Lithium secondary battery

Abstract

The present invention provides a lithium secondary battery which has a high energy density and excellent cycle characteristics. The present invention relates to a lithium secondary battery which is provided with a positive electrode and a negative electrode that does not contain a negative electrode active material, and which contains a compound that has a 1, 3, 5-triazine ring skeleton.

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, lithium secondary batteries, which are charged and discharged by the movement of 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 a lithium ion secondary battery, which has active materials capable of retaining lithium elements in the positive electrode and the negative electrode, and is charged and discharged by the exchange of lithium ions between the positive electrode active material and the negative electrode active material.

[0004] Also, in order to realize high energy density, lithium secondary batteries have been developed that use lithium metal as the negative electrode active material instead of materials that can insert lithium elements, such as carbonaceous materials. For example, Patent Document 1 discloses a lithium secondary battery equipped with an ultra-thin lithium metal anode to realize a volumetric energy density exceeding 1000 Wh / L and / or a mass energy density exceeding 350 Wh / kg during discharge at a rate of at least 1 C at room temperature. Patent Document 1 discloses that in such a lithium secondary battery, charging is performed by directly depositing additional lithium metal on the lithium metal as the negative electrode active material.

[0005] Also, for the purpose of further increasing the energy density and improving the productivity, lithium secondary batteries that do not use negative electrode active materials have been developed. For example, 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 in the negative electrode, 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. 2019-505971 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, it is difficult to sufficiently increase the energy density and capacity of a lithium secondary battery equipped with a negative electrode having a negative electrode active material due to the volume and mass occupied by the negative electrode active material. In addition, in the case of anode-free type lithium secondary battery equipped with a negative electrode not having a negative electrode active material, dendrite-like lithium metal is easily formed on the surface of the negative electrode by repeated charging and discharging, and short circuits and capacity reduction are easily caused, so that the cycle characteristics are insufficient.

[0009] In addition, in order to suppress the discrete growth of lithium metal during precipitation in anode-free lithium 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 includes a positive electrode and a negative electrode that does not have a negative electrode active material, and contains a compound having a 1,3,5-triazine ring skeleton.

[0012] Since such a lithium secondary battery does not have a negative electrode active material, the overall volume and mass of the battery are smaller and the energy density is, in principle, higher than that of a lithium secondary battery that has a negative electrode active material. In such a battery, lithium metal is deposited on the surface of the negative electrode, and the deposited lithium metal is electrolytically dissolved to charge and discharge the battery.

[0013] The present inventors have also found that in a compound having a 1,3,5-triazine ring skeleton, the nitrogen atom constituting the triazine ring and the hydrogen atom or the atom constituting the substituent bonded to the 2-, 4- or 6-position interact with lithium ions to stabilize the lithium ions, and have further found that an anode-free type lithium secondary battery containing such a compound having a 1,3,5-triazine ring skeleton has excellent cycle characteristics. Although the reason why the cycle characteristics of an anode-free type lithium secondary battery are improved by containing a compound having a 1,3,5-triazine ring skeleton is not necessarily clear, the present inventors speculate that this is because the compound stabilizes lithium ions inside the battery, thereby appropriately controlling the reaction rate of the lithium metal deposition reaction on the negative electrode surface and suppressing the non-uniform deposition reaction of lithium metal, i.e., the growth reaction of dendritic lithium metal.

[0014] The compound is preferably a compound having at least one thiol group bonded to a 1,3,5-triazine ring structure. According to such an embodiment, the compound having a 1,3,5-triazine ring structure interacts more favorably with the metal constituting the negative electrode, so that the growth reaction of the dendritic lithium metal is more suppressed, and the cycle characteristics of the battery tend to be further improved. From the same viewpoint, the compound is preferably a compound having at least two thiol groups bonded to a 1,3,5-triazine ring structure.

[0015] The compound preferably has a 1,3,5-triazine ring skeleton having substituents at all of the 2-, 4-, and 6-positions, and the substituents are selected from the group consisting of monovalent hydrocarbon groups optionally substituted with halogen atoms, hydroxy groups, alkoxy groups, thiol groups, and amino groups optionally substituted with unsubstituted hydrocarbon groups. According to such an embodiment, the cycle characteristics of the battery tend to be further improved.

[0016] The lithium secondary battery preferably further includes a separator or a solid electrolyte disposed between the positive electrode and the negative electrode. According to such an embodiment, the negative electrode and the positive electrode can be more reliably isolated from each other, and therefore, the battery can be more reliably prevented from being short-circuited.

[0017] At least a part of the compound is preferably coated on at least a part of the surface of the negative electrode facing the positive electrode. According to such an embodiment, when lithium ions are reduced on the surface of the negative electrode, the lithium ions are more reliably stabilized by the compound present on the surface of the negative electrode, so that the growth reaction of dendritic lithium metal is more suppressed, and the cycle characteristics of the battery tend to be further improved.

[0018] The lithium secondary battery preferably further includes an electrolyte solution containing the compound. According to such an embodiment, the lithium ions are more reliably stabilized by the compound inside the battery, so that the growth reaction of dendritic lithium metal is more suppressed, and the cycle characteristics of the battery tend to be more improved.

[0019] The lithium secondary battery preferably further comprises an electrolyte solution containing, as a solvent, a compound having at least one of a monovalent group represented by the following formula (A) and a monovalent group represented by the following formula (B), where in the following formula, the wavy line represents a binding site in the monovalent group. [ka] [ka] According to such an embodiment, the formation of a solid electrolyte interface layer (SEI layer) is promoted on the surface of the negative electrode, and thus the cycle characteristics of the battery are further improved. Since the SEI layer has ion conductivity, the reactivity of the lithium metal deposition reaction becomes uniform in the planar direction of the negative electrode surface on which the SEI layer is formed, and the growth of dendritic lithium metal on the negative electrode is suppressed.

[0020] The lithium secondary battery is charged and discharged by depositing lithium metal on the surface of the negative electrode and dissolving the deposited lithium through electrolysis.

[0021] 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, their alloys, 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, such a negative electrode is stable, which further improves the cycle characteristics of the secondary battery.

[0022] In a lithium secondary battery having a negative electrode that does not have a negative electrode active material, lithium metal is not formed on the surface of the negative electrode before initial charging and / or at the end of discharging. Therefore, the lithium secondary battery does not need to use highly flammable lithium metal during production, and is therefore excellent in safety and productivity.

[0023] The lithium secondary battery preferably has an energy density of 350 Wh / kg or more. Effect of the Invention

[0024] 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]

[0025] [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

[0026] 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.

[0027] [First embodiment] (lithium secondary battery) 1 is a schematic cross-sectional view of a lithium secondary battery according to the first embodiment. The lithium secondary battery 100 according to the first embodiment includes a positive electrode 120 and a negative electrode 130 that does not have a negative electrode active material. In the lithium secondary battery 100, a positive electrode current collector 110 is disposed on the side of the positive electrode 120 opposite to the surface facing the negative electrode 130, and a separator 140 is disposed between the positive electrode 120 and the negative electrode 130.

[0028] The lithium secondary battery 100 further contains a compound having a 1,3,5-triazine ring skeleton (hereinafter also referred to as a "triazine compound") not shown in FIG. 1. The triazine compound may be contained in any one or more of the components of the lithium secondary battery 100. Therefore, the triazine compound may be, for example, coated on at least a part of the surface of the positive electrode current collector 110 facing the negative electrode 130, may be contained in the positive electrode 120, may be coated on at least a part of the surface of the negative electrode 130 facing the positive electrode 120, or may be contained on the surface or inside of the separator 140. The surface of the separator 140 may be the surface on the negative electrode 130 side or the surface on the positive electrode 120 side. When the lithium secondary battery 100 includes an electrolyte, the triazine compound may be contained in the electrolyte. Each component of the lithium secondary battery 100 will be described below.

[0029] (Negative electrode) The negative electrode 130 does not have a negative electrode active material, that is, it does not have an active material that serves as a host for lithium metal and lithium (lithium metal or ions). Therefore, the lithium secondary battery 100 has a smaller overall volume and mass and, in principle, a higher energy density than a lithium secondary battery equipped with a negative electrode having a negative electrode active material. Here, the lithium secondary battery 100 is charged and discharged by depositing lithium metal on the negative electrode 130 and electrolytically dissolving the deposited lithium metal.

[0030] In this specification, "lithium metal is deposited on the negative electrode" means that lithium metal is deposited on at least one of the surface of the negative electrode coated with a triazine compound, the surface of the negative electrode not coated with a triazine compound, and the surface of a solid electrolyte interface layer (SEI layer) described later formed on the surface of the negative electrode. Therefore, in the lithium secondary battery 100, lithium metal may be deposited on, for example, the surface of the negative electrode 130 coated with a triazine compound (the interface between the negative electrode 130 and the separator 140) or the surface of the negative electrode 130 not coated with a triazine compound.

[0031] In this specification, the term "negative electrode active material" refers to a material for retaining lithium ions or lithium metal in the negative electrode 130, and may be referred to as a host material for lithium elements (typically lithium ions). The mechanism of such retention is not particularly limited, but examples include intercalation, alloying, and occlusion of metal clusters, and is typically intercalation.

[0032] Examples of such negative electrode active materials include, but are not particularly limited to, lithium metal and alloys containing lithium metal, carbon-based materials, metal oxides, and metals alloyed with lithium and alloys containing such metals. Examples of the carbon-based materials include, but are not particularly limited to, graphene, graphite, hard carbon, mesoporous carbon, carbon nanotubes, and carbon nanohorns. Examples of the metal oxides include, but are not particularly limited to, titanium oxide-based compounds, tin oxide-based compounds, and cobalt oxide-based compounds. Examples of the metals alloyed with lithium include silicon, germanium, tin, lead, aluminum, and gallium.

[0033] In this specification, when the negative electrode "has no negative electrode active material", it means that the content of the negative electrode active material in the negative electrode is 10% by mass or less based on the entire negative electrode. The content of the negative electrode active material in the negative electrode is preferably 5.0% by mass or less, may be 1.0% by mass or less, may be 0.1% by mass or less, or may be 0.0% by mass based on the entire negative electrode. Since the negative electrode has no negative electrode active material or the content of the negative electrode active material in the negative electrode is within the above range, the energy density of the lithium secondary battery 100 is high.

[0034] More specifically, regardless of the charge state of the battery, the content of the negative electrode active material other than lithium metal in the negative electrode 130 is 10% by mass or less, preferably 5.0% by mass or less, may be 1.0% by mass or less, may be 0.1% by mass or less, or may be 0.0% by mass based on the entire negative electrode. Also, at the time before initial charging and / or at the end of discharge, the content of lithium metal in the negative electrode 130 is 10% by mass or less, preferably 5.0% by mass or less, may be 1.0% by mass or less, may be 0.1% by mass or less, or may be 0.0% by mass based on the entire negative electrode.

[0035] The negative electrode 130 may have a lithium metal content of 10% by mass or less (preferably 5.0% by mass or less, 1.0% by mass or less, 0.1% by mass or less, or 0.0% by mass or less) relative to the entire negative electrode before initial charging or at the end of discharge; the lithium metal content of 10% by mass or less (preferably 5.0% by mass or less, 1.0% by mass or less, 0.1% by mass or less, or 0.0% by mass or less) relative to the entire negative electrode before initial charging or at the end of discharge. ); before the initial charge, the lithium metal content may be 10% by mass or less (preferably 5.0% by mass or less, may be 1.0% by mass or less, may be 0.1% by mass or less, or may be 0.0% by mass or less) relative to the entire negative electrode; or, at the end of discharge, the lithium metal content may be 10% by mass or less (preferably 5.0% by mass or less, may be 1.0% by mass or less, may be 0.1% by mass or less, or may be 0.0% by mass or less) relative to the entire negative electrode.

[0036] Therefore, a "lithium secondary battery having a negative electrode that does not have a negative electrode active material" can be expressed as an anode-free secondary battery, a zero anode secondary battery, or an anodeless secondary battery. Also, a "lithium secondary battery having a negative electrode that does not have a negative electrode active material" can be expressed as a "lithium secondary battery having a negative electrode that does not have a negative electrode active material other than lithium metal and does not have lithium metal before initial charging and / or at the end of discharge" or a "lithium secondary battery having a negative electrode current collector that does not have lithium metal before initial charging and / or at the end of discharge". Here, the term "before initial charging and / or at the end of discharge" may be replaced with the terms "before initial charging" or "at the end of discharge".

[0037] 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.

[0038] In the lithium secondary battery 100, when the battery voltage is 1.0 V or more and 3.5 V or less, the lithium metal content may be 10 mass % or less with respect to the entire negative electrode (preferably 5.0 mass % or less, 1.0 mass % or less, 0.1 mass % or less, or 0.0 mass % or less); when the battery voltage is 1.0 V or more and 3.0 V or less, the lithium metal content may be 10 mass % or less with respect to the entire negative electrode (preferably 5.0 mass % or less, 1.0 mass % or less, 0.1 mass % or less, or 0.0 mass % or less); or when the battery voltage is 1.0 V or more and 2.5 V or less, the lithium metal content may be 10 mass % or less with respect to the entire negative electrode (preferably 5.0 mass % or less, 1.0 mass % or less, 0.1 mass % or less, or 0.0 mass % or less).

[0039] In addition, in the lithium secondary battery 100, the mass M of lithium metal deposited on the negative electrode 130 when the battery voltage is 4.2 V is 4.2 The mass M of lithium metal deposited on the negative electrode 130 when the battery voltage is 3.0 V 3.0 Ratio of M 3.0 / M 4.2 is preferably 20% or less, more preferably 15% or less, and further preferably 10% or less. 3.0 / M 4.2 may be 8.0% or less, 5.0% or less, 3.0% or less, or 1.0% or less.

[0040] In a typical lithium secondary battery, the capacity of the negative electrode (capacity of the negative electrode active material) is set to be approximately the same as the capacity of the positive electrode (capacity of the positive electrode active material), but in the lithium secondary battery 100, the negative electrode 130 does not have a negative electrode active material that is a host material for lithium element, so there is no need to specify its capacity. Therefore, the lithium secondary battery 100 is not subject to the charge capacity restriction by the negative electrode, and therefore can in principle have a high energy density.

[0041] 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 a lithium secondary battery.

[0042] The negative electrode 130 is preferably made of at least one selected from the group consisting of Cu, Ni, Ti, Fe, and alloys thereof, and stainless steel (SUS), and more preferably made of at least one selected from the group consisting of Cu, Ni, and alloys thereof, and stainless steel (SUS). The negative electrode 130 is further preferably made of Cu, Ni, alloys thereof, or stainless steel (SUS). When such a negative electrode is used, the energy density and productivity of the battery tend to be further improved.

[0043] The negative electrode 130 is an electrode that does not contain lithium metal. Therefore, since there is no need to use highly flammable and reactive lithium metal during production, the lithium secondary battery 100 is excellent in safety, productivity, and cycle characteristics.

[0044] 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 lithium secondary battery 100 is further improved.

[0045] It is preferable that at least a part of the surface of the negative electrode 130 facing the positive electrode 120 is coated with a triazine compound so that the ratio of the triazine compound coated falls within the range described below. According to such an embodiment, the cycle characteristics of the battery tend to be further improved.

[0046] (Triazine compounds) The lithium secondary battery 100 has a high energy density because it includes a negative electrode 130 that does not have a negative electrode active material. However, the present inventors have found that if a negative electrode that does not have a negative electrode active material is simply used, lithium metal in a dendrite form is deposited on the negative electrode as the battery is charged and discharged, causing the battery to short circuit, or when the lithium metal deposited in a dendrite form dissolves, the root part of the lithium metal in a dendrite form dissolves, causing some of the lithium metal to peel off from the negative electrode and become inactive, thereby reducing the capacity of the battery. As a result of intensive research, the inventors have found that, in an anode-free type lithium secondary battery, by including a compound having a 1,3,5-triazine ring skeleton, the lithium metal deposited on the negative electrode is prevented from growing in a dendrite form, thereby solving the above problems.

[0047] The present inventors used molecular orbital calculations to investigate the stable structure when 1,3,5-triazine and lithium ions approach each other. As a result, it was found that the nitrogen atom of 1,3,5-triazine and the hydrogen atoms bonded to the 2-, 4-, or 6-positions interact with the lithium ion, thereby strongly stabilizing the lithium ion. Therefore, the present inventors speculate that the following factors contribute to the improvement of the cycle characteristics of anode-free lithium secondary batteries using a compound having a 1,3,5-triazine ring skeleton. However, the factors are not limited to the following. That is, when the lithium secondary battery 100 contains a triazine compound, as described above, the nitrogen atom constituting the triazine ring and the hydrogen atom or the atom constituting the substituent bonded to the 2nd, 4th or 6th position interact with the lithium ion, thereby stabilizing the lithium ion inside the battery. When the lithium ion is stabilized, the lithium ion is easily transported inside the battery, and the internal resistance of the battery is reduced. Furthermore, when the lithium ion is reduced to lithium metal on the surface of the negative electrode and when the lithium metal is oxidized and dissolved into lithium ion, the lithium ion is stabilized, so that the reaction rate of the deposition reaction of the lithium metal and the electrolytic dissolution reaction of the lithium metal are controlled, and local deposition and dissolution of the lithium metal are unlikely to occur. As a result, it is presumed that the non-uniform deposition reaction of the lithium metal, i.e., the growth reaction of the dendritic lithium metal, is suppressed, and the cycle characteristics of the battery are improved.

[0048] Therefore, the triazine compound may be contained in any one or more of the components of the lithium secondary battery 100. The triazine compound may be, for example, coated on at least a part of the surface of the positive electrode collector 110 facing the negative electrode 130, may be contained inside the positive electrode 120, may be coated on at least a part of the surface of the positive electrode 120 facing the negative electrode 130, may be coated on at least a part of the surface of the negative electrode 130 facing the positive electrode 120, or may be contained on the surface or inside the separator 140. The surface of the separator 140 containing the triazine compound may be the surface on the negative electrode 130 side or the surface on the positive electrode 120 side. When the lithium secondary battery 100 includes an electrolyte, the triazine compound may be contained in the electrolyte.

[0049] When the triazine compound is coated on at least a part of the surface of the negative electrode 130 facing the positive electrode 120, it is presumed that the reaction involving lithium ions (lithium oxidation reaction / reduction reaction) on the negative electrode surface can be effectively controlled, and such an embodiment is preferable. In an embodiment in which the triazine compound is coated on at least a part of the surface of the negative electrode 130 facing the positive electrode 120, from the viewpoint of strengthening the interaction between the triazine compound and the metal constituting the negative electrode, the triazine compound preferably has at least one thiol group, and more preferably has at least two thiol groups. In addition, when a triazine compound is contained in the electrolyte, lithium ions are effectively stabilized inside the battery, and therefore such an embodiment is also preferable. That is, an embodiment in which the triazine compound is coated on at least a part of the surface of the negative electrode 130 facing the positive electrode 120, and an embodiment in which the triazine compound is contained in the electrolyte are more preferable.

[0050] The triazine compound has a 1,3,5-triazine ring skeleton. Specifically, the triazine compound is represented by the following formula (1). Here, R is a hydrogen atom or any monovalent substituent. The triazine compound may be a polymer in which a plurality of 1,3,5-triazine ring skeletons are bonded via R. The polymerization number may be 10 or more, 50 or more, or 100 or more.

[0051] [ka]

[0052] R in formula (1) is not particularly limited, and may be a hydrogen atom, an optionally substituted monovalent hydrocarbon group, a hydroxyl group (-OH), an alkoxy group (-OR'), a thiol group (-SH), -SR', an amino group (-NH 2-n R' nand n is an integer of 0 to 2. ) and -OC(=O)-R'. Here, R' means a monovalent unsubstituted hydrocarbon group. The "hydrocarbon group" of the optionally substituted monovalent hydrocarbon group, the hydrocarbon group capable of substituting an amino group, and the hydrocarbon group in R' includes a group in which one hydrogen atom has been removed from a saturated or unsaturated branched or straight chain aliphatic hydrocarbon or an aromatic hydrocarbon, and the number of carbon atoms may be 1 to 100, 1 to 50, or 1 to 10. When the hydrocarbon group is optionally substituted, the hydrogen atoms in the hydrocarbon group may be partially or entirely substituted with fluorine atoms.

[0053] R in formula (1) is preferably selected from the group consisting of a hydrogen atom, a monovalent hydrocarbon group which may be substituted with a halogen atom, a hydroxy group, an alkoxy group, a thiol group, and an amino group which may be substituted with an unsubstituted hydrocarbon group, and more preferably selected from the group consisting of a hydrogen atom, a monovalent aliphatic hydrocarbon group having 1 to 3 carbon atoms (saturated or unsaturated, and branched or straight-chain) which may be substituted with a halogen atom, an alkoxy group having 1 to 3 carbon atoms (i.e., a methoxy group, an ethoxy group, or a propoxy group), a thiol group, and an amino group which may be substituted with an unsubstituted aliphatic hydrocarbon group having 1 to 5 carbon atoms (saturated or unsaturated, and branched or straight-chain). The halogen atom in the monovalent hydrocarbon group which may be substituted with a halogen atom is not particularly limited and may be a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, but is preferably a fluorine atom. In the amino group which may be substituted with an unsubstituted hydrocarbon group, the amino group may be unsubstituted, may be substituted with one hydrocarbon group, or may be substituted with two hydrocarbon groups. The hydrocarbon group which may substitute the amino group is preferably an unsubstituted aliphatic hydrocarbon group having 1 to 5 carbon atoms (saturated or unsaturated, and branched or linear), more preferably an unsubstituted saturated or unsaturated linear aliphatic hydrocarbon group having 2 to 5 carbon atoms, and even more preferably a butyl group and / or an allyl group (-CH 2 CH=CH 2 ).

[0054] The triazine compound is preferably a compound in which all R in the formula (1) are not hydrogen atoms, that is, a compound in which all of the 2-, 4- and 6-positions of the triazine ring are substituted with substituents. Among them, the triazine compound is more preferably a compound in which R in the formula (1) is selected from the group consisting of a monovalent hydrocarbon group which may be substituted with a halogen atom, a hydroxy group, an alkoxy group, a thiol group, and an amino group which may be substituted with an unsubstituted hydrocarbon group, and further preferably a compound in which R in the formula (1) is selected from the group consisting of a monovalent aliphatic hydrocarbon group having 1 to 3 carbon atoms (saturated or unsaturated, and branched or linear) which may be substituted with a halogen atom, an alkoxy group having 1 to 3 carbon atoms (i.e., a methoxy group, an ethoxy group, or a propoxy group), a thiol group, and an amino group which may be substituted with an unsubstituted aliphatic hydrocarbon group having 1 to 5 carbon atoms (saturated or unsaturated, and branched or linear).

[0055] In addition, in formula (1), it is preferable that at least one of the three R's is a thiol group, and more preferable that at least two of them are thiol groups. In other words, the triazine compound is preferably a compound having at least one thiol group bonded to a 1,3,5-triazine ring skeleton, and more preferable that at least two thiol groups are bonded to a 1,3,5-triazine ring skeleton. According to such an embodiment, the thiol group and the metal constituting the negative electrode interact more favorably, so that the triazine compound is more easily retained on the negative electrode surface, and the growth reaction of the dendritic lithium metal tends to be further suppressed.

[0056] Examples of the triazine compound include compounds represented by the following formulas (I), (II), (III), (IV) and (V) (hereinafter also abbreviated as "(I) to (V)"). [ka] [ka] [ka] [ka] [ka]

[0057] When the triazine compound is contained in the electrolytic solution, the triazine compound is preferably a compound represented by formulas (I) to (IV). The above-mentioned triazine compounds may be used alone or in combination of two or more.

[0058] The content of the triazine compound is not particularly limited, and may be 0.001% by mass or more, 0.005% by mass or more, 0.01% by mass or more, 0.05% by mass or more, 0.1% by mass or more, 0.5% by mass or more, 1.0% by mass or more, or 5.0% by mass or more, based on the mass of the entire battery. The content of the triazine compound may be 20% by mass or less, 15% by mass or less, or 10% by mass or less, based on the mass of the entire battery. Alternatively, the content of the triazine compound may be 5% by mass or less, or 1% by mass or less, based on the mass of the entire battery. The content of the triazine compound may be within a range that is a suitable combination of any of the above lower and upper limits. When the content of the triazine compound is equal to or more than the above lower limit, the effect of the triazine compound in stabilizing lithium ions in the battery tends to be effectively and reliably exhibited.

[0059] The triazine compound may be coated on at least a part of the surface of the negative electrode 130 facing the positive electrode 120. The expression "coated" on at least a part of the surface of the negative electrode with the triazine compound means that 10% or more of the surface of the negative electrode in terms of area ratio has the triazine compound. When the negative electrode 130 is coated with the triazine compound, the negative electrode surface is preferably coated with the triazine compound over an area ratio of 20% or more, 30% or more, 40% or more, or 50% or more, more preferably 70% or more, and even more preferably 80% or more.

[0060] The triazine compound may be coated on at least a part of the surface of the positive electrode current collector 110 facing the negative electrode 130. The phrase "coated" on at least a part of the surface of the positive electrode current collector with the triazine compound means that 10% or more of the surface of the positive electrode current collector in terms of area ratio has the triazine compound. When the positive electrode current collector 110 is coated with the triazine compound, preferably 20% or more, 30% or more, 40% or more, or 50% or more, more preferably 70% or more, and even more preferably 80% or more of the surface of the positive electrode current collector in terms of area ratio is coated with the triazine compound.

[0061] The triazine compound may be contained in the positive electrode 120. When the triazine compound is contained in the positive electrode 120, the content of the triazine compound in the positive electrode is preferably 0.01% by mass or more, more preferably 0.03% by mass or more, and even more preferably 0.05% by mass or more, based on the mass of the positive electrode. The content of the triazine compound in the positive electrode is preferably 5.0% by mass or less, more preferably 3.0% by mass or less, even more preferably 1.0% by mass or less, and even more preferably 0.5% by mass or less, based on the mass of the positive electrode. The content of the triazine compound in the positive electrode may be within a range that is an appropriate combination of any of the above lower limit values ​​and any of the above upper limit values.

[0062] The triazine compound may be coated on at least a part of the surface of the positive electrode 120 facing the negative electrode 130. The phrase "coated" on at least a part of the surface of the positive electrode with the triazine compound means that 10% or more of the surface of the positive electrode in terms of area ratio has the triazine compound. When the positive electrode 120 is coated with the triazine compound, the surface of the positive electrode is preferably coated with the triazine compound over an area ratio of 20% or more, 30% or more, 40% or more, or 50% or more, more preferably 70% or more, and even more preferably 80% or more.

[0063] The triazine compound may be contained on the surface and / or inside of the separator 140. The content of the triazine compound in the separator is preferably 0.01% by mass or more, more preferably 0.03% by mass or more, and even more preferably 0.05% by mass or more, based on the mass of the separator. The content of the triazine compound in the separator is preferably 5.0% by mass or less, more preferably 3.0% by mass or less, even more preferably 1.0% by mass or less, and even more preferably 0.5% by mass or less, based on the mass of the separator. The content of the triazine compound in the separator may be within a range that is an appropriate combination of any of the above lower limit values ​​and any of the above upper limit values.

[0064] When the lithium secondary battery 100 includes an electrolyte solution, the triazine compound may be contained in the electrolyte solution. The content of the triazine compound in the electrolyte solution is preferably 0.01% by mass or more, more preferably 0.03% by mass or more, and even more preferably 0.05% by mass or more, based on the mass of the electrolyte solution. The content of the triazine compound in the electrolyte solution is preferably 5.0% by mass or less, more preferably 3.0% by mass or less, even more preferably 1.0% by mass or less, and even more preferably 0.5% by mass or less, based on the mass of the electrolyte solution. The content of the triazine compound in the electrolyte solution may be within a range that is a suitable combination of any of the above lower limit values ​​and any of the above upper limit values.

[0065] The triazine compound may be contained in any of the above-mentioned components: the surface of the negative electrode, the surface of the positive electrode collector, the inside of the positive electrode, the surface of the positive electrode, the surface and / or the inside of the separator, and the electrolyte solution, or may be contained in two or more of these components. When the triazine compound is contained in two or more of the components: the surface of the negative electrode, the surface of the positive electrode collector, the inside of the positive electrode, the surface of the positive electrode, the surface and / or the inside of the separator, and the electrolyte solution, the preferred content and examples of the content of the triazine compound in each component are the same as those described above.

[0066] (positive electrode) The positive electrode 120 is not particularly limited as long as it has a positive electrode active material and is generally used in lithium secondary batteries, and a known material can be appropriately selected depending on the application of the lithium secondary battery. Since the positive electrode 120 has a positive electrode active material, it has high stability and output voltage.

[0067] In this specification, the term "positive electrode active material" refers to a material for retaining lithium element (typically, lithium ions) in the positive electrode 120, and may be referred to as a host material for lithium element (typically, lithium ions).

[0068] Examples of such positive electrode active materials include, but are not limited to, metal oxides and metal phosphates. Examples of the metal oxides include, but are not limited to, cobalt oxide compounds, manganese oxide compounds, and nickel oxide compounds. Examples of the metal phosphates include, but are not limited to, iron phosphate compounds, and cobalt phosphate compounds. Typical positive electrode active materials include LiCoO 2 , LiNi x Co y Mn z O(x+y+z=1), LiNi x Mn y O(x+y=1), LiNiO 2 , LiMn 2 O 4 , LiFePO, LiCoPO, LiFeOF, LiNiOF, and TiS 2The above positive electrode active materials may be used alone or in combination of two or more.

[0069] 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, known conductive assistants, binders, solid polymer electrolytes, and inorganic solid electrolytes.

[0070] The conductive assistant in the positive electrode 120 is not particularly limited, but examples thereof include carbon black, single-wall carbon nanotubes (SWCNT), multi-wall carbon nanotubes (MWCNT), carbon nanofibers (CF), acetylene black, etc. The binder is not particularly limited, but examples thereof include polyvinylidene fluoride, polytetrafluoroethylene, styrene butadiene rubber, acrylic resin, polyimide resin, etc.

[0071] 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 with respect to the entire positive electrode 120. The content of the conductive assistant may be, for example, 0.5% by mass to 30% by mass or less with respect to the entire positive electrode 120. The content of the binder may be, for example, 0.5% by mass to 30% by mass or less with respect to the entire positive electrode 120. 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 with respect to the entire positive electrode 120.

[0072] The positive electrode 120 may contain the triazine compound in the above-mentioned content therein, or at least a portion of the surface of the positive electrode 120 facing the negative electrode 130 may be coated with the triazine compound so that the coating ratio of the triazine compound falls within the above-mentioned range.

[0073] (Positive electrode current collector) A positive electrode current collector 110 is disposed on one side of the positive electrode 120. There are no particular limitations on the positive electrode current collector 110 as long as it is a conductor that does not react with lithium ions in the battery. Examples of such positive electrode current collectors include aluminum.

[0074] The average thickness of the positive electrode current collector 110 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 positive electrode current collector 110 in the lithium secondary battery 100 is reduced, and therefore the energy density of the lithium secondary battery 100 is further improved.

[0075] At least a part of the surface of the positive electrode current collector 110 facing the negative electrode 130 may be coated with a triazine compound so that the coating ratio of the triazine compound falls within the above-mentioned range. When the surface of the positive electrode current collector 110 is coated with a triazine compound, the positive electrode 120 is formed on the surface having the coating after the triazine compound is coated on the surface of the positive electrode current collector 110.

[0076] (Separator) The separator 140 is a member for preventing the battery from short-circuiting by isolating the positive electrode 120 and the negative electrode 130, while ensuring ionic conductivity of lithium ions that serve as charge carriers between the positive electrode 120 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 140 also plays a role in retaining the electrolyte. There are no limitations on the separator 140 as long as it plays the above role, and it is made of, for example, a porous polyethylene (PE) film, a polypropylene (PP) film, or a laminated structure thereof.

[0077] Separator 140 may be coated with a separator coating layer. The separator coating layer may coat both sides of separator 140, or may coat only one side. The separator coating layer is not particularly limited as long as it has ion conductivity and does not react with lithium ions, but it is preferably one that can firmly adhere separator 140 and the layer adjacent to separator 140. Such separator coating layers include, but are not particularly limited to, those containing binders such as polyvinylidene fluoride (PVDF), a composite material of styrene butadiene rubber and carboxymethyl cellulose (SBR-CMC), polyacrylic acid (PAA), lithium polyacrylate (Li-PAA), polyimide (PI), polyamideimide (PAI), and aramid. The separator coating layer may be added with inorganic particles such as silica, alumina, titania, zirconia, magnesium oxide, magnesium hydroxide, and lithium nitrate to the above binder. Note that separator 140 may be a separator without a separator coating layer, or may be a separator with a separator coating layer.

[0078] The average thickness of separator 140 is preferably 30 μm or less, more preferably 25 μm or less, and even more preferably 20 μm or less. According to such an aspect, since the volume occupied by separator 140 in lithium secondary battery 100 decreases, the energy density of lithium secondary battery 100 is further improved. Also, the average thickness of separator 140 is preferably 5 μm or more, more preferably 7 μm or more, and even more preferably 10 μm or more. According to such an aspect, the positive electrode 120 and the negative electrode 130 can be more reliably separated, and the occurrence of battery short circuit can be further suppressed.

[0079] The separator 140 may contain the triazine compound in the above-mentioned content. Alternatively, at least a part of the surface of the separator 140 may be coated with the triazine compound so that the content of the triazine compound falls within the above-mentioned range. When the surface of the separator is coated with the triazine compound, the surface may be the surface facing the negative electrode 130 or the surface facing the positive electrode 120.

[0080] (electrolyte) The lithium secondary battery 100 preferably further includes an electrolytic solution. In the lithium secondary battery 100, the electrolytic solution may be impregnated into the separator 140, or may be enclosed in a sealed container together with a laminate of the positive electrode current collector 110, the positive electrode 120, the separator 140, and the negative electrode 130. The electrolytic solution is a solution containing an electrolyte and a solvent and having ion conductivity, and acts as a conductive path for lithium ions. Therefore, according to an embodiment including the electrolytic solution, the internal resistance of the battery is further reduced, and the energy density, capacity, and cycle characteristics are further improved.

[0081] The solvent in the electrolytic solution is not particularly limited as long as it is generally used in lithium secondary batteries, and a known solvent such as an organic solvent can be appropriately selected depending on the application of the lithium secondary battery. As the solvent in the lithium secondary battery 100, a fluorinated alkyl compound having at least one of a monovalent group represented by the following formula (A) and a monovalent group represented by the following formula (B) is preferable. In other words, the lithium secondary battery 100 preferably contains such a fluorinated alkyl compound as a solvent. [ka] [ka] In the formula, the wavy line represents a bonding site in a monovalent group.

[0082] In general, in an anode-free type lithium secondary battery having an electrolyte, a solid electrolyte interface layer (SEI layer) is formed on the surface of the negative electrode, etc., by decomposing the solvent in the electrolyte. In a lithium secondary battery, the SEI layer suppresses further decomposition of the components in the electrolyte, as well as the irreversible reduction of lithium ions and the generation of gas caused thereby. In addition, since the SEI layer has ion conductivity, the reactivity of the lithium metal deposition reaction becomes uniform in the planar direction of the negative electrode surface on which the SEI layer is formed. Therefore, promoting the formation of the SEI layer is very important for improving the performance of an anode-free type lithium secondary battery. The present inventors have found that, in a lithium secondary battery 100 containing a triazine compound, when the above-mentioned alkyl fluoride compound is used as a solvent, an SEI layer is easily formed on the surface of the negative electrode, and the growth of dendritic lithium metal on the negative electrode is further suppressed, resulting in further improvement in cycle characteristics. Although the reason for this is not necessarily clear, the following factors are considered to be the cause.

[0083] During charging of the lithium secondary battery 100, especially during initial charging, it is believed that not only lithium ions but also the above-mentioned fluorinated alkyl compound, which is a solvent, is reduced on the negative electrode. In addition, it is believed that the part represented by the above formula (A) and the part represented by the above formula (B) in the fluorinated alkyl compound are substituted with a large number of fluorines, and therefore the reactivity of oxygen atoms is high, and the part represented by the above formula (A) and the part represented by the above formula (B) are easily desorbed in part or in whole. As a result, during charging of the lithium secondary battery 100, it is believed that the part represented by the above formula (A) and the part represented by the above formula (B) are adsorbed in part or in whole on the negative electrode surface, and an SEI layer is generated starting from the adsorbed part, so that the SEI layer is easily formed in the lithium secondary battery 100. In addition, since the negative electrode 130 has a triazine compound that is believed to interact with lithium ions, it is believed that many stabilized lithium ions are present near the negative electrode when the SEI layer is formed, and an SEI layer with a high concentration of lithium elements is formed. As a result, it is presumed that when the above-mentioned alkyl fluoride compound is used as a solvent in the lithium secondary battery 100 containing a triazine compound, an SEI layer having a suitable thickness and high ion conductivity is easily formed, thereby further improving the cycle characteristics.

[0084] Therefore, according to the embodiment including the electrolyte solution containing the above-mentioned fluorinated alkyl compound as a solvent, the SEI layer is easily formed, but the battery has low internal resistance and excellent rate performance. That is, the cycle characteristics and rate performance are further improved. The "rate performance" means the performance of being able to charge and discharge at a large current, and it is known that the rate performance is excellent when the battery has a low internal resistance.

[0085] In this specification, the phrase "contained as a solvent" means that the compound alone or a mixture with other compounds is liquid in the usage environment of the lithium secondary battery, and further, that the compound is capable of dissolving an electrolyte to produce an electrolyte solution in a solution phase.

[0086] Examples of such alkyl fluoride compounds include compounds having an ether bond (hereinafter referred to as "ether compounds"), compounds having an ester bond, and compounds having a carbonate bond. From the viewpoint of further improving the solubility of the electrolyte in the electrolytic solution and from the viewpoint of making it easier to form an SEI layer, the alkyl fluoride compound is preferably an ether compound.

[0087] Examples of ether compounds that are fluorinated alkyl compounds include ether compounds having both a monovalent group represented by formula (A) and a monovalent group represented by formula (B) (hereinafter also referred to as a "first fluorine solvent"), ether compounds having a monovalent group represented by formula (A) and not having a monovalent group represented by formula (B) (hereinafter also referred to as a "second fluorine solvent"), and ether compounds not having a monovalent group represented by formula (A) and having a monovalent group represented by formula (B) (hereinafter also referred to as a "third fluorine solvent").

[0088] Examples of the first fluorine solvent include 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl diethoxymethane, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl diethoxypropane, etc. From the viewpoint of effectively and reliably exerting the effect of the above-mentioned alkyl fluoride compound, the first fluorine solvent is preferably 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0089] Examples of the second fluorine solvent include 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, methyl-1,1,2,2-tetrafluoroethyl ether, ethyl-1,1,2,2-tetrafluoroethyl ether, propyl-1,1,2,2-tetrafluoroethyl ether, 1H,1H,5H-perfluoropentyl-1,1,2,2-tetrafluoroethyl ether, and 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether. From the viewpoint of effectively and reliably exerting the effect of the above-mentioned fluorinated alkyl compound, the second fluorine solvent is preferably 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, methyl-1,1,2,2-tetrafluoroethyl ether, ethyl-1,1,2,2-tetrafluoroethyl ether, and 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether.

[0090] Examples of the third fluorine solvent include difluoromethyl-2,2,3,3-tetrafluoropropyl ether, trifluoromethyl-2,2,3,3-tetrafluoropropyl ether, fluoromethyl-2,2,3,3-tetrafluoropropyl ether, and methyl-2,2,3,3-tetrafluoropropyl ether. From the viewpoint of effectively and reliably exerting the effect of the above-mentioned alkyl fluoride compound, the third fluorine solvent is preferably difluoromethyl-2,2,3,3-tetrafluoropropyl ether.

[0091] The electrolytic solution may contain a solvent that does not have either the monovalent group represented by formula (A) or the monovalent group represented by formula (B). Examples of such solvents include, but are not limited to, fluorine-free solvents such as dimethyl ether, triethylene glycol dimethyl ether, dimethoxyethane, 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, and triethyl phosphate, as well as fluorine-containing solvents such as methyl nonafluorobutyl ether, ethyl nonafluorobutyl ether, 1,1,1,2,2,3,4,5,5,5-decafluoro-3-methoxy-4-trifluoromethylpentane, methyl-2,2,3,3,3-pentafluoropropyl ether, 1,1,2,3,3,3-hexafluoropropyl methyl ether, ethyl-1,1,2,3,3,3-hexafluoropropyl ether, and tetrafluoroethyl tetrafluoropropyl ether.

[0092] The above-mentioned solvents, including the above-mentioned fluoroalkyl compounds, may be used alone or in combination of two or more kinds.

[0093] The content of the fluorinated alkyl compound in the electrolyte is not particularly limited, but is preferably 40% by volume or more, more preferably 50% by volume or more, even more preferably 60% by volume or more, and even more preferably 70% by volume or more, based on the total amount of the solvent components of the electrolyte. When the content of the fluorinated alkyl compound is within the above range, the SEI layer is more easily formed, and the cycle characteristics of the battery tend to be further improved. The upper limit of the content of the fluorinated alkyl compound is not particularly limited, and the content of the fluorinated alkyl compound may be 100% by volume or less, 95% by volume or less, 90% by volume or less, or 80% by volume or less, based on the total amount of the solvent components of the electrolyte. The content of the fluorinated alkyl compound may be within a range that appropriately combines any of the above lower limit values ​​and any of the above upper limit values.

[0094] 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. As the electrolyte, a lithium salt is preferably used. Examples of the lithium salt include, but are not limited to, LiI, LiCl, LiBr, LiF, LiBF 4 , LiPF 6 , LiAsF 6 , LiSO 3 CF 3 , LiN(SO 2 F) 2 , LiN(SO 2 CF 3 ) 2 , LiN(SO 2 CF 3 CF 3 ) 2 , LiBF 2 (C 2 O 4 ), LiB(O 2 C 2 H 4 ) 2 , LiB(O 2 C 2 H 4 )F 2 , LiB(OCOCF 3 ) 4 , LiNO 3 , and Li 2 SO 4 The above lithium salts may be used alone or in combination of two or more.

[0095] The concentration of the electrolyte in the electrolytic solution is not particularly limited, but is preferably 0.5M or more, more preferably 0.7M or more, even more preferably 0.9M or more, and even more preferably 1.0M 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 lower. The upper limit of the electrolyte concentration is not particularly limited, and the electrolyte concentration may be 10.0M or less, 5.0M or less, or 2.0M or less. The concentration of the electrolytic solution may be within a range that appropriately combines any of the above lower limit values ​​and any of the above upper limit values.

[0096] The electrolyte preferably contains a triazine compound, which tends to further improve the cycle characteristics of the battery.

[0097] (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 220 and a negative electrode terminal 210 for connecting the lithium secondary battery to an external circuit are joined to the positive electrode current collector 110 and the negative electrode 130, respectively, in the lithium secondary battery 100. The lithium secondary battery 200 is charged and discharged by connecting the negative electrode terminal 210 to one end of the external circuit and the positive electrode terminal 220 to the other end of the external circuit.

[0098] The lithium secondary battery 200 is charged by applying a voltage between the positive electrode terminal 220 and the negative electrode terminal 210 such that a current flows from the negative electrode terminal 210 through an external circuit to the positive electrode terminal 220. Charging the lithium secondary battery 200 causes deposition of lithium metal on the negative electrode.

[0099] In the lithium secondary battery 200, a solid electrolyte interface layer (SEI layer) may be formed on the surface of the negative electrode 130 (interface between the negative electrode 130 and the separator 140) by the first charge (initial charge) after the battery is assembled. 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.

[0100] When the positive electrode terminal 220 and the negative electrode terminal 210 of the charged lithium secondary battery 200 are connected, the lithium secondary battery 200 is discharged. This causes the lithium metal precipitated on the negative electrode to be electrolytically dissolved.

[0101] (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 capable of manufacturing a lithium secondary battery having the above-mentioned configuration, and examples thereof include the following methods.

[0102] First, the positive electrode 120 is prepared by a known manufacturing method or by purchasing a commercially available product. The positive electrode 120 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, relative to 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 predetermined thickness (e.g., 5 μm or more and 1 mm or less) as a positive electrode current collector, and press molded. The obtained molded body is punched out to a predetermined size by punching to obtain a positive electrode 120 formed on the positive electrode current collector 110.

[0103] When the surface of the positive electrode current collector 110 is coated with a triazine compound, the positive electrode current collector may be immersed in a solution containing a triazine compound (for example, an aqueous solution containing 0.01% by volume or more and 10% by volume or less of the triazine compound) and then dried in air before forming the positive electrode 120. At this time, one side of the positive electrode current collector may be masked to coat only one side with the triazine compound. When the triazine compound is contained in the positive electrode 120, the triazine compound may be further added in the step of obtaining the positive electrode mixture described above. The amount of the triazine compound added may be 0.01% by mass or more and 3.0% by mass or less, 0.03% by mass or more and 1.0% by mass or less, or 0.05% by mass or more and 0.5% by mass or less, based on the total amount of the positive electrode mixture. When coating the surface of the positive electrode with a triazine compound, a triazine compound may be mixed with a known conductive assistant and / or a known binder to obtain a slurry, and the slurry may be coated on the surface of the positive electrode.

[0104] Next, the negative electrode 130 can be prepared by washing the above-mentioned negative electrode material, for example, a metal foil having a thickness of 1 μm or more and 1 mm or less (for example, an electrolytic Cu foil), with a solvent containing sulfamic acid.

[0105] When the surface of the negative electrode 130 is coated with a triazine compound, the negative electrode obtained as described above may be further washed with dilute sulfuric acid, immersed in a commercially available cleaning agent containing a triazine compound (the content of the triazine compound is, for example, 0.01% by volume or more and 10% by volume or less) for 1 to 10 minutes, and then dried in the atmosphere to perform coating. At this time, the triazine compound may be coated only on one side of the negative electrode by masking the other side.

[0106] In addition, when coating the negative electrode 130 or the positive electrode current collector 110 with a triazine compound, a process of immersing the electrode plate in a solution containing the triazine compound may be performed by, for example, a roll-to-roll method.

[0107] Next, the separator 140 having the above-mentioned structure is prepared. The separator 140 may be produced by a conventionally known method, or a commercially available product may be used. When the triazine compound is contained inside the separator, the separator may be immersed in a solution containing the triazine compound (for example, an aqueous solution containing 0.01% by volume or more and 10% by volume or less of the triazine compound) and dried to contain the triazine compound. When the surface of the separator is coated with the triazine compound, the separator may be coated with a slurry obtained by mixing the above-mentioned resin such as polyvinylidene fluoride (PVDF) that may be contained in the separator coating layer, a filler such as alumina that may be contained in the separator coating layer, and the triazine compound, etc. The content of the triazine compound in the slurry may be, for example, 1 mass % or more and 20 mass % or less with respect to the entire slurry.

[0108] The electrolytic solution may be prepared by dissolving the above electrolyte (typically, a lithium salt) in the above solvent. When the electrolytic solution contains a triazine compound, the triazine compound may be added to the electrolytic solution so that the content of the triazine compound falls within the above-mentioned range.

[0109] The triazine compound may be contained in at least one of the above-mentioned components: the surface of the negative electrode, the surface of the positive electrode current collector, the inside of the positive electrode, the surface of the positive electrode, the surface and / or the inside of the separator, and the electrolyte.

[0110] Next, the positive electrode current collector 110 on which the positive electrode 120 is formed, the separator 140, and the negative electrode 130 obtained as above are laminated in this order to obtain a laminate as shown in Fig. 1. The laminate obtained as above 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.

[0111] [Second embodiment] (lithium secondary battery) 3 is a schematic cross-sectional view of a lithium secondary battery according to the second embodiment. The lithium secondary battery 300 according to the second embodiment includes a positive electrode 120 and a negative electrode 130 that does not have a negative electrode active material. In the lithium secondary battery 300, a positive electrode current collector 110 is disposed on the side of the positive electrode 120 opposite to the surface facing the negative electrode 130, and a solid electrolyte 310 is disposed between the positive electrode 120 and the negative electrode 130. The lithium secondary battery 300 may include an electrolytic solution such as that included in the lithium secondary battery 100.

[0112] The lithium secondary battery 300 further contains a compound having a 1,3,5-triazine ring skeleton (triazine compound) not shown in FIG. 3. The triazine compound may be contained in any one or more of the components of the lithium secondary battery 300. Therefore, the triazine compound may be, for example, coated on at least a part of the surface of the positive electrode current collector 110 facing the negative electrode 130, may be contained in the positive electrode 120, may be coated on at least a part of the surface of the negative electrode 130 facing the positive electrode 120, or may be contained on the surface or inside of the solid electrolyte 310. The surface of the solid electrolyte 310 may be on the negative electrode 130 side or on the positive electrode 120 side. When the lithium secondary battery 300 includes an electrolyte solution, the triazine compound may be contained in the electrolyte solution.

[0113] The configurations, examples, and preferred aspects of the positive electrode current collector 110, the positive electrode 120, the negative electrode 130, and the triazine compound are the same as those of the lithium secondary battery 100 of the first embodiment, and the lithium secondary battery 300 exhibits the same effects as the lithium secondary battery 100. Hereinafter, only the configuration of the lithium secondary battery 300 that differs from the lithium secondary battery 100 of the first embodiment will be described.

[0114] (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 surface of the negative electrode 130 is uniform, and the shape of the lithium metal precipitated on the surface of the negative electrode 130 can be made more uniform. That is, according to this embodiment, the lithium 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 are further improved.

[0115] 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. The solid electrolyte 310 is preferably ionically conductive and not electrically conductive. By making the solid electrolyte 310 ionically conductive and not electrically conductive, 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.

[0116] The solid electrolyte 310 is preferably one containing a resin and a lithium salt (gel electrolyte). Such resins are not particularly limited, but examples thereof include resins having ethylene oxide units in the chain and / or side chain, acrylic resins, vinyl resins, ester resins, nylon resins, polysiloxanes, polyphosphazenes, polyvinylidene fluoride, polymethyl methacrylate, polyamides, polyimides, aramids, polylactic acid, polyethylene, polystyrene, polyurethanes, polypropylene, polybutylene, polyacetal, polysulfones, and polytetrafluoroethylene. Alternatively, the solid electrolyte 310 may be a copolymer of polyethylene and / or polyethylene oxide, polyvinylidene fluoride, and a copolymer of polyvinylidene fluoride and hexafluoropropylene. The above-mentioned resins may be used alone or in combination of two or more.

[0117] The lithium salt contained in the gel electrolyte is not particularly limited, and examples thereof include the salts exemplified as the lithium salt that may be contained in the electrolyte solution of the lithium secondary battery 100. The above-mentioned lithium salts may be used alone or in combination of two or more kinds.

[0118] In general, the content ratio of the resin to the lithium salt in the gel 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 gel electrolyte, the content ratio of the resin to the lithium salt is adjusted so that the ratio ([Li] / [O]) is preferably 0.02 to 0.20, more preferably 0.03 to 0.15, and even more preferably 0.04 to 0.12.

[0119] The gel electrolyte 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 lithium salt. The salt other than lithium salt is not particularly limited, but includes, for example, salts of Na, K, Ca, and Mg. The solvent is not particularly limited, but includes, for example, those exemplified in the electrolyte solution that the lithium secondary battery 100 may contain. The above-mentioned solvents and salts other than lithium salts are used alone or in combination of two or more.

[0120] 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 120 and the negative electrode 130 can be more reliably isolated from each other, and the battery can be further prevented from being short-circuited.

[0121] The solid electrolyte 310 may contain a triazine compound therein. Alternatively, at least a part of the surface of the solid electrolyte 310 may be coated with a triazine compound. When the surface of the solid electrolyte is coated with a triazine compound, the surface may be the surface facing the negative electrode 130 or the surface facing the positive electrode 120.

[0122] The content of the triazine compound in the solid electrolyte is preferably 0.01% by mass or more, more preferably 0.03% by mass or more, and even more preferably 0.05% by mass or more, based on the mass of the solid electrolyte. The content of the triazine compound in the solid electrolyte is preferably 5.0% by mass or less, more preferably 3.0% by mass or less, even more preferably 1.0% by mass or less, and even more preferably 0.5% by mass or less, based on the mass of the solid electrolyte. The content of the triazine compound in the solid electrolyte may be within a range that is a suitable combination of any of the above lower and upper limits.

[0123] The triazine compound may be contained in any one of the components of the negative electrode surface, the positive electrode current collector surface, the positive electrode interior, the positive electrode surface, the solid electrolyte surface and / or interior, and the electrolyte solution, or may be contained in two or more of these components. When the triazine compound is contained in two or more of the components of the negative electrode surface, the positive electrode current collector surface, the positive electrode interior, the positive electrode surface, the solid electrolyte surface and / or interior, and the electrolyte solution, the preferred content and examples of the content of the triazine compound in each component are the same as those described above.

[0124] (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.

[0125] 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 gel electrolytes and a lithium salt (for example, the resin and lithium salt described above as the solid electrolyte 310 may contain) are dissolved in an organic solvent (for example, N-methylpyrrolidone, acetonitrile). The obtained solution is cast onto a molding substrate to a predetermined thickness, thereby obtaining 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 molding substrate is not particularly limited, but may be, for example, a PET film or a glass substrate.

[0126] When the triazine compound is contained inside the solid electrolyte, the triazine compound may be contained by immersing the solid electrolyte in a solution containing the triazine compound (for example, an aqueous solution containing 0.01 vol % or more and 10 vol % or less of the triazine compound) and drying it. When the surface of the solid electrolyte is coated with the triazine compound, the solid electrolyte may be coated with a slurry obtained by mixing the above-mentioned resin that may be contained in the solid electrolyte, the lithium salt that may be contained in the solid electrolyte, the triazine compound, etc. The content of the triazine compound in the slurry may be, for example, 1 mass % or more and 20 mass % or less with respect to the entire slurry.

[0127] [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.

[0128] For example, in the lithium secondary battery 100 of the first embodiment, the separators 140 may be formed on both sides of the negative electrode 130. In this case, the lithium secondary battery has each component laminated 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.

[0129] The lithium secondary battery 300 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.

[0130] The lithium secondary battery 100 may not have the separator 140. In such a case, it is desirable that the positive electrode 120 and the negative electrode 130 are fixed with a sufficient distance between them so that a short circuit of the battery does not occur due to contact between the positive electrode 120 and the negative electrode 130.

[0131] In the lithium secondary battery of this embodiment, a terminal for connecting to an external circuit may be attached to the positive electrode current collector and / or the negative electrode. For example, a metal terminal (e.g., Al, Ni, etc.) having a thickness of 10 μm to 1 mm may be bonded to one or both of the positive electrode current collector and the negative electrode. As a bonding method, a conventionally known method may be used, for example, ultrasonic welding may be used.

[0132] 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 800 Wh / L or more or 350 Wh / kg or more, more preferably 900 Wh / L or more or 400 Wh / kg or more, and even more preferably 1000 Wh / L or more or 450 Wh / kg or more.

[0133] 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. That is, when comparing the first discharge capacity after the 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 cycle is almost not reduced compared to the first discharge capacity after the initial charge. Here, the "number of times that can be expected in normal use" is, for example, 30 times, 50 times, 70 times, 100 times, 300 times, or 500 times, depending on the application of the lithium secondary battery. In addition, "the discharge capacity after the charge / discharge cycle is almost not reduced compared to the first discharge capacity after the initial charge" means, for example, that the discharge capacity after the charge / discharge cycle is 60% or more, 65% or more, 70% or more, 75% or more, 80% or more, or 85% or more compared to the first discharge capacity after the initial charge, depending on the application of the lithium secondary battery. EXAMPLES

[0134] 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.

[0135] [Manufacturing method of lithium secondary batteries] The steps for manufacturing the lithium secondary battery were carried out as follows.

[0136] (Preparation of negative electrode) A 10 μm electrolytic Cu foil was washed with dilute sulfuric acid, then immersed in a commercially available cleaning agent for 2 minutes and then dried. The obtained electrode was punched out to a specified size (45 mm × 45 mm) to obtain a negative electrode.

[0137] When the surface of the negative electrode was coated with the triazine compound, the triazine compound was added to the cleaning agent at a concentration of 0.05 mass % in the step of immersing the electrode in the cleaning agent containing the triazine compound, thereby coating the surface of the negative electrode with the triazine compound.

[0138] (Preparation of separator) A separator was produced by applying an aqueous slurry containing alumina, polyvinylidene fluoride (PVDF), a dispersant, and a surfactant to both sides of a 12 μm polyethylene microporous membrane (50 mm × 50 mm) using a comma coater, and then drying in a drying oven maintained at 60° C. The amount of slurry applied was adjusted so that the separator coating layer would be 2 μm thick.

[0139] When the triazine compound was coated on the surface of the separator, the triazine compound was added to the slurry in the step of applying the slurry so that the content of the triazine compound in the slurry was 10 mass %. The triazine compound was coated on the surface of the separator by applying the slurry containing the triazine compound.

[0140] (Preparation of positive electrode) 96.0 parts by mass of LiNi as the positive electrode active material 0.90 Co 0.08 Al 0.02 O 2 The mixture was mixed with 0.5 parts by mass of carbon nanotubes and 1.0 parts by mass of acetylene black as a conductive assistant, and 2.5 parts by mass of polyvinylidene fluoride (PVDF) as a binder to obtain a positive electrode mixture. The obtained positive electrode mixture was applied to one side of a 12 μm Al foil as a positive electrode current collector, and press molded. The obtained molded body was punched out to a predetermined size (40 mm × 40 mm) by punching to obtain a positive electrode formed on the positive electrode current collector.

[0141] When preparing a positive electrode containing a triazine compound, the triazine compound was added to the positive electrode mixture so that the content of the triazine compound was 0.1 mass% relative to the total positive electrode mixture. The positive electrode was prepared using the positive electrode mixture containing the triazine compound, thereby preparing a positive electrode containing the triazine compound.

[0142] (Preparation of electrolyte) The electrolyte was a mixture of dimethoxyethane (DME) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTFE) (mixture ratio: DME:TTFE = 20:80 volume%), with LiN(SO 2 F) 2 (LFSI) was dissolved to prepare a 1.2 M LFSI solution. When preparing an electrolyte solution containing a triazine compound, the triazine compound was added to the electrolyte solution so that the concentration of the triazine compound became a predetermined value shown in Table 1 below.

[0143] (Battery Assembly) Next, the positive electrode formed on the positive electrode current collector, the separator, and the negative electrode 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 current collector and the negative electrode, respectively, by ultrasonic welding, and then inserted into a laminate exterior body. Next, the above-mentioned electrolyte was injected into the exterior body. The exterior body was sealed to obtain a lithium secondary battery.

[0144] (Triazine compounds) As the triazine compound, compounds represented by the following formulae (I) to (V) were used. Hereinafter, for example, the compound represented by the following formula (I) will be referred to as "compound (I)" etc. [ka] [ka] [ka] [ka] [ka]

[0145] [Example 1] A lithium secondary battery was produced by the above-mentioned procedure, except that the negative electrode used had a surface coated with compound (I), and no triazine compound was added to the separator, positive electrode, or electrolyte.

[0146] [Examples 2 to 19] A lithium secondary battery was produced in the same manner as in Example 1. However, in each Example, the components (negative electrode, separator, positive electrode, or electrolyte) shown in Table 1 contained the triazine compound (any of compounds (I) to (V)) shown in Table 1. In the table, "-" means that each component does not contain a triazine compound. Also, "concentration (mass%)" means the concentration (mass%) of the triazine compound in the electrolyte. Therefore, for example, in Example 11, a lithium secondary battery was produced using an electrolyte containing 0.05 mass% of compound (I) and a negative electrode, a positive electrode, and a separator that did not contain a triazine compound.

[0147] [Comparative Example 1] As shown in Table 1, lithium secondary batteries were fabricated using the components of the battery that did not contain a triazine compound.

[0148] [Evaluation of capacity and cycle characteristics] The capacity and cycle characteristics of the lithium secondary batteries produced in each of the Examples and Comparative Examples were evaluated as follows.

[0149] The fabricated lithium secondary battery was CC charged at 3.2 mA until the voltage reached 4.2 V (initial charge), and then CC discharged at 3.2 mA until the voltage reached 3.0 V (hereinafter referred to as "initial discharge"). Next, the battery was CC charged at 13.6 mA until the voltage reached 4.2 V, and then CC discharged at 20.4 mA until the voltage reached 3.0 V, and this cycle was repeated 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") is shown in Table 1. Table 1 also shows the number of cycles at which the discharge capacity reached 80% of the initial capacity for each example (referred to as "cycles (times)" in the table).

[0150] [DC resistance measurement] The lithium secondary battery thus fabricated was CC-charged to 4.2 V at 5.0 mA, and then CC-discharged at 30 mA, 60 mA, and 90 mA for 30 seconds each. The lower limit voltage was set to 2.5 V, but in all cases, 2.5 V was not reached after 30 seconds of discharge. Between each discharge, CC charging was again performed at 5.0 mA to 4.2 V, and the next CC discharge was performed after the charging was completed. The current value I and voltage drop V obtained in the above manner were plotted, and the direct current resistance (DCR) (unit: Ω) was calculated from the slope of the IV characteristics obtained by linear approximation of each point. The results for each example are shown in Table 1.

[0151] [Table 1]

[0152] From Table 1, it can be seen that the examples containing a triazine compound have a higher number of cycles and are superior in cycle characteristics compared to Comparative Example 1 which does not contain a triazine compound. In addition, the examples containing a triazine compound have the same DC resistance compared to Comparative Example 1 which does not contain a triazine compound, and it can be seen that the rate performance is not deteriorated even when the triazine compound is contained. In other words, it can be seen that the lithium secondary battery of the present invention is superior in cycle characteristics and rate performance.

[0153] Furthermore, it can be seen from Table 1 that the embodiment in which the triazine compound is coated on the negative electrode or is contained in the electrolyte solution has particularly excellent cycle characteristics. [Industrial Applicability]

[0154] 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]

[0155] 100, 200, 300... lithium secondary battery, 110... positive electrode current collector, 120... positive electrode, 130... negative electrode, 140... separator, 210... negative electrode terminal, 220... positive electrode terminal, 310... solid electrolyte.

Claims

1. A lithium secondary battery, a positive electrode and a negative electrode including a negative electrode current collector having no negative electrode active material; Contains a compound having a 1,3,5-triazine ring skeleton (excluding 1,3,5-triazine-2,4,6-trithiol), The compound has a 1,3,5-triazine ring skeleton having substituents at all of the 2-, 4-, and 6-positions, one of the substituents is a thiol group; two of the substituents are selected from the group consisting of a monovalent hydrocarbon group optionally substituted with a halogen atom, a hydroxy group, an alkoxy group, and an amino group optionally substituted with an unsubstituted hydrocarbon group; The lithium secondary battery is a lithium secondary battery in which lithium metal is deposited on the surface of the negative electrode current collector, and charging and discharging are performed by electrolytic elution of the deposited lithium.

2. A lithium secondary battery, a positive electrode and a negative electrode including a negative electrode current collector having no negative electrode active material; Contains a compound having a 1,3,5-triazine ring skeleton (excluding 1,3,5-triazine-2,4,6-trithiol), The compound has a 1,3,5-triazine ring skeleton having substituents at all of the 2-, 4-, and 6-positions, two of the substituents are thiol groups; one of the substituents is selected from the group consisting of a monovalent hydrocarbon group optionally substituted with a halogen atom, a hydroxy group, and an alkoxy group; The lithium secondary battery is a lithium secondary battery in which lithium metal is deposited on the surface of the negative electrode current collector, and charging and discharging are performed by electrolytic elution of the deposited lithium.

3. A lithium secondary battery, a positive electrode and a negative electrode including a negative electrode current collector having no negative electrode active material; Contains a compound having a 1,3,5-triazine ring skeleton (excluding 1,3,5-triazine-2,4,6-trithiol), The compound has a 1,3,5-triazine ring skeleton having substituents at all of the 2-, 4-, and 6-positions, the substituent is selected from the group consisting of a monovalent hydrocarbon group optionally substituted with a halogen atom, a hydroxy group, and an alkoxy group; The lithium secondary battery is a lithium secondary battery in which lithium metal is deposited on the surface of the negative electrode current collector, and charging and discharging are performed by electrolytic elution of the deposited lithium.

4. A lithium secondary battery, a positive electrode and a negative electrode including a negative electrode current collector having no negative electrode active material; Contains a compound having a 1,3,5-triazine ring skeleton (excluding 1,3,5-triazine-2,4,6-trithiol), The compound is represented by the following formula (IV): The lithium secondary battery is a lithium secondary battery in which lithium metal is deposited on the surface of the negative electrode current collector, and charging and discharging are performed by electrolytic elution of the deposited lithium. 【Chemistry 1】

5. 5. The lithium secondary battery according to claim 1, further comprising a separator or a solid electrolyte disposed between the positive electrode and the negative electrode.

6. 6. The lithium secondary battery according to claim 1, wherein at least a portion of the compound is coated on at least a portion of a surface of the negative electrode facing the positive electrode.

7. Further comprising an electrolyte; 7. The lithium secondary battery according to claim 1, wherein the electrolyte contains the compound.

8. Further comprising an electrolyte; The lithium secondary battery according to any one of claims 1 to 7, wherein the electrolyte solution contains a compound having at least one of a monovalent group represented by the following formula (A) and a monovalent group represented by the following formula (B) as a solvent. 【Chemistry 2】 【Chemistry 3】 (In the formula, the wavy line represents a bonding site in a monovalent group.)

9. The lithium secondary battery according to any one of claims 1 to 8, wherein the negative electrode current collector 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 metal is formed on the surface of the negative electrode before initial charging and / or at the end of discharging.

11. 11. The lithium secondary battery according to claim 1, having an energy density of 350 Wh / kg or more.

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