Method for manufacturing positive electrode active material, positive electrode active material, and lithium ion secondary battery

Abstract

To provide a production method of a positive electrode active material capable of obtaining positive electrode active material with a small particle size.SOLUTION: A production method of a positive electrode active material including complex oxide, includes: a preparation process of preparing a precursor containing Li and Me (Me is at least one of Ni, Co, Mn, Al, and Fe); and a sintering step of sintering the precursor to obtain the composite oxide. In the preparation process, a water-soluble polymer is introduced into secondary particles constituting the precursor using a polymer-containing aqueous solution in which the water-soluble polymer is dissolved to thereby obtain the positive electrode active material.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a positive electrode active material, a positive electrode active material, and a lithium ion secondary battery.

Background Art

[0002] In recent years, with the rapid spread of electronic devices such as personal computers and mobile phones, the development of batteries used as their power sources has been underway. Also, in the automotive industry, the development of batteries used in hybrid vehicles (HEV), plug-in hybrid vehicles (PHEV), or battery electric vehicles (BEV) has been underway. Among various batteries, lithium ion secondary batteries have the advantage of high energy density.

[0003] A lithium ion secondary battery usually has a positive electrode layer, a negative electrode layer, and an electrolyte layer disposed between the positive electrode layer and the negative electrode layer. As the positive electrode active material used in the positive electrode layer, composite oxides containing Li are known. For example, Patent Document 1 discloses a method for manufacturing a positive electrode active material for a lithium ion secondary battery including a lithium nickel composite oxide. Also, Patent Document 1 discloses improving the crushability of a fired body using organic compound particles.

[0004] Patent Document 2 discloses a positive electrode active material for a non-aqueous secondary battery composed of composite oxide particles represented by the general formula LiNi a Co b Mn c O2 (a + b + c = 1, 0 < a < 1, 0 < b < 1, 0 < c < 1). Also, Patent Document 3 discloses a precursor of a positive electrode active material for a lithium ion secondary battery. Also, Patent Document 4 discloses a positive electrode active material for a lithium ion secondary battery composed of secondary particles in which primary particles are aggregated. Also, Patent Document 5 discloses a positive electrode active material of a non-aqueous electrolyte secondary battery obtained by firing a nickel composite hydroxide with a lithium compound.

Prior Art Documents

Patent Documents

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2020-113429 [Patent Document 2] JP 2016-081800 A [Patent Document 3] Japanese Patent Publication No. 2020-177860 [Patent Document 4] Patent Publication No. 2021-048071 [Patent Document 5] Patent Publication No. 2021-024764 Summary of the Invention [Problem to be solved by the invention]

[0006] In order to reduce the battery resistance, it is desirable to reduce the particle size of the positive electrode active material. The present disclosure has been made in view of the above-described circumstances, and a main object of the present disclosure is to provide a method for producing a positive electrode active material that can obtain a positive electrode active material having a small particle size. [Means for solving the problem]

[0007] The present disclosure provides a method for producing a cathode active material containing a composite oxide, the method comprising: a preparation step of preparing a precursor containing Li and Me (Me is at least one of Ni, Co, Mn, Al, and Fe); and a firing step of firing the precursor to obtain the composite oxide, wherein in the preparation step, a polymer-containing aqueous solution in which a water-soluble polymer is dissolved is used to introduce the water-soluble polymer into the interior of secondary particles constituting the precursor.

[0008] According to the present disclosure, by using a precursor in which a water-soluble polymer is introduced inside secondary particles, a positive electrode active material with a small particle size can be obtained.

[0009] In the above disclosure, the precursor may be a mixture having the Me compound containing Me and the Li compound containing Li, and at least one of the Me compound and the Li compound may be the secondary particles.

[0010] In the above disclosure, the preparation step includes a raw material solution preparation process in which the Me-containing Me raw material is dissolved in a solvent to prepare a raw material solution, a precipitate preparation process in which a Me compound containing Me is prepared as a precipitate from the raw material solution, a washing process in which the Me compound is washed, and a mixing process in which the washed Me compound is mixed with the Li compound, and the water-soluble polymer may be introduced into the interior of the secondary particles using the polymer-containing aqueous solution in at least one of the raw material solution preparation process, the precipitate preparation process, the washing process, and the mixing process.

[0011] In the above disclosure, the water-soluble polymer may be introduced into the interior of the secondary particles by washing the Me compound with the polymer-containing aqueous solution in the washing treatment.

[0012] In the above disclosure, the water-soluble polymer may include at least one of a cellulose derivative, a (meth)acrylic polymer, and a polyvinyl alcohol polymer.

[0013] In the above disclosure, the water-soluble polymer may include carboxymethyl cellulose, and the concentration of the carboxymethyl cellulose in the polymer-containing aqueous solution may be 0.5% by weight or more and 2.0% by weight or less.

[0014] In the above disclosure, the method for producing the positive electrode active material may include a crushing step of crushing the composite oxide after the firing step.

[0015] The present disclosure also provides a positive electrode active material containing a composite oxide, the composite oxide containing Li and Me (Me is at least one of Ni, Co, Mn, Al, and Fe), and the composite oxide having a particle diameter of 10% cumulative from the fine particle side in a volume-based cumulative particle size distribution, D 10 The cumulative 50% particle diameter is D 50 The cumulative particle diameter of 90% is D 90 In this case, D 50 is 0.3 μm or more and 1.2 μm or less, (D 90 -D 10 ) / D 50 is 0.9 or more and 1.7 or less, and the residual Na concentration in the composite oxide is 0.010 wt % or more and 0.134 wt % or less.

[0016] According to the present disclosure, by having a predetermined particle size, a positive electrode active material can be obtained that enables the production of a battery with low resistance.

[0017] The present disclosure also provides a lithium ion secondary battery having a positive electrode layer, a negative electrode layer, and an electrolyte layer disposed between the positive electrode layer and the negative electrode layer, wherein the positive electrode layer contains the above-described positive electrode active material.

[0018] According to the present disclosure, by using a predetermined positive electrode active material, a lithium ion secondary battery with low resistance can be obtained. [Effects of the Invention]

[0019] The method for producing a positive electrode active material according to the present disclosure has the effect of being able to obtain a positive electrode active material with a small particle size. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a flowchart illustrating a method for producing a positive electrode active material according to the present disclosure. [Figure 2] FIG. 2 is a schematic side view illustrating the firing step in the present disclosure. [Figure 3]1 is a flowchart illustrating a preparation process according to the present disclosure. [Figure 4] 1 is a schematic cross-sectional view illustrating a lithium-ion secondary battery according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0021] The method for producing a positive electrode active material, the positive electrode active material, and the lithium ion secondary battery according to the present disclosure will be described in detail below.

[0022] A. Method for manufacturing positive electrode active material FIG. 1 is a flowchart illustrating a method for producing a positive electrode active material according to the present disclosure. In FIG. 1, first, a precursor containing Li and Me (Me is at least one of Ni, Co, Mn, Al, and Fe) is prepared (preparation step). In the preparation step, a water-soluble polymer is dissolved in a polymer-containing aqueous solution, and the water-soluble polymer is introduced into the interior of secondary particles constituting the precursor. Next, the precursor is calcined to obtain a composite oxide (calcination step). Next, the calcined composite oxide is crushed (crushing step). This results in a positive electrode active material.

[0023] According to the present disclosure, a cathode active material with a small particle size can be obtained by using a precursor in which a water-soluble polymer is introduced into the interior of secondary particles. Furthermore, the use of a cathode active material with a small particle size reduces battery resistance. FIG. 2 is a schematic side view illustrating the calcination process of the present disclosure. As shown in FIG. 2, the precursor before calcination has secondary particles, and a water-soluble polymer (e.g., carboxymethyl cellulose, CMC) is introduced into the interior of the secondary particles. During calcination, the CMC decomposes, causing the structure of the secondary particles to collapse. As a result, a cathode active material (composite oxide) with a small particle size is obtained. Note that, for convenience, the cross section of the primary particles is depicted as a rectangle in FIG. 2, but this is not limited to a rectangle and other shapes, such as a circle, are also included. The shape of the primary particles may be, for example, rod-like or spherical.

[0024] As mentioned above, Patent Document 1 discloses that organic compound particles are used to improve the crushability of a fired body. However, solid organic compound particles cannot penetrate into the interior of secondary particles. Therefore, the structure of the secondary particles is not destroyed and is maintained. In particular, paragraph

[0089] of Patent Document 1 clearly states that the secondary particles themselves are not destroyed. In contrast, in the present disclosure, a water-soluble polymer is actively introduced into the interior of the secondary particles, thereby destroying the structure of the secondary particles during firing. This results in a positive electrode active material with a small particle size.

[0025] 1.Preparation process The preparation step in the present disclosure is a step of preparing a precursor containing Li and Me (Me is at least one of Ni, Co, Mn, Al, and Fe). In addition, in the preparation step, a water-soluble polymer is introduced into the interior of the secondary particles constituting the precursor using a polymer-containing aqueous solution in which the water-soluble polymer is dissolved. In other words, the water-soluble polymer is introduced into the interior of the secondary particles constituting the precursor.

[0026] In this disclosure, "secondary particles constituting the precursor" refers to secondary particles corresponding to at least one compound among one or more compounds constituting the entire precursor. Furthermore, "secondary particles" refers to particles formed by agglomeration of primary particles. Furthermore, "inside of secondary particles" refers to voids present between the agglomerated primary particles.

[0027] The precursor may also be a mixture of an Me compound containing Me and an Li compound containing Li. In this case, it is preferable that at least one of the Me compound and the Li compound is a secondary particle. A water-soluble polymer may be introduced into the Me compound, which is a secondary particle. A water-soluble polymer may also be introduced into the Li compound, which is a secondary particle.

[0028] The Me compound is not particularly limited as long as it contains Me and can synthesize a desired composite oxide by calcination. Examples of Me compounds include hydroxides containing Me and oxides containing Me. The precursor may contain only one type of Me compound, or two or more types of Me compounds. For example, when the precursor contains Ni, Co, and Mn as Me, one type of Me compound may be a single compound containing Ni, Co, and Mn. On the other hand, two or more types of Me compounds may be a mixture of a Ni compound, a Co compound, and a Mn compound.

[0029] The Li compound is not particularly limited as long as it contains Li and can be used to synthesize a desired composite oxide by firing. Examples of Li compounds include lithium carbonate, lithium hydroxide, lithium nitrate, and lithium acetate.

[0030] In the preparation process, a water-soluble polymer is introduced into the secondary particles constituting the precursor using a polymer-containing aqueous solution in which the water-soluble polymer is dissolved. The polymer-containing aqueous solution contains a water-soluble polymer and water. Examples of water-soluble polymers include cellulose derivatives such as carboxymethyl cellulose; (meth)acrylic polymers such as polyacrylic acid and polymethacrylic acid; and polyvinyl alcohol polymers such as polyvinyl alcohol and polyvinyl alcohol derivatives. The decomposition temperature of the water-soluble polymer is, for example, 600°C or lower, and may be 500°C or lower. On the other hand, the decomposition temperature of the water-soluble polymer is, for example, 120°C or higher, and may be 200°C or higher. The decomposition temperature of the water-soluble polymer refers to the temperature at which the water-soluble polymer thermally decomposes. The weight-average molecular weight of the water-soluble polymer is, for example, 1,000 or higher, and may be 10,000 or higher.

[0031] The concentration of the water-soluble polymer in the polymer-containing aqueous solution is not particularly limited, but is, for example, 0.1% by weight or more and 5% by weight or less. Furthermore, when the polymer-containing aqueous solution contains carboxymethylcellulose as the water-soluble polymer, the concentration of carboxymethylcellulose in the polymer-containing aqueous solution is, for example, 0.5% by weight or more. Furthermore, the concentration may be, for example, 2.0% by weight or less, or 1.5% by weight or less. The viscosity of the polymer-containing aqueous solution is, for example, 100 Pa·s or less, and preferably 80 Pa·s or less.

[0032] The method for introducing a water-soluble polymer into the secondary particles constituting the precursor using a polymer-containing aqueous solution is not particularly limited. For example, the polymer-containing aqueous solution may be brought into contact with the secondary particles constituting the precursor, allowing the polymer-containing aqueous solution to penetrate into the secondary particles constituting the precursor, and then dried to remove the water contained in the polymer-containing aqueous solution. The timing for introducing the water-soluble polymer is also not particularly limited. For example, the water-soluble polymer may be introduced into the mixture by adding a polymer-containing aqueous solution after mixing an Me compound and a Li compound, followed by drying. Alternatively, the water-soluble polymer may be introduced into at least one of the Me compound and the Li compound before mixing them. Alternatively, the water-soluble polymer may be introduced during the preparation of the Me compound.

[0033] Fig. 3 is a flowchart illustrating a preparation process in the present disclosure. In Fig. 3, first, a Me raw material containing Me is dissolved in a solvent to prepare a raw material solution (raw material solution preparation process). For example, a Ni-containing inorganic salt, a Co-containing inorganic salt, and a Mn-containing inorganic salt are dissolved in water to obtain a raw material solution. Next, a Me compound is prepared as a precipitate from the raw material solution (precipitate preparation process). For example, the raw material solution is neutralized to obtain a precipitate of the Me compound. Next, the Me compound is filtered and washed (washing process). Next, the washed Me compound is mixed with a Li compound (mixing process). This results in a precursor.

[0034] In the raw solution preparation process, a Me-containing raw material is dissolved in a solvent to prepare a raw material solution. Examples of the Me raw material include salts containing Me. Examples of such salts include sulfates, nitrates, and chlorides. Examples of the solvent include water. In the present disclosure, a water-soluble polymer may be introduced in the raw solution preparation process. For example, when dissolving the Me raw material in a solvent, a water-soluble polymer may be added at the same time, or a polymer-containing aqueous solution in which a water-soluble polymer is dissolved may be added.

[0035] In the precipitate preparation process, a Me compound containing Me is prepared as a precipitate from a raw material solution. The method for obtaining a precipitate of the Me compound is not particularly limited, and a common crystallization method can be used. Examples of crystallization methods include neutralization and concentration. For example, when the raw material solution is acidic, the Me compound can be obtained by adding an alkaline solution. Examples of alkaline solutions include a sodium hydroxide solution, a calcium hydroxide solution, and a potassium hydroxide solution. The Me compound is preferably a hydroxide. On the other hand, when the raw material solution is alkaline, the Me compound can be obtained by adding an acidic solution. A complexing agent may also be added to the raw material solution. Examples of the complexing agent include an aqueous ammonia solution. In the present disclosure, a water-soluble polymer may be introduced in the precipitate preparation process. For example, the water-soluble polymer may be added before or after neutralization of the raw material solution, or a polymer-containing aqueous solution in which the water-soluble polymer is dissolved may be added simultaneously when the raw material solution is neutralized.

[0036] In the cleaning process, the Me compound is cleaned using a cleaning solution. Examples of the cleaning solution include water. In the present disclosure, a water-soluble polymer may be introduced in the cleaning process. For example, a polymer-containing aqueous solution in which a water-soluble polymer is dissolved may be used as the cleaning solution.

[0037] In the mixing process, the washed Me compound and the Li compound are mixed. The Li compound is as described above. In the present disclosure, a water-soluble polymer may be introduced in the mixing process. For example, when mixing the Me compound and the Li compound, a polymer-containing aqueous solution in which a water-soluble polymer is dissolved may be added.

[0038] The shape of the precursor is not particularly limited, and may be a powder or a molded body.

[0039] 2. Firing process The calcination step in the present disclosure is a step of calcining the precursor to obtain the composite oxide. The calcination temperature in the calcination step is not particularly limited as long as it is a temperature at which the desired composite oxide can be obtained. The calcination temperature is preferably equal to or higher than the decomposition temperature of the water-soluble polymer. The calcination temperature is, for example, 500°C or higher, and may be 700°C or higher, or even 900°C or higher. On the other hand, the calcination temperature is, for example, 1500°C or lower. The calcination time is, for example, 1 hour or longer, and may be 5 hours or longer. On the other hand, the calcination time is, for example, 30 hours or shorter.

[0040] The firing atmosphere may be, for example, an oxygen-containing atmosphere. Examples of the oxygen-containing atmosphere include an atmospheric pressure atmosphere and an atmosphere in which oxygen gas is added to an inert gas. The firing method may be, for example, a method using a furnace such as a muffle furnace.

[0041] 3.Crushing process The crushing step in the present disclosure is a step of crushing the composite oxide after the firing step. By performing the crushing step, sintered necking between secondary particles is broken down. In the crushing step, the structure of the secondary particles themselves is not usually destroyed. Examples of methods for crushing the composite oxide include methods that apply mechanical energy, and a specific example is a jet mill. In addition, the crushing conditions are appropriately adjusted so as to obtain the positive electrode active material described below.

[0042] 4.Cathode active material The positive electrode active material in the present disclosure includes a composite oxide containing Li and Me (Me is at least one of Ni, Co, Mn, Al, and Fe).

[0043] The composite oxide may contain at least Ni as Me. Similarly, the composite oxide may contain at least Co as Me. Similarly, the composite oxide may contain at least Mn as Me. Furthermore, the composite oxide may contain at least one of Ni, Co, and Mn as Me. Similarly, the composite oxide may contain at least one of Ni, Co, and Al as Me. Furthermore, the composite oxide may contain at least one of Ni, Co, and Mn as Me. X Contains Me X A part of which is at least one of Al and Fe, Me Y may be substituted with.

[0044] In composite oxides, the particle size of the cumulative 10% from the fine particle side in the cumulative particle size distribution based on volume is defined as D 10 The cumulative 50% particle diameter is D 50 The cumulative particle diameter of 90% is D 90 D 50 is, for example, 0.3 μm or more, may be 0.4 μm or more, or may be 0.5 μm or more. 50 If D is too small, particles tend to aggregate. 50 is, for example, 1.2 μm or less, and may be 1.1 μm or less.

[0045] Also, (D 90 -D 10 ) / D 50 is an index showing the spread of particle size distribution. (D 90 -D 10 ) / D 50 is, for example, 0.9 or more, and may be 1.0 or more. 90 -D 10 ) / D 50 is, for example, 1.7 or less, and may be 1.5 or less. (D 90 -D 10 ) / D50 When the thickness is within the predetermined range, the filling rate of the positive electrode active material in the positive electrode layer is improved.

[0046] It is preferable that the composite oxide has a high bulk density, because this improves the energy density per volume. The bulk density of the composite oxide is, for example, 1.8 g / cm 3 or more, 2.1 g / cm 3 The bulk density of the composite oxide may be, for example, 3.0 g / cm or more. 3 less than or equal to 2.5 g / cm 3 It may be the following:

[0047] The composite oxide may contain residual Na. For example, when a sodium salt of a polymer is used as the water-soluble polymer, residual Na will be generated in the composite oxide after firing. The residual Na concentration in the composite oxide is, for example, 0.010 wt % or more, or may be 0.020 wt % or more, or may be 0.030 wt % or more. On the other hand, the residual Na concentration in the composite oxide is, for example, 0.134 wt % or less, or may be 0.100 wt % or less.

[0048] The composite oxide in the present disclosure preferably has a crystalline phase. Examples of the crystalline phase include a layered rock salt crystalline phase and a spinel crystalline phase. The present disclosure can also provide a positive electrode active material obtained by the above-described method for producing a positive electrode active material.

[0049] B. Positive electrode active material The positive electrode active material according to the present disclosure is a positive electrode active material containing a composite oxide, the composite oxide containing Li and Me (Me is at least one of Ni, Co, Mn, Al, and Fe), and the composite oxide having a particle diameter of 10% cumulative from the fine particle side in a volume-based cumulative particle size distribution, D 10 The cumulative 50% particle diameter is D 50 The cumulative particle diameter of 90% is D 90 In this case, D 50 is between 0.3 and 1.2, and (D 90 -D 10 ) / D50 is 0.9 or more and 1.7 or less, and the concentration of residual Na in the composite oxide is 0.01 wt % or more and 0.1 wt % or less.

[0050] According to the present disclosure, the cathode active material has a predetermined particle size, which allows a battery with low resistance to be obtained. Details of the cathode active material in the present disclosure are the same as those described above in "A. Cathode Active Material." The cathode active material in the present disclosure is used in a battery.

[0051] C. Lithium-ion secondary battery Fig. 4 is a schematic cross-sectional view illustrating a lithium-ion secondary battery according to the present disclosure. The lithium-ion secondary battery 10 shown in Fig. 4 includes a positive electrode layer 1, a negative electrode layer 2, an electrolyte layer 3 disposed between the positive electrode layer 1 and the negative electrode layer 20, a positive electrode current collector 4 that collects current from the positive electrode layer 1, and a negative electrode current collector 5 that collects current from the negative electrode layer 2. The positive electrode layer 1 contains the positive electrode active material described above in "B. Positive electrode active material."

[0052] According to the present disclosure, by using a predetermined positive electrode active material, a lithium ion secondary battery with low resistance can be obtained.

[0053] The positive electrode layer contains at least a positive electrode active material. The positive electrode active material is the same as that described above in "B. Positive Electrode Active Material." The positive electrode layer may contain at least one of an electrolyte, a conductive material, and a binder, as necessary. Details of the electrolyte will be described later. Examples of conductive materials include carbon materials. Examples of carbon materials include particulate carbon materials such as acetylene black (AB) and ketjen black (KB), and fibrous carbon materials such as carbon fiber, carbon nanotubes (CNT), and carbon nanofibers (CNF). Examples of binders include fluorine-containing binders such as polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). The thickness of the positive electrode layer is, for example, 0.1 μm or more and 1000 μm or less.

[0054] The negative electrode layer contains at least a negative electrode active material. Examples of the negative electrode active material include Li-based active materials such as metallic lithium and lithium alloys; carbon-based active materials such as graphite and hard carbon; oxide-based active materials such as lithium titanate; and Si-based active materials such as simple silicon, Si alloys, and silicon oxide. The negative electrode layer may contain at least one of an electrolyte, a conductive material, and a binder, as necessary. These materials are as described above. The thickness of the negative electrode layer is, for example, 0.1 μm or more and 1000 μm or less.

[0055] The electrolyte layer includes at least an electrolyte. Examples of the electrolyte include a liquid electrolyte (electrolytic solution), a gel electrolyte, and a solid electrolyte. The electrolytic solution includes, for example, a lithium salt and a solvent. Examples of the lithium salt include inorganic lithium salts such as LiPF6, LiBF4, LiClO4, and LiAsF6; and organic lithium salts such as LiCF3SO3, LiN(SO2CF3)2, LiN(SO2C2F5)2, and LiC(SO2CF3)3. Examples of the solvent include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).

[0056] Gel electrolytes are usually obtained by adding a polymer to an electrolytic solution. Examples of polymers include polyethylene oxide and polypropylene oxide. Examples of solid electrolytes include organic solid electrolytes such as polymer electrolytes; and inorganic solid electrolytes such as sulfide solid electrolytes and oxide solid electrolytes. The thickness of the electrolyte layer is, for example, 0.1 μm or more and 1000 μm or less. The electrolyte layer may have a separator.

[0057] Examples of applications of the lithium ion secondary battery of the present disclosure include power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), electric vehicles (BEVs), gasoline-powered automobiles, diesel-powered automobiles, etc. The lithium ion secondary battery of the present disclosure may also be used as a power source for mobile objects other than vehicles (for example, trains, ships, and aircraft), and may also be used as a power source for electrical appliances such as information processing devices.

[0058] The present disclosure is not limited to the above-described embodiments. The above-described embodiments are merely examples, and any configuration that is substantially identical to the technical idea described in the claims of the present disclosure and that provides similar effects is included within the technical scope of the present disclosure. [Example]

[0059] [Example 1] NiSO4, CoSO4, and MnSO4 were prepared as Me raw materials and dissolved in ion-exchanged water to prepare a raw material solution (concentration: 30 wt%). The molar ratio of Ni, Co, and Mn in the raw material solution was Ni:Co:Mn=1:1:1.

[0060] Next, a certain amount of NH3 aqueous solution (complexing agent) was placed in the reaction vessel, and the atmosphere was replaced with nitrogen while stirring with a stirrer. NaOH was added to the reaction vessel to adjust the pH to alkaline. While maintaining a constant pH inside the reaction vessel with NaOH, the raw material solution and NH3 aqueous solution were added dropwise to precipitate Me compounds (secondary hydroxide particles).

[0061] Next, the solution containing the Me compound was filtered, and the residue (Me compound) remaining on the filter paper was washed with a polymer-containing aqueous solution containing carboxymethylcellulose sodium salt (CMC-Na) dissolved at a concentration of 0.5 wt%. The solution was then dried at 120°C for 16 hours to evaporate the water. This introduced CMC into the Me compound.

[0062] Next, the CMC-infused Me compound and the Li compound (Li2CO3) were mixed in a mortar. The resulting mixture was fired in a muffle furnace at 1000°C for 10 hours to obtain a composite oxide. The resulting composite oxide was crushed using a jet mill to obtain a positive electrode active material.

[0063] [Example 2] A positive electrode active material was obtained in the same manner as in Example 1, except that the CMC concentration in the polymer-containing aqueous solution was changed to 1.0 wt %.

[0064] [Example 3] A positive electrode active material was obtained in the same manner as in Example 1, except that the CMC concentration in the polymer-containing aqueous solution was changed to 1.5% by weight.

[0065] [Example 4] A positive electrode active material was obtained in the same manner as in Example 1, except that the CMC concentration in the polymer-containing aqueous solution was changed to 2.0% by weight.

[0066] [Comparative Example 1] A positive electrode active material was obtained in the same manner as in Example 1, except that the CMC concentration in the polymer-containing aqueous solution was changed to 0 wt %.

[0067] [evaluation] (Particle size distribution measurement) The particle size distribution was measured for the positive electrode active materials obtained in Examples 1 to 4 and Comparative Example 1. For the measurement, a laser diffraction / scattering particle size distribution analyzer (MT3000, Microtrac Bell Corporation) was used to measure the particle diameter D of the cumulative 10% particle size from the fine particle side in the cumulative particle size distribution on a volume basis. 10 , cumulative 50% particle diameter D 50 , and cumulative 90% particle diameter D 90 The results are shown in Table 1.

[0068] (bulk density measurement) Bulk density measurements were performed on the positive electrode active materials obtained in Examples 1 to 4 and Comparative Example 1. For the measurements, a powder property evaluation device (Powder Tester PT-X, Hosokawa Micron Corporation) was used, with a tap stroke of 3 mm, 200 taps, and a speed of 100 taps / min. The results are shown in Table 1.

[0069] (Residual Na measurement) The amount of residual Na was measured for the positive electrode active materials obtained in Examples 1 to 4 and Comparative Example 1. For the measurement, an ICP optical emission spectrometer (ICPE-9800, Shimadzu Corporation) was used. The results are shown in Table 1.

[0070] (Initial resistance measurement) Batteries were fabricated using the positive electrode active materials obtained in Examples 1 to 4 and Comparative Example 1, and the initial resistance of the batteries was measured. The battery was fabricated as follows. First, the obtained positive electrode active material, a conductive material (acetylene black), and a binder (polyvinylidene fluoride) were weighed out in a weight ratio of positive electrode active material:conductive material:binder = 88:10:2, and then mixed. A dispersion medium was added to the obtained mixture, and the mixture was stirred to obtain a positive electrode slurry. The obtained positive electrode slurry was applied onto a positive electrode current collector using a film applicator (with a film thickness adjustment function, Allgood Co., Ltd.), and then dried at 80°C for 5 minutes. This resulted in a positive electrode structure having a positive electrode current collector and a positive electrode layer.

[0071] Next, the negative electrode active material (natural graphite) and binders (SBR and CMC) were mixed, and a dispersion medium was added to the resulting mixture, followed by stirring to obtain a negative electrode slurry. The resulting negative electrode slurry was applied to a negative electrode current collector using a film applicator, and then dried at 80°C for 5 minutes. This resulted in a negative electrode structure having a negative electrode current collector and a negative electrode layer.

[0072] The positive electrode layer of the positive electrode structure and the negative electrode layer of the negative electrode structure were arranged opposite each other with a separator interposed therebetween, wound, and then an electrolyte solution was injected to obtain a battery. The electrolyte solution used was a mixed solvent containing EC, DMC, and EMC in a volume ratio of EC:DMC:EMC = 3:4:3, in which LiPF6 was dissolved to a concentration of 1M.

[0073] The resulting battery was charged to 4.1 V and then discharged to 3.0 V. It was then charged to 3.7 V and left to stand at 60°C for 9 hours. The charging resistance was then measured at 3.7 V and 1 C for 10 seconds at -10°C, and this was taken as the initial resistance. The results are shown in Table 1. The initial resistance was calculated as a relative value with Comparative Example 1 taken as 100%.

[0074] (Dispersibility of active material) Positive electrode layers were fabricated in the same manner as described above using the positive electrode active materials obtained in Examples 1 to 4 and Comparative Example 1. The cross sections of the resulting positive electrode layers were observed with a scanning electron microscope (SEM) to evaluate the dispersibility of the positive electrode active material in the positive electrode layer. The dispersibility of the positive electrode active material was calculated according to the following formula using images (1 μm × 1 μm) obtained by dividing a cross-sectional image of the positive electrode layer (1000x magnification, 20 μm × 100 μm) into 20 sections.

[0075]

number

[0076] In the above formula, σ 2 is the dispersibility of the positive electrode active material, n is the number of divisions (n=20), and X i is the volume of the positive electrode active material in the i-th image, and X ave is the average of each volume of the positive electrode active material.

[0077] [Table 1]

[0078] As shown in Table 1, in Examples 1 to 4, the D of the positive electrode active material was lower than that of Comparative Example 1. 50In particular, in Examples 2 and 3, D 50 In addition, in Examples 1 to 4, the (D 90 -D 10 ) / D 50 It was suggested that this contributes to improving the filling rate of the positive electrode active material in the positive electrode layer. 90 -D 10 ) / D 50 was significantly high. Furthermore, Examples 1 to 4 had higher bulk densities than Comparative Example 1, and it was confirmed that this contributed to an improvement in energy density per volume. In particular, Examples 1 to 3 had significantly high bulk densities. Furthermore, Na residues resulting from CMC-Na were confirmed in Examples 1 to 4. Furthermore, in Example 3, the dispersibility of the positive electrode active material was significantly high. Furthermore, Examples 1 to 4 had lower initial resistances than Comparative Example 1, and it was confirmed that the battery performance was improved. In particular, Examples 1 to 3 had significantly lower initial resistances. [Explanation of symbols]

[0079] 1...Positive electrode layer 2...Anode layer 3...electrolyte layer 4...Positive electrode current collector 5...Negative electrode current collector 10...Lithium-ion secondary battery

Claims

1. A battery having a positive electrode layer, a negative electrode layer, and a separator disposed between the positive electrode layer and the negative electrode layer, the positive electrode layer is configured by disposing a composite oxide containing Li, Me (Me is at least one of Ni, Co, Mn, Al, and Fe), and Na on a surface of a positive electrode current collector; The composite oxide has a Na content of 0.010% by weight or more and 0.134% by weight or less, as determined by ICP emission spectroscopy; The dispersibility σ of the composite oxide in the positive electrode layer is calculated by the following formula: ２ is equal to or greater than 32.3 and equal to or less than 79.8, n is the number of divisions of the cross-sectional image of the positive electrode layer, and X ｉ is the volume of the complex oxide in the i-th image, and X ａｖｅ is the average volume of each of the composite oxides, In the composite oxide, when the particle diameter of the cumulative 10% from the fine particle side in the volume-based cumulative particle size distribution is defined as D10, the particle diameter of the cumulative 50% from the fine particle side is defined as D50, and the particle diameter of the cumulative 90% from the fine particle side is defined as D90, (D90-D10) / D50 is 0.9 or more and 1.7 or less, The battery, wherein the D 50 is 0.3 μm or more and 1.2 μm or less.

2. 10. The battery of claim 1, wherein the negative electrode layer contains graphite, SBR, and CMC.

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