JP5169181B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to an electricity storage device, and more particularly to a non-aqueous electrolyte secondary battery using a redox reaction of a nitroxide radical polymer.

The reduction in size and weight of portable battery-powered devices such as mobile phones is advancing more and more, and secondary batteries used in these devices are also required to be downsized. In addition, high output secondary batteries are required for notebook computers, mobile phones, electric vehicles, and the like.
Lithium ion secondary batteries widely used in portable battery-operated devices have a problem that it is difficult to charge and discharge a large current because the electrode reaction rate is low.
In contrast, a battery using a reaction between an oxidant state and a reductant state of a compound having a radical structure has a high reaction speed, and thus has a high energy density, a large capacity, and excellent stability. (For example, see Patent Documents 1 to 3).
JP 2002-151084 A JP 2002-304996 A JP 2002-298850 A

  A battery using a radical compound as an active material uses a fast reaction rate of radicals, and is expected to be charged / discharged at a large current density. However, the charge / discharge characteristics at a large current density were not sufficient. An object of the present invention is to provide a non-aqueous electrolyte secondary battery having a large electrode area and excellent large current charge / discharge characteristics.

In the present invention, a lithium-containing silicon oxide layer is formed on the negative electrode current collector surface, an active layer is disposed on the positive electrode current collector surface, and one surface of the active layer is in contact with the lithium-containing silicon oxide layer. The lithium-containing silicon oxide layer is composed of Li _x SiO (x is in the range of 1 to 4) and a binder, and the active layer is composed of lithium-containing silicon oxide in contact with the lithium-containing silicon oxide layer and nitroxide radical weight. It is a nonaqueous electrolyte secondary battery comprising a first layer in which coalescence is mixed and a second layer comprising a nitroxide radical polymer, a conductivity imparting material, and a binder.
The nitroxide radical polymer is the non-aqueous electrolyte secondary battery according to any one of the structural units represented by chemical formulas (1) to (8).

  The first layer of the active layer is the non-aqueous electrolyte secondary battery formed by intruding a solution containing a nitroxide radical polymer into a lithium-containing silicon oxide layer.

  According to the present invention, in the first layer in which the lithium-containing silicon oxide disposed on the negative electrode current collector side and the nitroxide radical polymer are mixed, the nitroxide radical polymer reacts with the lithium-containing silicon oxide layer, and the interface therebetween. A layer having a function as a separator is formed. In addition, since the interface between the nitroxide radical polymer and the lithium-containing silicon oxide layer can have a three-dimensional structure, a positive electrode made of a nitroxide radical polymer that is in contact with the layer having a function as a separator, Since the negative electrode made of the silicon oxide layer is in contact with a large electrode area, a non-aqueous electrolyte secondary battery excellent in large current charge / discharge characteristics can be obtained. In addition, since a layer having a function as a separator is formed by reaction, there is an advantage that it is not necessary to use a separate separator and the manufacturing process of the non-aqueous electrolyte secondary battery is greatly simplified.

  The present invention makes contact with each other by forming a layer having a function as a separator by a reaction between a nitroxy radical polymer used as a stable radical supply substance and a lithium-containing silicon oxide layer disposed on the negative electrode side. It is possible to increase the surface area of the interface between the positive electrode and the negative electrode, and since a separator made of a synthetic resin porous film is not disposed, an increase in electrical resistance due to the separator can be prevented, so charge / discharge characteristics at a large current Has been found to be able to provide a good secondary battery.

The present invention will be described below with reference to the drawings.
FIG. 1 is a cross-sectional view illustrating one embodiment of the nonaqueous electrolyte secondary battery of the present invention.
The non-aqueous electrolyte secondary battery 1 of the present invention has a negative electrode active layer 3 composed of a lithium-containing silicon oxide layer and a binder on the surface of a negative electrode current collector 2. A positive electrode active layer 4 is disposed in contact with the negative electrode active layer 3, and a positive electrode current collector 5 is disposed on the other surface of the positive electrode active layer 4.
The positive electrode active layer 4 has a first layer 6 in which lithium-containing silicon oxide and a nitroxide radical polymer are mixed on the surface in contact with the negative electrode active layer 3, and between the first layer 6 and the positive electrode current collector 5. And a second layer 7 made of a nitroxide radical polymer. Then, charging and discharging are performed through the negative electrode current collector 2 and the positive electrode current collector 5.

Hereinafter, each member of the nonaqueous electrolyte secondary battery of the present invention will be described.
The negative electrode current collector that is the first current collecting material can be made of copper, nickel, silver, or an alloy thereof having good conductivity and stably operating as a current collecting electrode during charging and discharging. As the shape, for example, a foil, a flat plate, or a mesh can be used.

A lithium-containing silicon oxide layer is formed on the surface of the negative electrode current collector. The lithium-containing silicon oxide layer not only acts as a negative electrode active material, but the lithium contained in the lithium-containing silicon oxide layer reacts with the nitroxide radical polymer, which is the positive electrode active material, to provide a separator function at the interface where both are associated. A layer is formed.
As a result, an electrical short circuit does not occur between the positive electrode and the negative electrode without using a separator made of a porous synthetic resin or the like.

As Li _x SiO forming the lithium-containing silicon oxide layer, x is preferably in the range of 1 to 4. When x is smaller than 1, it becomes difficult to form a layer having a separator function. On the other hand, when x is larger than 4, the volume change of the lithium-containing silicon oxide layer accompanying charging / discharging becomes large, and the capacity deterioration accompanying charging / discharging becomes large.

  The lithium-containing silicon oxide compound can be obtained by heating a predetermined amount of lithium and silicon monoxide to 1200 ° C. in a vacuum or an argon atmosphere. Among them, those synthesized by synthesis under an argon atmosphere are preferable.

  The lithium-containing silicon oxide preferably has a particle size of 5 μm to 20 μm. The lithium-containing silicon oxide particles are mixed with a binder such as polytetrafluoroethylene and applied to the surface of the negative electrode current collector. Thus, a negative electrode active material layer is formed. The lithium-containing silicon oxide and the binder are preferably 80/5 to 80/15 by mass ratio. When the lithium-containing silicon oxide is less than 80/5, the energy density of the battery is reduced, which is preferable. If it is greater than 80/5, the adhesion between the current collector and the active material is lowered, which is not preferable.

  The nitroxide radical polymer in the present invention acts as a positive electrode active material. The nitroxide radical polymer is a nitroxide radical polymer having a nitroxide radical partial structure represented by the following chemical formula in the reduced state and an oxoammonium cation (nitroxyl cation) partial structure in the oxidized state. Thus, it is a material that acts as a positive electrode active material by a reaction for exchanging electrons as described below.

The nitroxide radical polymer is preferably such that the state where the spin concentration in the equilibrium state is 10 ²¹ spin / g or more is continued for 1 second or longer. Structural units suitable as nitroxide radical polymers suitable as the nonaqueous electrolyte secondary battery of the present invention are shown in chemical formulas (1) to (8).

In these nitroxide radical polymers, since each radical is stabilized by a steric hindrance by a nearby bulky substituent or a resonance structure, the spin concentration in an equilibrium state is 10 ²¹ spin / g or more. Can continue for more than a second.
The polymer main chain is poly (meth) acrylic acid, polyalkyl (meth) acrylates, polyvinyl ethers, and poly (meth) acrylamide polymers have good electrochemical stability such as oxidation resistance and reduction resistance. This is particularly preferable.

In addition to nitroxide radical polymers, carbon black such as acetylene black and ketjen black, vapor grown carbon fiber (VGCF), mesophase pitch carbon fiber, carbon nanotubes and other conductivity-imparting agents are added to improve conductivity. It is preferable to do.
In order to enhance the binding property with the current collecting material, a binder such as polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer may be added.

In the nonaqueous electrolyte secondary battery of the present invention, a layer in which lithium-containing silicon oxide and a nitroxide radical polymer are mixed is formed in the first positive electrode active layer. This layer is formed by penetration of a nitroxide radical polymer into a void near the surface of a porous layer containing lithium-containing silicon oxide, and has a three-dimensional structured interface.
The nitroxide radical polymer should be dissolved in a solvent such as N-methyl-pyrrolidone, acetone or acetonitrile to adjust the solution viscosity, and impregnated so that the nitroxide radical polymer stays only on the surface layer of the lithium-containing silicon oxide layer. Is preferred.

The viscosity of the nitroxide radical polymer solution is desirably in the range of 5 to 0.01 Pa · s, and when the viscosity exceeds 5 Pa · s, it takes an excessive amount of time until the solution enters the void, which is not desirable. On the other hand, when the viscosity is less than 0.01 Pa · s, the nitroxide radical polymer solution reaches the deep part of the lithium-containing silicon oxide layer, so that it is difficult to adjust the impregnation amount.
Thus, in the non-aqueous electrolyte secondary battery of the present invention, a layer having a separator function is formed at the interface between the negative electrode active material layer and the positive electrode active material layer. No short circuit occurs. By reducing the three-dimensional structure of the contact portion, the effective area of the positive electrode and the negative electrode can be increased.

  Further, the material of the second layer may be applied on the first layer of the positive electrode active layer, or the second layer of the positive electrode active layer is applied on the positive electrode current collector, and then the first layer of the positive electrode active layer. The negative electrode formed with may be bonded together.

Further, in order to avoid direct contact between the conductive substance in the second active layer and Li _x SiO (x is in the range of 1 to 4), a layer mainly composed of a nitroxide radical polymer containing no conductive substance. So that Li _x SiO (x is in the range of 1 to 4) is not exposed to the surface when the first layer of the active layer is formed by applying the nitroxide radical polymer so that the is necessary.

  In the present invention, the positive electrode current collector is preferably made of aluminum, nickel, or an alloy thereof that is electrochemically stable in a charge / discharge environment. As the shape, for example, a foil, a flat plate, or a mesh can be used. Alternatively, a positive electrode current collector may be formed by forming a thin film by a method such as vapor deposition or sputtering of aluminum, nickel, or an alloy thereof on the surface of the second layer mainly composed of the nitroxide radical polymer.

As the non-aqueous electrolyte material, a non-aqueous electrolyte that is stable in the operating potential range of the non-aqueous electrolyte secondary battery of the present invention can be used, and the non-aqueous electrolyte used in a lithium ion battery or the like can be used. Although the electrolyte can be utilized, it is desirable that the electrolyte has an ionic conductivity of 10 ⁻⁵ to 10 ⁻¹ S / cm at 20 ° C., and an electrolytic solution in which a supporting electrolyte salt is dissolved in a solvent is most preferable.

Solvents include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, and vinylene carbonate), chain carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate, and lactones such as γ-butyrolactone. What mixed 2 or more types is preferable.
Examples of the supporting electrolyte salt include LiPF ₆ , LiAsF ₆ , LiAlCl ₄ , LiClO ₄ , LiBF ₄ , LiSbF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ SO _{2 2} ) and the like. These supporting electrolyte salts can be used alone or in combination of two or more. As other electrolytic solutions, ionic liquids such as quaternary ammonium-imide salts can be used.

The shape and appearance of the nonaqueous electrolyte secondary battery of the present invention are not particularly limited, and conventionally known ones can be employed. Examples of such a shape include a case where an electrode laminate or a wound body is sealed with a metal case, a resin case, or a laminate film composed of a metal foil such as an aluminum foil and a synthetic resin film. Examples of the external appearance of the battery include a cylindrical shape, a square shape, a coin shape, and a sheet shape.
Further, in a wound type or multi-layered type battery, it is necessary to stack or wind by interposing a separator in order to prevent the electrodes of both electrodes from contacting each other. In order to prevent the current collectors at both ends from coming into contact with each other, it is preferable to insulate the end of one current collector with a polyimide resin material or the like.

Hereinafter, the present invention will be described with reference to examples and comparative examples.
Example 1
After blending 1.36 g of lithium and 8.64 g of silicon monoxide (manufactured by High-Purity Chemical), heating at 1200 ° C. in an electric furnace under an argon atmosphere, quickly sandwiching between metal plates cooled with liquid nitrogen, Then, the particle size was adjusted to produce lithium-containing silicon oxide (LiSiO) particles having a number average particle size of 10 μm. The obtained lithium-containing silicon oxide particles and polyvinylidene fluoride (PVDF # 1100 made by Kureha) as a binder were kneaded at a mass ratio of 9: 1 to form a paste, which was pressed onto a copper foil having a thickness of 10 μm. A lithium-containing silicon oxide compound layer having a thickness of 120 μm was formed.
Next, on the surface of the lithium-containing silicon oxide compound layer, poly (2,2,6,6-tetramethylpiperidinoxymethacrylate) (PTMA) homopolymer having a molecular weight of 22000, which is composed of the repeating unit represented by the chemical formula (1). A solution in which a polymer substance and acetone are mixed (PTMA / acetone = 1/15, solution viscosity: 1 Pa · s) is dropped, impregnated to a depth of 70 μm from the surface of the layer, and then dried to form a homogenous lithium-containing silicon oxide compound and A first layer of a positive electrode active layer mixed with a polymer substance was formed.

Next, on the first layer of the positive electrode active layer, the above PTMA, graphitized vapor-grown carbon fiber as a conductivity-imparting agent, and polyvinylidene fluoride as a binder at a mass ratio of 5: 4: 1, A slurry obtained by mixing them with n-methylpyrrolidone was applied and then dried to form a second layer of the positive electrode active layer. An aluminum foil of a positive electrode current collector having a thickness of 20 μm was bonded to the surface of the second layer of the positive electrode active layer to obtain a laminate similar to that shown in FIG.
This laminated body is cut out into a disk shape having a diameter of 14 mm, accommodated in a stainless steel outer can, injected with propylene carbonate containing 1 mol / l LiPF ₆ supporting electrolyte salt as an electrolytic solution, sealed, and coin-type secondary battery The battery characteristics were evaluated by the following battery characteristic test method.

Battery characteristic test The manufactured coin-type secondary battery was charged and discharged at a constant current in a voltage range of a discharge stop voltage of 2 V and a charge stop voltage of 4 V. The charge / discharge test was performed in a thermostat set at 20 ° C.
The battery capacity was determined by charging to 4.2 V at a constant current of 0.1 mA and then discharging to 3.0 V. Next, the charging current is 1C. The discharge test was conducted at a current of 1C and a current of 100C. The test results are shown in Table 1.

Example 2
In Example 1, the homopolymer substance composed of the repeating unit represented by the chemical formula (1) used for the first layer and the second layer of the active layer is converted into the poly (2) composed of the repeating unit represented by the chemical formula (2). , 2,6,6-tetramethylpiperidinoxyacrylate) (PTAC) except that it was changed to a homopolymer material, a coin-type secondary battery was prepared in the same manner as in Example 1 and tested in the same manner as in Example 1. The test results are shown in Table 1.

Example 3
In Example 1, the homopolymer substance composed of the repeating unit represented by the chemical formula (1) used for the first layer and the second layer of the active layer is converted into the poly (2) composed of the repeating unit represented by the chemical formula (3). , 2,6,6-tetramethylpiperidinoxyvinyl) homopolymer material, a coin-type secondary battery was prepared in the same manner as in Example 1 and tested in the same manner as in Example 1. Is shown in Table 1.

Example 4
A coin-type secondary battery was prepared in the same manner as in Example 1 except that the lithium-containing silicon oxide in Example 1 was changed to Li ₄ SiO. The test was performed in the same manner as in Example 1, and the test results are shown in Table 1.

Comparative Example 1
The negative electrode of Example 1 was changed to Li-Si alloy foil (the atomic composition ratio of Si in the alloy was 30%), and the nitroxide radical polymer-containing solution used in Example 1 was applied to the surface and dried. Thus, a layer having a thickness of 120 μm was formed.

  Next, the PTMA used in Example 1, graphitized vapor-grown carbon fiber as a conductivity-imparting agent, and polyvinylidene fluoride as a binder at a mass ratio of 5: 4: 1 were mixed together. After applying a slurry mixed with methylpyrrolidone and drying, a coin-type secondary battery was produced in the same manner as in Example 1 except that the second layer of the positive electrode active layer was formed, and tested in the same manner as in Example 1. Did not work as a battery.

Comparative Example 2
The lithium-containing silicon oxide (LiSiO) particles having a number average particle diameter of 10 μm used in Example 1 and polytetrafluoroethylene as a binder were kneaded at a mass ratio of 9: 1 to form a paste, which was 10 μm thick. A negative electrode was prepared by pressure bonding to a copper foil to form a 120 μm thick lithium-containing silicon oxide compound layer.

Next, a poly (2,2,6,6-tetramethylpiperidinoxymethacrylate) (PTMA) homopolymer substance having a molecular weight of 22000 comprising the repeating unit represented by the chemical formula (1), graphitized as a conductivity-imparting agent Vapor-grown carbon fiber and polyvinylidene fluoride as a binder were blended at a mass ratio of 5: 4: 1, and a slurry obtained by mixing them with n-methylpyrrolidone was applied onto an aluminum foil having a thickness of 20 μm and dried. This was used as a positive electrode, and a separator made of polypropylene having a thickness of 25 μm was sandwiched between the positive and negative electrodes to obtain a laminate.
Using this laminate, a coin-type secondary battery was produced in the same manner as in Example 1. The test was conducted in the same manner as in Example 1, and the test results are shown in Table 1.

Table 1
100C discharge capacity / 1C discharge capacity (%)
Example 1 71
Example 2 66
Example 3 69
Example 4 56
Comparative Example 1
Comparative Example 2 13

  In the nonaqueous electrolyte secondary battery of the present invention, the same interface as the separator is formed on the surface where the nitroxide radical polymer and the lithium-containing silicon oxide layer are in contact with each other by the nitroxide radical polymer that has penetrated the lithium-containing silicon oxide layer. Therefore, there is no need to place a separator, and since the nitroxide radical polymer and the lithium-containing silicon oxide layer form an interface with a large surface area, a non-aqueous electrolyte secondary solution that can be charged and discharged at a high rate A battery can be provided.

It is sectional drawing explaining the nonaqueous electrolyte secondary battery of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Non-aqueous electrolyte secondary battery, 2 ... Negative electrode collector, 3 ... Negative electrode active layer, 4 ... Positive electrode active layer, 5 ... Positive electrode collector, 6 ... 1st layer, 7 ... 2nd layer

Claims (3)

A lithium-containing silicon oxide layer is formed on the negative electrode current collector surface, an active layer is disposed on the positive electrode current collector surface, and one surface of the active layer is in contact with the lithium-containing silicon oxide layer, The lithium-containing silicon oxide layer is composed of Li _x SiO (x is in the range of 1 to 4) and a binder, and the active layer is a mixture of lithium-containing silicon oxide in contact with the lithium-containing silicon oxide layer and a nitroxide radical polymer. A non-aqueous electrolyte secondary battery comprising a first layer and a second layer comprising a nitroxide radical polymer, a conductivity-imparting material, and a binder. The non-aqueous electrolyte secondary battery according to claim 1, wherein the nitroxide radical polymer includes a structural unit represented by any one of chemical formulas (1) to (8).

  3. The non-aqueous electrolysis according to claim 1, wherein the first layer of the active layer is formed by allowing a solution containing a nitroxide radical polymer to enter a lithium-containing silicon oxide layer. Liquid secondary battery.

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