Battery and method for manufacturing the same

Abstract

To provide a battery having good discharge capacity characteristics.SOLUTION: A battery that utilizes a deposition and dissolution reaction of metallic lithium as an anode reaction includes an anode current collector, a metal layer, an electrolyte layer, and a cathode active material layer in this order in the thickness direction, the metal layer contains a Li-Mg alloy phase and a Li-Ga alloy phase.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to a battery and a method for manufacturing the same. [Background technology]

[0002] Batteries typically have an electrolyte layer between a positive electrode active material layer and a negative electrode active material layer. In the field of batteries, batteries that utilize the deposition and dissolution reaction of metallic lithium as the negative electrode reaction are also known. For example, Patent Document 1 discloses an all-solid-state battery that utilizes the deposition-dissolution reaction of metallic lithium as the negative electrode reaction. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-184513 [Overview of the project] [Problems that the invention aims to solve]

[0004] Batteries that utilize the deposition and dissolution reaction of metallic lithium as the negative electrode reaction typically do not require a conventional negative electrode active material layer (a layer containing negative electrode active material particles that absorb and release Li) during the battery manufacturing process. Instead, the negative electrode active material layer (Li-containing layer) is formed during the initial charge, which has the advantage of easily improving energy density. On the other hand, batteries that utilize the deposition and dissolution reaction of metallic lithium as the negative electrode reaction still have room for further improvement in terms of discharge capacity characteristics.

[0005] This disclosure is made in view of the above circumstances and primarily aims to provide a battery with good discharge capacity characteristics. [Means for solving the problem]

[0006] [1] This battery utilizes the deposition and dissolution reaction of metallic lithium as the negative electrode reaction. It has a negative electrode current collector, a metal layer, an electrolyte layer, and a positive electrode active material layer in this order in the thickness direction. The battery has the metal layer containing a Li-Mg alloy phase and a Li-Ga alloy phase.

[0007] [2] The battery according to [1], wherein in the metal layer, the ratio of Ga to the total of Ga and Mg is 5 at% or more and 80 at% or less.

[0008] [3] The battery according to [1] or [2], wherein in the metal layer, the ratio of Ga to the total of Ga and Mg is 72 at% or more and 85 at% or less.

[0009] [4] A battery that utilizes the deposition and dissolution reaction of metallic lithium as a negative electrode reaction, It has a negative electrode current collector, a metal layer, an electrolyte layer, and a positive electrode active material layer in this order in the thickness direction. The battery has the metal layer containing a Mg-Ga alloy.

[0010] [5] A method for manufacturing a battery that utilizes the deposition and dissolution reaction of metallic lithium as a negative electrode reaction, A metal layer forming step of forming a metal layer containing a Mg-Ga alloy phase by a vapor deposition method, An assembling step of assembling the battery having a negative electrode current collector, the metal layer, an electrolyte layer, and a positive electrode active material layer in this order in the thickness direction, A method for manufacturing a battery having the above steps.

Effect of the Invention

[0011] The battery in the present disclosure has an effect of having good discharge capacity characteristics.

Brief Description of the Drawings

[0012] [Figure 1] It is a schematic cross-sectional view illustrating the battery in the present disclosure. [Figure 2]It is an explanatory diagram for explaining the state of the battery during charging in the present disclosure. [Figure 3] It is an explanatory diagram for explaining the state of the battery during discharging in the present disclosure. [Figure 4] It is the result of charge-discharge tests in the evaluation cells fabricated in Examples 1 to 5 and Comparative Examples 1 and 2. [Figure 5] It is the result of charge-discharge tests in the evaluation cells fabricated in Examples 1 to 5 and Comparative Examples 1 and 2. [Figure 6] It is a cross-sectional SEM image of the evaluation cell fabricated in Example 5.

Mode for Carrying Out the Invention

[0013] Hereinafter, the battery and its manufacturing method in the present disclosure will be described in detail with reference to the drawings. Each of the drawings shown below is schematically illustrated, and the sizes and shapes of each part are exaggerated as appropriate for ease of understanding.

[0014] A. Battery FIG. 1 is a schematic cross-sectional view illustrating the battery in the present disclosure. Specifically, FIG. 1(a) is a schematic cross-sectional view illustrating the battery before the first charge, and FIG. 1(b) is a schematic cross-sectional view illustrating the battery after the first charge.

[0015] As shown in FIGS. 1(a) and (b), the battery 10 has a negative electrode current collector 1, a metal layer 2, an electrolyte layer 3, and a positive electrode active material layer 4 in this order in the thickness direction D T Normally, a positive electrode current collector 5 is disposed on the side opposite to the electrolyte layer 3 with respect to the positive electrode active material layer 4. Further, as shown in FIG. 1(a), in the battery 10 before the first charge, the metal layer 2 contains a Mg-Ga alloy. The metal layer 2 is typically a vapor deposition layer having a Mg-Ga alloy phase. On the other hand, when the battery 10 shown in FIG. 1(a) is charged, the Mg-Ga alloy phase reacts with Li, and a Li-Mg alloy phase and a Li-Ga alloy phase are formed from the Mg-Ga alloy phase. As a result, as shown in FIG. 1(b), in the battery 10 after the first charge, the metal layer 2 contains a Li-Mg alloy phase and a Li-Ga alloy phase.

[0016] According to this disclosure, since the metal layer contains Mg and Ga, the battery will have good discharge capacity characteristics. As mentioned above, in batteries that utilize the deposition and dissolution reaction of metallic lithium as the negative electrode reaction, a general negative electrode active material layer (for example, a layer containing negative electrode active material particles that intercalate and deintercalate Li) is usually not provided during the manufacturing of the battery, and the negative electrode active material layer (Li-containing layer) is formed by the initial charge, which has the advantage of easily improving energy density. On the other hand, there is room for further improvement in the discharge capacity characteristics of batteries that utilize the deposition and dissolution reaction of metallic lithium as the negative electrode reaction.

[0017] In contrast, this disclosure uses a metal layer containing Mg and Ga. By using such a metal layer, good discharge capacity characteristics can be obtained. The reason why good discharge capacity characteristics can be obtained is presumed to be that by using a metal layer containing Mg and Ga, the increase in resistance at the negative electrode at the end of discharge can be suppressed. The effects obtained in this disclosure will be explained in detail below with reference to Figures 2 and 3.

[0018] As shown in Figure 2(a), the battery 10 has a negative electrode current collector 1, a metal layer 2, an electrolyte layer 3, a positive electrode active material layer 4, and a positive electrode current collector 5, in this order in the thickness direction. The metal layer 2 has an Mg-Ga alloy phase. Next, as shown in Figure 2(b), when charging of the battery 10 begins, a Li-Ga alloy phase is first formed from a portion of the Mg-Ga alloy phase. Since Ga has a higher reaction potential for Li insertion and deinsertion than Mg, Ga reacts with Li before Mg, and a Li-Ga alloy phase is formed. Next, as shown in Figures 2(c) and (d), as charging of the battery 10 progresses, a Li-Mg alloy phase is formed in addition to the Li-Ga alloy phase. Since the Li-Ga alloy phase is formed before the Li-Mg alloy phase, a state is obtained in which the Li-Ga alloy phase is dispersed relative to the Li-Mg alloy phase.

[0019] Next, as shown in Figure 3(a), when the charged battery 10 is discharged, the Li contained in the metal layer 2 moves to the positive electrode active material layer 4 via the electrolyte layer 3. At this time, since Mg has a lower reaction potential for Li insertion and deinsertion than Ga, Li is first desorbed from the Li-Mg alloy phase. As shown in Figure 3(b), the Li-Ga alloy phase has high Li ion conductivity, so a good ion conduction path is formed. As shown in Figure 3(c), it is presumed that the Li-Ga alloy phase is maintained even at the end of discharge, and it is presumed that this suppresses the increase in resistance at the negative electrode. As a result, it is presumed that good discharge capacity characteristics can be obtained.

[0020] The batteries described in this disclosure can be broadly classified into two embodiments depending on their State of Charge (SOC). The batteries described in this disclosure will be described below in two parts: the first embodiment and the second embodiment.

[0021] 1. First Embodiment As shown in Figure 3(a), the battery 10 in the first embodiment has a negative electrode current collector 1, a metal layer 2, an electrolyte layer 3, and a positive electrode active material layer 4 in this order in the thickness direction. Furthermore, the metal layer 2 contains a Li-Mg alloy phase and a Li-Ga alloy phase.

[0022] (1) Negative electrode The negative electrode in the first embodiment has a negative electrode current collector. Examples of materials for the negative electrode current collector include SUS, copper, nickel, and carbon. Examples of shapes for the negative electrode current collector include foil. The thickness of the negative electrode current collector is, for example, 1 μm or more and 500 μm or less.

[0023] The negative electrode has a metal layer. The metal layer contains a Li-Mg alloy phase and a Li-Ga alloy phase. The Li-Mg alloy phase is a metallic phase of an alloy containing Li and Mg, and may be a metallic phase of a binary alloy containing Li and Mg, or a metallic phase of an alloy containing other elements in addition to Li and Mg. In the latter case, it is preferable that Li and Mg are the main components in the Li-Mg alloy phase. "Main component" means the component that has the largest proportion (at%) among the components contained in the metallic phase. In the Li-Mg alloy phase, the total proportion of Li and Mg to all elements is, for example, 50 at% or more, may be 70 at% or more, or may be 90 at% or more.

[0024] The Li-Ga alloy phase is a metallic phase of an alloy containing Li and Ga, and may be a metallic phase of a binary alloy containing Li and Ga, or a metallic phase of an alloy containing other elements in addition to Li and Ga. In the latter case, it is preferable that Li and Ga are the main components in the Li-Ga alloy phase. In the Li-Ga alloy phase, the total proportion of Li and Ga to all elements is, for example, 50 at% or more, may be 70 at% or more, or may be 90 at% or more.

[0025] The metal layer contains both a Li-Ga alloy phase and a Li-Mg alloy phase. In particular, it is preferable that the Li-Ga alloy phase is dispersed relative to the Li-Mg alloy phase in the metal layer. That is, it is preferable that a sea-island structure is formed, with the Li-Mg alloy phase as the sea and the Li-Ga alloy phase as islands. This is because it is possible to suppress the increase in resistance at the negative electrode at the end of discharge. The size of the Li-Ga alloy phase is not particularly limited, but for example, it is between 0.1 μm and 5 μm. The size of the Li-Ga alloy phase can be determined from the distribution of Ga measured by SEM-EDX. The size of the Li-Ga alloy phase is the average value of the sizes measured from 100 or more samples.

[0026] In a metal layer, the ratio of Ga to the total of Ga and Mg (Ga / (Ga+Mg)) is not particularly limited. Ga / (Ga+Mg) may be, for example, 5 at% or more, 10 at% or more, 15 at% or more, 20 at% or more, or 25 at% or more. On the other hand, Ga / (Ga+Mg) may be, for example, 90 at% or less, or 85 at% or less.

[0027] The metal layer preferably does not contain a conductive material. Furthermore, the metal layer preferably does not contain a binder. A Li phase may be formed within the metal layer. A deposited Li layer may also be formed between the metal layer and the electrolyte layer. Furthermore, a deposited Li layer may be formed between the metal layer and the negative electrode current collector.

[0028] The metal layer is usually a dense layer. The porosity of the metal layer (the ratio of the area of ​​voids in the cross-section of the metal layer) is, for example, 5% or less, may be 3% or less, or may be 1% or less. In the first embodiment, the thickness of the metal layer is not particularly limited, but for example, it is 5 μm or more and 30 μm or less.

[0029] As shown in Figure 3(a), the metal layer 2 may be in direct contact with the negative electrode current collector 1. Similarly, the metal layer 2 may be in direct contact with the electrolyte layer 3. On the other hand, although not specifically shown, other layers may be placed between the metal layer and the negative electrode current collector. Similarly, other layers may be placed between the metal layer and the electrolyte layer. Also, as shown in Figure 3(c), the metal layer 2 after discharge may contain a Li-Mg alloy phase and a Li-Ga alloy phase. Depending on the SOC, the metal layer after discharge may contain a Li-free Mg phase and a Li-Ga alloy phase. Similarly, the metal layer after discharge may contain a Li-free Mg phase and a Li-free Ga phase.

[0030] (2) Positive electrode The positive electrode in the first embodiment comprises a positive electrode current collector and a positive electrode active material layer. The positive electrode active material layer contains at least a positive electrode active material. The positive electrode active material layer may also contain at least one of an electrolyte, a conductive material, and a binder.

[0031] Examples of positive electrode active materials include oxide active materials. Examples of oxide active materials include LiCoO2 and LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 Rock salt layered active materials such as O2, LiMn2O4, Li4Ti5O 12 Examples include spinel-type active materials such as LiFePO4 and olivine-type active materials such as LiFePO4. The shape of the positive electrode active material can be particulate, for example. The average particle size (D) of the positive electrode active material is... 50 ) is, for example, 0.5 μm or more and 50 μm or less. Average particle size (D 50 ) refers to the volume-cumulative particle size measured by a laser diffraction scattering particle size distribution analyzer.

[0032] Examples of electrolytes include solid electrolytes. Examples of solid electrolytes include inorganic solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, and halide solid electrolytes. Sulfide solid electrolytes preferably contain sulfur (S) as the main component of the anionic element. Oxide solid electrolytes preferably contain oxygen (O) as the main component of the anionic element. Halide solid electrolytes preferably contain halogen (X) as the main component of the anion. Among these, sulfide solid electrolytes are preferred.

[0033] The sulfide solid electrolyte preferably contains Li, M (where M is at least one of P, Sn, Al, Zn, In, Ge, Si, Sb, Ga, and Bi), and S. The sulfide solid electrolyte may also contain halogen elements such as F, Cl, Br, and I. Furthermore, in the sulfide solid electrolyte, some of the S elements may be substituted with O elements.

[0034] The sulfide solid electrolyte may be a glass-based (amorphous) sulfide solid electrolyte, a glass-ceramic sulfide solid electrolyte, or a crystalline sulfide solid electrolyte. Examples of the crystal phase contained in the sulfide solid electrolyte include, for example, LGPS-type crystal phase, Thio-LISICON-type crystal phase, and argyrodite-type crystal phase.

[0035] Examples of the sulfide solid electrolyte include, for example, Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-GeS2, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-P2S5-LiI-LiBr, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-Z m S n (where m and n are positive numbers. Z is either Ge, Zn, or Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (where x and y are positive numbers. M is either P, Si, Ge, B, Al, Ga, or In).

[0036] Other examples of the solid electrolyte include organic solid electrolytes such as polymer electrolytes and gel electrolytes. Also, a liquid electrolyte (electrolyte solution) can be used as the electrolyte.

[0037] Examples of the conductive material include, for example, carbon materials. Examples of the carbon materials include particulate carbon materials such as acetylene black (AB) and ketjen black (KB); fibrous carbon materials such as carbon fibers, carbon nanotubes (CNT), and carbon nanofibers (CNF). Also, examples of the binder include rubber-based binders such as butylene rubber (BR) and styrene-butadiene rubber (SBR), and fluoride-based binders such as polyvinylidene fluoride (PVDF). The thickness of the positive electrode active material layer is, for example, 1 μm or more and 500 μm or less.

[0038] Examples of materials for the positive electrode current collector include stainless steel (SUS), aluminum, nickel, and carbon. Examples of shapes for the positive electrode current collector include foil. The thickness of the positive electrode current collector is, for example, between 1 μm and 500 μm.

[0039] (3) Electrolyte layer The electrolyte layer in the first embodiment contains at least an electrolyte. The electrolyte is the same as described in "(2) Positive Electrode" above. In particular, it is preferable that the electrolyte layer contains a solid electrolyte. That is, it is preferable that the electrolyte layer is a solid electrolyte layer containing a solid electrolyte. A battery having a solid electrolyte layer is sometimes called an all-solid-state battery. In addition, the solid electrolyte layer may contain a binder in addition to the solid electrolyte. The binder is the same as described in "(2) Positive Electrode" above. The thickness of the electrolyte layer is, for example, 1 μm or more and 500 μm or less.

[0040] (4)Battery The battery in the first embodiment has a negative electrode current collector, a metal layer, an electrolyte layer, and a positive electrode active material layer, arranged in this order in the thickness direction. Furthermore, the battery usually has an outer casing that houses these components. Examples of outer casings include laminate-type casings and case-type casings.

[0041] The applications of batteries are not particularly limited, but examples include power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs), gasoline cars, and diesel cars. In particular, it is preferable that they be used as power sources for the drive of hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or battery electric vehicles (BEVs). Batteries may also be used as power sources for mobile devices other than vehicles (e.g., trains, ships, aircraft), or as power sources for electrical products such as information processing devices.

[0042] 2. Second Embodiment As shown in Figure 2(a), the battery 10 in the second embodiment has a negative electrode current collector 1, a metal layer 2, an electrolyte layer 3, and a positive electrode active material layer 4 in this order in the thickness direction. Furthermore, the metal layer 2 contains an Mg-Ga alloy. Details of each component other than the metal layer 2 are the same as those described in the first embodiment above.

[0043] The metal layer contains a Mg-Ga alloy. The Mg-Ga alloy is an alloy containing Mg and Ga, and may be a binary alloy containing Mg and Ga, or an alloy containing other elements in addition to Mg and Ga. In the latter case, it is preferable that Mg and Ga are the main components in the Mg-Ga alloy. In the Mg-Ga alloy, the total proportion of Mg and Ga to all elements is, for example, 50 at% or more, may be 70 at% or more, or may be 90 at% or more.

[0044] The metal layer may have a metallic phase (Mg-Ga alloy phase) of Mg-Ga alloy, or it may contain particles of Mg-Ga alloy. The particles of Mg-Ga alloy have an average particle size D 50 It is preferable that the nanoparticles have a diameter of 1 μm or less. Furthermore, in the metal layer, the ratio of Ga to the total of Ga and Mg (Ga / (Ga+Mg)) is not particularly limited. The preferred range for Ga / (Ga+Mg) is the same as that described in the first embodiment above. Furthermore, it is preferable that the metal layer does not contain a conductive material. Furthermore, it is preferable that the metal layer does not contain a binder. Furthermore, in the second embodiment, the metal layer usually does not contain Li.

[0045] The metal layer is usually a dense layer. The porosity of the metal layer (the ratio of the area of ​​voids in the cross-section of the metal layer) is, for example, 5% or less, but may be 3% or less, or 1% or less. The metal layer may also be a vapor-deposited film. It is preferable that the metal layer is in close contact with the negative electrode current collector. That is, it is preferable that the metal layer is arranged so as to cover the surface of the negative electrode current collector. A member having a negative electrode current collector and a metal layer arranged on the negative electrode current collector may be called a covered current collector. In the second embodiment, the thickness of the metal layer is not particularly limited, but may be, for example, 30 nm or more and 5 μm or less, 100 nm or more and 3 μm or less, or 500 nm or more and 2 μm or less.

[0046] The battery in the second embodiment has a negative electrode current collector, a metal layer, an electrolyte layer, and a positive electrode active material layer, arranged in this order in the thickness direction. Furthermore, the battery usually has an outer casing that houses these components. The configuration other than the metal layer is the same as described in "1. First Embodiment" above.

[0047] B. Battery manufacturing method In the battery manufacturing method described herein, a metal layer containing an Mg-Ga alloy phase is formed by a vapor deposition method (metal layer formation step). Subsequently, a battery having a negative electrode current collector, a metal layer, an electrolyte layer, and a positive electrode active material layer in this order in the thickness direction is assembled (assembly step). This yields, for example, the battery 10 shown in Figure 1(a). Subsequently, the battery is charged to form a Li-Mg alloy phase and a Li-Ga alloy phase from the Mg-Ga alloy phase contained in the metal layer (charging step). This yields, for example, the battery 10 shown in Figure 1(b).

[0048] According to this disclosure, a battery with good discharge capacity characteristics can be obtained by forming a specific metal layer.

[0049] 1.Metal layer formation process The metal layer formation process in this disclosure is a process of forming a metal layer containing a Mg-Ga alloy phase by a vapor deposition method. The metal layer obtained by the vapor deposition method is a vapor-deposited layer.

[0050] Examples of deposition methods include physical vapor deposition (PVD) such as ion plating, sputtering, and vacuum deposition. It is preferable to prepare Mg metal and Ga metal separately and perform binary deposition.

[0051] In this disclosure, it is preferable to form a metal layer on the negative electrode current collector by vapor deposition. This is because the negative electrode current collector has high smoothness, and a metal layer of uniform thickness can be obtained. In this case, the metal layer may be formed directly on the negative electrode current collector. Alternatively, the metal layer may be formed on the negative electrode current collector via another layer (for example, another vapor-deposited layer). Alternatively, in this disclosure, a metal layer may be formed on a solid electrolyte layer by vapor deposition. In this case, the metal layer may be formed directly on the solid electrolyte layer. Alternatively, the metal layer may be formed on the solid electrolyte layer via another layer (for example, another vapor-deposited layer).

[0052] 2. Assembly process The assembly process in this disclosure is a process of assembling the battery having a negative electrode current collector, the metal layer, the electrolyte layer, and the positive electrode active material layer in this order in the thickness direction. The method of assembling the battery is not particularly limited, and known methods can be employed.

[0053] 3.Charging process The charging step in this disclosure is a step in which the battery is charged after the assembly step described above, and a Li-Mg alloy phase and a Li-Ga alloy phase are formed from the Mg-Ga alloy phase contained in the metal layer. The charging conditions for the battery are appropriately selected according to the configuration of the battery.

[0054] 4.Battery The batteries obtained through the processes described above are the same as those described in "A. Batteries".

[0055] This disclosure is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of this disclosure and achieves similar effects is included within the technical scope of this disclosure. [Examples]

[0056] [Example 1] (Fabrication of the positive electrode) Lithium nickel-cobalt aluminate (NCA) was prepared as the positive electrode active material, a Li2-P2S5-based sulfide solid electrolyte containing LiI and LiBr was prepared as the solid electrolyte (SE), a PVDF-based binder was prepared as the binder, and vapor-grown carbon fiber (VGCF) was prepared as the conductive material. Next, each material was added to butyl butyrate in a weight ratio of NCA:SE:binder:conductive material = 84.7:13.4:0.6:1.27 to obtain a positive electrode slurry. The obtained positive electrode slurry was coated onto a positive electrode current collector (Al foil) with a coating gap of 225 μm, then pre-dried at 60°C and dried at 165°C for 1 hour. This obtained a positive electrode having a positive electrode current collector and a positive electrode active material layer. The basis weight of the positive electrode active material layer was 18.7 mg / cm². 2 The design capacity of the positive electrode active material layer is 3.0 mAh / cm². 2 That's what I decided.

[0057] (Preparation of a solid electrolyte layer) A Li2-P2S5-based sulfide solid electrolyte containing LiI and LiBr was prepared as the solid electrolyte (SE), and a PVDF-based binder was prepared as the binder. Next, each material was added to butyl butyrate in a weight ratio of SE:binder = 92.6:7.4 to obtain a slurry for the solid electrolyte layer. The obtained slurry was coated onto a release film with a coating gap of 325 μm, then pre-dried at room temperature for 3 hours, and dried at 165°C for 1 hour. This obtained a laminate having a release film and a solid electrolyte layer. The obtained laminate was punched out with a diameter of Φ14.5 mm, the solid electrolyte layers of the two punched-out members were stacked, and then pressed with a pressure of 7 tons. After pressing, the release films on both sides were peeled off to obtain a self-supporting solid electrolyte layer.

[0058] (Fabrication of the negative electrode) A stainless steel foil (SUS foil) was prepared as the negative electrode current collector. A metal layer (1.0 μm thick) containing an Mg-Ga alloy was formed on the SUS foil by binary deposition using an ion plating method. The target composition of the metal layer was Mg:Ga = 75:25 (at% basis), and the actual composition was Mg:Ga = 79:21 (at% basis). This resulted in obtaining a negative electrode with a negative electrode current collector and a metal layer.

[0059] (Creation of evaluation cells) The obtained positive electrode was punched out to a diameter of Φ11.28 mm, and the obtained negative electrode was punched out to a diameter of Φ14.5 mm. A self-supporting solid electrolyte layer was placed between them, and an aluminum positive electrode tab and a nickel negative electrode tab were attached, and the cell was vacuum-sealed in a laminate film. The sealed cell was subjected to a pressure of 392 MPa by cold isotropic pressing (CIP). Subsequently, the cell was restrained at 1 MPa using a constant-pressure jig with a spring inserted, so that the restraining pressure remained constant regardless of the volume change of the cell. This obtained an evaluation cell.

[0060] [Example 2] An evaluation cell was obtained in the same manner as in Example 1, except that the target composition in the metal layer was changed to Mg:Ga = 67:33 (at% basis). The actual composition in the metal layer was Mg:Ga = 73:27 (at% basis).

[0061] [Example 3] An evaluation cell was obtained in the same manner as in Example 1, except that the target composition in the metal layer was changed to Mg:Ga = 50:50 (at% basis). The actual composition in the metal layer was Mg:Ga = 47:53 (at% basis).

[0062] [Example 4] An evaluation cell was obtained in the same manner as in Example 1, except that the target composition in the metal layer was changed to Mg:Ga = 33:67 (at% basis). The actual composition in the metal layer was Mg:Ga = 30:70 (at% basis).

[0063] [Example 5] An evaluation cell was obtained in the same manner as in Example 1, except that the target composition in the metal layer was changed to Mg:Ga = 20:80 (at% basis). The actual composition in the metal layer was Mg:Ga = 24:76 (at% basis).

[0064] [Comparative Example 1] An evaluation cell was obtained in the same manner as in Example 1, except that a metal layer containing Mg metal was formed as the metal layer.

[0065] [Comparative Example 2] An evaluation cell was obtained in the same manner as in Example 1, except that a metal layer containing Ga metal was formed as the metal layer.

[0066] [evaluation] (Charge / Discharge Test) For the evaluation cells obtained in Examples 1-5 and Comparative Examples 1 and 2, first, a constant current (current density: 0.15 mA / cm²) was applied at a cutoff voltage in the range of 4.2V-3.0V. 2 (equivalent to 0.05C) - Constant voltage (cutoff current density: 0.03mA / cm²) 2The evaluation cells were charged and discharged at 60°C (equivalent to 0.01C) during the test.

[0067] Next, as a cycle test, a constant current (current density: 0.60 mA / cm²) was set at 25°C with a cutoff voltage in the range of 4.2V-3.0V. 2 (equivalent to 0.05C) - Constant voltage (charging only, cutoff current density: 0.03mA / cm²) 2 A test (equivalent to 0.01C) was conducted. The results are shown in Figure 4. Furthermore, the initial discharge capacity and the discharge capacity after 20 cycles in the cycle test are shown in Table 1 and Figure 5.

[0068] [Table 1]

[0069] As shown in Table 1, Figures 4 and 5, Examples 1 to 5 obtained higher discharge capacities than Comparative Examples 1 and 2. More specifically, as shown in Figure 5, Examples 1 to 5 obtained higher discharge capacities than those estimated from the straight line connecting Comparative Examples 1 and 2. As shown in Figure 4, among Examples 1 to 5, Examples 3 and 4 exhibited a unique phenomenon in which the discharge capacity decreased after the initial discharge, and then recovered through subsequent charging and discharging. In this respect, it was confirmed that a Ga / (Ga+Mg) ratio of 50 at% to 85 at% is preferable.

[0070] On the other hand, as shown in Figure 4, in Example 5, a remarkable result was obtained in which the discharge capacity did not decrease after the initial discharge, and the discharge capacity improved with subsequent charge-discharge cycles. In particular, when comparing Example 5 with Comparative Examples 1 and 2, the charge-discharge curves were completely different. Also, as shown in Figure 5, when comparing Examples 4, 5 and Example 2, it was confirmed that both the initial discharge capacity and the discharge capacity after 20 cycles were significantly higher in Example 5. Therefore, it was confirmed that a Ga / (Ga+Mg) ratio of around 76 at% (72 at% to 85 at%) is preferable.

[0071] (SEM observation) Cross-sectional observation was performed on the evaluation cell obtained in Example 5 using a scanning electron microscope (SEM). Specifically, the initial charge was performed at 60°C under the same conditions as above, and the cross-section was observed using SEM with secondary electron imaging at an applied voltage of 5kV. The results are shown in Figure 6. As shown in Figure 6, the metal layer placed between the solid electrolyte layer and the negative electrode current collector increased from 1.0 μm before the initial charge to approximately 15 μm. This is because the Mg and Ga contained in the metal layer alloyed with Li, respectively. In addition, although not specifically shown in the figures, analysis of elemental mapping by energy-dispersive X-ray spectroscopy (EDX) confirmed that Mg was relatively uniformly dispersed in the metal layer. In contrast, Ga was found to be locally dispersed. That is, it was confirmed that a sea-island structure was formed, with the Li-Mg alloy phase as the sea and the Li-Ga alloy phase as islands.

[0072] The reaction potential for Mg-Li insertion / deinsertion is 0.1V (vs Li / Li). + The reaction potential for Ga insertion and deinsertion of Li is lower than 0.1V~0.8V (vs Li / Li + ) is the extent of the relationship. Considering this relationship, it is presumed that during discharge, Li desorption from the Li-Mg alloy phase occurs first, and at that time, the Li-Ga alloy phase functions as a Li ion conduction path, resulting in a higher discharge capacity. In particular, in Example 5, it is presumed that the locally dispersed state of the Li-Ga alloy phase was effective for Li ion conduction. Furthermore, considering the binary phase diagram of the Mg-Ga alloy, in Example 5, a single phase of Ga5Mg2 was formed in the Mg-Ga alloy (before the first charge), and it is presumed that the Li insertion into Mg and Ga, which were mixed at the molecular level, affected the dispersion state of the Li-Ga alloy phase after the first charge. Furthermore, considering the difference in reaction potentials between Li insertion and deinsertion in Mg and Ga, it is presumed that Li-Ga redox occurred in the low-potential region (region below 3.5V) of the 60°C charge-discharge curve, and Li-Mg redox occurred in other regions. [Explanation of Symbols]

[0073] 1...Negative electrode current collector 2...metal layer 3 …electrolyte layer 4 …Positive electrode active material layer 5 …Positive current collector 10 … batteries

Claims

1. This battery utilizes the deposition and dissolution reaction of metallic lithium as the negative electrode reaction. The negative electrode current collector, metal layer, electrolyte layer, and positive electrode active material layer are arranged in this order in the thickness direction. The aforementioned metal layer contains a Li-Mg alloy phase and a Li-Ga alloy phase, in a battery.

2. The battery according to claim 1, wherein in the metal layer, the ratio of Ga to the total of Ga and Mg is 5 at% or more and 80 at% or less.

3. The battery according to claim 1, wherein in the metal layer, the ratio of Ga to the total of Ga and Mg is 72 at% or more and 85 at% or less.

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