JP6800417B2 - Positive electrode material for lithium ion secondary batteries, positive electrode for lithium ion secondary batteries and lithium ion secondary batteries - Google Patents

Description

The present embodiment relates to a positive electrode material for a lithium ion secondary battery, a positive electrode for a lithium ion secondary battery, and a lithium ion secondary battery.

A lithium ion secondary battery including a positive electrode containing a lithium iron-manganese-based composite oxide as a positive electrode material and a negative electrode containing a compound capable of occluding lithium ions as a negative electrode material is expected as a secondary battery having a high energy density. .. For example, Patent Document 1 discloses a lithium ion secondary battery using the lithium-iron-manganese-based composite oxide _{Li 1 + x (Fe y Mn} 1-y) 1-x O 2 in the positive electrode material. Since the lithium iron-manganese-based composite compound can redox oxygen in addition to the redox of the transition metal, the secondary battery using the lithium iron-manganese-based composite oxide can have a high energy density. ..

Japanese Unexamined Patent Publication No. 2005-154256 International Publication No. 2015/025844 Special Table 2012-505520 Japanese Unexamined Patent Publication No. 2000-1736663 Japanese Patent Publication No. 2014-5371818

Y. -K. Sun et al. , Advanced Materials. 24 (2012) 1192 G. R. Li, Electrochimica Acta. 78 (2012) 308

However, the lithium iron-manganese-based composite oxide described in Patent Document 1 has a problem that a large amount of gas is generated during charging and discharging. On the other hand, as a method for reducing the amount of gas generated, a positive electrode material coated with an inorganic substance such as Al ₂ O ₃ or Al F ₃ or the like has been proposed (Patent Documents 2 to 5 and Non-Patent Documents 1 and 2). However, even if Al ₂ O ₃ or Al F ₃ is coated with a lithium iron-manganese-based composite oxide, the effect of reducing the amount of gas generated is insufficient, and further improvement is desired. On the other hand, it is also required to show a high capacity retention rate even after the charge / discharge cycle.

An object of the present embodiment is to provide a positive electrode material for a lithium ion secondary battery capable of providing a lithium ion secondary battery that generates a small amount of gas and exhibits a high capacity retention rate even after a charge / discharge cycle.

The positive electrode material for a lithium ion secondary battery according to this embodiment has a layered rock salt type structure and has the following formula (1).
Li _x M1 _(y-p) Mn _p M2 _(z-q) Fe _q O _(2-δ) (1)
(In the formula (1), 1.050 ≦ x ≦ 1.320, 0.330 ≦ y ≦ 0.630, 0.060 ≦ z ≦ 0.500, 0 <p ≦ 0.630, 0.060 ≦ q ≤0.500, 0≤δ≤0.800, y≥p, z≥q, M1 is at least one element of Ti and Zr, and M2 is selected from the group consisting of Co, Ni and Mn. At least one kind of element)
At least a part of the surface of the lithium iron-manganese-based composite oxide shown in (1) is a positive electrode material for a lithium ion secondary battery coated with at least one type of fluoride selected from the group consisting of MgF ₂ and KF.

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

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

According to the present embodiment, it is possible to provide a positive electrode material for a lithium ion secondary battery capable of providing a lithium ion secondary battery that generates a small amount of gas and exhibits a high capacity retention rate even after a charge / discharge cycle.

It is sectional drawing which shows an example of the lithium iron-manganese-based composite oxide coated with the fluoride which concerns on this embodiment. It is sectional drawing which shows an example of the lithium ion secondary battery which concerns on this embodiment.

[Positive material for lithium-ion secondary batteries]
The positive electrode material for a lithium ion secondary battery according to this embodiment has a layered rock salt type structure and has the following formula (1).
Li _x M1 _(y-p) Mn _p M2 _(z-q) Fe _q O _(2-δ) (1)
(In the formula (1), 1.050 ≦ x ≦ 1.320, 0.330 ≦ y ≦ 0.630, 0.060 ≦ z ≦ 0.500, 0 <p ≦ 0.630, 0.060 ≦ q ≤0.500, 0≤δ≤0.800, y≥p, z≥q, M1 is at least one element of Ti and Zr, and M2 is selected from the group consisting of Co, Ni and Mn. At least one kind of element)
At least a part of the surface of the lithium iron-manganese-based composite oxide shown in (1) is a positive electrode material for a lithium ion secondary battery coated with at least one type of fluoride selected from the group consisting of MgF ₂ and KF.

As a result of examining in detail the mechanism by which the lithium iron-manganese-based composite oxide generates gas during charging and discharging, the electrolyte solvent is decomposed in the vicinity of iron on the surface of the lithium iron-manganese-based composite oxide, resulting in gas. Found to occur. Here, when the surface of the lithium iron-manganese-based composite oxide is coated with AlF ₃ or the like, the amount of gas generated is reduced as compared with the uncoated lithium iron-manganese-based composite oxide, but the effect is small. On the other hand, it was found that coating the surface of the lithium iron-manganese-based composite oxide with MgF ₂ and / or KF has a greater effect of reducing the amount of gas generated than coating with AlF ₃ or the like. The reason for this is that coating the surface of the lithium iron-manganese-based composite oxide with MgF ₂ and / or KF is closer to the iron on the surface of the lithium iron-manganese-based composite oxide than coating with AlF ₃ or the like. This is thought to be because a more dense protective film can be formed. Further, by using a lithium iron-manganese-based composite oxide coated with MgF ₂ and / or KF as a positive electrode material for a lithium ion secondary battery, a high capacity retention rate is exhibited even after a charge / discharge cycle, and a high energy density and a high energy density are obtained. A lithium ion secondary battery having output characteristics can be provided. Hereinafter, the details of this embodiment will be described.

(Lithium iron-manganese-based composite oxide)
The lithium iron-manganese-based composite oxide represented by the formula (1) (hereinafter, also referred to as a composite oxide) contains at least Mn. The composition p of Mn is 0 <p ≦ 0.630. When 0 <p, lithium can be contained in excess. Further, when p ≦ 0.630, Li ₂ Me1O ₃ (Me ₁ contains at least Mn) and LiMe 2O ₂ (Me ₂ contains at least Fe) can be in a solid solution state. p is preferably 0.100 ≦ p ≦ 0.600, more preferably 0.200 ≦ p ≦ 0.550, and even more preferably 0.300 ≦ p ≦ 0.500.

In the formula (1), M1 is at least one element of Ti and Zr. The y of the composition y-p of M1 is 0.330 ≦ y ≦ 0.630. By setting 0.330 ≦ y, lithium can be contained in excess. Further, when y ≦ 0.630, Li ₂ Me1O ₃ (Me1 contains at least Mn) and LiMe2O ₂ (Me2 contains at least Fe) can be in a solid solution state. y is preferably 0.350 ≦ y ≦ 0.600, more preferably 0.400 ≦ y ≦ 0.550, and even more preferably 0.450 ≦ y ≦ 0.500. The equation (1) satisfies y ≧ p. Further, the composition y-p of M1 may be 0. That is, the composite oxide represented by the formula (1) does not have to contain M1. Mn and M1 in the formula (1) correspond to Me1 of the Li ₂ Me1O ₃ .

The composite oxide represented by the formula (1) contains at least Fe. The composition q of Fe is 0.060 ≦ q ≦ 0.500. When 0.060 ≦ q, the lithium iron-manganese-based composite oxide can be activated. Further, when q ≦ 0.500, the capacity can be kept large. q is preferably 0.070 ≦ q ≦ 0.400, more preferably 0.080 ≦ q ≦ 0.300, and even more preferably 0.100 ≦ q ≦ 0.200.

In the formula (1), M2 is at least one element selected from the group consisting of Co, Ni and Mn. The z of the composition z−q of M2 is 0.060 ≦ z ≦ 0.500. When 0.060 ≦ z, the lithium iron-manganese-based composite oxide can be activated. Further, when z ≦ 0.500, lithium can be contained in excess. z is preferably 0.080 ≦ z ≦ 0.450, more preferably 0.100 ≦ z ≦ 0.400, and even more preferably 0.120 ≦ z ≦ 0.300. The equation (1) satisfies z ≧ q. Further, the composition zq of M2 may be 0. That is, the composite oxide represented by the formula (1) does not have to contain M2. Fe and M2 in the formula (1) correspond to Me2 of the LiMe2O ₂ .

In the formula (1), the composition x of Li is 1.050 ≦ x ≦ 1.320. By setting 1.050 ≦ x, the capacity can be increased. Further, when x ≦ 1.320, Li ₂ Me1O ₃ (Me ₁ contains at least Mn) and LiMe 2O ₂ (Me ₂ contains at least Fe) can be in a solid solution state. x is preferably 1.080 ≦ x ≦ 1.300, more preferably 1.120 ≦ x ≦ 1.280, and even more preferably 1.160 ≦ x ≦ 1.260.

In the above formula (1), δ in the composition 2-δ of the oxygen atom is a parameter indicating oxygen deficiency, and is 0 ≦ δ ≦ 0.800. By setting 0 ≦ δ, the capacity can be increased. Further, when δ ≦ 0.800, the crystal structure can be stabilized. δ is preferably 0.020 ≦ δ ≦ 0.500, more preferably 0.040 ≦ δ ≦ 0.300, and even more preferably 0.060 ≦ δ ≦ 0.200. The oxygen deficiency parameter δ can be determined by combustion infrared absorption method or fluorescent X-ray spectroscopy. It should be noted that δ varies depending not only on the blending ratio of Me1 and Me2 but also on the method for synthesizing the composite oxide.

The composition of each element in the formula (1) is a value measured by inductively coupled plasma emission spectroscopic analysis for Li and inductively coupled plasma mass analysis for other elements. Further, the composition of each element in the above formula (1) does not include fluoride used for surface coating.

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

(Fluoride)
At least a part of the surface of the lithium iron-manganese-based composite oxide according to the present embodiment is coated with at least one fluoride selected from the group consisting of MgF ₂ and KF. As a result, a dense protective film is formed in the vicinity of iron on the particle surface of the lithium iron-manganese-based composite oxide, and the amount of gas generated is reduced. In the present embodiment, as shown in FIG. 1, the entire surface of the lithium iron-manganese-based composite oxide 5 may be completely coated with fluoride 6, and a part of the surface of the lithium iron-manganese-based composite oxide may be covered. It may be covered with a compound. Whether or not at least a part of the surface of the lithium iron-manganese composite oxide is coated with MgF ₂ or KF is determined by scanning electron microscopy (energy dispersive X-ray analysis), transmission electron microscopy, and X-ray photoelectron. It can be judged by spectroscopic analysis, Auger electron spectroscopic analysis, and electron energy loss spectroscopic analysis.

At least a part of the surface of the lithium iron-manganese-based composite oxide may be coated with at least one fluoride selected from the group consisting of MgF ₂ and KF, but further, Na, Ca, and the like. From the viewpoint of capacity retention, it is preferable that the mixture is coated with a fluoride of at least one element selected from the group consisting of Al, Sn, Zn, Co, Pb, Ni, Fe, Cr, Bi, Mn and Sm. ..

The ratio of the fluoride to the lithium iron-manganese-based composite oxide coated with the fluoride (hereinafter, also referred to as a coating amount) is preferably 0.1% by mass or more and 15.0% by mass or less. .. When the coating amount is 0.1% by mass or more, the desorption of oxygen to the outside in the charge / discharge cycle can be sufficiently suppressed. Further, when the coating amount is 15.0% by mass or less, the storage and release of Li are not hindered. The coating amount is more preferably 0.2% by mass or more and 10.0% by mass or less, further preferably 0.5% by mass or more and 5.0% by mass or less, and 1.0% by mass or more. , 3.0% by mass or less is particularly preferable. When the fluoride of at least one element selected from the group consisting of Na, Ca, Al, Sn, Zn, Co, Pb, Ni, Fe, Cr, Bi, Mn and Sm is used as the coating amount. Is the coating amount including the fluoride. In this case, the ratio of the coating amount derived from at least one fluoride selected from the group consisting of MgF ₂ and KF to the total coating amount is preferably 80% by mass or more, and more preferably 90% by mass or more. It is preferably 95% by mass or more, and more preferably 95% by mass or more.

(Manufacturing method of positive electrode material for lithium ion secondary battery)
In the method for producing a positive electrode material for a lithium ion secondary battery according to the present embodiment, at least a part of the surface of a lithium iron-manganese-based composite oxide having a layered rock salt type structure and satisfying the above formula (1) is MgF _2. It is not particularly limited as long as it is coated with at least one fluoride selected from the group consisting of KF and KF. For example, the lithium iron-manganese-based composite oxide having a layered rock salt type structure and satisfying the above formula (1) is mixed with MgF ₂ and / or KF and then heat-treated to perform the lithium iron-manganese-based composite oxidation. At least a portion of the surface of the object can be coated with MgF ₂ and / or KF. Specifically, the following methods can be mentioned.

The method for producing the lithium iron-manganese-based composite oxide before coating with fluoride is not particularly limited, and it is produced by subjecting a metal raw material containing at least lithium, manganese and iron to a heat treatment such as firing or hydrothermal treatment. Can be done. On the other hand, in order to obtain a lithium iron-manganese-based composite oxide having more excellent electrochemical properties, it is preferable to mix constituent metal elements other than lithium more uniformly. From this point of view, for example, a method of obtaining a composite hydroxide such as iron or manganese from the liquid phase and firing it together with a lithium compound is preferable. This method is roughly divided into a composite hydroxide production step of producing a composite hydroxide containing a constituent metal other than lithium and a firing step of firing the composite hydroxide in the presence of lithium.

<Composite hydroxide manufacturing process>
The composite hydroxide can be produced by precipitating a water-soluble salt of the constituent metal by dropping it in an alkaline aqueous solution, performing air oxidation if necessary, and aging the hydroxide. The water-soluble salt of the constituent metal is not particularly limited, and examples thereof include anhydrous salts such as nitrates, sulfates, chlorides and acetates of the constituent metals, hydrates and the like. The alkali source is also not particularly limited, and examples thereof include lithium hydroxide and its hydrate, sodium hydroxide, potassium hydroxide, aqueous ammonia and the like. These may be used alone or in combination of two or more. The composite hydroxide can be obtained by gradually dropping a water-soluble salt of the constituent metal with respect to the 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 lower from the viewpoint of suppressing the formation of impurities such as spinel ferrite. When the water-soluble salt of the constituent metal is added dropwise at 0 ° C. or lower, it is preferable to add ethanol or the like as an antifreeze solution to the alkaline aqueous solution to prevent the solution from solidifying. It is preferable that the hydroxide obtained after dropping is wet-oxidized and aged by blowing air at room temperature for several hours or more. By washing the obtained aged product with water and filtering it, the desired composite hydroxide can be obtained.

<Baking process>
A predetermined lithium compound is added to the composite hydroxide according to the composition formula, mixed, and then calcined in a predetermined atmosphere. Then, if necessary, it is washed with water, filtered, and dried to remove the excess lithium compound, whereby a lithium iron-manganese-based composite oxide having the desired composition formula is obtained. The lithium compound is not particularly limited, and an anhydride or hydrate such as lithium carbonate, lithium hydroxide, lithium nitrate and lithium acetate can be used. These may be used alone or in combination of two or more. The firing temperature is preferably 1000 ° C. or lower from the viewpoint of preventing the volatilization of Li. As the firing atmosphere, an air atmosphere, an inert gas atmosphere, a nitrogen atmosphere, an oxygen atmosphere, or the like can be used. Through such a step, a lithium iron-manganese-based composite oxide before coating with a fluoride having a desired composition can be obtained.

<Coating process>
As the metal source of fluoride for coating, chlorides, hydroxides, carbonates, nitrates, acetates, alcoholates and the like containing Mg and / or K are preferable. These may be used alone or in combination of two or more. When the metal source is fluoride, either dry mixing or wet mixing may be used. When the metal source is other than fluoride, a fluoride source such as ammonium fluoride can be used in combination. As fluorides other than MgF ₂ and KF, fluorides of at least one element selected from the group consisting of Na, Ca, Al, Sn, Zn, Co, Pb, Ni, Fe, Cr, Bi, Mn and Sm are used. When included, two or more metal sources can be mixed at the same time.

When a metal source and, if necessary, a fluoride source are added to the solvent to prepare a mixed solution, the concentrations of the metal source and any fluoride source in the mixed solution are not particularly limited, but 0.002 to 0. .050% by mass is preferable. When the concentration is 0.002% by mass or more, the time required for evaporation of a solvent such as water or alcohol is shortened, so that the production efficiency is improved. Further, when the concentration is 0.050% by mass or less, the raw materials are sufficiently dissolved and a homogeneous mixed solution can be obtained.

For example, the lithium iron-manganese-based composite oxide is added to the mixed solution and mixed, and then the solvent is evaporated and the dried product obtained by drying is fired to cover at least a part of the surface with fluoride. The resulting lithium iron-manganese-based composite oxide is obtained. The drying method is not particularly limited, and examples thereof include a drying method using a rotary evaporator, a spray dryer, or the like, in addition to the usual drying method. The firing can be performed in a vacuum, an atmospheric atmosphere, an inert atmosphere, hydrogen, nitrogen, or a mixed atmosphere thereof, but from the viewpoint of cost reduction, it is preferably performed in the atmospheric atmosphere. The firing temperature is preferably 350 to 800 ° C. When the firing temperature is 350 ° C. or higher, the reaction is completed and reaction impurities and the like do not remain. Further, when the firing temperature is 800 ° C. or lower, the reaction of lithium in the lithium iron-manganese-based composite oxide can be suppressed, and the mixture of lithium compounds as impurities can be prevented.

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

The positive electrode can be produced by applying the positive electrode material according to the present embodiment onto a positive electrode current collector. For example, it can be produced by mixing the positive electrode material according to the present embodiment, the conductivity-imparting agent, the binder, and the solvent, applying the mixture on the positive electrode current collector, and drying the mixture. As the conductivity-imparting agent, a carbon material such as acetylene black or 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 and 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. The thickness of the positive electrode current collector is not particularly limited, but can be, for example, 5 to 50 μm.

The positive electrode material may also include a positive electrode material other than the positive electrode material according to the present embodiment. However, the proportion of the positive electrode material according to the present embodiment contained in the positive electrode material is preferably 80% by mass or more, more preferably 90% by mass or more, and further preferably 95% by mass or more. preferable. The ratio is particularly preferably 100% by mass, that is, the positive electrode material is made of the positive electrode material according to the present embodiment.

The amount of the conductivity-imparting agent added is preferably 1 to 10% by mass, more preferably 2 to 7% by mass. When the addition amount is 1% by mass or more, sufficient conductivity can be maintained. Further, when the addition amount is 10% by mass or less, the ratio of the positive electrode material mass can be increased, so that the capacity per mass can be increased. The amount of the binder added is preferably 1 to 10% by mass, more preferably 2 to 7% by mass. When the addition amount is 1% by mass or more, the occurrence of positive electrode peeling can be prevented. Further, when the addition amount is 10% by mass or less, the ratio of the positive electrode material mass can be increased, so that the capacity per mass can be increased.

The thickness of the positive electrode is not particularly limited, but is preferably, for example, 50 to 500 μm, and more preferably 100 to 400 μm.

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

FIG. 2 shows an example of the lithium ion secondary battery according to the present embodiment. In the lithium ion secondary battery shown in FIG. 2, the positive electrode is formed by forming the positive electrode material layer 1 containing the positive electrode material according to the present embodiment on the positive electrode current collector 1A. Further, the negative electrode is formed by forming the negative electrode material layer 2 on the negative electrode current collector 2A. These positive electrodes and negative electrodes are arranged facing each other via a separator 3 in a state of being immersed in an electrolytic solution, and are laminated. Further, 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 housed 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 material, and lithium ions are occluded in the negative electrode material, so that charging occurs. Further, by causing electrical contact between the positive electrode and the negative electrode outside the secondary battery, lithium ions are released from the negative electrode material and the lithium ions are occluded in the positive electrode material, which is the opposite of charging, so that discharge occurs.

As the electrolytic solution used in the lithium ion 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) and diethyl carbonate ( Chain carbonates such as DEC) and 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-methyltetraxide, dimethylsulfoxide, 1,3-dioxolane, formamide, acetamide, dimethylformamide, acetonitrile, propylnitrile , Nitromethane, ethyl monoglime, phosphate triesters, trimethoxymethane, dioxolane derivatives, sulfolanes, methyl sulfolanes, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, propylene carbonate derivatives, tetrahydrofuran Aprotonic organic solvents such as derivatives, ethyl ether, 1,3-propanesulton, anisole, N-methylpyrrolidone, and fluorinated carboxylic acid esters can be used. These may be used alone or in combination of two or more. Among these, from the viewpoint of stability at high voltage and viscosity of the solvent, it is preferable to use a mixed solution of cyclic carbonates and chain carbonates as the solvent.

Examples of lithium salts 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 ). ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiB ₁₀ Cl ₁₀ , lower aliphatic lithium carboxylate, chloroborane lithium, lithium tetraphenylborate, LiBr, LiI, LiSCN, LiCl, lithium bis (fluorosulfonyl) Examples thereof include imides such as imide. These may be used alone or in combination of two or more.

The concentration of the lithium salt as the supporting salt can be, for example, 0.5 to 3.0 mol / L, preferably 0.7 to 2.0 mol / L. When the concentration of the lithium salt is 0.5 mol / L or more, sufficient electrical conductivity can be obtained. Further, when the concentration of the lithium salt is 3.0 mol / L or less, the increase in density and viscosity can be suppressed.

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

As the negative electrode material, a material capable of occluding and releasing lithium can be used. For example, carbon materials such as graphite, hard carbon, soft carbon and amorphous carbon, Si oxides such as Li metal, Si, Sn, Al and SiO, Sn oxides, Li ₄ Ti ₅ O ₁₂ and TiO ₂ etc. Ti oxide, V-containing oxide, Sb-containing oxide, Fe-containing oxide, Co-containing oxide and the like can be used. One type of these negative electrode materials may be used, or two or more types may be used in combination. In particular, in the secondary battery according to the present embodiment, it is preferable to use SiO as the negative electrode material from the viewpoint of canceling the irreversible capacity in relation to the positive electrode material according to the present embodiment.

The negative electrode can be produced, for example, by mixing the negative electrode material, a conductivity-imparting agent, a binder, and a solvent, applying the mixture on the negative electrode current collector, and drying the mixture. 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, imidomid resin, polytetrafluoroethylene resin, polyamic acid and 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 and the like can be used. The thickness of the negative electrode current collector is not particularly limited, but can be, for example, 5 to 50 μm, preferably 10 to 40 μm. The thickness of the negative electrode is not particularly limited, but can be, for example, 10 to 100 μm, preferably 20 to 70 μm.

The lithium ion 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 an inert gas atmosphere, the positive electrode and the negative electrode according to the present embodiment are arranged to face each other via a separator without electrical contact. As the separator, a porous film containing polyethylene, polypropylene (PP), polyimide, polyamide or the like can be used.

The positive electrode and the negative electrode, which are arranged so as to face each other with the separator sandwiched between them, are formed into a cylindrical shape or a laminated shape and stored in the exterior body. As the exterior body, a battery can, a laminated film which is a laminated body 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 exterior body. A lithium ion secondary battery can be manufactured by sealing the exterior body leaving a part thereof, injecting an electrolytic solution from the part, and sealing the exterior body. Further, the activation treatment may be performed before using the lithium ion secondary battery.

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

Hereinafter, examples of this embodiment will be shown, but the present embodiment is not limited to these examples.

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

After aging, the composite hydroxide was washed with water and filtered, and then an equimolar amount of lithium carbonate was added and calcined at 850 ° C. for 5 hours in the air. After firing, the product is pulverized, washed several times with distilled water, filtered, and dried at 100 ° C., whereby the lithium iron-manganese-based composite oxide Li _1.200 Mn _0.490 Ni _0.105 Fe _{0 .105} O _1.890 was obtained.

<Coating with MgF ₂ >
A dry milling treatment was performed on a sample obtained by adding MgF ₂ to the lithium iron-manganese-based composite oxide for 3 minutes. Then, it was calcined at 400 ° C. for 5 hours in an atmosphere in nitrogen to obtain a lithium iron-manganese-based composite oxide whose surface was partially coated with 1.0% by mass of MgF ₂ .

<Preparation of positive electrode>
The positive electrode material contains 92% by mass of a lithium iron-manganese-based composite oxide whose surface is partially coated with 1.0% by mass of MgF ₂ , 4% by mass of Ketjenblack, and 4% by mass of polyvinylidene fluoride. The mixture was mixed with a solvent to prepare a slurry. The slurry was applied onto a positive electrode current collector which is an aluminum foil having a thickness of 20 μm, and the slurry was dried to prepare a positive electrode having a thickness of 175 μm.

<Manufacturing of negative electrode>
A mixture 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 is 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 prepared negative electrode was annealed at 350 ° C. for 3 hours in a nitrogen atmosphere to cure the polyamic acid.

<Manufacturing of lithium ion secondary battery>
After molding the positive electrode and the negative electrode, they were laminated with a porous film separator sandwiched between them. Then, the positive electrode tab and the negative electrode tab were welded to the positive electrode and the negative electrode, respectively, to prepare a power generation element. The power generation element was wrapped with an exterior body made of an aluminum laminated film, and three sides of the exterior body were sealed by heat fusion. Then, an EC / DEC electrolytic solution containing 1 mol / L LiPF ₆ was injected into the exterior body at an appropriate degree of vacuum. Then, the remaining one side of the exterior body was heat-sealed and sealed under reduced pressure to prepare a lithium ion secondary battery before the activation treatment.

<Activation treatment>
The lithium ion secondary battery before the activation treatment is charged to 4.5 V with a current of 20 mA / g per positive electrode material, and then discharged to 1.5 V with a current of 20 mA / g per positive electrode material, which is repeated twice. It was. After that, the sealing portion of the exterior body was once broken, the gas inside the secondary battery was released by reducing the pressure, and the lithium ion secondary battery was manufactured by resealing.

<Evaluation of lithium-ion secondary battery>
The lithium ion secondary battery was charged to 4.5 V with a constant current of 0.1 C in a constant temperature bath at 45 ° C., and further charged with a constant voltage of 4.5 V until the current reached 0.25 C. Then, the lithium secondary battery was discharged to 1.5 V with a current of 0.1 C. This charge / discharge cycle was repeated for 10 cycles, and the amount of gas generated and the capacity retention rate were measured. The amount of gas generated by the lithium ion secondary battery before and after the charge / discharge cycle was calculated from the mass difference before and after the charge / discharge cycle by measuring the mass of the lithium ion secondary battery in water before and after the charge / discharge cycle. Table 1 shows the initial capacity, the amount of gas generated after 10 cycles, and the capacity retention rate.

[Example 2]
A lithium ion secondary battery was produced and evaluated in the same manner as in Example 1 except that the coating amount of MgF ₂ was changed to 3.0% by mass. The results are shown in Table 1.

[Example 3]
The sample obtained by adding KF to the lithium iron-manganese-based composite oxide was stirred in 100 ml of distilled water, and then the powder was dried at 100 ° C. Then, it was calcined at 400 ° C. for 5 hours in an atmosphere in nitrogen to obtain a lithium iron-manganese-based composite oxide whose surface was partially coated with 1.0% by mass of KF. After that, a lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[Comparative Example 1]
Example 1 and Example 1 except that a lithium iron-manganese-based composite oxide (Li _1.200 Mn _0.490 Ni _0.105 Fe _0.105 O _1.890 ) not coated with fluoride was used as the positive electrode material. A lithium ion secondary battery was prepared in the same manner and evaluated. The results are shown in Table 1.

[Comparative Example 2]
The sample obtained by adding AlF ₃ to the lithium iron-manganese-based composite oxide was stirred in 100 ml of distilled water, and then the powder was dried at 100 ° C. Then, it was calcined at 400 ° C. for 5 hours in an atmosphere in nitrogen to obtain a lithium iron-manganese-based composite oxide whose surface was partially coated with 1.0% by mass of AlF ₃ . After that, a lithium ion secondary battery was prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[Comparative Example 3]
A lithium ion secondary battery was produced and evaluated in the same manner as in Comparative Example 2 except that the coating amount of AlF ₃ was changed to 3.0% by mass. The results are shown in Table 1.

As shown in Table 1, the positive electrode material obtained by coating the lithium iron-manganese-based composite oxide represented by the formula (1) according to the present embodiment with MgF ₂ or KF is an uncoated positive electrode or a positive electrode coated with AlF _3. Compared with the material, the amount of gas generated can be significantly reduced, and the capacity retention rate is high.

Since the lithium ion secondary battery according to the present embodiment has a high energy density and is also excellent in high output characteristics and high cycle characteristics, it can be used as a storage battery for power storage of electronic devices, electric vehicles, general households and facilities, etc. It can be widely used.

1 Positive electrode material layer 1A Positive electrode current collector 1B Positive electrode tab 2 Negative electrode material layer 2A Negative electrode current collector 2B Negative electrode tab 3 Separator 4 Exterior body 5 Lithium iron-manganese-based composite oxide 6 Fluoride

Claims (6)

It has a layered rock salt type structure and has the following formula (1).
Li _x M1 _(y-p) Mn _p M2 _(z-q) Fe _q O _(2-δ) (1)
(In the formula (1), 1.050 ≦ x ≦ 1.320, 0.330 ≦ y ≦ 0.630, 0.060 ≦ z ≦ 0.500, 0 <p ≦ 0.630, 0.060 ≦ q ≤0.500, 0≤δ≤0.800, y≥p, z≥q, M1 is at least one element of Ti and Zr, and M2 is selected from the group consisting of Co, Ni and Mn. At least one kind of element)
A positive electrode material for a lithium ion secondary battery in which at least a part of the surface of the lithium iron-manganese-based composite oxide represented by is coated with at least one type of fluoride selected from the group consisting of MgF ₂ and KF. At least a part of the surface of the lithium iron-manganese-based composite oxide is further selected from the group consisting of Na, Ca, Al, Sn, Zn, Co, Pb, Ni, Fe, Cr, Bi, Mn and Sm. The positive electrode material for a lithium ion secondary battery according to claim 1, which is coated with fluoride of at least one element. The lithium ion secondary battery according to claim 1 or 2, wherein the ratio of the fluoride to the lithium iron-manganese-based composite oxide coated with the fluoride is 0.1% by mass or more and 15.0% by mass or less. For positive electrode material. A positive electrode for a lithium ion secondary battery, which comprises the positive electrode material for a lithium ion secondary battery according to any one of claims 1 to 3. The lithium ion secondary battery including the positive electrode for the lithium ion secondary battery according to claim 4 and the negative electrode. The lithium ion secondary battery according to claim 5, wherein the negative electrode contains SiO as a negative electrode material.

Images