JP6252890B2 - Lithium iron manganese composite oxide and lithium ion secondary battery using the same - Google Patents

Description

  The present embodiment relates to a lithium iron manganese based composite oxide and a lithium ion secondary battery using the same.

  A lithium ion secondary battery comprising a positive electrode including a lithium iron manganese-based composite oxide as a positive electrode active material and a negative electrode including a material capable of occluding and releasing lithium ions as a negative electrode active material is expected as a high energy density secondary battery. Has been. For example, Patent Document 1 discloses a lithium ion secondary battery using a lithium iron manganese composite oxide as a positive electrode active material. On the other hand, Patent Documents 2 to 8 disclose techniques for substituting a part of elements of a composite oxide with fluorine atoms.

JP 2005-154256 A JP 2006-344425 A JP 2007-66745 A International Publication No. 03/069702 JP 2000-128539 A US Patent Application Publication No. 2010/0086854 JP 2013-503450 A International Publication No. 2013/069791

  However, the lithium ion secondary battery disclosed in the patent document has a problem in that the capacity of the secondary battery decreases with a charge / discharge cycle.

  An object of the present embodiment is to provide a lithium iron manganese based composite oxide that can provide a lithium ion secondary battery having a high capacity retention rate in a charge / discharge cycle.

The lithium iron manganese-based composite oxide according to the present embodiment has a layered rock salt structure, and has the following formula (1):
Li _x M ¹ _(yp) Mn _p M ² _(zq) Fe _q O _(2-δ-r) F _r (1)
(In the above formula (1), 1.05 ≦ x ≦ 1.32, 0.33 ≦ y ≦ 0.63, 0.06 ≦ z ≦ 0.50, 0 <p ≦ 0.63, 0.06 ≦ q ≦ 0.50, 0.01 ≦ r <2-δ, 0.06 ≦ δ ≦ 0.80, y ≧ p, z ≧ q, M ¹ is at least one element of Ti and Zr, M ² is at least one element selected from the group consisting of Co, Ni and Mn).

  The positive electrode active material for a lithium ion secondary battery according to this embodiment includes the lithium iron manganese composite oxide.

  The positive electrode for a lithium ion secondary battery according to this embodiment includes the positive electrode active material for a lithium ion secondary battery.

  The lithium ion secondary battery according to this embodiment includes the positive electrode for a lithium ion secondary battery and a negative electrode.

  According to the present embodiment, it is possible to provide a lithium iron manganese based composite oxide that can provide a lithium ion secondary battery having a high capacity retention rate in a charge / discharge cycle.

It is sectional drawing of an example of the lithium ion secondary battery which concerns on this embodiment.

[Lithium iron manganese complex oxide]
The lithium iron manganese-based composite oxide according to the present embodiment has a layered rock salt structure, and has the following formula (1):
Li _x M ¹ _(yp) Mn _p M ² _(zq) Fe _q O _(2-δ-r) F _r (1)
(In the above formula (1), 1.05 ≦ x ≦ 1.32, 0.33 ≦ y ≦ 0.63, 0.06 ≦ z ≦ 0.50, 0 <p ≦ 0.63, 0.06 ≦ q ≦ 0.50, 0.01 ≦ r <2-δ, 0 ≦ δ ≦ 0.80, y ≧ p, z ≧ q, M ¹ is at least one element of Ti and Zr, and M ² Is at least one element selected from the group consisting of Co, Ni and Mn).

Li ₂ Me ¹ O ₃ (Me ¹ contains at least Mn) and LiMe ² O ₂ (Me ² contains at least Fe), a lithium iron manganese-based composite oxide having a layered rock salt structure, Compared to lithium nickel manganese composite oxide and lithium cobalt manganese composite oxide in which Me ² contains at least Ni or Co instead of Fe, a positive electrode active material for lithium ion secondary battery (hereinafter referred to as positive electrode active material) When used as a battery, it is excellent in that a high energy density lithium ion secondary battery (hereinafter referred to as a secondary battery) is obtained. However, in the lithium iron manganese based composite oxide, oxygen is easily released in the charge / discharge cycle after activation.

When oxygen is desorbed in the charge / discharge cycle, the structure of the positive electrode active material changes from a layered rock salt structure to a spinel structure, and thus the capacity of the secondary battery decreases. Further, since Li ₂ O is generated on the negative electrode by the desorbed oxygen, the capacity of the secondary battery is reduced. Furthermore, since the secondary battery swells due to the desorption of oxygen and the resistance increases, the capacity of the secondary battery decreases.

The lithium iron manganese composite oxide (hereinafter referred to as composite oxide) according to the present embodiment is a composite oxide having a specific composition represented by the above formula (1), wherein some of the oxygen atoms are fluorine. Substituted by an atom. When the O ²⁻ site is substituted by F ^{2 −} , the bond between oxygen and metal is strengthened, so that diffusion of O ²⁻ can be prevented and desorption of oxygen can be suppressed. Thereby, when the complex oxide according to the present embodiment is used, the capacity of the secondary battery is maintained even in the charge / discharge cycle, and a high capacity maintenance rate is obtained. Details of this embodiment will be described below.

The composite oxide represented by the formula (1) contains at least Mn. The composition p of Mn is 0 <p ≦ 0.63. When 0 <p, lithium can be included excessively. Further, by satisfying p ≦ 0.63, Li ₂ Me ¹ O ₃ (Me ¹ contains at least Mn) and LiMe ² O ₂ (Me ² contains at least Fe) take a solid solution state. Can do. p is preferably 0.10 ≦ p ≦ 0.60, more preferably 0.20 ≦ p ≦ 0.55, and still more preferably 0.30 ≦ p ≦ 0.50.

In the formula (1), M ¹ is at least one element of Ti and Zr. The y of the composition yp of M ¹ is 0.33 ≦ y ≦ 0.63. When 0.33 ≦ y, excess lithium can be contained. Further, by satisfying y ≦ 0.63, Li ₂ Me ¹ O ₃ (Me ¹ contains at least Mn) and LiMe ² O ₂ (Me ² contains at least Fe) take a solid solution state. Can do. y is preferably 0.35 ≦ y ≦ 0.60, more preferably 0.40 ≦ y ≦ 0.55, and still more preferably 0.45 ≦ y ≦ 0.50. The formula (1) satisfies y ≧ p. Further, the composition yp of M ¹ may be zero. That is, the complex oxide represented by the formula (1) may not contain M ¹ . Mn and M ¹ in the formula (1) correspond to Me ¹ of the Li ₂ Me ¹ O ₃ .

  The composite oxide represented by the formula (1) contains at least Fe. The composition q of Fe is 0.06 ≦ q ≦ 0.50. By being 0.06 <= q, a lithium iron manganese system complex oxide can be activated. Further, since q ≦ 0.50, the capacity can be kept large. q is preferably 0.10 ≦ q ≦ 0.45, more preferably 0.13 ≦ q ≦ 0.40, and still more preferably 0.16 ≦ q ≦ 0.30.

In the formula (1), M ² is at least one element selected from the group consisting of Co, Ni and Mn. The z of the composition zq of M ² is 0.06 ≦ z ≦ 0.50. By being 0.06 <= z, a lithium iron manganese system complex oxide can be activated. Further, when z ≦ 0.50, excessive lithium can be contained. z is preferably 0.08 ≦ z ≦ 0.45, more preferably 0.10 ≦ z ≦ 0.40, and further preferably 0.12 ≦ z ≦ 0.30. The formula (1) satisfies z ≧ q. The composition zq of M ² may be zero. That is, the complex oxide represented by the formula (1) may not contain M ² . Fe and M ² in the formula (1) correspond to Me ² of the LiMe ² O ₂ .

In the formula (1), the composition x of Li is 1.05 ≦ x ≦ 1.32. By satisfying 1.05 ≦ x, the capacity can be increased. Further, by satisfying x ≦ 1.32, Li ₂ Me ¹ O ₃ (Me ¹ contains at least Mn) and LiMe ² O ₂ (Me ² contains at least Fe) are in a solid solution state. Can do. x is preferably 1.10 ≦ x ≦ 1.30, more preferably 1.16 ≦ x ≦ 1.28, and still more preferably 1.20 ≦ x ≦ 1.26.

  In the formula (1), δ in the oxygen atom composition 2-δ-r is a parameter indicating oxygen deficiency, and 0 ≦ δ ≦ 0.80. By satisfying 0 ≦ δ, the capacity can be increased. Further, when δ ≦ 0.80, the crystal structure can be stabilized. δ is preferably 0.02 ≦ δ ≦ 0.50, more preferably 0.04 ≦ δ ≦ 0.30, and further preferably 0.06 ≦ δ ≦ 0.20. Note that δ varies depending on the method for synthesizing the composite oxide.

In the formula (1), the composition r of F is 0.01 ≦ r <2-δ. When 0.01 ≦ r, the bond between oxygen and metal is sufficiently strengthened, so that diffusion of O ²⁻ can be prevented and desorption of oxygen can be suppressed. r is preferably 0.02 ≦ r ≦ 0.40, more preferably 0.10 <r ≦ 0.30, and still more preferably 0.11 ≦ r ≦ 0.20.

  In addition, the composition of each element in the formula (1) is a value measured by inductively coupled plasma emission spectrometry for Li, and by inductively coupled plasma mass spectrometry for the other elements.

  The composite oxide represented by the formula (1) has a layered rock salt structure. Since the composite oxide has a layered rock salt structure, charge and discharge can be stably repeated. Whether or not it has a layered rock salt structure can be determined by X-ray diffraction analysis. Further, it is not necessary that the entire complex oxide has a layered rock salt type structure, and it is sufficient that at least a part of the complex oxide has a layered rock salt type structure.

[Method for producing lithium iron manganese composite oxide]
The method for producing the lithium iron manganese based composite oxide is not particularly limited, and can be produced by performing a heat treatment such as firing or hydrothermal treatment on a metal raw material containing at least lithium, manganese, iron and a fluorine compound. . On the other hand, in order to obtain a lithium iron manganese-based composite oxide having more excellent electrochemical characteristics, it is preferable to mix constituent metal elements other than lithium more uniformly. From this point of view, it is preferable to obtain a composite hydroxide such as iron or manganese from the liquid phase by, for example, a coprecipitation method, and calcine it with lithium and a fluorine compound. This method can be broadly divided into a composite hydroxide production process for producing a composite hydroxide containing a constituent metal other than lithium and a firing process for firing in the presence of lithium and a fluorine compound.

<Composite hydroxide production process>
The composite hydroxide can be prepared by dropping a water-soluble salt of a constituent metal into an alkaline aqueous solution, performing air oxidation as necessary, and aging the hydroxide. The water-soluble salt of the constituent metal is not particularly limited, and examples thereof include anhydrous salts and hydrates such as nitrate, sulfate, chloride, and acetate of the constituent metal. The alkali source is not particularly limited, and examples thereof include lithium hydroxide and hydrates thereof, sodium hydroxide, potassium hydroxide, and aqueous ammonia. These may use 1 type and may use 2 or more types together. The composite hydroxide can be obtained by gradually dropping a water-soluble salt of a constituent metal into an alkaline aqueous solution over several hours. The temperature at which the water-soluble salt of the constituent metal is dropped is preferably 60 ° C. or less from the viewpoint of suppressing the generation of impurities such as spinel ferrite. In addition, when the water-soluble salt of the constituent metal is dropped at 0 ° C. or lower, it is preferable to prevent the solution from solidifying by adding ethanol or the like as an antifreeze to the alkaline aqueous solution. It is preferable to ripen the hydroxide by wet-oxidizing the hydroxide obtained after the dropwise addition by blowing air at room temperature for several hours or more. The resulting mature product is washed with water and filtered to obtain the desired composite hydroxide.

<Baking process>
A predetermined lithium compound and a fluorine compound are added to and mixed with the composite hydroxide according to the composition formula, and then fired in a predetermined atmosphere. Then, in order to remove an excess lithium compound as needed, a lithium iron manganese system complex oxide which has the target composition formula is obtained by performing washing processing, filtration, and drying. The lithium compound is not particularly limited, and an anhydride or hydrate such as lithium carbonate, lithium hydroxide, lithium nitrate, or lithium acetate can be used. The fluorine compound is not particularly limited, and ammonium fluoride, ammonium hydrogen fluoride, sodium fluoride, potassium fluoride, lithium fluoride, fluorine gas, and the like can be used. These may use 1 type and may use 2 or more types together. The firing temperature is preferably 1000 ° C. or less from the viewpoint of preventing Li volatilization. As the firing atmosphere, an air atmosphere, an inert gas atmosphere, a nitrogen atmosphere, an oxygen atmosphere, or the like can be used. If necessary, a pulverization treatment may be performed to adjust the particle size at the time of mixing the composite hydroxide before firing with the lithium compound and the fluorine compound or after firing.

[Positive electrode active material for lithium ion secondary battery]
The positive electrode active material for a lithium ion secondary battery according to the present embodiment includes the lithium iron manganese based composite oxide according to the present embodiment. When the positive electrode active material includes the lithium iron manganese composite oxide according to the present embodiment, desorption of oxygen is suppressed even in the charge / discharge cycle, and the capacity of the secondary battery is maintained.

  The proportion of the lithium iron manganese based composite oxide according to this embodiment contained in the positive electrode active material for a lithium ion secondary battery according to this embodiment is preferably 80% by mass or more, and 90% by mass or more. Is more preferably 95% by mass or more. The ratio may be 100% by mass.

[Positive electrode for lithium ion secondary battery]
The positive electrode for lithium ion secondary batteries according to the present embodiment (hereinafter referred to as positive electrode) includes the positive electrode active material for lithium ion secondary batteries according to the present embodiment.

  The positive electrode can be produced by applying the positive electrode active material according to the present embodiment on a positive electrode current collector. For example, it can be produced by mixing the positive electrode active material according to this embodiment, a conductivity imparting agent, a binder, and a solvent, applying the mixture onto the positive electrode current collector, and drying. As the conductivity imparting agent, a carbon material such as ketjen black, a metal material such as Al, a conductive oxide, or the like can be used. As the binder, polyvinylidene fluoride, acrylic resin, polytetrafluoroethylene resin, or the like can be used. As the solvent, N-methylpyrrolidone or the like can be used. As the positive electrode current collector, a metal thin film mainly containing aluminum or the like can be used. Although the thickness of a positive electrode electrical power collector is not specifically limited, For example, it can be 5-50 micrometers, and it is preferable that it is 10-40 micrometers.

  The addition amount of the conductivity imparting agent can be 1 to 10% by mass, and preferably 2 to 7% by mass. When the addition amount is 1% by mass or more, sufficient conductivity can be maintained. Moreover, since the ratio of positive electrode active material mass can be enlarged because this addition amount is 10 mass% or less, the capacity | capacitance per mass can be enlarged. The addition amount of the binder may be 1 to 10% by mass, and preferably 2 to 7% by mass. When the addition amount is 1% by mass or more, generation of positive electrode peeling can be prevented. Moreover, since the ratio of positive electrode active material mass can be enlarged because this addition amount is 10 mass% or less, the capacity | capacitance per mass can be enlarged.

  Although the thickness of a positive electrode is not specifically limited, For example, it can be 50-500 micrometers, and it is preferable that it is 100-400 micrometers.

[Lithium ion secondary battery]
The lithium ion secondary battery according to the present embodiment includes the positive electrode for a lithium ion secondary battery according to the present embodiment and a negative electrode.

  An example of the secondary battery according to the present embodiment is shown in FIG. In the secondary battery shown in FIG. 1, a positive electrode is configured by forming a positive electrode active material layer 1 containing a positive electrode active material according to the present embodiment on a positive electrode current collector 1A. Moreover, the negative electrode is comprised by forming the negative electrode active material layer 2 on the negative electrode collector 2A. These positive electrode and negative electrode are disposed so as to face each other through the separator 3 while being immersed in an electrolytic solution. The positive electrode is connected to the positive electrode tab 1B, and the negative electrode is connected to the negative electrode tab 2B. This power generation element is accommodated in the exterior body 4, and the positive electrode tab 1B and the negative electrode tab 2B are exposed to the outside.

  By applying a voltage to the positive electrode and the negative electrode, lithium ions are desorbed from the positive electrode active material, and lithium ions are occluded in the negative electrode active material, so that charging occurs. In addition, by causing electrical contact between the positive electrode and the negative electrode outside the secondary battery, lithium ions are released from the negative electrode active material contrary to the time of charging, and lithium ions are occluded in the positive electrode active material. Occur.

  As an electrolytic solution used in the secondary battery according to the present embodiment, a solution in which a lithium salt as a supporting salt is dissolved in a solvent can be used. Examples of the solvent include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and vinylene carbonate (VC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate ( DEC), chain carbonates such as dipropyl carbonate (DPC), aliphatic carboxylic acid esters such as methyl formate, methyl acetate and ethyl propionate, γ-lactones such as γ-butyrolactone, 1,2-diethoxy Chain ethers such as ethane (DEE) and ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, acetamide, dimethylform Muamide, dioxolane, acetonitrile, propyl nitrile, nitromethane, ethyl monoglyme, phosphoric acid triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2- Aprotic organic solvents such as oxazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ethyl ether, 1,3-propane sultone, anisole, N-methylpyrrolidone, and fluorinated carboxylic acid esters can be used. These may use 1 type and may use 2 or more types together. Among these, it is preferable to use a mixed solution of a cyclic carbonate and a chain carbonate as the solvent from the viewpoint of stability at a high voltage and the viscosity of the solvent.

Examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiAlCl ₄ , LiClO ₄ , LiBF ₄ , LiSbF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiC (CF ₃ SO ₂ ) ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiB ₁₀ Cl ₁₀ , lower aliphatic lithium lithium carboxylate, lithium chloroborane, lithium tetraphenylborate, LiBr, LiI, LiSCN, LiCl, imides, etc. . These may use 1 type and may use 2 or more types together.

  The density | concentration of the lithium salt which is a support salt can be 0.5-1.5 mol / L, for example, and it is preferable that it is 0.7-1.3 mol / L. Sufficient electric conductivity can be obtained when the concentration of the lithium salt is 0.5 mol / L or more. Moreover, when the density | concentration of lithium salt is 1.5 mol / L or less, the increase in a density and a viscosity can be suppressed.

  A polymer electrolyte obtained by adding a polymer or the like to the solvent of the electrolytic solution and solidifying the electrolytic solution in a gel form may be used.

As the negative electrode active material, a material capable of inserting and extracting lithium can be used. Examples of the negative electrode active material include carbon materials such as graphite, hard carbon, soft carbon, and amorphous carbon, Li metal, Si oxide such as Si, Sn, Al, and SiO, Sn oxide, and Li ₄ Ti ₅ O. ₁₂ , Ti oxide such as TiO ₂ , V-containing oxide, Sb-containing oxide, Fe-containing oxide, Co-containing oxide and the like can be used. These negative electrode active materials may be used alone or in combination of two or more. In particular, in the secondary battery according to the present embodiment, it is preferable to use SiO as the negative electrode active material from the viewpoint that the irreversible capacity is offset by the relationship with the positive electrode active material according to the present embodiment.

  The negative electrode can be produced, for example, by mixing the negative electrode active material, a conductivity imparting agent, a binder, and a solvent, applying the mixture onto a negative electrode current collector, and drying. As the conductivity imparting agent, for example, a carbon material, a conductive oxide, or the like can be used. As the binder, polyvinylidene fluoride, acrylic resin, styrene butadiene rubber, imide resin, imidoamide resin, polytetrafluoroethylene resin, polyamic acid, or the like can be used. As the solvent, N-methylpyrrolidone or the like can be used. As the negative electrode current collector, a metal thin film mainly containing aluminum, copper, or the like can be used. Although the thickness of a negative electrode collector is not specifically limited, For example, it can be 5-50 micrometers, and it is preferable that it is 10-40 micrometers. Moreover, although the thickness of a negative electrode is not specifically limited, For example, it is 10-100 micrometers, and it is preferable that it is 20-70 micrometers.

  The secondary battery according to the present embodiment can be manufactured by assembling using the positive electrode according to the present embodiment. For example, in a dry air or inert gas atmosphere, the positive electrode and the negative electrode according to the present embodiment are arranged to face each other with no electrical contact through the separator. As the separator, a porous film containing polyethylene, polypropylene (PP), polyimide, polyamide, or the like can be used.

  A material in which the positive electrode and the negative electrode are arranged opposite to each other with a separator interposed therebetween is formed into a cylindrical shape or a laminated shape, and is accommodated in the exterior body. As the exterior body, a battery can, a laminate film that is a laminate of a synthetic resin and a metal foil, or the like can be used. A positive electrode tab is connected to the positive electrode, and a negative electrode tab is connected to the negative electrode, so that these electrode tabs are exposed to the outside of the outer package. The secondary battery can be manufactured by sealing the exterior body while leaving a part, injecting an electrolyte from the part, and sealing the exterior body.

  The shape of the positive electrode and the negative electrode arranged opposite to each other with a separator interposed therebetween is not particularly limited, and may be a wound type, a laminated type, or the like. Further, the secondary battery may be a coin type, a laminate type, or the like. The shape of the secondary battery can be a square shape, a cylindrical shape, or the like.

  Examples of the present embodiment will be described below, but the present embodiment is not limited to these examples.

[Example 1]
<Synthesis of lithium iron manganese complex oxide>
Iron nitrate (III), manganese chloride (II), and nickel nitrate (II) weighed so as to have a predetermined atomic ratio were dissolved in distilled water to prepare an aqueous metal salt solution (total amount 0.25 mol / batch). Separately from this, a 1.25 mol / L lithium hydroxide aqueous solution was prepared, added with ethanol to be antifreeze, and then cooled to −10 ° C. in a thermostatic bath. A composite hydroxide was prepared by gradually dropping the metal salt aqueous solution into the alkaline solution over 2 hours or more. The alkali solution containing the composite hydroxide after the dropping was taken out from the thermostatic bath, air was blown into the solution to perform wet oxidation for 2 days, and then the composite hydroxide was aged at room temperature.

The composite hydroxide after aging was washed with water and filtered, and then added with an equimolar amount of lithium carbonate as compared with the molar amount charged, and calcined at 850 ° C. for 5 hours in the air. After firing, the product was crushed. The product was put in a solution obtained by dissolving 0.1 times mol of ammonium fluoride in distilled water with respect to the charged molar ratio and stirred well, and then the mixture was dried. The dried powder was pulverized, calcined at 800 ° C. for 1 hour in nitrogen, cooled, and the product was taken out from the electric furnace. This was washed several times with distilled water, filtered, and dried at 100 ° C. to obtain lithium iron manganese composite oxide Li _1.23 Mn _0.48 Ni _0.15 Fe _0.16 O _1.79 F _0.11 . As a result of X-ray diffraction measurement, it was confirmed that this substance has a layered rock salt structure.

<Preparation of positive electrode>
Lithium iron manganese composite oxide Li _1.23 Mn _0.48 Ni _0.15 Fe _0.16 O _1.79 F _0.11 as a positive electrode active material 92% by mass, ketjen black 4% by mass, and a mixture containing 4% by mass of polyvinylidene fluoride as a solvent A slurry was prepared by mixing. The slurry was applied onto a positive electrode current collector that was an aluminum foil having a thickness of 20 μm, and the slurry was dried to produce a positive electrode having a thickness of 175 μm.

<Production of negative electrode>
A slurry containing 85% by mass of SiO having an average particle size of 15 μm and 15% by mass of polyamic acid was mixed with a solvent to prepare a slurry. The slurry was applied onto a negative electrode current collector which was a copper foil having a thickness of 10 μm, and the slurry was dried to prepare a negative electrode having a thickness of 46 μm. The produced negative electrode was annealed at 350 ° C. for 3 hours in a nitrogen atmosphere to cure the polyamic acid.

<Production of lithium ion secondary battery>
After forming the positive electrode and the negative electrode, they were laminated with a porous film separator in between. Thereafter, a positive electrode tab and a negative electrode tab were welded to the positive electrode and the negative electrode, respectively, to produce a power generation element. The power generation element was wrapped in an outer package made of an aluminum laminate film, and three sides of the outer package were sealed by heat sealing. Thereafter, an EC / DEC electrolyte solution containing 1 mol / L LiPF ₆ was injected into the outer package at an appropriate degree of vacuum. Thereafter, the remaining one side of the outer package was heat-sealed and sealed under reduced pressure to prepare a lithium ion secondary battery before activation treatment.

<Activation processing>
About the lithium ion secondary battery before the activation treatment, after charging to 4.5 V at a current of 20 mA / g per positive electrode active material, the cycle is discharged to 1.5 V at a current of 20 mA / g per positive electrode active material. Repeated times. Thereafter, the sealing portion of the outer package was once broken and the internal pressure of the secondary battery was removed by degassing and resealing to produce a lithium ion secondary battery.

<Evaluation of lithium ion secondary battery>
The lithium ion secondary battery is charged to 4.5 V at a constant current of 40 mA / g per positive electrode active material in a constant temperature bath at 45 ° C. Charged. Thereafter, the lithium ion secondary battery was discharged to 1.5 V at a current of 10 mA / g. The lithium ion secondary battery is charged to 4.5 V at a constant current of 40 mA / g per positive electrode active material in a constant temperature bath at 45 ° C., and further at a constant voltage of 4.5 V until the current reaches 5 mA / g After charging, a charge / discharge cycle of discharging to 1.5 V with a current of 40 mA / g was repeated 100 times. From the ratio of the discharge capacity obtained in the first cycle and the discharge capacity obtained in the 100th cycle, the capacity retention rate after 100 cycles was determined. In Example 1, the capacity retention rate after 100 cycles was 82%.

[Comparative Example 1]
A lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1 except that lithium iron manganese-based composite oxide Li _1.19 Mn _0.47 Ni _0.16 Fe _0.17 O _1.99 was synthesized as the positive electrode active material, and this was used. . The capacity retention rate after 100 cycles in this Comparative Example 1 was 56%.

  The lithium ion secondary battery according to the present embodiment has a high energy density and is excellent in cycle characteristics. Therefore, the lithium ion secondary battery can be widely used as an electronic device, an electric vehicle, a storage battery for power storage in general households and facilities, and the like. it can.

DESCRIPTION OF SYMBOLS 1 Positive electrode active material layer 1A Positive electrode collector 1B Positive electrode tab 2 Negative electrode active material layer 2A Negative electrode collector 2B Negative electrode tab 3 Separator 4 Exterior body

Claims (9)

It has a layered rock salt structure and has the following formula (1)
Li _x M ¹ _(yp) Mn _p M ² _(zq) Fe _q O _(2-δ-r) F _r (1)
(In the above formula (1), 1.05 ≦ x ≦ 1.32, 0.33 ≦ y ≦ 0.63, 0.06 ≦ z ≦ 0.50, 0 <p ≦ 0.63, 0.06 ≦ q ≦ 0.50, 0.01 ≦ r <2-δ, 0.06 ≦ δ ≦ 0.80, y ≧ p, z ≧ q, M ¹ is at least one element of Ti and Zr, M ² is at least one element selected from the group consisting of Co, Ni and Mn)
Lithium iron manganese composite oxide represented by   2. The lithium iron manganese based composite oxide according to claim 1, wherein in the formula (1), r satisfies 0.10 <r ≦ 0.40.   3. The lithium iron manganese based composite oxide according to claim 1, wherein in the formula (1), q satisfies 0.16 ≦ q ≦ 0.45. 4. The lithium iron manganese composite oxide according to claim 1, wherein in the formula (1), δ satisfies 0.06 ≦ δ ≦ 0.50. 5.   The lithium iron manganese based composite oxide according to any one of claims 1 to 4, wherein at least a part of oxygen atoms is substituted with fluorine atoms.   The positive electrode active material for lithium ion secondary batteries containing the lithium iron manganese system complex oxide of any one of Claim 1 to 5.   The positive electrode for lithium ion secondary batteries containing the positive electrode active material for lithium ion secondary batteries of Claim 6.   A lithium ion secondary battery comprising the positive electrode for a lithium ion secondary battery according to claim 7 and a negative electrode.   The lithium ion secondary battery according to claim 8, wherein the negative electrode contains SiO as a negative electrode active material.

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