Method for producing positive electrode active material, and positive electrode active material

Abstract

To provide a method capable of improving cycle characteristics and rate characteristics of an O2 type positive electrode active material.SOLUTION: The method for producing a positive electrode active material according to the present disclosure includes: obtaining a first compound containing at least one element of Mn, Ni and Co; mixing the first compound, a second compound containing Na, and a third compound containing at least one element M selected from B, Mg, Al, K, Ca, Ti, V, Cr, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo and W to obtain a mixture; firing the mixture to obtain a Na-containing oxide having a P2 type structure; and exchanging at least part of Na of the Na-containing oxide for Li by ion exchange to obtain a Li-containing oxide having an O2 type structure.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This application discloses a method for manufacturing a positive electrode active material and a positive electrode active material.

Background Art

[0002] Positive electrode active materials having an O2-type structure are known. As disclosed in Patent Document 1, a positive electrode active material having an O2-type structure can be obtained by ion-exchanging at least a part of Na in a Na-containing transition metal oxide having a P2-type structure with Li.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Conventional positive electrode active materials having an O2-type structure have room for improvement in terms of capacity, cycle characteristics, and rate characteristics.

Means for Solving the Problems

[0005] As means for solving the above problems, this application discloses the following multiple aspects. <Aspect 1> A method for manufacturing a positive electrode active material, comprising: obtaining a first compound containing at least one element among Mn, Ni, and Co; mixing the first compound, a second compound containing Na, and a third compound containing at least one element M selected from B, Mg, Al, K, Ca, Ti, V, Cr, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W to obtain a mixture; firing the mixture to obtain a Na-containing oxide having a P2-type structure; and By ion exchange, at least a part of Na in the Na-containing oxide is exchanged with Li to obtain a Li-containing oxide having an O2-type structure. <Aspect 2> Using a transition metal ion and an ion source capable of forming a precipitate in an aqueous solution, and a transition metal compound, a precipitate is obtained as the first compound by a coprecipitation method. The production method of Aspect 1. <Aspect 3> The first compound is a salt containing at least one element among Mn, Ni, and Co. The second compound is a salt containing Na. The third compound is a salt containing element M. The production method of Aspect 1 or 2. <Aspect 4> The Li-containing oxide is Li a Na b Mn x-p Ni y-q Co z-r M p+q+r O2 (where 0 < a ≤ 1.00, 0 ≤ b ≤ 0.20, x + y + z = 1, 0.03 ≤ p + q + r < 0.17). The production method of any one of Aspects 1 to 3. <Aspect 5> A positive electrode active material, Having an O2-type structure, Li a Na b Mn x-p Ni y-q Co z-r M p+q+r O2 (where 0 < a ≤ 1.00, 0 ≤ b ≤ 0.20, x + y + z = 1, 0.03 ≤ p + q + r < 0.17, and M is at least one selected from B, Mg, Al, K, Ca, Ti, V, Cr, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W), and The ratio of the aggregation region of element M on the surface of the active material is less than 0.01 mm per 1.00 mm of the surface of the active material. 2 per 2 less than.

Advantages of the Invention

[0006] The positive electrode active material of the present disclosure has excellent capacity, cycle characteristics, and rate characteristics.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0008] 1. Method for manufacturing a positive electrode active material As shown in FIG. 1, a method for manufacturing a positive electrode active material according to an embodiment includes obtaining a first compound containing at least one element among Mn, Ni, and Co (step S1), mixing the first compound, a second compound containing Na, and a third compound containing at least one element M selected from B, Mg, Al, K, Ca, Ti, V, Cr, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W to obtain a mixture (step S2), firing the mixture to obtain a Na-containing oxide having a P2-type structure (step S3), and by ion exchange, exchanging at least a part of Na in the Na-containing oxide with Li to obtain a Li-containing oxide having an O2-type structure (step S4).

[0009] 1.1 Step S1 In step S1, a first compound containing at least one element among Mn, Ni, and Co is obtained. The first compound may be, for example, a salt containing at least one element among Mn, Ni, and Co. Specifically, the first compound may be at least one of a carbonate, a sulfate, a nitrate, and an acetate. Alternatively, the first compound may be a compound other than a salt. For example, the first compound may be a hydroxide. The first compound may be a combination of multiple types of compounds. The first compound does not contain the element M described below. The first compound may have various shapes. For example, the first compound may be in particulate form. The particle size of the particles composed of the first compound is not particularly limited.

[0010] In step S1, a transition metal ion, an ion source capable of forming a precipitate in an aqueous solution, and a transition metal compound may be used, and a precipitate as the above-mentioned first compound may be obtained by a coprecipitation method. The "transition metal ion and ion source capable of forming a precipitate" may be, for example, at least one selected from sodium salts such as sodium carbonate and sodium nitrate, sodium hydroxide, and sodium oxide. The transition metal compound may be the above-mentioned salts, hydroxides, etc. Specifically, in step S1, after preparing the ion source and the transition metal compound as solutions respectively, a precipitate may be obtained by dropping and mixing each solution. At this time, for example, water is used as the solvent. At this time, various sodium compounds may be used as the base, and an aqueous ammonia solution etc. may be added for adjustment of basicity. In the case of the coprecipitation method, for example, an aqueous solution of a transition metal compound and an aqueous solution of sodium carbonate are prepared, and by dropping and mixing each aqueous solution, a precipitate as the first compound is obtained. Alternatively, it is also possible to obtain the first compound by a sol-gel method. In particular, according to the coprecipitation method, it is easy to obtain a particulate and spherical first compound. As described above, the first compound does not contain the element M. In the manufacturing method of the present disclosure, the element M is not added during the coprecipitation synthesis of the first compound, and the element M is doped when the first compound is subjected to Na-doping firing in steps S2 and S3 described below.

[0011] 1.2 Step S2 In step S2, the first compound obtained in step S1 is mixed with a second compound containing Na and a third compound containing at least one element M selected from B, Mg, Al, K, Ca, Ti, V, Cr, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W to obtain a mixture. The second compound may be, for example, a salt containing Na such as a carbonate or a sulfate, or a compound other than a salt such as sodium oxide or sodium hydroxide. The third compound may be, for example, a salt containing element M such as a carbonate or a sulfate, or a compound other than a salt such as an oxide or a hydroxide.

[0012] The amount of the second compound mixed with respect to the first compound may be determined in consideration of the loss of Na during the subsequent firing. Also, the amount of the third compound mixed with respect to the first compound may be determined according to the chemical composition of the Na-containing oxide after firing. In step S2, the above first compound, second compound, and third compound may be mixed in the solid phase or in the liquid phase. For example, particles composed of the above first compound, particles composed of the second compound, and particles composed of the third compound may be mixed by a mortar, a ball mill, or the like. Further, in step S2, the surface of the particles composed of the first compound may be coated with the second compound or the third compound to obtain coated particles. The coated particles may be obtained by coating 40% or more, 50% or more, 60% or more, or 70% or more of the surface area of the particles composed of the first compound with the second compound and the third compound.

[0013] 1.3 Step S3 In step S3, the mixture obtained in step S2 is fired to obtain a Na-containing oxide having a P2-type structure. In step S3, the above mixture may be optionally shaped, optionally pre-fired, and then fired. The pre-firing of the mixture may be performed at a temperature lower than the firing temperature. For example, the pre-firing can be performed at a temperature of less than 700°C. The pre-firing time is not particularly limited. Alternatively, the pre-firing may be omitted.

[0014] In step S3, the final firing of the mixture may be performed, for example, at a temperature of 700 °C or higher and 1100 °C or lower. Preferably, it is 800 °C or higher and 1000 °C or lower. If the final firing temperature is too low, Na doping will not be performed. If the final firing temperature is too high, an O3-type structure is likely to be formed instead of the P2-type structure. The temperature rising conditions from the preliminary firing temperature to the final firing temperature are not particularly limited. The final firing time is also not particularly limited and may be, for example, 30 minutes or longer and 48 hours or shorter. The final firing atmosphere is also not particularly limited and may be, for example, an oxygen-containing atmosphere such as an air atmosphere or an inert gas atmosphere.

[0015] The Na-containing oxide obtained in step S3 contains, as constituent elements, at least at least one element of Mn, Ni, and Co, Na, element M, and O. In particular, when the constituent elements include at least Na, Mn, at least one of Ni and Co, element M, and O, among others, when the constituent elements include at least Na, Mn, Ni, Co, element M, and O, the performance of the positive electrode active material is more likely to be higher. More specifically, the Na-containing oxide obtained in step S3 is Na c Mn x-p Ni y-q Co z-r M p+q+rIt may have a chemical composition represented by O2 (where 0 < c ≤ 1.00, x + y + z = 1, and 0.03 ≤ p + q + r < 0.17). 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, and is 1.00 or less, and may be 0.90 or less, 0.80 or less, or 0.70 or less. Also, x is 0 or more, and 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, and 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, and 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 contribution of element M to charge and discharge is small. In this regard, in the above chemical composition, since p + q + r is less than 0.17, a high charge and discharge capacity is likely to be ensured. p + q + r may be 0.16 or less, 0.15 or less, 0.14 or less, 0.13 or less, 0.12 or less, 0.11 or less, or 0.10 or less. On the other hand, when element M is included, the P2-type structure and the O2-type structure are likely to be stabilized. In this regard, in the above chemical composition, p + q + r is 0.03 or more, and may be 0.04 or more, 0.05 or more, 0.06 or more, 0.07 or more, 0.08 or more, 0.09 or more, or 0.10 or more. The composition of O is approximately 2, but is not necessarily exactly 2.0 and is indefinite.

[0016] 1.4 Process S4 In step S4, at least a part of Na in the Na-containing oxide obtained in step S3 is exchanged with Li by ion exchange to obtain a Li-containing oxide having an O2-type structure. In step S4, for example, at least a part of Na in the Na-containing oxide can be replaced with Li by ion exchange using a lithium salt. For example, after mixing a Na-containing oxide having a P2-type structure and a lithium salt, the mixture is heated to a temperature equal to or higher than the melting point of the lithium salt to melt the lithium salt, whereby at least a part of Na can be replaced with Li by ion exchange. The lithium salt may be, for example, lithium halide. The lithium halide is preferably at least one of lithium chloride, lithium bromide, and lithium iodide. Alternatively, the lithium salt may be lithium nitrate. Alternatively, the lithium salt may be a mixed salt of lithium halide and lithium nitrate. When a mixed salt of lithium halide and lithium nitrate is used as the lithium salt, the lower the amount of lithium halide, the lower the melting point of the mixed salt tends to be.

[0017] The temperature in step S4 (for example, the heating temperature when heating and melting with contact of a lithium salt to perform ion exchange on Na-containing transition metal oxide particles) may be, for example, 600 °C or lower, 500 °C or lower, 400 °C or lower, 350 °C or lower, 300 °C or lower, 280 °C or lower, 250 °C or lower, 230 °C or lower, 200 °C or lower, or 170 °C or lower, and may also be room temperature or higher or 100 °C or higher. If the temperature is too high, an O3-type structure, which is a stable phase rather than an O2-type structure, is likely to be formed. In this regard, the temperature in step S4 is preferably 280 °C or lower. Further, when melting the lithium salt, as described above, it may be heated to a temperature equal to or higher than the melting point of the lithium salt. The time in step S2 (for example, the heating time when heating and melting with contact of a lithium salt to perform ion exchange on Na-containing transition metal oxide) may be adjusted so that most of the Na in the Na-containing transition metal oxide particles is replaced by Li. From the viewpoint of ensuring sufficient time for the lithium salt to melt, etc., the time in step S4 may be, for example, 10 minutes or longer or 30 minutes or longer, and may also be 12 hours or shorter or 6 hours or shorter. The atmosphere in step S4 is not particularly limited, and may be, for example, an oxygen-containing atmosphere such as an air atmosphere or an inert gas atmosphere. After ion exchange, some post-treatment such as washing may be performed on the Li-containing oxide having an O2-type structure.

[0018] 1.5 Effects Conventionally, when doping a Li-containing oxide having an O2-type structure with an element M, the element M was simultaneously added when obtaining a first compound containing a transition metal such as Mn. For example, after obtaining a precursor containing at least one of Mn, Ni, and Co and the element M, Na doping was performed on the precursor to obtain a Na-containing oxide having a P2-type structure, and then the Na-containing oxide was ion-exchanged to produce a Li-containing oxide having an O2-type structure. However, according to the findings of the present inventors, when the element M is simultaneously added when obtaining the first compound, fine particles having the element M as a nucleus are generated, and the fine particles tend to aggregate on the surface of the finally obtained Li-containing oxide. When obtaining the first compound by the coprecipitation method, when coprecipitating metal elements in an aqueous solution as salts, it is considered that metal elements having similar ionic radii are easily substituted for each other and tend to form a uniform compound. For example, since Mn, Ni, and Co have similar ionic radii, they easily form a uniform salt by coprecipitation. On the other hand, an element M having an ionic radius different from that of Mn, Ni, and Co is less likely to form a uniform salt with Mn, Ni, and Co. That is, during coprecipitation, fine particles having the element M as a nucleus are likely to be generated separately from the salts of Mn, Ni, and Co. The fine particles having the element M as a nucleus are considered not to substantially contribute to the battery reaction and to be one of the factors reducing the capacity of the positive electrode active material and the like.

[0019] In contrast, in the manufacturing method of the present disclosure, when obtaining the first compound in step S1, element M is not added simultaneously. When performing Na-doping firing on the first compound in steps S2 and S3, element M is doped together with Na. As a result, it becomes difficult to generate fine particles with element M as the nucleus, and while suppressing the aggregation of element M, element M is easily doped uniformly into the crystal structure of the positive electrode active material. By suppressing the aggregation of element M on the surface of the positive electrode active material, the insertion / extraction area of Li ions in the positive electrode active material becomes wider, and the capacity and the like are improved. Further, by doping element M into the positive electrode active material, the O2-type structure is stabilized, and the O2-type structure is less likely to collapse even when charge and discharge are repeated. Therefore, the cycle characteristics, rate characteristics, and the like of the positive electrode active material are improved. Such an effect of suppressing the aggregation of element M and the effect of stabilizing the crystal structure by element M are exhibited when the element M is at least one selected from B, Mg, Al, K, Ca, Ti, V, Cr, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W. Among them, when the element M is at least one selected from B, Mg, Al, K, Ca, Ti, V, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W, and among them, when it is one or both of Al and Mg, particularly when it is Al, a higher effect is more likely to be exhibited.

[0020] 2. Cathode active material As described above, by passing through steps S1 to S4, a cathode active material (Li-containing oxide having an O2-type structure) having an O2-type structure excellent in capacity, cycle characteristics, and rate characteristics can be manufactured. The cathode active material may have, for example, the following characteristics.

[0021] 2.1 Crystal structure The positive electrode active material of the present disclosure has at least an O2-type structure (belonging to the space group P63mc). The positive electrode active material may have an O2-type structure and may also have a crystal structure other than the O2-type structure. Examples of the crystal structure other than the O2-type structure include a T♯2-type structure (belonging to the space group Cmca) formed when Li is deintercalated / inserted from the O2-type structure, an O6-type structure (belonging to the space group R-3m, with the c-axis length being 2.5 nm or more and 3.5 nm or less, typically 2.9 nm or more and 3.0 nm or less, and different from the O3-type structure also belonging to the space group R-3m), and the like. The positive electrode active material may have an O2-type structure as the main phase, or may have a crystal structure other than the O2-type structure as the main phase, but in particular, those having an O2-type structure as the main phase are preferred. The positive electrode active material may be such that the crystal structure serving as the main phase changes depending on its charge / discharge state.

[0022] 2.2 Chemical composition The positive electrode active material of the present disclosure contains, as constituent elements, at least one element selected from at least Mn, Ni, and Co, Li, element M, and O. In particular, when it contains, as constituent elements, at least Mn and at least one of Ni and Co, Li, element M, and O, among others, when it contains, as constituent elements, at least Li, Mn, Ni, Co, element M, and O, it is easier to ensure higher performance. Further, due to the above-described manufacturing process, the positive electrode active material may contain Na as a constituent element. Also, the positive electrode active material may contain other impurity elements. Specifically, the positive electrode active material contains Li a Na b Mn x-p Ni y-q Co z-r M p+q+rIt may have a chemical composition represented by O2 (where 0 < a ≤ 1.00, 0 ≤ b ≤ 0.20, x + y + z = 1, and 0.03 ≤ p + q + r < 0.17). In this chemical composition, a may be 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, b may be 0 or more, may be greater than 0, and may be 0.20 or less, 0.15 or less, 0.10 or less, 0.05 or less, 0.04 or less, 0.03 or less, 0.02 or less, or 0.01 or less. 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 oxide having a P2-type structure obtained in the above step S3, and the description thereof is omitted here. In the prior art, when p + q + r is 0.03 or more, problems related to the aggregation of fine particles containing element M are likely to occur. In contrast, according to the positive electrode active material of the present disclosure, even when p + q + r is 0.03 or more, aggregation of fine particles can be suppressed. Further, in the above chemical composition, when the valence of element M is +n, the relationship 3.0 ≤ 4(x - p) + 2(y - q) + 3(z - r) + n(p + q + r) ≤ 3.5 may be satisfied. This is intended to be in a range close to the total valence of the metal in the Li-containing oxide being 3.33 valences (charge neutrality when a is 0.67). As described above, the Li-containing oxide having an O2-type structure passes through a Na-containing oxide having a P2-type structure during its synthesis, and the case where the Na composition at this time becomes charge neutral in the range of 0.5 or more and 1.0 or less corresponds to the case where the above relationship is satisfied.

[0023] 2.3 Aggregation region of element M The positive electrode active material of the present disclosure contains element M as described in the above chemical composition, and has a small aggregation region of element M on its surface. For example, the ratio of the aggregation region of element M occupying the active material surface is less than 0.01 mm per 1.00 mm of the active material surface. As described above, the conventional positive electrode active material has an aggregation region of element M on its surface, and the ratio of the aggregation region is 0.01 mm per 1.00 mm of the active material surface. 2 per 2 less than. As described above, the conventional positive electrode active material has an aggregation region of element M on its surface, and the ratio of the aggregation region is 0.01 mm per 1.00 mm of the active material surface. 2 per 2will far exceed this. In contrast, for the positive electrode active material of the present disclosure, the ratio of the agglomerated region is 1.00 mm on the surface of the active material 2 per 0.01 mm 2 or less, that is, the surface of the positive electrode active material has substantially no agglomerated region. Therefore, the positive electrode active material of the present disclosure has excellent capacity, rate characteristics, etc. Further, the positive electrode active material of the present disclosure has excellent cycle characteristics by having the above-described crystal structure and chemical composition.

[0024] In addition, the "ratio of the agglomerated region of element M on the surface of the active material" can be easily specified by observing the surface of the positive electrode active material by SEM and analyzing the element distribution on the surface by EDX. The "agglomerated region of element M" referred to in the present application is a region where element M is observed to agglomerate when element mapping of the surface of the active material is performed by SEM-EDX, and the diameter corresponding to the area circle is 0.1 μm or more (fine particles).

[0025] 2.4 Shape The positive electrode active material of the present disclosure 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 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, 500 nm or more, 800 nm or more, 1 μm or more, or 2 μm or more, and may also be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less. In addition, 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.

[0026] 3. Method for manufacturing a lithium ion battery The positive electrode active material produced as described above is used, for example, as a positive electrode active material of a lithium-ion battery. A method for manufacturing a lithium-ion battery may include, for example, manufacturing a positive electrode active material by the manufacturing method of the present disclosure, obtaining a positive electrode active material layer using the manufactured positive electrode active material, and obtaining a lithium-ion battery using the positive electrode active material layer. The method for manufacturing a lithium-ion battery of the present disclosure may be manufactured by a method similar to the conventional method except for obtaining a positive electrode active material layer using a specific positive electrode active material. For example, the methods described in Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2014-186937) and Japanese Unexamined Patent Application Publication No. 2021-068556 may be employed.

[0027] 4. Lithium-Ion Battery The technology of the present disclosure also has an aspect as a lithium-ion battery. For example, as shown in FIG. 2, a lithium-ion battery 100 according to an embodiment includes a positive electrode active material layer 10, an electrolyte layer 20, and a negative electrode active material layer 30, and is characterized in that the positive electrode active material layer 10 contains the positive electrode active material of the present disclosure. As shown in FIG. 2, the lithium-ion battery 100 may include a positive electrode current collector 40 and a negative electrode current collector 50. In the lithium-ion battery 100, the configurations other than the positive electrode active material are the same as those in the prior art. For example, the configurations described in Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2014-186937) and Japanese Unexamined Patent Application Publication No. 2021-068556 may be adopted.

Examples

[0028] As described above, an embodiment of the method for manufacturing a positive electrode active material of the present disclosure has been described. However, the method for manufacturing a positive electrode active material of the present disclosure can be variously modified other than the above embodiments without departing from the gist thereof. Hereinafter, the technology of the present disclosure will be described in more detail while showing examples, but the technology of the present disclosure is not limited to the following examples.

[0029] 1. Preparation of Positive Electrode Active Material 1.1 Example 1 1.1.1 Preparation of the First Compound (Coprecipitation Synthesis) Using Mn(NO3)2·6H2O, Ni(NO3)2·6H2O, and Co(NO3)2·6H2O as raw materials, they were dissolved in pure water so that the molar ratio of Mn, Ni, and Co was 5:2:2 to obtain a first solution. On the other hand, Na2CO3 was dissolved in pure water to a concentration of 12 wt% to obtain a second solution. The first solution and the second solution were simultaneously dropped into a beaker to co-precipitate and synthesize a first compound. At this time, the dropping rate was controlled so that the pH was 7.0 or more and less than 7.1. After the dropping was completed, the mixed solution was stirred at 50 °C and 300 rpm for 24 hours. Then, it was washed with pure water, and only the precipitated powder was separated by centrifugation. The obtained powder was dried at 120 °C for 48 hours and then crushed in an agate mortar to obtain a powder of the first compound containing Mn, Ni, and Co.

[0030] 1.1.2 Mixing The powder of the first compound, Na2CO3 as the second compound, and Al(NO3)3·9H2O as the third compound were mixed so that the composition ratio was Na 0.67 Mn 0.5 Ni 0.2 Co 0.2 Al 0.1 to form O2 to obtain a mixed powder.

[0031] 1.1.3 Firing The mixed powder was pressed with a load of 2 tons by the cold isostatic pressing method to produce pellets. The obtained pellets were pre-fired at 600 °C for 6 hours in an air atmosphere and then fired at 900 °C for 24 hours to synthesize a Na-containing oxide (Na 0.67 Mn 0.5 Ni 0.2 Co 0.2 Al 0.1 O2) having a P2-type structure.

[0032] 1.1.4 Ion Exchange LiNO3 and LiCl were mixed at a mass ratio of 88:12 to obtain a mixed salt. The obtained mixed salt and the above-mentioned Na-containing oxide were weighed so that the molar ratio of Li contained in the mixed salt to the Na-containing oxide was twice. After mixing the Na-containing oxide and the mixed salt, ion exchange was carried out at 150 °C for 1 hour in an air atmosphere. After ion exchange, water was added to dissolve the salt, and further washing with water was performed to obtain a Li-containing oxide having an O2-type structure as a positive electrode active material.

[0033] 1.2 Example 2 As the third compound, Mg(NO3)2·6H2O was used instead of Al(NO3)3·9H2O, and the first compound, the second compound, and the third compound were mixed with Na 0.67 Mn 0.5 Ni 0.2 Co 0.2 Mg 0.1 A Li-containing oxide having an O2-type structure as a positive electrode active material was obtained in the same manner as in Example 1, except that a mixed powder was obtained by mixing them so as to become O2.

[0034] 1.3 Comparative Example 1 When co-precipitating the first compound, Mn(NO3)2·6H2O, Ni(NO3)2·6H2O, and Co(NO3)2·6H2O were dissolved so as to have a molar ratio of 5:2:3, and without using the third compound, the first compound and the second compound were mixed with Na 0.67 Mn 0.5 Ni 0.2 Co 0.3 A Li-containing oxide having an O2-type structure as a positive electrode active material was obtained in the same manner as in Example 1, except that a mixed powder was obtained by mixing them so as to become O2.

[0035] 1.4 Comparative Example 2 1.4.1 Preparation of the first compound (co-precipitation synthesis) Using Mn(NO3)2·6H2O, Ni(NO3)2·6H2O, Co(NO3)2·6H2O, and Al(NO3)3·9H2O as raw materials, they were dissolved in pure water so that the molar ratio of Mn, Ni, Co, and Al was 5:2:2:1 to obtain a first solution. On the other hand, Na2CO3 was dissolved in pure water to a concentration of 12 wt% to obtain a second solution. The first solution and the second solution were simultaneously dropped into a beaker to co-precipitate and synthesize a first compound. At this time, the dropping rate was controlled so that the pH was 7.0 or more and less than 7.1. After the dropping was completed, the mixed solution was stirred at 50 °C and 300 rpm for 24 hours. Then, it was washed with pure water, and only the precipitated powder was separated by centrifugation. The obtained powder was dried at 120 °C for 48 hours and then pulverized in an agate mortar to obtain a powder of the first compound containing Mn, Ni, Co, and Al.

[0036] 1.4.2 Mixing, Firing, and Ion Exchange The powder of the first compound and Na2CO3 as the second compound were mixed so that the composition ratio was Na 0.67 Mn 0.5 Ni 0.2 Co 0.2 Al 0.1 O2 to obtain a mixed powder. Using the obtained mixed powder, molding, pre-firing, and main firing were carried out in the same manner as in Example 1 to synthesize a Na-containing oxide (Na 0.67 Mn 0.5 Ni 0.2 Co 0.2 Al 0.1 O2) having a P2-type structure, and using the Na-containing oxide, ion exchange was carried out in the same manner as in Example 1 to obtain a Li-containing oxide having an O2-type structure as a positive electrode active material.

[0037] 1.5 Comparative Example 3 Except that Mg(NO3)2·6H2O was used instead of Al(NO3)3·9H2O, in the same manner as in Comparative Example 2, a Na-containing oxide (Na 0.67 Mn 0.5 Ni 0.2 Co 0.2 Mg 0.1 O2) having a P2-type structure was synthesized, and a Li-containing oxide having an O2-type structure as a positive electrode active material was obtained.

[0038] 2. Identification of Chemical Composition and Crystal Structure of Cathode Active Material The chemical compositions of the cathode active materials of Examples 1 and 2 and Comparative Examples 1 to 3 were identified by ICP-AES. The results are shown in Table 1 below. As shown in Table 1, the intended chemical compositions were obtained. Also, X-ray diffraction measurements were performed on each cathode active material. The results are shown in Figure 3. As shown in Figure 3, it was confirmed that the cathode active materials of Examples 1 and 2 and Comparative Examples 1 to 3 all have an O2-type structure.

[0039] [Table 1]

[0040] 3. Observation of Cathode Active Material For each of the cathode active materials of Examples 1 and 2 and Comparative Examples 2 and 3, observations were made by SEM-EDX. The results are shown in Figure 4. A is the result related to Example 1, B is the result related to Example 2, C is the result related to Comparative Example 2, and D is the result related to Comparative Example 3. The EDX images of Example 1 and Comparative Example 2 show the distribution state of Al, and the EDX images of Example 2 and Comparative Example 3 show the distribution state of Mg. As shown in Figure 4, it can be seen that for the cathode active materials related to Comparative Examples 2 and 3, fine particles (with a circular equivalent diameter of 0.1 μm or more) containing Al and Mg are aggregated on their surfaces. The area of the aggregated region is much larger than 0.01 mm 2 per 1.00 mm of the surface of the cathode active material. 2 On the other hand, for the cathode active materials related to Examples 1 and 2, there is substantially no aggregated region of Al and Mg on the surface of the cathode active material (the area of the aggregated region is less than 0.01 mm 2 per 1.00 mm of the surface of the cathode active material), and it can be seen that Al and Mg are uniformly doped in the cathode active material. 2

[0041] 4. Fabrication of Coin Cell ​In 125 mL of an n-methylpyrrolidone solution in which 5 g of polyvinylidene fluoride (PVdF) was dissolved, 85 g of the above positive electrode active material particles (pulverized by ball milling) and 10 g of carbon black were added and uniformly kneaded to prepare a paste. This paste was applied unilaterally on an Al foil with a basis weight of 6 mg / cm 2 and dried to obtain a laminate having a positive electrode mixture layer on the Al foil. Thereafter, this laminate was pressed so that the thickness of the mixture layer was 45 μm and the density of the mixture layer was 2.4 g / cm 3 . Finally, the pressed laminate was cut out to a diameter of φ16 mm to obtain a positive electrode. On the other hand, a Li foil was cut out to a diameter of φ19 mm to obtain a negative electrode. Using these positive and negative electrodes, a CR2032 type coin cell was fabricated. Here, a porous separator made of PP was used as the separator, and as the electrolyte, a mixture of EC (ethylene carbonate) and DMC (dimethyl carbonate) in a volume ratio of 3:7, to which lithium hexafluorophosphate (LiPF6) was dissolved at a concentration of 1 mol / L as a supporting salt, was used.

[0042] 5. Evaluation of initial discharge capacity and charge-discharge cycle characteristics Regarding the fabricated coin cell, the initial discharge capacity and the capacity retention rate after 10 cycles were measured when charging and discharging were performed at a charge-discharge rate of 0.1C. For charging and discharging, in each cycle, charging was up to 4.8V and discharging was up to 2.0V.

[0043] 6. Evaluation of charge-discharge rate characteristics Regarding the fabricated coin cell, in a thermostatic bath maintained at 25°C, in a voltage range of 2.0 - 4.8V, charging was performed at 0.1C, and then discharging was performed at 0.1C, 0.5C, 1C, or 5C, and the discharge capacity at each rate was measured and evaluated by relativizing the discharge capacity at 0.1C as 100%.

[0044] 7. Evaluation results Table 2 below shows the evaluation results for each of the initial discharge capacity of the coin cell, the charge-discharge cycle characteristics of the coin cell, and the charge-discharge rate characteristics of the coin cell.

[0045]

Table 2

[0046] From the results shown in Table 1, the following can be understood. (1) The coin cell using the cathode active material according to Comparative Example 1 is inferior in cycle characteristics and rate characteristics. The cathode active material according to Comparative Example 1 does not contain an element M that stabilizes the crystal structure such as Al or Mg, and it is considered that the crystal structure collapses during charge and discharge, resulting in a decrease in cycle characteristics and rate characteristics. (2) The coin cells using the cathode active materials according to Comparative Examples 2 and 3 have a small capacity. In the cathode active materials according to Comparative Examples 2 and 3, fine particles derived from Al or Mg are aggregated on the surface, and the insertion / extraction area of Li ions in the cathode active material becomes small, which is considered to lead to a decrease in capacity. (4) The coin cells using the cathode active materials according to Examples 1 and 2 are excellent in capacity, cycle characteristics, and rate characteristics. The cathode active materials according to Examples 1 and 2 have a crystal structure stabilized by Al or Mg, and fine particles derived from Al or Mg are not aggregated on the surface of the active material, which is considered to lead to the compatibility of capacity, cycle characteristics, and rate characteristics.

[0047] In addition, in the above examples, the case of obtaining the first compound by coprecipitation synthesis was exemplified, but the method for obtaining the first compound is not limited to this. Also, in the above examples, the case of mixing the first compound, the second compound, and the third compound by powder mixing was exemplified, but the method for mixing the compounds is not limited to this. Further, in the above examples, the case of using a Li-containing oxide having a specific chemical composition as the cathode active material was exemplified, but the chemical composition of the cathode active material is not limited thereto.

Explanation of Symbols

[0048] 10 Cathode active material layer 20 Electrolyte layer 30 Anode active material layer 40 Cathode current collector 50 Anode current collector 100 Lithium ion battery

Claims

1. A method for producing a positive electrode active material, comprising: obtaining a first compound containing at least one element among Mn, Ni, and Co; mixing the first compound, a second compound containing Na, and a third compound containing at least one element M selected from B, Mg, Al, K, Ca, Ti, V, Cr, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W to obtain a mixture; firing the mixture to obtain a Na-containing oxide having a P2-type structure; and exchanging at least a part of Na in the Na-containing oxide with Li by ion exchange to obtain a Li-containing oxide having an O2-type structure. A method for producing a positive electrode active material.

2. The production method according to claim 1, comprising obtaining a precipitate as the first compound by a coprecipitation method using a transition metal ion, an ion source capable of forming a precipitate in an aqueous solution, and a transition metal compound. The production method according to claim 1.

3. The first compound is a salt containing at least one element among Mn, Ni, and Co, the second compound is a salt containing Na, and the third compound is a salt containing element M. The production method according to claim 1.

4. wherein the Li-containing oxide is Li ａ Na ｂ Mn ｘ－ｐ Ni ｙ－ｑ Co ｚ－ｒ M ｐ＋ｑ＋ｒ O ２ (where 0 < a ≤ 1.00, 0 ≤ b ≤ 0.20, x + y + z = 1, 0.03 ≤ p + q + r < 0.17) and having a chemical composition represented by The production method according to any one of claims 1 to 3.

5. A positive electrode active material, comprising: having an O2-type structure, Li ａ Na ｂ Mn ｘ－ｐ Ni ｙ－ｑ Co ｚ－ｒ M ｐ＋ｑ＋ｒ O ２ (where 0 < a ≤ 1.00, 0 ≤ b ≤ 0.20, x + y + z = 1, 0.03 ≤ p + q + r < 0.17, and M is at least one selected from B, Mg, Al, K, Ca, Ti, V, Cr, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, and W), and The ratio of the aggregation region of element M on the surface of the active material is less than 0.01 mm per 1.00 mm of the surface of the active material ２ per ２ 1.00 mm of the surface of the active material A positive electrode active material.

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