Manufacturing method of positive electrode material and positive electrode material

Abstract

To provide a manufacturing method for a positive electrode material that enables the manufacture of a lithium-ion secondary battery in which the decrease in initial battery capacity is suppressed and the decrease in battery capacity due to repeated charging and discharging is suppressed, and a positive electrode material.SOLUTION: A manufacturing method for a positive electrode material includes the steps of obtaining a mixture containing a positive electrode active material and one type of lithium alloy, and subjecting the mixture to a heat treatment.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a positive electrode material and a positive electrode material.

Background Art

[0002] In a lithium-ion secondary battery, a part of the lithium ions released from the positive electrode active material during the first charge reacts with the electrolyte on the surface of the negative electrode to form a film called SEI (Solid Electrolyte Interphase). Since the consumption of lithium ions associated with the formation of SEI causes a decrease in battery capacity, it is desirable to minimize it. As a measure for suppressing the consumption of lithium ions associated with the formation of SEI, it has been proposed to contain a lithium alloy in the positive electrode together with the positive electrode active material, and to complement the amount of lithium ions consumed for the formation of SEI by the lithium ions released from the lithium alloy during the first charge (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The method of containing a lithium alloy in the positive electrode is an effective means for suppressing a decrease in the initial battery capacity. On the other hand, metal ions derived from the lithium alloy from which lithium ions have been lost move to the negative electrode side and precipitate, and there is a risk that this precipitate becomes a resistance layer and causes a decrease in battery capacity. An object of the present disclosure is to provide a method for manufacturing a positive electrode material and a positive electrode material capable of manufacturing a lithium-ion secondary battery in which a decrease in the initial battery capacity is suppressed and a decrease in battery capacity due to repeated charge and discharge is suppressed.

Means for Solving the Problems

[0005] Means for solving the above problems include the following embodiments. <1> A step of obtaining a mixture containing a positive electrode active material and one kind of lithium alloy; And a step of performing heat treatment on the mixture, a method for manufacturing a positive electrode material. <2> The method for manufacturing a positive electrode material according to <1>, wherein the lithium alloy is selected from bismuth, tin, and antimony. <3> The method for manufacturing a positive electrode material according to <1> or <2>, wherein the temperature of the heat treatment is 350 ° C or higher. <4> The method for manufacturing a positive electrode material according to any one of <1> to <3>, wherein the content of the lithium alloy is 1 part by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the positive electrode active material in the previous stage. <5> A positive electrode material including a composite including a positive electrode active material and one kind of lithium alloy.

Advantages of the Invention

[0006] According to an embodiment of the present disclosure, there are provided a method for manufacturing a positive electrode material and a positive electrode material capable of manufacturing a lithium ion secondary battery in which a decrease in an initial battery capacity is suppressed and a decrease in battery capacity due to repeated charge and discharge is suppressed.

Embodiments for Carrying Out the Invention

[0007] In the present disclosure, a numerical range indicated by "~" means a range including the numerical values described before and after "~" as the minimum value and the maximum value, respectively. In the numerical ranges described step by step in the present disclosure, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in other step-by-step descriptions. In the numerical ranges described in the present disclosure, the upper limit value or the lower limit value described in a certain numerical range may be replaced with the value shown in the examples. In the present disclosure, the term "step" includes not only an independent step but also this term if the intended purpose of the step is achieved even when it cannot be clearly distinguished from other steps. In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. In the present disclosure, the amount of each component means the total amount of a plurality of substances when there are a plurality of substances corresponding to each component, unless otherwise specified.

[0008] <Method for manufacturing a positive electrode material> The method for manufacturing a positive electrode material of the present disclosure is a step of obtaining a mixture containing a positive electrode active material and one type of lithium alloy, and a step of performing heat treatment on the mixture.

[0009] A secondary battery manufactured using the positive electrode material manufactured by the method of the present disclosure contains a lithium alloy in the positive electrode. When lithium ions are released from the lithium alloy together with the positive electrode active material during the first charge of the secondary battery, the decrease in lithium ions consumed for the formation of the SEI is compensated. As a result, a decrease in the initial battery capacity is effectively suppressed.

[0010] Furthermore, a secondary battery manufactured using the positive electrode material manufactured by the method of the present disclosure has a suppressed decrease in battery capacity compared to a secondary battery manufactured using a positive electrode material not manufactured by the method of the present disclosure (specifically, a positive electrode material in which heat treatment of a mixture of a positive electrode active material and a lithium alloy has not been performed). As a factor for this, solid solution diffusion between the positive electrode active material and the lithium alloy occurs due to the heat treatment of the mixture of the positive electrode active material and the lithium alloy, and it is considered that a composite composed of the positive electrode active material and the lithium alloy is formed. It is considered that when the lithium alloy is incorporated into the composite, the movement of metal ions derived from the lithium alloy to the negative electrode side is suppressed, and the decrease in battery capacity is suppressed.

[0011] Hereinafter, the step of obtaining a mixture containing a positive electrode active material and one type of lithium alloy is also referred to as the first step, and the step of performing heat treatment on the mixture is also referred to as the second step.

[0012] (First step) In the first step, a mixture containing a positive electrode active material and one type of lithium alloy is obtained. The lithium alloy used in the first step preferably contains a metal element with an alloying potential with lithium of 0.5 V (vs. Li / Li + ). Since the metal element contained in the lithium alloy has the above alloying potential, the decrease in lithium ions released from the cathode active material and consumed for the formation of SEI during the first charge of the battery is effectively compensated. As a result, the decrease in the initial battery capacity is effectively suppressed.

[0013] Examples of metal elements with an alloying potential with lithium of 0.5 V (vs. Li / Li + ) or more include bismuth (Bi, alloying potential: 0.81 - 0.83 V), tin (Sn, alloying potential: 0.57 - 0.66 V), and antimony (Sb, alloying potential: 0.94 - 0.96 V). That is, examples of the lithium alloy contained in the cathode material include a lithium alloy containing bismuth (hereinafter also referred to as Li - Bi alloy), a lithium alloy containing tin (hereinafter also referred to as Li - Sn alloy), and a lithium alloy containing antimony (hereinafter also referred to as Li - Sb alloy).

[0014] Specifically, as the Li - Bi alloy, Li 3 Bi can be mentioned. Specifically, as the Li - Sb alloy, Li 3 Sb can be mentioned. Specifically, as the Li - Sn alloy, LiSn can be mentioned. From the viewpoint of suppressing the decrease in battery capacity due to repeated charge and discharge, the lithium alloy contained in the cathode material is preferably a Li - Bi alloy.

[0015] The cathode material contains one kind of lithium alloy. In the present disclosure, that the cathode material "contains one kind of lithium alloy" means that among the metal elements other than lithium that constitute the lithium alloy contained in the cathode material, there is only one kind of metal element with the highest content rate.

[0016] From the perspective of sufficiently compensating for the consumption of lithium ions associated with the formation of the SEI, the content of the lithium alloy contained in the positive electrode material is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and even more preferably 5 parts by mass or more with respect to 100 parts by mass of the positive electrode active material. From the perspective of ensuring sufficient energy density, the content of the lithium alloy contained in the positive electrode material is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 15 parts by mass or less with respect to 100 parts by mass of the positive electrode active material.

[0017] The lithium alloy may be in a particulate form. The volume average particle diameter of the particulate lithium alloy is not particularly limited and can be selected, for example, from the range of 1 μm to 50 μm.

[0018] In the present disclosure, the volume average particle diameter of the particles is the value (D50) when the volume cumulative is 50% in the volume-based particle size distribution measured by the laser diffraction / scattering method.

[0019] Examples of the positive electrode active material used in the first step include composite oxides of lithium and transition metals (hereinafter also referred to as lithium transition metal composite oxides). Examples of the lithium transition metal composite oxide include layered lithium transition metal composite oxides, spinel-type lithium transition metal composite oxides, olivine-type lithium transition metal composite oxides, and the like. Specific examples of the layered lithium transition metal composite oxide include compounds represented by LiMO 2 (where M is at least one transition metal selected from the group consisting of Ni, Co, and Mn), and compounds obtained by adding a different element to this compound. Examples of the different element include Al, Mg, La, Ti, Zn, B, W, Fe, Cr, V, Ru, Cu, Cd, Ag, Y, Sc, Ga, In, As, Sb, Pt, Au, Si, and the like. Specific examples of the spinel-type lithium transition metal composite oxide include LiMn 2 O 4 and the like. Specific examples of the olivine-type lithium transition metal composite oxide include LiMPO 4 (where M is Fe, Co, Ni, or Mn). The cathode active material contained in the cathode material may be a single type or two or more types.

[0020] Among the lithium transition metal composite oxides, a layered lithium transition metal composite oxide containing at least one selected from Ni, Co, and Mn as the transition metal is more preferable, and a layered lithium transition metal composite oxide containing Ni and at least one selected from Co and Mn as the transition metal is even more preferable, and a layered lithium transition metal composite oxide containing Ni, Co, and Mn as the transition metal (NCM, nickel cobalt manganese oxide) is even more preferable. The molar ratios of Ni, Co, and Mn contained in NCM may be selected, for example, such that the molar ratio of Ni to Co (Ni:Co) is in the range of 1:0.1 to 1:1, or the molar ratio of Ni to Mn (Ni:Mn) is in the range of 1:0.1 to 1:1.

[0021] The molar ratio of Ni to Co (Ni:Co) may be selected from the range of 1:0.1 to 1:0.5, 1:0.1 to 1:0.3, or 1:0.1 to 1:0.2. The molar ratio of Ni to Mn (Ni:Mn) may be selected from the range of 1:0.1 to 1:0.5, 1:0.1 to 1:0.3, or 1:0.1 to 1:0.2.

[0022] The cathode active material may be in particulate form. The volume average particle diameter of the particulate cathode active material is not particularly limited and can be selected, for example, from the range of 5 μm to 30 μm. When the cathode active material is secondary particles that are an aggregate of a plurality of primary particles, the above volume average particle diameter is the volume average particle diameter of the secondary particles.

[0023] The method for obtaining a mixture containing the cathode active material and one type of lithium alloy in the first step is not particularly limited, and a usual method can be adopted.

[0024] (Second step) In the second step, heat treatment of a mixture containing the positive electrode active material obtained in the first step and one type of lithium alloy is performed.

[0025] As shown in the examples described later, a battery manufactured using a positive electrode material obtained by performing heat treatment on a mixture of a positive electrode active material and a lithium alloy maintains a better battery capacity than a battery manufactured using a positive electrode material obtained without performing heat treatment on the mixture. As a factor for this, it is considered that solid solution diffusion occurs between the positive electrode active material and the lithium alloy by heat treatment of the mixture, and a composite composed of the positive electrode active material and the lithium alloy is formed. By having the lithium alloy incorporated into the composite, it is considered that the movement of metal ions derived from the lithium alloy to the negative electrode side is effectively suppressed.

[0026] The temperature of the heat treatment is preferably 350 °C or higher, and may be 450 °C or higher, 550 °C or higher, or 650 °C or higher. The temperature of the heat treatment may be 1000 °C or lower, 900 °C or lower, or 800 °C or lower. The time of the heat treatment is not particularly limited, and may be selected from between 30 minutes and 5 hours. The heat treatment is preferably performed in an inert atmosphere such as nitrogen or argon.

[0027] It is preferable that in the mixture after heat treatment, at least a part of the positive electrode active material and at least a part of the lithium alloy form a composite (such as a solid solution).

[0028] The mixture after heat treatment may be pulverized into particles. The volume average particle diameter of the particles obtained by pulverizing the mixture after heat treatment can be selected, for example, from the range of 5 μm to 30 μm.

[0029] <Positive Electrode Material> The positive electrode material of the present disclosure contains a composite composed of a positive electrode active material and one type of lithium alloy. The details and preferred embodiments of the cathode active material and the lithium alloy contained in the cathode material are the same as the details and preferred embodiments of the cathode active material and the lithium alloy used in the above-described method for manufacturing the cathode material.

[0030] A composite composed of a cathode active material contained in a cathode material and one type of lithium alloy may be in a state where solid solution diffusion between the cathode active material and the lithium alloy has occurred by heat treatment of a mixture of the cathode active material and the lithium alloy. The composite composed of a cathode active material contained in a cathode material and one type of lithium alloy may be in a particulate form. The volume average particle diameter of the particles obtained by crushing the mixture after heat treatment can be selected, for example, from the range of 5 μm to 30 μm.

[0031] The cathode material of the present disclosure may further contain other components used as a material for the cathode of a lithium-ion secondary battery. For example, the cathode material may be in a state of a mixture containing components other than the cathode active material and the lithium alloy, such as a conductive assistant and a binder. If necessary, a solvent may be added to the mixture to adjust the viscosity of the mixture.

[0032] Specific examples of the conductive assistant include carbon materials such as carbon black (acetylene black, thermal black, furnace black, etc.), carbon nanotubes, and graphite. The conductive material contained in the cathode material may be a single type or two or more types.

[0033] Specific examples of the binder include polyvinylidene fluoride (PVDF), polyethylene, polypropylene, polyethylene terephthalate, cellulose, nitrocellulose, carboxymethyl cellulose, polyethylene oxide, polyepichlorohydrin, polyacrylonitrile, styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), polyacrylate, polymethacrylate, and the like. The binder contained in the cathode material may be a single type or two or more types.

[0034] The positive electrode material of the present disclosure is used as a material for the positive electrode of a lithium-ion secondary battery. The positive electrode includes, for example, a current collector and a positive electrode layer disposed on the current collector, and the positive electrode layer contains the positive electrode material of the present disclosure. The positive electrode layer may be disposed on one side or both sides of the current collector.

[0035] Examples of the material constituting the current collector of the positive electrode include aluminum, aluminum alloy, nickel, titanium, stainless steel, etc. Examples of the shape of the current collector include foil, mesh, etc.

[0036] The positive electrode layer is disposed on the current collector, for example, by coating a slurry-like positive electrode material on one side or both sides of the current collector. If necessary, a pressing process may be performed to adjust the density of the positive electrode layer. The thickness of the positive electrode layer is not particularly limited and can be selected, for example, from the range of 10 μm to 100 μm.

[0037] A lithium-ion secondary battery obtained by using the positive electrode material of the present disclosure includes, for example, a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte. The negative electrode includes, for example, a current collector and a negative electrode layer disposed on the current collector and containing a negative electrode active material. Examples of the type of the negative electrode active material include carbon materials such as graphite, hard carbon, soft carbon, and activated carbon, silicon, metallic lithium, lithium alloy, lithium titanate (LTO), etc. Examples of the material constituting the current collector of the negative electrode include copper, copper alloy, nickel, titanium, stainless steel, etc. Examples of the shape of the current collector of the negative electrode include foil, mesh, etc. Examples of the separator include non-woven fabrics, cloths, and microporous films mainly composed of polyolefins such as polyethylene and polypropylene. The electrolyte may be either liquid or solid. As the liquid electrolyte (electrolyte solution), LiPF 6A known electrolyte dissolved in an organic solvent can be used without particular limitation. As the solid electrolyte, known solid electrolytes such as sulfide solid electrolytes, oxide solid electrolytes, and halide solid electrolytes can be used without particular limitation.

Examples

[0038] Hereinafter, the present disclosure will be described in more detail by way of examples. However, the invention of the present disclosure is not limited to these examples.

[0039] <Fabrication of Evaluation Battery> In the fabrication of the batteries of each example, NCM (LiNi 0.8 Co 0.1 Mn 0.1 O 2 ) as the positive electrode active material in the amounts shown in Table 1, and LiB 3 , Li 3 Sb and LiSn as lithium alloys were used respectively. The amounts of the respective components were adjusted so that the total volume of the positive electrode active material and the lithium alloy would be equal in each example.

[0040] In Examples 1 to 3, the mixture of the positive electrode active material and the lithium alloy shown in Table 1 was heat-treated in a nitrogen atmosphere at 700 °C for 2 hours, and then pulverized to obtain composite particles of the positive electrode active material and the lithium alloy. In Comparative Examples 1 to 5, the mixture of the positive electrode active material and the lithium alloy shown in Table 1 was not heat-treated.

[0041] A slurry-like positive electrode material was obtained by mixing a mixture of the positive electrode active material and the lithium alloy (93 g), carbon black (4 g) as a conductive aid, PVDF (3 g) as a binder, and a solvent (NMP). The obtained positive electrode material was coated on an aluminum foil and dried to obtain a positive electrode. An electrode body formed by laminating the obtained positive electrode, a separator (a polyethylene microporous film), and a negative electrode containing graphite as an active material in this order, and an electrolytic solution (LiPF 6A laminated evaluation battery was fabricated using a mixed solvent of ethylene carbonate / dimethyl carbonate / ethyl methyl carbonate containing

[0042] <Evaluation of Battery Performance> Based on the mass of the positive electrode active material contained in the battery, a current value of 210 mA / g was defined as the 1C rate, and CCCV charging and CCCV discharging were performed under the following conditions. The obtained CCCV capacity was taken as the capacity of the battery (initial discharge capacity). Lower limit voltage: 2.5 V Upper limit voltage: 4.25 V Charge / discharge current value: 0.2C Cut-off current value: 0.03C Subsequently, a cycle test (CC charging·CC discharging) of the battery was carried out. The number of cycles when the CC discharge capacity of the battery reached 40% or less of the initial discharge capacity is shown in Table 1. It can be judged that the larger the number of cycles shown in Table 1, the more the decrease in battery capacity due to repeated charge and discharge is suppressed.

[0043]

Table 1

[0044] As shown in Table 1, the batteries of Examples 1 to 3 in which the mixture of the positive electrode active material and the lithium alloy was heat-treated showed an excellent capacity retention rate compared to the batteries of Comparative Examples 1 to 5 in which the mixture of the positive electrode active material and the lithium alloy was not heat-treated.

[0045] <Evaluation of Metal Ion Release Amount from Lithium Alloy> After the cycle test, the cell was disassembled and the positive electrode was taken out. A sample solution was prepared from the positive electrode layer using an acid, and elemental analysis was performed by ICP-AES (ICP emission spectrometry). The concentrations of the metal elements in the lithium alloy used for the preparation of the positive electrode are shown in Table 2 as the ratios when the initial concentration is 100.

[0046]

Table 2

[0047] As shown in Table 2, in the batteries of Examples 1 to 3 in which the mixture of the positive electrode active material and the lithium alloy was heat-treated, the residual ratio of the metal element derived from the lithium alloy in the positive electrode was higher than that in the batteries of Comparative Examples 1 to 5 in which the mixture of the positive electrode active material and the lithium alloy was not heat-treated. The above results suggest that by performing heat treatment on the mixture of the positive electrode active material and the lithium alloy, the migration of the metal element derived from the lithium alloy to the negative electrode side is effectively suppressed.

Claims

1. Obtaining a mixture containing a positive electrode active material and one type of lithium alloy; and subjecting the mixture to a heat treatment.

2. 2. The method of claim 1, wherein the lithium alloy is selected from bismuth, tin, and antimony.

3. The method for producing a positive electrode material according to claim 1 or 2, wherein the heat treatment temperature is 350° C. or higher.

4. 3. The method for producing a positive electrode material according to claim 1, wherein the content of the lithium alloy is 1 part by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the positive electrode active material.

5. A positive electrode material comprising a composite of a positive electrode active material and one type of lithium alloy.

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