Lithium-ion secondary battery and method for producing the same

Abstract

A lithium-ion secondary battery (100), characterized in that it comprises:a positive electrode (50) including a positive active material layer (54);a negative electrode (60) including a negative active material layer (64);and a non-aqueous electrolyte, wherein the positive active material layer contains a positive active material and an inorganic phosphate compound, a BET specific surface area of the positive active material is 0.66 m2 / g to 1.15 m2 / g, the inorganic phosphate compound includes an alkali metal, an alkaline earth metal, and / or a hydrogen atom in a chemical formula, a content of the inorganic phosphate compound in the positive active material layer is 0.08 g / m2 to 0.225 g / m2 per unit surface area based on the BET specific surface area of the positive active material, and the lithium-ion secondary battery is configured to allow an open-circuit voltage of the lithium-ion secondary battery to be increased to 4.3 V or higher in terms of metallic lithium.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention

[0001] The present invention relates to a lithium ion secondary battery and a method for producing the same. 2. Description of the related art

[0002] In recent years, a lithium-ion secondary battery has been used to drive a motor of an electric vehicle, a hybrid electric vehicle, a fuel cell vehicle, or the like, or as an auxiliary power source therefor. Therefore, there is a need for higher output power and a longer cycle life.

[0003] To achieve high output power, an increase in the voltage of a battery, i.e., an increase in the voltage ceiling, is required during use. To achieve the increase in voltage, for example, the use of a high-potential positive active material (typically a lithium transition metal compound) that can suitably function as a positive active material even in the case of charging to a higher potential than the voltage ceiling of a general lithium-ion secondary battery in a typical use mode has been considered as a positive electrode material. The potential higher than the voltage ceiling in a typical use mode can be defined as a potential greater than or equal to 4.3 V (vs. Li / Li + ) in conjunction with a positive electrode potential.

[0004] However, in the lithium-ion secondary battery, which, as described above, has a high voltage greater than or equal to 4.3 V (vs. Li / Li + ) is realized as an open-circuit voltage (OCV). Depending on the non-aqueous electrolyte (non-aqueous electrolyte solution) used, the oxidative decomposition of the non-aqueous electrolyte in a high-voltage state is accelerated, and an acid (typically hydrogen fluoride (HF)) is generated in the electrolyte. Furthermore, the open-circuit voltage can also be considered an open-circuit potential. The generated acid causes the elution of transition metal components in the positive active material, and there is a concern that capacity deterioration may occur.

[0005] Japanese Patent Application Publication No. 2014-103098 (JP 2014- 103 098 A) describes a secondary battery with a non-aqueous electrolyte solution which, by incorporating phosphate or pyrophosphate with an alkali metal or a Group 2 element into a positive active material layer, achieves a high open circuit voltage greater than or equal to 4.3 V (vs. Li / Li + ). One object of the technique described in JP 2014-103098 A is to suppress capacity deterioration caused by the elution of transition metal by reacting phosphate or pyrophosphate as an acid-consuming material with an acid generated in the non-aqueous electrolyte solution (typically the aforementioned HF), and thus suppressing the elution of transition metal from the positive active material.

[0006] According to the technique described in JP 2014-103098 A, an inorganic phosphate compound contained in the positive active material layer prevents capacity deterioration caused by transition metal elution. However, if the content of the inorganic phosphate compound is too high, the influence of phosphate films increases, and this can lead to an increase in resistance. Consequently, capacity deterioration occurs. Therefore, there is a need to optimize the content of the inorganic phosphate compound, and the content of the inorganic phosphate compound relative to the weight of the positive active material is specified in JP 2014-103098 A. However, most of the oxidative decomposition reactions of the electrolyte solution, which cause metal elution, occur on the surface of the positive active material, and the amount of acid generated varies with the surface area of the active material.Accordingly, the optimal content varies depending on the performance of the positive active material, and there may be cases where the optimal content cannot be specified based on the weight of the positive active material.

[0007] Furthermore, the published patent applications JP 2003-173 770 A, US 2008 / 0 261 117 A1 and US 2002 / 0 086 210 A1 disclose lithium-ion secondary batteries and their manufacturing methods according to the prior art. SUMMARY OF THE INVENTION

[0008] The present invention provides a lithium ion secondary battery and a method for manufacturing the same.

[0009] A lithium-ion secondary battery according to a first aspect of the present invention includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The positive electrode includes a positive active material layer. The negative electrode includes a negative active material layer. The positive active material layer contains a positive active material and an inorganic phosphate compound. A BET specific surface area of the positive active material is 0.66 m². 2 / g up to 1.15 m 2 / g. The inorganic phosphate compound contains an alkali metal, an alkaline earth metal, and / or a hydrogen atom in a chemical formula. The content of the inorganic phosphate compound in the positive active material layer is 0.08 g / m 2 up to 0.225 g / m 2per unit surface area based on the BET specific surface area of the positive active material. The lithium-ion secondary battery is designed to allow an increase in the open-circuit voltage of the lithium-ion secondary battery to 4.3 V or higher with respect to metallic lithium.

[0010] Unless otherwise stated, in the specification, a "BET specific surface area (specific surface area)" is a measured value measured by a method that applies the BET theory, in which an adsorption process is dynamically analyzed by extending the Langmuir theory of localized single-molecule adsorption. In this configuration, since the inorganic phosphate compound reacts with acid, the acid in the electrolyte can be consumed. Therefore, the elution of transition metal from the positive active material can be effectively suppressed, and capacity deterioration caused by the elution of transition metal can be prevented. Furthermore, since the content of the inorganic phosphate compound can be determined based on the surface area orBy optimizing the surface area of the positive active material, even when using a positive active material with different specifications, an increase in resistance due to phosphate films can be effectively prevented. Therefore, according to the first aspect of the present invention, even in the lithium-ion secondary battery operating at a voltage value (open-circuit voltage of 4.3 V vs. Li / Li), the resistance can be increased significantly. + By using a voltage higher than a general voltage value (<0.05 V) or higher, the capacity deterioration caused by the elution of transition metal from the positive active material and the increase in resistance caused by the phosphate films can be suppressed in a compatible manner. Therefore, a lithium-ion secondary battery with high output and good cycle characteristics can be obtained.

[0011] In the first aspect of the present invention, the content of the inorganic phosphate compound in the first positive active material layer may be 0.08 g / m 2 up to 0.17 g / m 2 per unit surface area based on the specific BET surface area of the positive active material.

[0012] In the above embodiment, the content of the inorganic phosphate compound in the positive active material layer may be 0.08 g / m 2 up to 0.1 g / m 2 per unit surface area based on the specific BET surface area of the positive active material.

[0013] In the first aspect of the present invention, the inorganic phosphate compound may include a lithium phosphate.

[0014] Since the inorganic phosphate compound has high dielectric strength properties, the inorganic phosphate compound stably functions as an acid-consuming material even at the open-circuit voltage of the lithium-ion secondary battery according to the first aspect of the present invention. Therefore, even in the lithium-ion secondary battery (with an open-circuit voltage of 4.3 V vs. Li / Li), the acid-consuming material can be stably and consistently used. + ) or above), as in the first aspect of the present invention, can compatibly suppress the capacity deterioration caused by the elution of transition metal from the positive active material and the increase in resistance caused by the phosphate films. In this specification, "lithium phosphate" means "lithium-containing phosphorus salt" but is not limited to Li3PO4.

[0015] In the above embodiment, the lithium phosphate may include Li3PO4.

[0016] In the first aspect of the present invention, the positive active material may be a spinel positive active material containing Li, Ni and Mn.

[0017] The spinel positive active material exhibits high thermal stability and high electrical conductivity. Therefore, the spinel positive active material can increase the battery performance and durability of the lithium-ion secondary battery.

[0018] In the above embodiment, the spinel positive active material can be LiNi 0,5 Mn 1,5 O4 be.

[0019] Increasing the surface area of the active material, which is a reaction field for charge carriers, improves the output power. Since the lithium-ion secondary battery with the above configuration has the active material with a large surface area, high output power can be achieved.

[0020] A second aspect of the invention is a method for manufacturing a lithium-ion secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode includes a positive active material layer containing a positive active material, and the negative electrode includes a negative active material layer containing a negative active material. The method includes: obtaining a BET specific surface area of the positive active material of 0.66 m 2 / g up to 1.15 m 2 / g; and adding an inorganic phosphate compound to the positive active material layer to adjust an amount of the inorganic phosphate compound to 0.08 g / m 2 up to 0.225 g / m 2per unit surface area based on the BET specific surface area of the positive active material. The inorganic phosphate compound contains an alkali metal, an alkaline earth metal, and / or a hydrogen atom. The lithium-ion secondary battery is designed to allow an increase in the open-circuit voltage of the lithium-ion secondary battery to 4.3 V or higher with respect to metallic lithium.

[0021] According to the manufacturing process, the inorganic phosphate compound is included as an acid-consuming material, but its content is optimized with respect to the specific surface area of the positive active material. Therefore, the capacity deterioration caused by the elution of transition metal from the positive active material and the increase in resistance caused by the phosphate films can be prevented in a compatible manner. Therefore, the lithium-ion secondary battery can be manufactured with high output and good cycling characteristics.

[0022] In the second aspect of the present invention, the amount of inorganic phosphate added to the positive active material layer may be 0.08 g / m 2 up to 0.17 g / m 2 per unit surface area based on the specific BET surface area of the positive active material.

[0023] In the above embodiment, the amount of inorganic phosphate added to the positive active material layer may be 0.08 g / m 2 up to 0.1 g / m 2 per unit surface area based on the specific BET surface area of the positive active material. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Features, advantages, and technical and industrial significance of exemplary embodiments of the invention are described below with reference to the accompanying drawings, in which like reference numerals designate like elements. It shows: Fig. 1 is a perspective view schematically illustrating the external appearance of a lithium ion secondary battery according to an embodiment of the present invention; Fig. 2 is a longitudinal sectional view showing a sectional structure along the line II-II of Fig. 1 schematically illustrated; Fig. 3 is a manufacturing process diagram illustrating an example of a manufacturing method of the lithium ion secondary battery according to the embodiment of the present invention; Fig. 4 shows a graph of the relationship between the content ratio of lithium phosphate based on the weight of a positive active material and a capacity retention ratio; and Fig. Figure 5 shows a graph of the relationship between the lithium phosphate content per unit surface area (1 m 2 ) based on the specific BET surface area of the positive active material and the capacity retention ratio. DETAILED DESCRIPTION OF EMBODIMENTS

[0025] Embodiments of the present invention will be described below. Matters not specifically mentioned in the description and necessary for carrying out the present invention will be recognizable as design matters by those skilled in the art. The present invention can be carried out based on the contents disclosed in the specification and common technical knowledge in the art. In the following drawings, like elements and locations having the same effect are designated by like reference numerals, and overlapping descriptions may be omitted or simplified. In each of the drawings, dimensional relationships (length, width, thickness, and the like) do not necessarily reflect actual dimensional relationships.

[0026] Fig.1 is a view illustrating the external appearance of a lithium ion secondary battery 100 according to an embodiment of the present invention. Fig. 2 is a sectional view schematically illustrating the internal configuration of a battery case 30 according to this embodiment.

[0027] As in the Fig. 1 and Fig.As illustrated in Figure 2, the lithium-ion secondary battery 100 according to this embodiment is a so-called rectangular battery. The lithium-ion secondary battery 100 is formed by accommodating a flat wound electrode assembly 20 and a non-aqueous electrolyte (not shown) in a battery case (i.e., an outer container) 30 having a flat, rectangular shape. The battery case 30 is configured to include a case body 32 having a box shape (i.e., a rectangular parallelepiped shape with a bottom), one end of which (corresponding to an upper end portion in a typical use state of the lithium-ion secondary battery 100) has an opening, and a cover 34 that seals the opening of the case body 32. For the material of the battery case 30, for example, a metal material with light weight and good thermal conductivity is preferably used, such as aluminum, stainless steel, and nickel-plated steel.

[0028] As in the Fig. 1 and Fig. As illustrated in FIG. 2, the cover 34 is provided with a positive electrode terminal 42 and a negative electrode terminal 44 for external connection, a thin safety valve 36 configured to release the internal pressure of the battery case 30 when the internal pressure rises to a predetermined level or higher, and an injection port (not shown) for injecting the non-aqueous electrolyte (non-aqueous electrolyte solution). The battery case 30 of the lithium-ion secondary battery 100 may have not only the illustrated rectangular shape (box shape) but also other well-known shapes. For example, other shapes include a button shape, a layered shape, and the like, and a case shape can be appropriately selected from these.

[0029] As in Fig.As illustrated in FIG. 2, the wound electrode assembly 20 accommodated in the battery case 30 is manufactured by winding in the longitudinal direction a laminate in which a positive electrode 50 having a positive active material layer 54 formed along the longitudinal direction of one surface or both surfaces (here, both surfaces) of a long positive electrode collector 52 and a negative electrode 60 having a negative active material layer 64 formed along the longitudinal direction of one surface or both surfaces (here, both surfaces) of a long negative electrode collector 62 are stacked over two layers of long separators 70, and by forming the laminate in a flat shape. The wound electrode assembly 20 is formed, for example, by pressing and swaging the wound assembly obtained by winding the laminate in the flat shape from a lateral direction.The positive electrode collector 52, which is included in the positive electrode 50, is made of aluminum foil or the like. The negative electrode collector 62, which is included in the negative electrode 60, is made of copper foil or the like.

[0030] As in Fig.2, the central portion of the wound electrode assembly 20 in the winding axis direction thereof is provided with a wound core portion (i.e., a laminated structure in which the positive active material layer 54 of the positive electrode 50, the negative active material layer 64 of the negative electrode 60, and the separator 70 are laminated). Furthermore, portions of a positive active material layer non-formation portion 52a and a negative active material layer non-formation portion 62a extend from both end portions of the wound electrode assembly 20 in the winding axis direction in an outward direction from the wound core portion. A positive electrode collector plate 42a and a negative electrode collector plate 44a are provided at a positive electrode side extension portion (the positive active material layer non-formation portion 52a) and a negative electrode side extension portion (the positive active material layer non-formation portion 52a), respectively.a negative electrode side extending portion (the negative active material layer non-forming portion 62a) so as to be electrically connected to the positive electrode terminal 42 and the negative electrode terminal 44, respectively.

[0031] The positive active material layer 54 according to this embodiment contains a positive active material as the main component and an inorganic phosphate compound. One type or two or more types of materials previously used for the lithium-ion secondary battery 100 can be used as the positive active material without particular limitations. For example, oxides containing lithium and transition metal elements as metal components (lithium-transition metal composite oxides), such as lithium-nickel composite oxide (LiNiO2 or the like), lithium-cobalt composite oxide (LiCoO2 or the like), and lithium-manganese composite oxide (LiMn2O4 or the like), and phosphates containing lithium and transition metal elements as metal element components, such as lithium-manganese phosphate (LiMnPO4) and lithium-iron phosphate (LiFePO4), can be used.As a spinel positive active material, for example, lithium manganese composite oxide having a spinel structure represented by a general formula Li. p Mn 2-q M q O 4+αwhere p is 0.9≤p≤1.2, q is 0≤q<2 and typically 0≤q≤1 (for example, 0.2≤q≤0.6), and α is a value determined to satisfy charge neutrality conditions in a range of -0.2≤α≤0.2. In the case where q is greater than 0 (0 <q), ist M eine Art oder zwei oder mehr Arten ausgewählt aus beliebigen Metallelementen mit Ausnahme von Mn oder nicht-metallischen Elementen. M kann genauer gesagt Na, Mg, Ca, Sr, Ti, Zr, V, Nb, Cr, Mo, Fe, Co, Rh, Ni, Pd, Pt, Cu, Zn, B, Al, Ga, In, Sn, La, W, Ce oder dergleichen sein. Hieraus kann mindestens eine Art von Übergangsmetallelementen von Fe, Co und Ni bevorzugt eingesetzt werden. Konkrete Beispiele hierfür umfassen LiMn2O4 und LiCrMnO4. Hieraus wird ein Spinell-Positivaktivmaterial, das Li, Ni und Mn als die wesentlichen Elemente aufweist, bevorzugt.More specifically, lithium nickel manganese composite oxide with a spinel structure represented by a general formula Li. x (No y Mn 2-y-z M1 z )O 4+βM1 may not be present or may be any transition element except Ni and Mn or a typical metal element (e.g., one or two or more selected from Fe, Co, Cu, Cr, Zn, and Al). M1 preferably includes trivalent iron and / or Co. Otherwise, M1 may also be a semi-metallic element (e.g., one or two or more selected from B, Si, and Ge) or a non-metallic element. Furthermore, x 0.9≤x≤1.2, y is 0 <y, z ist 0≤z, y+z<2 (typischerweise gilt y+z≤1) und β wird auf ähnliche Weise erhalten wie α. In einer bevorzugten Ausführungsform ist y 0,2≤y≤1,0 (bevorzugter gilt 0,4≤y≤0,6, beispielsweise 0,45≤y≤0,55), z ist 0≤z<1,0 (beispielsweise gilt 0≤z≤0,3). Als ein besonders bevorzugtes konkretes Beispiel kann LiNi 0,5 Mn 1,5O4 or the like. Such a positive active material can become a high-potential positive active material capable of an open-circuit voltage (OCV) greater than or equal to 4.3 V with respect to metallic lithium (vs. Li / Li + ) and is therefore a suitable positive active material for the implementation of the present invention. Furthermore, the spinel positive active material (LiNi 0,5 Mn 1,5 O4 or the like) has high thermal stability and high electrical conductivity and can thus be used more preferably in terms of battery performance and durability.

[0032] The positive active material is not particularly limited, and, for example, a lithium transition metal composite powder consisting essentially of secondary particles having a cumulative 50% diameter point (median diameter (D50)) in a range of 1 μm to 25 μm (typically 2 μm to 10 μm, for example, 6 μm to 10 μm) in a volume-based particle size distribution obtained by a general laser diffraction particle size distribution measuring device is preferably used as the positive active material. Unless otherwise stated, a "particle size" in the specification refers to a median diameter in a volume-based particle size distribution obtainable by a general laser diffraction particle size distribution measuring device.

[0033] In addition, the positive active material used to form the positive active material layer 54 suitably has a BET specific surface area of at least 0.66 m 2 / g (for example 0.66 m 2 / g or more and 1.15 m 2 / g or less). As the surface area of the active material, which is a reaction field for charge carriers, is increased, the output power increases. Therefore, the positive active material formed as described above has a large surface area, thus realizing a high output power of the lithium-ion secondary battery.

[0034] The positive active material layer 54 may include components other than the positive active material, which is the main component described above, such as a conductive material and a binder. A carbon material such as carbon black, including acetylene black (AB), and other materials (graphite or the like) can be suitably used as the conductive material. Polyvinylidene fluoride (PVdF) or the like can be used as the binder.

[0035] Furthermore, the lithium-ion secondary battery disclosed herein includes the inorganic phosphate compound in the positive active material layer. The inorganic phosphate compound may be expressed in chemical formula as a compound containing one or more of an alkali metal, an alkaline earth metal, and a hydrogen atom. As the alkali metal element and the alkaline earth, one or more metals selected from the group consisting of lithium (Li), sodium (Na), potassium (K), magnesium (Mg), and calcium (Ca) are preferred. Examples of the inorganic phosphate compound include orthophosphoric acid (H3PO4) and pyrophosphate (H4P2O7) or salts thereof. For example, sodium salt (Na2P4O7), potassium salt (K4P2O7), or the like can be used.Typically, various inorganic phosphates can be used, for example, (NH4)3PO4, (NH4)2HPO4, (NH4)H2PO4, (NH4)M2PO4, (NH4)MPO4, M2HPO4, MH2PO4, M3PO4, M3(PO4)2, M4P2O7, and M2P2O7 (M in these formulas is an alkali metal or an alkaline earth metal such as Li, Na, K, Mg, or Ca). Of these, lithium phosphate containing lithium is preferred. In particular, Li3PO4 is preferred.

[0036] The inorganic phosphate compound (typically the inorganic phosphates described above) exhibits high withstand voltage properties and stably functions as an acid-consuming material even at the open-circuit voltage of the lithium-ion secondary battery 100 of this embodiment. Therefore, capacity deterioration caused by the elution of transition metal from the positive active material and an increase in resistance caused by the phosphate films can be compatibly suppressed.

[0037] The content (amount added) of the inorganic phosphate compound in the positive active material layer is preferably 0.08 g / m 2 up to 0.225 g / m 2 per surface unit (1 m 2 ) based on the BET specific surface area of the high-potential positive active material contained in the positive active material layer. More preferably, the content thereof is 0.08 g / m 2 up to 0.1 g / m 2According to this mixing ratio, both the capacity deterioration caused by the elution of transition metal from the positive active material and the increase in battery resistance caused by the addition of the inorganic phosphate compound components can be suppressed. The state of the inorganic phosphate compound present in the positive active material layer is not particularly limited, and the inorganic phosphate compound may be in a state of coating (adhering) to the positive active material (particles) or may be dispersed in the positive active material layer instead of adhering to the positive active material (particles). The inorganic phosphate compound is preferably in a state of being substantially homogeneously distributed in the positive active material layer.In this embodiment, the elution of the transition metal components over the entire positive active material layer 54 can be prevented.

[0038] The negative active material layer 64 contains at least the negative active material. For example, a carbon material such as graphite, hard carbon, or soft carbon can be used as the negative active material. The negative active material layer 64 may contain components other than the active material, such as a binder and a thickener. Styrene-butadiene rubber (SBR) or the like can be used as the binder. Carboxymethylcellulose (CMC) or the like can be used as the thickener.

[0039] For example, a porous layer (film) made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, or polyamide can be used as the separator 70. The porous layer may have a single-layer structure or a layered structure of two or more layers (for example, a three-layer structure in which PE layers are coated on both surfaces of a PP layer).

[0040] As the non-aqueous electrolyte, an electrolyte in which a predetermined carrier salt and an additive are contained in an organic solution (non-aqueous solvent) can typically be used.

[0041] As the non-aqueous solvent, various types of organic solvents used for the electrolyte of a general lithium-ion secondary battery 100, such as carbonates, ethers, esters, nitriles, sulfones, and lactones, can be used without particular restrictions. Specific examples include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). The non-aqueous solvents can be used singly or in an appropriate combination of two or more types. Otherwise, a fluorine-based solvent such as fluorinated carbonates, including monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC), and trifluorinated dimethyl carbonate (TFDMC), can be preferably used.For example, a mixed solvent containing MFEC and TFDMC in a volume ratio of 1:2 to 2:1 (e.g., 1:1) has high oxidation resistance and can be suitably used in combination with a high-potential electrode.

[0042] As the carrier salt, for example, lithium salts such as LiPF6, LiBF4, and LiClO4 can be suitably used. A particularly preferred carrier salt is LiPF6. The concentration of the carrier salt is preferably 0.7 mol / L or more and 1.3 mol / L or less, and is particularly preferably about 1.0 mol / L.

[0043] The non-aqueous electrolyte may further contain components other than the non-aqueous solvent and carrier salt, as long as the effects of the present invention are not significantly impaired. Such arbitrary components can be used, for example, for one or two or more purposes, such as increasing the output of the lithium-ion secondary battery 100, increasing storage stability (preventing capacity reduction during storage), increasing initial charge and discharge efficiency, and the like. Examples of the arbitrary components include various types of additives such as a gas generating agent including biphenyl (BP) and cyclohexylbenzene (CHB), a film former including an oxalate complex compound containing a boron atom and / or a phosphorus atom, vinylene carbonate (VC), and fluoroethylene carbonate (FEC), a dispersant, and a thickener.

[0044] Next, a method for manufacturing the lithium ion secondary battery 100 of the embodiment will be described. Fig. 3 is a manufacturing process diagram illustrating an example of a rough manufacturing process of the lithium-ion secondary battery 100 of the embodiment. Manufacturing of the lithium-ion secondary battery 100 begins with a manufacturing process S101 in which the battery case 30 is manufactured.

[0045] Next, the positive electrode 50 and the negative electrode 60 included in the electrode assembly are manufactured (manufacturing process S102). The manufacturing process S102 will be described in detail below.

[0046] First, the positive electrode 50 will be described. A paste-like (slurry-like) composition is prepared by dispersing the above-described positive active material (for example, LiNi 0,5 Mn 1,5O4, which is a high-potential positive active material), the inorganic phosphate compound, and other materials (a binder, a conductive material, and the like) optionally used in a suitable solvent. In the case where PVdF is used as the binder, N-methyl-2-pyrrolidone (NMP) is preferable as the solvent. The inorganic phosphate compound is a compound containing one or more of an alkali metal, an alkaline earth metal, and a hydrogen atom in the chemical formula. More preferably, the inorganic phosphate compound is a compound containing at least one type of lithium phosphate (typically Li3PO4). In this case, the BET specific surface area of the positive active material is obtained, and the inorganic phosphate compound is added to the positive active material so that the content of the inorganic phosphate compound is 0.08 g / m 2 up to 0.225 g / m 2(preferably 0.08 g / m 2 up to 0.1 g / m 2 ) per surface unit (1 m 2 ) based on the BET specific surface area. Next, after applying an appropriate amount of the composition to the surface of the positive electrode collector 52, the solvent is removed by drying, so that the positive active material layer 54 having desired properties can be applied to the positive electrode collector 52, thereby forming the positive electrode 50. Furthermore, the properties (e.g., average thickness, active material density, and the porosity of the active material layer) of the positive active material layer 54 can be controlled, if necessary, by appropriately performing a pressing process.

[0047] Next, the negative electrode 60 will be described. For example, the negative electrode 60 can be manufactured in the same manner as the above-described case of the positive electrode 50. That is, a paste-like (slurry-like) composition is prepared by dispersing the negative active material and materials used if necessary in a suitable solvent (e.g., ion-exchange water), an appropriate amount of the composition is applied to the surface of the negative electrode collector 62, and then the solvent is removed by drying, thereby forming the negative electrode. Furthermore, the properties (e.g., average thickness, active material density, and the porosity of the active material layer) of the negative active material layer 64 can be controlled if necessary by appropriately performing a pressing process.

[0048] Following the formation of the positive electrode 50 and the negative electrode 60 (manufacturing process S102), an electrode assembly is formed (manufacturing process S103). The electrode assembly is formed using the above-described positive electrode 50, the negative electrode 60, and the separator 70. For example, the positive electrode 50 and the negative electrode 60 are stacked and wound over the separator 70. Thus, the wound electrode assembly 20 is formed.

[0049] After forming the electrode assembly (manufacturing process S103), the lithium-ion secondary battery 100 is assembled (manufacturing process S104). In the manufacturing process S104, the wound electrode assembly 20 is housed in the battery case 30, the non-aqueous electrolyte is injected, and the battery case 30 is sealed with the cover, thereby creating the lithium-ion secondary battery 100.

[0050] According to the method for manufacturing the lithium-ion secondary battery 100 of the above-described embodiment, the content of the inorganic phosphate compound is optimized. Therefore, the lithium-ion secondary battery 100 can be manufactured that is capable of suppressing capacity deterioration caused by transition metal elution and resistance increase caused by phosphate films. That is, it is possible to provide the lithium-ion secondary battery 100 with high output and good cycle characteristics.

[0051] In the method for manufacturing the lithium-ion secondary battery 100 of the embodiment, the electrode assembly is formed after the battery case is formed. The embodiment of the present invention is not limited to this, and the battery case may also be formed after the electrode assembly is formed. That is, the manufacturing process S102 and the manufacturing process S103 may be performed before the manufacturing process S101.

[0052] The lithium-ion secondary battery 100 disclosed herein can be used for various purposes and, for example, can be suitably used as a driving power source mounted on a vehicle such as a plug-in hybrid vehicle (PHV), a hybrid vehicle (HV), and an electric vehicle (EV).

[0053] The following describes experimental examples relating to the present invention, but are not intended to limit the present invention to the experimental examples. In the following description, samples 1 to 3, 7 to 10, and 14 to 17 correspond to examples of the present invention. Furthermore, samples 4 to 6, 11 to 13, and 18 correspond to comparative examples of the present invention.

[0054] A layered cell battery of Sample 1 is described below. As a positive electrode mixture material, a spinel positive active material into which lithium phosphate (Li3PO4) was premixed, acetylene black (conductive material), and PVdF (binder) were mixed to a weight ratio of 89:8:3, and a slurry-like composition was prepared using NMP as a solvent. The spinel positive active material used here was LiNi. 0,5 Mn 1,5O4 with an average particle size of 13 µm and a specific BET surface area of 0.3 m 2 / g. In addition, Li3PO4 had a content corresponding to 1 wt.% when the content of the positive active material (LiNi 0,5 Mn 1,5 O4) was 100 and had a content corresponding to 0.033 g / m 2 per surface unit (1 m 2) based on the BET specific surface area of the positive active material. The positive electrode mixed material slurry was coated on a 15 μm-thick aluminum foil (positive electrode collector) and then dried to form a positive active material layer, and the resultant was subjected to roll pressing, thereby fabricating a positive electrode. The positive electrode was cut into a 5 cm × 5 cm square shape with a strip-shaped portion 10 mm wide extending from one corner. The active material layer was removed from the strip-shaped portion to expose the aluminum foil and form a terminal portion, thereby obtaining the positive electrode with the terminal portion.

[0055] As a negative electrode mixed material, graphite (a negative active material with an average particle size of 20 μm and a graphitization degree of ≥ 0.9), CMC (thickener), and SBR (binder) were mixed to obtain a weight ratio of 98:1:1, and a slurry was prepared by using water as a solvent. The negative electrode mixed material slurry was coated on a 10 μm-thick copper foil (negative electrode collector) and then dried to form a negative active material layer. The resultant was subjected to roll pressing, thereby preparing a negative electrode. By processing the negative electrode to have the same area and shape as those of the positive electrode with the terminal portion, the negative electrode with a terminal portion was obtained.

[0056] A non-aqueous electrolyte was prepared by dissolving LiPF6 to a concentration of 1 mol / L in a mixed solvent containing MFEC TFDMC in a volume ratio of 1:1.

[0057] The positive electrode with the terminal portion and the negative electrode with the terminal portion were stacked over a separator (a porous three-layer PE / PP / PE sheet) cut to an appropriate size and impregnated with the non-aqueous electrolyte, and covered with a layered film. The non-aqueous electrolyte was further injected, and the film was sealed, creating a layered cell-type battery.

[0058] In the same manner as Sample 1 described above, a layered cell type battery of Sample 2 was prepared, except that Li3PO4 had a content ratio corresponding to 3 wt% when the content of the positive active material was 100, and a content corresponding to 0.100 g / m 2 per surface unit (1 m 2 ) based on the specific BET surface area of the positive active material.

[0059] In the same manner as Sample 1 described above, a layered cell type battery of Sample 3 was prepared, except that Li3PO4 had a content ratio corresponding to 5 wt% when the content of the positive active material was 100, and a content corresponding to 0.167 g / m 2 per surface unit (1 m 2 ) based on the specific BET surface area of the positive active material.

[0060] In the same manner as Sample 1 described above, except that lithium phosphate (Li3PO4) was not used, a layered cell type battery of Sample 4 was prepared in which lithium phosphate was not included in the positive active material layer.

[0061] In the same manner as Sample 1 described above, a layered cell type battery of Sample 5 was prepared, except that Li3PO4 had a content ratio corresponding to 0.5 wt% when the content of the positive active material was 100, and a content corresponding to 0.017 g / m 2 per surface unit (1 m 2 ) based on the specific BET surface area of the positive active material.

[0062] In the same manner as Sample 1 described above, a layered cell type battery of Sample 6 was prepared, except that Li3PO4 had a content ratio corresponding to 10 wt% when the content of the positive active material was 100 and a content corresponding to 0.333 g / m 2 per surface unit (1 m 2 ) based on the specific BET surface area of the positive active material.

[0063] In the same manner as Sample 1 described above, a layered cell type battery of Sample 7 was prepared, except that the specific surface area of the positive active material was 0.66 m 2 / g, Li3PO4 had a content corresponding to 2 wt.% when the content of the positive active material was 100, and a content corresponding to 0.030 g / m 2 per surface unit (1 m 2 ) based on the specific BET surface area of the positive active material.

[0064] In the same manner as Sample 1 described above, a layered cell type battery of Sample 8 was prepared, except that the specific surface area of the positive active material was 0.66 m 2 / g, Li3PO4 had a content corresponding to 3 wt.% when the content of the positive active material was 100, and a content corresponding to 0.045 g / m 2 per surface unit (1 m 2 ) based on the specific BET surface area of the positive active material.

[0065] In the same manner as Sample 1 described above, a layered cell type battery of Sample 9 was prepared, except that the specific surface area of the positive active material was 0.66 m 2 / g, Li3PO4 had a content corresponding to 5 wt.% when the content of the positive active material was 100, and a content corresponding to 0.076 g / m 2 per surface unit (1 m 2) based on the specific BET surface area of the positive active material.

[0066] In the same manner as Sample 1 described above, a layered cell type battery of Sample 10 was prepared, except that the specific surface area of the positive active material was 0.66 m 2 / g, Li3PO4 had a content corresponding to 10 wt.% when the content of the positive active material was 100, and a content corresponding to 0.152 g / m 2 per surface unit (1 m 2 ) based on the specific BET surface area of the positive active material.

[0067] In the same manner as Sample 1 described above, except that the specific surface area of the positive active material was 0.66 m 2 / g and no Li3PO4 was used, a layered cell type battery of Sample 11 was constructed in which no Li3PO4 was included in the positive active material layer.

[0068] In the same manner as Sample 1 described above, a layered cell type battery of Sample 12 was prepared, except that the specific surface area of the positive active material was 0.66 m 2 / g, Li3PO4 had a content corresponding to 1 wt.% when the content of the positive active material was 100, and a content corresponding to 0.015 g / m 2 per surface unit (1 m 2 ) based on the specific BET surface area of the positive active material.

[0069] In the same manner as Sample 1 described above, a layered cell type battery of Sample 13 was prepared, except that the specific surface area of the positive active material was 0.66 m 2 / g, Li3PO4 had a content corresponding to 15 wt.% when the content of the positive active material was 100, and a content corresponding to 0.227 g / m 2per surface unit (1 m 2 ) based on the specific BET surface area of the positive active material.

[0070] In the same manner as Sample 1 described above, a layered cell type battery of Sample 14 was prepared, except that the specific surface area of the positive active material was 1.15 m 2 / g, Li3PO4 had a content corresponding to 3.4 wt.% when the content of the positive active material was 100, and a content corresponding to 0.028 g / m 2 per surface unit (1 m 2 ) based on the specific BET surface area of the positive active material.

[0071] In the same manner as Sample 1 described above, a layered cell type battery of Sample 15 was prepared, except that the specific surface area of the positive active material was 1.15 m 2 / g, Li3PO4 had a content corresponding to 5.1 wt.% when the content of the positive active material was 100, and a content corresponding to 0.042 g / m 2 per surface unit (1 m 2 ) based on the specific BET surface area of the positive active material.

[0072] In the same manner as Sample 1 described above, a layered cell type battery of Sample 16 was prepared, except that the specific surface area of the positive active material was 1.15 m 2 / g, Li3PO4 had a content corresponding to 10.2 wt.% when the content of the positive active material was 100, and a content corresponding to 0.083 g / m 2 per surface unit (1 m 2 ) based on the specific BET surface area of the positive active material.

[0073] In the same manner as Sample 1 described above, a layered cell type battery of Sample 17 was prepared, except that the specific surface area of the positive active material was 1.15 m 2 / g, Li3PO4 had a content corresponding to 15.3 wt.% when the content of the positive active material was 100, and a content corresponding to 0.125 g / m 2 per surface unit (1 m 2 ) based on the specific BET surface area of the positive active material.

[0074] In the same manner as Sample 1 described above, except that the specific surface area of the positive active material was 1.15 m 2 / g and no Li3PO4 was used, a layered cell type battery of Sample 18 was constructed in which no Li3PO4 was included in the positive active material layer.

[0075] The following describes a conditioning treatment performed on the test samples. Each of the battery cells of the above-described samples 1 to 18 was placed between two plates and subjected to a load of 350 kgf (350 kg / 25 cm 2 ). Each battery cell under load was subjected to a constant current charge to 4.9 V at a rate of 1.3 C, separated for 10 minutes, then subjected to a constant current discharge to 3.5 V at a rate of 1 / 3 C, and then separated for 10 minutes. This process was repeated three times. The following measurements were performed on the battery cells under load unless otherwise stated.

[0076] After the conditioning treatment, a test (endurance test) was performed on the battery cell of each of the samples, in which a process of performing a constant current charge to 4.9 V at a rate of 2 C in an environment at a temperature of 60°C and then performing a constant current discharge to 3.5 V at a rate of 2 C was repeated 200 times. Table 1 shows the capacity retention ratio (the ratio of the capacity after 200 cycles to the initial capacity) after performing the endurance test on each of the samples.

[0077] Samples 1 to 8, 11 to 15, and 18 are not part of the invention. Table 1 Samples Specific surface area of the positive active material (m 2 / G) Lithium phosphate content based on the weight of the positive active material (wt%) Lithium phosphate content per surface unit (1 m 2 ) based on specific BET surface area of the positive active material (g / m 2 ) Capacity retention ratio (%) 1 0,3 1 0,033 83,9 2 0,3 3 0,100 83,8 3 0,3 5 0,167 80,7 4 0,3 0 0 70,7 5 0,3 0,5 0,017 78,3 6 0,3 10 0,333 75,7 7 0,66 2 0,030 87,0 8 0,66 3 0,045 88,8 9 0,66 5 0,076 88,5 10 0,66 10 0,152 87,0 11 0,66 0 0 67,0 12 0,66 1 0,015 73,2 13 0,66 15 0,227 84,5 14 1,15 3,4 0,028 87,5 15 1,15 5,1 0,042 88,5 16 1,15 10,2 0,083 87,4 17 1,15 15,3 0,125 86,1 18 1,15 0 0 71,4

[0078] As shown in Table 1, it was found that, compared to samples 4, 11, and 18, in which no Li3PO4 was included in the positive active material, the batteries in the other samples containing Li3PO4 exhibited improved capacity retention ratios after the endurance test. This is believed to be because Li3PO4 present in the positive active material layer traps acid generated by the non-aqueous electrolyte solution in a high-voltage state and inhibits the reaction between the positive active material and the acid, thus preventing capacity deterioration caused by transition metal elution. Furthermore, it was found that when the Li3PO4 content was too high, the capacity retention ratio tended to decrease when a predetermined content was reached.

[0079] Fig.4 shows a graph of the relationship between the content ratio of lithium phosphate relative to the weight of the positive active material and the capacity retention ratio on the specific surface area of each of the positive active materials.

[0080] As in Fig. As shown in Figure 4, by plotting the content ratio relative to the weight of the positive active material, it was found that the specific surface areas of three types of positive active materials differed from each other in the optimal content ratio of lithium phosphate. Furthermore, it was found that with increasing specific surface area, the optimal lithium phosphate content tended to increase. This is believed to be because the decomposition of the non-aqueous electrolyte solution and the generation of acid were accelerated as the surface area of the positive active material increased, thus increasing the amount of lithium phosphate required for acid consumption.

[0081] Fig. Figure 5 shows a graph of the relationship between the lithium phosphate content per unit surface area (1 m 2 ) based on the specific BET surface area of the positive active material and the capacity retention ratio.

[0082] As in Fig. 5, when the content is represented in relation to the specific surface, unlike in Fig. 4, in which the content is shown relative to the weight of the positive active material, very similar optimal lithium phosphate content ranges were identified even when using different positive active materials. In view of the results, by representing the content relative to the specific surface area, it is possible to specify the optimal lithium phosphate content regardless of the specification of the positive active material. A specific lithium phosphate content relative to a surface unit (1 m 2) based on the BET specific surface area of the positive active material where the capacity retention ratio is 80% or higher is 0.08 g / m 2 up to 0.225 g / m 2 and preferably 0.08 g / m 2 up to 0.1 g / m 2 . If the specific surface area of the positive active material is 1.15 m 2 / g, the capacity retention ratio is always higher than when the specific surface area of the positive active material is 0.3 m 2 / g. Therefore, it is obvious that the capacity retention ratio is high even when the content of lithium phosphate relative to the weight of the positive active material is 0.225 g / m 2 amounts.

[0083] Although the present invention has been described in detail, the embodiments and samples are merely examples and are not limited thereto.

Claims

[1] Lithium-ion secondary battery (100), characterized by that it includes: a positive electrode (50) including a positive active material layer (54); a negative electrode (60) including a negative active material layer (64); and a non-aqueous electrolyte, where the positive active material layer contains a positive active material and an inorganic phosphate compound, a specific BET surface area of the positive active material 0.66 m 2 / g up to 1.15 m 2 / g, the inorganic phosphate compound contains an alkali metal, an alkaline earth metal and / or a hydrogen atom in a chemical formula, a content of the inorganic phosphate compound in the positive active material layer of 0.08 g / m 2 up to 0.225 g / m 2 per unit surface area based on the specific BET surface area of the positive active material, and the lithium-ion secondary battery is configured to allow an open circuit voltage of the lithium-ion secondary battery to be increased to 4.3 V or higher in terms of metallic lithium. [2] The lithium-ion secondary battery according to claim 1, wherein the content of the inorganic phosphate compound in the positive active material layer is 0.08 g / m 2 up to 0.17 g / m 2 per unit surface area based on the specific BET surface area of the positive active material. [3] The lithium-ion secondary battery according to claim 2, wherein the content of the inorganic phosphate compound in the positive active material layer is 0.08 g / m 2 up to 0.1 g / m 2 per unit surface area based on the specific BET surface area of the positive active material. [4] A lithium-ion secondary battery according to any one of claims 1 to 3, wherein the inorganic phosphate compound includes at least one lithium phosphate. [5] The lithium ion secondary battery according to claim 4, wherein the lithium phosphate includes Li3PO4. [6] The lithium ion secondary battery according to any one of claims 1 to 5, wherein the positive active material is a spinel positive active material containing Li, Ni and Mn. [7] The lithium-ion secondary battery according to claim 6, wherein the spinel positive active material is LiNi 0,5 Mn 1,5 O4 is. [8] A method for producing a lithium-ion secondary battery (100) comprising a positive electrode (50), a negative electrode (60) and a non-aqueous electrolyte, wherein the positive electrode comprises a positive active material layer (54) containing a positive active material and the negative electrode comprises a negative active material layer (64) containing a negative active material, the method characterized by is that it includes: Obtaining a specific BET surface area of the positive active material of 0.66 m2 / g up to 1.15 m 2 / g; and Adding an inorganic phosphate compound to the positive active material layer to adjust an amount of the inorganic phosphate compound to 0.08 g / m 2 up to 0.225 g / m 2 per unit surface area based on the specific BET surface area of the positive active material, where the inorganic phosphate compound contains an alkali metal, an alkaline earth metal and / or a hydrogen atom, and the lithium-ion secondary battery is configured to allow an open circuit voltage of the lithium-ion secondary battery to be increased to 4.3 V or higher in terms of metallic lithium. [9] The method according to claim 8, wherein the amount of inorganic phosphate added to the positive active material layer is 0.08 g / m 2 up to 0.17 g / m 2 per unit surface area based on the specific BET surface area of the positive active material. [10] The method according to claim 9, wherein the amount of inorganic phosphate added to the positive active material layer is 0.08 g / m 2 up to 0.1 g / m 2 per unit surface area based on the specific BET surface area of the positive active material.

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