Battery

Abstract

This battery is provided with a first electrode, a second electrode and an electrolyte solution; the first electrode comprises a collector and an active material layer; the active material layer contains Bi as a main component of the active material; and the electrolyte solution contains at least one substance that is selected from the group consisting of vinylene carbonate and fluoroethylene carbonate.

Description

[Technical Field]

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

[0002] In recent years, research and development of lithium secondary batteries has been actively conducted. Battery characteristics such as charge / discharge voltage, charge / discharge cycle life characteristics, and storage characteristics are greatly affected by the electrodes used. For this reason, efforts are being made to improve battery characteristics by improving the electrode active material.

[0003] For example, lithium secondary batteries that use aluminum, silicon, tin, or the like as electrodes that electrochemically alloy with lithium during charging have long been proposed. Patent Document 1 discloses a lithium secondary battery that includes a negative electrode containing a negative electrode material made of an alloy containing silicon, tin, and a transition metal, a positive electrode, and an electrolyte. Patent Document 2 discloses a lithium secondary battery that includes a negative electrode that uses a silicon thin film provided on a current collector as an active material, a positive electrode, and an electrolyte. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4898737 [Patent Document 2] Patent No. 3733065 Summary of the Invention [Problem to be solved by the invention]

[0005] The present disclosure provides a battery with good cycle characteristics. [Means for solving the problem]

[0006] The battery of the present disclosure comprises: A first electrode; A second electrode; An electrolyte; Equipped with the first electrode has a current collector and an active material layer, the active material layer contains Bi as a main component of the active material, The electrolyte solution contains at least one selected from the group consisting of vinylene carbonate and fluoroethylene carbonate. [Effects of the Invention]

[0007] According to the present disclosure, a battery having good cycle characteristics can be provided. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view schematically illustrating an example of the configuration of a battery 1000 according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a graph showing the relationship between the thickness of the active material layer made of a Bi plating layer and the density of the active material. [Figure 3] FIG. 3 is a graph showing an example of the X-ray diffraction pattern of an active material layer made of a Bi plating layer formed on a copper foil and of Bi powder. [Figure 4] FIG. 4 is a graph showing the relationship between the number of cycles and the discharge capacity density of the batteries according to Examples 1 and 2 and Comparative Examples 1 to 4. In FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] (Findings that formed the basis of this disclosure) As described in the section of the "Background Art," efforts are being made to improve the battery characteristics of lithium secondary batteries by improving the electrode active materials.

[0010] When lithium metal is used as the negative electrode active material, lithium secondary batteries with high energy density per weight and per volume can be obtained. However, in lithium secondary batteries with this configuration, lithium precipitates in a dendrite-like form during charging. Part of the precipitated lithium metal reacts with the electrolyte, resulting in low charge / discharge efficiency and poor cycle characteristics.

[0011] In response to this, carbon, particularly graphite, has been proposed as an anode. In carbon-based anodes, charging and discharging occur through the insertion and extraction of lithium into and from the carbon. In anodes with this structure, lithium metal does not precipitate in a dendritic form due to the charge-discharge mechanism. Furthermore, lithium secondary batteries employing such anodes have excellent reversibility due to the topotactic reaction, resulting in charge-discharge efficiencies approaching 100%. For these reasons, lithium secondary batteries employing anodes made of carbon, particularly graphite, have been put to practical use. However, the theoretical capacity density of graphite is 372 mAh / g, approximately one-tenth the theoretical capacity density of lithium metal (3884 mAh / g). Therefore, the active material capacity density of anodes using graphite is low. Furthermore, because the actual capacity density of graphite is nearly equal to the theoretical capacity density, the capacity of anodes using graphite is limited.

[0012] In response to these challenges, lithium secondary batteries have long been proposed that use electrodes made of aluminum, silicon, tin, or the like, which electrochemically alloy with lithium during charging. The capacity density of metals that alloy with lithium is significantly greater than that of graphite. Silicon, in particular, has a high theoretical capacity density. Therefore, electrodes made of aluminum, silicon, tin, or the like, which alloy with lithium, are promising as negative electrodes for batteries that exhibit high capacity, and various secondary batteries using such negative electrodes have been proposed (Patent Document 1).

[0013] However, negative electrodes using metals that alloy with lithium as described above expand when they absorb lithium and contract when they release lithium. Repeated expansion and contraction during charging and discharging causes the alloy, which is the electrode active material, to pulverize, deteriorating the current collection characteristics of the negative electrode, and thus failing to achieve sufficient cycle performance. Several attempts have been made to address these drawbacks. 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 these attempts, the active material, i.e., the metal that alloys with lithium, forms a thin film that adheres closely to the current collector, so that current collection performance is hardly impaired even when the negative electrode repeatedly expands and contracts due to the absorption and release of lithium.

[0014] However, forming the active material by sputtering or vapor deposition as described above is not practical due to the high manufacturing costs. Forming the active material by electroplating, which has low manufacturing costs, is practical, but electroplating silicon is very difficult. Furthermore, tin, which is easy to electroplat, has the problem of poor discharge flatness, making it difficult to use as a battery electrode.

[0015] Bismuth (Bi) is also an example of a metal that alloys with lithium. Bi forms compounds with lithium (Li), called LiBi and Li3Bi. There is almost no difference between the potentials of LiBi and Li3Bi. On the other hand, tin, which has poor discharge flatness, forms several 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 large potential differences between the multiple compounds formed with lithium, as tin does. For this reason, electrodes containing Bi as an active material have excellent discharge flatness because their potential is flat. Therefore, electrodes containing Bi as an active material are considered suitable as battery electrodes.

[0016] However, batteries equipped with electrodes containing Bi as an active material, particularly batteries equipped with electrodes containing an active material layer containing Bi as the main active material component, have not always been able to achieve good cycle characteristics.

[0017] Therefore, the present inventors have conducted extensive research to improve the cycle characteristics of a battery equipped with an electrode containing Bi as an active material, and as a result, have completed the battery of the present disclosure described below.

[0018] (Summary of one aspect of the present disclosure) The battery according to the first aspect of the present disclosure comprises: A first electrode; A second electrode; An electrolyte; Equipped with the first electrode has a current collector and an active material layer, the active material layer contains Bi as a main component of the active material, The electrolyte solution contains at least one selected from the group consisting of vinylene carbonate and fluoroethylene carbonate.

[0019] In the battery according to the first embodiment, a first electrode having an active material layer containing Bi as a main active material component is used in combination with an electrolyte solution containing at least one selected from the group consisting of vinylene carbonate and fluoroethylene carbonate, and this configuration allows the battery according to the first embodiment to have good cycle characteristics.

[0020] In the second aspect of the present disclosure, for example, in the battery according to the first aspect, the density of the active material is 6.0 g / cm 3 or more and 9.8g / cm 3 Here, the density of the active material refers to the density of the active material when the battery is in a fully discharged state when the first electrode is a negative electrode, and refers to the density of the active material when the battery is in a fully charged state when the first electrode is a positive electrode.

[0021] The battery according to the second embodiment has a high capacity and good cycle characteristics.

[0022] In a third aspect of the present disclosure, for example, in the battery according to the second aspect, the density of the active material is 7.5 g / cm3 or more and 9.8g / cm 3 It may be the following:

[0023] The battery according to the third embodiment has a higher capacity and good cycle characteristics.

[0024] In a fourth aspect of the present disclosure, for example, in the battery according to any one of the first to third aspects, when the height intensity of the maximum peak present in a diffraction angle 2θ range of 26° or more and 28° or less is defined as I(1) and the height intensity of the maximum peak present in a diffraction angle 2θ range of 37° or more and 39° or less is defined as I(2) in an X-ray diffraction pattern of the active material layer obtained by surface X-ray diffraction measurement using Cu-Kα radiation, the ratio of I(2) to I(1), I(2) / I(1), may be 0.29 or more.

[0025] The battery according to the fourth embodiment has a higher capacity and good cycle characteristics.

[0026] In a fifth aspect of the present disclosure, for example, in the battery according to the fourth aspect, the I(2) / I(1) may be 0.57 or less.

[0027] The battery according to the fifth embodiment has a higher capacity and good cycle characteristics.

[0028] In a sixth aspect of the present disclosure, for example, in the battery according to any one of the first to fifth aspects, the active material layer may contain simple Bi.

[0029] The battery according to the sixth embodiment has a higher capacity and good cycle characteristics.

[0030] In a seventh aspect of the present disclosure, for example, in the battery according to any one of the first to sixth aspects, the active material layer may contain at least one selected from the group consisting of LiBi and Li3Bi.

[0031] The battery according to the seventh embodiment has a higher capacity and good cycle characteristics.

[0032] In an eighth aspect of the present disclosure, for example, in the battery according to any one of the first to seventh aspects, the active material layer may contain only simple Bi as the active material.

[0033] The battery according to the eighth embodiment has a higher capacity and good cycle characteristics.

[0034] In a ninth aspect of the present disclosure, for example, in the battery according to any one of the first to eighth aspects, the current collector may contain Cu.

[0035] The battery according to the ninth embodiment has a higher capacity and good cycle characteristics.

[0036] In a tenth aspect of the present disclosure, for example, in the battery according to any one of the first to ninth aspects, the active material layer may be a plating layer.

[0037] According to the tenth aspect, a battery having a higher capacity per volume and good cycle characteristics can be obtained.

[0038] In an eleventh aspect of the present disclosure, for example, in the battery according to any one of the first to tenth aspects, the first electrode may be a negative electrode and the second electrode may be a positive electrode.

[0039] The battery according to the eleventh embodiment has a higher capacity and good cycle characteristics.

[0040] (Embodiments of the present disclosure) Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The following descriptions are all comprehensive or specific examples. The numerical values, compositions, shapes, film thicknesses, electrical characteristics, secondary battery structures, etc. shown below are merely examples and are not intended to limit the present disclosure.

[0041] FIG. 1 is a cross-sectional view schematically illustrating an example of the configuration of a battery 1000 according to an embodiment of the present disclosure.

[0042] The battery 1000 includes a first electrode 101, a second electrode 103, and an electrolyte 102. The first electrode 101 includes a current collector 100 and an active material layer 104. The active material layer 104 contains Bi as a main active material component. The second electrode 103 may include a current collector 105 and an active material layer 106.

[0043] The battery 1000 further includes, for example, a separator 107 and an exterior casing 108. The separator 107 is disposed between the first electrode 101 and the second electrode 103. The first electrode 101 and the second electrode 103 face each other with the separator 107 interposed therebetween. The first electrode 101, the second electrode 103, the separator 107, and the electrolyte solution 102 are housed in the exterior casing 108. The electrolyte solution 102 is, for example, an electrolyte solution impregnated in the first electrode 101, the second electrode 103, and the separator 107. The electrolyte solution 102 may fill the internal space of the exterior casing 108.

[0044] Battery 1000 is, for example, a lithium secondary battery. Hereinafter, an example will be described in which battery 1000 is a lithium secondary battery and the metal ions absorbed and released in active material layer 104 of first electrode 101 and second electrode 103 during charge and discharge are lithium ions.

[0045] The phrase "active material layer 104 contains Bi as the main active material component" means that "in active material layer 104, the component that is contained in the largest amount by molar ratio as the active material is Bi."

[0046] According to the above configuration, good charge-discharge cycle characteristics can be obtained.

[0047] The active material contained in the active material layer 104 is 6.0 g / cm 3 or more and 9.8g / cm 3 It may have the following densities:

[0048] According to the above configuration, better charge / discharge cycle characteristics can be obtained.

[0049] Here, in this specification, the density of the active material contained in the active material layer 104 of the first electrode 101 refers to the density of the active material contained in the active material layer 104 when the battery 1000 is in a fully discharged state if the first electrode 101 is a negative electrode, and refers to the density of the active material contained in the active material layer 104 when the battery 1000 is in a fully charged state if the first electrode 101 is a positive electrode. In other words, the density of the active material contained in the active material layer 104 of the first electrode 101 specified in this specification refers to the density of the active material contained in the active material layer 104 when lithium ions have been released from the active material layer 104 due to full charge or full discharge. Here, the "fully charged state" of the battery disclosed herein refers to a state in which the battery has been charged at a constant current (e.g., 0.05 C relative to the theoretical capacity) to a predetermined voltage (e.g., the negative electrode potential is 0 V vs. a lithium reference electrode). Furthermore, the "fully discharged state" of the battery of the present disclosure refers to a state in which the battery is discharged at a constant current (e.g., 0.05 C relative to the theoretical capacity) to a predetermined voltage (e.g., a negative electrode potential of 2 V versus a lithium reference electrode). The density of the active material contained in the active material layer 104 can be determined, for example, by removing the active material from the active material layer 104 and calculating the density of the removed active material using, for example, the Archimedes method. As an example, when the active material layer 104 is formed of a thin film essentially consisting of an active material, the density of the active material can be obtained by removing at least a portion of the thin film as a sample and calculating the density of the sample using, for example, the Archimedes method. Here, a thin film essentially consisting of an active material means a thin film having an active material content of 90 mass % or more.

[0050] The main component of the active material is Bi, and the density of the active material is 6.0 g / cm 3 or more and 9.8g / cm 3The active material layer 104 described below may be composed of, for example, Bi formed into a thin film (hereinafter referred to as "Bi thin film"). When the active material layer 104 is composed of a high-density Bi thin film that satisfies the density range described above and is provided in contact with the current collector 100, it can have high adhesion to the current collector 100. With this configuration, the active material, i.e., Bi, a metal that alloys with lithium, is in the form of a thin film and adheres to the current collector 100, so that even if Bi repeatedly expands and contracts due to the absorption and release of lithium, the electron conduction path can be maintained. Therefore, when the active material contained in the active material layer 104 of the first electrode 101 in the present disclosure is 6.0 g / cm 3 or more and 9.8g / cm 3 When the density satisfies the following range, the current collecting ability is unlikely to decrease even if the active material layer 104 repeatedly expands and contracts due to the absorption and release of Li. 3 or more and 9.8g / cm 3 If the following densities are satisfied, the battery 1000 of the present disclosure can have good cycle characteristics.

[0051] Furthermore, the active material layer 104 made of a Bi thin film that satisfies the above density range is an active material layer with a high active material density, and can provide sufficient electron conduction paths. Therefore, the first electrode 101 provided with the active material layer 104 made of a Bi thin film can achieve a higher capacity than an electrode in which the active material layer is formed of Bi powder. Therefore, when the active material contained in the active material layer 104 of the first electrode 101 is 6.0 g / cm 3 or more and 9.8g / cm 3 When the following density is satisfied, the battery 1000 of the present disclosure can achieve high capacity in addition to good cycle characteristics.

[0052] The density of the active material contained in the active material layer 104 is 6.5 g / cm 3 or more and 9.8g / cm 3 It may be less than 7.0 g / cm 3 or more and 9.8g / cm 3When the first electrode 101 includes the active material layer 104 containing such a higher density active material, the battery 1000 can have better cycle characteristics and a higher capacity.

[0053] The density of the active material contained in the active material layer 104 is 7.5 g / cm 3 or more and 9.8g / cm 3 In particular, it may be 7.5 g / cm 3 First electrode 101 including active material layer 104 containing the above-described high-density active material can further improve the cycle characteristics and capacity of battery 1000.

[0054] In the X-ray diffraction pattern of the active material layer 104 obtained by surface X-ray diffraction measurement using Cu-Kα radiation, when the height intensity of the maximum peak present in the diffraction angle 2θ range of 26° or more and 28° or less is defined as I(1) and the height intensity of the maximum peak present in the diffraction angle 2θ range of 37° or more and 39° or less is defined as I(2), the ratio of I(2) to I(1), I(2) / I(1), may be 0.29 or more.

[0055] Here, the maximum peak present in the diffraction angle 2θ range of 26° to 28° in the X-ray diffraction pattern corresponds to the peak derived from the (1,0,-1,2) plane of elemental Bi. Furthermore, the maximum peak present in the diffraction angle 2θ range of 37° to 39° in the X-ray diffraction pattern corresponds to the peak derived from the (1,0,-1,4) plane of elemental Bi. A peak intensity ratio I(2) / I(1) of 0.29 or greater indicates that the ratio of the (1,0,-1,4) plane to the (1,0,-1,2) plane of elemental Bi having a trigonal crystal structure of space group R-3m is high on the surface of the active material layer 104. This indicates that the orientation of the (1,0,-1,4) plane is stronger on the surface of the active material layer 104. An active material layer 104 having such orientation in the crystal structure of elemental Bi on its surface can have high adhesion to the current collector 100. Therefore, since the active material layer 104 has such surface orientation, the current collection performance is less likely to decrease even when the active material layer 104 repeatedly expands and contracts due to charging and discharging, and the battery 1000 of the present disclosure can have better cycle characteristics and higher capacity.

[0056] The peak intensity ratio I(2) / I(1) may be 0.57 or less.

[0057] According to the above configuration, better charge / discharge cycle characteristics can be obtained.

[0058] The X-ray diffraction pattern of active material layer 104 can be obtained by X-ray diffraction measurement by the θ-2θ method using Cu-Kα radiation with wavelengths of 1.5405 Å and 1.5444 Å, that is, wavelengths of 0.15405 nm and 0.15444 nm.

[0059] The diffraction angle of a peak in an X-ray diffraction pattern is defined as the angle at which the signal-to-noise ratio (i.e., the ratio of signal S to background noise N) is 1.3 or more and the peak width at half maximum is 10° or less. The half width is the maximum intensity of the X-ray diffraction peak. MAX When the intensity is I MAXThe width is expressed as the difference between the two diffraction angles that are half the value of the square root of the diffraction angle.

[0060] Active material layer 104, which contains Bi as the main component of the active material and is made of a Bi thin film that satisfies the density and surface orientation ranges described above, can be produced by, for example, electroplating. A method for producing first electrode 101 by producing active material layer 104 by electroplating is, for example, as follows.

[0061] First, a substrate for electroplating is prepared. In the case of the first electrode 101, for example, a current collector 100 serves as the substrate. As an example, copper foil is prepared as the current collector 100. After pre-degreasing the copper foil with an organic solvent, one side is masked and the foil is immersed in an acidic solvent for degreasing, thereby activating the copper foil surface. The activated copper foil is connected to a power source so that a current can be applied. The copper foil connected to the power source is immersed in a bismuth plating bath. The bismuth plating bath may contain, for example, Bi 3+ An organic acid bath containing ions and an organic acid is used. Then, a current is applied to the copper foil while controlling the current density and application time, thereby electroplating Bi on the unmasked surface of the copper foil. After electroplating, the copper foil is removed from the plating bath, washed with pure water, and dried. These methods yield a first electrode 101 equipped with an active material layer 104 formed by electroplating Bi. The bismuth plating bath used to form the active material layer 104 is not particularly limited and can be appropriately selected from known bismuth plating baths capable of depositing a thin film of simple Bi. The organic acid bath used in the bismuth plating bath may be an organic sulfonic acid bath, a gluconic acid and ethylenediaminetetraacetic acid (EDTA) bath, or a citric acid and EDTA bath. Alternatively, a sulfuric acid bath may be used as the bismuth plating bath. An additive may also be added to the bismuth plating bath.

[0062] Here, we will examine the relationship between the thickness of the active material layer produced by electroplating Bi and the density of the active material. Hereinafter, active material layer 104 produced by electroplating Bi may be referred to as an "active material layer made of a Bi-plated layer."

[0063] FIG. 2 is a graph showing the relationship between the thickness of an active material layer formed from a Bi plating layer and the density of the active material. The density of the active material in this case can be determined by measuring the density of the active material layer formed from the Bi plating layer. Samples of the active material layer formed from a Bi plating layer were prepared in the same manner as in Example 1 described below. However, the application time of current to the copper foil serving as the plating substrate was adjusted to target plating thicknesses of 1 μm, 3 μm, 5 μm, and 10 μm, and four active material layer samples were prepared. The relationship between the thickness of the active material layer and the density of the active material was determined from the mass, area, and thickness of the active material layer. The thickness of the obtained Bi plating layer was measured using an X-ray fluorescence analyzer (SEA6000VX, manufactured by Seiko Instruments Inc.). The thicknesses of the active material layer in the four samples were 1.5 μm, 4.5 μm, 6.2 μm, and 10 μm. As shown in the graph in FIG. 2, when the active material layer was a Bi plating layer, the density of the active material was 7.5 g / cm. 3 to 9.8 g / cm 3 It can be seen that

[0064] In addition, the surface structure of the active material layer made of Bi plating layer was analyzed by surface X-ray diffraction measurement. The sample of the active material layer made of Bi plating layer used for surface X-ray diffraction measurement was prepared in the same manner as the sample used to confirm the relationship between the thickness of the active material layer and the density of the active material. For comparison, X-ray diffraction measurement was also performed on Bi powder.

[0065] 3 is a graph showing an example of the X-ray diffraction patterns of an active material layer made of a Bi plating layer formed on a copper foil and of Bi powder. The X-ray diffraction pattern was measured from the surface of the Bi plating layer, i.e., in the thickness direction of active material layer 104, using an X-ray diffractometer (MiNi Flex, manufactured by RIGAKU) by the θ-2θ method using Cu-Kα rays with wavelengths of 1.5405 Å and 1.5444 Å.

[0066] Table 1 shows the calculated intensity ratio I(2) / I(1) between the maximum peak height intensity I(1) in the diffraction angle 2θ range of 26° to 28° and the maximum peak height intensity I(2) in the diffraction angle 2θ range of 37° to 39° in the X-ray diffraction patterns of Bi plating layers and Bi powder obtained by surface X-ray diffraction measurement using Cu-Kα radiation. Table 1 shows the measurement results for Bi plating layers of various thicknesses and three measurements of Bi powder.

[0067] [Table 1]

[0068] As shown in Table 1, the ratio I(2) / I(1) of the active material layer 104 fabricated by electroplating Bi is 0.29 or greater. Therefore, the surface of the active material layer 104 fabricated by electroplating Bi exhibits a higher ratio of the (1,0,-1,4) plane to the (1,0,-1,2) plane of the Bi element, which has a trigonal crystal structure with a space group of R-3m. This indicates that the (1,0,-1,4) plane is more strongly oriented on the surface of the active material layer 104. Furthermore, comparing the X-ray diffraction patterns of the Bi plating layer and the Bi powder in the X-ray diffraction patterns shown in FIG. 3, the peak intensity I(3) at a diffraction angle 2θ of 40° is higher in the Bi plating layer with a thickness of 3 μm or greater. This indicates that the Bi plating layer is oriented such that the (2,-1,-1,0) plane of the Bi element, which has a trigonal crystal structure with a space group of R-3m, is the surface. For Bi-plated layers with a thickness of less than 3 μm, the surface roughness of the copper foil substrate is also a factor, and it is thought that differences in the X-ray diffraction pattern due to orientation with Bi powder have not been fully confirmed.

[0069] Hereinafter, each component of the battery 1000 of this embodiment will be described in more detail, taking as an example a case where the first electrode 101 is a negative electrode and the second electrode 103 is a positive electrode.

[0070] [First electrode] As described above, the first electrode 101 has the current collector 100 and the active material layer 104. The active material layer 104 has the same configuration 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 absorbing and releasing lithium ions. Bi contained in the active material layer 104 functions as a negative electrode active material. The active material layer 104 contains, for example, elemental Bi.

[0071] Bi is an active material that absorbs and releases lithium ions at 0.8 V relative to lithium. Bi is a metal that alloys with lithium. During charging, Bi forms an alloy with lithium, thereby absorbing lithium. That is, a lithium-bismuth alloy is generated in the first electrode 101 during charging of the battery 1000. The lithium-bismuth alloy generated includes, for example, at least one selected from the group consisting of LiBi and Li3Bi. That is, during charging of the battery 1000, the active material layer 104 includes, for example, at least one selected from the group consisting of LiBi and Li3Bi. During discharging of the battery 1000, lithium is released from the lithium-bismuth alloy, and the lithium-bismuth alloy returns to Bi.

[0072] The active material layer 104 may contain only simple Bi as the active material.

[0073] The active material layer 104 may be disposed in direct contact with the surface of the current collector 100 .

[0074] The active material layer 104 may be in the form of a thin film.

[0075] The active material layer 104 may be a plated layer formed by depositing Bi by plating. The active material layer 104 may be a Bi plated layer provided in direct contact with the surface of the current collector 100.

[0076] When the active material layer 104 is a plated layer provided in direct contact with the surface of the current collector 100, the active material layer 104 adheres closely to the current collector 100. This makes it possible to suppress deterioration in the current collection characteristics of the first electrode 101, which occurs when the active material layer 104 repeatedly expands and contracts. This further improves the cycle characteristics of the battery 1000. Furthermore, when the active material layer 104 is a plated layer, the active material layer 104 contains Bi, an active material, at a high density, which allows for even higher capacity to be achieved.

[0077] The active material layer 104 may contain materials other than Bi.

[0078] The active material layer 104 may further contain a conductive material, if necessary.

[0079] Conductive materials include carbon materials, metals, inorganic compounds, and conductive polymers. Carbon materials include graphite, acetylene black, carbon black, ketjen black, carbon whiskers, needle coke, and carbon fibers. Graphite includes natural graphite and artificial graphite. Natural graphite includes lump graphite and flake graphite. Metals include copper, nickel, aluminum, silver, and gold. Inorganic compounds include tungsten carbide, titanium carbide, tantalum carbide, molybdenum carbide, titanium boride, and titanium nitride. These materials may be used alone or in combination.

[0080] The active material layer 104 may further contain a binder, if necessary.

[0081] Examples of binders include fluorine-containing resins, thermoplastic resins, ethylene propylene diene monomer (EPDM) rubber, sulfonated EPDM rubber, and natural butyl rubber (NBR). Examples of fluorine-containing resins include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluororubber. Examples of thermoplastic resins include polypropylene and polyethylene. These materials may be used alone or in combination.

[0082] 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.

[0083] The material of the current collector 100 is, for example, a single metal or an alloy. More specifically, it may be a single metal or an 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.

[0084] The current collector 100 may include copper (Cu).

[0085] 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 copper. Examples of metal foil containing copper include copper foil and copper alloy foil. The copper content in the metal foil may be 50% by mass or more, or may be 80% by mass or more. In particular, the metal foil may be a copper foil containing substantially only copper as the metal. The thickness of the current collector 100 may be, for example, 5 μm or more and 20 μm or less.

[0086] The current collector 100 may be a laminated film.

[0087] [Electrolyte] The electrolyte solution 102 includes, for example, a non-aqueous solvent and a lithium salt.

[0088] The electrolyte solution 102 contains at least one non-aqueous solvent selected from the group consisting of vinylene carbonate and fluoroethylene carbonate. The non-aqueous solvent may consist of only at least one selected from the group consisting of vinylene carbonate and fluoroethylene carbonate. That is, the ratio of the total mass of vinylene carbonate and fluoroethylene carbonate to the total mass of the non-aqueous solvent may be, for example, 100 mass%.

[0089] The electrolytic solution 102 may further contain other non-aqueous solvents other than vinylene carbonate and fluoroethylene carbonate.

[0090] Other examples of non-aqueous solvents include cyclic carbonate ester solvents, chain carbonate ester solvents, cyclic ether solvents, chain ether solvents, cyclic ester solvents, chain ester solvents, and fluorine-containing solvents. Examples of cyclic carbonate ester solvents include ethylene carbonate, propylene carbonate, and butylene carbonate. Examples of chain carbonate ester solvents include dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. Examples of cyclic ether solvents include tetrahydrofuran, 1,4-dioxane, and 1,3-dioxolane. Examples of chain ether solvents include 1,2-dimethoxyethane and 1,2-diethoxyethane. Examples of cyclic ester solvents include γ-butyrolactone. Examples of chain ester solvents include methyl acetate. Examples of fluorine-containing solvents include methyl fluoropropionate, fluorobenzene, fluoroethyl methyl carbonate, and fluorodimethylene carbonate. The electrolytic solution 102 may further contain one nonaqueous solvent selected from these as another nonaqueous solvent, or may further contain a mixture of two or more nonaqueous solvents selected from these as another nonaqueous solvent.

[0091] Examples of lithium salts include LiPF, LiBF, LiSbF, LiAsF, LiSOCF, LiN(SOCF), LiN(SOCF) , LiN(SOCF)(SOCF), or LiC(SOCF). 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.

[0092] [Second electrode] The second electrode 103 functions as a positive electrode. The second electrode 103 contains a material that can absorb and release metal ions such as lithium ions. The material is, for example, a positive electrode active material.

[0093] 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.

[0094] The active material layer 106 may be disposed on the surface of the current collector 105 so as to be in direct contact with the current collector 105 .

[0095] Examples of the positive electrode active material include lithium-containing transition metal oxides, transition metal fluorides, polyanion materials, fluorinated polyanion materials, transition metal sulfides, transition metal oxysulfides, and transition metal oxynitrides. Examples of 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 Examples of suitable cathode active materials include Li(Ni, Co, Mn)O2 ((x + y) < 1) and LiCoO2. In particular, when a lithium-containing transition metal oxide is used as the cathode active material, the electrode manufacturing cost can be reduced and the average discharge voltage of the battery can be increased. For example, the cathode active material may contain Li(Ni, Co, Mn)O2.

[0096] Examples of materials for the current collector 105 include metal materials, such as copper, stainless steel, iron, and aluminum.

[0097] The second electrode 103 may include a solid electrolyte. Any known solid electrolyte used in lithium secondary batteries can be used as the solid electrolyte. For example, a halide solid electrolyte, a sulfide solid electrolyte, an oxide solid electrolyte, a polymer solid electrolyte, or a complex hydride solid electrolyte may be used.

[0098] The halide solid electrolyte refers to a solid electrolyte containing a halogen element. The halide solid electrolyte may contain not only a halogen element but also oxygen. The halide solid electrolyte does not contain sulfur (S).

[0099] The halide solid electrolyte may be, for example, a material represented by the following composition 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 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.

[0100] "Semi-metallic elements" are B, Si, Ge, As, Sb, and Te.

[0101] "Metal elements" are all elements in groups 1 to 12 of the periodic table except hydrogen, and all elements in groups 13 to 16 except B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se. In other words, this is a group of elements that can become cations when forming inorganic compounds with halogen compounds.

[0102] In the composition formula (1), M may include Y, and X may include Cl and Br.

[0103] The sulfide solid electrolyte refers to a solid electrolyte containing sulfur (S). The sulfide solid electrolyte may contain not only sulfur but also a halogen element.

[0104] Examples of sulfide solid electrolytes include Li2S-P2S5, Li2S-SiS2, Li2S-B2S3, Li2S-GeS2, and Li 3.25 Ge 0.25 P 0.75 S4, or Li 10 GeP2S 12 etc. can be used.

[0105] Examples of oxide solid electrolytes include NASICON-type solid electrolytes, such as LiTi2(PO4)3 and its elemental substitution products, (LaLi)TiO3-based perovskite-type solid electrolytes, and Li 14 ZnGeO 16 , Li4SiO4, LiGeO4 and their element-substituted LISICON-type solid electrolytes, Li7La3Zr2O 12Garnet-type solid electrolytes, such as those typified by elemental substitution products thereof, Li3PO4 and its N-substituted products, and glasses or glass ceramics based on Li-BO compounds such as LiBO2 and Li3BO3 and to which Li2SO4, Li2CO3, etc. are added, can be used.

[0106] As the 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. A polymer compound having an ethylene oxide structure can contain a large amount of lithium salt. This can further increase ionic conductivity. As the lithium salt, LiPF6, LiBF4, LiSbF6, LiAsF6, LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), and LiC(SO2CF3)3 can be used. 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.

[0107] Examples of the complex hydride solid electrolyte that can be used include LiBH4-LiI and LiBH4-P2S5.

[0108] 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 well-dispersed state. This improves the charge / 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.

[0109] The positive electrode active material may have a larger median diameter than the solid electrolyte, which allows the positive electrode active material and the solid electrolyte to be well dispersed.

[0110] From the viewpoint of the energy density and output of the battery, the ratio of the volume of the positive electrode active material to the total volume of the positive electrode active material and the solid electrolyte in second electrode 103 may be 0.30 or more and 0.95 or less.

[0111] A coating layer may be formed on the surface of the positive electrode active material to prevent the solid electrolyte from reacting with the positive electrode active material. This can suppress an increase in the reaction overvoltage of the battery. Examples of coating materials included in the coating layer include a sulfide solid electrolyte, an oxide solid electrolyte, or a halide solid electrolyte.

[0112] 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.

[0113] The second electrode 103 may include a conductive material to enhance electronic conductivity.

[0114] The second electrode 103 may contain a binder.

[0115] The conductive material and binder may be the same materials that can be used for the active material layer 104 .

[0116] The second electrode 103 may contain a non-aqueous electrolyte, a gel electrolyte, or an ionic liquid for the purpose of facilitating the transfer of lithium ions and improving the output characteristics of the battery.

[0117] The nonaqueous electrolyte contains a nonaqueous solvent and a lithium salt dissolved in the nonaqueous solvent. Examples of the nonaqueous solvent include a cyclic carbonate ester solvent, a chain carbonate ester solvent, a cyclic ether solvent, a chain ether solvent, a cyclic ester solvent, a chain ester solvent, or a fluorine solvent. Examples of the cyclic carbonate ester solvent are ethylene carbonate, propylene carbonate, or butylene carbonate. Examples of the chain carbonate ester solvent are dimethyl carbonate, ethyl methyl carbonate, or diethyl carbonate. Examples of the cyclic ether solvent are tetrahydrofuran, 1,4-dioxane, or 1,3-dioxolane. Examples of the chain ether solvent are 1,2-dimethoxyethane or 1,2-diethoxyethane. An example of the cyclic ester solvent is γ-butyrolactone. An example of the chain ester solvent is methyl acetate. Examples of fluorine-containing solvents include fluoroethylene carbonate, methyl fluoropropionate, fluorobenzene, fluoroethyl methyl carbonate, and fluorodimethylene carbonate. One non-aqueous solvent selected from these may be used alone. Alternatively, a mixture of two or more non-aqueous solvents selected from these may be used.

[0118] Examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), and 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. The concentration of the lithium salt is, for example, in the range of 0.5 mol / L to 2 mol / L.

[0119] The gel electrolyte may be a polymer material impregnated with a non-aqueous electrolyte, such as polyethylene oxide, polyacrylonitrile, polyvinylidene fluoride, polymethyl methacrylate, or a polymer having an ethylene oxide bond.

[0120] Examples of cations contained in ionic liquids are: (i) aliphatic chain quaternary salts such as tetraalkylammonium or tetraalkylphosphonium; (ii) aliphatic cyclic ammoniums such as pyrrolidiniums, morpholiniums, imidazoliniums, tetrahydropyrimidiniums, piperaziniums, or piperidiniums, or (iii) Nitrogen-containing heterocyclic aromatic cations such as pyridiniums or imidazoliums.

[0121] An example of an anion found in ionic liquids is PF6 - , BF4 - , SbF6 - , AsF6 - , SO3CF3 - , N(SO2CF3)2 - , N(SO2C2F5)2 - , N(SO2CF3)(SO2C4F9) - , or C(SO2CF3)3 - is.

[0122] The ionic liquid may contain a lithium salt.

[0123] [Separator] The separator 107 has lithium ion conductivity. There are no particular limitations on the material of the separator 107 as long as it allows the passage of lithium ions. The material of the separator 107 can 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 of these materials, the safety of the battery 1000 can be sufficiently ensured. Examples of solid electrolytes include sulfide solid electrolytes such as Li2S-P2S5, Li7La3Zr2O 12 Examples of the electrolyte membrane include oxide solid electrolytes such as LLZ. Examples of the gel electrolyte include gel electrolytes containing fluororesins such as PVdF. Examples of the ion exchange resin membrane include cation exchange membranes and anion exchange membranes. Examples of the porous membrane include porous membranes made of polyolefin resin and porous membranes made of glass paper obtained by weaving glass fibers into nonwoven fabric.

[0124] [Exterior] The exterior 108 is made of a material obtained by laminating a metal foil such as an aluminum foil with a resin film such as a polyethylene terephthalate (PET) film, etc. The exterior 108 may also be a resin or metal container.

[0125] In the above, a configuration example in which the first electrode 101 is a negative electrode and the second electrode 103 is a positive electrode has been described, but the first electrode 101 may be a positive electrode and the second electrode 103 may be a negative electrode.

[0126] When the first electrode 101 is a positive electrode and the second electrode 103 is a negative electrode, the active material layer 104 is a positive electrode active material layer. That is, Bi contained in the active material layer 104 functions as a positive electrode active material. In this case, the second electrode 103, which is a negative electrode, is made of, for example, lithium metal.

[0127] The battery 1000 is basically composed of a first electrode 101, an electrolyte 102, and a second electrode 103, and is sealed in an airtight container to prevent air and moisture from getting in. The shape of the battery 1000 may be a coin type, a cylindrical type, a square type, a sheet type, a button type, a flat type, a laminated type, or the like. [Example]

[0128] Hereinafter, the present disclosure will be described in detail using examples and comparative examples. The following examples are merely illustrative, and the present disclosure is not limited to the following examples.

[0129] Example 1 <Preparation of the first electrode> As a pretreatment, copper foil (10 cm x 10 cm, thickness: 12 μm) was pre-degreased with an organic solvent, and then one side was masked and immersed in an acidic solvent to degrease the copper foil surface. Bismuth methanesulfonate was used as a soluble bismuth salt in 1.0 mol / L methanesulfonic acid. 3+The plating bath was prepared by adding ions to a concentration of 0.18 mol / L. The activated copper foil was connected to a power source so that a current could be applied, and then immersed in the plating bath. Then, the current density was increased to 2 A / dm 2 By controlling the temperature to 100°C, 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 acid bath, the masking was removed, and the foil was washed with pure water, dried, and punched out into a size of 2 cm x 2 cm to obtain a first electrode. That is, the first electrode of Example 1 had a configuration in which an active material layer made of a Bi plating layer was provided on a current collector made of copper foil. In the first electrode of Example 1, the density of the active material contained in the active material layer made of a Bi plating layer could be determined from the graph of FIG. 2 and was 7.5 g / cm 3 The X-ray diffraction pattern obtained by surface X-ray diffraction measurement of the active material layer made of the Bi plating layer is shown in FIG. 3, and the peak intensity ratio I(2) / I(1) is shown in Table 1. In the active material layer of the battery according to Example 1, the peak intensity ratio I(2) / I(1) was 0.29 or more.

[0130] <Preparation of test cell> The first electrode was used as the working electrode. A 0.34 mm thick Li metal counter electrode was used. The working electrode corresponds to the negative electrode of the secondary battery. The Li metal was doubly coated with a microporous separator (Asahi Kasei Corporation, Celgard 3401). A solution of LiPF6 dissolved in vinylene carbonate (VC) at a concentration of 1.0 mol / L was prepared as the electrolyte. A test cell was assembled using this working electrode, counter electrode, and electrolyte. The test cell prepared here is a single-electrode 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 active material in an amount sufficient to support the reaction at the working electrode is used as the counter electrode. Since this test cell is intended to test the performance of the first electrode as a negative electrode, a large excess of Li metal was used as the counter electrode, as is commonly used. The negative electrode whose performance has been tested using such a test cell can be used as a secondary battery, for example, by combining it with a positive electrode containing a positive electrode active material such as that described in the above embodiment, for example, a transition metal oxide containing Li.

[0131] <Charge / discharge cycle test> A charge / discharge test was performed on the test cell. 2 ), charging was performed to 0 V and discharging was performed to 2 V. This constituted one cycle. 2 ) corresponds to a constant current value of 0.5 IT. The charge-discharge cycle test was carried out at 25°C. FIG. 4 is a graph showing the relationship between the number of cycles and the discharge capacity density of the batteries according to Examples 1 and 2 and Comparative Examples 1 to 4. As shown in FIG. 4, the battery according to Example 1 had excellent cycle characteristics and a high discharge capacity density.

[0132] Example 2 <Preparation of the first electrode> The first electrode of Example 2 was prepared in the same manner as the first electrode of Example 1.

[0133] <Preparation of test cell> A battery serving as a test cell of Example 2 was fabricated in the same manner as the battery of Example 1, except that a solution of LiPF6 dissolved in fluoroethylene carbonate (FEC) at a concentration of 1.0 mol / L was used as the electrolyte.

[0134] <Charge / discharge cycle test> A charge-discharge cycle test was performed on the test cell prepared in Example 2 in the same manner as in Example 1. As shown in Fig. 4, the battery according to Example 2 had excellent cycle characteristics and a high discharge capacity density.

[0135] (Comparative Example 1) <Preparation of the first electrode> The first electrode of Comparative Example 1 was produced in the same manner as the first electrode of Example 1.

[0136] <Preparation of test cell> A test cell of Comparative Example 1 was fabricated in the same manner as the battery of Example 1, except that a solution of LiPF6 dissolved in ethylene carbonate (EC) at a concentration of 1.0 mol / L was used as the electrolyte. Two test cells of Comparative Example 1 were fabricated.

[0137] <Charge / discharge cycle test> A charge-discharge cycle test was performed using one of the two test cells prepared in Comparative Example 1 in the same manner as in Example 1. The other test cell was also subjected to a charge-discharge cycle test in the same manner as in Example 1, except that the end-of-discharge voltage was changed to 1.4 V. As shown in FIG. 4 , the battery according to Comparative Example 1 exhibited worse cycle characteristics than the batteries of Examples 1 and 2 at both end-of-discharge voltages of 2 V and 1.4 V. In the test with an end-of-discharge voltage of 2 V, the discharge capacity significantly decreased in the second charge-discharge cycle, and by the tenth charge-discharge cycle, the discharge capacity had decreased to approximately one-seventh of the initial discharge capacity. In the test with an end-of-discharge voltage of 1.4 V, the discharge capacity began to decrease in the fifth charge-discharge cycle, and by the tenth charge-discharge cycle, the discharge capacity had decreased to approximately half of the initial discharge capacity.

[0138] (Comparative Example 2) <Preparation of the first electrode> The first electrode of Comparative Example 2 was produced in the same manner as the first electrode of Example 1.

[0139] <Preparation of test cell> A battery serving as a test cell of Comparative Example 2 was fabricated in the same manner as the battery of Example 1, except that a solution in which LiPF6 was dissolved in propylene carbonate (PC) at a concentration of 1.0 mol / L was used as the electrolyte.

[0140] <Charge / discharge cycle test> A charge-discharge cycle test was performed on the test cell prepared in Comparative Example 2 in the same manner as in Example 1. As shown in Fig. 4, the discharge capacity of the battery according to Comparative Example 2 began to decrease at the fourth charge-discharge cycle, and at the tenth charge-discharge cycle, the discharge capacity had decreased to about 1 / 20 of the initial discharge capacity.

[0141] (Comparative Example 3) <Preparation of the first electrode> The first electrode of Comparative Example 3 was produced in the same manner as the first electrode of Example 1.

[0142] <Preparation of test cell> A battery serving as a test cell of Comparative Example 3 was fabricated in the same manner as the battery of Example 1, except that a solution of LiPF6 dissolved in methyl ethyl carbonate (MEC) at a concentration of 1.0 mol / L was used as the electrolyte.

[0143] <Charge / discharge cycle test> A charge-discharge cycle test was performed on the test cell prepared in Comparative Example 3 in the same manner as in Example 1. As shown in Fig. 4, the discharge capacity of the battery according to Comparative Example 3 began to decrease at the second charge-discharge cycle, and at the 10th charge-discharge cycle, the discharge capacity had decreased to about 1 / 30 of the initial discharge capacity.

[0144] Comparative Example 4 <Preparation of the first electrode> The first electrode of Comparative Example 4 was produced in the same manner as the first electrode of Example 1.

[0145] <Preparation of test cell> A battery serving as a test cell of Comparative Example 4 was fabricated in the same manner as the battery of Example 1, except that a solution in which LiPF6 was dissolved in a mixed solvent of ethylene carbonate (EC) at a concentration of 1.0 mol / L was used as the electrolyte. The mixed solvent was a mixture of EC and MEC in a volume ratio of EC:MEC = 1:1.

[0146] <Charge / discharge cycle test> A charge-discharge cycle test was performed on the test cell prepared in Comparative Example 4 in the same manner as in Example 1. However, the end-of-discharge voltage was changed to 1.4 V. As shown in FIG. 4 , the discharge capacity of the battery according to Comparative Example 4 began to decrease at the fifth charge-discharge cycle, and at the tenth charge-discharge cycle, the discharge capacity had decreased to about one-fifth of the initial discharge capacity.

[0147] From the results of Example 1, Example 2, and Comparative Examples 1 to 4, it was found that a battery using an electrolyte solution containing at least one selected from the group consisting of VC and FEC can have good cycle characteristics even when using an electrode including an active material layer containing Bi as the main active material component. [Industrial Applicability]

[0148] The battery of the present disclosure is used, for example, as a lithium secondary battery. [Explanation of symbols]

[0149] 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. A first electrode; A second electrode; An electrolyte; Equipped with the first electrode has a current collector and an active material layer, the current collector contains Cu, the active material layer contains Bi as a main component of the active material, the active material layer is a plating layer, the electrolyte solution contains at least one selected from the group consisting of vinylene carbonate and fluoroethylene carbonate, In an X-ray diffraction pattern of the active material layer obtained by surface X-ray diffraction measurement using Cu-Kα radiation, when the height intensity of the maximum peak present in a diffraction angle 2θ range of 26° to 28° is defined as I(1) and the height intensity of the maximum peak present in a diffraction angle 2θ range of 37° to 39° is defined as I(2), the ratio of I(2) to I(1), I(2) / I(1), is 0.29 or more, the first electrode is a negative electrode, The second electrode is a positive electrode. Lithium secondary battery.

2. The density of the active material is 6.0 g / cm 3 or more and 9.8 g / cm 3 2. The lithium secondary battery according to claim 1, wherein: Here, the density of the active material is the density of the active material when the battery is in a fully discharged state.

3. The density of the active material is 7.5 g / cm 3 or more and 9.8 g / cm 3 3. The lithium secondary battery according to claim 2, wherein:

4. The I(2) / I(1) is 0.57 or less. The lithium secondary battery according to claim 1 .

5. The active material layer contains simple Bi. The lithium secondary battery according to claim 1 .

6. The active material layer is made of LiBi and Li 3 Bi, The lithium secondary battery according to claim 1 .

7. the active material layer contains only simple Bi as an active material; The lithium secondary battery according to claim 1 .

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