Lithium secondary battery

Abstract

Provided is a rechargeable lithium battery that has high energy density and excels in a cycle characteristic. This rechargeable lithium battery comprises a positive electrode, a separator or a solid electrolyte, a negative electrode that does not have a negative electrode active material, and optionally, an electrolytic solution. Lithium metal is deposited on the surface of the negative electrode, and charging and discharging is carried out via electrodissolution of the deposited lithium. The rechargeable lithium battery includes an additive agent that, by being deposited together with the lithium metal during charging, inhibits anisotropic crystal growth of the lithium 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 electricity storage devices that are highly safe and capable of storing a large amount of electrical energy.

[0003] Among them, secondary batteries that charge and discharge by the movement of metal ions between the positive and negative electrodes are known to exhibit high voltage and high energy density, and a typical example is the lithium ion secondary battery. A typical lithium ion secondary battery is one in which an active material capable of retaining lithium is introduced into the positive and negative electrodes, and charging and discharging are performed by the exchange of lithium ions between the positive and negative active materials. In addition, as a secondary battery that does not use an active material in the negative electrode, a lithium metal secondary battery that retains lithium by depositing lithium metal on the surface of the negative electrode has been developed.

[0004] For example, Patent Document 1 discloses a high-energy density, high-power lithium metal anode secondary battery having a volumetric energy density exceeding 1000 Wh / L and / or a mass energy density exceeding 350 Wh / kg when discharged at room temperature at a rate of at least 1 C. Patent Document 1 discloses the use of an ultra-thin lithium metal anode to realize such a lithium metal anode secondary battery.

[0005] Patent Document 2 discloses a lithium secondary battery including a positive electrode, a negative electrode, a separator and an electrolyte interposed therebetween, in which metal particles are formed on a negative electrode current collector, and are transferred from the positive electrode by charging to form lithium metal on the negative electrode current collector in the negative electrode. Patent Document 2 discloses that such a lithium secondary battery can provide a lithium secondary battery with improved performance and life by solving problems caused by the reactivity of lithium metal and problems that occur during the assembly process. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 2019-517722 [Patent Document 2] Special Publication No. 2019-537226 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the present inventors have conducted detailed studies on conventional batteries, including those described in the above patent documents, and have found that at least one of the energy density and cycle characteristics is insufficient.

[0008] For example, a typical secondary battery that charges and discharges by transferring metal ions between a positive electrode active material and a negative electrode active material does not have sufficient energy density. In addition, a lithium metal secondary battery that retains lithium by depositing lithium metal on the surface of the negative electrode as described in the above patent document is prone to forming dendrites on the surface of the negative electrode due to repeated charging and discharging, which makes it prone to short circuits and capacity reduction. As a result, the cycle characteristics are insufficient.

[0009] In addition, in order to suppress the discrete growth of lithium metal precipitation in lithium metal secondary batteries, a method has been developed in which a large physical pressure is applied to the battery to keep the interface between the negative electrode and the separator at a high pressure. However, the application of such high pressure requires a large mechanical mechanism, which increases the weight and volume of the entire battery and reduces the energy density.

[0010] The present invention has been made in consideration of the above problems, and has an object to provide a lithium secondary battery having high energy density and excellent cycle characteristics. [Means for solving the problem]

[0011] A lithium secondary battery according to one embodiment of the present invention is a lithium secondary battery comprising a positive electrode, a separator, a negative electrode having no negative electrode active material, and an electrolyte, in which lithium metal is deposited on the surface of the negative electrode and the deposited lithium is electrolytically dissolved to perform charging and discharging, and which contains an additive that suppresses anisotropic crystal growth of lithium metal by being co-deposited with lithium metal during charging.

[0012] Such a lithium secondary battery has a high energy density because it is provided with a negative electrode that does not have a negative electrode active material, and lithium metal is deposited on the surface of the negative electrode, and the deposited lithium metal is electrolytically dissolved, thereby performing charging and discharging. In addition, in a lithium secondary battery containing such an additive, lithium and the additive undergo co-deposition during charging, and lithium metal with suppressed anisotropic crystal growth is deposited on the negative electrode, thereby suppressing the formation of dendritic lithium metal on the surface of the negative electrode, which causes a decrease in the cycle characteristics of the lithium secondary battery. Therefore, the lithium secondary battery has excellent cycle characteristics.

[0013] The additive may be contained in the electrolyte or the separator.

[0014] The electrolyte may contain an ether-based solvent, which tends to further suppress the anisotropic growth of lithium metal on the surface of the negative electrode.

[0015] The electrolyte may contain LiN(SO2F)2. According to such an embodiment, the anisotropic growth of lithium metal on the negative electrode surface tends to be further suppressed.

[0016] A lithium secondary battery according to one embodiment of the present invention is a lithium secondary battery comprising a positive electrode, a solid electrolyte, and a negative electrode having no negative electrode active material, in which lithium metal is deposited on the surface of the negative electrode and the deposited lithium is electrolytically dissolved to perform charging and discharging, and which contains an additive that suppresses anisotropic crystal growth of lithium metal by being co-deposited with the lithium metal during charging.

[0017] Such a lithium secondary battery has a high energy density because it is provided with a negative electrode that does not have a negative electrode active material, and lithium metal is deposited on the surface of the negative electrode, and the deposited lithium metal is electrolytically dissolved, thereby performing charging and discharging. In addition, in a lithium secondary battery containing such an additive, lithium and the additive undergo co-deposition during charging, and lithium metal with suppressed anisotropic crystal growth is deposited on the negative electrode, thereby suppressing the formation of dendritic lithium metal on the surface of the negative electrode, which causes a decrease in the cycle characteristics of the lithium secondary battery. Therefore, the lithium secondary battery has excellent cycle characteristics.

[0018] The additive may be contained in the solid electrolyte.

[0019] In a charged state, the content of the element derived from the additive in the lithium metal-containing deposit layer deposited on the negative electrode is preferably 0.001 atomic % or more and 10 atomic % or less with respect to the entire deposit layer. According to such an embodiment, anisotropic growth of lithium metal on the negative electrode surface tends to be further suppressed.

[0020] The additive is preferably a compound containing at least one element selected from Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, alkaline earth metal elements, alkali metal elements, copper, and zinc (excluding lithium, carbon, oxygen, and nitrogen). According to such an embodiment, the anisotropic growth of lithium metal on the negative electrode surface tends to be further suppressed.

[0021] The compound is preferably at least one selected from the group consisting of chlorides, fluorides, aromatic compounds, and metal complexes. According to such an embodiment, the anisotropic growth of lithium metal on the negative electrode surface tends to be further suppressed.

[0022] The negative electrode is preferably an electrode made of at least one selected from the group consisting of Cu, Ni, Ti, Fe, other metals that do not react with Li, alloys thereof, and stainless steel (SUS). According to such an embodiment, highly flammable lithium metal is not required during production, which leads to further improved safety and productivity. In addition, the stability of the negative electrode is further improved, which leads to further improved cycle characteristics of the lithium secondary battery.

[0023] In the lithium secondary battery, preferably, no lithium foil is formed on the surface of the negative electrode before the initial charge. According to such an embodiment, there is no need to use highly flammable lithium metal during production, which makes the battery safer and more productive.

[0024] The positive electrode may include a positive electrode active material. Effect of the Invention

[0025] According to the present invention, it is possible to provide a lithium secondary battery having high energy density and excellent cycle characteristics. [Brief description of the drawings]

[0026] [Figure 1] 1 is a schematic cross-sectional view of a lithium secondary battery according to a first embodiment of the present invention. [Diagram 2] FIG. 1 is a schematic cross-sectional view of a lithium secondary battery according to a first embodiment of the present invention; [Diagram 3] FIG. 2 is a schematic cross-sectional view of a lithium secondary battery according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] 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 are given the same reference numerals, and duplicated explanations will be omitted. Furthermore, unless otherwise specified, positional relationships such as up, down, left, and right are 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.

[0028] [First embodiment] (lithium secondary battery) Fig. 1 is a schematic cross-sectional view of a lithium secondary battery according to the first embodiment. As shown in Fig. 1, the lithium secondary battery 100 according to the first embodiment includes a positive electrode 110, a separator 120, a negative electrode 130 that does not have a negative electrode active material, and an electrolyte.

[0029] (Negative electrode) The negative electrode 130 does not have a negative electrode active material. In a lithium secondary battery having a negative electrode having a negative electrode active material, it is difficult to increase the energy density due to the presence of the negative electrode active material. On the other hand, the lithium secondary battery 100 of this embodiment has a negative electrode 130 that does not have a negative electrode active material, so such a problem does not occur. That is, the lithium secondary battery 100 of this embodiment has a high energy density because lithium metal is deposited on the surface of the negative electrode 130 and the deposited lithium metal is electrolytically dissolved to perform charging and discharging.

[0030] In this specification, the term "negative electrode active material" refers to a material for holding lithium ions or lithium metal (hereinafter referred to as "carrier metal"), which serves as a charge carrier in a battery, in the negative electrode 130, and may be referred to as a host material for the carrier metal. The mechanism of such holding is not particularly limited, but examples thereof include intercalation, alloying, and occlusion of metal clusters.

[0031] Examples of such negative electrode active materials include, but are not limited to, carbonaceous materials, metal oxides, and metals or alloys. Examples of the carbonaceous materials include, but are not limited to, graphene, graphite, hard carbon, mesoporous carbon, carbon nanotubes, and carbon nanohorns. Examples of the metal oxides include, but are not limited to, titanium oxide compounds, tin oxide compounds, and cobalt oxide compounds. Examples of the metals or alloys include, but are not limited to, silicon, germanium, tin, lead, aluminum, gallium, and alloys containing these metals as long as they can be alloyed with the carrier metal.

[0032] The negative electrode 130 is not particularly limited as long as it does not have a negative electrode active material and can be used as a current collector, and examples thereof include at least one selected from the group consisting of Cu, Ni, Ti, Fe, and other metals that do not react with Li, and alloys thereof, and stainless steel (SUS). When SUS is used for the negative electrode 130, various types of SUS that have been publicly known can be used. The above-mentioned negative electrode materials are used alone or in combination of two or more types. In this specification, the term "metal that does not react with Li" refers to a metal that does not react with lithium ions or lithium metal to form an alloy under the operating conditions of the secondary battery 100.

[0033] The negative electrode 130 is preferably an electrode that does not contain lithium. According to such an embodiment, highly flammable lithium metal does not need to be used during production, so the lithium secondary battery 100 is even more excellent in safety and productivity. From the same viewpoint and from the viewpoint of improving the stability of the negative electrode 130, the negative electrode 130 is more preferably made of at least one selected from the group consisting of Cu, Ni, and alloys thereof, and stainless steel (SUS). From the same viewpoint, the negative electrode 130 is more preferably made of Cu, Ni, or an alloy thereof, and particularly preferably made of Cu or Ni.

[0034] In this specification, "the negative electrode does not have a negative electrode active material" means that the content of the negative electrode active material in the negative electrode is 10 mass% or less with respect to the entire negative electrode. The content of the negative electrode active material in the negative electrode is preferably 5.0 mass% or less, more preferably 1.0 mass% or less, further preferably 0.1 mass% or less, and particularly preferably 0.0 mass% or less with respect to the entire negative electrode. Incidentally, the fact that the secondary battery 100 has a negative electrode that does not have a negative electrode active material means that the secondary battery 100 is an anode-free secondary battery, a zero anode secondary battery, or an anodeless secondary battery in the commonly used sense.

[0035] The average thickness of the negative electrode 130 is preferably 4 μm or more and 20 μm or less, more preferably 5 μm or more and 18 μm or less, and further preferably 6 μm or more and 15 μm or less. According to such an embodiment, the volume occupied by the negative electrode 130 in the lithium secondary battery 100 is reduced, and therefore the energy density of the secondary battery 100 is further improved.

[0036] (positive electrode) The positive electrode 110 is not particularly limited as long as it is generally used in lithium secondary batteries, but a known material can be appropriately selected depending on the application of the lithium secondary battery and the type of carrier metal. From the viewpoint of increasing the stability and output voltage of the lithium secondary battery 100, the positive electrode 110 preferably has a positive electrode active material.

[0037] In this specification, the term "positive electrode active material" refers to a material for holding a carrier metal in a positive electrode of a battery, and may be referred to as a host material for the carrier metal.

[0038] Such positive electrode active materials include, but are not limited to, metal oxides and metal phosphates. The metal oxides include, but are not limited to, cobalt oxide compounds, manganese oxide compounds, and nickel oxide compounds. The metal phosphates include, but are not limited to, iron phosphate compounds, and cobalt phosphate compounds. Typical positive electrode active materials include LiCoO2, LiNi x Co y Mn z O2(x+y+z=1), LiNi x Mn y O2 (x+y=1), LiNiO2, LiMn2O4, LiFePO4, LiCoPO4, FeF3, LiFeOF, LiNiOF, and TiS2. The above-mentioned positive electrode active materials may be used alone or in combination of two or more.

[0039] The positive electrode 110 may contain components other than the above-mentioned positive electrode active material. Such components are not particularly limited, but include, for example, known conductive assistants, binders, solid polymer electrolytes, and inorganic solid electrolytes.

[0040] The conductive assistant in the positive electrode 110 is not particularly limited, but examples thereof include carbon black, single-wall carbon nanotubes (SW-CNT), multi-wall carbon nanotubes (MW-CNT), carbon nanofibers, acetylene black, etc. The binder is not particularly limited, but examples thereof include polyvinylidene fluoride, polytetrafluoroethylene, styrene butadiene rubber, acrylic resin, polyimide resin, etc.

[0041] The content of the positive electrode active material in the positive electrode 110 may be, for example, 50% by mass or more and 100% by mass or less, based on the entire positive electrode 110. The content of the conductive assistant may be, for example, 0.5% by mass to 30% by mass or less, based on the entire positive electrode 110. The content of the binder may be, for example, 0.5% by mass to 30% by mass or less, based on the entire positive electrode 110. The total content of the solid polymer electrolyte and the inorganic solid electrolyte may be, for example, 0.5% by mass to 30% by mass or less, based on the entire positive electrode 110.

[0042] (Separator) The separator 120 is a member for preventing the battery from short-circuiting by isolating the positive electrode 110 and the negative electrode 130, while ensuring ionic conductivity of lithium ions that serve as charge carriers between the positive electrode 110 and the negative electrode 130, and is made of a material that does not have electronic conductivity and does not react with lithium ions. The separator 120 also plays a role in retaining the electrolyte. The separator 120 is not limited as long as it plays the above role, and is made of, for example, porous polyethylene (PE), polypropylene (PP), or a laminated structure thereof. For example, Erythotype P manufactured by Teijin Limited can be used as the separator 120.

[0043] The separator 120 may be coated with a separator coating layer. The separator coating layer may cover both sides of the separator 120, or may cover only one side. The separator coating layer is not particularly limited as long as it is a material that has ion conductivity and does not react with lithium ions, but it is preferable that the separator coating layer is capable of firmly bonding the separator 120 and a layer adjacent to the separator 120. Examples of such a separator coating layer include, but are not particularly 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 a binder such as aramid. The separator coating layer may include inorganic particles such as silica, alumina, titania, zirconia, magnesium oxide, magnesium hydroxide, and lithium nitrate added to the binder.

[0044] The average thickness of the separator 120 is preferably 20 μm or less, more preferably 18 μm or less, and even more preferably 15 μm or less. According to such an embodiment, the volume occupied by the separator 120 in the lithium secondary battery 100 is reduced, and the energy density of the lithium secondary battery 100 is further improved. Moreover, the average thickness of the separator 120 is preferably 5 μm or more, more preferably 7 μm or more, and even more preferably 10 μm or more. According to such an embodiment, the positive electrode 110 and the negative electrode 130 can be more reliably isolated from each other, and the battery can be further prevented from being short-circuited.

[0045] (electrolyte) The electrolyte (not shown in FIG. 1) serves to improve the ionic conductivity of lithium ions that serve as charge carriers between the positive electrode 110 and the negative electrode 130. The electrolyte may be impregnated into the separator 120, or may be enclosed in a sealed container together with a laminate of the positive electrode 110, the separator 120, and the negative electrode 130. The electrolyte is a solution that contains an electrolyte and a solvent and has ionic conductivity. Therefore, the lithium secondary battery 100 has low internal resistance, high energy density, and excellent cycle characteristics.

[0046] The electrolyte contained in the electrolytic solution is not particularly limited as long as it is a salt, and examples thereof include salts of Li, Na, K, Ca, and Mg. A lithium salt is preferably used as the electrolyte. The lithium salt is not particularly limited, and examples thereof include LiI, LiCl, LiBr, LiF, LiBF4, LiPF6, LiAsF6, LiSO3CF3, LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2CF3CF3)2, LiB(O2C2H4)2, LiB(O2C2H4)F2, LiB(OCOCF3)4, LiNO3, and Li2SO4. From the viewpoint of further improving the energy density and cycle characteristics of the lithium secondary battery 100, LiN(SO2F)2 is preferred as the lithium salt. In addition, when LiN(SO2F)2 is included as the lithium salt, the anisotropic growth of lithium metal on the negative electrode surface as described below tends to be further suppressed. The above lithium salts may be used alone or in combination of two or more.

[0047] The solvent contained in the electrolytic solution is not particularly limited, but examples thereof include ether-based solvents such as fluorinated ethers, and ester-based solvents such as fluorinated esters and fluorinated carbonates. More specifically, examples of the solvent include dimethoxyethane, dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, acetonitrile, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, propylene carbonate, chloroethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, trifluoromethylpropylene carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, nonafluorobutyl methyl ether, nonafluorobutyl ethyl ether, tetrafluoroethyl tetrafluoropropyl ether, 1,1,2,2-terafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2tetrafluoroethyl-2,2,2-trifluoroethyl ether, Methyl-1,1,2,2-tetrafluoroethyl ether, and Ethyl-1,1,2,2-tetrafluoroethyl Examples of the solvent include ether, trimethyl phosphate, and triethyl phosphate. From the viewpoint of further improving the energy density and cycle characteristics of the lithium secondary battery 100, the solvent is preferably an ether-based solvent. In addition, when an ether-based solvent is included as the solvent, as described later, the anisotropic growth of lithium metal on the negative electrode surface tends to be further suppressed. The above-mentioned solvents are used alone or in combination of two or more.

[0048] (Additives (anisotropic growth inhibitors)) 2 is a schematic cross-sectional view of one usage mode of the lithium secondary battery according to the first embodiment. In the lithium secondary battery 100 according to the first embodiment, a positive electrode current collector 210 is joined to a positive electrode 110, and a positive electrode terminal 230 and a negative electrode terminal 240 for connecting to an external circuit are joined to the positive electrode current collector 210 and the negative electrode 130, respectively, to constitute a lithium secondary battery 200.

[0049] The lithium secondary battery 200 is charged by applying a voltage between the positive electrode terminal 230 and the negative electrode terminal 240 such that a current flows from the negative electrode terminal 240 through an external circuit to the positive electrode terminal 230. By charging the lithium secondary battery 200, a deposit layer 220 containing lithium metal is precipitated at the interface between the negative electrode 130 and the separator 120. Furthermore, when the positive electrode terminal 230 and the negative electrode terminal 240 are connected to the charged lithium secondary battery 200, the lithium secondary battery 200 is discharged. The discharge proceeds by electrolytic dissolution of the deposit layer 220 precipitated at the interface between the negative electrode 130 and the separator 120.

[0050] In the conventional lithium secondary battery (hereinafter referred to as "lithium metal secondary battery"), in which lithium metal is deposited on the surface of the negative electrode and the deposited lithium is electrolytically dissolved to perform charging and discharging, the lithium metal deposited on the surface of the negative electrode is often composed of lithium metal alone. As a result of intensive research, the inventors of the present invention have inferred that the cycle characteristics of the conventional lithium metal secondary battery are poor because the anisotropic crystal growth of lithium metal on the surface of the negative electrode is not suppressed. That is, in the conventional lithium metal secondary battery, the lithium metal deposited on the surface of the negative electrode is composed of lithium metal alone, and the anisotropic crystal growth of lithium metal on the surface of the negative electrode is not suppressed, and the lithium metal deposited on the surface of the negative electrode grows in a dendrite shape. In addition, when the conventional lithium metal secondary battery is repeatedly charged and discharged, a part of the lithium metal grown in a dendrite shape falls off during the discharge of the battery, and the lithium metal that is not in electrical contact with the negative electrode and is inactive in the charging and discharging of the battery increases, and the capacity of the battery is reduced.

[0051] Therefore, the inventors have designed a lithium secondary battery to include an additive (hereinafter also referred to as an "anisotropic growth inhibitor") that suppresses anisotropic crystal growth of lithium metal by co-depositing with lithium metal during charging. That is, the lithium secondary battery 100 of the first embodiment shown in FIG. 1 includes an additive in addition to a positive electrode 110, a separator 120, a negative electrode 130 that does not have a negative electrode active material, and an electrolyte, and the additive co-deposits with lithium metal during charging of the battery to suppress anisotropic crystal growth of lithium metal. In this way, since the lithium secondary battery 100 includes an anisotropic growth inhibitor, the formation of dendritic lithium metal on the negative electrode surface, which causes a decrease in the cycle characteristics of the lithium secondary battery, is suppressed, and the cycle characteristics are excellent.

[0052] In this specification, "anisotropic crystal growth" means that lithium metal crystals grow only in a specific direction, and the growth direction is arbitrary. Therefore, lithium metal that has undergone anisotropic crystal growth will have a shape such as a needle, a dendrite, or a star. In addition, "suppressing anisotropic crystal growth" means suppressing lithium metal from growing only in a specific direction, in other words, promoting isotropic crystal growth of lithium metal. "Isotropic crystal growth" means that lithium metal crystals grow equally in all directions. Therefore, when lithium metal undergoes isotropic crystal growth on the surface of the negative electrode, the shape will be plate-like.

[0053] In addition, in this specification, "suppressing the formation of dendrites on the surface of the negative electrode" means suppressing the growth of lithium metal in a dendritic shape on the surface of the negative electrode. In other words, it means inducing the lithium metal formed on the surface of the negative electrode by charging and discharging the lithium secondary battery or repeating the charging and discharging to grow in a non-dendritic shape. Here, the "non-dendritic shape" is not particularly limited, but is typically a plate shape, a valley shape, or a hill shape.

[0054] In the lithium secondary battery 100 of the first embodiment shown in FIG. 1, the anisotropic growth inhibitor is contained in, for example, the electrolyte or the separator. From the viewpoint that the anisotropic growth inhibitor can be more easily co-precipitated with lithium metal during charging of the lithium secondary battery 100, it is preferable that the anisotropic growth inhibitor is dissolved in a solvent. Note that "the electrolyte contains an anisotropic growth inhibitor" is not limited to the case where the anisotropic growth inhibitor is dissolved in the solvent of the electrolyte, but also includes the case where the anisotropic growth inhibitor is precipitated as a solid in the electrolyte. In addition, "the separator contains an anisotropic growth inhibitor" includes the case where the anisotropic growth inhibitor is present in the electrolyte infiltrated into the separator, the case where a solid anisotropic growth inhibitor is contained inside the separator, and the case where a solid anisotropic growth inhibitor is applied to the surface of the separator.

[0055] The anisotropic growth inhibitor is not particularly limited as long as it is co-deposited with lithium metal during charging of the secondary battery 100 and inhibits the anisotropic crystal growth of lithium metal, but examples thereof include compounds containing at least one element selected from Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, alkaline earth metal elements, alkali metal elements, copper, and zinc (excluding lithium, carbon, oxygen, and nitrogen). Note that the Group 13 elements refer to boron, aluminum, gallium, and indium; the Group 14 elements refer to carbon, silicon, germanium, tin, and lead; the Group 15 elements refer to nitrogen, phosphorus, arsenic, antimony, and bismuth; the Group 16 elements refer to oxygen, sulfur, selenium, tellurium, and polonium; the alkaline earth metal elements refer to beryllium, magnesium, calcium, strontium, and barium; and the alkali metal elements refer to lithium, sodium, potassium, rubidium, and cesium.

[0056] From the viewpoint of further suppressing the anisotropic crystal growth of lithium metal, the anisotropic growth inhibitor is preferably a compound containing at least one element selected from Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, alkaline earth metal elements, alkali metal elements, copper, and zinc (limited to metal elements or semiconductor elements excluding lithium). From the same viewpoint, the anisotropic growth inhibitor is more preferably a compound containing at least one element selected from aluminum, gallium, germanium, tin, lead, antimony, bismuth, selenium, tellurium, magnesium, calcium, strontium, sodium, potassium, rubidium, copper, and zinc, more preferably a compound containing at least one element selected from aluminum, tin, antimony, bismuth, selenium, magnesium, potassium, copper, and zinc, and particularly preferably a compound containing at least one element selected from aluminum, tin, selenium, potassium, and copper.

[0057] When the lithium secondary battery 100 contains the anisotropic growth inhibitor as described above, when the lithium secondary battery 100 is charged, that is, when the electrode potential of the negative electrode is made positive with respect to the positive electrode, lithium metal is precipitated on the surface of the negative electrode and the above elements are precipitated (co-deposited) on the surface of the negative electrode at the same time. Therefore, instead of lithium metal alone, a co-deposit of the above elements and lithium is precipitated on the surface of the negative electrode. When lithium metal alone is precipitated, it is considered that anisotropic crystal growth is likely to occur because the crystal of lithium metal grows so as to expose a stable crystal face, but when the above elements are co-deposited with lithium, the crystallinity of lithium metal is reduced, so that the anisotropic crystal growth of lithium metal is suppressed. Furthermore, when lithium metal alone is precipitated, there are local active points on the surface where lithium metal is likely to be precipitated preferentially, and it is considered that anisotropic crystal growth is likely to occur at the active points, but when the above elements are co-deposited with lithium metal, the activity at such active points is reduced, and the anisotropic crystal growth of lithium metal is suppressed. However, the cause is not limited to this.

[0058] The anisotropic growth inhibitor may be at least one selected from the group consisting of chlorides, fluorides, bromides, iodides, aromatic compounds, and metal complexes containing the above elements. When the anisotropic growth inhibitor is the above compound, it is easy to obtain and tends to have a higher solubility in the solvent. From the same viewpoint, the anisotropic growth inhibitor is preferably at least one selected from the group consisting of chlorides, fluorides, aromatic compounds, and metal complexes containing the above elements.

[0059] Here, the aromatic compound is not particularly limited, but examples thereof include phenyl compounds, tolyl compounds, methoxyphenyl compounds, naphthyl compounds, furanyl compounds, coumarinyl compounds, pyrrolyl compounds, pyridyl compounds, imidazole compounds, pyrazole compounds, thiophenyl compounds, and compounds containing derivatives thereof. In addition, the metal complex is not particularly limited, but examples thereof include complexes of the above elements (limited to metal elements) with at least one selected from the group consisting of acetylacetone, trifluoromethanesulfonylimide, acesulfame, trifluoromethanesulfonic acid, ethyl acetoacetate, ethylenediamine, bipyridine, edetic acid, phenanthroline, porphyrin, and crown ether.

[0060] Since the lithium secondary battery 100 contains the above-mentioned anisotropic growth inhibitor, the deposition layer 220 containing lithium metal deposited on the negative electrode in the charged state of the lithium secondary battery 200 shown in FIG. 2 contains elements derived from the anisotropic growth inhibitor. The deposition layer 220 preferably contains at least one element selected from Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, alkaline earth metal elements, alkali metal elements, copper, and zinc (excluding lithium, carbon, oxygen, and nitrogen), more preferably at least one element selected from Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, alkaline earth metal elements, alkali metal elements, copper, and zinc (limited to metal elements or semiconductor elements excluding lithium), and even more preferably contains at least one element selected from Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, alkaline earth metal elements, alkali metal elements, copper, and zinc (limited to metal elements or semiconductor elements excluding lithium). The deposition layer 220 contains at least one element selected from aluminum, gallium, germanium, tin, lead, antimony, bismuth, selenium, tellurium, magnesium, calcium, strontium, sodium, potassium, rubidium, copper, and zinc, and more preferably contains at least one element selected from aluminum, tin, antimony, bismuth, selenium, magnesium, potassium, copper, and zinc, and particularly preferably contains at least one element selected from aluminum, tin, selenium, potassium, and copper. When the deposition layer 220 contains the above elements, anisotropic crystal growth of lithium metal in the deposition layer 220 is further suppressed.

[0061] In the deposition layer 220, the content of the element derived from the anisotropic growth inhibitor is preferably 0.001 atomic % or more and 10 atomic % or less, more preferably 0.005 atomic % or more and 5 atomic % or less, and even more preferably 0.010 atomic % or more and 3 atomic % or less, based on the entire deposition layer. According to such an embodiment, the anisotropic growth of lithium metal on the negative electrode surface tends to be further suppressed. The content of the element derived from the anisotropic growth inhibitor in the deposition layer 220 can be adjusted by the amount of the anisotropic growth inhibitor added, and the content of the element derived from the anisotropic growth inhibitor in the deposition layer 220 can be measured by a conventionally known method, for example, a method using an inductively coupled plasma mass spectrometer (ICP-MS).

[0062] The content of the anisotropic growth inhibitor is not particularly limited, but is preferably 0.1% by mass or more and 10% by mass or less, for example, based on the entire lithium secondary battery 100. The content of the anisotropic growth inhibitor may be 0.3% by mass or more and 10% by mass or less, or may be 0.5% by mass or more and 10% by mass or less, based on the entire lithium secondary battery 100. In addition, in the lithium secondary battery 100, when the anisotropic growth inhibitor is present in the electrolyte, the content of the anisotropic growth inhibitor is preferably 0.1% by mass or more and 30% by mass or less, more preferably 0.3% by mass or more and 20% by mass or less, even more preferably 0.5% by mass or more and 15% by mass or less, and particularly preferably 1.0% by mass or more and 10% by mass or less, based on the entire electrolyte. By the content of the anisotropic growth inhibitor being in the above range, the anisotropic growth of lithium metal on the negative electrode surface tends to be further suppressed.

[0063] In FIG. 2, a solid electrolyte interface layer (SEI layer) may be formed on the surface of the negative electrode 130. The SEI layer to be formed is not particularly limited, and may contain, for example, an inorganic compound containing lithium and an organic compound containing lithium. The typical average thickness of the SEI layer is 1 nm or more and 10 μm or less. When the SEI layer is formed in the lithium secondary battery 100, the deposition layer 220 may be precipitated at the interface between the negative electrode 130 and the SEI layer, or may be precipitated at the interface between the SEI layer and the separator 120.

[0064] (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 capable of manufacturing a lithium secondary battery having the above-mentioned configuration, and examples thereof include the following methods.

[0065] The positive electrode 110 is manufactured, for example, as follows. The above-mentioned positive electrode active material, a known conductive assistant, and a known binder are mixed to obtain a positive electrode mixture. The compounding ratio may be, for example, 50% by mass or more and 99% by mass or less of the positive electrode active material, 0.5% by mass or less and 30% by mass or less of the conductive assistant, and 0.5% by mass or less and 30% by mass or less of the binder, based on the entire positive electrode mixture. The obtained positive electrode mixture is applied to one side of a metal foil (e.g., Al foil) having a thickness of, for example, 5 μm to 1 mm, and press-molded. The obtained molded body is punched out to a predetermined size by a punching process to obtain the positive electrode 110.

[0066] Next, the separator 120 having the above-mentioned structure is prepared. The separator 120 may be produced by a conventionally known method, or a commercially available product may be used.

[0067] Next, the above-mentioned negative electrode material, for example, a metal foil (for example, electrolytic Cu foil) having a thickness of 1 μm or more and 1 mm or less, is washed with a solvent containing sulfamic acid, punched out to a predetermined size, and then ultrasonically cleaned with ethanol and dried to obtain the negative electrode 130.

[0068] The positive electrode 110, the separator 120, and the negative electrode 130 obtained as described above are laminated in this order to obtain a laminate. The obtained laminate is enclosed in a sealed container together with an electrolyte solution to obtain a lithium secondary battery 100. The sealed container is not particularly limited, but examples thereof include a laminate film.

[0069] In the above process, the anisotropic growth inhibitor may be added to the inside of the separator 120, may be applied to the surface of the separator 120, or may be added to the electrolyte. From the viewpoint of further suppressing the anisotropic growth of lithium metal on the negative electrode surface, the anisotropic growth inhibitor is added to the lithium secondary battery 100 by dissolving in the electrolyte.

[0070] [Second embodiment] (lithium secondary battery)

[0071] 3 is a schematic cross-sectional view of a lithium secondary battery according to the second embodiment. As shown in FIG. 3, the lithium secondary battery 300 according to the second embodiment includes a positive electrode 110, a solid electrolyte 310, and a negative electrode 130 that does not have a negative electrode active material, and is charged and discharged by depositing lithium metal on the surface of the negative electrode and electrolytically dissolving the deposited lithium, and contains an additive (anisotropic growth inhibitor) that suppresses anisotropic crystal growth of lithium metal by co-deposition with lithium metal during charging. The configurations and preferred aspects of the positive electrode 110, the negative electrode 130, and the anisotropic growth inhibitor are the same as those of the lithium secondary battery 100 according to the first embodiment, except for the points described below, and the lithium secondary battery 300 exhibits the same effects as the lithium secondary battery 100.

[0072] (solid electrolyte) Generally, in batteries with a liquid electrolyte, the physical pressure applied from the electrolyte to the negative electrode surface tends to vary depending on the location due to fluctuations in the liquid. On the other hand, since the lithium secondary battery 300 includes the solid electrolyte 310, the pressure applied from the solid electrolyte 310 to the negative electrode 130 surface becomes more uniform, and the shape of the carrier metal precipitated on the surface of the negative electrode 130 can be made more uniform. That is, according to this embodiment, the carrier metal precipitated on the surface of the negative electrode 130 is further prevented from growing in a dendritic shape, and the cycle characteristics of the lithium secondary battery 300 become more excellent.

[0073] The solid electrolyte 310 is not particularly limited as long as it is generally used in lithium solid secondary batteries, but a known material can be appropriately selected depending on the application of the lithium secondary battery 300 and the type of carrier metal. The solid electrolyte 310 preferably has ionic conductivity and no electronic conductivity. By having the solid electrolyte 310 have ionic conductivity and no electronic conductivity, the internal resistance of the lithium secondary battery 300 is further reduced and short circuits inside the lithium secondary battery 300 can be further suppressed. As a result, the energy density, capacity, and cycle characteristics of the lithium secondary battery 300 are further improved.

[0074] The solid electrolyte 310 is not particularly limited, but examples thereof include those containing a resin and a lithium salt. Examples of such resins are not particularly limited, but examples thereof include resins having an ethylene oxide unit in the main chain and / or side chain, acrylic resins, vinyl resins, ester resins, nylon resins, polysiloxanes, polyphosphazenes, polyvinylidene fluorides, polymethyl methacrylate, polyamides, polyimides, aramids, polylactic acids, polyethylenes, polystyrenes, polyurethanes, polypropylenes, polybutylenes, polyacetals, polysulfones, and polytetrafluoroethylenes. The above-mentioned resins are used alone or in combination of two or more.

[0075] The lithium salt contained in the solid electrolyte 310 is not particularly limited, but examples thereof include LiI, LiCl, LiBr, LiF, LiBF4, LiPF6, LiAsF6, LiSO3CF3, LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2CF3CF3)2, LiB(O2C2H4)2, LiB(O2C2H4)F2, LiB(OCOCF3)4, LiNO3, and Li2SO4. The above-mentioned lithium salts may be used alone or in combination of two or more.

[0076] In general, the content ratio of the resin to the lithium salt in the solid electrolyte is determined by the ratio ([Li] / [O]) of the oxygen atoms in the resin to the lithium atoms in the lithium salt. In the solid electrolyte 310, the content ratio of the resin to the lithium salt is adjusted so that the ratio ([Li] / [O]) is preferably 0.02 or more and 0.20 or less, more preferably 0.03 or more and 0.15 or less, and even more preferably 0.04 or more and 0.12 or less.

[0077] The solid electrolyte 310 may contain components other than the resin and lithium salt. Such components are not particularly limited, but include, for example, a solvent and a salt other than the lithium salt. The salt other than the lithium salt is not particularly limited, but includes, for example, salts of Li, Na, K, Ca, and Mg.

[0078] The solvent is not particularly limited, but may be, for example, any of those exemplified in the electrolyte solution contained in the lithium secondary battery 100 described above.

[0079] The average thickness of the solid electrolyte 310 is preferably 20 μm or less, more preferably 18 μm or less, and further preferably 15 μm or less. According to such an embodiment, the volume occupied by the solid electrolyte 310 in the lithium secondary battery 300 is reduced, and the energy density of the lithium secondary battery 300 is further improved. Also, the average thickness of the solid electrolyte 310 is preferably 5 μm or more, more preferably 7 μm or more, and further preferably 10 μm or more. According to such an embodiment, the positive electrode 110 and the negative electrode 130 can be more reliably isolated from each other, and the battery can be further prevented from being short-circuited.

[0080] In this specification, the term "solid electrolyte" includes gel electrolytes. The gel electrolyte is not particularly limited, but may include, for example, a polymer, an organic solvent, and a lithium salt. The polymer in the gel electrolyte is not particularly limited, but may include, for example, a copolymer of polyethylene and / or polyethylene oxide, polyvinylidene fluoride, and a copolymer of polyvinylidene fluoride and hexafluoropropylene.

[0081] (Additives (anisotropic growth inhibitors)) In the lithium secondary battery 300 of the second embodiment shown in Fig. 3, the anisotropic growth inhibitor is contained in, for example, the solid electrolyte. Note that "the solid electrolyte contains an anisotropic growth inhibitor" includes a case where the anisotropic growth inhibitor is present in the electrolytic solution infiltrated into the solid electrolyte, a case where a solid anisotropic growth inhibitor is contained inside the solid electrolyte, and a case where a solid anisotropic growth inhibitor is applied to the surface of the solid electrolyte.

[0082] The content of the anisotropic growth inhibitor is not particularly limited, but is preferably 0.1% by mass or more and 10% by mass or less, for example, based on the entire lithium secondary battery 300. The content of the anisotropic growth inhibitor may be 0.3% by mass or more and 10% by mass or less, or may be 0.5% by mass or more and 10% by mass or less, based on the entire lithium secondary battery 300. In addition, in the lithium secondary battery 300, when the anisotropic growth inhibitor is contained in the solid electrolyte, the content of the anisotropic growth inhibitor is preferably 0.1% by mass or more and 30% by mass or less, more preferably 0.3% by mass or more and 20% by mass or less, even more preferably 0.5% by mass or more and 15% by mass or less, and particularly preferably 1.0% by mass or more and 10% by mass or less, based on the entire solid electrolyte. By the content of the anisotropic growth inhibitor being in the above range, the anisotropic growth of lithium metal on the negative electrode surface tends to be further suppressed.

[0083] In FIG. 3, a solid electrolyte interface layer (SEI layer) may be formed on the surface of the negative electrode 130. The SEI layer to be formed is not particularly limited, and may contain, for example, an inorganic compound containing lithium and an organic compound containing lithium. A typical average thickness of the SEI layer is 1 nm or more and 10 μm or less. When the SEI layer is formed in the lithium secondary battery 300, a sediment layer may be precipitated at the interface between the negative electrode 130 and the SEI layer, or may be precipitated at the interface between the SEI layer and the solid electrolyte 310.

[0084] (Secondary battery manufacturing method) The lithium secondary battery 300 can be manufactured in the same manner as the manufacturing method of the lithium secondary battery 100 according to the first embodiment described above, except that a solid electrolyte is used instead of the separator.

[0085] The method for producing the solid electrolyte 310 is not particularly limited as long as it can obtain the above-mentioned solid electrolyte 310, but may be, for example, as follows. A resin conventionally used in solid electrolytes and a lithium salt (for example, the resin and lithium salt described above as the resin that the solid electrolyte 310 may contain) are dissolved in an organic solvent. The obtained solution is cast onto a molding substrate to a predetermined thickness to obtain the solid electrolyte 310. Here, the compounding ratio of the resin and the lithium salt may be determined by the ratio ([Li] / [O]) of the oxygen atoms of the resin to the lithium atoms of the lithium salt, as described above. The ratio ([Li] / [O]) is, for example, 0.02 or more and 0.20 or less. The organic solvent is not particularly limited, but acetonitrile may be used, for example. The molding substrate is not particularly limited, but PET film or glass substrate may be used, for example.

[0086] 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.

[0087] For example, the lithium secondary battery of the present embodiment may be a lithium solid secondary battery. According to such an embodiment, since it is not necessary to use an electrolyte, the problem of electrolyte leakage does not occur, and the safety of the battery is further improved.

[0088] The lithium secondary battery of this embodiment may not have a lithium foil formed between the separator or solid electrolyte and the negative electrode before initial charging. When the lithium secondary battery of this embodiment does not have a lithium foil formed between the separator or solid electrolyte and the negative electrode before initial charging, it is possible to manufacture the lithium secondary battery with even greater safety and productivity because it is not necessary to use highly flammable lithium metal.

[0089] In this specification, "high energy density" or "having a high energy density" means that the capacity per unit total volume or total mass of the battery is high, and is preferably 900 Wh / L or more or 400 Wh / kg or more, and more preferably 1000 Wh / L or more or 430 Wh / kg or more.

[0090] In addition, in this specification, "excellent cycle characteristics" means that the capacity of the battery is reduced at a low rate before and after a number of charge / discharge cycles that can be expected in normal use. In other words, when comparing the initial capacity with the capacity after a number of charge / discharge cycles that can be expected in normal use, the capacity after the charge / discharge cycles is almost not reduced compared to the initial capacity. Here, the "number of times that can be expected in normal use" is, for example, 50 times, 100 times, 500 times, 1000 times, 5000 times, or 10000 times, depending on the application of the lithium secondary battery. In addition, "the capacity after the charge / discharge cycle is almost not reduced compared to the initial capacity" means, for example, that the capacity after the charge / discharge cycle is 65% or more, 70% or more, 75% or more, 80% or more, 85% or more, or 90% or more compared to the initial capacity, depending on the application of the lithium secondary battery. EXAMPLES

[0091] 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.

[0092] [Example 1] LiNi as the positive electrode active material 0.8 Co 0.15 Al 0.05 A mixture of 96 parts by mass of O2, 2 parts by mass of carbon black as a conductive assistant, and 2 parts by mass of polyvinylidene fluoride (PVDF) as a binder was applied to one side of a 12 μm Al foil and press molded. The obtained molded body was punched out to a size of 4.0 cm × 4.0 cm by punching to obtain a positive electrode.

[0093] Next, an 8 μm electrolytic Cu foil was washed with a solvent containing sulfamic acid, and then punched out to a size of 4.5 cm×4.5 cm. The foil was then ultrasonically cleaned with ethanol and dried to obtain a negative electrode.

[0094] A separator whose surface was coated with a mixture of polyvinylidene fluoride (PVDF) and Li(NO3) was prepared.

[0095] As an electrolyte, a 4M LiN(SO2F)2 (hereinafter referred to as "LFSI") dimethoxyethane (hereinafter referred to as "DME") / 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (hereinafter referred to as "TTFE") / fluoroethylene carbonate (hereinafter referred to as "FEC") mixed solution (DME:TTFE:FEC = 8:1:1 (volume ratio)) was prepared.

[0096] The positive electrode, separator, and negative electrode obtained as above were laminated 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 and the negative electrode by ultrasonic welding, respectively, and then inserted into a laminate exterior body. Next, triphenylantimony was added as an anisotropic growth inhibitor to the electrolyte obtained as above so that the amount of triphenylantimony was 5 mass% relative to the entire electrolyte solution, and the electrolyte was injected into the exterior body. The exterior body was sealed to obtain a lithium secondary battery.

[0097] [Example 2] A lithium secondary battery was obtained in the same manner as in Example 1, except that Zn(N(SO2CF3)2)2 was used as the anisotropic growth inhibitor instead of triphenylantimony.

[0098] [Example 3] A lithium secondary battery was obtained in the same manner as in Example 1, except that Zn(SO3CF3)2 was used as the anisotropic growth inhibitor instead of triphenylantimony.

[0099] [Example 4] A lithium secondary battery was obtained in the same manner as in Example 1, except that magnesium acetylacetonate (Mg(Acac)2) was used as the anisotropic growth inhibitor instead of triphenylantimony.

[0100] [Example 5] A lithium secondary battery was obtained in the same manner as in Example 1, except that Mg(SO3CF3)2 was used as the anisotropic growth inhibitor instead of triphenylantimony.

[0101] [Example 6] A lithium secondary battery was obtained in the same manner as in Example 1, except that Mg(N(SO2CF3)2)2 was used as the anisotropic growth inhibitor instead of triphenylantimony.

[0102] [Example 7] A lithium secondary battery was obtained in the same manner as in Example 1, except that bismuth chloride (BiCl3) was used as the anisotropic growth inhibitor instead of triphenylantimony.

[0103] [Example 8] A lithium secondary battery was obtained in the same manner as in Example 1, except that triphenyldifluorobismuth was used as the anisotropic growth inhibitor instead of triphenylantimony.

[0104] [Example 9] A lithium secondary battery was obtained in the same manner as in Example 1, except that tetrabutylammonium difluorotriphenyltin was used as the anisotropic growth inhibitor instead of triphenylantimony.

[0105] [Example 10] A lithium secondary battery was obtained in the same manner as in Example 1, except that 6-methyl-1,2,3-oxathiazin-4(3H)-one 2,2-dioxide potassium (acesulfame potassium) was used as the anisotropic growth inhibitor instead of triphenylantimony.

[0106] [Example 11] A lithium secondary battery was obtained in the same manner as in Example 1, except that dimethylselenium was used instead of triphenylantimony as the anisotropic growth inhibitor.

[0107] [Example 12] A lithium secondary battery was obtained in the same manner as in Example 1, except that tris(ethyl acetoacetate)aluminum (III) was used as the anisotropic growth inhibitor instead of triphenylantimony.

[0108] [Example 13] A lithium secondary battery was obtained in the same manner as in Example 1, except that, as the anisotropic growth inhibitor, copper (I) trifluoromethanesulfonate-benzene complex was used instead of triphenylantimony.

[0109] [Comparative Example 1] A lithium secondary battery was obtained in the same manner as in Example 1, except that no anisotropic growth inhibitor was added to the electrolyte.

[0110] [Reference example 1] A lithium secondary battery was obtained in the same manner as in Comparative Example 1, except that a 20 μm Li foil was pressed onto one side of a 12 μm Cu foil as the negative electrode, and the negative electrode and separator were laminated so that the Li foil of the negative electrode faced the separator.

[0111] [Evaluation of energy density and cycle characteristics] The energy density and cycle characteristics of the lithium secondary batteries produced in each of the Examples and Comparative Examples were evaluated as follows.

[0112] The lithium secondary battery thus prepared was charged at 3.5 mA until the voltage reached 4.2 V, and then discharged at 3.5 mA until the voltage reached 3.0 V (hereinafter referred to as "initial discharge"). Next, the battery was charged at 7.0 mA until the voltage reached 4.2 V, and then discharged at 21 mA until the voltage reached 3.0 V, and this cycle was repeated 100 times in an environment at a temperature of 25°C. For each example, the capacity determined from the initial discharge (hereinafter referred to as "initial capacity") and the capacity determined from the discharge after the above 100 cycles (hereinafter referred to as "capacity retention rate") are shown in Table 1. For comparison, the initial capacity of Example 1 is taken as 100, and values ​​are shown. Here, the initial capacity of Example 1 was 70 mAh.

[0113] [Table 1]

[0114] From Table 1, it was found that, compared with Comparative Example 1 that does not contain an anisotropic growth inhibitor, Examples 1 to 13 that contain an anisotropic growth inhibitor have excellent initial capacity and capacity retention, high energy density, and excellent cycle characteristics. In addition, it was found that Examples 9 to 13 show a capacity retention rate equal to or higher than Reference Example 1 that has lithium foil on the negative electrode, and have extremely excellent cycle characteristics. Note that Reference Example 1 has lithium foil on the negative electrode surface before the initial charge, so it is necessary to use highly flammable lithium metal during production, which is inferior in safety and productivity and is not practically preferable. [Industrial Applicability]

[0115] INDUSTRIAL APPLICABILITY The lithium secondary battery of the present invention has high energy density and excellent cycle characteristics, and therefore has industrial applicability as an electricity storage device for various applications. [Explanation of symbols]

[0116] 100, 200, 300... Lithium secondary battery, 110... Positive electrode, 120... Separator, 130... Negative electrode, 210... Positive electrode current collector, 220... Deposition layer, 230... Positive electrode terminal, 240... Negative electrode terminal, 310... Solid electrolyte

Claims

1. A battery comprising a positive electrode, a separator, a negative electrode having no negative electrode active material, and an electrolyte; A lithium secondary battery in which lithium metal is deposited on the surface of the negative electrode and the deposited lithium is electrolytically dissolved to perform charging and discharging, Contains an additive that suppresses anisotropic crystal growth of lithium metal by co-depositing with lithium metal during charging; The additive is a compound containing at least one element selected from aluminum, tin, antimony, bismuth, selenium, tellurium, magnesium, potassium, copper, and zinc (excluding aromatic compounds in which hydrogen of a hydroxyl group is substituted with an alkali metal, aluminum oxide, magnesium oxide, and potassium nitrate). Lithium secondary battery.

2. 2. The lithium secondary battery in accordance with claim 1, wherein the additive is contained in the electrolyte or the separator.

3. 3. The lithium secondary battery according to claim 1, wherein the electrolyte solution contains an ether-based solvent.

4. The electrolyte is LiN(SO 2 F) 2 The lithium secondary battery according to any one of claims 1 to 3, comprising:

5. A battery comprising a positive electrode, a solid electrolyte, and a negative electrode having no negative electrode active material, A lithium secondary battery in which lithium metal is deposited on the surface of the negative electrode and the deposited lithium is electrolytically dissolved to perform charging and discharging, Contains an additive that suppresses anisotropic crystal growth of lithium metal by co-depositing with lithium metal during charging; The additive is a compound containing at least one element selected from aluminum, tin, antimony, bismuth, selenium, tellurium, magnesium, potassium, copper, and zinc (excluding aromatic compounds in which hydrogen of a hydroxyl group is substituted with an alkali metal, aluminum oxide, magnesium oxide, and potassium nitrate). Lithium secondary battery.

6. 6. The lithium secondary battery in accordance with claim 5, wherein the additive is contained in the solid electrolyte.

7. 7. The lithium secondary battery according to claim 1, wherein the content of the element derived from the additive in the deposition layer containing lithium metal deposited on the negative electrode in a charged state is 0.001 atomic % or more and 10 atomic % or less with respect to the entire deposition layer.

8. 8. The lithium secondary battery according to claim 1, wherein the compound is at least one selected from the group consisting of chlorides, fluorides, aromatic compounds, and metal complexes.

9. The lithium secondary battery according to any one of claims 1 to 8, wherein the negative electrode is an electrode made of at least one selected from the group consisting of Cu, Ni, Ti, Fe, and other metals that do not react with Li, and alloys thereof, and stainless steel (SUS).

10. 10. The lithium secondary battery according to claim 1, wherein no lithium foil is formed on the surface of the negative electrode before initial charging.

11. The lithium secondary battery according to any one of claims 1 to 10, wherein the positive electrode has a positive electrode active material.

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