Manufacturing method of non-aqueous electrolyte secondary battery

Abstract

The present invention provides a method for manufacturing a non-aqueous electrolyte secondary battery that suppresses the deterioration of input / output characteristics due to a decrease in the ionic conductivity of the non-aqueous electrolyte. [Solution] The manufacturing method comprises the steps of: injecting a first non-aqueous electrolyte containing a film-forming agent into the outer casing of a battery assembly in which electrodes are housed; a conditioning step of charging the battery assembly; an electrolyte discharge step of discharging the first non-aqueous electrolyte from the outer casing; and injecting a second non-aqueous electrolyte containing a cyclic carbonate as a non-aqueous solvent into the outer casing, wherein the second non-aqueous electrolyte contains at least one selected from the group consisting of a first compound represented by general formula (I) and a second compound represented by general formula (II) as a non-aqueous solvent. TIFF2026112194000016.tif2235 TIFF2026112194000017.tif2339

Description

[Technical Field]

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

[0002] Non-aqueous electrolyte secondary batteries, such as lithium-ion secondary batteries, have an electrode body including a positive electrode and a negative electrode, and a non-aqueous electrolyte in which a supporting salt is dissolved in a non-aqueous solvent. In such non-aqueous electrolyte secondary batteries, a portion of the non-aqueous electrolyte decomposes during initial charging, and a film called an SEI (Solid Electrolyte Interface) film, composed of the decomposition products, may form on the surface of the negative electrode. This film has the function of suppressing the reductive decomposition of the non-aqueous electrolyte by reacting with the negative electrode active material in direct contact. Therefore, the durability of the battery (cycle characteristics, high-temperature storage characteristics, etc.) can be improved.

[0003] Cyclic carbonates such as ethylene carbonate and propylene carbonate, which are suitably used as non-aqueous solvents in non-aqueous electrolytes, are known to form stable films. However, the films formed by the reductive decomposition of non-aqueous electrolytes consume charge carriers (e.g., lithium ions) in the non-aqueous electrolyte, and if the amount of film is large, it can degrade the cycle characteristics. Therefore, in recent years, film-forming agents (additives for film formation) have been added to non-aqueous electrolytes to form a stable film on the surface of the negative electrode in advance.

[0004] Furthermore, because cyclic carbonates are high dielectric constant solvents, they are suitably used as non-aqueous solvents in non-aqueous electrolytes. However, because cyclic carbonates have high viscosity, using only cyclic carbonates as a non-aqueous solvent increases the viscosity of the non-aqueous electrolyte, reducing ionic conductivity and consequently degrading the input / output characteristics of the battery. Therefore, cyclic carbonates are used in mixtures with chain-like carbonates such as dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, which have lower viscosity than cyclic carbonates.

[0005] Thus, various studies have been conducted on non-aqueous electrolytes to improve battery characteristics. One example of this is disclosed in Patent Documents 1 to 4.

[0006] The method for manufacturing a lithium-ion secondary battery described in Patent Document 1 includes the steps of: preparing a battery in which electrode bodies are housed in a battery case; injecting a first electrolyte containing a film-forming additive into the battery case; charging and discharging the battery in which the first electrolyte has been injected; discharging the first electrolyte from the charged and discharged battery; and injecting a second electrolyte containing less than 0.005 mol / L of a film-forming additive into the battery case from which the first electrolyte has been discharged.

[0007] In the technology described in Patent Document 1, a film-forming additive is added to the electrolyte, and a lithium-ion secondary battery is obtained in which a film derived from the film-forming additive is formed.

[0008] The method for manufacturing a non-aqueous electrolyte secondary battery described in Patent Document 2 includes the steps of: preparing an electrode body comprising a positive electrode containing a positive electrode active material and a negative electrode containing a negative electrode active material, wherein the electrode body contains sodium (Na) as an unavoidable impurity; housing the electrode body in a battery case; a first injection step of injecting a non-aqueous electrolyte that does not contain an oxalate complex compound containing boron (B) as a constituent element into the battery case; and a second injection step, after the first injection step, of injecting a non-aqueous electrolyte containing the oxalate complex compound into the battery case.

[0009] The technology described in Patent Document 2 prevents variations in the amount of coating due to the concentration of sodium components, and by forming a more favorable coating on the surface of the negative electrode active material, a non-aqueous electrolyte secondary battery is obtained in which the deposition of substances derived from the charge carrier is suppressed.

[0010] The method for manufacturing a non-aqueous electrolyte secondary battery described in Patent Document 3 involves performing a charging process using a non-aqueous electrolyte containing ethylene carbonate and vinylene carbonate, then, after discharging the non-aqueous electrolyte, injecting a non-aqueous electrolyte containing at least one selected from propylene carbonate (PC), fluorinated ethylene carbonate (FEC), and 1,3-dioxane (DOX) and ethylene carbonate.

[0011] The technology described in Patent Document 3 provides a non-aqueous electrolyte secondary battery with a large initial discharge capacity and minimal degradation of cycle characteristics even when the positive electrode charging potential is set to more than 4.3V and less than or equal to 5.1V relative to lithium.

[0012] The method for manufacturing a lithium-ion secondary battery described in Patent Document 4 is characterized in that it includes at least two electrolyte injection steps in which a non-aqueous electrolyte is injected into the inside of a battery precursor from an electrolyte inlet provided on the battery can or battery lid, and after the final electrolyte injection step, a step of sealing the electrolyte inlet, and at least one charging step after the first electrolyte injection step and before the final electrolyte injection step, wherein in the electrolyte injection step before the first charging step, a non-aqueous electrolyte containing an additive that can form a film on the negative electrode surface by charging is injected, and in the electrolyte injection step after the first charging step, a non-aqueous electrolyte with a lower concentration of the above-mentioned additive than the non-aqueous electrolyte used in the electrolyte injection step before the first charging step, or a non-aqueous electrolyte that does not contain the above-mentioned additive, is injected.

[0013] The technology described in Patent Document 4 can suppress battery swelling caused by gas generation during charging, and can also improve the battery's charge-discharge cycle characteristics. [Prior art documents] [Patent Documents]

[0014] [Patent Document 1] Japanese Patent Publication No. 2014-150027 [Patent Document 2] Japanese Patent Publication No. 2013-247009 [Patent Document 3] Japanese Patent Application Laid-Open No. 2009-110886 [Patent Document 4] Japanese Patent Application Laid-Open No. 2006-294282 [Summary of the Invention] [Problems to be Solved by the Invention]

[0015] However, even when using various single solvents or mixed solvents proposed by the techniques described in Patent Documents 1 to 4 as the non-aqueous solvent of the non-aqueous electrolyte, it may be difficult to sufficiently reduce the viscosity of the non-aqueous electrolyte. In this case, in the techniques described in Patent Documents 1 to 4, there is a problem that in a non-aqueous electrolyte secondary battery, there is a risk that sufficient input / output characteristics cannot be obtained due to a decrease in the ionic conductivity of the non-aqueous electrolyte. [Means for Solving the Problems]

[0016] The present disclosure has been made to solve such problems, and an object thereof is to provide a method for manufacturing a non-aqueous electrolyte secondary battery that suppresses a decrease in input / output characteristics due to a decrease in the ionic conductivity of the non-aqueous electrolyte.

[0017] The method for manufacturing a non-aqueous electrolyte secondary battery according to the present disclosure includes: a first injection step of injecting a first non-aqueous electrolyte containing a film-forming agent capable of forming a film on the surface of the negative electrode into the exterior body of a battery assembly in which an electrode body having a positive electrode and a negative electrode is housed in the exterior body; a conditioning step of charging the battery assembly after the first injection step; an electrolyte discharge step of discharging the first non-aqueous electrolyte from the exterior body after the conditioning step; and a second injection step of injecting a second non-aqueous electrolyte containing a cyclic carbonate as a non-aqueous solvent into the exterior body after the electrolyte discharge step, The second non-aqueous electrolyte contains, as a non-aqueous solvent, in addition to the cyclic carbonate, at least one selected from the group consisting of a first compound represented by the following general formula (I) and a second compound represented by the following general formula (II). [Chemistry] In formula (I), R 1 is a hydrocarbon group having 1 or 2 carbon atoms. [Chemistry] In formula (II), R 2 and R 3 are each a hydrocarbon group having 1 or 2 carbon atoms. [Advantages of the Invention]

[0018] According to the present disclosure, it is possible to provide a method for manufacturing a non-aqueous electrolyte secondary battery that suppresses a decrease in input / output characteristics due to a decrease in ionic conductivity of the non-aqueous electrolyte. [Brief Description of the Drawings]

[0019] [Figure 1] It is a cross-sectional view showing an overview of a non-aqueous electrolyte secondary battery manufactured by the method for manufacturing a non-aqueous electrolyte secondary battery according to Embodiment 1. [Figure 2] It is a flowchart showing the method for manufacturing a non-aqueous electrolyte secondary battery according to Embodiment 1. [Figure 3] It is a graph showing the results of comparing the non-aqueous electrolytes of Examples 1A to 122A with the non-aqueous electrolyte of Comparative Example 1. [Figure 4] It is a graph showing the results of comparing the non-aqueous electrolytes of Examples 1B to 87B with the non-aqueous electrolyte of Comparative Example 1. [Modes for Carrying Out the Invention]

[0020] Embodiment 1 Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. However, the present disclosure is not limited to the following embodiments. Also, for clarity of explanation, the following description and drawings are appropriately simplified. What is shown in the figures is a part of the whole, and many other configurations not shown are actually included. Furthermore, in the following description, the same or equivalent elements are denoted by the same reference numerals, and duplicate explanations are omitted.

[0021] The non-aqueous electrolyte secondary battery 10 manufactured by the manufacturing method of the non-aqueous electrolyte secondary battery according to this embodiment is a rechargeable battery such as a lithium-ion secondary battery or an electric double-layer capacitor. Hereinafter, one preferred embodiment of the manufacturing method of the non-aqueous electrolyte secondary battery 10 according to this embodiment will be described in detail as a manufacturing method for a lithium-ion secondary battery.

[0022] Lithium-ion secondary batteries charge and discharge by the conduction of lithium ions, which act as charge carriers, through the electrolyte between a positive electrode 30 and a negative electrode 40. Such lithium-ion secondary batteries are suitably used as power sources for vehicles such as electric vehicles (EVs), hybrid vehicles (HVs), and plug-in hybrid vehicles (PHEVs).

[0023] Here, Figure 1 is a cross-sectional view showing an overview of a non-aqueous electrolyte secondary battery manufactured by the manufacturing method of a non-aqueous electrolyte secondary battery according to Embodiment 1. As shown in Figure 1, the non-aqueous electrolyte secondary battery 10 is constructed by housing an electrode body 20 having a positive electrode 30 and a negative electrode 40, and a non-aqueous electrolyte, in a battery case 11.

[0024] The battery case 11 is one specific example of an outer casing. The outer casing may be, for example, a pouch made of aluminum laminate film. The battery case 11 has, for example, a flat rectangular parallelepiped shape. The battery case 11 is not limited to a rectangular parallelepiped shape, but may also be cylindrical, for example. The battery case 11 is made of a metal material such as aluminum, aluminum alloy, and stainless steel. The battery case 11 has a bottomed rectangular tubular case body 12 with an open top end, and a rectangular flat plate lid 13. The lid 13 is provided to close the opening of the case body 12 and is joined to the case body 12. The lid 13 seals the inside of the battery case 11 with the electrode body 20 and non-aqueous electrolyte contained inside the case body 12.

[0025] The lid 13 is provided with an inlet 14, a sealing member 15, a positive electrode terminal 16, and a negative electrode terminal 17. The inlet 14 is used when injecting a non-aqueous electrolyte into the battery case 11 and is a hole that penetrates the lid 13. The inlet 14 is airtightly sealed by the sealing member 15. In addition, the lid 13 is provided with a gas discharge valve that opens when the inside of the battery case 11 reaches a predetermined pressure to discharge gas generated inside the battery case 11.

[0026] The positive electrode terminal 16 is electrically connected to the positive electrode 30 via a positive electrode current collector terminal 18 attached to the portion of the electrode body 20 where the positive electrode current collector 31 is exposed, which is the end of the electrode body 20 on the positive electrode 30 side. The negative electrode terminal 17 is electrically connected to the negative electrode 40 via a negative electrode current collector terminal 19 attached to the portion of the electrode body 20 where the negative electrode current collector 41 is exposed, which is the end of the electrode body 20 on the negative electrode 40 side.

[0027] The electrode body 20 may have a positive and negative electrode 30 and 40, as well as a separator 50 interposed between the positive and negative electrodes 30 and 40. A wound electrode body can be suitably used as the electrode body 20, which consists of two elongated sheet-like positive electrode 30 and negative electrode 40, stacked with two elongated sheet-like separators 50 in between, and then wound and compressed in a flattened shape in the longitudinal direction.

[0028] Next, with reference to Figure 2, an example of a method for manufacturing the non-aqueous electrolyte secondary battery 10 according to this embodiment will be described. Figure 2 is a flowchart showing the method for manufacturing the non-aqueous electrolyte secondary battery according to Embodiment 1.

[0029] As shown in Figure 2, the method for manufacturing the non-aqueous electrolyte secondary battery 10 according to this embodiment (hereinafter also simply referred to as the manufacturing method) comprises a battery assembly construction step (step S1), a first injection step (step S2), a conditioning step (step S3), an aging step (step S4), an electrolyte discharge step (step S5), and a second injection step (step S6).

[0030] [Battery assembly construction process (Step S1)] Step S1 is a battery assembly construction step in which an electrode body 20 having a positive electrode 30 and a negative electrode 40 is housed in a battery case 11 which serves as an outer casing to construct a battery assembly. Note that the battery assembly construction step may be omitted if necessary.

[0031] The battery assembly construction process includes, for example, a preparation step of preparing a positive electrode 30, a negative electrode 40, and a separator 50; an electrode body manufacturing step of manufacturing an electrode body 20; an electrode body connection step of connecting the electrode body 20 to positive and negative electrode terminals 16 and 17; and an electrode body housing step of housing the electrode body 20, to which the positive and negative electrode terminals 16 and 17 are connected, inside the battery case 11.

[0032] In the preparation process, the positive electrode 30, negative electrode 40, and separator 50 to be used in the non-aqueous electrolyte secondary battery 10 to be manufactured are prepared. Any materials that can be used in lithium-ion secondary batteries can be used without particular restrictions as materials constituting the positive electrode 30, negative electrode 40, and separator 50.

[0033] (positive electrode 30) The positive electrode 30 comprises a positive electrode current collector 31 and a positive electrode composite layer 33 formed on the surface (one or both sides) of the positive electrode current collector 31, which contains positive electrode active material. In addition to the positive electrode active material, the positive electrode composite layer 33 may further contain any components such as a conductive material and a binder.

[0034] The positive electrode current collector 31 is made of a metal with good conductivity, such as aluminum or an aluminum alloy. In this embodiment, aluminum foil is used as the sheet-shaped positive electrode current collector 31, but the shape of the positive electrode current collector 31 is not limited to a sheet shape and can be appropriately changed according to the shape of the non-aqueous electrolyte secondary battery 10, etc.

[0035] Examples of positive electrode active materials include materials capable of intercalating and releasing lithium ions, such as lithium transition metal composite oxides like lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMn2O4), and lithium nickel-cobalt-manganate (NCM), and polyanionic compounds like lithium iron phosphate (LiFePO4). Such positive electrode active materials can be used individually or in combination of two or more. Furthermore, other metal elements may be added to the positive electrode active material.

[0036] The average particle size (D50) of the positive electrode active material is not particularly limited, but is preferably, for example, 1 μm to 30 μm. The average particle size (D50) of the positive electrode active material can be measured, for example, by particle size distribution measurement using laser diffraction scattering.

[0037] Examples of conductive materials include carbon black such as acetylene black, activated carbon, graphite, and carbon materials such as carbon nanotubes. Such conductive materials can be used individually or in combination of two or more.

[0038] As a binder, a polymer material that is soluble or dispersible in the solvent used can be used. The solvent is appropriately selected depending on the binder used. As solvents, for example, non-aqueous solvents such as N-methyl-2-pyrrolidone (NMP), mixed solvents combining non-aqueous solvents, or aqueous solvents such as water or mixed solvents mainly composed of water can be used.

[0039] When a non-aqueous solvent is used, polymer materials that can be dissolved or dispersed in the non-aqueous solvent, such as polyvinylidene fluoride (PVDF) or polyvinylidene chloride (PVDC), are used as binders. When an aqueous solvent is used, polymer materials that can be dissolved or dispersed in the aqueous solvent, such as polytetrafluoroethylene (PTFE), polyethylene oxide (PEO), or styrene-butadiene rubber (SBR), are used as binders.

[0040] The positive electrode 30 can be manufactured, for example, by the following procedure. A paste-like or slurry-like composition for forming a positive electrode composite layer is prepared by kneading a powder containing a positive electrode active material and, if necessary, a conductive material, a binder, etc., with a solvent capable of dissolving or dispersing the binder. The positive electrode 30 can be manufactured by coating at least one surface of the positive electrode current collector 31 with the composition thus prepared, except for the portion along one edge in the width direction, drying it, and then compressing (pressing) it.

[0041] (Negative electrode 40) The negative electrode 40 comprises a negative electrode current collector 41 and a negative electrode composite layer 43 containing negative electrode active material formed on the surface (one or both sides) of the negative electrode current collector 41. The negative electrode composite layer 43 may further contain any components other than the negative electrode active material, such as a binder and a thickener.

[0042] The negative electrode current collector 41 is made of a metal with good conductivity, such as copper or a copper alloy. In this embodiment, copper foil is used as the sheet-shaped negative electrode current collector 41, but the shape of the negative electrode current collector 41 is not limited to a sheet shape and can be appropriately changed according to the shape of the non-aqueous electrolyte secondary battery 10, etc.

[0043] Examples of negative electrode active materials include materials capable of intercalating and releasing lithium ions, such as carbon materials like graphite, hard carbon, and soft carbon, lithium transition metal composite oxides, and lithium transition metal composite nitrides. Such negative electrode active materials can be used individually or in combination of two or more. Furthermore, the surface of the negative electrode active material may be coated with an amorphous carbon film.

[0044] The average particle size (D50) of the negative electrode active material is not particularly limited, but is preferably, for example, 2 μm to 50 μm. The average particle size (D50) of the negative electrode active material can be determined, for example, by particle size distribution measurement using laser diffraction scattering.

[0045] As a binder, the same type as those exemplified for use in the positive electrode 30 can be used. As a thickener, for example, polymer materials such as carboxymethylcellulose (CMC) and polyvinyl alcohol (PVA) can be used. Alternatively, the polymer materials exemplified for use as binders can be used as thickeners.

[0046] The negative electrode 40 can be manufactured, for example, by the following procedure. A paste-like or slurry-like composition for forming a negative electrode composite layer is prepared by kneading a powder containing a negative electrode active material and, if necessary, a binder, a thickener, etc., with a solvent capable of dissolving or dispersing the binder. The negative electrode 40 can be manufactured by coating the surface of the negative electrode current collector 41 with the composition thus prepared, except for the portion along one edge in the width direction, drying it, and then compressing (pressing) it.

[0047] (Separator 50) As the separator 50, for example, a porous resin sheet made of a resin such as polyethylene (PE) or polypropylene (PP) can be used. Such a resin sheet 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). In addition, the separator 50 may have a heat-resistant layer (HRL) provided on its surface.

[0048] Next, in the electrode body manufacturing process, first, the positive electrode 30, the negative electrode 40, and the two separators 50 are stacked on top of each other so that the positive electrode composite layer 33 and the negative electrode composite layer 43 face each other via the separators 50. At this time, the positive electrode 30 and the negative electrode 40 are stacked with a slight offset in the width direction so that the exposed portions of the positive and negative electrode current collectors 31 and 41 protrude outward from both sides in the width direction of the separators 50. After that, the stacked positive electrode 30, the negative electrode 40, and the two separators 50 are wound in the longitudinal direction and compressed into a flat shape with a predetermined thickness to form a flat cylindrical electrode body 20.

[0049] Next, in the electrode connection process, first, the positive electrode current collector terminal 18 is joined to the exposed portion of the positive electrode current collector 31 of the electrode body 20, and the negative electrode current collector terminal 19 is joined to the exposed portion of the negative electrode current collector 41 of the electrode body 20. Next, the positive electrode current collector terminal 18 is joined to the positive electrode terminal 16 which is pre-attached to the cover 13, and the negative electrode current collector terminal 19 is joined to the negative electrode terminal 17 which is pre-attached to the cover 13. This electrically connects the positive and negative electrodes 30 and 40 of the electrode body 20 to the positive and negative electrode terminals 16 and 17. For joining, for example, ultrasonic welding or resistance welding can be used.

[0050] Next, in the electrode housing process, first, the electrode body 20, to which the positive and negative electrode terminals 16 and 17 are connected, is housed inside the case body 12 through the opening of the case body 12. Then, the opening of the case body 12 is closed with the lid 13, and the case bodies 12 and 13 are joined together to form the battery case 11. In this way, a battery assembly in which the electrode body 20 is housed inside the battery case 11 can be constructed. For joining, a joining method such as laser welding can be used.

[0051] [First injection process (Step S2)] Step S2 is a first injection step in which a first non-aqueous electrolyte containing a film-forming agent capable of forming a film on the surface of the negative electrode 40 is injected into the battery case 11 of the battery assembly, in which the electrode body 20 having a positive electrode 30 and a negative electrode 40 is housed in the battery case 11. The first injection step is performed after the battery assembly construction step.

[0052] As the first non-aqueous electrolyte, a non-aqueous electrolyte containing a film-forming agent can be used, which is obtained by dissolving a supporting salt (electrolyte) in a non-aqueous solvent (organic solvent). As the non-aqueous solvent for the first non-aqueous electrolyte, various aprotic solvents such as carbonates, esters, ethers, nitriles, sulfones, and lactones can be used. Among these, carbonates are preferred. Examples of carbonates include cyclic carbonates, linear carbonates, and compounds in which at least some of the hydrogen atoms of these carbonates are substituted with halogen atoms. Such non-aqueous solvents can be used individually or in combination of two or more.

[0053] Examples of cyclic carbonates include those having alkylene groups with 2 to 4 carbon atoms. Examples of cyclic carbonates having alkylene groups with 2 to 4 carbon atoms include ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Note that at least some of the hydrogen atoms in the alkylene group may be substituted.

[0054] Examples of linear carbonates include linear carbonates having an alkyl group with 3 to 7 carbon atoms. Examples of linear carbonates having an alkyl group with 3 to 7 carbon atoms include dimethyl carbonate (DMC), diethyl carbonate (DEC), di-n-propyl carbonate, diisopropyl carbonate, n-propylisopropyl carbonate, ethyl methyl carbonate (EMC), methyl-n-propyl carbonate, n-butyl ethyl carbonate, isobutyl ethyl carbonate, and t-butyl ethyl carbonate. Note that at least some of the hydrogen atoms in the alkyl group may be substituted.

[0055] From the viewpoint of improving charge-discharge efficiency, a combination of a cyclic carbonate, which is a high dielectric constant solvent, and a chain carbonate, which is a low viscosity solvent, is preferred as the non-aqueous solvent. Cyclic carbonates have a relatively high relative dielectric constant, which increases the degree of dissociation of the supporting salt and makes it easier to dissociate the supporting salt into cations and anions. Chain carbonates have a relatively low viscosity, which gives them high ion diffusion properties. More specifically, a combination of EC and DMC is preferred.

[0056] The cyclic carbonate content is preferably 20 wt% to 80 wt%, and more preferably 25 wt% to 35 wt%, relative to the total amount of non-aqueous solvent in the first non-aqueous electrolyte. This range promotes the dissociation of the supporting salt and suppresses an increase in the viscosity of the first non-aqueous electrolyte.

[0057] The content of the chain-like carbonate is preferably 20 wt% to 80 wt%, and more preferably 50 wt% to 70 wt%, relative to the total amount of non-aqueous solvent in the first non-aqueous electrolyte. By keeping it within this range, the viscosity of the first non-aqueous electrolyte can be reduced.

[0058] Examples of supporting salts include Li salts such as LiPF6, LiClO4, LiAsF6, LiBF4, and LiSO3CF3. Such supporting salts can be used individually or in combination of two or more. In particular, from the viewpoint of improving electrical properties, it is preferable that the supporting salt contains LiPF6.

[0059] The content of the supporting salt is not particularly limited, but from the viewpoint of suppressing a decrease in the ionic conductivity of the first non-aqueous electrolyte, it is preferable that it be 5 wt% to 40 wt%, and preferably 5 wt% to 20 wt%, relative to the total amount of the first non-aqueous electrolyte.

[0060] The film-forming agent is reduced and decomposed on the surface of the negative electrode 40 during initial charging, and a film derived from the decomposed film-forming agent is formed on the surface of the negative electrode 40. It is preferable to use various compounds as the film-forming agent that decompose at a lower voltage than other components in the first non-aqueous electrolyte and can form a film on the surface of the negative electrode 40.

[0061] Examples of film-forming agents include oxalato complex compounds and carbonates. Examples of oxalato complex compounds include (oxalato) borates represented by lithium bis(oxalato)borate (LiBOB), fluoro(oxalato)borates represented by lithium difluoro(oxalato)borate, and (oxalato) phosphates represented by lithium-tris(oxalato)phosphate. Examples of carbonates include vinylene carbonate (VC), vinyl ethyl carbonate (VEC), methylphenyl carbonate (MPC), and fluoroethylene carbonate (FEC). Such film-forming agents can be used individually or in combination of two or more. In particular, it is preferable that the film-forming agent contains LiBOB in order to form a high-quality film. The film-forming agent may substantially overlap with the non-aqueous solvent used in the first non-aqueous electrolyte.

[0062] The content of the film-forming agent in the first non-aqueous electrolyte is not particularly limited. From the viewpoint of sufficiently obtaining the effect of suppressing the reductive decomposition of the non-aqueous solvent by forming a sufficient film on the surface of the negative electrode 40, the content of the film-forming agent in the first non-aqueous electrolyte is preferably, for example, 0.1 wt% or more, and 0.5 wt% or more, relative to the total amount of the first non-aqueous electrolyte. On the other hand, from the viewpoint of suppressing an increase in battery resistance due to the excessive formation of a film on the surface of the negative electrode 40, the content of the film-forming agent in the first non-aqueous electrolyte is preferably, for example, 10 wt% or less, and 5 wt% or less, relative to the total amount of the first non-aqueous electrolyte.

[0063] The first non-aqueous electrolyte may contain various additives in addition to the non-aqueous solvent, supporting salt, and film-forming agent described above. The type of additive can be selected according to the application of the first non-aqueous electrolyte.

[0064] After injecting the first non-aqueous electrolyte, the pressure inside the battery case 11 may be appropriately reduced as needed to impregnate the electrode body 20 with the first non-aqueous electrolyte. After injecting the first non-aqueous electrolyte, the inlet 14 may be temporarily sealed with the sealing member 15 until the discharge of the first non-aqueous electrolyte begins or until the second non-aqueous electrolyte is injected.

[0065] [Conditioning Process (Step S3)] Step S3 is a conditioning step in which the battery assembly is charged after the first injection step.

[0066] In the conditioning process, the battery assembly is charged at least once (initial charge) within a voltage range in which a film can be formed on the surface of the negative electrode 40. This charging allows a film derived from the first non-aqueous electrolyte containing a film-forming agent to be formed on the surface of the negative electrode 40. The voltage range in which the film is formed on the surface of the negative electrode 40 varies depending on the materials used, and can be appropriately set according to the non-aqueous electrolyte secondary battery 10 to be manufactured.

[0067] The charging method is not particularly limited. For example, it may be a method of charging with a constant current (CC charging), a method of charging with a constant voltage (CV charging), or a method of charging with a constant current until a predetermined voltage is reached, and then charging with a constant voltage (CCCV charging). The charging rate during CC charging is not particularly limited, but from the viewpoint of forming a good quality coating on the surface of the negative electrode 40 in a short time, it is preferably, for example, 0.1C to 20C, and more preferably 0.5C to 10C.

[0068] [Aging process (Step S4)] Step S4 is an aging process performed on the battery assembly after the conditioning process and before the electrolyte discharge process. The aging process may be omitted if necessary.

[0069] In the aging process, the battery assembly is stored in a predetermined high-temperature environment for a predetermined time after initial charging. By performing aging after initial charging, the coating can be stabilized. The aging conditions can be adjusted as appropriate depending on the composition of the coating, etc.

[0070] [Electrolyte discharge process (Step S5)] Step S5 is an electrolyte discharge step in which the first non-aqueous electrolyte is discharged from the battery case 11 after the conditioning step. If an aging step is provided, the electrolyte discharge step is performed after the aging step.

[0071] In the electrolyte discharge step, after the film has been formed in the conditioning step, the first non-aqueous electrolyte containing unreacted film-forming agent is discharged. One method for discharging the first non-aqueous electrolyte is to disassemble the battery assembly, remove the electrode body 20 from inside the battery case 11, and then discharge the first non-aqueous electrolyte. In the electrolyte discharge step, it is preferable to discharge as much of the first non-aqueous electrolyte containing unreacted film-forming agent as possible.

[0072] [Second injection process (step S6)] Step S6 is a second injection step in which, after the electrolyte discharge step, a second non-aqueous electrolyte containing cyclic carbonate as a non-aqueous solvent is injected into the battery case 11. After injecting the second non-aqueous electrolyte, the pressure inside the battery case 11 may be appropriately reduced as needed to impregnate the electrode body 20 with the second non-aqueous electrolyte.

[0073] As the second non-aqueous electrolyte, a non-aqueous electrolyte can be used obtained by dissolving a supporting salt (electrolyte) in a non-aqueous solvent (organic solvent) containing a cyclic carbonate and at least one of the first compound and the second compound described later. As the supporting salt, the same type as the supporting salt exemplified for use in the first non-aqueous electrolyte can be used.

[0074] The content of the supporting salt is not particularly limited, but from the viewpoint of suppressing a decrease in the ionic conductivity of the second non-aqueous electrolyte, it is preferable that it be 5 wt% to 40 wt%, and more preferably 5 wt% to 20 wt%, relative to the total amount of the second non-aqueous electrolyte.

[0075] According to the manufacturing method of this embodiment, by including a cyclic carbonate, which is a high dielectric constant solvent, in the second non-aqueous electrolyte, it is possible to suppress the decrease in the degree of dissociation of the supporting salt due to a decrease in the relative dielectric constant of the second non-aqueous electrolyte.

[0076] Examples of cyclic carbonates include those similar to those exemplified as cyclic carbonates that may be included in the first non-aqueous electrolyte. In particular, because of their high dielectric constant, it is preferable that the cyclic carbonate be at least one selected from EC and PC.

[0077] The cyclic carbonate content is preferably 20 wt% to 80 wt%, and more preferably 25 wt% to 75 wt%, relative to the total amount of non-aqueous solvent in the second non-aqueous electrolyte. By setting it within this range, the dielectric constant of the second non-aqueous electrolyte can be adjusted to a suitable range, promoting the dissociation of the supporting salt, while also suppressing an increase in the viscosity of the second non-aqueous electrolyte.

[0078] The second non-aqueous electrolyte contains, as a non-aqueous solvent, a cyclic carbonate and at least one compound selected from the group consisting of a first compound represented by the following general formula (I) and a second compound represented by the following general formula (II). [ka] In formula (I), R 1 It is a hydrocarbon group having 1 or 2 carbon atoms. [ka] In formula (II), R 2 and R 3 These are hydrocarbon groups, each having either one or two carbon atoms.

[0079] Here, the first compound represented by formula (I) and the second compound represented by formula (II) have a narrower potential window compared to other non-aqueous solvents that can be used in non-aqueous electrolyte secondary batteries such as the cyclic carbonates mentioned above. As a result, in non-aqueous electrolyte secondary batteries with high voltages, they are prone to reductive decomposition on the surface of the negative electrode 40 during charging and discharging.

[0080] To address these problems, the manufacturing method according to this embodiment allows for the formation of a film on the surface of the negative electrode 40 by conditioning a battery assembly into which a first non-aqueous electrolyte containing a film-forming agent has been injected. Furthermore, in the manufacturing method according to this embodiment, the first non-aqueous electrolyte is drained after the film is formed, and then a second non-aqueous electrolyte containing the above-mentioned compound with a narrow potential window is injected. Therefore, the reductive decomposition of the second non-aqueous electrolyte during subsequent charging and discharging can be suppressed by the pre-formed film.

[0081] Furthermore, the first compound represented by formula (1) and the second compound represented by formula (2) have lower viscosity compared to other non-aqueous solvents that can be used in the non-aqueous electrolyte secondary battery 10, such as the cyclic carbonates mentioned above. Therefore, according to the manufacturing method of this embodiment, by including the above compounds, which are low-viscosity solvents, in the second non-aqueous electrolyte, the decrease in ionic conductivity due to an increase in the viscosity of the second non-aqueous electrolyte can be suppressed. As a result, the input / output characteristics of the non-aqueous electrolyte secondary battery 10 are improved.

[0082] The first and second compounds preferably have a viscosity of 0.3 mPa·s to 0.5 mPa·s at 25°C. This range allows for a sufficient reduction in the viscosity of the second non-aqueous electrolyte. The viscosity may be measured as shear viscosity (mPa·s) using a rotational viscometer such as a B-type viscometer.

[0083] The total content of the first and second compounds is preferably 5 wt% to 95 wt%, and more preferably 5 wt% to 70 wt%, relative to the total amount of non-aqueous solvent in the second non-aqueous electrolyte. By setting it within this range, the viscosity of the second non-aqueous electrolyte can be reduced and adjusted to a suitable range.

[0084] In the above formula (I), R 1 may have a halogen atom and may have an unsaturated bond. That is, in the above formula (I), R 1 is a hydrocarbon group or at least a part of the hydrocarbon group may be substituted with a halogen atom and may have a carbon-carbon unsaturated bond. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom. The unsaturated bond may be a double bond or a triple bond.

[0085] Specific examples of the first compound include chain esters such as methyl acetate (MA) and ethyl acetate (EA), unsaturated chain esters such as vinyl acetate and allyl acetate, and compounds in which at least a part of the hydrogen atoms of the hydrocarbon groups of these esters are substituted with halogen atoms. Among them, from the viewpoint of suppressing the decrease in ionic conductivity due to the increase in the viscosity of the second non-aqueous electrolyte, MA is preferable as the first compound.

[0086] In the above formula (II), at least one of R 2 and R 3 may have a halogen atom and may have an unsaturated bond. That is, in the above formula (II), at least one of R 2 and R 3 is a hydrocarbon group or at least a part of the hydrocarbon group may be substituted with a halogen atom and may have a carbon-carbon unsaturated bond. Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom. The unsaturated bond may be a double bond or a triple bond. Also, in the above formula (II), R 2 and R 3 may be the same as or different from each other.

[0087] Specific examples of the second compound include linear ketones such as methyl ethyl ketone (MEK), diethyl ketone (DEK), methyl propyl ketone (MPK), and ethyl propyl ketone (EPK), unsaturated linear ketones such as methyl vinyl ketone and ethyl vinyl ketone, and compounds in which at least some of the hydrogen atoms of the hydrocarbon groups of these ketones are substituted with halogen atoms. Among these, MEK is preferred as the second compound from the viewpoint of suppressing the decrease in ionic conductivity due to an increase in the viscosity of the second non-aqueous electrolyte.

[0088] The second non-aqueous electrolyte may further contain carbonates other than cyclic carbonates as a non-aqueous solvent, in addition to the cyclic carbonate, the first compound, and the second compound. From the viewpoint of reducing the viscosity of the second non-aqueous electrolyte, chain-like carbonates are preferred as the carbonates other than cyclic carbonates.

[0089] Examples of the linear carbonate include those similar to those exemplified as linear carbonates that may be included in the first non-aqueous electrolyte. In particular, it is preferable that the linear carbonate is at least one selected from DMC, DEC, and EMC.

[0090] The content of the chain-like carbonate is preferably 20 wt% to 80 wt%, and more preferably 25 wt% to 70 wt%, relative to the total amount of non-aqueous solvent in the second non-aqueous electrolyte. By setting it within this range, the viscosity of the second non-aqueous electrolyte can be reduced and adjusted to a suitable range.

[0091] The second non-aqueous electrolyte may further contain, as a non-aqueous solvent, cyclic carbonates, the first compound, and the second compound, as well as solvents other than carbonates, the first compound, and the second compound, to the extent that they do not impair the effects of the present disclosure.

[0092] When the first compound contains MA, the second non-aqueous electrolyte contains EC as a cyclic carbonate in addition to MA, and further contains DMC and EMC, and when the content of MA in the second non-aqueous electrolyte is A (wt%), the content of EC is B (wt%), the content of DMC is C (wt%), and the content of EMC is D (wt%), It is preferable that A+B+C+D=100, 6.0≦A≦55.9, and 40.0≦B≦74.2 are satisfied.

[0093] By using a non-aqueous solvent that combines MA, EC, DMC, and EMC to achieve the above-described composition, a second non-aqueous electrolyte with a dielectric constant equal to or greater than that of a non-aqueous electrolyte using a non-aqueous solvent that combines only EC, DMC, and EMC, and with low viscosity, can be obtained.

[0094] When MEK is included as the second compound, the second non-aqueous electrolyte contains EC as a cyclic carbonate in addition to MEK, and further contains DMC and EMC, and when the MEK content in the second non-aqueous electrolyte is A (wt%), the EC content is B (wt%), the DMC content is C (wt%), and the EMC content is D (wt%), It is preferable that A+B+C+D=100, 27.0≦A≦69.8, and 27.3≦B≦70.0 are satisfied.

[0095] By using a non-aqueous solvent that combines MEK, EC, DMC, and EMC to achieve the above-described composition, a second non-aqueous electrolyte with a dielectric constant equal to or greater than that of a non-aqueous electrolyte using a non-aqueous solvent that combines only EC, DMC, and EMC, and with low viscosity, can be obtained.

[0096] Furthermore, the second non-aqueous electrolyte may contain various additives in addition to the non-aqueous solvent and supporting salt described above. The type of additive can be selected according to the application of the second non-aqueous electrolyte.

[0097] After injecting the second non-aqueous electrolyte, the injection port 14 is sealed with the sealing member 15 to obtain the non-aqueous electrolyte secondary battery 10. Furthermore, the manufacturing method according to this embodiment may further include an activation step (step S7) after the second injection step, in which the non-aqueous electrolyte secondary battery 10 is subjected to conditioning and aging to activate the non-aqueous electrolyte secondary battery 10. The activation step can adjust the non-aqueous electrolyte secondary battery 10 to a usable state. [Examples]

[0098] The following describes some embodiments relating to this disclosure, but this disclosure is not intended to be limited to those shown in these embodiments.

[0099] [Preparation of the second non-aqueous electrolyte] Multiple types of non-aqueous electrolytes were prepared as secondary non-aqueous electrolytes using a non-aqueous solvent prepared by mixing two types selected from EC, DMC, and EMC with one type selected from MA and MEK. The performance of these electrolytes was evaluated based on the relative permittivity and viscosity calculated for each.

[0100] Non-aqueous electrolytes for Examples 1A to 122A were prepared by dissolving LiPF6 at a concentration of 1.0 mol / L in a non-aqueous solvent containing EC, DMC, EMC, and MA in the compositions shown in Tables 1 to 5 below. The content of EC, DMC, EMC, and MA in Tables 1 to 5 is expressed as wt% relative to the total amount of the non-aqueous solvent.

[0101] [Table 1]

[0102] [Table 2]

[0103] [Table 3]

[0104] [Table 4]

[0105] [Table 5]

[0106] Furthermore, non-aqueous electrolytes for Examples 1B to 87B were prepared by dissolving LiPF6 at a concentration of 1.0 mol / L in a non-aqueous solvent prepared by mixing EC, DMC, EMC, and MEK to the compositions shown in Tables 6 to 8 below. The content of EC, DMC, EMC, and MEK in Tables 6 to 8 is expressed as wt% relative to the total amount of the non-aqueous solvent.

[0107] [Table 6]

[0108] [Table 7]

[0109] [Table 8]

[0110] Furthermore, non-aqueous electrolytes for Comparative Examples 1 to 15 were prepared by dissolving LiPF6 at a concentration of 1.0 mol / L in a non-aqueous solvent containing EC, DMC, and EMC in the compositions shown in Table 9 below. Note that the content of EC, DMC, and EMC in Table 7 is expressed as wt% relative to the total amount of the non-aqueous solvent.

[0111] [Table 9]

[0112] For each of the non-aqueous electrolytes prepared in this manner—Examples 1A-122A, 1B-87B, and Comparative Examples 1-15—the relative permittivity and viscosity were calculated using classical MD calculations. The relative permittivity and viscosity obtained for the non-aqueous electrolytes of Examples 1A-122A and 1B-87B were then compared with the relative permittivity (19.54) and viscosity (1.035 mPa·s) obtained for the non-aqueous electrolyte of Comparative Example 1. The results are shown in Tables 1-8 and Figures 3 and 4.

[0113] First, Figure 3 is a graph showing the results of comparing the non-aqueous electrolytes of Examples 1A to 122A with the non-aqueous electrolyte of Comparative Example 1. The vertical axis of the graph in Figure 3 shows the wt% content of EC relative to the total amount of non-aqueous solvent. The horizontal axis of the graph in Figure 3 shows the wt% content of MA relative to the total amount of non-aqueous solvent. In the evaluation columns of Tables 1 to 5 and in the graph in Figure 3, a "○" is marked when the relative permittivity is 19.54 or higher and the viscosity is 1.035 mPa·s or lower, and a "×" is marked when the relative permittivity is less than 19.54 or the viscosity is greater than 1.035 mPa·s.

[0114] As shown in Tables 1-5 and Figure 3, when the MA content in the second non-aqueous electrolyte is A (wt%), the EC content is B (wt%), the DMC content is C (wt%), and the EMC content is D (wt%), the non-aqueous electrolytes of Examples 1A-50A that satisfy A+B+C+D=100, 6.0≦A≦55.9, and 40.0≦B≦74.2 were found to have a dielectric constant and low viscosity equivalent to or better than the non-aqueous electrolyte of Comparative Example 1.

[0115] Figure 4 is a graph showing the results of comparing the non-aqueous electrolytes of Examples 1B to 87B with the non-aqueous electrolyte of Comparative Example 1. The vertical axis of the graph in Figure 4 shows the wt% EC content relative to the total amount of non-aqueous solvent. The horizontal axis of the graph in Figure 4 shows the wt% MEK content relative to the total amount of non-aqueous solvent. In the evaluation columns of Tables 6 to 8 and in the graph in Figure 4, a "○" is used when the relative permittivity is 19.54 or higher and the viscosity is 1.035 mPa·s or lower, and a "×" is used when the relative permittivity is less than 19.54 or the viscosity is greater than 1.035 mPa·s.

[0116] As shown in Tables 6-8 and Figure 4, when the MEK content in the second non-aqueous electrolyte is A (wt%), the EC content is B (wt%), the DMC content is C (wt%), and the EMC content is D (wt%), the non-aqueous electrolytes of Examples 1B-26B that satisfy A+B+C+D=100, 27.0≦A≦69.8, and 27.3≦B≦70.0 have a dielectric constant and low viscosity equivalent to or better than the non-aqueous electrolyte of Comparative Example 1.

[0117] This disclosure is not limited to the embodiments described above, and can be modified as appropriate without departing from the spirit of the invention. For example, in the embodiments described above, an electrode body 20 which is a wound electrode body was used as an example, but the electrode body 20 is not limited to a wound electrode body, but may be a laminated electrode body in which a positive electrode 30 and a negative electrode 40 are stacked with a separator 50 in between. [Explanation of symbols]

[0118] 10 Nonaqueous electrolyte secondary battery 11 Battery case 12 Case body 13 Lid 14 Inlet 15 Sealing material 16 Positive terminal 17 Negative terminal 18 Positive current collection terminal 19 Negative current collection terminal 20 Electrode body 30 Positive electrode 31 Positive electrode current collector 33 Positive electrode composite layer 40 Negative electrode 41 Negative electrode current collector 43 Negative electrode composite layer 50 Separators

Claims

1. A first injection step involves injecting a first non-aqueous electrolyte containing a film-forming agent capable of forming a film on the surface of the negative electrode into the outer casing of a battery assembly in which an electrode body having a positive electrode and a negative electrode is housed within the outer casing, A conditioning step is performed after the first injection step, in which the battery assembly is charged. Following the conditioning step, an electrolyte discharge step is performed to discharge the first non-aqueous electrolyte from the outer casing, The process includes a second injection step in which, after the electrolyte discharge step, a second non-aqueous electrolyte containing a cyclic carbonate as a non-aqueous solvent is injected into the outer casing. The second non-aqueous electrolyte is A method for producing a non-aqueous electrolyte secondary battery, comprising, in addition to the cyclic carbonate, the non-aqueous solvent containing at least one selected from the group consisting of a first compound represented by the following general formula (I) and a second compound represented by the following general formula (II). 【Chemistry 1】 In formula (I), R １ It is a hydrocarbon group having one or two carbon atoms. 【Chemistry 2】 In formula (II), R ２ and R ３ Each of these is a hydrocarbon group having one or two carbon atoms.

2. The method for producing a non-aqueous electrolyte secondary battery according to claim 1, wherein the first compound and the second compound each have a viscosity of 0.3 mPa·s to 0.5 mPa·s at 25°C.

3. The method for producing a non-aqueous electrolyte secondary battery according to claim 1, wherein the total content of the first compound and the second compound is 5 wt% to 95 wt% relative to the total amount of the non-aqueous solvent in the second non-aqueous electrolyte.

4. The method for producing a non-aqueous electrolyte secondary battery according to claim 1, wherein the content of the cyclic carbonate is 20 wt% to 80 wt% relative to the total amount of the non-aqueous solvent in the second non-aqueous electrolyte.

5. The method for producing a non-aqueous electrolyte secondary battery according to claim 1, wherein the cyclic carbonate is at least one selected from ethylene carbonate and propylene carbonate.

6. The second non-aqueous electrolyte is A method for producing a non-aqueous electrolyte secondary battery according to claim 1, comprising methyl acetate as the first compound.

7. The second non-aqueous electrolyte is A method for producing a non-aqueous electrolyte secondary battery according to claim 1, comprising methyl ethyl ketone as the second compound.

8. The second non-aqueous electrolyte is The cyclic carbonate contains ethylene carbonate, It further contains dimethyl carbonate and ethyl methyl carbonate, When the content of methyl acetate in the second non-aqueous electrolyte is A (wt%), the content of ethylene carbonate is B (wt%), the content of dimethyl carbonate is C (wt%), and the content of ethyl methyl carbonate is D (wt%), A method for manufacturing a non-aqueous electrolyte secondary battery according to claim 6, satisfying A + B + C + D = 100, 6.0 ≤ A ≤ 55.9, and 40.0 ≤ B ≤ 74.

2.

9. The second non-aqueous electrolyte is The cyclic carbonate contains ethylene carbonate, It further contains dimethyl carbonate and ethyl methyl carbonate, When the content of methyl ethyl ketone in the second non-aqueous electrolyte is A (wt%), the content of ethylene carbonate is B (wt%), the content of dimethyl carbonate is C (wt%), and the content of ethyl methyl carbonate is D (wt%), A method for manufacturing a non-aqueous electrolyte secondary battery according to claim 7, satisfying A + B + C + D = 100, 27.0 ≤ A ≤ 69.8, and 27.3 ≤ B ≤ 70.

0.

10. The method for producing a non-aqueous electrolyte secondary battery according to claim 1, wherein the film-forming agent contains lithium bis(oxalato)borate.

11. A method for manufacturing a non-aqueous electrolyte secondary battery according to claim 1, further comprising an aging step of performing aging on the battery assembly after the conditioning step and before the electrolyte discharge step.

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