JP2014194842A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous secondary battery superior in discharge capacity and cycle characteristics.SOLUTION: A lithium ion secondary battery comprises: a positive electrode including a positive electrode active material including at least one foreign element selected from a group consisting of W, Nb, B, Zr and V; a negative electrode having a first layer including a carbon material as an active material and formed on a negative electrode current collector surface, and a second layer including lithium titanate as an active material and formed on the first layer; a separator disposed between the positive electrode and the negative electrode; and a nonaqueous electrolyte. The second layer has a thickness as large as 1-25% of the thickness of the first layer. The second layer includes a conducting agent which accounts for 3% or less in mass to 100 pts.mass of the lithium titanate.

Description

  The present invention relates to a lithium ion secondary battery.

  Lithium ion secondary batteries have high capacity, high energy density, and are easy to reduce in size and weight, and are therefore widely used as power sources for portable small electronic devices, for example. Examples of portable small electronic devices include mobile phones, personal digital assistants (PDAs), notebook personal computers, video cameras, and portable game machines.

  A typical lithium ion secondary battery includes a positive electrode containing a lithium cobalt composite oxide as a positive electrode active material, a negative electrode containing a carbon material as a negative electrode active material, and a polyolefin porous membrane (separator). As devices become smaller and lighter, demand for further increases in energy density of lithium ion secondary batteries is increasing. With conventional battery designs, the capacity is approaching the limit. Researches for long life, high output, and high charging voltage are widely conducted.

  Patent Document 1 discloses that the discharge capacity of a battery is improved by employing a positive electrode active material containing a different element.

  Further, for the purpose of suppressing a decrease in battery capacity due to metal elution, Patent Document 2 discloses a lithium ion secondary battery that employs lithium titanate as a negative electrode active material.

  In addition, for the purpose of providing a high-capacity and long-life lithium ion secondary battery, Patent Document 3 discloses a lithium material employing a negative electrode material in which a carbon material layer is provided on the negative electrode and a lithium titanate layer is provided on the surface thereof. An ion secondary battery is disclosed.

JP 2006-185794 A JP-A-6-275263 JP 2010-537389 A

  If a positive electrode active material containing a different element is used to increase the charging voltage of a lithium ion secondary battery, the different element contained in the positive electrode is eluted when the carbon material is used for the negative electrode, and the different kind of material eluted on the negative electrode surface. When the metal is deposited, there is a problem that an internal short circuit is caused and cycle characteristics are deteriorated.

  On the other hand, when lithium titanate is used for the negative electrode, since the redox potential (oxidation-reduction potential) of lithium titanate is high, good film formation is insufficient, and the nonaqueous electrolyte is decomposed during the charge / discharge cycle. As a result, gas is generated and cycle deterioration occurs. Furthermore, since lithium titanate has a low theoretical capacity, the capacity of the battery itself is reduced.

  An object of the present invention is to improve battery capacity and cycle characteristics in a lithium ion secondary battery cycled at a high charge voltage.

  Therefore, as a result of intensive studies, the inventors have made a carbon material layer and a carbon material layer on the negative electrode when a lithium ion secondary battery employing a positive electrode material containing a different element in the positive electrode is cycled at a high charge voltage. It has been found that by adopting a multi-layer structure in which a lithium titanate layer is provided on the surface, the redox potential of lithium titanate can be lowered, and the capacity and cycle characteristics of a lithium ion secondary battery are improved. .

  Further, by optimizing the thickness of the lithium titanate layer and the amount of the conductive agent, it is possible to suppress the decomposition of the nonaqueous electrolytic solution by precipitating different elements in the lithium titanate layer, As a result, it was found that cycle characteristics were improved.

  That is, the present invention employs a positive electrode active material containing a different element as a positive electrode, a first layer using a carbon material formed on the surface of the negative electrode current collector as an active material, and titanium on the first layer. A lithium ion secondary battery employing a negative electrode provided with a second layer comprising lithium acid as an active material, wherein the different element is at least one kind selected from the group consisting of tungsten, niobium, boron, zirconium and vanadium The second layer has a thickness of 1% to 25% with respect to the first layer, and the amount of the conductive agent contained in the second layer is 100 parts by mass of lithium titanate. By setting the amount to 3 parts by mass or less, the dissimilar elements can be deposited in the second layer and the decomposition of the non-aqueous electrolyte can be suppressed. As a result, even when the battery is charged at a high voltage, the capacity of the battery Lithium ion with excellent cycle characteristics It is possible to obtain a battery.

  ADVANTAGE OF THE INVENTION According to this invention, in the lithium ion secondary battery charged by high voltage, decomposition | disassembly of the non-aqueous electrolyte at the time of charging / discharging can be suppressed, and the capacity | capacitance and cycling characteristics of a battery can be improved.

Schematic cross-sectional view of a negative electrode material in one embodiment of the present invention 1 is a schematic cross-sectional view of a lithium ion secondary battery according to an embodiment of the present invention.

  First, the positive electrode for a lithium ion secondary battery used in the present invention will be described.

  A positive electrode for a lithium ion secondary battery includes a positive electrode current collector and a positive electrode active material layer formed on a surface of the positive electrode current collector, and the positive electrode active material includes a different additive element.

  As the positive electrode current collector, a current collector used for a positive electrode of a lithium ion secondary battery is not particularly limited. Specifically, aluminum, an aluminum alloy, or the like can be used in the form of a foil, a film, a film, a sheet, or the like. The thickness of the positive electrode current collector is usually 1 to 500 μm, and can be appropriately set according to the capacity and size of the lithium ion secondary battery.

  The positive electrode active material layer is obtained, for example, by mixing a lithium nickel composite oxide, a binder, a dispersion medium, and an additive such as a conductive agent as necessary to prepare a positive electrode mixture slurry. The obtained positive electrode mixture slurry can be applied to the surface of the positive electrode current collector, dried and rolled.

As a binder, the binder used for a lithium ion secondary battery can be mentioned without particular limitation. Specifically, polytetrafluoroethylene, polyvinylidene fluoride and modified products thereof, fluorine-containing polymers such as tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, styrene-butadiene rubber, etc. And polyolefin resins such as polyethylene, polypropylene, and the like. These can be used individually by 1 type and can also be used in combination of 2 or more type. As the conductive agent, a conductive agent used for a lithium ion secondary battery can be mentioned without particular limitation. Specifically, carbon blacks such as graphites, acetylene black, ketjen black, furnace black, lamp black and thermal black, carbon fibers, metal fibers and the like can be mentioned.

  The different element is a compound containing at least one different element selected from the group consisting of tungsten, niobium, boron, zirconium and vanadium.

  Below, the introduction method of the above-mentioned different element is demonstrated.

  As a first method, there is a method of attaching a different element to the surface of the lithium nickel composite oxide.

  For example, after preparing a solution containing a different element by dissolving an ethoxide compound containing the different element in a solvent such as ethanol, the lithium nickel composite oxide is dispersed in the solution containing the different element and heated to complete the solution. Remove the solvent. Thereafter, the obtained mixture of the different element and the lithium nickel composite oxide is heat-treated, whereby a lithium nickel composite oxide containing the different element is obtained. As heat processing conditions at this time, 300 to 700 degreeC and 12 to 24 hours are preferable.

  As the second method, there is a method in which a raw material mixture of a lithium nickel composite oxide and a different element compound are mixed and baked to add them internally.

  As the raw material mixture of the lithium nickel composite oxide, various raw materials conventionally used for producing lithium nickel composite oxide can be used without any particular limitation. Specifically, examples of the lithium compound include lithium hydroxide and lithium carbonate, and examples of the nickel compound include nickel hydroxide and nickel oxide. Examples of the different element compound include various oxides, carbonates, nitrates, hydroxides and the like.

  The mixing of the raw material mixture and the different element compound described above may be either dry mixing or wet mixing, but dry mixing is preferred from the standpoint of simplicity. Examples of the mixing device include a ball mill.

  By firing the obtained raw material mixture and the mixture with the different element compound in an air atmosphere, a lithium nickel composite oxide in which the different element is internally added can be obtained. As baking conditions at this time, 600 to 900 degreeC and 12 to 24 hours are preferable.

  Next, the negative electrode for a lithium ion secondary battery used in the present invention will be described with reference to FIG.

  The negative electrode for a lithium ion secondary battery includes a negative electrode current collector 10 and a first layer 11 using a carbon material formed on the surface of the negative electrode current collector 10 as an active material, and a lithium titanate layer is formed thereon. A second layer 12 as an active material is provided.

  Hereinafter, the manufacturing method of a negative electrode is demonstrated.

As a first method, first, a carbon material, a binder, a dispersion medium, and an additive such as a conductive agent as necessary are mixed to prepare a material mixture slurry, and then the obtained material mixture slurry is prepared. It apply | coats to the surface of the negative electrode collector 10, and it dries and rolls. Thereafter, a lithium titanate slurry prepared by mixing lithium titanate, a binder, a dispersion medium, and an additive such as a conductive agent is applied to the surface of the carbon material layer, dried and rolled.

  The second method is to first prepare a material mixture slurry by mixing a carbon material, a binder, a dispersion medium and, if necessary, an additive such as a conductive agent, and then preparing the obtained material mixture slurry. After coating on the surface of the negative electrode current collector 10, a lithium titanate slurry prepared by mixing lithium titanate, a binder, a dispersion medium, and an additive such as a conductive agent is formed on the surface of the carbon material layer. Apply and dry and roll two layers simultaneously.

  As the negative electrode current collector 10, a current collector used for a negative electrode of a lithium ion secondary battery is not particularly limited. Specifically, stainless steel, nickel, copper, or the like can be used in the form of a foil, a film, a film, a sheet, or the like. The thickness of the negative electrode current collector 10 can be appropriately set in the range of 1 μm to 500 μm according to the capacity, size, etc. of the lithium ion secondary battery.

  As the carbon material, a carbon material capable of inserting and extracting lithium used in a lithium ion secondary battery is not particularly limited. Specific examples include carbon materials such as graphite and amorphous carbon. As a binder, what is used for the negative electrode of a lithium ion secondary battery is used without limitation. Specific examples include polyolefins such as polyethylene and polypropylene; styrene-butadiene rubber (SBR) and modified products thereof. These can be used individually by 1 type and can also be used in combination of 2 or more type. Examples of the conductive agent include those exemplified as the conductive agent used for the positive electrode active material layer.

Lithium titanate is obtained by mixing a lithium compound and a titanium compound and then firing, for example, lithium titanate having a chemical formula of Li _{3 + 3x} Ti _6-3x-y My ₁₂ where x and y are Represents a molar ratio, 0 ≦ x ≦ 1/3, 0 ≦ y ≦ 0.25, M is Fe, Al, Ca, Co, B, Cr, Ni, Mg, Zr, Ga, V, Mn and Zn At least one selected from the group consisting of. Examples of the lithium compound include lithium hydroxide and lithium carbonate, and examples of the titanium compound include titanium oxide.

  The content ratio of the conductive agent of the second layer 12 using lithium titanate as an active material does not show electrode activity when the conductive agent is not included, but is 3 masses with respect to 100 parts by mass of lithium titanate. In the case where it exceeds 50%, the electrolyte solution is not sufficiently suppressed, and the cycle characteristics tend to be lowered.

  In addition, in the case where the thickness of the second layer 12 using the lithium titanate as an active material is less than 1% with respect to the thickness of the first layer 11 using the carbon material as an active material, The total amount of the different elements contained in the positive electrode active material eluted and deposited on the negative electrode is larger than the amount that can be deposited on lithium titanate, and the decomposition of the non-aqueous electrolyte cannot be suppressed, resulting in poor cycle characteristics. When it exceeds 25%, the influence of lithium titanate having a low theoretical capacity becomes prominent, and the capacity of the battery tends to decrease. It is desirable that it is 1% or more and 25% or less from the point that the capacity of the battery decreases.

When the mixture density of the first layer 11 made of a carbon material as an active material formed on the surface of the negative electrode current collector is less than 1.4 g / cc, the energy density per unit area On the other hand, if it exceeds 2.8 g / cc, the penetration of the non-aqueous electrolyte into the first layer 11 becomes insufficient, and the battery characteristics tend to deteriorate. From the point, it is more desirable that it is 1.4 g / cc or more and 2.8 g / cc or less.

  Moreover, the mixture density of the second layer 12 using the lithium titanate as an active material tends to decrease the energy density per unit area when it is less than 1.3 g / cc, If it exceeds 1.8 g / cc, the penetration of the non-aqueous electrolyte into the second layer 12 becomes insufficient, and the battery characteristics tend to be reduced. More preferably, it is 1.8 g / cc or less.

Further, if the BET specific surface area of lithium titanate is less than 2 m ² / g, the rate characteristics tend to be lowered, whereas if it exceeds 8 m ² / g, the conductive agent and the binder It is more desirable that the amount is ² m ² / g or more and 8 m ² / g or less from the viewpoint that the addition amount of the agent needs to be increased and the energy density per unit area tends to decrease.

  In addition, when the average particle size of lithium titanate is less than 0.5 μm, the surface area of the active material becomes large, so it is necessary to increase the addition amount of a conductive agent and a binding amount, and the energy density decreases. On the other hand, when the average particle size exceeds 10 μm, the rate characteristic tends to be lowered, so that it is more preferably 0.5 μm or more and 10 μm or less.

  Moreover, although the cycle characteristics are improved by setting the oil absorption of lithium titanate to 20 g / 100 g or less, the rate characteristics are improved by setting it to 50 g / 100 g or more. More desirably, it is 100 g or less.

  In addition, if the nonaqueous electrolyte contains at least one fluorinated solvent selected from the group consisting of fluoroethylene carbonate, methyl fluoropropionate, fluorobenzene, fluoroethyl methyl carbonate, and fluorodimethylene carbonate, the surface of the negative electrode is good. It is preferable from the point that a thick film can be formed.

  Next, the lithium ion secondary battery according to the present invention will be described.

  The lithium ion secondary battery according to the present invention includes a positive electrode employed in the above-described lithium nickel composite oxide containing different elements, and a first layer using a carbon material formed on the surface of the negative electrode current collector 10 as an active material. 11 and a second layer 12 comprising lithium titanate as an active material, a separator disposed between the positive electrode and the negative electrode, and a non-aqueous electrolyte.

  As shown in FIG. 2, in the lithium ion secondary battery 20, a positive electrode 21, a negative electrode 22, and a microporous separator 23 interposed between the positive electrode 21 and the negative electrode 22 are wound in a spiral shape. An electrode group 24 is provided. The electrode group 24 includes a positive-side insulating plate 25 at one end in the winding axis direction, and a negative-side insulating plate 26 at the other end. The electrode group 24 is housed together with a non-aqueous electrolyte in a battery case 27 that also serves as a negative electrode terminal. The battery case 27 is sealed with a sealing plate 28. The battery case 27 is electrically connected to the negative electrode 22 via the negative electrode lead 29, and the positive terminal 30 of the sealing plate 28 is electrically connected to the positive electrode 21 via the positive electrode lead 31.

  Hereinafter, although components other than the positive electrode 21 and the negative electrode 22 will be described, the components other than the positive electrode 21 and the negative electrode 22 are not particularly limited in the lithium ion secondary battery, and a known configuration is appropriately used as the lithium ion secondary battery. be able to.

The separator 23 is interposed between the positive electrode and the negative electrode. Examples of the separator 23 include microporous thin films, woven fabrics, and non-woven fabrics that have high ion permeability and sufficient mechanical strength. The material of the separator 23 is preferably a polyolefin such as polypropylene or polyethylene from the viewpoint that it has excellent durability and can exhibit a shutdown function when overheated. The thickness of the separator is generally 10 μm to 300 μm, preferably 10 μm to 40 μm. The separator may be a single layer film made of one kind of material, or a composite film or a multilayer film made of two or more kinds of materials. The porosity of the separator is preferably 30% to 70%, more preferably 35% to 60%. The porosity indicates the ratio of the volume of the hole portion to the total volume of the separator.

  The nonaqueous electrolytic solution includes a nonaqueous solvent and a lithium salt dissolved in the nonaqueous solvent.

  As the non-aqueous solvent, various non-aqueous solvents used for the non-aqueous electrolyte of the lithium ion secondary battery can be used. Specifically, cyclic carbonate solvents such as ethylene carbonate, propylene carbonate, butylene carbonate, chain carbonate solvents such as dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate, tetrahydrofuran, 1,4-dioxane, 1,3-dioxolane Cyclic ether solvents such as 1, 2-dimethoxyethane, chain ether solvents such as 1,2-diethoxyethane, cyclic ester solvents such as γ-butyrolactone, chain ester solvents such as methyl acetate, fluoroethylene carbonate, fluoro A fluorinated solvent that is at least one selected from the group consisting of methyl propionate, fluorobenzene, fluoroethyl methyl carbonate, and fluorodimethylene carbonate can be used. Moreover, these can be used individually by 1 type and can also be used in combination of 2 or more type.

Examples of the lithium salt include various lithium salts used as a solute in the non-aqueous electrolyte of a lithium ion secondary battery. _{Specifically, LiPF 6, LiBF 4, LiSbF} 6, LiAsF 6, LiSO 3 CF 3, LiN (SO 2 CF 3) 2, LiN (SO 2 C 2 F 5) 2, LiN (SO 2 CF 3) ( SO ₂ C ₄ F ₉ ), LiC (SO ₂ CF ₃ ) _{3 and the} like. These can be used individually by 1 type and can also be used in combination of 2 or more type. The concentration of the lithium salt is preferably 0.5 mol / L to 2 mol / L.

  In the above description, a wound cylindrical battery is illustrated as a specific embodiment of the lithium ion secondary battery, but the shape of the lithium ion secondary battery is not limited thereto. The lithium ion secondary battery can be appropriately selected not only in a cylindrical shape but also in a shape such as a coin shape, a square shape, a sheet shape, a button shape, a flat shape, and a stacked shape, depending on the application.

Example 1
(1) Preparation of lithium nickel composite oxide containing different elements Tungsten ethoxide was dissolved in dehydrated ethanol. Lithium nickel composite oxide (LiNi _0.8 Co _0.16 Al _0.04 O ₂ : NCA) was dispersed in the obtained solution. Next, the solvent was completely removed by heating with stirring. The obtained mixture was baked at 300 ° C. for 12 hours in an air atmosphere to obtain a lithium nickel composite oxide (W-NCA) containing a tungsten compound. The tungsten compound contained 0.5 mol% with respect to the lithium nickel composite oxide.

(2) Production of positive electrode 90 parts by mass of positive electrode active material particles, 3 parts by mass of a conductive agent, 87.5 parts by mass of a 2-methylpyrrolidone (NMP) solution of polyvinylidene fluoride (PVDF) (concentration of 8 parts by mass of PVDF, The positive electrode mixture slurry was obtained by mixing the solid content of PVDF (7 parts by mass). The obtained positive electrode mixture slurry was applied to both sides of a positive electrode current collector made of an aluminum foil having a thickness of 10 μm, dried and rolled to obtain a positive electrode having a total thickness of 140 μm provided with a positive electrode active material layer.

(3) Production of negative electrode 93.5 parts by mass of artificial graphite (C) powder and 12.5 parts by mass of modified styrene-butadiene rubber (solid content 40 parts by mass)) 1.5 parts by mass of sodium carboxymethylcellulose Thus, an artificial graphite mixture slurry was obtained. Next, 90 parts by mass of lithium titanate (Li ₄ Ti ₅ O ₁₂ : LTO), 3 parts by mass of a conductive agent, and 50 parts by mass of an NMP solution of PVDF (PVDF concentration of 8% by mass, PVDF solid content of 4 parts by mass) And lithium titanate mixture slurry was obtained. The obtained artificial graphite mixture slurry was applied to both sides of a negative electrode current collector made of a copper foil having a thickness of 10 μm, dried and rolled to obtain a negative electrode having a total thickness of 160 μm, and then the lithium titanate slurry was added to the artificial graphite layer. A negative electrode having a total thickness of 180 μm provided with a negative electrode active material layer was obtained by coating, drying and rolling on the substrate.

(4) Preparation of non-aqueous electrolyte Fluoroethylene carbonate (FEC), ethylene carbonate (EC), and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 1: 1: 6 to obtain a non-aqueous solvent. It was. A non-aqueous electrolyte (F / E / E) was prepared by dissolving LiPF ₆ in the non-aqueous solvent thus obtained to a concentration of 1.0 mol / L.

(5) Fabrication of lithium ion secondary battery Microporous separator (Polyethylene and polypropylene composite film, product number “2300” manufactured by Celgard Co., Ltd.), thickness inserted between the positive electrode, the negative electrode, the positive electrode, and the negative electrode An electrode group was obtained by winding a laminate of 25 μm in a spiral shape. Then, an aluminum positive electrode lead was welded to a part of the positive electrode current collector, and a nickel negative electrode lead was welded to a part of the negative electrode current collector. Such an electrode group was accommodated in a battery case having a bottomed substantially cylindrical shape having a diameter of 18 mm and a height of 65 mm. And 5.2 mL of nonaqueous electrolyte solution was inject | poured in the battery case.

(6) Evaluation of battery The cycle characteristics of the obtained lithium ion secondary battery were evaluated according to the following methods.

<Initial discharge capacity>
The lithium ion secondary battery was charged at a rate of 1 C with the end-of-charge voltage set to 4.4 V, and then discharged at a rate of 0.2 C with the end-of-discharge voltage set to 2.5 V. The discharge capacity obtained at this time was defined as the initial discharge capacity.

<Cycle characteristics>
The charge / discharge cycle under the following conditions was repeated for the lithium ion secondary battery. The environmental temperature at the time of charging / discharging was set to 25 degreeC. First, the maximum current value was set to 2.5 A, and constant current charging was performed until the voltage reached 4.4 V, and then constant voltage charging was performed at 4.2 V until the current value decreased to 50 mA. Next, the discharge end voltage was set to 2.5 V, and constant current discharge was performed at a rate of 0.2 C. The pause time between charging and discharging was 30 minutes. This charge / discharge cycle was taken as one cycle, and charge / discharge was repeated 100 cycles. The discharge capacity at the 100th cycle in the charge / discharge cycle was regarded as 100%, and the cycle characteristics were evaluated by expressing the discharge capacity when 100 cycles passed as a percentage as the capacity retention rate. The results are shown in Table 1.

(Example 2)
In the same manner as in Example 1, an artificial graphite slurry and a lithium titanate slurry were obtained. The obtained artificial graphite mixture slurry was applied to both sides of a negative electrode current collector made of a copper foil having a thickness of 10 μm, dried and rolled to obtain a negative electrode having a total thickness of 160 μm, and then the lithium titanate slurry was added to the artificial graphite layer. A negative electrode having a total thickness of 190 μm provided with a negative electrode active material layer was obtained by coating, drying and rolling on the substrate. A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that the obtained negative electrode was used.

(Example 3)
In the same manner as in Example 1, an artificial graphite slurry and a lithium titanate slurry were obtained. The obtained artificial graphite mixture slurry was applied to both sides of a negative electrode current collector made of a copper foil having a thickness of 10 μm, dried and rolled to obtain a negative electrode having a total thickness of 160 μm, and then the lithium titanate slurry was added to the artificial graphite layer. The negative electrode with a total thickness of 162 μm provided with the negative electrode active material layer was obtained by coating, drying and rolling on the substrate. A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that the obtained negative electrode was used.

Example 4
In the same manner as in Example 1, an artificial graphite mixture slurry was obtained. Next, 90 parts by mass of lithium titanate, 2 parts by mass of a conductive agent, and 100 parts by mass of PVDF NMP solution (PVDF concentration 8 parts by mass, PVDF solid content 8 parts by mass) were mixed to form titanium. A lithium acid mixture slurry was obtained. The obtained artificial graphite mixture slurry was applied to both sides of a negative electrode current collector made of a copper foil having a thickness of 10 μm, dried and rolled to obtain a negative electrode having a total thickness of 160 μm, and then the lithium titanate slurry was added to the artificial graphite layer. A negative electrode having a total thickness of 180 μm provided with a negative electrode active material layer was obtained by coating, drying and rolling on the substrate.

(Example 5)
In the same manner as in Example 1, an artificial graphite mixture slurry was obtained. Next, by mixing 90 parts by weight of lithium titanate, 1 part by weight of a conductive agent, and 112.5 parts by weight of a PVDF NMP solution (8 parts by weight of PVDF, 9 parts by weight of PVDF solid content) A lithium titanate mixture slurry was obtained. The obtained artificial graphite mixture slurry was applied to both sides of a negative electrode current collector made of a copper foil having a thickness of 10 μm, dried and rolled to obtain a negative electrode having a total thickness of 160 μm, and then the lithium titanate slurry was added to the artificial graphite layer. A negative electrode having a total thickness of 180 μm provided with a negative electrode active material layer was obtained by coating, drying and rolling on the substrate.

(Example 6)
Niobium ethoxide was dissolved in dehydrated ethanol. Lithium nickel composite oxide (LiNi _0.8 Co _0.16 Al _0.04 O ₂ : NCA) was dispersed in the obtained solution. Next, the solvent was completely removed by heating with stirring. The obtained mixture was baked at 300 ° C. for 12 hours in an air atmosphere to obtain a lithium nickel composite oxide (Nb—NCA) containing 0.5 mol% of a niobium compound with respect to the lithium nickel composite participant. . A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that the obtained positive electrode active material was used.

(Example 7)
Boron ethoxide was dissolved in dehydrated ethanol. Lithium nickel composite oxide (LiNi _0.8 Co _0.16 Al _0.04 O ₂ : NCA) was dispersed in the obtained solution. Next, the solvent was completely removed by heating with stirring. The obtained mixture was baked at 300 ° C. for 12 hours in an air atmosphere to obtain a lithium nickel composite oxide (B-NCA) containing 0.5 mol% of a boron compound with respect to the lithium nickel composite participant. . A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that the obtained positive electrode active material was used.

(Example 8)
Zirconium ethoxide was dissolved in dehydrated ethanol. Lithium nickel composite oxide (LiNi _0.8 Co _0.16 Al _0.04 O ₂ : NCA) was dispersed in the obtained solution. Next, the solvent was completely removed by heating with stirring. The obtained mixture was baked at 300 ° C. for 12 hours in an air atmosphere to obtain a lithium nickel composite oxide (Zr—NCA) containing 0.5 mol% of a zirconium compound with respect to the lithium nickel composite participant. . A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that the obtained positive electrode active material was used.

Example 9
Vanadium ethoxide was dissolved in dehydrated ethanol. Lithium nickel composite oxide (LiNi _0.8 Co _0.16 Al _0.04 O ₂ : NCA) was dispersed in the obtained solution. Next, the solvent was completely removed by heating with stirring. The obtained mixture was baked at 300 ° C. for 12 hours in an air atmosphere to obtain a lithium nickel composite oxide (V-NCA) containing 0.5 mol% of a vanadium compound with respect to the lithium nickel composite participant. . A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that the obtained positive electrode active material was used.

(Example 10)
EC and EMC were mixed with the non-aqueous electrolyte at a volume ratio of 1: 3 to obtain a non-aqueous solvent. A non-aqueous electrolyte (E / E) was prepared by dissolving LiPF ₆ in the non-aqueous solvent thus obtained to a concentration of 1.0 mol / L. A lithium ion secondary battery was produced and evaluated in the same manner as in Example 1 except that the obtained nonaqueous electrolytic solution was used.

(Comparative Example 1)
In the same manner as in Example 1, an artificial graphite slurry and a lithium titanate slurry were obtained. The obtained artificial graphite mixture slurry was applied to both sides of a negative electrode current collector made of a copper foil having a thickness of 10 μm, dried and rolled to obtain a negative electrode having a total thickness of 160 μm, and then the lithium titanate slurry was added to the artificial graphite layer. A negative electrode having a total thickness of 220 μm provided with a negative electrode active material layer was obtained by coating, drying and rolling on the substrate. A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that the obtained negative electrode was used.

(Comparative Example 2)
In the same manner as in Example 1, an artificial graphite slurry and a lithium titanate slurry were obtained. The obtained artificial graphite mixture slurry was applied to both sides of a negative electrode current collector made of a copper foil having a thickness of 10 μm, dried and rolled to obtain a negative electrode having a total thickness of 160 μm, and then the lithium titanate slurry was added to the artificial graphite layer. The negative electrode with a total thickness of 161 μm provided with the negative electrode active material layer was obtained by applying, drying and rolling onto the negative electrode. A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that the obtained negative electrode was used.

(Comparative Example 3)
In the same manner as in Example 1, an artificial graphite mixture slurry was obtained. Next, by mixing 90 parts by mass of lithium titanate, 5 parts by mass of a conductive agent, and 40 parts by mass of an NMP solution of PVDF (8% by mass of PVDF, 5 parts by mass of solid content of PVDF), titanium was mixed. A lithium acid mixture slurry was obtained. The obtained artificial graphite mixture slurry was applied to both sides of a negative electrode current collector made of a copper foil having a thickness of 10 μm, dried and rolled to obtain a negative electrode having a total thickness of 160 μm, and then the lithium titanate slurry was added to the artificial graphite layer. A negative electrode having a total thickness of 180 μm provided with a negative electrode active material layer was obtained by coating, drying and rolling on the substrate.

(Comparative Example 4)
In the same manner as in Example 1, an artificial graphite mixture slurry was obtained. Next, 90 parts by mass of lithium titanate and 80 parts by mass of NDF solution of PVDF (PVDF concentration of 8% by mass, PVDF solid content of 10 parts by mass) are mixed to obtain a lithium titanate mixture slurry. It was. The obtained artificial graphite mixture slurry was applied to both sides of a negative electrode current collector made of a copper foil having a thickness of 10 μm, dried and rolled to obtain a negative electrode having a total thickness of 160 μm, and then the lithium titanate slurry was added to the artificial graphite layer. A negative electrode having a total thickness of 180 μm provided with a negative electrode active material layer was obtained by coating, drying and rolling on the substrate.

(Comparative Example 5)
A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that a lithium nickel composite oxide containing no tungsten compound was used as the positive electrode active material.

(Comparative Example 6)
In the same manner as in Example 1, an artificial graphite mixture slurry was obtained. The obtained artificial graphite slurry was applied to both sides of a negative electrode current collector made of a copper foil having a thickness of 10 μm, dried and rolled to prepare a negative electrode having a total thickness of 180 μm provided with a negative electrode active material layer. A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that the obtained negative electrode was used.

(Comparative Example 7)
In the same manner as in Example 1, a lithium titanate mixture slurry was obtained. The obtained lithium titanate slurry was applied to both sides of a negative electrode current collector made of a copper foil having a thickness of 10 μm, dried, and rolled to prepare a negative electrode having a total thickness of 180 μm including a negative electrode active material layer. A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that the obtained negative electrode was used.

(Comparative Example 8)
A lithium nickel composite oxide containing no tungsten compound was used as the positive electrode active material. Further, an artificial graphite mixture slurry was obtained in the same manner as in Example 1. The obtained artificial graphite slurry was applied to both sides of a negative electrode current collector made of a copper foil having a thickness of 10 μm, dried and rolled to prepare a negative electrode having a total thickness of 180 μm provided with a negative electrode active material layer. A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that the obtained negative electrode was used.

(Comparative Example 9)
A lithium nickel composite oxide containing no tungsten compound element was used as the positive electrode active material. Moreover, it carried out similarly to Example 1, and obtained the lithium titanate mixture slurry. The obtained lithium titanate slurry was applied to both sides of a negative electrode current collector made of a copper foil having a thickness of 10 μm, dried, and rolled to prepare a negative electrode having a total thickness of 180 μm including a negative electrode active material layer. A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that the obtained negative electrode was used.

  The battery of Example 1 had good initial discharge capacity. This is because the lithium nickel composite oxide containing a tungsten compound was used as the positive electrode active material, the surface of the positive electrode active material was modified, the discharge capacity showed a good value, and the lithium titanate of the negative electrode was used as the active material. By controlling the thickness of the second layer 12 to be 13.3% with respect to the first layer 11 made of artificial graphite as an active material, the influence on the decrease in battery capacity of lithium titanate having a small theoretical capacity can be suppressed. This is thought to be due to the fact that

  Furthermore, Example 1 had a good capacity retention rate after 100 cycles. This is because the negative electrode potential of lithium titanate can be lowered by providing the negative electrode with the first layer 11 using artificial graphite as an active material and the second layer 12 using lithium titanate as an active material. It is considered that the gas generation due to the decomposition of the nonaqueous electrolytic solution containing the fluorinated solvent was suppressed by the formation of a good film of fluoroethylene carbonate on the negative electrode surface. Furthermore, it is considered that the amount of the conductive agent contained in the second layer 12 is 3 parts by mass with respect to 100 parts by mass of lithium titanate, so that decomposition of the non-aqueous electrolyte can be suppressed and cycle characteristics are improved.

  Further, the battery of Example 2 had a good initial discharge capacity. This is because the surface of the positive electrode active material is modified by using a lithium nickel composite oxide containing a tungsten compound as the positive electrode active material, and the initial discharge capacity shows a good value. By setting the thickness of the second layer 12 to 20% with respect to the first layer 11 made of artificial graphite as an active material, it is possible to suppress the influence on the decrease in battery capacity of lithium titanate having a small theoretical capacity. It is thought that it was made. However, although the initial discharge capacity is smaller than that of Example 1, the thickness of the second layer 12 using lithium titanate having a low theoretical capacity as the active material is larger than that of Example 1. This is considered to be due to the remarkable influence on the battery capacity reduction.

Furthermore, the battery of Example 2 had a good capacity retention rate after 100 cycles. This is because the redox potential of lithium titanate can be lowered by providing the negative electrode with the first layer 11 using artificial graphite as the active material and the second layer 12 using lithium titanate as the active material. It is considered that gas generation due to decomposition of the nonaqueous electrolytic solution containing the fluorinated solvent was suppressed by forming a good film of fluoroethylene carbonate on the surface. Furthermore, the amount of the conductive agent contained in the second layer 12 is 3 parts by mass with respect to 100 parts by mass of lithium titanate, so that the decomposition of the non-aqueous electrolyte can be suppressed, and the cycle characteristics are considered improved.

  The battery of Example 3 had good initial discharge capacity. This is because the lithium nickel composite oxide containing a tungsten compound was used as the positive electrode active material, the surface of the positive electrode active material was modified, the discharge capacity showed a good value, and the lithium titanate of the negative electrode was used as the active material. By setting the thickness of the second layer 12 to 1.3% with respect to the first layer 11 made of artificial graphite as an active material, the effect of lithium titanate having a small theoretical capacity on battery capacity reduction is reduced. It is thought that it was possible to suppress.

  Furthermore, the battery of Example 3 had a good capacity retention rate after 100 cycles. This is because the redox potential of lithium titanate can be lowered by providing the negative electrode with the first layer 11 using artificial graphite as the active material and the second layer 12 using lithium titanate as the active material. It is considered that gas generation due to decomposition of the nonaqueous electrolytic solution containing the fluorinated solvent was suppressed by forming a good film of fluoroethylene carbonate on the surface. Furthermore, the amount of the conductive agent contained in the second layer 12 is 3 parts by mass with respect to 100 parts by mass of lithium titanate, so that the decomposition of the non-aqueous electrolyte can be suppressed, and the cycle characteristics are considered improved. However, the capacity retention rate after 100 cycles is lower than that of Example 1, but this is because the different elements contained in the positive electrode active material are eluted and the total amount deposited on the negative electrode is in the lithium titanate. It is considered that the amount is larger than the amount that can be deposited, and the decomposition of the non-aqueous electrolyte cannot be suppressed and the cycle characteristics are deteriorated.

  The battery of Example 4 had good initial discharge capacity. This is because the lithium nickel composite oxide containing a tungsten compound was used as the positive electrode active material, the surface of the positive electrode active material was modified, the discharge capacity showed a good value, and the lithium titanate of the negative electrode was used as the active material. By setting the thickness of the second layer 12 to 13.3% with respect to the first layer 11 made of artificial graphite as an active material, the influence of lithium titanate having a small theoretical capacity on the decrease in battery capacity is reduced. It is thought that it was possible to suppress. However, the initial discharge capacity was lower than that in Example 1. This is presumably because the amount of the conductive agent contained in the second layer 12 was smaller than that in Example 1, and therefore, sufficient battery characteristics could not be expressed as compared with Example 1.

  Furthermore, the battery of Example 4 had a good capacity retention rate after 100 cycles. This is because the redox potential of lithium titanate can be lowered by providing the negative electrode with the first layer 11 using artificial graphite as an active material and the second layer 12 using lithium titanate as an active material. It is considered that gas generation due to decomposition of the nonaqueous electrolytic solution containing the fluorinated solvent was suppressed by forming a good film of fluoroethylene carbonate on the negative electrode surface. Furthermore, the amount of the conductive agent contained in the second layer 12 is set to 2 parts by mass with respect to 100 parts by mass of lithium titanate, so that the decomposition of the nonaqueous electrolytic solution can be suppressed, and the cycle characteristics are considered to be improved.

The battery of Example 5 had a good initial discharge capacity. This is because the lithium nickel composite oxide containing a tungsten compound was used as the positive electrode active material, the surface of the positive electrode active material was modified, the discharge capacity showed a good value, and the lithium titanate of the negative electrode was used as the active material. By setting the thickness of the second layer 12 to 13.3% with respect to the first layer 11 made of artificial graphite as an active material, the influence of lithium titanate having a small theoretical capacity on the decrease in battery capacity is reduced. It is thought that it was possible to suppress. However, the initial discharge capacity is lower than in Examples 1 and 2, but this is because the amount of the conductive agent contained in the second layer 12 was smaller than that in Example 1, so Compared to 2, it is considered that sufficient battery characteristics could not be expressed.

  Furthermore, the battery of Example 5 had a good capacity retention rate after 100 cycles. This is because the redox potential of lithium titanate can be lowered by providing the negative electrode with the first layer 11 using artificial graphite as the active material and the second layer 12 using lithium titanate as the active material. It is considered that the gas generation due to the decomposition of the nonaqueous electrolytic solution containing the fluorinated solvent was suppressed by the formation of a good film of fluoroethylene carbonate on the negative electrode surface. Furthermore, the amount of the conductive agent contained in the second layer 12 is set to 1 part by mass with respect to 100 parts by mass of lithium titanate, so that the decomposition of the nonaqueous electrolytic solution can be suppressed, and the cycle characteristics are considered to be improved.

  The battery of Example 6 exhibited a good initial discharge capacity equivalent to that of Example 1. This is because, by using a lithium nickel composite oxide containing a niobium compound as the positive electrode active material, the surface of the positive electrode active material is modified, the discharge capacity shows a good value, and the lithium titanate of the negative electrode is used as the active material. By setting the thickness of the second layer 12 to 13.3% with respect to the first layer 11 made of artificial graphite as an active material, the influence of lithium titanate having a small theoretical capacity on the decrease in battery capacity is reduced. It is thought that it was possible to suppress.

  Furthermore, the battery of Example 6 had a good capacity retention rate after 100 cycles. This is because the redox potential of lithium titanate can be lowered by providing the negative electrode with the first layer 11 using artificial graphite as an active material and the second layer 12 using lithium titanate as an active material. It is considered that gas generation due to decomposition of the nonaqueous electrolytic solution containing the fluorinated solvent was suppressed by forming a good film of fluoroethylene carbonate on the negative electrode surface. Furthermore, the amount of the conductive agent contained in the second layer 12 is 3 parts by mass with respect to 100 parts by mass of lithium titanate, so that the decomposition of the non-aqueous electrolyte can be suppressed, and the cycle characteristics are considered improved.

  The battery of Example 7 exhibited a good initial discharge capacity equivalent to that of Example 1. This is because, by using a lithium nickel composite oxide containing a boron compound as a positive electrode active material, the surface of the positive electrode active material is modified, the discharge capacity shows a good value, and the lithium titanate of the negative electrode is used as the active material. By setting the thickness of the second layer 12 to 13.3% with respect to the first layer 11 made of artificial graphite as an active material, the influence of lithium titanate having a small theoretical capacity on the decrease in battery capacity is reduced. It is thought that it was possible to suppress.

  Furthermore, in Example 7, the capacity retention rate after 100 cycles was good. This is because the redox potential of lithium titanate can be lowered by providing the negative electrode with the first layer 11 using artificial graphite as the active material and the second layer 12 using lithium titanate as the active material. It is considered that the gas generation due to the decomposition of the nonaqueous electrolytic solution containing the fluorinated solvent was suppressed by the formation of a good film of fluoroethylene carbonate on the negative electrode surface. Furthermore, the amount of the conductive agent contained in the second layer 12 is 3 parts by mass with respect to 100 parts by mass of lithium titanate, so that the decomposition of the non-aqueous electrolyte can be suppressed, and the cycle characteristics are considered improved.

The battery of Example 8 exhibited a good initial discharge capacity equivalent to that of Example 1. This is because, by using a lithium nickel composite oxide containing a zirconium compound as the positive electrode active material, the surface of the positive electrode active material is modified, the discharge capacity shows a good value, and the lithium titanate of the negative electrode is used as the active material. By setting the thickness of the second layer 12 to 13.3% with respect to the first layer 11 made of artificial graphite as an active material, the influence of lithium titanate having a small theoretical capacity on the decrease in battery capacity is reduced. It is thought that it was possible to suppress.

  Furthermore, the battery of Example 8 had a good capacity retention rate after 100 cycles. This is because the redox potential of lithium titanate can be lowered by providing the negative electrode with the first layer 11 using artificial graphite as the active material and the second layer 12 using lithium titanate as the active material. It is considered that the gas generation due to the decomposition of the nonaqueous electrolytic solution containing the fluorinated solvent was suppressed by the formation of a good film of fluoroethylene carbonate on the negative electrode surface. Furthermore, the amount of the conductive agent contained in the second layer 12 is 3 parts by mass with respect to 100 parts by mass of lithium titanate, so that the decomposition of the non-aqueous electrolyte can be suppressed, and the cycle characteristics are considered improved.

  The battery of Example 9 exhibited a good initial discharge capacity equivalent to that of Example 1. This is because, by using a lithium nickel composite oxide containing a vanadium compound as a positive electrode active material, the surface of the positive electrode active material is modified, the discharge capacity shows a good value, and the lithium titanate of the negative electrode is used as the active material. By setting the thickness of the second layer 12 to 13.3% with respect to the first layer 11 made of artificial graphite as an active material, the influence of lithium titanate having a small theoretical capacity on the decrease in battery capacity is reduced. It is thought that it was possible to suppress.

  Furthermore, the battery of Example 9 had a good capacity retention rate after 100 cycles. This is because the redox potential of lithium titanate can be lowered by providing the negative electrode with the first layer 11 using artificial graphite as the active material and the second layer 12 using lithium titanate as the active material. It is considered that the gas generation due to the decomposition of the nonaqueous electrolytic solution containing the fluorinated solvent was suppressed by the formation of a good film of fluoroethylene carbonate on the negative electrode surface. Furthermore, the amount of the conductive agent contained in the second layer 12 is 3 parts by mass with respect to 100 parts by mass of lithium titanate, so that the decomposition of the non-aqueous electrolyte can be suppressed, and the cycle characteristics are considered improved.

  Although the battery of Example 10 had good battery characteristics, the initial discharge capacity and the capacity retention after 100 cycles showed lower values than the battery of Example 1. From this, it can be considered that the inclusion of FEC in the non-aqueous electrolyte facilitates the formation of a good film on the negative electrode surface and improves the battery characteristics.

  In addition, the battery of Comparative Example 1 showed a lower initial discharge capacity than the batteries of Examples 1 to 9. This is because the thickness of the second layer 12 using lithium titanate as an active material is greater than 25% of the thickness of the first layer 11 using artificial graphite as an active material, so that lithium titanate having a low theoretical capacity is obtained. This is considered to be due to the remarkable influence on the decrease in battery capacity.

  On the other hand, the battery of Comparative Example 2 showed a lower capacity retention rate after 100 cycles than the batteries of Examples 1 to 9. This is because the thickness of the second layer 12 using lithium titanate as an active material is less than 1% with respect to the first layer 11 using artificial graphite as an active material, so that the different element contained in the positive electrode active material This is considered to be because the total amount of leached and deposited on the negative electrode is larger than the amount that can be deposited on lithium titanate, and the decomposition of the non-aqueous electrolyte cannot be suppressed, resulting in a decrease in cycle characteristics.

  Moreover, the battery of Comparative Example 3 showed a lower value of the capacity retention rate after 100 cycles than the batteries of Examples 1 to 9. This is because the amount of the conductive agent contained in the second layer 12 containing lithium titanate as an active material is 5% by mass with respect to 100 parts by mass of lithium titanate, so that the decomposition of the non-aqueous electrolyte can be suppressed. It is thought that it became.

Furthermore, the battery of Comparative Example 4 had a greatly reduced initial discharge capacity as compared with the batteries of Examples 1 to 9. This is considered to be because the second layer 12 containing lithium titanate as an active material did not contain a conductive agent, so that the conductivity of the second layer 12 was insufficient and no electrode activity appeared. It is done.

  Further, the battery of Comparative Example 5 showed a low value for both the initial discharge capacity and the capacity retention rate after 100 cycles as compared with the batteries of Examples 1 to 9. This is considered to be due to the use of a positive electrode active material that does not contain different elements.

  On the other hand, when compared with the batteries of Examples 1 to 9, the battery of Comparative Example 6 showed a low capacity retention rate after 100 cycles. This is because, because the negative electrode did not contain lithium titanate, the dissimilar elements contained in the eluted positive electrode were deposited on the negative electrode surface, so that decomposition of the non-aqueous electrolyte was not suppressed and cycle characteristics were reduced. Conceivable.

  Furthermore, the battery of Comparative Example 7 showed lower values for the initial discharge capacity and the capacity retention after 100 cycles than the batteries of Examples 1 to 9. This is because the use of a lithium titanate monolayer having a low theoretical capacity for the negative electrode resulted in a decrease in battery capacity and a high redox potential of lithium titanate, which prevented the formation of a film on the lithium titanate surface. This is considered to be sufficient because gas generation due to decomposition of the nonaqueous electrolytic solution containing the fluorinated solvent could not be suppressed, and the cycle characteristics deteriorated.

  Further, the battery of Comparative Example 8 showed a low value for the initial discharge capacity and the capacity retention after 100 cycles as compared with the batteries of Examples 1 to 9. This is due to the use of a positive electrode active material that does not contain foreign elements, and because the negative electrode does not contain lithium titanate, so that the foreign elements contained in the eluted positive electrode are deposited on the surface of the negative electrode. It is considered that the decomposition of the liquid was not suppressed and the cycle characteristics were deteriorated.

  Further, the battery of Comparative Example 9 showed lower values for the initial discharge capacity and the capacity retention after 100 cycles than the batteries of Examples 1 to 9. This is due to the use of a positive electrode active material that does not contain foreign elements, and because the redox potential of lithium titanate is high, the formation of a film on the lithium titanate surface is insufficient, and a non-fluorinated solvent is contained. It is considered that gas generation due to decomposition of the water electrolyte could not be suppressed and cycle characteristics were deteriorated.

  The lithium ion secondary battery of the present invention has a large discharge capacity even when charged at a high voltage, can suppress the decomposition of the non-aqueous electrolyte during the charge / discharge cycle, and has good cycle characteristics. Therefore, the lithium ion secondary battery of the present invention is useful as a power source for various portable electronic devices such as mobile phones, PDAs, notebook personal computers, digital cameras, and portable game machines. Further, it can be applied to the use of a driving power source for an electric vehicle, a hybrid vehicle and the like.

DESCRIPTION OF SYMBOLS 10 Negative electrode collector 11 1st layer 12 2nd layer 20 Lithium ion secondary battery 21 Positive electrode 22 Negative electrode 23 Separator 24 Electrode group 25 Positive electrode side insulating plate 26 Negative electrode side insulating plate 27 Battery case 28 Sealing plate 29 Negative electrode lead 30 Positive terminal 31 Positive lead

Claims (7)

A lithium ion secondary battery comprising: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; a separator disposed between the positive electrode and the negative electrode; and a non-aqueous electrolyte.
The positive electrode active material is a lithium nickel composite oxide containing a different element, and the different element is at least one kind of different element selected from the group consisting of tungsten, niobium, boron, zirconium and vanadium,
The negative electrode active material comprises a first layer formed on a current collector and a second layer formed on the first layer,
The first layer is a layer containing a carbon material, a thickener, and a binder,
The second layer is a layer containing lithium titanate, a conductive agent and a binder,
The second layer has a thickness of 1% to 25% with respect to the thickness of the first layer, and the conductive agent contained in the second layer is 100 parts by mass of the lithium titanate. The lithium ion secondary battery is characterized by being 3 parts by mass or less with respect to.   2. The lithium ion secondary battery according to claim 1, wherein the first layer has a mixture density of 1.4 g / cc or more and 2.8 g / cc or less.   3. The lithium ion secondary battery according to claim 1, wherein the second layer has a mixture density of 1.3 g / cc or more and 1.8 g / cc or less. The lithium ion secondary battery according to claim 1, wherein the lithium titanate has a BET specific surface area of ² m ² / g or more and 8 m ² / g or less.   The lithium ion secondary battery according to claim 1, wherein the lithium titanate has an average particle size of 0.5 μm or more and 10 μm or less.   The lithium ion secondary battery according to claim 1, wherein the lithium titanate has an oil absorption of 20 g / 100 g or more and 50 g / 100 g or less.   The non-aqueous electrolyte includes a fluorinated solvent that is at least one selected from the group consisting of fluoroethylene carbonate, methyl fluoropropionate, fluorobenzene, fluoroethyl methyl carbonate, and fluorodimethylene carbonate. Item 7. The lithium ion secondary battery according to any one of Items 1 to 6.