Power storage device and method for manufacturing power storage device

Abstract

Provided is a technique capable of suppressing an increase in the expansion rate of a plate after a charge / discharge cycle of a power storage device having a Si-containing negative electrode, and capable of reducing the rate of resistance increase. According to the technology disclosed herein, a power storage device is provided with 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) contains Si-containing particles as negative electrode active material particles, and the Si-containing particles are composite particles of a graphite substrate having voids and silicon disposed in the voids of the graphite substrate. In the thickness direction of the negative electrode active material layer (64), the hardness of the Si-containing particles contained in at least a portion of the divided layers is lower than the hardness of the Si-containing particles contained in the other layers.

Description

Technical Field

[0001] The present disclosure relates to an electric storage device and a method for manufacturing the electric storage device. Background Art

[0002] As an example of an electrical storage device, a secondary battery such as a lithium-ion secondary battery can be cited. In recent years, such secondary batteries have been suitable for use in portable power supplies such as personal computers and portable terminals, and in power supplies for vehicles such as battery-electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs).

[0003] The negative electrode active material disclosed in Patent Gazette No. 6385749 comprises a mixed powder of a first active material powder and a second active material powder, wherein the first active material powder is composed of at least one selected from Si, Si compounds, Sn, and Sn compounds, and the second active material powder is composed of plate-like graphite particles having a thickness of 0.3 nm to 100 nm and a length in the major axis direction of 0.1 μm to 500 μm. The invention is characterized in that an aromatic vinyl copolymer is adsorbed on the surface of the plate-like graphite particles, wherein the aromatic vinyl copolymer contains a vinyl aromatic monomer unit represented by the following formula (1): -(CH2-CHX)-(1). It should be noted that in formula (1), X represents a phenyl group, a naphthyl group, an anthracenyl group, or a pyrenyl group, and these groups may have a substituent. The same publication also states that this configuration improves the cycle characteristics and initial efficiency of the power storage device while achieving a higher capacity.

[0004] Patent Gazette No. 5522817 discloses a negative electrode active material composition for lithium secondary batteries. The composition comprises a negative electrode active material, a polyimide precursor compound, and a polymer with a glass transition temperature of 50°C or less. The polyimide precursor compound is polyamic acid. The polymer is polyvinylidene fluoride. The negative electrode active material is SnO, SnO2, SiO, or SiO x (0<x<2). The content of the polyimide precursor compound is 4.95 to 15 weight percent. The content of the polymer in the composition is 0.05 to 3 weight percent. The same publication also states that the use of the composition can prevent bending of the electrode plate, impart flexibility to the electrode plate, and improve the capacity and life characteristics of the lithium secondary battery.

[0005] Japanese Patent Publication No. 2006-196447 discloses a negative electrode for a lithium-ion secondary battery. The negative electrode comprises a current collector and an active material layer supported on the current collector. The active material layer comprises a first layer and a second layer alternately stacked in the thickness direction of the active material layer. The publication further states that the negative electrode can improve cycling characteristics by combining high lithium-ion conductivity with electron conductivity, enhancing high-rate charge and discharge characteristics, reducing the expansion rate of the active material when reacting with lithium ions, and distributing and alleviating the stress caused by the expansion throughout the active material layer.

[0006] International Publication No. 2020 / 031869 discloses a non-aqueous electrolyte secondary battery having a positive electrode, a negative electrode and an electrolyte. The negative electrode has a negative electrode mixture layer containing a first negative electrode active material and a negative electrode current collector to which the negative electrode mixture layer is attached. The first negative electrode active material includes a first lithium silicate phase containing lithium, silicon and oxygen, and first silicon particles dispersed in the first lithium silicate phase. The atomic ratio of oxygen to silicon in the first lithium silicate phase is A1:O / Si, which satisfies the relationship 2<A1≤3. Compared with the negative electrode current collector side of the negative electrode, the proportion of the first negative electrode active material in the negative electrode mixture layer on the surface side of the negative electrode becomes larger. The same publication also states that the above-mentioned structure can improve the cycle characteristics of the non-aqueous electrolyte secondary battery.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Patent No. 6385749

[0010] Patent Document 2: Patent No. 5522817

[0011] Patent Document 3: Japanese Patent Application Laid-Open No. 2006-196447

[0012] Patent Document 4: International Publication No. 2020 / 031869 Summary of the Invention

[0013] However, it is known that negative electrodes containing silicon (Si) experience significant expansion during charge and discharge, resulting in a hardened negative electrode plate and a reduction in reaction force characteristics. While active research and development efforts have been underway, as described in Patent Documents 1 to 4, there is still room for improvement in order to soften negative electrode plates containing high Si content without compromising the performance of electrical storage devices.

[0014] In view of the above circumstances, the present inventors have sought to suppress an increase in the plate expansion rate of an electrical storage device having a Si-containing negative electrode after charge and discharge cycles and to reduce the resistance increase rate of the electrical storage device.

[0015] According to the technology disclosed herein, an electrical storage device is disclosed, comprising a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The negative electrode active material layer contains Si-containing particles as the negative electrode active material particles. These Si-containing particles are composite particles composed of a graphite substrate having voids and silicon disposed within the voids of the graphite substrate. In the thickness direction of the negative electrode active material layer, the hardness of the Si-containing particles contained in at least one of the divided layers is lower than the hardness of the Si-containing particles contained in other layers. This configuration can suppress the increase in the plate expansion rate of an electrical storage device having a Si-containing negative electrode after charge and discharge cycles, and reduce the rate of increase in the electrical resistance of the electrical storage device.

[0016] According to the technology disclosed herein, a method for manufacturing an electrical storage device is disclosed, the electrical storage device comprising a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. The manufacturing method includes disposing a negative electrode active material layer on the negative electrode current collector, the negative electrode active material layer containing Si-containing particles as a negative electrode active material. The process of disposing the negative electrode active material layer includes: disposing a first layer using a first paste containing Si-containing particles having a relatively low hardness; and disposing a second layer using a second paste containing Si-containing particles having a relatively high hardness. The Si-containing particles are composite particles of a graphite substrate having voids and silicon disposed within the voids of the graphite substrate. According to the above configuration, for an electrical storage device having a negative electrode containing Si, it is possible to suppress an increase in the plate expansion rate after charge and discharge cycles and reduce the resistance increase rate of the electrical storage device. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a longitudinal cross-sectional view of the lithium-ion secondary battery 100 .

[0018] Figure 2 is a schematic diagram of the electrode body 20 .

[0019] Figure 3 is a schematic cross-sectional view of the negative electrode 60 .

[0020] Figure 4 is a schematic cross-sectional view of the negative electrode 260 .

[0021] Explanation of symbols

[0022] 20 electrode body

[0023] 30 shell

[0024] 42 positive terminal

[0025] 44 negative terminal

[0026] 50 positive electrode

[0027] 60, 260 negative electrode

[0028] 62, 262 negative electrode collector

[0029] 64, 264 negative electrode active material layer

[0030] 641, 2641, first floor

[0031] 642, 2642, second floor

[0032] 70 Isolators

[0033] 80 non-aqueous electrolyte

[0034] 100 lithium-ion secondary batteries DETAILED DESCRIPTION

[0035] An embodiment of the power storage device disclosed herein is described below. The embodiment described here does not particularly limit the technology disclosed herein. The technology disclosed herein is not limited to the embodiment described here unless otherwise specified. The accompanying drawings are schematically depicted and do not necessarily reflect the actual objects. In addition, for components and parts that play the same role, the same symbols are appropriately assigned, and repeated descriptions are sometimes omitted. In addition, the expression "A to B" indicating a numerical range means "above A and below B" and also includes "exceeding A and below B" unless otherwise specified.

[0036] In this specification, an "electrical storage device" refers to a device that charges and discharges electricity through the movement of charge carriers between a pair of electrodes (a positive electrode and a negative electrode) via an electrolyte. Examples of such devices include secondary batteries such as lithium-ion batteries, nickel-metal hydride batteries, and nickel-cadmium batteries, and capacitors such as lithium-ion capacitors and electric double-layer capacitors. The following describes an embodiment in which the electrical storage device is a lithium-ion secondary battery.

[0037] <First embodiment>

[0038] Figure 1 It is a longitudinal cross-sectional view of the lithium-ion secondary battery 100 . Figure 2 is a schematic diagram of the electrode body 20. Figure 1 As shown, the lithium-ion secondary battery 100 includes an electrode body 20 , a case 30 , and a non-aqueous electrolyte 80 .

[0039] like Figure 1 and Figure 2 As shown, the electrode body 20 is a wound electrode body formed by overlapping a long sheet of positive electrode 50 and a long sheet of negative electrode 60 with a long sheet of separator 70 interposed therebetween, and wound in the longitudinal direction of the sheet (hereinafter simply referred to as the "longitudinal direction"). In the electrode body 20, the exposed area 52a of the positive electrode 50 and the exposed area 62a of the negative electrode 60 are exposed outward from both ends in the short direction perpendicular to the longitudinal direction.

[0040] like Figure 1 and Figure 2 As shown, the positive electrode 50 has a long sheet-shaped positive electrode collector 52 and a positive electrode active material layer 54. The positive electrode collector 52 is, for example, aluminum foil. In this embodiment, the positive electrode collector 52 has an area where the positive electrode active material layer 54 is provided and an exposed area 52a where the positive electrode active material layer 54 is not provided but the surface of the positive electrode collector 52 is exposed. The positive electrode active material layer 54 is, for example, provided in a strip shape along the long side direction on one side or both sides (here, both sides) of the positive electrode collector 52. The positive electrode active material layer 54 is not provided at the end (the end on the left side in the figure) in the short side direction (hereinafter, also referred to as the "short side direction") of the sheet. The exposed area 52a here is a strip-shaped area at the end in the short side direction (the end on the left side in the figure). As Figure 1 As shown, the current collecting plate 42a is mounted on the exposed area 52a.

[0041] The positive electrode active material layer 54 contains, for example, a positive electrode active material. The positive electrode active material is not particularly limited as long as it can achieve the effects of the technology disclosed herein, and a positive electrode active material having a conventionally known composition for such an application can be used. Examples of the positive electrode active material include lithium composite oxides and lithium transition metal phosphate compounds. The crystal structure of the positive electrode active material is not particularly limited and may include a layered structure, a spinel structure, an olivine structure, and the like.

[0042] As the lithium composite oxide, a lithium transition metal composite oxide containing at least one of Ni, Co, and Mn as a transition metal element is preferred. Examples of the lithium transition metal composite oxide include lithium nickel composite oxides, lithium cobalt composite oxides, lithium manganese composite oxides, lithium nickel manganese composite oxides, lithium nickel cobalt manganese composite oxides, lithium nickel cobalt manganese composite oxides, lithium nickel cobalt aluminum composite oxides, and lithium iron nickel manganese composite oxides. These positive electrode active materials may be used alone or in combination of two or more.

[0043] It should be noted that in this specification, "lithium nickel cobalt manganese composite oxide" refers to a term that includes oxides containing one or more additional elements other than Li, Ni, Co, Mn, and O, in addition to oxides containing Li, Ni, Co, Mn, and O as constituent elements. Examples of additional elements include transition metal elements such as Mg, Ca, Al, Ti, V, Cr, Y, Zr, Nb, Mo, Hf, Ta, W, Na, Fe, Zn, and Sn; typical metal elements; and the like. Additional elements may also be semimetallic elements such as B, C, Si, and P; and nonmetallic elements such as S, F, Cl, Br, and I. This also applies to the aforementioned lithium nickel composite oxides, lithium cobalt composite oxides, lithium manganese composite oxides, lithium nickel manganese composite oxides, lithium nickel cobalt aluminum composite oxides, and lithium iron nickel manganese composite oxides.

[0044] Examples of lithium transition metal phosphate compounds include lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), and lithium manganese iron phosphate. As the positive electrode active material, for example, LiNi 0.33 Co 0.33 Mn 0.33 O2、LiNi 0.5 Co 0.2 Mn 0.3 O2、LiNi 0.6 Co 0.2 Mn 0.2 O2、LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNiO2, LiCoO2, LiFeO2, LiMn2O4, LiNi 0.5 Mn 1.5 O4, etc.

[0045] In addition to the positive electrode active material, the positive electrode active material layer 54 may also contain a conductive material, a binder, etc. As a conductive material, for example, carbon black such as acetylene black (AB); other carbon materials such as graphite can be mentioned. As a binder, for example, polyvinylidene fluoride (PVDF) can be mentioned. The content of the positive electrode active material relative to the entire positive electrode active material layer 54 is preferably 70% by mass or more, more preferably 80% to 97% by mass, and further preferably 85% to 96% by mass. The content of the conductive material relative to the entire positive electrode active material layer 54 is, for example, 0.1% to 20% by mass. The content of the binder relative to the entire positive electrode active material layer 54 is, for example, 0.5% to 15% by mass.

[0046] like Figure 1 and Figure 2 As shown, the negative electrode 60 has a long sheet-shaped negative electrode collector 62 and a negative electrode active material layer 64. The negative electrode collector 62 is, for example, copper foil. In this embodiment, the negative electrode collector 62 has an area where the negative electrode active material layer 64 is provided and an exposed area 62a on the surface where the negative electrode active material layer 64 is not provided but the negative electrode active material layer 64 is exposed. The negative electrode active material layer 64 is, for example, provided in a strip shape along the long side direction on one side or both sides (here both sides) of the negative electrode collector 62. The negative electrode active material layer 64 is not provided at the end in the short side direction (the end on the right side in the figure). The exposed area 62a here is a strip area at the end in the short side direction (the end on the right side in the figure). As Figure 1 As shown, the current collecting plate 44a is mounted on the exposed area 62a.

[0047] The negative electrode active material layer 64 contains, for example, a negative electrode active material. In the present embodiment, the negative electrode active material contains Si-containing particles. The Si-containing particles are, for example, composite particles of a graphite substrate having voids and silicon disposed within the voids of the graphite substrate (in the following description, the above particles are also referred to as "Si / C particles"). The graphite substrate can be, for example, porous, fibrous, or granular. In the present embodiment, the composite particles of the graphite substrate and silicon are particles in which the graphite substrate and silicon are integrated and move as a single particle.

[0048] Si-containing particles can be obtained by known methods. For example, Si, Si oxide, or other fine particles can be mixed with a carbon precursor (e.g., petroleum pitch, coal pitch, phenolic resin, etc.), carbonized, and spheroidized. Alternatively, a spherical graphite substrate and Si, Si oxide, or other fine particles can be mixed and dried in a dispersion medium, and the fine particles can be arranged in the pores of the graphite substrate.

[0049] The use of negative electrode active materials containing silicon (Si) can achieve further increases in capacity and energy density in energy storage devices. However, it is known that negative electrode active materials containing Si significantly expand and contract during charging and discharging of the energy storage device, resulting in stiffening of the negative electrode plate, which in turn reduces the durability of the energy storage device. The present inventors have conducted extensive research on a structure that suppresses expansion and contraction during charging and discharging while also suppressing increases in plate hardness in the negative electrode of an energy storage device using a negative electrode active material containing Si.

[0050] In the thickness direction of the negative electrode active material layer 64, the hardness of the Si-containing particles contained in at least one of the divided layers is, for example, lower than the hardness of the Si-containing particles contained in other layers. In this embodiment, the negative electrode active material layer 64 has at least two layers. One of the two layers contains Si-containing particles with relatively low hardness. The other of the two layers contains Si-containing particles with relatively high hardness. In the following description, the Si-containing particles with relatively low hardness are sometimes referred to as "first Si-containing particles" and the Si-containing particles with relatively high hardness are sometimes referred to as "second Si-containing particles." It should be noted that the layer structure of the negative electrode active material layer 64 will be further described later.

[0051] In the present embodiment, the hardness of the first Si-containing particle and the hardness of the second Si-containing particle are specified by the compressive elastic modulus of each particle. The compressive elastic modulus of the second Si-containing particle is approximately 1.5 times or more, for example, 1.7 times or more, relative to the compressive elastic modulus of the first Si-containing particle. From the perspective of better achieving the effect of the technology disclosed herein, it is preferably more than 2 times, more preferably more than 2.2 times. From the same perspective, the compressive elastic modulus of the second Si-containing particle is approximately 5 or less, for example, 4.5 or less, preferably 4 or less, more preferably 3.5 or less, relative to the compressive elastic modulus of the first Si-containing particle. The compressive elastic modulus of the first Si-containing particle and the compressive elastic modulus of the second Si-containing particle can be changed to a desired compressive elastic modulus, for example, according to the porosity of the graphite substrate, the type of the graphite substrate, the surface coating, etc.

[0052] The compressive modulus of the first Si-containing particles can be approximately 250 MPa or greater and less than 2000 MPa. To better suppress expansion and contraction of the negative electrode 60 during charge and discharge of the lithium-ion secondary battery 100, the compressive modulus of the first Si-containing particles is, for example, 1800 MPa or less, preferably 1600 MPa or less, and more preferably 1400 MPa or less. To achieve appropriate hardness of the negative electrode active material layer 64, the compressive modulus of the first Si-containing particles is, for example, 500 MPa or greater, preferably 750 MPa or greater, and more preferably 1000 MPa or greater. The compressive modulus of the second Si-containing particles can be approximately 2000 MPa to 5000 MPa or less. To suppress deformation of the negative electrode 60 during charge and discharge of the lithium-ion secondary battery 100, the compressive modulus of the second Si-containing particles is, for example, 4500 MPa or less, preferably 4000 MPa or less, and more preferably 3500 MPa or less. From the perspective of suppressing disconnection of the conductive path in the negative electrode active material layer 64 during charge and discharge of the lithium-ion secondary battery 100, the compressive elastic modulus of the second Si-containing particles is, for example, 2200 MPa or more, preferably 2400 MPa or more, more preferably 2600 MPa or more, and even more preferably 2800 MPa or more.

[0053] The compressive modulus of Si-containing particles (hereinafter, also referred to as "Si-containing particles" without specifically distinguishing between the first Si-containing particles and the second Si-containing particles) can be measured, for example, by using a commercially available testing machine. As a commercially available testing machine, for example, the micro compression testing machine "MCT-211" manufactured by Shimadzu Corporation can be preferably used. In the method for measuring the compressive modulus of Si-containing particles, first, a particle of the Si-containing particles is compressed in the vertical direction using a testing machine, and the displacement (compressive displacement) and stress (compressive stress) during compression are measured. Then, the average particle size of the Si-containing particles is divided by the compressive displacement to calculate the compression deformation. Next, the following formula (A) is used:

[0054] Compressive modulus (MPa) = Compression stress (Mpa) / Compression deformation (A) The compressive modulus of one Si-containing particle is calculated. In this embodiment, the compressive modulus is calculated for at least five Si-containing particles, and the arithmetic average thereof is obtained as the compressive modulus of the Si-containing particles. Here, at least five Si-containing particles have a particle size of 90% to 110% of the average particle size. The particle size of the Si-containing particles can be measured when measuring the compressive modulus using the above-mentioned testing machine. The average particle size of the Si-containing particles will be described later.

[0055] The average particle size of the Si-containing particles is approximately 0.5 μm to 20 μm. From the viewpoint of achieving the effect of the technology disclosed herein, the average particle size is, for example, 1 μm or more, preferably 3 μm or more, and more preferably 5 μm or more. From the same viewpoint, the average particle size is, for example, 15 μm or less, preferably 12 μm or less, and more preferably 10 μm or less. The average particle size of the first Si-containing particles and the average particle size of the second Si-containing particles may be the same or different. In this specification, the "average particle size" of the particles refers to the particle size distribution on a volume basis measured by a particle size distribution measurement based on a laser diffraction / light scattering method, which is equivalent to the particle size (D 50 particle size).

[0056] The negative electrode active material layer 64 may also contain graphite particles as a negative electrode active material. The graphite particles as the negative electrode active material may be, for example, artificial graphite, natural graphite, etc. The graphite particles may have a covering layer of amorphous carbon on the surface. Although not particularly limited, the graphite particles are, for example, roughly spherical in shape. In this specification, for graphite particles, "roughly spherical" means that the average aspect ratio of the graphite particles is 1 to 2 (preferably 1 to 1.5) based on electron microscope (SEM) observation. It should be noted that the average aspect ratio is obtained, for example, by obtaining a planar SEM observation image of the graphite particles, randomly selecting a plurality of (for example, 10 to 100) graphite particles from the SEM observation image and calculating the aspect ratio of each, and calculating the arithmetic average thereof. The average particle size of the graphite particles may be, for example, 5 μm to 30 μm, or 10 μm to 20 μm. The compressive elastic modulus of the graphite particles may be, for example, 100 MPa to 300 MPa, preferably 150 MPa to 200 MPa.

[0057] The content of the graphite particles is generally 20% to 80% by mass, preferably 40% to 75% by mass, and more preferably 50% to 70% by mass, based on the total mass of the negative electrode active material.

[0058] In addition to the negative electrode active material, the negative electrode active material layer 64 may also contain a conductive material. Examples of the conductive material include carbon nanotubes such as single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), and multi-walled carbon nanotubes (MWCNTs); carbon black such as acetylene black (AB); and carbon fibers. From the perspective of improving the cycle characteristics of the lithium-ion secondary battery 100, carbon nanotubes are preferred as the conductive agent, and single-walled carbon nanotubes are more preferred.

[0059] The proportion of the negative electrode active material relative to the total negative electrode active material layer 64 is, for example, 70% by mass or greater, preferably 80% by mass or greater, more preferably 90% by mass to 99% by mass, and may be 95% by mass to 99% by mass. Furthermore, the proportion of the conductive material relative to the total negative electrode active material layer 64 may be, for example, 0.01% by mass to 1% by mass.

[0060] In addition to the negative electrode active material, the negative electrode active material layer 64 may also contain a binder. Examples of the binder include carboxymethyl cellulose (CMC), polyacrylic acid (PAA), styrene-butadiene rubber (SBR), and polyvinylidene fluoride (PVDF). Among them, carboxymethyl cellulose (CMC), polyacrylic acid (PAA), and styrene-butadiene rubber (SBR) are preferably used. The proportion of the binder, when the entire negative electrode active material layer 64 is 100% by mass, may be, for example, 0.5% to 10% by mass.

[0061] Figure 3 is a schematic cross-sectional view of the negative electrode 60 . Figure 3 Schematically shows a partial cross-sectional structure of the negative electrode 60. Figure 3 As shown, the negative electrode active material layer 64 has a first region R1 and a second region R2. In this embodiment, the first region R1 is formed by dividing the negative electrode active material layer 64 in the thickness direction (in the Figure 3 The second region R2 is a region that is relatively close to the negative electrode current collector 62 when the negative electrode active material layer 64 is divided into two parts in the vertical direction.

[0062] exist Figure 3 In the embodiment shown, the negative electrode active material layer 64 includes a first layer 641 and a second layer 642. In this embodiment, the first layer 641 is provided on the second region R2. The second layer 642 is provided on the first region R1. Figure 3As shown, the first layer 641 is provided on the negative electrode current collector 62. In this embodiment, the second layer 642 is provided on the first region R1. The second layer 642 is provided on the first layer 641, and is located on the surface side of the negative electrode active material layer 64. The ratio (T1:T2) of the thickness T1 of the first layer 641 to the thickness T2 of the second layer 642 is not particularly limited. For example, the ratio (T1:T2) is 10:90 to 90:10.

[0063] In this embodiment, the first layer 641 contains first Si-containing particles. The second layer 642 contains second Si-containing particles. In this embodiment, the first layer 641 contains the first Si-containing particles and the second layer 642 contains the second Si-containing particles, which can be explained, for example, by the following steps. First, prepare the lithium-ion secondary battery 100 to be inspected. Next, disassemble the lithium-ion secondary battery 100 and remove the negative electrode 60. Next, divide the negative electrode active material layer 64 into 3 to 20 layers evenly spaced from the surface of the negative electrode active material layer 64 to the thickness of the negative electrode current collector 62. The compressive modulus of the Si-containing particles contained in each layer is measured according to the above steps. This compressive modulus measurement allows, for example, to determine whether each layer is either the first layer 641 or the second layer 642. When the negative electrode active material layer 64 contains both graphite particles and Si-containing particles, the two can be distinguished using analytical methods such as scanning electron microscopy energy dispersive X-ray spectroscopy (SEM-EDX).

[0064] The method for producing the negative electrode 60 (manufacturing method) includes, for example, forming a first layer 641 on the negative electrode current collector 62 using a first paste containing Si-containing particles with relatively low hardness (first Si-containing particles); and forming a second layer 642 using a second paste containing Si-containing particles with relatively high hardness (second Si-containing particles). This method can produce the negative electrode 60 having the aforementioned characteristics, and can also produce an electrical storage device (lithium-ion secondary battery 100) including the negative electrode 60.

[0065] In this embodiment, the production method (manufacturing method) of the negative electrode 60 includes a preparation step, a first mixing step, a second mixing step, a third mixing step, a first coating step, a first drying step, a first pressing step, a second coating step, a second drying step, and a second pressing step.

[0066] The preparation step is, for example, a step of preparing raw materials for the negative electrode active material layer 64. In this embodiment, the preparation step includes preparing graphite particles, first Si-containing particles, second Si-containing particles, a conductive agent, and a binder. The raw materials mentioned here are as described above.

[0067] The first mixing step is, for example, a step of dry-mixing graphite particles, first Si-containing particles or second Si-containing particles, and a first binder. In this embodiment, in the first mixing step, the graphite particles, first Si-containing particles, and first binder are dry-mixed to prepare a first mixed powder. Similarly, the graphite particles, second Si-containing particles, and first binder are dry-mixed to prepare a second mixed powder. The first binder is, for example, carboxymethyl cellulose and polyacrylic acid. For example, a conventional mixing device used for such applications can be used for dry mixing in the first mixing step without particular limitation.

[0068] The second mixing step is, for example, a step of solid-kneading the first mixed powder or the second mixed powder, the conductive agent, and the dispersion medium adjusted in the first mixing step. In this embodiment, in the second mixing step, the first mixed powder, the conductive agent, and water are solid-kneaded to obtain a first kneaded product. Similarly, the second mixed powder, the conductive agent, and water are solid-kneaded to obtain a second kneaded product. The solid content rate of the first kneaded product and the solid content rate of the second kneaded product are approximately 50% to 80%, preferably 60% to 70%. For the solid-phase kneading of the second mixing step, for example, a mixing device previously known for such a purpose can be used without particular limitation.

[0069] The third mixing step is, for example, a step of mixing the first or second kneaded product obtained in the second mixing step, a second binder, and a dispersion medium. In this embodiment, in the third mixing step, the first kneaded product, the second binder, and water are mixed to obtain a first paste. Similarly, the second kneaded product, the second binder, and water are mixed to obtain a second paste. The second binder is, for example, styrene-butadiene rubber. For mixing in the third mixing step, for example, a conventional mixing device used for such purposes can be used without particular limitation.

[0070] The first coating process is, for example, a process of coating the first paste or the second paste obtained in the third mixing process on the negative electrode collector 62. In the present embodiment, the second paste is coated in a strip-like manner on the copper foil serving as the negative electrode collector 62. The coating method is not particularly limited, and a conventionally known method can be used (the same also applies to the second coating process). The first drying process is, for example, a process of drying the second paste coated on the negative electrode collector 62 in the first coating process to obtain a dry film. The drying conditions are not particularly limited, and the conditions used to manufacture such a negative electrode can be appropriately used (the same also applies to the second drying process). The first pressing process is, for example, a process of pressing the dry film obtained in the first drying process to obtain the second layer 642. The pressing conditions are not particularly limited, and the conditions used to manufacture such a negative electrode can be appropriately used (the same also applies to the second pressing process).

[0071] The second coating step is, for example, a step of coating the first paste or the second paste obtained in the third mixing step on the dried film after the first pressing step. In this embodiment, the first paste is coated on the second layer 642 formed by the first pressing step. The second drying step is, for example, a step of drying the first paste coated on the second layer 642 in the second coating step to obtain a dried film. The second pressing step is, for example, a step of pressing the dried film obtained in the second drying step to obtain the first layer 641. It should be noted that the above-mentioned method for manufacturing the negative electrode 60 is only an example. The method for manufacturing the negative electrode 60 may, for example, not include some of the above-mentioned steps as needed, or may include any steps. In the above-mentioned method, although the first paste is applied and dried before the second paste is applied, the second paste may be applied after the first paste is applied but before drying, or the first and second pastes may be applied simultaneously. In addition, the second paste may be applied and dried after the first paste is applied and dried, and then pressed.

[0072] Examples of separator 70 include porous sheets (films) made of resin materials such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide. The porous sheet may have a single-layer structure or a laminated structure of two or more layers (e.g., a three-layer structure with PP layers laminated on both sides of a PE layer). A heat-resistant layer (HRL) may be provided on the surface of separator 70.

[0073] The shell 30 is, for example, an outer container for storing the electrode body 20 and the non-aqueous electrolyte 80. The shell 30 is a flat square shell. Figure 1 As shown, the shell 30 has a positive terminal 42, a negative terminal 44, a safety valve 36 and an injection hole (not shown). The positive terminal 42 is, for example, an external connection terminal on the positive electrode side. The positive terminal 42 is electrically connected to the positive electrode 50 of the electrode body 20 via the collector plate 42a. The negative terminal 44 is, for example, an external connection terminal on the negative electrode side. The negative terminal 44 is electrically connected to the negative electrode 60 of the electrode body 20 via the collector plate 44a. The safety valve 36 is, for example, a thin-walled portion set in a manner to release the internal pressure when the internal pressure of the shell 30 rises to a specified level or above. The injection hole is, for example, a portion for injecting the non-aqueous electrolyte 80 into the shell 30.

[0074] The non-aqueous electrolyte 80 contains, for example, a non-aqueous solvent and a supporting salt. Examples of the non-aqueous solvent include various organic solvents such as carbonates, ethers, esters, nitriles, sulfones, and lactones used for this purpose. Among them, carbonates are preferably used. Examples of carbonates include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC) (preferably monofluoroethylene carbonate), monofluoromethyldifluoromethyl carbonate (F-DMC), and dimethyl trifluorocarbonate (TFDMC). As the non-aqueous solvent, one non-aqueous solvent may be used alone, or two or more non-aqueous solvents may be used in combination. Examples of the supporting salt include lithium salts such as LiPF6, LiBF4, and LiClO4. The concentration of the supporting salt may be, for example, 0.7 mol / L to 1.4 mol / L. The non-aqueous electrolyte 80 may contain additives used for this purpose as needed. As additives, for example, a film forming agent such as LiB(C2O4)2(LiBOB) or LiBF2(C2O4); a gas generating agent such as biphenyl (BP) or cyclohexylbenzene (CHB); a thickener, etc. may be contained.

[0075] The lithium-ion secondary battery 100 can be used for various applications. Suitable applications include driving power supplies mounted on vehicles such as battery-electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs). The lithium-ion secondary battery 100 can be used, for example, as a storage battery for small power storage devices. The lithium-ion secondary battery 100 can also be used, for example, in the form of a battery pack comprising a plurality of batteries connected in series and / or in parallel.

[0076] In this embodiment, the lithium-ion secondary battery 100 includes a negative electrode current collector 62 and a negative electrode active material layer 64 disposed on the negative electrode current collector 62. The negative electrode active material layer 64 contains Si-containing particles as the negative electrode active material particles. The Si-containing particles are composite particles composed of a graphite substrate having voids and silicon disposed within the voids of the graphite substrate. In the thickness direction of the negative electrode active material layer 64, the hardness of the Si-containing particles contained in at least one of the divided layers is lower than the hardness of the Si-containing particles contained in other layers.

[0077] In the lithium-ion secondary battery 100, the negative electrode active material layer 64 contains Si-containing particles as the negative electrode active material. The Si-containing particles include a porous graphite substrate and Si disposed within the voids of the graphite substrate. As a result, when Si expands due to charge and discharge, the voids can mitigate the expansion of the Si, thereby suppressing increases in the thickness of the negative electrode 60. The negative electrode active material layer 64 comprises at least a layer containing Si-containing particles with relatively low hardness and a layer containing Si-containing particles with relatively high hardness, along the thickness direction. The layer containing Si-containing particles with relatively low hardness is more likely to follow the shape changes of the electrode plate during expansion and contraction during charge and discharge than the other layers. This can suppress increases in the electrode plate expansion rate after charge and discharge cycles. On the other hand, the layer containing Si-containing particles with relatively high hardness is less likely to deform during expansion and contraction during charge and discharge, making it less likely that the conductive path will be disconnected. This can suppress increases in the electrode plate expansion rate after charge and discharge cycles and reduce the rate of resistance increase. That is, the lithium-ion secondary battery 100 can achieve higher capacity and higher energy density while suppressing an increase in the electrode plate expansion rate due to expansion and contraction caused by charge and discharge cycles and reducing the resistance increase rate.

[0078] When the negative electrode active material layer 64 is divided into two regions along its thickness, with the region relatively close to the negative electrode current collector 62 designated as the first region R1 and the region relatively far from the negative electrode current collector 62 as the second region R2, the first layer 641 containing Si-containing particles (first Si-containing particles) with relatively low hardness can be provided in the second region R2. In the negative electrode active material layer 64, the further the second region R2 is from the negative electrode current collector 62, the more susceptible it is to expansion and contraction, and the more susceptible it is to deformation. Therefore, by providing the first layer 641 containing the first Si-containing particles in the second region R2, the negative electrode active material layer 64 follows the expansion and contraction of the negative electrode 60, alleviating the stress caused by this expansion and contraction. This further improves the effect of suppressing the increase in the plate expansion rate after charge and discharge cycles.

[0079] When the compressive modulus of the first Si-containing particles is set to 1, the compressive modulus of the second Si-containing particles can be at least 2 times that. By setting the compressive modulus of the first Si-containing particles and the compressive modulus of the second Si-containing particles in this manner, the effects of the technology disclosed herein can be better achieved.

[0080] The first Si-containing particles may have a compressive modulus of 250 MPa or greater and less than 2000 MPa. By setting the compressive modulus of the first Si-containing particles within the above range, the effects of the technology disclosed herein can be better achieved. The second Si-containing particles may have a compressive modulus of 2000 MPa to 5000 MPa. By setting the compressive modulus of the second Si-containing particles within the above range, the effects of the technology disclosed herein can be better achieved.

[0081] The ratio (T1:T2) of the thickness T1 of the first layer 641 to the thickness T2 of the second layer 642 may be 10:90 to 90:10. By setting the ratio of thickness T1 to thickness T2 within the above range, the effects of the technology disclosed herein can be better achieved.

[0082] The negative electrode active material layer 64 may further contain graphite particles. Graphite particles, compared to Si-containing particles, expand and contract less during charging and discharging of the lithium-ion secondary battery 100. Therefore, by including graphite particles in the negative electrode active material layer 64, the graphite particles assume a portion of the function of the negative electrode active material, thereby suppressing the degree of expansion and contraction.

[0083] The method for manufacturing a lithium-ion secondary battery 100 is a method for manufacturing an electrical storage device including a negative electrode current collector 62 and a negative electrode active material layer 64 disposed on the negative electrode current collector 62. The manufacturing method includes a step of disposing the negative electrode active material layer 64 on the negative electrode current collector 62. The negative electrode active material layer contains Si-containing particles as the negative electrode active material. The step of disposing the negative electrode active material layer 64 includes a step of disposing a first layer 641 using a first paste containing Si-containing particles with relatively low hardness (first Si-containing particles), and a step of disposing a second layer 642 using a second paste containing Si-containing particles with relatively high hardness (second Si-containing particles). The Si-containing particles are composite particles composed of a graphite substrate having voids and silicon disposed within the voids of the graphite substrate. In the lithium-ion secondary battery 100 manufactured by implementing the above-described manufacturing method, the increase in the plate expansion rate of the negative electrode 60 after charge and discharge cycles can be suppressed while reducing the rate of resistance increase.

[0084] In this manufacturing method, the preparation of the first paste and the preparation of the second paste may include the following steps: dry-mixing the first Si-containing particles or the second Si-containing particles and the first binder to obtain the first mixed powder or the second mixed powder; solid-phase kneading the first mixed powder or the second mixed powder, the conductive agent, and the dispersion medium to obtain the first kneaded product or the second kneaded product; and mixing the first kneaded product or the second kneaded product, the second binder, and the dispersion medium. In this way, the first paste and the second paste can be prepared that are preferably used to achieve the effects of the technology disclosed herein.

[0085] This manufacturing method may include applying the second paste on the negative electrode current collector 62 to form the second layer 642, and applying the first paste on the second layer 642 to form the first layer 641. This allows the manufacture of a negative electrode 60 having a structure that is preferably adapted to achieve the effects of the technology disclosed herein.

[0086] <Second embodiment>

[0087] Figure 4 is a schematic cross-sectional view of the negative electrode 260 . Figure 4 Schematically shows a partial cross-sectional structure of the negative electrode 260. Figure 4 As shown, the negative electrode active material layer 264 includes a first layer 2641 containing first Si-containing particles and a second layer 2642 containing second Si-containing particles. In this embodiment, the first layer 2641 is provided in the first region R1. The second layer 2642 is provided in the second region R2. Figure 3 As shown, the first layer 2641 is provided on the negative electrode collector 262. In this embodiment, the second layer 2642 is provided on the first layer 2641, here on the surface side of the negative electrode active material layer 264. In this embodiment, the first layer 2641 containing Si-containing particles (first Si-containing particles) with relatively high hardness is provided in the first region R1 relatively close to the negative electrode collector 262. As a result, the liquid fluidity of the electrolyte is improved on the side of the negative electrode active material layer 264 opposite to the negative electrode collector 262. Therefore, according to the above-mentioned configuration, the effect of reducing the resistance increase rate after the charge and discharge cycle, among the effects of the technology disclosed herein, can be achieved particularly well.

[0088] In this embodiment, the method for manufacturing the lithium-ion secondary battery 100 includes the steps of applying a first paste onto the negative electrode current collector 262 to form a first layer 2641, and applying a second paste onto the first layer 2641 to form a second layer 2642. Thus, it is possible to manufacture the lithium-ion secondary battery 100 that can particularly effectively achieve the effect of reducing the rate of increase in resistance after charge and discharge cycles, among the effects of the technology disclosed herein.

[0089] Hereinafter, test examples related to the technology disclosed herein will be described, but the technology disclosed herein is not intended to be limited to the scope shown in the following test examples.

[0090] [Manufacture of test unit]

[0091] <Example 1>

[0092] As negative electrode active materials, first Si-containing particles, second Si-containing particles, and graphite particles are prepared. The first Si-containing particles have a compressive elastic modulus of 1100 MPa, and are Si / C particles with an average particle size of 7 μm. The second Si-containing particles have a compressive elastic modulus of 3400 MPa, and are Si / C particles with an average particle size of 8 μm. As for the graphite particles, the compressive elastic modulus is 180 MPa, and the average particle size is 14 μm. As a conductive material, single-walled carbon nanotubes (SWCNTs) are prepared. As a binder, carboxymethyl cellulose (CMC), polyacrylic acid (PAA), and styrene-butadiene rubber (SBR) are prepared. Using the prepared materials, the first paste is prepared by kneading with water as a dispersion medium in a mass ratio of graphite particles: first Si-containing particles: SWCNTs: CMC: PAA: SBR = 60:40:0.1:1:1:2. The second paste was prepared by kneading the mixture with water as a solvent at a mass ratio of graphite particles: second Si-containing particles: SWCNT: CMC: PAA: SBR = 60:40:0.1:1:1:2.

[0093] The first and second pastes were prepared as follows. First, graphite particles, first or second Si-containing particles, CMC, and PAA were dry-mixed to form a mixed powder. SWCNTs (a water-soluble paste with a solids content of 2%) and water were then added to the mixed powder and solid-phase kneaded. SBR and water were further added to the solid-phase kneaded mixture and mixed. In this manner, the first and second pastes were prepared.

[0094] Next, the second paste was applied to both sides of a 10μm-thick copper foil and dried to form the second layer. Next, the first paste was applied to the second layer and dried to form the first layer. The first and second layers, formed on the copper foil, were punched to the desired thickness to produce a negative electrode plate processed to the specified dimensions. The ratio (T1:T2) of the thickness of the first layer (T1) to the thickness of the second layer (T2) was 50:50.

[0095] LiNi as the positive electrode active material was prepared 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (LNCM), acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were mixed with N-methylpyrrolidone (NMP) as a solvent at a mass ratio of LNCM:AB:PVdF = 100:1:1 to prepare a positive electrode paste. The paste was applied to both sides of a 10μm thick aluminum foil and dried. The foil was then punched to a predetermined thickness to produce a positive electrode plate of the specified dimensions.

[0096] As a separator, a separator sheet with HRL provided on a porous polyolefin sheet of a three-layer structure of PP / PE / PP was prepared. Wires were installed on the negative electrode and positive electrode prepared in the above manner, and the electrodes were stacked via separators to produce an electrode body. The electrode body was inserted into an outer packaging body composed of an aluminum laminate sheet and injected with a non-aqueous electrolyte, and the outside of the outer packaging body was sealed to produce the test unit of this example. As a non-aqueous electrolyte, LiPF6 as a supporting salt was dissolved at a concentration of 1 mol / L in a mixed solvent containing ethylene carbonate (EC), fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) in a volume ratio of EC:FEC:EMC:DMC=15:5:40:40.

[0097] <Example 2>

[0098] As the first Si-containing particles, Si / C particles with a compressive elastic modulus of 1300 MPa were used. As the second Si-containing particles, Si / C particles with a compressive elastic modulus of 2900 MPa were used. The test cell of this example was prepared using the same materials and procedures as in Example 1.

[0099] <Example 3>

[0100] The ratio of the thickness T1 of the first layer to the thickness T2 of the second layer (T1:T2) was set to 90:10. The test cell of this example was produced using the same materials and procedures as in Example 1 except for this.

[0101] <Example 4>

[0102] The ratio of the thickness T1 of the first layer to the thickness T2 of the second layer (T1:T2) was set to 10:90. The test cell of this example was produced using the same materials and procedures as in Example 1 except for this.

[0103] <Example 5>

[0104] A first paste containing first Si-containing particles was applied to a copper foil to form a first layer. A second paste containing second Si-containing particles was applied to the first layer to form a second layer. A test cell of this example was prepared using the same materials and procedures as in Example 1.

[0105] <Example 6>

[0106] The paste of Example 6 was prepared by kneading graphite particles: first Si-containing particles: second Si-containing particles: SWCNT: CMC: PAA: SBR in a mass ratio of 60:20:20:0.1:1:1:2 with water as a dispersion medium. The steps for preparing the paste of Example 6 are as follows. First, the graphite particles, the first Si-containing particles, the second Si-containing particles, CMC and PAA are dry-mixed to obtain a mixed powder. Then, SWCNT (a water-soluble paste with a solid content of 2%) and water are added to the mixed powder and solid-phase kneading is performed. SBR and water are further added to the solid-phase kneaded mixture and mixed. The paste of Example 6 was prepared in this way. Except for this, the test unit of this example was prepared using the same materials and steps as Example 1.

[0107] <Example 7>

[0108] The first paste was applied to both sides of the copper foil and dried, and then punched to a predetermined thickness to obtain a negative electrode plate processed to a predetermined size.

[0109] <Example 8>

[0110] The second paste was applied to both sides of the copper foil and dried, and then punched to a predetermined thickness to obtain a negative electrode plate processed to a predetermined size.

[0111] It should be noted that for the first Si-containing particles and the second Si-containing particles used in Examples 1 to 8, the compressive elastic modulus is a value measured using a commercially available testing machine (a micro compression testing machine "MCT-211" manufactured by Shimadzu Corporation) in accordance with the user guide of the device. First, using the testing machine, one particle is compressed in the vertical direction, and the displacement (compressive displacement) and stress (compressive stress) during compression are measured. Next, the average particle size of the Si-containing particles is divided by the compressive displacement to calculate the compression deformation. Next, the following formula (A) is used:

[0112] Compression modulus (MPa) = Compression stress (MPa) / Compression deformation (A)

[0113] The compressive modulus of one Si-containing particle is calculated. The compressive modulus of at least five Si-containing particles is calculated, and the arithmetic average is calculated to represent the compressive modulus of the Si-containing particle. The at least five Si-containing particles have a particle size that is 90% to 110% of the average particle size. The particle size of the Si-containing particles can be measured using a testing machine when measuring the compressive modulus.

[0114] [Measurement of plate hardness]

[0115] The plate hardness (spring constant) of the negative electrode of each example was measured. As a test machine for the measurement, a commercially available test machine (precision universal testing machine "AGX-10kNVD" manufactured by Shimadzu Corporation) was used. Here, first, the negative electrode plate was cut into a predetermined size, a load was applied in the stacking direction of the negative electrode plate, and the displacement was measured. Then, according to the following formula (B):

[0116] Spring constant (kN / mm) = load (kN) / displacement in thickness direction (mm) (B) The spring constant (plate hardness) of the negative electrode of each example was measured. The results are shown in the corresponding columns of Table 1.

[0117] [Measurement of resistance increase rate]

[0118] <Initial resistance measurement>

[0119] Place the test cell at 25°C. Charge the test cell with constant current-constant voltage (CCCV) until the depth of charge (SOC) reaches 50%. Then, place the test cell at 25°C for 1 hour. Then, discharge the cell with constant current (CC) at a constant current of 1C for 10 seconds. Then, according to the following formula (C):

[0120] Initial resistance = [open circuit voltage (OCV) - closed circuit voltage (CCV)] / discharge current (C)

[0121] The initial resistance of the test cell of each example was measured. In the above formula, the closed-circuit voltage is the voltage value 10 seconds after the start of discharge. The discharge current value is the current value 10 seconds after the start of discharge.

[0122] High-rate cycle test

[0123] The test cell was placed in an environment at 25°C. CCCV charging was performed on the test cell until the depth of charge (SOC) reached 50%. The test cell was then CC-charged at a current of 1.5C for 400 seconds, followed by CC-discharge at a current of 0.75C for 800 seconds. This charge-discharge cycle was repeated 400 times.

[0124] <Measurement of resistance increase rate>

[0125] The same operation as above was repeated for the test cell after 400 cycles to calculate the battery resistance. Then, the battery resistance was calculated according to the following formula (D):

[0126] Resistance increase rate (%) = [battery resistance at the 400th cycle / initial resistance] × 100 (D) The resistance increase rate of the test cell of each example was calculated. The results are shown in the corresponding columns of Table 1.

[0127] [Measurement of plate expansion rate]

[0128] First, the initial thickness T0 of the test unit of each example is measured. Select any three points from the upper part, the central part, and the lower part of the wide surface of the test unit of each example, respectively, and measure the thickness of the test unit at the three points, and take the arithmetic mean as the initial thickness T0. Next, the test unit of each example is CCCV charged (charged at a rate of 0.4C to 4.2V, and then cut off at 0.1C) under a 25°C environment, and then CC discharged (at a rate of 0.4C, cut off at 2.5V), and this is regarded as one cycle, and the charge and discharge are performed for 250 cycles. Then, the test unit of each example is discharged to 2.5V, disassembled under an argon atmosphere, and the negative electrode is taken out. The negative electrode is immersed in DMC and washed, and then dried, and the thickness of the same three points as when the initial thickness T0 was measured is measured, and the arithmetic mean is taken as the thickness T250 after 250 cycles. Then, based on the initial thickness T0 and the thickness T250 after 250 cycles, according to the following formula (E):

[0129] Plate expansion rate (%)

[0130] =(thickness after 250 cycles T250 / initial thickness T0)×100···Formula (E) was used to determine the plate expansion rate (%) of the test unit of each example. The results are shown in the corresponding columns of Table 1. It should be noted that examples in which the plate expansion rate (%) is 50% or less are evaluated as examples in which the plate expansion rate of the test unit is suppressed along with charging and discharging. In addition, the "central part" of the wide surface is the center of the wide surface. The "upper part" of the wide surface is an area closer to one end side than the center of the wide surface. The "lower part" of the wide surface is an area closer to the side opposite to the above-mentioned one end than the center of the wide surface.

[0131]

[0132] Regarding Examples 1 to 8, in the test cells of Examples 1 to 5, the negative electrode active material layer contained Si-containing particles (Si / C particles) as the negative electrode active material particles. These Si-containing particles were composite particles composed of a graphite substrate having voids and silicon disposed within the voids of the graphite substrate. In the thickness direction of the negative electrode active material layer, the hardness of the Si-containing particles contained in at least one of the divided layers (here, the first layer) was lower than the hardness of the Si-containing particles contained in the other layer (here, the second layer). As shown in Table 1, in Examples 1 to 5 having the above-described structure, compared to Examples 6 to 8, which had a single-layer structure, the increase in plate expansion after charge and discharge cycles was suppressed while also reducing the rate of resistance increase.

[0133] In the above embodiment, the negative electrode active material layer has a two-layer structure consisting of a first layer and a second layer. However, the technology disclosed herein does not limit the negative electrode active material layer to the above embodiment, as long as it includes a layer (first layer) containing Si particles with relatively low hardness. For example, in the negative electrode active material layer, the first layer may be sandwiched between the second layer and another second layer.

[0134] The technology disclosed here may include the technology described in the following items.

[0135] Item 1:

[0136] An electric storage device comprising a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector.

[0137] The negative electrode active material layer contains Si-containing particles as negative electrode active material particles. The Si-containing particles are composite particles of a graphite substrate having voids and silicon disposed in the voids of the graphite substrate.

[0138] In the thickness direction of the negative electrode active material layer, the hardness of the Si-containing particles contained in at least one of the divided layers is lower than the hardness of the Si-containing particles contained in the other layers.

[0139] Item 2:

[0140] According to the energy storage device described in item 1, when the above-mentioned negative electrode active material layer is divided into two in the thickness direction, the area relatively close to the above-mentioned negative electrode collector is used as the first area, and the area relatively far from the above-mentioned negative electrode collector is used as the second area, the first layer containing the above-mentioned Si-containing particles with relatively low hardness is arranged in the above-mentioned second area.

[0141] Item 3:

[0142] According to the energy storage device described in item 1, when the above-mentioned negative electrode active material layer is divided into two in the thickness direction, the area relatively close to the above-mentioned negative electrode collector is used as the first area, and the area relatively far from the above-mentioned negative electrode collector is used as the second area, the first layer containing the above-mentioned Si-containing particles with relatively low hardness is arranged in the above-mentioned first area.

[0143] Item 4:

[0144] The electrical storage device according to any one of items 1 to 3, wherein the compressive modulus of the Si-containing particles having a relatively low hardness is equal to or greater than 2 times the compressive modulus of 1.

[0145] Item 5:

[0146] The electrical storage device according to any one of items 1 to 4, wherein the Si-containing particles having relatively low hardness have a compressive elastic modulus of 250 MPa or more and less than 2000 MPa.

[0147] Item 6:

[0148] The electrical storage device according to any one of items 1 to 5, wherein the Si-containing particles having relatively high hardness have a compressive elastic modulus of 2000 MPa to 5000 MPa.

[0149] Item 7:

[0150] The electrical storage device according to any one of items 1 to 6, wherein the negative electrode active material layer comprises a first layer containing the Si-containing particles having a relatively low hardness and a second layer containing the Si-containing particles having a relatively high hardness.

[0151] The ratio of the thickness T1 of the first layer to the thickness T2 of the second layer (T1:T2) is 10:90 to 90:10.

[0152] Item 8:

[0153] The electrical storage device according to any one of items 1 to 7, wherein the negative electrode active material layer further contains graphite particles as the negative electrode active material.

[0154] Item 9:

[0155] A manufacturing method is a method for manufacturing an electric storage device comprising a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector.

[0156] The method comprises the steps of providing the negative electrode active material layer on the negative electrode current collector, wherein the negative electrode active material layer contains Si-containing particles as a negative electrode active material.

[0157] The process of providing the negative electrode active material layer includes:

[0158] a step of forming a first layer using a first paste containing Si-containing particles having a relatively low hardness, and

[0159] The process of forming the second layer using a second paste containing Si-containing particles having relatively high hardness,

[0160] The Si-containing particles are composite particles of a graphite substrate having voids and silicon disposed in the voids of the graphite substrate.

[0161] Item 10:

[0162] The manufacturing method according to item 9, wherein

[0163] The preparation of the first paste and the preparation of the second paste include:

[0164] a step of dry-mixing the Si-containing particles having a relatively low hardness or the Si-containing particles having a relatively high hardness with a first binder to obtain a first mixed powder or a second mixed powder;

[0165] a step of solid-phase kneading the first mixed powder or the second mixed powder with a conductive agent and a dispersion medium to obtain a first kneaded product or a second kneaded product; and

[0166] A step of mixing the first kneaded product or the second kneaded product with a second binder and a dispersion medium.

[0167] Item 11:

[0168] The manufacturing method according to item 9 or 10, comprising:

[0169] a step of applying the second paste on the negative electrode current collector to form a second layer, and

[0170] A step of applying the first paste on the second layer to form a first layer.

[0171] Item 12:

[0172] The manufacturing method according to item 9 or 10, comprising:

[0173] a step of applying the first paste on the negative electrode current collector to form a first layer, and

[0174] A step of applying the second paste on the first layer to form a second layer.

[0175] Item 13:

[0176] The manufacturing method according to any one of items 9 to 12, comprising:

[0177] A step of preparing Si-containing particles having a compressive modulus of 2 times or more, assuming that the compressive modulus of the Si-containing particles having relatively low hardness is 1, as the Si-containing particles having relatively high hardness.

[0178] Item 14:

[0179] The production method according to any one of items 9 to 13, wherein the Si-containing particles having relatively low hardness have a compressive elastic modulus of 250 MPa or more and less than 2000 MPa.

[0180] Item 15:

[0181] The production method according to any one of items 9 to 14, wherein the Si-containing particles having relatively high hardness have a compressive elastic modulus of 2000 MPa to 5000 MPa.

[0182] Item 16:

[0183] The production method according to any one of items 9 to 15, wherein the negative electrode active material layer further contains graphite particles as the negative electrode active material.

[0184] While the embodiments of the technology disclosed herein have been described above, these are merely examples and do not limit the scope of the patent application. The technology described in the scope of the patent application includes various modifications and alterations of the specific examples described above.

Claims

1. An electric storage device comprising a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector, The negative electrode active material layer contains Si-containing particles as negative electrode active material particles, wherein the Si-containing particles are composite particles of a graphite substrate having voids and silicon disposed in the voids of the graphite substrate. In the thickness direction of the negative electrode active material layer, the hardness of the Si-containing particles contained in at least one of the divided layers is lower than the hardness of the Si-containing particles contained in the other layers.

2. The power storage device according to claim 1, wherein When the negative electrode active material layer is divided into two in the thickness direction, the area relatively close to the negative electrode collector is defined as the first area, and the area relatively far from the negative electrode collector is defined as the second area, the first layer containing the Si-containing particles with relatively low hardness is provided in the second area.

3. The power storage device according to claim 1, wherein When the negative electrode active material layer is divided into two in the thickness direction, the area relatively close to the negative electrode collector is defined as the first area, and the area relatively far from the negative electrode collector is defined as the second area, the first layer containing the Si-containing particles with relatively low hardness is provided in the first area.

4. The electrical storage device according to any one of claims 1 to 3, wherein When the compressive elastic modulus of the Si-containing particles having a relatively low hardness is set to 1, the compressive elastic modulus of the Si-containing particles having a relatively high hardness is twice or more.

5. The electrical storage device according to any one of claims 1 to 3, wherein The Si-containing particles having relatively low hardness have a compressive elastic modulus of 250 MPa or more and less than 2000 MPa.

6. The electrical storage device according to any one of claims 1 to 3, wherein The Si-containing particles having relatively high hardness have a compressive elastic modulus of 2000 MPa to 5000 MPa.

7. The electrical storage device according to any one of claims 1 to 3, wherein The negative electrode active material layer includes a first layer containing the Si-containing particles having a relatively low hardness and a second layer containing the Si-containing particles having a relatively high hardness. The ratio of the thickness T1 of the first layer to the thickness T2 of the second layer, ie, T1:T2, is 10:90 to 90:

10.

8. The electrical storage device according to any one of claims 1 to 3, wherein The negative electrode active material layer further contains graphite particles as the negative electrode active material.

9. A method for manufacturing an electrical storage device comprising a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector. The method comprises the steps of providing the negative electrode active material layer on the negative electrode current collector, wherein the negative electrode active material layer contains Si-containing particles as a negative electrode active material. The process of providing the negative electrode active material layer includes: a step of forming a first layer using a first paste containing Si-containing particles having a relatively low hardness, and The process of forming the second layer using a second paste containing Si-containing particles having relatively high hardness, The Si-containing particles are composite particles of a graphite substrate having voids and silicon disposed in the voids of the graphite substrate.

10. The manufacturing method according to claim 9, wherein: The preparation of the first paste and the preparation of the second paste include: A step of dry-mixing the Si-containing particles having relatively low hardness or the Si-containing particles having relatively high hardness with a first binder to obtain a first mixed powder or a second mixed powder; a step of solid-phase kneading the first mixed powder or the second mixed powder with a conductive agent and a dispersion medium to obtain a first kneaded product or a second kneaded product; and A step of mixing the first kneaded product or the second kneaded product with a second binder and a dispersion medium.

11. The manufacturing method according to claim 9, wherein: include: a step of applying the second paste on the negative electrode current collector to form a second layer, and a step of applying the first paste on the second layer to form a first layer.

12. The manufacturing method according to claim 9, wherein: include: a step of applying the first paste on the negative electrode current collector to form a first layer, and A step of applying the second paste on the first layer to form a second layer.

13. The production method according to any one of claims 9 to 12, wherein The method includes the step of preparing Si-containing particles having a compressive modulus of at least twice that of the Si-containing particles having a relatively low hardness, when the compressive modulus of the Si-containing particles having a relatively low hardness is set to 1, as the Si-containing particles having a relatively high hardness.

14. The production method according to any one of claims 9 to 12, wherein The Si-containing particles having relatively low hardness have a compressive elastic modulus of 250 MPa or more and less than 2000 MPa.

15. The production method according to any one of claims 9 to 12, wherein The Si-containing particles having relatively high hardness have a compressive elastic modulus of 2000 MPa to 5000 MPa.

16. The production method according to any one of claims 9 to 12, wherein The negative electrode active material layer further contains graphite particles as the negative electrode active material.

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