Composite electrode active material, negative electrode layer, secondary battery and solid-state battery

Abstract

Reduce the internal resistance of the battery. [Solution] A composite electrode active material is used, which includes a granulated body containing primary particles containing silicon elements and a resin, and a solid electrolyte disposed on the surface of the granulated body.

Description

[Technical Field]

[0001] This disclosure relates to composite electrode active materials, negative electrode layers, secondary batteries, and solid-state batteries. [Background technology]

[0002] Silicon is attracting attention as a negative electrode active material because it has a high theoretical capacity. By using silicon as a negative electrode active material, it is possible to achieve a high energy density in batteries. Patent Document 1 describes that when silicon coated with a solid electrolyte is used, the internal resistance increases significantly compared to when silicon not coated with a solid electrolyte is used, which is a problem. Furthermore, Patent Document 1 discloses the use of a negative electrode that includes coated particles, which are made by coating a silicon-containing negative electrode active material with a sulfide solid electrolyte, and composite particles composed of a negative electrode active material and a sulfide solid electrolyte, in order to solve this problem.

[0003] Furthermore, Patent Document 2 discloses an active material composite particle comprising a granule containing silicon particles and a solid electrolyte, coated with a resin having carrier ion conductivity. According to the active material composite particle disclosed in Patent Document 2, excellent cycle characteristics can be achieved. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2021-128857 [Patent Document 2] Japanese Patent Publication No. 2024-034018 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] As disclosed in the aforementioned patent documents, there are examples of using granules containing silicon element particles and a solid electrolyte as a negative electrode active material. However, there are problems such as poor interfacial adhesion between the silicon exposed on the surface and the solid electrolyte, which leads to high internal resistance of the battery. Therefore, this disclosure aims to provide a composite electrode active material, a negative electrode layer, a secondary battery, and a solid-state battery that can reduce the internal resistance of the battery. [Means for solving the problem]

[0006] As a result of diligent research conducted by the inventors to achieve the above-mentioned objectives, we have found that good interfacial adhesion can be achieved by arranging a solid electrolyte on the surface of a granular material containing a silicon element primary and a resin, and have completed this disclosure. This disclosure encompasses the following: <1> A composite electrode active material comprising a granule containing primary particles containing silicon elements and a resin, and a solid electrolyte disposed on the surface of the granule. <2> The ratio of the particle size of the solid electrolyte to the particle size of the granulated material is 1.0 or less. <1> The composite electrode active material described above. <3> The ratio of the particle size of the solid electrolyte to the particle size of the granulated material is 0.4 or less. <1> The composite electrode active material described above. <4> The ratio of the particle size of the solid electrolyte to the particle size of the granulated material is 0.05 or less. <1> The composite electrode active material described above. <5> The solid electrolyte is a sulfide solid electrolyte. <1> ~ <4> A composite electrode active material described in any one of the following. <6> A negative electrode current collector and a negative electrode current collector arranged on one or both sides thereof <1> ~ <5> A negative electrode active material layer containing a composite electrode active material as described in any one of the following, and a negative electrode layer containing the above. <7> The negative electrode active material layer further comprises a solid electrolyte. <6> The negative electrode layer described above. <8> The negative electrode active material layer further comprises a conductive additive. <6> or <7> The negative electrode layer described above. <9> <6> A secondary battery comprising: a negative electrode layer as described above; a positive electrode layer including a positive electrode current collector and a positive electrode active material layer containing a positive electrode active material disposed on one or both sides of the positive electrode current collector; and an electrolyte layer disposed between the negative electrode layer and the positive electrode layer. <10>The secondary battery according to <9>, wherein the electrolyte layer includes a separator that insulates the negative electrode layer and the positive electrode layer, and a non-aqueous electrolyte. <11>The secondary battery according to <9> or <10>, wherein the negative electrode layer further includes a solid electrolyte in the negative electrode active material layer. <12>The secondary battery according to any one of <9> to <11>, wherein the negative electrode layer further includes a conductive assistant in the negative electrode active material layer. <13>A solid battery which is the secondary battery according to <9>, and wherein the electrolyte layer includes a solid electrolyte.

Advantages of the Invention

[0007] According to the composite electrode active material and the negative electrode layer of the present disclosure, the internal resistance of the battery can be reduced. Further, the secondary battery and the solid battery of the present disclosure have a low internal resistance and can have excellent battery performance.

Brief Description of the Drawings

[0008] [Figure 1] It is a cross-sectional view of a main part schematically showing one aspect of the secondary battery of the present disclosure.

Modes for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present disclosure will be described. The description is illustrative of the embodiments and does not limit the scope of the present disclosure.

[0010] In this specification, a numerical range indicated by using "~" indicates a range including the numerical values described before and after "~" as the minimum value and the maximum value, respectively. In the numerical ranges described step by step in this specification, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of the numerical ranges described in other step-by-step descriptions. Further, in the numerical ranges described in this specification, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples.

[0011] In this specification, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes, provided that their intended purpose is achieved.

[0012] In this specification, when embodiments are described with reference to the drawings, the configuration of the embodiments is not limited to the configuration shown in the drawings. Furthermore, the sizes of the members in each figure are conceptual, and the relative relationships between the sizes of the members are not limited thereto.

[0013] In this specification, each component may contain multiple substances. In this embodiment, when referring to the amount of each component in the composition, if there are multiple substances corresponding to each component in the composition, unless otherwise specified, it refers to the total amount of those multiple substances present in the composition.

[0014] The composite electrode active material of this disclosure comprises a granule containing primary particles containing silicon elements and a resin, and a solid electrolyte disposed on the surface of the granule. Because the composite electrode active material of this disclosure has a solid electrolyte disposed on the surface of the resin-containing granule, good interfacial adhesion can be formed between the solid electrolyte and the primary particles containing silicon elements within the composite electrode active material. Therefore, by using the composite electrode active material of this disclosure, the internal resistance of the battery can be reduced.

[0015] [Primary particles containing silicon] The primary particles containing silicon (hereinafter referred to as Si particles) relating to this disclosure preferably contain 60 at% or more of silicon (Si) in proportion to the elements excluding oxygen, more preferably 80 at% or more, and even more preferably 85 at% or more. These Si particles may also contain metallic elements other than silicon (Si), such as aluminum (Al), chromium (Cr), titanium (Ti), molybdenum (Mo), niobium (Nb), vanadium (V), and tungsten (W). Furthermore, these Si particles may also contain other elements other than silicon, such as alkali metal elements (such as sodium (Na)) including lithium (Li). Examples of other elements include alkali metal elements such as Li, as well as potassium (Ca), copper (Cu), magnesium (Mg), strontium (Sr), tin (Sn), iron (Fe), cobalt (Co), nickel (Ni), and phosphorus (P). Furthermore, these Si particles may contain impurities such as oxides. These Si particles may be amorphous or crystalline. The crystalline phase contained in these Si particles is not particularly limited.

[0016] The size of the Si particles relating to this disclosure is not particularly limited. The average primary particle diameter of these Si particles may be, for example, 10 nm or more, 30 nm or more, 50 nm or more, 100 nm or more, or 150 nm or more, or 10 μm or less, 5 μm or less, 3 μm or less, 2 μm or less, or 1 μm or less. Furthermore, a portion of the Si particles may form secondary particles. In this case, the average secondary particle diameter may be, for example, 100 nm or more, 1 μm or more, or 2 μm or more, or 20 μm or less, 15 μm or less, or 10 μm or less. The average primary particle diameter and the average secondary particle diameter can be adjusted as appropriate, for example, by appropriately changing the manufacturing conditions of the Si particles or by performing a classification process. The average primary particle diameter and the average secondary particle diameter of the Si particles are determined using the D50 value, which is the particle diameter (median diameter) at 50% of the cumulative value in the volume-based particle size distribution obtained by laser diffraction scattering.

[0017] The Si particles relating to this disclosure may be porous. The porous nature of the Si particles allows for the mitigation of expansion during charging due to the voids within the particles. There are no particular restrictions on the morphology of the voids in the porous particles. The porous particles may also contain nanoporous silicon. Nanoporous silicon refers to silicon having multiple pores with pore diameters on the order of nanometers (less than 1000 nm, preferably 100 nm or less). The porous particles may also contain pores with a diameter of 55 nm or less. Pores with a diameter of 55 nm or less are resistant to crushing by pressing. That is, porous particles containing pores with a diameter of 55 nm or less tend to maintain their porous nature even after pressing. For example, per gram of porous particles, 0.21 cm² of pores with a diameter of 55 nm or less may be present. 3 / g or more, 0.22cm 3 / g or more, or 0.23cm 3 It may contain more than / g, and 0.30cm 3 / g or less, 0.28cm 3 Less than / g, or 0.26cm 3 It may contain less than / g. The amount of pores with a diameter of 55 nm or less contained in porous particles can be determined from the pore size distribution by the DFT method in nitrogen gas adsorption.

[0018] When the Si particles relating to this disclosure are porous, their porosity is not particularly limited. The porosity may be, for example, 1% or more, 5% or more, 10% or more, or 20% or more, and may also be 80% or less, 70% or less, 60% or less, 50% or less, 40% or less, or 30% or less. The porosity can be determined, for example, by observation using a scanning electron microscope (SEM). A large number of samples is preferable, for example, 100 or more. The porosity can be the average value obtained from these samples.

[0019] [resin] The resin relating to this disclosure is capable of forming granules containing Si particles. The resin is not particularly limited, and various resins known as constituent materials for secondary batteries can be used. For example, the resin may be at least one selected from butadiene rubber (BR) binders, butylene rubber (IIR) binders, acrylate butadiene rubber (ABR) binders, styrene butadiene rubber (SBR) binders, polyvinylidene fluoride (PVdF) binders, polytetrafluoroethylene (PTFE) binders, polyimide (PI) binders, carboxymethylcellulose (CMC) binders, polyacrylate binders, polyacrylic acid ester binders, etc. PVdF binders, in particular, have high performance. The PVdF binder may be a copolymer having units derived from monomers other than VdF. The polymer may be used alone or in combination of two or more types.

[0020] [Granulated material] The granules relating to this disclosure include the Si particles and resin described above. Here, a granule means a mass in which multiple Si particles are bound together by resin. The number of Si particles contained in one granule is not particularly limited. The number of Si particles contained in one granule may be, for example, 2 or more, 5 or more, 10 or more, or 50 or more, or it may be 1000 or less, 500 or 100 or less.

[0021] The granulated material according to this disclosure, with the total amount of Si particles and resin being 100% by mass, may have a Si particle content of 40% by mass or more, 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, or 100% by mass or less, or 98% by mass or less. By setting the Si particle content within this range, the potential for intercalation and release of a predetermined carrier ion (e.g., lithium ions) (charge / discharge potential) can be increased, thereby further improving the performance of the secondary battery.

[0022] The particle size of the granules relating to this disclosure is not particularly limited, but may be, for example, 100 nm or more, 1 μm or more, or 2 μm or more, or 30 μm or less, 25 μm or less, 20 μm or less, 15 μm or less, or 10 μm or less. The particle size of the granules can be adjusted as appropriate by, for example, appropriately changing the average primary particle size of the Si particles, changing the type and amount of resin, or changing the mixing conditions between the resin and Si particles. By setting the particle size of the granules within this range, the potential for intercalation and release of a predetermined carrier ion (e.g., lithium ions) (charge / discharge potential) can be increased, and the performance of the secondary battery can be further improved. The particle size of the granules is determined using the D50 value, which is the particle size (median diameter) at 50% of the cumulative value in the volume-based particle size distribution obtained by laser diffraction scattering.

[0023] [Solid electrolyte] The solid electrolyte according to this disclosure preferably includes at least one solid electrolyte species selected from the group of solid electrolytes consisting of sulfide solid electrolytes, oxide solid electrolytes, and halide solid electrolytes. In particular, it is preferable to use at least one solid electrolyte selected from the group consisting of sulfide solid electrolytes and halide solid electrolytes as the solid electrolyte according to this disclosure. This is because these sulfide solid electrolytes and halide solid electrolytes are relatively flexible materials and can adhere well to primary particles containing silicon elements, thereby reducing the internal resistance of the battery. Among these, it is preferable to use a sulfide solid electrolyte as the solid electrolyte.

[0024] As a sulfide solid electrolyte, it is preferable to contain sulfur (S) as the main component of the anion element, and in addition to S, it is also preferable to contain, for example, Li element, A element, and S element. The A element is at least one selected from the group consisting of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In. The sulfide solid electrolyte may further contain at least one of O and halogen elements. Examples of the halogen element (X) include F, Cl, Br, I, etc. The composition of the sulfide solid electrolyte is not particularly limited, and examples include xLi2S·(100 - x)P2S5 (70 ≤ x ≤ 80), yLiI·zLiBr·(100 - y - z)(xLi2S·(1 - x)P2S5) (0.7 ≤ x ≤ 0.8, 0 ≤ y ≤ 30, 0 ≤ z ≤ 30).

[0025] The sulfide solid electrolyte may have a composition represented by the following general formula (1). Li 4-x Ge 1-x P x S4(0 < x < 1) ··· Formula (1) In formula (1), at least a part of Ge may be substituted by at least one selected from the group consisting of Sb, Si, Sn, B, Al, Ga, In, Ti, Zr, V, and Nb. Also, at least a part of P may be substituted by at least one selected from the group consisting of Sb, Si, Sn, B, Al, Ga, In, Ti, Zr, V, and Nb. A part of Li may be substituted by at least one selected from the group consisting of Na, K, Mg, Ca, and Zn. A part of S may be substituted by a halogen. The halogen is at least one of F, Cl, Br, and I.

[0026] As the oxide solid electrolyte, it is preferable to contain oxygen (O) as the main component of the anion element. For example, it may contain Li, Q element (Q represents at least one of Nb, B, Al, Si, P, Ti, Zr, Mo, W, and S), and O. Examples of the oxide solid electrolyte include garnet-type solid electrolyte, perovskite-type solid electrolyte, NASICON-type solid electrolyte, Li-P-O-based solid electrolyte, Li-B-O-based solid electrolyte, and the like. Examples of the garnet-type solid electrolyte include, for example, Li7La3Zr2O 12 、Li 7-x La3(Zr 2-x Nb x )O 12 (0 ≦ x ≦ 2), Li5La3Nb2O 12 and the like. Examples of the perovskite-type solid electrolyte include, for example, (Li, La)TiO3, (Li, La)NbO3, (Li, Sr)(Ta, Zr)O3, and the like. Examples of the NASICON-type solid electrolyte include, for example, Li(Al, Ti)(PO4)3, Li(Al, Ga)(PO4)3, and the like. Examples of the Li-P-O-based solid electrolyte include Li3PO4, LIPON (a compound in which a part of O in Li3PO4 is substituted by N), and examples of the Li-B-O-based solid electrolyte include Li3BO3, a compound in which a part of O in Li3BO3 is substituted by C, and the like.

[0027] As the halide solid electrolyte, a solid electrolyte containing Li, M, and X (M represents at least one of Ti, Al, and Y, and X represents F, Cl, or Br) is suitable. Specifically, Li 6-3z Y z X6 (X represents Cl or Br, and z satisfies 0 < z < 2), Li 6-(4-x)b (Ti 1-x Al x ) b F6 (0 < x < 1, 0 < b ≦ 1.5) is preferable. Among Li 6-3z Y z X6, Li3YX6 (X represents Cl or Br) is more preferable in terms of excellent lithium ion conductivity, and further, Li3YCl6 is preferable. Also, Li 6-(4-x)b (Ti 1-x Al x ) bF6 (0 < x < 1, 0 < b ≤ 1.5) is preferably included together with a solid electrolyte such as a sulfide solid electrolyte from the viewpoint of suppressing oxidative decomposition of the sulfide solid electrolyte or the like.

[0028] In the composite electrode active material of the present disclosure, a solid electrolyte is disposed on the surface of the granule described above. The state where the solid electrolyte is disposed on the surface of the granule means a mode in which part or all of the surface of the granule is covered with the solid electrolyte, a mode in which the solid electrolyte is embedded in the surface of the granule, and the like. For example, the composite electrode active material of the present disclosure may be one in which part of the surface of the granule is covered with the solid electrolyte and the solid electrolyte is embedded in a different part of the surface.

[0029] In the composite electrode active material of the present disclosure, it is preferable that the ratio of the particle size of the solid electrolyte to the particle size of the granule is 1.0 or less, and more preferably less than 1.0. That is, it is preferable to use a solid electrolyte having the same or smaller particle size compared to the particle size of the granule. Further, in the composite electrode active material of the present disclosure, the ratio of the particle size of the solid electrolyte to the particle size of the granule can be 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less. In particular, in the composite electrode active material of the present disclosure, it is preferable that the ratio of the particle size of the solid electrolyte to the particle size of the granule is 0.4 or less, more preferably 0.1 or less, and even more preferably 0.05 or less. By setting the relationship between the particle size of the granule and the particle size of the solid electrolyte within the above range in the composite electrode active material of the present disclosure, the resistance between the composite electrode active materials can be further reduced, and as a result, a secondary battery with a lower internal resistance can be obtained.

[0030] The particle size of the solid electrolyte in the composite electrode active material of this disclosure is preferably within the above-mentioned range with respect to the particle size of the granules, for example, it may be 100 nm or more, 1 μm or more, or 2 μm or more, or 30 μm or less, 25 μm or less, 20 μm or less, 15 μm or less, or 10 μm or less. Alternatively, the particle size of the solid electrolyte may be, for example, 40 nm or more, 400 nm or more, or 800 nm or more, or 12 μm or less, 10 μm or less, 8 μm or less, 6 μm or less, or 4 μm or less. Furthermore, the particle size of the solid electrolyte may be, for example, 10 nm or more, 100 nm or more, or 200 nm or more, or 3 μm or less, 2.5 μm or less, 2 μm or less, 1.5 μm or less, or 1 μm or less. By setting the particle size of the solid electrolyte within the above range, the resistance between the composite electrode active materials can be further reduced, resulting in a secondary battery with lower internal resistance. The particle size of the solid electrolyte is determined using the D50 value, which is the particle size (median diameter) at 50% of the cumulative value in the volume-based particle size distribution obtained by laser diffraction scattering.

[0031] Furthermore, the solid electrolyte content in the composite electrode active material of this disclosure is not particularly limited, but when the granules are considered as 100% by mass, it can be 20% by mass or more, 25% by mass or more, 30% by mass or more, 35% by mass or more, 40% by mass or more, 45% by mass or more, 50% by mass or more, 55% by mass or more, 60% by mass or more, 65% by mass or more, 70% by mass or more, 75% by mass or more, or 80% by mass or more. Furthermore, the solid electrolyte content is not particularly limited, but when the granules are considered as 100% by mass, it can be 80% by mass or less, 75% by mass or less, 70% by mass or less, 65% by mass or less, 60% by mass or less, 55% by mass or less, 50% by mass or less, 45% by mass or less, 40% by mass or less, 35% by mass or less, 30% by mass or less, 25% by mass or less, and 20% by mass or less. By setting the solid electrolyte content in the composite electrode active material within this range, the resistance between the composite electrode active materials can be reduced, resulting in a secondary battery with low internal resistance.

[0032] [Method for manufacturing composite electrode active material] The composite electrode active material of this disclosure can be manufactured by a manufacturing method that includes the steps of manufacturing a granule and arranging a solid electrolyte on the surface of the manufactured granule.

[0033] In the process of producing granules, the Si particles and resin described above are mixed to produce the granules. Specifically, first, the resin is dissolved or dispersed in an organic solvent, and then the Si particles are added and mixed to prepare a slurry. After that, the solvent is dried by a method such as spray drying to produce the granules. There are no particular restrictions on the mixing method when preparing the slurry; it may be mixed manually using a mortar and pestle, or it may be mixed mechanically using various mixing devices.

[0034] Subsequently, in the step of distributing a solid electrolyte on the surface of the prepared granules, first, the granules prepared as described above and the solid electrolyte are added to an organic solvent and stirred and mixed. Then, by drying and removing the organic solvent, the composite electrode active material of this disclosure can be prepared. Through the above steps, a composite electrode active material can be produced that includes granules containing Si particles and resin, and a solid electrolyte distributed on the surface of the granules.

[0035] [Negative electrode layer] The negative electrode layer of this disclosure comprises a negative electrode current collector and a negative electrode active material layer containing the composite electrode active material of this disclosure, disposed on one or both sides of the negative electrode current collector. The negative electrode layer of this disclosure can have its internal resistance lowered by containing the composite electrode active material described above. The negative electrode layer of this disclosure may contain any components other than the composite electrode active material described above.

[0036] The negative electrode active material layer may contain a solid electrolyte as an optional component. The solid electrolyte included in the negative electrode active material layer may be at least one solid electrolyte selected from the group of solid electrolytes consisting of sulfide solid electrolytes, oxide solid electrolytes, and halide solid electrolytes as described in the [Solid Electrolytes] section above. Furthermore, the solid electrolyte included in the negative electrode active material layer and the solid electrolyte included in the composite electrode active material of this disclosure may be the same or different.

[0037] Furthermore, the negative electrode active material layer may contain conductive additives as optional components. Examples of conductive additives include carbon materials such as vapor-processed carbon fiber (VGCF), acetylene black (AB), Ketjenblack (KB), carbon nanotubes (CNT), and carbon nanofibers (CNF); and metallic materials such as nickel, aluminum, and stainless steel. The conductive additive may be in particulate or fibrous form, for example, and its size is not particularly limited. One type of conductive additive may be used alone, or two or more types may be used in combination.

[0038] The negative electrode active material layer can be prepared by applying a slurry, which is a mixture of the composite electrode active material of this disclosure and optional components such as a solid electrolyte and a conductive additive, to the negative electrode current collector. Here, the slurry can be prepared by adding the composite electrode active material, optional components such as a solid electrolyte and a conductive additive to a solvent in which the material described in the [Resin] section above is dissolved or dispersed, and then kneading the mixture.

[0039] Here, the content of the composite electrode active material in the negative electrode active material layer may be, for example, 40% or more by mass, 50% or more by mass, 60% or more by mass, or 70% or more by mass, with the entire negative electrode active material layer (total solid content) being 100% by mass, or it may be 100% or less by mass or 90% or less by mass. The shape of the negative electrode active material layer is not particularly limited, and for example, it may be a sheet-like negative electrode active material layer having a substantially flat surface. The thickness of the negative electrode active material layer is not particularly limited, and for example, it may be 0.1 μm or more, 1 μm or more, or 10 μm or more, or it may be 2 mm or less, 1 mm or less, or 500 μm or less.

[0040] Furthermore, the negative electrode layer of this disclosure may contain a solid electrolyte, a liquid electrolyte (electrolyte solution), or a combination thereof. In particular, a higher effect is more easily obtained when the negative electrode active material layer contains at least a solid electrolyte. That is, it is preferable that the negative electrode layer of this disclosure contains the above-mentioned active material composite particles and a solid electrolyte arranged around them. It is preferable that the negative electrode active material layer contains a solid electrolyte, in particular a sulfide solid electrolyte, and moreover a sulfide solid electrolyte containing Li, S, and P as constituent elements.

[0041] As the negative electrode current collector, any of the materials commonly used as negative electrode current collectors in batteries can be used. The negative electrode current collector may be in the form of foil, plate, mesh, perforated metal, or foam. The negative electrode current collector may be a metal foil or metal mesh, or a carbon sheet. The negative electrode current collector may consist of multiple foils or sheets. Examples of metals constituting the negative electrode current collector include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, and stainless steel. In particular, from the viewpoint of ensuring reduction resistance and avoiding alloying with lithium, the negative electrode current collector may contain at least one metal selected from Cu, Ni, and stainless steel. The negative electrode current collector may have some kind of coating layer on its surface for purposes such as adjusting resistance. Furthermore, the negative electrode current collector may be a metal foil or substrate on which the above metals are plated or vapor-deposited. Also, if the negative electrode current collector consists of multiple metal foils, there may be some kind of layer between the multiple metal foils. The thickness of the negative electrode current collector is not particularly limited. For example, it may be 0.1 μm or more, or 1 μm or more, or 1 mm or less, or 100 μm or less.

[0042] [Secondary battery] The secondary battery of this disclosure comprises a negative electrode layer as described above, a positive electrode layer including a positive electrode current collector and a positive electrode active material layer containing a positive electrode active material disposed on one or both sides of the positive electrode current collector, and an electrolyte layer disposed between the negative electrode layer and the positive electrode layer. The secondary battery of this disclosure can have its internal resistance reduced by including the negative electrode layer as described above.

[0043] In the secondary battery of this disclosure, the positive electrode layer only needs to be capable of functioning appropriately as the positive electrode of the secondary battery, and its composition is not particularly limited. The positive electrode active material layer includes at least a positive electrode active material and may optionally include an electrolyte, a conductive additive, and a binder. The positive electrode active material layer may also contain various other additives. As the positive electrode active material, known positive electrode active materials for secondary batteries can be used. As the positive electrode active material, for example, at least one selected from various lithium-containing compounds, elemental sulfur and sulfur compounds, etc. Lithium-containing compounds as positive electrode active materials include lithium cobaltate, lithium nickelate, Li 1±α Ni 1 / 3 Co 1 / 3 Mn 1 / 3 O 2±δ Lithium manganate, spinel-type lithium compounds (Li 1+x Mn 2-x-y M y Various lithium-containing oxides may be used, such as heteroatom-substituted Li-Mn spinel (e.g., O4, where M is one or more selected from Al, Mg, Co, Fe, Ni, and Zn), lithium titanate, and metallic lithium phosphate (e.g., LiMPO4, where M is one or more selected from Fe, Mn, Co, and Ni). In particular, a higher effect can be expected when the positive electrode active material contains a lithium-containing oxide that includes at least Li, at least one of Ni, Co, and Mn, and O as constituent elements. The positive electrode active material may be used alone or in combination of two or more types.

[0044] The shape of the positive electrode active material can be any shape that is common for positive electrode active materials in batteries. The positive electrode active material may be, for example, particulate. The positive electrode active material may be solid, hollow, have voids, or be porous. The positive electrode active material may be primary particles or secondary particles formed by the aggregation of multiple primary particles. In addition, a protective layer containing an ion-conducting oxide may be formed on the surface of the positive electrode active material. This makes it easier to suppress reactions between the positive electrode active material and sulfides (e.g., sulfide solid electrolytes). Examples of ion-conducting oxides include Li3BO3, LiBO2, Li2CO3, LiAlO2, Li4SiO4, Li2SiO3, Li3PO4, Li2SO4, Li2TiO3, and Li4Ti5O 12 Examples include Li2Ti2O5, Li2ZrO3, LiNbO3, Li2MoO4, and Li2WO4.

[0045] The electrolyte contained in the positive electrode active material layer may be a solid electrolyte, a liquid electrolyte (electrolyte solution), or a combination thereof. In particular, a higher effect can be expected when the positive electrode active material layer contains at least a solid electrolyte. As the solid electrolyte, those listed in the [Solid Electrolyte] section above can be used. As the conductive additive contained in the positive electrode active material layer, those listed in the [Negative Electrode Layer] section above can be used. As the resin contained in the positive electrode active material layer, those listed in the [Resin] section above can be used.

[0046] The positive electrode current collector can be any of the commonly used positive electrode current collectors for batteries. The positive electrode current collector may be in the form of foil, plate, mesh, perforated metal, or foam. The positive electrode current collector may be composed of metal foil or metal mesh. Metal foil, in particular, offers superior handling. The positive electrode current collector may consist of multiple foils. Examples of metals that can constitute the positive electrode current collector include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, and stainless steel. In particular, the positive electrode current collector may contain Al to ensure oxidation resistance. The positive electrode current collector may have some kind of coating layer on its surface for purposes such as adjusting resistance. Furthermore, the positive electrode current collector may be a metal foil or substrate on which the above metals are plated or vapor-deposited.

[0047] The electrolyte layer in the secondary battery of this disclosure may be a layer that does not contain a liquid electrolyte but contains a solid electrolyte (solid battery), a layer that does not contain a solid electrolyte but contains a liquid electrolyte (non-aqueous electrolyte), or a layer that contains both a solid electrolyte and a liquid electrolyte. As one embodiment of the secondary battery of this disclosure, the lithium-ion secondary battery 1 shown in Figure 1 comprises a positive electrode layer 2 including a positive electrode current collector 5 and a positive electrode active material layer 6, a negative electrode layer 3 including a negative electrode current collector 7 and a negative electrode active material layer 8, and an electrolyte layer 4 disposed between the positive electrode layer 2 and the negative electrode layer 3. When the electrolyte layer 4 contains a liquid electrolyte, it is preferable that the electrolyte layer 4 has a separator that holds the liquid electrolyte and insulates the positive electrode layer 2 and the negative electrode layer 3. Furthermore, when the electrolyte layer 4 contains a solid electrolyte, the electrolyte layer 4 may optionally contain a binder or the like in addition to the solid electrolyte. In particular, when using the negative electrode active material and negative electrode of this disclosure, it is preferable that the electrolyte layer 4 does not contain a liquid electrolyte but contains a solid electrolyte, or contains both a liquid electrolyte and a solid electrolyte (solid battery).

[0048] The liquid electrolyte can be any non-aqueous electrolyte typically used in non-aqueous lithium-ion secondary batteries. The non-aqueous electrolyte may be a composition containing a supporting salt in a non-aqueous solvent. Examples of non-aqueous solvents include organic electrolytes, fluorinated solvents, propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and materials selected from the group consisting of two or more combinations thereof. Examples of supporting salts include materials selected from the group consisting of Li(FSO2)2N, LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, LiC4F9SO3, LiN(CF3SO2)2, LiC(CF3SO2)3, lithium compounds (lithium salts) of LiI, and materials selected from the group consisting of two or more combinations thereof.

[0049] The separator used in the liquid electrolyte can be any separator commonly used in non-aqueous lithium-ion secondary batteries, such as those containing resins like polyethylene (PE), polypropylene (PP), polyester, and polyamide. The separator may have a single-layer structure or a multi-layer structure. [Examples]

[0050] The present disclosure will be described in more detail below using examples, but the technical scope of the present disclosure is not limited to the following examples.

[0051] <Example 1> 1. Fabrication of the positive electrode layer The organic solvent contains 0.4% by mass of styrene-butadiene rubber (SBR) binder, 2% by mass of conductive additive (vapor-grown carbon fiber: VGCF), 12.6% by mass of Li2S-P2S5 solid electrolyte, and LiNi as the positive electrode active material. 0.8 Co 0.15 Mn 0.05 85% by mass of O2 was added. The mixture was then kneaded using an ultrasonic homogenizer to obtain a cathode slurry. The obtained cathode slurry was coated onto an aluminum foil to create a cathode layer.

[0052] 2. Fabrication of the negative electrode layer A binder solution was prepared by dissolving or dispersing 2% by mass of a vinyl-based binder in an organic solvent. A slurry was prepared by adding 15% by mass of Si particles (average primary particle size: 1.5 μm) to this binder solution. The obtained slurry was dried by spray drying to prepare granules in which Si particles and resin were compounded. Next, a Li2S-P2S5-based solid electrolyte having a predetermined particle size was added to the granules in a ratio of 50% by mass relative to the granules and stirred and mixed. After that, the solvent was removed and the mixture was pulverized in a mortar. This prepared a composite electrode active material in which the solid electrolyte was arranged on the surface of the granules. Next, the prepared composite electrode active material was added to a solvent in a ratio of 58% by mass, SBR binder in a ratio of 2% by mass, conductive additive (carbon nanotube) in a ratio of 0.4% by mass, and Li2S-P2S5-based solid electrolyte in a ratio of 49.6% by mass. The mixture was then kneaded using an ultrasonic homogenizer to obtain a negative electrode slurry. The obtained negative electrode slurry was coated onto a Cu foil to create a negative electrode layer. The particle sizes of the granules and solid electrolyte were measured using the D50 value obtained with a laser scattering particle size analyzer. In this example, the particle size of the granules was 1 μm, and the particle size of the Li2S-P2S5-based solid electrolyte placed on the surface of the granules was also 1 μm. In other words, in this example, the ratio of the particle size of the Li2S-P2S5-based solid electrolyte to the particle size of the granules was 1.0.

[0053] 3. Preparation of the solid electrolyte layer 0.6% by mass of acrylate butadiene rubber (ABR) binder and 99.4% by mass of Li2S-P2S5 solid electrolyte were added to an organic solvent. The mixture was then kneaded using an ultrasonic homogenizer to obtain an electrolyte layer slurry. The obtained electrolyte layer slurry was coated onto an aluminum foil to prepare a solid electrolyte layer.

[0054] 4. Fabrication of lithium-ion secondary batteries The positive electrode layer, negative electrode layer, and solid electrolyte layer prepared in steps 1-3 above were each formed into strips. Next, the positive electrode layer and the solid electrolyte layer were bonded together so that their composite material surfaces faced each other, and then bonded at 165°C and 50kN / cm². 2The roller was roll-pressed under the following pressure. Then, the solid electrolyte layer was transferred to the positive electrode layer by peeling off the Al foil of the solid electrolyte layer. Similarly, the composite surface of another solid electrolyte layer was bonded to the composite surface of the negative electrode layer at 25°C and 50kN / cm². 2 The material was roll-pressed under pressure. Then, the solid electrolyte layer was transferred to the negative electrode layer by peeling off the Al foil of the solid electrolyte layer.

[0055] The negative electrode layer, onto which the solid electrolyte layer was transferred, was punched out with a φ13.00 mm punching machine, and the positive electrode layer, onto which the solid electrolyte layer was transferred, was punched out with a φ11.28 mm punching machine. Separately, the solid electrolyte layer punched out with a φ13.00 mm punching machine was transferred to the negative electrode, onto which the solid electrolyte layer was transferred, using a uniaxial press machine. The resulting negative electrode layer and positive electrode layer were placed facing each other to form a battery. Finally, current extraction tabs were attached to each of the positive and negative electrode layers, and the assembly was sealed in aluminum laminate using a vacuum sealer and restrained at a pressure of 5 MPa to fabricate a lithium-ion secondary battery.

[0056] 5. Battery Resistance Evaluation For the lithium-ion secondary battery (all-solid-state battery) prepared as described above, the voltage was adjusted to 3.7V, and the resistance value was calculated from the voltage drop after 5 seconds of discharge at a 5C rate. The resistance value was normalized by setting the resistance value of the lithium-ion secondary battery prepared in Comparative Example 1 (described later) to 100.

[0057] <Example 2> In this example, a lithium-ion secondary battery was fabricated in the same manner as in Example 1, except that the particle size of the granules was 5 μm and the particle size of the Li2S-P2S5-based solid electrolyte placed on the surface of the granules was 1 μm. That is, in Example 2, the ratio of the particle size of the Li2S-P2S5-based solid electrolyte to the particle size of the granules was set to 0.2.

[0058] <Example 3> In this example, a lithium-ion secondary battery was fabricated in the same manner as in Example 1, except that the particle size of the granules was 10 μm and the particle size of the Li2S-P2S5-based solid electrolyte placed on the surface of the granules was 1 μm. That is, in Example 3, the ratio of the particle size of the Li2S-P2S5-based solid electrolyte to the particle size of the granules was 0.1.

[0059] <Example 4> In this example, a lithium-ion secondary battery was fabricated in the same manner as in Example 1, except that the particle size of the granules was 15 μm and the particle size of the Li2S-P2S5-based solid electrolyte placed on the surface of the granules was 0.6 μm. That is, in Example 4, the ratio of the particle size of the Li2S-P2S5-based solid electrolyte to the particle size of the granules was 0.04.

[0060] <Example 5> In this example, a lithium-ion secondary battery was fabricated in the same manner as in Example 1, except that the particle size of the granules was 15 μm and the particle size of the Li2S-P2S5-based solid electrolyte arranged on the surface of the granules was 0.3 μm. Specifically, in Example 5, the ratio of the particle size of the Li2S-P2S5-based solid electrolyte to the particle size of the granules was set to 0.02.

[0061] <Example 6> In this example, a lithium-ion secondary battery was fabricated in the same manner as in Example 1, except that the particle size of the granules was 25 μm and the particle size of the Li2S-P2S5-based solid electrolyte placed on the surface of the granules was 1 μm. Specifically, in Example 6, the ratio of the particle size of the Li2S-P2S5-based solid electrolyte to the particle size of the granules was set to 0.04.

[0062] <Comparative Example 1> In this comparative example, a lithium-ion secondary battery was fabricated in the same manner as in Example 1, except that a granular material with a particle size of 15 μm was used as the negative electrode active material. That is, in Comparative Example 1, a lithium-ion secondary battery was fabricated using a negative electrode active material that did not have a Li2S-P2S5-based solid electrolyte on the surface of the granular material.

[0063] <Result> Table 1 shows the results of measuring the resistance values ​​of the lithium-ion secondary batteries prepared in Examples 1-5 and Comparative Example 1. As mentioned above, the resistance values ​​are shown normalized to 100, with the resistance value of the lithium-ion secondary battery in Comparative Example 1 being set to 100.

[0064] [Table 1]

[0065] As shown in Table 1, it was found that the internal resistance of a secondary battery can be reduced by using a composite electrode active material, which consists of a granule containing Si particles and resin with a solid electrolyte on its surface, as the negative electrode active material. In particular, it was found that the smaller the particle size of the solid electrolyte on the surface is compared to the granule, the greater the resistance reduction effect. Specifically, comparing Example 4 and Example 6, it was found that even with the same particle size ratio (solid electrolyte / granule), the resistance reduction effect was greater when the particle size of the solid electrolyte on the surface was smaller. [Explanation of symbols]

[0066] 1...Lithium-ion secondary battery, 2...Positive electrode layer, 3...Negative electrode layer, 4...Electrolyte layer, 5...Positive electrode current collector, 6...Positive electrode active material layer, 7...Negative electrode current collector, 8...Negative electrode active material layer

Claims

1. A granulated body containing primary particles containing silicon elements and a resin, A solid electrolyte disposed on the surface of the granular material, A composite electrode active material containing the above.

2. The composite electrode active material according to claim 1, wherein the ratio of the particle size of the solid electrolyte to the particle size of the granulated material is 1.0 or less.

3. The composite electrode active material according to claim 1, wherein the ratio of the particle size of the solid electrolyte to the particle size of the granulated material is 0.4 or less.

4. The composite electrode active material according to claim 1, wherein the ratio of the particle size of the solid electrolyte to the particle size of the granulated material is 0.05 or less.

5. The composite electrode active material according to claim 1, wherein the solid electrolyte is a sulfide solid electrolyte.

6. A negative electrode current collector, and a negative electrode active material layer comprising the composite electrode active material described in any one of claims 1 to 5, disposed on one or both sides of the negative electrode current collector, A negative electrode layer containing this layer.

7. The negative electrode layer according to claim 6, wherein the negative electrode active material layer further comprises a solid electrolyte.

8. The negative electrode layer according to claim 6, wherein the negative electrode active material layer further comprises a conductive additive.

9. The negative electrode layer according to claim 6, A positive electrode layer comprising a positive electrode current collector and a positive electrode active material layer containing positive electrode active material disposed on one or both sides of the positive electrode current collector, An electrolyte layer disposed between the negative electrode layer and the positive electrode layer, A secondary battery equipped with the following features.

10. The secondary battery according to claim 9, wherein the electrolyte layer includes a separator that insulates the negative electrode layer from the positive electrode layer and a non-aqueous electrolyte.

11. The secondary battery according to claim 9, wherein the negative electrode layer further comprises a solid electrolyte in the negative electrode active material layer.

12. The secondary battery according to claim 9, wherein the negative electrode layer further comprises a conductive additive in the negative electrode active material layer.

13. A secondary battery according to claim 9, wherein the electrolyte layer includes a solid electrolyte.

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