JP5445148B2 - Secondary battery and charging method thereof - Google Patents

Description

The present invention relates to a positive electrode and a secondary battery for a secondary _{battery, Li 2 NiPO 4 F, LiNiPO} 4, LiCoPO 4, Li 2 CoPO 4 F or the like, a secondary battery charging reaction at a high potential by using a positive electrode active material is performed Can be suitably used.

Conventionally, carbon powder is mixed with a positive electrode active material of a secondary battery to impart necessary electron conductivity to the positive electrode. For example, lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), solid solutions thereof, lithium manganate (LiMn ₂ O ₄ ), and the like are used as positive electrode active materials for lithium ion batteries. Carbon as a conductive additive is mixed with the material to provide the necessary electronic conductivity for the positive electrode, and a fluororesin such as polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (PVdF) is used as a binder. Thus, the positive electrode is formed.

  In order to meet the demand for higher output and higher speed charging, the raw material is carbonized when manufacturing the electrode, or the electrode active material, the conductive additive and the solvent are mixed and pulverized by a wet method, and then the solvent is removed. (Patent Document 1) and improving the electronic conductivity. Moreover, the polymer material which coat | covered the surface with the metal is used as a conductive support agent (patent document 2), or a metal particle is included in the active material layer as a conductive assistant agent (patent document 3). Improvements have also been proposed.

JP 2008-147024 A JP 2007-311057 A JP 2006-164823 A

However, the above _{Li 2 NiPO 4 F, LiNiPO 4} , LiCoPO 4, Li 2 CoPO 4 The positive electrode active material charging reaction at a high potential of F or the like is performed, a graphite powder was added to these positive electrode active material as a conductive additive And the like may be oxidized at a high potential during charging, or the solvent may be decomposed by an electrochemical reaction on the graphite powder.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a positive electrode for a secondary battery in which a positive electrode active material having a high energy density, in which a charging reaction is performed at a high potential, can be effectively utilized. And

  The positive electrode for a secondary battery of the present invention is a positive electrode for a secondary battery in which an aggregate of particles made of a positive electrode active material is formed into a predetermined shape, and the particles made of the positive electrode active material include conductive diamond-like carbon and The glassy carbon is attached.

In the positive electrode for an organic electrolyte secondary battery of the present invention, an aggregate of particles made of a positive electrode active material is formed into a predetermined shape, and the particles made of the positive electrode active material include conductive diamond-like carbon and / or glassy. Carbon is attached. For this reason, the conductive diamond-like carbon and / or glassy carbon plays a role of a conductive auxiliary agent and imparts electronic conductivity, which is a necessary characteristic for the positive electrode for the secondary battery. Moreover, according to the test results of the present inventors, conductive diamond-like carbon and glassy carbon have a wider potential window than graphite, are stable at a high potential, and are less likely to decompose the solvent. For this reason, there is little possibility that the conductive diamond-like carbon or glassy carbon is oxidized or the solvent is decomposed at a high potential during charging. For this reason, the positive electrode active material with a high energy density in which a charging reaction is performed at a high potential can be effectively utilized.

Here, the conductive diamond-like carbon (hereinafter sometimes simply referred to as diamond-like carbon or DLC) is a diamond bond (SP ₃ hybrid orbital bond between carbons) and a graphite bond (SP ₂ between carbons). Among carbons having an amorphous structure in which both the bonds of hybrid orbital bonds are mixed, those having conductivity of 1000 Ωcm or less. However, in addition to the amorphous structure, those having a phase composed of a crystal structure partially composed of a graphite structure (that is, a hexagonal crystal structure composed of SP ₂ hybrid orbital bonds) and thereby exhibiting conductivity are also included. . Diamond-like carbon having properties intermediate between graphite and diamond adjusts the conductivity by adjusting the ratio of SP ₂ hybrid orbital bonds and SP ₃ hybrid orbital bonds of the carbon atoms constituting diamond-like carbon during film formation. be able to.

Glassy carbon (hereinafter sometimes abbreviated as GC) is a non-directional assembly of hexagonal mesh surfaces of several nanometers, which is the basic structure of graphite-based materials. Carbon that has a structure that is difficult to develop and has a structure close to amorphous.

  The conductive diamond-like carbon and / or glassy carbon is preferably attached to the particles made of the positive electrode active material by a dry plating method. If it is like this, electroconductive diamond-like carbon and / or glassy carbon can be adhered to the whole surface of the particle | grains which consist of positive electrode active materials uniformly with sufficient adhesiveness. Here, the dry plating method refers to all methods in which conductive diamond-like carbon and / or glassy carbon is attached to the surface of particles made of a positive electrode active material in a vacuum or in a gas phase.

The dry plating method for attaching the conductive diamond-like carbon to the powder of the positive electrode active material is not particularly limited. For example, CVD, thermal CVD, plasma CVD (high frequency, microwave, direct current, etc.), PVD method And vacuum deposition, ion plating (direct current excitation, high frequency excitation), sputtering (bipolar sputtering, magnetron sputtering, ECR sputtering), laser ablation, ion beam deposition, ion implantation, and the like.
The dry plating method for adhering the glassy carbon to the positive electrode active material powder is not particularly limited. However, the ion beam is applied to the glassy carbon target in a vacuum and deposited on the surface of the positive electrode active material by a sputtering phenomenon. It is possible to employ a sputtering method, a method in which the powder of the positive electrode active material is subjected to plasma heat treatment in an atmosphere containing a hydrocarbon gas, or the like.
Furthermore, the positive electrode active material of the coating process and the positive electrode active material of the conductive diamond-like carbon to the powder of glassy carbon on the powder coating method to both employed, and conductive diamond-like carbon powder of the positive electrode active material A positive electrode active material to which both glassy carbons are attached can also be used as a positive electrode material.

As the positive electrode active material used in the positive electrode for secondary battery of the present _invention, Li ₂ NiPO _{4 F,} it may comprise at least one LiNiPO 4, LiCoPO ₄ and _Li 2 CoPO ₄ F. Since these positive electrode active materials are charged at a high potential, there is an advantage that the energy density is large. However, there is a possibility that the graphite is oxidized or the solvent is decomposed with the conventional conductive assistant made of graphite. . On the other hand, in the positive electrode for a secondary battery of the present invention, even if the potential is high, stable diamond-like carbon works as a conductive assistant, and the potential window is wide so that the solvent is not easily decomposed. For this reason, it can use suitably as a lithium ion battery which can utilize effectively the advantage of these positive electrode active materials with a large energy density.

Further, according to the inventors of the test results, the electrolyte solution containing the nitrile compound is charged in a wide since it has a potential _{window, Li 2 NiPO 4 F, LiNiPO} 4, LiCoPO 4 and _Li 2 CoPO ₄ F higher potential of such It exists stably in the charged region of the positive electrode active material, and can withstand decomposition. For this reason, it is suitable as an electrolytic solution for the positive electrode for the secondary battery of the present invention. For this reason, the secondary battery of this invention was equipped with the positive electrode for secondary batteries of Claim 1 or 2, and the electrolyte solution containing a nitrile compound, It was characterized by the above-mentioned.

It is a cross-sectional schematic diagram of the secondary battery of the embodiment. It is an expansion schematic diagram of the positive electrode for secondary batteries of an embodiment. The potential of the experimental Examples 1 and 2 and a lithium-ion battery electrolyte solution obtained by dissolving LiPF ₆ of the electrode of Comparative Examples 1 to 3 - a current curve. The potential of the experimental Examples 1 and 2 and a lithium-ion battery electrolyte solution obtained by dissolving LiBF ₄ in Comparative Examples 1 to 3 of the electrode - is a current curve. It is an electric potential-current curve in the electrolyte solution for lithium ion batteries which melt | dissolved LiTFSI of the electrode of Experimental example 2 and Comparative Examples 1-3. The potential of the experimental examples 3 and 4及 beauty lithium ion battery electrolyte solution obtained by dissolving NaPF ₆ in Comparative Example 4 of the electrode - is a current curve. 2 is a graph showing charge / discharge characteristics of a lithium ion battery electrode of Example 1. FIG.

(Embodiment)
Hereinafter, embodiments embodying the present invention will be described.
First, a positive electrode active material powder is prepared, and diamond-like carbon and / or glassy carbon is adhered to the surface of the positive electrode active material powder by dry plating.
Although it does not specifically limit as a dry-type plating method for making diamond-like carbon adhere to the powder of a positive electrode active material, For example, an ionization vapor deposition method can be used. In other words, benzene or hydrocarbon gas is introduced into a vacuum chamber, ions are generated in a DC arc discharge plasma, and collided with a positive active material powder biased to a DC negative voltage with energy corresponding to the bias voltage. In this method, diamond-like carbon is attached to the surface of the positive electrode active material powder.

  As another method for attaching the diamond-like carbon to the powder of the positive electrode active material, a high frequency plasma method can be given. In this method, methane gas is used as a raw material, and a capacitively coupled plasma electrode is used.

  Furthermore, diamond-like carbon can be attached to the powder of the positive electrode active material by thermal decomposition of hydrocarbon gas (for example, JP 2008-260670 A).

Further, diamond-like carbon can be attached to the surface of the positive electrode active material powder by a sputtering method (for example, Japanese Patent Application Laid-Open No. 2004-339564).
That is, in a vacuum, electrons are accelerated by an electric field and collided with argon gas to ionize argon, which is accelerated by the electric field and collided with a solid carbon target to be sputtered, and diamond-like carbon is formed on the positive electrode active material powder. (At this time, a negative bias voltage applied to the positive electrode active material may be applied).

A positive electrode active material powder having diamond-like carbon attached to the surface is prepared by various dry plating methods as described above, and polytetraethylene (PTFE), polyvinylidene fluoride (PVdF), or the like as a binder is prepared. And a positive electrode for a secondary battery according to the embodiment is obtained. As the positive electrode active material, for example, _{Li 2 NiPO 4 F, LiNiPO 4} , LiCoPO 4, Li 2 CoPO 4 either F or the like, or may be a mixture thereof. These mixing ratios may be appropriately determined in consideration of the electron conductivity required for the positive electrode, the addition amount of the fluororesin necessary for exhibiting the function as the binder, and the like.

  Further, as a method for adhering the glassy carbon to the positive electrode active material powder, the positive electrode active material powder is 0.1 to 30 torr and 400 to 1100 ° C. containing hydrocarbon gas such as methane, ethane, and propane. A method of performing a plasma heat treatment in an atmosphere can be employed (see Japanese Patent Application Laid-Open No. 11-43770).

Furthermore, the positive electrode active material of the coating process and the positive electrode active material of the conductive diamond-like carbon to the powder of glassy carbon on the powder coating method to both employed, and conductive diamond-like carbon powder of the positive electrode active material A positive electrode active material to which both glassy carbons are attached can also be used as a positive electrode material.

  A lithium ion battery 8 as shown in FIG. 1 can be manufactured using the positive electrode for a lithium ion battery thus formed. That is, the separator 1 through which the electrolytic solution can permeate is sandwiched between the positive electrode 2 for a lithium ion battery and the negative electrode 3 made of graphite to form a joined body 4 and immersed in the electrolytic solution. Then, the joined body 4 is accommodated so that the negative electrode 3 is in contact with the negative electrode current collecting case 6 loaded with the packing 5, and the positive electrode current collector plate 7 is inserted from the positive electrode 2 side for the lithium ion battery. The current collecting case 6 and the positive current collecting plate 7 are caulked and sealed. Thus, the lithium ion battery 8 of the embodiment can be manufactured.

  In the lithium ion battery positive electrode 2 of the lithium ion battery 8 of the above embodiment, as shown in FIG. 2, diamond-like carbon 2b and fluororesin powder 2c are attached on the positive electrode active material powder 2a, and the fluororesin powder 2c. However, the powder is held as a binder to maintain the electrode shape. The diamond-like carbon 2b plays a role as a conductive auxiliary agent responsible for electron conductivity. As will be described later, the diamond-like carbon 2b has a wider potential window than the simple carbon black powder or graphite powder in the electrolyte solution of the lithium ion battery. For this reason, even at a high potential in the charging process of the positive electrode active material, it stably exists and hardly decomposes the electrolyte solvent. For this reason, the conductive auxiliary agent is not oxidized at a high potential during charging or the solvent is not decomposed. As a result, a charging reaction is performed at a high potential, and a positive electrode active material having a high energy density is obtained. It can be used effectively.

<Experimental example>
Hereinafter, in order to prove the effect of the invention of the positive electrode for a secondary battery of the present invention, various conductive substance powders are mixed with PTFE powder to prepare a disk-shaped electrode by a hot press method, and a potential-current curve is obtained. It was measured.

(Experimental example 1)
In Experimental Example 1, conductive diamond-like carbon (DLC) powder (average particle size 0.03 μm) and PTFE powder were mixed at a mass ratio of 80:20, and a disk-shaped electrode of 8 mmφ was produced by hot pressing. .

(Experimental example 2)
In Experimental Example 2, glassy carbon powder (average particle size 0.5 μm) and PTFE powder were mixed at a mass ratio of 80:20, and an 8 mmφ disk-shaped electrode was produced by hot pressing.

(Comparative Example 1)
Comparative Example 1 is a commercially available glassy carbon plate itself.

(Comparative Example 2)
In Comparative Example 2, carbon black (“HS-100” manufactured by Denki Kagaku Kogyo Co., Ltd.) and PTFE powder were mixed at a mass ratio of 80:20, and a disk-shaped electrode of 8 mmφ was produced by hot pressing.

(Comparative Example 3)
In Comparative Example 3, carbon black (“HS-100” manufactured by Denki Kagaku Kogyo Co., Ltd.) was heat-treated in a vacuum at 3000 ° C. for 3 hours and graphitized and PTFE powder were mixed at a mass ratio of 80:20. A disk-shaped electrode of 8 mmφ was prepared by hot pressing.

<Measurement of potential-current curve>
The electrodes of Experimental Examples 1 and 2 and Comparative Examples 1 to 3 prepared as described above were subjected to potential scanning in the electrolyte solution for lithium ion batteries, and a potential-current curve was measured. The electrolytic solution was prepared as follows. That is, a mixed solution is prepared so that ethylene carbonate, dimethyl carbonate, and sebaconitrile are in a mass ratio of 25:25:50, and the lithium electrolyte (any one of LiPF ₆ , LiBF _4, and LiTFSI) is 1 mol / L. The so-dissolved solution was used as an electrolytic solution and placed in a three-electrode electrolytic cell container.

The potential-current curve was measured using the above electrode (area 1.0 cm ² ) as a working electrode, a platinum net as a counter electrode, and Li metal as a reference electrode. The sweep speed was 5 mV / sec.

The results are shown in FIGS.
(Measurement results in an electrolyte solution for lithium ion batteries in which LiPF ₆ was dissolved)
In the electrode of Experimental Example 1 using diamond-like carbon powder and the electrode of Experimental Example 2 using glassy carbon powder, almost no current flows up to 7 V (vs Li / Li ⁺ ) as shown in FIG. It was found that the electrode had a wider potential window than the glassy carbon plate electrode of Comparative Example 1.
On the other hand, it was found that in the electrode of Comparative Example 2 using carbon black, when the voltage exceeded 3.6 V (vs Li / Li ⁺ ), current started to flow rapidly and the potential window was narrow.
Further, in the electrode of Comparative Example 3 using carbon black that was heat-treated and graphitized, the potential window was slightly wider than that of the electrode of Comparative Example 2, but when it exceeded 4 V, an oxidation current began to flow, and Experimental Example 1 and Compared with the electrode of Experimental Example 2, it was found that the potential window was narrow.

(Measurement results in an electrolyte solution for lithium ion batteries in which LiBF ₄ is dissolved)
In addition, as shown in FIG. 4, the electrode of Experimental Example 1 using diamond-like carbon powder and the electrode of Experimental Example 2 using glassy carbon powder in the electrolyte solution for lithium ion batteries in which LiBF ₄ was dissolved Similar to the measurement in the lithium ion battery electrolyte in which LiPF ₆ was dissolved, it was found to have a wide potential window.

(Measurement results in an electrolyte solution for lithium ion batteries in which LiTFSI is dissolved)
Furthermore, as shown in FIG. 5, it was found that the electrode of Experimental Example 2 using the glassy carbon powder had a wide potential window even in the measurement in the electrolyte solution for lithium ion batteries in which LiTFSI was dissolved. As a result, and in a measurement result (see FIG. 3) in the electrolyte solution for lithium ion batteries in which LiPF ₆ was dissolved and a measurement result (see FIG. 4) in the electrolyte solution for lithium ion batteries in which LiBF ₄ was dissolved, Since the electrode using diamond-like carbon has a wide potential window like the electrode using glassy carbon, the glassy carbon was also used in the electrolyte for lithium ion batteries in which LiTFSI was dissolved. It is clear that the electrode has a wide potential window.

<Application example to sodium ion battery>
The above is an experimental example related to the measurement of a potential-current curve in an electrolytic solution of a solution in which LiPF ₆ is dissolved, assuming a lithium ion battery. The present invention can be applied to a sodium ion battery in addition to a lithium ion battery. In order to prove this, a solution in which NaPF ₆ was dissolved was also measured for a potential-current curve in the electrolytic solution.

(Experimental example 3)
In Experimental Example 3, glassy carbon powder (average particle size 0.5 μm) and PTFE powder were mixed at a weight ratio of 90:10, and a disk-shaped electrode of 8 mmφ was produced by hot pressing.

(Experimental example 4)
In Experimental Example 4, conductive diamond-like carbon powder (average particle size 0.03 μm) and PTFE powder were mixed at a weight ratio of 90:10, and a disk-shaped electrode of 8 mmφ was produced by hot pressing.

(Comparative Example 4)
In Comparative Example 4, carbon black (trade name: Denka Black, manufactured by Denki Kagaku Kogyo Co., Ltd.) and PTFE powder were mixed at a weight ratio of 90:10, and an 8 mmφ disk-shaped electrode was produced by hot pressing.

<Measurement of potential-current curve>
The electrodes of Experimental Examples 3 and 4 and Comparative Example 4 produced as described above were subjected to potential scanning in an electrolytic solution for sodium ion batteries, and a potential-current curve was measured. The electrolytic solution was prepared as follows. That is, a mixed solution was prepared such that ethylene carbonate, dimethyl carbonate, and sebaconitrile were in a volume ratio of 25:25:50, and a solution in which NaPF ₆ was dissolved to 0.5 mol / L was used as an electrolytic solution. Placed in a triode electrolytic cell container.

The potential-current curve was measured using the above electrode (area 1.0 cm ² ) as a working electrode, a platinum net as a counter electrode, and sodium metal as a reference electrode. The sweep speed was 5 mV / sec.

As a result, as shown in FIG. 6, in the electrodes of Experimental Example 3 using glassy carbon powder and Experimental Example 4 using conductive diamond-like carbon, almost no current flows up to 7 V (vs. Li / Li ⁺ ). It was found to have a wide potential window. On the other hand, in the electrode of Comparative Example 4 using carbon black as an electrode, the current rose in the vicinity of 4 V (vs. Li / Li ⁺ ), and it was found that the potential window was narrow compared to Experimental Examples 3 and 4. .

  From the above results, the positive electrode in which glassy carbon or diamond-like carbon is attached to the positive electrode active material powder of the sodium ion battery is decomposed even in the positive electrode that is at a high potential during charging, as in the case of the lithium ion battery. It was also found that there is little risk of decomposing the solvent. And from this result, it turned out that the positive electrode active material for sodium ion batteries with a high energy density in which a charging reaction is performed at a high potential can be effectively utilized.

  From the above results, the lithium ion battery of the embodiment in which diamond-like carbon and / or glassy carbon was attached to the positive electrode active material powder of the lithium ion battery by dry plating, and further mixed with fluororesin powder. It can be seen that the positive electrode for the battery is not decomposed and is less likely to decompose the solvent even in the positive electrode that is at a high potential during charging for a lithium ion battery. From this result, it can be seen that a positive electrode active material having a high energy density in which a charging reaction is performed at a high potential can be effectively utilized. The same applies to sodium ion batteries. In order to prove the above, in Example 1, the positive electrode for lithium batteries was produced by the method shown below, and the charge / discharge characteristics were measured.

Example 1
Li ₂ CoPO ₄ F powder coated with conductive DLC by plasma CVD method, conductive assistant (glassy carbon), and PTFE powder are mixed in a mortar at a weight ratio of 70: 25: 5, and pressure-molded. A sheet was formed and used as the lithium battery electrode of Example 1.

(Comparative Example 5)
In the electrode of Comparative Example 5, a powder of Li ₂ CoPO ₄ F not coated with conductive DLC as a positive electrode active material, a conductive assistant (glassy carbon), and PTFE powder were mixed in a mortar at a weight ratio of 70: 25: 5. These were mixed and pressure-molded to form a sheet, which was used as the lithium battery electrode of Comparative Example 5.

For the lithium battery electrode of Example 1 produced as described above, the discharge rate was 0.01 C, and the charge / discharge characteristics were examined. As a result, as shown in FIG. 7, it was found that charging is possible even at a charging potential of 5 V (vs Li / Li ⁺ ) or higher. On the other hand, in Comparative Example 5 in which the conductive diamond-like carbon coating was not performed, the discharge capacity was significantly smaller than that in Example 1. This is presumed to be due to the poor electronic conductivity between the glassy carbon, which is a conductive aid, and the Li ₂ CoPO ₄ F, which is a positive electrode active material.
When the conductive DLC is coated, electrons are exchanged smoothly.

  The present invention is applied to a secondary battery such as a lithium ion battery or a sodium ion battery. Here, a secondary battery such as a lithium ion battery or a sodium ion battery includes an electrolytic solution, a positive electrode, a negative electrode, a separator, and a case.

(Electrolytic solution for lithium ion battery)
The electrolytic solution for a lithium ion battery contains a Li salt (electrolyte) and an organic solvent.
As the Li salt, a general Li salt for a Li ion battery can be used. For example, LiPF ₆ (lithium hexafluorophosphate), LiBF ₄ (lithium tetrafluoroborate), LiTFSI (lithium bis (trifluoromethanesulfonyl) imide), LiTFS (lithium trifluoromethanesulfonate), LiBETI (lithium bis ( Pentafluoroethanesulfonyl) imide) or two or more thereof can be used.
Among them, for those redox potential of the positive electrode is more than 4.5V, it is preferable to use LiPF _6, and / or LiBF _4. In the case of using a LiTFSI and LiTFS and LiBETI, it is preferable to add LiPF ₆ or LiBF _4.

As the organic solvent, a general solvent used for a Li ion battery can be adopted. Such an organic solvent is preferably one or more selected from cyclic carbonates, cyclic carboxylic acid esters and chain carbonates. More preferably, a cyclic carbonate and a chain carbonate are used in combination. Specifically, it is particularly preferable to use ethylene carbonate and dimethyl carbonate in combination. The blending ratio of both is not particularly limited. As the cyclic carboxylic acid ester, γ-butyrolactone can be used.
Furthermore, a nitrile compound can be used as an organic solvent. Here, as the nitrile compound, a chain saturated hydrocarbon dinitrile compound in which a nitrile group is bonded to both ends of a chain saturated hydrocarbon compound, a chain ether in which a nitrile group is bonded to at least one terminal of a chain ether compound. Mention may be made of at least one nitrile compound among nitrile compounds and cyanoacetic acid esters.

Examples of the chain saturated hydrocarbon dinitrile compound in which nitrile groups are bonded to both ends of the chain saturated hydrocarbon compound include succinonitrile NC (CH ₂ ) ₂ CN, glutaronitrile NC (CH ₂ ) ₃ CN, adiponitrile In addition to linear dinitrile compounds such as NC (CH ₂ ) ₄ CN, sebaconitrile NC (CH ₂ ) ₈ CN, dodecanedinitrile NC (CH ₂ ) ₁₀ CN, 2-methylglutaronitrile NCCH (CH ₃ ) _CH 2 _CH 2 CN may have a branched as such. These chain saturated hydrocarbon dinitrile compounds are not particularly limited in carbon number, but are preferably 20 or less. More preferably, it is 7-12.

Examples of the chain ether nitrile compound in which a nitrile group is bonded to at least one end of the chain ether compound include oxydipropionitrile NCCH ₂ CH ₂ —O—CH ₂ CH ₂ CN and 3-methoxypropionitrile CH _{3. -O-CH} 2 CH 2 CN, and the like. These chain ether nitrile compounds are not particularly limited in carbon number, but are preferably 20 or less.
Examples of cyanoacetic acid esters include methyl cyanoacetate, ethyl cyanoacetate, propyl cyanoacetate, and butyl cyanoacetate. These cyanoacetic acid esters are not particularly limited in carbon number, but are preferably 20 or less.

These nitrile compounds have the effect of expanding the potential window particularly in the positive direction in the electrolytic solution.
A dinitrile compound is preferable from the viewpoint of the action of expanding the potential window. Of these, the use of sebacononitrile is more preferable.
However, since a nitrile compound has high viscosity, it is preferable to use together with the above-mentioned chain carbonate ester, cyclic carbonate ester, and / or cyclic carboxylic acid ester. More preferably, a nitrile compound, a chain carbonate ester and a cyclic carbonate ester are used in combination. Dimethyl carbonate can be employed as the chain carbonate, and ethylene carbonate can be employed as the cyclic carbonate.
In this case, the blending ratio of the nitrile compound in the whole organic solvent is preferably 1 to 90% by volume. More preferably, it is 5-70 volume%, More preferably, it is 10-50 volume%.

  Moreover, it is also preferable to add about 0.1 to 3% of various additives (for example, vinylene carbonate, fluoroethylene carbonate, ethylene sulfite). Thereby, a corrosion-resistant film is formed on the negative electrode side, and the corrosion resistance is improved.

The concentration of the Li salt is 0.01 mol / L or more and is lower than the saturated state. When the concentration of the Li salt is less than 0.01 mol / L, ion conduction by Li ions is reduced, and the electric resistance of the electrolytic solution is increased, which is not preferable. On the other hand, exceeding the saturation state is not preferable because the dissolved Li salt precipitates due to environmental changes such as temperature.

(Sodium ion battery electrolyte)
The electrolyte for sodium ion batteries contains Na salt (electrolyte) and an organic solvent.
As the Na salt, those conventionally known as Na salts for Na ion batteries can be used. For example, for example, NaClO ₄ , NaPF ₆ , NaBF ₄ , NaCF ₃ SO ₃ , NaN (CF ₃ SO ₂ ) ₂ , NaN (FSO ₂ ) ₂ , NaN (C ₂ F ₅ SO ₂ ) ₂ , NaC (CF ₃ SO ₂ ) ₃ etc. are mentioned. The mixing ratio of the solvent and the solute is not particularly limited and is appropriately set according to the purpose.
Moreover, it is also preferable to add about 0.1 to 3% of various additives (for example, vinylene carbonate, fluoroethylene carbonate, ethylene sulfite). Thereby, a corrosion-resistant film is formed on the negative electrode side, and the corrosion resistance is improved.

As the organic solvent, a general one used for a Na ion battery can be adopted. As such an organic solvent, one kind or two or more kinds selected from cyclic carbonates, cyclic carboxylic acid esters and chain carbonates are preferable. More preferably, a cyclic carbonate and a chain carbonate are used in combination. Specifically, it is particularly preferable to use ethylene carbonate and dimethyl carbonate in combination. The blending ratio of both is not particularly limited. As the cyclic carboxylic acid ester, γ-butyrolactone or propylene carbonate can be used.
As the chain carbonate, in addition to dimethyl carbonate, diethyl carbonate or ethyl methyl carbonate can be used.
Furthermore, a nitrile compound can be used as an organic solvent. Here, as the nitrile compound, a chain saturated hydrocarbon dinitrile compound in which a nitrile group is bonded to both ends of a chain saturated hydrocarbon compound, a chain ether in which a nitrile group is bonded to at least one terminal of a chain ether compound. Mention may be made of at least one nitrile compound among nitrile compounds and cyanoacetic acid esters.

Examples of the chain saturated hydrocarbon dinitrile compound in which nitrile groups are bonded to both ends of the chain saturated hydrocarbon compound include succinonitrile NC (CH ₂ ) ₂ CN, glutaronitrile NC (CH ₂ ) ₃ CN, adiponitrile In addition to linear dinitrile compounds such as NC (CH ₂ ) ₄ CN, sebaconitrile NC (CH ₂ ) ₈ CN, dodecanedinitrile NC (CH ₂ ) ₁₀ CN, 2-methylglutaronitrile NCCH (CH ₃ ) _CH 2 _CH 2 CN may have a branched as such. These chain saturated hydrocarbon dinitrile compounds are not particularly limited in carbon number, but are preferably 7 to 20. More preferably, it is 10-12.

Examples of the chain ether nitrile compound in which a nitrile group is bonded to at least one end of the chain ether compound include oxydipropionitrile NCCH ₂ CH ₂ —O—CH ₂ CH ₂ CN and 3-methoxypropionitrile CH _{3. -O-CH} 2 CH 2 CN, and the like. These chain ether nitrile compounds are not particularly limited in carbon number, but are preferably 20 or less.
Examples of cyanoacetic acid esters include methyl cyanoacetate, ethyl cyanoacetate, propyl cyanoacetate, and butyl cyanoacetate. These cyanoacetic acid esters are not particularly limited in carbon number, but are preferably 20 or less.

These nitrile compounds have the effect of expanding the potential window particularly in the positive direction in the electrolytic solution. A dinitrile compound is preferable from the viewpoint of the action of expanding the potential window. Of these, the use of sebacononitrile is more preferable.
However, since a nitrile compound has high viscosity, it is preferable to use together with the above-mentioned chain carbonate ester, cyclic carbonate ester, and / or cyclic carboxylic acid ester. More preferably, a nitrile compound, a chain carbonate ester and a cyclic carbonate ester are used in combination. Dimethyl carbonate can be employed as the chain carbonate, and ethylene carbonate can be employed as the cyclic carbonate.
In this case, the blending ratio of the nitrile compound in the whole organic solvent is preferably 1 to 90% by volume. More preferably, it is 15-70 volume%, More preferably, it is 30-50 volume%.

  The concentration of Na salt is 0.01 mol / L or more, which is lower than the saturated state. If the concentration of Na salt is less than 0.01 mol / L, ion conduction due to Na ions is reduced, and the electric resistance of the electrolytic solution is increased, which is not preferable. On the other hand, exceeding the saturated state is not preferable because a dissolved Na salt is precipitated due to environmental changes such as temperature.

(Positive electrode)
The positive electrode includes a positive electrode active material and a current collector.
(Positive electrode active material for lithium ion battery)
The positive electrode active material for a lithium ion battery refers to “a material in which lithium is inserted / extracted in the crystal structure at a higher potential than that of the negative electrode, and oxidation / reduction is performed accordingly”.
Examples of the positive electrode active material include (1) an oxide system, (2) a phosphate system having an olivine type crystal structure, and (3) an olivine fluoride system.

(1) Oxide-based 1-1 specific substances As oxide-based materials, Li _1-x CoO ₂ (x = 0 to 1: layered structure), Li _1-x NiO ₂ (x = 0 to ₁ : layered structure) ), Li _1-x Mn ₂ O ₄ (x = 0 to 1: spinel structure), Li _2−y MnO ₃ system (y = 0 to 2) and their solid solutions (here, the solid solution is the above oxide system) In which the metal atoms are mixed in a free ratio.). Moreover, what doped the metal atom of these with the other metal atom is also contained. The dopant is not particularly limited as long as the electrochemical characteristics can be changed in the oxidation-reduction reaction. For example, one or more of Li, Mg, Al, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, and Mo can be used.
1-2 Characteristics The general discharge potential of this positive electrode active material is less than 5 V (vs Li / Li ⁺ ). However, LiNi _0.5 Mn _1.5 O ₄ partially substituted with Ni in the LiMn ₂ O ₄ system has a discharge potential of 4.7 V, and takes into account overvoltage when performing rapid charging, and 5 V May require a charging voltage exceeding. Further, since LiCoMnO ₄ starts with a discharge voltage of about 5.2V, the charge voltage also exceeds 5V. In addition, oxide systems generally decompose at less than 300 ° C., and have a relatively large exothermic reaction as oxygen is generated. Therefore, a control circuit that does not cause overcharging is required.

(2) Phosphate-based 2-1 specific substance having olivine-type crystal structure As phosphate-based substances having olivine-type crystal structure, Li _1-x NiPO ₄ (x = 0 to ₁ ), Li _1-x CoPO ₄ (x = 0 to ₁ ), Li _1-x MnPO ₄ (x = 0 to ₁ ), Li _1-x FePO ₄ (x = 0 to 1) and their solid solutions (herein the solid solution is the above-mentioned phosphorus In the acid salt positive electrode active material, it refers to a material in which metal atoms are mixed in a free ratio. Moreover, what doped the metal atom of these with the other metal atom is also contained. The dopant is not particularly limited as long as the electrochemical characteristics can be changed in the oxidation-reduction reaction. For example, one or more of Mg, Al, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, and Mo can be used (see JP 2008-130525 A).
2-2 Characteristics The oxidation-reduction potential of this positive electrode active material is attracting attention because, unlike the above oxide system, if it is less than 300 ° C., the exothermic reaction is small, oxygen is not generated, and safety is high. Of the phosphate systems, the LiCoPO ₄ system has a discharge potential of about 4.8 V, and an electrolyte having a withstand voltage of 5 V or more is required for rapid charging. It is suggested that the discharge potential of LiNiPO ₄ is 5.2 V (vs Li / Li ⁺ ).

(3) Olivine fluoride system 3-1 Specific substances Li _2-x NiPO ₄ F (x = 0-2), Li _2-x CoPO ₄ F (x = 0-2) are known, and other Li _{2 -x MnPO 4 F (x = 0~2} ), Li 2-x FePO 4 F (x = 0~2) are considered.
Further, these solid solutions (herein, the solid solution refers to a material in which metal atoms are mixed in a free ratio in the olivine fluoride-based positive electrode active material) can also be mentioned. Furthermore, the thing which doped the metal atom of these with another metal atom is also contained. The dopant is not particularly limited as long as the electrochemical characteristics can be changed in the oxidation-reduction reaction. For example, one or more of Mg, Al, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, and Mo can be used.
3-2 Characteristics Similar to the olivine system, the redox potential of this positive electrode active material is different from that of the above oxide system. The effect of battery ignition is considered to be small, and is attracting attention in terms of safety. Moreover, the electric capacity density (mAh / g) of a battery can be made higher than the said phosphate system (refer Unexamined-Japanese-Patent No. 2003-229126). However, for example, the Li ₂ CoPO ₄ F system has an average discharge potential of about 4.8 V, and an electrolytic solution having a withstand voltage of 5 V or more is required for rapid charging. Further, the discharge potential of the Li ₂ NiPO ₄ F system is about 5.2 V (vs Li / Li ⁺ ), and an electrolytic solution having a withstand voltage at 5 V or more is required.

(4) Others In addition, lithium-free FeF ₃ , a conjugated polymer using an organic conductive material, a chevrel phase compound, or the like can also be used. In addition, transition metal chalcogenides, vanadium oxides and lithium salts thereof, niobium oxides and lithium salts thereof, and a plurality of different positive electrode active materials may be used in combination.
The average particle diameter of the positive electrode active material particles is not particularly limited, but is preferably 10 nm to 30 μm.

(Positive electrode active material for sodium ion batteries)
The positive electrode active material for a sodium ion battery is a material that can be reversibly oxidized and reduced by charge and discharge, and is required to be a material that can reversibly intercalate and deintercalate sodium ions. The
Examples of such positive electrode active materials include NaFeO ₂ , NaNiO ₂ , NaCoO ₂ , NaMnO ₂ , NaFe _1-x M ¹ _x O ₂ , and NaNi _1-x M ¹ _x described in JP-A-2009-129741. O ₂ , NaCo _1-x M ¹ _x O ₂ , NaMn _1-x M ¹ _x O ₂ (where M ¹ is one or more elements selected from the group consisting of trivalent metals, and 0 ≦ x <0 .5)) and the like. Among these, a composite oxide mainly containing iron and sodium, and using a composite oxide having a hexagonal crystal structure as a positive electrode active material, a high discharge voltage can be obtained. A secondary battery having a high density can be obtained.

More preferably, the positive electrode active material is a composite oxide mainly containing iron and sodium, has a hexagonal crystal structure, and has an interplanar spacing of 2 in the X-ray diffraction analysis of the composite oxide. A complex oxide having a value obtained by dividing the intensity of a peak of 20 angstroms by the intensity of a peak of 5.36 angstroms in plane spacing is 2 or less. In heating a metal compound mixture containing a sodium compound and an iron compound in a temperature range of 400 ° C. or more and 900 ° C. or less, the atmosphere is heated as an inert atmosphere in a temperature range of less than 100 ° C. during the temperature increase. Is preferred.
Moreover, what doped the transition metal atom of these compounds with the other metal atom may be used. The dopant is not particularly limited as long as the electrochemical characteristics can be changed in the oxidation-reduction reaction.

(Current collector for positive electrode)
The positive electrode current collector is a conductive substrate carrying a positive electrode active material.
The molding material for the current collector of the positive electrode is required to be stable during charging. In particular, when using a phosphate-based and olivine fluoride-based positive electrode active material having an olivine-type crystal structure with a high redox potential, it is preferable to use a material excellent in corrosion resistance.
For example, when LiPF ₆ or LiBF ₄ is used as the electrolyte, austenitic stainless steel, Ni, Al, Ti, or the like can be used, but it is preferable to select them appropriately in consideration of the operating potential of the positive electrode active material to be used. For example, when LiPF ₆ is used as the electrolyte, it can be used even at 6 V with respect to the Li / Li ⁺ electrode. However, when LiBF ₄ is used as the electrolyte, SUS304 is 5.8 V or less with respect to the Li / Li ⁺ electrode. It can be used only when charge / discharge is possible. Further, when LiTFSI is used as the electrolyte, it is preferable that LiPF ₆ coexists in order to form a corrosion-resistant film on the surface of the positive electrode current collector. LiBETI and LiTFS are the same as in LiTFSI.
In addition, a conductive metal material such as Al coated with conductive DLC (diamond-like carbon) by a well-known method can be used as a current collector. When the electrolyte is a lithium salt such as LiBF ₄ or LiPF ₆ that easily forms a fluoride film, a thick fluoride film is formed on the aluminum and the corrosion resistance is improved, but the electronic conductivity is lowered, and consequently The increase in output accompanying the increase in ohmic overvoltage is impeded. If the conductive metal material such as Al is coated with the conductive DLC, the fluoride film is generated only in a very small area of the defective portion of the conductive DLC. For this reason, even if the voltage is increased, the decrease in electron conductivity is negligible, and it is possible to prevent the decrease in output due to the increased voltage, which is a concern.
Here, the conductive diamond-like carbon is carbon having an amorphous structure in which both bonds of diamond bonds (SP ₃ hybrid orbital bonds between carbons) and graphite bonds (SP ₂ hybrid orbital bonds between carbons) are mixed. Among them, the one whose conductivity is 1000 Ωcm or less. However, in addition to the amorphous structure, those having a phase composed of a crystal structure partially composed of a graphite structure (that is, a hexagonal crystal structure composed of SP ₂ hybrid orbital bonds) and thereby exhibiting conductivity are also included. . Diamond-like carbon having properties intermediate between graphite and diamond adjusts the conductivity by adjusting the ratio of SP ₂ hybrid orbital bonds and SP ₃ hybrid orbital bonds of the carbon atoms constituting diamond-like carbon during film formation. be able to.
Of course, you may coat | cover the said corrosion-resistant electroconductive metal material with electroconductive DLC.
The shape and structure of the current collector can be arbitrarily designed according to the structure of the positive electrode active material and the battery.

(Pretreatment of positive electrode)
The positive electrode for a lithium ion battery or the positive electrode for a sodium ion battery is a positive electrode in an electrolyte for pretreatment in which a lithium salt (or sodium salt) is dissolved in an organic solvent containing 1% by volume or more of a nitrile compound before being incorporated into the battery. An immersion treatment step for immersing the electrode is performed, and a positive voltage treatment step for applying a positive voltage to the electrode is further performed. The electrode thus pretreated has a wide potential window even when used in an electrolyte solution containing no nitrile compound or in a lithium ion battery using an electrolyte solution with a small amount of nitrile compound added. It becomes difficult to disassemble (see Japanese Patent Application No. 2009-180007). The reason why the electrode has such a wide potential window is presumed to be that a corrosion-resistant film containing nitrogen as a component is formed on the electrode.

(Negative electrode)
The negative electrode includes a negative electrode active material and a current collector.
(Anode active material for lithium ion battery)
The negative electrode active material for lithium ion batteries refers to “a material in which lithium is inserted / extracted in the crystal structure at a lower potential than that of the positive electrode, and oxidation / reduction is performed accordingly”.
Examples of the negative electrode active material for a lithium ion battery include various carbon materials such as artificial graphite, natural graphite, and hard carbon, lithium titanate (Li ₄ Ti ₅ O ₁₂ ), H ₂ Ti ₁₂ O ₂₅ , and H ₂ Ti _6. Examples thereof include O ₁₃ and Fe ₂ O ₃ . Moreover, the composite material which mixed these suitably can also be mentioned. Furthermore, there may be mentioned Si fine particles and Si thin films, and fine particles and thin films in which these Si are Si-based alloys such as Si—Ni, Si—Cu, Si—Nb, Si—Zn, Si—Sn. Further, SiO oxide, Si-SiO ₂ composite, Si-SiO ₂ - can be given complex, etc., such as carbon.

(Anode active material for sodium ion battery)
The negative electrode active material for a sodium ion battery is a “substance that allows sodium ions to enter and exit as a negative electrode of a secondary battery and reversibly repeat oxidation and reduction”. In the present invention, Li ₄ Ti ₅ O ₁₂ is used.

(Current collector for negative electrode)
The current collector for the negative electrode can be formed of a general-purpose conductive metal material, Cu, Al, Ni, Ti, austenitic stainless steel, or the like.
However, when a nitrile compound is used for the electrolytic solution (including combined use with other organic solvents), it is necessary to select appropriately according to the Li salt in the electrolytic solution. That is, when LiPF ₆ or LiBF ₄ is used as the electrolyte, austenitic stainless steel, Ni, Al, Ti, or the like can be used. However, it is necessary to select appropriately according to the operating potential of the negative electrode active material to be used. In the case of using carbon or Si as the negative electrode active material, when LiBF ₄ is used as the electrolyte, a current collector made of Al, Ni, Ti, austenitic stainless or the like other than Cu can be used. In the case where lithium titanate or a Fe ₂ O ₃ based compound is used as the negative electrode active material, all of the above materials containing Cu are applicable. On the other hand, when LiPF _{6 is} used as the electrolyte, Al, Ni and Ti are preferable, and austenitic stainless steel and Cu are not preferable. In addition, when LiTFSI, LiBETI, or LiTFS is used as the electrolyte, any of Ni, Ti, Al, Cu, and austenitic stainless steel can be used.

(Electroconductive member for positive electrode)
Some positive electrode active materials have low electrical conductivity. Therefore, it is preferable to provide a sufficient electron conduction path between the positive electrode active material and the current collector by interposing a conductive electron conduction member.
Here, the form of the electron conducting member is not particularly limited as long as an electron conducting path can be formed between the positive electrode active material and the current collector. For example, carbon black such as acetylene black, graphite powder, diamond-like carbon, glassy Conductive powder (conductive aid) such as carbon can be used. Diamond-like carbon and glassy carbon have a much wider potential window than carbon black and graphite, and are excellent in corrosion resistance when a high potential is applied, and therefore can be suitably used. Moreover, it is also preferable that metal fine particles are supported on these conductive assistants. Examples of the metal fine particles include Pt, Au, Ni and the like. These may be used alone or an alloy thereof.
As an electron conductive material, a positive electrode active material used in the present invention can be used in combination with a conductive thin film (gold thin film or the like) in which a positive electrode active material is embedded in addition to a conductive film made of diamond-like carbon.

(Electroconductive member for negative electrode)
The thing similar to the electron conductive member for positive electrodes can be used.

(Separator)
The separator is immersed in the electrolytic solution, separates the positive electrode and the negative electrode, prevents a short circuit therebetween, and allows the passage of Li ions.
Examples of such separators include porous films made of polyolefin resins such as polyethylene and polypropylene.

(Case)
The case is formed of a material having corrosion resistance against the electrolytic solution. The shape can be arbitrarily designed according to the intended use of the battery.
When using an electrolytic solution in which a lithium salt is dissolved, a base material made of austenitic stainless steel, a case made of Ti, Ni and / or Al can be used. However, there are cases where it is necessary to select appropriately depending on the operating potential of the positive electrode and negative electrode active material to be used.
When the case also serves as a current collector or is electrically coupled to the current collector, the case is formed of the same or the same material as the current collector forming material of each electrode.

  The present invention is not limited to the description of the embodiment of the invention. Various modifications may be included in the present invention as long as those skilled in the art can easily conceive without departing from the description of the scope of claims.

  The positive electrode for a secondary battery of the present invention can be suitably used as a positive electrode for a secondary battery that can effectively utilize a positive electrode active material having a high energy density in which a charging reaction is performed at a high potential.

2a ... Positive electrode active material 2b ... Conductive diamond-like carbon 2c ... Fluorine resin powder 2 ... Positive electrode for secondary battery 3 ... Negative electrode

Claims (4)

A positive electrode for a secondary battery in which an aggregate of particles made of a positive electrode active material is formed into a predetermined shape ;
And a secondary battery having a charging potential of 5 V (vs Li / Li ⁺ ) or higher,
Conductive diamond-like carbon and / or glassy carbon is attached to the particles made of the positive electrode active material . 2. The secondary battery according to claim 1, wherein the conductive diamond-like carbon and / or glassy carbon is attached to the positive electrode active material by a dry plating method . The secondary battery according to claim 1, wherein the organic electrolyte contains a dinitrile compound.   A positive electrode for a secondary battery, which is a particle made of a positive electrode active material and in which an aggregate of particles to which conductive diamond-like carbon and / or glassy carbon is attached is formed into a predetermined shape, and an organic electrolyte A secondary battery charging method,
  The charging potential applied to the positive electrode for the secondary battery is 5 V (vs Li / Li ⁺ ) A rechargeable battery charging method characterized by the above.

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