JP2010165491A - Electrode active material and secondary battery using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode active material capable of being made a secondary battery without mounting a separator to prevent short-circuit between a positive electrode and a negative electrode. <P>SOLUTION: In the electrode active material composed of a copolymer of a monomer having an organic radical group and a monomer having an oxyethylene unit, a ratio of the organic radical group is made to be 1 time or more and 40 times or less of that of the oxyethylene unit. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrode active material and a secondary battery using the same. More specifically, the present invention relates to an electrode active material using an organic compound, and an organic radical battery that repeats charge and discharge using an electrode reaction of the electrode active material.

  In recent years, the performance of portable electronic devices such as notebook computers and mobile phones has been increasing. As a power source for these electronic devices, a secondary battery having a high energy density and a long life is expected.

  Currently, lithium ion batteries using a lithium-containing transition metal compound as a positive electrode and a lithium storage compound such as a carbon material as a negative electrode are widely used as power sources for such electronic devices.

  However, the energy density of this type of lithium ion secondary battery is approaching the theoretical limit, and development of a new secondary battery that realizes a high capacity is required. In addition, since this type of lithium ion secondary battery has a low electrode reaction rate, the battery performance is significantly lowered when a large current is passed. In addition, when downsizing, the capacity and output are often much lower than expected, and it is necessary to charge for a long time.

  Therefore, in order to solve such problems, in recent years, research and development of secondary batteries using an organic radical compound as a reaction product or product of an electrode reaction have been actively conducted.

  A secondary battery using an organic radical compound as an electrode active material charges and discharges using a radical oxidation-reduction reaction, and thus has a high reaction rate. Therefore, it has the characteristics that it has high output and charging is completed in a relatively short time.

  Patent Document 1 discloses a secondary battery electrode that secures the conductivity of the electrode, has excellent output characteristics, particularly low temperature characteristics, and has a high energy density as a secondary battery containing a nitroxyl radical compound in the electrode. ing. As nitroxyl radical compounds, piperidyl group-containing high molecular weight polymers and copolymers are described.

  Further, Non-Patent Document 1 discloses a micro battery using 2,2,6,6-tetramethylpiperidinoxyl-7-yl methacrylate (PTMA) as a positive electrode active material. In the microbattery, a positive electrode made of PTMA is impregnated with an electrolytic solution to be gelled. Since PTMA gel exhibits high ionic conductivity and low electronic conductivity, it serves as an electrolyte at the same time as a positive electrode active material, and is an organic radical constructed without a separator that prevents a short circuit between the positive and negative electrodes. A battery is disclosed.

JP 2007-213992 A

208th ECS Meeting, 2005 Abstract # 1246

  However, the organic radical compound itself such as the nitroxyl radical compound described in Patent Document 1 and PTMA described in Non-Patent Document 1 does not have ionic conductivity. Therefore, as described in Patent Document 1 and Non-Patent Document 1, an electrolytic solution used in a normal lithium ion secondary battery or the like must be used.

  Moreover, in order to prevent the short circuit between positive and negative electrodes like the secondary battery described in patent document 1, it is also necessary to interpose a separator.

  As described above, although secondary batteries using various organic radical compounds as electrode active materials have been proposed, secondary batteries that function without using an electrolytic solution and a separator have not yet been obtained.

  Therefore, the present invention provides an electrode active material having both a charge / discharge function based on an electrochemical redox reaction of an organic radical and an ion conduction function of a polymer electrolyte, and a secondary battery using the same. .

The present invention is an electrode active material comprising a copolymer of a monomer having an organic radical group and a monomer having an oxyethylene unit.
The ratio of the oxyethylene unit is 1 to 40 times that of the organic radical group.

  Moreover, it is preferable that the said organic radical group contains at least 1 sort (s) chosen from the group which consists of a nitroxyl radical group, a ferdazyl radical group, or a nitronyl nitroxide radical group. In the present invention, the radical group is a stable free radical, that is, a substituent composed of an atomic group containing a stable radical.

  The present invention is also directed to a secondary battery using the electrode active material.

The secondary battery of the present invention is a secondary battery that charges and discharges by a battery electrode reaction. The electrode active material is included in any one of a reaction starting material, a product, and an intermediate product in at least a discharge reaction of the battery electrode reaction.
Furthermore, the secondary battery of the present invention preferably has a positive electrode current collector, a positive electrode, a negative electrode, and a negative electrode current collector.
Moreover, it is preferable that the positive electrode is mainly composed of the electrode active material and contains a conductive additive so as not to reach the negative electrode from the surface on the positive electrode current collector side of the positive electrode to the inside.

  According to the electrode active material of the present invention, since the main component is a copolymer of a monomer having an organic radical group and a monomer having an oxyethylene unit, the separator or electrolyte used in a lithium ion secondary battery is usually used. Even if it is not used, since the portion of the oxyethylene unit plays the role of an electrolyte, a secondary battery can be realized without using a separator and an electrolytic solution.

The electrode active material and secondary battery of the present invention will be described in detail below.

First, the electrode active material of the present invention will be described. Hereinafter, although a concrete compound form is illustrated, the present invention is not limited to such a compound form. The electrode active material used in the present invention is a polymer compound having both a charge / discharge reaction function and an ion conduction function. Thus, a secondary battery that can function without using a separator and an electrolytic solution can be obtained. The charge / discharge reaction function includes an electrochemical redox reaction of organic radicals. The ion conduction function includes ion conduction by a polymer electrolyte such as a polymer having an oxyethylene unit. Therefore, the present inventors can obtain a polymer compound having both a charge / discharge reaction function and an ion conduction function by copolymerizing a monomer having an organic radical group and a monomer having an oxyethylene unit or the like. Found.

The ratio of the oxyethylene unit is 1 to 40 times that of the organic radical group. When the ratio of oxyethylene units is 1 time or less of the organic radical group, it is insufficient to play a role as an electrolyte, and when it is 40 times or more, the capacity decreases. Therefore, the ratio of oxyethylene units is preferably 1 to 40 times.
Examples of the organic radical group include a stable radical group. Specifically, as shown in FIG. 1, piperidinoxy radical group (a), proxy radical group (b), pyrrolinoxy radical group (c), di-tert-butyl nitroxy radical group (d), As shown by azaadamantyl radical group (e), trimethyldiazaadamantyl radical group (f), bridged alicyclic compound nitroxy radical group as shown in (g) of FIG. 1, (h) to (l) And stable radical groups such as aromatic nitroxyl radical groups. Among these, it is preferable to include at least one selected from the group consisting of a nitroxyl radical group, a ferdazyl radical group, or a nitronyl nitroxide radical group. In the present invention, the organic radical group only needs to contain at least one of the radical groups, and these radical groups can be combined.

Next, the secondary battery of the present invention will be described in detail.
The secondary battery of the present invention is a secondary battery that charges and discharges by a battery electrode reaction, and uses the above-described electrode active material as an electrode material. The electrode active material is characterized in that it is contained in at least one of reaction starting materials, products and intermediate products in the charge / discharge reaction of the battery electrode reaction. The secondary battery of the present invention is composed of at least a positive electrode current collector, a positive electrode, a negative electrode, and a negative electrode current collector, and the positive electrode is mainly composed of the electrode active material. In addition, since the electrode active material is an insulator, it is preferable that a conductive assistant is included on the positive electrode current collector side of the positive electrode in order to reduce contact resistance with the current collector.
Furthermore, it is preferable that a conductive additive is contained so as not to reach the negative electrode from the surface on the positive electrode current collector side of the positive electrode to the inside.
An example of the structure of the secondary battery of the present invention is shown in FIG. The secondary battery shown in FIG. 2 has a configuration in which the negative electrode 4 and the positive electrode 3 are overlapped.
As the negative electrode 4, conventionally known negative electrode materials used for lithium secondary batteries and the like can be used. For example, it is possible to use a conductive polymer such as lithium metal or lithium alloy, other single metal or alloy, polyacetylene, polyphenylene, polyaniline, or polypyrrole.
Examples of the material of the negative electrode current collector 5 and the positive electrode current collector 1 include nickel, aluminum, copper, gold, silver, titanium, an aluminum alloy, stainless steel, and a carbon material.

Moreover, since the electrode active material of this invention is an insulator, it is preferable that the positive electrode 3 contains a conductive support agent in the positive electrode collector 1 side. It is preferable that the conductive additive 2 is contained inside the surface of the positive electrode 3 on the positive electrode current collector 1 side so as not to reach the negative electrode 4.
In addition, examples of the conductive auxiliary material include vapor-grown carbon fibers, carbon materials such as acetylene black and ketjen black, and materials used as conductive auxiliary agents in lithium ion secondary batteries can be used. It is.

Further, when producing the positive electrode, a supporting salt serving as a charge carrier is added to the copolymer as the electrode active material. As the supporting salt, a supporting salt generally used for lithium ion secondary batteries and the like can be used. Specifically, 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 , Etc. can be selected and used.

  Other supporting salts include quaternary ammonium salts such as tetraammonium tetrafluoroborate and tetraethylammonium tetrafluoroborate, quaternary phosphonium salts such as tetraethylphosphonium tetrafluoroborate, and tetrafluoroborate. A salt selected from imidazolium salts such as ethyl methyl borohydride and the like can be used. These materials may be used alone or in combination of two or more.

  Examples of the polymer compound of the present invention and a secondary battery using the same will be described below.

[Example 1]
[Synthesis of electrode active material]
First, 2,2,6,6-tetramethyl-4-piperidyl methacrylate: 8 g and 2- (2-ethoxyethoxy) ethyl acrylate: 8 g were dissolved in 100 mL of toluene, and azoisobutyronitrile: 0.03 g was added. Then, the mixture was stirred at 50 ° C. for 12 hours for reaction.

  Next, the obtained reaction solution was dropped into a large amount of methanol to precipitate, and the product was isolated.

Next, the product thus obtained was dissolved in tetrahydrofuran. And it was dripped at methanol and reprecipitated, the obtained compound was taken out and dissolved in dichloromethane: 100 mL.
Next, 5 g of metachloroperbenzoic acid: 5 g was added to the obtained solution, and the mixture was stirred at room temperature for 12 hours to be reacted, and reddish brown 2,2,6,6-tetramethyl-4- represented by the following formula (1) A copolymer of piperidinoxy methacrylate and 2- (2-ethoxyethoxy) ethyl acrylate was synthesized.

Electron spin resonance (ESR) measurement of a copolymer of 2,2,6,6-tetramethyl-4-piperidinoxymethacrylate and 2- (2-ethoxyethoxy) ethyl acrylate was performed. As a result, the spin concentration was 1.12 × 10 ²¹ g ⁻¹ .
The spin concentration means the number of unpaired electrons (radicals) per unit mass, and in general, the radical concentration can be represented by the spin concentration. Therefore, to determine the molality x _A monomer having an organic radical group contained in the copolymer from the resulting spin concentration from the following equation (1). In the following formula (1), sp is the spin concentration, and N _A is the Avogadro constant. Further, the molality of a monomer having an oxyethylene unit and x _B.

Further, the copolymerization ratio x _A : x _B of the monomer having an organic radical group and the monomer having an oxyethylene unit is obtained from the following formula (2), and the ratio z of the oxyethylene unit to the organic radical group is obtained from the following formula (3). Asked. Here, the molecular weight of the monomer having a M _A is an organic radical group, M _B is the molecular weight of the monomer having an oxyethylene unit. N is the number of oxyethylene units (—CH ₂ CH ₂ O—) contained in one molecule of the monomer having an oxyethylene unit. In the case of the compound represented by the chemical formula (1), n is 2.
As a result of the above calculation, it was found that the copolymerization ratio x _A : x _B of the obtained copolymer was 1: 1.6, and the ratio of oxyethylene units was 3.2 times that of the organic radical group.

[Production of secondary battery]
The obtained copolymer: 23.7 g and LiPF ₆ : 0.1 g were dissolved in tetrahydrofuran.
Next, this solution was cast on a conductive additive made of vapor-grown carbon fiber coated with polyvinylidene fluoride as a binder, the solvent was dried, and then punched into a circle with a diameter of 12 mm to produce a positive electrode.
Next, the negative electrode which stuck lithium on both surfaces of copper foil was laminated | stacked on this positive electrode. Thereafter, the negative electrode case is joined to the positive electrode case with the insulating packing disposed on the periphery, and the outer case is sealed by a caulking machine, whereby 2,2,6,6-tetramethyl-4-piperidino is used as the positive electrode active material. A sealed coin-type battery having a copolymer of xyl methacrylate and 2- (2-ethoxyethoxy) ethyl acrylate and metallic lithium as a negative electrode active material was produced.
[Confirmation of secondary battery operation]
The secondary battery produced as described above was charged with a constant current of 0.02 mA until the voltage reached 4.0 V, and then discharged to 2.0 V with a constant current of 0.02 mA. As a result, it was found that this battery was a secondary battery having a charging / discharging voltage of 3.6 V and a discharge capacity of 0.1 mAh, although it did not have a separator and an electrolytic solution that are usually used.
Moreover, when charging and discharging were repeated 100 cycles in the range of 4.0 to 2.0 V, the initial capacity of 80% or more was maintained even after 100 cycles. That is, it was found that secondary charge with a long cycle life can be obtained with little decrease in capacity even after repeated charge and discharge.

Comparative Example 1

[Synthesis of electrode active material]
A polymer compound was synthesized in the same manner as in Example 1. However, the addition amount of 2,2,6,6-tetramethyl-4-piperidyl methacrylate was 12 g, and the addition amount of 2- (2-ethoxyethoxy) ethyl acrylate was 2 g.

The spin concentration of the obtained copolymer was 2.1 × 10 ²¹ g ⁻¹ . Further, the copolymerization ratio and the ratio of oxyethylene units were calculated in the same manner as in Example 1. As a result, the copolymerization ratio x _A : x _B was 1: 0.25, and the ratio of oxyethylene units was 0.50 of the organic radical group. It turned out to be double.
[Production of secondary battery]
A secondary battery was produced in the same manner as in Example 1 except that the copolymer synthesized by the above method was used as the positive electrode active material.
[Confirmation of secondary battery operation]
The secondary battery produced as described above was charged with a constant current of 0.02 mA until the voltage reached 4.0 V, and then discharged to 2.0 V with a constant current of 0.02 mA. As a result, it was found that the voltage flat portion indicating the progress of the charge / discharge reaction was hardly observed, and it did not operate as a secondary battery.

Comparative Example 2

[Synthesis of electrode active material]
A polymer compound was synthesized in the same manner as in Example 1. However, the addition amount of 2,2,6,6-tetramethyl-4-piperidyl methacrylate was 1 g, and the addition amount of 2- (2-ethoxyethoxy) ethyl acrylate was 15 g.

The spin concentration of the obtained copolymer was 1.5 × 10 ²⁰ g ⁻¹ . Further, as a result of calculating the copolymerization ratio and the ratio of the oxyethylene units in the same manner as in Example 1, the copolymerization ratio x _A : x _B was 1: 20.2, and the ratio of the oxyethylene units was 40.4 of the organic radical group. It turned out to be double.
[Production of secondary battery]
A secondary battery was produced in the same manner as in Example 1 except that the copolymer synthesized by the above method was used as the positive electrode active material.
[Confirmation of secondary battery operation]
The secondary battery produced as described above was charged with a constant current of 0.02 mA until the voltage reached 4.0 V, and then discharged to 2.0 V with a constant current of 0.02 mA. As a result, a charge / discharge voltage of 3.6 V was shown, but the discharge capacity was 0.01 mAh or less, and it was found that the battery could not be used as a secondary battery.
[Example 2]
[Synthesis of electrode active material]
2,2,6,6-tetramethyl-4-piperidyl methacrylate: 8 g and methoxypolyethylene glycol monomethacrylate (average molecular weight 500): 8 g were dissolved in 100 mL of toluene, and azoisobutyronitrile: 0.03 g was added. The mixture was stirred at 70 ^° C. for 12 hours for reaction.
Next, the obtained reaction solution was dropped into a large amount of methanol to precipitate, and the product was isolated.
Next, the product thus obtained was dissolved in tetrahydrofuran. And it was dripped at methanol and reprecipitated, the obtained compound was taken out and dissolved in dichloromethane: 100 mL.
Next, after adding 5 g of metachloroperbenzoic acid to the resulting solution, the reaction was allowed to proceed at room temperature for 12 hours, and the reddish brown 2,2,6,6-tetramethyl-4-piperidi represented by the following formula (2) A copolymer of noxymethacrylate and methoxypolyethylene glycol monomethacrylate was synthesized.

The spin concentration of the obtained copolymer was 1.14 × 10 ²¹ g ⁻¹ . Moreover, as a result of calculating the copolymerization ratio and the ratio of oxyethylene units in the same manner as in Example 1, the copolymerization ratio x _A : x _B was 1: 0.53, and the ratio of oxyethylene units was 5.0 of the organic radical group. It turned out to be double.
[Production of secondary battery]
A secondary battery was produced in the same manner as in Example 1 except that the copolymer synthesized by the above method was used as the positive electrode active material.
[Confirmation of secondary battery operation]
The secondary battery produced as described above was charged with a constant current of 0.02 mA until the voltage reached 4.0 V, and then discharged to 2.0 V with a constant current of 0.02 mA. As a result, the charge / discharge voltage was 3.6 V, and the secondary battery was found to have a discharge capacity of 0.2 mAh.
Moreover, when charging and discharging were repeated 100 cycles in the range of 4.0 to 2.0 V, the initial capacity of 80% or more was maintained even after 100 cycles. That is, it was found that a secondary battery with a small capacity reduction and a long cycle life can be obtained even when charging and discharging are repeated.
[Example 3]
[Synthesis of electrode active material]
In the same manner as in Example 2, a polymer compound represented by the following formula (3) was synthesized. However, methoxypolyethylene glycol monomethacrylate (average molecular weight 1100) was used instead of methoxypolyethyleneglycol monomethacrylate (average molecular weight 500).

The spin concentration of the obtained copolymer was 1.5 × 10 ²¹ g ⁻¹ . Further, as a result of calculating the copolymerization ratio and the ratio of oxyethylene units in the same manner as in Example 1, the copolymerization ratio x _A : x _B was 1: 0.14, and the ratio of oxyethylene units was 3.2 of the organic radical group. It turned out to be double.

[Production of secondary battery]
A secondary battery was produced in the same manner as in Example 1 except that the copolymer synthesized by the above method was used as the positive electrode active material.
[Confirmation of secondary battery operation]
The secondary battery produced as described above was charged with a constant current of 0.02 mA until the voltage reached 4.0 V, and then discharged to 2.0 V with a constant current of 0.02 mA. As a result, the charge / discharge voltage was 3.6 V, and the secondary battery was found to have a discharge capacity of 0.2 mAh.
Moreover, when charging and discharging were repeated 100 cycles in the range of 4.0 to 2.0 V, the initial capacity of 80% or more was maintained even after 100 cycles. That is, it was found that a secondary battery with a small capacity reduction and a long cycle life can be obtained even when charging and discharging are repeated.
[Example 4]
[Synthesis of electrode active material]
First, 5.4 g of phenylhydrazine was dissolved in 90 mL of pyridine, and further 6.8 g of 4-vinylbenzaldehyde was added and stirred for 1 hour to react.
Next, 4 mL of glacial acetic acid was added to the reaction solution and stirred for 1 hour, and an aqueous solution of dialine diazonium salt was added dropwise to the solution to obtain red crystals. It was confirmed by ¹ H-NMR measurement that the obtained crystal was 1,5-diphenyl-3- (4-vinylphenyl) formazan.
1,5 Diphenyl-3- (4-vinylphenyl) formazan obtained as described above: 5.0 g was dissolved in dimethylformamide: 500 mL, and potassium hydrogen sulfate (KHSO ₄ ): 14 g and a formalin solution (37%): 138 mL was added and diluted. Then, it neutralized using 2N sodium hydroxide aqueous solution, and the deep blue needle-like crystal | crystallization of 1, 5- diphenyl-3- (4-vinylphenyl) ferdazil was obtained.

  Next, 1.6 g of 1,5-diphenyl-3- (4-vinylphenyl) ferdadil thus obtained was added to 1.6 mL of anhydrous tetrahydrofuran: 1.6 g together with 1.6 g of 2- (2-ethoxyethoxy) ethyl acrylate. 1,5-diphenyl-3- (4-vinylphenyl) ferdadil represented by the following formula (4) and 2- (2-ethoxy) A copolymer of ethoxy) ethyl acrylate was synthesized.

ESR measurement of the obtained copolymer was performed. As a result, the spin concentration was 8.3 × 10 ²⁰ g ⁻¹ . Moreover, as a result of calculating the copolymerization ratio and the ratio of oxyethylene units in the same manner as in Example 1, the copolymerization ratio x _A : x _B was 1: 2.0, and the ratio of oxyethylene units was 4.0 of the organic radical group. It turned out to be double.

[Create secondary battery]
A secondary battery was produced in the same manner as in Example 1 except that the copolymer synthesized by the above method was used as the positive electrode active material.
[Confirmation of secondary battery operation]
The secondary battery produced as described above was charged with a constant current of 0.02 mA until the voltage reached 4.0 V, and then discharged to 2.0 V with a constant current of 0.02 mA. As a result, it was found that the charge / discharge voltage was 2.8 V, and the secondary battery had a discharge capacity of 0.11 mAh. Moreover, when charging and discharging were repeated 100 cycles in the range of 4.0 to 2.0 V, the initial capacity of 80% or more was maintained even after 100 cycles. That is, it was found that a secondary battery with a small capacity reduction and a long cycle life can be obtained even when charging and discharging are repeated.

It is a structural formula of various stable radical groups. It is sectional drawing which shows one Embodiment of the structure of the secondary battery which concerns on this invention.

1 Positive current collector
2 Conductive aid 3 Positive electrode 4 Negative electrode 5 Negative electrode current collector

Claims (4)

An electrode active material comprising a copolymer of a monomer having an organic radical group and a monomer having an oxyethylene unit,
The electrode active material whose ratio of the said oxyethylene unit is 1 to 40 times the said organic radical group.   2. The electrode active material according to claim 1, wherein the organic radical group contains at least one selected from the group consisting of a nitroxyl radical group, a ferdazyl radical group or a nitronyl nitroxide radical group. A secondary battery that charges and discharges by a battery electrode reaction,
The electrode active material according to any one of claims 1 and 2 is included in at least one of a reaction starting material, a product, and an intermediate product in a discharge reaction of the battery electrode reaction. Next battery. A positive electrode current collector, a positive electrode, a negative electrode and a negative electrode current collector;
The positive electrode mainly comprises the electrode active material,
The secondary battery according to claim 3, wherein a conductive additive is contained so as not to reach the negative electrode from the surface on the positive electrode current collector side of the positive electrode to the inside.

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