JP6314751B2 - Binder for lithium ion secondary battery, negative electrode for lithium ion secondary battery and lithium ion secondary battery - Google Patents

Description

  The present invention relates to a binder for a lithium ion secondary battery, a negative electrode for a lithium ion secondary battery, and a lithium ion secondary battery used for a high capacity negative electrode using an alloy-based negative electrode active material.

  In recent years, lithium ion secondary batteries have been widely used in portable electronic devices such as mobile phones and notebook PCs because of their high energy density. Taking a mobile phone as an example, in addition to a telephone call function and mail transmission / reception, functions introduced into an application have been remarkably evolving and increasing along with the increase in functions such as a Web browser and a music playback function.

  The lithium ion secondary battery is mainly composed of a positive electrode, a negative electrode, a separator that insulates the positive electrode from the negative electrode, and an electrolyte solution that allows lithium ions to move between the positive electrode and the negative electrode. The negative electrode is formed by applying various active material layers to both or one side of a current collector made of metal foil. For example, a positive electrode is used in which an active material layer containing lithium cobalt oxide or the like is applied to a current collector made of aluminum foil, while an active material layer containing graphite or the like is made of copper foil as the negative electrode. What was apply | coated to the electrical power collector is used.

  In recent years, graphite (theoretical capacity: 372 mAh / g) has been used as a negative electrode active material as a negative electrode of a lithium ion secondary battery that is commonly used. As the process progresses, there is an urgent need to respond to further increases in capacity.

  In particular, high-capacity negative electrode active materials include lithium metal and alloy-based negative electrode materials such as silicon (Si), silicon compounds (eg, SiO), and tin (Sn) that can be alloyed with lithium. In particular, silicon has a high theoretical capacity of 4199 mAh / g.

  However, when silicon or a silicon compound is used as the negative electrode active material, the expansion and contraction of the electrode accompanying the insertion and desorption of lithium ions due to charge / discharge is significantly larger than when graphite is used as the negative electrode active material. Therefore, in a lithium ion secondary battery using an alloy-based negative electrode material such as silicon as a negative electrode active material, the negative electrode active material layer expands and contracts due to repeated charging and discharging, so that a large stress load is applied to the negative electrode active material layer. work.

  As a result, there are problems such as cracks generated in the negative electrode active material layer formed on the current collector and peeling between the negative electrode active material layer and the current collector. As a result, the conductive paths between the negative electrode active material and the negative electrode active material and between the negative electrode active material and the current collector are blocked, and as a result, the cycle characteristics of the lithium ion secondary battery are degraded.

  With respect to the negative electrode exhibiting such a large volume expansion, Patent Document 1 describes that the cycle characteristics are improved by using polyamideimide having specific tensile strength, tensile elongation, and elastic modulus as the negative electrode binder.

  However, even when the polyamideimide of Patent Document 1 is used as the negative electrode binder, it was found that the volume expansion of the negative electrode active material layer was not sufficiently suppressed, and good cycle characteristics could not be obtained.

JP 2011-48969 A

  The present invention has been made in order to solve the above-described conventional problems, and suppresses volume expansion of the negative electrode active material layer accompanying lithium insertion and desorption from the negative electrode of a lithium ion secondary battery, and has excellent cycle characteristics. It aims at providing the binder for lithium ion secondary batteries, the negative electrode for lithium ion secondary batteries, and a lithium ion secondary battery using the same.

ただし、式（１）内のＸは、以下、式（２−１）または式（２−２）を示す。

（ただし、Ｒ_１、Ｒ_２は水素、アルキル基からなる群より選ばれる置換基を示す。また、式（２−２）内のＹは、−Ｏ−、−Ｓ−、−Ｃ（＝Ｏ）−、−ＳＯ_２−、−Ｃ（＝Ｏ）Ｏ−、−（ＣＨ_２）_ｎ−、−Ｃ（ＣＦ_３）_２−、−Ｃ（ＣＨ_３）_２−を示す。なお、−（ＣＨ_２）_ｎ−のｎは、０以上５以下の整数である。）

（ただし、上記ａ及びｂは、ｍｏｌ％を表し、ａ＋ｂ＝１００である） In order to solve the above problems, a binder for a lithium ion secondary battery of the present invention (hereinafter sometimes referred to as a negative electrode binder) includes a polyamideimide having repeating units of the following formulas (1) and (3). It is characterized by

However, X in Formula (1) represents Formula (2-1) or Formula (2-2) below.

(However, R ₁ and R ₂ represent a substituent selected from the group consisting of hydrogen and an alkyl group. Y in the formula (2-2) is —O—, —S—, —C (═O). _{) -, - SO 2 -,} - C (= O) O -, - (CH 2) n -, - C (CF 3) 2 -, - C (CH 3) 2 - shows a Note, -. (CH ₂ ) _n in n- is an integer of 0 or more and 5 or less.)

(However, a and b represent mol%, and a + b = 100)

  By using the negative electrode binder of the present invention for a negative electrode for a lithium ion secondary battery (hereinafter sometimes referred to as “negative electrode”), the expansion and contraction of the negative electrode active material layer caused by charging / discharging, that is, volume expansion is suppressed. be able to. Although the detailed cause has not been clarified, it is presumed that the cycle characteristics as a lithium ion secondary battery have been improved by the following phenomenon.

The negative electrode active material in the negative electrode active material layer is at least partially covered with the negative electrode binder of the present invention. Polyamideimide, which is a negative electrode binder of the present invention, has a trifluoromethyl group (—CF ₃ group) in its structure. For this reason, the —CF ₃ group acts as a water repellency, so It is considered that excessive wettability with the liquid is suppressed and the reaction with lithium ions is alleviated. This presumes that the rapid deterioration of the negative electrode active material is alleviated.

  In the negative electrode binder of the present invention, the ratio of a in the formula (1) is preferably 50 to 99 mol%, and the ratio of b in the formula (3) is preferably 50 to 1 mol%. In addition, when the ratio of a and b is added, it will be set as the relationship of 100 mol%.

  In the case where the ratio of a and b in formula (1) and formula (3) is used as a binder, the volume expansion of the negative electrode active material layer due to charge / discharge is suitably suppressed, Cycle characteristics as an ion secondary battery are improved.

Moreover, in the infrared absorption spectrum of the negative electrode binder of the present invention, 1780 cm ⁻¹ / 1510 cm ⁻¹ (cyclic imide bond amount) with respect to the infrared absorption spectrum intensity ratio of 1360 cm ⁻¹ / 1510 cm ⁻¹ (total imide bond amount). ) Is preferably 0.21 or more.

  When the infrared absorption spectrum intensity ratio attributed to the cyclic imide bond amount of the polyamideimide as the negative electrode binder is 0.21 or more, the lithium ion secondary Cycle characteristics when used as a battery are improved.

  ADVANTAGE OF THE INVENTION According to this invention, the volume expansion of a negative electrode active material layer can be prevented, and the negative electrode for lithium ion secondary batteries which can improve cycling characteristics, and a lithium ion secondary battery can be provided.

It is sectional drawing showing the structure of a lithium ion secondary battery.

  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 separator 18 is charged and discharged. The electrolyte solution, which is a lithium ion transfer medium between the positive and negative electrodes, is held.

  The positive electrode 10 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. Yes.

  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. The laminate film is configured as a three-layer structure in which, for example, polypropylene, aluminum, and nylon are laminated in this order.

ただし、式（１）内のＸは、以下、式（２−１）または式（２−２）を示す。

（ただし、Ｒ_１、Ｒ_２は水素、アルキル基からなる群より選ばれる置換基を示す。また、式（２−２）内のＹは、−Ｏ−、−Ｓ−、−Ｃ（＝Ｏ）−、−ＳＯ_２−、−Ｃ（＝Ｏ）Ｏ−、−（ＣＨ_２）_ｎ−、−Ｃ（ＣＦ_３）_２−、−Ｃ（ＣＨ_３）_２−を示す。なお、−（ＣＨ_２）_ｎ−のｎは、０以上５以下の整数である。）

（ただし、上記ａ及びｂは、ｍｏｌ％を表し、ａ＋ｂ＝１００である） <Binder for lithium ion secondary battery>
The binder for a lithium ion secondary battery according to the present invention used for a negative electrode for a lithium ion secondary battery (hereinafter sometimes referred to as a negative electrode binder) is a repeating unit of the following formula (1) and the following formula (3). Including polyamideimide.

However, X in Formula (1) represents Formula (2-1) or Formula (2-2) below.

(However, R ₁ and R ₂ represent a substituent selected from the group consisting of hydrogen and an alkyl group. Y in the formula (2-2) is —O—, —S—, —C (═O). _{) -, - SO 2 -,} - C (= O) O -, - (CH 2) n -, - C (CF 3) 2 -, - C (CH 3) 2 - shows a Note, -. (CH ₂ ) _n in n- is an integer of 0 or more and 5 or less.)

(However, a and b represent mol%, and a + b = 100)

  By using the negative electrode binder in the negative electrode 20 for a lithium ion secondary battery, it is possible to suppress the expansion and contraction of the negative electrode active material layer 24 during charging and discharging. The negative electrode binder has a structure composed of the polyamideimide of the above formula (1) and the above formula (3), and thus becomes a polyamideimide having a trifluoromethyl group in a part of the molecule.

  In the negative electrode 20 for a lithium ion secondary battery composed of the binder, deterioration of the negative electrode active material during charging / discharging is suppressed, and as a result, volume expansion of the negative electrode active material layer 24 is suppressed. For the above reasons, when the negative electrode 20 for a lithium ion secondary battery is used in the lithium ion secondary battery 100, excellent cycle characteristics are exhibited.

  Further, the ratio of a in formula (1) of the negative electrode binder is preferably 50 to 99 mol%, and the ratio of b in formula (3) is preferably 50 to 1 mol%.

  The polyamide imides prepared so that the ratios of a and b in the formula (1) and the formula (3) are 50 to 99 mol% and 50 to 1 mol%, respectively, are used as the negative electrode binder. The expansion and contraction of the material layer 24 is suppressed, and as a result, the problem of deterioration of the negative electrode active material is improved, whereby excellent cycle characteristics can be exhibited.

Further in the infrared absorption spectrum of the negative electrode ^binder, to infrared absorption spectrum intensity ratio of 1360cm ^-1 / 1510cm -1 (total imide bond ^amount), infrared 1780cm ^-1 / 1510cm -1 (cyclic imide bond amount) The absorption spectrum intensity ratio is preferably 0.21 or more.

In the infrared absorption spectrum of the negative electrode binder of the present ^invention, with respect to the infrared absorption spectrum intensity ratio of 1360 cm -1 / 1510 cm ^-1 (total imide bond ^amount), 1780 cm -1 / 1510 cm ^-1 of the (cyclic imide bond amount) By setting the infrared absorption spectrum intensity ratio to 0.21 or more, the negative electrode binder having a high degree of polymerization (high molecular weight) can be obtained, and the volume expansion of the negative electrode active material layer can be suppressed. Furthermore, the adhesion between the negative electrode current collector 22 and the negative electrode active material layer 24 and / or the negative electrode active materials can be strongly maintained.

  The degree of polymerization of the 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 desirably a temperature at which the polyamideimide in the present invention is not decomposed. However, when the polyamideimide is used as a lithium ion secondary battery, the battery characteristics are not impaired. For example, a temperature at which a part of the polyamideimide is decomposed may be used.

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

<Negative electrode active material>
As the negative electrode active material of the negative electrode 20 for a lithium ion secondary battery in this embodiment, a negative electrode active material that can be alloyed with lithium is used. In particular, silicon having a high capacity is desirable. Silicon may be contained alone, in an alloy, or may be contained in a compound, and particles may be formed in a state where two or more of them are mixed. _{Specifically,} M y Si (M is at least one element other than Si, y is greater than zero) as the silicon compound represented by the chemical formula, for example _{SiB 4, SiB 6, Mg 2} Si _{, Ni 2 Si, TiSi 2,} MoSi 2, NiSi 2, CaSi 2, CrSi 2, Cu 5 Si, FeSi 2, MnSi 2, NbSi 2, TaSi 2, VSi 2, WSi 2, ZnSi 2 , and the like. Examples of the oxide compound, nitrogen compound, or carbonized compound containing silicon include SiC, Si ₃ N ₄ , Si ₂ N ₂ O, SiO _x (0 <x ≦ 2), LiSiO, and the like. Furthermore, as an alloy of silicon, for example, at least one selected from the group consisting of tin, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony and chromium in addition to silicon The thing containing is mentioned.

In addition, examples of the negative electrode active material other than silicon include metallic tin. Metal tin may be contained alone, in an alloy, in a compound, or in a state in which two or more of them are mixed. Specifically, as a tin compound represented by a chemical formula of N _w Sn (N is one or more elements other than Sn and w is a numerical value of 0 or more), for example, Mg ₂ Sn can be given. Examples of the tin-containing oxide compound, nitrogenated compound, or carbonized compound include SnO _z (0 <z ≦ 2) and LiSnO. Furthermore, as an alloy of tin, for example, at least one selected from the group consisting of silicon, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony and chromium in addition to tin The thing containing is mentioned.

  Further, the negative electrode active material is not limited to the above-mentioned materials, and any other negative electrode for lithium ion secondary batteries is not particularly limited as long as it is a material capable of electrochemically inserting and extracting lithium ions. In addition, when a negative electrode active material having a large expansion and contraction is used, a more suitable effect can be exhibited.

<Polyamideimide binder>
The binder for a lithium ion secondary battery described above aims to maintain the form of the negative electrode active material layer 24 by binding members constituting the negative electrode active material layer 24, and the negative electrode active material layer 24 and the negative electrode current collector 22. Is added for the purpose of maintaining the electrode structure of the negative electrode 20 for a lithium ion secondary battery. As the binder used for the negative electrode 20 for a lithium ion secondary battery, the polyamideimide described above can be used. As the polyamideimide, the above-mentioned aromatic polyamideimide is preferable from the viewpoints of solubility in a solvent, workability, cost, etc. in addition to strength, elongation, elasticity, and electrolytic solution resistance.

  Examples of the method for producing the polyamideimide constituted by the above formulas (1) and (3) include an isocyanate method produced from an acid component and an isocyanate component, or a diamine method (acid chloride method) produced from an acid chloride and an amine. However, the isocyanate method is preferred from the viewpoint of production cost.

  When synthesizing polyamideimide by the isocyanate method, trimellitic anhydride contained in the formula (1) and the formula (3) is an essential component as an acid component. A part thereof can be replaced with another polybasic acid or its anhydride as long as it is not impaired. For example, tetracarboxylic acids such as pyromellitic acid, biphenyl tetracarboxylic acid, biphenyl sulfone tetracarboxylic acid, benzophenone tetracarboxylic acid, biphenyl ether tetracarboxylic acid, ethylene glycol bis trimellitate, propylene glycol bis trimellitate and anhydrides thereof, Aliphatic dicarboxylic acids such as oxalic acid, adipic acid, malonic acid, sebacic acid, azelaic acid, dodecanedicarboxylic acid, dicarboxypolybutadiene, dicarboxypoly (acrylonitrile-butadiene), dicarboxypoly (styrene-butadiene), 1,4 Cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 4,4′-dicyclohexylmethanedicarboxylic acid, dimer acid and other alicyclic dicarboxylic acids, terephthalic acid Isophthalic acid, diphenyl sulfone dicarboxylic acid, diphenyl ether dicarboxylic acid, aromatic dicarboxylic acids such as naphthalene dicarboxylic acid, trimesic acid, and trifunctional carboxylic acids such as cyclohexane tricarboxylic acid. Of these, trimellitic anhydride is most preferred, followed by benzophenone tetracarboxylic anhydride, biphenyltetracarboxylic anhydride, pyromellitic acid, and the like.

  When the polyamideimide is synthesized by the isocyanate method, the diisocyanate corresponding to the formula (1) and the formula (3) is an essential component. For example, the diisocyanate components listed below can be used. p-phenylene diisocyanate, m-phenylene diisocyanate, 4,4′-diphenylmethane diisocyanate, 4,4′-diphenyl ether diisocyanate, diphenylcarbonyl-3,3′-diisocyanate, 4-isocyanatobenzoic acid 4-isocyanatophenyl, 4 , 4′-diphenylsulfone diisocyanate, diphenyl sulfide-2,4′-diisocyanate, xylylene diisocyanate, tolylene diisocyanate, tolidine diisocyanate, 2,2-bis (4-isocyanatophenyl) hexafluoropropane, 1-isocyanate Aromatic diisocyanates such as -4- [1- (4-isocyanatophenyl) -1-methylethyl] benzene and the like, and among these, p-phenylene diisocyanate. , M-phenylene diisocyanate, 4,4′-diphenylmethane diisocyanate, 4,4′-diphenyl ether diisocyanate, xylylene diisocyanate, tolylene diisocyanate, tolidine diisocyanate and the like, more preferably p-phenylene diisocyanate, m- Phenylene diisocyanate, 4,4′-diphenylmethane diisocyanate.

  In addition, when manufacturing a polyamideimide by the diamine method, the carboxylic acid of the said acid component can be changed into a carboxylic acid chloride, and it can manufacture by changing an isocyanate component into a corresponding amine.

  Polyamideimide can be easily synthesized by stirring in a polar solvent while heating to 60 to 200 ° C. Examples of the solvent used for the synthesis by the isocyanate method include N-methyl-2-pyrrolidone, N, N′-dimethylformamide, N, N′-dimethylacetamide, 1,3-dimethyl-2-imidazolidinone, tetra Examples include methylurea, sulfolane, dimethylsulfoxide, γ-butyrolactone, cyclohexanone, and cyclopentanone. Among these, N-methyl-2-pyrrolidone is preferable. It is also possible to replace some of these solvents with hydrocarbon organic solvents such as toluene and xylene, ether organic solvents such as diglyme, triglyme and tetrahydrofuran, and ketone organic solvents such as methyl ethyl ketone and methyl isobutyl ketone. is there.

  In addition, the molecular weight of the polyamideimide can be easily prepared by adjusting the reaction temperature and reaction time during the synthesis. In the polyamideimide according to the present embodiment, the weight average molecular weight (Mw) is preferably 4,000 to 100,000, and more preferably 5,000 to 60,000. By using the polyamideimide according to this embodiment having a weight average molecular weight of 4,000 to 100,000 as a negative electrode binder, the binding properties of the active material and the active material and the active material and the current collector can be strongly retained. In addition, the conductive path between the negative electrode active materials is excellent, and the charge / discharge cycle characteristics are good. Furthermore, cycling characteristics are more excellent by using the polyamideimide which concerns on this embodiment whose weight average molecular weight becomes 5,000-60,000 as a negative electrode binder. Although details about the cause have not been elucidated, when the weight average molecular weight is 5,000 to 60,000, a very small amount of the polyamideimide according to the present embodiment is decomposed and / or electrolytic solution in the charge and discharge process. It is believed that the cycle characteristics are further improved by acting on a part of a suitable solid electrolyte interface (SEI) film containing fluorine on the negative electrode active material surface.

  In addition, the said weight average molecular weight can calculate the weight average molecular weight (Mw) of standard polyamide conversion of the said polyamideimide using size exclusion chromatography (SEC).

  In synthesizing the polyamideimide, a catalyst may be used as necessary to accelerate the reaction. For example, triethylamine, diethylenetriamine, triethylenediamine, 1,8-diazabicyclo [5.4.0] -7-undecene. Amines such as sodium fluoride, potassium fluoride and cesium fluoride, organic bases such as sodium methoxide and sodium ethoxide, and inorganic bases such as sodium hydroxide and potassium hydroxide. The amount of the catalyst is preferably 0 mol% or more and 10 mol% or less, and more preferably 0.1 mol% or more and 5 mol% or less with respect to the acid component.

  In addition, as a binder used for the said negative electrode 20, you may use together the polyamideimide in this invention, and another binder in combination with at least 1 or more. Examples of other binders include polyamide imide and polyimide, and examples of polyamide imide include various known polyamide imides. More specifically, for example, commercially available products such as “HPC series (trade name)” manufactured by Hitachi Chemical Co., Ltd. and “Viromax (trade name)” manufactured by Toyobo Co., Ltd. can be used. In addition, as said polyamideimide, what has an aromatic ring in a molecular chain, ie, an aromatic polyamideimide, is more preferable. Furthermore, the polyamideimide combined with the polyamideimide of the present invention may be used alone or in combination of two or more. Examples of the polyimide include various known polyimides, and any of thermoplastic polyimide and thermosetting polyimide can be used. In the case of a thermosetting polyimide, either a condensation type polyimide or an addition type polyimide may be used. More specifically, for example, “Semicofine (trade name)” manufactured by Toray Industries, “PIX series (trade name)” manufactured by Hitachi Chemical DuPont Microsystems, “HCI series (trade name)” manufactured by Hitachi Chemical, Ube Commercial products such as “U-Varnish (trade name)” manufactured by Kosan Co., Ltd. can be used. Similarly, when the polyimide is combined with the polyamideimide of the present invention, only one type may be used, or two or more types may be used in combination.

<Positive electrode active material>
As the positive electrode active material used in the lithium ion secondary battery, a lithium composite oxide is used. Specifically, similar materials having different composition ratios of the respective materials and elements shown below can be used. (LiCoO ₂ ), lithium manganate (LiMn ₂ O ₄ ), lithium nickelate (LiNiO ₂ ), lithium nickel cobaltate (LiNiCoO ₂ ), lithium iron phosphate (LiFePO ₄ ), LiMO ₂ (M = Ni, Co, Mn), LiMO ₂ (M = Ni, Co, Al), LiFeMnO ₂ , Li ₂ PtO ₃ , LiMnNiO ₄ , LiNiMnO ₂ , LiCrMnO ₄ , LiFe (SO ₄ ) ₃ , LiMVO ₄ , (M = Mn, Ni, Co) ), LiCoPO ₄ , Li ₃ V ₂ (PO ₄ ) ₃ , and the like. The material is not limited to this material, 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 organic 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, ketjen black, furnace black, channel black and thermal black, carbon fibers such as vapor grown carbon fiber (VGCF) and carbon nanotube, and carbon materials such as graphite. 1 type (s) or 2 or more types can be used.

<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. Copper and a copper alloy are particularly preferable, and a foil made of an electrolytic copper foil and a rolled copper foil 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.

In the negative electrode current collector 22 in the present embodiment, when the negative electrode 20 is produced in combination with a high capacity negative electrode active material such as silicon or a silicon compound, the negative electrode current collector 22 has a tensile strength of 50 N / mm ² or more. The negative electrode current collector 22 having 200 N / mm ² or more is more preferable.

The tensile strength of the negative electrode current collector 22 is not limited to the above, but the reason is that in the various research results so far, when the negative electrode current collector 22 having a tensile strength smaller than 50 N / mm ² is used. In the charging / discharging, the negative electrode active material layer 24 tends to be easily broken due to expansion and contraction. In other words, in order to more effectively suppress the breakage of the negative electrode 20 due to charge / discharge and the falling off of the negative electrode active material layer 24, it is desirable to use the negative electrode current collector 22 having a predetermined tensile strength. The effect of is exhibited suitably.

  Although the copper foil thickness which is the said negative electrode collector 22 in this embodiment is not specifically limited, A copper foil of about 5-30 micrometers can be used conveniently. When the copper foil thickness is less than 5 μm, the relative tensile strength of the copper foil tends to be weakened, and the copper foil is easily broken or deformed by the volume expansion due to charging / discharging of the negative electrode active material layer 24. May occur easily.

  Further, the surface roughness Ra of the copper foil is not particularly limited, but from the viewpoint of adhesion to the negative electrode active material layer 24, a current collector having a predetermined surface roughness is preferred. As the surface roughness Ra of the copper foil, a copper foil of 0.05 μm or more may be used. In addition, Ra is arithmetic mean roughness Ra prescribed | regulated to JISB0601.

<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, polyamideimide, and the like. Examples thereof include a heat-resistant porous film, a composite film of the polyolefin-based porous film and a highly heat-resistant porous film, and a nonwoven fabric 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%.

<Electrolyte>
The electrolytic solution is impregnated in the separator 18 as described above, 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 electrolytic solution include cyclic carbonates such as ethylene carbonate (EC) and propylene carbonate (PC), and chain structures such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). A chain carboxylic acid ester such as carbonate, methyl acetate (MA), ethyl acetate (EA), methyl propionate (MP), ethyl propionate (EP), or γ-butyrolactone (GBL), γ-valerolactone ( Cyclic carboxylic acid esters such as GVL). Any one of these or a mixture of two or more can be used as a solvent. Further, the solvent is not limited to the above listed solvents, and is not particularly limited as long as the characteristics are not impaired when the electrolyte salt is dissolved to form the lithium ion secondary battery 100.

  In addition, a cyclic carbonate having an unsaturated bond such as vinylene carbonate (VC), or a fluorinated cyclic carbonate such as fluoroethylene carbonate (FEC) or difluoroethylene carbonate (DFEC) is mixed with the above solvent as a solvent. Can be used.

As electrolyte salt, lithium salt is mentioned, for example, 1 type may be used independently, and 2 or more types may be mixed and used for it. Lithium salts include LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiClO ₄ , LiB (C ₆ H ₅ ) ₄ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ , LiAlCl ₄ , LiSiF ₆ , LiCl, lithium bisoxalate borate, LiBr, or the like can be used, and one kind or two or more kinds can be used. 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 negative electrode active material, the conductive additive, and the binder described above 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 said 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, and the negative electrode active material layer 24 on the negative electrode current collector 22 While improving the adhesiveness with the negative electrode collector 22, it becomes a negative electrode sheet which has a predetermined density.

  The negative electrode sheet 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 not higher than the thermal decomposition of the binder in a vacuum or an inert gas atmosphere, thereby increasing the degree of polymerization due to the binder, and the interface between the negative electrode active material layer 24 and the negative electrode current collector 22. And the adhesiveness between negative electrode active materials can further be improved. 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 produce 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 said 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 or both surfaces of the positive electrode current collector 12 by a roll press or the like, and the positive electrode active material layer 14, the positive electrode current collector 12, At the same time, the positive electrode sheet having a predetermined density is obtained.

  The positive electrode sheet 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 already 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 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. In order to prevent the negative electrode 20 and the positive electrode 10 from coming into direct contact with each other, the separator 18 can be suitably used by punching out a larger electrode size than both electrodes using a mold.

  Next, in the negative electrode 20 of the electrode body 30, a 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 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 lithium ion secondary battery 100 can store electric capacity.

  Although the present invention has been described in detail with the embodiments, the present invention is not limited to the above-described embodiments, and various modifications can be made. For example, in the above 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 said embodiment, this invention is further demonstrated in detail in the following examples and comparative examples. However, the present invention is not limited to the embodiments described below.

<Synthesis of Polyamideimide A>
In a four-necked flask equipped with a condenser and a nitrogen gas inlet, trimellitic anhydride (TMA) (manufactured by Wako Pure Chemical Industries, Ltd.) 1 mol, 4,4′-diphenylmethane diisocyanate (MDI) (manufactured by Aldrich) 0 99 mol, 2,2-bis (4-isocyanatophenyl) hexafluoropropane (Tokyo Chemical Industry Co., Ltd.) 0.01 mol, potassium fluoride 0.01 mol (Pure Chemical Co., Ltd.) as a catalyst, solid content concentration 20% The mixture was charged with N-methyl-2-pyrrolidone (NMP) so that the temperature became 120 ° C. with stirring and reacted for about 1 hour, then heated to 180 ° C. and reacted for about 3 hours. Imide A was obtained. The molar ratio of the formula (1) and the formula (3) of the polyamideimide A was 99/1.

<Synthesis of Polyamideimide B>
Trimellitic anhydride (TMA) (manufactured by Wako Pure Chemical Industries, Ltd.) 1 mol, 4,4′-diphenylmethane diisocyanate (MDI) (manufactured by Aldrich) 0.9 mol, 2,2-bis (4-isocyanatophenyl) hexa 0.1 mol of fluoropropane (manufactured by Tokyo Chemical Industry Co., Ltd.) and 0.01 mol of potassium fluoride (manufactured by Junsei Chemical Co., Ltd.) as a catalyst are charged together with N-methyl-2-pyrrolidone (NMP) so that the solid concentration is 20%. Polyamideimide B was obtained at the same synthesis temperature and reaction time as polyamideimide A. The molar ratio of the formula (1) and the formula (3) of the polyamideimide B was 91/9.

<Synthesis of Polyamideimide C>
Trimellitic anhydride (TMA) (manufactured by Wako Pure Chemical Industries, Ltd.) 1 mol, 4,4′-diphenylmethane diisocyanate (MDI) (manufactured by Aldrich) 0.8 mol, 2,2-bis (4-isocyanatophenyl) hexa Charge 0.2 mol of fluoropropane (manufactured by Tokyo Chemical Industry Co., Ltd.) and 0.01 mol of potassium fluoride (manufactured by Junsei Chemical Co., Ltd.) as a catalyst together with N-methyl-2-pyrrolidone (NMP) so that the solid content concentration is 20%. Polyamideimide B was obtained at the same synthesis temperature and reaction time as polyamideimide A. The molar ratio of the formula (1) and the formula (3) of the polyamideimide C was 82/18.

<Synthesis of Polyamideimide D>
Trimellitic anhydride (TMA) (manufactured by Wako Pure Chemical Industries) 1 mol, 4,4'-diphenylmethane diisocyanate (MDI) (manufactured by Aldrich) 0.5 mol, 2,2-bis (4-isocyanatophenyl) hexa Charge 0.5 mol of fluoropropane (manufactured by Tokyo Chemical Industry Co., Ltd.) and 0.01 mol of potassium fluoride (manufactured by Junsei Chemical Co., Ltd.) as a catalyst together with N-methyl-2-pyrrolidone (NMP) so that the solid concentration is 20%. Polyamideimide D was obtained at the same synthesis temperature and reaction time as polyamideimide A. The molar ratio of the formula (1) and the formula (3) of the polyamideimide D was 50/50.

<Preparation of negative electrode for lithium ion secondary battery>
Example 1
80 wt% of SiO disproportionated by heat treatment at 1000 ° C. under reduced pressure as a negative electrode active material, 5 wt% of acetylene black as a conductive additive, and 15 wt% of polyamideimide A synthesized by an isocyanate method as a binder, A paste-like negative electrode slurry was prepared by mixing and dispersing a solvent of N-methyl-2-pyrrolidone. 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. In addition, the thickness of the coating film of the negative electrode active material layer apply | coated to both surfaces of the said copper foil was adjusted to the substantially same film thickness. 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 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. A negative electrode for a lithium ion secondary battery according to Example 1 was produced. The heat treatment was performed in a vacuum.

<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 said 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 negative electrode sheet 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 prepared negative electrode and positive electrode were laminated through a polyethylene separator having a thickness of 16 μm and a size of 22 × 33 mm, thereby preparing 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 said negative electrode and a positive electrode are equipped with each active material layer on both surfaces, they are comprised by three negative electrodes, two positive electrodes, and four separators.
Further, in the negative electrode of the electrode body, a nickel negative electrode lead is attached to the protruding end portion of the copper foil not provided with the negative electrode active material layer, while the positive electrode of the electrode body is provided with aluminum without the positive electrode active material layer. An aluminum positive electrode lead was attached to the protruding end of the foil by an ultrasonic welding machine. Then, this electrode body is inserted into an aluminum laminate film outer package and heat-sealed except for one peripheral portion to form a closed portion, and EC / DEC is blended at a ratio of 3: 7 in the outer package. Example 1 After injecting an electrolyte containing 1M (mol / L) LiPF ₆ as a lithium salt into the solvent, the remaining one part was sealed with a heat seal while reducing the pressure with a vacuum sealer. The lithium ion secondary battery which concerns on was produced. The lithium ion secondary battery produced above was measured for expansion rate from the discharge capacity retention rate after 100 cycles and the cell thickness after 100 cycles.

(Example 2)
The negative electrode for lithium ion secondary batteries and the lithium ion secondary battery according to Example 2 were the same as in Example 1 except that the binder used for the negative electrode for lithium ion secondary batteries was changed to polyamideimide B. A negative electrode for a secondary battery and a lithium ion secondary battery were produced.

(Example 3)
The negative electrode for lithium ion secondary batteries and the lithium ion secondary battery according to Example 3 were the same as in Example 1 except that the binder used for the negative electrode for lithium ion secondary batteries was changed to polyamideimide C. A negative electrode for a secondary battery and a lithium ion secondary battery were produced.

Example 4
The negative electrode for lithium ion secondary batteries and the lithium ion secondary battery according to Example 4 were the same as in Example 1 except that the binder used for the negative electrode for lithium ion secondary batteries was changed to polyamideimide D. A negative electrode for a secondary battery and a lithium ion secondary battery were produced.

<Synthesis of Polyamideimide E>
Trimellitic anhydride (TMA) (manufactured by Wako Pure Chemical Industries, Ltd.) 1 mol, 4,4′-diphenylmethane diisocyanate (MDI) (manufactured by Aldrich) 1 mol, 0.01 mol of potassium fluoride (manufactured by Junsei Chemical Co., Ltd.) as a catalyst N-methyl-2-pyrrolidone (NMP) was charged so that the solid content concentration was 20%, and polyamideimide E was obtained at the same synthesis temperature and reaction time as polyamideimide A. The molar ratio of the formula (1) and the formula (3) of the polyamideimide E was 100/0.

(Comparative Example 1)
A negative electrode for a lithium ion secondary battery and a lithium ion secondary battery according to Comparative Example 1 were prepared in the same manner as in Example 1 except that the negative electrode binder was changed to polyamideimide E. An ion secondary battery was produced.

<Heat treatment temperature>
The negative electrode for lithium ion secondary batteries according to the present invention was heat-treated at various temperatures to produce negative electrodes having different degrees of polymerization of the negative electrode binder constituting the negative electrode. Hereinafter, more preferred embodiments of the negative electrode for lithium ion secondary battery and the embodiment of the lithium ion secondary battery will be described in detail with reference to examples and comparative examples. In the following examples, the polyamideimide B synthesized in Example 2 (the ratios of a and b in the formula (1) and the formula (3) are 91 mol% and 9 mol%, respectively) will be described in detail as an example. explain.

(Example 5)
The lithium ion secondary battery negative electrode and the lithium ion secondary battery according to Example 5 are the same as Example except that the heat treatment temperature of the lithium ion secondary battery negative electrode according to Example 2 was changed from 300 ° C to 150 ° C. The negative electrode for lithium ion secondary batteries and the lithium ion secondary battery were produced by the same method as 2.

  Separately from the above, a negative electrode binder (polyamideimide B) was applied in the form of a film, and NMP as a solvent was dried at a heat treatment temperature of 150 ° C. under vacuum to produce a polyamideimide film in Example 5.

(Example 6)
The negative electrode for lithium ion secondary power and the lithium ion secondary battery according to Example 6 were the same as those in Example except that the heat treatment temperature of the negative electrode for lithium ion secondary battery according to Example 2 was changed from 300 ° C to 200 ° C. The negative electrode for lithium ion secondary batteries and the lithium ion secondary battery were produced by the same method as 2.

  Separately from the above, a negative electrode binder (polyamideimide B) was applied in the form of a film, and NMP as a solvent was dried at a heat treatment temperature of 200 ° C. under vacuum to produce a polyamideimide film in Example 6.

(Example 7)
Since the negative electrode for lithium ion secondary electricity and the lithium ion secondary battery according to Example 7 are the same as those of Example 2, the manufacturing method is omitted. In addition, the heat processing temperature of the said negative electrode for lithium ion secondary batteries was implemented at 300 degreeC same as Example 2. FIG.

  Separately from the above, a negative electrode binder (polyamideimide B) was applied in a film form, and NMP as a solvent was dried at a heat treatment temperature of 300 ° C. under vacuum to produce a polyamideimide film in Example 7.

(Example 8)
The lithium ion secondary battery negative electrode and the lithium ion secondary battery according to Example 8 are the same as those in Example except that the heat treatment temperature of the lithium ion secondary battery negative electrode according to Example 2 was changed from 300 ° C to 350 ° C. The negative electrode for lithium ion secondary batteries and the lithium ion secondary battery were produced by the same method as 2.

  Separately from the above, a negative electrode binder (polyamideimide B) was applied in the form of a film, and NMP as a solvent was dried at a heat treatment temperature of 350 ° C. under vacuum to produce a polyamideimide film in Example 8.

Example 9
The lithium ion secondary battery negative electrode and the lithium ion secondary battery according to Example 9 were the same as those in Example except that the heat treatment temperature of the lithium ion secondary battery negative electrode according to Example 2 was changed from 300 ° C to 500 ° C. The negative electrode for lithium ion secondary batteries and the lithium ion secondary battery were produced by the same method as 2.

  Separately from the above, a negative electrode binder (polyamideimide B) was applied in the form of a film, and NMP as a solvent was dried at a heat treatment temperature of 500 ° C. under vacuum to produce a polyamideimide film in Example 9.

<Combination of binder>
The polyamideimide negative electrode binder of the example according to the present invention can exhibit excellent cycle characteristics as a lithium ion secondary battery even when mixed with another binder. Examples and comparative examples of lithium ion secondary batteries when combining the binders of the examples and commercially available binders, lithium ion secondary batteries when combining the binders of the comparative examples and commercially available binders, An example will be described in detail.

(Example 10)
In the lithium ion secondary battery negative electrode and lithium ion secondary battery according to Example 10, the binder used for the lithium ion secondary battery negative electrode was polyamide imide B in the present invention and a commercially available polyamide imide (manufactured by Hitachi Chemical Co., Ltd., “ “HPC series (trade name)” was prepared so as to be 50 vol%: 50 vol%, and a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery were produced in the same manner as in Example 2 except that.

(Comparative Example 2)
In the lithium ion secondary battery negative electrode and lithium ion secondary battery according to Comparative Example 2, the binder used for the negative electrode for the lithium ion secondary battery was polyamide imide F in the present invention and a commercially available polyamide imide (manufactured by Hitachi Chemical Co., Ltd., “ “HPC series (trade name)” was prepared so as to be 50 vol%: 50 vol%, and a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery were produced in the same manner as in Comparative Example 1 except that.

<Evaluation>
The following evaluation was performed about the lithium ion secondary battery and the polyamide-imide film which were produced by the Example and the comparative example.

(Cycle test)
The lithium ion secondary batteries produced in Examples and Comparative Examples were repeatedly charged and discharged under the following charge / discharge test conditions and evaluated for cycle characteristics. In addition, charging / discharging was implemented at 25 degreeC. The charging / discharging test conditions were as follows: constant current charging until a constant current of 1.0 C was 4.2 V, then discharging until a battery voltage of 2.5 V was reached with a constant current of 1.0 C, and the above was performed for one cycle. And evaluated by the discharge capacity maintenance rate after 100 cycles. Note that 1C is a current value at which charging / discharging is completed in just one hour after constant current charging or constant current discharging of a battery cell having a nominal capacity value.

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

(Thickness expansion)
In the lithium ion secondary batteries of Examples and Comparative Examples, the expansion coefficient of thickness was calculated by measuring the thickness of the cell before charging and discharging and at the time when 100 cycles were completed. The thickness expansion coefficient was defined by the following calculation formula.

  Expansion rate (%) = (cell thickness before charge / discharge (mm) −cell thickness after charge / discharge (mm)) / cell thickness before charge / discharge (mm) × 100 (%)

(Presence or absence of peeling of negative electrode active material layer after cycle)
The lithium ion secondary batteries of Examples and Comparative Examples that ended 100 cycles were disassembled in the globepox and the negative electrode was taken out. The negative electrode taken out was washed with an electrolytic solution with dimethyl carbonate (DMC) and dried at 40 ° C., and then the peeled state of the negative electrode active material layer from the current collector in the negative electrode was visually evaluated.

(Infrared spectroscopy)
Polyamideimide films prepared in Examples and Comparative Examples were obtained by using a Fourier transform infrared spectrophotometer (manufactured by Thermo Nicolet, product number: Nexus 670 + SMART ENDURANCE Diamond ATR), and obtained the chemical structure of the binder from the obtained absorption spectra. Analyzed.

In the polyamideimide, the absorption spectrum of the imide group is mainly (ν _C—N : 1380 cm ⁻¹ , ν _C═O : 1780 cm ⁻¹ ), and the absorption spectrum of the amide group is (ν _N—H : 1525 cm ⁻¹⁾ . ^{_{ν C = O: 1660cm -1)}} , the absorption spectrum of the benzene ring ^{_{(ν C = C: 1510cm -1}} , ν C = O: was 1590 cm ^-1). The infrared absorption wavelength indicates the peak of the absorption spectrum of the meaning group. Further, the spectral ratio shown below represents the peak intensity ratio normalized at 1510 cm ⁻¹ .

The total imide linkage of the polyamideimide, absorption spectrum ratio of the 1380 cm ^-1 and ^{1510cm -1 (1380cm -1 / 1510cm -1} ), cyclic imide bond content in the main chain, and 1780 cm ^-1 1510 cm ^{- 1} with the absorption spectrum ratio ^{(1780cm -1} / ^1510cm -1), whereas, an amide bond amount was expressed in the absorption spectrum ratio of the 1525 cm ^-1 and ^{1510cm -1 (1525cm -1 / 1510cm -1} ).

  Moreover, the cyclic imide bond amount in the total imide bond amount was calculated as a relative ratio by the following calculation formula.

  Cyclic imide bond content ratio in total imide bond content = Absorption spectrum ratio of cyclic imide bond content / Absorption spectrum ratio of total imide bond content

In the polyamideimide, in the negative electrodes and / or lithium ion secondary batteries according to Examples 1 to 4 and Comparative Example 1 in which the molar ratios of a and b in the formulas (1) and (3) were variously prepared. Table 1 shows the results of cycle characteristics, thickness expansion coefficient after cell cycle.

  As is clear from Table 1 above, the ratio (a / b) of a and b in the formula (1) and the formula (3) constituting the polyamideimide is 50 to 99 mol% / 50 to 1 mol%. In Examples 1 to 4, it was found that the cycle characteristics after 100 cycles when a lithium ion secondary battery was used showed a high capacity retention rate of 80% or more. On the other hand, in the lithium ion secondary battery using the polyamideimide that does not have the structure of the formula (3) in Comparative Example 1, the negative electrode active material does not peel off, but the cycle characteristics are deteriorated and the cell thickness is large. Was confirmed.

  Taking as an example a negative electrode using polyamideimide B according to an embodiment of the present invention as a negative electrode binder, the amount of cyclic imide bonds, which is the chemical structure of the polyamideimide contained in the negative electrode active material layer, was variously adjusted, Table 2 shows the results of the cycle characteristics when an ion secondary battery is obtained.

As is clear from Example 5 to Example 9 in Table 2, when the strength ratio of the cyclic imide bond amount constituting the polyamideimide is 0.21 or more with respect to the strength ratio of the total imide bond amount, lithium Cycle characteristics when using an ion secondary battery were good.

Table 3 shows the results of the cycle characteristics as a lithium ion secondary battery when the polyamideimide B in the present invention is taken as an example and combined with another negative electrode binder.

  As is clear from the results in Table 3, it was confirmed that the polyamideimide as the negative electrode binder in the present invention exhibited excellent cycle characteristics as a lithium ion secondary battery even when combined with other polyamideimides. It was done.

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 (5)

The binder for lithium ion secondary batteries characterized by including the polyamideimide which has a repeating unit of following formula (1) and formula (3).

However, X in Formula (1) represents Formula (2-1) or Formula (2-2) below.

(However, R ₁ and R ₂ represent a substituent selected from the group consisting of hydrogen and an alkyl group. Y in the formula (2-2) is —O—, —S—, —C (═O). _{) -, - SO 2 -,} - C (= O) O -, - (CH 2) n -, - C (CF 3) 2 -, - C (CH 3) 2 - shows a Note, -. (CH ₂ ) _n in n- is an integer of 0 or more and 5 or less.)

(However, a and b represent mol%, and a + b = 100)   2. The binder for a lithium ion secondary battery according to claim 1, wherein the ratio of a in the formula (1) is 50 to 99 mol% and the ratio of b in the formula (3) is 50 to 1 mol%. At infrared absorption ^{spectroscopy,} infrared absorption spectrum of 1360 cm -1 / 1510 cm ^-1 with respect to the infrared absorption spectrum intensity ratio of (total imide bond ^amount), 1780 cm -1 / 1510 cm ^-1 (cyclic imide bond amount) The binder for a lithium ion secondary battery according to claim 1 or 2, wherein the strength ratio is 0.21 or more.   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 comprising a negative electrode active material capable of being alloyed with lithium, a conductive material A negative electrode for a lithium ion secondary battery, comprising an auxiliary agent and a binder, wherein the binder comprises the binder for a lithium ion secondary battery according to any one of claims 1 to 3.   A lithium ion secondary battery comprising the negative electrode for a lithium ion secondary battery according to claim 4.

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