WO2019017199A1

WO2019017199A1 - Positive electrode active material

Info

Publication number: WO2019017199A1
Application number: PCT/JP2018/025295
Authority: WO
Inventors: 明後藤; 裕輔山本; 尚杉江; 泰行森下; 泰彰岡山
Original assignee: 株式会社豊田自動織機
Priority date: 2017-07-21
Filing date: 2018-07-04
Publication date: 2019-01-24

Abstract

The present invention provides a novel positive electrode active material for providing a lithium-ion secondary battery that exhibits a superior capacity. This positive electrode active material is characterized by exhibiting a crystal structure attributable to the space group Fm-3m and by being represented by compositional formula (1): Li1+xNbyFeaMnbPcXdOe, wherein X is selected from among halogens, and x, y, a, b, c, d, and e satisfy 0<x<1, 0<y<0.5, 0.25≤a+b<1, 0≤a<1, 0≤b<1, 0<c≤0.05, 0≤d≤0.2, and 1.8≤e≤2.2.

Description

Positive electrode active material

The present invention relates to a positive electrode active material of a lithium ion secondary battery.

Lithium ion secondary batteries are small in size and large in capacity, and thus are used as batteries of various devices such as mobile phones and laptop computers. The lithium ion secondary battery includes a positive electrode, a negative electrode, and an electrolyte as main components. The positive electrode includes a current collector and a positive electrode active material layer formed on the surface of the current collector and containing a positive electrode active material.

As a positive electrode active material of a lithium ion secondary battery, various materials are known to be used, and a material that can be an excellent positive electrode active material is being explored. For example, Patent Document 1 reports that a new composite oxide containing lithium, niobium, and iron or manganese can be used as a positive electrode active material of a lithium ion secondary battery.

International Publication No. 2014/156153

In recent years, a lithium ion secondary battery excellent in capacity is required from the industrial world, and a new positive electrode active material for realizing it is required.

The present invention has been made in view of such circumstances, and an object thereof is to provide a new positive electrode active material for providing a lithium ion secondary battery excellent in capacity.

The inventors of the present invention conducted research on the complex oxide described in Patent Document 1 and found that there is room for improvement in terms of capacity. And as a result of earnest examination of this inventor, it discovered that the performance as a positive electrode active material of the said complex oxide improves by doping a certain element. The present invention has been completed based on the findings of the present inventor.

The positive electrode active material of the present invention exhibits a crystal structure attributable to the space group Fm-3m, and is characterized by being represented by the following composition formula (1).
Li _{1 + x} Nb _y Fe _a Mn _b P _c X _d O _e (1)
In the composition formula (1), X is selected from halogen elements. x, y, a, b, c, d and e are 0 <x <1, 0 <y <0.5, 0.25 ≦ a + b <1, 0 ≦ a <1, 0 ≦ b <1, 0 <C ≦ 0.05, 0 ≦ d ≦ 0.2, and 1.8 ≦ e ≦ 2.2 are satisfied.

According to the positive electrode active material of the present invention, a lithium ion secondary battery excellent in capacity can be provided.

7 is a SEM image of a positive electrode active material of Comparative Example 1; 7 is a SEM image of the positive electrode active material of Example 1. 7 is a SEM image of the positive electrode active material of Example 2. 7 is a SEM image of the positive electrode active material of Example 3. 5 is an X-ray diffraction chart of a positive electrode active material of Example 1. 7 is a charge / discharge curve at 25 ° C. of the lithium ion secondary battery of Example 1. 7 is a charge / discharge curve at 60 ° C. of the lithium ion secondary battery of Example 1. 7 is a charge / discharge curve at 25 ° C. of the lithium ion secondary battery of Example 2. FIG. 7 is a charge / discharge curve at 60 ° C. of the lithium ion secondary battery of Example 2. FIG.

Below, the form for implementing this invention is demonstrated. Incidentally, unless otherwise specified, the numerical range “ab” described in the present specification includes the lower limit a and the upper limit b in that range. And a numerical range can be constituted by combining these arbitrarily including the upper limit and lower limit, and the numerical value listed in the example. Furthermore, numerical values arbitrarily selected from these numerical ranges can be used as new upper and lower numerical values.

The positive electrode active material of the present invention exhibits a crystal structure attributable to the space group Fm-3m, and is characterized by being represented by the following composition formula (1).
Li _{1 + x} Nb _y Fe _a Mn _b P _c X _d O _e (1)
In the composition formula (1), X is selected from halogen elements. x, y, a, b, c, d and e are 0 <x <1, 0 <y <0.5, 0.25 ≦ a + b <1, 0 ≦ a <1, 0 ≦ b <1, 0 <C ≦ 0.05, 0 ≦ d ≦ 0.2, and 1.8 ≦ e ≦ 2.2 are satisfied.
In "Fm-3m", "-3" represents 3 with an upper line.

First, x, y, a, b and e in the composition formula (1) will be described. About this description, a part of description of patent document 1 is referred.

As x, a range of 0.1 ≦ x <0.7 is preferable, a range of 0.2 ≦ x ≦ 0.6 is more preferable, and a range of 0.3 ≦ x ≦ 0.5 is more preferable. As y, a range of 0.05 ≦ y <0.5 is preferable, a range of 0.1 ≦ y ≦ 0.45 is more preferable, a range of 0.2 ≦ y ≦ 0.4 is more preferable, and 0. The range of 3 ≦ y ≦ 0.35 is more preferable.

For a and b, it is preferable to satisfy the relationship of 0.25 ≦ a + b ≦ 0.75, more preferably 0.3 ≦ a + b ≦ 0.7, and 0.35 ≦ a + b ≦ 0. It is further preferable to satisfy the relationship of .5. With respect to y, a and b, it is preferable to satisfy the relationship 0.8 ≦ 2y + a + b ≦ 1.2, and it is more preferable to satisfy the relationship 0.9 ≦ 2y + a + b ≦ 1.15.

As e, a range of 1.85 ≦ e ≦ 2.15 is preferable, and a range of 1.9 ≦ e ≦ 2.1 is more preferable.

P is contained in the positive electrode active material represented by composition formula (1). Since the lattice constant of the crystal structure of the positive electrode active material is increased by the addition of P, it can be said that the distance between crystal planes of the positive electrode active material of the present invention is wider than that of the conventional P-free positive electrode active material. Since the distance between crystal planes can be a conductive path of lithium ions, the positive electrode active material of the present invention can be said to have a wide conductive path of lithium ions and excellent ion conductivity. Due to these matters, in the positive electrode active material of the present invention, compared to the complex oxide described in the conventional Patent Document 1, the charge and discharge for releasing and introducing lithium ions are performed smoothly, so the capacity It is advantageous in terms of

As c indicating the composition ratio of P, it is preferable to satisfy 0.001 ≦ c ≦ 0.04, it is more preferable to satisfy 0.005 ≦ c ≦ 0.03, and 0.005 ≦ c ≦ 0. It is more preferable to satisfy .025, and it is particularly preferable to satisfy 0.01 ≦ c ≦ 0.02. If the amount of P present is too small, it may be difficult to confirm the effect of P addition. On the other hand, when P is added in excess, the amount of P that can be introduced into the crystal of the positive electrode active material of the present invention is saturated, so P is a phosphate on the surface of the positive electrode active material of the present invention Will also exist in the form of Therefore, excessive addition of P is wasteful.

As X, F, Cl, Br, and I can be illustrated. Although X is not essential in the positive electrode active material represented by the composition formula (1), the addition of X is expected to have the same effect as the addition of P. As the positive electrode active material represented by the composition formula (1), a material in which P and X coexist is preferable.

As d indicating the composition ratio of X, it is preferable to satisfy 0 <d ≦ 0.2, more preferably to satisfy 0 <d ≦ 0.15, and satisfy 0.01 <d ≦ 0.12 Is more preferable, and it is particularly preferable to satisfy 0.05 <d ≦ 0.11.

The manufacturing method of the positive electrode active material of this invention is demonstrated.
In order to produce the positive electrode active material of the present invention, it may be synthesized by applying a solid phase method or a coprecipitation method employed when producing a general positive electrode active material. In the case of the solid phase method, the positive electrode of the present invention can be prepared by mixing and calcining lithium source, niobium source, iron source and / or manganese source, P source, and optionally X source in the desired ratio. Can produce substances. In the case of the coprecipitation method, the hydroxide is precipitated to be a precipitate from an aqueous solution in which niobium salt, iron salt and / or manganese salt is mixed in the desired ratio, and then the precipitate, lithium source, P The positive electrode active material of the present invention can be produced by mixing and firing a source and, if necessary, an X source. The calcination temperature in the solid phase method and coprecipitation method is preferably 500 to 1200 ° C., more preferably 700 to 1100 ° C., still more preferably 800 to 1000 ° C., particularly preferably 850 to 950 ° C., most preferably 880 to 920 ° C. preferable. The firing is preferably performed in an inert gas atmosphere such as helium or argon.

Examples of lithium sources include lithium oxide, lithium hydroxide, lithium carbonate, lithium hydrogen carbonate and lithium fluoride. Examples of the niobium source or niobium salt include niobium oxide, niobium hydroxide, niobium sulfate, niobium nitrate, niobium chloride, niobium fluoride and lithium niobate. Examples of the iron source or iron salt include iron oxide, iron hydroxide, iron sulfate, iron nitrate, iron chloride and iron fluoride. Examples of the manganese source or manganese salt include manganese oxide, manganese hydroxide, manganese sulfate, manganese nitrate, manganese chloride and manganese fluoride. Examples of P sources include phosphoric acid, phosphates and phosphates, and derivatives thereof. Examples of the X source include lithium fluoride, niobium fluoride, iron fluoride and manganese fluoride when X is fluorine. In addition, since it is reasonable to adopt a compound that can be a lithium source or an X source as the P source, it is preferable to adopt a lithium phosphate lithium salt or LiPX ₆ as the P source.

As the P source, a compound having a melting point or decomposition temperature lower than the calcination temperature is preferable. By employing a compound having a melting point or a decomposition temperature lower than the calcination temperature as the P source, it becomes possible to provide an excellent reaction field at the time of calcination. As a result, the reactivity of each raw material is improved, and adverse side reactions can be suppressed. Therefore, mixing of low-capacity impurities such as LiMnO ₂ and Li ₃ NbO ₄ is suppressed in the positive electrode active material of the present invention manufactured using a compound having a melting point or decomposition temperature lower than the firing temperature as the P source. It can be said that. Examples of suitable P sources in terms of melting point or decomposition temperature include LiPF ₆ and Li ₃ PO ₄ .

After synthesis, the positive electrode active material of the present invention is preferably subjected to a grinding step to prepare a powder of an appropriate particle size distribution. The pulverizing step is preferably carried out in the coexistence of the positive electrode active material of the present invention and the conductive auxiliary agent described later. The average particle diameter of the powder of the positive electrode active material of the present invention is preferably 0.5 to 50 μm, more preferably 1 to 30 μm, and still more preferably 3 to 10 μm. In the present specification, the average particle size is meant the 50% cumulative diameter when measuring samples with conventional laser diffraction scattering particle size distribution measuring apparatus (D _50).

Hereinafter, the positive electrode for a lithium ion secondary battery comprising the positive electrode active material of the present invention is referred to as "the positive electrode of the present invention", and the lithium ion secondary battery comprising the positive electrode active material of the present invention is referred to as "lithium ion of the present invention It is called a secondary battery.

The positive electrode of the present invention comprises a positive electrode active material layer containing the positive electrode active material of the present invention, and a current collector. The positive electrode active material layer is formed on the current collector. The blending ratio of the positive electrode active material of the present invention in the positive electrode active material layer can be, for example, 30 to 100% by mass, 40 to 90% by mass, and 50 to 80% by mass.

The current collector refers to a chemically inert electron conductor for keeping current flowing to the electrode during discharge or charge of the lithium ion secondary battery. The material of the current collector is not particularly limited as long as it is a metal that can withstand a voltage suitable for the active material to be used. The material of the current collector is at least one selected from silver, copper, gold, aluminum, tungsten, cobalt, zinc, nickel, iron, platinum, tin, indium, titanium, ruthenium, tantalum, chromium, molybdenum, and stainless steel Etc. can be exemplified. The current collector may be coated with a known protective layer. What processed the surface of a collector by a well-known method may be used as a collector.

When the potential of the positive electrode is set to 4 V or more based on lithium, it is preferable to use aluminum as a current collector for the positive electrode.

Specifically, it is preferable to use an aluminum or an aluminum alloy as the positive electrode current collector. Here, aluminum refers to pure aluminum, and aluminum having a purity of 99.0% or more is referred to as pure aluminum. An alloy obtained by adding various elements to pure aluminum is called an aluminum alloy. Examples of aluminum alloys include Al-Cu, Al-Mn, Al-Fe, Al-Si, Al-Mg, Al-Mg-Si, and Al-Zn-Mg.

As aluminum or aluminum alloy, specifically, for example, A1000 series alloys (pure aluminum series) such as JIS A1085 and A1N30, A3000 series alloys such as JIS A3003 and A3004 (Al-Mn series), JIS A8079, A8021 etc. A 8000 series alloys (Al-Fe series).

The current collector can take the form of a foil, a sheet, a film, a line, a rod, a mesh or the like. Therefore, as the current collector, for example, metal foils such as copper foil, nickel foil, aluminum foil, and stainless steel foil can be suitably used. When the current collector is in the form of a foil, a sheet or a film, the thickness is preferably in the range of 1 μm to 100 μm.

The positive electrode active material layer may contain a known positive electrode active material in addition to the positive electrode active material of the present invention. The positive electrode active material layer preferably contains a binder and a conductive auxiliary. What is mentioned later may be suitably adopted suitably as a binder and a conductive support agent contained in a positive electrode active material layer.

Specifically, the lithium ion secondary battery of the present invention comprises the positive electrode of the present invention, a negative electrode, a separator, and an electrolytic solution.

The negative electrode includes a current collector and a negative electrode active material layer formed on the current collector. The negative electrode active material layer contains a known negative electrode active material, and preferably further contains a binder and a conductive additive. The current collector of the negative electrode may be appropriately selected from those described for the positive electrode of the present invention. Hereinafter, both the positive electrode active material and the negative electrode active material may be collectively referred to as "active material", and both the positive electrode active material layer and the negative electrode active material layer may be collectively referred to as the "active material layer". .

As the binder, fluorine-containing resins such as polyvinylidene fluoride, polytetrafluoroethylene and fluororubber, thermoplastic resins such as polypropylene and polyethylene, imide resins such as polyimide and polyamideimide, alkoxysilyl group-containing resin, carboxymethyl cellulose Known materials such as styrene butadiene rubber may be employed.

The blending ratio of the binder in the active material layer is preferably, in mass ratio, active material: binder = 1: 0.005 to 1: 0.5. When the amount of the binder is too small, the formability of the electrode decreases, and when the amount of the binder is too large, the energy density of the electrode decreases.

A conductive aid is added to enhance the conductivity of the electrode. Therefore, the conductive additive may be optionally added when the conductivity of the electrode is insufficient, and may not be added when the conductivity of the electrode is sufficiently excellent. The conductive support agent may be any chemically active high electron conductor, and carbon black fine particles such as carbon black, graphite, vapor grown carbon fiber, and various metal particles are exemplified. Ru. Examples of the carbon black include acetylene black, ketjen black (registered trademark), furnace black, channel black and the like. These conductive assistants can be added to the active material layer singly or in combination of two or more. The compounding ratio of the conductive aid in the active material layer is preferably, in mass ratio, active material: conductive aid = 1: 0.01 to 1: 0.7. If the amount of the conductive additive is too small, efficient conductive paths can not be formed. If the amount of the conductive additive is too large, the formability of the active material layer deteriorates and the energy density of the electrode decreases.

In order to form an active material layer on the surface of a current collector, current collection can be performed using conventionally known methods such as roll coating, die coating, dip coating, doctor blade method, spray coating, and curtain coating. The active material may be applied to the surface of the body. Specifically, the active material, the binder, the solvent, and the conductive auxiliary agent as needed may be mixed to form a slurry, and the slurry may be applied to the surface of the current collector and then dried. Examples of the solvent include N-methyl-2-pyrrolidone, methanol, methyl isobutyl ketone and water. The dried one may be compressed to increase the electrode density. Alternatively, a mixture containing an active material, a binder, and, if necessary, a conductive auxiliary may be prepared, and the mixture may be pressed onto the current collector to form an active material layer on the surface of the current collector. Good.

The separator separates the positive electrode and the negative electrode, and allows lithium ions to pass while preventing a short circuit due to the contact of the both electrodes. As the separator, a known one may be employed, and polytetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamide, polyaramid (Aromatic polyamide), polyester, synthetic resin such as polyacrylonitrile, polysaccharide such as cellulose, amylose, fibroin Examples thereof include porous bodies, non-woven fabrics, and woven fabrics using one or more of electrically insulating materials such as natural polymers and ceramics such as keratin, lignin and suberin. In addition, the separator may have a multilayer structure.

The electrolytic solution contains a non-aqueous solvent and an electrolyte dissolved in the non-aqueous solvent.

As the non-aqueous solvent, cyclic carbonate, cyclic ester, chain carbonate, chain ester, ethers and the like can be used. Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate. Examples of cyclic esters include gamma butyrolactone, 2-methyl-gamma butyrolactone, acetyl-gamma butyrolactone, and gamma valerolactone. Examples of chain carbonates include dimethyl carbonate, diethyl carbonate, dibutyl carbonate, dipropyl carbonate, and ethyl methyl carbonate. Examples of chain esters include propionic acid alkyl ester, malonic acid dialkyl ester, acetic acid alkyl ester and the like. As the ethers, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dibutoxyethane can be exemplified. As the non-aqueous solvent, a compound in which part or all of hydrogens in the chemical structure of the above specific solvent is substituted with fluorine may be adopted.

Examples of the electrolyte include lithium salts such as LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , and LiN (CF ₃ SO ₂ ) ₂ .

As an electrolytic solution, 0.5 mol / liter of a lithium salt such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ and the like in a nonaqueous solvent such as fluoroethylene carbonate, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate and diethyl carbonate A solution dissolved at a concentration of about L to 1.7 mol / L can be exemplified.

The specific manufacturing method of the lithium ion secondary battery of this invention is described.
For example, the positive electrode and the negative electrode sandwich a separator to form an electrode body. The electrode body may be any of a laminated type in which a positive electrode, a separator and a negative electrode are stacked, or a wound type in which a laminate of a positive electrode, a separator and a negative electrode is wound. After connecting the current collector of the positive electrode and the current collector of the negative electrode to the positive electrode terminal and the negative electrode terminal leading to the outside using a current collection lead or the like, an electrolytic solution is added to the electrode body to form a lithium ion secondary battery. Good.

The shape of the lithium ion secondary battery of the present invention is not particularly limited, and various shapes such as cylindrical, square, coin, and laminate types can be adopted.

The lithium ion secondary battery of the present invention may be mounted on a vehicle. The vehicle may be a vehicle using electric energy from a lithium ion secondary battery for all or part of its power source, and may be, for example, an electric vehicle or a hybrid vehicle. When a lithium ion secondary battery is mounted on a vehicle, a plurality of lithium ion secondary batteries may be connected in series to form a battery pack. As an apparatus which mounts a lithium ion secondary battery, various household appliances driven by a battery, such as a personal computer and a mobile communication apparatus, as well as a vehicle, an office apparatus, an industrial apparatus and the like can be mentioned. Furthermore, the lithium ion secondary battery of the present invention can be used in wind power generation, solar power generation, hydroelectric power generation, storage devices and power smoothing devices for electric power systems, power sources for power and / or accessories of ships, etc., aircraft, Power supply source for power of spacecraft and / or accessories, auxiliary power supply for vehicles not using electricity as power source, power supply for mobile home robots, power supply for system backup, power supply for uninterruptible power supply, You may use for the electrical storage apparatus which stores temporarily the electric power required for charge in the charge station etc. for electric vehicles.

As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment. In the range which does not deviate from the summary of the present invention, it can carry out with various forms which gave change, improvement, etc. which a person skilled in the art can make.

Below, various specific examples are shown and this invention is more concretely demonstrated to it. The present invention is not limited by these specific examples.

(Comparative example 1)
Li ₂ CO ₃ , Nb ₂ O ₅ and Mn ₂ O ₃ were weighed so that the element ratio Li: Nb: Mn was 1.3: 0.3: 0.4, and these powders were put into a ball mill . Then, mixing with a ball mill was performed at about 100 rpm for 24 hours to obtain a mixture. After molding the mixture, the mixture was fired by heating at 950 ° C. for 12 hours in an argon gas atmosphere to manufacture a positive electrode active material of Comparative Example 1 which is a fired product. The theoretical composition of the positive electrode active material of Comparative Example 1 is Li _1.3 Nb _0.3 Mn _0.4 O ₂ .

The positive electrode active material of Comparative Example 1 and acetylene black as a conductive additive were weighed so as to have a mass ratio of 5: 2, and charged into a ball mill. And the mixing by a ball mill was performed for 0.5 hours at 300 rpm, and it was set as the mixture of the comparative example 1 containing the positive electrode active material of the comparative example 1, and acetylene black.

The mixture of Comparative Example 1, acetylene black, and polytetrafluoroethylene as a binder were mixed in a mortar to obtain a clay-like composition for a positive electrode active material layer. In the composition for the positive electrode active material layer, the mass ratio of the positive electrode active material of Comparative Example 1, acetylene black to polytetrafluoroethylene was 5: 3: 2.
A mesh-like aluminum was prepared as a current collector, and the composition for the positive electrode active material layer was pressure-bonded to this, whereby the positive electrode of Comparative Example 1 was obtained.

Lithium foil was prepared and used as a negative electrode. A polyethylene porous membrane was prepared as a separator. Further, an electrolyte was prepared by dissolving LiPF ₆ at a concentration of 1 mol / L in a solvent in which 5 parts by volume of ethylene carbonate and 5 parts by volume of diethyl carbonate were mixed. The separator was sandwiched between the positive electrode and the negative electrode of Comparative Example 1 to form an electrode body. The electrode body was covered with a pair of laminate films, and the three sides were sealed, and then the electrolytic solution was injected into the bag-like laminate film. Thereafter, by sealing the other side, the lithium ion secondary battery of Comparative Example 1 was manufactured, in which the four sides were airtightly sealed and the electrode body and the electrolytic solution were sealed.

(Comparative example 2)
The positive electrode active material of Comparative Example 2, the mixture of Comparative Example 2, the positive electrode of Comparative Example 2, and the lithium ion secondary battery of Comparative Example 2 are the same as in Comparative Example 1 except that the firing temperature is 900.degree. Manufactured.

Example 1
LiPF ₆ was added to the ball mill together with Li ₂ CO ₃ , Nb ₂ O ₅ and Mn ₂ O _{3 in} an amount equivalent to 1% by mass with respect to Li _1.3 Nb _0.3 Mn _0.4 O ₂ The positive electrode active material of Example 1, the mixture of Example 1, the positive electrode of Example 1, and the secondary lithium ion of Example 1 are the same as Comparative Example 1 except that the baking temperature is set to 900 ° C. The battery was manufactured. The theoretical composition of the positive electrode active material of Example 1 is Li _1.306 Nb _0.3 Mn _0.4 P _0.006 F _0.036 O ₂ .

(Example 2)
LiPF ₆ was added to the ball mill together with Li ₂ CO ₃ , Nb ₂ O ₅ and Mn ₂ O _{3 in} an amount equivalent to 2% by mass with respect to Li _1.3 Nb _0.3 Mn _0.4 O ₂ In the same manner as in Comparative Example 1 except that the baking temperature was set to 900 ° C., the positive electrode active material of Example 2, the mixture of Example 2, the positive electrode of Example 2, and the secondary lithium ion of Example 2 The battery was manufactured. The composition of the theoretical positive electrode active material of Example 2 _is _{_{_{_{Li 1.312 Nb 0.3 Mn 0.4 P 0.012}}}} F 0.072 O 2.

(Example 3)
LiPF ₆ was added to the ball mill together with Li ₂ CO ₃ , Nb ₂ O ₅ and Mn ₂ O _{3 in} an additive amount corresponding to 3% by mass with respect to Li _1.3 Nb _0.3 Mn _0.4 O ₂ In the same manner as in Comparative Example 1 except that the baking temperature was set to 900 ° C., the positive electrode active material of Example 3, the mixture of Example 3, the positive electrode of Example 3, and the secondary lithium ion of Example 3 The battery was manufactured. The theoretical composition of the positive electrode active material of Example 3 is Li _1.318 Nb _0.3 Mn _0.4 P _0.018 F _0.108 O ₂ .

Table 1 shows a list of production methods of positive electrode active materials of Comparative Examples 1 to 2 and Examples 1 to 3.

(Evaluation example 1)
The positive electrode active material of Comparative Example 1, Example 1, Example 2 and Example 3 was observed with a scanning electron microscope (SEM). 1 shows a SEM image of the positive electrode active material of Comparative Example 1, FIG. 2 shows a SEM image of the positive electrode active material of Example 1, FIG. 3 shows a SEM image of the positive electrode active material of Example 2, FIG. 4 shows the positive electrode of Example 3. The SEM image of the positive electrode active material of an active material is shown, respectively.
From the SEM image of the positive electrode active material of Comparative Example 1, a positive electrode active material with a particle diameter of about 1 μm was observed. From the SEM images of the positive electrode active materials of Example 1, Example 2 and Example 3, it was confirmed that as the addition amount of LiPF ₆ increased, the degree of the particles to be bound tended to increase.

Moreover, Nb, Mn, P, and O were targeted for the positive electrode active material of Example 2 by SEM-EDX combining a scanning electron microscope (SEM) and an energy dispersive X-ray analyzer (EDX). As a result of analysis, it was confirmed that these elements were dispersed and present in the positive electrode active material of Example 2.

(Evaluation example 2)
The positive electrode active materials of Comparative Example 1, Comparative Example 2, Example 1, Example 2, and Example 3 were analyzed by a powder X-ray diffractometer using a Cu-Kα ray. The X-ray diffraction chart of the positive electrode active material of Example 1 is shown in FIG.
In the X-ray diffraction charts of all the positive electrode active materials, diffraction patterns showing crystal structures attributable to the space group Fm-3m were observed.

Comparing the X-ray diffraction chart of the positive electrode active material of Comparative Example 1 whose firing temperature is 950 ° C. with the X-ray diffraction chart of the positive electrode active material of Comparative Example 2 whose firing temperature is 900 ° C. In the line diffraction chart, the peaks derived from the impurities LiMnO ₂ and Li ₃ NbO ₄ were strongly observed. Therefore, under the production conditions in which LiPF ₆ is not added, it can be said that the firing temperature of 950 ° C. is more advantageous than the firing temperature of 900 ° C.
On the other hand, in the X-ray diffraction charts of the positive electrode active materials of Examples 1 to 3 with a baking temperature of 900 ° C., almost no peaks derived from the impurities LiMnO ₂ and Li ₃ NbO ₄ were observed. In view of the result of Comparative Example 2 in which the baking temperature is 900 ° C., in Examples 1 to 3, the addition of LiPF ₆ improves the reactivity of each raw material at the time of baking and suppresses the adverse side reaction. It can be said that it was possible.

Also, it was found that the position of the X-ray diffraction peak shifted to the left as the addition amount of LiPF ₆ increased to 0%, 1% and 2%. From the Bragg's condition: 2 d sin θ = n λ, the shift of the position of the X-ray diffraction peak to the left means that sin θ becomes smaller, that is, the crystal plane distance d becomes larger. Therefore, as the addition amount of LiPF ₆ increases, it can be said that the interplanar spacing of the crystal structure that can be assigned to the space group Fm-3m increases.

(Evaluation example 3)
The positive electrode active materials of Example 1 and Example 2 were analyzed by a powder X-ray diffractometer using radiation light. Also in the X-ray diffraction chart of any positive electrode active material, a diffraction pattern showing a crystal structure attributable to the space group Fm-3m was observed.
The X-ray diffraction chart of the positive electrode active material of Example 1 showed some peaks derived from LiMnO _{2 as} an impurity, while the X-ray diffraction chart of the positive electrode active material of Example ₂ was derived from LiMnO ₂ Peak was not observed.
In addition, in both X-ray diffraction charts, a peak derived from Li ₃ PO ₄ was slightly observed. The intensity of the peak derived from Li ₃ PO ₄ was larger in the X-ray diffraction chart of the positive electrode active material of Example 2. It can be said that the amount of Li ₃ PO ₄ formed tends to increase as the amount of addition of LiPF ₆ increases.

(Evaluation example 4)
The positive electrode active materials of Example 1 and Example 2 were subjected to elemental analysis using inductively coupled plasma emission spectrometry (ICP-AES) and ion chromatography (IC). The results are shown in Table 2. The mass% of Li, Nb, Mn and P is the analysis result by ICP-AES, and the mass% of F is the analysis result by IC. The mass% of O was calculated by subtracting the mass% of Li, Nb, Mn, P and F from 100%.

(Evaluation example 5)
The lithium ion secondary batteries of Comparative Example 1, Example 1, Example 2 and Example 3 were charged to a voltage of 4.8 V at a current rate of 13.5 mA / g under conditions of 25 ° C. and 60 ° C. The amount of discharge when discharged to a voltage of 1.5 V at 13.5 mA / g was measured. The results of the discharge capacity per unit mass of each positive electrode active material are shown in Table 3. The charge / discharge curve at 25 ° C. of the lithium ion secondary battery of Example 1 is shown in FIG. 6, and the charge / discharge curve at 60 ° C. of the lithium ion secondary battery of Example 1 is shown in FIG. The charge-discharge curve at 25 ° C. of the lithium ion secondary battery is shown in FIG. 8, and the charge-discharge curve at 60 ° C. of the lithium ion secondary battery of Example 2 is shown in FIG.

It was supported that the positive electrode active material of the present invention can preferably contribute to charge and discharge. In particular, the value of the discharge capacity at 60 ° C. in Example 1 and Example 2 can be said to be extremely high. The addition of LiPF ₆ can suppress the formation of low-capacity impurities (LiMnO ₂ and Li ₃ NbO ₄ ), and the point of the increase in crystal plane spacing due to P addition and F addition increases the discharge capacity It is considered to have brought

Further, from the results in Table 3, in accordance with the amount of LiPF ₆ is increased as 0 → 1 → 2% by weight, although the discharge capacity of each temperature conditions also increased, the amount of LiPF ₆ is 2 → 3 wt% And it was found that the discharge capacity decreased. When the addition amount of LiPF ₆ is too large, it is considered that an excessive amount of Li ₃ PO _{4 as} an impurity is generated, which becomes a resistance factor, and the discharge capacity per unit mass of the positive electrode active material is reduced.
From the above results, the preferable range of the addition amount of LiPF ₆ is 0.5 to 2.5% by mass, the more preferable range is 1 to 2.2% by mass, and the more preferable range is 1.5 It is considered to be ̃2.1 mass%.

(Example 4)
An additive amount of Li ₃ PO ₄ equivalent to 1% by mass with respect to Li _1.3 Nb _0.3 Mn _0.4 O ₂ is introduced into a ball mill together with Li ₂ CO ₃ , Nb ₂ O ₅ and Mn ₂ O ₃ The positive electrode active material of Example 4, the mixture of Example 4, the positive electrode of Example 4, and the lithium ion secondary battery of Example 4 were manufactured in the same manner as in Comparative Example 1 except for the above. The composition of the theoretical positive electrode active material of Example _4, a _{_{_{_{Li 1.324 Nb 0.3 Mn 0.4 P 0.008}}}} O 2.032.

(Example 5)
Li _1.3 Nb _0.3 Mn _0.4 amount of _Li 3 PO ₄ and _Li 1.3 1 mass relative to _Nb 0.3 _Mn 0.4 _{O 2} which relative O ₂ equivalent to 1 wt% %, And the positive electrode active material of Example 5 in the same manner as Comparative Example 1 except that LiF was added to the ball mill together with Li ₂ CO ₃ , Nb ₂ O ₅ and Mn ₂ O ₃ . The mixture of Example 5, the positive electrode of Example 5, and the lithium ion secondary battery of Example 5 were manufactured. The composition of the positive electrode active theoretical material of Example 5 _are _{_{_{_{Li 1.359 Nb 0.3 Mn 0.4 P 0.008}}}} F 0.035 O 2.032.

(Comparative example 3)
Except that LiF was added to the ball mill together with Li ₂ CO ₃ , Nb ₂ O ₅ and Mn ₂ O _{3 in} an additive amount corresponding to 1 mass% with respect to Li _1.3 Nb _0.3 Mn _0.4 O ₂ In the same manner as in Comparative Example 1, a positive electrode active material of Comparative Example 3, a mixture of Comparative Example 3, a positive electrode of Comparative Example 3, and a lithium ion secondary battery of Comparative Example 3 were manufactured. The theoretical composition of the positive electrode active material of Comparative Example 3 is Li _1.335 Nb _0.3 Mn _0.4 F _0.035 O ₂ .

(Evaluation example 6)
The positive electrode active materials of Example 4, Example 5, and Comparative Example 3 were analyzed by a powder X-ray diffractometer using a Cu-Kα ray.
In the X-ray diffraction charts of all the positive electrode active materials, diffraction patterns showing crystal structures attributable to the space group Fm-3m were observed.

(Evaluation example 7)
For the lithium ion secondary batteries of Example 4 and Example 5 and Comparative Example 3, the amount of discharge was measured in the same manner as in Evaluation Example 5. The results are shown in Table 4.

From Table 4, in comparison with the lithium ion secondary battery of Example 4 to which Li ₃ PO ₄ is added and the lithium ion secondary battery of Comparative Example 3 to which LiF is added, both of Li ₃ PO ₄ and LiF are compared. It turns out that the lithium ion secondary battery of Example 5 added is excellent in discharge capacity.
In the positive electrode active material of the present invention, it is considered that co-addition of P and X is particularly preferable.

Claims

What is claimed is: 1. A positive electrode active material, which has a crystal structure that can be assigned to a space group Fm-3m and is represented by the following composition formula (1).
Li 1 + x Nb y Fe a Mn b P c X d O e (1)
In the composition formula (1), X is selected from halogen elements. x, y, a, b, c, d and e are 0 <x <1, 0 <y <0.5, 0.25 ≦ a + b <1, 0 ≦ a <1, 0 ≦ b <1, 0 <C ≦ 0.05, 0 ≦ d ≦ 0.2, and 1.8 ≦ e ≦ 2.2 are satisfied.
The positive electrode active material according to claim 1, which satisfies 0.8 ≦ 2 y + a + b ≦ 1.2.
The positive electrode active material according to claim 1, wherein 0 <c ≦ 0.025 is satisfied.
A positive electrode for a lithium ion secondary battery comprising the positive electrode active material according to any one of claims 1 to 3.
The lithium ion secondary battery which comprises the positive electrode for lithium ion secondary batteries of Claim 4.
Mixing a lithium source, a niobium source, an iron source and / or a manganese source, and a P source into a mixture,
The method for producing a positive electrode active material according to any one of claims 1 to 3, comprising the step of firing the mixture.