Battery

Abstract

A battery (1000) according to the present disclosure comprises a first electrode (101), a second electrode (103), and an electrolyte (102). The first electrode (101) has a base material that is a porous body, and an active material layer that is positioned on the surface of the base material. The active material layer includes Bi. The active material layer may include Bi as the main component of the active material. In the battery (1000), the first electrode (101) may be a negative electrode and the second electrode (102) may be a positive electrode, for example.

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

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

[0009] The battery of the present disclosure includes a first electrode, a second electrode, and an electrolyte. The first electrode has a porous substrate and an active material layer located on the surface of the substrate, and the active material layer contains Bi.

[0010] According to the present 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 the present disclosure. [Figure 2] FIG. 2 is a partially enlarged cross-sectional view schematically showing a configuration example of a first electrode in a battery according to an embodiment of the present disclosure. [Figure 3] FIG. 3 is a graph showing the relationship between the number of cycles and the discharge capacity density of test cells according to Example 1, Example 2, Comparative Example 1, and Comparative Example 2. [Figure 4] FIG. 4 is a graph showing the relationship between the number of cycles and the discharge capacity density of test cells according to Example 1 and Examples 3 to 7.

Modes for Carrying Out the Invention

[0012] (Findings on which the present disclosure is based) As described in the column of [Background Art], in lithium secondary batteries, improvement of electrode active materials is aimed at improving battery characteristics.

[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 found that when Bi is formed as an active material on the surface of a porous substrate, the cycle characteristics of the battery are improved, leading to the completion of this disclosure.

[0021] (Summary of one aspect of this disclosure) A battery according to a first aspect of the present disclosure comprises a first electrode, a second electrode, and an electrolyte, wherein the first electrode has a porous substrate and an active material layer located on the surface of the substrate, and the active material layer contains Bi.

[0022] The battery according to the first embodiment comprises an electrode having a porous substrate and an active material layer containing Bi located on the surface of the substrate. Therefore, the battery according to the first embodiment has improved cycle characteristics.

[0023] In a second aspect of this disclosure, for example, in the battery according to the first aspect, the active material layer may include elemental Bi.

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

[0025] In a third aspect of this disclosure, for example, in a battery according to the first or second aspect, the active material layer may contain Bi as the main component of the active material.

[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 the battery according to the third aspect, the active material layer may substantially consist only of Bi as the active material.

[0028] The battery according to the fourth embodiment has improved capacity 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 include at least one selected from the group consisting of LiBi and Li3Bi.

[0030] The battery according to the fifth embodiment has improved capacity and improved cycle characteristics.

[0031] In a sixth aspect of this disclosure, for example, in a battery according to any one of the first to fifth aspects, the substrate may include at least one selected from the group consisting of Cu and Ni.

[0032] The battery according to the sixth embodiment 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 active material layer may be a plating layer.

[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 electrolyte may include an aprotic solvent and a lithium salt dissolved in the aprotic solvent.

[0036] The battery according to the eighth embodiment can realize a lithium-ion battery having improved capacity and improved cycle characteristics.

[0037] In a ninth aspect of this disclosure, for example, in the battery according to the eighth aspect, the aprotic solvent may include at least one selected from the group consisting of vinylene carbonate and fluoroethylene carbonate.

[0038] The battery according to the ninth embodiment has improved capacity and improved cycle characteristics.

[0039] In a tenth aspect of this disclosure, for example, in a battery according to any one of the first to ninth aspects, the first electrode may be a negative electrode and the second electrode may be a positive electrode.

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

[0041] (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.

[0042] 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.

[0043] The battery 1000 comprises a first electrode 101, a second electrode 103, and an electrolyte 102. Figure 2 is a schematic partially enlarged cross-sectional view showing an example of the configuration of the first electrode 101 in the battery 1000 according to an embodiment of the present disclosure. As shown in Figure 2, the first electrode 101 has a porous substrate 108 and an active material layer 109 located on the surface of the substrate 108. The active material layer 109 contains Bi. The active material layer 109 contains, for example, Bi alone.

[0044] As shown in Figure 1, the battery 1000 according to this embodiment may further include, for example, a first current collector 104 in contact with the first electrode 101. Furthermore, the battery 1000 according to this embodiment may further include, for example, a second current collector 105 in contact with the second electrode 103. By providing the first electrode 101 and the second current collector 105, electricity can be extracted from the battery 1000 with high efficiency.

[0045] The battery 1000 further comprises, for example, a separator 106 and an outer casing 107. The separator 106 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 106. The first electrode 101, the second electrode 103, the separator 106, and the electrolyte 102 are housed in the outer casing 107. The electrolyte 102 is, for example, an electrolyte impregnated into the first electrode 101, the second electrode 103, and the separator 106. The electrolyte 102 may fill the internal space of the outer casing 107.

[0046] Furthermore, in the battery 1000, an active material layer 109 containing Bi is formed on the surface of a porous substrate 108 at the first electrode 101. The active material layer 109 is also formed on the inner walls of the pores in the substrate 108, for example, as shown in Figure 2. Therefore, in the battery 1000, the area of ​​the active material layer 109 that can come into contact with the electrolyte is larger when the active material layer 109 is formed on the surface of the porous substrate 108 than when it is formed on the surface of a foil-like substrate. Consequently, the battery 1000 according to this embodiment can improve capacity.

[0047] In the first electrode 101 shown in Figure 2, the active material layer 109 is formed as a thin film on the inner wall of the pores in the substrate 108, and the pores exist with a relatively high porosity. However, the first electrode 101 is not limited to this configuration. For example, the first electrode 101 may have a structure in which the active material layer 109 almost completely fills the inside of the pores in the substrate 108, resulting in a low porosity. Even if the first electrode 101 has such a structure, the boundary between the substrate 108 and the active material layer 109 can be clearly identified, and it can be said that in the first electrode 101, the substrate 108 is a porous body and the active material layer 109 is formed on the surface of the substrate 108. The active material layer 109 may be formed on a part of the inner wall of multiple pores, or it may be formed on almost the entire surface.

[0048] Battery 1000 is, for example, a lithium secondary battery. The following explanation will use the case where the metal ions intercepted and released in the active material layer 109 of the first electrode 101 and the second electrode 103 during charging and discharging of battery 1000 are lithium ions as an example.

[0049] As described above, the base material 108 is a porous body. In this specification, a porous body means a structure having a plurality of pores, including open pores that open to the outside. Examples of porous bodies in this specification include meshes and porous structures. A porous structure is a structure composed of a porous material having a plurality of pores, and the size of the pores is not particularly limited. An example of a porous structure is a foam. A porous structure may also be a three-dimensional mesh structure in which the pores are in communication with each other. In this specification, "pore" includes both those that are filled with, for example, an active material layer and those that are not. That is, even those that are filled with, for example, an active material layer are considered to be "pores".

[0050] The base material 108 is, for example, conductive. The base material 108 may be formed of a conductive material such as metal, or it may be a porous body made of a non-conductive material such as resin (for example, foamed resin) with a conductive film made of a conductive material provided on its surface. The base material 108 may be, for example, a metal mesh or a porous metal. The base material 108 can function as a current collector for the first electrode 101. That is, if a first current collector 104 is provided, for example, the first current collector 104 and the base material 108 function as current collectors for the first electrode 101. If a first current collector 104 is not provided, for example, the base material 108 functions as a current collector for the first electrode 101.

[0051] The base material 108 may include at least one selected from the group consisting of, for example, Cu and Ni. The base material 108 may be, for example, nickel mesh or porous nickel.

[0052] As described above, the active material layer 109 contains elemental Bi. The active material layer 109 may also contain Bi as its main component. Here, "the active material layer 109 contains Bi as its main component" is defined as "the Bi content in the active material layer 109 is 50% by mass or more." The Bi content in the active material layer 109 can be determined, for example, by confirming the presence of Bi in the active material layer 109 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 109.

[0053] With the above configuration, improved charge-discharge cycle characteristics can be obtained.

[0054] The active material layer 109, which mainly contains Bi, may be composed of, for example, a Bi thin film (hereinafter referred to as "Bi thin film").

[0055] The active material layer 109, composed of a Bi thin film, can be fabricated, for example, by electroplating. A method for manufacturing the first electrode 101 by fabricating the active material layer 109 by electroplating is as follows.

[0056] First, the substrate for electroplating is prepared. As the substrate for electroplating, for example, a porous material that can constitute the substrate 108 when the first electrode 101 is formed is used. For example, a metal mesh or a porous metal can be used as the substrate for electroplating. For example, a nickel mesh or porous nickel may be used as the substrate for electroplating. The porous material used as the substrate for electroplating is not particularly limited in structure, as it only needs to be able to constitute the substrate 108 when the first electrode is formed through processes such as electroplating and pressure treatment. It can be appropriately selected according to the desired structure of the first electrode 101. As an example, the porous material used as the substrate for electroplating may be, for example, 0.014 m 2 / cm 3 More than 0.036m 2 / cm 3 It may have the following specific surface areas.

[0057] As an example, a nickel mesh is prepared as the base material for electroplating. After pre-degreasing the nickel mesh with an organic solvent, it is immersed in an acidic solvent for degreasing to activate the surface of the nickel mesh. The activated nickel mesh is connected to a power source so that current can be applied. The nickel mesh connected to the power source is immersed in a bismuth plating bath. As the bismuth plating bath, for example, an organic acid bath containing Bi 3+ ions and an organic acid is used. Then, by controlling the current density and the application time and applying current to the nickel mesh, Bi is electroplated on the surface of the nickel mesh. After electroplating, the nickel mesh is recovered from the plating bath, and after removing the masking, it is washed and dried with pure water. By these methods, a Bi plating layer is formed on the surface of the nickel mesh. The bismuth plating bath used for forming the Bi plating layer is not particularly limited, and it can be appropriately selected from known bismuth plating baths capable of depositing a single Bi thin film. In the bismuth plating bath, as the organic acid bath, an organic sulfonic acid bath, a gluconic acid and ethylenediaminetetraacetic acid (EDTA) bath, or a citric acid and EDTA bath can be used. Further, a sulfuric acid bath, for example, may be used for the bismuth plating bath. An additive may also be added to the bismuth plating bath.

[0058] Even when porous nickel, for example, is used as the base material for electroplating, a Bi plating layer can be formed by the same method as described above.

[0059] The active material composed of the Bi thin film has a density of, for example, 6.0 g / cm 3 or more and 9.8 g / cm 3 or less. The density of the active material composed of the Bi thin film may be 6.5 g / cm 3 or more and 9.8 g / cm 3 or less, or 7.0 g / cm 3 or more and 9.8 g / cm 3The following may also apply. The density of the active material composed of a Bi thin film can be determined, for example, by calculating it using the Archimedes method. For example, if the active material layer 109 is composed of a thin film substantially made of the active material, the density of the active material can be obtained by taking at least a portion of the thin film as a sample and calculating the density of the sample using, for example, the Archimedes method.

[0060] 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.

[0061] [First electrode] As described above, the first electrode 101 has a porous substrate 108 and an active material layer 109 located on the surface of the substrate 108. The configuration of the substrate 108 and the active material layer 109 is as described above.

[0062] The first electrode 101 functions as a negative electrode. Therefore, the active material layer 109 contains a negative electrode active material that has the property of intercalating and releasing lithium ions. The active material layer 109 contains Bi, which functions as the negative electrode active material.

[0063] Bi is a metallic element that alloys with lithium. When Bi functions as the negative electrode active material, lithium is intercalated during charging by Bi forming an alloy with lithium. That is, in the active material layer 109, a lithium-bismuth alloy is formed when the battery 1000 is charged. The formed 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 109 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 Bi.

[0064] Bi, 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 reaction is for the case where the lithium bismuth alloy produced during charging is Li3Bi. Charging: Bi+3Li + +3e - →Li3Bi Discharge: Li3Bi→Bi+3Li + +3e - The active material layer 109 may contain substantially only Bi as the active material. In this case, the battery 1000 can have improved capacity and improved cycle characteristics. Note that "the active material layer 109 contains substantially only Bi as the active material" means, for example, that the amount of other active materials besides Bi in the active material layer 109 is 1% by mass or less. The active material layer 109 may contain only Bi as the active material.

[0065] The active material layer 109 does not necessarily have to contain a solid electrolyte.

[0066] The active material layer 109 may be disposed in direct contact with the surface of the substrate 108. Furthermore, if the battery 1000 includes a first current collector 104, the substrate 108 may be disposed in contact with the first current collector 104.

[0067] The active material layer 109 may be in the form of a thin film.

[0068] The active material layer 109 may be a plating layer. The active material layer 109 may be a plating layer provided in direct contact with the surface of the substrate 108. That is, as described above, the active material layer 109 may be a Bi plating layer formed on the surface of the substrate 108.

[0069] If the active material layer 109 is a plating layer provided in direct contact with the surface of the substrate 108, the active material layer 109 adheres firmly to the substrate 108. This further suppresses the deterioration of the current collection characteristics of the first electrode 101 that occurs when the active material layer 109 repeatedly expands and contracts. Therefore, the charge and discharge characteristics of the battery 1000 are further improved. Furthermore, if the active material layer 109 is a plating layer, the active material layer 109 contains a high density of Bi, which alloys with lithium, thus enabling even higher capacity.

[0070] The active material layer 109 may contain materials other than Bi or Bi-containing alloys. The Bi-containing alloys referred to here are, for example, lithium bismuth alloys produced by charging reactions (e.g., LiBi and Li3Bi).

[0071] The active material layer 109 may further contain a conductive material.

[0072] 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.

[0073] The active material layer 109 may further contain a binder.

[0074] 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.

[0075] The thickness of the active material layer 109 is not particularly limited and may be, for example, 0.1 μm or more and 100 μm or less.

[0076] The material of the base material 108 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 base material 100 may be stainless steel.

[0077] The base material 108 may contain nickel (Ni).

[0078] The structure of the base material 108 is as described above. The base material 108 may be considered as the current collector of the first electrode 101 or as part of the current collector.

[0079] The thickness of the first electrode 101 may be 10 μm or more and 2000 μm or less. That is, the overall thickness of the porous substrate 108, on which the active material layer 109 is provided on the surface, may be 10 μm or more and 2000 μm or less. Having such a thickness for the first electrode 101 allows the battery to operate at high output.

[0080] [First current collector] In the battery 1000 according to this embodiment, the first current collector 104 may or may not be provided. The first current collector 104 may be provided in contact with the first electrode 101, for example. The first current collector 104 may be provided in contact with the base material 108 of the first electrode 101, for example. By providing the first current collector 104, electricity can be extracted from the battery 1000 with high efficiency.

[0081] The material of the first current collector 104 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 first current collector 104 may be stainless steel.

[0082] The first current collector 104 may contain nickel (Ni).

[0083] The first current collector 104 may be in the form of a plate or foil. From the viewpoint of easily ensuring high conductivity, the first current collector 104 may be a metal foil. The thickness of the first current collector 104 may be, for example, 5 μm or more and 20 μm or less.

[0084] The first current collector 104 may be a laminated film.

[0085] [Electrolyte] The electrolyte 102 includes, for example, an aprotic solvent and a lithium salt dissolved in the aprotic solvent.

[0086] Aprotic solvents are not particularly limited. Examples of aprotic solvents include 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 vinylene carbonate, fluoroethylene carbonate, 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, 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.

[0087] The electrolyte 102 may contain at least one selected from the group consisting of vinylene carbonate and fluoroethylene carbonate as an aprotic solvent. By including these solvents in the electrolyte 102, the battery 1000 has improved cycle characteristics.

[0088] 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.

[0089] [Second electrode] The second electrode 103 functions as the positive electrode. The second electrode 103 contains a material capable of intercalating and releasing metal ions such as lithium ions. This material is, for example, the positive electrode active material.

[0090] The second electrode 103 contains a positive electrode active material.

[0091] The second electrode 103 may be positioned on the surface of the second current collector 105, in direct contact with the second current collector 105.

[0092] As positive electrode active materials, for example, lithium-containing transition metal oxides, transition metal fluorides, polyanionic materials, fluorinated polyanionic materials, transition metal sulfides, transition metal oxysulfides, or transition metal oxynitrides can be used. An example of a lithium-containing transition metal oxide is LiNi 1-x-y Co x Al y O2((x+y)<1), LiNi 1-x-y Co x Mn y Examples include O2((x+y)<1) or LiCoO2. 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 also contain Li(Ni,Co,Mn)O2.

[0093] 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.

[0094] 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).

[0095] The halide solid electrolyte may be, for example, a material represented by the following compositional formula (1).

[0096] 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 metal elements and metalloid elements other than Li, and X is at least one selected from the group consisting of F, Cl, Br, and I.

[0097] "Metallic elements" are B, Si, Ge, As, Sb, and Te.

[0098] "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 combined with halogen elements to create inorganic compounds.

[0099] In compositional formula (1), M may contain Y, and X may contain Cl and Br.

[0100] 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.

[0101] 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.

[0102] Examples of oxide solid electrolytes include NASICON-type solid electrolytes represented by LiTi2(PO4)3 and its elemental substitutions, (LaLi)TiO3-based perovskite-type solid electrolytes, and Li14 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.

[0103] As a polymer solid electrolyte, for example, a compound of a polymer compound and a lithium salt can be used. The polymer compound may have an ethylene oxide structure. Polymer 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.

[0104] Examples of complex hydride solid electrolytes that can be used include LiBH4-LiI and LiBH4-P2S5.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] The second electrode 103 may contain a conductive material for the purpose of enhancing electronic conductivity.

[0111] The second electrode 103 may contain a binder.

[0112] The same materials that can be used for the first electrode 101 may be used as the conductive material and binder.

[0113] 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.

[0114] The non-aqueous electrolyte contains a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent. Examples of the non-aqueous solvent and lithium salt are the same as those exemplified in the description of the electrolyte. The concentration of the lithium salt is, for example, in the range of 0.5 mol / liter to 2 mol / liter.

[0115] 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.

[0116] Examples of cations contained in ionic liquids include (i) aliphatic quaternary salts such as tetraalkylammonium or tetraalkylphosphonium, (ii) aliphatic cyclic ammonium compounds such as pyrrolidiniums, morpholiniums, imidazoliniums, tetrahydropyrimidiniums, piperadiniums, or piperidiniums, or (iii) nitrogen-containing heterocyclic aromatic cations such as pyridiniums or imidazoliums.

[0117] An example of anion found in ionic liquids is PF6. - BF4 - SbF6 - AsF6 - , SO3CF3 - , N(SO2CF3)2 - , N(SO2C2F5)2 - , N(SO2CF3)(SO2C4F9) - , or C(SO2CF3)3 - That is the case.

[0118] The ionic liquid may contain a lithium salt.

[0119] [Second current collector] In the battery 1000 according to this embodiment, the second current collector 105 may or may not be provided. The second current collector 105 is provided, for example, in contact with the second electrode 103. By providing the second current collector 105, electricity can be extracted from the battery 1000 with high efficiency.

[0120] The material of the second current collector 105 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 second current collector 105 may be stainless steel.

[0121] The second current collector 105 may contain nickel (Ni).

[0122] The second current collector 105 may be in the form of a plate or foil. From the viewpoint of easily ensuring high conductivity, the second current collector 105 may be a metal foil. The thickness of the second current collector 105 may be, for example, 5 μm or more and 20 μm or less.

[0123] [Separator] The separator 106 is lithium ion conductive. The material of the separator 106 is not particularly limited, as long as the passage of lithium ions is permitted. The material of the separator 106 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 106 is made from these materials, the safety of the battery 1000 can be sufficiently ensured. As for the solid electrolyte, 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.

[0124] [Exterior] The outer casing 107 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 107 may also be a resin or metal container.

[0125] 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.

[0126] When the first electrode 101 is the positive electrode and the second electrode 103 is the negative electrode, the active material layer 109 is the positive electrode active material layer. That is, the Bi contained in the active material layer 109 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.

[0127] 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, prismatic, sheet-shaped, button-shaped, flat, or stacked. [Examples]

[0128] 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.

[0129] (Example 1) <Fabrication of the first electrode> As a pretreatment, a nickel mesh (2cm x 2cm, thickness: 50μm, manufactured by Niraco Co., Ltd., "NI-318200") was pre-degreased with an organic solvent, and then degreased by immersion in an acidic solvent to activate the nickel mesh 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 mesh was connected to a power supply so that current could be applied, and then immersed in the plating bath. Subsequently, the current density was set to 2 A / dm². 2 By controlling the process, Bi was electroplated onto one side of the nickel mesh to a thickness of approximately 1 μm. After electroplating, the nickel mesh was recovered from the acidic bath, washed with pure water, and dried.

[0130] <Preparation of test cells> The first electrode was used as the working electrode. 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 was prepared by dissolving LiPF6 in vinylene carbonate (VC) at a concentration of 1.0 mol / L. Using this working electrode, counter electrode, and electrolyte, a battery was assembled as the test cell of Example 1. The test cell prepared here is a unipolar test cell using a working electrode and a counter electrode, and is used to test the performance of one electrode in a secondary battery. Specifically, the electrode under test is used as the working electrode, and an appropriate amount of active material sufficient 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.

[0131] <Charge-discharge cycle test> A charge-discharge cycle test was performed on the test cell. 0.6mA (0.15mA / cm²) 2Charging was performed to 0V and discharging to 2V at a constant current value of (equivalent to 0.5IT). Charging and discharging were repeated as one cycle, and the cycle characteristics were evaluated. The charge-discharge cycle test was conducted at 25°C. Figure 3 is a graph showing the relationship between the number of cycles and the discharge capacity density of the test cell in Example 1. In Example 1, the capacity retention rate of the cell decreased to about 50% after 20 cycles, but thereafter it decreased gradually, maintaining a capacity retention rate of about 30% even after 100 cycles.

[0132] (Example 2) <Fabrication of the first electrode> As a pretreatment, porous nickel (2cm x 2cm, thickness: 1.6mm, manufactured by Niraco Co., Ltd., "NI-318161") was pre-degreased with an organic solvent, and then degreased by immersion in an acidic solvent to activate the surface of the porous nickel. 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 porous nickel 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 set to 2 A / dm². 2 By controlling the process, Bi was electroplated onto the porous nickel surface to a thickness of approximately 1 μm. After electroplating, the porous nickel was recovered from the acidic bath, washed with pure water, and dried.

[0133] <Preparation of test cells> The first electrode from Example 2 was used as the working electrode. Except for this point, the test cell was prepared in the same manner as in Example 1.

[0134] <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 3 is a graph showing the relationship between the number of cycles and the discharge capacity density of the test cell in Example 2. In Example 2, the capacity retention rate of the cell decreased to about 50% after 20 cycles, but thereafter it decreased gradually, maintaining a capacity retention rate of about 20% even after 50 cycles.

[0135] (Reference example 1) <Fabrication of the first electrode> As a pretreatment, the Ni foil was pre-degreased with an organic solvent, then one side was masked and the Ni foil surface was activated by immersion in an acidic solvent. 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 current could be applied, and then immersed in the plating bath. Subsequently, the current density was set to 2 A / dm². 2 By controlling the process, Bi was electroplated onto the unmasked Ni foil surface to a thickness of approximately 1 μm. After electroplating, the Ni foil was recovered from the acidic bath, the masking was removed, and the foil 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 Ni foil.

[0136] <Preparation of test cells> The first electrode from Reference Example 1 was used as the working electrode. Aside from this, the test cell was prepared in the same manner as in Example 1.

[0137] <Charge-discharge cycle test> A charge-discharge cycle test was performed on the test cell. The charge-discharge cycle test was conducted in the same manner as in Example 1. Figure 3 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. In the cell of Reference Example 1, the capacity retention rate decreased significantly at 20 cycles.

[0138] (Reference example 2) <Fabrication of the first electrode> The first electrode was fabricated using the same method as in Reference Example 1, except that Cu foil was used instead of Ni foil.

[0139] <Preparation of test cells> The first electrode from Reference Example 2 was used as the working electrode. Aside from this, the test cell was prepared in the same manner as in Example 1.

[0140] <Charge-discharge cycle test> A charge-discharge cycle test was performed on the test cell. The charge-discharge cycle test was conducted in the same manner as in Example 1. Figure 3 is a graph showing the relationship between the number of cycles and the discharge capacity density of the test cell related to Reference Example 2. In the cell of Reference Example 2, the capacity retention rate decreased significantly at 20 cycles.

[0141] (Example 3) <Preparation of test cells> A test cell was prepared in the same manner as in Example 1, except that the solvent of the electrolyte was changed from vinylene carbonate (VC) to fluoroethylene carbonate (FEC).

[0142] <Charge-discharge cycle test> A charge-discharge cycle test was performed using the test cell of Example 3 in the same manner as in Example 1. However, the constant current value was changed to 0.05 mA. A charge-discharge cycle test was also performed on the test cell of Example 1 under the same conditions. Figure 4 is a graph showing the relationship between the number of cycles and the discharge capacity density of the test cells of Example 1 and Example 3. As shown in Figure 4, when FEC was used as the solvent, better cycle characteristics were obtained than with VC.

[0143] (Example 4) <Preparation of test cells> A test cell was prepared in the same manner as in Example 1, except that the solvent of the electrolyte was changed from vinylene carbonate (VC) to ethylene carbonate (EC).

[0144] <Charge-discharge cycle test> A charge-discharge cycle test was performed using the test cell of Example 4 in the same manner as in Example 1. However, the constant current value was changed to 0.05 mA. In this example, a charge-discharge cycle test was also performed with a discharge voltage up to 1.4 V. Figure 4 is a graph showing the relationship between the number of cycles and the discharge capacity density of the test cell of Example 4.

[0145] (Example 5) <Preparation of test cells> A test cell was prepared in the same manner as in Example 1, except that the solvent of the electrolyte was changed from vinylene carbonate (VC) to propylene carbonate (PC).

[0146] <Charge-discharge cycle test> A charge-discharge cycle test was performed using the test cell of Example 5 in the same manner as in Example 1. However, the constant current value was changed to 0.05 mA. Figure 4 is a graph showing the relationship between the number of cycles and the discharge capacity density of the test cell of Example 5.

[0147] (Example 6) <Preparation of test cells> A test cell was prepared in the same manner as in Example 1, except that the solvent of the electrolyte was changed from vinylene carbonate (VC) to methyl ethyl carbonate (MEC).

[0148] <Charge-discharge cycle test> A charge-discharge cycle test was performed using the test cell of Example 6 in the same manner as in Example 1. However, the constant current value was changed to 0.05 mA. Figure 4 is a graph showing the relationship between the number of cycles and the discharge capacity density of the test cell of Example 6.

[0149] (Example 7) <Preparation of test cells> A test cell was prepared in the same manner as in Example 1, except that the solvent of the electrolyte was changed from vinylene carbonate (VC) to a mixed solvent of EC and MEC (EC:MEC = 1:1 (volume ratio)).

[0150] <Charge-discharge cycle test> A charge-discharge cycle test was performed using the test cell of Example 7 in the same manner as in Example 1. However, the constant current value was changed to 0.05 mA, and the discharge voltage was limited to 1.4 V. Figure 4 is a graph showing the relationship between the number of cycles and the discharge capacity density of the test cell of Example 7. [Industrial applicability]

[0151] The battery described herein can be used, for example, as a lithium secondary battery. [Explanation of symbols]

[0152] 1000 batteries 101 First electrode 102 Electrolyte 103 Second electrode 104 First current collector 105 Second current collector 106 Separator 107 Exterior 108 Base material 109 Active material layer

Claims

1. First electrode and The second electrode and Electrolyte and Equipped with, The first electrode is, A porous substrate, The substrate has an active material layer located on its surface, The active material layer contains Bi, The active material layer is a plating layer. battery.

2. The active material layer contains Bi elemental, The battery according to claim 1.

3. The active material layer contains Bi as the main component of the active material. The battery according to claim 1.

4. The active material layer contains substantially only Bi as the active material. The battery according to claim 3.

5. The active material layer consists of LiBi and Li 3 Includes at least one selected from the group consisting of Bi, The battery according to claim 1.

6. The substrate comprises at least one selected from the group consisting of Cu and Ni. The battery according to claim 1.

7. The electrolyte comprises an aprotic solvent and a lithium salt dissolved in the aprotic solvent. The battery according to claim 1.

8. The aprotic solvent comprises at least one selected from the group consisting of vinylene carbonate and fluoroethylene carbonate. The battery according to claim 7.

9. The first electrode is a negative electrode, The second electrode is the positive electrode. The battery according to claim 1.

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