JP2021157936A - Negative electrode active material, negative electrode, and secondary battery - Google Patents

Abstract

To provide a negative electrode active material having an improved reversible capacity as compared with LixFeNb11O29, which is a non-replacement material.SOLUTION: A negative electrode active material according to the present invention is represented by a general formula of Fe1-xNb11-yO29-z-aAx+y+z(0≤x≤1, 0≤y≤11, and -10≤z≤10 are satisfied, and A is one or more selected from the group consisting of Al, Si, B, P, C, Ge, and Bi), and a part or all of the surface is covered with A.SELECTED DRAWING: Figure 1

Description

The present invention relates to a negative electrode active material, a negative electrode and a secondary battery.

Conventionally, graphite, which has been generally used as a negative electrode active material, has a theoretical capacity of about 372 mAh / g. A secondary battery using graphite as a negative electrode active material has a problem that the capacity is reduced after a plurality of cycles or after storage, and as a result, the battery life is shortened. The decrease in capacity is due to the formation of a Solid Electrolyte Interface (hereinafter, SEI), which is an organic film, around the graphite in the negative electrode because the potential drops to about 0.1 V based on Li metal during battery operation. Since the formation potential of SEI, which is an organic film, is 0.7 V on the basis of lithium metal, attention is focused on negative electrode active materials having a potential higher than 0.7 V.

As such a negative electrode active material exceeding 0.7 V, Patent Document 1 describes a battery active material containing an orthorhombic oxide represented by _{the general formula Li x} M1M2 ₂ O _{6 (0 ≦ x ≦ 5).} Is disclosed. Here, M1 is at least one selected from the group consisting of Fe and Mn, and M2 is at least one selected from the group consisting of Nb, Ta and V. Further, Patent Document 2 describes a lithium-free mixed titanium niobium oxide containing at least one trivalent metal and having a molar ratio of Nb / Ti greater than 2, which is the material and formula of the following formula (I). A lithium-free mixed titanium niobium oxide selected from the group comprising the material of (II) is disclosed.
M _x Ti _{1-2 x} Nb _{2 + x} O _{7 ± δ} (I): 0 <x ≦ 0.20, −0.3 ≦ δ ≦ 0.3
MxTi _2-2x Nb _{10 + x} O _{29 ± δ} (II): 0 <x ≦ 0.40, −0.3 ≦ δ ≦ 0.3

On the other hand, in recent years, a material-based negative electrode active material called _{Li x} FeNb ₁₁ O ₂₉ , which has a crystal structure different from that of the above compound and has a potential exceeding 0.7 V, has been reported. The problem with this negative electrode active material is that the reversible capacity appears lower than the theoretical capacity. Specifically, although it has been reported that the reversible capacity is increased by adjusting the particle shape and the firing atmosphere as shown in Non-Patent Document 1, 270 mAh / g is the maximum in Non-Patent Document 1, and the theoretical capacity is theoretical. It is lower than 380 mAh / g. Therefore, a technique for improving the reversible capacity of _{Li x} FeNb ₁₁ O _{29 is required.}

Japanese Unexamined Patent Publication No. 2014-11526 Japanese Patent Application Laid-Open No. 2016-510304

X.Lou et al., ChemElectroChem 4 (2017) 3171-3180

_{When Li x} FeNb ₁₁ O ₂₉ is used as the negative electrode active material without element substitution, when the charge reaction, which is the reaction at the time of the first Li desorption, is carried out after the discharge reaction, which is the reaction at the time of the first Li insertion. There is a problem that the reversible capacity, which is the capacity generated in the above, is lower than the theoretical capacity of 380 mAh / g. In this case, there is a problem that the energy density of the battery is lowered.

Therefore, an object of the present invention is to provide a negative electrode active material having an improved _{reversible capacity as compared with Li x FeNb 11} O ₂₉ , which is a non-replacement material.

The features of the present invention for solving the above problems are as follows, for example.
General composition formula: Fe _1-x Nb _11-y O _29-z-a A _{x + y + z} (0 ≦ x ≦ 1, 0 ≦ y ≦ 11, -10 ≦ z ≦ 10, where A is Al, Si, B, A negative electrode active material represented by (one or more selected from the group consisting of P, C, Ge and Bi).

According to the present invention, the reversible capacity of the secondary battery can be improved. Issues, configurations and effects other than those described above will be clarified by the following description of the embodiments.

It is a perspective view of the electrode body included in a secondary battery. It is the XRD measurement result of the negative electrode active material in Examples 1 to 3 and Comparative Example 1. It is the XRD measurement result of the negative electrode active material in Examples 4-5 and Comparative Example 1. It is the XRD measurement result of the negative electrode active material in Examples 6 to 7 and Comparative Example 1. It is the XRD measurement result of the negative electrode active material in Examples 8-10 and Comparative Example 1. It is the XRD measurement result of the negative electrode active material in Examples 11 to 13 and Comparative Example 1. It is the XRD measurement result of the negative electrode active material in Example 14 and Comparative Example 1. It is the XRD measurement result of the negative electrode active material in Comparative Examples 1-6. It is a measurement result of SEM and EDX of the negative electrode active material in an Example.

Hereinafter, embodiments of the present invention will be described with reference to the drawings and the like. The following description shows specific examples of the contents of the present invention, and the present invention is not limited to these explanations. It can be changed and modified. Further, in all the drawings for explaining the present invention, those having the same function may be designated by the same reference numerals, and the repeated description thereof may be omitted.

The "~" described in the present specification is used to mean that the numerical values described before and after the "~" are used as the lower limit value and the upper limit value. When the upper limit value or the lower limit value is 0, the upper limit value or the lower limit value is not included. In the numerical range described stepwise in the present specification, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value described in another stepwise. The upper limit value or the lower limit value of the numerical range described in the present specification may be replaced with the value shown in the examples.

In the present specification, the embodiment will be described by taking a lithium ion secondary battery as an example as the secondary battery. A lithium ion secondary battery is an electrochemical device that creates a potential difference between electrodes by occlusion of lithium ions into the electrodes and discharge from the electrodes, thereby storing or making available electrical energy.

The object of the present invention also includes a secondary battery called by a name different from that of the lithium ion secondary battery, for example, a lithium ion battery, a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte secondary battery, and the like. The technical idea of the present invention can also be applied to a sodium ion secondary battery, a magnesium ion secondary battery, a calcium ion secondary battery, a zinc secondary battery, an aluminum ion secondary battery and the like.

When a material is selected and used from the material group exemplified in the following description, the material may be used alone or in combination of a plurality of materials as long as it does not contradict the contents disclosed in the present specification. Is also good. Further, materials other than the material group exemplified in the following description may be used as long as they do not contradict the contents disclosed in the present specification.

<Secondary battery>
FIG. 1 is a perspective view of an electrode body 400 included in a secondary battery. This secondary battery includes a positive electrode 100, a negative electrode 200, a separator 300, and an exterior body (not shown). The secondary battery of FIG. 1 is a laminated type laminated battery. The secondary battery may be a cylindrical battery, a square battery, a button battery, or the like, instead of the laminated battery.

As shown in FIG. 1, the positive electrode 100 has a positive electrode mixture layer 110, a positive electrode current collector 120, and a positive electrode tab 130. In the illustrated positive electrode 100, the positive electrode mixture layer 110 is formed on both sides of the flat plate-shaped positive electrode current collector 120. The positive electrode tab 130 is provided at the end of the positive electrode current collector 120 as a flat plate-shaped projecting piece.

The negative electrode 200 has a negative electrode mixture layer 210, a negative electrode current collector 220, and a negative electrode tab 230. In the illustrated negative electrode 200, the negative electrode mixture layer 210 is formed on both sides of the flat plate-shaped negative electrode current collector 220. The negative electrode tab 230 is provided at the end of the negative electrode current collector 220 as a flat plate-shaped projecting piece.

As shown in FIG. 1, the positive electrode 100, the separator 300, and the negative electrode 200 are laminated in this order to form one electrode body 400. In the secondary battery, a plurality of electrode bodies 400 can be laminated and built in the exterior body. The electrode bodies 400 are electrically insulated from each other by being laminated with the separator 300 interposed therebetween.

These current collectors, electrode tabs and the like can be bonded to each other by various methods such as spot welding and ultrasonic bonding. The electrode bodies 400 built in the outer body may be electrically connected in parallel, or a part or all of the plurality of electrode bodies 400 may be electrically connected in series.

In the exterior body, the electrolytic solution is injected into the inner space where the electrode body 400 is built. The electrode body 400 housed in the outer body is held in a state of being immersed in the electrolytic solution. The electrode body 400 and the electrolytic solution are sealed by an exterior body or the like to prevent contact with moisture, air or the like.

Examples of the exterior body include a bag-shaped laminated container. The laminated container can be formed by laminating a multilayer film with a heat seal, an adhesive or the like. The multilayer film can be formed by laminating various films such as polyethylene, polypropylene, polyamide, polyester, and aluminum foil.

The exterior body can be provided as a metal can instead of the laminated container. The metal can can be formed by using, for example, an aluminum alloy, stainless steel, nickel-plated steel, or the like. The secondary battery may be a laminated type in which electrode bodies 400 are stacked, or may be a wound type in which strip-shaped electrode bodies are spirally wound.

<Positive electrode>
The positive electrode mixture layer 110 of the positive electrode 100 is formed by using a positive electrode mixture having a positive electrode active material. The positive electrode mixture layer 110 may contain a carbon material, a binder, and the like together with the positive electrode active material. Further, the positive electrode mixture layer 110 may contain a solid electrolyte. When a solid electrolyte having high ionic conductivity is used for the positive electrode mixture layer 110, the ionic conductivity in the positive electrode can be improved.

Examples of the positive electrode active material include various active materials such as LiCo-based composite oxide, LiNi-based composite oxide, LiMn-based composite oxide, LiCoNiMn-based composite oxide, LiFePO _4- based composite oxide, and LiMnPO _4- based composite oxide. Substances can be used. Specific examples of the composite oxide include LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiCo _1/3 Ni _1/3 Mn _1/3 O _2, and the like, and these transition metals are Co, Ni, Mn, Al, and the like. Examples thereof include composite oxides substituted with various different elements such as Ti.

As the carbon material, for example, carbon black, carbon nanofibers, conductive polymer and the like can be used. Examples of carbon black include Ketjen black, acetylene black, furnace black, thermal black, graphite and the like. Examples of carbon nanofibers include pitch-based carbon nanotubes and PAN-based carbon nanotubes. Examples of the conductive polymer include polyacetylene, polyaniline, polyacene and the like.

As the binder forming the positive electrode mixture layer 110, for example, polyvinylidene fluoride (PVDF), acrylic acid ester resin, methacrylic acid ester resin, or the like can be used.

As the positive electrode current collector 120, for example, a metal foil made of aluminum, stainless steel, titanium or the like, a perforated foil, an expanded metal, a foamed metal plate or the like can be used. The thickness of the positive electrode current collector 120 is preferably 10 nm to 1 mm, more preferably 1 to 100 μm, from the viewpoint of achieving both mechanical strength and energy density. The positive electrode tab 130 can be formed of the same material as the positive electrode current collector 120.

<Negative electrode>
The negative electrode mixture layer 210 of the negative electrode 200 is formed by using a negative electrode mixture having a negative electrode active material. The negative electrode mixture layer 210 may contain a carbon material, a binder, and the like together with the negative electrode active material. Further, the negative electrode mixture layer 210 may contain a solid electrolyte. When a solid electrolyte having high ionic conductivity is used for the negative electrode mixture layer 210, the ionic conductivity in the negative electrode can be improved.

As the negative electrode active material, a conversion-based metal oxide is used as described later. The conversion-based metal oxide means a metal oxide that undergoes a conversion reaction to reduce and generate a metal. In the conversion reaction between the metal oxide and lithium ion, a single metal is produced by the reduction of the metal oxide, and lithium oxide is produced by the oxidation of lithium.

According to the conversion-type metal oxide, by reversibly causing a conversion reaction and its reverse reaction, lithium ions can be occluded when the secondary battery is discharged and lithium ions can be released when the secondary battery is charged. According to the conversion-type metal oxide, a potential difference required for charging and discharging can be generated between the electrodes by such a redox reaction, an accompanying alloying reaction, or the like.

As the binder for forming the negative electrode mixture layer 210, for example, styrene-butadiene rubber, polyvinylidene fluoride (PVDF), acrylic acid ester resin, methacrylic acid ester resin and the like can be used. As the binder, a thickening resin such as carboxymethyl cellulose may be used in combination.

Similar to the positive electrode mixture layer 110, a carbon material such as carbon black, carbon nanofibers, or a conductive polymer can be used for the negative electrode mixture layer 210.

As the negative electrode current collector 220, for example, a metal foil made of copper, stainless steel, titanium, nickel or the like, a perforated foil, an expanded metal, a foamed metal plate or the like can be used. The thickness of the negative electrode current collector 220 is preferably 10 nm to 1 mm, more preferably 1 to 100 μm, from the viewpoint of achieving both mechanical strength and energy density. The negative electrode tab 230 can be formed of the same material as the negative electrode current collector 220.

<Mixed mixture layer formation method>
In the positive electrode mixture layer 110 and the negative electrode mixture layer 210, an active material, a binder, a carbon material, etc. are kneaded in a solvent to prepare a mixture, and the prepared mixture is applied to a current collector. It can be formed by drying the coated mixture. The mixture layer formed on the current collector is press-molded so that the active material and the like have a predetermined density. If necessary, the current collector formed from the mixture layer can be punched, cut, or the like to form an electrode.

Mixing and kneading of the mixture can be performed using various devices such as a planetary mixer, a dispenser mixer, a butterfly mixer, a twin-screw kneader, a ball mill, and a bead mill. As the solvent for dispersing the raw material and the mixture, various solvents such as 1-methyl-2-pyrrolidone (NMP), water, and γ-butyrolactone can be used depending on the electrode. As a method of applying the mixture, various methods such as a roll coating method, a doctor blade method, a die coating method, a dipping method, and a spray method can be used.

<Separator>
The separator 300 is mainly provided to prevent a short circuit between the electrodes. As the separator 300, a polyolefin resin such as polyethylene, polypropylene, or a polyethylene-polypropylene copolymer, a microporous film made of glass fiber or the like, a non-woven fabric, or the like can be used. A solid electrolyte may be used as the separator 300. By using a solid electrolyte exhibiting high ionic conductivity and low conductivity, the electrode bodies 400 can be electrically connected in series, or the secondary battery can be converted into an all-solid-state battery.

Examples of the solid electrolyte include sulfide-based solid electrolytes _{such as Li 10} Ge ₂ PS ₁₂ and Li ₂ SP ₂ S ₅ , garnet-type solid electrolytes such as _{Li 7} La ₃ Zr ₂ O _{12 , and La 2 /. Various solid electrolytes such as perovskite type solid electrolytes such as 3-x} Li _3x TiO ₃ , NASICON type solid electrolytes, semi-solid electrolytes in which ionic liquids are supported on resins and inorganic particles, and gel electrolytes using polymer gels. Can be used.

Depending on the material, the separator 300 may be formed in a sheet shape and arranged between the electrodes, or may be formed on the electrodes by coating or the like. The thickness of the separator 300 is preferably several nm to several mm from the viewpoint of achieving both electron insulation and energy density.

<Electrolytic solution>
The electrolytic solution has a composition having an electrolyte that serves as a carrier of electric charges and a solvent that disperses and dissolves the electrolyte. Various additives may be added to the electrolytic solution for the purpose of improving the cycle characteristics and stability of the secondary battery, the flame retardancy of the electrolytic solution, and the like. However, when a solid electrolyte is used as the separator 300, it is not necessary to use an electrolytic solution. Instead of immersing the positive electrode 100, the negative electrode 200, etc. in the electrolytic solution, a solid electrolyte may be filled between these electrodes.

As the electrolyte, for _{example, LiPF 6, LiBF 4, LiClO} 4, LiCF 3 SO 3, LiCF 3 CO 2, LiAsF 6, LiSbF 6, or a lithium imide salt such as lithium bis (fluorosulfonyl) imide, lithium bis oxalate borate Lat (LiBOB) or the like can be used. As the electrolyte, LiPF ₆ is particularly preferable.

Various solvents such as ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), propylene carbonate, butylene carbonate, γ-butyrolactone, phosphate triester, trimethoxymethane, dioxolane, diethyl ether, and sulfolane. Solvents can be used.

<Negative electrode active material>
As the negative electrode active material, Fe Nb ₁₁ O ₂₉ having the space group Amma has a general composition formula, Fe _{1-x Nb 11-y} O _29-z-a A _{x + y + z} (0 ≦ x ≦ 1, 0 ≦ y ≦ 11). , -10 ≦ z ≦ 10), and the element A belonging to the 13th, 14th, and 15th groups is added. In the above composition formula, a means an oxygen deficiency or an excessively introduced amount of oxygen, and the range of a is usually between -5 and 5. Also, x + y + z is not 0. The total amount of A added does not necessarily have to be elementally substituted with the active material, and may be precipitated on the surface of the material to cover a part or all of the active material. Specifically, as A, one or more selected from the group consisting of Al, Si, B, P, C, Ge and Bi can be used. _{When A is deposited on the surface of FeNb 11} O ₂₉ or is coated with A instead of element substitution, the structure of A is, for example, amorphous A, an oxide of A, or a single crystal of A. It may be a crystal. As the base material of the negative electrode active material to which A is added, an active material in which any metal element is elementally substituted for one or both of the Fe site and the Nb site of _{FeNb 11} O _{29 is used.} You may.

The synthesis method is not limited, but it is preferable to use, for example, the following method. _{That is, as the element source of the additive element A, Fe 2} O so that Fe and Nb have a desired chemical quantitative ratio together with an oxide, an oxo acid, and an organic compound containing the elements A of groups 13, 14, and 15. It can be obtained _{by weighing 3} and Nb ₂ O ₅ , mixing them with a ball mill, ball milling them in ethanol at room temperature, and then _{sintering them in an N 2 atmosphere.} At this time, the sintering temperature and the sintering time _{can be set arbitrarily as long as FeNb 11} O ₂₉ having the space group Amma can be synthesized, and the structure of A deposited and coated on the surface is controlled. The sintering temperature and time can be adjusted.

The reversible capacity of the negative electrode active material thus produced is increased as compared with the reversible capacity of _{FeNb 11} O _{29. The reason why the increase in the reversible capacity is obtained in FeNb 11} O ₂₉ to which the element A is added is not necessarily clear, but a combination of the following causes can be considered. That is, the presence of the additive element A suppresses the Ostwald growth of the active material, promotes fine particle formation, and improves the conductivity of FeNb ₁₁ O ₂₉ , which has low electron conductivity, by substituting some elements for oxygen sites. The presence of A as a precipitate having good _{conductivity ensures the electron conductivity of the FeNb 11} O ₂₉ negative electrode as an electrode, and the additive element improves the diffusibility of Li during charging and discharging.

The negative electrode active material according to the present embodiment has a _{general composition formula, Fe 1-x} Nb _11-y O, by adding element A while maintaining a crystal structure based on the space group Amma _{represented by FeNb 11} O _{29. 29-z-a} A _{x + y + z} (0 ≦ x ≦ 1, 0 ≦ y ≦ 11, -10 ≦ z ≦ 10) is sufficient, and the total amount of added A does not necessarily have to be replaced with an active material. , It may be deposited on the surface of the material, or a part or all of the surface of the active material may be covered with A. Examples of the method for confirming whether or not the desired active material has been synthesized include the following methods. That is, powder X-ray diffraction (hereinafter referred to as XRD) is performed on the powder obtained after material synthesis, and it is confirmed that the main phase in the obtained peak corresponds to the space group Amma. .. In addition, when confirming whether or not element substitution is performed and how much chemical ratio is contained in the active material, high frequency inductively coupled plasma optical emission spectrometer (ICP) emission is performed. Spectral analysis may be used. Specifically, after dissolving the oxide as the main phase in an acid solution or the like, ICP emission spectroscopy is used to introduce a solution sample into the plasma, so that the unique elements generated from each element are substituted. It can be confirmed by confirming the existence of the element from the spectrum of the above, obtaining the concentration of the element from the intensity of the spectrum, and calculating the chemical ratio.

The size of the negative electrode active material is not particularly limited, but the primary particles of the negative electrode active material have a circle-equivalent diameter measured by approximating a circle on an electron microscope image, preferably 100 μm or less, more preferably. The primary particle size may be 10 μm or less, more preferably 5 μm or less, and 0.5 μm or less as long as good crystallinity can be ensured. The particles may have a solid structure, some primary particles may have a hollow structure, or substantially all of the primary particles may have a hollow structure. Further, the primary particles may have only open pores or may have open pores and closed pores. The shape and structure of the negative electrode active material can be confirmed by, for example, observation using a scanning electron microscope (SEM).

In order to ensure conductivity, a material described later can be used as the carbon material introduced together with the active material into the electrode.

Oxides, oxo acids, and organic compounds used as the element source of the element A to be added include, for example, silicon oxide, boron oxide, boric acid, phosphoric acid, iron phosphate, sucrose, lactose, starch, amylose, and cellulose. , Mannan, germanium oxide, bismuth oxide and the like can be used. Of the above, a plurality of types of raw materials may be used as the element source of the element A to be added. Specific examples of the metal oxide is _{used, Al 2 O 3, SiO 2} , H 3 BO 3, B 2 O 3, H 3 PO 4, FePO 4 · 2 (H 2 O), GeO 2, Bi 2 O 3 And so on.

<Carbon material>
In addition, as carbon materials introduced into the active material in order to ensure conductivity, artificial graphite, natural graphite, non-graphitized carbons, vapor phase carbon fiber, carbon black, carbon nanofibers, fullerenes, graphene, etc. are used. Can be used. Examples of carbon black include Ketjen black, acetylene black, furnace black, thermal black, graphite and the like. Examples of carbon nanofibers include pitch-based carbon nanotubes and PAN-based carbon nanotubes.

Among these, a better network of carbon materials can be formed by using a carbon material having a particle size that has a particularly good affinity for metal oxides. Specifically, in order to increase the affinity, it is preferable to use a carbon material having a particle size of the primary particles of the carbon material equal to or smaller than the particle size of the metal oxide. Among these, Ketjen Black has a small particle size of the primary particles, which is preferable for ensuring conductivity. Further, a material obtained by heating and pressurizing these carbon materials in a polar solvent may be used as the carbon material.

<Manufacturing method of negative electrode active material>
_{As a method for synthesizing a general composition formula, Fe 1-x} Nb _11-y O _29-z-a A _{x + y + z} (0 ≦ x ≦ 1, 0 ≦ y ≦ 11, -10 ≦ z ≦ 10), which is a negative electrode active material. Can be synthesized, for example, by using a general solid phase reaction method. Hereinafter will be described by taking a method of synthesizing _FeNb 11 _{Si x O 29-x} as a negative electrode active material as an example. The negative electrode active material can be produced by a production method including a mixing step of raw material powder and a sintering step.

First, in the mixing step, the raw materials of the negative electrode active material are mixed. As raw materials, Fe ₂ O ₃ , SiO ₂ , and Nb ₂ O ₅ can be used. The size of these raw material powders is not particularly limited, it is preferable to use a material having a small particle diameter than FeNb 11 Si _z O _29-z after synthesis. This is because Ostwald grows in the sintering process, and the synthesized substance tends to have a larger particle size than the raw material powder. A crusher such as a ball mill may be used for mixing the materials in the mixing step. Both wet and dry methods are effective, but it is preferable to use the wet method for uniform mixing. Examples of the solvent for making it wet include water, ethanol and the like. The raw material powder is dispersed in a solvent such as water or ethanol, and then mixed at 300 rpm for 1 hour or more using an appropriate ball to obtain a suspension dispersed in the solvent. By separating the solvent from the suspension, a mixed powder in which the raw materials are mixed substantially uniformly can be obtained. As a method for separating the solvent, centrifugation, vacuum distillation of the solvent using an evaporator, filtration or the like can be used.

Next, in the sintering step, the mixed powder obtained in the mixing step is sintered under a predetermined temperature and atmosphere. Specifically, it is a step of putting the mixed powder in a sintering container and then putting it in an electric furnace for sintering. Examples of the sintering temperature include 600 ° C. to 1450 ° C., preferably 800 ° C. to 1350 ° C., and most preferably 900 ° C. to 1250 ° C. If the sintering temperature is too high, the crystal structure is transformed from the Amma structure. On the other hand, if it is sintered too much at a low temperature, a desired Amma structure cannot be obtained. Further, when the temperature is increased to 1250 ° C. or higher, the particle size tends to be coarsened. The sintering time is 2 hours or more, more preferably 4 hours or more. From the viewpoint of more uniformly sintering the material, a sintering time of 2 hours or more is required. On the other hand, when sintering is performed at a high temperature for a long time, the particle size tends to be coarse. The atmosphere during sintering, an oxygen atmosphere, may be in the synthesis of an oxidizing atmosphere such as air atmosphere, and N ₂ atmosphere, Ar atmosphere, may be synthesized in a reducing atmosphere such as CO atmosphere. In the synthesis under an oxidizing atmosphere, the _{amount of a represented by FeNb 11} O _29-a tends to be small, and the amount of x tends to be large under a reducing atmosphere. However, a crystal having an Amma structure as the main phase crystal structure can be obtained in either atmosphere. Incidentally, the atmosphere in the case of sintering the carbon source, N ₂ atmosphere, Ar atmosphere, is synthesized in a reducing atmosphere such as CO atmosphere preferred. This is because in an oxidizing atmosphere, the carbon source becomes a gas such as CO by combustion, and the amount of carbon used for element substitution and coating decreases. The addition of C may be obtained by sintering at a temperature of from 900 to 1250 ° C. is mixed with the raw material _powder, mixing the carbon source with a ball mill or the like together with powder of _FeNb 11 _{O 29} after synthesizing the _FeNb 11 _{O 29} Then, by sintering again at a temperature of 600 to 800 ° C., more preferably 650 ° C. to 750 ° C., a general composition formula, Fe _1-x Nb _11-y O _29-z-a A _{x + y + z} (0 ≦ x ≦). 1, 0 ≦ y ≦ 11, -10 ≦ z ≦ 10) may be combined.

After that, these materials may be reduced in x amount by performing post-annealing in an oxidizing atmosphere at a lower temperature, for example, a temperature of about 300 ° C. to 600 ° C.

Usually, the primary particles in the present invention synthesized by the solid phase reaction method may be classified if necessary. Further, the negative electrode active material may be obtained by combining the classified primary particles with different particle size groups.

The negative electrode active material obtained by the above manufacturing method can be used as a material for the negative electrode 200. The negative electrode active material can be kneaded with a binder, a carbon material, or the like in a solvent to prepare a negative electrode mixture. The negative electrode mixture layer 210 as shown in FIG. 1 can be formed by applying the prepared negative electrode mixture to the negative electrode current collector 220 and drying the applied negative electrode mixture.

Further, the negative electrode active material obtained by the above manufacturing method is a secondary battery including a positive electrode 100, a negative electrode 200, and a separator 300 by forming a negative electrode mixture layer 210 as shown in FIG. Can be done. Such secondary batteries include, for example, a power source for mobile bodies such as mobile phones and portable personal computers, a power source for electric vehicles, hybrid vehicles, railway vehicles, hybrid railway vehicles, ships, etc., a stationary power source for power storage, and the like. It can be used for various purposes.

Hereinafter, the present invention will be specifically described with reference to examples, but the technical scope of the present invention is not limited thereto.

<Example 1>
<Preparation of negative electrode active material>
The negative electrode active material was synthesized by the following procedure using the solid phase reaction method. _{First, Fe 2} O ₃ , RuO ₂ , and H ₃ BO ₃ are weighed so that the chemical ratio of Fe, Nb, and B is 1: 11: 0.5, and the amount of powder is 2 g in total. Was adjusted. Then, a zirconium ball having a diameter of 3 mm was put into a ball mill pot containing 40 g of the zirconium ball. Then, after putting 6 g of ethanol into the mill pot, the ball mill was carried out at a speed of 300 rpm for 1 hour. Then, ethanol was separated from the suspension using an evaporator, and then vacuum dried at 60 ° C. for 10 hours or more. Then, the material was placed on a sintering dish and sintered in an electric furnace at 1250 ° C. under Air to obtain the desired product.

<Identification of crystal phase>
When the crystal phase was identified using XRD, a crystal phase in which the main phase belonged to the space group Amma was obtained. FIG. 2 shows the XRD result.

<Manufacturing of negative electrode 200>
The negative electrode 200 was synthesized by the following procedure. The synthesized negative electrode active material, carbon material, and binder were mixed and kneaded by adding N-methyl-2-pyrrolidone: NMP to prepare a slurry-like negative electrode mixture. Ketjen black was used as the carbon material. As the binder, an acrylic binder was used. The mixing ratio was set to negative electrode active material: Ketjen black: binder = 80 wt%: 10 wt%: 10 wt% in terms of solid content ratio. The prepared negative electrode mixture was applied onto the current collector foil and dried to form a negative electrode mixture layer, and then the negative electrode mixture layer was pressed to a predetermined density to obtain a negative electrode.

<Measurement of reversible capacity>
A unipolar cell, which is a lithium ion secondary battery, was produced by using the produced negative electrode and metallic lithium as a counter electrode. Assuming that the capacity of the negative electrode active material is 380 mAh / g, the weight of the negative electrode active material in the electrode is calculated, and the current value calculated when multiplied by 380 mAh / g is set to 1C. The unipolar cell was discharged to a final voltage of 0.8 V with a constant current of 0.2 C, Li was inserted, and then charged to a final voltage of 3 V with a constant current of 0.2 C. The combination of the discharge process and the charge process was measured as one cycle. The reversible capacity was defined as the capacity generated when charging to 3 V after discharging and inserting Li. As a result of the measurement, it was clarified that the reversible capacity was 270.6 mAh / g.

<Example 2>
<Preparation of negative electrode active material>
_{In the negative electrode active material in this example, Fe 2} O ₃ , RuO ₂ , and H ₃ BO ₃ are weighed and mixed so that the chemical ratio of Fe, Nb, and B is 1: 11: 1.0. Was prepared in the same manner as in Example 1 except that the above was carried out.

<Identification of crystal phase>
When the crystal phase was identified using XRD, a crystal phase in which the main phase belonged to the space group Amma was obtained. FIG. 2 shows the XRD result.

<Manufacturing of negative electrode 200>
The method for producing the negative electrode was the same as in Example 1.

<Measurement of reversible capacity>
The method for measuring the reversible capacity was the same as in Example 1. As a result, the reversible capacity was 260.1 mAh / g.

<Example 3>
<Preparation of negative electrode active material>
_{The negative electrode active material in this example contains Fe 2} O ₃ and Al ₂ O ₃ so that the chemical ratio of Fe and Al and Nb and B is 0.5: 0.5: 11: 0.25. Nb ₂ O ₅ and H ₃ BO ₃ were weighed and mixed, and the mixture was prepared in the same manner as in Example 1.

<Identification of crystal phase>
When the crystal phase was identified using XRD, a crystal phase in which the main phase belonged to the space group Amma was obtained. FIG. 2 shows the XRD result.

<Manufacturing of negative electrode 200>
The method for producing the negative electrode was the same as in Example 1.

<Measurement of reversible capacity>
The method for measuring the reversible capacity was the same as in Example 1. As a result, the reversible capacity was 268.9 mAh / g.

<Comparative example 1>
<Preparation of negative electrode active material>
The negative electrode active material in this example was prepared as follows. _{First, Fe 2} O ₃ and Nb ₂ O ₅ were weighed so that the chemical ratio of Fe and Nb was 1:11, and the amount of powder was adjusted so as to have a total of 2 g. Then, a zirconium ball having a diameter of 3 mm was put into a ball mill pot containing 40 g of the zirconium ball. Then, after putting 6 g of ethanol into the mill pot, the ball mill was carried out at a speed of 300 rpm for 1 hour. Then, after separating ethanol from the suspension by centrifugation, it was vacuum dried at 60 ° C. for 10 hours or more. Then, the material was placed on a sintering dish and sintered in an electric furnace at 1250 ° C. under Air to obtain the desired product.

<Identification of crystal phase>
When the crystal phase was identified using XRD, a crystal phase having a main phase of FeNb ₁₁ O _29-x belonging to the space group Amma was obtained. FIG. 2 shows the XRD result.

<Manufacturing of negative electrode 200>
The method for producing the negative electrode was the same as in Example 1.

<Measurement of reversible capacity>
The method for measuring the reversible capacity was the same as in Example 1. As a result, the reversible capacity was 249.8 mAh / g.

<Example 4>
<Preparation of negative electrode active material>
The negative electrode active material was synthesized by the following procedure using the solid phase reaction method. _{First, Fe 2} O ₃ , Al ₂ O ₃ , and SiO ₂ are weighed so that the chemical ratio of Fe, Nb, and Si is 1: 11: 0.25, and the amount of powder is 2 g in total. Was adjusted. Then, a zirconium ball having a diameter of 3 mm was put into a ball mill pot containing 40 g of the zirconium ball. Then, after putting 6 g of ethanol into the mill pot, the ball mill was carried out at a speed of 300 rpm for 1 hour. Then, after separating ethanol from the suspension by centrifugation, it was vacuum dried at 60 ° C. for 10 hours or more. Then, the material was placed on a sintering dish and sintered in an electric furnace at 1250 ° C. under Air to obtain the desired product.

<Identification of crystal phase>
When the crystal phase was identified using XRD, a crystal phase in which the main phase belonged to the space group Amma was obtained. FIG. 3 shows the XRD result.

<Manufacturing of negative electrode 200>
The method for producing the negative electrode was the same as in Example 1.

<Measurement of reversible capacity>
The method for measuring the reversible capacity was the same as in Example 1. As a result, the reversible capacity was 269.6 mAh / g.

<Example 5>
<Preparation of negative electrode active material>
_{For the negative electrode active material in this example, Fe 2} O ₃ , RuO ₂ , and SiO ₂ are weighed and mixed so that the chemical ratio of Fe, Nb, and Si is 1: 11: 0.5. It was synthesized in the same manner as in Example 4 except for the above.

<Identification of crystal phase>
When the crystal phase was identified using XRD, a crystal phase in which the main phase belonged to the space group Amma was obtained. FIG. 3 shows the XRD result.

<Manufacturing of negative electrode 200>
The method for producing the negative electrode was the same as in Example 1.

<Measurement of reversible capacity>
The method for measuring the reversible capacity was the same as in Example 1. As a result, the reversible capacity was 270.7 mAh / g.

<Example 6>
<Preparation of negative electrode active material>
The negative electrode active material was synthesized by the following procedure using the solid phase reaction method. First, Fe and Nb, and stoichiometric ratios of P 1: 11: and _Fe 2 _{O 3} so as to be _0.25, and _{FePO 4 · 2 (H 2 O} ), except that weighed _Nb 2 _{O 5} is performed The same as in Example 4.

<Identification of crystal phase>
When the crystal phase was identified using XRD, a crystal phase in which the main phase belonged to the space group Amma was obtained. FIG. 4 shows the XRD result.

<Manufacturing of negative electrode 200>
The method for producing the negative electrode was the same as in Example 1.

<Measurement of reversible capacity>
The method for measuring the reversible capacity was the same as in Example 1. As a result, the reversible capacity was 255.6 mAh / g.

<Example 7>
<Preparation of negative electrode active material>
Negative electrode active material in this embodiment, stoichiometric ratio of Fe and Nb and P 1: 11: and _Fe 2 _{O 3} so that the _0.5, FePO 4 · 2 and _{(H 2 O), Nb 2} O It was synthesized in the same manner as in Example 4 except that _{5 was weighed.}

<Identification of crystal phase>
When the crystal phase was identified using XRD, a crystal phase in which the main phase belonged to the space group Amma was obtained. FIG. 4 shows the XRD result.

<Manufacturing of negative electrode 200>
The method for producing the negative electrode was the same as in Example 1.

<Measurement of reversible capacity>
The method for measuring the reversible capacity was the same as in Example 1. As a result, the reversible capacity was 253.6 mAh / g.

<Example 8>
<Preparation of negative electrode active material>
_{For the negative electrode active material in this example, Fe 2} O ₃ and Nb ₂ O ₅ were weighed so that the chemical ratio of Fe and Nb was 1:11, and the mixing step was carried out. Then, a sintering process for 4 hours was carried out under Air at 1250 ° C. to obtain _{FeNb 11} O _{29 without element substitution. Then, FeNb} 11 _{O 29} and the molar ratio of C 1: As a 0.025, a weight ratio of about 100: _FeNb so that 7 wt% 11 _{O 29} and weighed sucrose _{(C 12 H} 22 _{O 11)} After that, a zirconium ball having a diameter of 3 mm was put into a ball mill pot containing 40 g of the ball. Then, 6 g of ethanol was put into a mill pot, and a ball mill was performed at a speed of 300 rpm for 1 hour. Then, ethanol was separated from the suspension using an evaporator and vacuum dried at 60 ° C. for 10 hours or more. Then, the material was placed on a sintering dish and sintered in an electric furnace at 730 ° C. under Ar to obtain the desired product. At this time, it is considered that some carbon remains as a coating layer on the surface of the active material at the same time as the element substitution with FNO.

<Identification of crystal phase>
When the crystal phase was identified using XRD, a crystal phase in which the main phase belonged to the space group Amma was obtained. FIG. 5 shows the XRD result.

<Manufacturing of negative electrode 200>
The method for producing the negative electrode was the same as in Example 1.

<Measurement of reversible capacity>
The method for measuring the reversible capacity was the same as in Example 1. As a result, the reversible capacity was 241.2 mAh / g. Although the reversible capacity was reduced as compared with Comparative Example 1, when the reversible capacity of FeNb ₁₁ O ₂₉ itself was calculated using the amount of carbon source added, it could be estimated to be 258.1 mAh / g, and the reversible capacity of the negative electrode active material could be calculated. Is considered to have improved. The residual amount of carbon remaining after sintering is less than the charged amount of 7 wt%.

<Example 9>
<Preparation of negative electrode active material>
_{The negative electrode active material in this example is a mixing step in which Fe 2} O ₃ and Nb ₂ O ₅ and sucrose are weighed so that the chemical ratio of Fe, Nb, and C is 1: 11: 0.025. Was carried out. Then, ethanol was separated from the suspension using an evaporator and vacuum dried at 60 ° C. for 10 hours or more. Then, place the material on the Shoyuisara, 900 ° C. in an electric furnace to obtain a desired product by sintering under N _2.

<Identification of crystal phase>
When the crystal phase was identified using XRD, a crystal phase in which the main phase belonged to the space group Amma was obtained. FIG. 5 shows the XRD result.

<Manufacturing of negative electrode 200>
The method for producing the negative electrode was the same as in Example 1.

<Measurement of reversible capacity>
The method for measuring the reversible capacity was the same as in Example 1. As a result, the reversible capacity was 257.7 mAh / g.

<Example 10>
<Preparation of negative electrode active material>
_{The negative electrode active material in this example is a mixing step in which Fe 2} O ₃ and Nb ₂ O ₅ and sucrose are weighed so that the chemical ratio of Fe, Nb, and C is 1: 11: 0.025. Was carried out. Then, ethanol was separated from the suspension using an evaporator, and then vacuum dried at 60 ° C. for 10 hours or more. Then, place the material on the Shoyuisara, 1050 ° C. in an electric furnace to obtain a desired product by sintering under N _2.

<Identification of crystal phase>
When the crystal phase was identified using XRD, a crystal phase in which the main phase belonged to the space group Amma was obtained. FIG. 5 shows the XRD result.

<Manufacturing of negative electrode 200>
The method for producing the negative electrode was the same as in Example 1.

<Measurement of reversible capacity>
The method for measuring the reversible capacity was the same as in Example 1. As a result, the reversible capacity was 262.0 mAh / g.

<Example 11>
<Preparation of negative electrode active material>
_{In the negative electrode active material in this example, Fe 2} O ₃ , Nb ₂ O ₅ , and Ge _{O 2} are weighed and mixed so that the chemical ratio of Fe, Nb, and Ge is 1: 11: 0.5. Was synthesized in the same manner as in Example 4 except that.

<Identification of crystal phase>
When the crystal phase was identified using XRD, a crystal phase in which the main phase belonged to the space group Amma was obtained. FIG. 6 shows the XRD result.

<Manufacturing of negative electrode 200>
The method for producing the negative electrode was the same as in Example 1.

<Measurement of reversible capacity>
The method for measuring the reversible capacity was the same as in Example 1. As a result, the reversible capacity was 255.3 mAh / g.

<Example 12>
<Preparation of negative electrode active material>
_{For the negative electrode active material in this example, Fe 2} O ₃ , Nb ₂ O ₅ , and Ge _{O 2} are weighed so that the chemical ratio of Fe, Nb, and Ge is 0.5: 11: 0.5. Synthesis was carried out in the same manner as in Example 4 except that the mixing step was carried out.

<Identification of crystal phase>
When the crystal phase was identified using XRD, a crystal phase in which the main phase belonged to the space group Amma was obtained. FIG. 6 shows the XRD result.

<Manufacturing of negative electrode 200>
The method for producing the negative electrode was the same as in Example 1.

<Measurement of reversible capacity>
The method for measuring the reversible capacity was the same as in Example 1. As a result, the reversible capacity was 254.1 mAh / g.

<Example 13>
<Preparation of negative electrode active material>
_{For the negative electrode active material in this example, Fe 2} O ₃ , Nb ₂ O ₅ , and Ge _{O 2} are weighed so that the chemical ratio of Fe, Nb, and Ge is 0.5: 11: 1.0. Synthesis was carried out in the same manner as in Example 4 except that the mixing step was carried out.

<Identification of crystal phase>
When the crystal phase was identified using XRD, a crystal phase in which the main phase belonged to the space group Amma was obtained. FIG. 6 shows the XRD result.

<Manufacturing of negative electrode 200>
The method for producing the negative electrode was the same as in Example 1.

<Measurement of reversible capacity>
The method for measuring the reversible capacity was the same as in Example 1. As a result, the reversible capacity was 254.1 mAh / g.

<Example 14>
<Preparation of negative electrode active material>
_{The negative electrode active material in this example weighs Fe 2} O ₃ , Nb ₂ O ₅ , and Bi ₂ O ₃ so that the chemical ratio of Fe, Nb, and Bi is 0.5: 11: 0.5. The mixture was synthesized in the same manner as in Example 4 except that the mixing step was carried out.

<Identification of crystal phase>
When the crystal phase was identified using XRD, a crystal phase in which the main phase belonged to the space group Amma was obtained. FIG. 7 shows the XRD result.

<Manufacturing of negative electrode 200>
The method for producing the negative electrode was the same as in Example 1.

<Measurement of reversible capacity>
The method for measuring the reversible capacity was the same as in Example 1. As a result, the reversible capacity was 265.0 mAh / g.

<Comparative example 2>
<Preparation of negative electrode active material>
_{For the negative electrode active material in this example, Fe 2} O ₃ , Nb ₂ O _5, and Mg O are weighed and mixed so that the chemical ratio of Fe, Nb, and Mg is 1: 11: 0.25. It was synthesized in the same manner as in Example 4 except that it was carried out.

<Identification of crystal phase>
When the crystal phase was identified using XRD, a crystal phase in which the main phase belonged to the space group Amma was obtained. FIG. 8 shows the XRD result.

<Manufacturing of negative electrode 200>
The method for producing the negative electrode was the same as in Example 1.

<Measurement of reversible capacity>
The method for measuring the reversible capacity was the same as in Example 1. As a result, the reversible capacity was 249.2 mAh / g.

<Comparative example 3>
<Preparation of negative electrode active material>
_{For the negative electrode active material in this example, Fe 2} O ₃ , Nb ₂ O _5, and Mg O are weighed and mixed so that the chemical ratio of Fe, Nb, and Mg is 1: 11: 0.5. It was synthesized in the same manner as in Example 4 except that it was carried out.

<Identification of crystal phase>
When the crystal phase was identified using XRD, a crystal phase in which the main phase belonged to the space group Amma was obtained. FIG. 8 shows the XRD result.

<Manufacturing of negative electrode 200>
The method for producing the negative electrode was the same as in Example 1.

<Measurement of reversible capacity>
The method for measuring the reversible capacity was the same as in Example 1. As a result, the reversible capacity was 236.2 mAh / g.

<Comparative example 4>
<Preparation of negative electrode active material>
_{In the negative electrode active material in this example, Fe 2} O ₃ , Nb ₂ O ₅ , _{and Ca CO 3} are weighed and mixed so that the chemical ratio of Fe, Nb, and Ca is 1: 11: 0.5. Was synthesized in the same manner as in Example 4 except that.

<Identification of crystal phase>
When the crystal phase was identified using XRD, a crystal phase in which the main phase belonged to the space group Amma was obtained. FIG. 8 shows the XRD result.

<Manufacturing of negative electrode 200>
The method for producing the negative electrode was the same as in Example 1.

<Measurement of reversible capacity>
The method for measuring the reversible capacity was the same as in Example 1. As a result, the reversible capacity was 234.6 mAh / g.

<Comparative example 5>
<Preparation of negative electrode active material>
_{In the negative electrode active material in this example, Fe 2} O ₃ , Nb ₂ O ₅ , _{and Ca CO 3} are weighed and mixed so that the chemical ratio of Fe, Nb, and Ca is 1: 11: 1.0. Was synthesized in the same manner as in Example 4 except that.

<Identification of crystal phase>
When the crystal phase was identified using XRD, a crystal phase in which the main phase belonged to the space group Amma was obtained. FIG. 8 shows the XRD result.

<Manufacturing of negative electrode 200>
The method for producing the negative electrode was the same as in Example 1.

<Measurement of reversible capacity>
The method for measuring the reversible capacity was the same as in Example 1. As a result, the reversible capacity was 212.1 mAh / g.

<Comparative Example 6>
<Preparation of negative electrode active material>
_{In the negative electrode active material in this example, Fe 2} O ₃ , Nb ₂ O ₅ , and Li ₂ CO ₃ are weighed and mixed so that the chemical ratio of Fe, Nb, and Li is 1:11:10. Was synthesized in the same manner as in Example 4 except that.

<Identification of crystal phase>
When the crystal phase was identified using XRD, a crystal phase in which the main phase did not belong to the space group Amma was obtained. FIG. 8 shows the XRD result.

<Manufacturing of negative electrode 200>
The method for producing the negative electrode was the same as in Example 1.

<Measurement of reversible capacity>
The method for measuring the reversible capacity was the same as in Example 1. As a result, the reversible capacity was 83.5 mAh / g.

<Measurement result>
Table 1 shows the parameters and measurement results of Examples and Comparative Examples. In particular, in the sample to which C was added, as shown in the example, the sample was _{sintered in an N 2} atmosphere so that the C source did not disappear as _{CO, CO 2,} etc., but in Example 8, it was sintered. Since it is difficult to obtain the crystal structure of Amma when sintered at a temperature of 900 ° C. or lower, the active material of the present invention _{was obtained by synthesizing FeNb 11} O _{29 at 1250 ° C. and then mixing the carbon source.} ..

<Discussion>
From the results of Examples 1 to 14 and Comparative Example 1, the material coated with a part _{of FeNb 11} O ₂₉ by element substitution with an element belonging to Group 13 to Group 15 or by precipitating on the surface is not substituted. It was clarified that the reversible capacity was improved as compared with Comparative Example 1. In addition, from Example 3, it was found that the effect of increasing the reversible capacity also appeared in the simultaneous substitution material of Al and B, which exceeded the performance of Comparative Example 1, and simultaneous application with other element substitutions was also effective in improving the reversible capacitance. It turned out that there was. From the above, it was found that when an attempt was made to replace an element using an element belonging to groups 13 to 15, performance improvement was obtained as compared with a non-replacement material. The cause of this is not clear, but it is considered to be a combination of the following causes. That is, the presence of the additive element A suppresses the Ostwald growth of the active material, promotes fine particle formation, and improves the conductivity of FeNb ₁₁ O ₂₉ , which has low electron conductivity, by substituting some elements for oxygen sites. The presence of A as a precipitate having good _{conductivity ensures the electron conductivity of the FeNb 11} O ₂₉ negative electrode as an electrode, and the additive element improves the diffusibility of Li during charging and discharging.

FIG. 9 shows the SEM-EDX measurement results of the material to which B, Si, P, and C were added in comparison with the sample to which no addition was added. From FIG. 9, it can be seen that Si, P, and C are uniformly dispersed on the surface and inside of the primary particles of the material, and the particle size is smaller than that when these elements are not added, and crystal growth is suppressed. It became clear that there was. Therefore, the reversible capacity may be improved. In addition, it can be seen that B, Si, P, and C are dispersed without agglutination. Therefore, it can be considered that a part of the active material or the whole of the active material is covered by being partially replaced by the active material or precipitated on the surface of the active material.

On the other hand, as shown in the comparative example, the reversible capacitance was significantly reduced by the substitution of Mg and Ca, which are the elements of Group 2. It is considered that the cause of these problems is that in group 1 and group 2 element substitutions, element substitution with Li sites proceeds, and as a result of the sites that can store Li ions being occupied by different elements, the reversible capacity decreases.

Further, in Comparative Example 6 in which Li was replaced with an element, the reversible capacity was significantly reduced, and as shown in FIG. 8, the main phase was not the space group Amma, and impurities other than those derived from _{FeNb 11} O _{29, which were designated as ▽ in the figure, were used.} The peak became the prime minister. _{This means that the structure of FeNb 11} O ₂₉ derived from Amma is not a stable phase at the temperature at which the solid phase reaction proceeds, and it means that it is inappropriate to proceed with element substitution by the solid phase reaction method. do.

Since the reversible capacity of the heavy elements of Groups 15 and 14 also increased due to substitution, it was considered that the elements of Groups 13 to 15 could be expected to improve the reversible capacity regardless of the number of elements. .. From the above, it was clarified that the reversible capacity tends to be improved by adding the elements belonging to the 13th to 15th groups.

100 Positive electrode 110 Positive electrode mixture layer 120 Positive electrode current collector 130 Positive electrode tab 200 Negative electrode 210 Negative electrode mixture layer 220 Negative electrode current collector 230 Negative electrode tab 300 Separator 400 Electrode body

Claims (4)

General composition formula: Fe _1-x Nb _11-y O _29-z-a A _{x + y + z} (0 ≦ x ≦ 1, 0 ≦ y ≦ 11, -10 ≦ z ≦ 10, where A is Al, Si, B, A negative electrode active material represented by (one or more selected from the group consisting of P, C, Ge and Bi). The negative electrode active material according to claim 1, wherein a part or all of the surface is coated with the A. A negative electrode having the negative electrode active material according to claim 1. A secondary battery including a positive electrode, the negative electrode according to claim 3, and a separator.

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