Battery

Abstract

This battery comprises a first electrode, a second electrode, and an electrolyte solution. The first electrode includes a current collector and an active substance layer. The active substance layer contains BiNi. The BiNi has a crystal structure where the space group is attributed to C2 / m.

Description

[Technical Field]

[0001] This disclosure relates to batteries. [Background technology]

[0002] In recent years, research and development of lithium-ion secondary batteries has been actively pursued. The type of electrodes used significantly influences battery characteristics such as charge / discharge voltage, charge / discharge cycle life, and storage characteristics. Therefore, efforts are being made to improve battery characteristics by improving the electrode active materials.

[0003] For example, lithium secondary batteries that use aluminum, silicon, tin, etc., which electrochemically alloy with lithium during charging, as electrodes have been proposed for a long time. Patent Document 1 discloses a lithium secondary battery comprising a negative electrode, a positive electrode, and an electrolyte, the negative electrode material being made of an alloy having silicon, tin, and a transition metal.

[0004] Patent Document 2 discloses a lithium secondary battery comprising a negative electrode, a positive electrode, and an electrolyte, the negative electrode being a silicon thin film provided on a current collector as an active material.

[0005] Bismuth (Bi) is an example of a metal that alloys with lithium. Non-patent document 1 discloses a negative electrode containing Bi as the negative electrode active material, which is made using Bi powder. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent No. 4898737 [Patent Document 2] Patent No. 3733065 [Non-patent literature]

[0007] [Non-Patent Document 1] Synthesis and Electrochemical Properties of Amorphous Polymer Anode Active Material for Lithium Batteries Composed of Reaction Products of Polyacrylic Acid and Metal Oxides, by Hiroyuki Yamaguchi, Doctoral Thesis, Tohoku University, 2015

Summary of the Invention

Problems to be Solved by the Invention

[0008] This disclosure provides a battery having improved cycle characteristics.

Means for Solving the Problems

[0009] The battery of this disclosure comprises a first electrode, a second electrode, an electrolyte, and the first electrode has a current collector and an active material layer, the active material layer contains BiNi, the BiNi has a crystal structure belonging to the space group C2 / m.

Effects of the Invention

[0010] According to this disclosure, a battery having improved cycle characteristics can be provided.

Brief Description of the Drawings

[0011] [Figure 1] FIG. 1 is a cross-sectional view schematically showing a configuration example of a battery according to an embodiment of this disclosure. [Figure 2] FIG. 2 is a graph showing an example of an X-ray diffraction pattern of an active material layer composed of a BiNi thin film formed on a nickel foil. [Figure 3A] FIG. 3A is a graph showing the results of an initial charge-discharge test of a test cell according to Example 1-1. [Figure 3B] FIG. 3B is a graph showing the results of a second charge-discharge test of a test cell according to Example 1-1. [Figure 4A] FIG. 4A is a graph showing the results of an initial charge-discharge test of a test cell according to Example 1-2. [Figure 4B] Figure 4B is a graph showing the results of the second charge-discharge test of the test cell according to Example 1-2. [Figure 5A] Figure 5A is a graph showing the results of the initial charge-discharge tests of the test cells according to Examples 1-3. [Figure 5B] Figure 5B is a graph showing the results of the second charge-discharge test of the test cells according to Examples 1-3. [Figure 6A] Figure 6A is a graph showing the results of the initial charge-discharge tests of the test cells according to Examples 1-4. [Figure 6B] Figure 6B is a graph showing the results of the second charge-discharge test of the test cells according to Examples 1-4. [Figure 7A] Figure 7A is a graph showing the results of the initial charge-discharge tests of the test cells according to Examples 1-5. [Figure 7B] Figure 7B is a graph showing the results of the second charge-discharge test of the test cells according to Examples 1-5. [Figure 8A] Figure 8A is a graph showing the results of the initial charge-discharge tests of the test cells according to Examples 1-6. [Figure 8B] Figure 8B is a graph showing the results of the second charge-discharge test of the test cells according to Examples 1-6. [Figure 9A] Figure 9A is a graph showing the results of the initial charge-discharge tests of the test cells according to Examples 1-7. [Figure 9B] Figure 9B is a graph showing the results of the second charge-discharge test of the test cell according to Example 1-7. [Figure 10A] Figure 10A is a graph showing the results of the initial charge-discharge tests of the test cells according to Examples 1-8. [Figure 10B] Figure 10B is a graph showing the results of the second charge-discharge test of the test cell according to Example 1-8. [Figure 11A] Figure 11A is a graph showing the results of the initial charge-discharge tests of the test cells according to Examples 1-9. [Figure 11B] Figure 11B is a graph showing the results of the second charge-discharge test of the test cells according to Examples 1-9. [Figure 12A] Figure 12A is a graph showing the results of the initial charge-discharge tests of the test cells according to Examples 1-10. [Figure 12B] Figure 12B is a graph showing the results of the second charge-discharge test of the test cell according to Example 1-10. [Figure 13] Figure 13 is a graph showing the results of the initial charge-discharge tests of the test cells according to Examples 1-11. [Figure 14] Figure 14 is a graph showing the results of the initial charge-discharge tests of the test cells according to Examples 1-12. [Figure 15] Figure 15 is a graph showing the relationship between the number of cycles and the discharge capacity density of the test cells related to Examples 1-1 to 1-8. [Figure 16] Figure 16 is a graph showing the relationship between the number of cycles and the discharge capacity density of the test cells for Examples 1-1 to 1-4. [Figure 17] Figure 17 is a graph showing the relationship between the number of cycles and the discharge capacity density of the test cells related to Examples 1-1 and 1-9. [Figure 18] Figure 18 is a graph showing the relationship between the number of cycles and the discharge capacity density of the test cells according to Examples 1-10. [Figure 19] Figure 19 is a graph showing the relationship between the number of cycles and the discharge capacity density of the test cells in Examples 1-11 and 1-12. [Figure 20] Figure 20 is a graph showing the X-ray diffraction pattern of the active material layer composed of a BiNi thin film fabricated on nickel foil in Example 2. [Figure 21A] Figure 21A is a graph showing the results of the initial charge-discharge test of the test cell according to Example 2. [Figure 21B] Figure 21B is a graph showing the results of the second charge-discharge test of the test cell according to Example 2. [Figure 22] Figure 22 is a graph showing the relationship between the number of cycles and the discharge capacity density of the test cells in Examples 2 and 3. [Figure 23]Figure 23 is a graph showing the X-ray diffraction pattern of the active material layer composed of a BiNi thin film fabricated on nickel foil in Example 3. [Figure 24A] Figure 24A is a graph showing the results of the initial charge-discharge test of the test cell according to Example 3. [Figure 24B] Figure 24B is a graph showing the results of the second charge-discharge test of the test cell according to Example 3. [Figure 25] Figure 25 is a graph showing an example of the X-ray diffraction patterns of the active material layer in the test cell according to Example 1-1 before charging, after charging, and after discharging. [Figure 26] Figure 26 is a photograph of the first electrode in Example 1-1 after 500 charge-discharge cycles. [Figure 27] Figure 27 is a graph showing the X-ray diffraction pattern of BiNi powder prepared from the powder raw material in Example 4. [Figure 28A] Figure 28A is a graph showing the results of the initial charge-discharge test of the test cell according to Example 4-1. [Figure 28B] Figure 28B is a graph showing the results of the second charge-discharge test of the test cell according to Example 4-1. [Figure 29A] Figure 29A is a graph showing the results of the initial charge-discharge test of the test cell according to Example 4-2. [Figure 29B] Figure 29B is a graph showing the results of the second charge-discharge test of the test cell according to Example 4-2. [Figure 30] Figure 30 is a graph showing the relationship between the number of cycles up to 50 and the discharge capacity density for the test cells according to Examples 4-1 and 4-2. [Figure 31] Figure 31 is a graph showing the relationship between the number of cycles up to 10 and the discharge capacity density for the test cells according to Examples 4-1 and 4-2. [Figure 32A] Figure 32A is a graph showing the results of the initial charge-discharge test of the test cell related to Reference Example 1. [Figure 32B] Figure 32B is a graph showing the results of the second charge-discharge test of the test cell related to Reference Example 1. [Figure 33] Figure 33 is a graph showing the relationship between the number of cycles and the discharge capacity density of the test cell related to Reference Example 1. [Figure 34A] Figure 34A is a graph showing the results of the initial charge-discharge test of the test cell related to Comparative Example 1. [Figure 34B] Figure 34B is a graph showing the results of the second charge-discharge test of the test cell related to Comparative Example 1. [Figure 35] Figure 35 is a graph showing the relationship between the number of cycles up to 10 and the discharge capacity density for the test cell related to Comparative Example 1. [Modes for carrying out the invention]

[0012] (Knowledge that forms the basis of this disclosure) As described in the [Background Technology] section, improvements in lithium secondary batteries are being made to battery characteristics by improving the electrode active material.

[0013] When lithium metal is used as the negative electrode active material, a lithium secondary battery with high energy density per unit weight and per unit volume can be obtained. However, in lithium secondary batteries with this configuration, lithium deposits in a dendrite-like manner during charging. Because some of the deposited lithium metal reacts with the electrolyte, there is a problem of low charge-discharge efficiency and poor cycle characteristics.

[0014] In response to this, the use of carbon, particularly graphite, as the negative electrode has been proposed. In a negative electrode using carbon, charging and discharging occur through the insertion and removal of lithium from the carbon. In a negative electrode with such a configuration, lithium metal does not precipitate in a dendrite-like manner due to the charge-discharge mechanism. Furthermore, in lithium secondary batteries employing a negative electrode with such a configuration, the reaction is topotactic, resulting in excellent reversibility and nearly 100% charge-discharge efficiency. For these reasons, lithium secondary batteries employing negative electrodes made of carbon, particularly graphite, have been put into practical use. However, the theoretical capacity density of graphite is 372 mAh / g, which is about 1 / 10 of the theoretical capacity density of lithium metal, which is 3884 mAh / g. Therefore, the active material capacity density of a negative electrode using graphite is low. Moreover, since the actual capacity density of graphite has almost reached its theoretical capacity density, there is a limit to how high a capacity can be achieved with a negative electrode using graphite.

[0015] In response to these issues, lithium-ion secondary batteries using aluminum, silicon, tin, etc., which electrochemically alloy with lithium during charging, have long been proposed. The capacity density of metals that alloy with lithium is significantly higher than that of graphite. In particular, the theoretical capacity density of silicon is high. Therefore, electrodes using aluminum, silicon, tin, etc., which alloy with lithium, are promising as negative electrodes for batteries exhibiting high capacity, and various secondary batteries using these as negative electrodes have been proposed (Patent Document 1).

[0016] However, negative electrodes using metals that alloy with lithium, as described above, expand when they absorb lithium and contract when they release lithium. When such expansion and contraction are repeated during charging and discharging, the alloy itself, which is the electrode active material, becomes pulverized by charging and discharging, degrading the current collection characteristics of the negative electrode, and thus sufficient cycle characteristics have not been obtained. Several attempts have been made to improve these shortcomings. For example, attempts have been made to deposit silicon on a roughened current collector by sputtering or vapor deposition, or to deposit tin by electroplating (Patent Document 2). In this attempt, the active material, i.e., the metal that alloys with lithium, is in close contact with the current collector as a thin film, so even when the negative electrode repeatedly expands and contracts due to the absorption and release of lithium, the current collection performance hardly deteriorates.

[0017] However, as mentioned above, forming the active material by sputtering or vapor deposition results in high manufacturing costs, making it impractical. Forming the active material by electroplating, which is inexpensive, is more practical, but silicon is extremely difficult to electroplat. Furthermore, tin, which is easily electroplated, has poor discharge flatness, making it unsuitable for use as a battery electrode.

[0018] Another metal that alloys with lithium is bismuth (Bi). Bi forms compounds called LiBi and Li3Bi with lithium (Li). The potentials of LiBi and Li3Bi are almost the same. On the other hand, tin, which has poor discharge flatness, forms several types of compounds with lithium, and the potentials of each compound are quite different from each other. In other words, Bi does not have the property of having a large difference in potential between the multiple types of compounds it forms with lithium, as tin does. For this reason, electrodes containing Bi as an active material have a flat potential and therefore excellent discharge flatness. Consequently, electrodes containing Bi as an active material are considered suitable as electrodes for batteries.

[0019] However, Bi has poor malleability and ductility, making it difficult to manufacture in the form of metal sheets or foils, and the resulting form is small spheres or powder. For this reason, electrodes containing Bi as an active material have been investigated that are manufactured by coating Bi powder onto a current collector. However, electrodes manufactured using such Bi powder have not been able to obtain sufficient cycle characteristics because they become pulverized after repeated charging and discharging, resulting in deterioration of current collection characteristics. For example, Non-Patent Literature 1 describes the manufacture of an electrode containing Bi as an active material using Bi powder and PVdF (polyvinylidene fluoride) or PI (polyimide) as a binder. Non-Patent Literature 1 describes the charging and discharging of a battery manufactured using this electrode. However, the results of the initial charge-discharge curve and cycle characteristics of the manufactured electrode are both very poor. Although measured at a very low rate equivalent to 0.042C, the initial charge-discharge efficiency is low and the cycle degradation is severe, making it unsuitable for practical use. Regarding this cyclic degradation, Non-Patent Literature 1 suggests that as the Bi active material expands during Li insertion and contracts during Li desorption, the active material becomes smaller, preventing electron conduction paths from being formed, and thus a decrease in capacity occurs.

[0020] As described above, the inventors focused on Bi, which does not exhibit a large difference in potential between the various compounds formed with Li and has excellent discharge flatness, and diligently investigated batteries that could improve cycle characteristics. As a result, the inventors discovered a new technological concept in which the cycle characteristics of a battery can be improved when BiNi having a specific crystal structure, specifically a crystal structure in which the space group belongs to C2 / m, is used as the active material, and have completed this disclosure.

[0021] (Summary of one aspect of this disclosure) The battery relating to the first aspect of this disclosure is First electrode and The second electrode and Electrolyte and Equipped with, The first electrode comprises a current collector and an active material layer. The active material layer contains BiNi, The BiNi material has a crystal structure whose space group belongs to C2 / m.

[0022] The battery according to the first embodiment comprises electrodes containing BiNi as an active material, having a crystal structure whose space group belongs to C2 / m. Therefore, the battery according to the first embodiment has improved cycle characteristics.

[0023] In the second embodiment, for example, in the battery according to the first embodiment, when the height intensity of the maximum peak located in the diffraction angle 2θ range of 29° to 31° is defined as I(1) and the height intensity of the maximum peak located in the diffraction angle 2θ range of 41° to 43° is defined as I(2), the ratio of I(2) to I(1), I(2) / I(1), may be 0.28 or less.

[0024] The battery according to the second embodiment has high initial efficiency and improved cycle characteristics.

[0025] In a third aspect of this disclosure, for example, in a battery of the first or second aspect, the active material layer may include at least one selected from the group consisting of LiBi and Li3Bi.

[0026] The battery according to the third embodiment has improved capacity and improved cycle characteristics.

[0027] In a fourth aspect of this disclosure, for example, in a battery according to any one of the first to third aspects, the active material layer may not contain a solid electrolyte.

[0028] According to the fourth embodiment, a battery is obtained that has a higher capacity per unit volume and improved cycle characteristics.

[0029] In a fifth aspect of this disclosure, for example, in a battery according to any one of the first to fourth aspects, the active material layer may contain BiNi as the main component of the active material.

[0030] According to the fifth embodiment, it has improved capacity and improved cycle characteristics.

[0031] In a sixth aspect of this disclosure, for example, in the battery according to the fifth aspect, the active material layer may contain substantially only BiNi as the active material.

[0032] According to the sixth embodiment, it has improved capacity and improved cycle characteristics.

[0033] In a seventh aspect of this disclosure, for example, in a battery according to any one of the first to sixth aspects, the current collector may contain Ni.

[0034] The battery according to the seventh embodiment has improved capacity and improved cycle characteristics.

[0035] In the eighth aspect of this disclosure, for example, in a battery according to any one of the first to seventh aspects, the active material layer may be a heat-treated plated layer.

[0036] According to the eighth aspect, a battery is obtained that has a higher capacity per unit volume and improved cycle characteristics.

[0037] In the ninth aspect of this disclosure, for example, in a battery according to any one of the first to eighth aspects, the electrolyte may include an aprotic solvent and a lithium salt dissolved in the aprotic solvent.

[0038] The battery according to the ninth embodiment can realize a lithium-ion battery having improved capacity and improved cycle characteristics.

[0039] In a tenth aspect of this disclosure, for example, in the battery according to the ninth aspect, the aprotic solvent may include at least one selected from the group consisting of vinylene carbonate, 2-methyltetrahydrofuran, fluoroethylene carbonate, and ethylene carbonate.

[0040] The battery according to the tenth embodiment has improved capacity and improved cycle characteristics.

[0041] In the eleventh aspect of this disclosure, for example, in the battery according to the ninth aspect, the aprotic solvent may include vinylene carbonate and a linear carbonate.

[0042] The battery according to the 11th embodiment has improved cycle characteristics.

[0043] In a twelfth aspect of this disclosure, for example, in a battery according to any one of the first to eleventh aspects, the first electrode may be a negative electrode and the second electrode may be a positive electrode.

[0044] The battery according to the 12th embodiment has improved capacity and improved cycle characteristics.

[0045] (Embodiments of the present disclosure) Embodiments of this disclosure will be described below with reference to the drawings. The following descriptions are general or specific examples. The numerical values, compositions, shapes, film thicknesses, electrical properties, and secondary battery structures shown below are examples and are not intended to limit this disclosure.

[0046] Figure 1 is a schematic cross-sectional view showing an example of the configuration of a battery 1000 according to an embodiment of this disclosure.

[0047] The battery 1000 comprises a first electrode 101, a second electrode 103, and an electrolyte 102. The first electrode 101 has a current collector 100 and an active material layer 104. The active material layer 104 contains BiNi. This BiNi has a monoclinic crystal structure whose space group is assigned to C2 / m.

[0048] The battery 1000 further comprises, for example, a separator 107 and an outer casing 108. The separator 107 is positioned between the first electrode 101 and the second electrode 103. The first electrode 101 and the second electrode 103 face each other through the separator 107. The first electrode 101, the second electrode 103, the separator 107, and the electrolyte 102 are housed in the outer casing 108. The electrolyte 102 is, for example, an electrolyte impregnated into the first electrode 101, the second electrode 103, and the separator 107. The electrolyte 102 may fill the internal space of the outer casing 108.

[0049] In battery 1000, the active material layer 104 contains BiNi as the active material, which has a monoclinic crystal structure with a space group assigned to C2 / m. By using BiNi as the active material, the problems of pulverization and side reactions with the electrolyte during charging and discharging of Bi active materials formed using Bi powder are solved. Therefore, the reduction of electron conduction pathways within the active material layer 104 due to repeated charging and discharging is suppressed. As a result, battery 1000 has improved cycle characteristics.

[0050] Battery 1000 is, for example, a lithium secondary battery. The following explanation of the features of this technology is based on the example where the metal ions intercepted and released in the active material layer 104 of the first electrode 101 and the second electrode 103 during charging and discharging of battery 1000 are lithium ions.

[0051] The active material layer 104 may contain BiNi as its main component. Here, "the active material layer 104 contains BiNi as its main component" is defined as "the BiNi content in the active material layer 104 is 50% by mass or more." The BiNi content in the active material layer 104 can be determined, for example, by confirming that Bi and Ni are present in the active material layer 104 through elemental analysis by EDX (energy-dispersive X-ray spectroscopy), and then calculating the ratio of the compounds contained by performing Rietveld analysis on the X-ray diffraction results of the active material layer 104.

[0052] With the above configuration, improved charge-discharge cycle characteristics can be obtained.

[0053] The active material layer 104, which mainly contains BiNi, may be composed of, for example, BiNi formed in the form of a thin film (hereinafter referred to as "BiNi thin film").

[0054] In the X-ray diffraction pattern of the active material layer 104 obtained by surface X-ray diffraction measurement using Cu-Kα rays, when the height intensity of the maximum peak located in the diffraction angle 2θ range of 29° to 31° is defined as I(1), and the height intensity of the maximum peak located in the diffraction angle 2θ range of 41° to 43° is defined as I(2), the ratio of I(2) to I(1), I(2) / I(1), may be 0.28 or less.

[0055] Here, the maximum peak in the X-ray diffraction pattern within the diffraction angle range of 2θ from 29° to 31° corresponds to the peak originating from the (2,2,1) plane of the intermetallic compound BiNi. Similarly, the maximum peak in the X-ray diffraction pattern within the diffraction angle range of 2θ from 41° to 43° corresponds to the peak originating from the (2,2,3) plane of the intermetallic compound BiNi. A peak intensity ratio I(2) / I(1) of 0.28 or less means that, on the surface of the active material layer 104, the proportion of the (2,2,3) plane to the (2,2,1) plane of BiNi, which has a monoclinic crystal structure with space group C2 / m, is low. In other words, it means that the orientation of the (2,2,1) plane is stronger on the surface of the active material layer 104. An active material layer 104 with such orientation in the crystal structure of BiNi on its surface can have high adhesion to the current collector 100. Therefore, because the active material layer 104 has such surface orientation, even if the active material layer 104 repeatedly expands and contracts due to charging and discharging, a decrease in current collection performance is less likely to occur. Accordingly, the battery 1000 of this disclosure can have improved cycle characteristics and a higher capacity.

[0056] The X-ray diffraction pattern of the active material layer 104 can be obtained by X-ray diffraction measurements using the θ-2θ method with Cu-Kα rays having wavelengths of 1.5405 Å and 1.5444 Å, i.e., wavelengths of 0.15405 nm and 0.15444 nm.

[0057] The diffraction angle of a peak in an X-ray diffraction pattern is defined as the angle that shows the maximum intensity of the peak-shaped portion where the signal-to-noise ratio (i.e., the ratio of signal S to background noise N) is 1.3 or greater and the full width at half maximum (FWHM) is 10° or less. FWHM is the maximum intensity of the X-ray diffraction peak. MAX When the intensity is I MAX This refers to the width represented by the difference between two diffraction angles that are half the value of the given value.

[0058] The active material layer 104, which is composed of a BiNi thin film containing BiNi as the main component and satisfying the above-mentioned surface orientation properties, can be manufactured, for example, by electroplating. A method for manufacturing the first electrode 101 by manufacturing the active material layer 104 by electroplating is as follows, for example.

[0059] First, a substrate for electroplating is prepared. For the first electrode 101, for example, a current collector 100 serves as the substrate. For example, a current collector containing Ni is prepared as the current collector 100. The manufacturing method of the first electrode 101 includes, for example, creating a Bi plating layer on a Ni-containing current collector by electroplating, and heating the current collector and the Bi plating layer to diffuse the Ni contained in the current collector into the Bi plating layer, thereby obtaining an electrode in which an active material layer containing BiNi is formed on the current collector. The heating temperature of the current collector and the Bi plating layer is, for example, 250°C or higher, and may be 350°C or higher.

[0060] The manufacturing method for the first electrode 101 will be explained in more detail.

[0061] First, the substrate for electroplating is prepared. For the first electrode 101, for example, the current collector 100 serves as the substrate. As an example, nickel foil is prepared as the current collector 100. After the nickel foil is pre-degreased with an organic solvent, one side is masked and the surface of the nickel foil is activated by immersion in an acidic solvent to degrease it. The activated nickel foil is connected to a power supply so that current can be applied. The nickel foil connected to the power supply is immersed in a bismuth plating bath. As a bismuth plating bath, for example, Bi 3+ An organic acid bath containing ions and organic acids is used. Subsequently, the current density and application time are controlled, and an electric current is applied to the nickel foil, thereby electroplating Bi onto the unmasked nickel foil surface. After electroplating, the nickel foil is recovered from the plating bath, the masking is removed, and then it is washed with pure water and dried. By these methods, a Bi plating layer is created on the nickel foil surface. The bismuth plating bath used to create the Bi plating layer is not particularly limited and can be appropriately selected from known bismuth plating baths capable of depositing a thin film of elemental Bi. In the bismuth plating bath, an organic sulfonic acid bath, a gluconic acid and ethylenediaminetetraacetic acid (EDTA) bath, or a citric acid and EDTA bath may be used as the organic acid bath. In addition, a sulfuric acid bath may be used as the bismuth plating bath. Additives may also be added to the bismuth plating bath.

[0062] Table 1 shows the target thickness of the Bi-plated layer produced by electroplating Bi, and the actual thickness of the Bi-plated layer produced.

[0063] Samples of the Bi-plated layer were prepared using the same method as in Example 1 described below. However, the current application time to the nickel foil, which was the plating substrate, was adjusted to aim for a plating thickness of 5 μm, and the samples were prepared accordingly. The thickness of the obtained Bi-plated layer was measured using a Seiko Instruments SEA6000VX X-ray fluorescence spectrometer. The average thickness of the Bi layer in the five samples was 5.7 μm, 5.1 μm, 5.1 μm, 5.7 μm, and 5.8 μm.

[0064] [Table 1]

[0065] Next, the nickel foil and the Bi plating layer formed on the nickel foil are heated. This heat treatment allows for the solid-phase diffusion of Ni from the nickel foil to the Bi plating layer, thereby creating an active material layer composed of a BiNi thin film. Here, a sample in which Bi has been electroplated onto nickel foil is subjected to a heat treatment, for example, at a temperature of 250°C or higher in a non-oxidizing atmosphere for 30 minutes to less than 100 hours, thereby allowing for the solid-phase diffusion of Ni from the nickel foil to the Bi plating layer and creating an active material layer composed of a BiNi thin film.

[0066] For the above-mentioned sample, which was electroplated with Bi to a thickness of approximately 5 μm onto nickel foil, an active material layer composed of a BiNi thin film was fabricated by heat treatment at 400°C for 60 hours in an argon atmosphere. Furthermore, the surface structure of the fabricated BiNi thin film active material layer was analyzed by surface X-ray diffraction measurement.

[0067] Figure 2 is a graph showing an example of the X-ray diffraction pattern of an active material layer composed of a BiNi thin film fabricated on nickel foil. The X-ray diffraction pattern was measured using the θ-2θ method with Cu-Kα rays at wavelengths of 1.5405 Å and 1.5444 Å, using an X-ray diffractometer (RIGAKU, MiNi Flex) from the surface of the active material layer, i.e., in the thickness direction of the active material layer 104. From the X-ray diffraction pattern shown in Figure 2, the phases of BiNi, whose space group is assigned to C2 / m as a crystal structure, and the nickel foil as a current collector and Ni contained in the active material layer were identified. Note that the X-ray diffraction pattern shown in Figure 2 is the X-ray diffraction pattern obtained by surface X-ray diffraction measurement of the active material layer at the first electrode fabricated in Example 1 described later.

[0068] In the X-ray diffraction pattern of the active material layer obtained by surface X-ray diffraction measurement using Cu-Kα rays, as shown in Figure 2, the peak intensity ratio I(2) / I(1) of the active material layer, calculated from the intensity ratio I(2) / I(1) of the maximum peak height intensity I(1) in the diffraction angle 2θ range of 29° to 31° and the maximum peak height intensity I(2) in the diffraction angle 2θ range of 41° to 43°, was 0.28 or less.

[0069] From the X-ray diffraction pattern results described above, it was confirmed that on the surface of the active material layer 104, which was fabricated by electroplating Bi onto a current collector 100 containing Ni to create a Bi plating layer, and then heating the Bi plating layer on the current collector 100 together with the current collector 100, the ratio of (2,2,3) planes to (2,2,1) planes of BiNi, which has a monoclinic crystal structure whose space group belongs to C2 / m, was low. In other words, it was confirmed that the orientation of the (2,2,1) plane was strong on the surface of the active material layer 104. From this, it was found that by fabricating a Bi plating layer on a current collector containing Ni, and then heat-treating the resulting Bi plating layer on the current collector containing Ni, it is possible to orient BiNi, which has a monoclinic crystal structure whose space group belongs to C2 / m, so that the (2,2,1) plane becomes the surface. An electrode provided with a BiNi thin film having such orientation as the active material layer can further improve the cycle characteristics of the battery.

[0070] The following describes in more detail the configuration of the battery 1000 of this embodiment, using the case where the first electrode 101 is the negative electrode and the second electrode 103 is the positive electrode as an example.

[0071] [First electrode] As described above, the first electrode 101 has a current collector 100 and an active material layer 104. The composition of the active material layer 104 is as described above. The first electrode 101 functions as a negative electrode. Therefore, the active material layer 104 contains a negative electrode active material that has the property of intercalating and releasing lithium ions. The active material layer 104 contains BiNi having a crystalline structure whose space group belongs to C2 / m, and this BiNi functions as a negative electrode active material. The active material layer 104 contains BiNi as an active material.

[0072] Bi is a metallic element that alloys with lithium. On the other hand, Ni does not alloy with lithium, so it is presumed that alloys containing Ni reduce the load on the crystal structure of the negative electrode active material during the desorption and insertion of lithium atoms during charging and discharging, thereby suppressing the decrease in the battery's capacity retention rate. When BiNi functions as the negative electrode active material, lithium is intercalated when Bi forms an alloy with lithium during charging. That is, a lithium-bismuth alloy is generated in the active material layer 104 when the battery 1000 is charged. The generated lithium-bismuth alloy includes, for example, at least one selected from the group consisting of LiBi and Li3Bi. That is, when the battery 1000 is charged, the active material layer 104 includes, for example, at least one selected from the group consisting of LiBi and Li3Bi. When the battery 1000 is discharged, lithium is released from the lithium-bismuth alloy, and the lithium-bismuth alloy returns to BiNi.

[0073] BiNi, used as the negative electrode active material, reacts during charging and discharging of the battery 1000, for example, as follows. Note that the following example of reactions is for the case where the lithium bismuth alloy produced during charging is Li3Bi. Charging: BiNi+3Li + +3e - →Li3Bi+Ni Discharge: Li3Bi + Ni → BiNi + 3Li + +3e -

[0074] The active material layer 104 may contain substantially only BiNi as the active material. In this case, the battery 1000 can have improved capacity and improved cycle characteristics. Note that "the active material layer 104 contains substantially only BiNi as the active material" means, for example, that the amount of other active materials besides BiNi in the active material layer 104 is 1% by mass or less. The active material layer 104 may contain only BiNi as the active material.

[0075] The active material layer 104 does not necessarily have to contain a solid electrolyte.

[0076] The active material layer 104 may be disposed in direct contact with the surface of the current collector 100.

[0077] The active material layer 104 may be in the form of a thin film.

[0078] The active material layer 104 may be a heat-treated plating layer. The active material layer 104 may be a heat-treated plating layer provided in direct contact with the surface of the current collector 100. That is, as described above, the active material layer 104 may be a layer formed by heat-treating a Bi plating layer formed on the current collector 100 containing Ni.

[0079] If the active material layer 104 is a heat-treated plating layer provided in direct contact with the surface of the current collector 100, the active material layer 104 adheres firmly to the current collector 100. This further suppresses the deterioration of the current collection characteristics of the first electrode 101 that occurs when the active material layer 104 repeatedly expands and contracts. Therefore, the cycle characteristics of the battery 1000 are further improved. Furthermore, if the active material layer 104 is a heat-treated plating layer, the active material layer 104 contains a high density of Bi, which alloys with lithium, thus enabling even higher capacity.

[0080] The active material layer 104 may contain materials other than BiNi.

[0081] The active material layer 104 may further contain a conductive material.

[0082] Examples of conductive materials include carbon materials, metals, inorganic compounds, and conductive polymers. Examples of carbon materials include graphite, acetylene black, carbon black, Ketjenblack, carbon whiskers, needle coke, and carbon fibers. Examples of graphite include natural graphite and artificial graphite. Examples of natural graphite include lump graphite and flake graphite. Examples of metals include copper, nickel, aluminum, silver, and gold. Examples of inorganic compounds include tungsten carbide, titanium carbide, tantalum carbide, molybdenum carbide, titanium boride, and titanium nitride. These materials may be used individually or in combination.

[0083] The active material layer 104 may further contain a binder.

[0084] Examples of binders include fluororesins, thermoplastics, ethylene propylene diene monomer (EPDM) rubber, sulfonated EPDM rubber, and natural butyl rubber (NBR). Examples of fluororesins include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluororubber. Examples of thermoplastics include polypropylene and polyethylene. These materials may be used individually or in combination.

[0085] The thickness of the active material layer 104 is not particularly limited and may be, for example, 1 μm or more and 100 μm or less.

[0086] The material of the current collector 100 is, for example, a single metal or alloy. More specifically, it may be a single metal or alloy containing at least one selected from the group consisting of copper, chromium, nickel, titanium, platinum, gold, aluminum, tungsten, iron, and molybdenum. The current collector 100 may also be stainless steel.

[0087] The current collector 100 may contain nickel (Ni).

[0088] The current collector 100 may be in the form of a plate or foil. From the viewpoint of easily ensuring high conductivity, the negative electrode current collector may be a metal foil, or a metal foil containing nickel. Examples of nickel-containing metal foils include nickel foil and nickel alloy foil. The nickel content in the metal foil may be 50% by mass or more, or 80% by mass or more. In particular, the metal foil may be a nickel foil containing substantially only nickel as the metal. The current collector 100 may be a metal foil formed of a metal other than nickel, with a Ni layer, such as a Ni plating layer, formed on its surface.

[0089] The current collector 100 may be a laminated film.

[0090] [Electrolyte] The electrolyte 102 includes, for example, an aprotic solvent and a lithium salt dissolved in the aprotic solvent.

[0091] Aprotic solvents are not particularly limited. Examples of aprotic solvents include cyclic carbonate solvents, linear carbonate (linear carbonate) solvents, cyclic ether solvents, linear ether solvents, cyclic ester solvents, linear ester solvents, or fluorine solvents. Examples of cyclic carbonate solvents are vinylene carbonate, fluoroethylene carbonate, ethylene carbonate, propylene carbonate, or butylene carbonate. Examples of linear carbonate solvents are dimethyl carbonate, methyl ethyl carbonate, or diethyl carbonate. Examples of cyclic ether solvents are tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, or 1,3-dioxolane. Examples of linear ether solvents are 1,2-dimethoxyethane, or 1,2-diethoxyethane. An example of a cyclic ester solvent is γ-butyrolactone. An example of a linear ester solvent is methyl acetate. Examples of fluorinated solvents include methyl fluoropropionate, fluorobenzene, fluoroethyl methyl carbonate, or fluorodimethylene carbonate. The electrolyte 102 may contain one solvent selected from these, or a mixture of two or more non-aqueous solvents selected from these.

[0092] The electrolyte 102 may contain at least one selected from the group consisting of vinylene carbonate, 2-methyltetrahydrofuran, fluoroethylene carbonate, and ethylene carbonate as an aprotic solvent. By including these solvents in the electrolyte 102, the battery 1000 has improved cycle characteristics.

[0093] The electrolyte 102 may contain vinylene carbonate and a linear carbonate as an aprotic solvent. By including a mixed solvent containing vinylene carbonate and a linear carbonate in the electrolyte 102, the battery 1000 has improved cycle characteristics.

[0094] The chain-like carbonates are not particularly limited. Examples of chain-like carbonates include dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate.

[0095] When the aprotic solvent in electrolyte 102 contains a mixed solvent comprising vinylene carbonate and linear carbonate, the ratio of vinylene carbonate to linear carbonate is not particularly limited. For example, the ratio of linear carbonate to vinylene carbonate (linear carbonate / vinylene carbonate) may be greater than 0 and less than or equal to 99 in volume.

[0096] The aprotic solvent contained in the electrolyte 102 may consist only of vinylene carbonate and linear carbonate. That is, the ratio of the total mass of vinylene carbonate and linear carbonate to the total mass of the nonaqueous solvent may be, for example, 100% by mass.

[0097] If the aprotic solvent in electrolyte 102 contains a mixed solvent containing vinylene carbonate and linear carbonate, electrolyte 102 may further contain other aprotic solvents other than vinylene carbonate and linear carbonate. In this case, the total mass percentage of the other aprotic solvents is, for example, 10% by mass or less. Examples of other aprotic solvents include cyclic carbonate solvents, cyclic ether solvents, linear ether solvents, cyclic ester solvents, linear ester solvents, or fluorine solvents. Examples of cyclic carbonate solvents are fluoroethylene carbonate, ethylene carbonate, propylene carbonate, or butylene carbonate. Examples of cyclic ether solvents are tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, or 1,3-dioxolane. Examples of linear ether solvents are 1,2-dimethoxyethane or 1,2-diethoxyethane. An example of a cyclic ester solvent is γ-butyrolactone. An example of a linear ester solvent is methyl acetate. Examples of fluorine solvents are methyl fluoropropionate, fluorobenzene, fluoroethylmethyl carbonate, or fluorodimethylene carbonate.

[0098] Examples of the lithium salt include LiPF6, LiBF4, LiSbF6, LiAsF6, LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), or LiC(SO2CF3)3. One lithium salt selected from these may be used alone. Alternatively, a mixture of two or more lithium salts selected from these may be used.

[0099] [Second electrode] The second electrode 103 functions as a positive electrode. The second electrode 103 contains a material capable of occluding and releasing metal ions such as lithium ions. The material is, for example, a positive electrode active material.

[0100] The second electrode 103 may have a current collector 105 and an active material layer 106. The active material layer 106 contains a positive electrode active material.

[0101] The active material layer 106 may be disposed on the surface of the current collector 105, directly contacting the current collector 105.

[0102] As the positive electrode active material, for example, lithium-containing transition metal oxides, transition metal fluorides, polyanion materials, fluorinated polyanion materials, transition metal sulfides, transition metal oxysulfides, or transition metal oxynitrides, etc. may be used. Examples of the lithium-containing transition metal oxides include LiNi 1-x-y Co x Al y O2((x + y)<1), LiNi 1-x-y Co x Mn y O2((x + y)<1) or LiCoO2, etc. can be mentioned. In particular, when a lithium-containing transition metal oxide is used as the positive electrode active material, the manufacturing cost of the electrode can be reduced and the average discharge voltage of the battery can be increased. For example, the positive electrode active material may contain Li(Ni,Co,Mn)O2.

[0103] Examples of the material of the current collector 105 include metal materials. Examples of the metal materials include copper, stainless steel, iron, aluminum, etc.

[0104] The second electrode 103 may contain a solid electrolyte. Known solid electrolytes used in lithium-ion batteries can be used as the solid electrolyte. For example, a halide solid electrolyte, sulfide solid electrolyte, oxide solid electrolyte, polymer solid electrolyte, or complex hydride solid electrolyte may be used.

[0105] A halide solid electrolyte refers to a solid electrolyte containing a halogen element. A halide solid electrolyte may also contain oxygen in addition to the halogen element. A halide solid electrolyte does not contain sulfur (S).

[0106] The halide solid electrolyte may be, for example, a material represented by the following compositional formula (1). Li α M β X γ ...Equation (1) Here, α, β, and γ are values ​​greater than 0, M is at least one selected from the group consisting of metallic elements and metalloid elements other than Li, and X is at least one selected from the group consisting of F, Cl, Br, and I.

[0107] "Metallic elements" are B, Si, Ge, As, Sb, and Te.

[0108] "Metallic elements" refer to all elements in groups 1 through 12 of the periodic table, excluding hydrogen, as well as all elements in groups 13 through 16, excluding B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se. In other words, they are the elements that can form cations when forming halogen compounds and inorganic compounds.

[0109] In compositional formula (1), M may contain Y, and X may contain Cl and Br.

[0110] A sulfide solid electrolyte refers to a solid electrolyte containing sulfur (S). A sulfide solid electrolyte may also contain halogen elements in addition to sulfur.

[0111] Examples of sulfide solid electrolytes include Li2S-P2S5, Li2S-SiS2, Li2S-B2S3, Li2S-GeS2, Li 3.25 Ge 0.25 P 0.75 S4, or Li 10 GeP2S 12 These may be used.

[0112] Examples of oxide solid electrolytes include NASICON-type solid electrolytes, such as LiTi2(PO4)3 and its elemental substitutions, and (LaLi)TiO3-based perovskite-type solid electrolytes, Li 14 ZnGe4O 16 , LiSICON-type solid electrolytes such as Li4SiO4, LiGeO4 and their elemental substitutions, Li7La3Zr2O 12 Garnet-type solid electrolytes, such as those represented by elemental substitutions thereof, Li3PO4 and its N-substituted counterparts, and glass or glass ceramics based on Li-BO compounds such as LiBO2 and Li3BO3, with Li2SO4, Li2CO3, etc., added, can be used.

[0113] As a polymeric solid electrolyte, for example, a compound of a polymer and a lithium salt can be used. The polymer may have an ethylene oxide structure. Polymeric compounds having an ethylene oxide structure can contain a large amount of lithium salt. Therefore, the ionic conductivity can be further increased. Examples of lithium salts that can be used include LiPF6, LiBF4, LiSbF6, LiAsF6, LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), and LiC(SO2CF3)3. One lithium salt selected from the exemplified lithium salts can be used alone. Alternatively, a mixture of two or more lithium salts selected from the exemplified lithium salts can be used.

[0114] Examples of complex hydride solid electrolytes that can be used include LiBH4-LiI and LiBH4-P2S5.

[0115] The positive electrode active material may have a median diameter of 0.1 μm or more and 100 μm or less. When the positive electrode active material has a median diameter of 0.1 μm or more, the positive electrode active material and the solid electrolyte can form a good dispersion state. This improves the charge and discharge characteristics of the battery. When the positive electrode active material has a median diameter of 100 μm or less, the lithium diffusion rate improves. This allows the battery to operate at high power.

[0116] The positive electrode active material may have a larger median diameter than the solid electrolyte. This allows the positive electrode active material and the solid electrolyte to form a good dispersion state.

[0117] From the viewpoint of the battery's energy density and output, the ratio of the volume of the positive electrode active material to the sum of the volume of the positive electrode active material and the volume of the solid electrolyte in the second electrode 103 may be 0.30 or more and 0.95 or less.

[0118] To prevent the solid electrolyte from reacting with the positive electrode active material, a coating layer may be formed on the surface of the positive electrode active material. This can suppress the rise in the reaction overpotential of the battery. Examples of coating materials included in the coating layer are sulfide solid electrolytes, oxide solid electrolytes, or halide solid electrolytes.

[0119] The thickness of the second electrode 103 may be 10 μm or more and 500 μm or less. When the thickness of the second electrode 103 is 10 μm or more, a sufficient energy density of the battery can be ensured. When the thickness of the second electrode 103 is 500 μm or less, the battery can operate at high power.

[0120] The second electrode 103 may contain a conductive material for the purpose of enhancing electronic conductivity.

[0121] The second electrode 103 may contain a binder.

[0122] The same materials that can be used for the active material layer 104 may be used as the conductive material and binder.

[0123] The second electrode 103 may contain a non-aqueous electrolyte, a gel electrolyte, or an ionic liquid in order to facilitate the transfer of lithium ions and improve the output characteristics of the battery.

[0124] Non-aqueous electrolytes include a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent. Examples of non-aqueous solvents are cyclic carbonate solvents, linear carbonate solvents, cyclic ether solvents, linear ether solvents, cyclic ester solvents, linear ester solvents, or fluorine solvents. Examples of cyclic carbonate solvents are ethylene carbonate, propylene carbonate, or butylene carbonate. Examples of linear carbonate solvents are dimethyl carbonate, ethyl methyl carbonate, or diethyl carbonate. Examples of cyclic ether solvents are tetrahydrofuran, 1,4-dioxane, or 1,3-dioxolane. Examples of linear ether solvents are 1,2-dimethoxyethane, or 1,2-diethoxyethane. An example of a cyclic ester solvent is γ-butyrolactone. An example of a linear ester solvent is methyl acetate. Examples of fluorinated solvents include fluoroethylene carbonate, methyl fluoropropionate, fluorobenzene, fluoroethyl methyl carbonate, or fluorodimethylene carbonate. One non-aqueous solvent selected from these may be used alone, or a mixture of two or more non-aqueous solvents selected from these may be used.

[0125] Examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), or LiC(SO2CF3)3. One lithium salt selected from these may be used alone, or a mixture of two or more lithium salts selected from these may be used. The concentration of the lithium salt is, for example, in the range of 0.5 mol / liter to 2 mol / liter.

[0126] As the gel electrolyte, polymer materials impregnated with a non-aqueous electrolyte can be used. Examples of polymer materials include polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, or polymers having ethylene oxide bonds.

[0127] Examples of cations contained in ionic liquids are: (i) aliphatic chain quaternary salts such as tetraalkylammonium or tetraalkylphosphonium, (ii) Aliphatic cyclic ammonium compounds such as pyrrolidiniums, morpholiniums, imidazoliniums, tetrahydropyrimidiniums, piperadiniums, or piperidiniums, (iii) Nitrogen-containing heterocyclic aromatic cations such as pyridiniums or imidazoliums.

[0128] An example of anion contained in an ionic liquid is PF6. - BF4 - SbF6 - AsF6 - , SO3CF3 - , N(SO2CF3)2 - , N(SO2C2F5)2 - , N(SO2CF3)(SO2C4F9) - , or C(SO2CF3)3 - That is the case.

[0129] The ionic liquid may contain a lithium salt.

[0130] [Separator] The separator 107 is lithium ion conductive. The material of the separator 107 is not particularly limited, as long as the passage of lithium ions is permitted. The material of the separator 107 may be at least one selected from the group consisting of solid electrolytes, gel electrolytes, ion exchange resin membranes such as lithium cation exchange resins, semipermeable membranes, and porous membranes. If the separator 107 is made from these materials, the safety of the battery 1000 can be sufficiently ensured. As for solid electrolytes, sulfide solid electrolytes such as Li2S-P2S5 and Li7La3Zr2O 12 Examples of oxide solid electrolytes include (LLZ). Examples of gel electrolytes include gel electrolytes containing fluororesins such as PVdF. Examples of ion exchange resin membranes include cation exchange membranes and anion exchange membranes. Examples of porous membranes include porous membranes made of polyolefin resin and porous membranes made of glass paper obtained by weaving glass fibers into a nonwoven fabric.

[0131] [Exterior] The outer casing 108 is made of a material obtained by laminating a metal foil, such as aluminum foil, with a resin film, such as polyethylene terephthalate (PET) film. The outer casing 108 may also be a resin or metal container.

[0132] In the above description, an example configuration was explained in which the first electrode 101 is the negative electrode and the second electrode 103 is the positive electrode. However, the first electrode 101 may also be the positive electrode and the second electrode 103 may be the negative electrode.

[0133] When the first electrode 101 is the positive electrode and the second electrode 103 is the negative electrode, the active material layer 104 is the positive electrode active material layer. That is, the Bi contained in the active material layer 104 functions as the positive electrode active material. In this case, the second electrode 103, which is the negative electrode, is made of, for example, lithium metal.

[0134] The battery 1000 has a basic configuration of a first electrode 101, an electrolyte 102, and a second electrode 103, and is sealed in a sealed container to prevent contamination from air and moisture. The shape of the battery 1000 can be coin-shaped, cylindrical, rectangular, sheet-shaped, button-shaped, flat, or stacked. [Examples]

[0135] The details of this disclosure are disclosed below with reference to examples and reference examples. The following examples are illustrative and this disclosure is not limited to the following examples.

[0136] (Example 1) <Fabrication of the first electrode> As a pretreatment, nickel foil (10cm x 10cm, thickness: 10μm) was pre-degreased with an organic solvent, then one side was masked and degreased by immersion in an acidic solvent, activating the nickel foil surface. In 1.0 mol / L of methanesulfonic acid, bismuth methanesulfonate was added as a soluble bismuth salt. 3+ A plating bath was prepared by adding ions to a concentration of 0.18 mol / L. The activated nickel foil was connected to a power supply so that current could be applied, and then immersed in the plating bath. Subsequently, a current density of 2 A / dm² was applied. 2Under controlled conditions, Bi was electroplated to a thickness of approximately 1 μm onto the unmasked nickel foil surface. After electroplating, the nickel foil was recovered from the acidic bath, the masking was removed, and it was washed and dried with pure water. Subsequently, the Bi-plated nickel foil was heat-treated at 400°C for 60 hours in an electric furnace under an argon atmosphere. After the heat treatment, surface X-ray diffraction measurements were performed on the Bi-plated layer on the nickel foil. The X-ray diffraction pattern obtained from this measurement is shown in Figure 2. From this X-ray diffraction pattern, it was confirmed that BiNi with a monoclinic crystal structure belonging to the space group C2 / m was formed. Furthermore, it was confirmed from the X-ray diffraction pattern that single-phase BiNi was formed on the nickel foil. In other words, a laminate was obtained consisting of a current collector made of nickel foil and an active material layer made of BiNi with a crystal structure belonging to the space group C2 / m, which was placed in direct contact with the surface of the current collector. The peak intensity ratio I(2) / I(1) of the active material layer, calculated from this X-ray diffraction pattern, was 0.28 or less. Subsequently, the resulting laminate was punched out to 2 cm × 2 cm to fabricate the first electrode. The thickness of the obtained first electrode was 12 μm.

[0137] <Preparation of test cells> The first electrode was used as the working electrode. A 0.34 mm thick piece of Li metal was used as the counter electrode. The working electrode corresponds to the negative electrode of a secondary battery. The Li metal was double-coated with a microporous separator (Asahi Kasei Corporation, Cellguard 3401). As the electrolyte, a solution of LiPF6 dissolved at a concentration of 1.0 mol / L in each solvent shown in Table 2 was prepared. Using this working electrode, counter electrode, and electrolyte, batteries as test cells for Examples 1-1 to 1-9 were assembled. The test cells prepared here are unipolar test cells using a working electrode and a counter electrode, and are used to test the performance of one electrode in a secondary battery. Specifically, the electrode under test is used as the working electrode, and a sufficient amount of appropriate active material to support the reaction of the working electrode is used as the counter electrode. Since this test cell tests the performance of the first electrode as the negative electrode, a large excess of Li metal was used as the counter electrode, as is commonly done. The negative electrode whose performance has been tested using such a test cell can be used as a secondary battery by combining it with a positive electrode containing a positive electrode active material, such as a transition metal oxide containing Li, as described in the above embodiment.

[0138] [Table 2]

[0139] <Charge / Discharge Test> A charge-discharge test was performed on the test cell. 0.6mA (0.15mA / cm²) 2 Charging was performed to 0V and discharging to 2V at a constant current value. This was considered one cycle. The discharge cycle test was conducted at 25°C.

[0140] Figure 3A is a graph showing the results of the initial charge-discharge test of the test cell according to Example 1-1. Figure 3B is a graph showing the results of the second charge-discharge test of the test cell according to Example 1-1.

[0141] Figure 4A is a graph showing the results of the initial charge-discharge test of the test cell according to Example 1-2. Figure 4B is a graph showing the results of the second charge-discharge test of the test cell according to Example 1-2.

[0142] Figure 5A is a graph showing the results of the initial charge-discharge test of the test cell according to Example 1-3. Figure 5B is a graph showing the results of the second charge-discharge test of the test cell according to Example 1-3.

[0143] Figure 6A is a graph showing the results of the initial charge-discharge test of the test cell according to Example 1-4. Figure 6B is a graph showing the results of the second charge-discharge test of the test cell according to Example 1-4.

[0144] Figure 7A is a graph showing the results of the initial charge-discharge test of the test cell according to Example 1-5. Figure 7B is a graph showing the results of the second charge-discharge test of the test cell according to Example 1-5.

[0145] Figure 8A is a graph showing the results of the initial charge-discharge test of the test cell according to Example 1-6. Figure 8B is a graph showing the results of the second charge-discharge test of the test cell according to Example 1-6.

[0146] Figure 9A is a graph showing the results of the initial charge-discharge test of the test cell according to Example 1-7. Figure 9B is a graph showing the results of the second charge-discharge test of the test cell according to Example 1-7.

[0147] Figure 10A is a graph showing the results of the initial charge-discharge test of the test cell according to Example 1-8. Figure 10B is a graph showing the results of the second charge-discharge test of the test cell according to Example 1-8.

[0148] Figure 11A is a graph showing the results of the initial charge-discharge test of the test cell according to Example 1-9. Figure 11B is a graph showing the results of the second charge-discharge test of the test cell according to Example 1-9.

[0149] Figure 12A is a graph showing the results of the initial charge-discharge test of the test cell according to Example 1-10. Figure 12B is a graph showing the results of the second charge-discharge test of the test cell according to Example 1-10.

[0150] Figure 13 is a graph showing the results of the initial charge-discharge tests of the test cells according to Examples 1-11.

[0151] Figure 14 is a graph showing the results of the initial charge-discharge tests of the test cells according to Examples 1-12.

[0152] From the charge-discharge test results of the test cells in Examples 1-1 to 1-12, it was confirmed that batteries equipped with electrodes containing BiNi as the active material exhibit excellent discharge flatness. In Examples 1-7 and 1-9, the second charge-discharge capacity decreased from the initial charge-discharge capacity, but in the other test cells, a charge-discharge capacity similar to the initial charge-discharge capacity was obtained in the second charge-discharge.

[0153] <Charge-discharge cycle test> Under the same conditions as in the charge-discharge test, charging and discharging were repeatedly performed, with each cycle counting as one, and the cycle characteristics were evaluated. Figure 15 is a graph showing the relationship between the number of cycles and discharge capacity density for the test cells of Examples 1-1 to 1-8. Figure 16 is a graph showing the relationship between the number of cycles and discharge capacity density for the test cells of Examples 1-1 to 1-4. Figure 17 is a graph showing the relationship between the number of cycles and discharge capacity density for the test cells of Examples 1-1 and 1-9. Figure 18 is a graph showing the relationship between the number of cycles and discharge capacity density for the test cell of Example 1-10. Figure 19 is a graph showing the relationship between the number of cycles and discharge capacity density for the test cells of Examples 1-11 and 1-12.

[0154] <Evaluation of the crystal structure of the active material layer before charging, after charging, and after discharging> Surface X-ray diffraction measurements were performed on the active material layer of the first electrode of the test cell of Example 1-1 before charging, after charging, and after discharging. Figure 25 is a graph showing an example of the X-ray diffraction pattern of the active material layer of the test cell of Example 1-1 before charging, after charging, and after discharging. According to Figure 25, before charging, BiNi with a monoclinic crystal structure and belonging to the space group C2 / m, and Ni with a cubic crystal structure and belonging to the space group Fm-3m can be identified, and compounds originating from the active material and current collector can be identified, respectively. After charging, Li3Bi with a cubic crystal structure and belonging to the space group Fm-3m, and Ni with a cubic crystal structure and belonging to the space group Fm-3m can be identified. That is, Li3Bi is formed after charging, and the charging reaction is: BiNi + 3Li + +3e - →It was confirmed that the reaction Li3Bi+Ni was progressing. Furthermore, after charging and discharging, BiNi with a monoclinic crystal structure belonging to the space group C2 / m and Ni with a cubic crystal structure belonging to the space group Fm-3m could be identified. Also, the discharge reaction was: Li3Bi+Ni→BiNi+3Li + +3e - This confirmed that the charge-discharge reaction was reversible in terms of the composition of the compound before charging.

[0155] <Evaluation of electrodes after charge-discharge cycle testing> The electrodes of the test cell in Example 1-1, which underwent the above charge-discharge cycle test, were examined after 500 cycles. Figure 26 is a photograph of the first electrode in Example 1-1 after 500 charge-discharge cycles. From the photograph in Figure 26, it was confirmed that the first electrode in Example 1-1 had not deteriorated even after 500 charge-discharge cycles and was in a very clean condition.

[0156] (Example 2) <Fabrication of the first electrode> In Example 2, the first electrode was fabricated in the same manner as in Example 1, except that the heat treatment conditions were changed from 400°C for 60 hours. In Example 2, after heat treatment at 250°C for 0.5 hours, further heat treatment at 350°C for 0.5 hours was performed. In Example 2, as in Example 1, surface X-ray diffraction measurements were performed on the Bi plating layer on the nickel foil after the heat treatment. Figure 20 is a graph showing the X-ray diffraction pattern of the active material layer composed of a BiNi thin film fabricated on the nickel foil in Example 2. From this X-ray diffraction pattern, it was confirmed that BiNi with a monoclinic crystal structure belonging to the space group C2 / m was produced. Furthermore, the X-ray diffraction pattern confirmed that single-phase BiNi was formed on the nickel foil. In other words, in Example 2, as in Example 1, a first electrode was obtained composed of a current collector made of nickel foil and an active material layer made of BiNi having a crystal structure belonging to the space group C2 / m, which was placed in direct contact with the surface of the current collector. The peak intensity ratio I(2) / I(1) of the active material layer, calculated from this X-ray diffraction pattern, was 0.28 or less.

[0157] <Preparation of test cells> In Example 2, the first electrode was used as the working electrode, and a solution of LiPF6 dissolved in VC at a concentration of 1.0 mol / L was used as the electrolyte. Except for these points, the test cell was prepared in the same manner as in Example 1.

[0158] <Charge / Discharge Test> A charge-discharge test was performed on the test cell. The charge-discharge test was conducted in the same manner as in Example 1. Figure 21A is a graph showing the results of the initial charge-discharge test of the test cell according to Example 2. Figure 21B is a graph showing the results of the second charge-discharge test of the test cell according to Example 2. From the results of the charge-discharge test of the test cell according to Example 2, it was confirmed that the battery equipped with electrodes containing BiNi as the active material exhibits excellent discharge flatness. Furthermore, in the second charge-discharge, a charge-discharge capacity similar to the initial charge-discharge capacity was obtained.

[0159] <Charge-discharge cycle test> A charge-discharge cycle test was performed on the test cells. The discharge test was performed in the same manner as in Example 1. Figure 22 is a graph showing the relationship between the number of cycles and the discharge capacity density of the test cells related to Examples 2 and 3.

[0160] (Example 3) <Fabrication of the first electrode> In Example 3, the first electrode was fabricated in the same manner as in Example 1, except that the heat treatment conditions were changed from 400°C for 60 hours. In Example 3, heat treatment was performed at 250°C for 0.5 hours. In Example 3, as in Example 1, surface X-ray diffraction measurements were performed on the Bi plating layer on the nickel foil after heat treatment. Figure 23 is a graph showing the X-ray diffraction pattern of the active material layer composed of a BiNi thin film fabricated on the nickel foil in Example 3. From this X-ray diffraction pattern, two phases were confirmed: BiNi with a monoclinic crystal structure belonging to the C2 / m space group, BiNi with a monoclinic crystal structure belonging to the C2 / m space group, and Bi3Ni with an orthorhombic crystal structure belonging to the Pnma space group. In other words, in Example 3, a first electrode was obtained composed of a current collector made of nickel foil and an active material layer containing BiNi and Bi3Ni placed in direct contact with the surface of the current collector.

[0161] <Preparation of test cells> In Example 3, the first electrode was used as the working electrode, and a solution of LiPF6 dissolved in VC at a concentration of 1.0 mol / L was used as the electrolyte. Except for these points, the test cell was prepared in the same manner as in Example 1.

[0162] <Charge / Discharge Test> A charge-discharge test was performed on the test cell. The charge-discharge test was conducted in the same manner as in Example 1. Figure 24A is a graph showing the results of the initial charge-discharge test of the test cell according to Example 3. Figure 24B is a graph showing the results of the second charge-discharge test of the test cell according to Example 3. From the results of the charge-discharge test of the test cell according to Example 3, it was confirmed that the battery equipped with electrodes containing BiNi as the active material exhibits excellent discharge flatness. Furthermore, in the second charge-discharge, a charge-discharge capacity similar to the initial charge-discharge capacity was obtained.

[0163] <Charge-discharge cycle test> A charge-discharge cycle test was performed on the test cells. The discharge test was performed in the same manner as in Example 1. Figure 22 is a graph showing the relationship between the number of cycles and the discharge capacity density of the test cells related to Examples 2 and 3.

[0164] (Example 4) <Fabrication of the first electrode> As powder raw materials, Bi2O3 (bismuth trioxide "BIO10PB" manufactured by Kojunka Chemical Co., Ltd.), NiO (nickel monoxide "NIO04PB" manufactured by Sumitomo Metal Mining Co., Ltd.), and carbon (Denka Black manufactured by Denka Co., Ltd.) were mixed in a mortar. The molar ratio of Bi2O3, NiO, and carbon was Bi2O3:NiO:Carbon = 2:4:5. The resulting mixture was calcined in a nitrogen atmosphere using an electric furnace to produce BiNi powder. The calcination was carried out at 800°C for 4 hours.

[0165] Figure 27 is a graph showing the X-ray diffraction pattern of BiNi powder prepared from powder raw materials in Example 4. The X-ray diffraction pattern was measured after crushing the calcined BiNi powder in a mortar. The measurement was performed using the θ-2θ method with Cu-Kα rays at wavelengths of 1.5405 Å and 1.5444 Å, using an X-ray diffractometer (RIGAKU, MiNi Flex). From the obtained X-ray diffraction pattern, it was confirmed that BiNi was formed and that the BiNi had a monoclinic crystal structure belonging to the space group C2 / m. In addition, although the obtained powder was mostly BiNi, it was confirmed that Bi3Ni and Ni were also present. Furthermore, from this X-ray diffraction pattern, it was confirmed that the peak intensity ratio I(2) / I(1) in the active material layer of the first electrode according to Example 4 was greater than 0.28.

[0166] The obtained BiNi powder and acetylene black (AB) (manufactured by Denka Co., Ltd., "Denka Black") as a conductive agent were dispersed in a PVdF solution with N-methyl-2-pyrrolidone (NMP) to prepare a slurry. PVdF was used as a binder. In this slurry, the mass ratio of BiNi powder, AB, and PVdF was BiNi powder:AB:PVdF = 8:1:1. After coating this slurry onto nickel foil (10cm × 10cm), the solvent NMP was removed, and the foil was shaped and punched out to a 2cm × 2cm size to form the first electrode.

[0167] <Preparation of test cells> In Example 4, the first electrode was used as the working electrode, and a solution of LiPF6 dissolved in VC or a mixed solvent at a concentration of 1.0 mol / L was used as the electrolyte. Except for these points, the test cell was prepared in the same manner as in Example 1. The test cell in which VC was used as the solvent for the electrolyte is designated as the test cell of Example 4-1. In addition, a solvent in which EC, MEC, and DMC were mixed as the electrolyte was used in a volume ratio of EC:MEC:DMC = 6:7:7. The test cell in which this mixed solvent was used as the solvent for the electrolyte is designated as the test cell of Example 4-2.

[0168] <Charge / Discharge Test> A charge-discharge test was performed on the test cell. 0.6mA (0.15mA / cm²) 2 Charging was performed to 0V and discharging to 2V using a constant current value. This was considered one cycle. The charge-discharge cycle test was conducted at 25°C.

[0169] Figure 28A is a graph showing the results of the initial charge-discharge test of the test cell according to Example 4-1. Figure 28B is a graph showing the results of the second charge-discharge test of the test cell according to Example 4-1.

[0170] Figure 29A is a graph showing the results of the initial charge-discharge test of the test cell according to Example 4-2. Figure 29B is a graph showing the results of the second charge-discharge test of the test cell according to Example 4-2.

[0171] <Charge-discharge cycle test> Under the same conditions as in the charge-discharge test, charging and discharging were repeatedly performed, with each cycle counting as one cycle, and the cycle characteristics were evaluated. Figure 30 is a graph showing the relationship between the number of cycles up to 50 and the discharge capacity density for the test cells of Examples 4-1 and 4-2. Figure 31 is a graph showing the relationship between the number of cycles up to 10 and the discharge capacity density for the test cells of Examples 4-1 and 4-2.

[0172] (Reference example 1) <Fabrication of the first electrode> As a pretreatment, the copper foil was initially degreased with an organic solvent, then one side was masked and immersed in an acidic solvent to degrease it further, activating the copper foil surface. In 1.0 mol / L of methanesulfonic acid, bismuth methanesulfonate was added as a soluble bismuth salt. 3+ A plating bath was prepared by adding ions to a concentration of 0.18 mol / L. The activated copper foil was connected to a power supply so that an electric current could be applied, and then immersed in the plating bath. Subsequently, the current density was 2 A / dm². 2 Under controlled conditions, Bi was electroplated onto the unmasked copper foil surface to a thickness of approximately 1 μm. After electroplating, the copper foil was recovered from the acidic bath, the masking was removed, and it was washed with pure water, dried, and punched out to a size of 2 cm x 2 cm to obtain the first electrode. In other words, the first electrode of Reference Example 1 had a configuration in which an active material layer consisting of a Bi plating layer was provided on a current collector made of copper foil.

[0173] <Preparation of test cells> The first electrode from Reference Example 1 was used as the working electrode, and a solution of LiPF6 dissolved in VC at a concentration of 1.0 mol / L was used as the electrolyte. Except for these points, the test cell was prepared in the same manner as in Example 1.

[0174] <Charge / Discharge Test> A charge-discharge test was performed on the test cell. The charge-discharge test was performed in the same manner as in Example 1. Figure 32A is a graph showing the results of the initial charge-discharge test of the test cell according to Reference Example 1. Figure 32B is a graph showing the results of the second charge-discharge test of the test cell according to Reference Example 1. From Figures 32A and 32B, it can be seen that the battery according to Reference Example 1, in which a Bi plating layer was used in the active material layer, exhibited excellent discharge flatness, and furthermore, the charge-discharge capacity was almost maintained even after the second charge-discharge.

[0175] <Charge-discharge cycle test> A charge-discharge cycle test was performed on the test cell. The discharge test was performed in the same manner as in Example 1. Figure 33 is a graph showing the relationship between the number of cycles and the discharge capacity density of the test cell according to Reference Example 1. When the number of cycles shown in Figure 33 is compared with the number of cycles shown in Figures 15 and 16 of the cell of Example 1-1, which uses the same electrolyte, it was confirmed that the battery equipped with a first electrode containing BiNi as the active material has superior charge-discharge cycle characteristics compared to the battery equipped with a first electrode containing Bi as the active material.

[0176] (Comparative Example 1) <Fabrication of the first electrode> A slurry was prepared by dispersing Bi powder (manufactured by Kojun Chemical Laboratory Co., Ltd., 3N purity fine powder, particle size approximately 1 μm to 2 μm) and AB (manufactured by Denka Co., Ltd., "Denka Black") as a conductive agent in an NMP solution of PVdF. PVdF was used as a binder. In this slurry, the mass ratio of Bi powder, AB, and PVdF was Bi powder:AB:PVdF = 8:1:1. After this slurry was applied to a copper foil (10 cm × 10 cm), the NMP solvent was removed, and the foil was shaped and punched out to 2 cm × 2 cm to prepare as the first electrode.

[0177] <Preparation of test cells> The test cell was assembled in the same manner as in Example 1, except that the first electrode prepared in Comparative Example 1 was used.

[0178] <Charge / Discharge Test> A charge-discharge test was performed on the test cell. 0.6mA (0.15mA / cm²) 2 Charging was performed to 0V and discharging to 2V using a constant current value. This was considered one cycle. The charge-discharge cycle test was conducted at 25°C.

[0179] Figure 34A is a graph showing the results of the initial charge-discharge test of the test cell according to Comparative Example 1. Figure 34B is a graph showing the results of the second charge-discharge test of the test cell according to Comparative Example 1. From Figures 34A and 34B, it can be seen that the battery according to Comparative Example 1, in which Bi powder was used in the active material layer, had very poor initial discharge characteristics, and the charge-discharge capacity decreased even further in the second test.

[0180] <Charge-discharge cycle test> Under the same conditions as in the charge-discharge test, the charge-discharge cycle was repeatedly performed, with each cycle counting as one, and the cycle characteristics were evaluated. Figure 35 is a graph showing the relationship between the number of cycles up to 10 and the discharge capacity density for the test cell of Comparative Example 1. From the results shown in Figure 35, it was confirmed that the battery of Comparative Example 1, in which Bi powder was used in the active material layer, had very poor cycle characteristics.

[0181] The batteries in Examples 1 to 4, which had a first electrode containing BiNi, exhibited improved cycle characteristics compared to batteries with a first electrode containing Bi. In particular, the batteries in Examples 1 to 3, in which the active material layer containing BiNi had high orientation such that I(2) / I(1) was 0.28 or less, exhibited superior cycle characteristics. Furthermore, as shown in Figure 15, for example, it was confirmed that cycle characteristics were further improved when the electrolyte solvent contained at least one selected from the group consisting of VC, 2MeTHF, FEC, and EC. Also, according to Figures 15, 18, and 19, the batteries in Examples 1-10, 1-11, and 1-12, which used an electrolyte containing a mixed solvent of vinylene carbonate and a linear carbonate, exhibited superior cycle characteristics compared to the batteries in Examples 1-6 and 1-8, which used an electrolyte containing only one type of linear carbonate as the solvent. [Industrial applicability]

[0182] The battery described herein can be used, for example, as an all-solid-state lithium secondary battery. [Explanation of Symbols]

[0183] 1000 batteries 100 Current collector 101 First electrode 102 Electrolyte 103 Second electrode 104 Active material layer 105 Current collector 106 Active material layer 107 Separator 108 Exterior

Claims

1. First electrode and The second electrode and Electrolyte and Equipped with, The first electrode comprises a current collector and an active material layer. The current collector contains Ni, The active material layer contains BiNi, The BiNi mentioned above has a crystal structure whose space group belongs to C2 / m. Nonaqueous electrolyte secondary battery.

2. In the X-ray diffraction pattern of the active material layer obtained by surface X-ray diffraction measurement using Cu-Kα rays, Let I(1) be the height intensity of the maximum peak that exists in the diffraction angle range 2θ from 29° to 31°. When I(2) is the height intensity of the maximum peak that exists in the diffraction angle range 2θ of 41° to 43°, The ratio of I(2) to I(1), I(2) / I(1), is 0.28 or less. The non-aqueous electrolyte secondary battery according to claim 1.

3. The active material layer consists of LiBi and Li 3 Includes at least one selected from the group consisting of Bi, A non-aqueous electrolyte secondary battery according to claim 1 or 2.

4. The active material layer does not contain a solid electrolyte. A non-aqueous electrolyte secondary battery according to any one of claims 1 to 3.

5. The active material layer contains BiNi as the main component of the active material. A non-aqueous electrolyte secondary battery according to any one of claims 1 to 4.

6. The active material layer contains substantially only BiNi as the active material. The non-aqueous electrolyte secondary battery according to claim 5.

7. The electrolyte comprises an aprotic solvent and a lithium salt dissolved in the aprotic solvent. A non-aqueous electrolyte secondary battery according to any one of claims 1 to 6.

8. The aprotic solvent comprises at least one selected from the group consisting of vinylene carbonate, 2-methyltetrahydrofuran, fluoroethylene carbonate, and ethylene carbonate. The non-aqueous electrolyte secondary battery according to claim 7.

9. The aprotic solvent includes vinylene carbonate and linear carbonate. The non-aqueous electrolyte secondary battery according to claim 7.

10. The first electrode is a negative electrode, The second electrode is the positive electrode. A non-aqueous electrolyte secondary battery according to any one of claims 1 to 9.

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