JP6900735B2 - Battery positive electrode, battery positive electrode manufacturing method and battery - Google Patents

Description

The present invention relates to a positive electrode for a battery, a method for manufacturing a positive electrode for a battery, and a battery.

A positive electrode for a non-aqueous electrolyte battery is usually produced by using a positive electrode paste in which a positive electrode active material, a conductive agent, and a binder are dispersed in a dispersion medium. Specifically, a positive electrode is obtained by applying this positive electrode paste to a conductive base material such as aluminum foil and passing it through a drying oven to volatilize and remove the dispersion medium.

In order to increase the productivity of the positive electrode, it is considered to increase the line speed in the above coating process. However, when the line speed is increased, the residence time in the drying oven is shortened, resulting in insufficient drying. As one of the methods capable of drying in a short time, there is a method of increasing the solid content concentration in the positive electrode paste, that is, reducing the content of the dispersion medium. However, in this case, since the viscosity of the positive electrode paste is increased, there is an inconvenience that the coatability is lowered, such as fading during coating.

Therefore, in order to suppress an increase in the viscosity of the positive electrode paste, a positive electrode paste containing a copolymer having a specific structure has been proposed (see Patent Document 1). According to this positive electrode paste, the dispersibility of the conductive agent or the like is enhanced by containing the copolymer, and as a result, the viscosity can be reduced.

International Publication No. 2013/151062

However, a battery using a positive electrode obtained by a positive electrode paste containing the above-mentioned copolymer has a disadvantage that the resistance increase rate with repeated charging and discharging is large. The inventors have found that the cause of this is the high solubility of the copolymer contained in the positive electrode paste in the electrolytic solution. That is, it is presumed that the copolymer in which the copolymer is eluted from the positive electrode into the electrolytic solution causes clogging of the separator existing between the positive electrode and the negative electrode, thereby increasing the resistance. On the other hand, it is considered that increasing the molecular weight of the copolymer reduces the solubility of the copolymer in the electrolytic solution. However, simply increasing the molecular weight of the copolymer is not preferable because the viscosity of the paste is unlikely to decrease.

The present invention has been made based on the above circumstances, and an object of the present invention is a positive electrode for a battery capable of suppressing an increase in battery resistance due to repeated charging and discharging, and a positive electrode for such a battery. It is an object of the present invention to provide a manufacturing method and a battery in which an increase in resistance due to repeated charging and discharging is suppressed.

（式（１）〜（３）中、Ｒ^１、Ｒ^２、Ｒ^３、Ｒ^５、Ｒ^６、Ｒ^７、Ｒ^９、Ｒ^１０、Ｒ^１１、及びＲ^１２は、それぞれ独立して、水素原子、メチル基又はエチル基である。Ｒ^４は、炭素数８〜３０の１価の炭化水素基である。Ｒ^８は、炭素数２〜４の直鎖状又は分岐状のアルキレン基である。ｐは、１〜５０の数である。） One aspect of the present invention made to solve the above problems includes a positive electrode active material, a conductive agent, a binder and a copolymer, and the copolymer is a structural unit represented by the following formula (1). (A), the structural unit (b) represented by the following formula (2) and the structural unit (c) represented by the following formula (3), and the structural unit (c) in the copolymer. It is a positive electrode for a battery having a content of 15% by mass or more and 45% by mass or less.

(In formulas (1) to (3), R ¹ , R ² , R ³ , R ⁵ , R ⁶ , R ⁷ , R ⁹ , R ¹⁰ , R ¹¹ , and R ¹² are independent hydrogen atoms, respectively. , Methyl group or ethyl group. R ⁴ is a monovalent hydrocarbon group having 8 to 30 carbon atoms. R ⁸ is a linear or branched alkylene group having 2 to 4 carbon atoms. p is a number from 1 to 50.)

（式（１）〜（３）中、Ｒ^１、Ｒ^２、Ｒ^３、Ｒ^５、Ｒ^６、Ｒ^７、Ｒ^９、Ｒ^１０、Ｒ^１１、及びＲ^１２は、それぞれ独立して、水素原子、メチル基又はエチル基である。Ｒ^４は、炭素数８〜３０の１価の炭化水素基である。Ｒ^８は、炭素数２〜４の直鎖状又は分岐状のアルキレン基である。ｐは、１〜５０の数である。） Another aspect of the present invention made to solve the above problems includes using a positive electrode paste for a battery containing a positive electrode active material, a conductive agent, a binder, a copolymer and a dispersion medium, and has the same weight. The coalescence contains a structural unit (a) represented by the following formula (1), a structural unit (b) represented by the following formula (2), and a structural unit (c) represented by the following formula (3). This is a method for producing a positive electrode for a battery, wherein the content of the structural unit (c) in the copolymer is 15% by mass or more and 45% by mass or less.

(In formulas (1) to (3), R ¹ , R ² , R ³ , R ⁵ , R ⁶ , R ⁷ , R ⁹ , R ¹⁰ , R ¹¹ , and R ¹² are independent hydrogen atoms, respectively. , Methyl group or ethyl group. R ⁴ is a monovalent hydrocarbon group having 8 to 30 carbon atoms. R ⁸ is a linear or branched alkylene group having 2 to 4 carbon atoms. p is a number from 1 to 50.)

Another aspect of the present invention made to solve the above problems is a battery including the positive electrode for the battery.

According to the present invention, a positive electrode for a battery capable of suppressing an increase in battery resistance due to repeated charging and discharging, a method for manufacturing such a positive electrode for a battery, and an increase in resistance due to repeated charging and discharging are suppressed. Batteries can be provided.

FIG. 1 is an external perspective view showing a battery according to an embodiment of the present invention. FIG. 2 is a schematic view showing a power storage device configured by assembling a plurality of batteries according to an embodiment of the present invention.

The positive electrode for a battery according to an embodiment of the present invention contains a positive electrode active material, a conductive agent, a binder and a copolymer, and the copolymer is a structural unit (a) represented by the following formula (1). , The structural unit (b) represented by the following formula (2) and the structural unit (c) represented by the following formula (3) are contained, and the content of the structural unit (c) in the copolymer is , 15% by mass or more and 45% by mass or less, which is a positive electrode for a battery.

（式（１）〜（３）中、Ｒ^１、Ｒ^２、Ｒ^３、Ｒ^５、Ｒ^６、Ｒ^７、Ｒ^９、Ｒ^１０、Ｒ^１１、及びＲ^１２は、それぞれ独立して、水素原子、メチル基又はエチル基である。Ｒ^４は、炭素数８〜３０の１価の炭化水素基である。Ｒ^８は、炭素数２〜４の直鎖状又は分岐状のアルキレン基である。ｐは、１〜５０の数である。）

(In formulas (1) to (3), R ¹ , R ² , R ³ , R ⁵ , R ⁶ , R ⁷ , R ⁹ , R ¹⁰ , R ¹¹ , and R ¹² are independent hydrogen atoms, respectively. , Methyl group or ethyl group. R ⁴ is a monovalent hydrocarbon group having 8 to 30 carbon atoms. R ⁸ is a linear or branched alkylene group having 2 to 4 carbon atoms. p is a number from 1 to 50.)

Since the copolymer contained in the positive electrode for a battery has the structural unit (c) having an amide group in the side chain at a predetermined ratio, its solubility in an electrolytic solution is high when compared with the same molecular weight. Low. Therefore, according to the positive electrode for the battery, the elution of the copolymer into the electrolytic solution is small, and as a result, an increase in the resistance of the battery due to repeated charging and discharging can be suppressed. Further, usually, the positive electrode for a battery uses a positive electrode paste for a battery (hereinafter, also simply referred to as “paste” or the like) containing the positive electrode active material, a conductive agent, a binder, a copolymer and a dispersion medium. It is formed. At this time, since the copolymer has the structural unit (a) and the structural unit (b), this paste can suppress an increase in viscosity when the solid content concentration is increased, and has good coatability. Etc. This is because the structural unit (a) having a hydrophobic group is strongly adsorbed on the particle surface of the conductive agent in the paste, and the structural unit (b) having a polyoxyalkylene group brings a strong three-dimensional repulsive force between the particles. It is presumed that this produces an effect of suppressing the aggregation of particles in the paste and lowers the viscosity of the paste. As described above, since the above-mentioned copolymer can reduce the solubility in the electrolytic solution without increasing the molecular weight, both the reduction in the viscosity of the paste and the suppression of elution from the formed positive electrode into the electrolytic solution are achieved at the same time. be able to. Therefore, the positive electrode for the battery can suppress an increase in the resistance of the battery due to repeated charging and discharging.

The mass ratio of the structural unit (a) to the structural unit (b) of the copolymer (constituent unit (a) / structural unit (b)) is preferably 0.5 or more and 5 or less. By setting the mass ratio of the structural unit (a) to the structural unit (b) within the above range, the effect of reducing the viscosity of the paste for forming the positive electrode for the battery can be further enhanced, and the productivity can be enhanced.

The weight average molecular weight of the copolymer is preferably 15,000 or more and 100,000 or less. As a result, the effect of suppressing the elution of the copolymer into the electrolytic solution and the effect of reducing the viscosity of the paste can be enhanced in a well-balanced manner. As a result, the effect of suppressing the increase in resistance of the positive electrode for the battery and the effect of improving productivity can be enhanced in a well-balanced manner.

The content of the copolymer is preferably 0.5 parts by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the conductive agent. By setting the content of the copolymer in the above range, it is possible to exert a good effect of reducing the viscosity of the paste while suppressing the amount of the copolymer eluted in the electrolytic solution. That is, the effect of suppressing the increase in resistance of the positive electrode for the battery and the effect of improving productivity can be enhanced in a well-balanced manner.

（式（１）〜（３）中、Ｒ^１、Ｒ^２、Ｒ^３、Ｒ^５、Ｒ^６、Ｒ^７、Ｒ^９、Ｒ^１０、Ｒ^１１、及びＲ^１２は、それぞれ独立して、水素原子、メチル基又はエチル基である。Ｒ^４は、炭素数８〜３０の１価の炭化水素基である。Ｒ^８は、炭素数２〜４の直鎖状又は分岐状のアルキレン基である。ｐは、１〜５０の数である。） The method for producing a positive electrode for a battery according to an embodiment of the present invention includes using a positive electrode paste for a battery containing a positive electrode active material, a conductive agent, a binder, a copolymer and a dispersion medium, and the above-mentioned copolymer , The structural unit (a) represented by the following formula (1), the structural unit (b) represented by the following formula (2), and the structural unit (c) represented by the following formula (3). This is a method for producing a positive electrode for a battery, wherein the content of the structural unit (c) in the copolymer is 15% by mass or more and 45% by mass or less.

(In formulas (1) to (3), R ¹ , R ² , R ³ , R ⁵ , R ⁶ , R ⁷ , R ⁹ , R ¹⁰ , R ¹¹ , and R ¹² are independent hydrogen atoms, respectively. , Methyl group or ethyl group. R ⁴ is a monovalent hydrocarbon group having 8 to 30 carbon atoms. R ⁸ is a linear or branched alkylene group having 2 to 4 carbon atoms. p is a number from 1 to 50.)

According to the manufacturing method, it is possible to obtain a positive electrode for a battery capable of suppressing an increase in battery resistance due to repeated charging and discharging. Further, according to the production method, since a paste having good coatability in which an increase in viscosity is suppressed is used, productivity can be improved.

The battery according to an embodiment of the present invention is a battery including the positive electrode for the battery.

Since the battery includes the positive electrode for the battery in which the elution of the copolymer is suppressed, the increase in resistance due to repeated charging and discharging is suppressed. Further, since the positive electrode of the battery can be formed by using a paste having good coatability in which an increase in viscosity is suppressed, the productivity is also high.

Hereinafter, a battery positive electrode, a method for manufacturing the battery positive electrode, and a battery according to an embodiment of the present invention will be described in detail.

<Positive electrode for batteries>
The positive electrode for a battery according to an embodiment of the present invention has a conductive base material and a positive electrode mixture layer laminated directly on the base material or via an intermediate layer.

[Base material]
The base material has conductivity. As the material of the base material, metals such as aluminum, titanium, and tantalum, or alloys thereof are used. Among these, aluminum and aluminum alloys are preferable from the viewpoint of balance of potential resistance, high conductivity and cost. Further, examples of the form of forming the positive electrode base material include foil, a vapor-deposited film, and the like, and foil is preferable from the viewpoint of cost. That is, aluminum foil is preferable as the positive electrode base material. Examples of aluminum or aluminum alloy include A1085P and A3003P specified in JIS-H-4000 (2014).

[Positive electrode mixture layer]
The positive electrode mixture layer contains a positive electrode active material, a conductive agent, a binder and a copolymer. The positive electrode mixture layer may further contain other components (functional materials other than the copolymer, fillers, etc.). As will be described later, this positive electrode mixture layer can be suitably produced by a positive electrode paste for a battery containing a positive electrode active material, a conductive agent, a binder, a copolymer and a dispersion medium.

[Positive electrode active material]
The positive electrode active material is a substance capable of occluding and releasing ions such as lithium. Examples of the positive electrode active material include _{composite oxides represented by Li x} MO _y (M represents at least one kind of transition metal) ( _{Li x} CoO ₂ having a _{layered α-NaFeO type 2} crystal structure, Li _x NiO _2). , Li _x MnO ₃ , Li _x Ni _α Co _(1-α) O ₂ , Li _x Ni _α Mn _β Co _(1-α-β) O ₂ , Li _{1 + w} Ni _α Mn _β Co _{(1-α-β-) w)} O _2, etc., Li _x Mn ₂ O ₄ , Li _x Ni _α Mn _(2-α) O _4, etc.), Li _w Me _x (AO _y ) _z (Me is at least one kind of transition). Represents a metal, where A represents, for example, P, Si, B, V, etc.) and a polyanion compound (LiFePO ₄ , LiMnPO ₄ , LiNiPO ₄ , LiCoPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , Li ₂ MnSiO. ₄ , Li ₂ CoPO ₄ F, etc.). The elements or polyanions in these compounds may be partially substituted with other elements or anion species. As the positive electrode active material, one of these compounds may be used alone, or two or more of these compounds may be mixed and used.

The positive electrode active material is Li _{1 + x} Ni _a Co _b Mn _c D _d O ₂ (D is an element other than Li, Co, Mn, Ni and O. X ≧ 0, a> 0, b ≧ 0, c. A compound represented by ≧ 0, 0 ≦ d ≦ 0.2, x + a + b + c + d = 1) can be used.

Examples of the element D in the above formula include metal elements such as aluminum, calcium, titanium, chromium, iron, cobalt and copper, and non-metal elements such as halogen and carbon. The element represented by D may be one kind or two or more kinds. The upper limit of x may be, for example, 0.5, 0.2, or 0.1. The upper limit of a may be, for example, 0.8, 0.6, 0.55, or 0.4. The lower limit of a may be, for example, 0.1. The upper limit of b may be, for example, 0.6 or 0.4. The lower limit of b may be, for example, 0.1. The upper limit of c may be, for example, 0.6 or 0.4. The lower limit of c may be, for example, 0.1. The upper limit of d may be preferably 0.1, more preferably 0.05.

The lower limit of the content of the positive electrode active material in the positive electrode mixture layer can be, for example, 50% by mass, 60% by mass, 80% by mass, or 90% by mass. preferable. On the other hand, the upper limit of this content can be, for example, 99% by mass or 98% by mass.

[Conducting agent]
The conductive agent is not particularly limited as long as it is a conductive material that does not adversely affect the battery performance. Examples of such a conductive agent include natural or artificial graphite, carbon black such as furnace black, acetylene black, and Ketjen black, metals, conductive ceramics, and the like, and acetylene black is preferable.

Further, when a conductive agent having a large specific surface area is used, the charge / discharge performance (output, etc.) of the positive electrode can be improved, which is preferable. However, when such a conductive agent is used, the paste viscosity tends to increase. is there. However, the above-mentioned copolymer is preferable because the effect of reducing the paste viscosity becomes larger when a conductive agent having a large specific surface area is used. Specifically, the lower limit of the specific surface area of the conductive agent is ^{1 m} 2 / g, more preferably ^{10 m} 2 / g, particularly preferably ^{30 m} 2 / g. On the other hand, the upper limit is preferably 200 meters ² / g, more preferably ^{100m 2 / g, 80m 2 /} g is particularly preferred. Further, the specific surface area refers to the BET specific surface area obtained by the BET method.

As the lower limit of the content of the conductive agent in the positive electrode mixture layer, for example, 1% by mass is preferable, and 2% by mass is more preferable. By setting the content of the conductive agent to the above lower limit or more, good conductivity can be exhibited. On the other hand, the upper limit of this content can be, for example, 20% by mass, but 10% by mass is preferable, and 5% by mass is more preferable. By setting the content of the conductive agent to the above upper limit or less, it is possible to improve the adhesion of the positive electrode mixture layer to the base material or the like.

[Binder]
The binder is a component that fixes a positive electrode active material, a conductive agent, and the like. As the binder, a thermoplastic resin such as vinylidene fluoride resin (polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer, etc.), polytetrafluoroethylene (PTFE), polyethylene, polypropylene, polyimide, etc. Elastomers such as ethylene-propylene-diene rubber (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber; and thermoplastic polymers.

Further, as the binder, it is particularly preferable to use vinylidene fluoride resin because of its good compatibility with the copolymer in the positive electrode paste.

Here, since the copolymer is not suitable as a binder for the positive electrode paste, the copolymer is not included in the binder here.

As the lower limit of the content of the binder in the positive electrode mixture layer, for example, 1% by mass is preferable, 2% by mass is more preferable, and 2.5% by mass is further preferable. By setting the content of the binder to the above lower limit or more, it is possible to improve the adhesion of the positive electrode mixture layer to the base material or the like. On the other hand, the upper limit of this content is, for example, 20% by mass, preferably 10% by mass, and more preferably 6% by mass.

[Copolymer]
The copolymer has a structural unit (a) represented by the following formula (1), a structural unit (b) represented by the following formula (2), and a structural unit (c) represented by the following formula (3). Contains. The copolymer may further contain another structural unit (d). The copolymer can increase the dispersibility of the conductive agent in the paste and reduce the viscosity of the paste.

In formulas (1) to (3), R ¹ , R ² , R ³ , R ⁵ , R ⁶ , R ⁷ , R ⁹ , R ¹⁰ , R ¹¹ , and R ¹² are independent hydrogen atoms, respectively. It is a methyl group or an ethyl group. R ⁴ is a monovalent hydrocarbon group having 8 to 30 carbon atoms. R ⁸ is a linear or branched alkylene group having 2 to 4 carbon atoms. p is a number from 1 to 50.

(Structural unit (a))
The copolymer, by including the structural unit having R ⁴ is a hydrophobic group (a), it is possible to satisfactorily adsorbed on the particle surfaces of the conductive agent in the paste.

As the above R ¹ and R ² , a hydrogen atom is preferable. As the R ^3, preferably a hydrogen atom or a methyl group, more preferably a methyl group. By using R ^{1 to} R ³ as these atoms or groups, it is possible to enhance the adsorptivity to a conductive agent or the like, the effect of reducing the viscosity of the paste, the ease of introduction during copolymerization, and the like.

Examples of the monovalent hydrocarbon group having 8 to 30 carbon atoms in the R ^4, an alkyl group, an alkenyl group, or an aliphatic hydrocarbon group, an alkynyl group, and aromatic hydrocarbon group. Among these, an aliphatic hydrocarbon group is preferable, and an alkyl group and an alkenyl group are preferable. Further, ^{as the lower limit of the number of carbon atoms of R 4} , 10 is preferable, 12 is more preferable, 13 is further preferable, and 18 is particularly preferable. On the other hand, the upper limit of the number of carbon atoms is preferably 26, more preferably 22, and even more preferably 20. By ^{limiting R 4} to these, it is possible to enhance the adsorptivity to the conductive agent and the like, the effect of reducing the viscosity of the paste, and the like. Specific examples of the ^{group represented by R 4} include an octyl group, a 2-ethylhexyl group, a decyl group, a lauryl group, a myristyl group, a cetyl group, a stearyl group, an oleyl group, and a behenyl group.

Examples of the monomer giving the structural unit (a) include 2-ethylhexyl (meth) acrylate, octyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate, isostearyl (meth) acrylate, and behenyl (meth) acrylate. And so on. Among these, lauryl (meth) acrylate, stearyl (meth) acrylate and behenyl (meth) acrylate are preferable from the viewpoint of adsorptivity to a conductive agent and the like and the effect of reducing the viscosity of the paste. One type of these monomers may be used, or two or more types may be used.

The lower limit of the content of the structural unit (a) in the copolymer is preferably 10% by mass, more preferably 20% by mass, and even more preferably 30% by mass. On the other hand, as the upper limit of this content, 80% by mass is preferable, 70% by mass is more preferable, and 60% by mass is further preferable. By setting the content of the structural unit (a) within the above range, the adsorptivity to the conductive agent, the effect of reducing the viscosity of the paste, and the like can be enhanced.

(Constituent unit (b))
By containing the structural unit (b) having a polyoxyalkylene group, the copolymer can provide a strong three-dimensional repulsive force between the particles adsorbed by the copolymer. As a result, the effect of suppressing the aggregation of particles in the paste is generated, and the increase in the viscosity of the paste can be suppressed.

As the above R ⁵ and R ⁶ , a hydrogen atom is preferable. As the R ^7, preferably a hydrogen atom or a methyl group, more preferably a methyl group. As the R ^9, preferably a methyl group and an ethyl group, more preferably a methyl group. By using R ^{5 to} R ⁷ and R ⁹ as these atoms or groups, the effect of reducing the viscosity of the paste, the ease of introduction during copolymerization, and the like can be enhanced.

Examples of the linear or branched alkylene group having 2 to 4 carbon atoms in the R ^8, an ethylene group and propylene group are preferred, and more preferably an ethylene group. By using R ⁸ as these groups, the effect of reducing the viscosity of the positive electrode paste, the ease of introduction at the time of copolymerization, and the like can be enhanced. In R ⁸ may contain more alkylene groups.

The p is the average addition number of moles of alkylene oxide (-R 8 ^-O-), but is not limited to an integer. As the upper limit of p, 40 is preferable, 25 is more preferable, 10 is more preferable, 7 is more preferable, and 4 is more preferable. By setting p to the above upper limit or less, the solubility in the electrolytic solution can be further reduced.

Examples of the monomer giving the structural unit (b) include methoxypoly (ethylene glycol / propylene glycol) (meth) acrylate, ethoxypoly (ethylene glycol / propylene glycol) (meth) acrylate, and poly (ethylene glycol / propylene glycol) mono (meth). Acrylate and the like can be mentioned. Of these, methoxypolyethylene glycol methacrylate is preferable. One type of these monomers may be used, or two or more types may be used.

As the lower limit of the content of the structural unit (b) in the copolymer, 5% by mass is preferable, 10% by mass is more preferable, and 15% by mass is further preferable. On the other hand, as the upper limit of this content, 60% by mass is preferable, 50% by mass is more preferable, and 40% by mass is further preferable. By setting the content of the structural unit (b) in the above range, the effect of reducing the viscosity of the paste and the effect of suppressing elution into the electrolytic solution can be further enhanced.

(Constituent unit (c))
By having the structural unit (c) having an amide group, the copolymer can exert an effect of suppressing elution of the copolymer into an electrolytic solution at the positive electrode for a battery.

As the above R ¹⁰ and R ¹¹ , a hydrogen atom is preferable. As the R ^12, preferably a hydrogen atom or a methyl group, more preferably a methyl group. By using R ^{10 to} R ¹² as these atoms or groups, the effect of suppressing elution into the electrolytic solution, the ease of introduction during copolymerization, and the like can be enhanced.

Examples of the monomer giving the structural unit (c) include (meth) acrylamide and 2-butenoic acid amide, and (meth) acrylamide is preferable. One type of these monomers may be used, or two or more types may be used.

The lower limit of the content of the structural unit (c) in the copolymer is 15% by mass, preferably 17.5% by mass, more preferably 20% by mass, and even more preferably 26% by mass. By setting the content of the structural unit (c) to the above lower limit or more, the effect of suppressing elution into the electrolytic solution can be enhanced. On the other hand, the upper limit of this content is 45% by mass, preferably 40% by mass, more preferably 37.5% by mass, and even more preferably 35% by mass. By setting the content of the structural unit (c) to the above upper limit or less, the viscosity reducing effect of the paste can be further enhanced.

(Structural unit (d))
The monomer that gives the other structural unit (d) is not particularly limited as long as it can be copolymerized with the monomer that gives the structural unit (a), the structural unit (b), and the structural unit (c). ..

Examples of the monomer giving the structural unit (d) include acid monomers such as (meth) acrylic acid; methyl (meth) acrylic acid, ethyl (meth) acrylic acid, butyl (meth) acrylic acid, isobutyl (meth) acrylic acid, ( (Meta) acrylates such as tert-butyl (meth) acrylate, benzyl (meth) acrylate, cyclohexyl (meth) acrylate, isobolonyl (meth) acrylate, dimethylaminoethyl (meth) acrylate; N, N -(Meta) acrylamides such as dimethyl (meth) acrylamide, tert-butyl (meth) acrylamide, N-isopropyl (meth) acrylamide; styrenes such as styrene and p-methylstyrene; vinyl esters such as vinyl acetate; 2 -Vinylpyridines such as vinylpyridine; Vinylpyrrolidones such as vinylpyrrolidone and the like can be mentioned. One type of these monomers may be used, or two or more types may be used.

The upper limit of the content of the structural unit (d) in the copolymer is preferably 60% by mass, more preferably 40% by mass, further preferably 20% by mass, further preferably 5% by mass, and 1% by mass. May be%. By setting the content of the structural unit (d) to the above upper limit or less, the effect of suppressing elution into the electrolytic solution and the effect of reducing the viscosity of the paste can be further enhanced.

It is preferable that the copolymer does not have a structural unit derived from a monomer having two or more polymerizable groups (crosslinkable monomer) among the structural units (d). Here, from the viewpoint of the effect of reducing the viscosity of the paste, it is preferable that the copolymer is dissolved in the dispersion medium in the paste. It can also be used in a partially dissolved state. When the copolymer contains a structural unit derived from a crosslinkable monomer, the solubility of the copolymer in the dispersion medium tends to decrease, and the viscosity reducing effect of the paste tends to decrease. The upper limit of the content of the structural unit derived from the crosslinkable monomer in the copolymer is preferably 5% by mass, more preferably 1% by mass, still more preferably 0.1% by mass. By setting the content of the structural unit derived from the crosslinkable monomer to the above upper limit or less, the viscosity reducing effect of the paste can be enhanced.

(Constituent unit ratio)
In the above copolymer, the lower limit of the mass ratio of the structural unit (a) to the structural unit (b) (constituent unit (a) / structural unit (b)) is preferably 0.5, more preferably 0.75. Preferably, 1 is even more preferred. On the other hand, as the upper limit of this mass ratio, 5 is preferable, 4 is more preferable, and 3 is further preferable. By setting the mass ratio of the structural unit (a) to the structural unit (b) within the above range, the effect of reducing the viscosity of the paste can be further enhanced.

In the above copolymer, the lower limit of the mass ratio of the structural unit (b) to the structural unit (c) (constituent unit (b) / structural unit (c)) is preferably 0.2, more preferably 0.4. Preferably, 0.6 is even more preferred. On the other hand, as the upper limit of this mass ratio, 5 is preferable, 4 is more preferable, 3 is more preferable, and 1 is further preferable in some cases. By setting the mass ratio of the structural unit (b) to the structural unit (c) in the above range, the effect of suppressing elution into the electrolytic solution and the effect of reducing the viscosity of the paste when compared with the same molecular weight can be further enhanced. Can be done.

In the above copolymer, the lower limit of the mass ratio of the structural unit (a) to the structural unit (c) (constituent unit (a) / structural unit (c)) is preferably 0.2, more preferably 0.5. Preferably, 0.8 is even more preferred. On the other hand, as the upper limit of this mass ratio, 5 is preferable, 4 is more preferable, and 3 is further preferable. By setting the mass ratio of the structural unit (a) to the structural unit (c) within the above range, the effect of suppressing elution into the electrolytic solution and the effect of reducing the viscosity of the paste can be further enhanced.

(Molecular weight)
As the lower limit of the weight average molecular weight measured by gel permeation chromatography (GPC) of the above copolymer, 5,000 is preferable, 7,500 is more preferable, 10,000 is further preferable, and 15,000 is further more preferable. Preferably, 18,000 is particularly preferred. By setting the weight average molecular weight to the above lower limit or more, the solubility in the electrolytic solution can be further reduced, and the viscosity reducing effect of the paste can be more sufficiently exhibited. On the other hand, as the upper limit of the weight average molecular weight, 500,000 is preferable, 250,000 is more preferable, 100,000 is further preferable, and 70,000 is particularly preferable. By setting the weight average molecular weight to the above upper limit or less, the effect of reducing the viscosity of the paste can be further enhanced, and the synthesis becomes easy.

The lower limit of the content of the copolymer in the positive electrode mixture layer may be 0.1 part by mass with respect to 100 parts by mass of the conductive agent, but 0.5 part by mass is preferable and 1 part by mass is preferable. Parts are more preferable, and 1.5 parts by mass is further preferable. By setting the content of the copolymer to the above lower limit or more, the dispersibility of the conductive agent can be further enhanced, and the viscosity reducing effect of the paste can be further enhanced. On the other hand, the upper limit of this content may be 40 parts by mass, but 30 parts by mass is preferable, 20 parts by mass is more preferable, 10 parts by mass is further preferable, 5 parts by mass is more preferable, and 3 parts by mass is preferable. Part is particularly preferable. By setting the content of the copolymer to the above upper limit or less, the battery output can be maintained in a good state, and the amount of elution into the electrolytic solution can be suppressed.

The lower limit of the content of the copolymer in the positive electrode mixture layer is, for example, 0.01% by mass. By setting the content of the copolymer to the above lower limit or more, it is possible to exert a sufficient effect of reducing the viscosity of the paste. On the other hand, the upper limit of this content may be, for example, 3% by mass, preferably 2% by mass, and more preferably 1.5% by mass. By setting the content of the copolymer to the above upper limit or less, the amount of elution into the electrolytic solution can be further reduced, and the adhesion of the positive electrode mixture layer to the substrate or the like can be improved.

The positive electrode for a battery may further contain a copolymer other than the above-mentioned copolymer. However, the lower limit of the content of the copolymer with respect to the total of the copolymer and the copolymer other than the copolymer (excluding the copolymer used as a binder) is preferably 40% by mass. 60% by mass is more preferable, and 80% by mass is further preferable.

(Method for synthesizing copolymer)
The method for synthesizing the above-mentioned copolymer is not particularly limited, and the method used for the polymerization of ordinary (meth) acrylic acid esters is used. The copolymer can be synthesized by, for example, a free radical polymerization method, a living radical polymerization method, an anion polymerization method, a living anion polymerization method, or the like. For example, when the free radical polymerization method is used, each monomer giving the structural unit (a), the structural unit (b), the structural unit (c) and, if necessary, the structural unit (d) is polymerized by the solution polymerization method. Can be done by From the viewpoint of ease of synthesis and solubility in a solvent, it is preferable to synthesize by solution polymerization.

Examples of the solvent used for solution polymerization include aliphatic hydrocarbons (hexane, heptane, etc.), aromatic hydrocarbons (toluene, xylene, etc.), lower alcohols (ethanol, isopropanol, etc.), ketones (acetone, methyl ethyl ketone, etc.). , Ether (tetracarbon, diethylene glycol dimethyl ether, etc.), and other organic solvents such as dimethyl sulfoxide, dimethylformamide, and N-methylpyrrolidone can be used. The amount of the solvent is preferably 0.5 to 10 times the mass ratio with respect to the total amount of the monomers.

As the polymerization initiator used in the synthesis of the copolymer, a known radical polymerization initiator can be used. Examples of the radical polymerization initiator include azo-based polymerization initiators, hydroperoxides, dialkyl peroxides, diacyl peroxides, ketone peroxides and the like. The lower limit of the amount of the polymerization initiator is preferably 0.01 mol%, more preferably 0.1 mol%, still more preferably 0.2 mol%, based on the total amount of the monomer components. On the other hand, as the upper limit, 5 mol% is preferable, 3 mol% is more preferable, and 2 mol% is further preferable. The polymerization reaction is preferably carried out in a temperature range of 60 ° C. or higher and 180 ° C. or lower under a nitrogen stream, and the reaction time is preferably 0.5 hours or longer and 20 hours or lower.

In addition, a known chain transfer agent for adjusting the molecular weight can be used. Examples of the chain transfer agent include isopropyl alcohol and mercapto compounds such as mercaptoethanol.

In the above-mentioned copolymer, the arrangement of the structural unit (a), the structural unit (b), the structural unit (c) and the structural unit (d) contained as needed may be any of random, block, gradient, graft and the like. But it may be.

<Manufacturing method of positive electrode for batteries>
The positive electrode for a battery can be suitably produced by using a positive electrode paste for a battery containing the positive electrode active material, the conductive agent, the binder, the copolymer and the dispersion medium. That is, the method for producing a positive electrode for a battery according to an embodiment of the present invention includes using a positive electrode paste for a battery containing a positive electrode active material, a conductive agent, a binder, a copolymer, and a dispersion medium. Specifically, it can be produced by applying the positive electrode paste for a battery to a base material and drying it. Details of the positive electrode active material, the conductive agent, the binder and the copolymer are as described above.

The dispersion medium is a component that uniformly disperses a positive electrode active material, a conductive agent, a binder, a copolymer and the like. In the paste, the copolymer is preferably dissolved in the dispersion medium in order to further enhance the viscosity reducing effect.

As the dispersion medium, one capable of dissolving the copolymer can be used. Non-aqueous dispersion media such as aprotic polar solvents such as N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMA) and dimethyl sulfoxide (DMSO), water, etc. may be used. it can. The dispersion medium is preferably a non-aqueous dispersion medium, and more preferably an aprotic polar solvent, from the viewpoint of solubility of the copolymer and prevention of bringing excess water into the battery. NMP is particularly preferable because of the high solubility of the copolymer. The non-aqueous dispersion medium means a dispersion medium other than water, and is a dispersion medium that does not substantially contain water.

The solid content concentration (content of components other than the dispersion medium) of the paste can be, for example, 40% by mass or more and 70% by mass or less.

The paste can be prepared by mixing and stirring a positive electrode active material, a conductive agent, a binder, a copolymer, a dispersion medium and the like. A known stirring device such as a planetary mixer, a bead mill, or a jet mill can be used for this mixing and stirring. When charging each component into the stirring device, the stirring blade may be rotated while charging. As a result, it is possible to suppress the mechanical load of the stirring device, suppress the bulk of the components in the stirring container, perform preliminary mixing of each component, and the like. Further, the whole amount may not be added at once, but may be added in a plurality of times. As a result, the mechanical load of the stirring device can be suppressed.

As described above, the positive electrode for a battery can be obtained by applying the paste to a base material and drying it. Consolidation can also be performed with a press to increase the density of the positive electrode. A die head, a comma reverse roll, a direct roll, a gravure roll, or the like can be used for applying the paste. Drying after coating can be performed by heating, airflow, infrared irradiation, or the like alone or in combination. Further, the positive electrode can be pressed by a roll press machine or the like.

In the positive electrode thus obtained, dissolution / elution of the copolymer in the electrolytic solution is suppressed, and as a result, an increase in resistance due to repeated charging / discharging of the battery can be suppressed.

<Battery>
The battery according to an embodiment of the present invention is a non-aqueous electrolyte secondary battery having a positive electrode, a negative electrode, and a non-aqueous electrolyte (electrolyte solution). The positive electrode and the negative electrode usually form an electrode body laminated or wound via a separator. The electrode body is housed in a case, and the case is filled with the non-aqueous electrolyte. The non-aqueous electrolyte is interposed between the positive electrode and the negative electrode. Further, as the above case, a known metal case, a resin case, etc., which are usually used as a case for a secondary battery, can be used.

[Positive electrode]
As the positive electrode, the positive electrode for a battery according to the embodiment of the present invention described above is used.

[Negative electrode]
The negative electrode has a negative electrode base material and a negative electrode mixture layer arranged directly on the negative electrode base material or via an intermediate layer.

As the material of the negative electrode base material, a metal such as copper, nickel, stainless steel, nickel-plated steel or an alloy thereof is used, and copper or a copper alloy is preferable. That is, copper foil is preferable as the negative electrode base material. Examples of the copper foil include rolled copper foil and electrolytic copper foil.

The negative electrode mixture layer is formed of a so-called negative electrode mixture containing a negative electrode active material. Further, the negative electrode mixture forming the negative electrode mixture layer contains optional components such as a conductive agent, a binder, and a filler, if necessary. As the optional component such as the conductive agent and the binder, the same one as that of the positive electrode mixture layer can be used.

As the negative electrode active material, a material capable of occluding and releasing lithium ions is usually used. Specific examples of the negative electrode active material include metals or semi-metals such as Si and Sn; metal oxides or semi-metal oxides such as Si oxide and Sn oxide; polyphosphate compounds; graphite and amorphous. Examples thereof include carbon materials such as carbon (graphitizable carbon or non-graphitizable carbon).

Further, the negative electrode mixture layer contains typical non-metal elements such as B, N, P, F, Cl, Br and I, and typical metal elements such as Li, Na, Mg, Al, K, Ca, Zn, Ga and Ge. , Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, Zr, Ta, Hf, Nb, W and the like.

[Separator]
The separator plays a role of separating the positive electrode and the negative electrode and holding a non-aqueous electrolyte. As the material of the separator, for example, a woven fabric, a non-woven fabric, a porous resin film or the like is used. Among these, a porous resin film is preferable. As the main component of the porous resin film, polyolefins such as polyethylene and polypropylene are preferable from the viewpoint of strength. Further, a porous resin film obtained by combining these resins with a resin such as aramid or polyimide may be used.

[Non-aqueous electrolyte]
As the non-aqueous electrolyte, a non-aqueous electrolyte solution containing a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent is usually used. The non-aqueous electrolyte may contain other additives.

As the non-aqueous solvent, a known non-aqueous solvent usually used as a non-aqueous solvent for a general non-aqueous electrolyte secondary battery can be used. The non-aqueous solvent refers to a solvent other than water, and is a solvent that does not substantially contain water. Examples of the non-aqueous solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate and butylene carbonate, and chain carbonates such as diethyl carbonate, dimethyl carbonate and ethyl methyl carbonate.

As the electrolyte salt, a known electrolyte salt usually used as an electrolyte salt of a general non-aqueous electrolyte secondary battery can be used. Examples of the electrolyte salt include lithium salt, sodium salt, potassium salt, magnesium salt, onium salt and the like, but lithium salt is preferable.

Examples of the lithium salt include inorganic lithium salts such _{as LiPF 6} , LiPO ₂ F ₂ , LiBF ₄ , LiClO ₄ , LiN (SO ₂ F) _{2 , LiSO 3} CF ₃ , LiN (SO ₂ CF _{3 ) 2} , and LiN (SO). ₂ C ₂ F ₅ ) ₂ , LiN (SO ₂ CF ₃ ) (SO ₂ C ₄ F ₉ ), LiC (SO ₂ CF ₃ ) ₃ , LiC (SO ₂ C ₂ F ₅ ) _{3 and} other fluorinated hydrocarbon groups Lithium salt having the above can be mentioned. Of these, inorganic lithium salts are preferred.

As the non-aqueous electrolyte, a solid electrolyte may be used instead of the non-aqueous electrolyte solution. Further, the non-aqueous electrolyte solution and the solid electrolyte may be used in combination. Examples of the solid electrolyte include an inorganic solid electrolyte and a polymer solid electrolyte. The non-aqueous electrolyte may be in the form of a gel.

Since the battery includes the positive electrode for the battery in which the elution of the copolymer is suppressed, the increase in resistance due to repeated charging and discharging is suppressed.
Further, by manipulating the composition and molecular weight of the copolymer and the content in the positive electrode mixture layer, it can be formed by using a paste having good coatability in which an increase in viscosity is further suppressed. Such a paste is preferable because it can increase the productivity of the positive electrode of the battery. Specifically, since it is possible to increase the solid content concentration of the paste, it is possible to shorten the drying time of the paste by reducing the content of the dispersant in the paste, and it is possible to shorten the drying time of the paste. You can increase the speed. In addition, costs can be expected by shortening the paste feeding time and reducing the mechanical load such as stirring.

<Other Embodiments>
The present invention is not limited to the above embodiment, and can be implemented in various modifications and improvements in addition to the above embodiment. In the above embodiment, the battery is mainly a non-aqueous electrolyte secondary battery, but other batteries may be used. Examples of other batteries include primary batteries and batteries using an electrolytic solution containing water as a solvent. Further, the positive electrode mixture in the positive electrode for the battery does not have to form a clear layer. For example, it may be a positive electrode in which a positive electrode mixture is supported on a mesh-like base material.

FIG. 1 shows a schematic view of a rectangular battery 1 (non-aqueous electrolyte secondary battery) according to an embodiment of the present invention. The figure is a perspective view of the inside of the container. In the battery 1 shown in FIG. 1, the electrode body 2 is housed in the battery container 3. The electrode body 2 is formed by winding a positive electrode having a positive electrode active material and a negative electrode having a negative electrode active material through a separator. The positive electrode is electrically connected to the positive electrode terminal 4 via the positive electrode lead 4', and the negative electrode is electrically connected to the negative electrode terminal 5 via the negative electrode lead 5'. Further, a non-aqueous electrolyte is injected into the battery container 3. The specific configuration of each element such as the positive electrode is as described above.

The configuration of the battery according to the present invention is not particularly limited, and examples thereof include a cylindrical battery, a square battery (rectangular battery), and a flat battery. The present invention can also be realized as a power storage device including a plurality of the above batteries. An embodiment of the power storage device is shown in FIG. In FIG. 2, the power storage device 30 includes a plurality of power storage units 20. Each power storage unit 20 includes a plurality of batteries 1. The power storage device 30 can be mounted as a power source for automobiles such as electric vehicles (EV), hybrid electric vehicles (HEV), and plug-in hybrid vehicles (PHEV).

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples.

The abbreviations of the raw materials used in the examples are as follows.
-SMA: Stearyl methacrylate (manufactured by Shin-Nakamura Chemical Co., Ltd., product number: NK-ester S)
PEG (2) MA: Methoxypolyethylene glycol methacrylate (manufactured by Shin-Nakamura Chemical Industry Co., Ltd., product number: NK ester M-20G, average number of moles of ethylene oxide added p = 2)
PEG (9) MA: Methoxypolyethylene glycol methacrylate (manufactured by Shin-Nakamura Chemical Industry Co., Ltd., product number: NK-ester M-90G, average number of moles of ethylene oxide added p = 9)
・ MAAm: Methacrylamide (manufactured by Wako Pure Chemical Industries, Ltd.)
・ MAA: Methacrylic acid (manufactured by Wako Pure Chemical Industries, Ltd.)
-DMAAm: Dimethylacrylamide (manufactured by Wako Pure Chemical Industries, Ltd.)
-NMP: N-methyl-2-pyrrolidone (manufactured by Wako Pure Chemical Industries, Ltd.)
-V-65B: 2,2'-azobis (2,4-dimethylvaleronitrile) (manufactured by Wako Pure Chemical Industries, Ltd.)

[Synthesis Example 1] Synthesis of Copolymer H As a monomer solution for initial preparation, a solution consisting of 4.8 g of SMA, 2.8 g of PEG (2) MA, 22.4 g of MAAm and 86.7 g of NMP, and A mixed solution consisting of 0.8 g of V-65B and 3.3 g of NMP was prepared as the initial charge initiator solution. Next, as the dropping monomer solution 1, a mixed solution consisting of 106.1 g of SMA, 61.9 g of PEG (2) MA, and 24.7 g of NMP, and as the dropping monomer solution 2, 67.6 g of MAAm, And 135.3 g of NMP mixed solution, as the dropping monomer solution 3, 21.7 g of SMA, 12.7 g of PEG (2) MA, and 20.0 g of NMP mixed solution, dropping initiator solution. A mixed solution consisting of 6.7 g of V-65B and 26.7 g of NMP as No. 1 and a mixed solution of 0.8 g of V-65B and 3.3 g of NMP as the dropping initiator solution 2 were prepared.
The initial preparation monomer was placed in a separable flask equipped with a reflux tube, a stirrer, a thermometer, a nitrogen introduction tube, and a dropping funnel, and the inside of the reaction vessel was replaced with nitrogen for 1 hour or more while stirring and heating at 65 ° C. After confirming that the temperature in the tank reached 65 ° C., the initial preparation initiator solution was added with stirring. After stirring for 10 minutes, the dropping monomer solution 1, the dropping monomer solution 2, and the dropping initiator solution 1 were added dropwise into the tank over 160 minutes. Then, the dropping monomer solution 3 and the dropping initiator solution 2 were dropped into the tank over 20 minutes. After completion of the dropping, the mixture was further stirred at 65 ° C. for 1 hour. The temperature was raised to 80 ° C. while continuing stirring, and it was confirmed that the temperature in the tank reached 80 ° C., and the mixture was further stirred for 2 hours. Then 600 g of NMP was added and stirred until a homogeneous solution was obtained. After dilution, the mixture was air-cooled to 40 ° C. or lower to obtain a copolymer H.

[Synthesis Example 2] Synthesis of Copolymer I As a monomer solution for initial preparation, a solution consisting of 4.8 g of SMA, 2.8 g of PEG (2) MA, 22.4 g of MAAm and 89.3 g of NMP, and A mixed solution consisting of 0.2 g of V-65B and 0.7 g of NMP was prepared as the initial charge initiator solution. Next, as the dropping monomer solution 1, 106.1 g of SMA, 61.9 g of PEG (2) MA, 8.2 g of NMP, and 67.6 g of MAAm as the dropping monomer solution 2. And 135.3 g of NMP mixed solution, as the dropping monomer solution 3, 21.7 g of SMA, 12.7 g of PEG (2) MA, and 17.9 g of NMP mixed solution, dropping initiator solution. A mixed solution consisting of 1.4 g of V-65B and 43.2 g of NMP as 1 and a mixed solution of 0.2 g of V-65B and 5.4 g of NMP as the dropping initiator solution 2 were prepared.
The initial preparation monomer was placed in a separable flask equipped with a reflux tube, a stirrer, a thermometer, a nitrogen introduction tube, and a dropping funnel, and the inside of the reaction vessel was replaced with nitrogen for 1 hour or more while stirring and heating at 65 ° C. After confirming that the temperature in the tank reached 65 ° C., the initial preparation initiator solution was added with stirring. After stirring for 10 minutes, the dropping monomer solution 1, the dropping monomer solution 2, and the dropping initiator solution 1 were added dropwise into the tank over 160 minutes. Then, the dropping monomer solution 3 and the dropping initiator solution 2 were dropped into the tank over 20 minutes. After completion of the dropping, the mixture was further stirred at 65 ° C. for 1 hour. Then, 150 g of NMP was added while continuing stirring, and the temperature was raised to 80 ° C. It was confirmed that the temperature in the tank reached 80 ° C., and the mixture was further stirred for 2 hours. Then 450 g of NMP was added and stirred until a homogeneous solution was obtained. After dilution, it was air-cooled to 40 ° C. or lower to obtain copolymer I.

[Comparative Synthesis Example 1] Synthesis of Copolymer O A solution consisting of 90 g of NMP was prepared as a solution for initial preparation. Next, as dropping monomer solution 1, SMA of 132.6 g, PEG of 77.4g (2) MA, 90g of D Maam, and a mixed solution consisting of NMP 300 g, V of 3g as dropping initiator solution 1 A mixed solution consisting of -65B and 60 g of NMP was prepared.
The initial preparation monomer was placed in a separable flask equipped with a reflux tube, a stirrer, a thermometer, a nitrogen introduction tube, and a dropping funnel, and the inside of the reaction vessel was replaced with nitrogen for 1 hour or more while stirring and heating at 65 ° C. After confirming that the temperature in the tank reached 65 ° C., the dropping monomer solution 1 and the dropping initiator solution 1 were dropped into the tank over 180 minutes. After completion of the dropping, the mixture was further stirred at 65 ° C. for 1 hour. Then, the temperature was raised to 80 ° C., it was confirmed that the temperature in the tank reached 80 ° C., and the mixture was further stirred for 2 hours. The copolymer O was obtained by air cooling to 40 ° C. or lower.

[Synthesis Examples 3 to 12 and Comparative Synthesis Examples 2 to 3] Synthesis of copolymers A to G and JN The copolymers C to G are an initial monomer solution, an initial initiator solution, a dropping monomer solution 1, and dropping. The composition of the monomer solution 2, the dropping monomer solution 3, the dropping initiator solution 1 and the dropping initiator solution 2 is as shown in Table 1, and the same as in Synthesis Example 1 above except for the amount of the diluting solvent and the polymerization temperature. Each was synthesized by the method of.
The copolymers A, B, J, K and L contain an initial monomer solution, an initial initiator solution, a dropping monomer solution 1, a dropping monomer solution 2, a dropping monomer solution 3, a dropping initiator solution 1 and a dropping initiator solution 2. The compositions were as shown in Table 1, and the solutions were synthesized by the same method as in Synthesis Example 2 above, except for the amount of the diluting solvent and the polymerization temperature.
The copolymers M and N had the composition of the initial monomer solution, the initial initiator solution, the dropping monomer solution 1, the dropping monomer solution 2, and the dropping initiator solution 1 as shown in Table 1, and other than the polymerization temperature. Was synthesized by the same method as in Comparative Synthesis Example 1 above.

[Measurement of weight average molecular weight of copolymer]
The weight average molecular weight of each of the obtained copolymers was calculated by gel permeation chromatography (GPC) measurement. The detailed conditions are as shown below. All weight average molecular weights are polystyrene-equivalent molecular weights. As a sample, a 0.3 mass% N, N-dimethylformamide solution was prepared and passed through a 0.2 μm PTFE filter. The measurement results are shown in Table 1.
Measuring device: HLC-8320GPC (manufactured by Tosoh)
Column: α-M + α-M (manufactured by Tosoh)
Detector: Differential Refractometer (RI)
Eluent: 60 mmol / L H ₃ PO ₄ , 50 mmol / L LiBr DMF solution flow rate: 1 mL / min
Column temperature: 40 ° C
Sample solution injection volume: 10 μL

[Measurement of viscosity of acetylene black (AB) paste]
Using acetylene black (AB) (Denka black powder manufactured by Denka) as a conductive agent, polyvinylidene fluoride (12% by mass NMP solution of # 1100 manufactured by Kureha) as a binder, and NMP as a non-aqueous solvent. AB paste was prepared. The mass ratio of the conductive agent and the binder was 50:50 (in terms of solid content). The AB paste was prepared through a kneading step using a multi-blender mill with a solid content of 15% by mass by adjusting the amount of NMP.
To 20 g of the above AB paste, 4% by mass of each copolymer was added to AB, and defoaming and stirring was performed using a rotation / revolution mixer (Awatori Rentaro AR-100) (stirring: 2000 rpm × 4 min, defoaming). Foam: 2200 rpm x 1 min). A rheometer was used to measure the viscosity. The measurement was carried out under the conditions shown below. The obtained AB paste viscosity is shown in Table 1. The viscosity of the AB paste to which no copolymer was added was 42000 mPa · s.
Measuring device: Modular Compact Rheometer MCR 302 (manufactured by Antonio Par)
Jig: 25mm Parallel plate Gap width: 0.5mm
Temperature: 20 ° C
Shear velocity range: 0.1-400s ^-1
Measurement point interval: 1s

[Measurement of dissolution rate]
For the purpose of confirming the solubility of the copolymer in the electrolytic solution, the solubility in the solvent used in the electrolytic solution was measured. The obtained copolymer solution was placed in a petri dish and dried under reduced pressure at 140 ° C. under a nitrogen stream for 12 hours or more. To 1 g of the obtained copolymer, 9 g of a mixed solvent (volume ratio 50/50) of ethylene carbonate and diethylene carbonate was added to prepare a 10% suspension. The obtained suspension was allowed to stand at 40 ° C. for 1 hour. Then, it was filtered through a 0.5 μm PTFE filter to remove the undissolved copolymer. The filtered solution was dried at 140 ° C. under reduced pressure and a nitrogen stream to measure the mass of the copolymer dissolved in the mixed solvent. The solubility in the mixed solvent was determined from the following formula. The dissolution rates obtained are shown in Table 1.

[Appearance evaluation]
27.3 g of the 27.5% by mass copolymer A / NMP solution and 22.7 g of NMP were added to the sample bottle to prepare 50 g of the 15% by mass NMP solution of the copolymer A. The prepared solution was allowed to stand at 60 ° C. for 1 hour, and then the appearance was visually evaluated. Copolymers B to O were also evaluated in the same manner. The evaluation results are shown in Table 1. A transparent one indicates that the copolymer is sufficiently dissolved in NMP, and a white turbidity indicates that at least a part of the copolymer is not dissolved in NMP.

As shown in Table 1, it can be seen that the copolymers A to L have low solubility in the electrolytic solution. Therefore, it can be seen that the elution of the copolymer into the electrolytic solution is reduced from the positive electrode obtained from the positive electrode paste for batteries containing the copolymers A to L. Further, as shown in Table 1, the AB paste containing the copolymers A to L has a sufficiently low viscosity, and the copolymers A to L have sufficient solubility in NMP, which is a dispersion medium. It turns out that it has. The copolymer J having a large molecular weight has a relatively low solubility in NMP and a relatively high paste viscosity. On the other hand, it can be seen that the copolymer G having a small molecular weight dissolves slightly in the electrolytic solution. It can also be seen that some of the copolymers I, J, and L are not dissolved in NMP.

[Examples 1 to 7, Comparative Example 1]
In order to confirm the adhesion of the positive electrode mixture layer using the positive electrode paste containing the copolymer, the following adhesion test was performed. The adhesion test 1 simulates the processing performance of the electrode plate (slit process, etc.), and the adhesion test 2 simulates the winding performance of the electrode plate.

[Preparation of positive electrode paste]
Each paste was prepared using the copolymers shown in Table 2 synthesized in the above synthesis example, and the positive electrode active material, the conductive agent, the binder, and the non-aqueous dispersion medium. The positive electrode active material is LiNi _1/3 Mn _1/3 Co _1/3 O ₂ , the conductive agent is acetylene black (BET specific surface area: 68 m ² / g), and the binder is PVDF (Kureha's "# 1100" 12). % NMP solution), NMP was used as the non-aqueous dispersion medium. The mass ratio (content in solid content) of the positive electrode active material (active material), the binder, the conductive agent and the copolymer was as shown in Table 2. The positive electrode paste was prepared through a kneading step using a multi-blender mill after adjusting the solid content by adjusting the amount of the non-aqueous solvent. In this Example and Comparative Example, the solid content of the positive electrode paste refers to a material contained in the positive electrode paste, which is composed of a positive electrode active material, a binder, a conductive agent and a copolymer, that is, a material other than a non-aqueous dispersion medium. ..

[Manufacturing of positive electrode plate]
Each of the obtained positive electrode pastes is applied to one side of an aluminum foil having a thickness of 20 μm as a base material using a doctor blade, and sufficiently dried to form a mixture layer (positive electrode mixture layer). ), Each of the positive electrode plates (positive electrodes) of Examples 1 to 7 and Comparative Example 1 was prepared. The coating mass of the positive electrode plate after drying was 17 mg / cm ² .

[Adhesion test 1]
The mixed material layer coated portion of the positive electrode plate after drying was cut to a length of 30 mm × 60 mm using a cutting machine, and the mixed material layer of the cut portion was observed. In the cut portion, it was judged that the mixture layer having a width of 1 mm or more falling off or peeling off had poor adhesion, and the positive electrode plate having a width of 1 mm or more had no problem. The results of adhesion are shown in Table 2 as "B" for the positive electrode plate having poor adhesion and "A" for the positive electrode plate having no problem.

[Adhesion test 2]
Similar to the adhesion test 1, the mixed material layer coated portion of the positive electrode plate after drying was cut to a length of 30 mm × 60 mm using a cutting machine. The cut positive electrode plate was bent twice around an intermediate point in the long side direction. The first time, it was bent 180 ° so that the uncoated surfaces were in contact with each other, and then returned to the state before bending. The second time, it was bent 180 ° so that the coated surfaces were in contact with each other, and then returned to the state before bending. At the end of the first bending (returned before bending) and at the end of the second bending (returned before bending), the state of the mixture layer falling off was confirmed. The width at which the mixture layer fell off and peeled off was measured in the short side direction of the positive electrode plate at the bent portion (intermediate point in the long side direction). Then, the mixture layer dropout rate was calculated by the following formula.
Mixing material layer dropout rate (%) = {Width (mm) / 30 (mm) of mixed material layer falling off} x 100
Table 2 shows the dropout rate of the mixture layer.

[result]
From the results of the adhesion test 1, it was found that in the case of Comparative Example 1 in which the binder was not used separately from the copolymer in the positive electrode paste, poor adhesion occurred. As described above, a positive electrode paste containing a copolymer and not using a binder and a positive electrode containing a copolymer and a positive electrode mixture layer containing no binder are used in batteries such as lithium batteries. It can be said that it is not suitable.

Further, from the adhesion test 2, in Example 7 in which the content of the copolymer in the solid content (positive electrode mixture layer) of the positive electrode paste exceeds 2% by mass, the mixture layer falls off and peels off when the positive electrode plate is bent. Turned out to be possible. In an electrode body in which a positive electrode having a long strip shape, a first separator, a negative electrode and a second separator are superposed and wound flat around a winding axis, both ends in a direction orthogonal to the winding axis. The electrode plate of the curved portion of the above is bent at a relatively acute angle, and may have a shape that can be temporarily bent when it is inserted into a case or the like. As in Example 7, where the mixture layer falls off or peels off when the electrode plate is bent, the mixture layer may fall off or peel off in the wound electrode body. Therefore, the content of the copolymer in the solid content of the positive electrode paste (positive electrode mixture layer) is preferably 2% by mass or less.

[Examples 8 to 14, Comparative Example 2]
(Preparation of positive electrode paste)
The copolymers and positive electrode active materials shown in Table 3, acetylene black as a conductive agent (BET specific surface area: 68 m ² / g), polyvinylidene fluoride (PVDF) as a binder, and NMP as a non-aqueous dispersion medium. To prepare a positive electrode paste. The mass ratio of the positive electrode active material, the conductive agent, and the binder was 94: 3: 3 (in terms of solid content). The amount of the copolymer added was defined as parts by mass with respect to 100 parts by mass of the conductive agent shown in Table 3.

(Preparation of positive electrode)
The obtained positive electrode paste is applied to both sides of an aluminum foil (positive electrode base material) having a thickness of 15 μm, leaving a non-coated portion (positive electrode mixture layer non-forming region), and dried to prepare a positive electrode mixture layer. did. Then, a roll press was performed to prepare a positive electrode.

(Preparation of negative electrode)
Negative electrode mixture is made by mixing graphite and non-graphitizable carbon, which are negative electrode active materials, styrene-butadiene rubber (SBR), which is a binder, carboxymethyl cellulose (CMC), which is a thickener, and water, which is a dispersion medium. A paste (material for forming a negative electrode mixture layer) was prepared. The mass ratio of graphite to non-graphitizable carbon was 80:20, and the total mass of graphite and non-graphitizable carbon to the mass ratio of SBR to CMC was 96: 2: 2. The negative electrode mixture paste was prepared by adjusting the solid content by adjusting the amount of water and then performing a kneading step using a multi-blender mill. This negative electrode paste was applied to both sides of the copper foil, leaving a non-coated portion (negative electrode mixture layer non-forming region), and dried to prepare a negative electrode mixture layer. Then, a roll press was performed to prepare a negative electrode.

A polyethylene microporous film having a length of 1300 mm, a width of 34 mm, and a thickness of 25 μm was used as a separator, and ethylene carbonate (EC): diethyl carbonate (DMC): ethyl methyl carbonate (EMC) = 25:35:40 (volume) as a non-aqueous electrolyte. A solution in which 1 mol / L of _{LiPF 6} was dissolved in the mixed solvent of (ratio) was used.

The produced positive electrode, separator, and negative electrode were superposed in order, and this was wound around a rectangular polyethylene core in an oval spiral shape to form an electrode body.

The electrode body was housed in a battery case made of square aluminum, and the positive electrode lead was led out from the positive electrode and welded to the battery lid, and the negative electrode lead was led out from the negative electrode and welded to the negative electrode terminal, and then the electrolytic solution was injected. Next, the battery lid and the battery case were laser-welded to maintain the airtightness inside the battery case, and a small square battery was obtained.

(Measurement of ACR increase rate)
Each of the obtained batteries was constantly charged to 4.2 V at a charging current of 1 hour rate (1 CmA) in an environment of 45 ° C., and then continuously charged at 4.2 V at a constant voltage for a total of 3 hours. Then, it was discharged to 2.75 V with a discharge current of 1 CmA. This charge / discharge was performed for 500 cycles. The AC battery resistance value (ACR) was measured before and after 500 cycles of charging and discharging, and the rate of increase was determined. The results are shown in Table 3.

As shown in Table 3, Examples 8 to 8 using a positive electrode prepared from a positive electrode paste containing a copolymer A, B, H or I containing the structural unit (c) represented by the above formula (3). At 14, it can be seen that the ACR increase rate is low. On the other hand, Comparative Example 2 using the copolymer N not containing the structural unit (c) represented by the above formula (3) has a high ACR increase rate. It is presumed that this is due to the high solubility of the copolymer N, which does not contain the structural unit (c) represented by the above formula (3), in the electrolytic solution, as shown in Table 1.

The present invention can be applied to electronic devices such as personal computers and communication terminals, batteries used as power sources for automobiles and the like, and positive electrodes thereof.

1 Battery 2 Electrode 3 Battery container 4 Positive terminal 4'Positive lead 5 Negative terminal 5'Negative lead 20 Power storage unit 30 Power storage device

Claims (8)

A positive electrode active material, conductive agent, including the positive-electrode mixture layer and the binder and copolymers,
The copolymer is a structural unit (a) represented by the following formula (1), a structural unit (b) represented by the following formula (2), and a structural unit (c) represented by the following formula (3). Contains,
The content of the structural unit (b) in the copolymer is 10% by mass or more and 60% by mass or less.
The content of the structural units of said copolymer (c) is state, and are 15 wt% to 45 wt% or less,
The content of the copolymer in the positive electrode mixture layer is 0.01% by mass or more and 3% by mass or less.
A positive electrode for a battery comprising an electrolytic solution containing at least one non-aqueous solvent selected from the group consisting of cyclic carbonate and chain carbonate.

(Formula (1) in ^{~ (3), R 1,} R 2, R 3, R 5, R 6, R 7 and R ⁹ are each independently hydrogen atom, a methyl group or an ethyl group .R ^{Reference numeral 4} is a monovalent hydrocarbon group having 8 to 30 carbon atoms. R ⁸ is a linear or branched alkylene group having 2 to 4 carbon atoms. R ¹⁰ and R ¹¹ are hydrogen atoms. R ¹² is a hydrogen atom or a methyl group. P is a number from 1 to 50.) The positive electrode for a battery according to claim 1, wherein the mass ratio (constituent unit (a) / structural unit (b)) of the structural unit (a) and the structural unit (b) of the copolymer is 0.5 or more and 5 or less. .. The positive electrode for a battery according to claim 1 or 2, wherein the weight average molecular weight of the copolymer is 15,000 or more and 100,000 or less. The positive electrode for a battery according to claim 1, claim 2 or claim 3, wherein the content of the copolymer is 0.5 parts by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the conductive agent. The positive electrode active material is Li _{1 + x} Ni _a Co _b Mn _c D _d O ₂ (D is an element other than Li, Co, Mn, Ni and O. X ≧ 0, a> 0, b ≧ 0, c ≧ 0, 0 ≦ d ≦ 0.2, x + a + b + c + d = 1). The positive electrode for a battery according to any one of claims 1 to 4, which is a compound. It comprises using a positive electrode paste for a battery containing a positive electrode active material, a conductive agent, a binder, a copolymer and a dispersion medium.
The copolymer is a structural unit (a) represented by the following formula (1), a structural unit (b) represented by the following formula (2), and a structural unit (c) represented by the following formula (3). Contains,
The content of the structural unit (b) in the copolymer is 10% by mass or more and 60% by mass or less.
The content of the structural units of said copolymer (c) is state, and are 15 wt% to 45 wt% or less,
The content of the copolymer in the solid content of the positive electrode paste for batteries is 0.01% by mass or more and 3% by mass or less.
A method for producing a positive electrode for a battery, which comprises an electrolytic solution containing at least one non-aqueous solvent selected from the group consisting of cyclic carbonate and chain carbonate.

(Formula (1) in ^{~ (3), R 1,} R 2, R 3, R 5, R 6, R 7 and R ⁹ are each independently hydrogen atom, a methyl group or an ethyl group .R ^{Reference numeral 4} is a monovalent hydrocarbon group having 8 to 30 carbon atoms. R ⁸ is a linear or branched alkylene group having 2 to 4 carbon atoms. R ¹⁰ and R ¹¹ are hydrogen atoms. R ¹² is a hydrogen atom or a methyl group. P is a number from 1 to 50.) The positive electrode active material is Li _{1 + x} Ni _a Co _b Mn _c D _d O ₂ (D is an element other than Li, Co, Mn, Ni and O. X ≧ 0, a> 0, b ≧ 0, c ≧ 0, 0 ≦ d ≦ 0.2, x + a + b + c + d = 1). The method for producing a positive electrode for a battery according to claim 6, which is a compound. Positive electrode and battery of any one of claims 1 to 5
A battery comprising an electrolytic solution containing at least one non-aqueous solvent selected from the group consisting of cyclic carbonates and chain carbonates.

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