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

Abstract

The invention relates to a positive electrode active material, a positive electrode, a lithium ion battery, and a manufacturing method of the positive electrode active material. The positive electrode active material has a composition represented by LixNiaCobMncM1dM2eO2, and the TM interlayer distance (D) is equal to or greater than # imgabs 0 # and equal to or less than # imgabs 1 #. (In the composition, 0.1 < = x < = 1.5, 0.5 < = a < = 1.0, 0 < = b < = 0.3, 0 < = c < = 0.3, a + b + c = 1.0, 0.0005 < = d < = 0.050, and 0.0005 < = e < = 0.050, M1 represents at least one element selected from the group consisting of Ba, Pr, La, Y, Sr, Ce, Se, Hf, Rh, Zr, and Sn, and M2 represents at least one element selected from the group consisting of W, Re, Sb, Sn, Ta, Os, Ir, Mo, Nb, Tc, Ru, Ga, Ag, Pd, Ge, As, Zr, In, Pt, Al, and Ti. )

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 producing the positive electrode active material. Background Art

[0002] Conventionally, various additive elements have been added to positive electrode active materials used in batteries in order to improve the resistance characteristics of the batteries.

[0003] For example, Japanese Patent Publication No. 2022-513681 discloses a positive electrode active material, a method for producing the positive electrode active material, and a positive electrode and a secondary battery containing the positive electrode active material. The positive electrode active material comprises a nickel-cobalt-manganese lithium transition metal oxide containing 60 mol% or more of nickel relative to the total molar number of metals excluding lithium, the nickel-cobalt-manganese lithium transition metal oxide being doped with a doping element M1 (the doping element M1 being a metal element containing Al) and a doping element M2 (the doping element M2 being one or more metal elements selected from Mg, La, Ti, Zn, B, W, Ni, Co, Fe, Cr, V, Ru, Cu, Cd, Ag, Y, Sc, Ga, In, As, Sb, Pt, Au, and Si), the nickel-cobalt-manganese lithium transition metal oxide containing 100 to 10,000 ppm of the doping element M1, and containing the doping elements M1 and M2 in a weight ratio of 50:50 to 99:1.

[0004] In addition, Japanese Patent Publication No. 2021-177491 discloses a positive electrode active material for a lithium secondary battery, which includes nickel-based lithium metal oxide particles doped with Zr and Al, wherein the nickel-based lithium metal oxide particles are composed of a core portion having a molar content of nickel within a certain range, and a shell portion surrounding the outer surface of the core portion, with a concentration gradient (gradient) in which the molar content of nickel gradually decreases in the direction from the boundary surface with the core portion to the outermost shell. Summary of the Invention

[0005] Problems to be solved by the invention

[0006] In existing positive electrode active materials, additive elements are added to improve battery resistance, for example. However, certain additive elements sometimes have difficulty incorporating into the crystal structure of the positive electrode active material, making it difficult to contribute to improved resistance. Therefore, further improvements are needed to reduce battery resistance when using these positive electrode active materials in lithium-ion batteries.

[0007] The present disclosure has been made in view of the above-mentioned actual situation, and its purpose is to provide a positive electrode active material that can achieve low battery resistance when used in a battery, a positive electrode including the positive electrode active material, a lithium ion battery including the positive electrode, and a method for producing the positive electrode active material.

[0008] Means for solving problems

[0009] Means for solving the above-mentioned problems include the following.

[0010] <1>

[0011] The positive electrode active material is composed of Li x Ni a Co b Mn c M1 d M2 e The composition represented by O2, the distance D between TM layers is Above and the following,

[0012] In the composition, 0.1≤x≤1.5, 0.5≤a≤1.0, 0≤b≤0.3, 0≤c≤0.3, a+b+c=1.0, 0.0005≤d≤0.050, and 0.0005≤e≤0.050, the M1 represents at least one element selected from Ba, Pr, La, Y, Sr, Ce, Se, Hf, Rh, Zr and Sn, and the M2 represents at least one element selected from W, Re, Sb, Sn, Ta, Os, Ir, Mo, Nb, Tc, Ru, Ga, Ag, Pd, Ge, As, Zr, In, Pt, Al and Ti.

[0013] <2>

[0014] The positive electrode active material according to <1>, wherein the combination of the M1 element and the M2 element is at least one combination selected from the group consisting of Ba-W, Pr-W, La-W, Hf-W, Sr-Nb, Pr-Ta, YW, Sr-W, Ce-W, Pr-Re, Ba-Re, Sr-Sb, Se-W, Y-Re, Sr-Re, Rh-W, Zr-W, Sr-Sn, Y-Ta, Y-Sb, Sr-Os, Sr-Ta, Ce-Re, La-Re, Ba-Ta, Sr-Ir, Sn-W, Sr-Mo, Ba-Ti, Ba-Zr, and Ba-Al.

[0015] <3>

[0016] The positive electrode active material according to <1>, wherein the combination of the M1 element and the M2 element is at least one combination selected from La—W, Pr—W, and Sr—Nb.

[0017] <4>

[0018] The positive electrode active material according to any one of <1> to <3>, wherein a satisfies 0.7≤a≤1.0.

[0019] <5>

[0020] The positive electrode active material according to any one of <1> to <4>, wherein the M1 element is Sr.

[0021] <6>

[0022] The positive electrode active material according to any one of <1> to <4>, wherein the M1 element is at least one element selected from La and Ce.

[0023] <7>

[0024] The positive electrode active material according to any one of <1> to <6>, wherein the M2 element is W.

[0025] <8>

[0026] A positive electrode comprising the positive electrode active material according to any one of <1> to <7>.

[0027] <9>

[0028] A lithium-ion battery comprising the positive electrode according to <8>.

[0029] <10>

[0030] A method for producing a positive electrode active material, comprising:

[0031] a step of mixing raw materials respectively containing Ni, Co, and Mn, a raw material containing Li, a raw material containing an element represented by M1, and a raw material containing an element represented by M2 to obtain a mixture; and

[0032] The mixture is heated in an oxygen atmosphere at a heating rate A of 1°C / min to 10°C / min to a maximum reaching temperature X-100°C, and then heated from the maximum reaching temperature X-100°C to the maximum reaching temperature X at a heating rate B of 0.1°C / min to 5°C / min and slower than the heating rate A, to be fired.

[0033] The M1 represents at least one element selected from Ba, Pr, La, Y, Sr, Ce, Se, Hf, Rh, Zr and Sn, and the M2 represents at least one element selected from W, Re, Sb, Sn, Ta, Os, Ir, Mo, Nb, Tc, Ru, Ga, Ag, Pd, Ge, As, Zr, In, Pt, Al and Ti.

[0034] Effects of the Invention

[0035] According to the present disclosure, there are provided a positive electrode active material capable of achieving low battery resistance when used in a battery, a positive electrode including the positive electrode active material, a lithium ion battery including the positive electrode, and a method for producing the positive electrode active material. DETAILED DESCRIPTION

[0036] The following describes an embodiment as an example of the present disclosure. These descriptions and examples are for illustration of the embodiment and do not limit the scope of the invention.

[0037] In the numerical ranges described in this specification, the upper limit or lower limit described in one numerical range can be replaced by the upper limit or lower limit of the numerical range described in another stage. In addition, in the numerical ranges described in this specification, the upper limit or lower limit of the numerical range can be replaced by the value shown in the Examples.

[0038] Each component may contain a variety of compatible substances.

[0039] When referring to the amount of each component in a composition, if a plurality of substances corresponding to each component are present in the composition, the amount refers to the total amount of the plurality of substances present in the composition unless otherwise specified.

[0040] The term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes as long as the intended effect of the process is achieved.

[0041] <Positive electrode active material>

[0042] The positive electrode active material according to the embodiment of the present disclosure has a x Ni a Co b Mn c M1 d M2 e The composition represented by O2.

[0043] Moreover, the distance between TM layers (D) is Above and the following.

[0044] (In the composition, 0.1≤x≤1.5, 0.5≤a≤1.0, 0≤b≤0.3, 0≤c≤0.3, a+b+c=1.0, 0.0005≤d≤0.050, and 0.0005≤e≤0.050; M1 represents at least one element selected from Ba, Pr, La, Y, Sr, Ce, Se, Hf, Rh, Zr, and Sn; and M2 represents at least one element selected from W, Re, Sb, Sn, Ta, Os, Ir, Mo, Nb, Tc, Ru, Ga, Ag, Pd, Ge, As, Zr, In, Pt, Al, and Ti.)

[0045] So far, for the purpose of improving the resistance characteristics in the battery, additional elements (so-called doping elements) have been added to the positive electrode active material. It should be noted that in the positive electrode active material, a crystal structure having a Li layer containing the Li element and a TM layer containing a transition metal (transition metal) such as Ni, Co, and Mn is formed. However, it is difficult for specific doping elements to enter the crystal structure of the positive electrode active material, and the structure stabilization effect is small. Therefore, from the perspective of reducing the battery resistance when the positive electrode active material is used in a lithium ion battery, further improvement is needed.

[0046] The positive electrode active material involved in the embodiment of the present disclosure includes two doping elements, M1 and M2. By combining the doping elements of M1 and M2, it is possible to make the doping elements exist in large quantities in the crystal structure of the positive electrode active material, greatly improving the structural stabilization effect. It is believed that this is because the element represented by M1 (M1 element) has a large average ion radius and is therefore difficult to enter the crystal structure of the positive electrode active material, and by combining with the element represented by M2 (M2 element), it becomes easy to enter the crystal structure. As a result, the TM interlayer distance (D) in the crystal structure of the positive electrode active material becomes the above-mentioned range, that is, the interlayer distance becomes larger.

[0047] Furthermore, due to the enhanced structural stabilization effect, Ni mixing (cation mixing) into the Li layer during charge and discharge in the lithium ion battery is suppressed, and the obstruction of Li ion movement during charge and discharge is suppressed, thereby suppressing an increase in battery resistance.

[0048] Next, the positive electrode active material according to the embodiment of the present disclosure will be described in detail.

[0049] (composition)

[0050] The positive electrode active material according to the embodiment of the present disclosure has a x Ni a Co b Mn c M1 d M2e The composition represented by O2.

[0051] (In the composition, 0.1≤x≤1.5, 0.5≤a≤1.0, 0≤b≤0.3, 0≤c≤0.3, a+b+c=1.0, 0.0005≤d≤0.050, and 0.0005≤e≤0.050; M1 represents at least one element selected from Ba, Pr, La, Y, Sr, Ce, Se, Hf, Rh, Zr, and Sn; and M2 represents at least one element selected from W, Re, Sb, Sn, Ta, Os, Ir, Mo, Nb, Tc, Ru, Ga, Ag, Pd, Ge, As, Zr, In, Pt, Al, and Ti.)

[0052] In the composition of the particles of compound A, the Li ratio x is 0.1 to 1.5, preferably 0.3 to 1.4, and more preferably 0.5 to 1.2, from the viewpoint of resistance characteristics in the battery.

[0053] The Ni ratio a is 0.5 to 1.0, preferably 0.6 to 0.9, and more preferably 0.7 to 0.8, from the perspective of resistance characteristics in the battery. It should be noted that the Ni ratio a can be increased, in which case the ratio a is preferably 0.6 to 1.0 (0.6 ≤ a ≤ 1.0), and more preferably 0.7 to 1.0 (0.7 ≤ a ≤ 1.0).

[0054] The ratio b of Co is 0 or more and 0.3 or less, preferably 0 or more and 0.2 or less, and more preferably 0.1 or more and 0.2 or less, from the viewpoint of resistance characteristics in the battery.

[0055] The Mn ratio c is 0 or more and 0.3 or less, preferably 0 or more and 0.2 or less, and more preferably 0.1 or more and 0.2 or less, from the viewpoint of resistance characteristics in the battery.

[0056] In addition, the total ratio (a+b+c) of Ni, Co, and Mn is 1.0.

[0057] The ratio d of the M1 element is 0.0005 or more and 0.05 or less, preferably 0.001 or more and 0.040 or less, and more preferably 0.003 or more and 0.030 or less, from the viewpoint of resistance characteristics in the battery.

[0058] The ratio e of the M2 element is 0.0005 or more and 0.05 or less, preferably 0.001 or more and 0.040 or less, and more preferably 0.003 or more and 0.030 or less, from the viewpoint of resistance characteristics in the battery.

[0059] The positive electrode active material contains an M1 element and an M2 element as additional elements. M1 represents at least one element selected from Ba, Pr, La, Y, Sr, Ce, Se, Hf, Rh, Zr, and Sn, and M2 represents at least one element selected from W, Re, Sb, Sn, Ta, Os, Ir, Mo, Nb, Tc, Ru, Ga, Ag, Pd, Ge, As, Zr, In, Pt, Al, and Ti.

[0060] The positive electrode active material contains the above-mentioned M1 element and M2 element as additional elements, so that the battery resistance can be reduced when the positive electrode active material is used in a battery.

[0061] It should be noted that from the viewpoint of reducing battery resistance, the combination of the M1 element and the M2 element is preferably at least one combination selected from Ba-W, Pr-W, La-W, Hf-W, Sr-Nb, Pr-Ta, YW, Sr-W, Ce-W, Pr-Re, Ba-Re, Sr-Sb, Se-W, Y-Re, Sr-Re, Rh-W, Zr-W, Sr-Sn, Y-Ta, Y-Sb, Sr-Os, Sr-Ta, Ce-Re, La-Re, Ba-Ta, Sr-Ir, Sn-W, Sr-Mo, Ba-Ti, Ba-Zr and Ba-Al.

[0062] Furthermore, from the viewpoint of reducing battery resistance, the combination of the M1 element and the M2 element is more preferably at least one combination selected from the group consisting of La—W, Pr—W, and Sr—Nb.

[0063] As the M1 element, for example, Sr is preferable.

[0064] Furthermore, from the viewpoint of resistance characteristics in the battery, etc., the M1 element is preferably at least one element selected from La and Ce.

[0065] As the M2 element, for example, W is preferable.

[0066] (TM layer distance (D))

[0067] The distance (D) between TM layers of the positive electrode active material according to the embodiment of the present disclosure is Above and the following.

[0068] The positive electrode active material forms a crystal structure comprising a Li layer containing the element Li and a TM layer containing a transition metal such as Ni, Co, or Mn. Furthermore, a TM layer distance (D) within the above range indicates that the TM layer is sufficiently large, meaning that a large amount of the M1 element, with its large ionic radius, is incorporated into the TM layer. This enhances the structural stabilization of the positive electrode active material and suppresses increases in battery resistance.

[0069] If the distance between TM layers (D) is less than On the other hand, the greater the distance between TM layers (D) is, the greater the resistance of the battery will be. It is more difficult to form a TM layer with a large interlayer distance.

[0070] The distance (D) between TM layers is preferably Above and The following are more preferably Above and the following.

[0071] Here, the method for measuring the TM interlayer distance (D) is explained. First, X-ray diffraction (XRD) diffraction is performed on the positive electrode active material, and Rietveld analysis (Fullprof) is performed on the XRD diffraction data. It should be noted that Fullprof is an application for Rietveld analysis of XRD diffraction data, which can calculate the lattice constant and atomic coordinates of the material.

[0072] Then, find the c-axis length (C h ) and the z coordinate of oxygen (Z oxy ). It should be noted that the so-called Chi2 value is a convergence index value obtained by fitting the XRD diffraction data using the least squares method, and the Chi2 value is minimized when the deviation between the XRD diffraction data and the curve fitting is minimized.

[0073] Then, the TM interlayer distance (D) is calculated based on the following formula.

[0074] Formula: D = 2[(1 / 3)-Z oxy ]C h

[0075] It should be noted that the positive electrode active material has a crystal structure having a Li layer containing Li element and a TM layer. The interlayer distance of the Li layer is not particularly limited, and is, for example, Above and The following, further about.

[0076] <Method for producing positive electrode active material>

[0077] Next, a method for producing a positive electrode active material according to an embodiment of the present disclosure will be described. The positive electrode active material according to the embodiment of the present disclosure described above can be produced by the method for producing a positive electrode active material according to an embodiment of the present disclosure described below.

[0078] The manufacturing method of the positive electrode active material involved in the embodiment of the present disclosure includes: a process of mixing raw materials containing Ni, Co and Mn, a raw material containing Li, a raw material containing an element represented by M1, and a raw material containing an element represented by M2 to obtain a mixture; and a sintering process of heating the mixture in an oxygen atmosphere at a heating rate A of 1°C / minute to a maximum reaching temperature X-100°C, and heating the mixture from the maximum reaching temperature X-100°C to the maximum reaching temperature X at a heating rate B of 0.1°C / minute to 5°C / minute and slower than the heating rate A.

[0079] (M1 represents at least one element selected from Ba, Pr, La, Y, Sr, Ce, Se, Hf, Rh, Zr, and Sn, and M2 represents at least one element selected from W, Re, Sb, Sn, Ta, Os, Ir, Mo, Nb, Tc, Ru, Ga, Ag, Pd, Ge, As, Zr, In, Pt, Al, and Ti.)

[0080] In the positive electrode active material, the M1 element, which has a large ionic radius, has the characteristic of being difficult to enter the TM layer in the crystal structure. However, in the method for manufacturing the positive electrode active material according to the embodiment of the present disclosure, the M1 element and the M2 element are used in combination, and the sintering temperature is gradually increased as the maximum reaching temperature X is approached. Specifically, the temperature increase rate from the maximum reaching temperature X-100°C to the maximum reaching temperature X is slowed down. As a result, the M1 element enters the TM layer near X-100°C, and the added elements in the TM layer diffuse near the maximum reaching temperature X°C. Therefore, the M1 element and the M2 element can be present in large quantities in the crystal structure of the positive electrode active material, and the TM layer distance (D) can be made within the above-mentioned range, that is, the interlayer distance is increased.

[0081] It should be noted that the method for producing a positive electrode active material according to an embodiment of the present disclosure preferably includes the following steps (1) to (5).

[0082] (1) Step of preparing a solution by dissolving raw materials containing Ni, Co, and Mn (raw material dissolution)

[0083] (2) Adding the above solution to an alkaline solution to precipitate the hydroxide (crystallization)

[0084] (3) A step of collecting a precipitate from the alkaline solution

[0085] (4) A step of mixing the precipitate with a raw material containing Li, a raw material containing an element represented by M1, and a raw material containing an element represented by M2 to obtain a mixture (mixing)

[0086] (5) Step of firing the mixture (firing)

[0087] Each step is described below in detail.

[0088] (1) Step of preparing a solution by dissolving raw materials containing Ni, Co, and Mn

[0089] A solution is prepared by dissolving a raw material containing Ni, a raw material containing Co, and a raw material containing Mn.

[0090] For example, a solution can be prepared by dissolving a raw material containing Ni, a raw material containing Co, and a raw material containing Mn in a solvent such as water. The concentration of the solution is preferably in the range of 10 to 40 mass %. The Ni / Co / Mn ratio is preferably 1.0 / 0.8 to 1.2 / 0.8 to 1.2 (atm %) relative to Ni:1.0.

[0091] Examples of raw materials containing Ni include sulfates such as NiSO 4 , examples of raw materials containing Co include sulfates such as CoSO 4 , and examples of raw materials containing Mn include sulfates such as MnSO 4 .

[0092] (2) Adding a solution to an alkaline solution to precipitate hydroxide

[0093] Next, the solution is added to the alkaline solution to precipitate the hydroxide. As a result, particles formed from the hydroxides of Ni, Co, and Mn are crystallized, and the particles are obtained as a precipitate. In this step, for example, the alkaline solution for hydroxide precipitation is controlled to a certain pH (e.g., pH 10-12), and the solution and NH3 are simultaneously added dropwise to precipitate the transition metal hydroxides.

[0094] (3) Step of taking precipitate from alkaline solution

[0095] Next, a precipitate is taken from the alkaline solution.

[0096] Methods for collecting the precipitated particles include, for example, filtration and water washing. Examples include a method in which the precipitate (particles) is first removed by filtration, then washed with water, and then the washed liquid is filtered to remove the precipitate (particles). The washed precipitate (particles) may be further dried.

[0097] (4) A step of mixing the precipitate with a raw material containing Li, a raw material containing an element represented by M1, and a raw material containing an element represented by M2 to obtain a mixture.

[0098] Next, the collected precipitate (particles) is mixed with a raw material containing Li, a raw material containing the element represented by M1, and a raw material containing the element represented by M2 to obtain a mixture. For example, the collected precipitate particles can be mixed with the raw material containing Li, the raw material containing the element represented by M1, and the raw material containing the element represented by M2 in a mortar.

[0099] Examples of raw materials containing Li include Li 2 CO 3 and LiOH.

[0100] As raw materials containing M1 (i.e., at least one element selected from Ba, Pr, La, Y, Sr, Ce, Se, Hf, Rh, Zr and Sn), oxides of each element (such as BaO, Pr2O3, La2O3 and SrO) and the like can be listed.

[0101] As raw materials containing M2 (i.e., at least one element selected from W, Re, Sb, Sn, Ta, Os, Ir, Mo, Nb, Tc, Ru, Ga, Ag, Pd, Ge, As, Zr, In, Pt, Al and Ti), oxides of each element (such as W2O3, MoO3 and NbO) can be listed.

[0102] (5) Process of firing the mixture

[0103] Next, a mixture of the collected precipitate (particles), a raw material containing Li, a raw material containing the element represented by M1, and a raw material containing the element represented by M2 is calcined. For example, the first mixture can be calcined in a calcining furnace (muffle furnace, etc.).

[0104] As the heating conditions during sintering, the temperature is raised to the maximum achieved temperature X-100°C at a heating rate A of 1°C / minute to 10°C / minute, and the temperature is raised from the maximum achieved temperature X-100°C to the maximum achieved temperature X at a heating rate B of 0.1°C / minute to 5°C / minute, which is slower than the heating rate A. By adjusting the heating conditions as described above, the M1 element and the M2 element can be present in large quantities in the crystal structure of the positive electrode active material, and the TM interlayer distance (D) can be adjusted to the above range, that is, the interlayer distance can be increased.

[0105] The temperature increase rate A to the maximum ultimate temperature X-100° C. is 1° C. / minute to 10° C. / minute, preferably 3° C. / minute to 6° C. / minute.

[0106] The heating rate B from the maximum temperature X-100°C to the maximum temperature X is 0.1°C / min to 5°C / min and slower than the heating rate A, preferably 0.5°C / min to 2°C / min.

[0107] The time for heating from the maximum achieved temperature X-100° C. to the maximum achieved temperature X° C. is preferably 20 minutes to 1000 minutes, more preferably 50 minutes to 200 minutes.

[0108] The firing conditions preferably have a maximum temperature X of 500° C. to 1500° C., more preferably 800° C. to 1200° C. The firing is performed in an oxygen atmosphere, and the heating time after reaching the maximum temperature X can be set to 5 hours to 20 hours.

[0109] In order to make the positive electrode active material have a predetermined particle size, the mixture after calcination may be crushed. Examples of the crushing method include a crushing method using a pulverizer (eg, a jet mill).

[0110] Through these steps, the positive electrode active material according to the embodiment of the present disclosure can be obtained.

[0111] Lithium-ion batteries

[0112] The lithium-ion battery according to the embodiment of the present disclosure includes the positive electrode active material according to the embodiment of the present disclosure. The lithium-ion battery includes, for example, a negative electrode, a positive electrode, a separator, and an electrolyte.

[0113] The lithium-ion battery according to the embodiments of the present disclosure may be a solid-state battery having a solid electrolyte or a liquid-type battery having a liquid electrolyte. Furthermore, it may be a bipolar battery having a positive electrode active material layer and a negative electrode active material layer on both sides of a current collector that functions as a positive electrode current collector and a negative electrode current collector.

[0114] (positive electrode)

[0115] The positive electrode includes, for example, a positive electrode current collector and a positive electrode active material layer fixed on the positive electrode current collector.

[0116] The positive electrode active material layer contains the positive electrode active material according to the embodiment of the present disclosure as the positive electrode active material. The details of the positive electrode active material have been described above and are therefore omitted here.

[0117] The positive electrode active material layer may further include a conductive material in addition to the positive electrode active material, and may further include other components such as a binder and various additives. Examples of the conductive material include non-graphitizable carbon, acetylene black, carbon black and other easily graphitizable carbons, graphite, etc. Examples of the binder include halogenated vinyl resins such as polyvinylidene fluoride (PVdF).

[0118] The positive electrode current collector is preferably a conductive member made of a metal with good conductivity (such as aluminum). It may also be a current collector that functions as both a positive electrode current collector and a negative electrode current collector (i.e., a bipolar battery).

[0119] (negative electrode)

[0120] The negative electrode, for example, includes a negative electrode current collector and a negative electrode active material layer fixed to the negative electrode current collector. The negative electrode current collector is preferably a conductive member made of a metal with good conductivity (e.g., copper). It should be noted that the current collector may function as both a positive electrode current collector and a negative electrode current collector (i.e., a bipolar battery).

[0121] The negative electrode active material layer contains a negative electrode active material. As the negative electrode active material, for example, graphite-based carbon such as natural graphite, artificial graphite, and amorphous coated graphite can be exemplified. The proportion of graphite in the graphite-based carbon is about 50% by mass or more, preferably 80% by mass or more. The negative electrode active material layer can be composed only of the negative electrode active material, and as needed, it can contain components other than the negative electrode active material, such as a thickener, a binder, etc. As a thickener, for example, a cellulose such as carboxymethyl cellulose (CMC) can be exemplified. As a binder, for example, rubbers such as styrene butadiene copolymer (SBR) and halogenated vinyl resins such as polyvinylidene fluoride (PVdF) can be exemplified.

[0122] (Separator)

[0123] The separator is an electrically insulating porous film. The separator electrically isolates the positive electrode and the negative electrode. The separator may have a thickness of, for example, 5 to 30 μm. The separator may be composed of, for example, a porous polyethylene (PE) film, a porous polypropylene (PP) film, etc. The separator may have a multilayer structure. For example, the separator may be composed by stacking a porous PP film, a porous PE film, and a porous PP film in sequence. The separator may have a heat-resistant layer on its surface. The heat-resistant layer contains a heat-resistant material. Examples of the heat-resistant material include metal oxide particles such as aluminum oxide, and high-melting-point resins such as polyimide.

[0124] (Electrolyte)

[0125] The battery according to the embodiment of the present disclosure may further be a liquid-based battery having an electrolyte solution, and a non-aqueous electrolyte solution is particularly preferred.

[0126] Solvent

[0127] The non-aqueous electrolyte solution contains a solvent (non-aqueous solvent) and an electrolyte.

[0128] Examples of the solvent (non-aqueous solvent) include ethyl carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), propylene carbonate (PC), fluoroethylene carbonate (FEC), N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(fluorosulfonyl)imide (DEME), 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMI), and 1-ethyl-2,3-dimethylimidazolium bis(fluorosulfonyl)imide (DEMI-FSI).

[0129] Electrolytes

[0130] Examples of the electrolyte in the electrolyte solution include lithium salts, such as lithium bis(fluorosulfonyl)imide (LiFSI), LiPF6 (lithium hexafluorophosphate), lithium tetrafluoroborate (LiBF4), and Li[N(CF3SO2)2].

[0131] The amount of the electrolyte may be, for example, 1.0 to 2.0 mol / L, preferably 1.0 to 1.5 mol / L.

[0132] In addition to the solvent and electrolyte, the electrolyte may contain various additives, such as thickeners, film-forming agents, and gas generators. The electrolyte is typically a non-aqueous electrolyte that is liquid at room temperature (e.g., 25±10°C). The electrolyte is typically liquid under the operating environment of the battery (e.g., a temperature range of -20°C to +60°C).

[0133] (use)

[0134] Examples of applications of the battery include power sources for hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), and battery electric vehicles (BEV).

[0135] Example

[0136] The present disclosure will be described below based on examples, but the present disclosure is not limited to these examples.

[0137] <Example 1>

[0138] (Synthesis of Positive Electrode Active Material)

[0139] The following method was used to synthesize the x Ni a Co b Mn c M1 d M2 eA positive electrode active material having a composition represented by O2, x, a, b, c, d, and e having the ratios shown in Table 1, and using the elements described in Table 1 as the element represented by M1 and the element represented by M2.

[0140] Raw material solution

[0141] NiSO4, CoSO4, and MnSO4 were dissolved in ion-exchanged water to obtain a raw material solution. The ratio of Ni / Co / Mn was 1 / 1 / 1 (atm%), and the concentration of the aqueous solution was 30% by mass.

[0142] ·crystallization

[0143] A certain amount of NH3 aqueous solution is placed in a reaction vessel and nitrogen is replaced while stirring with a stirrer. NaOH is added to the reaction vessel to adjust the pH to alkaline. Next, while controlling the pH in the reaction vessel to a certain level (pH 10-12), the raw material solution and NH3 are added dropwise to precipitate the transition metal hydroxide.

[0144] Washing, filtering, drying

[0145] The precipitated transition metal hydroxide is taken out by filtration, ion exchange water is added, stirred with a spoon to disperse it, and washed with water.

[0146] Next, the washed liquid is filtered to take out the transition metal hydroxide.

[0147] Next, the filtered transition metal hydroxide was dried at 120° C. for 16 hours to evaporate moisture.

[0148] Mixture of Li raw material, M1 raw material and M2 raw material

[0149] The dried transition metal hydroxide, Li2CO3 and LiOH as Li raw materials, BaO as M1 raw material, and W2O3 as M2 raw material were mixed in a mortar.

[0150] Burning and crushing

[0151] A mixture of the transition metal hydroxide, the Li raw material, the M1 raw material, and the M2 raw material was calcined in a calcination furnace (muffle furnace). The calcination conditions were as follows: the maximum temperature (X) was 800°C, the heating rate (°C / min) to the maximum temperature (X) - 100°C, and the heating rate (°C / min from the maximum temperature (X) - 100°C to the maximum temperature (X) were as shown in Table 2, the heating time after reaching the maximum temperature was 10 hours, and calcination was performed in an oxygen atmosphere.

[0152] Next, the fired mixture is pulverized using a pulverizer (jet mill) to reduce the mixture to a predetermined particle size.

[0153] In this manner, the positive electrode active material of Example 1 was obtained.

[0154] <Examples 2 to 6>

[0155] The positive electrode active materials of each embodiment were obtained in the same manner as in Example 1, except that the M1 raw material in Example 1 was changed from BaO to Pr2O3 (Example 2), La2O3 (Example 3) and SrO (Examples 4 to 6), and the M2 raw material was changed from W2O3 to W2O3 (Examples 2 to 4), MoO3 (Example 5) and NbO (Example 6).

[0156] Comparative Example 1

[0157] Except that the M1 raw material and the M2 raw material in Example 1 are not added, the sintering conditions are such that the heating rate (°C / minute) until the maximum reached temperature (X)-100°C and the heating rate (°C / minute) from the maximum reached temperature (X)-100°C to the maximum reached temperature (X) are the conditions described in Table 2 (i.e., all are set to the same heating rate). In the same manner as in Example 1, the positive electrode active material of Comparative Example 1 is obtained.

[0158] <Comparative Examples 2 and 4>

[0159] Except that the M1 raw material in Example 1 is changed from BaO to ZrO (Comparative Example 2) and La2O3 (Comparative Example 4), and the M2 raw material is changed from W2O3 to Al2O3 (Comparative Example 2) and W2O3 (Comparative Example 4), the sintering conditions are such that the heating rate (°C / minute) until the maximum reached temperature (X)-100°C and the heating rate (°C / minute) from the maximum reached temperature (X)-100°C to the maximum reached temperature (X) are the conditions described in Table 2 (i.e., the same heating rate is set), the positive electrode active materials of Comparative Examples 2 and 4 are obtained in the same manner as in Example 1.

[0160] Comparative Example 3

[0161] The positive electrode active material of Comparative Example 3 was obtained in the same manner as in Example 1, except that the M1 raw material and the M2 raw material in Example 1 were changed to the four raw materials of Al2O3, MgO, TiO2 and La2O3, and the sintering conditions were such that the heating rate (°C / minute) to the maximum reached temperature (X)-100°C and the heating rate (°C / minute) from the maximum reached temperature (X)-100°C to the maximum reached temperature (X) were the same as in Table 2 (i.e., the heating rate was the same).

[0162] [Production of battery cells]

[0163] Battery cells were produced using the positive electrode active materials obtained in the examples and comparative examples.

[0164] Battery cell composition

[0165] Winding cylinder

[0166] Positive electrode composition: Positive electrode active material / acetylene black (conductive material) / polyvinylidene fluoride = 88 / 10 / 2 (mass %)

[0167] Negative electrode composition: natural graphite / styrene butadiene rubber (SBR) / carboxymethyl cellulose (CMC)

[0168] Electrolyte composition: electrolyte = LiPF6 (1M), solvent = ethylene carbonate (EC) / dimethyl carbonate (DMC) / ethyl methyl carbonate (EMC) = 3 / 4 / 3 (volume %)

[0169] Electrode production

[0170] The positive electrode and the negative electrode were coated on the current collector using a film coater with a film thickness adjustment function (Allgood Co., Ltd.), and dried in a dryer at 80° C. for 5 minutes to produce a battery cell.

[0171] [TM layer distance (D)]

[0172] The TM interlayer distance (D) was determined for the positive electrode active material layers obtained in each of the Examples and Comparative Examples using the above-mentioned method. The results are shown in Table 1.

[0173] [Ni-mix]

[0174] The Ni-mixing of the positive electrode active material layer obtained in each of Examples and Comparative Examples was calculated by the following method.

[0175] First, X-ray diffraction (XRD) diffraction was performed on the positive electrode active material, and Rietveld analysis (Fullprof) was performed on the XRD diffraction data. Next, the Ni-mixing amount was arbitrarily input and the Chi2 value was calculated. The Ni-mixing with the lowest Chi2 value was defined as the "Ni-mixing" in each positive electrode active material.

[0176] [Determination of resistance increase rate after cycling]

[0177] The battery resistance of the battery cells obtained in each Example and Comparative Example was measured before and after cycling under the following test conditions. The results are shown in Table 1: the ratio of the battery resistance after cycling (resistance increase (%)), with the battery resistance before cycling being 100%. The closer the resistance increase is to 100%, the better the battery performance.

[0178] The test conditions were: 60° C., 2C rate, and 300 cycles of charge and discharge between SOC 0% and 100%.

[0179]

Table 1

[0180]

[0181]

Table 2

[0182]

[0183] As shown in Table 1, it can be seen that the positive electrode active materials of each embodiment containing both the X1 element and the X2 element and having the TM layer distance (D) falling within the above-mentioned range can achieve lower battery resistance than the positive electrode active materials of each comparative example having the TM layer distance (D) outside the above-mentioned range.

Claims

1. The positive electrode active material is composed of Li x Ni a Co b Mn c M1 d M2 e The composition represented by O2, the distance D between TM layers is Above and the following, In the composition, 0.1≤x≤1.5, 0.5≤a≤1.0, 0≤b≤0.3, 0≤c≤0.3, a+b+c=1.0, 0.0005≤d≤0.050, and 0.0005≤e≤0.050, the M1 represents at least one element selected from Ba, Pr, La, Y, Sr, Ce, Se, Hf, Rh, Zr and Sn, and the M2 represents at least one element selected from W, Re, Sb, Sn, Ta, Os, Ir, Mo, Nb, Tc, Ru, Ga, Ag, Pd, Ge, As, Zr, In, Pt, Al and Ti.

2. The positive electrode active material according to claim 1, wherein The combination of the M1 element and the M2 element is at least one combination selected from Ba-W, Pr-W, La-W, Hf-W, Sr-Nb, Pr-Ta, YW, Sr-W, Ce-W, Pr-Re, Ba-Re, Sr-Sb, Se-W, Y-Re, Sr-Re, Rh-W, Zr-W, Sr-Sn, Y-Ta, Y-Sb, Sr-Os, Sr-Ta, Ce-Re, La-Re, Ba-Ta, Sr-Ir, Sn-W, Sr-Mo, Ba-Ti, Ba-Zr and Ba-Al.

3. The positive electrode active material according to claim 1, wherein The combination of the M1 element and the M2 element is at least one combination selected from La—W, Pr—W, and Sr—Nb.

4. The positive electrode active material according to claim 1, wherein The a is 0.7≤a≤1.

0.

5. The positive electrode active material according to claim 1, wherein The M1 element is Sr.

6. The positive electrode active material according to claim 1, wherein The M1 element is at least one element selected from La and Ce.

7. The positive electrode active material according to claim 1, wherein The M2 element is W. 8 . A positive electrode comprising the positive electrode active material according to claim 1 .

9. A lithium ion battery comprising the positive electrode according to claim 8.

10. A method for producing a positive electrode active material, comprising: a step of mixing raw materials respectively containing Ni, Co, and Mn, a raw material containing Li, a raw material containing an element represented by M1, and a raw material containing an element represented by M2 to obtain a mixture; and The mixture is heated in an oxygen atmosphere at a heating rate A of 1°C / min to 10°C / min to a maximum reaching temperature X-100°C, and then heated from the maximum reaching temperature X-100°C to the maximum reaching temperature X at a heating rate B of 0.1°C / min to 5°C / min and slower than the heating rate A, to be fired. The M1 represents at least one element selected from Ba, Pr, La, Y, Sr, Ce, Se, Hf, Rh, Zr and Sn, and the M2 represents at least one element selected from W, Re, Sb, Sn, Ta, Os, Ir, Mo, Nb, Tc, Ru, Ga, Ag, Pd, Ge, As, Zr, In, Pt, Al and Ti.

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