JP5398302B2 - Lithium ion secondary battery - Google Patents

Description

  The present invention relates to a lithium ion secondary battery, and in particular, a lithium electrode in which an electrode group in which a positive electrode plate and a negative electrode plate containing a lithium transition metal double oxide are arranged via a separator is infiltrated with an electrolytic solution and accommodated in a battery container. The present invention relates to an ion secondary battery.

  In the conventional lithium ion secondary battery, a lithium transition metal double oxide capable of inserting and extracting lithium ions is used as a positive electrode active material. Among them, the use of spinel-type lithium manganate has been proposed because of its excellent safety and low cost raw materials. When this lithium manganate is used, there are advantages in terms of safety, but the crystal structure of the positive electrode active material by elution of manganese (transition metal) ions by cycling (repetition of charge / discharge), storage and storage of batteries It is known that the reversibility of the positive electrode active material that occludes and releases lithium ions is reduced, causing capacity deterioration.

  Further, in the lithium ion secondary battery, a non-aqueous electrolyte solution in which a lithium-containing electrolyte such as a lithium salt is dissolved in an organic solvent is used. When moisture is mixed in the battery, the lithium-containing electrolyte is decomposed in the non-aqueous electrolyte by reaction with moisture. For this reason, the movement of lithium ions released from the positive electrode active material is hindered, causing a decrease in capacity and output, and further a decrease in life. In order to remove moisture in the non-aqueous electrolyte, for example, a technique of mixing an adsorbent into the non-aqueous electrolyte is disclosed (see Patent Document 1).

JP-A-7-262999

However, when lithium fluoride such as lithium hexafluorophosphate (LiPF ₆ ) or lithium chloride such as lithium perchlorate (LiClO ₄ ) is used as the lithium-containing electrolyte, it is included in the lithium ion secondary battery. Even if the amount of moisture is small, the lithium-containing electrolyte is decomposed, and an acid such as hydrogen fluoride (HF) or perchloric acid (HClO ₄ ) is generated. Since this acid promotes the elution of transition metal ions from the lithium transition metal complex oxide, as described above, it causes problems such as capacity deterioration and life reduction. In the technique of Patent Document 1, although an adsorbent for removing water is mixed, since the lithium-containing electrolyte is decomposed even with a very small amount of water, it cannot be said that removal of water with the adsorbent is sufficient. Therefore, when a lithium transition metal double oxide such as lithium manganate is used as the positive electrode active material, in order to extend the life of the lithium ion secondary battery, the acid generated by the decomposition of the lithium-containing electrolyte is neutralized. Alternatively, it is considered important to suppress the generation of acid.

  An object of the present invention is to provide a lithium ion secondary battery capable of suppressing a decrease in capacity and extending its life in view of the above-described case.

In order to solve the above problems, the present invention includes an electrode group of wound via a separator and a positive electrode plate and negative electrode plate comprising a lithium transition metal complex oxide in about the axis is infiltrated into non-aqueous electrolyte cell In the lithium ion secondary battery housed in a container, the non-aqueous electrolyte is a mixture of a lithium-containing electrolyte in an organic solvent, and is a solid-state inorganic oxide that neutralizes acids generated by decomposition of the lithium-containing electrolyte. An acid neutralizing agent that is a product and a water absorbent that is a porous material are present in at least one of the axial core of the electrode group and the outer periphery of the electrode group, and the inorganic oxide is at least alumina, silica And the porous material is made of at least one selected from zeolite-based compounds and cellulose-based compounds.

In the present invention, the acid neutralizing agent, which is an inorganic oxide present in at least one of the axial core of the electrode group and the outer peripheral portion of the electrode group, is made into a solid state, so that it is liquid and mixed with the non-aqueous electrolyte. As compared with the case where it is present in the aqueous solution, the effect on the non-aqueous electrolyte is suppressed, and when the lithium-containing electrolyte in the non-aqueous electrolyte is decomposed by reaction with moisture to generate an acid, the generated acid is an acid neutralizer. The elution of transition metal ions due to the decomposition of the lithium transition metal complex oxide is suppressed , and a water absorbent that is a porous material is present on at least one of the axial core of the electrode group and the outer periphery of the electrode group it is, it is possible to achieve Runode the decomposition of contaminating moisture is absorbed lithium-containing electrolyte in the battery is suppressed, the suppression and long life capacity reduction.

In this case, it is possible to the Lithium transition metal complex oxide with a spinel-type lithium manganate. The non-aqueous electrolyte may contain a phosphazene flame retardant. An acid neutralizing agent or a water absorbent may be further present in at least one of the separator, the positive electrode plate, and the negative electrode plate.

According to the present invention , the acid neutralizing agent, which is an inorganic oxide present in at least one of the axial core of the electrode group and the outer peripheral portion of the electrode group, is made solid, so that the liquid non-aqueous electrolyte and Compared to the case where it exists in a mixed form, the effect on the non-aqueous electrolyte is suppressed, and when the lithium-containing electrolyte in the non-aqueous electrolyte decomposes by reaction with moisture to produce an acid, the generated acid is in the acid. Elution of transition metal ions due to decomposition of the lithium transition metal double oxide is suppressed by neutralizing with a hydrating agent, and a water absorbent that is a porous substance is present on at least one of the axial core of the electrode group and the outer periphery of the electrode group. and it has, it is possible to achieve Runode is suppressed decomposition of entrained moisture is absorbed lithium-containing electrolyte into the battery, the suppressing long life capacity reduction, there can be provided an advantage.

It is sectional drawing which fractures | ruptures partially and shows typically the cylindrical lithium ion secondary battery of embodiment to which this invention is applied. It is a graph which shows the change of the capacity | capacitance maintenance factor with respect to the leaving days when the cylindrical lithium ion secondary battery of embodiment is left.

  Hereinafter, an embodiment in which the present invention is applied to an 18650 type cylindrical lithium ion secondary battery will be described with reference to the drawings.

  As shown in FIG. 1, the columnar lithium ion secondary battery 20 of the present embodiment includes a bottomed cylindrical battery can 9 made of nickel-plated steel. The battery can 9 contains an electrode group 7 in which a belt-like positive electrode plate 4 and a belt-like negative electrode plate 5 are wound in a spiral shape with a separator 6 interposed therebetween.

  Under the electrode group 7, the other end of the nickel tab terminal joined at one end to the negative electrode current collector constituting the negative electrode plate 5 is led out. The other end of the nickel tab terminal is welded to the inner bottom surface of the battery can 9 that also serves as the negative electrode external terminal.

  On the other hand, on the upper side of the electrode group 7, the other end of the aluminum tab terminal joined at one end to the positive electrode current collector constituting the positive electrode plate 4 is led out. Above the electrode group 7, a disc-shaped upper lid that has a built-in safety valve and also serves as a positive external terminal is disposed. The other end of the aluminum tab terminal is joined to the lower surface of the upper lid by welding. The upper lid is caulked and fixed to the upper part of the battery can 9 via an insulating gasket. For this reason, the inside of the lithium ion secondary battery 20 is sealed.

  In the electrode group 7, the positive electrode plate 4 and the negative electrode plate 5 are wound through a polyethylene microporous membrane separator 6 through which lithium ions can pass so that the two electrode plates do not directly contact each other. An axis 1 made of polytetrafluoroethylene (hereinafter abbreviated as PTFE) is used at the winding center of the electrode group 7. In this example, the separator 6 has a width (length in the longitudinal direction of the battery can 9) of 58 mm and a thickness of 40 μm. The aluminum tab terminal and the nickel tab terminal are led out to the opposite end surfaces of the electrode group 7, respectively. An insulation coating is applied to the entire circumference of the electrode group 7 in order to prevent electrical contact between the electrode group 7 and the battery can 9.

  The positive electrode plate 4 constituting the electrode group 7 has an aluminum foil as a positive electrode current collector. The thickness of the aluminum foil is set to 20 μm in this example. A positive electrode mixture containing a lithium transition metal double oxide as a positive electrode active material is applied to both surfaces of the aluminum foil. In this example, lithium manganate powder having a spinel crystal structure is used as the lithium transition metal double oxide. In addition to the positive electrode active material, the positive electrode mixture contains carbon powder as a conductive material and polyvinylidene fluoride (hereinafter abbreviated as PVdF) as a binder (binder). In this example, the blending ratio of the lithium manganate powder, the carbon powder, and the PVdF is set to 80:10:10 (% by weight). When the positive electrode mixture is applied to the aluminum foil, the viscosity is adjusted with a dispersion solvent N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP) to prepare a slurry. This slurry is applied to both sides of the aluminum foil. The positive electrode plate 4 is rolled after being dried, cut into a width of 54 mm, and formed into a strip shape.

  On the other hand, the negative electrode plate 5 has a copper foil as a negative electrode current collector. The thickness of the copper foil is set to 10 μm in this example. A negative electrode mixture containing a carbon material such as amorphous carbon powder or graphite powder capable of occluding and releasing lithium ions as a negative electrode active material is applied to both surfaces of the copper foil. In addition to the negative electrode active material, PVdF is blended in the negative electrode mixture as a binder. In this example, the blending ratio of the carbon material and PVdF is set to 90:10 (% by weight). When the negative electrode mixture is applied to the copper foil, the viscosity is adjusted with the dispersion solvent NMP to prepare a slurry. This slurry is applied to both sides of the copper foil. The negative electrode plate 5 is dried and then rolled, cut into a width of 56 mm, and formed in a strip shape.

  In the electrode group 7, a water absorbent and an acid neutralizing agent are present. The water absorbent and the acid neutralizing agent are contained in at least one of the shaft core 1, the outer peripheral portion of the electrode group 7, the separator 6, the positive electrode plate 4, and the negative electrode plate 5. In this example, as shown in FIG. 1, a water absorbent and an acid neutralizer are contained in the shaft core 1 and the thin film 3 wound around the outer periphery of the electrode group 7. The thin film 3 is disposed between the separator 6 and the positive electrode plate 4 or the negative electrode plate 5 located on the outer periphery of the electrode group 7. That is, the water absorbent and the acid neutralizer are present at two locations, the shaft core 1 and the outer peripheral portion of the electrode group 7, respectively. The acid neutralizing agent is a solid inorganic oxide that has a neutralizing action on the acid generated by the decomposition of the lithium salt in the non-aqueous electrolyte. In this example, alumina (aluminum oxide) is used. ing. The water absorbent is a solid porous material, and in this example, molecular sieves (molecular sieves) are used.

  The shaft core 1 containing the acid neutralizing agent alumina and the water absorbent molecular sieve is manufactured as follows. That is, alumina, molecular sieve, and PTFE were mixed at a ratio of 60: 35: 5 (% by weight), and then formed into a cylindrical shape having a diameter of 3 mm and a length of 55 mm. Then, it vacuum-dried at 120 degreeC for 12 hours. Alumina and molecular sieves were each vacuum-dried at 150 ° C. for 24 hours before use.

  Moreover, in order to make a water absorber and an acid neutralizer exist in the outer peripheral part of the electrode group 7, the thin film 3 containing an acid neutralizer and a water absorber is used. The thin film 3 is produced as follows. That is, alumina, molecular sieve, and PTFE were mixed at a ratio of 60: 35: 5 (% by weight), and then formed into a thin film having a thickness of 100 μm. Then, it vacuum-dried at 120 degreeC for 12 hours.

A non-aqueous electrolyte is injected into the battery can 9. The injection amount of the non-aqueous electrolyte is set to 4.5 ml in this example. For this reason, the non-aqueous electrolyte is infiltrated into the electrode group 7. The non-aqueous electrolyte includes lithium fluoride as a lithium salt (lithium-containing electrolyte) in a 1: 1: 1 volume ratio of ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC). Some lithium hexafluorophosphate (LiPF ₆ ) dissolved at 1.0 mol / liter is used. The non-aqueous electrolyte contains a liquid phosphazene compound having phosphorus and nitrogen as a basic skeleton as a flame retardant. The phosphazene compound is a cyclic compound represented by the general formula (NPR ₂ ) ₃ or (NPR ₂ ) ₄ , and R in the general formula represents a halogen element such as fluorine or chlorine or a monovalent substituent. As monovalent substituents, alkoxy groups such as methoxy group and ethoxy group, aryloxy groups such as phenoxy group and methylphenoxy group, alkyl groups such as methyl group and ethyl group, aryl groups such as phenyl group and tolyl group, Examples thereof include an amino group containing a substituted amino group such as a methylamino group, an alkylthio group such as a methylthio group and an ethylthio group, and an arylthio group such as a phenylthio group. In this example, the content ratio of the flame retardant in the nonaqueous electrolytic solution is set to 15 vol (volume)%.

(Action etc.)
Next, the operation and the like of the lithium ion secondary battery 20 of the present embodiment will be described.

  In the lithium ion secondary battery 20 of this embodiment, the acid neutralizer alumina is contained in the thin film 3 wound around the shaft core 1 and the electrode group 7. For this reason, even if lithium hexafluorophosphate in the non-aqueous electrolyte is decomposed by a small amount of water mixed in the lithium ion secondary battery 20 and hydrofluoric acid is generated, the reaction with alumina causes fluorination. Hydrogen acid can be neutralized. For this reason, elution of manganese ions from lithium manganate of the positive electrode active material by hydrofluoric acid can be suppressed. Thereby, since the conductivity of lithium ions in the non-aqueous electrolyte is ensured, the capacity reduction can be suppressed and the life can be extended.

  Further, in the lithium ion secondary battery 20 of the present embodiment, the shaft core 1 and the thin film 3 contain a water absorbent molecular sieve together with an acid neutralizer alumina. For this reason, even if a very small amount of water is mixed in the lithium ion secondary battery 20, the water can be adsorbed and removed by the action of the molecular sieve. Thereby, since a trace amount of water | moisture content in a nonaqueous electrolyte solution is removed, decomposition | disassembly of lithium hexafluorophosphate in a nonaqueous electrolyte solution can be suppressed.

  Furthermore, in the lithium ion secondary battery 20 of the present embodiment, the acid neutralizing agent and the water absorbent are present in two places, the axial core 1 of the electrode group 7 and the thin film 3 disposed on the outer periphery of the electrode group 7. doing. For this reason, neutralization of hydrofluoric acid with an acid neutralizer and removal of water with a water absorbent can be performed efficiently. In addition, when the acid neutralizing agent or the water absorbent is in a liquid state, it may be considered that the reaction with the nonaqueous electrolytic solution, the inhibition of lithium ion mobility, and the like occur, affecting the nonaqueous electrolytic solution. In this embodiment, since the acid neutralizer and the water absorbent contained in the shaft core 1 and the thin film 3 are both solid, the influence on the non-aqueous electrolyte can be suppressed.

  Furthermore, in the present embodiment, a liquid phosphazene compound is contained as a flame retardant in the nonaqueous electrolytic solution. Since this phosphazene compound decomposes in a high temperature environment such as when the battery is abnormal and exhibits a fire extinguishing action, self-digestibility is imparted to the non-aqueous electrolyte. For this reason, when the lithium ion secondary battery 20 is exposed to an abnormally high temperature environment or when a battery abnormality occurs, gas ejection or leakage of the nonaqueous electrolyte occurs due to decomposition of the nonaqueous electrolyte. However, since the ignition to the ejected gas or the leaked non-aqueous electrolyte is suppressed, the safety of the battery can be ensured.

In this embodiment, the 18650 type cylindrical lithium ion secondary battery is illustrated, but the present invention is not limited to the cylindrical type, and a lithium ion secondary battery such as a coin type, a button type, or a square type is used. It is also possible to apply to. There is no particular limitation on the battery size .

  In the present embodiment, alumina is exemplified as the acid neutralizing agent, but the present invention is not limited to this, and neutralizes the acid generated by the decomposition of the lithium salt dissolved in the non-aqueous electrolyte. It may be in a solid state showing. As the acid neutralizing agent, for example, an oxide such as silicon or magnesium, that is, an inorganic oxide such as silica or magnesium oxide can be used, and at least one selected from alumina, silica and magnesium oxide is used. It is preferable.

  Furthermore, in this embodiment, the molecular sieve was exemplified as the water absorbent, but the water absorbent that can be used in the present invention is not particularly limited. As the water absorbent, for example, a zeolite-based or cellulose-based solid porous material can be used, and it is preferable to use at least one of a zeolite-based compound and a cellulose-based compound as a material.

  Furthermore, in the present embodiment, an example in which the acid neutralizer and the water absorbent are contained in the shaft core 1 and the thin film 3 wound around the outer periphery of the electrode group 7 is shown, but the present invention is limited to this. It is not a thing. An acid neutralizer or water absorbent may be present in the electrode group 7, and is contained in at least one of the shaft core 1, the outer periphery of the electrode group 7, the separator 6, the positive electrode plate 4, and the negative electrode plate 5. Can be made. For example, when a stacked electrode group is used instead of the wound electrode group 7, the shaft core 1 is not used, so that an acid neutralizer or a water absorbent is blended in the positive electrode mixture or the negative electrode mixture. Thus, the positive electrode plate 4 and the negative electrode plate 5 may be included. Moreover, you may make it contain separately, without making an acid neutralizer and a water absorber contain together. For example, the shaft core 1 can contain an acid neutralizing agent, and the thin film 3 can contain a water absorbent.

  Furthermore, in the present embodiment, when the shaft core 1 and the thin film 3 containing the acid neutralizing agent and the water absorbent are formed, PTFE is exemplified as the polymer material, but the present invention is limited to this. is not. Examples of the polymer material for forming the shaft core 1 and the thin film 3 include polyethylene oxide, polyacrylonitrile, polymethyl methacrylate, polyethylene, polystyrene, polybutadiene, butyl rubber, nitrile rubber, styrene / butadiene rubber, polysulfide rubber, nitrocellulose, Polymers such as cyanoethyl cellulose, various latexes, acrylonitrile, vinyl fluoride, vinylidene fluoride, propylene fluoride, chloroprene fluoride, and the like may be used.

  Moreover, in this embodiment, although lithium manganate which has a spinel crystal structure was illustrated as a positive electrode active material, this invention is not limited to this. For example, lithium cobaltate or lithium nickelate, or a material obtained by substituting or doping a part of lithium or manganese in these crystals with other elements may be used. Although there is no particular limitation on the crystal structure, it is preferable to use lithium manganate having a spinel crystal structure from the viewpoint of stability of the crystal structure in consideration of extending the life.

  Furthermore, in this embodiment, although the example which sets the content rate of the flame retardant in nonaqueous electrolyte solution to 15 vol% was shown, this invention is not limited to this, A content rate is 10 vol% or more It has been confirmed that the effects described above can be obtained. If the content of the flame retardant is less than 10 vol%, it becomes difficult to impart flame retardancy and self-digestibility to the non-aqueous electrolyte. On the other hand, if it exceeds 25 vol%, ion conduction during charge / discharge is hindered, And output will be reduced. For this reason, it is preferable to make the content rate of a flame retardant into the range of 10-25 vol%.

  Furthermore, in the present embodiment, PVdF is exemplified as a binder when the positive electrode plate 4 and the negative electrode plate 5 are produced. However, the present invention is not limited to this, for example, PTFE, polyethylene, polystyrene, polybutadiene, Polymers such as butyl rubber, nitrile rubber, styrene / butadiene rubber, polysulfide rubber, nitrocellulose, cyanoethyl cellulose, various latexes, acrylonitrile, vinyl fluoride, vinylidene fluoride, propylene fluoride, chloroprene, and mixtures thereof May be used.

Furthermore, in the present embodiment, EC, DMC, and DEC are exemplified as the organic solvent of the nonaqueous electrolytic solution, but the present invention is not particularly limited to the organic solvent to be used. For example, as the organic solvent, propylene carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, Sulfolane, methyl sulfolane, acetonitrile, propionitrile, etc. or a mixed solvent of two or more of these may be used, and the mixing ratio is not limited. Moreover, although lithium hexafluorophosphate of lithium fluoride is exemplified as the lithium salt to be dissolved in the organic solvent, the present invention is not limited to this. As lithium salts that can be used in other than this embodiment, for example, may be used lithium chloride such as LiClO _4, the LiAsF 6, LiBF lithium fluoride, and mixtures thereof, such as _4. These lithium salts also generate acids such as perchloric acid and hydrogen fluoride by reacting with water, so that the battery life can be improved by adding an acid neutralizer and a water absorbent as described above. Can do.

  Next, examples of the lithium ion secondary battery 20 manufactured according to the present embodiment will be described. In addition, it describes together about the lithium ion secondary battery of the comparative example produced for the comparison.

Example 1
In Example 1, the electrode group 7 was produced using the axial core 1 containing the acid neutralizing agent alumina and the water absorbent molecular sieve, and the lithium ion secondary battery 20 was produced.

(Example 2)
In Example 2, the thin film 3 containing the acid neutralizing agent alumina and the water absorbent molecular sieve was cut into a width of 6 cm and a length of 6 cm, and arranged on the outer periphery of the electrode group 7 to be a lithium ion secondary battery 20. Was made.

(Example 3)
In Example 3, a lithium ion secondary battery 20 was manufactured by using the shaft 1 used in Example 1 and arranging the thin film 3 used in Example 2 on the outer periphery of the electrode group 7.

(Comparative Example 1)
In Comparative Example 1, a lithium ion secondary battery in which a water absorbent and an acid neutralizer were not present in the battery can was produced. That is, the shaft core 1 was produced only with PTFE without blending a water absorbent and an acid neutralizer. The battery of Comparative Example 1 is a conventional lithium ion secondary battery.

(Evaluation)
About the lithium ion secondary battery of each Example and the comparative example, the capacity | capacitance maintenance factor was measured. In the capacity maintenance rate measurement, each lithium ion secondary battery was charged at a constant current and a constant voltage up to 4.2 V to be in a fully charged state, and discharged to measure an initial discharge capacity. After being fully charged again, it was left in an environment of 40 ° C. The discharge capacity was measured every month, and the ratio to the initial discharge capacity was calculated as the capacity maintenance rate.

  As shown in FIG. 2, in the lithium ion secondary battery of Comparative Example 1, the capacity retention rate greatly decreased with an increase in the number of days left. On the other hand, in the lithium ion secondary battery 20 of Example 1 to Example 3 in which the acid neutralizing agent alumina and the water absorbent molecular sieve were present in the battery, the decrease in capacity maintenance rate was suppressed to a small level. It was found that Accordingly, it has been clarified that the life of the lithium ion secondary battery 20 can be extended. Moreover, compared with Example 1 which made the acid neutralizer and water absorbent exist in the inside of the shaft core 1, and Example 2 made to exist in the outer peripheral part of the electrode group 7, the inside of the shaft core 1 and the electrode group It was found that the capacity retention rate of Example 3 that was present both in the outer peripheral portion of 7 increased. From this, it was found that the place where the acid neutralizing agent and the water absorbent are present is not limited to one place, but is preferably present both in the shaft core 1 and in the outer peripheral portion of the electrode group 7.

  Since the present invention provides a lithium ion secondary battery capable of suppressing a decrease in capacity and extending its life, and contributes to the manufacture and sale of lithium ion secondary batteries, it has industrial applicability.

DESCRIPTION OF SYMBOLS 3 Thin film 4 Positive electrode plate 5 Negative electrode plate 6 Separator 7 Electrode group 9 Battery can 20 Cylindrical lithium ion secondary battery (lithium ion secondary battery)

Claims (4)

In the positive electrode plate and the negative electrode plate and a lithium-ion secondary battery electrode group wound with a separator interposed therebetween is infiltrated into non-aqueous electrolyte housed in a battery container comprising a lithium transition metal complex oxide in about the axis, The non-aqueous electrolyte is an organic solvent mixed with a lithium-containing electrolyte, and is a solid substance, an acid neutralizer that is an inorganic oxide that neutralizes acid generated by decomposition of the lithium-containing electrolyte, and a porous substance And a water absorbent that is present in at least one of the axis of the electrode group and the outer periphery of the electrode group, and the inorganic oxide is at least one selected from alumina, silica, and magnesium oxide, A lithium ion secondary battery, wherein the porous material is made of at least one selected from a zeolite compound and a cellulose compound.   The lithium ion secondary battery according to claim 1, wherein the lithium transition metal complex oxide is spinel-type lithium manganate.   The lithium ion secondary battery according to claim 1 or 2, wherein the non-aqueous electrolyte contains a phosphazene-based flame retardant.   The lithium ion secondary according to claim 1, wherein the acid neutralizer or the water absorbent is further present in at least one of the separator, the positive electrode plate, and the negative electrode plate. battery.

Images