Solid electrolyte battery and method for manufacturing the same

Abstract

The present invention addresses the problem of taking measures to a battery resistance increase associated with charge and discharge cycles with respect to a solid electrolyte battery. The configuration of the present invention is as described below. The present invention provides a solid electrolyte battery which comprises a positive electrode layer, a negative electrode layer and a solid electrolyte layer that is formed between the positive electrode layer and the negative electrode layer, and which is characterized in that: the negative electrode layer comprises a first negative electrode layer 1, and a second negative electrode layer 2 that is superposed on the first negative electrode layer 1 so as to be in contact with the solid electrolyte layer 3; the active material of the first negative electrode layer 1 is a crystalline carbon 11; the active material of the second negative electrode layer 2 is an amorphous carbon 21; a negative electrode layer solid electrolyte 32 is mixed into the first negative electrode layer 1 and the second negative electrode layer 2; and (average particle diameter (D50) of negative electrode layer solid electrolyte 32) < (average particle diameter (D50) of crystalline carbon 2) < (average particle diameter (D50) of amorphous carbon 1) is satisfied.

Description

[Technical Field]

[0001] The present invention relates to a secondary battery, and more particularly to a solid electrolyte battery. [Background technology]

[0002] Lithium-ion secondary batteries, which charge and discharge by absorbing and releasing lithium ions at electrodes, are widely used in various fields, including electric vehicles, as high-energy-density batteries.

[0003] On the other hand, as the discharge capacity per unit weight or unit volume increases, ensuring safety becomes an issue, and solid electrolyte batteries have recently been developed as batteries that can ensure even greater safety. Solid electrolyte batteries are batteries that use a solid electrolyte instead of the liquid electrolyte used until now. Because solid electrolyte batteries do not use a liquid electrolyte, they are less likely to catch fire even when the discharge capacity per unit weight or unit volume increases, making them highly safe batteries.

[0004] There are various challenges to overcome in practical application of solid electrolyte batteries. For example, achieving both high capacity and long-term cycle durability is one issue. Patent Document 1 addresses this issue. Patent Document 1 discloses a multilayer negative electrode for a lithium-ion secondary battery, in which the negative electrode active material is composed of a lower layer containing graphite and an upper layer containing hard carbon. On the other hand, solid electrolyte batteries have the problem of requiring high confining pressure during charge and discharge in order to maintain adhesion between the positive electrode layer, solid electrolyte layer, and negative electrode layer. Patent Document 1 does not disclose any issues related to the confining pressure. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-53142 Summary of the Invention [Problem to be solved by the invention]

[0006] In solid electrolyte batteries that use graphite as the negative electrode active material, repeated expansion and contraction of the graphite during charging and discharging reduces the mechanical strength of the interface with the bonded solid electrolyte layer. As a result, microvoids form between the negative electrode layer and the solid electrolyte layer, reducing uniform reactivity. This reduction in uniform reactivity, or the occurrence of uneven reaction, can lead to issues such as a significant increase in battery resistance with charge-discharge cycles. To prevent this decrease in uniform reactivity, the battery is sandwiched between metal plates and externally restrained during charging and discharging. Charging and discharging with the restraining pressure reduced uniform reactivity, or the occurrence of uneven reaction, resulting in a significant increase in battery resistance with charge-discharge cycles. This results in a problem of reduced battery durability. [Means for solving the problem]

[0007] The present invention solves the above-mentioned problems by providing the following main specific means: a solid electrolyte battery including a positive electrode layer, a negative electrode layer, and a solid electrolyte layer formed between the positive electrode layer and the negative electrode layer, the negative electrode layer having a first negative electrode layer and a second negative electrode layer stacked on the first negative electrode layer and in contact with the solid electrolyte layer, the active material of the first negative electrode layer is crystalline carbon, the active material of the second negative electrode layer is amorphous carbon, an anode layer solid electrolyte is mixed in the first anode layer and the second anode layer, and the average particle size (D50) of the anode layer solid electrolyte is smaller than the average particle size (D50) of the amorphous carbon and smaller than the average particle size (D50) of the crystalline carbon. [Effects of the Invention]

[0008] By using the present invention, it is possible to obtain effects such as suppressing an increase in resistance after charge / discharge cycles. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view of a solid electrolyte battery according to Example 1. [Figure 2] FIG. 2 is a detailed cross-sectional view of FIG. [Figure 3]FIG. 10 is a cross-sectional view of a solid electrolyte battery according to Example 2. [Figure 4] 1 is a table comparing the configurations and performances of Example 1, Example 2, and a comparative example. [Figure 5] FIG. 10 is a cross-sectional view of Example 3, and is a schematic cross-sectional view showing a state in which a restraining pressure is applied to the solid electrolyte battery shown in Example 1 using a restraining member. [Figure 6] FIG. 7 is a plan view corresponding to FIG. [Figure 7] FIG. 10 is a cross-sectional view of Comparative Example 2, and is a schematic cross-sectional view showing a state in which a restraining pressure is applied to the solid electrolyte battery shown in Comparative Example 1 using a restraining member. [Figure 8] 1 shows cycle test results showing a comparison of durability between solid electrolytes of Examples 3 and 4 and Comparative Examples 2 and 3. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described in detail below using examples. [Example]

[0011] Fig. 1 is a cross-sectional view of a lithium ion secondary battery, which is a solid electrolyte battery according to Example 1. In Fig. 1, the lithium ion secondary battery has a configuration in which a first anode layer 1, a second anode layer 2, a solid electrolyte layer 3, and a cathode layer 4 are stacked between a negative electrode current collector 5 and a positive electrode current collector 6. The active material of the first anode layer 1 is crystalline carbon 11, and the active material of the second anode layer 2 is amorphous carbon 21.

[0012] FIG. 2 is a detailed cross-sectional view of FIG. 1, depicting the details of the first anode layer 1, the second anode layer 2, and the solid electrolyte layer 3. In FIG. 2, the dotted line between the first anode layer and the second anode layer is a virtual line indicating the boundary between the first anode layer and the second anode layer. The specific configuration of FIG. 2 will be described later, but the operation of the configuration of FIG. 2 is outlined as follows.

[0013] The second anode layer adjacent to the electrolyte layer 3 includes amorphous carbon 21, which expands and contracts less than crystalline carbon 11 due to the insertion and desorption of lithium ions. This prevents void formation between the anode layer and the electrolyte layer, even after repeated charging and discharging, and ensures high adhesion. Furthermore, the presence of amorphous carbon 21 or an anode layer solid electrolyte 32 smaller than crystalline carbon 11 ensures the above-mentioned adhesion. In other words, high adhesion is achieved between the crystalline carbon 11 in the first anode layer and its surroundings, or between the amorphous carbon 21 in the second anode layer and its surroundings.

[0014] As shown in FIG. 2, the first negative electrode layer 1 is composed of crystalline carbon 11 and a negative electrode layer solid electrolyte 32. The active material of the first negative electrode layer 1 is crystalline carbon 11, formed, for example, of graphite. Graphite is a layered compound consisting of multiple graphene layers, and Li ions are inserted or extracted between the graphene layers. The average particle size (D50) of the crystalline carbon 11 is preferably approximately 30 μm to 2 μm, for example, 16 μm. Hereinafter, in this specification, unless otherwise specified, the average particle size (D50) will be referred to as the average particle size or simply the particle size. The average particle size (D50) can be defined as the particle size corresponding to 50% of the cumulative volume on a particle size distribution curve. The average particle size (D50) can be measured, for example, using a laser diffraction method. For example, the average particle size (D50) of the positive electrode active material can be measured by introducing the material into a commercially available laser diffraction particle size distribution measuring device, irradiating it with ultrasound, and then calculating the average particle size (D50) corresponding to 50% of the cumulative volume in the measuring device.

[0015] In FIG. 2, the spaces between the graphite 11, which is crystalline carbon 11, are filled with fine particles of anode layer solid electrolyte 32. The average particle size of the anode layer solid electrolyte 32 is, for example, 0.5 μm. That is, the average particle size of the anode layer solid electrolyte 32 is smaller than the average particle size of the crystalline carbon 11. In FIG. 2, a binder, a conductive additive, and voids are present in the blank spaces in the first anode layer 1. The same applies to the second anode layer 2, etc.

[0016] The particle diameter of the solid electrolyte 31 constituting the solid electrolyte layer 3 shown in Figure 2 is different from the particle diameter of the anode layer solid electrolyte 32 mixed in the first anode layer 1 and the second anode layer 2. Furthermore, the material of the particles of the solid electrolyte 31 constituting the solid electrolyte layer 3 may be different from the material of the particles of the anode layer solid electrolyte 32 mixed in the first anode layer 1 and the second anode layer 2. Hereinafter, for the sake of distinction, the electrolyte in the solid electrolyte layer 3 will be referred to as the solid electrolyte 31, and the solid electrolyte filled in the first anode layer 1 and the second anode layer 2 will be referred to as the anode layer solid electrolyte 32.

[0017] The thickness of the first negative electrode layer 1 is not particularly limited, but is set in the range of about 20 to 500 μm depending on the required performance of the battery. In Example 1, it is 80 μm, and in Example 2, it is 48 μm.

[0018] In FIG. 2, the second anode layer 2 is composed of amorphous carbon 21 and an anode layer solid electrolyte 32. The active material of the second anode layer 2 is amorphous carbon 21, such as hard carbon. Hard carbon is also called "non-graphitizable carbon" and is obtained by, for example, heat treating a thermosetting resin such as phenolic resin in an inert gas atmosphere. In hard carbon, the number of graphene layers is small, and Li ions are inserted and removed not only between the graphene layers but also between the particles.

[0019] The average particle size of the hard carbon, which is the amorphous carbon 21, is in the range of 1 μm to 20 μm, for example, 5 μm. The anode layer solid electrolyte 32 mixed in the second anode layer 2 is the same as the anode layer solid electrolyte 32 mixed in the first anode layer. That is, the average particle size of the anode layer solid electrolyte 32 is, for example, 0.5 μm, which is smaller than the average particle size of the crystalline carbon 11. The average particle size of the amorphous carbon 21 is also smaller than the average particle size of the crystalline carbon 11.

[0020] The thickness of the second anode layer 2 is not particularly limited, but is set to a range of approximately 5 to 500 μm depending on the required performance of the battery. However, since a thick second anode layer 2 leads to a decrease in battery capacity, in order to maintain a high battery capacity, the thickness of the second anode layer 2 is preferably 120 μm or less. In Example 1, the thickness of the second anode layer 2 is 12 μm, and in Example 2, the thickness of the second anode layer 2 is 84 μm.

[0021] When the active material is amorphous carbon 21, conductive ions can be inserted and extracted from multiple directions, improving input / output characteristics, particularly at high current densities. Furthermore, expansion and contraction of the negative electrode layer due to the insertion and extraction of Li ions can be suppressed. However, because amorphous carbon 21 is hard, there are issues such as increased contact resistance with the negative electrode layer solid electrolyte 32. In response to this issue, the present invention suppresses the increase in contact resistance by making the average particle size of the negative electrode layer solid electrolyte 32 smaller than the average particle size of the amorphous carbon 21.

[0022] The amorphous carbon 21 used as the active material of the second negative electrode layer 2 may be soft carbon. Soft carbon is also called "easily graphitizable carbon" and is a mixture of amorphous parts, turbostratic structures, and graphite-like structures. For example, it can be obtained by heat treating pitch-based carbon or thermoplastic resin. In the following examples, hard carbon is used as the amorphous carbon 21, but similar performance can be obtained when soft carbon is used.

[0023] A solid electrolyte layer 3 is formed on the second negative electrode layer 2. The solid electrolyte 31 used in the solid electrolyte layer 3 includes oxide-based and sulfide-based solid electrolytes. Examples of oxide-based solid electrolytes include Li7La3Zr2O12-Zr2O12 (LLZ) and Li3BO3-Li2SO4. Examples of sulfide-based solid electrolytes include Li10GeP2S12 (LGPS) and Li6PS5Cl-based (argyrodite).

[0024] In this embodiment, a Li6PS5Cl-based (argyrodite) sulfide-based solid electrolyte is used, which can reduce electrical resistance and is more advantageous in terms of output characteristics. However, the solid electrolyte 31 in the present invention is not limited to a Li6PS5Cl-based (argyrodite) solid electrolyte, and other solid electrolytes can also be used. The thickness of the solid electrolyte layer 3 is, for example, 0.1 μm to 300 μm, and preferably 10 μm to 30 μm.

[0025] The solid electrolyte 31 constituting the solid electrolyte layer 3 is different from the anode layer solid electrolyte 32 mixed in the first anode layer 1 and the second anode layer 2. In particular, as shown in FIG. 2 , the average particle size of the anode layer solid electrolyte 32 is smaller than the average particle size of the solid electrolyte 31 constituting the solid electrolyte layer 3. However, the solid electrolyte 31 and the anode layer solid electrolyte 32 may be made of the same material. In Examples 1 and 2, the solid electrolyte 31 and the anode layer solid electrolyte 32 are made of the same material.

[0026] The features of the present invention described above are as follows: the average particle size of crystalline carbon 11, which is the active material of first anode layer 1, is greater than the average particle size of amorphous carbon 21, which is the active material of second anode layer 2, and is greater than the average particle size of anode layer solid electrolyte 32 mixed in both first anode layer 1 and second anode layer 2. Furthermore, the average particle size of solid electrolyte 31 constituting solid electrolyte layer 3 is greater than the average particle size of anode layer solid electrolyte 32 mixed in first anode layer 1 and second anode layer 2.

[0027] In addition to the above-described configurations, the present invention can also have the following configurations. The first configuration is that the average particle size of the anode layer solid electrolyte 32 in the first anode layer 1 is smaller than the average particle size of the crystalline carbon 11, preferably 1 / 10 or less. This configuration improves adhesion between the crystalline carbon 11 constituting the active material in the first anode layer 1 and the anode layer solid electrolyte 32 arranged therearound. Even after charge-discharge cycles, this configuration can suppress a decrease in adhesion due to cycles of expansion and contraction of the active material (e.g., crystalline carbon 11), thereby suppressing an increase in battery resistance. Furthermore, this configuration can provide effects such as suppressing the formation of lithium dendrites during rapid charging.

[0028] The second configuration is that the average particle size of the anode layer solid electrolyte 32 in the second anode layer 2 is smaller than the average particle size of the amorphous carbon 21, preferably 1 / 10 or less. This configuration improves adhesion between the amorphous carbon 21 constituting the active material in the second anode layer 2 and the anode layer solid electrolyte 32 arranged therearound. Even after charge-discharge cycles, this configuration can suppress a decrease in adhesion due to cycles of expansion and contraction of the active material (e.g., amorphous carbon 21), thereby suppressing an increase in battery resistance. This also provides the effect of suppressing the formation of lithium dendrites during rapid charging.

[0029] In the third configuration, the average particle size of the anode layer solid electrolyte 32 in the second anode layer 2 is smaller than that of the anode layer solid electrolyte 32 in the first anode layer 1. The second anode layer 2 is closer to the solid electrolyte layer 3, so the reaction is more active. According to the third configuration, the active material 21 in the second anode layer 2 where the reaction is more active is and negative Since high adhesion to the electrode layer solid electrolyte 32 can be obtained, it is possible to obtain effects such as suppressing an increase in battery resistance after charge / discharge cycles and suppressing the formation of lithium dendrites during rapid charging.

[0030] In a fourth configuration, the average particle size of the anode layer solid electrolyte 32 in the second anode layer 2 is smaller than the average particle size of the anode layer solid electrolyte 32 in the first anode layer 1. According to the fourth configuration, in the first anode layer 1 containing crystalline carbon 11 having a larger expansion coefficient than amorphous carbon 21, high adhesion can be obtained between the crystalline carbon 11 and the anode layer solid electrolyte 32. This can provide effects such as suppressing an increase in battery resistance after charge / discharge cycles and suppressing the formation of lithium dendrites during rapid charging.

[0031] Furthermore, in addition to the above configurations 1 to 4, by disposing the first anode layer 1 and the solid electrolyte layer 3 with the second anode layer 2 interposed therebetween, it is possible to suppress a decrease in the adhesion of the interface between the first anode layer 1 and other layers due to the expansion and contraction, and further suppress an increase in electrical resistance. Alternatively, instead of the above, the solid electrolyte 31 and the anode layer solid electrolyte 32 may have the same average particle shape. This configuration provides excellent cost-effectiveness in handling the solid electrolyte. In addition, when forming the solid electrolyte layer 3 into a thin film, it is easy to control the film thickness, improving manufacturability.

[0032] As described above, the present invention includes various embodiments. However, in the following description, for ease of understanding, the anode layer solid electrolyte mixed in the first anode layer 1 and the second anode layer 2 will be simply referred to as the anode layer solid electrolyte 32 unless otherwise specified.

[0033] In the second anode layer 2, the average particle size of the anode layer solid electrolyte 32 is preferably 1 / 10 or less of the average particle size of the amorphous carbon 21. If it is 1 / 10 or less, the anode layer solid electrolyte 32 can be easily arranged on the outer edge of the relatively large amorphous carbon 21, thereby reducing the contact resistance between the anode layer solid electrolyte 32 and the amorphous carbon 21. The average particle size of the anode layer solid electrolyte 32 can be reduced to about 0.1 μm.

[0034] In the example shown below, the average particle size of the anode layer solid electrolyte 32 is 0.5 μm, and the average particle size of the amorphous carbon 21 of the second anode layer 2 is 5 μm, so the ratio of the average particle size of the anode layer solid electrolyte 32 to the average particle size of the amorphous carbon 21 of the second anode layer 2 is 1 / 10. Even when the average particle size of the anode layer solid electrolyte 32 is other than 0.5 μm or the average particle size of the amorphous carbon 21 of the second anode layer 2 is other than 5 μm, it is desirable that the ratio (the average particle size of the anode layer solid electrolyte 32 to the average particle size of the amorphous carbon 21 of the second anode layer 2) be 1 / 10 or less.

[0035] In the present invention, the negative electrode has a two-layer structure, but the energy density of the second negative electrode layer 2, which uses hard carbon as the active material, is lower than the energy density of the first negative electrode layer 1, which uses graphite as the active material. Therefore, when it is desired to increase the energy density of the lithium-ion secondary battery, the thickness of the second negative electrode layer 2, which uses hard carbon, is reduced. In this case, for example, the thickness of the second negative electrode layer 2 becomes smaller than the thickness of the solid electrolyte layer 3.

[0036] 1 and 2, a positive electrode layer 4 is laminated on a solid electrolyte layer 3. The positive electrode layer 4 used in the present invention is not particularly limited. For example, the positive electrode active material may be a layered rock salt complex oxide positive electrode material such as LiCoO2 (lithium cobalt oxide) or LiNiO2 (lithium nickel oxide), or a spinel complex oxide positive electrode material such as LiMn2O4 (lithium manganese oxide).

[0037] The average particle size of the positive electrode active material is not particularly limited, but is, for example, 0.1 to 50 μm. The thickness of the positive electrode layer is not particularly limited, but is, for example, 0.5 to 500 μm. A positive electrode current collector 6 is disposed on the positive electrode layer 4.

[0038] 1 and 2 will be described in detail below. The negative electrode current collector 5 may be made of, for example, stainless steel, copper, nickel, or carbon. The negative electrode current collector 5 has a thickness of, for example, 1 μm to 20 μm. In Example 1, a stainless steel foil having a thickness of 10 μm was used as the negative electrode current collector 5.

[0039] Examples of materials that can be used for the positive electrode current collector 6 include stainless steel, copper, nickel, titanium, iron, and carbon. The thickness of the positive electrode current collector 6 is, for example, 1 μm to 20 μm. In Example 1, an aluminum foil with a thickness of 20 μm was used as the positive electrode current collector 6.

[0040] (First negative electrode layer) The first negative electrode layer 1 was produced as follows. In Example 1, graphite was used as the crystalline carbon 11 serving as the active material of the first negative electrode layer 1. The graphite 11, the negative electrode layer solid electrolyte 32, and a binder were mixed together, and a solvent was added to form a slurry. This slurry was applied to the negative electrode current collector plate 5 to achieve a desired basis weight. The mixture was then dried to remove the solvent, and the first negative electrode layer 1 was produced.

[0041] In Example 1, the average particle size of the graphite in the first negative electrode layer 1 was 16 μm. The negative electrode layer solid electrolyte 32 mixed with the graphite was a Li6PS5Cl-based (argyrodite) with an average particle size of 0.5 μm. In Example 1, the thickness of the first negative electrode layer was 80 μm.

[0042] (Second negative electrode layer) The second negative electrode layer 2 was also basically formed by the same process as the first negative electrode layer 1. In Example 1, hard carbon was used as the amorphous carbon 21 serving as the active material of the second negative electrode layer 2. The hard carbon 21, the negative electrode layer solid electrolyte 32, and a binder were mixed, and a solvent was added to form a slurry. This slurry was applied to a PET (Polyethylene Terephthalate) substrate to achieve a target basis weight. The mixture was then dried to remove the solvent, and the second negative electrode layer 2 was formed.

[0043] The hard carbon 21 in the second anode layer 2 has an average particle size of 5 μm. The anode layer solid electrolyte 32 mixed with the hard carbon is a Li6PS5Cl-based (argyrodite) with an average particle size of 0.5 μm, similar to the first anode layer 1. The thickness of the second anode layer 2 is 12 μm. A thinner second anode layer 2 increases the battery's energy density, but makes layer formation more difficult. The ratio of the thickness of the second anode layer 2 to the total thickness of the first anode layer 1 and the second anode layer 2 is 12 μm / 92 μm=0.13.

[0044] (2-layer negative electrode stack) A laminate in which the first anode layer 1 was formed on the anode current collector 5 and a laminate in which the second anode layer 2 was formed on the PET substrate were overlapped so that the first anode layer 1 and the second anode layer 2 faced each other, and the second anode layer 2 was bonded onto the first anode layer 1 by roll pressing. The PET substrate was then peeled off from the second anode layer 2, and a laminate of the first anode layer 1 and the second anode layer 2 was formed on the anode current collector 5. This lamination method using bonding has the advantage that the first anode layer 1 and the second anode layer 2 can each be formed under optimal conditions.

[0045] In addition to the above, the configuration in which the second anode layer 2 is laminated on the first anode layer 1 can also be formed by a method in which the second anode layer 2 is applied onto the first anode layer 1. That is, as described above, the first anode layer 1 is formed on the anode current collector 5, and then a slurry for forming the second anode layer 2 is applied thereon, followed by drying, and the second anode layer 2 is laminated on the first anode layer 1.

[0046] (Creation and stacking of solid electrolyte layers) The solid electrolyte 31 in the solid electrolyte layer 3 was made of Li6PS5Cl (argyrodite), but its average particle size was larger than that of the negative electrode layer solid electrolyte 32. The solid electrolyte 31 was mixed with a binder, and a solvent was added to create a slurry. This slurry was applied to a PET (Polyethylene Terephthalate) substrate, and then dried to remove the solvent, creating the solid electrolyte layer 3. The thickness of the solid electrolyte layer 3 was set to 20 μm.

[0047] A laminate in which the first anode layer 1 and the second anode layer 2 were formed on the anode current collector 5 and a laminate in which the solid electrolyte layer 3 was formed on the PET substrate were overlapped so that the second anode layer 2 and the solid electrolyte layer 3 faced each other, and the solid electrolyte layer 3 was bonded onto the second anode layer 2 by roll pressing. Thereafter, the PET substrate was peeled off from the solid electrolyte layer 3, and a laminate in which the first anode layer 1, the second anode layer 2, and the solid electrolyte layer 3 were formed on the anode current collector 5 was produced.

[0048] In addition to the above, the configuration in which the solid electrolyte layer 3 is laminated on the laminate of the first anode layer 1 and the second anode layer 2 can also be formed by a method in which the solid electrolyte layer 3 is applied on the second anode layer 2. That is, the first anode layer 1 and the second anode layer 2 are formed on the anode current collector 5 as described above, and then a slurry for forming the solid electrolyte layer 3 is applied thereon. After that, the resulting mixture is dried, and the solid electrolyte layer 3 is laminated on the second anode layer 2.

[0049] (Creation and stacking of positive electrode layer) The positive electrode active material, solid electrolyte, and binder were mixed, and a solvent was added to form a slurry. This slurry was applied to the positive electrode current collector plate 6 to achieve the desired coating weight. After that, the slurry was dried to remove the solvent, and the positive electrode layer 4 was formed. The positive electrode active material was LiNi, a layered rock salt type composite oxide positive electrode material with an average particle size of 4 μm. 0.5 Co 0.2 Mn 0.3 (lithium-nickel-cobalt-manganese oxide) was used. In Example 1, the thickness of the positive electrode layer 4 was set to 80 μm.

[0050] A laminate in which a first anode layer 1, a second anode layer 2, and a solid electrolyte layer 3 are formed on an anode current collector 5, and a laminate in which a cathode layer 4 is formed on a cathode current collector 6 are overlapped so that the cathode layer 4 and the solid electrolyte layer 3 face each other, and the cathode layer 4 is bonded onto the solid electrolyte layer 3 by roll pressing. Through the above process, the lithium ion secondary battery of Example 1 is manufactured.

[0051] In the laminate formed in this manner, the average particle size of crystalline carbon 11, which is the active material of first anode layer 1, is greater than the average particle size of amorphous carbon 21, which is the active material of second anode layer 2, and greater than the average particle size of anode layer solid electrolyte 32 mixed in the first and second anode layers. Furthermore, the average particle size of solid electrolyte 31 constituting solid electrolyte layer 3 is greater than the average particle size of anode layer solid electrolyte 32 mixed in the first and second anode layers 1 and 2.

[0052] Of the configurations of Example 1 described above, the configurations of the first negative electrode layer 1 and the second negative electrode layer 2 are shown in the row for Example 1 in the table at the top of FIG. 4. The table at the top of FIG. 4 shows examples of the physical configurations of the first negative electrode layer 1 and the second negative electrode layer 2 in Example 1, Example 2, and the comparative example. The table at the bottom of FIG. 4 lists the characteristics in Example 1, Example 2, and the comparative example. The comparison of characteristics will be described later. [Example]

[0053] FIG. 3 is a cross-sectional view of a lithium-ion secondary battery, which is a solid electrolyte battery according to Example 2. The specific materials of the first anode layer 1, second anode layer 2, solid electrolyte layer 3, and cathode layer 4 in Example 2 are the same as those in Example 1. Example 2 differs from Example 1 in the thickness of each layer. The first anode layer 1 in Example 2 is 48 μm thick, and the second anode layer 2 is 84 μm thick. In contrast, the first anode layer 1 in Example 1 is 80 μm thick, and the second anode layer 2 is 12 μm thick. Therefore, in Example 2, the influence of the second anode layer 2, which uses hard carbon 21 as the active material, is more pronounced. The ratio of the total thickness of the first anode layer 1 and the second anode layer 2 to the thickness of the second anode layer 2 is 84 μm / 132 μm=0.64.

[0054] In Example 2, the total thickness of the first anode layer 1 and the second anode layer 2 is larger than that of Example 1. However, the following relationship is also satisfied in Example 2: average particle size of crystalline carbon 11, which is the active material of the first anode layer 1 > average particle size of amorphous carbon 21, which is the active material of the second anode layer 2 > average particle size of anode layer solid electrolyte 32 mixed in the first anode layer 1 and the second anode layer 2. Furthermore, the average particle size of solid electrolyte 31 constituting solid electrolyte layer 3 > average particle size of anode layer solid electrolyte 32 mixed in the first anode layer 1 and the second anode layer 2.

[0055] In addition to the above configuration, Example 2 also employs the following configuration to achieve the same effects as those described in Example 1, such as suppressing an increase in battery resistance after charge / discharge cycles and suppressing the formation of lithium dendrites during rapid charging. Specifically, in a first configuration, the average particle size of the anode layer solid electrolyte 32 in the first anode layer 1 is smaller than the average particle size of the crystalline carbon 11, preferably by at least 1 / 10. In a second configuration, the average particle size of the anode layer solid electrolyte 32 in the second anode layer 2 is smaller than the average particle size of the amorphous carbon 21, preferably by at least 1 / 10. In a third configuration, the average particle size of the anode layer solid electrolyte 32 in the second anode layer 2 is smaller than the average particle size of the anode layer solid electrolyte 32 in the first anode layer 1. In a fourth configuration, the average particle size of the anode layer solid electrolyte 32 in the second anode layer 2 is smaller than the average particle size of the anode layer solid electrolyte 32 in the first anode layer 1.

[0056] The manufacturing methods for each layer, such as the first anode layer 1, the second anode layer 2, the solid electrolyte layer 3, and the cathode layer 4, are the same as those in Example 1. Of the configurations of Example 2, the configurations of the first anode layer 1 and the second anode layer 2 are shown in the row for Example 2 in the table at the top of FIG. 4. The table at the bottom of FIG. 4 lists the characteristics of Examples 1, 2, and the comparative example. The comparison of characteristics will be explained later. Comparative Example 1

[0057] In the comparative example, the negative electrode layer is formed as a single layer, as in the conventional case. Graphite, which is crystalline carbon 11, is used as the active material of the negative electrode layer. The average particle size of the graphite is, for example, 16 μm. The thickness of the negative electrode layer is 87 μm. The method for forming the negative electrode layer is the same as that described in the manufacturing method of the first negative electrode layer 1 in Example 1. The configurations and lamination methods of the solid electrolyte layer 3 and the positive electrode layer 4 are also the same as those described in Example 1. Evaluation Result 1

[0058] FIG. 4 is a table comparing Example 1, Example 2, and Comparative Example. The upper table compares the configurations of the first negative electrode layer 1 and the second negative electrode layer 2 in each example described above. Note that the negative electrode layer in the Comparative Example is a single layer with the same configuration as the first negative electrode layer, so it is listed in the column for the first negative electrode layer. The thickness ratio at the right end of the upper table is (thickness of the second negative electrode layer) / (thickness of the first negative electrode layer + thickness of the second negative electrode layer).

[0059] The table at the bottom of Figure 4 compares the performance of the lithium ion secondary batteries according to Example 1, Example 2, and Comparative Example. The performance of the lithium ion secondary batteries is compared in terms of energy density (%), durability, and input characteristics.

[0060] The energy density of the battery is higher when graphite is used for the negative electrode than when hard carbon is used. Therefore, the energy density of the comparative example is the highest. In the table at the bottom of Figure 4, the numerical values ​​(%) in the energy density column indicate the energy densities of Examples 1 and 2, with the energy density of the comparative example set at 100.

[0061] Durability was evaluated by measuring the change in direct current resistance (DCR) after 200 cycles of the cycle test as a percentage increase (%). The smaller the increase in DCR, the better. In the comparative example, the DCR after 200 cycles was 210%, while in Example 1 it was 142% and in Example 2 it was 140%, demonstrating that the present invention achieved excellent results.

[0062] The input characteristics are evaluated at 25°C, using the discharge capacity at 0.1C as the denominator, and the charge capacity rate at which 4.35V is reached at 4C and 6C charging. Here, 0.1C means fully charging from a completely discharged state over 10 hours, and 4C means fully charging from a completely discharged state over 1 / 4 hour.

[0063] In Example 1, the battery capacity was 52% at 4C charging and 37% at 6C charging. In Example 2, the battery capacity was 41% at 4C charging and 25% at 6C charging. In contrast, in the comparative example, Li dendrites precipitated during charging, causing a short circuit between the negative and positive electrodes, and the voltage did not reach 4.35V.

[0064] As described above, the present invention can realize a highly reliable and durable lithium ion secondary battery. Furthermore, the present invention can suppress the precipitation of Li dendrites. Therefore, the rigidity of the jig (metal plate) used to restrain the housing can be reduced, enabling the battery to be made lighter. The detailed reasons for this are as follows.

[0065] That is, a solid electrolyte battery including the laminate described above can suppress an increase in resistance after charge / discharge cycles. Furthermore, in addition to at least the above effects, lithium precipitation during high-rate charging can be suppressed. As a result, effects such as suppression of short circuits and reduction of the battery's restraint pressure can be obtained. For example, in a solid electrolyte battery, in order to suppress the risk of lithium dendrites precipitating in voids during high-rate charging and causing an internal short circuit in the battery, it is conceivable to sandwich the battery between metal plates and restrain it from the outside. In this case, the higher the restraint pressure, the more rigid the metal plates must be. For this reason, it is important to prevent the weight and volume of the metal plates from increasing, which leads to a decrease in energy density. This solid electrolyte battery can reduce the restraint pressure.

[0066] Examples 3 and 4 shown below are configurations in which a confining pressure is applied to the solid electrolyte battery of Example 1. Comparative Examples 2 and 3 are configuration examples in which a confining pressure is applied to the solid electrolyte battery of Comparative Example 1. FIG. 8 is a table comparing the durability of the batteries of Examples 3 and 4 with those of Comparative Examples 2 and 3. [Example]

[0067] FIG. 5 is a cross-sectional view of a solid electrolyte battery according to Example 3. FIG. 5 is a cross-sectional view showing a state in which pressure is applied to the solid electrolyte battery of Example 1 using a restraining member 40. The cross-section of FIG. 5 is a schematic cross-sectional view to give an idea of ​​the restraining pressure. That is, in an actual solid electrolyte battery, the first to sixth layers shown in Example 1 are wound in multiple layers with insulating sheets interposed between them and housed in a battery case. Then, pressure is applied from the outside of the battery case using, for example, a support plate or the like shown in FIG. 5. The same applies to Example 4 and Comparative Examples 2 and 3.

[0068] 5, a first anode layer 1, a second anode layer 2, a solid electrolyte layer 3, and a cathode layer 4 are sandwiched between an anode current collector plate 5 and a cathode current collector plate 6. As described in Example 1, the first anode layer 1, the second anode layer 2, and the solid electrolyte layer 3 are sandwiched between an anode current collector plate 5 and a cathode current collector plate 6. layer A solid electrolyte 32 is mixed in. In Fig. 5, the restraining member 40 is composed of support plates 41, bolts 42, and nuts 43 that sandwich the solid electrolyte battery from above and below via an insulating sheet 7. In Fig. 5, the upper and lower support plates 41 are fastened together by the long bolts 42 and nuts 43, applying restraining pressure to the solid electrolyte battery.

[0069] FIG. 6 is a plan view of FIG. 5 viewed from above. Bolts 42 and nuts 43 for fastening the upper and lower support plates 41 are arranged at the four corners of the support plate 41. The support plate 41 applies pressure to the solid electrolyte battery from above and below, so a certain degree of rigidity is required. In the product, for example, stainless steel with a thickness of approximately 10 mm is used. However, since the energy density of the battery is counted including the restraining member 40, it is desirable that the weight of the restraining member 40 be as small as possible. However, if the restraining pressure is small, the durability of the battery cannot be ensured.

[0070] In Example 3, a solid electrolyte battery having the same configuration as in Example 1 according to the present invention is used, so only a small confining pressure is required. The confining pressure in Example 3 is 0.1 t / cm 2where t is tons. The durability of the solid electrolyte battery was evaluated based on the DCR (%) and capacity retention rate (%) after 300 cycles at 60°C. The results are shown in Figure 8, which shows superior durability to the comparative example. Details of Figure 8 will be explained later. [Example]

[0071] The structure of Example 4 is the same as that of Example 3. That is, the solid electrolyte battery of Example 1 is clamped and subjected to a constraining pressure by a constraining member 40, as shown in Figures 5 and 6. The constraining pressure in Example 4 is 0.05 t / cm, which is smaller than that in Example 3. 2 The durability of the solid electrolyte battery in this case is shown in FIG. 8. Details of FIG. 8 will be explained later, but this example also shows superior durability to the comparative example. Comparative Example 2

[0072] FIG. 7 is a cross-sectional view of a solid electrolyte battery according to Comparative Example 2. FIG. 7 is a cross-sectional view showing a state in which pressure is applied to the solid electrolyte battery of Comparative Example 1 using a restraining member 40 via an insulating sheet 7. The cross section of FIG. 7 is a schematic cross-sectional view for providing an idea of ​​the restraining pressure. As shown in FIG. 7, in Comparative Examples 1 and 2, there is no second negative electrode layer. The plan view of FIG. 7 viewed from above is the same as FIG. 6. The restraining pressure in Comparative Example 1 is 0.1 t / cm, the same as in Example 3. 2 The durability of the solid electrolyte battery in this case is shown in FIG. 8. Details of FIG. 8 will be explained later. Comparative Example 3

[0073] The structure of Comparative Example 3 is the same as that of Comparative Example 2. That is, the solid electrolyte battery of Comparative Example 1 is clamped and subjected to a constraining pressure by a constraining member 40, as shown in Fig. 7. The constraining pressure in Comparative Example 3 is 0.05 t / cm, which is smaller than that in Comparative Example 2. 2 The durability of the solid electrolyte battery in this case is shown in Figure 8. Evaluation Result 2

[0074] 8 is a table comparing Example 3, Example 4, Comparative Example 2, and Comparative Example 3, and the upper table shows the configurations of each Example and Comparative Example as explained above. Note that Comparative Example 2 and Comparative Example 3 each have only one negative electrode layer, and have the same configuration as the first negative electrode layer, so they are listed in the column for the first negative electrode layer. The confining pressure (sometimes referred to as confining pressure) in Example 3 and Comparative Example 2 was 0.1 t / cm 2 The confining pressure in Example 4 and Comparative Example 3 was 0.05 t / cm 2 is.

[0075] The table at the bottom of Figure 8 compares the durability of the solid electrolyte batteries of Example 3, Example 4, Comparative Example 2, and Comparative Example 2. Durability was evaluated by the change in DC resistance (DCR) (%) and capacity retention (%) after 300 cycles at 60°C. The cycle test involved charging the battery at a charging current of 1C, leaving it for 30 minutes, and then discharging it at a discharging current of, for example, 1C. The battery was then left for 30 minutes and charged again at a charging current of 1C. The solid electrolyte battery used in this cycle test had a terminal voltage of 4.35V when fully charged and 3V when fully discharged. Figure 8 compares the initial changes in DC resistance and capacity after repeating this cycle 300 times at 60°C. The capacity retention after 300 cycles can also be interpreted as a comparison of the discharge capacity at the first cycle and the discharge capacity at the 300th cycle.

[0076] In Figure 8, the same confining pressure (0.1t / cm 2 ), Example 3 has improved DCR and capacity retention compared to Comparative Example 2. 2 ), both DCR and capacity retention are improved in Example 4 compared to Comparative Example 3. Therefore, the effect of the configuration of the present invention on durability is fully recognized.

[0077] When Fig. 8 is examined in more detail, the effect of the present invention is evident when the confining pressure (0.05 t / cm 2 ) is more difficult to achieve with the confining pressure (0.1t / cm 2) is more significant than in the case of the confining pressure (0.1t / cm 2 ), comparing Example 3 with Comparative Example 2, Example 3 shows an improvement of 410 / 480=0.854, or 14.6%, over Comparative Example 2. On the other hand, when the confining pressure (0.05 t / cm 2 In this case, when Example 4 and Comparative Example 3 are compared in terms of DCR, Example 4 has an improvement of 415 / 549=0.756, ie, 24.4%, over Comparative Example 3.

[0078] On the other hand, the capacity retention rate is affected by the confining pressure (0.1t / cm 2 ), comparing Example 3 with Comparative Example 2, Example 3 shows an improvement of 70 / 67=1.045, or 4.5%, over Comparative Example 2. On the other hand, when the confining pressure (0.05 t / cm 2 8 ), comparing the capacity retention rate between Example 4 and Comparative Example 3, Example 4 has an improvement of 69 / 62=01.113, or 11.3%, over Comparative Example 3. As such, the results shown in Fig. 8 clearly demonstrate the effect of the present invention, that is, the configuration of the present invention can suppress deterioration in durability even when the confining pressure is reduced.

[0079] REFERENCE SIGNS LIST 1...first negative electrode layer, 2...second negative electrode layer, 3...solid electrolyte layer, 4...positive electrode layer, 5...negative electrode current collector, 6...positive electrode current collector, 7...insulating sheet, 11...crystalline carbon, 12...amorphous carbon, 31...solid electrolyte, 32...negative electrode layer solid electrolyte, 40...restraint member, 41...support plate, 42...bolt, 43 …nut

[0080] By the way, if the confining pressure is increased, the durability of the solid electrolyte battery can be improved. However, if the confining pressure is increased, the thickness of the support plate must be increased, and this reduces the energy efficiency of the solid electrolyte battery. A feature of the present invention is that it is possible to prevent a decrease in durability even when the confining pressure is reduced. Referring to Figure 8, according to the present invention, the change in DCR is as follows: 2) to (0.05t / cm 2 ), the change in capacity retention rate is only slight, from 410% to 415%. 2 ) to (0.05t / cm 2 ), the change from 70% to 69% is slight. Considering these data, by using the configuration of the present invention, the confining pressure is (0.01 t / cm 2 ), it can be reasonably estimated that the durability of the solid electrolyte battery can be maintained at a practical level.

[0081] In the above examples, graphite is used as the crystalline carbon 11 in the active material of the first anode layer 1, hard carbon is used as the crystalline carbon 11 in the active material of the second anode layer 2, Li6PS5Cl (argyrodite) is used as the anode layer solid electrolyte 32 mixed in the first anode layer 1 and the second anode layer, and Li6PS5Cl (argyrodite) is used as the solid electrolyte 31 in the solid electrolyte layer 3. However, the present invention is not limited thereto, and other crystalline carbons, amorphous carbons, and solid electrolytes can be used. Alternatively, the first negative electrode layer or the second negative electrode layer can contain crystalline carbon or amorphous carbon as, for example, a main component, and further contain a known active material. [Explanation of symbols]

[0082] REFERENCE SIGNS LIST 1...first negative electrode layer, 2...second negative electrode layer, 3...solid electrolyte layer, 4...positive electrode layer, 5...negative electrode current collector, 6...positive electrode current collector, 7...insulating sheet, 11...crystalline carbon, 12...amorphous carbon, 31...solid electrolyte, 32...negative electrode layer solid electrolyte, 40...restraint member, 41...support plate, 42...bolt, 42...nut

Claims

1. A solid electrolyte battery including a positive electrode layer, a negative electrode layer, and a solid electrolyte layer formed between the positive electrode layer and the negative electrode layer, the negative electrode layer includes a first negative electrode layer and a second negative electrode layer stacked on the first negative electrode layer and in contact with the solid electrolyte layer, the active material of the first negative electrode layer is crystalline carbon, the active material of the second negative electrode layer is amorphous carbon, an anode layer solid electrolyte is mixed in the first anode layer and the second anode layer; the average particle size (D50) of the negative electrode layer solid electrolyte < the average particle size (D50) of the amorphous carbon < the average particle size (D50) of the crystalline carbon, the solid electrolyte layer is made of a solid electrolyte, A solid electrolyte battery, characterized in that the average particle size (D50) of the solid electrolyte of the negative electrode layer is smaller than the average particle size (D50) of the solid electrolyte.

2. 2. The solid electrolyte battery according to claim 1, wherein the average particle size (D50) of the solid electrolyte in the negative electrode layer is 1 / 10 or less of the average particle size (D50) of the amorphous carbon in the second negative electrode layer.

3. 2. The solid electrolyte battery according to claim 1, wherein the thickness of the second anode layer is smaller than the thickness of the first anode layer.

4. 2. The solid electrolyte battery according to claim 1, wherein the second negative electrode layer has a thickness of 12 μm or less.

5. the crystalline carbon is graphite; 2. The solid electrolyte battery according to claim 1, wherein the amorphous carbon is hard carbon or soft carbon.

6. 2. The solid electrolyte battery according to claim 1, wherein the solid electrolyte of the solid electrolyte layer and the solid electrolyte of the negative electrode layer are made of a sulfide-based solid electrolyte.

7. 2. The solid electrolyte battery according to claim 1, wherein the solid electrolyte of the solid electrolyte layer and the solid electrolyte of the negative electrode layer are made of a Li6PS5Cl system (argyrodite).

8. A solid electrolyte battery including a positive electrode layer, a negative electrode layer, and a solid electrolyte layer formed between the positive electrode layer and the negative electrode layer, the negative electrode layer includes a first negative electrode layer and a second negative electrode layer stacked on the first negative electrode layer and in contact with the solid electrolyte layer, the active material of the first negative electrode layer is crystalline carbon, the active material of the second negative electrode layer is amorphous carbon, an anode layer solid electrolyte is mixed in the first anode layer and the second anode layer; the average particle size (D50) of the negative electrode layer solid electrolyte < the average particle size (D50) of the amorphous carbon < the average particle size (D50) of the crystalline carbon, the solid electrolyte layer is made of a solid electrolyte, the average particle size (D50) of the negative electrode layer solid electrolyte is smaller than the average particle size (D50) of the solid electrolyte, a negative electrode current collector plate is laminated on the outside of the negative electrode layer; a positive electrode current collector plate is laminated on the outside of the positive electrode layer; a first support plate is laminated on the outer side of the negative electrode current collector plate; a second support plate is laminated on the outer side of the positive electrode current collector plate; By sandwiching the solid electrolyte battery between the first support plate and the second support plate, a confining pressure of (0.11 t / cm ２ ) to (0.01t / cm ２ ) a solid electrolyte battery characterized in that pressure is applied to the battery.

9. By sandwiching the solid electrolyte battery between the first support plate and the second support plate, a confining pressure of (0.11 t / cm ２ ) to (0.04t / cm ２ 9. The solid electrolyte battery according to claim 8, wherein pressure is applied so that

10. 1. A method for manufacturing a solid electrolyte battery including a positive electrode layer, a negative electrode layer, and a solid electrolyte layer formed between the positive electrode layer and the negative electrode layer, comprising: the negative electrode layer includes a first negative electrode layer and a second negative electrode layer stacked on the first negative electrode layer and in contact with the solid electrolyte layer, the active material of the first negative electrode layer is crystalline carbon, the active material of the second negative electrode layer is amorphous carbon, an anode layer solid electrolyte is mixed in the first anode layer and the second anode layer; the average particle size (D50) of the negative electrode layer solid electrolyte < the average particle size (D50) of the amorphous carbon < the average particle size (D50) of the crystalline carbon, the solid electrolyte layer is made of a solid electrolyte, the average particle size (D50) of the negative electrode layer solid electrolyte is smaller than the average particle size (D50) of the solid electrolyte, a negative electrode current collector plate is laminated on the outside of the negative electrode layer; a positive electrode current collector plate is laminated on the outside of the positive electrode layer; a first support plate is laminated on the outer side of the negative electrode current collector plate; laminating a second support plate on the outer side of the positive electrode current collector plate; a step of sandwiching and pressing the solid electrolyte battery between the first support plate and the second support plate; placing the solid electrolyte battery in a battery charging device so that it can be charged; and charging the disposed solid electrolyte battery by the charging device, In the charging step, the solid electrolyte battery is charged with a current of 0.11 t / cm ２ ) to (0.01t / cm ２ ) and pressing the mixture.

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