JP2018120848A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery which can be charged and discharged without causing the dissolution of a coating formed on a current collector surface.SOLUTION: A lithium ion secondary battery 1 comprises a negative electrode 3, a positive electrode 4 and an electrolyte solution. The negative electrode 3 includes: a current collector 31; and a coating 32 covering the surface of the current collector 31. The coating includes at least one kind of metal selected from a group consisting of tin, lead, aluminum and zinc. The electrolyte solution contains a phosphoric ester solvent, and a supporting electrolyte, of which pH is in a range of 4 to 10.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a lithium ion secondary battery.

  Conventionally, there has been known a lithium ion secondary battery that includes a negative electrode, a positive electrode, and an electrolytic solution, and the negative electrode includes a current collector and a negative electrode active material film formed on the surface of the current collector. . The use of tin having a theoretical capacity larger than that of a carbon material as a negative electrode active material of the lithium ion secondary battery has been studied. For example, a thickness of 10 to 300 μm formed on the surface of the current collector by electroplating. Lithium ion secondary batteries having a tin film are known. (For example, refer to Patent Document 1).

  In addition, it is known that lead (Pb), aluminum (Al), or zinc (Zn) is used as the negative electrode active material (see, for example, Patent Document 2).

  In the conventional lithium ion secondary battery, the positive electrode includes lithium cobaltate, lithium nickelate, lithium manganate, etc. as a positive electrode active material, the electrolyte includes a carbonate-based solvent, and a fluorine-containing lithium salt as a supporting salt. ing. As the carbonate solvent, at least one solvent selected from the group consisting of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, and γ-butyrolactone can be used. As the fluorine-containing lithium salt, at least one compound selected from the group consisting of lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium trifluoromethanesulfonate can be used.

JP 2001-68094 A JP 2004-95264 A

  However, in a lithium ion secondary battery using a current collector provided with a tin film as a negative electrode and an electrolytic solution containing a carbonate solvent and a supporting salt, a certain amount of time has passed while the tin film is in contact with the electrolytic solution. As a result, charging / discharging may not be possible, or durability against charging / discharging cycles may be reduced.

  Further, when the current collector is provided with any one of a lead film, an aluminum film, and a zinc film, there are the same disadvantages as in the case of the tin film.

  The present invention eliminates such inconveniences, and when the negative electrode contains at least one metal selected from the group consisting of tin, lead, aluminum, and zinc, the negative electrode is in contact with the electrolyte to some extent. An object of the present invention is to provide a lithium ion secondary battery that can be charged / discharged over time or has excellent charge / discharge characteristics.

  The present inventor uses a current collector having a tin film on the surface as a negative electrode, and in a lithium ion secondary battery using an electrolytic solution containing a carbonate-based solvent and a supporting salt, the tin film is in contact with the electrolytic solution. The reason why charging and discharging may become impossible after a certain amount of time has been studied.

  As a result, when the pH of the electrolytic solution containing the carbonate solvent and the supporting salt is about 3.1 to 3.9, the amphoteric metal tin is in contact with the electrolytic solution for a certain amount of time. It has been found that it dissolves as time passes.

  When a certain amount of time has passed while the tin coating is in contact with the electrolytic solution, tin begins to dissolve from the interface portion where the electrolytic solution and the tin coating are in contact, and the dissolution of tin gradually proceeds. As a result, charging / discharging may not be possible, or durability against charging / discharging cycles may be reduced. Here, since lead (Pb), aluminum (Al), and zinc (Zn) are amphoteric metals like tin (Sn), lead (Pb), aluminum (Al), zinc (Zn) or Even when a coating made of a mixture of these metals is used, the coating dissolves when it comes into contact with the electrolytic solution in the same manner as the tin coating, and as a result, charging / discharging may not be possible. The durability against the discharge cycle is considered to be reduced. The inventor has further studied in accordance with the above findings and has reached the present invention.

  Therefore, in order to achieve the above object, a lithium ion secondary battery of the present invention is a lithium ion secondary battery comprising a negative electrode, a positive electrode, and an electrolyte layer positioned between the negative electrode and the positive electrode. And at least one metal selected from the group consisting of tin, lead, aluminum, and zinc, and the electrolyte layer includes an electrolytic solution containing a solvent and a supporting salt and having a pH in the range of 4 to 10. Features.

  In the lithium ion secondary battery of the present invention, the negative electrode contains at least one metal selected from the group consisting of tin, lead, aluminum, and zinc. The negative electrode includes a current collector and a surface of the current collector. And a film made of at least one metal selected from the group consisting of tin, lead, aluminum, and zinc, and the negative electrode itself is tin, lead, It may be in the form of at least one metal selected from the group consisting of aluminum and zinc, or an alloy containing at least one metal selected from the group consisting of tin, lead, aluminum and zinc.

  Further, in the negative electrode, instead of the metal film, at least one metal powder selected from the group consisting of tin, lead, aluminum, and zinc, a binder, and a conductive auxiliary agent such as a carbon material are dispersed in a solvent. You may provide the membrane | film | coat formed by apply | coating the made slurry on a collector. At this time, the metal powder preferably has an average particle diameter of 10 nm to 100 μm.

  Further, in the lithium ion secondary battery of the present invention, the electrolyte layer may be in a form in which a separator made of a synthetic resin is impregnated with the electrolyte solution, and the electrolyte solution containing a gelling material is included in the separator. It may be in the form of being impregnated and gelled. Examples of the gelling material include polymerization initiators or polymers such as polyvinylidene fluoride / hexafluoropropylene (PVDF-HFP), (poly) acrylonitrile, (poly) acrylic acid, and polymethyl methacrylate. Moreover, the said electrolyte solution containing the said gelatinization material can be gelatinized by heating or using a gelatinization initiator.

  In the lithium ion secondary battery of the present invention, when the pH of the electrolyte contained in the electrolyte layer is in the range of 4 to 10, the amphoteric metal tin, lead, aluminum, zinc or a mixture of these metals is substantially present. Does not dissolve.

  Therefore, according to the lithium ion secondary battery of the present invention, the electrolytic solution contained in the electrolyte layer is in contact with the negative electrode containing at least one metal selected from the group consisting of tin, lead, aluminum, and zinc. In this case, it is possible to prevent any of the metals, their alloys, or their metal powders from being dissolved. As a result, according to the lithium ion secondary battery of the present invention, the negative electrode can be charged / discharged even after a certain period of time with the negative electrode in contact with the electrolytic solution, or excellent charge / discharge characteristics are obtained. be able to.

  When the pH of the electrolyte is less than 4 or exceeds 11, at least one metal selected from the group consisting of tin, lead, aluminum, and zinc, which are amphoteric metals, an alloy thereof, or a metal powder thereof is dissolved. To do.

  In the lithium ion secondary battery of the present invention, the solvent preferably contains a phosphate ester. The said electrolyte solution can make the pH into the range of 4-10 reliably because the said solvent contains phosphate ester.

  Moreover, the lithium ion secondary battery of this invention WHEREIN: It is preferable that the said phosphate ester is equipped with a C3 or less hydrocarbon group in a side chain. The phosphate ester can have an appropriate viscosity and a high solubility in the supporting salt by providing a hydrocarbon group having 3 or less carbon atoms in the side chain. When the hydrocarbon group has more than 3 carbon atoms in the hydrocarbon group, the viscosity becomes too high and handling may be difficult.

  In the lithium ion secondary battery of the present invention, when the negative electrode is made of an alloy containing at least one metal selected from the group consisting of tin, lead, aluminum, and zinc, charging and discharging of the lithium ion secondary battery are repeated. Capacity deterioration can be suppressed. The reason for this is considered to be that metals other than tin, lead, aluminum, or zinc contained in the alloy function as a buffer against expansion, contraction of tin, lead, aluminum, or zinc in the negative electrode. Alternatively, when a metal other than tin, lead, aluminum, or zinc contained in the alloy is a metal that does not react with lithium ions, the metal that does not react with lithium ions serves as a skeleton that retains the electrode structure of the negative electrode. It is thought to function.

  In this case, the alloy preferably has a content of at least one metal selected from the group consisting of tin, lead, aluminum, or zinc of 30% by mass or more of the total amount. When the content of at least one metal selected from the group consisting of tin, lead, aluminum, or zinc is less than 30% by mass of the total amount of the alloy, the energy density of the lithium ion secondary battery is reduced. It will be.

  Further, in the lithium ion secondary battery of the present invention, when the electrolyte layer is composed of the gelled electrolyte containing a gelled material, the gelled electrolyte is converted into active material fine particles and active material electrolysis. It is considered that it acts as a barrier that suppresses diffusion into the liquid and can improve the capacity of the lithium ion secondary battery.

The typical sectional view showing an example of the structure of the lithium ion secondary battery of the present invention. The lithium ion secondary battery of this invention WHEREIN: The graph which shows the charging / discharging characteristic in the case of using tin foil or tin alloy foil itself as a negative electrode. The lithium ion secondary battery of this invention WHEREIN: The graph which shows the charging / discharging characteristic in the case of using aluminum foil or aluminum alloy foil itself as a negative electrode. The lithium ion secondary battery of this invention WHEREIN: The graph which shows the charging / discharging characteristic in the case of providing the negative electrode containing aluminum powder.

  Next, embodiments of the present invention will be described in more detail with reference to the accompanying drawings.

  As shown in FIG. 1, the lithium ion secondary battery 1 of the present embodiment includes a negative electrode 3 disposed inside a cell 2, a positive electrode 4, and a separator 5 positioned between the negative electrode 3 and the positive electrode 4. And the electrolyte layer 6 is formed by impregnating the separator 5 with an electrolytic solution.

  The negative electrode 3 includes a current collector 31 and a coating 32 that covers one surface of the current collector 31, and is disposed so that the coating 32 faces the electrolyte layer 6. A negative electrode lead 33 is connected to the current collector 31. The film 32 only needs to cover at least one surface of the current collector 31, and may cover both the front and back surfaces of the current collector 31.

  The current collector 31 of the negative electrode 3 is not particularly limited as long as it is a material having electrical conductivity. For example, a metal made of copper, steel, titanium, or the like can be used. As the current collector 31, a foil of the metal or an alloy thereof may be used, or a mesh-like body or an expanded metal may be used. When the current collector 31 is a metal or alloy foil, its thickness is preferably thin in order to improve the energy density of the battery, but if it is too thin, handling is difficult and productivity is reduced. A range of 1 to 100 μm is preferable.

  As the film 32, a film of any one of tin, lead, aluminum, and zinc, a film of a mixture of these metals, or a film of an alloy containing these metals can be used.

  The film 32 can be formed on the current collector 31 by plating, fusing, sputtering, vapor deposition, or the like of at least one metal selected from the group consisting of tin, lead, aluminum, and zinc. When the film 32 is formed by a plating method, it may be coprecipitated with a metal such as copper, nickel, or silver.

  The film 32 may be formed by ultrasonically welding or friction welding a foil of one kind of metal selected from the group consisting of tin, lead, aluminum, and zinc or an alloy thereof onto the current collector 31. Good. Further, the coating 32 is coated on the current collector 31 with a slurry in which at least one metal powder selected from the group consisting of tin, lead, aluminum, and zinc is dispersed together with a conductive aid such as a binder or a carbon material. It may be formed by working and drying. The metal powder may be coated with nickel, copper, silver, gold or the like.

  When the film 32 is a tin film, it can be formed by, for example, an electroless plating method. In this case, the current collector 31 is immersed in an acid such as nitric acid, hydrochloric acid or sulfuric acid, or washed with water to remove dust, oxide film, etc. on the surface, and then a tin salt such as tin chloride is added to the acid such as sulfuric acid. It can be carried out by immersing in a plating bath in which sodium diphosphite as a reducing agent is dissolved and raising the temperature of the plating bath to a predetermined temperature. The plating bath may be obtained by dissolving a tin salt such as tin chloride and sodium diphosphite as a reducing agent in an alkaline solution such as sodium hydroxide instead of sulfuric acid.

  For example, the tin coating 32 has a thickness in the range of 10 nm or more and less than 50 μm. The thickness of the tin film 32 can be managed by the temperature of the plating bath and the immersion time.

  The tin film 32 formed by the above electroless plating method is a porous body having pores having a pore diameter in the range of 0.01 to 300 nm, and the porosity of the porous body is in the range of 0.01 to 20% by volume. It is.

  Moreover, when the film | membrane 32 is an aluminum film, it can form by the electroplating method or the electroless-plating method, for example. In this case, what dissolved aluminum chloride etc. in organic solvents, such as acetone and an ionic liquid, can be used as a plating bath.

  In addition, the lithium ion secondary battery 1 of this embodiment does not include the film 32, and the current collector 31 itself is made of any one of tin, lead, aluminum, and zinc, or an alloy containing these metals. It may be a thing.

  On the other hand, the positive electrode 4 includes a current collector 41 and a positive electrode mixture layer 42 formed on one surface of the current collector 41, and the positive electrode mixture layer 42 is disposed so as to face the electrolyte layer 6. . A positive electrode lead 43 is connected to the current collector 41. The positive electrode mixture layer 42 only needs to be formed on at least one surface of the current collector 41, and may be formed on both the front and back surfaces of the current collector 41.

  The current collector 41 of the positive electrode 4 is not particularly limited as long as it is a material having electrical conductivity. For example, a material made of aluminum, copper, steel, titanium, or the like can be used. The current collector 41 may use a foil of the metal or an alloy thereof, or may use a mesh-like body or an expanded metal. When the current collector 41 is the metal or alloy foil, its thickness is preferably thin in order to improve the energy density of the battery, but if it is too thin, handling is difficult and productivity is reduced. It is preferable to set it as the range of 5-50 micrometers.

  The positive electrode mixture layer 42 in the positive electrode 4 is prepared by mixing a suitable amount of a positive electrode active material and a binder such as polyvinylidene fluoride (PVDF) and diluting with N-methylpyrrolidone, a doctor blade method or the like. Thus, the current collector 41 can be formed by coating and coating. The positive electrode mixture layer 42 preferably has a higher content of the positive electrode active material with respect to the total amount. For example, the content is preferably 85% by mass or more. The positive electrode mixture layer 42 may contain a conductive additive in addition to the positive electrode active material and the binder.

Examples of the positive electrode active material include LiMnO ₂ , Li _x Mn ₂ O ₄ (0 <x <2), Li ₂ MnO ₃ , Li _x Mn _1.5 Ni _0.5 O ₄ (0 <x <2), and the like. Lithium manganate having a layered structure or lithium manganate having a spinel structure, LiCo ₂ O ₂ , LiNiO ₂ or a compound obtained by substituting a part of its transition metal with another metal, LiNi _1/3 Co _1/3 Mn _{1 /} Lithium transition metal oxides in which specific transition metals such as ₃ O ₂ do not exceed half of the total, compounds in which Li is excessive in excess of the stoichiometric composition in these lithium transition metal oxides, and olivine structures such as LiFePO ₄ And the like.

In addition, as the positive electrode active material, some of these metal oxide metals may be Al, Fe, P, Ti, Si, Pb, Sn, In, Bi, Ag, Ba, Ca, Hg, Pd, Pt, Te. A material substituted with Zn, La, or the like can also be used. In _{particular, Li α Ni β Co γ Al} δ O 2 (β + γ + δ = 1, β ≧ 0.4, γ ≦ 0.2) or _{Li α Ni β Co γ Mn δ} O 2 (β + γ + δ = 1, β ≧ 0.4 Γ ≦ 0.2).

  As the positive electrode active material, any one of the above compounds may be used alone, or two or more may be used in combination.

Further, as the positive electrode active material, iron sulfide, iron disulfide, sulfur, polysulfide, Li ₃ VO ₄ or the like can be used, and radical materials such as a nitroxyl compound having a nitroxyl radical partial structure can also be used.

  As the electrolytic solution contained in the electrolyte layer 6, a phosphate ester represented by the following general formula (1) as a solvent and a lithium salt dissolved as a supporting salt in the solvent can be used.

In the general formula (1), R ¹ , R ² , and R ³ are linear hydrocarbon groups such as alkyl groups, alkenyl groups, and alkynyl groups, or groups obtained by substituting some of the hydrogens with fluorine. They may be the same or different. Moreover, since the viscosity of the linear hydrocarbon group becomes too high when the number of carbon atoms increases and handling becomes difficult, the linear hydrocarbon group preferably has 7 or less carbon atoms, more preferably 3 or less carbon atoms.

  As the phosphoric acid ester, for example, trimethyl phosphate, triethyl phosphate, tristrifluoroethyl phosphate, and the like are preferable because they have an appropriate viscosity and high solubility in the lithium salt as the supporting salt.

Examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiAlCl ₄ , LiClO ₄ , LiBF ₄ , LiSbF ₆ , Li ₂ SO ₄ , Li ₃ PO ₄ , Li ₂ HPO ₄ , LiH ₂ PO ₄ , LiCF ₃ SO ₃ , LiC. ₄ F ₉ SO ₃ , LiN (FSO ₂ ) ₂ consisting of imide anions, LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₂ F ₅ SO _{2), LiN (CF 3 SO} 2) (C 4 F 9 SO 2), LiN containing a five-membered ring structure _{(CF 2 SO 2) 2 (} CF 2), LiN having a six-membered ring structure _(CF 2 SO ₂ ) ₂ (CF ₂ ) _{2 and the} like. Further, as the lithium salt, LiPF ₅ (CF ₃ ), LiPF ₅ (C ₂ F ₅ ), LiPF ₅ (C ₃ F ₇ ), LiPF _{4 in which} at least one fluorine atom of LiPF ₆ is substituted with a fluorinated alkyl group. (CF ₃ ) ₂ , LiPF ₄ (CF ₃ ) (C ₂ F ₅ ), LiPF ₃ (CF ₃ ) _{3 and the} like can also be mentioned. Moreover, it can replace with the said lithium salt, a sodium salt can also be used, and this lithium salt and this sodium salt can also be used together.

  Moreover, if pH of electrolyte solution is 4-10, you may add the additive of the quantity of 50 mass% or less with respect to electrolyte solution whole quantity. Additives include vinylene carbonate (VC), vinyl ethylene carbonate (VEC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), propylene carbonate (PC), ether Group-containing dimethoxyethane, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, triethylene glycol dimethyl ether, (anhydrous) succinic acid, (anhydrous) maleic acid, γ-butyrolactone, γ-valerolactone, ethylene sulfite, sulfolane, ionic liquid, boron Examples thereof include acid esters, acetonitrile, phosphazene and the like, or those obtained by fluorinating some of the hydrogen groups.

  The concentration of the supporting salt in the electrolytic solution is preferably in the range of 0.1 to 3 mol / L, and more preferably in the range of 0.6 to 1.5 mol / L.

  In the lithium ion secondary battery 1 according to this embodiment, the separator 5 may be impregnated with the electrolyte solution to form the electrolyte layer 6. The separator 5 is impregnated with the electrolyte solution added with the gelling material and then heated. The electrolyte layer 6 may be formed by gelation. As the separator 5, what consists of synthetic resins, such as polyethylene, can be used, for example. Examples of the gelling material include polymers such as polyvinylidene fluoride / hexafluoropropylene (PVDF-HFP), (poly) acrylonitrile, (poly) acrylic acid, and polymethyl methacrylate. The gelation of the gelling material may be performed using a polymerization initiator instead of heating.

  Next, examples and comparative examples of the present invention are shown.

[Example 1]
In this example, first, a copper foil (50 mm × 50 mm) having a thickness of 20 μm was used as a current collector 31, the surface was washed with sulfuric acid, one surface was masked with epoxy tape, and heated to 50 ° C. The film was immersed in an electroless plating bath to form a 1.1 μm thick tin film 32 on the unmasked surface. The tin coating 32 was a porous body having pores with a pore diameter in the range of 0.1 to 300 nm, and the porosity of the porous body was 0.1% by volume. Next, the current collector 31 on which the tin film 32 was formed was cut into a size of 26 mm × 44 mm to form the negative electrode 3.

Next, LiCoO ₂ as a positive electrode active material, a conductive assistant, and polyvinylidene fluoride (PVDF) as a binder are mixed at a mass ratio of 92: 4: 4 to prepare a slurry, and the resulting slurry Was applied to a 15 μm-thick aluminum foil (50 mm × 50 mm) as a current collector 41 by a doctor blade method to form a positive electrode mixture layer 42. Next, the current collector 41 on which the positive electrode mixture layer 42 was formed was cut into a size of 25 mm × 44 mm to obtain the positive electrode 4.

  Next, a 25 μm thick polyethylene separator (30 mm × 50 mm) is disposed as the separator 5 between the negative electrode 3 and the positive electrode 4, and the polyethylene layer is impregnated with an electrolytic solution to form an electrolyte layer 6. The cell was vacuum-sealed to produce a lithium ion secondary battery 1.

As the electrolytic solution, triethyl phosphate (TEP) was used as a solvent, and LiPF ₆ was dissolved in the solvent at a concentration of 1.0 mol / L. Here, when the pH of the electrolyte solution at 25 ° C. was measured with a pH meter (trade name: LAQUA, manufactured by Horiba, Ltd.), it was 9.1.

  Next, the lithium ion secondary battery 1 obtained in this example was left at 25 ° C. for 1 week.

  Next, the lithium ion secondary battery 1 obtained in this example is charged to an upper limit potential of 4.05 V with a charging current of 0.1 mA in an environment of 25 ° C., and after a pause of 10 minutes, to 2.5 V Discharged.

  In the lithium ion secondary battery 1 obtained in this example, the tin film 32 was not dissolved, and charging / discharging was possible.

[Comparative Example 1]
In Comparative Example 1, except that a mixed solvent in which ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed at a volume ratio of 30:30:40 was used as the solvent of the electrolytic solution. A lithium ion secondary battery 1 was fabricated in exactly the same manner as in Example 1. Here, when the pH of the electrolyte solution at 25 ° C. was measured in the same manner as in Example 1, it was 3.1.

  Next, the lithium ion secondary battery 1 obtained in this comparative example was left at 25 ° C. for 1 week.

  Next, the lithium ion secondary battery 1 obtained in this comparative example was charged at a charging current of 0.1 mA in an environment of 25 ° C., but charged to the upper limit potential of 4.05 V even after 20 hours. I couldn't. When the lithium ion secondary battery 1 obtained in this comparative example was disassembled, it was confirmed that the tin film 32 was dissolved.

[Comparative Example 2]
In Comparative Example 2, the same procedure as in Example 1 was used except that a mixed solvent in which propylene carbonate (PC) and diethyl carbonate (DMC) were mixed at a volume ratio of 50:50 was used as a solvent for the electrolytic solution. A lithium ion secondary battery 1 was produced. Here, when the pH of the electrolyte solution at 25 ° C. was measured in the same manner as in Example 1, it was 3.9.

  Next, the lithium ion secondary battery 1 obtained in this comparative example was left at 25 ° C. for 1 week.

  Next, the lithium ion secondary battery 1 obtained in this comparative example was charged at a charging current of 0.1 mA in an environment of 25 ° C., but charged to the upper limit potential of 4.05 V even after 20 hours. I couldn't. When the lithium ion secondary battery 1 obtained in this comparative example was disassembled, it was confirmed that the tin film 32 was dissolved.

[Comparative Example 3]
In Comparative Example 3, a lithium ion secondary battery 1 was produced in the same manner as in Example 1 except that propylene carbonate (PC) was used as a solvent for the electrolytic solution. Here, when the pH of the electrolyte solution at 25 ° C. was measured in the same manner as in Example 1, it was 3.2.

  Next, the lithium ion secondary battery 1 obtained in this comparative example was left at 25 ° C. for 1 week.

  Next, the lithium ion secondary battery 1 obtained in this comparative example was charged at a charging current of 0.1 mA in an environment of 25 ° C., but charged to the upper limit potential of 4.05 V even after 20 hours. I couldn't. When the lithium ion secondary battery 1 obtained in this comparative example was disassembled, it was confirmed that the tin film 32 was dissolved.

[Example 2]
In this example, first, a tin foil having a thickness of 10 μm was punched into a diameter of 15 mm to form a current collector 31, and the current collector 31 itself was used as a negative electrode 3.

Next, LiNi _0.5 Mn _0.3 Co _0.2 O ₂ as the positive electrode active material, acetylene black as the conductive auxiliary agent, and polyvinylidene fluoride (PVDF) as the binder were 94: 3: 3. A slurry was prepared by mixing at a mass ratio of 1.5 μm, and the resulting slurry was applied to a 15 μm thick aluminum foil as a current collector 41 by a doctor blade method to form a positive electrode mixture layer 42. Next, the current collector 41 on which the positive electrode mixture layer 42 was formed was punched out into a size of 14 mm in diameter to obtain the positive electrode 4.

Next, a polyethylene cell having a thickness of 20 μm (diameter 20 mm) is disposed as the separator 5 between the negative electrode 3 and the positive electrode 4, and the separator 5 is impregnated with an electrolytic solution to form an electrolyte layer 6. The lithium ion secondary battery 1 was produced. The electrolytic solution was prepared by mixing triethyl phosphate (TEP) and dimethyl carbonate (DMC) at a volume ratio of 50:50 to form a mixed solvent, and LiPF ₆ was added at a concentration of 1.0 mol / L to the mixed solvent. The dissolved one was used. The pH of the electrolytic solution was measured to be 4.1 in the same manner as in Example 1.

  Next, using the lithium ion secondary battery 1 obtained in this example, 10 hours after fabrication, the lithium ion secondary battery 1 was charged with a voltage in the range of 2.5 to 3.8 V and a current amount of 1C. The discharge was repeated. FIG. 2 shows the change in discharge capacity with respect to the number of charge / discharge cycles as the charge / discharge characteristics at this time.

Example 3
In this example, exactly the same as Example 2 except that a mixed solvent in which triethyl phosphate (TEP) and dimethyl carbonate (DMC) were mixed at a volume ratio of 75:25 was used as the solvent of the electrolytic solution. Thus, a coin cell type lithium ion secondary battery 1 was produced. The pH of the electrolytic solution was 7.7 when measured in the same manner as in Example 1.

  Next, charge / discharge of the lithium ion secondary battery 1 was repeated in the same manner as in Example 2 except that the lithium ion secondary battery 1 obtained in this example was used. FIG. 2 shows the change in discharge capacity with respect to the number of charge / discharge cycles as the charge / discharge characteristics at this time.

Example 4
In the present example, a tin alloy foil having a thickness of 10 μm made of a tin alloy containing 10% by mass of copper with respect to the total amount is punched into a size of 15 mm in diameter as a current collector 31. A coin cell type lithium ion secondary battery 1 was produced in exactly the same manner as in Example 3 except that. It was 7.7 when pH of the electrolyte solution used for the lithium ion secondary battery 1 of the present Example was measured in the same manner as in Example 1.

  Next, charge / discharge of the lithium ion secondary battery 1 was repeated in the same manner as in Example 2 except that the lithium ion secondary battery 1 obtained in this example was used. FIG. 2 shows the change in discharge capacity with respect to the number of charge / discharge cycles as the charge / discharge characteristics at this time.

[Comparative Example 4]
In this comparative example, exactly the same as Example 2 except that a mixed solvent in which triethyl phosphate (TEP) and dimethyl carbonate (DMC) were mixed at a volume ratio of 40:60 was used as the solvent of the electrolytic solution. Thus, a coin cell type lithium ion secondary battery 1 was produced. The pH of the electrolyte was measured to be the same as in Example 1 and was 3.7.

  Next, charge / discharge of the lithium ion secondary battery 1 was repeated in the same manner as in Example 2 except that the lithium ion secondary battery 1 obtained in this comparative example was used. FIG. 2 shows the change in discharge capacity with respect to the number of charge / discharge cycles as the charge / discharge characteristics at this time.

Example 5
In this example, an aluminum foil having a thickness of 15 μm is punched into a diameter of 15 mm to form a current collector 31, the current collector 31 itself is a negative electrode 3, and triethyl phosphate (TEP) is used as a solvent for the electrolyte. A coin cell type lithium ion secondary battery 1 was produced in exactly the same manner as in Example 2 except that a mixed solvent in which fluoroethylene carbonate (FEC) was mixed at a volume ratio of 75:25 was used. The pH of the electrolyte was measured to be the same as in Example 1 and was 6.72.

  Next, charging / discharging with respect to the lithium ion secondary battery 1 was repeated with the electric current amount of 1C with the voltage of the range of 2.5-4.15V using the lithium ion secondary battery 1 obtained by the present Example. FIG. 3 shows the change in discharge capacity with respect to the number of charge / discharge cycles as the charge / discharge characteristics at this time.

Example 6
In this embodiment, a 15 μm thick aluminum alloy foil made of an aluminum alloy containing 10% by mass of copper with respect to the total amount is punched out to a diameter of 15 mm to form a current collector 31, and the current collector 31 itself is connected to the negative electrode 3. A coin cell type lithium ion secondary battery 1 was produced in exactly the same manner as in Example 5 except that. It was 6.72 when pH of the electrolyte solution used for the lithium ion secondary battery 1 of the present Example was measured in the same manner as in Example 1.

  Next, charge / discharge of the lithium ion secondary battery 1 was repeated in the same manner as in Example 5 except that the lithium ion secondary battery 1 obtained in this example was used. FIG. 3 shows the change in discharge capacity with respect to the number of charge / discharge cycles as the charge / discharge characteristics at this time.

Example 7
In the present embodiment, a 15 μm thick aluminum alloy foil made of an aluminum alloy containing 15% by mass of Li with respect to the total amount is punched into a diameter of 15 mm to form a current collector 31, and the current collector 31 itself is connected to the negative electrode 3. A coin cell type lithium ion secondary battery 1 was produced in exactly the same manner as in Example 5 except that. It was 6.72 when pH of the electrolyte solution used for the lithium ion secondary battery 1 of the present Example was measured in the same manner as in Example 1.

  Next, charge / discharge of the lithium ion secondary battery 1 was repeated in the same manner as in Example 5 except that the lithium ion secondary battery 1 obtained in this example was used. FIG. 3 shows the change in discharge capacity with respect to the number of charge / discharge cycles as the charge / discharge characteristics at this time.

Example 8
In this example, first, triethyl phosphate (TEP) and fluoroethylene carbonate (FEC) were mixed at a volume ratio of 75:25 to form a mixed solvent, and LiPF ₆ was added to the mixed solvent at 1.2 mol / L. And a polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) as a gelling material were mixed at a mass ratio of 90:10 to prepare an electrolytic solution.

  Next, a coin cell type lithium ion secondary battery 1 was produced in exactly the same manner as in Example 5 except that the electrolytic solution containing the gelling material was used. It was 6.3 when the pH of the electrolyte was measured in the same manner as in Example 1. In this example, the lithium ion secondary battery 1 was held at a temperature of 60 ° C. for 1 hour to gel the electrolyte solution to form the electrolyte layer 6, then returned to room temperature and left for 10 hours.

  Next, charge / discharge of the lithium ion secondary battery 1 was repeated in the same manner as in Example 5 except that the lithium ion secondary battery 1 obtained in this example was used. FIG. 3 shows the change in discharge capacity with respect to the number of charge / discharge cycles as the charge / discharge characteristics at this time.

[Comparative Example 5]
In this comparative example, exactly the same as Example 5 except that a mixed solvent in which ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate were mixed at a volume ratio of 30:30:40 was used as the solvent of the electrolytic solution. Thus, a coin cell type lithium ion secondary battery 1 was produced. When the pH of the electrolyte was measured in the same manner as in Example 1, it was 3.1.

  Next, charge / discharge of the lithium ion secondary battery 1 was repeated in the same manner as in Example 5 except that the lithium ion secondary battery 1 obtained in this comparative example was used. FIG. 3 shows the change in discharge capacity with respect to the number of charge / discharge cycles as the charge / discharge characteristics at this time.

Example 9
In this example, first, aluminum powder (particle size: 150 nm), acetylene black as a conductive additive, and polyvinylidene fluoride (PVDF) as a binder are mixed at a mass ratio of 80:10:10, and N -Dispersed in methyl-2-pyrrolidone (NMP) to prepare a slurry. In this case, the mass ratio of conductive assistant / binder is 1. The slurry was applied to a copper foil having a thickness of 10 μm as the current collector 31 to form a film 32. Next, the current collector 31 on which the film 32 was formed was cut into a diameter of 15 mm to form the negative electrode 3. Next, a positive electrode 4 was produced in the same manner as in Example 2.

Next, triethyl phosphate (TEP) and fluoroethylene carbonate (FEC) are mixed at a volume ratio of 75:25 to form a mixed solvent, and LiPF ₆ is dissolved in the mixed solvent at a concentration of 1.0 mol / L. Thus, an electrolytic solution was prepared.

  Next, a coin cell-type lithium ion secondary battery 1 was produced in the same manner as in Example 2 except that the negative electrode 3 and the positive electrode 4 produced in this example and the electrolyte prepared in this example were used. did. The pH of the electrolyte was measured to be the same as in Example 1 and was 6.72.

  Next, using the lithium ion secondary battery 1 obtained in this example, charging and discharging of the lithium ion secondary battery 1 was repeated with a current amount of 1 C at a voltage in the range of 2.5 to 4.0 V. FIG. 4 shows the change in discharge capacity with respect to the number of charge / discharge cycles as the charge / discharge characteristics at this time.

Example 10
In this example, first, aluminum powder (particle size 150 nm), acetylene black as a conductive additive, and polyvinylidene fluoride (PVDF) as a binder were mixed in a mass ratio of 85: 5: 10. A slurry was prepared exactly as in Example 9. In this case, the mass ratio of conductive assistant / binder is 0.5. Next, the coin cell type lithium ion secondary was exactly the same as in Example 9, except that the slurry was used to form the film 32 so that the amount of aluminum contained in the film 32 was the same as in Example 9. Battery 1 was produced. It was 6.72 when pH of the electrolyte solution used for the lithium ion secondary battery 1 of the present Example was measured in the same manner as in Example 1.

  Next, charge / discharge of the lithium ion secondary battery 1 was repeated in the same manner as in Example 9 except that the lithium ion secondary battery 1 obtained in this example was used. FIG. 4 shows the change in discharge capacity with respect to the number of charge / discharge cycles as the charge / discharge characteristics at this time.

[Comparative Example 6]
In this comparative example, as the solvent of the electrolytic solution, except that a mixed solvent in which ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed at a volume ratio of 30:30:40 was used. A lithium ion secondary battery 1 was produced in exactly the same manner as in Example 9. In this case, the mass ratio of conductive assistant / binder is 1. When the pH of the electrolyte was measured in the same manner as in Example 1, it was 3.1.

  Next, charge / discharge of the lithium ion secondary battery 1 was repeated in the same manner as in Example 9 except that the lithium ion secondary battery 1 obtained in this comparative example was used. FIG. 4 shows the change in discharge capacity with respect to the number of charge / discharge cycles as the charge / discharge characteristics at this time.

Example 11
In this example, first, a lead foil having a thickness of 20 μm was punched into a diameter of 15 mm to form the current collector 31, and the current collector 31 itself was used as the negative electrode 3. Next, a 50 μm thick Li foil was punched out to a diameter of 16 mm to form a current collector 41, and the current collector 41 itself was used as a counter electrode 4. And using the said negative electrode 3 and the counter electrode 4, except having used the mixed solvent which mixed triethyl phosphate (TEP) and fluoroethylene carbonate (FEC) by the volume ratio of 75:25 as a solvent of the said electrolyte solution. A coin cell type lithium ion secondary battery 1 was produced in exactly the same manner as in Example 5. The pH of the electrolyte was measured to be the same as in Example 1 and was 6.72.

  Next, using the lithium ion secondary battery 1 obtained in this example, charging and discharging of the lithium ion secondary battery 1 with a voltage in the range of 0.1 to 2.5 V and a current amount of 0.1 C are performed in two cycles. went. Table 1 shows the discharge and charge capacities during charging and discharging.

[Comparative Example 7]
In this comparative example, exactly the same as Example 11 except that a mixed solvent in which ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate were mixed at a volume ratio of 30:30:40 was used as the solvent of the electrolytic solution. Thus, a coin cell type lithium ion secondary battery 1 was produced. When the pH of the electrolyte was measured in the same manner as in Example 1, it was 3.1.

  Next, the lithium ion secondary battery 1 was charged and discharged two cycles in exactly the same manner as in Example 11 except that the lithium ion secondary battery 1 obtained in this comparative example was used. Table 1 shows the discharge and charge capacities during charging and discharging.

Example 12
In this example, a coin cell type lithium ion secondary battery 1 was fabricated in exactly the same manner as in Example 11 except that a zinc foil having a thickness of 20 μm was used as the current collector 31. It was 6.72 when pH of the electrolyte solution used for the lithium ion secondary battery 1 of the present Example was measured in the same manner as in Example 1.

  Next, the lithium ion secondary battery 1 obtained in this example was used to charge and discharge the lithium ion secondary battery 1 with a current amount of 0.1 C at a voltage in the range of 0.1 to 2.5 V. . The initial charge / discharge efficiency (charge capacity / discharge capacity) at this time is shown in Table 2.

[Comparative Example 8]
In this comparative example, a mixed solvent in which ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed at a volume ratio of 30:30:40 was used as the solvent of the electrolytic solution. A coin cell type lithium ion secondary battery 1 was produced in the same manner as in Example 12 except for the above. When the pH of the electrolyte was measured in the same manner as in Example 1, it was 3.1.

  Next, the lithium ion secondary battery 1 was charged and discharged in exactly the same manner as in Example 12 except that the lithium ion secondary battery 1 obtained in this comparative example was used. The initial coulomb efficiency (charge capacity / discharge capacity) at this time is shown in Table 2.

  The lithium ion secondary battery of Example 1 in which the negative electrode 3 includes a current collector 31 and a tin film 32 formed on the surface of the current collector 31, and the pH of the electrolyte contained in the electrolyte layer 6 is 9.1. According to 1, it is clear that the tin coating 32 does not dissolve even after one week has passed while the negative electrode 3 is in contact with the electrolytic solution, and charging and discharging are possible.

  On the other hand, the negative electrode 3 includes a current collector 31 and a tin coating 32 formed on the surface of the current collector 31, and the pH of the electrolyte contained in the electrolyte layer 6 is in the range of 3.1 to 3.9 less than 4. According to the lithium ion secondary batteries 1 of Comparative Examples 1 to 3, the tin film 32 is dissolved after one week while the negative electrode 3 is in contact with the electrolytic solution and cannot be charged. it is obvious.

  Further, from FIG. 2, according to the lithium ion secondary battery 1 of Examples 2 and 3, in which the negative electrode 3 is made of tin foil, and the pH of the electrolytic solution contained in the electrolyte layer 6 is in the range of 4.1 to 7.7. Thus, it is clear that the capacity deterioration can be suppressed even when the charge / discharge cycle is repeated, and the negative electrode 3 is made of a tin alloy foil, and the pH of the electrolyte contained in the electrolyte layer 6 is 7.7. According to the lithium ion secondary battery 1 of the present invention, it is clear that the effect of suppressing the deterioration of the capacity is further excellent.

  On the other hand, according to the lithium ion secondary battery 1 of Comparative Example 4 in which the negative electrode 3 is made of tin foil and the pH of the electrolyte contained in the electrolyte layer 6 is 3.7, which is less than 4, when the charge / discharge cycle is repeated It is clear that the capacity is significantly degraded.

  Further, from FIG. 3, the negative electrode 3 is made of an aluminum foil or an aluminum alloy foil, and the pH of the electrolyte contained in the electrolyte layer 6 is in the range of 6.3 to 6.72. According to the battery 1, it is clear that the capacity deterioration can be suppressed even when the charge / discharge cycle is repeated. Further, according to the lithium ion secondary battery 1 of Example 7 in which the negative electrode 3 is made of Li-aluminum alloy foil, or the lithium ion secondary battery 1 of Example 8 in which the electrolytic solution containing the gelling material is gelled. Thus, it is clear that the capacity can be improved as compared with the lithium ion secondary batteries 1 of Examples 5 and 6.

  The reason why the capacity of the lithium ion secondary battery 1 of Example 7 in which the negative electrode 3 is made of Li-aluminum alloy foil is improved as compared with the lithium ion secondary battery 1 of Examples 5 and 6 is that lithium in the aluminum alloy It can be considered that the load on the negative electrode 3 was reduced because the reaction of the following formula (2) with less volume expansion occurred mainly in addition to being able to be taken out as a capacity.

2LiAl + Li → Li ₃ Al ₂ (2)
In addition, the reason why the capacity of the lithium ion secondary battery 1 of Example 8 in which the electrolytic solution containing the gelling material is gelled is improved as compared with the lithium ion secondary battery 1 of Examples 5 and 6. This is probably because the gelled electrolyte acts as a barrier that suppresses the formation of fine particles of the active material and diffusion of the active material into the electrolyte.

  On the other hand, according to the lithium ion secondary battery 1 of Comparative Example 5 in which the negative electrode 3 is made of an aluminum foil and the pH of the electrolyte contained in the electrolyte layer 6 is 3.1 less than 4, the charge / discharge cycle is repeated. It is clear that the capacity is significantly degraded.

  Further, from FIG. 4, the negative electrode 3 is provided with a coating 32 made of aluminum powder, a conductive additive, and a binder, and the pH of the electrolyte contained in the electrolyte layer 6 is 6.72. According to the secondary battery 1, it is clear that the charge / discharge operation can be confirmed. Here, Example 9 where the conductive auxiliary agent / binder (mass ratio) is 1 has a higher cycle capacity retention rate than Example 10 where the conductive auxiliary agent / binder (mass ratio) is 0.5. More preferred. That is, the conductive auxiliary agent / binder (mass ratio) is more preferably larger than 0.5.

  Meanwhile, the lithium ion secondary battery 1 of Comparative Example 6 in which the negative electrode 3 is provided with a film 32 made of aluminum powder, a conductive additive, and a binder, and the pH of the electrolyte contained in the electrolyte layer 6 is 3.1 less than 4. According to the above, it is clear that the charge / discharge capacity after the third charge / discharge cycle is hardly obtained, and the capacity deterioration is remarkable. The reason why the lithium ion secondary battery 1 of Comparative Example 6 can hardly obtain a capacity after the third charge / discharge cycle is that the aluminum powder contained in the coating 32 is an electrolysis whose pH is 3.1 less than 4. It is considered that the negative electrode 3 does not function as an electrode because it is dissolved by the liquid.

  Also, from Table 1, according to the lithium ion secondary battery 1 of Example 11 in which the negative electrode 3 is made of a lead foil and the pH of the electrolyte contained in the electrolyte layer 6 is 6.72, the second charge / discharge cycle is performed. It is clear that the capacity can be obtained without dissolving the lead foil.

  On the other hand, according to the lithium ion secondary battery 1 of Comparative Example 7 in which the negative electrode 3 is made of lead foil and the pH of the electrolyte contained in the electrolyte layer 6 is 3.1 less than 4, the second charge / discharge cycle is performed. It is clear that almost no capacity can be obtained. The reason why the lithium ion secondary battery 1 of Comparative Example 7 can hardly obtain a capacity in the second charge / discharge cycle is that the negative electrode 3 made of lead foil has an electrolyte solution with a pH of 3.1 less than 4. It is thought that it dissolves and does not function as an electrode.

  Further, from Table 2, according to the lithium ion secondary battery 1 of Example 12 in which the negative electrode 3 is made of zinc foil and the pH of the electrolytic solution contained in the electrolyte layer 6 is 6.72, it is contained in the electrolyte layer 6. It is apparent that the initial coulomb efficiency is greatly improved as compared with the lithium ion secondary battery 1 of Comparative Example 8 in which the pH of the electrolytic solution is 3.1 which is less than 4. The reason why the initial Coulomb efficiency is low in the lithium ion secondary battery 1 of Comparative Example 8 is that the negative electrode 3 made of zinc foil is dissolved by an electrolyte solution having a pH of 3.1 less than 4, and does not function as an electrode. This is probably because of this.

  DESCRIPTION OF SYMBOLS 1 ... Lithium ion secondary battery, 3 ... Negative electrode, 4 ... Positive electrode (counter electrode), 6 ... Electrolyte layer, 31 ... Current collector, 32 ... Tin film | membrane.

Claims (5)

In a lithium ion secondary battery comprising a negative electrode, a positive electrode, and an electrolyte layer located between the negative electrode and the positive electrode,
The negative electrode includes at least one metal selected from the group consisting of tin, lead, aluminum, and zinc,
The electrolyte layer includes an electrolyte solution containing a solvent and a supporting salt and having a pH in the range of 4 to 10.   The lithium ion secondary battery according to claim 1, wherein the solvent contains a phosphate ester.   3. The lithium ion secondary battery according to claim 2, wherein the phosphate ester has a hydrocarbon group having 3 or less carbon atoms in a side chain. 4.   4. The lithium ion secondary battery according to claim 1, wherein the electrolyte layer includes the gelled electrolyte solution containing a gelling material. 5. .   5. The lithium ion secondary battery according to claim 1, wherein the negative electrode is made of an alloy containing at least one metal selected from the group consisting of tin, lead, aluminum, and zinc. A lithium ion secondary battery characterized by the above.