Lithium secondary battery

Abstract

The present invention provides a lithium secondary battery which has a high energy density. The present invention pertains to a lithium secondary battery in which lithium metal has been deposited on the surface of the negative electrode and charge and discharge occurs due to the electrodissolution of the deposited lithium, wherein the negative electrode specifically comprises an Mg alloy or Mg metal.

Description

[Technical Field]

[0001] The present invention relates to a lithium secondary battery. [Background technology]

[0002] In recent years, technology for converting natural energy such as solar or wind power into electrical energy has been attracting attention. Accordingly, various secondary batteries have been developed as energy storage devices that are highly safe and can store large amounts of electrical energy.

[0003] Among these, lithium secondary batteries, which charge and discharge by transferring lithium ions between a positive electrode and a negative electrode, are known to exhibit high voltage and high energy density. A typical lithium secondary battery is the lithium-ion secondary battery (LIB), which has active materials capable of retaining lithium elements in the positive electrode and negative electrode, and charges and discharges by transferring lithium ions between the positive electrode active material and the negative electrode active material.

[0004] Furthermore, in order to achieve a high energy density, lithium secondary batteries (lithium metal batteries; LMBs) have been developed that use lithium metal as the negative electrode active material instead of materials that can insert lithium ions, such as carbon materials. For example, Patent Document 1 discloses a rechargeable battery that uses a lithium metal-based electrode as the negative electrode.

[0005] Furthermore, with the aim of achieving even higher energy density and improving productivity, lithium secondary batteries have been developed that use negative electrodes that do not have negative electrode active materials such as carbon materials or lithium metal. For example, Patent Document 2 discloses a lithium secondary battery that includes a positive electrode, a negative electrode, a separator membrane interposed between them, and an electrolyte, in which metal particles are formed on the negative electrode current collector of the negative electrode, and these particles are transferred from the positive electrode upon charging to form lithium metal on the negative electrode current collector within the negative electrode. Patent Document 2 discloses that such a lithium secondary battery can solve problems caused by the reactivity of lithium metal and problems that arise during the assembly process, thereby providing a lithium secondary battery with improved performance and lifespan. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 2006-500755 [Patent Document 2] Special Publication No. 2019-505971 Summary of the Invention [Problem to be solved by the invention]

[0007] Lithium secondary batteries, such as those in Patent Documents 1 and 2, in which lithium metal is deposited on the surface of the negative electrode and charging and discharging is performed by electrolytic elution of the deposited lithium, have a high energy density in principle, but it is desired to provide lithium secondary batteries with even higher energy density.

[0008] The present invention has been made in view of the above problems, and has an object to provide a lithium secondary battery with high energy density. [Means for solving the problem]

[0009] In a lithium secondary battery according to one embodiment of the present invention, charging and discharging are performed by depositing lithium metal on the surface of the negative electrode and electrolytically dissolving the deposited lithium metal, and the negative electrode is essentially made of an Mg alloy or Mg metal.

[0010] Lithium secondary batteries, which are charged and discharged by depositing lithium metal on the surface of the negative electrode and electrolytically dissolving the deposited lithium metal, have a smaller overall battery volume and mass and, in principle, a higher energy density than lithium ion secondary batteries that have a negative electrode active material for retaining lithium ions in the negative electrode. Furthermore, because the negative electrode is essentially made of magnesium metal or its alloy, which has a low specific gravity, the battery mass is small and the energy density is high.

[0011] Preferably, a plurality of recesses are formed on the surface of the negative electrode on which the lithium metal is deposited. In this embodiment, the mass of the negative electrode itself is further reduced, and the surface area of ​​the reaction field of the negative electrode is increased in the recesses, resulting in a lithium secondary battery with even better energy density and / or cycle characteristics.

[0012] The recesses are preferably filled with a gel electrolyte, which makes it possible to further improve the energy density of the lithium secondary battery.

[0013] The negative electrode preferably has a plurality of through-holes formed therein, penetrating the negative electrode between the surface on which the lithium metal is deposited and the surface opposite to the surface on which the lithium metal is deposited. In such an embodiment, the mass of the negative electrode itself is further reduced, and the through-holes increase the surface area of ​​the reaction field of the negative electrode, resulting in a lithium secondary battery with even better energy density and / or cycle characteristics.

[0014] The through holes are preferably filled with a gel electrolyte, and according to this embodiment, the energy density of the lithium secondary battery is further improved.

[0015] The average thickness of the negative electrode is 3.0 μm or more and 30 μm or less. According to such an embodiment, the energy density of the lithium secondary battery is further improved.

[0016] The specific gravity of the negative electrode is preferably 1.0 g / cm 3 More than 3.5g / cm 3 According to such an embodiment, the energy density of the lithium secondary battery is further improved.

[0017] The Mg alloy preferably contains 50 mol % or more of Mg atoms relative to the total number of moles of atoms in the Mg alloy. According to such an embodiment, the energy density of the lithium secondary battery is further improved.

[0018] The Mg alloy is preferably an alloy consisting of Mg and at least one selected from the group consisting of Al, Li, Zn, Mn, Fe, Si, Cu, Ni, and Ca. According to such an embodiment, the cycle characteristics and / or energy density of the lithium secondary battery are further improved.

[0019] In the lithium secondary battery, preferably, no lithium foil is formed on the surface of the negative electrode before initial charging. According to such an embodiment, the safety and / or energy density of the lithium secondary battery are further improved.

[0020] The lithium secondary battery preferably has an energy density of 425 Wh / kg or more. [Effects of the Invention]

[0021] According to the present invention, a lithium secondary battery with high energy density can be provided. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a schematic cross-sectional view of a lithium secondary battery according to an embodiment of the present invention. [Figure 2] FIG. 1 is a schematic cross-sectional view of a lithium secondary battery according to an embodiment of the present invention. [Figure 3] FIG. 2 is a schematic cross-sectional view of another aspect of the negative electrode according to the present embodiment. [Figure 4] FIG. 2 is a schematic cross-sectional view of another aspect of the negative electrode according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, an embodiment of the present invention (hereinafter referred to as "the present embodiment") will be described in detail with reference to the drawings as necessary. In the drawings, the same elements will be given the same reference numerals, and duplicate explanations will be omitted. Furthermore, unless otherwise specified, positional relationships such as up, down, left, and right will be based on the positional relationships shown in the drawings. Furthermore, the dimensional ratios of the drawings are not limited to those shown in the drawings.

[0024] [Present embodiment] (lithium secondary battery) Fig. 1 is a schematic cross-sectional view of a lithium secondary battery according to this embodiment. As shown in Fig. 1, the lithium secondary battery 100 of this embodiment includes a positive electrode 120, a negative electrode 140, a separator 130 disposed between the positive electrode 120 and the negative electrode 140, and an ion-conductive material not shown in Fig. 1. The positive electrode 120 has a positive electrode current collector 110 on the surface opposite to the surface facing the separator 130. Note that although the negative electrode 140 is depicted as a flat plate in Fig. 1, the negative electrode 140 is not limited to a flat plate and may take various forms, including those described below.

[0025] The lithium secondary battery according to this embodiment is charged and discharged by depositing lithium metal on the surface of the negative electrode and electrolytically dissolving the deposited lithium. That is, the lithium secondary battery according to this embodiment is charged and discharged by a method different from that of a lithium ion battery (LIB). The detailed differences will be described later in the description of each configuration. Each component of the lithium secondary battery 100 will be described below.

[0026] (Negative electrode) The negative electrode is essentially made of an Mg alloy or Mg metal, and has a smaller mass than electrodes (e.g., Cu, Ni, or SUS electrodes) used as negative electrodes in conventional lithium secondary batteries, so the lithium secondary battery of this embodiment has a high energy density.

[0027] In lithium secondary batteries, a method of reducing the thickness of the negative electrode is typically used to increase the energy density. However, reducing the thickness of the negative electrode reduces mechanical strength, potentially resulting in cutting, bending, and / or breakage of the negative electrode. Furthermore, when manufacturing a lithium secondary battery using a thin negative electrode, handling is difficult, which tends to increase the time and cost required for manufacturing the lithium secondary battery. Therefore, a method that can increase the energy density without reducing the thickness of the negative electrode is preferred. The present inventors have investigated various low-specific-gravity negative electrode materials and found that Mg alloys or Mg metal are suitable for sufficiently increasing the energy density of lithium secondary batteries without reducing the thickness of the negative electrode.

[0028] Mg has a specific gravity of approximately 1.74 g / cm 3 As shown in Table 1, Mg has a low specific gravity among metals. Therefore, alloys containing Mg atoms also tend to have a low specific gravity compared to other alloys. Furthermore, Mg has high electrical conductivity, making it suitable for use as an electrode. Furthermore, it has been found that Mg alloys or Mg metal exhibit superior resistance to degradation due to reactions with lithium ions during charging and discharging of lithium secondary batteries compared to other light metals or alloys of other light metals. Examples of metal elements with low specific gravity include Al and Ca. However, metals such as Al and Ca tend to have reduced corrosion resistance and / or toughness due to reactions with lithium ions during charging and discharging, and are therefore not suitable as negative electrode materials for lithium secondary batteries that are repeatedly charged and discharged. In other words, negative electrodes essentially consisting of Mg alloys or Mg metal have better properties as negative electrode materials, such as electrical conductivity and durability, compared to other metal materials with low specific gravity. Therefore, by using a negative electrode essentially consisting of an Mg alloy or Mg metal, it is possible to further increase the energy density of a lithium secondary battery without reducing the thickness of the negative electrode.

[0029] [Table 1]

[0030] The lithium secondary battery of this embodiment is charged and discharged by depositing lithium metal on the surface of the negative electrode when the battery is charged, and then electrolytically dissolving the deposited lithium when the battery is discharged. Therefore, the negative electrode 140 functions as a negative electrode current collector.

[0031] It is preferable that the lithium secondary battery 100 has no lithium foil formed on the surface of the negative electrode 140 (the interface between the negative electrode 140 and the separator 130) before initial charging. According to such an embodiment, there is no need to directly handle highly reactive lithium metal during production, and therefore a lithium secondary battery with better cycle characteristics, safety, and / or productivity can be obtained. In this embodiment, when the lithium secondary battery 100 is initially charged, Mg exposed on the surface of the negative electrode 140 reacts with Li supplied from the electrolyte or the like, forming a thin Mg-Li alloy on the negative electrode 140. After that, a layer containing mainly lithium metal is deposited on the Mg-Li alloy layer. In this embodiment, the lithium metal deposited on the negative electrode 140 is lithium metal derived from the positive electrode 120.

[0032] In this specification, "lithium metal" refers to lithium in a metallic state, including lithium containing impurities other than lithium. Furthermore, the term "lithium" refers to elemental lithium, lithium atoms, or lithium ions. In this specification, the term "before initial charging" refers to the state of the battery from assembly to the first charging, and the term "at the end of discharging" refers to the state of the battery when the voltage is between 1.0 V and 3.8 V, preferably between 1.0 V and 3.0 V.

[0033] The lithium secondary battery of this embodiment differs from a lithium ion battery (LIB) in the following respects. In a lithium ion battery (LIB), the negative electrode contains a host material of lithium element (lithium ion or lithium metal), and when the battery is charged, the material is filled with lithium element, and the host material releases the lithium element, thereby discharging the battery. That is, in a LIB, the host material of the negative electrode holds the lithium element, whereas in the lithium secondary battery of this embodiment, as described above, the lithium metal is formed directly on the surface of the negative electrode, which is a difference between the two.

[0034] In a lithium ion battery (LIB), the amount of negative electrode active material must be larger than the mass of the negative electrode current collector (which may correspond to the negative electrode in this embodiment). Therefore, even if the specific gravity of the negative electrode current collector is reduced, the effect of improving the energy density is limited, and the above-mentioned effect cannot be expected in the lithium secondary battery of this embodiment.

[0035] The negative electrode of this embodiment may contain components other than Mg alloys and Mg metal, as long as the effects of this embodiment are not impaired. Examples of components other than Mg alloys include metal atoms that do not alloy with Mg metal, and unavoidable impurities such as non-metallic substances. Examples of components other than Mg metal include metal atoms other than Mg metal, and unavoidable impurities such as non-metallic substances.

[0036] The negative electrode of this embodiment may essentially consist of Mg metal. In this case, the negative electrode may contain unavoidable impurities to the extent that the effects of this embodiment are not impaired. Such unavoidable impurities are not particularly limited, and may be, for example, Fe, Mn, Co, P, and S. The negative electrode of this embodiment may be made of an Mg alloy. In this case, the negative electrode is made of Mg metal and one or more metals that can be alloyed with Mg metal. The negative electrode of this embodiment may essentially consist of an Mg alloy. In this case, the negative electrode may contain unavoidable impurities such as metal atoms that do not alloy with Mg metal and substances other than metals. Such unavoidable impurities are not particularly limited, but may be, for example, Fe, Mn, Co, P, and S.

[0037] The Mg alloy used for the negative electrode 140 is not particularly limited as long as it can be used as a negative electrode of a lithium secondary battery and contains Mg. From the viewpoint of improving the durability and electronic conductivity of the negative electrode while increasing the energy density of the lithium secondary battery 100, the Mg alloy used for the negative electrode 140 preferably contains, in addition to Mg, at least one selected from the group consisting of Al, Li, Zn, Mn, Fe, Si, Cu, Ni, and Ca. From the same viewpoint, the Mg alloy used for the negative electrode 140 more preferably contains at least one selected from the group consisting of Al, Li, Zn, Mn, and Fe, even more preferably contains at least one selected from the group consisting of Li, Zn, and Fe, and even more preferably contains Li or Zn. The Mg alloy may consist of Mg metal and at least one metal selected from the group consisting of Al, Li, Zn, Mn, Fe, Si, Cu, Ni, and Ca. The Mg alloy may consist essentially of Mg metal and at least one metal selected from the group consisting of Al, Li, Zn, Mn, Fe, Si, Cu, Ni, and Ca. In this embodiment, the metal other than Mg metal may be at least one metal selected from the group consisting of Al, Li, Zn, Mn, and Fe, the group consisting of Li, Zn, and Fe, or the group consisting of Li and Zn.

[0038] Examples of Mg alloys used for the negative electrode 140 include known alloys such as AZ31, AZ31B, AZ61, AZ91, AM60, AM80, and LZ91. The chemical compositions of the respective Mg alloys are shown in Table 2, for example.

[0039] [Table 2]

[0040] As the negative electrode 140 of this embodiment, preferably, Mg metal or AZ31B, AZ91, AM60, or LZ91 is used, and more preferably, LZ91 is used. The Mg alloy or Mg metal used as the negative electrode 140 may be produced by a known method, or a commercially available product may be used.

[0041] The upper limit of the specific gravity of the negative electrode 140 consisting essentially of an Mg alloy or Mg metal is not particularly limited, and is, for example, 4.0 g / cm 3 From the viewpoint of increasing the energy density of the lithium secondary battery 100, the upper limit of the specific gravity of the negative electrode 140 is 3.8 g / cm 3 It is preferable that the concentration is 3.5 g / cm or less. 3 More preferably, it is 3.0 g / cm or less. 3 More preferably, it is 2.5 g / cm or less. 3 Even more preferably, the following: The lower limit of the specific gravity of the negative electrode 140 essentially made of an Mg alloy or Mg metal is not particularly limited, and is, for example, 0.9 g / cm 3 More than 1.0g / cm 3 More than 1.1g / cm 3 More than 1.2g / cm 3 or more, or 1.3 g / cm 3 It may be more than that. The specific gravity of typical Mg alloys and Mg metal is 1.78 g / cm for AZ31B at 20°C. 3 , AZ91 is 1.83g / cm 3 , AM60 is 1.81g / cm 3 , LZ91 is 1.50g / cm 3 , Mg metal is 1.74 g / cm 3 is.

[0042] The capacity of the negative electrode 140 for the alloying reaction with lithium metal is not particularly limited, and is, for example, 30% or less of the capacity of the positive electrode active material in the positive electrode 120. This capacity may be 25% or less, 20% or less, 15% or less, or 10% or less. The capacity of the positive electrode active material in the positive electrode 120 and the capacity of the negative electrode 140 for the alloying reaction with lithium metal can be measured by a conventionally known method.

[0043] In the lithium secondary battery 100 of this embodiment, the capacity of the alloying reaction with lithium metal in the negative electrode 140 is sufficiently small compared to the capacity of the positive electrode active material in the positive electrode 120. Therefore, it can be said that the lithium secondary battery 100 is charged and discharged by depositing lithium metal on the surface of the negative electrode and electrolytically dissolving the deposited lithium.

[0044] The average thickness of the negative electrode 140 is not particularly limited and is, for example, 1.0 μm or more and 60 μm or less. From the viewpoint of increasing the energy density of the lithium secondary battery 100 while improving the stability of the negative electrode 140, the average thickness of the negative electrode 140 is preferably 2.0 μm or more and 45 μm or less, more preferably 3.0 μm or more and 30 μm or less, even more preferably 5.0 μm or more and 28 μm or less, still more preferably 8.0 μm or more and 25 μm or less, and particularly preferably 10 μm or more and 20 μm or less.

[0045] In this embodiment, the average thickness can be measured by a known measurement method. For example, the lithium secondary battery can be cut in the thickness direction and the exposed cut surface can be observed with a scanning electron microscope (SEM) or a transmission electron microscope (TEM). In this embodiment, the "average thickness" and "thickness" are obtained by calculating the arithmetic mean of measurements taken three or more times, preferably five or more times.

[0046] When the Mg metal used in the negative electrode 140 contains impurities, the content of Mg atoms in the Mg metal is not particularly limited and may be, for example, more than 99.0 mass% relative to the total mass of the Mg metal. From the viewpoint of increasing the energy density of the lithium secondary battery 100, the Mg metal used in the negative electrode 140 preferably contains Mg atoms in an amount of 99.2 mass% or more, more preferably 99.5 mass% or more, and even more preferably 99.8 mass% or more relative to the total mass of the metal.

[0047] The Mg alloy used in the negative electrode 140 is not particularly limited as long as it contains Mg, and the content of Mg atoms in the Mg alloy is also not particularly limited. The content of Mg atoms in the Mg alloy may be, for example, 50 mol% or more relative to the total number of moles of atoms in the Mg alloy. From the viewpoint of increasing the energy density of the lithium secondary battery 100, the Mg alloy used in the negative electrode 140 preferably contains 55 mol% or more, more preferably 60 mol% or more, even more preferably 70 mol% or more, and even more preferably 80 mol% or more of Mg atoms relative to the total number of moles of atoms in the Mg alloy. The upper limit of the content of Mg atoms in the Mg alloy is not particularly limited, and may be 99 mol% or less, 97 mol% or less, 95 mol% or less, 92 mol% or less, or 85 mol% or less relative to the total number of moles of atoms in the Mg alloy.

[0048] The content of Mg atoms in the Mg alloy used for the negative electrode 140 may be, for example, 60% by mass or more and 99% by mass or less, relative to the total mass of the Mg alloy. From the viewpoint of improving the properties of the negative electrode 140 while increasing the energy density of the lithium secondary battery 100, the Mg alloy preferably contains 65% by mass or more and 98% by mass or less, more preferably 70% by mass or more and 97% by mass or less, even more preferably 75% by mass or more and 95% by mass or less, and still more preferably 80% by mass or more and 90% by mass or less of Mg atoms, relative to the total mass of the metal.

[0049] When the Mg alloy contains Al, the Al content is not particularly limited and may be, for example, 0.010 to 12 mass% relative to the total mass of the Mg alloy. The Al content in the Mg alloy may be 0.050 to 10 mass%, 0.10 to 8.0 mass%, 0.50 to 7.0 mass%, 1.0 to 5.0 mass%, or 2.0 to 4.0 mass%.

[0050] When the Mg alloy contains Li, the Li content is not particularly limited and may be, for example, 0.010 to 15 mass% relative to the total mass of the Mg alloy. The Li content in the Mg alloy may be 0.10 to 14 mass%, 1.0 to 13 mass%, 3.0 to 12 mass%, 5.0 to 11 mass%, 7.0 to 10 mass%, or 8.5 to 9.5 mass%.

[0051] When the Mg alloy contains Zn, the Zn content is not particularly limited and may be, for example, 0.0010 to 10% by mass relative to the total mass of the Mg alloy. The Zn content in the Mg alloy may be 0.0050 to 8.0% by mass, 0.010 to 5.0% by mass, 0.1 to 3.0% by mass, or 0.5 to 2.0% by mass.

[0052] When the Mg alloy contains Mn, Fe, Si, Cu, Ni, or Ca, the contents of Mn, Fe, Si, Cu, Ni, or Ca are not particularly limited, and may, for example, each independently be 0.0001% by mass to 7.0% by mass relative to the total mass of the Mg alloy. The contents of the above metal elements may each independently be 0.0005% by mass to 3.0% by mass, 0.001% by mass to 1.0% by mass, 0.005% by mass to 0.5% by mass, or 0.01% by mass to 0.1% by mass. The contents of each metal element are independent and may be different from one another.

[0053] The crystal structure of the Mg metal or Mg alloy used in the negative electrode 140 is not particularly limited, and examples thereof include an hcp (hexagonal close-packed) structure, a bcc (body-centered cubic) structure, and a mixed phase structure of an hcp structure and a bcc structure. The crystal structure of the negative electrode 140 may be a mixed phase structure of an hcp structure and a bcc structure, or a bcc structure.

[0054] FIG. 3 shows an embodiment of a negative electrode different from the negative electrode 140. The negative electrode 310 is the negative electrode 140 with a plurality of recesses 320 formed therein. The recesses 320 are formed on the surface on which lithium metal is deposited, i.e., the surface facing the separator. The negative electrode 310 may have the same chemical composition, average thickness, capacity, and the like as the negative electrode 140. In the lithium secondary battery 100, the negative electrode 140 may be replaced with a negative electrode 410.

[0055] 4 shows an embodiment of a negative electrode different from the negative electrode 140. The negative electrode 410 is the negative electrode 140 with a plurality of through-holes 420 formed therein. The negative electrode 410 may have the same chemical composition, average thickness, capacity, and the like as the negative electrode 140. The negative electrode 410 may be used in place of the negative electrode 140 in the lithium secondary battery 100.

[0056] The negative electrode 310 or the negative electrode 410 has a plurality of recesses 320 or through-holes 420, which reduces the mass of the negative electrode and increases the area on which lithium metal can be deposited, thereby improving the energy density and / or cycle characteristics of the lithium secondary battery 100.

[0057] The recess 320 or the through-hole 420 may be filled with an ion-conductive material, which will be described later. Such an ion-conductive material is not particularly limited, and examples thereof include an electrolytic solution, a gel electrolyte, and a polymer electrolyte. From the viewpoint of further improving the energy density while maintaining the stability and / or cycle characteristics of the lithium secondary battery, the recess 320 or the through-hole 420 is preferably filled with an electrolytic solution or a gel electrolyte, and more preferably with a gel electrolyte. The electrolytic solution, gel electrolyte, and polymer electrolyte filled in the recess 320 or the through-hole 420 are not particularly limited, and the materials described below may be used.

[0058] The shape of the recesses 320 or the through-holes 420 is not particularly limited, and may be, for example, circular, elliptical, rectangular, polygonal, or the like on the surface (the surface facing the separator). From the viewpoint of improving the productivity of the lithium secondary battery 100, the shape of the recesses 320 or the through-holes 420 may be circular. The method for forming the plurality of recesses 320 or the through-holes 420 is not particularly limited, and a known method may be used. Examples of methods for forming the plurality of recesses 320 include etching, stamping, scratching, and the like. Examples of methods for forming the plurality of through-holes 420 include laser processing, punching, etching, and the like.

[0059] The average pore size of the recesses 320 or through-holes 420 is not particularly limited and is, for example, 0.20 μm or more and 100 μm or less. From the viewpoint of improving the energy density and productivity of the lithium secondary battery 100, the pore size of the recesses 320 or through-holes 420 is preferably 0.30 μm or more and 75 μm or less, more preferably 0.50 μm or more and 50 μm or less, and even more preferably 1.0 μm or more and 30 μm or less. The pore size of the recesses 320 or through-holes 420 may be 3.0 μm or more, 5.0 μm or more, 10 μm or more, or 15 μm or more. In this specification, the "average pore size" of the recesses 320 or through-holes 420 refers to the average value of the circle-equivalent diameters of the recesses 320 or through-holes 420 on the surface of the negative electrode 310 or the surface of the negative electrode 410 facing the separator. The average value is calculated from at least five through-holes. The depth of the recess 320 may be 5% or more, 10% or more, 20% or more, or 30% or more of the thickness of the negative electrode 310. The depth of the recess 320 may be 80% or less, 70% or less, 60% or less, or 50% or less of the thickness of the negative electrode 310.

[0060] The porosity of the negative electrode 310 or 410 is not particularly limited and is, for example, 1% or more and 40% or less. From the viewpoint of improving the energy density and productivity of the lithium secondary battery 100, the porosity of the negative electrode 310 or 410 may be 2% or more and 30% or less, 3% or more and 25% or less, 4% or more and 20% or less, or 5% or more and 15% or less. In this specification, the "porosity" of the negative electrode 310 or 410 refers to the ratio (S2 / (S1+S2)) of the area of ​​the through-hole portion to the sum of the area of ​​the metal portion (S1) and the area of ​​the through-hole portion (S2) on the surface of the negative electrode 310 or 410 facing the separator.

[0061] In the negative electrode 140, a portion or all of the surface facing the separator 130 may be coated with a coating agent. The compound used as the coating agent is not particularly limited and may be a compound containing an aromatic ring to which two or more elements selected from the group consisting of N, S, and O are independently bonded, i.e., a compound having a structure in which two or more N, S, or O are independently bonded to an aromatic ring. Examples of aromatic rings include aromatic hydrocarbons such as benzene, naphthalene, azulene, anthracene, and pyrene, and heteroaromatic compounds such as furan, thiophene, pyrrole, imidazole, pyrazole, pyridine, pyridazine, pyrimidine, and pyrazine. Among these, aromatic hydrocarbons are preferred, with benzene and naphthalene being more preferred, and benzene being even more preferred. The above-mentioned negative electrode coating agents may be used alone or in combination. Coating the negative electrode with such a coating agent can further improve the cycle characteristics of the lithium secondary battery. Furthermore, if necessary, a conductive additive or a lithium salt, which will be described later, may be mixed into the above-mentioned negative electrode coating agent.

[0062] The negative electrode coating agent is not particularly limited, and examples thereof include benzotriazole (BTA), imidazole (IM), triazine thiol (TAS), polybenzimidazole, polyimide, polysulfone (PSU), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), and derivatives thereof.

[0063] In the negative electrode 140, a part or all of the surface facing the separator 130 may be covered with a thin film of a metal other than Mg. That is, in one aspect of this embodiment, the negative electrode may have a thin film of a metal other than Mg formed on an Mg alloy or Mg metal. Such a thin film of a metal may have a thickness that is much thinner than that of the Mg alloy or Mg metal. The thin metal film to be coated may be, for example, one that has low reactivity with Li metal. Examples of such metals include Cu, Au, Ag, and Pt. By coating the negative electrode 140 with a thin metal film that has low reactivity with Li metal, the lithium secondary battery 100 tends to have even better cycle characteristics. The thickness of the metal thin film is not particularly limited, and may be, for example, 1 / 10 or less, 1 / 50 or less, or 1 / 100 or less of the thickness of the Mg metal or Mg alloy. Specifically, the thickness of the metal thin film may be 10 nm or more and 60 nm or less, or 20 nm or more and 30 nm or less. The method for forming the metal thin film is not particularly limited, and examples thereof include vapor deposition, sputtering, and CVD.

[0064] (ion-conducting materials) The lithium secondary battery 100 includes an ion-conductive material, although this is not shown in FIG. 1. In this specification, the term "ion-conductive material" refers to a substance that contains at least an electrolyte (i.e., a salt) and has ion conductivity, and is a material that acts as a conduction path for lithium ions. Therefore, the lithium secondary battery 100 that includes the ion-conductive material has a further reduced internal resistance and further improved energy density, capacity, and cycle characteristics. The ion-conductive material may be present as a material filling the battery case (pouch), may be impregnated into the separator, may be present as an ion-conductive material layer separate from the layers illustrated in FIG. 1, or may fill pores in the negative electrode and / or positive electrode.

[0065] The ion-conductive material is not particularly limited as long as it is a material generally used in lithium secondary batteries, and can be appropriately selected depending on the application of the lithium secondary battery, etc. Specific examples include an electrolytic solution, a gel electrolyte, and a polymer electrolyte. The ion-conductive material may be an electrolytic solution or a gel electrolyte, or may be a gel electrolyte. An electrolyte solution is a material containing at least a solvent and an electrolyte (salt). Both polymer electrolytes and gel electrolytes contain a polymer and a salt, and a gel electrolyte is specifically defined as one that has become gel-like by containing an electrolyte solution or a solvent. Polymer electrolytes are not particularly limited, but examples include solid polymer electrolytes that primarily contain a polymer and an electrolyte, and semi-solid polymer electrolytes that primarily contain a polymer, an electrolyte, and a plasticizer.

[0066] The solvent that can be contained in the electrolytic solution, polymer electrolyte, and gel electrolyte as the ion-conductive material is not particularly limited as long as it is a non-aqueous solvent, and may be a polar solvent or a non-polar solvent. The solvent component may be selected by comprehensively considering the stability, volatility, solubility of the electrolyte used, etc. inside the lithium secondary battery 100. As the solvent component, either a fluorinated solvent having fluorine atoms or a non-fluorinated solvent having no fluorine atoms may be used, or a combination of both may be used.

[0067] The fluorinated solvent is not particularly limited as long as it functions as a solvent, and examples thereof include ether compounds, ester compounds, carbonate compounds, and phosphate ester compounds, all of which have at least one fluorine atom. The number of carbon atoms in the fluorinated solvent is not particularly limited, and may be, for example, 2 to 50, 2 to 40, 3 to 20, or 3 to 15. The number of fluorines in the fluorinated solvent is also not particularly limited, and may be, for example, 1 to 70, 2 to 50, 2 to 30, 3 to 20, or 4 to 15.

[0068] A preferred embodiment of the fluorinated solvent is one having a monovalent group represented by the following formula (A) or (B). In this embodiment, the fluorinated solvent is preferably an ether compound. In this embodiment, the fluorinated solvent may have both the monovalent group represented by formula (A) and the monovalent group represented by formula (B). According to these embodiments, the cycle characteristics of the lithium secondary battery 100 tend to be further improved. [ka] [ka] In the formula, the wavy line represents a bonding site in a monovalent group.

[0069] Non-limiting examples of fluorinated solvents include 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTFE), 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (TFEE), ethyl-1,1,2,2-tetrafluoroethyl ether (ETFE), methyl-1,1,2,2-tetrafluoroethyl ether (TFME), 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (OFTFE), difluoromethyl Examples of suitable fluoroisopropyl ethers include methyl-2,2,3,3-tetrafluoropropyl ether (DFTFE), methyl perfluorobutyl ether (NV7100), ethyl perfluorobutyl ether (NV7200), 1,1,1,2,2,3,4,5,5,5-decafluoro-3-methoxy-4-trifluoromethylpentane (NV7300), methyl-2,2,3,3,3-pentafluoropropyl ether, methyl-1,1,2,3,3,3-hexafluoropropyl ether, and ethyl-1,1,2,3,3,3-hexafluoropropyl ether.

[0070] The non-fluorine-containing solvent is not particularly limited as long as it functions as a solvent, and examples thereof include ether compounds, ester compounds, carbonate compounds, and phosphate ester compounds. The number of carbon atoms in the non-fluorine-containing solvent is not particularly limited, and may be, for example, 2 to 50, 2 to 40, 3 to 20, or 3 to 15. Non-limiting specific examples of the fluorine-free solvent include triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,2-dimethoxyethane, dimethoxyethane (DME), dimethoxypropane (DMP), 1,2-dimethoxypropane, 2,2-dimethoxypropane, dimethoxybutane (DMB), 1,3-dimethoxybutane, 1,2-dimethoxybutane, 2,2-dimethoxybutane, 2,3-dimethoxybutane, diethylene glycol dimethyl ether, acetonitrile, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, chloroethylene carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, trimethyl phosphate, triethyl phosphate, and 12-crown-4.

[0071] The ion-conductive material may contain either a fluorinated solvent or a non-fluorinated solvent, or may contain both. In this embodiment, the lithium secondary battery 100 may contain, as the fluorinated solvent, one of the above-mentioned solvents alone or in combination of two or more thereof, and similarly, may contain, as the non-fluorinated solvent, one of the above-mentioned solvents alone or in combination of two or more thereof.

[0072] The above-mentioned fluorinated solvents and / or non-fluorinated solvents can be freely combined and used in any ratio. The blending ratio of the fluorinated solvent and the non-fluorinated solvent is not particularly limited, and the ratio of the fluorinated solvent to the total solvent may be 0% by volume or more and 100% by volume or less, or the ratio of the non-fluorinated solvent to the total solvent may be 0% by volume or more and 100% by volume or less.

[0073] The salts that can be contained as electrolytes in the electrolytic solution, polymer electrolyte, and gel electrolyte are not particularly limited, and examples thereof include salts of Li, Na, K, Ca, and Mg. The lithium secondary battery 100 preferably contains a lithium salt as an electrolyte. Such lithium salts are not particularly limited as long as they function as an electrolyte, and examples thereof include LiI, LiCl, LiBr, LiF, LiBF, LiPF, LiAsF, LiSOCF, LiN(SOF), LiN(SOCF), LiN(SOCFCF), LiBF(CO), LiB(CO), LiB(OCOCF), LiNO, and LiSO. Examples of salts of Na, K, Ca, and Mg include Na, K, Ca, and Mg. + , K. + , Ca 2+ , and Mg 2+ and any of the anions in the lithium salts described above. The above salts may be used alone or in combination of two or more thereof. The above lithium salts may be used alone or in combination of two or more thereof.

[0074] The concentration of the electrolyte in the electrolytic solution is not particularly limited, but is preferably 0.5 M or more, more preferably 0.7 M or more, even more preferably 0.9 M or more, and even more preferably 1.0 M or more. When the concentration of the electrolyte is within the above range, the SEI layer is more easily formed and the internal resistance tends to be further reduced, which tends to further improve the cycle characteristics and rate characteristics of the battery. The upper limit of the electrolyte concentration is not particularly limited, and the electrolyte concentration may be equal to or less than the saturated concentration, for example, 10.0 M or less, 5.0 M or less, or 2.0 M or less.

[0075] Materials constituting the polymer electrolyte or gel electrolyte are not particularly limited as long as they are generally used in lithium secondary batteries, and known materials can be appropriately selected. Polymers (resins) that can be contained in the polymer electrolyte or gel electrolyte include, but are not limited to, resins having ethylene oxide units in the main chain and / or side chain, such as polyethylene oxide (PEO), acrylic resins, vinyl resins, ester resins, nylon resins, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polysiloxane, polyphosphazene, polymethyl methacrylate, polyamide, polyimide, aramid, polylactic acid, polyethylene, polystyrene, polyurethane, polypropylene, polybutylene, polyacetal, polysulfone, polytetrafluoroethylene, and vinylidene fluoride-hexafluoropropylene copolymers. These polymers can be used alone or in combination.

[0076] In the polymer electrolyte or gel electrolyte, the content ratio of the polymer to the lithium salt may be determined by the ratio ([Li] / [O]) of oxygen atoms in the polymer to lithium atoms in the lithium salt. In the polymer electrolyte or gel electrolyte, the content ratio of the polymer to the lithium salt may be adjusted so that the ratio ([Li] / [O]) is, for example, 0.02 to 0.20, 0.03 to 0.15, or 0.04 to 0.12.

[0077] The plasticizer contained in the semi-solid polymer electrolyte is not particularly limited, but examples thereof include components similar to the solvent that can be contained in the gel electrolyte, and various oligomers.

[0078] (separator) The separator 130 is a component that prevents the battery from short-circuiting by isolating the positive electrode 120 and the negative electrode 140, while ensuring ionic conductivity of lithium ions, which serve as charge carriers between the positive electrode 120 and the negative electrode 140. That is, the separator 130 has the function of physically and / or electrically isolating the positive electrode 120 and the negative electrode 140, and the function of ensuring ionic conductivity of lithium ions. Therefore, the separator 130 is not electronically conductive and is made of a material that does not react with lithium ions. The separator 130 may also serve to retain the electrolyte. As such a separator, one kind of material having the above two functions may be used alone, or two or more kinds of materials having one of the above functions may be used in combination. The separator is not particularly limited as long as it has the above function, but examples thereof include insulating porous materials, polymer electrolytes, gel electrolytes, and inorganic solid electrolytes, and is typically at least one selected from the group consisting of insulating porous materials, polymer electrolytes, and gel electrolytes.

[0079] When the separator includes an insulating porous member, the pores of the member are filled with an ion-conductive substance, which allows the member to exhibit ion conductivity. The substance to be filled may be, for example, the ion-conductive material described above, and may be at least one of an electrolytic solution, a polymer electrolyte, and a gel electrolyte. An insulating porous material, a polymer electrolyte, or a gel electrolyte can be used singly or in combination as the separator 130. When an insulating porous material is used alone as the separator, the lithium secondary battery must further include an ion-conductive material.

[0080] The material constituting the insulating porous member is not particularly limited, but examples thereof include insulating polymer materials, specifically polyethylene (PE) and polypropylene (PP). That is, the separator 130 may be a porous polyethylene (PE) film, a porous polypropylene (PP) film, or a laminated structure thereof.

[0081] The separator 130 may be coated with a separator coating layer. The separator coating layer may cover both sides of the separator 130 or only one side. The separator coating layer is not particularly limited as long as it is ion-conductive and does not react with lithium ions, but it is preferable that it be capable of firmly bonding the separator 130 to a layer adjacent to the separator 130. Examples of such separator coating layers include, but are not limited to, polyvinylidene fluoride (PVDF), a mixture of styrene butadiene rubber and carboxymethyl cellulose (SBR-CMC), polyacrylic acid (PAA), lithium polyacrylate (Li-PAA), polyimide (PI), polyamideimide (PAI), and those containing a binder such as aramid. The separator coating layer may contain inorganic particles such as silica, alumina, titania, zirconia, magnesium oxide, magnesium hydroxide, or lithium nitrate added to the binder. The separator 130 may be a separator without a separator coating layer, or may be a separator with a separator coating layer.

[0082] The average thickness of the separator 130, including the separator coating layer, is preferably 30 μm or less, more preferably 25 μm or less, and even more preferably 20 μm or less. According to such an embodiment, the volume occupied by the separator 130 in the lithium secondary battery 100 is reduced, thereby further improving the energy density of the lithium secondary battery 100. In addition, the average thickness of the separator 130 is preferably 5.0 μm or more, more preferably 7.0 μm or more, and even more preferably 10 μm or more. According to such an embodiment, the positive electrode 120 and the negative electrode 140 can be reliably isolated from each other, and short-circuiting of the battery can be further prevented.

[0083] (positive electrode) The positive electrode 120 is not particularly limited as long as it is a material generally used in lithium secondary batteries, and known materials can be appropriately selected depending on the application of the lithium secondary battery. From the viewpoint of improving the stability and output voltage of the battery, the positive electrode 120 preferably contains a positive electrode active material. When the positive electrode has a positive electrode active material, lithium ions are typically charged into and desorbed from the positive electrode active material by charging and discharging the battery.

[0084] In this specification, the term "positive electrode active material" refers to a material that causes an electrode reaction, i.e., an oxidation reaction and a reduction reaction, at the positive electrode. Specifically, the positive electrode active material may be a host material for lithium element (typically, lithium ion).

[0085] Such positive electrode active materials are not particularly limited, but include, for example, metal oxides and metal phosphates. Examples of the metal oxides include, but are not particularly limited, cobalt oxide-based compounds, manganese oxide-based compounds, and nickel oxide-based compounds. Examples of the metal phosphates include, but are not particularly limited, iron phosphate-based compounds and cobalt phosphate-based compounds. Typical positive electrode active materials include LiCoO2, LiNi x Co y Mn z O(x+y+z=1), LiNi x Co y Al z O(x+y+z=1), LiNi x Mn y O(x+y=1), LiNiO2, LiMn2O4, LiFePO4, LiCoPO4, LiFeOF, LiNiOF, and LiTiS2. The above-mentioned positive electrode active materials may be used singly or in combination of two or more.

[0086] The positive electrode 120 may contain components other than the above-mentioned positive electrode active material. Such components are not particularly limited, but may include, for example, a conductive additive, a binder, and an ion-conductive material.

[0087] The ion-conductive material in the positive electrode 120 may be one of those described above (for example, the gel electrolyte or polymer electrolyte described above). The ion-conductive material in the positive electrode 120 may be a gel electrolyte. According to such an embodiment, the function of the gel electrolyte improves the adhesive strength between the positive electrode and the positive electrode current collector, making it possible to attach a thinner positive electrode current collector, thereby further improving the energy density of the battery. When attaching the positive electrode current collector to the surface of the positive electrode, a positive electrode current collector formed on release paper may be used.

[0088] The conductive additive in the positive electrode 120 is not particularly limited, but examples thereof include carbon black, single-walled carbon nanotubes (SWCNT), multi-walled carbon nanotubes (MWCNT), carbon nanofibers (CF), and acetylene black. The binder is not particularly limited, but examples thereof include polyvinylidene fluoride, polytetrafluoroethylene, styrene butadiene rubber, acrylic resin, and polyimide resin.

[0089] The content of the positive electrode active material in the positive electrode 120 may be, for example, 50% by mass or more and 100% by mass or less, based on the entire positive electrode 120. The content of the conductive additive may be, for example, 0.50% by mass or more and 30% by mass or less, based on the entire positive electrode 120. The content of the binder may be, for example, 0.50% by mass or more and 30% by mass or less, based on the entire positive electrode 120. The content of the ion conductive material may be, for example, 0.50% by mass or more and 30% by mass or less, preferably 5.0% by mass or more and 20% by mass or less, and more preferably 8.0% by mass or more and 15% by mass or less, based on the entire positive electrode 120.

[0090] The average thickness of the positive electrode 120 is preferably 20 μm or more and 100 μm or less, more preferably 30 μm or more and 80 μm or less, and even more preferably 40 μm or more and 70 μm or less, although the average thickness of the positive electrode can be adjusted appropriately depending on the desired battery capacity.

[0091] (Positive electrode current collector) A positive electrode current collector 110 is disposed on one side of the positive electrode 120. The positive electrode current collector is not particularly limited as long as it is a conductor that does not react with lithium ions in the battery. An example of such a positive electrode current collector is aluminum. The positive electrode current collector 110 may not be provided, in which case the positive electrode itself functions as a current collector. The positive electrode current collector functions to donate and receive electrons to the positive electrode (particularly the positive electrode active material). The positive electrode current collector 110 is in physical and / or electrical contact with the positive electrode 120.

[0092] In this embodiment, the average thickness of the positive electrode current collector is preferably 1.0 μm or more and 15 μm or less, more preferably 2.0 μm or more and 10 μm or less, and even more preferably 3.0 μm or more and 6.0 μm or less. According to such an embodiment, the volume occupied by the positive electrode current collector in the lithium secondary battery 100 is reduced, and therefore the energy density of the lithium secondary battery 100 is further improved.

[0093] (Use of lithium secondary batteries) 2 shows one mode of use of the lithium secondary battery of this embodiment. In the lithium secondary battery 200, a positive electrode terminal 210 and a negative electrode terminal 220 are joined to the positive electrode current collector 110 and the negative electrode 140, respectively, for connecting the lithium secondary battery 200 to an external circuit. The lithium secondary battery 200 is charged and discharged by connecting the negative electrode terminal 220 to one end of the external circuit and the positive electrode terminal 210 to the other end of the external circuit. The external circuit may be, for example, a resistor, a power source, an apparatus, a device, another battery, or a potentiostat.

[0094] More specifically, the lithium secondary battery 200 is charged by connecting an external power source to the positive electrode terminal 210 and the negative electrode terminal 220 and applying a voltage between the positive electrode terminal 210 and the negative electrode terminal 220 such that a current flows from the negative electrode terminal 220 (negative electrode 140) through an external circuit to the positive electrode terminal 210 (positive electrode 120). It is presumed that a solid electrolyte interface layer (SEI layer) is formed on the surface of the negative electrode 140 (the interface between the negative electrode 140 and the separator 130) during initial charging of the lithium secondary battery 200, but the lithium secondary battery 200 does not necessarily have an SEI layer. Charging the lithium secondary battery 200 causes deposition of lithium metal at the interface between the negative electrode 140 and the SEI layer, the interface between the negative electrode 140 and the separator 130, and / or the interface between the SEI layer and the separator 130. Furthermore, when the negative electrode 140 of the lithium secondary battery 200 has recesses or through-holes, an SEI layer may be formed at the interface between the recesses or through-holes of the negative electrode and the ion-conductive material by initial charging. When a lithium secondary battery having a negative electrode 140 with recesses or through-holes is charged, lithium metal may also be deposited on the surface of the recesses or through-holes.

[0095] When the positive electrode terminal 210 and the negative electrode terminal 220 of the charged lithium secondary battery 200 are connected via a desired external circuit, the lithium secondary battery 200 is discharged. As a result, the lithium metal deposited on the negative electrode is electrolytically dissolved. If an SEI layer is formed in the lithium secondary battery 200, the lithium metal formed at at least one of the interface between the negative electrode and the SEI layer, the interface between the negative electrode and the separator, and / or the interface between the SEI layer and the separator is electrolytically dissolved. Furthermore, if the negative electrode of the lithium secondary battery 200 has recesses or through-holes, lithium metal produced on the surfaces of the recesses or through-holes may also be electrolytically dissolved by discharge.

[0096] (Lithium secondary battery manufacturing method) The method for manufacturing the lithium secondary battery 100 as shown in FIG. 1 is not particularly limited as long as it is a method that can manufacture a lithium secondary battery having the above-described configuration, and examples thereof include the following methods.

[0097] The positive electrode current collector 110 and the positive electrode 120 are manufactured, for example, as follows. The positive electrode active material described above is mixed with at least one of a conductive additive, an ion-conductive material, and a binder to obtain a positive electrode mixture. The compounding ratios may be, for example, 50% by mass to 99% by mass of the positive electrode active material, 0.5% by mass to 30% by mass of the conductive additive, 0.5% by mass to 30% by mass of the binder, and 0.5% by mass to 30% by mass of the ion-conductive material, relative to the total positive electrode mixture. The obtained positive electrode mixture is applied to one side of a metal foil (e.g., Al foil) having a predetermined thickness (e.g., 1.0 μm to 1.0 mm) as a positive electrode current collector, and press-molded. The obtained molded body is punched to a predetermined size by a punching process to obtain the positive electrode current collector 110 and the positive electrode 120.

[0098] Next, an Mg alloy or Mg metal is prepared as the negative electrode material, for example, with a thickness of 1.0 μm or more and 1.0 mm or less, and after washing with a solvent, it is punched out to a predetermined size, and then ultrasonically cleaned with ethanol and dried to obtain the negative electrode 140. When a negative electrode having recesses or through holes is used (see FIGS. 3 and 4), the negative electrode 140 obtained as described above may be further processed (etching, stamping, laser processing, punching, etc.) to form multiple recesses or through holes. If necessary, the surface of the negative electrode material may be coated with the above-mentioned coating agent and then dried in the atmosphere to carry out a coating treatment.

[0099] Next, the separator 130 having the above-described structure is prepared. The separator 130 may be manufactured by a conventionally known method, or a commercially available separator may be used.

[0100] When an electrolyte solution is used as the ion-conductive material, the electrolyte solution may be prepared by dissolving an electrolyte (e.g., a lithium salt) in a solution obtained by using one of the above-mentioned solvents alone or by mixing two or more of them as the solvent. The mixing ratio of the solvent and the electrolyte may be appropriately adjusted so that the contents or concentrations of the solvent and the electrolyte fall within the above-mentioned ranges. Thereafter, the positive electrode current collector 110 having the positive electrode 120 formed thereon obtained as described above, the separator 130, and the negative electrode 140 are stacked in this order so that the positive electrode 120 faces the separator 130, thereby obtaining a laminate. The obtained laminate is sealed in a sealed container together with an electrolyte solution, thereby obtaining a lithium secondary battery 100.

[0101] When a gel electrolyte or a polymer electrolyte is used as the ion-conductive material, the gel electrolyte or polymer electrolyte may be prepared by a known manufacturing method or by purchasing a commercially available product. The gel electrolyte or polymer electrolyte may be produced, for example, by mixing the above-mentioned polymer, the above-mentioned solvent, and / or the above-mentioned electrolyte (e.g., lithium salt). The mixing ratio of the solvent and the electrolyte may be appropriately adjusted so that the content or concentration of the polymer, solvent, and electrolyte falls within the above-mentioned ranges. Then, in the lamination process in which each component is laminated in order, a gel-like ion-conductive material is applied between each component, or a solid ion-conductive material is adhered to the components to produce a laminate. The resulting laminate is sealed in a sealed container to produce a lithium secondary battery. The laminate may also be sealed in a sealed container together with an electrolyte solution.

[0102] The sealed container is not particularly limited, but examples thereof include a laminate film.

[0103] [Variations] The above-described embodiment is an example for explaining the present invention, and is not intended to limit the present invention to only this embodiment. The present invention can be modified in various ways without departing from the gist of the invention.

[0104] Although each component of the lithium secondary battery 100 is a flat plate, the shape of the lithium secondary battery of this embodiment is not particularly limited. For example, in addition to a flat plate shape, the lithium secondary battery may be cylindrical, rectangular, or other shapes. Furthermore, although the lithium secondary battery 100 includes one of each type of component, the lithium secondary battery of this embodiment may have a layered structure including multiple components of each type.

[0105] For example, in the lithium secondary battery 100 of this embodiment, the components may be stacked (may be multiple layers) in the following order: positive electrode current collector / positive electrode / separator / negative electrode / separator / positive electrode / positive electrode current collector. According to such an embodiment, the capacity of the lithium secondary battery can be further improved.

[0106] In the lithium secondary battery of this embodiment, terminals for connecting to an external circuit may be attached to the positive electrode current collector and / or the negative electrode. For example, metal terminals (e.g., Al, Ni, etc.) having a thickness of 10 μm to 1.0 mm may be bonded to one or both of the positive electrode current collector and the negative electrode. A conventionally known method may be used as the bonding method, and ultrasonic welding may be used, for example.

[0107] In this specification, "high energy density" or "having a high energy density" means that the capacity per total mass or volume of the battery is high, and is preferably 800 Wh / L or more or 400 Wh / kg or more, and more preferably 900 Wh / L or more or 425 Wh / kg or more.

[0108] In this specification, "excellent cycle characteristics" means that the rate of decrease in battery capacity is low before and after a number of charge-discharge cycles that can be expected in normal use. In other words, when comparing the first discharge capacity after initial charge with the discharge capacity after a number of charge-discharge cycles that can be expected in normal use, the discharge capacity after the charge-discharge cycles is almost no decrease compared to the first discharge capacity after initial charge. [Example]

[0109] The present invention will be described in more detail below using examples and comparative examples, but the present invention is not limited to the following examples.

[0110] [Example 1] A lithium secondary battery was fabricated as follows. First, a 30 μm thick Mg alloy foil (AZ31B) was washed with a solvent containing sulfamic acid and then rinsed with water. The Mg alloy foil was then immersed in a solution containing 1H-benzotriazole as an anode coating agent, dried, and then rinsed with water to obtain an Mg alloy foil coated with an anode coating agent. The obtained Mg alloy foil was punched to a predetermined size (36.3 cm × 36.3 cm) to obtain an anode.

[0111] A separator having a thickness of 16 μm and a predetermined size (38 cm×38 cm) was prepared, in which both sides of a 12 μm polyethylene microporous membrane were coated with 2.0 μm polyvinylidene fluoride (PVdF).

[0112] Next, LiNi 0.85 Co 0.12 Al 0.03 A mixture of 96 parts by mass of O2, 2.0 parts by mass of carbon black as a conductive additive, and 2.0 parts by mass of polyvinylidene fluoride (PVdF) as a binder was applied to one side of a 12 μm thick Al foil as a positive electrode current collector and press-molded. The resulting molded body was punched out to a predetermined size (36.3 cm × 36.3 cm) to obtain a positive electrode formed on the positive electrode current collector.

[0113] The electrolyte was prepared by dissolving LiN(SO2F)2 (LiFSI) in dimethoxyethane (DME) to prepare a 1.0 M LiFSI solution. The specific gravity of the prepared electrolyte was 1.45 g / cm 3 It was.

[0114] The positive electrode current collector, positive electrode, separator, and negative electrode obtained as described above were stacked in this order to obtain a laminate. Furthermore, a 100 μm Al terminal and a 100 μm Ni terminal were joined to the positive electrode current collector and negative electrode, respectively, by ultrasonic welding, and then inserted into a laminate exterior body. The electrolyte solution prepared as described above was then poured into the exterior body. The exterior body was sealed to obtain a lithium secondary battery.

[0115] [Examples 2 to 4] A lithium secondary battery was obtained in the same manner as in Example 1, except that an Mg alloy foil having a thickness shown in Table 3 was used as the negative electrode.

[0116] [Examples 5 to 8] A lithium secondary battery was obtained in the same manner as in Example 1, except that an Mg metal foil having a thickness shown in Table 3 was used as the negative electrode.

[0117] [Examples 9 to 12] A lithium secondary battery was obtained in the same manner as in Example 1, except that an Mg alloy foil (LZ91) having a thickness shown in Table 4 was used as the negative electrode.

[0118] [Example 13] Using a 20 μm thick LZ91 Mg alloy foil, an Mg alloy foil (36.3 cm × 36.3 cm) coated with a negative electrode coating agent was obtained in the same manner as in Example 1. Next, circular through-holes with an average pore diameter of 20 μm were formed on the Mg alloy foil by laser processing so that the porosity was 5.0%, to obtain a negative electrode. A lithium secondary battery was obtained in the same manner as in Example 1, except that the negative electrode obtained as described above was used.

[0119] [Example 14] A lithium secondary battery was obtained in the same manner as in Example 13, except that through-holes with an average pore size of 10 μm were formed in the Mg alloy foil of the negative electrode so that the porosity was 10%.

[0120] [Example 15] In the same manner as in Example 13, a negative electrode, a positive electrode with a positive electrode current collector formed thereon, and a separator were prepared. Next, a gel electrolyte was prepared as follows. Dimethoxyethane (DME) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTFE) were mixed in a volume ratio of 2:8, and LiN(SO2F)2 (LiFSI) was dissolved in the solution to a concentration of 1.2 M. An equal amount of vinylidene fluoride-hexafluoropropylene copolymer was added to the solution (electrolyte:vinylidene fluoride-hexafluoropropylene copolymer = 1:1) to prepare a gel electrolyte. The specific gravity of the resulting gel electrolyte was 1.35 g / cc. A positive electrode current collector, a positive electrode, a separator, and a negative electrode were stacked in this order to obtain a laminate. A gel electrolyte was applied to the interface between each component. The through-holes formed in the negative electrode were filled with the gel electrolyte. A 100 μm Al terminal and a 100 μm Ni terminal were joined to the positive electrode current collector and the negative electrode, respectively, by ultrasonic welding, and then inserted into a laminate exterior. The exterior was then sealed without injecting an electrolyte solution, yielding a lithium secondary battery.

[0121] [Example 16] A lithium secondary battery was obtained in the same manner as in Example 15, except that through-holes with a pore diameter of 10 μm were formed in the Mg alloy foil of the negative electrode so that the porosity was 10%.

[0122] [Example 17] A lithium secondary battery was obtained in the same manner as in Example 15, except that the same Mg alloy foil without through holes as in Example 10 was used as the Mg alloy foil for the negative electrode.

[0123] [Comparative Example 1] A lithium secondary battery was fabricated as follows. First, as a method for producing a negative electrode, a commercially available electrolytic Cu foil having a thickness of 8.0 μm was used and washed in the same manner as in Example 1 to prepare a negative electrode coated negative electrode.

[0124] The positive electrode, positive electrode current collector, separator, and electrolyte were prepared in the same manner as in Example 1.

[0125] The positive electrode current collector with the positive electrode formed thereon, the separator, and the negative electrode were stacked in this order, with the positive electrode facing the separator, to obtain a laminate. Furthermore, as in Example 1, a 100 μm Al terminal and a 100 μm Ni terminal were joined to the positive electrode current collector and the negative electrode, respectively, by ultrasonic welding, and then inserted into a laminate exterior body. The electrolyte solution prepared as described above was then poured into the exterior body, and the exterior body was sealed to obtain a lithium secondary battery.

[0126] [Comparative Examples 2 to 3] A lithium secondary battery was obtained in the same manner as in Comparative Example 1, except that an electrolytic Cu foil having a thickness shown in Table 5 was used as the negative electrode.

[0127] [Energy density evaluation] The energy density of the lithium secondary batteries fabricated in the examples and comparative examples was evaluated. The product of the charge / discharge capacity and average discharge voltage of the fabricated lithium secondary battery divided by the total weight of the battery is defined as the energy density (Wh / kg). The higher the energy density, the better the battery performance.

[0128] [Table 3]

[0129] [Table 4]

[0130] [Table 5]

[0131] It can be seen from Tables 3 to 5 that Examples 1 to 17, which used negative electrodes made of Mg alloys or Mg metal, had higher energy densities than Comparative Examples 1 to 3, which did not. It can be seen that Examples 13 to 16, which have through holes on the surface of the negative electrode, have even higher energy densities than examples with negative electrodes of equivalent thickness. It can also be seen that Examples 15 to 17, which use a gel electrolyte instead of a liquid electrolyte, have even higher energy densities than examples using a liquid electrolyte. INDUSTRIAL APPLICABILITY

[0132] The lithium secondary battery of the present invention has high energy density and is therefore industrially applicable as an electricity storage device for a variety of uses. [Explanation of symbols]

[0133] 100, 200... lithium secondary battery, 110... positive electrode current collector, 120... positive electrode, 130... separator, 130, 310, 410... negative electrode, 210... positive electrode terminal, 220... negative electrode terminal, 320... recess, 420... through hole.

Claims

1. A lithium secondary battery that is charged and discharged by depositing lithium metal on the surface of a negative electrode and electrolytically dissolving the deposited lithium metal, The negative electrode is made of one or more Mg alloys or Mg metals selected from the group consisting of AZ31, AZ31B, AZ61, AZ91, AM60, AM80, and LZ91. Lithium secondary battery.

2. 2. The lithium secondary battery according to claim 1, wherein a plurality of recesses are formed on the surface of the negative electrode on which the lithium metal is deposited.

3. 3. The lithium secondary battery according to claim 2, wherein the recess is filled with a gel electrolyte.

4. The lithium secondary battery according to any one of claims 1 to 3, wherein the negative electrode has a plurality of through holes formed therein, the through holes penetrating between the surface of the negative electrode on which the lithium metal is deposited and the surface opposite to the surface.

5. 5. The lithium secondary battery according to claim 4, wherein the through-holes are filled with a gel electrolyte.

6. 6. The lithium secondary battery according to claim 1, wherein the average thickness of the negative electrode is 3.0 μm or more and 30 μm or less.

7. The specific gravity of the negative electrode is 3.5 g / cm 3 The lithium secondary battery according to any one of claims 1 to 6, wherein:

8. 8. The lithium secondary battery according to claim 1, wherein the Mg alloy contains 50 mol % or more of Mg atoms.

9. A lithium secondary battery described in any one of claims 1 to 8, wherein no lithium foil is formed on the surface of the negative electrode before initial charging.

10. 10. The lithium secondary battery according to claim 1, having an energy density of 425 Wh / kg or more.

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