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

Abstract

Disclosed is a positive electrode active material for a lithium ion battery, which has a small volume change accompanying charge and discharge and can improve the cycle characteristics of the battery when applied to the battery. A positive electrode active material for a lithium ion battery has an irregular rock salt structure belonging to the space group Fm-3m and has a composition represented by Li 1+x Ti y V z O2, where 0

Description

Technical Field

[0001] This application discloses a positive electrode active material for a lithium-ion battery, a method for manufacturing the same, and a lithium-ion battery. Background Art

[0002] In Patent Document 1, a positive electrode active material for a lithium-ion battery is disclosed, which has a layered rock salt structure belonging to the space group R-3m and has a composition represented by Li 1+x Ti y V z D a O2 (D: doping element, 0 ≤ x < 1, 0 < y < 0.5, 0.3 ≤ z < 1, 0 ≤ a ≤ 0.2). In addition, in Non-Patent Document 1, an electrode active material is disclosed, which has a layered rock salt structure and has a composition represented by (1 - x)LiVO2·xLi2TiO3 (0 ≤ x ≤ 0.6).

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2019-091580

[0006] Non-Patent Documents

[0007] Non-Patent Document 1: Journal of Power Sources 174 (2007) 1007-1011 Summary of the Invention

[0008] According to the insight of the present inventors, the positive electrode active material having a layered rock salt structure has a large volume change during charge and discharge. This becomes a factor that reduces the cycle characteristics of the battery when applied to a lithium-ion battery.

[0009] As one of the means for solving the above problems, this application discloses a positive electrode active material for a lithium-ion battery, which has an irregular rock salt structure belonging to the space group Fm-3m and has a composition represented by Li 1+x Ti y V z O2 (0 < x ≤ 0.20, 0 < y ≤ 0.40, 0.40 ≤ z ≤ 0.85).

[0010] As one of the means for solving the above problems, this application discloses a lithium-ion battery having the positive electrode active material disclosed herein.

[0011] The positive electrode active material for a lithium-ion battery disclosed herein can be manufactured, for example, by the following method. That is, the manufacturing method disclosed herein can be a manufacturing method including the following steps,

[0012] A process for producing an intermediate material having a layered rock salt structure and having a composition represented by Li 1+x Ti y V z O2 (0 < x ≤ 0.20, 0 < y ≤ 0.40, 0.40 ≤ z ≤ 0.85); and

[0013] A process for obtaining a positive electrode active material by subjecting the intermediate material to dry mechanical grinding, the positive electrode active material having an irregular rock salt structure belonging to the space group Fm-3m and having a composition represented by Li 1+x Ti y V z O2 (0 < x ≤ 0.20, 0 < y ≤ 0.40, 0.40 ≤ z ≤ 0.85).

[0014] The positive electrode active material of the present disclosure has a small volume change during charge and discharge. By applying such a positive electrode active material to a lithium ion battery, the cycle characteristics of the battery can be easily improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 An example of a method for manufacturing a positive electrode active material for a lithium ion battery is shown.

[0016] Figure 2 An example of the configuration of a positive electrode and a lithium ion battery is schematically shown.

[0017] Figure 3 The X-ray diffraction peaks of the intermediate material before dry mechanical grinding and the X-ray diffraction peaks of the positive electrode active material after dry mechanical grinding are compared.

[0018] Figure 4 The powder X-ray diffraction peaks of the positive electrode active material according to the examples are shown.

[0019] Figure 5 Regarding the positive electrode active material according to the examples, the displacement change of the X-ray diffraction peaks during charge and discharge is shown.

[0020] REFERENCE SIGNS LIST

[0021] 10 Positive electrode

[0022] 11 Positive electrode active material layer

[0023] 12 Positive electrode current collector

[0024] 20 Electrolyte layer

[0025] 30 Negative electrode

[0026] 31 Negative electrode active material layer

[0027] 32 Negative current collector

[0028] 100 Lithium-ion battery Detailed implementation mode

[0029] 1. Positive active material for lithium-ion battery

[0030] The positive active material for lithium-ion battery of the present disclosure has an irregular rock salt structure belonging to the space group Fm-3m, and has a composition represented by Li 1+x Ti y V z O2 (0 < x ≤ 0.20, 0 < y ≤ 0.40, 0.40 ≤ z ≤ 0.85).

[0031] 1.1 Crystal structure

[0032] Regarding the positive active material with a layered rock salt structure that has been known for a long time, the reversible transition metal movement during charge and discharge is difficult, and with the insertion or extraction of Li, the volume is likely to expand or contract greatly in one dimension. In contrast, the positive active material of the present disclosure has an irregular rock salt structure belonging to the space group Fm-3m. According to such a positive active material, the volume change is easily suppressed by the movement of V. For example, even if a volume change occurs, it is likely to be isotropic expansion and contraction, and it is difficult to generate a one-dimensional volume change. The lattice constant change of the crystal structure of the positive active material of the present disclosure during charge and discharge is suppressed to, for example, 1% or less. In this way, by using a positive active material with a small volume change during charge and discharge in a lithium-ion battery, the cycle characteristics of the battery are easily improved.

[0033] 1.2 Composition

[0034] The positive active material of the present disclosure has a composition represented by Li 1+x Ti y V z O2. Here, the relationship of 0 < x ≤ 0.20, 0 < y ≤ 0.40, and 0.40 ≤ z ≤ 0.85 is satisfied. In the case of having such a composition, it is easy to maintain the above-mentioned irregular rock salt structure and easy to exert the above-mentioned effects. In addition, in the case of having such a composition, it is easy to obtain a high charge-discharge capacity.

[0035] x exceeds 0 and can be 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, 0.06 or more, 0.07 or more, 0.08 or more, 0.09 or more, 0.10 or more, or 0.11 or more. In addition, x is 0.20 or less and can be 0.19 or less, 0.18 or less, 0.17 or less, 0.16 or less, 0.15 or less, or 0.14 or less.

[0036] When y is greater than 0, it can be 0.01 or more, 0.03 or more, 0.05 or more, 0.07 or more, 0.09 or more, 0.10 or more, 0.11 or more, 0.13 or more, 0.15 or more, 0.17 or more, 0.19 or more, 0.21 or more, or 0.22 or more. Additionally, y is 0.40 or less, and can be 0.39 or less, 0.38 or less, 0.37 or less, 0.36 or less, 0.35 or less, 0.34 or less, 0.33 or less, 0.32 or less, 0.31 or less, 0.30 or less, or 0.29 or less.

[0037] When z is 0.40 or more, it can be 0.42 or more, 0.44 or more, 0.46 or more, 0.48 or more, 0.50 or more, 0.52 or more, 0.54 or more, 0.56 or more, or 0.57 or more. Additionally, z is 0.85 or less, and can be 0.83 or less, 0.81 or less, 0.79 or less, 0.77 or less, 0.75 or less, 0.73 or less, 0.71 or less, 0.69 or less, or 0.67 or less.

[0038] 1.3 Others

[0039] The positive electrode active material of the present disclosure only needs to have the above crystal structure and composition, and the other components are not particularly limited.

[0040] 1.3.1 Shape

[0041] The shape of the positive electrode active material can be, for example, particulate, thin film, etc., as long as an appropriate shape is selected according to the form of the battery. When the positive electrode active material is particulate, the particles can be solid particles or hollow particles. The particles of the positive electrode active material can be primary particles or secondary particles formed by aggregation of multiple primary particles. The average particle diameter (D50) of the particles of the positive electrode active material can be, for example, 1 nm or more, 5 nm or more, or 10 nm or more, and can also be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less. Furthermore, the average particle diameter D50 mentioned in this application refers to the particle diameter (median diameter) corresponding to the cumulative value of 50% in the volume-based particle size distribution obtained by the laser diffraction-scattering method.

[0042] 1.3.2 Protective layer

[0043] A protective layer containing a Li-ion conductive oxide may also be formed on the surface of the positive electrode active material of the present disclosure. Thereby, reactions such as the reaction between the positive electrode active material and a sulfide (such as a sulfide solid electrolyte described later) are easily suppressed. Examples of the Li-ion conductive oxide include Li3BO3, LiBO2, Li2CO3, LiAlO2, Li4SiO4, Li2SiO3, Li3PO4, Li2SO4, Li2TiO3, Li4Ti5O 12 , Li2Ti2O5, Li2ZrO3, LiNbO3, Li2MoO4, Li2WO4. The Li-ion conductive oxide may also be an oxide obtained by substituting a part of the elements with doping elements such as P and B. The coverage rate (area ratio) of the protective layer may be, for example, 70% or more, 80% or more, or 90% or more. The thickness of the protective layer may be, for example, 0.1 nm or more or 1 nm or more, and may be 100 nm or less or 20 nm or less.

[0044] 2. Method for manufacturing positive electrode active material for lithium ion battery

[0045] The positive electrode active material of the present disclosure can be manufactured, for example, by the following method. As Figure 1 shown, the manufacturing method according to one embodiment may be a method including step S1 and step S2,

[0046] Step S1: Produce an intermediate substance having a layered rock salt structure and having a composition represented by Li 1+x Ti y V z O2 (0 < x ≤ 0.20, 0 < y ≤ 0.40, 0.40 ≤ z ≤ 0.85);

[0047] Step S2: Obtain a positive electrode active material by subjecting the intermediate substance to dry mechanical grinding. The positive electrode active material has an irregular rock salt structure belonging to the space group Fm-3m and has a composition represented by Li 1+x Ti y V z O2 (0 < x ≤ 0.20, 0 < y ≤ 0.40, 0.40 ≤ z ≤ 0.85).

[0048] 2.1 Step S1

[0049] In step S1, an intermediate substance is produced. The intermediate substance has a layered rock salt structure (belonging to the space group R-3m) and has a composition represented by Li 1+x Ti y V zComposition represented by O2(0 < x ≤ 0.20, 0 < y ≤ 0.40, 0.40 ≤ z ≤ 0.85). The intermediate substance can be produced, for example, by arbitrarily shaping a mixture of a Li source, a Ti source, and a V source and then firing it.

[0050] 2.1.1 Raw Materials

[0051] As the Li source constituting the mixture, for example, Li2CO3 can be cited. In addition, as the Ti source, for example, TiO2 can be cited. Moreover, as the V source, for example, V2O3 can be cited. By using Li2CO3, TiO2, and V2O3 as the Li source, Ti source, and V source respectively, it is easy to form the target layered rock salt structure in the intermediate substance. Therefore, it is easy to form the target irregular rock salt structure in the positive electrode active material as the final product. Alternatively, as the raw materials constituting the mixture, raw materials other than the above can also be used. In addition, a compound (such as a composite oxide) that also serves as at least two of the Li source, Ti source, and V source can also be used. The composition ratios of Li, Ti, and V contained in the mixture can be appropriately determined according to the composition ratio of the positive electrode active material as the final product. It is also possible to adjust so that Li is contained in excess in the mixture. Thus, even when Li volatilizes during the firing in step S1 or when Li is consumed due to side reactions in step S2 described later, the insufficient amount of Li can be filled. That is, it is easy to obtain the composition as the target in the positive electrode active material as the final product.

[0052] 2.1.2 Mixing Means

[0053] The method of mixing the Li source, Ti source, and V source is not particularly limited. The Li source, Ti source, and V source can be uniformly mixed, for example, by wet mechanical grinding using a solvent. As the solvent, an organic solvent such as ethanol can be used. Wet mechanical grinding can be carried out, for example, using a mechanical mixing mechanism such as a planetary ball mill. The mixing conditions (mixing time, rotation speed, number of repetitions, etc.) in wet mechanical grinding are not particularly limited as long as they are conditions that can uniformly mix the Li source, Ti source, and V source to the extent that the target layered rock salt structure can be formed after firing described later.

[0054] 2.1.3 Shaping

[0055] The above mixture can also be shaped into pellets or the like before firing. The size and shape of the shaped body are not particularly limited.

[0056] 2.1.4 Firing

[0057] By firing the above mixture or shaped body, an intermediate substance having a layered rock salt structure and the above composition is obtained. The firing atmosphere is not particularly limited. For example, it can be an oxygen-containing atmosphere such as an air atmosphere or an air atmosphere, or an inert gas atmosphere such as an Ar atmosphere. In particular, in the case of an inert gas atmosphere, it is easy to obtain the target intermediate substance. Regarding the firing temperature, as long as a layered rock salt structure can be obtained, it is not particularly limited. For example, it can be 800 °C or higher or 850 °C or higher, and can be 1000 °C or lower or 950 °C or lower. The firing time (holding time at the firing temperature) is also not particularly limited. For example, it can be 5 hours or longer, 7 hours or longer, 10 hours or longer, or 12 hours or longer, and can be 100 hours or shorter, 50 hours or shorter, or 20 hours or shorter.

[0058] 2.2 Process S2

[0059] In Process S2, by subjecting the above intermediate substance to dry mechanical grinding, a positive electrode active material having an irregular rock salt structure belonging to the space group Fm-3m and having a composition represented by Li 1+x Ti y V z O2 (0 < x ≤ 0.20, 0 < y ≤ 0.40, 0.40 ≤ z ≤ 0.85) is obtained. That is, by subjecting the above intermediate substance to dry mechanical grinding that substantially does not use a solvent, the layered rock salt structure in the intermediate substance changes, thereby obtaining a positive electrode active material having an irregular rock salt structure. Dry mechanical grinding can be carried out, for example, using a mechanical mixing mechanism such as a planetary ball mill. The conditions of dry mechanical grinding (mixing time, rotation speed, number of repetitions, etc.) are not particularly limited. For example, in the case of using a planetary ball mill, the rotation speed can be 500 to 700 rpm, the rotation time can be 10 to 20 minutes, the rest time can be 1 to 5 minutes, rotation and rest can be repeated multiple times, and in addition, the repetition of rotation and rest can be taken as one set and this set can be repeated multiple times. By adjusting the conditions of dry mechanical grinding, it is possible to control, for example, the microcrystal size of the positive electrode active material.

[0060] 2.3 Supplement

[0061] Furthermore, in the manufacturing method of the present disclosure, from the above mixture through the intermediate substance to the positive electrode active material, the composition ratios of Li, Ti, and V may vary or may remain substantially the same without variation. Additionally, in the above description, a solid-state reaction method was used to produce the intermediate substance having a layered rock salt structure, but the method for producing the intermediate substance is not limited thereto. Also, in the above description, dry mechanical grinding was performed on the intermediate substance having a layered rock salt structure, but there is also room to adopt other methods as a method for obtaining the positive electrode active material having an irregular rock salt structure. However, in terms of what the present inventors have confirmed, by performing dry mechanical grinding on the intermediate substance having a layered rock salt structure after producing it, it is easy to stably and easily obtain the target irregular rock salt structure.

[0062] 3. Positive electrode for lithium-ion battery

[0063] Another aspect of the technology of the present disclosure is for a positive electrode for a lithium-ion battery. That is, the positive electrode of the present disclosure contains the above positive electrode active material. As Figure 2 shown, the positive electrode 10 according to one embodiment may be a positive electrode including a positive electrode active material layer 11 and a positive electrode current collector 12. In this case, the positive electrode active material layer 11 may contain the above positive electrode active material.

[0064] 3.1 Positive electrode active material layer

[0065] The positive electrode active material layer 11 contains at least the above positive electrode active material, and may further optionally contain an electrolyte, a conductive additive, a binder, and the like. The respective contents of the positive electrode active material, the electrolyte, the conductive additive, and the binder in the positive electrode active material layer 11 may be appropriately determined according to the target battery performance. For example, when the entire positive electrode active material layer 11 (the entire solid component) is set to 100% by mass, the content of the positive electrode active material may be 40% by mass or more, 50% by mass or more, or 60% by mass or more, and may be 100% by mass or less or 90% by mass or less. The shape of the positive electrode active material layer 11 is not particularly limited. For example, it may be a sheet-like positive electrode active material layer 11 having a substantially flat surface. The thickness of the positive electrode active material layer 11 is not particularly limited. For example, it may be 0.1 μm or more or 1 μm or more, and may be 2 mm or less or 1 mm or less.

[0066] 3.1.1 Positive electrode active material

[0067] The positive electrode active material layer 11 may be a layer containing only the above-mentioned positive electrode active material having an irregular rock salt structure as the positive electrode active material. Alternatively, the positive electrode active material layer 11 may contain, in addition to the above-mentioned positive electrode active material, a different type of positive electrode active material (other positive electrode active materials). From the viewpoint of further enhancing the effects brought about by the technology of the present disclosure, the content of the other positive electrode active materials in the positive electrode active material layer 11 may be small. For example, the above-mentioned positive electrode active material having an irregular rock salt structure may account for 50% by mass or more, 60% by mass or more, 70% by mass or more, 80% by mass or more, 90% by mass or more, 95% by mass or more, or 99% by mass or more of all the positive electrode active materials contained in the positive electrode active material layer 11.

[0068] 3.1.2 Electrolyte

[0069] The electrolyte may be a solid electrolyte or a liquid electrolyte (electrolyte solution). When the positive electrode 10 is a positive electrode for a solid battery (a battery including a solid electrolyte), a solid electrolyte may be included as the electrolyte in the positive electrode active material layer 11. In addition, when the positive electrode 10 is a positive electrode for an electrolyte solution battery, an electrolyte solution may be included as the electrolyte in the positive electrode active material layer 11, or the electrolyte solution is in contact with the positive electrode active material layer 11. Furthermore, when the positive electrode 10 is a positive electrode for an electrolyte solution battery, it is sufficient that the positive electrode active material layer 11 and the electrolyte solution are in contact at least after the battery is constructed. The same applies to the negative electrode 30 described later.

[0070] As the solid electrolyte, any electrolyte known as a solid electrolyte for a battery may be used. The solid electrolyte may be an inorganic solid electrolyte or an organic polymer electrolyte. In particular, the inorganic solid electrolyte has a higher ionic conductivity and better heat resistance than the organic polymer electrolyte. Examples of the inorganic solid electrolyte include lithium lanthanum zirconate, LiPON, Li 1+X Al X Ge 2-X(PO4)3, Li-SiO-based glasses, Li-Al-S-O-based glasses and other oxide solid electrolytes; Li2S-P2S5, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Si2S-P2S5, Li2S-P2S5-LiI-LiBr, LiI-Li2S-P2S5, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li2S-P2S5-GeS2 and other sulfide solid electrolytes. The performance of sulfide solid electrolytes, especially those containing Li2S-P2S5, is high. The solid electrolyte can be amorphous or crystalline. The solid electrolyte can be, for example, in the form of particles. The solid electrolyte can be used alone or in combination of two or more.

[0071] The electrolyte can contain, for example, lithium ions as carrier ions. The electrolyte can be an aqueous electrolyte or a non-aqueous electrolyte. The composition of the electrolyte only needs to be the same as the well-known composition of the electrolyte for a lithium-ion battery. For example, as the electrolyte, an electrolyte obtained by dissolving a lithium salt in a carbonate-based solvent at a specified concentration can be used. Examples of the carbonate-based solvent include fluoroethylene carbonate (FEC), ethylene carbonate (EC), dimethyl carbonate (DMC), etc. Examples of the lithium salt include LiPF6, etc.

[0072] 3.1.3 Conductive aids

[0073] Examples of the conductive aids include carbon materials such as vapor-grown carbon fiber (VGCF), acetylene black (AB), Ketjenblack (KB), carbon nanotube (CNT), carbon nanofiber (CNF), etc.; metal materials such as nickel, aluminum, stainless steel, etc. The conductive aids can be, for example, in the form of particles or fibers, and their size is not particularly limited. The conductive aids can be used alone or in combination of two or more.

[0074] 3.1.4 Binder

[0075] Examples of the binder include, for example, butadiene rubber (BR)-based binder, isobutylene rubber (IIR)-based binder, acrylate butadiene rubber (ABR)-based binder, styrene butadiene rubber (SBR)-based binder, polyvinylidene fluoride (PVdF)-based binder, polytetrafluoroethylene (PTFE)-based binder, polyimide (PI)-based binder, etc. The binder can be used alone or in combination of two or more.

[0076] 3.2 Positive current collector

[0077] Such as Figure 2As shown, the positive electrode 10 may include a positive electrode current collector 12 in contact with the above-described positive electrode active material layer 11. The positive electrode current collector 12 may be a current collector commonly used as the positive electrode current collector of a battery. In addition, the positive electrode current collector 12 may be in the form of a foil, a plate, a net, a punched metal, a foam body, etc. The positive electrode current collector 12 may be composed of a metal foil or a metal net. In particular, a metal foil has excellent operability and the like. The positive electrode current collector 12 may also be composed of multiple foils. Examples of the metal constituting the positive electrode current collector 12 include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, etc. In particular, from the viewpoint of ensuring oxidation resistance, etc., the positive electrode current collector 12 may be a current collector containing Al. The positive electrode current collector 12 may also have a certain coating on its surface for the purpose of adjusting resistance, etc. In addition, the positive electrode current collector 12 may be a current collector obtained by plating or vapor-depositing the above-described metal on a metal foil or a substrate. In addition, when the positive electrode current collector 12 is composed of multiple metal foils, there may also be a certain layer between the multiple metal foils. The thickness of the positive electrode current collector 12 is not particularly limited. For example, it may be 0.1 μm or more, or 1 μm or more, and may be 1 mm or less, or 100 μm or less.

[0078] 3.3 Others

[0079] The positive electrode 10 may also include components commonly provided as the positive electrode of a battery in addition to the above-described components. For example, it may include tabs, terminals, etc. The positive electrode 10 can be manufactured by a known method except that the above-described active material having an irregular rock-salt structure is used as the positive electrode active material. For example, by forming the positive electrode mixture containing the above-described various components in a dry or wet manner, etc., the positive electrode active material layer 11 can be easily formed. The positive electrode active material layer 11 may be formed together with the positive electrode current collector 12, or may be formed separately from the positive electrode current collector 12.

[0080] 4. Lithium-ion battery

[0081] Another aspect of the technology of the present disclosure is for a lithium-ion battery. That is, the lithium-ion battery of the present disclosure has the positive electrode active material of the present disclosure. As described above, the positive electrode active material of the present disclosure has a small volume change during charge and discharge, so when applied to a lithium-ion battery, it is easy to improve the cycle characteristics of the battery. The configuration of the lithium-ion battery of the present disclosure is not particularly limited as long as it has the positive electrode active material of the present disclosure. For example, as Figure 2 shown, the lithium-ion battery 100 according to an embodiment may be a battery having a positive electrode 10, an electrolyte layer 20, and a negative electrode 30. Regarding the positive electrode 10, as shown above.

[0082] 4.1 Electrolyte layer

[0083] The electrolyte layer 20 contains at least an electrolyte. In the case where the lithium-ion battery 100 is a solid battery, the electrolyte layer 20 contains a solid electrolyte, and may also optionally contain an adhesive or the like. In this case, the contents of the solid electrolyte and the adhesive or the like in the electrolyte layer 20 are not particularly limited. On the other hand, in the case where the lithium-ion battery 100 is an electrolyte battery, the electrolyte layer 20 contains an electrolyte solution, and may also have a separator or the like for holding the electrolyte solution and preventing contact between the positive electrode active material layer 11 and the negative electrode active material layer 31. The thickness of the electrolyte layer 20 is not particularly limited. For example, it can be 0.1 μm or more or 1 μm or more, and can be 2 mm or less or 1 mm or less.

[0084] Regarding the solid electrolyte, the electrolyte solution, the adhesive, etc., as described above. The separator may be any separator commonly used in lithium-ion batteries. For example, separators made of resins such as polyethylene (PE), polypropylene (PP), polyester, and polyamide can be cited. The separator can be a single-layer structure or a multi-layer structure. As a multi-layer structure separator, for example, a PE / PP two-layer structure separator, or a PP / PE / PP or PE / PP / PE three-layer structure separator can be cited. The separator can also be a separator made of non-woven fabric such as cellulose non-woven fabric, resin non-woven fabric, and glass fiber non-woven fabric.

[0085] 4.2 Negative electrode

[0086] As Figure 2 shown, the negative electrode 30 can be a negative electrode having a negative electrode active material layer 31 and a negative electrode current collector 32.

[0087] 4.2.1 Negative electrode active material layer

[0088] The negative electrode active material layer 31 contains at least a negative electrode active material, and may also optionally contain an electrolyte, a conductive additive, an adhesive, etc. The content of each of the negative electrode active material, the electrolyte, the conductive additive, and the adhesive in the negative electrode active material layer 31 can be appropriately determined according to the target battery performance. For example, when the entire negative electrode active material layer 31 (the entire solid component) is set to 100% by mass, the content of the negative electrode active material can be 40% by mass or more, 50% by mass or more, or 60% by mass or more, and can be 100% by mass or less or 90% by mass or less. The shape of the negative electrode active material layer 31 is not particularly limited. For example, it can be a sheet-like negative electrode active material layer having a substantially flat surface. The thickness of the negative electrode active material layer 31 is not particularly limited. For example, it can be 0.1 μm or more or 1 μm or more, and can be 2 mm or less or 1 mm or less.

[0089] As the negative electrode active material, various materials with a lower potential for lithium ion insertion / extraction (charge / discharge potential) compared to the above-mentioned positive electrode active material can be used. For example, silicon-based active materials such as Si, Si alloys, and silicon oxides; carbon-based active materials such as graphite and hard carbon; various oxide-based active materials such as lithium titanate; metallic lithium, lithium alloys, etc. The negative electrode active material can be used alone or in combination of two or more.

[0090] The shape of the negative electrode active material may be any shape that is typically possessed by the negative electrode active material of a battery. For example, the negative electrode active material can be in the form of particles. The negative electrode active material particles can be primary particles or secondary particles formed by aggregation of multiple primary particles. The average particle diameter (D50) of the negative electrode active material particles can be, for example, 1 nm or more, 5 nm or more, or 10 nm or more, and can also be 500 μm or less, 100 μm or less, 50 μm or less, or 30 μm or less. Alternatively, the negative electrode active material can also be in the form of a sheet (foil, film) such as a metallic lithium foil. That is, the negative electrode active material layer 31 can also be composed of sheets of the negative electrode active material.

[0091] As the electrolyte that can be contained in the negative electrode active material layer 31, the above-mentioned solid electrolyte and electrolyte solution can be cited. As the conductive assistant that can be contained in the negative electrode active material layer 31, the above-mentioned carbon material and the above-mentioned metal material can be cited. The binder that can be contained in the negative electrode active material layer 31 can be appropriately selected from the substances exemplified as the binders that can be contained in the above-mentioned positive electrode active material layer 11, for example.

[0092] 4.2.2 Negative Electrode Current Collector

[0093] As Figure 2As shown in the figure, the negative electrode 30 may include a negative electrode current collector 32 that contacts the above-mentioned negative electrode active material layer 31. The negative electrode current collector 32 may be a current collector commonly used as the negative electrode current collector of a battery. In addition, the negative electrode current collector 32 may be in the form of a foil, a plate, a mesh, a perforated metal, a foam body, etc. The negative electrode current collector 32 may be a metal foil or a metal mesh, or may be a carbon sheet. In particular, the metal foil has excellent operability and the like. The negative electrode current collector 32 may also be composed of multiple foils or sheets. Examples of the metal constituting the negative electrode current collector 32 include Cu, Ni, Cr, Au, Pt, Ag, Al, Fe, Ti, Zn, Co, stainless steel, etc. In particular, from the viewpoints of ensuring reducibility resistance and being difficult to alloy with lithium, the negative electrode current collector 32 may be a current collector including at least one metal selected from Cu, Ni, and stainless steel. The negative electrode current collector 32 may also have a certain coating on its surface for the purpose of adjusting resistance and the like. In addition, the negative electrode current collector 32 may be a current collector obtained by plating or vapor-depositing the above-mentioned metal on a metal foil or a substrate. In addition, when the negative electrode current collector 32 is composed of multiple metal foils, a certain layer may also be provided between the multiple metal foils. The thickness of the negative electrode current collector 32 is not particularly limited. For example, it may be 0.1 μm or more or 1 μm or more, and may be 1 mm or less or 100 μm or less. The negative electrode 30 may also include components commonly provided as the negative electrode of a battery in addition to the above-mentioned components. For example, it may include a tab, a terminal, etc.

[0094] 4.3 Others

[0095] The lithium-ion battery 100 may be a battery in which the above-mentioned components are housed inside an exterior body. The exterior body may be a publicly known exterior body used as the exterior body of a battery. In addition, multiple batteries 100 may be electrically connected arbitrarily and may be overlapped arbitrarily to form a battery pack. In this case, the battery pack may be housed inside a publicly known battery case. The lithium-ion battery 100 may also include self-evident components such as terminals required in addition to this. Examples of the shape of the lithium-ion battery 100 include a coin type, a laminated type, a cylindrical shape, and a rectangular shape.

[0096] 5. Manufacturing Method of Lithium-Ion Battery

[0097] The lithium-ion battery 100 can be manufactured by applying a publicly known method. For example, the manufacturing method of the lithium-ion battery 100 includes a step of laminating the above-mentioned positive electrode 10, electrolyte layer 20, and negative electrode 30. The following shows a specific example of the manufacturing method of the lithium-ion battery 100. However, the manufacturing method of the lithium-ion battery 100 is not limited to the following method. For example, each layer may also be formed by dry forming or the like.

[0098] (1) The positive electrode active material that constitutes the positive electrode active material layer and the like are dispersed in a solvent to obtain a paste for the positive electrode layer. The solvent used in this case is not particularly limited, and water or various organic solvents can be used, such as N-methylpyrrolidone (NMP). The paste for the positive electrode layer is applied to the surface of the positive electrode current collector using a doctor blade or the like, and then dried to form a positive electrode active material layer on the surface of the positive electrode current collector, thereby fabricating a positive electrode.

[0099] (2) The negative electrode active material that constitutes the negative electrode active material layer and the like are dispersed in a solvent to obtain a paste for the negative electrode layer. The solvent used in this case is not particularly limited, and water or various organic solvents can be used, such as N-methylpyrrolidone (NMP). The paste for the negative electrode layer is applied to the surface of the negative electrode current collector using a doctor blade or the like, and then dried to form a negative electrode active material layer on the surface of the negative electrode current collector, thereby fabricating a negative electrode. Alternatively, a metal foil as the negative electrode active material can be used as the negative electrode as it is.

[0100] (3) The layers are stacked such that the electrolyte layer (solid electrolyte layer or separator) is sandwiched between the negative electrode and the positive electrode to obtain a laminate having a negative electrode current collector, a negative electrode active material layer, an electrolyte layer, a positive electrode active material layer, and a positive electrode current collector in this order. Other components such as terminals are installed on the laminate as needed.

[0101] (4) The laminate is housed in a battery case. In the case of an electrolyte battery, an electrolyte is filled into the battery case, the laminate is immersed in the electrolyte, and the laminate is sealed in the battery case, thereby fabricating a secondary battery. Further, in the case of an electrolyte battery, the electrolyte can also be included in the negative electrode active material layer, the separator, and the positive electrode active material layer at the stage of (3) above.

[0102] Examples

[0103] Examples are shown below to further elaborate on the technology of the present disclosure in detail, but the technology of the present disclosure is not limited by the following examples.

[0104] 1. Synthesis of Positive Electrode Active Material

[0105] 1.1 Examples 1 to 6

[0106] A positive electrode active material having an irregular rock salt structure was synthesized by the following method.

[0107] 1.1.1 Preparation of Intermediate Substance

[0108] Weigh Li2CO3 (in excess of 3%), TiO2, and V2O3, which are used as raw materials, in such a way that they form a specified ratio, and then mix them by wet ball milling (wet BM), which is a type of wet mechanical grinding. The conditions for wet BM are shown in Table 1 below. After that, form the mixture into pellets. Place the formed pellets on a boat-shaped aluminum plate, wrap them with Cu foil, and then sinter them in an Ar atmosphere at 900 °C for 12 hours to obtain an intermediate substance. By changing the composition of the raw materials, various changes are made to the values of x, y, and z, and a variety of intermediate substances are obtained. According to the X-ray diffraction peaks and elemental analysis, all the intermediate substances have a layered rock salt structure and have a composition represented by Li 1+x Ti y V z O2 (0 < x ≤ 0.20, 0 < y ≤ 0.40, 0.40 ≤ z ≤ 0.85).

[0109] 1.1.2 Dry mechanical grinding

[0110] By subjecting each intermediate substance to dry ball milling (dry BM), which is a type of dry mechanical grinding, a positive electrode active material was obtained. The conditions for dry BM are shown in Table 1 below. The positive electrode active material has an irregular rock salt structure belonging to the space group Fm-3m and has a composition represented by Li 1+x Ti y V z O2 (0 < x ≤ 0.20, 0 < y ≤ 0.40, 0.40 ≤ z ≤ 0.85). Figure 3 An example of the X-ray diffraction peak of the intermediate substance before dry mechanical grinding and an example of the X-ray diffraction peak of the positive electrode active material after dry mechanical grinding are shown.

[0111] Table 1

[0112]

[0113] 1.2 Comparative Examples 1 - 3

[0114] Prepared various positive electrode active materials having a layered rock salt structure (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.85 Co 0.10 Al 0.05 O2, LiNi 0.5 Mn 0.5 O2).

[0115] 1.3 Comparative Examples 4, 5

[0116] LiVO₂ was prepared as a Ti-free positive electrode active material. In addition, Li₂TiO₃ was prepared as a V-free positive electrode active material. Furthermore, the specific synthesis methods of LiVO₂ and Li₂TiO₃ follow the synthesis methods of the Li-Ti-V-O-based positive electrode active materials described in the above Examples 1 to 6.

[0117] 2. XRD Measurement and Results

[0118] 2.1 Powder XRD

[0119] Powder X-ray diffraction measurement was performed on the positive electrode active materials related to the examples. Specifically, using a non-reflecting sample plate, X-ray diffraction analysis was performed using an X-ray diffractometer SmartLab (using CuKα as the radiation source). Figure 4 The X-ray diffraction peaks of the positive electrode active material in the case of x = 0.14, y = 0.29, and z = 0.57 are shown.

[0120] As Figure 4 shown, it was confirmed that peaks attributable to an irregular rock salt structure could be observed. The positive electrode active materials related to Examples 1 to 6 are all active materials having an irregular rock salt structure belonging to the space group Fm-3m.

[0121] 2.2 In-situ XRD during Cycling (Operando XRD)

[0122] Changes in the crystal structure during charge and discharge were observed by synchrotron radiation X-ray diffraction measurement. In Table 2 below, for Example 1 and Comparative Examples 1 to 3, the maximum volume change rate with respect to the c-axis during charge and discharge is shown. In addition, in Figure 5 a case, an example of the displacement change of the X-ray diffraction peak of the positive electrode active material related to the example during charge and discharge is shown.

[0123] Table 2

[0124] Composition Maximum volume change rate (C-axis) Example 1 <![CDATA[Li 8 / 7 Ti 2 / 7 V 4 / 7 O2]]> 0.46％ Comparative Example 1 <![CDATA[LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2]]> 2.0％ Comparative Example 2 <![CDATA[LiNi 0.85 Co 0.10 Al 0.05 O2]]> 2.5％ Comparative Example 3 <![CDATA[LiNi 0.5 Mn 0.5 O2]]> 1.4％

[0125] From the results shown in Table 2 and Figure 5 it is clearly understood that for the positive electrode active materials related to the examples, only a very small volume change of less than 1% occurs during charge and discharge. In contrast, it is known that for positive electrode active materials having a layered rock salt structure such as Comparative Examples 1 to 3, a large volume change of more than 1% occurs during charge and discharge. From the above results, it can be said that when the positive electrode active materials related to the examples are applied to lithium ion batteries, mechanical degradation and the like caused by the volume change of the active material during the charge and discharge process can be suppressed, and it is easy to improve the cycle characteristics of the battery.

[0126] 3. Fabrication and Evaluation of Lithium Ion Batteries

[0127] The above-mentioned positive electrode active material, acetylene black as a conductive assistant, and PVdF as a binder were weighed at a ratio of 76.5:13.5:10.0 by mass, and then dispersed and mixed in N-methylpyrrolidone to obtain a positive electrode mixture slurry. The positive electrode mixture slurry was coated on an Al current collector foil and vacuum dried at 120 °C overnight to obtain a positive electrode. Using this positive electrode, a non-aqueous electrolyte (electrolyte: 1 M LiPF6, solvent: a solvent obtained by mixing ethylene carbonate (EC) and dimethyl carbonate (DMC) at 30 vol%:70 vol%), and a metallic lithium foil as a negative electrode, a coin cell (CR2032) was fabricated. Regarding the fabricated coin cell, the charge-discharge characteristics were evaluated under the conditions of a voltage range of 1.2 to 4.3 V and 10 mA / g in a thermostatic bath maintained at room temperature. Table 3 below shows the discharge capacities of the positive electrodes of the examples and comparative examples.

[0128] Table 3

[0129] Composition Discharge capacity (mAh / g) Example 2 <![CDATA[Li 1.05 Ti 0.10 V 0.85 O2]]> 211 Example 3 <![CDATA[Li 1.11 Ti 0.22 V 0.67 O2]]> 245 Example 4 <![CDATA[Li 1.14 Ti 0.29 V 0.57 O2]]> 270 Example 5 <![CDATA[Li 1.17 Ti 0.33 V 0.50 O2]]> 213 Example 6 <![CDATA[Li 1.20 Ti 0.40 V 0.40 O2]]> 181 Comparative Example 4 <![CDATA[LiVO2]]> 156 Comparative Example 5 <![CDATA[Li2TiO3]]> 0

[0130] As shown in Table 3, it can be seen that: compared with the positive electrode active materials represented by LiVO2 and Li2TiO3, the positive electrode active material having an irregular rock salt structure and having a composition represented by Li 1+x Ti y V z O2 can ensure a sufficient discharge capacity when applied to the positive electrode of a lithium-ion battery.

[0131] As described above, a positive electrode active material having the following requirements (1) and (2) has a small volume change during charge and discharge, for example, even when used in a wide SOC range with a reversible capacity of 250 mAh / g or more, and can improve the cycle characteristics of a lithium-ion battery. In addition, a sufficient discharge capacity can also be obtained as the positive electrode.

[0132] (1) It has an irregular rock salt structure belonging to the space group Fm-3m.

[0133] (2) It has a composition represented by Li 1+x Ti y V z O2 (0

Claims

1. A manufacturing method of a cathode active material for a lithium-ion battery, comprising: Process for producing an intermediate material, the intermediate material having a layered rock salt structure and having a composition represented by Li 1+x Ti y V z O2, wherein, 0 < x ≤ 0.20, 0 < y ≤ 0.40, 0.40 ≤ z ≤ 0.85; and A step of obtaining a positive electrode active material by subjecting the intermediate material to dry mechanical grinding, the positive electrode active material having an irregular rock salt structure belonging to the space group Fm-3m and having a composition represented by Li 1+x Ti y V z O2, where 0 < x ≤ 0.20, 0 < y ≤ 0.40, 0.40 ≤ z ≤ 0.85.

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