Lithium ion secondary battery

Abstract

The lithium ion secondary battery is a lithium ion secondary battery in which a positive electrode layer containing a positive electrode active material and a negative electrode layer containing a negative electrode active material are sequentially stacked with an interlayer solid electrolyte layer therebetween, and a ratio t1 / t2 of an average thickness t1 of the thickest interlayer solid electrolyte layer in the interlayer solid electrolyte layer to an average thickness t2 of the thinnest interlayer solid electrolyte is 1.02 ≤ t1 / t2 ≤ 1.99.

Description

TECHNICAL FIELD

[0001] The present application relates to a lithium ion secondary battery.

[0002] This application claims priority from Japanese Patent Application No. 2020-009573 filed on January 24, 2020, the contents of which are incorporated herein by reference. BACKGROUND

[0003] In recent years, the development of electronic technology is remarkable, and the miniaturization, thinning, and multifunctionalization of portable electronic devices have been achieved. Along with this, there is a strong demand for miniaturization, thinning, and improvement of reliability for batteries that become power sources for electronic devices.

[0004] In the lithium ion secondary battery that is widely used as a battery that becomes a power source for electronic devices at present, a liquid electrolyte (electrolyte) such as an organic solvent has been used as a medium for moving ions, that is, an electrolyte. However, in a battery using a liquid electrolyte, there is a possibility that the electrolyte leaks due to external impact or the like, and the function of the battery decreases, and it is required to further improve the reliability of the lithium ion secondary battery.

[0005] Therefore, as one countermeasure for improving the reliability of the lithium ion secondary battery, the development of a lithium ion secondary battery using a solid electrolyte instead of a liquid electrolyte as an electrolyte, which is laminated or wound by sandwiching it between electrodes, is being promoted.

[0006] However, it is known that the ionic conductivity of a solid electrolyte is lower than that of a liquid electrolyte, and various studies have been conducted to improve the output characteristics of a lithium ion secondary battery using a solid electrolyte.

[0007] In Patent Literature 1, it is disclosed that by mixing a solid electrolyte in an electrode, and controlling the ratio of the solid electrolyte to the electrode active material in the thickness direction of the electrode, and the porosity of the electrode, the rate characteristics are improved.

[0008] In Patent Literature 2, it is disclosed that by mixing a solid electrolyte in an electrode, and controlling the difference between the resistivity accompanying the movement of ions in the electrode and the resistivity accompanying the movement of electrons to be 0 kΩ·cm or more and 100 kΩ·cm or less, the charge and discharge efficiency can be improved.

[0009] In Patent Literature 3, it is disclosed that by making the standard deviation of the thickness of the electrolyte film be 5.0 μm or less, a solid electrolyte film having excellent battery characteristics can be obtained.

[0010] Prior Art Documents

[0011] Patent Literature

[0012] Patent Literature 1: Japanese Patent Application Publication No. 2012-104270

[0013] Patent Literature 2: International Publication No. 2014 / 002858

[0014] Patent Literature 3: Japanese Patent Application Laid-Open No. 2017-157362 SUMMARY

[0015] PROBLEMS TO BE SOLVED BY THE INVENTION

[0016] However, with the multi-functionality of electronic devices, there is a demand for lithium ion secondary batteries having higher output characteristics when using a solid electrolyte.

[0017] The present application provides a lithium ion secondary battery having high output characteristics when using a solid electrolyte as an electrolyte, which solves the above problem.

[0018] METHOD FOR SOLVING THE PROBLEM

[0019] The inventors conducted intensive studies, and as a result, it was clarified that by setting the thicknesses of the plurality of solid electrolyte layers in the thickness direction within the lithium ion secondary battery to a specific ratio, the output characteristics are improved, and the present application was completed.

[0020] That is, in order to solve the above problem, the following means is provided.

[0021] In the lithium ion secondary battery of the present mode, a positive electrode layer containing a positive electrode active material and a negative electrode layer containing a negative electrode active material are sequentially stacked with a solid electrolyte layer interposed therebetween, and in the solid electrolyte layer, the ratio t1 / t2 of the average thickness t1 of the thickest solid electrolyte layer to the average thickness t2 of the thinnest solid electrolyte layer is 1.02 ≤ t1 / t2 ≤ 1.99.

[0022] By adopting such a structure, the output of the lithium ion secondary battery using a solid electrolyte can be improved. This is based on the following principle. Compared to the case where the average thickness of the solid electrolyte layer contained in the lithium ion secondary battery is uniform, the charge and discharge reactions in the positive electrode layer and the negative electrode layer with the solid electrolyte layer interposed therebetween proceed more quickly, thereby generating a deviation of the electric charge between the positive electrode layer and the negative electrode layer within the lithium ion battery. Through this deviation of the electric charge, the charge and discharge reactions of the solid electrolyte layer with a thick average thickness are promoted.

[0023] By setting the ratio of the average thickness of the solid electrolyte layer to the range of the present application, a deviation of the electric charge between the positive electrode layer and the negative electrode layer is generated, and the occurrence of non-uniform reactions within the lithium ion secondary battery accompanying the difference in the average thickness of the solid electrolyte layer is suppressed, thereby improving the output characteristics.

[0024] In the lithium ion secondary battery of the above-described aspect, the standard deviation σ of the average thickness t of each of the solid electrolyte layers can be 0.15 ≤ σ ≤ 1.66 (μm).

[0025] Thus, the occurrence of uneven reactions in the lithium ion secondary battery is suppressed, and a moderate deviation of electric charges is generated uniformly in the lithium ion secondary battery, and thus a high output characteristic can be obtained.

[0026] In the lithium ion secondary battery of the above-described aspect, at least a portion between the positive electrode layer or the negative electrode layer and the solid electrolyte layer can have an intermediate layer containing a constituent element of the positive electrode layer or the negative electrode layer and the solid electrolyte.

[0027] Thus, the transfer of lithium ions between the positive electrode layer, the negative electrode layer, and the solid electrolyte layer can be appropriately performed. That is, by reducing the interface resistance, the generation of a deviation of electric charges and the subsequent charge-discharge reactions are further promoted, and a high output characteristic can be obtained.

[0028] In the lithium ion secondary battery of the above-described aspect, the average thickness T of the average thickness t of each of the solid electrolyte layers can be 4.8 ≤ T ≤ 9.8 (μm).

[0029] Thus, the insulation between the positive electrode layer and the negative electrode layer can be sufficiently ensured, and the transfer of lithium ions can be appropriately performed. Thus, a high output characteristic can be obtained.

[0030] Effects of the Invention

[0031] The present application can provide a lithium ion secondary battery having a high output characteristic. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 A part of a cross-sectional view in a stacking direction of a lithium ion secondary battery of the present embodiment is shown.

[0033] Figure 2 A part of a cross-sectional view in a stacking direction of a lithium ion secondary battery of a modification of the present embodiment is shown.

[0034] Explanation of Reference Numerals

[0035] 1 … … Lithium ion secondary battery

[0036] 20 … … Stacked body

[0037] 30 … … Positive electrode

[0038] 31 … … Positive electrode current collector layer

[0039] 32 … … Positive electrode active material layer

[0040] 40 … … Negative electrode

[0041] 41 …… negative current collector layer

[0042] 42 …… negative active material layer

[0043] 50 …… solid electrolyte layer

[0044] 60 …… positive external electrode

[0045] 70 …… negative external electrode

[0046] 80 …… edge layer DETAILED DESCRIPTION

[0047] Hereinafter, the present application will be described in detail with appropriate reference to the accompanying drawings. In the drawings used in the following description, in order to easily understand the features of the present application, sometimes a portion to be a feature is shown enlarged for convenience. Therefore, the dimensional ratio and the like of each constituent element recited in the drawings are sometimes different from the actual ones. The materials, dimensions, shapes, and the like exemplified in the following description are one example, and the present application is not limited thereto, and can be implemented by appropriately changing them within a range where the effects are exerted without changing the gist thereof. For example, the structures recited in different embodiments can be appropriately combined and implemented.

[0048] First, the directions are defined. One direction of one face of the positive electrode layer 30 (refer to Figure 1 ) is set as the x direction, and a direction orthogonal to the x direction is set as the y direction. The x direction is, for example, a direction in which the positive external electrode 60 and the negative external electrode 70 sandwich the laminated body 20. The x direction and the y direction are one example of in-plane directions. The z direction is a direction orthogonal to the x direction and the y direction. The z direction is one example of a laminating direction. Hereinafter, sometimes the +z direction is expressed as "up" and the -z direction is expressed as "down". The up and down do not necessarily coincide with the direction in which the gravity is applied.

[0049] (Lithium ion secondary battery)

[0050] First, the lithium ion secondary battery of the present embodiment will be described.

[0051] As shown in Figure 1 , the lithium ion secondary battery 1 includes a laminated body 20 in which a positive electrode layer 30 and a negative electrode layer 40 are laminated with a solid electrolyte layer 50 interposed therebetween. The laminated body 20 is, for example, sandwiched in the laminating direction by an outer layer 55 to be described later. The positive electrode layer 30 has a positive electrode current collector layer 31 and a positive electrode active material layer 32. The negative electrode layer 40 has a negative electrode current collector layer 41 and a negative electrode active material layer 42.

[0052] On the same plane as the positive electrode layer 30 and the negative electrode layer 40, the edge layer 80 is formed. The laminate 20 is a 6-faceted body having 2 end faces and 2 side faces formed as faces parallel to the stacking direction, and an upper face and a lower face formed as faces orthogonal to the stacking direction. The positive electrode current collector layer 31 is exposed on the 1st end face, and the negative electrode current collector layer 41 is exposed on the 2nd end face.

[0053] Further, the 1st end face and the 2nd end face are opposed to each other, and the 1st side face and the 2nd side face are opposed to each other. Further, as described later, the positive electrode current collector layer 31 and the negative electrode current collector layer 41 are also exposed on a part of the 1st side face and the 2nd side face.

[0054] The positive electrode external electrode 60 electrically connected to the positive electrode current collector layer 31 is disposed so as to cover the 1st end face side of the laminate 20. Further, the electrical connection is made by connecting the positive electrode external electrode 60 to the positive electrode current collector layer 31 of the positive electrode layer 30 exposed on the 1st end face, the 1st side face, and the 2nd side face of the laminate 20.

[0055] The negative electrode external electrode 70 electrically connected to the negative electrode current collector layer 41 is disposed so as to cover the 2nd end face side of the laminate 20. Further, the electrical connection is made by connecting the negative electrode external electrode 70 to the negative electrode current collector layer 41 of the negative electrode layer 40 exposed on the 2nd end face, the 1st side face, and the 2nd side face of the laminate 20.

[0056] Here, as the description in the following description, either or both of the positive electrode active material and the negative electrode active material are sometimes collectively referred to as an active material, either or both of the positive electrode active material layer 32 and the negative electrode active material layer 42 are sometimes collectively referred to as an active material layer, either or both of the positive electrode current collector layer 31 and the negative electrode current collector layer 41 are sometimes collectively referred to as a current collector layer, either or both of the positive electrode layer 30 and the negative electrode layer 40 are sometimes collectively referred to as an electrode layer, the 1st end face and the 2nd end face are sometimes collectively referred to as an end face, the 1st side face and the 2nd side face are sometimes collectively referred to as a side face, and the positive electrode external electrode 60 and the negative electrode external electrode 70 are sometimes collectively referred to as an external electrode.

[0057] In order to eliminate the step difference of the solid electrolyte layer 50 from the positive electrode layer 30 and the step difference of the solid electrolyte layer 50 from the negative electrode layer 40, it is preferable to provide the edge layer 80 of the lithium ion secondary battery 1 of the present embodiment in a case where the step difference is large. The edge layer 80 is preferably provided on the same plane as the positive electrode layer 30 and the negative electrode layer 40. Due to the presence of the edge layer 80, the step difference of the solid electrolyte layer 50 from the positive electrode layer 30 and the negative electrode layer 40 is eliminated, so the denseness of the solid electrolyte layer 50 from the electrode layer is high, and it is difficult to cause interlayer peeling (delamination), warping caused by the firing of the lithium ion secondary battery.

[0058] (Solid electrolyte layer)

[0059] The solid electrolyte layer 50 of the lithium ion secondary battery 1 of the present embodiment is sandwiched by the positive electrode layer 30 and the negative electrode layer 40 in the z direction. In Figure 1 In the present embodiment, a case where there are three solid electrolyte layers 50a, 50b, 50c is exemplified. The solid electrolyte layer 50a is the thinnest solid electrolyte layer in thickness, and the solid electrolyte layer 50b is the thickest solid electrolyte layer in thickness. The solid electrolyte layer 50c has a thickness between the solid electrolyte layer 50a and the solid electrolyte layer 50b. Among them, the thickness of each solid electrolyte layer 50 is judged by the average thickness.

[0060] The ratio t1 / t2 of the average thickness t1 of the thickest solid electrolyte layer 50b to the average thickness t2 of the thinnest solid electrolyte layer 50a is 1.02 ≤ t1 / t2 ≤ 1.99. Here, the average thickness of the solid electrolyte layer 50 is the average thickness in the in-plane direction of only one solid electrolyte layer 50, for example, the average thickness in the x direction. Among them, in the present embodiment, the average thickness of the solid electrolyte layer 50 is the average thickness in the z direction. Figure 1 In the present embodiment, a case where the thickness of the two solid electrolyte layers 50 sandwiching the positive electrode layer 30, the negative electrode layer 40, and the solid electrolyte layer 50b in the z direction is the same, and the thickness of the solid electrolyte layer sandwiched thereby is thin, is exemplified, but it can be different respectively, and the thickness of the taught solid electrolyte layer can also be thick.

[0061] By adopting such a structure, the output of the lithium ion secondary battery using a solid electrolyte can be improved. This is based on the following principle. With respect to the case where the average thickness of the solid electrolyte layer is uniform, the charge and discharge reaction in the positive electrode layer and the negative electrode layer across the solid electrolyte layer of which the average thickness is thin proceeds more quickly, thereby generating a deviation of the electric charge between the positive electrode layer and the negative electrode layer within the lithium ion battery. Through this deviation of the electric charge, the charge and discharge reaction of the solid electrolyte layer of which the average thickness is thick is promoted.

[0062] By setting the ratio of the average thickness of the thinnest solid electrolyte layer 50a to the average thickness of the thickest solid electrolyte layer 50b within the range of the present application, a deviation of the electric charge between the positive electrode layer and the negative electrode layer is generated, and the occurrence of a non-uniform reaction within the lithium ion secondary battery accompanying the difference in the average thickness of the solid electrolyte layer 50 is suppressed, thereby improving the output characteristics.

[0063] In addition, in the solid electrolyte layer 50 of the present embodiment, the ratio t1 / t2 of the average thickness t1 of the thickest solid electrolyte layer 50b to the average thickness t2 of the thinnest solid electrolyte layer 50a is preferably 1.02 ≤ t1 / t2 ≤ 1.99.

[0064] By setting t1 / t2 to the above range, the difference in the charge imbalance between the positive electrode layer and the negative electrode layer in the lithium ion battery becomes small, and thus the charge imbalance between the positive electrode layer and the negative electrode layer as a whole of the lithium ion secondary battery becomes close, whereby the occurrence of the uneven reaction in the lithium ion secondary battery is suppressed, and thus the output characteristics are improved.

[0065] The average thickness of each of the solid electrolyte layers in the solid electrolyte layer 50 of the present embodiment can be found by cross-sectional SEM observation of the lithium ion secondary battery 1. In the cross section of the lithium ion secondary battery 1, the average of the thicknesses at five points that approximately equally divide the solid electrolyte layer 50 is set as the average thickness of the solid electrolyte layer 50, the thickness of the solid electrolyte layer 50b having the thickest average thickness is set as t1, and the thickness of the solid electrolyte layer 50a having the thinnest average thickness is set as t2.

[0066] The solid electrolyte layer 50 of the present embodiment is preferably such that the standard deviation σ of the average thickness t in all of the solid electrolyte layers is 0.15 ≤ σ ≤ 1.66 (μm).

[0067] Thus, the occurrence of the uneven reaction in the lithium ion secondary battery is suppressed, and a moderate charge imbalance is generated uniformly in the lithium ion secondary battery, whereby high output characteristics are obtained.

[0068] In addition, the solid electrolyte layer 50 of the present embodiment is more preferably such that the standard deviation σ of the average thickness in all of the solid electrolyte layers is 0.55 ≤ σ ≤ 1.24 (μm).

[0069] The solid electrolyte layer 50 of the present embodiment is preferably such that the average thickness T of the average thickness t of each of the solid electrolyte layers in the lithium ion secondary battery of the above-described mode is 4.8 ≤ T ≤ 9.8 (μm).

[0070] Thus, the insulation between the positive electrode layer and the negative electrode layer is sufficiently ensured, and the transfer of lithium ions is appropriately performed. Thus, high output characteristics are obtained.

[0071] The solid electrolyte layer 50 of the present embodiment is composed of a solid electrolyte as a main component. As the solid electrolyte, a publicly known material can be used, and for example, lithium titanium aluminum phosphate Li 1+x Al x Ti 2-x (PO4)3 (0 ≤ x ≤ 0.6), lithium germanium phosphate Li 1.5 Ge 2.0 (PO4)3, lithium aluminum germanium phosphate Li 1.5 Al 0.5 Ge 1.5 (PO4)3, Li 3+x1 Si x1 P 1-x1O4 (0.4 ≤ x1 ≤ 0.6), Li 3.4 V 0.4 Ge 0.6 O4, lithium germanium phosphate (LiGe2(PO4)3), Li2O-V2O5-SiO2, Li2O-P2O5-B2O3, Li3PO4, Li 0.5 La 0.5 TiO3, Li 14 Zn(GeO4)4, Li7La3ZrO 12 , Li 3.6 Si 0.6 P 0.4 O4, Li3BO3-Li2SO4 glass ceramic, Li3BO3-Li2SO4-Li2CO3 glass ceramic, polyethylene oxide, and the like.

[0072] The solid electrolyte of the present embodiment can also use a solid electrolyte that has undergone a change in composition through a change in the composition ratio or substitution of a different element, as long as it is capable of obtaining the characteristics of a solid electrolyte.

[0073] The solid electrolyte layer 50 of the present embodiment preferably contains lithium titanium aluminum phosphate, lithium germanium aluminum phosphate, or the like, or an oxide such as Li 0.5 La 0.5 TiO3, Li 3.6 Si 0.6 P 0.4 O4 as a solid electrolyte.

[0074] In the solid electrolyte that constitutes the solid electrolyte layer 50 of the present embodiment, the main component refers to a constituent that occupies the largest proportion as a constituent component of the solid electrolyte layer 50.

[0075] As a subcomponent that constitutes the solid electrolyte layer 50 of the present embodiment, a sintering filler used when forming the solid electrolyte layer, a decomposition product thereof, and the like can be given.

[0076] (Positive electrode layer and negative electrode layer)

[0077] The positive electrode layer 30 and the negative electrode layer 40 are each provided a plurality of times within the laminate 20. The positive electrode layer 30 and the negative electrode layer 40 are alternately laminated with the solid electrolyte layer therebetween.

[0078] The positive electrode layer 30 has a positive electrode current collector layer 31 and a positive electrode active material layer 32 containing a positive electrode active material. The negative electrode layer 40 has a negative electrode current collector layer 41 and a negative electrode active material layer 42 containing a negative electrode active material.

[0079] The positive electrode current collector layer 31 and the negative electrode current collector layer 41 are excellent in conductivity. The positive electrode current collector layer 31 and the negative electrode current collector layer 41 are, for example, silver, palladium, gold, platinum, aluminum, copper, nickel. Copper is difficult to react with the positive electrode active material, the negative electrode active material, and the solid electrolyte. For example, if the positive electrode current collector layer 31 and the negative electrode current collector layer 41 use copper, the internal resistance of the lithium ion secondary battery 1 can be reduced. The substance constituting the positive electrode current collector layer 31 and the negative electrode current collector layer 41 can be the same or different.

[0080] The positive electrode active material layer 32 is formed on one face or both faces of the positive electrode current collector layer 31. The face of the positive electrode current collector layer 31 on which the opposite negative electrode layer 40 is not present can also be free of the positive electrode active material layer 32. In addition, the negative electrode active material layer 42 is formed on one face or both faces of the negative electrode current collector layer 41. The face of the negative electrode current collector layer 41 on which the opposite positive electrode layer 30 is not present can also be free of the negative electrode active material layer 42. For example, the positive electrode layer 30 or the negative electrode layer 40 located in the uppermost layer or the lowermost layer of the laminate 20 can also have no positive electrode active material layer 32 or negative electrode active material layer 42 on one face.

[0081] The positive electrode active material layer 32 and the negative electrode active material layer 42 contain positive electrode active materials and negative electrode active materials that donate and accept electrons. In addition, a conductive aid, an ion-conductive aid, a binder, or the like can be contained. The positive electrode active material and the negative electrode active material are preferably capable of efficiently intercalating and deintercalating lithium ions.

[0082] The positive electrode active material and the negative electrode active material can use a publicly known material, and are, for example, a transition metal oxide, a transition metal complex oxide. The positive electrode active material and the negative electrode active material are specifically, for example, a lithium manganese complex oxide Li2Mn a Ma 1-a O3 (0.8 ≤ a ≤ 1, Ma = Co, Ni), lithium cobaltate (LiCoO2), lithium nickelate (LiNiO2), lithium manganese spinel (LiMn2O4), a complex metal oxide represented by the general formula: LiNi x Co y Mn z O2 (x + y + z = 1, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1), a lithium vanadium compound (LiV2O5), an olivine-type LiMbPO4 (where Mb is one or more elements selected from Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, Zr), a lithium vanadium phosphate (Li3V2(PO4)3 or LiVOPO4), a Li-excess system solid solution positive electrode represented by Li2MnO3-LiMcO2 (Mc = Mn, Co, Ni), a lithium titanate (Li4Ti5O 12 ), a titanium oxide (TiO2) Li s Ni t Cou Al v O2(0.9 < s < 1.3, 0.9 < t + u + v < 1.1) and the like.

[0083] In addition, as the positive electrode active material and the negative electrode active material, it is preferable to use a phosphoric acid compound typified by olivine-type LiMbPO4(where Mb is an element selected from one or more of Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, Zr) and lithium vanadium phosphate (Li3V2(PO4)3or LiVOPO4) as a main component.

[0084] The positive electrode active material and the negative electrode active material of the present embodiment can also use a material that has undergone a change in composition by changing the composition ratio or substituting different elements, as long as it is within a range in which the characteristics of the positive electrode active material and the negative electrode active material can be obtained.

[0085] In the positive electrode active material and the negative electrode active material that constitute the positive electrode layer 30 and the negative electrode layer 40 of the present embodiment, the main component refers to a component that constitutes the positive electrode active material and the negative electrode active material in the largest proportion.

[0086] As the conductive aid, for example, carbon materials such as carbon black, acetylene black, ketjen black, carbon nanotubes, graphite, graphene, and activated carbon; and metal materials such as gold, silver, palladium, platinum, copper, and tin can be listed.

[0087] As the ion conductive aid, for example, a solid electrolyte can be listed. Specifically, the same material as that used for the solid electrolyte layer 50 can be used as the solid electrolyte.

[0088] In the case of using a solid electrolyte as the ion conductive aid, the same material is preferably used for the ion conductive aid and the solid electrolyte used for the solid electrolyte layer 50.

[0089] In addition, in the case of using a solid electrolyte as the ion conductive aid, different solid electrolytes can also be used in the positive electrode active material layer 32 and the negative electrode active material layer 42, respectively.

[0090] There is no clear distinction between the active material that constitutes the positive electrode active material layer 32 or the negative electrode active material layer 42, and by comparing the potentials of two compounds, a compound that shows a higher potential can be used as the positive electrode active material, and a compound that shows a lower potential can be used as the negative electrode active material.

[0091] (Positive electrode current collector and negative electrode current collector)

[0092] The material of the positive electrode current collector layer 31 and the negative electrode current collector layer 41 of the lithium ion secondary battery 1 according to the present embodiment preferably uses a material having a large electrical conductivity, and for example, silver, palladium, gold, platinum, aluminum, copper, nickel, or the like is preferably used. In particular, copper is difficult to react with the oxide-based lithium ion conductor, and further has an effect of reducing the internal resistance of the stacked all-solid-state battery, and thus is more preferable. The material of the positive electrode current collector layer 31 and the negative electrode current collector layer 41 can use the same material, or can use different materials.

[0093] In addition, the positive electrode current collector layer 31 and the negative electrode current collector layer 41 can each include a positive electrode active material and a negative electrode active material, respectively. The content ratio of the active material contained in each current collector is not particularly limited as long as the function as a current collector is exerted. For example, the positive electrode current collector / positive electrode active material, or the negative electrode current collector / negative electrode active material is preferably in the range of 90 / 10 to 70 / 30 in terms of volume ratio.

[0094] If the positive electrode current collector layer 31 and the negative electrode current collector layer 41 each include a positive electrode active material and a negative electrode active material, respectively, the adhesion of the positive electrode current collector layer 31 to the positive electrode active material layer 32 and the negative electrode current collector layer 41 to the negative electrode active material layer 42 is improved.

[0095] (intermediate layer)

[0096] The lithium ion secondary battery 1 according to the present embodiment can have an intermediate layer 90 between at least any one of the positive electrode layer 30 and the solid electrolyte layer 50 and the negative electrode layer 40 and the solid electrolyte layer 50. Figure 1 In the drawing, an example in which the intermediate layer 90 is present between the surface of the lowermost positive electrode layer 30 in the z direction and the solid electrolyte layer 50b is shown, but the number and the position of the intermediate layer 90 formed are not limited to this example.

[0097] The intermediate layer 90 according to the present embodiment is preferably a layer containing constituent elements of the positive electrode layer 30 or the negative electrode layer 40 and the solid electrolyte layer 50.

[0098] By being a layer containing constituent elements of the positive electrode layer 30 or the negative electrode layer 40 and the solid electrolyte layer 50, the positive electrode layer 30, the negative electrode layer 40, and the solid electrolyte layer 50 are mutually compatible with the intermediate layer 90, and thus the interface resistance is reduced, the generation of the deviation of the electric charge and the subsequent charge-discharge reaction are further promoted, and a high output characteristic can be obtained.

[0099] (edge layer)

[0100] The edge layer 80 of the lithium ion secondary battery 1 of the present embodiment is preferably provided in order to eliminate the step difference between the solid electrolyte layer 50 and the positive electrode layer 30, and the step difference between the solid electrolyte layer 50 and the negative electrode layer 40. By the presence of such an edge layer 80, the step difference between the solid electrolyte layer 50 and the positive electrode layer 30 and the negative electrode layer 40 is eliminated, so the density of the laminate 20 with the positive electrode layer 30 and the negative electrode layer 40 becomes high, and it is difficult to cause interlayer peeling (delamination) or warping due to the firing of the lithium ion secondary battery 1.

[0101] The material constituting the edge layer 80 can use the same material as the solid electrolyte used for the solid electrolyte layer 50.

[0102] In addition, the solid electrolyte constituting the edge layer 80 is preferably the same constitution as the solid electrolyte constituting the solid electrolyte layer 50.

[0103] (Outer layer)

[0104] The lithium ion secondary battery 1 of the present embodiment can be provided with an outer layer (cover layer) 55 on both of the two main surfaces of the laminate 20 exposed in the z direction as needed. In the present embodiment, the outer layer on the upper side in the stacking direction is set as the first outer layer (uppermost surface outer layer) 55A, and the outer layer on the lower side in the stacking direction is set as the second outer layer (lowermost surface outer layer) 55B. The outer layer 55 can use the same material as the solid electrolyte layer, but is not included in the solid electrolyte layer of the present embodiment.

[0105] (Method for manufacturing lithium ion secondary battery)

[0106] The lithium ion secondary battery 1 of the present embodiment can be manufactured in the following order. Each of the materials of the positive electrode current collector layer 31, the positive electrode active material layer 32, the solid electrolyte layer 50, the negative electrode current collector layer 41, the negative electrode active material layer 42, the edge layer 80, and the intermediate layer 90 is pasted. The method of pasting is not particularly limited, and for example, a paste can be obtained by mixing the powders of the above-described materials in a medium. Here, the medium is a general term for a medium in a liquid phase, and includes solvents, binders, and the like. The binder contained in the paste for forming a green sheet or a printed layer is not particularly limited, and poly(vinyl acetal) resin, cellulose resin, acrylic resin, polyurethane resin, vinyl acetate resin, polyvinyl alcohol resin, or the like can be used, and the slurry can contain at least one of these resins.

[0107] In addition, a plasticizer can be contained in the paste. The type of the plasticizer is not particularly limited, and dioctyl phthalate, diisononyl phthalate, or the like can be used.

[0108] By this method, the paste for the positive electrode current collector layer, the paste for the positive electrode active material layer, the paste for the solid electrolyte layer, the paste for the negative electrode active material layer, the paste for the negative electrode current collector layer, the paste for the edge layer, and the paste for the intermediate layer are produced.

[0109] The paste for the solid electrolyte layer produced as described above is applied to a substrate such as polyethylene terephthalate (PET) or the like at a desired thickness, and dried as necessary to produce a green sheet 5 for the solid electrolyte. The method of producing the green sheet 5 for the solid electrolyte is not particularly limited, and a publicly known method such as a doctor blade method, a die coater, a comma coater, a gravure coater, or the like can be used. Next, the intermediate layer 90, the positive electrode active material layer 32, the positive electrode current collector layer 31, and the positive electrode active material layer 32 are sequentially printed by screen printing on the green sheet 5 for the solid electrolyte to form the intermediate layer 90 and the positive electrode layer 30. Further, in order to fill the step difference between the green sheet 5 for the solid electrolyte and the positive electrode layer 30, the edge layer 80 is formed by screen printing in a region other than the positive electrode layer, and a positive electrode layer unit is produced.

[0110] The negative electrode layer unit can also be produced by the same method as the positive electrode layer unit, and the negative electrode layer 40 and the edge layer 80 are formed by screen printing on the green sheet 5 for the solid electrolyte to produce a negative electrode layer unit.

[0111] At this time, by adjusting the application thickness of the paste for the solid electrolyte, the positive electrode layer unit and the negative electrode layer unit having different thicknesses of the solid electrolyte layer are produced.

[0112] Then, the positive electrode layer unit and the negative electrode layer unit are alternately shifted so that the respective one ends are not aligned, and are laminated, and further, if necessary, an outer layer (cover layer) can be provided on both main surfaces of the above-described laminate exposed in the z direction. Among them, the outer layer can use the same material as the solid electrolyte. Hereinafter, the sheet material for providing the outer layer is sometimes referred to as a sheet material for the outermost layer. In addition, in the present embodiment, the outer layer is not treated as the solid electrolyte layer 50 of the laminate 1.

[0113] The above-described manufacturing method is a method of producing a parallel type lithium ion secondary battery, and the manufacturing method of a series type lithium ion secondary battery can be performed as long as the positive electrode layer and the negative electrode layer are laminated so that the one end of the positive electrode layer and the one end of the negative electrode layer are aligned, that is, without being shifted.

[0114] The laminated substrate thus produced is pressed using a mold, warm isostatic pressing (WIP), cold isostatic pressing (CIP), isostatic pressing, or the like, and the adhesiveness can be improved. The pressing is preferably performed while heating, and can be performed at 40 to 95°C, for example. In the method for manufacturing the all-solid-state lithium-ion secondary battery of the present embodiment, the laminated substrate can be produced in advance with consideration of the position in the z direction at which the laminated substrate is to be cut later, and the laminated substrate can be cut at a predetermined position in the z direction to obtain a plurality of desired laminates.

[0115] The laminated substrate thus produced can be cut into laminates of lithium-ion secondary batteries that are not yet fired using a cutting device.

[0116] By debinding and firing the laminate of the lithium-ion secondary battery, a lithium-ion secondary battery can be manufactured. The debinding and firing can be performed at a temperature of 600 to 1000°C in a nitrogen atmosphere. The debinding and firing can be performed for a period of 0.1 to 6 hours, for example.

[0117] Further, in order to efficiently extract a current from the laminate 20 of the lithium-ion secondary battery 1, an external electrode can be provided. The external electrode is connected in parallel to the positive electrode layer 30 and the negative electrode layer 40 alternately and is joined via a portion of the opposite two end surfaces E1, E2 and the opposite two side surfaces S1, S2 of the laminate. Thus, a pair of external electrodes is formed in a manner of sandwiching the end surfaces of the laminate. As a method for forming the external electrode 12, a sputtering method, a screen printing method, or a dip coating method, or the like can be given. In the screen printing method or the dip coating method, a paste for the external electrode containing a metal powder, a resin, and a solvent is produced and formed into the external electrode 12. Subsequently, a sintering process for volatilizing the solvent and a plating process for forming a terminal electrode on the surface of the external electrode are performed. On the other hand, in the sputtering method, the external electrode and the terminal electrode can be formed directly, and thus the sintering process and the plating process are not required.

[0118] In order to improve the moisture resistance and the impact resistance, the laminate of the lithium-ion secondary battery 1 can be sealed in a coin cell, for example. The sealing method is not particularly limited, and the laminate after firing can be sealed with a resin, for example. Alternatively, the laminate can be sealed by applying or dip-coating an insulator paste such as an Al2O3 paste around the laminate and performing a heat treatment on the insulator paste.

[0119] In the above embodiment, a method for manufacturing a laminate-type all-solid-state battery having a process of forming an edge layer using an edge layer paste is exemplified, but the method for manufacturing a lithium-ion secondary battery of the present embodiment is not limited to this example. For example, the process of forming an edge layer using an edge layer paste can be omitted. The edge layer can be formed by deforming a solid electrolyte layer paste during the manufacturing process of the lithium-ion secondary battery, for example.

[0120] (Modified example)

[0121] Figure 2 A cross-sectional view of a lithium-ion secondary battery 1A, which is a modified example, is shown. In the lithium-ion secondary battery 1A, the same reference numerals are assigned to the same structures as those of the lithium-ion secondary battery 1, and the description thereof is omitted.

[0122] Figure 2 The lithium-ion secondary battery 1A shown differs from the lithium-ion secondary battery 1 in that it does not have the intermediate layer 90. Figure 1

[0123] Even the lithium-ion secondary battery 1A, which is a modified example, can achieve the same effects as the lithium-ion secondary battery 1.

[0124] Thus far, specific examples of the lithium-ion secondary battery according to the embodiment have been described. The characteristic structures of the embodiment can also be combined as appropriate.

[0125] [Examples]

[0126] Hereinafter, the present application will be described in further detail using examples and comparative examples based on the above-described embodiment.

[0127] (Example 1)

[0128] (Production of active material powder)

[0129] As the active material powder, lithium vanadium phosphate produced by the following method was used. As the production method thereof, Li2CO3, V2O5, and NH4H2PO4 were used as starting materials, dispersed in pure water, and then wet-mixed for 12 hours using a ball mill. After the mixing, the powder obtained by the dehydration drying was calcined at 850°C for 2 hours in a nitrogen-hydrogen mixed gas. After the calcination, the powder was dispersed in pure water and then wet-pulverized for 1 hour using a ball mill. After the pulverization, the dehydration drying was performed, and lithium vanadium phosphate was obtained as the active material powder.

[0130] The active material powder obtained was analyzed using an X-ray diffractometer, and as a result, it was confirmed that the lithium vanadium phosphate had the same crystal structure as NASICON (sodium superionic conductor) type Li3V2(PO4)3.

[0131] (Production of paste for active material layer)

[0132] The paste for the active material layer was a paste obtained by adding 15 parts of ethyl cellulose as a binder and 65 parts of dihydromyrcenol as a solvent to 100 parts of the obtained active material powder and mixing and dispersing the same, as the paste for the active material layer.

[0133] (Production of paste for solid electrolyte layer-01)

[0134] ​As the solid electrolyte, a solid electrolyte powder-01 produced by the following method was used. As the production method thereof, Li2CO3, Al2O3, TiO2, and NH4H2PO4 were used as starting materials, dispersed in pure water, and then wet-mixed for 12 hours using a ball mill. After the mixing, dehydration drying was performed, and then the obtained powder was calcined at 800°C in the atmosphere for 2 hours. After the calcination, the powder was dispersed in pure water, and then wet-pulverized for 8 hours using a ball mill. After the pulverization, dehydration drying was performed, and the solid electrolyte powder-01 was obtained.

[0135] The obtained solid electrolyte powder-01 was analyzed using an X-ray diffractometer, and as a result, it was confirmed that it was an aluminum titanium lithium phosphate having the same crystal structure as NASICON-type LiTi2(PO4)3.

[0136] Next, 100 parts of the obtained solid electrolyte powder-01 was mixed with 100 parts of ethanol and 200 parts of toluene as solvents using a ball mill. Then, 16 parts of a polyvinyl butyral-based adhesive and 4.8 parts of butyl benzyl phthalate were further added and mixed, and a paste-01 for a solid electrolyte layer was produced.

[0137] (Production of a sheet-01 for a solid electrolyte layer)

[0138] Using the obtained paste-01 for a solid electrolyte layer, a sheet was formed using a doctor blade method with a PET film as a base material, and a sheet for a solid electrolyte layer was obtained. At this time, by adjusting the thickness in the range of 5 to 15 μm, a plurality of sheets-01 for a solid electrolyte layer having different thicknesses were produced.

[0139] (Production of a sheet-01 for an outermost layer)

[0140] Using the obtained paste-01 for a solid electrolyte layer, a sheet having a thickness of 30 μm was formed using a doctor blade method with a PET film as a base material, and a sheet-01 for an outermost layer was obtained.

[0141] (Production of a paste for a current collector layer)

[0142] As the current collector, the obtained active material powder and Cu powder were mixed in such a manner that the volume ratio becomes 80 / 20. After the mixing, 100 parts of the obtained mixture, 10 parts of ethyl cellulose as an adhesive, and 50 parts of dihydromyrcenol as a solvent were mixed and dispersed, and a paste for a current collector layer was produced.

[0143] (Production of a paste-01 for an edge layer)

[0144] For the edge layer paste-01, 100 parts of the obtained solid electrolyte powder-01 was mixed with 100 parts of ethanol and 100 parts of toluene as solvents by a ball mill, and then 16 parts of polyvinyl butyral-based binder and 4.8 parts of butyl benzyl phthalate were further added and mixed to produce the edge layer paste-01.

[0145] (Production of the external electrode paste)

[0146] The external electrode paste of the thermosetting type was produced by mixing and dispersing silver powder with an epoxy resin and a solvent.

[0147] Using these pastes, a lithium ion secondary battery was produced as follows.

[0148] (Production of the electrode layer unit)

[0149] On the solid electrolyte layer sheet-01 having a thickness of 8 μm, an active material layer having a thickness of 5 μm was formed by screen printing, and dried at 80°C for 10 minutes. Then, a current collector layer having a thickness of 5 μm was formed thereon by screen printing in the same printing pattern, and dried at 80°C for 10 minutes. Further, an active material layer having a thickness of 5 to 10 μm was formed thereon again by screen printing in the same printing pattern, and dried at 80°C for 10 minutes, thereby producing an electrode layer on the solid electrolyte layer sheet-01. Then, an edge layer having a height approximately the same as that of the above electrode layer was formed on the outer periphery of one end of the electrode layer by screen printing, and dried at 80°C for 10 minutes. Then, by peeling the PET film, a sheet of the electrode layer unit was obtained.

[0150] Similarly, using the solid electrolyte sheet-01 having different thicknesses, sheets of a plurality of electrode layer units having different thicknesses of the solid electrolyte layer were obtained.

[0151] (Production of the lowermost outer layer unit)

[0152] On the outermost layer sheet-01, a current collector layer having a thickness of 5 μm was formed by screen printing, and dried at 80°C for 10 minutes. Further, an active material layer having a thickness of 5 to 10 μm was formed thereon again by screen printing in the same printing pattern, and dried at 80°C for 10 minutes, thereby producing an electrode layer having the active material layer on only one side of the outermost layer sheet-01. Then, an edge layer having a height approximately the same as that of the above electrode layer was formed on the outer periphery of one end of the electrode layer by screen printing, and dried at 80°C for 10 minutes. Then, by peeling the PET film of the outermost layer sheet-01, a sheet of the lowermost outer layer unit was obtained.

[0153] (Production of the uppermost outer layer unit)

[0154] On the solid electrolyte layer sheet-01 having a thickness of 8 μm, an active material layer having a thickness of 5 to 10 μm was formed using screen printing in the same printing pattern, and dried at 80°C for 10 minutes. Further, a current collector layer having a thickness of 5 μm was formed again on it using screen printing, and dried at 80°C for 10 minutes, whereby an electrode layer in which the active material layer existed only on one side of the solid electrolyte layer sheet-01 was produced. Next, on the outer periphery of one end of the electrode layer, an edge layer having a height approximately the same as the plane of the above electrode layer was formed using screen printing, and dried at 80°C for 10 minutes. Next, the outermost layer sheet-01 was laminated on the electrode layer, and the PET film of the solid electrolyte layer sheet-01 and the outermost layer sheet-01 was peeled, whereby a sheet of the upper surface outermost layer unit was obtained.

[0155] (Production of the laminate)

[0156] Using the obtained plurality of electrode layer units, a laminate was produced by alternately laminating 50 layers while shifting each one end by one. Further, on both main surfaces in the lamination direction of the laminate, the lower surface outermost layer unit and the lower surface outermost layer unit were laminated by one layer while shifting each by one. Further, as the outer layer solid electrolyte layer, the solid electrolyte sheet was laminated by four layers on the lower surface outermost layer unit and by five layers on the upper surface outermost layer unit, whereby the outer layer was formed. Next, after heat pressure bonding by pressing with a mold, cutting was performed, and a laminate of an unburned lithium ion secondary battery was produced. Next, the produced laminate was heated at a temperature increasing rate of 200°C / hour to a burn temperature of 750°C in nitrogen gas, and maintained at this temperature for two hours, and debinder / burn processing was performed by natural cooling, whereby a laminate of a lithium ion secondary battery was obtained.

[0157] (External electrode forming step)

[0158] The paste for external electrodes was applied so as to cover both end surfaces of the obtained laminate of the lithium ion secondary battery and the positive and negative electrodes exposed on both side surfaces, and heat curing was performed at 150°C for 30 minutes, and a pair of external electrodes was formed.

[0159] The battery in which a pair of external electrodes was formed on the laminate of the lithium ion secondary battery was used as the evaluation battery in Example 1.

[0160] (Measurement of the thickness of the solid electrolyte layer)

[0161] The thickness of the solid electrolyte layer in the lithium ion secondary battery produced in Example 1 was measured using a scanning electron microscope (SEM). In the cross section of the lithium ion secondary battery, the thickness of each of the 49 layers of the solid electrolyte layer, excluding the outermost solid electrolyte layer, in the 50-layer stack was measured at 5 points, and the average value thereof was taken as the thickness of each of the solid electrolyte layers.

[0162] The average thickness tl of the thickest interlayer solid electrolyte layer in the lithium ion secondary battery produced in Example 1 was 10.70 μm, and the average thickness t2 of the thinnest interlayer solid electrolyte was 5.98 μm, and tl / t2 = 1.79. In addition, the average value of the thickness of each of the 49 layers of the solid electrolyte layer was calculated as the average thickness of the solid electrolyte layer, and the result was T = 8.67 μm.

[0163] The standard deviation σ of the thickness of the solid electrolyte layer in the lithium ion secondary battery produced in Example 1 was calculated from the thickness of each of the solid electrolyte layers, and the result was σ = 1.02 μm.

[0164] (Examples 2 to 9, Comparative Examples 1 to 4)

[0165] In producing the stack, the values of tl, t2, and T were changed by changing the electrode layer unit used, and otherwise, the evaluation battery was produced in the same manner as in Example 1.

[0166] (Example 10)

[0167] (Production of Paste-02 for Solid Electrolyte Layer)

[0168] As the solid electrolyte, a solid electrolyte powder-02 produced by the following method was used. As the production method thereof, Li2CO3, Al2O3, GeO2, and NH4H2PO4 were used as starting materials, and after being dispersed in pure water, wet mixing was performed using a ball mill for 12 hours. After the mixing, dehydration drying was performed, and then the obtained powder was calcined at 800°C in the atmosphere for 2 hours. After the calcination, the powder was dispersed in pure water, and wet pulverization was performed using a ball mill for 8 hours. After the pulverization, dehydration drying was performed, and the solid electrolyte powder-02 was obtained.

[0169] The obtained solid electrolyte powder-02 was analyzed using an X-ray diffractometer, and as a result, it was confirmed to be an aluminum germanium lithium phosphate having the same crystal structure as NASICON-type LiGe2(PO4)3.

[0170] Then, 100 parts of the obtained solid electrolyte powder-02 was mixed with 100 parts of ethanol and 200 parts of toluene as solvents using a ball mill. Then, 16 parts of a polyvinyl butyral-based adhesive and 4.8 parts of butyl benzyl phthalate were further added and mixed, and the paste-02 for solid electrolyte layer was produced.

[0171] (Production of the sheet for the solid electrolyte layer-02)

[0172] Using the obtained paste for the solid electrolyte layer-02, a sheet was formed by a doctor blade method with a PET film as a substrate, and a sheet for the solid electrolyte layer B was obtained. At this time, by adjusting the thickness in the range of 5 to 15 μm, a plurality of sheets for the solid electrolyte layer-02 having different thicknesses were produced.

[0173] (Production of the sheet for the outermost layer-02)

[0174] Using the obtained paste for the solid electrolyte layer-02, a sheet having a thickness of 30 μm was formed by a doctor blade method with a PET film as a substrate, and a sheet for the outermost layer-02 was obtained.

[0175] (Production of the paste for the edge layer-02)

[0176] To the paste for the edge layer-02, 100 parts of the obtained solid electrolyte powder-02 was added with 100 parts of ethanol and 100 parts of toluene as solvents, and wet mixing was performed with a ball mill, and then 16 parts of a polyvinyl butyral-based adhesive and 4.8 parts of butyl benzyl phthalate were further added and mixed, and the paste for the edge layer-02 was produced.

[0177] (Example 10)

[0178] Except for using the sheet for the solid electrolyte-02, the sheet for the outermost layer-02, and the paste for the edge layer-02, the evaluation battery of Example 10 was produced in the same manner as Example 1.

[0179] (Examples 11 to 18, Comparative Examples 5 to 8)

[0180] In producing the laminated body, the values of ti, t2, T were changed by changing the electrode layer unit used, and otherwise, the evaluation batteries of Examples 11 to 18, Comparative Examples 5 to 8 were produced in the same manner as Example 10.

[0181] (Evaluation of output characteristics)

[0182] The batteries for evaluation produced in the present examples and comparative examples were subjected to charge and discharge under the following charge and discharge conditions, whereby the output characteristics were evaluated. The charge and discharge current is hereinafter expressed in terms of C rate (charge rate). The C rate is expressed in terms of nC (pA) (n is a numerical value), and refers to a current capable of charging and discharging the nominal capacity (pAh) in 1 / n (h). For example, 1C refers to a charge and discharge current capable of charging the nominal capacity in 1 h, and if 2C, it refers to a charge and discharge current capable of charging the nominal capacity in 0.5 h. For example, in the case of a lithium ion secondary battery having a nominal capacity of 100 pAh, a current of 0.1C is 10 pA (calculation formula 100 pAh x 0.1 = 10 pA). Similarly, a current of 0.2C is 20 pA, and a current of 1C is 100 pA.

[0183] The output characteristic evaluation conditions were performed under the following conditions. In a normal temperature environment, constant current charging (CC charging) was performed at a constant current of 0.2C rate until the battery voltage became 1.6 V, and then constant voltage charging (CV charging) was performed until the current value of 0.05C rate. After charging, after a rest time of 5 minutes, discharging was performed at a constant current of 0.2C rate to a battery voltage of 0 V (CC discharging). The obtained discharge capacity was set as the 0.2C discharge capacity.

[0184] After that, in a normal temperature environment, constant current charging (CC charging) was performed at a constant current of 0.2C rate until the battery voltage reached 1.6 V, and then constant voltage charging (CV charging) was performed until the current value of 0.05C rate. After charging, after a rest time of 5 minutes, discharging was performed at a constant current of 1.0C rate to a battery voltage of 0 V (CC discharging). The obtained discharge capacity was set as the 1.0C discharge capacity.

[0185] The ratio of the above 1.0C discharge capacity to the 0.2C discharge capacity was calculated as the output characteristic in the present example by the following formula (1).

[0186] Output characteristic (%) = (1.0C discharge capacity ÷ 0.2C discharge capacity) x 100... (1)

[0187] The evaluation results of t1, t2, T, and the calculated standard deviation σ of the solid electrolyte layer and the output characteristics in Examples 1 to 18 and Comparative Examples 1 to 8 are shown in Table 1 below.

[0188] [Table 1]

[0189]

[0190] From the results of Examples 1 to 9 and Comparative Examples 1 to 4, it was confirmed that the ratio t1 / t2 of the average thickness t1 of the thickest solid electrolyte layer to the average thickness t2 of the thinnest solid electrolyte layer, t1 / t2, in the range of 1.02 ≤ t1 / t2 ≤ 1.99, enables excellent output characteristics to be obtained.

[0191] (Examples 19 to 26)

[0192] In the production of the laminated body, the standard deviation σ in the average thickness of the solid electrolyte layer was changed by changing the electrode layer unit used, and otherwise, the evaluation batteries of Examples 10 to 17 were produced in the same manner as in Example 1, and were evaluated in the same manner as in Example 1. The evaluation results are shown in Table 2.

[0193] (Examples 27 to 34)

[0194] In the production of the laminated body, the standard deviation σ in the average thickness of the solid electrolyte layer was changed by changing the electrode layer unit used, and otherwise, the evaluation batteries of Examples 27 to 34 were produced in the same manner as in Example 10, and were evaluated in the same manner as in Example 1. The evaluation results are shown in Table 2.

[0195] [Table 2]

[0196]

[0197] From the results of Examples 19 to 34, it was confirmed that the standard deviation σ in the average thickness of the solid electrolyte layer in the range of 0.15 ≤ σ ≤ 1.66 μm enables excellent output characteristics to be obtained.

[0198] (Example 35)

[0199] (Production of the paste for the intermediate layer)

[0200] As the base material for the intermediate layer, the powder of lithium vanadium phosphate and the powder of lithium titanium aluminum phosphate produced in Example 1 were wet-mixed for 16 hours using a ball mill, and were dehydrated and dried. After drying, the obtained powder was calcined at 850°C for 2 hours in a nitrogen-hydrogen mixed gas. After wet-pulverizing the calcined product using a ball mill, dehydrating and drying were performed, and a base material powder for the intermediate layer was obtained.

[0201] To 100 parts of the obtained base material powder for the intermediate layer, 15 parts of ethyl cellulose as a binder and 65 parts of dihydroterpineol as a solvent were added, and were mixed and dispersed, and a paste for the intermediate layer was produced.

[0202] In the production of the electrode layer unit, the paste for the intermediate layer was used on the solid electrolyte sheet, and a 2-μm-thick intermediate layer was formed using screen printing, and otherwise, the electrode layer unit was produced in the same manner as in Example 3.

[0203] (Example 36)

[0204] In the preparation of the paste for the intermediate layer, titanium oxide (TiO2) was used as the base material powder for the intermediate layer, and otherwise, the electrode layer unit was prepared in the same manner as in Example 35.

[0205] (Example 37)

[0206] In the preparation of the paste for the intermediate layer, aluminum oxide (Al2O3) was used as the base material powder for the intermediate layer, and otherwise, the electrode layer unit was prepared in the same manner as in Example 35.

[0207] (Example 38)

[0208] In the preparation of the paste for the intermediate layer, zirconium oxide (ZrO2) was used as the base material powder for the intermediate layer, and otherwise, the electrode layer unit was prepared in the same manner as in Example 35.

[0209] (Example 39)

[0210] In the preparation of the paste for the intermediate layer, zirconium oxide (ZrO2) was used as the base material powder for the intermediate layer, and otherwise, the electrode layer unit was prepared in the same manner as in Example 12.

[0211] The cross section of the obtained electrode layer unit was observed using a scanning electron microscope energy dispersive X-ray spectrometer (SEM-EDS), and the constituent elements contained in the intermediate layer were analyzed.

[0212] Except for using the obtained electrode layer unit, the evaluation battery of Examples 35 to 39 was prepared in the same manner as in Example 3, and evaluation was performed in the same manner as in Example 1. The evaluation results are shown in Table 3.

[0213] [Table 3]

[0214]

[0215] It was confirmed from the results of Examples 35 to 38 that the output characteristics were improved by the presence of the intermediate layer between the solid electrolyte layer and the electrode layer. In addition, it was confirmed from the comparison between Example 38 and Example 39 that the output characteristics were improved not by the composition of the intermediate layer but by the elements constituting the intermediate layer.

[0216] (Example 40)

[0217] In the preparation of the paste for the active material, a positive active material paste was prepared using lithium iron phosphate (LiFePO4) as the active material powder, and a negative active material paste was prepared using lithium titanate (Li4Ti5O12) as the active material powder. 12 ) as the active material powder.

[0218] In addition to using the paste for the positive electrode active material layer and the paste for the negative electrode active material layer, the sheet of the electrode layer unit was produced in the same manner as in Example 1. The electrode layer unit produced using the paste for the positive electrode active material layer was used as the positive electrode layer unit, and the electrode layer unit produced using the paste for the negative electrode active material layer was used as the negative electrode layer unit.

[0219] In the production of the laminate, the obtained plurality of positive electrode layer units and negative electrode layer units were stacked while being alternately offset in a manner that the one end of the positive electrode layer unit and the one end of the negative electrode layer unit were not coincident, and otherwise, the evaluation battery of Example 40 was produced in the same manner as in Example 1.

[0220] (Examples 41 to 48, Comparative Examples 9 to 12)

[0221] In the production of the laminate, the standard deviation σ of the average thickness of the solid electrolyte layer was changed by changing the positive electrode layer unit and the negative electrode layer unit used, and otherwise, the evaluation batteries of Examples 41 to 48 and Comparative Examples 9 to 12 were produced in the same manner as in Example 39.

[0222] (Evaluation of output characteristics)

[0223] The evaluation conditions of the output characteristics were performed under the following conditions. In a normal temperature environment, constant current charging (CC charging) was performed at a constant current of 0.2C rate until the battery voltage reached 3.0V, and then constant voltage charging (CV charging) was performed until the current value of 0.05C rate. After charging, after a rest time of 5 minutes, discharging was performed at a constant current of 0.2C rate to a battery voltage of 1.5V (CC discharging). The obtained discharge capacity was set as the 0.2C discharge capacity.

[0224] After that, in a normal temperature environment, constant current charging (CC charging) was performed at a constant current of 0.2C rate until the battery voltage reached 3.0V, and then constant voltage charging (CV charging) was performed until the current value of 0.05C rate. After charging, after a rest time of 5 minutes, discharging was performed at a constant current of 1.0C rate to a battery voltage of 1.5V (CC discharging). The obtained discharge capacity was set as the 1.0C discharge capacity.

[0225] The ratio of the above 1.0C discharge capacity to the 0.2C discharge capacity was calculated as the output characteristics in the present example by the following formula (2).

[0226] Output characteristics (%) = (1.0C discharge capacity ÷ 0.2C discharge capacity) x 100 … (2)

[0227] The evaluation results of t1, t2, T, and the calculated standard deviation σ of the solid electrolyte layer and the output characteristics in Examples 40 to 48 and Comparative Examples 9 to 12 are shown in Table 4.

[0228] [Table 4]

[0229]

[0230] From the results of Examples 40 to 48 and Comparative Examples 9 to 12, it was confirmed that even in lithium ion secondary batteries in which the positive active material and the negative active material are different, excellent output characteristics can be obtained in the range where the ratio t1 / t2 of the average thickness t1 of the thickest solid electrolyte layer to the average thickness t2 of the thinnest solid electrolyte layer is 1.02 ≤ t1 / t2 ≤ 1.99.

[0231] (Example 49)

[0232] (Production of the paste for solid electrolyte layer-03)

[0233] As the solid electrolyte, the solid electrolyte powder-03 produced by the following method was used. As the production method thereof, first, Li2CO3 and SiO2 were mixed, and firing was performed at 800°C, thereby synthesizing a precursor. The obtained precursor was mixed with Li3PO4, and pressing was performed under a pressure of 34.5 MPa, and firing was performed at 1000°C. Then, heat treatment was performed at 400°C, thereby removing impurities on the surface. After the heat treatment, dry pulverization was performed for 8 hours using a ball mill, thereby obtaining the solid electrolyte powder-03.

[0234] The obtained solid electrolyte powder-03 was analyzed using an X-ray diffractometer, and as a result, it was confirmed to be a compound having the same crystal structure as Li 3.6 Si 0.6 P 0.4 O4.

[0235] Next, 100 parts of the obtained solid electrolyte powder-03 was mixed with 100 parts of ethanol and 200 parts of toluene as solvents using a ball mill. Then, 16 parts of a polyvinyl butyral-based adhesive and 4.8 parts of butyl benzyl phthalate were further added and mixed, thereby producing the paste for solid electrolyte layer-03.

[0236] (Production of the sheet for solid electrolyte layer-03)

[0237] Using the obtained paste for solid electrolyte layer-03, a sheet was formed using a doctor blade method with a PET film as a substrate, thereby obtaining a sheet for solid electrolyte layer. At this time, by adjusting the thickness in the range of 5 to 15 μm, a plurality of sheets for solid electrolyte layer-03 having different thicknesses were produced.

[0238] (Production of sheet material-03 for outermost layer)

[0239] Using the obtained paste for solid electrolyte layer-03, a sheet material was formed to a thickness of 30 μm using a doctor blade method with a PET film as a substrate, to obtain a sheet material-03 for outermost layer.

[0240] (Production of paste-03 for edge layer)

[0241] To the paste-03 for edge layer, 100 parts of the obtained solid electrolyte powder-03 was added with 100 parts of ethanol and 100 parts of toluene as solvents, and wet mixed using a ball mill, and then further 16 parts of a polyvinyl butyral-based adhesive and 4.8 parts of butyl benzyl phthalate were added and mixed, to produce the paste-03 for edge layer.

[0242] When producing the laminated body, the sheet material-03 for solid electrolyte, the sheet material-03 for outermost layer, and the paste-03 for edge layer were used, and otherwise, the evaluation battery of Example 49 was produced in the same manner as Example 40.

[0243] (Examples 50 to 57, Comparative Examples 13 to 16)

[0244] When producing the laminated body, the standard deviation σ in the average thickness of the solid electrolyte layer was changed by changing the positive electrode layer unit and the negative electrode unit used, and otherwise, the evaluation batteries of Examples 50 to 57 and Comparative Examples 13 to 16 were produced in the same manner as Example 49.

[0245] (Evaluation of output characteristics)

[0246] The evaluation results of t1, t2, T, and the calculated standard deviation σ of the solid electrolyte layer and the output characteristics in Examples 49 to 57 and Comparative Examples 13 to 16 are shown in Table 5. Among them, the evaluation of the output characteristics was performed under the same conditions as Example 40.

[0247] [Table 5]

[0248]

[0249] (Example 58)

[0250] (Production of paste-04 for solid electrolyte layer)

[0251] As the solid electrolyte, a solid electrolyte powder-04 produced by the following method was used. As the production method thereof, first, LiCO3, La(OH)3, ZrO2 were dispersed in ethanol as a starting material, and wet mixing was performed for 12 hours using a ball mill. After the mixing, the powder obtained after the drying was heat-treated at 900°C for 5 hours. After the heat treatment, dry pulverization was performed for 12 hours using a ball mill, whereby the solid electrolyte powder-04 was obtained.

[0252] The obtained solid electrolyte powder-04 was analyzed using an X-ray diffractometer, and as a result, it was confirmed to have a crystal structure identical to that of Li7La3Zr2O 12 a compound having the same crystal structure.

[0253] Next, 100 parts of the obtained solid electrolyte powder-04 was mixed with 100 parts of ethanol and 200 parts of toluene as solvents using a ball mill. Then, 16 parts of a polyvinyl butyral-based adhesive and 4.8 parts of butyl benzyl phthalate were further added and mixed, whereby a paste-04 for a solid electrolyte layer was produced.

[0254] (Production of a sheet-04 for a solid electrolyte layer)

[0255] Using the obtained paste-04 for a solid electrolyte layer, a sheet was formed using a doctor blade method with a PET film as a base material, whereby a sheet for a solid electrolyte layer was obtained. At this time, by adjusting the thickness in the range of 5 to 15 μm, a plurality of sheets-04 for a solid electrolyte layer having different thicknesses were produced.

[0256] (Production of a sheet-04 for an outermost layer)

[0257] Using the obtained paste-04 for a solid electrolyte layer, a sheet having a thickness of 30 μm was formed using a doctor blade method with a PET film as a base material, whereby a sheet-04 for an outermost layer was obtained.

[0258] (Production of a paste-04 for an edge layer)

[0259] As for the paste-04 for an edge layer, 100 parts of the obtained solid electrolyte powder-04 was mixed with 100 parts of ethanol and 100 parts of toluene as solvents using a ball mill, and then 16 parts of a polyvinyl butyral-based adhesive and 4.8 parts of butyl benzyl phthalate were further added and mixed, whereby a paste-04 for an edge layer was produced.

[0260] When the laminate was produced, the sheet-04 for a solid electrolyte, the paste-04 for an edge layer, and the sheet-04 for an outermost layer were used, and in addition thereto, the evaluation battery of Example 58 was produced in the same manner as in Example 40.

[0261] (Examples 59 to 66, Comparative Examples 17 to 20)

[0262] In the production of the laminated body, the standard deviation σ of the average thickness of the solid electrolyte layer was changed by changing the positive electrode layer unit and the negative electrode unit used, and evaluation batteries of Examples 59 to 66 and Comparative Examples 17 to 20 were produced in the same manner as in Example 58 except for this.

[0263] (Output characteristic evaluation)

[0264] The evaluation results of t1, t2, T, and the standard deviation σ of the solid electrolyte layer and the output characteristics calculated in Examples 58 to 66 and Comparative Examples 17 to 20 are shown in Table 6. Among them, the output characteristic evaluation was performed under the same conditions as in Example 40.

[0265] [Table 6]

[0266]

[0267] (Example 67)

[0268] (Production of paste for solid electrolyte layer-05)

[0269] As the solid electrolyte, a solid electrolyte powder-05 produced by the following method was used. As the production method thereof, first, LiCO3, La2O3, TiO2 were used as starting materials, and dry mixing was performed using a marquis mortar. After mixing, the obtained powder was heat-treated at 1100°C for 12 hours, and then sintered at 1250°C for 5 hours. After sintering, quenching to room temperature was performed, and then dry pulverization was performed using a ball mill for 12 hours, thereby obtaining the solid electrolyte powder-05.

[0270] The obtained solid electrolyte powder-05 was analyzed using an X-ray diffractometer, and as a result, it was confirmed to be a compound having the same crystal structure as Li 0.56 Li 0.31 TiO3.

[0271] Next, 100 parts of the obtained solid electrolyte powder-05 was mixed with 100 parts of ethanol and 200 parts of toluene as solvents using a ball mill. Then, 16 parts of a polyvinyl butyral-based adhesive and 4.8 parts of butyl benzyl phthalate were further added and mixed, thereby producing a paste for a solid electrolyte layer-05.

[0272] (Production of sheet for solid electrolyte layer-05)

[0273] Using the obtained solid electrolyte layer paste-05, a sheet was formed by a doctor blade method with a PET film as a substrate, and a solid electrolyte layer sheet was obtained. At this time, by adjusting the thickness in the range of 5 to 15 μm, a plurality of solid electrolyte layer sheets-05 having different thicknesses were produced.

[0274] (Production of the outermost layer sheet-05)

[0275] Using the obtained solid electrolyte layer paste-05, a sheet having a thickness of 30 μm was formed by a doctor blade method with a PET film as a substrate, and the outermost layer sheet-05 was obtained.

[0276] (Production of the edge layer paste-05)

[0277] To the edge layer paste-05, 100 parts of the obtained solid electrolyte powder-05 was added 100 parts of ethanol and 100 parts of toluene as solvents, and wet mixing was performed using a ball mill. Next, 16 parts of a polyvinyl butyral-based adhesive and 4.8 parts of butyl benzyl phthalate were further added and mixed, and the edge layer paste-05 was produced.

[0278] In the active material paste production, lithium manganate (LiMn2O4) was used as the active material powder to produce the positive electrode active material paste and the negative electrode active material paste.

[0279] In the production of the laminated body, the obtained positive electrode active material layer paste and the negative electrode active material layer paste, the solid electrolyte sheet-05, the outermost layer sheet-05, and the edge layer paste-05 were used, and in addition, the evaluation battery of Example 67 was produced in the same manner as in Example 40.

[0280] (Examples 68 to 75, Comparative Examples 21 to 24)

[0281] In the production of the laminated body, the standard deviation σ of the average thickness of the solid electrolyte layer was changed by changing the positive electrode layer unit and the negative electrode unit used, and in addition, the evaluation batteries of Examples 68 to 75 and Comparative Examples 21 to 24 were produced in the same manner as in Example 67.

[0282] (Output characteristic evaluation)

[0283] The output characteristic evaluation conditions were performed under the following conditions. In a normal temperature environment, constant current charging (CC charging) was performed at a constant current of 0.2 C rate until the battery voltage became 2.0 V, and then constant voltage charging (CV charging) was performed until the current value of 0.05 C rate. After charging, after a rest time of 5 minutes, discharging was performed at a constant current of 0.2 C rate to a battery voltage of 0.5 V (CC discharging). The obtained discharge capacity was set as the 0.2 C discharge capacity.

[0284] After that, in a normal temperature environment, constant current charging (CC charging) was performed at 0.2C rate until the battery voltage became 2.0V, after which constant voltage charging (CV charging) was performed until the current value of 0.05C rate. After the charging, after a rest time of 5 minutes, discharging was performed at 1.0C rate constant current to the battery voltage of 0.5V (CC discharging). The obtained discharging capacity was set as the 1.0C discharging capacity.

[0285] The ratio of the above 1.0C discharging capacity to the 0.2C discharging capacity was calculated as the output characteristics in this example by the following formula (3).

[0286] Output characteristics (%) = (1.0C discharging capacity ÷ 0.2C discharging capacity) x 100... (3)

[0287] The evaluation results of t1, t2, T, and the calculated standard deviation σ of the solid electrolyte layer and the output characteristics in Examples 67 to 68 and Comparative Examples 21 to 24 are shown in Table 7.

[0288] [Table 7]

[0289]

[0290] (Example 76)

[0291] (Production of paste-06 for solid electrolyte layer)

[0292] As the solid electrolyte, solid electrolyte powder-06 produced by the following method was used. As the production method thereof, first, LiOH-H2O, H3BO3 were mixed, put in an alumina crucible, and heat-treated at 600°C for 3 hours under an atmospheric atmosphere, thereby obtaining a precursor A. Next, Li2SO4-H2O was heat-treated at 300°C for 2 hours under an atmospheric atmosphere, thereby obtaining a precursor B. The obtained precursor A and the precursor B were mixed, and mechanically ground with a ball mill for 100 hours, thereby obtaining the solid electrolyte powder-06.

[0293] The obtained solid electrolyte powder-06 was analyzed with an X-ray diffraction device, and as a result, it was confirmed to be a compound having the same crystal structure as that of Li3BO3-Li2SO4 glass ceramic.

[0294] Next, 100 parts of the obtained solid electrolyte powder-06 was added with 100 parts of ethanol and 200 parts of toluene as solvents, and wet-mixed with a ball mill. Then, 16 parts of a polyvinyl butyral-based adhesive and 4.8 parts of butyl benzyl phthalate were further put in and mixed, and paste-06 for a solid electrolyte layer was produced.

[0295] (Production of the sheet for the solid electrolyte layer-06)

[0296] Using the obtained paste for the solid electrolyte layer-06, a sheet was formed by a doctor blade method with a PET film as a substrate, to obtain a sheet for the solid electrolyte layer. At this time, by adjusting the thickness in the range of 5 to 15 μm, a plurality of sheets for the solid electrolyte layer-06 having different thicknesses were produced.

[0297] (Production of the sheet for the outermost layer-06)

[0298] Using the obtained paste for the solid electrolyte layer-06, a sheet having a thickness of 30 μm was formed by a doctor blade method with a PET film as a substrate, to obtain a sheet for the outermost layer-06.

[0299] (Production of the paste for the edge layer-06)

[0300] To the paste for the edge layer-06, 100 parts of the obtained solid electrolyte powder-06 was added with 100 parts of ethanol and 100 parts of toluene as solvents, and wet-mixed by a ball mill, and then further 16 parts of a polyvinyl butyral-based adhesive and 4.8 parts of butyl benzyl phthalate were put in and mixed, to produce the paste for the edge layer-06.

[0301] In the production of the laminate, the sheet for the solid electrolyte-06, the sheet for the outermost layer-06, and the paste for the edge layer-06 were used, and otherwise, the evaluation battery of Example 76 was produced in the same manner as in Example 40.

[0302] (Examples 77 to 84, Comparative Examples 25 to 28)

[0303] In the production of the laminate, the average thickness standard deviation σ of the solid electrolyte layer was changed by changing the positive electrode layer unit and the negative electrode unit used, and otherwise, the evaluation batteries of Examples 77 to 84 and Comparative Examples 25 to 28 were produced in the same manner as in Example 67.

[0304] (Evaluation of output characteristics)

[0305] The evaluation results of t1, t2, T, and the calculated standard deviation σ of the solid electrolyte layer and the output characteristics in Examples 76 to 84 and Comparative Examples 25 to 28 are shown in Table 8. Among them, the output characteristics were evaluated under the same conditions as in Example 40.

[0306] [Table 8]

[0307]

[0308] (Example 85)

[0309] (Production of the paste for the solid electrolyte layer-07)

[0310] As the solid electrolyte, a solid electrolyte powder-07 was used, which was produced by the following method. As the production method thereof, first, LiOH-H2O and H3BO3 were mixed and put in an alumina crucible, and heat treatment was performed at 600°C for 3 hours under an atmospheric air atmosphere, whereby a precursor A was obtained. Next, Li2SO4-H2O was heat-treated at 300°C for 2 hours under an atmospheric air atmosphere, whereby a precursor B was obtained. Li2CO3 was mixed in the obtained precursors A and B, and mechanical grinding was performed for 100 hours using a ball mill, whereby the solid electrolyte powder-07 was obtained.

[0311] The obtained solid electrolyte powder-07 was analyzed using an X-ray diffractometer, and as a result, it was confirmed that it was a compound having the same crystal structure as that of the Li3BO3-Li2SO4-Li2CO3 glass ceramic.

[0312] Next, 100 parts of the obtained solid electrolyte powder-07 was mixed with 100 parts of ethanol and 200 parts of toluene as solvents using a ball mill in a wet manner. Then, 16 parts of a polyvinyl butyral-based adhesive and 4.8 parts of butyl benzyl phthalate were further put in and mixed, whereby a paste-07 for a solid electrolyte layer was produced.

[0313] (Production of a sheet-07 for a solid electrolyte layer)

[0314] Using the obtained paste-07 for a solid electrolyte layer, a sheet was formed using a doctor blade method with a PET film as a substrate, and a sheet for a solid electrolyte layer was obtained. At this time, by adjusting the thickness in the range of 5 to 15 μm, a plurality of sheets-07 for a solid electrolyte layer having different thicknesses were produced.

[0315] (Production of a sheet-07 for an outermost layer)

[0316] Using the obtained paste-07 for a solid electrolyte layer, a sheet having a thickness of 30 μm was formed using a doctor blade method with a PET film as a substrate, and a sheet-07 for an outermost layer was obtained.

[0317] (Production of a paste-07 for an edge layer)

[0318] As for the paste-07 for an edge layer, 100 parts of the obtained solid electrolyte powder-06 was mixed with 100 parts of ethanol and 100 parts of toluene as solvents using a ball mill in a wet manner, and next, 16 parts of a polyvinyl butyral-based adhesive and 4.8 parts of butyl benzyl phthalate were further put in and mixed, whereby the paste-07 for an edge layer was produced.

[0319] When the laminated body was produced, the solid electrolyte sheet-07, the outermost layer sheet-07, the edge layer paste-07 were used, and the evaluation battery of Example 85 was produced in the same manner as in Example 40, except for this.

[0320] (Examples 86 to 93, Comparative Examples 29 to 32)

[0321] When the laminated body was produced, the average thickness standard deviation σ in the solid electrolyte layer was changed by changing the positive electrode layer unit and the negative electrode unit used, and the evaluation batteries of Examples 86 to 93 and Comparative Examples 29 to 32 were produced in the same manner as in Example 85, except for this.

[0322] (Evaluation of output characteristics)

[0323] The evaluation results of t1, t2, T, and the calculated standard deviation σ of the solid electrolyte layer and the output characteristics in Examples 85 to 93 and Comparative Examples 29 to 32 are shown in Table 9. Among them, the output characteristics were evaluated under the same conditions as in Example 40.

[0324] [Table 9]

[0325]

[0326] (Example 94)

[0327] (Production of solid electrolyte sheet-08)

[0328] As the solid electrolyte sheet, the solid electrolyte sheet-08 produced by the following method was used. As the production method thereof, first, in an argon atmosphere glove box, after dissolving polyethylene oxide (PEO) having a mixed molecular weight of 5 million and LiCF3SO3 (LiTFS) in acetonitrile, it was added dropwise to a Teflon sheet ("Teflon" is a registered trademark). After the dropwise addition, the Teflon sheet was formed into a sheet using a doctor blade method as a base material, and after drying at room temperature for 24 hours, vacuum drying was performed at 60°C, thereby obtaining the solid electrolyte layer sheet-07. At this time, by adjusting the thickness in the range of 5 to 15 μm, a plurality of solid electrolyte layer sheets-08 having different thicknesses were produced.

[0329] (Production of positive electrode sheet)

[0330] 100 parts of LiFePO4, 10 parts of acetylene black, and 10 parts of polyvinylidene fluoride (PVDF) were weighed and dispersed in N-methylpyrrolidone as a solvent to obtain a positive electrode slurry. The obtained positive electrode slurry was coated onto a portion of one side of a 10 μm thick aluminum foil with a thickness of 30 μm and dried at 100 °C to remove the solvent. After removing the solvent, the positive electrode slurry was also coated onto a portion of the other side of the aluminum foil with a thickness of 30 μm and dried at 100 °C to remove the solvent, thereby forming active material layers on both sides of the aluminum foil.

[0331] After forming active material layers on both sides of the aluminum foil, it is rolled using a roll mill and then punched into an electrode size of 27mm × 30mm using a die to produce a positive electrode sheet. At this point, the sheet is punched in a form that includes a portion of the area without an active material layer.

[0332] (Fabrication of negative electrode sheet)

[0333] Weigh 100 parts of Li4Ti5O as the negative electrode active material. 12 10 parts acetylene black and 10 parts polyvinylidene fluoride were dispersed in N-methylpyrrolidone as a solvent to obtain a positive electrode slurry. The obtained positive electrode slurry was coated onto a portion of one side of a 10 μm thick aluminum foil with a thickness of 30 μm, and dried at 100°C to remove the solvent. After removing the solvent, the positive electrode slurry was also coated onto a portion of the other side of the aluminum foil with a thickness of 30 μm, and the solvent was removed by drying at 100°C, thereby forming an active material layer on both sides of the aluminum foil.

[0334] After forming active material layers on both sides of the aluminum foil, it is rolled using a roll mill and then punched into an electrode size of 28mm × 31mm using a die to produce a negative electrode sheet. At this point, the sheet is punched in a form that includes a portion of the area without an active material layer.

[0335] (Creating a layered body)

[0336] 23 positive electrode sheets and 24 negative electrode sheets were stacked with a solid electrolyte sheet-08 in between, and then hot-pressed at 50°C to form a laminate. Aluminum wires were then attached to the areas of the positive electrode sheets and the negative electrode sheets where no active material layer was present, respectively, using an ultrasonic welding machine. The laminate was then welded to an aluminum laminate for the outer casing, and the laminate was folded to insert the electrode body into the outer casing. A closed portion was formed by heat-sealing one side around the outer casing, and the opening was sealed using a vacuum sealing machine while depressurizing the opening. This produced the evaluation battery of Example 94.

[0337] (Examples 95-102, Comparative Examples 33-36)

[0338] When fabricating the laminate, the thickness of the solid electrolyte sheet-08 used was adjusted, and the standard deviation σ of the average thickness in the solid electrolyte layer was changed. Otherwise, the evaluation batteries of Examples 95 to 102 and Comparative Examples 33 to 36 were fabricated in the same manner as in Example 94.

[0339] (Output Characteristic Evaluation)

[0340] Table 10 shows the evaluation results of t1, t2, T, the calculated standard deviation σ of the solid electrolyte layer, and the output characteristics in Examples 94-102 and Comparative Examples 33-36. The output characteristics were evaluated under the same conditions as in Example 40.

[0341] [Table 10]

[0342]

[0343] The results in Tables 5-9 confirm that even by changing the composition of the solid electrolyte powder used in the solid electrolyte sheet, excellent output characteristics can be obtained by controlling the ratio t1 / t2 of the average thickness t1 of the thickest solid electrolyte layer to the average thickness t2 of the thinnest solid electrolyte layer. Furthermore, the results in Table 10 confirm that the output characteristics are improved even when the battery configuration is different.

[0344] Industrial availability

[0345] According to the present invention, lithium-ion secondary batteries with high output characteristics can be provided. They are suitable for use as power sources for portable electronic devices, and can also be used as batteries for electric vehicles, homes, and industries.

Claims

1. A lithium-ion secondary battery, wherein, The lithium-ion secondary battery is composed of a positive electrode layer containing positive electrode active material and a negative electrode layer containing negative electrode active material, separated by a solid electrolyte layer. It has multiple solid electrolyte layers stacked with the positive electrode layer or the negative electrode layer in between. Among the average thicknesses t of the plurality of solid electrolyte layers, the ratio t1 / t2 of the average thickness t of the thickest solid electrolyte layer to the average thickness t2 of the thinnest solid electrolyte layer is 1.02≤t1 / t2≤1.

99.

2. The lithium-ion secondary battery as described in claim 1, wherein, The standard deviation σ of the average thickness t of each of the plurality of solid electrolyte layers is 0.15≤σ≤1.66, where the unit of σ is μm.

3. The lithium-ion secondary battery as described in claim 1, wherein, At least a portion of the space between the positive electrode layer or the negative electrode layer and the solid electrolyte layer has an intermediate layer, the intermediate layer having the constituent elements of the positive electrode layer or the negative electrode layer and the solid electrolyte layer.

4. The lithium-ion secondary battery as described in claim 1, wherein, The average thickness T of each of the plurality of solid electrolyte layers is 4.8 ≤ T ≤ 9.8, where the unit of T is μm.

5. The lithium-ion secondary battery as described in claim 1, wherein, t1 / t2 is above 1.21 and below 1.

79.

6. The lithium-ion secondary battery as described in claim 2, wherein, The standard deviation σ is above 0.21 and below 1.24.

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