Method for manufacturing non-aqueous electrolyte secondary battery

Abstract

To provide a method for manufacturing a non-aqueous electrolyte secondary battery that can suppress a decrease in capacity retention rate even when high-rate charging and discharging are repeated using an electrolyte solution containing LiFSO3.SOLUTION: A method for manufacturing a non-aqueous electrolyte secondary battery includes a first step of injecting a first electrolyte solution containing at least one of LiPF6 and LiBF4 into an exterior housing that includes an electrode body to obtain a battery assembly, a second step including a step of charging the battery assembly such that the voltage becomes 3.5 V or higher, and a third step of injecting a second electrolyte solution containing LiFSO3 into the exterior housing of the battery assembly after the second step.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[0002] LiFSO is used as the electrolyte for non-aqueous electrolyte secondary batteries. 3 For example, Patent Document 1 describes LiPF 6 and LiFSO 3 It is disclosed that the use of an electrolyte solution containing the above improves the initial charge capacity, input / output characteristics, and internal impedance characteristics of the battery. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2013-152956 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, LiFSO 3 It has been found that in a battery using an electrolyte solution containing the above, the capacity retention rate decreases when high-rate charging and discharging is repeated.

[0005] This disclosure is based on the LiFSO 3 The present invention aims to provide a method for producing a non-aqueous electrolyte secondary battery that can suppress a decrease in capacity retention rate even when high-rate charging and discharging are repeated using an electrolyte solution containing the above compound. [Means for solving the problem]

[0006] [1] A method for producing a nonaqueous electrolyte secondary battery including an electrode assembly, comprising: The electrode assembly includes a positive electrode plate having an active material layer, The exterior housing containing the electrode assembly is filled with LiPF 6 and LiBF 4a first step of injecting a first electrolytic solution containing at least one of the following to obtain a battery assembly; a second step including charging the battery assembly to a voltage of 3.5 V or greater; The battery assembly after the second step is provided with a LiFSO 3 and a third step of injecting a second electrolytic solution containing the above. [2] LiFSO in the first electrolyte 3 The manufacturing method according to [1], wherein the content of is 0.1 mass% or less. [3] The first electrolyte is LiFSO 3 The method according to [1] or [2], which does not include [4] The manufacturing method according to any one of [1] to [3], wherein the second step further includes an aging step of holding the battery assembly after the charging step at 40° C. or higher for 5 hours or more. [5] The manufacturing method according to [4], wherein the second step includes a step of removing gas present within the battery assembly after the charging step and before the aging step. [6] The manufacturing method according to any one of [1] to [4], wherein the second step includes a step of removing gas present within the battery assembly after the charging step. [7] The manufacturing method according to any one of [1] to [6], wherein the second step is performed while applying a confining pressure of 0.5 MPa or more to the battery assembly in a stacking direction of the positive electrode plates. [8] The electrode body is a wound type electrode body or a laminated type electrode body including a positive electrode plate having an active material layer, When the electrode body is a wound type electrode body, the length of the active material layer in a direction parallel to the winding axis is 150 mm or more, When the electrode body is a laminated electrode body, The laminated electrode body has a square or rectangular shape in a plan view, The method according to any one of [1] to [7], wherein the length of the active material layer in a direction parallel to one side of the square or a direction parallel to a longer side of the rectangle is 150 mm or more. [9] The first electrolyte is LiPF 6 The method according to any one of [1] to [8], comprising: Effect of the Invention

[0007] According to the nonaqueous electrolyte secondary battery of the present disclosure, LiFSO 3 Even when high-rate charge and discharge are repeated using an electrolyte solution containing the above, a decrease in capacity retention rate can be suppressed. [Brief description of the drawings]

[0008] [Figure 1] 2 is a flowchart showing a method for manufacturing a nonaqueous electrolyte secondary battery according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] (Method of manufacturing non-aqueous electrolyte secondary battery) 1 is a flow chart showing a method for manufacturing a nonaqueous electrolyte secondary battery according to an embodiment. The nonaqueous electrolyte secondary battery according to this embodiment (hereinafter also referred to as "the battery") is, for example, a lithium ion secondary battery that performs charging and discharging by absorbing and releasing lithium ions. The battery includes an electrode body, which includes a positive electrode plate having a positive electrode active material layer (active material layer).

[0010] The manufacturing method of the present battery is as follows: The exterior housing that houses the electrode body contains LiPF 6 and LiBF 4 a first step of injecting a first electrolytic solution containing at least one of the following to obtain a battery assembly; a second step including charging the battery assembly to a voltage of 3.5 V or greater; After the second process, LiFSO 3 and a third step of injecting a second electrolytic solution containing the same.

[0011] The electrode assembly typically includes a positive electrode plate and a negative electrode plate. The positive electrode plate has a positive electrode active material layer including a positive electrode active material, and the negative electrode plate has a negative electrode active material layer including a negative electrode active material. The electrode assembly can include, for example, a positive electrode plate, a negative electrode plate, and a separator interposed between the positive electrode plate and the negative electrode plate.

[0012] The electrolyte in this battery is LiFSO 3 Since it contains LiFSO, the output resistance can be reduced. 3 By manufacturing the present battery including the above-mentioned method, it is possible to obtain a present battery in which the decrease in the capacity retention rate can be suppressed even when the battery is repeatedly charged and discharged at a high rate. The reason why the decrease in the capacity retention rate is suppressed is presumed to be as follows.

[0013] In a non-aqueous electrolyte secondary battery (hereinafter also referred to as a "battery"), when charging and discharging are repeated, the electrolyte is pushed out from the electrode body due to the expansion of the negative electrode active material, etc. At this time, the salt concentration of the electrolyte becomes relatively small at the end side of the electrode body, causing uneven charging and discharging, and the potential of the positive electrode plate at the end side of the electrode body increases, and the positive electrode active material and FSO 3 - This causes the transition metals in the positive electrode active material to dissolve, and the dissolved transition metals accumulate on the negative electrode plate, which is thought to result in a decrease in the capacity retention rate when the battery is repeatedly charged and discharged at a high rate. 6 and LiBF 4 After injecting a first electrolyte solution containing at least one of the above, in the second step, charging is performed so that the voltage becomes 3.5 V or higher, thereby forming a LiF film on the surface of the positive electrode active material contained in the positive electrode plate. Then, in the third step, LiFSO 3 Therefore, even if the potential of the positive plate increases due to repeated charging and discharging, the LiF film on the surface of the positive active material prevents the positive active material from being separated from the FSO 3 - This suppresses the reaction with LiFSO and prevents the transition metal from leaching out of the positive electrode active material. 3It is believed that by including this, it is possible to suppress a decrease in the capacity retention rate when charging and discharging at a high rate is repeated while keeping the output resistance small.

[0014] (1st step) The first step is a step of injecting a first electrolytic solution into an outer casing to obtain a battery assembly. This allows the electrode body to be impregnated with the first electrolytic solution. The first step may include a step of housing the electrode body in the outer casing before injecting the first electrolytic solution.

[0015] The first electrolyte is usually a non-aqueous electrolyte, preferably containing LiPF as a supporting electrolyte in a non-aqueous solvent such as an organic solvent. 6 and LiBF 4 The supporting salt contained in the first electrolyte solution is LiPF 6 and LiBF 4 The first electrolyte may contain at least one of the above, or may contain both. The first electrolyte is preferably LiPF 6 Including LiBF 4 It does not have to include.

[0016] Examples of non-aqueous solvents that may be included in the first electrolytic solution include ethylene carbonate (EC), dimethyl carbonate (DMC), propylene carbonate (PC), butylene carbonate (BC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC). The first electrolytic solution may include one or more of these non-aqueous solvents, and preferably includes at least one of EC, DMC, and EMC, more preferably includes EC and DMC, and further preferably includes at least EC. The nonaqueous solvent used in the first electrolytic solution preferably contains two or more of EC, DMC, and EMC in a mixing ratio of EC:DMC:EMC=5-40:0-70:0-70 (volume ratio), or may contain EC:DMC:EMC=10-40:20-70:0-50 (volume ratio), or may contain EC:DMC=30-40:60-70 (volume ratio). In this specification, the notation "x to y" (x and y represent numerical values) indicates that the range is from x to y.

[0017] LiPF contained in the first electrolyte 6 and LiBF 4 The concentration of LiPF may be, for example, 0.5 mol / L or more and 1.5 mol / L or less, 0.6 mol / L or more and 1.2 mol / L or less, or 0.7 mol / L or more and 1.0 mol / L or less. 6 and LiBF 4 When the first electrolyte contains one of the two, the concentration is that of the other, and the first electrolyte contains LiPF 6 and LiBF 4 If both are included, LiPF 6 and LiBF 4 The above concentration is the total concentration of LiPF per 1 L of nonaqueous solvent (if two or more nonaqueous solvents are included, the total concentration of the nonaqueous solvents). 6 and LiBF 4 is the number of moles.

[0018] The first electrolyte is LiPF 6 and LiBF 4 Supporting salts other than LiFSO may be included. 3 The content of LiFSO in the first electrolyte is preferably small. 3 The content of LiFSO in the first electrolyte solution is preferably 0.1 mass % or less. 3 The content [mass%] of LiFSO relative to the total amount of the first electrolyte 3 The amount of LiFSO in the first electrolyte 3 The content of LiFSO in the first electrolyte may be 0.05 mass% or less, or may be zero. 3 Since the content of LiFSO is within the above range, in the first step, 3 FSO produced by ionization 3 - This makes it possible to prevent the LiF film from directly contacting the surface of the positive electrode active material. Therefore, in the second step, the formation of the LiF film on the surface of the positive electrode active material is not easily hindered, and the positive electrode active material and the FSO 3 -Therefore, the reaction with the electrolyte can be suppressed, and the decrease in the capacity retention rate can be suppressed.

[0019] (2nd process) The second step includes a step of charging the battery assembly so that the voltage is 3.5 V or more. The charging step is a step of charging the battery assembly to 3.5 V or more for the first time. The voltage in the charging step may be 3.6 V or more, or 3.8 V or more, and is usually 4.2 V or less. This allows a LiF film to be formed on the surface of the positive electrode active material included in the battery assembly.

[0020] The second step may further include an aging step of holding the battery assembly after the charging step at 30° C. or higher for 5 hours or more. The temperature at which the aging step is carried out may be 35° C. or higher, or 40° C. or higher, and is usually 70° C. or lower. The time for carrying out the aging step may be 6 hours or more, or 7 hours or more, and is usually 20 hours or less. In the aging step, the battery assembly after charging is preferably held at 40° C. or higher for 5 hours or more. This makes it easier to sufficiently form a LiF film on the surface of the positive electrode active material, and makes it easier to further suppress the decrease in the capacity retention rate when charging and discharging at a high rate are repeated.

[0021] The second step may further include a step of removing gas present in the battery assembly after the charging step (hereinafter, also referred to as a "defoaming step"). When the second step includes an aging step, the defoaming step is preferably performed after the charging step and before the aging step. This makes it easier to form a uniform LiF film on the surface of the positive electrode active material, and makes it easier to further suppress a decrease in the capacity retention rate when charging and discharging at a high rate are repeated.

[0022] The degassing step can be a method of reducing the pressure inside the battery assembly. By reducing the pressure inside the battery assembly, it is also possible to easily impregnate the entire electrode assembly with the first electrolytic solution.

[0023] The second step is preferably performed while applying a confining pressure of 0.5 MPa or more to the battery assembly in the stacking direction of the positive electrode plates. The stacking direction of the positive electrode plates is usually the same as the stacking direction of the positive electrode plates and the negative electrode plates. The confining pressure may be 0.5 MPa or more and 5 MPa or less, 1 MPa or more and 4 MPa or less, or 2 MPa or more and 4 MPa or less. The confining pressure can be set to a predetermined value by adjusting the press pressure during confinement. When the second step is performed while applying the confining pressure, it is preferable to constrain the battery assembly before the charging step, but the battery assembly may be constrained after the charging step.

[0024] When the second step includes at least one of an aging step and a defoaming step in addition to a charging step, all steps included in the second step are preferably performed while applying the above-mentioned confining pressure. The confining pressure may be applied to one battery assembly, or to a battery assembly group (battery pack) in which two or more battery assemblies are arranged so as to be electrically connected. The battery assembly group is preferably arranged so that the battery assemblies are adjacent to each other, and the battery assemblies are arranged so that the stacking directions of the positive electrode plates of the battery assemblies are in the same direction. When the present battery is confined under the above-mentioned confining pressure, repeated high-rate charging and discharging easily causes unevenness in the salt concentration of the electrolyte, which tends to reduce the capacity retention rate, and therefore it is preferable to manufacture the battery by the manufacturing method of the present battery.

[0025] (3rd step) The third step is to insert LiFSO 3 This is a step of injecting a second electrolyte solution containing LiPF 6 and LiBF 4 At least one of these and LiFSO 3 As described above, in the third step, after the LiF film is formed on the surface of the positive electrode active material in the second step, the second electrolyte is injected into the exterior body. Therefore, the LiFSO 3 FSO produced by ionization 3 -This prevents the FSO from coming into direct contact with the surface of the positive electrode active material. This prevents the positive electrode active material from coming into direct contact with the FSO even when the battery is repeatedly charged and discharged at a high rate. 3 - This suppresses the reaction with LiFSO, which helps prevent the decrease in capacity retention rate. 3 Since the output resistance can be reduced,

[0026] LiFSO in the second electrolyte 3 The content of LiFSO in the second electrolyte is preferably 0.5% by mass or more and 2% by mass or less, and may be 0.6% by mass or more and 1.8% by mass or less, or may be 0.7% by mass or more and 1.5% by mass or less. 3 The content of LiFSO in the total amount of the second electrolyte is 3 is the amount.

[0027] The second electrolyte is usually a non-aqueous electrolyte, preferably containing LiFSO as a supporting electrolyte in a non-aqueous solvent such as an organic solvent. 3 The non-aqueous solvent contained in the second electrolytic solution is preferably EC and DMC. The non-aqueous solvent contained in the second electrolytic solution may be the same as or different from the non-aqueous solvent contained in the first electrolytic solution. The second electrolytic solution preferably contains EC and DMC. The non-aqueous solvent used in the second electrolytic solution preferably contains two or more of EC, DMC, and EMC in a mixing ratio of EC:DMC:EMC=5-40:0-70:0-70 (volume ratio), may be in a mixing ratio of EC:DMC:EMC=10-40:20-70:0-50 (volume ratio), or may be in a mixing ratio of EC:DMC=30-40:60-70 (volume ratio).

[0028] The second electrolyte is LiFSO 3 It may contain a supporting salt other than LiPF 6 and LiBF 4 and preferably LiPF 6 The second electrolyte may contain, for example, the same supporting salt as that contained in the first electrolyte, and the first electrolyte may contain LiPF 6When the second electrolyte contains LiPF 6 The second electrolyte contains LiPF 6 and LiBF 4 The concentration of LiPF may be, for example, 0.5 mol / L or more and 1.5 mol / L or less, 0.6 mol / L or more and 1.2 mol / L or less, or 0.7 mol / L or more and 1.0 mol / L or less. 6 and LiBF 4 When the second electrolyte contains one of the two, the concentration is that of the other, and the second electrolyte contains LiPF 6 and LiBF 4 If both are included, LiPF 6 and LiBF 4 The above concentration is the total concentration of LiPF per 1 L of non-aqueous solvent. 6 and LiBF 4 is the number of moles.

[0029] The battery assembly after the third step contains a mixed electrolyte solution of the first electrolyte solution and the second electrolyte solution. 6 and LiBF 4 The concentration of LiPF is preferably 0.5 mol / L or more and 1.5 mol / L or less, may be 0.7 mol / L or more and 1.4 mol / L or less, or may be 0.8 mol / L or more and 1.2 mol / L or less. The above total concentration is the ratio of LiPF to 1 L of the nonaqueous solvent in the mixed electrolyte. 6 and LiBF 4 The total concentration is the total number of moles of LiPF 6 and LiBF 4 When one of the two is contained, the concentration of that one is LiPF 6 and LiBF 4 If both are included, LiPF 6 and LiBF 4 is the total concentration of

[0030] (electrode body) As described above, the electrode assembly may include, for example, a positive electrode plate, a negative electrode plate, and a separator. The electrode assembly may be a wound type electrode assembly or a laminated type electrode assembly.

[0031] When the electrode body is a wound electrode body, the length of the positive electrode active material layer and the negative electrode active material layer in the direction parallel to the winding axis may be independently 130 mm or more, preferably 150 mm or more, 150 mm or more to 350 mm or less, 180 mm or more to 350 mm or less, or 200 mm or more to 300 mm or less. When the electrode body is a laminated electrode body, the planar shape of the laminated electrode body is preferably a square or a rectangle. In this case, in the laminated electrode body, the length of the positive electrode active material layer and the negative electrode active material layer in the direction parallel to one side of the square, or the length of the positive electrode active material layer and the negative electrode active material layer in the direction parallel to the long side of the rectangle may be independently 130 mm or more, preferably 150 mm or more, 150 mm or more to 350 mm or less, 180 mm or more to 350 mm or less, or 200 mm or more to 300 mm or less.

[0032] The electrode body may have at least one of the positive electrode active material layer and the negative electrode active material layer within the above-mentioned length range, but it is preferable that the lengths of both the positive electrode active material layer and the negative electrode active material layer are within the above-mentioned range. In a large-sized nonaqueous electrolyte secondary battery in which at least one of the positive electrode active material layer and the negative electrode active material layer has the above-mentioned length, when high-rate charging and discharging is repeated, unevenness in the salt concentration of the electrolyte is likely to occur depending on the position of the electrode body, so it is preferable to manufacture the battery by the manufacturing method of this battery.

[0033] The positive electrode plate can have a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector. The positive electrode current collector is, for example, a metal foil made of an aluminum material such as aluminum or an aluminum alloy. The positive electrode active material layer contains a positive electrode active material. Examples of the positive electrode active material include layered or spinel-based lithium transition metal oxides (e.g., LiNiCoMnO 2 , LiNiO 2 , LiCoO 2 , LiFeO 2 , LiMn 2 O 4 , LiNi 0.5 Mn1.5 O 4 , LiCrMnO 4 , LiFePO 4 , LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 ) are mentioned.

[0034] The positive electrode active material layer may contain one or both of a binder and a conductive assistant in addition to the positive electrode active material. Examples of the binder include styrene butadiene rubber (SBR), polyvinylidene fluoride (PVdF), and polytetrafluoroethylene (PTFE). Examples of the conductive assistant include carbon materials such as fibrous carbon, carbon black (acetylene black, ketjen black, etc.), coke, and activated carbon. Examples of the fibrous carbon include carbon nanotubes (hereinafter also referred to as "CNTs"). The CNTs may be single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes such as double-walled carbon tubes (DWCNTs).

[0035] The negative electrode plate may have a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector. The negative electrode current collector is, for example, a metal foil made of a copper material such as copper or a copper alloy. The negative electrode active material layer includes a negative electrode active material. Examples of the negative electrode active material include a carbon-based active material containing a carbon (C) atom such as graphite; and a metal-based active material containing a metal element such as a metal oxide or a metal element containing an element selected from the group consisting of silicon (Si), tin (Sn), antimony (Sb), bismuth (Bi), titanium (Ti), and germanium (Ge). The negative electrode active material layer may include a Si-based active material containing a silicon element as a metal-based active material.

[0036] Examples of the Si-based active material include silicon alone, SiC (a composite material of silicon and carbon, for example, silicon nanoparticles dispersed in porous carbon particles), SiOx, LixSiyOz, etc. The Si-based active material expands and contracts greatly with charging and discharging, and repeated high-rate charging and discharging easily causes unevenness in the salt concentration of the electrolyte. Therefore, when the negative electrode active material layer contains a Si-based active material, it is preferable to manufacture the battery by the present battery manufacturing method.

[0037] The negative electrode active material layer may contain one or both of a binder and a conductive assistant in addition to the negative electrode active material. Examples of the binder include cellulose-based binders such as carboxymethyl cellulose (CMC), methyl cellulose (MC), and hydroxypropyl cellulose; styrene butadiene rubber (SBR), polyacrylic acid (PAA), acrylonitrile butadiene rubber (NBR), polyvinylidene fluoride (PVdF), and polytetrafluoroethylene (PTFE). Examples of the conductive assistant include those mentioned above.

[0038] The separator may be a porous sheet (film, nonwoven fabric, etc.) made of a resin such as polyethylene, polypropylene, polyester, cellulose, or polyamide. The porous sheet may have a single-layer structure or a multi-layer structure of two or more layers. The separator may have a functional layer on the surface of the porous sheet. The functional layer may be at least one of a heat-resistant layer and an adhesive layer for bonding to a positive electrode plate and a negative electrode plate.

[0039] (Exterior body) The exterior body is a housing that houses the electrode assembly and has an opening for housing the electrode assembly. The opening of the exterior body can be sealed with a sealing plate. The exterior body and the sealing plate are preferably made of metal and can be formed using aluminum, an aluminum alloy, iron, an iron alloy, or the like, and can be formed using, for example, an aluminum laminate film. EXAMPLES

[0040] The present disclosure will be described more specifically below with reference to examples and comparative examples. Example 1 (Preparation of positive electrode plate) LiNiCoMnO as a positive electrode active material 2 , acetylene black (AB) as a conductive additive, polyvinylidene fluoride (PVdF) as a binder, and LiNiCoMnO 2 :AB:pVdF=100:1:1 (mass ratio), which was mixed with N-methylpyrrolidone (NMP) to obtain a positive electrode mixture slurry. The positive electrode mixture slurry was applied to an aluminum foil as a positive electrode current collector, dried, and compressed to a predetermined thickness to form a positive electrode active material layer on the aluminum foil, and then cut out to a predetermined width to obtain a positive electrode plate. The positive electrode plate had, in the width direction, a region where the positive electrode active material layer was formed on the aluminum foil, and a region where the positive electrode active material layer was not formed and the aluminum foil was exposed. The width of the positive electrode active material layer of the positive electrode plate (the length in the direction parallel to the winding axis of the electrode body described later) was 150 mm.

[0041] (Preparation of negative electrode plate) Graphite as the negative electrode active material, styrene butadiene rubber (SBR) as the binder, and carboxymethyl cellulose (CMC) were used in a ratio of graphite:SBR:CMC=100:1:1 (mass ratio), and this was mixed with water to obtain a negative electrode mixture slurry. The negative electrode mixture slurry was applied to a copper foil as a negative electrode current collector, dried, and compressed to a predetermined thickness to form a negative electrode active material layer on the copper foil, and then cut out to a predetermined width to obtain a negative electrode plate. The negative electrode plate had, in the width direction, a region where the negative electrode active material layer was formed on the copper foil and a region where the negative electrode active material layer was not formed and the copper foil was exposed. The width of the negative electrode active material layer of the negative electrode plate (the length in the direction parallel to the winding axis of the electrode body described later) was 154 mm.

[0042] (Preparation of electrode body) A separator having a three-layer structure of polypropylene / polyethylene / polypropylene was prepared. The positive and negative plates obtained above were stacked with the separator interposed therebetween and wound to obtain a wound electrode body. The wound electrode body had a positive current collector exposed at one end in a direction parallel to the winding axis, and a negative current collector exposed at the other end. An aluminum plate for external current collection was welded to the area where the positive current collector of the wound electrode body was exposed, and a copper plate for external current collection was welded to the area where the negative current collector was exposed, and then the wound electrode body was housed in an exterior body formed of an aluminum laminate film.

[0043] (Preparation of the first electrolyte) LiPF as supporting salt 6 A mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) (EC / DMC = 30 / 70 (volume ratio)) was used as the non-aqueous solvent, and LiPF 6 The concentration of LiPF was adjusted to 0.7 mol / L. 6 and the mixed solvent were mixed to prepare a first electrolytic solution.

[0044] (Preparation of the second electrolyte) LiPF as supporting salt 6 and LiFSO 3 A mixed solvent of EC and DMC (EC / DMC = 30 / 70 (volume ratio)) was used as the non-aqueous solvent, and LiPF 6 The concentration of LiFSO is 0.7 mol / L. 3 The concentration of LiPF was 3% by mass. 6 , LiFSO 3 and the mixed solvent were mixed to prepare a second electrolytic solution.

[0045] (Preparation of non-aqueous electrolyte secondary battery) A first electrolyte solution was injected into the exterior housing containing the wound electrode body prepared above to obtain a battery assembly (first step). Next, stainless steel restraining plates were placed on each of the two surfaces of the battery assembly parallel to the winding axis of the wound electrode body (i.e., two surfaces perpendicular to the lamination direction of the positive and negative electrode plates of the wound electrode body), and the battery assembly was sandwiched between the two restraining plates. The four corners of the two restraining plates were fastened to each other using bolts and nuts, and a load was applied using a press machine to adjust the battery assembly so that a restraining pressure of 0.5 MPa was applied. After the battery assembly in a state in which the set restraining pressure was applied was charged to 3.5 V at a current value of C / 10, the pressure was reduced to a gauge pressure of -50 kPa, and the pressure was maintained for one minute, and the reduced pressure state was released. This operation was repeated three times to perform a degassing step to remove gas present in the battery assembly (second step). Next, the exterior body was sealed, and the battery was discharged at a current value of C / 10 to a potential of 3 V. The exterior body was then opened, and the second electrolytic solution was poured in (third step), and the exterior body was sealed again to obtain a nonaqueous electrolyte secondary battery. The first electrolytic solution and the second electrolytic solution were poured in such a ratio by mass that the first electrolytic solution:the second electrolytic solution was 60:40.

[0046] Example 2 A nonaqueous electrolyte secondary battery was obtained in the same manner as in Example 1, except that after the degassing step, the exterior body was sealed and an aging step was carried out by keeping it at 30° C. for 5 hours.

[0047] Example 3 A nonaqueous electrolyte secondary battery was obtained in the same manner as in Example 1, except that after the battery assembly was charged to 3.5 V, an aging step of holding the battery assembly at 40° C. for 5 hours was carried out without carrying out a defoaming step.

[0048] Example 4 A nonaqueous electrolyte secondary battery was obtained in the same manner as in Example 1, except that after the degassing step, the exterior body was sealed and an aging step was carried out by holding it at 40° C. for 5 hours.

[0049] Comparative Example 1 (Preparation of comparative electrolyte) LiPF as supporting salt 6 and LiFSO 3A mixed solvent of EC and DMC (EC / DMC = 30 / 70 (volume ratio)) was used as the non-aqueous solvent, and LiPF 6 The concentration of LiFSO is 0.7 mol / L. 3 The concentration of LiPF was adjusted to 1.2% by mass. 6 , LiFSO 3 and the mixed solvent were mixed to prepare a comparative electrolyte solution.

[0050] (Preparation of non-aqueous electrolyte secondary battery) A comparative electrolyte solution was injected into an exterior housing housing the wound electrode body produced by the procedure described in Example 1 to obtain a battery assembly. The battery assembly was restrained by the procedure described in Example 1. The battery assembly in a state in which the set restraining pressure was applied was charged to 3.5 V at a current value of C / 10, and then a degassing process was performed by the procedure described in Example 1. Subsequently, an aging process was performed in which the battery assembly was held at 40° C. for 5 hours to obtain a nonaqueous electrolyte secondary battery.

[0051] <Evaluation> (Initial activation) In an environment of 25° C., the nonaqueous electrolyte secondary battery obtained above was charged to 4.2 Vcccv (constant current / constant voltage) at a current value of C / 10, and stored for 24 hours at 60° C. After that, the battery was discharged to a potential of 3 V at a current value of C / 10, thereby performing initial activation of the nonaqueous electrolyte secondary battery.

[0052] [Evaluation of output resistance] The initially activated non-aqueous electrolyte secondary battery was charged at a current value of C / 3 in an environment of 25° C. until the SOC (charge rate) reached 50%, and then rested for 30 minutes, after which the voltage V0 of the non-aqueous electrolyte secondary battery was measured. Then, in an environment of 25° C., the battery was discharged for 10 seconds at a current value of 2C, and the voltage V1 of the non-aqueous electrolyte secondary battery at the 10th second was measured. The resistance of the non-aqueous electrolyte secondary battery was calculated according to the following formula. Resistance [Ω] = (V0-V1) / 2C current value

[0053] The resistance value of each Example was converted into a relative value when the resistance value of Comparative Example 1 was set to 100 (standard), and those with this converted value of 100 or less were evaluated as A, and those with a converted value exceeding 100 were evaluated as B. The results are shown in Table 1.

[0054] [Cycle test] In an environment of 25°C, the above initially activated non-aqueous electrolyte secondary battery was charged to 4.2Vcccv (constant current / constant voltage) at a current value of 1C, and discharged to a potential of 3V at a current value of 1C, which constituted one charge / discharge cycle, and this cycle was repeated. The retention rate of the discharge capacity W500 at the 500th cycle relative to the discharge capacity W1 at the 1st cycle was calculated as the capacity retention rate [%] according to the following formula. The results are shown in Table 1. Capacity maintenance rate [%]=(W500 / W1)×100

[0055] [Table 1]

[0056] The nonaqueous electrolyte secondary batteries obtained in Examples 1 to 4 and Comparative Example 1 all contained LiFSO 3 Since the first electrolyte solution contains LiFSO, the output resistance can be reduced. Since the first to third steps are included in Examples 1 to 4, the capacity retention rate in the cycle test was better than that in Comparative Example 1. In Examples 1 to 4, the first electrolyte solution contains LiFSO 3Since it does not contain LiF, it is presumed that the LiF film is formed on the surface of the positive electrode active material by the charging performed in the second step, and the elution of the positive electrode active material in the cycle test is suppressed, and the capacity retention rate was good. From the comparison between Example 1 and Examples 2 and 4, it is considered that the LiF film is easily formed sufficiently on the surface of the positive electrode active material by performing the aging step, and the capacity retention rate in the cycle test is easily improved. From the comparison between Example 2 and Example 4, it is considered that the LiF film is easily formed sufficiently on the surface of the positive electrode active material when the temperature of the aging step is high, and the capacity retention rate in the cycle test is easily improved. From the comparison between Example 3 and Example 4, it is considered that the LiF film is easily formed sufficiently on the surface of the positive electrode active material by performing the defoaming step before the aging step, and the capacity retention rate in the cycle test is easily improved.

Claims

1. A method for producing a nonaqueous electrolyte secondary battery including an electrode assembly, comprising: The electrode assembly includes a positive electrode plate having an active material layer, The electrode assembly is accommodated in an exterior housing, and LiPF ６ and LiBF ４ a first step of injecting a first electrolytic solution containing at least one of the following to obtain a battery assembly; a second step including charging the battery assembly to a voltage of 3.5 V or greater; The battery assembly after the second step is provided with LiFSO ３ and a third step of injecting a second electrolytic solution containing the above.

2. LiFSO in the first electrolyte ３ The method according to claim 1 , wherein the content of is 0.1 mass % or less.

3. The first electrolyte solution is LiFSO ３ The method of claim 1 , which does not include

4. The manufacturing method according to any one of claims 1 to 3, wherein the second step further includes an aging step of holding the battery assembly after the charging step at 40°C or higher for 5 hours or more.

5. The manufacturing method according to claim 4 , wherein the second step includes a step of removing gas present within the battery assembly after the charging step and before the aging step.

6. The manufacturing method according to any one of claims 1 to 3, wherein the second step includes a step of removing gas present within the battery assembly after the charging step.

7. The method according to any one of claims 1 to 3, wherein the second step is performed while applying a confining pressure of 0.5 MPa or more to the battery assembly in a stacking direction of the positive electrode plates.

8. The electrode body is a wound type electrode body or a laminated type electrode body including a positive electrode plate having an active material layer, When the electrode body is a wound type electrode body, the length of the active material layer in a direction parallel to a winding axis is 150 mm or more, When the electrode body is a laminated electrode body, The laminated electrode body has a square or rectangular shape in a plan view, The method according to any one of claims 1 to 3, wherein a length of the active material layer in a direction parallel to one side of the square or a direction parallel to a longer side of the rectangle is 150 mm or more.

9. The first electrolyte solution is LiPF ６ The method according to any one of claims 1 to 3, comprising:

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