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

Abstract

To provide a positive electrode active material suppressed in expansion / contraction, a positive electrode, a lithium ion battery, and a method for manufacturing the positive electrode active material.SOLUTION: The positive electrode active material includes a lithium metal-containing complex oxide. The lithium metal-containing complex oxide is represented by the following expression (1): LiaNixCoyMnzMbO2, x, y, z, and b satisfying relations 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 being either a lanthanoid or a transition element with a d-orbital electron count of 4 or less.SELECTED DRAWING: Figure 4

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 (Patent Document 1) discloses adding a specific element for the purpose of increasing the battery capacity in a lithium metal composite oxide containing lithium, nickel, cobalt, and manganese.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In Patent Document 1, improvement in battery capacity has been achieved by adding a specific element. However, there is room for improvement in suppressing cracking of the positive electrode active material particles, which is the main cause of deterioration of the positive electrode active material.

[0005] An object of the present disclosure 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 in which expansion and contraction are suppressed.

Means for Solving the Problems

[0006] [1] including a lithium metal-containing composite oxide, The lithium metal-containing composite oxide is represented by the following formula (1): Li a Ni x Co y Mn 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. M is a positive electrode active material that is a lanthanoid or a transition element with 4 or fewer electrons in the d orbit.

[0007] Since the M element, which is a lanthanoid or a transition element with 4 or fewer electrons in the d orbit, contributes electrons to charge and discharge, doping the positive electrode active material does not reduce the capacity. Also, the spatial spread of d / f electrons is considered to support the structure of the positive electrode active material even when the lithium filling rate is low.

[0008] [2] The positive electrode active material according to [1], wherein the M is at least one selected from the group consisting of Nd, Sm, Gd, and La.

[0009] [3] A positive electrode comprising the positive electrode active material according to [1] or [2].

[0010] [4] A lithium-ion battery comprising the positive electrode according to [3].

[0011] [5] A precursor preparation step of preparing a precursor containing M, A mixing step of preparing a lithium mixture by mixing the precursor and lithium, A firing step of preparing a lithium metal-containing composite oxide by firing the lithium mixture, A pulverizing step of manufacturing a positive electrode active material by pulverizing the lithium metal-containing composite oxide, and includes The firing step is performed at a temperature of 600 to 700 °C for 48 to 52 hours, and is a method for manufacturing a positive electrode active material.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

MODE FOR CARRYING OUT THE INVENTION

[0013] Hereinafter, embodiments of the present disclosure (hereinafter may be abbreviated as "the present embodiment"), and examples of the present disclosure (hereinafter may be abbreviated as "the present examples") will be described. However, the present embodiment and the present examples do not limit the technical scope of the present disclosure.

[0014] <Positive Electrode Active Material> The positive electrode active material of the present embodiment is a positive electrode active material containing a lithium metal-containing composite oxide. The positive electrode active material of the present embodiment may be a positive electrode active material composed of a lithium metal-containing composite oxide. The positive electrode active material is in the form of particles. The positive electrode active material can have any size. The positive electrode active material may have, for example, a D50 of 1 μm or more and 30 μm or less, or a D50 of 5 μm or more and 20 μm or less. "D50" in this specification is defined as the particle diameter at which the cumulative frequency from the smaller particle diameter becomes 50% in the volume-based particle size distribution. The volume-based particle size distribution can be measured by a laser diffraction particle size distribution measuring device.

[0015] 《Particle Structure》 The positive electrode active material contains secondary particles formed by aggregation of a plurality of primary particles. The positive electrode active material may, for example, consist substantially of secondary particles. The secondary particles are formed by aggregation of 50 or more primary particles. The number of primary particles contained in the secondary particles is measured in a SEM (scanning electron microscope) image of the secondary particles. The magnification of the SEM image may be, for example, from 10,000 times to 30,000 times. The secondary particles may be formed by aggregation of 100 or more primary particles. In the secondary particles, there is no upper limit to the number of primary particles. The secondary particles may be formed by aggregation of, for example, 10,000 or fewer primary particles. The secondary particles may be formed by aggregation of, for example, 1,000 or fewer primary particles. The primary particles can have any shape. The primary particles may be, for example, spherical, columnar, massive, or the like.

[0016] 《Composition》 The positive electrode active material can reversibly intercalate and deintercalate lithium ions. The positive electrode active material can have any crystal structure. The positive electrode active material may have, for example, a layered rock salt structure, a spinel structure, an olivine structure, or the like. The positive electrode active material can have any chemical composition. The chemical composition of the positive electrode active material can be measured, for example, by high frequency inductively coupled plasma atomic emission spectrometry (ICP-AES) or the like.

[0017] The positive electrode active material contains a lithium metal-containing composite oxide. The lithium metal-containing composite oxide has a composition represented by the following formula (1).

[0018] Li a Ni x Co y Mn 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. M is a lanthanoid or a transition element having 4 or fewer electrons in the d orbital.

[0019] Element M, which is a lanthanoid or a transition element with 4 or fewer electrons in the d orbital, does not reduce the capacity even when doped into the cathode active material because electrons contribute to charge and discharge. Also, the spatial spread of d / f electrons supports the structure of the cathode active material even when the filling rate of Li is low. Therefore, by adding element M, the expansion and contraction of the cathode active material accompanying charge and discharge can be suppressed.

[0020] Examples of element M include lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), tungsten (W), etc. Among these, as element M, from the viewpoint of suppressing capacity reduction, La, Nd, Sm, and Gd are preferable.

[0021] In the above formula (1), b satisfies the relationship of 0 < b ≤ 0.15. When b exceeds 0.15, since the ratio of element M is large, there is a possibility that the structure of the cathode active material cannot be supported. b may be 0.01 or more, and may be 0.02 or more. b may be 0.10 or less, may be 0.07 or less, and may be 0.04 or less.

[0022] <Manufacturing method of cathode active material> Figure 1 is a schematic flowchart of the manufacturing method of the cathode active material in this embodiment. Hereinafter, "the manufacturing method of the cathode active material in this embodiment" may be abbreviated as "this manufacturing method". This manufacturing method includes at least (a) a precursor preparation step, (b) a mixing step, (c) a firing step, and (d) a pulverization step.

[0023] 《(a) Precursor preparation step》 In the precursor preparation process, a precursor (composite hydroxide) containing a salt of element M is prepared. The precursor is prepared, for example, by the following procedure.

[0024] For example, an acidic aqueous solution is prepared by dissolving a nickel salt, a cobalt salt, a manganese salt, and a salt of element M in water at a predetermined ratio. The nickel salt is not particularly limited, and for example, nickel sulfate, nickel nitrate, nickel chloride, etc. can be used. The cobalt salt is not particularly limited, and for example, cobalt sulfate, cobalt nitrate, cobalt chloride, etc. can be used. The manganese salt is not particularly limited, and for example, manganese sulfate, manganese nitrate, manganese chloride, etc. can be used. The salt of element M is not particularly limited, and for example, a sulfate salt of element M, a nitrate salt of element M, a hydrochloride salt of element M, etc. can be used.

[0025] The nickel salt, cobalt salt, manganese salt, and salt of element M are mixed so that the molar ratios of nickel, cobalt, manganese, and element M are "x:y:z:b". x, y, z, and b satisfy the relationships of x + y + z + b = 1, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1, and 0 < b ≤ 0.15.

[0026] For example, a neutralization reaction occurs when an alkaline aqueous solution is dropped into the acidic aqueous solution. The alkaline aqueous solution is prepared, for example, by mixing water, an ammonium ion donor, and a pH adjuster. The ammonium ion donor is not particularly limited, and for example, aqueous ammonia, ammonium sulfate aqueous solution, etc. can be used. The pH adjuster is not particularly limited, 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.

[0027] For example, by washing, filtering, and drying the precipitate, a dried product (precursor) is produced. Washing is performed, for example, by taking out the composite hydroxide by filtering the precipitate and then washing with water. Drying is carried out at a predetermined temperature for a predetermined time. The drying temperature may be, for example, 100 to 150 °C. The drying time may be, for example, 1 to 24 hours.

[0028] 《(b) Mixing step》 In the mixing step, a lithium salt is mixed with the precursor obtained in the precursor production step to produce a lithium mixture. The lithium salt is not particularly limited, and for example, lithium carbonate, lithium hydroxide, lithium nitrate, etc. can be used.

[0029] 《(c) Firing step》 In the firing step, a lithium metal-containing composite oxide is produced by firing the lithium mixture obtained in the mixing step. For firing, for example, a muffle furnace or the like may be used. The firing may be carried out, for example, in an inert gas atmosphere, in dry air, or in an oxygen atmosphere.

[0030] The firing temperature may be, for example, 500 to 1000 °C. When the firing temperature is less than 500 °C, Li and the precursor may not react sufficiently, and excess Li or unreacted precursor may remain, or the crystallinity of the obtained lithium metal-containing composite oxide may be insufficient. When the firing temperature exceeds 1000 °C, the external surface area of the obtained lithium metal-containing composite oxide may decrease, or abnormal sintering may occur between the secondary particles of the lithium metal-containing composite oxide, and the number of amorphous secondary particles may increase.

[0031] The firing time may be, for example, 5 to 60 hours. If the firing time is less than 5 hours, Li and the precursor may not react sufficiently, and excess Li or unreacted precursor may remain, or the crystallinity of the resulting lithium metal-containing composite oxide may be insufficient. If the firing temperature exceeds 60 hours, the outer surface area of the resulting lithium metal-containing composite oxide may decrease, abnormal sintering may occur between the secondary particles of the lithium metal-containing composite oxide, and the number of amorphous secondary particles may increase.

[0032] In the firing step, it is preferable that the firing temperature is 600 to 700 °C and the firing time is 48 to 52 hours. By performing the firing step under these conditions, the doping rate of the M element is improved.

[0033] 《(d) Crushing Step》 In the crushing step, the lithium metal-containing composite oxide obtained by the firing step is crushed. Thereby, a positive electrode active material having a desired particle size can be obtained. For crushing, for example, a jet mill or the like may be used. The crushing may be carried out, for example, in an inert gas atmosphere or in a nitrogen atmosphere.

[0034] <Lithium Ion Battery> FIG. 2 is a schematic diagram showing an example of the lithium ion battery (hereinafter may be abbreviated as "battery") of the present embodiment. The battery 100 includes a case 90. The case 90 has an arbitrary form. The case 90 may be, for example, rectangular or cylindrical. The case 90 may be made of, for example, metal, or may be a pouch made of an aluminum (Al) laminate film or the like. A positive electrode terminal 91 and a negative electrode terminal 92 may be provided on the case 90.

[0035] The case 90 houses the electrode body 50 and the 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.

[0036] FIG. 3 is a schematic diagram showing an example of the electrode body of the present 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 may be a wound type. The positive electrode 20, the separator 40, and the negative electrode 30 may all be strip-shaped sheets. The electrode body 50 may be formed, for example, by laminating the positive electrode 20, the separator 40 (the first sheet), the negative electrode 30, and the separator 40 (the second sheet) in this order. After winding, the electrode body 50 may be formed into a flat shape.

[0037] 《Positive Electrode》 The positive electrode 20 may include a positive electrode current collector and a positive electrode active material layer. The positive electrode current collector may include, for example, aluminum (Al) foil or the like. The positive electrode active material layer contains the above-described positive electrode active material. As long as the positive electrode 20 contains the above-described positive electrode active material, the positive electrode 20 may further contain an additional positive electrode active material. The positive electrode active material layer may further contain, for example, a conductive material, a binder, and the like.

[0038] The conductive material may include, for example, acetylene black (AB) or the like. The binder may include, for example, PVDF or the like. The blending amounts of the conductive material and the binder may be, for example, 0.1 to 10 parts by mass with respect to 100 parts by mass of the positive electrode active material.

[0039] 《Negative Electrode》 The negative electrode 30 may include a negative electrode current collector and a negative electrode active material layer. The negative electrode current collector may include, for example, copper (Cu) foil or the like. The negative electrode active material layer contains a negative electrode active material. The negative electrode active material may include, for example, at least one selected from the group consisting of graphite, soft carbon, and hard carbon. The negative electrode active material layer may further contain, for example, a conductive material, a binder, and the like.

[0040] The conductive material may include, for example, carbon nanotubes (CNTs) or the like. The binder may include, for example, carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), or the like. The blending amounts of the conductive material and the binder may be, for example, 0.1 to 10 parts by mass with respect to 100 parts by mass of the negative electrode active material.

[0041] 《Separator》 The separator 40 is porous. The separator 40 can permeate the electrolytic solution. The separator 40 separates the positive electrode 20 and the negative electrode 30. The separator 40 is electrically insulating. The separator 40 may include, for example, polyolefin resins such as polyethylene (PE), polypropylene (PP), or the like. The separator 40 may have, for example, a single-layer structure or a multilayer structure. The separator 40 may be composed substantially of a PE layer, or may be formed by laminating a PP layer, a PE layer, and a PP layer in this order. A heat-resistant layer may be formed, for example, on the surface of the separator 40.

[0042] 《Electrolytic Solution》 The electrolytic solution contains a solvent and a Li salt. The solvent is aprotic. The solvent may contain any component. The solvent may include, for example, at least one selected from the group consisting of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC).

[0043] The Li salt is a supporting electrolyte. The Li salt is dissolved in the solvent. The Li salt may include, for example, at least one selected from the group consisting of LiPF6 and LiBF4. The Li salt may have, for example, a molar concentration of 0.5 mol / L or more and 2.0 mol / L or less.

[0044] The electrolyte may further contain an optional additive. For example, the electrolyte may contain an additive in an amount of 0.01% by mass or more and 5% by mass or less. The additive may contain, for example, at least one selected from the group consisting of vinylene carbonate (VC) and vinyl ethylene carbonate (VEC).

Example

[0045] <No.1> 《Manufacture of the positive electrode active material》 (Precursor preparation step) An acidic aqueous solution was obtained by dissolving nickel sulfate and manganese sulfate in ion-exchanged water.

[0046] Ammonia water was supplied to the reaction vessel and stirred with a stirrer. Next, an alkaline aqueous solution was prepared by supplying an aqueous sodium hydroxide solution to the reaction vessel. While the alkaline aqueous solution in the reaction vessel was stirred by the stirrer, the acidic aqueous solution was dropped into the alkaline aqueous solution. During the dropping of the acidic aqueous solution, ammonia water and the aqueous sodium hydroxide solution were appropriately added so that the ammonia concentration and pH of the reaction solution became constant.

[0047] The precipitate after the reaction was filtered, washed with water, and filtered again to obtain a composite hydroxide. The obtained composite hydroxide was dried at 120 °C for 16 hours to obtain a precursor.

[0048] (Mixing step) The above precursor and lithium carbonate were mixed in a mortar to obtain a lithium mixture.

[0049] (Firing step) The above lithium mixture was fired in a muffle furnace set at 600 to 700 °C for 50 hours to obtain a lithium metal-containing composite oxide.

[0050] (Crushing step) The above lithium metal-containing composite oxide was crushed using a jet mill to obtain the positive electrode active material of No.1.

[0051] <No.2-1,2,3,4~No.16-1,2,3,4> Nickel sulfate, manganese sulfate, and the sulfate of element M were 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 were obtained by the same process as No.1. The element M contained in the positive electrode active material of each No. is as shown in Figs. 5 and 6.

[0052] 《Manufacture of Lithium-Ion Batteries》 As the positive electrode material, 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 were prepared. The positive electrode was fabricated using the above materials.

[0053] As the negative electrode material, natural graphite as the negative electrode active material, CMC and SBR as the binder, and Cu foil as the negative electrode current collector were prepared. The negative electrode was fabricated using the above materials.

[0054] As the separator, a porous resin (PP / PE / PP) with PP layers laminated on both sides of the PE layer was prepared. As the electrolyte, a mixture of EC, DMC, and EMC containing a supporting salt (LiPF6) dissolved at a concentration of 1 mol / L was prepared. Using the above positive electrode, negative electrode, separator, and electrolyte, test cells for evaluation of No.1~16 were manufactured.

[0055] <Evaluation> 《c-axis length》 At 100% SOC, the test battery was disassembled to recover the positive electrode active material. Using an X-ray diffractometer, X-rays were irradiated onto the positive electrode active material of each No. after production (positive electrode active material at 0% SOC) and the positive electrode active material of each No. after the above recovery under the following measurement conditions to obtain an X-ray diffraction pattern. From the obtained X-ray diffraction pattern, the crystal peak data was subjected to Rietveld analysis, and the lattice constant was calculated to calculate the c-axis length in the crystal. Then, by obtaining 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 were confirmed. The results are shown in Figs. 4 to 6. Note that "SOC (State Of Charge)" indicates the percentage of the charge capacity of the battery at that time with respect to the full charge capacity of the battery.

[0056] [Measurement Conditions] X-ray output: 45 kV, 200 mA X-ray source: CuKα ray (wavelength: 1.54051 Å), single crystal monochromator Diffraction angle: 10 to 120° Measurement temperature: room temperature (25 °C) Scanning speed: 1 second / step Also, from the obtained X-ray diffraction pattern, the composition of each positive electrode active material was confirmed. The ratio of the M element contained in each positive electrode active material was calculated from the difference in the c-axis length of the positive electrode active material of each No. obtained above and the ionic radius of each M element. The compositions of each positive electrode active material are shown in Figs. 5 and 6.

[0057] 《Rate of Capacity Degradation》 The initial capacity (initial discharge capacity) of each test battery was measured by the following constant current-constant voltage charging and constant current discharging. Also, the rate of capacity degradation of each test battery other than No. 1 was calculated by the following formula (2). The results are shown in Figs. 5 and 6.

[0058] Constant current-constant voltage charging: current = 0.1C, upper limit voltage = 4.3, cut-off current = 0.02C Constant current discharging: current = 0.2C, cut-off voltage = 3V (Initial capacity of No. 1 test battery - Initial capacity of each test battery) / Initial capacity of No. 1 test battery × 100 ··· (2) <Results> As shown in FIGS. 4 to 6, the difference in the c-axis length of the positive electrode active material other than No. 1 containing the M element was shorter than the difference in the c-axis length of the No. 1 positive electrode active material not containing the M element. 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 are suppressed.

[0059] Also, as shown in FIGS. 5 and 6, by adding the M element to the positive electrode active material, the capacity of the test battery decreases, but in Nos. 10 to 13, it can be seen that the rate of capacity decrease due to the addition of the M element is smaller than the rate of capacity decrease of other Nos. 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 the capacity of the battery can be suppressed.

[0060] This embodiment and these examples are illustrative in all respects. This embodiment and these examples are not restrictive. The technical scope of the present disclosure includes all modifications within the meaning and scope equivalent to the description of the claims. For example, any configurations are extracted from this embodiment and these examples, and their arbitrary combinations are also initially planned.

Description of Reference Numerals

[0061] 20 Positive electrode, 30 Negative electrode, 40 Separator, 50 Electrode body, 90 Case, 91 Positive electrode terminal, 92 Negative electrode terminal, 100 Lithium ion battery.

Claims

1. comprising a lithium metal-containing composite oxide, wherein the lithium metal-containing composite oxide is represented by the following formula (1): Li ａ Ni ｘ Co ｙ Mn ｚ M ｂ O ２ (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, 0 < b ≦ 0.15, and M is a lanthanoid or a transition element having 4 or less electrons in the d orbital, and is a positive electrode active material.

2. The positive electrode active material according to Claim 1, wherein the M is at least one selected from the group consisting of 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 precursor preparation step of preparing a precursor containing M; a mixing step of preparing a lithium mixture by mixing the precursor and lithium; a firing step of preparing a lithium metal-containing composite oxide by firing the lithium mixture; a pulverizing step of producing a positive electrode active material by pulverizing the lithium metal-containing composite oxide, and the firing step is performed at a temperature of 600°C to 700°C for 48 to 52 hours, and is a method for producing a positive electrode active material.

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