JP2015130310A - Renewal method of lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a renewal method capable of prolonging a charging/discharging cycle lifetime of a lithium ion secondary battery and suppressing expansion.SOLUTION: Regarding the lithium ion secondary battery in which a battery case includes a nonaqueous electrolyte injection port and the nonaqueous electrolyte injection port is sealed by a sealing member formed from an elastic body, the renewal method of the lithium ion secondary battery includes, on the stage where discharge capacity becomes smaller than initial discharge capacity by repeating charge and discharge from assembly of the battery, piercing the sealing member with a tube, supplying a nonaqueous electrolyte into the battery case via the tube, and pulling the tube out of the sealing member thereafter. A nonaqueous electrolyte (1) to be used for assembling the battery contains a chemical compound of which the reduction potential in an anode is 1.3 V or lower relatively to a metal Li potential, and for a nonaqueous electrolyte (2) to be supplied into the battery case, the content of the chemical compound is less than the content in the nonaqueous electrolyte (1) or the chemical compound is not contained.

Description

  The present invention relates to a regeneration method capable of extending the charge / discharge cycle life of a lithium ion secondary battery.

  Lithium ion secondary batteries can be used again by charging even if the capacity decreases due to use, and thus are used in many applications including power supply for portable electronic devices.

  However, in the lithium ion secondary battery, the capacity after charging becomes smaller than the initial (immediately after assembly) as the number of times of charging and discharging proceeds. Therefore, in lithium ion secondary batteries, many studies have been made to improve charge / discharge cycle characteristics so that a decrease in capacity can be suppressed as much as possible even after repeated charge / discharge.

  Various causes can be considered for the capacity reduction of the lithium ion secondary battery due to repeated charge / discharge, and one of them is that the non-aqueous electrolyte of the lithium ion secondary battery is reduced by repeated charge / discharge. Can be mentioned. This occurs because the non-aqueous electrolyte is decomposed due to the reaction between the negative electrode and the positive electrode and the non-aqueous electrolyte accompanying charging and discharging of the lithium ion secondary battery.

  Therefore, many techniques for suppressing the decomposition reaction of the nonaqueous electrolytic solution in the lithium ion secondary battery have been proposed.

  On the other hand, it is also conceivable to regenerate the lithium ion secondary battery by reinjecting the non-aqueous electrolyte into the lithium ion secondary battery after repeated charging and discharging. In Patent Document 1, the exterior body has a liquid injection part having a structure in which an injection needle for injecting a non-aqueous electrolyte can be inserted, so that the non-aqueous electrolyte can be re-injected even after long-term use. A lithium ion secondary battery has been proposed.

JP 2008-41548 A

  By the way, the present inventors have clarified that the problem of swelling increases when the nonaqueous electrolyte is reinjected into a lithium ion secondary battery that has been used.

  This invention is made | formed in view of the said situation, The objective is to provide the reproduction | regenerating method which can prolong the charging / discharging cycle life of a lithium ion secondary battery, and can suppress a swelling.

  The method for regenerating a lithium ion secondary battery of the present invention that has achieved the above object is a battery case formed of a bottomed cylindrical outer can and a lid plate that seals the opening of the outer can. A method for regenerating a lithium ion secondary battery containing a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte, wherein the lithium ion secondary battery has a nonaqueous electrolyte inlet in the battery case. And the non-aqueous electrolyte injection port is sealed by a sealing member made of an elastic body, and charge and discharge are repeated from the assembly of the lithium ion secondary battery, so that the discharge capacity is more than the initial discharge capacity. A step of piercing the sealing member with a tube, replenishing the battery case with a non-aqueous electrolyte through the tube, and subsequently removing the tube from the sealing member, Lithium ion secondary battery The non-aqueous electrolyte (1) used during assembly and the non-aqueous electrolyte (2) to be replenished in the battery case contain a compound whose reduction potential at the negative electrode is 1.3 V or less with respect to the metal Li potential. And the content of the compound in which the reduction potential at the negative electrode is 1.3 V or less with respect to the metal Li potential is higher than the content in the non-aqueous electrolyte (1). Or the non-aqueous electrolyte (1) used at the time of assembling the lithium ion secondary battery contains a compound whose reduction potential at the negative electrode is 1.3 V or less with respect to the metal Li potential, And the nonaqueous electrolyte (2) replenished in the said battery case is characterized by not containing the said compound whose reduction potential in a negative electrode is 1.3 V or less with respect to metal Li potential.

  ADVANTAGE OF THE INVENTION According to this invention, the regeneration method which can prolong the charging / discharging cycle life of a lithium ion secondary battery, and can suppress a swelling can be provided.

It is a fragmentary longitudinal cross-sectional view which represents typically an example of the lithium ion secondary battery used with the reproduction | regenerating method of this invention. It is a perspective view of the lithium ion secondary battery shown in FIG.

  The method for regenerating a lithium ion secondary battery according to the present invention reduced the amount of the lithium ion secondary battery whose charge capacity had decreased from the initial discharge capacity due to repeated charge and discharge by decomposition associated with the charge and discharge. By replenishing the non-aqueous electrolyte, characteristics such as the capacity of the lithium ion secondary battery are further restored to a level where they can be used continuously.

  In the regeneration method of the present invention, when the discharge capacity is smaller than the initial discharge capacity after repeated charging and discharging from the assembly of the lithium ion secondary battery, a tube is pierced into the sealing member, and the battery case is passed through the tube. And a step of replenishing the non-aqueous electrolyte, and then removing the tube from the sealing member.

  As used herein, “initial discharge capacity of a lithium ion secondary battery” refers to initial charge / discharge after completion of a lithium ion secondary battery (charging and discharging during a battery manufacturing process called so-called chemical conversion treatment or pre-charging). Rather, it means the discharge capacity required by charging and discharging to use the battery. In the regeneration method of the present invention, the discharge capacity after repeating the charge / discharge of the lithium ion secondary battery is smaller than the initial discharge capacity. The charging / discharging conditions are not particularly limited, but can be determined, for example, based on the charging / discharging conditions employed in the examples described later.

  In the recycling method of the present invention, a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte are contained in a battery case formed by a bottomed cylindrical outer can and a lid plate that seals the opening of the outer can. Use a lithium ion secondary battery. The lithium ion secondary battery has a non-aqueous electrolyte inlet in the battery case, and a sealing member for sealing the non-aqueous electrolyte inlet is made of an elastic body and has a syringe needle. The tube can be stabbed, and the battery case can be replenished with the non-aqueous electrolyte through this tube. Then, after injecting the non-aqueous electrolyte into the battery case, when the tube is pulled out from the sealing member, the hole through the tube is closed because the sealing member is made of an elastic body. The sealed state can be maintained. Therefore, according to the regeneration method of the present invention using such a lithium ion secondary battery, the lithium ion secondary battery can be used without removing or disassembling part of the battery case according to the lithium ion secondary battery. The non-aqueous electrolyte can be supplemented to restore the characteristics.

  In the regeneration method of the present invention, the non-aqueous electrolyte solution (2) to be replenished in the battery case is different from the non-aqueous electrolyte solution (1) used at the time of assembling the lithium ion secondary battery with a specific additive content. Use a different one.

  An organic solvent solution of a lithium salt is used as a non-aqueous electrolyte for a lithium ion secondary battery. Normally, this non-aqueous electrolyte has characteristics of a lithium ion secondary battery in addition to a lithium salt and an organic solvent. Various additives are added for the purpose of enhancing the content.

  Among such additives, there is a compound whose reduction potential at the negative electrode is 1.3 V or less with respect to the metal Li potential. In a lithium ion secondary battery, with charge / discharge, for example, the nonaqueous electrolyte comes into contact with the negative electrode surface, the components in the nonaqueous electrolyte are decomposed, the amount of nonaqueous electrolyte is reduced, and the capacity is reduced. Problems can arise. However, in a lithium ion secondary battery using a non-aqueous electrolyte containing a compound whose reduction potential at the negative electrode is 1.3 V or less with respect to the metal Li potential, the compound reacts on the surface of the negative electrode due to charge and discharge. This film prevents direct contact between the negative electrode and the non-aqueous electrolyte, so that the decomposition of the non-aqueous electrolyte on the negative electrode surface accompanying charge / discharge of the battery is suppressed.

  However, the nonaqueous electrolyte used for replenishing the battery case and the nonaqueous electrolyte used when assembling the lithium ion secondary battery have a reduction potential at the negative electrode of 1.3 V or less with respect to the metal Li potential. When the same amount of the compound is contained, when a lithium ion secondary battery replenished with a nonaqueous electrolyte is used, the amount of swelling (for example, a charged battery is stored at a high temperature of about 85 ° C.). The amount of swelling).

  A compound having a reduction potential of 1.3 V or less with respect to the metal Li potential at the negative electrode may generate gas by being oxidized on the positive electrode side. Therefore, if the amount in the non-aqueous electrolyte is too large, Causes the ion secondary battery to swell.

  In a lithium ion secondary battery, a film is formed by the decomposition of the compound in the non-aqueous electrolyte by charge / discharge during chemical conversion treatment during assembly and charge / discharge during actual use. Even after the lapse of time, the unreacted compound usually remains in the nonaqueous electrolytic solution. The compound remaining in the non-aqueous electrolyte is a negative electrode exposed by a defect when a film is formed on the surface of the negative electrode due to an increase in the number of charge / discharge cycles of the lithium ion secondary battery. It reacts with the surface and plays a role in repairing defective parts of the film. Therefore, in an ordinary lithium ion secondary battery, the amount of the compound in the non-aqueous electrolyte is determined so that a certain amount of the compound remains even after a predetermined number of charge / discharge cycles.

  Therefore, if the non-aqueous electrolyte used for refilling the battery case is the same as the non-aqueous electrolyte used for assembling the lithium ion secondary battery, the regenerated lithium ion When the amount of the compound in the non-aqueous electrolyte of the secondary battery is too large, the amount of gas generated inside becomes extremely large when stored in a high temperature environment with full charge, and the battery case expands greatly. It is thought that.

  Therefore, in the regeneration method of the present invention, the nonaqueous electrolyte (2) to be replenished into the battery case has a reduction potential at the negative electrode as compared with the nonaqueous electrolyte (1) used when assembling the lithium ion secondary battery. A compound having a low content of a compound of 1.3 V or less with respect to the metal Li potential, or a compound having a reduction potential at the negative electrode that does not contain a compound of 1.3 V or less with respect to the metal Li potential. Decided to use. In the regeneration method of the present invention, this prevents generation of excess gas in the non-aqueous electrolyte solution of the unreacted compound in the regenerated lithium ion secondary battery, thereby generating gas during storage. The amount is reduced and the occurrence of swelling is suppressed.

  As described above, an organic solvent solution of lithium salt is used for the non-aqueous electrolyte solution related to the lithium ion secondary battery used in the regeneration method of the present invention.

The lithium salt related to the non-aqueous electrolyte is not particularly limited as long as it dissociates in a solvent to form Li ⁺ ions and hardly causes a side reaction such as decomposition in a voltage range used as a battery. For example, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ and other inorganic lithium salts, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1} SO ₃ (n ≧ 2), LiN (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group] and the like can be used. .

  The organic solvent related to the non-aqueous electrolyte is not particularly limited as long as it dissolves the lithium salt and does not cause a side reaction such as decomposition in a voltage range used as a battery. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate; chain esters such as methyl propionate; cyclic esters such as γ-butyrolactone; dimethoxyethane; Chain ethers such as diethyl ether, 1,3-dioxolane, diglyme, triglyme and tetraglyme; cyclic ethers such as dioxane, tetrahydrofuran and 2-methyltetrahydrofuran; nitriles such as acetonitrile, propionitrile and methoxypropionitrile; ethylene Sulfites such as glycol sulfite; and the like. These may be used in combination of two or more. In order to obtain a battery with better characteristics, it is desirable to use a combination that can obtain high conductivity, such as a mixed solvent of ethylene carbonate and chain carbonate.

  The concentration of the lithium salt in the non-aqueous electrolyte is preferably 0.5 to 1.5 mol / l, and more preferably 0.9 to 1.25 mol / l.

  And the non-aqueous electrolyte used for a lithium ion secondary battery contains the compound whose reduction potential in a negative electrode is 1.3V or less with respect to metal Li potential. 2-propynyldiethylphosphonoacetate (PDEA), 4-fluoro-1,3-dioxolan-2-one (FEC), vinylene carbonate (VC), vinylethylene carbonate (VEC), etc. Only seeds may be used, or two or more kinds may be used in combination.

  In the non-aqueous electrolyte used for the lithium ion secondary battery, the content of the compound having a reduction potential at the negative electrode of 1.3 V or less with respect to the metal Li potential is from the viewpoint of ensuring a good effect by using the compound. The content is preferably 2% by mass or more, and more preferably 3.5% by mass or more. In addition, from the viewpoint of better suppressing the battery swelling that can be caused by the compound, in the non-aqueous electrolyte used for the lithium ion secondary battery, the reduction potential at the negative electrode is 1.3 V or less with respect to the metal Li potential. The content of the compound is preferably 7% by mass or less, and more preferably 5% by mass or less. However, in the non-aqueous electrolyte (2) used for replenishing the battery case of the lithium ion secondary battery, the content of the compound whose reduction potential at the negative electrode is 1.3 V or less with respect to the metal Li potential is , 0% by mass.

  And as above-mentioned, the non-aqueous electrolyte (2) used for the replenishment in the battery case concerning a lithium ion secondary battery is more than the non-aqueous electrolyte (1) used for the assembly of a lithium ion secondary battery. The content of the compound having a reduction potential at the negative electrode of 1.3 V or less with respect to the metal Li potential is low, or the compound has a reduction potential at the negative electrode of 1.3 V or less with respect to the metal Li potential. Use something that doesn't exist.

  The content of the compound in which the reduction potential at the negative electrode is 1.3 V or less with respect to the metal Li potential in the nonaqueous electrolytic solution (2) is the same as the content of the compound in the nonaqueous electrolytic solution (1) and nonaqueous electrolysis. It is preferable to determine from the state of the lithium ion secondary battery at the time of replenishment of the liquid (2).

  Lithium ion secondary batteries have a compound in which the reduction potential at the negative electrode is 1.3 V or less with respect to the metal Li potential, depending on the degree of discharge capacity that is reduced by repeated charge and discharge from the initial discharge capacity. The amount remaining in the non-aqueous electrolyte varies. Therefore, depending on the content of the compound in the non-aqueous electrolyte (1) used for the assembly of the lithium ion secondary battery and the degree of decrease in the discharge capacity after repeated charge and discharge from the initial discharge capacity Since the approximate amount of the compound remaining in the non-aqueous electrolyte solution of the lithium ion secondary battery can be grasped, a suitable content of the compound in the non-aqueous electrolyte solution (2) can be estimated.

  Specifically, a compound in which the reduction potential at the negative electrode in the non-aqueous electrolyte in the lithium ion secondary battery after replenishing the non-aqueous electrolyte (2) is 1.3 V or less with respect to the metal Li potential is used. In the non-aqueous electrolyte (2) so that the content does not exceed 50% by mass of the content in the non-aqueous electrolyte (1) that the lithium ion secondary battery had at the time of assembly. It is preferable to set the content of the compound.

  For example, when the discharge capacity of a lithium ion secondary battery is reduced to about 80% immediately after assembly due to repeated charge and discharge, the compound remaining in the non-aqueous electrolyte in the lithium ion secondary battery It has been empirically found that the amount is about 10% by mass of the non-aqueous electrolyte (1) used for assembling the lithium ion secondary battery.

  Therefore, when replenishing the non-aqueous electrolyte (2) into the battery case when the discharge capacity of the lithium ion secondary battery is 80% ± 3% of the initial discharge capacity immediately after assembly. When the content of the non-aqueous electrolyte (1) of the compound whose reduction potential at the negative electrode is 1.3 V or less with respect to the metal Li potential is a (mg), the reduction potential at the negative electrode is relative to the metal Li potential. Use a non-aqueous electrolyte (2) containing a compound of 1.3 V or less at 0.4 × a (mg) or less, or use a non-aqueous electrolyte (2) not containing the compound. It is preferable. In addition, when the non-aqueous electrolyte (2) contains the compound and replenishes, when a defect portion is generated in the film derived from the compound formed on the negative electrode surface, the effect of repairing the defect portion is improved. From the viewpoint of ensuring the rechargeability of the non-aqueous electrolyte (2) in the battery case, the discharge capacity of the lithium ion secondary battery becomes 80% ± 3% of the initial discharge capacity immediately after assembly. In the case of carrying out, when the content of the non-aqueous electrolyte (1) of the compound whose reduction potential at the negative electrode is 1.3 V or less with respect to the metal Li potential is a (mg), the reduction potential at the negative electrode is It is preferable to use a nonaqueous electrolytic solution (2) containing a compound of 1.3 V or less with respect to the metal Li potential in an amount of 0.2 × a (mg) or more.

  In addition, when the discharge capacity of the lithium ion secondary battery is reduced to about 60% immediately after assembly due to repeated charge and discharge, the compound remaining in the non-aqueous electrolyte in the lithium ion secondary battery It has been empirically found that the amount is about 5% by mass of the non-aqueous electrolyte (1) used for assembling the lithium ion secondary battery.

  Therefore, when replenishing the non-aqueous electrolyte (2) into the battery case when the discharge capacity of the lithium ion secondary battery is 60% ± 3% of the initial discharge capacity immediately after assembly. When the content of the nonaqueous electrolyte (1) of the compound whose reduction potential at the negative electrode is 1.3 V or less with respect to the metal Li potential is b (mg), the reduction potential at the negative electrode is relative to the metal Li potential. The non-aqueous electrolyte (2) containing a compound of 1.3 V or less at 0.45 × b (mg) or less is used, or the non-aqueous electrolyte (2) not containing the compound is used. It is preferable. In addition, when the non-aqueous electrolyte (2) contains the compound and replenishes, when a defect portion is generated in the film derived from the compound formed on the negative electrode surface, the effect of repairing the defect portion is improved. From the viewpoint of ensuring the rechargeability of the non-aqueous electrolyte (2) into the battery case, the discharge capacity of the lithium ion secondary battery becomes 60% ± 3% of the initial discharge capacity immediately after assembly. In the case of carrying out, when the content of the non-aqueous electrolyte (1) of the compound whose reduction potential at the negative electrode is 1.3 V or less with respect to the metal Li potential is b (mg), the reduction potential at the negative electrode is It is preferable to use a nonaqueous electrolytic solution (2) containing a compound of 1.3 V or less with respect to the metal Li potential at 0.25 × b (mg) or more.

  In the non-aqueous electrolyte (1) used for assembling the lithium ion secondary battery and the non-aqueous electrolyte (2) supplemented in the battery case, the reduction potential at the negative electrode is 1.3 V or less with respect to the metal Li potential. In addition to the compound, an additive having an action capable of improving the characteristics of the lithium ion secondary battery can be contained. Examples of such additives include 1,3-propane sultone, 1,3-dioxane, nitrile compounds (succinonitrile, glutaronitrile, adiponitrile, etc.) and the like.

  The nonaqueous electrolytic solution (1) used for assembling the lithium ion secondary battery and the nonaqueous electrolytic solution (2) to be replenished in the battery case are the same in terms of the types of lithium salt and organic solvent and the concentration of the lithium salt. It may be different as long as the battery characteristics are not impaired.

  In the method of the present invention, regeneration treatment after use of the lithium ion secondary battery [replenishment of the non-aqueous electrolyte (2) after the capacity is reduced from the initial capacity through repeated charge and discharge of the lithium ion secondary battery] It may be performed only once, but the deterioration of components (electrodes, separators, etc.) other than the non-aqueous electrolyte of the lithium ion secondary battery is such that it does not prevent further use of the battery. Alternatively, the reproduction process may be performed twice or more.

  The positive electrode according to the lithium ion secondary battery used in the regeneration method of the present invention has, for example, a structure having a positive electrode mixture layer containing a positive electrode active material, a conductive additive and a binder on one side or both sides of a current collector Is used.

As the positive electrode active material, a conventionally known positive electrode active material for a lithium ion secondary battery, for example, an active material capable of inserting and extracting lithium ions is used. As a specific example of such a positive electrode active material, for example, a layered structure represented by Li _{1 + x} MO ₂ (−0.1 <x <0.1, M: Co, Ni, Mn, Al, Mg, etc.) Lithium-containing transition metal oxide, LiMn ₂ O ₄ and spinel-structured lithium manganese oxide obtained by substituting some of its elements with other elements, LiMPO ₄ (M: Co, Ni, Mn, Fe, etc.) Type compounds. Specific examples of the lithium-containing transition metal oxide having a layered structure include LiCoO ₂ and LiNi _1-x Co _xy Al _y O ₂ (0.1 ≦ x ≦ 0.3, 0.01 ≦ y ≦ 0. 2) and other oxides containing at least Co, Ni and Mn (LiMn _1/3 Ni _1/3 Co _1/3 O ₂ , LiMn _5/12 Ni _5/12 Co _1/6 O ₂ , LiNi _{3 / 5} Mn _1/5 Co _1/5 O ₂ etc.).

  Examples of the conductive additive related to the positive electrode mixture layer include graphite (graphite carbon material) such as natural graphite (flaky graphite, etc.) and artificial graphite; acetylene black, ketjen black, channel black, furnace black, lamp black. And carbon materials such as carbon black, carbon black, and the like. In addition, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), or the like can be used for the binder related to the positive electrode mixture layer.

  For the positive electrode, for example, a positive electrode mixture-containing composition in the form of a paste or slurry in which a positive electrode active material, a conductive additive and a binder are dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP) is prepared ( However, the binder may be dissolved in a solvent), and this is applied to one or both sides of the current collector, dried, and then subjected to a calendering process as necessary. However, the positive electrode is not limited to those manufactured by the above manufacturing method, and may be manufactured by other methods.

  Moreover, you may form the lead body for electrically connecting with the other member in a lithium ion secondary battery according to a conventional method to a positive electrode as needed.

  The thickness of the positive electrode mixture layer is preferably, for example, 10 to 100 μm per one side of the current collector. Moreover, as a composition of a positive mix layer, it is preferable that the quantity of a positive electrode active material is 60-95 mass%, for example, it is preferable that the quantity of a binder is 1-15 mass%, and the quantity of a conductive support agent. Is preferably 3 to 20% by mass.

  As the current collector for the positive electrode, the same one as used for the positive electrode of a conventionally known non-aqueous electrolyte secondary battery can be used. For example, an aluminum foil having a thickness of 10 to 30 μm is preferable.

  The negative electrode for the lithium ion secondary battery used in the regeneration method of the present invention includes, for example, a negative electrode active material and a binder, and further, a negative electrode mixture layer containing a conductive auxiliary agent if necessary, a current collector The thing of the structure which has in one side or both sides of is used.

  Examples of the negative electrode active material include graphite materials such as natural graphite (flaky graphite), artificial graphite, and expanded graphite; graphitizable carbonaceous materials such as coke obtained by calcining pitch; furfuryl alcohol resin ( Carbon materials such as non-graphitizable carbonaceous materials such as amorphous carbon obtained by low-temperature firing of PFA), polyparaphenylene (PPP), and phenol resins. In addition to the carbon material, lithium or a lithium-containing compound can also be used as the negative electrode active material. Examples of the lithium-containing compound include lithium alloys such as Li—Al, and alloys containing elements that can be alloyed with lithium such as Si and Sn. Furthermore, oxide-based materials such as Sn oxide and Si oxide can also be used.

  As the binder and the conductive auxiliary agent related to the negative electrode mixture layer, the same materials as those exemplified above as the binder and the conductive auxiliary agent related to the positive electrode mixture layer can be used.

  The negative electrode is prepared, for example, by preparing a paste-like or slurry-like negative electrode mixture-containing composition in which a negative electrode active material and a binder and, if necessary, a conductive additive are dispersed in a solvent such as NMP or water (however, The binder may be dissolved in a solvent), and this is applied to one or both sides of the current collector, dried, and then subjected to a calendering process as necessary. However, the negative electrode is not limited to those manufactured by the above manufacturing method, and may be manufactured by other methods.

  Moreover, you may form the lead body for electrically connecting with the other member in a lithium ion secondary battery according to a conventional method to a negative electrode as needed.

  The thickness of the negative electrode mixture layer is preferably 10 to 100 μm per side of the current collector per side of the current collector. Moreover, as a composition of a negative mix layer, it is preferable that the quantity of a negative electrode active material is 80-95 mass%, for example, it is preferable that the quantity of a binder is 1-20 mass%, and uses a conductive support agent. When it does, it is preferable that the quantity is 1-10 mass%.

  As the current collector for the negative electrode, a foil made of copper or nickel, a punching metal, a net, an expanded metal, or the like can be used, but a copper foil is usually used. In the negative electrode current collector, when the thickness of the entire negative electrode is reduced in order to obtain a battery having a high energy density, the upper limit of the thickness is preferably 30 μm, and the lower limit is preferably 5 μm.

  The separator according to the lithium ion secondary battery used in the regeneration method of the present invention has a property that the pores are closed at 80 ° C. or higher (more preferably 100 ° C. or higher) and 170 ° C. or lower (more preferably 150 ° C. or lower). That is, it is preferable to have a shutdown function, and a separator used in a normal lithium ion secondary battery, for example, a microporous membrane made of polyolefin such as polyethylene (PE) or polypropylene (PP) is used. Can do. The microporous film constituting the separator may be, for example, one using only PE or one using PP, or a laminate of a PE microporous film and a PP microporous film. There may be. The thickness of the separator is preferably 10 to 30 μm, for example.

  The positive electrode and the negative electrode are a laminated body (laminated electrode body) configured by being stacked with the separator interposed therebetween, or a wound body (wound electrode body) formed by further winding the laminated body in a spiral shape. ) In the form of lithium ion secondary batteries.

  1 and 2 show an example of a lithium ion secondary battery used in the regeneration method of the present invention. FIG. 1 is a partial longitudinal sectional view schematically showing a lithium ion secondary battery, and FIG. 2 is a perspective view of the lithium ion secondary battery shown in FIG.

  The lithium ion secondary battery shown in FIGS. 1 and 2 is in a battery case formed by a bottomed cylindrical (square tube) outer can 4 and a lid plate 9 that seals the opening of the outer can 4. After the positive electrode 1 and the negative electrode 2 are laminated via the separator 3 and wound in a spiral shape, a flat wound electrode body that is pressure-molded so as to have a flat cross section, a non-aqueous electrolyte, Is housed. In FIG. 1, in order to avoid complication, the layers of the positive electrode 1 and the negative electrode 2 are not shown separately, and the non-aqueous electrolyte is not shown. Further, in FIG. 1, the inner peripheral portion of the flat wound electrode body 6 is not shown in cross section.

  The outer can 4 is made of an aluminum alloy or the like. In the lithium ion secondary battery shown in FIG. 1, the outer can 4 also serves as a positive electrode terminal. An insulator 5 made of a PE sheet is disposed at the bottom of the outer can 4. From the flat wound electrode body 6 including the positive electrode 1, the negative electrode 2 and the separator 3, a positive electrode lead body 7 and a negative electrode lead body 8 connected to one ends of the positive electrode 1 and the negative electrode 2 are drawn out. The cover plate 9 is made of an aluminum alloy or the like, and a terminal 11 made of stainless steel or the like is attached to the cover plate 9 via an insulating packing 10 made of PP or the like. A lead plate 13 made of stainless steel or the like is attached via an insulator 12.

  And this cover plate 9 is inserted in the opening part of the armored can 4, and the opening part of the armored can 4 is sealed by welding the junction part of both, and the inside of a battery (battery case) is sealed. The lid plate 9 is provided with a cleavage vent 15 as a mechanism for discharging the internal gas to the outside when the temperature of the battery rises.

  Further, in the lithium ion secondary battery of FIG. 1, the lid plate 9 is provided with a non-aqueous electrolyte inlet, and a sealing member 14 is inserted into the non-aqueous electrolyte inlet, thereby sealing the battery. Is secured. As described above, the sealing member 14 can pierce a tube such as an injection needle for replenishing the non-aqueous electrolyte (2) at a stage where the capacity is reduced by repeatedly charging and discharging the lithium ion secondary battery. In addition, the battery is made of an elastic body so that the airtightness of the battery can be maintained even after the tube is pulled out.

  Examples of the elastic body that can constitute the sealing member include butyl rubber.

  In the lithium ion secondary battery shown in FIGS. 1 and 2, the outer can 5 and the cover plate 9 function as a positive electrode terminal by directly welding the positive electrode lead body 7 to the cover plate 9, and the negative electrode lead body 8 is used as the lead plate. 13 is connected to the negative electrode lead body 8 and the terminal 11 through the lead plate 13 so that the terminal 11 functions as a negative electrode terminal. However, depending on the material of the outer can 4, The sign may be reversed.

  The regeneration method of the present invention is applied to various lithium ion secondary batteries such as large lithium ion secondary batteries such as in-vehicle and industrial batteries and small lithium ion secondary batteries used for portable devices. This is a useful method for reproduction.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention.

Example 1
<Preparation of positive electrode>
LiCoO _{2 as} positive electrode active material: 100 parts by mass, NMP solution containing PVDF as binder at a concentration of 10% by mass: 20 parts by mass, artificial graphite as conductive aid: 1 part by mass and Ketjen Black: 1 The slurry was mixed with a mass part using a planetary mixer, and NMP was added to adjust the viscosity to prepare a positive electrode mixture-containing slurry.

  The positive electrode mixture-containing slurry is applied to both surfaces of an aluminum foil (positive electrode current collector) having a thickness of 15 μm, and then vacuum-dried at 120 ° C. for 12 hours to form a positive electrode mixture layer on both surfaces of the aluminum foil. Formed. Thereafter, calendar treatment was performed to adjust the thickness and density of the positive electrode mixture layer, and a nickel lead body was welded to the exposed portion of the aluminum foil to produce a strip-like positive electrode having a length of 375 mm and a width of 43 mm. The positive electrode mixture layer in the obtained positive electrode had a thickness of 55 μm per one side.

<Production of negative electrode>
Water is added to 97.5 parts by mass of natural graphite having a number average particle diameter of 10 μm as a negative electrode active material, 1.5 parts by mass of SBR as a binder, and 1 part by mass of CMC as a thickener. And mixed to prepare a negative electrode mixture-containing paste. This negative electrode mixture-containing paste was applied to both sides of a copper foil having a thickness of 8 μm, and then vacuum-dried at 120 ° C. for 12 hours to form negative electrode mixture layers on both sides of the copper foil. Thereafter, calendar treatment was performed to adjust the thickness and density of the negative electrode mixture layer, and a nickel lead body was welded to the exposed portion of the copper foil to produce a strip-shaped negative electrode having a length of 380 mm and a width of 44 mm. The negative electrode mixture layer in the obtained negative electrode had a thickness of 65 μm per one surface.

<Preparation of non-aqueous electrolyte>
LiPF ₆ was dissolved at a concentration of 1 mol / L in a mixed solvent of ethylene carbonate, methyl ethyl carbonate and diethyl carbonate in a volume ratio of 2: 3: 1, and FEC was added in an amount of 2% by mass, and VC was 2%. A non-aqueous electrolyte solution (1) used for assembling a lithium ion secondary battery was prepared by dissolving each in an amount of mass%.

  Further, in the same manner as in the non-aqueous electrolyte (1) except that FEC was dissolved in an amount of 1.05% by mass and VC was dissolved in an amount of 1.05% by mass, respectively, a lithium ion secondary solution was obtained. A non-aqueous electrolyte (2a) for replenishing the battery case of the battery was prepared.

<Assembly of lithium ion secondary battery>
The strip-shaped positive electrode and the strip-shaped negative electrode are stacked with a microporous polyethylene separator (porosity: 41%) having a thickness of 16 μm, wound in a spiral shape, and then pressed so as to be flat. Thus, a flat wound electrode body was obtained. The flat wound electrode body was placed in an aluminum alloy outer can having a thickness of 5 mm, a width of 42 mm, and a height of 61 mm, and an aluminum alloy lid plate was placed on the opening of the outer can and welded to form a battery case. Subsequently, 4 g of the non-aqueous electrolyte (1): 4 g was injected into the battery from the non-aqueous electrolyte injection port provided on the cover plate, and a chemical conversion treatment [constant current charging to 4.2 V at a current value of 800 mA, Subsequently, a constant voltage charge of 4.2 V is performed (total charge time of constant current charge and constant voltage charge is 2.5 hours, and then a discharge is performed until the voltage reaches 3 V at 160 mA). A battery case was sealed by inserting a sealing member made of butyl rubber into the electrolyte inlet, and a lithium ion secondary battery was obtained. This lithium ion secondary battery has 80 mg of FEC and 80 mg of VC (the total of both is 160 mg) by injecting the above-mentioned amount of the non-aqueous electrolyte (1).

<Charge / discharge treatment of lithium ion secondary battery>
About the said lithium ion secondary battery, constant current charge was carried out until it became 4.2V with the electric current value of 800 mA, and then 4.2V constant current charge was performed (the total charge time of constant current charge and constant voltage charge is 2). .5 hours), and thereafter, a series of operations for discharging until 160 V at 3 V was taken as one cycle, and this charge / discharge cycle was repeated. Then, charging and discharging were stopped when the discharge capacity fell below 80% of the discharge capacity at the first cycle (specifically, 78%, and the number of cycles at that time was 612). In addition, about the part of lithium ion secondary battery which performed this charging / discharging process, when the total amount of FEC and VC which remain | survived inside was investigated, it was 16 mg.

<Replenishment of non-aqueous electrolyte>
Next, the lithium ion secondary battery after the charge / discharge cycle treatment was supplemented with 3 g of the non-aqueous electrolyte (2a), and a regeneration treatment was performed. The replenishment of the non-aqueous electrolyte (2) is performed by putting the non-aqueous electrolyte (2a) into a syringe having an injection needle first, and inserting the syringe needle into the sealing member sealing the lid plate. This was performed by injecting a non-aqueous electrolyte (2a) into the stab battery case. And when replenishment of the non-aqueous electrolyte (2a) was completed, the injection needle was pulled out from the sealing member, and it was confirmed that the non-aqueous electrolyte (2a) did not leak from the sealing member. By replenishing this non-aqueous electrolyte (2a), 31.5 mg of FEC and 31.5 mg of VC (a total of 63 mg of both) were newly introduced into the battery case.

<High temperature storage characteristics evaluation of regenerated lithium ion secondary battery>
About the lithium ion secondary battery after a regeneration process, the constant current charge and the constant voltage charge were performed on the same conditions as the time of the said charging / discharging process. Next, the charged lithium ion secondary battery was placed in a thermostat set at 85 ° C., stored for 24 hours, and the thickness of the battery after removal was measured. And the amount of swelling was computed from the calculated | required thickness according to a following formula.

Battery swell amount = 100 × (t ₁ −t ₀ ) / t ₀
Here, in the above formula, t ₁ is the thickness (mm) of the battery after regenerating and performing constant current-constant voltage charging and storing at 85 ° C. for 24 hours, and t ₀ is the battery immediately after assembly. (That is, the thickness of the outer can used for assembling the battery, mm.).

  In addition, for a battery different from the battery that has undergone the regeneration process, the charge / discharge process under the above conditions before the regeneration process is performed for the same number of cycles as the battery that has undergone the regeneration process, and then the regeneration process is performed. The amount of swelling after high-temperature storage was determined under the same conditions as the battery used.

<Evaluation of charge / discharge cycle characteristics of lithium ion secondary battery before and after regeneration treatment>
About the lithium ion secondary battery (battery different from what was used for the said high temperature storage characteristic evaluation) after a reproduction | regeneration process, a charge / discharge cycle is performed on the same conditions as the time of the said charge / discharge process, and a lithium ion secondary battery The number of cycles capable of maintaining 80% of the initial discharge capacity after assembly was determined. Then, the total number of cycles and the number of charge / discharge cycles applied to the lithium ion secondary battery during the charge / discharge process before the regeneration process are combined to determine the initial discharge capacity of the lithium ion secondary battery before and after the regeneration process. The number of cycles capable of maintaining 80% capacity was calculated.

Comparative Example 1
The lithium ion secondary was the same as in Example 1, except that the same nonaqueous electrolyte (1) as that prepared in Example 1 was used as the nonaqueous electrolyte to replenish the lithium ion secondary battery during the regeneration process. The battery was charged / discharged and regenerated. Note that 60 mg of FEC and 60 mg of VC (total of both 120 mg) were newly introduced into the battery case by replenishment of the non-aqueous electrolyte (1) during the regeneration process.

  And about the lithium ion secondary battery after a regeneration process, high temperature storage characteristic evaluation (measurement of the swelling amount of a battery) and charge / discharge cycle characteristic evaluation were performed by the same method as Example 1. FIG.

  Table 1 shows the results of the high-temperature storage characteristic evaluation and the charge / discharge cycle characteristic evaluation in the lithium ion secondary batteries according to Example 1 and Comparative Example 1.

  As shown in Table 1, in the lithium ion secondary battery according to Example 1, the number of cycles that can maintain 80% of the initial discharge capacity immediately after assembly in the charge / discharge cycle characteristics evaluation before and after the regeneration treatment is a comparative example. Although it was slightly less than the battery of 1, it was very much. Therefore, the regeneration treatment applied to the lithium ion secondary battery according to Example 1 can prolong the charge / discharge cycle life of the lithium ion secondary battery. Further, the lithium ion secondary battery according to Example 1 has a small amount of swelling at the time of high temperature storage characteristic evaluation after the regeneration process after the regeneration process, compared with the battery according to Comparative Example 1, and the high temperature storage characteristic before the regeneration process. It was equivalent to the amount of swelling at the time of evaluation, and it was possible to satisfactorily suppress the swelling that could occur with the regeneration process.

Example 2
Lithium ions were obtained in the same manner as the non-aqueous electrolyte (1) in Example 1 except that FEC was dissolved in an amount of 1.2% by mass and VC was dissolved in an amount of 1.2% by mass. A non-aqueous electrolyte (2b) for replenishing the battery case of the secondary battery was prepared.

  For a lithium ion secondary battery produced in the same manner as that produced in Example 1, the charge / discharge treatment was repeated under the same conditions as in Example 1, and the discharge capacity fell below 60% of the discharge capacity in the first cycle (specifically 59%, and the number of cycles at that time was 715). In addition, about the part of lithium ion secondary battery which performed this charging / discharging process, when the total amount of FEC and VC which remain | survived inside was investigated, it was 8 mg.

  The lithium ion secondary battery after the charge / discharge treatment was supplemented with the nonaqueous electrolyte solution (2b) in the same manner as in Example 1 to perform a regeneration treatment. By replenishing this non-aqueous electrolyte (2b), 36 mg of FEC and 36 mg of VC (total of both 72 mg) are newly introduced into the battery case.

  The lithium ion secondary battery after the regeneration treatment was evaluated for high-temperature storage characteristics (measurement of battery swelling) by the same method as in Example 1.

  Moreover, about the lithium ion secondary battery (Battery different from what was used for the said high temperature storage characteristic evaluation) after a reproduction | regeneration process, a charge / discharge cycle is performed on the same conditions as the time of the said charge / discharge process, and a lithium ion secondary The number of cycles capable of maintaining 60% of the initial discharge capacity after battery assembly was determined. Then, the total number of cycles and the number of charge / discharge cycles applied to the lithium ion secondary battery during the charge / discharge process before the regeneration process are combined to determine the initial discharge capacity of the lithium ion secondary battery before and after the regeneration process. The number of cycles that can maintain a capacity of 60% was calculated.

Comparative Example 2
The lithium ion secondary was the same as in Example 2, except that the same nonaqueous electrolyte (1) as that prepared in Example 1 was used as the nonaqueous electrolyte to replenish the lithium ion secondary battery during the regeneration process. The battery was charged / discharged and regenerated. Note that 60 mg of FEC and 60 mg of VC (total of both 120 mg) were newly introduced into the battery case by replenishment of the non-aqueous electrolyte (1) during the regeneration process.

  And about the lithium ion secondary battery after a regeneration process, high temperature storage characteristic evaluation (measurement of the swelling amount of a battery) and charge / discharge cycle characteristic evaluation were performed by the same method as Example 1. FIG.

  Table 2 shows the results of the high-temperature storage characteristic evaluation and the charge / discharge cycle characteristic evaluation in the lithium ion secondary batteries according to Example 2 and Comparative Example 2.

  As shown in Table 2, the lithium ion secondary battery according to Example 2 has a comparative example in which the number of cycles capable of maintaining 60% of the initial discharge capacity immediately after assembly is evaluated at the time of charge / discharge cycle characteristics evaluation before and after the regeneration process. Although it was slightly less than the battery of 2, it was very much. Therefore, the regeneration treatment applied to the lithium ion secondary battery according to Example 2 can extend the charge / discharge cycle life of the lithium ion secondary battery. Further, the lithium ion secondary battery according to Example 2 has a small swelling amount at the time of high temperature storage characteristic evaluation after the regeneration process after the regeneration process, compared with the battery according to Comparative Example 2, and the high temperature storage characteristic before the regeneration process. It was equivalent to the amount of swelling at the time of evaluation, and it was possible to satisfactorily suppress the swelling that could occur with the regeneration process.

1 Positive electrode 2 Negative electrode 3 Separator

Claims (4)

A lithium ion secondary battery in which a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte are accommodated in a battery case formed by a bottomed cylindrical outer can and a lid plate that seals the opening of the outer can. Is a method of playing
The lithium ion secondary battery has a non-aqueous electrolyte inlet in the battery case, and the non-aqueous electrolyte inlet is sealed by a sealing member made of an elastic body,
In the stage where the discharge capacity is smaller than the initial discharge capacity by repeating charge and discharge from the assembly of the lithium ion secondary battery, a tube is pierced into the sealing member, and the non-aqueous electrolyte is inserted into the battery case through the tube. And then removing the tube from the sealing member,
The non-aqueous electrolyte (1) used when assembling the lithium ion secondary battery and the non-aqueous electrolyte (2) to be replenished in the battery case have a reduction potential at the negative electrode of 1. The content of the compound containing 3 V or less and the reduction potential at the negative electrode of 1.3 V or less with respect to the metal Li potential in the non-aqueous electrolyte (2) is the non-aqueous electrolyte. Less than the content in (1), or
The non-aqueous electrolyte (1) used at the time of assembling the lithium ion secondary battery contains a compound whose reduction potential at the negative electrode is 1.3 V or less with respect to the metal Li potential, and in the battery case The method of regenerating a lithium ion secondary battery, wherein the nonaqueous electrolyte solution (2) to be replenished does not contain the compound having a reduction potential at the negative electrode of 1.3 V or less with respect to the metal Li potential. The replenishment of the non-aqueous electrolyte (2) into the battery case is performed when the discharge capacity of the lithium ion secondary battery is 80% ± 3% of the initial discharge capacity immediately after assembly,
When the content of the compound in which the reduction potential at the negative electrode is 1.3 V or less with respect to the metal Li potential is a (mg) in the non-aqueous electrolyte (1), the non-aqueous electrolyte (2) Uses a compound in which the reduction potential at the negative electrode is 1.3 V or less with respect to the metal Li potential and the content of the compound is 0.4 × a (mg) or less, or does not contain the compound. The method for regenerating a lithium ion secondary battery according to claim 1.   The replenishment of the non-aqueous electrolyte (2) into the battery case was performed when the discharge capacity of the lithium ion secondary battery was 60% ± 3% of the initial discharge capacity immediately after assembly. When the content in the non-aqueous electrolyte (1) of the compound having a reduction potential of 1.3 V or less with respect to the metal Li potential is b (mg), the non-aqueous electrolyte (2) The content of the compound having a reduction potential at the negative electrode of 1.3 V or less with respect to the metal Li potential is 0.45 × b (mg) or less, or does not contain the compound. The method for regenerating a lithium ion secondary battery according to claim 1.   4. The compound according to claim 1, wherein the compound having a reduction potential at a negative electrode of 1.3 V or less with respect to a metal Li potential is 4-fluoro-1,3-dioxolan-2-one and / or vinylene carbonate. The regeneration method of the lithium ion secondary battery as described.