Method for manufacturing a positive electrode active material, method for manufacturing a sodium ion battery, positive electrode active material, and sodium ion battery

Abstract

To disclose a method of increasing the capacity of a P2 type positive electrode active material.SOLUTION: A method of manufacturing a positive electrode active material according to the present disclosure includes obtaining an Na-containing transition metal oxide having a P2 type structure, and further doping the Na-containing transition metal oxide with Na.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present application discloses a method for manufacturing a positive electrode active material, a method for manufacturing a sodium ion battery, a positive electrode active material, and a sodium ion battery. [Background technology]

[0002] As disclosed in Patent Document 1, a sodium-containing transition metal oxide having a P2 type structure is known as a positive electrode active material. Here, the sodium-containing transition metal oxide having a P2 type structure is used as a positive electrode active material for, for example, a sodium ion battery. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-201588 Summary of the Invention [Problem to be solved by the invention]

[0004] It is difficult to say that the potential of conventional positive electrode active materials having a P2 structure has been fully exploited in terms of reversible capacity. [Means for solving the problem]

[0005] The present application discloses the following aspects as means for solving the above problems. <Aspect 1> A method for producing a positive electrode active material, Obtaining a sodium-containing transition metal oxide having a P2 type structure, and Further doping the Na-containing transition metal oxide with Na. A method for producing a positive electrode active material. <Aspect 2> The manufacturing method of embodiment 1, By bringing a reducing solution containing Na ions into contact with the Na-containing transition metal oxide, the Na-containing transition metal oxide is further doped with Na. Production method. <Aspect 3> A method for manufacturing a sodium ion battery, comprising: manufacturing a positive electrode active material by the method of Aspect 1 or 2; obtaining a positive electrode active material layer using the manufactured positive electrode active material; and obtaining a sodium ion battery using the positive electrode active material layer. A method for manufacturing a sodium ion battery. <Aspect 4> A positive electrode active material, comprising: having a P2-type structure; Na a Mn x-p Ni y-q Co z-r M p+q+r O2 (where 0.70 < a ≤ 1.40, x + y + z = 1, 0 ≤ p + q + r < 0.17, and M is at least one element selected from B, Mg, Al, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W), having a chemical composition represented by Positive electrode active material. <Aspect 5> A sodium ion battery, comprising a positive electrode active material layer, an electrolyte layer, and a negative electrode active material layer, where the positive electrode active material layer contains the positive electrode active material of Aspect 4. Sodium ion battery.

Advantages of the Invention

[0006] The positive electrode active material of the present disclosure has a high capacity.

Brief Description of the Drawings

[0007] [Figure 1] An example of the process for manufacturing a positive electrode active material is shown. [Figure 2] An example of the process for manufacturing a sodium ion battery is shown. [Figure 3] 1 shows a schematic diagram of an example of the configuration of a sodium ion battery. [Figure 4] 1 shows the X-ray diffraction patterns of the positive electrode active materials of Comparative Example, Example 1, and Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0008] 1. Manufacturing method of positive electrode active material As shown in FIG. 1, a method for producing a positive electrode active material according to one embodiment includes obtaining a Na-containing transition metal oxide having a P2-type structure (step S1), and further doping the Na-containing transition metal oxide with Na (step S2).

[0009] 1.1 Process S1 In step S1, the Na-containing transition metal oxide having a P2 type structure can be obtained, for example, by obtaining a precursor containing Na and a transition metal element, optionally shaping the precursor, optionally pre-firing the precursor, and then performing main firing.

[0010] In step S1, the precursor may be obtained by, for example, mixing a transition metal source and a Na source. The transition metal source may be, for example, a transition metal salt such as a carbonate, sulfate, nitrate, or acetate, or a transition metal compound such as a transition metal hydroxide. The transition metal element may be at least one of Mn, Ni, and Co. The transition metal source may be Me(CO3) x (Me is at least one transition metal element selected from Mn, Ni, and Co, and x is the valence of Me), or a salt represented by Me(SO4) x or a salt represented by Me(NO3) x or a salt represented by Me(CH3COO) x or a salt represented by Me(OH) xThe Na source may be, for example, a Na salt such as a carbonate or a sulfate, or a Na compound such as sodium oxide or sodium hydroxide. The amount of the Na source to be mixed with the transition metal source may be determined taking into account the amount of Na lost during subsequent calcination. In step S1, the surfaces of particles made of the transition metal source may be coated with the Na source to obtain coated particles as precursors. Here, the coated particles may be obtained by coating at least a portion of the surfaces of particles made of the transition metal source with the Na source. The coated particles may be obtained by coating 40 area % or more, 50 area % or more, 60 area % or more, or 70 area % of the surfaces of particles made of the transition metal source with the Na source.

[0011] In step S1, the precursor may be obtained by mixing, for example, a transition metal source, a Na source, and an M source containing the element M. Here, the element M is at least one selected from B, Mg, Al, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W. The element M can further stabilize the P2 type structure. The M source may be, for example, a salt such as a nitrate, sulfate, carbonate, or acetate, or a compound other than a salt such as a hydroxide. The amount of the M source in the precursor may be appropriately determined depending on the target composition of the Na-containing transition metal oxide after firing.

[0012] In step S1, the precursor may be obtained by, for example, obtaining a precipitate using an ion source capable of forming a precipitate in an aqueous solution with transition metal ions and a transition metal compound, and then mixing the precipitate with a Na source and, optionally, an element M source. Examples of ion sources capable of forming a precipitate with transition metal ions include sodium salts such as sodium carbonate and sodium nitrate, sodium hydroxide, and sodium oxide. Examples of transition metal compounds include salts and hydroxides such as nitrates, sulfates, carbonates, and acetates. In step S1, the ion source and the transition metal compound may be prepared as solutions, and then the solutions may be added dropwise and mixed to obtain a precipitate. In this case, various sodium compounds may be used as bases, and aqueous ammonia or the like may be added to adjust the basicity. More specifically, in step S1, the precipitate may contain at least one transition metal element selected from Mn, Ni, and Co. The precipitate may be obtained by a solution method such as a coprecipitation method or a sol-gel method. In the case of the coprecipitation method, for example, Me(SO4) x An aqueous solution of Na2CO3 and an aqueous solution of Na2CO3 are prepared, and the respective aqueous solutions are added dropwise and mixed to obtain a precipitate. After collecting the precipitate, the precipitate may be mixed with a Na source. The amount of Na source to be mixed with the precipitate may be determined taking into account the amount of Na lost during subsequent calcination. Alternatively, the surfaces of particles made of the precipitate may be coated with a Na salt to obtain coated particles as precursors. The coverage rate and other details of the coated particles are as described above.

[0013] In step S1, the precursor obtained as described above is pre-baked at a temperature equal to or lower than that of the main baking. For example, pre-baking can be performed at a temperature lower than 700°C. The pre-baking time is not particularly limited. Alternatively, pre-baking may be omitted.

[0014] In step S1, the precursor may be calcined at a temperature of, for example, 700°C or higher and 1100°C or lower. The temperature is preferably 800°C or higher and 1000°C or lower. If the calcination temperature is too low, Na doping will not occur, and if the calcination temperature is too high, an O3 structure will likely form rather than a P2 structure. The temperature rise conditions from the pre-calcination temperature to the calcination temperature are not particularly limited. The calcination time is also not particularly limited, and may be, for example, 30 minutes to 10 hours. The calcination atmosphere is also not particularly limited, and may be, for example, an oxygen-containing atmosphere such as air or an inert gas atmosphere.

[0015] In step S1, after the main firing, the Na-containing transition metal oxide having a P2 type structure may be doped with the element M. That is, after synthesizing a Na-containing transition metal oxide having a P2 type structure that does not contain the element M, the oxide may be doped with the element M. The doping with the element M may be performed by, for example, ion exchange.

[0016] The Na-containing transition metal oxide having a P2-type structure obtained by step S1 may contain, for example, as constituent elements, at least one element selected from Mn, Ni, and Co, Na, and O. In particular, when the constituent elements contain at least Na, Mn, at least one of Ni and Co, and O, and especially when the constituent elements contain at least Na, Mn, Ni, Co, and O, the performance of the positive electrode active material is likely to be further improved. More specifically, the Na-containing transition metal oxide obtained by step S1 contains Na c Mn x-p Ni y-q Co z-r M p+q+rO2 (where 0 < c ≤ 0.70, x + y + z = 1, and 0 ≤ p + q + r < 0.17, and the element M is at least one selected from B, Mg, Al, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W). It may have a chemical composition represented by this. When the Na-containing transition metal oxide has such a chemical composition, the P2-type structure is likely to be maintained. In the above chemical composition, c is greater than 0, and may be 0.10 or more, 0.20 or more, 0.30 or more, 0.40 or more, 0.50 or more, or 0.60 or more. Also, x is 0 or more, may be 0.10 or more, 0.20 or more, 0.30 or more, 0.40 or more, or 0.50 or more, and is 1.00 or less, and may be 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, or 0.50 or less. Also, y is 0 or more, may be 0.10 or more or 0.20 or more, and is 1.00 or less, and may be 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, 0.30 or less, or 0.20 or less. Also, z is 0 or more, may be 0.10 or more, 0.20 or more, or 0.30 or more, and is 1.00 or less, and may be 0.90 or less, 0.80 or less, 0.70 or less, 0.60 or less, 0.50 or less, 0.40 or less, or 0.30 or less. The element M has little contribution to charge and discharge. In this regard, in the above chemical composition, since p + q + r is less than 0.17, it is easy to ensure a high charge and discharge capacity. p + q + r may be 0.15 or less, 0.13 or less, 0.11 or less, 0.09 or less, 0.07 or less, 0.06 or less, 0.05 or less, or 0.04 or less. On the other hand, since the element M is contained, the P2-type structure is likely to be stabilized. In this regard, in the above chemical composition, p + q + r is 0 or more, and may be greater than 0, 0.01 or more, 0.02 or more, or 0.03 or more. The composition of O is approximately 2, but it is not necessarily exactly 2.0 and is indefinite.

[0017] 1.2 Process S2 By undergoing the above-mentioned step S1, a Na-containing transition metal oxide having a P2-type structure can be obtained. However, according to the knowledge of the present inventors, it is difficult to obtain a sufficient amount of Na contained in the Na-containing transition metal oxide by simply undergoing the above-mentioned step S1. For example, the molar ratio of Na (above) in the Na-containing transition metal oxide after the above-mentioned calcination is only 0.70 or less, and the potential of the reversible capacity of the P2-type positive electrode active material cannot be fully utilized.

[0018] In contrast, in step S2, the Na-containing transition metal oxide obtained in step S1 is further doped with Na, thereby increasing the molar ratio of Na in the Na-containing transition metal oxide (the above-mentioned a) to more than 0.70. In step S2, for example, the Na-containing transition metal oxide may be further doped with Na without applying a driving force by voltage. For example, the Na-containing transition metal oxide may be doped with Na by contacting a Na doping source with the Na-containing transition metal oxide.

[0019] Specifically, in step S2, it is preferable to contact the Na-containing transition metal oxide with a reducing solution containing Na ions to further dope the Na-containing transition metal oxide. The "reducing solution" refers to a solution having reducing properties, and may be, for example, a solution containing an electrophile. The reducing solution may be obtained, for example, by dissolving an electrophile and a Na source in a solvent. The solvent may be any of various organic solvents capable of dissolving the electrophile and the Na source. The solvent is preferably, for example, an ether-based solvent such as tetrahydrofuran or dimethoxyethane. The electrophile may be any of various substances that dissolve in the above-mentioned solvents. The electrophile is preferably an aromatic organic compound such as biphenyl. The Na source may be any of various substances that dissolve in the above-mentioned solvents to generate Na ions. The Na source may be metallic sodium or a Na compound.

[0020] The concentrations of the electrophile and Na ions contained in the reducing solution may be appropriately determined depending on the desired doping amount. According to the inventors' findings, the greater the amount of Na ions contained in the reducing solution relative to the amount of Na-containing transition metal oxide contacted with the reducing solution, the greater the amount of Na doping of the Na-containing transition metal oxide. For example, when the Na-containing transition metal oxide is immersed in the reducing solution, the molar ratio of Na ions contained in the reducing solution to the Na-containing transition metal oxide immersed in the reducing solution (Na ions / Na-containing transition metal oxide) may be 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, 0.5 or more, 0.6 or more, 0.7 or more, or 0.8 or more, or may be 2.0 or less, 1.5 or less, 1.0 or less, 0.9 or less, 0.8 or less, 0.7 or less, 0.6 or less, 0.5 or less, 0.4 or less, 0.3 or less, or 0.2 or less. In particular, when the molar ratio (Na ions / Na-containing transition metal oxide) is 0.1 or more and 0.8 or less, a positive electrode active material with excellent performance is likely to be obtained. The molar ratio of the electrophile to the Na ions contained in the reducing solution (electrophile / Na ions) is not particularly limited, and may be, for example, 0.5 or more and 2.0 or less, 0.7 or more and 1.5 or less, or 0.9 or more and 1.1 or less.

[0021] In step S2, for example, simply contacting the Na-containing transition metal oxide with the reducing solution described above can further dope the Na-containing transition metal oxide with Na. The contact mode between the reducing solution and the Na-containing transition metal oxide is not particularly limited. For example, the Na-containing transition metal oxide may be immersed in the reducing solution, or the reducing solution may be sprayed onto the Na-containing transition metal oxide. The temperature during contact is also not particularly limited, and the solution may be heated or not heated. Furthermore, the Na-containing transition metal oxide may be immersed in the reducing solution and then stirred. The time for contacting the Na-containing transition metal oxide with the reducing solution is also not particularly limited, and may be appropriately determined depending on the desired doping amount. The contact time may be, for example, 1 minute or more, 30 minutes or more, or 1 hour or more, or 48 hours or less, 40 hours or less, or 30 hours or less.

[0022] 2.Cathode active material As described above, through steps S1 and S2, a cathode active material having a P2 structure (a P2 type Na-containing transition metal oxide) can be produced, which has a larger Na content and a higher capacity than conventional cathode active materials. The cathode active material obtained through steps S1 and S2 may have, for example, the following characteristics.

[0023] 2.1 Crystal structure The positive electrode active material has at least a P2 type structure (belonging to the space group P63mc). The positive electrode active material has the P2 type structure, and may also have a crystal structure other than the P2 type structure. Examples of crystal structures other than the P2 type structure include various crystal structures (P3 type structure, etc.) formed when Na is desorbed from the P2 type structure. The positive electrode active material may have the P2 type structure as the main phase, or may have a crystal structure other than the P2 type structure as the main phase. The crystal structure of the positive electrode active material may change depending on the charge / discharge state.

[0024] 2.2 Chemical composition The positive electrode active material may contain, as constituent elements, at least one element selected from Mn, Ni, and Co, Na, and O. In particular, when the constituent elements include at least Mn, at least one of Ni and Co, Na, and O, and especially when the constituent elements include at least Na, Mn, Ni, Co, and O, even higher performance is likely to be ensured. However, in the positive electrode active material, for example, Na may be almost completely released upon charging, and the molar concentration of Na may approach 0. The positive electrode active material may also contain the above-mentioned element M. The positive electrode active material may also contain other impurity elements.

[0025] The chemical composition of the positive electrode active material with P2 structure is Na a Mn x-p Ni y-q Co z-r M p+q+rIt may also be represented by O2 (where 0.70 < a ≤ 1.40, x + y + z = 1, 0 ≤ p + q + r < 0.17, and M is at least one element selected from B, Mg, Al, K, Ca, Ti, V, Cr, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W). In this chemical composition, a is greater than 0.70, and may be greater than 0.80, greater than 0.90, greater than 1.00, or greater than 1.00, and is at most 1.40, and may be at most 1.35, at most 1.30, at most  1.25, at most 1.20, at most 1.15, or at most 1.10. For x, y, z, p, q, r, and the composition of O, they may be the same as those exemplified as the chemical composition of the Na-containing transition metal oxide obtained in step S1, and the description thereof is omitted here.

[0026] 2.3 Shape [[ID=*5]] The positive electrode active material may be in the form of particles. The positive electrode active material particles may be solid particles, hollow particles, or may have voids. The positive electrode active material particles may be primary particles, or may be secondary particles formed by aggregation of a plurality of primary particles. The average particle diameter (D50) of the positive electrode active material particles may be, for example, 1 nm or more, 5 nm or more, or 10 nm or more, and may be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less. Note that the average particle diameter D50 referred to in the present application is the particle diameter (median diameter) at the integrated value of 50% in the volume-based particle size distribution determined by the laser diffraction / scattering method.

[0027] 2.4 Others The positive electrode active material may contain components resulting from the above manufacturing process as impurities. For example, the positive electrode active material may contain components derived from the reducing solution. Specifically, the positive electrode active material may contain an aromatic organic compound such as biphenyl. Further, the positive electrode active material may contain an ether compound such as tetrahydrofuran or dimethoxyethane.

[0028] 3. Manufacturing Method of Sodium Ion Battery The cathode active material produced as described above is used, for example, as the cathode active material of a sodium ion battery. A method for producing a sodium ion battery according to one embodiment may include, for example, as shown in FIG. 2 , producing a cathode active material by the production method of the present disclosure, obtaining a cathode active material layer using the produced cathode active material, and producing a sodium ion battery using the cathode active material layer. Thus, the method for producing a sodium ion battery according to the present disclosure may be performed by a conventional method, except that, after producing the cathode active material according to the present disclosure, a cathode active material layer is obtained using the cathode active material. For example, the method is as follows. (1) The cathode active material and the like of the present disclosure are dispersed in a solvent to obtain a cathode layer slurry. The solvent used in this case is not particularly limited, and water or various organic solvents can be used. The cathode layer slurry is then applied to the surface of a cathode current collector using a doctor blade or the like, and then dried to form a cathode active material layer on the surface of the cathode current collector, resulting in a cathode. (2) A negative electrode layer slurry is obtained by dispersing the negative electrode active material and the like in a solvent. The solvent used in this case is not particularly limited, and water or various organic solvents can be used. The negative electrode layer slurry is then applied to the surface of a negative electrode current collector using a doctor blade or the like, and then dried to form a negative electrode active material layer on the surface of the negative electrode current collector, resulting in a negative electrode. (3) The layers are stacked so that the electrolyte layer (solid electrolyte layer or separator) is sandwiched between the negative electrode and the positive electrode to obtain a laminate having, in this order, the negative electrode current collector, the negative electrode active material layer, the electrolyte layer, the positive electrode active material layer, and the positive electrode current collector. Other members such as terminals are attached to the laminate as necessary. (4) The laminate is housed in a battery case, and in the case of an electrolyte battery, the battery case is filled with an electrolyte, and the laminate is immersed in the electrolyte and sealed in the battery case to form a sodium ion battery. In the case of an electrolyte battery, the negative electrode active material layer, separator, and positive electrode active material layer may be impregnated with the electrolyte at the step (3) above.

[0029] 4. Sodium-ion battery The technology of the present disclosure also has an aspect as a sodium ion battery. For example, as shown in FIG. 3, a sodium ion battery 100 according to one embodiment has a positive electrode active material layer 10, an electrolyte layer 20, and a negative electrode active material layer 30, and the positive electrode active material layer 10 is characterized in that it contains the positive electrode active material of the present disclosure. As shown in FIG. 3, the sodium ion battery 100 may also include a positive electrode current collector 40 and a negative electrode current collector 50. The configuration of the sodium ion battery 100 other than the positive electrode active material is the same as that of a conventional battery, and may employ, for example, the configuration described in Patent Document 1 (JP 2012-201588 A). [Example]

[0030] As described above, one embodiment of the method for producing a positive electrode active material of the present disclosure has been described, but the method for producing a positive electrode active material of the present disclosure can be modified in various ways other than the above embodiment without departing from the gist thereof. Hereinafter, the technology of the present disclosure will be described in more detail with reference to examples, but the technology of the present disclosure is not limited to the following examples.

[0031] 1. Preparation of positive electrode active material 1.1 Coprecipitation synthesis of transition metal sources MnSO4·5H2O, NiSO4·6H2O, and CoSO4·7H2O were weighed to the desired composition ratio and dissolved in distilled water to a concentration of 1.2 mol / L to obtain the first solution. In a separate container, Na2CO3 was dissolved in distilled water to a concentration of 1.2 mol / L to obtain the second solution. Next, 500 mL of each of the first and second solutions was added dropwise at a rate of approximately 4 mL / min to a reaction vessel containing 1000 mL of pure water. After the addition, the mixture was stirred at 150 rpm for 1 hour at room temperature. The precipitate was washed with pure water and separated into solid and liquid using a centrifuge. The resulting precipitate was dried overnight at 120°C, crushed in a mortar, and then air-classified to remove fine particles, yielding mixed salt particles containing Mn, Ni, and Co (transition metal source).

[0032] 1.2 Mixing of transition metal source and sodium source (Na coating) Na2CO3 was stirred in distilled water using a stirrer until it was completely dissolved, to prepare an aqueous solution of Na2CO3. The mixed salt particles were mixed in the aqueous solution of Na2CO3 to prepare a slurry. The Na2CO3 and the mixed salt particles were then dried and mixed into Na 0.7 Mn 0.5 Ni 0.2 Co 0.3 The resulting slurry was dried by spray drying. Specifically, a spray drying apparatus DL410 was used, with a slurry delivery rate of 30 mL / min, an inlet temperature of 200°C, and a circulating air volume of 0.8 m 3 The surfaces of the mixed salt particles were coated with Na2CO3 under the conditions of 0.3 MPa spray air pressure and 0.5 MPa spraying speed.

[0033] 1.3 Sintering of coated particles The coated particles were fired in an electric furnace using an alumina crucible under atmospheric conditions. Specifically, the coated particles were subjected to the "first heating step," "pre-firing step," "second heating step," "main firing step," and "furnace cooling step" shown in Table 1 below. The fired product was then removed from the electric furnace at 250°C and pulverized in a mortar in a dry atmosphere with a dew point of -30°C or lower to obtain a sodium-containing transition metal oxide having a P2 structure.

[0034] [Table 1]

[0035] 1.4 Na-doped (Examples 1 and 2) Biphenyl was mixed and dissolved in tetrahydrofuran (THF) in a glove box (Ar atmosphere) to obtain a biphenyl solution at a concentration of 1 mol / L. Metallic Na was then added to the biphenyl solution in an amount equal to the moles of biphenyl, and the mixture was stirred for 2 hours to obtain a reduced solution containing 1 mol / L of Na ions. The Na-containing transition metal oxide was then added to the resulting reduced solution, immersed, and stirred for 24 hours. After stirring, the Na-containing transition metal oxide was washed with THF and subjected to solid-liquid separation by vacuum filtration. The resulting precipitate was dried overnight at 120°C to obtain a positive electrode active material (the Na-containing transition metal oxide further doped with Na). The molar ratio (Na ions / Na-containing transition metal oxide) of the Na ions contained in the reduced solution to the Na-containing transition metal oxide immersed in the reduced solution was varied as shown in Table 2 below to obtain the positive electrode active materials of Examples 1 and 2.

[0036] 1.5 Comparative Example Without doping with Na, the Na-containing transition metal oxide after cooling outside the furnace and pulverizing in a mortar was used as it was as the positive electrode active material.

[0037] 2. Identification of the chemical composition and crystalline structure of the positive electrode active material The chemical composition of each of the positive electrode active materials of Examples 1 and 2 and the Comparative Example was determined by ICP analysis. X Mn 0.5 Ni 0.2 Co 0.3 The positive electrode active materials of Examples 1 and 2 and the Comparative Example all had a chemical composition represented by O2, i.e., the transition metal composition ratios were the same but the Na composition ratios were different. Furthermore, X-ray diffraction measurements were performed on each of the positive electrode active materials of Examples 1 and 2 and the Comparative Example to identify their crystal structures. FIG. 4 shows the respective X-ray diffraction patterns. As shown in FIG. 4, the positive electrode active materials of Examples 1 and 2 and the Comparative Example all had a P2-type crystal structure.

[0038] 3. Coin Cell Fabrication The positive electrode active material, acetylene black (AB) as a conductive material, and PVdF as a binder were weighed out to a mass ratio of positive electrode active material:AB:PVdF = 85:10:5, and dispersed and mixed in N-methyl-2-pyrrolidone to obtain a positive electrode slurry. The positive electrode slurry was applied to an Al foil and vacuum dried overnight at 120 °C to obtain a positive electrode. A coin cell (CR2032) was fabricated using the obtained positive electrode, an electrolyte (solvent: EC / DMC, electrolyte: NaPF6, concentration: 1M), and a metallic Na foil as a negative electrode.

[0039] 4. Coin Cell Evaluation The coin cell was charged and discharged in a thermostatic bath maintained at 25° C. at a voltage range of 1.5-4.5 V and a 0.1 C rate (1 C=200 mA / g), and the initial charge capacity and initial discharge capacity were measured.

[0040] 5. Evaluation Results Table 2 below shows the "molar ratio (Na ion / Na-containing transition metal oxide) between the Na ions contained in the reducing solution and the Na-containing transition metal oxide immersed in the reducing solution" in the Na doping step, and the amount of Na determined by ICP analysis (Na X Mn 0.5 Ni 0.2 Co 0.3 The graph shows the X value of O2 and the initial charge / discharge capacity of the coin cell.

[0041] [Table 2]

[0042] As shown in Table 2, the positive electrode active material according to the Comparative Example, which was not doped with Na after the main firing, had an X value below 0.70, whereas the positive electrode active materials according to Examples 1 and 2, which were further doped with Na in a separate step after the main firing, had an X value above 0.70. As a result, the coin cells according to Examples 1 and 2 had significantly higher initial charge capacities and initial discharge capacities than the coin cells according to the Comparative Example. In other words, it was found that by further doping Na after obtaining a Na-containing transition metal oxide having a P2 structure, it is possible to maximize the capacity potential of a P2-type positive electrode active material.

[0043] In the above examples, the case where coated particles containing Na and a transition metal are obtained through coprecipitation and spray drying is illustrated, but the conditions for preparing the precursor before the main calcination are not limited thereto. Furthermore, in the above examples, the case where coated particles and a P2-type Na-containing transition metal oxide having a specific chemical composition are prepared and the Na-containing transition metal oxide is further doped with Na is illustrated, but the chemical composition of the P2-type positive electrode active material is not limited thereto. Furthermore, in the above examples, the case where Na is doped using a specific reducing solution is illustrated, but the type of reducing solution is not limited thereto. In addition, various conditions can be changed after the main calcination as long as Na can be further doped in a step separate from the main calcination. [Explanation of symbols]

[0044] 10 Cathode active material layer 20 Electrolyte layer 30 Negative electrode active material layer 40 Positive electrode current collector 50 Negative electrode current collector 100 sodium-ion batteries

Claims

1. A method for producing a positive electrode active material, Obtaining a Na-containing transition metal oxide having a P2 type structure; and and contacting the Na-containing transition metal oxide with a reducing solution containing Na ions to further dope the Na-containing transition metal oxide with Na. A method for producing a positive electrode active material.

2. A method for manufacturing a sodium ion battery, comprising: Producing a positive electrode active material by the method of claim 1; Obtaining a positive electrode active material layer using the produced positive electrode active material; and Obtaining a sodium ion battery using the positive electrode active material layer. How sodium-ion batteries are manufactured.

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