JP2016027561A - Negative electrode binder for lithium ion secondary battery, negative electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a binder for a lithium ion secondary battery which is superior in charge and discharge cycle characteristics.SOLUTION: A negative electrode binder for a lithium ion secondary battery comprises: a polyamide imide having repeating structural units expressed by the formulas (1) and (2), where Ar represents substituted/unsubstituted one or two aryl groups; and "a" and "b" each represent an appropriate integer.SELECTED DRAWING: None

Description

  The present invention relates to a negative electrode binder for a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery.

  In recent years, portable electronic devices such as video cameras, mobile phones, and notebook computers have been widely used, and there is a strong demand for miniaturization, weight reduction, and long life. Accordingly, as a power source for portable electronic devices, development of a battery, in particular, a lithium ion secondary battery that is lightweight and obtains a high energy density is in progress.

  In particular, lithium ion secondary batteries that use the insertion and extraction of lithium ions for charge / discharge reactions are expected to have higher energy density than lead batteries and nickel cadmium batteries.

  The lithium ion secondary battery is mainly composed of a positive electrode, a negative electrode, a separator for insulating the positive electrode and the negative electrode, and an electrolyte solution for allowing lithium ions to move between the positive electrode and the negative electrode, as described above. The positive electrode and the negative electrode described above are obtained by applying various active material layers to both surfaces or one surface of a current collector made of a metal foil. The positive electrode has a positive electrode active material layer on the positive electrode current collector, and includes, for example, a positive electrode active material such as lithium cobaltate, lithium nickelate, lithium manganate, and lithium iron phosphate. On the other hand, the negative electrode has a negative electrode active material layer on a negative electrode current collector, and includes a negative electrode active material containing, for example, natural graphite or artificial graphite.

  Recently, however, there has been a demand for higher battery capacity as electronic devices become more sophisticated and multifunctional, and in response to this, a new negative electrode active material that replaces graphite (theoretical capacity 372 mAh / g). Is being considered.

  Examples of high-capacity negative electrode active materials that can replace graphite include lithium metal and alloy-based negative electrode materials such as silicon (Si), silicon oxide (for example, SiO), and tin (Sn) that can be alloyed with lithium. However, since silicon (4199 mAh / g) and silicon oxide (2000 mAh / g) exhibit high theoretical capacity, a significant improvement in battery capacity is expected.

  However, when silicon is used as the negative electrode active material, a large amount of stress is applied to the negative electrode because the negative electrode active material layer expands and contracts violently during charge and discharge. As a result, a crack occurs in the negative electrode active material layer formed on the current collector, peeling occurs between the negative electrode active material layer and the current collector, or the apparent thickness of the negative electrode active material layer increases. There is a problem such as.

  Thereby, while the battery capacity is increased, the negative electrode active material—the negative electrode active material, and the negative electrode active material—the current collector are obtained by such volume expansion (hereinafter sometimes referred to as expansion / contraction). As a result, the charge / discharge cycle characteristics, which are important characteristics of the lithium ion secondary battery, are deteriorated, and the thickness is unintentionally increased.

  In response to the above-described problems, for example, it has been proposed to use polyimide or polyamideimide as a binder for high strength as a binder having high strength (for example, Patent Document 1, Patent Document 2, and Patent Document 3). However, the market demand is not limited recently, and further improvement of charge / discharge cycle characteristics is required.

JP 2007-242405 A JP 2010-205609 A JP 2011-048969 A

  This invention is made | formed in view of the above-mentioned situation, and is providing the negative electrode binder for lithium ion secondary batteries which is excellent in charging / discharging cycling characteristics, the negative electrode for lithium ion secondary batteries, and a lithium ion secondary battery. .

In order to solve the above-described problems, the negative electrode binder for a negative electrode for a lithium ion secondary battery of the present invention (hereinafter sometimes referred to as “negative electrode binder”) is a repeating structure of the following formulas (1) and (2): Polyamideimide having a unit is included. However, the value of a and b in a formula shows the copolymerization ratio of each structural unit by a molar ratio.

Furthermore, Ar in Formula (2) represents an aryl group having an aromatic ring, and represents any one of Formula (3), Formula (4), and Formula (5). R _{1 to} R ₄ , R ₆ and R ₇ are each independently a hydrogen atom, hydroxyl group, alkyl group, methyl group, halogen, substituted alkyl group, alkoxy group, aryl group, substituted aryl group, nitro group, cyano group And a substituent selected from the group consisting of a thiol group, a methyl halide group and the like. R ₅ in the formula (4) is —O—, —S—, —C (═O) —, —SO ₂ —, —C (═O) O—, — (CH ₂ ) _n —, _{-C (CF 3) 2 -,} - C (CH 3) 2 - shows a. Note that _{n in} — (CH ₂ ) _n — is an integer of 0 or more and 5 or less. )

  According to the negative electrode binder according to the present invention, the charge / discharge cycle characteristics are greatly improved. Although the detailed cause is not clarified as the reason, one of the reasons is as follows from our earnest examination.

  The negative electrode binder according to the present invention is partially decomposed and / or dissolved in the charging process, so that the decomposed product and / or dissolved material contains fluorine ions on the surface of the negative electrode active material in the initial charging process. This contributes to the formation of a solid electrolyte membrane (SEI membrane). The formation of the SEI film acts on the insertion / release reaction between the negative electrode active material and lithium ions, and as a result, the charge / discharge cycle is improved.

  Further, in the negative electrode binder according to the present invention, the molar ratio of a in the above formula (1) is 0.1 to 70 mol%, and the molar ratio of b in the above formula (2) is 30 to 99.9. It is preferable that it is mol%. However, a and b show the ratio of copolymerization, and when the molar ratio of a and b is added together, the relationship of 100 mol% shall be satisfied.

  In the polyamideimide in which the molar ratio a of the polyamideimide of the formula (1) having fluorine in the structure as a trifluoromethyl group is 0.1 to 70 mol%, SEI containing fluorine formed on the surface of the negative electrode active material Since the amount of fluorine ions necessary to form a film is a sufficient amount and further maintains the physical strength as a binder necessary to suppress expansion, the volume expansion of the negative electrode active material is further suppressed, In addition, it is considered that good charge / discharge cycle characteristics can be obtained.

  In particular, in the case of polyamideimide in which the molar ratio of a in the formula (1) is 1 to 40 mol%, the volume expansion of the negative electrode active material is further suppressed, and better charge / discharge cycle characteristics are obtained.

  Furthermore, the negative electrode binder according to the present invention preferably has a weight average molecular weight (Mw) of 4,000 to 100,000.

  When the weight average molecular weight (Mw) is 4,000 to 100,000, volume expansion of the negative electrode active material is further suppressed, and better charge / discharge cycle characteristics are obtained.

  When the above-mentioned weight average molecular weight (Mw) is 4,000 to 100,000, the volume of the negative electrode binder is maintained by strongly holding the binding property between the active material and the active material and the active material and the current collector. The expansion is suppressed, and as a result, the charge / discharge cycle characteristics are improved because the conductive paths between the active materials and between the active material and the current collector are excellent. Furthermore, since the viscosity as the handling of the binder is optimal, the dispersibility in coating is improved, and the binder can be uniformly dispersed in the negative electrode active material layer. The weight average molecular weight can be easily adjusted in various ways depending on the stirring time and reaction temperature during synthesis.

  Particularly when the weight average molecular weight (Mw) is 5,000 to 80,000, more excellent charge / discharge cycle characteristics can be obtained.

  Furthermore, a negative electrode for a lithium ion secondary battery according to the present invention is a negative electrode for a lithium ion secondary battery comprising a current collector and a negative electrode active material layer formed on the current collector, the negative electrode active material layer described above Includes a negative electrode active material, a conductive additive, and a negative electrode binder according to the present invention, and the negative electrode active material includes at least one of silicon (Si) and a silicon compound.

  Further, in the negative electrode for a lithium ion secondary battery according to the present invention, in the negative electrode active material layer formed on the current collector, at least the negative electrode binder according to the present invention is in the range of 5.0 wt% or more and 40 wt% or less. It is preferable that it is contained within.

  When the content of the negative electrode binder is 5.0 to 40% by weight, in addition to the volume expansion and charge / discharge cycle characteristics of the negative electrode, a lithium ion secondary battery showing an excellent capacity retention rate even at a high rate is obtained. . When the content of the binder is less than 5.0% by weight, the strength of the negative electrode active material layer is weak, and good cycle characteristics may not be obtained. On the other hand, if the amount exceeds 40% by weight, the binder acts as a resistor, so that the rate characteristics may deteriorate.

  Furthermore, the lithium ion secondary battery according to the present invention is a lithium ion secondary battery comprising a negative electrode and a positive electrode, a separator disposed between the negative electrode and the positive electrode, and an electrolyte solution, wherein the negative electrode is It is a negative electrode for lithium ion secondary batteries according to the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the negative electrode binder for lithium ion secondary batteries which is excellent in charging / discharging cycling characteristics, the negative electrode for lithium ion secondary batteries, and a lithium ion secondary battery can be provided.

It is sectional drawing showing the structure of a lithium ion secondary battery. SEM-EDX spectrum of the negative electrode SiO _x active material surface using the polyamide-imide binder according to Example 3 after 10 cycles of charge and discharge SEM-EDX spectrum of SiO _x active material surface of negative electrode using polyamideimide binder according to Comparative Example 1 after 10 cycles of charge and discharge SEM-EDX spectrum of the surface of the SiO _x active material of the negative electrode using the polyamideimide binder according to Example 3 before charging and discharging SEM-EDX spectrum of the surface of the SiO _x active material of the negative electrode using the polyamideimide binder according to Comparative Example 1 before charging and discharging

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In addition, this invention is not limited to the following embodiment. The constituent elements described below include those that can be easily assumed by those skilled in the art and those that are substantially the same. Furthermore, the constituent elements described below can be appropriately combined.

<Lithium ion secondary battery>
FIG. 1 shows a cross-sectional view of a lithium ion secondary battery 100. A lithium ion secondary battery 100 in FIG. 1 includes a positive electrode 10 and a negative electrode 20, a separator 18 disposed between the positive electrode 10 and the negative electrode 20, and an electrolyte solution containing an electrolyte. The electrolyte solution described above, which is a lithium ion transfer medium between the positive and negative electrodes in FIG.

  The positive electrode 10 described above includes a positive electrode active material layer 14 containing a positive electrode active material that absorbs and releases lithium ions, a conductive additive, and a binder on at least one main surface of the positive electrode current collector 12. The negative electrode 20 includes a negative electrode active material layer 24 containing a negative electrode active material that absorbs and releases lithium ions, a conductive additive, and a binder on at least one main surface of the negative electrode current collector 22. Has been.

  There is no restriction | limiting in particular as a shape of a lithium ion secondary battery, For example, any, such as a cylindrical type, a square type, a coin type, a flat type, a laminate film type, may be sufficient. In the present invention, a laminate film is used as the outer package 50, and in the following examples, a laminate film type battery is produced and evaluated. As the above-mentioned laminate film, for example, a film having a three-layer structure in which polypropylene, aluminum, and nylon are laminated in this order can be used.

  Hereinafter, preferred embodiments of the negative electrode binder for a lithium ion secondary battery, the negative electrode 20 for a lithium ion secondary battery, and the lithium ion secondary battery 100 according to the present embodiment will be described in more detail.

<Negative electrode active material>
As the negative electrode active material that can be alloyed with lithium, silicon, tin, and germanium are preferable, and silicon having a high capacity is particularly preferable. Silicon may be used alone, may be used as an alloy, may be used as a compound, or two or more of them may be used in combination.

Further, a compound containing silicon oxide, that is, a compound containing silicon and oxygen as constituent elements can be cited as a high-capacity negative electrode active material used in the present invention. (However, the atomic ratio x of O to Si is 0.5 ≦ x ≦ 1.5. Hereinafter, it is expressed as “SiO _x ”).

The SiO _x may contain a microcrystalline or amorphous phase of Si. In this case, the atomic ratio of Si and O is a ratio including Si microcrystalline or amorphous Si. That is, SiO _x includes a structure in which Si (for example, microcrystalline Si) is dispersed in an amorphous SiO ₂ matrix, and this amorphous SiO ₂ is dispersed in the SiO ₂ matrix. It is sufficient that the atomic ratio x satisfies 0.5 ≦ x ≦ 1.5 in combination with Si. For example, in the case of a compound in which Si is dispersed in an amorphous SiO ₂ matrix and the molar ratio of SiO ₂ to Si is 1: 1, x = 1, so that the structural formula is represented by SiO. The

In addition, when SiO _x or other oxides (silicon, tin, or germanium oxides) are used, the surface is preferably covered with carbon. Since these oxides have poor conductivity, when used as a negative electrode active material, a conductive additive is used to ensure good battery characteristics, and the oxide and the conductive material in the negative electrode active material layer are electrically conductive. It is necessary to improve the mixing and dispersion with the auxiliary agent to form an excellent conductive network. Therefore, if the surface of the oxide is coated with carbon, for example, a conductive network in the negative electrode is formed better than when the oxide and a conductive additive made of a carbon material are mixed and used.

  Further, the negative electrode active material is not limited to the above-described materials, and any other material that can electrochemically occlude / release lithium ions is not particularly limited. In particular, in the case where a negative electrode active material that expresses a high capacity with large expansion and contraction is used for the negative electrode 20 for a lithium ion secondary battery, the negative electrode binder of the present embodiment can exhibit a more suitable effect.

  Furthermore, a carbon-based negative electrode active material may be used in combination with the silicon-based negative electrode active material described above, and for example, crystalline carbon, amorphous carbon, or a combination thereof may be used. Examples of the crystalline carbon include natural graphite or artificial graphite such as amorphous, plate-like, scale-like, spherical, and fibrous. Examples of the amorphous carbon include soft carbon or hard carbon. Examples include mesophase pitch carbide and calcined coke.

<Negative electrode binder for lithium ion secondary battery>
The negative electrode binder for a lithium ion secondary battery according to the present invention used for the negative electrode 20 for a lithium ion secondary battery (hereinafter sometimes referred to as “negative electrode binder”) is a repetition of the following formulas (1) and (2): A polyamideimide having a structural unit is used. However, the value of a and b in a formula shows the copolymerization ratio of each structural unit by a molar ratio.

Furthermore, Ar in Formula (2) represents an aryl group having an aromatic ring, and represents any one of Formula (3), Formula (4), and Formula (5). R _{1 to} R ₄ , R ₆ and R ₇ are each independently a hydrogen atom, hydroxyl group, alkyl group, methyl group, halogen, substituted alkyl group, alkoxy group, aryl group, substituted aryl group, nitro group, cyano group And a substituent selected from the group consisting of a thiol group, a methyl halide group and the like. R ₅ in the formula (4) is —O—, —S—, —C (═O) —, —SO ₂ —, —C (═O) O—, — (CH ₂ ) _n —, _{-C (CF 3) 2 -,} - C (CH 3) 2 - shows a. Note that _{n in} — (CH ₂ ) _n — is an integer of 0 or more and 5 or less. )

  In the negative electrode 20 for a lithium ion secondary battery composed of the above-described negative electrode binder, a part of the negative electrode binder of the present embodiment is decomposed and / or dissolved in the charge / discharge process, so that the decomposed product and / or the dissolved product is obtained. However, it contributes to the formation of a solid electrolyte membrane (SEI membrane) containing fluorine ions on the surface of the negative electrode active material in the charging process. In the lithium ion secondary battery 100 using the negative electrode 20 for the lithium ion secondary battery according to the present embodiment, the charge / discharge cycle characteristics are excellent by acting on the insertion / extraction reaction of lithium ions due to the presence of the SEI film. Indicates. The partial decomposition and / or dissolution of the negative electrode binder described above means a very slight degree, and the negative electrode active material layer does not fall off or collapse due to the above-described decomposition and / or dissolution of the negative electrode binder. Means degree.

  According to the negative electrode binder of this embodiment, the above-mentioned polyamideimide is composed of repeating structural units of the above formulas (1) and (2), and the molar ratio of a in the above formula (1) is 0.00. It is preferably 1 to 70 mol%, and the molar ratio of b in the formula (2) is preferably 30 to 99.9 mol%. However, a and b show the ratio of copolymerization, and when the molar ratio of a and b is added together, the relationship of 100 mol% shall be satisfied.

  By using as a negative electrode binder polyamideimide prepared by adjusting the molar ratio of a and b in formula (1) and formula (2) to 0.1 to 70 mol% and 30 to 99.9 mol%, respectively, Since the amount of fluorine ions necessary to form a SEI film containing fluorine formed on the active material surface is sufficient, and further maintains the physical strength as a binder necessary to suppress expansion, Volume expansion of the negative electrode active material is further suppressed, and good charge / discharge cycle characteristics are obtained.

  In particular, in the case of polyamideimides prepared so that the molar ratios of a and b in formula (1) and formula (2) are 1 to 40 mol% and 60 to 99 mol%, respectively, more excellent suppression and expansion of expansion and contraction are achieved. Discharge cycle characteristics can be obtained.

  Furthermore, as the above-mentioned polyamideimide relating to the negative electrode binder of the present embodiment, the weight average molecular weight (Mw) is preferably 4,000 to 100,000.

  When the weight average molecular weight (Mw) described above, the negative electrode active material layer is strongly held by the polyamideimide described above, and each of the negative electrode active material, the conductive additive, and the negative electrode current collector can be firmly bound. Excellent charge / discharge cycle characteristics.

  In particular, the weight average molecular weight (Mw) is more preferably 5,000 to 80,000. Thereby, more excellent charge / discharge cycle characteristics can be obtained.

  In addition, the weight average molecular weight of the above-mentioned negative electrode binder can be increased by heat treatment at a predetermined temperature. The polyamideimide molecule and the polyamideimide molecule constituting the polyamideimide are newly polycondensed by heat treatment, and the mechanical strength as the polyamideimide can be increased.

  The upper limit of the temperature of the heat treatment is preferably a temperature that does not cause the polyamideimide in the present embodiment to decompose, but the battery characteristics are not impaired when the polyamideimide is used as a lithium ion secondary battery. If it is a range, the temperature which a part of polyamideimide decomposes | disassembles may be sufficient.

<Polyamideimide>
Polyamideimide, which is a negative electrode binder for a lithium ion secondary battery described above, is a lithium ion secondary battery in which members constituting the negative electrode active material layer 24 or the negative electrode active material layer 24 and the negative electrode current collector 22 are bound together. It is added for the purpose of maintaining the electrode structure of the negative electrode 20 for use. As the negative electrode binder contained in the negative electrode 20 for a lithium ion secondary battery, the aforementioned polyamideimide can be used.

Polyamideimide production methods include acid chloride method using aromatic diamine and trimellitic anhydride monochloride, isocyanate method in which aromatic diisocyanate derived from aromatic diamine and trimellitic anhydride are reacted, aromatic diamine and It can be produced by a direct polymerization method in which trimellitic anhydride is reacted by heating to a high temperature in the presence of a dehydration catalyst. The polyamideimide of the present embodiment can be produced by an acid chloride method, and is obtained by polymerizing trimellitic anhydride monochloride (TMAC) and a diamine component as an acid component monomer. As long as the effects of the present embodiment are not impaired, the following acid component monomers may be used as copolymerization components.

  As acid component monomers, trimellitic acid, terephthalic acid, isophthalic acid, 4,4′-biphenyldicarboxylic acid, pyromellitic acid, 3,3′-benzophenone tetracarboxylic acid, 4,4′-benzophenone tetracarboxylic acid, 3, 3'-biphenylsulfonetetracarboxylic acid, 4,4'-biphenylsulfonetetracarboxylic acid, 3,3'-biphenyltetracarboxylic acid, 4,4'-biphenyltetracarboxylic acid, adipic acid, sebacic acid, maleic acid, fumar Acid, dimer acid, stilbene dicarboxylic acid, or acid anhydrides thereof or acid chlorides thereof can be used.

  On the other hand, as a diamine component monomer, 2,2'-bis (trifluoromethyl) benzidine (TFMB) is an essential component, and a diamine component monomer corresponding to the structure of the above formula (2) is a necessary component. Furthermore, other diamine component monomers can be used as copolymerization components as long as the effects of the present invention are not impaired.

  Examples of the diamine component monomer that can be used for polyamideimide include 2,2′-bis (trifluoromethyl) benzidine (TFMB), m-phenylenediamine (m-PDA), p-phenylenediamine (p-PDA), 4 , 4'-diaminodiphenyl ether, 3,4-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane (DADPM), m-xylylenediamine, p-xylylenediamine, 2,2'-benzidine disulfonic acid (BDSA), 1 , 4-Naphthalenediamine, 1,5-naphthalenediamine, 2,6-naphthalenediamine, 2,7-naphthalenediamine, 2,2′-bis (4-aminophenyl) propane, 2,2′-bis (4- Aminophenyl) hexafluoropropane, 4,4'-diaminodiphenyl Lufone, 3,3′-diaminodiphenyl sulfone, 3,4-diaminobiphenyl, 4,4′-diaminobenzophenone, hexamethylene diamine, tetramethylene diamine, isophorone diamine, isopropylidene dianiline, 3,3′-diaminobenzophenone, Dicyclohexyl-4,4′-diamine, o-tolidine, 2,4-tolylenediamine, 1,3-bis (3-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 1,4 -Bis (4-aminophenoxy) benzene, 2,2-bis [4- (4-aminophenoxy) phenyl] propane, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (3-amino Phenoxy) phenyl] sulfone, 4,4′-bis (4-aminophenoxy) bi Eniru, 2,2-bis [4- (4-aminophenoxy) phenyl] hexafluoropropane, 4,4'-diaminodiphenyl sulfide, etc. 3,3'-diaminodiphenyl sulfide and the like.

  The polyamideimide used in the present embodiment is a copolymer produced from the above-mentioned acid component and diamine component, and having a repeating structural unit represented by the above formula (1) and formula (2). (1) and the molar ratio of a and b in the above formula (2) are in the range of 0.1 to 70 mol% and 30 to 99.9 mol%, respectively, for the lithium ion secondary battery. As a negative electrode binder, more excellent charge / discharge cycle characteristics can be exhibited.

<Production method of polyamideimide>
The production of the polyamideimide of the present embodiment is preferably carried out using the acid component monomer and diamine component monomer described above by the conventionally known acid chloride method (Japanese Patent Publication No. 42-15637). To obtain polyamideimide by reacting trimellitic anhydride chloride with at least two or more kinds of diamine component monomers described above at a low temperature of, for example, 40 ° C. or less to obtain a polyamic acid, followed by heat ring closure or chemical ring closure. Can do.

In addition, as an organic solvent used when polymerizing the polyamideimide of this embodiment, for example, N, N-dimethylacetamide, N, N-dimethylformamide, N-methyl-2-pyrrolidone, dimethylsulfoxide, cresol are used. Polar solvents such as N, N-dimethylacetamide and N-methyl-2-pyrrolidone are preferable.

  Moreover, the polymer of polyamic acid can be isolated by pouring the obtained polyamic acid polymerization solution into a solvent such as water or acetone during high-speed stirring.

  The polyamideimide resin of the present embodiment is produced by an acid chloride method. In the acid chloride method, a polyamic acid is obtained in the first stage as described above, and then subjected to heat ring closure (or chemical ring closure) to obtain polyamide. It can be produced by a two-stage polymerization method that synthesizes an imide.

  The polymer of polyamic acid synthesized and isolated in the first stage is heated in an air atmosphere at 150 to 300 ° C., in vacuum, or in an inert gas in the process of imide ring closure in the second stage. Polyamideimide can be obtained by heating under or chemical ring closure using acetic anhydride or the like.

<Heated imide ring closure>
In producing the polyamideimide of the present embodiment, it is preferable to dry in a vacuum or heat to close in an inert gas, particularly in the second stage heated imide cyclization process. That is, in the production of the polyamideimide of the present embodiment, it is preferable to produce the polyamic acid by heat-cyclization by heat-cyclization imidization at a temperature of 150 ° C. or more and 300 ° C. or less under vacuum drying.

<Polyamideimide varnish>
The polyamideimide of this embodiment can be dissolved in an aprotic polar solvent having a boiling point of 160 ° C. or higher to form a polyamideimide varnish.

  As an aprotic polar solvent having a boiling point of 160 ° C. or higher used in the above-mentioned polyamideimide varnish, aprotic polar solvents such as N-methyl-2-pyrrolidone and N, N-dimethylacetamide are soluble and solvent-dried. From the viewpoint of sex.

  In addition, amide solvents such as dimethylformamide, sulfur solvents such as dimethyl sulfoxide and sulfolane, nitro solvents such as nitromethane and nitroethane, ether solvents such as diglyme and tetrahydrofuran, cyclohexanone, as long as the characteristics as varnish are not impaired Ketone solvents such as methyl ethyl ketone, nitrile solvents such as acetonitrile and propionitrile, γ-butyrolactone, tetramethylurea and the like can be used as the mixed solvent.

  The method for producing the polyamide-imide varnish of the present embodiment is not particularly limited, but is produced by appropriately combining a stirrer, dissolver, homogenizer, three rolls, sand mill, ball mill, etc. according to the intended viscosity and concentration. Can do.

The ratio of the polyamideimide in the varnish is 5 wt% to 30 wt% of the polyamideimide and 95 wt% to 70 wt% of the aprotic polar solvent with respect to 100 wt% of the polyamideimide varnish, depending on the logarithmic viscosity of the polyamideimide. It is preferable. More preferably, the polyamideimide is 10 to 20 wt% and the aprotic polar solvent is 90 to 80 wt% from the handling property as a varnish for producing the paste.

<Positive electrode active material>
As a positive electrode active material used for a lithium ion secondary battery, a material capable of inserting and extracting lithium ions, for example, a lithium-containing compound such as lithium oxide, lithium sulfide, or an intercalation compound containing lithium is preferable. Two or more of these may be mixed and used. In particular, in order to increase the energy density, a lithium composite oxide represented by the general formula Li _x MO ₂ or an intercalation compound containing lithium is preferable. Note that M is preferably one or more transition metals, specifically, at least one of cobalt (Co), nickel, manganese (Mn), iron, aluminum, vanadium (V), and titanium (Ti). preferable. x varies depending on the charge / discharge state of the battery, and is usually a value in the range of 0.05 ≦ x ≦ 1.10. In addition, manganese spinel (LiMn ₂ O ₄ ) having a spinel crystal structure, lithium iron phosphate (LiFePO ₄ ) having an olivine crystal structure, and the like are preferable because they can provide a high energy density.

Specifically, lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), LiNi _x Co _y Mn _z M _a O ₂ (x + y + z + a = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, 0 ≦ a ≦ 1, M is one or more elements selected from Al, Mg, Nb, Ti, Cu, Zn, Cr), lithium vanadium compound (LiV ₂ O ₅ ), olivine type LiMPO ₄ (where M represents one or more elements selected from Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, and Zr, or VO), lithium titanate (Li ₄ Ti ₅ O _{12 ), LiNi x Co y Al z} O 2 (0.9 <x + y + z <1.1) , and the like. Further, the material is not limited to these materials, and any other positive electrode active material that electrochemically inserts and desorbs lithium ions is not particularly limited.

  Examples of the binder used for the positive electrode 10 include polyamide-imide, polyvinylidene fluoride (PVDF), polyimide, polyurethane, ethylene vinyl alcohol, polyacrylate, and other solvent-based binders, carboxymethyl cellulose (CMC), and styrene-butadiene. An aqueous binder such as a polymer can be suitably used.

<Conductive aid>
In the negative electrode active material layer 24 and the positive electrode active material layer 14, a conductive additive may be additionally added for the purpose of improving conductivity. The conductive auxiliary agent used in the present embodiment is not particularly limited, and a known material can be used. Examples include carbon blacks such as acetylene black (AB), ketjen black, furnace black, channel black, thermal black, carbon vapor such as vapor grown carbon fiber (VGCF), carbon nanotube, and carbon materials such as graphite. These can be used alone or in combination of two or more.

<Current collector>
The current collector is made of a conductive material, and an active material layer is disposed on one main surface or both surfaces thereof. Although the material which comprises a collector is not specifically limited as a lithium ion secondary battery of this embodiment, As a negative electrode collector 22 used for the negative electrode 20, copper, stainless steel, nickel, titanium, or Metal foils such as these alloys can be used. In particular, copper, a copper alloy, and stainless steel are preferable. From the viewpoint of cost, a copper foil manufactured using an electrolytic copper foil and a rolled copper foil can be suitably used. From the viewpoint of strength, a rolled foil of stainless steel or copper alloy can be suitably used. As the positive electrode current collector 12 used for the positive electrode 10, a metal foil such as aluminum, stainless steel, nickel, titanium, or an alloy thereof can be used. In particular, the positive electrode current collector 12 is preferably an aluminum foil.

<Separator>
The separator 18 is disposed between the negative electrode 20 and the positive electrode 10, prevents a short circuit of current due to contact between both electrodes, and further allows lithium ions to pass through by being impregnated with an electrolyte solution containing an electrolyte salt. is there. The separator 18 includes, for example, a porous film having a large number of minute pores. Specific examples of the separator 18 include polyolefin-based porous films such as polyethylene and polypropylene, polyimide, and polyamideimide. Examples thereof include a highly heat-resistant porous film, a composite film of the above-described polyolefin-based porous film and a highly heat-resistant porous film, and nonwoven fabrics such as aromatic polyamide, polyimide, and polyamideimide. The separator 18 preferably has, for example, a thickness in the range of 5 μm to 50 μm, and a porosity representing a void volume ratio in the total volume of 20% to 60%.

<Electrolytic solution (solvent)>
As described above, the electrolytic solution is impregnated in the separator 18 and includes, for example, a solvent and an electrolyte salt dissolved in the solvent, and may include an additive as necessary. Examples of the solvent for the electrolyte solution include cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC), chains such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). Chain carbonate ester, chain carboxylate such as methyl acetate (MA), ethyl acetate (EA), methyl propionate (MP), ethyl propionate (EP), or γ-butyrolactone (GBL), γ-valerolactone And cyclic carboxylic acid esters such as (GVL). Any one of these may be used as a solvent by mixing two or more. Further, the solvent is not limited to the above-described solvents, and is not particularly limited as long as the electrolyte salt is dissolved to obtain the lithium ion secondary battery 100 and the characteristics are not impaired.

  Examples of the solvent include cyclic carbonates having an unsaturated bond such as vinylene carbonate (VC), fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC), 1,3- Flame retardant liquids such as sulfur-containing compounds such as propane sultone (PS) and phosphazene compounds can be mixed and used as a solvent.

<Electrolytic solution (electrolyte salt)>
Examples of the electrolyte salt contained in the electrolytic solution include a lithium salt, which dissociates in the electrolytic solution and supplies lithium ions. As the lithium salt, is not particularly limited, for _{example, LiPF 6, LiBF 4, LiAsF} 6, LiClO 4, LiB (C 6 H 5) 4, LiCH 3 SO 3, LiC (SO 2 CF 3) ₃ , LiN (CF ₃ SO ₂ ) ₂ (also referred to as LiTFSI), LiN (C ₂ F ₅ SO ₂ ) ₂ (also referred to as LiBETI), LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiN (CF ₃ SO ₂ ) (C ₂ F ₅ SO ₂ ), LiN (CF ₃ SO ₂ ) (C ₃ F ₇ SO ₂ ), LiN (CF ₃ SO _{2) (C 4 F 9 SO} 2), LiN (SO 2 F) 2 ( also known sometimes referred to as _{LiFSI), LiAlCl 4, LiSiF 6} , LiCl, LiC BO ₈ (aka, sometimes referred to as LiBOB), or the like can be mentioned LiBr, can be used those selected from any combination of one, or two or more thereof. In particular, LiPF ₆ can be suitably used because it can obtain high ionic conductivity.

<Method for producing lithium ion secondary battery>
The lithium ion secondary battery 100 of this embodiment can be manufactured as follows, for example.

  First, the negative electrode 20 can be manufactured as follows. For example, the above-described negative electrode active material, conductive additive, and binder are mixed and dispersed in a solvent such as N-methyl-2-pyrrolidone to prepare a paste-like negative electrode slurry. Next, the negative electrode active material layer 24 having a predetermined thickness is applied to one or both surfaces of the negative electrode current collector 22 such as a copper foil, and the solvent is dried in a drying furnace using, for example, a comma roll coater. I let you. In addition, when apply | coating to both surfaces of the above-mentioned negative electrode collector 22, it is desirable that the thickness of the coating film used as the negative electrode active material layer 24 is the same film thickness on both surfaces. The negative electrode 20 on which the negative electrode active material is formed is bonded to one or both sides of the negative electrode current collector 22 by using a roll press or the like to form the negative electrode active material layer 24 on the negative electrode current collector 22. In addition, the adhesion to the negative electrode current collector 22 is improved, and at the same time, the negative electrode sheet has a predetermined density.

  The negative electrode sheet described above is punched into a predetermined electrode size using a mold to form the negative electrode 20 for the lithium ion secondary battery of this embodiment. The area of the negative electrode 20 is preferably larger than the area of the positive electrode 10. This is because the area of the negative electrode 20 is made larger than the area of the opposing positive electrode 10 to prevent an internal short circuit due to lithium deposition.

  The negative electrode 20 is heat-treated at a temperature equal to or lower than the temperature at which the binder is thermally decomposed in vacuum or in an inert gas atmosphere, whereby the negative electrode active material layer 24 and the negative electrode current collector 22 The adhesion between the interface and the negative electrode active materials can be further enhanced. Further, if the surface of the negative electrode current collector 22 has a certain surface roughness, an anchor effect acts between the binder and the negative electrode current collector 22 by allowing the binder to enter the uneven portions of the surface, Furthermore, the adhesion is improved. Therefore, peeling of the negative electrode active material layer 24 from the negative electrode current collector 22 due to expansion / contraction of the volume of the active material during occlusion / release of lithium ions can be suppressed.

  The positive electrode 10 can be manufactured as follows. For example, the above-described positive electrode active material, conductive additive, and binder are mixed and dispersed in a solvent such as N-methyl-2-pyrrolidone to prepare a paste-like positive electrode slurry. Next, the positive electrode active material layer 14 having a predetermined thickness is applied to one surface or both surfaces of the positive electrode current collector 12 such as an aluminum foil, and the solvent is dried in a drying furnace. I let you. In addition, when apply | coating to both surfaces of the above-mentioned positive electrode collector 12, it is desirable that the thickness of the coating film used as the positive electrode active material layer 14 is the same film thickness on both surfaces. The positive electrode 10 on which the positive electrode active material layer 14 is formed is pressure-bonded to one side or both sides of the positive electrode current collector 12 by a roll press or the like, so that the positive electrode active material layer 14 and the positive electrode current collector 12 are pressed. As a result, the positive electrode sheet having a predetermined density is obtained.

  The positive electrode sheet described above is punched into a predetermined electrode size using a mold to form the positive electrode 10 for the lithium ion secondary battery of this embodiment. As described above, the area of the positive electrode 10 is preferably smaller than the area of the negative electrode 20. This is because, by making the area of the positive electrode 10 slightly smaller than the area of the opposing negative electrode 20, it is possible to easily prevent the occurrence of an internal short circuit due to lithium deposition.

  Further, similarly to the negative electrode 20, the above-described positive electrode 10 may be appropriately heat-treated depending on the binder used.

Subsequently, the electrode body 30 can be manufactured by laminating the negative electrode 20 and the positive electrode 10 via the separator 18. This is used as one electrode body, and an electrode body composed of an arbitrary number of layers can be manufactured by the same manufacturing method. As the separator 18 described above, in order to prevent the negative electrode 20 and the positive electrode 10 from being in direct contact with each other, a separator having a larger electrode size than both electrodes using a mold can be suitably used.

  Next, in the negative electrode 20 of the electrode body 30 described above, the negative electrode lead 62 made of nickel is attached to the protruding end portion of the copper foil where the negative electrode active material layer 24 is not provided. An aluminum positive electrode lead 60 is attached to the protruding end portion of the aluminum foil not provided with the active material layer 14 by an ultrasonic welding machine. Then, the electrode body 30 is inserted into an aluminum laminate film exterior body 50 and heat-sealed except for one peripheral portion to form a closed portion, and a predetermined amount of electrolytic solution is placed in the exterior body 50. After the injection, the remaining one portion is sealed by heat sealing while reducing the pressure, and the lithium ion secondary battery 100 can be manufactured.

  In the lithium ion secondary battery 100, when charged, for example, lithium ions are released from the positive electrode active material layer 14 and inserted in the negative electrode active material layer 24 through the electrolytic solution. Further, when discharging is performed, for example, lithium ions are released from the negative electrode active material layer 24 and are occluded in the positive electrode active material layer 14 through the electrolytic solution. Therefore, the above-described lithium ion secondary battery 100 can store electric capacity.

  Although the present invention has been described in detail with the above embodiments, the present invention is not limited to the above-described embodiments, and various modifications can be made. For example, in the above-described embodiment, a lithium ion secondary battery having a laminate film structure has been described. However, the present invention also applies to a lithium ion secondary battery having a structure in which a positive electrode and a negative electrode are folded or stacked. Can be applied. Furthermore, the present invention can also be suitably applied to lithium ion secondary batteries such as coin type, square type, and flat type.

  Hereinafter, based on the above-mentioned embodiment, the present invention will be described in further detail using the following examples and comparative examples. However, the present invention is not limited to the embodiments described below.

Example 1
[Production of polyamideimide]
610 mL of dimethylacetamide (hereinafter referred to as DMAc) as a polymerization solvent and 2,2′-bis (trifluoromethyl) as a diamine component in a reaction vessel (2000 ml glass four-necked flask) with a cooling tube and a nitrogen gas inlet Benzidine (hereinafter referred to as TFMB) 0.1 g (0.0003 mol), 4,4′-diaminodiphenyl ether (ODA) 60.01 g (0.297 mol), and triethylamine 30.36 g (0.3 mol) as a dehydrochlorinating agent And the solution was stirred to completely dissolve these diamine components. Then, 63.17 g (0.30 mol) of trimellitic anhydride monochloride (hereinafter referred to as TMAC) was gradually added so that the temperature of the polymerization reaction solution did not exceed 40 ° C. After the addition was completed, the polymerization solution was heated at 30 ° C. While maintaining the mixture, the mixture was stirred and reacted to obtain a polymerization solution.

  The obtained polymerization solution was re-precipitated in 1.7 L of distilled water and separated by filtration to obtain a polyamic acid powder. Furthermore, the obtained polyamic acid powder was subjected to imide ring closure by drying at 150 ° C. for 2 hours and then at 260 ° C. for 2 hours in a vacuum dryer to obtain polyamideimide powder.

  The aforementioned polyamideimide powder was dissolved in N-methyl-2-pyrrolidone solvent so as to be 20 wt% to obtain a polyamideimide varnish.

The above-mentioned polyamideimide varnish was heat-treated at 150 ° C. for 1 hour under vacuum drying.
-Methyl-2-pyrrolidone solvent was dried, and the obtained product was subjected to the above process using a Fourier transform infrared spectrophotometer (FT-IR), a pyrolysis gas chromatograph mass spectrometer, and a nuclear magnetic resonance method (NMR). The chemical structure of the polyamideimide was analyzed, and the weight average molecular weight (Mw) in terms of standard polystyrene of the polyamideimide was calculated using size exclusion chromatography (SEC).

In the analysis of polyamideimide by FT-IR, the absorption spectrum of the imide group is ν _C—N : 1380 cm ⁻¹ , ν _C═O : 1780 cm ⁻¹ , and the absorption spectrum of the amide group is ν _N—H : 1525cm ^-1, ν _C = O: that polyamideimide with 1590 cm ^-1, is synthesized: 1660 cm ^-1, the absorption spectrum of the benzene ^{_{ring, ν C = C: 1510cm -1}} , ν C = O confirmed.

<Preparation of negative electrode for lithium ion secondary battery>
As a negative electrode active material, 80 wt% of SiO (hereinafter referred to as SiO _x ) that has been disproportionated by heat treatment at 1000 ° C. under reduced pressure, 5 wt% of acetylene black as a conductive auxiliary agent, and further as a binder The polyamide-imide varnish synthesized according to Example 1 was adjusted so that the polyamide-imide was 15 wt% as a solid content, and added and mixed and dispersed. Finally, a solvent of N-methyl-2-pyrrolidone was added and adjusted to a predetermined viscosity to prepare a paste-like negative electrode slurry. Then, using a comma roll coater, the negative electrode active material layer was uniformly applied on both surfaces of the copper foil having a thickness of 10 μm so as to have a predetermined thickness. Next, the N-methyl-2-pyrrolidone solvent in the negative electrode active material was dried in an air atmosphere at 110 ° C. in a drying furnace. The negative electrode on which the negative electrode active material was formed was pressure-bonded to both surfaces of the negative electrode current collector by a roll press to obtain a negative electrode sheet having a predetermined density.

  The above negative electrode sheet is punched into an electrode size of 21 × 31 mm using an electrode mold, heated to 300 ° C. at a high temperature of 30 ° C./min in a heat treatment furnace, held for 1 hour, and then rapidly cooled to room temperature. Thus, a negative electrode for a lithium ion secondary battery according to Example 1 was produced. The above heat treatment was performed in a vacuum.

(Examples 2 to 10)
Except having changed the molar ratio of the diamine component to the value shown in Table 1, polyamic acid was polymerized in the same procedure as in Example 1, and imide ring-closing treatment was performed by heating to obtain a polyamideimide powder. Each of the obtained polyamideimide powders was dissolved in an N-methyl-2-pyrrolidone solvent so as to be 20 wt% to prepare a polyamideimide varnish. In addition, the physical property of each polyamideimide obtained in Examples 2 to 10 was evaluated in the same procedure as in Example 1.

  Furthermore, in the same procedure as in Example 1, negative electrodes for lithium ion secondary batteries according to Examples 2 to 10 were produced.

(Comparative Examples 1 and 2)
Polyamic acid is polymerized in the same procedure as in Example 1 except that the diamine component is ODA only or TFMB only, and the molar ratio is changed to the values shown in Table 1, and the imide ring-closing treatment is performed by heating. A powder was obtained. Each of the obtained polyamideimide powders was dissolved in an N-methyl-2-pyrrolidone solvent so as to be 20 wt% to prepare a polyamideimide varnish. In addition, also in the physical property of each polyamideimide obtained by the comparative example, it measured in the procedure similar to Example 1. FIG.

  Furthermore, in the same procedure as in Example 1, negative electrodes for lithium ion secondary batteries according to Comparative Examples 1 and 2 were produced.

(Examples 11 to 17)
Polyamic acid powder was prepared in the same procedure as in Example 3, and the polyamideimide powder adjusted to the weight average molecular weight (Mw) shown in Table 2 was changed by changing the drying temperature and drying time in imide ring closure. Obtained. In addition, each obtained polyamideimide powder was dissolved in N-methyl-2-pyrrolidone solvent so that it might become 20 wt%, and the polyamideimide varnish was produced. Furthermore, each polyamideimide varnish described above was heat-treated at 150 ° C. under vacuum drying, and the resulting product was analyzed for weight average molecular weight (Mw) by size exclusion chromatography (SEC).

  Furthermore, in the same procedure as in Example 1, negative electrodes for lithium ion secondary batteries according to Examples 11 to 17 were produced.

(Examples 18 to 23)
In the production of the negative electrode for a lithium ion secondary battery according to Example 3, the procedure similar to that of Example 1 was performed except that the amount of polyamideimide contained in the negative electrode active material layer was changed to the amount shown in Table 3. The negative electrode for each lithium ion secondary battery which concerns on Examples 18-23 was produced.

(Examples 24-26)
In the production of the lithium ion secondary batteries according to Examples 3, 5, and 8, the active material contained in the negative electrode active material layer was changed to a material in which SiO _x and graphite were mixed at a weight ratio of 1: 9. Except for the above, the negative electrodes for lithium ion secondary batteries according to Examples 24 to 26 were produced in the same procedure as in Example 1.

(Comparative Examples 3 and 4)
In the production of lithium ion secondary batteries according to Comparative Examples 1 and 2, except that the active material contained in the negative electrode active material layer was changed to a mixture of SiO _x and graphite in a weight ratio of 1: 9. The negative electrode for a lithium ion secondary battery according to Comparative Examples 3 and 4 was prepared in the same procedure as Comparative Example 1.

(Examples 27 to 29)
In the production of the lithium ion secondary batteries according to Examples 3, 5, and 8, the active material contained in the negative electrode active material layer was changed to Si, and the same procedure as in Example 1 was followed. A negative electrode for a lithium ion secondary battery according to No. 29 was produced.

(Comparative Examples 5 and 6)
In the production of the lithium ion secondary batteries according to Comparative Examples 1 and 2, the same procedure as in Comparative Example 1 was applied to Comparative Examples 5 and 6 except that Si was used as the active material contained in the negative electrode active material layer. Such a negative electrode for a lithium ion secondary battery was produced.

(Examples 30 to 32)
In the production of the lithium ion secondary batteries according to Examples 3, 5, and 8, except that Si and SiO _x were mixed at a weight ratio of 1: 9 as the active material contained in the negative electrode active material layer. Produced the negative electrodes for lithium ion secondary batteries according to Examples 30 to 32 in the same procedure as in Example 1.

(Comparative Examples 7 and 8)
In the production of lithium ion secondary batteries according to Comparative Examples 1 and 2, as a negative electrode active material contained in the negative electrode, except that Si and SiO _x were mixed in a weight ratio of 1: 9, a comparison was made. In the same procedure as in Example 1, negative electrodes for lithium ion secondary batteries according to Comparative Examples 7 and 8 were produced.

(Examples 33 to 35)
In the production of lithium ion secondary batteries according to Examples 3, 5, and 8, except that Si and graphite were mixed in a weight ratio of 1: 9 as an active material contained in the negative electrode active material layer. The negative electrodes for lithium ion secondary batteries according to Examples 33 to 35 were produced in the same procedure as in Example 1.

(Comparative Examples 9 and 10)
Comparative Example 1 except that in the production of lithium ion secondary batteries according to Comparative Examples 1 and 2, the negative electrode active material contained in the negative electrode was changed to a mixture of Si and graphite in a weight ratio of 1: 9. 1 was used to produce a negative electrode for a lithium ion secondary battery according to Comparative Examples 9 and 10.

<Preparation of positive electrode for lithium ion secondary battery>
96 wt% of lithium cobaltate (LiCoO ₂ ) as a positive electrode active material, 2 wt% of ketjen black as a conductive additive, 2 wt% of PVDF as a binder, and a solvent of N-methyl-2-pyrrolidone are mixed and dispersed. Thus, a paste-like positive electrode slurry was prepared. Then, using a comma roll coater, the positive electrode active material layer was uniformly applied so that the positive electrode slurry had a predetermined thickness on both surfaces of an aluminum foil having a thickness of 20 μm. Next, the N-methyl-2-pyrrolidone solvent in the positive electrode active material was dried in an air atmosphere at 110 ° C. in a drying furnace. In addition, the thickness of the coating film of the positive electrode active material layer apply | coated to both surfaces of the above-mentioned aluminum foil was adjusted to the substantially same film thickness. The positive electrode on which the positive electrode active material was formed was pressure-bonded to both surfaces of the positive electrode current collector by a roll press to obtain a positive electrode sheet having a predetermined density.

  The positive electrode sheet described above was punched into an electrode size of 20 × 30 mm using an electrode mold to produce a positive electrode for a lithium ion secondary battery.

<Production of lithium ion secondary battery>
The above-prepared negative electrodes of Examples 1 to 22 and Comparative Examples 1 to 9 and the positive electrode were laminated via a polyethylene separator having a thickness of 16 μm and a size of 22 × 33 mm to prepare an electrode body. This was used as one electrode body, and an electrode body composed of four layers was produced by the same production method. In addition, since the above-mentioned negative electrode and positive electrode are provided with each active material layer on both surfaces, they are composed of three negative electrodes, two positive electrodes, and four separators. Furthermore, in the negative electrode of the electrode body described above, a negative electrode lead made of nickel is attached to the protruding end portion of the copper foil not provided with the negative electrode active material layer, while the positive electrode active material layer is not provided in the positive electrode of the electrode body. An aluminum positive electrode lead was attached to the protruding end portion of the aluminum foil by an ultrasonic fusion machine. Then, this electrode body was fused to an aluminum laminate film for an exterior body, and the above-mentioned electrode body was inserted into the exterior body by folding the above-mentioned laminate film. A closed portion is formed by heat-sealing except for one side around the outer package body, and 1 mol concentration of LiPF as a lithium salt in a solvent in which EC / DEC is blended at a ratio of 3: 7 from this opening. _The electrolyte solution to which ₆ was added was injected. And the opening part of the above-mentioned exterior body was sealed by heat sealing, reducing pressure with a vacuum sealing machine, and the lithium ion secondary battery which concerns on an Example and a comparative example was produced.

<Evaluation>
The lithium ion secondary batteries produced in the examples and comparative examples were evaluated for the following battery characteristics.

(Charge / discharge cycle characteristics)
The lithium ion secondary batteries produced in Examples 1 to 35 and Comparative Examples 1 to 10 were repeatedly charged and discharged under the following charge / discharge test conditions, and the charge / discharge cycle characteristics were evaluated. The charge / discharge cycle test conditions were a constant current and constant voltage charge (CC-CV charge) at a constant current of 0.5 C and a charge capacity measured at a constant current of 0.5 C at a temperature of 25 ° C. Thereafter, the battery was discharged at a constant current (CC discharge) at a constant current of 1.0 C until the battery voltage became 2.5 V, and the discharge capacity was measured. This was defined as one cycle, and the charge / discharge cycle characteristics were evaluated by the discharge capacity retention rate after repeating this for 300 cycles.

  Note that 0.5 C is a current value at which charging and discharging are completed in two hours when a battery cell having a capacity of a nominal capacity value is subjected to constant current charging or constant current discharging. In the case of 1C, it means a current value at which charging and discharging are completed in one hour.

The discharge capacity maintenance rate after 300 cycles is defined by the following calculation formula.
Discharge capacity maintenance rate after 300 cycles (%) = (discharge capacity after 300 cycles / discharge capacity after 1 cycle) × 100

(Battery cell thickness expansion)
The expansion rate of the cell thickness was evaluated by measuring the cell thickness before charging / discharging of each lithium ion secondary battery produced in Examples and Comparative Examples and the thickness of the cell at the end of 300 cycles. The expansion coefficient was defined by the following calculation formula.
Expansion rate (%) = (cell thickness after 300 cycles (mm) −cell thickness before charge / discharge (mm)) / cell thickness before charge / discharge (mm) × 100

(result)
Table 1 shows the results of the battery characteristics of the lithium ion secondary batteries according to Examples 1 to 10 and Comparative Examples 1 and 2 in which the molar ratios of a and b in the above formulas (1) and (2) were variously prepared. Show. In addition, about the charging / discharging cycling characteristics and the thickness expansion coefficient of a battery cell, the measurement result of the comparative example 1 is set to 100%, and it shows as a relative ratio with respect to the measurement result of the comparative example 1.

  From the result of Table 1, in the lithium ion secondary battery using the polyamideimide having the repeating unit structure of the formula (1) and the formula (2) as the binder for the negative electrode, the expansion coefficient of the battery cell is lowered, and the charge / discharge cycle characteristics It turned out to be excellent. On the other hand, it was found that when a polyamideimide having no repeating unit structure of the formulas (1) and (2) was used for the negative electrode binder, the battery cell had a high expansion coefficient and the charge / discharge cycle characteristics were lowered. In particular, it has been found that a remarkable effect is obtained when the molar ratio a in the formula (1) is 0.1 to 70%.

The lithium ion secondary batteries of Example 3 and Comparative Example 1 in which 10 charge / discharge cycles were completed were decomposed in a dry room, the negative electrode was taken out and washed with DMC (dimethyl carbonate), and then the negative electrode SiO _x active material. FIG. 2 and FIG. 3 show the results of EDX spectra when the surface was subjected to point analysis with a SEM-EDX (energy dispersive X-ray spectroscopy) apparatus at a magnification of 20,000 times. Further, examples not subjected to a charge and discharge 3, and SEM-EDX result of Spectrum of SiO _x active material of each negative electrode of Comparative Example 1 shown in FIGS.

In the SiO _x active material after 10 cycles of the lithium ion secondary battery produced in Example 3, fluorine (F) was detected in addition to silicon (Si), oxygen (O), and carbon (C). On the other hand, in the SiO _x active material after 10 cycles in Comparative Example 1, no fluorine was detected. Also, fluorine was not detected in the SiO _x active material of Example 3 and Comparative Example 1 that were not charged / discharged. Therefore, in the negative electrode using the polyamideimide according to the present invention, it was confirmed that a solid electrolyte film (SEI film) containing fluorine ions was formed on the surface of the SiO _x active material during the charge / discharge process.

Table 2 shows lithium ion secondary batteries when the negative electrodes for lithium ion secondary batteries according to Example 3 and Examples 11 to 17 using polyamideimides having different weight average molecular weights are used in the polyamideimide in the present invention. The results of the expansion coefficient and charge / discharge cycle characteristics are shown. As in Table 1, the charge / discharge cycle characteristics and the battery cell thickness expansion coefficient are shown as relative ratios to the measurement results of Example 11 with the measurement results of Example 11 being 100%.

  From Table 2, in the polyamideimide of this invention, when the weight average molecular weight (Mw) became the range of 4,000-100,000, it was confirmed that the charging / discharging cycle of a lithium ion secondary battery is excellent. In particular, it was found that when the weight average molecular weight (Mw) is in the range of 5,000 to 80,000, a more excellent charge / discharge cycle can be obtained.

Table 3 shows the results of studying the relationship between the content of polyamideimide in the negative electrode active material layer and the battery characteristics in the lithium ion secondary battery according to the present invention.

  From Table 3, in the negative electrode for a lithium ion secondary battery, when the content of the polyamideimide according to the present example contained in the negative electrode active material layer is in the range of 5 to 40 wt%, the cell expansion coefficient and the charge In addition to the discharge cycle characteristics, it was confirmed that the rate characteristics were excellent.

Table 4 shows the results of the battery characteristics of the lithium ion secondary batteries according to Examples 24-26 and Comparative Examples 3-4 when SiO _x and graphite are combined as the negative electrode active material. As in Table 1, the charge / discharge cycle characteristics and the battery cell thickness expansion coefficient are shown as relative ratios to the measurement results of Comparative Example 3, with the measurement results of Comparative Example 3 being 100%.

Table 5 shows the results of the battery characteristics of the lithium ion secondary batteries according to Examples 27 to 29 and Comparative Examples 5 to 6 when Si is used as the negative electrode active material. As in Table 1, the charge / discharge cycle characteristics and the battery cell thickness expansion coefficient are shown as relative ratios to the measurement results of Comparative Example 5, with the measurement results of Comparative Example 5 being 100%.

Table 6 shows the results of the battery characteristics of the lithium ion secondary batteries according to Examples 30 to 32 and Comparative Examples 7 to 8 when Si and SiO _x are combined as the negative electrode active material. As in Table 1, the charge / discharge cycle characteristics and the battery cell thickness expansion coefficient are shown as relative ratios to the measurement results of Comparative Example 7, with the measurement results of Comparative Example 7 being 100%.

Table 7 shows the results of the battery characteristics of the lithium ion secondary batteries according to Examples 33 to 35 and Comparative Examples 9 to 10 when Si and graphite are combined as the negative electrode active material. As in Table 1, the charge / discharge cycle characteristics and the battery cell thickness expansion coefficient are shown as relative ratios to the measurement result of Comparative Example 9, with the measurement result of Comparative Example 9 being 100%.

  Even when various negative electrode active materials are used, when the polyamide imide of this example is used as a negative electrode binder, the expansion rate of the battery cell and the charge / discharge are better than when the polyamide imide of the comparative example is used. It was confirmed that cycle characteristics were obtained.

DESCRIPTION OF SYMBOLS 100 ... Lithium ion secondary battery, 10 ... Positive electrode (synonymous: Positive electrode for lithium ion secondary batteries), 12 ... Positive electrode collector, 14 ... Positive electrode active material layer, 60 ... Positive electrode Lead,
20 ... negative electrode (synonymous: negative electrode for lithium ion secondary battery), 22 ... negative electrode current collector, 24 ... negative electrode active material layer, 62 ... negative electrode lead, 18 ... separator, 30 ..Electrode body, 50 ... exterior body

Claims (7)

The negative electrode binder for lithium ion secondary batteries characterized by including the polyamideimide which has a repeating structural unit of following formula (1) and formula (2). However, although the value of a and b in a formula is arbitrary, the copolymerization ratio of each structural unit is shown by a molar ratio.

Ar in Formula (2) represents an aryl group having an aromatic ring, and represents any one of Formula (3), Formula (4), and Formula (5). R _{1 to} R ₄ , R ₆ and R ₇ are each independently a hydrogen atom, hydroxyl group, alkyl group, methyl group, halogen, substituted alkyl group, alkoxy group, aryl group, substituted aryl group, nitro group, cyano group And a substituent selected from the group consisting of a thiol group, a methyl halide group and the like. R ₅ in the formula (4) is —O—, —S—, —C (═O) —, —SO ₂ —, —C (═O) O—, — (CH ₂ ) _n —, _{-C (CF 3) 2 -,} - C (CH 3) 2 - shows a. Note that _{n in} — (CH ₂ ) _n — is an integer of 0 or more and 5 or less. )

  2. The lithium ion secondary battery according to claim 1, wherein the molar ratio of a is 0.1 to 70 mol%, and the molar ratio of b is 30 to 99.9 mol%. Negative electrode binder.   The negative electrode binder for a lithium ion secondary battery according to claim 1 or 2, wherein the weight average molecular weight (Mw) is 4,000 to 100,000.   A negative electrode for a lithium ion secondary battery comprising a current collector and a negative electrode active material layer formed on the current collector, wherein the negative electrode active material layer comprises a negative electrode active material, a conductive additive, and 1 to 3 and a negative electrode binder for a lithium ion secondary battery according to any one of 1 to 3, wherein the negative electrode active material contains at least one of silicon (Si) and a silicon compound. Negative electrode for ion secondary battery.   A negative electrode for a lithium ion secondary battery comprising a current collector and a negative electrode active material layer formed on the current collector, wherein the negative electrode active material layer comprises a negative electrode active material, a conductive additive, and The negative electrode binder for lithium ion secondary batteries according to any one of 1 to 3 and a binder other than that are included, and at least one of silicon (Si) and a silicon compound is included as the negative electrode active material. The negative electrode for lithium ion secondary batteries characterized by the above-mentioned.   6. The negative electrode active material layer, wherein the negative electrode binder for a lithium ion secondary battery is contained in a range of at least 5.0 wt% or more and 40 wt% or less. Negative electrode for lithium ion secondary battery.   It is a lithium ion secondary battery provided with the separator arrange | positioned between a negative electrode and a positive electrode, a negative electrode, and a positive electrode, and electrolyte solution, Comprising: The said negative electrode is any one of Claims 4-6. A lithium ion secondary battery, which is a negative electrode for a lithium ion secondary battery.

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