Negative electrode precursor, negative electrode precursor laminate, negative electrode structure, secondary battery, and method for manufacturing negative electrode precursor

Abstract

A negative electrode precursor for manufacturing a negative electrode having a high utilization rate of a negative electrode active material. A negative electrode precursor to be applied to manufacturing of a negative electrode for a secondary battery, the negative electrode precursor comprising a resin substrate and a particle layer held by the resin substrate, wherein the particle layer includes first particles containing a carbon allotrope and exhibiting conductivity, and second particles containing a material capable of alloying with lithium, and an arrangement of at least one of the first particles and the second particles has a pattern structure having periodicity in a predetermined direction within the particle layer.

Description

Negative electrode precursor, negative electrode precursor laminate, negative electrode structure, secondary battery, and method for manufacturing negative electrode precursor

[0001] This disclosure relates to a negative electrode precursor, a negative electrode precursor stack, a negative electrode structure, a secondary battery, and a method for manufacturing a negative electrode precursor.

[0002] Generally, rechargeable batteries consist of electrodes (positive and negative electrodes) and an electrolyte, and charging and discharging occur through the movement of ions between the electrodes via the electrolyte. Such rechargeable batteries are used in a wide range of applications, from small devices such as mobile phones to large devices such as electric vehicles.

[0003] Particles containing conductive carbon allotropes such as graphite are commonly used as negative electrode active materials in secondary batteries, and capacities close to the theoretical capacity have already been achieved. To further increase the negative electrode capacity, silicon materials, which have a theoretical capacity about 10 times larger than graphite, are attracting attention. However, silicon materials undergo large volume changes due to the insertion and removal of Li, which limits the lifespan and utilization rate of secondary batteries. Therefore, composite negative electrodes mixing graphite and silicon are being investigated. Patent document 1 discloses a negative electrode in which the silicon content on the current collector side is increased by applying slurries with different silicon concentrations during manufacturing twice. By increasing the silicon concentration on the current collector side, it is possible to maintain a high capacity while reducing the discharge load of the graphite / silicon composite negative electrode. On the other hand, Patent document 2 discloses a method for manufacturing electrodes by arranging active material particles in a pattern on a resin substrate.

[0004] International Publication No. 2016 / 035289, Japanese Patent Publication No. 2019-137061

[0005] However, according to the inventors' research, the method described in Patent Document 1 is based on the premise of using a liquid electrolyte, and the method of permeating the electrolyte by creating a gap during negative electrode molding is difficult to apply to solid-state batteries because it increases interfacial resistance. Furthermore, when using a graphite negative electrode in a solid-state battery, the interface with the current collector and solid electrolyte may not be sufficiently formed. Therefore, if the graphite is molded thickly to increase the capacity of the negative electrode, the utilization rate may not be sufficient. Also, when using a composite negative electrode of silicon and graphite, the volume change of silicon due to Li insertion and removal is large, so it is necessary to lower the Si particle addition rate or control the utilization rate to a lower capacity than the theoretical capacity. On the other hand, Patent Document 2 shows that it is possible to operate as an all-solid-state battery by controlling the arrangement of the positive electrode active material, but Patent Document 2 does not disclose specific applications to the negative electrode or the effects of particle arrangement. This disclosure relates to a negative electrode precursor for manufacturing a negative electrode with a high utilization rate of the negative electrode active material. This disclosure also relates to a negative electrode precursor laminate, a negative electrode structure, and a secondary battery using the above negative electrode precursor. Furthermore, this disclosure relates to a method for producing the above-mentioned negative electrode precursor.

[0006] At least one aspect of the present disclosure relates to a negative electrode precursor applied to the manufacture of a negative electrode of a secondary battery, the negative electrode precursor comprising a resin substrate and a particle layer held on the resin substrate, the particle layer comprising: first particles containing an allotrope of carbon and exhibiting conductivity; and second particles containing a material that alloys with lithium, wherein the arrangement of at least one of the first particles and the second particles has a pattern structure having periodicity in a predetermined direction within the particle layer.

[0007] Furthermore, at least one aspect of the present disclosure relates to a negative electrode structure for use in a secondary battery, wherein the negative electrode structure contains a particle layer, the particle layer comprises a first particle containing an allotrope of carbon and exhibiting conductivity, and a second particle containing a material that alloys with lithium, and the arrangement of at least one of the first particle and the second particle has a pattern structure having periodicity in a predetermined direction within the particle layer.

[0008] Furthermore, at least one aspect of the present disclosure relates to a method for manufacturing a negative electrode precursor applied to a secondary battery, the manufacturing method comprising: a preparation step of preparing a resin substrate having an adhesive portion; a first step of arranging first particles containing an allotrope of carbon and exhibiting conductivity in a pattern on the surface of the adhesive portion; and a second step of arranging second particles containing a material that alloys with lithium in a region of the surface of the adhesive portion where the first particles are not arranged, wherein the pattern arrangement has a pattern structure having periodicity in a predetermined direction.

[0009] This disclosure provides a negative electrode precursor for manufacturing a negative electrode having a high utilization rate of the negative electrode active material. Furthermore, this disclosure provides a negative electrode precursor laminate, a negative electrode structure, and a secondary battery using the negative electrode precursor. In addition, this disclosure provides a method for manufacturing the negative electrode precursor.

[0010] Figure 1 is a schematic diagram of the negative electrode precursor. Figure 2 is a diagram showing the manufacturing method of the negative electrode precursor. Figure 3 is a schematic diagram showing the configuration of the particle arrangement apparatus. Figure 4 is a schematic diagram of the negative electrode precursor stack. Figure 5 is a schematic diagram of the negative electrode structure. Figure 6 is a diagram showing the manufacturing method of the negative electrode structure. Figure 7 is a schematic diagram of the secondary battery. Figure 8 is the TG-DTA measurement result of the negative electrode precursor. Figure 9 is an SEM-EDX image of the surface of the negative electrode precursor (photograph used as a substitute for drawing). Figure 10 is an SEM-EDX image of the cross-section of the negative electrode precursor (photograph used as a substitute for drawing). Figure 11 is the FFT power spectrum of the surface of the negative electrode precursor (photograph used as a substitute for drawing). Figure 12 is the initial charge-discharge curve. Figure 13 is a diagram showing the rate characteristics. Figure 14 shows the XRD measurement results. Figure 15 shows the cycle test results. Figure 16 is a schematic diagram showing the effect of pattern arranging graphite and silicon particles. Figure 17 is a schematic diagram of negative electrode precursor 1 and negative electrode precursor 3. Figure 18 is a schematic diagram of the evaluated half-cell.

[0011] In this disclosure, the expressions "XX or greater and YY or less" and "XX to YY" that represent numerical ranges mean numerical ranges that include the lower and upper limits, which are the endpoints, unless otherwise specified. When numerical ranges are described in steps, any combination of the upper and lower limits of each numerical range is also disclosed.

[0012] Furthermore, in this disclosure, a statement such as "at least one selected from the group consisting of XX, YY, and ZZ" means any of the following: XX, YY, ZZ, a combination of XX and YY, a combination of XX and ZZ, a combination of YY and ZZ, or a combination of XX, YY, and ZZ. Note that if XX is a group, multiple elements may be selected from XX, and the same applies to YY and ZZ.

[0013] The inventors of this invention recognized that, as described above, there is a problem with the utilization rate of the active material in a composite negative electrode comprising particles containing conductive carbon allotropes such as graphite and particles containing materials that alloy with lithium such as silicon. In particular, in solid-state batteries, the interface is due to contact between solids, which increases interfacial resistance and reduces the efficiency of Li ions and electron transfer.

[0014] The inventors investigated manufacturing a negative electrode by randomly arranging first particles containing an allotrope of carbon, such as graphite, which exhibits conductivity, and second particles containing a material that alloys with lithium, such as silicon. Specifically, they investigated manufacturing a negative electrode by randomly arranging graphite particles and silicon particles, but a sufficient utilization rate of the negative electrode active material could not be obtained. Graphite and other particles have a flattened shape, and Li ions penetrate and are retained from the edge side. However, the basal surface side tends to come into contact more often with the solid electrolyte and current collector through which Li ions and electrons pass during the pressurization process when forming the battery. Therefore, it is thought that effective exchange of ions and electrons becomes difficult when graphite and silicon particles are randomly arranged. A schematic diagram of this is shown in Figure 16. Furthermore, due to volume fluctuations associated with charging and discharging, silicon particles may develop gaps between adjacent particles, resulting in a reduced contact interface.

[0015] To solve the above problems, the inventors investigated the arrangement of a first particle containing an allotrope of carbon and exhibiting conductivity, and a second particle containing a material that alloys with lithium, within the particle layer of the negative electrode precursor. The inventors found that by arranging at least one of the first and second particles to have a periodic pattern structure, the utilization rate is improved and the above problems can be solved. The inventors believe the reason for this is as follows.

[0016] The following explanation uses graphite particles as the first particles, which contain allotropes of carbon and exhibit conductivity, and silicon particles as the second particles, which contain a material that alloys with lithium, as examples. Because at least one of the graphite particles and silicon particles has a periodic pattern structure, unlike in the case of random arrangement, the graphite particles can be adjacent to the silicon particles. Unlike graphite particles, silicon particles are not restricted in the direction in which Li ions and electrons intercalate. Therefore, it is thought that ion conduction paths are more easily formed from adjacent silicon particles to the edge surface of graphite particles, and the utilization rate of graphite is improved.

[0017] Furthermore, since silicon particles are surrounded by highly flexible graphite particles, gaps caused by volume changes in the silicon particles themselves can be reduced, thereby improving utilization. In addition, by arranging particles with a periodic pattern structure, it is possible to construct ion and electron conduction paths not only in the plane but also three-dimensionally. Based on the above mechanism, it is believed that arranging particles with a periodic pattern structure significantly improves utilization.

[0018] <Negative Electrode Precursor> Figure 1 shows a schematic diagram of a negative electrode precursor 1 applied to the manufacture of a negative electrode for a secondary battery. The negative electrode precursor 1 has a resin substrate 5 and a particle layer 31 held on the resin substrate 5. The particle layer 31 includes at least a first particle 2 containing an allotrope of carbon and exhibiting conductivity, and a second particle 3 containing a material that alloys with lithium. The first particle 2 and the second particle 3 are held on the resin substrate 5, for example, via an adhesive layer 4 acting as an adhesive portion.

[0019] Furthermore, at least one of the first particles and the second particles is arranged to have a pattern structure with periodicity in a predetermined direction within the particle layer. In Figure 1, the double-headed arrow X indicates the lamination direction of the resin substrate and the particle layer. The predetermined direction within the particle layer may be a direction perpendicular to the lamination direction, that is, a direction along the surface on which the particle layer is laminated in the resin substrate. The particle layer in the negative electrode precursor may consist of multiple layers, but is preferably a single layer.

[0020] (First particles containing allotropes of carbon and exhibiting conductivity) The first particles containing allotropes of carbon and exhibiting conductivity (hereinafter also referred to as "carbon material particles") are not particularly limited and known particles can be used. The carbon material particles are flattened in shape. Examples of carbon material particles include at least one selected from the group consisting of natural graphite, artificial graphite, mesophase carbon microspheres, non-graphitizable carbon, easily graphitizable carbon, cokes, graphites, glassy carbons, calcined organic polymer compounds, carbon fibers, activated carbon, carbon black, hard carbon, soft carbon, carbon nanotubes, carbon nanofibers, carbon nanohorns, graphene, and highly oriented pyrolysis graphite (HOPG).

[0021] The carbon material particles are preferably particles that include at least one selected from the group consisting of natural graphite, artificial graphite, mesophase carbon microspheres, hard carbon, soft carbon, carbon nanotubes, and carbon nanofibers. From the viewpoint of conductivity and cost, the carbon material particles are preferably at least one selected from the group consisting of artificial graphite and natural graphite, and more preferably artificial graphite.

[0022] The carbon material particle content is, for example, 50 to 99.9% by mass, preferably 50 to 90% by mass, more preferably 50 to 80% by mass, and even more preferably 50 to 70% by mass, based on the particles contained in the particle layer (for example, the total of particles containing conductive carbon allotropes and particles containing materials that alloy with lithium).

[0023] (Second particles containing a material alloying with lithium) The particle layer of the negative electrode precursor contains second particles containing a material alloying with lithium. Examples of the material alloying with lithium include materials used as negative electrode active materials. The second particles containing a material alloying with lithium are, for example, particles containing at least one selected from the group consisting of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, Ra, Ti, Ag, Zn, Cd, Al, Ga, In, Si, Ge, Sn, Pb, Sb, Bi, Au, and V.

[0024] The second particles containing a material alloying with lithium are preferably particles containing at least one selected from the group consisting of Ag, Al, Au, Ge, Sb, Si, Sn, Ti, V, and Zn. Only one type of negative electrode active material may be used, or two or more types may be used in combination. Among the materials capable of alloying with lithium, the second particles containing a material alloying with lithium are preferably particles containing Si, and particularly preferably particles of a silicon-based material containing Si.

[0025] Examples of the silicon-based material include Si, SiB ４ , SiB ６ , Mg ２ Si, Ni ２ Si, TiSi ２ , MoSi ２ , CoSi ２ , NiSi ２ , CaSi ２ , CrSi ２ , Cu ５ Si, FeSi ２ , MnSi ２ , NbSi ２ , TaSi ２ , VSi ２ , WSi ２ , ZnSi ２ , SiC, Si ３ N ４ , Si ２ N ２ O, SiO, SiO ２ , SnSiO ３ , LiSiO. The second particles containing a material alloying with lithium are particularly preferably Si particles.

[0026] These particles preferably have a particle size of 10 μm or less in order to minimize volume changes associated with the insertion and removal of Li. Furthermore, from the viewpoint of handling, a particle size of 10 nm or more is preferable. Specifically, the volume-based median diameter (D50) of the second particle containing the material to be alloyed with lithium is preferably 10 nm to 10 μm, more preferably 50 nm to 8 μm, even more preferably 100 nm to 7 μm, and even more preferably 1 to 5 μm.

[0027] The content of the second particles containing the material that alloys with lithium is, for example, 0.1 to 50% by mass, preferably 1.0 to 50% by mass, more preferably 10 to 50% by mass, even more preferably 20 to 50% by mass, and even more preferably 30 to 50% by mass, based on the total amount of particles in the particle layer (for example, the first particles containing an allotrope of carbon and exhibiting conductivity, and the second particles containing the material that alloys with lithium).

[0028] When the content is 1.0% by mass or more, the effect of improving the utilization rate is more easily obtained. When the content is 50% by mass or less, the volume change of the negative electrode active material during charging and discharging is small and easy to control, and the effect of improving the utilization rate is more easily obtained.

[0029] (Other materials) Other materials used for the negative electrode may include solid electrolytes, conductive materials, etc., to the extent that they do not impair the effects of the present disclosure.

[0030] (Resin Substrate) One example of a method for arranging particles on a resin substrate is the method described in Japanese Patent Publication No. 2019-137061, which involves arranging particles on a resin substrate. The resin substrate used in this case is a substrate containing resin. By using a substrate made of organic material such as resin, it is possible to easily remove the substrate by heating in the manufacturing process of the electrode substrate described later. Details of the method for arranging carbon material particles on a resin substrate will be described later.

[0031] The resin included in the resin substrate material is not particularly limited, but for example, polyesters such as polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET), as well as polyamides such as nylon, can be used. Among these, PET is preferred from the viewpoint of decomposition temperature and the low toxicity of gases generated during thermal decomposition. The thickness of the resin substrate is, for example, 0.1 to 1000 μm, and preferably 1 to 100 μm.

[0032] (Arrangement of first particles containing carbon allotropes and exhibiting conductivity, and second particles containing a material that alloys with lithium) The arrangement of the first and second particles in the negative electrode precursor and negative electrode structure forms a pattern structure having periodicity in a predetermined direction within the particle layer. A periodic pattern structure refers to a pattern in which the same particle arrangement is repeated at regular intervals or periods.

[0033] Specifically, SEM-EDX images of the carbon component of the particle layer or SEM-EDX images of the material component alloyed with lithium are acquired. The acquired images are binarized and then subjected to a two-dimensional Fourier transform to obtain an FFT power spectrum. When peak detection processing is performed on the obtained FFT power spectrum, if there is at least one peak other than the origin, it is determined that there is a periodic pattern structure.

[0034] The predetermined direction within the particle layer is a predetermined direction in a plane parallel to the layer of the particle layer. The predetermined direction may be the lamination direction of the resin substrate and the particle layer, or it may be a direction perpendicular to the lamination direction of the resin substrate and the particle layer. Furthermore, the predetermined direction may be an oblique direction, such as the diagonal direction of the particle layer. This is because if a pattern structure is formed in the predetermined direction within the particle layer, carbon material particles and particles containing materials that alloy with lithium are more likely to be adjacent to each other, ion conduction paths are more easily formed, and the above-mentioned effect of improving utilization rate is obtained.

[0035] In the negative electrode precursor, it is preferable that a predetermined direction within the particle layer is perpendicular to the lamination direction of the resin substrate and the particle layer. Therefore, in the SEM-EDX image of the carbon component observed from the lamination direction on the outer surface of the particle layer of the negative electrode precursor, it is preferable that the carbon material particles have a periodic pattern structure. Furthermore, in the SEM-EDX image of the material component alloyed with lithium observed from the lamination direction on the outer surface of the particle layer of the negative electrode precursor, it is preferable that the second particles have a periodic pattern structure.

[0036] It is preferable that the arrangement of the first particles and the arrangement of the second particles each have a pattern structure having periodicity in a predetermined direction within the particle layer. That is, it is preferable that the first particles and the second particles form a pattern structure in the particle layer. Furthermore, let cross-section A be the cross section obtained by cutting the negative electrode precursor in the stacking direction. Let cross-section B be the cross section obtained by cutting the negative electrode precursor in the stacking direction, with the cutting direction changed by 90° from that of cross-section A. In the SEM-EDX images observed of cross-sections A and B, it is preferable that the first particles and / or the second particles have a pattern structure having periodicity in at least one (preferably both) of cross-sections A and B.

[0037] In the negative electrode structure described later, the predetermined direction within the particle layer is not particularly limited. The predetermined direction within the particle layer is a predetermined direction in a plane parallel to the layers of the particle layer. The predetermined direction may be, for example, the stacking direction of the particle layer, a direction perpendicular to the stacking direction of the particle layer, or an oblique direction within the particle layer, such as the diagonal direction of the particle layer.

[0038] From the viewpoint of efficiently forming ion conduction and electron conduction paths at the contact points with the current collector and solid electrolyte layer that are in contact with the negative electrode structure, it is preferable that a predetermined direction within the particle layer of the negative electrode structure is perpendicular to the stacking direction of the particle layer. Therefore, it is preferable that the carbon material particles have a periodic pattern structure in the SEM-EDX image of the carbon component observed from the stacking direction on the outer surface of the particle layer of the negative electrode structure. Furthermore, it is preferable that the second particles have a periodic pattern structure in the SEM-EDX image of the material component alloyed with lithium observed from the stacking direction on the outer surface of the particle layer of the negative electrode structure.

[0039] In the negative electrode structure, it is preferable that the arrangement of the first particles and the arrangement of the second particles each have a pattern structure having periodicity in a predetermined direction within the particle layer. Furthermore, the cross section obtained by cutting the negative electrode structure in the stacking direction is defined as cross section A. The cross section obtained by cutting the negative electrode structure in the stacking direction with the cutting direction changed by 90° from the cutting direction of cross section A is defined as cross section B. In the SEM-EDX images observed of cross sections A and B, it is preferable that at least one (preferably both) of cross sections A and B has a pattern structure in which the first particles and / or the second particles have periodicity.

[0040] By arranging particles in a periodic pattern structure, it becomes possible to efficiently construct ion and electron conduction paths for the arranged particles, thereby improving the utilization rate of the electrode active material. Furthermore, by using a periodic pattern, even when stacking negative electrode precursors to obtain a negative electrode structure or negative electrode, ion and electron conduction paths can be formed between the upper and lower layers of the particle layer. In other words, unused particles can be eliminated throughout the entire three-dimensional structure of the negative electrode, and efficient conduction paths can be constructed.

[0041] Examples of such periodic pattern structures include one-dimensional grid (line) patterns, zigzag patterns, two-dimensional grid patterns, staggered patterns, sea-island patterns, honeycomb patterns, and the like. The periodic pattern structure preferably includes at least one of the following: one-dimensional grid (line) patterns, two-dimensional grid patterns, staggered patterns, and sea-island patterns including hole patterns. It is more preferably a one-dimensional grid (line) pattern, a two-dimensional grid pattern, a staggered pattern, or a sea-island pattern. Particularly preferred are one-dimensional grid (line) patterns or hole patterns. A hole pattern refers to a sea-island pattern in which the island portions are circular.

[0042] The pattern shape is preferably determined so that ion conduction and electron conduction paths can be connected to each particle, and further preferably so that the paths can properly contact each other when stacked. Moreover, it is preferable that the pattern allows paths to connect even without sufficient alignment during stacking. For example, in a line pattern, changing the angle at which the upper and lower layers are attached will always create a point where the lines meet, thus connecting the paths. Another example is a configuration in which the orientation of the pattern structure of adjacent layers differs by 90° in multiple particle layers. In a sea-island pattern as well, by appropriately designing the area ratio of the island portions, the island portions can always be made to contact each other vertically.

[0043] When peak detection processing is performed on the FFT power spectrum, examples of peaks in each pattern are shown below. In a one-dimensional grid (line) pattern, if the vertical lines are equally spaced with a width of 10 μm, for example, in the direction of an angle of 0° from the wavenumber (0,0), the horizontal component of wavenumber 10 μm... －１ A peak is observed at the position indicated. However, if there is some variation in the line pattern width, for example, if the variation is ±2 μm, then the range is 8 to 12 μm. －１ , and the multiple components are 16-24 μm －１ In some cases, two or more peaks may be observed with a periodicity such as the above.

[0044] Furthermore, if the image is acquired with the above line pattern tilted at 45°, the power spectrum will, for example, have a horizontal and vertical component at a wavenumber of 10 μm in the direction of a 45° angle relative to the wavenumber (0,0). －１ A peak is observed at this position.

[0045] In the case of a two-dimensional grid pattern consisting of equally spaced vertical lines with a width of 10 μm and equally spaced horizontal lines with a width of 5 μm, for example, the horizontal component wavenumber is 10 μm in the directions of angles 0°, 30°, and 90° relative to the wavenumber (0,0). －１ , 10 μm －１ , 0 μm －１ , wavenumber of the vertical component 0 μm －１ , 5 μm －１ , 5 μm －１ A peak is observed at the position indicated by ,.

[0046] In a hole pattern where a circle with a diameter of 10 μm is considered an island, and the origins of three adjacent circles form an equilateral triangle with side lengths of 12 μm, for example, the horizontal component wavenumbers at angles of 0°, 45°, and 90° relative to the wavenumber (0,0) are each 21 μm. －１ , 12 μm －１ , 0 μm －１ The wavenumber of the vertical component is 0 μm. －１ , 12 μm －１ , 21 μm －１ A peak is observed at the position indicated by ,.

[0047] The period of the periodic pattern structure is, for example, 0.05 μm to 50 μm, preferably 1 to 20 μm, and more preferably 5 to 15 μm. The period of the pattern structure corresponds to the -1 power of the wavenumber of the horizontal or vertical component relative to the peak when peak detection processing is performed on the FFT power spectrum.

[0048] The periodicity of the pattern structure is preferably determined by the particle size of the carbon isotope particles used, and is preferably 1 to 5 times the volume-based median diameter D50. When the periodicity of the pattern structure is 1 or more times the volume-based median diameter D50, the particles can be sufficiently packed, making it easier to improve the negative electrode capacity. When the periodicity of the pattern structure is 5 or less, it becomes easier to construct ion conduction and electron conduction paths in each particle, making it easier to obtain the effect of improving utilization efficiency.

[0049] <Method for Manufacturing a Negative Electrode Precursor> An example of a method for manufacturing a negative electrode precursor will be described in detail below with reference to the drawings. The method for manufacturing a negative electrode precursor includes, for example, the following steps: (1) A preparation step of preparing a resin substrate having an adhesive portion. (2) A first step of arranging particles P1 in a pattern on the surface of the adhesive portion (S101 in Figure 2). (3) A second step of arranging particles P2 in areas on the surface of the adhesive portion where particles P1 are not arranged (S102 in Figure 2).

[0050] Particle P1 and particle P2 are two particles, one of which is a first particle containing an allotrope of carbon and exhibiting conductivity, and the other is a second particle containing a material that alloys with lithium. Particle P1 may be the first particle containing an allotrope of carbon and exhibiting conductivity, or particle P2 may be the first particle containing an allotrope of carbon and exhibiting conductivity. Preferably, particle P1 is the first particle containing an allotrope of carbon and exhibiting conductivity, and particle P2 is the second particle containing a material that alloys with lithium.

[0051] In other words, the method for producing a negative electrode precursor preferably comprises: a preparation step of preparing a resin substrate having an adhesive portion; a first step of arranging first particles containing an allotrope of carbon and exhibiting conductivity in a pattern on the surface of the adhesive portion; and a second step of arranging second particles containing a material that alloys with lithium in areas on the surface of the adhesive portion where the first particles are not arranged.

[0052] (Preparation Step) As a preparation step, a resin substrate equipped with an adhesive portion is prepared. In this disclosure, "equipped with an adhesive portion" means that an adhesive portion is provided on part or all of the surface of the resin substrate. As the resin substrate, a substrate containing the above-mentioned resin can be used. The method of providing the adhesive portion is not particularly limited, but a method of applying an adhesive to the surface of the resin substrate is preferred. That is, the transfer member may contain an adhesive, or it may contain a substrate having an adhesive portion. For example, the adhesive portion may be an adhesive layer. An adhesive tape may be used as the resin substrate equipped with an adhesive portion.

[0053] The adhesive is not particularly limited, and known adhesives can be used. Examples of adhesives include acrylic adhesives, urethane adhesives, rubber adhesives, silicone adhesives, thermoplastic resins whose adhesive strength changes due to external disturbances such as heat and light, and photocurable resins.

[0054] (First and Second Steps) The first step is to arrange particles P1 in a pattern on the surface of the adhesive portion of the resin substrate. The second step is to arrange particles P2 on the surface of the adhesive portion of the resin substrate where particles P1 are not present. In Figure 2, the second step (S102) is shown following the first step (S101), but the order of the first and second steps is not particularly limited. That is, the step of arranging particles P2 on the surface of the adhesive portion may be performed first, followed by the step of arranging particles P1.

[0055] Particle P1 is a first particle that contains an allotrope of carbon, such as graphite particles, and exhibits conductivity. Particle P2 is a second particle that contains a material that alloys with lithium, for example. In other words, in the method for producing the negative electrode precursor, the first and second steps can also be rephrased as steps for arranging the first and second particles on the surface of the adhesive portion.

[0056] The particle size of the primary particles of particle P1 is not particularly limited, but for example, the cumulative 50% particle size in the volume-based particle size distribution is preferably 0.01 to 10.0 μm, more preferably 0.05 to 7.0 μm, and even more preferably 1.0 to 7.0 μm.

[0057] The particle size of the primary particles of particle P2 is not particularly limited. For example, the cumulative 50% particle size in the volume-based particle size distribution of primary particles of particle P2 is preferably 0.01 to 10.0 μm, more preferably 0.05 to 7.0 μm, and even more preferably 1.0 to 7.0 μm.

[0058] The ratio (P1:P2) of the primary particle size of particle P1 to the primary particle size of particle P2 is not particularly limited. The ratio (P1:P2) is, for example, 1:2 to 2:1.

[0059] Particles P1 and P2 may be interchangeable, or the same particles may be used. That is, particle P1 may be a second particle containing a material that alloys with lithium, and particle P2 may be a first particle containing an allotrope of carbon and exhibiting conductivity.

[0060] In addition, additional steps may be added between each process. Examples include a step of adding a third particle P3 and a step of rubbing the particles. Examples of the third particle P3 include graphite particles, other active material particles, and solid electrolyte particles. Preferably, of the particles contained in the particle layer, for example, 50 to 100% by mass, 80 to 100% by mass, and 90 to 100% by mass are first particles containing an allotrope of carbon and exhibiting conductivity, and second particles containing a material that alloys with lithium.

[0061] Figure 3 is a schematic diagram showing the configuration of a particle placement apparatus for arranging particles on a resin substrate. For example, electrophotography can be used for the particle placement apparatus. The particle placement apparatus includes a first storage container 21a for storing and supplying a first substrate 11a, a first belt device 22a for transporting the first substrate 11a, and a pattern forming device 23 for forming an uneven pattern on the first substrate 11a. The first belt device 22a drives a belt 224a with rollers 222a.

[0062] As the first substrate a, a substrate containing the resin described above can be used. As a method for forming the uneven pattern in the pattern forming apparatus 23, a UV imprint method, a thermal imprint method, a UV inkjet method, a printing method, a laser etching method, etc., can be used. Alternatively, a substrate with an uneven pattern already formed on its surface may be used as the first substrate 11a. The uneven pattern can be selected from the periodic pattern structures described above. Recesses can be formed so that particles P1 are filled into the periodic pattern structures described above.

[0063] The particle placement apparatus includes a first filling device 24a that places particles P1 into the recesses of an uneven pattern formed on a first substrate 11a. The filling device 24a is a device that fills the recesses with particles P1 by rubbing magnetic particles, on which particles P1 are supported on the surface, on the substrate 11a using magnetic force. By making the particle size of the magnetic particles used at this time larger than the period of the uneven pattern formed on the substrate 11a, only the particles to be placed are filled into the recesses.

[0064] The particle placement device includes a second storage container 21b for storing and supplying a second substrate 11b, and a second belt device 22b for transporting the second substrate 11b. The second belt device 22b drives a belt 224b with rollers 222b. As the second substrate b, the resin substrate having the adhesive portion described above can be used. The particle placement device has a transfer section 25a where rollers 223a and 223b, respectively, of the first belt device 22a and the second belt device 22b face each other.

[0065] After the particles P1 are placed in the recesses of the uneven pattern, the substrate 11a is transported to the transfer section 25a by the first belt device 22a. In the transfer section 25a, the particles P1 are transferred from the first substrate 11a to the second substrate 11b. As a result, the particles P1 are arranged in a pattern on the surface of the adhesive section.

[0066] Furthermore, the particle placement device includes a second filling device 24b that places particles P2 on the surface of the adhesive portion on the second substrate 11b in areas where particles P1 have not been transferred. After the particles P1 have been transferred to the second substrate 11b, the second substrate 11b is transported to the second filling device 24b by a second belt device 22b.

[0067] The filling device 24b also fills particles P2 using the same mechanism as the filling device 24a. Since particles P1 are already arranged in a pattern on the surface of the adhesive portion, particles P2 will be placed in areas of the surface of the adhesive portion where particles P1 are not present. Furthermore, because particles P1 are arranged in a pattern, particles P2 can also be arranged in a pattern. Note that devices that are not relevant to explaining the effects of this disclosure, such as a peeling and recovery device for peeling and recovering the substrate 11a after transfer from the first belt device 22a and various cleaning devices, are not shown in illustration or detailed description.

[0068] In the particle placement apparatus, the pattern forming apparatus 23, the first filling apparatus 24a, and the transfer section 25a correspond to the first placement means for arranging particles P1 in a pattern on the first substrate 11a. The second filling apparatus 24b corresponds to the second placement means for arranging particles P2 in areas on the second substrate 11b where particles P1 are not present. Through these steps, a negative electrode precursor having a particle layer 31 is manufactured.

[0069] <Negative Electrode Precursor Laminate> A schematic diagram of the negative electrode precursor laminate 7 is shown in Figure 4. The negative electrode precursor laminate 7 is made up of stacked negative electrode precursors 1. For example, the negative electrode precursor laminate 7 can be obtained by stacking the aforementioned negative electrode precursors 1 on a substrate 6. In this case, examples of substrates that can be used include current collector metal, solid electrolyte layer, and transfer substrate.

[0070] When stacking the negative electrode precursors 1, negative electrode precursors with different patterns may be used on the top and bottom, or they may be used in combination with precursors without patterns. Furthermore, negative electrode precursors made of different active materials may be used. In particular, at the solid electrolyte interface and the current collector interface, by arranging the members that form the interfacial bonding layer in the same way as the negative electrode precursors, it is possible to reduce the interfacial resistance when used as a negative electrode. As shown in Figure 4, it is preferable to stack negative electrode precursors 1 having the same pattern structure alternately with the pattern orientation changed by 90°.

[0071] The number of layers of the negative electrode precursor 1 is determined by the amount of active material and electrode area required when it is used as a secondary battery. A number of layers from 1 to about 30 is preferable. One or more layers make it easier to function as a negative electrode. Thirty or fewer layers make it easier to remove the resin substrate during the degreasing process when manufacturing the negative electrode structure.

[0072] When fabricating a negative electrode structure, if a negative electrode precursor has a large number of carbon particles with a low coefficient of thermal expansion arranged by heat treatment, it is preferable to laminate the negative electrode precursor on a transfer substrate with a relatively low coefficient of thermal expansion. This makes it easier to suppress peeling and cracking due to the difference in thermal expansion with the substrate.

[0073] (Current Collector) The current collector can be made of any known material without particular limitations. The current collector is, for example, a metal. Examples of current collectors include aluminum, stainless steel, platinum, gold, copper, copper-nickel, nickel, tungsten, etc. The above metals that can be used as current collectors may also be used as metal foil or mesh.

[0074] (Solid Electrolyte Layer) The solid electrolyte layer is made by solidifying solid electrolyte particles to a thickness that does not cause short circuits. As for the solid electrolyte, any type of solid electrolyte is acceptable, as long as it has electrical insulating properties and ionic conductivity, such as sulfide-based or oxide-based solid electrolytes.

[0075] As a sulfide-based solid electrolyte, Li ７ P ３ S １１ Li ３ PS ４ Li ８ P ２ S ９ Li １３ GeP ３ S １６ Li １０ GeP ２ S １２ These are some examples. Sulfide-based solid electrolytes can be formed into a solid electrolyte layer by cold-pressing the powder to break down the bonding between particles.

[0076] As an oxide-based solid electrolyte, Li is used as a NASCICON type. ２－ｘ Al ｘ Ge ２－ｘ (PO ４ ) ３ (LAGP), Li １＋ｘ Al ｘ Ti ２－ｘ (PO ４ ) ３ Examples include (LATP) and its substituted derivatives. Garnet-type examples include lithium lanthanum zirconate Li ７ La ３ Zr ２ O １２ Examples include , and their substituted derivatives. Perovskite types include La ２／３－ｘ Li ３ｘ TiO ３Examples include (LLTO) and their substituted derivatives. As a boric acid-based example, Li ３ BO ３ (LBO), Li ６－ｘ R １－ｘ M ｘ (BO ３ ) ３ Examples include (where R is Yb, Er, Ho, Tm, La, Nd, or Sm, and M is Zr, Ce, or Sn), and their substituted derivatives.

[0077] The above oxide-based solid electrolyte powder can be formed into pellets by pressurizing them, and a solid electrolyte layer can be obtained by sintering each pellet at a predetermined temperature.

[0078] (Transfer Substrate) In order to remove the resin substrate from the negative electrode precursor by heat treatment, the transfer substrate is preferably made of an inorganic material. The substrate 6 may be a current collector or a solid electrolyte layer.

[0079] Since carbon-based materials generally have a low coefficient of linear thermal expansion, materials with a low coefficient of linear thermal expansion are selected for transfer substrates. Examples of transfer substrates with a low coefficient of linear thermal expansion include metals such as Invar, SuperInvar, 42-Invar, Kovar, tungsten, and platinum, as well as ceramic materials such as silicon, sapphire, diamond, silicon carbide, aluminum nitride, silicon nitride, alumina, yttria, cermet, and cordierite. These materials may be used individually or in combination. For example, foil-like forms of these materials can be used as transfer substrates.

[0080] <Negative Electrode Structure> This disclosure provides a negative electrode structure for use in a secondary battery. The negative electrode structure contains a particle layer, the particle layer comprising particles containing conductive allotropes of carbon and particles containing a material that alloys with lithium, and the arrangement of the conductive allotropes of carbon has a pattern structure having periodicity in a predetermined direction within the particle layer.

[0081] A schematic diagram of the negative electrode structure 8 is shown in Figure 5. It is obtained by removing the resin substrate 5 of the negative electrode precursor 1 from the negative electrode precursor laminate 7 described above. That is, it consists of a particle layer and the substrate 6 described above. When the resin substrate 5 of the negative electrode precursor 1 is removed from the substrate 6, the upper and lower layers come into contact while the particle arrangement remains the same, and ion conduction and electron conduction paths are formed.

[0082] The negative electrode structure has at least one particle layer. There may be multiple particle layers. The number of particle layers can be, for example, 1 to 30, preferably 1 to 20, and more preferably 1 to 10. From the viewpoint of improving utilization, when there are multiple particle layers, it is preferable that, for example, 50 to 100%, preferably 80 to 100%, and more preferably 90 to 100% of the particle layers have a periodic pattern structure. It is particularly preferable that all particle layers have a periodic pattern structure. For example, in the negative electrode precursor and negative electrode structure, it is preferable that the carbon material particles and the particles containing the material to be alloyed with lithium are arranged such that the distance between the carbon material particles and the particles containing the material to be alloyed with lithium is preferably in the range of 0 to 20 μm, more preferably 0 to 10 μm, and even more preferably 0 to 5 μm.

[0083] <Method for Manufacturing a Negative Electrode Structure> An example of a method for manufacturing a negative electrode structure will be described in detail below with reference to the drawings. The negative electrode is formed by laminating negative electrode precursors on a substrate, removing the resin substrate by heat treatment, and obtaining the negative electrode structure. The negative electrode structure may be a fired or sintered product of the negative electrode precursor or the negative electrode precursor laminate. The method for manufacturing the negative electrode structure consists of the following two steps (Step I and Step II).

[0084] (I) A step of laminating a negative electrode precursor onto a current collector, a transfer substrate member, or a solid electrolyte layer to obtain a negative electrode precursor laminate (S201 in Figure 6) (II) A step of removing the resin substrate from the negative electrode precursor laminate by heating to obtain a negative electrode structure (S202 in Figure 6)

[0085] In other words, the negative electrode structure can be manufactured by a manufacturing method that includes the steps of: stacking negative electrode precursors on a substrate or solid electrolyte layer to obtain a negative electrode precursor laminate; and removing the resin substrate contained in the negative electrode precursor from the negative electrode precursor laminate by heating. The details of each step in the manufacturing method of the negative electrode structure will be described below.

[0086] (Step I) Step I is the process of attaching and laminating negative electrode precursors onto a substrate. As for the lamination method, negative electrode precursors cut to a predetermined size may be laminated on the substrate, or they may be cut to a predetermined area after lamination. It is preferable that the negative electrode precursors are laminated alternately with the direction of the pattern changed by 90°. That is, it is preferable that the negative electrode structure has multiple particle layers, and the orientation of the periodic pattern structure in each of the multiple particle layers is 90° different from the orientation of the periodic pattern structure in the adjacent particle layer (Figure 5).

[0087] Subsequently, the process may include steps to improve the adhesion between the substrate and the negative electrode precursor. Specifically, this may include heating and pressurizing processes. Heating and pressurizing may be performed independently or simultaneously. The heating temperature is preferably between 30°C and 200°C, depending on the type of resin component. The pressurizing pressure is preferably between 5 MPa and 500 MPa. The pressurizing method is preferably such that the pressure is applied evenly to the entire negative electrode precursor. In particular, isotropic pressurization is preferred to prevent particle movement and disruption of the arrangement due to pressurization.

[0088] (Step II) Step II is a step of heat-treating the negative electrode precursor laminated on the substrate. Step II is a step of degreasing at least a portion of the resin in the negative electrode precursor by heat treatment. As a means of heating, a firing furnace used for firing ceramics and the like can be used. It may also be combined with a means of pressurization. As a means of pressurization, it is sufficient to simply place a metal plate or a ceramic plate on top of the carbon-containing layer, but a hot press machine or the like may also be used. As the atmospheric gas for Step II, an oxidizing atmosphere (O ２ ), inert atmosphere (Ar, N ２ (etc.) and reducing atmosphere (Ar-H ２) can be used, but sintering may also be carried out in the atmosphere.

[0089] In a heat treatment apparatus, it is preferable to exhaust the released gas to the outside of the heating furnace using a depressurization means. By maintaining an oxidizing atmosphere inside the heating furnace, i.e., an atmosphere containing oxygen gas such as air, using an atmospheric gas supply means, the resin substrate can be burned and removed. On the other hand, depending on the active material particles or solid electrolyte particles used, heating in an oxidizing atmosphere may cause decomposition or compositional changes. In such cases, an inert atmosphere (Ar, N) may be used. ２ (etc.) and reducing atmosphere (Ar-H ２ It is preferable to heat it using ).

[0090] When degreasing the negative electrode precursor or the negative electrode precursor laminate, it is preferable to heat it at a temperature above the thermal decomposition temperature of the substrate having the adhesive portion in the negative electrode precursor, and at a temperature below the thermal decomposition temperature of each particle in the negative electrode precursor. The temperature at which the negative electrode precursor is heated is preferably 200°C to 700°C, more preferably 300°C to 600°C, and even more preferably 400°C to 550°C. It is preferable to maintain the upper limit temperature during heating for 30 minutes or more, and more preferably for 1 hour or more.

[0091] The thermal decomposition temperature is the temperature at which a material begins to lose weight when the temperature is gradually increased under the heating atmosphere in a heat treatment apparatus. Therefore, by heating the negative electrode precursor at a temperature above the thermal decomposition temperature of the base material 5, the base material 5 of the negative electrode precursor can be decomposed, reducing its weight and allowing the resin base material to be removed from the negative electrode precursor.

[0092] The heating temperature is preferably above the thermal decomposition temperature of the substrate 5, and more preferably above the thermal decomposition temperature of the substrate 5. Specifically, it is preferable to heat to a temperature above the temperature at which the initial mass of the substrate 5 becomes 70% by mass when thermogravimetric analysis is performed by raising the temperature from room temperature (25°C) at a rate of 5°C / min under the atmosphere (typically air) during heating in the heat treatment apparatus. Specifically, for example, a temperature of 385°C or higher is preferable.

[0093] Furthermore, when thermogravimetric analysis is performed in a similar manner, it is more preferable to heat the substrate 5 to a temperature above the temperature at which it becomes 50% by mass of the initial mass of the substrate 5, and even more preferable to heat it to a temperature above the temperature at which it becomes 20% by mass of the initial mass of the substrate 5.

[0094] Specifically, the temperature is preferably 400°C or higher, and more preferably 450°C or higher. This makes it possible to shorten the time required to remove the resin substrate and to increase the removal rate of the resin substrate.

[0095] Thus, when removing the substrate 5 by heating with a heat treatment apparatus, it is preferable that the particle layer, active material particles, and solid electrolyte particles in the negative electrode precursor have a higher thermal decomposition temperature than the substrate 5. In other words, it is preferable that the thermal decomposition temperature of the substrate having the adhesive portion is lower than the thermal decomposition temperature of the substrate of the transfer member and the thermal decomposition temperature of the carbon-containing layer.

[0096] For example, the thermal decomposition temperature or melting point of the substrate is usually in the range of 1000°C to 3500°C, and the thermal decomposition temperature of the carbon-containing layer is usually in the range of 600 to 900°C. The thermal decomposition temperature of the resin substrate having an adhesive portion is preferably, for example, 300 to 500°C.

[0097] Generally, inorganic materials tend to have higher thermal decomposition temperatures than organic materials, so it is preferable that the active material particles and solid electrolyte particles are made of inorganic materials. Furthermore, it is preferable that the active material particles have a softening point temperature higher than the thermal decomposition temperature of the base material 5. Through the above-described heat treatment, it is preferable that 50% or more by mass of the resin base material in the carbon-containing layer is removed, more preferably 80% or more by mass, and even more preferably 90% or more by mass.

[0098] Alternatively, the resin component may be heat-treated at a temperature and atmosphere that removes components other than element C, i.e., carbonizes it. In this case, it is preferable that the resin substrate is burned or gasified and released to the outside as a gas. When the resin substrate gasified by thermal decomposition is released as a gas to the outside of the negative electrode precursor laminate, it may push up the particle layer formed on the resin substrate and disrupt its shape. For this reason, it is preferable to reduce the thickness of the resin substrate to reduce the impact on the particle layer.

[0099] Specifically, the thickness (μm) of the resin substrate is preferably 10 times or less the thickness of the particle layer on the resin substrate, more preferably 5 times or less, and even more preferably 2 times or less. Here, the thickness of the particle layer refers to the difference between the maximum and minimum values ​​of z in the region (x, y, z) where each particle on the resin substrate exists, when the planar direction of the resin substrate is (x, y) and the lamination direction of the resin substrate is (z).

[0100] In the negative electrode precursor, the thickness of the resin substrate is preferably 1 μm or more and 1 mm or less. In the negative electrode precursor, the thickness of the particle layer is, for example, 0.1 to 100 μm, preferably 1 to 50 μm, and more preferably 2 to 10 μm.

[0101] The thickness of the particle layer on the resin substrate is calculated by observing the cross-section of the particle layer using a BIB-SEM, determining the region where the particles exist (x, z) using image processing software, and then finding the difference between the maximum and minimum values ​​of z, with the resin substrate surface as x and the layering direction of the resin substrate as z.

[0102] The thickness of the resin substrate may be determined from a BIB-SEM or measured using a digital thickness gauge or the like. Furthermore, in SEM observation using a BIB-SEM, methods for identifying carbon allotrope particles, active material particles, solid electrolyte particles, substrate, and adhesive portion include elemental composition analysis by EDX.

[0103] (Transfer Process) The transfer process is necessary when the negative electrode precursor is laminated on a substrate different from the battery components such as the current collector and solid electrolyte in process I. Since carbon material particles generally have a low coefficient of thermal expansion, when heated on the current collector metal, the particle layer may peel off or crack due to the difference in expansion rates. Therefore, it is possible to form a negative electrode structure by laminating it on a substrate with a low coefficient of thermal expansion, degreasing it, and then transferring it back onto the current collector metal. The transfer process is a process in which the negative electrode laminate on the substrate is sandwiched between the current collector and the negative electrode, and the particle layer of the negative electrode is transferred from the substrate to the current collector metal side or the solid electrolyte layer side by applying pressure.

[0104] The preferred method of pressurization is vacuum degassing, isotropic pressurization, or the use of a general hydraulic press or roller pressurizer. In particular, it is preferable to combine vacuum degassing and isotropic pressurization. The pressurization is preferably performed at 5 MPa to 500 MPa. This allows the particle layer to be transferred from the substrate of the transfer member to the current collector metal side or the solid electrolyte layer side.

[0105] <Secondary Battery> A schematic diagram of the secondary battery 9 is shown in Figure 7. Using the negative electrode structure 8 manufactured above, the package contains a solid electrolyte layer 11, a positive electrode 10, a positive electrode current collector 12, and a negative electrode current collector 13. The secondary battery includes a current collector, a positive electrode, a solid electrolyte layer, and a negative electrode. For example, the secondary battery is stacked in the order of positive electrode current collector 12, positive electrode 10, solid electrolyte layer 11, negative electrode structure 8, and negative electrode current collector 13.

[0106] <Method for Manufacturing a Secondary Battery> The secondary battery 9 can be manufactured by using the negative electrode structure described above as the negative electrode. A positive electrode layer and a solid electrolyte layer necessary for a secondary battery are prepared, and the positive electrode current collector, positive electrode layer, solid electrolyte layer, negative electrode, and negative electrode current collector are stacked in that order, and then vacuum-packed with aluminum laminate film to form a secondary battery.

[0107] When using a sulfide-based solid electrolyte, a stainless steel cell with a structure that can apply a certain confinement pressure can also be used. After compacting the solid electrolyte in the cell, a negative electrode and a positive electrode are placed on both sides of the solid electrolyte layer, and a current collector is placed on each electrode to apply confinement pressure, thereby creating a secondary battery for evaluation. When using a sulfide-based solid electrolyte, it is preferable to perform all assembly operations in a low dew point environment. In particular, it is preferable to perform the operations in a glove box with a dew point adjusted to -70°C or lower, substituted with Ar.

[0108] The positive electrode layer can be obtained by using the particle arrangement apparatus illustrated in Figure 3, arranging the material particles to be used for the positive electrode on a resin substrate, then laminating and degreasing by heating. In this process, the positive electrode layer can be created by using particle P1 as the positive electrode active material and particle P2 as the solid electrolyte particle.

[0109] As the material particles used for the positive electrode, there may be mentioned positive electrode active materials, solid electrolytes, conductive aids, etc. The positive electrode active material particles are not particularly limited, and known ones can be used. For example, composite oxides containing lithium can be used. Specifically, for example, LiCoO ２ and other active material particles of the Li-Co oxide system, LiMO ２ (M is one element selected from the group consisting of Ni, Mn, and Co) and other active material particles, Li-PO ４ oxide-based active material particles, lithium vanadium compounds (Li ３ V ２ (PO ４ ), ３ LiVOPO ４ ), olivine-type phosphate-based compounds (LiMPO ４ (M is one or more elements selected from the group consisting of Co, Ni, Mn, Fe, Mg, V, Nb, Ti, Al, and Zr)), etc.

[0110] As the solid electrolyte particles, there is no particular limitation, and ion-conductive solids usually used in all-solid-state batteries can be used. For example, Li-B oxide-based solid electrolyte particles, Li-Yb oxide-based solid electrolyte particles, NASICON-type solid electrolyte particles (LiAlTi(PO ４ ), ３ LiAlGe(PO ４ ), ３ etc.), perovskite-type oxide-based solid electrolyte particles (Li ｘ La （１－ｘ）／３ TiO ３ , LixLa （１－ｘ）／３ NbO ３ etc.), garnet-type oxide-based solid electrolyte particles (Li ７ La ３ Zr[[ID=A4]] ２ O １２ , etc.), Li-P-O-based solid electrolyte particles (Li ３ PO ４ , LiPON (Li ３ PO ４Examples include particles in which some of the oxygen atoms are replaced with nitrogen atoms. Among the above solid electrolyte particles, Li-B oxide-based solid electrolyte particles and Li-Yb oxide-based solid electrolyte particles can be sintered at relatively low temperatures (below 700°C), thereby suppressing reactions with positive electrode active material particles during sintering and maintaining ionic conductivity. The solid electrolyte particles may be commercially available products or may be prepared separately as materials.

[0111] Examples of Li-B oxide solid electrolyte particles include Li ３ BO ３ Yes, Li ３ BO ３ Particles in which some of the O is replaced with C can be used. In addition, as Li-Yb oxide solid electrolyte particles, for example, the compound described in Japanese Patent Application Publication No. 2022-130301 can be used, for example Li ５．９ Yb ０．８１ La ０．０９ Zr ０．１ (BO ３ ) ３ These can be used. These solid electrolyte particles may be amorphous beforehand by methods such as planetary ball milling.

[0112] The obtained positive electrode substrate can be laminated over the required area onto aluminum foil, which can also be used as a positive electrode current collector, and the resin component can be degreased by heat treatment to obtain the positive electrode layer. Pressurization may be applied between each step as needed.

[0113] As the solid electrolyte layer, the solid electrolyte particles used in the positive electrode can be used. Also, as the sulfide-based solid electrolyte, Li ７ P ３ S １１ Li ３ PS ４ Li ８ P ２ S ９ Li １３ GeP ３ S １６ Li １０ GeP ２ S １２ These are some examples. Sulfide-based solid electrolytes can be formed into a solid electrolyte layer by cold-pressing the powder to break down the bonding between particles.

[0114] The current collector metals described above can be used as current collectors. The secondary battery has a stacked structure consisting of a positive electrode current collector, a positive electrode, a solid electrolyte layer, a negative electrode structure, and a negative electrode current collector in that order. Furthermore, a restraining pressure may be applied as needed. The positive electrode current collector, positive electrode, solid electrolyte layer, negative electrode structure, and negative electrode current collector that constitute the secondary battery are packaged to prevent contact with the outside air.

[0115] The present disclosure will be described in more detail below using examples, but the present disclosure is not limited to these examples. In the following examples, unless otherwise specified, the number of copies is by mass.

[0116] (Preparation of Negative Electrode Precursors 1-3) Negative electrode precursors were molded using the negative electrode precursor manufacturing method described above. Specifically, a particle layer was formed on a resin substrate using the particle layer forming apparatus shown in Figure 3. A first substrate a having an uneven pattern capable of forming the arrangement patterns described in Table 1 was used, and the thickness of the particle layer was set to 5 μm. Table 1 shows the particles P1, P2 and the particle arrangement patterns used in the preparation. The resin substrate used was PET substrate ultra-thin 5 μm double-sided tape No. 5600 (manufactured by Nitto Denko), cut to 72 mm x 72 mm. Schematic diagrams of the prepared negative electrode precursors 1 and 3 are shown in Figure 17.

[0117]

[0118] The line pattern is a pattern formed by alternating lines of particle P1 with a thickness of 7 μm and lines of particle P2 with a thickness of 3 μm. The hole pattern is a pattern in which the centers of three adjacent circles (holes) with a diameter of 7 μm are arranged to form an equilateral triangle with sides of 8 μm. The percentages in Table 1 indicate the area ratio of each pattern constituting the negative electrode precursor to the particle arrangement surface of the negative electrode precursor. In the case of the line pattern, it is the occupancy ratio corresponding to the ratio of line widths, and in the case of the hole pattern, it indicates the area ratio of holes to gaps. The materials in Table 1 are as follows: Graphite: KS-6 (manufactured by TIMREX) Si: Si powder particle size (D50) 5.0 μm (manufactured by Toyoshima Seisakusho)

[0119] (Measurement of carbon particle-silicon particle ratio) To confirm the ratio of carbon particles to Si particles in the fabricated negative electrode precursors 1 and 3, TG-DTA measurement (NEXTA-STA200, Hitachi High-Tech) was performed. The measurement was performed using powder obtained by degreasing the negative electrode precursor on a silicon substrate at 510°C for 1 hour to remove the base resin. The measurement conditions were to heat to 900°C in an air atmosphere at a heating rate of 20°C / min, and then hold the temperature for 10 minutes. The measurement results are shown in Figure 8.

[0120] The Si particle ratio of the negative electrode precursor was determined from the residue after measurement. TG-DTA measurements were also performed on Si particles alone under the same conditions, and the Si particle ratio was calculated after correcting for the weight increase due to oxidation of the Si particles. Similarly, TG-DTA measurements were performed on carbon particles alone, and the disappearance of more than 99.9% of the carbon particles was confirmed. Table 2 shows the ratios of carbon particles and Si particles in negative electrode precursors 1 and 3. As shown in Table 2, it was confirmed that the ratios of carbon particles and Si particles were almost equal in negative electrode precursors 1 and 3.

[0121] The percentages in Table 2 represent mass percentages.

[0122] (Fabrication of Negative Electrode Structure 1) Six layers of the fabricated negative electrode precursor 1 were laminated onto a tungsten foil (50 μm thick, manufactured by Nilaco) in a line pattern, rotating each layer by 90° to obtain a negative electrode precursor laminate 1. The negative electrode precursor laminate 1 was degreased by heating it in a muffle furnace at 510°C for 1 hour. Then, an unpolished SUS304 disc with a diameter of 10 mm and a thickness of 0.5 mm was placed on the degreased laminate 1, and the particle layer was transferred onto the SUS disc by cold isostatic pressing (CIP) to obtain a negative electrode structure 1. The weight of the particles transferred onto the SUS disc was measured and determined to be the weight of the negative electrode active material.

[0123] (Fabrication of negative electrode structure 2) Negative electrode structure 2 was obtained by the same method as negative electrode structure 1, except that negative electrode precursor 2 was used.

[0124] (Fabrication of negative electrode structure 3) The negative electrode structure 3 was obtained by the same method as the negative electrode structure 1, except that the negative electrode precursor 3 was used.

[0125] (SEM-EDX Observation of Negative Electrode Precursor and Negative Electrode Structure) The method for SEM-EDX measurement of the surface and cross-section of the negative electrode precursor and negative electrode structure is described below. Surface observation of the negative electrode precursor and negative electrode structure was performed using a scanning electron microscope (SEM), and the surface of the particle layer was photographed from the stacking direction. The electron microscope used was a Zeiss ULTRA55, and the images were taken under the following conditions. The imaging area was the area in which the particle layer could be observed.

[0126] Detector: ESB (backscattered electron imaging) Observation conditions: Acceleration voltage 3kV Magnification: 500x Filter: 1500V bias applied to the ESB filter Next, elemental and compositional analysis of each particle was performed using SEM-EDX (Bruker XFlash Detector 630M) to distinguish between carbon particles and Si particles contained in the negative electrode. Figure 9 shows observation images of the surfaces of negative electrode precursors 1 to 3. EDX images of C and Si are also shown. In the EDX images of C or Si, the white areas represent the regions where C or Si is present, respectively. In negative electrode precursor 1, a periodic pattern structure can be observed on the surface of the particle layer, where C and Si are alternately arranged in lines. On the other hand, in negative electrode precursor 3, no such pattern is observed, and C and Si are randomly arranged.

[0127] Cross-sectional observation of the negative electrode precursors and negative electrode structures was performed using a BIB-SEM. The BIB-SEM imaging conditions are described below. Negative electrode precursors 1-3 and negative electrode structures 1-3 were each cut with a wire saw (DWS3400 / wire diameter 170 μm, diamond diameter 30 μm). Specifically, the negative electrode precursors or negative electrode structures were cut in the stacking direction so that the particle layer and resin substrate were exposed on the cut surface. Then, the cut surface was processed using a broad ion beam with Ar (JEOL SM-09010 Cross Section Polisher). The conditions for cross-sectional processing were a voltage of 6 kV and a current of 150-200 mA. As a BIB-SEM image, the cross-section in the stacking direction of the particle layer was captured using an electron microscope (ULTRA55) under the following conditions. The imaging area was the area in which the particle layer could be observed.

[0128] Detector: ESB (backscattered electron image) Observation conditions: Acceleration voltage 8kV Magnification: 5000x Filter: 1500V bias applied to the ESB filter Next, elemental and compositional analysis of each particle was performed using SEM-EDX (Bruker XFlash Detector 630M) to identify carbon particles, Si particles, and current collector parts contained in the negative electrode. Figure 10 shows observation images of cross-sections of negative electrode structures 1 and 3. EDX images of C and Si are also shown. In the EDX images of C or Si, the white areas represent the regions where C or Si is present, respectively.

[0129] (Determination of Periodic Pattern Structures) The presence or absence of periodic pattern structures was determined as follows: SEM-EDX images of the carbon components were obtained using the method described above. If peaks were detected when the obtained images were subjected to a two-dimensional Fourier transform, then a periodic structure was present, and the presence of a pattern structure was determined. On the other hand, if no peaks were observed and the image was uniform, the absence of a pattern structure was determined.

[0130] The presence or absence of a periodic pattern structure in the negative electrode precursor and negative electrode structure was determined specifically as follows. The following explanation uses the negative electrode precursor as an example. The SEM-EDX image of carbon in the surface observation image of the negative electrode precursor shown in Figure 9 was used to determine the presence or absence of a pattern structure. Note that to confirm the pattern structure of the second particle, a similar determination can be made using the SEM-EDX image of the material component alloyed with lithium, such as Si. The image size was set to 256 x 200 pixels.

[0131] Image processing of SEM-EDX images of carbon was performed using OpenCV. After converting the images to grayscale, scales and other elements were cut off. The resulting images were normalized to have an average brightness of 100 and a standard deviation of ±35. Next, the images were binarized with a brightness threshold of 125, resulting in images where the carbon portions were represented by black pixels. A two-dimensional Fast Fourier Transform (FFT) was performed on the binarized images to obtain the FFT power spectrum. The obtained FFT power spectrum is shown in Figure 11.

[0132] Next, peak detection processing was performed on the obtained FFT power spectrum. The peak detection process was carried out in the following steps: After applying a 3x3 maximum value filter to the power spectrum, elements other than pixels with the same value as the original image were set to 0, and the peaks were detected. Subsequently, intensity peaks with a value of 50% or less of the maximum peak were removed as noise, and these were used as the final peaks.

[0133] The surface of the negative electrode precursor was evenly divided into 10 sections, and one SEM-EDX image of carbon was obtained from each of the 10 sections, for a total of 10 SEM-EDX images. Peak detection processing was performed on all 10 SEM-EDX images using FFT power spectroscopy. If at least one peak was found in eight or more images other than the origin, it was determined that the measured negative electrode precursor had a periodic pattern structure.

[0134] In comparative example negative electrode precursor 3, no peaks other than the origin were observed, and it was determined that there was no periodic pattern structure. On the other hand, in negative electrode precursor 1 of Example 1, a horizontal component of 12 μm was observed in the direction of 0° angle relative to the wavenumber (0,0). －１ , 23 μm －１ A peak was observed in the region, and it was determined that there was a pattern structure with linear periodicity at approximately 10 μm. In Figure 11, the white arrows indicate peak positions other than the origin (wavenumber (0,0)). In the negative electrode precursor 2 of Example 2, horizontal components of 16 μm were also observed at angles of 0°, 45°, and 90° relative to wavenumber (0,0). －１ Both the horizontal and vertical components are 9 μm. －１ , vertical component 16μm －１ A peak was observed at a specific location, and it was determined that a periodic pattern structure was present.

[0135] (Fabrication of half-cell in Example 1) All assembly operations of the half-cell were performed in a glove box with a dew point of -70°C or lower. A pressurized cell made of SUS was used, and a solid electrolyte material (80Li) was used. ２ S・20P ２ S ５A glass (glass) was pressurized and formed. Then, the current collector SUS304, the negative electrode structure 1, the solid electrolyte layer, the counter electrode In-Li foil, and the current collector SUS304 were arranged in that order to obtain a primary assembly. The obtained primary assembly was screwed together with a torque of 6.0 Nm, thereby applying a restraining pressure of 370 MPa in the stacking direction to obtain the half-cell of Example 1. A schematic diagram is shown in Figure 18. The assembled half-cell was sealed in a sealed container to serve as a measurement cell.

[0136] (Preparation of the comparative example half-cell) The comparative example half-cell was obtained in the same manner as the half-cell of Example 1, except that the negative electrode structure 1 was changed to the negative electrode structure 3.

[0137] (Charge / Discharge Measurement) The following charge / discharge tests were performed using the high-performance electrochemical measurement system VMP300 (manufactured by Bio-Logic). Using the half-cells obtained in Example 1 and Comparative Example, a current value of 10 μA / cm was used until the voltage reached 0.01 V relative to lithium metal. ２ A CC charging test was then performed. After that, the current was set to 10 μA / cm² until the voltage reached 1.20 V (based on lithium metal). ２ A CC discharge test was conducted, and a CC charge-discharge curve was obtained. The initial charge-discharge curve is shown in Figure 12.

[0138] In Example 1, the charging capacity was 1960 mAh / g, which is 96% of the theoretical capacity, while in Comparative Example 1, the charging capacity was 1229 mAh / g, which is 62% of the theoretical capacity. This result indicates that the utilization rate of the negative electrode active material in Example 1 is higher than in Comparative Example 1, in which silicon particles were arranged randomly. The Coulomb efficiency remained unchanged at approximately 86% in both cases.

[0139] Next, the current values ​​were set to 50, 100, and 500 μA / cm². ２ A rate characteristic test was conducted. The results are shown in Figure 13. In both Example 1 and the Comparative Example, it can be seen that as the current value increases, the charging capacity and discharging capacity decrease.

[0140] (XRD measurement) For the half-cells of Example 1 and the Comparative Example, the current value was measured at 100 μA / cm using the electrochemical measurement system described above. ２The battery was charged until the voltage reached 0.01V relative to lithium metal. After charging, the half-battery was disassembled in the glove compartment and the negative electrode portion was removed. The removed negative electrode portion was subjected to XRD measurement using an X-ray diffractometer (MiniFlex, Rigaku Corporation) to evaluate the amount of Li in the carbon material within the negative electrode. The results are shown in Figure 14.

[0141] In the comparative example, LiC ６ LiC １２ While the peaks for C are large, in Example 1, LiC ６ The peak was larger, indicating that a large amount of Li was intercalated within the carbon particles. This also shows that the utilization rate of graphite was improved in Example 1.

[0142] (Cycle Test) The cycle characteristics of the fabricated half-cell were tested using the same cutoff value as in the charge-discharge test, with a current value of 100 μA / cm². ２ The cycle characteristics were measured by repeatedly performing CC charge-discharge measurements. The results are shown in Figure 15. In both Example 1 and the Comparative Example, no significant decrease in efficiency was observed up to 10 cycles, indicating that they were functioning as secondary batteries.

[0143] This disclosure is not limited to the embodiments described above, and various modifications and alterations are possible without departing from the spirit and scope of this disclosure. Accordingly, the following claims are attached to make the scope of this disclosure public. This application claims priority based on Japanese Patent Application No. 2024-201199, filed on 18 November 2024, the entire contents of which are incorporated herein by reference.

Claims

1. A negative electrode precursor applicable to the manufacture of a negative electrode of a secondary battery, wherein the negative electrode precursor comprises a resin substrate and a particle layer held on the resin substrate, the particle layer comprises a first particle containing an allotrope of carbon and exhibiting conductivity, and a second particle containing a material that alloys with lithium, and the arrangement of at least one of the first particle and the second particle has a pattern structure having periodicity in a predetermined direction within the particle layer.

2. The negative electrode precursor according to claim 1, wherein each of the arrangements of the first particles and the arrangement of the second particles has a pattern structure having periodicity in a predetermined direction within the particle layer.

3. The negative electrode precursor according to claim 1 or 2, wherein the first particle is a particle comprising at least one selected from the group consisting of natural graphite, artificial graphite, mesophase carbon microspheres, hard carbon, soft carbon, carbon nanotubes, and carbon nanofibers.

4. The negative electrode precursor according to any one of claims 1 to 3, wherein the second particle is a particle comprising at least one selected from the group consisting of Ag, Al, Au, Ge, Sb, Si, Sn, Ti, V, and Zn.

5. The negative electrode precursor according to any one of claims 1 to 4, wherein the second particle is a Si-containing particle.

6. The negative electrode precursor according to any one of claims 1 to 5, wherein the periodic pattern structure includes at least one of a one-dimensional grid (line) pattern, a two-dimensional grid pattern, a staggered pattern, and a sea-island pattern.

7. The negative electrode precursor according to any one of claims 1 to 6, wherein the period of the periodic pattern structure is 0.05 μm to 50 μm.

8. A negative electrode precursor laminate comprising negative electrode precursors according to any one of claims 1 to 7.

9. A negative electrode structure for use in a secondary battery, wherein the negative electrode structure contains a particle layer, the particle layer comprises a first particle containing an allotrope of carbon and exhibiting conductivity, and a second particle containing a material that alloys with lithium, and the arrangement of at least one of the first particle and the second particle has a pattern structure having periodicity in a predetermined direction within the particle layer.

10. A secondary battery, wherein the secondary battery comprises a current collector, a positive electrode, a solid electrolyte layer, and a negative electrode, and the negative electrode is the negative electrode structure described in claim 9.

11. A method for manufacturing a negative electrode precursor applied to a secondary battery, the manufacturing method comprising: a preparation step of preparing a resin substrate having an adhesive portion; a first step of arranging first particles containing an allotrope of carbon and exhibiting conductivity in a pattern on the surface of the adhesive portion; and a second step of arranging second particles containing a material that alloys with lithium in a region of the surface of the adhesive portion where the first particles are not arranged, wherein the pattern arrangement has a pattern structure having periodicity in a predetermined direction.

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