JP2013175311A - Positive electrode material for sodium secondary battery, manufacturing method thereof, sodium secondary battery electrode using the positive electrode material for sodium secondary battery, nonaqueous sodium secondary battery having the sodium secondary battery electrode, and electric device having the nonaqueous sodium secondary battery incorporated therein - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode material for a sodium secondary battery, a manufacturing method thereof, a sodium secondary battery electrode using the positive electrode material for a sodium secondary battery, a nonaqueous sodium secondary battery having the sodium secondary battery electrode and an electric device having a nonaqueous sodium secondary battery incorporated therein which allow the achievement of an excellent charge/discharge capacity and an excellent capacity-keeping rate.SOLUTION: The positive electrode material for a sodium secondary battery comprises: a transition metal oxide solid solution having a crystal structure of a space group R-3 m (No.166). The positive electrode material has lattice constants which satisfy the conditions of 2.80≤a≤3.00 Å and 16.0≤c≤16.6 Å, and diffraction peaks of (003)plane and (104)plane which meet the condition of 1.1≤I(104)/I(003)≤1.3.

Description

  The present invention provides a sodium secondary battery positive electrode material excellent in charge and discharge capacity and capacity retention rate, a method for producing the sodium secondary battery positive electrode material, a sodium secondary battery electrode using the sodium secondary battery positive electrode material, The present invention relates to a non-aqueous sodium secondary battery including the sodium secondary battery electrode, and an electric device using the non-aqueous sodium secondary battery.

Lithium-ion batteries are secondary batteries with high energy density, so they have been put to practical use as small power sources for mobile phones and laptop computers, and large power sources for electric vehicles. Is done.
However, lithium, which is a charge carrier, is a rare metal and its resources are unevenly distributed in South America and China. Therefore, raw material prices are high and there is concern about the stable supply of raw materials.

  As a next-generation secondary battery replacing the lithium secondary battery, a sodium secondary battery has been studied. Sodium is abundant in seawater, the sixth most abundant element on earth, and is an inexpensive and readily available element. In other words, it is a very attractive element in Japan, which is not blessed with lithium resources. Further, the current collector of the negative electrode is a copper foil in a lithium ion battery, but there is also an advantage that an inexpensive aluminum foil can be used in a sodium ion battery. Further, sodium is an alkali metal element similar to lithium and has similar properties, and the theory of sodium ion batteries has been studied for a long time.

As a sodium secondary battery positive electrode active material, Patent Document 1 discloses a positive electrode represented by a chemical formula of Na _a Li _b M _x O _{2 ± α} and a sodium secondary battery using sodium metal as a negative electrode.
Patent Document 2 discloses a sodium secondary battery using sodium metal for a positive electrode and a negative electrode obtained by electrochemically desorbing lithium from a lithium-containing composite oxide.
However, since the ion radius of the sodium ion is about 1.3 times larger than that of the lithium ion, the volume expansion / contraction change of the positive electrode material accompanying charge / discharge is large, and the occlusion amount of the sodium ion is also small. Therefore, in these conventional sodium secondary batteries, a sufficient charge / discharge capacity and a sufficient capacity retention rate are not obtained at present.

JP 2007-287661 A JP 2007-073424 A JP 2006-12613 A

Chemistry of Materials, 2001, 13, 2951 52nd Battery Symposium Abstracts, 2B10 Journal of Solid State Chemistry, 1981, 81, 203

  The present invention has been made in view of the above-described state of the art, and a main object thereof is to provide a sodium secondary battery that is superior in charge / discharge capacity and capacity retention rate as compared with the conventional art.

  The positive electrode material for a sodium secondary battery of the present invention is a transition metal oxide solid solution having a crystal structure of space group R-3m (No. 166), and has a lattice constant of 2.80Å ≦ a ≦ 3.00Å, 16. 0Å ≦ c ≦ 16.6Å, and diffraction peaks of the (003) plane and the (104) plane are 1.1 ≦ I (104) / I (003) ≦ 1.3.

Sodium secondary battery positive electrode material of the present invention, the composition formula _1: is represented by _{Na A (Mn B M1 C)} O D, the number A of Na atoms in the composition formula 1 is 0.7 to 1.2, Mn atoms Number B of 0.4 to 0.6, the sum of the number B of Mn atoms and the number C of M1 atoms is 0.7 to 1.0, and the number D of O atoms is 1.8 to 2.2. The M1 is preferably one or more selected from the group consisting of Fe, Co, Ni, Nb, and Mo.

According to another aspect, the sodium secondary battery positive electrode material of the present invention, the composition formula _{2: Na A (Mn B M1} C M2 E) is represented by _{O D,} the number A of Na atoms in the composition formula 2 0 0.7 to 1.2, Mn atom number B is 0.4 to 0.6, M2 atom number E is 0.01 to 0.1, Mn atom number B, M1 atom number C, and M2 atom number The sum with the number E is 0.7 to 1.0, the number D of O atoms is 1.8 to 2.2, and the M1 is selected from the group consisting of Fe, Co, Ni, Nb, and Mo. Preferably, M2 is at least one selected from the group consisting of Ti, V, Cr, Zr, and W.

According to another aspect, the sodium secondary battery positive electrode material of the present invention, the composition formula _{3: Na} A is represented by _{(Mn B M1 C M2 E)} O D F G, the number of Na atoms in the composition formula 3 A Is 0.7 to 1.2, the number B of Mn atoms is 0.4 to 0.6, the number E of M2 atoms is 0.01 to 0.1, the number B of Mn atoms and the number of M1 atoms C and M2 The sum with the number E of atoms is 0.7 to 1.0, the number D of O atoms is 1.8 to 2.2, the number G of F atoms is 0.01 to 0.2, and M1 is , Fe, Co, Ni, Nb, Mo are preferably one or more selected from the group consisting of Mo, and M2 is preferably one or more selected from the group consisting of Ti, V, Cr, Zr, and W. .

According to another aspect, the sodium secondary battery positive electrode material of the present invention is represented by the composition formula 4: Na _A Li _J (Mn _B M1 _C ) O _D , and the number J of Li atoms in the composition formula 4 is 0. ~ 0.4, the sum of the number J of Li atoms and the number A of Na atoms is 0.7 to 1.2, the number B of Mn atoms is 0.4 to 0.6, the number B of Mn atoms and M1 atoms The number of oxygen atoms is 0.7 to 1.0, the number of O atoms D is 1.8 to 2.2, and M1 is selected from the group consisting of Fe, Co, Ni, Nb, and Mo. It is preferable that it is 1 or more types.

  According to the sodium secondary battery positive electrode material of the present invention, it is possible to provide a sodium secondary battery that is superior in charge / discharge capacity and capacity retention rate as compared to conventional sodium secondary batteries.

The sodium secondary battery positive electrode material of the present invention can further contain Na ₃ V ₂ (PO ₄ ) ₃ . Thereby, the impedance of a sodium secondary battery can be reduced and, as a result, rate characteristics can be improved.

  A method for producing a positive electrode material for a sodium secondary battery according to the present invention is a method for producing a positive electrode material for a sodium secondary battery according to any one of claims 2 to 6, wherein lithium is electrochemically or from a high lithium-containing transition metal oxide. This is a method for producing a positive electrode material for a sodium secondary battery that is chemically desorbed and then occluded with sodium.

In the method for producing a positive electrode material for a sodium secondary battery of the present invention, the high lithium-containing transition metal oxide is represented by the composition formula 5: Li _K (Mn _B M1 _C ) O _D , and the Li atom of the composition formula 5 The number K is 1.0 to 1.2, the number B of Mn atoms is 0.4 to 0.6, the sum of the number B of Mn atoms and the number C of M1 atoms is 0.7 to 1.0, O atoms The number D of these is 1.8 to 2.2, and the M1 is preferably at least one selected from the group consisting of Fe, Co, Ni, Nb, and Mo.

According to another aspect, in the method for producing a positive electrode material for a sodium secondary battery of the present invention, the high lithium-containing transition metal oxide is represented by a composition formula 6: Li _K (Mn _B M1 _C M2 _E ) O _D. In the compositional formula 6, the number K of Li atoms is 1.0 to 1.2, the number B of Mn atoms is 0.4 to 0.6, the number E of M2 atoms is 0.01 to 0.1, and the Mn atoms The sum of the number B of M, the number C of M1 atoms and the number E of M2 atoms is 0.7 to 1.0, the number D of O atoms is 1.8 to 2.2, and the M1 is Fe, Preferably, the M2 is one or more selected from the group consisting of Co, Ni, Nb, and Mo, and the M2 is one or more selected from the group consisting of Ti, V, Cr, Zr, and W.

According to another aspect, in the method for producing a positive electrode material for a sodium secondary battery of the present invention, the high lithium-containing transition metal oxide is represented by the composition formula 7: Li _K (Mn _B M1 _C M2 _E ) O _D F _G In the composition formula 7, the number K of Li atoms is 1.0 to 1.2, the number B of Mn atoms is 0.4 to 0.6, the number E of M2 atoms is 0.01 to 0.1, The sum of the number B of Mn atoms, the number C of M1 atoms, and the number E of M2 atoms is 0.7 to 1.0, the number D of O atoms is 1.8 to 2.2, and the number G of F atoms is 0. 0.01 to 0.2, where M1 is one or more selected from the group consisting of Fe, Co, Ni, Nb, and Mo, and M2 is selected from Ti, V, Cr, Zr, and W. It is preferable that it is 1 or more types selected from the group which consists of.

  The method for producing a positive electrode material for a sodium secondary battery according to the present invention comprises preparing a first half battery using the high lithium-containing transition metal oxide as a positive electrode and a Li metal as a negative electrode, and charging the first half battery. A step of detaching from the positive electrode of the first half-cell, and a second half-cell having a positive electrode as the positive electrode of the first half-cell from which Li has been desorbed and a negative electrode of Na metal as the second half-cell It is preferable to include a step of occluding Na in the positive electrode of the second half battery by discharging.

In the said manufacturing method, it is preferable to perform charging until it reaches 4.6 to 5.0 V (vs. Li / Li ⁺ ), and until discharging reaches 1 to 2 V (vs. Na ^/ Na ⁺ ). .

  According to the method for producing a positive electrode material for a sodium secondary battery of the present invention, since the sodium secondary battery positive electrode material having the above-described crystal structure is obtained, the charge / discharge capacity and capacity are compared with those of a conventional sodium secondary battery. A sodium secondary battery having an excellent maintenance rate can be provided.

  The electrode for sodium secondary batteries of the present invention uses, as an active material, the positive electrode material for sodium secondary batteries or the positive electrode material for sodium secondary batteries obtained by the method for producing the positive electrode material for sodium secondary batteries.

  The electrode for a sodium secondary battery of the present invention further includes a conductive additive and a binder. When the total of the active material, the conductive additive and the binder is 100% by weight, the binder is included in an amount of 1 to 25% by weight. Carboxymethyl cellulose (CMC) is preferred.

  It is preferable that the binder of the electrode for a sodium secondary battery of the present invention further contains 10 to 50% by weight of an acrylic resin with respect to 100% by weight of CMC.

  According to the electrode for sodium secondary batteries of the present invention, it is possible to provide a sodium secondary battery that is superior in charge / discharge capacity and capacity retention rate as compared to conventional sodium secondary batteries.

The non-aqueous sodium secondary battery of this invention is equipped with the positive electrode which consists of the said electrode for sodium secondary batteries.
The nonaqueous sodium secondary battery of the present invention preferably further comprises a tin sulfide negative electrode and an EC electrolyte solution in which sodium hexafluorophosphate is dissolved.

  According to the non-aqueous sodium secondary battery of the present invention, it is possible to provide a sodium secondary battery that is superior in charge / discharge capacity and capacity retention rate as compared to conventional sodium secondary batteries.

  The non-aqueous sodium secondary battery of the present invention can be used for electrical equipment.

  According to the present invention, by being a sodium secondary battery positive electrode material that is a transition metal oxide solid solution having a structure defined by the above space group and lattice constant, the charge / discharge capacity and the capacity retention ratio are improved as compared with the conventional case. An excellent sodium secondary battery can be provided.

In the XRD pattern of Li _1.2 (Ni _0.10 Mn _0.45 Co _0.25 ) O ₂ and electrochemically produced Na _A (Ni _0.10 Mn _0.45 Co _0.25 ) O ₂ is there. It is the charge / discharge characteristic of electrochemically produced Na _A (Ni _0.10 Mn _0.45 Co _0.25 ) O ₂ . It is an XRD pattern in each J amount of _{Na A Li J (Mn B M1} C) O D. It is a graph showing the change of the cycle life in 60 degreeC by the difference in a binder. It is a charging / discharging curve at 60 degreeC of the electrode which used the polyacrylic resin for the binder. Transition metal oxide solid solution to 5 _{wt% Na 3 V 2 (PO 4} ) a charge-discharge curve at each rate of ₃ positive electrode was added. Transition metal oxide solid solution in 0, 5, 10, 20 _{wt% Na 3 V 2 (PO 4} ) 3 is a graph showing the rate characteristics of the positive electrode added. It is a graph which shows the rate characteristic of the positive electrode in each electrolyte solution.

  Hereinafter, a sodium secondary battery positive electrode material of the present invention, a method for producing the sodium secondary battery positive electrode material, a sodium secondary battery electrode using the sodium secondary battery positive electrode material, and the sodium secondary battery electrode are provided. Embodiments of a non-aqueous sodium secondary battery and an electric device using the non-aqueous sodium secondary battery will be described.

The positive electrode material for a sodium secondary battery of the present invention is a transition metal oxide solid solution having a crystal structure of space group R-3m (No. 166), and has a lattice constant of 2.80Å ≦ a ≦ 3.00Å, 16. 0Å ≦ c ≦ 16.6Å, and the (003) plane and (104) plane diffraction peaks are 1.1 ≦ I (104) / I (003) ≦ 1.3. .
By using this positive electrode material as an active material, it is possible to obtain a sodium secondary battery that is superior in charge / discharge capacity and capacity retention rate as compared with the conventional material.
When a sodium secondary battery is configured using a positive electrode active material as a sodium secondary battery positive electrode material whose lattice constant or diffraction peak ratio is outside this range, the charge / discharge capacity is reduced, and the discharge capacity is reduced when the discharge cycle is repeated. Since it falls and the capacity maintenance rate deteriorates, it is not preferable.

Sodium secondary battery positive electrode material of the present invention, the composition formula _1: is represented by _{Na A (Mn B M1 C)} O D, the number A of Na atoms in the composition formula 1 is 0.7 to 1.2, Mn atoms Number B of 0.4 to 0.6, the sum of the number B of Mn atoms and the number C of M1 atoms is 0.7 to 1.0, and the number D of O atoms is 1.8 to 2.2. The M1 is preferably a secondary battery positive electrode material that is at least one selected from the group consisting of Fe, Co, Ni, Nb, and Mo.

Alternatively, the composition formula _2: is represented by _{Na A (Mn B M1 C M2} E) O D, the number A of Na atoms in the composition formula 2 is 0.7 to 1.2, the number B of Mn atoms 0.4 -0.6, the number E of M2 atoms is 0.01-0.1, the sum of the number B of Mn atoms, the number C of M1 atoms, and the number E of M2 atoms is 0.7-1.0, O atoms The number D is 1.8 to 2.2, and the M1 is one or more selected from the group consisting of Fe, Co, Ni, Nb, and Mo, and the M2 is Ti, V, Cr It is preferable that it is a sodium secondary battery positive electrode material which is 1 or more types selected from the group which consists of, Zr, and W.
These elements M2 are formula _1: in _Na A (Mn _B M1 C) a transition metal oxide solid solution in the crystal represented by _{O D,} mainly, those present in a part and replaced by M1 site element M1 It is. For this reason, an element having an ion size close to the M1 ion size is preferable.
When the ratio in the raw material composition of the number of moles of M2 to the total number of moles of M2 and M1 is T, and T = M2 / (M2 + M1), T is preferably in the range of 0.01 to 0.1.

Alternatively, the composition formula _3: represented by _{Na A (Mn B M1 C M2} E) O D F G, the number A of Na atoms in the composition formula 3 is 0.7 to 1.2, the number B of Mn atoms 0 .4 to 0.6, the number E of M2 atoms is 0.01 to 0.1, the sum of the number B of Mn atoms, the number C of M1 atoms and the number E of M2 atoms is 0.7 to 1.0, The number D of O atoms is 1.8 to 2.2, the number G of F atoms is 0.01 to 0.2, and M1 is selected from the group consisting of Fe, Co, Ni, Nb, and Mo. Preferably, the M2 is a sodium secondary battery positive electrode material that is at least one selected from the group consisting of Ti, V, Cr, Zr, and W.
In the above composition formula, the fluorine element F is, formula _2: are those present in the _{Na A (Mn B M1 C M2} E) O D part and replaced by O site O present in the crystals, fluorine The transition metal oxide solid solution substituted with the element F has a slight decrease in the initial charge / discharge capacity, but the charge / discharge cycle characteristics are improved by about 5 to 10%, and at the same time, the discharge voltage is increased by about 0.02 to 0.1V. To do. However, when the amount of substitution of the fluorine element F increases, the binding energy between Na and F increases, and the insertion / extraction of Na ions does not easily occur, so the positive electrode capacity decreases.
The substitution amount G of fluorine element F may be in the range of 0.01 ≦ G ≦ 0.2. However, in order to sufficiently exhibit the substitution effect of fluorine element F, 0.01 ≦ G ≦ 0. A range of 05 is preferred.

Alternatively, the composition formula _{4: Na} A _Li J is represented by _{(Mn B M1 C) O D} , the number J of Li atoms in the composition formula 4 is 0 to 0.4, the number of the number J and Na atoms Li atom A Is 0.7 to 1.2, the number B of Mn atoms is 0.4 to 0.6, the sum of the number B of Mn atoms and the number C of M1 atoms is 0.7 to 1.0, O The number D of atoms is 1.8 to 2.2, and M1 is a positive electrode material for a sodium secondary battery that is at least one selected from the group consisting of Fe, Co, Ni, Nb, and Mo. preferable.

  If the number A of Na atoms (or the sum of the number J of Li atoms and the number A of Na atoms) exceeds 1.2, the basic skeleton structure of the Na-containing transition metal oxide solid solution tends to be unstable. It is difficult to obtain stable charge / discharge characteristics.

  On the other hand, when the number A of Na atoms (or the sum of the number J of Li atoms and the number A of Na atoms) is less than 0.7, the amount of sodium ions (and lithium ions) that can be occluded and released is reduced. This is not preferable because a high charge / discharge capacity cannot be obtained.

The material for a sodium secondary battery of the present invention can further contain sodium vanadium phosphate (Na ₃ V ₂ (PO ₄ ) ₃ ).
Thereby, rate characteristics can be improved.

<Method for producing positive electrode material>
Next, the manufacturing method of the positive electrode material for sodium secondary batteries of this invention is demonstrated.

The method for producing a positive electrode material for a sodium secondary battery according to the present invention comprises desorbing lithium electrochemically or chemically from a high lithium-containing transition metal oxide (starting material of the positive electrode material of the present invention), and then storing sodium. It is a manufacturing method of the positive electrode material for sodium secondary batteries to be made.
In the method for producing a positive electrode material for a sodium secondary battery according to the present invention, “electrochemically” refers to the transfer of electrons between substances and various incidental phenomena, and “chemically” refers to substances This is due to a chemical reaction between them.
For example, as a method of electrochemical production, in Non-Patent Document 1, a half battery having LiFePO ₄ as a positive electrode and a counter electrode as a Li foil is prepared, and Li is desorbed by charging. Examples thereof include a method of producing a half battery having a positive electrode and a counter electrode made of Na foil and inserting Na. As a chemical production method, as described in Patent Document 3 and Non-Patent Documents 2 and 3, a lithium compound is dispersed in an acetonitrile solution in which NO ₂ BF ₄ , NO ₂ PF ₆ or MoF ₆ is dissolved. And removing lithium from the compound, and then inserting lithium into a dissolved acetonitrile solution such as lithium iodide.

The high lithium-containing transition metal oxide, the composition formula _5: is represented by _{Li K (Mn B M1 C)} O D, the number K of Li atoms in the composition formula 5 is 1.0 to 1.2, the Mn atoms The number B is 0.4 to 0.6, the sum of the number B of Mn atoms and the number C of M1 atoms is 0.7 to 1.0, and the number D of O atoms is 1.8 to 2.2. The M1 may be a high lithium-containing transition metal oxide that is at least one selected from the group consisting of Fe, Co, Ni, Nb, and Mo.

Further, as a high lithium-containing transition metal oxide, the composition formula _6: is represented by _{Li K (Mn B M1 C M2} E) O D, the number K of Li atoms in the composition formula 6 is 1.0 to 1.2, The number B of Mn atoms is 0.4 to 0.6, the number E of M2 atoms is 0.01 to 0.1, and the sum of the number B of Mn atoms, the number C of M1 atoms, and the number E of M2 atoms is 0. 0.7 to 1.0, the number D of O atoms is 1.8 to 2.2, and the M1 is one or more selected from the group consisting of Fe, Co, Ni, Nb, and Mo, The M2 may be a high lithium-containing transition metal oxide that is one or more selected from the group consisting of Ti, V, Cr, Zr, and W.

Further, as a high lithium-containing transition metal oxide, the composition formula _7: is represented by _{Li K (Mn B M1 C M2} E) O D F G, the number K of Li atoms in the composition formula 7 is 1.0 to 1. 2, the number B of Mn atoms is 0.4 to 0.6, the number E of M2 atoms is 0.01 to 0.1, the sum of the number B of Mn atoms, the number C of M1 atoms, and the number E of M2 atoms Is 0.7 to 1.0, the number of O atoms D is 1.8 to 2.2, the number G of F atoms is 0.01 to 0.2, and M1 is Fe, Co, Ni, Use a high lithium content transition metal oxide which is one or more selected from the group consisting of Nb and Mo, and wherein M2 is one or more selected from the group consisting of Ti, V, Cr, Zr and W. Can do.

  By using the high lithium-containing transition metal oxide as a starting material, the sodium secondary battery positive electrode material of the present invention can be obtained.

  Hereinafter, the manufacturing method of the sodium secondary battery positive electrode material of this invention is demonstrated for every process.

1. Desorption of Li First, lithium is desorbed (pulled out) from the transition metal oxide containing high lithium. The following method is mentioned as an example.

First, a first half battery is fabricated using a high lithium-containing transition metal oxide as a positive electrode and Li metal as a negative electrode. Li can be desorbed from the positive electrode by charging the first half-cell.
This charging is preferably performed up to 4.6 to 5.0 V (vs. Li / Li ⁺ ).
As a result, a large amount of lithium in the transition metal oxide having a high lithium content can be eliminated, and lithium can be prevented from remaining in the transition metal oxide having a high lithium content.

In the sodium secondary battery positive electrode material represented by composition formula 4: Na _A Li _J (Mn _B M1 _C ) O _D of the present invention, the initial discharge capacity increases as the number of lithium atoms J increases, that is, the remaining amount of lithium increases. Becomes smaller.
Therefore, it is preferable to remove lithium in the high lithium-containing transition metal oxide as a starting material as much as possible.

As an electrolytic solution of the first half battery, a solution containing Li ions can be used, and an electrolytic solution used in a lithium ion battery can be suitably used. For example, as the supporting salt of the electrolytic solution, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiTiF ₄ , LiVF ₅ , LiAsF, LiSbF ₆ , LiCF ₃ SO ₃ , Li (C ₂ F ₅ SO ₂ ) ₂ N, LiB (C _{2 O 4) 2, LiB 10} Cl 10, LiB 12 Cl 12, LiCF 3 COO, Li 2 S 2 O 4, LiNO 3, Li 2 SO 4, LiPF 3 (C 2 F 5) 3, LiB (C 6 F ₅ ) ₄ and salts such as Li (CF ₃ SO ₂ ) ₃ C can be used. In addition, 1 type may be used independently among the said salts, and 2 or more types may be combined. Solvents are not particularly limited, but cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate, ethers such as tetrahydrofuran, hydrocarbons such as hexane, and lactones such as γ-butyllactone. System, etc. can be used.

2. Disassembly of the battery, washing of the electrode Since the positive electrode from which Li has been desorbed has Li ions attached around it, it is preferable to remove this by washing. Cleaning is preferably performed using the same solvent as the electrolyte of the first half battery, but is not particularly limited as long as it is a solvent that can dissolve the electrolyte.

3. Occlusion of Na Next, the positive electrode of the first half battery from which Li is desorbed by the above process is used as the positive electrode, and the second half battery is manufactured using Na metal as the negative electrode. By discharging the second half-cell, Na can be stored in the positive electrode of the second half-cell.
This discharge is preferably in the range of a cutoff potential of 1 to 2 V (vs. Na ^/ Na ⁺ ).
The smaller the cut-off potential at the time of discharge, the greater the number of sodium atoms to be occluded, and a positive electrode having a large charge / discharge capacity can be obtained. However, when the cut-off potential is less than 1 V (vs. Na / Na ⁺ ), excess sodium that does not remain in the basic skeleton of the Na-containing transition metal oxide solid solution easily precipitates on the electrode surface. Sometimes short circuit.
On the other hand, when the cut-off potential at the time of discharge is 2 V (vs. Na ^/ Na ⁺ ) or more, the number of occluded sodium atoms becomes small, and the positive electrode material of the present invention having a sufficient discharge capacity cannot be obtained.
Therefore, the cut-off potential at the time of discharge is within the range of 1 to 2 V (vs. Na ^/ Na ⁺ ), so that a sufficient charge / discharge capacity can be obtained without short-circuiting when the battery is assembled.

As an electrolytic solution of the second half battery, a solution containing Na ions can be used, and an electrolytic solution used in a Na ion battery can be preferably used. For example, as the supporting salt of the electrolytic solution, NaPF ₆ , NaBF ₄ , NaClO ₄ , NaTiF ₄ , NaVF ₅ , NaAsF, NaSbF ₆ , NaCF ₃ SO ₃ , Na (C ₂ F ₅ SO ₂ ) ₂ N, NaB (C _{2 O 4) 2, NaB 10} Cl 10, NaB 12 Cl 12, NaCF 3 COO, Na 2 S 2 O 4, NaNO 3, Na 2 SO 4, NaPF 3 (C 2 F 5) 3, NaB (C 6 F ₅ ) ₄ and salts such as Na (CF ₃ SO ₂ ) ₃ C can be used. In addition, 1 type may be used independently among the said salts, and 2 or more types may be combined. Solvents are not particularly limited, but cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate, ethers such as tetrahydrofuran, hydrocarbons such as hexane, and lactones such as γ-butyllactone. System, etc. can be used.

  Through the above steps, lithium can be eliminated from the high lithium-containing transition metal oxide that is a starting material, and sodium can be occluded. Thereby, the sodium secondary battery positive electrode material of this invention can be obtained.

  The sodium secondary battery material of the present invention can be used as an active material to form the sodium secondary battery electrode of the present invention.

  In addition, the positive electrode material of the sodium secondary battery according to the present invention uses a carbon-based material or alloy that occludes sodium as the negative electrode so that lithium in the transition metal oxide containing high lithium is desorbed. Can do.

<Method for producing positive electrode>
The sodium secondary battery electrode of the present invention can contain the sodium secondary battery positive electrode active material of the present invention and a binder, and optionally a conductive additive.
For example, an appropriate solvent (N-methyl-2-pyrrolidone (NMP), water) is added to a mixture (positive electrode mixture) containing a binder and, if necessary, a conductive additive added in addition to the positive electrode active material. A positive electrode active material mixture paste composition, a positive electrode active material mixture slurry, and the like obtained by sufficiently kneading and adding alcohol, xylene, toluene, etc.) to the surface of the current collector, drying, and pressing Thus, a positive electrode active material-containing layer can be formed on the surface of the current collector to form the positive electrode of the first half battery.

  The positive electrode of the first half battery preferably contains 1 to 25% of the binder when the total of the active material, the binder and the conductive auxiliary agent added as necessary is 100% by weight.

  The binder material is not particularly limited as long as it is normally used. For example, carboxymethyl cellulose (CMC), polyvinylidene fluoride (PVDF), polyimide (PI), polytetrafluoroethylene (PTFE), Polyamide, polyamideimide, polyacryl, styrene butadiene rubber (SBR), styrene-ethylene-butylene-styrene copolymer (SEBS), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), ethylene acetic acid copolymer (EVA), etc. These materials may be used alone or in combination of two or more.

In general, when a binder using water as a solvent (hereinafter referred to as an aqueous binder) is used as a positive electrode binder, lithium as a starting material dissolves in water. However, in the present invention, lithium is previously extracted electrochemically and then sodium is occluded, so that even if an aqueous binder is used, there is no problem of a decrease in the practical amount.
Of the above water-based binders, CMC is preferably used. When CMC is used as a binder, not only the high temperature durability of the positive electrode is improved, but also the output characteristics are improved.
This is presumably because CMC does not swell in a high-temperature electrolyte solution, and thus suppresses an increase in electrode resistance and does not weaken the bonding force.

More preferably, the aqueous binder further contains an acrylic resin.
Sufficient positive electrode characteristics can be obtained with only an aqueous binder, but by including an acrylic resin, volume expansion / contraction associated with charge / discharge is suppressed, and the cycle life characteristics of the positive electrode are improved.
However, if the content of the acrylic resin is too large, the ion conductivity and the electron conductivity become poor, and sufficient rate characteristics cannot be obtained. Moreover, when there are too few, sufficient binding force cannot be acquired.
Therefore, when it contains an acrylic resin, it is preferably contained in an amount of 10 to 50% by weight, more preferably 15 to 30% by weight, based on 100% by weight of CMC.

  As the conductive auxiliary agent, a commonly used carbon material such as acetylene black (AB), ketjen black (KB), graphite, carbon fiber, carbon tube, graphene, amorphous carbon or the like is used alone. Or two or more of them may be used in combination. More preferably, the conductive aid of the carbon material can form a conductive three-dimensional network structure (for example, flaky conductive material (flaked aluminum powder, flake stainless steel powder, etc.), carbon fiber, carbon tube, Crystalline carbon or the like) is preferably added. If the conductive three-dimensional network structure is formed, a sufficient current collecting effect can be obtained, and the volume expansion of the electrode during Na occlusion / release can be effectively suppressed.

  The current collector is not particularly limited as long as it is a material having electronic conductivity and capable of energizing the held negative electrode material. For example, conductive materials such as C, Ti, Cr, Mo, Ru, Rh, Ta, W, Os, Ir, Pt, Au, and Al, and alloys containing two or more of these conductive materials (for example, stainless steel ) Can be used. The current collector is preferably C, Al, stainless steel or the like from the viewpoint of high electrical conductivity and good stability and oxidation resistance in the electrolytic solution, and Al or the like is more preferable from the viewpoint of material cost.

Although there is no restriction | limiting in particular in the shape of an electrical power collector, A foil-like base material, a three-dimensional base material, etc. can be used. However, when a three-dimensional substrate (foamed metal, mesh, woven fabric, non-woven fabric, expanded, etc.) is used, an electrode with a high capacity density can be obtained even with a binder that lacks adhesion to the current collector. In addition, high rate charge / discharge characteristics are also improved.
Even in the case of a foil-like current collector, the capacity can be increased by forming a primer layer on the current collector surface in advance. The primer layer only needs to have good adhesion between the active material layer and the current collector and have conductivity. For example, a primer layer can be formed by applying a binder mixed with a carbon-based conductive additive on a current collector in a thickness of 0.1 μm to 50 μm.

  The conductive auxiliary for the primer layer is preferably carbon powder. If it is a metal-based conductive additive, it is possible to increase the capacity density, but the input / output characteristics deteriorate. If the conductive additive is carbon-based, the capacity density can be increased using CMC, and the input / output characteristics are improved. Examples of the carbon-based conductive assistant include KB, AB, VGCF, graphite, graphene, carbon tube, and the like. One of these may be used, or two or more may be used in combination. Among these, KB or AB is preferable from the viewpoint of conductivity and cost.

  The binder for the primer layer is not limited as long as it can bind the carbon-based conductive additive. However, when the primer layer is formed using an aqueous binder such as PVA, CMC, or sodium alginate, the primer layer melts when the active material layer is formed, and the effect is often not exhibited remarkably. Therefore, when using such an aqueous binder, the primer layer may be crosslinked in advance. Examples of the cross-linking material include a zirconia compound, a boron compound, a titanium compound, and the like.

The primer layer thus prepared is a foil-shaped current collector, and not only can the capacity density be increased using CMC, but also the polarization becomes small and high even when charging / discharging with a high current. The rate charge / discharge characteristics are improved.
The primer layer is not only effective for the foil-shaped current collector but also has the same effect for a three-dimensional substrate.

  According to the electrode manufactured in the above-described process, it functions as a positive electrode for a sodium secondary battery.

<Negative electrode>
The negative electrode combined with the positive electrode for sodium secondary batteries of the present invention may be a negative electrode used in sodium ion batteries, and may be an electrode containing a negative electrode active material capable of occluding and releasing sodium.
For example, hard carbon, Mg, Al, Si, P, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Y, Zr, Nb, Mo, Pd One or more elements selected from Ag, Cd, In, Sn, Sb, W, Pb and Bi, alloys or oxides using these elements, halides, chalcogenides, and the like may be used.
Especially, it is preferable to contain the negative electrode active material (Y) which can occlude and discharge | release sodium, Na ( _alpha ) X ( _beta ), and a binder. However, X is one or more elements selected from F, Cl, Br, I, O, S, Se and Te, α is 1 to 2, and β is 1 to 5.
Here, the negative electrode active material (Y) capable of occluding and releasing sodium can occlude sodium ions in the initial charge, and can occlude and release sodium ions during subsequent charging and discharging. If it is a thing, it will not specifically limit. For example, Na, hard carbon, Mg, Al, Si, P, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, Y, Zr, Nb, Mo One or more elements selected from Pd, Ag, Cd, In, Sn, Sb, W, Pb, and Bi, and alloys using these elements are preferable.

  The negative electrode active material (Y) preferably has a discharge plateau region that can be observed within a range of 0 to 1 V (vs. sodium potential) and has a high discharge capacity. Among the above examples, Sn, Ge, Sb, etc. The alloys are preferably A1-Ge, Si-Ge, Si-Sn, Zn-Sn, Ge-Ag, Ge-Sn, Ge-Sb, Ag-Sn, Ag-Ge, Sn-Sb, Sn-Cu. Each combination of Sn-Ni and the like is preferable. In addition, even if it uses 2 or more types of negative electrode active materials (Y), there is no problem.

Na _α X _β is a compound which becomes a sodium compound in the initial charge (sodium ion occlusion process) and does not react electrochemically in the subsequent charge / discharge process, that is, a compound which has been reduced by sodium and decomposed into a buffer layer. . This buffer layer functions to suppress the volume change of the negative electrode material during the process of occlusion / release of sodium ions. As the buffer layer, a substance having sodium ion conductivity is preferable.

As long as it is a material that can achieve the above-mentioned purpose, there is no particular limitation. Examples of Na _α X _β include sodium halide (NaF, NaCl, NaBr, NaI, etc.), chalcogen sodium (Na ₂ O, Na ₂ O ₂ , Na ₂ O ₃ , Na ₂ S, Na ₂ Se, Na ₂ Te, etc.), sodium nitride (Na ₃ N), sodium nitride phosphate (NaPON), sodium oxalate (Na ₂ C ₂ O ₄ ), NaC ₁ O _{3, NaA1Cl 4, Na 2 SO} 4, NaNO 3, Na 3 PO 4, Na 4 SiO 4, Na 3 VO 4, Na 4 GeO 4, Na 4 SiO 4, Na 4 ZrO 4, NaMoO 4, NaA1F 4, Na ₃ Ni ₂ , NaBF ₄ , NaCF ₃ SO _{3 and the} like can be mentioned, and one or more of these can be used. However, sodium nitride (Na ₃ N), sodium nitride phosphate (NaPON), sodium oxalate (Na ₂ C ₂ O ₄ ), NaC ₁ O ₃ , NaA 1 Cl ₄ , Na ₂ SO ₄ , NaNO ₃ , Na ₃ PO ₄ , Na ₄ SiO ₄ , Na ₃ VO ₄ , Na ₄ GeO ₄ , Na ₄ ZrO ₄ , NaMoO ₄ , NaA1F ₄ , Na ₃ Ni ₂ , NaBF ₄ , NaCF ₃ SO _3, etc. have a large bulk density, so the battery capacity density It is difficult to improve. Therefore, Na _α X _β is sodium halide (NaF, NaCl, NaBr, NaI, etc.), chalcogen sodium (Na ₂ O, Na ₂ O ₂ , Na ₂ O ₃ , Na ₂ S, Na ₂ Se, Na ₂ Te). Etc.) is preferable.

  Moreover, the discharge plateau of the material that can achieve the above-mentioned object is 0.2 to 0.6 V, which is higher than the discharge plateau near 0 V of the hard carbon negative electrode. When the discharge plateau of the negative electrode is increased, the energy density of the entire battery is decreased. On the other hand, charge and discharge can be performed at a potential equal to or higher than the deposition potential of sodium.

It is preferable that the negative electrode active material (Y) capable of occluding and releasing sodium and Na _α X _β are mixed at the molecular level rather than being simply mixed.
Here, "Y and Na _alpha X _beta are uniformly mixed at the molecular level", when sodium reduction of Y _alpha X _beta, is decomposed into Y and Na _alpha X _beta, Y and Na _alpha X _beta is It means a uniformly mixed state.
Since Y and Na _α X _β are uniformly mixed at the molecular level, the expansion / contraction stress of Y due to charge / discharge can be effectively relieved.

The negative electrode for a sodium secondary battery according to the present invention contains a binder in addition to the negative electrode active material and Na _α X _β . The type of the binder is not particularly limited, and for example, a commonly used binder such as PVdF can be used. From the viewpoint of improving the discharge capacity of the secondary battery, a binder containing polyimide is used. preferable. In addition to the above, the negative electrode for a sodium secondary battery according to the present invention may contain a conductive additive as necessary in order to improve conductivity. There are no particular restrictions on the type of conductive aid, and for example, commonly used conductive aids such as KB, AB, graphite, VGCF, Cu powder, Al powder, and Ni powder may be included.

In the negative electrode for sodium secondary batteries according to the present invention, it is preferable that T obtained by the following formula (1) is in the range of 0.10 to 0.85. If the negative electrode has T in this range, the discharge capacity is good and the cycle life is also good. The lower limit of T is more preferably 0.40, and still more preferably 0.50. The upper limit of T is preferably 0.75, and more preferably 0.70.
_{T = M B / (M A} + M B) (1)
However, the meaning of each symbol in the formula (1) is as follows.
M _A : Number of moles of negative electrode active material (Y) (mol)
M _B : number of moles of Na _α X _β (mol)

  When T is 0.50 or more, a long-life negative electrode can be obtained while the discharge capacity per mass of the active material is in a favorable range of about 200 to 400 mAh / g. On the other hand, when T is less than 0.50, a negative electrode having a high discharge capacity of 300 to 500 mAh / g per mass of the active material is obtained although the cycle life is slightly inferior.

Although it does not specifically limit as a collector used for the negative electrode for sodium secondary batteries of this invention, For example, Cu, Al, Ni, Cr, Ti, Fe, or these alloys can be used. Of these, Cu, Al, Fe, or alloys thereof are preferably used in consideration of cost, ease of manufacture, and the like. However, if S, F, Cl, Br, I, or the like is contained as the negative electrode material, the current collector is corroded by heat treatment, and therefore, it is preferable to use Al, Al alloy, or stainless steel having high corrosion resistance. For example, when SnS ₂ is used as the negative electrode active material, if Cu is used for the current collector, copper sulfide is generated by the heat treatment, and the strength of the current collector is extremely reduced, which may not function as an electrode.

The negative electrode used for the sodium ion battery which concerns on this invention can be manufactured through the process of following (1)-(3), for example.
(1) Y _α X _β [wherein Y is one or two of Sn or Ge, X is one or more elements selected from F, Cl, Br, I, O, S, Se and Te, α is 1 ~ 2, β is 1-5] and a step of obtaining a slurry containing a binder,
(2) applying the slurry to an aluminum current collector, subjecting the slurry to heat treatment to obtain a negative electrode precursor, and
(3) A step of performing a heat treatment of holding metal sodium on the active material layer of the negative electrode precursor and holding it at a temperature of 20 to 150 ° C. for 1 hour or more.

Here, Y _α X _β is decomposed into a substance that can occlude and release sodium ions in addition to the buffer layer, rather than the compound that decomposes only into the buffer layer as described above, in the process of initial charging. Compounds are more preferred. For this reason, examples of Y _α X _β include oxides such as SnO, SnO ₂ , and SnC ₂ O ₄ , chalcogenides such as SnS and SnS ₂ , and halides such as SnF ₂ , SnCl ₂ , SnI ₂ , and SnI _4. And selenides such as SnSe and tellurides such as SnTe. Among them, it is preferable to use one or both of Sn fluoride and sulfide. Further, when β is large, the discharge capacity can be increased and the cycle life can be improved. Therefore, β is preferably 2 or more. Among these, SnS, SnS ₂ and SnF ₂ have particularly good cycle life.

Y _α X _β is particularly preferably a Sn compound. _{Specifically, SnO, SnO 2, SnS,} SnS 2, SnSe, SnSe 2, SnTe, SnTe 2, SnF 2, SnCl 2, SnBr 2, SnI 2, and the like. This is because Na is reduced during the initial charge, and an active material (Y) and a buffer layer (Na _α X _β ) that are uniformly mixed at the molecular level are constructed. Further, the buffer layer (Na _α X _β ) becomes ionic conductive. This is because the cycle life is good because it is excellent.

Here, when Y _α X _β is used as the negative electrode active material precursor, there is a problem that the initial irreversible capacity increases. If this initial irreversible capacity is large, even if all the batteries are manufactured, they may not operate normally. Therefore, it is preferable that the negative electrode is doped with sodium in advance to compensate the capacity. The sodium doping method is not particularly limited. For example, (i) metal sodium is attached to a portion where the negative electrode material of the present invention on the negative electrode current collector is not present, and a local cell is formed by injecting the liquid. A method of doping sodium into the active material, (ii) a method of forming a metal sodium film on the negative electrode material of the present invention by vapor deposition or sputtering, and doping sodium into the negative electrode material of the present invention by solid phase reaction, (iii) ) A method of electrochemically doping sodium into the negative electrode before battery construction in an electrolytic solution, and (iv) Sodium metal is added and mixed during the production of the composite powder used in the present invention. Examples thereof include a method of doping sodium into the negative electrode material.

  However, in the above (i), since sodium metal is locally present, it is difficult for sodium ions to diffuse uniformly throughout the negative electrode. In (ii) above, a large-scale apparatus such as a vapor deposition apparatus or a sputtering apparatus is required, and there is room for improvement in productivity. In the above (iii), it is necessary to configure a battery for sodium doping in advance. In (iv) above, since the obtained negative electrode material is sodium, it is soft and difficult to handle, and there is a tendency that a slurry cannot be produced in a normal atmosphere (in a humid air).

  In order to eliminate such problems, the slurry is applied to an aluminum current collector, and heat treatment is performed on the negative electrode precursor active material layer obtained by applying heat treatment to the aluminum current collector. It is effective to do. Thereby, a sodium ion can be uniformly doped in the whole negative electrode, without using a special apparatus. The thickness of the metal sodium foil is preferably 1 to 30 μm, more preferably 5 to 20 μm, considering the ease of handling and the ability to dope sodium ions uniformly. preferable.

  As a condition of the heat treatment for doping sodium ions, it is possible to dope the negative electrode material of the present invention with sodium even at a low temperature, but since the reaction rate is slow, it should be at least 1 hour at 20 to 150 ° C. Is preferred. This heat treatment is preferably performed in an electrolytic solution. If the heating temperature is set to this condition, sodium ions can be doped without damaging the electrode itself and without evaporating the electrolyte. The lower limit of the heat treatment temperature is preferably 30 ° C., and the upper limit is preferably 90 ° C.

  According to the electrode having the above-described configuration, it functions as a negative electrode for a sodium secondary battery.

<Battery>
Using the positive electrode comprising the electrode for the sodium secondary battery of the present invention, the non-aqueous sodium secondary battery of the present invention can be obtained.
The non-aqueous sodium secondary battery of the present invention can use the positive electrode and the negative electrode.
The electrolyte solution is not particularly limited as a solvent for the electrolyte solution, but is a cyclic carbonate system such as ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate, an ether system such as tetrahydrofuran, a hydrocarbon system such as hexane, A lactone system such as γ-butyllactone can be used. Among these, it is preferable to provide EC type electrolyte solution from a viewpoint of rate characteristics.
Usually, since EC is solid at room temperature, EC alone does not function as an electrolyte. However, when used as a mixed solvent with PC, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), etc., it functions as an electrolyte that can be used at room temperature.
EC (ethylene carbonate) -DEC (diethylene carbonate) and EC-DMC (dimethyl carbonate) are preferably used as the solvent for the EC electrolyte solution, and EC-DEC is particularly preferably used.

Although it does not specifically limit as a support salt of electrolyte solution, The salt generally used for a sodium secondary battery can be used. For example, NaPF ₆ , NaBF ₄ , NaClO ₄ , NaTiF ₄ , NaVF ₅ , NaAsF, NaSbF ₆ , NaCF ₃ SO ₃ , Na (C ₂ F ₅ SO ₂ ) ₂ N, NaB (C ₂ O ₄ ) ₂ , NaB _{10 Cl 10, NaB 12 Cl 12,} NaCF 3 COO, Na 2 S 2 O 4, NaNO 3, Na 2 SO 4, NaPF 3 (C 2 F 5) 3, NaB (C 6 F 5) 4, and Na (CF A salt such as ₃ SO ₂ ) ₃ C can be used. In addition, 1 type may be used independently among the said salts, and 2 or more types may be combined.

Among these, sodium hexafluorophosphate (NaPF ₆ ), sodium perchlorate (NaClO ₄ ), sodium tetrafluoroborate (NaBF ₄ ), and the like are preferably used, and NaPF ₆ is particularly preferably used. By using NaPF ₆ as a salt, the effect of improving the discharge capacity and cycle life of the positive electrode and improving the cycle life of the negative electrode is enhanced. The concentration of the electrolytic solution (the concentration of the salt in the solvent) is not particularly limited, but is preferably 0.1 to 3 mol / L, and more preferably 0.5 to 2 mol / L.

  Although it does not specifically limit as a structure of a sodium secondary battery, It can apply to the existing battery forms and structures, such as a laminated type battery and a wound type battery.

  According to the sodium secondary battery having the above-described structure, it functions as a secondary battery by charge / discharge reactions shown in the following chemical formulas (1) to (3). The following chemical formula (1) shows the main charge / discharge reaction of the positive electrode of the present invention. Next, chemical formulas (2) and (3) show main charge / discharge reactions of the negative electrode of the present invention.

  The non-aqueous sodium secondary battery of the present invention can be used for electric devices such as mobile communication devices and portable electronic devices.

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

<Synthesis of Na _A (Ni _0.10 Mn _0.45 Co _0.25 ) O ₂ by Electrochemical Method>
1. Desorption of Li Li _1.2 (Ni _0.10 Mn _0.45 Co _0.25 ) O ₂ as positive electrode, Li metal as negative electrode, EC-DEC containing 1 mol / L LiPF ₆ as supporting salt as electrolyte The half cell used was prepared and charged to 4.6 V (vs. Li ^/ Li ⁺ ).

2. Disassembly of the battery, washing of the electrode The positive electrode from which Li was detached was taken out and washed with dimethyl carbonate to remove the Li electrolyte adhering to the electrode.

3. A half-cell using an electrode after the occlusion cleaning of Na as a positive electrode, Na metal as a negative electrode and EC-DEC containing 1 mol / L NaPF ₆ as a supporting salt as an electrolyte was prepared, and 1 V (vs. Na / Na ⁺ ) Was discharged. Moreover, it carried out also when discharging to 2 V (vs. Na ^/ Na ⁺ ).

  The sodium-containing compound which maintained the crystal structure of the solid solution system by the said process was obtained.

<X-Ray Diffraction of Na _A (Ni _0.10 Mn _0.45 Co _0.25 ) O ₂ Synthesized by Electrochemical Method>
Li _1.2 (Ni _0.10 Mn _0.45 Co _0.25 ) O ₂ (Sample B) and Na _A (Ni _0.10 Mn _0.45 Co _0.25 ) synthesized by the electrochemical method described above. ) O ₂ (Sample A) was subjected to X-ray diffraction measurement using an X-ray diffractometer (manufactured by MAC Science, CuKα ₁ line λ = 1.54056Å), and crystallinity was evaluated. The XRD patterns of the samples A and B are shown in FIG.

The (003) plane peak observed at around 18 ° in sample A was observed at around 16 ° in sample B. That is, the shift of the peak to a low angle means that the lattice constant of Li _1.2 (Ni _0.10 Mn _0.45 Co _0.25 ) O ₂ is increased. Since sodium has a larger ion size than lithium, it can be seen that Li and Na are substituted.
Further, since the peak intensity of the (104) plane depends on the amount of sodium existing between the layers, the relative intensity increases as the sodium amount increases compared to the (003) plane observed near 16 °.
In sample B, I (104) / I (003) was 1.2.
From the XRD pattern of FIG. 1, the lattice constants of samples A and B were obtained. The results are shown in Table 1 below.

The charge / discharge characteristics of the obtained Na _A (Ni _0.10 Mn _0.45 Co _0.25 ) O ₂ were measured.
The positive electrode composition was prepared by mixing 90% by mass of active material, 5% by mass of AB and 5% by mass of PVdF binder to prepare a slurry-like mixture, and after applying and drying on a 20 μm thick aluminum foil, The aluminum foil and the coating film were tightly bonded, and then heat-treated (during decompression, 180 ° C., 1 hour or longer). As a counter electrode, a metal sodium foil having a capacity about 50 times the calculated capacity of the test electrode was used, a glass filter as a separator, and 1 mol / L NaPF ₆ (EC: DEC = 1: 1 vol.%) As an electrolyte. The provided coin cell (CR2032) was produced.
FIG. 2 shows the charge / discharge characteristics of electrochemically produced Na _A (Ni _0.10 Mn _0.45 Co _0.25 ) O ₂ . The lower diagram shows the case where the cutoff potential is 2-4.2 V (Na / Na ⁺ ), and the upper diagram shows the case where the cutoff potential is 1-4.2 V (Na / Na ⁺ ).
In the case of a cut-off potential of 2-4.2 V (Na / Na ⁺ ), the initial discharge capacity was 252 mAh / g, and the number A of inserted Na atoms calculated from the discharge capacity was 0.83.
In the case of a cut-off potential of 1-4.2 V (Na / Na ⁺ ), the initial discharge capacity was 275 mAh / g, and the number A of inserted Na atoms calculated from the discharge capacity was 0.91.
From this result, it can be seen that the lower the cut-off potential during discharge, the greater the number of stored Na atoms and the greater the initial discharge capacity.

Next, the influence of the amount of lithium in the sodium-containing transition metal oxide on the discharge characteristics was examined.
In the method for synthesizing Na _A (Ni _0.10 Mn _0.45 Co _0.25 ) O ₂ by the electrochemical method, the cutoff potential at the time of Li desorption in the first half cell is 4.1, 4. Li atom in sodium-containing transition metal oxide represented by Na _A Li _J (Mn _B M1 _C ) O _D by setting to 0, 3.8, 3.6, 3.3 V (Li / Li ⁺ ) Obtained were compounds having a number J of 0.13, 0.16, 0.27, 0.43, and 0.59, respectively.

Figure 3 _is a XRD pattern of each J amount of _{Na A Li J (Mn B M1} C) O D.
From this XRD pattern, it was found that the crystal structure was a single phase when the amount of lithium J = 0 to 0.4, and that the crystal structure became a two-phase when it exceeded 0.4.
The positive electrode composition is active material: AB: PVdF = 90: 5: 5% by mass, Na foil as the counter electrode, 1 mol / L NaPF ₆ (EC: DEC = 1: 1 vol.%) As the electrolyte, and Al foil as the current collector (20 [mu] m) using a charge and discharge cutoff potential 2-4.2V (Na / Na _^+), was measured initial discharge capacity at each J amount of _{Na a Li J (Mn B M1} C) O D.
The results are shown in Table 2 below.

  From the results shown in Table 2, it can be seen that the larger the residual amount of lithium in the active material, the smaller the initial discharge capacity. In particular, when the number of lithium atoms exceeds 0.4, the initial discharge capacity decreases. It can also be seen that the crystal structure is a single phase when the number of lithium atoms J = 0 to 0.4, and that the crystal structure becomes a two-phase when the number exceeds 0.4.

Subsequently, the change of the high temperature characteristic (60 degreeC) of the sodium secondary battery by the difference in a binder was investigated.
Three types of binders were examined: PVdF, CMC (carboxymethylcellulose), and CMC with an acrylic resin added.
Na _A (Ni _0.10 Mn _0.45 Co _0.25 ) obtained by the above electrochemical method (4.6 V charge (vs. Li ^/ Li ⁺ ) and then 2 V discharge (vs. Na / Na ⁺ )). ) Using O ₂ as the active material, the positive electrode composition was prepared by mixing 90% by mass of the active material, 5% by mass of AB and 5% by mass of the binder to prepare a slurry-like mixture, which was applied and dried on a 20 μm thick aluminum foil After that, the aluminum foil and the coating film were closely bonded by a roll press machine, and then heat-treated (under reduced pressure, 180 ° C., 1 hour or more). As a counter electrode, a metal sodium foil having a capacity about 50 times the calculated capacity of the test electrode was used, a glass filter as a separator, and 1 mol / L NaPF ₆ (EC: DEC = 1: 1 vol.%) As an electrolyte. The provided coin cell (CR2032) was produced, and it charged / discharged to 60 cycles with the cut-off potential 2-4.2V (Na / Na ^<+> ).

FIG. 4 is a graph showing changes in cycle life due to the difference in binder, and Table 3 below shows the values numerically.
FIG. 5 is a charge / discharge curve of an electrode using an acrylic resin as a binder in a 60 ° C. environment.

  From this result, it is understood that when CMC and polyacryl are used as the binder, the discharge capacity can be maintained as compared with PVdF that has been conventionally used even in a high cycle under a high temperature environment. In particular, it can be seen that the capacity retention rate is improved by using polyacryl as a binder.

Next, the charge / discharge characteristics when Na ₃ V ₂ (PO ₄ ) ₃ was added to the positive electrode were examined.
Na _A (Ni _0.10 Mn _0.45 Co _0.25 ) obtained by the above electrochemical method (4.6 V charge (vs. Li ^/ Li ⁺ ) and then 2 V discharge (vs. Na / Na ⁺ )). ) Using O ₂ as the active material, the positive electrode composition was prepared by mixing 90% by mass of the active material, 5% by mass of AB and 5% by mass of the PVdF binder to prepare a slurry-like mixture, which was applied onto an aluminum foil having a thickness of 20 μm. After drying, the aluminum foil and the coating film were tightly bonded with a roll press, and then heat-treated (under reduced pressure at 180 ° C. for 1 hour or more). As a counter electrode, a metal sodium foil having a capacity about 50 times the calculated capacity of the test electrode was used, a glass filter as a separator, and 1 mol / L NaPF ₆ (EC: DEC = 1: 1 vol.%) As an electrolyte. The equipped coin cell (CR2032) was produced, and it charged / discharged to 15 cycles with the discharge rate 0.05C-1C.

FIG. 6 is a charge / discharge curve of a positive electrode in which 5 mass% Na ₃ V ₂ (PO ₄ ) ₃ is added to a transition metal oxide solid solution, and Table 4 below shows numerical values thereof.
FIG. 7 is a graph showing rate characteristics of a positive electrode in which 0, 5, 10, 20 mass% Na ₃ V ₂ (PO ₄ ) ₃ is added to a transition metal oxide solid solution.

When the discharge rate is 1C, Na ₃ V ₂ (PO ₄ ) ₃ added in an amount of 5 to 20% by mass is superior to those in which Na ₃ V ₂ (PO ₄ ) ₃ is not added to the positive electrode material. You can see that
Therefore, it can be seen that the rate characteristics are improved by adding Na ₃ V ₂ (PO ₄ ) ₃ to the positive electrode material.

Next, the influence of the electrolyte solvent and the supporting salt on the charge / discharge characteristics of the positive electrode was examined.
As the electrolytic solution, combinations shown in Table 5 below were used.
Na _A (Ni _0.10 Mn _0.45 Co _0.25 ) O obtained by 4.6 V charge (vs. Li ^/ Li ⁺ ) and 2 V discharge (vs. Na / Na ⁺ )) ₂ was used as the active material, and the positive electrode composition was prepared by mixing 90% by mass of the active material, 5% by mass of AB and 5% by mass of the PVdF binder to prepare a slurry mixture, and applying and drying on a 20 μm thick aluminum foil The aluminum foil and the coating film were tightly bonded with a roll press machine, and then heat-treated (under reduced pressure at 180 ° C. for 1 hour or more). As a counter electrode, a metal sodium foil having a capacity about 50 times the calculated capacity of the test electrode was used, a glass filter as a separator, and 1 mol / L NaPF ₆ (EC: DEC = 1: 1 vol.%) As an electrolyte. The equipped coin cell (CR2032) was produced, and it charged / discharged to 12 cycles with the discharge rate 0.05C-1C.

  FIG. 8 is a graph showing the rate characteristics of the positive electrode in each electrolytic solution, and Table 5 below shows the numerical values.

From this result, the initial discharge capacity is electrolytic solution 4> electrolytic solution 2> electrolytic solution 1> electrolytic solution 3, and the rate characteristics are electrolytic solution 4≈electrolytic solution 2≈electrolytic solution 1> electrolytic solution 3. Recognize.
Therefore, it can be seen that the supporting salt is PF ₆ > ClO ₄ ^— and the solvent is EC-DEC≈EC-DMC> PC.

<All battery tests>
Na _A (Ni _0.10 Mn _0.45 Co _0.25 ) obtained by the above electrochemical method (4.6 V charge (vs. Li ^/ Li ⁺ ) and then 2 V discharge (vs. Na / Na ⁺ )) the O ₂ as the active material, the positive electrode composition, the active material 90% by weight, AB5 wt%, CMC binder 4 mass%, a mixture of 1 wt% of acrylic resin to prepare a slurry mixture, of a thickness of 20μm aluminum After coating and drying on the foil, the aluminum foil and the coating film were closely bonded with a roll press, and then heat-treated (under reduced pressure at 180 ° C. for 1 hour or more).

As a counter electrode, SnS was used as a negative electrode active material precursor, and a slurry mixture was prepared by mixing 80% by mass of a negative electrode active material precursor, 5% by mass of KB, and 15% by mass of a PI binder, and an aluminum foil having a thickness of 20 μm. After coating and drying, the aluminum foil and the coating film were closely bonded with a roll press machine, and then heat-treated (under reduced pressure at 230 ° C. for 1 hour or more). Subsequently, after a metal sodium foil of 10 μm was pressure-bonded on the negative electrode active material layer, it was heat-treated for 2 hours in an electrolytic solution (1 mol / L NaPF ₆ / EC: DEC (50:50 vol%)) at 50 ° C. A volume of sodium was doped.

Using a 1 mol / L NaPF ₆ (EC: DEC = 1: 1 vol.%) As the positive electrode, negative electrode, and electrolyte, a coin cell of a sodium ion total battery (nominal capacity 2.25 mAh) was prepared, and in a 60 ° C. environment. The test was conducted up to 100 cycles at a cutoff potential of 1-4.
Moreover, the negative electrode which uses hard carbon as a negative electrode active material was produced, and the whole battery test was done similarly. The conditions are the same except that SnS is changed to hard carbon.
Table 6 shows the cycle life of a sodium ion all battery in which Na _A (Ni _0.10 Mn _0.45 Co _0.25 ) O ₂ positive electrode and sodium-doped SnS negative electrode or hard carbon negative electrode are combined in a 60 ° C. environment. The test results are shown.

As is apparent from Table 6, it can be seen that the SnS negative electrode and the hard carbon negative electrode reversibly operate as a battery.

<Synthesis of Na _A (Ni _0.10 Mn _0.45 Co _0.25 ) O _1.98 F _0.02 by Electrochemical Method>
1. Desorption of Li _1.2 (Ni _0.10 Mn _0.45 Co _0.25 ) O _1.98 F _0.02 as positive electrode, Li metal as negative electrode, EC containing 1 mol / L LiPF ₆ as supporting salt -A half-cell using DEC as the electrolyte was prepared and charged to 4.6 V (vs. Li ^/ Li ⁺ ).

2. Disassembly of the battery, washing of the electrode The positive electrode from which Li was detached was taken out and washed with dimethyl carbonate to remove the Li electrolyte adhering to the electrode.

3. A half-cell using an electrode after the occlusion cleaning of Na as a positive electrode, Na metal as a negative electrode and EC-DEC containing 1 mol / L NaPF ₆ as a supporting salt as an electrolyte was prepared, and 2 V (vs. Na / Na ^It was also performed when discharging to ⁺ ).

By the above process, Na _A (Ni _0.10 Mn _0.45 Co _0.25 ) O _1.98 F _0.02 was obtained, which maintained the crystal structure of the solid solution system.
The charge / discharge characteristics of the obtained Na _A (Ni _0.10 Mn _0.45 Co _0.25 ) O _1.98 F _0.02 were measured.
The composition of the positive electrode was as follows: active material: acetylene black (AB): polyvinylidene fluoride (PVdF) = 90: 5: 5 mass%, Na foil as the counter electrode, 1 mol / L NaPF ₆ as the electrolyte (EC: DEC = 1: 1 vol) Al) (20 μm) was used as a current collector.

  As a result, the initial discharge capacity was 243 mAh / g, and the atomic number A of inserted Na calculated from the discharge capacity was 0.80.

<Synthesis of Na _A (Mn _0.45 Ni _0.35 ) O ₂ by Electrochemical Method>
1. Desorption of Li Half cell using Li _1.2 (Mn _0.45 Ni _0.35 ) O ₂ as positive electrode, Li metal as negative electrode, EC-DEC containing 1 mol / L LiPF ₆ as supporting salt as electrolyte And charged to 4.6 V (vs. Li ^/ Li ⁺ ).

2. Disassembly of the battery, washing of the electrode The positive electrode from which Li was detached was taken out and washed with dimethyl carbonate to remove the Li electrolyte adhering to the electrode.

3. A half-cell using an electrode after the occlusion cleaning of Na as a positive electrode, Na metal as a negative electrode and EC-DEC containing 1 mol / L NaPF ₆ as a supporting salt as an electrolyte was prepared, and 2 V (vs. Na / Na ^It was also performed when discharging to ⁺ ).

By the above process, Na _A (Mn _0.45 Ni _0.35 ) O ₂ maintaining the crystal structure of the solid solution system was obtained.
The charge / discharge characteristics of the obtained Na _A (Mn _0.45 Ni _0.35 ) O ₂ were measured.
The composition of the positive electrode was as follows: active material: acetylene black (AB): polyvinylidene fluoride (PVdF) = 90: 5: 5 mass%, Na foil as the counter electrode, 1 mol / L NaPF ₆ as the electrolyte (EC: DEC = 1: 1 vol) Al) (20 μm) was used as a current collector.

  As a result, the initial discharge capacity was 237 mAh / g, and the number of inserted Na atoms A calculated from the discharge capacity was 0.78.

<Synthesis of Na _A (Mn _0.45 Fe _0.35 ) O ₂ by Electrochemical Method>
1. Desorption of Li Half cell using Li _1.2 (Mn _0.45 Fe _0.35 ) O ₂ as positive electrode, Li metal as negative electrode, EC-DEC containing 1 mol / L LiPF ₆ as supporting salt as electrolyte And charged to 4.6 V (vs. Li ^/ Li ⁺ ).

2. Disassembly of the battery, washing of the electrode The positive electrode from which Li was detached was taken out and washed with dimethyl carbonate to remove the Li electrolyte adhering to the electrode.

3. A half-cell using an electrode after the occlusion cleaning of Na as a positive electrode, Na metal as a negative electrode and EC-DEC containing 1 mol / L NaPF ₆ as a supporting salt as an electrolyte was prepared, and 2 V (vs. Na / Na ^It was also performed when discharging to ⁺ ).

By the above process, Na _A (Mn _0.45 Fe _0.35 ) O ₂ maintaining the crystal structure of the solid solution system was obtained.
The charge / discharge characteristics of the obtained Na _A (Mn _0.45 Fe _0.35 ) O ₂ were measured.
The composition of the positive electrode was as follows: active material: acetylene black (AB): polyvinylidene fluoride (PVdF) = 90: 5: 5 mass%, Na foil as the counter electrode, 1 mol / L NaPF ₆ as the electrolyte (EC: DEC = 1: 1 vol) Al) (20 μm) was used as a current collector.

  As a result, the initial discharge capacity was 228 mAh / g, and the atomic number A of inserted Na calculated from the discharge capacity was 0.75.

<Synthesis of Na _A (Mn _0.45 Co _0.3 W _0.05 ) O ₂ by Electrochemical Method>
1. Desorption of Li Li _1.2 (Mn _0.45 Co _0.3 W _0.05 ) O ₂ as positive electrode, Li metal as negative electrode, EC-DEC containing 1 mol / L LiPF ₆ as supporting salt as electrolyte The half cell used was prepared and charged to 4.6 V (vs. Li ^/ Li ⁺ ).

2. Disassembly of the battery, washing of the electrode The positive electrode from which Li was detached was taken out and washed with dimethyl carbonate to remove the Li electrolyte adhering to the electrode.

3. A half-cell using an electrode after the occlusion cleaning of Na as a positive electrode, Na metal as a negative electrode and EC-DEC containing 1 mol / L NaPF ₆ as a supporting salt as an electrolyte was prepared, and 2 V (vs. Na / Na ^It was also performed when discharging to ⁺ ).

By the above process, Na _A (Mn _0.45 Co _0.3 W _0.05 ) O ₂ maintaining the crystal structure of the solid solution system was obtained.
The charge / discharge characteristics of the obtained Na _A (Mn _0.45 Co _0.3 W _0.05 ) O ₂ were measured.
The composition of the positive electrode was as follows: active material: acetylene black (AB): polyvinylidene fluoride (PVdF) = 90: 5: 5 mass%, Na foil as the counter electrode, 1 mol / L NaPF ₆ as the electrolyte (EC: DEC = 1: 1 vol) Al) (20 μm) was used as a current collector.

  As a result, the initial discharge capacity was 236 mAh / g, and the number of inserted Na atoms A calculated from the discharge capacity was 0.77.

<Synthesis of Na _A (Mn _0.45 Ni _0.05 Co _0.25 Ti _0.03 Zr _0.02 ) O ₂ by Electrochemical Method>
1. Desorption of Li Li _1.2 (Mn _0.45 Ni _0.05 Co _0.25 Ti _0.03 Zr _0.02 ) O ₂ as positive electrode, Li metal as negative electrode, 1 mol / L LiPF ₆ as supporting salt A half cell using the EC-DEC thus prepared as an electrolyte was prepared and charged to 4.6 V (vs. Li ^/ Li ⁺ ).

2. Disassembly of the battery, washing of the electrode The positive electrode from which Li was detached was taken out and washed with dimethyl carbonate to remove the Li electrolyte adhering to the electrode.

3. A half-cell using an electrode after the occlusion cleaning of Na as a positive electrode, Na metal as a negative electrode and EC-DEC containing 1 mol / L NaPF ₆ as a supporting salt as an electrolyte was prepared, and 2 V (vs. Na / Na ^It was also performed when discharging to ⁺ ).

By the above process, Na _A (Mn _0.45 Ni _0.05 Co _0.25 Ti _0.03 Zr _0.02 ) O ₂ maintaining the crystal structure of the solid solution system was obtained.
The charge / discharge characteristics of the obtained Na _A (Mn _0.45 Ni _0.05 Co _0.25 Ti _0.03 Zr _0.02 ) O ₂ were measured.
The composition of the positive electrode was as follows: active material: acetylene black (AB): polyvinylidene fluoride (PVdF) = 90: 5: 5 mass%, Na foil as the counter electrode, 1 mol / L NaPF ₆ as the electrolyte (EC: DEC = 1: 1 vol) Al) (20 μm) was used as a current collector.

  As a result, the initial discharge capacity was 241 mAh / g, and the atomic number A of inserted Na calculated from the discharge capacity was 0.79.

  The present invention is suitably used as a main power source for mobile communication devices, portable electronic devices, electric bicycles, electric motorcycles, electric vehicles and the like.

Claims (19)

  A transition metal oxide solid solution having a crystal structure of space group R-3m (No. 166), with lattice constants of 2.80Å ≦ a ≦ 3.00Å, 16.4Å ≦ c ≦ 17Å, (003) A sodium secondary battery positive electrode material, wherein the diffraction peak of the surface and the (104) plane is 1.1 ≦ I (104) / I (003) ≦ 1.3. Formula _1: is represented by _{Na A (Mn B M1 C)} O D,
The number A of Na atoms in the composition formula 1 is 0.7 to 1.2, the number B of Mn atoms is 0.4 to 0.6, and the sum of the number B of Mn atoms and the number C of M1 atoms is 0.00. 7 to 1.0, the number D of O atoms is 1.8 to 2.2,
The sodium secondary battery positive electrode material according to claim 1, wherein the M1 is one or more selected from the group consisting of Fe, Co, Ni, Nb, and Mo. Formula _2: is represented by _{Na A (Mn B M1 C M2} E) O D,
The number A of Na atoms in the composition formula 2 is 0.7 to 1.2, the number B of Mn atoms is 0.4 to 0.6, the number E of M2 atoms is 0.01 to 0.1, The sum of the number B, the number C of M1 atoms, and the number E of M2 atoms is 0.7 to 1.0, and the number D of O atoms is 1.8 to 2.2,
The M1 is one or more selected from the group consisting of Fe, Co, Ni, Nb, and Mo, and the M2 is one or more selected from the group consisting of Ti, V, Cr, Zr, and W. The sodium secondary battery positive electrode material according to claim 1. Formula _3: represented by _{Na A (Mn B M1 C M2} E) O D F G,
The number A of Na atoms in the composition formula 3 is 0.7 to 1.2, the number B of Mn atoms is 0.4 to 0.6, the number E of M2 atoms is 0.01 to 0.1, The sum of the number B, the number C of M1 atoms and the number E of M2 atoms is 0.7 to 1.0, the number D of O atoms is 1.8 to 2.2, and the number G of F atoms is 0.01 to 0.2,
The M1 is one or more selected from the group consisting of Fe, Co, Ni, Nb, and Mo, and the M2 is one or more selected from the group consisting of Ti, V, Cr, Zr, and W. The sodium secondary battery positive electrode material according to claim 1. Composition formula 4: Na _A Li _J (Mn _B M1 _C ) O _D
The number J of Li atoms in the composition formula 4 is 0 to 0.4, the sum of the number J of Li atoms and the number A of Na atoms is 0.7 to 1.2, and the number B of Mn atoms is 0.4 to 0.4. 0.6, the sum of the number B of Mn atoms and the number C of M1 atoms is 0.7 to 1.0, the number D of O atoms is 1.8 to 2.2,
The sodium secondary battery positive electrode material according to claim 1, wherein the M1 is one or more selected from the group consisting of Fe, Co, Ni, Nb, and Mo. The sodium secondary battery positive electrode material according to claim 1, further comprising Na ₃ V ₂ (PO ₄ ) ₃ .   The method for producing a positive electrode material for a sodium secondary battery according to claim 2, wherein lithium is electrochemically or chemically desorbed from a high lithium-containing transition metal oxide and then occluded by sodium. A method for producing a positive electrode material for a sodium secondary battery. The high lithium-containing transition metal oxide, the composition formula _5: is represented by _{Li K (Mn B M1 C)} O D, the number K of Li atoms in the composition formula 5 is 1.0 to 1.2, the Mn atoms The number B is 0.4 to 0.6, the sum of the number B of Mn atoms and the number C of M1 atoms is 0.7 to 1.0, and the number D of O atoms is 1.8 to 2.2. The method for producing a positive electrode material for a sodium secondary battery according to claim 7, wherein M1 is at least one selected from the group consisting of Fe, Co, Ni, Nb, and Mo. The high lithium-containing transition metal oxide, the composition formula _6: is represented by _{Li K (Mn B M1 C M2} E) O D, the number K of Li atoms in the composition formula 6 is 1.0 to 1.2, Mn The number B of atoms is 0.4 to 0.6, the number E of M2 atoms is 0.01 to 0.1, and the sum of the number B of Mn atoms, the number C of M1 atoms, and the number E of M2 atoms is 0. 7 to 1.0, the number of O atoms D is 1.8 to 2.2, and the M1 is at least one selected from the group consisting of Fe, Co, Ni, Nb, and Mo, The method for producing a positive electrode material for a sodium secondary battery according to claim 7, wherein M2 is at least one selected from the group consisting of Ti, V, Cr, Zr, and W. The high lithium-containing transition metal oxide, the composition formula _7: is represented by _{Li K (Mn B M1 C M2} E) O D F G, the number K of Li atoms in the composition formula 7 is 1.0 to 1.2 The number B of Mn atoms is 0.4 to 0.6, the number E of M2 atoms is 0.01 to 0.1, the sum of the number B of Mn atoms, the number C of M1 atoms, and the number E of M2 atoms is 0.7 to 1.0, the number D of O atoms is 1.8 to 2.2, the number G of F atoms is 0.01 to 0.2, and M1 is Fe, Co, Ni, Nb The sodium according to claim 7, wherein the M2 is one or more selected from the group consisting of Ti, V, Cr, Zr, and W. A method for producing a positive electrode material for a secondary battery.   Desorbing Li from the positive electrode of the first half-cell by creating a first half-cell using the high lithium-containing transition metal oxide as the positive electrode and Li metal as the negative electrode and charging the first half-cell; The second half cell is created by using the positive electrode of the first half cell from which Li has been detached as the positive electrode and Na metal as the negative electrode, and discharging the second half cell, whereby Na becomes the positive electrode of the second half cell. The method for producing a positive electrode material for a sodium secondary battery according to any one of claims 7 to 10, further comprising a step of occlusion. The charging is performed until reaching 4.6 to 5.0 V (vs. Li / Li ⁺ ), and the discharging is performed until reaching 1 to 2 V (vs. Na ^/ Na ⁺ ). 11. A method for producing a positive electrode material for a sodium secondary battery according to 11.   The positive electrode material for sodium secondary batteries according to claim 1, or the positive electrode material for sodium secondary batteries obtained by the method for producing a positive electrode material for sodium secondary batteries according to claim 7 as an active material. An electrode for a sodium secondary battery, comprising:   When the total of the said active material, the said conductive support agent, and the said binder is 100 weight% further including a conductive support agent and a binder, the said binder is included 1-25 weight%, The said binder is carboxymethylcellulose (CMC). The electrode for sodium secondary batteries according to claim 13, wherein the electrode is provided.   The sodium secondary battery electrode according to claim 14, wherein the binder further contains 10 to 50% by weight of an acrylic resin with respect to 100% by weight of CMC.   A non-aqueous sodium secondary battery comprising a positive electrode comprising the sodium secondary battery electrode according to claim 13.   The nonaqueous sodium secondary battery according to claim 16, further comprising a tin sulfide negative electrode and an EC electrolyte solution in which sodium hexafluorophosphate is dissolved.   The non-aqueous sodium secondary battery according to claim 17, wherein the negative electrode is an alloy compound containing tin sulfide.   An electrical apparatus using the non-aqueous sodium secondary battery according to claim 17 or 18.