as a binder preferably in a state dispersed in water. That is, as an example of usable aqueous binder, ethylene-propylene copolymer aqueous dispersion, ethylene-methacrylic acid copolymer aqueous dispersion, ethylene-acrylic acid copolymer aqueous dispersion, propylene- Examples include an aqueous dispersion of a butene copolymer, an aqueous dispersion of an acrylonitrile-styrene copolymer, and an aqueous dispersion of a methyl methacrylate-butadiene-styrene copolymer.

  The positive electrode mixture layer 12 contains other components such as a dispersant such as a surfactant and a thickener such as carboxymethylcellulose (CMC), methylcellulose (MC), and hydroxypropylmethylcellulose (HPMC). Also good.

  As shown in FIG. 2, the negative electrode 20 includes a negative electrode current collector 21 and a negative electrode mixture layer 22 formed on the negative electrode current collector 21. The negative electrode mixture layer 22 is a mixture layer containing a negative electrode active material and a binder. The negative electrode mixture layer 22 may contain a conductive additive as necessary. The negative electrode mixture layer 22 can be formed, for example, by applying a paste (negative electrode paste) mixed using an appropriate solvent according to the properties of the binder to the negative electrode current collector 21 and drying it. At that time, the thickness and porosity may be adjusted by a roll press or the like.

  The negative electrode current collector 21 is configured using a conductive material. The negative electrode current collector 21 can be configured using a metal material such as copper, nickel, stainless steel, nickel-plated steel, or the like. As the shape, various shapes such as a sheet (foil or thin film), a plate, a columnar body, a coil, a foamed body, a porous body, and an expanded lattice can be adopted.

The negative electrode active material is a material that absorbs and releases lithium ions. Examples of such a negative electrode active material include metal lithium; lithium titanate such as Li ₄ Ti ₅ O ₁₂ ; graphite; and amorphous carbon such as soft carbon and hard carbon. Illustrated.

  The conductive assistant is a material added for the purpose of improving the conductivity in the negative electrode mixture layer 22 as necessary. As such a conductive assistant, various conductive materials can be used. As the conductive additive for the negative electrode, the same material as the conductive additive for the positive electrode described above can be used.

  The binder (negative electrode binder) is a material added for the purpose of binding the negative electrode active material. The binder also plays a role of binding the negative electrode active material and the negative electrode current collector 21. In the case where the negative electrode mixture layer 22 includes a conductive additive, the binder also serves to bind the negative electrode active material and the negative electrode current collector 21 to the conductive additive. As the binder for the negative electrode, an aqueous binder can be used, and a solvent-based binder can also be used. As the aqueous binder, the same material as the above-described positive electrode aqueous binder can be used.

  The solvent-based binder is a binder in which an organic solvent is used when mixing with a negative electrode active material or the like to form a paste. As the solvent binder, polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), polyacrylonitrile (PAN), or the like can be used. When solvent-based binders are used, they can be preferably used in a state of being dissolved in an aprotic polar solvent which is an example of an organic solvent. As the aprotic polar solvent, an aprotic amide solvent such as N-methyl-2-pyrrolidone (NMP) or N, N-dimethylformamide (DMF) can be used. That is, as an example of a solvent-based binder that can be used for a negative electrode, an N-methyl-2-pyrrolidone (NMP) solution of polyvinylidene fluoride (PVDF) can be cited.

  The negative electrode mixture layer 22 may contain other components such as a dispersant and a thickener as in the positive electrode mixture layer 12.

  The separator 30 separates the positive electrode 10 and the negative electrode 20 and holds a nonaqueous electrolyte. As the separator 30, various materials can be used as appropriate, and for example, a synthetic resin microporous film, a woven fabric, a non-woven fabric, or the like can be used. As the synthetic resin microporous membrane, for example, a polyethylene microporous membrane, a polypropylene microporous membrane, and a polyolefin microporous membrane such as a microporous membrane obtained by combining these can be preferably used.

  The power generation element 3 including the positive electrode 10, the negative electrode 20, and the separator 30 is accommodated in the container 5. A nonaqueous electrolyte is also accommodated in the container 5. The power generation element 3 is immersed in the nonaqueous electrolyte in the container 5, and the power generation element 3 is impregnated with the nonaqueous electrolyte.

  The non-aqueous electrolyte is an electrolyte obtained by dissolving a supporting electrolyte in a non-aqueous solvent (a solvent other than water). As the non-aqueous solvent, an organic solvent can be preferably used. Examples of such an organic solvent include carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), and methyl ethyl carbonate (MEC); Esters such as γ-butyrolactone and methyl formate can be suitably used. You may use these 2 or more types of mixed solvents.

A lithium salt is used as the supporting electrolyte contained in the nonaqueous electrolyte. As the lithium salt, either an inorganic lithium salt or an organic lithium salt can be used. Examples of the inorganic lithium salt include lithium fluoride salts such as LiPF ₆ , LiAsF ₆ , LiBF ₄ and LiSbF ₆ ; lithium chloride salts such as LiAlCl ₄ ; and lithium perhalogenates such as LiClO ₄ , LiBrO ₄ and LiIO _4. Etc. can be illustrated. Two or more of these may be used in combination.

  In the present invention, the non-aqueous electrolyte contains a sulfur-containing compound. Here, the “sulfur-containing compound” represents a sulfur-containing compound that is intentionally added. As the sulfur-containing compound, any of a sulfur-containing organic compound and a sulfur-containing inorganic compound can be used. In the present invention, since a non-aqueous electrolyte is used, it is preferable to use a sulfur-containing organic compound as the sulfur-containing compound in consideration of the stability in the non-aqueous electrolyte. Moreover, as a sulfur-containing organic compound, it is preferable to use a sulfate ester compound or a sultone compound (cyclic sulfonate ester compound). These may be used in combination.

  As the sulfate ester compound, both cyclic sulfate esters and chain sulfate esters can be used. Examples of cyclic sulfates include ethylene glycol sulfate and propylene glycol sulfate (PEGLST). Examples of the chain sulfates include dimethyl sulfate, diethyl sulfate, and dipropyl sulfate. These derivatives can also be used. Two or more of these may be used in combination.

  As the sultone compound (cyclic sulfonic acid ester compound), both saturated sultones and unsaturated sultones can be used. Examples of saturated sultone include 1,3-propane sultone and 1,4-butane sultone. Examples of unsaturated sultone include 1,3-propene sultone (RPS). These derivatives can also be used. Two or more of these may be used in combination.

  Among these, 1,3-propene sultone (RPS) and propylene glycol sulfate (PEGLST), which are cyclic sulfur-containing organic compounds, are particularly preferable because of their low self-degradability and easy handling.

  If the amount of the sulfur-containing compound added to the non-aqueous electrolyte exceeds 4.0% by mass, side reactions due to the excess sulfur-containing compound increase, which may cause a reduction in capacity and battery swelling. In view of this point, it is preferable that the content of the sulfur-containing compound with respect to the mass of the nonaqueous electrolyte is 4.0% by mass or less. Moreover, when the addition amount of the sulfur-containing compound with respect to the nonaqueous electrolyte is less than 0.1% by mass, the formation of a protective film on the positive electrode and the negative electrode becomes insufficient, resulting in a decrease in capacity and battery swelling. There is a case. It is preferable that the content of the sulfur-containing compound relative to the mass of the nonaqueous electrolyte is 0.1% by mass.

  It should be noted that other compounds may be added to the nonaqueous electrolyte for the purpose of improving charge / discharge characteristics or making it nonflammable.

  The container 5 that houses the power generation element 3 and the nonaqueous electrolyte (including various additives) functions as a battery case that constitutes an outer can of the nonaqueous electrolyte secondary battery 1. As shown in FIG. 1, in the present embodiment, the container 5 is formed in a square box shape. The container 5 is comprised using metal materials, such as aluminum and aluminum alloy, for example. In a state where the power generation element 3 and the nonaqueous electrolyte (including various additives) are accommodated in the container 5, the lid member 6 made of a metal material is fixed to the opening of the container 5 and sealed. Yes.

  In the present embodiment, the lid member 6 also serves as a positive electrode terminal. In addition, a negative electrode terminal 61 is provided at the center of the lid member 6. An insulating member 62 made of an insulating material such as a resin is interposed between the lid member 6 and the negative electrode terminal 61 to ensure electrical insulation between the two electrode terminals. The positive electrode 10 is connected to a lid member 6 as a positive electrode terminal via a positive electrode lead 15. The negative electrode 20 is connected to the negative electrode terminal 61 via the negative electrode lead 25. The lid member 6 is also provided with a safety valve 63 for releasing gas to the outside when the internal pressure in the sealed container reaches a predetermined pressure.

  In the nonaqueous electrolyte secondary battery 1 as described above, the present invention uses an aqueous binder as a binder for binding the positive electrode active material, and adds a sulfur-containing compound to the nonaqueous electrolyte. It has the feature in the point which combined. Thereby, while achieving low environmental load and cost reduction, it is possible to suppress the decrease in capacity and the expansion of the battery and contribute to the improvement of the battery characteristics. Hereinafter, this point will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited to these examples.

[Example 1]
A nonaqueous electrolyte secondary battery 1 having the form shown in FIG. 1 was produced according to the following procedure.
<1> Production of Positive Electrode 94 parts by mass of LiMn _0.33 Ni _0.33 Co _0.33 O ₂ powder as a positive electrode active material, 3.5 parts by mass of acetylene black as a conductive additive, and a binder 2 parts by mass of acrylic resin particles made of ethyl acrylate (using 40% by mass acrylic resin particle water dispersion), 0.5 parts by mass of carboxymethyl cellulose (CMC) as a thickener, and water in a mixer The positive electrode paste was prepared by mixing. Next, the obtained positive electrode paste was applied to both surfaces of a positive electrode current collector 11 made of aluminum foil having a thickness of 20 μm by a doctor blade method, and a positive electrode mixture layer 12 was formed on the positive electrode current collector 11. Thereafter, the positive electrode mixture layer 12 was vacuum-dried at 130 ° C. for 24 hours to obtain the positive electrode 10. A positive electrode lead 15 was attached to the positive electrode 10.

<2> Production of negative electrode 95 parts by mass of natural graphite as a negative electrode active material, N-methyl-2-pyrrolidone (NMP) solution of 5 parts by mass of polyvinylidene fluoride (PVDF) as a binder, and N-methyl- 2-Pyrrolidone (NMP) was mixed to prepare a negative electrode paste. Next, the obtained negative electrode paste was applied to both surfaces of a copper foil negative electrode current collector 21 having a thickness of 10 μm by a doctor blade method to form a negative electrode mixture layer 22 on the negative electrode current collector 21. Thereafter, the negative electrode mixture layer 22 was vacuum-dried at 150 ° C. for 14 hours to obtain the negative electrode 20. A negative electrode lead 25 was attached to the negative electrode 20.

<3> Preparation of nonaqueous electrolyte In a mixed solvent of ethylene carbonate (EC): diethyl carbonate (DEC) = 30: 70 (volume ratio), LiPF ₆ as a supporting electrolyte was dissolved so as to be 1 mol / L, A non-aqueous electrolyte was prepared. Moreover, 1,3-propene sultone (PRS) was added as an additive so that the ratio with respect to the total mass of a nonaqueous electrolyte might be 1 mass%.

<4> Production of Battery The positive electrode and the negative electrode laminated through a polyethylene microporous membrane separator were wound to form a power generation element 3, and the power generation element 3 was housed in an aluminum square container 5. Thereafter, the positive electrode 10 was connected to the lid member 6 via the positive electrode lead 15, the negative electrode 20 was connected to the negative electrode terminal 61 via the negative electrode lead 25, and the lid member 6 was attached to the container 5 by laser welding. Then, after injecting a nonaqueous electrolyte (including an additive) under reduced pressure, the injection port was sealed by laser welding. Thereby, a rectangular nonaqueous electrolyte secondary battery 1 (referred to as battery A) having a design capacity of 570 mAh was produced.

[Example 2]
A battery B was produced in the same manner as in Example 1 except that LiFePO ₄ powder was used as the positive electrode active material in the battery A of Example 1. The design capacity of this battery B is 450 mAh.

[Example 3]
A battery C was produced in the same manner as in Example 1, except that in the battery A of Example 1, LiNi _0.82 Co _0.15 Al _0.03 O ₂ powder was used as the positive electrode active material. The design capacity of this battery C is 700 mAh.

[Example 4]
In the battery A of Example 1, a battery D was produced in the same manner as in Example 1 except that propylene glycol sulfate (PEGLST) was used as an additive.

[Example 5]
In the battery B of Example 2, a battery E was produced in the same manner as in Example 2 except that propylene glycol sulfate (PEGLST) was used as an additive.

[Example 6]
In the battery C of Example 3, a battery F was produced in the same manner as in Example 3 except that propylene glycol sulfate (PEGLST) was used as an additive.

[Example 7]
In the battery B of Example 2, a battery G was produced in the same manner as in Example 2 except that an aqueous dispersion of styrene-butadiene rubber (SBR) was used as the binder.

[Example 8]
In the battery B of Example 2, a battery H was produced in the same manner as in Example 2 except that an aqueous dispersion of olefin resin particles made of polyethylene was used as the binder.

[Example 9]
In the battery B of Example 2, a battery I was produced in the same manner as in Example 2 except that the amount of 1,3-propene sultone (PRS) added to the nonaqueous electrolyte was 0.1% by mass.

[Example 10]
In the battery B of Example 2, a battery J was produced in the same manner as in Example 2 except that the amount of 1,3-propene sultone (PRS) added to the nonaqueous electrolyte was 4% by mass.

[Example 11]
In the battery B of Example 2, a battery K was produced in the same manner as in Example 2 except that the amount of 1,3-propene sultone (PRS) added to the nonaqueous electrolyte was 0.08% by mass.

[Example 12]
In the battery B of Example 2, a battery L was produced in the same manner as in Example 2 except that the amount of 1,3-propene sultone (PRS) added to the nonaqueous electrolyte was 4.2% by mass.

[Comparative Example 1]
93 parts by mass of LiMn _0.33 Ni _0.33 Co _0.33 O ₂ powder as a positive electrode active material, 3 parts by mass of acetylene black as a conductive additive, and polyvinylidene fluoride (PVDF) as a binder 4 parts by mass (N-methyl-2-pyrrolidone (NMP) 12% by mass) and N-methyl-2-pyrrolidone (NMP) were mixed with a mixer to prepare a positive electrode paste. Next, the obtained positive electrode paste was applied to both surfaces of a positive electrode current collector made of aluminum foil having a thickness of 20 μm to form a positive electrode mixture layer on the positive electrode current collector. Then, this positive mix layer was vacuum-dried at 100 degreeC for 24 hours, and the positive electrode was obtained. Further, a negative electrode was obtained in the same manner as in Example 1. Using these positive and negative electrodes, a square nonaqueous electrolyte was obtained in the same manner as in Example 1 except that vinylene carbonate (VC) was added to the nonaqueous electrolyte instead of 1,3-propene sultone (PRS). A secondary battery (referred to as battery M) was produced. In addition, the ratio of vinylene carbonate (VC) with respect to the total mass of a nonaqueous electrolyte was 1 mass%.

[Comparative Example 2]
In the battery M of Comparative Example 1, a battery N was produced in the same manner as in Comparative Example 1 except that LiFePO ₄ powder was used as the positive electrode active material. The design capacity of the battery N is 450 mAh.

[Comparative Example 3]
In the battery M of Comparative Example 1, a battery O was produced in the same manner as in Comparative Example 1 except that LiNi _0.82 Co _0.15 Al _0.03 O ₂ powder was used as the positive electrode active material. The design capacity of this battery O is 700 mAh.

[Comparative Example 4]
In the battery M of Comparative Example 1, a battery P was produced in the same manner as in Comparative Example 1 except that an aqueous dispersion of acrylic resin particles was used as the binder.

[Comparative Example 5]
In the battery N of Comparative Example 2, a battery Q was produced in the same manner as in Comparative Example 2, except that an aqueous dispersion of acrylic resin particles was used as the binder.

[Comparative Example 6]
In the battery O of Comparative Example 3, a battery R was produced in the same manner as in Comparative Example 3, except that an aqueous dispersion of acrylic resin particles was used as the binder.

[Comparative Example 7]
In the battery N of Comparative Example 2, a battery S was produced in the same manner as in Comparative Example 2, except that an aqueous dispersion of styrene-butadiene rubber (SBR) was used as the binder.

[Comparative Example 8]
In the battery N of Comparative Example 2, a battery T was produced in the same manner as in Comparative Example 2, except that an aqueous dispersion of olefin resin particles was used as the binder.

[Evaluation test]
A charge / discharge test was performed using each of the batteries A to T according to Examples 1 to 12 and Comparative Examples 1 to 8. Batteries A, C, D, F, M, O, P, R of which the positive electrode active material is LiMn _0.33 Ni _0.33 Co _0.33 O ₂ or LiNi _0.82 Co _0.15 Al _0.03 O ₂ Is charged at a constant current of 1 CmA (570 mA or 700 mA depending on the positive electrode active material) at 25 ° C. to 4.2 V, and charged at a constant voltage of 4.2 V so that the charging time is 3 hours. The battery was discharged to 2.5 V at a constant current of 1 CmA (same as above), and the discharge capacity at that time was measured. On the other hand, the batteries B, E, G to L, N, Q, S, and T whose positive electrode active material is LiFePO ₄ are charged to 3.5 V with a constant current of 1 CmA (450 mA) at 25 ° C., and the charging time is 3 After charging at a constant voltage of 3.5 V so as to reach time, the battery was discharged to 2.0 V with a constant current of 1 CmA (same as above), and the discharge capacity at that time was measured. Moreover, the thickness of the battery case before and after charging / discharging was measured, respectively, and the battery expansion coefficient was calculated. The results of these evaluation tests are summarized in Table 1.

  From the results shown in Table 1, the following matters became clear.

  Referring to the results of Comparative Examples 1 to 3, an N-methyl-2-pyrrolidone (NMP) solution of polyvinylidene fluoride (PVDF) was used as a binder for binding the positive electrode active material, and vinylene carbonate ( VC) is added to the non-aqueous electrolyte, so that the discharge capacity is maintained high regardless of the type of the positive electrode active material (in other words, the actual discharge capacity is obtained as designed), and battery swelling is avoided. Can be confirmed. This is considered to be because a part of the side reaction product generated by the oxidative decomposition of vinylene carbonate (VC) forms a protective film covering the negative electrode.

  On the other hand, when the results of Comparative Examples 1 to 3 and the results of Comparative Examples 4 to 6 are compared, the binder for the positive electrode is an acrylic resin that is an aqueous binder while using vinylene carbonate (VC) as an additive. It can be seen that the discharge capacity decreases (in other words, the actual discharge capacity cannot be obtained as designed) and the battery swells only by replacing the particle with the water dispersion. Further, comparing the results of Comparative Example 2 with the results of Comparative Examples 7 and 8, the positive electrode binder was an aqueous dispersion of styrene-butadiene rubber (SBR), which is an aqueous binder, or olefin resin particles. It can be seen that the same result is obtained when the water dispersion is merely used. This is because aqueous binders such as acrylic resin and styrene-butadiene rubber (SBR) have higher reactivity at the positive electrode than solvent-based binders such as polyvinylidene fluoride (PVDF), and vinylene carbonate (VC). It is considered that the discharge capacity maintaining effect and the battery swelling avoidance effect cannot be sufficiently obtained only by forming the protective film by the above method on the negative electrode.

  On the other hand, if the results of Comparative Examples 1 to 3 and the results of Examples 1 to 3 are compared, the positive electrode binder is replaced with an aqueous dispersion of acrylic resin particles that are aqueous binders. Accordingly, it can be seen that by replacing the additive with 1,3-propene sultone (PRS), the discharge capacity is kept high and battery swelling is avoided regardless of the type of the positive electrode active material. Further, comparing the results of Comparative Example 2 with the results of Examples 7 and 8, the positive electrode binder was an aqueous dispersion of styrene-butadiene rubber (SBR), which is an aqueous binder, or olefin resin particles. It turns out that the same effect is acquired by replacing with an aqueous dispersion and replacing an additive with 1, 3- propene sultone (PRS) according to it. Although the detailed reaction mechanism has not been specified yet, a protective film is formed not only on the negative electrode but also on the positive electrode by adding a sulfur-containing organic compound such as 1,3-propene sultone (PRS) to the non-aqueous electrolyte. It is thought that it is because it is formed. Therefore, even when an aqueous binder having high reactivity at the positive electrode is used, it is considered that the discharge capacity maintaining effect and the battery swelling avoidance effect can be sufficiently obtained.

  Further, referring to the results of Examples 2, 9, and 10, when the amount of 1,3-propene sultone (PRS) added to the non-aqueous electrolyte is in the range of 0.1% by mass or more and 4.0% by mass or less, It can be seen that the discharge capacity is kept high and battery swelling is avoided regardless of the amount added. On the other hand, referring to the results of Example 11, when the amount of 1,3-propene sultone (PRS) added to the non-aqueous electrolyte is less than 0.1% by mass, the discharge capacity decreases and the battery swells. I understand. Also, referring to the results of Example 12, it can be seen that when the amount of 1,3-propene sultone (PRS) added to the non-aqueous electrolyte exceeds 4.0% by mass, the discharge capacity decreases. This is because, when the amount of sulfur-containing organic compound such as 1,3-propene sultone (PRS) is too small, the formation of protective coatings on the positive electrode and the negative electrode is insufficient, while when it is excessive, excessive sulfur-containing compounds are present. This is thought to be due to an increase in side reactions caused by organic compounds. Considering this, the amount of the sulfur-containing organic compound added to the non-aqueous electrolyte is preferably 0.1% by mass or more and 4.0% by mass or less.

  However, referring to the results of Example 12, when the amount of 1,3-propene sultone (PRS) added to the non-aqueous electrolyte exceeds 4.0% by mass, the discharge capacity decreases. There is no battery swelling. In consideration of this, when a slight decrease in the discharge capacity can be allowed, the amount of the sulfur-containing organic compound added to the nonaqueous electrolyte can exceed 4.0% by mass. As one aspect, the amount of the sulfur-containing organic compound added to the nonaqueous electrolyte may be, for example, 0.1% by mass or more and 5.0% by mass or less, or 0.1% by mass or more and 6.0% by mass or less. It may be.

  In addition, if the result of the comparative example 5 and the result of Example 11 and 12 are compared, the reduction of the discharge capacity by the addition amount of 1, 3- propene sultone (PRS) with respect to a nonaqueous electrolyte being too small or excessive, and Compared with battery swelling, battery swelling is caused by replacing the positive electrode binder with an aqueous dispersion of acrylic resin particles, which is an aqueous binder, while using vinylene carbonate (VC) as an additive. It can be seen that the degree is low. Therefore, the combination of using an aqueous binder as the positive electrode binder and adding a sulfur-containing compound to the nonaqueous electrolyte greatly contributes to the discharge capacity maintenance effect and the battery swelling avoidance effect. I understand that

Comparison between Example 1 and Comparative Example 4 in which the positive electrode active material is LiMn _0.33 Ni _0.33 Co _0.33 O ₂ , Comparison between Example 2 and Comparative Example 5 in which the positive electrode active material is LiFePO ₄ , and positive electrode When the results of Example 3 and Comparative Example 6 in which the active material is LiNi _0.82 Co _0.15 Al _0.03 O ₂ are compared, respectively, the positive electrode active material LiNi _0.82 Co _0.15 Al _0.03 O _{When 2} was used, the recovery of the discharge capacity was large. From this, it was found that in the present invention, when a Ni-based active material is used as the positive electrode active material, a greater effect than other positive electrode active materials can be obtained. Here, the Ni-based active material refers to a positive electrode active material having a Ni molar ratio of 50% or more in the entire molar ratio of metals other than Li.

  As described above, the non-aqueous electrolyte secondary battery according to the present invention is characterized by the combination of using an aqueous binder as the positive electrode binder and adding a sulfur-containing compound to the non-aqueous electrolyte. Have. As is clear from the above study, by adding a sulfur-containing compound to the nonaqueous electrolyte, even when an aqueous binder is used as the binder for the positive electrode, the decrease in discharge capacity and battery swelling are suppressed. Thus, the battery characteristics can be improved.

  It should be understood that the embodiments disclosed herein and examples embodying the same are illustrative in all respects, and the scope of the present invention is not limited thereby. Those skilled in the art will readily understand that modifications can be made as appropriate without departing from the spirit of the present invention based on the above-described embodiments and examples. Accordingly, other embodiments modified without departing from the spirit of the present invention are naturally included in the scope of the present invention.

  For example, the positive electrode material, the negative electrode material, the nonaqueous electrolyte, and the like can be appropriately selected according to the performance and specifications required for the nonaqueous electrolyte secondary battery.

  Further, for example, the sulfur-containing compound as the positive electrode aqueous binder or additive is not limited to the compounds exemplified in the present specification, and various compounds each having specified characteristics can be used. .

  The present invention can be used for a nonaqueous electrolyte secondary battery such as a lithium ion secondary battery.

DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte secondary battery 10 Positive electrode 12 Positive electrode mixture layer 20 Negative electrode 22 Negative electrode mixture layer

Claims (4)

A positive electrode and a non-aqueous electrolyte;
The positive electrode contains an aqueous binder as a binder,
A non-aqueous electrolyte secondary battery, wherein the non-aqueous electrolyte contains a compound containing sulfur.   The nonaqueous electrolyte secondary battery according to claim 1, wherein the compound containing sulfur includes at least one selected from a sulfate ester compound and a sultone compound.   The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein a content of the sulfur-containing compound with respect to a mass of the nonaqueous electrolyte is 4.0 mass% or less. A method for producing a non-aqueous electrolyte secondary battery comprising a positive electrode and a non-aqueous electrolyte,
Using an aqueous binder as the positive electrode binder,
A method for producing a non-aqueous electrolyte secondary battery, wherein a non-aqueous electrolyte containing a compound containing sulfur is used as the non-aqueous electrolyte.