Nonaqueous secondary battery

Abstract

This nonaqueous secondary battery is provided with a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a nonaqueous electrolyte solution. The negative electrode is formed by laminating a negative electrode current collector, a binder layer, and a negative electrode composite material layer in this order. The adhesive layer contains a conductive auxiliary agent. The ratio of the average length of the conductive auxiliary agent to the average thickness of the adhesive layer is 1.8 or more.

Description

Technical Field

[0001] The present disclosure relates to a non-aqueous secondary battery. Background Art

[0002] A lithium secondary battery using a non-aqueous electrolyte (hereinafter also referred to as a "non-aqueous secondary battery") is used for information and communication technology (such as personal computers, smartphones, etc.), vehicle-mounted, power storage, etc.

[0003] Japanese Patent Application Laid-Open No. 2004-273181 discloses an electrode plate for a battery. The electrode plate is an electrode plate in which a binder layer (hereinafter also referred to as an "adhesive layer") and an active material layer (hereinafter also referred to as a "composite material layer") are sequentially laminated on at least one surface of a current collector. The binder layer is made of a polyamideimide resin containing carbon. As the carbon, graphite, carbon black, or acetylene black is specifically disclosed. Summary of the Invention

[0004] However, in the electrode body disclosed in Japanese Patent Application Laid-Open No. 2004-273181, in order to increase the energy density (specifically, to improve the electron conductivity of the negative electrode), the content of carbon in the binder layer is increased. If the content of carbon in the binder layer is increased, the strength of the binder layer for bonding the negative electrode composite material layer to the negative electrode current collector (hereinafter also referred to as the "bonding strength of the negative electrode") may decrease. There is also a need for a non-aqueous secondary battery in which a decrease in the discharge rate characteristics of the non-aqueous secondary battery is suppressed.

[0005] The present disclosure has been made in view of the above circumstances. A problem to be solved by one embodiment of the present disclosure is to provide a non-aqueous secondary battery having excellent bonding strength and electron conductivity of a negative electrode and suppressing a decrease in discharge rate characteristics.

[0006] The technical solutions for solving the above problems include the following embodiments. <1> A non-aqueous secondary battery, comprising a positive electrode, a negative electrode, a spacer disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte, the negative electrode being formed by sequentially laminating a negative electrode current collector, a binder layer, and a negative electrode composite material layer, the binder layer containing a conductive auxiliary agent, a ratio (A / B) of an average length (A) of the conductive auxiliary agent to an average thickness (B) of the binder layer being 1.8 or more. <2> The non-aqueous secondary battery according to <1> above, wherein the ratio (A / B) is 2.5 or more. <3> The non-aqueous secondary battery according to <1> or <2> above, wherein The content of the conductive additive is 0.8 mass% or more relative to the total amount of the adhesive layer. <4>The non-aqueous secondary battery according to any one of <1> to <3> above, wherein, The adhesive layer contains a styrene-butadiene copolymer. <5>The non-aqueous secondary battery according to any one of <1> to <4> above, wherein, The thickness of the negative electrode composite material layer is 100 μm or more.

[0007] According to the present disclosure, there is provided a non-aqueous secondary battery having excellent adhesive strength and electronic conductivity of the negative electrode, and in which a decrease in discharge rate characteristics is suppressed. Detailed Description

[0008] In the present disclosure, a numerical range indicated by using "to" means a range including the numerical values described before and after "to" as the minimum value and the maximum value, respectively. In the numerical ranges described stepwise in the present disclosure, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the upper limit value or the lower limit value of another numerically described stepwise range. In the numerical ranges described in the present disclosure, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the value shown in the examples. In the present disclosure, a combination of two or more preferred modes is a more preferred mode. In the present disclosure, regarding the amounts of the respective components, when there are multiple substances corresponding to the respective components, unless otherwise specified, it means the total amount of the multiple substances. In the present disclosure, the expression "step" is not limited to an independent step, and even if it cannot be clearly distinguished from other steps, as long as the desired purpose of the step can be achieved, it is also included in this expression. (1) Non-aqueous secondary battery

[0009] The non-aqueous secondary battery of the present disclosure includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte. The negative electrode is formed by sequentially laminating a negative electrode current collector, an adhesive layer, and a negative electrode composite material layer. The adhesive layer contains a conductive additive. The ratio (A / B) of the average length (A) of the conductive additive to the average thickness (B) of the adhesive layer is 1.8 or more.

[0010] Since the non-aqueous secondary battery of the present disclosure has the above configuration, the adhesive strength and electronic conductivity of the negative electrode are excellent, and a decrease in discharge rate characteristics is suppressed. This effect is presumably based on the following reasons, but is not limited thereto. In the present disclosure, the ratio (A / B) is 1.8 or more. Therefore, compared with a configuration where the ratio (A / B) is less than 1.8 (for example, a configuration where the conductive additive is composed of at least one of graphite, carbon black, and acetylene black), even if the amount of the conductive additive in the adhesive layer is small, a conductive path is likely to be formed in the adhesive layer. As a result, it is speculated that in the non-aqueous secondary battery of the present disclosure, the adhesion strength and electron conductivity of the negative electrode are excellent, and a decrease in the discharge rate characteristics is suppressed.

[0011] As the monomer structure of the non-aqueous secondary battery, there is no particular limitation, and examples include a wound type and a laminated type. The wound type is formed by winding a strip-shaped electrode body in which a negative electrode, a spacer, and a positive electrode are sequentially laminated. The laminated type is formed by laminating sheet-shaped electrode bodies in which a negative electrode, a spacer, and a positive electrode are sequentially laminated. (1.1) Negative electrode

[0012] The negative electrode is formed by sequentially laminating a negative electrode current collector, an adhesive layer, and a negative electrode composite material layer. (1.1.1) Negative electrode current collector

[0013] As the negative electrode current collector, any known current collector (such as a copper foil) may be used. (1.1.2) Adhesive layer

[0014] The ratio (A / B) of the adhesive layer is preferably 2.5 or more. Thereby, a decrease in the discharge rate characteristics of the non-aqueous secondary battery is suppressed. The ratio (A / B) may be 4.0 or more, or may be 5.0 or more. The ratio (A / B) may be 7.0 or less, or may be 4.0 or less.

[0015] Regarding the thickness (B) of the adhesive layer, as long as the ratio (A / B) is 1.8 or more, there is no particular limitation. The thickness (B) of the adhesive layer may be 3 μm or more, may be 5 μm or more, or may be 8 μm or more. The thickness (B) of the adhesive layer may be 13 μm or less, or may be 8 μm or less. The thickness (B) of the adhesive layer is measured by observation with an electron microscope (SEM). (1.1.2.1) Conductive additive

[0016] The average length (A) of the conductive additive is not particularly limited, and may be 8 μm or more, may be 13 μm or more, or may be 20 μm or more. The average length (A) of the conductive additive may be 35 μm or less. The average length (A) of the conductive additive is measured by observation with an electron microscope (SEM).

[0017] Regarding the conductive additive, as long as the ratio (A / B) is 1.8 or more, there is no particular limitation, and it preferably contains carbon nanotubes, and is preferably carbon nanotubes.

[0018] The content of the conductive additive is not particularly limited. The content of the conductive additive can be 0.3% by mass or more, can be 0.8% by mass or more, and can also be 1.0% by mass or more with respect to the total amount of the adhesive layer. The content of the conductive additive can be 2.2% by mass or less, and can also be 1.2% by mass or less.

[0019] When the ratio (A / B) is 2.5 or more, the content of the conductive additive is preferably 0.8% by mass or more with respect to the total amount of the adhesive layer. Thereby, the through - resistance of the negative electrode composite layer is lower. (1.1.2.2) Adhesive

[0020] The adhesive layer bonds the negative electrode composite layer and the negative electrode current collector. The adhesive layer usually contains an adhesive in addition to the conductive additive. Examples of the adhesive include vinyl halide resins, rubbers, polyolefin resins, etc. Examples of the vinyl halide resin include polyvinylidene fluoride (PVdF), copolymer of polyvinylidene fluoride and hexafluoropropylene (PVdF - HFP), etc. Examples of the rubber include styrene - butadiene rubber (SBR), butadiene rubber (BR), acrylate butadiene rubber (ABR), acrylonitrile - butadiene rubber (NBR), butyl rubber (isobutylene - isoprene rubber), etc. Examples of the polyolefin resin include polyethylene, polypropylene, etc. The adhesive can be used alone or in combination of two or more.

[0021] When the ratio (A / B) is 2.5 or more and the content of the conductive additive is 0.8% by mass or more, the adhesive layer preferably contains styrene - butadiene rubber. Thereby, the bonding strength of the negative electrode composite layer is more excellent, and the decrease in the discharge rate characteristics of the non - aqueous secondary battery is suppressed.

[0022] The content of the adhesive is not particularly limited. The content of the adhesive can be 99.7% by mass or less, can be 99.2% by mass or less, and can also be 99.0% by mass or less with respect to the total amount of the adhesive layer. The content of the conductive additive can be 97.8% by mass or more, and can also be 98.8% by mass or more. (1.1.2.3) Other components

[0023] The adhesive layer may or may not contain other components. Examples of other components include electrolyte supporting salts (lithium salts) for improving ionic conductivity, polymer electrolytes, additives (such as propylene carbonate trifluoride, etc.). (1.1.3) Negative electrode composite layer

[0024] The negative electrode composite material layer contains a negative electrode layer active material capable of occluding and releasing charge carriers (such as carbon (such as natural graphite, artificial graphite), compounds capable of alloying with lithium (such as silicon, tin, etc.), etc.). The negative electrode composite material layer may also contain, as needed, a conductive aid (such as acetylene black, etc.) for improving electron conductivity, a binder, an electrolyte support salt (lithium salt) for improving ion conductivity, a polymer electrolyte, and an additive (such as propylene carbonate trifluoride, etc.). As the binder, the same binders as those exemplified as the binder for the binder layer can be cited.

[0025] The thickness of the negative electrode composite material layer is not particularly limited, and is preferably 100 μm or more. Thereby, the energy density of the non-aqueous secondary battery is increased. From the perspective of achieving a higher energy density, the thickness of the negative electrode composite material layer is more preferably 150 μm or more, and further preferably 180 μm or more. The thickness of the negative electrode composite material layer can be 250 μm or less. (1.2) Positive electrode

[0026] The positive electrode may have a positive electrode current collector (such as aluminum foil, etc.) and a positive electrode composite material layer. The positive electrode composite material layer is laminated on at least one main surface of the positive electrode current collector.

[0027] The positive electrode composite material layer contains a positive electrode active material. The positive electrode active material releases or occludes lithium ions from / to the non-aqueous electrolyte. Any known positive electrode active material (such as LiNiO 2 , LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 etc.) may be used. The positive electrode composite material layer may also contain a known conductive material (such as carbon black, etc.), lithium phosphate, and a binder. As the binder, the same binders as those exemplified as the binder for the binder layer can be cited. (1.3) Spacer

[0028] The spacer maintains the spacing between the positive electrode and the negative electrode to prevent the occurrence of contact short circuit, and allows lithium ions to pass through. As the spacer, for example, a porous resin sheet or a non-woven fabric can be cited. As the material of the porous resin sheet, for example, polyolefins (such as polypropylene, polyethylene, etc.) can be cited. As the material of the non-woven fabric, for example, polypropylene, polyethylene terephthalate, methyl cellulose, etc. can be cited. The spacer can be a known structure. (1.4) Non-aqueous electrolyte

[0029] The non-aqueous electrolyte may contain a non-aqueous solvent and a lithium salt. As the lithium salt, for example, LiClO 4 , LiAsF 6 , LiPF 6 , LiBF4 , LiCF 3 SO 3 , LiN(FSO 2 ) 2 , LiN(CF 3 SO 2 ) 2 etc. As non-aqueous solvents, cyclic carbonates (such as ethylene carbonate, etc.), chain carbonates (such as dimethyl carbonate, methyl ethyl carbonate, etc.), cyclic esters (such as γ-butyrolactone, γ-valerolactone, etc.), chain esters (such as methyl formate, methyl acetate, etc.), ethers (such as 1,2-dimethoxyethane, ethoxymethoxyethane, etc.) can be cited, etc. The non-aqueous electrolyte can contain additives (such as vinylene carbonate, lithium bis(oxalato)borate, etc.) etc. (1.5) Case

[0030] Non-aqueous secondary batteries usually have a case. The case houses the positive electrode, negative electrode, separator, and non-aqueous electrolyte. As the case, there is no particular limitation, and laminated films (such as aluminum sheets, etc.), battery cans (such as cylindrical, square, coin-shaped, etc.) can be cited, etc.

[0031] Hereinafter, the present disclosure will be further described in detail using examples, but the invention of the present disclosure is not limited to these examples. [1] Examples 1 to 11 and Comparative Examples 1 to 11 [1.1] Positive electrode

[0032] LiNi which is a positive electrode active material 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 , a conductive aid, and a solution containing polyvinylidene fluoride (PVdF) as a binder were mixed to prepare a slurry. The mass ratio of the positive electrode active material, conductive aid, and binder (positive electrode active material: conductive aid: binder) was 87:10:3. The "solution containing PVdF" means a mixed solution of PVdF and a solvent. The slurry was coated on an aluminum foil as a positive electrode current collector to obtain a positive electrode sheet. Using (diameter: 12 mm) punch to cut the positive electrode sheet to obtain a positive electrode. The positive electrode is formed by laminating a positive electrode current collector and a positive electrode composite material layer in sequence. [1.2] Negative electrode [1.2.1] Binder layer

[0033] As a solution containing a binder (hereinafter also referred to as "binder-containing solution"), a solution containing styrene-butadiene rubber (SBR) and a solution containing polyvinylidene fluoride (PVdF) were prepared. The "solution containing SBR" means a mixed solution of SBR and a solvent. The "solution containing PVdF" means a mixed solution of PVdF and a solvent.

[0034] As a conductive additive, carbon nanotubes (CNTs) with an average length of 10 μm, CNTs with an average length of 15 μm, and CNTs with an average length of 30 μm were prepared.

[0035] The binder-containing solution containing the binder shown in Table 1 and the conductive additive shown in Table 1 were mixed in the ratio shown in Table 1 to obtain a dispersion. The dispersion was coated on a copper foil serving as a negative electrode current collector and dried at 80 °C. Thus, a negative electrode current collector with a binder layer was obtained. The negative electrode current collector with a binder layer includes a negative electrode current collector and a binder layer formed on one main surface of the negative electrode current collector. [1.2.2] Negative electrode composite material layer

[0036] As a negative electrode active material, an artificial graphite-based material coated with an amorphous coating having an average particle size of 15 μm was prepared. The negative electrode active material, styrene-butadiene rubber (SBR) as a binder, carboxymethyl cellulose (CMC) as a thickener, and water as a dispersion solvent were mixed to obtain a slurry. The slurry was coated on the binder layer of the negative electrode current collector with a binder layer to obtain a negative electrode sheet. Using (Diameter: 12 mm) punch to punch the negative electrode sheet to obtain a negative electrode. The negative electrode is formed by sequentially laminating a negative electrode current collector, a binder layer, and a negative electrode composite material layer. The capacity of the negative electrode is about 1.1 relative to the capacity of the positive electrode. [1.2.3] Non-aqueous electrolyte

[0037] LiPF was added to the mixed solvent as an electrolyte 6 , to obtain a non-aqueous electrolyte. The mixed solvent is composed of ethylene carbonate (EC) and ethyl methyl carbonate (EMC). The volume ratio of EC to EMC (EC:EMC) is 30:70. The concentration of LiPF in the non-aqueous electrolyte 6 is 1.0 M (mol / L). [1.2.4] Spacer

[0038] As a spacer, a three-layer porous membrane was prepared. The porous membrane is formed by sequentially laminating a polypropylene layer, a polyethylene layer, and a polypropylene layer. The air permeability of the porous membrane obtained by the Gurley test method is 300 seconds. [1.2.5] Battery

[0039] The positive electrode and the negative electrode were used to form a monomer (electrode body) facing each other with a spacer interposed therebetween, and an evaluation battery was fabricated by laminating and sealing together with the non-aqueous electrolyte. [2] Evaluation [2.1] 1.0C rated discharge rate [2.1.1] Activation

[0040] In a constant temperature bath at 25 °C, the initial charging is set to a constant current mode, and charging is performed at a current value of 0.1C until 4.30V. After that, using the constant current mode, it is discharged at a current value of 0.3C until 3.00V. This is repeated three times. [2.1.2] Initial characteristic evaluation

[0041] Using the constant current - constant voltage method, charging is performed at a current value of 0.1C until 4.30V, and constant voltage charging is carried out until the current value during constant voltage charging reaches 1 / 50C, reaching a full charge state. After that, using the constant current mode, it is discharged at a current value of 0.2C until 3.00V. The capacity at this time is taken as the initial capacity. [2.1.3] Long - term input - output characteristic evaluation

[0042] Using the constant current mode, charging is performed at a current value of 0.1C until 4.30V, and constant voltage charging is carried out until the current value during constant voltage charging reaches 1 / 50C, reaching a full charge state. After that, using the constant current mode, it is discharged at a current value of 1.0C until 3.00V. The capacity at this time is measured.

[0043] The ratio of the capacity measured in the long - term input - output characteristic evaluation to the initial capacity measured in the initial characteristic evaluation is taken as the "1.0C rated discharge rate". The measurement results are shown in Table 1. The allowable range of the 1.0C rated discharge rate is "57% or more". [2.2] Peel strength

[0044] A peel test is carried out to measure the peel strength of the negative composite material layer. Specifically, a specified tape is attached to the negative electrode, and the stress when peeled off at a constant speed is measured. The stress when the negative composite material layer is peeled is taken as the "peel stress". The measurement results are shown in Table 1. The allowable range of the peel strength is "0.18 N / cm or more". [2.3] Composite material formability

[0045] The evaluation method of the composite material formability is carried out in accordance with JIS K6854 - 11999. Specifically, using the measurement results of the peel strength in the peel test, the composite material formability (i.e., the adhesiveness required to produce the monomers of the examples) is evaluated according to the following evaluation criteria. The evaluation results are shown in Table 1. In addition, to produce the monomers of the examples, a peel strength of 0.10 N / m 2 or more is required.

[0046] A: The peel strength is 0.10 N / m 2 or more. B: The peel strength is less than 0.10 N / m 2 . [2.4] Through - hole resistance

[0047] In order to evaluate the electron conductivity between the negative electrode composite material layer and the negative electrode current collector (i.e., the electron conductivity of the negative electrode), the through - resistance was measured. Specifically, one terminal of the measuring device was electrically connected to the negative electrode composite material layer of the negative electrode, and the other terminal of the measuring device was electrically connected to the negative electrode current collector of the negative electrode, and an electric current was passed through the negative electrode composite material layer of the negative electrode and the negative electrode current collector of the negative electrode. The electron resistance value between the terminals was taken as the "through - resistance". The measurement results are shown in Table 1. The allowable range of the through - resistance is "2.10 Ω / cm or less". Table 1

[0048] In Table 1, the "amount of binder" represents the proportion (mass%) of the binder relative to the total amount of the negative electrode composite material layer. "SBR" represents styrene - butadiene rubber. "PVdF" represents polyvinylidene fluoride. The "addition amount of the binder" represents the proportion (mass%) of CNT relative to the total amount of the binder layer. The "*" at the 1.0C rated discharge rate indicates that the measurement could not be performed.

[0049] In Comparative Examples 1 to 11, the ratio (A / B) is not 1.8 or more. Thus, the measured values of the 1.0C rated discharge rate in Comparative Examples 5 to 11 are not "57% or more". The peel strength in Comparative Examples 1 to 5 is not "0.18 N / cm or more". The through - resistance in Comparative Examples 8 to 10 is not "2.10 Ω / cm or less". As a result, it can be seen that the non - aqueous secondary batteries in Comparative Examples 1 to 11 are not "non - aqueous secondary batteries with excellent bonding strength and electron conductivity of the negative electrode and with the reduction of the discharge rate characteristics suppressed".

[0050] In Examples 1 to 11, the ratio (A / B) is 1.8 or more. Thus, the measured values of the 1.0C rated discharge rate in Examples 1 to 11 are "57% or more". The peel strength in Examples 1 to 11 is "0.18 N / cm or more". The through - resistance in Examples 1 to 11 is "2.10 Ω / cm or less". As a result, it can be seen that the non - aqueous secondary batteries in Examples 1 to 11 are "non - aqueous secondary batteries with excellent bonding strength and electron conductivity of the negative electrode and with the reduction of the discharge rate characteristics suppressed".

Claims

1. A non-aqueous secondary battery, The invention comprises a positive electrode, a negative electrode, a separator arranged between the positive electrode and the negative electrode, and a non-aqueous electrolyte. The negative electrode is formed by sequentially stacking a negative electrode current collector, a binder layer, and a negative electrode composite material layer. The adhesive layer contains a conductive auxiliary agent, The ratio of the average length of the conductive auxiliary agent to the average thickness of the adhesive layer is 1.8 or more.

2. The nonaqueous secondary battery according to claim 1, wherein The ratio is 2.5 or more.

3. The non-aqueous secondary battery according to claim 2, wherein: The content of the conductive auxiliary agent is 0.8% by mass or more based on the total amount of the adhesive layer.

4. The non-aqueous secondary battery according to claim 3, wherein: The adhesive layer includes a styrene-butadiene copolymer.

5. The nonaqueous secondary battery according to any one of claims 1 to 4, wherein The thickness of the negative electrode composite material layer is greater than 100 μm.

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