Solid-state battery and method for manufacturing a solid-state battery

Abstract

The present invention provides a solid-state battery and a method for manufacturing a solid-state battery, in which the bonding state between the negative electrode layer and the solid electrolyte layer is well maintained. [Solution] A solid-state battery comprising a structure in which a solid electrolyte layer, a negative electrode layer, and a negative electrode current collector are arranged in this order, wherein the negative electrode layer contains negative electrode active material particles, and when the negative electrode layer is divided in the thickness direction into a region X on the solid electrolyte side and a region Y on the negative electrode current collector side, the degree of orientation X of the negative electrode active material particles in region X is greater than the degree of orientation Y of the negative electrode active material particles in region Y.

Description

[Technical Field]

[0001] This disclosure relates to a solid-state battery and a method for manufacturing a solid-state battery. [Background technology]

[0002] The practical application of rechargeable batteries that use a solid electrolyte (hereinafter also called solid-state batteries) is being considered as secondary batteries that can be used repeatedly by recharging. The electrodes of solid-state batteries may contain solid active material along with the active material to promote the movement of ions between particles of the active material within the electrode.

[0003] It is known that the negative electrode active material contained in the negative electrode of a secondary battery undergoes significant volume changes during battery charging (ion absorption) and battery discharging (ion release). Furthermore, it has been pointed out that repeated expansion and contraction of the negative electrode active material during charging and discharging alters the bonding state between the active material particles and the solid electrolyte within the negative electrode, which can cause battery degradation. As a negative electrode active material in which volume changes associated with battery charging and discharging are suppressed, Patent Document 1 discloses a Si-based active material in which secondary particles are composed of multiple primary particles whose ratio of the length of the long side to the length of the short side is within a specific range. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-13702 [Overview of the project] [Problems that the invention aims to solve]

[0005] Solid-state batteries have a layer containing a solid electrolyte (hereinafter also referred to as the solid electrolyte layer) placed between the positive electrode and the negative electrode. The solid electrolyte layer serves as a separator that isolates the positive electrode and the negative electrode, and as a pathway for ions to move between the positive electrode and the negative electrode. Deterioration of the junction between the negative electrode and the solid electrolyte layer has been cited as a factor in the increase in resistance associated with the charging and discharging of solid-state batteries. In view of the above circumstances, this disclosure aims to provide a solid-state battery and a method for manufacturing a solid-state battery in which the bonding state between the negative electrode layer and the solid electrolyte layer is well maintained. [Means for solving the problem]

[0006] The means for solving the above problems include the following embodiments. <1> The structure includes a solid electrolyte layer, a negative electrode layer, and a negative electrode current collector arranged in this order. The aforementioned negative electrode layer contains negative electrode active material particles, A solid-state battery in which, when the negative electrode layer is divided in the thickness direction into a region X on the solid electrolyte side and a region Y on the negative electrode current collector side, the degree of orientation X of the negative electrode active material particles in region X is greater than the degree of orientation Y of the negative electrode active material particles in region Y. <2> The negative electrode active material particles contain the element Si. <1> Solid-state batteries as described above. <3> The structure includes a positive electrode layer, a solid electrolyte layer, a negative electrode layer, and a negative electrode current collector arranged in this order on both sides of the positive electrode current collector. <1> or <2> Solid-state batteries as described above. <4> <1> ~ <3> A method for manufacturing a solid battery as described in any one of the items, This includes transferring the negative electrode layer formed on the support to the solid electrolyte layer. A method for manufacturing a solid-state battery, wherein the negative electrode layer formed on the support comprises a negative electrode layer Y formed on the support and a negative electrode layer X formed on the negative electrode layer Y, and the degree of orientation X of the negative electrode active material particles in the negative electrode layer X is greater than the degree of orientation Y of the negative electrode active material particles in the negative electrode layer Y. <5> Forming positive electrode layers on both sides of the positive electrode current collector, Forming a solid electrolyte layer on the positive electrode layer, This includes, in this order, forming a negative electrode layer on the solid electrolyte layer, <4> A method for manufacturing a solid-state battery as described above. [Effects of the Invention]

[0007] According to the present disclosure, there are provided a solid battery in which a bonding state between a negative electrode layer and a solid electrolyte layer is maintained well, and a method for manufacturing the solid battery.

Brief Description of the Drawings

[0008] [Figure 1] It is a cross-sectional view schematically showing an example of a configuration of a negative electrode structure included in a solid battery. [Figure 2] It is a diagram for explaining the concept of the degree of orientation of negative electrode active material particles in a negative electrode layer. [Figure 3] It is a cross-sectional view schematically showing an example of a positive electrode center laminate structure included in a solid battery.

Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments which are an example of the present disclosure will be described. These descriptions and examples are illustrative of the embodiments and do not limit the scope of the present disclosure.

[0010] In the present disclosure, a numerical range represented using "~" means a range including the numerical values described before and after "~" as a lower limit value and an upper limit value. In a numerical range described stepwise in the present disclosure, an upper limit value or a lower limit value described in one numerical range may be replaced with an upper limit value or a lower limit value of another numerically described stepwise range. Further, in the numerical range described in the present disclosure, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples. In the present disclosure, the amount of each component in a composition means the total amount of the plurality of substances present in the composition when there are a plurality of substances corresponding to each component in the composition, unless otherwise specified. In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. In the present disclosure, the term "step" includes not only an independent step but also the term if the intended purpose of the step is achieved even when it cannot be clearly distinguished from other steps. In the present disclosure, the "solid-state battery" means a secondary battery that uses at least a solid electrolyte as an electrolyte. Therefore, the solid-state batteries of the present disclosure include batteries that are referred to by different names such as all-solid-state batteries and semi-solid-state batteries.

[0011] <Solid-state battery> One embodiment of the present disclosure is including a structure in which a solid electrolyte layer, a negative electrode layer, and a negative electrode current collector are arranged in this order, the negative electrode layer contains negative electrode active material particles, when the negative electrode layer is divided into a region X on the solid electrolyte side and a region Y on the negative electrode current collector side in the thickness direction, the orientation degree X of the negative electrode active material particles in the region X is greater than the orientation degree Y of the negative electrode active material particles in the region Y, which is a solid-state battery.

[0012] The negative electrode layer of a solid-state battery is generally press-treated at a high pressure to increase the density of the negative electrode layer. When the press treatment is performed on the negative electrode layer, the negative electrode active material particles contained in the negative electrode layer change from a randomly oriented state to an oriented state along the surface direction of the negative electrode layer. On the other hand, the volume of the negative electrode active material particles changes with the charge and discharge of the battery. The degree of this volume change is larger in the major axis direction than in the minor axis direction of the negative electrode active material particles. Therefore, when the ratio of the particles oriented along the surface direction of the negative electrode layer among the negative electrode active material particles contained in the negative electrode layer increases, the stress generated at the interface between the negative electrode layer and the adjacent layer tends to increase due to the volume change of the negative electrode active material particles. The stress generated at the interface between the negative electrode layer and the adjacent layer may affect the bonding state between the negative electrode layer and the adjacent layer. Thus, when the press treatment for increasing the density of the negative electrode layer is performed, the stress generated due to the volume change of the negative electrode active material particles increases, and the bonding state between the negative electrode layer and the adjacent layer may be affected by the increased stress.

[0013] As a result of the study by the present inventors, it was found that the influence of the stress generated due to the volume change of the negative electrode active material particles on the bonding state between the negative electrode layer and the adjacent layer is greater in the bonding state between the negative electrode material and the solid electrolyte layer than in the bonding state between the negative electrode material and the current collector. In the solid-state battery of this disclosure, the degree of orientation X of the negative electrode active material particles in region X on the solid electrolyte layer side of the negative electrode layer is greater than the degree of orientation Y of the negative electrode active material particles in region Y on the negative electrode current collector side. In other words, the solid-state battery of this disclosure suppresses the generation of stress at the interface between the negative electrode layer and the solid electrolyte layer by selectively suppressing the decrease in the degree of orientation of negative electrode active material particles in the region of the negative electrode layer on the solid electrolyte layer side. In other words, the solid-state battery of this disclosure makes it possible to maintain a good bonding state between the negative electrode layer and the solid electrolyte layer while ensuring sufficient density throughout the negative electrode layer. The above effect is particularly pronounced when the volume change of the negative electrode active material particles is large (for example, when the negative electrode active material particles contain Si).

[0014] In the following explanation, the structure in which the solid electrolyte layer, the negative electrode layer, and the negative electrode current collector in a solid-state battery are arranged in this order is also referred to as the "negative electrode structure."

[0015] An example of the configuration of the negative electrode structure included in the solid-state battery of this disclosure is shown in Figure 1. As shown in Figure 1, the negative electrode structure consists of a solid electrolyte layer 30, a negative electrode layer 40, and a negative electrode current collector 50, arranged in this order. Although not shown in the diagram, the negative electrode layer 40 contains negative electrode active material particles. Furthermore, when the negative electrode layer 40 is divided in the thickness direction into a region X on the solid electrolyte 30 side and a region Y on the negative electrode current collector 50 side, the degree of orientation X of the negative electrode active material particles in region X is greater than the degree of orientation Y of the negative electrode active material particles in region Y.

[0016] In this disclosure, the degree of orientation of the negative electrode active material particles is determined by the magnitude of the angle between the direction of the long axis of the negative electrode active material particles and the thickness direction of the negative electrode layer. In this disclosure, the long axis of the negative electrode active material particle means the straight line at which the length of the straight line connecting two points located on the contour line of the projected image of the negative electrode active material particle (i.e., the distance between the two points) is the maximum value.

[0017] Figure 2 illustrates the concept of the degree of orientation of negative electrode active material particles. As shown in Figure 2(a), when the angle between the direction of the long axis of the negative electrode active material particles and the thickness direction of the negative electrode layer is 0°, the degree of orientation of the particles is set to 90°. As shown in Figure 2(b), if the angle between the direction of the long axis of the negative electrode active material particles and the thickness direction of the negative electrode layer is 45°, then the degree of orientation of the particles is set to 45°. As shown in Figure 2(c), if the angle between the direction of the long axis of the negative electrode active material particles and the thickness direction of the negative electrode layer is 90°, the degree of orientation of the particles is considered to be 0°.

[0018] In this disclosure, the degree of orientation of the negative electrode active material particles contained in the negative electrode layer is determined based on the projection image of the negative electrode active material particles observed in the cross-section of the negative electrode layer. In this disclosure, the degree of orientation X of the negative electrode active material particles in region X of the negative electrode layer is the arithmetic mean of the degree of orientation X of 100 negative electrode active material particles selected from the negative electrode active material particles observed in region X. In this disclosure, the degree of orientation Y of the negative electrode active material particles in region Y of the negative electrode layer is the arithmetic mean of the degree of orientation Y of 100 negative electrode active material particles selected from the negative electrode active material particles observed in region Y.

[0019] In the negative electrode structure, the ratio of the region X on the solid electrolyte layer side to the region Y on the current collector side in the negative electrode layer is not particularly limited and can be determined according to the desired characteristics of the negative electrode layer (such as the density of the negative electrode layer). For example, the ratio of the thickness of region X to the thickness of region Y (thickness of region X:thickness of region Y) can be selected from the ranges of 8:2 to 2:8, 7:3 to 3:7, or 6:4 to 4:6. The ratio of the thickness of region X to the thickness of region Y may also be 1:1.

[0020] In a negative electrode structure, the negative electrode layer may consist of multiple negative electrode layers or a single layer. If the negative electrode layer consists of multiple negative electrode layers, the boundaries between the negative electrode layers may or may not coincide with the boundaries between region X and region Y. From the viewpoint of controlling the orientation of negative electrode active material particles so as to satisfy the condition that the orientation X of negative electrode active material particles in region X is greater than the orientation Y of negative electrode active material particles in region Y, it is preferable that the negative electrode layer is composed of a negative electrode layer corresponding to region X and a negative electrode layer corresponding to region Y.

[0021] In a negative electrode structure, the relationship between the degree of orientation X of negative electrode active material particles in region X of the negative electrode layer and the degree of orientation Y of negative electrode active material particles in region Y is not particularly limited as long as the degree of orientation X is greater than the degree of orientation Y (i.e., the condition X / Y > 1.0 is satisfied), and can be determined according to the desired properties of the negative electrode material (such as the density of the negative electrode material). For example, the relationship between the degree of orientation X and the degree of orientation Y may satisfy the conditions that X / Y is 1.1 or greater, 1.2 or greater, or 1.5 or greater. For example, the relationship between the degree of orientation X and the degree of orientation Y may satisfy the condition that X / Y is 5.0 or less, 3.0 or less, or 2.0 or less.

[0022] The solid-state battery of this disclosure may include a plurality of negative electrode structures. The number of negative electrode structures included in the solid-state battery of this disclosure is not particularly limited and can be selected from, for example, 2 to 100.

[0023] If the solid-state battery of this disclosure includes multiple negative electrode structures, even if all of the negative electrode structures satisfy the orientation degree conditions described above (i.e., the orientation degree X of the negative electrode active material particles in region X of the negative electrode layer is greater than the orientation degree Y of the negative electrode active material particles in region Y), only a portion of the negative electrode structures may satisfy the orientation degree conditions described above. From the viewpoint of maintaining a good bonding state between the negative electrode layer and the solid electrolyte layer, it is preferable that 50% or more of the negative electrode structures included in the solid battery of this disclosure, based on the number, satisfy the orientation degree conditions described above, more preferably 70% or more of the negative electrode structures, based on the number, satisfy the orientation degree conditions described above, and even more preferably 80% or more of the negative electrode structures, based on the number, satisfy the orientation degree conditions described above.

[0024] (Method for fabricating the negative electrode structure) In the solid-state battery of this disclosure, a negative electrode structure in which the degree of orientation X of negative electrode active material particles in region X of the negative electrode layer is greater than the degree of orientation Y of negative electrode active material particles in region Y can be fabricated, for example, by the following method.

[0025] First, a negative electrode layer Y corresponding to region Y of the negative electrode layer is formed on the support, and a press treatment is performed as necessary. The method for forming the negative electrode layer Y on the support is not particularly limited and can be selected from coating methods, transfer methods, etc. From the viewpoint of workability, a transfer method that can perform the formation of the negative electrode layer Y and the press treatment in one step is preferred. Next, a negative electrode layer X corresponding to region X of the negative electrode layer is formed on the negative electrode layer Y, and a press treatment is performed as necessary. The method for forming the negative electrode layer X on the negative electrode layer Y is not particularly limited and can be selected from coating methods, transfer methods, etc. From the viewpoint of workability, a transfer method that can perform the formation of the negative electrode layer X and the press treatment in one step is preferred. Next, the negative electrode layer X and the solid electrolyte layer are joined together to obtain the negative electrode structure. The solid electrolyte layer joined to the negative electrode layer X may have a positive electrode layer formed on the other side, or it may not have a positive electrode layer formed on the other side.

[0026] The support used in the above method may be a negative electrode current collector or a different material from the negative electrode current collector. An example of a different material from the negative electrode current collector is a temporary support that is removed from the negative electrode layer Y after the negative electrode layer X and the solid electrolyte layer have been joined together. When using a temporary support in the above method, the negative electrode structure is obtained by removing the temporary support from the negative electrode layer Y and then joining the negative electrode layer Y and the negative electrode current collector.

[0027] In the negative electrode structure manufactured by the above method, the negative electrode layer X is subjected to pressure fewer times (during pressing or transfer) compared to the negative electrode layer Y. Therefore, according to the above method, it is possible to manufacture a negative electrode structure in which the degree of orientation X of the negative electrode active material particles in region X of the negative electrode layer is greater than the degree of orientation Y of the negative electrode active material particles in region Y.

[0028] The solid-state battery of this disclosure may include a structure in which a positive electrode layer, a solid electrolyte layer, a negative electrode layer, and a negative electrode current collector are arranged in this order on both sides of the positive electrode current collector (hereinafter also referred to as a positive electrode center stacked structure).

[0029] An example of a positive electrode center stacked structure included in the solid-state battery of this disclosure is shown in Figure 3. As shown in Figure 3, the positive electrode center stacked structure 100 is arranged in the following order: first negative electrode current collector 50A, first negative electrode layer 40A, first solid electrolyte layer 30A, first positive electrode layer 20A, positive electrode current collector 10, second positive electrode layer 20B, second solid electrolyte layer 30B, second negative electrode layer 40B, and second negative electrode current collector layer 50B.

[0030] A solid-state battery having a positive electrode center stacked structure can be manufactured, for example, by a method including the steps shown below. In the following explanation, the first negative electrode layer and the second negative electrode layer may be referred to as the "negative electrode layer" without distinction, the first negative electrode current collector and the second negative electrode current collector may be referred to as the "negative electrode current collector" without distinction, the first positive electrode layer and the second positive electrode layer may be referred to as the "positive electrode layer" without distinction, the first positive electrode current collector and the second positive electrode current collector may be referred to as the "positive electrode current collector" without distinction, and the first solid electrolyte layer and the second solid electrolyte layer may be referred to as the "solid electrolyte layer" without distinction.

[0031] (Process 1) In step 1, positive electrode layers are formed on both sides of the positive electrode current collector to obtain a laminate 1 (layer structure: first positive electrode layer / positive electrode current collector / second positive electrode layer). The method for forming the positive electrode layers on both sides of the positive electrode current collector is not particularly limited and can be selected from coating methods, transfer methods, etc. Press treatment may be applied to the laminate 1 as needed. If necessary, end fillers may be placed at the ends of the positive electrode layers formed on both sides of the positive electrode current collector. The end fillers serve functions such as shaping the ends of the positive electrode layers and preventing the positive electrode layers from coming into contact with the negative electrode layers, which expand during charging. The material of the end fillers can be selected from electrically insulating materials such as resins.

[0032] (Process 2) In step 2, a solid electrolyte layer is formed on the positive electrode layer formed on both sides of the positive electrode current collector to obtain a laminate 2 (layer configuration: first solid electrolyte layer / first positive electrode layer / positive electrode current collector / second positive electrode layer / second solid electrolyte layer). The method for forming the solid electrolyte layer on the positive electrode layer is not particularly limited and can be selected from coating methods, transfer methods, etc. From the viewpoint of workability, a transfer method that can perform the formation of the solid electrolyte layer and the pressing process in one step is preferred.

[0033] (Step 3) In step 3, a negative electrode layer is formed on the solid electrolyte layer formed on the positive electrode layer to obtain a laminate 3 (layer structure: first negative electrode layer / first solid electrolyte layer / first positive electrode layer / positive electrode current collector / second positive electrode layer / second solid electrolyte layer / second negative electrode layer). The method for forming the negative electrode layer on the solid electrolyte layer is not particularly limited and can be selected from coating methods, transfer methods, etc. From the viewpoint of workability, a transfer method that can perform the formation of the negative electrode layer and the pressing process in one step is preferred.

[0034] (Step 4) In step 4, a negative electrode current collector is placed on the negative electrode layer formed on the solid electrolyte layer to obtain a laminate 4 (layer configuration: first negative electrode current collector / first negative electrode layer / first solid electrolyte layer / first positive electrode layer / positive electrode current collector / second positive electrode layer / second solid electrolyte layer / second negative electrode layer / second negative electrode current collector). If necessary, the laminate 4 may be subjected to a press treatment. If the negative electrode layer formed on the solid electrolyte layer in step 3 is in contact with the negative electrode current collector, step 4 can be omitted.

[0035] The negative electrode layer of a solid-state battery manufactured by the method including the above process is subjected to less pressure (during pressing or transfer) compared to the positive electrode layer. Therefore, the method including the above steps allows for sufficient pressure to be applied to the positive electrode layer to increase its density while controlling the pressure applied to the negative electrode layer to a desired degree. For this reason, solid-state batteries including a positive electrode center stacked structure tend to have an excellent balance of battery characteristics.

[0036] According to the method including the above steps, a solid-state battery can be easily manufactured in which the degree of orientation X of the negative electrode active material particles in the region X on the solid electrolyte layer side of the negative electrode layer is greater than the degree of orientation Y of the negative electrode active material particles in the region Y on the negative electrode current collector side. A solid-state battery in which the degree of orientation X of negative electrode active material particles in region X of the negative electrode layer is greater than the degree of orientation Y of negative electrode active material particles in region Y can be obtained, for example, by performing the formation of the negative electrode layer in step 3 of the above method by a transfer method (specifically, by transferring the negative electrode layer X of the negative electrode structure produced by the negative electrode structure fabrication method described above to the solid electrolyte layer).

[0037] The following describes the components that make up the solid-state battery of this disclosure. In the following description, the negative electrode current collector and the positive electrode current collector may be referred to as "current collector" without distinction, the negative electrode layer and the positive electrode layer may be referred to as "electrode" without distinction, and the negative electrode active material and the positive electrode active material may be referred to as "electrode active material" without distinction.

[0038] (Current collector) The type of current collector included in the solid-state battery of this disclosure is not particularly limited and can be selected and used from known current collectors. Specifically, the material of the current collector may be a metal selected from Ag, Cu, Au, Al, Ni, Fe, and Ti, or an alloy containing these metals. In some embodiments of this disclosure, the positive electrode current collector may contain Al, and the negative electrode current collector may contain Cu. The thickness of the current collector is not particularly limited and can be selected considering the type and size of the battery obtained using the current collector. The thickness of the current collector may be, for example, 5 μm or more, 10 μm or more, or 20 μm or more. The thickness of the current collector may be, for example, 120 μm or less, 80 μm or less, or 60 μm or less.

[0039] (electrode layer) The electrode layer included in the solid-state battery of this disclosure contains at least an electrode active material and may optionally contain a binder, a conductive material, a solid electrolyte, etc. Examples of negative electrode active materials include carbon materials, active materials containing Si elements, metallic lithium, lithium-containing alloys, metals or alloys that can be alloyed with lithium, oxides, and transition metal nitrides. Examples of carbon materials include graphite materials, amorphous carbon materials, carbon black, and activated carbon. Examples of graphite materials include natural graphite and artificial graphite. Examples of amorphous carbon materials include hard carbon, soft carbon, coke, mesocarbon microbeads (MCMB), and mesophase pitch carbon fiber (MCF). Graphite materials may be coated with metal or amorphous carbon. Active materials containing the Si element include elemental silicon, silicon alloys (for example, alloys of Si with one or more metals selected from the group consisting of Sn, Ti, Fe, Ni, Cu, Co, and Al), porous silicon, silicon clathrate compounds, silicon oxides, and the like.

[0040] Specifically, examples of positive electrode active materials include composite oxides containing lithium and transition metals (hereinafter also referred to as composite oxides). Examples of composite oxides include composite oxides having a layered crystal structure, composite oxides having a spinel-type crystal structure, and composite oxides having an olivine-type crystal structure. Specific examples of composite oxides having a layered crystal structure include compounds represented as LiMO2 (where M is at least one transition metal selected from the group consisting of Ni, Co, and Mn), and compounds to which heterogeneous elements are added. Representative examples of composite oxides having a layered crystal structure include LCO (lithium cobaltate), NCM (lithium nickel-cobalt-manganate), and NCA (lithium nickelate or lithium nickel-cobalt-aluminate). LiMn2O4 is a specific example of a composite oxide having a spinel-type crystal structure. A specific example of a composite oxide having an olivine-type crystal structure is LiMPO4 (where M is Fe, Co, Ni, or Mn).

[0041] The electrode active material contained in the electrode layer may be a single type or a combination of two or more types. The electrode active material may take the form of, for example, fibers, spheres, flakes, etc. The volume-average particle size of the electrode active material may be selected from, for example, a range of 5 μm to 50 μm. The volume-average particle size of the electrode active material is defined as the value (D50) at which the cumulative amount from the smaller diameter side in the volume-based particle size distribution obtained using the laser diffraction-scattering method becomes 50%.

[0042] Examples of binders include polyvinylidene fluoride (PVdF), polyethylene, polypropylene, polyethylene terephthalate, cellulose, nitrocellulose, carboxymethylcellulose, polyethylene oxide, polyepichlorohydrin, polyacrylonitrile, styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), polyacrylate, polymethacrylate, and polytetrafluoroethylene (PTFE). The binder contained in the electrode layer may be a single type or a combination of two or more types.

[0043] Examples of conductive materials include carbon materials, metals, conductive oxides, and conductive nitrides. Specifically, carbon materials include graphite, carbon black (acetylene black, thermal black, furnace black, etc.), carbon nanotubes (CNTs), carbon nanofibers (CNFs), and vapor-grown carbon fibers (VGCFs). TM Examples include: The conductive material contained in the electrode layer may be a single type or a combination of two or more types.

[0044] Examples of solid electrolytes included in the electrode layer include sulfide solid electrolytes, oxide solid electrolytes, and polymer solid electrolytes. From the viewpoint of battery performance, sulfide solid electrolytes and polymer solid electrolytes are preferred as solid electrolytes, and from the viewpoint of thermal stability, sulfide solid electrolytes are more preferred. The solid electrolyte contained in the electrode layer may be a single type or a combination of two or more types.

[0045] Examples of sulfide solid electrolytes include compounds containing a metal element that acts as a conductive ion and sulfur (S). Examples of metallic elements include Li, Na, K, Mg, and Ca. Among these, Li is preferred as a metallic element. The sulfide solid electrolyte may contain Li and S, and at least one selected from the group consisting of P, Si, Ge, Al, and B. Among these, a sulfide solid electrolyte containing Li, S, and P (hereinafter also referred to as an LPS-type sulfide solid electrolyte) is preferred. From the viewpoint of ionic conductivity, sulfide solid electrolytes may contain halogen elements such as Cl, Br, and I. From the viewpoint of chemical stability, sulfide solid electrolytes may contain oxygen (O).

[0046] Specifically, LPS-type sulfide solid electrolytes include Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, LiBr-LiI-Li2S-P2S5, and Li2S-P2S5-Z. m S n (In the formulas, m and n are positive numbers, and Z is Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y Examples include (where x and y are positive numbers, and M is P, Si, Ge, B, Al, Ga, or In)

[0047] In the above, the term "Li2S-P2S5" refers to a sulfide solid electrolyte obtained using Li2S and P2S5 as raw materials, and the same applies to other terms.

[0048] Among LPS-type sulfide solid electrolytes, sulfide solid electrolytes obtained using Li2S and P2S5 are preferred, and sulfide solid electrolytes satisfying the following formula are more preferred. Li 3+x+5y P 1-y S4 (0 < x ≤ 0.6, 0 < y ≤ 0.2)

[0049] As the oxide solid electrolyte, compounds having a NASICON (Na3Zr2PSi2O 12 )-type crystal structure can be mentioned. Compounds having a NASICON-type crystal structure have high ionic conductivity and excellent stability in the atmosphere. As compounds having a NASICON-type crystal structure, lithium-containing phosphates can be mentioned. As the phosphate, a composite lithium phosphate salt with Ti (for example, Li 1+x Al x Ti 2-x (PO4)3), and compounds in which all or part of Ti in the composite lithium phosphate salt is substituted with a tetravalent transition metal such as Ge, Sn, Hf, Zr or a trivalent transition metal such as Al, Ga, In, Y, La, etc. can be mentioned. Specifically, as compounds having a NASICON-type crystal structure, Li-Al-Ge-P-O-based materials (Li 1+x Al x Ge 2-x (PO4)3), Li-Al-Zr-P-O-based materials (Li 1+x Al x Zr 2-x (PO4)3), Li-Al-Ti-P-O-based materials (Li 1+x Al x Ti 2-x (PO4)3), etc. can be mentioned.

[0050] Examples of polymeric solid electrolytes include mixtures (complexes) of polymer compounds and electrolyte salts. Specific examples of polymer compounds include polyether-based polymer compounds such as polyethylene oxide (PEO) and polypropylene oxide (PPO), polyamine-based polymer compounds such as polyethyleneimine (PEI), and polysulfide-based polymer compounds such as polyalkylene sulfide (PAS). Among these, polyether-based polymer compounds are preferred.

[0051] (solid electrolyte layer) The solid electrolyte layer included in the solid battery of this disclosure includes a solid electrolyte. The type of solid electrolyte included in the solid electrolyte layer is not particularly limited and may be selected from the solid electrolytes that may be included in the electrode layer as described above. If the electrode layer contains a solid electrolyte, the solid electrolyte contained in the electrode layer and the electrolyte contained in the solid electrolyte layer may be the same or different. The solid electrolyte layer may contain only one type of solid electrolyte or a combination of two or more types. The solid electrolyte layer may contain a composite solid electrolyte comprising an inorganic solid electrolyte and a polymer electrolyte.

[0052] The solid electrolyte layer may contain a liquid electrolyte (electrolyte) along with the solid electrolyte. For example, the solid electrolyte layer may contain an electrolyte in an amount of less than 10% by mass relative to the total amount of electrolyte.

[0053] If the solid-state battery of this disclosure includes an electrolyte solution as the electrolyte, the type of electrolyte solution is not particularly limited, and known electrolyte solutions can be used. Specific examples of electrolytes include liquids obtained by dissolving lithium salts such as LiPF6 and LiFSi in an organic solvent. Specific examples of organic solvents include cyclic or linear carbonates such as ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). The solvent may be a mixture of two or more solvents, or a mixture containing both cyclic and linear carbonates. The solvent may contain additives such as vinylene carbonate (VC).

[0054] (Exterior) The solid-state battery of this disclosure may further include an outer casing. The outer casing houses an electrode laminate comprising at least a current collector, an electrode layer, and a solid electrolyte layer. Examples of outer casings include laminate-type outer casings and case-type outer casings. A laminate-type outer casing may be formed from a laminate (laminate film) having a metal layer containing a metal such as aluminum and a heat-seal layer containing a resin that melts upon heating.

[0055] (Restraining member) The battery of this disclosure may further include a restraining member. The restraining member applies restraining pressure in the thickness direction to the electrode stack described above. The restraining pressure applied in the thickness direction of the electrode stack may be, for example, 0.1 MPa or more, 1 MPa or more, or 5 MPa or more. The restraining pressure applied in the thickness direction of the electrode stack may be, for example, 100 MPa or less, 50 MPa or less, or 20 MPa or less.

[0056] (Applications of solid-state batteries) The applications of the solid-state batteries of this disclosure are not particularly limited. Typical applications include power sources for vehicles, electronic equipment, and electric storage systems. Of these, the batteries of this disclosure are preferably used as power sources for vehicles, and more preferably as power sources for hybrid vehicles, plug-in hybrid vehicles, or electric vehicles. Examples of vehicles include electric four-wheeled vehicles, electric two-wheeled vehicles, gasoline-powered vehicles, and diesel-powered vehicles. Examples of electric four-wheeled vehicles include battery electric vehicles (BEVs), plug-in hybrid electric vehicles (PHEVs), and hybrid electric vehicles (HEVs). Examples of electric two-wheeled vehicles include electric motorcycles and electric-assist bicycles.

[0057] <Method of manufacturing solid-state batteries> One embodiment of this disclosure is, The method for manufacturing a solid battery as described above in this disclosure, This includes transferring the negative electrode layer formed on the support to the solid electrolyte layer. The negative electrode layer formed on the support comprises a negative electrode layer Y formed on the support and a negative electrode layer X formed on the negative electrode layer Y, wherein the degree of orientation X of the negative electrode active material particles in the negative electrode layer X is greater than the degree of orientation Y of the negative electrode active material particles in the negative electrode layer Y, in a method for manufacturing a solid-state battery.

[0058] According to the method of this disclosure, a solid-state battery can be manufactured in which the junction between the negative electrode layer and the solid electrolyte layer is well maintained.

[0059] The negative electrode layer transferred to the solid electrolyte layer in the method disclosed herein can be formed, for example, by the following method.

[0060] First, a negative electrode layer Y is formed on the support, and pressing is performed as necessary. The method for forming the negative electrode layer Y on the support is not particularly limited and can be selected from coating methods, transfer methods, etc. From the viewpoint of workability, a transfer method that can perform the formation of the negative electrode layer Y and the pressing in a single step is preferred. Next, a negative electrode layer X is formed on the negative electrode layer Y, and pressing is performed as necessary. The method for forming the negative electrode layer X on the negative electrode layer Y is not particularly limited and can be selected from coating methods, transfer methods, etc. From the viewpoint of workability, a transfer method that can perform the formation of the negative electrode layer X and the pressing in a single process is preferred. The support may be the negative electrode current collector or a different material from the negative electrode current collector. An example of a different material from the negative electrode current collector is a temporary support that is removed from the negative electrode layer after the negative electrode layer has been transferred to the solid electrolyte layer. When using a temporary support in the above method, a solid-state battery including the negative electrode structure of this disclosure can be obtained by removing the temporary support from the negative electrode layer Y and then joining the negative electrode layer Y and the negative electrode current collector.

[0061] The negative electrode layer X formed by the above method is subjected to less pressure (during pressing or transfer) compared to the negative electrode layer Y. Therefore, it is easy to create a state in which the degree of orientation X of the negative electrode active material particles in the negative electrode layer X is greater than the degree of orientation Y of the negative electrode active material particles in the negative electrode layer Y. By transferring the negative electrode layer formed on the support using the above method to a solid electrolyte layer, a solid-state battery can be manufactured that includes a negative electrode structure in which the degree of orientation X of the negative electrode active material particles in region X is greater than the degree of orientation Y of the negative electrode active material particles in region Y.

[0062] The solid-state battery manufactured by the method of this disclosure may be a solid-state battery including a positive electrode center stacked structure. That is, the method of this disclosure is Forming positive electrode layers on both sides of the positive electrode current collector, Forming a solid electrolyte layer on the positive electrode layer, The process may include, in this order, forming a negative electrode layer on the solid electrolyte layer.

[0063] According to the above method, a solid-state battery can be manufactured that includes a positive electrode center stacked structure and maintains a good junction between the negative electrode layer and the solid electrolyte layer. In the above method, the method for forming the positive electrode layer, the solid electrolyte layer, and the negative electrode layer is not particularly limited and can be selected from coating methods, transfer methods, etc. [Explanation of Symbols]

[0064] 30: Solid electrolyte layer 40: Negative electrode layer 50: Negative electrode current collector

Claims

1. The structure includes a solid electrolyte layer, a negative electrode layer, and a negative electrode current collector arranged in this order. The aforementioned negative electrode layer contains negative electrode active material particles, A solid-state battery in which, when the negative electrode layer is divided in the thickness direction into a region X on the solid electrolyte side and a region Y on the negative electrode current collector side, the degree of orientation X of the negative electrode active material particles in region X is greater than the degree of orientation Y of the negative electrode active material particles in region Y.

2. The solid battery according to claim 1, wherein the negative electrode active material particles contain the element Si.

3. A solid-state battery according to claim 1 or claim 2, comprising a structure in which a positive electrode layer, a solid electrolyte layer, a negative electrode layer, and a negative electrode current collector are arranged in this order on both sides of a positive electrode current collector.

4. A method for manufacturing a solid battery according to any one of claims 1 to 3, This includes transferring the negative electrode layer formed on the support to the solid electrolyte layer. A method for manufacturing a solid-state battery, wherein the negative electrode layer formed on the support comprises a negative electrode layer Y formed on the support and a negative electrode layer X formed on the negative electrode layer Y, and the degree of orientation X of the negative electrode active material particles in the negative electrode layer X is greater than the degree of orientation Y of the negative electrode active material particles in the negative electrode layer Y.

5. Forming positive electrode layers on both sides of the positive electrode current collector, Forming a solid electrolyte layer on the positive electrode layer, A method for manufacturing a solid battery according to claim 4, comprising, in this order, forming a negative electrode layer on the solid electrolyte layer.

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