Secondary battery

Abstract

A secondary battery includes a positive electrode including a positive electrode active material, a negative electrode, and an electrolyte including a polycarbonic compound. The positive electrode active material includes a lithium-nickel complex oxide of a layered rock salt type and a boron compound. A crystallite size of a (104) plane of the positive electrode active material calculated using X-ray diffraction and the Scherrer formula is 40.0 nm or more and 74.5 nm or less. An element concentration ratio calculated based on a B1s spectrum, a Ni2p 3 / 2 spectrum, a Co2p 3 / 2 spectrum, a Mn2p 1 / 2 spectrum, and an Al2s spectrum of the positive electrode active material detected using X-ray photoelectron spectroscopy is 0.15 or more and 0.90 or less.

Description

TECHNICAL FIELD

[0001] The present technology relates to a secondary battery. BACKGROUND

[0002] Since various electronic devices such as mobile phones are becoming widespread, development of a secondary battery as a power source that is small and light and at the same time can obtain a high energy density is being promoted. The secondary battery has a positive electrode and a negative electrode and an electrolyte solution, and various studies have been made on the constitution of the secondary battery.

[0003] Specifically, in order to improve the cycle characteristics and the like, a dinitrile compound is contained in the electrolyte solution (for example, refer to Patent Documents 1 to 3), and in some cases, the dinitrile compound is used in combination with 4-fluoro-1,3-dioxolan-2-one (for example, refer to Patent Document 4). In addition, in order to improve the cycle characteristics and the like, while a lithium-containing composite oxide of a nickel-based is used as a positive electrode active material, the surface of the lithium-containing composite oxide is modified by a surface modification compound containing a specific element (for example, refer to Patent Document 5).

[0004] PRIOR ART DOCUMENTS

[0005] PATENT DOCUMENTS

[0006] Patent Document 1: Japanese Patent Application Publication No. 2013-051207

[0007] Patent Document 2: Japanese Patent Application Publication No. 2012-138335

[0008] Patent Document 3: Japanese Patent Application Publication No. 2008-108586

[0009] Patent Document 4: Japanese Patent Application Laid-Open No. 2016-536776

[0010] Patent Document 5: Japanese Patent Application Laid-Open No. 2015-144108 SUMMARY

[0011] Various studies have been made in order to improve the performance of the secondary battery, but the capacity characteristics, the expansion characteristics, and the cycle characteristics are all insufficient, and there is room for improvement.

[0012] The present technology was completed in view of such a point, and aims to provide a secondary battery that can obtain excellent capacity characteristics, excellent expansion characteristics, and excellent cycle characteristics.

[0013] The secondary battery of one embodiment of the present technology includes a positive electrode including a positive electrode active material, a negative electrode, and an electrolyte including a polycarbonitrile compound. The positive electrode active material includes a lithium-nickel composite oxide of a layered rock salt type represented by the following formula (1) and a boron compound. The crystallite size of the (104) plane of the positive electrode active material calculated using X-ray diffraction and the Scherrer formula is greater than or equal to 40.0 nm and less than or equal to 74.5 nm. The element concentration ratio represented by the following formula (2) calculated from the B1s spectrum, the Ni2p 3 / 2 spectrum, the Co2p 3 / 2 spectrum, the Mn2p 1 / 2 spectrum, and the Al2s spectrum is greater than or equal to 0.15 and less than or equal to 0.90.

[0014] Li a Ni 1-b M b O c …(1)

[0015] (M is at least one of Co, Fe, Mn, Cu, Zn, Al, Cr, V, Ti, Mg, and Zr. a, b, and c satisfy 0.8 < a < 1.2, 0 ≤ b ≤ 0.5, and 0 < c < 3.)

[0016] R = I2 / I1 … (2)

[0017] (R is an element concentration ratio. I1 is the Ni concentration (atomic %) calculated from the Ni2p 3 / 2 spectrum, the Co2p 3 / 2 spectrum, the Mn2p 1 / 2 spectrum, and the Al2s spectrum. I2 is the B concentration (atomic %) calculated from the B1s spectrum.)

[0018] Here, the "polycarbonitrile compound" refers to a general term for a compound including two or more nitrile groups (-CN). In addition, the "boron compound" refers to a general term for a compound including boron as a constituent element. Note that details of the polycarbonitrile compound and the boron compound will be described later.

[0019] According to the secondary battery of one embodiment of the present technology, the positive electrode active material of the positive electrode includes a lithium-nickel composite oxide and a boron compound, the electrolyte includes a polycarbonitrile compound, the crystallite size of the (104) plane of the positive electrode active material is greater than or equal to 40.0 nm and less than or equal to 74.5 nm, and the element concentration ratio of the positive electrode active material is greater than or equal to 0.15 and less than or equal to 0.90, whereby excellent capacity characteristics, excellent expansion characteristics, and excellent cycle characteristics can be obtained.

[0020] Note that the effects of the present technology are not necessarily limited to those described here, and can be any of a series of effects related to the present technology described later. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a perspective view showing the configuration of a secondary battery of one embodiment of the present technology.

[0022] Figure 2 is a perspective view showing the configuration of a battery element shown in Figure 1

[0023] Figure 3 is a plan view showing the configuration of a positive electrode current collector shown in Figure 2

[0024] Figure 4 is a plan view showing the configuration of a negative electrode current collector shown in Figure 2

[0025] Figure 5 is a plan view schematically showing the configuration of a positive electrode active material.

[0026] Figure 6 is a perspective view showing the configuration of a secondary battery of Modification 1.

[0027] Figure 7 is a block diagram showing the configuration of an application example of a secondary battery. DETAILED DESCRIPTION

[0028] Hereinafter, one embodiment of the present technology will be described in detail with reference to the drawings. Note that the order of description is as follows.

[0029] 1. Secondary battery

[0030] 1-1. Configuration

[0031] 1-1-1. Configuration of secondary battery

[0032] 1-1-2. Physical properties of positive electrode active material

[0033] 1-2. Operation

[0034] 1-3. Manufacturing method

[0035] 1-3-1. Manufacturing method of positive electrode active material

[0036] 1-3-2. Manufacturing method of secondary battery

[0037] 1-4. Action and effect

[0038] 2. Modification

[0039] ​​​3. Uses of secondary batteries

[0040] <1. Secondary Battery>

[0041] First, a secondary battery according to one embodiment of this technology will be described.

[0042] The secondary battery described here utilizes the adsorption and release of electrode reactants to obtain battery capacity. It includes a positive electrode, a negative electrode, and an electrolyte in liquid form. In this secondary battery, to prevent the deposition of electrode reactants on the surface of the negative electrode during charging, 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 that of the positive electrode per unit area.

[0043] There are no particular restrictions on the types of substances used in the electrode reactions, but specifically, they are light metals such as alkali metals and alkaline earth metals. Alkali metals include lithium, sodium, and potassium, while alkaline earth metals include beryllium, magnesium, and calcium.

[0044] The following examples illustrate the use of lithium as the electrode reactant. A secondary battery that utilizes the adsorption and release of lithium to obtain battery capacity is called a lithium-ion secondary battery. In this type of lithium-ion secondary battery, lithium is adsorbed and released in ionic form.

[0045] <1-1. Composition>

[0046] Here, after explaining the structure of the secondary battery, the physical properties of the positive electrode active material will be explained.

[0047] <1-1-1. The Composition of a Secondary Battery>

[0048] Figure 1 This diagram shows the three-dimensional configuration of a secondary battery 10, which is a secondary battery according to one embodiment of the present technology. Figure 2 express Figure 1 The cross-sectional structure of the battery element 20 shown is as follows. Figure 3 express Figure 2 The planar configuration of the positive current collector 21A shown is as follows, and at the same time Figure 4 express Figure 2 The planar configuration of the negative current collector 22A is shown.

[0049] Among them, Figure 1 The image shows the battery element 20 separated from the outer packaging film 30 (film components 30A, 30B). Figure 2 Multiple positive current collectors 21A are shown in the figure. Figure 3 The exposed portions 21N shown are in their state before they are joined together, while multiple negative current collectors 22A are also shown. Figure 4 The exposed portions 22N shown are in their state before they are joined together.

[0050] like Figure 1 As shown, the secondary battery 10 includes a battery element 20, an outer packaging film 30, a positive electrode lead 41, and a negative electrode lead 42. The secondary battery 10 described here is a laminated film type non-aqueous electrolyte secondary battery, using a flexible (or supple) outer packaging component (outer packaging film 30) to house the battery element 20. This secondary battery 10 enables miniaturization, weight reduction, and thinning.

[0051] [Outer packaging film]

[0052] As described above, the outer packaging film 30 houses the battery element 20, and therefore houses the positive electrode 21 and negative electrode 22, as well as the electrolyte, which will be described later.

[0053] like Figure 1 As shown, the outer packaging film 30 includes two separate film-shaped components (film components 30A and 30B), which overlap each other with the battery element 20 in between. The outer peripheral portions of the four sides of each of the film components 30A and 30B are bonded to each other, thus forming an adhesive portion at the periphery of the outer packaging film 30. Therefore, the outer packaging film 30 has a bag-like structure capable of sealing the battery element 20 inside. It should be noted that a recessed portion 31 (so-called deep-drawn portion) for accommodating the battery element 20 is provided in the film component 30A.

[0054] Specifically, membrane components 30A and 30B are each a three-layer laminate consisting of a weld layer, a metal layer, and a surface protective layer, stacked sequentially from the inside. In this case, with membrane components 30A and 30B overlapping each other, the outer peripheral portions of the four sides of the opposing weld layers are welded together. The weld layer contains a polymer compound such as polypropylene. The metal layer contains a metal material such as aluminum. The surface protective layer contains a polymer compound such as nylon. The outer peripheral portions of the four sides of the opposing weld layers can also be bonded together using an adhesive.

[0055] The composition (number of layers) of the outer packaging film 30 is not particularly limited, so it can be one or two layers, or even four or more layers. That is, the outer packaging film 30 is not limited to laminated film, but can also be a single-layer film.

[0056] A sealing film 33 is inserted between the outer packaging film 30 and the positive electrode lead 41, while a sealing film 34 is inserted between the outer packaging film 30 and the negative electrode lead 42. The sealing films 33 and 34 are each components that prevent external gases from entering the interior of the outer packaging film 30, and include any one or more polymeric compounds such as polyolefins that provide sealing for each of the positive electrode lead 41 and the negative electrode lead 42. The polyolefin is polyethylene, polypropylene, modified polyethylene, or modified polypropylene, etc. One or both of the sealing films 33 and 34 may be omitted.

[0057] [Battery element]

[0058] As shown in Figure 1 and Figure 2 , a battery element 20 is housed inside an outer packaging film 30, and includes a positive electrode 21, a negative electrode 22, a separator 23, and an electrolyte (not shown). The battery element 20 has a main surface 20A and a main surface 20B on the opposite side of the main surface 20A, the main surface 20A having an edge portion 20C in a long side direction and an edge portion 20D in a short side direction. The electrolyte is impregnated in each of the positive electrode 21, the negative electrode 22, and the separator 23.

[0059] Here, the battery element 20 is a structure in which the positive electrode 21 and the negative electrode 22 are alternately stacked with the separator 23 interposed therebetween (a stacked electrode body). Thus, the positive electrode 21 and the negative electrode 22 face each other with the separator 23 interposed therebetween.

[0060] (Positive electrode)

[0061] As shown in Figure 2 , the positive electrode 21 includes a positive electrode current collector 21A having a pair of surfaces and two positive electrode active material layers 21B formed on both surfaces of the positive electrode current collector 21A. Of these, the positive electrode active material layer 21B can be formed on only one surface of the positive electrode current collector 21A.

[0062] As shown in Figure 3 , the positive electrode current collector 21A includes a formed portion 21M in which the positive electrode active material layer 21B is formed and an exposed portion 21N in which the positive electrode active material layer 21B is not formed. As described above, the positive electrode active material layer 21B is formed on both surfaces of the formed portion 21M. The exposed portion 21N is a portion that is provided so as to protrude from a part of the formed portion 21M and has a width that is narrower than that (a dimension in the X-axis direction) of the formed portion 21M. Of these, as shown by the double-dotted line in Figure 3 , the exposed portion 21N can have the same width as that of the formed portion 21M. The plurality of exposed portions 21N are joined to each other, and thus the positive electrode lead 41 is connected to the plurality of exposed portions 21N that are joined to each other.

[0063] The positive electrode current collector 21A contains any one or two or more of a conductive material such as a metal material, which is aluminum, nickel, stainless steel, or the like. The positive electrode active material layer 21B contains any one or two or more of a positive electrode active material that can occlude and release lithium, and can further contain a positive electrode binder, a positive electrode conductive agent, or the like. The method of forming the positive electrode active material layer 21B is not particularly limited, but is specifically any one or two or more of a coating method or the like.

[0064] The positive electrode active material contains a lithium-containing compound, and more specifically, the positive electrode active material contains a lithium-nickel composite oxide and a boron compound. This is because, while achieving a high energy density, decomposition reactions of the electrolyte solution caused by the positive electrode 21 at the time of charge and discharge are suppressed. Thus, a high battery capacity can be obtained even if the voltage is low. In addition, since the generation of gas caused by decomposition reactions of the electrolyte solution at the time of charge and discharge is suppressed, the secondary battery is less likely to expand. Furthermore, the decomposition reactions of the electrolyte solution are suppressed, so the discharge capacity is less likely to decrease even if the charge and discharge are repeated.

[0065] The lithium-nickel composite oxide contains any one or two or more of the compounds represented by the following formula (1). Here, the composition of lithium is different depending on the state of charge and discharge, and the value of a represents the value in the fully discharged state.

[0066] Li a Ni 1-b M b O c …(1)

[0067] (M is at least one of Co, Fe, Mn, Cu, Zn, Al, Cr, V, Ti, Mg, and Zr. a, b, and c satisfy 0.8

[0068] As is clear from formula (1), the lithium-nickel composite oxide is an oxide containing lithium and nickel as constituent elements, and further contains an additional metal element (M).

[0069] As is clear from the range of the value of b (0

[0070] The content of nickel (the value of 1-b) is determined depending on the content of the additional metal element (M) (the value of b). In this case, as described above, the value of b is not particularly limited as long as it satisfies the condition of 0

[0071] Here, b preferably satisfies 0.1

[0072] Specific examples of the lithium-nickel composite oxide are LiNiO2, LiNi0.50 Co 0.20 Al 0.30 O2, LiNi 0.60 Co 0.20 Al 0.20 O2, LiNi 0.80 Co 0.15 Al 0.05 O2, LiNi 0.90 Co 0.07 Al 0.03 O2, LiNi 0.92 Co 0.05 Al 0.03 O2, LiNi 0.50 Co 0.20 Mn 0.30 O2 and LiNi 0.60 Co 0.20 Mn 0.20 O2, etc. Among them, the specific examples of lithium nickel composite oxides can be other compounds not shown here, as long as they meet the conditions shown in formula (1).

[0073] As mentioned above, "boron compounds" refers to the general term for compounds that contain boron as a constituent element. Specific examples of boron compounds are any one or more of boric acid (H3BO3), lithium tetraborate (Li2B4O7), ammonium pentaborate (NH4B5O8), lithium metaborate (LiBO2), and boron oxide (B2O3).

[0074] The specific composition of the positive electrode active material comprising lithium nickel composite oxide and boron compound is not particularly limited. Here, as described later, the surface of the lithium nickel composite oxide is covered with boron compound. That is, the positive electrode active material comprises lithium nickel composite oxide and boron compound covering the surface of the lithium nickel composite oxide. This is because the surface electrochemical stabilization of the lithium nickel composite oxide makes it easier to suppress the decomposition reaction of the electrolyte on the surface of the lithium nickel composite oxide.

[0075] To improve the performance of the secondary battery 10, the positive electrode active material, comprising lithium-nickel composite oxide and boron compound, has specified physical properties. Details regarding the physical properties of the positive electrode active material will be described later.

[0076] It should be noted that, in addition to containing the aforementioned lithium-nickel composite oxides and boron compounds, the positive electrode active material may also contain one or more other lithium-containing compounds. These other lithium-containing compounds can be lithium-containing compounds with a layered rock salt crystal structure, lithium-containing compounds with a spinel crystal structure, or lithium-containing compounds with an olivine crystal structure. Specific examples of other lithium-containing compounds with a layered rock salt crystal structure are lithium composite oxides such as LiCoO2. Specific examples of lithium-containing compounds with a spinel crystal structure are lithium composite oxides such as LiMn2O4. Specific examples of lithium-containing compounds with an olivine crystal structure are LiFePO4, LiMnPO4, and LiMn... 0.5 Fe 0.5 Lithium phosphate compounds such as PO4.

[0077] In addition, the positive electrode active material may also contain one or more compounds that do not contain lithium as a constituent element (non-lithium compounds). Specific examples of non-lithium compounds are MnO2, V2O5, and V6O. 13 Inorganic compounds such as NiS and MoS.

[0078] The positive electrode binder comprises one or more polymeric materials such as polyvinylidene fluoride, polytetrafluoroethylene, polyacrylonitrile, styrene-butadiene rubber, and carboxymethyl cellulose. However, the positive electrode binder can also be a copolymer of two or more polymeric materials.

[0079] The positive electrode conductive agent includes any one or more carbon materials such as graphite, carbon black, and Ketjen black. However, the positive electrode conductive agent can be a metallic material or a conductive polymer material, as long as it is a conductive material.

[0080] (negative electrode)

[0081] like Figure 2 As shown, the negative electrode 22 includes a negative electrode current collector 22A with one side facing each other and two negative electrode active material layers 22B formed on both sides of the negative electrode current collector 22A. Alternatively, the negative electrode active material layer 22B may be disposed on only one side of the negative electrode current collector 22A.

[0082] like Figure 4 As shown, the negative electrode current collector 22A includes a forming portion 22M in which a negative electrode active material layer 22B is formed, and an exposed portion 22N in which the negative electrode active material layer 22B is not formed. As described above, the negative electrode active material layer 22B is formed on both sides of the forming portion 22M. The exposed portion 22N is a portion that extends outward from a part of the forming portion 22M and has a width narrower than the width (dimension in the X-axis direction) of the forming portion 22M. The exposed portion 22N is arranged in a manner that does not overlap with the exposed portion 21N. Wherein, as Figure 4The exposed portions 22N can have the same width as the width of the formed portions 22M, as indicated by the double-dot chain line. Since the plurality of exposed portions 22N are engaged with each other, the negative electrode lead 42 is connected to the plurality of exposed portions 22N engaged with each other.

[0083] The negative electrode current collector 22A includes any one or two or more of a conductive material such as a metal material, which is copper, aluminum, nickel, stainless steel, or the like. The negative electrode active material layer 22B includes any one or two or more of a negative electrode active material capable of occluding and releasing lithium, and can further include a negative electrode binder and a negative electrode conductive agent, or the like. Details related to the negative electrode binder are the same as details related to the positive electrode binder, and details related to the negative electrode conductive agent are the same as details related to the positive electrode conductive agent. The method of forming the negative electrode active material layer 22B is not particularly limited, but specifically, it is any one or two or more of a coating method, a vapor phase method, a liquid phase method, an atomization method, and a firing method (sintering method), or the like.

[0084] The kind of the negative electrode active material is not particularly limited, but specifically, the negative electrode active material is a carbon material, a metal-based material, or the like. The carbon material is a readily graphitizable carbon, a hardly graphitizable carbon, graphite, or the like, and the graphite is natural graphite, artificial graphite, or the like. The metal-based material is a material including any one or two or more of a metal element and a semi-metal element capable of forming an alloy with lithium, and the metal element and the semi-metal element are silicon, tin, or the like. Among them, the metal-based material can be a single body, can be a compound, can be a mixture of two or more of them, or can be a material including phases of two or more of them.

[0085] Specific examples of the metal-based material are SiB4, SiB6, Mg2Si, Ni2Si, TiSi2, MoSi2, CoSi2, NiSi2, CaSi2, CrSi2, Cu5Si, FeSi2, MnSi2, NbSi2, TaSi2, VSi2, WSi2, ZnSi2, SiC, Si3N4, Si2N2O, SiO x (0 < x < 2, preferably 0.2 < x < 1.4), LiSiO, SnO w (0 < w < 2), SnSiO3, LiSnO, and Mg2Sn, or the like.

[0086] Note that the kind of the negative electrode active material can be a metal oxide and a high molecular material, or the like. Specific examples of the metal oxide are a lithium complex oxide, an iron oxide, a ruthenium oxide, a molybdenum oxide, or the like, and the lithium complex oxide is a lithium titanium complex oxide such as lithium titanate (Li4Ti5O 12 ) or the like. Specific examples of the high molecular material are polyacetylene, polyaniline, polypyrrole, or the like.

[0087] (Separator)

[0088] AsFigure 2 The separator 23 is a porous film that is interposed between the positive electrode 21 and the negative electrode 22, prevents contact between the positive electrode 21 and the negative electrode 22, and allows lithium ions to pass therethrough. The separator 23 includes any one or two or more of a high molecular material and a ceramic material. Specific examples of the high molecular material are polyethylene, polypropylene, polytetrafluoroethylene, and the like, and can also be a copolymer of two or more thereof. Note that the separator 23 can be a single layer or multiple layers.

[0089] (Electrolyte)

[0090] The electrolyte includes any one or two or more of a multi-nitrile compound. As described above, the "multi-nitrile compound" refers to a general term for a compound including two or more nitrile groups. This is because the generation of gas due to the decomposition reaction of the electrolyte caused by the positive electrode 21 at the time of charge and discharge is further inhibited, and thus the secondary battery is less likely to expand, and the decomposition reaction of the electrolyte is further inhibited, and thus the capacity is less likely to decrease even if the charge and discharge are repeated.

[0091] In detail, the multi-nitrile compound has the following properties: it is hardly decomposed and remains in the electrolyte at the time of the first charge and discharge (stabilization of the secondary battery described later), and it gradually reacts (decomposes) while forming a coating film on the surface of the positive electrode 21 at the time of the second and subsequent charge and discharge. Thus, even if a fresh surface of the positive electrode active material having high reactivity is generated due to breakage of the positive electrode active material at the time of the second and subsequent charge and discharge, the coating film from the multi-nitrile compound is formed so as to cover the fresh surface, and thus the decomposition reaction of the electrolyte in the fresh surface is inhibited, and the generation of unnecessary gas due to the decomposition reaction of the electrolyte is also inhibited. The breakage of the positive electrode active material includes not only breakage of the positive electrode active material, but also generation of cracks and the like in the positive electrode active material. Thus, even if the charge and discharge are repeated at the time of the second and subsequent charge and discharge, the secondary battery is less likely to expand, and the discharge capacity is less likely to decrease.

[0092] The multi-nitrile compound includes two or more nitrile groups and a central group that bonds the two or more nitrile groups. Since the type of the central group is not particularly limited, it can be a chain hydrocarbon group, a cyclic hydrocarbon group, or a group in which one or two or more chain hydrocarbon groups and one or two or more cyclic hydrocarbon groups are bonded to each other.

[0093] Note that the chain hydrocarbon group can be linear or branched, and can include one or two or more side chains, and the cyclic hydrocarbon group can include one ring or two or more rings. In addition, each of the chain hydrocarbon group and the cyclic hydrocarbon group can include one or two or more unsaturated carbon bonds (>C=C<), and each of the chain hydrocarbon group and the cyclic hydrocarbon group can have one or two or more ether bonds (-O-).

[0094] Specifically, the polycarbonitrile compound is a dicarbonitrile compound and a tricarbonitrile compound, etc. The dicarbonitrile compound contains two nitrile groups, while the tricarbonitrile compound contains three nitrile groups. Of course, the polycarbonitrile compound can also be a compound containing four or more nitrile groups.

[0095] Specific examples of the dicarbonitrile compound are succinonitrile (carbon number = 2), glutaronitrile (carbon number = 3), adiponitrile (carbon number = 4), pimelonitrile (carbon number = 5), suberonitrile (carbon number = 6), and sebaconitrile (carbon number = 8), etc. The specific examples of the series of dicarbonitrile compounds described herein contain a chain-like saturated hydrocarbon group (alkylene group) as a central group, and the carbon number in parentheses indicates the carbon number of the alkylene group. In addition, a specific example of the dicarbonitrile compound is ethylene glycol bis(propionitrile) ether, etc. This ethylene glycol bis(propionitrile) ether contains a chain-like saturated hydrocarbon group (alkylene group) with two ether bonds introduced thereinto as a central group.

[0096] Specific examples of the tricarbonitrile compound are 1,3,5-cyclohexanetricarbonitrile and 1,3,6-hexanetricarbonitrile, etc. The 1,3,5-cyclohexanetricarbonitrile contains a cyclic saturated hydrocarbon group as a central group, while the 1,3,6-hexanetricarbonitrile contains a branched chain saturated hydrocarbon group as a central group.

[0097] Among them, the electrolytic solution preferably contains two or more kinds of polycarbonitrile compounds different from each other. This is because the decomposition rate of the polycarbonitrile compound differs mainly depending on the carbon number of the central group (length of carbon chain). By using two or more kinds of polycarbonitrile compounds different from each other in combination, the coating film from the polycarbonitrile compound is easily formed continuously compared to the case where only one kind of polycarbonitrile compound is used. Thus, the secondary battery is stable and difficult to swell, and the discharge capacity is stable and difficult to decrease.

[0098] Specifically, the polycarbonitrile compound preferably contains one or both of a dicarbonitrile compound and a tricarbonitrile compound. This is because the coating film from the polycarbonitrile compound is easily formed, and thus the secondary battery is difficult to swell sufficiently, and the discharge capacity is difficult to decrease sufficiently.

[0099] The content of the polycarbonitrile compound in the electrolytic solution is not particularly limited, and is preferably 0.5 to 3.0% by weight, and more preferably 1.5 to 2.0% by weight. This is because the coating film from the polycarbonitrile compound is easily formed, and thus the secondary battery is more difficult to swell, and the discharge capacity is more difficult to decrease. Among them, in the case where two or more kinds of polycarbonitrile compounds different from each other are used in combination, the content of the polycarbonitrile compound described above is the sum of the contents of the respective polycarbonitrile compounds.

[0100] Note that the electrolytic solution can also contain a solvent and an electrolyte salt, as long as it contains the polycarbonitrile compound described above.

[0101] The solvent includes any one or two or more of nonaqueous solvents (organic solvents), and the electrolyte solution including the nonaqueous solvent is a so-called nonaqueous electrolyte solution. The nonaqueous solvent is an ester-based compound, an ether-based compound, or the like, and more specifically, the nonaqueous solvent is a carbonate-based compound, a carboxylate-based compound, a lactone-based compound, or the like. This is because the dissociation property of the electrolyte salt is improved, and a high ion mobility can be obtained.

[0102] Specifically, the carbonate-based compound is a cyclic carbonate and a chain carbonate, or the like. Specific examples of the cyclic carbonate are ethylene carbonate and propylene carbonate, or the like, and specific examples of the chain carbonate are dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, or the like.

[0103] The carboxylate-based compound is a carboxylate, or the like. Specific examples of the carboxylate are ethyl acetate, ethyl propionate, propyl propionate, and ethyl trimethyl acetate, or the like.

[0104] The lactone-based compound is a lactone, or the like. Specific examples of the lactone are γ-butyrolactone and γ-valerolactone, or the like. Note that the ether-based compound can be 1,2-dimethoxyethane, tetrahydrofuran, 1,3-dioxolane, 1,4-dioxane, or the like, in addition to the above-described lactone-based compound.

[0105] In addition, the nonaqueous solvent can be an unsaturated cyclic carbonate, a halogenated carbonate, a sulfonate, a phosphate, an anhydride, a mononitrile compound, an isocyanate compound, or the like. This is because the chemical stability of the electrolyte solution is improved.

[0106] Specific examples of the unsaturated cyclic carbonate are vinylene carbonate (1,3-dioxol-2-one), vinyl ethylene carbonate (4-vinyl-1,3-dioxolan-2-one), and methylene ethylene carbonate (4-methylene-1,3-dioxolan-2-one), or the like. Specific examples of the halogenated carbonate are monofluoro ethylene carbonate (4-fluoro-1,3-dioxolan-2-one) and difluoro ethylene carbonate (4,5-difluoro-1,3-dioxolan-2-one), or the like. Specific examples of the sulfonate are 1,3-propane sultone and 1,3-propylene sultone, or the like. Specific examples of the phosphate are trimethyl phosphate and triethyl phosphate, or the like.

[0107] The anhydride is a cyclic dicarboxylic anhydride, a cyclic disulfonic anhydride, and a cyclic carboxylic sulfonic anhydride, or the like. Specific examples of the cyclic dicarboxylic anhydride are succinic anhydride, glutaric anhydride, and maleic anhydride, or the like. Specific examples of the cyclic disulfonic anhydride are 1,2-ethane disulfonic anhydride and 1,3-propane disulfonic anhydride, or the like. Specific examples of the cyclic carboxylic sulfonic anhydride are sulfobenzoic anhydride, sulfopropionic anhydride, and sulfobutyric anhydride, or the like.

[0108] Specific examples of the mononitrile compound are acetonitrile, or the like. Specific examples of the isocyanate compound are hexamethylene diisocyanate, or the like.

[0109] Electrolyte salts include one or more of light metal salts such as lithium salts. Specific examples of lithium salts are lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(fluorosulfonyl)imide (LiN(FSO2)2), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF3SO2)2), lithium tri(trifluoromethanesulfonyl)methyl (LiC(CF3SO2)3), lithium difluorooxalateborate (LiBF2(C2O4)), and lithium bis(oxalate)borate (LiB(C2O4)2), etc.

[0110] The content of the electrolyte salt is not particularly limited, but specifically it is 0.3 mol / kg to 3.0 mol / kg relative to the solvent. This is because it allows for high ionic conductivity.

[0111] [Positive and negative leads]

[0112] The positive lead 41 is the positive terminal connected to the positive electrode 21 (a plurality of exposed portions 21N joined together), and contains one or more conductive materials such as aluminum. The negative lead 42 is the negative terminal connected to the negative electrode 22 (a plurality of exposed portions 22N joined together), and contains one or more conductive materials such as copper, nickel, and stainless steel. The shape of the positive lead 41 and the negative lead 42 is not particularly limited, but specifically, it can be one or more of the following: a thin plate shape and a mesh shape.

[0113] Here, as Figure 1 As shown, the positive electrode lead 41 and the negative electrode lead 42 are each led out from the inside of the outer packaging film 30 towards the outside in a common direction. However, the positive electrode lead 41 and the negative electrode lead 42 can also be led out in different directions.

[0114] In addition, such as Figure 1 As shown, the number of positive leads 41 is one. However, the number of positive leads 41 is not particularly limited, and therefore can be two or more. In particular, when the number of positive leads 41 is two or more, the resistance of the secondary battery decreases. The explanation regarding the number of positive leads 41 is the same as the explanation regarding the number of negative leads 42; therefore, the number of negative leads 42 is not limited to one, and can also be two or more.

[0115] <1-1-2. Physical Properties of Positive Electrode Active Materials>

[0116] Figure 5 The planar configuration of the positive electrode active material 100 is schematically shown, in which, as described above, the surface of the lithium-nickel composite oxide is covered with a boron compound. Therefore, as... Figure 5 As shown, the positive electrode active material 100 includes a central portion 110 and a covering portion 120.

[0117] The center portion 110 is a plurality of particles containing a lithium-nickel composite oxide. The covering portion 120 covers the surface of the center portion 110 and contains a boron compound. As shown in FIG. 1, the covering portion 120 covers the entire surface of the center portion 110. Here, the covering portion 120 can cover only a part of the surface of the center portion 110. In this case, the covering portion 120 can cover the surface of the center portion 110 at a plurality of positions spaced apart from each other. Figure 5

[0118] In the positive electrode active material 100, a plurality of primary particles G1 containing a lithium-nickel composite oxide are aggregated, and thus a secondary particle G2 (the center portion 110) is formed from the plurality of primary particles G1. As a result, the surface of the secondary particle G2 is covered with the boron compound (the covering portion 120). Note that it is considered that a part of the boron compound is solid-solved in the primary particle G1.

[0119] [Physical properties]

[0120] Here, as described above, in order to improve the performance of the secondary battery 10, the positive electrode active material 100, that is, the center portion 110 (lithium-nickel composite oxide) whose surface is covered with the covering portion 120 (boron compound) has prescribed physical properties.

[0121] Specifically, the crystallite size Z (nm) of the (104) plane of the positive electrode active material 100 calculated using the X-ray diffraction (XRD) method and the Scherrer formula is 40.0 nm to 74.5 nm.

[0122] In addition, the element concentration ratio R represented by the following formula (2) calculated from the boron (B) 1s spectrum, the nickel (Ni) 2p 3 / 2 spectrum, the cobalt (Co) 2p 3 / 2 spectrum, the manganese (Mn) 2p 1 / 2 spectrum, and the aluminum (Al) 2s spectrum of the positive electrode active material 100 detected using the X-ray Photoelectron Spectroscopy (XPS) method is 0.15 to 0.90. The element concentration ratio R is a parameter indicating the distribution state of boron in the surface of the positive electrode active material 100.

[0123] R = I2 / I1...(2)

[0124] (R is the element concentration ratio. I1 is the intensity of the Ni2p 3 / 2 spectrum, I2 is the intensity of the B 1s spectrum, and R is the element concentration ratio.) 3 / 2 spectrum, I2 is the intensity of the B 1s spectrum, and R is the element concentration ratio.) 1 / 2 ​The sum of the Ni concentration (atomic %), the Co concentration (atomic %), the Mn concentration (atomic %), and the Al concentration (atomic %) calculated from the Al2s spectrum. I2 is the B concentration (atomic %) calculated from the B1s spectrum.

[0125] As described above, the positive electrode active material contains a lithium-nickel composite oxide and a boron compound, and more specifically, the positive electrode active material 100 includes a center portion 110 (lithium-nickel composite oxide) and a covering portion 120 (boron compound).

[0126] In this case, the reason why the two conditions described above with respect to the crystallite size Z and the element concentration ratio R are satisfied at the same time is that the element concentration ratio R is optimized in relation to the crystallite size Z, and thus the surface state (the respective distributions of the boron and the residual lithium component) of the positive electrode active material 100 is optimized. The residual lithium component is a lithium reactant such as lithium carbonate (Li2CO3). Thus, the amount of the residual lithium component is sufficiently suppressed on the surface of the positive electrode active material 100, and the surface of the center portion 110 is sufficiently protected by the covering portion 120.

[0127] Therefore, while the generation of gas caused by the residual lithium component is suppressed, the lithium ion is easily occluded and released in the center portion 110, and at the same time, the decomposition reaction of the electrolyte solution is suppressed on the surface of the center portion 110. In this case, in particular, even if the secondary battery 10 (positive electrode active material 100) is used (charged and discharged) or stored in a high-temperature environment, the decomposition reaction of the electrolyte solution is effectively suppressed.

[0128] Therefore, in the positive electrode 21, not only the generation of gas caused by the decomposition reaction of the electrolyte solution is suppressed, but also the generation of gas caused by the residual lithium component is suppressed, and thus the amount of the generated gas is significantly reduced. Therefore, while the high energy density is maintained, the secondary battery is difficult to significantly expand at the time of charging and discharging, and at the same time, the discharge capacity is difficult to decrease even if the charging and discharging is repeatedly performed.

[0129] Here, the crystallite size Z is preferably 50.0 nm to 70.0 nm, and at the same time, the element concentration ratio R is preferably 0.30 to 0.60. This is because the amount of the generated gas is further reduced, and thus the secondary battery is further difficult to expand at the time of charging and discharging, and at the same time, the discharge capacity is further difficult to decrease even if the charging and discharging is repeatedly performed.

[0130] [Measurement method and measurement conditions]

[0131] The crystallite size Z is a parameter calculated on the basis of the analysis result of the positive electrode active material 100 using XRD, and as described above, is calculated using the Scherrer formula represented by the following formula (3).

[0132] Z = Kλ / B cos θ...(3)

[0133] (K is a constant of the Scherrer. λ is the wavelength of the X-ray (nm). B is the spread (°) based on the half-value width of the crystallite size Z. θ is the Bragg angle, that is, the value of half of the diffraction angle 2θ (°).)

[0134] In the case where the positive electrode active material 100 is analyzed using XRD, a full-automatic multipurpose X-ray diffractometer SmartLab manufactured by Rigaku Corporation can be used. In this case, the following conditions are set: goniometer = SmartLab, accessory = standard χ cradle, monochromator = Bent, scan mode = 2θ / θ, scan type = FT, X-ray = Cu Kα ray, irradiation intensity = 45 kV / 200 mA, incident slit = 1 / 2 deg, light-receiving slit 1 = 1 / 2 deg, light-receiving slit 2 = 0.300 mm, start = 15, stop = 90, step = 0.02. Accordingly, in the Scherrer formula shown in Equation (3), K = 0.89, λ (wavelength of Cu Kα ray) = 0.15418 nm, and B = half-value width.

[0135] In the case where the positive electrode active material 100 is analyzed using XPS, an X-ray photoelectron spectroscopy analyzer Quantera SXM manufactured by ULVAC-PHI, Inc. can be used. In the analysis results of this XPS (B1s spectrum, Ni2p 3 / 2 spectrum, Co2p 3 / 2 spectrum, Mn2p 1 / 2 spectrum, and Al2s spectrum), the peak intensity of a series of spectra is automatically measured. Thus, the B concentration, the Ni concentration, the Co concentration, the Mn concentration, and the Al concentration are calculated (converted) on the basis of the measurement results, and thus the element concentration ratio R is calculated. Note that the range that can be analyzed in the case of using XPS is a narrow range near the surface of the positive electrode active material 100.

[0136] <1-2. Operation>

[0137] During charging of the secondary battery 10, lithium is released from the positive electrode 21, and the lithium is occluded in the negative electrode 22 via the electrolyte. In addition, during discharging of the secondary battery 10, lithium is released from the negative electrode 22, and the lithium is occluded in the positive electrode 21 via the electrolyte. During these charge and discharge, lithium is occluded and released in an ionic state.

[0138] <1-3. Manufacturing method>

[0139] Reference Figure 5 After the manufacturing method of the positive electrode active material 100 is described, the manufacturing method of the secondary battery 10 using the positive electrode active material 100 is described. Figures 1-4

[0140] ​<1-3-1. Method for manufacturing positive electrode active material>

[0141] Here, a method for manufacturing the positive electrode active material 100 including the center portion 110 and the covering portion 120 will be described. In manufacturing the positive electrode active material 100, the following processes are sequentially performed in the order of a precursor preparation process, a first firing process, a water washing process, and a covering process (second firing process) as described below.

[0142] [precursor preparation process]

[0143] First, as raw materials, a supply source of lithium (lithium compound), a supply source of nickel (nickel compound), and a supply source of an additional metal element (M in formula (1)) (additional compound) are prepared as necessary. Hereinafter, a case where the additional compound (additional metal element) is used will be described. The lithium compound can be an inorganic compound or an organic compound, and the kind of the lithium compound can be one kind or two or more kinds. The description of the lithium compound here is the same as the description of the nickel compound and the additional compound.

[0144] Specific examples of the lithium compound as the inorganic compound are lithium hydroxide, lithium carbonate, lithium nitrate, lithium fluoride, lithium chloride, lithium bromide, lithium iodide, lithium chlorate, lithium perchlorate, lithium bromate, lithium iodate, lithium oxide, lithium peroxide, lithium sulfide, lithium hydrosulfide, lithium sulfate, lithium bisulfate, lithium nitride, lithium azide, lithium nitrite, lithium phosphate, lithium dihydrogen phosphate, and lithium bicarbonate, etc. Specific examples of the lithium compound as the organic compound are methyl lithium, vinyl lithium, isopropyl lithium, butyl lithium, phenyl lithium, lithium oxalate, and lithium acetate, etc.

[0145] Subsequently, after dissolving the nickel compound and the additional compound using an aqueous solvent such as pure water, a coprecipitate (nickel complex coprecipitated hydroxide) is obtained using a coprecipitation method. In this case, the mixing ratio of the nickel compound and the additional compound is adjusted according to the composition of the finally obtained center portion 110 (lithium-nickel complex oxide). In addition, as the alkali compound for coprecipitation, any one or two or more kinds of hydroxides such as sodium hydroxide (NaOH) and ammonium hydroxide (NH4OH) are used. Subsequently, the nickel complex coprecipitated hydroxide is washed with water, and then the nickel complex coprecipitated hydroxide is dried.

[0146] Finally, the precursor is obtained by mixing the lithium compound, the nickel complex coprecipitated hydroxide, and the additional compound with each other. In this case, the mixing ratio of the nickel compound, the nickel complex coprecipitated hydroxide, and the additional compound is adjusted according to the composition of the finally obtained center portion 110 (lithium-nickel complex oxide).

[0147] [first firing process]

[0148] The precursor is fired. Thus, a compound (lithium-nickel composite oxide) containing lithium, nickel, and an additional metal element as constituent elements is formed, and thus the center portion 110 containing the lithium-nickel composite oxide is obtained. In the lithium-nickel composite oxide thus obtained, since most of the plurality of primary particles G1 are agglomerated, most of the plurality of primary particles G1 form secondary particles G2.

[0149] The conditions such as the firing temperature are not particularly limited, and thus can be arbitrarily set. Among them, the firing temperature is preferably 650°C to 850°C. This is because the lithium-nickel composite oxide having a stable composition is easily manufactured with good reproducibility.

[0150] In detail, when the firing temperature is lower than 650°C, the lithium compound is difficult to diffuse, and at the same time, the crystal structure of the R3m layered rock salt type is difficult to sufficiently form. On the other hand, when the firing temperature is higher than 850°C, the loss of lithium due to volatilization of the lithium compound is easily caused in the crystal structure of the lithium-nickel composite oxide, and at the same time, the tendency of the composition of the lithium-nickel composite oxide to become a non-stoichiometric composition due to the mixing of other atoms into the lithium-deficient sites (empty sites) is enhanced. The other atoms are nickel (Ni + ) and the like having an ionic radius substantially the same as that of lithium (Li 2+ ).

[0151] Note that when nickel is mixed into the lithium 3d sites, the mixed region of the nickel is a cubic rock salt phase (rock salt region). The rock salt region is electrochemically inert, and at the same time, the nickel mixed into the lithium sites has a property of easily hindering the solid-phase diffusion of the lithium single phase. Thus, the decrease in the performance (including the resistance characteristics) of the secondary battery 10 is easily induced.

[0152] Note that in order to suppress the occurrence of an unnecessary reduction reaction at the time of firing the precursor, it is preferable to fire the precursor in an oxygen atmosphere. The reduction reaction is a reduction reaction of nickel (Ni 3+ → Ni 2+ ) and the like.

[0153] In particular, in the first firing process described here, by adjusting the firing temperature, the crystallite size Z can be controlled.

[0154] [Water washing process]

[0155] The center portion 110 (lithium-nickel composite oxide) is washed with a water-based solvent such as pure water. In this case, the center portion 110 can also be washed mechanically using a blender or the like as needed. The conditions such as the washing time are not particularly limited, and thus can be arbitrarily set.

[0156] [Covering process (second firing process)]

[0157] After the mixture is obtained by mixing the center portion 110 (lithium-nickel composite oxide) and the boron compound with each other, the mixture is fired. In this case, the mixing ratio of the center portion 110 and the boron compound is adjusted so that the amount of boron present in (coverage amount of) the surface of the center portion 110 reaches a desired value. Thus, by fixing the boron compound to the surface of the center portion 110, the covering portion 120 containing the boron compound is formed because the surface of the center portion 110 is covered with the boron compound. Therefore, the positive electrode active material 100 including the center portion 110 (lithium-nickel composite oxide) and the covering portion 120 (boron compound) is obtained.

[0158] In particular, in the covering process (second firing process) described herein, by adjusting the amount of addition of the boron compound, the element concentration ratio R can be controlled, i.e., the state of covering the surface of the lithium-nickel composite oxide with the boron compound can be controlled.

[0159] <1-3-2. Method for manufacturing secondary battery>

[0160] In manufacturing the secondary battery 10, after the positive electrode 21 and the negative electrode 22 are produced and the electrolyte is prepared, the secondary battery is produced using the positive electrode 21, the negative electrode 22, and the electrolyte, as described below.

[0161] [Production of positive electrode]

[0162] First, the positive electrode active material 100 is mixed with a positive electrode binder, a positive electrode conductive agent, and the like to obtain a positive electrode mixture. Subsequently, the positive electrode mixture is dispersed in a solvent for dispersion to prepare a paste-like positive electrode mixture slurry. The kind of the solvent for dispersion is not particularly limited, and is any one or two or more of organic solvents such as N-methyl-2-pyrrolidone. Subsequently, the positive electrode active material layer 21B is formed by applying the positive electrode mixture slurry to both surfaces of the positive electrode current collector 21A (formed portion 21M). Finally, the positive electrode active material layer 21B is compression-molded using a roll press. Thus, the positive electrode active material layer 21B is formed on both surfaces of the positive electrode current collector 21A, and the positive electrode 21 is produced.

[0163] [Production of negative electrode]

[0164] First, a negative electrode active material is mixed with a negative electrode binder and a negative electrode conductive agent, and the like, to obtain a negative electrode mixture. Subsequently, the negative electrode mixture is dispersed in a solvent for dispersion to prepare a paste-like negative electrode mixture slurry. The solvent for dispersion is not particularly limited, and is any one or two or more of organic solvents such as N-methyl-2-pyrrolidone and methyl ethyl ketone. Subsequently, the negative electrode mixture slurry is applied to both surfaces of the negative electrode current collector 22A (formed portion 22M) to form a negative electrode active material layer 22B. Finally, the negative electrode active material layer 22B is compression molded using a roll press. Thus, the negative electrode active material layer 22B is formed on both surfaces of the negative electrode current collector 22A, and thus the negative electrode 22 is produced.

[0165] [Preparation of electrolyte solution]

[0166] After the electrolyte salt is added to the solvent, the polycarbonyl compound is added to the solvent. Thus, the electrolyte salt and the polycarbonyl compound are each dispersed or dissolved in the solvent, and thus the electrolyte solution is prepared.

[0167] [Assembly of secondary battery]

[0168] First, a laminate is formed by alternately stacking the positive electrode 21 and the negative electrode 22 with the separator 23 interposed therebetween. The laminate has the same configuration as that of the battery element 20, except that the electrolyte solution does not penetrate into each of the positive electrode 21, the negative electrode 22, and the separator 23. Subsequently, after the plurality of exposed portions 21N are joined to each other, the plurality of exposed portions 21N that are joined to each other are connected to the positive electrode lead 41. In addition, after the plurality of exposed portions 22N are joined to each other, the plurality of exposed portions 22N that are joined to each other are connected to the negative electrode lead 42. The joining method and the connecting method are not particularly limited, and are any one or two or more of ultrasonic welding, resistance welding, and brazing.

[0169] Subsequently, after the laminate is housed inside the recessed portion 31, the film members 30A, 30B are overlapped with each other with the laminate interposed therebetween. Subsequently, by bonding the outer peripheral edge portions of the three sides other than one side of each of the film members 30A, 30B to each other, the laminate is housed inside the bag-shaped outer packaging film 30. The method of bonding the film members 30A, 30B to each other is not particularly limited, and thus a heat fusion method can be used, or an adhesive can be used.

[0170] Finally, after the electrolytic solution is injected into the inside of the bag-shaped outer packaging film 30, the outer packaging film 30 is sealed by adhering the remaining outer peripheral edge portions of the film members 30A, 30B to each other. In this case, the gasket film 33 is interposed between the outer packaging film 30 (film members 30A, 30B) and the positive electrode lead 41, and the gasket film 34 is interposed between the outer packaging film 30 and the negative electrode lead 42. Thus, the electrolytic solution infiltrates into the laminate, and therefore, while the battery element 20 is produced as a laminated electrode body, the positive electrode lead 41 and the negative electrode lead 42 are drawn out from the inside of the outer packaging film 30 to the outside, and the battery element 20 is accommodated in the inside of the outer packaging film 30. Therefore, the battery element 20 is enclosed in the inside of the outer packaging film 30, and thus the secondary battery 10 is assembled.

[0171] [Stabilization of secondary battery]

[0172] The assembled secondary battery 10 is subjected to charge and discharge. Various conditions such as ambient temperature, number of times of charge and discharge (number of times of cycle), and conditions of charge and discharge can be arbitrarily set. Thus, the coating film is formed on the surface of each of the positive electrode 21 and the negative electrode 22, and therefore, the state of the secondary battery is electrochemically stabilized. Thus, the secondary battery using the outer packaging film 30, that is, the laminate film type secondary battery is completed.

[0173] <1-4. Effects and advantages>

[0174] In the secondary battery 10, the positive electrode active material of the positive electrode 21 contains a lithium-nickel complex oxide and a boron compound, and the electrolytic solution contains a polycarbonic compound. In addition, the crystallite size Z of the (104) plane of the positive electrode active material is 40.0 nm to 74.5 nm, and the element concentration ratio R of the positive electrode active material is 0.15 to 0.90.

[0175] Thus, as described above, the decomposition reaction of the electrolytic solution caused by the positive electrode 21 is suppressed, and therefore, while maintaining a high energy density, the secondary battery is difficult to expand at the time of charge and discharge, and even if the charge and discharge is repeated, the discharge capacity is difficult to decrease. In this case, the coating film from the polycarbonic compound is continuously formed even at the time of charge and discharge after the second time, and therefore, the decomposition reaction of the electrolytic solution is continuously suppressed. In addition, not only the generation of gas caused by the decomposition reaction of the electrolytic solution is suppressed, but also the generation of gas caused by the residual of the residual lithium component is suppressed, and therefore, the amount of generated gas is significantly reduced. Thus, while the capacity of the battery is guaranteed, the secondary battery is difficult to expand at the time of charge and discharge, and even if the charge and discharge is repeated, the discharge capacity is difficult to decrease, and therefore, excellent capacity characteristics, excellent expansion characteristics, and excellent cycle characteristics can be obtained.

[0176] In particular, if the positive electrode active material 100 includes a central portion 110 (lithium-nickel composite oxide) and a covering portion 120 (boron compound), the surface of the lithium-nickel composite oxide is easily electrochemically stabilized. Therefore, the decomposition reaction of the electrolyte on the surface of the lithium-nickel composite oxide is easily suppressed, thus achieving better results.

[0177] In addition, since b in equation (1) satisfies 0.1≤b≤0.2, if 1-b satisfies 0.8≤1-b≤0.9, then while maintaining high energy density, the decomposition reaction of electrolyte caused by positive electrode 21 during charging and discharging is further suppressed, thus achieving better results.

[0178] In addition, if the polynitrile compound contains one or both of the dinitrile compounds such as succinic anhydride and the trinitrile compounds such as ethylene glycol bis(propionitrile) ether, a coating derived from the polynitrile compound is easily formed, thus achieving better results.

[0179] In addition, if the crystallite size Z is 50.0 nm to 70.0 nm, or the element concentration ratio R is 0.30 to 0.60, the amount of gas generated is further reduced, thus achieving better results.

[0180] In addition, if the content of polynitrile compound in the electrolyte is 0.5% to 3.0% by weight, preferably 1.5% to 2.0% by weight, it is easier to form a coating from the polynitrile compound, thus achieving better results.

[0181] Furthermore, if the secondary battery has a flexible outer packaging film 30, and the battery elements 20 (positive electrode 11, negative electrode 12 and electrolyte) are housed inside the outer packaging film 30, then even if an outer packaging film 30 that is prone to expansion is used, the secondary battery will not expand effectively, thus achieving better results.

[0182] In addition, if the secondary battery is a lithium-ion secondary battery, sufficient battery capacity can be stably obtained by utilizing the absorption and release of lithium, thus achieving better results.

[0183] <2. Variations>

[0184] The configuration of the secondary battery 10 described above can be appropriately modified as explained below. It should be noted that any two or more of the variations described below can be combined with each other.

[0185] [Variation Example 1]

[0186] like Figure 1 As shown, two outer packaging films 30 (film components 30A and 30B) are used. However, as with Figure 1 corresponding Figure 6As shown, a single foldable outer packaging film 30 can also be used instead of two outer packaging films 30. This single outer packaging film 30 has a structure in which one side of film component 30A and one side of film component 30B opposite to the side of film component 30A are connected to each other.

[0187] In this case, after folding one outer packaging film 30, the outer periphery portions of three opposite sides of the outer packaging film 30 are joined together, thereby sealing the battery element 20 inside the bag-shaped outer packaging film 30. Similarly, in this case, since the battery element 20 is housed inside the outer packaging film 30, the same effect can be obtained.

[0188] [Variation Example 2]

[0189] A membrane 23 is used as a porous membrane. However, although not specifically illustrated here, a laminated membrane containing layers of polymer compounds may be used instead of the porous membrane 23.

[0190] Specifically, the laminated separator includes: a porous membrane having one and two faces and a polymer compound layer disposed on one or both sides of the porous membrane. This is because the separator improves the adhesion to both the positive electrode 21 and the negative electrode 22, making it difficult for the battery element 20 to shift position. Therefore, even if electrolyte decomposition reactions occur, the secondary battery is unlikely to expand. The polymer compound layer contains polymers such as polyvinylidene fluoride (PVDF). This is because PVDF and similar materials have excellent physical strength and are electrochemically stable.

[0191] It should be noted that one or both of the porous membrane and the polymer compound layer may contain any one or more types of insulating particles. This is because multiple insulating particles dissipate heat during the heating of the secondary battery, thus improving the battery's safety (heat resistance). Insulating particles include inorganic particles and resin particles. Specific examples of inorganic particles include alumina, aluminum nitride, boehmite, silicon dioxide, titanium dioxide, magnesium oxide, and zirconium oxide. Specific examples of resin particles include acrylic resin and styrene resin.

[0192] In the case of fabricating a laminated membrane, after preparing a precursor solution containing a polymer compound and an organic solvent, the precursor solution is coated onto one or both sides of the porous membrane. Alternatively, the porous membrane can be impregnated in the precursor solution. In this case, multiple insulating particles can be added to the precursor solution as needed.

[0193] When using this layered separator, the same effect can be obtained because lithium ions can move between the positive electrode 21 and the negative electrode 22.

[0194] [Variation Example 3]

[0195] An electrolyte layer is used as the electrolyte. However, although not specifically shown in the figure, an electrolyte layer can also be used as the electrolyte instead of the electrolyte.

[0196] In the battery element 20 using the electrolyte layer, the positive electrode 21 and the negative electrode 22 are stacked with the separator 23 and the electrolyte layer interposed therebetween. The electrolyte layer is interposed between the positive electrode 21 and the separator 23, and also interposed between the negative electrode 22 and the separator 23.

[0197] Specifically, the electrolyte layer contains an electrolyte and a high molecular compound, and the electrolyte is held by the high molecular compound in the electrolyte layer. This is because leakage of the electrolyte is prevented. The electrolyte is as described above. The high molecular compound contains polyvinylidene fluoride or the like. In forming the electrolyte layer, a precursor solution containing the electrolyte, the high molecular compound, and an organic solvent or the like is prepared, and the precursor solution is applied to one or both surfaces of the positive electrode 21 and the negative electrode 22.

[0198] Even in the case where the electrolyte layer is used, lithium ions can move between the positive electrode 21 and the negative electrode 22 with the electrolyte layer interposed therebetween, and thus the same effects can be obtained.

[0199] <3. Uses of the secondary battery>

[0200] Next, the uses (application examples) of the secondary battery described above will be described.

[0201] The use of the secondary battery is not particularly limited as long as it is mainly a machine, a device, an apparatus, a system (an assembly of a plurality of machines or the like), or the like, which can use the secondary battery as a power source for driving or a power storage source for power accumulation or the like. The secondary battery used as the power source can be a main power source or an auxiliary power source. The main power source is a 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 that is used instead of the main power source or a power source that is switched from the main power source as needed. In the case where the secondary battery is used as the auxiliary power source, the type of the main power source is not limited to the secondary battery.

[0202] Specific examples of the use of the secondary battery are as follows. Electronic equipment (including portable electronic equipment) such as a video recorder, a digital camera, a mobile phone, a notebook computer, a cordless phone, a stereo headset, a portable radio, a portable television, and a portable information terminal. Portable living apparatus such as an electric shaver. Storage devices such as a backup power source and a memory card. Electric power tools such as a power drill and a power saw. A battery pack mounted as a detachable power source on a notebook computer or the like. Medical electronic equipment such as a pacemaker and a hearing aid. Electric vehicles such as an electric automobile (including a hybrid automobile). A power storage system such as a household battery system that accumulates power in advance for emergency situations or the like.

[0203] Secondary batteries are effective in applications such as electronic devices, battery packs, electric vehicles, energy storage systems, and power tools. Battery packs can use single cells or battery arrays. Electric vehicles are vehicles that operate (drive) using secondary batteries as a power source; as mentioned above, they are automobiles (hybrid vehicles, etc.) that also possess a power source other than the secondary battery. Energy storage systems are systems that use secondary batteries as a source of energy storage. In household energy storage systems, electricity is stored in the secondary batteries, which serve as the energy storage source, allowing the use of household electrical products, etc.

[0204] Here, specific application examples of secondary batteries will be explained. The following application examples are only examples and can be modified as appropriate.

[0205] Figure 7 This describes the frame structure of the battery pack. The battery pack described here is a simplified type (so-called pouch) that uses a single rechargeable battery and is used in electronic devices such as smartphones.

[0206] like Figure 7 As shown, the battery pack includes a power supply 61 and a circuit board 62. The circuit board 62 is connected to the power supply 61 and includes a positive terminal 63, a negative terminal 64, and a temperature sensing terminal 65. The temperature sensing terminal 65 is a so-called T-terminal.

[0207] The power supply 61 includes a secondary battery. In this secondary battery, the positive lead is connected to the positive terminal 63, and the negative lead is connected to the negative terminal 64. The power supply 61 can be connected to an external source via the positive terminal 63 and the negative terminal 64, thus enabling charging and discharging. The circuit board 62 includes a control unit 66, a switch 67, a thermistor (Positive Temperature Coefficient (PTC) element) 68, and a temperature detection unit 69. However, the PTC element 68 may be omitted.

[0208] The control unit 66 includes a central processing unit (CPU) and memory, and controls the overall operation of the battery pack. The control unit 66 detects and controls the operating status of the power supply 61 as needed.

[0209] Note that if the battery voltage of the power supply 61 (secondary battery) reaches the overcharge detection voltage or the overdischarge detection voltage, the control section 66 causes the switch 67 to be cut off so that the current path of the power supply 61 does not flow with the charge current. In addition, when a large current flows at the time of charging or discharging, the control section 66 blocks the charge current by causing the switch 67 to be cut off. The overcharge detection voltage and the overdischarge detection voltage are not particularly limited. If one example is cited, the overcharge detection voltage is 4.2 V ± 0.05 V, and the overdischarge detection voltage is 2.4 V ± 0.1 V.

[0210] The switch 67 includes a charge control switch, a discharge control switch, a charge diode, a discharge diode, and the like, and switches whether the power supply 61 is connected to the external device or not in accordance with the instruction of the control section 66. The switch 67 includes a Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) or the like, and the charge and discharge currents are detected on the basis of the on-resistance of the switch 67.

[0211] The temperature detection section 69 includes a temperature detection element such as a thermistor, and measures the temperature of the power supply 61 using the temperature detection terminal 65, and outputs the measurement result of the temperature to the control section 66. The measurement result of the temperature measured by the temperature detection section 69 is used in the case where the control section 66 performs charge and discharge control at the time of abnormal heat generation, and in the case where the control section 66 performs correction processing at the time of calculation of the remaining capacity, and the like.

[0212] Embodiment

[0213] An embodiment of the present technology will be described.

[0214] (Experimental Examples 1 to 24)

[0215] Synthesis Figure 5 The positive electrode active material 100 shown in the drawing was synthesized, and the secondary battery 10 (lithium ion secondary battery) of the laminate film type shown in the drawing was manufactured. Figures 1-4 After the secondary battery 10 (lithium ion secondary battery) of the laminate film type shown in the drawing was manufactured, the performance of the secondary battery 10 was evaluated.

[0216] [Synthesis of Positive Electrode Active Material]

[0217] The positive electrode active material 100 was synthesized in the following order.

[0218] In the precursor production step, first, after a nickel compound (nickel sulfate (NiSO4)) and an additional compound (cobalt sulfate (CoSO4)) are put into an aqueous solvent (pure water), the aqueous solvent is stirred, thereby obtaining a mixed aqueous solution. In this case, the mixing ratio of the nickel compound and the cobalt compound (molar ratio of nickel to cobalt) is adjusted so that the composition of the lithium nickel composite oxide finally obtained is the composition shown in Tables 1 and 2.

[0219] Subsequently, while the mixed aqueous solution is stirred, an alkaline compound (sodium hydroxide (NaOH) and ammonium hydroxide (NH4OH)) is added to the mixed aqueous solution, thereby obtaining a plurality of particulate precipitates (secondary particles G2 of nickel-cobalt composite coprecipitated hydroxide) using a coprecipitation method.

[0220] Subsequently, after the nickel-cobalt composite coprecipitated hydroxide is washed with an aqueous solvent (pure water), the nickel-cobalt composite coprecipitated hydroxide is dried.

[0221] Finally, by adding a lithium compound (lithium hydroxide monohydrate (LiOH H2O)) and an additional compound (aluminum hydroxide (Al(OH)3)) to the nickel-cobalt composite coprecipitated hydroxide, a precursor is obtained. In this case, the mixing ratio of the nickel-cobalt composite coprecipitated hydroxide, the lithium compound, and the additional compound (molar ratio of lithium, nickel, cobalt, and aluminum) is adjusted so that the composition of the lithium nickel composite oxide finally obtained is the composition shown in Tables 1 and 2.

[0222] In the first firing step, the precursor is fired in an oxygen atmosphere. In this case, the firing temperature is adjusted in the range of 650°C to 900°C. Thereby, a plurality of particulate lithium nickel composite oxides are synthesized, and thus a center portion 110 including the lithium nickel composite oxides is obtained. The composition of the lithium nickel composite oxides is as shown in Tables 1 and 2.

[0223] In the water washing step, first, 50 g of the center portion 110 and an aqueous solvent (pure water) 500 ml (= 500 cm 3 ) are put into a beaker having a volume of 1000 ml (= 1000 cm 3 ). Subsequently, the center portion 110 is washed with the aqueous solvent by stirring the aqueous solvent using a stirrer. In this case, the washing time is adjusted in the range of 60 minutes to 150 minutes. Subsequently, after the aqueous solvent is transferred to a suction filter, the filtrate is dehydrated (dehydration time = 10 minutes). Subsequently, the filtrate is dried (drying temperature = 120°C). Subsequently, the filtrate is pulverized using an agate mortar, and the pulverized product is vacuum dried (drying time = 100°C). Thereby, the water-washed center portion 110 is obtained.

[0224] In the covering process (second firing process), the center portion 110 and the boron compound (boric acid (H3BO3)) were mixed with each other to obtain a mixture. In this case, the mixing amount of the boron compound, i.e., the ratio of the mass of the boron compound to the mass of the center portion 110, was adjusted in the range of 0.05 to 0.55 mass%. Thereafter, the mixture was fired in an oxygen atmosphere. In this case, the firing temperature was adjusted in the range of 200 to 450°C. Thus, as shown in FIG. 1, the surface of the center portion 110 (lithium-nickel composite oxide) was covered with the covering portion 120 (boron compound), and thus the positive electrode active material 100 was obtained. Figure 5

[0225] After the positive electrode active material 100 was analyzed by XRD, the crystallite size Z (nm) was calculated based on the analysis result (peak of (104) plane) using the Scherrer formula, and the results shown in Tables 1 and 2 were obtained. In addition, after the positive electrode active material 100 was analyzed by XPS, the element concentration ratio R was calculated based on the analysis result, and the results shown in Tables 1 and 2 were obtained.

[0226] Note that, in the synthesis of the positive electrode active material 100, as shown in Tables 1 and 2, the crystallite size Z was changed by changing the firing temperature in the first firing process, and the element concentration ratio R was changed by adjusting the mixing ratio of the boron compound in the covering process (second firing process).

[0227] [Table 1]

[0228]

[0229] [Table 2]

[0230]

[0231] [Manufacture of Secondary Battery]

[0232] A laminated film-type secondary battery 10 was manufactured by the following sequence.

[0233] (Manufacture Process of Positive Electrode)

[0234] ​First, a positive electrode mixture was obtained by mixing the above-mentioned positive electrode active material 100 (the center portion 110 and the cover portion 120) 95.5 parts by mass, a positive electrode binder (polyvinylidene fluoride) 1.9 parts by mass, a positive electrode conductive agent (carbon black) 2.5 parts by mass, and a dispersing agent (polyvinylpyrrolidone) 0.1 part by mass with each other. Subsequently, after the positive electrode mixture was put into an organic solvent (N-methyl-2-pyrrolidone), the organic solvent was stirred, whereby a paste-like positive electrode mixture slurry was prepared. Subsequently, after the positive electrode mixture slurry was coated on both surfaces of the formed portion 21M in the positive electrode current collector 21A (aluminum foil having a thickness of 15 μm) using a coating device, the positive electrode mixture slurry was dried, whereby the positive electrode active material layer 21B was formed. Finally, the positive electrode active material layer 21B was compression-molded using a roll press, whereby the positive electrode active material layer 21B was formed on both surfaces of the positive electrode current collector 21A, and thus the positive electrode 21 was produced.

[0235] (Production procedure of negative electrode)

[0236] First, a negative electrode mixture was obtained by mixing a negative electrode active material (graphite) 90 parts by mass and a negative electrode binder (polyvinylidene fluoride) 10 parts by mass with each other. Subsequently, after the negative electrode mixture was put into an organic solvent (N-methyl-2-pyrrolidone), a paste-like negative electrode mixture slurry was prepared by stirring the organic solvent. Subsequently, after the negative electrode mixture slurry was coated on both surfaces of the formed portion 22M in the negative electrode current collector 22A (copper foil having a thickness of 15 μm) using a coating device, the negative electrode mixture slurry was dried, whereby the negative electrode active material layer 22B was formed. Finally, the negative electrode active material layer 22B was compression-molded using a roll press, whereby the negative electrode active material layer 22B was formed on both surfaces of the negative electrode current collector 22A, and thus the negative electrode 22 was produced.

[0237] (Preparation procedure of electrolyte solution)

[0238] An electrolyte salt (lithium hexafluorophosphate) was added to a solvent (ethylene carbonate and ethyl methyl carbonate), and after the solvent was stirred, a polycarbonic compound (succinonitrile (SN) as a dinitrile compound) was added to the stirred solvent, and the solvent was stirred. In this case, the mixture ratio (mass ratio) of the solvent was set to ethylene carbonate:ethyl methyl carbonate = 50:50, and the content of the electrolyte salt was set to 1 mol / kg with respect to the solvent. The content (wt%) of the polycarbonic compound in the electrolyte solution is shown in Tables 1 and 2. Thus, the electrolyte salt and the polycarbonic compound were dispersed or dissolved in the solvent, respectively, and thus the electrolyte solution was prepared.

[0239] Note that, for comparison, the electrolyte solution was prepared in the same procedure except that the polycarbonic compound was not used.

[0240] (Assembly procedure of secondary battery)

[0241] First, the positive electrode 21 and the negative electrode 22 are alternately stacked through the separator 23 (a microporous polyethylene film having a thickness of 25 μm) to form a stack. Subsequently, the plurality of exposed portions 21N are joined to each other using ultrasonic welding, and the plurality of exposed portions 22N are joined to each other using ultrasonic welding. Subsequently, the positive electrode lead 41 is connected to the plurality of exposed portions 21N joined to each other using ultrasonic welding, and the negative electrode lead 42 is connected to the plurality of exposed portions 22N joined to each other using ultrasonic welding.

[0242] Subsequently, two film members 30A, 30B are prepared. As each of the film members 30A, 30B, a moisture-proof aluminum laminated film in which a fusion layer (a polypropylene film having a thickness of 30 μm), a metal layer (an aluminum foil having a thickness of 40 μm), and a surface protective layer (a nylon film having a thickness of 25 μm) are sequentially stacked is prepared. Subsequently, after the stack is accommodated in the recessed portion 31, the outer peripheral edge portions of three sides of each of the film members 30A, 30B (a heat fusion resin layer) are heat-fused to each other using heat fusion to accommodate the stack in the bag-shaped outer packaging film 30.

[0243] Finally, after the electrolyte solution is injected into the bag-shaped outer packaging film 30, the outer packaging film 30 is sealed using heat fusion. In this case, the sealing film 33 (a polypropylene film having a thickness of 15 μm) is interposed between the outer packaging film 30 and the positive electrode lead 41, and the sealing film 34 is interposed between the outer packaging film 30 and the negative electrode lead 42. Thus, the stack is impregnated with the electrolyte solution, and the battery element 20 as a stacked electrode body is produced. In addition, each of the positive electrode lead 41 and the negative electrode lead 42 is drawn out to the outside from the inside of the outer packaging film 30, and the battery element 20 is accommodated in the inside of the outer packaging film 30. Thus, the battery element 20 is enclosed in the inside of the outer packaging film 30, and the secondary battery 10 is assembled.

[0244] (Stabilization process of secondary battery)

[0245] The secondary battery 10 is subjected to charge and discharge in one cycle in a thermostat (temperature = 60°C). At the time of charging, constant current charging is performed at a current of 0.1 C until the voltage reaches 4.2 V, and constant voltage charging is performed at the voltage of 4.2 V until the current reaches 0.05 C. At the time of discharging, constant current discharging is performed at a current of 0.1 C until the voltage reaches 2.5 V. 0.1 C means a current value at which the battery capacity (theoretical capacity) is completely discharged in 10 hours, and 0.05 C means a current value at which the battery capacity is completely discharged in 20 hours. Thus, a coating film is formed on the surface of each of the positive electrode 21 and the negative electrode 22, and the state of the secondary battery 10 is electrochemically stabilized. Thus, the secondary battery 10 of the laminated film type is completed.

[0246] [Evaluation of performance]

[0247] The performance (capacity characteristics, expansion characteristics, and cycle characteristics) of the secondary battery 10 was evaluated, and the results shown in Tables 1 and 2 were obtained.

[0248] (capacity characteristics)

[0249] In studying the capacity characteristics, the secondary battery was charged and discharged in a normal temperature environment (temperature = 23°C), whereby the battery capacity (so-called initial capacity) was measured. The charge and discharge conditions were the same as in the stabilization process of the secondary battery. Note that in Tables 1 and 2, as the value of the battery capacity, the value after normalization by setting the value of the battery capacity in Experimental Example 4 to 100 is shown.

[0250] (expansion characteristics)

[0251] First, after charging the secondary battery in a normal temperature environment, the thickness of the secondary battery (thickness before storage) was measured. Subsequently, after storing (storage period = 24 hours) the charged secondary battery in a constant temperature chamber (temperature = 60°C), the thickness of the secondary battery (thickness after storage) was measured again. Finally, the expansion rate (%) = [(thickness after storage - thickness before storage) / thickness before storage] x 100 was calculated. The charging conditions were the same as in the stabilization process of the secondary battery.

[0252] (cycle characteristics)

[0253] First, the secondary battery was charged and discharged in a normal temperature environment, whereby the discharge capacity (discharge capacity at the 1st cycle) was measured. Subsequently, the secondary battery was repeatedly charged and discharged in the environment until the total number of cycles reached 300 cycles, whereby the discharge capacity (discharge capacity at the 300th cycle) was measured. Finally, the capacity maintenance rate (%) = (discharge capacity at the 300th cycle / discharge capacity at the 1st cycle) x 100 was calculated. Except that the current at the time of charging was changed to 1C and the current at the time of discharging was changed to 3C, the charge and discharge conditions were the same as in the stabilization process of the secondary battery. 1C means a current value at which the battery capacity is completely discharged in 1 hour, and 3C means a current value at which the battery capacity is completely discharged in 1 / 3 hour.

[0254] [Investigation]

[0255] As shown in Tables 1 and 2, in the secondary battery in which the positive electrode active material 100 includes the center portion 110 (lithium-nickel composite oxide) and the covering portion 120 (boron compound), the capacity characteristics (battery capacity), the expansion characteristics (expansion rate), and the cycle characteristics (capacity maintenance rate) varied depending on the composition (composition of lithium-nickel composite oxide) and the physical properties (crystallite size Z and element concentration ratio R) of the positive electrode active material 100 and the composition (presence or absence of polycarbonitrile compound) of the electrolyte.

[0256] That is, in the case where the electrolytic solution does not contain the polycarbonic compound (Experimental Example 24), although a high battery capacity is obtained, the expansion rate increases, and at the same time, the capacity maintenance rate decreases. In contrast, in the case where the electrolytic solution contains the polycarbonic compound (Experimental Examples 1 to 23), depending on each of the composition of the lithium-nickel composite oxide, the crystallite size Z, and the element concentration ratio R, the battery capacity, the expansion rate, and the capacity maintenance rate each greatly change in quality.

[0257] Specifically, in the case where the three conditions that the lithium-nickel composite oxide is the compound represented by formula (1), the crystallite size Z is 40.0 nm to 74.5 nm, and the element concentration ratio R is 0.15 to 0.90 are satisfied at the same time (Experimental Examples 2 to 6, 8 to 12, 15 to 18, 21, and 22), unlike the case where the three conditions are not satisfied at the same time (Experimental Examples 1, 7, 13, 14, 19, 20, and 23), the expansion rate decreases and the capacity maintenance rate increases while the battery capacity is secured.

[0258] In particular, in the case where the three conditions are satisfied at the same time, a series of favorable tendencies described below are obtained.

[0259] First, since b in formula (1) satisfies 0.1 ≤ b ≤ 0.2, if 1 - b satisfies 0.8 ≤ 1 - b ≤ 0.9 (Experimental Examples 4 and 5), the expansion rate sufficiently decreases and the capacity maintenance rate sufficiently increases while the high battery capacity is maintained.

[0260] Second, by using the dicarbonic compound (succinonitrile) as the polycarbonic compound, as described above, the expansion rate decreases and the capacity maintenance rate increases while the battery capacity is secured.

[0261] Third, if the crystallite size Z is 50.0 nm to 70.0 nm (Experimental Examples 4, 9 to 11), the expansion rate sufficiently decreases and the capacity maintenance rate sufficiently increases while the high battery capacity is maintained.

[0262] Fourth, if the element concentration ratio R is 0.3 to 0.6% (Experimental Examples 4, 16, and 17), the expansion rate sufficiently decreases and the capacity maintenance rate sufficiently increases while the high battery capacity is maintained.

[0263] (Experimental Examples 25 to 48)

[0264] As shown in Tables 3 and 4, in addition to changing the kind and content (wt%) of the polycarbonitrile compound, respectively, the secondary battery 10 was produced by the same procedure, and the performance of the secondary battery 10 was evaluated. Here, as the polycarbonitrile compound, a tricarbonitrile compound was newly used in addition to other dicarbonitrile compounds. As the other dicarbonitrile compounds, glutaronitrile (GN), adiponitrile (AN), pimelonitrile (PN), suberonitrile (SUN), secononitrile (SEN), and ethylene glycol bis(propionitrile) ether (EGPNE) were used. As the tricarbonitrile compound, 1,3,5-cyclohexanetricarbonitrile (CHTCN) and 1,3,6-hexanetricarbonitrile (HTCN) were used. Note that in addition to adiponitrile alone, butanediol and adiponitrile were used.

[0265] [Table 3]

[0266]

[0267] [Table 4]

[0268]

[0269] As shown in Tables 3 and 4, in the case of using a dicarbonitrile compound (Examples 25 to 46) and in the case of using a tricarbonitrile compound (Examples 47 and 48), as in Example 4 described above, the expansion rate was reduced while the battery capacity was secured, and the capacity maintenance rate was increased.

[0270] In addition, if the content of the polycarbonitrile compound in the electrolyte solution is 0.5 to 3.0 wt% (Examples 4, 25 to 35), the expansion rate is sufficiently reduced while the battery capacity is secured, and the capacity maintenance rate is sufficiently increased. In this case, the content of the polycarbonitrile compound in the electrolyte solution is 1.5 to 2.0 wt% (Examples 4, 27, 32, and 33), and the expansion rate is further reduced.

[0271] [Summary]

[0272] According to the results shown in Tables 1 to 4, when the positive electrode active material includes a lithium-nickel complex oxide and a boron compound, the electrolyte solution includes a polycarbonitrile compound, the crystallite size Z of the (104) plane of the positive electrode active material is 40.0 to 74.5 nm, and the element concentration ratio R of the positive electrode active material is 0.15 to 0.90, the expansion rate is reduced while the battery capacity is secured, and the capacity maintenance rate is increased. Therefore, excellent capacity characteristics, excellent expansion characteristics, and excellent cycle characteristics are obtained in the secondary battery.

[0273] The present technology has been described above based on one embodiment and examples, but the configuration of the present technology is not limited to the configuration described in one embodiment and examples, and various modifications can be made.

[0274] The battery structure of the secondary battery is described as a laminated film type, but the battery structure is not particularly limited. Specifically, the battery structure can also be a cylindrical type, a square type, a coin type, a button type, or the like.

[0275] In addition, the element structure of the battery element is described as a stacked type, but the element structure of the battery element is not particularly limited. Specifically, the element structure can also be a jelly-roll type in which electrodes (a positive electrode and a negative electrode) are wound, a multiple-fold type in which electrodes (a positive electrode and a negative electrode) are folded in a zigzag shape, or the like.

[0276] Furthermore, the electrode reaction substance is described as lithium, but the electrode reaction substance is not particularly limited. Specifically, the electrode reaction substance can also be another alkali metal such as sodium and potassium, or an alkaline earth metal such as beryllium, magnesium, and calcium. In addition, the electrode reaction substance can also be another light metal such as aluminum.

[0277] The effects described in this specification are merely illustrative, and thus the effects of the present technology are not limited to the effects described in this specification. Therefore, other effects can be obtained with respect to the present technology.

Claims

1. A secondary battery comprising: a positive electrode including a positive electrode active material; a negative electrode; and an electrolyte including a polynitrile compound, wherein the positive electrode active material includes a lithium-nickel composite oxide of a layered rock salt type represented by the following formula (1) and a boron compound, wherein a crystallite size of a (104) plane of the positive electrode active material calculated using an X-ray diffraction method and a Scherrer formula is 40.0 nm or more and 74.5 nm or less, wherein M is at least one of Co, Fe, Mn, Cu, Zn, Al, Cr, V, Ti, Mg, and Zr, and a, b, and c satisfy 0.8 < a < 1.2, 0 ≤ b ≤ 0.5, and 0 < c < 3, wherein R = I2 / I1... (2), wherein I1 is an intensity of a peak of the (104) plane of the lithium-nickel composite oxide, and wherein I2 is an intensity of a peak of the (104) plane of the lithium-nickel composite oxide and the boron compound.

2. The secondary battery according to claim 1, wherein the positive electrode active material includes: a central portion including the lithium-nickel composite oxide; and a covering portion covering a surface of the central portion, including the boron compound.

3. The secondary battery according to claim 1 or 2, wherein the b in the formula (1) satisfies 0.1 ≤ b ≤ 0.

2.

4. The secondary battery according to any one of claims 1 to 3, wherein the polynitrile compound includes at least one of a dicarbonitrile compound and a tricarbonitrile compound, wherein the dicarbonitrile compound includes at least one of butanedinitrile, pentanedinitrile, hexanedinitrile, heptanedinitrile, octanedinitrile, decanedinitrile, and ethyleneglycol bis(propionitrile) ether, and wherein the tricarbonitrile compound includes at least one of 1,3,5-cyclohexanetricarbonitrile and 1,3,6-hexanetricarbonitrile.

5. The secondary battery according to any one of claims 1 to 4, wherein the crystallite size is 50.0 nm or more and 70.0 nm or less.

6. The secondary battery according to any one of claims 1 to 5, wherein the element concentration ratio is 0.30 or more and 0.60 or less. The element concentration ratio represented by the following formula (2) calculated from the B1s spectrum of the positive electrode active material detected using an X-ray photoelectron spectroscopy analysis method, the Ni2p 3 / 2 spectrum, the Co2p 3 / 2 spectrum, the Mn2p 1 / 2 spectrum, and the Al2s spectrum is 0.15 or greater and 0.90 or less. Li a Ni 1-b M b O c …(1), wherein 7. The secondary battery according to any one of claims 1 to 6, wherein a content of the polynitrile compound in the electrolyte is 0.5% by weight or more and 3.0% by weight or less.

8. The secondary battery according to claim 7, wherein the content of the polynitrile compound in the electrolyte is 1.5% by weight or more and 2.0% by weight or less. wherein R is an element concentration ratio, Ii is a Ni2p 3 / 2 spectrum, Co2p 3 / 2 spectrum, Mn2p 1 / 2 spectrum, and Al2s spectrum, I2 is a B concentration calculated based on a B1s spectrum, the Ni concentration, Co concentration, Mn concentration, Al concentration, and B concentration being in atomic %.

9. The secondary battery according to any one of claims 1 to 8, further comprising: a flexible outer packaging member that accommodates the positive electrode, the negative electrode, and the electrolyte.

10. The secondary battery according to any one of claims 1 to 9, wherein the secondary battery is a lithium-ion secondary battery. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

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