Method for manufacturing non-aqueous electrolyte secondary batteries

Abstract

This invention provides a method for manufacturing a non-aqueous electrolyte secondary battery in which the increase in resistance when exposed to high temperatures for extended periods is suppressed. [Solution] The method for manufacturing a non-aqueous electrolyte secondary battery according to the present disclosure comprises the steps of: preparing a battery assembly comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte; and performing initial charging on the battery assembly. The positive electrode comprises a positive electrode current collector and a positive electrode active material layer supported by the positive electrode current collector. The positive electrode active material layer contains a positive electrode active material and Li3PS4. The content ratio of Li3PS4 in the positive electrode active material layer is 1% by mass to 10% by mass. The initial charging is performed up to a voltage that is equal to or greater than the decomposition start potential of Li3PS4.

Description

[Technical Field]

[0001] This disclosure relates to a method for manufacturing a non-aqueous electrolyte secondary battery. [Background technology]

[0002] In recent years, non-aqueous electrolyte secondary batteries, such as lithium-ion secondary batteries, have been suitably used in portable power supplies for personal computers and mobile devices, as well as in power supplies for vehicle propulsion systems such as battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs).

[0003] The positive electrode of a non-aqueous electrolyte secondary battery typically comprises a positive electrode active material layer containing a positive electrode active material. To improve the performance of non-aqueous electrolyte secondary batteries, a technique is known in which an additive that forms a film on the surface of the positive electrode active material (so-called positive electrode additive) is incorporated into the 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 incorporating a thiophosphate ester or thiophosphate ester salt into 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 when a high-potential positive electrode active material is used by incorporating lithium phosphate into the positive electrode active material layer. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2002-352804 [Patent Document 2] Japanese Patent Publication No. 2016-062644 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, as a result of the inventors' intensive studies, it has been found that in the above prior art, there is room for improvement in the high-temperature storage characteristics of non-aqueous electrolyte secondary batteries. Specifically, there is room for improvement in suppressing the increase in resistance when non-aqueous electrolyte secondary batteries are placed at high temperatures for a long time.

[0006] Therefore, an object of the present disclosure is to provide a method capable of manufacturing a non-aqueous electrolyte secondary battery in which an increase in resistance when placed at high temperatures for a long time is suppressed.

Means for Solving the Problems

[0007] The method for manufacturing a non-aqueous electrolyte secondary battery according to the present disclosure includes a step of preparing a battery assembly including a positive electrode, a negative electrode, and a non-aqueous electrolyte, and a step of performing an initial charge on the battery assembly. The positive electrode includes a positive electrode current collector and a positive electrode active material layer supported by the positive electrode current collector. The positive electrode active material layer contains a positive electrode active material and Li3PS4. The content ratio of Li3PS4 in the positive electrode active material layer is 1% by mass to 10% by mass. The initial charge is performed up to a voltage that is equal to or higher than the decomposition start potential of Li3PS4.

[0008] According to such a configuration, it is possible to provide a method capable of manufacturing a non-aqueous electrolyte secondary battery in which an increase in resistance when placed at high temperatures for a long time is suppressed.

Brief Description of the Drawings

[0009] [Figure 1] It is a flowchart showing each step of the method for manufacturing a non-aqueous electrolyte secondary battery according to an embodiment of the present invention. [Figure 2] It is a schematic diagram for explaining the configuration of a wound electrode body of a non-aqueous electrolyte secondary battery manufactured according to an embodiment of the present invention. [Figure 3] It is a cross-sectional view schematically showing the configuration of a non-aqueous electrolyte secondary battery manufactured according to an embodiment of the present invention.

Mode for Carrying Out the Invention

[0010] Embodiments relating to this disclosure will be described below with reference to the drawings. Matters not mentioned herein but necessary for the implementation of this disclosure can be understood as design matters for those skilled in the art based on prior art in the relevant field. This disclosure can be implemented based on the contents disclosed herein and common technical knowledge in the relevant field. In the following drawings, members and parts that perform the same function are denoted by the same reference numerals. Also, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect actual dimensional relationships. In this specification, the numerical range expressed as "A~B" includes A and B.

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

[0012] The present invention will be described in detail below, as an example, with respect to an embodiment where the non-aqueous electrolyte secondary battery is a flattened rectangular lithium-ion secondary battery, but the present invention is not intended to be limited to the embodiment described therein.

[0013] Figure 1 shows each step of the manufacturing method for a non-aqueous electrolyte secondary battery according to this embodiment. Figure 2 schematically shows the configuration of the electrode body of a lithium-ion secondary battery, an example of a non-aqueous electrolyte secondary battery obtained by the manufacturing method according to this embodiment. Figure 3 schematically shows the internal structure of a lithium-ion secondary battery, an example of a non-aqueous electrolyte secondary battery obtained by the manufacturing method according to this embodiment.

[0014] The method for manufacturing a non-aqueous electrolyte secondary battery according to this embodiment includes, as shown in Figure 1, a step of preparing a battery assembly comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte (hereinafter also referred to as the "assembly preparation step") S101, and a step of performing initial charging on the battery assembly (hereinafter also referred to as the "initial charging step") S102, as essential steps. Furthermore, the method for manufacturing a non-aqueous electrolyte secondary battery according to this embodiment may further include, as an optional step, a step of performing aging treatment on the battery assembly that has undergone initial charging (hereinafter also referred to as the "aging step") S103. In the method for manufacturing a non-aqueous electrolyte secondary battery according to this embodiment, the positive electrode comprises a positive electrode current collector and a positive electrode active material layer supported by the positive electrode current collector. The positive electrode active material layer contains a positive electrode active material and Li3PS4. The content ratio of Li3PS4 in the positive electrode active material layer is 1% by mass to 10% by mass. The initial charging is performed up to a voltage that is equal to or greater than the decomposition start potential of the Li3PS4.

[0015] First, the assembly preparation process S101 will be explained. In the assembly preparation process S101, a battery assembly 100 is prepared, which includes a positive electrode 50, a negative electrode 60, and a non-aqueous electrolyte 80.

[0016] The positive electrode 50 used in the assembly preparation process S101 typically comprises, for example, a positive electrode current collector 52 and a positive electrode active material layer 54 supported by the positive electrode current collector 52, as shown in Figure 2. The positive electrode active material layer 54 may be provided on one side of the positive electrode current collector 52 or on both sides, but is preferably provided on both sides. The positive electrode 50 typically has a portion 52a where the positive electrode active material layer is not formed (i.e., a portion where the positive electrode current collector 52 is exposed without the positive electrode active material layer 54 being formed), as shown in Figure 2.

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

[0018] The dimensions of the positive electrode current collector 52 are not particularly limited and can be determined as appropriate according to the battery design. When aluminum foil is used as the positive electrode current collector 52, its 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 Li3PS4. As the positive electrode active material, a known positive electrode active material used in lithium-ion secondary batteries may be used. Specifically, for example, lithium composite oxides, lithium transition metal phosphate compounds, etc., can be used as the positive electrode active material. The crystal structure of the positive electrode active material is not particularly limited and may be a layered structure, spinel structure, olivine structure, etc.

[0020] Preferably, lithium transition metal composite oxides are lithium transition metal composite oxides containing at least one of Ni, Co, and Mn as a transition metal element. Specific examples 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, "lithium nickel cobalt manganese composite oxide" is a term that encompasses not only oxides whose constituent elements are Li, Ni, Co, Mn, and O, but also oxides that contain one or more additive elements other than these. Examples of such additive elements include transition metal elements and main group metal elements such as Mg, Ca, Al, Ti, V, Cr, Y, Zr, Nb, Mo, Hf, Ta, W, Na, Fe, Zn, and Sn. The additive elements may also be metalloid elements such as B, C, Si, and P, or nonmetallic elements such as S, F, Cl, Br, and I. This also applies to the lithium nickel composite oxide, lithium cobalt composite oxide, lithium manganese composite oxide, lithium nickel manganese composite oxide, lithium nickel cobalt aluminum composite oxide, lithium iron nickel manganese composite oxide, etc.

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

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

[0024] Li3PS4 is decomposed by the initial charging in the following initial charging step S102, and a film derived from Li3PS4 is formed on the surface of the positive electrode active material. Initial charging is performed at a voltage that is above the decomposition initiation potential of Li3PS4. However, since it is only necessary to apply a voltage to the lithium-ion secondary battery that is above the decomposition initiation potential of Li3PS4 only during initial charging, the upper limit potential of the positive electrode active material in the general usage of lithium-ion secondary batteries may be lower than the decomposition initiation potential of Li3PS4.

[0025] From the viewpoint of battery characteristics and the stability of the crystal structure during initial charging, a lithium composite oxide having a layered structure is preferred as the positive electrode active material. The lithium composite oxide is preferably Ni-containing. Therefore, lithium nickel cobalt manganese-based composite oxides and lithium nickel cobalt aluminum-based composite oxides are preferred as positive electrode active materials, with lithium nickel cobalt manganese-based composite oxides being more preferred.

[0026] The ratio of Ni to the total amount 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 or more and 25 μm or less, preferably 1 μm or more and 20 μm or less, and more preferably 3 μm or more and 15 μm or less. The average particle diameter (D50) of the positive electrode active material can be determined, for example, by laser diffraction scattering.

[0028] The content of positive electrode active material in the positive electrode active material layer 54 (i.e., the content of 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% by mass or more, preferably 85% by mass or more, and more preferably 87% by mass or more.

[0029] Li3PS4 is a component (so-called positive electrode additive) that is added to the positive electrode to form a film on the surface of the positive electrode active material during the initial charging process S102.

[0030] A higher content of Li3PS4 in the positive electrode active material layer 54 enhances the effect of suppressing resistance increase when the lithium-ion secondary battery 100 is subjected to high temperatures for a long period of time. Therefore, the content of Li3PS4 in the positive electrode active material layer 54 (i.e., the mass ratio of Li3PS4 to the total mass of all components in the positive electrode active material layer) is 1% by mass or more, preferably 2% by mass or more, more preferably 2.5% by mass or more, and even more preferably 3% by mass or more. On the other hand, a higher content of Li3PS4 tends to increase the initial resistance. Therefore, the content of Li3PS4 in the positive electrode active material layer 54 is 10% by mass or less, preferably 8% by mass or less, more preferably 7.5% by mass or less, and even more preferably 7% by mass or less.

[0031] The positive electrode active material layer 54 may contain only Li3PS4 as a positive electrode additive, or it may further contain other positive electrode additives within a range that does not significantly impair the effects of the present invention.

[0032] The positive electrode active material layer 54 may contain components other than the positive electrode active material and Li3PS4 (i.e., optional components). Examples of such optional components include conductive materials and binders. Suitable conductive materials include carbon materials such as carbon black (e.g., acetylene black), carbon nanotubes (CNTs), and graphite. Suitable binders include polyvinylidene fluoride (PVDF). When CNTs are used as the conductive material, the positive electrode active material layer 54 may further contain a CNT dispersant.

[0033] The content of conductive material in the positive electrode active material layer 54 is not particularly limited, but is preferably 0.1% by mass or more and 15% by mass or less, and more preferably 0.5% by mass or more and 13% by mass or less. The content of binder in the positive electrode active material layer 54 is not particularly limited, but is preferably 1% by mass or more and 15% by mass or less, and more preferably 1.5% by mass or more and 10% by mass or less.

[0034] The thickness of the positive electrode active material layer 54 is not particularly limited, but is, for example, 10 μm or more and 300 μm or less, and preferably 20 μm or more and 200 μm or less.

[0035] The positive electrode sheet 50 may contain an insulating layer (not shown) at the boundary between the portion 52a where the positive electrode active material layer is not formed and the positive electrode active material layer 54. This insulating layer may contain, for example, ceramic particles.

[0036] The positive electrode 50 can be prepared by manufacturing it according to a known method. For example, the positive electrode 50 can be prepared by manufacturing a positive electrode paste containing a positive electrode active material, Li3PS4, and an optional component, coating the positive electrode paste onto the positive electrode current collector 52, drying it, and pressing it as necessary. In this specification, the term "paste" is used to include forms also known as "slurry" and "ink."

[0037] The negative electrode 60 used in the assembly preparation step S101 may be a known negative electrode used in lithium-ion secondary batteries. Typically, the negative electrode 60 comprises, for example, a negative electrode current collector 62 and a negative electrode active material layer 64 supported by the negative electrode current collector 62, as shown in Figure 2. The negative electrode active material layer 64 may be provided on one side of the negative electrode current collector 62 or on both sides, but is preferably provided on both sides. Typically, the negative electrode 60 has a portion 62a where the negative electrode active material layer is not formed (i.e., a portion where the negative electrode current collector 62 is exposed without the negative electrode active material layer 64), as shown in Figure 2.

[0038] As the negative electrode current collector 62, a known negative electrode current collector used in lithium-ion secondary batteries may be used, and examples include a sheet or foil made of a metal with good conductivity (e.g., copper, nickel, titanium, stainless steel, etc.). Copper foil is preferred as the negative electrode current collector 62.

[0039] The dimensions of the negative electrode current collector 62 are not particularly limited and can be determined as appropriate according to the battery design. When copper foil is used as the negative electrode current collector 62, its thickness is not particularly limited, but is, for example, 5 μm to 35 μm, and preferably 7 μm to 20 μm.

[0040] The negative electrode active material layer 64 contains a negative electrode active material. As the negative electrode active material, carbon materials such as graphite, hard carbon, and soft carbon may be used. The graphite may be natural graphite or artificial graphite, or amorphous carbon-coated graphite in which graphite is coated with an amorphous carbon material.

[0041] The average particle size (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 size (D50) of the negative electrode active material can be determined, for example, by laser diffraction scattering.

[0042] The negative electrode active material layer 64 may contain components other than the active material, such as a binder or a thickener. Examples of binders include styrene-butadiene rubber (SBR) and polyvinylidene fluoride (PVDF). Examples of thickeners include carboxymethylcellulose (CMC).

[0043] 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.

[0044] The thickness of the negative electrode active material layer 64 is not particularly limited, but is, for example, 10 μm or more and 300 μm or less, and preferably 20 μm or more and 200 μm or less.

[0045] The negative electrode 60 can be prepared by manufacturing it according to a known method. For example, the negative electrode 60 can be prepared by manufacturing a negative electrode paste containing a negative electrode active material and optional components, coating the negative electrode paste onto the negative electrode current collector 62, drying it, and pressing it if necessary.

[0046] The positive electrode 50 and the negative electrode 60 are typically used as an electrode body 20, which is formed by stacking the positive electrode 50 and the negative electrode 60 with a separator 70 in between. 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.

[0047] Examples of the separator 70 include porous sheets (films) made of resins such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide. Such porous sheets may have a single-layer structure or a laminated structure of two or more layers (for example, a three-layer structure in which PP layers are laminated on both sides of a PE layer). A heat-resistant layer (HRL) may be provided on the surface of the separator 70.

[0048] 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 obtained by the Gurley test method of the separator 70 is not particularly limited, but is preferably 350 seconds / 100 cc or less.

[0049] The electrode body 20 can be manufactured according to known methods. If the electrode body 20 is a wound electrode body as shown in the illustrated example, it can be prepared, for example, as follows.

[0050] First, the positive electrode sheet 50 and the negative electrode sheet 60 are stacked on top of each other with a separator sheet 70 interposed between them. Then, another separator sheet 70 is stacked. At this time, as shown in Figure 2, the portion 52a of the positive electrode sheet 50 that does not have a positive electrode active material layer and the portion 62a of the negative electrode sheet 60 that does not have a negative electrode active material layer are stacked on top of each other so that they protrude in opposite directions from the widthwise edges of the two separator sheets 70.

[0051] The resulting laminate is wound up. This winding of the laminate can be carried out according to known methods. For example, it can be done by using a winding machine equipped with a known core and winding the laminate onto the outer surface of the core. The winding conditions may be the same as known conditions.

[0052] Next, the wound laminate is pressed to produce a flattened wound electrode body. This pressing process can be carried out by pressing the laminate wound in the above winding step using a known press device that is used for the general manufacture of flattened wound electrode bodies. The pressing conditions may be the same as known conditions.

[0053] Meanwhile, a battery case 30 is prepared. Specifically, as shown in Figure 3, a body of the battery case 30 having an opening and a lid for the battery case 30 are prepared. The opening is sized to allow the wound electrode body 20 to be inserted. The lid is sized to close 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 above a predetermined level, and an inlet (not shown) for injecting a non-aqueous electrolyte. For example, a lightweight metal material with good thermal conductivity, such as aluminum, is used for the battery case 30.

[0054] Furthermore, a non-aqueous electrolyte 80 is prepared. The non-aqueous electrolyte 80 typically contains a non-aqueous solvent and a supporting salt (electrolyte salt). As the non-aqueous solvent, various organic solvents such as carbonates, ethers, esters, nitriles, sulfones, and lactones commonly used in the electrolytes of lithium-ion secondary batteries can be used without particular limitation. Among these, carbonates and esters are preferred, and specific examples include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC), monofluoromethyldifluoromethyl carbonate (F-DMC), trifluorodimethyl carbonate (TFDMC), methyl acetate, and methyl propionate. Such non-aqueous solvents can be used individually or in appropriate combinations of two or more.

[0055] Suitable supporting salts include lithium salts such as LiPF6, LiBF4, and lithium bis(fluorosulfonyl)imide (LiFSI), preferably LiPF6. The concentration of the supporting salt is preferably 0.7 mol / L or more and 1.3 mol / L or less.

[0056] Furthermore, the non-aqueous electrolyte 80 may contain various additives other than those described above, as long as they do not significantly impair the effects of the present invention. For example, film-forming agents such as vinylene carbonate (VC) and oxalat complexes; gas generating agents such as biphenyl (BP) and cyclohexylbenzene (CHB); thickeners; etc.

[0057] Next, the positive electrode terminal 42 and positive electrode current collector plate 42a and the negative electrode terminal 44 and negative electrode current collector plate 44a are attached to the lid of the battery case 30. The positive electrode current collector plate 42a and the negative electrode current collector plate 44a are welded to the exposed portions 52a and 62a of the positive electrode active material layer at the ends of the wound electrode body 20 by ultrasonic welding, resistance welding, etc. Then, the wound electrode body 20 is placed inside the battery case 30 through the opening, and the battery case 30 body and lid are welded together by laser welding, etc.

[0058] Next, the non-aqueous electrolyte 80 is injected through the inlet 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 injecting the non-aqueous electrolyte 80, the battery assembly 100 can be obtained by sealing the inlet. The sealing of the inlet can be carried out according to a known method.

[0059] Next, the initial charging process S102 will be described. In the initial charging process S102, the battery assembly 100 is subjected to initial charging. This initial charging is carried out up to a voltage that is above the decomposition initiation potential of Li3PS4. This decomposes the Li3PS4 in the positive electrode active material layer 54, allowing a film derived from Li3PS4 to form on the surface of the positive electrode active material.

[0060] Here, Li3PS4 has a relatively low decomposition initiation potential as a cathode additive. For example, the decomposition initiation potential of Li3PO3, which is well known as a cathode additive, is 4.50V (vsLi + The voltage is lower than / Li) (i.e., 4.50V based on metallic lithium). Therefore, when the battery assembly 100 is initially charged, Li3PS4 can be efficiently decomposed, and a high-quality film can be formed on the surface of the positive electrode active material layer. As a result, the increase in resistance when the lithium-ion secondary battery 100 is placed under high temperature conditions for a long period of time can be suppressed.

[0061] Because the decomposition initiation potential of Li3PS4 is relatively low, in this embodiment, the lower limit voltage for initial charging is when the potential of the positive electrode 50 is 4.30V (vsLi +The voltage at which it becomes (vsLi). The lower limit voltage of the initial charge is preferably such that the potential of the positive electrode 50 is 4.33 V (vsLi + The voltage at which it becomes (vsLi), and more preferably the potential of the positive electrode 50 is 4.35 V (vsLi + The voltage at which it becomes (vsLi). On the other hand, if the upper limit voltage of the initial charge is made too high, excessive decomposition of the non-aqueous electrolyte 80, structural deterioration of the positive electrode active material, etc. may occur. Therefore, the upper limit voltage of the initial charge is preferably such that the positive electrode potential is 4.70 V (vsLi + The voltage at which it becomes (vsLi), and more preferably the positive electrode potential is 4.50 V (vsLi + The voltage at which it becomes (vsLi).

[0062] Therefore, the initial charge is preferably carried out until the potential of the positive electrode 50 reaches 4.30 V (vsLi + / Li) to 4.70 V (vsLi + / Li), more preferably until the voltage reaches 4.30 V (vsLi + / Li) to 4.50 V (vsLi + / Li), even more preferably until the voltage reaches 4.33 V (vsLi + / Li) to 4.50 V (vsLi + / Li), and particularly preferably until the voltage reaches 4.35 V (vsLi + / Li) to 4.50 V (vsLi + / Li).

[0063] The initial charge 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, discharge is usually performed. In the initial charge, the charging may be performed only once, or may be performed a plurality of times (e.g., 2 to 3 times).

[0064] The battery assembly 100 that has undergone this initial charging process S102 can be made into a completed lithium-ion secondary battery 100. In the lithium-ion secondary battery 100, a high-quality film derived from Li3PS4 is formed on the surface of the positive electrode active material, and this film suppresses the decomposition of the non-aqueous electrolyte 80 during storage. As a result, the lithium-ion secondary battery 100 exhibits suppressed resistance increase when placed under high temperatures for extended periods. Therefore, according to the manufacturing method of this embodiment, a lithium-ion secondary battery 100 with excellent durability can be manufactured.

[0065] Next, the aging process S103 will be described. In the manufacturing method of the non-aqueous electrolyte secondary battery according to this embodiment, it is preferable to further perform the aging process S103, which involves applying an aging treatment to the battery assembly 100 that has been initially charged in the previous step. The aging process S103 can further modify the coating formed on the electrodes.

[0066] The aging process is preferably performed with the battery assembly 100 charged to a voltage above the decomposition initiation potential of Li3PS4. This further decomposes the Li3PS4 in the positive electrode active material layer 54, allowing for the formation of a Li3PS4-derived film on the positive electrode active material surface, thereby further improving the quality of the film.

[0067] Specifically, this voltage of the battery assembly 100 is preferably such that the potential of the positive electrode 50 is 4.30V (vsLi + The voltage is greater than or equal to the voltage at which / Li), and more preferably the potential of the positive electrode 50 is 4.33V (vsLi + The voltage is greater than or equal to the voltage at which / Li), and more preferably the potential of the positive electrode 50 is 4.35V (vsLi + The voltage is greater than or equal to / Li.

[0068] If the voltage of the battery assembly 100 is too high during the aging process S103, excessive decomposition of the non-aqueous electrolyte 80 and structural deterioration of the positive electrode active material may occur. Therefore, the voltage of the battery assembly 100 is preferably such that the positive electrode potential is 4.70V (vsLi +The voltage is below the voltage at which / Li) occurs, and more preferably the positive electrode potential is 4.50V (vsLi + The voltage is below the value of / Li.

[0069] Therefore, the aging process is performed such that the potential of the positive electrode 50 is preferably 4.30V (vsLi + / Li)~4.70V(vsLi + A voltage that results in / Li, more preferably 4.30V (vsLi + / Li)~4.50V(vsLi + A voltage that is equal to / Li, more preferably 4.33V(vsLi + / Li)~4.50V(vsLi + A voltage that results in / Li, particularly preferably 4.35V(vsLi + / Li)~4.50V(vsLi + This is done while the battery is charged to a voltage of ( / Li).

[0070] The temperature of the aging process is not particularly limited, but a temperature higher than room temperature is preferred. Specifically, the temperature of the aging process is preferably 40°C to 100°C, and more preferably 40°C to 75°C. The duration of the aging process is not particularly limited. The duration of the aging process is preferably 1 hour to 72 hours, and more preferably 4 hours to 24 hours.

[0071] Therefore, it is particularly preferable that the aging process be carried out at a temperature in the range of 40°C to 75°C for 4 to 24 hours.

[0072] The aging process S103 can be carried out according to a known method. Specifically, for example, it can be carried out by adjusting the charge state of the battery assembly 100 using a known voltage application device (not shown) and then leaving it in a constant temperature bath or the like.

[0073] As described above, a lithium-ion secondary battery 100 with a further modified coating can be obtained. This coating further suppresses the decomposition of the non-aqueous electrolyte 80 during storage. As a result, the increase in resistance when the lithium-ion secondary battery 100 is placed under high temperatures for a long period of time is further suppressed, and thus a lithium-ion secondary battery 100 with superior durability can be obtained.

[0074] The lithium-ion secondary battery 100 can be used for various applications. Specific applications include portable power supplies for personal computers, portable electronic devices, and mobile terminals; power supplies for vehicle propulsion systems such as battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); and storage batteries for small-scale power storage devices, with vehicle propulsion power supplies being particularly preferred. The lithium-ion secondary battery 100 can also typically be used in the form of a battery pack, where multiple batteries are connected in series and / or parallel.

[0075] As an example, a rectangular lithium-ion secondary battery 100 equipped with a flattened wound electrode body 20 has been described. However, the manufacturing method of the non-aqueous electrolyte secondary battery disclosed herein can also be used to manufacture a lithium-ion secondary battery equipped with a stacked electrode body (i.e., an electrode body in which multiple positive electrodes and multiple negative electrodes are alternately stacked). Furthermore, the manufacturing method of the non-aqueous electrolyte secondary battery disclosed herein can also be used to manufacture coin-type lithium-ion secondary batteries, button-type lithium-ion secondary batteries, cylindrical lithium-ion secondary batteries, and laminate-case type lithium-ion secondary batteries. In addition, the manufacturing method of the non-aqueous electrolyte secondary battery disclosed herein can also be used to manufacture non-aqueous electrolyte secondary batteries other than lithium-ion secondary batteries.

[0076] The following describes examples relating to the present invention, but the present invention is not intended to be limited to those shown in these examples.

[0077] Examples 1-4 and Comparative Examples 1-3 [Fabrication of lithium-ion secondary battery assemblies] LiNi as a positive electrode active material powder0.5 Co 0.2 Mn 0.3 O2 (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 to this mixture in the amounts shown in Table 1 for the positive electrode active material layer, and then mixed with N-methylpyrrolidone (NMP). This prepared a slurry for forming the positive electrode active material layer. This slurry was applied to both sides of an aluminum foil and dried to form the positive electrode active material layer. The total basis weight of both sides at this time was 15 mg / cm³. 2 Next, the positive electrode active material layer was prepared, with a density of 2.5 g / cm³. 3 A positive electrode sheet was obtained by rolling and pressing it in such a manner.

[0078] As the negative electrode active material, natural graphite (C), styrene-butadiene rubber (SBR) as a binder, and carboxymethylcellulose (CMC) as a thickener were mixed with deionized water in a mass ratio of C:SBR:CMC = 97:2:1 to prepare a slurry for forming the negative electrode active material layer. This slurry was applied to both sides of a copper foil and then dried to form the negative electrode active material layer. The total basis weight of both sides at this time was 9 mg / cm². 2 Next, the negative electrode active material layer was prepared, with a density of 1.2 g / cm³. 3 A negative electrode sheet was obtained by rolling and pressing it in such a manner.

[0079] Furthermore, a porous polyolefin membrane was prepared as a separator. The fabricated positive electrode sheet and negative electrode sheet were stacked with the separator in between to create a laminated electrode body. Terminals were attached to this electrode body, and it was housed in an aluminum battery case.

[0080] 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. A non-aqueous electrolyte was prepared by dissolving LiPF6 at a concentration of 1.1 mol / L in this mixed solvent. After pouring the prepared non-aqueous electrolyte into a battery case, the battery case was sealed to obtain a battery assembly.

[0081] [Initial charging] The obtained battery assembly was placed in a constant temperature bath at 25°C. The battery assembly was charged with a constant current of 0.1C up to a predetermined upper voltage limit, and then discharged with a constant current down to 3.0V. This predetermined upper voltage limit is determined by the positive electrode potential (vsLi) shown in Table 1. + The voltage was set to ( / Li). This charge-discharge cycle was performed twice as an initial charge.

[0082] <Aging process> The battery assembly after initial charging should have the positive electrode potential (vsLi) as shown in Table 1. + The voltage was adjusted to a value of ( / Li). Then, the battery assembly was placed in a 60°C constant temperature bath and subjected to a 12-hour aging process. In this manner, a lithium-ion secondary battery was obtained.

[0083] [Initial characteristic evaluation] The lithium-ion secondary batteries prepared in each example and comparative example were charged with a constant current of 0.1C up to the same upper voltage limit as the initial charge, and then discharged with a constant current down to 3.0V. The discharge capacity at this time was measured and defined as the initial capacity.

[0084] This initial capacity was defined as SOC 100%, and the lithium-ion secondary battery was adjusted to SOC 50% at 25°C. Then, the lithium-ion secondary battery was placed in a constant temperature chamber at -10°C and discharged for 10 seconds at a current of 10C. The voltage change ΔV was measured, and the output resistance of the lithium-ion secondary battery was calculated as the initial resistance using this voltage change ΔV and the current value.

[0085] [Evaluation of high-temperature storage characteristics] Lithium-ion secondary batteries were adjusted to a state of charge (SOC) of 80% at a temperature of 25°C. These lithium-ion secondary batteries were then stored in a constant temperature chamber at 60°C for 60 days. Afterward, the output resistance after storage was measured using the same method as for the initial resistance. The resistance increase rate (%) was calculated using the formula: (Output resistance after high-temperature storage / Initial resistance) × 100. The results are shown in Table 1.

[0086] [Table 1]

[0087] Comparative Example 1 is an example where no positive electrode additive was used, while Comparative Examples 2 and 3 are examples where trilithium phosphate and thiophosphate ester were used as positive electrode additives, respectively. A comparison of Example 1 and Comparative Examples 1-3 shows that when Li3PS4 is used as the positive electrode additive, a very high effect in suppressing resistance increase during high-temperature storage is obtained.

[0088] Furthermore, Examples 2-4 are examples in which the voltage of the lithium-ion secondary battery during the aging process was raised to a level above the decomposition initiation potential of Li3PS4. A comparison of Example 1 with Examples 2-4 shows that raising the voltage of the lithium-ion secondary battery during the aging process to a level above the decomposition initiation potential of Li3PS4 results in a greater suppression of resistance increase during high-temperature storage.

[0089] From the above, it can be seen that the method for manufacturing a non-aqueous electrolyte secondary battery according to this disclosure makes it possible to manufacture a non-aqueous electrolyte secondary battery in which the increase in resistance when exposed to high temperatures for a long period of time is suppressed.

[0090] Although specific examples of the present invention have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The technologies described in the claims include various modifications and changes to the specific examples illustrated above.

[0091] In other words, the method for manufacturing a non-aqueous electrolyte secondary battery according to the present disclosure is as described in the following sections [1] to [8]. [1] A step of preparing a battery assembly comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, The process of applying initial charge to the aforementioned battery assembly, A method for manufacturing a non-aqueous electrolyte secondary battery, comprising: The positive electrode comprises a positive electrode current collector and a positive electrode active material layer supported by the positive electrode current collector. The positive electrode active material layer contains a positive electrode active material and Li3PS4, The content ratio of Li3PS4 in the positive electrode active material layer is 1% by mass to 10% by mass. A manufacturing method wherein the initial charging is performed up to a voltage that is above the decomposition initiation potential of Li3PS4. [2] The manufacturing method according to item [1], wherein the content of Li3PS4 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 4.30V (vsLi + / Li)~4.70V(vsLi + The manufacturing method described in section [1] or [2], which is carried out up to a voltage of / Li. [4] The manufacturing method according to any one of items [1] to [3], further comprising the step of performing an aging treatment on the battery assembly after the initial charging step. [5] The manufacturing method according to item [4], wherein the aging treatment is performed while the battery assembly is charged to a voltage equal to or greater than the decomposition initiation potential of Li3PS4. [6] The aging process brings the battery assembly to a potential of 4.30V (vsLi) + / Li)~4.70V(vsLi + The manufacturing method described in item [4] or [5], which is carried out while the device is charged to a voltage of / Li. [7] The manufacturing method according to any one of items [4] to [6], wherein the aging treatment is carried out at a temperature in the range of 40°C to 75°C for 4 to 24 hours. [8] The manufacturing method according to any one of items [1] to [7], 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. [Explanation of Symbols]

[0092] 20 Electrode body 30 Battery Cases 36 Safety valve 42 Positive terminal 42a Positive electrode current collector plate 44 Negative terminal 44a Negative current collector plate 50 Positive electrode sheets (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 sheets (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 Sheets (Separators) 100 Battery assemblies, lithium-ion rechargeable batteries

Claims

1. A process for preparing a battery assembly comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, The process of applying initial charge to the aforementioned battery assembly, A method for manufacturing a non-aqueous electrolyte secondary battery, comprising: The positive electrode comprises a positive electrode current collector and a positive electrode active material layer supported by the positive electrode current collector. The positive electrode active material layer comprises a positive electrode active material and Li ３ PS ４ It contains, Li in the positive electrode active material layer ３ PS ４ The content ratio is 1% by mass to 10% by mass. The initial charge is Li ３ PS ４ A manufacturing method in which the process is carried out up to a voltage that exceeds the decomposition initiation potential.

2. Li in the positive electrode active material layer ３ PS ４ The manufacturing method according to claim 1, wherein the content ratio of is 3% by mass to 7% by mass.

3. The initial charging is performed until the potential of the positive electrode reaches a voltage of 4.30 V (vs Li ＋ / Li) to 4.70 V (vs Li ＋ / Li). The manufacturing method according to claim 1

4. The manufacturing method according to claim 1, further comprising the step of performing an aging treatment on the battery assembly after the step of performing the initial charging.

5. The aging process described above causes the battery assembly to Li ３ PS ４ The manufacturing method according to claim 4, which is carried out while the device is charged to a voltage that is above the decomposition initiation potential.

6. The aging process brings the battery assembly to a potential of 4.30V (vsLi) for the positive electrode. ＋ / Li) ~ 4.70V (vsLi ＋ The manufacturing method according to claim 4, which is carried out while the device is charged to a voltage of / Li.

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

8. The manufacturing 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-based composite oxides and lithium nickel cobalt aluminum-based composite oxides.

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