JP6187903B2 - Method for producing positive electrode material for sodium secondary battery - Google Patents

Description

The present invention relates to the production how Luna thorium secondary battery positive electrode material having a high capacity maintenance rate and has a high charge-discharge capacity.

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 material, Patent Document 1 describes Na _a Mn _1-b M ¹ _b O ₂ (M ¹ is Fe or Ni), and a molar ratio of Na: Mn: M ¹ a: (1 -B): Disclosed is a sodium-containing transition gold oxide in which b is a value in the range of more than 0.5 and less than 1, and b is a value in the range of 0.001 to 0.5. .
However, in Patent Document 1, although the metal oxide of Example 4 in Table 1 of paragraph [0074] has an initial discharge capacity of 162 mAh / g, the discharge capacity maintenance ratio at the 10th cycle with respect to the initial discharge capacity is 76. % Is a low value. On the other hand, the metal oxide of Example 3 has a discharge capacity retention rate of 85%, but the initial discharge capacity is a low value of 141 mAh / g, and both the initial discharge capacity and the capacity retention rate are sufficient. Nothing is disclosed.

Patent Document 2 includes Na _a Li _b Mn _x M _y O _{2 ± α} , where M includes one or more selected from the group consisting of iron, cobalt, and nickel, and the a is 0.6 or more. 1.1 or less, b is 0 or more and 0.5 or less, the sum of x and y is 0.9 or more and 1.1 or less, and α is 0 or more and 0.1 or less. A sodium secondary battery positive electrode material made of an oxide is disclosed.
As shown in FIG. 5, the positive electrode material described in Patent Document 2 has an initial discharge capacity of 169 mAh / g, but the capacity retention rate has not been verified.

Non-Patent Document 1 discloses an oxide represented by NaNi _1/3 Mn _1/3 Co _1/3 O _{2 in} which Li in a ternary positive electrode already put into practical use in a lithium secondary battery is replaced with Na. It has been reported that a reversible capacity of about 120 mAh / g can be obtained when used as a positive electrode material.
However, the positive electrode material described in Non-Patent Document 1 is also not sufficient in both initial discharge capacity and capacity retention rate.

  Since sodium ions have an ion radius that is about 1.3 times larger than lithium ions, the volume expansion / contraction change of the positive electrode material accompanying charge / discharge is large, and the amount of occlusion of sodium ions is also reduced. Therefore, in these conventional sodium secondary batteries, a sufficient charge / discharge capacity and a sufficient capacity retention rate are not obtained at present.

JP 2009-209037 A JP 2007-287661 A

Chemistry of Materials, 24, 1846-1853 (2012)

The present invention has been made in view of the current state of the prior art described above, and its main purpose is to provide a method for producing a sodium secondary battery having a high charge / discharge capacity and a high capacity retention ratio as compared with the prior art. It is to provide.

Sodium secondary battery positive electrode material consists of sodium-containing transition metal oxide represented by a composition formula _{Na x (Mn y Co 1-} y-z Ni z) O 2, the composition ratio, 0.5 <x ≦ 1.0, 0.60 ≦ y ≦ 0.80, 0.05 ≦ z ≦ 0.20, 0.05 ≦ 1-yz ≦ 0.25, a positive electrode material for sodium secondary battery It is.

The sodium secondary battery positive electrode material has a composition ratio of 0.65 ≦ y ≦ 0.80, 0.10 ≦ z ≦ 0.20, 0.10 ≦ 1-yz ≦ 0.25. Is more preferable.

According to the above- mentioned sodium secondary battery positive electrode material, by providing the above-mentioned specific composition, a sodium secondary battery having a high charge / discharge capacity and a high capacity retention rate as compared with a conventional sodium secondary battery is provided. can do.
Specifically, by setting the specific composition as described above, the initial discharge capacity is 150 mAh / g or more, and the capacity maintenance ratio at the 15th cycle ((discharge capacity at the 15th cycle / discharge capacity at the 1st cycle)) × 100 ) Can be 80% or more. This value of “initial discharge capacity 150 mAh / g” is comparable to the initial discharge capacity of the lithium secondary battery. Moreover, the value of “capacity maintenance rate (15 ^th / 1 ^st ) 80%” is also superior to the conventional sodium secondary battery, and the present invention has both a high charge / discharge capacity and a high capacity maintenance rate. Therefore, it is an excellent positive electrode material.

Method for producing a sodium secondary battery positive electrode material of the present _{invention, Na x (Mn y Co 1} -y-z Ni z) O 2 ( although Shikichu, 0.5 <x ≦ 1.0,0.6 0 ≦ y ≦ 0.80, 0.05 ≦ z ≦ 0.20, 0.05 ≦ 1-yz ≦ 0.25), so as to include a sodium compound, manganese, cobalt, and nickel the compound is mixed sodium and the mixture was synthesized by baking at 500 to 1000 ° C., to gas oxygen concentration is 10 to 30 vol%, wherein that you have to flow in the atmosphere during firing two It is a manufacturing method of a secondary battery positive electrode material.

  In the method for producing a positive electrode material for a sodium secondary battery according to the present invention, the y is 0.65 ≦ y ≦ 0.80, the z is 0.10 ≦ z ≦ 0.20, and the 1-yz is 0.10. It is preferable that the range is ≦ 1-yz ≦ 0.25.

  In the manufacturing method of the sodium secondary battery positive electrode material of this invention, it is preferable that a calcination temperature is 700-900 degreeC, and it is more preferable that it is 800-900 degreeC.

  In the method for producing a sodium secondary battery positive electrode material of the present invention, the oxygen concentration in the atmosphere during firing is preferably 10 to 30% by volume. Moreover, it is preferable that gas flows in the atmosphere at the time of baking.

  According to the method for producing a positive electrode material for a sodium secondary battery of the present invention, the above-mentioned specific composition, the firing temperature is set to the above-mentioned specific range, and the atmosphere during firing is controlled, whereby the conventional sodium secondary battery is controlled. It is possible to provide a sodium secondary battery having a high charge / discharge capacity as compared with the battery and a high capacity retention rate.

Sodium secondary battery electrode, as an active material, using a positive electrode material for sodium secondary batteries obtained by the method for producing a cathode material for a sodium secondary battery according to any one of claims 1 to 4.

According to the electrode for the sodium secondary battery, can be compared with the conventional sodium secondary battery, it provides a sodium secondary battery having a high capacity maintenance rate and has a high charge-discharge capacity.

The sodium secondary battery includes a positive electrode composed of the sodium secondary battery electrode.
The sodium secondary battery preferably includes a negative electrode containing Sn or a Sn compound.

According to the sodium secondary battery, it is possible to provide a sodium secondary battery having a high capacity maintenance rate and has a high charge-discharge capacity as compared with the conventional sodium secondary battery.

The sodium secondary battery can be used for electrical equipment.

According to the present invention, sodium-containing transition metal oxide represented by a composition formula _{Na x (Mn y Co 1-} y-z Ni z) O 2, composition ratio, 0.5 <x ≦ 1.0 0.60 ≦ y ≦ 0.80, 0.05 ≦ z ≦ 0.20, 0.05 ≦ 1-yz ≦ 0.25, and a sodium secondary battery positive electrode material Thus, it is possible to provide a sodium secondary battery having a high charge / discharge capacity and a high capacity retention rate as compared with the conventional case.

It is a graph which shows the relationship between the atomic ratio of manganese (Mn) of samples A, G, J, K, L, M, and N and the initial discharge capacity. In the composition of Mn—Co—Ni, a region showing a high initial discharge capacity of 150 mAh / g or more, a region showing a high capacity maintenance rate of 15th cycle capacity retention rate (15 ^th / 1 ^st ) of 80% or more, It is a graph which shows. It is a graph which shows the relationship between the discharge capacity of a sodium secondary battery using the positive electrode material from which the baking temperature at the time of manufacture differs in the same composition as the sample J, and cycle number. It is a charging / discharging curve of the sodium secondary battery using the positive electrode material synthesize | combined with the same composition as the sample J at the baking temperature of 700 degreeC. It is a charging / discharging curve of the sodium secondary battery using the positive electrode material synthesize | combined with the same composition as the sample J at the calcination temperature of 900 degreeC. It is the XRD pattern of each sodium containing transition metal oxide synthesize | combined with the same composition as the sample J at the baking temperature of 600 degreeC, 700 degreeC, and 800 degreeC. It is an electron micrograph of each sodium containing transition metal oxide synthesize | combined by the same composition as the sample J at baking temperature (a) 900 degreeC and (b) 700 degreeC.

  Hereinafter, the sodium secondary battery positive electrode material of the present invention, the method for producing the sodium secondary battery positive electrode material, the sodium secondary battery electrode using the sodium secondary battery positive electrode material, and the sodium secondary battery equipped with the sodium secondary battery electrode An embodiment of a secondary battery and an electric device using the sodium secondary battery will be described.

Sodium secondary battery positive electrode material of the present invention comprises sodium-containing transition metal oxide represented by a composition formula _{Na x (Mn y Co 1-} y-z Ni z) O 2, Na atomic ratio of the composition formula x is 0.5 <x ≦ 1.0, Mn atomic ratio y is 0.60 ≦ y ≦ 0.80, Ni atomic ratio z is 0.05 ≦ z ≦ 0.20, Co atomic ratio 1− yz is 0.05 <= 1-yz <= 0.25. In the composition formula, the Mn atom number ratio y is 0.65 ≦ y ≦ 0.80, the Ni atom number ratio z is 0.10 ≦ z ≦ 0.20, and the Co atom number ratio 1-yz is 0.00. It is more preferable that 10 ≦ 1-yz ≦ 0.25.
By using a positive electrode material having this composition range as an active material, a sodium secondary battery having a high charge / discharge capacity and a high capacity retention rate as compared with the conventional one can be obtained. Specifically, the initial discharge capacity can be set to 150 mAh / g or more and the capacity maintenance ratio (15 ^th / 1 ^st ) of the 15th cycle can be set to 80% or more, and further, the initial discharge capacity can be set to 200 mAh / g or more. it can.
If the manganese (Mn) atomic ratio y is smaller than 0.6, it is not preferable because sufficient initial discharge capacity cannot be obtained. When the manganese (Mn) atomic ratio y is larger than 0.8, the initial discharge capacity is increased, but the capacity retention rate is lowered, which is not preferable.
Further, when the nickel (Ni) atomic ratio z is smaller than 0.05, a sufficient initial discharge capacity cannot be obtained, which is not preferable. On the other hand, when the nickel (Ni) atomic number ratio z is larger than 0.20, a sufficient capacity retention rate cannot be obtained, which is not preferable. This is because nickel (Ni) undergoes oxidation-reduction represented by the following formula, which is effective for increasing the capacity, but the stability of the structure decreases as the amount of insertion and desorption of Na increases. This is probably because of this.

Further, when the cobalt (Co) atomic number ratio 1-yz is smaller than 0.05, a sufficient capacity retention rate cannot be obtained, which is not preferable. On the other hand, when the cobalt (Co) atomic ratio 1-yz is larger than 0.25, the charge / discharge region is increased in potential, so that the energy density of the battery can be improved, but the electrolytic solution is likely to be decomposed. This is not preferable because it is difficult to obtain sufficient life characteristics.
Further, when the sodium (Na) atomic number ratio x is 0.5 or less, the Na source for forming the layered compound is insufficient, so that it is difficult to obtain a single phase during synthesis, which is not preferable. On the other hand, when the sodium (Na) atomic ratio x exceeds 1, it is not preferable because unreacted sodium compounds are likely to remain in the active material.

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

Sodium secondary battery positive electrode material of the present invention _is made of a sodium-containing transition metal oxide represented by _{Na x (Mn y Co 1-} y-z Ni z) O 2, the sodium-containing transition metal oxides As raw materials, at least one kind of sodium metal or sodium compound, at least one kind of manganese metal or manganese compound, at least one kind of cobalt metal or cobalt compound, at least one kind of nickel metal or nickel compound, Na _x (Mn _y Co _1-yz Ni _z ) O ₂ (wherein, the Na atom number ratio x is 0.5 <x ≦ 1.0, the Mn atom number ratio y is 0.65 ≦ y ≦ 0.80, Ni The atomic ratio z is 0.05 ≦ z ≦ 0.20, and the Co atomic ratio 1-yz is 0.05 ≦ 1-yz ≦ 0.25). Weighing and And the mixture can be synthesized by firing.

More preferably, the sodium-containing transition metal oxide forming the sodium secondary battery positive electrode material of the present invention contains, as a raw material, at least one kind of sodium metal or sodium compound, at least one kind of manganese metal or manganese compound, cobalt metal or at least one cobalt compound, at least one nickel metal or a nickel _{compound, Na x (Mn y Co 1} -y-z Ni z) O 2 ( provided that where each of the Na atomic ratio x 0.5 <x ≦ 1.0, Mn atomic ratio y is 0.65 ≦ y ≦ 0.80, Ni atomic ratio z is 0.10 ≦ z ≦ 0.20, Co atomic ratio 1-yz is 0.05. It can synthesize | combine by weighing and mixing so that it may become a chemical composition represented by <= 1-yz <0.25), and baking this mixture.

  The firing temperature can be in the range of 500 to 1000 ° C, more preferably in the range of 700 to 900 ° C, and still more preferably in the range of 800 to 900 ° C. By setting it as this calcination temperature, the sodium secondary battery positive electrode material which has a high charge retention capacity and a high capacity | capacitance maintenance factor compared with the past can be obtained. When the firing temperature is less than 500 ° C., the firing time becomes long and the practicality is lacking. On the other hand, if the firing temperature exceeds 1000 ° C., the crystal grains tend to be large, and the discharge capacity and capacity retention during charge / discharge are lowered, which is not preferable.

The atmosphere during firing may be a non-oxygen atmosphere (for example, a reducing atmosphere or an inert atmosphere), but is preferably in the presence of oxygen (for example, in air or an oxygen-containing nitrogen atmosphere). As for the density | concentration of oxygen, it is more preferable that it is the range of 10-30 volume%, and it is further more preferable that it is 15-25 volume%. In addition, it is preferable that the atmosphere at the time of baking always flows.
Although the gas flow rate at the time of a flow is not specifically limited, From the uniformity of positive electrode material, it is preferable that a gas flow rate is 10-500 mL / min.
By controlling the atmosphere during firing so as to achieve the oxygen concentration described above, the oxygen deficiency of the positive electrode material is reduced, and a sodium secondary battery positive electrode material having a high charge / discharge capacity can be obtained. If the oxygen concentration is less than 10% by volume, the amount of oxygen supplied during firing is insufficient and the sample is difficult to synthesize uniformly. Conversely, if the oxygen concentration exceeds 30% by volume, an excessive oxidizing atmosphere tends to occur. May not be obtained.

As the sodium raw material, at least one of sodium (metallic sodium) and a sodium compound is used. The sodium compound is not particularly limited as long as it contains sodium. For example, acetate such as CH ₃ COONa, CH ₃ COONa · 3H ₂ O, nitrate such as NaNO ₃ , hydroxide such as NaOH, Na ₂ Examples thereof include oxides such as O and Na ₂ O ₂ and carbonates such as Na ₂ CO ₃ . Or the compound etc. which are already sodium manganese oxide and sodium nickel oxide are mentioned.

As the manganese raw material, at least one of manganese (metallic manganese) and a manganese compound is used. The manganese compound is not particularly limited as long as it contains manganese, and examples thereof include oxides such as MnO, Mn ₂ O ₃ , Mn ₃ O ₄ , and MnO ₂ , and hydroxides such as MnOH and MnOOH. .

As the cobalt raw material, at least one of cobalt (metal cobalt) and a cobalt compound is used. The cobalt compound is not particularly limited as long as it contains cobalt, and examples thereof include oxides such as CoO, Co ₂ O ₃ , and Co ₃ O ₄ . Or the hydroxide etc. which are already manganese cobalt compounds are mentioned.

  As the nickel raw material, at least one of nickel (metallic nickel) and a nickel compound is used. The nickel compound is not particularly limited as long as it contains nickel, and examples thereof include oxides such as NiO and hydroxides such as NiOH and NiOOH. Or the hydroxide already used as the manganese nickel compound, the hydroxide used as the manganese cobalt nickel compound, etc. are mentioned.

First, a mixture containing these is prepared. The mixing ratio of the respective elements _{are, Na x (Mn y Co 1} -y-z Ni z) O 2 ( although Shikichu, Na atomic ratio x is 0.5 <x ≦ 1.0, Mn atomic ratio y Is 0.60 ≦ y ≦ 0.80, Ni atom number ratio z is 0.05 ≦ z ≦ 0.20, Co atom number ratio 1-yz is 0.05 ≦ 1-yz ≦ 0.25. ) So that the chemical composition is the same. Or _{Na x (Mn y Co 1-} y-z Ni z) O 2 ( although Shikichu, Na atomic ratio x is 0.5 <x ≦ 1.0, the number of Mn atomic ratio y is 0.65 ≦ y ≦ 0.80, Ni atomic ratio z is 0.10 ≦ z ≦ 0.20, and Co atomic ratio 1−yz is 0.10 ≦ 1-yz ≦ 0.25). It is more preferable to mix them. Further, since sodium easily volatilizes during heating, it is better to make the amount slightly charged, and preferably 0.6 <x ≦ 1.0. Moreover, a mixing method is not specifically limited as long as these can be mixed uniformly, For example, what is necessary is just to mix by a wet type or a dry type using well-known mixers, such as a mixer.

  The mixture is then fired. The firing temperature is in the above range. The firing atmosphere is not particularly limited, and may be usually performed in an oxidizing atmosphere or air.

  The firing time can be appropriately changed according to the firing temperature and the like. The cooling method is not particularly limited, but may be natural cooling (cooling in the furnace) or slow cooling.

  After firing, the fired product may be pulverized by a known method as necessary, and the above firing step may be performed. However, in order to suppress sodium volatilization, it is preferable to perform firing once. Note that the degree of pulverization may be appropriately adjusted according to the firing temperature and the like.

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

  The positive electrode of the half-cell 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 usually 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.

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 reduced. On the other hand, charge and discharge can be performed at a potential equal to or higher than the precipitation potential of sodium, and therefore, the possibility of dendrite precipitation is reduced, which is preferable in terms of safety.

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 conditions for the heat treatment for doping sodium ions, it is possible to dope the negative electrode material with sodium even at a low temperature. However, since the reaction rate is slow, it is preferably at 20 to 150 ° C. for at least 1 hour. 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>
The positive electrode comprising the sodium secondary battery electrode of the present invention can be used to make the sodium secondary battery of the present invention.
The sodium secondary battery of the present invention can use the positive electrode and the negative electrode.
The electrolytic solution is not particularly limited as a solvent, but cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate, ethers such as tetrahydrofuran, hydrocarbons such as hexane, γ-butyl, etc. Lactones such as lactones 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 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 sodium manganese cobalt nickel composite oxide>
Sodium carbonate (Na ₂ CO ₃ ) powder having a purity of 99% or more, manganese (II, III) (Mn ₃ O ₄ ), nickel manganese cobalt hydroxide (NiMnCo) OH ₂ , Na: (Mn + Co + Ni) = Weighing was performed so that the atomic ratio of 1: 1 and the atomic ratios of Mn, Co and Ni were as shown in Table 1. After mixing these in a mortar, they were filled in an alumina crucible and baked in the air at 900 ° C. for 10 hours using an electric furnace. Thereafter, it was naturally cooled in an electric furnace to obtain a sodium manganese cobalt nickel composite oxide.

<Test 1: Comparison of initial discharge capacity and capacity maintenance rate of each sample>
Charge-discharge characteristics of the resulting _{Na 1 (Mn y Co 1-} y-z Ni z) O 2 was 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. Table 2 shows the initial discharge capacity and the capacity retention rate at 15 cycles of each sample.

  From the results in Table 2, high initial discharge capacities of 150 mAh / g or more were obtained for samples A, B, C, D, E, J, K, L, M, and N. In particular, in Sample J, a very high initial discharge capacity of 200 mAh / g or more was obtained. From this result, it can be seen that a high initial discharge capacity can be obtained with a transition metal oxide having a composition containing about 65% or more of Mn by atomic ratio and containing Ni as an essential component.

FIG. 1 shows the atomic ratios of manganese (Mn) in samples A, G, J, K, L, M, and N, each containing cobalt (Co) and nickel (Ni) and having different atomic ratios of manganese (Mn). It is a graph which shows the relationship of initial stage discharge capacity.
From this graph, it can be said that the atomic ratio of manganese (Mn) should be about 60% or more in order to achieve the initial discharge capacity of 150 mAh / g.

In addition, a high capacity retention rate of 80% or more was obtained even after 15 cycles of Samples A, B, D, F, J, and M. From this result, it can be seen that a high capacity retention ratio can be achieved in a composition containing Co as an essential component and having an Ni atomic ratio of about 25% or less.
The reason for this is considered that Co is oxidized and reduced at a high potential, so that the structure can be stabilized to a high potential. In addition, since Ni is oxidized and reduced represented by the following formula, it is effective for increasing the capacity. However, it is considered that the stability of the structure is lowered by increasing the amount of insertion and desorption of Na.

FIG. 2 shows a region showing a high initial discharge capacity of 150 mAh / g or more in the composition of Mn—Co—Ni, and a high capacity maintenance rate of 15% cycle capacity retention rate (15 ^th / 1 ^st ) of 80% or more. It is a graph which shows the area | region which shows.
According to the results of the above test, there are a high initial discharge capacity region and a high capacity retention rate region as shown in Table 2. The composition range having a high initial discharge capacity and a high capacity retention rate is a range where the high initial discharge capacity region and the high capacity retention rate region shown in FIG. 2 overlap.
From a range these two regions _{overlap, Na x (Mn y Co 1} -y-z Ni z) in _{O 2} sodium-containing transition metal oxide represented by, Na atomic ratio x is 0.5 <x ≦ 1. 0, Mn atomic ratio y is 0.60 ≦ y ≦ 0.80, Ni atomic ratio z is 0.05 ≦ z ≦ 0.20, Co atomic ratio 1-yz is 0.05 ≦ 1- It can be seen that both high initial discharge capacity and high capacity retention ratio can be achieved in the range of yz ≦ 0.25.
Samples A, B, D, J, and M were able to achieve both an initial discharge capacity of 150 mAh / g or more and a capacity retention rate of 80% or more (15 ^th / 1 ^st ). In particular, Sample J showed very excellent values for both the initial discharge capacity and the capacity retention rate as compared with the conventional material.

<Test 2: Cycle characteristics of samples prepared at different firing temperatures>
Next, the influence on the capacity retention rate due to the difference in the firing temperature when synthesizing the sodium manganese cobalt nickel composite oxide was examined. The composition of the sample was the same as that of Sample J in Table 1. The results are shown in Table 3 and FIG.

As shown in Table 3, as the firing temperature increased, the capacity retention rate after 40 cycles was improved. The initial discharge capacity was the highest 220 mAh / g when fired at 800 ° C.
From this result, in order to obtain a high initial discharge capacity and a high capacity retention rate, it can be said that the firing temperature is preferably 700 to 900 ° C, more preferably 800 to 900 ° C.

<Test 3: Charge / Discharge Curves of Samples Produced at Different Firing Temperatures>
Next, FIGS. 4 and 5 show charge / discharge curves of a sample (J-2) fired at 700 ° C. with the same composition as the sample J and a sample (J-4) fired at 900 ° C. with the same composition as the sample J.

  As shown in FIGS. 4 and 5, the sample (J-4) fired at 900 ° C. had a smaller polarization during charge / discharge than the sample (J-2) fired at 700 ° C. This is presumably because high-temperature firing has higher crystallinity.

<XRD pattern and electron micrograph (SEM photograph) of samples prepared at different firing temperatures>
Further, samples (J-1, J-2, J-3) obtained at the firing temperatures of 600 ° C., 700 ° C., and 800 ° C. shown in Table 3 were used as X-ray diffractometers (manufactured by MAC Science, CuKα ₁ line). X-ray diffraction measurement was performed using λ = 1.54056 mm) to evaluate crystallinity. Furthermore, the crystal | crystallization of the sample (J-2) baked at 700 degreeC and the sample (J-4) baked at 900 degreeC was confirmed using the electron micrograph (SEM). The XRD pattern is shown in FIG. 6, and the SEM photograph is shown in FIG.

From the XRD pattern, it can be seen that the crystal structure of the composite has changed depending on the firing temperature. It can be seen that the 800 ° C. calcined sample (J-3) has a smaller peak width near 15 °, and has higher crystallinity than the 600 ° C. calcined sample (J-1) and 700 ° C. calcined sample (J-2).
Moreover, even if it sees a SEM photograph, it turns out that the 900 degreeC baking sample (J-4) has higher crystallinity than the 700 degreeC baking sample (J-2).
This shows that a sample with higher crystallinity can be obtained as the firing temperature increases.

  When it has high crystallinity, the ion conductivity in the crystal is improved and the interface resistance is lowered, which contributes to the improvement of battery characteristics.

<Test 4: Optimization of atmosphere during firing>
Next, Samples A-1 to A-4 were prepared under the same conditions as Sample A, except that the atmosphere shown in Table 4 was used with the same composition as Sample A, and these samples were used as positive electrode materials. The initial discharge capacity was measured under the same conditions as in Test 1. The firing temperature was 900 ° C. Table 4 summarizes the initial discharge capacity.
Note that “with flow” at the time of firing means that the value of the gas flow rate is 100 mL / min.

As shown in Table 4, the sample (A-1) produced with 20% oxygen-80% nitrogen (with flow) in the firing atmosphere has an initial discharge capacity as compared with the sample without flow (A-2). Was found to improve. In addition, a sample (A-3) produced with 5% oxygen-95% nitrogen (no flow) in a firing atmosphere and a sample (A-4) produced with 40% oxygen-60% nitrogen (no flow) were 20 Compared to the sample (A-2) prepared with% oxygen-80% nitrogen (no flow), the initial discharge capacity was lowered. Therefore, it can be seen that the oxygen concentration at the time of firing is preferably in the range of more than 5% and less than 40.
From these results, it can be seen that the amount of oxygen in the atmosphere during firing is an important factor for obtaining a high initial discharge capacity.

<Test 5: Test with all batteries>
Using the above J as an active material, the positive electrode composition was prepared by mixing 90% by mass of active material, 5% by mass of AB, 2.5% by mass of CMC, and 2.5% by mass of acrylic resin to prepare a slurry mixture having a thickness of 20 μm. After coating and drying on the aluminum foil, the aluminum foil and the coating film were closely bonded with a roll press machine, and then heat-treated (under reduced pressure at 160 ° C. for 10 hours 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 the negative electrode active material precursor, 2% by mass of KB, and 18% by mass of a PI binder, and an aluminum foil having a thickness of 40 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 the above positive electrode, negative electrode and 1 mol / L NaPF ₆ (EC: DEC = 1: 1 vol.%) As the electrolyte, a coin cell of a sodium ion total battery (nominal capacity 2 mAh) was prepared and cut in a 30 ° C. environment. When charging / discharging was performed at an off potential of 1-4.4 V, it was confirmed that the battery functions as a battery.

  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 (4)

At least one sodium metal or sodium compound, at least one manganese metal or manganese compound, at least one of cobalt metal or cobalt compound, at least one nickel metal or a nickel _{compound, Na x (Mn y Co 1} -y _-z Ni _{z) O 2} (although Shikichu, 0.5 <x ≦ 1.0,0.6 0 ≦ y ≦ 0.80,0.05 ≦ z ≦ 0.20,0.05 ≦ 1-y -Z ≦ 0.25) is mixed so that the chemical composition is represented, and the mixture is synthesized by firing at 500 to 1000 ° C. ,
Method for producing a sodium secondary battery positive electrode material gas oxygen concentration in the atmosphere during firing is 10 to 30% by volume, it characterized that you have to flow. The y is in the range of 0.65 ≦ y ≦ 0.80, the z is in the range of 0.10 ≦ z ≦ 0.20, and the 1-yz is in the range of 0.10 ≦ 1−yz ≦ 0.25. The manufacturing method of the sodium secondary battery positive electrode material of Claim 1 characterized by the above-mentioned. The said baking temperature is 700-900 degreeC, The manufacturing method of the positive electrode material for sodium secondary batteries of Claim 1 or 2 characterized by the above-mentioned. The said baking temperature is 800-900 degreeC, The manufacturing method of the positive electrode material for sodium secondary batteries of Claim 3 characterized by the above-mentioned.