JP2012174537A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous secondary battery which can suppress influences of hydrogen fluoride generated in the battery.SOLUTION: The nonaqueous electrolyte is a gel consisting of polyvalent cations, an anionic group high polymer material crosslinked with the cations and a dispersant, which includes a neutralization component disposed at a position touchable by the electrolyte. The neutralization component, although in a stable state normally, reacts with polyvalent cations in the neutralization component and is thereby neutralized when hydrogen fluoride or similar other acid occurs. The neutralization component is decomposed by reaction with the polyvalent cations, making it possible for acid to be neutralized by new polyvalent cations. Since anions as counter ions of the polyvalent cations are turned into a high polymer material, the neutralization component does not dissolve in the electrolyte and it becomes less likely that the neutralization component adversely affects battery performance. Furthermore, because anions left after the polyvalent cations have reacted are a high polymer material, no gas is generated and, hence, there is no progress in a rise of the internal pressure of the battery.

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and relates to a non-aqueous electrolyte secondary battery that can effectively neutralize an acid generated by battery deterioration.

  In recent years, non-aqueous electrolyte secondary batteries such as lithium batteries having a large capacity, high output, and high energy density have attracted attention as power sources for driving automobiles and portable devices.

  As a lithium battery, a power generation element in which a positive electrode and a negative electrode, which are formed with a composite layer mainly composed of an electrode active material capable of receiving lithium ions on the surface of a current collecting member such as a metal foil, are arranged opposite to each other with a separator interposed therebetween. Is known which is sealed in a battery container together with a non-aqueous electrolyte.

  By the way, the non-aqueous electrolyte secondary battery has a problem that the battery performance deteriorates when moisture enters the inside of the battery container. Specifically, when moisture is present inside the battery container, this moisture reacts with the non-aqueous electrolyte to generate hydrogen fluoride, and the generated hydrogen fluoride is a power generation element such as positive and negative electrodes, electrodes, positive and negative electrodes and electrodes. Corrosion of members constituting the battery, such as leads and battery containers, to reduce performance such as battery capacity and battery life.

  For this reason, the nonaqueous electrolyte secondary battery is devised so that it can be sealed so that moisture does not enter the battery container as much as possible, but it is difficult to completely prevent it. Therefore, the member which anticipated deterioration by hydrogen fluoride is employ | adopted, or the neutralizing agent which can neutralize the hydrogen fluoride to produce | generate is contained.

  As a prior art, a non-aqueous electrolyte battery in which calcium carbonate, which is a calcium salt, is added as a neutralizing agent in a non-aqueous electrolyte is disclosed (Patent Document 1).

Japanese Patent No. 3281701 Japanese Patent Laid-Open No. 2002-151024

  However, in the invention disclosed in Patent Document 1, it has been found that the addition of calcium carbonate has an adverse effect on battery performance, such as undesirable effects on battery reaction and increased internal resistance of the battery. .

  The calcium carbonate added in the invention of Patent Document 1 is difficult to dissolve in the electrolytic solution, but does not completely dissolve. The dissolved calcium carbonate becomes calcium ions. The produced calcium ions will affect the battery reaction.

  For example, a film is gradually formed on the electrode surface as the battery reaction progresses, but the internal resistance of the battery increases because calcium ions are less permeable to the film formed on the electrode surface than lithium ions. become.

  Further, when hydrogen fluoride reacts with calcium carbonate, carbon dioxide is generated and the internal pressure of the battery increases.

  The present invention has been completed in view of the above circumstances. That is, it is possible to provide a nonaqueous electrolyte secondary battery including a member capable of effectively neutralizing an acid such as hydrogen fluoride generated inside the battery while suppressing adverse effects on battery performance as much as possible. It should be a challenge.

  As a result of intensive studies for the purpose of solving the above-mentioned problems, the present inventors have included a polyvalent cation as a cation that reacts with an acid such as hydrogen fluoride, and an anion as a counter ion of the polyvalent cation is a polymer material. As a result, it has been found that the neutralizing member is not eluted in the electrolyte and the risk of adversely affecting battery performance can be reduced. The present invention has been completed based on the above findings.

  By containing polyvalent ions as cations contained in the neutralizing member, they can bind to the anions of the polymer material and crosslink the polymer materials. Therefore, when no acid is generated, the polyvalent cation remains in the neutralizing member as a cross-linking point of the anionic group-containing polymer material, and does not elute in the electrolyte, thereby reducing the influence on the battery reaction.

  Moreover, the polyvalent cation and acid which are contained can react easily by making a neutralization member into a gel. The polyvalent cation in the neutralizing member reacts with the acid from the surface. Therefore, the internal polyvalent cation can be stably present in the neutralizing member. Further, since the reaction with the polyvalent cation proceeds sequentially according to the generation of the acid and the neutralizing member is decomposed, the neutralizing member can supply the polyvalent cation according to the amount of acid generated.

  In other words, since the neutralizing member is stably present in the battery when no acid is generated, the influence of the neutralizing member on the battery performance can be reduced and the generated acid can be effectively neutralized. it can.

  In addition, after the polyvalent cation reacts, the remaining anion is a polymer material, so no gas is generated and the internal pressure of the battery does not increase.

  Patent Document 2 describes a sealing material made of a metal ion cross-linked product of ethylene / (meth) acrylic acid copolymer. This metal ion cross-linked product is gelled by the presence of copolymerized ethylene. Therefore, a rapid reaction between the contained metal ions and the acid cannot be expected.

The nonaqueous electrolyte secondary battery according to claim 1 that solves the above problem is a nonaqueous electrolyte secondary battery comprising a positive and negative electrode capable of occluding and releasing lithium ions, and a nonaqueous electrolyte,
A gel comprising a polyvalent cation, an anionic group-containing polymer material cross-linked with the polyvalent cation, and a dispersion medium, and having a neutralizing member disposed at a position in contact with the electrolyte And

  The neutralizing member provided in the nonaqueous electrolyte secondary battery of the present invention is in a stable state under normal conditions, but when an acid such as hydrogen fluoride is generated, it is reacted and neutralized with the polyvalent cation in the neutralizing member. The By reacting with the polyvalent cation, the neutralizing member is decomposed, and the acid can be neutralized with a new polyvalent cation.

  As a result, it is possible to increase the durability of battery components such as battery containers. For example, when a battery container formed from a laminate film is adopted, a non-aqueous electrolyte secondary battery is sealed by heat-sealing a resin film constituting the laminate film. The size of is set so that the strength of the sealed portion can be maintained for a necessary period or longer. Conventionally, the sealing portion has been enlarged by the amount of deterioration due to acid such as hydrogen fluoride. However, since the deterioration due to acid can be suppressed by employing the neutralizing member of the present invention, the sealing portion is relatively small. it can.

  In the non-aqueous electrolyte secondary battery according to claim 2 for solving the above-mentioned problems, the anionic group of the anionic group-containing polymer material is a carboxyl group.

  This is because a carboxyl group can be easily introduced into a polymer material, and a polyvalent cation bonded due to the presence of hydrogen fluoride or the like can be easily released.

  In the nonaqueous electrolyte secondary battery according to claim 3 for solving the above-mentioned problems, the anionic group-containing polymer material is a carboxyl group-containing polysaccharide or poly (meth) acrylic acid. These polymer materials have high stability in the battery and are inexpensive.

  In the non-aqueous electrolyte secondary battery according to claim 4 for solving the above-mentioned problem, the polyvalent cation is an ion of an alkaline earth metal.

  In the nonaqueous electrolyte secondary battery according to claim 5 for solving the above-mentioned problem, the polyvalent cation is at least one of calcium ions and barium ions.

  Alkaline earth metals (especially calcium or barium) can form insolubles with many acids, and can effectively neutralize and remove the generated acid.

  The non-aqueous electrolyte secondary battery according to claim 6 for solving the above-mentioned problems is characterized in that the neutralizing member is fixed by an acrylic adhesive material. Acrylic adhesives have excellent chemical resistance and physical properties, and are excellent in durability.

The non-aqueous electrolyte secondary battery according to claim 7 for solving the above-described problem is a battery container that houses the positive and negative electrodes and the electrolyte and has a communication part that communicates the inside and the outside;
A lead that electrically connects the inside and outside of the battery container through the communication portion of the battery container;
A sealing material for sealing the communication portion of the main body,
The neutralizing member is disposed adjacent to the lead or the sealing material.

  Compared to battery containers, sealing materials and leads have many performances that must be satisfied in addition to acid durability, so acid durability may not be sufficient. In such cases, a neutralizing member should be provided adjacent to them. Can sufficiently protect the sealing material and leads.

It is a partial cross section figure of the test battery used in the Example. It is an enlarged view of the junction part of the positive and negative electrode lead | read | reed and current collector of the test battery used in the Example. It is an expanded sectional view of the junction part of a positive and negative electrode lead and current collector of a test battery used in an example, and the junction part (communication part) of a lead and a battery container. It is a partial cross section figure which shows the other aspect of the test battery used in the Example.

  The nonaqueous electrolyte secondary battery of the present invention will be described in detail based on the embodiment. The nonaqueous electrolyte secondary battery of this embodiment includes positive and negative electrodes capable of inserting and extracting lithium ions, a nonaqueous electrolyte, and other members selected as necessary. In addition, it has a neutralizing member. The neutralizing member to be contained is a gel composed of a polyvalent cation, an anionic group-containing polymer material crosslinked with the polyvalent cation, and a dispersion medium. And it arrange | positions in the position which can contact nonaqueous electrolyte.

The positive and negative electrodes include an active material capable of occluding and releasing lithium ions. Examples of the positive electrode active material include lithium-containing transition metal oxides. The lithium-containing transition metal oxide is a material capable of removing and inserting Li ⁺ , and can be exemplified by a lithium-metal composite oxide having a layered structure or a spinel structure. Specifically, Li ₁ -Z NiO ₂ , Li ₁ -Z MnO ₂ , Li ₁ -Z Mn ₂ O ₄ , Li ₁ -Z CoO ₂ and other metal oxide materials, Li ₁ -Z βPO ₄ (β is And LiFePO ₄ which is Fe), and one or more of them can be included. Z in this illustration shows the number of 0-1. A material obtained by adding or substituting a transition metal such as Li, Mg, Al, or Co, Ti, Nb, or Cr may be used. Moreover, not only these lithium-metal composite oxides are used alone, but also a plurality of them can be mixed and used. Moreover, a conductive polymer material, a material having a radical, or the like can be employed alone or mixed.

  As the negative electrode active material, one or more compounds selected from the group consisting of carbon materials such as graphite and amorphous carbon, metal materials capable of forming an alloy with lithium, titanium oxide, and vanadium oxide can be employed. In these active materials, insertion / extraction of lithium (ion) proceeds as the battery reaction proceeds.

  When these positive electrode active materials and negative electrode active materials are used to form an electrode, it can be used in a state in which a composite material layer is formed on a current collector after forming a composite material together with other necessary members. Other necessary members include a conductive material and a binder.

  Examples of the conductive material include ketjen black, acetylene black, carbon black, graphite, carbon nanotube, and amorphous carbon. Moreover, conductive polymers (polyaniline, polypyrrole, polythiophene, polyacetylene, polyacene, etc.) whose aspect ratio is not limited can be exemplified.

  The binder is preferably formed of a polymer material, and is desirably a material that is chemically and physically stable in the atmosphere in the secondary battery. For example, fluorine-based polymer materials (such as polyvinylidene fluoride) and polysaccharides (such as carboxymethyl cellulose) can be used. In addition, a conductive polymer can be used as the binder.

  Such a composite material layer is formed on the surface of an appropriate current collector. An example of the current collector is a foil formed of an electrochemically stable metal. Examples of the method of forming the electrode mixture layer on the surface of the current collector include a method in which the material constituting the mixture layer is dispersed or dissolved in an appropriate dispersion medium and then applied to the surface of the current collector and dried. it can.

  A separator can be interposed between the positive and negative electrodes. The separator is a sheet-like member, and is a member that achieves both electrical insulation and ion conduction. When the electrolyte is liquid, the separator also plays a role of holding the liquid supporting electrolyte. For the purpose of ensuring the insulation between the positive electrode and the negative electrode, the separator preferably adopts a form that is larger than the area of the positive electrode and the negative electrode. The separator can be formed of a porous film having communication holes communicating with the front and back surfaces, or an ion conductive material such as a solid electrolyte. Examples of the porous film include polyolefin films such as polypropylene and polyethylene, and porous films made of polyester, polyamide, and fluororesin.

  Although it does not specifically limit as a non-aqueous electrolyte, What melt | dissolved the supporting salt with respect to the thing which melt | dissolved supporting salt in solvents, such as an organic solvent, the ionic liquid which is liquid itself, and an ionic liquid can be illustrated. By adopting a fluorine-containing salt as the non-aqueous electrolyte, hydrogen fluoride is generated due to water mixing.

  As an organic solvent, the organic solvent used for the nonaqueous electrolyte of a normal nonaqueous electrolyte secondary battery can be illustrated. For example, carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, lactones, oxolane compounds and the like can be used. In particular, propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and the like, and mixed solvents thereof are suitable. Among these organic solvents mentioned in the examples, in particular, by using one or more nonaqueous solvents selected from the group consisting of carbonates and ethers, the nonaqueous electrolyte is excellent in solubility, dielectric constant and viscosity, Since the charging / discharging efficiency of a battery is also high, it is preferable.

An ionic liquid will not be specifically limited if it is an ionic liquid normally used for the electrolyte solution of a lithium secondary battery. For example, examples of the cation component of the ionic liquid include N-methyl-N-propylpiperidinium and dimethylethylmethoxyammonium cation, and examples of the anion component include BF ⁴⁻ , N (SO ₂ CF ₃ ) ^2−. Etc.

The electrolyte is not particularly limited. For example, LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiSbF ₆ , LiSCN, LiClO ₄ , LiAlCl ₄ , NaClO ₄ , BClO ₄ , NaI, and salt compounds such as derivatives thereof. Among these, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiN (FSO ₂ ) ₂ , LiN (CF _{3 SO 2) (C 4 F 9} SO 2), derivatives of _{LiCF 3 SO 3, LiN (CF} 3 SO 2) 2 derivative, and _LiC (CF 3 _{SO 2)} 1 or more selected from the group consisting of ₃ derivatives It is preferable to use the salt of from the viewpoint of electrical characteristics.

  Examples of other members include battery containers and leads. The battery container is a member that houses positive and negative electrodes, a non-aqueous electrolyte, and the like. The lead is a member that is electrically connected to the positive and negative electrodes, and is a member that extracts power from the positive and negative electrodes. A part or all of the battery container may be made of a conductor such as metal and may also be used as a lead. The material of the lead is preferably made of the same material as that of the current collector.

  A battery container has a communication part which connects the inside and the outside, and the communication part is sealed with a sealing material. By providing the communication part, it is possible to easily put the positive and negative electrodes inside the battery container or put the non-aqueous electrolyte. Moreover, a lead can also be passed through the communicating portion. When the lead is passed through the communication part, the lead is also sealed with a sealing material. As the sealing material, polyethylene, polypropylene, polyphenylene sulfide, and modified products thereof can be used. It is desirable that the sealing material be bonded to the communication part or the lead by heating or the like.

  The neutralizing member is a gel composed of a polyvalent cation, an anionic group-containing polymer material crosslinked with the polyvalent cation, and a dispersion medium. The neutralizing member is disposed at a position where it can contact the nonaqueous electrolyte. In particular, the seal material and the lead can be effectively protected from the acid by being arranged adjacent to or close to the seal material and the lead. In particular, it is desirable to coat so as to protect a member such as a sealing material from coming into contact with the electrolyte. The neutralization member being a gel includes not only the case where the entire neutralization member is a gel but also the case where only the surface layer portion is a gel. Moreover, as long as the form of the neutralizing member can be generally maintained in the battery, a part thereof may be in a sol state or a part thereof may be dissolved.

  Moreover, you may use the neutralization member instead of the binder used for the electrode mentioned above. The arrangement of the neutralizing member is preferably fixed in the battery by some method. In that case, it can fix with an acrylic adhesive material. The acrylic pressure-sensitive adhesive material is obtained by polymerizing acrylic acid or acrylic acid ester alone or with other monomers.

  The neutralizing member preferably contains 100 ppm or more of polyvalent cations based on the mass of the entire neutralizing member. The content of the neutralizing member is a polyvalent cation in an amount (or more) that can neutralize (preferably neutralize without excess or deficiency) all the acids that are considered to be generated inside during the lifetime assumed for the battery of the present invention. It is desirable to set to include.

Examples of polyvalent cations include alkaline earth metals, Group 8 elements (such as iron Fe), Group 11 elements (such as copper Cu), Group 12 metals (such as zinc Zn), and Group 13 metals (such as aluminum Al). Can be mentioned. Examples thereof include divalent cations such as Ca ²⁺ , Ba ²⁺ , Mg ²⁺ , Cu ²⁺ and Zn ^2+, and trivalent cations such as Al ³⁺ and Fe ³⁺ . When a metal is used for the positive and negative current collectors and the positive and negative current collectors and is in contact with the electrolyte, it is desirable that the reactivity is higher than ions derived from the metal. For example, when copper or nickel is employed as the negative electrode or its current collector and aluminum is employed as the positive electrode or its current collector, it is desirable to employ an alkaline earth metal element as the polyvalent cation. Among the alkaline earth metals, it is particularly desirable to select calcium or barium ions. In addition, not only a polyvalent cation but also a monovalent cation may be mixed in the neutralizing member.

  The anionic group-containing polymer material has a chemical structure in which an anionic group is bonded to a polymer base material that is a polymer compound. Examples of the anionic group include a carboxyl group, a phospho group, a sulfo group, and a sulfate group, and a carboxyl group is particularly preferable. As the polymer substrate, a material capable of stably existing without dissolving an anionic group-containing polymer material containing a polyvalent cation in the battery can be selected. Here, whether it can exist stably changes also with the quantity and kind of anionic group couple | bonded. The anionic group-containing polymer material alone after the polyvalent cation is consumed may be dissolved in the battery, but it is desirable that the battery reaction is not affected.

  The polymer substrate can be selected from polysaccharides and general polymer compounds. As a selection criterion for a polymer base material, an anionic group-containing polymer material (in which a polyvalent cation is bonded) in which an anionic group is introduced to the polymer base material, the polyvalent cation contained therein is easily released. Thus, the one that gels is selected. As the dispersion medium to be gelled, it is desirable to use a polar solvent contained in the electrolyte. Furthermore, with regard to anionic group-containing polymer materials (those from which polyvalent cations are eluted), not only those that swell by non-aqueous electrolytes but also those that dissolve, A part having a polyvalent cation dissolves in the non-aqueous electrolyte and appears on the surface quickly, so that the acid can react quickly with the polyvalent cation.

  The polysaccharide that can be employed in the polymer substrate or the anionic group-containing polymer material is not particularly limited, and various polysaccharides (such as homoglycan and heteroglycan) can be used. Homoglycans include glucans (cellulose, starch, glycogen, caronin, laminaran, dextran, etc.), fructans (inulin, levan, etc.), mannans (such as elephant palm mannan), xylan (such as rice straw xylan), galacturonan (pectinic acid, etc.) ), Mannuronan (such as alginic acid), N-acetylglucosamine polymer (such as chitin), and derivatives thereof. Heteroglycans include diheteroglycans (guaran, konjac mannan, heparin, chondroitin sulfate, hyaluronic acid, etc.), triheteroglycans (gelatin gum, female kit gum, gummy gum and other plant mucilages, gums, bacterial polysaccharides, etc.) Examples include tetraheteroglycans (viscous substances such as gum arabic, gums, bacterial polysaccharides, etc.), and derivatives thereof.

In addition to the anionic group, the anionic group-containing polymer material having a polysaccharide as a polymer substrate may be —NH ₂ , —CN, —OH, —NHCONH ₂ , — (OCH ₂ CH ₂ ) —, —NR _3. It may have a hydrophilic group such as X (wherein R represents an alkyl group, X represents a halogen atom), SO ₃ NH ₂ CO—, —N (SO ₃ H) —.

  Examples of the polymer substrate (anionic group-containing polymer material) having a structure other than the polysaccharide include polyacrylic acid and polymethacrylic acid.

(Manufacture of test batteries)
A laminate type cell having the configuration shown in FIGS.
Production of positive and negative electrodes 2, 3 and electrolyte Positive electrode: 85 parts by mass of LiNi _0.8 Co _0.17 Al _0.03 O ₂ as a positive electrode active material, 12 parts by mass of acetylene black as a conductive material, carboxy Disperse 1 part by mass of methylcellulose sodium salt (CMC · Na) and 1 part by mass of polyethylene oxide (PEO) in 80 parts by mass of water, and further add 1 part by mass of polytetrafluoroethylene (PTFE) as a binder. Added and dispersed into a slurry. This slurry was applied to both surfaces of the positive electrode current collector 1 made of aluminum, dried and press-molded to obtain a positive electrode plate. Thereafter, the positive electrode plate was cut into a predetermined size, and the electrode mixture at the portion where the lead 6 for current extraction was welded was scraped to produce a sheet-like positive electrode 2.

  Negative electrode: 98 parts by mass of graphite carbon material powder as a negative electrode active material and 1 part by mass of CMC · Na were dispersed in water to form a slurry. This slurry was applied to both surfaces of a copper negative electrode current collector 4, dried and press-molded to obtain a negative electrode plate. Then, this negative electrode plate was cut into a predetermined size, and the electrode composite material at the portion where the lead 7 for current extraction was welded was scraped to produce a sheet-like negative electrode 3.

Nonaqueous electrolyte: 1 mol / L of LiPF ₆ as a supporting salt in a mixed solvent composed of 25% by volume of ethylene carbonate, 40% by volume of ethyl methyl carbonate, 30% by volume of dimethyl carbonate, and 5% by volume of diethyl carbonate An electrolytic solution was prepared by dissolving at a concentration of.
-Production of protective film 10 (gel-like film: neutralizing member) As the anionic group-containing polymer material, polysaccharides, polyvalent carboxylic acid polymers, or derivatives thereof shown in Table 1 were employed. These anionic groups may be contained in the form of a sodium salt or the like. As the polyvalent cation, calcium ions or barium ions were used as shown in Table 1. The step of preparing a gel containing a polyvalent cation is prepared by preparing a 5% by mass calcium carbonate aqueous solution in the case of calcium ions and a 1% by mass barium chloride aqueous solution in the case of barium ions. An anionic group-containing polymer material was dissolved at a concentration of 1% by mass or less and then poured into a mold to remove moisture. The concentration of the anionic group-containing polymer material is considered to increase the number of ionic crosslinking points when it is concentrated from a low concentration, so the initial concentration of the anionic group-containing polymer material was lowered.

  Even when used in the form of a sodium salt as an anionic group-containing polymer material, an ionic cross-linked product can be obtained without problems by increasing the amount of the aqueous solution of the polyvalent cation and increasing the concentration of the polyvalent cation to a large excess. It was.

  The removal of moisture prevents the polyvalent cations such as calcium carbonate adhering to and near the surface of the gel film from being mixed into the battery. After evaporating the water to a certain extent and removing it from the mold, the surface was washed with pure water to remove the polyvalent cations present on the surface and in the vicinity of the surface, and then vacuum dried at 60 ° C.

  The vacuum drying was performed until the moisture concentration detected by the Karl Fischer method was 100 ppm or less in order to reduce the amount of moisture brought into the battery.

  The thickness and size of the protective film 10 do not greatly contribute to the neutralization performance of hydrogen fluoride, and the mass of the added protective film (the amount of polyvalent cation contained) may affect the amount that can be neutralized. Since it has been found in preliminary tests, the form of the protective film 10 disposed in the battery is equal to or less than the thickness of the battery container to be used, and is set in a range that does not hinder battery performance and assembly properties. It was confirmed that the produced protective film 10 can neutralize the produced hydrogen fluoride in the electrolyte solution by releasing polyvalent cations contained in accordance with the amount of hydrogen fluoride produced from the electrolyte solution. . Moreover, when hydrogen fluoride did not exist, it confirmed that the elution to the non-aqueous electrolyte of the polyvalent cation in a protective film did not become a problem.

  An adhesive layer 11 made of an acrylic pressure-sensitive adhesive material is applied in advance to the manufactured protective film 10, and the protective film 10 is a part A where the positive electrode lead 7 and the negative electrode lead 6 are joined to the battery container 9 using the adhesive layer 11. It was fixed at a position where the electrolyte solution would not touch the (communication part) so as to cover from the inside of the battery. A polypropylene sealing material 5 was firmly bonded in advance to a portion A where the positive electrode lead 7 and the negative electrode lead 6 were bonded to the battery container 9.

  The conductor which comprises the leads 6 and 7 by using an acrylic adhesive material as a joining method of the protective film 10. As a result of being able to adhere to both the sealing material 5 and the polyolefin in the laminated interior constituting the battery case 9, the choice of installation location is expanded. As the acrylic adhesive material, any adhesive material that does not dissolve in the electrolytic solution may be used. In this example, Coponil 5820 (manufactured by Nippon Synthetic Chemical) was used. Although a method of thermocompression bonding the protective film 10 directly to a predetermined place was also attempted, since the protective film becomes sticky when heated, workability is better when directly bonded using an acrylic adhesive than thermocompression bonding. Improved. In addition, instead of (or in addition to) the portions (FIGS. 1 to 3) adjacent to the leads 6 and 7, the protective film 10 is disposed adjacent to the joint portion of the battery container 9 as shown in FIG. It can also be arranged. By arrange | positioning here, the junction part (heat-fusion part) of the battery container 9 can be protected from the hydrogen fluoride etc. which are produced | generated.

  In the case of using barium ions, since the atomic weight of barium is larger than the atomic weight of calcium (40.1) (137.3), the mass to be included was adjusted so that the number of moles was the same.

The amount of ions to be included in the protective film 10 is assumed to be neutralizable by assuming that half of the LiPF ₆ molecules contained in the electrolyte will be consumed by the HF reaction by the end of the battery life. . Therefore, first, for the obtained protective film test examples 1 to 5, the amount of ions contained is determined by atomic absorption method, and the cutout dimensions are adjusted so that the ion concentration is constant with respect to the electrolytic solution. did. In this study, the size of the protective film was adjusted so that the calcium ion was 2 mass% and the barium ion was 7 mass% based on the mass of the electrolyte (25 g: 1M LiPF ₆ ).

Comparative Example 1 was prepared based on Patent Document 1, and Comparative Example 2 was prepared based on Patent Document 2 to create a member corresponding to a protective film (neutralizing member). The amount of cation added inside was the same number of moles as the amount added in the protective film of the example.
-Manufacture of the battery The positive electrode 2 and the negative electrode 3 described above, and the separator 8 made of porous polyolefin and punched into a predetermined size were sequentially laminated to assemble the electrode body. The current collector 1 of the positive electrode 2 and the current collector 4 of the negative electrode 4 of this electrode body were bundled together, and the leads 6 and 7 to which the protective film 10 was bonded were joined by ultrasonic welding (joint portions 61 and 71). . Each of the leads 6 and 7 is sandwiched between two laminated film joining parts (peripheral parts) constituting the battery container 9, and the joining part of the laminated film is heat-sealed in a reduced pressure state to obtain the test battery of this test example. Obtained. In addition, the electrolyte solution was inject | poured before heat sealing | fusion.
(Battery evaluation)
Table 1 also shows the results (high temperature storage test results) of comparing the discharge capacities of the batteries after storage using these test batteries. As experimental conditions for this high-temperature storage test, the fully charged battery was stored at 60 ° C. and 95% RH for 3 months, the discharge capacity (mAh) of the battery was measured, and the rate of change was calculated. At the same time, the peel strength change rate (%) between the lead and the battery container, the visual observation of gas generation inside the battery, and the evaluation of the internal resistance were also performed. The internal resistance was compared using the relative ratio as an index when the internal resistance was 1.0 when no polyvalent cations such as calcium or barium ions were included.

In the measurement of the battery capacity, the test batteries before and after the test were discharged at a constant current up to 3.0 V at a current value corresponding to 0.2 C, and the discharge capacity at this time was defined as the initial discharge capacity and the discharge capacity after the high-temperature storage test. From the discharge capacity and the initial discharge capacity after this high-temperature storage test, the change rate (%) of the discharge capacity was determined according to the following equation. Discharge capacity change rate (%) = [(discharge capacity after high-temperature storage test) / (initial discharge capacity)] × 100
The peel strength was measured according to JIS-K-6854-2 (180 ° C peel test). The ion content was measured by atomic absorption.

  As is clear from Table 1, in any of Test Examples 1 to 5, there is no reduction in the peel strength of the joint and no significant reduction in the capacity retention rate after the high-temperature storage test, and the reduced pressure state of the battery is also maintained. I found out. Therefore, it was suggested that the hydrogen fluoride generated in the electrolyte during the high-temperature storage test was neutralized and rendered harmless.

  In addition, since no significant increase in internal resistance was observed, it was found that there was no adverse effect on the energization resistance and there was little adverse effect on the charge / discharge characteristics.

  In particular, when chitosan was used as the anionic group-containing polymer material (Test Example 3), even better performance was obtained compared to the test batteries of other test examples. This is thought to be due to the addition of the effect of neutralizing hydrogen fluoride by the amino group of chitosan in the chemical structure.

  On the other hand, in the test battery of Comparative Example 1, it was found that hydrogen fluoride was neutralized because the capacity retention rate was 95% and the peel strength was also maintained. However, battery swelling was observed. That is, it is considered that the internal pressure of the battery was increased by the carbon dioxide gas generated by the reaction between calcium carbonate and hydrogen fluoride. When the test battery of Comparative Example 1 was observed in more detail, creep detachment was observed on a part of the negative electrode tab film which was not recognized in other test batteries. Therefore, it was found that when the test battery of Comparative Example 1 was used for a long period of time, the fused portion might be creep broken by the gas pressure. In addition, although the internal resistance in the test battery did not change before and after storage at high temperature, it remained high (5.2 times) compared to the case where calcium carbonate was not added, and the output decreased. It has been found that it can be a factor that accelerates heat generation of batteries and batteries.

  Next, in Comparative Example 2, in the test battery after the high-temperature storage test, the peel strength was greatly reduced, the capacity retention rate was also reduced, and the internal resistance was increased. This is presumed to be because the acrylic resin cured by radical reaction (which does not become a gel) is used, so there is no function of slow release of ions from the electrolyte and hydrogen fluoride cannot be neutralized. it can. That is, it is considered that the nickel plating layer on the surface of the negative electrode lead 7 was corroded by the generated hydrogen fluoride. In addition, since the expansion of the battery container (relaxation of the reduced pressure state) was observed with the generation of gas derived from the decomposition of the electrolytic solution, when it was used for a long period of time, it was creep-ruptured as in Comparative Example 1. It turns out that there is a possibility.

  As described above, the batteries of Test Examples 1 to 5 embodying the secondary battery of the present invention have a protective film (neutralizing member) in the battery, so that the product generated in the battery (hydrogen fluoride) It has become clear that it is possible to suppress a decrease in battery performance due to the above. In particular, it was found that calcium ions as polyvalent cations can achieve the same effect with a smaller addition amount than barium ions. Moreover, from the result that it is desirable to employ chitosan as the anionic group-containing polymer material, the anionic group-containing polymer material contains not only an anionic group (carboxyl group) but also a cationic group (amino group, etc.). I found it desirable.

DESCRIPTION OF SYMBOLS 2 ... Positive electrode 1 ... Positive electrode collector 3 ... Negative electrode 4 ... Negative electrode collector 5 ... Sealing material 6 ... Positive electrode lead 7 ... Negative electrode lead 8 ... Separator 9 ... Battery container 10 ... Protective film (neutralization member)
11 ... Adhesive layer (made of acrylic adhesive)
A ... Joining part (communication part)

Claims (7)

A non-aqueous electrolyte secondary battery comprising positive and negative electrodes capable of inserting and extracting lithium ions and a non-aqueous electrolyte,
A gel comprising a polyvalent cation, an anionic group-containing polymer material crosslinked with the polyvalent cation, and a dispersion medium, and having a neutralizing member disposed at a position in contact with the non-aqueous electrolyte A non-aqueous electrolyte secondary battery.   The nonaqueous electrolyte secondary battery according to claim 1, wherein the anionic group of the anionic group-containing polymer material is a carboxyl group.   The nonaqueous electrolyte secondary battery according to claim 2, wherein the anionic group-containing polymer material is a carboxyl group-containing polysaccharide or poly (meth) acrylic acid.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the polyvalent cation is an alkaline earth metal ion.   The nonaqueous electrolyte secondary battery according to claim 4, wherein the polyvalent cation is at least one of calcium ions and barium ions.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the neutralizing member is fixed by an acrylic adhesive material. A battery container that houses the positive and negative electrodes and the electrolyte, and has a communication portion that communicates inside and outside;
A lead that electrically connects the inside and outside of the battery container through the communication portion of the battery container;
A sealing material for sealing the communication portion of the main body,
The non-aqueous electrolyte secondary battery according to claim 1, wherein the neutralizing member is disposed adjacent to the lead or the sealing material.

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