Method for manufacturing nonaqueous electrolyte secondary battery and negative electrode active material

Abstract

The present invention relates to a manufacturing method of a nonaqueous electrolyte secondary battery and a negative electrode active material. A negative electrode active material is prepared by mixing first graphite particles and second graphite particles. A negative electrode containing the negative electrode active material is manufactured. A nonaqueous electrolyte secondary battery containing the negative electrode, a positive electrode, and an electrolyte is manufactured. The first graphite particles have a first particle size distribution on a number basis. The second graphite particles have a second particle size distribution on a number basis. A relationship of "D250 / D150 ≤ 0.50" is satisfied. D150 represents D50 in the first particle size distribution. D250 represents D50 in the second particle size distribution. A relationship of "R2 ≤ R1" is satisfied. R1 represents an arithmetic average of circularity of the first graphite particles. R2 represents an arithmetic average of circularity of the second graphite particles.

Description

Technical Field

[0001] This technology relates to a method for manufacturing non-aqueous electrolyte secondary batteries and a negative electrode active material. Background Technology

[0002] Japanese Patent Application Publication No. 2013-197082 discloses a carbon material for batteries containing spherical graphite. Summary of the Invention

[0003] Spherical graphite particles have been developed as the negative electrode active material for non-aqueous electrolyte secondary batteries (hereinafter referred to as "batteries"). As described in the text, spherical graphite particles have an approximately spherical shape. Indicators of sphericity include, for example, the roundness of particle images.

[0004] Spherical graphite particles exhibit good filling properties. By employing spherical graphite particles, improvements in energy density, for example, can be expected. However, spherical graphite particles also tend to be difficult to crush. Generally, the negative electrode of a battery undergoes compression processing. Because the particles are difficult to crush during compression, there is a tendency for voids to easily form within the negative electrode. Electrolyte can permeate into these voids. Due to the formation of voids, improvements in input / output characteristics, for example, can be expected. Furthermore, if the particles are crushed, the active surface (edge ​​surface) of the graphite may sometimes be exposed, reducing storage characteristics. Because the particles are difficult to crush, improvements in storage characteristics can be expected.

[0005] However, there is room for improvement in the cycle durability of spherical graphite particles. Specifically, in a negative electrode containing spherical graphite particles, there is a tendency for the contact points between the particles to become point-like. During charging and discharging, the particles repeatedly expand and contract. Due to the volume changes of the particles, the contact points between them may be lost. It is believed that the loss of these contact points disrupts the conductive path, resulting in a decrease in capacity retention.

[0006] For example, using conductive materials (such as carbon black) to form conductive paths is also considered. However, conductive materials do not significantly improve battery capacity. Adding conductive materials to the negative electrode may even reduce the battery's energy density.

[0007] The purpose of this technology is to improve cycle durability.

[0008] The following describes the structure and effects of this technology. The mechanism of action described in this specification includes assumptions. The mechanism of action does not limit the scope of this technology.

[0009] [1] The manufacturing methods of non-aqueous electrolyte secondary batteries include the following (A), (B) and (C).

[0010] (A) A negative electrode active material is prepared by mixing a first graphite particle and a second graphite particle.

[0011] (B) Manufacturing a negative electrode containing a negative electrode active material.

[0012] (C) Manufacturing a non-aqueous electrolyte secondary battery containing a negative electrode, a positive electrode and an electrolyte.

[0013] The first graphite particles have a first particle size distribution based on the number of particles. The second graphite particles have a second particle size distribution based on the number of particles.

[0014] The following relationship (I) must be satisfied:

[0015] D250 / D150≤0.50…(I).

[0016] In equation (I) above, D150 represents D50 in the first particle size distribution. D250 represents D50 in the second particle size distribution.

[0017] Furthermore, the following relationship (II) is satisfied:

[0018] R2≤R1…(II).

[0019] In equation (II) above, R1 represents the arithmetic mean of the roundness of the first graphite particles. R2 represents the arithmetic mean of the roundness of the second graphite particles.

[0020] The negative electrode active material of this technology comprises first graphite particles and second graphite particles. The second graphite particles can be considered small particles. As shown in equation (I) above, the second graphite particles have a D50 of less than 1 / 2 that of the first graphite particles. Conductive pathways are expected to be formed by the second graphite particles entering the gaps between the first graphite particles. Unlike general conductive materials (such as carbon black), the second graphite particles contribute to the battery capacity.

[0021] Furthermore, as shown in equation (II) above, the arithmetic mean of the roundness (hereinafter also referred to as "average roundness") between the first and second graphite particles satisfies a specific relationship. That is, the average roundness (R2) of the smaller particle is less than or equal to the average roundness (R1) of the larger particle. Due to charging and discharging, the smaller particles repeatedly expand and contract. Due to the volume change of the smaller particles, the junction between the smaller and larger particles may be lost. According to the novel insight of this technology, by ensuring that the average roundness (R2) of the smaller particles is less than or equal to the average roundness (R1) of the larger particles, it is expected that the junction between the smaller and larger particles will be less likely to be lost.

[0022] Based on the above, improved cycle durability can be expected in the batteries of this technology.

[0023] [2] The following relationships (III) and (IV) can be satisfied:

[0024] 0.94≤R1…(III)

[0025] 0.90≤R2 <R1…(IV)。

[0026] By further satisfying the relationships in equations (III) and (IV) above, improvements in cycle durability can be expected.

[0027] [3] The following relationship (V) can be satisfied:

[0028] 0.05≤M2 / M1≤0.10…(V).

[0029] In the above formula (V), M1 represents the mass of the first graphite particle contained in the negative electrode active material. M2 represents the mass of the second graphite particle contained in the negative electrode active material.

[0030] By further satisfying the relationship of the above equation (V), improvements in cycle durability can be expected.

[0031] [4] The following relationship (VI) can be satisfied:

[0032] 0.70≤(D190-D110) / D150≤0.80…(VI).

[0033] In equation (VI) above, D110 represents D10 in the first particle size distribution. D190 represents D90 in the first particle size distribution.

[0034] Furthermore, the following relationship (VII) can be satisfied:

[0035] 0.97≤(D290-D210) / D250…(VII).

[0036] In equation (VII) above, D210 represents D10 in the second particle size distribution. D290 represents D90 in the second particle size distribution.

[0037] The value “(D90-D10) / D50” is also known as the “span value”. The span value is an indicator of the diffusion of the particle size distribution. It is believed that the smaller the span value, the sharper the particle size distribution. By further satisfying the relationship between equations (VI) and (VII) above, improvements in cycle durability can be expected.

[0038] [5] The standard deviation of the roundness of the second graphite particle can be above 0.08.

[0039] With a standard deviation of over 0.08 for the sphericity of the second graphite particles, improved cycle durability can be expected. It is believed that because the sphericity of the small particles has a specific deviation, the junction between the small and large particles is less likely to be lost.

[0040] [6] The negative electrode active material has a third particle size distribution based on the number of particles.

[0041] The following relationship (VIII) can be satisfied:

[0042] 0.87≤(D390-D310) / D350≤0.99…(VIII).

[0043] In equation (VIII) above, D310 represents D10 in the third granularity distribution. D350 represents D50 in the third granularity distribution. D390 represents D90 in the third granularity distribution.

[0044] The negative electrode active material is a mixture of first graphite particles and second graphite particles. By mixing the first graphite particles and the second graphite particles in a manner that satisfies the relationship in equation (VIII) above, improved cycle durability can be expected.

[0045] [7] The negative electrode active material is used in a non-aqueous electrolyte secondary battery. The negative electrode active material comprises first graphite particles and second graphite particles. The first graphite particles have a first particle size distribution based on the number of particles. The second graphite particles have a second particle size distribution based on the number of particles.

[0046] The following relationship (I) must be satisfied:

[0047] D250 / D150≤0.50…(I).

[0048] In equation (I) above, D150 represents D50 in the first particle size distribution. D250 represents D50 in the second particle size distribution.

[0049] Furthermore, the following relationship (II) is satisfied:

[0050] R2≤R1…(II).

[0051] In equation (II) above, R1 represents the arithmetic mean of the roundness of the first graphite particles. R2 represents the arithmetic mean of the roundness of the second graphite particles.

[0052] The above and other objects, features, aspects and advantages of this technology will become clear from the following detailed description of the technology in conjunction with the accompanying drawings. Attached Figure Description

[0053] Figure 1 A schematic flowchart illustrating the manufacturing method of the non-aqueous electrolyte secondary battery in this embodiment is provided.

[0054] Figure 2 This is a schematic diagram illustrating an example of the configuration of the electrode body in this embodiment.

[0055] Figure 3 A schematic diagram illustrating an example of the configuration of a non-aqueous electrolyte secondary battery in this embodiment. Detailed Implementation

[0056] The following describes embodiments of the present technology (also referred to as "the present embodiment" in this specification); however, the following description does not limit the scope of the present technology. For example, the effects mentioned in this specification are not intended to limit the scope of the present technology to achieving all of the effects.

[0057] <Definitions of terms, etc.>

[0058] In this specification, the terms "comprise," "include," "have," and their variations (such as "be composed of," "encompass," "involve," "contain," "carry," "support," "hold," etc.) are open-ended. Open-ended forms may include additional elements beyond the essential elements, or they may not. The term "consist of" is a closed-ended form. The term "consist essentially of" is a semi-closed-ended form. Semi-closed-ended forms may include additional elements beyond the essential elements, without hindering the purpose of this technology. For example, elements commonly conceived in the art (such as unavoidable impurities) may be included as additional elements.

[0059] In this specification, the expressions “may” and “can” are not used in a mandatory sense, meaning “must”, but rather in a permissive sense, meaning “possible to have”.

[0060] In this specification, the singular forms (a, an, and the) include the plural forms unless otherwise specified. For example, "particle" can include not only "a single particle" but also "a collection of particles (powder, powder, or a group of particles)".

[0061] In this specification, unless otherwise specified, the order in which two or more steps, actions, and operations are described in the method is not limited. For example, two or more steps may be performed simultaneously.

[0062] In this specification, unless otherwise specified, numerical ranges such as "1% to 10%" and "1% to 10%" include both upper and lower limits. That is, "1% to 10%" and "1% to 10%" represent a numerical range of "above 1% and below 10%". Furthermore, any value arbitrarily selected from the numerical range can be set as a new upper and lower limit. For example, a new numerical range can be set by arbitrarily combining values ​​within the numerical range with values ​​described in other parts of this specification.

[0063] In this specification, all numerical values ​​are described using the term "approximately". "Approximately" can refer to, for example, ±5%, ±3%, ±1%, etc. All numerical values ​​are approximate values ​​that may vary depending on the application of this technology. All numerical values ​​are expressed in significant figures. All measured values ​​may be rounded to account for the number of significant figures. All numerical values ​​may include, for example, errors associated with detection limits, etc.

[0064] In this specification, when a compound is represented by a stoichiometric formula such as "LiCoO2", the stoichiometric formula is merely a representative example. The composition ratio can be non-stoichiometric. For example, when lithium cobalt oxide is represented as "LiCoO2", unless otherwise specified, lithium cobalt oxide is not limited to the composition ratio of "Li / Co / O = 1 / 1 / 2", and can contain Li, Co, and O in any composition ratio.

[0065] Geometric terms used in this specification (such as "perpendicular") should not be interpreted in a strict sense. For example, "perpendicular" can also deviate slightly from the strict meaning of "perpendicular." Geometric terms used in this specification may include tolerances and errors in design, operation, and manufacturing. Dimensional relationships in the drawings may sometimes differ from actual dimensional relationships. To aid in understanding this technology, dimensional relationships (length, width, thickness, etc.) in the drawings may sometimes be altered. Furthermore, some components may sometimes be omitted.

[0066] In this specification, "at least one of the first graphite particle and the second graphite particle" may be collectively referred to as "graphite particle". The ratio of the D50 of the second graphite particle to the D50 of the first graphite particle is also denoted as "particle size ratio". The arithmetic mean of roundness is also denoted as "average roundness". The ratio of the mass of the second graphite particle to the mass of the first graphite particle is also denoted as "mixing ratio". For example, "first particle size distribution based on number" is also denoted as "first particle size distribution", etc.

[0067] Regarding "particle size distribution" in this specification, "D10", "D50", and "D90" are defined as follows: D10 represents the particle size in the number-based particle size distribution where the cumulative frequency from the smallest particle size side is 10%. D50 represents the particle size in the number-based particle size distribution where the cumulative frequency from the smallest particle size side is 50%. D90 represents the particle size in the number-based particle size distribution where the cumulative frequency from the smallest particle size side is 90%.

[0068] In this specification, the particle size distribution based on volume is converted to a particle size distribution based on number. The particle size distribution based on volume can be determined using a laser diffraction particle size distribution measuring device. The measurement sequence can be as follows: Prepare the test object (graphite particles). Prepare the test sample (particle dispersion) by mixing the test object, dispersant, and dispersion medium. The dispersant can be the product name "Tritton X-100". The dispersion medium can be ion-exchanged water. Determine the particle size distribution based on volume by introducing the test sample into the laser diffraction particle size distribution measuring device.

[0069] The "roundness" in this specification is determined by the following formula (IX):

[0070] R = L0 / L···(IX).

[0071] In equation (IX) above, "R" represents the circularity. "L0" represents the circumference of a circle with the same area as the particle image. "L" represents the perimeter of the particle image. The circularity of a perfect circle is 1.

[0072] Particle images can be obtained using a flow cytometry particle image analyzer. For example, a wet flow cytometry particle size and shape analyzer, such as the "FPIA-3000" manufactured by Sismex, can be used. The measurement sequence can be as follows: Prepare the target particle (graphite particles). Prepare a sample (particle dispersion) by mixing the target particle, dispersant, and dispersion medium. Supply the sample to the flow cell of the flow cytometry particle image analyzer. Image the sample passing through the flow cell using a flash lamp and an optical microscope. Analyze the images of each particle in the image to determine the roundness of each particle. The detection range is 0.25–100 μm. The arithmetic mean of the roundness of 100 or more particles is considered the "arithmetic mean of roundness (average roundness)". Furthermore, the standard deviation is calculated based on the roundness of 100 or more particles.

[0073] <Manufacturing Method of Non-Aqueous Electrolyte Secondary Batteries>

[0074] Figure 1A schematic flowchart of the manufacturing method of the non-aqueous electrolyte secondary battery in this embodiment is provided. The manufacturing method of the non-aqueous electrolyte secondary battery in this embodiment (hereinafter also referred to as "this manufacturing method") includes "(A) preparation of negative electrode active material", "(B) manufacturing of negative electrode" and "(C) manufacturing of battery".

[0075] (A) Preparation of Negative Electrode Active Materials

[0076] This manufacturing method involves preparing a negative electrode active material by mixing first graphite particles and second graphite particles. Any powder mixer can be used in this manufacturing method. Dry mixing or wet mixing can be performed in this manufacturing method.

[0077] (Mix ratio)

[0078] Regarding the second graphite particles, they are mixed with the first graphite particles at a predetermined mixing ratio. In this embodiment, the "mixing ratio" is the ratio (M2 / M1) of the mass of the second graphite particles (M2) to the mass of the first graphite particles (M1). The mixing ratio can be, for example, 0.025 to 0.125. The mixing ratio can also be, for example, 0.05 to 0.10. With a mixing ratio of 0.05 to 0.10, improved cycle durability can be expected.

[0079] (Graphite particles)

[0080] The graphite particles in this embodiment comprise graphite. For example, the graphite particles may be substantially composed of graphite. Graphite may include synthetic graphite and natural graphite, etc. As long as the graphite particles contain graphite, additional components may be included. For example, the graphite particles may include a surface coating. The surface coating may, for example, include amorphous carbon, etc.

[0081] (First graphite particle)

[0082] The first graphite particle can be considered a large particle. It has a relatively large particle size compared to the second graphite particle. The first graphite particle can contribute to improvements in energy density, input / output characteristics, and storage properties. The first graphite particle has a first particle size distribution based on the number of particles. D150 is the D50 of this first particle size distribution. D150 can be, for example, 15–20 μm.

[0083] (Second graphite particle)

[0084] The second graphite particles can be considered small particles. They have a relatively smaller particle size compared to the first graphite particles. These second graphite particles can form conductive paths between larger particles. They can contribute to improved cycle durability. The second graphite particles have a second particle size distribution based on the number of particles. D250 is the D50 in this second particle size distribution. D250 can be, for example, 5–9 μm.

[0085] (particle size ratio)

[0086] In this embodiment, the "particle size ratio (D250 / D150)" is obtained by dividing the D250 of the second graphite particle by the D150 of the first graphite particle. The particle size ratio is 0.50 or less. An improved cycle durability is expected when the particle size ratio is 0.50 or less. This is believed to be because small particles easily enter the gaps between larger particles. For example, the particle size ratio can be 0.45 or less, 0.43 or less, or 0.41 or less. For example, the particle size ratio can be 0.39 or more.

[0087] (Average roundness)

[0088] The average roundness is the arithmetic mean of the roundness. In this embodiment, the average roundness (R2) of the second graphite particle is less than or equal to the average roundness (R1) of the first graphite particle. That is, the relationship "R2 ≤ R1" is satisfied. Therefore, it is expected that the junction between the small and large particles is less likely to be lost. The average roundness (R2) of the second graphite particle can also be less than the average roundness (R1) of the first graphite particle. That is, the relationship "R2 < R1" can also be satisfied.

[0089] The average sphericity (R1) of the first graphite particle can be, for example, 0.94 or higher, 0.95 or higher, or between 0.94 and 0.95. A higher average sphericity (R1) of the first graphite particle can, for example, lead to improved input-output characteristics. The average sphericity (R2) of the second graphite particle can be, for example, 0.90 or higher, 0.92 or higher, less than 0.94, or between 0.90 and 0.92.

[0090] (Standard deviation of roundness)

[0091] The standard deviation (σ²) of the sphericity of the second graphite particle can be, for example, 0.08 or higher. With a standard deviation (σ²) of 0.08 or higher, improved cycle durability can be expected. It is believed that because the sphericity of small particles has a specific deviation, the junction between small and large particles is less likely to be lost. The standard deviation (σ²) can be, for example, 0.15 or lower.

[0092] The standard deviation (σ1) of the sphericity of the first graphite particle can, for example, be less than 0.05. The standard deviation (σ1) can also be greater than 0.03.

[0093] (Span value)

[0094] The first granularity distribution can be sharper than the second granularity distribution. That is, the first granularity distribution can have a smaller span value than the second granularity distribution. Therefore, improved cycle durability can be expected.

[0095] D110 is D10 in the first granularity distribution. D190 is D90 in the first granularity distribution. For example, the span value of the first granularity distribution [(D190-D110) / D150] can be 0.70 to 0.80.

[0096] D210 is D10 in the second granularity distribution. D290 is D90 in the second granularity distribution. The span value of the second granularity distribution [(D290-D210) / D250] can be, for example, greater than 0.97, greater than 1.05, or between 0.97 and 1.05.

[0097] The negative electrode active material (a mixture of first and second graphite particles) has a third particle size distribution. D310 is D10 in the third particle size distribution. D350 is D50 in the third particle size distribution. D390 is D90 in the third particle size distribution.

[0098] The third granularity distribution can have a specific span value. That is, the span value of the third granularity distribution [(D390-D310) / D350] can be, for example, 0.87 to 0.99. Therefore, improved cycle durability can be expected. The span value of the third granularity distribution can also be, for example, 0.89 to 0.99.

[0099] (Optional ingredients)

[0100] The negative electrode active material can be prepared by including additional components, provided it contains first and second graphite particles. For example, in addition to the first and second graphite particles, silicon (Si), silicon oxide (SiO), tin (Sn), tin oxide (SnO), and Li4Ti5O can also be mixed in. 12 The total mass fraction of the first and second graphite particles in the negative electrode active material can be, for example, 50% or more, 80% or more, 90% or more, 95% or more, or essentially 100%. This total mass fraction is calculated by dividing the total mass of the first and second graphite particles by the total mass of the negative electrode active material.

[0101] (B) Manufacturing of the Negative Electrode

[0102] This manufacturing method includes manufacturing a negative electrode containing a negative electrode active material. The negative electrode can be manufactured by any method. For example, it can be manufactured by coating a slurry. For example, a slurry can be prepared by mixing the negative electrode active material, a binder, and a dispersion medium. The slurry can be prepared using any mixer, disperser, etc. The solid component of the slurry may, for example, contain the negative electrode active material and the binder. For example, the solid component of the slurry may consist substantially of 0.1% to 10% binder by mass fraction and the balance being the negative electrode active material. The slurry may, for example, have a solid component concentration of 40% to 80%. "Solid component concentration" refers to the total mass fraction of components other than the dispersion medium.

[0103] The adhesive may contain optional components. For example, the adhesive may contain at least one selected from sodium carboxymethyl cellulose (CMC-Na) and styrene-butadiene rubber (SBR). The dispersion medium may be appropriately selected depending on the type of adhesive, etc. The dispersion medium may contain, for example, water.

[0104] Figure 2 This is a schematic diagram illustrating an example of the structure of the electrode body in this embodiment.

[0105] For example, a negative electrode substrate 21 can be prepared. The negative electrode substrate 21 may, for example, contain copper (Cu) foil. The negative electrode substrate 21 may, for example, have a thickness of 5 to 30 μm. By coating a slurry onto the surface of the negative electrode substrate 21 and allowing it to dry, a negative electrode active material layer 22 can be formed. In this embodiment, any coating machine can be used. The negative electrode active material layer 22 may be formed only on one side of the negative electrode substrate 21, or it may be formed on both the front and back sides. The negative electrode active material layer 22 can be formed with a portion of the negative electrode substrate 21 exposed. The exposed portion of the negative electrode substrate 21 can, for example, be used for current collector processing. Thus, a negative electrode raw sheet is manufactured.

[0106] Regarding the negative electrode material sheet, it can be processed into a specified shape according to the morphology of the electrode body 50. For example, the negative electrode active material layer 22 can be compressed using a calender or similar device. The compressed negative electrode active material layer 22 can, for example, have a thickness of 10 to 200 μm. The compressed negative electrode active material layer 22 can, for example, have a thickness of 0.8 to 1.6 g / cm³. 3 The density. For example, the negative electrode material sheet can be cut using a cutting machine. For example, the negative electrode material sheet can be cut into strips. Thus, negative electrode 20 can be manufactured.

[0107] (C) Battery Manufacturing

[0108] Figure 3 A schematic diagram illustrating an example of the configuration of a non-aqueous electrolyte secondary battery in the embodiment.

[0109] This manufacturing method includes manufacturing a battery 100 comprising a negative electrode 20, a positive electrode 10, and an electrolyte (not shown).

[0110] (positive electrode)

[0111] This manufacturing method includes preparing the positive electrode 10 (refer to...). Figure 2 The positive electrode 10 can be prepared by any method. For example, similar to the negative electrode 20, the positive electrode 10 can be manufactured by coating a slurry. The positive electrode 10 includes a positive electrode substrate 11 and a positive electrode active material layer 12. The positive electrode substrate 11 may, for example, include aluminum (Al) foil. The positive electrode substrate 11 may, for example, have a thickness of 10 to 30 μm. The positive electrode active material layer 12 is formed on the surface of the positive electrode substrate 11. The positive electrode active material layer 12 may be formed only on one side of the positive electrode substrate 11, or it may be formed on both the front and back sides. The positive electrode active material layer 12 may, for example, have a thickness of 10 to 200 μm. The positive electrode active material layer 12 may, for example, include a positive electrode active material, a conductive material, and a binder. For example, the positive electrode active material layer 12 may consist essentially of 0.1 to 10% binder, 0.1 to 10% conductive material, and the balance positive electrode active material by mass fraction.

[0112] The positive electrode active material may contain optional components. For example, it may contain at least one selected from LiCoO2, LiNiO2, LiMnO2, LiMn2O4, Li(NiCoMn)O2, Li(NiCoAl)O2, and LiFePO4. Here, for example, in the composition formula of "Li(NiCoMn)O2", the sum of the composition ratios within parentheses is 1 (Ni + Co + Mn = 1). As long as the sum of the composition ratios is 1, the composition ratio of each element (Ni, Co, Mn) is arbitrary. The conductive material may contain optional components. For example, it may contain carbon black. The binder may contain optional components. For example, it may contain polyvinylidene fluoride (PVdF).

[0113] (Electrode)

[0114] This manufacturing method includes forming an electrode body 50 (see reference). Figure 2 The electrode body 50 can have any shape. For example, the electrode body 50 can be a stacked type or a wound type. For example, a separator 30 is prepared. One separator 30 or two separators 30 can be used. For example, a stacked body can be formed by sequentially stacking the separator 30, the negative electrode 20, the separator 30, and the positive electrode 10. The electrode body 50 can be formed by winding the stacked body into a vortex shape. The electrode body 50 can be formed, for example, into a flat shape.

[0115] (Separator)

[0116] The separator 30 is a porous sheet. The separator 30 allows the electrolyte to pass through. The separator 30 can, for example, have an air permeability of 100–400 s / 100 mL. In this specification, "air permeability" refers to the "air resistance" specified in JIS P 8117:2009. Air permeability can be determined using the Gurley test.

[0117] The separator 30 is electrically insulating. The separator 30 may, for example, contain a polyolefin resin. The separator 30 may, for example, be substantially composed of a polyolefin resin. The polyolefin resin may, for example, contain at least one selected from polyethylene (PE) and polypropylene (PP). The separator 30 may, for example, have a single-layer structure. The separator 30 may, for example, be substantially composed of a PE layer. The separator 30 may, for example, have a multi-layer structure. The separator 30 may, for example, be formed by sequentially stacking a PP layer, a PE layer, and another PP layer. A heat-resistant layer (ceramic particle layer), for example, may be formed on the surface of the separator 30.

[0118] (Outer packaging)

[0119] Prepare outer packaging 90 (refer to) Figure 3 The outer packaging 90 can have any shape. For example, the outer packaging 90 can be a container made of Al alloy or a pouch made of Al laminate. The outer packaging 90 can be, for example, square or cylindrical.

[0120] The outer packaging 90 may include, for example, a sealing plate 91 and an outer packaging can 92. The sealing plate 91 may have a positive terminal 81 and a negative terminal 82. Electrode bodies 50 are connected to the positive terminal 81 and the negative terminal 82. The electrode bodies 50 are housed in the outer packaging can 92. The sealing plate 91 and the outer packaging can 92 may be joined, for example, by laser welding. The sealing plate 91 may also have an injection port (not shown). Electrolyte can be injected into the outer packaging 90 through the injection port. The electrolyte can impregnate the electrode bodies 50. After the electrolyte is injected, the outer packaging 90 is sealed by closing the injection port. Thus, a battery 100 can be manufactured.

[0121] Battery 100 may have a rated capacity of, for example, 1 to 400 Ah. Battery 100 can be used in any application. For example, battery 100 can be used as a main power source or auxiliary power source in electric vehicles. By connecting multiple batteries 100, a battery module or battery pack can be formed.

[0122] (electrolyte)

[0123] The electrolyte is a liquid electrolyte. Any electrolyte used can form, for example, a gel electrolyte. The electrolyte comprises a solvent and a supporting electrolyte. The solvent is aprotic. The solvent may contain optional components. For example, the solvent may contain at least one selected from ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), 1,2-dimethoxyethane (DME), methyl formate (MF), methyl acetate (MA), methyl propionate (MP), and γ-butyrolactone (GBL).

[0124] The supporting electrolyte is dissolved in a solvent. The supporting electrolyte may, for example, contain at least one selected from LiPF6, LiBF4, and LiN(FSO2)2. The supporting electrolyte may, for example, have a molar concentration of 0.5–2.0 mol / L, or a molar concentration of 0.8–1.2 mol / L.

[0125] In addition to the solvent and supporting electrolyte, the electrolyte may further contain optional additives. For example, the electrolyte may contain 0.01 to 5% additives by mass fraction. The additives may, for example, contain at least one selected from vinylene carbonate (VC), lithium difluorophosphate (LiPO2F2), lithium fluorosulfonate (FSO3Li), and lithium bis(oxalato)borate (LiBOB).

[0126] [Example]

[0127] The following describes embodiments of the present technology (also referred to as "the present embodiments" in this specification). However, the following description does not limit the scope of the present technology.

[0128] Various experimental batteries (pouch batteries) are manufactured using the manufacturing methods described in Nos. 1 to 12 below.

[0129] <No.1>

[0130] (A) Preparation of Negative Electrode Active Materials

[0131] Prepare the following materials.

[0132] First graphite particle: Graphite A (the powder properties are shown in Table 1 below).

[0133] Second graphite particle: graphite C (powder properties are shown in Table 1 below).

[0134] The negative electrode active material was prepared by mixing 95 parts by mass of first graphite particles and 5 parts by mass of second graphite particles. That is, the mixing ratio (M2 / M1) was 0.05. The powder properties (range values) of the negative electrode active material are shown in Table 1 below.

[0135] (B) Manufacturing of the Negative Electrode

[0136] Prepare the following materials.

[0137] Adhesives: CMC-Na, SBR

[0138] Dispersion medium: water

[0139] Negative electrode substrate: Cu foil

[0140] A slurry is prepared by mixing 100 parts by mass of negative electrode active material, 0.7 parts by mass of CMC-Na, 1 part by mass of SBR, and an appropriate amount of dispersion medium. The slurry is then coated onto the surface of a negative electrode substrate to form a negative electrode active material layer. This layer is then dried. The negative electrode active material layer is then compressed using a calender. This produces a negative electrode raw material sheet. The negative electrode raw material sheet is then cut into strips to manufacture the negative electrode.

[0141] (C) Battery Manufacturing

[0142] Prepare the following materials.

[0143] Positive electrode active material: Li(NiCoMn)O2

[0144] Conductive material: Acetylene black

[0145] Adhesive: PVdF

[0146] Dispersion medium: N-methyl-2-pyrrolidone

[0147] Positive electrode substrate: Al foil

[0148] A slurry is prepared by mixing 97.5 parts by weight of positive electrode active material, 1 part by weight of conductive material, 1.5 parts by weight of binder, and a suitable amount of dispersion medium. The slurry is then coated onto the surface of a positive electrode substrate to form a positive electrode active material layer. The positive electrode active material layer is dried. The positive electrode active material layer is then compressed using a calender. This produces a positive electrode raw material sheet. The positive electrode raw material sheet is cut into strips to manufacture the positive electrode.

[0149] Prepare a PP separator. The separator has a single-layer structure. Lead tabs are attached to the positive and negative electrodes respectively. A laminate is formed by stacking the positive electrode, separator, and negative electrode in sequence. The electrode body is formed by winding the laminate into a vortex shape.

[0150] Prepare the outer packaging. The outer packaging is a bag made of Al laminated film. The electrode body is contained within the outer packaging. Prepare the electrolyte. The electrolyte consists of the following components.

[0151] Solvent: "EC / EMC = 3 / 7 (volume ratio)"

[0152] Supported electrolyte: LiPF6 (1.0 mol / L)

[0153] Additive: Vitamin C (2% by volume)

[0154] Electrolyte is injected into the outer packaging. After injection, the outer packaging is sealed using a heat-sealing machine. This process produces the test battery.

[0155] <No.2>

[0156] The test cell was manufactured in the same manner as described in No. 1, except that graphite B was used as the first graphite particle instead of graphite A. The powder properties of graphite B are shown in Table 1 below.

[0157] <No.3>

[0158] Except for changing the mixing ratio (M2 / M1) to 0.10, the test cells were manufactured in the same manner as those described in No.1.

[0159] <No.4>

[0160] Except that graphite G was used instead of graphite A as the first graphite particle, the test cell was manufactured in the same manner as described in No. 1. The powder properties of graphite G are shown in Table 1 below.

[0161] <No.5>

[0162] The test cell was manufactured in the same manner as described in No. 1, except that graphite F was used as the second graphite particle instead of graphite C. The powder properties of graphite F are shown in Table 1 below.

[0163] <No.6>

[0164] The test cell was manufactured in the same manner as described in No. 5, except that graphite B was used instead of graphite A as the first graphite particle.

[0165] <No.7>

[0166] Except for changing the mixing ratio (M2 / M1) to 0.025, the test cells were manufactured in the same manner as those described in No.1.

[0167] <No.8>

[0168] Except for changing the mixing ratio (M2 / M1) to 0.125, the test cells were manufactured in the same manner as those described in No.1.

[0169] <No.9>

[0170] The test cell was manufactured in the same manner as described in No. 1, except that graphite D was used as the second graphite particle instead of graphite C. The powder properties of graphite D are shown in Table 1 below.

[0171] <No.10>

[0172] The test cell was manufactured in the same manner as described in No. 1, except that graphite E was used as the second graphite particle instead of graphite C. The powder properties of graphite E are shown in Table 1 below.

[0173] <No.11>

[0174] The test cell was manufactured in the same manner as described in No. 2, except that graphite D was used instead of graphite C as the second graphite particle.

[0175] <No.12>

[0176] Except for changing the mixing ratio (M2 / M1) to 0, the test battery was manufactured in the same manner as that described in No.1. That is, the negative electrode active material described in No.12 consists only of first graphite particles (graphite A).

[0177] <Evaluation>

[0178] The system was subjected to 200 charge-discharge cycles at a temperature of 25°C. One cycle represents one round of charging and discharging.

[0179] The test battery was charged to 4.25V using a constant current charging rate of 1 / 3 It. Then, it was charged at a constant voltage of 4.25V until the current decreased to 1 / 20 It. After charging, the test battery was discharged to 3.0V using a constant current discharge rate of 1 / 3 It. Note that "1 It" is defined as the current required to fully discharge the test battery's rated capacity in one hour.

[0180] The capacity retention rate at the 200th cycle is calculated by dividing the discharge capacity of the 1st cycle by the discharge capacity of the 200th cycle. The capacity retention rate is expressed as a percentage. A higher capacity retention rate generally indicates better cycle durability.

[0181]

[0182] <Results>

[0183] Regarding the test batteries manufactured using the manufacturing methods described in Nos. 1 to 8, their cycle durability is better compared to that of the test batteries manufactured using the manufacturing methods described in Nos. 9 to 12. In the manufacturing methods described in Nos. 1 to 8, the relationships "D250 / D150≤0.50" and "R2≤R1" are satisfied.

[0184] By satisfying the relationship “0.05≤M2 / M1≤0.10”, we can see the tendency for improved cycle durability (see No.1, 3, 7, 8).

[0185] By satisfying the relationships “0.70≤(D190-D110) / D150≤0.80” and “0.97≤(D290-D210) / D250”, we can see the tendency for improved cycle durability (see No.1, 3, 4).

[0186] By satisfying the relationship “0.08≤σ2”, we can see the tendency for improved cycle durability (see No.1, 2, 5, 6).

[0187] By satisfying the relationship “0.87≤(D390-D310) / D350≤0.99”, we can see the tendency for improved cycle durability (see No.1~3, 7, 8).

[0188] This embodiment and these embodiments are illustrative in all respects and are not restrictive. The scope of this technology includes all modifications within the meaning and scope equivalent to the claims. For example, it is foreseeable that any configuration extracted from this embodiment and these embodiments and combined in any way.

Claims

1. A method for manufacturing a nonaqueous electrolyte secondary battery, comprising: (A) preparing a negative electrode active material by mixing first graphite particles and second graphite particles; (B) manufacturing a negative electrode comprising the negative electrode active material; and (C) manufacturing a nonaqueous electrolyte secondary battery comprising the negative electrode, a positive electrode, and an electrolyte, wherein the first graphite particles have a first particle size distribution on a number basis, the second graphite particles have a second particle size distribution on a number basis, a relationship of formula (I) is satisfied: D250 / D150 < 0.50... (I), in the formula (I), D150 represents D50 in the first particle size distribution, D250 represents D50 in the second particle size distribution, and a relationship of formula (III) and formula (IV) is satisfied: 0.94 < Rl... (III) 0.90 < R2 < Rl... (IV) in the formula (III) and formula (IV), Rl represents an arithmetic average of circularity of the first graphite particles, R2 represents an arithmetic average of circularity of the second graphite particles, and a standard deviation of circularity of the second graphite particles is 0.08 or more and 0.15 or less. a relationship of formula (V) is satisfied: 0.05 < M2 / Ml < 0.10... (V), in the formula (V), Ml represents a mass of the first graphite particles contained in the negative electrode active material, and M2 represents a mass of the second graphite particles contained in the negative electrode active material. a relationship of formula (VI) is satisfied: 0.70 < (D190-D110) / D150 < 0.80... (VI), in the formula (VI), D110 represents D10 in the first particle size distribution, D190 represents D90 in the first particle size distribution, and a relationship of formula (VII) is satisfied: 0.97 < (D290-D210) / D250... (VII), in the formula (VII), D210 represents D10 in the second particle size distribution, and D290 represents D90 in the second particle size distribution.

4. The method for manufacturing a nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein a mixture of the first graphite particles and the second graphite particles has a third particle size distribution on a number basis, a relationship of formula (VIII) is satisfied: 0.87 < (D390-D310) / D350 < 0.99... (VIII), in the formula (VIII), D310 represents D10 in the third particle size distribution, D350 represents D50 in the third particle size distribution, and D390 represents D90 in the third particle size distribution.

5. A negative electrode active material for a nonaqueous electrolyte secondary battery, comprising first graphite particles and second graphite particles, the first graphite particles having a first particle size distribution on a number basis, the second graphite particles having a second particle size distribution on a number basis, and a relationship of formula (I) being satisfied: D250 / D150 < 0.50... (I), in the formula (I), D150 represents D50 in the first particle size distribution, D250 represents D50 in the second particle size distribution, and ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 2. The method for manufacturing a nonaqueous electrolyte secondary battery according to claim 1, wherein ​ ​ ​ ​ ​ 3. The method for manufacturing a nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ satisfy the following relationships of formula (III) and formula (IV): 0.94 ≤ R1... (III) 0.90 ≤ R2 < R1... (IV), in the formula (III) and formula (IV), R1 represents an arithmetic average of the circularity of the first graphite particles, R2 represents an arithmetic average of the circularity of the second graphite particles, a standard deviation of the circularity of the second graphite particles is 0.08 or more and 0.15 or less.

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