Manufacturing method of non-aqueous electrolyte secondary battery

Abstract

To provide a method capable of manufacturing a non-aqueous electrolyte secondary battery, in which resistance increase at the time when it is located under a long period high temperature is suppressed.SOLUTION: A manufacturing method of a non-aqueous electrolyte secondary battery to be disclosed, contains: a step of preparing a battery assembly having a positive electrode, a negative electrode, and a non-aqueous electrolyte; a step of exciting initial charging to the battery assembly; and a step of exciting aging processing to the battery assembly to which the initial charging is executed. The positive electrode comprises: a positive electrode collector; and a positive electrode activation layer supported by the positive electrode collector. The positive electrode active material layer contains: a positive electrode active material; and a thiophospheric acid. A content ratio of the thiophospheric acid in the positive electrode active material layer is 1 mass% to 10 mass%. The initial charging is performed until a voltage becomes a dissolution start potential or more of the thiophospheric acid. The aging processing is performed in a state where the battery assembly is charged to the voltage that becomes the dissolution start potential of the thiophospheric acid.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing a non-aqueous electrolyte secondary battery. [Background technology]

[0002] In recent years, nonaqueous electrolyte secondary batteries such as lithium ion secondary batteries have been suitably used as portable power sources for personal computers, mobile terminals, and the like, and as power sources for driving vehicles such as electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), among others.

[0003] The positive electrode of a non-aqueous electrolyte secondary battery typically includes a positive electrode active material layer containing a positive electrode active material. For the purpose of improving the performance of a non-aqueous electrolyte secondary battery, a technique is known in which an additive (so-called positive electrode additive) that forms a coating on the surface of a positive electrode active material is contained in a positive electrode active material layer. For example, Patent Document 1 describes that the cycle characteristics of a non-aqueous electrolyte secondary battery are improved by containing a thiophosphate ester or a thiophosphate ester salt in the positive electrode active material layer. For example, Patent Document 2 describes that the output characteristics and cycle characteristics of a non-aqueous electrolyte secondary battery are improved by containing lithium phosphate in the positive electrode active material layer when a high-potential positive electrode active material is used. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2002-352804 A [Patent Document 2] JP 2016-062644 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, as a result of intensive research, the present inventors have found that in the above-mentioned conventional techniques, there is room for improvement in the high-temperature storage characteristics of nonaqueous electrolyte secondary batteries, specifically, there is room for improvement in suppressing an increase in resistance when a nonaqueous electrolyte secondary battery is placed under high temperatures for a long period of time.

[0006] SUMMARY OF THE PRESENT DISCLOSURE An object of the present invention is to provide a method for producing a non-aqueous electrolyte secondary battery in which an increase in resistance when placed at high temperatures for a long period of time is suppressed. [Means for solving the problem]

[0007] The method for manufacturing a non-aqueous electrolyte secondary battery disclosed herein includes the steps of preparing a battery assembly including a positive electrode, a negative electrode, and a non-aqueous electrolyte, performing an initial charge on the battery assembly, and performing an aging treatment on the battery assembly that has been initially charged. The positive electrode includes a positive electrode current collector and a positive electrode active material layer supported on the positive electrode current collector. The positive electrode active material layer contains a positive electrode active material and a thiophosphate. The content of the thiophosphate in the positive electrode active material layer is 1% by mass to 10% by mass. The initial charge is performed up to a voltage equal to or higher than the decomposition start potential of the thiophosphate. The aging treatment is performed in a state in which the battery assembly is charged to a voltage equal to or higher than the decomposition start potential of the thiophosphate.

[0008] According to this configuration, it is possible to provide a method for manufacturing a nonaqueous electrolyte secondary battery in which an increase in resistance when placed at high temperatures for a long period of time is suppressed. [Brief description of the drawings]

[0009] [Figure 1] 2 is a flowchart showing each step of a method for producing a nonaqueous electrolyte secondary battery according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram illustrating the configuration of a wound electrode body of a nonaqueous electrolyte secondary battery produced according to one embodiment of the present invention. [Diagram 3] 1 is a cross-sectional view that illustrates a schematic configuration of a nonaqueous electrolyte secondary battery produced according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Matters not mentioned in this specification but necessary for carrying out the present invention can be understood as design matters for a person skilled in the art based on the prior art in the relevant field. The present invention can be carried out based on the contents disclosed in this specification and the technical common sense in the relevant field. In addition, in the following drawings, members and parts having the same function are described with the same reference numerals. Furthermore, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect the actual dimensional relationships. In addition, the numerical range expressed as "A to B" in this specification includes A and B.

[0011] In this specification, the term "secondary battery" refers to an electricity storage device that can be repeatedly charged and discharged. In addition, in this specification, the term "lithium ion secondary battery" refers to a secondary battery that uses lithium ions as a charge carrier and realizes charging and discharging by the transfer of charge associated with the lithium ions between the positive and negative electrodes.

[0012] Hereinafter, as an example, the present invention will be described in detail with respect to an embodiment in which the nonaqueous electrolyte secondary battery is a flat prismatic lithium ion secondary battery; however, it is not intended that the present invention be limited to the embodiment described above.

[0013] Fig. 1 shows each step of the method for producing a nonaqueous electrolyte secondary battery according to the present embodiment. Fig. 2 shows a schematic configuration of an electrode body of a lithium ion secondary battery as an example of a nonaqueous electrolyte secondary battery obtained by the method for producing the present embodiment. Fig. 3 shows a schematic internal structure of a lithium ion secondary battery as an example of a nonaqueous electrolyte secondary battery obtained by the method for producing the present embodiment.

[0014] As shown in FIG. 1, the method for producing a non-aqueous electrolyte secondary battery according to this embodiment includes a step S101 of preparing a battery assembly including a positive electrode, a negative electrode, and a non-aqueous electrolyte (hereinafter also referred to as an "assembly preparation step"), a step S102 of initially charging the battery assembly (hereinafter also referred to as an "initial charging step"), and a step S103 of aging the battery assembly that has been initially charged (hereinafter also referred to as an "aging step"). The positive electrode includes a positive electrode current collector and a positive electrode active material layer supported on the positive electrode current collector. The positive electrode active material layer contains a positive electrode active material and a thiophosphate. The content of the thiophosphate in the positive electrode active material layer is 1% by mass to 10% by mass. The initial charging is performed up to a voltage equal to or higher than the decomposition start potential of the thiophosphate. The aging treatment is performed in a state where the battery assembly is charged to a voltage equal to or higher than the decomposition start potential of the thiophosphate. Hereinafter, each step of the method for producing a nonaqueous electrolyte secondary battery according to this embodiment will be described.

[0015] First, the assembly preparation step S101 will be described. In the assembly preparation step S101, a battery assembly including a positive electrode 50, a negative electrode 60, and a non-aqueous electrolyte 80 is prepared.

[0016] The positive electrode 50 used in the assembly preparation step S101 may be a known positive electrode used in a lithium ion secondary battery. The positive electrode 50 typically includes a positive electrode collector 52 and a positive electrode active material layer 54 supported by the positive electrode collector 52, as shown in FIG. 2, for example. The positive electrode active material layer 54 may be provided on one side or both sides of the positive electrode collector 52, but is preferably provided on both sides. The positive electrode 50 typically includes a positive electrode active material layer non-formed portion 52a (i.e., a portion where the positive electrode active material layer 54 is not formed and the positive electrode collector 52 is exposed) as shown in FIG. 2.

[0017] A known positive electrode current collector used in lithium ion secondary batteries may be used as the positive electrode current collector 52, and examples thereof include a sheet or foil made of a metal having good electrical conductivity (e.g., aluminum, nickel, titanium, stainless steel, etc.). As the positive electrode current collector 52, aluminum foil is preferred.

[0018] The dimensions of the positive electrode current collector 52 are not particularly limited and may be appropriately determined depending on the battery design. When an aluminum foil is used as the positive electrode current collector 52, the thickness is not particularly limited, but is, for example, 5 μm or more and 35 μm or less, and preferably 7 μm or more and 20 μm or less.

[0019] The positive electrode active material layer 54 contains a positive electrode active material and a thiophosphate. As the positive electrode active material, a known positive electrode active material used in a lithium ion secondary battery may be used. Specifically, for example, as the positive electrode active material, a lithium composite oxide, a lithium transition metal phosphate compound, or the like may be used. The crystal structure of the positive electrode active material is not particularly limited, and may be a layered structure, a spinel structure, an olivine structure, or the like.

[0020] The lithium composite oxide is preferably a lithium transition metal composite oxide containing at least one of Ni, Co, and Mn as a transition metal element, and specific examples thereof include lithium nickel-based composite oxides, lithium cobalt-based composite oxides, lithium manganese-based composite oxides, lithium nickel manganese-based composite oxides, lithium nickel cobalt manganese-based composite oxides, lithium nickel cobalt aluminum-based composite oxides, and lithium iron nickel manganese-based composite oxides.

[0021] In this specification, the term "lithium nickel cobalt manganese composite oxide" includes oxides containing Li, Ni, Co, Mn, and O as constituent elements, as well as oxides containing one or more additional elements other than those. Examples of such additional elements include transition metal elements and typical metal elements such as Mg, Ca, Al, Ti, V, Cr, Y, Zr, Nb, Mo, Hf, Ta, W, Na, Fe, Zn, and Sn. The additional element may be a semimetal element such as B, C, Si, or P, or a nonmetal element such as S, F, Cl, Br, or I. This also applies to the above-mentioned lithium nickel composite oxide, lithium cobalt composite oxide, lithium manganese composite oxide, lithium nickel manganese composite oxide, lithium nickel cobalt aluminum composite oxide, and lithium iron nickel manganese composite oxide.

[0022] Examples of the lithium transition metal phosphate compound include lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), and lithium manganese iron phosphate.

[0023] These positive electrode active materials may be used alone or in combination of two or more.

[0024] The thiophosphate is decomposed by the initial charge in the next initial charge step S102, and a coating derived from the thiophosphate is formed on the surface of the positive electrode active material. The initial charge is performed at a voltage equal to or higher than the decomposition onset potential of the thiophosphate. However, since it is only necessary to apply a voltage equal to or higher than the decomposition onset potential of the thiophosphate to the lithium ion secondary battery only during the initial charge, the upper limit potential of the positive electrode active material in a general use mode of the lithium ion secondary battery may be lower than the decomposition onset potential of the thiophosphate.

[0025] From the viewpoint of battery characteristics and stability of crystal structure during initial charging, the positive electrode active material is preferably a lithium composite oxide having a layered structure. The lithium composite oxide preferably contains Ni. Therefore, the positive electrode active material is preferably a lithium nickel cobalt manganese composite oxide and a lithium nickel cobalt aluminum composite oxide, and more preferably a lithium nickel cobalt manganese composite oxide.

[0026] The ratio of Ni to the total of metal elements other than Li in the lithium composite oxide is preferably 20 mol % to 60 mol %, and more preferably 30 mol % to 50 mol %.

[0027] The average particle diameter (median diameter: D50) of the positive electrode active material is not particularly limited, but is, for example, 0.05 μm to 25 μm, preferably 1 μm to 20 μm, and more preferably 3 μm to 15 μm. The average particle diameter (D50) of the positive electrode active material can be determined, for example, by a laser diffraction scattering method.

[0028] The content of the positive electrode active material in the positive electrode active material layer 54 (i.e., the content of the positive electrode active material relative to the total mass of the positive electrode active material layer 54) is not particularly limited, but is, for example, 80 mass% or more, preferably 85 mass% or more, and more preferably 87 mass% or more.

[0029] The thiophosphate is a component (so-called positive electrode additive) that is added to the positive electrode to form a coating on the surface of the positive electrode active material by initial charging in the next initial charging step S102. The thiophosphate is a salt of a thiophosphate anion represented by the following formula (1) and a cation. The thiophosphate is typically an inorganic salt and therefore typically does not contain an organic group. The thiophosphate anion is a trivalent anion, and the cation is a monovalent, divalent, or trivalent cation (particularly a metal cation).

[0030] [ka]

[0031] Since the thiophosphate anion contributes greatly to the formation of the coating, the type of cation is not particularly limited. Examples of the cation include Li + , Na + , K + Alkali metal cations such as Mg 2+ , Ca 2+ , Sr 2+ , B.A. 2+ Alkaline earth metal cations such as Zn 2+ Group 12 element cations such as Al 3+ and the like. Among these, alkali metal cations are preferred. Thus, the preferred thiophosphate is an alkali metal salt of thiophosphoric acid.

[0032] From the viewpoint of availability, sodium thiophosphate is particularly preferred as the thiophosphate, and from the viewpoint of battery performance, lithium thiophosphate is particularly preferred as the thiophosphate.

[0033] The larger the content of the thiophosphate in the positive electrode active material layer 54, the higher the effect of suppressing the increase in resistance when the lithium ion secondary battery 100 is placed under high temperature for a long period of time. Therefore, the content of the thiophosphate in the positive electrode active material layer 54 (i.e., the mass ratio of the thiophosphate to the total mass of all components of the positive electrode active material layer) is 1 mass% or more, preferably 2 mass% or more, more preferably 2.5 mass% or more, and even more preferably 3 mass% or more. On the other hand, if the content of the thiophosphate is large, the initial resistance tends to increase. Therefore, the content of the above positive electrode additive in the positive electrode active material layer 54 is 10 mass% or less, preferably 8 mass% or less, more preferably 7.5 mass% or less, and even more preferably 7 mass% or less.

[0034] The positive electrode active material layer 54 may contain only a thiophosphate as a positive electrode additive, or may further contain other positive electrode additives within a range that does not significantly impair the effects of the present invention.

[0035] The positive electrode active material layer 54 may contain components (i.e., optional components) other than the above positive electrode active material and thiophosphate. Examples of the optional components include a conductive material, a binder, and the like. As the conductive material, for example, a carbon material such as carbon black (e.g., acetylene black), carbon nanotubes (CNT), graphite, and the like may be suitably used. As the binder, for example, polyvinylidene fluoride (PVDF) and the like may be used. When CNT is used as the conductive material, the positive electrode active material layer 54 may further contain a dispersant for CNT.

[0036] The content of the conductive material in the positive electrode active material layer 54 is not particularly limited, but is preferably from 0.1% by mass to 15% by mass, and more preferably from 0.5% by mass to 13% by mass. The content of the binder in the positive electrode active material layer 54 is not particularly limited, but is preferably from 1% by mass to 15% by mass, and more preferably from 1.5% by mass to 10% by mass.

[0037] The thickness of the positive electrode active material layer 54 is not particularly limited, but is, for example, from 10 μm to 300 μm, and preferably from 20 μm to 200 μm.

[0038] The positive electrode sheet 50 may contain an insulating layer (not shown) at the boundary between the positive electrode active material layer non-forming portion 52a and the positive electrode active material layer 54. The insulating layer contains, for example, ceramic particles.

[0039] Positive electrode 50 can be prepared by a known method, for example, by preparing a positive electrode paste containing a positive electrode active material, a thiophosphate, and any optional components, applying the positive electrode paste to positive electrode current collector 52, drying, and pressing as necessary, thereby preparing positive electrode 50. Note that in this specification, the term "paste" is used as a term that also includes forms called "slurry" and "ink."

[0040] The negative electrode 60 used in the assembly preparation step S101 may be a known negative electrode used in a lithium ion secondary battery. The negative electrode 60 typically includes a negative electrode current collector 62 and a negative electrode active material layer 64 supported by the negative electrode current collector 62, for example, as shown in FIG. 2. The negative electrode active material layer 64 may be provided on one side or both sides of the negative electrode current collector 62, but is preferably provided on both sides. The negative electrode 60 typically includes a negative electrode active material layer non-formed portion 62a (i.e., a portion where the negative electrode active material layer 64 is not formed and the negative electrode current collector 62 is exposed) as shown in FIG. 2.

[0041] A known negative electrode current collector used in lithium ion secondary batteries may be used as the negative electrode current collector 62, and examples thereof include a sheet or foil made of a metal having good electrical conductivity (e.g., copper, nickel, titanium, stainless steel, etc.). Copper foil is preferable as the negative electrode current collector 62.

[0042] The dimensions of the negative electrode current collector 62 are not particularly limited and may be appropriately determined depending on the battery design. When a copper foil is used as the negative electrode current collector 62, the thickness is not particularly limited, but is, for example, 5 μm or more and 35 μm or less, and preferably 7 μm or more and 20 μm or less.

[0043] The negative electrode active material layer 64 contains a negative electrode active material. As the negative electrode active material, for example, a carbon material such as graphite, hard carbon, soft carbon, etc. The graphite may be natural graphite or artificial graphite, or may be amorphous carbon-coated graphite in which graphite is coated with an amorphous carbon material.

[0044] The average particle diameter (median diameter: D50) of the negative electrode active material is not particularly limited, but is, for example, 0.1 μm to 50 μm, preferably 1 μm to 25 μm, and more preferably 5 μm to 20 μm. The average particle diameter (D50) of the negative electrode active material can be determined, for example, by a laser diffraction scattering method.

[0045] The negative electrode active material layer 64 may contain components other than the active material, such as a binder, a thickener, etc. As the binder, for example, styrene butadiene rubber (SBR), polyvinylidene fluoride (PVDF), etc. may be used. As the thickener, for example, carboxymethyl cellulose (CMC), etc. may be used.

[0046] The content of the negative electrode active material in the negative electrode active material layer 64 is preferably 90% by mass or more, and more preferably 95% by mass or more and 99% by mass or less. The content of the binder in the negative electrode active material layer 64 is preferably 0.1% by mass or more and 8% by mass or less, and more preferably 0.5% by mass or more and 3% by mass or less. The content of the thickener in the negative electrode active material layer 64 is preferably 0.3% by mass or more and 3% by mass or less, and more preferably 0.5% by mass or more and 2% by mass or less.

[0047] The thickness of the negative electrode active material layer 64 is not particularly limited, but is, for example, not less than 10 μm and not more than 300 μm, and preferably not less than 20 μm and not more than 200 μm.

[0048] The negative electrode 60 can be prepared by making according to a known method. For example, the negative electrode 60 can be prepared by making a negative electrode paste containing a negative electrode active material and optional components, applying the negative electrode paste to a negative electrode current collector 62, drying, and pressing as necessary.

[0049] The positive electrode 50 and the negative electrode 60 are typically used as an electrode body 20 in which the positive electrode 50 and the negative electrode 60 are stacked with a separator 70 interposed therebetween. The electrode body 20 may be a stacked electrode body or a wound electrode body. In the illustrated example, the electrode body 20 is a wound electrode body.

[0050] The separator 70 may be a porous sheet (film) made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, or polyamide. Such a porous sheet may have a single-layer structure or a laminated structure of two or more layers (for example, a three-layer structure in which a PP layer is laminated on both sides of a PE layer). A heat-resistant layer (HRL) may be provided on the surface of the separator 70.

[0051] The thickness of the separator 70 is not particularly limited, but is, for example, 5 μm to 50 μm, and preferably 10 μm to 30 μm. The air permeability of the separator 70 obtained by the Gurley test method is not particularly limited, but is preferably 350 sec / 100 cc or less.

[0052] The electrode assembly 20 can be produced according to a known method. When the electrode assembly 20 is a wound electrode assembly as in the illustrated example, it can be prepared, for example, as follows.

[0053] First, the positive electrode sheet 50 and the negative electrode sheet 60 are overlapped with a separator sheet 70 interposed therebetween. The separator sheet 70 is then laminated. At this time, as shown in FIG. 2, the positive electrode sheet 50 and the negative electrode sheet 60 are overlapped such that the positive electrode active material layer non-forming portion 52a and the negative electrode sheet 60 are overlapped such that they protrude in opposite directions from the widthwise ends of the two separator sheets 70.

[0054] The obtained laminate is wound. The winding of the laminate can be carried out according to a known method. For example, the laminate can be wound on the outer peripheral surface of a winding core using a winding machine equipped with a known winding core. The winding conditions may be the same as known conditions.

[0055] Next, the wound laminate is pressed to produce a flat wound electrode body. This pressing can be performed by pressing the laminate wound in the above-mentioned winding step using a known pressing device used in the manufacture of a general flat wound electrode body. The pressing conditions may be the same as known conditions.

[0056] On the other hand, the battery case 30 is prepared. Specifically, as shown in FIG. 3, a body of the battery case 30 having an opening and a lid of the battery case 30 are prepared. The opening has a dimension that allows the wound electrode body 20 to be inserted. The lid has a dimension that closes the opening of the body of the battery case 30. The lid is also provided with a thin-walled safety valve 36 that is set to release the internal pressure when the internal pressure of the battery case 30 rises to a predetermined level or higher, and an injection port (not shown) for injecting a non-aqueous electrolyte. The battery case 30 is made of a lightweight metal material with good thermal conductivity, such as aluminum.

[0057] In addition, a nonaqueous electrolyte 80 is prepared. The nonaqueous electrolyte 80 typically contains a nonaqueous solvent and a supporting salt (electrolyte salt). As the nonaqueous solvent, various organic solvents such as carbonates, ethers, esters, nitriles, sulfones, and lactones that are used in general electrolytes of lithium ion secondary batteries can be used without any particular limitation. Among them, carbonates and esters are preferable, and specific examples thereof include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC), monofluoromethyl difluoromethyl carbonate (F-DMC), trifluorodimethyl carbonate (TFDMC), methyl acetate, and methyl propionate. Such nonaqueous solvents can be used alone or in appropriate combination of two or more.

[0058] As the supporting salt, for example, a lithium salt such as LiPF6, LiBF4, lithium bis(fluorosulfonyl)imide (LiFSI) (preferably LiPF6) can be suitably used. The concentration of the supporting salt is preferably 0.7 mol / L or more and 1.3 mol / L or less.

[0059] The non-aqueous electrolyte 80 may contain components (eg, various additives) other than the above-mentioned components, so long as the effects of the present invention are not significantly impaired.

[0060] For example, when the non-aqueous electrolyte 80 contains an oxalato complex as a film-forming agent, the increase in resistance when the electrolyte is placed under high temperature for a long period of time can be further suppressed. Examples of the oxalato complex include lithium difluoro(oxalato)borate (LiBF2(C2O4)), lithium bis(oxalato)borate (LiB(C2O4)2), lithium tetrafluoro(oxalato)phosphate (LiPF4(C2O4)), and lithium difluorobis(oxalato)phosphate (LiPF2(C2O4)2). Among these, lithium bis(oxalato)borate (LiBOB) is preferred because of its high film-forming ability.

[0061] The concentration of the oxalate complex in the non-aqueous electrolyte 80 is, for example, 0.1% by mass or more and 1.5% by mass or less, preferably 0.3% by mass or more and 1.5% by mass or less, and more preferably 0.5% by mass or more and 1.5% by mass or less. From the viewpoint of achieving both initial resistance and high-temperature storage characteristics, the concentration of the oxalate complex in the non-aqueous electrolyte 80 is preferably 0.5% by mass or more and 1.0% by mass or less.

[0062] Examples of other additives include film-forming agents such as vinylene carbonate (VC); gas generating agents such as biphenyl (BP) and cyclohexylbenzene (CHB); and thickeners.

[0063] Next, the positive terminal 42 and the positive current collector 42a, and the negative terminal 44 and the negative current collector 44a are attached to the lid of the battery case 30. The positive current collector 42a and the negative current collector 44a are welded by ultrasonic welding, resistance welding, or the like to the positive active material layer non-forming portion 52a and the negative active material layer non-forming portion 62a exposed at the ends of the wound electrode body 20, respectively. Then, the wound electrode body 20 is housed inside the battery case 30 body through its opening, and the body and the lid of the battery case 30 are welded by laser welding, or the like.

[0064] Next, the non-aqueous electrolyte 80 is injected through the injection port of the lid of the battery case 30. The injection of the non-aqueous electrolyte 80 can be carried out according to a known method. After the injection of the non-aqueous electrolyte 80, the injection port is sealed to obtain the battery assembly 100. The injection port can be sealed according to a known method.

[0065] Next, the initial charging step S102 will be described. In the initial charging step S102, the battery assembly 100 is initially charged. This initial charging is performed up to a voltage equal to or higher than the decomposition start potential of the thiophosphate. This decomposes the thiophosphate in the positive electrode active material layer 54, and a coating derived from the thiophosphate can be formed on the surface of the positive electrode active material.

[0066] Here, as a positive electrode additive, thiophosphate has a relatively low decomposition potential. For example, the decomposition potential of Li3PO3 is 4.50 V (vs Li + / Li) (i.e., 4.50 V based on metallic lithium), whereas the decomposition potential of sodium thiophosphate (Na3PSO3) is 4.35 V (vsLi + / Li). Therefore, when the battery assembly 100 is initially charged, the thiophosphate can be efficiently decomposed, and a high-quality coating can be formed on the surface of the positive electrode active material layer. As a result, an increase in resistance when the lithium-ion secondary battery 100 is placed under high temperatures for a long period of time can be suppressed.

[0067] The upper limit voltage of the initial charge depends on the type of thiophosphate. However, if the upper limit voltage of the initial charge is set too high, excessive decomposition of the non-aqueous electrolyte 80 and structural deterioration of the positive electrode active material may occur. Therefore, the upper limit voltage of the initial charge is preferably set to a value at which the positive electrode potential is 4.70 V (vs Li + / Li), and more preferably, the positive electrode potential is 4.50V (vs. Li + / Li).

[0068] The initial charge is when the potential of the positive electrode 50 is 4.35V (vs Li + / Li)~4.70V(vsLi +It is preferable to perform the test up to a voltage of 4.35V (vsLi + / Li)~4.50V(vsLi + It is more preferable to perform the process until the voltage becomes 0.1 / Li.

[0069] The initial charging can be performed according to a known method. Specifically, it can be performed by applying a predetermined voltage between the positive electrode 50 and the negative electrode 60 using a known voltage application device (not shown). The current value is not particularly limited, but is preferably 1 C or less, and more preferably 0.1 C or more and 0.5 C or less. After charging, discharging is usually performed. In the initial charging, charging may be performed only once, or may be performed multiple times (for example, 2 to 3 times).

[0070] Next, the aging step S103 will be described. In the aging step S103, an aging treatment is performed on the battery assembly 100 that has been initially charged in the previous step. This aging treatment is performed in a state where the battery assembly 100 is charged to a voltage equal to or higher than the decomposition start potential of the thiophosphate. This further decomposes the thiophosphate in the positive electrode active material layer 54, and further forms a coating derived from the thiophosphate on the surface of the positive electrode active material, thereby further improving the quality of the coating.

[0071] If the voltage of the battery assembly 100 in the aging step S103 is too high, excessive decomposition of the nonaqueous electrolyte 80, structural deterioration of the positive electrode active material, etc. may occur. Therefore, the voltage of the battery assembly 100 is preferably set to a positive electrode potential of 4.70 V (vs Li + / Li), and more preferably, the positive electrode potential is 4.50 V (vs. Li + / Li).

[0072] Therefore, the aging treatment is preferably performed when the potential of the positive electrode 50 is 4.35 V (vs Li + / Li)~4.70V(vsLi + / Li), more preferably 4.35V (vsLi + / Li)~4.50V(vsLi +This is done while the battery is charged to a voltage of 0.1 V / Li.

[0073] The temperature of the aging treatment is not particularly limited, but is preferably a temperature higher than room temperature. Specifically, the temperature of the aging treatment is preferably 40° C. to 100° C., more preferably 40° C. to 75° C. The time of the aging treatment is not particularly limited. The time of the aging treatment is preferably 1 hour to 72 hours, more preferably 4 hours to 24 hours.

[0074] Therefore, it is particularly preferable that the aging treatment is carried out at a temperature within the range of 40° C. to 75° C. for 4 hours to 24 hours.

[0075] The aging step S103 can be performed according to a known method, for example, by adjusting the state of charge of the battery assembly 100 using a known voltage application device (not shown) and leaving it in a thermostatic bath or the like.

[0076] In the aging step S103, the thiophosphate is decomposed and a coating film derived from the thiophosphate is formed on the surface of the positive electrode active material. Therefore, by performing the initial charging step S102 and the aging step S103, the thiophosphate can be efficiently decomposed and a coating film can be effectively formed on the surface of the positive electrode active material.

[0077] By going through the above steps, a lithium ion secondary battery 100 can be obtained. In the lithium ion secondary battery 100, a high-quality coating derived from a thiophosphate is formed on the surface of the positive electrode active material, and this coating can suppress decomposition of the non-aqueous electrolyte 80 during storage. As a result, in the lithium ion secondary battery 100, an increase in resistance when it is placed under high temperatures for a long period of time is suppressed. Therefore, according to the manufacturing method of this embodiment, a lithium ion secondary battery 100 with excellent durability can be manufactured.

[0078] The lithium ion secondary battery 100 can be used for various purposes. Specific applications include portable power sources for personal computers, portable electronic devices, portable terminals, etc.; power sources for driving vehicles such as electric vehicles (BEVs), hybrid vehicles (HEVs), and plug-in hybrid vehicles (PHEVs); and storage batteries for small power storage devices, among which a power source for driving vehicles is preferred. The lithium ion secondary battery 100 can also be used in the form of a battery pack typically consisting of a plurality of batteries connected in series and / or parallel.

[0079] As an example, a rectangular lithium ion secondary battery 100 including a flat wound electrode assembly 20 has been described. However, the method for manufacturing a nonaqueous electrolyte secondary battery disclosed herein can also be used to manufacture a lithium ion secondary battery including a laminated electrode assembly (i.e., an electrode assembly in which multiple positive electrodes and multiple negative electrodes are alternately laminated). Furthermore, the method for manufacturing a nonaqueous electrolyte secondary battery disclosed herein can also be used to manufacture a coin-type lithium ion secondary battery, a button-type lithium ion secondary battery, a cylindrical lithium ion secondary battery, and a laminate case-type lithium ion secondary battery. Furthermore, the method for manufacturing a nonaqueous electrolyte secondary battery disclosed herein can also be used to manufacture nonaqueous electrolyte secondary batteries other than lithium ion secondary batteries.

[0080] Examples of the present invention will be described below, but it is not intended that the present invention be limited to those shown in these examples.

[0081] Examples 1 to 6 and Comparative Examples 1 to 6 [Preparation of Lithium Ion Secondary Battery Assembly] LiNi as a positive electrode active material powder 0.5 Co 0.2 Mn 0.3O2 (NCM), acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were mixed in a mass ratio of NCM:AB:PVdF=90:5:5. The positive electrode additives shown in Table 1 were added thereto so that the content ratio in the positive electrode active material layer was the amount shown in Table 1, and mixed with N-methylpyrrolidone (NMP). In this way, a slurry for forming a positive electrode active material layer was prepared. This slurry was applied to both sides of an aluminum foil and then dried to form a positive electrode active material layer. The total basis weight of both sides at this time was 15 mg / cm. 2 Next, the positive electrode active material layer was 3 A positive electrode sheet was obtained by rolling and pressing the sheet so as to obtain a positive electrode sheet.

[0082] A negative electrode active material layer forming slurry was prepared by mixing natural graphite (C) as a negative electrode active material, styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener with ion-exchanged water in a mass ratio of C:SBR:CMC=97:2:1. This slurry was applied to both sides of a copper foil and then dried to form a negative electrode active material layer. The total weight of both sides was 9 mg / cm. 2 Next, the negative electrode active material layer was 3 A roll press treatment was performed so that a negative electrode sheet was obtained.

[0083] A polyolefin porous film was prepared as a separator. The prepared positive electrode sheet and negative electrode sheet were laminated with the separator interposed therebetween to prepare a laminated electrode body. Terminals were attached to this electrode body, which was then housed in an aluminum battery case.

[0084] A mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 25:40:35 was prepared. In Examples 1 and 2 and Comparative Examples 1 to 6, LiPF6 was dissolved in this mixed solvent at a concentration of 1.1 mol / L to prepare a non-aqueous electrolyte. In Examples 3 to 6, LiPF6 was dissolved in this mixed solvent at a concentration of 1.1 mol / L, and lithium bis(oxalato)borate (LiBOB) was further dissolved in the amount shown in Table 1 to prepare a non-aqueous electrolyte. The prepared non-aqueous electrolyte was poured into a battery case, and then the battery case was sealed to obtain a battery assembly.

[0085] [Initial charging] The obtained battery assembly was placed in a thermostatic chamber at 25° C. The battery assembly was charged at a constant current of 0.1 C up to a predetermined upper limit voltage, and then discharged at a constant current up to 3.0 V. This predetermined upper limit voltage was determined by the positive electrode potential (vs Li + This charge and discharge was repeated twice as the initial charge.

[0086] [Aging treatment] After the initial charge, the battery assembly was charged at a positive electrode potential (vs Li + The battery assembly was then placed in a thermostatic chamber at 60° C. and aged for 12 hours. In this manner, a lithium ion secondary battery was obtained.

[0087] [Initial characteristic evaluation] The lithium ion secondary batteries prepared in each of the Examples and Comparative Examples were charged at a constant current of 0.1 C to the same upper limit voltage as the initial charge, and then discharged at a constant current to 3.0 V. The discharge capacity at this time was measured and used as the initial capacity.

[0088] This initial capacity was taken as SOC100%, and the lithium ion secondary battery was adjusted to SOC50% at 25°C. The lithium ion secondary battery was then placed in a thermostatic chamber at -10°C and discharged at a current value of 10C for 10 seconds. The voltage change amount ΔV at this time was measured, and the output resistance of the lithium ion secondary battery was calculated as the initial resistance using this voltage change amount ΔV and the current value. The results are shown in Table 1.

[0089] [Evaluation of high-temperature storage characteristics] The lithium ion secondary battery was adjusted to SOC 80% in a temperature environment of 25°C. This lithium ion secondary battery was placed in a thermostatic chamber at 60°C and stored for 60 days. Thereafter, the output resistance after storage was measured in the same manner as for the initial resistance. The resistance increase rate (%) was calculated from the formula: (output resistance after high-temperature storage / initial resistance) x 100. The results are shown in Table 1.

[0090] [Table 1]

[0091] The decomposition potential of sodium thiophosphate (Na3PSO3) is 4.35V (vsLi + / Li). Comparative Example 1 and Comparative Example 2 are examples in which the voltage in the aging process is lowered, and a coating derived from thiophosphoric acid is not formed in the aging process. Comparative Example 3 is an example in which the voltage in the initial charging process and the aging process is lowered, and a coating derived from thiophosphoric acid is not formed in the initial charging process and the aging process. Comparison of Comparative Example 1 and Comparative Example 2 with Comparative Example 3 shows that the increase in resistance during high-temperature storage can be suppressed by performing an initial charge on the battery assembly to a voltage equal to or higher than the decomposition start potential of Na3PSO3 to form a coating. In addition, comparison of Examples 1 and 2 with Comparative Examples 1 and 2 shows that the increase in resistance during high-temperature storage can be further suppressed by performing an aging treatment while the battery assembly is charged to a voltage equal to or higher than the decomposition start potential of Na3PSO3, and further forming a coating.

[0092] Comparative Example 4 is an example in which no positive electrode additive was used, and Comparative Examples 5 and 6 are examples in which trilithium phosphate and a thiophosphate ester were used as the positive electrode additive, respectively. A comparison of Examples 1 and 2 and Comparative Examples 4 to 6 shows that when the positive electrode additive is a thiophosphate, the effect of suppressing the increase in resistance during high-temperature storage can be obtained.

[0093] Moreover, LiBOB was contained in the non-aqueous electrolyte in Examples 3 to 6. These results show that when LiBOB is contained in the non-aqueous electrolyte, the effect of suppressing the increase in resistance during high-temperature storage is further enhanced.

[0094] From the above, it can be seen that the method for manufacturing a nonaqueous electrolyte secondary battery disclosed herein makes it possible to manufacture a nonaqueous electrolyte secondary battery in which an increase in resistance when placed under high temperatures for a long period of time is suppressed.

[0095] Although the specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples exemplified above.

[0096] That is, the method for producing a nonaqueous electrolyte secondary battery disclosed herein includes the following items [1] to [7]. [1] preparing a battery assembly including a positive electrode, a negative electrode, and a non-aqueous electrolyte; administering an initial charge to the battery assembly; subjecting the initially charged battery assembly to an aging treatment; A method for producing a non-aqueous electrolyte secondary battery comprising the steps of: The positive electrode includes a positive electrode current collector and a positive electrode active material layer supported on the positive electrode current collector, the positive electrode active material layer contains a positive electrode active material and a thiophosphate, the content of the thiophosphate in the positive electrode active material layer is 1% by mass to 10% by mass, The initial charging is performed up to a voltage equal to or higher than the decomposition start potential of the thiophosphate, The aging treatment is carried out in a state where the battery assembly is charged to a voltage equal to or higher than a decomposition start potential of the thiophosphate. [2] The method according to item [1], wherein the content of the thiophosphate in the positive electrode active material layer is 3% by mass to 7% by mass. [3] The initial charge is performed when the potential of the positive electrode is 4.35 V (vs Li + / Li)~4.50V(vsLi + / Li), The aging treatment is performed by aging the battery assembly such that the potential of the positive electrode is 4.35 V (vs Li + / Li)~4.50V(vsLi + The manufacturing method according to item [1] or [2], wherein the battery is charged to a voltage of 0.1 V / Li. [4] The method according to any one of items [1] to [3], wherein the aging treatment is carried out at a temperature in the range of 40° C. to 75° C. for 4 hours to 24 hours. [5] The method according to any one of items [1] to [4], wherein the thiophosphate is an alkali metal salt of thiophosphoric acid. [6] The method according to any one of items [1] to [5], wherein the positive electrode active material is at least one composite oxide selected from the group consisting of lithium nickel cobalt manganese-based composite oxides and lithium nickel cobalt aluminum-based composite oxides. [7] The method according to any one of items [1] to [6], wherein the non-aqueous electrolyte contains lithium bis(oxalato)borate. [Explanation of symbols]

[0097] 20 Wound electrode body 30 Battery case 36 Safety valve 42 Positive terminal 42a Positive current collector 44 Negative terminal 44a Negative current collector plate 50 Positive electrode sheet (positive electrode) 52 Positive electrode current collector 52a Portion where positive electrode active material layer is not formed 54 Cathode active material layer 60 Negative electrode sheet (negative electrode) 62 Negative electrode current collector 62a Part where negative electrode active material layer is not formed 64 Negative electrode active material layer 70 Separator sheet (separator) 100 Battery assembly, lithium ion secondary battery

Claims

1. Providing a battery assembly including a positive electrode, a negative electrode, and a non-aqueous electrolyte; administering an initial charge to the battery assembly; subjecting the initially charged battery assembly to an aging treatment; A method for producing a non-aqueous electrolyte secondary battery comprising the steps of: The positive electrode includes a positive electrode current collector and a positive electrode active material layer supported on the positive electrode current collector, the positive electrode active material layer contains a positive electrode active material and a thiophosphate, the content of the thiophosphate in the positive electrode active material layer is 1% by mass to 10% by mass, The initial charging is performed up to a voltage equal to or higher than the decomposition starting potential of the thiophosphate, The aging treatment is performed in a state where the battery assembly is charged to a voltage equal to or higher than a decomposition start potential of the thiophosphate.

2. The method according to claim 1, wherein the content of the thiophosphate in the positive electrode active material layer is 3% by mass to 7% by mass.

3. The initial charge is performed when the potential of the positive electrode is 4.35 V (vs. Li ＋ / Li) to 4.50V (vs Li ＋ / Li), The aging treatment is performed by subjecting the battery assembly to a charging condition in which the potential of the positive electrode is 4.35 V (vs. Li ＋ / Li) to 4.50V (vs Li ＋ The method according to claim 1, wherein the method is carried out in a charged state to a voltage of 0.1 V / Li.

4. The method according to claim 1, wherein the aging treatment is carried out at a temperature in the range of 40° C. to 75° C. for 4 hours to 24 hours.

5. The method according to claim 1 , wherein the thiophosphate is an alkali metal salt of thiophosphoric acid.

6. 2. The method according to claim 1, wherein the positive electrode active material is at least one composite oxide selected from the group consisting of lithium nickel cobalt manganese composite oxides and lithium nickel cobalt aluminum composite oxides.

7. The method according to claim 1 , wherein the non-aqueous electrolyte contains lithium bis(oxalato)borate.

Images