Secondary battery

Abstract

To achieve a secondary battery capable of charging and discharging with a new mechanism.SOLUTION: A secondary battery (1) comprises: a positive electrode (10) comprising a first layer (11) including a solid electrolyte; and a negative electrode (20) comprising a second layer (21) including a semiconductor. The first layer and the second layer are in contact with each other. The first layer includes a material that is represented by Li(1-x)Nb(1+y)O(3-z), where at least one of x, y, and z is larger than 0.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to secondary batteries. [Background technology]

[0002] Patent Document 1 discloses a secondary battery that stores electrons. The secondary battery includes an n-type oxide semiconductor and an oxide insulator, and has a structure containing carbon atoms, hydrogen atoms, or carbon atoms and hydrogen atoms as an electricity storage layer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-14128 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of one embodiment of the present disclosure is to realize a secondary battery that can be charged and discharged using a new mechanism. [Means for solving the problem]

[0005] In order to solve the above problems, a secondary battery according to one embodiment of the present disclosure includes a positive electrode having a first layer including a solid electrolyte and a negative electrode having a second layer including a semiconductor, the first layer and the second layer being in contact with each other, and the first layer containing Li (1-x) Nb (1+y) O (3-z) and includes a material in which at least one of x, y, and z is greater than 0. [Effects of the Invention]

[0006] According to one aspect of the present disclosure, a secondary battery capable of being charged and discharged by a new mechanism can be realized. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a schematic diagram illustrating an outline of a secondary battery according to a first embodiment. [Figure 2] 3 is a schematic diagram showing the operation of the secondary battery according to the first embodiment during charging. FIG. [Figure 3] 3 is a schematic diagram showing the operation of the secondary battery according to the first embodiment during discharge. FIG. [Figure 4] 10 is a graph showing an example of charge and discharge in a comparative example of a secondary battery. [Figure 5] FIG. 2 is a diagram showing an image of the boundary between the first layer and the second layer in the secondary battery. [Figure 6] FIG. 1 is a diagram comparing the first layers of Examples 1 and 2 and a comparative example. [Figure 7] FIG. 10 is a diagram comparing the first layers of Example 3 and the comparative example. [Figure 8] FIG. 10 is a diagram comparing the first layers of Example 4 and the comparative example. [Figure 9] 10A and 10B are schematic diagrams showing modified examples of the shapes of the first and second layers. [Figure 10] 10A and 10B are schematic diagrams showing modified examples of the interface between the first layer and the second layer. [Figure 11] 10A and 10B are schematic diagrams showing modified examples of the region where the first layer and the second layer face each other. [Figure 12] 10 is a schematic diagram illustrating an example of a secondary battery according to a second embodiment. FIG. [Figure 13] 10 is a schematic diagram showing another example of a secondary battery according to the second embodiment. FIG. [Figure 14] FIG. 10 is a schematic diagram illustrating an outline of a secondary battery according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] [Embodiment 1] An embodiment of the present disclosure will be described in detail below.

[0009] (Structure of secondary battery) Fig. 1 is a schematic diagram showing an outline of a secondary battery 1 according to embodiment 1. As shown in Fig. 1, the secondary battery 1 includes a positive electrode 10 and a negative electrode 20. The positive electrode 10 includes a first layer 11 and a positive electrode current collector foil 12. The negative electrode 20 includes a second layer 21 and a negative electrode current collector foil 22. In the secondary battery 1, the positive electrode current collector foil 12, the first layer 11, the second layer 21, and the negative electrode current collector foil 22 are arranged in this order.

[0010] The first layer 11 may be a layer containing a solid electrolyte. The first layer 11 may further contain a substance other than the solid electrolyte. However, at least a portion of the solid electrolyte contained in the first layer 11 may be in continuous contact from the positive current collector foil 12 to the second layer 21, so that the positive current collector foil 12 and the second layer 21 are electrically joined by the solid electrolyte. The materials constituting the first layer 11 will be described later.

[0011] The second layer 21 may contain a semiconductor. The type of semiconductor is not particularly limited. The second layer 21 may further contain a material other than a semiconductor. However, at least a portion of the semiconductor contained in the second layer 21 may be in continuous contact from the negative electrode current collector foil 22 to the first layer 11, thereby electrically connecting the negative electrode current collector foil 22 and the first layer 11 via the semiconductor. Specifically, the second layer 21 may contain one or more of single-crystal Si, single-crystal Ge, amorphous Si, and an oxide semiconductor. Specific examples of oxide semiconductors include NiO, ZnO, TiO2, Al2O3, SnO2, Cu2O, CdO, WO3, and MoO2. By using a semiconductor contained in the second layer 21 with a high carrier concentration, the capacity of the secondary battery 1 is increased.

[0012] A specific example of the semiconductor contained in the second layer 21 is single crystal Si doped with P. By doping Si, which has four valence electrons, with P, which has five valence electrons, one of the valence electrons of P functions as a free electron. However, the semiconductor contained in the second layer 21 is not limited to this. The semiconductor contained in the second layer 21 is not limited to an n-type semiconductor, and may be a p-type semiconductor.

[0013] 1, the first layer 11 and the second layer 21 have a rectangular parallelepiped shape. However, the shapes of the first layer 11 and the second layer 21 are not limited to this.

[0014] In the secondary battery 1, the first layer 11 and the second layer 21 are in contact with each other. This allows the ions of the solid electrolyte contained in the first layer 11 and the free electrons (carriers) or holes (carriers) of the semiconductor contained in the second layer 21 to operate as described below, and the secondary battery 1 functions as a secondary battery.

[0015] There are no particular limitations on the contact area between the first layer 11 and the second layer 21. However, by increasing the contact area between the first layer 11 and the second layer 21, the capacity of the secondary battery 1 can be increased compared to when the contact area is small.

[0016] The thickness of the first layer 11 may be 1 μm or more and 60 μm or less, for example, 10 μm. When the thickness of the first layer 11 is 1 μm or more, the occurrence of a short circuit between the positive electrode current collector foil 12 and the negative electrode current collector foil 22 can be reduced. Furthermore, when the thickness of the first layer 11 is 20 μm or less, the internal resistance of the first layer 11 can be reduced.

[0017] The thickness of the second layer 21 may be 1 μm or more and 180 μm or less, for example, 20 μm. When the thickness of the second layer 21 is 1 μm or more, it is possible to ensure the generation of the amount of carriers necessary for the secondary battery 1 to function as a secondary battery. Furthermore, when the thickness of the second layer 21 is 60 μm or less, it is possible to reduce the migration distance of the carriers and the internal resistance caused by the migration distance, thereby increasing the capacity of the secondary battery 1.

[0018] The ratio of the thickness of the second layer 21 to the thickness of the first layer 11 may be not less than 1 and not more than 30. When the ratio is within the above range, the capacity per unit volume of the secondary battery 1 can be increased compared to when the ratio is outside the above range.

[0019] The positive electrode current collector foil 12 may be a metal foil in contact with the first layer 11. The negative electrode current collector foil 22 may be a metal foil in contact with the second layer 21. Terminals (not shown) for charging and discharging the secondary battery 1 may be connected to the positive electrode current collector foil 12 and the negative electrode current collector foil 22.

[0020] The positive electrode current collector foil 12 and the negative electrode current collector foil 22 may be made of, for example, but not limited to, SUS (stainless steel), Cu, or Al. The positive electrode current collector foil 12 and the negative electrode current collector foil 22 may be made of different materials or the same material.

[0021] The thickness of the positive electrode current collector foil 12 and the negative electrode current collector foil 22 may be 0.1 μm or more and 100 μm or less, for example, 10 μm. The thickness of the positive electrode current collector foil 12 and the negative electrode current collector foil 22 may be the same as or different from each other.

[0022] (Secondary battery manufacturing method) The secondary battery 1 may be manufactured, for example, as follows. First, a mixture of solid electrolyte powder and a binder, which is the material for the first layer 11, is applied onto the positive electrode current collector foil 12 to form the first layer 11 in a sheet shape. Next, the sheet-shaped first layer 11 may be rolled to a thickness of 30% to 60%. A mixture of semiconductor powder and a binder, which is the material for the second layer 21, is applied onto the rolled first layer 11 to form the second layer 21 in a sheet shape. The sheet-shaped second layer 21 may be rolled to a thickness of 30% to 60%. Thereafter, the negative electrode current collector foil 22 is disposed on the second layer 21, thereby manufacturing the secondary battery 1.

[0023] The binder may be any known binder, such as a polymer binder, without any particular limitations. The binders for the first layer 11 and the second layer 21 may be the same or different in type.

[0024] The method for manufacturing the secondary battery 1 is not limited to the above example. For example, the material for the first layer 11 may be applied to the positive electrode current collector foil 12, the material for the second layer 21 may be applied to the negative electrode current collector foil 22, and then the first layer 11 and the second layer 21 may be bonded to each other.

[0025] Furthermore, instead of the above-described coating, the first layer 11 and the second layer 21 may be formed, for example, by vapor deposition of the materials for the first layer 11 and the second layer 21. However, when the first layer 11 and the second layer 21 are formed by coating, it becomes easier to manufacture the first layer 11 and the second layer 21 and to increase their areas.

[0026] Furthermore, parameters such as particle size (particle size or surface area) or the volume or mass ratio of the particles to the binder in the materials of the first layer 11 and the second layer 21 also affect the capacity of the secondary battery 1. By appropriately setting these parameters, the capacity of the secondary battery 1 can be further increased.

[0027] For example, the average particle size of the particles in the material of first layer 11 may be 0.01 μm or more and 50 μm or less. Alternatively, the average particle size of the particles in the material of first layer 11 may be 0.05 μm or more and 20 μm or less. Alternatively, the average particle size of the particles in the material of first layer 11 may be 0.1 μm or more and 5 μm or less.

[0028] When the average particle diameter is 50 μm or less, the specific surface area of ​​the particles is larger than when the average particle diameter exceeds 50 μm. As a result, the charge flowing from the second layer 21 is more likely to penetrate into defects in the first layer 11. Furthermore, when the average particle diameter is less than 0.01 μm, the specific surface area becomes too large, making it difficult to form into a sheet shape. In this case, it is necessary to increase the amount of binder that acts as a binding material for the particles, which increases the resistance value of the first layer 11.

[0029] The average particle size of the particles in the material of second layer 21 may be 0.01 μm or more and 100 μm or less. The average particle size of the particles in the material of second layer 21 may be 0.5 μm or more and 60 μm or less. The average particle size of the particles in the material of second layer 21 may be 1 μm or more and 40 μm or less.

[0030] Defects occur in the material of the second layer 21 during the process of reducing the particle size. Charges that should flow to the first layer 11 are trapped in the defects, reducing the amount of charge that flows to the first layer 11. As a result, the capacity of the secondary battery 1 decreases. By setting the average particle size of the particles in the material of the second layer 21 to 0.01 μm or more, the occurrence of defects and the reduction in capacity of the secondary battery 1 are reduced. Furthermore, if the average particle size exceeds 100 μm, pinholes will occur on the surface of the second layer 21. This increases the resistance value of the second layer 21, causing a reduction in the capacity of the secondary battery 1.

[0031] The specific surface area of ​​the particles in the material of the first layer 11 and the second layer 21 is 5 m 2 / g or more and 20m 2 / g or less. 2 / g or more, the grain boundaries and the resistance at the grain boundaries can be reduced, and the capacity of the secondary battery 1 can be increased. 2 By setting the porosity to be not more than 1 / g, the porosity in the first layer 11 and the second layer 21 and the resistance caused by the porosity can be reduced, and the capacity of the secondary battery 1 can be increased.

[0032] Furthermore, the ratio (mass ratio) of the mass of the binder to the mass of the material of the first layer 11 and the second layer 21 may be 1 mass % or more and 10 mass % or less. By setting the mass ratio to 1 mass % or more, it is possible to ensure the amount of binder necessary for forming the first layer 11 and the second layer 21 into a sheet shape according to the specific surface area of ​​the particles. By setting the mass ratio to 10 mass % or less, it is possible to set the amount of binder to an amount that does not inhibit the movement of carriers or ions.

[0033] (Secondary battery operation) FIG. 2 is a schematic diagram showing the operation of the secondary battery 1 during charging. FIG. 3 is a schematic diagram showing the operation of the secondary battery 1 during discharging. The operation of the secondary battery 1 during charging and discharging will be described with reference to FIGS. 2 and 3. In the example shown in FIGS. 2 and 3, the first layer 11 contains LiNbO3. Therefore, in the first layer 11, Li + The ions 11a contribute to the charging and discharging of the secondary battery 1. In the example shown in FIGS. 2 and 3, the second layer 21 contains an n-type semiconductor. Therefore, in the second layer 21, free electrons 21a contribute to the charging and discharging of the secondary battery 1. For ease of visibility, in FIGS. 2 and 3, only a portion of the Li + Only the ions 11a and the free electrons 21a are labeled.

[0034] As shown in FIG. 2, when the secondary battery 1 is being charged, a current flows in the direction indicated by the white arrow 31. At this time, electrons 35 move in the opposite direction to the white arrow 31. As the electrons 35 flow into the second layer 21, free electrons 21a in the second layer 21 move toward the interface between the second layer 21 and the first layer 11, and accumulate near the interface between the second layer 21 and the first layer 11. At the same time, some metallic Li atoms in the first layer 11 are ionized to form Li + Ions 11a are generated. Li + The ions 11 a are attracted to the free electrons 21 a accumulated at the interface between the second layer 21 and the first layer 11 , and segregate near the interface between the first layer 11 and the second layer 21 .

[0035] As shown in FIG. 3, when the secondary battery 1 is discharged, a current flows in the direction indicated by the white arrow 32. At this time, electrons 35 move in the opposite direction to the white arrow 32. As the electrons 35 flow out of the second layer 21, the free electrons 21a that had accumulated in the second layer 21 near the interface between the second layer 21 and the first layer 11 return to their original positions. At the same time, in the first layer 11, the Li ions that had segregated in the first layer 11 near the interface between the first layer 11 and the second layer 21 also return to their original positions. + Ion 11a returns to its original position. At this time, Li + Some of the ions 11a combine with the electrons 35 that have flowed into the first layer 11 and return to metallic Li atoms.

[0036] If the second layer 21 contains a p-type semiconductor instead of an n-type semiconductor, holes rather than free electrons become carriers in the second layer 21. In this case, when the secondary battery 1 is charged, the holes in the second layer 21 accumulate near the surface opposite the interface between the second layer 21 and the first layer 11, i.e., in the negative electrode current collecting foil 22. When the secondary battery 1 is discharged, the holes in the second layer 21 return to their original positions from the surface opposite the interface between the second layer 21 and the first layer 11. Li in the first layer 11 + The behavior of the ions 11a is the same as when the second layer 21 contains an n-type semiconductor.

[0037] (IR drop) Fig. 4 is a graph showing an example of charging and discharging in a comparative example of the secondary battery 1. In Fig. 4, the horizontal axis represents the time (minutes) elapsed since the start of charging, the vertical axis on the left represents the voltage (V) of the secondary battery 1, and the vertical axis on the right represents the current (μA) of the secondary battery 1. In the graph of Fig. 4, positive current values ​​represent the charging current to the secondary battery 1, and negative current values ​​represent the discharging current from the secondary battery 1.

[0038] In the example shown in FIG. 4, the first layer 11 was made of LiNbO3. The second layer 21 was made of P-doped single crystal Si powder. In the example shown in FIG. 4, the secondary battery 1 was charged for 5 minutes from the start of charging, and then the OCV (Open Circuit Voltage) was measured for 5 minutes from the end of charging. Thereafter, the secondary battery 1 started discharging. Discharging of the secondary battery 1 continued for approximately 13 minutes.

[0039] In the example shown in FIG. 4, the voltage of the secondary battery 1 reached its maximum value at the end of charging. However, the voltage of the secondary battery 1 dropped during the OCV measurement period. In this way, the secondary battery 1 experiences a phenomenon known as self-discharge, in which the voltage drops when left standing after charging. This means that the charged charge is transferred and released, reducing the capacity of the secondary battery 1.

[0040] As an index of self-discharge, an IR (Intensity of Current-Resistance) drop, which is a value obtained by subtracting the voltage value after OCV measurement from the maximum voltage value of the secondary battery 1, can be used. It is considered that the smaller the IR drop, the smaller the self-discharge of the secondary battery 1. The magnitude of the IR drop depends on, for example, the material of the first layer 11.

[0041] (1st layer material) In this embodiment, the first layer 11 is Li (1-x) Nb (1+y) O (3-z) The material is represented by the formula: where at least one of x, y, and z is greater than 0. This material is LiNbO3 with defects in its crystal structure. In this specification, defects do not occur naturally, but are intentionally created.

[0042] Fig. 5 is a diagram showing an image of the boundary between the first layer 11 and the second layer 21 in the secondary battery 1. The boundary between the first layer 11 and the second layer 21 shown in Fig. 5 does not represent a physical shape but an energy level.

[0043] In FIG. 5, reference numeral 501 indicates a case where the first layer 11 is formed of a material that does not cause defects in the crystal structure of LiNbO3. In the case shown by reference numeral 501, the energy level at the boundary between the first layer 11 and the second layer 21 is flat. Therefore, the force holding the free electrons 21a at the boundary between the first layer 11 and the second layer 21 is weak. Therefore, in the case shown by reference numeral 501, the free electrons 21a can easily move at the boundary between the first layer 11 and the second layer 21.

[0044] Reference numeral 502 indicates a case where the first layer 11 is formed from a material in which crystal structure defects are generated in oxygen in LiNbO3. In the case shown by reference numeral 502, traps 61 due to oxygen defects are generated at the energy level at the boundary between the first layer 11 and the second layer 21. As a result, some of the free electrons 21a are held in the traps 61. Therefore, the case shown by reference numeral 502 has a smaller IR drop value than the case shown by reference numeral 501.

[0045] Such LiNbO3 is LiNbO (3-z) The value of z is expressed as, for example, 0<z≦0.5であってよい。z> When z is 0, traps 61 are generated at the boundary between the first layer 11 and the second layer 21, and the IR drop value is reduced. When z≦0.5, LiNbO3 having a crystal structure of the trigonal space group R3c is maintained. When LiNbO3 is formed from a material in which crystal structure defects are generated in Li and oxygen, the LiNbO (3-z) It is expressed as:

[0046] Reference numeral 503 indicates a case where the first layer 11 is formed from a material in which crystal structure defects are generated in the Li in LiNbO3. In the case shown by reference numeral 503, traps 62 due to Li defects are generated at the energy level at the boundary between the first layer 11 and the second layer 21. As a result, some of the free electrons 21a are held in the traps 62. The traps 62 are deeper than the traps 61 due to oxygen defects. Therefore, the IR drop value is even smaller in the case shown by reference numeral 503 than in the case shown by reference numeral 502.

[0047] Such LiNbO3 is Li (1-x) Nb (1+y) O3. The values ​​of x and y are, for example, 0 <x≦0.2、かつ0<y≦0.05であってよい。x> When x≦0.2 and y≦0.05, a Li ion-doped ferrite having a crystal structure of the trigonal space group R3c with Li defects is obtained. (1-x) Nb (1+y) For example, if x>0.2, LiNb3O8, which does not store charge, is generated. In this case, LiNbO3 is not a single phase but is in a phase-split state.

[0048] Reference numeral 504 illustrates a case where the first layer 11 is formed from a material in which random crystal structure defects are generated in both Li and O at the surface of LiNbO3. In the case illustrated by reference numeral 504, both traps 61 due to oxygen defects and traps 62 due to Li defects are generated at the energy level at the boundary between the first layer 11 and the second layer 21. In the case illustrated by reference numeral 504, the generation of traps 62 reduces the IR drop value compared to the case illustrated by reference numeral 502 in which only traps 61 are generated. On the other hand, in the case illustrated by reference numeral 504, the generation of traps 61 also reduces the IR drop value compared to the case illustrated by reference numeral 502 in which only traps 62 are generated.

[0049] Such LiNbO3 is Li (1-x) Nb (1+y) O (3-z) The values ​​of x, y, and z are expressed as, for example, 0 <x≦0.5、-0.5≦y<0、かつ0<z≦1であってよい。x> 0, y<0 and z>0, which means that Li has a crystal structure in the trigonal space group R3c. (1-x) Nb (1+y) O (3-z) is generated, and traps 62 due to defects of Li, Nb, and O are generated at the energy level at the boundary between the first layer 11 and the second layer 21, reducing the IR drop value. Furthermore, if x>0.5, y<-0.5, or z>1, the crystal cannot have a crystal structure of the trigonal space group R3c.

[0050] (Li (1-x) Nb (1+y) (O3 manufacturing method) Li (1-x) Nb (1+y) LiNbO3 can be produced by varying the conditions, such as the molar ratio of Li and Nb in the raw materials, in common synthesis methods for LiNbO3, such as the sintering method, sol-gel method, hydraulic synthesis method, or pulverization method. For example, in the sintering method, the molar ratio of Li and Nb is set to 1:1 to 1.3, and sintering is performed in a hydrogen or air atmosphere at 500 to 1100°C for 1 to 10 hours. (1-x) Nb (1+y)In the case of the pulverization method, LiNbO3 can be obtained by pulverizing LiNbO3 using a pulverizer such as a vibration ball mill, cutter mill, planetary rotating ball mill, jet mill, mortar, or sand mill at a rotation speed of 100 to 600 rpm for 1 to 24 hours. (1-x) Nb (1+y) You can get O3.

[0051] For example, in the firing method, Li vacancies can be formed by firing at 800 to 1100°C in an electric furnace under atmospheric conditions. (1-x) Nb (1+y) In the firing method, LiNbO3 with defects in O can be produced by firing at 500 to 1000°C in a controlled atmosphere furnace under a mixed atmosphere of H2 / Ar. (3-z) Furthermore, the crushing method can produce Li with random defects on the surface. (1-x) Nb (1+y) O (3-z) can be manufactured.

[0052] (Example) Table 1 shows examples 1 to 4 of the secondary battery 1 and a comparative example.

[0053] [Table 1] In Examples 1 and 2, Li (1-x) Nb (1+y) The secondary battery 1 has a first layer 11 formed of LiNbO3, that is, LiNbO3 having defects in Li. Examples 1 and 2 differ from each other in the size of the defects in Li. Example 2 has larger defects in Li than Example 1.

[0054] The Li forming the first layer 11 in the secondary battery 1 of Examples 1 and 2 (1-x) Nb (1+y)O3 was produced by the following procedure. Li2CO3 manufactured by Honjo Chemical Co., Ltd. and Nb2O5 manufactured by Toshima Manufacturing Co., Ltd. were mixed by hand and formed into a disk shape with a diameter of 10 mm and a thickness of 5 mm. In Example 1, 0.68 g of Li2CO3 and 2.72 g of Nb2O3 were weighed out so that the molar ratio of Li:Nb was 1:1.08. In Example 2, 0.64 g of Li2CO3 and 2.73 g of Nb2O5 were weighed out so that the molar ratio of Li:Nb was 1:1.174. The mixture was then fired in air for 4 hours using an electric furnace. The firing temperature was 1000°C in Example 1 and 800°C in Example 2.

[0055] Example 3 is LiNbO (3-z) In other words, the secondary battery 1 has a first layer 11 formed of LiNbO3 having defects in O. (3-z) was obtained by heat treating LiNbO3 manufactured by Toshima Manufacturing Co., Ltd. in a reducing atmosphere of Ar:H2=30cc:70cc at a temperature of 1000°C for 4 hours.

[0056] Example 4 is Li (1-x) Nb (1+y) O (3-z) In other words, the secondary battery 1 has a first layer 11 formed of LiNbO3 having random defects in both Li and O on the surface. Regarding Example 4, it is unclear how many defects the LiNbO3 has. (1-x) Nb (1+y) O (3-z) was obtained by grinding LiNbO3 manufactured by Toshima Manufacturing Co., Ltd. for 5 hours at a rotation speed of 500 rpm using a planetary ball mill.

[0057] The comparative example is a secondary battery 1 in which the first layer 11 is formed of defect-free LiNbO3. The LiNbO3 forming the first layer 11 in the comparative example secondary battery 1 is LiNbO3 manufactured by Toshima Manufacturing Co., Ltd.

[0058] (Comparison of Examples 1 and 2 with Comparative Example) FIG. 6 is a diagram comparing the first layer 11 of Examples 1 and 2 and the Comparative Example. Reference numeral 601 is a graph showing the results of XRD (X-ray diffraction) analysis of Examples 1 and 2 and the Comparative Example. In Reference numeral 601, the horizontal axis represents angle, and the vertical axis represents the intensity of reflected light. In Reference numeral 601, graph 601a represents Example 1, graph 601b represents Example 2, and graph 601c represents the Comparative Example. In the XRD analysis, no significant difference was observed between Examples 1 and 2 and the Comparative Example.

[0059] In particular, all of the peaks attributable to the trigonal space group R3c, which is the crystal structure of LiNbO3, were confirmed in all of graphs 601a to 601c. From this, it can be said that it was confirmed that the atoms constituting LiNbO3 were in solid solution with each other in all of Examples 1 and 2 and the Comparative Example.

[0060] Reference numeral 602 is a graph showing the lattice distances of Examples 1 and 2 and the comparative example. In reference numeral 602, the horizontal axis indicates the type of the comparative example and Examples 1 and 2, and the vertical axis indicates the lattice distance. Generally, LiNbO3 crystals have a rectangular parallelepiped shape with a square base. In reference numeral 602, the vertical axis on the left indicates the lattice distance in the direction along each side of the base of the crystal. Also, the vertical axis on the right indicates the lattice distance in the height direction of the crystal. In reference numeral 602, graph 602a indicates the lattice distance in the direction along each side of the base of the crystal. Also, graph 602b indicates the lattice distance in the height direction of the crystal.

[0061] As shown by reference numeral 602, the lattice spacing was different from that of the comparative example in both Examples 1 and 2. Specifically, the lattice spacing was smallest in the comparative example, followed by Examples 1 and 2 in the order of increasing in both the direction along each side of the base of the crystal and the height direction.

[0062] Reference numeral 603 indicates the results of CL (Cathod Luminescence) measurements for Examples 1 and 2 and the Comparative Example. In Reference numeral 603, the horizontal axis indicates wavelength, and the vertical axis indicates the measured light intensity. In Reference numeral 603, graph 603a indicates Example 1, graph 603b indicates Example 2, and graph 603c indicates the Comparative Example.

[0063] In CL measurements, LiNbO3 has a peak near 480 nm. As the intensity of this peak decreases, it indicates that the number of O defects decreases and the number of non-luminescent defects increases. Non-luminescent defects are, for example, Li defects. The peak intensity near 480 nm in graphs 603a and 603b is significantly lower than the peak intensity near 480 nm in graph 603c. The measurement results suggest that the number of Li defects is higher in Example 1 and Example 2 than in the comparative example.

[0064] (Comparison between Example 3 and Comparative Example) FIG. 7 is a diagram comparing the first layer 11 of Example 3 and the comparative example. Reference numeral 701 is a graph showing the results of XRD analysis of Example 3 and the comparative example. In reference numeral 701, the horizontal axis represents angle, and the vertical axis represents the intensity of reflected light. In reference numeral 701, graph 701a represents Example 1, and graph 701b represents the comparative example. In the XRD analysis, no significant difference was observed between Example 3 and the comparative example.

[0065] In particular, all peaks belonging to the trigonal space group R3c, which is the crystal structure of LiNbO3, were confirmed in graph 701a as in graphs 601a to 601c in Fig. 6. From this, it can be said that it was confirmed that the atoms constituting LiNbO3 were in solid solution with each other in Example 3 as well.

[0066] Reference numeral 702 is a graph showing the lattice distances of Example 3 and Comparative Example. In reference numeral 702, the horizontal axis indicates the type of Comparative Example and Example 3. The vertical axis on the left indicates the lattice distance in the direction along each side of the bottom surface of the crystal. The vertical axis on the right indicates the lattice distance in the height direction of the crystal.

[0067] In the graph 702, graph 702a shows the interlattice distance in the direction along each side of the bottom surface of the crystal. Graph 702b shows the interlattice distance in the height direction of the crystal. As shown by the reference numeral 702, the interlattice distance in Example 3 was also different from that in the comparative example. Specifically, the interlattice distance in the direction along each side of the bottom surface of the crystal was smaller in Example 3 than in the comparative example. On the other hand, the interlattice distance in the height direction of the crystal was larger in Example 3 than in the comparative example.

[0068] Reference numeral 703 indicates the results of CL measurements for Example 3 and the Comparative Example. In Reference numeral 703, the horizontal axis indicates wavelength and the vertical axis indicates the measured light intensity. In Reference numeral 703, graph 703a indicates Example 3, and graph 703b indicates the Comparative Example.

[0069] As described above, in the CL measurement, LiNbO3 has a peak near 480 nm. As the intensity of this peak increases, it indicates that the number of O defects increases and the number of non-luminescent defects decreases. The peak intensity near 480 nm in graph 703a is significantly higher than the peak intensity near 480 nm in graph 703b. This measurement result suggests that the number of O defects is increased in Example 3 compared to the comparative example.

[0070] (Comparison between Example 4 and Comparative Example) FIG. 8 is a diagram comparing the first layer 11 of Example 4 and the comparative example. Reference numeral 801 is a graph showing the results of XRD analysis of Example 3 and the comparative example. In reference numeral 801, the horizontal axis represents angle, and the vertical axis represents the intensity of reflected light. In reference numeral 801, graph 801a represents Example 4, and graph 801b represents the comparative example. In the XRD analysis, no significant difference was observed between Example 4 and the comparative example.

[0071] In particular, all peaks belonging to the trigonal space group R3c, which is the crystal structure of LiNbO3, were confirmed in graph 801a as in graphs 601a to 601c in Fig. 6. From this, it can be said that in Example 4, there was no change in the crystal structure due to milling, and it was confirmed that the crystal structure was the same as that of LiNbO3 belonging to the trigonal space group R3c.

[0072] Reference numeral 802 is a graph showing the lattice distances of Example 4 and Comparative Example. In reference numeral 802, the horizontal axis indicates the type of Comparative Example and Example 4. The vertical axis on the left indicates the lattice distance in the direction along each side of the bottom surface of the crystal. The vertical axis on the right indicates the lattice distance in the height direction of the crystal.

[0073] In the graph 802, graph 802a shows the interlattice distance in the direction along each side of the base of the crystal. Graph 802b shows the interlattice distance in the height direction of the crystal. As shown by the reference numeral 802, the interlattice distance in Example 4 was also different from that in the comparative example. Specifically, the interlattice distance in Example 4 was smaller than that in the comparative example in both the direction along each side of the base of the crystal and the height direction.

[0074] Reference numeral 803 shows the results of CL measurements for Example 4 and the Comparative Example. In Reference numeral 803, the horizontal axis represents wavelength and the vertical axis represents the measured light intensity. In Reference numeral 803, graph 803a represents Example 4, and graph 803b represents the Comparative Example.

[0075] The peak intensity near 480 nm in graph 803a was lower than the peak intensity near 480 nm in graph 80b. The measurement results suggest that the number of Li defects in Example 4 was increased compared to the comparative example. However, the degree of decrease in the peak intensity near 480 nm in Example 4 was smaller than the degree of decrease in the peak intensity near 480 nm in Examples 1 and 2. This is thought to be because the number of O defects also increased in Example 4, and the increase in peak intensity due to the increase in O defects alleviated the decrease in peak intensity due to the increase in Li defects.

[0076] (IR drop and battery capacity evaluation) The IR drop of the secondary batteries 1 of Examples 1 to 4 and the comparative example was evaluated by a constant current charge / discharge test. Specifically, each secondary battery 1 was charged at a current value of 1 μA for 5 minutes, and then OCV measurement was performed for 5 minutes. The secondary battery 1 was then discharged at a current value of 1 μA until the output voltage reached 0 V to check its operation. If the secondary battery 1 does not function as a battery, i.e., if no current flows, the voltage drops to 0 V in an extremely short time, such as less than 1 second, from the start of discharge after OCV measurement. If discharging continues for, for example, 10 minutes or more, it can be said that the secondary battery functioned as a battery. In a series of charge / discharge cycles, the difference between the voltage at the end of charging and the voltage at the end of OCV measurement was taken as the IR drop value.

[0077] Furthermore, the battery capacity of the secondary batteries 1 of Examples 1 to 4 and Comparative Example was evaluated by a constant voltage charge / discharge test. Specifically, each secondary battery 1 was charged for 10 minutes at a voltage value of 4 V, and then OCV measurement was performed for 10 minutes. Thereafter, the secondary battery 1 was discharged at a current value of 1 μA until the output voltage reached 0 V. In a series of charge / discharge operations, the capacity of the secondary battery 1 was calculated using the time from the start of discharge until the output voltage reached 0 V.

[0078] As shown in Table 1, in all of Examples 1 to 4, the IR drop was reduced compared to the comparative example. In particular, in Example 2, the IR drop was significantly reduced compared to the other Examples. Furthermore, in all of Examples 1 to 4, the battery capacity was increased compared to the comparative example.

[0079] (Effect of secondary batteries) As described above, the secondary battery 1 has a smaller IR drop than when the first layer 11 is made of, for example, LiNbO3, which does not have defects in its crystal structure. In other words, the capacity loss due to self-discharge is reduced. Therefore, the secondary battery 1 can be realized as a secondary battery that can be charged and discharged using a new mechanism.

[0080] Furthermore, the above-described effects of the secondary battery 1 can also be said to improve the energy efficiency of the secondary battery 1. Such effects will contribute to achieving, for example, Goal 7 of the Sustainable Development Goals (SDGs) advocated by the United Nations, "Affordable and clean energy."

[0081] (Variation 1) Fig. 9 is a schematic diagram showing modified shapes of the first layer 11 and the second layer 21 of the secondary battery 1. In Fig. 9, different modified shapes of the first layer 11 and the second layer 21 are indicated by reference numerals 901, 902, and 903.

[0082] 1, the first layer 11 is formed larger than the second layer 21 in the direction along the interface between the first layer 11 and the second layer 21. However, in the secondary battery 1, the first layer 11 and the second layer 21 may be formed to have the same size, as indicated by reference numeral 901. Alternatively, the second layer 21 may be formed larger than the first layer 11, as indicated by reference numeral 902.

[0083] 1, the first layer 11 and the second layer 21 are formed to have the same thickness. However, in the secondary battery 1, the second layer 21 may be formed to be thicker than the first layer 11, as indicated by the reference numeral 903.

[0084] (Variation 2) Fig. 10 is a schematic diagram showing modified examples of the interface between the first layer 11 and the second layer 21 of the secondary battery 1. In Fig. 10, different modified examples of the interface between the first layer 11 and the second layer 21 are indicated by reference numerals 1001, 1002, 1003, and 1004.

[0085] As described above, in the secondary battery 1, the capacity can be increased by increasing the contact area between the first layer 11 and the second layer 21. For example, as indicated by reference numeral 1001, the interface between the first layer 11 and the second layer 21 may not be smooth but may have irregularities. As indicated by reference numeral 1002, a portion of the second layer 21 may be embedded in the first layer 11 to the extent that the first layer 11 does not contact the negative electrode current collector foil 22. As indicated by reference numeral 1003, a portion of the first layer 11 may be embedded in the second layer 21 to the extent that the second layer 21 does not contact the positive electrode current collector foil 12. As indicated by reference numeral 1004, the first layer 11 and the second layer 21 may not be rectangular parallelepipeds, and the interface may be inclined with respect to the positive electrode current collector foil 12 and the negative electrode current collector foil 22.

[0086] (Variation 3) Fig. 11 is a schematic diagram showing a second modified example of the region where the first layer 11 and the second layer 21 face each other in the secondary battery 1. In Fig. 11, different modified examples of the region where the first layer 11 and the second layer 21 face each other are indicated by reference numerals 1101 and 1102.

[0087] As described above, in the secondary battery 1, the capacity can be increased by increasing the contact area between the first layer 11 and the second layer 21. However, the entire area where the first layer 11 and the second layer 21 face each other does not necessarily need to be in contact with each other. For example, as indicated by reference numeral 1101, a cavity 41 may be formed in at least a part of the area where the first layer 11 and the second layer 21 face each other. Furthermore, as indicated by reference numeral 1102, a buried layer 42 made of a material different from the first layer 11 and the second layer 21 may be buried in at least a part of the area where the first layer 11 and the second layer 21 face each other.

[0088] [Embodiment 2] In the first embodiment, the secondary battery 1 includes only one pair of the first layer 11 and the second layer 21. However, the secondary battery 1 may include a plurality of pairs of the first layer 11 and the second layer 21.

[0089] FIG. 12 is a schematic diagram showing an example of a secondary battery 2 according to embodiment 2. As shown in FIG. 12, the secondary battery 2 may include two pairs of a first layer 11 and a second layer 21. The two first layers 11 may be electrically connected to each other. The two second layers 21 may be electrically connected to each other. Furthermore, the secondary battery 2 may include three or more pairs of a first layer 11 and a second layer 21. In addition to the effects of the secondary battery 1 according to embodiment 1, such a secondary battery 1 further achieves the effect of improving the capacity of the secondary battery 1 compared to a battery including only one pair of a first layer 11 and a second layer 21.

[0090] In this case, the secondary battery 1 may include the same number of positive electrode current collector foils 12 as the plurality of first layers 11, and the same number of negative electrode current collector foils 22 as the plurality of second layers 21. Alternatively, at least two first layers 11 may share a single positive electrode current collector foil 12, and at least two second layers 21 may share a single negative electrode current collector foil 22.

[0091] (Variation) Fig. 13 is a schematic diagram showing modified examples of the secondary battery 2. In Fig. 13, different modified examples of the secondary battery 2 are indicated by reference numerals 1301, 1302, 1303, and 1304.

[0092] In the secondary battery 2, as indicated by reference numeral 1301, a plurality of first layers 11 and second layers 21 may be alternately positioned between the positive electrode current collector foil 12 and the negative electrode current collector foil 22.

[0093] In the secondary battery 2 shown at 1301, the secondary battery 2 has two first layers 11 and two second layers 21. However, the secondary battery 2 may have three or more first layers 11 and two or more second layers 21.

[0094] Furthermore, as indicated by reference numeral 1302 , a plurality of first layers 11 and second layers 21 may be present between the positive electrode current collector foil 12 and the negative electrode current collector foil 22 .

[0095] The secondary battery 2 may further include an intermediate current collector foil 50 in contact with both the first layer 11 and the second layer 21. For example, as indicated by reference numeral 1303, the positive current collector foil 12, the first layer 11, the second layer 21, the intermediate current collector foil 50, the first layer 11, the second layer 21, and the negative current collector foil 22 may be arranged in this order and in contact with one another. The material of the intermediate current collector foil 50 may be, for example, stainless steel (SUS), Cu, or Al, but is not limited to these. The material of the intermediate current collector foil 50 may be the same as or different from the material of the positive current collector foil 12 and the negative current collector foil 22. When the secondary battery 2 includes the intermediate current collector foil 50, the electrical connection between the positive current collector foil 12 and the negative current collector foil 22 is improved compared to when the secondary battery 2 does not include the intermediate current collector foil 50.

[0096] Alternatively, as indicated by reference numeral 1304, the first layer 11, the second layer 21, and the negative electrode current collector foil 22 may be positioned in this order on both sides of the positive electrode current collector foil 12 in contact with each other.

[0097] [Embodiment 3] 14 is a schematic diagram showing an outline of a secondary battery 3 according to embodiment 3. As shown in FIG. 14, the secondary battery 3 differs from the secondary battery 1 in that the second layer 21 is replaced by a second layer 21A.

[0098] The second layer 21A may contain the same type of semiconductor as the semiconductor contained in the second layer 21. The second layer 21A may further contain a solid electrolyte. The type of solid electrolyte contained in the second layer 21 may be the same as or different from the solid electrolyte contained in the first layer 11.

[0099] In the secondary battery 3, the contact area between the solid electrolyte and the semiconductor can be increased compared to the secondary battery 1. At this time, ion segregation and carrier accumulation occur at the boundary between the first layer 11 and the second layer 21A, as well as at the individual grain boundaries between the solid electrolyte and the semiconductor. Therefore, the capacity of the secondary battery 3 is increased compared to the secondary battery 1.

[0100] As described in the second embodiment, the secondary battery 3 may have a plurality of pairs of the first layer 11 and the second layer 21A. This further increases the capacity of the secondary battery 3 compared to the secondary battery 2.

[0101] The present disclosure is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present disclosure. [Explanation of symbols]

[0102] 1,2,3 Secondary battery 10 positive electrode 11 1st layer 20 negative electrode 21,21A 2nd layer

Claims

1. a positive electrode having a first layer including a solid electrolyte; a negative electrode having a second layer including a semiconductor; the first layer and the second layer are in contact with each other; The first layer is Li （１－ｘ） Nb （１＋ｙ） O （３－ｚ） A secondary battery comprising a material represented by the formula:

2. 2. The secondary battery according to claim 1, wherein 0<x≦0.2 and 0<y≦0.

05.

3. 3. The secondary battery according to claim 1, wherein 0<z≦0.

5.

4. 2. The secondary battery according to claim 1, wherein 0<x≦0.5, −0.5≦y<0, and 0<z≦1.

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