JP2018156876A - Positive electrode for lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery capable of suppressing heat generation of a positive electrode mixture layer in response to an instantaneous temperature rise occurring at a time of internal short circuit while maintaining cycle characteristics and high capacity of the lithium secondary battery.SOLUTION: The positive electrode for a lithium ion secondary battery includes: a current collector; and a positive electrode mixture layer coated on the current collector. The positive electrode mixture layer includes: a layer A containing a positive electrode active material, a conduction aid, and a binding component; and a layer B containing a positive electrode active material, a conduction aid, a binding component, and a PTC function imparting component.SELECTED DRAWING: None

Description

  The present invention relates to a positive electrode for a lithium ion secondary battery and a lithium ion secondary battery using the same.

  In recent years, lithium ion secondary batteries have been widely used as electronic devices such as mobile phones and notebook computers, electric vehicles, and power storages for power storage. In particular, recently, there has been a rapid increase in demand for batteries with high capacity, high output, and high energy density that can be mounted on hybrid vehicles and electric vehicles. This lithium ion secondary battery has the advantage of high energy density, but uses lithium metal and a non-aqueous electrolyte, so a sufficient countermeasure for safety is required.

  For example, a positive electrode of a lithium secondary battery disclosed in Patent Document 1 has a mixture layer of two or more layers containing a lithium-containing oxide as a positive electrode active material on the surface of a current collecting base material. A positive electrode active material having a high heat generation starting temperature is used for the surface layer. This conventional technique increases the safety of the surface layer portion of the positive electrode, which has the greatest risk of heat generation of the composite layer itself, by facing the negative electrode, thereby suppressing the occurrence of thermal runaway. In addition, in the lower composite layer having a lower heat generation start temperature than the outermost composite layer, a lithium-containing composite oxide having a high capacity density can be used, so that the battery capacity can be improved. .

  The invention described in Patent Document 2 includes a current collecting base material and a positive electrode coating film composed of a plurality of mixture layers on the current collecting base material, and the positive electrode coating film has a heat generation start temperature as a positive electrode active material. Two or more different lithium-containing compounds, and at least one lithium-containing compound of the two or more lithium-containing compounds has an exothermic onset temperature of 300 ° C. or higher and is closest to the current collecting base material. In the one mixture layer, the positive electrode for a lithium secondary battery contains at least one lithium-containing compound having a heat generation start temperature of 300 ° C. or higher. In this invention, the positive electrode coating film is composed of a plurality of mixture layers, and the heat generation start temperature is 300 in the first mixture layer closest to the current collecting base material that generates high Joule heat due to an internal short circuit in the nail penetration test. By containing at least one lithium-containing compound at or above ° C., heat generation of the positive electrode due to an internal short circuit is reliably suppressed.

JP 2003-036838 A Japanese Patent No. 5032800

  However, it is preferable to change the type of the positive electrode active material in the positive electrode mixture layer, because the degree of deformation of the positive electrode active material due to expansion and contraction of the crystal lattice accompanying charge / discharge changes and leads to deterioration of the current collecting structure in the positive electrode mixture layer. Absent.

  The problem to be solved by the present invention is lithium that can suppress the heat generation of the positive electrode mixture layer in response to an instantaneous temperature rise that occurs during an internal short circuit while maintaining the cycle characteristics and high capacity of the lithium ion secondary battery. It is to provide an ion secondary battery.

  The positive electrode for lithium ion secondary batteries concerning one Embodiment of this invention is equipped with a collector and the positive mix layer apply | coated on this collector. The positive electrode mixture layer includes a layer A including a positive electrode active material, a conductive additive, and a binder component, and a layer B including a positive electrode active material, a conductive auxiliary agent, a binder component, and a PTC function-imparting component. And

  The positions of the layer A and the layer B in the positive electrode mixture layer are not particularly limited. In the thickness direction of the positive electrode mixture layer, the layer B is provided on the current collector side, and the layer A sandwiches the layer B and collects the current. By being provided on the side opposite to the body, that is, on the separator side, when the temperature rises due to an internal short circuit, the action of the PTC function-imparting component contained in layer B between the current collector and the positive electrode mixture layer Thus, the cutting action of the conductive path can be effectively obtained, and the performance of the high temperature storage test and the cycle durability test can be expected to be improved by the action of the binder component contained in the layer A, which is preferable.

  In addition, by providing layer A on the current collector side and layer B on the separator side, when the temperature rises due to an internal short circuit, due to the action of the PTC function-imparting component contained in layer B, the shutdown temperature before the separator, Lithium ion diffusion is inhibited at the contact interface between the separator and the positive electrode mixture layer, and a blocking action of the lithium ion pathway can be effectively obtained. It is preferable because performance improvement in the cycle durability test can be expected.

  Layer A may contain a PTC function-imparting component at a lower concentration than layer B, but preferably does not contain a PTC function-imparting component from the viewpoint of a high-temperature storage test or a cycle durability test.

  In the positive electrode for a lithium ion secondary battery of the present invention, at least a part of a binder composed of a mixture of a binder component and a PTC function-imparting component melts in response to an instantaneous temperature rise when an internal short circuit occurs. Thus, there is an advantage that the conductive path of the positive electrode mixture layer is cut, thereby suppressing the heat generation at the time of internal short circuit of the battery.

It is sectional drawing at the time of the nail penetration test of the positive mix layer which concerns on one Embodiment of this invention. It is sectional drawing at the time of the nail penetration test of the positive mix layer which concerns on other embodiment of this invention. The typical DSC curve of the binder material sample measured in Examples 1 and 2 and Comparative Example 3 is shown.

  Hereinafter, the positive electrode for lithium ion secondary batteries of this invention and a lithium ion secondary battery using the same are demonstrated. First, the layered structure of the positive electrode mixture layer applied on the current collector and the state at the time of the nail penetration test will be described based on the drawings, and then each component of the battery will be described in detail.

[Positive electrode for lithium ion secondary battery]
FIG. 1 is a schematic view showing an embodiment when an internal short circuit occurs due to nail penetration in the positive electrode. A positive electrode 10 for a lithium ion secondary battery shown in FIG. 1 has a positive electrode mixture layer 14 on one side of a current collector 13. The positive electrode mixture layer 14 includes a positive electrode active material capable of inserting and extracting lithium, a conductive additive, a binder component, and optionally a PTC function-imparting component, and is composed of two layers, a layer A11 and a layer B12. . The positive electrode mixture layer 14 may be applied to at least one surface of the current collector 13, and may be applied to both surfaces of the current collector 13 in some cases. In other embodiments, one or more intermediate layers may be included.

  The positive electrode active material, the conductive additive and the binder component contained in the layers A11 and B12 may be the same or different, but from the viewpoint of ensuring the uniformity of the positive electrode mixture layer, What consists of a composition is preferable. On the other hand, the PTC function-imparting component constituting the binder together with the binder component may be contained at least in the layer B12, and the layer A11 does not contain the PTC function-imparting agent or has a lower concentration than the layer B. A function-imparting component may be included. Here, the density | concentration of the PTC function provision component in each layer is a mass ratio of the PTC function provision component contained in each layer with respect to the mass of each whole layer. From the viewpoint of battery characteristics, the binder contained in the layer A is preferably composed only of a binder component, for example, polyvinylidene fluoride (PVDF). Further, the concentration of the PTC function-imparting component contained in the layer B is not particularly limited as long as it can contribute to the disconnection of the conductive path between the current collector 13 and the positive electrode mixture layer 14 at the time of an internal short circuit, but typically The total amount of the layer B is 0.5 to 5% by mass, preferably about 1 to 3% by mass.

As shown in FIG. 1, at the time of an internal short circuit by nail penetration, when the nail 15 penetrating the negative electrode and having a negative potential penetrates the positive electrode mixture layer 14, the positive electrode current collector 13 or the positive electrode current collector 13 and the positive electrode combination Since a large amount of thermal energy is released at the interface portion of the agent layer 14, it is important to suppress thermal runaway of the entire battery by increasing the resistance of this portion (layer B12) and reducing the heat generation rate during heat generation. it is conceivable that.
Although the average thickness of layer B12 is not specifically limited, It is preferable to set it as 5-30 micrometers on the single side | surface of a collector, and it is more preferable to set it as 10-20 micrometers. The average thickness of the layer A can be appropriately adjusted based on the average thickness of the entire positive electrode mixture layer, but is usually 5 to 20 times, preferably about 10 to 15 times the average thickness of the layer B. It is preferable to have an average thickness of about 30 μm to about 100 μm on one side of the current collector.

  FIG. 2 is a cross-sectional view of the positive electrode during an internal short circuit due to nail penetration in another embodiment. A positive electrode 20 for a lithium ion secondary battery shown in FIG. 2 has a positive electrode mixture layer 24 on one side of a current collector 23, and a positive electrode active material capable of occluding and releasing lithium, as well as FIG. It comprises an agent, a binder component, and optionally a PTC function-imparting component, and consists of two layers, layer A22 and layer B21. The positive electrode active material, the conductive additive, and the binder component contained in the layer A22 and the layer B21 are the same as those in FIG. On the other hand, in this embodiment, the PTC function provision component which comprises a binder with a binder component is contained in layer B21. That is, the binder contained in the layer A22 may be composed of only the binder component or may contain a PTC function-imparting component at a lower concentration than the layer B. In FIG. 2, even when an internal short circuit due to nail penetration does not penetrate the positive electrode mixture layer 24, a large current is applied to the surface of the positive electrode at the moment when the nail 25 penetrating the negative electrode and reaching the negative electrode potential touches the positive electrode. Flows to generate large Joule heat, and the positive electrode starts to thermally decompose by this heat, thereby releasing large energy and causing thermal escape. Therefore, in the present embodiment, a PTC function-imparting component is added to the binder contained in the layer B21 of the positive electrode mixture layer 24, the resistance of this portion is increased during heat generation, the heat generation rate is decreased, and the entire battery is reduced. We decided to suppress thermal runaway. About the average thickness of layer B21, it is the same as that of the average thickness of layer B12 mentioned above.

Although the mechanism for increasing the resistance of the specific portion in the positive electrode mixture layer by adding the PTC function-imparting component to the layer B12 or the layer B21 is not necessarily clear, the short-circuited portion of the lithium ion secondary battery Due to the temperature rise, the binder (mixture of the binder component and the PTC function-imparting component) in the positive electrode mixture layer at this portion melts. At this time, a fibril (fiber) -shaped structure is formed by wrapping together a positive electrode active material and a conductive additive whose binder is an inorganic substance, thereby changing the local structure in the positive electrode mixture layer, and It is estimated that at least a part of the conductive path in the agent layer is cut and the resistance of the part increases. Since such a function is exhibited by a decrease in the melting start temperature and / or the melting peak temperature of the binding material, the binding material of the present embodiment has a normal melting start temperature of a single binding component and The temperature is lower than the melting peak temperature. In addition, since the battery temperature is controlled by the balance between heat generation and heat dissipation, it is considered that the thermal runaway of the battery can be suppressed by increasing the resistance in the initial stage of heat generation due to an internal short circuit to suppress the heat generation rate.
Hereinafter, each component of the lithium ion secondary battery according to the present embodiment will be described in detail.

(Positive electrode active material)
The positive electrode active material is not particularly limited as long as it is a material capable of occluding and releasing lithium, and is a positive electrode active material usually used for lithium ion secondary batteries. Specifically, in addition to an oxide having lithium (Li) and nickel (Ni) as constituent metal elements, at least one metal element other than lithium and nickel (that is, a transition metal element other than Li and Ni and (Or a typical metal element) is also meant to include an oxide containing a constituent metal element in a proportion equivalent to or less than nickel in terms of the number of atoms. Examples of the metal element other than Li and Ni include, for example, Co, Mn, Al, Cr, Fe, V, Mg, Ca, Na, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, It may be one or more metal elements selected from the group consisting of La and Ce. These positive electrode active materials may be used alone or in combination.

In a preferred embodiment, the positive electrode active material has, for example, the general formula (1): Li _t Ni _1-xy Co _x Al _y O ₂ (where 0.95 ≦ t ≦ 1.15, 0 ≦ x ≦ 0.3, 0.1 ≦ y ≦ 0.2, and x + y <0.5 are satisfied.) Lithium nickel cobalt aluminum-based oxide (NCA). A specific example of NCA is LiNi _0.8 Co _0.15 Al _0.05 O ₂ .

In another preferred embodiment, the positive electrode active material may be, for example, the general formula (2): LiNi _a Co _b Mn _c O ₂ (where 0 <a <1, 0 <b <1, 0 <c < 1 and satisfying a + b + c = 1). A lithium nickel cobalt manganese-based oxide (NCM) is given. NCM has a high energy density per volume and excellent thermal stability.
The content of the positive electrode active material in the positive electrode mixture layer is usually 10% by mass or more, preferably 30% by mass or more, more preferably 50% by mass or more, and particularly preferably 70% by mass or more. Moreover, it is 99.9 mass% or less normally, Preferably it is 99 mass% or less.

(Conductive aid)
The positive electrode mixture layer preferably contains a conductive additive. As the conductive auxiliary agent used in the present invention, a known conductive auxiliary agent can be used. The known conductive aid is not particularly limited as long as it is a carbon material having conductivity, but graphite, carbon black, conductive carbon fiber (carbon nanotube, carbon nanofiber, carbon fiber), fullerene, etc. It can be used alone or in combination of two or more. Examples of commercially available carbon black include Toka Black # 4300, # 4400, # 4500, # 5500 (Tokai Carbon Co., Furnace Black), Printex L and the like (Degussa Co., Furnace Black), Raven 7000, 5750, 5250, 5000 ULTRA III, 5000 ULTRA, etc., Conductex SC ULTRA, Conductex 975 ULTRA, etc., PUER BLACK100, 115, 205, etc. (manufactured by Colombian, Furnace Black), # 2350, # 2400B, # 2600B, # 30050B, # 3030B, # 3030B, # 3030B 3350B, # 3400B, # 5400B, etc. (Mitsubishi Chemical Corporation, furnace black), MONARCH1400, 1300, 900, VulcanXC-7 2R, BlackPearls2000, LITX-50, LITX-200, etc. (Cabot, Furnace Black), Ensaco250G, Ensaco260G, Ensaco350G, SuperP-Li (manufactured by TIMCAL), Ketjen Black EC-300J, EC-600JD (manufactured by Akzo) ), Denka Black, Denka Black HS-100, FX-35 (manufactured by Denki Kagaku Kogyo Co., Ltd., acetylene black) and the like, for example, natural graphite such as artificial graphite, flake graphite, massive graphite, earth graphite, etc. However, it is not limited to these. The content of the conductive additive contained in the positive electrode mixture layer is preferably 1% by mass or more, and is preferably about 1 to 10% by mass, for example.

(Binder)
As a binder, the polyvinylidene fluoride (PVDF) as a binder component and the PTC function provision component depending on the case are included. The purpose of using the binder component to produce the electrode is to first ensure the adhesion of the powdered active material without substantially obscuring the electrochemically active active material surface. It is to do. This effect depends on the wettability of the binder component. Also, the binder component needs to have adhesion to the current collector metal, which is achieved by the presence of polar groups in the binder component. Also, the binder component must be able to handle sufficient flexibility to handle the electrode and dimensional changes of the active material during the charge / discharge cycle. The binder component must have specific electrochemical properties and must be compatible with the non-aqueous electrolyte solution used. Finally, because the reducing and oxidizing agents used as active materials are extremely powerful, the binder must have the lowest possible reactivity that can withstand extreme operating conditions without degradation. I must.

  The mechanical and electrochemical properties of PVDF are suitable for the numerous purposes described above required for the binder component. Although it has been reported that the melting point of PVDF alone is about 180 ° C., it is considered that the melting point of the lithium ion secondary battery is slightly lowered because it is in contact with the nonaqueous electrolyte. Further, by including a PTC function-imparting component, the binder of the present embodiment melts when the temperature of the lithium ion secondary battery rises, and increases the resistance of the positive electrode mixture layer from a lower temperature range, thereby recharging the lithium ion secondary battery. Can prevent thermal runaway. Since the binder contains the PTC function-imparting component, either or both of the melting start temperature and the melting peak temperature are lowered as compared with PVDF alone. From the viewpoint of suppressing thermal runaway, it is preferable that the melting start temperature and / or the melting peak temperature of the binder is low, but if it is too low, the function as the binder is hindered. Therefore, the melting start temperature of the binder is preferably about 60 ° C. to about 150 ° C., more preferably about 65 ° C. to about 130 ° C., and further preferably about 70 ° C. to about 100 ° C.

  The melting peak temperature (melting point) of the binder may also decrease, and the melting peak temperature of the binder is preferably 70 ° C to 130 ° C under the above measurement conditions. The melting peak temperature of the binder is preferably 70 ° C. or higher from the viewpoint of thermal stability. On the other hand, from the viewpoint of safety, the melting point of the binder is preferably 130 ° C. or lower. More preferably, it is less than 130 degreeC, It is more preferable that it is 120 degrees C or less, It is still more preferable that it is 110 degrees C or less.

  The “PTC function imparting component” in the present embodiment refers to a component that imparts a PTC function to the binder or enhances the PTC function by lowering the melting start temperature and / or the melting peak temperature of the PVDF. The relationship between the PTC (positive temperature coefficient) function in which the resistance value increases as the temperature rises and the melting of PVDF is considered as follows. For example, when a short-circuit current flows through an electrode formed by binding an electrode active material and a conductive additive, the temperature of the electrode increases due to short-circuit heat generation. At this time, when the binder melts, an inorganic electrode active material and a conductive auxiliary agent are wound together to form a fibril (fibre) -shaped structure, which changes the shape of the electrode, and the conductive path in the electrode. It is estimated that at least a part of the electrode is cut to increase the resistance of the electrode. Since such a function is exhibited by a decrease in the melting start temperature and / or the melting peak temperature of the binding material, the binding material of the present embodiment has a normal melting start temperature of a single binding component and The temperature is lower than the melting peak temperature.

  Therefore, the binder of the present embodiment is a mixture of PVDF as a binding component and a PTC function-imparting component, and the mixture is measured by differential scanning calorimetry in the presence of a non-aqueous electrolyte. The melting start temperature and / or the melting peak temperature can be selected as compared with the case of only PVDF measured under the same conditions. In the present embodiment, the melting start temperature means the temperature at which the endotherm analyzed by differential scanning calorimetry (hereinafter also referred to as DSC) rises from the baseline, and specifically, JIS7121 (plastic The temperature at the intersection of a straight line obtained by extending the base line on the low temperature side to the high temperature side and the tangent line drawn at the point where the gradient is maximized on the low temperature side curve of the melting peak is defined. Alternatively, the endothermic amount due to melting of the binder may be calculated from the peak area of the DSC curve, and the temperature when reaching about one-half of the total endothermic amount may be used as an index. This is because, when the melting start temperature of the binder is lowered, the endothermic heat starts from a lower temperature, and the PTC function is exhibited when a certain endothermic amount is reached.

[Measuring method of melting point and melting start temperature]
For example, using a high-sensitivity differential scanning calorimeter DSC7000X device manufactured by Hitachi High-Tech Science Co., Ltd., PVDF and PTC function-imparting component are dissolved in an organic solvent or mixed in a mortar or the like as a powder and then dried. About 5 mg is packed in an aluminum pan, and a nonaqueous electrolyte is added to this to make a sample. The nonaqueous electrolyte to be added to the sample is preferably an electrolytic solution in which a lithium salt containing at least LiPF ₆ as an electrolyte is dissolved in a solvent mixture in which an organic solvent selected from cyclic carbonates and chain carbonates is used alone or in combination. . In this embodiment, a non-aqueous electrolyte in which 1M lithium hexafluorophosphate (LiPF ₆ ) is dissolved in a 3: 7 mixed solution of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) is used. For example, the temperature is raised from room temperature to about 200 ° C. at a rate of 5 ° C./min. It can obtain | require from the endothermic curve obtained at this time.

  The PTC function-imparting component is not particularly limited as long as it is a substance that can lower the melting start temperature and the melting peak temperature of PVDF used as a binder component, but is compatible with PVDF that is a crystalline polymer ( Compatible), preferably crystalline or non-crystalline polymeric compounds. In this specification, the term “compatible” refers to a state in which two different substances, particularly polymers, are uniformly mixed. These are completely compatible or partially compatible. May be. It can be determined that the mixed sample is transparent or has a film-forming ability so as to be uniformly mixed. For example, it is a compound containing a carbonyl group or a cyano group. A carbonyl group has a structure of —C (═O) —, and an oxygen atom has a much higher electronegativity than a carbon atom, so that an electron of a C═O bond is an electrically positive carbon atom. It exists in the vicinity of oxygen atoms having a higher electronegativity than in the vicinity. Similarly, the cyano group is a strong electron-withdrawing group having a triple structure between a carbon atom and a nitrogen atom, with electrons biased on the nitrogen atom. One or a plurality of carbonyl groups and cyano groups may be contained. For example, a dione compound containing two carbonyl groups is also included in the PTC function-imparting component of the present invention.

In general, it is known that when a crystalline polymer and an amorphous polymer are compatible, the melting point of the crystalline polymer is lowered. The factor that most affects the melting point drop is a thermodynamic parameter χ ₁₂ value representing the strength of interaction between the two polymers, and is derived by the Flory-Huggins theory. Based on this theory, it is said that a melting point drop occurs in a compatible crystalline / amorphous polymer blend system when the χ ₁₂ value shows a negative value. In a preferred embodiment, the compatible substance is a carboxyl group (—COOH), a carboxylic acid ester (—COO—R), a carbonate group (R—O— (C═O) —O—R ′), an imide group ( R-CONHCO-R ′), or a crystalline or non-crystalline polymer containing an amide group (R—C═ONH—R ′).

  In this embodiment, the specific reason why the PTC function-imparting component made of such a compatible material lowers the melting point of PVDF is not clear, but the electrical properties of these additives derived from a carbonyl group or a cyano group It is presumed that having (polarity) enhances the interaction with PDVF and exhibits its melting point lowering effect.

  Therefore, in a preferred embodiment, the PTC function-imparting component is acrylic acid (AAc), methacrylic acid (MAc), barbituric acid (BTA), acetylacetone, polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), Polyvinyl acetate (PVAc), di-2-ethylhexyl phthalate (DEHP), polybutylene succinate (PBS), polycarbonate (PC), polyacrylonitrile (PAN), polyamide (PA), polyimide (PI), polyamideimide ( PAI) and one or more selected from the group consisting of derivatives (copolymers) thereof.

Examples of the methacrylic acid ester having good compatibility with PVDF include the following compounds. Methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, hexyl methacrylate, octyl methacrylate, dodecyl methacrylate, stearyl methacrylate, 2-ethylhexyl methacrylate, phenyl methacrylate, benzyl methacrylate, methoxyethyl methacrylate, ethoxyethyl methacrylate, n-butoxyethyl methacrylate, isobutoxyethyl methacrylate, t-butoxyethyl methacrylate, phenoxyethyl methacrylate, methacryl Nonylphenoxyethyl acid, 3-methoxybutyl methacrylate, Blemmer PME-100 (trade name, manufactured by NOF Corporation), Blemmer PME-200 (trade name) Nippon Oil & Fats Co., Ltd.).
Among the methacrylic acid esters, the following are preferably used from the viewpoint of easy availability and compatibility with PVDF. Methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, dodecyl methacrylate, stearyl methacrylate, 2-ethylhexyl methacrylate are preferred, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, More preferred is t-butyl methacrylate. A vinyl monomer may be used individually by 1 type, and may use 2 or more types together.

  Moreover, as a fluorinated alkyl methacrylate, the following compounds can be used conveniently. 2,2,2-trifluoroethyl methacrylate, 2,2,3,3-tetrafluoropropyl methacrylate, 2,2,3,3,3-pentafluoropropyl methacrylate, 2,2,3,4,4,4 -Hexafluorobutyl methacrylate, 2,2,3,3,4,4,5,5-octafluoropentyl methacrylate, 2,2,2-trifluoroethyl α-fluoroacrylate, 2,2,3,3-tetra Fluoropropyl alpha fluoroacrylate, 2,2,3,3,3-pentafluoropropyl alpha fluoroacrylate, 2,2,3,3,4,4,5,5-octafluoropentyl alpha fluoroacrylate and the like.

As one embodiment of the present invention, the PTC function-imparting component includes an amide, an imide, a maleimide, a dione compound, and the like.
As the amide, a primary amide is particularly preferable, and examples thereof include N-vinyl amide, divinyl amide, silyl (vinyl) amide, and glyoxylated vinyl amide.

Specific examples of the imide include divinylimide such as N-vinylimide, N-vinylphthalimide, and vinylacetamide.
Examples of maleimides include monomaleimide, bismaleimide, trismaleimide, and polymaleimide.

  Specific examples of bismaleimide include, for example, N, N′-bismaleimide-4,4′-diphenylmethane, 1,1 ′-(methylenedi-4,1-phenylene) bismaleimide, N, N ′-(1, 1′-biphenyl-4,4′-diyl) bismaleimide, N, N ′-(4-methyl-1,3-phenylene) bismaleimide, 1,1 ′-(3,3′-dimethyl-1,1 '-Biphenyl-4,4'-diyl) bismaleimide, N, N'-ethylenedimaleimide, N, N'-(1,2-phenylene) dimaleimide, N, N '-(1,3-phenylene) dimaleimide N, N'-thiodimaleimide, N, N'-dithiodimaleimide, N, N'-ketone dimaleimide, N, N'-methylene bismaleimide, bismaleimide methyl ether, 1,2-bis Maleimide-1,2-d Njioru, N, N'-4,4'-diphenyl ether - bismaleimide, 4,4'-bismaleimide - diphenyl sulfone and the like.

  The dione compound used in the present embodiment refers to a β-diketo compound having a carbon atom between two carbonyl carbons, or barbituric acid and derivatives thereof. Examples of dione compounds include barbituric acid and its derivatives, acetylacetone and its derivatives, and the like.

  It is preferable that the content rate of these PTC function provision components contained in the said binder is 0-50 mass%, More preferably, it is 1-40 mass%, More preferably, it is 5-30 mass%. It is. When there is more content of a PTC function provision component than 50 mass%, there exists a possibility that the bond strength with a positive electrode active material may decline as a binder.

  The binder of the present embodiment is a mixture obtained by dissolving polyvinylidene fluoride (PVDF) as a binder component and a PTC function-imparting component in a common solvent that dissolves them together, and then substituting the solvent for precipitation. It is preferable to prepare. This is because the binder prepared by this method exists in a state where the binding component and the PTC function-imparting component are uniformly mixed at the molecular level.

  In another embodiment, a powder mixture of polyvinylidene fluoride (PVDF) and a PTC function-imparting component may be prepared by mixing with a powder mixer such as a ball mill or a rocking mixer or a known crusher. Good. This is because it is easily uniformized in a solvent for preparing the electrolytic solution or electrode mixture layer to become a binder.

(PVDF copolymer)
Alternatively, as another embodiment, a polyvinylidene fluoride (PVDF) copolymer containing PVDF as a binding component and a PTC function-imparting component in the molecule may be used as the binding material. In this case, in the presence of the non-aqueous electrolyte, it is preferable that the melting start temperature and / or the melting peak temperature of the PVDF copolymer is lower than that of PVDF, which is a vinylidene fluoride single polymer. For example, it has a melting start temperature and / or a melting peak temperature at 50 ° C. to 100 ° C., more preferably 60 ° C. to 90 ° C. As such a PVDF copolymer, PVDF-HFP (hexafluoropropylene), PVDF-PEO (polyoxyethylene), or the like can be used.

(Current collector)
Various types of current collectors can be used in the present embodiment, but metals and alloys are usually used. Specifically, examples of the positive electrode current collector include aluminum, nickel, and SUS, and examples of the negative electrode current collector include copper, nickel, and SUS.

(Other ingredients)
In addition to the positive electrode active material, the positive electrode mixture layer included in the positive electrode for a lithium ion secondary battery according to this embodiment may include an appropriate component used for producing the positive electrode mixture layer. . For example, when the positive electrode mixture layer is formed from a mixture slurry, the positive electrode mixture layer may contain various blending components derived from the mixture slurry. Examples of various compounding components derived from such a mixture slurry include thickeners and other additives such as surfactants, dispersants, wetting agents, and antifoaming agents.

(Negative electrode active material)
Negative electrode active materials include metallic lithium, lithium-containing alloys, metals or alloys that can be alloyed with lithium, oxides that can be doped / undoped with lithium ions, and transition metals that can be doped / undoped with lithium ions At least one selected from the group consisting of nitrides and carbon materials capable of doping and undoping lithium ions (may be used alone or a mixture containing two or more of these may be used) Can be used.

Examples of metals or alloys that can be alloyed with lithium (or lithium ions) include silicon, silicon alloys, tin, and tin alloys. Further, lithium titanate may be used.
Among these, carbon materials that can be doped / undoped with lithium ions are preferable. Examples of such carbon materials include carbon black, activated carbon, graphite materials (artificial graphite, natural graphite), amorphous carbon materials, and the like. The form of the carbon material may be any of a fibrous form, a spherical form, a potato form, and a flake form.

  Specific examples of the amorphous carbon material include hard carbon, coke, mesocarbon microbeads (MCMB) fired at 1500 ° C. or less, and mesopause bitch carbon fiber (MCF).

Examples of the graphite material include natural graphite and artificial graphite. As artificial graphite, graphitized MCMB, graphitized MCF, and the like are used. Further, as the graphite material, a material containing boron can be used. As the graphite material, those coated with a metal such as gold, platinum, silver, copper and tin, those coated with amorphous carbon, and those obtained by mixing amorphous carbon and graphite can be used.
These carbon materials may be used alone or in combination of two or more.

(Method for forming positive electrode mixture layer)
The mixture layer included in the positive electrode for the lithium ion secondary battery of the present invention is applied by applying the positive electrode mixture slurry containing the positive electrode active material, the conductive additive, and the binder to the surface of the current collector and then drying. Can be manufactured. In this case, it is preferable to form the positive electrode mixture slurry by dispersing the positive electrode active material and the conductive additive in a solution obtained by dissolving the above-described binder in a solvent. The amount of the binder contained in the positive electrode mixture slurry can be, for example, about 1 to 10% by mass of the total solid components. When the content of the binder is less than 1% by mass, the effect of blocking the conductive path is reduced when the temperature of the mixture layer is increased. On the other hand, since the binder generally exhibits insulating properties, if its content is more than 10% by mass, the contact resistance in the mixture layer increases and the battery capacity decreases, which is not preferable.

  The solvent contained in the mixture slurry also serves as a common solvent for preparing the binder, and is a non-proton represented by N-methylpyrrolidone, dimethyl sulfoxide, propylene carbonate, dimethylformamide, γ-butyrolactone, etc. Polar solvent or a mixture thereof can be selected.

In applying and drying the mixture slurry to the current collector, the application and drying method is not particularly limited. For example, methods such as slot die coating, slide coating, curtain coating, or gravure coating may be used. Examples of the drying method include drying with warm air, hot air, low-humidity air, vacuum drying, and (far) infrared rays. Although it does not specifically limit about drying time and drying temperature, Drying time is normally 1 minute-30 minutes, and drying temperature is 40 to 180 degreeC normally.
In order to form a plurality of layers having different concentrations of the PTC function-imparting component, there is a method in which a plurality of mixture slurry is prepared and applied sequentially. For example, when providing a layer having a high content of the PTC function-imparting component in the lower layer, a positive electrode mixture layer containing a predetermined concentration (for example, 2% by mass) of the PTC function-imparting component on both sides of the Al current collector foil is provided on one side. Application and drying are performed so as to have a predetermined thickness (for example, 15 μm). Next, a positive electrode material mixture layer containing no PTC function-imparting component is applied to the upper layer so that one surface has a predetermined thickness (for example, 85 μm). When this is pressed to a desired density, for example, a two-layer positive electrode mixture layer having a single side of about 70 μm can be formed. In order to produce a multi-layer coating, either single-sided sequential coating or double-sided sequential coating may be used. In the method for producing a composite layer, after applying and drying the above-mentioned composite slurry on a current collector, a die press or roll It is preferable to have a step of reducing the porosity of the active material layer by pressurization using a press or the like.

For example, the electrolyte solution is preferably one that is usually used in a lithium ion secondary battery, and specifically has a form in which a supporting salt (lithium salt) is dissolved in an organic solvent. Examples of the lithium salt include lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium perchlorate (LiClO ₄ ), lithium hexafluoroarsenate (LiAsF ₆ ), six Inorganic acid anion salts such as lithium fluorotantalate (LiTaF ₆ ), lithium tetrachloroaluminate (LiAlCl ₄ ), lithium decachlorodecaborate (Li ₂ B ₁₀ Cl ₁₀ ), lithium trifluoromethanesulfonate (LiCF ₃₎ Organic acids such as SO ₃ ), lithium bis (trifluoromethanesulfonyl) imide (Li (CF ₃ SO ₂ ) ₂ N), lithium bis (pentafluoroethanesulfonyl) imide (Li (C ₂ F ₅ SO ₂ ) ₂ N) List at least one lithium salt selected from anionic salts Can. Among these, lithium hexafluorophosphate (LiPF ₆ ) is preferable.

  Examples of the organic solvent include cyclic carbonates, fluorine-containing cyclic carbonates, chain carbonates, fluorine-containing chain carbonates, aliphatic carboxylic acid esters, fluorine-containing aliphatic carboxylic acid esters, and γ-lactone. , Fluorine-containing γ-lactones, cyclic ethers, fluorine-containing cyclic ethers, chain ethers, and at least one organic solvent selected from the group consisting of fluorine-containing chain ethers can be used.

  Examples of cyclic carbonates include propylene carbonate (PC), ethylene carbonate (EC), and butylene carbonate (BC). Moreover, as a fluorine-containing cyclic carbonate, fluoroethylene carbonate (FEC) can be mentioned, for example. Further, examples of the chain carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), and dipropyl carbonate (DPC). Can be mentioned. Examples of the aliphatic carboxylic acid esters include methyl formate, methyl acetate, and ethyl propionate. Furthermore, examples of γ-lactones include γ-butyrolactone. Examples of cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, and 1,4-dioxane. Furthermore, examples of the chain ethers include 1,2-ethoxyethane (DEE), ethoxymethoxyethane (EME), diethyl ether, 1,2-dimethoxyethane, and 1,2-dibutoxyethane. . Other examples include nitriles such as acetonitrile and amides such as dimethylformamide. These can be used alone or in combination of two or more.

  The electrolyte includes organic sulfone compounds such as sultone derivatives and cyclic sulfonate esters, organic disulfone compounds such as disulfone derivatives and cyclic disulfonate esters, vinylene carbonate derivatives, ethylene carbonate derivatives, ester derivatives, divalent phenol derivatives, ethylene Additives such as glycol derivatives, terphenyl derivatives, and phosphate derivatives may be added. These form a film on the surface of the negative electrode active material, reduce gas generation in the battery, and further improve the capacity retention rate.

  Examples of the organic sulfone compounds include 1,3-propanesulfone (saturated sultone) and 1,3-propene sultone (unsaturated sultone). Examples of organic disulfone compounds include methylene methanedisulfonate. Examples of the vinylene carbonate derivative include vinylene carbonate (VC). Moreover, as an ethylene carbonate derivative, fluoroethylene carbonate (FEC) can be mentioned, for example. Furthermore, examples of the ester derivative include 4-biphenylyl acetate, 4-biphenylyl benzoate, 4-biphenylyl benzyl carboxylate, and 2-biphenylyl propionate. Examples of the divalent phenol derivative include 1,4-diphenoxybenzene and 1,3-diphenoxybenzene. Furthermore, examples of the ethylene glycol derivative include 1,2-diphenoxyethane, 1- (4-biphenylyloxy) -2-phenoxyethane, and 1- (2-biphenylyloxy) -phenoxyethane. . Examples of the terphenyl derivative include o-terphenyl, m-terphenyl, p-terephenyl, 2-methyl-o-terphenyl, and 2,2-dimethyl-o-terphenyl. Further, examples of the phosphate derivative include triphenyl phosphate.

  Examples of the separator include a microporous film made of polyolefin such as polyethylene (PE) and polypropylene (PP), a porous flat plate, and a nonwoven fabric.

It is considered that the heat generation suppressing action exhibited by the positive electrode for a lithium ion secondary battery according to the present invention during an internal short circuit or the like is due to the melting point lowering action of the PTC function-imparting component contained in the binder. Therefore, a typical example will be described below.
[Reference Examples 1 to 34] Measurement of melting point of binder in the presence of non-aqueous electrolyte by DSC <List of components imparting PTC function>
Table 1 below shows a list of compounds used as PTC function-imparting components.

<Sample preparation>
PVDF and various PTC function-imparting components (powder) were mixed at a predetermined ratio for about 15 minutes using an agate mortar. For example, when the mixing ratio of PVDF (powder) and PTC function-imparting component (powder) was 1: 1, 0.1 g was weighed and mixed. This mixed powder was vacuum dried at room temperature (25 ° C.) for 10 hours or more.
3 mg of the sample was weighed and put into SUS-PAN for DSC measurement weighed in advance. Subsequently, 6 mg of an electrolytic solution (1M-LiPF ₆ / 3EC7EMC) was added to the SUS-PAN (powder: electrolytic solution = 1: 2 by weight ratio). At that time, it was visually confirmed that almost all of the powder was immersed in the liquid. The lid (weighed in advance) was quickly set (weighed) and hermetically sealed with a dedicated press.

<Measurement>
Using a high-sensitivity differential scanning calorimeter DSC7000X manufactured by Hitachi High-Tech Science, the melting temperature was measured under conditions of a scanning speed of 5 ° C./min and room temperature → 210 ° C.

  <Result>

The PVDF manufacturer name and product name used in Reference Examples 1 to 34, and the melting temperature of PVDF alone measured by DSC as a comparative example are shown.

Table 3 shows the melting start temperature and the peak temperature (melting point) when 75% by mass of the binder component (PVDF) and 25% by mass of the PTC function-imparting component or 50% by mass of each are mixed.

As shown in Tables 2 and 3, it was found that the mixture of the PVDF and the PTC function-imparting component started melting at about 70 ° C and had a peak temperature in the vicinity of 90 ° C to 130 ° C.
Moreover, the DSC chart of the sample measured in Example 1, 2 and Comparative Example 2 is shown in FIG. From the results shown in FIG. 3, it can be seen that the melting start temperature and melting point of PVDF, which is a binder component, are clearly reduced by the addition of the PTC function-imparting component.

[Example 1]
Positive electrode fabrication (lower layer)
1. Slurry preparation (A)
The slurry preparation used 5 L planetary dispa.
NCM523 (made by Umicore, composition formula LiNi _0.5 Co _0.2 Mn _0.3 O ₂ ) 920 g, Super-P (conductive carbon made by TIMCAL) 20 g, KS-6 (flaky graphite made by TIMREX) After mixing 20 g for 10 minutes, 50 g of N-methylpyrrolidone (NMP) was added and further mixed for 20 minutes.
Next, 10 g of a BMI-1000 / BTA = 2/1 mixture dissolved in NMP (100 g) and an 8% -PVDF solution (Kureha PVDFW # 7200 dissolved in NMP) (125 g) were added and kneaded for 30 minutes. Thereafter, 100 g of a 10% solution obtained by dissolving 10 g of a BMI-1000 / BTA = 2/1 solution in NMP and 125 g of an 8% -PVDF solution were added and kneaded for 30 minutes. Thereafter, 106 g of NMP was added to adjust the viscosity and mixed for 30 minutes, followed by vacuum defoaming for 30 minutes. Thus, a slurry having a solid content concentration of 60% was prepared.

2. Coating / Drying A die coater was used for slurry coating. The slurry was applied to one side of an aluminum foil (thickness 20 μm, width 200 mm) so that the coating weight after drying was 3.0 mg / cm ² (applying thickness was about 15 μm) and dried. Next, the slurry was applied to an aluminum foil on the opposite surface (uncoated surface) in a similar manner so that the coating weight was 3.0 mg / cm ² and dried.

Positive electrode fabrication (upper layer)
1. Slurry preparation (B)
The slurry preparation used 5 L planetary dispa.
NCM523 (made by Umicore, composition formula LiNi _0.5 Co _0.2 Mn _0.3 O ₂ ) 920 g, Super-P (conductive carbon made by TIMCAL) 20 g, KS-6 (flaky graphite made by TIMREX) After mixing 20 g for 10 minutes, 50 g of N-methylpyrrolidone (NMP) was added and further mixed for 20 minutes.

  Next, 230 g of 8% -PVDF solution (Kureha PVDFW # 7200 dissolved in NMP) was added and kneaded for 30 minutes, and then 230 g of 8% -PVDF solution was added and kneaded for 30 minutes. Next, 100 g of a solution dissolved in NMP was added and kneaded for 30 minutes. Thereafter, vacuum defoaming was performed for 30 minutes. Thus, a slurry having a solid content concentration of 62% was prepared.

2. Coating / Drying A die coater was used for slurry coating. The slurry is applied to one side of the sheet coated with the lower layer so that the coating weight after drying is 17.0 mg / cm ² (the coating thickness is about 85 μm, the total coating amount on one side is 20.0 mg / cm ² ) and dried. did. Next, the slurry was applied to the opposite surface in the same manner so that the coating weight was 17.0 mg / cm ² and dried.
The double-sided positive electrode roll thus obtained was dried in a vacuum drying oven at 130 ° C. for 12 hours.

3. Press A 35-ton press was used. The gap (gap) between the upper and lower rolls was adjusted, and the positive electrode was compressed so that the press density was 2.9 ± 0.05 g / cm ³ (the coating thickness after pressing was about 75 μm).

4). Slit The electrode was slit to obtain a positive electrode C-1 so that an electrode application area (surface: 56 mm × 334 mm, back: 56 mm × 408 mm) and a tab welding margin were obtained.

Production of negative electrode Slurry preparation A 5 L planetary dispa was used for slurry preparation.
After mixing 930 g of natural graphite and 1 g of Super-P (conductive carbon, BET specific surface area 62 m ² / g) for 10 minutes, 500 g of NMP was added and further mixed for 20 minutes. Next, 500 g of 8% -PVDF solution (PVDF dissolved in NMP) was added and kneaded for 30 minutes, and then 250 g of 8% -PVDF solution was further added and kneaded for 30 minutes. Thereafter, 32 g of NMP was added to adjust the viscosity and mixed for 30 minutes, followed by vacuum defoaming for 30 minutes. Thus, a slurry having a solid content concentration of 45% was prepared.

2. Coating / Drying A die coater was used for slurry coating.
The slurry was applied to one side of a copper foil (thickness 10 μm) and dried so that the coating weight after drying was 11.0 mg / cm ² . Next, the slurry was applied to a copper foil on the opposite surface (uncoated surface) in the same manner so that the coating weight was 11.0 mg / cm ² and dried. The double-sided coated (22.0 mg / cm ² ) negative electrode roll thus obtained was dried at 120 ° C. for 12 hours in a vacuum drying oven.

3. Press A small press was used.
The gap (gap) between the upper and lower rolls was adjusted, and the negative electrode was compressed so that the press density was 1.45 ± 0.05 g / cm ³ .

4). Slit The electrode was slit so that an electrode application area (front surface: 58 mm × 372 mm, back surface: 58 mm × 431 mm) and a tab welding margin were obtained, and negative electrode A-1 was obtained.

Battery fabrication Winding type battery (design capacity 1Ah)
1. For the winding separator, a polyethylene porous membrane (60.5 mm × 450 mm) having a porosity of 45% and a thickness of 25 μm was used (S-1).
The negative electrode A-1 (front surface / back surface), the separator (S-1), the positive electrode C-1 (back surface / front surface), and the separator (S-1) were wound and pressed. Next, an aluminum tab was joined to the blank portion of the positive electrode C-1 with an ultrasonic bonding machine, and a nickel tab was joined to the blank portion of the negative electrode A-1 with an ultrasonic bonding machine. This was sandwiched between laminate sheets and heat-sealed on the three sides.

2. Electrolyte Injection Before the electrolyte injection, the above was dried under reduced pressure at 70 ° C. × 12 h in a vacuum dryer. An electrolyte solution (1 mol-LiPF ₆ , EC / DEC = 3/7 (vol. Ratio), additive VC 1.0 wt%) 4.7 ± 0.1 g was injected, and then heat-sealed while evacuating. .

3. Activation treatment The battery after electrolyte injection was maintained for 24 hours. Next, the battery was charged at a constant current of 0.05 C for 4 hours (0.05 C-CC) and then rested for 12 hours. Thereafter, the battery was charged with constant current and constant voltage (0.1C-CCCV) at 0.1 C to 4.2 V, paused for 30 minutes, and then discharged with constant current (0.1 C-CC) at 0.1 C up to 2.8 V. Furthermore, after charging / discharging cycle (4.2V charging at 0.1C-CCCV and 2.8V discharging at 0.1C-CC) was repeated 5 times, the battery was fully charged at 4.2V (SOC 100%). The state was stored at 25 ° C. for 5 days. Thus, a battery D-1 was obtained.

[Example 2]
A positive electrode roll produced in the same manner as in Example 1 was slit to obtain a positive electrode C-2 so that an electrode application area (front and back surfaces: 174 mm × 94 mm) and a tab welding margin were obtained.
A negative electrode roll produced in the same manner as in Example 1 was slit to obtain a positive electrode C-2 so that an electrode application area (front and back surfaces: 180 mm × 100 mm) and a tab welding margin were obtained.

Battery fabrication Multi-layer battery (design capacity 5Ah)
An aluminum tab was joined to the blank portion of the positive electrode C-2 with an ultrasonic joining machine. A nickel tab was joined to the blank portion of the negative electrode A-2 with an ultrasonic joining machine.

1. As the laminated separator, a polyethylene porous membrane (183 mm × 100 mm) having a porosity of 45% and a thickness of 25 μm was used (S-2).
The negative electrode A-2, the separator (S-2), the positive electrode C-2, the separator (S-2), and the negative electrode A-2 were laminated in this order so as to form a positive electrode 5 layer and a negative electrode 6 layer. Subsequently, the laminate sheet was sandwiched and heat-sealed on the three sides.

2. Electrolyte Injection Before the electrolyte injection, the above was dried under reduced pressure at 70 ° C. × 12 h in a vacuum dryer. 19.6 ± 0.3 g of electrolyte (1 mol-LiPF ₆ , EC / DEC = 3/7 (vol. Ratio), additive VC 1.0 wt%) was injected, and then heat-sealed while evacuating. .
3. Activation treatment An activation treatment was performed in the same manner as in Example 1 to obtain a battery D-2.

[Test Example 1 and Comparative Test Example 1]
A nail penetration test was performed using the wound battery (design capacity 1 Ah) produced in Example 1. A nail having a diameter of 6 mm was inserted into the middle part of the battery (cell) at a speed of 20 mm / second, and the positive electrode and the negative electrode were short-circuited inside the battery container. As a result of investigating the presence or absence of battery rupture and expansion, and ignition and smoke from the battery, ignition was recognized only 3 times out of 10 nail penetration tests conducted using the battery manufactured with the same specifications. The remaining 7 times only smoked slightly.
As Comparative Test Example 1, a positive electrode using only PVDF as a binder was applied without adding a mixture of BMI-1000 / BTA = 2/1 in Example 1, and a wound battery (design capacity 1 Ah) Was made. When a similar nail penetration test was performed, ignition was observed in 5 out of 10 times.

[Test Example 2]
Using PMMA (molecular weight 15,000) instead of the mixture of BMI-1000 / BTA = 2/1 in Example 1 and using a stacked battery (design capacity 5 Ah) manufactured by the method described in Example 2. The same nail penetration test (nail diameter 6 mm, nail penetration speed 20 mm / second) as in Test Example 1 was conducted. As a result, no ignition was observed once in 10 times. In this test example, a clear difference was recognized as compared with Comparative Test Example 1 described above.

[Test Example 3 and Comparative Test Example 2]
A wound battery (design capacity: 1 Ah) manufactured using NCA instead of NCM523 which is the positive electrode active material of Example 1 and using BMI-1000 instead of the mixture of BMI-1000 / BTA = 2/1 is used. Then, the same nail penetration test as in Test Example 1 (nail diameter 3 mm, nail penetration speed 10 mm / second) was performed. As a result, ignition was recognized in 6 out of 10 times. On the other hand, as Comparative Test Example 2, NCA was used instead of NCM523 which is the positive electrode active material of Example 1, and only PVDF was used as a binder without adding a mixture of BMI-1000 / BTA = 2/1. In the wound battery (design capacity 1 Ah) coated with the positive electrode used, ignition was observed in all 10 times, and a clear difference in heat generation was recognized.

10, 20 Positive electrode 11, 22 Layer A
12, 21 layer B
13, 23 Cathode current collector 14, 24 Cathode mixture layer 15, 25 Nail

Claims (10)

A positive electrode for a lithium ion secondary battery comprising a current collector and a positive electrode mixture layer applied on the current collector,
The positive electrode mixture layer includes a layer A including a positive electrode active material, a conductive additive and a binder component, and a layer B including a positive electrode active material, a conductive additive, a binder component and a PTC function-imparting component. A positive electrode for a lithium ion secondary battery.   The layer B is provided on the current collector side in the thickness direction of the positive electrode mixture layer, and the layer A is provided on the opposite side of the current collector across the layer B. Item 2. A positive electrode for a lithium ion secondary battery according to Item 1.   The layer A is provided on the current collector side in the thickness direction of the positive electrode mixture layer, and the layer B is provided on the opposite side of the current collector across the layer A. Item 2. A positive electrode for a lithium ion secondary battery according to Item 1.   The binder component contains polyvinylidene fluoride (PVDF), and the PTC function-imparting component is melted by a mixture of the binder component and the PTC function-imparting component measured by differential scanning calorimetry in the presence of a non-aqueous electrolyte. The positive electrode for a lithium ion secondary battery according to any one of claims 1 to 3, wherein the starting temperature and / or the melting peak temperature is lowered as compared with the case of only the binder component.   5. The lithium ion secondary battery according to claim 1, wherein the positive electrode active material is lithium nickel cobalt aluminum oxide (NCA) and / or lithium nickel cobalt manganese oxide (NCM). Positive electrode.   The positive electrode for a lithium ion secondary battery according to any one of claims 1 to 5, wherein the PTC function-imparting component is a compound containing a carbonyl group or a cyano group.   The positive electrode for a lithium ion secondary battery according to any one of claims 1 to 5, wherein the PTC function-imparting component is an amorphous polymer that is compatible with the binder component.   The lithium ion secondary according to any one of claims 1 to 7, wherein the content of the PTC function-imparting component is 0 to 50 mass% with respect to the total amount of the mixture of the binding component and the PTC function-imparting component. Battery positive electrode.   The positive electrode for a lithium ion secondary battery according to claim 1, comprising a polyvinylidene fluoride copolymer in place of the binder component and the PTC function-imparting component contained in the layer B.   A lithium ion secondary battery comprising the positive electrode according to any one of claims 1 to 9, a separator, and a nonaqueous electrolyte.

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