Secondary battery

Abstract

[Problem] To provide a means capable of sufficiently improving initial capacity and cycle durability of a secondary battery using a sulfide solid electrolyte containing sulfur and phosphorus and a high-nickel positive electrode active material. [Solution] In a secondary battery provided with a power generating element formed by sequentially stacking a positive electrode, a solid electrolyte layer, and a negative electrode, the positive electrode includes a positive electrode active material layer containing a positive electrode active material formed of a so-called high-nickel lithium-containing composite oxide, the solid electrolyte layer contains a sulfide solid electrolyte containing sulfur and phosphorus, and the negative electrode includes a negative electrode active material layer containing a negative electrode active material, and one or two or more kinds of additive elements selected from the group consisting of B, P, S, and Si are present at a molar concentration higher than that of Ni in a surface layer region within 100 nm from the surface of a particle of the lithium-containing composite oxide.

Description

Technical Field

[0001] This invention relates to secondary batteries. Background Technology

[0002] In recent years, there has been an urgent need to reduce carbon dioxide emissions in order to combat global warming. Within the automotive industry, the reduction in carbon dioxide emissions from the introduction of electric vehicles (EVs) and hybrid electric vehicles (HEVs) is highly anticipated, and the development of non-aqueous electrolyte secondary batteries, such as those for engine-driven secondary batteries, which are key to their practical application, is actively underway.

[0003] As a secondary battery for engine propulsion, lithium-ion secondary batteries, compared to those used in consumer electronics such as mobile phones and laptops, require extremely high power characteristics and high energy density. Therefore, lithium-ion secondary batteries, possessing the highest theoretical energy density among all existing batteries, are attracting significant attention and their development is currently progressing rapidly.

[0004] The commonly used lithium-ion secondary batteries currently employ organic electrolytes that are flammable. These liquid-based lithium-ion secondary batteries require stricter safety measures against leakage, short circuits, and overcharging than other types of batteries.

[0005] Therefore, in recent years, research and development of all-solid-state batteries, including all-solid-state lithium-ion secondary batteries using oxide-based and sulfide-based solid electrolytes, has been actively underway. Solid electrolytes are materials that primarily utilize ion conductors capable of ion conduction within a solid state. Therefore, in principle, all-solid-state lithium-ion secondary batteries do not experience the various problems caused by flammable organic electrolytes, as seen in conventional liquid-based lithium-ion secondary batteries. Furthermore, by using high-potential / high-capacity positive electrode materials and high-capacity negative electrode materials, significant improvements in battery power density and energy density can typically be achieved.

[0006] However, in all-solid-state lithium-ion secondary batteries that combine a sulfide solid electrolyte with a positive electrode active material formed from metal oxides, problems such as increased battery resistance and decreased power characteristics sometimes occur due to the low electronic conductivity of metal oxides. Furthermore, as a measure to address this problem, adding conductive materials relatively reduces the content of the positive electrode active material, resulting in a decrease in the battery's energy density.

[0007] To suppress the occurrence of such problems, for example, Patent Document 1 discloses the following technology: by forming a reaction inhibition layer containing carbonaceous material and lithium oxides such as LiNbO3 on the surface of the positive electrode active material as a composite positive electrode active material, the decrease in battery resistance of the all-solid-state battery is prevented and the power characteristics are improved.

[0008] Existing technical documents

[0009] Patent documents

[0010] Patent Document 1: International Publication No. 2013 / 022034 Summary of the Invention

[0011] The problem the invention aims to solve

[0012] In a secondary battery where a sulfide solid electrolyte containing sulfur and phosphorus was used as the electrolyte layer, the inventors investigated the use of a high-nickel-based positive electrode active material as a high-capacity positive electrode active material. The results showed that sufficient performance was not obtained in terms of initial capacity and cycle durability. Therefore, the inventors attempted to improve these performance characteristics using the technology described in Patent Document 1.

[0013] However, the technology disclosed in Patent Document 1 cannot adequately improve the initial capacity and cycle durability of secondary batteries that use sulfide solid electrolytes containing sulfur and phosphorus and high-nickel cathode active materials.

[0014] Therefore, the object of the present invention is to provide a solution that can significantly improve the initial capacity and cycle durability of a secondary battery using a sulfide solid electrolyte containing sulfur and phosphorus and a high-nickel cathode active material.

[0015] Solution for solving the problem

[0016] The inventors conducted in-depth research to solve the aforementioned problems. Their findings revealed that by introducing a specified element into the surface region of the lithium-containing composite oxide particles in a positive electrode active material composed of a lithium-containing composite oxide having a defined central portion, and combining it with a sulfide solid electrolyte containing sulfur and phosphorus, the aforementioned problems can be solved, thus completing this invention.

[0017] According to one aspect of the present invention, a secondary battery is provided, which includes a power generation element, said power generation element being formed by sequentially stacking a positive electrode, a solid electrolyte layer, and a negative electrode.

[0018] The positive electrode includes a positive electrode active material layer, which contains a positive electrode active material formed from a lithium-containing composite oxide with the following chemical formula (1) at its center:

[0019] Li 1+q Ni x Co y Mn z M p O2(1)

[0020] In equation (1), -0.02≤q≤0.20, x+y+z+p=1, 0.5≤x≤1.0, 0≤y≤0.5, 0≤z≤0.5, 0≤p≤0.1, and M is one or more elements selected from the group consisting of Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr and Cr.

[0021] The solid electrolyte layer contains a sulfide solid electrolyte containing sulfur and phosphorus.

[0022] The negative electrode includes a layer of negative electrode active material containing negative electrode active material.

[0023] In the surface region within 100 nm of the aforementioned lithium-containing composite oxide particles, one or more additive elements selected from the group consisting of B, P, S and Si are present at a molar concentration higher than that of Ni.

[0024] The effects of the invention

[0025] According to the present invention, the initial capacity and cycle durability of secondary batteries using sulfide solid electrolytes containing sulfur and phosphorus and high-nickel cathode active materials can be significantly improved. Attached Figure Description

[0026] Figure 1 A perspective view showing the appearance of a flat, stacked, all-solid-state lithium-ion secondary battery, which is one embodiment of the lithium-ion secondary battery of the present invention.

[0027] Figure 2 For along Figure 1 The sectional view shown is along line 2-2.

[0028] Figure 3 A cross-sectional view of a bipolar all-solid-state lithium-ion secondary battery, which is one embodiment of the lithium-ion secondary battery of the present invention, is shown for illustrative purposes. Detailed Implementation

[0029] Secondary Batteries

[0030] One aspect of the present invention is a secondary battery comprising a power generation element, wherein the power generation element is formed by sequentially stacking a positive electrode, a solid electrolyte layer, and a negative electrode.

[0031] The positive electrode contains a positive electrode active material, which is formed from a lithium-containing composite oxide with the following chemical formula (1) in its central part:

[0032] Li 1+q Ni x Co y Mn z M pO2(1)

[0033] In equation (1), -0.02≤q≤0.20, x+y+z+p=1, 0.5≤x≤1.0, 0≤y≤0.5, 0≤z≤0.5, 0≤p≤0.1, and M is one or more elements selected from the group consisting of Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr and Cr.

[0034] The solid electrolyte layer contains a sulfide solid electrolyte containing sulfur and phosphorus.

[0035] The negative electrode contains a negative electrode active material.

[0036] In the surface region within 100 nm of the aforementioned lithium-containing composite oxide particles, one or more additive elements selected from the group consisting of B, P, S and Si are present at a molar concentration higher than that of Ni.

[0037] Hereinafter, the embodiment of the positive electrode for a secondary battery according to the present invention will be described with reference to the accompanying drawings. However, the scope of protection of the present invention should be determined based on the claims and is not limited to the embodiments described below. It should be noted that the scale of the drawings is exaggerated for ease of explanation and may sometimes differ from the actual scale.

[0038] Figure 1 A perspective view showing the appearance of a flat, stacked, all-solid-state lithium-ion secondary battery, which is one embodiment of the lithium-ion secondary battery of the present invention. Figure 2 For along Figure 1 The cross-sectional view shown is along line 2-2. By forming a stacked structure, the battery can be made compact and have a high capacity. It should be noted that in this specification, examples are listed... Figure 1 and Figure 2 The flat, stacked type lithium-ion secondary battery shown is used as an example to illustrate this in detail. However, when considering the internal electrical connection configuration (electrode structure) of the lithium-ion secondary battery of this type, it can also be applied to either non-bipolar (internal parallel connection type) batteries or bipolar (internal series connection type) batteries.

[0039] like Figure 1 As shown, the stacked battery 10a has a rectangular, flat shape, with a negative current collector 25 and a positive current collector 27 extending from its two sides for extracting electricity. The power generation element 21 is covered by the battery casing material (laminated film 29) of the stacked battery 10a, and its perimeter is heat-sealed, so that the power generation element 21 is sealed in a state where the negative current collector 25 and the positive current collector 27 are extended to the outside.

[0040] It should be noted that the lithium-ion secondary battery of this method is not limited to a flat, stacked shape. The wound lithium-ion secondary battery can be cylindrical, or it can be deformed into a rectangular flat shape, etc., without particular limitation. For the aforementioned cylindrical shape, the outer shell material can be a laminated film, or a conventional cylindrical can (metal can), etc., without particular limitation. Preferably, the power generation element is housed inside a laminated film containing aluminum. This method achieves weight reduction.

[0041] In addition, regarding Figure 1 There are no particular restrictions on the removal of the current collectors (25, 27) shown. The negative current collector 25 and the positive current collector 27 can be led out from the same side, or they can be divided into multiple parts and taken out from different sides, etc., without limitation. Figure 1 As shown in the diagram. Additionally, in wound lithium-ion batteries, for example, terminals can be formed using a cylindrical can (metal can) instead of tabs.

[0042] like Figure 2 As shown, the stacked battery 10a of this embodiment has a structure in which a flat, roughly rectangular power generation element 21, in which the actual charge-discharge reaction takes place, is sealed inside a laminated film 29, which serves as the battery casing material. Here, the power generation element 21 has a configuration in which a positive electrode, a solid electrolyte layer 17, and a negative electrode are stacked. The positive electrode has a structure in which a positive electrode active material layer 15 containing a positive electrode active material is disposed on both sides of the positive electrode current collector 11'. The negative electrode has a structure in which a negative electrode active material layer 13 containing a negative electrode active material is disposed on both sides of the negative electrode current collector 11'. Specifically, a positive electrode active material layer 15 and an adjacent negative electrode active material layer 13 are stacked sequentially with the positive electrode, the solid electrolyte layer, and the negative electrode separated by a solid electrolyte layer 17. Thus, the adjacent positive electrode, the solid electrolyte layer, and the negative electrode constitute a single cell layer 19. Therefore, it can be said that... Figure 1 The stacked battery 10a shown has a configuration formed by stacking multiple single cell layers 19 and connecting them in parallel.

[0043] like Figure 2 As shown, the outermost positive current collectors of the two outermost layers of the power generation element 21 are each provided with a positive active material layer 15 on only one side, but active material layers can also be provided on both sides. That is, the current collector with active material layers on both sides can be used directly as the outermost current collector without forming a dedicated outermost current collector with an active material layer on only one side. In addition, depending on the situation, the negative active material layer 13 and the positive active material layer 15 can be used as the negative and positive electrodes respectively without using current collectors (11', 11").

[0044] The negative current collector 11' and the positive current collector 11" have the following structure: a negative current collector plate (tab) 25 and a positive current collector plate (tab) 27, respectively connected to each electrode (positive and negative), are respectively installed and led out to the outside of the laminated film 29, which is used as the battery casing material, by clamping it to the end of the laminated film 29. The positive current collector plate 27 and the negative current collector plate 25 are respectively installed on the positive current collector 11" and the negative current collector 11' of each electrode by means of positive and negative leads (not shown) through ultrasonic welding, resistance welding, etc., as needed.

[0045] The main components of the lithium-ion secondary battery of this method are described below.

[0046] [Current Collector]

[0047] A current collector has the function of mediating the movement of electrons from the electrode active material layer. There are no particular restrictions on the materials used to construct the current collector. Materials used to construct the current collector include, for example, metals and conductive resins.

[0048] Specifically, as metals, aluminum, nickel, iron, stainless steel, titanium, and copper can be used. In addition to these, cladding materials of nickel and aluminum, copper and aluminum, etc., can be used. Alternatively, a foil formed by covering a metal surface with aluminum can also be used. From the viewpoints of electronic conductivity, battery operating potential, and the adhesion of the negative electrode active material generated by sputtering the current collector, aluminum, stainless steel, copper, and nickel are preferred.

[0049] In addition, as a conductive resin, examples of non-conductive polymer materials include resins in which conductive fillers are added as needed.

[0050] Examples of non-conductive polymer materials include polyethylene (PE; high-density polyethylene (HDPE), low-density polyethylene (LDPE), etc.), polypropylene (PP), polyethylene terephthalate (PET), polyether nitrile (PEN), polyimide (PI), polyamide-imide (PAI), polyamide (PA), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl methacrylate (PMA), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), or polystyrene (PS). Such non-conductive polymer materials can exhibit excellent potential resistance or solvent resistance.

[0051] Conductive fillers can be added to the aforementioned conductive or non-conductive polymer materials as needed. In particular, when the resin, which serves as the substrate for current collectors, is formed solely of non-conductive polymers, conductive fillers are essential to impart conductivity to the resin.

[0052] Conductive fillers can be used without particular restrictions as long as they are conductive materials. For example, metals and conductive carbon can be cited as materials with excellent conductivity, potential resistance, or lithium-ion blocking properties. As for metals, there are no particular restrictions, but it is preferable to include at least one metal selected from the group consisting of Ni, Ti, Al, Cu, Pt, Fe, Cr, Sn, Zn, In, and Sb, or alloys or metal oxides containing these metals. Similarly, as for conductive carbon, there are no particular restrictions. It is preferable to include at least one carbon selected from the group consisting of acetylene black, Vulcan (registered trademark), BLACK PEARL (registered trademark), carbon nanofibers, Ketjenblack (registered trademark), carbon nanotubes, carbon nanohorns, carbon nanospheres, and fullerenes.

[0053] There is no particular limitation on the amount of conductive filler added, as long as it is sufficient to impart sufficient conductivity to the current collector. It is usually 5 to 80% of the total mass of the current collector.

[0054] It should be noted that the current collector can be a single-layer structure formed from an elemental material, or it can be a stacked structure formed by appropriately combining layers formed from these materials. From the viewpoint of lightweighting the current collector, it is preferable to include at least a conductive resin layer formed from a conductive resin. Furthermore, from the viewpoint of blocking the movement of lithium ions between the single-cell layers, a metal layer can be provided in a portion of the current collector. Moreover, the negative electrode active material layer and the positive electrode active material layer described later only need to be conductive and capable of performing the current collection function; it is not necessary to use a current collector that is a component different from these electrode active material layers. In this approach, the negative electrode active material layer described later directly constitutes the negative electrode, and the positive electrode active material layer described later directly constitutes the positive electrode.

[0055] [Negative electrode (negative electrode active material layer)]

[0056] In this type of secondary battery, the negative electrode active material layer 13 contains a negative electrode active material. There are no particular limitations on the type of negative electrode active material; examples include carbon materials, metal oxides, and metal active materials. Examples of carbon materials include natural graphite, artificial graphite, mesophase carbon microspheres (MCMB), highly oriented graphite (HOPG), hard carbon, and soft carbon. Examples of metal oxides include Nb₂O₅ and Li₄Ti₅O₅. 12Furthermore, silicon-based and tin-based anode active materials can also be used. Here, silicon and tin belong to Group 14 elements and are known to be anode active materials that can significantly improve the capacity of non-aqueous electrolyte secondary batteries. These elements can absorb and release a large number of charge carriers (lithium ions, etc.) per unit volume (mass), thus becoming high-capacity anode active materials. Here, elemental Si is preferred as a silicon-based anode active material. Similarly, SiO2, which is heterogeneously divided into two phases—a Si phase and a silicon oxide phase—is also preferred. x Silicon oxides such as (0.3≤x≤1.6). In this case, the range of x is more preferably 0.5≤x≤1.5, and even more preferably 0.7≤x≤1.2. Furthermore, silicon-containing alloys (silicon-containing alloy-based anode active materials) can also be used. On the other hand, as anode active materials containing tin (tin-based anode active materials), examples include elemental Sn, tin alloys (Cu-Sn alloys, Co-Sn alloys), amorphous tin oxides, and tin-silicon oxides. Among these, SnB is an example of an amorphous tin oxide. 0.4 P 0.6 O 3.1 Additionally, SnSiO3 is an example of a tin-silicon oxide. Furthermore, lithium-containing metals can be used as the negative electrode active material. There are no particular limitations on this negative electrode active material as long as it contains lithium; lithium alloys other than metallic lithium can also be used. Examples of lithium-containing alloys include alloys of Li with at least one of In, Al, Si, and Sn. Depending on the situation, two or more negative electrode active materials can be used together. It should be noted that negative electrode active materials other than those mentioned above can also be used. The negative electrode active material preferably contains metallic lithium, a silicon-based negative electrode active material, or a tin-based negative electrode active material, and is particularly preferably containing metallic lithium.

[0057] The shape of the negative electrode active material can be, for example, particulate (spherical, fibrous), or thin film. When the negative electrode active material is in particulate form, its average particle size (D) 50 For example, a particle size range of 1 nm to 100 μm is preferred, a range of 10 nm to 50 μm is more preferred, a range of 100 nm to 20 μm is even more preferred, and a range of 1 nm to 20 μm is particularly preferred. It should be noted that, in this specification, the average particle size (D) of the active material is... 50 The value of ) can be determined using the laser diffraction scattering method.

[0058] The content of negative electrode active material in the negative electrode active material layer is not particularly limited, but is preferably in the range of 40 to 99% by mass, and more preferably in the range of 50 to 90% by mass.

[0059] The negative electrode active material layer preferably also includes a solid electrolyte. By including a solid electrolyte, the ionic conductivity of the negative electrode active material layer can be improved. Examples of solid electrolytes include sulfide solid electrolytes and oxide solid electrolytes, with sulfide solid electrolytes being preferred.

[0060] Examples of sulfide solid electrolytes include LiI-Li2S-SiS2, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li2S-P2S5, LiI-Li3PS4, LiI-LiBr-Li3PS4, Li3PS4, Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, and Li2S-P2S5-Z. m S n (where m and n are positive numbers, and Z is any one of Ge, Zn, and Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, Li2S-SiS2-Li x MO y (Where x and y are positive numbers, and M is any one of P, Si, Ge, B, Al, Ga, and In.) It should be noted that the description of "Li2S-P2S5" refers to a sulfide solid electrolyte made using a raw material composition containing Li2S and P2S5, and the same applies to other descriptions.

[0061] Sulfide solid electrolytes can have, for example, a Li3PS4 framework, a Li4P2S7 framework, or a Li4P2S6 framework. Examples of sulfide solid electrolytes with a Li3PS4 framework include LiI-Li3PS4, LiI-LiBr-Li3PS4, and Li3PS4. Furthermore, examples of sulfide solid electrolytes with a Li4P2S7 framework include Li-PS system solid electrolytes known as LPS (e.g., Li7P3S). 11 Additionally, as a sulfide solid electrolyte, Li can be used, for example. (4-x) Ge (1-x) P xLGPS as shown in S4 (where 0 < x < 1), etc. Among them, the sulfide solid electrolyte contained in the active material layer is preferably a sulfide solid electrolyte containing P element, and the sulfide solid electrolyte is more preferably a material with Li2S-P2S5 as the main component. Furthermore, the sulfide solid electrolyte may contain halogen (F, Cl, Br, I).

[0062] In addition, when the sulfide solid electrolyte is of the Li2S-P2S5 system, the ratio of Li2S and P2S5 is preferably within the range of Li2S:P2S5 = 50:50 to 100:0 in terms of molar ratio, and preferably Li2S:P2S5 = 70:30 to 80:20 among them.

[0063] In addition, the sulfide solid electrolyte can be a sulfide glass, a crystallized sulfide glass, or a crystalline material obtained by a solid-phase method. It should be noted that the sulfide glass can be obtained, for example, by mechanically grinding (such as a ball mill) the raw material composition. In addition, the crystallized sulfide glass can be obtained, for example, by heat-treating the sulfide glass at a temperature above the crystallization temperature. In addition, the ionic conductivity (such as Li ion conductivity) of the sulfide solid electrolyte at room temperature (25 °C) is preferably 1×10 -5 S / cm or more, more preferably 1×10 -4 S / cm or more. It should be noted that the value of the ionic conductivity of the solid electrolyte can be measured by the alternating current impedance method.

[0064] As the oxide solid electrolyte, for example, compounds having a NASICON-type structure can be cited. As an example of a compound having a NASICON-type structure, a compound represented by the general formula Li 1+x Al x Ge 2-x (PO4)3 (0 ≤ x ≤ 2) (LAGP), a compound represented by the general formula Li 1+x Al x Ti 2-x (PO4)3 (0 ≤ x ≤ 2) (LATP), etc. can be cited. In addition, as other examples of the oxide solid electrolyte, LiLaTiO (such as Li 0.34 La 0.51 TiO3), LiPON (such as Li 2.9 PO 3.3 N 0.46 ), LiLaZrO (such as Li7La3Zr2O 12 ), etc. can be cited.

[0065] Examples of solid electrolyte shapes include spherical, ellipsoidal, and other particle shapes, as well as thin film shapes. When a solid electrolyte is in particle shape, its average particle size (D) 50 There is no particular limitation, but 40 μm or less is preferred, more preferably 20 μm or less, and even more preferably 10 μm or less. On the other hand, the average particle size (D) 50 Preferably, the micrometer size is 0.01 μm or larger, and more preferably, 0.1 μm or larger.

[0066] The content of solid electrolyte in the negative electrode active material layer is preferably in the range of 1 to 60% by mass, more preferably in the range of 10 to 50% by mass.

[0067] In addition to the aforementioned negative electrode active material and solid electrolyte, the negative electrode active material layer may also contain at least one of conductive additives and binders.

[0068] Examples of conductive additives include, but are not limited to, metals such as aluminum, stainless steel (SUS), silver, gold, copper, and titanium, alloys or metal oxides containing these metals; carbon fibers (specifically, vapor-deposited carbon fibers (VGCF), polyacrylonitrile-based carbon fibers, pitch-based carbon fibers, rayon-based carbon fibers, activated carbon fibers, etc.), carbon nanotubes (CNTs), and carbon black (specifically, acetylene black, Ketjenblack (registered trademark), furnace black, channel black, thermal lamp black, etc.). Additionally, granular ceramic materials or materials obtained by coating the aforementioned metal materials around a resin material using methods such as plating can also be used as conductive additives. From the viewpoint of electrical stability, it is preferable that these conductive additives include at least one element selected from the group consisting of aluminum, stainless steel, silver, gold, copper, titanium, and carbon; more preferably, at least one element selected from the group consisting of aluminum, stainless steel, silver, gold, and carbon; and even more preferably, at least one type of carbon. These conductive additives can be used alone or in combination of two or more.

[0069] The conductive additive is preferably in granular or fibrous form. When the conductive additive is in granular form, the shape of the granules is not particularly limited and can be any shape such as powder, sphere, rod, needle, plate, column, irregular shape, scale, spindle, etc.

[0070] The average particle size (primary particle size) of the conductive additive in particulate form is not particularly limited, but from the viewpoint of the battery's electrical characteristics, 0.01 to 10 μm is preferred. It should be noted that in this specification, "particle size of the conductive additive" refers to the maximum distance L between any two points on the outline of the conductive additive. The value of the "average particle size of the conductive additive" is calculated using observation methods such as scanning electron microscopy (SEM) and transmission electron microscopy (TEM), by averaging the particle sizes observed in several to tens of fields of view.

[0071] When the negative electrode active material layer contains a conductive additive, the content of the conductive additive in the negative electrode active material layer is not particularly limited. Relative to the total mass of the negative electrode active material layer, it is preferably 0 to 10% by mass, more preferably 2 to 8% by mass, and even more preferably 4 to 7% by mass. If it is within this range, a more robust electron conduction pathway can be formed in the negative electrode active material layer, which can effectively improve the battery characteristics.

[0072] On the other hand, as an adhesive, there are no particular limitations; for example, the following materials can be cited.

[0073] Examples include: polybutylene terephthalate, polyethylene terephthalate, polyvinylidene fluoride (PVDF) (compounds obtained by replacing hydrogen atoms with other halogen elements), polyethylene, polypropylene, polymethylpentene, polybutene, polyether nitrile, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR), ethylene / propylene / diene copolymer, styrene-butadiene / styrene block copolymer and its hydrides, styrene / isoprene / styrene block copolymer and its hydrides, etc., thermoplastic polymers such as tetrafluoroethylene / hexafluoropropylene copolymer (FEP), tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer (PFA), ethylene / tetrafluoroethylene copolymer (ETFE), polyvinyl chloride trifluoroethylene (PC). Fluoropolymers such as TFE, ethylene / chlorotrifluoroethylene copolymer (ECTFE), and polyvinylidene fluoride (PVF), as well as vinylidene fluoride-hexafluoropropylene fluororubbers (VDF-HFP), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene fluororubbers (VDF-HFP-TFE), vinylidene fluoride-pentafluoropropylene fluororubbers (VDF-PFP), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene fluororubbers (VDF-PFP-TFE), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene fluororubbers (VDF-PFMVE-TFE), and vinylidene fluoride-chlorotrifluoroethylene fluororubbers (VDF-CTFE), and epoxy resins, are preferred. Among these, polyimide, styrene-butadiene rubber, carboxymethyl cellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, and polyamide are preferred.

[0074] The thickness of the negative electrode active material layer also varies depending on the target secondary battery structure, preferably in the range of 0.1 to 1000 μm.

[0075] [Solid electrolyte layer]

[0076] In this type of secondary battery, the solid electrolyte layer is a layer sandwiched between the positive electrode active material layer and the negative electrode active material layer, and must contain a sulfide solid electrolyte containing sulfur and phosphorus.

[0077] There is no particular limitation on the specific form of the sulfide solid electrolyte contained in the solid electrolyte layer, and the sulfide solid electrolyte containing phosphorus exemplified in the column of the negative electrode active material layer can be similarly adopted. Specifically, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li2S-P2S5, LiI-Li3PS4, LiI-LiBr-Li3PS4, Li3PS4, Li2S-P2S5, Li2S-P2S5-LiI, Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2-P2S5-LiI, Li2S-P2S5-Z m S n (where m and n are positive numbers, and Z is any one of Ge, Zn, and Ga), Li2S-SiS2-Li3PO4, LiI-Li3PS4, LiI-LiBr-Li3PS4, Li3PS4, LPS (Li-P-S-based solid electrolyte (e.g., Li7P3S 11 )), LGPS (Li (4-x) Ge (1-x) P x S4 (where 0 < x < 1)), etc. Among them, the sulfide solid electrolyte contained in the solid electrolyte layer is more preferably a material with Li2S-P2S5 as the main component. Depending on the situation, a solid electrolyte other than the above-mentioned phosphorus-containing sulfide solid electrolyte can also be used in combination. Among them, the ratio of the content of the above-mentioned specified sulfide solid electrolyte in the total amount of the solid electrolyte of 100% by mass is preferably 50% by mass or more, more preferably 70% by mass or more, further preferably 80% by mass or more, still preferably 90% by mass or more, particularly preferably 95% by mass or more, and most preferably 100% by mass.

[0078] The solid electrolyte layer may further contain a binder in addition to the above-mentioned specified sulfide solid electrolyte. For the binder that can be contained in the solid electrolyte layer, the examples and preferred forms described in the column of the negative electrode active material layer can also be similarly adopted.

[0079] The thickness of the solid electrolyte layer also varies depending on the composition of the target lithium-ion secondary battery. From the perspective of improving the volumetric energy density of the battery, it is preferably 600 μm or less, more preferably 500 μm or less, and further preferably 400 μm or less. On the other hand, there is no particular limitation on the lower limit value of the thickness of the solid electrolyte layer, and it is preferably 10 μm or more, more preferably 50 μm or more, and further preferably 100 μm or more.

[0080] [Positive electrode active material layer]

[0081] In this type of secondary battery, the positive electrode active material layer contains a so-called high-nickel-based positive electrode active material. Specifically, the positive electrode active material contained in the positive electrode active material layer of this type of secondary battery is formed from a lithium-containing composite oxide with the following chemical formula (1) in the center:

[0082] Li 1+q Ni x Co y Mn z M p O2(1)

[0083] In formula (1), -0.02≤q≤0.20, x+y+z+p=1, 0.5≤x≤1.0, 0≤y≤0.5, 0≤z≤0.5, 0≤p≤0.1, and M is one or more elements selected from the group consisting of Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr and Cr.

[0084] In general formula (1), q is -0.02 ≤ q ≤ 0.20. From the viewpoint of increasing the initial discharge capacity, q is preferably 0 ≤ q ≤ 0.10. Furthermore, in general formula (1), x is 0.50 ≤ x ≤ 1.0. From the viewpoint of increasing the initial discharge capacity, x is preferably 0.50 ≤ x < 1.0, more preferably 0.55 ≤ x ≤ 0.95, even more preferably 0.60 ≤ x ≤ 0.90, and particularly preferably 0.70 ≤ x ≤ 0.85. Furthermore, in general formula (1), y and z are 0 ≤ (y, z) ≤ 0.50. From the viewpoint of excellent safety, 0 < (y, z) ≤ 0.50 is preferred, more preferably 0.05 ≤ (y, z) ≤ 0.45, and even more preferably 0.10 ≤ (y, z) ≤ 0.40. x / z is preferably greater than 1, more preferably 1.2 or more, and even more preferably 1.5 to 99.

[0085] One characteristic of the positive electrode active material of this method is that the composition of the surface region of the lithium-containing composite oxide particles constituting the positive electrode active material is different from the composition of the central portion shown in the above general formula (1). Specifically, it has the following characteristic: in the surface region within 100 nm of the surface of the lithium-containing composite oxide particles having the composition of the above-mentioned central portion (general formula (1)), one or more additive elements selected from the group consisting of B, P, S and Si are present at a molar concentration higher than that of Ni. In other words, in the above-mentioned surface region, at least one element among B, P, S and Si coexists at a molar concentration higher than that of Ni. It should be noted that in this invention, the additive element "present in the surface region at a molar concentration higher than that of Ni" must be one or more. Therefore, if the molar concentration of any additive element in the surface region is less than or equal to the molar concentration of Ni, even if the total molar concentration of the multiple additive elements is greater than the molar concentration of Ni, it is not included in the scope of this invention.

[0086] The elemental composition of the surface region within 100 nm of the lithium-containing composite oxide particles can be analyzed using X-ray photoelectron spectroscopy (XPS). Similarly, the composition of the central region of the aforementioned lithium-containing composite oxide can also be analyzed using XPS. It should be noted that during XPS measurements, a charge correction is applied to shift the peak of C1s to 284.6 eV.

[0087] There are no particular restrictions on the concentration (amount) of the added elements in the surface region. The concentration of the added elements is preferably 1 to 30 mol%, more preferably 17 to 30 mol%, relative to the molar percentage of all elements in the surface region. It should be noted that the concentration of the added elements in the surface region when multiple added elements are present is the total concentration of all added elements. Furthermore, there are no particular restrictions on the curve of the concentration change of the added elements in the depth direction of the surface region. For example, it can be a sloping curve where the concentration of the added elements gradually decreases from the surface to the depth direction. Alternatively, it can be a curve where the concentration of the added elements temporarily increases and then decreases from the surface to the depth direction, or it can be a curve where the concentration of the added elements in the depth direction of the surface region is substantially uniform and decreases sharply towards the center.

[0088] Here, as mentioned above, in addition to the aforementioned added elements, Ni must also be present in the surface region. In the case of y>0 or z>0 in general formula (1), Mn or Co elements are also present respectively. This indicates that the aforementioned added elements are present by permeation (doping) into the surface region of the lithium-containing composite oxide having the composition shown in general formula (1). In other words, this indicates that the positive electrode active material of this method is not simply a substance containing added elements covering (coating) the surface of the lithium-containing composite oxide. It should be noted that there is no particular limitation on the concentration (amount) of Ni in the surface region. The concentration of Ni is preferably less than 10 mol%, more preferably 2 to 7 mol%, relative to the molar percentage of all elements in the surface region. Furthermore, there is no particular limitation on the value of the ratio of O (oxygen) concentration to Ni concentration (O / Ni) in the surface region. From the viewpoint of further embodying the effects of the present invention, it is preferably 20.0 or less, more preferably 2.9 to 20.0.

[0089] The positive electrode active material used in this secondary battery is a particulate lithium-containing composite oxide having the above-described structure. Here, the lithium-containing composite oxide can be in the form of monodisperse primary particles or in the form of secondary particles formed by the aggregation of primary particles. From the viewpoint of further embodying the effects of the present invention, the lithium-containing composite oxide is preferably in the form of primary particles. Furthermore, for the same reason, the average particle size of the lithium-containing composite oxide particles, measured as the 50% cumulative diameter (D50) of the particle size distribution obtained by laser diffraction scattering, is preferably 10 μm or less, more preferably 3.6 to 6.3 μm.

[0090] Here, there are no particular limitations on the method for manufacturing the positive electrode active material (lithium-containing composite oxide) of this embodiment having the above-described structure, and conventionally known insights may be appropriately referenced. Such a positive electrode active material (lithium-containing composite oxide) may be manufactured, for example, by the manufacturing method disclosed in Japanese Patent Application Publication No. 2020-35693 or by a method that may be appropriately modified thereto.

[0091] Here, a brief description of the manufacturing method of the positive electrode active material (lithium-containing composite oxide) disclosed in this publication is provided. In this method, firstly, an aqueous solution containing a transition metal raw material comprising one or more transition metal compounds and an aqueous solution for nucleation of ammonium ions are controlled at a specified pH, a specified ammonium ion concentration, and a specified oxygen concentration in an atmosphere, and are supplied to a crystallization reaction tank to generate nuclei (nucleation generation step). Next, the nuclei generated in the nucleation generation step are subjected to particle growth (particle growth step). This yields a transition metal composite hydroxide, which serves as a raw material for synthesizing the lithium-containing composite oxide. Then, the transition metal composite hydroxide obtained above is subjected to heat treatment (heat treatment step). Next, the heat-treated transition metal composite hydroxide is mixed with a lithium compound to form a lithium mixture (mixing step). Finally, the mixture formed in the mixing step is calcined (calcination step). This yields a lithium-containing composite oxide. Here, the manufacturing method disclosed in this publication, as a method for having additive elements different from those of the present invention present on the surface of the transition metal composite hydroxide, discloses the following method: slurrying the transition metal composite hydroxide obtained above in an aqueous solution (or an alkanoic solution of the additive element) containing the additive element, controlling the pH to a predetermined level, and further adding the aqueous solution to precipitate the additive element on the surface of the composite hydroxide using a crystallization reaction; and blowing the transition metal composite hydroxide obtained above with an aqueous solution or slurry containing the additive element and drying it. Furthermore, the following methods are also disclosed: spray drying a slurry containing the transition metal composite hydroxide and a salt containing the additive element; and mixing the transition metal composite hydroxide and the salt containing the additive element using a solid-phase method. When manufacturing the positive electrode active material (lithium-containing composite oxide) of this method, the additive elements (B, P, S, Si) of the present invention can be used instead of the additive elements disclosed in the above publication, and the same method can be employed.

[0092] Although the positive electrode active material of this method is a so-called high-nickel positive electrode active material, by having the composition of the above-mentioned surface region, the initial discharge capacity and cycle durability of the secondary battery using a sulfide solid electrolyte containing sulfur and phosphorus can be significantly improved. The mechanism by which this effect is achieved by forming the structure of the present invention is not fully elucidated, but the following mechanism is presumed. That is, in the conventionally known high-nickel positive electrode active material having the composition shown in the above-mentioned general formula (1), even in the surface region, the concentration of Ni element is as high as in the center, and in the surface region, Ni atoms form metal-oxygen (Ni-O) bonds with oxygen atoms. This metal-oxygen bond is different from a covalent bond and becomes unstable during charging, and therefore, it breaks down as the charging reaction proceeds. On the other hand, the sulfide solid electrolyte containing sulfur and phosphorus is prone to oxidation (combination with oxygen) reaction by contact with a positive electrode active material with a high potential (≥3V (relative to lithium)), and the generation of active oxygen atoms generated by the breaking down of the metal-oxygen bonds in the above-mentioned positive electrode active material accelerates the progress of this oxidation reaction.

[0093] In contrast, in the positive electrode active material of this method, by adding elements to the composition of the central part, the concentrations of Ni and O elements in the composition of the surface region are relatively reduced. As a result, it becomes less likely to generate active oxygen atoms that promote the oxidation reaction that occurs when the aforementioned sulfide solid electrolyte comes into contact with the high-potential positive electrode active material. In addition, in the surface region, the aforementioned added elements (B, P, S, Si) form covalent bonds with O atoms, and therefore are electrochemically stable, which also plays a role in suppressing the generation of active oxygen atoms. As a result of these, it is believed that the present invention can achieve effects such as preventing the oxidation reaction of the sulfide solid electrolyte that occurs during charging, improving the initial discharge capacity and cycle durability. Here, from the viewpoint of further embodying the effects of the present invention, it is preferable that B (boron) is present in the surface region as an added element. This is because the atomic radius of B (boron) is smaller than that of other added elements (P, S, Si), and as an added element present in the surface region, it is least likely to hinder the absorption and release of lithium ions in the lithium-containing composite oxide. That is, by adding element B (boron), in addition to the effects of the present invention, an improved power characteristic with a reduction in battery resistance (reaction resistance) is also obtained.

[0094] It should be noted that, based on the research of the inventors, the present invention does not achieve the desired effect according to the technology described in Patent Document 1 (International Publication No. 2013 / 022034). This is presumed to be because the reaction inhibition layer peels off due to the expansion and contraction of the active material during charging and discharging, and the shear force applied during the mixing process in the slurry preparation step. Furthermore, the layer containing lithium oxide also presents a fundamental problem in principle, as it increases the resistance in the direction of lithium ion and electron conduction. Moreover, a separate reaction inhibition layer is required, thus increasing manufacturing costs.

[0095] Depending on the circumstances, positive electrode active materials other than the aforementioned lithium-containing composite oxides may also be used. Preferably, the content of the aforementioned lithium-containing composite oxides in 100% by mass of the total positive electrode active material is 50% by mass or more, more preferably 70% by mass or more, further preferably 80% by mass or more, even more preferably 90% by mass or more, particularly preferably 95% by mass or more, and most preferably 100% by mass.

[0096] The content of positive electrode active material in the positive electrode active material layer is not particularly limited, but from the viewpoint of preventing a decrease in the energy density of the secondary battery, it is preferably in the range of 55% to 95% by mass. It should be noted that the positive electrode active material layer may also contain conductive additives and / or binders, and the specific and preferred methods for these can be described in the section on negative electrode active material layer above.

[0097] [Positive current collector and negative current collector]

[0098] There are no particular limitations on the materials used to construct the current collectors (25, 27), and conventionally known highly conductive materials can be used as current collectors for secondary batteries. Preferred materials for the current collectors include, for example, aluminum, copper, titanium, nickel, stainless steel (SUS), and their alloys. From the viewpoints of lightweight, corrosion resistance, and high conductivity, aluminum and copper are more preferred, and aluminum is particularly preferred. It should be noted that the positive current collector 27 and the negative current collector 25 can be made of the same material or different materials.

[0099] [Positive lead and negative lead]

[0100] Furthermore, although the illustration is omitted, an electrical connection can be made between the current collectors (11, 12) and the current collector plates (25, 27) using positive and negative leads. The materials used in lithium-ion secondary batteries can be the same as those used in the positive and negative leads. It should be noted that the portion removed from the casing is preferably covered with heat-resistant and insulating heat-shrink tubing to prevent leakage current from contact with peripheral equipment or wiring, thus avoiding damage to the product (e.g., automotive parts, especially electronic devices).

[0101] [Battery casing material]

[0102] As for the battery casing material, known metal can casings can be used; alternatively, materials such as... Figure 1 and Figure 2 The illustration shows a bag-shaped casing using a laminated film 29 containing aluminum to cover the power generation element. This laminated film can be, for example, a three-layer structure consisting of PP, aluminum, and nylon stacked sequentially, but is not limited thereto. From the viewpoint of high power output, excellent cooling performance, and suitability for large-scale motor batteries used in EVs and HEVs, a laminated film containing aluminum is ideal. Furthermore, from the perspective of easily adjusting the overall pressure applied to the power generation element from the outside, the casing is more preferably a laminated film containing aluminum.

[0103] This type of stacked battery, composed of multiple single-cell layers connected in parallel, achieves high capacity and excellent cycle durability. Therefore, this type of stacked battery is suitable for use as a power source for EVs and HEVs.

[0104] The above describes one embodiment of a lithium-ion secondary battery, but the present invention is not limited to the configuration described in the above embodiment and may be appropriately modified based on the claims.

[0105] For example, as a type of battery to which the present invention is applicable, a bipolar battery comprising a bipolar electrode is also mentioned, the bipolar electrode having: a positive electrode active material layer electrically connected to one side of a current collector, and a negative electrode active material layer electrically connected to the opposite side of the current collector.

[0106] Figure 3 A cross-sectional view of a bipolar lithium-ion secondary battery (hereinafter also simply referred to as "bipolar battery") as an embodiment of the lithium-ion secondary battery of the present invention is shown for illustrative purposes. Figure 3 The bipolar battery 10b shown has a structure in which a roughly rectangular power generation element 21, in which the actual charging and discharging reaction takes place, is sealed inside a laminated film 29, which serves as the battery casing.

[0107] like Figure 3 As shown, the power generation element 21 of the bipolar battery 10b of this method has multiple bipolar electrodes 23, on which a positive electrode active material layer 15 electrically connected to one side of the current collector 11 is formed, and a negative electrode active material layer 13 electrically connected to the opposite side of the current collector 11 is formed. Each bipolar electrode 23 is stacked with a solid electrolyte layer 17 to form the power generation element 21. It should be noted that the solid electrolyte layer 17 has a structure in which the solid electrolyte is formed in layers. Figure 3As shown, a solid electrolyte layer 17 is sandwiched between the positive active material layer 15 of a bipolar electrode 23 and the negative active material layer 13 of another bipolar electrode 23 adjacent to the aforementioned bipolar electrode 23.

[0108] The adjacent positive electrode active material layer 15, solid electrolyte layer 17, and negative electrode active material layer 13 constitute a single cell layer 19. Therefore, it can be said that the bipolar battery 10b has a configuration consisting of stacked single cell layers 19. It should be noted that in the outermost current collector 11a on the outermost positive electrode side of the power generation element 21, the positive electrode active material layer 15 is formed only on one side. In addition, in the outermost current collector 11b on the outermost negative electrode side of the power generation element 21, the negative electrode active material layer 13 is formed only on one side.

[0109] and then, Figure 3 In the bipolar battery 10b shown, a positive current collector plate (positive electrode tab) 25 is arranged adjacent to the outermost current collector 11a on the positive electrode side, and it is extended and extended from the laminated film 29, which serves as the battery casing. On the other hand, a negative current collector plate (negative electrode tab) 27 is arranged adjacent to the outermost current collector 11b on the negative electrode side, and it is similarly extended and extended from the laminated film 29.

[0110] It should be noted that the number of times the single cell layer 19 is stacked is adjusted according to the desired voltage. Furthermore, in the bipolar battery 10b, if sufficient power can be ensured even with minimal reduction in battery thickness, the number of times the single cell layer 19 is stacked can be reduced. In the bipolar battery 10b, to prevent external impacts and environmental degradation during use, the following structure can be formed: the power generation element 21 is depressurized and sealed into the laminated film 29, which serves as the battery casing, and the positive current collector 27 and the negative current collector 25 are removed and placed outside the laminated film 29.

[0111] Furthermore, the secondary battery of this method does not have to be entirely solid-state. That is, the solid electrolyte layer may further contain a conventionally known liquid electrolyte (electrolyte). There is no particular limitation on the amount of liquid electrolyte (electrolyte) that can be contained in the solid electrolyte layer; the preferred amount is one that maintains the shape of the solid electrolyte layer formed by the solid electrolyte and prevents leakage of the liquid electrolyte (electrolyte).

[0112] The usable liquid electrolyte (electrolyte) has a form in which lithium salts are dissolved in an organic solvent. Examples of usable organic solvents include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl methyl carbonate (EMC), methyl propionate (MP), methyl acetate (MA), methyl formate (MF), 4-methyldioxolane (4MeDOL), dioxolane (DOL), 2-methyltetrahydrofuran (2MeTHF), tetrahydrofuran (THF), dimethoxyethane (DME), propylene carbonate (PC), butylene carbonate (BC), dimethyl sulfoxide (DMSO), and γ-butyrolactone (GBL). From the viewpoint of further improving rapid charging characteristics and power characteristics, the organic solvent is preferably a chain carbonate, more preferably at least one selected from the group consisting of diethyl carbonate (DEC), methyl methyl carbonate (EMC), and dimethyl carbonate (DMC), and even more preferably selected from methyl methyl carbonate (EMC) and dimethyl carbonate (DMC).

[0113] Examples of lithium salts include Li(FSO2)2N (lithium bis(fluorosulfonyl)imide; LiFSI), Li(C2F5SO2)2N, LiPF6, LiBF4, LiClO4, LiAsF6, and LiCF3SO3. Among these, Li(FSO2)2N (LiFSI) is preferred from the perspective of battery power and charge-discharge cycle characteristics.

[0114] Liquid electrolytes (electrolytes) may further contain additives in addition to the above-mentioned components. Specific examples of such compounds include ethylene carbonate, vinylene carbonate, methyl vinylene carbonate, dimethyl vinylene carbonate, phenyl vinylene carbonate, diphenyl vinylene carbonate, ethyl vinylene carbonate, diethyl vinylene carbonate, vinylene carbonate, 1,2-divinylene carbonate, 1-methyl-1-vinylene carbonate, 1-methyl-2-vinylene carbonate, 1-ethyl-1-vinylene carbonate, 1-ethyl-2-vinylene carbonate, vinylene carbonate, allyl ethylene carbonate, ethyleneoxymethyl ethylene carbonate, allyloxymethyl ethylene carbonate, acryloyloxymethyl ethylene carbonate, methacryloyloxymethyl ethylene carbonate, ethynyl ethylene carbonate, propynyl ethylene carbonate, propynyloxymethyl ethylene carbonate, methylene ethylene carbonate, and 1,1-dimethyl-2-methylene ethylene carbonate. These additives can be used alone or in combination of two or more. In addition, the amount of additives used in electrolytes can be adjusted appropriately.

[0115] [Battery Pack]

[0116] A battery pack is composed of multiple connected batteries. Specifically, it uses at least two batteries, connected in series, parallel, or both. By connecting them in series or parallel, the capacity and voltage can be freely adjusted.

[0117] Multiple batteries can be connected in series or parallel to form a small, detachable battery pack. Furthermore, this detachable small battery pack can be further connected in series or parallel to form a large-capacity, high-power battery pack (battery module, battery bag, etc.) suitable for vehicle drive power and auxiliary power supplies requiring high volumetric energy density and high volumetric power density. The number of batteries connected to form a battery pack, or the stacking of several small battery packs to form a large-capacity battery pack, depends on the battery capacity and power of the vehicle (electric vehicle) to be equipped with it.

[0118] [vehicle]

[0119] Batteries or battery packs formed by combining multiple batteries can be mounted in vehicles. In this invention, because a long-life battery with excellent long-term reliability can be constructed, using such a battery can create plug-in hybrid electric vehicles with long driving ranges and electric vehicles with long driving ranges on a single charge. This is because by using batteries or battery packs formed by combining multiple batteries in, for example, hybrid vehicles, fuel cell vehicles, and electric vehicles (including four-wheeled vehicles (sedans, trucks, buses, and other commercial vehicles, light vehicles, etc.), as well as two-wheeled vehicles (motorcycles) and three-wheeled vehicles), vehicles with long lifespans and high reliability are formed. However, the application is not limited to automobiles; for example, it can be applied to various power sources for other vehicles, such as trams, and can also be used as a power source for uninterruptible power supply devices, etc.

[0120] Example

[0121] The present invention will be further described in detail below through embodiments. However, the scope of protection of the present invention is not limited to the following embodiments.

[0122] Example of fabrication of experimental battery cells

[0123] [Comparative Example 1]

[0124] As a positive electrode active material, LiNi is prepared. 0.8 Mn 0.1 Co 0.1The lithium-containing composite oxide has a uniform composition of O2 and exhibits a secondary particle morphology as an aggregate of primary particles. It should be noted that the average particle size (D50) of this lithium-containing composite oxide (secondary particles), determined by laser diffraction scattering, is 11.5 μm. Furthermore, the elemental composition of the surface region within a depth of 100 nm from the surface of the prepared lithium-containing composite oxide particles was determined by X-ray photoelectron spectroscopy (XPS). The results show that, in terms of the percentage of all elements, Ni is 15 mol% and O is 57 mol%. Additionally, the ratio of O (oxygen) concentration to Ni concentration (O / Ni) in the surface region, calculated from these values, is 3.8. It should be noted that during XPS measurements, a charge correction was performed by shifting the C1s peak to 284.6 eV.

[0125] On the other hand, as a solid electrolyte, LPS (Li2S-P2S5 (mixing ratio 80:20 (mol%)) is prepared as a sulfide solid electrolyte containing sulfur and phosphorus with lithium-ion conductivity. Furthermore, acetylene black is prepared as a conductive aid.

[0126] Weigh 60 parts by mass of the positive electrode active material, 6 parts by mass of the conductive additive, and 34 parts by mass of the sulfide solid electrolyte prepared above, and mix them using a bench mill to prepare the positive electrode mixture.

[0127] Then, LPS (Li2S-P2S5 (mixing ratio 80:20 (mol%)) as the same sulfide solid electrolyte as described above is placed in a jig (glass ceramic tube), and the solid electrolyte layer (a circular plate shape with a diameter of 10 mm and a thickness of 600 μm) is formed by pressing with a molding pressure of 400 [MPa] to produce a solid electrolyte layer.

[0128] Next, the positive electrode mixture prepared above is placed on one side of the solid electrolyte layer prepared above, and the mixture is pressed into powder under a molding pressure of 200 [MPa] to form a positive electrode active material layer (a circular plate shape with a diameter of 10 mm and a thickness of 70 μm).

[0129] Next, a Li-In electrode, formed from a laminate of lithium metal foil (100 μm thick) and indium metal foil (100 μm thick), was prepared as the negative electrode. This Li-In electrode was then positioned on the other side of the solid electrolyte layer prepared above, with the indium metal foil located on the solid electrolyte layer side. Next, the fixture was tightened with a constraint pressure of 100 MPa, and leads for extracting current were connected to each electrode to fabricate the test battery cell for this comparative example.

[0130] [Comparative Example 2]

[0131] As a positive electrode active material, LiNi is prepared.0.8 Mn 0.1 Co 0.1 The lithium-containing composite oxide has a uniform composition of O2 and is an aggregate of primary particles with a secondary particle morphology. It should be noted that the average particle size (D50) of this lithium-containing composite oxide (secondary particles), determined by laser diffraction scattering, is 10.5 μm. Furthermore, the elemental composition of the surface region within a depth of 100 nm from the surface of the prepared lithium-containing composite oxide particles was determined by X-ray photoelectron spectroscopy (XPS). The results show that, in terms of the proportions of all elements, Ni is 10 mol% and O is 56 mol%. Additionally, the ratio of O (oxygen) concentration to Ni concentration (O / Ni) in the surface region, calculated from these values, is 5.6.

[0132] The lithium-containing composite oxide prepared above was used as the positive electrode active material. Otherwise, the test battery cell of this comparative example was made in the same manner as in Comparative Example 1 above.

[0133] [Comparative Example 3]

[0134] As a positive electrode active material, LiNi is prepared. 0.8 Mn 0.1 Co 0.1 The lithium-containing composite oxide has a uniform composition of O2 and is an aggregate of primary particles with a secondary particle morphology. It should be noted that the average particle size (D50) of this lithium-containing composite oxide (secondary particles), determined by laser diffraction scattering, is 10.2 μm. Furthermore, the elemental composition of the surface region within a depth of 100 nm from the surface of the prepared lithium-containing composite oxide particles was determined by X-ray photoelectron spectroscopy (XPS). The results show that, in terms of the percentage of all elements, Ni is 12 mol% and O is 55 mol%. Additionally, the ratio of O (oxygen) concentration to Ni concentration (O / Ni) in the surface region, calculated from these values, is 4.6.

[0135] The lithium-containing composite oxide prepared above was used as the positive electrode active material. Otherwise, the test battery cell of this comparative example was made in the same manner as in Comparative Example 1 above.

[0136] [Comparative Example 4]

[0137] As a positive electrode active material, LiNi is prepared. 0.8 Mn 0.1 Co 0.1A lithium-containing composite oxide with a uniform O2 composition and a primary particle morphology. It should be noted that the average particle size (D50) of this lithium-containing composite oxide (primary particles), determined by laser diffraction scattering, is 4.5 μm. Furthermore, the elemental composition of the surface region within a depth of 100 nm from the surface of the prepared lithium-containing composite oxide particles was determined by X-ray photoelectron spectroscopy (XPS). The results show that, in terms of the percentage of all elements, Ni is 13 mol% and O is 60 mol%. Additionally, the ratio of O (oxygen) concentration to Ni concentration (O / Ni) in the surface region, calculated from these values, is 4.6.

[0138] The lithium-containing composite oxide prepared above was used as the positive electrode active material. Otherwise, the test battery cell of this comparative example was made in the same manner as in Comparative Example 1 above.

[0139] [Example 1]

[0140] As a positive electrode active material, the central part contains LiNi 0.8 Mn 0.1 Co 0.1 A lithium-containing composite oxide with a uniform O2 composition, a surface region containing boron (B), and a primary particle morphology. It should be noted that the average particle size (D50) of this lithium-containing composite oxide (primary particles), determined by laser diffraction scattering, is 3.6 μm. Furthermore, the elemental composition of the surface region within 100 nm of the prepared lithium-containing composite oxide particles was determined by X-ray photoelectron spectroscopy (XPS), and the results, in terms of the percentages of all elements, are: Ni 5 mol%, O 36 mol%, and B 24 mol%. Additionally, the ratio of O (oxygen) concentration to Ni concentration (O / Ni) in the surface region, calculated from these values, is 7.2.

[0141] The lithium-containing composite oxide prepared above was used as the positive electrode active material. Otherwise, the test battery cell of this comparative example was made in the same manner as in Comparative Example 1 above.

[0142] [Example 2]

[0143] As a positive electrode active material, the central part contains LiNi 0.8 Mn 0.1 Co 0.1A lithium-containing composite oxide with a uniform O2 composition, a surface region containing boron (B), and a primary particle morphology. It should be noted that the average particle size (D50) of this lithium-containing composite oxide (primary particles), determined by laser diffraction scattering, is 3.6 μm. Furthermore, the elemental composition of the surface region within a depth of 100 nm from the surface of the prepared lithium-containing composite oxide particles was determined by X-ray photoelectron spectroscopy (XPS), and the results, in terms of the percentage of all elements, are: Ni 7 mol%, O 20 mol%, and B 30 mol%. Additionally, the ratio of O (oxygen) concentration to Ni concentration (O / Ni) in the surface region, calculated from these values, is 2.9.

[0144] The lithium-containing composite oxide prepared above was used as the positive electrode active material. Otherwise, the test battery cell of this comparative example was made in the same manner as in Comparative Example 1 above.

[0145] [Example 3]

[0146] As a positive electrode active material, the central part has LiNi 0.8 Mn 0.1 Co 0.1 A lithium-containing composite oxide with a uniform O2 composition, a surface region containing boron (B), and a primary particle morphology. It should be noted that the average particle size (D50) of this lithium-containing composite oxide (primary particles), determined by laser diffraction scattering, is 4.3 μm. Furthermore, the elemental composition of the surface region within 100 nm of the prepared lithium-containing composite oxide particles was determined by X-ray photoelectron spectroscopy (XPS), and the results, in terms of the percentages of all elements, are: Ni 2 mol%, O 40 mol%, and B 17 mol%. Additionally, the ratio of O (oxygen) concentration to Ni concentration (O / Ni) in the surface region, calculated from these values, is 20.0.

[0147] The lithium-containing composite oxide prepared above was used as the positive electrode active material. Otherwise, the test battery cell of this comparative example was made in the same manner as in Comparative Example 1 above.

[0148] [Example 4]

[0149] As a positive electrode active material, the central part contains LiNi 0.8 Mn 0.1 Co 0.1A lithium-containing composite oxide with a uniform O2 composition, a surface region containing boron (B), and a primary particle morphology. It should be noted that the average particle size (D50) of this lithium-containing composite oxide (primary particles), determined by laser diffraction scattering, is 4.6 μm. Furthermore, the elemental composition of the surface region within 100 nm of the prepared lithium-containing composite oxide particles was determined by X-ray photoelectron spectroscopy (XPS), and the results, in terms of the percentages of all elements, are: Ni 3 mol%, O 40 mol%, and B 17 mol%. Additionally, the ratio of O (oxygen) concentration to Ni concentration (O / Ni) in the surface region, calculated from these values, is 13.3.

[0150] The lithium-containing composite oxide prepared above was used as the positive electrode active material. Otherwise, the test battery cell of this comparative example was made in the same manner as in Comparative Example 1 above.

[0151] [Example 5]

[0152] As a positive electrode active material, the central part contains LiNi 0.8 Mn 0.1 Co 0.1 A lithium-containing composite oxide with a uniform O2 composition, a surface region containing boron (B), and a primary particle morphology. It should be noted that the average particle size (D50) of this lithium-containing composite oxide (primary particles), determined by laser diffraction scattering, is 3.6 μm. Furthermore, the elemental composition of the surface region within 100 nm of the prepared lithium-containing composite oxide particles was determined by X-ray photoelectron spectroscopy (XPS), and the results, in terms of the percentages of all elements, are: Ni 3 mol%, O 57 mol%, and B 17 mol%. Additionally, the O / Ni ratio (O / Ni) calculated from these values ​​is 19.0.

[0153] The lithium-containing composite oxide prepared above was used as the positive electrode active material. Otherwise, the test battery cell of this comparative example was made in the same manner as in Comparative Example 1 above.

[0154] Evaluation Examples of Test Battery Cells

[0155] For the test battery cells prepared in the above comparative examples and embodiments, the discharge capacity per unit mass of the positive electrode active material was determined according to the following method.

[0156] First, the test battery cell is clamped between two 5mm thick stainless steel plates with a clamping pressure of 1000 kgf / cm². 2 The pressurization is achieved by using a flatbed press with a hydraulic lifter.

[0157] One hour after pressurization, the test battery cells were placed inside a constant temperature bath set to 25°C and connected to a charge / discharge device for charge / discharge testing to determine their charge / discharge capacity. During charging, a current equivalent to 0.05C was applied, with the upper limit voltage set to 3.6V (vs. Li-In negative electrode), and CC-CV charging was performed. This charging process ended either when the current value decreased to 0.01C or after 40 hours from the start of charging. After charging, the cells were left to stand for one hour before discharging. During discharging, a current equivalent to 0.05C was applied, with the lower limit voltage set to 1.9V (vs. Li-In negative electrode), and CC discharge was performed. The capacity (discharge capacity) was then measured during the discharge process. The discharge capacity per unit mass of the active material used in each test battery cell was standardized and calculated as the initial discharge capacity. The results are shown in Table 1 below.

[0158] Furthermore, the above charge-discharge treatment was considered as one cycle, and a total of 50 charge-discharge cycles were performed. During this process, a one-hour rest period was also set between charge-discharge treatments, during which the test battery cells were placed. Moreover, as an indicator of cycle durability, the percentage of the discharge capacity at the 50th cycle relative to the initial discharge capacity was calculated as the capacity retention rate after 50 cycles. The results are shown in Table 1 below. It should be noted that for Comparative Example 1, the initial discharge capacity was an extremely small value; therefore, the capacity retention rate could not be evaluated.

[0159] [Table 1]

[0160]

[0161] As shown in Table 1, by using a positive electrode active material formed from a lithium-containing composite oxide with specified additive elements present in the surface region, the initial capacity and cycle durability of secondary batteries using sulfide solid electrolytes containing sulfur and phosphorus and high-nickel positive electrode active materials can be significantly improved.

[0162] Explanation of reference numerals in the attached figures

[0163] 10. 10a stacked battery

[0164] 10b bipolar battery,

[0165] 11 collectors,

[0166] 11' negative current collector,

[0167] 11” positive current collector,

[0168] 13 negative electrode active material layer,

[0169] 15 positive electrode active material layers

[0170] 17. Solid electrolyte layer

[0171] 19 single-cell layers

[0172] 21 power generation components

[0173] 25 negative current collector,

[0174] 27 Positive current collector,

[0175] 29-layer laminated film.

Claims

1. A secondary battery comprising a power generation element, said power generation element being formed by sequentially stacking a positive electrode, a solid electrolyte layer, and a negative electrode. The positive electrode includes a positive electrode active material layer, which contains a positive electrode active material formed from a lithium-containing composite oxide with the following chemical formula (1) in its central part: Li 1+q Ni x Co y Mr z M p O2(1) In formula (1), -0.02≤q≤0.20, x+y+z+p=1, 0.5≤x≤1.0, 0≤y≤0.5, 0≤z≤0.5, 0≤p≤0.1, and M is one or more elements selected from the group consisting of Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr and Cr. The solid electrolyte layer contains a sulfide solid electrolyte containing sulfur and phosphorus. The negative electrode includes a layer of negative electrode active material containing negative electrode active material. In the surface region within 100 nm of the lithium-containing composite oxide particles, one or more additive elements selected from the group consisting of B, S, and Si are present at a molar concentration higher than that of Ni, and Ni is present in the surface region. The amount of Ni in the surface region is 2 to 7 moles.

2. A secondary battery comprising a power generation element, said power generation element being formed by sequentially stacking a positive electrode, a solid electrolyte layer, and a negative electrode. The positive electrode includes a positive electrode active material layer, which contains a positive electrode active material formed from a lithium-containing composite oxide with the following chemical formula (1) in its central part: Li 1+q Ni x Co y Mr z M p O2(1) In formula (1), -0.02≤q≤0.20, x+y+z+p=1, 0.5≤x≤1.0, 0≤y≤0.5, 0≤z≤0.5, 0≤p≤0.1, and M is one or more elements selected from the group consisting of Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr and Cr. The solid electrolyte layer contains a sulfide solid electrolyte containing sulfur and phosphorus. The negative electrode includes a layer of negative electrode active material containing negative electrode active material. In the surface region within 100 nm of the lithium-containing composite oxide particles, phosphorus (P) as an additive element exists at a higher molar concentration than nitrogen (Ni), with the concentration of P being 17-30 mol%, and nitrogen is present in the surface region. The amount of Ni in the surface region is 2 to 7 moles.

3. The secondary battery according to claim 1, wherein, The added element contains B.

4. The secondary battery according to claim 1 or 2, wherein, The ratio of the concentration of O (oxygen) to the concentration of Ni in the surface region (O / Ni) is 20.0 or less.

5. The secondary battery according to claim 1 or 2, wherein, The lithium-containing composite oxide is in the form of primary particles, and the average particle size (D50) of the lithium-containing composite oxide is less than 10 μm.

6. The secondary battery according to claim 1 or 2, wherein, The positive electrode active material accounts for 55-95% of the total solid components of the positive electrode by mass.

7. The secondary battery according to claim 1 or 2, wherein, In the chemical formula (1), 0.60≤x≤0.

90.

8. The secondary battery according to claim 1 or 2 is an all-solid-state lithium-ion secondary battery.

9. A positive electrode active material for a secondary battery, which is formed from a lithium-containing composite oxide with a central portion having the following chemical formula (1): Li 1+q Ni x Co y Mr z M p O2(1) In formula (1), -0.02≤q≤0.20, x+y+z+p=1, 0.5≤x≤1.0, 0≤y≤0.5, 0≤z≤0.5, 0≤p≤0.1, and M is one or more elements selected from the group consisting of Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr and Cr. In the surface region within 100 nm of the lithium-containing composite oxide particles, one or more additive elements selected from the group consisting of B, S, and Si are present at a molar concentration higher than that of Ni, and Ni is present in the surface region. The amount of Ni in the surface region is 2 to 7 moles.

10. A positive electrode active material for a secondary battery, which is formed from a lithium-containing composite oxide with a central portion having the following chemical formula (1): Li 1+q Ni x Co y Mr z M p O2(1) In formula (1), -0.02≤q≤0.20, x+y+z+p=1, 0.5≤x≤1.0, 0≤y≤0.5, 0≤z≤0.5, 0≤p≤0.1, and M is one or more elements selected from the group consisting of Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr and Cr. In the surface region within 100 nm of the lithium-containing composite oxide particles, phosphorus (P) as an additive element exists at a higher molar concentration than nitrogen (Ni), with the concentration of P being 17-30 mol%, and nitrogen is present in the surface region. The amount of Ni in the surface region is 2 to 7 moles.

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