Positive electrode for secondary battery and secondary battery

Abstract

The secondary battery includes a positive electrode, a negative electrode, and an electrolytic solution, where the positive electrode includes a positive electrode active material layer containing a layered rock salt type lithium nickel composite oxide represented by the following formula (1). When analyzing the positive electrode active material layer using X-ray photoelectron spectroscopy on the surface of the positive electrode active material layer, the ratio X of the atomic concentration of Al to the atomic concentration of Ni satisfies the condition represented by the following formula (2). When analyzing the positive electrode active material layer using X-ray photoelectron spectroscopy inside the positive electrode active material layer (depth = 100 nm), the ratio Y of the atomic concentration of Al to the atomic concentration of Ni satisfies the condition represented by the following formula (3). The ratio Z of the ratio X to the ratio Y satisfies the condition represented by the following formula (4). In the surface analysis of the positive electrode using X-ray photoelectron spectroscopy, a B1s spectrum, an S2p spectrum, an F1s spectrum, and a Ni3p spectrum are detected. The ratio IBN of the intensity of the B1s spectrum to the intensity of the Ni3p spectrum satisfies the condition represented by the following formula (5). The ratio ISN of the intensity of the S2p spectrum to the intensity of the Ni3p spectrum satisfies the condition represented by the following formula (6). The ratio IFN of the intensity of the F1s spectrum to the intensity of the Ni3p spectrum satisfies the condition represented by the following formula (7). Li a Ni 1‑b‑c‑ d Co b Al c M d O e …(1) (M is at least one of Fe, Mn, Cu, Zn, Cr, V, Ti, Mg, and Zr. a, b, c, d, and e satisfy 0.8 < a < 1.2, 0.06 ≤ b ≤ 0.18, 0.015 ≤ c ≤ 0.05, 0 ≤ d ≤ 0.08, 0 < e < 3, 0.1 ≤ (b + c + d) ≤ 0.22, and 4.33 ≤ (1 - b - c - d) / b ≤ 15.0.) 0.30 ≤ X ≤ 0.70…(2) 0.16 ≤ Y ≤ 0.37…(3) 1.30 ≤ Z ≤ 2.52…(4) 0.9 ≤ IBN ≤ 1.8…(5) 0.4 ≤ ISN ≤ 1.2…(6) 8 ≤ IFN ≤ 13…(7).

Description

Technical Field

[0001] The present technology relates to a positive electrode for a secondary battery and a secondary battery. Background Art

[0002] Since various electronic devices such as mobile phones are becoming popular, development of secondary batteries is underway as a power source that is small, lightweight, and capable of achieving a high energy density. The secondary battery includes a positive electrode (positive electrode for a secondary battery), a negative electrode, and an electrolyte, and various studies have been conducted on the structure of the secondary battery.

[0003] Specifically, in order to obtain excellent thermal stability and the like, a layer containing LiAlO2 is provided on the surface of lithium transition metal composite oxide particles, and Al derived from the LiAlO2 is solid-dissolved in the vicinity of the surface of the lithium transition metal composite oxide particles (for example, refer to Patent Document 1).

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Patent Laid-Open No. 2010-129471 Summary of the Invention

[0007] Various studies have been conducted to improve the battery characteristics of secondary batteries, but there is still room for improvement because the battery characteristics are not yet sufficient.

[0008] The present technology has been completed in view of the above problems, and an object thereof is to provide a positive electrode for a secondary battery and a secondary battery capable of obtaining excellent battery characteristics.

[0009] The positive electrode for a secondary battery according to one embodiment of the present technology includes a positive electrode active material layer, and the positive electrode active material layer includes a layered rock salt-type lithium nickel composite oxide represented by the following formula (1). When the positive electrode active material layer is analyzed by X-ray photoelectron spectroscopy on the surface of the positive electrode active material layer, the ratio X of the atomic concentration of Al to the atomic concentration of Ni satisfies the condition represented by the following formula (2). When the positive electrode active material layer is analyzed by X-ray photoelectron spectroscopy inside the positive electrode active material layer (depth = 100 nm), the ratio Y of the atomic concentration of Al to the atomic concentration of Ni satisfies the condition represented by the following formula (3). The ratio Z of the ratio X to the ratio Y satisfies the condition represented by the following formula (4). In the surface analysis using X-ray photoelectron spectroscopy, B1s spectrum, S2p spectrum, F1s spectrum, and Ni3p spectrum are detected. The ratio IBN of the intensity of the B1s spectrum to the intensity of the Ni3p spectrum satisfies the condition represented by the following formula (5). The ratio ISN of the intensity of the S2p spectrum to the intensity of the Ni3p spectrum satisfies the condition represented by the following formula (6). The ratio IFN of the intensity of the F1s spectrum to the intensity of the Ni3p spectrum satisfies the condition represented by the following formula (7).

[0010] Li a Ni 1-b-c-d Co b Al c M d O e …(1)

[0011] (M is at least one of Fe, Mn, Cu, Zn, Cr, V, Ti, Mg, and Zr. a, b, c, d, and e satisfy 0.8 < a < 1.2, 0.06 ≤ b ≤ 0.18, 0.015 ≤ c ≤ 0.05, 0 ≤ d ≤ 0.08, 0 < e < 3, 0.1 ≤ (b + c + d) ≤ 0.22, and 4.33 ≤ (1 - b - c - d) / b ≤ 15.0.)

[0012] 0.30 ≤ X ≤ 0.70…(2)

[0013] 0.16 ≤ Y ≤ 0.37…(3)

[0014] 1.30 ≤ Z ≤ 2.52…(4)

[0015] 0.9 ≤ IBN ≤ 1.8…(5)

[0016] 0.4 ≤ ISN ≤ 1.2…(6)

[0017] 8 ≤ IFN ≤ 13…(7)

[0018] A secondary battery according to an embodiment of the present technology includes a positive electrode, a negative electrode, and an electrolyte. The positive electrode has the same structure as that of the positive electrode for a secondary battery according to an embodiment of the present technology described above.

[0019] It should be noted that the detailed procedures for analyzing the positive electrode active material layer (the procedures for determining each of the ratios X, Y, and Z) and the positive electrode (the procedures for determining each of the ratios IBN, ISN, and IFN) using X-ray photoelectron spectroscopy will be described later.

[0020] In the positive electrode for a secondary battery or the secondary battery according to an embodiment of the present technology, the positive electrode active material layer contains the above-mentioned layered rock salt-type lithium nickel composite oxide. The analysis results (ratios X, Y, and Z) of the positive electrode active material layer using X-ray photoelectron spectroscopy satisfy the above conditions, and the analysis results (ratios IBN, ISN, and IFN) of the positive electrode using X-ray photoelectron spectroscopy satisfy the above conditions. Therefore, excellent battery characteristics can be obtained.

[0021] It should be noted that the effects of the present technology are not necessarily limited to the effects described herein, and may be any of the series of effects related to the present technology described later. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 FIG. is a perspective view showing the structure of a secondary battery according to an embodiment of the present technology.

[0023] Figure 2 FIG. is showing Figure 1 a cross-sectional view of the structure of the battery element shown.

[0024] Figure 3 FIG. is an enlarged cross-sectional view showing Figure 2 the structure of the positive electrode shown.

[0025] Figure 4 FIG. is a block diagram showing the structure of an application example of the secondary battery. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] Hereinafter, an embodiment of the present technology will be described in detail with reference to the drawings. It should be noted that the order of description is as follows.

[0027] 1. Secondary battery (positive electrode for secondary battery)

[0028] 1-1. Structure

[0029] 1-2. Physical properties

[0030] 1-3. Operation

[0031] 1-4. Manufacturing method

[0032] 1-5. Functions and Effects

[0033] 2. Variation Examples

[0034] 3. Uses of Secondary Batteries

[0035] <1. Secondary Battery (Positive Electrode for Secondary Battery)>

[0036] First, a secondary battery according to an embodiment of the present technology will be described. It should be noted that the positive electrode for the secondary battery according to an embodiment of the present technology (hereinafter simply referred to as "positive electrode") is a part (a constituent element) of the secondary battery. Therefore, the positive electrode will be described together below.

[0037] The secondary battery described here is a secondary battery that obtains battery capacity by insertion and extraction of electrode reaction substances, and includes a positive electrode, a negative electrode, and an electrolytic solution as a liquid electrolyte. In this secondary battery, in order to prevent the electrode reaction substances from depositing on the surface of the negative electrode during the charging process, the charging capacity of the negative electrode is greater than the discharging capacity of the positive electrode. That is, the electrochemical capacity per unit area of the negative electrode is set to be greater than the electrochemical capacity per unit area of the positive electrode.

[0038] The type of the electrode reaction substance is not particularly limited. Specifically, it is a light metal such as an alkali metal and an alkaline earth metal. The alkali metal is lithium, sodium, potassium, etc., and the alkaline earth metal is beryllium, magnesium, calcium, etc.

[0039] Hereinafter, the case where the electrode reaction substance is lithium will be taken as an example. A secondary battery that obtains battery capacity by insertion and extraction of lithium is a so-called lithium-ion secondary battery. In this lithium-ion secondary battery, lithium is inserted and extracted in an ionic state.

[0040] <1-1. Structure>

[0041] Figure 1 The three-dimensional structure of the secondary battery is shown, Figure 2 is shown Figure 1 the cross-sectional structure of the battery element 20 shown. In addition, Figure 1 shows the state where the exterior film 10 and the battery element 20 are separated from each other, Figure 2 only shows a part of the battery element 20.

[0042] As Figure 1 and Figure 2 shown, this secondary battery includes an exterior film 10, a battery element 20, a positive electrode lead 31 and a negative electrode lead 32, and sealing films 41 and 42. The secondary battery described here is a laminated film type secondary battery that uses a flexible (or soft) exterior component (exterior film 10) as the exterior component for housing the battery element 20.

[0043] [Outer packaging film]

[0044] As Figure 1 shown, the outer packaging film 10 is a flexible outer packaging component that houses the battery element 20 (i.e., the positive electrode 21, negative electrode 22, electrolyte, etc. described later), and has a bag-like structure.

[0045] Here, the outer packaging film 10 is a single film-like component that can be folded along the folding direction R. A recessed portion 10U (so-called deep-drawn deep part) for housing the battery element 20 is provided on the outer packaging film 10.

[0046] The structure (material, number of layers, etc.) of the outer packaging film 10 is not particularly limited, and it can be a single-layer film or a multi-layer film.

[0047] Here, the outer packaging film 10 is a three-layer laminated film in which a welding layer, a metal layer, and a surface protection layer are laminated in order from the inside. The welding layer contains a polymer compound such as polypropylene. The metal layer contains a metal material such as aluminum. The surface protection layer contains a polymer compound such as nylon. In the state where the outer packaging film 10 is folded, the outer peripheral edge portions of the opposed outer packaging films 10 (welding layers) are welded to each other.

[0048] [Sealing film]

[0049] As Figure 1 shown, the sealing films 41 and 42 are sealing components for preventing the intrusion of external air, etc. into the inside of the outer packaging film 10. The sealing film 41 is inserted between the outer packaging film 10 and the positive electrode lead 31, and the sealing film 42 is inserted between the outer packaging film 10 and the negative electrode lead 32. In addition, one or both of the sealing films 41 and 42 can be omitted.

[0050] Specifically, the sealing film 41 contains a polymer compound such as polyolefin that has a sealing property with respect to the positive electrode lead 31, and the polyolefin is polypropylene or the like.

[0051] The structure of the sealing film 42 is the same as that of the sealing film 41 except that it has a sealing property with respect to the negative electrode lead 32. That is, the sealing film 42 contains a polymer compound such as polyolefin that has a sealing property with respect to the negative electrode lead 32.

[0052] [Battery element]

[0053] As Figure 1 and Figure 2 shown, the battery element 20 is a power generation element housed inside the outer packaging film 10, and it includes a positive electrode 21, a negative electrode 22, a separator 23, and an electrolyte (not shown).

[0054] Here, the battery element 20 is a so-called wound electrode body. That is, in the battery element 20, the positive electrode 21 and the negative electrode 22 are laminated with each other with the separator 23 interposed therebetween, and the positive electrode 21, the negative electrode 22, and the separator 23 are wound around a winding axis (an imaginary axis extending in the Y-axis direction). That is, the positive electrode 21 and the negative electrode 22 are wound around with the separator 23 interposed therebetween and facing each other.

[0055] Since the battery element 20 has a flat three-dimensional shape, the shape of the cross-section of the battery element 20 that intersects the winding axis (the cross-section along the XZ plane) is a flat shape defined by a major axis and a minor axis. The major axis is an imaginary axis extending in the X-axis direction and having a length larger than that of the minor axis, and the minor axis is an imaginary axis extending in the Z-axis direction intersecting the X-axis direction and having a length smaller than that of the major axis. Here, the cross-sectional shape of the battery element 20 is a flat and substantially elliptical shape.

[0056] (Positive electrode)

[0057] The positive electrode 21 is a positive electrode for a secondary battery according to an embodiment of the present technology. As Figure 2 shown, it includes a positive electrode active material layer 21B. Here, the positive electrode 21 includes the positive electrode active material layer 21B, a positive electrode current collector 21A that supports the positive electrode active material layer 21B, and a coating film 21C that covers the surface of the positive electrode active material layer 21B.

[0058] The positive electrode current collector 21A has a pair of surfaces on which the positive electrode active material layer 21B is disposed. The positive electrode current collector 21A includes a conductive material such as a metal material, and the metal material is aluminum or the like.

[0059] The positive electrode active material layer 21B contains a positive electrode active material capable of intercalating and deintercalating lithium. Here, it is disposed on both surfaces of the positive electrode current collector 21A. In addition, the positive electrode active material layer 21B may further contain a positive electrode binder, a positive electrode conductive agent, etc., and may be disposed only on one surface of the positive electrode current collector 21A. The method for forming the positive electrode active material layer 21B is not particularly limited. Specifically, it is a coating method or the like.

[0060] Specifically, the positive electrode active material layer 21B contains any one or more of the layered rock salt-type lithium nickel composite oxides represented by the following formula (1) as the positive electrode active material. This is because a high energy density can be obtained.

[0061] Li a Ni 1-b-c-d Co b Al c M d O e …(1)

[0062] (M is at least one of Fe, Mn, Cu, Zn, Cr, V, Ti, Mg, and Zr. a, b, c, d, and e satisfy 0.8 < a < 1.2, 0.06 ≤ b ≤ 0.18, 0.015 ≤ c ≤ 0.05, 0 ≤ d ≤ 0.08, 0 < e < 3, 0.1 ≤ (b + c + d) ≤ 0.22, and 4.33 ≤ (1 - b - c - d) / b ≤ 15.0.)

[0063] From the conditions for a to e shown in formula (1), it can be seen that this lithium nickel composite oxide is a composite oxide containing Li, Ni, Co, and Al as constituent elements and has a layered rock salt-type crystal structure. That is, the lithium nickel composite oxide contains two transition metal elements (Ni and Co) as constituent elements.

[0064] In addition, from the range of values that d can take (0 ≤ d ≤ 0.08), it can be seen that the lithium nickel composite oxide can also contain an additional element M as a constituent element. The type of the additional element M can be any one or two or more of the above-mentioned Fe, Mn, Cu, Zn, Cr, V, Ti, Mg, and Zr, and there is no particular limitation.

[0065] In particular, from the range of values that (b + c + d) can take (0.1 ≤ (b + c + d) ≤ 0.22), it can be seen that the range of values that (1 - b - c - d) can take is 0.78 ≤ (1 - b - c - d) ≤ 0.9. Therefore, the lithium nickel composite oxide contains Ni among the two transition metal elements (Ni and Co) as the main component. This is because a high energy density can be obtained.

[0066] In addition, from the range of values that (1 - b - c - d) / b can take (4.33 ≤ (1 - b - c - d) / b ≤ 15.0), it can be seen that in the lithium nickel composite oxide containing two transition metal elements (Ni and Co) as constituent elements, the molar ratio of Ni (1 - b - c - d) is sufficiently large relative to the molar ratio of Co (b). That is, the ratio of the molar ratio of Ni to the molar ratio of Co (NC ratio = (1 - b - c - d) / b) is sufficiently large within an appropriate range. This is because, while ensuring the energy density, the discharge capacity is not easily reduced even during repeated charge and discharge. It should be noted that the value of the NC ratio is the value after rounding the third decimal place.

[0067] Here, since the molar ratio of the additional element M (d) satisfies d ≥ 0, the lithium nickel composite oxide can contain the additional element M as a constituent element or may not contain the additional element M as a constituent element. Among them, since d satisfies d > 0, the lithium nickel composite oxide preferably contains the additional element M as a constituent element. This is because, in the positive electrode active material (lithium nickel composite oxide) during charge and discharge, lithium ions can be easily input and output smoothly.

[0068] The specific composition of the lithium nickel composite oxide only needs to satisfy the conditions shown in formula (1), and there is no particular limitation. The specific composition of the lithium nickel composite oxide will be described in detail in the following examples.

[0069] It should be noted that in addition to the above-mentioned lithium nickel composite oxide, the positive electrode active material may further contain any one or two or more of lithium compounds. In addition, the lithium compounds described herein do not include the lithium nickel composite oxide that has been described.

[0070] The lithium compound is a general term for compounds containing lithium as a constituent element. More specifically, it is a compound containing lithium and one or two or more transition metal elements as constituent elements. The types of lithium compounds are not particularly limited. Specifically, they are oxides, phosphate compounds, silicate compounds, boric acid compounds, etc. Specific examples of oxides are LiNiO2, LiCoO2, LiMn2O4, etc., and specific examples of phosphate compounds are LiFePO4, LiMnPO4, etc.

[0071] The positive electrode binder contains any one or two or more of synthetic rubbers and polymer compounds, etc. The synthetic rubber is styrene-butadiene rubber, etc., and the polymer compound is polyvinylidene fluoride, etc. The positive electrode conductive agent contains any one or two or more of conductive materials such as carbon materials. The carbon material is graphite, carbon black, acetylene black, Ketjen black, etc. In addition, the conductive material can also be a metal material, a polymer compound, etc.

[0072] Here, regarding the physical properties of the positive electrode 21 (positive electrode active material layer 21B) containing the positive electrode active material (lithium nickel composite oxide), it satisfies the specified physical property conditions in order to improve the battery characteristics of the secondary battery. The details of the physical property conditions of the positive electrode 21 (positive electrode active material layer 21B) will be described later.

[0073] The coating film 21C is a film formed on the surface of the positive electrode active material layer 21B by the charge and discharge of the secondary battery. More specifically, it is a deposition film deposited on the surface of the positive electrode active material layer 21B due to decomposition reactions of the electrolyte during charge and discharge, etc.

[0074] The coating film 21C is mainly formed on the surface of the positive electrode active material layer 21B according to the charge and discharge during the stabilization treatment of the secondary battery described later, that is, the first charge and discharge after the secondary battery is assembled. In addition, the coating film 21C can also be additionally formed on the surface of the positive electrode active material layer 21B according to the charge and discharge after the stabilization treatment of the secondary battery, that is, the charge and discharge after the secondary battery is completed.

[0075] Note that the coating film 21C may cover the entire surface of the positive electrode active material layer 21B, or may cover only a part of the surface of the positive electrode active material layer 21B. Of course, in the latter case, a plurality of coating films 21C may cover the surface of the positive electrode active material layer 21B at a plurality of separated positions from each other.

[0076] Here, since the positive electrode active material layer 21B is disposed on both surfaces of the positive electrode current collector 21A, the positive electrode 21 includes two positive electrode active material layers 21B. In addition, the coating film 21C is provided to cover the surfaces of the respective two positive electrode active material layers 21B, so the positive electrode 21 includes two coating films 21C. In addition, it may be set that the coating film 21C covers only the surface of one of the two positive electrode active material layers 21B, so the positive electrode 21 includes one coating film 21C.

[0077] In the surface analysis of the positive electrode 21 (coating film 21C) using X-ray Photoelectron Spectroscopy (XPS), a predetermined XPS spectrum (B1s spectrum, S2p spectrum, F1s spectrum, and Ni3p spectrum) is detected. That is, since the positive electrode active material layer 21B contains the above-mentioned lithium nickel composite oxide, the positive electrode active material layer 21B contains Ni as a constituent element. In contrast, the coating film 21C may contain B, S, and F as constituent elements.

[0078] More specifically, as described later, when the electrolytic solution contains a boron-containing compound, a sulfur-containing compound, and a fluorine-containing compound, the coating film 21C is formed due to the decomposition reaction of the electrolytic solution. Therefore, as described above, the coating film 21C contains B, S, and F as constituent elements.

[0079] Here, regarding the physical properties of the positive electrode 21 (coating film 21C), in order to improve the battery characteristics of the secondary battery, the physical property conditions are satisfied. The details of the physical properties of the positive electrode 21 (coating film 21C) will be described later.

[0080] (Negative electrode)

[0081] As Figure 2 shown, the negative electrode 22 includes a negative electrode current collector 22A and a negative electrode active material layer 22B.

[0082] The negative electrode current collector 22A has a pair of surfaces on which the negative electrode active material layer 22B is disposed. The negative electrode current collector 22A includes a conductive material such as a metal material, and the metal material is copper or the like.

[0083] The negative electrode active material layer 22B contains any one or more of negative electrode active materials capable of intercalating and deintercalating lithium. Here, the negative electrode active material layer 22B is disposed on both surfaces of the negative electrode current collector 22A. In addition, the negative electrode active material layer 22B may further contain a negative electrode binder, a negative electrode conductive agent, etc., and the negative electrode active material layer 22B may be disposed only on one surface of the negative electrode current collector 22A. The details of the negative electrode binder and the negative electrode conductive agent are the same as the details of the positive electrode binder and the positive electrode conductive agent, respectively. The method for forming the negative electrode active material layer 22B is not particularly limited. Specifically, it is any one or more of a coating method, a vapor phase method, a liquid phase method, a spraying method, and a firing method (sintering method), etc.

[0084] The negative electrode active material is a carbon material, a metal-based material, etc. This is because a high energy density can be obtained. The carbon material is easily graphitizable carbon, hardly graphitizable carbon, graphite (natural graphite and artificial graphite), etc. The metal-based material is a general term for materials containing any one or two or more of metal elements and semi-metal elements capable of forming an alloy with lithium as constituent elements, and the metal elements and semi-metal elements are silicon, tin, etc. The metal-based material may be a monomer, an alloy, a compound, a mixture of two or more of them, or a material containing two or more phases of them. Specific examples of the metal-based material are TiSi2 and SiO x (0 < x ≤ 2, or 0.2 < x < 1.4), etc.

[0085] (Separator)

[0086] As Figure 2 shown, the separator 23 is an insulating porous membrane between the positive electrode 21 and the negative electrode 22, and allows lithium ions to pass through while preventing contact (short circuit) between the positive electrode 21 and the negative electrode 22. The separator 23 contains a polymer compound such as polyethylene.

[0087] (Electrolyte)

[0088] The electrolyte is impregnated in each of the positive electrode 21, the negative electrode 22, and the separator 23, and contains a solvent and an electrolyte salt.

[0089] The solvent contains any one or two or more of non-aqueous solvents (organic solvents) such as carbonate-based compounds, carboxylate-based compounds, and lactone-based compounds, and the electrolyte containing the non-aqueous solvent is a so-called non-aqueous electrolyte. The electrolyte salt contains any one or two or more of light metal salts such as lithium salts.

[0090] It should be noted that, as described above, in order to detect three XPS spectra (B1s spectrum, S2p spectrum, and F1s spectrum) in the surface analysis of the positive electrode 21 using XPS, the electrolytic solution may further contain a boron-containing compound, a sulfur-containing compound, and a fluorine-containing compound.

[0091] Boron-containing compounds are a general term for compounds containing B as a constituent element. The types of boron-containing compounds are not particularly limited. Specifically, they are any one or two or more of boron-containing lithium salts, etc.

[0092] Specific examples of boron-containing lithium salts are lithium tetrafluoroborate, lithium difluorooxalate borate, and lithium bis(oxalato)borate, etc.

[0093] Sulfur-containing compounds are a general term for compounds containing S as a constituent element. The types of sulfur-containing compounds are not particularly limited. Specifically, they are any one or two or more of cyclic disulfonic anhydrides and alkynyl sulfonates, etc. That is, the sulfur-containing compound can be only a cyclic disulfonic anhydride, only an alkynyl sulfonate, or both a cyclic disulfonic anhydride and an alkynyl sulfonate.

[0094] Cyclic disulfonic anhydrides are cyclic compounds obtained by dehydrating disulfonic anhydrides. Specific examples of cyclic disulfonic anhydrides are 1,2-ethanedisulfonic anhydride and 1,3-propanedisulfonic anhydride, etc. In addition, the cyclic disulfonic anhydride can be 1,2-benzenedisulfonic anhydride, etc.

[0095] Alkynyl sulfonates are sulfonic acids containing a carbon-carbon triple bond. Specific examples of alkynyl sulfonates are propargyl benzenesulfonate and propargyl methanesulfonate, etc.

[0096] Fluorine-containing compounds are a general term for compounds containing F as a constituent element. The types of fluorine-containing compounds are not particularly limited. Specifically, they are any one or two or more of fluorine-containing lithium salts, etc.

[0097] Specific examples of fluorine-containing lithium salts are lithium hexafluorophosphate, lithium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, and lithium tris(trifluoromethanesulfonyl)methide, etc. In addition, the fluorine-containing lithium salt can also be lithium hexafluoroarsenate (LiAsF6), etc.

[0098] In addition, a compound containing both B and F as constituent elements does not belong to the fluorine-containing compound, but belongs to the boron-containing compound. Therefore, as described above, a lithium salt (lithium tetrafluoroborate) containing both boron and fluorine as constituent elements is not a fluorine-containing compound (fluorine-containing lithium salt), but a boron-containing compound (boron-containing lithium salt).

[0099] The content of the boron-containing compound in the electrolytic solution is not particularly limited and can be arbitrarily set. The same applies to the content of the sulfur-containing compound in the electrolytic solution and the content of the fluorine-containing compound in the electrolytic solution.

[0100] It should be noted that, for the sake of clarity, if the following four XPS spectra (B1s spectrum, S2p spectrum, F1s spectrum, and Ni3p spectrum) are detected in the surface analysis of the positive electrode 21 using XPS, and the following three intensity ratios (intensity ratios IBN, ISN, IFN) satisfy the specified conditions, the electrolyte does not necessarily have to contain a boron compound, a sulfur compound, and a fluorine compound. In this case, the electrolyte may not contain all of the boron compound, the sulfur compound, and the fluorine compound, but may contain only any one or two of the boron compound, the sulfur compound, and the fluorine compound.

[0101] Specifically, even if the electrolyte initially (when preparing the electrolyte) contains all of the boron compound, the sulfur compound, and the fluorine compound, but all of the boron compound, the sulfur compound, and the fluorine compound are consumed for forming the coating film 21C during charge and discharge in the stabilization treatment of the secondary battery, in the completed secondary battery, the electrolyte may not contain the boron compound, the sulfur compound, and the fluorine compound.

[0102] In addition, even if the electrolyte initially contains all of the boron compound, the sulfur compound, and the fluorine compound, but any one or two of the boron compound, the sulfur compound, and the fluorine compound are consumed for forming the coating film 21C during charge and discharge in the stabilization treatment of the secondary battery, in the completed secondary battery, the electrolyte may contain only the remaining one or two of the boron compound, the sulfur compound, and the fluorine compound.

[0103] [Positive electrode lead]

[0104] As Figure 1 shown, the positive electrode lead 31 is connected to the positive terminal of the battery element 20 (positive electrode 21) and is led out from the inside of the outer packaging film 10 to the outside. The positive electrode lead 31 contains a conductive material such as aluminum, and the shape of the positive electrode lead 31 is any one of a thin plate shape, a mesh shape, etc.

[0105] [Negative electrode lead]

[0106] As Figure 1 shown, the negative electrode lead 32 is connected to the negative terminal of the battery element 20 (negative electrode 22). Here, the negative electrode lead 32 is led out from the inside of the outer packaging film 10 to the outside in the same direction as the positive electrode 21. The negative electrode lead 32 contains a conductive material such as copper, and the details of the shape of the negative electrode lead 32 are the same as the details of the shape of the positive electrode lead 31.

[0107] <1-2. Physical properties>

[0108] In this secondary battery, as described above, in order to improve battery characteristics, when the positive electrode active material (lithium nickel composite oxide) is included, the physical properties of the positive electrode 21 (positive electrode active material layer 21B) satisfy the specified physical property conditions, and the physical properties of the positive electrode 21 (coating film 21C) satisfy the specified physical property conditions.

[0109] [Physical property conditions 1 to 3]

[0110] Specifically, the analysis results (physical properties) of the positive electrode active material layer 21B using XPS simultaneously satisfy the following three conditions (physical property conditions 1 to 3) described below.

[0111] Here, before explaining physical property conditions 1 to 3 respectively, the preconditions for explaining these physical property conditions 1 to 3 will be explained.

[0112] Figure 3 Magnified Figure 2 The cross-sectional structure of the positive electrode 21 shown. Figure 3 The positions P1 and P2 shown represent two analysis positions when analyzing the positive electrode active material layer 21B using XPS. Position P1 is the position of the surface of the positive electrode active material layer 21B when observing the positive electrode active material layer 21B from the surface in the depth direction (Z-axis direction). Position P2 is the position inside the positive electrode active material layer 21B when observing the positive electrode active material layer 21B from the surface in the same direction. More specifically, it is the position at a depth D of 100 nm from the surface of the positive electrode active material layer 21B (depth D = 100 nm).

[0113] As described above, the positive electrode active material layer 21B contains a layered rock salt type lithium nickel composite oxide as the positive electrode active material, and this lithium nickel composite oxide contains Ni and Al as constituent elements.

[0114] In this case, when analyzing the positive electrode active material layer 21B using XPS, as its analysis result, two XPS spectra (Ni2p3 / 2 spectrum and Al2s spectrum) are detected. The Ni2p3 / 2 spectrum is the XPS spectrum derived from Ni atoms in the lithium nickel composite oxide, and the Al2s spectrum is the XPS spectrum derived from Al atoms in the lithium nickel composite oxide.

[0115] Thus, based on the spectral intensity of the Ni2p3 / 2 spectrum, the atomic concentration (atomic %) of Ni is calculated, and based on the spectral intensity of the Al2s spectrum, the atomic concentration (atomic %) of Al is calculated.

[0116] (Physical property condition 1)

[0117] On the surface of the positive electrode active material layer 21B (position P1), when the positive electrode active material layer 21B is analyzed by XPS, the concentration ratio X (=atomic concentration of Al / atomic concentration of Ni), which is the ratio of the atomic concentration of Al to the atomic concentration of Ni, satisfies the condition represented by the following formula (2).

[0118] 0.30 ≤ X ≤ 0.70…(2)

[0119] This concentration ratio X is a parameter representing the magnitude relationship between the amount of Ni atoms and the amount of Al atoms present at position P1. From the condition represented by formula (2), it can be seen that on the surface of the positive electrode active material layer 21B (position P1), the amount of Al atoms present is appropriately reduced compared to the amount of Ni atoms.

[0120] (Physical property condition 2)

[0121] Inside the positive electrode active material layer 21B (position P2), when the positive electrode active material layer 21B is analyzed by XPS, the concentration ratio Y (=atomic concentration of Al / atomic concentration of Ni), which is the ratio of the atomic concentration of Al to the atomic concentration of Ni, satisfies the condition represented by the following formula (3).

[0122] 0.16 ≤ Y ≤ 0.37…(3)

[0123] This concentration ratio Y is a parameter representing the magnitude relationship between the amount of Ni atoms and the amount of Al atoms present at position P2. From the condition represented by formula (3), it can be seen that inside the positive electrode active material layer 21B (position P2), the amount of Al atoms present is appropriately reduced compared to the amount of Ni atoms. In addition, by comparing Physical property conditions 1 and 2, it can be seen that the amount of Al atoms present is appropriately increased on the surface (position P1) compared to the inside (position P2), and conversely, it is appropriately reduced on the inside (position P2) compared to the surface (position P1).

[0124] (Physical property condition 3)

[0125] Regarding the above concentration ratios X and Y, the relative ratio Z (=concentration ratio X / concentration ratio Y), which is the ratio of the concentration ratio X to this concentration ratio Y, satisfies the condition represented by the following formula (4).

[0126] 1.30 ≤ Z ≤ 2.52…(4)

[0127] This relative ratio Z is a parameter representing the magnitude relationship between the amount of Al atoms present at position P1 and the amount of Al atoms present at position P2. From the condition represented by formula (4), it can be seen that in the positive electrode active material layer 21B, the amount of Al atoms present gradually decreases from the surface (position P1) to the inside (position P2), and thus an appropriate concentration gradient is generated with respect to the amount of Al atoms present (atomic concentration).

[0128] (Reasons for satisfying Physical Property Conditions 1 to 3)

[0129] The simultaneous satisfaction of Physical Property Conditions 1 to 3 is because, while achieving a high energy density, it is possible to suppress the reduction in discharge capacity and the generation of gas even during repeated charge and discharge, and it is possible to improve the input / output property of lithium ions not only during the first charge and discharge but also thereafter. It should be noted that the detailed reasons for the simultaneous satisfaction of Physical Property Conditions 1 to 3 will be described later.

[0130] (Analysis steps)

[0131] The analysis steps (steps for determining each of the concentration ratios X, Y, and the relative ratio Z) of the positive electrode active material layer 21B using XPS are as follows.

[0132] First, discharge the secondary battery, and then recover the positive electrode 21 (positive electrode active material layer 21B) by disassembling the secondary battery. Next, wash the positive electrode 21 with pure water and then dry the positive electrode 21. Next, obtain a specimen for analysis by cutting the positive electrode 21 into a rectangular shape (10 mm × 10 mm).

[0133] Next, analyze the specimen using an XPS analyzer. In this case, as the XPS analyzer, use the scanning type X-ray photoelectron spectroscopy analyzer PHI Quantera SXM manufactured by ULVAC-PHI, Inc. In addition, as the analysis conditions, light source = monochromatic Al Kα ray (1486.6 eV), vacuum degree = 1 × 10 -9 Torr (≈ 133.3 × 10 - 9 Pa), analysis range (diameter) = 100 μm, analysis depth = several nm, presence / absence of a neutralization gun = present.

[0134] Thereby, on the surface (position P1) of the positive electrode active material layer 21B, detect the Ni2p3 / 2 spectrum and the Al2s spectrum, respectively, and calculate the atomic concentration (atomic %) of Ni and the atomic concentration (atomic %) of Al, respectively. Therefore, calculate the concentration ratio X based on the atomic concentration of Ni and the atomic concentration of Al.

[0135] Next, repeat the above calculation operation of the concentration ratio X 20 times, and then calculate the average value of the 20 concentration ratios X as the final concentration ratio X (the concentration ratio X for determining whether Physical Property Condition 1 is satisfied). Using the average value as the value of the concentration ratio X is to improve the calculation accuracy (reproducibility) of the concentration ratio X.

[0136] Next, except for changing the analysis depth in the analysis conditions from several nm to 100 nm, and converting the acceleration voltage = 1 kV and sputtering rate = SiO2 as new analysis conditions to 6 nm to 7 nm, the same analysis steps as those in the analysis steps when calculating the concentration ratio X are performed. Thus, inside the positive electrode active material layer 21B (position P2), the atomic concentration (atomic %) of Ni and the atomic concentration (atomic %) of Al are calculated respectively, and the concentration ratio Y is calculated based on the atomic concentration of Ni and the atomic concentration of Al. In this case, by using the average value as the value of the final concentration ratio Y, the calculation accuracy (reproducibility) of the concentration ratio Y can also be improved.

[0137] Finally, the relative ratio Z is calculated based on the concentration ratios X and Y. Thus, the concentration ratios X and Y are determined respectively, and the relative ratio Z is determined.

[0138] [Physical property conditions 4 - 6]

[0139] In addition, in order to better suppress the decrease in discharge capacity and the generation of gas even during repeated charge and discharge, the analysis results (physical properties) of the positive electrode 21 using XPS simultaneously satisfy the following three physical property conditions (physical property conditions 4 - 6).

[0140] Here, as Figure 2 shown, since the positive electrode 21 includes the coating film 21C, the coating film 21C is analyzed in the surface analysis of the positive electrode 21 using XPS. Thus, the physical properties of the positive electrode 21 (coating film 21C) satisfy the specified physical property conditions.

[0141] Specifically, as described above, the positive electrode active material layer 21B contains a layered rock salt type lithium nickel composite oxide as the positive electrode active material, and the lithium nickel composite oxide contains Ni as a constituent element. In addition, as described above, the coating film 21C covers the surface of the positive electrode active material layer 21B and contains B, S, and F as constituent elements.

[0142] In this case, when performing surface analysis on the positive electrode 21 (coating film 21C) using XPS, as the analysis result, four XPS spectra (B1s spectrum, S2p spectrum, F1s spectrum, and Ni3p spectrum) are detected. The B1s spectrum is the XPS spectrum derived from B atoms in the electrolytic solution (boron-containing compound). The S2p spectrum is the XPS spectrum derived from S atoms in the electrolytic solution (sulfur-containing compound). The F1s spectrum is the XPS spectrum derived from F atoms in the electrolytic solution (fluorine-containing compound). The Ni3p spectrum is the XPS spectrum derived from Ni atoms in the positive electrode active material layer 21B (lithium nickel composite oxide).

[0143] Based on the analysis results of the positive electrode 21 (coated film 21C) using this XPS, three intensity ratios (intensity ratios IBN, ISN, IFN) are calculated, and these three intensity ratios satisfy the conditions described below.

[0144] (Physical property condition 4)

[0145] The intensity ratio IBN (= IB / IN), which is the ratio of the intensity IB of the B1s spectrum to the intensity IN of the Ni3p spectrum, satisfies the condition expressed by the following formula (5).

[0146] 0.9 ≤ IBN ≤ 1.8…(5)

[0147] (Physical property condition 5)

[0148] The intensity ratio ISN (= IS / IN), which is the ratio of the intensity IS of the S2p spectrum to the intensity IN of the Ni3p spectrum, satisfies the condition expressed by the following formula (6).

[0149] 0.4 ≤ ISN ≤ 1.2…(6)

[0150] (Physical property condition 6)

[0151] The intensity ratio IFN (= IF / IN), which is the ratio of the intensity IF of the F1s spectrum to the intensity IN of the Ni3p spectrum, satisfies the condition expressed by the following formula (7).

[0152] 8 ≤ IFN ≤ 13…(7)

[0153] (Reasons for satisfying physical property conditions 4 to 6)

[0154] The intensity ratios IBN, ISN, and IFN satisfy the above conditions respectively because, in the positive electrode 21 containing the positive electrode active material (lithium nickel composite oxide), the bonding states (oxidation states) of constituent atoms such as O atoms and Ni atoms in the crystal structure of the positive electrode active material are optimized. Thereby, the crystal structure of the positive electrode active material is stabilized, and the surface state of the positive electrode 21 is electrochemically stabilized using the coated film 21C. Therefore, during charge and discharge, the decomposition reaction of the electrolyte on the surface of the positive electrode 21 can be suppressed, and thus the generation of gas due to the decomposition reaction of the electrolyte can be suppressed. Based on the above, even if the positive electrode 21 contains a lithium nickel composite oxide, the expansion of the secondary battery can be suppressed during charge and discharge.

[0155] (Analysis steps)

[0156] The analysis procedure for the positive electrode 21 (coated film 21C) using XPS is the same as the above-described analysis procedure for the positive electrode active material layer 21B using XPS, except that four XPS spectra (B1s spectrum, S2p spectrum, F1s spectrum, and Ni3p spectrum) are detected by surface analysis of the coated film 21C, and then three intensity ratios (intensity ratios IBN, ISN, IFN) are calculated.

[0157] It should be noted that in the case where the electrolytic solution contains a boron-containing compound, the intensity IB of the B1s spectrum varies according to the content of the boron-containing compound in the electrolytic solution. Similarly, in the case where the electrolytic solution contains a sulfur-containing compound, the intensity IS of the S2p spectrum varies according to the content of the sulfur-containing compound in the electrolytic solution, and the intensity IF of the F1s spectrum varies according to the content of the fluorine-containing compound in the electrolytic solution.

[0158] Therefore, the intensity ratio IBN can be controlled according to the content of the boron-containing compound in the electrolytic solution. Similarly, the intensity ratio ISN can be controlled according to the content of the sulfur-containing compound in the electrolytic solution, and the intensity ratio IFN can be controlled according to the content of the fluorine-containing compound in the electrolytic solution.

[0159] <1-3. Operations>

[0160] When the secondary battery is charged, in the battery element 20, lithium is deintercalated from the positive electrode 21, and this lithium is intercalated into the negative electrode 22 via the electrolytic solution. In addition, when the secondary battery is discharged, in the battery element 20, lithium is deintercalated from the negative electrode 22, and this lithium is intercalated into the positive electrode 21 via the electrolytic solution. During these charge and discharge processes, lithium is intercalated and deintercalated in an ionic state.

[0161] <1-4. Manufacturing Method>

[0162] After manufacturing the positive electrode active material (lithium nickel composite oxide), a secondary battery is fabricated using this positive electrode active material.

[0163] [Manufacture of Positive Electrode Active Material]

[0164] The positive electrode active material (lithium nickel composite oxide) is manufactured by the following-described procedure using a coprecipitation method and a firing method (primary firing process).

[0165] First, as raw materials, a supply source of Ni (nickel compound) and a supply source of Co (cobalt compound) are prepared.

[0166] The nickel compound is any one or two or more of the compounds containing Ni as a constituent element. Specifically, it is an oxide, carbonate, sulfate, hydroxide, etc. Regarding the details of the cobalt compound, except that Co is contained instead of Ni as a constituent element, it is the same as the details regarding the nickel compound.

[0167] Next, a mixed aqueous solution is prepared by introducing a mixture of a nickel compound and a cobalt compound into an aqueous solvent. The type of the aqueous solvent is not particularly limited, and specifically, it is pure water or the like. The details of the type of the aqueous solvent described herein are the same in the following description. The mixing ratio of the nickel compound and the cobalt compound (molar ratio of Ni to Co) can be arbitrarily set according to the composition of the finally manufactured positive electrode active material (lithium nickel composite oxide).

[0168] Next, any one or more of the alkali compounds are added to the mixed aqueous solution. The type of the alkali compound is not particularly limited, and specifically, it is a hydroxide or the like. Thus, since a plurality of particulate precipitates are granulated (co-precipitation method), a precursor for synthesizing a lithium nickel composite oxide (secondary particles of nickel cobalt composite co-precipitated hydroxide) can be obtained. In this case, as will be described in detail in the following examples, secondary particles of a Bi-model design containing two types of particles (large particle size particles and small particle size particles) can also be used.

[0169] Thereafter, the precursor is washed using an aqueous solvent.

[0170] Next, as other raw materials, a supply source of Li (lithium compound) and a supply source of Al (aluminum compound) are prepared. In this case, a supply source of an additional element M (additional compound) can also be prepared.

[0171] The lithium compound is any one or more of the compounds containing Li as a constituent element, and specifically, it is an oxide, a carbonate, a sulfate, a hydroxide, or the like. The details of the aluminum compound are the same as those of the lithium compound except that Al is contained as a constituent element instead of Li. The details of the additional compound are the same as those of the lithium compound except that the additional element M is contained as a constituent element instead of Li.

[0172] Next, a precursor mixture is obtained by mixing the precursor, the lithium compound, and the aluminum compound with each other. In this case, a precursor mixture containing the additional compound can also be obtained by mixing the additional compound in the precursor or the like. The mixing ratio of the precursor, the lithium compound, and the aluminum compound (molar ratio of Ni, Co, Li, and Al) can be arbitrarily set according to the composition of the finally manufactured positive electrode active material (lithium nickel composite oxide). The same applies to the mixing ratio of the additional compound (molar ratio of the additional element M).

[0173] Finally, the precursor mixture is fired in an oxygen atmosphere (firing method). Conditions such as the firing temperature and firing time can be arbitrarily set. Thus, the precursor, the lithium compound, and the aluminum compound react with each other, and a lithium nickel composite oxide containing Li, Ni, Co, and Al as constituent elements is synthesized. Therefore, a positive electrode active material (lithium nickel composite oxide) can be obtained. Of course, when the precursor mixture contains an additional compound, a positive electrode active material (lithium nickel composite oxide) further containing an additional element M as a constituent element can be obtained.

[0174] In this case, in the firing process of the precursor mixture, Al atoms in the aluminum compound sufficiently diffuse into the interior of the precursor, and thus a concentration gradient is generated such that the abundance (atomic concentration) of Al atoms gradually decreases from the surface (position P1) to the interior (position P2).

[0175] It should be noted that when manufacturing the positive electrode active material (lithium nickel composite oxide), by changing conditions such as the firing temperature during the firing of the precursor mixture, the concentration ratios X and Y can be adjusted respectively, and thus the relative ratio Z can also be adjusted.

[0176] [Manufacture of secondary battery]

[0177] Through the steps described below, a secondary battery is manufactured using the above positive electrode active material (lithium nickel composite oxide). Hereinafter, the case of manufacturing the positive electrode 21 including the coating film 21C and preparing an electrolytic solution containing a boron compound, a sulfur compound, and a fluorine compound will be described.

[0178] (Manufacture of positive electrode)

[0179] First, a positive electrode mixture is made by mixing the positive electrode active material, the positive electrode binder, the positive electrode conductive agent, etc. with each other, and then the positive electrode mixture is put into an organic solvent or the like to prepare a paste-like positive electrode mixture slurry. Next, the positive electrode mixture slurry is coated on both sides of the positive electrode current collector 21A to form a positive electrode active material layer 21B. Finally, as described later, after assembling the secondary battery using an electrolytic solution containing a boron compound, a sulfur compound, and a fluorine compound, the secondary battery is subjected to a stabilization treatment (charge-discharge treatment), and thus a coating film 21C containing B, S, and F as constituent elements is formed on the surface of the positive electrode active material layer 21B. Thereafter, the positive electrode active material layer 21B can be compression-molded using a roll press or the like. In this case, the positive electrode active material layer 21B can be heated, or the compression molding can be repeated multiple times. Thus, the positive electrode active material layer 21B and the coating film 21C are formed on both sides of the positive electrode current collector 21A to manufacture the positive electrode 21.

[0180] (Manufacture of negative electrode)

[0181] The negative electrode 22 is fabricated through the same steps as those for fabricating the positive electrode 21 described above. Specifically, a negative electrode mixture is made by mixing a negative electrode active material, a negative electrode binder, a negative electrode conductive agent, etc. Then, the negative electrode mixture is put into an organic solvent or the like, thereby preparing a paste-like negative electrode mixture slurry. Thereafter, the negative electrode mixture slurry is coated on both surfaces of the negative electrode current collector 22A, thereby forming a negative electrode active material layer 22B. Of course, the negative electrode active material layer 22B can also be compression molded. Thus, the negative electrode active material layer 22B is formed on both surfaces of the negative electrode current collector 22A, and the negative electrode 22 is fabricated.

[0182] (Preparation of the electrolyte solution)

[0183] After the electrolyte salt is put into the solvent, a boron-containing compound, a sulfur-containing compound, and a fluorine-containing compound are added to the solvent. Thus, the electrolyte salt is dispersed or dissolved in the solvent, thereby preparing the electrolyte solution.

[0184] (Assembly of the secondary battery)

[0185] First, the positive electrode lead 31 is connected to the positive electrode 21 (positive electrode current collector 21A) using a welding method or the like, and the negative electrode lead 32 is connected to the negative electrode 22 (negative electrode current collector 22A) using a welding method or the like.

[0186] Next, the positive electrode 21 and the negative electrode 22 are stacked on top of each other with the separator 23 in between, and then the positive electrode 21, the negative electrode 22, and the separator 23 are wound, thereby fabricating a wound body. This wound body has the same structure as that of the battery element 20 except that the electrolyte solution is not impregnated in each of the positive electrode 21, the negative electrode 22, and the separator 23. Next, the wound body is pressed using a press or the like to form the wound body into a flat shape.

[0187] Next, the wound body is housed inside the recessed portion 10U, and then the outer packaging film 10 is folded so that the outer packaging films 10 face each other. Next, using a heat fusion method or the like, the outer peripheral edge portions of two sides of the facing outer packaging films 10 (welded layers) are welded to each other, thereby housing the wound body inside the bag-shaped outer packaging film 10.

[0188] Finally, the electrolyte solution is injected into the inside of the bag-shaped outer packaging film 10, and then the outer peripheral edge portions of the remaining one side of the outer packaging film 10 (welded layer) are welded to each other using a heat fusion method or the like. In this case, the sealing film 41 is inserted between the outer packaging film 10 and the positive electrode lead 31, and the sealing film 42 is inserted between the outer packaging film 10 and the negative electrode lead 32. Thus, the wound body is impregnated with the electrolyte solution, the battery element 20 as a wound electrode body is fabricated, and the battery element 20 is sealed inside the bag-shaped outer packaging film 10, and the secondary battery is assembled.

[0189] (Stabilization of secondary battery)

[0190] The assembled secondary battery is charged and discharged. Various conditions such as ambient temperature, number of charge and discharge cycles (cycle number), and charge and discharge conditions can be arbitrarily set. Thereby, a coating film is formed on the surface of the negative electrode 22 or the like, so that the state of the secondary battery is electrochemically stabilized.

[0191] In this case, since the electrolytic solution contains a boron-containing compound, a sulfur-containing compound, and a fluorine-containing compound, a coating film 21C is formed on the surface of the positive electrode active material layer 21B by the stabilization treatment (charge and discharge treatment) of the secondary battery.

[0192] Therefore, a secondary battery using the exterior film 10, that is, a laminated film type secondary battery, is completed.

[0193] <1-5. Functions and effects>

[0194] According to this secondary battery, the positive electrode active material layer 21B of the positive electrode 21 contains a layered rock salt type lithium nickel composite oxide as the positive electrode active material, and the analysis results (concentration ratios X, Y, and relative ratio Z) of the positive electrode active material layer 21B using XPS simultaneously satisfy the physical property conditions 1 to 3, and the analysis results (intensity ratios IBN, ISN, IFN) of the positive electrode 21 using XPS simultaneously satisfy the physical property conditions 4 to 6.

[0195] In this case, based on the composition of the positive electrode active material (lithium nickel composite oxide) and the physical property conditions 1 to 6, a series of functions described below can be obtained.

[0196] First, since the positive electrode active material (lithium nickel composite oxide) contains the transition metal element Ni as the main component, a high energy density can be obtained.

[0197] Second, Al contained as a constituent element in the lithium nickel composite oxide exists in the form of columns in the crystal structure of the layered rock salt type (transition metal layer), and it does not contribute to the redox reaction. Therefore, Al has the property of being able to inhibit the crystal structure change but not participating in the charge and discharge reaction.

[0198] Here, since the physical property condition 1 is satisfied, an appropriate and sufficient amount of Al atoms exists on the surface (position P1) of the positive electrode active material layer 21B. In this case, during charge and discharge (during insertion and extraction of lithium ions), the crystal structure of the lithium nickel composite oxide hardly changes near the surface of the positive electrode active material layer 21B, so this positive electrode active material layer 21B is not easily expanded or contracted. It should be noted that in the change of the crystal structure of the lithium nickel composite oxide, it also includes unexpected phenomena such as the pulling out of Li. Thus, during charge and discharge, the positive electrode active material is not easily broken, so highly reactive fresh surfaces are not easily generated in this positive electrode active material. Therefore, the electrolyte is not easily decomposed on the fresh surface of the positive electrode active material, so even if charge and discharge are repeated, the discharge capacity is not easily reduced, and gas is not easily generated due to the decomposition reaction of the electrolyte during charge and discharge.

[0199] In this case, in particular, even when the secondary battery is used (charged, discharged, or stored) in a high-temperature environment, the discharge capacity is not easily reduced sufficiently, and gas is not easily generated sufficiently. In addition, in the positive electrode active material, since fresh surfaces are not easily generated, a resistive coating film is not easily formed, and the crystal structure is not easily changed (such as the structural change from hexagonal crystal to cubic crystal), and this crystal structure change is the main cause of the increase in resistance.

[0200] Third, since the physical property condition 2 is satisfied, the amount of Al atoms present in the interior (position P2) of the positive electrode active material layer 21B is appropriately and sufficiently reduced compared to the surface (position P1). In this case, not only during the first charge and discharge but also thereafter, in the inner part near the surface of the positive electrode active material layer 21B, lithium ions can be easily input and output without being overly affected by Al atoms. Thus, the charge and discharge reactions can proceed smoothly and sufficiently, thereby ensuring the energy density, and lithium ions can be easily and stably inserted and extracted during charge and discharge.

[0201] Fourth, since the physical property condition 3 is satisfied, in the positive electrode active material layer 21B, the amount of Al atoms present in the interior (position P2) is appropriately reduced compared to the surface (position P1). More specifically, the amount of Al present gradually decreases from the surface (position P1) to the interior (position P2) without a sharp decrease. In this case, in the positive electrode active material layer 21B, the advantages related to the first effect based on the above physical property condition 1 and the advantages related to the second effect based on the above physical property condition 2 can be obtained with good balance. Thus, compared with the case where the physical property condition 3 is not satisfied, there is no trade-off relationship where obtaining one of the two advantages makes it impossible to obtain the other, so both of these advantages can be effectively obtained.

[0202] Fifth, since physical property conditions 4 to 6 are satisfied, the state of the positive electrode 21 is stabilized. Specifically, in the positive electrode 21 containing the positive electrode active material (lithium nickel composite oxide), since the bonding state (oxidation state) of constituent atoms such as Ni atoms in the crystal structure of the positive electrode active material is optimized, the crystal structure of the positive electrode active material is stabilized, and the surface state of the positive electrode active material layer 21B is electrochemically stabilized. Moreover, since the bonding states of constituent atoms such as B atoms, S atoms, and F atoms in the positive electrode 21 are optimized, the surface state of the positive electrode 21 is more stable electrochemically. Thereby, even if the positive electrode 21 contains a lithium nickel composite oxide, the decomposition reaction of the electrolytic solution on the surface of the positive electrode 21 during charge and discharge can be suppressed, and thus the generation of gas due to the decomposition reaction of the electrolytic solution can be suppressed.

[0203] As described above, different from the case where physical property conditions 1 to 6 are not satisfied simultaneously, high energy density can be obtained, and even when repeated charge and discharge are performed, a decrease in discharge capacity and generation of gas can be suppressed, and the input / output property of lithium ions can be improved not only during the first charge and discharge but also thereafter. Therefore, excellent battery characteristics can be obtained.

[0204] In this case, in particular, as a method for manufacturing the positive electrode active material, by using the coprecipitation method and the firing method (single firing process), different from the case of using the coprecipitation method and the firing method (double firing process), physical property conditions 1 to 3 are substantially satisfied simultaneously, and thus battery characteristics can be improved.

[0205] Specifically, as will be described in detail in the following examples, in the case of using the coprecipitation method and the firing method (double firing process), the same as in the case of using the coprecipitation method and the firing method (single firing process), in the positive electrode active material layer 21B, the abundance of Al atoms decreases inside (position P2) compared to the surface (position P1). However, the abundance of Al atoms increases excessively on the surface (position P1), and the abundance of Al atoms decreases excessively inside (position P2), so both physical property conditions 1 and 2 are not satisfied. Or, the abundance of Al atoms decreases sharply inside (position P2) compared to the surface (position P1), so physical property condition 3 is not satisfied. Thereby, due to the above-described trade-off relationship caused by not satisfying physical property conditions 1 to 3 simultaneously, it is difficult to improve battery characteristics.

[0206] In contrast, in the case of using the coprecipitation method and the firing method (single firing process), different from the case of using the coprecipitation method and the firing method (double firing process), in the positive electrode active material layer 21B, the amount of Al atoms present on the surface (position P1) increases appropriately, and the amount of Al atoms present inside (position P2) decreases appropriately. Therefore, both physical property conditions 1 and 2 are satisfied. Moreover, the amount of Al atoms present gradually decreases from the surface (position P1) to the inside (position P2), so physical property condition 3 is satisfied. Therefore, by simultaneously satisfying physical property conditions 1 to 3, the above-mentioned trade-off relationship can be broken, and thus the battery characteristics can be improved.

[0207] In addition, since d in formula (1) satisfies d > 0, if the lithium nickel composite oxide contains the additional element M as a constituent element, lithium ions can be easily and smoothly input and output in the positive electrode active material (lithium nickel composite oxide) during charge and discharge, and thus a higher effect can be obtained.

[0208] In addition, if the secondary battery includes a flexible outer packaging film 10, in the case of using the flexible outer packaging film 10 that is prone to obvious deformation (expansion), the expansion of the secondary battery can also be effectively suppressed, and thus a higher effect can be obtained.

[0209] In addition, if the positive electrode 21 includes a coating film 21C (containing B, S, and F as constituent elements), and the coating film 21C is analyzed in the surface analysis of the positive electrode 21 using XPS, the surface state of the positive electrode 21 can be easily electrochemically stabilized by using the coating film 21C, and thus a higher effect can be obtained.

[0210] In addition, if the electrolytic solution contains a boron-containing compound, a sulfur-containing compound, and a fluorine-containing compound, it is easy to detect three XPS spectra (B1s spectrum, S2p spectrum, and F1s spectrum), and the three intensity ratios (intensity ratios IBN, ISN, IFN) are easy to satisfy the above-mentioned conditions, and thus a higher effect can be obtained.

[0211] In this case, if the boron-containing compound contains a boron-containing lithium salt, the sulfur-containing compound contains one or both of cyclic disulfonic anhydride and sulfonyloxyalkyne ester, and the fluorine-containing compound contains a fluorine-containing lithium salt, it is easy to stably detect the three XPS spectra, and the three intensity ratios are more likely to satisfy the above-mentioned conditions, and thus a higher effect can be obtained.

[0212] In addition, if the secondary battery is a lithium-ion secondary battery, sufficient battery capacity can be stably obtained by using the insertion and extraction of lithium, and thus a higher effect can be obtained.

[0213] In addition, according to the positive electrode 21, the positive electrode active material layer 21B contains a layered rock salt type lithium nickel composite oxide as the positive electrode active material. The analysis results (concentration ratios X, Y, and relative ratio Z) of the positive electrode active material layer 21B using XPS simultaneously satisfy the physical property conditions 1 to 3, and the analysis results (intensity ratios IBN, ISN, IFN) of the positive electrode 21 using XPS simultaneously satisfy the physical property conditions 4 to 6. Therefore, for the above reasons, excellent battery characteristics can be obtained in the secondary battery using the positive electrode 21.

[0214] <2. Modified Example>

[0215] Next, a modified example of the above secondary battery will be described. As described below, the structure of the secondary battery can be appropriately changed. In addition, any two or more of the series of modified examples described below can be combined with each other.

[0216] [Modified Example 1]

[0217] The above secondary battery uses the separator 23 as a porous membrane. However, although not specifically illustrated here, a laminated separator including a polymer compound layer can be used instead of the separator 23 as a porous membrane.

[0218] Specifically, the laminated separator includes a porous membrane having a pair of surfaces and a polymer compound layer disposed on one or both surfaces of the porous membrane. This is because, since the adhesion of the separator to each of the positive electrode 21 and the negative electrode 22 is improved, positional deviation (winding deviation of each of the positive electrode 21, the negative electrode 22, and the separator) of the battery element 20 is not likely to occur. Thus, even if a decomposition reaction of the electrolyte solution or the like occurs, the secondary battery is not likely to expand. The polymer compound layer includes a polymer compound such as polyvinylidene fluoride. This is because polyvinylidene fluoride and the like have excellent physical strength and electrochemical stability.

[0219] It should be noted that one or both of the porous membrane and the polymer compound layer may include any one or two or more of a plurality of insulating particles. This is because when the secondary battery generates heat, the plurality of insulating particles dissipate heat, so the safety (heat resistance) of the secondary battery is improved. The insulating particles are inorganic particles and resin particles, etc. Specific examples of the inorganic particles are particles such as alumina, aluminum nitride, boehmite, silica, titanium oxide, magnesium oxide, and zirconia. Specific examples of the resin particles are particles such as acrylic resin and styrene resin.

[0220] In the case of manufacturing the laminated separator, a precursor solution containing a polymer compound and an organic solvent, etc. is prepared, and then the precursor solution is coated on one or both surfaces of the porous membrane. In this case, a plurality of insulating particles can also be added to the precursor solution as needed.

[0221] When the laminated separator is used, lithium ions can also move between the positive electrode 21 and the negative electrode 22, so the same effect can be obtained.

[0222] [Variant Example 2]

[0223] The above secondary battery uses an electrolytic solution as a liquid electrolyte. However, although not specifically illustrated here, an electrolyte layer as a gel electrolyte can also be used instead of the electrolytic solution.

[0224] In the battery element 20 using the electrolyte layer, the positive electrode 21 and the negative electrode 22 are laminated on each other with the separator 23 and the electrolyte layer in between, and then the positive electrode 21, the negative electrode 22, the separator 23, and the electrolyte layer are wound. The electrolyte layer is interposed between the positive electrode 21 and the separator 23, and is also interposed between the negative electrode 22 and the separator 23.

[0225] Specifically, the electrolyte layer contains an electrolytic solution and a polymer compound, and in this electrolyte layer, the electrolytic solution is held by the polymer compound. This is because leakage of the liquid can be prevented. The structure of the electrolytic solution is as described above. The polymer compound includes polyvinylidene fluoride and the like. When forming the electrolyte layer, after preparing a precursor solution containing an electrolytic solution, a polymer compound, an organic solvent, etc., the precursor solution is coated on one side or both sides of each of the positive electrode 21 and the negative electrode 22.

[0226] Even when the electrolyte layer is used, lithium ions can move between the positive electrode 21 and the negative electrode 22 via the electrolyte layer, so the same effect can be obtained.

[0227] <3. Uses of the Secondary Battery>

[0228] Next, the uses (application examples) of the above secondary battery will be described.

[0229] The uses of the secondary battery are not particularly limited as long as they are machines, equipment, appliances, devices, and systems (aggregates of multiple devices, etc.) that can utilize the secondary battery mainly as a driving power source or a power storage source for power accumulation, etc. The secondary battery used as a power source can be a main power source or an auxiliary power source. The main power source is the power source that is preferentially used, regardless of the presence or absence of other power sources. The auxiliary power source can be a power source used instead of the main power source, or a power source switched from the main power source as needed. When using the secondary battery as an auxiliary power source, the type of the main power source is not limited to a secondary battery.

[0230] Specific examples of the uses of secondary batteries are as follows. Electronic devices such as cameras, digital still cameras, mobile phones, notebook computers, cordless phones, stereo headphones, portable radios, portable televisions, and portable information terminals (including portable electronic devices). Portable living appliances such as electric shavers. Storage devices such as backup power supplies and memory cards. Electric tools such as electric drills and electric saws. A battery pack that is mounted as a detachable power source on a notebook computer or the like. Medical electronic devices such as pacemakers and hearing aids. Electric vehicles such as electric cars (including hybrid vehicles). Power storage systems such as home battery systems that store electricity in advance for emergencies or the like. In these uses, one secondary battery or multiple secondary batteries can be used.

[0231] Among them, it is effective for the battery pack to be applied to relatively large devices such as electric vehicles, power storage systems, and electric tools. The battery pack can use a single cell or a battery pack. An electric vehicle is a vehicle that operates (runs) using a secondary battery as a driving power source. As described above, it can also be a car (such as a hybrid vehicle) that has a driving source other than the secondary battery. A power storage system is a system that uses a secondary battery as a power storage source. In a home power storage system, since electricity is stored in the secondary battery as a power storage source, this electricity can be used to operate home electrical products and the like.

[0232] Here, an example of the application of a secondary battery will be specifically described. The structure of the application example described below is only one example, and thus can be appropriately changed.

[0233] Figure 4 Shows the frame structure of the battery pack. The battery pack described here is a simple type of battery pack (so-called soft pack) that uses one secondary battery and is mounted on electronic devices represented by smartphones.

[0234] As Figure 4 shown, the battery pack includes a power source 51 and a circuit board 52. The circuit board 52 is connected to the power source 51 and includes a positive terminal 53, a negative terminal 54, and a temperature detection terminal 55 (so-called T terminal).

[0235] The power source 51 includes one secondary battery. In this secondary battery, the positive lead is connected to the positive terminal 53, and the negative lead is connected to the negative terminal 54. Since this power source 51 can be connected to the outside through the positive terminal 53 and the negative terminal 54, charging and discharging can be performed through the positive terminal 53 and the negative terminal 54. The circuit board 52 includes a control unit 56, a switch 57, a thermistor element (Positive Temperature Coefficient (PTC): positive temperature coefficient element) 58, and a temperature detection unit 59. In addition, the PTC element 58 can also be omitted.

[0236] The control unit 56 includes a central processing unit (CPU: Central Processing Unit) and a memory, etc., and controls the operation of the entire battery pack. The control unit 56 detects and controls the usage status of the power supply 51 as needed.

[0237] It should be noted that when the voltage of the power supply 51 (secondary battery) reaches the overcharge detection voltage or the overdischarge detection voltage, the control unit 56 cuts off the switch 57 to prevent the charging current from flowing through the current path of the power supply 51. In addition, when a large current flows during charging or discharging, the control unit 56 blocks the charging current by cutting off the switch 57. The overcharge detection voltage and the overdischarge detection voltage are not particularly limited. For example, the overcharge detection voltage is 4.2V ± 0.05V, and the overdischarge detection voltage is 2.4V ± 0.1V.

[0238] The switch 57 includes a charge control switch, a discharge control switch, a charging diode, a discharging diode, etc., and switches the connection between the power supply 51 and the external device according to the instruction of the control unit 56. The switch 57 includes a metal-oxide-semiconductor field-effect transistor (MOSFET: Metal-Oxide-Semiconductor Field-Effect Transistor), etc., and detects the charge and discharge current based on the on-resistance of the switch 57.

[0239] The temperature detection unit 59 includes a temperature detection element such as a thermistor, measures the temperature of the power supply 51 using the temperature detection terminal 55, and outputs the measurement result of the temperature to the control unit 56. The measurement result of the temperature measured by the temperature detection unit 59 is used when the control unit 56 performs charge and discharge control in case of abnormal heat generation, and for the control unit 56 to perform correction processing when calculating the remaining capacity, etc.

[0240] Examples

[0241] Examples of the present technology will be described.

[0242] <Examples 1 to 8 and Comparative Examples 9 to 15>

[0243] As described below, a positive electrode active material was manufactured, a secondary battery was manufactured using the positive electrode active material, and then the battery characteristics of the secondary battery were evaluated.

[0244] [Manufacture of the positive electrode active material in Examples 1 to 8 and Comparative Examples 9 to 14]

[0245] The following steps were used to manufacture a positive electrode active material (lithium nickel composite oxide) using coprecipitation and firing (primary firing process) as the manufacturing methods.

[0246] First, as raw materials, powdery nickel compound (nickel sulfate (NiSO4)) and powdery cobalt compound (cobalt sulfate (CoSO4)) were prepared. Next, a mixture was obtained by mixing the nickel compound and the cobalt compound with each other. In this case, the mixing ratio of the nickel compound and the cobalt compound was adjusted so that the mixing ratio (molar ratio) of Ni to Co was 85.4:14.6. In addition, the mixing ratio of the nickel compound and the cobalt compound was changed by changing the mixing ratio (molar ratio) of Co according to the mixing ratio (molar ratio) of Ni.

[0247] Next, the mixture was put into an aqueous solvent (pure water), and then the aqueous solvent was stirred to obtain a mixed aqueous solution.

[0248] Next, while stirring the mixed aqueous solution, an alkali compound (sodium hydroxide (NaOH) and ammonium hydroxide (NH4OH)) was added to the mixed aqueous solution (coprecipitation method). As a result, multiple particulate precipitates were granulated in the mixed aqueous solution to obtain a precursor (secondary particles of nickel cobalt composite coprecipitated hydroxide). The composition of this precursor is shown in Table 1. In this case, in order to finally obtain secondary particles of the positive electrode active material having two different average particle diameters (median particle diameter D50 (μm)) (Bi-model design including large particle diameter particles and small particle diameter particles), two kinds of secondary particles with different average particle diameters were granulated by controlling their average particle diameters.

[0249] Next, as other raw materials, powdery lithium compound (lithium hydroxide monohydrate (LiOH·H2O)) and powdery aluminum compound (aluminum hydroxide (Al(OH)3)) were prepared.

[0250] Next, a precursor mixture was obtained by mixing the precursor, the aluminum compound, and the lithium compound with each other. In this case, the mixing ratio of the precursor and the aluminum compound was adjusted so that the mixing ratio (molar ratio) of Ni, Co, and Al was 82.0:14.0:4.0, and the addition amount (weight%) of the aluminum compound relative to the precursor was 1.12 wt%. In addition, the mixing ratio of the precursor and the aluminum compound and the lithium compound was adjusted so that the mixing ratio (molar ratio) of Ni, Co, and Al to Li was 103:100. It should be noted that the mixing ratio of the precursor and the aluminum compound was changed by changing the mixing ratio (molar ratio) of Ni and Co according to the mixing ratio (molar ratio) of Al. In addition, the mixing ratio of the precursor and the aluminum compound and the lithium compound was changed by changing the mixing ratio (molar ratio) of Ni, Co, and Al according to the mixing ratio (molar ratio) of Li.

[0251] In the column of "Addition period" shown in Table 1, the period when the aluminum compound was added during the manufacturing process of the positive electrode active material is shown. "After coprecipitation" means that after obtaining the precursor using the coprecipitation method, the aluminum compound was added to the precursor before the subsequent firing process.

[0252] Finally, the precursor mixture was fired in an oxygen atmosphere. The firing temperature (°C) is as shown in Table 1. Thus, the powdery layered rock salt type lithium nickel composite oxide represented by the formula (1) was synthesized.

[0253] In the column of "Firing times" shown in Table 1, the number of firing processes performed during the manufacturing process of the positive electrode active material is shown. Here, since the firing process is performed after forming the precursor using the coprecipitation method, the number of firing times is one.

[0254] Therefore, the positive electrode active material (lithium nickel composite oxide) was obtained. The composition and NC ratio of this lithium nickel composite oxide are as shown in Table 2.

[0255] It should be noted that in the case of manufacturing the positive electrode active material, a powdery manganese compound (manganese sulfate (MnSO4)) was further prepared as other raw materials, and then the manganese compound was further mixed in the precursor to obtain a precursor mixture. Except for this, a lithium nickel composite oxide containing manganese as a constituent element of the additional element M was synthesized through the same steps.

[0256] In the column of "Additional element M" shown in Table 2, the presence or absence of the additional element M is shown, and in the case where the lithium nickel composite oxide contains the additional element M as a constituent element, the type of the additional element M is shown.

[0257] [Manufacture of the positive electrode active material in Comparative Example 15]

[0258] For comparison, through the steps described below, as the manufacturing method, the coprecipitation method and the firing method (two firing processes) were used instead of the coprecipitation method and the firing method (one firing process) to manufacture the positive electrode active material (lithium nickel composite oxide).

[0259] In this case, first, through the above steps, a precursor (secondary particles of nickel cobalt composite coprecipitated hydroxide) was obtained using the coprecipitation method. Next, a mixture of the precursor and a powdery lithium compound (lithium hydroxide monohydrate) was obtained, and then this mixture was fired (the first firing process). The mixing ratio (molar ratio) of the precursor and the lithium compound is as described above, and the firing temperature (°C) and the like in the first firing process are as shown in Table 1. Thus, a powdery composite oxide as the fired product was obtained.

[0260] Next, a mixture of the composite oxide and the powdery aluminum compound (aluminum hydroxide) was obtained, and then the mixture was fired in an oxygen atmosphere (second firing step). In this case, the addition amount of the aluminum compound relative to the composite oxide was 0.41% by weight. The firing temperature (°C) in the second firing step is shown in Table 1. Thus, a powdery layered rock salt type lithium nickel composite oxide (lithium nickel cobaltate covered with Al on the surface) was synthesized, and thus the positive electrode active material was obtained. The composition and NC ratio of the positive electrode active material are shown in Table 2.

[0261] Here, since the aluminum compound is added after the first firing step and before the second firing step, as shown in the "addition period" column of Table 1, the addition period of the aluminum compound is after the first firing. In addition, here, since two firing steps are performed as the manufacturing method of the positive electrode active material, as shown in the "number of firings" column of Table 1, the number of firings is two.

[0262] [Table 1]

[0263]

[0264] [Table 2]

[0265]

[0266] [Manufacture of secondary batteries in Examples 1 to 8 and Comparative Examples 9 to 15]

[0267] The laminated film type secondary battery (lithium ion secondary battery) shown below was manufactured through the steps described below. Figures 1 to 3

[0268] (Fabrication of positive electrode)

[0269] First, 95.5 parts by mass of the positive electrode active material (lithium nickel composite oxide), 1.9 parts by mass of the positive electrode binder (polyvinylidene fluoride), 2.5 parts by mass of the positive electrode conductive agent (carbon black), and 0.1 part by mass of the dispersant (polyvinylpyrrolidone) were mixed with each other to prepare a positive electrode mixture. Next, the positive electrode mixture was put into an organic solvent (N-methyl-2-pyrrolidone), and then the organic solvent was stirred to prepare a paste-like positive electrode mixture slurry. Next, the positive electrode mixture slurry was coated on both sides of the positive electrode current collector 21A (a strip-shaped aluminum foil with a thickness of 15 μm), and then the positive electrode mixture slurry was dried to form a positive electrode active material layer 21B. Next, the positive electrode active material layer 21B was compression-molded using a roll press.

[0270] Finally, as described later, after assembling a secondary battery using an electrolytic solution containing a boron compound, a sulfur compound, and a fluorine compound, the secondary battery is subjected to a stabilization treatment (charge-discharge treatment), whereby a coating film 21C is formed on the surface of the positive electrode active material layer 21B. Thus, the positive electrode 21 was fabricated.

[0271] After fabricating the positive electrode 21, the physical properties (concentration ratios X, Y, and relative ratio Z) of the positive electrode 21 (positive electrode active material layer 21B) were analyzed using XPS, and the results are shown in Table 2. Note that the analysis procedure of the positive electrode active material layer 21B using XPS was as described above.

[0272] (Fabrication of the negative electrode)

[0273] First, 90 parts by mass of a negative electrode active material (graphite) and 10 parts by mass of a negative electrode binder (polyvinylidene fluoride) were mixed with each other to prepare a negative electrode mixture. Next, the negative electrode mixture was put into an organic solvent (N-methyl-2-pyrrolidone), and then the organic solvent was stirred to prepare a paste-like negative electrode mixture slurry. Next, the negative electrode mixture slurry was coated on both surfaces of a negative electrode current collector 22A (a strip-shaped copper foil with a thickness of 15 μm), and then the negative electrode mixture slurry was dried to form a negative electrode active material layer 22B. Finally, the negative electrode active material layer 22B was compression-molded using a roll press. Thus, the negative electrode 22 was fabricated.

[0274] (Preparation of the electrolytic solution)

[0275] An electrolyte salt (lithium hexafluorophosphate (LiPF6)) was added to a solvent (ethylene carbonate and ethyl methyl carbonate), and then the solvent was stirred. In this case, the mixing ratio (weight ratio) of the solvents was ethylene carbonate:ethyl methyl carbonate = 50:50, and the content of the electrolyte salt relative to the solvent was 1 mol / kg.

[0276] Next, a boron compound, a sulfur compound, and a fluorine compound were added to the solvent to which the electrolyte salt had been added, and then the solvent was stirred. In this case, lithium tetrafluorophosphate (LiBF4) was used as the boron compound, 1,3-propanedisulfonic anhydride (PDSA) was used as the sulfur compound, and an additional lithium hexafluorophosphate (LiPF6) was used as the fluorine compound. In addition, the content of the boron compound in the electrolytic solution was 1 wt%, the content of the sulfur compound in the electrolytic solution was 1 wt%, and the content of the fluorine compound in the electrolytic solution was 15 wt%. Thus, the electrolytic solution was prepared.

[0277] (Assembly of the secondary battery)

[0278] First, the positive electrode lead 31 (strip-shaped aluminum foil) is welded to the positive electrode 21 (positive electrode current collector 21A), and the negative electrode lead 32 (strip-shaped copper foil) is welded to the negative electrode 22 (negative electrode current collector 22A).

[0279] Next, the positive electrode 21 and the negative electrode 22 are laminated with each other with the separator 23 (microporous polyethylene film with a thickness of 25 μm) interposed therebetween, and then the positive electrode 21, the negative electrode 22, and the separator 23 are wound to form a wound body. Next, the wound body is pressed using a press to form a wound body having a flat shape.

[0280] Next, the outer packaging film 10 is folded so as to sandwich the wound body accommodated in the recessed portion 10U, and then the outer peripheral edge portions of the two sides in the outer packaging film 10 (welding layer) are heat-sealed to each other, thereby accommodating the wound body inside the bag-shaped outer packaging film 10. As the outer packaging film 10, an aluminum laminated film in which a welding layer (polypropylene film with a thickness of 30 μm), a metal layer (aluminum foil with a thickness of 40 μm), and a surface protective layer (nylon film with a thickness of 25 μm) are laminated in order from the inside is used.

[0281] Finally, after injecting the electrolytic solution into the inside of the bag-shaped outer packaging film 10, the outer peripheral edge portions of the remaining one side in the outer packaging film 10 (welding layer) are heat-sealed to each other in a reduced-pressure environment. In this case, the sealing film 41 (polypropylene film with a thickness of 5 μm) is inserted between the outer packaging film 10 and the positive electrode lead 31, and the sealing film 42 (polypropylene film with a thickness of 5 μm) is inserted between the outer packaging film 10 and the negative electrode lead 32. Thereby, the electrolytic solution is impregnated into the wound body, thereby manufacturing the battery element 20 as a wound electrode body, and the battery element 20 is sealed inside the bag-shaped outer packaging film 10 to assemble a secondary battery.

[0282] (Stabilization of the secondary battery)

[0283] The secondary battery is charged and discharged for 1 cycle in a normal temperature environment (temperature = 25°C). During charging, constant current charging is performed at a current of 0.1C until the voltage reaches 4.2V, and then constant voltage charging is performed at the voltage of 4.2V until the current reaches 0.005C. The conditions of the normal temperature environment described here (temperature = 25°C) are the same in the following description. During discharging, constant current discharging is performed at a current of 0.1C until the voltage reaches 2.5V. 0.1C refers to the current value at which the battery capacity (theoretical capacity) is completely discharged in 10 hours, and 0.005C refers to the current value at which the battery capacity is completely discharged in 200 hours.

[0284] Thus, as described above, a coating film 21C is formed on the surface of the positive electrode active material layer 21B to fabricate the positive electrode 21. In addition, a coating film is formed on the surface of the negative electrode 22 and the like to stabilize the state of the secondary battery. Thus, the laminated film type secondary battery is completed.

[0285] After fabricating the secondary battery, the physical properties (intensity ratios IBN, ISN, IFN) of the positive electrode 21 (coating film 21C) were analyzed using XPS. As a result, the intensity ratio IBN = 1.2, the intensity ratio ISN = 0.9, and the intensity ratio IFN = 9. It should be noted that the analysis procedure of the positive electrode 21 (coating film 21C) using XPS is as described above.

[0286] [Evaluation of Battery Characteristics]

[0287] The battery characteristics (initial capacity characteristics, cycle characteristics, load characteristics, and swelling characteristics) of the secondary battery were evaluated, and the results shown in Table 2 were obtained.

[0288] (Initial Capacity Characteristics)

[0289] By charging and discharging the secondary battery for 1 cycle in a normal temperature environment, the discharge capacity (initial capacity) was measured. The charge-discharge conditions were the same as those during the stabilization of the secondary battery described above. It should be noted that the value of the initial capacity shown in Table 2 is a normalized value with the initial capacity value in Example 1 being 100.

[0290] (Cycle Characteristics)

[0291] First, by charging and discharging the secondary battery in a high temperature environment (temperature = 60°C), the discharge capacity (discharge capacity of the first cycle) was measured. The conditions of the high temperature environment described here (temperature = 60°C) are the same in the following description. Next, the secondary battery was repeatedly charged and discharged in the same environment until the total number of cycles reached 100 cycles, and thus the discharge capacity (discharge capacity of the 100th cycle) was measured. The charge-discharge conditions were the same as those during the stabilization of the secondary battery described above. Finally, the cycle retention rate (%) = (discharge capacity of the 100th cycle / discharge capacity of the first cycle) × 100 was calculated.

[0292] (Load Characteristics)

[0293] First, by charging and discharging the secondary battery in a normal temperature environment, the discharge capacity (the discharge capacity of the first cycle) was measured. Except that the charging current and the discharging current were changed from 0.1C to 0.2C respectively, the charging and discharging conditions were the same as those during the stabilization of the above secondary battery. Next, by charging and discharging the secondary battery again in the same environment, the discharge capacity (the discharge capacity of the second cycle) was measured. The charging and discharging conditions were the same as those during the stabilization of the above secondary battery except that the discharging current was changed from 0.1C to 10C. 0.2C refers to the current value that completely discharges the battery capacity in 5 hours, and 10C refers to the current value that completely discharges the battery capacity in 0.1 hours. Finally, the load retention rate (%) = (the discharge capacity of the second cycle (discharging current = 10C) / the discharge capacity of the first cycle (discharging current = 0.2C)) × 100 was calculated.

[0294] (Swelling characteristics)

[0295] First, the secondary battery was charged in a normal temperature environment, and then the thickness of the secondary battery (the thickness before storage) was measured. The charging conditions were the same as those during the stabilization of the above secondary battery. Next, the charged secondary battery was stored in a high temperature environment (storage period = 24 hours), and then the thickness of the secondary battery (the thickness after storage) was measured. Finally, the swelling rate (%) = [(the thickness after storage - the thickness before storage) / the thickness before storage] × 100 was calculated.

[0296] [Discussion]

[0297] As shown in Table 2, the battery characteristics of the secondary battery vary according to the analysis results (physical properties) of the positive electrode active material layer 21B using XPS.

[0298] Specifically, when the physical property conditions 1 to 3 were not satisfied simultaneously (Comparative Examples 9 to 15), a trade-off relationship occurred where any one of the initial capacity, cycle retention rate, load retention rate, and swelling rate increased while the others decreased. Therefore, each of the initial capacity, cycle retention rate, load retention rate, and swelling rate could not be improved.

[0299] In particular, when the positive electrode active material (lithium nickel composite oxide) was manufactured using the coprecipitation method and the firing method (primary firing process) (Comparative Example 15), due to the excessive increase in the relative ratio of Z, the above-mentioned trade-off relationship occurred.

[0300] In contrast, when the physical property conditions 1 to 3 were satisfied simultaneously (Examples 1 to 8), the above-mentioned trade-off relationship was broken, and therefore each of the initial capacity, cycle retention rate, load retention rate, and swelling rate could be improved.

[0301] In this case, particularly when the positive electrode active material (lithium nickel composite oxide) contains an additional element M (Mn) as a constituent element, compared with the case where the lithium nickel composite oxide does not contain the additional element M as a constituent element, while substantially maintaining a high load retention rate, the initial capacity increases. In addition, even when using the flexible outer packaging film 10 in which deformation (expansion) is likely to be conspicuous, the expansion rate can be sufficiently suppressed.

[0302] <Examples 16 to 21 and Comparative Examples 22 to 27>

[0303] Except for changing the strength ratios IBN, ISN, and IFN as shown in Table 3, respectively, secondary batteries were manufactured through the same steps, and then the battery characteristics (initial capacity characteristics, cycle characteristics, load characteristics, and expansion characteristics) of the secondary batteries were evaluated.

[0304] In order to change the strength ratios IBN, ISN, and IFN, respectively, in the production process of the electrolytic solution, the addition amounts of the boron-containing compound, sulfur-containing compound, and fluorine-containing compound were changed. The addition amounts (contents (wt%)) of the boron-containing compound, sulfur-containing compound, and fluorine-containing compound in the electrolytic solution are shown in Table 3. In Table 3, for the sake of simplifying the expression content, the boron-containing compound is expressed as "B-containing compound", the sulfur-containing compound is expressed as "S-containing compound", and the fluorine-containing compound is expressed as "F-containing compound".

[0305] [Table 3]

[0306]

[0307] As shown in Table 3, the battery characteristics of the secondary battery also vary according to the analysis results (physical properties) of the positive electrode 21 (coated film 21C) using XPS.

[0308] Specifically, in the case where the physical property conditions 4 to 6 are not satisfied simultaneously (Comparative Examples 22 to 27), the above-mentioned trade-off relationship occurs, and thus, each of the initial capacity, cycle retention rate, load retention rate, and expansion rate cannot be improved.

[0309] On the contrary, in the case where the physical property conditions 4 to 6 are satisfied simultaneously (Examples 1, 16 to 21), since the above-mentioned trade-off relationship is broken, each of the initial capacity, cycle retention rate, load retention rate, and expansion rate can be improved.

[0310] [Summary]

[0311] As can be seen from the results shown in Table 2 and Table 3, if the positive electrode active material layer 21B contains a layered rock salt type lithium nickel composite oxide as the positive electrode active material, the analysis results (concentration ratios X, Y, and relative ratio Z) of the positive electrode 21 (positive electrode active material layer 21B) using XPS simultaneously satisfy the physical property conditions 1 to 3, and the analysis results (intensity ratios IBN, ISN, IFN) of the positive electrode 21 using XPS simultaneously satisfy the physical property conditions 4 to 6, then each of the initial capacity characteristics, cycle characteristics, load characteristics, and swelling characteristics can be improved. Therefore, excellent battery characteristics can be obtained in the secondary battery.

[0312] As described above, although one embodiment and examples have been used to illustrate the present technology, the structure of the present technology is not limited to the structure described in one embodiment and examples, and various modifications can be made.

[0313] Specifically, although the case where the battery structure of the secondary battery is a laminated film type has been described, the battery structure is not particularly limited, and thus can be a cylindrical type, a square type, a coin type, a button type, etc.

[0314] In addition, although the case where the element structure of the battery element is a wound type has been described, the element structure of the battery element is not particularly limited, and thus a laminated type in which electrodes (positive electrode and negative electrode) are laminated, a repeatedly folded type in which electrodes (positive electrode and negative electrode) are folded in a Z shape, etc. can be adopted.

[0315] Furthermore, although the case where the electrode reaction material is lithium has been described, the electrode reaction material is not particularly limited. Specifically, as described above, the electrode reaction material can be other alkali metals such as sodium and potassium, and can also be alkaline earth metals such as beryllium, magnesium, and calcium. In addition, the electrode reaction material can also be other light metals such as aluminum.

[0316] It should be noted that the use of the above positive electrode is not limited to secondary batteries, and thus the positive electrode can also be applied to other electrochemical devices such as capacitors.

[0317] The effects described in this specification are merely examples, and thus the effects of the present technology are not limited to the effects described in this specification. Therefore, the present technology can also obtain other effects.

Claims

1. A secondary battery comprising a positive electrode including a positive electrode active material layer, a negative electrode, and an electrolyte solution, wherein the positive electrode active material layer contains a layered rock salt type lithium nickel composite oxide represented by the following formula (1), when analyzing the positive electrode active material layer on the surface of the positive electrode active material layer using X-ray photoelectron spectroscopy, the ratio X of the atomic concentration of Al to the atomic concentration of Ni satisfies the condition represented by the following formula (2), when analyzing the positive electrode active material layer at a depth of 100 nm inside the positive electrode active material layer using the X-ray photoelectron spectroscopy, the ratio Y of the atomic concentration of Al to the atomic concentration of Ni satisfies the condition represented by the following formula (3), the ratio Z of the ratio X to the ratio Y satisfies the condition represented by the following formula (4), in the surface analysis of the positive electrode using the X-ray photoelectron spectroscopy, a B1s spectrum, an S2p spectrum, an F1s spectrum, and a Ni3p spectrum are detected, the ratio IBN of the intensity of the B1s spectrum to the intensity of the Ni3p spectrum satisfies the condition represented by the following formula (5), the ratio ISN of the intensity of the S2p spectrum to the intensity of the Ni3p spectrum satisfies the condition represented by the following formula (6), the ratio IFN of the intensity of the F1s spectrum to the intensity of the Ni3p spectrum satisfies the condition represented by the following formula (7), Li a Ni 1-b-c-d Co b Al c M d O e (1) wherein M is at least one of Fe, Mn, Cu, Zn, Cr, V, Ti, Mg, and Zr, and a, b, c, d, and e satisfy 0.8 < a < 1.2, 0.06 ≤ b ≤ 0.18, 0.015 ≤ c ≤ 0.05, 0 ≤ d ≤ 0.08, 0 < e < 3, 0.1 ≤ (b + c + d) ≤ 0.22, and 4.33 ≤ (1 - b - c - d) / b ≤ 15.0, 0.30≤X≤0.70(2) 0.16≤Y≤0.37(3) 1.30≤Z≤2.52(4) 0.9 ≤ IBN ≤ 1.8 (5) 0.4 ≤ ISN ≤ 1.2 (6) 8 ≤ IFN ≤ 13 (7).

2. The secondary battery according to claim 1, wherein d in the formula (1) satisfies d > 0.

3. The secondary battery according to claim 1 or 2, wherein it further includes a flexible outer package member for housing the positive electrode, the negative electrode, and the electrolyte solution.

4. The secondary battery according to any one of claims 1 to 3, wherein the positive electrode further includes a coating film covering the surface of the positive electrode active material layer, the coating film contains B, S, and F as constituent elements, in the surface analysis of the positive electrode using the X-ray photoelectron spectroscopy, the coating film is analyzed.

5. The secondary battery according to any one of claims 1 to 4, wherein the electrolyte solution contains a boron-containing compound, a sulfur-containing compound, and a fluorine-containing compound.

6. The secondary battery according to claim 5, wherein the boron-containing compound contains a boron-containing lithium salt, the sulfur-containing compound contains at least one of cyclic disulfonic anhydride and sulfonic acid alkynyl ester, the fluorine-containing compound contains a fluorine-containing lithium salt.

7. The secondary battery according to any one of claims 1 to 6, wherein the secondary battery is a lithium ion secondary battery.

8. A positive electrode for a secondary battery, comprising a positive electrode active material layer, The positive electrode active material layer contains a layered rock salt type lithium nickel composite oxide represented by the following formula (1), When analyzing the positive electrode active material layer using X-ray photoelectron spectroscopy on the surface of the positive electrode active material layer, the ratio X of the atomic concentration of Al to the atomic concentration of Ni satisfies the condition represented by the following formula (2), When analyzing the positive electrode active material layer using the X-ray photoelectron spectroscopy at a depth of 100 nm inside the positive electrode active material layer, the ratio Y of the atomic concentration of Al to the atomic concentration of Ni satisfies the condition represented by the following formula (3), The ratio Z of the ratio X to the ratio Y satisfies the condition represented by the following formula (4), In the surface analysis using the X-ray photoelectron spectroscopy, B1s spectrum, S2p spectrum, F1s spectrum and Ni3p spectrum are detected, The ratio IBN of the intensity of the B1s spectrum to the intensity of the Ni3p spectrum satisfies the condition represented by the following formula (5), The ratio ISN of the intensity of the S2p spectrum to the intensity of the Ni3p spectrum satisfies the condition represented by the following formula (6), The ratio IFN of the intensity of the F1s spectrum to the intensity of the Ni3p spectrum satisfies the condition represented by the following formula (7), Li a Ni 1-b-c-d Co b Al c M d O e (1) In the formula, M is at least one of Fe, Mn, Cu, Zn, Cr, V, Ti, Mg and Zr, and a, b, c, d and e satisfy 0.8 < a < 1.2, 0.06 ≤ b ≤ 0.18, 0.015 ≤ c ≤ 0.05, 0 ≤ d ≤ 0.08, 0 < e < 3, 0.1 ≤ (b + c + d) ≤ 0.22 and 4.33 ≤ (1 - b - c - d) / b ≤ 15.0, 0.30≤X≤0.70(2) 0.16≤Y≤0.37(3) 1.30≤Z≤2.52(4) 0.9 ≤ IBN ≤ 1.8 (5) 0.4 ≤ ISN ≤ 1.2 (6) 8 ≤ IFN ≤ 13 (7).

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