JP2006210208A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery having high energy density superior even when an active material of high Si content in cycle characteristics because current collecting characteristics of the negative electrode are reduced and cycle characteristics are inferior because swelling and contraction accompanying charge and discharge is large when using active material with large Si content. <P>SOLUTION: This is the nonaqueous electrolyte secondary battery composed of the positive electrode in which lithium ions can be stored and released, the negative electrode consisting of a negative electrode active material containing Si, and nonaqueous electrolyte composed of Li-ion conductive nonaqueous electrolyte, and contains high polymer containing lithiated carboxyl group in the negative electrode pillar. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and more specifically, the present invention relates to a non-aqueous electrolyte secondary battery having high energy density and excellent long-term cycle characteristics.

  In general, non-aqueous electrolyte secondary batteries have a high energy density and can be reduced in size and weight, so that the demand as a main power source for various electronic devices and a power source for memory backup is increasing year by year. In recent years, with the remarkable development of portable electronic devices and the like, there is a strong demand for non-aqueous electrolyte secondary batteries with a high energy density from the viewpoints of further miniaturization, higher performance, and maintenance-free devices.

  On the other hand, in the manufacture of mobile devices, as a method for mounting components on a printed circuit board, reflow soldering capable of soldering a large number of electronic components at a high density is often employed. For reflow soldering, a solder cream or the like is applied to the part to be soldered on the board, and the parts are mounted in a furnace in a high-temperature atmosphere set so that the soldered part is 200 to 260 ° C. This is a method of performing soldering by melting the solder by passing the solder. For this reason, non-aqueous electrolyte secondary batteries for memory backup applications themselves are also required to have heat resistance, and studies have been made on the use of heat-resistant materials for battery components such as electrolytes, separators, and gaskets. Has been done.

  Since battery characteristics largely depend on the positive electrode and negative electrode characteristics, many studies on these positive and negative electrodes have been conducted. The positive electrode mixture and the negative electrode mixture are composed of an active material responsible for an electron transfer reaction, a conductive agent for imparting electron conductivity in the electrode, and a binder for joining them together.

  The binder serves to bond the active material and the conductive agent and to bind the mixture and the current collector.

  Conventionally, fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) have been used as binders for active materials for non-aqueous electrolyte secondary batteries. These resins are stable with respect to the non-aqueous electrolyte and have good characteristics for binding the active material and the conductive additive. However, PTFE, PVDF, etc., which are fluororesins, for example, in the case of active materials such as Si and Sn that undergo large volume changes accompanying lithium ion insertion and desorption reactions, maintain the adhesion of the mixture due to volume changes associated with charge and discharge. There was a problem that the mixture was not separated and the adhesion between the mixture and the current collector was lowered. As a result, the current collection performance decreases with charge / discharge, the utilization factor of the electrode active material decreases, and as a result, the charge / discharge cycle life is poor.

  With respect to such a problem, Patent Document 1 contains a water-soluble polymer such as an acrylic acid polymer in the electrode mixture of the positive electrode and / or the negative electrode, thereby improving the current collecting performance of the electrode. As compared with the case where a fluororesin is used as a binder, an electrode configuration having a high energy density, excellent high-rate charge / discharge characteristics, and excellent long-term cycle characteristics is obtained.

In Patent Document 2, a lithium salt of polyacrylic acid or methacrylic acid is used as a binder for a lithium ion secondary battery in which the negative electrode is a carbonaceous material and the positive electrode is a composite metal oxide. It is said that a slurry excellent in applicability to the body can be obtained and a lithium ion secondary battery excellent in charge / discharge cycle characteristics can be obtained.
Japanese Patent Laid-Open No. 9-289022 Japanese Patent Laid-Open No. 2001-282859

  The negative electrode active material containing Si has an extremely large expansion / contraction during charge / discharge compared to the carbonaceous negative electrode active material used in the lithium ion secondary battery. Further, the expansion / contraction behavior during charging / discharging depends on the amount of Si used in the active material. That is, when the amount of Si used in the active material increases, the energy density per active material increases, but when the amount of Li insertion / extraction associated with charge / discharge is also increased, the volume change of the active material also increases. Therefore, when using an active material with a high Si content, the volume change associated with charging / discharging increases, so in the binder or acrylic acid polymer used in conventional lithium ion secondary batteries, the amount added There is a need to improve the adhesiveness of the mixture by increasing the amount.

  In addition, since a high molecular polymer such as an acrylic acid polymer or a methacrylic acid polymer has a carboxyl group represented by the chemical formula (—COOH) in the repeating unit of the polymer, lithium and carboxyl groups are not charged during charge and discharge. An irreversible side reaction occurs between them, resulting in lithium that cannot be used for charging and discharging. Furthermore, accumulation of gas generated by the side reaction causes an increase in battery internal resistance. For these reasons, a non-aqueous electrolyte secondary battery using a polyacrylic acid polymer as a binder cannot satisfy the long-term cycle life characteristics.

  Therefore, the present invention provides a high energy density non-aqueous electrolyte secondary battery that solves the above problems, suppresses a decrease in battery capacity when charging and discharging are repeated, and has excellent cycle characteristics. Objective.

  The present invention has been made as a result of various studies to solve the above-described problems, and includes a positive electrode capable of occluding and releasing lithium ions, a negative electrode made of a negative electrode active material containing Si, and a lithium ion conductive non-conductive material. A non-aqueous electrolyte secondary battery comprising a water electrolyte, wherein the negative electrode contains a polymer containing a lithiated carboxyl group, and the polymer containing a lithiated carboxyl group is a binder By using as, the adhesive force as a binder increases, As a result, the nonaqueous electrolyte secondary battery excellent in the charge / discharge cycle characteristic can be provided. Furthermore, since the activity of the carboxyl group can be reduced by lithiation, the side reaction occurring between the lithium ion and the carboxyl group involved in the battery reaction can be suppressed, and the amount of gas generated by the side reaction can also be suppressed. An increase in battery internal resistance can also be suppressed.

  According to the present invention, a non-aqueous electrolyte secondary battery having a very high energy density and excellent charge / discharge cycle characteristics can be provided by using a polymer containing a lithiated carboxyl group as a binder. .

  The present invention is a nonaqueous electrolyte secondary battery comprising a positive electrode capable of occluding and releasing lithium ions, a negative electrode having Si in the negative electrode, and a lithium ion conductive nonaqueous electrolyte, wherein a lithiumated carboxyl group is formed in the negative electrode. As a high molecular polymer containing a lithiated carboxyl group to be used, a carboxyl group (—COOH) in a high molecular polymer having a carboxyl group that is an acidic compound, For example, the carboxyl group (—COOH) can be lithium-chlorinated to (—COOLi) by neutralizing with lithium hydroxide.

When the high molecular polymer having a carboxyl group is neutralized, the adhesive force as a binder becomes strong. This reason can be presumed to be due to the structural change accompanying lithium chloride of the polymer having a carboxyl group. The degree of dissociation of the carboxyl group of the polymer is increased by lithium chloride. For this reason, repulsive force due to electric charge is generated between the carboxyl groups, and the polymer chain tends to extend in a linear rod shape as compared with before lithium chloride. As a result, the effective charge in the polymer increases, and the electrostatic interaction that acts between the polymer and the active material, conductive agent, and current collector is strengthened. Will be stronger.

  Examples of the lithiated polymer having a carboxyl group include lithiated acrylic acid polymer, lithiated methacrylic acid polymer, lithiated fumaric acid polymer, lithiated maleic acid polymer, and lithiated itacone. Among them, the use of a lithiated acrylic acid polymer, a lithiated methacrylic acid polymer, or a lithiated acrylic acid-methacrylic acid copolymer is particularly effective in improving charge / discharge cycle characteristics.

  Furthermore, in the present invention, it has been confirmed that the use of a polymer containing a lithiated carboxyl group whose neutralization degree is adjusted to 40% or more and 100% or less as a binder is effective in improving charge / discharge characteristics. It was. The “degree of neutralization” in the present invention is the number of lithiated carboxyl groups (—COOLi) relative to the number of carboxyl groups contained in the polymer before lithiation. That is, the degree of neutralization is 100% in a polymer containing a completely neutralized lithiated carboxyl group.

  In addition, considering the battery characteristics, it is appropriate to keep the addition amount of the polymer having a lithiated carboxyl group in the mixture to the minimum amount that can maintain the adhesion of the mixture and the adhesion to the current collector. In view of the above, the polymer having a lithiated carboxyl group in the mixture is preferably in the range of 0.5 to 30% by weight with respect to the weight of the negative electrode active material.

  Furthermore, the polymer having a lithiated carboxyl group of the present invention may be a polymer having a carboxyl group crosslinked.

  In the present invention, the active material having Si used for the negative electrode means a simple substance of Si, a Si alloy, SiO or the like, and includes any of single crystal, polycrystal and amorphous.

  Moreover, when Si simple substance is used as the negative electrode active material, since the Si content in the active material becomes the largest, it is possible to increase the capacity of the battery, but for the purpose of imparting electronic conductivity to the negative electrode active material. It is more preferable to introduce a high electron conductive material such as Fe, Ti, Co, or Cu that can be alloyed with Si.

  Among these, when an active material having a high Si content is used as the negative electrode active material, the high molecular weight polymer containing a lithiated carboxyl group of the present invention is mixed as a binder, so that the binder can be bound as compared to before the lithiation treatment. Adhesive strength of the agent is improved, and the activity of the carboxyl group can be reduced by lithiation of the carboxyl group, so that irreversible side reactions can be suppressed, and charge / discharge cycle characteristics can be greatly improved.

  Further, the use of the polymer containing a lithiated carboxyl group of the present invention as a negative electrode active material having a relatively low Si content such as SiO improves the charge / discharge cycle characteristics due to the above effects. This is effective because it is possible to reduce the binder content in the mixture.

Some negative electrode active materials do not contain lithium at the time of manufacture, but when acting as a negative electrode active material, they can be used by making them contain lithium by chemical means, electrochemical means, etc. Become.

  The negative electrode may be, for example, the above-described negative electrode active material, graphite, such as natural graphite (such as flake graphite), artificial graphite, or expanded graphite, acetylene black, ketjen black, channel black, furnace black, lamp black, if necessary. Carbon blacks such as thermal black, conductive fibers such as carbon fibers and metal fibers, metal powders such as copper and nickel, and organic conductive materials such as polyphenylene derivatives may be included alone or as a mixture thereof. it can. An electron conduction assistant such as carbon black or graphite is added, and a binder and an aqueous solvent are further added and mixed to form a mixture or paint. In preparing the mixture or paint, the binder is dissolved in an aqueous solvent in advance to form a solution, and the binder solution is mixed with the negative electrode active material to prepare the mixture or paint.

  Although the addition amount of a electrically conductive agent is not specifically limited, 1-50 weight% is preferable with respect to a negative electrode active material, and 1-40 weight% is especially preferable. Moreover, since the negative electrode material of the present invention itself has electronic conductivity, it can function as a battery without adding a conductive material.

  The nonaqueous electrolyte used in the present invention is composed of a solvent and a supporting electrolyte that dissolves in the solvent. Examples of non-aqueous solvents include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), cyclic carbonates such as vinylene carbonate (VC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl. Chain carbonates such as methyl carbonate (EMC) and dipropyl carbonate (DPC), aliphatic carboxylic acid esters such as methyl formate, methyl acetate, methyl propionate and ethyl propionate, and γ-lactones such as γ-butyrolactone Chain ethers such as 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE) and ethoxymethoxyethane (EME), cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, dimethylsulfate Hoxide, 1,3-dioxolane, formamide, acetamide, dimethylformamide, dioxolane, acetonitrile, propylnitrile, nitromethane, ethyl monoglyme, phosphate triester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl -2-imidazolidinone, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ethyl ether, 1,3-propane sultone, anisole, dimethyl sulfoxide, N-methylpyrrolidone, butyl diglyme, methyl tetraglyme An aprotic organic solvent such as γ-butyl lactone can be used, and one kind or a mixture of two or more kinds thereof can be used. In addition, when imparting reflow resistance to a battery, one or two of ethylene carbonate, propylene carbonate, sulfolane, butyl diglyme, methyl tetraglyme, γ-butyl lactone, etc., having a boiling point of 200 ° C. or higher at normal pressure It is preferable to use a solvent obtained by mixing the above.

Examples of the supporting electrolyte dissolved in these solvents include LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAlCl ₄ , LiSbF ₆ , LiSCN, LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li (CF ₃ SO ₂ ) ₂ , LiAsF _6. , LiB ₁₀ Cl ₁₀ , lower aliphatic lithium carboxylate, LiCl, LiBr, LiI, chloroborane lithium, lithium tetraphenylborate, LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₃ ) _2, etc. These can be used alone or in combination of two or more in an electrolyte solution using these.

The supporting electrolyte in the electrolytic solution is not particularly limited. Among these, imides such as LiN (CF ₃ SO ₂ ) ₂ and LiN (C ₂ F ₅ SO ₃ ) ₂ may be included. More preferred.

  The battery of the present invention is preferably produced in a dehumidified atmosphere or an inert atmosphere, but it is also desirable that the battery components are dried before battery assembly. As a method for drying the pellets, hot air, vacuum, infrared rays, far infrared rays, and electron beams can be used alone or in combination.

  However, when the polymer containing a lithiated carboxyl group of the present invention is used as a binder for the negative electrode, the polymer itself is a very strong hydrophilic compound. There is a possibility that moisture removal may be insufficient, and the negative electrode may absorb moisture during the manufacturing process. In that case, the battery will eventually contain moisture, and when a fluorinated support electrolyte is used, the lithium salt in the electrolyte will hydrolyze inside the battery, generating hydrogen fluoride, phosphoric acid, etc. End up. And the problem that the capacity | capacitance of a positive electrode and a negative electrode falls resulting from the generated hooker hydrogen, phosphoric acid, etc. arises, This problem is remarkable especially at high temperature, and the capacity | capacitance degradation after high temperature storage becomes a big problem. .

  Lithium imide salt is a stable compound and does not react with water to generate hydrogen fluoride, phosphoric acid or the like. For this reason, hydrogen fluoride, phosphoric acid, etc. are not generated even when the amount of water contained in the battery is relatively large by using a water-soluble compound as the binder. That is, the capacity does not decrease due to the lithium salt, and capacity deterioration at the time of high temperature insulation does not become a problem.

Therefore, in the non-aqueous electrolyte secondary battery according to the present invention, by containing the above lithium imide salt as a supporting electrolyte contained in the non-aqueous electrolyte, hydrogen fluoride and phosphoric acid in the non-aqueous electrolyte are included. Since generation can be reduced and prevented, it is possible to reduce or prevent a decrease in capacity of the positive electrode and the negative electrode due to hydrogen fluoride or phosphoric acid. This effect does not change even at high temperatures, and can be obtained in the same manner as normal temperatures. That is, it is possible to reduce and prevent a decrease in capacity even at a high temperature of 60 ° C. or higher at which LiPF _{6 as} a conventional supporting electrolyte becomes particularly unstable. Thereby, in the present invention, it is possible to reduce and prevent capacity deterioration after storage at high temperature, and it is possible to realize a non-aqueous electrolyte secondary battery excellent in high temperature stability.

A particularly preferable non-aqueous electrolyte in the present invention is an electrolytic solution containing LiN (CF ₃ SO ₃ ) ₂ or LiN (C ₂ F ₅ SO ₃ ) ₂ as a supporting electrolyte. The amount of these lithium salts dissolved in the non-aqueous solvent Is not particularly limited, but is preferably 0.2 to 2.0 mol / l. In particular, 0.5 to 1.5 mol / l is more preferable.

In addition to the electrolytic solution, the following solid electrolyte can also be used. The solid electrolyte is classified into an inorganic solid electrolyte and an organic solid electrolyte. Well-known inorganic solid electrolytes include Li nitrides, halides, oxyacid salts, and the like. Among _{them, Li 4 SiO 4, Li 4} SiO 4 -LiI-LiOH, xLi 3 PO 4 - (1-x) Li 4 SiO 4, Li 2 SiS 3, Li 3 PO4-Li 2 S-SiS 2, phosphosulfurized Compounds and the like are effective. For organic solid electrolytes, for example, polymer materials such as polyethylene oxide, polypropylene oxide, polyphosphazene, polyaziridine, polyethylene sulfide, polyvinyl alcohol, polyvinylidene fluoride, polyhexafluoropropylene, and their derivatives, mixtures, and composites are effective. is there.

In addition, a lithium-containing or non-containing compound can be used for the positive electrode material used in the present invention. For example, Li _x CoO ₂ , Li _x NiO ₂ , Li _x MnO ₂ , Li ₄ Mn ₅ O ₁₂ , Li ₂ Mn ₄ O ₉ , Li _x Co _y Ni _1-y O ₂ , Li _x Co _y M _{1-y O z, Li x Ni 1-} y M y O z, Li x Mn 2 O 4, Li x Mn 2-y M y O 4 (M = Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, B) (where x = 0 to 1.2, y = 0 to 0.9, z = 2.0 to 2.3). It is done. Here, said x value is a value before the start of charging / discharging, and it increases / decreases by charging / discharging. However, other positive electrode materials such as transition metal chalcogenides, vanadium oxides and lithium compounds thereof, niobium oxides and lithium compounds thereof, conjugated polymers using organic conductive substances, and chevrel phase compounds can also be used. . It is also possible to use a mixture of a plurality of different positive electrode materials.

  Further, the positive electrode conductive agent used in the present invention may be any electron conductive material that does not cause a chemical change at the charge / discharge potential of the positive electrode material used. For example, graphite such as natural graphite (such as flake graphite), artificial graphite, carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, and conductive such as carbon fiber and metal fiber Conductive fibers, metal powders such as carbon fluoride and aluminum, conductive whiskers such as zinc oxide and potassium titanate, conductive metal oxides such as titanium oxide, or organic conductive materials such as polyphenylene derivatives, etc. It can be included as a mixture thereof. Among these conductive agents, artificial graphite and acetylene black are particularly preferable. Although the addition amount of a electrically conductive agent is not specifically limited, 1-50% is preferable by weight ratio with respect to positive mix, and 1-30% is especially preferable.

  Moreover, as a binder for positive electrodes used for this invention, any of a thermoplastic resin and a thermosetting resin may be sufficient. Preferred binders in the present invention include, for example, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene. -Hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene -Tetrafluoroethylene copolymer (ETFE resin), polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene Polymer, ethylene-chlorotrifluoroethylene copolymer (ECTFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer, ethylene-acrylic Examples thereof include an acid copolymer, an ethylene-methacrylic acid copolymer, an ethylene-methyl acrylate copolymer, and an ethylene-methyl methacrylate copolymer, and these materials can be used alone or as a mixture.

  Moreover, even if the high molecular weight polymer containing the lithiated carcarboxyl group of the present invention is added to the positive electrode, the same effect as when used for the negative electrode can be obtained. Therefore, the binder of this research is effective when used for either the positive electrode or the negative electrode, and may be used for both the positive electrode and the negative electrode.

  In addition, as the separator used in the present invention, an insulating microporous thin film having a large ion permeability and a predetermined mechanical strength is used. A sheet, a nonwoven fabric or a woven fabric made of a single or combined polymer such as polypropylene, polyethylene, polyphenylene sulfide, polyethylene terephthalate, polyamide, polyimide, or glass fiber is used because of its organic solvent resistance and hydrophobicity. The thickness of the separator is generally 10 to 300 μm. The porosity is determined according to the permeability of the electrons and ions, the material, and the film pressure, but is generally preferably 30 to 80%. In general, inexpensive polypropylene is used. However, in order to impart reflow resistance to the battery, it is preferable to use polypropylene sulfide, polyethylene terephthalate, polyamide, polyimide, or the like having a heat distortion temperature of 230 ° C. or higher.

A polymer in which an organic electrolytic solution composed of a solvent and a lithium salt dissolved in the solvent is absorbed and held in a polymer material is included in the positive electrode mixture and the negative electrode mixture, and the organic electrolytic solution is absorbed and held. It is also possible to constitute a battery in which a porous separator made of is integrated with a positive electrode and a negative electrode. The polymer material may be any material that can absorb and hold the organic electrolyte solution.

  Insulation gaskets use polymers such as polypropylene, polyphenylene sulfide, polyetherketone, polyamide, polyimide, liquid crystal polymer alone or in combination, or a combination of fillers such as inorganic fibers, etc. in terms of stability to electrolyte and heat resistance. It is done. In general, inexpensive polypropylene is used. However, in order to impart reflow resistance to the battery, it is preferable to use polyphenylene sulfide, polyether ketone, polyimide, or liquid crystal polymer having a heat distortion temperature of 230 ° C. or higher. .

  Furthermore, in order to improve the confidentiality of the battery, the gasket may be coated with a sealing material. At this time, it is also possible to coat either or both of the inner wall portion and the outer peripheral portion of the gasket. Further, instead of coating the outer peripheral portion of the gasket, a sealing material may be coated in advance on the inner wall portion of the positive electrode can. As a kind of the sealing material, there are asphalt pitch, butyl rubber, fluorinated oil, etc., but when the sealing material is transparent, it is preferable to color it to clarify the presence or absence of application.

Example 1
Examples of the present invention will be described in detail below. However, the contents of the present invention are not limited to these examples.

  FIG. 1 is a cross-sectional view of a nonaqueous electrolyte secondary battery of the present invention. In this example, a battery having a battery size of 6.8 mm in diameter and 2.1 mm in thickness was produced. In FIG. 1, the positive electrode can 1 also serves as a positive electrode terminal and is made of stainless steel having excellent corrosion resistance. The negative electrode can 2 also serves as a negative electrode terminal and is made of stainless steel made of the same material as the positive electrode can 1. The gasket 3 insulates the positive electrode can 1 and the negative electrode can 2 and is made of polypropylene. A pitch is applied to the surface where the positive electrode can 1 and the negative electrode can 2 are in contact with the gasket 3. The positive electrode 4 is obtained by mixing manganese dioxide and lithium hydroxide in a molar ratio of 2: 1 and then firing in air at 400 ° C. for 12 hours, lithium manganate, acetylene black as a conductive agent, binder A mixture of a fluororesin aqueous dispersion and a weight ratio of solids of 88: 6: 6 is molded into a pellet having a diameter of 4 mm and a thickness of 1.0 mm, and then at 250 ° C. for 12 hours. It is dry. The negative electrode 5 has a diameter of 4 mm obtained by mixing a negative electrode active material containing Si, graphite as a conductive agent, and a polymer containing a lithiated carboxyl group as a binder in a weight ratio of 70:20:10. This was formed into a pellet having a thickness of 0.3 mm and then dried at 200 ° C. for 12 hours. In order to alloy with lithium, a lithium foil is pressure-bonded to the surface of the negative electrode 5 during battery assembly, and lithium is occluded in the presence of an electrolytic solution to make an lithium alloy electrochemically, and this is used as the negative electrode. Yes. Further, a separator 6 made of a polypropylene nonwoven fabric was disposed between the positive electrode 4 and the negative electrode 5.

  Hereinafter, the case where a Ti 41 wt% -Si 59 wt% alloy is used as the negative electrode active material will be described.

  Ti 41 wt% -Si 59 wt% alloy was put into a vibrating ball mill container with Ti and Si at a weight ratio of 41:59, then mechanical milling was performed using stainless steel balls with a diameter of 15 mm, and then classified into particles of 63 μm or less. It was produced by sizing.

For the electrolyte, a mixed solvent of PC: EC: DME = 1: 1: 1 is used as an organic solvent in a volume ratio, and LiN (CF ₃ SO ₂ ) ₂ is dissolved as a supporting electrolyte in a ratio of 1 mol / l. It was used. A battery container composed of the positive electrode can 1, the negative electrode can 2 and the gasket 3 is filled with 15 μl.

  Electrode in which Ti 41 wt% -Si 59 wt% alloy as a negative electrode active material, carbon black as a conductive agent, and lithium acrylic acid polymer as a binder are mixed in a weight ratio of 100: 20: 10 as a solid content. A mixture was prepared. The electrode mixture was molded into a pellet shape having a diameter of 4 mm and a thickness of 0.3 mm, and then dried at 200 ° C. for 12 hours to form a positive electrode 4. A coin-type test cell was produced using the electrode produced as described above, and was designated as battery A1.

  In addition, as a binder, instead of a lithiated acrylic acid polymer (neutralization degree 100%), a lithiated methacrylic acid polymer (neutralization degree 100%), a lithiated acrylic acid-methacrylic acid copolymer (neutralization degree) The batteries manufactured in the same manner as the battery A1 except that 100%) are used are referred to as a battery A2 and a battery A3, respectively.

  On the other hand, in the batteries A1 to A3, the binder was not lithiated, and an acrylic acid polymer (neutralization degree 0%), a methacrylic acid polymer (neutralization degree 0%), acrylic acid-methacrylic acid The batteries using the copolymer (degree of neutralization 0%) were designated as battery a1, battery a2, and battery a3, respectively. In addition, the neutralization treatment is not lithiated, but sodium or potassium with sodium hydroxide, potassium hydroxide or the like, sodium-treated acrylic acid polymer (neutralization degree 100%), potassium-treated acrylic acid polymer (neutralized) The batteries produced in the same manner as the battery A1 except that the degree of use was 100%) were designated as battery a4 and battery a5, respectively.

  And as charging / discharging of a test cell, 200 cycles were performed in the voltage range of 2.0V to 3.3V with a constant current of 0.1 mA in both charging and discharging. Table 1 shows the initial battery internal resistance and the battery internal resistance after 200 cycles, the battery capacity retention rate after 200 cycles when the initial value is 100, and the strength of the negative electrode pellet, as measured by the 1 kHz AC impedance method. In the measurement of the strength of each negative electrode pellet of the batteries A1 to A3 and the batteries a1 to a5, the negative electrode pellet 12 was placed on the jig 11 as shown in FIG. The pushing rod 13 is pressed against the placed negative electrode pellet 12, and the weight applied to the pellet with the pushing rod 13 is gradually increased, and the maximum weight when the negative electrode pellet 12 is broken is simply determined as the strength of each negative electrode pellet. did. In measuring the strength, each negative electrode pellet was previously dried at 200 ° C. for 12 hours.

As shown in Table 1, in the case of a negative electrode active material having Si, when a polymer containing a lithiated carboxyl group is used as a negative electrode binder, a polymer containing a carboxyl group that has not been lithiated is converted into a negative electrode binder. It was confirmed that the battery internal resistance was decreased and the pellet strength was increased as compared with the case of using as an adhesive, and the battery capacity retention rate was improved. By using a lithiated binder, the adhesion between the negative electrode constituent materials is improved, and the pellet strength is increased, so that the binding of the mixture is maintained even after cycling, and it can be assumed that the cycle characteristics have been improved. . In addition, when the neutralization treatment of the polymer having a carboxyl group is not lithiated but sodium or potassium, the effect of suppressing the reduction in discharge capacity is small as shown in Table 1. . This is because in the case of sodium or potassium, the strength of the pellet is increased and the bonding between the negative electrode constituent materials becomes firm. However, since side reactions that occur during charging and discharging cannot be suppressed, the decrease in battery capacity can be suppressed. It is estimated that there was not.

(Example 2)
Instead of the Ti 41 wt% -Si 59 wt% alloy of the battery A1 and the battery a1, Ti 23 wt% -Si 77 wt% alloy and Ti 5 wt% -Si 95 wt% alloy prepared by changing the mixing ratio of Ti and Si were used as the negative electrode. A case where the active material is used will be described. The other production conditions were the same. In a Ti 23 wt% -Si 77 wt% alloy, a battery using a lithiated acrylic acid polymer (neutralization degree 100%) was designated as battery B1, and an acrylic acid polymer not subjected to lithiation treatment (neutralization degree 0%). The battery used is battery b1. In addition, in a Ti 5 wt% -Si 95 wt% alloy, a battery using a lithiated acrylic acid polymer (neutralization degree 100%) was designated as battery B2, and an acrylic acid polymer (neutralization degree 0) was not subjected to lithiation treatment. %) Was designated as battery b2, and the others were made in the same manner as battery A1 and battery a1, and coin-type test cells were produced to evaluate the battery characteristics. Table 2 shows the results of the batteries A1 and a1.

  In the case of a negative electrode active material having Si, as the Si content in the negative electrode active material increases, the active material greatly expands and contracts, and the cycle characteristics tend to deteriorate. However, when a polymer containing a lithiated carboxyl group is used as the binder for the negative electrode, the strength as the binder increases, so that it functions effectively as a binder even when the Si content is high, so that cycle characteristics The improvement was confirmed.

(Example 3)
In place of the Ti 41 wt% -Si 59 wt% alloy of the battery A1, a commercially available Si simple substance was pulverized and sized into particles of 63 μm or less as the negative electrode active material, and the lithium binder polymer ( Battery C is obtained using a neutralization degree 100%, and battery c is obtained using an acrylic acid polymer (neutralization degree 0%) that has not been lithiated as a negative electrode binder. Otherwise, a coin-type test cell was prepared in the same manner as the battery A1, and the battery characteristics were evaluated. The results are shown in Table 3.

  In the case where Si alone is a negative electrode active material, it is a high capacity active material, but it is known that the cycle life is very poor due to extremely large expansion and contraction. However, as shown in Table 3, the capacity maintenance rate after 200 cycles of the battery using a polymer containing a carboxyl group that has not been lithiated is less than 5%, but it contains a lithiated carboxyl group. Using a polymer, the battery capacity retention rate was about 40%, and it was confirmed that the cycle characteristics could be greatly improved.

Example 4
In place of the Ti 41 wt% -Si 59 wt% alloy of the battery A1, a commercially available SiO pulverized and sized particles having a particle size of 63 μm or less were used as the negative electrode active material. Battery D is a battery using a degree of sum (100%), and battery d is a battery using an acrylic acid polymer (neutralization degree 0%) that has not been lithiated as a negative electrode binder. Otherwise, a coin-type test cell was prepared in the same manner as the battery A1, and the battery characteristics were evaluated. The results are shown in Table 4.

The Si content in SiO was 50 mol%, and since the Si content was small, the expansion and shrinkage of the negative electrode was small, and the presence or absence of lithiation treatment of the polymer containing a carboxyl group did not affect the charge / discharge cycle characteristics. I guess that. However, when SiO is used for the negative electrode active material, lithium and oxygen in SiO react to generate Li ₂ O, and therefore lithium that can participate in charging and discharging is reduced. In comparison, it can be inferred that the capacity retention rate after 200 cycles has decreased. However, since the polymer polymer containing a carboxylated lithium group has a high binder strength, the amount of binder added can be reduced. Even when the active material is SiO, the carboxyl group of the present invention can be reduced. Use of the polymer polymer containing is effective in terms of increasing the battery capacity.

(Example 5)
Instead of the lithiated acrylic acid polymer (neutralization degree: 100%) of the battery A1, a lithiated acrylic acid polymer prepared to have various neutralization degrees was used as the negative electrode binder. Produced batteries F1 to F9 in the same manner as battery A1, and evaluated battery characteristics. FIG. 3 shows the relationship between the degree of neutralization at this time and the pH value of the lithiated acrylic acid polymer produced by the neutralization treatment (1 wt% aqueous solution). The results are shown in Table 5 together with the value of the battery A1.

As shown in Table 5, as the degree of neutralization of the acrylic acid polymer increased, the negative electrode pellet strength increased and the battery capacity retention rate increased. In particular, when the degree of neutralization is 40% or more, the capacity maintenance rate is 80% or more even after 200 cycles, and it is understood that the capacity maintenance rate is remarkably improved as compared with the case of less than 10%. It can also be seen that the capacity retention rate is lowered when the degree of neutralization exceeds 100%, that is, when neutralization is performed excessively. Therefore, when an acrylic acid polymer is used as a binder, it is charge / discharge to use a lithium salt prepared to a neutralization degree of 40 to 100%, more preferably 60 to 100%. It was confirmed that it was effective by improving the characteristics. This is because an aqueous solution containing an excessively neutralized lithiated acrylic acid polymer becomes strongly alkaline, so that an active material containing Si reacts with an aqueous solution in a strong alkaline state during the preparation of a mixture, so that a high capacity negative electrode active It is presumed that this is due to the deterioration of the properties as a substance.

  In addition, although the case of the lithiated lithium acrylate polymer adjusted to various degree of neutralization was demonstrated as a binder, the binder was lithiated methacrylic acid, lithium adjusted to various degree of neutralization. It was confirmed that the same results were obtained for the case of the acrylated acrylic acid-methacrylic acid polymer.

(Example 6)
The negative electrode active material, Ti 41 wt% -Si 59 wt% alloy, the conductive agent carbon black, and the lithiated acrylic acid polymer as the binder in a weight ratio of solids of 100: 20: 0.3 (active material) 100: 20: 0.5 (0.5% by weight binder relative to the active material), 100: 20: 1.0 (based on the active material) 100: 20: 5.0 (5.0% by weight binder with respect to the active material), 100: 20: 20 (bound with respect to the active material) The ratio of the binder is 20% by weight), 100: 20: 30 (the binder is 30% by weight with respect to the active material), and the ratio is 100: 20: 40 (the binder is 40% by weight with respect to the active material). The batteries using the mixed electrode mixture are designated as battery G1, battery G2, battery G3, battery G4, battery G5, battery G6, and battery G7, respectively. It was. Otherwise, a coin-type test cell was prepared in the same manner as the battery A1, and the battery characteristics were evaluated. The results are shown in Table 6 together with the value of the battery A1.

  As shown in Table 6, as the amount of the binder in the negative electrode mixture increased, the negative electrode pellet strength increased and the battery capacity retention rate increased. In particular, when the amount of the binder is 0.5% by weight or more, the capacity maintenance rate is 80% or more even after 200 cycles, and the capacity maintenance rate is remarkably improved as compared with the case of less than 0.5% by weight. I understand that. In addition, it can be seen that the capacity retention rate is reduced when the amount of the binder exceeds 30%, that is, when the binder is used in excess. This is because when the binder is excessively added, the insulating binder increases, the conductivity in the negative electrode mixture decreases, and the capacity retention rate decreases because the battery internal resistance increases. I can guess. When an acrylic acid polymer is used as a binder, the neutralization degree is adjusted to 0.5 to 30% by weight, more preferably 1, 0 to 20% by weight with respect to the negative electrode active material. It was confirmed that the use was effective in improving the charge / discharge characteristics.

(Example 7)
Further, LiN (C ₂ F ₅ SO ₂ ) ₂ , LiClO ₄ , LiPF ₆ , LiCF ₃ SO ₃ is used as the supporting electrolyte instead of LiN (CF ₃ SO ₂ ) ₂ that is the supporting electrolyte of the battery A1, and the negative electrode The batteries using the lithiated acrylic acid polymer of the present invention (neutralization degree 100%) as the binder are referred to as a battery H1, a battery h1, a battery h2, and a battery h3, respectively. Otherwise, a coin-type test cell was prepared in the same manner as the battery A1, and the battery characteristics were evaluated. The results are shown in Table 7 together with the value of the battery A1.

As shown in Table 7, when LiN (C ₂ F ₅ SO ₂ ) ₂ was used instead of LiN (CF ₃ SO ₂ ) ₂ , the capacity retention was almost the same, but LiClO ₄ , LiPF ₆ When LiCF ₃ SO ₃ was used, it was confirmed that the capacity retention rate decreased. From this, when using a lithiated acrylic acid polymer as a binder, it is possible to use an imide-based lithium salt such as LiN (CF ₃ SO ₂ ) ₂ or LiN (C ₂ F ₅ SO ₂ ) ₂ . It was confirmed that it was more effective in suppressing the decrease in discharge capacity.

(Example 8)
Instead of Ti 41 wt% -Si 59 wt% alloy which is the active material of battery A1, Fe 41 wt% -Si 59 wt% alloy, Co 41 wt% -Si 59 wt% alloy, Ni 41 wt% -Si 59 wt% alloy, Cu 41 wt% -Si 59 The batteries using the wt% alloy as the negative electrode active material are referred to as a battery J1, a battery J2, a battery J3, and a battery J4, respectively. Otherwise, a coin-type test cell was prepared in the same manner as the battery A1, and the battery characteristics were evaluated. The results are shown in Table 8 together with the value of the battery A1.

  As shown in Table 8, instead of Ti 41 wt% -Si 59 wt% alloy, Fe 41 wt% -Si 59 wt% alloy, Co 41 wt% -Si 59 wt% alloy, Ni 41 wt% -Si 59 wt% alloy, Cu 41 wt% -Si 59 When the weight% alloy was used, the discharge capacity retention rate was almost the same.

  In the above examples, a test was performed using a coin-type battery, but similar results were obtained in a test using a cylindrical battery or a stacked battery using a polymer electrolyte.

  The present invention provides a non-aqueous electrolyte having an excellent cycle life by using a polymer having a neutralized carboxyl group as a positive or negative electrode binder of a non-aqueous electrolyte secondary battery for the positive or negative electrode. A secondary battery can be provided, and an optimal non-aqueous electrolyte secondary battery can be provided as a main power source and a memory backup power source for various electronic devices such as mobile phones and digital cameras.

Sectional drawing of the coin-type battery in the Example of this invention Schematic diagram of the state of measuring the negative electrode pellet strength in the present invention The figure which shows the relationship between the neutralization degree of lithiated acrylic acid polymer, and pH value

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode can 2 Negative electrode can 3 Gasket 4 Positive electrode 5 Negative electrode 6 Separator 11 Jig 12 Negative electrode pellet 13 Push rod

Claims (6)

A non-aqueous electrolyte secondary battery comprising a positive electrode capable of occluding and releasing lithium ions, a negative electrode active material containing Si, and a lithium ion conductive non-aqueous electrolyte, wherein a lithium ion carboxyl group is formed in the negative electrode. A non-aqueous electrolyte secondary battery comprising a high molecular weight polymer. The polymer containing a lithiated carboxyl group is at least one selected from the group consisting of a lithiated acrylic acid polymer, a lithiated methacrylic acid polymer, and a lithiated acrylic acid-methacrylic acid copolymer. The nonaqueous electrolyte secondary battery according to claim 1. 3. The nonaqueous electrolyte secondary battery according to claim 1, wherein a degree of neutralization in the polymer containing the lithiated carboxyl group is 40% or more and 100% or less. 4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the content of the polymer containing the lithiated carboxyl group is 0.5 to 30% by weight based on the weight of the negative electrode active material. The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode active material includes at least one metal selected from the group consisting of Fe, Ti, Co, Ni, and Cu. The nonaqueous electrolyte secondary battery according to claim 1, wherein the nonaqueous electrolyte contains at least one of LiN (CF ₃ SO ₂ ) ₂ and LiN (C ₂ F ₅ SO ₂ ) _2. .

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