JP2019021445A - Suppressing method of separator wrinkle in first charging method of lithium ion secondary battery and manufacturing method of lithium ion secondary battery - Google Patents

Abstract

To provide a suppressing method of a separator wrinkle in a first charging method of a lithium ion secondary battery in which charging at the time of initial charging is made uniform and separator wrinkle is effectively suppressed.SOLUTION: In a suppressing method of a separator wrinkle in an initial first charging method of a lithium ion secondary battery including an exterior body, an electrode group housed in the exterior body and having a positive electrode and a negative electrode alternately stacked with a separator interposed therebetween, and a nonaqueous electrolytic solution accommodated in the exterior body, and the initial charge includes at least two charging steps in a state where the nonaqueous electrolytic solution is injected into the exterior body containing the electrode group and then the exterior body is sealed, and the lithium ion secondary battery is left to stand after the first charging step and gas evacuation is done after the second charging step.SELECTED DRAWING: None

Description

  The present invention relates to a method for suppressing separator flaws in an initial charging method for a lithium ion secondary battery and a method for manufacturing a lithium ion secondary battery including the initial charging method.

  Secondary batteries are used in a wide range of applications as power sources for portable devices, electric vehicles, houses, or business facilities. Among secondary batteries, a lithium ion secondary battery has a high discharge voltage suitable for these applications, and has become the mainstream of current secondary batteries.

  One of the manufacturing processes of a lithium ion secondary battery is initial charging. In the first charge, gas is generated in the secondary battery by electrolyzing a small amount of water contained in the members constituting the secondary battery and by partially decomposing the organic solvent constituting the non-aqueous electrolyte. To do. The generated gas is a by-product when forming SEI (Solid Electrolyte Interface) that stabilizes the negative electrode surface. If charging and discharging are repeated while the generated gas stays in the secondary battery, the performance, safety and reliability of the secondary battery are lowered.

  Patent Documents 1 to 4 describe a method for solving a decrease in performance, safety and reliability of a secondary battery associated with the generated gas.

JP 2000-90974 A JP 2003-331916 A JP 2010-9983 A Japanese Patent Application Laid-Open No. 2006-126953

  However, in the methods described in Patent Documents 1 to 4, it is difficult to appropriately remove the gas staying between the electrode plates. In addition, the methods described in Patent Documents 1 to 4 generate gas depending on the battery system different from the conventional battery voltage, the composition of the electrolytic solution to be used, and the type of additive, with the recent development of various battery materials. May not be applicable due to changes in timing.

  Furthermore, the methods described in Patent Documents 1 to 4 cannot effectively suppress the generation of soot in the insulating separator interposed between the positive electrode and the negative electrode with gas generation.

  That is, a secondary battery in which charging is not uniform at the time of initial charging often has a phenomenon in which wrinkles are generated in the separator interposed between the positive electrode and the negative electrode. A portion where charging is not uniform becomes a bank like a crater-like depression as compared with a portion where charging is uniform as charging progresses. Since the gas tends to stay in the depression, wrinkles are generated in the separator due to the internal pressure stress of the staying gas. If wrinkles occur in the separator along the non-uniformly charged portion, the battery reaction during charging / discharging may be significantly inhibited. For example, there is a problem that lithium is deposited along the edge of the separator due to repeated charge and discharge, and the safety and reliability of the secondary battery are lowered.

  The present invention relates to a method for suppressing separator wrinkles in an initial charging method of a lithium ion secondary battery that effectively suppresses generation of wrinkles of the separator by uniformizing charging at the time of initial charging, and a lithium ion secondary battery including the initial charging method It aims at providing the manufacturing method of.

In order to solve the above-described problem, according to an embodiment of the present invention, an exterior body, an electrode group that is housed in the exterior body, in which a positive electrode and a negative electrode are alternately stacked with a separator interposed therebetween, and the exterior body are housed. A separator soot suppression method in the initial charging method of a lithium ion secondary battery provided with a non-aqueous electrolyte,
The initial charging includes at least two charging steps in a state where the outer body is sealed and sealed after injecting the non-aqueous electrolyte into the outer body housing the electrode group,
There is provided a method for suppressing separator flaws in an initial charging method of a lithium ion secondary battery, characterized in that the apparatus is left after the first charging step and gas is exhausted after the second charging step.

  According to the present invention, by effectively suppressing the occurrence of wrinkles in the separator, lithium deposition associated with repeated charging and discharging is suppressed, and the safety and reliability of the lithium ion secondary battery in the end of life state are ensured. Of a lithium ion secondary battery capable of ensuring safety and reliability in a simple process, including a separator flaw suppression method in the initial charging method of a lithium ion secondary battery that can be performed, and the initial charging method A manufacturing method can be provided.

It is a figure which shows the charge curve after the charge start of the 1st time in initial charge. It is a perspective view which shows the lithium ion secondary battery which concerns on embodiment. It is sectional drawing which follows the III-III line of FIG.

  Hereinafter, the separator flaw suppression method in the initial charge method of the lithium ion secondary battery according to the embodiment will be described in detail.

First, an exterior body and an electrode group are prepared, and the electrode group is accommodated in the exterior body. The electrode group has a structure in which a plurality of positive electrodes and negative electrodes are alternately stacked with a separator interposed therebetween. A non-aqueous electrolyte is injected into the exterior body containing the electrode group, and the exterior body is sealed and sealed, and then the first charge of the lithium ion secondary battery is started. In addition, it is preferable to pressurize a secondary battery with the pressure of 0.1-100 kgf / cm < ² > immediately after the assembly of a secondary battery and before first charge. By performing such pretreatment, it is possible to more effectively prevent the occurrence of wrinkles in the separator. Moreover, it becomes possible to let a nonaqueous electrolyte solution adapt to the structural member of an electrode group by leaving still after a pressurization process and before first charge.

  The first charging is performed by connecting the secondary battery and the charging device. After completing the first charge, the secondary battery and the charging device are shut off and allowed to stand. Thereafter, the second charging is performed, and the gas generated in the exterior body is exhausted before the secondary battery reaches a fully charged state.

  Here, the full charge refers to a state of charge (SOC) in which the amount of charge corresponding to the rated capacity of the secondary battery is 100% charged.

In the secondary battery to which the first charging is applied, the positive electrode and the negative electrode of the electrode group in the outer package are never used and are not optimized, that is, the non-aqueous electrolyte is sufficiently impregnated in the electrode group. There is no state. When such a secondary battery is charged for the first time, lithium may be electrodeposited on the negative electrode surface due to overvoltage, and an SEI film must be formed on the negative electrode surface. There is. The SEI film suppresses excessive reaction between the carbon material on the negative electrode surface and the non-aqueous electrolyte, and stabilizes the reaction on the negative electrode surface. Although the generation of the SEI film is a known fact, it has a negative electrode potential of 1.2 to 0.8 V (vs. Li / Li ⁺ ) at the first charge. However, at the time of the initial charge, the potential holding time is short, and it becomes difficult to sufficiently form the SEI film on the negative electrode surface.

  For this reason, the first charging step is the charging curve after the start of the first charging, where the horizontal axis is the battery voltage V, and the vertical axis is the amount of change in charge [Ah] / the amount of change in battery voltage [V]. It is preferable that the process is performed under the condition that at least one inflection point appears in the first charging step, which is (dQ / dV). FIG. 1 shows a charge curve after the first charge start in the first charge. The inflection point shown in FIG. 1 is a peak between a certain capacity range, and is presumed to be a peak of the formation reaction of the SEI film. The amount of charged electricity at which the peak falls depends on the current value at the time of charging, but appears within a range of about 1 to 5% of the rated capacity of the secondary battery. For this reason, it is preferable to perform the amount of charge electricity of the 1st charge process in the range of 1-5% of the rated capacity of a secondary battery. In the charging curve after the start of charging in the first charging step, a condition where an inflection point appears, that is, the amount of charged electricity is in the range of 1 to 5% of the rated capacity of the secondary battery, and a low current value (≦ 0.1 ItA ), A dense SEI film can be formed on the negative electrode surface.

  By allowing it to stand after the first charging step, the impregnation of the nonaqueous electrolyte into the pores of the electrodes (positive electrode and negative electrode) can be further promoted. As a result, the reduction of the nonaqueous electrolytic solution on the electrode surface can be suppressed, and a nonuniform electrode reaction can also be suppressed. The standing time is preferably about 8 to 24 hours.

  Since the second charging step is performed after passing through the first charging step and the stationary step, the second charging step can be executed with a larger current value than the first charging step. The role of the second charging step is to sufficiently generate gas in the exterior body. For this reason, it is preferable that the amount of charged electricity in the second charging step is higher than that in the first charging step. Specifically, the amount of electricity charged in the second charging process is preferably 38 to 78% of the rated capacity of the secondary battery, although it depends on the degree of gas generation.

  After the gas generation in the exterior body by the second charging process ends, the process proceeds to the gas exhausting process. In the exhaust process, the sealing of the secondary battery is temporarily released by a known method, and the gas in the exterior body is exhausted. The gas exhaust step is preferably performed in a dry environment. Further, in the exhaust process, the exhaust time can be shortened by applying pressure to the exterior body from the outside, or by reducing the pressure by putting the secondary battery in the chamber, thereby facilitating exhaust of the gas.

  In the third charging step, charging is performed up to the upper limit voltage determined by the manufacturer under the same conditions as the current value in the second charging step, that is, full charging including the first charging step and the second charging step is performed. However, the third and subsequent charging steps are not necessarily required and may be omitted.

  Next, each member of the lithium ion secondary battery described above will be described in detail.

<Exterior body>
The exterior body has a bag shape using a laminated film in which a heat-fusible resin film (inner layer), a metal foil, and at least one protective resin film (outer layer) are laminated in this order. The inner layer can be formed from a polyolefin-based resin. The metal layer can be formed from aluminum foil or stainless steel foil. The outer layer can be formed from nylon alone, polyethylene terephthalate (PET) alone, or a laminated film of nylon and PET.

<Positive electrode>
The positive electrode includes a current collector and a positive electrode layer formed on at least one surface of the current collector and including a positive electrode active material, a conductive material, and a binder.

  As the current collector, for example, a metal foil such as an aluminum foil, a copper foil or a stainless steel foil, a porous metal such as porous aluminum, or the like can be used.

The positive electrode active material is not particularly limited as long as it can be used for a lithium ion secondary battery. For example, LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiFePO ₄ , LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , LiCo _0.15 Ni _0.8 Al _0.05 O ₂ , LiNi _0.5 Mn _1.5 O ₄ can be used.

  The conductive material is not particularly limited, and a known or commercially available material can be used. Examples thereof include carbon black such as acetylene black and ketjen black, carbon nanotube, carbon fiber, activated carbon, graphite and the like.

  A binder is not specifically limited, A well-known or commercially available thing can be used. For example, polyvinylidene fluoride, polytetrafluoroethylene (PTFE), polyvinylpyrrolidone (PVP), polyvinyl chloride (PVC), polyethylene (PE), polypropylene (PP), ethylene-propylene copolymer, styrene butadiene rubber (SBR) And acrylic resin.

  The positive electrode layer is allowed to further contain a thickener or dispersant. Examples of thickeners include sodium cellulose sulfate, methyl cellulose ether, methyl ethyl cellulose ether, ethyl cellulose ether, carboxymethyl cellulose ether. Examples of the dispersant include a cationic surfactant and a nonionic surfactant.

  The positive electrode can be produced, for example, by applying a slurry containing a positive electrode active material, a conductive material, a binder and a solvent to at least one surface of a current collector to form a coating film, and then drying and pressurizing. .

  The solvent is not particularly limited, and known or commercially available solvents can be used. The solvent is preferably N-methyl-2-pyrrolidone when polyvinylidene fluoride is used as the binder. The solvent is preferably water when styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinyl alcohol, carboxymethyl cellulose or the like is used as the binder.

<Negative electrode>
The negative electrode includes a current collector and a negative electrode layer formed on at least one surface of the current collector and including a negative electrode active material, a conductive material, and a binder.

  The current collector is not particularly limited, and a metal foil such as an aluminum foil, a copper foil or a stainless steel foil, porous aluminum or the like can be used.

The negative electrode active material is not particularly limited. For example, natural graphite or artificial graphite, mesocarbon microbeads (MCMB), carbon materials such as hard carbon or soft carbon, and lithium such as Al, Si, and Sn are occluded and released. Metal materials that can be used or alloy materials thereof, oxide materials such as SiO, SiO ₂ , and lithium titanate (Li ₄ Ti ₅ 0 ₁₂ ) can be used.

  The binder is not particularly limited. For example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride, fluorine rubber, styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), core shell binder, polyvinyl alcohol, polyimide Polyamideimide or the like can be used.

  As the conductive material, the same materials as those used for the positive electrode described above, for example, carbon black such as acetylene black and ketjen black, activated carbon or graphite can be used. Note that the conductive agent may not be included in the negative electrode layer.

<Separator>
As the separator, a nonwoven fabric or a porous sheet made of a synthetic resin such as polyolefin such as polyethylene (PE) or polypropylene (PP) or polytetrafluoroethylene (PTFE) can be used.

<Non-aqueous electrolyte>
The nonaqueous electrolytic solution contains an electrolyte salt containing lithium ions and an organic solvent.

The electrolyte salt is not particularly limited, and a known lithium salt can be applied. For example, lithium such as LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiCF ₃ CFO, LiSO ₃ CF ₃ , LiCF ₂ CF ₂ SO ₃ , LiClO ₄ , LiN (COCF ₂ CF ₃ ) ₂ , LiN (SO ₂ CF ₃ ) ₂ Mention may be made of salts. These lithium salts can be used alone or in a mixture of two or more.

  The solvent is preferably a mixed solvent of a main solvent and a sub solvent. As the main solvent, for example, ethylene carbonate, γ-butyrolactone, diethyl carbonate, or dimethyl carbonate can be used. As the auxiliary solvent, propylene carbonate, sulfolane, dimethoxyethane, diethoxyethane, 2-methyl-tetrahydrofuran, various glymes and the like can be used.

  The concentration of the electrolyte salt dissolved in the solvent is not particularly limited, and is preferably, for example, 0.3 mol / L to 3.0 mol / L.

  The nonaqueous electrolyte solution further includes an organic substance having an unsaturated bond in the molecule and capable of reductive polymerization at the time of charging. By adding such an organic substance to the non-aqueous electrolyte, an effective solid electrolyte interface coating can be formed on the surface of the negative electrode active material, and decomposition of the non-aqueous electrolyte can be suppressed. Organic substances having an unsaturated bond in the molecule and capable of reductive polymerization at the time of charging are, for example, fluoroethylene carbonate, vinylene carbonate (VC), carbonates such as vinyl ethylene carbonate and derivatives thereof, unsaturated carboxylic acid esters, Phosphate esters, borate esters, alcohols, and the like can be used. Among these, it is preferable to use vinylene carbonate (VC). In order to obtain a stable solid electrolyte interface coating, such an organic substance is desirably added in an amount of 0.1 wt% to 10 wt%, more preferably 1 wt% to 5 wt% with respect to the nonaqueous electrolyte. By making the addition amount of the organic substance in the range of 0.1 wt% to 10 wt%, it can be reduced at the time of charging to form a stable film on the surface of the negative electrode active material layer, and the electrolyte material can be decomposed. Can be prevented. When the amount of the organic substance added is less than 0.1% by weight, it is difficult to sufficiently form a stable film on the surface of the negative electrode active material. On the other hand, when the amount of the organic substance added exceeds 10% by weight, the amount to be reduced increases, so that the formed solid electrolyte interface film becomes thick and the battery impedance may increase.

  The manufacturing method of the lithium ion secondary battery which concerns on embodiment contains the initial charging method of the lithium ion secondary battery mentioned above.

  The shape of the lithium secondary battery manufactured by the method according to the embodiment is not particularly limited, and examples thereof include a coin type, a button type, a sheet type, a stacked type, a cylindrical type, a rectangular shape, and a flat type.

  Hereinafter, the structure of the lithium secondary battery according to the embodiment will be described with reference to the drawings, taking a laminated lithium secondary battery as an example. FIG. 2 is a perspective view showing an example of a stacked lithium secondary battery, and FIG. 3 is a cross-sectional view taken along line III-III in FIG.

  The laminated lithium secondary battery 1 includes a bag-shaped exterior body 2 made of a laminate film. A flat electrode group 3 is accommodated in the exterior body 2. The laminate film has a structure in which, for example, a plurality of (for example, two) plastic films are laminated with a metal foil such as an aluminum foil sandwiched between the films. Of the two plastic films, one of the plastic films is a heat-fusible resin film. The outer package 2 is formed by stacking two laminated films so that the heat-fusible resin films face each other, interposing the electrode group 3 between the laminated films, and sandwiching the two laminated film portions around the electrode group 3 The electrode group 3 is housed in an airtight manner by heat-sealing each other and sealing.

  As shown in FIG. 3, the electrode group 3 has a structure in which a plurality of positive electrodes 4, negative electrodes 5, and separators 6 interposed between the positive electrodes 4 and 5 are stacked so that the negative electrode 5 is located in the outermost layer. The positive electrode 4 includes a positive electrode current collector 41 and positive electrode layers 42 and 42 formed on both surfaces of the current collector 41. The negative electrode 5 located in the outermost layer includes a negative electrode current collector 51 and a negative electrode layer 52 formed on the surface of the current collector 51 facing the separator 6. The negative electrode 5 located between the positive electrodes 4 excluding the negative electrode 5 located in the outermost layer is composed of a negative electrode current collector 51 and negative electrode layers 52 and 52 made of metallic lithium formed on both surfaces of the current collector 51. Has been.

  The positive electrode 4 includes a positive electrode lead 43 in which a positive electrode current collector 41 extends from, for example, the right side surface of the positive electrode layer 42. Each positive electrode lead 43 is bundled on the tip side in the exterior body 2 and joined to each other. One end of the positive electrode terminal 7 is joined to the joint portion of the positive electrode lead 43, and the other end extends to the outside through the sealing portion of the exterior body 2. The negative electrode 5 has a negative electrode lead 53 in which a negative electrode current collector 51 extends from, for example, the left side surface of the negative electrode layer 52. Each negative electrode lead 53 is bundled on the tip side in the exterior body 2 and joined to each other. One end of the negative electrode terminal 8 is joined to the joint portion of the negative electrode lead 53, and the other end extends to the outside through the sealing portion of the exterior body 2.

  Examples will be described in detail below.

Example 1
<Positive electrode>
90 parts by mass of lithium iron phosphate (LiFePO ₄ ), 5 parts by mass of polyvinylidene fluoride, and 5 parts by mass of carbon black as a conductive material were dissolved and dispersed in N-methylpyrrolidone (NMP) to prepare a positive electrode slurry. . This positive electrode slurry was applied to both sides of an aluminum foil having a thickness of 20 μm, dried, and then pressurized to obtain a positive electrode.

<Negative electrode>
A negative electrode slurry was prepared by dispersing in 98 parts by weight of graphite, 1 part by weight of carboxymethyl cellulose (CMC), 1 part by weight of styrene butadiene rubber (SBR) and ion-exchanged water as a solvent. This negative electrode slurry was applied to both sides of a copper foil having a thickness of 10 μm, dried, and then pressurized to obtain a negative electrode.

<Separator>
A separator was prepared by opening a large number of fine holes in a three-layer film having a thickness of 25 μm in which a polyethylene film obtained by a dry uniaxial stretching method was sandwiched between two polypropylene films. The type is used.

<Non-aqueous electrolyte>
In the non-aqueous electrolyte, 1.3 mol / L of LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) (volume ratio 2: 5: 3). In addition, 3% by weight of vinylene carbonate (VC) was added as an additive.

<Al laminate>
An Al laminate was produced by laminating an inner layer made of a polyolefin resin having a thickness of 80 μm, a heat-fusible inner layer, an intermediate layer made of an aluminum foil having a thickness of 40 μm, and an outer layer made of polyethylene terephthalate in this order. This Al laminate had a total thickness of 153 μm.

<Assembly of lithium ion secondary battery>
A positive electrode and a separator cut to a predetermined size were covered with two separators with respect to one positive electrode. The separator was thermally welded to the positive electrode so as not to peel off. Seven combinations of the positive electrode and the separator and eight negative electrodes were alternately stacked to obtain a stacked electrode group. This laminated electrode group had a battery capacity of about 3 Ah.

  Terminal tabs were connected to the positive electrode unformed part of the positive electrode and the negative electrode non-formed part of the negative electrode of the laminated electrode group, respectively, by ultrasonic welding. The laminated electrode group with tabs is sandwiched between two Al laminate films so that the terminal tabs protrude to the outside so that the inner layers having heat-fusibility are opposed to each other, and positioned on the three sides of the Al laminate film. The inner layer having the heat-fusibility is thermally welded to obtain an outer package. After injecting a non-aqueous electrolyte from one side of the outer package that was left unsealed, it was vacuum sealed to obtain a sealed lithium ion secondary battery. The amount of the non-aqueous electrolyte was adjusted at about 7 to 8 g / Ah. The degree of vacuum (degree of vacuum) in the sealing process was 1 hPa.

The lithium ion secondary battery immediately after the sealing step was pressurized at a pressure of 1 kgf / cm ² and then allowed to stand for 3 hours while maintaining the pressurized state.

  Next, the sealed lithium ion secondary battery was charged for the first time. The conditions for the first charge are as follows.

  1) The first charging step was performed at 0.01 ItA for 2 hours while maintaining the pressurized state.

  2) After the 1st charge process, it left still for 16 hours, maintaining a pressurization state.

  3) The second charging step was carried out at 0.057 ItA for 8.4 hours while maintaining the pressurized state. The amount of electricity charged until the second charging step was 50% of the rated capacity.

  4) The gas exhaust process was performed by releasing the pressure applied to the secondary battery and further temporarily releasing the sealing.

  5) In the third charging step, the lithium ion secondary battery was again sealed and charged to 4.25 V at 0.057 ItA while being pressurized at the same pressure as described above.

  6) Pressurization to the secondary battery was released, and sealing was temporarily released to perform a gas exhaust process.

  After the completion of all the steps, it was disassembled in a fully charged state within 16 hours, and visual inspection and photography were recorded. By these operations, the charged state of the electrode group and the state of the separator were investigated. The results are shown in Table 1 below.

(Example 2)
A sealed lithium ion secondary battery that had undergone the same steps as in Example 1 was charged for the first time under the following conditions.

  1) The first charging step was performed at 0.01 ItA for 2 hours while maintaining the pressurized state.

  2) After the 1st charge process, it left still for 16 hours, maintaining a pressurization state.

  3) The second charging step was carried out at 0.057 ItA for 8.4 hours while maintaining the pressurized state. The amount of electricity charged until the second charging step was 50% of the rated capacity.

  4) The gas exhaust process was performed by releasing the pressure applied to the secondary battery and further temporarily releasing the sealing.

  5) In the third charging step, the lithium ion secondary battery was again sealed and charged to 4.25 V at 0.057 ItA while being pressurized at the same pressure as described above.

  The results of investigating the charged state of the electrode group and the state of the separator by the same method as in Example 1 are shown in Table 1 below.

(Example 3)
A sealed lithium ion secondary battery that had undergone the same steps as in Example 1 was charged for the first time under the following conditions.

  1) The first charging step was performed at 0.01 ItA for 2 hours while maintaining the pressurized state.

  2) After the 1st charge process, it left still for 16 hours, maintaining a pressurization state.

  3) The second charging step was performed for 6.7 hours at 0.057 ItA while maintaining the pressurized state. The amount of electricity charged until the second charging step was 40% of the rated capacity.

  4) The gas exhaust process was performed by releasing the pressure applied to the secondary battery and further temporarily releasing the sealing.

  5) In the third charging step, the lithium ion secondary battery was again sealed and charged to 4.25 V at 0.057 ItA while being pressurized at the same pressure as described above.

  The results of investigating the charged state of the electrode group and the state of the separator by the same method as in Example 1 are shown in Table 1 below.

Example 4
A sealed lithium ion secondary battery that had undergone the same steps as in Example 1 was charged for the first time under the following conditions.

  1) The first charging step was performed at 0.01 ItA for 2 hours while maintaining the pressurized state.

  2) After the 1st charge process, it left still for 16 hours, maintaining a pressurization state.

  3) The second charging step was performed at 0.057 ItA for 10.2 hours while maintaining the pressurized state. The amount of electricity charged until the second charging step was 60% of the rated capacity.

  4) The gas exhaust process was performed by releasing the pressure applied to the secondary battery and further temporarily releasing the sealing.

  5) In the third charging step, the lithium ion secondary battery was again sealed and charged to 4.25 V at 0.057 ItA while being pressurized at the same pressure as described above.

  The results of investigating the charged state of the electrode group and the state of the separator by the same method as in Example 1 are shown in Table 1 below.

(Example 5)
A sealed lithium ion secondary battery that had undergone the same steps as in Example 1 was charged for the first time under the following conditions.

  1) The first charging step was performed at 0.01 ItA for 2 hours while maintaining the pressurized state.

  2) After the 1st charge process, it left still for 16 hours, maintaining a pressurization state.

  3) The second charging step was performed at 0.057 ItA for 13.7 hours while maintaining the pressurized state. The amount of electricity charged until the second charging step was 80% of the rated capacity.

  4) The gas exhaust process was performed by releasing the pressure applied to the secondary battery and further temporarily releasing the sealing.

  5) In the third charging step, the lithium ion secondary battery was again sealed and charged to 4.25 V at 0.057 ItA while being pressurized at the same pressure as described above.

  The results of investigating the charged state of the electrode group and the state of the separator by the same method as in Example 1 are shown in Table 1 below.

(Comparative Example 1)
A sealed lithium ion secondary battery that had undergone the same steps as in Example 1 was charged for the first time under the following conditions.

  1) The first charging step was performed at 0.01 ItA for 2 hours while maintaining the pressurized state.

  2) After the 1st charge process, it left still for 16 hours, maintaining a pressurization state.

  3) The second charging step was carried out at 0.057 ItA for 8.4 hours while maintaining the pressurized state. The amount of electricity charged until the second charging step was 50% of the rated capacity.

  4) The third charging step was performed without exhausting the gas. In the third charging step, the battery was charged to 4.25 V at 0.057 ItA while maintaining the pressurized state.

  5) Pressurization to the secondary battery was released, and further, the sealing was temporarily released to perform the gas exhaust process.

  The results of investigating the charged state of the electrode group and the state of the separator by the same method as in Example 1 are shown in Table 1 below.

(Comparative Example 2)
A sealed lithium ion secondary battery that had undergone the same steps as in Example 1 was charged for the first time under the following conditions.

  1) The first charging step was performed at 0.01 ItA for 2 hours while maintaining the pressurized state.

  2) It charged to 4.25V with 0.057 ItA, maintaining a pressurization state without performing stationary and gas exhaustion.

  3) The pressure on the secondary battery was released, and the sealing was temporarily released to perform the gas exhaust process.

  The results of investigating the charged state of the electrode group and the state of the separator by the same method as in Example 1 are shown in Table 1 below.

(Comparative Example 3)
A sealed lithium ion secondary battery that had undergone the same steps as in Example 1 was charged for the first time under the following conditions.

  1) The first charging step was performed at 0.01 ItA for 2 hours while maintaining the pressurized state.

  2) The 2nd charge process was performed without leaving still. The second charging step was performed at 0.057 ItA for 8.4 hours while maintaining the pressurized state. The amount of electricity charged until the second charging step was 50% of the rated capacity.

  3) The pressure on the secondary battery was released, and the sealing was temporarily released to perform the gas exhaust process.

  4) In the third charging step, the lithium ion secondary battery was again sealed and charged to 4.25 V at 0.057 ItA while being pressurized at the same pressure as in Example 1.

  The results of investigating the charged state of the electrode group and the state of the separator by the same method as in Example 1 are shown in Table 1 below.

(Comparative Example 4)
1) The first charging step was performed at 0.01 ItA for 2 hours while maintaining the pressurized state.

  2) The 2nd charge process was performed without leaving still. The second charging step was performed at 0.057 ItA for 8.4 hours while maintaining the pressurized state. The amount of electricity charged until the second charging step was 50% of the rated capacity.

  3) The pressure on the secondary battery was released, and the sealing was temporarily released to perform the gas exhaust process.

  4) In the third charging step, the lithium ion secondary battery was again sealed and charged to 4.25 V at 0.057 ItA while being pressurized at the same pressure as in Example 1.

  5) Pressurization to the secondary battery was released, and further, the sealing was temporarily released to perform the gas exhaust process.

The results of investigating the charged state of the electrode group and the state of the separator by the same method as in Example 1 are shown in Table 1 below.

  As is apparent from Table 1, after the nonaqueous electrolyte is injected into the exterior body containing the electrode group, the exterior body is sealed and sealed, and includes at least two charging steps. It can be seen that the initial charging in Examples 1 to 5 where the process is left after the process and the gas is exhausted after the second charging process has a uniform charged state of the electrode group and can prevent generation of wrinkles on the separator.

  On the other hand, in the first discharges of Comparative Examples 1 to 4 that deviate from the methods of Examples 1 to 5, it can be seen that the charged state of the electrode group becomes uneven and wrinkles are generated in the separator.

    DESCRIPTION OF SYMBOLS 1 ... Lithium secondary battery, 2 ... Exterior body, 3 ... Laminated electrode group, 4 ... Positive electrode, 5 ... Negative electrode, 6 ... Separator, 41 ... Positive electrode collector, 42 ... Positive electrode layer, 51 ... Negative electrode collector, 52 ... negative electrode layer.

Claims (4)

Initial charging of a lithium ion secondary battery comprising: an exterior body; an electrode group that is housed in the exterior body, and alternately stacks positive and negative electrodes with a separator interposed therebetween; and a non-aqueous electrolyte contained in the exterior body A separator wrinkle suppression method in the method,
The initial charging includes at least two charging steps in a state where the outer body is sealed and sealed after injecting the non-aqueous electrolyte into the outer body housing the electrode group,
A separator soot suppression method in an initial charging method of a lithium ion secondary battery, wherein the method is left after the first charging step and gas is exhausted after the second charging step.   In the first charging, the amount of charged electricity in the second charging step is made larger than the amount of charged electricity in the first charging step, and the amount of charged electricity in the first charging step and the second charging step. The method for suppressing separator wrinkles in the initial charging method for a lithium ion secondary battery according to claim 1, wherein the total amount of the lithium ion secondary battery is in a capacity range of 40 to 80% of the rated capacity.   The first charging step of the first charging is a charging curve after the start of the first charging, where the horizontal axis is the battery voltage V, and the vertical axis is the storage amount change amount / battery voltage change amount (dQ / dV). And under the condition that at least one inflection point appears, and after charging in the range of the amount of charge under the magnitude relationship of the amount of charge in the first and second charging steps, Gas separator exhaust is performed, The separator flaw suppression method in the initial charge method of the lithium ion secondary battery of Claim 2 characterized by the above-mentioned.   The manufacturing method of the lithium ion secondary battery containing the initial charging method of the lithium ion secondary battery of any one of Claims 1-3.

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