A negative electrode for a secondary battery, a method for manufacturing the negative electrode, and a secondary battery using the negative electrode

Abstract

The present invention provides a negative electrode containing Si-containing particles and graphite particles, which can suppress capacity degradation when a secondary battery is repeatedly charged and discharged. [Solution] The negative electrode of the secondary battery of this disclosure comprises a negative electrode current collector and a negative electrode active material layer supported by the negative electrode current collector. The negative electrode active material layer contains graphite, first Si-containing particles, and second Si-containing particles. The Si content in the first Si-containing particles is smaller than the Si content in the second Si-containing particles. When the density of a molded body obtained by pressing 1 g of particles uniaxially at 25°C and 60 MPa to form a tablet with a diameter of 20 mm is defined as the compaction density, the compaction density of the first Si-containing particles is 0.9 g / cm³. 3 The above conditions are met, and the compaction density of the second Si-containing particles is 0.9 g / cm³. 3 It is less than.

Description

Technical Field

[0001] The present disclosure relates to a negative electrode of a secondary battery and a method for manufacturing the same. The present disclosure also relates to a secondary battery using the negative electrode.

Background Art

[0002] In recent years, secondary batteries have been suitably used as portable power sources such as personal computers and mobile terminals, and as power sources for driving vehicles such as battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs).

[0003] In the application of power sources for driving vehicles, particularly in the application of power sources for driving BEVs, from the viewpoint of extending the cruising range of vehicles, further increase in the capacity of secondary batteries is desired. As a high-capacity negative electrode active material, Si-containing particles are known, and it is known that the capacity of secondary batteries can be increased by using Si-containing particles (for example, see Patent Document 1). Patent Document 1 discloses a technique of using, as a negative electrode active material, Si-containing particles and graphite particles such as natural graphite in combination.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, while Si-containing particles have a high capacity, they have a large volume change due to expansion / contraction during charge / discharge of the secondary battery. Therefore, when Si-containing particles and graphite particles are used in combination, the filling property of these particles decreases when the secondary battery is repeatedly charged and discharged, and conduction path breakage or the like may occur. Therefore, when Si-containing particles and graphite particles are used in combination, there is a problem that the cycle characteristics of the secondary battery deteriorate. Specifically, there is a problem that the capacity deterioration is large when the secondary battery is repeatedly charged and discharged.

[0006] In view of the above circumstances, an object of the present disclosure is to provide a negative electrode containing Si-containing particles and graphite particles, which can suppress capacity deterioration when the secondary battery is repeatedly charged and discharged.

Means for Solving the Problems

[0007] The negative electrode of the secondary battery of the present disclosure includes a negative electrode current collector and a negative electrode active material layer supported on the negative electrode current collector. The negative electrode active material layer contains graphite, first Si-containing particles, and second Si-containing particles. The Si content ratio in the first Si-containing particles is smaller than the Si content ratio in the second Si-containing particles. When the density of a molded body obtained by pressing 1 g of particles uniaxially at 25 °C and 60 MPa into a tablet shape with a diameter of 20 mm is defined as the consolidation density, the consolidation density of the first Si-containing particles is 0.9 g / cm 3 or more, and the consolidation density of the second Si-containing particles is 0.9 g / cm 3 less than.

[0008] According to such a configuration, it is possible to provide a negative electrode containing Si-containing particles and graphite particles, which can suppress capacity deterioration when the secondary battery is repeatedly charged and discharged.

[0009] From another aspect, the method for manufacturing a negative electrode of a secondary battery of the present disclosure includes a step of preparing a negative electrode paste containing graphite particles, first Si-containing particles, second Si-containing particles, and a dispersion medium, a step of coating the negative electrode paste on a negative electrode current collector, a step of drying the coated negative electrode paste to form a negative electrode active material layer, and a step of pressing the negative electrode active material layer. The Si content ratio in the first Si-containing particles is smaller than the Si content ratio in the second Si-containing particles. When the density of a molded body obtained by pressing 1 g of particles uniaxially at 25 °C and 60 MPa into a tablet shape with a diameter of 20 mm is defined as the consolidation density of the particles, the consolidation density of the first Si-containing particles is 0.9 g / cm 3 or more, and the consolidation density of the second Si-containing particles is 0.9 g / cm 3 less than.

[0010] The negative electrode obtained by this configuration can provide the secondary battery with excellent resistance to capacity degradation when repeatedly charged and discharged.

[0011] From another perspective, the secondary battery of this disclosure comprises a positive electrode, a negative electrode, and an electrolyte. The negative electrode is the negative electrode described above.

[0012] This configuration makes it possible to provide a secondary battery with excellent resistance to capacity degradation when repeatedly charged and discharged. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic cross-sectional view showing the configuration of the negative electrode of a secondary battery according to one embodiment of the present disclosure. [Figure 2] Figure 1 is a schematic cross-sectional view showing the composition of particles contained in the negative electrode active material layer of the negative electrode. [Figure 3] This is a schematic cross-sectional view showing the configuration of a lithium-ion secondary battery constructed using the negative electrode of a secondary battery according to one embodiment of the present disclosure. [Figure 4] Figure 3 is a schematic exploded view showing the configuration of the wound electrode body of a lithium-ion secondary battery. [Modes for carrying out the invention]

[0014] Embodiments relating to this disclosure will be described below with reference to the drawings. Matters not mentioned herein but necessary for the implementation of this disclosure can be understood as design matters for those skilled in the art based on prior art. This disclosure can be implemented based on the contents disclosed herein and common technical knowledge in the art. In the following drawings, members and parts that perform the same function are denoted by the same reference numerals. Also, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect actual dimensional relationships. In this specification, the numerical range expressed as "A~B" includes A and B.

[0015] In this specification, "secondary battery" refers to an energy storage device that can be repeatedly charged and discharged. Furthermore, in this specification, "lithium-ion secondary battery" refers to a secondary battery that uses lithium ions as a charge carrier and achieves charging and discharging through the transfer of charge associated with lithium ions between the positive and negative electrodes.

[0016] The negative electrode disclosed herein is used in secondary batteries, and preferably in lithium-ion secondary batteries. One embodiment of the negative electrode disclosed herein will be specifically described with reference to Figure 1. Figure 1 is a schematic cross-sectional view showing an example of the negative electrode 60 according to this embodiment, and is a cross-sectional view along the thickness direction and the width direction. The negative electrode 60 according to this embodiment shown in Figure 1 is the negative electrode of a lithium-ion secondary battery.

[0017] As shown in the figure, the negative electrode 60 comprises a negative electrode current collector 62 and a negative electrode active material layer 64 supported by the negative electrode current collector 62. In other words, the negative electrode 60 comprises a negative electrode current collector 62 and a negative electrode active material layer 64 provided on the negative electrode current collector 62. The negative electrode active material layer 64 may be provided on only one side of the negative electrode current collector 62, or it may be provided on both sides of the negative electrode current collector 62 as in the illustrated example. It is preferable that the negative electrode active material layer 64 is provided on both sides of the negative electrode current collector 62.

[0018] As shown in the illustrated example, a portion 62a without a negative electrode active material layer 64 may be provided at one end of the negative electrode 60 in the width direction. In the portion 62a without a negative electrode active material layer, the negative electrode current collector 62 is exposed, and the portion 62a can function as a current collector. However, the configuration for collecting current from the negative electrode 60 is not limited to this.

[0019] The shape of the negative electrode current collector 62 is foil-like (or sheet-like) in the illustrated example, but is not limited thereto. The negative electrode current collector 62 may take various forms such as rod-like, plate-like, or mesh-like. As with conventional lithium-ion secondary batteries, a metal with good conductivity (e.g., copper, nickel, titanium, stainless steel, etc.) can be used as the material for the negative electrode current collector 62, and copper is particularly preferred. Copper foil is especially preferred as the negative electrode current collector 62.

[0020] The dimensions of the negative electrode current collector 62 are not particularly limited and can be determined as appropriate according to the battery design. When copper foil is used as the negative electrode current collector 62, its thickness is not particularly limited, but is, for example, 5 μm or more and 35 μm or less, and preferably 6 μm or more and 20 μm or less.

[0021] The negative electrode active material layer 64 contains a negative electrode active material. The negative electrode active material used includes at least graphite particles, first Si-containing particles, and second Si-containing particles. This will be explained in detail using Figure 2. Figure 2 is a schematic cross-sectional view showing the particles contained in the negative electrode active material layer 64 shown in Figure 1. As shown in Figure 2, the negative electrode active material layer 64 contains graphite particles 12, first Si-containing particles 14, and second Si-containing particles 16. Note that Figure 2 is a schematic diagram, and therefore the number and distribution of particles are not limited to those shown in Figure 2.

[0022] The graphite constituting the graphite particles 12 may be natural graphite or artificial graphite, or it may be amorphous carbon-coated graphite in which the graphite is coated with an amorphous carbon material.

[0023] The shape of the graphite particles 12 is not particularly limited and may be flaky, spherical, or the like. Preferably, the graphite particles 12 are spheroidized graphite particles. When the graphite particles 12 are spherical, the circularity of the graphite particles 12 is preferably 0.85 to 1, more preferably 0.88 to 1, and even more preferably 0.90 to 1.

[0024] In this specification, "circularity" refers to the ratio of the circumference of a perfect circle having the same area as the projected area of ​​the particle to the circumference of the particle projection image (i.e., circularity = circumference of a perfect circle having the same area as the projected area of ​​the particle / circumference of the particle projection image). Therefore, the closer the circularity is to 1, the closer the particle projection image is to a perfect circle, and the closer the particle is to a perfect sphere. Circularity can be determined, for example, by using a commercially available static automatic image analyzer to determine the circularity of 100 or more particles and calculating the average value.

[0025] The average particle size (D50) of the graphite particles 12 is not particularly limited. The average particle size (D50) of the graphite particles 12 is, for example, 1 μm to 30 μm, preferably 5 μm to 25 μm, more preferably 10 μm to 23 μm, and even more preferably 12 μm to 20 μm.

[0026] In this specification, "average particle size (D50)" refers to the median diameter (D50), which is the particle size corresponding to the cumulative frequency of 50% by volume from the smaller particle size side in a volume-based particle size distribution based on laser diffraction and scattering methods. The average particle size (D50) can be determined using commercially available laser diffraction and scattering type particle size distribution analyzers.

[0027] When 1 g of graphite particles 12 are compressed uniaxially to form a tablet shape with a diameter of 20 mm, the density of the molded body is 1.7 g / cm³. 3 The molding pressure at which this occurs is preferably 20 MPa or less, and more preferably 10 MPa to 18 MPa. This molding pressure can be easily measured using an automatic powder resistance measuring system (e.g., "MCP-PD600" manufactured by Nitto Seiko Analytech Co., Ltd.) and a 20 mm diameter probe (corresponding to a mold).

[0028] The proportion of graphite particles 12 to the total of graphite particles 12, first Si-containing particles 14, and second Si-containing particles 16 is preferably 40% to 90% by mass, more preferably 45% to 85% by mass, and even more preferably 50% to 80% by mass.

[0029] For example, the first Si-containing particles 14 and the second Si-containing particles 16 can be particles of a Si-C composite material. Si-C composite materials typically contain carbon domains and Si-containing domains. However, the first Si-containing particles 14 and the second Si-containing particles 16 do not have to be Si-C composite materials; they may be Si particles, Si oxide particles, etc.

[0030] Carbon domains are, for example, carbonized forms of carbon precursors (e.g., petroleum pitch, coal pitch, phenolic resin, etc.); graphite, etc. Preferably, carbon domains constitute a carbon matrix. Therefore, a Si-C composite material is preferably a material in which multiple Si-containing domains are dispersed within a carbon matrix. In this case, the carbon matrix is ​​advantageous because it can mitigate volume changes due to the expansion / contraction of the Si-containing domains.

[0031] The Si-containing domain contains Si, for example, Si, Si oxide (SiO x It is composed of Si, Si nitride (SiNx), Si carbide (SiCx), etc. The Si-containing domain is preferably Si and Si oxide (SiO x It consists of at least one of the following. The Si-containing domains may be fine particles. The oxygen content in the Si-containing domains is preferably 10% by mass or less.

[0032] The average particle diameter of the Si-containing domains is, for example, 50 nm or less, and may be between 5 nm and 50 nm. The "average particle diameter of the Si-containing domains" can be determined as follows: First, the negative electrode active material layer 64 is processed with FIB (Focused Ion Beam) to prepare a sample for scanning transmission electron microscopy (STEM) observation. Then, the sample is subjected to elemental analysis by EDX elemental mapping, and BF images (bright-field images) and HAADF images (high-angle scattering annular dark-field images) are obtained. The diameter of the Si-containing domains can be determined from the contrast and shape obtained from the BF and HAADF images. The diameters of 10 or more arbitrarily selected Si-containing domains are determined, and their average value is taken as the "average particle diameter of the Si-containing domains" here.

[0033] Si-C composite materials include, for example, those in which fine particles containing Si are dispersed inside a carbon material; or those in which fine particles containing Si are embedded in the pores of granulated porous graphite; and so on. Si-C composite materials may also include those in which fine particles containing Si are attached to the surface of carbon particles; or those in which carbon fine particles are attached to the surface of Si-containing particles. From the viewpoint of suppressing volume changes of Si, materials in which Si nanoparticles are dispersed inside a carbon material and materials in which Si nanoparticles are dispersed in the pores of a porous carbon material are preferred, and materials in which Si nanoparticles are dispersed in the pores of a porous carbon material are more preferred.

[0034] The Si content (S1) in the first Si-containing particle 14 is smaller than the Si content (S2) in the second Si-containing particle 16. The Si content (S1) in the first Si-containing particle 14 and the Si content (S2) in the second Si-containing particle 16 are not particularly limited as long as this relationship is satisfied. However, if these Si content ratios are too low, the effect of improving cycle characteristics will be small, and the effect of increasing the capacity of the secondary battery may be too small. On the other hand, if these Si content ratios are too high, the volume change due to expansion / contraction of the first Si-containing particle 14 and the second Si-containing particle 16 may become too large when the secondary battery is repeatedly charged and discharged.

[0035] Therefore, the Si content (S1) in the first Si-containing particle 14 is preferably 20% to 55% by mass, and more preferably 25% to 45% by mass. The Si content (S2) in the second Si-containing particle 16 is preferably 45% to 80% by mass, and more preferably 55% to 75% by mass.

[0036] Furthermore, the ratio (S1 / S2) of the Si content (S1) in the first Si-containing particle 14 to the Si content (S2) in the second Si-containing particle 16 is preferably 0.10 to 0.90, more preferably 0.20 to 0.80, and even more preferably 0.40 to 0.75.

[0037] Here, the density of the molded body obtained by pressing 1 g of particles uniaxially at 25°C and 60 MPa to form a tablet shape with a diameter of 20 mm is defined as the consolidation density. This consolidation density serves as an index of the packing property of the particles. The higher the consolidation density of the particles, the higher the packing property of the particles. The consolidation density of the first Si-containing particles 14 is 0.90 g / cm 3 or more. On the other hand, the consolidation density of the second Si-containing particles 16 is less than 0.90 g / cm 3 .

[0038] Thus, in the present disclosure, as the negative electrode active material, in addition to the graphite particles 12, the first Si-containing particles 14 with a low Si content ratio and a high consolidation density and the second Si-containing particles 16 with a high Si content ratio and a low consolidation density are used in combination. In particular, the consolidation density of the conventionally used Si-containing particles is usually less than 0.90 / cm 3 . Therefore, the first Si-containing particles 14 have a higher consolidation density than the conventionally used Si-containing particles. According to such a combination of particles, it is possible to suppress the capacity degradation when the secondary battery is repeatedly charged and discharged. The reason is considered as follows.

[0039] One of the causes of capacity degradation when the secondary battery is repeatedly charged and discharged is the disconnection of the conductive path. Si-containing particles with a small Si content ratio have a small expansion and contraction during charge and discharge of the secondary discharge. Therefore, by increasing the consolidation density of the first Si-containing particles 14 with a low Si content ratio as in the present disclosure, that is, by enhancing the packing property of the first Si-containing particles 14 with a low Si content ratio, the packing state around the first Si-containing particles 14 can be maintained even after the secondary battery is repeatedly charged and discharged. Thereby, the disconnection of the conductive path when the secondary battery is repeatedly charged and discharged can be suppressed.

[0040] On the other hand, Si-containing particles with a high Si content exhibit significant expansion and contraction during charging and discharging of the secondary battery. Therefore, as disclosed herein, by setting a low compaction density for the high Si-content second Si-containing particles 16, that is, by setting a low packing density for the high Si-content second Si-containing particles 16, deformation around the second Si-containing particles 16 due to expansion / contraction can be suppressed even after repeated charging and discharging of the secondary battery. This makes it possible to suppress the disconnection of the conductive path when the secondary battery is repeatedly charged and discharged.

[0041] Therefore, by using a combination of first Si-containing particles 14 with a low Si content and high pressure density, and second Si-containing particles 16 with a high Si content and low pressure density, it is possible to suppress capacity degradation caused by the breakdown of conductive paths when a secondary battery is repeatedly charged and discharged.

[0042] The compaction density of the first Si-containing particle 14 is preferably 0.95 g / cm³. 3 The above, and more preferably 1.00 g / cm³ 3 The above is preferable, and more preferably 1.1 g / cm³. 3 The above is the most preferred, and is particularly preferably 1.2 g / cm³. 3 That concludes the explanation. On the other hand, the compaction density of the first Si-containing particle 14 is 2.3 g / cm³. 3 Below 2.0g / cm 3 Below 1.8g / cm 3 The following, or 1.5 g / cm³ 3 The following is acceptable:

[0043] The compaction density of the second Si-containing particle 16 is preferably 0.88 g / cm³. 3 The following, and more preferably 0.86 g / cm³ 3 The following, and more preferably 0.85 g / cm³ 3 The following applies. On the other hand, the compaction density of the second Si-containing particle 16 is preferably 0.50 g / cm³. 3 The above is more accurate, and more preferably 0.65 g / cm³ 3 The above is preferable, and more preferably 0.75 g / cm³ 3 The above is the most preferred, and is particularly preferably 0.83 g / cm³.3 That's all.

[0044] Furthermore, the compaction density can be easily measured, for example, by using an automated powder resistance measurement system (e.g., "MCP-PD600" manufactured by Nitto Seiko Analytech Co., Ltd.) and a 20 mm diameter probe (equivalent to a mold).

[0045] Furthermore, the compaction density is affected by the circularity of the Si-containing particles. Increasing the circularity of the Si-containing particles tends to increase the compaction density. Therefore, if the circularity of the Si-containing particles is set to 0.85 to 1 (especially 0.90 to 1), the compaction density will be 0.90 g / cm³. 3 This tends to be the case. On the other hand, if the circularity of the Si-containing particles is less than 0.85, the compaction density becomes 0.90 g / cm³. 3 It tends to be less than that.

[0046] Furthermore, the particle size of the Si-containing particles also affects the compaction density. Therefore, 0.90 g / cm³ 3 Because it is easy to adjust the compaction density to the above, the average particle size (D50) of the first Si-containing particles 14 is preferably 2 μm to 10 μm, and more preferably 5 μm to 10 μm. Also, 0.90 g / cm³ 3 Because it is easy to adjust the compaction density to less than 1, the average particle size (D50) of the second Si-containing particles 16 is preferably 2 μm to 10 μm, more preferably 5 μm to 10 μm, and even more preferably 6 μm to 9 μm.

[0047] The true density of the Si-containing particles also affects the compaction density. Therefore, the compaction density can be finely adjusted by adjusting the composition (proportion of constituent elements) of the first Si-containing particles 14 and the second Si-containing particles 16.

[0048] The ratio of the average particle diameter (D50) of graphite particles 12 to the average particle diameter (D50) of first Si-containing particles 14 (D50 of graphite particles 12 / D50 of first Si-containing particles 14) is not particularly limited. Particularly from the viewpoint of high packing performance, the ratio (D50 of graphite particles 12 / D50 of first Si-containing particles 14) is preferably 1.0 to 8.0, more preferably 1.0 to 5.0, even more preferably 1.2 to 3.0, and particularly preferably 1.4 to 2.5.

[0049] The ratio of the average particle diameter (D50) of graphite particles 12 to the average particle diameter (D50) of secondary Si-containing particles 16 (D50 of graphite particles 12 / D50 of secondary Si-containing particles 16) is not particularly limited. Particularly from the viewpoint of high packing performance, the ratio (D50 of graphite particles 12 / D50 of secondary Si-containing particles 16) is preferably 1.0 to 8.0, more preferably 1.0 to 5.0, even more preferably 1.2 to 3.0, and particularly preferably 1.4 to 2.5.

[0050] The mass ratio of the first Si-containing particles 14 to the second Si-containing particles 16 is not particularly limited as long as the effects of this disclosure are obtained, and is, for example, 10:90 to 90:10. The mass ratio (first:second) is preferably 20:80 to 80:20, more preferably 30:70 to 70:30, even more preferably 35:65 to 70:30, and particularly preferably 45:55 to 60:40.

[0051] The total content ratio of the first Si-containing particles 14 and the second Si-containing particles 16 to the total of the graphite particles 12, first Si-containing particles 14, and second Si-containing particles 16 is preferably 10% to 60% by mass, more preferably 15% to 55% by mass, and even more preferably 20% to 50% by mass.

[0052] The first Si-containing particles 14 and the second Si-containing particles 16 can be manufactured according to known methods. Various methods for manufacturing particles of Si-C composite materials are known (see, for example, Japanese Patent Publication No. 2015-38862, International Publication No. 2014 / 046144, and the prior art documents cited in said International Publication).

[0053] The negative electrode active material layer 64 may contain components other than the negative electrode active material, such as binders and conductive materials. Examples of binders include styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC), polyacrylic acid (PAA), and polyvinylidene fluoride (PVDF). CMC also functions as a thickening agent. Examples of conductive materials include carbon black such as acetylene black, carbon fibers, and carbon nanotubes (CNTs). CNTs are particularly preferred. When CNTs are used as the conductive material, the negative electrode active material layer 64 may contain a CNT dispersant.

[0054] The content of the negative electrode active material in the negative electrode active material layer 64 (i.e., relative to the total mass of the negative electrode active material layer 64) is preferably 90% by mass or more, and more preferably 95% by mass or more. The content of the binder in the negative electrode active material layer is preferably 0.1% by mass or more and 8% by mass or less, and more preferably 0.5% by mass or more and 5% by mass or less. The content of the conductive material in the negative electrode active material layer 64 is preferably 0.01% by mass or more and 3% by mass or less, and more preferably 0.05% by mass or more and 1% by mass or less.

[0055] The thickness of the negative electrode active material layer 64 is not particularly limited, but is, for example, 10 μm or more and 400 μm or less, and preferably 20 μm or more and 300 μm or less.

[0056] The density of the negative electrode active material layer 64 is not particularly limited, but for example, 0.7 g / cm³ 3 The above is preferable, preferably 1.0 g / cm³. 3 The above is more preferable, or 1.2 g / cm³. 3 That concludes the explanation. On the other hand, the density of the negative electrode active material layer 64 is, for example, 2.3 g / cm³. 3 The following is the case: 2.0 g / cm³ 3 The following is acceptable:

[0057] The negative electrode 60 may include components other than the negative electrode current collector 62 and the negative electrode active material layer 64. For example, an insulating layer (not shown) adjacent to the negative electrode active material layer 64 may be provided on the portion 62a where the negative electrode active material layer is not formed. This insulating layer may contain, for example, an insulating inorganic filler.

[0058] The negative electrode 60 can be suitably manufactured by a manufacturing method comprising the steps of: preparing a negative electrode paste containing graphite particles 12, first Si-containing particles 14, second Si-containing particles 16, and a dispersion medium (hereinafter also referred to as the "paste preparation step"); coating the prepared negative electrode paste onto the negative electrode current collector 62 (hereinafter also referred to as the "coating step"); drying the coated negative electrode paste to form a negative electrode active material layer 64 (hereinafter also referred to as the "drying step"); and pressing the negative electrode active material layer 64 (hereinafter also referred to as the "pressing step"). In this manufacturing method, the Si content ratio (S1) in the first Si-containing particles 14 is smaller than the Si content ratio (S2) in the second Si-containing particles 16. The compaction density of the first Si-containing particles 14 is 0.9 g / cm³. 3 The above-mentioned compaction density of the second Si-containing particle 16 is 0.9 g / cm³. 3 It is less than.

[0059] In this specification, "paste" refers to a mixture in which some or all of the solid components are dispersed in a dispersion medium, and includes so-called "slurry," "ink," etc.

[0060] The paste preparation process can be carried out by mixing graphite particles 12, first Si-containing particles 14, second Si-containing particles 16, and optional components (e.g., binder, conductive material, etc.) with a dispersion medium (e.g., water) using a known mixing device, stirring device, etc., according to a known method.

[0061] The coating process can be carried out according to known methods. Specifically, for example, the coating process can be carried out by coating the obtained negative electrode paste onto the negative electrode current collector 62 using a coating device such as a gravure coater, comma coater, slit coater, or die coater.

[0062] The drying process can be carried out according to a known method. Specifically, for example, the negative electrode active material layer 64 is formed by removing the dispersion medium from the negative electrode current collector 62 coated with the negative electrode paste using a drying apparatus such as a drying oven. This allows the drying process to be carried out. The drying temperature and drying time can be appropriately determined according to the solid content concentration of the negative electrode paste and are not particularly limited. The drying temperature is, for example, 60°C to 200°C, preferably 70°C to 150°C. The drying time is, for example, 10 seconds to 30 minutes, preferably 30 seconds to 10 minutes.

[0063] The pressing process can be carried out according to a known method. Specifically, the pressing process can be performed by applying pressure to the formed negative electrode active material layer 64 using a roller press or the like. The pressing process compresses the negative electrode active material layer 64 to a predetermined density, thereby densely packing the graphite particles 12, first Si-containing particles 14, and second Si-containing particles 16. In this way, the negative electrode 60 is obtained.

[0064] The negative electrode 60 according to this embodiment can provide the secondary battery with excellent resistance to capacity degradation when repeatedly charged and discharged. Furthermore, since the negative electrode 60 according to this embodiment uses a negative electrode active material containing Si, the capacity of the secondary battery can be increased. Therefore, the secondary battery using the negative electrode 60 according to this embodiment has high capacity and excellent cycle characteristics.

[0065] Therefore, from another perspective, the secondary battery disclosed herein comprises a positive electrode, a negative electrode, and an electrolyte. The negative electrode is the negative electrode 60 according to the above-described embodiment. Hereinafter, an embodiment of the secondary battery disclosed herein will be described with reference to Figures 3 and 4, using a lithium-ion secondary battery as an example. The following configuration example is a flat rectangular lithium-ion secondary battery having a flat wound electrode body and a flat battery case.

[0066] The lithium-ion secondary battery 100 shown in Figure 3 is a sealed lithium-ion secondary battery 100 constructed by housing a flat-shaped wound electrode body 20 and a non-aqueous electrolyte (not shown) in a flat rectangular battery case (i.e., outer container) 30. The battery case 30 is provided with a positive electrode terminal 42 and a negative electrode terminal 44 for external connection, and a thin-walled safety valve 36 that is set to release the internal pressure when the internal pressure of the battery case 30 rises above a predetermined level. The battery case 30 is also provided with an inlet (not shown) for injecting the non-aqueous electrolyte. The positive electrode terminal 42 is electrically connected to a positive electrode current collector plate 42a. The negative electrode terminal 44 is electrically connected to a negative electrode current collector plate 44a. As the material of the battery case 30, for example, a lightweight metal material with good thermal conductivity such as aluminum is used.

[0067] As shown in Figures 3 and 4, the wound electrode body 20 has a configuration in which a positive electrode sheet 50 and a negative electrode sheet 60 are superimposed on each other via two elongated separator sheets 70 and wound in the longitudinal direction. The positive electrode sheet 50 has a configuration in which a positive electrode active material layer 54 is formed along the longitudinal direction on one or both sides (here, both sides) of an elongated positive electrode current collector 52. The negative electrode sheet 60 has a configuration in which a negative electrode active material layer 64 is formed along the longitudinal direction on one or both sides (here, both sides) of an elongated negative electrode current collector 62. The portion 52a where the positive electrode active material layer is not formed (i.e., the portion where the positive electrode current collector 52 is exposed without the positive electrode active material layer 54 being formed) and the portion 62a where the negative electrode active material layer is not formed (i.e., the portion where the negative electrode current collector 62 is exposed without the negative electrode active material layer 64 being formed) are formed to protrude outward from both ends of the winding axis direction of the wound electrode body 20 (i.e., the sheet width direction perpendicular to the longitudinal direction). The positive electrode current collector plate 42a and the negative electrode current collector plate 44a are joined to the positive electrode active material layer not formed portion 52a and the negative electrode active material layer not formed portion 62a, respectively.

[0068] As the positive electrode current collector 52 constituting the positive electrode sheet 50, a known positive electrode current collector used in lithium-ion secondary batteries may be used, and examples include a sheet or foil made of a metal with good conductivity (e.g., aluminum, nickel, titanium, stainless steel, etc.). Aluminum foil is preferred as the positive electrode current collector 52.

[0069] The dimensions of the positive electrode current collector 52 are not particularly limited and can be determined as appropriate according to the battery design. When aluminum foil is used as the positive electrode current collector 52, its thickness is not particularly limited, but is, for example, 5 μm or more and 35 μm or less, and preferably 7 μm or more and 20 μm or less.

[0070] The positive electrode active material layer 54 contains a positive electrode active material. As the positive electrode active material, a known composition of positive electrode active material used in lithium-ion secondary batteries may be used. Specifically, for example, lithium composite oxides, lithium transition metal phosphate compounds, etc., can be used as the positive electrode active material. The crystal structure of the positive electrode active material is not particularly limited and may be a layered structure, spinel structure, olivine structure, etc.

[0071] Preferably, lithium transition metal composite oxides are lithium transition metal composite oxides containing at least one of Ni, Co, and Mn as a transition metal element. Specific examples include lithium nickel-based composite oxides, lithium cobalt-based composite oxides, lithium manganese-based composite oxides, lithium nickel-manganese-based composite oxides, lithium nickel-cobalt-manganese-based composite oxides, lithium nickel-cobalt-aluminum-based composite oxides, and lithium iron-nickel-manganese-based composite oxides.

[0072] In this specification, "lithium nickel cobalt manganese composite oxide" is a term that encompasses not only oxides whose constituent elements are Li, Ni, Co, Mn, and O, but also oxides that contain one or more additive elements other than these. Examples of such additive elements include transition metal elements and main group metal elements such as Mg, Ca, Al, Ti, V, Cr, Y, Zr, Nb, Mo, Hf, Ta, W, Na, Fe, Zn, and Sn. The additive elements may also be metalloid elements such as B, C, Si, and P, or nonmetallic elements such as S, F, Cl, Br, and I. This also applies to the lithium nickel composite oxide, lithium cobalt composite oxide, lithium manganese composite oxide, lithium nickel manganese composite oxide, lithium nickel cobalt aluminum composite oxide, lithium iron nickel manganese composite oxide, etc.

[0073] Examples of lithium transition metal phosphate compounds include lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), and lithium manganese iron phosphate.

[0074] These positive electrode active materials may be used individually or in combination of two or more. Lithium nickel cobalt manganese composite oxides are particularly preferred as positive electrode active materials due to their excellent properties, such as initial resistance characteristics.

[0075] The average particle size (D50) of the positive electrode active material is not particularly limited, but is, for example, 0.05 μm or more and 25 μm or less, preferably 1 μm or more and 20 μm or less, and more preferably 3 μm or more and 15 μm or less.

[0076] The positive electrode active material layer 54 may contain components other than the positive electrode active material, such as trilithium phosphate, conductive material, binder, etc. Suitable conductive materials include carbon black such as acetylene black (AB); carbon fibers such as vapor-processed carbon fiber (VGCF) and carbon nanotubes (CNT); and other carbon materials (e.g., graphite). Suitable binders include polyvinylidene fluoride (PVdF), etc.

[0077] The content of positive electrode active material in the positive electrode active material layer 54 (i.e., the content of positive electrode active material relative to the total mass of the positive electrode active material layer 54) is not particularly limited, but is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 85% by mass or more and 99% by mass or less. The content of trilithium phosphate in the positive electrode active material layer 54 is not particularly limited, but is preferably 0.1% by mass or more and 15% by mass or less, and more preferably 0.2% by mass or more and 10% by mass or less. The content of conductive material in the positive electrode active material layer 54 is not particularly limited, but is preferably 0.1% by mass or more and 20% by mass or less, and more preferably 0.3% by mass or more and 15% by mass or less. The content of binder in the positive electrode active material layer 54 is not particularly limited, but is preferably 0.4% by mass or more and 15% by mass or less, and more preferably 0.5% by mass or more and 10% by mass or less.

[0078] The thickness of the positive electrode active material layer 54 per side is not particularly limited, but is usually 10 μm or more, and preferably 20 μm or more. On the other hand, the thickness is usually 400 μm or less, and preferably 300 μm or less.

[0079] The negative electrode sheet 60 used is the negative electrode 60 described above.

[0080] Examples of the separator 70 include porous sheets (films) made of resins such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide. Such porous sheets may have a single-layer structure or a laminated structure of two or more layers (for example, a three-layer structure in which PP layers are laminated on both sides of a PE layer). A heat-resistant layer (HRL) may be provided on the surface of the separator 70.

[0081] The thickness of the separator 70 is not particularly limited, but is, for example, 5 μm to 50 μm, and preferably 10 μm to 30 μm. The air permeability obtained by the Gurley test method of the separator 70 is not particularly limited, but is preferably 350 seconds / 100 cc or less.

[0082] Non-aqueous electrolytes typically contain a non-aqueous solvent and a supporting salt (electrolyte salt). As the non-aqueous solvent, organic solvents commonly used in lithium-ion secondary battery electrolytes, such as carbonates, ethers, esters, nitriles, sulfones, and lactones, can be used without particular limitation. Among these, carbonates are preferred, with specific examples including ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), monofluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), monofluoromethyldifluoromethyl carbonate (F-DMC), and trifluorodimethyl carbonate (TFDMC). Such non-aqueous solvents can be used individually or in appropriate combinations of two or more. For example, the non-aqueous solvent may consist solely of carbonates. As another example, non-aqueous solvents include carbonates and esters such as methyl acetate.

[0083] Suitable supporting salts include lithium salts such as LiPF6, LiBF4, and lithium bis(fluorosulfonyl)imide (LiFSI), preferably LiPF6. The concentration of the supporting salt is preferably 0.7 mol / L or more and 1.3 mol / L or less.

[0084] Furthermore, the above-mentioned non-aqueous electrolyte may contain components other than those described above, such as film-forming agents like vinylene carbonate (VC) and oxalat complexes; gas-generating agents like biphenyl (BP) and cyclohexylbenzene (CHB); thickeners; and other additives, as long as they do not significantly impair the effects of the present disclosure.

[0085] The lithium-ion secondary battery 100 exhibits suppressed capacity degradation during repeated charging and discharging, and also boasts high capacity. The lithium-ion secondary battery 100 can be used in a variety of applications. Suitable applications include power supplies for vehicles such as electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs). Furthermore, the lithium-ion secondary battery 100 can be used as a storage battery for small-scale power storage devices. The lithium-ion secondary battery 100 can also typically be used in the form of a battery pack, consisting of multiple batteries connected in series and / or parallel.

[0086] The above describes a rectangular lithium-ion secondary battery 100 equipped with a flattened wound electrode body 20 as an example. However, lithium-ion secondary batteries can also be configured as lithium-ion secondary batteries equipped with a stacked electrode body (i.e., an electrode body in which multiple positive electrodes and multiple negative electrodes are stacked alternately). Furthermore, lithium-ion secondary batteries can also be configured as cylindrical lithium-ion secondary batteries, laminated case type lithium-ion secondary batteries, and the like.

[0087] Furthermore, according to known methods, the lithium-ion secondary battery 100 can also be configured as an all-solid-state lithium-ion secondary battery using a solid electrolyte instead of a non-aqueous electrolyte.

[0088] Furthermore, while the negative electrode 60 according to this embodiment is suitable as the negative electrode of a lithium-ion secondary battery, it can be constructed and used as the negative electrode of other secondary batteries, and other secondary batteries can be constructed according to known methods.

[0089] The following describes examples relating to this disclosure in detail, but this disclosure is not intended to be limited to those shown in such examples.

[0090] <Fabrication of the negative electrode> [Example 1] The following materials were prepared as the negative electrode active material. First Si-containing particles: Si-C composite material, Si content ratio = 40% by mass, average particle diameter (D50) = 7μm, consolidation density 1.2g / cm 3 Second Si-containing particles: Si-C composite material, Si content ratio = 62% by mass, average particle diameter (D50) = 6μm, consolidation density 0.85g / cm 3 Graphite particles (first and second graphite particles): Average particle size (D50) = 15 μm. 1 g of graphite particles is compressed uniaxially to achieve a density of 1.7 g / cm³. 3 Furthermore, the molding pressure when forming a tablet shape with a diameter of 20 mm was 15 MPa.

[0091] The Si content of the first Si-containing particles and the second Si-containing particles was measured using a commercially available ICP-OEC instrument. The average particle size (D50) of each particle was measured using a commercially available laser diffraction / scattering particle size distribution analyzer. The compaction density of the first Si-containing particles and the second Si-containing particles was measured by the following method.

[0092] One g of either primary or secondary Si-containing particles was weighed out as a powder measurement sample and placed on the probe (20 mm in diameter) of the automatic powder resistance measurement system "MCP-PD600" (manufactured by Nitto Seikou Analytech Co., Ltd.). At 25°C, the load and displacement when pressurized in a uniaxial direction were measured using this automatic powder resistance measurement system. Based on this, the bulk density of the molded body at a pressure of 60 MPa was determined and defined as the consolidation density. In addition, one g of graphite particles was weighed out as a powder measurement sample and placed on the probe (20 mm in diameter) of the automatic powder resistance measurement system "MCP-PD600" (manufactured by Nitto Seikou Analytech Co., Ltd.). At 25°C, the load and displacement when pressurized in a uniaxial direction were measured using this automatic powder resistance measurement system. Based on this, the density of the molded body was determined to be 1.7 g / cm³. 3 The molding pressure was then calculated.

[0093] As binders, carboxymethylcellulose (CMC), polyacrylic acid (PAA), and styrene-butadiene rubber (SBR) were prepared. In addition, a dispersion of single-walled carbon nanotubes (SWCNTs) was prepared as a conductive material.

[0094] A negative electrode paste containing graphite particles, primary Si-containing particles, secondary Si-containing particles, CMC, PAA, SBR, and SWCNT in a mass ratio of 60:20:20:1:1:1:0.1 was prepared using the following procedure.

[0095] First, graphite particles, primary Si-containing particles, secondary Si-containing particles, CMC, and PAA were dry-blended using a planetary mixer. The resulting mixture, SWCNT dispersion, and dispersion medium were kneaded using a planetary mixer. SBR and further dispersion medium were added to this mixture and uniformly mixed to prepare a negative electrode paste.

[0096] The prepared negative electrode paste was applied to the surface of a 10 μm thick copper foil and dried to form a negative electrode active material layer. After roll pressing the negative electrode active material layer, the resulting sheet was processed to a predetermined size to obtain a negative electrode sheet.

[0097] [Example 2] As a first Si-containing particle, the compressed density is 1.0 g / cm³. 3 The negative electrode sheet of Example 2 was obtained in the same manner as in Example 1, except that particles of a Si-C composite material with a Si content of 51% by mass were used.

[0098] [Example 3] The negative electrode sheet of Example 3 was obtained in the same manner as in Example 1, except that the composition of the negative electrode paste was changed, specifically, a negative electrode paste containing graphite particles, primary Si-containing particles, secondary Si-containing particles, CMC, PAA, SBR, and SWCNT in a mass ratio of 60:16:24:1:1:1:0.1 was used.

[0099] [Example 4] The negative electrode sheet of Example 4 was obtained in the same manner as in Example 1, except that the composition of the negative electrode paste was changed, specifically, a negative electrode paste containing graphite particles, primary Si-containing particles, secondary Si-containing particles, CMC, PAA, SBR, and SWCNT in a mass ratio of 60:12:28:1:1:1:0.1 was used.

[0100] [Example 5] As a Si-2 particle, it has a compressed density of 0.8 g / cm³. 3 The negative electrode sheet of Example 5 was obtained in the same manner as in Example 1, except that particles of a Si-C composite material with a Si content of 64% by mass were used.

[0101] [Example 6] As particles containing secondary Si, the compressed density is 0.72 g / cm³. 3 The negative electrode sheet of Example 6 was obtained in the same manner as in Example 1, except that particles of a Si-C composite material with a Si content of 58% by mass were used.

[0102] [Comparative Example 1] As a first Si-containing particle, the compressed density is 0.8 g / cm³. 3 Using particles of a Si-C composite material with a Si content of 43% by mass, the second Si-containing particles had a compressed density of 1.1 g / cm³. 3 A negative electrode sheet for Comparative Example 1 was obtained in the same manner as in Example 1, except that particles of a Si-C composite material with a Si content of 60% by mass were used.

[0103] [Comparative Example 2] As a particle containing secondary Si, the compressed density is 1.1 g / cm³. 3 A negative electrode sheet for Comparative Example 2 was obtained in the same manner as in Example 1, except that particles of a Si-C composite material with a Si content of 60% by mass were used.

[0104] [Comparative Example 3] As a first Si-containing particle, the compressed density is 0.8 g / cm³. 3 Using particles of a Si-C composite material with a Si content of 43% by mass, the second Si-containing particles had a compressed density of 0.85 g / cm³. 3A negative electrode sheet for Comparative Example 3 was obtained in the same manner as in Example 1, except that particles of a Si-C composite material with a Si content of 62% by mass were used.

[0105] [Comparative Example 4] A negative electrode sheet for Comparative Example 4 was obtained in the same manner as in Example 1, except that a negative electrode paste containing graphite particles, primary Si-containing particles, CMC, PAA, SBR, and SWCNT in a mass ratio of 60:40:1:1:1:0.1 was used, instead of using secondary Si-containing particles.

[0106] [Comparative Example 5] A negative electrode sheet for Comparative Example 5 was obtained in the same manner as in Example 1, except that a negative electrode paste containing graphite particles, secondary Si-containing particles, CMC, PAA, SBR, and SWCNT in a mass ratio of 60:40:1:1:1:0.1 was used, instead of using primary Si-containing particles.

[0107] <Fabrication of lithium-ion secondary batteries for evaluation> LiNi as a positive electrode active material powder 1 / 3 Co 1 / 3 Mn 1 / 3 A positive electrode paste was prepared by mixing O2 (NCM), acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder with N-methylpyrrolidone (NMP) in a mass ratio of NCM:AB:PVdF = 100:1:1. This paste was applied to the surface of a 15 μm thick aluminum foil and dried to form a positive electrode active material layer. After roll pressing the positive electrode active material layer, the resulting sheet was processed to a predetermined size to obtain a positive electrode sheet.

[0108] A separator made of porous polyolefin was prepared. Leads were attached to the negative electrode sheet and positive electrode sheet prepared above, and the electrodes were laminated via the separator to create an electrode body. This was then placed in an aluminum laminate film case along with a non-aqueous electrolyte. The non-aqueous electrolyte used was a mixed solvent containing ethylene carbonate (EC), fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 15:5:35:45, with LiPF6 dissolved as a supporting salt at a concentration of 1.0 mol / L. The case was then sealed to obtain a lithium-ion secondary battery for evaluation.

[0109] <Cycle Characteristics Evaluation> Each of the lithium-ion secondary batteries prepared for evaluation was placed in an environment of 25°C. Each evaluation lithium-ion secondary battery was charged with a constant current of 0.4C up to 4.2V, and then charged with a constant voltage until the current value was 0.1C. Next, each evaluation lithium-ion secondary battery was discharged with a constant current of 0.4C up to 2.5V. The discharge capacity at this time was measured to determine the initial capacity.

[0110] The above charge-discharge cycle was repeated 200 times, with each cycle being considered one. The discharge capacity after 200 cycles was determined using the same method as for the initial capacity. As an indicator of cycle characteristics, the capacity retention rate (%) was calculated using the formula: (discharge capacity after 200 charge-discharge cycles / initial capacity) × 100. The results are shown in Table 1.

[0111] [Table 1]

[0112] From the results in Table 1, the Si content in the first Si-containing particles is smaller than the Si content in the second Si-containing particles, and the compaction density of the first Si-containing particles is 0.9 g / cm³. 3 Furthermore, the compaction density of the secondary Si-containing particles is 0.9 g / cm³. 3When the value is less than [value missing], it can be seen that the capacity retention rate after 200 charge-discharge cycles is remarkably high. Therefore, it can be seen that the negative electrode of this disclosure can suppress capacity degradation when a secondary battery is repeatedly charged and discharged.

[0113] The specific examples of this disclosure have been described in detail above, but these are merely illustrative and do not limit the scope of the claims. The technologies described in the claims include various modifications and changes to the specific examples described above.

[0114] In other words, the negative electrode of the secondary battery of this disclosure, the method for manufacturing the same, and the secondary battery are as described in the following sections [1] to

[10] . [1] Negative electrode current collector and The negative electrode active material layer supported by the negative electrode current collector, The negative electrode of a secondary battery, The negative electrode active material layer contains graphite, first Si-containing particles, and second Si-containing particles. The Si content in the first Si-containing particle is smaller than the Si content in the second Si-containing particle. When the density of a molded body obtained by pressurizing 1 g of particles uniaxially at 25°C and 60 MPa to form a tablet with a diameter of 20 mm is defined as the compaction density, the compaction density of the first Si-containing particles is 0.9 g / cm³. 3 The above conditions are met, and the compaction density of the second Si-containing particles is 0.9 g / cm³. 3 The negative electrode, which is less than [a certain value]. [2] The compaction density of the first Si-containing particles is 0.95 g / cm³. 3 More than 1.8g / cm 3 The negative electrode is as follows, as described in item [1]. [3] The compaction density of the second Si-containing particles is 0.65 g / cm³. 3 More than 0.85g / cm 3 The negative electrode as described in item [1] or [2] below. [4] The negative electrode according to any one of items [1] to [3], wherein the mass ratio of the first Si-containing particles to the second Si-containing particles is 20:80 to 80:20. [5] The negative electrode according to any one of items [1] to [4], wherein the ratio of the Si content in the first Si-containing particles to the Si content in the second Si-containing particles is 0.10 to 0.90. [6] The negative electrode according to any one of items [1] to [5], wherein the Si content in the first Si-containing particles is 20% to 55% by mass, and the Si content in the second Si-containing particles is 45% to 80% by mass. [7] The negative electrode according to any one of items [1] to [6], wherein the content ratio of the graphite particles to the total of the graphite particles, the first Si-containing particles, and the second Si-containing particles is 40% by mass to 90% by mass. [8] The ratio of the average particle diameter (D50) of the graphite particles to the average particle diameter (D50) of the first Si-containing particles is 1.0 to 8.0. The negative electrode according to any one of items [1] to [7], wherein the ratio of the average particle diameter (D50) of the graphite particles to the average particle diameter (D50) of the second Si-containing particles is 1.0 to 8.0. [9] A step of preparing a negative electrode paste containing graphite particles, first Si-containing particles, second Si-containing particles, and a dispersion medium. A step of applying the negative electrode paste to the negative electrode current collector, The steps include drying the coated negative electrode paste to form a negative electrode active material layer, and A step of pressing the negative electrode active material layer, Equipped with, The Si content in the first Si-containing particle is smaller than the Si content in the second Si-containing particle. When the density of a molded body obtained by shaping 1 g of particles into a tablet with a diameter of 20 mm by uniaxial pressure at 25°C and 60 MPa is defined as the compaction density of the particles, the compaction density of the first Si-containing particles is 0.9 g / cm³. 3 The above conditions are met, and the compaction density of the second Si-containing particles is 0.9 g / cm³. 3 Less than, A method for manufacturing the negative electrode of a secondary battery.

[10] Positive electrode and, The negative electrode and, Electrolytes, A secondary battery equipped with, A secondary battery wherein the negative electrode is the negative electrode described in any one of items [1] to [8]. [Explanation of Symbols]

[0115] 12 Graphite Particles 14 1st Si-containing particles 16 2nd Si-containing particles 20 Wound electrode body 30 Battery Cases 36 Safety valve 42 Positive terminal 42a Positive electrode current collector plate 44 Negative terminal 44a Negative current collector plate 50 Positive electrode sheets (positive electrode) 52 Positive electrode current collector 52a Portion where positive electrode active material layer is not formed 54 Cathode active material layer 60 Negative electrode sheets (negative electrode) 62 Negative electrode current collector 62a Part where negative electrode active material layer is not formed 64 Negative electrode active material layer 70 Separator Sheets (Separators) 100 Lithium-ion rechargeable batteries

Claims

1. Negative electrode current collector and The negative electrode active material layer supported by the negative electrode current collector, The negative electrode of a secondary battery, The negative electrode active material layer contains graphite, first Si-containing particles, and second Si-containing particles. The Si content in the first Si-containing particle is smaller than the Si content in the second Si-containing particle. When the density of a molded body obtained by pressing 1 g of particles uniaxially at 25°C and 60 MPa to form a tablet with a diameter of 20 mm is defined as the compaction density, the compaction density of the first Si-containing particle is 0.9 g / cm³. ３ The above conditions are met, and the compaction density of the second Si-containing particle is 0.9 g / cm³. ３ The negative electrode, which is less than [a certain value].

2. The compaction density of the first Si-containing particle is 0.95 g / cm³. ３ 1.8g / cm or more ３ The negative electrode according to claim 1, which is as follows:

3. The compaction density of the second Si-containing particle is 0.65 g / cm³. ３ 0.85g / cm or more ３ The negative electrode according to claim 1, which is as follows:

4. The negative electrode according to claim 1, wherein the mass ratio of the first Si-containing particles to the second Si-containing particles is 20:80 to 80:

20.

5. The negative electrode according to claim 1, wherein the ratio of the Si content in the first Si-containing particles to the Si content in the second Si-containing particles is 0.10 to 0.

90.

6. The negative electrode according to claim 1, wherein the Si content in the first Si-containing particles is 20% to 55% by mass, and the Si content in the second Si-containing particles is 45% to 80% by mass.

7. The negative electrode according to claim 1, wherein the content ratio of the graphite particles to the total of the graphite particles, the first Si-containing particles, and the second Si-containing particles is 40% by mass to 90% by mass.

8. The ratio of the average particle diameter (D50) of the graphite particles to the average particle diameter (D50) of the first Si-containing particles is 1.0 to 8.

0. The negative electrode according to claim 1, wherein the ratio of the average particle diameter (D50) of the graphite particles to the average particle diameter (D50) of the second Si-containing particles is 1.0 to 8.

0.

9. A process for preparing a negative electrode paste containing graphite particles, first Si-containing particles, second Si-containing particles, and a dispersion medium. A step of applying the negative electrode paste to the negative electrode current collector, The steps include drying the coated negative electrode paste to form a negative electrode active material layer, and A step of pressing the negative electrode active material layer, Equipped with, The Si content in the first Si-containing particle is smaller than the Si content in the second Si-containing particle. When the density of a molded body obtained by pressing 1 g of particles uniaxially at 25°C and 60 MPa to form a tablet with a diameter of 20 mm is defined as the compaction density of the particles, the compaction density of the first Si-containing particles is 0.9 g / cm³. ３ The above conditions are met, and the compaction density of the second Si-containing particle is 0.9 g / cm³. ３ Less than, A method for manufacturing the negative electrode of a secondary battery.

10. Positive electrode and, The negative electrode and, Electrolytes, A secondary battery equipped with, A secondary battery wherein the negative electrode is the negative electrode described in claim 1.

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