JP6068237B2 - Electrolyte-negative electrode structure and lithium ion secondary battery comprising the same - Google Patents

Description

  The present invention relates to an electrolyte-negative electrode structure and a lithium ion secondary battery including the same.

  In recent years, in order to increase the battery capacity of lithium ion secondary batteries, a high capacity material capable of occluding lithium ions by reacting with lithium ions such as silicon, silicon oxide and tin oxide to form a compound is used. Use as a substance is under consideration. For example, a negative electrode formed by depositing a negative electrode active material layer made of silicon on a copper foil as a current collector, and a separator disposed in contact with the negative electrode are impregnated with an electrolyte solution in which a supporting salt is dissolved in an organic solvent. There has been proposed a lithium ion secondary battery comprising an electrolyte as described above (see Patent Document 1).

International Publication No. 01/029913

  However, in the lithium ion secondary battery, the negative electrode active material layer greatly expands and contracts as lithium ions are occluded and released by charging and discharging. As a result, when charging / discharging is repeated, the negative electrode active material layer is cracked by the stress generated by the expansion and contraction, and the negative electrode active material layer is peeled off from the current collector, resulting in a decrease in cycle performance. There is an inconvenience.

  An object of the present invention is to provide a configuration that can eliminate such inconvenience and can suppress a decrease in cycle performance when charging and discharging are repeated for a lithium ion secondary battery. Furthermore, this invention also aims at providing a lithium ion secondary battery provided with the said structure.

In order to achieve such an object, the present invention provides an electrolyte-negative electrode structure used in a lithium ion secondary battery, in which a negative electrode active material layer made of a material capable of occluding lithium ions is formed on a current collector. A negative electrode, inorganic particles having lithium ion conductivity, an organic polymer capable of binding the inorganic particles and impregnating a polymer gel, and holding an electrolyte having lithium ion conductivity and the organic polymer The negative electrode active material layer and the solid electrolyte are integrated using the organic polymer as a medium, and the inorganic particles have the chemical formula Li _7-y La _3. during _{-x a x Zr 2-y M} y O 12 ( wherein, a is Y, Nd, Sm, is any one metal selected from the group consisting of Gd, x is in the range of 0 ≦ x <3 And M is Nb or T And y is in the range of 0 ≦ y <2, and a composite metal oxide having a garnet structure and a coating film that covers the surface of the composite metal oxide, The film includes one or more metal oxides selected from the group consisting of Li, Y, and Zr.

  In the electrolyte-negative electrode structure of the present invention, the solid electrolyte is impregnated with the inorganic particles by the organic polymer, and the organic polymer is impregnated with the polymer gel that holds the electrolytic solution. . And the said solid electrolyte and the negative electrode active material layer formed on the said collector are joined and integrated by the said organic polymer. Moreover, when the inorganic particles constituting the solid electrolyte are provided with a coating film made of the oxide on the surface of the composite metal oxide, the solid electrolyte and the negative electrode active material layer are more closely attached. As described above, when the electrolyte-negative electrode structure is used for a lithium ion secondary battery, even if the negative electrode active material layer repeatedly expands and contracts due to charge and discharge, the solid-state stress generated by the expansion and contraction is increased. It can be mitigated by the electrolyte.

In the electrolyte-negative electrode structure according to the present invention, the inorganic particles may have the chemical formula Li _7-y La _3-x A _x Zr _{2- y My} O ₁₂ (wherein A represents Y, Nd, Sm, Gd). Any one metal selected from the group consisting of: x is in the range of 0 ≦ x <3, M is Nb or Ta, and y is in the range of 0 ≦ y <2. And a composite metal oxide having a garnet-type structure.

In the composite metal oxide, the reduction potential based on the potential of the Li ⁺ / Li electrode reaction is smaller than lithium, silicon, tin or the like used as the negative electrode active material layer made of a material capable of occluding lithium ions. For this reason, the electrolyte-negative electrode structure of the present invention suppresses the occurrence of a redox reaction at the interface between the solid electrolyte and the negative electrode active material layer separately from the battery reaction when used in a lithium ion secondary battery. And it can prevent that this solid electrolyte reduces and deteriorates.

  Therefore, according to the electrolyte-negative electrode structure of the present invention, it is possible to prevent the negative electrode active material layer from being peeled off from the current collector by the stress and to prevent the solid electrolyte from deteriorating. It is possible to suppress a decrease in cycle performance.

  Moreover, in the electrolyte-negative electrode structure of the present invention, the coating film covering the composite metal oxide constituting the inorganic particles preferably contains a Zr oxide, and more effectively suppresses the deterioration in cycle performance. Can be obtained.

  Furthermore, the electrolyte-negative electrode structure of the present invention can be applied to a lithium ion secondary battery.

Explanatory sectional drawing which shows the structure of a lithium ion secondary battery provided with the electrolyte-negative electrode structure of this embodiment. Sectional image which shows the junction surface of the electrolyte-negative electrode structure of this embodiment. The graph which shows the cycle performance of a lithium ion secondary battery provided with the electrolyte-negative electrode structure of this embodiment.

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

  As shown in FIG. 1, a lithium ion secondary battery 1 of this embodiment includes a positive electrode 2 containing a positive electrode active material, a negative electrode 5 formed by forming a negative electrode active material layer 4 on a negative electrode current collector 3, A solid electrolyte 6 disposed between the positive electrode 2 and the negative electrode 5. In the lithium ion secondary battery 1, the negative electrode active material layer 4 and the solid electrolyte 6 are integrated to form an electrolyte-negative electrode structure 7.

  As the positive electrode 2, for example, one formed by pressure-bonding a positive electrode active material layer on a positive electrode current collector can be used.

  As the positive electrode current collector, for example, a metal foil or a metal plate made of aluminum, stainless steel, or the like can be used.

The positive electrode active material layer includes, for example, a positive electrode active material such as a transition metal oxide, a composite oxide of lithium and a transition metal oxide, a transition metal sulfide, or an organic compound. Specifically, as the transition metal oxide, for example, MnO, V ₂ O ₃ , V ₆ O ₁₂ , TiO ₂ or the like can be used. In addition, as a composite oxide of lithium and a transition metal oxide, for example, lithium nickelate, lithium cobaltate, or the like can be used. As examples of the transition metal sulfides, for example, can be used TiS, FeS, and MoS ₂ and the like. As the organic compound, polyaniline, polypyrrole, polyacene, disulfide compounds, polysulfide compounds, N-fluoropyridinium salts, and the like can be used. Furthermore, lithium iron phosphate having an olivine structure can be used as the positive electrode active material.

  The negative electrode 5 includes a negative electrode current collector 3 and a negative electrode active material layer 4 that is pressure-bonded to one surface of the negative electrode current collector 3 and contains a negative electrode active material.

  For the negative electrode current collector 3, for example, a metal foil or a metal plate made of copper or SUS can be used.

  The negative electrode active material layer 4 includes, for example, a negative electrode active material such as a metal or carbon made of a high capacity material capable of occluding lithium. As the metal, for example, lithium, silicon, tin, and oxides and alloys containing these metals can be used.

  The solid electrolyte 6 includes inorganic particles having lithium ion conductivity, an organic polymer that binds the inorganic particles and can be impregnated with a polymer gel, and holds an electrolytic solution having lithium ion conductivity and the organic polymer. The polymer gel is impregnated into.

The inorganic particles include a powdered composite metal oxide and a coating film that covers the surface of the composite metal oxide. The complex metal oxide chemical formula _{Li 7-y La 3-x} A x Zr 2-y M y O 12 ( wherein, A is Y, Nd, Sm, any one selected from the group consisting of Gd X is in the range of 0 ≦ x <3, M is Nb or Ta, and y is in the range of 0 ≦ y <2, and has a garnet-type structure. The coating film includes an oxide of one or more metals selected from the group consisting of Li, Y, and Zr.

  The inorganic particles can be prepared, for example, as follows. First, in addition to the Li compound, the La compound, and the Zr compound, if necessary, any one metal compound selected from the group consisting of Y, Nd, Sm, and Gd, and an Nb or Ta compound. The mixture is pulverized and mixed with a pulverizing and mixing device such as a ball mill or a mixer to obtain a mixture.

As the Li compound, for example, a LiOH or a hydrate _{thereof, Li 2 CO 3, LiNO 3} , CH 3 COOLi like. Examples of the La compound include La ₂ O ₃ , La (OH) ₃ , La ₂ (CO ₃ ) ₃ , La (NO ₃ ) ₃ , (CH ₃ COO) ₃ La, and the like. Examples of the Zr compound include Zr ₂ O ₂ , ZrO (NO ₃ ) ₂ , ZrO (CH ₃ COO) ₂ , Zr (OH) ₂ CO ₃ , ZrO _{2 and the} like.

Examples of the Y compound include Y ₂ O ₃ , Y ₂ (CO ₃ ) ₃ , Y (NO ₃ ) ₃ , (CH ₃ COO) ₃ Y, and the like. Examples of the Nd compound include Nd ₂ O ₃ , Nd ₂ (CO ₃ ) ₃ , Nd (NO ₃ ) ₃ , (CH ₃ COO) ₃ Nd, and the like. Examples of the Sm compound include Sm ₂ O ₃ , Sm ₂ (CO ₃ ) ₃ , Sm (NO ₃ ) ₃ , (CH ₃ COO) ₃ Sm, and the like. Examples of the Gd compound include Gd ₂ O ₃ , Gd ₂ (CO ₃ ) ₃ , Gd (NO ₃ ) ₃ , (CH ₃ COO) ₃ Gd, and the like.

Examples of the Nb compound include Nb ₂ O ₅ , NbO ₂ , NbCl ₅ , LiNbO _{3 and the} like. Examples of the Ta compound include Ta ₂ O ₅ , TaCl ₅ , LiTaO _{3 and the} like.

  The resulting mixture is then primarily fired at a temperature in the range of 850-950 ° C. for a time in the range of 5-7 hours. Next, the fired body obtained by the primary firing is pulverized and mixed again by a ball mill, a mixer or the like using a mixing device, and then held at a temperature in the range of 1000 to 1200 ° C. for 6 to 12 hours. The powdery composite metal oxide is prepared by secondary firing.

  In order to use the powdery composite metal oxide as a lithium ion conductive material, it is preferable to have a particle size of 20 μm or less, particularly preferably 10 μm or less. When many particles having a particle size larger than 20 μm are contained, the inorganic particles obtained by the baking are pulverized by, for example, a ball mill, a mixer or the like, and mixed by a mixing device so as to have a particle size of 20 μm or less. To. By setting the particle size of the inorganic particles to 20 μm or less, the density of the inorganic particles present in the solid electrolyte 6 can be increased, and the solid electrolyte 6 itself can be formed thin to reduce the resistance. .

  Next, one or more metal compounds selected from the group consisting of Li, La, and Zr are added to a solvent and mixed by stirring to prepare a solution in which the metal compound is dissolved or dispersed. .

  Examples of the compound containing Li include lithium alkoxide compounds such as lithium oxide, lithium peroxide, lithium hydroxide, lithium carbonate, lithium acetate, lithium nitrate, lithium chloride, lithium fluoride, and lithium ethoxide. .

  Examples of the compound containing Y include yttrium alkoxide compounds such as yttrium oxide, yttrium hydroxide, yttrium carbonate, yttrium acetate, yttrium nitrate, yttrium chloride, yttrium fluoride, yttrium phosphate, yttrium acetylacetonate, and yttrium isopropoxide. Etc. can be used.

  Zr-containing compounds include zirconium hydroxide, zirconium oxide, carbonate basic zirconium, zirconium oxyacetate, zirconium oxynitrate, zirconium chloride, zirconium oxychloride, zirconium fluoride, zirconium acetylacetonate, zirconium ethoxide, and other zirconium alkoxides. A compound or the like can be used.

  As the solvent, water, methanol, ethanol, 2-propanol, butanol, ethylene glycol, toluene, cyclohexane and the like can be used, and a mixture thereof can also be used.

  Next, the obtained powdered composite metal oxide is mixed by adding to a solution in which one or more metal compounds selected from the group consisting of Li, Y, and Zr are dissolved or dispersed and stirring. Then, the solution is adhered to the surface of the composite metal oxide. At this time, the solution of the one or more kinds of metals is surely adhered to the surface of the composite metal oxide by making the total amount thereof be 1 to 10 mol% with respect to the composite metal oxide. Can be made. Further, by performing the stirring at a temperature of 40 to 80 ° C. for 1 minute to 6 hours, the solution is surely adhered to the surface of the composite metal oxide and the coating film is adjusted to an appropriate thickness. can do. Further, instead of mixing the powdery composite metal oxide and the solution, a solution in which the powdered composite metal oxide is dissolved or dispersed in the solvent, and the compound of one or more kinds of metals is added. A solution dissolved or dispersed in a solvent may be mixed, or the mixed metal oxide and the one or more metal compounds may be mixed and then dissolved or dispersed in the solvent.

  Next, by heating the composite metal oxide having a solution containing the one or more metal compounds attached to the surface to remove the solvent in the solution, the one or more metal compounds are obtained. The composite metal oxide adhered to the surface is obtained. The removal of the solvent can be performed, for example, as follows. First, a mixed solution obtained by mixing the composite metal oxide and a solution containing one or more kinds of metal compounds is filtered, and the composite metal oxidation in which the solution containing the one or more kinds of metal compounds is attached to the surface The product and the solvent are separated. Next, the solvent in the solution adhering to the surface of the powdered composite metal oxide is removed by heating the residue obtained by the filtration. Alternatively, by treating a mixed solution obtained by mixing the composite metal oxide and the solution containing the one or more metal compounds with a rotary evaporator, the solution in the solution attached to the surface of the powdered composite metal oxide The solvent may be removed.

Next, firing the composite metal oxide having one or more metal compounds selected from the group consisting of Li, Y, and Zr attached to the surface at a temperature of 300 to 800 ° C. for 1 to 6 hours. To oxidize the one or more metal compounds. As described above, the inorganic particles in which the surface of the composite metal oxide is coated with the coating film containing an oxide of one or more metals selected from the group consisting of Li, Y, and Zr can be obtained. Examples of the oxide of one or more metals selected from the group consisting of Li, Y, and Zr include, for example, Li ₂ O, Li ₂ O ₂ , Y ₂ O ₃ , LiYO ₂ , ZrO ₂ , and Li ₂ ZrO _3. , Li ₄ Zr ₃ O ₈ , Li ₆ Zr ₂ O ₇ , Zr _1-x Y _x O _{2−x / 2} (0 <x <0.6), La _2−x Y _x Zr ₂ O ₇ (0 < x <1) and the like can be mentioned, among which Y ₂ O ₃ , LiYO ₂ , ZrO ₂ , and Li ₂ ZrO ₃ can be preferably used. The coating film containing one or more metal oxides preferably has a thickness of 100 nm or less in order to prevent an increase in resistance and weight.

  The organic polymer constituting the solid electrolyte 6 is required to act as a binder for the inorganic particles and to be impregnated with the polymer gel and to be stable at the operating voltage of the lithium secondary battery. Examples of the organic polymer include polyolefins such as polyethylene and polypropylene, fluorine resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride, polyimide, acrylic resin, styrene butadiene rubber (SBR), and carboxymethyl cellulose (CMC). One or two or more resins selected from the group can be used.

  The polymer gel constituting the solid electrolyte 6 is composed of an electrolytic solution composed of a lithium salt as a supporting salt and an organic solvent that dissolves the lithium salt, and a polymer that holds the electrolytic solution. In order to achieve both lithium ion conductivity and mechanical strength as the polymer gel, the polymer gel preferably holds the electrolytic solution in a range of 30 to 95% by mass, and 50 to 95% by mass. It is particularly preferred to retain a range of the electrolyte.

Examples of the lithium salt, for _example, can be used _{LiPF 6, LiBF 4, LiClO 4} , LiCF 3 SO 3, LiN (CF 3 SO 2) 2 and the like.

  Examples of the organic solvent include cyclic esters such as ethylene carbonate (EC), propylene carbonate (PC), and γ-butyrolactone (γ-BL), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). ) And the like can be used.

  As the polymer constituting the polymer gel, for example, a thermoplastic organic polymer such as polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), or the like can be used.

  In the solid electrolyte 6, the inorganic particles and the organic polymer have a mass ratio of 99: 1 to 95: 5, and the inorganic particles, the polymer gel, and the organic polymer are mixed in 77: 8: 15 to 38: A volume ratio in the range of 32:30 is preferable. In this way, the inorganic particles and the polymer gel can be uniformly dispersed in the solid electrolyte 6 to form a lithium ion conduction path throughout the solid electrolyte 6, and excellent lithium ion conductivity. Can be obtained. Further, the organic polymer binds the inorganic particles, so that the structure as the solid electrolyte 6 can be surely formed.

  In the electrolyte-negative electrode structure 7, the solid electrolyte 6 and the negative electrode active material layer 4 are joined and integrated by the organic polymer.

  The electrolyte-negative electrode structure 7 can be formed, for example, as follows. First, a paste formed by mixing the inorganic particles and the organic polymer is formed on the negative electrode active material layer 4 of the negative electrode 5 by a casting method using a doctor blade, and then dried. 5 and a dry body 6a of the paste are formed. Next, by pressurizing the obtained laminate, the negative electrode 5 and the dry body 6a are joined and integrated to form the joined body 7a.

  Next, an electrolytic solution having lithium ion conductivity and a polymer powder constituting the polymer gel are mixed to prepare a sol-like liquid. Next, the obtained sol-like liquid is pressed into the joined body 7a to impregnate the dried body 6a of the joined body 7a, and then naturally cooled to gel the sol-like liquid, thereby forming an electrolyte-negative electrode structure. The body 7 can be obtained.

  In the electrolyte-negative electrode structure 7 of the present embodiment, the solid electrolyte 6 includes the inorganic particles bound by an organic polymer and the organic polymer impregnated with the polymer gel that holds the electrolytic solution. Yes. The solid electrolyte 6 and the negative electrode active material layer 4 formed on the negative electrode current collector 3 are joined and integrated by the organic polymer. Further, the inorganic particles constituting the solid electrolyte 6 are provided with the coating film made of the oxide on the surface of the composite metal oxide, whereby the solid electrolyte 6 and the negative electrode active material layer 4 are more closely adhered to each other. . As described above, when the electrolyte-negative electrode structure 7 is used in the lithium ion secondary battery 1, even if the negative electrode active material layer 4 repeatedly expands and contracts due to charge and discharge, the stress generated by the expansion and contraction is solid. It can be relaxed by the electrolyte 6.

Moreover, in the electrolyte-negative electrode structure 7 of this embodiment, the inorganic particles constituting the solid electrolyte 6 include a composite metal oxide represented by the chemical formula and having a garnet structure. The composite metal oxide has a reduction potential in the range of −1.67 to −0.06 V, based on the potential of the Li ⁺ / Li electrode reaction. On the other hand, the high-capacity material that can occlude lithium ions constituting the negative electrode active material layer 4 has a reduction potential of 0.5 V for silicon, 0.5 V for silicon oxide, and 1.0 V for tin, for example. That is, the composite metal oxide has a lower reduction potential than the high-capacity material capable of occluding lithium ions. Therefore, when the electrolyte-negative electrode structure 7 of the present embodiment is used for the lithium ion secondary battery 1, an oxidation-reduction reaction occurs at the interface between the solid electrolyte 6 and the negative electrode active material layer 4 separately from the battery reaction. It is possible to prevent the solid electrolyte 6 from being reduced and deteriorated.

  Therefore, according to the electrolyte-negative electrode structure 7 of the present embodiment, it is possible to prevent the negative electrode active material layer 4 from being peeled off from the negative electrode current collector 3 due to the stress and to prevent the solid electrolyte 6 from deteriorating. Therefore, a decrease in cycle performance can be suppressed.

  Moreover, since the electrolyte-negative electrode structure 7 is in good contact with the solid electrolyte 6 and the negative electrode active material layer 4 that are integrated, the contact resistance between the solid electrolyte 6 and the negative electrode active material layer 4 is good. Can be suppressed.

  In addition, the electrolyte-negative electrode structure 7 can handle the solid electrolyte 6 in a state supported by the negative electrode 5 instead of handling the solid electrolyte 6 alone as in the prior art, and can obtain excellent handling properties. The solid electrolyte 6 can be secured to a required strength to avoid breakage.

  The reduction potential is calculated by using a first principle calculation method, specifically, a first principle electronic state calculation program VASP (Vienna Ab initio Simulation Package), GGA (Generalized Gradient Approximation) / PAW (Projector Augmented). Wave) method can be calculated under the conditions of cutoff energy 480 eV and k point = 3 × 3 × 3.

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

[Example 1]
[1. Preparation of oxide-coated inorganic particles]
In this example, lithium hydroxide monohydrate was first subjected to dehydration treatment by heating at 350 ° C. for 6 hours in a vacuum atmosphere to obtain lithium hydroxide anhydride. In addition, lanthanum oxide was dehydrated and decarboxylated by heating at 950 ° C. for 24 hours in an air atmosphere.

  Next, in addition to the obtained lithium hydroxide anhydride and dehydrated and decarboxylated lanthanum oxide, zirconium oxide is added so that the molar ratio is Li: La: Zr = 7.7: 3: 2. After mixing, using a planetary ball mill, the mixture was pulverized and mixed at 360 rpm for 3 hours to obtain a mixed raw material.

  The obtained mixed raw material was accommodated in an alumina crucible, and held in an air atmosphere at a temperature of 900 ° C. for 6 hours to perform primary firing, thereby obtaining a powdery primary fired product.

Next, the obtained primary fired product was pulverized for 3 hours at 360 rpm using a planetary ball mill, and then stored in an alumina crucible, and kept in an air atmosphere at a temperature of 1050 ° C. for 6 hours to obtain a secondary product. By firing, a powdered composite metal oxide was obtained. The composite metal oxide is represented by a chemical formula Li ₇ La ₃ Zr ₂ O ₁₂ , is composed of a composite metal oxide having a garnet structure, and has lithium ion conductivity. The chemical formula Li ₇ La ₃ Zr ₂ O ₁₂ corresponds to the case where x = 0 and y = 0 in the Li _7-y La _3-x A _x Zr _{2- y My} O ₁₂ . The obtained powdery composite metal oxide had an average particle size of 8.5 μm.

  Next, the obtained powdery composite metal oxide is added to a solution obtained by dissolving 5 mol% of zirconium ethoxide in ethanol with respect to the composite metal oxide, and 1 at a temperature of 50 ° C. using a hot stirrer. By mixing for a period of time, the solution containing zirconium ethoxide was adhered to the surface of the composite metal oxide.

Next, the composite metal oxide having a solution containing zirconium ethoxide attached to the surface is subjected to solid filtration by suction filtration, and then the obtained residue is dried under reduced pressure at a temperature of 120 ° C. for 12 hours. Thus, 2-propanol contained in the filtrate was removed. Next, the filtrate from which 2-propanol was removed was heated to a temperature of 600 ° C. at a rate of 5 ° C./min, and held at a temperature of 600 ° C. for 6 hours to obtain inorganic particles. In the obtained inorganic particles, the surface of the composite metal oxide having a garnet structure represented by the chemical formula Li ₇ La ₃ Zr ₂ O ₁₂ is covered with a coating layer containing zirconium oxide.

[2. Preparation of paste containing inorganic particles and organic polymer]
Next, as an organic polymer, 40% by mass of styrene butadiene rubber (SBR) dispersion and 1.5% by mass of carboxymethylcellulose (CMC) aqueous solution were used, and the obtained inorganic particles, SBR, and CMC were used. The mixture was obtained by mixing at a mass ratio of 98: 1: 1 and stirring using a rotation / revolution mixer. Next, after defoaming the obtained mixture, the inorganic particles, SBR, and CMC were dispersed as a paste containing inorganic particles and an organic polymer by mixing using a thin-film swirling mixer. A paste was prepared.

[3. Production of negative electrode]
Next, Si powder (average particle size 10 μm), Ketjen black (trade name: EC600JD, Lion Corporation, hereinafter abbreviated as KB), flaky copper powder (Mitsui Metal Mining Co., Ltd.), solid A polyamic acid solution containing 40% by mass (trade name: SKYBOND700, I.S.T.) is mixed at a mass ratio of 75: 5: 5: 15 and stirred using a rotation / revolution mixer. This gave a mixture. Next, after defoaming the obtained mixture, the second paste in which the Si powder, KB, copper powder, and polyamic acid are dispersed is obtained by mixing using a thin film swirling mixer. It was.

  Next, a thin film made of the second paste is formed on the negative electrode current collector 3 made of an electrolytic copper foil (Fukuda Metal Foil Powder Co., Ltd.) having a thickness of about 40 μm by a casting method using a doctor blade, Thereafter, the polyamic acid was polymerized and imidized by heating at a temperature of 300 ° C. under a vacuum of 200 Pa to form the negative electrode active material layer 4 having a thickness of about 50 μm. As a result, a negative electrode 5 in which the negative electrode active material layer 4 was formed on the negative electrode current collector 3 was obtained.

[4. Preparation of electrolyte-negative electrode structure]
Next, a thin film made of the first paste is formed on the negative electrode active material layer 4 of the obtained negative electrode 5 by a casting method using a doctor blade, and dried by heating at a temperature of 70 ° C. for 2 hours. Thus, a laminate composed of the negative electrode 5 and the dried body 6a of the first paste was formed. Next, after cutting the obtained laminate into a circle having a diameter of 17 mm, the negative electrode active material layer 4 and the dry body 6a of the first paste are joined and integrated by pressurizing with a pressure of 20 MPa, and then 200 Pa. The joined body 7a was formed by heating at a temperature of 150 ° C. under a vacuum of.

  Next, a cross section of the obtained bonded body 7a was observed by SEM. FIG. 2 shows a cross-sectional image of the joined body 7a. From FIG. 2, it is clear that the dry body 6a made of the inorganic particles and the organic polymer and the negative electrode active material layer 4 are integrated.

Next, LiPF ₆ as a supporting salt is dissolved at a concentration of 0.8 mol / L in an organic solvent obtained by mixing ethylene carbonate (EC) and propylene carbonate (PC) at a volume ratio of 1: 1. An electrolytic solution having ionic conductivity was prepared. 88 parts by mass of the obtained electrolytic solution and polyacrylonitrile powder (molecular weight: 150,000) were mixed at a temperature of 120 ° C. in an argon atmosphere to prepare a sol-like liquid.

  Next, the joined body 7a is impregnated with the sol-like liquid by press-fitting and allowed to stand at room temperature for 12 hours, so that the pores present in the joined body 7a are filled with the sol-like liquid and the sol-like liquid is filled. Was naturally cooled and gelled. Thus, an electrolyte-negative electrode structure 7 in which the solid electrolyte 6 and the negative electrode active material layer 4 of the negative electrode 5 were integrated was formed. In the obtained electrolyte-negative electrode structure 7, the volume ratio of the inorganic particles to the organic polymer composed of SBR and CMC was 81.8: 18.2.

[5. Preparation of positive electrode and lithium ion secondary battery]
Next, carbon-coated LiFePO ₄ powder (manufactured by Hosen Co., Ltd.), ketjen black (trade name: EC600JD, manufactured by Lion Corporation) as a conductive additive, and polytetrafluoroethylene (as a binder) PTFE) at a mass ratio of 88: 6: 6 using ethanol as a solvent to obtain a positive electrode mixture.

The obtained positive electrode mixture was formed into a pellet shape with a die having a diameter of 16 mm, and then pressed onto a stainless mesh (SUS316L) as a positive electrode current collector, whereby LiFePO as a positive electrode active material was formed on the positive electrode current collector. _A positive electrode 2 formed by forming a positive electrode active material layer containing ₄ was obtained.

  Next, the lithium ion secondary battery 1 was produced by sticking the positive electrode 2 to the solid electrolyte 6 of the electrolyte-negative electrode structure 7 obtained in this example.

[6. (Evaluation of cycle performance of lithium ion secondary battery)
The lithium ion secondary battery provided with the electrolyte-negative electrode structure 7 obtained in this example was mounted on an electrochemical measurement device (manufactured by Toho Giken Co., Ltd.). Next, an operation of applying a current between the positive electrode 2 and the negative electrode 5 at a temperature of 25 ° C. to charge the cell voltage to 4.0 V and then discharging the cell voltage to 2.0 V is performed. The cycle performance was evaluated by repeating 100 cycles. The current application was performed at a current density of 0.375 mA / cm ² . The discharge capacity density at the end of each cycle is shown in FIG. 3, and the discharge capacity density at the 100th cycle is shown in Table 1.

[Example 2]
In this example, first, instead of the solution in which 5 mol% of zirconium ethoxide was dissolved in ethanol, 5 mol% of zirconium ethoxide and 5 mol% of lithium ethoxide were dissolved in ethanol with respect to the composite metal oxide. Inorganic particles were prepared in the same manner as in Example 1 except that the solution was used. In the obtained inorganic particles, the surface of the composite metal oxide having a garnet structure represented by the chemical formula Li ₇ La ₃ Zr ₂ O ₁₂ is coated with a coating layer containing zirconium oxide and lithium zirconate.

  Next, a lithium ion secondary battery 1 was produced in the same manner as in Example 1 except that the inorganic particles obtained in this example were used.

  Next, the cycle performance was evaluated in exactly the same manner as in Example 1 except that the lithium ion secondary battery 1 obtained in this example was used. Table 1 shows the discharge capacity density at the 100th cycle.

Example 3
In this example, first, instead of the solution of 5 mol% of zirconium ethoxide dissolved in ethanol, 5 mol% of yttrium isopropoxide and 5 mol% of lithium isopropoxide were added to the composite metal oxide. Inorganic particles were prepared in the same manner as in Example 1 except that a solution dissolved in a propanol solution was used. In the obtained inorganic particles, the surface of the composite metal oxide having a garnet structure represented by the chemical formula Li ₇ La ₃ Zr ₂ O ₁₂ is coated with a coating layer containing yttrium oxide and lithium yttrium oxide.

  Next, a lithium ion secondary battery 1 was produced in the same manner as in Example 1 except that the inorganic particles obtained in this example were used.

  Next, the cycle performance was evaluated in exactly the same manner as in Example 1 except that the lithium ion secondary battery 1 obtained in this example was used. Table 1 shows the discharge capacity density at the 100th cycle.

Example 4
In this example, first, instead of the solution of 5 mol% of zirconium ethoxide dissolved in ethanol, 5 mol% of yttrium isopropoxide and 10 mol% of lithium isopropoxide were added to the composite metal oxide. Inorganic particles were prepared in the same manner as in Example 1 except that a solution dissolved in a propanol solution was used. In the obtained inorganic particles, the surface of the composite metal oxide having a garnet structure represented by the chemical formula Li ₇ La ₃ Zr ₂ O ₁₂ is coated with a coating layer containing yttrium oxide and lithium yttrium oxide.

  Next, a lithium ion secondary battery 1 was produced in the same manner as in Example 1 except that the inorganic particles obtained in this example were used.

  Next, the cycle performance was evaluated in exactly the same manner as in Example 1 except that the lithium ion secondary battery 1 obtained in this example was used. Table 1 shows the discharge capacity density at the 100th cycle.

[Comparative Example 1]
In this comparative example, the powdery composite metal oxide was prepared exactly as in Example 1, and the composite metal oxide was used as inorganic particles. The obtained inorganic particles do not have a coating layer on the surface of the composite metal oxide.

  Next, a lithium ion secondary battery 1 was produced in the same manner as in Example 1 except that the inorganic particles obtained in this comparative example were used.

  Next, the cycle performance was evaluated in the same manner as in Example 1 except that the lithium ion secondary battery 1 obtained in this comparative example was used. The discharge capacity density at the end of each cycle is shown in FIG. 3, and the discharge capacity density at the 100th cycle is shown in Table 1.

  From FIG.

  From FIG. 3, the lithium ion secondary battery 1 of Example 1 in which the inorganic particles constituting the electrolyte-negative electrode structure 7 have a coating layer containing zirconium oxide on the surface of the composite metal oxide is As compared with the lithium ion secondary battery 1 of Comparative Example 1 having no coating layer on the surface, it is clear that the cycle performance is excellent when charging and discharging are repeated.

  Further, from Table 1, the inorganic particles constituting the electrolyte-negative electrode structure 7 are coated with the oxide of one or more metals selected from the group consisting of Li, Y, and Zr on the surface of the composite metal oxide. Compared with the lithium ion secondary battery 1 of Comparative Example 1 in which the lithium ion secondary battery of Example 1-4 including the layer does not include any coating layer on the surface of the composite metal oxide, the 100th cycle It is clear that it has an excellent discharge capacity density in charge and discharge. Moreover, it is clear that the lithium ion secondary battery 1 of Example 1-2 in which the inorganic particles have a coating layer containing a Zr oxide has a particularly excellent discharge capacity density in charge and discharge at the 100th cycle.

  DESCRIPTION OF SYMBOLS 1 ... Lithium ion secondary battery, 3 ... Current collector (negative electrode current collector), 4 ... Negative electrode active material layer, 5 ... Negative electrode, 6 ... Solid electrolyte, 7 ... Electrolyte-negative electrode structure.

Claims (3)

An electrolyte-negative electrode structure used in a lithium ion secondary battery,
A negative electrode formed by forming a negative electrode active material layer made of a material capable of occluding lithium ions on a current collector;
Inorganic particles having lithium ion conductivity, organic polymers that bind the inorganic particles and can be impregnated with a polymer gel, and high electrolytes that retain an electrolyte having lithium ion conductivity and are impregnated in the organic polymer A solid electrolyte containing a molecular gel,
The negative electrode active material layer and the solid electrolyte are integrated using the organic polymer as a medium,
Inorganic particles, the chemical formula _{Li 7-y La 3-x} A x Zr 2-y M y O 12 ( wherein, A is Y, Nd, Sm, any one metal selected from the group consisting of Gd X is in the range of 0 ≦ x <3, M is Nb or Ta, and y is in the range of 0 ≦ y <2, and a composite metal oxide having a garnet-type structure, A coating film that covers the surface of the composite metal oxide, the coating film including an oxide of one or more metals selected from the group consisting of Li, Y, and Zr Electrolyte-negative electrode structure. The electrolyte-negative electrode structure according to claim 1,
The coating film comprises an electrolyte-negative electrode structure containing a Zr oxide. A negative electrode formed by forming a negative electrode active material layer made of a material capable of occluding lithium ions on a current collector;
Inorganic particles having lithium ion conductivity, organic polymers that bind the inorganic particles and can be impregnated with a polymer gel, and high electrolytes that retain an electrolyte having lithium ion conductivity and are impregnated in the organic polymer A solid electrolyte containing a molecular gel,
The negative electrode active material layer and the solid electrolyte are integrated using the organic polymer as a medium,
Inorganic particles, the chemical formula _{Li 7-y La 3-x} A x Zr 2-y M y O 12 ( wherein, A is Y, Nd, Sm, any one metal selected from the group consisting of Gd X is in the range of 0 ≦ x <3, M is Nb or Ta, and y is in the range of 0 ≦ y <2, and a composite metal oxide having a garnet-type structure, A coating film that covers the surface of the composite metal oxide, wherein the coating film includes an oxide of one or more metals selected from the group consisting of Li, Y, and Zr. A lithium ion secondary battery comprising: