Positive electrode active material for lithium-ion secondary batteries, method for manufacturing positive electrode active material for lithium-ion secondary batteries

Abstract

To provide a positive electrode active material for a lithium ion secondary battery, which can enhance cycle characteristics when used for a lithium ion secondary battery.SOLUTION: The positive electrode active material for a lithium ion secondary battery contains lithium metal composite oxide particles and one or more kinds of additive particles selected from aluminum oxide particles, titanium oxide particles, magnesium oxide particles, silicon oxide particles, and zirconium oxide particles. The positive electrode active material for a lithium ion secondary battery has a specific surface area of 0.25 m2 / g or more and 4.0 m2 / g or less.SELECTED DRAWING: Figure 2A

Description

[Technical Field]

[0001] This invention relates to a positive electrode active material for lithium-ion secondary batteries and a method for producing a positive electrode active material for lithium-ion secondary batteries. [Background technology]

[0002] In recent years, with the widespread use of portable electronic devices such as mobile phones and laptop computers, there has been a strong demand for the development of small, lightweight rechargeable batteries with high energy density and durability. Furthermore, there is a strong demand for high-output rechargeable batteries for use in power tools and electric vehicles, including hybrid cars. In addition to the above-mentioned required characteristics, there is also a growing need for rechargeable batteries with high durability that do not degrade easily even after repeated use.

[0003] Lithium-ion batteries are a type of secondary battery that meets these requirements. A lithium-ion battery consists of a negative electrode, a positive electrode, and an electrolyte, and the active materials of the negative and positive electrodes are materials that can detach and insert lithium. As mentioned above, lithium-ion batteries have high energy density, power output characteristics, and durability.

[0004] While research and development are currently thriving on lithium-ion secondary batteries, lithium-ion secondary batteries using layered or spinel-type lithium metal composite oxides as the cathode material are particularly gaining practical application as batteries with high energy density, as they can achieve high voltages of around 4V.

[0005] Currently, lithium-cobalt composite oxide (LiCoO2), which is relatively easy to synthesize, lithium nickel composite oxide (LiNiO2), which uses nickel that is cheaper than cobalt, and lithium nickel cobalt manganese composite oxide (LiNiO2) are used as positive electrode materials for such lithium-ion secondary batteries. 1 / 3 Co 1 / 3 Mn 1 / 3 Lithium manganese composite oxide (LiMn2O4) and lithium nickel manganese composite oxide (LiNi) using manganese (O2).0.5 Mn 0.5 Lithium metal composite oxides such as O2 have been proposed.

[0006] In recent years, there has been a growing demand for further improvements in the performance of lithium-ion secondary batteries. Therefore, there has been a need for positive electrode active materials for lithium-ion secondary batteries that can enhance battery performance when used in such batteries, and various studies have been conducted to address this.

[0007] For example, Patent Document 1 proposes coating particles for lithium-ion secondary batteries, comprising positive electrode active material particles and a metal sulfide compounded on the surface of the positive electrode active material particles, wherein the total mass of the metal sulfide is 1.0 to 5.0% by mass relative to the total mass of the positive electrode active material particles, and the metal sulfide has a layered structure. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 2016-100101 [Overview of the project] [Problems that the invention aims to solve]

[0009] Incidentally, in recent years, there has been a demand for positive electrode active materials for lithium-ion secondary batteries that can improve cycle characteristics when used in lithium-ion secondary batteries.

[0010] Therefore, in view of the problems of the above-mentioned conventional technology, one aspect of the present invention aims to provide a positive electrode active material for lithium-ion secondary batteries that can improve cycle characteristics when used in lithium-ion secondary batteries. [Means for solving the problem]

[0011] To solve the above problems, according to one aspect of the present invention, Lithium metal composite oxide particles, aluminum oxide particles, titanium oxide particles, magnesium oxide particles, and Silicon dioxide granules Child It includes one or more selected additive particles, The additive particles are a mixture dispersed and arranged on the surface of the lithium metal composite oxide particles. Specific surface area is 0.25 m² 2 / g or more 4.0m 2 This provides a positive electrode active material for lithium-ion secondary batteries that is less than or equal to / g. [Effects of the Invention]

[0012] According to one aspect of the present invention, it is possible to provide a positive electrode active material for lithium-ion secondary batteries that can improve cycle characteristics when used in lithium-ion secondary batteries. [Brief explanation of the drawing]

[0013] [Figure 1] A diagram illustrating the configuration of the laminate-type battery fabricated in the experimental example. [Figure 2A] SEM image of the positive electrode active material obtained in Experimental Example 4. [Figure 2B] SEM image of the positive electrode active material obtained in Experimental Example 8. [Figure 3A] SEM image of the positive electrode active material obtained in Experimental Example 13. [Figure 3B] SEM image of the positive electrode active material obtained in Experimental Example 16. [Figure 4] SEM image of the positive electrode active material obtained in Experimental Example 22. [Figure 5] SEM image of the positive electrode active material obtained in Experimental Example 25. [Figure 6A] SEM image of the positive electrode active material obtained in Experimental Example 26. [Figure 6B] A partially enlarged view of Figure 6A. [Figure 7] Cross-sectional SEM image of the positive electrode active material obtained in Experimental Example 28. [Figure 8] Cross-sectional SEM image of the positive electrode active material obtained in Experimental Example 30. [Figure 9A] SEM image of the positive electrode active material obtained in Experimental Example 32. [Figure 9B] Partial enlarged view of FIG. 9A. [Figure 9C] SEM image of the positive electrode active material obtained in Experimental Example 34. [Figure 9D] Partial enlarged view of FIG. 9C.

Mode for Carrying Out the Invention

[0014] Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments, and various modifications and substitutions can be made to the following embodiments without departing from the scope of the present invention. [Positive Electrode Active Material for Lithium-Ion Secondary Battery] The positive electrode active material for a lithium-ion secondary battery of the present embodiment (hereinafter, also simply referred to as "positive electrode active material") can include lithium metal composite oxide particles and one or more types of additive particles selected from aluminum oxide particles, titanium oxide particles, magnesium oxide particles, silicon oxide particles, and zirconium oxide particles.

[0015] And the positive electrode active material of the present embodiment can have a specific surface area of 0.25 m 2 / g or more and 4.0 m 2 / g or less.

[0016] The positive electrode active material of the present embodiment can include lithium metal composite oxide particles and additive particles as described above. In addition, the positive electrode active material of the present embodiment can also be composed only of lithium metal composite oxide particles and additive particles. However, even in this case, the case of containing unavoidable impurities is not excluded.

[0017] Hereinafter, the lithium metal composite oxide particles and the additive particles contained in the positive electrode active material of the present embodiment will be described. (Lithium Metal Composite Oxide Particles) Lithium metal composite oxide particles are particles of lithium metal composite oxide, which is an oxide containing lithium and any metal component.

[0018] The specific composition of the lithium metal composite oxide is not particularly limited, and various lithium metal composite oxides capable of inserting and deinserting lithium ions, i.e., capable of intercalating and deintercalating lithium ions, can be suitably used. As the lithium metal composite oxide, one or more types selected from, for example, lithium metal composite oxides having a spinel-type structure, lithium metal composite oxides having a layered structure, and lithium metal composite oxides having an olivine-type structure can be used.

[0019] A lithium metal composite oxide having a spinel-type structure can contain, for example, lithium (Li), manganese (Mn), nickel (Ni), and element M1 (M1) in a molar ratio of Li:Mn:Ni:M1 = a1:2-x1-y1:x1:y1. However, it is preferable that a1, x1, and y1 in the above formula satisfy the following conditions: 0.96≦a1≦1.25, 0.40≦x1≦0.60, and 0≦y1≦0.20, respectively.

[0020] Element M1 can be one or more elements selected from the group consisting of magnesium (Mg), aluminum (Al), silicon (Si), titanium (Ti), chromium (Cr), iron (Fe), cobalt (Co), copper (Cu), and zinc (Zn).

[0021] Lithium metal composite oxides having a spinel-type structure include, for example, those with the general formula Li a1 Mn 2-x1-y1 Ni x1 M1 y1 O 4+α It can be expressed as follows. Note that a1, x1, and y1 in the above general formula have already been described, so their explanation is omitted here. Furthermore, it is preferable that α is, for example, -0.2 ≤ α ≤ 0.2.

[0022] A layered lithium metal composite oxide can contain, for example, lithium (Li), nickel (Ni), cobalt (Co), and element M2 (M2) in a molar ratio of Li:Ni:Co:M2 = a2:1-x2-y2:x2:y2. However, it is preferable that a2, x2, and y2 in the above formula satisfy 0.95≦a2≦1.50, 0≦x2≦0.35, and 0≦y2≦0.35, respectively. Furthermore, element M2 can be one or more elements selected from magnesium (Mg), calcium (Ca), aluminum (Al), silicon (Si), iron (Fe), chromium (Cr), manganese (Mn), vanadium (V), molybdenum (Mo), tungsten (W), niobium (Nb), titanium (Ti), zirconium (Zr), and tantalum (Ta).

[0023] Lithium metal composite oxides with a layered structure are, for example, those with the general formula Li a2 Ni 1-x2-y2 Co x2 M2 y2 O 2+β It can be expressed as follows. Note that a2, x2, and y2 in the above general formula have already been described, so their explanation is omitted here. Furthermore, it is preferable that β is, for example, 0 ≤ β ≤ 0.10.

[0024] Lithium metal composite oxides having an olivine-type structure can, for example, contain lithium (Li), element M3 (M3), phosphorus (P), and oxygen (O), and have the general formula LiM3PO 4+γ It can be expressed as follows. Element M3 can be one or more elements selected from, for example, Co, Ni, Mn, Fe, Mg, Nb, Ti, Al, Zr, or VO. γ is preferably, for example, -0.2 ≤ γ ≤ 0.2.

[0025] The average particle size of the lithium metal composite oxide particles is not particularly limited, but is preferably 2 μm to 20 μm, and more preferably 3 μm to 18 μm.

[0026] This is because by setting the average particle size of the lithium metal composite oxide particles to 20 μm or less, the surface area of ​​the lithium metal composite oxide particles can be sufficiently increased, thereby promoting the absorption and release of lithium ions with the electrolyte.

[0027] Setting the average particle size of lithium metal composite oxide particles to 2 μm or more improves handling ease, which is preferable.

[0028] The average particle size of lithium metal composite oxide particles can be evaluated in the same manner as the added particles described later. (added particles) The inventors of this invention investigated positive electrode active materials for lithium-ion secondary batteries that can improve cycle characteristics when used in lithium-ion secondary batteries. As a result, they found that a positive electrode active material containing lithium metal composite oxide particles and additive particles can improve cycle characteristics when used in lithium-ion secondary batteries.

[0029] Although the cause is not clear, the following mechanism is hypothesized to improve cycle characteristics.

[0030] By adding additive particles to lithium metal composite oxide particles, the additive particles can be dispersed and arranged on the surface of the lithium metal composite oxide particles. For example, one or more types of additive particles can be selected from aluminum oxide particles, titanium oxide particles, magnesium oxide particles, silicon oxide particles, and zirconium oxide particles. Aluminum oxide, titanium oxide particles, magnesium oxide particles, silicon oxide particles, and zirconium oxide particles, which are used as additive particles, are corrosion-resistant. Therefore, it is believed that the dispersion and arrangement of additive particles on the surface of lithium metal composite oxide particles can suppress the reaction between the electrolyte and the surface of the lithium metal composite oxide particles that degrades the lithium metal composite oxide. In other words, it is thought that the additive particles act as an artificial-Solid Electrolyte Interphase (SEI), suppressing the aforementioned side reaction between the electrolyte and the surface of the lithium metal composite oxide particles.

[0031] However, since the added particles are only positioned on the surface of the lithium metal composite oxide particles, they hardly hinder the movement of lithium ions between the electrolyte and the lithium metal composite oxide particles. Therefore, compared to a battery without added particles, cycle characteristics can be improved while maintaining or enhancing other battery characteristics.

[0032] As described above, one or more particles selected from aluminum oxide particles, titanium oxide particles, magnesium oxide particles, silicon oxide particles, and zirconium oxide particles can be used as additive particles. That is, the additive particles may be any of aluminum oxide particles, titanium oxide particles, magnesium oxide particles, silicon oxide particles, and zirconium oxide particles, or they may be a mixture of two or more particles selected from aluminum oxide particles, titanium oxide particles, magnesium oxide particles, silicon oxide particles, and zirconium oxide particles.

[0033] When titanium dioxide particles are used as additive particles, the type of crystalline phase of the titanium dioxide contained is not particularly limited. Furthermore, the crystalline phase is not particularly limited to single-phase or co-phase. However, from the viewpoint of particularly improving cycle characteristics, it is preferable that the crystalline phase of titanium dioxide contained in the titanium dioxide particles is either a single-phase rutile phase or a predominant phase among the rutile phase, anatase phase, and brookite phase. Here, the dominant phase refers to the phase with the highest mass ratio.

[0034] When zirconium oxide particles are used as additive particles, the type of crystalline phase of the contained zirconium oxide is not particularly limited. Furthermore, the crystalline phase is not particularly limited to single-phase or conjugate phase, and calcium, magnesium, hafnium, etc., may be added to the zirconium oxide to stabilize it as cubic zirconium. However, from the viewpoint of particularly improving the cycle characteristics, it is preferable that the crystalline phase of the zirconium oxide contained in the zirconium oxide particles is predominantly tetragonal among monoclinic, tetragonal, and cubic phases. Here, "primary phase" refers to the phase with the highest mass ratio.

[0035] In the positive electrode active material of this embodiment, the state of the added particles is not particularly limited, but it is preferable that they are dispersed on the surface of the lithium metal composite oxide particles and modify the surface of the lithium metal composite oxide particles.

[0036] The average particle size of the additive particles used in the positive electrode active material of this embodiment is not particularly limited, but for example, it is preferable that the average particle size is 300 nm or less, and more preferably 10 nm or more and 200 nm or less.

[0037] By setting the average particle size of the additive particles to 300 nm or less, the additive particles can be uniformly dispersed on the surface of the lithium metal composite oxide particles when added to them. In this case, the movement of lithium ions between the electrolyte and the lithium metal composite oxide particles is not hindered, and the cycle characteristics can be particularly improved while maintaining the battery characteristics. Furthermore, according to the inventors' studies, the lithium-ion secondary battery using the positive electrode active material of this embodiment can suppress the positive electrode resistance at low temperatures and at room temperature with a SOC of 50% after repeated charging and discharging compared to a lithium-ion secondary battery using a positive electrode active material without additive particles. Note that SOC stands for State of Charge and can also be rephrased as charge rate.

[0038] The lower limit of the average particle size of the additive particles used is not particularly limited, but as mentioned above, setting it to 10 nm or more is preferable because it provides excellent handling characteristics.

[0039] The method for determining the average particle size of the added particles is not particularly limited, but it can be observed and measured using a scanning electron microscope (SEM) or a transmission electron microscope (TEM). Specifically, for example, first, the added particles are observed using an SEM or the like to obtain an image. The magnification used for observation is not particularly limited, but it is preferably 50,000x or higher. There is also no particular upper limit to the magnification, but from the viewpoint of efficient observation, it is preferably 1,000,000x or less, and more preferably 100,000x or less. From the obtained image, 100 added particles are arbitrarily selected, and a circumscribed circle is drawn around the contour of each selected particle, and the diameter of the circumscribed circle is taken as the particle size of each particle. The average value of the particle sizes of the 100 evaluated particles can then be taken as the average particle size of the added particles.

[0040] If 100 added particles are not present in a single field of view, observation can be performed in multiple fields of view, and 100 particles can be selected from a total of these fields.

[0041] The specific surface area of ​​the additive particles used is not particularly limited, but in the case of aluminum oxide particles, for example, 20m 2 / g or more 180m 2 It is preferable that the amount be less than or equal to 65m 2 / g or more 180m 2 It is more preferable that the specific surface area of ​​the aluminum oxide particles be less than / g. 2 By using a concentration of 1 / g or higher, sufficiently fine particles can be produced. Therefore, when added to lithium metal composite oxide particles, they can be dispersed particularly uniformly on the surface of the lithium metal composite oxide particles. Furthermore, in this process, the movement of lithium ions between the electrolyte and the lithium metal composite oxide particles is not hindered, and the cycle performance can be improved while maintaining battery characteristics.

[0042] Furthermore, the specific surface area of ​​the aluminum oxide particles used is 180 m². 2 It is preferable to keep the amount below / g because it improves handling.

[0043] When the added particles are titanium dioxide particles, the specific surface area of ​​the titanium dioxide particles is not particularly limited, but for example, 30 m 2 / g or more 180m 2 It is preferable that the specific surface area of ​​the titanium dioxide particles is 30 m² or less. 2 By using a concentration of 1 / g or higher, sufficiently fine particles can be produced. Therefore, when added to lithium metal composite oxide particles, they can be dispersed particularly uniformly on the surface of the lithium metal composite oxide particles. Furthermore, in this process, the movement of lithium ions between the electrolyte and the lithium metal composite oxide particles is not hindered, and the cycle performance can be improved while maintaining battery characteristics.

[0044] Furthermore, the specific surface area of ​​the titanium dioxide particles used is 180 m². 2 It is preferable to keep the amount below / g because it improves handling.

[0045] When the added particles are magnesium oxide particles, the specific surface area of ​​the magnesium oxide particles is not particularly limited, but for example, 65 m 2 / g or more 180m 2 It is preferable that the amount be less than or equal to / g. The specific surface area of ​​the magnesium oxide particles is 65 m². 2 By using a concentration of 1 / g or higher, sufficiently fine particles can be produced. Therefore, when added to lithium metal composite oxide particles, they can be uniformly dispersed on the surface of the lithium metal composite oxide particles. Furthermore, this process does not hinder the movement of lithium ions between the electrolyte and the lithium metal composite oxide particles, thereby improving cycle performance while maintaining battery characteristics.

[0046] Furthermore, the specific surface area of ​​the magnesium oxide used is 180 m². 2 It is preferable to keep the amount below / g because it improves handling.

[0047] When the added particles are silicon dioxide particles, the specific surface area of ​​the silicon dioxide particles is not particularly limited, but for example, 30 m 2 / g or more 250m 2It is preferable that the amount is less than or equal to / g. The specific surface area of ​​silicon dioxide particles is 30m². 2 By using a concentration of 1 / g or higher, sufficiently fine particles can be produced. Therefore, when added to lithium metal composite oxide particles, they can be uniformly dispersed on the surface of the lithium metal composite oxide particles. Furthermore, this process does not hinder the movement of lithium ions between the electrolyte and the lithium metal composite oxide particles, thereby improving cycle performance while maintaining battery characteristics.

[0048] Furthermore, the specific surface area of ​​the silicon dioxide particles used is 250 m². 2 It is preferable to keep the amount below / g because it improves handling.

[0049] When the added particles are zirconium oxide particles, the specific surface area of ​​the zirconium oxide particles is not particularly limited, but for example, 30 m 2 / g or more 250m 2 It is preferable that the specific surface area of ​​the zirconium oxide particles be 30 m² or less. 2 By using a concentration of 1 / g or higher, sufficiently fine particles can be produced. Therefore, when added to lithium metal composite oxide particles, they can be dispersed particularly uniformly on the surface of the lithium metal composite oxide particles. Furthermore, in this process, the movement of lithium ions between the electrolyte and the lithium metal composite oxide particles is not hindered, and the cycle performance can be improved while maintaining battery characteristics.

[0050] Furthermore, the specific surface area of ​​the zirconium oxide particles used is 250 m². 2 It is preferable to keep the amount below / g because it improves handling.

[0051] The amount of additive particles added to the lithium metal composite oxide particles is not particularly limited. For example, the ratio of additive particles to lithium metal composite oxide particles is preferably 0.025% by mass or more and 3.0% by mass or less, and more preferably 0.05% by mass or more and 2.0% by mass or less.

[0052] By setting the ratio of added particles to lithium metal composite oxide particles to 0.025% by mass or more, a sufficient amount of added particles can be placed on the surface of the lithium metal composite oxide particles, thereby particularly improving the cycle characteristics.

[0053] However, since the added particles do not insert or remove lithium ions, excessive addition may reduce the battery capacity when used in lithium-ion secondary batteries. For this reason, the ratio of added particles to lithium metal composite oxide particles is preferably 3.0% by mass or less.

[0054] The specific surface area of ​​the positive electrode active material in this embodiment is 0.25 m². 2 / g or more 4.0m 2 It can be less than / g, and 0.29m 2 / g or more 3.8m 2 It is preferable that the value be less than or equal to / g.

[0055] The specific surface area of ​​the positive electrode active material in this embodiment is 0.25 m². 2 This is because a value of 1 / g or more means that a sufficient amount of added particles are positioned on the surface of the lithium metal composite oxide particles. Therefore, it is possible to suppress the reaction that degrades the lithium metal composite oxide between the electrolyte and the surface of the lithium metal composite oxide particles, thereby improving the cycle characteristics.

[0056] On the other hand, the specific surface area of ​​the positive electrode active material in this embodiment is 4.0 m². 2 By keeping the amount below / g, it is possible to suppress the excessive placement of additive particles on the surface of lithium metal composite oxide particles, thereby significantly increasing the battery capacity when used in lithium-ion secondary batteries.

[0057] In this embodiment, the positive electrode active material preferably has a predetermined specific surface area depending on the particle structure of the lithium metal composite oxide that serves as the base material.

[0058] For example, if the lithium metal composite oxide used as the base material has a porous structure, the specific surface area of ​​the positive electrode active material in this embodiment is 1.0 m². 2 / g or more 4.0m 2It is preferable that it be less than or equal to / g, and 1.2m 2 / g or more 3.8m 2 It is more preferable that the value be less than or equal to / g.

[0059] Furthermore, for example, if the lithium metal composite oxide used as the base material has a hollow structure, the specific surface area of ​​the positive electrode active material in this embodiment is 0.50 m². 2 / g or more 2.5m 2 It is preferable that it be less than or equal to / g, and 0.55m 2 / g or more 2.3m 2 It is more preferable that the value be less than or equal to / g.

[0060] Furthermore, if the lithium metal composite oxide used as the base material has a solid structure, the specific surface area of ​​the positive electrode active material in this embodiment is 0.25 m². 2 / g or more 2.0m 2 It is preferable that it be less than or equal to / g, and 0.29m 2 / g or more 1.8m 2 It is more preferable that the value be less than or equal to / g.

[0061] A porous structure refers to a particle structure in which voids are contained and dispersed throughout the entire particle. In the case of a porous structure, the average value of the porosity measured in the cross-section of the lithium metal composite oxide particles is 15% or more. In the case of a porous structure, there is no particular upper limit to the average value of the porosity measured in the cross-section of the lithium metal composite oxide particles, but it is preferably 85% or less.

[0062] A hollow structure refers to a particle structure having a hollow portion consisting of a space located in the center of the particle, and an outer shell portion located outside the hollow portion. In the case of a hollow structure, the average value of the porosity measured in the cross-section of the lithium metal composite oxide particle is 15% or more. In the case of a hollow structure, there is no particular upper limit to the average value of the porosity measured in the cross-section of the lithium metal composite oxide particle, but it is preferably 85% or less.

[0063] Furthermore, a solid structure refers to a particle that contains very few voids inside, and the average value of the porosity measured in the cross-section of the particle is less than 15%.

[0064] The average value of the porosity in the particle cross-section of lithium metal composite oxide can be determined by the following procedure.

[0065] First, the group of lithium metal composite oxide particles to be measured are embedded in resin, and then the cross-section of the particle group is exposed by cutting it with a cross-section polisher (CP), and this exposed cross-section is imaged using a scanning electron microscope. Next, the obtained cross-sectional image of the particle group is analyzed using image analysis software to identify voids as black regions and dense parts such as the outer shell as white regions. Then, the porosity of each particle is calculated for the cross-sections of 20 or more particles using the following formula (A).

[0066] (Void ratio (%)) = [Area of ​​black region / (Area of ​​black region + Area of ​​white region) × 100] ... (A) The particles used to calculate the porosity are those whose particle size can be confirmed from the particle size distribution, etc. 50 It is desirable to select particles that are substantially equal to the particle size. Here, D 50 A particle whose particle size is substantially equal to that of a particle with particle size D 50 Particles with a size of ±1.0 μm or less are preferable.

[0067] By calculating the average porosity of each individual particle, the average porosity of the lithium metal composite oxide can be determined. [Method for manufacturing positive electrode active material for lithium-ion secondary batteries] Next, an example of the configuration of the method for manufacturing the positive electrode active material for lithium-ion secondary batteries according to this embodiment (hereinafter also simply referred to as "method for manufacturing the positive electrode active material") will be described.

[0068] The method for producing the positive electrode active material of this embodiment allows for the production of the positive electrode active material described above. Therefore, some of the matters already explained will be omitted.

[0069] The method for producing a positive electrode active material for lithium-ion secondary batteries according to this embodiment may include a mixing step of mixing lithium metal composite oxide particles with one or more additive particles selected from aluminum oxide particles, titanium oxide particles, magnesium oxide particles, silicon oxide particles, and zirconium oxide particles.

[0070] Furthermore, in the mixing process, the specific surface area of ​​the resulting positive electrode active material is 0.25 m². 2 / g or more 4.0m 2 It can be mixed so that the amount is less than or equal to / g.

[0071] Since lithium metal composite oxide particles and additive particles have already been explained in the section on positive electrode active materials for lithium-ion secondary batteries, their explanation will be omitted here. It is preferable to use particles with an average particle size of 300 nm or less as the additive particles.

[0072] In the mixing process, a general mixer can be used to mix the lithium metal composite oxide particles with the added particles. For example, one or more types selected from shaker mixers, Redigge mixers, Julia mixers, V-blenders, etc., can be used. The mixing conditions in the mixing process are not particularly limited, but it is preferable to select conditions such that the raw material components are sufficiently mixed without destroying the physical structure of the raw material particles, such as the lithium metal composite oxide particles.

[0073] The mixing ratio of lithium metal composite oxide particles to additive particles is not particularly limited. For example, as described above, it is preferable to weigh and mix both materials so that the ratio of additive particles to lithium metal composite oxide particles is 0.025% by mass or more and 3.0% by mass or less.

[0074] However, in the mixing process, the specific surface area of ​​the positive electrode active material obtained after the mixing process is 0.25 m². 2 / g or more 4.0m 2 It is preferable to select lithium metal composite oxide particles and additive particles, and to select their mixing ratio, so that the amount is less than or equal to / g. [Lithium-ion rechargeable battery] The lithium-ion secondary battery of this embodiment (hereinafter also referred to as "secondary battery") may have a positive electrode containing the positive electrode active material described above.

[0075] The following describes an example configuration of the secondary battery of this embodiment, with each component explained separately. The secondary battery of this embodiment includes, for example, a positive electrode, a negative electrode, and a non-aqueous electrolyte, and is composed of components similar to those of a general lithium-ion secondary battery. The embodiments described below are merely illustrative, and the lithium-ion secondary battery of this embodiment can be implemented in various modified and improved forms based on the knowledge of those skilled in the art, including the embodiments described below. Furthermore, the secondary battery does not particularly limit its applications. (positive electrode) The positive electrode of the secondary battery of this embodiment may include the positive electrode active material described above.

[0076] An example of a method for manufacturing a positive electrode is described below. First, the positive electrode active material (in powder form), conductive material, and binder are mixed to form a positive electrode mixture. Then, activated carbon and solvents for purposes such as viscosity adjustment are added as needed, and this mixture is kneaded to produce a positive electrode mixture paste.

[0077] The mixing ratio of each material in the positive electrode composite is a factor that determines the performance of the lithium-ion secondary battery, and therefore can be adjusted according to the application. The mixing ratio of the materials can be the same as that of the positive electrode of a known lithium-ion secondary battery. For example, if the total mass of the solid content of the positive electrode composite excluding the solvent is 100% by mass, the positive electrode active material can be contained in a ratio of 60% to 95% by mass, the conductive material in a ratio of 1% to 20% by mass, and the binder in a ratio of 1% to 20% by mass.

[0078] The resulting positive electrode composite paste is applied to the surface of a current collector, for example, made of aluminum foil, and dried to remove the solvent, thereby producing a sheet-like positive electrode. If necessary, it can be pressurized using a roll press or the like to increase the electrode density. The sheet-like positive electrode thus obtained can be cut to an appropriate size according to the intended battery and used in the manufacture of the battery.

[0079] As conductive materials, for example, graphite (natural graphite, artificial graphite, and expanded graphite, etc.) or carbon black-based materials such as acetylene black and Ketjenblack (registered trademark) can be used.

[0080] The binder serves to hold the active material particles together, and one or more of the following can be used: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose resins, and polyacrylic acid.

[0081] If necessary, a solvent that dissolves the binder and disperses the positive electrode active material, conductive material, etc., can be added to the positive electrode mixture. Specifically, organic solvents such as N-methyl-2-pyrrolidone can be used as the solvent. In addition, activated carbon can be added to the positive electrode mixture to increase the electrical double layer capacity.

[0082] The method for manufacturing the positive electrode is not limited to the examples given above, and other methods may be used. For example, it can be manufactured by press-molding the positive electrode composite material and then drying it under a vacuum atmosphere. (Negative electrode) The negative electrode can be made of metallic lithium, lithium alloy, or the like. Alternatively, the negative electrode may be formed by mixing a binder with a negative electrode active material capable of intercalating and deintercalating lithium ions, adding a suitable solvent to make a paste, applying the paste to the surface of a metal foil current collector such as copper, drying it, and compressing it as needed to increase the electrode density.

[0083] As the negative electrode active material, for example, natural graphite, artificial graphite, and calcined organic compounds such as phenolic resin, and powdered carbon materials such as coke can be used. In this case, as with the positive electrode, a fluororesin such as PVDF can be used as the negative electrode binder, and an organic solvent such as N-methyl-2-pyrrolidone can be used as the solvent for dispersing these active materials and binders. (Separator) A separator can be placed between the positive and negative electrodes as needed. The separator separates the positive and negative electrodes and holds the electrolyte. Known materials can be used, such as a thin film made of polyethylene or polypropylene with numerous micropores. (Non-aqueous electrolyte) As a non-aqueous electrolyte, for example, a non-aqueous electrolyte solution can be used.

[0084] As a non-aqueous electrolyte, for example, a lithium salt dissolved in an organic solvent can be used as a supporting salt. Alternatively, a lithium salt dissolved in an ionic liquid may be used as a non-aqueous electrolyte. An ionic liquid is a salt composed of cations and anions other than lithium ions, and is liquid at room temperature.

[0085] As the organic solvent, one of the following may be used alone or in combination with another: cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate; linear carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate; ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran, and dimethoxyethane; sulfur compounds such as ethyl methyl sulfone and butanesultone; and phosphorus compounds such as triethyl phosphate and trioctyl phosphate.

[0086] As supporting salts, LiPF6, LiBF4, LiClO4, LiAsF6, LiN(CF3SO2)2, and their composite salts can be used. Furthermore, the non-aqueous electrolyte may contain radical scavengers, surfactants, and flame retardants.

[0087] Furthermore, solid electrolytes may be used as non-aqueous electrolytes. Solid electrolytes have the property of being able to withstand high voltages. Examples of solid electrolytes include inorganic solid electrolytes and organic solid electrolytes.

[0088] Examples of inorganic solid electrolytes include oxide-based solid electrolytes and sulfide-based solid electrolytes.

[0089] The oxide-based solid electrolyte is not particularly limited, and for example, one containing oxygen (O) and having lithium ion conductivity and electronic insulation properties can be suitably used. Examples of oxide-based solid electrolytes include lithium phosphate (Li3PO4) and Li3PO4N. X LiBO2N X , LiNbO3, LiTaO3, Li2SiO3, Li4SiO4-Li3PO4, Li4SiO4-Li3VO4, Li2O-B2O3-P2O5, Li2O-SiO2, Li2O-B2O3-ZnO, Li 1+X Al X Ti 2-X (PO4)3(0≦X≦1), Li 1+X Al X Ge 2-X (PO4)3(0≦X≦1), LiTi2(PO4)3, Li 3X La 2 / 3-X TiO3(0≦X≦2 / 3), Li5La3Ta2O 12 Li7La3Zr2O 12 Li6BaLa2Ta2O 12 Li 3.6 Si 0.6 P 0.4 One or more types selected from O4, etc., can be used.

[0090] The sulfide-based solid electrolyte is not particularly limited, and for example, one or more that contain sulfur (S) and have lithium-ion conductivity and electronic insulation properties can be suitably used. For example, one or more sulfide-based solid electrolytes selected from Li2S-P2S5, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-Li2S-B2S3, Li3PO4-Li2S-Si2S, Li3PO4-Li2S-SiS2, LiPO4-Li2S-SiS, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, etc. can be used.

[0091] Furthermore, other inorganic solid electrolytes may be used besides those mentioned above; for example, Li3N, LiI, Li3N-LiI-LiOH, etc., may be used.

[0092] The organic solid electrolyte is not particularly limited as long as it is a polymer compound exhibiting ionic conductivity; for example, polyethylene oxide, polypropylene oxide, or copolymers thereof can be used. Furthermore, the organic solid electrolyte may contain a supporting salt (lithium salt). (Shape and composition of secondary batteries) As described above, the lithium-ion secondary battery of this embodiment can be made into various shapes, such as cylindrical or stacked. Regardless of the shape adopted, if the secondary battery of this embodiment uses a non-aqueous electrolyte, the positive electrode and negative electrode can be stacked with a separator in between to form an electrode body, the resulting electrode body can be impregnated with a non-aqueous electrolyte, and the positive electrode current collector and the positive electrode terminal that is open to the outside, and the negative electrode current collector and the negative electrode terminal that is open to the outside can be connected using current collector leads or the like, and the battery can be sealed in a battery case.

[0093] As previously described, the secondary battery of this embodiment is not limited to a form using a non-aqueous electrolyte solution as the non-aqueous electrolyte; for example, a secondary battery using a solid non-aqueous electrolyte, i.e., an all-solid-state battery, can also be used. In the case of an all-solid-state battery, the components other than the positive electrode active material can be changed as necessary.

[0094] The secondary battery of this embodiment can be used for various applications. Because the secondary battery of this embodiment can be a high-capacity, high-output secondary battery, it is suitable for powering small portable electronic devices (such as notebook personal computers and mobile phone terminals) that always require high capacity, and is also suitable for powering electric vehicles that require high output.

[0095] Furthermore, since the secondary battery of this embodiment can be miniaturized and have a high output, it is suitable as a power source for electric vehicles where mounting space is limited. Moreover, the secondary battery of this embodiment can be used not only as a power source for electric vehicles that are driven purely by electrical energy, but also as a power source for so-called hybrid vehicles that are used in conjunction with combustion engines such as gasoline engines and diesel engines. [Examples]

[0096] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way by these examples.

[0097] First, we will explain the evaluation method for the positive electrode active material and secondary battery obtained in the following experimental example. (Evaluation of positive electrode active material) The following evaluations were performed on the obtained positive electrode active material.

[0098] (a) Average particle size of added particles and lithium metal composite oxide particles First, using a scanning electron microscope (SEM, Hitachi High-Technologies Corporation, S-4700), the added particles contained in the positive electrode active material prepared in the following experimental example were observed at 50,000x magnification, and images were obtained. From the obtained images, 100 added particles were selected, and a circumscribed circle was drawn around the contour of each selected particle. The diameter of this circumscribed circle was defined as the particle size of each particle. The average particle size of the 100 evaluated particles was then defined as the average particle size of the added particles in the positive electrode active material.

[0099] The average particle size was measured for lithium metal composite oxide particles in the same manner.

[0100] (b) Specific surface area The specific surface area of ​​the positive electrode active material and the added particles of the raw materials was measured using a fluidized gas adsorption specific surface area measuring device (MultiSorb, manufactured by Yuasa Ionics Corporation).

[0101] (c) SEM observation The cathode active materials prepared in the following experimental examples 4, 8, 13, 16, 22, 25, 26, 32, and 34 were observed using a scanning electron microscope (Scanning Electron Microscope S-4700, manufactured by Hitachi High-Technologies Corporation).

[0102] Furthermore, the cross-sectional views of the particles of the positive electrode active material prepared in experimental examples 28 and 30 were observed. (Evaluation of battery characteristics) The positive electrode resistance and cycle characteristics were evaluated before and after cycling using laminated batteries fabricated in the following experimental examples. Note that positive electrode resistance was evaluated only for experimental examples 1-5, 8-21, and 24-34. For samples where positive electrode resistance was not evaluated, the same conditioning process was followed, except for the absence of positive electrode resistance measurement, before evaluating the cycle characteristics.

[0103] The laminated batteries prepared in each of the following experimental examples were subjected to a current density of 0.3 mA / cm² in a constant temperature bath maintained at 25°C. 2 The conditioning process involved charging the battery to a cutoff voltage of 4.2V, letting it rest for 10 minutes, and then discharging it to a cutoff voltage of 2.5V. This cycle was repeated five times. The initial discharge capacity was defined as the capacity at which the battery discharged to 2.5V after one cycle under the same conditions following the conditioning.

[0104] Next, the laminated battery was charged to 50% of its initial discharge capacity, given a 10-minute rest period, and then discharged at a 1C rate for 10 seconds. The change in voltage during this 10-second discharge at the 1C rate was then measured.

[0105] According to Ohm's law, the voltage change was divided by the current to calculate the resistance (DC-IR), which was then used as the DC resistance of the battery at SOC 50%, 1C, 10 seconds, and 25°C. In this case, since the laminate-type batteries fabricated in the following multiple experimental examples use the same components other than the positive electrode active material, the above DC resistance of the battery is considered to be an evaluation of the resistance of the positive electrode active material.

[0106] Furthermore, after cooling the laminated battery to -10°C, the DC resistance of the battery, i.e., the positive electrode resistance, was measured in the same manner (positive electrode resistance before cycling).

[0107] In Tables 1 and 2, the column for positive electrode resistance before cycling shows the positive electrode resistance measured at 25°C in the 25°C column and the positive electrode resistance measured at -10°C in the -10°C column. The positive electrode resistance after cycling, which will be discussed later, is shown in the same manner.

[0108] After measuring the positive electrode resistance before cycling, or after measuring the initial discharge capacity, the current density was measured at 2.0 mA / cm² in a constant temperature bath maintained at 45°C. 2 The battery was charged to a predetermined cutoff voltage, rested for 10 minutes, and then discharged at a 2C rate to a cutoff voltage of 2.5V. This cycle was repeated 500 times. The capacity retention rate, which is the ratio of the discharge capacity at the 500th cycle after conditioning to the discharge capacity at the first cycle, was calculated and evaluated. For the repeated charge-discharge described above, experimental examples 1-9, 17, 18, 21-25, and 28-31 were charged to a cutoff voltage of 4.3V, while experimental examples 10-16, 19, 20, 26, 27, and 32-34 were charged to a cutoff voltage of 4.2V. Table 1 shows the discharge capacity at the first cycle, the discharge capacity at the 500th cycle, and the cycle capacity retention rate (capacity retention rate).

[0109] After 500 charge-discharge cycles, the DC resistance of the battery, i.e., the positive electrode resistance, was measured and calculated at 25°C and -10°C in the same manner as before the 500 charge-discharge cycles (positive electrode resistance after cycles).

[0110] Hereinafter, the manufacturing conditions and evaluation results of the positive electrode active material and the like in each experimental example will be described. Experimental examples 1 to 7, 10, 11, 13 to 15, 17 to 26, 28, 30, 32, 33 are examples, and experimental examples 8, 9, 12, 16, 27, 29, 31, 34 are comparative examples. [Experimental Example 1] (1) Manufacture of positive electrode active material 100 g of particles of a lithium metal composite oxide having a layered structure represented by LiNi 0.52 Mn 0.28 Co 0.20 O2 and 0.053 g of aluminum oxide particles having an average particle diameter of 54 nm and a specific surface area of 104 m 2 / g were sufficiently mixed using a shaker mixer device to obtain the positive electrode active material of this experimental example (mixing step). As the shaker mixer device, the type: TURBULA TypeT2C manufactured by Willy E. Bachofen (WAB) was used. The mixing step was also carried out using the same shaker mixer device in the following other experimental examples.

[0111] Regarding the particles of the lithium metal composite oxide used in this experimental example, the structure of the particle cross-section was observed, and the average value of the porosity in the cross-section was calculated. Specifically, after embedding the particle group of the lithium metal composite oxide in resin, the cross-section of the particle group was exposed by cutting with a cross-section polisher (CP), and the exposed cross-section of the particle group was imaged using a scanning electron microscope. As a result, it was confirmed that the particles of the lithium metal composite oxide have a solid structure with almost no voids.

[0112] Regarding the cross-sectional image of the obtained particle group, the void part was identified as a black region and the dense part as a white region by analyzing it with image analysis and measurement software (WinRoof6.1.1 manufactured by Mitani Shoko Co., Ltd.), and the porosity was determined for 20 particles.

[0113] As the 20 particles for which the porosity was determined, the particle size was D at 50% of the volume integration value in the particle size distribution previously determined by the laser diffraction / scattering method for the lithium metal composite oxide particles 50Particles with a particle size equal to the particle size were selected. The particle size of each particle was defined as the diameter of the circumscribed circle of the particle in the captured cross-sectional image. In the following other experimental examples, particles were selected in the same manner to determine the porosity.

[0114] Next, the average porosity of the lithium metal composite oxide particles was calculated. As a result, it was confirmed that the lithium metal composite oxide particles used in this experiment had an average porosity of 5% or less. Similarly, it was confirmed that the solid lithium metal composite oxide particles used in other experimental examples 1 to 27 and 32 to 34 also had a porosity of 5% or less.

[0115] Furthermore, when the average particle size of the lithium metal composite oxide particles and aluminum oxide particles contained in the positive electrode active material obtained after the mixing process was measured using the evaluation method described above, it was confirmed that they were the same as before mixing. In the following other experimental examples, namely Experimental Examples 2 to 34, it was confirmed that there was no change in the average particle size of the lithium metal composite oxide particles and the average particle size of the added particles before and after mixing, and they remained the same.

[0116] Furthermore, the specific surface area of ​​the positive electrode active material obtained after mixing was measured to be 0.29 m². 2 It was confirmed that the value was / g. (2) Manufacturing of secondary batteries A laminate-type battery with the structure shown in Figure 1 was fabricated using the following procedure, and the battery was evaluated as described above.

[0117] As shown in Figure 1, the laminated battery 10 has a structure in which an electrolyte is impregnated into a laminate of a positive electrode film 11, a separator 12, and a negative electrode film 13, and then sealed with a laminate 14. A positive electrode tab 15 is connected to the positive electrode film 11, and a negative electrode tab 16 is connected to the negative electrode film 13, with the positive electrode tab 15 and negative electrode tab 16 being exposed outside the laminate 14.

[0118] A slurry was prepared by dispersing 20.0 g of the obtained positive electrode active material, 2.35 g of acetylene black, and 1.18 g of polyvinylidene fluoride in N-methyl-2-pyrrolidone (NMP) and spreading it on an aluminum foil for 1 cm. 2 The positive electrode active material was coated so that 7.0 mg was present per Al foil. Next, the slurry containing the positive electrode active material was coated onto the Al foil and dried in air at 120°C for 30 minutes to remove NMP. The Al foil coated with the positive electrode active material was cut into strips 66 mm wide and roll-pressed with a load of 1.2 t to produce a positive electrode film. The positive electrode film was then cut into a rectangle of 50 mm x 30 mm and dried in a vacuum dryer at 120°C for 12 hours, and used as the positive electrode film 11 of the laminate-type battery 10.

[0119] Furthermore, a negative electrode film 13 was prepared by coating a copper foil with a negative electrode composite paste, which is a mixture of graphite powder with an average particle size of about 20 μm and polyvinylidene fluoride. For the separator 12, a polyethylene porous film with a thickness of 20 μm was used, and for the electrolyte, a 3:7 mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) with 1 M LiPF6 as the supporting electrolyte (manufactured by Ube Industries, Ltd.) was used.

[0120] In a dry room controlled to a dew point of -60°C, the laminate of the positive electrode film 11, separator 12, and negative electrode film 13 was impregnated with an electrolyte, sealed with a laminate 14, and a laminate-type battery 10 was fabricated, and the evaluation described above was performed.

[0121] The evaluation results are shown in Table 1. [Experimental Examples 2-7] The positive electrode active material and secondary battery were prepared and evaluated in the same manner as in Experimental Example 1, except that the amount of aluminum oxide particles added was as shown in Table 1. The evaluation results are shown in Table 1.

[0122] Figure 2A shows the SEM image of the positive electrode active material obtained in Experimental Example 4. [Experimental Example 8] LiNi having a layered structure with an average particle size of 13.0 μm, without the addition of aluminum oxide particles. 0.52 Mn 0.28 Co0.20 Particles of a lithium metal composite oxide represented by O2 were used as the positive electrode active material. The particles of the lithium metal composite oxide used had a solid structure. And, regarding such a positive electrode active material, evaluation was carried out in the same manner as in Experimental Example 1.

[0123] Also, a secondary battery was fabricated and evaluated in the same manner as in Experimental Example 1, except that the above positive electrode active material was used. The evaluation results are shown in Table 1.

[0124] The SEM image of the positive electrode active material obtained in Experimental Example 8 is shown in FIG. 2B. [Experimental Example 9] As the aluminum oxide particles, aluminum oxide particles having an average particle size of 3.1 μm and a specific surface area of 0.92 m 2 / g, which were obtained by pulverizing aluminum oxide particles having an average particle size of 46.2 μm with a jet mill, were used. And, the addition amount of the above aluminum oxide particles with respect to 100 g of the particles of the lithium metal composite oxide was 0.26 g. Except for the above points, a positive electrode active material and a secondary battery were fabricated and evaluated in the same manner as in Experimental Example 1. The evaluation results are shown in Table 1. [Experimental Example 10] Lithium nickel 0.82 Manganese 0.10 Cobalt 0.05 Aluminum 0.03 100 g of particles of a lithium metal composite oxide having a layered structure represented by O2 and 0.26 g of aluminum oxide particles having an average particle size of 54 nm and a specific surface area of 104 m 2 / g were sufficiently mixed using a shaker mixer device to obtain the positive electrode active material of this experimental example (mixing step). The particles of the lithium metal composite oxide used had a solid structure.

[0125] Also, when the specific surface area of the positive electrode active material obtained after mixing was measured, it was confirmed to be 0.51 m 2 / g.

[0126] A secondary battery was fabricated and evaluated in the same manner as in Experimental Example 1, except that the obtained positive electrode active material was used. The evaluation results are shown in Table 1.

[0127] [Experimental Example 11] The positive electrode active material and secondary battery were prepared and evaluated in the same manner as in Experimental Example 10, except that the amount of aluminum oxide particles added was as shown in Table 1. The evaluation results are shown in Table 1.

[0128] [Experimental Example 12] LiNi 0.82 Mn 0.10 Co 0.05 Al 0.03 Particles of a lithium metal composite oxide having a layered structure represented by O2 were used as the positive electrode active material. This positive electrode active material was evaluated in the same manner as in Experimental Example 10. The lithium metal composite oxide particles used had a solid structure.

[0129] Furthermore, a secondary battery was fabricated and evaluated in the same manner as in Experimental Example 10, except for the use of the positive electrode active material described above. The evaluation results are shown in Table 1.

[0130] [Experimental Example 13] LiNi has an average particle size of 14.7 μm. 0.85 Mn 0.1 Co 0.05 100g of lithium metal composite oxide particles having a layered structure represented by O2, and a particle with an average particle size of 54nm and a specific surface area of ​​104m² 2 0.13 g of aluminum oxide particles (at a concentration of / g) were thoroughly mixed using a shaker mixer to obtain the positive electrode active material for this experiment (mixing step). The lithium metal composite oxide particles used had a solid structure.

[0131] Furthermore, the specific surface area of ​​the positive electrode active material obtained after mixing was measured to be 1.03 m². 2 It was confirmed that the value was / g.

[0132] A secondary battery was fabricated and evaluated in the same manner as in Experimental Example 1, except that the obtained positive electrode active material was used. The evaluation results are shown in Table 1.

[0133] Figure 3A shows an SEM image of the positive electrode active material obtained in Experimental Example 13. [Experimental Examples 14, 15] The positive electrode active material and secondary battery were prepared and evaluated in the same manner as in Experimental Example 13, except that the amount of aluminum oxide particles added was as shown in Table 1. The evaluation results are shown in Table 1.

[0134] [Experimental Example 16] LiNi 0.85 Mn 0.1 Co 0.05 Particles of a lithium metal composite oxide having a layered structure represented by O2 were used as the positive electrode active material. This positive electrode active material was evaluated in the same manner as in Experimental Example 13. The lithium metal composite oxide particles used had a solid structure.

[0135] Furthermore, a secondary battery was fabricated and evaluated in the same manner as in Experimental Example 13, except for the use of the positive electrode active material described above. The evaluation results are shown in Table 1.

[0136] Figure 3B shows an SEM image of the positive electrode active material from experimental example 16. [Experimental Example 17] Instead of aluminum oxide particles, we used particles with an average particle size of 84 nm and a specific surface area of ​​55 m². 2 Except for using 0.41 g of titanium oxide particles at a concentration of / g, the lithium metal composite oxide particles and titanium oxide particles were mixed in the same manner as in Experimental Example 1 to obtain the positive electrode active material for this experiment (mixing step).

[0137] The lithium metal composite oxide particles used were LiNi, which has the same average particle size of 13.0 μm as in Experimental Example 1. 0.52 Mn 0.28 Co 0.20 The study used lithium metal composite oxide particles having a layered structure represented by O2. Furthermore, the lithium metal composite oxide particles used had a solid structure.

[0138] Furthermore, it was confirmed that the titanium dioxide particles, which are added particles, contain a single phase of rutile crystalline titanium dioxide.

[0139] The lithium metal composite oxide particles and titanium oxide particles contained in the positive electrode active material obtained after the mixing process were measured using the evaluation method described above, and it was confirmed that they were the same as those before mixing. The same result was confirmed in the following other experimental examples.

[0140] Furthermore, the specific surface area of ​​the positive electrode active material obtained after mixing was measured to be 0.45 m². 2 It was confirmed that the value was / g.

[0141] A secondary battery was fabricated and evaluated in the same manner as in Experimental Example 1, except for the use of the positive electrode active material described above. The evaluation results are shown in Table 1.

[0142] [Experimental Example 18] The positive electrode active material and secondary battery were prepared and evaluated in the same manner as in Experimental Example 17, except that the amount of titanium dioxide particles added was as shown in Table 1. The evaluation results are shown in Table 1.

[0143] [Experimental Example 19] Instead of aluminum oxide particles, we used particles with an average particle size of 84 nm and a specific surface area of ​​55 m². 2 Except for using 0.20 g of titanium oxide particles at a concentration of / g, the lithium metal composite oxide particles and titanium oxide particles were mixed in the same manner as in Experimental Example 13 to obtain the positive electrode active material of this experiment (mixing step).

[0144] Furthermore, the lithium metal composite oxide particles used were LiNi, which has the same average particle size of 14.7 μm as in Experimental Example 13. 0.85 Mn 0.1 Co 0.05 The study used lithium metal composite oxide particles having a layered structure represented by O2. Furthermore, the lithium metal composite oxide particles used had a solid structure.

[0145] The titanium dioxide particles, which are added as additives, were confirmed to contain a single rutile phase in their crystalline structure.

[0146] Furthermore, the specific surface area of ​​the positive electrode active material obtained after the mixing process was measured to be 1.11 m². 2 It was confirmed that the value was / g.

[0147] A secondary battery was fabricated and evaluated in the same manner as in Experimental Example 13, except that the obtained positive electrode active material was used. The evaluation results are shown in Table 1.

[0148] [Experimental Example 20] Instead of aluminum oxide particles, we used particles with an average particle size of 84 nm and a specific surface area of ​​55 m². 2 Except for using 0.20 g of titanium oxide particles at a concentration of / g, the lithium metal composite oxide particles and titanium oxide particles were mixed in the same manner as in Experimental Example 13 to obtain the positive electrode active material of this experiment (mixing step).

[0149] Furthermore, the lithium metal composite oxide particles used were LiNi, which has the same average particle size of 14.7 μm as in Experimental Example 13. 0.85 Mn 0.1 Co 0.05 The study used lithium metal composite oxide particles having a layered structure represented by O2. Furthermore, the lithium metal composite oxide particles used had a solid structure.

[0150] The titanium dioxide particles, which are added particles, were confirmed to be cophase containing rutile and anatase phases in a mass ratio of 8:2. The rutile phase is the dominant phase.

[0151] Furthermore, the specific surface area of ​​the positive electrode active material obtained after the mixing process was measured to be 1.05 m². 2 It was confirmed that the value was / g.

[0152] A secondary battery was fabricated and evaluated in the same manner as in Experimental Example 13, except that the obtained positive electrode active material was used. The evaluation results are shown in Table 1. [Experimental Example 21] As additive particles, in addition to aluminum oxide particles, titanium oxide particles used in Experimental Example 17 were used. 0.13 g of aluminum oxide particles and 0.17 g of titanium oxide particles were used. Except for the above, the lithium metal composite oxide particles, aluminum oxide particles, and titanium oxide particles were mixed in the same manner as in Experimental Example 1 to obtain the positive electrode active material of this experiment (mixing step).

[0153] The lithium metal composite oxide particles used were LiNi, which has the same average particle size of 13.0 μm as in Experimental Example 1. 0.52 Mn 0.28 Co 0.20 Particles of a lithium metal composite oxide having a layered structure represented by O2 were used. The lithium metal composite oxide particles used had a solid structure.

[0154] Furthermore, the specific surface area of ​​the positive electrode active material obtained after the mixing process was measured to be 0.40 m². 2 It was confirmed that the value was / g.

[0155] A secondary battery was fabricated and evaluated in the same manner as in Experimental Example 1, except that the obtained positive electrode active material was used. The evaluation results are shown in Table 1. [Experimental Example 22] Instead of aluminum oxide particles, we used particles with an average particle size of 30 nm and a specific surface area of ​​65 m². 2 Except for using 0.102 g of magnesium oxide particles at a concentration of / g, the lithium metal composite oxide particles and magnesium oxide particles were mixed in the same manner as in Experimental Example 1 to obtain the positive electrode active material for this experiment (mixing step).

[0156] The lithium metal composite oxide particles used were LiNi, which has the same average particle size of 13.0 μm as in Experimental Example 1. 0.52 Mn 0.28 Co 0.20 The study used lithium metal composite oxide particles having a layered structure represented by O2. Furthermore, the lithium metal composite oxide particles used had a solid structure.

[0157] As described in Experimental Example 1, when the average particle size of the lithium metal composite oxide particles and magnesium oxide particles contained in the positive electrode active material obtained after the mixing process was measured using the evaluation method described above, it was confirmed that it was the same as before mixing.

[0158] Furthermore, the specific surface area of ​​the positive electrode active material obtained after mixing was measured to be 0.62 m². 2 It was confirmed that the value was / g.

[0159] A secondary battery was fabricated and evaluated in the same manner as in Experimental Example 1, except for the use of the positive electrode active material described above. The evaluation results are shown in Table 2.

[0160] Figure 4 shows the SEM image of the positive electrode active material obtained in Experimental Example 22. [Experimental Example 23] The positive electrode active material and secondary battery were prepared and evaluated in the same manner as in Experimental Example 22, except that the amount of magnesium oxide particles added was as shown in Table 2. The evaluation results are shown in Table 2. [Experimental Example 24] Instead of aluminum oxide particles, we used particles with an average particle size of 167 nm and a specific surface area of ​​207 m². 2 Except for using 0.155 g of silicon oxide particles at a concentration of / g, the lithium metal composite oxide particles and silicon oxide particles were mixed in the same manner as in Experimental Example 1 to obtain the positive electrode active material for this experiment (mixing step).

[0161] The lithium metal composite oxide particles used were LiNi, which has the same average particle size of 13.0 μm as in Experimental Example 1. 0.52 Mn 0.28 Co 0.20 The study used lithium metal composite oxide particles having a layered structure represented by O2. Furthermore, the lithium metal composite oxide particles used had a solid structure.

[0162] As described in Experimental Example 1, when the average particle size of the lithium metal composite oxide particles and silicon oxide particles contained in the positive electrode active material obtained after the mixing process was measured using the evaluation method described above, it was confirmed that it was the same as before mixing.

[0163] Furthermore, the specific surface area of ​​the positive electrode active material obtained after mixing was measured to be 0.38 m². 2 It was confirmed that the value was / g.

[0164] A secondary battery was fabricated and evaluated in the same manner as in Experimental Example 1, except for the use of the positive electrode active material described above. The evaluation results are shown in Table 2. [Experimental Example 25] The positive electrode active material and secondary battery were prepared and evaluated in the same manner as in Experimental Example 24, except that the amount of silicon dioxide particles added was as shown in Table 2. The evaluation results are shown in Table 2.

[0165] Figure 5 shows the SEM image of the positive electrode active material obtained in Experimental Example 25. [Experimental Example 26] 100g of lithium metal composite oxide particles having a layered structure represented by LiNiO2, with an average particle size of 12.9μm, and a particle with an average particle size of 10nm and a specific surface area of ​​221m². 2 0.82 g of zirconium oxide particles (at a concentration of / g) were placed in a nitrogen-purged container and thoroughly mixed using a shaker mixer to obtain the positive electrode active material for this experiment (mixing step). The lithium metal composite oxide particles used had a solid structure.

[0166] The added zirconium oxide particles were confirmed to have a tetragonal single-phase crystalline structure.

[0167] The specific surface area of ​​the positive electrode active material obtained after mixing was measured to be 1.68 m². 2 It was confirmed that the value was / g.

[0168] A secondary battery was fabricated and evaluated in the same manner as in Experimental Example 1, except for the use of the obtained positive electrode active material. The evaluation results are shown in Table 2.

[0169] SEM images of the positive electrode active material obtained in Experimental Example 26 are shown in Figures 6A and 6B. Figure 6B is a magnified view of a portion of Figure 6A. [Experimental Example 27] Without the addition of zirconium oxide particles, lithium metal composite oxide particles having a layered structure represented by LiNiO2 and an average particle size of 12.9 μm were used as the positive electrode active material. This positive electrode active material was then evaluated in the same manner as in Experimental Example 26.

[0170] Furthermore, a secondary battery was fabricated and evaluated in the same manner as in Experimental Example 26, except for the use of the positive electrode active material described above. The evaluation results are shown in Table 2. [Experimental Example 28] LiNi has an average particle size of 5.2 μm. 0.50 Mn 0.30 Co 0.20 100g of lithium metal composite oxide particles having a layered structure represented by O2, and a particle with an average particle size of 54nm and a specific surface area of ​​104m² 2 0.32 g of aluminum oxide particles, which are present in a quantity of / g, were thoroughly mixed using a shaker mixer to obtain the positive electrode active material for this experimental example (mixing step).

[0171] In this experiment, the structure of the particle cross-section of the lithium metal composite oxide particles used was observed, and the average value of the porosity in the cross-section was calculated. Specifically, after embedding the lithium metal composite oxide particle group in resin, the cross-section of the particle group was exposed by cutting it with a cross-section polisher (CP), and the exposed cross-section of the particle group was imaged using a scanning electron microscope. As a result, it was confirmed that the lithium metal composite oxide particles have a hollow structure consisting of a hollow part with a space located in the center and an outer shell located outside the hollow part.

[0172] From the cross-sectional images of the obtained particle group, the average porosity of the lithium metal composite oxide particles was calculated using the method and conditions described in Experimental Example 1. As a result, it was confirmed that the average porosity of the hollow lithium metal composite oxide used in this experiment was 15% or more.

[0173] The specific surface area of ​​the positive electrode active material obtained after mixing was measured to be 2.05 m². 2 It was confirmed that the value was / g.

[0174] A secondary battery was fabricated and evaluated in the same manner as in Experimental Example 1, except for the use of the obtained positive electrode active material. The evaluation results are shown in Table 2.

[0175] Figure 7 shows an SEM image of the cross-section of the positive electrode active material obtained in Experimental Example 28. [Experimental Example 29] Without adding aluminum oxide particles, the LiNi used in Experimental Example 28 had a hollow structure with an average particle size of 5.2 μm. 0.50 Mn 0.30 Co 0.20 Particles of a lithium metal composite oxide having a layered structure represented by O2 were used as the positive electrode active material. This positive electrode active material was then evaluated in the same manner as in Experimental Example 28.

[0176] Furthermore, a secondary battery was fabricated and evaluated in the same manner as in Experimental Example 1, except for the use of the positive electrode active material described above. The evaluation results are shown in Table 2. [Experimental Example 30] LiNi has an average particle size of 5.2 μm. 0.50 Mn 0.30 Co 0.20 100g of lithium metal composite oxide particles having a layered structure represented by O2, and a particle with an average particle size of 54nm and a specific surface area of ​​104m² 2 0.32 g of aluminum oxide particles, which are present in a quantity of / g, were thoroughly mixed using a shaker mixer to obtain the positive electrode active material for this experimental example (mixing step).

[0177] In this experiment, the structure of the particle cross-section of the lithium metal composite oxide particles used was observed, and the average value of the porosity in the cross-section was calculated. Specifically, after embedding the lithium metal composite oxide particle group in resin, the cross-section of the particle group was exposed by cutting it with a cross-section polisher (CP), and this exposed cross-section was imaged using a scanning electron microscope. As a result, it was confirmed that the lithium metal composite oxide particles possess a porous structure in which voids are dispersed throughout the entire particle.

[0178] From the cross-sectional images of the obtained particle group, the average porosity of the lithium metal composite oxide particles was calculated using the method and conditions described in Experimental Example 1. As a result, it was confirmed that the average porosity of the porous lithium metal composite oxide used in this experiment was 15% or more.

[0179] The specific surface area of ​​the positive electrode active material obtained after mixing was measured to be 3.18 m². 2 It was confirmed that the value was / g.

[0180] A secondary battery was fabricated and evaluated in the same manner as in Experimental Example 1, except for the use of the obtained positive electrode active material. The evaluation results are shown in Table 2.

[0181] Figure 8 shows an SEM image of the cross-section of the positive electrode active material obtained in experimental example 30. [Experimental Example 31] LiNi, which has a porous structure with an average particle size of 5.2 μm, was used in Experimental Example 30 without the addition of aluminum oxide particles. 0.50 Mn 0.30 Co 0.20 Particles of a lithium metal composite oxide having a layered structure represented by O2 were used as the positive electrode active material. This positive electrode active material was then evaluated in the same manner as in Experimental Example 30.

[0182] Furthermore, a secondary battery was fabricated and evaluated in the same manner as in Experimental Example 1, except for the use of the positive electrode active material described above. The evaluation results are shown in Table 2. [Experimental Example 32] LiNi has an average particle size of 2.3 μm. 0.88 Mn 0.07 Co 0.05 100g of lithium metal composite oxide particles having a layered structure represented by O2, and a particle with an average particle size of 54nm and a specific surface area of ​​104m² 2 0.26 g of aluminum oxide particles (at a concentration of / g) were thoroughly mixed using a shaker mixer to obtain the positive electrode active material for this experiment (mixing step). The lithium metal composite oxide particles used had a solid structure.

[0183] The specific surface area of ​​the positive electrode active material obtained after mixing was measured to be 1.33 m².2 It was confirmed that the value was / g.

[0184] A secondary battery was fabricated and evaluated in the same manner as in Experimental Example 1, except for the use of the obtained positive electrode active material. The evaluation results are shown in Table 2.

[0185] SEM images of the positive electrode active material obtained in Experimental Example 32 are shown in Figures 9A and 9B. Figure 9B is a magnified view of a portion of Figure 9A. [Experimental Example 33] The positive electrode active material and secondary battery were prepared and evaluated in the same manner as in Experimental Example 32, except that the amount of aluminum oxide particles added was as shown in Table 2. The evaluation results are shown in Table 1. [Experimental Example 34] LiNi 0.88 Mn 0.07 Co 0.05 Particles of a lithium metal composite oxide having a layered structure represented by O2 were used as the positive electrode active material. This positive electrode active material was then evaluated in the same manner as in Experimental Example 32.

[0186] Furthermore, a secondary battery was fabricated and evaluated in the same manner as in Experimental Example 32, except for the use of the positive electrode active material described above. The evaluation results are shown in Table 2.

[0187] SEM images of the positive electrode active material obtained in Experimental Example 34 are shown in Figures 9C and 9D. Figure 9D is a magnified view of a portion of Figure 9C.

[0188] [Table 1]

[0189] [Table 2] As shown in Tables 1 and 2, in Experimental Examples 1 to 7, in which aluminum oxide particles were added, the cycle characteristics were confirmed to be higher compared to Experimental Example 8, in which aluminum oxide particles were not added. A similar trend was observed between other experimental examples with added aluminum oxide particles and those without. Specifically, this was observed between Experimental Examples 10 and 11 and Experimental Example 12, between Experimental Examples 13 to 15 and Experimental Example 16, between Experimental Example 28 and Experimental Example 29, and between Experimental Example 30 and Experimental Example 31. Furthermore, a similar trend was observed when titanium oxide particles, magnesium oxide particles, silicon oxide particles, and zirconium oxide particles were used as added particles. Specifically, a similar trend was observed between Experimental Examples 17 and 18, in which titanium oxide particles were added, and Experimental Example 8, in which titanium oxide particles were not added, and between Experimental Examples 19 and 20, in which titanium oxide particles were added, and Experimental Example 16, in which titanium oxide particles were not added. Furthermore, similar trends were observed between experimental examples 22 and 23, which included magnesium oxide particles, and experimental example 8, which did not include magnesium oxide particles, as well as between experimental examples 24 and 25, which included silicon oxide particles, and experimental example 8, which did not include silicon oxide particles. A similar trend was also observed between experimental example 26, which included zirconium oxide particles, and experimental example 27, which did not include zirconium oxide particles.

[0190] Furthermore, a similar trend was observed between Experimental Example 21, in which aluminum oxide particles and titanium oxide particles were added as additives, and Experimental Example 8, in which no additive particles were added.

[0191] Before cycling, although the positive electrode resistances of the secondary batteries in Experimental Examples 1 to 5 were equivalent to that of the secondary battery in Experimental Example 8, it was confirmed that after cycling, the increase in the positive electrode resistance was suppressed and could be maintained significantly lower compared to Experimental Example 8. Similar tendencies were also confirmed between Experimental Examples 10 and 11 and Experimental Example 12, between Experimental Examples 13 to 15 and Experimental Example 16, between Experimental Examples 17, 18, 21 and Experimental Example 8, between Experimental Examples 19, 20 and Experimental Example 16, between Experimental Examples 24, 25 and Experimental Example 8, between Experimental Examples 26 and 27, between Experimental Examples 28 and 29, between Experimental Examples 30 and 31, and between Experimental Examples 32, 33 and Experimental Example 34.

[0192] This is presumably because in Experimental Examples 1 to 5, Experimental Examples 10, 11, Experimental Examples 13 to 15, Experimental Examples 17 to 21, Experimental Examples 24 to 26, Experimental Example 28, Experimental Example 30, Experimental Example 32, and Experimental Example 33, the additive particles were dispersed on the surface of the lithium metal composite oxide particles, and the reaction that deteriorates the lithium metal composite oxide between the lithium metal composite oxide particles and the electrolyte could be suppressed.

[0193] Among Experimental Examples 19 and 20 to which titanium oxide particles were added, in Experimental Example 19, titanium oxide particles in which the crystal phase of the contained titanium oxide was a rutile phase single phase were used. On the other hand, in Experimental Example 20, titanium oxide particles in which the crystal phase of the contained titanium oxide was a co-phase of a rutile phase and anatase phase and the rutile phase was the main phase were used. Comparing the results of both experimental examples, it was confirmed that the cycle characteristics were higher in the case of Experimental Example 19. From this result, it was confirmed that when using titanium oxide particles as an additive element, it is preferable that the titanium oxide particles contain a rutile phase, and particularly preferable that the rutile phase is the main phase.

[0194] Also, according to the SEM images of Experimental Examples 4 and 8 disclosed in FIGS. 2A and 2B, when comparing Experimental Example 4 to which aluminum oxide particles were added and Experimental Example 8 to which no aluminum oxide particles were added, it was confirmed that in Experimental Example 4, fine aluminum oxide particles were dispersed on the particle surface of the lithium metal composite oxide, modifying the lithium metal composite oxide particles.

[0195] It was similarly confirmed from the SEM images of Experimental Examples 13 and 16 disclosed in FIGS. 3A and 3B that the additive particles were dispersed and modified on the particle surface of the lithium metal composite oxide. Further, the same was confirmed from the SEM images of Experimental Example 22 disclosed in FIG. 4, the SEM image of Experimental Example 25 disclosed in FIG. 5, the SEM images of Experimental Example 26 disclosed in FIGS. 6A and 6B, and the SEM images of Experimental Example 32 disclosed in FIGS. 9A and 9B. Incidentally, the SEM images of Experimental Examples 22 and 25 in FIGS. 4 and 5 can be compared with the SEM image of Experimental Example 8 shown in FIG. 2B. The SEM images of Experimental Example 32 disclosed in FIGS. 9A and 9B can be compared with the SEM images of Experimental Example 34 disclosed in FIGS. 9C and 9D.

[0196] According to the SEM image of Experimental Example 28 disclosed in FIG. 7, it can be confirmed that the lithium metal composite oxide particles of the positive electrode active material obtained in Experimental Example 28 have a hollow structure having a hollow portion and an outer shell portion arranged so as to surround the hollow portion.

[0197] According to the SEM image of Experimental Example 30 disclosed in FIG. 8, it can be confirmed that the lithium metal composite oxide particles of the positive electrode active material obtained in Experimental Example 30 have a porous structure in which voids are dispersed throughout the particles.

[0198] The positive electrode active material for a lithium ion secondary battery and the method for manufacturing the positive electrode active material for a lithium ion secondary battery have been described in the embodiments, examples, etc. However, the present invention is not limited to the above embodiments and examples. Various modifications and changes are possible within the scope of the gist of the present invention described in the claims.

Claims

1. It comprises lithium metal composite oxide particles and one or more additive particles selected from aluminum oxide particles, titanium oxide particles, magnesium oxide particles, and silicon oxide particles. The additive particles are a mixture dispersed and arranged on the surface of the lithium metal composite oxide particles. Specific surface area is 0.25 m² ２ / g or more 4.0m ２ Positive electrode active material for lithium-ion secondary batteries with a value of less than / g.

2. The positive electrode active material for a lithium-ion secondary battery according to claim 1, wherein the average particle size of the added particles is 300 nm or less.

3. The positive electrode active material for a lithium-ion secondary battery according to claim 1 or claim 2, wherein the ratio of the added particles to the lithium metal composite oxide particles is 0.025% by mass or more and 3.0% by mass or less.

4. The process includes a mixing step of mixing lithium metal composite oxide particles with one or more additive particles selected from aluminum oxide particles, titanium oxide particles, magnesium oxide particles, and silicon oxide particles. In the mixing step, the specific surface area of ​​the positive electrode active material for lithium-ion secondary batteries obtained after the mixing step is 0.25 m². ２ / g or more 4.0m ２ A method for producing a positive electrode active material for a lithium-ion secondary battery, comprising mixing the materials such that the amount is less than or equal to / g, and the added particles are dispersed and arranged on the surface of the lithium metal composite oxide particles to form a mixture.

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