JP6120160B2 - Cathode active material for sodium ion battery and method for producing the same - Google Patents

Description

  The present invention belongs to the technical field of secondary batteries, and particularly relates to a novel electrode active material constituting a non-aqueous sodium ion secondary battery and a secondary battery using the same.

  A sodium battery is a secondary battery having a positive electrode, a negative electrode, and a non-aqueous electrolyte. A typical secondary battery is a lithium battery. Lithium batteries have already been put into practical use as small power sources for mobile phones and laptop computers, and can be used as large power sources such as power sources for automobiles such as electric vehicles and hybrid vehicles, and distributed power storage power sources. The demand is increasing. However, in the production of materials constituting lithium batteries, since raw materials containing rare metal elements such as lithium are often used, in order to meet the increasing demand for large-scale power supplies, the stability of rare metal elements There is a concern about the supply.

  On the other hand, sodium batteries are being considered as one of secondary batteries for large-scale storage batteries that can solve the concerns regarding the supply of rare metal elements. In the sodium battery, raw materials that are rich in resources and inexpensive are used for the production of the material constituting the battery. Therefore, it is expected that a large-scale power supply can be supplied in large quantities by putting sodium batteries into practical use.

  As a material constituting a conventional sodium battery, as a positive electrode material, an insertion reaction positive electrode active material such as an oxide containing both sodium and transition metal such as sodium manganate is used, and as a negative electrode material, It is disclosed that a sodium metal hexafluorophosphate that is an electrolyte salt is dissolved in a nonaqueous solvent obtained by mixing ethylene carbonate and diethyl carbonate as a nonaqueous electrolyte using sodium metal (for example, Patent Document 1).

Moreover, the electrode active material used for a sodium battery is an important material which determines the charging / discharging characteristic of a battery, and various studies have been conducted so far. For example, perovskite type iron fluoride (FeF ₃ ) or rutile type FeOF is used as a positive electrode material, sodium metal is used as a negative electrode material, and sodium perchlorate, which is an electrolyte salt, is used as a non-aqueous electrolyte in polypropylene carbonate. It has been reported (for example, refer to Patent Document 2).
.

Regarding perovskite-type FeF ₃ that is also used as a positive electrode for lithium-ion batteries, there is no synthesis report example, although LiFeF ₃ produced upon initial discharge is expected as a promising positive electrode material. . For such a composition, the first charge is performed on the LiF-FeF ₂ nanocomposite positive electrode using LiF and FeF ₂ as raw materials, thereby generating FeF ₃ by the first charge as shown in the following formula (1). After the first charge, it has been reported that a reversible charge / discharge reaction as shown in the formula (2) occurs to show good battery characteristics (for example, see Non-Patent Document 1).

LiF + FeF ₂ → Li ⁺ + FeF ₃ (1)
Li ⁺ + FeF ₃ ⇔LiFeF ₃ (2)

JP 2006-216509 A JP 2008-243646 A

S. W. Kim, K. W. Nam, D. H. Seo, J. Hong, H. Kim, H. Gwon, K. Kang, Nano Today 7, 168-178 (2012)

However, with regard to the rutile FeOF, not only the positive electrode for lithium ion batteries but also the positive electrode for sodium ion batteries expected to replace the positive electrode for lithium ion batteries, the positive electrode material corresponding to the above formulas (1) and (2) Has not yet been synthesized. That is, in order to build a reversible battery system such as the following formula (3), it is necessary to synthesize a MOF positive electrode and a C ₆ Na negative electrode storing Na in advance, but a C ₆ Na negative electrode storing Na can also be directly synthesized. However, even if it can be made, it has a problem that it cannot be handled in the atmosphere because it is low in potential and easily oxidized.

MOF + C ₆ Na⇔NaMOF + C ₆ (3)

  By using a mixture of sodium fluoride (NaF) and a divalent metal oxide (metal oxide) (MO), the positive electrode active material for a sodium ion battery of the present invention is charged as follows by first charging the negative electrode: 4) By generating the initial charge reaction as shown in the formula, the MOF positive electrode is electrolytically generated on the positive electrode side in the battery without causing extra gas generation, and the reversible charge / discharge reaction shown in the formula (5) is made possible thereafter. It is characterized by that.

Positive electrode side: NaF + MO → Na ⁺ + e ⁻ + MOF
Negative electrode side: 6C + Na ⁺ + e ⁻ → C ₆ Na
Total reaction (initial charge): NaF + MO + 6C → MOF + C ₆ Na (4)
Subsequent charge / discharge reaction: MOF + C ₆ Na⇔NaMOF + C ₆ (5)

  According to the present invention, it is possible to obtain a positive electrode active material that functions as NaMOF (M is a transition metal) for which no synthesis report has been reported so far. Moreover, in this invention, the sodium battery provided with the positive electrode and negative electrode containing a positive electrode active material, and the electrolyte intervening between them is provided, and a favorable charging / discharging characteristic is acquired. In particular, in the invention provided with the carbon negative electrode, a sodium battery having good safety, cost, and characteristics is provided.

The schematic of the sodium battery layer concerning the present invention is shown. The XRD pattern result and SEM image of the positive electrode active material NaF-FeO mixed positive electrode manufactured by this invention are shown. The charging / discharging curve at the time of using sodium metal for the negative electrode of the positive electrode active material NaF-FeO mixed positive electrode manufactured by this invention is shown. The charging / discharging curve at the time of using hard carbon for the negative electrode of the positive electrode active material NaF-FeO mixed positive electrode manufactured by this invention is shown. The XRD pattern result and SEM image of the positive electrode active material NaF-MnO mixed positive electrode manufactured by this invention are shown. The charging / discharging curve at the time of using a sodium metal for the negative electrode of the positive electrode active material NaF-MnO mixed positive electrode manufactured by this invention is shown. The charging / discharging curve at the time of using hard carbon for the negative electrode of the positive electrode active material NaF-MnO mixed positive electrode manufactured by this invention is shown. The XRD pattern result and SEM image of the positive electrode active material NaF-TiO mixed positive electrode manufactured by this invention are shown. The charging / discharging curve at the time of using sodium metal for the negative electrode of the positive electrode active material NaF-TiO mixed positive electrode manufactured by this invention is shown.

  The electrode active material for a sodium ion secondary battery according to the present invention is characterized by comprising NaF and a divalent metal oxide (MO). Of these, carbon or sodium metal is preferable for the negative electrode, and transition metals such as Fe, Mn, Co, Ti, V, and Ni are preferable for the positive electrode because of potential and ease of handling. In addition, the charge / discharge reaction of the electrode active material for a sodium ion secondary battery obtained in the present invention is to cause a reversible charge / discharge reaction as shown in formula (7) after the initial charge as shown in formula (6) below. Features.

NaF + M ²⁺ O → Na ⁺ + M ³⁺ OF (charging reaction at the first charging) (6)
Na ⁺ + M ³⁺ OF⇔NaM ²⁺ OF (charge / discharge reaction after initial discharge) (7)

  The NaF-MO mixed positive electrode of the present invention can be produced, for example, by dry-mixing NaF and a divalent metal oxide in an inert atmosphere. Furthermore, it is preferable to add and mix a carbon source for the purpose of improving electrical conductivity (rate characteristics).

  As the divalent metal oxide, FeO, MnO, TiO, VO, CoO or NiO can be used, and among these, FeO, MnO or TiO is particularly preferable from the viewpoint of easy handling. These metal oxides can also be used as a mixture.

Such addition of the carbon source may be performed in a plurality of times (for example, in two stages). In this case, the primary aim is often pulverization / mixing in the first stage and carbon coating in the second stage.
In the first stage, acetylene black, graphite, carbon nanotubes, or the like can be used as the carbon source, and among these, acetylene black is particularly preferable from the viewpoint of ease of handling. In the second stage, furnace black, channel black, acetylene black, ketjen black, thermal black, and the like can be used, but acetylene black is preferred because of its high conductivity when used as an electrode. (For example, see Example 1 below)

  When preparing the NaF-MO mixed positive electrode, the specific means applied to pulverization / mixing is not particularly limited, and various means conventionally used for the purpose of pulverization / mixing of solid substances can be applied. However, since NaF is water-soluble, it is preferable to use a ball mill under dry conditions (for example, a relative humidity of 10% or less). It is preferable to use it.

The above positive electrode active material may be used as it is as a positive electrode of a sodium ion secondary battery, but a composite with a known conductive material may be formed in order to improve the rate characteristics of the electrode.
That is, according to the present invention, from the viewpoint of improving the rate characteristics, the NaF-MO mixed positive electrode, which is the electrode active material obtained as described above, is pulverized and mixed together with carbon fine particles in an inert atmosphere to obtain a carbon coat. can do. As the inert atmosphere, vacuum, nitrogen gas, argon gas, or the like can be used. For example, argon gas can be used.

  For example, as an example of the production method of the present invention, NaF and FeO are mixed in an inert atmosphere for 10 hours to 72 hours, acetylene black is added, and further mixed in an inert atmosphere for 10 hours to 48 hours. A NaF—FeO mixed positive electrode is obtained (for example, see Example 1 described later).

  The average particle diameter of the positive electrode for sodium batteries according to the present invention is, for example, preferably in the range of 0.1 to 50 μm, more preferably in the range of 0.1 to 10 μm, and particularly preferably in the range of 0.5 to 3 μm. . If the average particle size of the positive electrode active material for sodium battery is too small, the handleability may be deteriorated. If the average particle size of the positive electrode active material for sodium battery is too large, it is difficult to obtain a flat active material layer. Because there is a fear. In addition, in the battery characteristic evaluation at a low rate, an active material having a large average particle diameter is advantageous for increasing energy density. However, when battery characteristics at a high rate are required, the active material average particle diameter is It can be handled by controlling it to be smaller. In addition, the average particle diameter of the positive electrode active material for sodium batteries according to the present invention is obtained by measuring and averaging the particle diameter of the positive electrode active material for sodium batteries observed with, for example, a scanning electron microscope (SEM). be able to.

  According to this invention, the sodium ion non-aqueous secondary battery positive electrode containing the electrode active material NaF-MO obtained by the above is provided.

FIG. 1 is a diagram showing an example of a layer configuration of a sodium battery according to the present invention, and is a diagram schematically showing a cross section cut in a stacking direction. The sodium battery according to the present invention is not necessarily limited to this example.
The sodium battery 10 includes a positive electrode 6 including a positive electrode active material layer 2 and a positive electrode current collector 4, a negative electrode 7 including a negative electrode active material layer 3 and a negative electrode current collector 5, and an electrolyte layer 1 sandwiched between the positive electrode 6 and the negative electrode 7. Is provided.
Hereinafter, the positive electrode, the negative electrode, and the electrolyte layer used in the sodium battery according to the present invention, and the separator and the battery case suitably used in the sodium battery according to the present invention will be described in detail.

  The positive electrode used in the present invention preferably comprises a positive electrode active material layer containing the above-mentioned positive electrode active material, and in addition to this, a positive electrode current collector and a positive electrode connected to the positive electrode current collector Provide leads.

[Current collector]
As the current collector, a conductor such as aluminum, nickel, stainless steel, or copper is used. Examples of the shape of the current collector include a foil shape, a net shape, and a porous shape. Among these, aluminum foil is preferable because it is stable at the positive electrode operating potential of the secondary battery, easily processed into a thin film, and inexpensive.

[binder]
As the binder, a thermoplastic resin is used. Specifically, polyvinylidene fluoride (hereinafter sometimes referred to as “PVDF”), polytetrafluoroethylene (hereinafter sometimes referred to as “PTFE”). Fluorine resins such as tetrafluoroethylene / hexafluoropropylene / vinylidene fluoride copolymer, hexafluoropropylene / vinylidene fluoride copolymer and tetrafluoroethylene / perfluorovinyl ether copolymer; polyethylene And polyolefin resins such as polypropylene. These thermoplastic resins are used alone or in combination of two or more.

[Method for producing positive electrode for sodium secondary battery]
A positive electrode for a sodium secondary battery is manufactured by supporting (stacking) a positive electrode mixture containing an active material, a conductive material, and a binder on a current collector.
As a method of supporting the positive electrode mixture on the current collector, (1) a method of pressure-forming the positive electrode mixture, (2) mixing the organic solvent and the positive electrode mixture, and preparing a paste of the positive electrode mixture The paste is applied to a current collector, and the paste applied to the current collector is dried and then fixed by pressing or the like.

  Examples of the method of applying the paste to the current collector include a slit die coating method, a screen coating method, a curtain coating method, a knife coating method, a gravure coating method, and an electrostatic spray method. In the present invention, a plurality of these coating methods may be used in combination.

[Production method of negative electrode]
The negative electrode is generally produced by supporting (stacking) a negative electrode mixture containing an active material, a conductive material and a binder on a current collector.
As a method of supporting the negative electrode mixture on the current collector, (1) a method of pressure-molding the negative electrode mixture, and (2) mixing the organic solvent and the negative electrode mixture to prepare a paste of the negative electrode mixture The paste is applied to a current collector, and the paste applied to the current collector is dried and then fixed by pressing or the like.

[Negative electrode active material]
As the negative electrode active material, sodium metal or an alloy containing sodium is desirable for increasing the energy density. However, when a negative electrode having a sodium-containing composition is used, a reducing or inert gas atmosphere is indispensable in the production process. Carbon materials such as hard carbon are suitable for reducing the manufacturing cost and increasing the safety of the battery. Other negative electrode candidates include metal elements containing a group 14 element of the periodic table capable of inserting and desorbing sodium ions alone or as a main component, for example, germanium (Ge), tin (Sn), lead (Pb) Etc. Since the positive electrode active material of the present invention contains sodium, a material that does not contain sodium can also be used as the negative electrode.

[Nonaqueous electrolyte]
The non-aqueous electrolyte in the present invention is a liquid or solid composed of a substance containing alkali ions, and mainly contains sodium ions as alkali ions.
The non-aqueous electrolyte may contain alkali ions other than sodium ions. As alkali ions other than sodium ions, either lithium ions or potassium ions, or both lithium ions and potassium ions are preferable.

  The content ratio of sodium ions contained in the nonaqueous electrolyte is preferably 50% by mass or more of the total alkali ions, more preferably 75% by mass or more, and further preferably 80% by mass or more (100% by mass). Included).

The nonaqueous electrolyte in the present invention is usually used as a nonaqueous electrolytic solution containing an electrolyte and an organic solvent.
Examples of the electrolyte include NaClO ₄ , NaPF ₆ , NaAsF ₆ , NaSbF ₆ , NaBF ₄ , NaCF ₃ SO ₃ , NaN (SO ₂ CF ₃ ) ₂ , lower aliphatic carboxylic acid sodium salt, and NaAlCl ₄ . You may use the mixture which mixed 2 or more types for these.
The electrolyte preferably includes at least one sodium salt selected from the group consisting of NaClO ₄ , NaPF ₆ , NaAsF ₆ , NaSbF ₆ , NaBF ₄ , NaCF ₃ SO ₃ and NaN (SO ₂ CF ₃ ) _2. .

  Examples of the organic solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, isopropyl methyl carbonate, vinylene carbonate, 4-trifluoromethyl-1,3-dioxolan-2-one, 1,2- Carbonates such as di (methoxycarbonyloxy) ethane; 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropyl methyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, tetrahydrofuran, 2 -Ethers such as methyltetrahydrofuran; Esters such as methyl formate, methyl acetate and γ-butyrolactone; Nitriles such as acetonitrile and butyronitrile; N, N-dimethylformami Amides such as N, N-dimethylacetamide; carbamates such as 3-methyl-2-oxazolidone; sulfur-containing compounds such as sulfolane, dimethyl sulfoxide and 1,3-propane sultone; Those having a substituent introduced therein are used.

In the present invention, a solid electrolyte may be used as the nonaqueous electrolyte instead of the nonaqueous electrolyte.
As the solid electrolyte, for example, a so-called gel in which an electrolytic solution is held in a polymer solid electrolyte such as a polymer containing at least one selected from a polyethylene oxide polymer, a polyorganosiloxane chain, and a polyoxyalkylene chain. type and _{electrolytes, Na 2 S-SiS 2,} Na 2 S-GeS 2, Na 2 S-P 2 S 5, Na 2 S-B 2 S 3, Na 2 S-SiS 2 -Na 3 PO 4, Na Examples thereof include sulfide-containing electrolytes such as ₂ S—SiS ₂ —Na ₂ SO ₄ ; inorganic solid electrolytes such as NASICON type electrolytes such as NaZr ₂ (PO ₄ ) ₃ .
By using such a solid electrolyte, the safety of the sodium secondary battery may be further improved.
In the sodium battery of the present invention, when a solid electrolyte is used, the solid electrolyte may function as a separator. In that case, a separator may not be required.

[Separator]
The sodium battery of the present invention usually further includes a separator.
As the separator, for example, a material such as a porous film made of a material such as a polyolefin resin such as polyethylene or polypropylene, a fluororesin, or a nitrogen-containing aromatic polymer, a nonwoven fabric, or a woven fabric is used.

The thickness of the separator is preferably as thin as possible as long as the mechanical strength is maintained in that the volume energy density of the battery is increased and the internal resistance is reduced.
In general, the thickness of the separator is preferably about 5 to 200 μm, more preferably about 5 to 40 μm.

  Examples of the shape of the electrode group include a shape in which a cross section when the electrode group is cut in a direction perpendicular to the winding axis forms a circle, an ellipse, a rectangle, a rectangle with a corner, or the like. It is done.

  Examples of the shape of the sodium battery include a paper shape, a coin shape, a cylindrical shape, and a square shape.

The sodium battery thus obtained has a large discharge capacity retention rate when charging and discharging are repeated, and is excellent in charge / discharge cycle characteristics, as compared with conventional sodium batteries. Furthermore, the production | generation of sodium dendrite can also be suppressed and it is excellent in the stability as a secondary battery.
In addition, sodium dendrite is a dendritic crystal of sodium that is deposited on an electrode with repeated charge and discharge. When the positive electrode and the negative electrode are short-circuited by this sodium dendrite, the sodium secondary battery will not function.

  Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to these examples.

(Manufacture of positive electrode active material for sodium batteries)
Example 1
The molar ratio of NaF: FeO = 1.2 so that sodium fluoride (NaF, manufactured by Soekawa Chemical Co., Ltd.) and iron oxide (FeO, manufactured by Wako Pure Chemical Industries, Ltd.) is Na-excess from the composition of formula (6) described above. : 1 and weighed in a planetary ball mill container capable of controlling the atmosphere, and sealed with 40 g of zirconia balls having a diameter of 3 mm in an argon atmosphere. This was subjected to a ball mill for 24 hours under the condition of 600 rpm. Thereafter, acetylene black as a carbon source was further added as an active material: acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd., HS-100) at a ratio of 70% by mass to 5% by mass, and this was added to a ball mill for 24 hours at 600 rpm. Provided. Next, acetylene black was weighed so that the ratio of the obtained mixture: carbon source (acetylene black) was 75% by mass: 20% by mass and placed in a planetary ball mill container whose atmosphere could be controlled. Sealed together with 20 g of zirconia balls in an argon atmosphere. This was subjected to a ball mill for 3 hours under the condition of 400 rpm to produce a NaF—FeO mixed positive electrode.

(Structural analysis of positive electrode active material for sodium batteries)
The positive electrode active material for sodium batteries of Example 1 was subjected to X-ray diffraction measurement. Detailed measurement conditions are as follows.
X-ray diffractometer: TTRIII (Rigaku)
Measurement range: 2θ = 10-80 °
Measurement interval: 0.02 °
Scanning speed: 0.02 ° / min
Measurement voltage: 50 kV
Measurement current: 300 mA

FIG. 2A is a graph showing an XRD pattern of a NaF—FeO mixed positive electrode which is a positive electrode active material for a sodium battery of Example 1. FIG. The XRD pattern of the obtained positive electrode active material matches the XRD peak obtained from the ICDD data of sodium fluoride (NaF) and iron oxide (FeO) shown as a reference. All the XRD peaks of the obtained NaF—FeO mixed positive electrode of Example 1 are attributed to the peaks of NaF and FeO. FIG. 2B shows the result of SEM observation in order to observe the particle diameter of the prepared NaF—FeO mixed positive electrode. As a result, it was confirmed that the primary particle diameter of the obtained NaF—FeO mixed positive electrode was 1 μm or less.
From the above, it was confirmed that the positive electrode active material for sodium battery of Example 1 was a mixture of NaF and FeO, and no other compound was produced when a planetary ball mill was used.

(Production of sodium battery using sodium metal negative electrode)
(Example 2)
As a positive electrode active material, a positive electrode active material for sodium battery manufactured by the method of Example 1 and subjected to carbon coating treatment and PVdF (Kureha, # 3505) as a binder were prepared. The positive electrode active material after carbon coating and the binder were mixed such that the positive electrode active material after carbon coating: the binder = 95% by mass: 5% by mass to prepare a positive electrode mixture. Further, N-methyl-2-pyrrolidone (manufactured by Nacalai Tesque) was appropriately added as a dispersant to the positive electrode mixture.
An aluminum foil was prepared as a positive electrode current collector.
After applying the adjusted positive electrode mixture to the aluminum foil as the positive electrode current collector, it was dried at 80 ° C. for 30 minutes under vacuum conditions.
Sodium metal (manufactured by Aldrich) was prepared as the negative electrode.
As an electrolytic solution, 1 mol / L NaClO ₄ (solvent PC) was prepared.
A coin cell (SUS2032 type) was prepared as a battery case. The positive electrode current collector, the positive electrode mixture, the electrolyte layer, and the negative electrode are housed in a battery case in the order of aluminum foil, positive electrode mixture layer, electrolyte layer, and sodium metal, and the sodium of Example 2 A battery was manufactured.
The above steps were all performed in a glove box under an argon atmosphere.

(Manufacture of sodium battery using carbon negative electrode)
(Example 3)
The same operation as in Example 2 was performed except that the negative electrode material used was changed from sodium metal to hard carbon.

(Sodium battery charge / discharge test)
A charge / discharge test was performed on the sodium batteries of Example 2 and Example 3. Specifically, first, charging was performed in a constant current mode under the following conditions of current density, with 4.5 V as the upper limit. Next, the battery was discharged to 1.0 V, 1.3 V, or 1.5 V, and the obtained capacity was defined as the discharge capacity.
Current density of Examples 2 and 3: 10 mA / g (0.011 mA / cm ² )

  FIG. 3 is a charge / discharge curve of a sodium battery using the NaF—FeO mixed positive electrode of Example 2. FIG. 4 is a charge / discharge curve of a sodium battery using the NaF—FeO mixed positive electrode of Example 3. When sodium metal was used as the negative electrode as shown in FIG. 4, the initial discharge capacity was 150 mAh / g. On the other hand, even when the carbon material was used as the negative electrode as shown in FIG. 4, the initial discharge capacity was 60 mAh / g (positive electrode weight conversion). Thus, it has been found that good charge / discharge can be achieved by using the positive electrode active material for a sodium secondary battery of the present invention.

(Manufacture of positive electrode active material for sodium batteries)
Example 4
The same procedure as in Example 1, Example 2, and Example 3 was performed except that FeO was changed to manganese oxide (MnO).

  FIG. 5A is a graph showing an XRD pattern of a NaF—MnO mixed positive electrode which is a positive electrode active material for a sodium battery of Example 4. The XRD pattern of the obtained active material coincides with the XRD peak obtained from the ICDD data of sodium fluoride (NaF) and manganese oxide (MnO) shown as reference, and the obtained NaF-MnO mixed positive electrode All XRD peaks are attributed to NaF and MnO peaks. FIG. 5B shows the result of SEM observation in order to observe the particle diameter of the prepared NaF—MnO mixed positive electrode. As a result, it was confirmed that the primary particle diameter of the obtained NaF—MnO mixed positive electrode was 1 μm or less.

  FIG. 6 is a charge / discharge curve of a sodium battery using a NaF—MnO mixed positive electrode, which is a positive electrode active material for a sodium battery of Example 4, created by the same method as in Example 2. FIG. 7 is a charge / discharge curve of a sodium battery using a NaF—MnO mixed positive electrode, which is a positive electrode active material for a sodium battery of Example 4, created by the same method as in Example 3. When sodium metal was used as the negative electrode as shown in FIG. 6, the initial discharge capacity was 150 mAh / g. On the other hand, even when a carbon material is used as the negative electrode as shown in FIG. 7, the initial discharge capacity is 60 mAh / g (positive electrode weight conversion), and the same charge and discharge as the NaF—FeO mixed positive electrode is possible. It was found.

(Manufacture of positive electrode active material for sodium batteries)
(Example 5)
Example 1 and Example 2 were performed except that FeO was changed to titanium oxide (TiO).

  FIG. 8A is a graph showing an XRD pattern of a NaF—TiO mixed positive electrode which is a positive electrode active material for a sodium battery of Example 5. The XRD pattern of the obtained active material coincides with the XRD peak obtained from the ICDD data of sodium fluoride (NaF) and titanium oxide (TiO) shown as reference, and the obtained NaF-TiO mixed positive electrode All XRD peaks are attributed to NaF and TiO peaks. FIG. 8B shows the result of SEM observation in order to observe the particle diameter of the prepared NaF—TiO mixed positive electrode. As a result, it was confirmed that the primary particle diameter of the obtained NaF—TiO mixed positive electrode was 1 μm or less.

  FIG. 9 is a charge / discharge curve of a sodium battery using a NaF—TiO mixed positive electrode, which is a positive electrode active material for a sodium battery of Example 5, created in the same manner as in Example 2. When sodium metal was used as the negative electrode as shown in FIG. 9, the initial discharge capacity was 90 mAh / g, and it was found that good charge / discharge was possible.

In the above examples, since similar characteristics are obtained when M is single, it is considered that good battery characteristics can be obtained even when M is plural.

DESCRIPTION OF SYMBOLS 1 Electrolyte layer 2 Positive electrode layer 3 Negative electrode layer 4 Positive electrode collector 5 Negative electrode collector 6 Positive electrode 7 Negative electrode 10 Sodium battery

Claims (4)

  Sodium ion secondary characterized by comprising a mixture of sodium fluoride (NaF) and divalent metal oxide (MO) (M is at least one metal element of Fe, Mn, Ti, V, Co, Ni) Positive electrode active material for batteries.   The positive electrode active material for a sodium ion secondary battery according to claim 1, wherein M is at least one of Fe, Mn, and Ti.   A sodium ion secondary battery comprising the active material according to claim 1 on a positive electrode and sodium metal or carbon on a negative electrode.   It is characterized by mixing sodium fluoride (NaF) and divalent metal oxide (MO) (M is at least one metal element of Fe, Mn, Ti, V, Co, and Ni) in an inert atmosphere and dry type. The manufacturing method of the positive electrode active material for sodium ion secondary batteries of Claim 1.