JP2016111013A - Secondary battery electrode, secondary battery, and manufacturing methods therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: a secondary battery electrode including a conductive assistant appropriately designed in particle diameter; a secondary battery; and manufacturing methods therefor.SOLUTION: A method for manufacturing a secondary battery electrode of the present invention comprises a select step for selecting an electrode active material having an average particle diameter D(μm), a first conductive assistant having an average particle diameter d(μm), and a second conductive assistant having an average particle diameter d(μm) larger than d(μm). The average particle diameter d(μm) satisfies the condition given by the expression (1) below, and an electrode formation step for applying an electrode mixture material including the electrode active material, the first conductive assistant and the second conductive assistant to a current collector, to form an electrode mixture material layer: D×((3/2)-1)≤d≤D Expression(1).SELECTED DRAWING: None

Description

  The present invention relates to an electrode for a secondary battery, a secondary battery, and a manufacturing method thereof.

  A lithium ion secondary battery is a secondary battery having a high charge / discharge capacity and capable of high output. At present, lithium ion secondary batteries are mainly used as a power source for portable electronic devices, and further expected as a power source for electric vehicles that are expected to be widely used in the future.

  Usually, an electrode for a lithium ion secondary battery is prepared by mixing a fine conductive additive such as acetylene black or ketjen black (registered trademark) in addition to an active material powder in order to improve conductivity. In such a conventional electrode, the conductivity of the electrode mixture layer is ensured by a continuation of innumerable point contacts between fine conductive assistants of about several tens of nanometers. There is a contact resistance at the point where the conductive assistants are in point contact, and the contact resistance increases in the process of cycling, storage, and the like, and further deterioration may occur by cutting (cutting the conductive path). As a means for reducing point contact, introduction of a conductive aid having a relatively large particle size is conceivable. In Patent Document 1, carbon particles having an average particle diameter of 8 to 45 μm are added as a second conductive auxiliary agent in the first conductive auxiliary agent composed of carbon particles having an average particle diameter of 0.01 to 1 μm in order to improve storage characteristics. Is disclosed. Patent Document 2 discloses that a second conductive assistant having a large particle diameter is introduced to reduce resistance.

JP-A-11-283628 JP 2006-179367 A

However, simply adding the second conductive additive having a particle size slightly larger than that of the first conductive additive is insufficient to effectively suppress the conduction path breakage. In addition, when the particle size of the second conductive additive is too large, the conductivity in the electrode varies, and the electrode may be deteriorated due to uneven reaction. Therefore, a more preferable particle size design is required for the conductive assistant.
This invention is made | formed in view of this situation, and makes it a subject to provide the electrode for secondary batteries and secondary battery which have the conductive support agent by which the appropriate particle size design was made, and these manufacturing methods.

  As a result of diligent search, the present inventor has found a new relationship between the particle size of the conductive additive and the particle size of the electrode active material that can suppress the increase in the internal resistance of the battery after the cycle.

The manufacturing method of the electrode for secondary batteries of the present invention includes an electrode active material having an average particle diameter D (μm), a first conductive additive having an average particle diameter d _c1 (μm), and the d _c1 (μm). A selection step of selecting a second conductive auxiliary agent having a large average particle diameter d _c2 (μm) and the d _c2 (μm) satisfying the condition of the following formula (1):
An electrode forming step of forming an electrode mixture layer by applying an electrode mixture having the electrode active material, the first conductive additive, and the second conductive additive on a current collector. And
D × ((3/2) ^1/2 −1) ≦ d _c2 ≦ D (1)

The electrode for a secondary battery of the present invention includes an electrode active material having an average particle diameter D (μm), a first conductive additive having an average particle diameter d _c1 (μm), and an average particle larger than the above d _c1 (μm). It has a diameter d _c2 (μm), and the d _c2 (μm) has a second conductive additive that satisfies the condition of the following formula (1).
D × ((3/2) ^1/2 −1) ≦ d _c2 ≦ D (1)

  The secondary battery of the present invention is characterized by having the secondary battery electrode manufactured by the above-described secondary battery electrode manufacturing method or the secondary battery electrode described above.

  Since the present invention has the above-described configuration, it is possible to provide an electrode for a secondary battery, a secondary battery, and a method for manufacturing the same, each having a conductive additive having an appropriate particle size design.

It is a section explanatory view of the electrode compound material layer of the present invention. It is a perspective view of the electrode active material arrange | positioned with a close-packed structure. It is explanatory drawing which shows the relationship between the regular tetrahedron and its gravity center for calculating | requiring the distance between the center of an electrode active material, and the center of the clearance gap between electrode active materials. It is explanatory drawing which shows the relationship between an electrode active material, a 2nd conductive support agent, and a 1st conductive support agent. It is a figure which shows the alternating current impedance measurement result of the lithium ion secondary battery of Example 1. It is a figure which shows the alternating current impedance measurement result of the lithium ion secondary battery of the comparative example 1.

An electrode for a secondary battery, a manufacturing method thereof, and a secondary battery according to an embodiment of the present invention will be described in detail. In addition, in this specification, an electrode compound material means the mixture (solid content) containing the electrode active material before apply | coating to a collector. The electrode mixture layer refers to a layer (solid content) formed by applying an electrode mixture on a current collector. M ^* , m _c1 ^* , m _c2 ^* are the masses of the electrode active material, the first conductive auxiliary agent, and the second conductive auxiliary agent in the electrode composite layer when the electrode composite layer is 100% by mass in order. Although it is described as a ratio (mass%), M ^* , m _c1 ^* , and _{mc 2} ^* are, in order, the electrode active material in the electrode mixture when the electrode mixture is 100 mass%, the first conductive assistant. May be read as the mass ratio (% by mass) of the agent and the second conductive additive.

(Method for producing secondary battery electrode and secondary battery electrode)
The manufacturing method of the electrode for secondary batteries of this invention has a selection process and an electrode formation process. An adjustment step or / and a determination step may be performed between the selection step and the electrode formation step. Hereinafter, the selection process, the adjustment process, the determination process, and the electrode formation process will be described in order. The relationship between the electrode active material, the first conductive auxiliary agent, and the average particle size of the second conductive auxiliary agent described in each step is such that the electrode active material, the first conductive auxiliary agent, and the second conductive auxiliary agent are monodispersed spheres. This is a parameter based on the ideal model.

(1) Selection Step In the selection step, an electrode active material having an average particle diameter D (μm), a first conductive assistant having an average particle diameter d _c1 (μm), and a second conductivity having an average particle diameter d _c2 (μm). Select the auxiliaries. Here, the average particle diameter d _c2 (μm) of the second conductive auxiliary agent is larger than the average particle diameter d _c1 (μm) of the first conductive auxiliary agent (d _c2 > d _c1 ) and the electrode active material The average particle diameter D (μm) has the relationship of the following formula (1).
D × ((3/2) ^1/2 −1) ≦ d _c2 ≦ D (1)

  Formula (1) has shown the range of these average particle sizes for the electrode active material, the 1st conductive support agent, and the 2nd conductive support agent to arrange | position arrangement | positioning which raises electroconductivity in an electrode compound-material layer. The range of these average particle diameters can be applied to both the case where the electrode mixture layer is a positive electrode mixture layer and / or the case where it is a negative electrode mixture layer. This embodiment can be applied particularly effectively when the electrode active material is poor in conductivity and requires a conductive assistant.

  As shown in FIG. 1, the surface of the electrode active material 3 is covered with the first conductive additive 1. The second conductive auxiliary agent 2 having an average particle size larger than that of the first conductive auxiliary agent 1 fills the gap 4 between the electrode active materials 3, thereby allowing the second conductive auxiliary agent 2 to conduct long-distance conduction between the electrode active materials 3. Ensure sex. In this specification, “gap” refers to a three-dimensional space surrounded by at least three electrode active materials 3.

The upper limit of the average particle diameter d _c2 (μm) of the second conductive additive is the average particle diameter D (μm) of the electrode active material. When d _c2 (μm) is larger than D (μm), there is a possibility that uneven conductivity occurs in the electrode mixture layer. The upper limit of d _c2 (μm) is preferably D × 4/5.

The lower limit of the average particle diameter d _c2 (μm) of the second conductive additive is D × ((3/2) ^1/2 −1). When d _c2 (μm) is less than D × ((3/2) ^1/2 −1), the second conductive assistant becomes difficult to contact the electrode active material surrounding the gap, and the conductivity in the gap is reduced. May not contribute.

In the case where the electrode active material has a close-packed structure, the lower limit of the average particle diameter d _c2 (μm) of the second conductive additive is a size that just fits in the gap between the electrode active materials. This will be described in detail below.

FIG. 2 shows the electrode active material 3 arranged with a close-packed structure. The electrode active material 3 is a sphere having a particle diameter D (μm), and the second conductive additive 2 is a sphere having a particle diameter _dc2 (μm).

  A gap 4 is formed between the electrode active materials 3 arranged at a high density so as to have a close-packed structure. The center of the second conductive additive 2 having a size that just fits in the gap 4 is located at the center of gravity of a regular tetrahedron 6 formed by connecting the centers of the four electrode active materials 3 surrounding the gap 4.

FIG. 3 shows the relationship between a regular tetrahedron and its center of gravity. In FIG. 3, A, B, C, and D indicate the vertices of a regular tetrahedron, G indicates the centroid of the regular tetrahedron, G ₁ indicates the centroid of the triangle BCD surrounded by the vertices B, C, and D, G ₂ indicates the center of gravity of the triangle ACD surrounded by the vertices A, C, and D, G ₃ indicates the center of gravity of the triangle ABD surrounded by the vertices A, B, and D, and G ₄ is surrounded by the vertices A, B, and C The center of gravity of the triangle ABC is shown. In the triangle ABG ₁ surrounded by the vertex A, the vertex B, and the center of gravity G ₁ , ∠AG ₁ B is a right angle, and the length of the line segment AB is D (μm). If the center of the line segment BC is P, ∠BPG ₁ is a right angle and ∠G ₁ BP is 30 °. The length of the line segment BP is 1/2 × D. From the three-square theorem, the length of the line segment BG ₁ is D / √3, and the length of the line segment AG ₁ is √ (2/3) × D. From the nature of the centroid of the tetrahedron, the ratio of the length of the line segment GA line segment GG ₁ 1: 3. The length of the line segment AG is D × √ (2/3) × 3/4.

From the above, the distance E (μm) between the center of the tetrahedron formed by connecting the centers of the adjacent electrode active materials 3 and the center of the electrode active material 3 is D × √ (2/3) X3 / 4. As shown in FIG. 2, since the second conductive additive 2 is in contact with the electrode active material 3 surrounding the gap 4, the radius of the second conductive auxiliary agent 2 having a size that just fits in the gap 4 is equal to the adjacent electrode active material 3. A value obtained by subtracting the half value of the particle diameter D (μm) of the electrode active material 3 from the distance E between the center of gravity of the regular tetrahedron formed by connecting the centers of the materials 3 and the center of the electrode active material 3 (D × √ (2/3) × 3 / 4−½ × D). Twice the radius of the second conductive additive is the particle size d _c2 (μm). Therefore, the particle size d _c2 of the second conductive additive having a size that just fits in the gap 4 is 2 × (D × √ (2/3) × 3 / 4−1 / 2 × D) = D ((3 / 2) ^{1 /} 2-1). Therefore, the average particle diameter d _c2 (μm) of the second conductive additive has the relationship of the formula (1) with the average particle diameter D (μm) of the positive electrode active material.

Prior to the selection step, at least an average particle diameter D (μm) of the electrode active material, an average particle diameter d _c1 (μm) of the first conductive assistant, and an average particle diameter d _c2 (μm) of the second conductive assistant One should be measured. In the selection step, based on at least one of D (μm), d _c1 (μm) _, and d _c2 (μm) measured in advance, d _c2 > d _c1 and the relationship satisfying the above formula (1) is satisfied. As such, the remaining parameters of unmeasured D (μm), d _c1 (μm) _, and d _c2 (μm) may be determined.

Each average particle diameter D (μm), d _c1 (μm) _{, and} d _c2 (μm) mean D50 of each component, that is, the median diameter measured on a volume basis. Each average particle diameter D (μm), d _c1 (μm) _, d _c2 (μm) can be measured by a laser diffraction particle size distribution measuring method. The average particle diameter D of the electrode active material ([mu] m), the average particle of the first conductive additive diameter _{d c1} ([mu] m), and the average particle diameter _{d c2} (μm) of the second conductive _additive, in d _{c2> d c1} It may be adjusted by pulverization, classification, or the like so that the relationship is satisfied and satisfies the above formula (1).

Moreover, you may measure the average particle diameter D (micrometer) of an electrode active material previously. You may select the 2nd conductive support agent of the average particle diameter _dc2 (micrometer) which satisfy _{| fills} conditions of said Formula (1) based on measured D (micrometer).

Further, D (μm), d _c1 (μm), and d _c2 (μm) are preferably in the following ranges.

  The average particle diameter D of the electrode active material is preferably 0.6 μm or more and 60 μm or less, and more preferably 1 μm or more and 30 μm or less. When the average particle diameter D of the electrode active material is too small, the electrode active material may be difficult to handle. When the average particle diameter D of the electrode active material is excessive, the charge carriers are difficult to reach the inside of the electrode active material, and the battery capacity and rate characteristics may be reduced.

The average particle diameter d _c1 of the first conductive auxiliary agent is preferably 0.003 μm or more and 0.3 μm or less, further 0.01 μm or more and 0.1 μm or less, and 0.02 μm or more and 0.08 μm. More preferred. When the average particle diameter _dc1 of the first conductive auxiliary agent is too small, the handleability of the first conductive auxiliary agent may be reduced. When the average particle diameter _dc1 of the first conductive auxiliary agent is excessive, it becomes difficult to uniformly coat the surface of the electrode active material, and the conductivity of the surface of the electrode active material may be reduced.

The average particle diameter _dc2 of the second conductive additive is preferably 0.3 μm or more and 30 μm or less, more preferably 1 μm or more and 10 μm or less, and most preferably 2 μm or more and 8 μm or less. In this case, the subject of this invention can be achieved more effectively.

The ratio (d _c2 / d _c1 ) between the average particle diameter d _c2 (μm) of the second conductive auxiliary agent and the average particle diameter d _c1 (μm) of the first conductive auxiliary agent is preferably 10 or more and 1000 or less, and more preferably 50 It is preferably 500 or more and preferably 70 or more and 250 or less. When the above ratio (d _c2 / d _c1 ) is too small, the average particle size of the second conductive auxiliary agent and the average particle size of the first conductive auxiliary agent are too close. May be lost.

  The electrode active material used in the present embodiment is a material that can occlude and release metal ions such as lithium ions. Since the electrode active material used in the present embodiment is poor in conductivity, it is preferable to have a large necessity for mixing a conductive additive in the electrode mixture layer. The electrode active material used in this embodiment may be either a positive electrode active material or a negative electrode active material. The electrode active material when the electrode mixture layer is a positive electrode mixture layer is particularly referred to as a positive electrode active material, and the electrode active material when the electrode mixture layer is a negative electrode mixture layer is particularly referred to as a negative electrode active material.

Examples of the positive electrode active material include lithium composite metal oxides. As the lithium composite metal oxide represented by the general _{formula: Li a Ni b Co c Mn} d D e O f (0.2 ≦ a ≦ 1.2, b + c + d + e = 1,0 ≦ e <1, D is Li, Fe, At least one element selected from Cr, Cu, Zn, Ca, Mg, S, Si, Na, K, Al, Zr, Ti, P, Ga, Ge, V, Mo, Nb, W, La, 1.7 ≦ f ≦ 2.1), Li ₂ MnO ₃ can be mentioned. As the lithium composite metal oxide represented by the general _{formula: Li x A y Mn 2-} y O 4 (A is a transition metal element, Li, Ca, Mg, S , Si, Na, K, Al, P, Ga , And at least one element selected from Ge, a spinel compound represented by 0 <x ≦ 2.2, 0 ≦ y ≦ 1), and a solid solution composed of a mixture of a spinel compound and a layered compound, LiMPO ₄ , LiMVO ₄ or Li ₂ MSiO ₄ (wherein M is selected from at least one of Co, Ni, Mn, and Fe).

For example, as the layered compound, LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNi _0.5 Co _0.3 Mn _0.2 O ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , at least one selected from LiNi _0.5 Mn _0.5 O ₂ , LiNi _0.75 Co _0.1 Mn _0.15 O ₂ , LiMnO ₂ , LiNiO ₂ , and LiCoO ₂ . Examples of the spinel compound include LiNi _0.5 Mn _1.5 O ₄ and LiMn ₂ O ₄ . Examples of the polyanion compound include LiFePO ₄ , LiCoPO ₄ , Li ₂ CoPO ₄ F, Li ₂ MnSiO ₄ , and Li ₂ FeSiO ₄ .

As the negative electrode active material, a material that can occlude and release metal ions such as lithium ions can be used. Therefore, the negative electrode active material may be a simple substance, an alloy, or a compound that can occlude and release metal ions such as lithium ions. For example, silicon etc. are mentioned as a negative electrode active material. When silicon or the like is used for the negative electrode active material, a silicon atom reacts with a plurality of lithiums, so that it becomes a high-capacity active material. However, there is a problem that volume expansion and contraction due to insertion and extraction of lithium becomes significant. In order to reduce the fear, it is preferable to employ a silicon-based material such as SiO _x (0.3 ≦ x ≦ 1.6) that disproportionates to silicon alone and silicon dioxide.

In addition, as the negative electrode active material, oxides such as Nb ₂ O ₅ , TiO ₂ , Li ₄ Ti ₅ O ₁₂ , WO ₂ , MoO ₂ , Fe ₂ O ₃ , or Li _3-x M _x N (M = A nitride represented by (Co, Ni, Cu) may be employed.

  The present invention can also be applied when a conductive material is used as the negative electrode active material. By applying the particle size design of the present invention to the first conductive assistant and the second conductive assistant of the present invention, it is possible to suppress the disconnection of the conductive path between the conductive negative electrode active materials. Examples of conductive materials that can be used as the negative electrode active material include Li, group 14 elements such as carbon, germanium, and tin, group 13 elements such as aluminum and indium, group 12 elements such as zinc and cadmium, antimony, and bismuth. Group 15 elements, alkaline earth metals such as magnesium and calcium, and group 11 elements such as silver and gold. These can be used as alloys or compounds. Specific examples of alloys or compounds include tin-based materials such as Ag-Sn alloy, Cu-Sn alloy, Co-Sn alloy, crystalline carbon-based materials such as various graphites, and amorphous carbon such as hard carbon and soft carbon. System materials.

  The electrode active material used for the electrode for the secondary battery according to the embodiment of the present invention is not necessarily used alone, and may be used as a mixed electrode active material including two or more kinds.

  The first conductive assistant and the second conductive assistant need only be chemically inert electronic high conductors, such as carbon black, graphite, acetylene black, ketjen black (registered trademark), Examples include phase grown carbon fiber (VGCF) and various metal particles. These may be used alone or in combination of two or more as the first conductive assistant and the second conductive assistant.

(2) Adjustment process In the adjustment process, the mass ratio of the electrode active material and the mass ratio of the second conductive additive when the electrode mixture layer is 100 mass% are expressed in terms of M ^* (mass%) and m _c2 ^* ( Mass%), the true density of the electrode active material is ρ (g / cm ³ ), the true density of the second conductive additive is ρ _c2 (g / cm ³ ), and the average particle diameter of the electrode active material is D ( μm), and the average particle diameter of the second conductive additive is d _c2 (μm), so that M ^* (mass%) and m _c2 ^* (mass%) satisfy the condition of the following formula (2) Next, the compounding ratio of the electrode active material and the second conductive additive is adjusted.
0.1 <(M ^* × ρ _c2 × d _c2 ³ ) / ( _{mc 2} ^* × ρ × D ³ ) <10 Equation (2)

  As shown in FIG. 2, when the electrode active materials 3 are arranged in a close-packed manner in the electrode mixture layer and have a cubic or hexagonal close-packed structure, the number of electrode active materials 3 and the number of gaps 4 between the electrode active materials 3 are Almost equal. It is preferable that the second conductive additive is contained in most of the gaps 4 between the electrode active materials 3. For this reason, it is preferable that the number of the electrode active materials 3 and the number of the 2nd conductive support agents 2 in an electrode compound-material layer are substantially equal.

The number of electrode active materials in the electrode mixture layer is determined by dividing the total volume V (cm ³ ) of the electrode active material in the electrode mixture layer by the volume W (cm ³ ) per electrode active material. . The total mass of the electrode active material in the electrode mixture layer is M (g), the true density of the electrode active material is ρ (g / cm ³ ), and the average particle diameter of the electrode active material is D (μm). In this case, the number N of electrode active materials in the electrode mixture layer is represented by the following formula (3).
^{N = V / W = 10 12} × (M / ρ) / (4π × (D / 2) 3/3) ··· (3)

The number n _c2 of the second conductive assistants in the electrode mixture layer is the total volume v _c2 (cm ³ ) of the second conductive assistants in the electrode mixture layer, and the volume w _c2 per second conductive assistant ( It is obtained by dividing by cm ³ ). The total mass of the second conductive additive in the electrode mixture layer is m _c2 (g), the true density of the second conductive additive is ρ _c2 (g / cm ³ ), and the average particle diameter of the second conductive additive Is represented by d _c2 (μm), the number n _c2 of the second conductive additive in the electrode mixture layer is represented by the following formula (4).
_{n c2 = v c2 / w c2} = 10 12 × (m c2 / ρ c2) / (4π × (d c2 / 2) 3/3) ··· (4)

The ratio (N / n _c2 ) between the number N of electrode active materials and the number n _c2 of second conductive assistants in the electrode mixture layer is expressed by the following formula (5).
_{N / n c2 = ((M} / ρ) / (4π × (D / 2) 3/3)) / ((m c2 / ρ c2) / (4π × (d c2 / 2) 3/3)) = (M × ρ _c2 × d _c2 ³ ) / (m _c2 × ρ × D ³ ) (5)

Here, when the mass ratio of the electrode active material and the mass ratio of the second conductive additive when the electrode mixture layer is 100 mass% are M ^* (mass%) and m _c2 ^* (mass%), Equation (5) is equal to (M ^* × ρ _c2 × _{dc 2} ³ ) / ( _{mc 2} ^* × ρ × D ³ ).

When (M ^* × ρ _c2 × d _c2 ³ ) / (m _c2 ^* × ρ × D ³ ) is 0.1 or less, the second conductive auxiliary agent is more than the number of gaps between the electrode active materials. Therefore, there is a possibility that the second conductive auxiliary agent that does not contribute to the conductivity in the gap increases. There is a risk that the amount of the electrode active material is relatively small, and the battery capacity is reduced. On the other hand, when (M ^* × ρ _c2 × d _c2 ³ ) / (m _c2 ^* × ρ × D ³ ) is 10 or more, the second conductive additive does not enter many of the gaps between the electrode active materials, The conductivity of the gap cannot be achieved, and the internal resistance of the battery may increase.

(M ^* × ρ _c2 × d _c2 ³ ) / (m _c2 ^* × ρ × D ³ ) is preferably 0.3 or more and 4 or less, and more preferably 0.5 or more and 3.5 or less. Most desirable. In this case, the internal resistance of the battery can be further suppressed.

Prior to the adjusting step, it is preferable to measure the true density ρ (g / cm ³ ) of the electrode active material and the true density ρ _c2 (g / cm ³ ) of the second conductive additive. Based on ρ (g / cm ³ ) and ρ _c2 (g / cm ³ ) that have become known by measurement or the like, M (g) and m _c2 (g) in the electrode mixture layer are _expressed by the formula (2). It is good to adjust to satisfy the condition. In addition, the mass ratio M ^* (mass%) of the electrode active material in the electrode mixture layer is determined in advance, and M ^* (mass%) and the known ρ (g / cm ³ ) and ρ _c2 (g / cm ^3). ), The mass ratio m _c2 ^* (mass%) of the second conductive additive in the electrode mixture layer may be determined so as to satisfy the condition of the formula (2).

In order for the mass ratio M ^* (mass%) of the electrode active material in the electrode mixture layer and the mass ratio m _c2 ^* (mass%) of the second conductive additive to satisfy the condition of the formula (2) The M ^* (mass%) and _mc2 ^* (mass%) in the electrode mixture before being applied on the current collector may satisfy the condition of the formula (2).

(3) Determination step Further, the product of the number of first conductive additives in the electrode mixture layer and the cross-sectional area per first conductive additive is S _c1 (m ² ), and the electrode mixture layer When the total surface area of the electrode active material in the electrode is S (m ² ) and the total surface area of the second conductive additive in the electrode mixture layer is S _c2 (m ² ), S _c1 (m ² ) and S _{c2 (m} ²⁾ is to satisfy the condition of following equation (6), may make a decision step of determining the amount of the first conductive additive and a second conductive additive.
S + S _c2 ≦ S _c1 ... Formula (6)

S _c1 (m ² ), which is the product of the number of first conductive aids in the electrode mixture layer and the cross-sectional area per first conductive aid, is the first conductive aid contained in the electrode mixture layer. It means the covering area that can be covered with the whole agent. The cross-sectional area per 1st conductive support agent says the area of the cross section which passes along the center of this spherical body when the 1st conductive support agent is assumed to be a spherical body.

  In order to cause the entire electrode active material to react as efficiently and uniformly as possible, it is desirable that the first conductive auxiliary agent cover the entire surface of the electrode active material and collect current. Therefore, it is desirable to use an amount that can cover at least the surface of the electrode active material as the first conductive additive. When forming an electrode mixture layer made of materials having different particle sizes, the first conductive auxiliary agent 1 has not only the surface of the electrode active material 3 but also the surface of the second conductive auxiliary agent 2 as shown in FIG. It is envisaged to coat. For this reason, it is preferable that the covering area of the first conductive auxiliary agent 1 is equal to or larger than the sum of the surface area of the electrode active material 3 and the surface area of the second conductive auxiliary agent 2. In this case, the first conductive auxiliary agent 1 has a covering area sufficient to cover the entire surface of the electrode active material 3, and can further reduce the resistance in the electrode mixture layer and efficiently. Reaction and current collection.

In the determining step, the product S _c1 (m ² ) of the number of first conductive aids in the electrode mixture layer and the cross-sectional area per first conductive aid, the total surface area S (m ² ) of the electrode active material, The total surface area S _c2 (m ² ) of the second conductive additive may be calculated according to the following formula (7), formula (8), formula (9), formula (10), and formula (11).

When the average particle diameter of the first conductive auxiliary agent is d _c1 (μm), the volume w _c1 (cm ³ ) per first conductive auxiliary agent is expressed by the following formula (7).
^{_{w c1 (cm 3) = 4π}} × (d c1 × 10 -4 / 2) 3/3 = π × (d c1 × 10 -4) 3/6 = π × d c1 3 × 10 -12 / 6 ··・ Formula (7)

When the total mass of the first conductive auxiliary agent in the electrode mixture layer is m _c1 (g) and the true density of the first conductive auxiliary agent is ρ _c1 (g / cm ³ ), the total mass of the first conductive auxiliary agent The number n _c1 of the first conductive additives in m _c1 (g) is represented by the following formula (8).
n _c1 (pieces) = (m _c1 / ρ _c1 ) × (1 / w _c1 ) = (m _c1 / ρ _c1 ) × (1 / (π × d _c1 ³ × 10 ⁻¹² / 6)) = 6 m _c1 × 10 ¹² / (π × ρ _c1 × d _c1 ³ ) (8)

The product S _c1 (m ² ) of the cross-sectional area (m ² ) per first conductive auxiliary agent and the number n _{c1 of} the first conductive auxiliary agents is represented by the following formula (9).
S _c1 (m ² ) = π (d _c1 × 10 ⁻⁶ / 2) ² × n _c1 = π (d _c1 × 10 ⁻⁶ / 2) ² × 6 m _c1 × 10 ¹² / (π × ρ _c1 × d _c1 ³ ) = 3 m _c1 / (2ρ _c1 × d _c1 ) (9)

When the BET specific surface area of the second conductive auxiliary agent is s _c2 (m ² / g) and the total mass of the second conductive auxiliary agent in the electrode mixture layer is m _c2 (g), The total surface area S _c2 (m ² ) of the second conductive additive therein is represented by the following formula (10).
S _c2 (m ² ) = s _c2 × m _c2 Formula (10)

The BET specific surface area of the electrode active material and ^{_{s am (m 2 / g)}} , when the total mass of the electrode active material in the electrode mixture layer was M (g), the electrode active material in the electrode mixture layer The total surface area S (m ² ) is represented by the following formula (11).
_{^{S (m 2) = s am}} × M ··· formula (11)

Substituting Expression (9), Expression (10), and Expression (11) into Expression (6), S + S _c2 ≦ S _c1 can be expressed by the following Expression (12).
s _am × M + s _c2 × m _c2 ≦ 3 m _c1 / (2ρ _c1 × d _c1 ) (12)

When the electrode mixture layer is 100% by mass, the mass ratio of the electrode active material is M ^* , the mass ratio of the first conductive auxiliary agent is m _c1 ^* , and the mass ratio of the second conductive auxiliary agent is m _c2. ^{When *} , Formula (12) is represented by the following (13).
s _am × M ^* + s _c2 × m _c2 ^* ≦ 3 m _c1 ^* / (2ρ _c1 × d _c1 ) (13)

After the selection step or the adjustment step, the mass ratio M ^* of the electrode active material in the electrode mixture layer and the mass ratio m _c1 ^{* of} the first conductive additive so as to have the relationship of the above formula (6) or formula (13) ^. And the mass ratio m _c2 ^* of the second conductive additive may be determined.

When the total electrode mixture layer is 100% by mass, the mass ratio M ^* of the electrode active material is preferably 55% by mass to 99% by mass, and more preferably 80% by mass to 98% by mass, 85%. It is preferable that they are mass% or more and 98 mass% or less. If the mass ratio M ^* of the electrode active material is too small, the battery capacity may be reduced.

The total of the mass ratio m _c1 ^* of the first conductive auxiliary agent and the mass ratio m _c2 ^* of the second conductive auxiliary agent (m _c1 ^* + m _c2 ^* ) is 0 when the entire electrode mixture layer is 100 mass%. It is preferably 5% by mass or more and 50% by mass, and more preferably 1% by mass or more and 30% by mass or less. In this case, a decrease in battery capacity can be suppressed while improving or maintaining the conductivity in the electrode mixture layer.

In the electrode mixture layer, the total of the mass ratio M ^* of the electrode active material, the mass ratio m _c1 ^* of the first conductive auxiliary agent, and the mass ratio m _c2 ^* of the second conductive auxiliary agent (m _c1 ^* + m _c2 ^* ) The ratio is preferably M ^* _:( m _c1 ^* + m _c2 ^* ) = 99: 1 to 70:30. This is because if the first and second conductive assistants are too small, an efficient conductive path cannot be formed, and if there are too many conductive assistants, the energy density of the electrode becomes low.

(4) Electrode forming step Next, in the electrode forming step, an electrode mixture having an electrode active material, a first conductive auxiliary agent, and a second conductive auxiliary agent satisfying the conditions set in the above step is formed on the current collector. The electrode mixture layer is formed by coating. After forming the electrode mixture layer on the current collector, the electrode active material, the first conductive auxiliary agent, and the second conductive auxiliary agent contained in each electrode composite layer are the steps (1) to (3) described above. It may be confirmed that the above condition is satisfied.

  In addition to the electrode active material, the second conductive auxiliary agent, and the first conductive auxiliary agent, the electrode mixture includes a binder as necessary. The binder serves to bind the electrode active material and the conductive additive to the surface of the current collector. Examples of the binder include fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene, and fluororubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, and alkoxysilyl group-containing resins. be able to.

  The blending ratio of the binder in the electrode mixture is preferably a mass ratio of electrode active material: binder = 99: 1 to 70:30. This is because when the amount of the binder is too small, the moldability of the electrode is lowered, and when the amount of the binder is too large, the energy density and conductivity of the electrode are lowered.

  In order to form the electrode mixture layer on the surface of the current collector, a conventionally known method such as a roll coating method, a die coating method, a dip coating method, a doctor blade method, a spray coating method, or a curtain coating method is used. What is necessary is just to apply | coat an electrode compound material on the surface of an electrical conductor. Specifically, an appropriate solvent is added to the electrode mixture to form a paste, which is applied to the surface of the current collector and then dried to form an electrode mixture layer. Examples of the solvent include N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone, and water. In order to increase the electrode density, the electrode mixture layer after drying may be compressed.

  The electrode mixture layer may be compressed by pressing the electrode in the thickness direction. The electrode active material in the electrode mixture layer can be arranged in a state close to a close-packed structure by pressurization. In addition, the second conductive additive can be suitably arranged in the gap between the electrode active materials.

  The current collector refers to a chemically inert electronic high conductor that keeps a current flowing through an electrode during discharge or charging of a lithium ion secondary battery. As the current collector, at least one selected from silver, copper, gold, aluminum, tungsten, cobalt, zinc, nickel, iron, platinum, tin, indium, titanium, ruthenium, tantalum, chromium, molybdenum, and stainless steel, etc. Metal materials can be exemplified. The current collector may be covered with a known protective layer. What collected the surface of the electrical power collector by the well-known method may be used as an electrical power collector.

  The current collector can take the form of a foil, a sheet, a film, a linear shape, a rod shape, a mesh, or the like. Therefore, for example, a metal foil such as a copper foil, a nickel foil, an aluminum foil, and a stainless steel foil can be suitably used as the current collector. When the current collector is in the form of foil, sheet or film, the thickness is preferably in the range of 1 μm to 100 μm.

  The electrode for a secondary battery of the present invention is an electrode manufactured by the above manufacturing method. The electrode for a secondary battery of the present invention has an electrode active material, a first conductive auxiliary agent, and a second conductive auxiliary agent, and includes the electrode active material and the second conductive auxiliary agent having the relationship of the above formula (1). Have. According to the electrode active material, the first conductive aid and the second conductive aid having this relationship, the internal resistance of the battery and its increase can be kept low. Furthermore, the electrode active material, the first conductive auxiliary agent, and the second conductive auxiliary agent preferably have at least one relationship of the formula (2), the formula (6), and the formula (13). According to the electrode having the electrode active material, the first conductive aid and the second conductive aid, the internal resistance of the battery and its increase can be further reduced.

(Secondary battery)
The secondary battery of the present embodiment includes the above-described secondary battery electrode. The secondary battery may be a non-aqueous secondary battery using a non-aqueous electrolyte solution. The secondary battery electrode may be either a positive electrode or a negative electrode, and both the positive electrode and the negative electrode may be the above secondary battery electrode.

  A separator is used for the secondary battery as necessary. The separator separates the electrode and the negative electrode, and allows metal ions to pass through while preventing a short circuit of current due to contact between both electrodes. As separators, natural resins such as polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamide, polyaramid (Aromatic polymer), polyester, polyacrylonitrile and other polysaccharides, cellulose, amylose and other polysaccharides, fibroin, keratin, lignin and suberin Examples thereof include porous bodies, nonwoven fabrics, and woven fabrics using one or more electrically insulating materials such as polymers and ceramics. The separator may have a multilayer structure.

  If necessary, a separator is sandwiched between the positive electrode and the negative electrode to form an electrode body. The electrode body may be either a stacked type in which the positive electrode, the separator and the negative electrode are stacked, or a wound type in which the positive electrode, the separator and the negative electrode are sandwiched. After connecting between the positive electrode current collector and the negative electrode current collector to the positive electrode terminal and the negative electrode terminal connected to the outside using a current collecting lead or the like, an electrolyte is added to the electrode body to form a secondary battery. Good.

The non-aqueous electrolytic solution is obtained by dissolving a metal salt that is an electrolyte in an organic solvent. As the organic solvent, an aprotic organic solvent such as propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC) or the like is used. Can do. As the electrolyte to be dissolved, lithium salts such as LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , and LiN (CF ₃ SO ₂ ) ₂ can be used.

As a non-aqueous electrolyte, for example, an organic solvent such as ethylene carbonate, dimethyl carbonate, propylene carbonate, and dimethyl carbonate is mixed with a lithium metal salt such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ from 0.5 mol / L. A solution dissolved at a concentration of about 1.7 mol / L can be used.

  The shape of the secondary battery of the present invention is not particularly limited, and various shapes such as a cylindrical shape, a square shape, a coin shape, and a laminate shape can be adopted.

  The secondary battery of the present invention may be mounted on a vehicle. The vehicle may be a vehicle that uses electric energy from the secondary battery for all or part of its power source, and may be, for example, an electric vehicle, a hybrid vehicle, or the like. When a secondary battery is mounted on a vehicle, a plurality of secondary batteries may be connected in series to form an assembled battery. Examples of devices equipped with secondary batteries include various home appliances driven by batteries, office devices, industrial devices, and the like, such as personal computers and portable communication devices, in addition to vehicles. Further, the secondary battery according to the present invention includes wind power generation, solar power generation, hydroelectric power generation and other power system power storage devices and power smoothing devices, power of power sources for ships, etc. and / or power supply sources for auxiliary equipment, aircraft, spacecraft Power supply for auxiliary power and / or auxiliary equipment, auxiliary power source for vehicles that do not use electricity as a power source, power source for mobile home robots, power source for system backup, power source for uninterruptible power supply, electric vehicle You may use for the electrical storage apparatus which temporarily stores the electric power required for charge in the charging station for a vehicle.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment. The present invention can be implemented in various forms without departing from the gist of the present invention, with modifications and improvements that can be made by those skilled in the art.

Example 1
The lithium ion secondary battery of Example 1 has a positive electrode, a negative electrode, an electrolytic solution, and a separator.

The positive electrode includes a positive electrode mixture layer and a current collector covered with the positive electrode mixture layer. The positive electrode mixture layer includes a positive electrode active material, a first conductive auxiliary agent, a second conductive auxiliary agent, and a binder. The positive electrode active material is made of LiNi _0.5 Co _0.2 Mn _0.3 O ₂ having an average particle diameter D of 6 μm. The first conductive auxiliary agent is made of acetylene black (AB) and has an average particle diameter d _c1 of 0.035 μm (Denka Black granular product (trade name), manufactured by Denki Kagaku Kogyo Co., Ltd.). The second conductive additive is made of graphite, the average particle diameter _{d c2} is 3.5 [mu] m (product name KS6L, IMERYS production). The binder is made of polyvinylidene fluoride (PVDF, manufactured by Kureha Battery Materials Japan, product number # 7300). The current collector is made of an aluminum foil having a thickness of 20 μm. When the positive-electrode mixture layer is 100 mass%, the mass ratio m _c2 ^* and a binder mass ratio m _c1 ^* and the second conductive additive weight ratio M ^* a first conductive additive of the positive electrode active material The mass ratio is 90: 5: 3: 2 in percentage.

  In order to produce the positive electrode, the following steps were performed.

(1) Selection Step First, LiNi _0.5 Co _0.2 Mn _0.3 O ₂ as a positive electrode active material, PVDF as a binder, and AB as a first conductive auxiliary agent and a second conductive auxiliary agent. Got ready. The average particle diameter d _c1 having an average particle diameter D and the first conductive additive of the positive electrode active material was measured by a laser diffraction method. D was 6 μm and d _c1 was 0.035 μm. The range of the average particle diameter _dc2 of the second conductive additive was determined according to the formula (1) using D, and 6 ((3/2) ^1/2 −1) ≦ _{dc 2} ≦ 6, that is, 1.3 ≦ d _c2 ≦ 6. A second conductive aid that _falls within this range and has an average particle size d _c2 greater than d _c1 was selected. The average particle diameter _dc2 of the selected second conductive additive was 3.5 μm.

(2) the true density of the adjustment process known positive electrode active material [rho, was confirmed true density [rho _c2 true density [rho _c1, and a second conductive additive of the first conductive additive (AB) (graphite). The true density ρ of the positive electrode active material was 4.70 g / cm ³ . The true density ρ _c1 of the first conductive additive was 1.95 g / cm ³ (true density 1 of acetylene black described in “Nanomaterial Information Providing Sheet” (material name: acetylene black, provided by Denki Kagaku Kogyo Co., Ltd.) 0.8-2.1 g / cm ³ average value). The true density ρ _c2 of the second conductive additive was 2.26 g / cm ³ (IMERYS analysis table published). The positive electrode active mass ratio of the mass ratio M ^* and the second conductive auxiliary material m _c2 ^* in the positive-electrode mixture layer formed on the collector is, so as to satisfy the relationship of formula (2), a cathode active material The compounding ratio with the 2nd conductive support agent was adjusted. In Example 1, M ^* was 90% by mass, and _mc2 ^* was 3% by mass. (M ^* × ρ _c2 × _{dc 2} ³ ) / ( _{mc 2} ^* × ρ × D ³ ) was 2.86.

(3) Determination process The specific surface area s _am of the known positive electrode active material and the specific surface area s _c2 of the second conductive additive were confirmed by the BET method. The specific surface area s _am of the positive electrode active material was 0.43 m ² / g, and the specific surface area s _c2 of the second conductive additive was 19.2 m ² / g. When the positive-electrode mixture layer is 100 mass% mass ratio M ^* of the positive electrode active ^material, the mass ratio of the mass ratio m _c1 ^* and the second conductive additive of the first conductive additive m _c2 ^* is the formula (13) M ^* , m _c1 ^* and m _c2 ^* were determined so as to satisfy the conditions. In Example 1, the left side (s _am × M ^* + s _c2 × m _c2 ^* ) of the formula (13) is 96.3 m ² , and the right side of the formula (13) (3 m _c1 ^* / (2ρ _c1 × d _c1 ) ) Was 109.9 m ² . _{M c1} ^* was determined to be 5% by mass so as to satisfy the relationship of the formula (13).

In addition, the product of the number of the first conductive assistants in the positive electrode mixture layer 100g and the cross-sectional area per first conductive assistant is _Sc1 , the total surface area of the positive electrode active material is S, and the second conductive when the total surface area of the aid and the _{S c2, S c1} and _{S c2} were determined so as to satisfy the condition of equation (6). Was determined the _{S c1} by the equation (9), was 109.9m ^2. Was determined the _{S c2} by the equation (10) was 57.6m ^2. Was determined to S by the equation (11) was 38.7m ^2. S _c1 , S, and S _c2 satisfied the relationship of Expression (6).

As the amount of the positive electrode active material satisfying the formulas (6) and (13), the first conductive auxiliary agent and the second conductive auxiliary agent, M ^* is 90% by mass, m _c1 ^* is 5% by mass, and m _c2 ^* is 3 The mass was determined.

(4) Positive electrode forming step In the positive electrode forming step, in addition to the positive electrode active material, the first conductive auxiliary agent, and the second conductive auxiliary agent, a binder was added and mixed to obtain a positive electrode mixture. The mass ratio of the positive electrode active material, the first conductive auxiliary agent, the second conductive auxiliary agent, and the binder when the positive electrode mixture is 100% by mass is 90% by mass, 5% by mass, 3% by mass, The content was 2% by mass. N-methyl-2-pyrrolidone (NMP) as a solvent was added to the positive electrode mixture to obtain a paste. This paste was applied to the surface of an aluminum foil as a current collector using a doctor blade, and dried at 80 ° C. for 20 minutes, whereby NMP was removed by volatilization to form a positive electrode mixture layer. The basis weight of the positive electrode mixture layer after drying was 6 mg / cm ² . The aluminum foil having the positive electrode mixture layer formed on the surface was compressed using a roll press machine, and the aluminum foil and the positive electrode mixture layer were firmly bonded. The joined product was heated with a vacuum dryer at 120 ° C. for 6 hours, cut into a predetermined shape (25 mm × 30 mm), and a positive electrode having a positive electrode mixture layer thickness of about 25 μm was obtained.

The negative electrode is composed of a negative electrode mixture layer and a current collector covered with the negative electrode mixture layer. The negative electrode mixture layer has a negative electrode active material and a binder. In order to produce a negative electrode, 98 parts by mass of graphite as a negative electrode active material and 1 part by mass of styrene-butadiene rubber (SBR) and 1 part by mass of carboxymethyl cellulose (CMC) as a binder were mixed. This mixture was dispersed in an appropriate amount of ion-exchanged water to prepare a slurry-like negative electrode mixture. The slurry-like negative electrode mixture was applied to a copper foil having a thickness of 20 μm, which is a negative electrode current collector, in a film shape using a doctor blade to form a negative electrode mixture layer. The basis weight of the negative electrode mixture layer after drying was 4 mg / cm ² . The current collector on which the negative electrode mixture layer was formed was dried at 80 ° C. for 20 minutes and then pressed, and the joined product was heated at 120 ° C. for 6 hours with a vacuum dryer, cut into a predetermined shape (26 mm × 31 mm), A negative electrode having a material layer thickness of about 34 μm was obtained.

In order to prepare an electrolytic solution, a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) was prepared. The component ratio of the mixed solvent was EC / DEC = 3: 7 in volume ratio. LiPF ₆ as an electrolyte was dissolved in a mixed solvent so as to be 1 mol / L to obtain an electrolytic solution.

  A laminate type lithium ion secondary battery was manufactured using the positive electrode, the negative electrode, and the electrolytic solution. Specifically, a rectangular sheet (27 × 32 mm, thickness 25 μm) made of a porous resin film having a three-layer structure of polypropylene / polyethylene / polypropylene is sandwiched between the positive electrode and the negative electrode to form an electrode plate group. . The electrode plate group was covered with a set of two laminated films, and the three sides were sealed, and then the electrolyte solution was poured into the bag-like laminated film. Thereafter, the remaining one side was sealed to obtain a laminate type lithium ion secondary battery in which the four sides were hermetically sealed and the electrode plate group and the electrolyte were sealed. Note that the positive electrode and the negative electrode have a tab that can be electrically connected to the outside, and a part of the tab extends to the outside of the laminated lithium ion secondary battery.

  The alternating current impedance before and after the cycle test of the obtained lithium ion secondary battery was measured. When performing a cycle test, CC charge (constant current charge) to 4.1 V with a 1 C rate current load in a thermostat controlled at room temperature (25 ° C.), then CC discharge (constant current) to 3.0 V. This was repeated 200 cycles. For example, 1C means a constant current value for fully charging or discharging the battery in one hour. The AC impedance was measured in the frequency range of 0.02 Hz to 1 MHz using a Solaron 147055BEC (Solartron) for lithium ion secondary batteries before and after the cycle test with the voltage adjusted to 3.5V. The results are shown in FIG.

  Two arcs were seen in the complex impedance plane plot obtained by the measurement. The arc on the left side of the figure (that is, the side where the real part of the complex impedance is small) is called the first arc. The arc on the right side in the figure is called the second arc, and the electronic resistance (resistance of the conductive path) was analyzed based on the size of these arcs. The analysis results are shown in FIG. As shown in FIG. 5, in Example 1, the increase of two circular arcs is not seen, and it is considered that the increase in electronic resistance is suppressed.

(Comparative Example 1)
The lithium ion secondary battery of Comparative Example 1 does not include the second conductive auxiliary agent in the positive electrode mixture layer, and the mixing ratio of the positive electrode active material, the first conductive auxiliary agent, and the binder is 90% by mass: 8 % By mass: The same as the lithium ion secondary battery of Example 1 except that the content is 2% by mass.

The process for producing the positive electrode was as follows.
That is, (1) the selection process was performed in the same manner as the selection process of Example 1. The positive electrode active material and the first conductive auxiliary used were the same as the positive electrode active material and the first conductive auxiliary of Example 1, and their average particle diameter D, d _c1 , true density ρ _, ρ _c1 and specific surface area. s _am was the same as in Example 1.

(2) In the adjusting step, the mass ratio M ^* of the positive electrode active material in the positive electrode mixture layer formed on the current collector was 90% by mass. Equation (2) could not be calculated because the second conductive aid was not used.

(3) In the determining step, Equation (13) was calculated using the mass ratio M ^* of the positive electrode active material and the mass ratio m _c1 ^* of the first conductive additive. Left _{^{(s am × M * + s}} c2 × m c2 *) of formula (13) is 38.7m ^2, the right side of the equation ^{_{(13) (3m c1 * /}} (2ρ c1 × d c1)) is 175.8m ² .
Further, when the product of the number of the first conductive assistants in the positive electrode mixture layer 100g and the cross-sectional area per first conductive assistant is _Sc1, and the total surface area of the positive electrode active material is S, the formula (9) was determined to _{S c1,} it was 175.8m ^2. Was 0 m ² was determined to _{S c2} by the equation (10). Was determined to S by the equation (11) was 38.7m ^2. S _c1 , S, and S _c2 satisfied the relationship of Expression (6). As the amounts of the positive electrode active material, the first conductive auxiliary agent, and the second conductive auxiliary agent, M ^* was determined to be 90 mass%, m _c1 ^* was determined to be 8 mass%, and m _c2 ^* was determined to be 0 mass%.

  (4) In the positive electrode forming step, the mass ratio of the positive electrode active material, the first conductive auxiliary agent, the second conductive auxiliary agent, and the binder when the positive electrode mixture is 100% by mass is 90% by mass, Except for the points of 8% by mass, 0% by mass and 2% by mass, the same procedure as in (4) Positive electrode forming step of Example 1 was performed. Thus, the positive electrode of Comparative Example 1 was obtained.

  Using the obtained positive electrode of Comparative Example 1, a lithium ion secondary battery was produced in the same manner as in Example 1, and this was used as the lithium ion secondary battery of Comparative Example 1.

  The impedance of the lithium ion secondary battery of Comparative Example 1 before and after the cycle test was measured. The results are shown in FIG. Further, as shown in FIG. 6, the first arc on the left side is larger than the result of Example 1 in FIG. This is thought to be due to the disconnection of the conductive path between the positive electrode active materials and the increase in the electronic resistance of the positive electrode.

Table 1 shows the parameters of Formula (1), Formula (2), and Formula (6) of Example 1 and Comparative Example 1. In Tables 2 and 3, the resistance of the first arc of the lithium ion secondary batteries in Example 1 and Comparative Example 1, the resistance increase amount after the cycle test, and the resistance increase rate were obtained. When the resistance of the first arc before the cycle test is Z _before and the resistance of the first arc after the cycle test is Z _after , the resistance increase rate (%) is 100 × (Z _after −Z _before ) / Z _before Calculated by Table 2 shows the result of calculation using the value of the first arc rounded to the third decimal place after rounding off to the fourth decimal place, and Table 3 shows the resistance of the first arc to the third decimal place. Results calculated using values rounded to the first decimal place. The resistance increase rate (%) in Tables 2 and 3 was rounded to the first decimal place by rounding off the second decimal place.

  As shown in Tables 2 and 3, the resistance increase rate of the first arc of the secondary battery of Example 1 was significantly suppressed as compared with that of the secondary battery of Comparative Example 1. This is considered to be due to the fact that the conductive path was not easily cut in the positive electrode mixture layer by introducing the second conductive additive into the positive electrode mixture layer in Example 1.

(Example 2)
In the lithium ion secondary battery of Example 2, the mass ratio M ^* of the positive electrode active material, the mass ratio m _c1 ^* of the first conductive additive, and the second conductivity when the positive electrode mixture layer of the positive electrode is 100 mass%. The mass ratio m _c2 ^* of the auxiliary agent and the mass ratio of the binder differ from the lithium ion secondary battery of Example 1 in that the mass ratio is 90: 7.13: 0.87: 2.

The process for producing the positive electrode was as follows.
That is, (1) the selection process was performed in the same manner as the selection process of Example 1. The positive electrode active material, the first conductive auxiliary agent, and the second conductive auxiliary agent used are the same as the positive electrode active material, the first conductive auxiliary agent, and the second conductive auxiliary agent of Example 1, and their average particle diameter D, d _c1 , d _c2 , true density ρ 1 _, ρ _c1 , ρ _c2 and specific surface areas s _am , s _c2 were the same as those in Example 1.

(2) In the adjustment step, the mass ratio M ^* of the positive electrode active material in the positive electrode mixture layer formed on the current collector is 90% by mass, and the mass ratio m _c2 ^* of the second conductive additive is 0.87 mass. %. (M ^* × ρ _c2 × d _c2 ³ ) / ( _{mc 2} ^* × ρ × D ³ ) in the formula (2) was 9.85.

(3) In the determination step, the left side (s _am × M ^* + s _c2 × m _c2 ^* ) of formula (13) is 55.4 m ² , and the right side of formula (13) (3m _c1 ^* / (2ρ _c1 × d) _c1 )) was 156.7 m ² . M _c1 ^* was determined to be 7.13 mass% so as to satisfy the relationship of the formula (13).
In addition, the product of the number of the first conductive assistants in the positive electrode mixture layer 100g and the cross-sectional area per first conductive assistant is _Sc1 , the total surface area of the positive electrode active material is S, and the second conductive when the total surface area of the aid and the _{S c2, S c1} and _{S c2} were determined so as to satisfy the condition of equation (6). Was determined the _{S c1} by the equation (9), was 156.7m ^2. Was determined the _{S c2} by the equation (10) was 16.7 m ^2. Was determined to S by the equation (11) was 38.7m ^2. S _c1 , S, and S _c2 satisfied the relationship of Expression (6). As the amount of the positive electrode active material satisfying the formulas (6) and (13), the first conductive auxiliary agent and the second conductive auxiliary agent, M ^* is 90% by mass, m _c1 ^* is 7.13% by mass, m _c2 ^* Was determined to be 0.87 mass%.

  (4) In the positive electrode forming step, the mass ratio of the positive electrode active material, the first conductive auxiliary agent, the second conductive auxiliary agent, and the binder when the positive electrode mixture is 100% by mass is 90% by mass, Except for the points set to 7.13% by mass, 0.87% by mass, and 2% by mass, the same procedure as in (4) Positive electrode forming step of Example 1 was performed. Thus, the positive electrode of Example 2 was obtained.

  Using the obtained positive electrode of Example 2, a lithium ion secondary battery was produced in the same manner as in Example 1, and this was used as the lithium ion secondary battery of Example 2.

(Example 3)
In the lithium ion secondary battery of Example 3, the mass ratio M ^* of the positive electrode active material, the mass ratio m _c1 ^* of the first conductive additive, and the second conductivity when the positive electrode mixture layer of the positive electrode is 100 mass%. The mass ratio m _c2 ^* of the auxiliary agent and the mass ratio of the binder differ from the lithium ion secondary battery of Example 1 in that the mass ratio is 90: 7.6: 0.4: 2.

The process for producing the positive electrode was as follows.
That is, (1) the selection process was performed in the same manner as the selection process of Example 1. The positive electrode active material, the first conductive auxiliary agent, and the second conductive auxiliary agent used are the same as the positive electrode active material, the first conductive auxiliary agent, and the second conductive auxiliary agent of Example 1, and their average particle diameter D, d _c1 , d _c2 , true density ρ 1 _, ρ _c1 , ρ _c2 and specific surface areas s _am , s _c2 were the same as those in Example 1.

(2) In the adjustment step, the mass ratio M ^* of the positive electrode active material in the positive electrode mixture layer formed on the current collector is 90 mass%, and the mass ratio m _c2 ^* of the second conductive additive is 0.4 mass. %. (M ^* × ρ _c2 × _{dc 2} ³ ) / ( _{mc 2} ^* × ρ × D ³ ) in the formula (2) was 21.5.

(3) In the determination step, the left side (s _am × M ^* + s _c2 × m _c2 ^* ) of formula (13) is 46.4 m ² , and the right side of formula (13) (3m _c1 ^* / (2ρ _c1 × d) _c1 )) was 167.0 m ² . _{M c1} ^* was determined to be 7.6% by mass so as to satisfy the relationship of the formula (13).
In addition, the product of the number of the first conductive assistants in the positive electrode mixture layer 100g and the cross-sectional area per first conductive assistant is _Sc1 , the total surface area of the positive electrode active material is S, and the second conductive when the total surface area of the aid and the _{S c2, S c1} and _{S c2} were determined so as to satisfy the condition of equation (6). Was determined the _{S c1} by the equation (9), was 167.0m ^2. Was determined the _{S c2} by the equation (10), it was 7.7 m ^2. Was determined to S by the equation (11) was 38.7m ^2. S _c1 , S, and S _c2 satisfied the relationship of Expression (6). As the amount of the positive electrode active material satisfying the formulas (6) and (13), the first conductive auxiliary agent and the second conductive auxiliary agent, M ^* is 90% by mass, m _c1 ^* is 7.6% by mass, m _c2 ^* Was determined to be 0.4 mass%.

  (4) In the positive electrode forming step, the mass ratio of the positive electrode active material, the first conductive auxiliary agent, the second conductive auxiliary agent, and the binder when the positive electrode mixture is 100% by mass is 90% by mass, Except for points of 7.6% by mass, 0.4% by mass and 2% by mass, the same procedure as in (4) positive electrode forming step of Example 1 was performed. Thus, the positive electrode of Example 3 was obtained.

  Using the obtained positive electrode of Example 3, a lithium ion secondary battery was produced in the same manner as in Example 1, and this was used as the lithium ion secondary battery of Example 3.

Example 4
In the lithium ion secondary battery of Example 4, the positive electrode active material mass ratio M ^* , the first conductive additive mass ratio m _c1 ^*, and the second conductivity when the positive electrode mixture layer of the positive electrode is 100 mass%. The mass ratio m _c2 ^* of the auxiliary agent and the mass ratio of the binder differ from the lithium ion secondary battery of Example 1 in that the mass ratio is 90: 7.92: 0.08: 2.

The process for producing the positive electrode was as follows.
That is, (1) the selection process was performed in the same manner as the selection process of Example 1. The positive electrode active material, the first conductive auxiliary agent, and the second conductive auxiliary agent used are the same as the positive electrode active material, the first conductive auxiliary agent, and the second conductive auxiliary agent of Example 1, and their average particle diameter D, d _c1 , d _c2 , true density ρ 1 _, ρ _c1 , ρ _c2 and specific surface areas s _am , s _c2 were the same as those in Example 1.

(2) In the adjustment step, the mass ratio M ^* of the positive electrode active material in the positive electrode mixture layer formed on the current collector is 90 mass%, and the mass ratio m _c2 ^* of the second conductive additive is 0.08 mass. %. (M ^* × ρ _c2 × d _c2 ³ ) / ( _{mc 2} ^* × ρ × D ³ ) in the formula (2) was 107.4.

(3) In the determining step, the left side (s _am × M ^* + s _c2 × m _c2 ^* ) of the formula (13) is 40.2 m ² , and the right side (3m _c1 ^* / (2ρ _c1 × d) of the formula (13). _c1 )) was 174.1 m ² . M _c1 ^* was determined to be 7.92% by mass so as to satisfy the relationship of the formula (13).
In addition, the product of the number of the first conductive assistants in the positive electrode mixture layer 100g and the cross-sectional area per first conductive assistant is _Sc1 , the total surface area of the positive electrode active material is S, and the second conductive when the total surface area of the aid and the _{S c2, S c1} and _{S c2} were determined so as to satisfy the condition of equation (6). Was determined the _{S c1} by the equation (9), was 174.1m ^2. Was determined the _{S c2} by the equation (10), it was 1.5 m ^2. Was determined to S by the equation (11) was 38.7m ^2. S _c1 , S, and S _c2 satisfied the relationship of Expression (6). As the amount of the positive electrode active material satisfying the formulas (6) and (13), the first conductive auxiliary agent and the second conductive auxiliary agent, M ^* is 90% by mass, m _c1 ^* is 7.92% by mass, m _c2 ^* Was determined to be 0.08 mass%.

  (4) In the positive electrode forming step, the mass ratio of the positive electrode active material, the first conductive auxiliary agent, the second conductive auxiliary agent, and the binder when the positive electrode mixture is 100% by mass is 90% by mass, Except for the points of 7.92% by mass, 0.08% by mass, and 2% by mass, the same procedure as in (4) positive electrode formation step of Example 1 was performed. Thus, the positive electrode of Example 4 was obtained.

  Using the obtained positive electrode of Example 4, a lithium ion secondary battery was produced in the same manner as in Example 1, and this was used as the lithium ion secondary battery of Example 4.

(Comparative Example 2)
The lithium ion secondary battery of Comparative Example 2 does not include the first conductive additive in the positive electrode mixture layer, and the mixing ratio of the positive electrode active material, the second conductive auxiliary agent, and the binder is 90% by mass: 8 % By mass: The same as the lithium ion secondary battery of Example 1 except that the content is 2% by mass.

The process for producing the positive electrode was as follows.
That is, (1) the selection step was performed in the same manner as the selection step of Example 1. The positive electrode active material and the second conductive auxiliary used were the same as the positive electrode active material and the second conductive auxiliary of Example 1, and their average particle diameter D, d _c2 , true density ρ _, ρ _c2 and specific surface area. s _am and s _c2 were the same as those in Example 1.

(2) In the adjustment step, the mass ratio M ^* of the positive electrode active material in the positive electrode mixture layer formed on the current collector is 90% by mass, and the mass ratio m _c2 ^* of the second conductive additive is 2% by mass. did. (M ^* × ρ _c2 × _{dc 2} ³ ) / ( _{mc 2} ^* × ρ × D ³ ) in the formula (2) was 1.07.

(3) In the determination step, the formula (13) was calculated using the mass ratio M ^* of the positive electrode active material and the mass ratio m _c2 ^* of the second conductive additive. The left side (s _am × M ^* + s _c2 × m _c2 ^* ) of the equation (13) is 192.3 m ² , and the right side (3m _c1 ^* / (2ρ _c1 × d _c1 )) of the equation (13) is 0. It was.
In addition, the product of the number of the first conductive assistants in the positive electrode mixture layer 100g and the cross-sectional area per first conductive assistant is _Sc1 , the total surface area of the positive electrode active material is S, and the second conductive The total surface area of the auxiliary agent was S _c2, and S _c1 was determined by the formula (9), and was 0 m ² . Was determined the _{S c2} by the equation (10), it was 153.6m ^2. Was determined to S by the equation (11) was 38.7m ^2. S _c1 , S, and S _c2 did not satisfy the relationship of the formula (6). As the amounts of the positive electrode active material, the first conductive auxiliary agent, and the second conductive auxiliary agent, M ^* was determined to be 90 mass%, m _c1 ^* was determined to be 0 mass%, and m _c2 ^* was determined to be 8 mass%.

  (4) In the positive electrode forming step, the mass ratio of the positive electrode active material, the first conductive auxiliary agent, the second conductive auxiliary agent, and the binder when the positive electrode mixture is 100% by mass is 90% by mass, Except for the points of 0% by mass, 8% by mass and 2% by mass, the same procedure as in (4) Positive electrode forming step of Example 1 was performed. Thus, the positive electrode of Comparative Example 2 was obtained.

  Using the obtained positive electrode of Comparative Example 2, a lithium ion secondary battery was produced in the same manner as in Example 1, and this was used as the lithium ion secondary battery of Comparative Example 2.

  Various parameters of Examples 2 to 4 and Comparative Example 2 are shown in Table 1. Moreover, the impedance before and behind the cycle test of the lithium ion secondary batteries of Examples 2 to 4 and Comparative Example 2 was measured in the same manner as in Example 1, and the results are shown in Tables 2 and 3.

  For the lithium ion secondary batteries of Examples 1 to 4 in which both the first conductive auxiliary and the second conductive auxiliary are included in the positive electrode, Comparative Example 1 including one of the first conductive auxiliary and the second conductive auxiliary in the positive electrode Compared with the lithium ion secondary battery of 2, the resistance increase rate after the cycle test was remarkably low. Among Examples 1 to 4, the lithium ion secondary batteries of Examples 1 and 2 that satisfy the condition of Expression (2) are compared to Examples 3 and 4 that do not satisfy the condition of Expression (2). The resistance increase rate was low. Although the resistance increase rate is different between Table 2 and Table 3, the value of Table 2 calculated by determining the resistance of the first arc to the third decimal place is more reliable than the value of Table 3. it is conceivable that.

1: First conductive auxiliary agent, 2: Second conductive auxiliary agent, 3: Electrode active material, 4: Gaps

Claims (12)

An electrode active material having an average particle diameter D (μm), a first conductive assistant having an average particle diameter d _c1 (μm), an average particle diameter d _c2 (μm) larger than the d _c1 (μm) and a selection step of selecting a second conductive additive in which d _c2 (μm) satisfies the condition of the following formula (1):
An electrode forming step of forming an electrode mixture layer by applying an electrode mixture having the electrode active material, the first conductive additive, and the second conductive additive on a current collector. A method for producing a secondary battery electrode.
D × ((3/2) ^1/2 −1) ≦ d _c2 ≦ D (1) The mass ratio of the electrode active material and the mass ratio of the second conductive additive when the electrode mixture layer is 100% by mass are M ^* and _mc2 ^* in percentage, and the true density of the electrode active material is ρ (G / cm ³ ), the true density of the second conductive auxiliary agent is ρ _c2 (g / cm ³ ), the average particle diameter of the electrode active material is D (μm), and the second conductive auxiliary agent When the average particle size is _dc2 (μm), the electrode active material and the second conductive additive are blended so that the M ^* and the _mc2 ^* satisfy the condition of the following formula (2). The manufacturing method of the electrode for secondary batteries of Claim 1 which has the adjustment process which adjusts ratio.
0.1 <(M ^* × ρ _c2 × d _c2 ³ ) / ( _{mc 2} ^* × ρ × D ³ ) <10 Equation (2) The product of the number of the first conductive additives in the electrode mixture layer and the cross-sectional area per one first conductive additive is S _c1 (m ² ), and the When the total surface area of the electrode active material is S (m ² ) and the total surface area of the second conductive additive in the electrode mixture layer is S _c2 (m ² ), the S, S _c1 (m ² ) and S _c2 (m ² ) so that the condition of the following formula (6) is satisfied, the electrode active material, the first conductive auxiliary agent, and the second conductive auxiliary agent included in the electrode mixture layer The manufacturing method of the electrode for secondary batteries of Claim 1 or 2 which has the determination process which determines mass ratio.
S + S _c2 ≦ S _c1 ... Formula (6) The specific surface area of the electrode active material is s _am (m ² / g), the specific surface area of the second conductive auxiliary agent is s _c2 (m ² / g), and the true density of the first conductive auxiliary agent is ρ _c1. (G / cm ³ ), the average particle diameter of the first conductive auxiliary agent is d _c1 (μm), and the mass ratio of the first conductive auxiliary agent when the electrode mixture layer is 100% by mass, the weight ratio of the second conductive additive, and the mass ratio of the positive electrode active material ^{_m c1} _{*, m} c2 _*, when the ^{M *,} wherein ^{M *,} wherein _{m c1} ^* and the _{m c2} ^* the following equation (13 4) having a step of determining a mass ratio of the positive electrode active material, the first conductive auxiliary agent and the second conductive auxiliary agent to be included in the electrode mixture layer so as to satisfy the condition of The manufacturing method of the electrode for secondary batteries of Claim 1.
s _am × M ^* + s _c2 × m _c2 ^* ≦ 3 m _c1 ^* / (2ρ _c1 × d _c1 ) (13)   The method for producing a secondary battery electrode according to claim 1, wherein the secondary battery electrode is a positive electrode. An electrode active material having an average particle diameter D (μm), a first conductive assistant having an average particle diameter d _c1 (μm), an average particle diameter d _c2 (μm) larger than the d _c1 (μm) and An electrode for a secondary battery, comprising: an electrode mixture layer having a second conductive additive satisfying a condition of the following formula (1), wherein d _c2 (μm) is satisfied.
D × ((3/2) ^1/2 −1) ≦ d _c2 ≦ D (1) The mass ratio of the electrode active material and the mass ratio of the second conductive additive when the electrode mixture layer is 100% by mass are M ^* and _mc2 ^* in percentage, and the true density of the electrode active material is ρ (G / cm ³ ), the true density of the second conductive auxiliary agent is ρ _c2 (g / cm ³ ), the average particle diameter of the electrode active material is D (μm), and the second conductive auxiliary agent The secondary battery electrode according to claim 6, wherein the M ^* and the m _c2 ^* satisfy the condition of the following formula (2) when the average particle diameter is d _c2 (μm).
0.1 <(M ^* × ρ _c2 × d _c2 ³ ) / ( _{mc 2} ^* × ρ × D ³ ) <10 Equation (2) The product of the number of the first conductive additives in the electrode mixture layer and the cross-sectional area per one first conductive additive is S _c1 (m ² ), and the When the total surface area of the electrode active material is S (m ² ) and the total surface area of the second conductive additive in the electrode mixture layer is S _c2 (m ² ), the S and S _c1 (m ^The secondary battery electrode according to claim 6 or 7, wherein ² ) and S _c2 (m ² ) satisfy a condition of the following formula (6).
S + S _c2 ≦ S _c1 ... Formula (6) The specific surface area of the electrode active material is s _am (m ² / g), the specific surface area of the second conductive auxiliary agent is s _c2 (m ² / g), and the true density of the first conductive auxiliary agent is ρ _c1. (G / cm ³ ), the average particle diameter of the first conductive auxiliary agent is d _c1 (μm), and the mass ratio of the first conductive auxiliary agent when the electrode mixture layer is 100% by mass, the weight ratio of the second conductive additive, and the mass ratio of the positive electrode active material ^{_m c1} _{*, m} c2 _*, when the ^{M *,} wherein ^{M *,} wherein _{m c1} ^* and the _{m c2} ^* the following equation (13 The electrode for secondary batteries of any one of Claims 6-8 which satisfy | fills the conditions of.
s _am × M ^* + s _c2 × m _c2 ^* ≦ 3 m _c1 ^* / (2ρ _c1 × d _c1 ) (13)   It is a positive electrode, The electrode for secondary batteries of any one of Claims 6-9.   The manufacturing method of the secondary battery using the electrode for secondary batteries manufactured by the manufacturing method of the electrode for secondary batteries of Claim 5.   A secondary battery comprising the secondary battery electrode according to claim 10.

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