Lithium-ion secondary battery

Abstract

To provide a lithium-ion secondary battery that achieves both output characteristics and energy density.SOLUTION: The lithium-ion secondary battery includes a negative electrode including niobium-titanium oxide as a negative electrode active material in a mixture layer and a non-aqueous electrolyte including lithium alkoxysulfonate represented by RSOOO-Li+ (wherein R is at least one material selected from the group consisting of OCH3 and OC2H5).SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In recent years, lithium-ion batteries with anodes using titanium oxide as the anode active material have been put to practical use. Titanium oxide has a higher potential relative to metallic lithium than carbon-based materials, but titanium oxide also has the drawback of having a low capacity per mass and a low energy density.

[0003] For this reason, monoclinic Nb-Ti composite oxides (hereinafter sometimes referred to as "TNO" or "niobium titanium oxide") such as TiNb2O7 have been investigated as negative electrode active materials. Negative electrodes using this TNO as the negative electrode active material in the composite layer (hereinafter sometimes referred to as "TNO negative electrodes") have a theoretical capacity of 387 mAh / g, which is equivalent to that of conventional carbon-based negative electrodes, and the use of this material may potentially solve the problem of low energy density, a drawback of using titanium oxides to date (see Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6636758 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the electrochemical behavior of this TNO anode is different from that of conventional titanium oxide anodes, and therefore simply replacing titanium oxide with TNO does not allow for the construction of a lithium-ion secondary battery that achieves both high output and high energy density.

[0006] In particular, TNO anodes exhibit a behavior different from that of conventional titanium oxides, in that a solid electrolyte interface (hereinafter sometimes referred to as "SEI film") forms during charging. This SEI film forms on the surface of the anode, leading to an increase in internal resistance. As a result, the high output that is a major feature of lithium-ion secondary batteries using titanium oxide as the anode active material cannot be achieved, resulting in a decline in output characteristics, which is a major factor hindering their practical application.

[0007] Although the details are unclear, it is thought that niobium (Nb) in the TNO anode acts as a catalyst in forming the SEI film, and unless this issue is resolved, lithium-ion secondary batteries using TNO anodes will not be practical. Furthermore, the formation of the SEI film is related to the material composition of the anode active material and the composition of the electrolyte, and if the electrolyte used in lithium-ion secondary batteries using conventional titanium oxides is applied directly to the TNO anode, it will result in a decrease in output characteristics.

[0008] Therefore, the present invention has been made in consideration of the above-mentioned problems, and an object of the present invention is to provide a lithium ion secondary battery that achieves both output characteristics and energy density. [Means for solving the problem]

[0009] In order to solve the above problems, the present inventors have investigated the electrolyte composition when a TNO negative electrode is used. As a result of extensive investigation, they have found that when a TNO negative electrode is used and a non-aqueous electrolyte containing a specific lithium alkoxysulfonate as an electrolyte additive, the effects unique to this combination are produced, and it is possible to increase the energy density of a lithium-ion secondary battery by about 1.7 times compared to when lithium titanate is used, without significantly reducing the output characteristics of the battery. This finding led to the completion of the present invention.

[0010] In order to solve the above problems, the lithium ion secondary battery of the present invention comprises a negative electrode containing niobium titanium oxide as a negative electrode active material in a mixture layer, and a negative electrode containing niobium titanium oxide as a negative electrode active material in a mixture layer. - Li +(wherein R is at least one substance selected from the group consisting of OCH3 and OC2H5), and a non-aqueous electrolyte solution containing lithium alkoxysulfonate represented by the formula:

[0011] The content of the lithium alkoxysulfonate in the non-aqueous electrolyte solution is preferably 0.5 to 2.0% by mass. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a lithium ion secondary battery that achieves both output characteristics and energy density. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic cross-sectional view of a coin-type battery, which is an example of the lithium ion secondary battery of the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional view of a stacked battery, which is an example of the lithium ion secondary battery of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] The following provides examples of the forms and configurations of the present invention, but the present invention is not limited to these. All aspects that are in line with the intentions of the claims, the means for solving the problems, the effects of the invention, etc., are included in the present invention.

[0015] The present invention relates to a lithium ion secondary battery using a TNO negative electrode, and has the following two features.

[0016] The first point is the use of a negative electrode containing niobium titanium oxide in a composite layer as the negative electrode active material. While the TNO negative electrode has been described above, the present invention aims to solve the problem by utilizing the unique effects of the TNO negative electrode and the electrolyte additive. Therefore, the effects of the present invention cannot be obtained with lithium ion secondary batteries that use lithium titanate as the negative electrode active material, let alone carbon materials, which are typical negative electrode active materials for lithium ion secondary batteries.

[0017] The second point is the use of lithium alkoxysulfonate (see [Chemical Formula 1]) as an electrolyte additive. In the present invention, by using lithium alkoxysulfonate shown in [Chemical Formula 1] as an electrolyte additive, this additive penetrates into the SEI coating, lowering the coating density and thereby achieving the effect of reducing internal resistance. Therefore, the decomposition of the lithium alkoxysulfonate itself is not intended by the present invention.

[0018] [ka]

[0019] Furthermore, in the present invention, the content of lithium alkoxysulfonate in the non-aqueous electrolyte is preferably 0.5 to 2.0 mass%. As described above, lithium alkoxysulfonate exerts its effect by penetrating into the SEI coating. Therefore, if the content is less than 0.5 mass%, the number of additive molecules penetrating into the SEI coating will also be reduced. As a result, the coating density will not decrease, and the effect of reducing internal resistance may not be achieved. On the other hand, if the content is more than 2.0 mass%, due to the solubility of lithium alkoxysulfonate in the non-aqueous electrolyte, some of the lithium alkoxysulfonate may remain undissolved depending on the temperature of the non-aqueous electrolyte, making it impossible to prepare a non-aqueous electrolyte with a concentration greater than 2.0 mass%.

[0020] Even more preferably, if the content of lithium alkoxysulfonate in the non-aqueous electrolyte is 1.0 to 2.0 mass %, the effect of reducing internal resistance can be sufficiently obtained, and the solubility in the non-aqueous electrolyte can also be sufficiently ensured.

[0021] (Method for determining lithium alkoxysulfonate in non-aqueous electrolyte) The content of lithium alkoxysulfonate in the non-aqueous electrolyte can be determined by preparing a calibration curve as follows, and measuring the non-aqueous electrolyte as a sample by ion chromatography.

[0022] <Creating a calibration curve> A calibration curve was prepared by appropriately changing the amount of lithium alkoxysulfonate.

[0023] <Quantitative method for lithium alkoxysulfonate> If the non-aqueous electrolyte solution to be quantified, whose lithium alkoxysulfonate content is unknown, is measured by ion chromatography, and a peak appears at the same retention time as the solution for which the calibration curve was prepared, the electrolyte solution contains lithium alkoxysulfonate. The amount of addition can be determined from the peak area measured by ion chromatography and the calibration curve.

[0024] [Lithium-ion secondary battery] The lithium ion secondary battery of the present invention can be composed of, for example, a positive electrode, a negative electrode, a separator, a non-aqueous electrolyte, terminals, and an exterior body, all of which are described below.

[0025] <Positive electrode> The positive electrode is composed of, for example, a positive electrode active material composite electrode layer and a current collector.

[0026] (Positive active material composite electrode layer) The positive electrode active material composite electrode layer can be composed of, for example, a positive electrode active material, a conductive material, a binder, and a solvent. 1 / 3 Ni 1 / 3 Mn 1 / 3 O2, LiCo 0.15 Ni 0.8 Al 0.05 O2, LiNi 0.5 Mn 1.5 Examples include compounds such as LiNi. In a more preferred embodiment, the positive electrode active material can contain a lithium composite oxide in which the atomic ratio of Ni is 50% or more. Examples of such oxides include oxides in which the atomic ratio of nickel is 50% or more among the cation species other than lithium contained as the positive electrode active material in the positive electrode active material composite electrode layer. Specifically, LiNi 0.5 Co 0.2 Mn0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, and LiCo 0.15 Ni 0.80 Al 0.05 In the present invention, high energy density is mentioned as an issue, and therefore, a high energy density can be achieved by increasing the battery capacity, but a material with a nickel atomic ratio of 50% or more is characterized by a large unit capacity, and by using the above oxide, the amount of the positive electrode active material composite electrode layer in the positive electrode can be reduced and the electrode thickness can be made thinner, thereby achieving a high energy density.

[0027] For example, when graphite is used as the negative electrode active material and a nickel-containing oxide is used as the positive electrode active material, the nickel content in the positive electrode active material has a small effect on energy density. This is because lithium-containing graphite has a reduction potential nearly equal to that of lithium, making it the most noble of all materials. On the other hand, the oxidation potential, which varies by approximately 0.1 V depending on the amount of nickel in the positive electrode active material, is small. Therefore, while the average discharge voltage for a graphite negative electrode varies only within a range of approximately 4.3 ± 0.05 V, for a TNO negative electrode, it varies within a range of approximately 2.8 ± 0.05 V. Therefore, the effect of the nickel content in the positive electrode active material on energy density becomes significant.

[0028] Furthermore, the reason why a nickel atomic ratio of 50% or more is preferred is that a nickel atomic ratio of less than 50% not only makes it difficult to achieve a high capacity on the positive electrode side, but also takes into consideration the early loss of the benefits of the present invention, which is thought to be due to the disintegration of active material particles caused by the elution of manganese and aluminum contained in the positive electrode active material. In this invention, TNO is used as the negative electrode active material, making it possible to use esters and ethers, which are not usable in general lithium-ion batteries, as electrolyte solvents. At the same time, these components have a high affinity for manganese and aluminum ions, and are thought to be more susceptible to elution than general electrolytes containing only carbonate. Although the details are unclear, it is thought that due to the relationship between the positive charge of manganese and aluminum and the electronegativity with carbon, the electrons used in the covalent bond lean toward oxygen, resulting in δ - It is thought that the charged ester oxygen or ether oxygen coordinates to form a complex, thereby increasing the stability of manganese and aluminum in the electrolyte.

[0029] The conductive material is not particularly limited in the present invention, and known or commercially available materials such as carbon black such as acetylene black or ketjen black, carbon nanotubes, carbon fibers, activated carbon, and graphite can be used.

[0030] There are no particular limitations on the binder, and known or commercially available binders can be used, such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinylpyrrolidone (PVP), polyvinyl chloride (PVC), polyethylene (PE), polypropylene (PP), ethylene-propylene copolymer, styrene-butadiene rubber (SBR), and acrylic resin.

[0031] The solvent is not particularly limited in the present invention, and various solvents can be selected depending on the positive electrode active material or binder used. Specifically, when PVDF is used as the binder, it is preferable to use N-methyl-2-pyrrolidone as the solvent, while when a rubber-based binder such as styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinyl alcohol, or carboxymethyl cellulose (CMC) is used, water is suitable as the solvent.

[0032] (current collector) The current collector is not particularly limited in the present invention, but aluminum foil is generally used as a current collector for the positive electrode of a lithium ion battery, and porous aluminum current collectors may also be used depending on the application.

[0033] The positive electrode can be produced, for example, by the following method. First, a positive electrode active material, a conductive additive, a binder, and the like are dispersed in a solvent to prepare a positive electrode slurry. Next, the positive electrode slurry is applied to one or both surfaces of a positive electrode current collector, and then dried, for example, at 80°C under vacuum to form a positive electrode active material composite electrode layer. A positive electrode can be produced by these steps.

[0034] Although the positive electrode described above is composed of a positive electrode active material composite electrode layer and a current collector, the present invention is not limited to this, and when a half cell is used instead of a full cell, for example, metallic lithium may be used as a counter electrode instead of the positive electrode.

[0035] <Negative electrode> The negative electrode is composed of a negative electrode active material composite electrode layer and a current collector.

[0036] (Negative active material composite electrode layer) The negative electrode active material composite electrode layer (sometimes referred to as "composite layer" in this specification) is composed of a negative electrode active material, a conductive material, a binder, and a solvent. In the present invention, only niobium titanium oxides, which are monoclinic Nb-Ti composite oxides, are applicable as the negative electrode active material, and in particular, TiNb2O7 and Ti2Nb 10 O 29 It is highly effective in the following cases.

[0037] The content of niobium titanium oxide in the negative electrode active material composite electrode layer is preferably 80% to 95% by mass. Furthermore, the average secondary particle diameter of the niobium titanium oxide used is preferably 5 μm to 20 μm. Furthermore, the average secondary particle diameter in this specification refers to the particle diameter at 50% of the cumulative value in the particle size distribution determined by laser diffraction / scattering.

[0038] The conductive material is not particularly limited in the present invention, and known or commercially available materials such as carbon black such as acetylene black or ketjen black, carbon nanotubes, carbon fibers, activated carbon, and graphite can be used.

[0039] There are no particular limitations on the binder, and known or commercially available binders can be used, such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinylpyrrolidone (PVP), polyvinyl chloride (PVC), polyethylene (PE), polypropylene (PP), ethylene-propylene copolymer, styrene-butadiene rubber (SBR), and acrylic resin.

[0040] The solvent used for the binder is not particularly limited in the present invention, and various solvents can be selected depending on the active material or binder used. Specifically, when PVDF is used as the binder, it is preferable to use N-methyl-2-pyrrolidone as the solvent, while when a rubber-based binder such as styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinyl alcohol, or carboxymethyl cellulose (CMC) is used, water is suitable as the solvent.

[0041] (current collector) The current collector is not particularly limited in the present invention, but aluminum foil is suitable as the current collector for the TNO negative electrode, and porous aluminum current collectors may also be used depending on the application.

[0042] The negative electrode can be produced, for example, by the following method. First, niobium titanium oxide, a conductive additive, a binder, and the like are dispersed in a solvent to prepare a negative electrode slurry. Next, the negative electrode slurry is applied to one or both surfaces of a negative electrode current collector, and then dried, for example, at 80°C under vacuum to form a negative electrode active material composite electrode layer. The negative electrode can be produced by these steps.

[0043] <Separator> The separator interposed between the positive electrode and the negative electrode can be a commonly used nonwoven fabric or porous sheet made of a synthetic resin such as a polyolefin resin such as PE (polyethylene) or PP (polypropylene), or PTFE (polytetrafluoroethylene). The nonwoven fabric or porous sheet may have a single layer or a multilayer structure.

[0044] <Non-aqueous electrolyte> The non-aqueous electrolyte solution contains an electrolyte, an electrolyte solvent, and the above-mentioned lithium alkoxysulfonate as an electrolyte additive, and is a non-aqueous electrolyte solution that can be used in the lithium ion secondary battery of the present invention.

[0045] The electrolyte is not particularly limited, but is preferably an electrolyte salt containing lithium ions commonly used in lithium ion secondary batteries. For example, lithium salts such as LiBF4 and LiPF6 can be used. These electrolytes may be used alone or in combination of two or more. The concentration of the electrolyte salt is not particularly limited, and may be, for example, about 0.3 M (mol / L) to 3 M relative to the electrolyte solvent.

[0046] More specifically, an electrolyte containing, for example, 0.5M to 3M LiPF6 and / or LiBF4, but not containing LiFSI, LiBOB, or LiPO2F2, can be used.

[0047] If the content of LiPF6 and / or LiBF4 is less than 0.5M, the amount of ions in the electrolyte may be insufficient to achieve high output. If the content is more than 3M, the viscosity of the electrolyte may become too high, which may increase penetration into the separator and the resistance of the electrolyte, making it difficult to achieve high output. Therefore, taking into consideration high output and the resistance of the electrolyte, the content is preferably 0.5M to 3M.

[0048] Furthermore, in the present invention, it is preferable not to include LiFSI, LiBOB, or LiPO2F2. This is because these electrolytes all undergo reductive decomposition on the anode side during charging, forming an excessive SEI, making it impossible to achieve the high output that is the effect of the present invention. Although the details are unclear, the niobium in TNO, the anode active material in the present invention, acts as a catalyst and may specifically react and decompose with carbonate, a component of the electrolyte, to produce hydrofluoric acid.

[0049] In the present invention, high-power characteristics are mentioned as a problem, and the ionic conductivity of the electrolyte is an important parameter in solving this problem. The ionic conductivity of the electrolyte will be discussed later, but this is an approach from the nonaqueous solvent side, and the parameters that have the greatest impact on the ionic conductivity of the electrolyte are the type and amount of electrolyte. In particular, LiPF6 and / or LiBF4 have large anions, allowing for good ion dissociation, making it possible to construct high-power lithium-ion batteries. Furthermore, they are suitable for the present invention because they are less likely to adversely affect TNO, which is used as the negative electrode active material in the present invention.

[0050] As the electrolyte solvent, a non-aqueous electrolyte used in an electrolyte-based lithium ion secondary battery can be used.

[0051] The non-aqueous electrolyte preferably contains a cyclic solvent and / or a chain solvent as the non-aqueous solvent. The cyclic solvent preferably contains a cyclic carbonate and / or a cyclic ester, and the chain solvent preferably contains a chain carbonate and / or a chain ether. The cyclic carbonate is related to the degree of dissociation of the electrolyte components, and the chain carbonate is related to the viscosity of the electrolyte.

[0052] Cyclic carbonates have a high dielectric constant, which contributes to improving the lithium ion conductivity of electrolytes. The Born equation, which describes the solvation energy of ionic species in electrolytes, includes the dielectric constant, and as the dielectric constant increases, the Gibbs free energy becomes more negative. A negative Gibbs free energy indicates that the reaction proceeds spontaneously, and the larger its absolute value, the more likely the reaction is to proceed. Therefore, when cyclic carbonates are included in non-aqueous solvents, the dissociation of the cation and anion components of the electrolyte is promoted, increasing the proportion of the electrolyte present as ions in the non-aqueous solvent, leading to improved lithium ion conductivity.

[0053] Furthermore, since this lithium ion conductivity is a parameter directly related to the rate characteristics of a battery, it is preferable to include a cyclic carbonate in the non-aqueous solvent. Furthermore, chain carbonates are related to the viscosity of the non-aqueous solvent. As mentioned above, cyclic carbonates have a high dielectric constant, but they often also have a high viscosity. The viscosity of the non-aqueous solvent is directly related to the fluidity of the electrolyte and contributes to the permeability of the electrolyte into the separator. If areas of the separator where the electrolyte does not permeate are created, current will not flow through those areas, preventing the battery from achieving its inherent performance and resulting in a deterioration in all battery performance. Chain carbonates can be used to prevent this, and although they do not have a high dielectric constant, they are characterized by low viscosity. As such, since cyclic and chain carbonates have different roles, it is preferable to include both as non-aqueous solvent components to construct better lithium ion batteries. In the present invention, it is preferable to include at least one of these components.

[0054] Furthermore, γ-butyrolactone, a cyclic ester, is a compound that possesses the properties of both a cyclic carbonate and an ester. While γ-butyrolactone alone could be used in lithium-ion batteries as an electrolyte solvent component, it has not been used until now because graphite is often used as the negative electrode material, and in this case, γ-butyrolactone molecules may enter between the graphite layers, potentially promoting graphite decomposition. The present invention requires the use of TNO as the negative electrode active material, which eliminates the aforementioned problem of γ-butyrolactone entering between the active material layers, allowing the inherent performance of γ-butyrolactone to be fully demonstrated.

[0055] The cyclic carbonate is preferably ethylene carbonate and / or propylene carbonate, and does not include vinylene carbonate, fluoroethylene carbonate, or vinylethylene carbonate.

[0056] Among cyclic carbonates, the effects of the present invention are enhanced when ethylene carbonate and propylene carbonate are used. Ethylene carbonate has an extremely high dielectric constant among cyclic carbonates, making it an ideal material for maintaining high-rate performance. Propylene carbonate also has properties similar to those of ethylene carbonate, but like γ-butyrolactone, propylene carbonate has not been used until now because, when the negative electrode active material is graphite, molecules may enter between the layers, promoting decomposition. However, the present invention requires the use of TNO instead of graphite as the negative electrode active material, which eliminates the problem of molecules entering between the active material layers as described above, allowing the inherent performance of propylene carbonate to be fully demonstrated.

[0057] In the present invention, it is preferable that vinylene carbonate, fluoroethylene carbonate, and vinylethylene carbonate are not contained. The reason for this is that the SEI formation specific to the TNO negative electrode is involved, and if these carbonates are contained, there is a risk of SEI over-formation to the extent that it inhibits current flow, resulting in a decrease in battery capacity and rate characteristics.

[0058] The chain carbonate is preferably at least one selected from dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

[0059] As described above, the chain carbonate is used for the purpose of reducing the viscosity of the electrolyte solution. Chain carbonates having methyl or ethyl groups have extremely low viscosity among chain carbonates, and therefore, by using such chain carbonates, the high rate characteristics that are the effect of the present invention can be fully exhibited.

[0060] The non-aqueous electrolyte may also contain 0.1% by mass to 5% by mass of at least one selected from cyclic ethers: 1,3-dioxane, adiponitrile, and succinonitrile.

[0061] 1,3-Dioxane has advantageous characteristics as an electrolyte for high-power batteries, such as a lower viscosity than chain carbonates and a high dielectric constant, but it has a fatal drawback of having an oxidative decomposition potential of approximately 2.2 V, which is about 1 V lower than chain carbonates, and it is easily oxidatively decomposed on the positive electrode side, so it has not been used much in lithium-ion battery electrolytes until now. However, in the present invention, it was found that a content in the range of 0.1% by mass to 5% by mass does not adversely affect battery performance, and by including this compound in an appropriate amount as an electrolyte component, the characteristics of a lower viscosity than chain carbonates and a high dielectric constant can be utilized, resulting in effective results in achieving both high energy density and high power characteristics, which are the effects of the present invention.

[0062] Adiponitrile and succinonitrile are compounds known as additives for improving safety or reliability, and it is also preferable for these compounds to be contained within the above-mentioned mass% range in the present invention. These compounds coordinate with metal ions eluted from the current collector and active material to form complexes, which are thought to deactivate highly active metal ion species and enable the suppression of leakage current and gas generation, leading to the long-term maintenance of the effects of the present invention.

[0063] In particular, in the present invention, as described above, the positive electrode active material composite electrode layer can contain a lithium composite oxide having an atomic ratio of Ni of 50% or more as the positive electrode active material, and due to its ionization tendency, nickel tends to be more likely to dissolve out of the cation species contained in the positive electrode active material. In the present invention, by including such dinitriles in the electrolyte, nickel ions generated in large quantities during overcharge are captured in the form of a complex, preventing battery deterioration, and thereby enabling the effects of the present invention, namely, high energy density and high output characteristics, to be achieved for a long period of time.

[0064] However, because 1,3-dioxane, adiponitrile, and succinonitrile have strong coordinating power, if their content in the non-aqueous electrolyte exceeds 5% by mass, a high proportion of them will capture ions necessary for charging and discharging, resulting in a decrease in cycle characteristics, and therefore, as mentioned above, it is recommended to use them in the range of 0.1% by mass to 5% by mass.

[0065] In addition to the cyclic carbonates and cyclic esters, sulfolane can be used as the electrolyte solvent. In addition, dimethoxyethane, diethoxyethane, various glymes, etc. can be used as the chain ethers in the chain solvent by mixing them with the main solvent.

[0066] The effect of including lithium alkoxysulfonate as an electrolyte additive is as described above. Examples of lithium alkoxysulfonate include lithium methoxysulfonate and lithium ethoxysulfonate. The electrolyte additive contains at least one of these. Specific combinations include lithium methoxysulfonate alone, lithium ethoxysulfonate alone, and a combination containing both lithium methoxysulfonate and lithium ethoxysulfonate. The total content of all lithium alkoxysulfonates in the non-aqueous electrolyte is 0.5% to 2.0% by mass, preferably 1.0% to 2.0% by mass. The saturated concentration of lithium methoxysulfonate is 2.0% by mass, and if the total additive concentration is greater than 2.0% by mass, it is mixed with lithium ethoxysulfonate. Furthermore, RSOOO - Li + The substance where R is OCH3 is lithium methoxysulfonate, and the substance where R is OC2H5 is lithium ethoxysulfonate.

[0067] Terminal Metal is generally used for the terminals. There are no restrictions on the material or shape, but in the present invention, aluminum and copper are suitable as materials, and a shape that will not be deformed by wiring or the like is suitable.

[0068] <Exterior body> The exterior body can be made of, for example, a can or a laminate. There are no restrictions on the material or shape, but stainless steel is a suitable can material, and a laminate material made of aluminum foil coated with a plastic film is a suitable material. The shape can be changed depending on the cell capacity, and generally, the larger the cell capacity, the larger the shape.

[0069] The shape of the lithium ion secondary battery of the present invention is not particularly limited, but examples thereof include coin type, button type, sheet type, laminate type, cylindrical type, prismatic type, and flat type.

[0070] The structure of the lithium ion secondary battery of the present invention will be described below with reference to the drawings, taking a coin-type lithium ion secondary battery as an example. Figure 1 is a schematic cross-sectional view of a coin-type battery shown as an example of the lithium ion secondary battery of the present invention.

[0071] The coin-type lithium-ion secondary battery 1 includes a positive electrode 2, a negative electrode 3, and a separator 4 disposed between the positive electrode 2 and the negative electrode 3. The positive electrode 2, the negative electrode 3, and the separator 4 are housed between a first external terminal 5 located on the lower side and a second external terminal 6 located on the upper side. The contact portions of the first external terminal 5 and the second external terminal 6 are insulated by a gasket 7.

[0072] The positive electrode 2 is composed of a positive electrode current collector 21 located on the inner surface of the first external terminal 5 and connected thereto, and a positive electrode active material composite electrode layer 22 provided on the surface of the positive electrode current collector 21 facing the separator 4. The negative electrode 3 is composed of a negative electrode current collector 31 located on the inner surface of the second external terminal 6 and connected thereto, and a composite material layer 32 provided on the surface of the negative electrode current collector 31 facing the separator 4. The separator 4 is impregnated with, for example, a non-aqueous electrolyte. The second external terminal 6 is inserted into the first external terminal 5 with its lower end and both side surfaces wrapped in gaskets 7, and the lower open end of the first external terminal 5 is bent toward the gasket 7 to crimp and fix the second external terminal 6 to the first external terminal 5, and the abutting portions of the first external terminal 5 and the second external terminal 6 are insulated by the gasket 7.

[0073] Next, with reference to FIG. 2, a stacked battery, which is an example of the lithium ion secondary battery of the present invention, will be described.

[0074] The laminated lithium secondary battery 100 includes a bag-shaped exterior body 200 made of laminate film. An electrode group 300 having a laminated structure is housed inside the exterior body 200. The laminate film has a structure in which, for example, multiple (e.g., two) plastic films are laminated together with a metal foil such as aluminum foil sandwiched between them. One of the two plastic films is a heat-sealable resin film. The exterior body 200 is made by stacking two laminate films with the heat-sealable resin films facing each other, and housing the electrode group 300 between these laminate films. The two laminate film portions around the electrode group 300 are heat-sealed to each other to seal the electrode group 300, thereby hermetically housing the electrode group 300.

[0075] The electrode group 300 has a structure in which a positive electrode 400, a negative electrode 500, and a separator 600 interposed between the positive electrode 400 and the negative electrode 500 are stacked in multiple layers, with the negative electrode 500 positioned as the outermost layer and the separator 600 positioned between the negative electrode 500 and the inner surface of the exterior body 200. The positive electrode 400 is composed of a positive electrode current collector 410 and a positive electrode active material composite electrode layer 420 formed on both sides of the current collector 410. The negative electrode 500 is composed of a negative electrode current collector 510 and a composite layer 520 formed on both sides of the current collector 510.

[0076] The positive electrode 400 has a positive electrode lead 700 in which a positive electrode current collector 410 extends from, for example, the left side surface of the positive electrode active material composite electrode layer 420. The positive electrode leads 700 are bundled at their tip ends within the exterior body 200 and joined to each other. One end of a positive electrode tab 800 is joined to the joint of the positive electrode lead 700, and the other end extends to the outside through a sealed portion of the exterior body 200. The negative electrode 500 has a negative electrode lead 900 in which a negative electrode current collector 510 extends from, for example, the right side surface of the composite layer 520. The negative electrode leads 900 are bundled at their tip ends within the exterior body 200 and joined to each other. One end of a negative electrode tab 1000 is joined to the joint of the negative electrode lead 900, and the other end extends to the outside through a sealed portion of the exterior body 200. A nonaqueous electrolyte is injected into the exterior body 200. The injection portion of the exterior body 200 is sealed after the non-aqueous electrolyte is injected. [Example]

[0077] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0078] <Example 1-1> (1) Preparation of electrolyte LiPF6 was dissolved in a solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 3:7 so that the concentration of LiPF6 was 1.0 M, and 0.5% by weight of lithium methoxysulfonate was further added to the solution, followed by stirring with a magnetic stirrer for 1 hour to prepare the electrolyte solution of the present invention.

[0079] (2) Preparation of test cell TiNb2O7 particles obtained by hydrothermal synthesis were used as the active material, and the active material, conductive material, and binder were mixed in a solvent to prepare a slurry. Acetylene black manufactured by Denka Corporation was used as the conductive material, and KF polymer manufactured by Kureha Corporation was used as the binder. The mass ratio of the active material, conductive material, and binder was 85:10:5. N-methylpyrrolidone manufactured by Kanto Chemical Co., Ltd. was used as the solvent. The obtained slurry was applied to one side of a 20 μm thick aluminum foil with a basis weight of 50 g / m 2 After coating, the mixture was pressed, punched out to a diameter of 13 mm, and dried to evaporate the solvent, thereby obtaining a negative electrode.

[0080] The resulting negative electrode, a Φ14 lithium metal counter electrode, and a Φ15 glass separator were placed inside the exterior of a 2032-type coin cell, with the coated surface of the negative electrode facing the lithium metal through the separator, and the prepared electrolyte was added. After placing the lid, the periphery was crimped using a crimping machine to create a test cell.

[0081] (3) Charge / discharge test Charge and discharge tests were performed using a charge and discharge tester (TOSCAT-3000) manufactured by Toyo Systems Co., Ltd. To measure the discharge capacity, the fabricated test cell was first charged at a constant current / constant voltage of 0.1 ItA to 1.5 V and then left for 15 minutes. It was then discharged at a constant current of 0.1 ItA to 2.5 V, yielding a capacity of 252 mAh / g of active material. The cell was then charged at a constant current / constant voltage of 0.1 ItA to 1.5 V, left for 15 minutes, and then discharged at 5.0 ItA, yielding a capacity ratio of 89% vs. 0.1 ItA. Here, "89% vs. 0.1 ItA" refers to the discharge capacity ratio at 5.0 ItA relative to 0.1 ItA, and the same applies below. These results are shown in the table under "5.0 ItA Discharge Capacity Ratio."

[0082] <Example 1-2> A test cell was prepared and tested in the same manner as in Example 1-1, except that no lithium methoxysulfonate was added to the electrolyte and the amount of lithium ethoxysulfonate added was 0.5 wt %. A discharge capacity of 250 mAh / g-active material and a capacity ratio of 87% vs. 0.1 ItA were obtained.

[0083] <Examples 1-3> A test cell was prepared and tested in the same manner as in Example 1-1, except that no lithium methoxysulfonate was added to the electrolyte and the amount of lithium ethoxysulfonate added was 1.0 wt %. A discharge capacity of 250 mAh / g-active material and a capacity ratio of 87% vs. 0.1 ItA were obtained.

[0084] <Examples 1-4> A test cell was prepared and tested in the same manner as in Example 1-1, except that no lithium methoxysulfonate was added to the electrolyte and the amount of lithium ethoxysulfonate added was 1.5 wt %. A discharge capacity of 249 mAh / g-active material and a capacity ratio of 87% vs. 0.1 ItA were obtained.

[0085] <Examples 1-5> A test cell was prepared and tested in the same manner as in Example 1-1, except that the amount of lithium methoxysulfonate added to the electrolyte was 0.5 wt % and the amount of lithium ethoxysulfonate added was 0.5 wt %, and a discharge capacity of 251 mAh / g-active material and a capacity ratio of 85% vs. 0.1 ItA were obtained.

[0086] <Examples 1-6> A test cell was prepared and tested in the same manner as in Examples 1-5, except that the amount of lithium ethoxysulfonate added to the electrolyte was 1.0 wt %. A discharge capacity of 249 mAh / g of active material and a capacity ratio of 91% vs. 0.1 ItA were obtained.

[0087] <Examples 1-7> A test cell was prepared and tested in the same manner as in Examples 1-5, except that the amount of lithium methoxysulfonate added to the electrolyte was 0.2 wt % and the amount of lithium ethoxysulfonate added was 0.3 wt %, and a discharge capacity of 248 mAh / g-active material and a capacity ratio of 88% vs. 0.1 ItA were obtained.

[0088] <Example 1-8> A test cell was prepared and tested in the same manner as in Examples 1-5, except that the amount of lithium ethoxysulfonate added to the electrolyte was 1.5 wt %. A discharge capacity of 245 mAh / g of active material and a capacity ratio of 90% vs. 0.1 ItA were obtained.

[0089] <Examples 1-9> A test cell was prepared and tested in the same manner as in Examples 1-5, except that the amount of lithium methoxysulfonate added to the electrolyte was 0.4 wt %. A discharge capacity of 250 mAh / g-active material and a capacity ratio of 78% vs. 0.1 ItA were obtained.

[0090] <Examples 1-10> A test cell was prepared and tested in the same manner as in Examples 1-5, except that no lithium methoxysulfonate was added to the electrolyte and the amount of lithium ethoxysulfonate added was 0.4 wt %. A discharge capacity of 249 mAh / g-active material and a capacity ratio of 79% vs. 0.1 ItA were obtained.

[0091] <Comparative Example 1> A test cell was prepared and tested in the same manner as in Example 1-1, except that an electrolyte solution without lithium methoxysulfonate was used. A discharge capacity of 247 mAh / g-active material and a capacity ratio of 70% vs. 0.1 ItA were obtained.

[0092] <Conventional Example 1> A test cell was prepared and tested in the same manner as in Example 1-1, except that lithium titanate was used as the negative electrode active material particles and an electrolyte solution without lithium methoxysulfonate was used. A discharge capacity of 150 mAh / g-active material and a capacity ratio of 99% vs. 0.1 ItA were obtained.

[0093] The results of charge / discharge tests for Examples 1-1 to 1-10, Comparative Example 1, and the Conventional Example are shown in Table 1. The discharge capacities at 0.1 ItA were approximately 1.7 times larger in the Examples and Comparative Examples than in the Conventional Example, demonstrating that the TNO active materials used in the Examples and Comparative Examples are advantageous for achieving high energy densities in lithium-ion batteries. In the overall evaluation section of Table 1, a case in which the 0.1 ItA discharge capacity was higher than 240 mAh / g and the ratio of the 0.1 ItA discharge capacity to the 5.0 ItA discharge capacity was 80 or more was evaluated as ⊚; a case in which the 0.1 ItA discharge capacity was higher than 200 mAh / g and the ratio of the 0.1 ItA discharge capacity to the 5.0 ItA discharge capacity was 75 or more was evaluated as ◯, although inferior to ⊚; and all other cases were evaluated as ×. The same evaluations were also conducted for the overall evaluation section of the other tables below unless otherwise specified.

[0094] [Table 1]

[0095] Examples 1-1 to 1-8 satisfy claims 1 and 2 of the present invention. Compared to Conventional Example 1, the 0.1 ItA discharge capacities of Examples 1-1 to 1-8 are at least 95 mAh / g greater than the 0.1 ItA discharge capacity of Conventional Example 1. Compared to Comparative Example 1, the 0.1 ItA discharge capacities of Examples 1-1 to 1-8 are comparable to that of Comparative Example 1, but the 5.0 ItA discharge capacity ratios are at least 15% greater than the 5.0 ItA discharge capacity ratio of Comparative Example 1. This result demonstrates the compatibility of output characteristics and energy density, which are the effects of the present invention. Furthermore, Examples 1-9 and 1-10 are included in claim 1 but not claim 2. Although the 0.1 ItA discharge capacity of Examples 1-9 and 1-10 was similar to that of Comparative Example 1, the 5.0 ItA discharge capacity ratio of Examples 1-9 and 1-10 was improved by at least 8% compared to Comparative Example 1, and although it was inferior to Examples 1-1 to 1-8, the effect was confirmed.

[0096] From the above, it was found that in all of the examples, both the output characteristics and energy density, which are the effects of the invention, were achieved, but the effect of the invention was greater in the range included in claim 2. Furthermore, lithium methoxysulfonate does not dissolve when added alone up to 2.0 M without adding lithium ethoxysulfonate, so experiments were conducted up to the saturated concentration of 0.5 M. Lithium ethoxysulfonate does not dissolve when added alone up to 2.0 M without adding lithium methoxysulfonate, so experiments were conducted up to the saturated concentration of 1.5 M.

[0097] <Example 2-1> A test cell was prepared and tested in the same manner as in Example 1-1, except that the ethylene carbonate in the electrolyte was replaced with propylene carbonate (PC). A discharge capacity of 252 mAh / g-active material and a capacity ratio of 86% vs. 0.1 ItA were obtained.

[0098] <Example 2-2> A test cell was prepared and tested in the same manner as in Example 1-1, except that the solvent component in the electrolyte was γ-butyrolactone (GBL). A discharge capacity of 247 mAh / g-active material and a capacity ratio of 90% vs. 0.1 ItA were obtained.

[0099] <Example 2-3> A test cell was prepared and tested in the same manner as in Example 1-1, except that ethylene carbonate in the electrolyte was replaced with γ-butyrolactone, and a discharge capacity of 255 mAh / g-active material and a capacity ratio of 88% vs. 0.1 ItA were obtained. Table 2 shows the results of Examples 2-1 to 2-3.

[0100] <Example 2-4> A test cell was prepared and tested in the same manner as in Example 1-1, except that the ethylene carbonate in the electrolyte was replaced with propylene carbonate and the dimethyl carbonate in the electrolyte was replaced with γ-butyrolactone. A discharge capacity of 250 mAh / g-active material and a capacity ratio of 85% vs. 0.1 ItA were obtained. Table 2 shows the results of Examples 2-1 to 2-4.

[0101] [Table 2]

[0102] All levels of Examples 2-1 to 2-4 demonstrated the effect of the present invention, which is to achieve both output characteristics and energy density. These electrolyte solvents are liquid at room temperature, and GBL and DMC have low viscosity, so it is presumed that the above configuration did not adversely affect performance.

[0103] <Example 3-1> A test cell was prepared and tested in the same manner as in Example 1-1, except that propylene carbonate was added to the electrolyte and the volume ratio of ethylene carbonate, dimethyl carbonate, and propylene carbonate was 1.5:7:1.5. A discharge capacity of 245 mAh / g of active material and a capacity ratio of 88% vs. 0.1 ItA were obtained. Table 3 shows the results of Examples 3-1, 1-1, and 2-1.

[0104] [Table 3]

[0105] Example 3-1 is a system in which two cyclic carbonates, EC and PC, were added to the electrolyte, and the results demonstrated the effects of the present invention. EC is a solid at room temperature and becomes a highly viscous liquid when melted at around 40°C, but this electrolyte system also contains a low-viscosity chain carbonate, and it is believed that the results were satisfactory within the scope of the electrolyte composition.

[0106] <Example 4-1> A test cell was prepared and tested in the same manner as in Example 1-1, except that ethyl methyl carbonate (EMC) was used as the chain carbonate in the electrolyte, and a discharge capacity of 248 mAh / g-active material and a capacity ratio of 90% vs. 0.1 ItA were obtained.

[0107] <Example 4-2> A test cell was prepared and tested in the same manner as in Example 1-1, except that diethyl carbonate (DEC) was used as the chain carbonate in the electrolyte, and a discharge capacity of 248 mAh / g-active material and a capacity ratio of 88% vs. 0.1 ItA were obtained.

[0108] <Example 4-3> A test cell was prepared and tested in the same manner as in Example 1-1, except that the same amounts of dimethyl carbonate and ethyl methyl carbonate were used as the chain carbonate in the electrolyte. A discharge capacity of 253 mAh / g-active material and a capacity ratio of 90% vs. 0.1 ItA were obtained.

[0109] <Example 4-4> A test cell was prepared and tested in the same manner as in Example 1-1, except that the same amounts of dimethyl carbonate and diethyl carbonate were used as the chain carbonate in the electrolyte. A discharge capacity of 251 mAh / g-active material and a capacity ratio of 87% vs. 0.1 ItA were obtained.

[0110] <Example 4-5> A test cell was prepared and tested in the same manner as in Example 1-1, except that the same amounts of ethyl methyl carbonate and diethyl carbonate were used as the chain carbonate in the electrolyte, and a discharge capacity of 247 mAh / g-active material and a capacity ratio of 85% vs. 0.1 ItA were obtained. Table 4 shows the results of Examples 4-1 to 4-5 and 1-1.

[0111] [Table 4]

[0112] All levels of Examples 4-1 to 4-5 showed results that enabled the realization of both output characteristics and energy density, which are the effects of the present invention. These electrolyte solvents, except for EC, are liquid at room temperature and have low viscosity, so it is presumed that the results were satisfactory even with the above configuration.

[0113] <Example 5-1> A test cell was prepared and tested in the same manner as in Example 1-1, except that 0.1 wt% of 1,3-dioxane (1,3-DO) was added to 100 wt% of the electrolyte solution. A discharge capacity of 252 mAh / g of active material and a capacity ratio of 90% vs. 0.1 ItA were obtained.

[0114] <Example 5-2> A test cell was prepared and tested in the same manner as in Example 1-1, except that 2.5 wt% of 1,3-dioxane was added to 100 wt% of the electrolyte solution. A discharge capacity of 250 mAh / g-active material and a capacity ratio of 92% vs. 0.1 ItA were obtained.

[0115] <Example 5-3> A test cell was prepared and tested in the same manner as in Example 1-1, except that 5.0 wt% of 1,3-dioxane was added to 100 wt% of the electrolyte solution. A discharge capacity of 246 mAh / g-active material and a capacity ratio of 92% vs. 0.1 ItA were obtained.

[0116] <Example 5-4> A test cell was prepared and tested in the same manner as in Example 1-1, except that 0.1 wt% adiponitrile (AZN) was added to 100 wt% of the electrolyte solution. A discharge capacity of 254 mAh / g-active material and a capacity ratio of 90% vs. 0.1 ItA were obtained.

[0117] <Example 5-5> A test cell was prepared and tested in the same manner as in Example 1-1, except that 2.5 wt% adiponitrile was added to 100 wt% of the electrolyte solution. A discharge capacity of 249 mAh / g-active material and a capacity ratio of 88% vs. 0.1 ItA were obtained.

[0118] <Examples 5-6> A test cell was prepared and tested in the same manner as in Example 1-1, except that 5.0 wt% adiponitrile was added to 100 wt% of the electrolyte solution. A discharge capacity of 242 mAh / g-active material and a capacity ratio of 87% vs. 0.1 ItA were obtained.

[0119] <Examples 5-7> A test cell was prepared and tested in the same manner as in Example 1-1, except that 0.1 wt% of succinonitrile (SCN) was added to 100 wt% of the electrolyte solution. A discharge capacity of 252 mAh / g-active material and a capacity ratio of 90% vs. 0.1 ItA were obtained.

[0120] <Examples 5-8> A test cell was prepared and tested in the same manner as in Example 1-1, except that 2.5 wt% of succinonitrile was added to 100 wt% of the electrolyte solution. A discharge capacity of 250 mAh / g-active material and a capacity ratio of 88% vs. 0.1 ItA were obtained.

[0121] <Examples 5-9> A test cell was prepared and tested in the same manner as in Example 1-1, except that 5.0 wt% of succinonitrile was added to 100 wt% of the electrolyte solution. A discharge capacity of 243 mAh / g-active material and a capacity ratio of 90% vs. 0.1 ItA were obtained.

[0122] <Examples 5-10> A test cell was prepared and tested in the same manner as in Example 1-1, except that 6.0 wt% of 1,3-dioxane was added to 100 wt% of the electrolyte solution. A discharge capacity of 215 mAh / g-active material and a capacity ratio of 92% vs. 0.1 ItA were obtained.

[0123] <Example 5-11> A test cell was prepared and tested in the same manner as in Example 1-1, except that 6.0% by weight of adiponitrile was added to 100% by weight of the electrolyte solution. A discharge capacity of 213 mAh / g-active material and a capacity ratio of 92% vs. 0.1 ItA were obtained.

[0124] <Example 5-12> A test cell was prepared and tested in the same manner as in Example 1-1, except that 6.0% by weight of succinonitrile was added to 100% by weight of the electrolyte solution. A discharge capacity of 210 mAh / g-active material and a capacity ratio of 92% vs. 0.1 ItA were obtained.

[0125] <Example 5-13> A test cell was prepared and tested in the same manner as in Example 1-1, except that 0.08 wt% of 1,3-dioxane was added to 100 wt% of the electrolyte solution. A discharge capacity of 239 mAh / g-active material and a capacity ratio of 85% vs. 0.1 ItA were obtained.

[0126] <Example 5-14> A test cell was prepared and tested in the same manner as in Example 1-1, except that 1.0 wt % of 1,3-dioxane and 1.0 wt % of adiponitrile were added to 100 wt % of the electrolyte solution. A discharge capacity of 247 mAh / g of active material and a capacity ratio of 86% vs. 0.1 ItA were obtained.

[0127] <Example 5-15> A test cell was prepared and tested in the same manner as in Example 1-1, except that 0.08 wt % of 1,3-dioxane and 1.0 wt % of succinonitrile were added to 100 wt % of the electrolyte solution. A discharge capacity of 250 mAh / g of active material and a capacity ratio of 87% vs. 0.1 ItA were obtained.

[0128] <Example 5-16> A test cell was fabricated and tested in the same manner as in Example 1-1, except that 1.0 wt% adiponitrile and 1.0 wt% succinonitrile were added to 100 wt% of the electrolyte solution, and a discharge capacity of 248 mAh / g-active material and a capacity ratio of 86% vs. 0.1 ItA were obtained. Table 5 shows the results of Examples 5-1 to 5-16.

[0129] [Table 5]

[0130] In all levels of Examples 5-1 to 5-9 and Examples 5-14 to 5-16, the results demonstrated the ability to achieve both output characteristics and energy density, which are the effects of the present invention. It is believed that 1,3-dioxane exhibited a high dielectric constant, while adiponitrile and succinonitrile contributed to improved safety and reliability. Furthermore, in Examples 5-10 to 5-13, in which the amounts added were greater than 5.0 wt% or less than 0.1 wt%, respectively, the 0.1 ItA discharge capacity was higher than 200 mAh / g, and the ratio of the 0.1 ItA discharge capacity to the 5.0 ItA discharge capacity was 75 or greater. These results demonstrate that adding 0.1 to 5 wt% of 1,3-dioxane, adiponitrile, and succinonitrile, respectively, resulted in good battery characteristics.

[0131] <Comparative Example 6-1> A test cell was prepared and tested in the same manner as in Example 1-1, except that no electrolyte was added to the electrolytic solution, and a discharge capacity of 0 mAh / g-active material and a capacity ratio of 0% vs. 0.1 ItA were obtained.

[0132] <Example 6-1> A test cell was prepared and tested in the same manner as in Example 1-1, except that the electrolyte concentration was 0.5M, and a discharge capacity of 250mAh / g-active material and a capacity ratio of 82% vs. 0.1 ItA were obtained.

[0133] <Example 6-2> A test cell was prepared and tested in the same manner as in Example 1-1, except that the electrolyte concentration was 1.5 M. A discharge capacity of 252 mAh / g-active material and a capacity ratio of 86% vs. 0.1 ItA were obtained.

[0134] <Example 6-3> A test cell was prepared and tested in the same manner as in Example 1-1, except that the electrolyte concentration was 3.0 M. A discharge capacity of 253 mAh / g-active material and a capacity ratio of 83% vs. 0.1 ItA were obtained.

[0135] <Example 6-4> A test cell was prepared and tested in the same manner as in Example 1-1, except that the electrolyte concentration was 4.0 M, and a discharge capacity of 246 mAh / g-active material and a capacity ratio of 75% vs. 0.1 ItA were obtained.

[0136] <Example 6-5> A test cell was prepared and tested in the same manner as in Example 1-1, except that lithium tetrafluoroborate was used as the electrolyte and the concentration was 0.5 M. A discharge capacity of 245 mAh / g-active material and a capacity ratio of 82% vs. 0.1 ItA were obtained.

[0137] <Example 6-6> A test cell was prepared and tested in the same manner as in Example 1-1, except that lithium tetrafluoroborate was used as the electrolyte and the concentration was 1.5 M. A discharge capacity of 248 mAh / g-active material and a capacity ratio of 86% vs. 0.1 ItA were obtained.

[0138] <Examples 6-7> A test cell was prepared and tested in the same manner as in Example 1-1, except that lithium tetrafluoroborate was used as the electrolyte and the concentration was 3.0 M. A discharge capacity of 249 mAh / g-active material and a capacity ratio of 83% vs. 0.1 ItA were obtained.

[0139] <Examples 6-8> A test cell was prepared and tested in the same manner as in Example 1-1, except that lithium tetrafluoroborate was used as the electrolyte and the concentration was 4.0 M. A discharge capacity of 242 mAh / g-active material and a capacity ratio of 75% vs. 0.1 ItA were obtained.

[0140] <Examples 6-9> A test cell was prepared and tested in the same manner as in Example 1-1, except that LiFSI was used as the electrolyte and the concentration was 1.5M. A discharge capacity of 246 mAh / g-active material and a capacity ratio of 75% vs. 0.1 ItA were obtained.

[0141] <Examples 6-10> A test cell was fabricated and tested in the same manner as in Example 1-1, except that LiBOB was used as the electrolyte and the concentration was 1.5M. A discharge capacity of 248 mAh / g-active material and a capacity ratio of 75% vs. 0.1 ItA were obtained.

[0142] <Example 6-11> A test cell was fabricated and tested in the same manner as in Example 1-1, except that LiPF2O2 was used as the electrolyte and the concentration was 1.5 M. A discharge capacity of 246 mAh / g-active material and a capacity ratio of 75% vs. 0.1 ItA were obtained. Table 6 shows the results of Examples 6-1 to 6-11 and Comparative Example 6-1.

[0143] [Table 6]

[0144] At all levels, Examples 6-1 to 6-3 and Examples 6-5 to 6-7, the results demonstrated that the effects of the present invention, namely, output characteristics and energy density, were compatible. However, when more than 3M of each was added, as in Examples 6-4 and 6-8, the resistance of the electrolyte increased, resulting in a slight deterioration in the 5.0 ItA discharge capacity ratio. Therefore, if the amount of electrolyte added is too large, the viscosity of the electrolyte increases, adversely affecting the discharge rate characteristics, so an appropriate concentration is required. Furthermore, when LiFSI, LiBOB, or LFO was added, the effect was not as good as that of LiPF6 or LiBF4, resulting in a slight deterioration in the 5.0 ItA discharge capacity ratio. Note that Comparative Example 6-1 does not function as a battery because it does not contain an electrolyte. From the above, it was found that adding 0.5 to 3.0M of LiPF6 or LiBF4 showed good battery characteristics.

[0145] <Example 7-1> The metallic lithium counter electrode is LiNi 0.5 Co 0.2 Mn 0.3 The positive electrode was changed to one using O2 (NCM), and the coin cell was further changed to a 1 Ah laminate cell. Specifically, an electrode element was fabricated by alternately stacking a positive electrode with a positive current collector lead and a negative electrode with a negative current collector lead on a separator connected in a zigzag pattern. The separator was made of a polyethylene substrate layer with a polypropylene surface layer on both sides (PE / PP / PE). The separator was 20 μm thick. Next, the positive and negative electrode leads were bundled together, and the positive terminal was connected to the bundled positive lead by ultrasonic welding, and the negative terminal was connected to the bundled negative lead by ultrasonic welding. The fabricated electrode element was 4.8 mm thick and had a rated capacity of 1 Ah. The "rated capacity" mentioned here refers to the discharge capacity when a constant current-constant voltage charge (cutoff current: 0.05C) is performed at an upper limit voltage of 4.2V and a current value of 0.5C, followed by a constant current discharge at a lower limit voltage of 2.7V and a current value of 0.2C.

[0146] Next, two laminate films were prepared as exterior bodies, each having a structure in which a heat-sealed resin layer made of polyolefin, a metal layer made of aluminum foil, and a protective layer made of nylon resin and polyester resin were laminated in that order. The heat-sealed resin layers of the two laminate films were placed facing each other, and the laminate films were overlapped so that the adhesive surfaces of the laminate films faced each other, allowing the electrode groups to be housed in the two housing recesses. The electrode groups were arranged so that the portions of the heat-sealed resin portions of each terminal passed between the edges of the two laminate films, leaving a portion of each terminal exposed to the outside. In this state, the heat-sealed resin layers of the laminate films were heat-sealed to each other along three edges, including the two edges from which the tabs of the laminate films extended. Next, the electrolyte prepared above was injected into the one edge of the exterior body that was not heat-sealed. Next, the remaining edge of the exterior body was heat-sealed under reduced pressure to create a test cell.

[0147] Tests were carried out in the same manner as in Example 1-1, and a discharge capacity of 1012 mAh / g, a discharge average voltage of 2.35 V, and a capacity ratio of 89% vs. 0.1 ItA were obtained.

[0148] <Example 7-2> Positive electrode: LiNi 0.6 Co 0.2 Mn 0.2 A test cell was fabricated and tested in the same manner as in Example 7-1, except that O2 was used, and a discharge capacity of 1020 mAh / g-active material, an average discharge voltage of 2.34 V, and a capacity ratio of 92% vs. 0.1 ItA were obtained.

[0149] <Example 7-3> Positive electrode: LiNi 0.8 Co 0.1 Mn 0.1 A test cell was fabricated and tested in the same manner as in Example 7-1, except that O2 was used, and a discharge capacity of 999 mAh / g-active material, an average discharge voltage of 2.38 V, and a capacity ratio of 89% vs. 0.1 ItA were obtained.

[0150] <Example 7-4> Positive electrode: LiNi 0.5 Mn 0.5A test cell was fabricated and tested in the same manner as in Example 7-1, except that O2 was used, and a discharge capacity of 1010 mAh / g-active material, an average discharge voltage of 3.00 V, and a capacity ratio of 80% vs. 0.1 ItA were obtained.

[0151] <Example 7-5> A test cell was fabricated and tested in the same manner as in Example 7-1, except that the positive electrode was LiNiO2, and a discharge capacity of 996 mAh / g-active material, an average discharge voltage of 2.44 V, and a capacity ratio of 85% vs. 0.1 ItA were obtained.

[0152] <Example 7-6> Positive electrode: LiNi 0.33 Co 0.33 Mn 0.33 A test cell was fabricated and tested in the same manner as in Example 7-1, except that O2 was used. A discharge capacity of 950 mAh / g of active material, an average discharge voltage of 2.37 V, and a capacity ratio of 92% vs. 0.1 ItA were obtained. Table 7 shows the results of Examples 7-1 to 7-6. In the overall evaluation section of Table 7, cases where the ratio of the 0.1 ItA discharge capacity to the 5.0 ItA discharge capacity was higher than 75 and the 0.1 ItA discharge capacity was higher than 950 mAh / g were evaluated as ⊚; cases where the 0.1 ItA discharge capacity was lower than ⊚ but higher than 900 mAh / g were evaluated as ◯; and cases where the 0.1 ItA discharge capacity was lower than 900 mAh / g were evaluated as x.

[0153] [Table 7]

[0154] In Examples 7-1 to 7-6, the results showed that the effects of the present invention, namely, the output characteristics and energy density, could be achieved at any level. However, if the nickel ratio in the positive electrode active material were to fall below 33.3%, the discharge capacity would decrease and it would be impossible to ensure the energy density, so the nickel ratio must be greater than 33.3%.

[0155] The objective of this invention is to achieve both high output characteristics and high energy density in lithium-ion batteries. This was achieved only when TNO was used as the negative electrode active material and 0.5 to 2.0 wt.% of lithium methoxysulfonate and lithium ethoxysulfonate were added as electrolyte additives. The effect was not achieved with TNO alone or the additives alone, demonstrating that the invention is due to the unique effect of the combination. While the output characteristics were inferior to those achieved with lithium titanate as the negative electrode active material, the difference was only about 10%, and considering that the use of TNO increased the discharge capacity by approximately 1.7 times, it goes without saying which battery configuration is superior.

[0156] As described above, by using lithium niobium titanate as the negative electrode active material and lithium methoxysulfonate and lithium ethoxysulfonate as electrolyte additives in lithium-ion batteries, it is possible to create batteries that combine good output characteristics and energy density. This battery is expected to be used in a wide range of fields, including mobility applications such as electric vehicles and drones, as well as natural energy storage applications. The inventions described in the original claims of this application are set forth below. [1] a negative electrode containing niobium titanium oxide as a negative electrode active material in a mixture layer; RSOOO - Li + (where R is OCH 3 , O.C. 2 H 5 and a non-aqueous electrolyte solution containing a lithium alkoxysulfonate represented by the formula (at least one substance selected from the group consisting of: [2] The lithium ion secondary battery according to [1], wherein the content of the lithium alkoxysulfonate in the non-aqueous electrolyte solution is 0.5 to 2.0% by mass. [3] The lithium ion secondary battery according to [1] or [2], wherein the non-aqueous electrolyte contains at least one non-aqueous solvent selected from the group consisting of cyclic carbonates, chain carbonates, and γ-butyrolactone. [4] The lithium ion secondary battery according to any one of [1] to [3], wherein the cyclic carbonate is ethylene carbonate and / or propylene carbonate, and does not include vinylene carbonate, fluoroethylene carbonate, or vinylethylene carbonate. [5] The lithium ion secondary battery according to any one of [1] to [4], wherein the chain carbonate is at least one selected from dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. [6] The lithium ion secondary battery according to any one of [1] to [5], wherein the non-aqueous electrolyte solution contains 0.1 wt % to 5 wt % of at least one selected from cyclic ethers: 1,3-dioxane, adiponitrile, and succinonitrile. [7] 0.5M to 3M LiPF as electrolyte 6 and / or LiBF 4 Includes LiFSi, LiBOB and LiPO 2 F 2 Lithium-ion secondary batteries of any of [1] to [6], excluding [1] to [6]. [8] The lithium ion secondary battery according to any one of [1] to [7], comprising a positive electrode containing a lithium composite oxide in which Ni is present in an atomic ratio of 50% or more in a composite layer. [9] Lithium composite oxide is LiNi 0.5 Co 0.2 Mn 0.3 O 2 , LiNi 0.6 Co 0.2 Mn 0.2 O 2 , and LiNi 0.8 Co 0.1 Mn 0.1 O 2 [8] The lithium-ion secondary battery according to [8], wherein the lithium-ion secondary battery is at least one selected from the following:

[10] A non-aqueous electrolyte solution for use in any one of the lithium-ion secondary batteries [1] to [9]. [Explanation of symbols]

[0157] 1...lithium ion secondary battery, 2...positive electrode, 3...negative electrode, 4...separator, 5...first external terminal, 6...second external terminal, 7...gasket, 21...positive electrode current collector, 22...positive electrode active material composite electrode layer, 31...negative electrode current collector, 32...composite layer, 100...laminated lithium secondary battery, 200...casing, 300...electrode group, 400...positive electrode, 500...negative electrode, 600...separator, 410...positive electrode current collector, 420...positive electrode active material composite electrode layer, 510...negative electrode current collector, 520...composite layer, 700...positive electrode lead, 800...positive electrode tab, 900...negative electrode lead, 1000...negative electrode tab.

Claims

1. a negative electrode containing niobium titanium oxide as a negative electrode active material in a mixture layer; RSOOO － Li ＋ (where R is OCH ３ and O.C. ２ H ５ a non-aqueous electrolyte solution containing a lithium alkoxysulfonate represented by the formula (I), A lithium-ion secondary battery comprising:

2. 2. The lithium ion secondary battery according to claim 1, wherein the content of the lithium alkoxysulfonate in the non-aqueous electrolyte is 0.5 to 2.0 mass %.

3. 3. The lithium ion secondary battery according to claim 1, wherein the non-aqueous electrolyte contains at least one non-aqueous solvent selected from the group consisting of cyclic carbonates, chain carbonates, and γ-butyrolactone.

4. 4. The lithium ion secondary battery according to claim 3, wherein the cyclic carbonate is ethylene carbonate and / or propylene carbonate, and does not include vinylene carbonate, fluoroethylene carbonate, or vinylethylene carbonate.

5. 4. The lithium ion secondary battery according to claim 3, wherein the chain carbonate is at least one selected from the group consisting of dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

6. 6. The lithium ion secondary battery according to claim 1, wherein the non-aqueous electrolyte solution further contains at least one cyclic ether selected from the group consisting of 1,3-dioxane, adiponitrile, and succinonitrile, and the content of the cyclic ether is 0.1% by weight to 5% by weight.

7. The nonaqueous electrolyte solution contains an electrolyte, and the electrolyte is 0.5M to 3M LiPF ６ and / or LiBF ４ LiFSi, LiBOB and LiPO ２ F ２ The lithium ion secondary battery according to any one of claims 1 to 6, which does not contain

8. The lithium ion secondary battery according to any one of claims 1 to 7, further comprising a positive electrode containing a lithium composite oxide in which Ni is 50 atomic % or more in the mixture layer.

9. The lithium composite oxide is LiNi ０．５ Co ０．２ Mn ０．３ O ２ , LiNi ０．６ Co ０．２ Mn ０．２ O ２ , and LiNi ０．８ Co ０．１ Mn ０．１ O ２ The lithium ion secondary battery according to claim 8, wherein the lithium ion secondary battery is at least one selected from the group consisting of:

Images