Method for manufacturing non-aqueous electrolyte secondary battery

Abstract

To provide a manufacturing method of a non-aqueous electrolyte secondary battery.SOLUTION: A manufacturing method disclosed here, contains: a construction step (step S1) of constructing an assembly by housing an electrode body in a battery case; a first impregnation step (step S2) of injecting a first non-aqueous electrolyte, which contains difluorophosphate and a non-fluorination carbonate and does not actually contain fluoroethylene carbonate, into the battery case, and impregnating it into the electrode body; a second impregnation step (step S4) of injecting a second non-aqueous electrolyte containing the fluoroethylene carbonate into the battery case, and impregnating it into the electrode body; and a charging step (step S5) of charging the assembly.SELECTED DRAWING: Figure 4

Description

[Technical Field]

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

[0002] Conventionally, non-aqueous electrolyte secondary batteries have been known, each comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte. In non-aqueous electrolyte secondary batteries, a portion of the non-aqueous electrolyte (typically an additive or non-aqueous solvent) contained in the non-aqueous electrolyte decomposes during initial charging, and a coating (solid electrolyte interface film: SEI film) containing the decomposition product is deposited on the surface of the electrode (positive electrode and / or negative electrode). This coating stabilizes the interface between the electrode and the non-aqueous electrolyte, which can improve battery performance.

[0003] As a related prior art, for example, Patent Document 1 describes a manufacturing method in which a first nonaqueous electrolyte solution containing a predetermined additive but not a difluorophosphate is injected into a battery case, an initial charge / discharge cycle is performed, and then a second nonaqueous electrolyte solution containing a difluorophosphate but not a predetermined additive is injected into the battery case, and a second charge / discharge cycle is performed. Patent Document 1 describes that by injecting the electrolyte solution in a stepwise manner as described above, it is possible to prevent a coating derived from difluorophosphate from reacting with the additive to form a high-resistance coating. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-28875 Summary of the Invention [Problem to be solved by the invention]

[0005] Recently, non-aqueous electrolyte secondary batteries have become known that contain a Si (silicon)-containing material in the negative electrode and fluoroethylene carbonate (FEC) as an additive in the non-aqueous electrolyte solution for the purpose of increasing capacity, etc. However, according to the studies of the present inventors, it has been newly discovered that when manufacturing such a battery, for example by applying the technology of Patent Document 1, adding FEC as an additive to the first non-aqueous electrolyte solution and adding difluorophosphate to the second non-aqueous electrolyte solution, the battery characteristics (for example, initial resistance and cycle characteristics) are actually reduced compared to, for example, adding FEC and difluorophosphate together at once.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for producing a nonaqueous electrolyte secondary battery which contains a Si-containing material in the negative electrode and has excellent battery characteristics. [Means for solving the problem]

[0007] The present invention provides a method for producing a nonaqueous electrolyte secondary battery comprising an electrode assembly having a positive electrode and a negative electrode, a nonaqueous electrolyte, and a battery case, the negative electrode containing a Si-containing material. The method includes an assembly step of housing the electrode assembly in the battery case to construct an assembly, a first impregnation step of injecting a first nonaqueous electrolyte containing a difluorophosphate and a non-fluorinated carbonate and substantially free of fluoroethylene carbonate into the battery case to impregnate the electrode assembly, a second impregnation step of injecting a second nonaqueous electrolyte containing fluoroethylene carbonate into the battery case after the first impregnation step to impregnate the electrode assembly, and a charging step of charging the assembly after the second impregnation step.

[0008] The inventors of the present invention have conducted extensive research and found that fluoroethylene carbonate (FEC), for example, has a carbonate skeleton and is therefore easily adsorbed to the positive electrode (specifically, the surface of the positive electrode active material). Therefore, it has been suggested that adding FEC to the first nonaqueous electrolyte solution as described in Patent Document 1 reduces the absolute amount of FEC acting on the Si-containing material in the negative electrode, thereby reducing the effect of adding FEC to the Si-containing material.

[0009] Therefore, in the present invention, when using a combination of difluorophosphate and FEC, the electrode body is impregnated with a first nonaqueous electrolyte containing difluorophosphate in a first impregnation step, and then the electrode body is impregnated with a second nonaqueous electrolyte containing FEC in a second impregnation step. This allows the difluorophosphate to be favorably adsorbed onto the positive electrode in the first impregnation step, thereby forming a high-quality protective coating containing a component derived from the difluorophosphate on the surface of the positive electrode. Furthermore, the second impregnation step allows the FEC to be favorably disposed near the negative electrode while suppressing adsorption of FEC to the positive electrode, thereby stably forming a protective coating containing a component derived from FEC on the surface of the negative electrode, particularly on the surface of the Si-containing material. Therefore, the technology disclosed herein can favorably manufacture a nonaqueous electrolyte secondary battery with excellent battery characteristics (e.g., initial resistance and cycle characteristics). [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a perspective view schematically showing a nonaqueous electrolyte secondary battery according to one embodiment. [Figure 2] FIG. 2 is a schematic vertical cross-sectional view taken along line II-II in FIG. [Figure 3] FIG. 3 is a schematic diagram showing the configuration of the electrode body. [Figure 4] FIG. 4 is a flowchart of a manufacturing method according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, some preferred embodiments of the technology disclosed herein will be described with reference to the drawings. It should be noted that matters necessary for carrying out the present invention other than those specifically mentioned in this specification (for example, the general configuration and manufacturing process of a non-aqueous electrolyte secondary battery that does not characterize the present invention) can be understood as design matters for those skilled in the art based on prior art in the relevant field. The present invention can be carried out based on the contents disclosed in this specification and common general technical knowledge in the relevant field.

[0012] In this specification, the term "nonaqueous electrolyte secondary battery" refers to any battery that can be repeatedly charged and discharged by the transfer of charge carriers between a positive electrode and a negative electrode via a nonaqueous electrolyte. The concept of nonaqueous electrolyte secondary batteries encompasses so-called storage batteries such as lithium ion secondary batteries, and capacitors such as lithium ion capacitors and electric double layer capacitors. In this specification, the expression "A to B" indicating a range includes not only the meaning of A or more but also the meaning of "greater than A" and "smaller than B."

[0013] <Battery 100> First, a nonaqueous electrolyte secondary battery (hereinafter simply referred to as battery) 100 manufactured by the manufacturing method disclosed herein will be described. FIG. 1 is a perspective view of the battery 100. FIG. 2 is a schematic longitudinal cross-sectional view taken along line II-II in FIG. 1. In the following description, the symbols L, R, F, Rr, U, and D in the drawings represent left, right, front, rear, top, and bottom, and the symbols X, Y, and Z in the drawings represent the short side direction of the battery 100, the long side direction perpendicular to the short side direction, and the up-down direction perpendicular to the short side and long side directions, respectively. However, these directions are merely used for convenience of explanation and do not limit the installation form of the battery 100 in any way.

[0014] 2, the battery 100 includes a battery case 10, an electrode assembly 20, a positive electrode terminal 30, a negative electrode terminal 40, a positive electrode current collector 50, a negative electrode current collector 60, and a nonaqueous electrolyte (not shown). The battery 100 here is a lithium ion secondary battery. The battery 100 is preferably a lithium ion secondary battery.

[0015] The battery case 10 is a housing that houses the electrode assembly 20 and the nonaqueous electrolyte. As shown in FIG. 1, the battery case 10 has a flat, bottomed, rectangular parallelepiped (rectangular) outer shape. The material of the battery case 10 may be the same as that used conventionally and is not particularly limited. The battery case 10 is preferably made of a metal, more preferably made of, for example, aluminum, an aluminum alloy, iron, or an iron alloy. However, in other embodiments, the battery case 10 may be in the shape of a bag made of, for example, a laminate film. As shown in FIG. 2, the battery case 10 includes an exterior body 12 having an opening 12h and a sealing plate (lid) 14 that closes the opening 12h. The sealing plate 14 is attached to the exterior body 12 so as to close the opening 12h. The battery case 10 is integrated by joining (e.g., welding) the sealing plate 14 to the periphery of the opening 12h of the exterior body 12. The battery case 10 is hermetically sealed (sealed).

[0016] As shown in Fig. 2, the sealing plate 14 is provided with a liquid inlet 15 and two terminal outlet holes 18, 19. The liquid inlet 15 is for injecting a non-aqueous electrolyte into the battery case 10 after the sealing plate 14 is assembled to the exterior body 12. The liquid inlet 15 is preferably provided in the sealing plate 14. The liquid inlet 15 is sealed with a sealing member 16. The terminal outlet holes 18, 19 are formed at both ends of the sealing plate 14 in the long side direction Y (the left end and the right end in Fig. 2). The terminal outlet holes 18, 19 penetrate the sealing plate 14 in the thickness direction (the up-down direction Z).

[0017] As shown in Fig. 2, the positive electrode terminal 30 and the negative electrode terminal 40 extend from the inside to the outside of the sealing plate 14 through the terminal lead-out holes 18, 19. Here, the positive electrode terminal 30 and the negative electrode terminal 40 are crimped to the peripheral portion of the sealing plate 14 surrounding the terminal lead-out holes 18, 19 by crimping. Crimped portions 30c, 40c are formed on the ends of the positive electrode terminal 30 and the negative electrode terminal 40 on the side of the exterior body 12 (the lower ends in Fig. 2).

[0018] The positive electrode terminal 30 is electrically connected to the positive electrode tab group 23 of the electrode assembly 20 via a positive electrode current collector 50 inside the battery case 10. The positive electrode terminal 30 is insulated from the sealing plate 14 by a positive electrode insulating member 70 and a gasket 90. The positive electrode terminal 30 is preferably made of metal, and more preferably made of, for example, aluminum or an aluminum alloy. The negative electrode terminal 40 is electrically connected to the negative electrode tab group 25 of the electrode assembly 20 via a negative electrode current collector 60 inside the battery case 10. The negative electrode terminal 40 is insulated from the sealing plate 14 by a negative electrode insulating member 80 and a gasket 90. The negative electrode terminal 40 is preferably made of metal, and more preferably made of, for example, copper or a copper alloy.

[0019] 2, the electrode assembly 20 is housed inside the battery case 10 (more specifically, inside the exterior body 12). The number of electrode assemblies 20 arranged inside one battery case 10 is not particularly limited, and may be one or two or more (plural).

[0020] FIG. 3 is a schematic diagram showing the configuration of the electrode assembly 20. As shown in FIG. 3, the electrode assembly 20 includes a positive electrode 22, a negative electrode 24, and a separator 26. Here, the electrode assembly 20 is a flat wound electrode assembly. The electrode assembly 20 is configured by stacking a strip-shaped positive electrode 22 and a strip-shaped negative electrode 24 with a strip-shaped separator 26 interposed between them and winding them around a winding axis WL. However, the electrode assembly 20 may also be a laminated electrode assembly in which a square-shaped (typically rectangular) positive electrode and a square-shaped (typically rectangular) negative electrode are stacked in an insulated state.

[0021] The positive electrode 22 may be the same as a conventional one and is not particularly limited. The positive electrode 22 has a positive electrode current collector 22c, a positive electrode active material layer 22a and a positive electrode protective layer 22p adhered to at least one surface of the positive electrode current collector 22c. However, the positive electrode protective layer 22p is not essential and may be omitted in other embodiments. The positive electrode current collector 22c is strip-shaped. The positive electrode current collector 22c is made of a conductive metal such as aluminum, an aluminum alloy, nickel, or stainless steel. In this example, the positive electrode current collector 22c is a metal foil, specifically, an aluminum foil.

[0022] A plurality of positive electrode tabs 22t are provided at one end of the positive electrode current collector 22c in the long side direction Y (the left end in FIG. 3). The positive electrode tab 22t is part of the positive electrode current collector 22c and is made of metal foil (aluminum foil). The plurality of positive electrode tabs 22t are stacked at one end of the positive electrode current collector 22c in the long side direction Y (the left end in FIG. 3) to form a positive electrode tab group 23 as shown in FIG. 2. A positive electrode current collector 50 is attached to (more specifically, joined to) the positive electrode tab group 23. The positive electrode tab group 23 is electrically connected to the positive electrode terminal 30 via the positive electrode current collector 50.

[0023] The positive electrode active material layer 22a is provided in a strip shape along the longitudinal direction of the strip-shaped positive electrode current collector 22c. The positive electrode active material layer 22a contains a positive electrode active material capable of reversibly absorbing and releasing charge carriers. The positive electrode active material is not particularly limited and may be the same as conventional materials. The positive electrode active material preferably contains a lithium transition metal composite oxide. The crystal structure of the lithium transition metal composite oxide is not particularly limited and may be a layered structure, a spinel structure, an olivine structure, or the like. In some embodiments, the lithium transition metal composite oxide preferably has a layered rock-salt crystal structure of space group C2 / m (so-called lithium-excess crystal structure) from the viewpoint of achieving a high energy density. An example of such a compound is a lithium-excess transition metal composite oxide represented by the following formula (I). A specific example is Li(Li 1 / 3 Mn 2 / 3 As will be described in the test examples below, when the positive electrode contains a lithium-excess transition metal composite oxide, the effects of the technology disclosed herein are exhibited at a particularly high level.

[0024] Li(Li a Ni x Mn y M z )O2 formula (I) In formula (I), a, x, y, and z satisfy 0.1 ≦ a ≦ 0.4, 0 ≦ x ≦ 0.5, 0.5 ≦ y ≦ 0.7, 0 ≦ z ≦ 0.2, and a + x + y + z = 1. When 0 < z, M is one or more elements selected from Co, Al, Mg, Ca, Ti, V, Cr, Si, Y, Zr, Nb, Mo, Hf, Ta, and W.

[0025] In formula (I), it is preferable that a satisfies 0.2 ≦ a ≦ 0.4. In one example, a = 1 / 3. It is preferable that x satisfies 0 ≦ x ≦ 0.2. In one example, x = 0. It is preferable that y satisfies 0.6 ≦ y ≦ 0.7. In one example, y = 2 / 3. It is preferable that z satisfies 0 ≦ z ≦ 0.1. In one example, z = 0.

[0026] In some other embodiments, the lithium transition metal composite oxide preferably has a layered rock salt crystal structure of the space group R-3m. Examples of such a compound include a lithium transition metal composite oxide represented by the following formula (II): LiMeO2 (Me is one or more transition metal elements other than Li). It is preferable that Me contains at least one of Ni, Co, and Mn, and more preferably contains all of Ni, Co, and Mn. That is, a lithium nickel cobalt manganese-containing composite oxide is more preferable.

[0027] The positive electrode active material layer 22a may contain optional components other than the positive electrode active material, such as a binder, a conductive material, various additive components, etc. As the binder, for example, polyvinylidene fluoride (PVdF) etc. can be preferably used. As the conductive material, for example, a carbon material such as acetylene black (AB) etc. can be preferably used.

[0028] The positive electrode protective layer 22p is provided between the positive electrode current collector 22c and the positive electrode active material layer 22a in the long side direction Y. The positive electrode protective layer 22p is provided in a strip shape along the positive electrode active material layer 22a. The positive electrode protective layer 22p contains an inorganic filler (e.g., alumina). The positive electrode protective layer 22p may contain optional components other than the inorganic filler, such as a conductive material, a binder, various additive components, etc. The conductive material and the binder may be the same as those exemplified as those that may be contained in the positive electrode active material layer 22a.

[0029] The negative electrode 24 includes a negative electrode current collector 24c and a negative electrode active material layer 24a fixed to at least one surface of the negative electrode current collector 24c. The negative electrode current collector 24c is strip-shaped. The negative electrode current collector 24c is made of a conductive metal such as copper, a copper alloy, nickel, or stainless steel. In this example, the negative electrode current collector 24c is a metal foil, specifically, a copper foil.

[0030] A plurality of negative electrode tabs 24t are provided at one end of the negative electrode current collector 24c in the long side direction Y (the right end in FIG. 3). The negative electrode tab 24t is part of the negative electrode current collector 24c and is made of metal foil (copper foil). The plurality of negative electrode tabs 24t are stacked at one end of the negative electrode current collector 24c in the long side direction Y (the right end in FIG. 3) to form a negative electrode tab group 25 as shown in FIG. 2. A negative electrode current collector 60 is attached (more specifically, joined) to the negative electrode tab group 25. The negative electrode tab group 25 is electrically connected to the negative electrode terminal 40 via the negative electrode current collector 60.

[0031] The negative electrode active material layer 24a is provided in a strip-like shape along the longitudinal direction of the strip-shaped negative electrode current collector 24c. The negative electrode active material layer 24a includes a negative electrode active material capable of reversibly absorbing and releasing charge carriers. In this embodiment, the negative electrode active material essentially includes a Si-containing material from the viewpoint of increasing capacity, etc. Preferred examples of the Si-containing material include Si, SiO (silicon oxide), SiC-containing materials (including silicon carbide and SiC composites in which carbon is dispersed inside silicon particles), SiN-containing materials (silicon nitride), and porous particles in which nano-Si particles are dispersed. Among these, it is preferable to include at least one of Si, SiO, and SiC-containing materials. Although not particularly limited, when the total amount of the negative electrode active material is taken as 100% by mass, the content of the Si-containing material is typically 50% by mass or less, for example, 1 to 30% by mass is preferable, and 5 to 20% by mass is more preferable.

[0032] From the viewpoint of achieving high levels of battery characteristics (e.g., high capacity and cycle characteristics), the negative electrode active material preferably contains graphite, such as artificial graphite or natural graphite, in addition to the Si-containing material. In this case, the content of graphite is preferably higher than that of the Si-containing material, on a mass basis. Although not particularly limited, when the total of the Si-containing material and graphite is taken as 100 mass%, the content of the Si-containing material is typically 50 mass% or less, for example, preferably 1 to 30 mass%, and more preferably 5 to 20 mass%. The negative electrode active material may contain negative electrode active materials other than the Si-containing material and graphite. Specific examples of negative electrode active materials other than the Si-containing material and graphite include carbon materials such as hard carbon, soft carbon, and amorphous carbon.

[0033] The negative electrode active material layer 24a may contain optional components other than the negative electrode active material, such as a binder, a dispersant, a conductive material, and various additives. Suitable binders include rubbers such as styrene butadiene rubber (SBR) and acrylic resins such as polyacrylic acid (PAA). Suitable dispersants include celluloses such as carboxymethyl cellulose (CMC). Suitable conductive materials include carbon materials such as carbon fibers and carbon nanotubes.

[0034] The separator 26 is a member that insulates the positive electrode active material layer 22a of the positive electrode 22 from the negative electrode active material layer 24a of the negative electrode 24. The separator 26 may be the same as a conventional separator and is not particularly limited. The separator 26 is preferably a porous resin sheet made of a polyolefin resin such as polyethylene (PE) or polypropylene (PP). The separator 26 may have a heat resistance layer (HRL) or an adhesive layer on the surface of a substrate portion made of a porous resin sheet. The configuration of the heat resistance layer or adhesive layer may be the same as a conventional one.

[0035] The non-aqueous electrolyte may be the same as conventional ones and is not particularly limited. The non-aqueous electrolyte typically contains a non-aqueous solvent and a supporting salt (electrolyte salt). As the non-aqueous solvent, one or more of those known to be usable in non-aqueous electrolyte secondary batteries can be used. Examples of the non-aqueous solvent include organic solvents such as carbonates, ethers, esters, nitriles, sulfones, and lactones. The non-aqueous solvent preferably contains a carbonate.

[0036] Carbonates are divided into non-fluorinated carbonates and fluorinated carbonates depending on whether they contain fluorine (F) as a constituent element. Carbonates are also divided into chain carbonates and cyclic carbonates depending on their chemical structure. Chain carbonates are acyclic (chain) carbonate compounds with a carbonate skeleton (O-CO-O). Cyclic carbonates are carbonate compounds with a carbonate skeleton closed in a ring by a C-C bond.

[0037] In this embodiment, the non-aqueous solvent preferably contains at least a non-fluorinated carbonate. Examples of non-fluorinated carbonates include non-fluorinated chain carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC), and non-fluorinated cyclic carbonates such as ethylene carbonate (EC), vinylene carbonate (VC), and propylene carbonate (PC). The non-fluorinated carbonate preferably contains at least one of DMC, DEC, EMC, EC, and VC. More preferably, the non-fluorinated carbonate contains a non-fluorinated chain carbonate and a non-fluorinated cyclic carbonate.

[0038] In a preferred embodiment, the non-aqueous solvent contains fluoroethylene carbonate (FEC) in addition to a non-fluorinated carbonate. However, as will be described in detail in the section on the manufacturing method, FEC may be electrically decomposed during a charging process or the like during battery manufacturing and consumed to form a coating on the negative electrode active material layer 24a, etc. Therefore, in the state of the battery 100, FEC may or may not be contained (remain) in the non-aqueous electrolyte. The non-aqueous solvent may further contain a fluorinated carbonate other than FEC, such as a fluorinated chain carbonate or a fluorinated cyclic carbonate other than FEC.

[0039] The supporting salt is not particularly limited as long as it contains a charge carrier, and one or more salts that have been known to be usable in non-aqueous electrolyte secondary batteries can be used. In the case of a lithium ion secondary battery, examples of the supporting salt include fluorine-containing lithium salts such as LiPF6 and LiBF4. The supporting salt preferably contains LiPF6.

[0040] The non-aqueous electrolyte may further contain additional components (additives). As the additive, for example, one or more of the additives known to be able to be added to the non-aqueous electrolyte, such as a film-forming agent, may be used. In a preferred embodiment, the non-aqueous electrolyte contains a difluorophosphate. The difluorophosphate is PO2F2 - The difluorophosphate salt is a salt of a cation and an anion represented by the formula:

[0026] . Examples of the cation include alkali metal ions such as Li, Na, and K, and ammonium ions, with Li being preferred. A specific example of the difluorophosphate salt is lithium difluorophosphate (lithium difluorophosphate (LiDFP), LiPO2F2).

[0041] <Method of manufacturing the battery 100> 4 is a flowchart of a manufacturing method according to one embodiment. As shown in FIG. 4, the battery 100 can be manufactured by a manufacturing method including, for example, a construction step (step S1), a first impregnation step (step S2), an initial charging step (step S3), a second impregnation step (step S4), and a charging step (step S5) in this order. However, the initial charging step (step S3) is optional and can be omitted. Furthermore, other steps may be included at any stage.

[0042] The construction step (step S1) is a step of housing the electrode body 20 in the battery case 10 to construct an assembly (a combination of the battery case 10 and the electrode body 20). In a preferred embodiment, this step includes an electrode fabrication step (step S1-1), an electrode body fabrication step (step S1-2), an arrangement step (step S1-3), and a welding and joining step (step S1-4). Furthermore, other steps may be included at any stage.

[0043] First, in the electrode preparation step (step S1-1), the positive electrode 22 and the negative electrode 24 are each prepared. The positive electrode 22 can be prepared, for example, by mixing a positive electrode active material, a conductive material, a binder, and a dispersion solvent to prepare a positive electrode composite slurry, and then applying the prepared positive electrode composite slurry to the positive electrode current collector 22c by a conventionally known method, drying it, and appropriately pressing it. As the positive electrode active material, one type from the above-mentioned materials can be used alone, or two or more types can be mixed and used as appropriate. Among them, the lithium-excess transition metal composite oxide represented by the above formula (I) and the lithium transition metal composite oxide represented by the above formula (II) can be preferably used.

[0044] The negative electrode 24 can be fabricated, for example, by mixing a negative electrode active material, a binder, a dispersant, and a dispersion solvent to prepare a negative electrode composite slurry, applying the prepared negative electrode composite slurry to the negative electrode current collector 24c by a conventionally known method, drying, and appropriately pressing. The negative electrode active material essentially uses a Si-containing material (preferably at least one of Si, SiO, and SiC-containing materials), and one or more of the above-mentioned materials can also be used. In particular, graphite can be preferably used in addition to the Si-containing material. While the present embodiment fabricates electrodes (positive electrode 22 and / or negative electrode 24), in other embodiments, commercially available electrodes may be purchased.

[0045] Next, in the electrode assembly fabrication step (step S1-2), the positive electrode 22 and negative electrode 24 fabricated above are opposed to each other with the separator 26 interposed therebetween to fabricate the electrode assembly 20. Next, in the placement step (step S1-3), the electrode assembly 20 is placed inside the exterior housing 12. For example, the electrode assembly 20 is accommodated inside the exterior housing 12 through the opening 12h of the exterior housing 12. Next, in the welding and joining step (step S1-4), the sealing plate 14 is fitted into the opening 12h of the exterior housing 12 and welded to the periphery of the opening 12h to integrate the exterior housing 12 and the sealing plate 14.

[0046] The first impregnation step (step S2) is a step of injecting a first nonaqueous electrolyte into the battery case 10 to impregnate the electrode assembly 20 with the nonaqueous electrolyte. In this step, the first nonaqueous electrolyte is first prepared. The first nonaqueous electrolyte essentially contains a difluorophosphate and a non-fluorinated carbonate. LiPO2F2 is preferably used as the difluorophosphate. Although not particularly limited, from the viewpoint of achieving a high level of the effects of the technology disclosed herein, it is preferable to add the difluorophosphate to the first nonaqueous electrolyte so that its proportion in the total nonaqueous electrolyte (the sum of the first nonaqueous electrolyte and a second nonaqueous electrolyte described below) before the charging step is approximately 0.1 mass % or more, for example, 0.5 mass % or more. On the other hand, from the viewpoint of suppressing an increase in resistance, it is preferable to add the difluorophosphate to the first nonaqueous electrolyte solution so that the proportion of the difluorophosphate in the entire nonaqueous electrolyte solution before the charging step is approximately 5% by mass or less, for example, 2% by mass or less, or 1% by mass or less.

[0047] The non-fluorinated carbonate is typically a non-aqueous solvent for dissolving the difluorophosphate. The non-fluorinated carbonate may be selected from the above-mentioned materials, either singly or in combination. It is particularly preferred that the non-fluorinated carbonate contains at least one of DMC, DEC, EMC, EC, and VC. It is more preferred that the non-fluorinated carbonate contains a non-fluorinated chain carbonate (e.g., one or more of DMC, DEC, and EMC) and a non-fluorinated cyclic carbonate (e.g., EC and / or VC). While not particularly limited, the proportion of the non-fluorinated chain carbonate in the first non-aqueous electrolyte is preferably greater than the proportion of the non-fluorinated cyclic carbonate, by volume.

[0048] In a preferred embodiment, the first nonaqueous electrolyte solution contains a supporting salt (lithium salt in the case of a lithium ion secondary battery) in addition to a difluorophosphate and a non-fluorinated carbonate. As the supporting salt, one of the above-mentioned materials can be used alone or in combination of two or more, and LiPF6 is particularly preferred.

[0049] In this embodiment, the first nonaqueous electrolyte solution is substantially free of FEC. According to the inventors' investigations, FEC, for example, has a carbonate skeleton and is therefore easily adsorbed to the surface of the positive electrode 22 (specifically, the surface of the positive electrode active material). Therefore, adding FEC to the first nonaqueous electrolyte solution may reduce the absolute amount of FEC acting on the Si-containing material of the negative electrode 24, thereby potentially reducing the effect of adding FEC to the Si-containing material. Furthermore, the effect of the difluorophosphate salt added in the second impregnation step (step S4) described below on the surface of the positive electrode 22 (specifically, the surface of the positive electrode active material) may be reduced, resulting in increased resistance of the positive electrode (particularly, interfacial resistance with the nonaqueous electrolyte solution). It is more preferable that the first nonaqueous electrolyte solution be substantially free of fluorinated carbonates in general (i.e., fluorinated carbonates other than FEC).

[0050] In this specification, the term "substantially free" refers to the inclusion of a trace amount of the target component, provided that the effect of the technology disclosed herein is not significantly impaired, and refers to the proportion of the target component relative to the total (e.g., the proportion of FEC relative to the total first nonaqueous electrolyte solution) being less than 0.1 mass%. The proportion of the target component relative to the total (e.g., the proportion of FEC relative to the total first nonaqueous electrolyte solution) is preferably less than 0.05 mass%, more preferably less than 0.01 mass%.

[0051] In this step, the prepared first nonaqueous electrolyte solution is then injected into the battery case 10 through the injection hole 15 in the sealing plate 14. Injection may be performed at atmospheric pressure, or may be performed under reduced pressure in the battery case 10, for example, to improve the impregnation of the nonaqueous electrolyte solution into the electrode assembly 20. The first nonaqueous electrolyte solution injected through the injection hole 15 is impregnated into the electrode assembly 20. In other words, the first nonaqueous electrolyte solution is uniformly distributed throughout the electrode assembly 20. In this embodiment, the first nonaqueous electrolyte solution contains a difluorophosphate and is substantially free of FEC. Difluorophosphate is a material that readily interacts with and is readily adsorbed to the surface of an active material. Therefore, in this step, the difluorophosphate contained in the first nonaqueous electrolyte solution can be specifically adsorbed onto the surface of the positive electrode 22 (specifically, the surface of the positive electrode active material).

[0052] In a preferred embodiment, after the injection, the assembly is left (held) for a predetermined time. This allows the nonaqueous electrolyte to be evenly distributed in the long side direction Y, even when the electrode assembly 20 is relatively long, thereby thoroughly impregnating the electrode assembly 20 with the first nonaqueous electrolyte. The leaving temperature may be room temperature (e.g., 25°C ± 10°C, approximately 25°C ± 5°C), or a high temperature of approximately 35 to 45°C may be used, for example, for the purpose of improving the impregnation of the nonaqueous electrolyte into the electrode assembly 20. The leaving time is not particularly limited, as it depends on, for example, the size of the electrode assembly 20 (particularly the length in the long side direction Y), the viscosity of the first nonaqueous electrolyte, whether or not pressure is applied, the leaving temperature, and other factors. However, for example, 5 minutes or more is preferable, 10 minutes or more is more preferable, and 1 hour or more is particularly preferable. From the viewpoint of production efficiency, the leaving time is preferably within 240 hours (10 days), more preferably within 48 hours (2 days), and particularly preferably within 24 hours (1 day).

[0053] The initial charging step (step S3) is a step of charging the assembly into which the first nonaqueous electrolyte solution has been injected at least once. The charging of the assembly can be carried out in the same manner as in the past. Typically, an external power source is connected between the positive and negative electrode terminals of the assembly, and charging is carried out until the assembly reaches a predetermined voltage. Although not particularly limited, it is preferable to charge until the voltage reaches approximately 4 V or more, preferably 4.1 V or more, 4.2 V or more, for example, 4.2 V. When a lithium-excess transition metal composite oxide is used as the positive electrode active material, it is more preferable to charge until the voltage reaches approximately 4.6 V or more, preferably 4.7 V or more, for example, 4.7 V, from the viewpoint of achieving an electrochemically active state and achieving high capacity. The charge / discharge rate can be, for example, about 0.1 to 2 C. As a result, the difluorophosphate contained in the first nonaqueous electrolyte solution is typically electrolyzed (mainly oxidatively decomposed) before other components (non-fluorinated carbonate and supporting salt) in the first nonaqueous electrolyte solution, and a high-quality protective coating containing components derived from the difluorophosphate is formed, particularly on the surface (more specifically, the surface of the positive electrode active material) of the positive electrode 22. Therefore, the protective effect of the difluorophosphate can reduce the resistance of the positive electrode 22.

[0054] Charging may be performed once, or may be repeated two or more times, for example, with a discharge in between. Discharging may also be performed after charging. In a preferred embodiment, the assembly may be discharged until the state of charge (SOC) is approximately 20% or less, preferably 10% or less, for example, 0%. Alternatively, the assembly may be discharged until the voltage is approximately 3.5 V or less, 3.0 V or less, for example, 3.0 V. This step may be performed in a room temperature environment (e.g., about 25°C ± 10°C, 25°C ± 5°C), or may be performed in a high-temperature environment of about 35 to 45°C, for example, for the purpose of promoting film formation.

[0055] The second impregnation step (step S4) is a step of injecting a second nonaqueous electrolyte into the battery case 10 to impregnate the electrode assembly 20 with the nonaqueous electrolyte. In this step, the second nonaqueous electrolyte is first prepared. The second nonaqueous electrolyte essentially contains fluoroethylene carbonate (FEC). Although not particularly limited, from the viewpoint of achieving a high level of the effects of the technology disclosed herein, it is preferable to add FEC to the second nonaqueous electrolyte so that the proportion of FEC in the total amount of carbonates (e.g., the total amount of non-fluorinated carbonate and FEC) in the entire nonaqueous electrolyte (the total amount of the first nonaqueous electrolyte and the second nonaqueous electrolyte) before the charging step is approximately 1% by volume or more, for example, 5% by volume or more. On the other hand, from the viewpoint of suppressing an increase in resistance, it is preferable to add FEC to the second nonaqueous electrolyte solution so that the proportion of FEC in the total amount of carbonates is approximately 30% by volume or less, for example, 20% by volume or less, or 10% by volume or less.

[0056] In a preferred embodiment, the second non-aqueous electrolyte contains a non-fluorinated carbonate in addition to FEC. The non-fluorinated carbonate may be the same as or different from that added to the first non-aqueous electrolyte. The non-fluorinated carbonate preferably contains a non-fluorinated chain carbonate (e.g., one or more of DMC, DEC, and EMC). The second non-aqueous electrolyte preferably does not substantially contain a non-fluorinated cyclic carbonate (e.g., EC and / or VC).

[0057] The second non-aqueous electrolyte may contain a supporting salt (lithium salt in the case of a lithium ion secondary battery). The supporting salt may be the same as or different from that added to the first non-aqueous electrolyte.

[0058] The second electrolyte may contain a difluorophosphate salt as long as it does not significantly impair the effects of the technology disclosed herein. In a preferred embodiment, the second nonaqueous electrolyte is substantially free of a difluorophosphate salt (e.g., LiPO2F2). This prevents excessive coating from being formed on the positive electrode 22 during the charging step (step S5) described below, allowing the effects of the technology disclosed herein to be exhibited at a high level.

[0059] Next, in this step, the prepared second nonaqueous electrolyte solution is injected into the battery case 10 through the injection hole 15 in the sealing plate 14. The injection may be performed at atmospheric pressure, or may be performed with the battery case 10 under reduced pressure, for example, to improve the impregnation of the nonaqueous electrolyte solution into the electrode assembly 20. The second nonaqueous electrolyte solution injected through the injection hole 15 is impregnated into the electrode assembly 20. In other words, the second nonaqueous electrolyte solution is evenly distributed throughout the electrode assembly 20. This allows the FEC contained in the second nonaqueous electrolyte solution to be suitably disposed, for example, near the negative electrode 24 (more specifically, near the negative electrode active material).

[0060] In a preferred embodiment, after the injection, the assembly is left (held) for a predetermined time. This allows the nonaqueous electrolyte to be evenly distributed in the long side direction Y, even when the electrode assembly 20 is relatively long, thereby thoroughly impregnating the electrode assembly 20 with the second nonaqueous electrolyte. The leaving temperature may be room temperature (e.g., 25°C ± 10°C, approximately 25°C ± 5°C), or a high temperature of approximately 35 to 45°C may be used, for example, for the purpose of improving the impregnation of the nonaqueous electrolyte into the electrode assembly 20. The leaving time is not particularly limited, as it depends on, for example, the size of the electrode assembly 20 (particularly the length in the long side direction Y), the viscosity of the second nonaqueous electrolyte, whether or not the electrode assembly 20 is decompressed, the leaving temperature, and other factors. However, for example, 5 minutes or more is preferable, 10 minutes or more is more preferable, and 1 hour or more is particularly preferable. From the viewpoint of production efficiency, the leaving time is preferably within 240 hours (10 days), more preferably within 48 hours (2 days), and particularly preferably within 24 hours (1 day).

[0061] The charging step (step S5) is a step of charging the assembly into which the second nonaqueous electrolyte solution has been injected at least once. The charging of the assembly can be performed in accordance with the initial charging step (step S3). Although not particularly limited, in a preferred embodiment, the assembly is charged until the state of charge (SOC) reaches approximately 80% or more, preferably 90% or more, for example, 100%. Alternatively, it is preferable to charge the assembly until the voltage reaches approximately 4 V or more, preferably 4.1 V or more, 4.2 V or more, for example, 4.2 V. Note that when the initial charging step (step S3) is performed, the SOC or voltage may be as described above even when a lithium-excess transition metal composite oxide is used as the positive electrode active material. However, when a lithium-excess transition metal composite oxide is used as the positive electrode active material and the initial charging step (step S3) is omitted, it is preferable to charge the assembly until the voltage reaches approximately 4.6 V or more, preferably 4.7 V or more, for example, 4.7 V, in order to achieve a high capacity in an electrochemically active state. The charge / discharge rate can be, for example, about 0.1 to 2 C. As a result, the FEC contained in the second nonaqueous electrolyte is typically electrolyzed (mainly by reductive decomposition) before other components (e.g., non-fluorinated carbonate and supporting salt) in the nonaqueous electrolyte. A protective coating containing components derived from the FEC is then stably formed, particularly on the surface of the negative electrode 24 (specifically, on the surface of the negative electrode active material, particularly on the surface of the Si-containing material). Therefore, the protective effect of the FEC can enhance the durability of the negative electrode 24. In this manner, the battery 100 can be suitably manufactured.

[0062] <Uses of Battery 100> Battery 100 can be used for a variety of purposes, but because it has reduced resistance and excellent durability, it can be suitably used as a power source (driving power source) for motors mounted on vehicles such as passenger cars and trucks. The type of vehicle is not particularly limited, and examples include plug-in hybrid electric vehicles (PHEVs), hybrid electric vehicles (HEVs), and battery electric vehicles (BEVs).

[0063] Hereinafter, several examples of the present invention will be described, but it is not intended that the present invention be limited to these examples.

[0064] <Test Example I (Examples 1 and 2, Comparative Examples 1 and 2)> <Construction of non-aqueous electrolyte secondary battery> First, a positive electrode and a negative electrode were prepared. The positive electrode was prepared as follows. First, Li (Li 1 / 3 Mn 2 / 3 )O2, AB as a conductive material, and PVdF as a binder were mixed in a mass ratio of active material:AB:PVdF = 100:1:1, and the fluidity was adjusted with a dispersion solvent (NMP) to prepare a positive electrode composite slurry. Next, the prepared positive electrode composite slurry was applied to an Al foil as a positive electrode current collector, dried, and pressed to a predetermined thickness. The mixture was then cut to a predetermined size to prepare a positive electrode.

[0065] The negative electrode was fabricated as follows. First, graphite and SiO (Si-containing material) as negative electrode active materials were mixed in a mass ratio of graphite:SiO = 95:5 to obtain a mixture. Next, 1 part by mass of SBR as a binder and 1 part by mass of CMC as a dispersant were added to the obtained mixture (100 parts by mass), and the fluidity was adjusted with a dispersion solvent (water) to prepare a negative electrode composite slurry. Next, the prepared negative electrode composite slurry was applied to Cu foil as a negative electrode current collector, dried, and pressed to a predetermined thickness. Then, the mixture was cut to a predetermined size to prepare a negative electrode.

[0066] Next, an assembly was constructed. First, the positive electrode and negative electrode prepared above were placed opposite each other with a separator (a porous sheet consisting of three layers of PP / PE / PP) interposed between them to prepare an electrode body. Next, the electrode body was housed in a bag-shaped battery case made of aluminum laminate film to construct an assembly. This process was repeated to prepare multiple assemblies (construction process).

[0067] (Example 1) First, non-aqueous electrolytes A and B were prepared. The following two types of non-aqueous electrolytes were prepared so that the composition of the entire non-aqueous electrolyte (total amount of electrolyte injected) before the charging step was LiPF6 (1 mol / L) as a supporting electrolyte, LiPO2F2 (0.5 mass%) as a difluorophosphate, and FEC+EC+EMC (volume ratio 1:4:15) as a non-aqueous solvent. ·Non-aqueous electrolyte A: LiPF6 (1mol / L), LiPO2F2 (0.625% by mass), EC+EMC (1:3 by volume) ·Non-aqueous electrolyte B: LiPF6 (1mol / L), FEC+EMC (1:3 by volume)

[0068] Next, nonaqueous electrolyte A (a nonaqueous electrolyte containing LiPO2F2 but not containing FEC) was injected into the battery case in an amount of 80% of the total amount of electrolyte to be injected, and the battery case was left standing for 12 hours, thereby impregnating the electrode body with nonaqueous electrolyte A (first impregnation step). Next, nonaqueous electrolyte B (a nonaqueous electrolyte containing FEC but not containing LiPO2F2) was injected into the battery case in an amount of 20% of the total amount of electrolyte to be injected, and the battery case was sealed and left standing for 12 hours, thereby impregnating the electrode body with nonaqueous electrolyte B (second impregnation step). After the second impregnation step, the assembly was charged at a constant current of 0.1 C to 4.7 V, and then discharged at a constant current of 0.1 C to 3.0 V (charging step). In this manner, a nonaqueous electrolyte secondary battery (Example 1) was constructed.

[0069] Comparative Example 1 First, the following two types of non-aqueous electrolytes C and D were prepared. ·Non-aqueous electrolyte C: LiPF6 (1mol / L), FEC+EC+EMC (volume ratio 1:3:12) ·Non-aqueous electrolyte D: LiPF6 (1mol / L), LiPO2F2 (2.5% by mass), EC+EMC (1:3 by volume) A nonaqueous electrolyte secondary battery (Comparative Example 1) was constructed in the same manner as in Example 1 above, except that in the first impregnation step, nonaqueous electrolyte C (nonaqueous electrolyte containing FEC and not containing LiPO2F2) was injected in an amount of 80% of the total amount of electrolyte to be injected, and in the second impregnation step, nonaqueous electrolyte D (nonaqueous electrolyte containing LiPO2F2 and not containing FEC) was injected in an amount of 20% of the total amount of electrolyte to be injected.

[0070] Comparative Example 2 First, one type of non-aqueous electrolyte solution E was prepared. Non-aqueous electrolyte E: LiPF6 (1 mol / L), LiPO2F2 (0.5 mass%), FEC+EC+EMC (volume ratio 1:4:15) as non-aqueous solvent Then, a nonaqueous electrolyte secondary battery (Comparative Example 2) was constructed in the same manner as in Example 1 above, except that in the first impregnation step, nonaqueous electrolyte E (nonaqueous electrolyte containing FEC and LiPO2F2) was injected and the second impregnation step was not performed.

[0071] (Example 2) An initial charging step was carried out between the first impregnation step and the second impregnation step in Example 1 above. The charge / discharge conditions in the initial charging step were the same as those in the charging step in Example 1 (constant current charging of the assembly to 4.7 V at a charge rate of 0.1 C, followed by constant current discharging to 3.0 V at a discharge rate of 0.1 C). In addition, in the charging step in Example 2, the charging voltage was set to 4.2 V. A nonaqueous electrolyte secondary battery (Example 2) was constructed in the same manner as in Example 1 above, except for these conditions.

[0072] <Evaluation of initial characteristics (initial capacitance and initial resistance)> The battery was charged at a constant current of 0.1C to 4.2V at a charge rate of 0.1C in a 25°C environment, and then discharged at a constant current of 0.1C to 3.0V. The discharge capacity was recorded as the initial capacity. Next, the battery's state of charge was adjusted to 50% SOC in a 25°C environment, and after a 1-hour rest, a 10-second constant-current discharge was performed at a constant current of 5C. The initial resistance (mΩ) was calculated from the open-circuit voltage (V0) immediately before discharge and the closed-circuit voltage (V1) after 10 seconds of discharge using the following formula: initial resistance = (V0 - V1) / 5C current value. The results are shown in Table 1.

[0073] <Evaluation of cycle characteristics> The battery was subjected to 100 charge / discharge cycles at 25°C, consisting of a constant current charge to 4.2 V at a charge rate of 0.4 C, followed by a constant current discharge to 3.0 V at a discharge rate of 0.4 C. The "post-cycle capacity" was measured in the same manner as for the initial capacity, and the capacity retention rate (%) was calculated using the following formula: capacity retention rate = (post-cycle capacity / initial capacity) x 100. The results are shown in Table 1.

[0074] [Table 1]

[0075] As shown in Table 1, Comparative Example 1, in which nonaqueous electrolyte C (nonaqueous electrolyte containing FEC) was injected in the first impregnation step and nonaqueous electrolyte D (nonaqueous electrolyte containing LiPO2F2) was injected in the second impregnation step, exhibited worse battery characteristics than Comparative Example 2, in which nonaqueous electrolyte E (nonaqueous electrolyte containing FEC and LiPO2F2) was added in the first impregnation step. The reasons for this are thought to be: (1) because FEC has a high adsorption property to the positive electrode, adding FEC in the first impregnation step also caused FEC to be adsorbed to the positive electrode, reducing the absolute amount of FEC acting on the Si-containing material in the negative electrode and reducing the effect of adding FEC; and (2) because FEC was adsorbed to the positive electrode in the first impregnation step, the effect of difluorophosphate added in the second impregnation step on the positive electrode was reduced.

[0076] In contrast to Comparative Examples 1 and 2, Example 1, in which nonaqueous electrolyte A containing LiPO2F2 was added in the first impregnation step and nonaqueous electrolyte B containing FEC was added in the second impregnation step, exhibited relatively reduced battery resistance and improved cycle characteristics. While not intended to be particularly restrictive, the reasons for this are thought to be (1) the difluorophosphate added in the first impregnation step specifically adsorbed to the positive electrode surface, forming a high-quality protective coating; and (2) the addition of FEC in the second impregnation step suppressed FEC adsorption to the positive electrode while increasing the absolute amount of FEC acting on the Si-containing material in the negative electrode. As a result, the positive electrode surface was reduced in resistance due to the protective effect of the difluorophosphate, and the negative electrode surface (particularly the surface of the Si-containing material) was made highly durable due to the protective effect of the FEC. These results demonstrate the significance of the technology disclosed herein.

[0077] Furthermore, Example 2, in which the first charge was performed between the first impregnation step and the second impregnation step, had even better cycle characteristics than Example 1. Although no particular limitation is intended, the reason for this is thought to be that in Example 2, the oxidative decomposition of FEC was suppressed by performing high-voltage treatment in a state in which FEC was not contained.

[0078] Test Example II (Examples 3 and 4, Comparative Examples 3 and 4) In this test example, LiNi was used as the positive electrode active material. 0.8 Co 0.1 Mn 0.1 Examples 1 and 2 of Test Example I, Comparative Examples 1 and 2, and nonaqueous electrolyte secondary batteries (Examples 3 and 4, Comparative Examples 3 and 4) were constructed and evaluated, except that O2 (NCM811) was used and the charging voltage during the charging process (or initial charging process) was 4.2 V. The results are shown in Table 2.

[0079] [Table 2]

[0080] As shown in Table 2, similar effects were obtained even when the type of positive electrode active material was different. Therefore, it was found that the effects of the technology disclosed herein can be exerted regardless of the type of positive electrode active material.

[0081] Although several embodiments of the present invention have been described above, the above embodiments are merely examples. The present invention can be implemented in various other forms. The present invention can be implemented based on the contents disclosed in this specification and the common general technical knowledge in the relevant field. The technology described in the claims includes various modifications and alterations of the above-exemplified embodiments. For example, it is possible to replace part of the above-described embodiments with other modifications, or to add other modifications to the above-described embodiments. Furthermore, if a technical feature is not described as essential, it may be deleted as appropriate.

[0082] In the embodiment of Fig. 1 described above, the external shape of the battery 100 is a rectangular parallelepiped (square). However, this is not limiting. In other embodiments, the battery 100 may be, for example, a sheet, a cylinder, a button, a coin, or the like.

[0083] 4 includes the initial charging step (step S3), but as mentioned above, the initial charging step (step S3) is optional and can be omitted. In that case, in the charging step (step S5), a coating containing a component derived from difluorophosphate is formed on the positive electrode 22 side, and a coating containing a component derived from FEC is formed on the negative electrode 24 side.

[0084] As described above, specific aspects of the technology disclosed herein include those described in the following sections. Item 1: A method for producing a non-aqueous electrolyte secondary battery comprising an electrode assembly having a positive electrode and a negative electrode, a non-aqueous electrolyte, and a battery case, wherein the negative electrode contains a Si-containing material, the method comprising: an assembly step of accommodating the electrode assembly in the battery case to construct an assembly; a first impregnation step of injecting a first non-aqueous electrolyte solution containing a difluorophosphate and a non-fluorinated carbonate and substantially no fluoroethylene carbonate into the battery case to impregnate the electrode assembly; a second impregnation step of injecting a second non-aqueous electrolyte solution containing fluoroethylene carbonate into the battery case after the first impregnation step to impregnate the electrode assembly; and a charging step of charging the assembly after the second impregnation step. Item 2: The manufacturing method according to Item 1, further comprising an initial charging step of charging the assembly after the first liquid injection step and before the second liquid injection step. Item 3: The method according to item 1 or 2, wherein the second non-aqueous electrolyte solution is substantially free of difluorophosphate. Item 4: The method according to any one of Items 1 to 3, wherein the first nonaqueous electrolyte solution contains a supporting salt. Item 5: The manufacturing method according to any one of Items 1 to 4, wherein the Si-containing material is at least one of Si, SiO, and SiC. Item 6: The production method according to any one of Items 1 to 5, wherein the non-fluorinated carbonate is at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, and vinylene carbonate. [Explanation of symbols]

[0085] 10 Battery case 20 Electrode body 22 Positive electrode 22a Cathode active material layer 24 Negative electrode 24a Negative electrode active material layer 100 batteries S1 construction process S2 1st impregnation process S3 Initial charging process S4 2nd impregnation process S5 charging process

Claims

1. A method for manufacturing a non-aqueous electrolyte secondary battery comprising: an electrode assembly having a positive electrode and a negative electrode; a non-aqueous electrolyte; and a battery case, wherein the negative electrode contains a Si-containing material, a construction step of housing the electrode body in the battery case to construct an assembly; a first impregnation step of injecting a first nonaqueous electrolyte solution containing a supporting salt, a difluorophosphate, and a non-fluorinated carbonate but not containing fluoroethylene carbonate into the battery case to impregnate the electrode body; an initial charging step of charging the assembly until a voltage reaches 4 V or more after the first impregnation step, thereby forming a coating containing a component derived from the difluorophosphate on the surface of the positive electrode; a second impregnation step of injecting a second nonaqueous electrolyte solution containing fluoroethylene carbonate into the battery case and impregnating the electrode body after the initial charging step; a charging step of charging the assembly after the second impregnation step to form a coating containing a component derived from the fluoroethylene carbonate on the surface of the negative electrode; A method for manufacturing a non-aqueous electrolyte secondary battery, comprising:

2. In the initial charging step, the assembly is charged until the voltage reaches 4.6 V or more. The method of claim 1.

3. the second non-aqueous electrolyte does not contain a difluorophosphate; The method according to claim 1 or 2.

4. In the first impregnation step, the difluorophosphate is added to the first non-aqueous electrolyte so that the proportion of the difluorophosphate in the entire non-aqueous electrolyte before the charging step is 0.5 mass % or more and 1 mass % or less. The method according to claim 1 or 2.

5. The Si-containing material is at least one of Si, SiO, and SiC-containing materials. The method according to claim 1 or 2.

6. The non-fluorinated carbonate is at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethylene carbonate, and vinylene carbonate. The method according to claim 1 or 2.

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