JP2012129095A - Bipolar electrode for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a bipolar electrode for a nonaqueous electrolyte secondary battery exhibiting excellent cycle stability.SOLUTION: A bipolar electrode for a nonaqueous electrolyte secondary battery is constituted by forming a positive electrode containing a positive electrode active material excellent in cycle stability which is represented by LiMMnO(wherein 0≤x≤0.2 and 0<y≤0.6 are satisfied, and M represents at least one selected from a group consisting of group II to XIII elements belonging to the third and fourth periods) on one surface of a collector, and a negative electrode containing lithium titanate on the other surface.

Description

  The present invention relates to a bipolar electrode for a non-aqueous electrolyte secondary battery, a non-aqueous electrolyte secondary battery using the bipolar electrode, and an assembled battery using the non-aqueous electrolyte secondary battery.

  In recent years, non-aqueous electrolyte secondary batteries have been actively researched and developed for portable devices, electric bicycles, hybrid cars, electric cars, and household power storage applications. This nonaqueous electrolyte secondary battery needs to be used by connecting a plurality of batteries in series in order to develop an output corresponding to each application. However, when a plurality of batteries are connected in series, there is a problem that the output density and energy density are reduced because the output decreases due to the electrical resistance of the connection part of each battery and the connection part requires a space. In order to solve this problem, a bipolar battery as disclosed in Patent Document 1 has been developed. A bipolar battery has a structure in which a plurality of bipolar electrodes, each having a positive electrode on one side of a current collector and a negative electrode on the other, are stacked via an electrolyte layer, that is, a single cell is connected in series in the stacking direction within the battery. Battery. With this configuration, since the battery can be increased in voltage and compact, it is possible to increase the output density and energy density of the battery. However, in this bipolar battery, when the capacity of a part of the single battery portion is reduced due to electrode deterioration, even if charging is completed earlier than other single battery parts, the current continues to flow until the other battery is fully charged. For this reason, there is a problem in that the unit cell portion with reduced capacity is overcharged and the battery is damaged. In particular, when lithium manganate is used for the positive electrode as in Patent Document 1, the problem is likely to occur because the stability during cycle operation is low.

JP 2004-171955 A

  An object of the present invention is to provide a bipolar electrode for a nonaqueous electrolyte secondary battery that exhibits excellent cycle stability. That is, it is to provide a bipolar electrode for a non-aqueous electrolyte secondary battery using a positive electrode active material excellent in cycle stability.

  In view of the above circumstances, as a result of repeated extensive studies by the present inventors, by improving the stability of the electrode using lithium manganate doped with a different element, the occurrence of variations in each electrode during cycle operation is suppressed, and the cycle The inventors have succeeded in obtaining a bipolar battery with good stability and have completed the present invention.

That is, the present invention, Li ₁ on one face of the current collector _{+ x M y Mn 2 - x} - y O 4 (0 ≦ x ≦ 0.2,0 <y ≦ 0.6, M is 2 to 13 A positive electrode containing a positive electrode active material represented by at least one selected from the group consisting of elements belonging to the group and belonging to the third to fourth periods), a negative electrode containing lithium titanate on the other surface, It is a bipolar electrode for water electrolyte secondary batteries.

In the non-aqueous electrolyte secondary battery bipolar electrode of the present _{invention, Li 1 + x M y Mn} 2 - x - y O 4 (0 ≦ x ≦ 0.2,0 <y ≦ 0.6) M contained in the It is preferably at least one selected from the group consisting of Al, Mg, Zn, Ni, Co, Fe and Cr.

  In the bipolar electrode for a non-aqueous electrolyte secondary battery of the present invention, the lithium titanate preferably has a spinel structure.

  In the bipolar electrode for a non-aqueous electrolyte secondary battery of the present invention, the current collector is preferably aluminum.

In the bipolar electrode for a nonaqueous electrolyte secondary battery of the present invention, the positive electrode capacity and the negative electrode capacity preferably satisfy the following formula (1).
1 ≦ B / A ≦ 1.2 (1)
(However, A is the electric capacity per 1 cm ² of the positive electrode, B: electric capacity per 1 cm ^{2 of the} negative electrode)
The nonaqueous electrolyte secondary battery of the present invention includes the bipolar electrode for a nonaqueous secondary battery of the present invention.

  The assembled battery of the present invention is formed by connecting a plurality of nonaqueous secondary batteries of the present invention.

  By using the bipolar electrode for a non-aqueous electrolyte secondary battery of the present invention, a non-aqueous electrolyte secondary battery excellent in cycle stability can be provided.

  An embodiment of the present invention will be described as follows. The present invention is not limited to the following description.

<1. Positive electrode>
Positive in the bipolar electrode of the present invention is _{Li 1 + x M y Mn 2} - x - y O 4 (0 ≦ x ≦ 0.2,0 <y ≦ 0.6, M is 2-13 Group a and the third to And a positive electrode active material (hereinafter, also referred to as “positive electrode active material of the present invention”) represented by at least one selected from the group consisting of elements belonging to four periods. M is at least one selected from elements belonging to Groups 2 to 13 and belonging to the 3rd to 4th periods, but Al, Mg, Zn, Ni, Co, Fe, and Cr are effective in improving stability. Are preferred, Al, Mg, Zn, Ni and Cr are more preferred, and Al, Mg, Zn and Ni are even more preferred. When x <0, the capacity of the positive electrode active material tends to decrease. Further, when x> 0.2, there is a tendency that many impurities such as lithium carbonate are included. When y = 0, the stability of the positive electrode active material tends to be low. Further, when y> 0.6, a large amount of impurities such as M oxide tends to be contained.

  The positive electrode active material of the present invention preferably has a spinel structure. The spinel structure is preferable because the expansion and contraction of the active material in the lithium ion insertion / extraction reaction is small.

  The positive electrode active material of the present invention preferably has a half width of (400) plane of powder X-ray diffraction by CuKα of 0.5 ° or less. When it is larger than 0.5 °, the crystallinity of the positive electrode active material is low, and thus the stability of the electrode may be lowered.

  The positive electrode active material of the present invention preferably has a lithium content of 90% or more in the 8a site according to the Rietveld analysis method by X-ray diffraction. If it is less than 90%, there are many defects in the crystal of the positive electrode active material, and the stability of the electrode may be lowered.

  The particle diameter of the positive electrode active material of the present invention is preferably 0.5 μm or more and 50 μm or less, and more preferably 1 μm or more and 30 μm or less from the viewpoint of handling. The particle diameter here is a value obtained by measuring the size of each particle from the SEM and TEM images and calculating the average particle diameter.

The specific surface area of the positive electrode active material of the present invention is preferably 0.1 m ² / g or more and 50 m ² / g or less because a desired output density is easily obtained. The specific surface area can be calculated by measurement by the BET method.

The positive electrode active material of the present invention preferably has a bulk density of 0.2 g / cm ³ or more and 2.0 g / cm ³ or less. 0.2 g / cm economically be disadvantageous because it requires a large amount of solvent in the step of preparing the slurry below in the case of less than ^3, 2.0 g / cm ³ conductive agent described later is greater than, it is mixed with a binder It tends to be difficult.

  The positive electrode active material of the present invention can be obtained by heat-treating a lithium compound, a manganese compound, and an M compound at 500 ° C. or higher and 1500 ° C. or lower. When the temperature is lower than 500 ° C. or higher than 1500 ° C., a positive electrode active material having a desired structure may not be obtained. The heat treatment may be performed by mixing a lithium compound, a manganese compound, and a compound of M, or may be heat-treated with a lithium compound after heat-treating the manganese compound and the M compound. In order to improve the crystallinity of the positive electrode active material, after the heat treatment, the heat treatment may be performed again at 500 ° C. or more and 1500 ° C. or less. The temperature of the reheating treatment may be the same as or different from the initial temperature. The heat treatment may be performed in the presence of air or in the presence of an inert gas such as nitrogen or argon. Although it does not specifically limit in heat processing, For example, a box furnace, a tubular furnace, a tunnel furnace, a rotary kiln etc. can be used.

  As the lithium compound, for example, lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, lithium oxalate, lithium halide and the like can be used. These lithium compounds may be used alone or in combination of two or more.

  As the manganese compound, for example, manganese oxide such as manganese dioxide, manganese carbonate, manganese nitrate, manganese hydroxide and the like can be used. These manganese compounds may be used alone or in combination of two or more.

As the compound of M, for example, carbonate, oxide, nitrate, hydroxide, sulfate and the like can be used. _{Li 1 + x M y Mn 2} - x - amount of M contained in _y O ₄ can be controlled by the amount of the compound of M in the heat treatment. One type of M compound may be used, or two or more types may be used.

  The compounding ratio of the lithium compound, the manganese compound and the compound of M is such that the atomic ratio of lithium, manganese and M is 1 + x (lithium), 2-xy (manganese), and y (M), respectively, where 0 ≦ x ≦ It is selected in a range satisfying 0.2, 0 <y ≦ 0.6. For example, when a positive electrode active material having an atomic ratio of 1.5 of Mn / Li is produced, a slight width may be provided around the blending ratio of 1.5 depending on the properties of the raw materials and heating conditions.

  The surface of the positive electrode active material of the present invention may be covered with a carbon material, a metal oxide, a polymer, or the like in order to improve conductivity or stability.

  The positive electrode of the present invention may contain a conductive additive. Although it does not specifically limit as a conductive support material, A carbon material is preferable. Examples thereof include natural graphite, artificial graphite, vapor grown carbon fiber, carbon nanotube, acetylene black, ketjen black, and furnace black. These carbon materials may be used alone or in combination of two or more.

  The amount of the conductive additive contained in the positive electrode of the present invention is preferably 1 part by weight or more and 30 parts by weight or less, more preferably 2 parts by weight or more and 15 parts by weight or less with respect to 100 parts by weight of the positive electrode active material. If it is the said range, the electroconductivity of a positive electrode will be ensured. Moreover, adhesiveness with the below-mentioned binder is maintained, and adhesiveness with a collector can fully be obtained.

  The positive electrode of the present invention may contain a binder. The binder is not particularly limited, and for example, at least one selected from the group consisting of polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber, polyimide, and derivatives thereof can be used. . The binder is preferably dissolved or dispersed in a non-aqueous solvent or water from the viewpoint of easy production of the positive electrode. The non-aqueous solvent is not particularly limited, and examples thereof include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, methyl acetate, ethyl acetate, and tetrahydrofuran. You may add a dispersing agent and a thickener to these.

  The amount of the binder contained in the positive electrode of the present invention is preferably 1 part by weight or more and 30 parts by weight or less, more preferably 2 parts by weight or more and 15 parts by weight or less with respect to 100 parts by weight of the positive electrode active material. If it is the said range, the adhesiveness of a positive electrode active material and a conductive support material will be maintained, and adhesiveness with a collector can fully be acquired.

  Examples of the method for producing the positive electrode of the present invention include a method of producing a positive electrode active material, a conductive additive, and a binder by coating a current collector on the current collector. A method of producing a positive electrode by preparing a slurry with a solvent and coating the obtained slurry on a current collector and then removing the solvent is preferable.

  Although the production of the slurry is not particularly limited, it is preferable to use a ball mill, a planetary mixer, a jet mill, or a thin film swirl mixer because the positive electrode active material, the conductive additive, the binder, and the solvent can be mixed uniformly. Although the preparation of the slurry is not particularly limited, it may be prepared by mixing the positive electrode active material, the conductive additive, and the binder and then adding a solvent, or the positive electrode active material, the conductive additive, the binder, and the solvent may be combined together. You may mix and produce.

  The solid content concentration of the slurry is preferably 30 wt% or more and 80 wt% or less. If it is less than 30 wt%, the viscosity of the slurry tends to be too low. On the other hand, if it is higher than 80 wt%, the viscosity of the slurry tends to be too high, so that it may be difficult to form an electrode described later.

  The solvent used for the slurry is preferably a non-aqueous solvent or water. The non-aqueous solvent is not particularly limited, and examples thereof include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, methyl acetate, ethyl acetate, and tetrahydrofuran. Moreover, you may add a dispersing agent and a thickener to these.

  Formation of the positive electrode on the current collector is not particularly limited. For example, a method of removing the solvent after applying the slurry with a doctor blade, a die coater, a comma coater, or the like, or a method of removing the solvent after applying with a spray. preferable. The method for removing the solvent is preferable because it is easy to dry using an oven or a vacuum oven. Examples of the atmosphere for removing the solvent include air, an inert gas, and a vacuum state. The temperature at which the solvent is removed is not particularly limited, but is preferably 60 ° C. or higher and 250 ° C. or lower. When the temperature is lower than 60 ° C., it may take time to remove the solvent. When the temperature is higher than 250 ° C., the binder may be deteriorated. The positive electrode may be formed before or after forming the negative electrode described later.

  The thickness of the positive electrode of the present invention is preferably 10 μm or more and 200 μm or less. If it is less than 10 μm, it may be difficult to obtain a desired capacity, while if it is thicker than 200 μm, it may be difficult to obtain a desired output density.

The density of the positive electrode of the present invention is preferably 1.0 g / cm ³ or more and 4.0 g / cm ³ or less. If it is less than 1.0 mg / cm ³ , the contact with the positive electrode active material and the conductive additive becomes insufficient, and the electronic conductivity may decrease. On the other hand, if it is larger than 4.0 g / cm ³ , the electrolytic solution is less likely to penetrate into the positive electrode, and the lithium conductivity may decrease.

  The positive electrode of the present invention may be compressed to a desired thickness and density. Although compression is not specifically limited, For example, it can carry out using a roll press, a hydraulic press, etc. The electrode may be compressed before or after the later-described negative electrode is formed.

The positive electrode of the present invention preferably has an electric capacity per 1 cm ² of positive electrode of 0.5 mAh to 3.0 mAh. When it is less than 0.5 mAh, the size of a battery having a desired capacity tends to increase, and when it exceeds 3.0 mAh, it tends to be difficult to obtain a desired output density. The electric capacity per 1 cm ² of the positive electrode may be calculated by measuring charge / discharge characteristics after preparing a positive electrode and then preparing a half battery using lithium metal as a counter electrode.

The electric capacity per 1 cm ^{2 of the} positive electrode of the positive electrode is not particularly limited, but is controlled by the weight of the positive electrode formed per unit area of the current collector, for example, by the coating thickness at the time of the slurry coating described above. Can do.

<2. Negative electrode>
The negative electrode in the bipolar electrode of the present invention contains lithium titanate. Since lithium titanate has a noble potential of lithium ion insertion / extraction reaction higher than 1 V (vs. Li ⁺ / Li), a current collector generally used for a positive electrode, for example, Aluminum or the like can be used. In this case, since the negative electrode can be formed on the back surface of the current collector on which the positive electrode is formed, it is not necessary to provide a separate current collector for the negative electrode. In other words, bipolar electrodes using lithium titanate as the negative electrode active material can form positive and negative electrodes on the front and back of the same current collector, respectively, reducing the amount of materials and reducing costs by simplifying the bipolar electrode manufacturing process. In addition, the output density of the battery can be improved by reducing the thickness of the bipolar electrode.

The lithium titanate preferably has a spinel structure, and a molecular formula represented by Li ₄ Ti ₅ O ₁₂ is preferable. In the case of the spinel structure, the expansion and contraction of the active material in the reaction of insertion / extraction of lithium ions is small. Lithium titanate may contain a small amount of elements other than lithium such as Nb and titanium, for example.

  Lithium titanate preferably has a half width of (400) plane of powder X-ray diffraction by CuKα of 0.5 ° or less. If it is larger than 0.5 °, the crystallinity of lithium titanate is low, and the stability of the electrode may be lowered.

  The lithium titanate preferably has a lithium content of 90% or more in the 8a site according to the Rietveld analysis by X-ray diffraction. If it is less than 90%, since there are many defects in the crystal of lithium titanate, the stability of the electrode may be lowered.

  Lithium titanate can be obtained by heat-treating a lithium compound and a titanium compound at 500 ° C. or higher and 1500 ° C. or lower. When the temperature is lower than 500 ° C. or higher than 1500 ° C., lithium titanate having a desired structure tends to be difficult to obtain. In order to improve the crystallinity of lithium titanate, after the heat treatment, the heat treatment may be performed again at a temperature of 500 ° C. or higher and 1500 ° C. or lower. The temperature of the reheating treatment may be the same as or different from the initial temperature. The heat treatment may be performed in the presence of air or in the presence of an inert gas such as nitrogen or argon. Although it does not specifically limit in heat processing, For example, a box furnace, a tubular furnace, a tunnel furnace, a rotary kiln etc. can be used.

  As the lithium compound, for example, lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, lithium oxalate, lithium halide and the like can be used. These lithium compounds may be used alone or in combination of two or more.

  Although it does not specifically limit as a titanium compound, For example, titanium oxides, such as titanium dioxide and a titanium monoxide, can be used.

  The compounding ratio of the lithium compound and the titanium compound may be slightly widened depending on the properties of the raw materials and the heating conditions, and the atomic ratio of lithium and titanium, and Ti / Li = 1.25.

  The surface of the lithium titanate may be covered with a carbon material, a metal oxide, a polymer, or the like in order to improve conductivity or stability.

  The particle size of lithium titanate is preferably 0.5 μm or more and 50 μm or less, and more preferably 1 μm or more and 30 μm or less from the viewpoint of handling. The particle diameter is a value obtained by measuring the size of each particle from SEM and TEM images and calculating the average particle diameter.

The specific surface area of lithium titanate is preferably 0.1 m ² / g or more and 50 m ² / g or less because a desired output density is easily obtained. The specific surface area may be calculated by measurement using a mercury porosimeter or BET method.

The lithium titanate preferably has a bulk density of 0.2 g / cm ³ or more and 1.5 g / cm ³ or less. 0.2 g / cm in the case of less than ³ tend to be economically disadvantageous because it requires a large amount of solvent in the step of preparing the slurry described below, 1.5 g / cm ³ greater than the later of conductive agent, and a binder Tend to be difficult to mix.

  In the present invention, the negative electrode may contain a conductive additive. Although it does not specifically limit as a conductive support material, A carbon material is preferable. Examples thereof include natural graphite, artificial graphite, vapor grown carbon fiber, carbon nanotube, acetylene black, ketjen black, and furnace black. These carbon materials may be used alone or in combination of two or more.

  In the present invention, the amount of the conductive additive contained in the negative electrode is preferably 1 part by weight or more and 30 parts by weight or less, more preferably 2 parts by weight or more and 15 parts by weight or less with respect to 100 parts by weight of the negative electrode active material. If it is the said range, the electroconductivity of a negative electrode will be ensured. Moreover, adhesiveness with the below-mentioned binder is maintained, and adhesiveness with a collector can fully be obtained.

  In the present invention, the negative electrode may contain a binder. Although not particularly limited, for example, at least one selected from the group consisting of polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber, polyimide, and derivatives thereof can be used. The binder is preferably dissolved or dispersed in a non-aqueous solvent or water from the viewpoint of easy production of the negative electrode. The non-aqueous solvent is not particularly limited, and examples thereof include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, methyl acetate, ethyl acetate, and tetrahydrofuran. You may add a dispersing agent and a thickener to these.

  In the present invention, the amount of the binder contained in the negative electrode is preferably 1 part by weight or more and 30 parts by weight or less, more preferably 2 parts by weight or more and 15 parts by weight or less with respect to 100 parts by weight of the negative electrode active material. If it is the said range, the adhesiveness of a negative electrode active material and a conductive support material will be maintained, and adhesiveness with a collector can fully be acquired.

  As a preferred embodiment of the negative electrode in the present invention, it is produced by forming a mixture of a negative electrode active material, a conductive additive and a binder on a current collector. From the ease of the production method, the above mixture and solvent are used. A method of preparing a negative electrode by removing the solvent after preparing the slurry and coating the obtained slurry on a current collector is preferable.

  The production of the slurry is not particularly limited, but it is preferable to use a ball mill, a planetary mixer, a jet mill, or a thin film swirl mixer because the negative electrode active material, the conductive additive, the binder, and the solvent can be mixed uniformly. Although the preparation of the slurry is not particularly limited, it may be prepared by mixing the negative electrode active material, the conductive additive, and the binder and then adding a solvent, or the negative electrode active material, the conductive additive, the binder, and the solvent together. You may mix and produce.

  The solid content concentration of the slurry is preferably 30 wt% or more and 80 wt% or less. If it is less than 30 wt%, the viscosity of the slurry tends to be too low, whereas if it is higher than 80 wt%, the viscosity of the slurry tends to be too high, and it may be difficult to form an electrode described later.

  The solvent used for the slurry is preferably a non-aqueous solvent or water. The non-aqueous solvent is not particularly limited, and examples thereof include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, methyl acetate, ethyl acetate, and tetrahydrofuran. Moreover, you may add a dispersing agent and a thickener to these.

  The formation of the negative electrode on the current collector is not particularly limited. For example, there is a method of removing the solvent after applying the slurry with a doctor blade, a die coater, a comma coater or the like, or a method of removing the solvent after applying with a spray. preferable. The method for removing the solvent is preferable because it is easy to dry using an oven or a vacuum oven. Examples of the atmosphere include room temperature or high temperature air, an inert gas, and a vacuum state. The negative electrode may be formed before or after the above-described positive electrode is formed. Moreover, you may compress a negative electrode using a roll press machine etc. after negative electrode preparation. The electrode may be compressed before or after the positive electrode is formed.

  In the present invention, the thickness of the negative electrode is preferably 10 μm or more and 200 μm or less. If it is 10 μm or less, it may be difficult to obtain a desired capacity, and if it is thicker than 200 μm, it may be difficult to obtain a desired output density.

In the present invention, the density of the negative electrode is preferably 1.0 g / cm ³ or more and 4.0 g / cm ³ or less. If it is less than 1.0 mg / cm ³ , the contact with lithium titanate and the conductive additive becomes insufficient, and the electronic conductivity may be lowered. When it is larger than 4.0 g / cm ³ , an electrolyte solution described later hardly penetrates into the negative electrode, and lithium conductivity may be lowered. The negative electrode may be compressed to a desired thickness and density. Although compression is not specifically limited, For example, it can carry out using a roll press, a hydraulic press, etc. The electrode may be compressed before or after the above-described positive electrode is formed.

In the present invention, the electric capacity per 1 cm ² of the negative electrode is preferably 0.5 mAh or more and 3.6 mAh or less. If it is less than 0.5 mAh, the size of the battery having a desired capacity may be increased. On the other hand, if it is more than 3.6 mAh, it may be difficult to obtain a desired output density. Calculation of the electric capacity per 1 cm < ² > of a negative electrode can be calculated by measuring a charging / discharging characteristic after producing a half cell which made lithium metal a counter electrode after negative electrode preparation.

Although the electric capacity per 1 cm ² of the negative electrode of the negative electrode is not particularly limited, it can be controlled by the method of controlling by the weight of the negative electrode formed per unit area of the current collector, for example, the coating thickness at the time of the negative electrode coating described above. it can.

<3. Bipolar electrode>
The bipolar electrode of the present invention is formed by forming a positive electrode on one surface of a current collector and a negative electrode on the other surface.

In the bipolar electrode of the present invention, it is preferable that the positive electrode capacitance and the negative electrode capacitance satisfy the following formula (1).
1 ≦ B / A ≦ 1.2 (1)
In the above formula (1), A represents the electric capacity per 1 cm ² of the positive electrode, and B represents the electric capacity per 1 cm ² of the negative electrode.

  When B / A is less than 1, the potential of the negative electrode may become the deposition potential of lithium during overcharge. On the other hand, when B / A is greater than 1.2, there is a large amount of lithium titanate not involved in the battery reaction. As a result, side reactions may occur.

In the bipolar electrode of the present invention, the area ratio of the positive electrode and the negative electrode is not particularly limited, but preferably satisfies the following formula (2).
1 ≦ D / C ≦ 1.2 (2)
(However, C represents the area of the positive electrode, and D represents the area of the negative electrode.)
When D / C is less than 1, for example, when B / A = 1 as described above, the capacity of the negative electrode is smaller than that of the positive electrode, so that the potential of the negative electrode may become a lithium deposition potential during overcharge. On the other hand, when D / C is greater than 1.2, the portion of the negative electrode that is not in contact with the positive electrode is large, and thus lithium titanate that is not involved in the battery reaction may cause a side reaction. Although control of the area of a positive electrode and a negative electrode is not specifically limited, For example, in the case of slurry coating, it can carry out by controlling the coating width.

Current collector used in the bipolar electrode, 0.5V is preferred metals are (vs.Li ⁺ / Li) stable in an atmosphere which is more noble _{than, Li 1 + x M y Mn} 2 - x - y O 4 ( A positive electrode active material represented by 0 ≦ x ≦ 0.2, 0 <y ≦ 0.6, and M is at least one selected from the group consisting of elements belonging to Group 2-13 and belonging to the third to fourth periods; Aluminum is particularly preferred because of its high stability against the potential of lithium ion insertion and desorption reactions of lithium titanate. The aluminum is not particularly limited because it is stable in the positive electrode and negative electrode reaction atmospheres, but is preferably high-purity aluminum represented by JIS standards 1030, 1050, 1085, 1N90, 1N99 and the like.

  The surface roughness Ra of the current collector is preferably 0.05 μm or more and 0.5 μm or less. If the thickness is less than 0.05 μm, the adhesion between the positive electrode and the negative electrode may be lowered. If the thickness is more than 0.5 μm, it may be difficult to form the positive electrode and the negative electrode uniformly. The surface roughness Ra can be measured using a light wave interference type surface roughness measuring instrument or the like.

  The electrical resistance of the current collector is preferably 5 μΩ · cm or less. If it is higher than 5 μΩ · cm, the battery performance may be reduced. Electrical resistance can be measured by the four probe method.

  The thickness of the current collector is not particularly limited, but is preferably 10 μm or more and 100 μm or less. If it is less than 10 μm, handling is difficult from the viewpoint of production, and if it is thicker than 100 μm, it is disadvantageous from an economic viewpoint.

  In addition, the thing which coat | covered aluminum on the surface of materials (copper, SUS, nickel, titanium, and those alloys) other than aluminum can also be used for a collector.

<4. Non-aqueous electrolyte secondary battery>
The nonaqueous electrolyte secondary battery using the bipolar electrode of the present invention is, for example, a battery including a laminate having a structure in which the bipolar electrode of the present invention is sandwiched between separators and the positive electrode side and the negative electrode side of adjacent bipolar electrodes are opposed to each other. Can be mentioned. The positive electrode, the negative electrode, and the separator may contain an electrolyte solution that is responsible for lithium ion conduction. Moreover, in the layer where each positive electrode side and the negative electrode side face each other, an insulating material may be disposed around the positive electrode and the negative electrode in order to prevent liquid junction.

  A separator is not specifically limited, For example, a woven fabric, a nonwoven fabric, a microporous film etc. are mentioned. The material of the separator is not particularly limited, and for example, nylon, cellulose, polysulfone, polyethylene, polypropylene, polybutene, polyacrylonitrile, polyimide, polyamide, and a composite of two or more thereof are used. The separator may include various plasticizers, antioxidants, flame retardants, and may be coated with a metal oxide or the like.

  The thickness of the separator is preferably 10 μm or more and 100 μm or less. When the thickness is less than 10 μm, the positive electrode and the negative electrode may be in contact with each other. When the thickness is greater than 100 μm, the resistance of the battery may be increased. From the viewpoint of economy and handling, it is more preferably 15 μm or more and 50 μm or less.

The size ratio of the separator and the area ratio of the bipolar electrode on the negative electrode side is not particularly limited, but it is preferable to satisfy the following formula (3).
1 ≦ F / E ≦ 1.5 (3)
(However, E represents the area of the negative electrode, and F represents the area of the separator.)
When F / E is less than 1, the positive electrode and the negative electrode are in contact with each other, and when F / E is greater than 1.5, the volume required for the exterior increases, and the output density of the battery may decrease.

  The electrolytic solution is not particularly limited, but an electrolytic solution in which a solute is dissolved in a liquid solvent can be used. As the solvent, for example, acetonitrile, dimethyl carbonate, methyl ethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl uppropyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyl lactone, 1,2-dimethoxyethane, etc. should be used. Can do. These solvents may be used alone or as a mixture of two or more. However, in view of the ease of dissolving the solute described below and the high conductivity of lithium ions, a mixture of two or more of these solvents. Is preferably used. In place of the electrolyte, a gel electrolyte in which the polymer is impregnated with the electrolyte, a solid polymer electrolyte such as polyethylene oxide or propylene oxide, or an inorganic solid electrolyte such as sulfide glass or oxynitride may be used. it can.

Although the solute is not particularly limited, for example, LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) _{2 and the} like are preferable because they are easily dissolved in a solvent. The concentration of the solute contained in the electrolytic solution is preferably 0.5 mol / L or more and 2.0 mol / L or less. If it is less than 0.5 mol / L, the desired lithium ion conductivity may not be exhibited. On the other hand, if it is higher than 2.0 mol / L, the solute may not be dissolved any more.

  The electrolyte solution may contain a trace amount of additives such as a flame retardant and a stabilizer.

  It is preferable that the insulators disposed in the periphery of the positive electrode and the negative electrode have sealing properties and heat resistance against electrolyte penetration, moisture from the outside, oxygen penetration, and the like. Although the said insulator is not specifically limited, For example, a urethane resin, a silicon resin, an epoxy resin, a polyethylene resin, a polypropylene resin, a polyimide resin, rubber | gum etc. can be used.

  The nonaqueous electrolyte secondary battery of the present invention may be packaged with a laminate film after being laminated with a plurality of the above laminates, or may be packaged with a metal can. Further, the exterior may be provided with a mechanism for releasing the generated gas. The number of stacked layers can be stacked until a desired voltage value is expressed.

  The nonaqueous electrolyte secondary battery of the present invention can be formed into an assembled battery by connecting a plurality of the nonaqueous electrolyte secondary batteries. The assembled battery of the present invention can be produced by appropriately connecting in series or in parallel according to a desired size, capacity, and voltage. Moreover, it is preferable that a control circuit is attached to the assembled battery in order to confirm the state of charge of each battery and improve safety.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited at all by these Examples, In the range which does not change the summary, it can change suitably.

(Production of bipolar electrode / positive electrode side)
The positive electrode active material Li _1.1 Al _0.1 Mn _1.8 O ₄ was produced by the method described in the literature (Electrochemical and Solid-State Letters, 9 (12), A557 (2006)). 100 parts by weight of this positive electrode active material, 6.8 parts by weight of a conductive additive (acetylene black), and 6.8 parts by weight of a binder (solid content concentration 12 wt%, NMP solution) were mixed to prepare a slurry. The slurry was applied to an aluminum foil (20 μm) and then vacuum dried at 150 ° C. to produce a positive electrode (50 cm ² ).

The capacity of the positive electrode was measured by the following charge / discharge test.
In the same manner as described above, an electrode coated on one surface of an aluminum foil was punched into a working electrode of 16 mmΦ, and a Li metal was punched out of 16 mmΦ as a counter electrode. Using these electrodes, the working electrode (single-sided coating) / separator / Li metal were laminated in this order in the test cell (HS cell, manufactured by Hosen Co., Ltd.), and the electrolyte (ethylene carbonate / dimethyl carbonate = 3/7 vol%). , LiPF ₆ , 1 mol / L) was added to prepare a half battery. The half-cell was allowed to stand at 25 ° C. for one day, and then connected to a charge / discharge test apparatus (HJ1005SD8, manufactured by Hokuto Denko). This half-cell was subjected to constant current charging (end voltage: 4.5 V) and constant current discharge (end voltage: 3.5 V) at 25 ° C. and 0.4 mA five times, and the fifth result was taken as the positive electrode capacity. As a result, the capacity of the positive electrode was 1.0 mAh / cm ² .

(Manufacture of bipolar electrode and negative electrode side)
The negative electrode active material Li ₄ Ti ₅ O ₁₂ was prepared by the method described in the literature (Journal of Electrochemical Society, 142, 1431 (1995)). 100 parts by weight of this negative electrode active material, 6.8 parts by weight of a conductive additive (acetylene black), and 6.8 parts by weight of a binder (solid content concentration 12 wt%, NMP solution) were mixed to prepare a slurry. After applying the slurry prepared on the back surface of the aluminum foil (20 μm) on which the positive electrode was formed, the negative electrode (50 cm ² ) was prepared by vacuum drying at 150 ° C. Then, it roll-pressed so that each electrode density might be 2.0 mg / cm < ³ >.

The capacity of the negative electrode was measured by the following charge / discharge test.
An electrode was applied to one side of the aluminum foil under the same conditions as described above, and a working electrode was punched out to 16 mmΦ. Li metal was punched out to 16 mmΦ as a counter electrode. Using these electrodes, the working electrode (single-sided coating) / separator / Li metal were laminated in this order in the test cell (HS cell, manufactured by Hosen Co., Ltd.), and the electrolyte (ethylene carbonate / dimethyl carbonate = 3/7 vol%). , LiPF ₆ , 1 mol / L) was added to prepare a half battery. The half-cell was allowed to stand at 25 ° C. for one day, and then connected to a charge / discharge test apparatus (HJ1005SD8, manufactured by Hokuto Denko). The half-cell was subjected to constant current discharge (end voltage: 1.0 V) and constant current charge (end voltage: 2.0 V) at 25 ° C. and 0.4 mA five times, and the fifth result was defined as the positive electrode capacity. As a result, the capacity of the negative electrode was 1.2 mAh / cm ² .

(Manufacture of bipolar batteries)
The bipolar battery of Example 1 was produced as follows. As the electrodes at both ends of the laminate, an electrode in which a positive electrode or a negative electrode alone was applied on one side of an aluminum foil was used. Cellulose unwoven cloth (25 μm, 55 cm ² ) was used as the separator. First, the prepared positive electrode (single-sided coating), negative electrode (single-sided coating), bipolar electrode, and separator are laminated in the order of positive electrode (single-sided coating) / separator / bipolar electrode / separator / negative electrode (single-sided coating). did. Next, aluminum tabs were vibration welded to the positive and negative electrodes at both ends, and then placed in a bag-like aluminum laminate sheet. Finally, 2 mL of an electrolytic solution (ethylene carbonate / dimethyl carbonate = 3/7 vol%, LiPF ₆ , 1 mol / L) was added, and then sealed under reduced pressure to produce a bipolar battery of Example 1.

LiNi _0.5 Mn _1.5 O ₄ was prepared as a positive electrode active material by the method described in the literature (Journal of PowerSources, 81-82, 90 (1999)). A bipolar electrode and a bipolar battery were produced in the same manner as in Example 1 except that the produced LiNi _0.5 Mn _1.5 O ₄ was used as the positive electrode active material.

(Comparative Example 1)
As a positive electrode active material, LiMn ₂ O ₄ was obtained by mixing manganese dioxide and lithium hydroxide and then heat-treating in air at 1000 ° C. for 12 hours. A bipolar electrode and a bipolar battery were produced in the same manner as in Example 1 except that the obtained LiMn ₂ O ₄ was used as the positive electrode active material.

(Measurement of cycle characteristics)
The batteries of Example 1, Example 2, and Comparative Example 1 were connected to a charge / discharge device (HJ1005SD8, manufactured by Hokuto Denko), and 25 ° C., 50 mA constant current charge, and 50 mA constant current discharge were repeated 100 times. The charge end voltage and discharge end voltage of Example 1 and Comparative Example 1 at this time were 6 V and 4 V, respectively, and the charge end voltage and discharge end voltage of Example 2 were 7 V and 5 V, respectively. Table 1 shows the 100th discharge capacity when the first discharge capacity is 100.

  As is clear from Table 1, the cycle stability of the bipolar batteries of Example 1 and Example 2 of the present invention is higher than that of the bipolar battery of Comparative Example 1.

Claims (7)

On one face of the current collector _{Li 1 + x M y Mn 2} - x - y O 4 (0 ≦ x ≦ 0.2,0 <y ≦ 0.6, M is 2-13 Group a and the third to For a non-aqueous electrolyte secondary battery in which a positive electrode containing a positive electrode active material represented by at least one selected from the group consisting of elements belonging to four cycles) and a negative electrode containing lithium titanate are formed on the other surface Bipolar electrode. _{Li 1 + x M y Mn 2} - x - y O 4 (0 ≦ x ≦ 0.2,0 <y ≦ 0.6) M contained in the, Al, Mg, Zn, Ni , Co, Fe and Cr The bipolar electrode for a nonaqueous electrolyte secondary battery according to claim 1, which is at least one selected from the group consisting of:   The bipolar electrode for a non-aqueous secondary battery according to claim 1 or 2, wherein the lithium titanate has a spinel structure.   The bipolar electrode for nonaqueous secondary batteries according to any one of claims 1 to 3, wherein the current collector is aluminum. The bipolar electrode for a non-aqueous secondary battery according to any one of claims 1 to 4, wherein the electric capacity of the positive electrode and the electric capacity of the negative electrode satisfy the following formula (1).
1 ≦ B / A ≦ 1.2 (1)
(However, A is the electric capacity per 1 cm ² of the positive electrode, B: electric capacity per 1 cm ^{2 of the} negative electrode)   A nonaqueous electrolyte secondary battery comprising the bipolar electrode for a nonaqueous secondary battery according to claim 1.   An assembled battery comprising a plurality of nonaqueous secondary batteries according to claim 6 connected.