Positive electrode active material, positive electrode, lithium ion battery, and method for producing positive electrode active material

Abstract

Provided are: a positive electrode active material in which expansion and contraction are suppressed; a positive electrode; a lithium ion battery; and a method for producing the positive electrode active material. A positive electrode active material including a composite oxide of a lithium-containing metal, the composite oxide being represented by formula (1): LiaNixCoyMnzMbO2 (1) in which x, y, z, a and b satisfy x + y + z + b = 1, 0 < = x < = 1, 0 < = y < = 1, 0 < = z < = 1, 0 lt; a < = 1, 0lt; m is a lanthanide element or a transition element having an electron number of 4 or less in the d orbital.

Description

Technical Field

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

[0002] Japanese Unexamined Patent Application Publication No. 2013-229339 discloses adding a specific element to a lithium metal composite oxide containing lithium, nickel, cobalt, and manganese for the purpose of increasing battery capacity and the like. Summary of the Invention

[0003] In Japanese Unexamined Patent Application Publication No. 2013-229339, an increase in battery capacity was achieved by adding a specific element. However, there is room for improvement in terms of the cracking of positive electrode active material particles, which is a main cause of the deterioration of the positive electrode active material.

[0004] An object of the present invention is to provide a positive electrode active material, a positive electrode, a lithium ion battery, and a method for manufacturing a positive electrode active material that suppress expansion and contraction. 1

[0006] A positive electrode active material,

[0007] comprising a lithium-containing metal composite oxide,

[0008] The lithium-containing metal composite oxide is represented by the following formula (1):

[0009] Li a Ni x Co y Mn z M b O2 (1)

[0010] In the above formula (1),

[0011] x, y, z, a, and b satisfy the relationships of x + y + z + b = 1, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, 0 < a ≤ 1, and 0 < b ≤ 0.15,

[0012] M is a lanthanide element or a transition element having 4 or less electrons in the d orbital.

[0013] The lanthanide element or the transition element having 4 or less electrons in the d orbital, i.e., the M element, does not cause a decrease in capacity even when doped into the positive electrode active material because the electrons contribute to charge and discharge. In addition, it is considered that the spatial expansion of the d / f electrons can support the structure of the positive electrode active material even when the lithium filling rate is low. 2

[0015] In the positive electrode active material according to 1,

[0016] M is at least one selected from Nd, Sm, Gd, and La. 3

[0018] A positive electrode

[0019] contains the positive electrode active material described in 1 or 2. 4

[0021] A lithium-ion battery

[0022] contains the positive electrode described in 3. 5

[0024] A method for manufacturing a positive electrode active material, comprising:

[0025] A precursor production step of producing a precursor containing M;

[0026] A mixing step of producing a lithium mixture by mixing the precursor and lithium;

[0027] A firing step of producing a lithium-containing metal composite oxide by firing the lithium mixture; and

[0028] A crushing step of manufacturing a positive electrode active material by crushing the lithium-containing metal composite oxide,

[0029] The firing step is carried out at a temperature of 600 to 700 °C for 48 to 52 hours. Description of the Drawings

[0030] Hereinafter, the features, advantages, and technical and industrial significance of the exemplary embodiments of the present invention will be described with reference to the drawings. In the drawings, the same reference numerals denote the same elements.

[0031] Figure 1 is a schematic flowchart of the method for manufacturing a positive electrode active material according to this embodiment.

[0032] Figure 2 is a schematic diagram showing an example of the lithium-ion battery according to this embodiment.

[0033] Figure 3 is a schematic diagram showing an example of the electrode body according to this embodiment.

[0034] Figure 4 is a coordinate diagram showing the value of the c-axis length of each positive electrode active material from No. 2 to 16 relative to b.

[0035] Figure 5 is a table showing the sample compositions and evaluation results of the examples and comparative examples.

[0036] Figure 6 is a table showing the sample compositions and evaluation results of the examples and comparative examples. DETAILED DESCRIPTION

[0037] Hereinafter, an embodiment of the present disclosure (hereinafter may be referred to as “the present embodiment”) and an example of the present disclosure (hereinafter may be referred to as “the present example”) will be described. However, the present embodiment and the example do not limit the technical scope of the present disclosure.

[0038] Positive active material

[0039] The positive electrode active material of the present embodiment is a positive electrode active material comprising a composite oxide containing lithium metal. The positive electrode active material of the present embodiment may also be a positive electrode active material composed of a composite oxide containing lithium metal. The positive electrode active material is a particle. The positive electrode active material may have any size. The D50 of the positive electrode active material may be, for example, greater than 1 μm and less than 30 μm, or may be greater than 5 μm and less than 20 μm. "D50" in this specification is defined as the particle size at which the cumulative frequency from the smaller particle size in the volume-based particle size distribution reaches 50%. The volume-based particle size distribution can be measured by a laser diffraction particle size distribution measuring device.

[0040] Particle structure

[0041] The positive electrode active material contains secondary particles formed by the aggregation of multiple primary particles. The positive electrode active material may also be substantially composed of secondary particles, for example. The secondary particles are formed by the aggregation of more than 50 primary particles. The number of primary particles contained in the secondary particles is measured in the SEM image (scanning electron microscope) of the secondary particles. The magnification of the SEM image may also be, for example, 10,000 times to 30,000 times. The secondary particles may be formed, for example, by the aggregation of more than 100 primary particles. There is no upper limit to the number of primary particles in the secondary particles. The secondary particles may also be formed, for example, by the aggregation of less than 10,000 primary particles. The secondary particles may also be formed, for example, by the aggregation of less than 1,000 primary particles. The primary particles may have any shape. The primary particles may also be, for example, spherical, columnar, blocky, etc.

[0042] composition

[0043] The positive electrode active material can reversibly absorb and release lithium ions. The positive electrode active material can have any crystal structure. The positive electrode active material can also have, for example, a layered rock salt structure, a spinel structure, an olivine structure, etc. The positive electrode active material can have any chemical composition. The chemical composition of the positive electrode active material can be determined, for example, by high-frequency inductively coupled plasma emission spectrometry (ICPAES) or the like.

[0044] The positive electrode active material contains a lithium-containing metal composite oxide. The lithium-containing metal composite oxide has a composition represented by the following formula (1).

[0045] Li a Ni x Co y Mn z M b O2 (1)

[0046] In the above formula (1), x, y, z, a, and b satisfy the relationships of x + y + z + b = 1, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, 0 < a ≤ 1, and 0 < b ≤ 0.15. M is a lanthanide element or a transition element with 4 or fewer electrons in the d orbital.

[0047] The lanthanide element or the transition element with 4 or fewer electrons in the d orbital, that is, the M element, does not cause a decrease in capacity even when doped into the positive electrode active material because the electrons contribute to charge and discharge. In addition, even when the filling rate of Li is low, the spatial expansion of d / f electrons can support the structure of the positive electrode active material. Therefore, by adding the M element, the expansion and contraction of the positive electrode active material accompanying charge and discharge can be suppressed.

[0048] Examples of the M element include lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), Pm, samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), etc. In addition, examples of the M element include dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), scandium (Sc), titanium (Ti), vanadium (V), etc. In addition, examples of the M element include chromium (Cr), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), tungsten (W), etc. Among them, from the viewpoint of suppressing capacity decline, La, Nd, Sm, and Gd are preferred as the M element.

[0049] In the above formula (1), b satisfies the relationship of 0 < b ≤ 0.15. When b exceeds 0.15, since the ratio of the M element is large, the structure of the positive electrode active material may not be supported. b can be 0.01 or more, and can also be 0.02 or more. b can be 0.10 or less, can be 0.07 or less, and can also be 0.04 or less.

[0050] Manufacturing method of positive electrode active material

[0051] Figure 1 is a schematic flowchart of the manufacturing method of the positive electrode active material of the present embodiment. Hereinafter, "the manufacturing method of the positive electrode active material of the present embodiment" may be abbreviated as "the present manufacturing method". The present manufacturing method includes at least (a) a precursor production step, (b) a mixing step, (c) a firing step, and (d) a crushing step.

[0052] (a) Precursor production process

[0053] In the precursor production process, a precursor (composite hydroxide) containing a salt of element M is produced. The precursor is produced, for example, in the following order.

[0054] For example, an acidic aqueous solution is produced by dissolving a nickel salt, a cobalt salt, a manganese salt, and a salt of element M in water in a predetermined ratio. There is no particular limitation on the nickel salt, and for example, nickel sulfate, nickel nitrate, nickel chloride, etc. can be used. There is no particular limitation on the cobalt salt, and for example, cobalt sulfate, cobalt nitrate, cobalt chloride, etc. can be used. There is no particular limitation on the manganese salt, and for example, manganese sulfate, manganese nitrate, manganese chloride, etc. can be used. There is no particular limitation on the salt of element M, and for example, a sulfate of element M, a nitrate of element M, a hydrochloride of element M, etc. can be used.

[0055] The nickel salt, the cobalt salt, the manganese salt, and the salt of element M are mixed so that the molar ratio of nickel, cobalt, manganese, and element M becomes "x:y:z:b". x, y, z, and b satisfy the relationship of x + y + z + b = 1, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, and 0 < b ≤ 0.15.

[0056] For example, a neutralization reaction is caused by dropping a basic aqueous solution into the acidic aqueous solution. The basic aqueous solution is prepared, for example, by mixing water, an ammonium ion donor, and a pH adjuster. There is no particular limitation on the ammonium ion donor, and for example, ammonia water, ammonium sulfate aqueous solution, etc. can be used. There is no particular limitation on the pH adjuster, and for example, sodium hydroxide, potassium hydroxide, etc. can be used. A precipitate is produced by the neutralization reaction. The precipitate contains a composite hydroxide.

[0057] For example, a dried product (precursor) is produced by washing, filtering, and drying the precipitate. Washing is carried out, for example, by filtering the precipitate to remove the composite hydroxide and then performing water washing. Drying is carried out at a predetermined temperature for a predetermined time. The drying temperature can also be, for example, 100 to 150 °C. The drying time can also be, for example, 1 to 24 hours.

[0058] (b) Mixing process

[0059] In the mixing process, a lithium salt is mixed with the precursor obtained in the precursor production process to produce a lithium mixture. There is no particular limitation on the lithium salt, and for example, lithium carbonate, lithium hydroxide, lithium nitrate, etc. can be used.

[0060] (c) Firing process

[0061] In the firing process, a composite oxide containing a lithium metal is produced by firing the lithium mixture obtained in the mixing process. The firing can be carried out using, for example, a muffle furnace. The firing can be carried out, for example, in an inert gas atmosphere, in dry air, or in an oxygen atmosphere.

[0062] The firing temperature can also be, for example, 500 to 1000 °C. When the firing temperature is lower than 500 °C, Li does not react sufficiently with the precursor, and residual Li and unreacted precursor may remain, resulting in insufficient crystallinity of the composite oxide containing the lithium metal. When the firing temperature exceeds 1000 °C, the external surface area of the composite oxide containing the lithium metal decreases, abnormal sintering occurs between the secondary particles of the composite oxide containing the lithium metal, and amorphous secondary particles may increase.

[0063] The firing time can be, for example, 5 to 60 hours. When the firing time is less than 5 hours, Li does not react sufficiently with the precursor, and residual Li and unreacted precursor may remain, resulting in insufficient crystallinity of the composite oxide containing the lithium metal. When the firing temperature exceeds 60 hours, the external surface area of the composite oxide containing the lithium metal decreases, abnormal sintering occurs between the secondary particles of the composite oxide containing the lithium metal, and amorphous secondary particles may increase.

[0064] In the firing process, it is preferable that the firing temperature is 600 to 700 °C and the firing time is 48 to 52 hours. By carrying out the firing process under these conditions, the doping rate of the M element is increased.

[0065] (d) Crushing process

[0066] In the crushing process, the composite oxide containing the lithium metal obtained by the firing process is crushed. Thereby, a positive electrode active material having a desired particle size can be obtained. Crushing can be carried out using, for example, a jet mill. Crushing can be carried out, for example, in an inert gas atmosphere or in a nitrogen atmosphere.

[0067] Lithium-ion battery

[0068] Figure 2 is a schematic diagram showing an example of the lithium-ion battery (hereinafter may be simply referred to as "battery") of the present embodiment. The battery 100 includes a housing 90. The housing 90 has an arbitrary shape. The housing 90 can be, for example, square or cylindrical. The housing 90 can be, for example, made of metal or a soft package made of an aluminum (Al) laminated film. A positive electrode terminal 91 and a negative electrode terminal 92 can also be provided on the housing 90.

[0069] The housing 90 houses an electrode body 50 and an electrolytic solution. The electrolytic solution is impregnated in the electrode body 50. The electrode body 50 is connected to the positive electrode terminal 91 and the negative electrode terminal 92.

[0070] Figure 3 This is a schematic diagram showing an example of the electrode body of this embodiment. The electrode body 50 includes a positive electrode 20, a separator 40, and a negative electrode 30. The electrode body 50 has an arbitrary structure. For example, the electrode body 50 can also be a wound type. The positive electrode 20, the separator 40, and the negative electrode 30 can all be strip-shaped sheets. For example, the electrode body 50 can also be formed by laminating the positive electrode 20, the separator 40 (the first sheet), the negative electrode 30, and the separator 40 (the second sheet) in sequence. After winding, the electrode body 50 can also be formed into a flat shape.

[0071] Positive electrode

[0072] The positive electrode 20 can also include a positive electrode current collector and a positive electrode active material layer. The positive electrode current collector can include, for example, aluminum (Al) foil, etc. The positive electrode active material layer contains the above-mentioned positive electrode active material. As long as the positive electrode 20 contains the above-mentioned positive electrode active material, the positive electrode 20 can also contain an additional positive electrode active material. The positive electrode active material layer can also include, for example, a conductive material, an adhesive, etc.

[0073] The conductive material can include, for example, acetylene black (AB), etc. The adhesive can include, for example, PVDF, etc. The compounding amounts of the conductive material and the adhesive can be, for example, 0.1 to 10 parts by mass relative to 100 parts by mass of the positive electrode active material.

[0074] Negative electrode

[0075] The negative electrode 30 can also include a negative electrode current collector and a negative electrode active material layer. The negative electrode current collector can include, for example, copper (Cu) foil, etc. The negative electrode active material layer contains the negative electrode active material. The negative electrode active material can include, for example, at least one selected from graphite, soft carbon, and hard carbon. The negative electrode active material layer can also include, for example, a conductive material, an adhesive, etc.

[0076] The conductive material can include, for example, carbon nanotubes (CNT), etc. The adhesive can include, for example, carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), etc. The compounding amounts of the conductive material and the adhesive can be, for example, 0.1 to 10 parts by mass relative to 100 parts by mass of the negative electrode active material.

[0077] Separator

[0078] The separator 40 is porous. The separator 40 can permeate the electrolyte. The separator 40 separates the positive electrode 20 and the negative electrode 30. The separator 40 has electrical insulation properties. The separator 40 can include, for example, polyolefin resins such as polyethylene (PE), polypropylene (PP), etc. The separator 40 can have a single-layer structure, or can have a multi-layer structure. For example, the separator 40 can be substantially composed of a PE layer, or can be formed by laminating a PP layer, a PE layer, and a PP layer in sequence. For example, a heat-resistant layer can also be formed on the surface of the separator 40.

[0079] Electrolyte

[0080] The electrolyte contains a solvent and a Li salt. The solvent is aprotic. The solvent may contain optional components. The solvent may also contain, for example, at least one selected from ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC).

[0081] The Li salt is a supporting electrolyte. The Li salt is dissolved in the solvent. The Li salt may also contain, for example, at least one selected from LiPF6 and LiBF4. The molar concentration of the Li salt may also be, for example, 0.5 mol / L or more and 2.0 mol / L or less.

[0082] The electrolyte may further contain optional additives. The electrolyte may also contain, for example, 0.01% by mass or more and 5% by mass or less of additives. The additives may also contain, for example, at least one selected from vinylene carbonate (VC) and vinyl ethyl carbonate (VEC), etc.

[0083] No.1

[0084] Manufacture of the positive electrode active material

[0085] Precursor preparation process

[0086] An acidic aqueous solution is obtained by dissolving nickel sulfate and manganese sulfate in ion-exchanged water.

[0087] Ammonia water is supplied to the reaction vessel and stirred with a stirrer. Then, an alkaline aqueous solution is prepared by supplying an aqueous sodium hydroxide solution to the reaction vessel. While stirring the alkaline aqueous solution in the reaction vessel with a stirrer, the acidic aqueous solution is dropped into the alkaline aqueous solution. During the dropping of the acidic aqueous solution, ammonia water and an aqueous sodium hydroxide solution are appropriately added so that the ammonia concentration and pH value of the reaction solution are constant.

[0088] The precipitate after the reaction is filtered and washed with water, and then filtered again to obtain a composite hydroxide. The obtained composite hydroxide is dried at 120 °C for 16 hours to obtain a precursor.

[0089] Mixing process

[0090] The above precursor and lithium carbonate are mixed with a mortar to obtain a lithium mixture.

[0091] Firing process

[0092] A lithium-containing metal composite oxide is obtained by firing the above lithium mixture in a muffle furnace set at 600 - 700 °C for 50 hours.

[0093] Crushing process

[0094] The above lithium-containing metal composite oxide is crushed using a jet mill to obtain the positive electrode active material of No.1.

[0095] No.2-1, 2, 3, 4~No.16-1, 2, 3, 4

[0096] Nickel sulfate, manganese sulfate and the sulfate of element M are dissolved in ion-exchanged water to obtain an acidic aqueous solution. Except for this change, the positive electrode active materials of No.2-1, 2, 3, 4~No.16-1, 2, 3, 4 are obtained through the same process as No.1. The M element contained in the positive electrode active material of each No. (number) is as Figure 5 and 6 shown.

[0097] Manufacture of lithium-ion battery

[0098] As the material for the positive electrode, the positive electrode active materials of No.1~16, AB as the conductive material, PVdF as the binder, and Al foil as the positive electrode current collector are prepared. The positive electrode is made from the above materials.

[0099] As the material for the negative electrode, natural graphite as the negative electrode active material, CMC and SBR as the binders, and Cu foil as the negative electrode current collector are prepared. The negative electrode is made from the above materials.

[0100] As the separator, a porous resin (PP / PE / PP) with PP layers laminated on both sides of the PE layer is prepared. As the electrolyte, an electrolyte in which a supporting salt (LiPF6) is dissolved at a concentration of 1 mol / L in a mixed solvent containing EC, DMC and EMC is prepared. Through the above positive electrode, negative electrode, separator and electrolyte, test batteries for evaluation of No.1~16 are manufactured.

[0101] Evaluation

[0102] c-axis length

[0103] At 100% SOC, the positive electrode active material is recovered by disassembling the test battery. Through an X-ray diffractometer, under the following measurement conditions, X-rays are irradiated on the positive electrode active material of each No. after manufacture (positive electrode active material at 0% SOC) and the positive electrode active material of each No. after the above recovery to obtain an X-ray diffraction pattern. Based on the obtained X-ray diffraction pattern, Rietveld analysis is performed on the crystal peak data to calculate the lattice constant, and thus the c-axis length in the crystal is calculated. Then, by finding the difference between the c-axis length of the positive electrode active material at 100% SOC and the c-axis length of the positive electrode active material at 0% SOC, the expansion and contraction of the positive electrode active material are confirmed. The results are shown in Figures 4 to 6Furthermore, "SOC (State Of Charge)" represents the percentage of the charging capacity of the battery at that moment relative to the full charging capacity of the battery.

[0104] Measurement conditions

[0105] X-ray output power: 45 kV, 200 mA

[0106] X-ray source: CuKα ray (wavelength: )), single crystal monochromator

[0107] Diffraction angle: 10 to 120°

[0108] Measurement temperature: room temperature (25 °C)

[0109] Scanning speed: 1 second / step

[0110] In addition, the composition of each positive electrode active material is confirmed based on the obtained X-ray diffraction pattern. The ratio of the M element contained in each positive electrode active material is calculated from the difference in the c-axis length of the positive electrode active materials of each No. obtained above and the ionic radius of each M element. The composition of each positive electrode active material is shown in Figure 5 and Figure 6 .

[0111] Capacity degradation rate

[0112] Through the following constant current-constant voltage charging and constant current discharging, the initial capacity (initial discharge capacity) of each test battery is measured. In addition, the capacity degradation rate of each test battery other than No. 1 is calculated by the following formula (2). The results are shown in Figure 5 and Figure 6 .

[0113] Constant current-constant voltage charging: current = 0.1C, upper limit voltage = 4.3, cut-off current = 0.02C

[0114] Constant current discharging: current = 0.2C, cut-off voltage = 3V

[0115] (Initial capacity of the test battery of No. 1 - Initial capacity of each test battery) / Initial capacity of the test battery of No. 1 × 100 (2)

[0116] Results

[0117] As Figures 4 to 6 shown, compared with the difference in the c-axis length of the positive electrode active material of No. 1 that does not contain the M element, the difference in the c-axis length of the positive electrode active materials other than No. 1 that contain the M element is shorter. That is, it can be seen that by adding the M element to the positive electrode active material, the expansion and contraction of the positive electrode active material can be suppressed.

[0118] In addition, it can be seen that as Figure 5 andFigure 6 As shown in the figure, by adding the M element to the positive electrode active material, the capacity of the test battery decreases, but in No. 10 to 13, the capacity decrease rate caused by the addition of the M element is smaller than the capacity decrease rate of other No. That is, it can be seen that by using La, Nd, Sm and Gd as the M element, not only the expansion and contraction of the positive electrode active material can be suppressed, but also the decrease in battery capacity can be suppressed.

[0119] The present embodiment and the present example are illustrative in all aspects. The present embodiment and the present example are not restrictive. The technical scope of the present disclosure includes all changes within the meaning and scope equivalent to the description of the scope of the claim. For example, it is intended from the outset to include the situation where any structure is extracted from the present embodiment and the present example and they are arbitrarily combined.

Claims

1. A positive electrode active material, comprising a lithium-containing metal composite oxide, wherein the lithium-containing metal composite oxide is represented by the following formula (1): Li a Ni x Co y Mr z M b O2(1) In the above formula (1), x, y, z, a, and b satisfy the relationships of x + y + z + b = 1, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, 0 < a ≤ 1, and 0 < b ≤ 0.15, and M is a lanthanide element or a transition element having 4 or less electrons in the d orbital.

2. The positive electrode active material according to claim 1, wherein the M is at least one selected from Nd, Sm, Gd, and La.

3. A positive electrode, comprising the positive electrode active material according to claim 1 or 2.

4. A lithium ion battery, comprising the positive electrode according to claim 3.

5. A method for manufacturing a positive electrode active material, comprising: a precursor production step of producing a precursor containing M; a mixing step of producing a lithium mixture by mixing the precursor and lithium; a firing step of producing a lithium-containing metal composite oxide by firing the lithium mixture; and a crushing step of manufacturing the positive electrode active material by crushing the lithium-containing metal composite oxide, wherein the firing step is carried out at a temperature of 600°C to 700°C for 48 to 52 hours.

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