Solid electrolyte laminate, solid secondary battery, and method for producing same

Abstract

Provided is a solid electrolyte laminate for a solid secondary battery, said solid electrolyte laminate being capable of achieving a solid secondary battery in which a short circuit and / or deterioration in battery capacity can be suppressed even when a charge-discharge cycle is repeated during charging at a large current. A solid electrolyte laminate (4) in which three or more electrolyte layers including a solid electrolyte are laminated, the solid electrolyte laminate (4) being provided with: a first electrolyte layer (1) having a support; and a second electrolyte layer (2) and a third electrolyte layer (3) that are disposed so as to sandwich the first electrolyte layer (1) and that do not have a support. The film thickness (T2) of the second electrolyte layer (2) is 1.5-5 times the film thickness (T3) of the third electrolyte layer (3).

Description

Technical Field

[0001] The present invention relates to a solid electrolyte laminate, a solid secondary battery using the solid electrolyte laminate, and a method for manufacturing the solid secondary battery. Background Art

[0002] As a secondary battery having a high energy density, lithium ion secondary batteries have been widely popularized. In recent years, as a powerful means to achieve carbon neutrality, the conversion of gasoline vehicles to electric vehicles has been required, and the use of batteries for this purpose has gradually accelerated.

[0003] However, when a lithium ion secondary battery is used for an electric vehicle, compared with the gasoline filling time of a gasoline vehicle, the long charging time becomes a bottleneck in its popularization. Therefore, charging performance at a large current that can be charged in a shorter time is required.

[0004] As a technology capable of achieving charging at a large current, a lithium ion solid secondary battery using a solid electrolyte (in this specification, sometimes simply referred to as a "solid secondary battery") has been proposed. Most solid electrolytes have a lithium ion transference number of 1, and in addition, with the improvement of ionic conductivity in recent years, they have gradually become batteries essentially suitable for flowing a large current.

[0005] In a solid secondary battery using a solid electrolyte, the solid electrolyte is in powder form or gel form. The solid electrolyte layer that has these solid electrolytes and serves as a separator is preferably formed thinly to improve the energy density. At the same time, similar to the polyolefin-based separator used in existing lithium ion secondary batteries using an organic electrolyte, it is desired that at least a part of it be self-supporting. By making at least a part of the solid electrolyte layer self-supporting, the handling of the powder-like or gel-like solid electrolyte becomes easy, and thus, it becomes easy to achieve the enlargement of the battery area and the improvement of mass productivity.

[0006] In this regard, a solid electrolyte laminate using a sheet having a large number of through holes as a support has been proposed (for example, refer to Patent Documents 1 to 3).

[0007] Prior Art Documents

[0008] Patent Documents

[0009] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2016-31789

[0010] Patent Document 2: Japanese Unexamined Patent Application Publication No. 2017-208250

[0011] Patent Document 3: Japanese Unexamined Patent Application Publication No. 2021-150204 Summary of the Invention

[0012] Problems to be Solved by the Invention

[0013] However, in the solid secondary batteries of the prior art examples using a solid electrolyte sheet (solid electrolyte laminate) described in Patent Documents 1 to 3, there are the following problems: particularly, short circuits are likely to occur during charging at high currents, and in addition, the battery capacity is likely to decrease when repeating charge-discharge cycles. Therefore, there is a demand for a solid secondary battery that can suppress short circuits during charging at high currents and / or suppress deterioration of the battery capacity even when repeating charge-discharge cycles.

[0014] An object of the present invention is to provide: a solid electrolyte laminate that can realize a solid secondary battery capable of suppressing short circuits during charging at high currents and / or suppressing a decrease in battery capacity even when repeating charge-discharge cycles. In addition, an object of the present invention is to provide: a solid secondary battery using the above solid electrolyte laminate and a method for manufacturing the solid secondary battery.

[0015] Solutions to the Problems

[0016] One aspect of the present invention is as follows: [1]

[0018] A solid electrolyte laminate in which three or more electrolyte layers containing a solid electrolyte are laminated, the solid electrolyte laminate comprising:

[0019] a first electrolyte layer having a support; and

[0020] a second electrolyte layer and a third electrolyte layer that are disposed sandwiching the first electrolyte layer and do not have a support,

[0021] wherein the film thickness (T2) of the second electrolyte layer is 1.5 to 5 times that of the film thickness (T3) of the third electrolyte layer; [2]

[0023] The solid electrolyte laminate according to item 1, wherein the support includes a woven fabric; [3]

[0025] The solid electrolyte laminate according to item 2, wherein the film thickness (T2) of the second electrolyte layer is 0.2 to 2 times that of the collective fiber width of the woven fabric; [4]

[0027] The solid electrolyte laminate according to item 1, wherein the support includes at least one of a non-woven fabric and short fibers; [5]

[0029] The solid electrolyte laminate according to item 4, wherein the support includes a non-woven fabric, and

[0030] The film thickness (T2) of the second electrolyte layer is 3 to 20 times that of the average diameter of the fibers constituting the support body; [6]

[0032] A solid secondary battery, comprising: a positive electrode, a negative electrode, and the solid electrolyte laminate according to any one of Items 1 to 5,

[0033] The second electrolyte layer is in contact with the positive electrode or the negative electrode.

[0034] In addition, another aspect of the present invention is as follows: [7]

[0036] A method for manufacturing a solid secondary battery, the manufacturing method comprising the following steps:

[0037] Step (1), providing a second B electrolyte layer without a support body on either the positive electrode composite layer or the negative electrode composite layer;

[0038] Step (2), forming a first electrolyte layer having a support body, and then providing a second A electrolyte layer and a third electrolyte layer without a support body in a manner of sandwiching the first electrolyte layer {wherein, the film thickness (T2A) of the second A electrolyte layer is substantially equal to the film thickness (T3) of the third electrolyte layer}, to obtain a laminate precursor; and

[0039] Step (3), laminating the positive electrode composite layer, the laminate precursor, and the negative electrode composite layer in such a manner that the second A electrolyte layer and the second B electrolyte layer face each other, so that the total film thickness (T2; T2A + T2B) of the second A electrolyte layer and the second B electrolyte layer is 1.5 to 5 times that of the film thickness (T3) of the third electrolyte layer. Description of the Drawings

[0040] Figure 1 A cross-sectional view showing a configuration example of a solid electrolyte laminate according to an embodiment of the present invention.

[0041] Figure 2 A cross-sectional view schematically showing the analysis sites in Example 3 and Comparative Example 4.

[0042] Figure 3 A view showing a manufacturing example of a solid electrolyte laminate according to an embodiment of the present invention. Detailed Embodiments

[0043] One aspect of the present invention is a solid electrolyte laminate which is a solid electrolyte laminate in which three or more electrolyte layers containing a solid electrolyte are laminated. The solid electrolyte laminate includes: a first electrolyte layer having a support; and a second electrolyte layer and a third electrolyte layer which are disposed sandwiching the first electrolyte layer and do not have a support. The film thickness (T2) of the second electrolyte layer is 1.5 to 5 times that of the third electrolyte layer (T3).

[0044] In addition, another aspect of the present invention is a method for manufacturing a solid secondary battery, the manufacturing method including the following steps:

[0045] Step (1) of providing a second B electrolyte layer without a support on either the positive electrode composite material layer or the negative electrode composite material layer;

[0046] Step (2) of forming a first electrolyte layer having a support, and then providing a second A electrolyte layer and a third electrolyte layer without a support in a manner of sandwiching the first electrolyte layer {wherein the film thickness (T2A) of the second A electrolyte layer is substantially the same as the film thickness (T3) of the third electrolyte layer}, to obtain a laminate precursor; and

[0047] Step (3) of laminating the positive electrode composite material layer, the laminate precursor, and the negative electrode composite material layer in such a manner that the second A electrolyte layer faces the second B electrolyte layer, whereby the total film thickness (T2; T2A + T2B) of the second A electrolyte layer and the second B electrolyte layer is 1.5 to 5 times that of the third electrolyte layer (T3).

[0048] According to the solid electrolyte laminate of the above aspect, it is possible to provide a solid electrolyte laminate for a solid secondary battery that can suppress short circuits during charging at high currents and / or suppress deterioration of battery capacity even during repeated charge and discharge cycles, although a solid electrolyte layer having a support is used.

[0049] Hereinafter, embodiments of the present invention (hereinafter referred to as "the present embodiments") will be described with reference to the drawings. However, the present invention is not limited to the content shown in the present embodiments and the drawings, and various modifications can be made without departing from the gist thereof.

[0050] In this specification, the upper limit value or the lower limit value of a numerically defined range described stepwise can be replaced with the upper limit value or the lower limit value of another numerically defined range described stepwise, or can also be replaced with the value shown in the examples. The scales, shapes, lengths, etc. shown in the drawings are sometimes exaggerated for further clarity.

[0051] In this specification, a solid electrolyte layer having a support and a solid electrolyte layer without a support are regarded as different layers from each other. Further, in this specification, when the constitution (composition, shape, etc.) of the support is different, and when the composition of the solid electrolyte or the like in the support is different, they are regarded as different layers from each other. Here, when the solid electrolyte layers B (layer B1 and layer B2) without a support are separated by a solid electrolyte layer having a support, the layer B1 and the layer B2 are regarded as independent different layers. On the other hand, regardless of whether the constitution (composition, shape, etc.) is the same or different, when the solid electrolyte layers B (layer B1 and layer B2) without a support are stacked in contact with each other, the layer B1 and the layer B2 are collectively regarded as one solid electrolyte layer.

[0052] [Solid electrolyte laminate]

[0053] 〔Schematic constitution〕

[0054] An example of the solid electrolyte laminate of the present embodiment (in this specification, sometimes simply referred to as "laminate".) is shown in Figure 1 . Figure 1 It is a cross-sectional view schematically showing an example of a solid electrolyte laminate 4 including a three-layer structure.

[0055] The solid electrolyte laminate 4 of the present embodiment is a solid electrolyte laminate 4 in which three or more electrolyte layers containing a solid electrolyte are stacked,

[0056] The solid electrolyte laminate 4 includes:

[0057] A first electrolyte layer 1 having a support; and

[0058] A second electrolyte layer 2 and a third electrolyte layer 3 that are disposed sandwiching the first electrolyte layer 1 and do not have a support,

[0059] The film thickness (T2) of the second electrolyte layer 2 is 1.5 to 5 times that of the third electrolyte layer 3.

[0060] The laminate 4 has the following structure: The second electrolyte layer 2 and the third electrolyte layer 3 on both sides of the laminate 4 ( Figure 1 the upper surface side and the lower surface side in) are disposed so as to sandwich at least one first electrolyte layer 1 having a support. The film thickness (T2) of the second electrolyte layer 2 on a single surface side of the laminate 4 that does not have a support is 1.5 to 5 times, preferably 1.5 to 4.0 times, that of the third electrolyte layer 3 on the other single surface side that also does not have a support. In the figure, the second electrolyte layer 2 is shown on the upper surface side, and the third electrolyte layer 3 is shown on the lower surface side, but their arrangements may be reversed.

[0061] A thick, supportless solid electrolyte layer (here, the second electrolyte layer 2) is disposed in a manner that it is joined to the negative electrode composite material layer, whereby short circuits accompanied by the precipitation of Li metal during charging can be suppressed. Additionally, a supportless solid electrolyte layer (here, the second electrolyte layer 2) is disposed in a manner that it is joined to the positive electrode composite material layer, whereby a reduction in battery capacity accompanied by local degradation of the positive electrode active material can be suppressed.

[0062] The first electrolyte layer 1 can be a single layer, or can be two or more layers having supports with different constitutions (composition, shape, etc.), or can be two or more layers having different compositions such as a solid electrolyte and a binder. The second electrolyte layer 2 and the third electrolyte layer 3 can have the same constitution as each other or can have different constitutions. The second electrolyte layer and the third electrolyte layer 3 can have a compositional distribution in the film thickness direction and / or the plane direction.

[0063] The laminate 4 exhibits the function of a solid secondary battery by joining the second electrolyte layer 2 and the third electrolyte layer 3 to the positive electrode composite material layer or the negative electrode composite material layer. It should be noted that in the present invention, the solid electrolyte layer does not contain an active material, and thus is distinguished from the positive electrode composite material layer and the negative electrode composite material layer that function as active material layers. Among them, within the range that does not impair the effects of the present invention and within the range that does not function as an active material layer, the solid electrolyte layer can also contain any active material.

[0064] The laminate 4 does not necessarily have to be a sheet (solid electrolyte sheet) that has self-supporting strength by itself. Among them, when the whole or a part of the structure body (the first electrolyte layer 1) having a support has self-supporting strength, it is related to the improvement of the strength of the laminate 4 as a whole. Therefore, from the viewpoints of preventing the detachment of the solid electrolyte, preventing the occurrence of cracks in the solid electrolyte layer, and making it easier to increase the area of the battery through these, and the improvement of mass productivity based on the improvement of operability, etc., it is preferred.

[0065] In the laminate 4, there is no limit to the upper limit of the number of solid electrolyte layers, but it is preferably 7 or less, more preferably 5 or less, and still more preferably 4 or less. The film thickness of the laminate 4 is not particularly limited, but if the film thickness is too thick, the energy density of the solid secondary battery is likely to decrease, and if the film thickness is too thin, the possibility of short circuits occurring in the solid secondary battery is likely to increase. Therefore, the film thickness is preferably 7 to 80 μm, more preferably 10 to 70 μm, and still more preferably 13 to 60 μm. Figure 1 In this case, the film thickness of the laminate 4 is the sum of the film thickness of the first electrolyte layer 1, the film thickness (T2) of the second electrolyte layer 2, and the film thickness (T3) of the third electrolyte layer 3.

[0066] 〔Solid electrolyte layer having a support〕

[0067] The solid electrolyte layer can be roughly divided into a solid electrolyte layer with a support and a solid electrolyte layer without a support. Among them, the volume ratio of the solid electrolyte in the solid electrolyte layer with a support (here, the first electrolyte layer 1) is not particularly limited. If the volume ratio is too small, the resistance of the battery tends to increase, and thus the capacity is likely to decrease. On the other hand, if the volume ratio is too large, the proportion of the support tends to decrease, and thus the strengthening effect of the solid electrolyte layer based on the support is likely to decrease. Therefore, the volume ratio of the solid electrolyte is preferably 10 to 90%, more preferably 15 to 80%, and still more preferably 20 to 70%.

[0068] The thickness of the solid electrolyte layer with a support can be substantially the same as the thickness of the support. Specifically, the thickness of the solid electrolyte layer with a support can be 0.95 to 1.05 times the thickness of the support.

[0069] <Support>

[0070] The support is not particularly limited, and any of woven fabric, non-woven fabric, microporous membrane, and a sheet formed with a large number of through-holes can be used. There are no limitations on its constitution (composition, shape, etc.) and the constitution of the opening part (size, shape, etc.). The support is not limited to being formed in a sheet shape, and the short fibers in the solid electrolyte layer obtained by compounding fine short fibers with the solid electrolyte are also included in the concept of "support" in this specification. In this case, the short fibers can be physically bonded to each other or exist dispersed in the solid electrolyte layer without bonding.

[0071] In this embodiment, the support preferably includes a woven fabric (in one embodiment, the support is a woven fabric). In addition, the support preferably includes at least one of non-woven fabric and short fibers (in one embodiment, the support is at least one of non-woven fabric and short fibers).

[0072] (Woven fabric)

[0073] As the above support, a woven fabric can be used. The woven fabric is formed by bundling multiple single filaments, which are the basic units of fibers, with a bundling agent as needed and then weaving them. Here, when using a woven fabric as the above support, in this specification, the average value obtained by looking down at the width of the bundled single-filament bundle in the thickness direction of the woven fabric and measuring the length is defined as the "aggregate fiber width". As the method of looking down, an optical microscope or a scanning electron microscope (SEM) can be used. When there is a distribution along the aggregate fiber width, measure the widths of multiple of them, calculate the arithmetic mean, and regard it as the aggregate fiber width. It should be noted that the aggregate fiber width is represented by the symbol 8 in Figure 2 is represented by the symbol 8.

[0074] The width of the assembled fibers and the number of bundled fibers are not particularly limited. If the width of the assembled fibers is too large, the opening rate of the support is likely to decrease. In addition, if it is too small, the strength of the fibers is likely to decrease, and therefore, weaving the woven fabric becomes difficult. Therefore, the width of the assembled fibers is preferably 3 to 200 μm, more preferably 5 to 100 μm, and further preferably 7 to 90 μm. The weaving method of the woven fabric can be appropriately plain weave, twill weave, satin weave, gauze weave, etc. Among them, there is no particular limitation as long as the shape can be maintained.

[0075] (Non-woven fabric)

[0076] As the support, a nonwoven fabric can be used. The average fiber diameter of the fibrous material constituting the nonwoven fabric is not particularly limited. If the average fiber diameter is too thick, the opening ratio of the support is likely to decrease, and if it is too small, the strength of the support is likely to decrease. Therefore, the average fiber diameter is preferably 0.3 to 25 μm, and more preferably 0.5 to 22 μm.

[0077] The weight per unit area of ​​the nonwoven fabric is not particularly limited. If the weight per unit area is too large, the opening diameter and the opening ratio are likely to decrease, and thus the resistance of the battery is likely to increase. In addition, if the weight per unit area is too small, the strength as a support is likely to decrease due to the small proportion of the fibrous material. Therefore, the weight per unit area of ​​the nonwoven fabric is preferably 1.0 to 10.0 g / m 2 , more preferably 1.5 to 8.0 g / m 2 , more preferably 2.0 to 6.0 g / m 2 .

[0078] The porosity of the nonwoven fabric relative to the film thickness is not particularly limited. If the porosity is too small, the proportion of the solid electrolyte is likely to decrease, so the resistance of the battery is likely to increase. In addition, if the porosity is too large, the proportion of fibrous materials is likely to decrease, so the strength as a support is likely to decrease. Therefore, the porosity of the nonwoven fabric is preferably 30 to 90%, more preferably 40 to 85%, and further preferably 50 to 80%.

[0079] (microporous membrane)

[0080] As the above-mentioned support, a microporous membrane can be used. The composition of the pores in the microporous membrane (average pore size and its distribution width, etc.) is not particularly limited. If the average pore size is too small, it is easy to become difficult to fill the opening, especially in the case of a granular solid electrolyte. In addition, if it is too large, especially in the case of a granular solid electrolyte, the particles are easy to fall off from the opening. Therefore, the average pore size in the microporous membrane is preferably 0.5 to 5 μm, more preferably 1 to 4 μm.

[0081] (Sheet with a large number of through holes formed)

[0082] As the above-mentioned support, a sheet such as a net (a sheet formed with a large number of through-holes) can be used. The structure of the through-holes in the sheet (such as the average pore diameter and shape) is not particularly limited. For example, the shape of the through-holes is not limited to a square or a circle, etc., and can also be a rectangle, a rhombus, an ellipse, etc. As a method for forming the through-holes, the following methods can be cited: a method of opening physically using a mold and a drill, etc.; a method of opening using a laser; a method of opening using photolithography and thermal lithography; etc. In addition, a support in which incisions are introduced into the sheet and stretched to both sides to flare the through-holes can also be used.

[0083] (Short fiber)

[0084] As the above-mentioned support, fine short fibers can be used. The structure of the short fibers (such as the average fiber diameter, its distribution, and the average length, etc.) is not particularly limited. Similar to the non-woven fabric, if the average fiber diameter is too thick, the aperture ratio of the support is likely to decrease, and if it is too small, the strength of the support is likely to decrease. Therefore, the average fiber diameter is preferably 0.3 to 25 μm, more preferably 0.5 to 20 μm. In addition, if the average length is too long, the fibers are likely to aggregate when compounded with the solid electrolyte, and thus it is difficult to obtain a uniform composite. In addition, if the average length is too short, the effect of imparting the strength of the support is likely to decrease when compounded with the solid electrolyte. Therefore, the average length of the short fibers is preferably 10 to 2000 μm, more preferably 20 to 1000 μm, and further preferably 30 to 500 μm.

[0085] (Others)

[0086] The material of the support is not limited to the above. Any material that can enhance the solid electrolyte layer having the support can be used as the support material. For example,

[0087] Polyolefins such as polypropylene and polyethylene;

[0088] Polyesters such as polystyrene, aromatic polyamide, polyamideimide, polyimide, nylon, polyethylene terephthalate (PET);

[0089] Polyarylate, cellulose and its modified forms;

[0090] Any resin such as the above can be used as the material of the support.

[0091] In addition, metals such as Al 2 O 3 、 glass, nickel, etc.; various inorganic substances; etc. can also be used as the material of the support. It should be noted that from the viewpoint of not easily causing the occurrence of battery short-circuit accompanied by contact with the electrode, it is preferable to use a material with high insulation as the material of the support.

[0092] The film thickness of the support is not particularly limited. If the film thickness is too thick, the energy density of the battery is likely to decrease. If the film thickness is too thin, the strength of the support is likely to decrease. Therefore, the film thickness of the support is preferably 2 to 40 μm, more preferably 3 to 35 μm, and still more preferably 4 to 30 μm.

[0093] The measurement of the above film thickness can be carried out by a conventionally known method. For example, the support is clamped by a commercially available micrometer (e.g., high-precision digital mechanical micrometer MDH-25MB manufactured by Mitutoyo Corporation, etc.), and different positions of the support are measured multiple times. The arithmetic mean value is calculated based on the results obtained thereby to obtain the film thickness.

[0094] When fibrous materials (non-woven fabrics, short fibers, etc.) are used as the support, the average fiber diameter is not particularly limited. If the average fiber diameter is too large, the thickness of the support is likely to increase. If it is too small, the thickness of the support is likely to become thinner. Therefore, from the viewpoint of suppressing the occurrence of problems related to the aforementioned thickness, the average fiber diameter of the fibrous material is preferably 0.5 to 20 μm, more preferably 1 to 15 μm, and still more preferably 2 to 10 μm.

[0095] The measurement of the average fiber diameter and its distribution of the fibrous materials contained in the solid electrolyte layer can be carried out by a conventionally known method. For example, the above can be obtained through the following steps: a step of cutting the solid electrolyte laminate to expose the cross-section; a step of measuring multiple parts of the fiber part in the cross-section that has been smoothly polished by a cross-section polishing machine, etc., using SEM-based cross-section observation; and a step of calculating the arithmetic mean value and distribution of the measured fiber diameters.

[0096] The porosity of the support is not particularly limited. If the porosity is too small, the resistance of the battery is likely to increase, and thus the capacity is likely to decrease. In addition, if the porosity is too large, the strength of the support is likely to decrease. Therefore, the porosity of the support is preferably 10 to 90%, more preferably 15 to 80%, and still more preferably 20 to 70%.

[0097] The porosity of the support is defined as follows: when looking at the support from the thickness direction, the ratio of the area of the opposite side of the observation surface of the support observed through the support to the area of the surface regarded as the observation object.

[0098] The volume ratio of the support in the solid electrolyte layer having a support is not particularly limited. If this volume ratio is too large, the resistance of the battery is likely to increase, and thus the capacity is likely to decrease. In addition, if the volume ratio is too small, the proportion of the support is likely to decrease, and thus the strength derived from the support is likely to decrease. Therefore, the above volume ratio is preferably 10 to 90%, more preferably 20 to 85%, and still more preferably 30 to 80%.

[0099] 〔Solid electrolyte layer without a support〕

[0100] Regarding the solid electrolyte layer without a support, the film thickness of the solid electrolyte layer without a support located on the single surface side of the laminate 4 (here, the film thickness (T2) of the second electrolyte layer 2) is 1.5 to 5 times, more preferably 1.5 to 4 times, the film thickness of the solid electrolyte layer without a support located on the other single surface side (here, the film thickness (T3) of the third electrolyte layer 3). The second electrolyte layer 2 and the third electrolyte layer 3 are respectively in contact with the solid electrolyte layer with a support (the first electrolyte layer 1). In this regard, for the film thickness (T2) of the second electrolyte layer 2, when the support included in the first electrolyte layer 1 is a woven fabric, it is preferably 0.2 to 2 times the width of the collective fibers of the woven fabric, and when the support is a non-woven fabric, it is preferably 2 to 20 times, or 3 to 20 times, the average fiber diameter of the non-woven fabric.

[0101] Without being bound by theory, the present inventors have found from the results of the experiments shown in the examples and the results of the solid battery simulation based on the Newman model that the short circuit and deterioration are accelerated by the following mechanism. That is, the present inventors have found that the presence of the support causes state unevenness such as electrolyte potential and SOC inside the solid battery, and problems such as the occurrence of a short circuit accompanied by Li precipitation and the deterioration of the active material are accelerated due to this unevenness. It should be noted that the present inventors have also found that, in addition to the above reasons, the following phenomena occur in the solid secondary battery of the prior art examples, thereby causing short circuit and deterioration.

[0102] The movement and diffusion path of Li ions is restricted by the support;

[0103] The bonding property at the interface between the solid electrolyte sheet and the positive electrode and / or the negative electrode is reduced, thereby increasing the impedance of the battery;

[0104] Compared with a lithium solid secondary battery without a support, it becomes particularly easy to cause the precipitation of Li metal on the surface of the negative electrode during charging at a large current and the short circuit caused thereby;

[0105] As the charge-discharge cycle progresses, the positive electrode active material deteriorates locally, and the reduction of the battery capacity progresses.

[0106] Moreover, the present inventors have found that problems such as these short circuits and deteriorations are not caused by an increase in the impedance of the battery in which the separator is a solid electrolyte sheet, and have further found that they are related to the film thickness of the solid electrolyte layer without a support having a relatively thick film thickness ( Figure 1 In this case, it is the film thickness T2 of the second electrolyte layer 2).

[0107] In addition, the inventors et al. have found a specific relationship that suppresses problems such as the occurrence of short circuits accompanied by Li precipitation and the deterioration of active materials (specifically, the film thickness of the above-mentioned solid electrolyte layer with a relatively thick film thickness without a support), and furthermore, have found a suitable relationship between them and the width and / or diameter of the collective fibers. The present invention has been made through the in-depth efforts of the inventors et al.

[0108] The film thickness of the solid electrolyte layer without a support is not particularly limited. If the film thickness is too thick, the energy density of the battery is likely to decrease. On the other hand, if the film thickness is too thin, the possibility of the battery short-circuiting is likely to increase. Therefore, the film thickness of the solid electrolyte layer without a support is preferably 2 to 60 μm, more preferably 4 to 50 μm, and even more preferably 6 to 40 μm. The film thickness here refers to the respective film thicknesses of the solid electrolyte layers without a support. For example, it refers to Figure 1 the film thickness (T2) of the second electrolyte layer 2 and the film thickness (T3) of the third electrolyte layer 3 in

[0109] The measurement of the film thickness of the solid electrolyte layer can be carried out by a conventionally known method. For example, it can be obtained through the following steps: a step of cutting the solid electrolyte laminate to expose the cross-section; a step of observing the cross-section of the solid electrolyte laminate that has been smoothly polished with a cross-section polishing machine or the like using SEM and measuring the film thickness at multiple positions; and a step of calculating the arithmetic average of the multiple measured film thicknesses.

[0110] 〔Solid Electrolyte〕

[0111] The solid electrolyte is preferably one that can be used alone, or held on the surface of a support, or contained in a support so as to be able to maintain a layer form, and more preferably one that can conduct ions. In general, the higher the ionic conductivity of the electrolyte used in the battery, the more preferable it is, and the present invention is no exception. Examples of solid electrolytes include sulfide-based solid electrolytes, polymer-based solid electrolytes, gel-based electrolytes, hydride-based solid electrolytes, and oxide-based solid electrolytes. Among them, the following substances are excluded: those that cannot maintain a layer form even when held on the surface of a support and flow; and those that cannot maintain a layer form even when contained in a support and flow.

[0112] Even when the layer thickness decreases due to the pressurization of the battery based on constraints or the like, it can be used as a solid electrolyte. As the layer thickness decreases, the solid electrolyte flows, and thus, it is not preferable that more than half of the solid electrolyte is extruded from the layer.

[0113] As the solid electrolyte filled in the opening of the support, a sulfide-based solid electrolyte, a polymer solid electrolyte, a gel electrolyte, and a hydride-based solid electrolyte, which are preferably soft and easily deformable to facilitate filling, are preferred. If necessary, a binder component, a viscosity modifier, and other components required for filling and coating can also be added.

[0114] As the sulfide-based solid electrolyte, for example, in the glass-based and glass-ceramic-based, there can be mentioned: Li 2 S-P 2 S 5 、Li 2 S-P 2 S 3 、Li 2 S-P 2 S 3 -P 2 S 5 、Li 2 S-P 2 S 5 -GeS 2 、Li 2 S-P 2 S 5 -B 2 S 3 、Li 2 S-SiS 2 、Li 2 S-SiS 2 -P 2 O 5 、LiI-Li 2 S-SiS 2 、LiI-Li 2 S-P 2 S 5 、LiI-Li 2 S-P 2 O 5 、LiI-Li 3 PO 4 -P 2 S 5 、LiI-Li 2 S-SiS 2 -P 2 S 5 、Li 2 S-SiS 2 -Li 3 PO 4 、LiBr-Li 2 S-SiS 2 、Li 2 S-GeS 2 、Li 2 S-GeS2 -ZnS, Li 2 S - GeS 2 -Sb 2 S 5 、Li 2 S - GeS 2 -Ga 2 S 3 、Li 2 S - GeS 2 -Al 2 S 3 、LiI - Li 2 S - GeS 2 、Li 2 S - GeS 2 -Li 3 PO 4 、Li 2 S - Ga 2 S 3 、Li 2 S - B 2 S 3 、Li 2 S - Al 2 S 3 、Li 2 S - SiS 2 -Al 2 S 3 、LiI - Li 2 S - B 2 S 3 、Li 2 S - B 2 S 3 -Li 3 PO 4 、Li 2 S - P 2 S 5 -LiBr, Li 2 S - P 2 S 5 -Li 3 N, Li 2 S - P 2 S 5 -LiBH 4 etc.

[0115] In the crystal system, examples include: Li 6 PS 5 X (where X = Cl, Br, I), Li 7-x PS 6-x X x (where X = Cl, Br, I, 0 ≤ x ≤ 1.8), etc., and Li 3.4P 0.6 Si 0.4 S 4 、Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 、Li 4-x Ge 1-x P x S 4 (where 0 ≤ x ≤ 1), Li 10 GeP 2 S 11.7 O 0.3 etc.

[0116] As the polymer solid electrolyte and the gel electrolyte, those that can be used are: those in which an electrolyte salt is dissolved in a polymer compound to exhibit ionic conductivity; and those in which an electrolyte salt, a polymer, and a monomer are dissolved in a solvent and gelled, and then exhibit ionic conductivity. Specifically, when using a lithium salt as the electrolyte salt, examples of the lithium salt include: lithium hexafluorophosphate (LiPF 6 ), lithium bis(fluorosulfonyl)imide (Li(FSO 2 ) 2 )N), lithium bis(trifluoromethanesulfonyl)imide (Li(CF 3 SO 2 ) 2 N), lithium perchlorate (LiClO 4 ), lithium hexafluoroarsenate (LiAsF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium trifluoromethanesulfonate (LiCF 3 SO 3 ), lithium bis(trifluoromethanesulfonyl)imide [LiN(CF 3 SO 3 ) 2 and other lithium salts known in the past.

[0117] As the polymer that dissolves an electrolyte salt by itself to exhibit ionic conductivity, for example, those that can be used are: polyethylene glycol, polymers having a main chain of polyacrylic acid, polymethacrylic acid, polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyphosphazene, polysilane, etc., and copolymers thereof, and polymers having a polyoxyethylene structure in the side chain, etc.

[0118] In a gel electrolyte in which an electrolyte salt is dissolved together with a polymer and a monomer in an electrolyte solvent and then gelates to exhibit ionic conductivity, the polymer and monomer used are not particularly limited. Examples of the polymer include polyvinyl chloride, polyacrylonitrile, polyethylene, polypropylene, polyester, polyacrylate, and copolymers thereof. Examples of the monomer include carborane-based materials such as o-carborane, m-carborane, p-carborane; adamantane-based materials such as 2-adamantanone, 1-adamantanone, 1-adamantanecarbonitrile, 2-adamantanecarbonitrile; dinitrile compounds such as succinonitrile, methyl succinonitrile, tetramethyl succinonitrile, azobisisobutyronitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelaonitrile, sebaconitrile; and sulfolane compounds such as sulfolane, ethyl methyl sulfone, 3-methyl sulfolane; etc.

[0119] As the above electrolyte solvent, a mixed solvent of a cyclic carbonate and a linear carbonate can be cited. As the cyclic carbonate, ethylene carbonate (EC) or propylene carbonate (PC) can be typically cited. Additionally, as the linear carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), etc. can be typically cited. However, it is not limited to these.

[0120] As the electrolyte solvent, an ionic liquid can also be used. Specifically, for example, 1,2-ethylmethylimidazolium bis(fluorosulfonyl)imide, 1,2-ethylmethylimidazolium bis(trifluoromethylsulfonyl)imide, 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (abbreviation: EMImFSI), N-methylpropylpyrrolidinium bis(fluorosulfonyl)imide, N-methylpropylpyrrolidinium bis(trifluoromethylsulfonyl)imide, diethylmethylmethoxyethylammonium bis(trifluoromethylsulfonyl)imide, diethylammonium bis(fluorosulfonyl)imide, diallyldimethylammonium (trifluoromethylsulfonyl)imide, diallyldimethylammonium (fluorosulfonyl)imide, etc. can be cited. However, it is not limited to these.

[0121] As the hydride-based solid electrolyte, those having ionic conductivity are preferred. For example, LiBH 4 , LiAlH 4 , Li 3 AlH 6 , LiBH(Et) 3 , LiBH(s-Bu) 3 , LiNH 2 , Li 2 NH, Li[OC(CH 3 ) 3 3 AlH, Li(OCH 3 ) 3 AlH, Li(OC 2 H​5 ) 3 H, LiBH 4 A solid electrolyte with a molar ratio of 1:1 to 20:1 of LiI, Li 2 B 12 H 12 and Li 3 MoH 9 And other spin complex ion classes, as well as those formed by various solid solutions of them, etc.

[0122] As an oxide-based solid electrolyte, for example, there can be cited: Li 7 La 3 Zr 2 O 12 (LLZ), Li x La Y TiO 3 [where x = 0.3 to 0.7, Y = 0.3 to 0.7] (LLT), Li with a LISICON (Lithium super ionic conductor) type crystal structure 3.5 Zn 0.25 GeO 4 And LiTi with a NASICON (Natrium super ionic conductor) type crystal structure 2 P 3 O 12 And so on. However, it is not limited to these.

[0123] Phosphorus compounds containing Li, P, and O can also be used as solid electrolytes. For example, Li 3 PO 4 can also be preferably selected. By replacing a part of the oxygen in Li 3 PO 4 with nitrogen, LiPON, LiPOD (where D is at least one selected from transition metals), LiAON (where A is at least one selected from the group consisting of Si, B, Ge, Al, C, Ga, etc.) can be obtained. Li 3 N using N instead of P can also be used.

[0124] Among them, from the viewpoint of having a high ionic conductivity, as a solid electrolyte, a sulfide-based solid electrolyte is preferred. In addition, from the viewpoint of being electrochemically stable, a thiogermanate-type sulfide-based solid electrolyte in the crystal system is more preferred.

[0125] When using a powdery sulfide-based solid electrolyte, if its average particle size becomes smaller, it becomes easier to fill the solid electrolyte into the openings of the support. On the other hand, when the solid electrolyte is treated as a slurry, the dispersibility in the solid electrolyte slurry tends to decrease, so it becomes difficult to obtain a uniform solid electrolyte sheet. In addition, if the average particle size becomes larger, the proportion of large particle size solid electrolyte particles tends to increase. Therefore, not only is it difficult to fill the solid electrolyte into the openings of the support, but it also becomes difficult to obtain a solid electrolyte layer with a uniform thickness. Thus, the average particle size of the sulfide-based solid electrolyte is preferably 0.1 to 10 μm.

[0126] The average particle size and particle size distribution of the powdery solid electrolyte can be determined by known general methods. Specifically, for example, a dry particle size distribution measuring device using laser diffraction / scattering (e.g., laser diffraction / scattering type particle size distribution measuring device LA-960V2 manufactured by Horiba, Ltd.) can be used. The solid electrolyte can be used alone or in combination of two or more kinds.

[0127] <Binder>

[0128] The solid electrolyte layer may contain a binder to improve the adhesion between the support and the solid electrolyte layer and / or between the solid electrolyte layers. As the binder, known substances can be used, for example, styrene-based thermoplastic elastomers such as SBS (styrene-butadiene block polymer), SEBS (styrene-ethylene-butadiene-styrene block polymer), styrene-styrene-butadiene-styrene block polymer, styrene-butadiene rubber, butadiene rubber, natural rubber, isoprene rubber, EPDM (ethylene-propylene-diene terpolymer), nitrile rubber, chloroprene rubber, and their partially hydrogenated or fully hydrogenated products, cellulose such as carboxymethyl cellulose, copolymers of polyacrylate, PVDF (polyvinylidene fluoride), PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene copolymer), and their carboxylic acid modified products, polymethacrylate, polyvinyl alcohol, ethylene-vinyl alcohol copolymer, acrylic latex, polyimide, polyamide, polyamideimide, etc. In addition, polystyrene, polyolefin, olefin-based thermoplastic elastomer, polycycloolefin, silicone resin, etc. can be mentioned. They can be used alone or in combination of two or more kinds.

[0129] 〔Method for forming solid electrolyte layer and method for forming laminate〕

[0130] As a method for forming a solid electrolyte layer, a usual forming method can be adopted. For example, the following methods can be cited: a method of dissolving or dispersing a solid electrolyte and a binder in a solvent to obtain a slurry or a solution, then coating the slurry or solution of the solid electrolyte, and then drying it; a method of coating a powder of a solid electrolyte material and then removing excess powder using a squeegee or the like; etc.

[0131] In a solid electrolyte layer having a support, it is necessary to fill the opening of the support with the solid electrolyte. At this time, the support can be held on a sheet and a film that serve as a substrate, and a slurry or a solution of the solid electrolyte can be coated or powder-coated from above it, so that while filling and holding the solid electrolyte in the opening of the support, a solid electrolyte layer having a support integrated with the above sheet and film is temporarily fabricated. At this time, it is preferable to perform a release treatment on the surface of the above sheet and film that is in contact with the solid electrolyte layer so that the above sheet and film can be peeled off and removed from the solid electrolyte layer later.

[0132] The method for forming a solid electrolyte layer without a support is the same as that for forming a solid electrolyte layer with a support. That is, the following methods can be used: a method of coating a slurry or a solution of a solid electrolyte on the above sheet and film that serve as a substrate, on a solid electrolyte layer having a support, on other solid electrolyte layers without a support, on a positive composite material layer, or on a negative composite material layer, and a method of powder-coating a solid electrolyte material.

[0133] In the above method, preferably, first, a solid electrolyte layer without a support is fabricated on a sheet and a film that serve as a substrate, then a support is placed thereon, and a solid electrolyte is further overlapped by coating a slurry or a solution or powder-coating, thereby forming a laminate. Thereby, a solid electrolyte laminate having a desired film thickness and including the following constitution can be obtained on the above sheet and film:

[0134] A solid electrolyte layer without a support,

[0135] A solid electrolyte layer having a support, and

[0136] A solid electrolyte layer without a support

[0137] of the solid electrolyte laminate. Then, the above sheet and film are peeled off, and thus it can be regarded as a self-supporting solid electrolyte sheet, or the above sheet and film are peeled off while being transferred to a positive electrode or a negative electrode or the like, and thus it can also be regarded as a solid electrolyte laminate.

[0138] As the above sheet and film that serve as a substrate, for example, a stainless steel foil, a PET film, etc. can be cited. However, there is no particular limitation.

[0139] In this embodiment, if the solid electrolyte layers are stacked in the aforementioned manner, after peeling off the sheet and the film due to the shrinkage stress during drying and the residual stress after compression of the solid electrolyte material, there is a possibility that the solid electrolyte laminate will warp. Depending on the type and material of the support, warping becomes significant in many cases when the difference in the film thickness of the solid electrolyte layers ( Figure 1 in Figure 1 , the difference between the film thickness (T2) of the second electrolyte layer 2 and the film thickness (T3) of the third electrolyte layer 3) is large. When the solid electrolyte laminate is treated as a self-supporting solid electrolyte sheet, this warping easily induces cracks and notches in the solid electrolyte layer and easily causes short circuits in the battery. Therefore, it is preferable to suppress warping.

[0140] Therefore, in this embodiment, it is preferable to adopt the following method: laminate a positive electrode or a negative electrode having a solid electrolyte layer without a support provided to either the positive electrode composite layer or the negative electrode composite layer with the solid electrolyte laminate, and then bond them, so that finally the film thickness of the solid electrolyte layer without a support in contact with either the positive electrode composite layer or the negative electrode composite layer becomes at least 1.5 times and at most 5 times the film thickness of the other solid electrolyte layer without a support, and a laminate is formed. This can be cited as a preferable method in the case of a solid electrolyte laminate with a large warping when forming a solid electrolyte sheet having self-supporting strength.

[0141] At this time, for a solid electrolyte laminate in which the thicknesses of the two substantially supportless solid electrolyte layers are the same, the above-mentioned sheet and film as the base material can be peeled off and treated as a solid electrolyte sheet having self-supporting strength, or it can be transferred to either the positive electrode composite layer or the negative electrode composite layer and then the above-mentioned sheet and film can be peeled off.

[0142] The solid electrolyte layer and its laminate of the present invention are pressurized as needed to compress the solid electrolyte material. When the solid electrolyte is formed of particles, it is desirable to improve the bonding property between the particles and at the same time fill the openings of the support.

[0143] The method of pressurizing the solid electrolyte is not particularly limited. For example, methods such as roll pressurization, flat plate pressurization, and hydrostatic pressurization can be cited. Since roll pressurization can perform pressurization continuously, it is preferable from the viewpoint of improving the productivity of the solid electrolyte laminate.

[0144] When pressurizing the solid electrolyte, it is more preferable to pressurize while heating. At this time, hot roll pressurization, hot flat plate pressurization, and hot hydrostatic pressurization can be used. The temperature at this time depends on the material of the support and the type of the solid electrolyte, and is, for example, 60 to 250 °C.

[0145] Regarding the pressure for pressing the solid electrolyte layer and its laminate, in the case of flat pressing or static pressing, etc., it is, for example, 30 to 1000 MPa. Further, in the case of the line pressure of roll pressing, it is, for example, 0.1 to 5 ton / cm.

[0146] 〔Method for producing slurry or solution of solid electrolyte and solid electrolyte layer using the same〕

[0147] The slurry or solution of the solid electrolyte described above contains: a solid electrolyte, a solvent for dispersing or dissolving it (the concept of "solvent" in this specification includes a dispersion medium), and additives (known additives such as a binder and a thickener) added as required.

[0148] As the solvent, as long as it can disperse or dissolve the solid electrolyte and the additives well and does not cause a large obstacle to the battery characteristics of the solid electrolyte and the support, for example, methanol, ethanol, 1-propanol, 2-butanol, ethylene glycol, propylene glycol, glycerol, 1,6-hexanediol, 1,3-butanediol, 1,4-butanediol, ethylene glycol monomethyl ether, ethylene glycol monobutyl ether, diethylene glycol, dipropylene glycol, propylene glycol monomethyl ether, diethylene glycol monomethyl ether, triethylene glycol, polyethylene glycol, propylene glycol dimethyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, diethylene glycol monobutyl ether, diethylene glycol dibutyl ether, dimethyl ether, ethyl ether, dibutyl ether, etc., tetrahydrofuran, dioxane, N,N-dimethylformamide, 1-methyl-2-pyrrolidone, 2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, ε-caprolactam, formamide, N-methylformamide, acetamide, N-methylacetamide, N,N-dimethylacetamide, N-methylpropionamide, triethylamine, tributylamine, acetone, methyl ethyl ketone, diethyl ketone, diacetone, dibutyl ketone, diisobutyl ketone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, amyl acetate, hexyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate, isobutyl isobutyrate, amyl butyrate, methyl valerate, ethyl valerate, propyl valerate, butyl valerate, methyl caproate, ethyl caproate, propyl caproate, butyl caproate, hexene, heptene, cyclohexene, toluene, various o-, m-, p-xylenes, decalin, 1,2,3,4-tetrahydronaphthalene, mesitylene, anisole, hexane, pentane, heptane, 2-ethylhexane, cyclohexane, methylcyclohexane, ethylcyclohexane, decalin, octane, nonane, decane, pentane, cyclopentane, cyclooctane, acetonitrile, propionitrile, butyronitrile.

[0149] When using a sulfide-based solid electrolyte, a low-polarity solvent with low reactivity with the sulfide-based solid electrolyte is particularly preferred. Examples thereof include hexane, pentane, 2-ethylhexane, heptane, octane, nonane, decane, cyclohexane, hexene, heptene, cyclohexene, toluene, xylene, decalin, 1,2,3,4-tetrahydronaphthalene, mesitylene, methoxybenzene, etc.

[0150] The above solvents can be used alone or in combination of two or more. In addition, the water content of the solvent is preferably low. The water content is preferably 50 mass ppm or less, more preferably 30 mass ppm or less, still more preferably 10 mass ppm or less, and the closer to 0 mass ppm, the more preferred. When using a sulfide-based solid electrolyte, a low water content is particularly preferred.

[0151] As a method for coating the slurry or solution of the solid electrolyte, for example, generally known methods such as a doctor blade coating method, a dip coating method, spin coating, comma coating, gravure coating, a spray coating method, a rod coater coating method, etc. can be used.

[0152] When producing a solid electrolyte layer by a known wet coating method, for the purpose of adjusting viscosity, etc., known thickeners can also be added, such as cellulose compounds such as carboxymethyl cellulose, methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, etc.; ammonium salts or alkali metal salts of the above cellulose compounds; polyvinyl alcohol-based polymers or copolymers thereof such as polyvinyl alcohol, modified polyvinyl alcohol, ethylene-vinyl alcohol copolymer; saponification products of copolymers of unsaturated carboxylic acids such as (meth)acrylic acid, maleic acid, or fumaric acid and vinyl esters; etc.

[0153] After coating the slurry or solution of the solid electrolyte, it is dried to remove the solvent, thereby obtaining a solid electrolyte layer. As the drying temperature, for example, 30 to 300 °C is preferred, 60 to 250 °C is more preferred, and 70 to 200 °C is particularly preferred. Drying can also be carried out in a vacuum or under reduced pressure. By heating within this temperature range, it is easy to suppress the deterioration of the solid electrolyte and the support.

[0154] [Positive electrode]

[0155] The positive electrode functions as the positive electrode of a solid secondary battery and can be a known one. The preferred positive electrode contains a positive electrode active material and a solid electrolyte, and may also contain a conductive assistant, a binder, and additives similar to those that can be contained in the solid electrolyte layer as the case may be.

[0156] When the positive electrode contains a material that can electrochemically absorb and release ions as the positive electrode active material, there is a tendency to obtain a high voltage and a high energy density, so it is preferred. As such materials, for example, Li-containing compounds represented by the following general formulas (2a) and (2b), and other Li-containing compounds can be cited:

[0157] Li x MO 2 (2a)

[0158] Li Y M 2 O 4 (2b)

[0159] {In the formula, each M is independently one or more metals selected from transition metals, x is a number from 0 to 1.3, and Y is a number from 0 to 2.}.

[0160] As the Li-containing compounds represented by the above general formulas (2a) and (2b), for example, there can be mentioned: lithium cobalt oxides represented by LiCoO 2 ; lithium manganese oxides represented by LiMnO 2 , LiMn 2 O 4 and Li 2 Mn 2 O 4 ; lithium nickel oxides represented by LiNiO 2 ; lithium-containing complex metal oxides represented by Li z MO 2 (In the formula, M is one or more elements selected from the group consisting of Ni, Mn, Co, Al, and Mg, and z is a number greater than 0.9 and less than 1.2). According to need, other metal elements can be further added to M.

[0161] As other Li-containing compounds, as long as they contain Li, examples of such other Li-containing compounds include: composite oxides containing Li and transition metal elements, metal chalcogenides having Li, phosphoric compounds containing Li and transition metal elements, and metal silicate compounds containing Li and transition metal elements (e.g., Li t M u SiO 4 , where M has the same meaning as in the above formula (2a), t is a number from 0 to 1, and u is a number from 0 to 2). From the viewpoint of obtaining a higher voltage, as other Li-containing compounds, composite oxides containing Li and one or more transition metal elements selected from the group consisting of cobalt (Co), nickel (Ni), manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), chromium (Cr), vanadium (V), and titanium (Ti), and phosphoric compounds are particularly preferred.

[0162] As other Li compounds, more specifically, composite oxides containing Li and transition metal elements or metal chalcogenides containing Li and transition metal elements, and metal phosphates having Li are more preferably used, and composite oxides containing Li and transition metal elements and metal phosphates having Li are further preferably used. Compounds represented by the following general formulas (3a) and (3b) can be cited as examples:

[0163] Li v M I O 2 (3a)

[0164] Li w M II PO 4 (3b)

[0165] {In the formula, M I and M II are each one or more transition metal elements, and the values of v and w vary depending on the charge and discharge state of the battery. v is a number from 0.05 to 1.10, and w is a number from 0.01 to 1.10.}.

[0166] The compound represented by the above general formula (3a) has a layered structure, and the compound represented by the above general formula (3b) has an olivine structure. From the viewpoint of stabilizing the structure, etc., these compounds can be: those in which a part of the transition metal element is replaced by Al, Mg or other transition metal elements; those in which these metal elements are included in the grain boundaries; those in which a part of the oxygen atoms is replaced by fluorine atoms, etc.; those in which at least a part of the surface of the positive electrode active material is covered with other positive electrode active materials.

[0167] As the positive electrode active material, only the Li-containing compound as described above can be used, or other positive electrode active materials can be used in combination with the Li-containing compound.

[0168] As such other positive electrode active materials, for example, metal oxides or metal chalcogenides having a tunnel structure and a layered structure; sulfur; conductive polymers, etc. can be cited. As metal oxides or metal chalcogenides having a tunnel structure and a layered structure, for example, MnO 2 、FeO 2 、FeS 2 、V 2 O 5 、V 6 O 13 、TiO 2 、TiS 2 、MoS 2 and NbSe 2Oxides, sulfides, selenides, etc. of metals other than lithium represented thereby. As the conductive polymer, for example, conductive polymers represented by polyaniline, polythiophene, polyacetylene, and polypyrrole are exemplified.

[0169] As the positive electrode active material in the present embodiment, those obtained by arbitrarily coating the surface of the above positive electrode active material can be used. As the material to be coated, an ion conductive material containing Li, Nb, P, and O can be cited, but it is not limited thereto. The positive electrode active material can be used alone or in combination of two or more.

[0170] The mass ratio of the positive electrode active material in the positive electrode composite material layer is preferably 60% by mass or more, more preferably 70% by mass or more, and further preferably 80% by mass or more. The average particle diameter (primary particle diameter) of the positive electrode active material is preferably 0.05 to 100 μm, more preferably 1 to 20 μm, and further preferably 2 to 15 μm. The average particle diameter of the positive electrode active material can be measured by an existing particle diameter measuring device (for example, a laser diffraction / scattering type particle size distribution meter, a dynamic light scattering type particle size distribution meter, etc.).

[0171] As the solid electrolyte, the same substances as those used in the solid electrolyte layer described above can be cited, and they can be the same as those possessed by the solid electrolyte layer. As the mass ratio of the solid electrolyte, it is preferably 8 to 40% by mass, more preferably 12 to 35% by mass, and further preferably 15 to 30% by mass.

[0172] As the conductive aid, for example, carbon blacks represented by graphite, acetylene black, and Ketjen black, activated carbon, various cokes, and carbon fibers such as carbon nanotubes can be cited. It can also be metal powders such as aluminum, titanium, and stainless steel. The number average particle diameter (primary particle diameter) of the conductive aid is preferably 10 nm to 10 μm, more preferably 20 nm to 1 μm. The number average particle diameter of the conductive aid is measured in the same manner as the number average particle diameter of the positive electrode active material. As the mass ratio of the conductive aid, it is preferably 0.5 to 10% by mass, more preferably 0.8 to 6% by mass, and further preferably 1.1 to 4% by mass.

[0173] As the binder, the same substances as those optionally contained in the above solid electrolyte layer can be cited, and they can be the same as those possessed by the solid electrolyte layer. As the mass ratio of the binder, it is preferably 0 to 4% by mass, more preferably 0.3 to 3% by mass, and further preferably 0.6 to 2% by mass.

[0174] The positive electrode is obtained, for example, as follows. That is, first, for a specified amount of positive electrode active material and solid electrolyte, a conductive assistant, a binder, an additive, etc. are added as needed and mixed to obtain a positive electrode composite material. The obtained positive electrode composite material is dispersed in a solvent to prepare a slurry containing the positive electrode composite material. As the solvent, a conventionally well-known solvent can be used without particular limitation, and a solvent exemplified when wet-producing the aforementioned solid electrolyte layer can be suitably used. Then, the slurry containing the positive electrode composite material is coated on a positive electrode current collector and dried to form a positive electrode composite material layer.

[0175] The positive electrode current collector is composed of, for example, a metal foil such as an aluminum foil, a nickel foil, a titanium foil, a stainless steel foil, or a sheet made of a resin containing a conductive material and having conductivity. The surface of the positive electrode current collector can be subjected to carbon coating and can be processed into a mesh shape or a foam shape. The thickness of the positive electrode current collector is preferably 5 to 35 μm, more preferably 7 to 30 μm, and further preferably 9 to 25 μm.

[0176] The positive electrode can be manufactured, for example, by coating the aforementioned slurry containing the positive electrode composite material on the aforementioned current collector and drying. The manufacture, coating, and drying of the slurry can be carried out by conventionally well-known methods.

[0177] As a method for manufacturing the slurry, for example, a rotation revolution mixer, a planetary mixer, a bead mill, a film rotation type mixer, etc. can be cited. As a method for coating the slurry, for example, a doctor blade coating method, an immersion coating method, spin coating, comma coating, gravure coating, a spray coating method, a rod coater coating method, etc., which are commonly well-known methods, can be used.

[0178] By compressing the positive electrode composite material layer obtained after drying as needed by roll pressing or the like, a positive electrode having a positive electrode composite material layer formed on the positive electrode current collector is obtained. The thickness of the compressed positive electrode composite material is preferably 10 to 400 μm, more preferably 20 to 350 μm, and further preferably 30 to 300 μm.

[0179] [Negative Electrode]

[0180] The negative electrode only needs to electrochemically absorb and release ions as the negative electrode of a solid secondary battery and can be a well-known negative electrode. A preferred negative electrode contains a negative electrode active material and a solid electrolyte, and may also contain a conductive assistant, a binder, and the same additives as those that can be contained in the solid electrolyte layer according to circumstances.

[0181] The negative electrode preferably contains one or more materials selected from the group consisting of materials capable of absorbing and releasing Li ions and metallic Li as the negative electrode active material. Examples of such materials include: metallic Li, amorphous carbon (hard carbon), artificial graphite, natural graphite, pyrolytic carbon, coke, vitreous carbon, fired bodies of organic high molecular compounds, mesophase carbon microbeads, carbon fibers, activated carbon, graphite, colloidal carbon, and carbon materials represented by carbon black; materials containing elements capable of forming alloys with Li, etc. Examples of the above-mentioned coke include: pitch coke, needle coke, and petroleum coke. The fired body of an organic high molecular compound is obtained by firing and carbonizing a high molecular material such as phenolic resin or furan resin at an appropriate temperature. In the carbon material, in addition to carbon, it may also contain foreign elements or foreign compounds such as O, B, P, N, S, Si, SiC, SiO 2 , B 4 C and other foreign elements or foreign compounds. The content of the foreign elements or foreign compounds is preferably 0 to 10% by mass.

[0182] As the above-mentioned material containing elements capable of forming alloys with Li, it can be a single substance, alloy or compound of a metal or semi-metal, and can have one or two or more phases in at least a part thereof.

[0183] In this specification, in the "alloy", in addition to those formed by two or more metal elements, it also includes those having one or more metal elements and one or more semi-metal elements. In addition, as long as the alloy has the properties of a metal as a whole, it may also contain non-metal elements. A solid solution, eutectic (eutectic mixture), or intermetallic compound, or two or more of these can coexist in the structure of the alloy.

[0184] Examples of the metal elements and semi-metal elements capable of forming alloys with Li include: titanium (Ti), tin (Sn), lead (Pb), aluminum (Al), indium (In), silicon (Si), zinc (Zn), antimony (Sb), bismuth (Bi), gallium (Ga), germanium (Ge), arsenic (As), silver (Ag), hafnium (Hf), zirconium (Zr), and yttrium (Y). Among these, metal elements and semi-metal elements in Group 4 or Group 14 of the long-period type periodic table are preferred. Particularly preferred are titanium, silicon, or tin, which have a large ability to absorb and release Li and can obtain a high energy density.

[0185] Examples of the alloy of tin include those having one or more elements selected from the group consisting of silicon, magnesium (Mg), nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium (Ti), germanium, bismuth, antimony, and chromium (Cr) as the second constituent element other than tin.

[0186] As an alloy of silicon, for example, one or more elements selected from the group consisting of magnesium, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, and chromium can be cited as the second constituent element other than silicon.

[0187] As a compound of titanium, a compound of tin, and a compound of silicon, for example, those having oxygen (O) or carbon (C) can be cited. In this case, in addition to titanium, tin, or silicon, the above-described second constituent element may also be included.

[0188] The negative electrode may also contain a metal compound capable of occluding and releasing Li ions in the range of 0.4 to 3 V vs. Li / Li + as a negative electrode active material. As such a metal compound, for example, metal oxides, metal sulfides, and metal nitrides can be cited.

[0189] As metal oxides, for example, titanium oxides, lithium titanium oxides (lithium-titanium composite oxides), tungsten oxides (e.g., WO 3 ), amorphous tin oxides (e.g., SnB 0.4 P 0.6 O 3.1 ), tin silicon oxides (e.g., SnSiO 3 ), and silicon oxide (SiO) can be cited. Among these, titanium oxides and lithium titanium oxides are preferred.

[0190] As lithium titanium oxides, for example, lithium titanate having a spinel structure {e.g., Li 4 +aTi 5 O 12 (wherein a can vary in the range of -1 ≤ a ≤ 3 according to the charge-discharge reaction)}, lithium titanate having an orthorhombic manganese structure {e.g., Li 2 +bTi 3 O 7 (wherein b can vary in the range of -1 ≤ b ≤ 3 according to the charge-discharge reaction)}, etc. can be cited.

[0191] As titanium oxides, those containing Li before charge-discharge or not containing Li can be used. As titanium oxides not containing Li before charge-discharge (during synthesis), for example, titanium oxide (e.g., TiO 2 , H 2 Ti 12 O 25 ), titanium composite oxides containing Ti and at least one element selected from the group consisting of P, V, Sn, Cu, Ni, and Fe, etc. can be cited. As TiO 2 , anatase-type and low-crystalline ones with a heat treatment temperature of 300 to 500 °C are preferred. As titanium composite oxides, for example, TiO 2 -P 2 O5 and TiO 2 -V 2 O 5 and TiO 2 -P 2 O 5 -SnO 2 and TiO 2 -P 2 O 5 -MeO (wherein Me is at least one element selected from the group consisting of Cu, Ni, and Fe). The titanium composite oxide preferably has a microstructure with low crystallinity, coexistence of a crystalline phase and an amorphous phase, or an amorphous phase alone. By having such a microstructure, the cycle performance of the solid secondary battery can be significantly improved.

[0192] As the titanium oxide containing Li before charge-discharge (during synthesis), for example, Li c TiO 2 (where 0 < c ≤ 1.1) etc.

[0193] As the metal sulfide, for example, titanium sulfide (such as TiS 2 ), molybdenum sulfide (such as MoS 2 ), and iron sulfide (such as FeS, FeS 2 , Li g FeS 2 (where g is 0 ≤ g ≤ 1)). As the metal nitride, for example, lithium cobalt nitride (such as Li d Co e N, 0 < d < 4, 0 < e < 0.5).

[0194] For the solid secondary battery in this embodiment, from the viewpoint of increasing the battery voltage, the negative electrode preferably contains a material that stores lithium ions at a potential lower than 0.4V vs. Li / Li + as the negative electrode active material. As such a material, for example, in addition to amorphous carbon (hard carbon), artificial graphite, natural graphite, graphite, pyrolytic carbon, coke, vitreous carbon, fired bodies of organic high molecular compounds, mesophase carbon microbeads, carbon fibers, activated carbon, graphite, colloidal carbon, and carbon materials represented by carbon black, metal lithium, metal oxides, metal nitrides, lithium alloys, tin alloys, silicon alloys, intermetallic compounds, organic compounds, inorganic compounds, metal complexes, organic high molecular compounds, etc. can also be cited.

[0195] The negative electrode active material can be used alone or in combination of two or more. The mass ratio of the negative electrode active material in the negative electrode composite layer is preferably 50% by mass or more, more preferably 60% by mass or more, and further preferably 65% by mass or more.

[0196] The number average particle diameter (primary particle diameter) of the negative electrode active material is preferably 0.1 to 30 μm, more preferably 1 to 20 μm. The number average particle diameter of the negative electrode active material is measured in the same manner as that of the positive electrode active material. As the solid electrolyte, conductive assistant, binder, and additive that can be contained in the negative electrode, the same substances as those that can be used in the aforementioned positive electrode composite material layer can be used.

[0197] As the mass ratio of the solid electrolyte, it is preferably 10 to 50% by mass, more preferably 15 to 40% by mass, and further preferably 20 to 35% by mass. As the mass ratio of the conductive assistant, it is preferably 0 to 10% by mass, more preferably 0.5 to 6% by mass, and further preferably 1 to 4% by mass. As the mass ratio of the binder, it is preferably 0 to 5% by mass, more preferably 0.5 to 4% by mass, and further preferably 1 to 3% by mass.

[0198] The negative electrode is obtained, for example, as follows. That is, first, for a specified amount of the above-mentioned negative electrode active material and solid electrolyte, a conductive assistant, binder, additive, etc. are added as needed and mixed to obtain a negative electrode composite material. The obtained negative electrode composite material is dispersed in a solvent to prepare a slurry containing the negative electrode composite material. As the solvent, there is no particular limitation, and conventionally well-known solvents can be used, and the solvents exemplified when forming the aforementioned solid electrolyte layer by a wet method can be suitably used. Next, the slurry containing the negative electrode composite material is coated on a negative electrode current collector and dried to form a negative electrode composite material layer.

[0199] As the negative electrode current collector, it is composed of, for example, a metal foil such as a copper foil, nickel foil, or stainless steel foil. The negative electrode current collector can be in a form in which carbon coating is applied to its surface or in a form processed into a mesh. The thickness of the negative electrode current collector is preferably 5 to 40 μm, more preferably 6 to 35 μm, and further preferably 7 to 30 μm.

[0200] As the coating method of the slurry, for example, generally well-known methods such as a doctor blade coating method, dip coating method, spin coating, comma coating, gravure coating, spray coating method, and bar coater coating method can be used.

[0201] If necessary, the negative electrode composite material layer obtained after drying is compressed by roll pressing or the like to obtain a negative electrode having a negative electrode composite material layer formed on the negative electrode current collector. The thickness of the compressed negative electrode composite material layer is preferably 10 to 300 μm, more preferably 20 to 280 μm, and further preferably 30 to 250 μm.

[0202] [Exterior of the solid secondary battery]

[0203] The configuration of the exterior of the solid secondary battery is not particularly limited. For example, any battery exterior such as a battery can or a laminated film exterior body can be used. As the battery can, for example, a metal can formed of steel or aluminum can be used. As the laminated film exterior body, for example, the following can be used: two laminated films each formed of a three-layer structure of a heat-melt resin / metal film / resin are overlapped with the heat-melt resin side facing inward, and the ends are sealed by heat sealing.

[0204] In the case of using the laminated film exterior body, a positive terminal (or a lead plate connected to the positive terminal) and a negative terminal (or a lead plate connected to the negative terminal) can be respectively connected to the positive electrode current collector and the negative electrode current collector, and the laminated film exterior body can be sealed in a state where the ends of the two terminals (or lead plates) are led out to the outside of the exterior body.

[0205] [Method for manufacturing a solid secondary battery]

[0206] Figure 3 FIG. is a diagram schematically showing a manufacturing example of the solid electrolyte laminate 4 of the present embodiment. One aspect of the present invention is the manufacturing method of the above-mentioned solid secondary battery, and includes the following steps:

[0207] Step (1), a second B electrolyte layer 2B without a support is provided on either the positive electrode composite layer or the negative electrode composite layer (denoted by the symbol "11" in the figure).

[0208] Step (2), a first electrolyte layer 1 with a support is formed, and then a second A electrolyte layer 2A and a third electrolyte layer 3 without a support are provided in a manner of sandwiching the first electrolyte layer 1 {wherein the film thickness (T2A) of the second A electrolyte layer is substantially equal to the film thickness (T3) of the third electrolyte layer}, to obtain a laminate precursor; and

[0209] Step (3), the positive electrode composite layer, the laminate precursor 4, and the negative electrode composite layer are laminated in such a manner that the second A electrolyte layer 2A and the second B electrolyte layer 2B face each other, so that the total film thickness (T2; T2A + T2B) of the second A electrolyte layer 2A and the second B electrolyte layer 2B is 1.5 to 5 times the film thickness (T3) of the third electrolyte layer 3.

[0210] Thus, the above-mentioned secondary battery can be suitably manufactured.

[0211] In the above manufacturing method, in step (3), the second B electrolyte layer manufactured in step (1) and the second A electrolyte layer manufactured in step (2) are laminated to obtain the second electrolyte layer ( Figure 1The second electrolyte layer 2) shown. It should be noted that "substantially equivalent" in step (2) means that the ratio (T2A / T3) of the film thickness (T2A) of the second A electrolyte layer to the film thickness (T3) of the third electrolyte layer is 0.85 or more or 0.95 or more, and 1.15 or less or 1.05 or less.

[0212] The solid secondary battery of the present embodiment has at least the solid electrolyte laminate of the present embodiment between the above-mentioned positive electrode and the above-mentioned negative electrode. And, for the solid electrolyte layer without a support located on a single surface side of the solid electrolyte laminate and having a relatively thick film thickness, in the case of suppressing a short circuit accompanied by the precipitation of lithium metal, it is preferably used in combination with the negative electrode composite material layer, and in the case of suppressing a decrease in battery capacity accompanied by local deterioration of the positive electrode active material, it is preferably used in combination with the positive electrode composite material layer.

[0213] It is possible to laminate and bond in the same manner a positive electrode or a negative electrode provided with a solid electrolyte layer without a support to either the positive electrode composite material layer or the negative electrode composite material layer, and a solid electrolyte laminate, that is, a solid electrolyte sheet, having a self-supporting strength and having the same thickness as the solid electrolyte layer without a support within a range where warping of the solid electrolyte laminate does not pose a problem. As a method for the above bonding, for example, there can be mentioned: a method of laminating the above positive electrode, the above solid electrolyte sheet, and the above negative electrode, and then pressurizing with a roll, a flat plate, cold isostatic pressing, or hot isostatic pressing as needed after including a laminate film exterior body or the like.

[0214] Next, the above laminate is housed in a battery case (battery exterior) and sealed, whereby the solid secondary battery of the present embodiment can be manufactured. The shape of the solid secondary battery of the present embodiment is not particularly limited, and for example, a cylindrical shape, an elliptical shape, a square tube shape, a button shape, a coin shape, a flat shape, a laminated shape, etc. are suitable.

[0215] The solid secondary battery of the present embodiment can function as a battery through primary charging. There is no particular limitation on the method of primary charging in the present embodiment. The primary charging is preferably performed at 0.01 to 1 C, more preferably at 0.05 to 0.5 C, and further preferably at 0.1 to 0.2 C. It should be noted that 1 C means a current that can discharge the rated capacity (equivalent to the fully charged capacity) of a determined battery within 1 hour. The above primary charging can be performed multiple times.

[0216] The solid secondary battery of the present embodiment can also be used as a battery pack in which a plurality of batteries are connected in series or in parallel. From the viewpoint of suppressing the deterioration of the active material and the solid electrolyte and managing the charge and discharge state of the battery pack, the use voltage range for each one is preferably 2.25 to 5 V, more preferably 2.5 to 4.75 V, and particularly preferably 2.75 V to 4.5 V.

[0217] Example

[0218] Hereinafter, examples are listed to illustrate the present invention. It should be noted that the following examples are Figure 3 an example of the embodiment shown. However, the present invention is not limited to these examples.

[0219] [Example 1]

[0220] [Production of laminate precursor]

[0221] As the sulfide-based solid electrolyte, a powder (average particle size 3 μm) of argyrodite-type sulfide solid electrolyte Li 7-x PS 6-x Cl x (wherein x≈1); and

[0222] a binder solution in which 5% by mass of a rubber-based resin is dissolved in 100% by mass of a low-polarity organic solvent that does not react with the sulfide-based solid electrolyte.

[0223] Then, weighing is carried out so that the mass ratio of the sulfide solid electrolyte to the rubber-based resin becomes 96.0:4.0. In order to adjust the viscosity, the above-mentioned low-polarity organic solvent is further added, and kneading is carried out in a rotary mixer, whereby a solid electrolyte slurry is obtained.

[0224] A poly(ethylene terephthalate) (PET) film with a thickness of about 38 μm and one side being demolded as the base material is placed on a tabletop coater with the demolded surface facing upward. Then, for the demolded surface, while setting a prescribed gap, the solid electrolyte slurry is coated with a spreader. Then, it is dried in a dryer at normal pressure for 1 hour at a temperature of 70 °C, whereby a sheet with a solid electrolyte layer laminated on the PET film is obtained. Next, the aforementioned sheet is placed on a tabletop coater with the solid electrolyte layer facing upward, and a glass fiber woven fabric (support: aggregate fiber width of about 84 μm, interval of aggregate fiber width of about 179 μm, thickness of about 18 μm, and aperture ratio of about 46%) is placed thereon. Next, while further setting a prescribed gap from the glass fiber woven fabric, the solid electrolyte slurry is coated with a spreader. Then, it is dried in a dryer at normal pressure for 1 hour at a temperature of 70 °C, and then depressurized and dried in a dryer for 20 hours at a temperature of 70 °C. Thus, a laminate precursor (Example 1) in which a solid electrolyte layer, a solid electrolyte layer containing a glass fiber woven fabric, and a solid electrolyte layer are sequentially laminated on a PET film is obtained.

[0225] [Production of solid electrolyte sheet]

[0226] Note that at a pressure of 392 MPa, the obtained laminate precursor is pressed onto a PET film, whereby the PET film is peeled off from the laminate. Thus, a solid electrolyte sheet with self-supporting strength and no observable warpage is obtained.

[0227] [Fabrication of the positive electrode]

[0228] Prepare a powder (average particle size: 5 μm) of LiNi in which a composite oxide of Li and Nb is formed on the surface as a positive electrode active material; 0.5 Co 0.2 Mn 0.3 O 2 ;

[0229] A powder (average particle size: 0.6 μm) of a lithium superionic conductor Li 7-x PS 6-x Cl x (where x ≈ 1);

[0230] Carbon fibers (Resonac Holdings Corporation's "VGCF" (trade name)) as a conductive additive; and

[0231] A binder solution in which 5% by mass of a rubber-based resin is dissolved in 100% by mass of a low-polarity organic solvent that does not react with the sulfide-based solid electrolyte.

[0232] Then, weigh them so that the mass ratio of the positive electrode active material, the sulfide solid electrolyte, the carbon fibers, and the rubber-based resin becomes 82.7:15.3:1.2:0.8. To adjust the viscosity, further add the above-mentioned low-polarity organic solvent and knead in a planetary mixer to obtain a positive electrode paste.

[0233] Place an aluminum foil with a thickness of 20 μm on a tabletop coater, set a specified gap, and coat the positive electrode paste with a spreader. Then, dry it in a dryer at 100 °C for 1 hour under normal pressure and then at 100 °C for 20 hours under reduced pressure to obtain the positive electrode.

[0234] [Fabrication of the negative electrode]

[0235] Prepare natural graphite powder (average particle size: 16 μm) as a negative electrode active material;

[0236] A powder (average particle size: 0.6 μm) of a lithium superionic conductor Li 7-x PS 6-x Cl x (where x ≈ 1); and

[0237] A binder solution in which 5% by mass of a rubber-based resin is dissolved in 100% by mass of a low-polarity organic solvent that does not react with the sulfide-based solid electrolyte.

[0238] Then, the negative electrode active material, the sulfide solid electrolyte, and the rubber-based resin are weighed so that the weight ratio becomes 67.5:30.5:2. To adjust the viscosity, the above low-polarity organic solvent is further added, and kneading is performed in a rotation-revolution mixer, whereby a negative electrode paste is obtained.

[0239] A stainless steel foil with a total thickness of 10 μm and carbon coated on its surface is placed on a tabletop coater. Then, for the carbon-coated surface, while setting a prescribed gap, the negative electrode paste is coated with a spreader. Then, it is dried in a dryer at a temperature of 100°C for 1 hour under normal pressure, and then dried in a dryer at a temperature of 100°C for 20 hours under reduced pressure, whereby a negative electrode is obtained.

[0240] [Fabrication of the solid electrolyte layer applied to the negative electrode composite layer]

[0241] A stainless steel foil with a total thickness of 10 μm and carbon coated on its surface is placed on a tabletop coater. Then, for the carbon-coated surface, while setting a prescribed gap, the same solid electrolyte paste as that used by the user in the fabrication of the solid electrolyte sheet is coated with a spreader. Then, it is dried in a dryer at a temperature of 70°C for 1 hour under normal pressure, whereby a sheet having a solid electrolyte layer laminated on the stainless steel foil is obtained.

[0242] The negative electrode is placed on the workpiece under roll pressing with the negative electrode composite layer facing upward, and the above stainless steel foil is placed thereon in such a manner that the negative electrode composite layer is in contact with the solid electrolyte layer, and roll pressing is performed, whereby the solid electrolyte layer is transferred to the negative electrode composite layer. Thus, a negative electrode formed of a negative electrode current collector foil - negative electrode composite layer - solid electrolyte layer is obtained.

[0243] [Fabrication of the solid secondary battery]

[0244] The above positive electrode, the above negative electrode, and the above solid electrolyte sheet are each blanked into a prescribed size. Then, they are overlapped in the order of the positive electrode composite layer, the solid electrolyte sheet, and the negative electrode composite layer, whereby a laminate is obtained. The obtained laminate is covered with a stainless steel foil, and its outer side is further covered with an aluminum laminated film, and then vacuum-sealed, whereby the laminate is placed in a packaging material. For the laminate placed in the packaging material, densification of the laminate and pressurization of the bonding surface are performed by a method based on hot isostatic pressing.

[0245] After taking out the pressurized laminate from the packaging material, the lead plates are ultrasonically welded to the positive electrode and the negative electrode, respectively. Next, the laminate with the lead plates installed is covered with an aluminum laminate, and then depressurized and sealed, whereby a solid secondary battery is produced.

[0246] [Structure of the solid electrolyte laminate]

[0247] After cutting the obtained solid secondary battery with a sharp razor blade, in a non-atmosphere-exposed environment, using a cross-section polishing machine with an argon ion beam, the cross-section is smoothed, and this cross-section is observed with an SEM. The film thicknesses of the respective layers in the solid electrolyte laminate are as follows: the layer on the side in contact with the positive electrode composite layer (the layer without a support) is 10 μm, the layer with a support having a glass fabric is 10 μm, and the layer on the side in contact with the negative electrode composite layer (the layer without a support) is 35 μm.

[0248] [Charge and discharge evaluation of the solid secondary battery]

[0249] The produced solid secondary battery is constrained with a stainless steel constraint jig in such a manner that the constraint pressure applied to the battery cell becomes 0.15 tons / cm 2 . Charge and discharge evaluation is carried out in this state.

[0250] (Initial charge and discharge)

[0251] In this project of "initial charge and discharge", based on the reference capacity of 204 mAh / g at 4.35 V of the positive electrode active material, 1C current is determined. It should be noted that "1.0C" as the current value of 1C is the current value of the amount of electricity that a fully charged battery can discharge in 1 hour.

[0252] Constant temperature: In a constant temperature bath at 25 °C, using a charge and discharge device (manufactured by Toyo System.Co., Ltd., product name: TOSCAT-3000), after a constant current of 0.1C, charging is carried out at a constant voltage of 4.35 V until the termination current becomes 0.01C. After that, after a constant current of 0.1C, discharging is carried out at a constant voltage of 3.0 V until the termination current becomes 0.01C (charge and discharge of the first cycle). The charge and discharge of the second cycle and the third cycle are carried out under the same conditions as the first cycle.

[0253] (Charge load characteristic evaluation)

[0254] In this project of "charge load characteristic evaluation", in the 0.1C constant current discharge of the third cycle of the above initial charge and discharge, the discharge capacity from full charge until it becomes 3.0 V is determined as the rated capacity of this battery, and based on this, 1C current is determined. It should be noted that the 1C current in this charge load characteristic evaluation is expressed as a current density of approximately 2.9 mA / cm2 。

[0255] After the initial charge and discharge, in the same thermostat at 25 °C, using the same charge and discharge device, after discharging at a constant current of 0.1 C, charging is carried out at a constant voltage of 4.35 V until the termination current becomes 0.01 C. Then, after discharging at a constant current of 0.1 C, discharging is carried out at a constant voltage of 3.0 V until the termination current becomes 0.01 C. The charge-discharge efficiency (%) at this time = [(discharge capacity) / (charge capacity)] × 100 becomes 99.8%.

[0256] After that, charging is carried out at a constant current of 1 C until the termination voltage becomes 4.35 V, then after discharging at a constant current of 0.1 C, discharging is carried out at a constant voltage of 3.0 V until the termination current becomes 0.01 C (charge-discharge condition A). The charge-discharge efficiency at this time becomes 100.0%.

[0257] After that, the charging current values are made 2 C, 3 C, 4 C, 5 C, 6 C, and except for this, the charge and discharge are repeatedly carried out in the same manner as the charge-discharge condition A. The charge-discharge efficiencies at each charging current value are shown in Table 1. It should be noted that when the charge-discharge efficiency at each charging current becomes lower than 95%, or when a voltage drop of 40 mV or more occurs during charging, it is determined that the battery has short-circuited. The results of the charge-discharge evaluation are shown in Table 1. Results with a charge-discharge efficiency of 95% or more up to 5 C of about 14.4 mA / cm 2 are obtained, and it can be seen that high short-circuit resistance is also exhibited at high current densities.

[0258] [Example 2]

[0259] As the support, a non-woven fabric formed of PET resin (support: average fiber diameter of about 7 μm, thickness of about 22 μm, and basis weight of 5 g / m 2 ) is used instead of glass woven fabric, and except for this, a solid secondary battery is fabricated in the same manner as in Example 1.

[0260] The film thicknesses of the respective layers in the solid electrolyte laminate are as follows: the layer on the side in contact with the positive electrode composite layer (the layer without a support) is 9 μm, the layer with the PET non-woven fabric support is 27 μm, and the layer on the side in contact with the negative electrode composite layer (the layer without a support) is 25 μm.

[0261] The results of the charge-discharge evaluation carried out in the same manner as in Example 1 are shown in the same Table 1. Results with a charge-discharge efficiency of 95% or more up to 5 C of about 14.4 mA / cm 2 are obtained, and it can be seen that high short-circuit resistance is also exhibited at high current densities.

[0262] [Comparative Example 1]

[0263] A solid secondary battery was fabricated in the same manner as in Example 1, except that the solid electrolyte layer was not provided on the negative composite material layer.

[0264] The film thicknesses of the respective layers in the solid electrolyte laminate were as follows: the layer on the side in contact with the positive composite material layer (the layer without a support) was 10 μm, the layer with a support of glass woven fabric was 11 μm, and the layer on the side in contact with the negative composite material layer (the layer without a support) was 11 μm.

[0265] The results of charge-discharge evaluation performed in the same manner as in Example 1 are also shown in Table 1. As a result, a sharp voltage drop occurred during 3C charging, resulting in a short circuit. After the short circuit, the voltage did not increase, and it was difficult to perform charging beyond that. From the above, it can be seen that in Comparative Example 1, short circuits are likely to occur when the current density is gradually increased.

[0266] [Comparative Example 2]

[0267] A solid secondary battery was fabricated in the same manner as in Example 2, except that the solid electrolyte layer was not provided on the negative composite material layer.

[0268] The film thicknesses of the respective layers in the solid electrolyte laminate were as follows: the layer on the side in contact with the positive composite material layer (the layer without a support) was 7 μm, the layer with a support of PET nonwoven fabric was 27 μm, and the layer on the side in contact with the negative composite material layer (the layer without a support) was 9 μm.

[0269] The results of charge-discharge evaluation performed in the same manner as in Example 1 are also shown in Table 1. As a result, the charge-discharge efficiency became lower than 95% during 3C charging, and a sharp voltage drop occurred during 5C charging and subsequent charging, resulting in a short circuit. After the short circuit, the voltage did not increase, and it was difficult to perform charging beyond that. From this, it can be seen that in Comparative Example 2, short circuits are likely to occur when the current density is gradually increased.

[0270] [Comparative Example 3]

[0271] A solid secondary battery was fabricated in the same manner as in Example 1, except that the solid electrolyte layer provided on the negative composite material layer was thickened. However, warping occurred in the negative electrode with the thicker solid electrolyte layer. Due to this warping, wrinkles were generated on the surface of the packaging material when the laminate was placed in the packaging material and pressed.

[0272] The film thicknesses of the respective layers in the solid electrolyte laminate were as follows: the layer on the side in contact with the positive composite material layer (the layer without a support) was 9 μm, the layer with a support of glass woven fabric was 11 μm, and the layer on the side in contact with the negative composite material layer (the layer without a support) was 52 μm.

[0273] The charge-discharge evaluation was carried out in the same manner as in Example 1. However, just after the start of the initial charge-discharge, a voltage drop occurred, the voltage did not rise, and it was difficult to perform charging beyond that. From this, it can be seen that in Comparative Example 3, the battery does not function easily.

[0274] It should be noted that in the method of giving the solid electrolyte layer thickness to the negative composite material layer as in Comparative Example 3, it was also confirmed that short circuits occurred frequently in the extremely initial stage of the initial charge-discharge at a low current density. In this method, many ruptures were confirmed in the solid electrolyte layer, and it is speculated that this rupture is one of the reasons for the short circuit in the initial stage.

[0275] [Comparative Example 3A]

[0276] A solid secondary battery was fabricated in the same manner as in Example 1, except that no solid electrolyte layer was given to the negative composite material layer and the gap during applicator coating was changed.

[0277] The film thicknesses of the respective layers in the solid electrolyte laminate were as follows: the layer on the side in contact with the positive composite material layer (the layer without a support) was 20 μm, the layer with a support of glass cloth was 12 μm, and the layer on the side in contact with the negative composite material layer (the layer without a support) was 23 μm.

[0278] The charge-discharge evaluation was carried out in the same manner as in Example 1. The result of a short circuit occurring with a sharp voltage drop during 2C charging was obtained. After the short circuit, the voltage did not increase, and it was also difficult to perform charging beyond that. From the above, it can be seen that in Comparative Example 3A, short circuits are likely to occur when the current density is gradually increased.

[0279] [Example 3]

[0280] A solid secondary battery was fabricated in the same manner as in Example 1, except that a solid electrolyte layer was given to the positive composite material layer instead of the negative composite material layer.

[0281] The film thicknesses of the respective layers in the solid electrolyte laminate were as follows: the layer on the side in contact with the positive composite material layer (the layer without a support) was 34 μm, the layer with a support of glass cloth was 11 μm, and the layer on the side in contact with the negative composite material layer (the layer without a support) was 11 μm.

[0282] After the initial charge and discharge were completed, the temperature of the thermostat was changed to 60°C. Then, charging was performed at a constant current of 1C determined according to the same definition as that in the evaluation of the charge load characteristics in Example 1 until the termination voltage reached 4.35V, and then discharging was performed until the termination voltage reached 3.0V. This cycle was repeated 100 times. After that, the temperature of the thermostat was changed to 25°C, and after a constant current of 0.1C, charging was performed at a constant voltage of 4.35V until the termination current reached 0.01C. Then, after discharging at a constant current of 0.1C, discharging was performed at a constant voltage of 3.0V until the termination current reached 0.01C. Thus, the residual capacity retention rate per 100 cycles (charge-discharge condition B) when the aforementioned rated capacity was 100% was confirmed at 1C and 0.1C constant currents. The change in the residual capacity retention rate during charge and discharge at 1C constant current when charge-discharge condition B was repeated 3 times is shown in Table 2.

[0283] [Comparative Example 4]

[0284] A solid secondary battery was fabricated in the same manner as in Comparative Example 1, and charge-discharge condition B was repeated 3 times in the same manner as in Example 3. The change in the residual capacity retention rate at this time is shown in Table 2.

[0285] It should be noted that the "reference example" in Table 2 is a solid secondary battery with a solid electrolyte layer thickness of 26μm fabricated in the same manner as in Example 1 except that it does not have a support.

[0286] After the charge-discharge evaluation of the solid secondary battery was completed, it was cut with a sharp razor blade, and in a non-atmosphere-exposed environment, cross-section smoothing was performed using a cross-section polishing machine using an argon ion beam. After that, using a focused ion beam processing observation device (VERSA3D manufactured by FEI), thinning processing was performed at a stage temperature of -130°C. After that, using a scanning transmission electron microscope with a spherical aberration correction mechanism (JEM-ARM200F manufactured by JEOL Ltd.), the positive electrode active material at a position several μm from the positive electrode composite material layer side of the solid electrolyte layer was observed. For example, using the electron energy loss spectroscopy analysis device (GIF Quantum ER manufactured by Gatan Inc.) attached to the same device, the electronic state of the constituent elements in the cross-section of the solid battery and the crystal structure reflected thereby were observed.

[0287] Figure 2Schematically shows a configuration example of the above cross-section. As shown in the figure, in the solid electrolyte laminate 4, bundles 6 formed by bundling glass filaments 5 are dispersed in the plane direction. In the figure, openings 7 are shown between these bundles 6, and the width of the bundles 6 in the plane direction is shown as the width 8 of the collective fibers. The positive electrode composite layer 10 is in contact with the solid electrolyte laminate 4 in the plane direction. In the positive electrode composite layer 10, a plurality of positive electrode active materials 9 are schematically shown. The positive electrode active material 9 located directly below the bundle 6 in the thickness direction is denoted by the symbol 8A as the "positive electrode active material directly below the center of the width of the collective fibers", and the positive electrode active material 9 located directly below the opening 7 in the thickness direction is denoted by the symbol 7A as the "positive electrode active material directly below the center of the opening".

[0288] For the positive electrode active materials 7A and 8A directly below the center of the opening and directly below the center of the width of the collective fibers, the peak displacement amounts of the electron energy loss spectra of Ni, Mn, and Co were measured. Specifically, the measurement was performed from the outermost surface of the positive electrode active material 9 toward the inside, and the range from the surface where the peak displacement was confirmed (corresponding to the range where the active material deteriorated) was analyzed. For the ranges where the average peak displacement of Ni, Mn, and Co was confirmed, the case of the positive electrode active material without the charge-discharge process and the positive electrode active materials 7A and 8A directly below the center of the opening 7 and the center of the width 8 of the collective fibers are shown below. That is, the ranges where the above peak displacement was confirmed are as follows: 5.7 nm directly below the center of the opening 7 and 1.8 nm directly below the center of the width 8 of the collective fibers. In addition, in the case without the charge-discharge process, the ranges where the above peak displacement was confirmed were both 0.4 nm. It was confirmed that there was a significant difference in the ranges where the peak displacement was confirmed directly below the center of the opening and directly below the center of the width of the collective fibers. From this, it can be seen that the deterioration of the positive electrode active material in the opening further progresses. In other words, it is presumed to be the reason for the reduction of the remaining capacity.

[0289] [Table 1]

[0290]

[0291] [Table 2]

[0292]

[0293] From the above, it was confirmed that the solid electrolyte laminate and the solid secondary battery belonging to the examples are excellent in suppressing short circuits at high currents and the capacity deterioration is suppressed as compared with the comparative examples.

[0294] Industrial applicability

[0295] The solid secondary battery using the solid electrolyte laminate of the present invention can be used as a storage battery for electric vehicles, hybrid electric vehicles, electric two-wheelers, electric bicycles, stationary power storage systems, mobile communication devices, mobile electronic devices, etc.

[0296] This application is based on Japanese Patent Application No. 2022-176682 filed on November 2, 2022, the entire disclosure of which is incorporated herein by reference.

[0297] Explanation of reference numerals

[0298] 1: Solid electrolyte layer with a support (first electrolyte layer)

[0299] 2: Solid electrolyte layer without a support (second electrolyte layer)

[0300] 3: Solid electrolyte layer without a support (third electrolyte layer)

[0301] 4: Solid electrolyte laminate

[0302] 5: Glass monofilament

[0303] 6: Bundle formed by bundling glass monofilaments

[0304] 7: Opening

[0305] 7A: Positive electrode active material directly below the center of the opening

[0306] 8: Width of the collective fiber

[0307] 8A: Positive electrode active material directly below the center of the width of the collective fiber

[0308] 9: Positive electrode active material

[0309] 10: Positive electrode composite layer

[0310] 11: Positive electrode composite layer or negative electrode composite layer

[0311] T2: Film thickness of the solid electrolyte layer without a support (second electrolyte layer)

[0312] T3: Film thickness of the solid electrolyte layer without a support (third electrolyte layer)

Claims

1. A solid electrolyte laminate in which three or more electrolyte layers containing a solid electrolyte are laminated, the solid electrolyte laminate comprising: a first electrolyte layer having a support; and a second electrolyte layer and a third electrolyte layer that are disposed sandwiching the first electrolyte layer and do not have a support, wherein a film thickness (T2) of the second electrolyte layer is 1.5 to 5 times that of the film thickness (T3) of the third electrolyte layer.

2. The solid electrolyte laminate according to claim 1, wherein the support includes a woven fabric.

3. The solid electrolyte laminate according to claim 2, wherein the film thickness (T2) of the second electrolyte layer is 0.2 to 2 times that of the aggregate fiber width of the woven fabric.

4. The solid electrolyte laminate according to claim 1, wherein the support includes at least one of a non-woven fabric and short fibers.

5. The solid electrolyte laminate according to claim 4, wherein the support includes a non-woven fabric, and the film thickness (T2) of the second electrolyte layer is 3 to 20 times that of the average diameter of the fibers constituting the support.

6. A solid secondary battery comprising: a positive electrode, a negative electrode, and the solid electrolyte laminate according to any one of claims 1 to 5, wherein the second electrolyte layer is in contact with the positive electrode or the negative electrode.

7. A method for manufacturing a solid secondary battery, the manufacturing method including the following steps: Step (1), providing a second B electrolyte layer without a support on either a positive electrode composite layer or a negative electrode composite layer; Step (2), forming a first electrolyte layer having a support, and then providing a second A electrolyte layer and a third electrolyte layer without a support in a manner sandwiching the first electrolyte layer to obtain a laminate precursor, wherein a film thickness (T2A) of the second A electrolyte layer is substantially equal to a film thickness (T3) of the third electrolyte layer; and Step (3), laminating the positive electrode composite layer, the laminate precursor, and the negative electrode composite layer such that the second A electrolyte layer faces the second B electrolyte layer, whereby a total film thickness (T2; T2A + T2B) of the second A electrolyte layer and the second B electrolyte layer is 1.5 to 5 times that of the film thickness (T3) of the third electrolyte layer.

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