JP2011091019A - Collector for positive electrode of secondary battery, collector for negative electrode of secondary battery, positive electrode of secondary battery, negative electrode of secondary battery, and secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a collector exhibiting excellent corrosion resistance and having fewer ohmic loss in a lithium ion battery using electrolyte with cyclic carbonic acid ester such as ethylene carbonate and/or chained carbonic acid ester such as dimethyl carbonate, and further with various nitriles added. <P>SOLUTION: The collector for a positive electrode of a secondary battery is a collector of a positive electrode used for a lithium (or sodium) ion battery having electrolyte solution having lithium salt dissolved in a solvent including cyclic carbonic acid ester and/or chained carbonic acid ester, and nitrile, and is made of at least one kind out of austenite stainless steel, titanium, nickel, and aluminum. The collector for a negative electrode of a secondary battery is a collector for a negative electrode used for a lithium (or sodium) ion battery having electrolyte solution wherein lithium salt (or sodium salt) is dissolved in a solvent including cyclic carbonic acid ester, chained carbonic acid ester, and nitrile, and is made of at least one kind out of titanium, nickel, aluminum, and austenite stainless steel. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention can be suitably used for a lithium ion battery or a sodium ion battery using an electrolytic solution to which a nitrile compound is added, a secondary battery positive electrode current collector, a secondary battery negative electrode current collector, a secondary battery The present invention relates to a positive electrode for a battery, a negative electrode for a secondary battery, and a secondary battery.

  Conventionally, in a lithium ion battery, aluminum is used as a current collector material in contact with the positive electrode active material, and copper is used as a current collector material in contact with the negative electrode active material. Then, charging and discharging are performed through these current collectors. Since the current collector is placed in a harsh corrosive environment, it is required to have corrosion resistance, and it is required not to alter the electrolyte or electrolyte.

JP 2004-235091 A

We, _Li 2 NiPO ₄ F which has been proposed as a positive electrode active material for high energy density lithium-ion _battery, for LiNiPO 4, LiCoPO ₄ and _Li 2 CoPO ₄ F, withstand high potential during charging electrolyte An application has already been filed for the liquid (Japanese Patent Application No. 2008-322910). These electrolytes are electrolyses obtained by adding various nitriles to a mixed solvent of a cyclic carbonate such as ethylene carbonate and a chain carbonate such as dimethyl carbonate, which has been conventionally used as a solvent for an electrolyte for a lithium battery. It is a liquid and has a feature that the electrolytic solution is hardly decomposed even at a high potential during charging.
Also, a positive electrode active material having a high energy density has been found for sodium ion batteries. For example, NaFeO ₂ , NaNiO ₂ , NaCoO ₂ , NaMnO ₂ , NaFe _1-x M ¹ _x O ₂ , NaNi _1-x M ¹ _x O ₂ , NaCo _{1-x described in} JP2009-129741A. 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. In such a secondary battery using a positive electrode active material for a sodium ion battery having a high energy density, an application has already been filed for an electrolyte for a sodium ion battery that can withstand a high potential during charging (Japanese Patent Application No. 2009-285997). . This electrolyte is also an electrolyte obtained by adding various nitriles to a mixed solvent of a cyclic carbonate such as ethylene carbonate and a chain carbonate such as dimethyl carbonate, and the electrolyte is decomposed even at a high potential during charging. It is difficult.

  However, conventional electrolyte materials for lithium ion batteries and sodium ion batteries that can withstand these high potentials may not be used, and current collectors that are suitable for these electrolytes There was no problem.

For example, _Li 2 NiPO ₄ F as a cathode active material of a lithium ion _{battery, LiNiPO 4, LiCoPO 4, Li} 2 CoPO 4 when the positive electrode active material F such as used in the above electrolytic solution, a large polarization voltage to the electrodes during charging Will be applied. For this reason, when the electrolyte is a salt that is difficult to form a corrosion-resistant film made of fluoride, such as LiTFSI or LiBETI, when a current collector made of aluminum is used, there is a problem that the aluminum is corroded.

In addition, when the electrolyte is a salt that easily forms a corrosion-resistant film made of fluoride, such as LiBF ₄ or LiPF ₆ , aluminum exposed to a high potential increases the thickness of the corrosion-resistant film and increases the electric resistance. Becomes larger. For this reason, there has been a problem that the passivation proceeds from the contact area between the current collector forming the electron path and the conductive additive, the ohmic overvoltage is increased, and high output is hindered.

  Furthermore, it was not understood what kind of current collecting material for the negative electrode was appropriate for the electrolytic solution to which the above various nitriles were added.

  The above has described the problems related to the current collector for lithium ion batteries, but similar problems existed for sodium ion batteries.

  The present invention has been made in view of the above-described conventional situation, and an electrolytic solution in which various nitriles were further added to a mixed solvent of a cyclic carbonate such as ethylene carbonate and a chain carbonate such as dimethyl carbonate was used. An object to be solved is to provide a current collector having excellent corrosion resistance and low ohmic loss in a lithium ion battery.

As described above, the inventors, _Li 2 NiPO ₄ F which has been proposed as a positive electrode active material for high energy density lithium-ion _battery, for LiNiPO 4, LiCoPO ₄ and _Li 2 CoPO ₄ F, a high potential during charging An application has already been filed for an electrolyte solution that can withstand (Japanese Patent Application No. 2008-322910). In addition, an application has already been filed for an electrolyte solution that can withstand a high potential during charging for a positive electrode active material for a sodium ion battery having a high energy density (Japanese Patent Application No. 2009-285997). These electrolytic solutions are mixed with a mixed solvent of a cyclic carbonate such as ethylene carbonate and a chain carbonate such as dimethyl carbonate, which has been used as a solvent for an electrolyte for a lithium (or sodium) ion battery. It is an electrolytic solution to which nitrile is added.

Such a lithium (sodium) ion battery using a positive electrode active material having a high energy density, such as Li ₂ NiPO ₄ F, using an electrolytic solution to which various nitriles capable of widening the potential window is used. ) The charging voltage is higher than that of the ion battery. For this reason, the current collector made of aluminum may be corroded, the thickness of the corrosion-resistant film may increase, and the electrical resistance may increase. For this reason, the present inventors have conducted intensive research on a positive electrode current collecting material that can withstand a high potential region and can form a corrosion-resistant film having a low electric resistance. As a result, in an electrolytic solution in which nitrile is added to a mixed solvent of a cyclic carbonate and a chain carbonate, the austenitic stainless steel, titanium, and nickel are found to have excellent corrosion resistance as a current collecting base material constituting the current collector. The present invention has been completed.

  That is, the current collector for the positive electrode of the secondary battery of the present invention is lithium (or sodium) provided with an electrolytic solution in which a lithium salt is dissolved in a solvent containing a cyclic carbonate and / or a chain carbonate and a nitrile. A current collector for a positive electrode used for an ion battery, comprising at least one of austenitic stainless steel, titanium, nickel and aluminum.

  The current collector for a secondary battery positive electrode of the present invention comprises at least one of austenitic stainless steel, titanium, nickel and aluminum. Here, “titanium, nickel, and aluminum” means that the current collector base material is made of pure titanium, pure nickel, and pure aluminum, as well as cyclic carbonates and / or chains even if other components are included. In the mixed solvent containing the carbonic acid ester and the nitrile, it is meant to include a current collector base material on which a corrosion-resistant film is formed during charging.

When the current collector for the positive electrode of the secondary battery of the present invention is composed of titanium and / or nickel, the positive voltage repeats in the cyclic voltammographic measurement when the potential sweep is repeated in the electrolyte for the lithium (or sodium) ion battery. Since the current becomes smaller at the potential in the direction, it is considered that a corrosion-resistant film is formed, so that excellent corrosion resistance is exhibited and the potential window is widened.
Moreover, also when the collector for secondary battery positive electrodes consists of austenitic stainless steel, the outstanding corrosion resistance is shown. Particularly preferred is austenitic stainless steel to which molybdenum is added. Examples of the austenitic stainless steel containing molybdenum include SUS316, SUS316L, and SUS317.

On the other hand, a current collector made of aluminum such as LiBF ₄ or LiPF ₆ can be used with a conventionally used aluminum even in the case of a salt that easily forms a corrosion-resistant film made of fluoride. .

  As described above, the current collector for the positive electrode of the secondary battery according to the present invention is extremely excellent in corrosion resistance and electronic conductivity, and has a wide potential window, so that the lithium ion battery or sodium ion battery having a high charging voltage is used. It can be suitably used as a current collector.

The current collector for a positive electrode of a lithium ion battery according to the present invention is exposed to a high potential region during charging in an electrolyte solution of a lithium ion battery, whereby a fluorine compound, an oxygen compound, a nitrogen compound, a carbon compound, a phosphorus compound, and a boron compound. A passive film consisting of is formed. For this reason, the current collector is extremely excellent in corrosion resistance. The lithium ion battery positive electrode current collector of the present invention is 4.5 V (VSLi / Li ⁺ ) or more (preferably 5 V) in the lithium ion battery electrolyte or sodium ion battery electrolyte before being incorporated in the battery. It is preferable to perform a pretreatment at a high potential of (VSLi / Li ⁺ ) or higher, more preferably 6 V (VSLi / Li ⁺ ) or higher). In this case, a passive film made of a fluorine compound, an oxygen compound, a nitrogen compound, a carbon compound, a phosphorus compound and a boron compound is already formed when the battery is incorporated into the battery, so that current collection with excellent corrosion resistance is provided from the beginning. Become a body.

On the other hand, the current collector for the negative electrode of the secondary battery of the present invention is required to be a current collector that is stable at a low potential where the negative electrode active material is charged and discharged and that does not decompose or alter the electrolyte. There is. For the current collector material that can be used in a lithium ion battery including an electrolytic solution in which a lithium salt is dissolved in a solvent containing a cyclic carbonate and / or a chain carbonate and a nitrile, As a result of extensive research, titanium, nickel, aluminum, and austenitic stainless steel are suitable, and copper that has been used as a current collector for negative electrodes can be used depending on the combination of electrolyte, electrolyte, and negative electrode active material. is there. For example, when LiPF ₆ is used as the electrolyte and lithium titanate or Fe ₂ O ₃ based material is used as the negative electrode active material, it can be used.

That is, the current collector for a secondary battery negative electrode of the present invention is a lithium (or sodium) ion battery including an electrolytic solution in which a lithium salt is dissolved in a solvent containing a cyclic carbonate, a chain carbonate, and a nitrile. A negative electrode current collector to be used, comprising at least one of titanium, nickel, aluminum, copper, and austenitic stainless steel.
The lithium ion battery negative electrode current collector is also exposed to a high potential region to form a passive film composed of a fluorine compound, an oxygen compound, a nitrogen compound, a carbon compound, a phosphorus compound, and a boron compound. For this reason, the current collector is extremely excellent in corrosion resistance. Incidentally, the current collector of the present invention is a lithium-ion battery electrolyte solution and a sodium ion battery electrolyte solution 4.5V (VSLi / Li ⁺⁾ or more before it is incorporated into the cell (preferably 5V (VSLi / Li ⁺ ) Or more, and more preferably, pre-treatment for setting a high potential of 6 V (VSLi / Li ⁺ ) or more) is performed. In this case, a passive film made of a fluorine compound, an oxygen compound, a nitrogen compound, a carbon compound, a phosphorus compound and a boron compound is already formed when the battery is incorporated into the battery, so that current collection with excellent corrosion resistance is provided from the beginning. Become a body.

By supporting the positive electrode (negative electrode) active material on the current collector for the secondary battery positive electrode (negative electrode) of the present invention, the positive electrode (negative electrode) for the secondary battery of the present invention is obtained.
In addition, the secondary battery of the present invention includes the positive electrode (negative electrode) for the secondary battery of the present invention.
When the current collector for the positive electrode of the secondary battery of the present invention is made of at least one of nickel, aluminum, and titanium, the electrolyte contains LiTFSI and / or LiBETI in addition to LiPF ₆ and / or LiBF _4. It is preferable. This is because LiTFSI and LiBETI alone are unlikely to form a corrosion-resistant film on nickel, aluminum, and titanium, but an excellent corrosion-resistant film is formed by coexisting with LiPF ₆ and / or LiBF ₄ . In addition, LiTFSI (lithium bis (trifluoromethanesulfonyl) imide) has an effect that the decomposition temperature is particularly high and the heat resistance is improved, the solubility is high, and the specific conductivity can be increased.

2 is a cyclic voltammogram of a titanium electrode measured in Experimental Example 1. FIG. 4 is a cyclic voltammogram of a nickel electrode measured in Experimental Example 2. FIG. 5 is a cyclic voltammogram of an aluminum electrode measured in Experimental Example 3. FIG. It is an electric potential current curve of various metals in example 4 of an experiment. It is an electric potential current curve of various metals in example 5 of an experiment. It is the electric potential current curve of the nickel in Experimental example 6. It is an electric potential current curve of aluminum in example 7 of an experiment. It is the electric potential current curve of titanium in Experimental Example 8. It is a graph which shows the surface presence rate of each element calculated | required from the XPS measurement (wide scan) result about the electrical power collector of Test Examples 1-5. It is a graph which shows the surface presence rate of the nitrogen calculated | required from the XPS measurement (nitrogen narrow scan) result of the electrical power collector of Test Examples 1-5, and the ratio of the bonding state of those elements. It is a graph which shows the surface presence rate of the phosphorus calculated | required from the XPS measurement (phosphorus narrow scan) result, and the ratio of the bonding state of those elements about the electrical power collector of Test Examples 1-5. It is a graph which shows the surface presence rate of the fluorine calculated | required from the XPS measurement (fluorine narrow scan) result, and the ratio of the bonding state of those elements about the electrical power collector of Test Examples 1-5. It is the electric potential current curve of titanium in Experimental Example 9. It is the electric potential current curve of the nickel in Experimental example 10. It is the electric potential current curve of the aluminum in Experimental example 11. It is a potential current curve of SUS316L in Experimental Example 12. It is a cross-sectional schematic diagram of the lithium ion battery of an embodiment.

<Experimental example>
An experimental example which proves the effect of the current collector of the present invention will be described below.
(Experimental example 1)
In Experimental Example 1, an electrode made of pure titanium was subjected to potential scanning in an electrolyte for a lithium ion battery, and a cyclic voltammogram was measured. The solvent of the electrolytic solution is ethylene carbonate: dimethyl carbonate: sevacononitrile = 25: 25: 50 (volume ratio) or ethylene carbonate: dimethyl carbonate = 50: 50 (volume ratio), and LiPF ₆ is 1 mol / L. The so-dissolved solution was used as an electrolytic solution and placed in a three-electrode electrolytic cell container.

  The cyclic voltammogram was measured using a titanium electrode as a working electrode, a platinum net as a counter electrode, and Li metal as a reference electrode. The measurement was performed by scanning the reference electrode three times between 3V and 8V, and measuring the potential-current curve. The sweep speed was 5 mV / sec.

As a result, as shown in FIG. 1, in any electrolyte solution, the potential sweep after the second cycle has a smaller current than the first cycle, so a film is formed on the titanium electrode by the potential sweep. Is done. In fact, as will be described later, the formation of a film was confirmed from the surface analysis by XPS.
Further, in the electrolyte solution of ethylene carbonate: dimethyl carbonate: sebacononitrile = 25: 25: 50 (volume ratio), the potential window becomes wider than the electrolyte solution of ethylene carbonate: dimethyl carbonate = 50: 50 (volume ratio), It was found that the current at the second cycle was extremely small and the potential window was greatly expanded.

(Experimental example 2)
In Experimental Example 2, an electrode made of pure nickel was subjected to potential scanning in an electrolyte for a lithium ion battery, and a cyclic voltammogram was measured. The measurement conditions are the same as in Experimental Example 1, and detailed description thereof is omitted.

  As a result, as shown in FIG. 2, in any electrolyte solution, the potential sweep after the second cycle has a smaller current than the first cycle, and a film is formed on the nickel electrode by the potential sweep. It has been suggested. In addition, the electrolyte window of ethylene carbonate: dimethyl carbonate: sebaconitrile = 25: 25: 50 (volume ratio) is found to have a wider potential window than the electrolyte solution of ethylene carbonate: dimethyl carbonate = 50: 50 (volume ratio). It was.

(Experimental example 3)
In Experimental Example 3, an electrode made of pure aluminum was subjected to potential scanning in an electrolyte for a lithium ion battery, and a cyclic voltammogram was measured. The measurement conditions are the same as in Experimental Example 1, and detailed description thereof is omitted.

  As a result, as shown in FIG. 3, in any electrolyte solution, the potential sweep after the second cycle has a smaller current than the first cycle, and a film is formed on the aluminum electrode by the potential sweep. It has been suggested. In addition, in the electrolyte of ethylene carbonate: dimethyl carbonate: sebacononitrile = 25: 25: 50 (volume ratio), the current is much smaller than the electrolyte of ethylene carbonate: dimethyl carbonate = 50: 50 (volume ratio), It was found that the potential window widened. As a result, aluminum that can be used in conventional electrolytes can also be used without problems. However, it is considered that the ohmic loss is large due to the formation of an insulating film.

  Based on the above results, titanium or nickel is configured as a current collector for a positive electrode used in a lithium ion battery including an electrolytic solution in which a lithium salt is dissolved in a solvent containing a cyclic carbonate, a chain carbonate, and a nitrile. It was found that if a positive electrode current collector made of a current collector base material as a component was used, excellent corrosion resistance was exhibited, ohmic loss was small, and low output due to an increase in ohmic overvoltage could be prevented.

(Experimental example 4)
In Experimental Example 4, SUS304, SUS316, SUS316L, pure nickel, pure titanium, and pure aluminum were subjected to a potential sweep to the positive potential side, and a potential-current curve was measured. Further, potential sweeping was performed on SUS304, SUS316, SUS316L, pure nickel, pure titanium, pure aluminum, and pure copper to the negative potential side, and a potential-current curve was measured.
The solvent of the electrolytic solution is ethylene carbonate: dimethyl carbonate: sebaconitrile = 25: 25: 50 (volume ratio), and a solution obtained by dissolving LiBF ₄ so as to be 1 mol / L is used as the electrolytic solution. Put in.

  In measuring the potential-current curve, the above-mentioned various electrodes were used as the working electrode, a platinum net as the counter electrode, and Li metal as the reference electrode. The sweep speed was 5 mV / sec.

As a result, as shown in FIG. 4, in the potential sweep to the high potential side, the potential at which the oxidation current exceeds 50 μA / cm ² (electrode area is 0.5 cm ² ) is SUS304 <SUS316 <nickel <SUS316 <aluminum. <Titanium in order, and in titanium, the oxidation current was about 5 μA / cm ² even at the upper limit of the measurement range of 8.6 V (v..s. Li / Li ⁺ ).
The oxidation current on the high potential side indicates the oxidation of the electrode and the electrolytic solution. Therefore, from the above results, when the electrolyte solution is ethylene carbonate: dimethyl carbonate: sebaconitrile = 25: 25: 50 (volume ratio) and LiBF ₄ is dissolved to 1 mol / L, the positive electrode Titanium, aluminum, SUS304, SUS316L, nickel and SUS316 can be applied as the material of the current collector for use (SUS304 can also be used depending on the potential of the positive electrode active material), preferably titanium, aluminum, SUS316L and nickel. Further preferred were titanium, aluminum and SUS316L.

On the other hand, in the potential sweep to the low potential side, the potential at which the reduction current exceeds −50 μA / cm ² (electrode area is 0.5 cm ² ) is 1.7V for Cu and Li for Li / Li ⁺ . 0.8V, SUS316 was 0.2V, SUS304 was 0.15V, and SUS316L was 0.15V, and nickel and titanium were not exceeded.
The reduction current on the low potential side is considered to indicate the reduction of the electrolytic solution, and the smaller the reduction current, the less the alteration of the electrolytic solution. Therefore, from the above results, when the electrolyte solution is ethylene carbonate: dimethyl carbonate: sebaconitrile = 25: 25: 50 (volume ratio) and LiBF ₄ is dissolved to 1 mol / L, the negative electrode It was found that nickel, titanium, SUS316L, SUS304, SUS316, and aluminum are preferable as a material for the current collector, and nickel, titanium, and SUS316L are particularly preferable. It has been found that Cu, which has been conventionally used as a negative electrode current collector, is not preferable, and aluminum is not so preferable.

(Experimental example 5)
In Experimental Example 5, LiPF ₆ was used as an electrolyte, and this was dissolved so as to be 1 mol / L. Otherwise, the potential-current curve was measured in the same manner as in Experimental Example 4.

As a result, as shown in FIG. 5, in the potential sweep to the high potential side, the oxidation current of any metal exceeds 50 μA / cm ^{2 up} to 7.5 V (v..s. Li / Li ⁺ ). However, it was found that any of SUS304, SUS316, SUS316L, pure nickel, pure titanium, and pure aluminum can be sufficiently used as the positive electrode current collector.

On the other hand, in the potential sweep to the low potential side, the potential where the reduction current exceeds −50 μA / cm ² is 1.2V for Cu, 1.1V for SUS316, and 0.1V for SUS316L with respect to Li / Li ⁺ . Al was 0.2V, SUS304 was 0.1V, and nickel and titanium were not exceeded.
The reduction current on the low potential side is considered to indicate the reduction of the electrolytic solution, and the smaller the reduction current, the less the alteration of the electrolytic solution. Therefore, from the above results, when the electrolyte solution is ethylene carbonate: dimethyl carbonate: sebaconitrile = 25: 25: 50 (volume ratio) and further LiPF ₆ is dissolved to 1 mol / L, the negative electrode It has been found that nickel, titanium, aluminum and SUS304 are preferable as the current collector material, and nickel and titanium are particularly preferable.
However, the operating potential of the negative electrode active material varies depending on the type. When a lithium titanate or Fe ₂ O ₃ negative electrode active material is used, the oxidation-reduction potential is about 1.5 V, It becomes higher than the deposition potential. For this reason, in a lithium ion battery using a negative electrode active material having such a high oxidation-reduction potential, copper, SUS316, or SUS316L can be used as a material for the current collector for the negative electrode.

(Experimental example 6)
In Experimental Example 6, an electrolytic solution containing LiTFSI and LiPF _{6 in} a ratio of 1: 0 to 1: 1 as a lithium salt was used. That is, ethylene carbonate, dimethyl carbonate and sebaconitrile are mixed so that the mass ratio is 25:25:50, and a solution in which LiTFSI (1 mol / L) and LiPF ₆ (0 to 1 mol / L) are dissolved is mixed here. It was made into electrolyte solution and put into the tripolar electrolytic cell container. And the potential sweep to the positive electric potential side was performed about the nickel plate, and the electric potential current curve was measured. The measurement conditions were the same as in Experimental Examples 1-5.

(Experimental example 7)
In Experimental Example 7, the same electrolytic solution as in Experimental Example 6 was used, and potential sweeping of aluminum to the positive potential side was performed to measure a potential-current curve. The measurement conditions were the same as in Experimental Examples 1-5.

(Experimental example 8)
In Experimental Example 8, an electrolytic solution containing LiTFSI and LiPF ₆ at a ratio of 1: 0 to 1: 0.5 was used. That is, ethylene carbonate, dimethyl carbonate, and sebaconitrile were mixed at a mass ratio of 25:25:50, and LiTFSI (1 mol / L) and LiPF ₆ (0 to 0.5 mol / L) were dissolved therein. Using an electrolytic solution as the solution, potential sweeping of titanium toward the positive potential side was performed, and a potential-current curve was measured. The measurement conditions were the same as in Experimental Examples 1-5.

<Result>
In Experimental Example 6 using a nickel plate, as shown in FIG. 6, when the lithium salt is LITFSI alone, and the concentration of LITFSI is 1 mol / L, LiPF ₆ is 0.1 mol / L, which is 1/10 of that. When the amount is small, the potential window is not so wide. However, when LiPF ₆ is added at 0.5 mol / L or more, the potential window is large and spreads in the noble direction, and a passive film having excellent corrosion resistance is formed. I found out.
Also in Experimental Example 7 using an aluminum plate, as shown in FIG. 7, it was found that the potential window widens dramatically by making LiTFSI coexist with LiPF ₆ . Similarly, in Experimental Example 8 using a titanium plate, as shown in FIG. 8, it was found that LiTFSI coexists with LiPF ₆ so that the potential window is dramatically expanded.

From the measurement results of the potential current curves of Experimental Example 6, Experimental Example 7, and Experimental Example 8 above, it was found that the potential window was dramatically expanded by coexisting LiTFSI with LiPF ₆ in nickel, aluminum, and titanium. . Since LiBETI has the same chemical structure as LITFSI and LiBF ₄ has the same chemical structure as LiPF ₆ , LiBETI may be used instead of LiBETI, or LiBF ₄ may be used instead of LiPF _6. However, it is natural that a similar corrosion-resistant film can be formed.

(Measurement of XPS)
Test example 1 to test example 4
In Test Examples 1 to 4, a surface analysis by XPS was performed in order to confirm the surface film formation when a positive potential was applied to the current collector in the electrolyte.
That is, a solvent obtained by mixing sebacononitrile, ethylene carbonate (EC), and dimethyl carbonate (DMC) at a volume ratio of 50:25:25 as an organic solvent, and LiPF ₆ (hexafluoride) as a lithium salt. An electrolytic solution in which lithium phosphate) is dissolved to 1 mol / L is prepared. Then, this electrolytic solution is put into a glass cell for electrochemical measurement, and various current collector materials (nickel in Test Example 1, titanium in Test Example 2, aluminum in Test Example 3, and glassy carbon in Test Example 4) are used as electrodes. Immersion was performed, and a potential operation (scanning speed: 5 mV / sec) was performed from a natural potential to 7 V using a platinum wire as a counter electrode and Li / Li ⁺ as a reference electrode. Thereafter, the current collector material was pulled up, washed with DMC, and measured by XPS.

XPS is a measurement method in which information on the type, valence, and bonding state of elements existing on the surface is obtained by irradiating the surface of the sample with soft X-rays and measuring the energy of photoelectrons emitted from the surface. Since the mean free path of photoelectrons is several nm, the detection region in the depth direction of the surface analysis by XPS is several nm, so that analysis on the extreme surface can be performed. The measurement conditions are as follows.
Measuring device: Quantera SXI (PHI)
Excitation X-ray: monochromatic AlKα _1,2 line
X-ray diameter: 200 μm
Photoelectron escape angle: 45 ° (inclination of detector with respect to sample surface)
Pretreatment method: Sampling and transport of the sample to the apparatus were performed in an argon atmosphere.
Data processing: Smoothing was performed by 9-point smoothing, and horizontal axis correction was performed with the C1 _S main peak at 284.6 eV.

Test example 5
In Test Example 5, an electrolyte solution in which LiBF ₄ (lithium tetrafluoride) was dissolved as a lithium salt to a concentration of 1 mol / L was used, the electrode was glassy carbon, and the others were XPS in the same manner as in Test Examples 1 to 4. Measurements were made.

<Result>
-About the presence rate of the element which exists in the surface Table 1 and the presence rate of the element which exists on the collector surface calculated | required from the result of the XPS wide scan are shown in FIG. From Table 1 and FIG. 9, it was found that in Test Examples 1 to 4, a large amount of nitrogen, phosphorus and fluorine were present, and other oxygen and carbon were also present. Nitrogen is attributed to the nitrile contained in the electrolytic solution, and phosphorus is attributed to LiPF ₆ added as the electrolyte. That is, it was found that nitrile and LiPF ₆ cause an electrode reaction at a high potential, and a corrosion-resistant passive film composed of a fluorine compound, an oxygen compound, a nitrogen compound, a carbon compound, and a phosphorus compound is formed on the electrode surface.
Further, in Test Example 5 in which LiBF ₄ was added as an electrolyte, boron attributed to LiBF ₄ was detected, and it was found that a corrosion-resistant passive film made of a boron compound was formed on the electrode surface.

  Further, in Test Example 1, nickel as a base material of the current collector was hardly detected, whereas in Examples 2 and 3, Ti and Al as base materials were considerably detected. From this, it was suggested that a particularly dense corrosion-resistant film is formed on the nickel-based current collector.

-Nitrogen surface abundance ratio and bonding state The nitrogen surface abundance ratio and bonding state ratio were determined from a wide scan and a nitrogen narrow scan. The results are shown in FIG. As can be seen from this figure, the presence of nitrogen was large on the electrode surfaces of Test Examples 1 to 5, and the bonding state was CN triple bond or CN single bond and ammonium salt, -NO. In Test Example 3 using a Ti substrate, nitrides were also confirmed on Ti.

-Phosphorus surface abundance ratio and binding state Phosphorus surface abundance ratio and binding state ratio were determined from wide scan and phosphorous narrow scan. The results are shown in FIG. As can be seen from this figure, the phosphorus existing on the electrode surfaces of Test Examples 1 to 5 was attributed to the phosphorus compound related to the PF bond (B-F bond in Test Example 5).

-Fluorine surface abundance ratio and bonding state Fluorine surface abundance ratio and bonding state ratio were determined from wide scan and fluorine narrow scan. The results are shown in FIG. As can be seen from this figure, the fluorine present on the electrode surfaces of Test Examples 1 to 5 was mostly fluorine attributed to C—F bonds or PF bonds (B—F bonds in Test Example 5).

From the result of the surface analysis by XPS as described above, it was found that the surface film formed on the current collectors of Test Examples 1 to 4 had the following properties.
(1) A film containing nitrogen and fluorine as components is formed on the electrode surface.
(2) A large amount of nitrogen is present on the electrode surface, and the bonding state of nitrogen is a CN triple bond, a CN single bond, an ammonium salt, or -NO. Further, when titanium is used as the substrate, nitrides are also present.
(3) When LiPF ₆ is used as the electrolyte, a phosphorus compound related to the PF bond is detected in the film.
(4) Fluorine is mostly fluorine attributed to C—F bonds or PF bonds.
(5) When LiBF ₄ is used as the electrolyte, a boron compound is detected in the film.

(Experimental example 9)
In Experimental Example 9, an electrode made of pure titanium was subjected to potential scanning in an electrolyte for sodium ion batteries, and a cyclic voltammogram was measured. The solvent of the electrolytic solution was ethylene carbonate: dimethyl carbonate: sebaconitrile = 25: 25: 50 (volume ratio), and a solution in which NaPF ₆ was dissolved to a concentration of 0.5 mol / L was used as the electrolytic solution. Placed in cell container.

  The cyclic voltammogram was measured using a titanium electrode as a working electrode, a platinum net as a counter electrode, and Li metal as a reference electrode. The measurement was performed by scanning in the positive and negative directions with respect to the reference electrode, and the potential-current curve was measured. The sweep speed was 5 mV / sec.

(Experimental example 10)
In Experimental Example 10, a pure nickel plate was used as the electrode. Others are the same as those of Experimental Example 9, and detailed description thereof is omitted.

(Experimental example 11)
In Experimental Example 11, a pure aluminum plate was used as the electrode. Others are the same as those of Experimental Example 9, and detailed description thereof is omitted.

(Experimental example 12)
In Experimental Example 12, a plate made of SUS316L was used as the electrode. Others are the same as those of Experimental Example 9, and detailed description thereof is omitted.

<Result>
As a result, in Experimental Example 9 using titanium, a large current flowed at a potential higher than 5 V (v..s. Li / Li ⁺ ) in the first cycle as shown in FIG. After that, almost no current flowed.
In Experimental Example 10 using nickel, as shown in FIG. 14, a large current flowed at a potential higher than 4.5 V (v..s. Li / Li ⁺ ) in the first cycle. After the cycle, 7V (v..s. Li / Li ⁺ ) almost no current flowed.
Furthermore, also in Experimental Example 11 using aluminum and Experimental Example 12 using SUS316L, as shown in FIGS. 15 and 16, in the potential sweep after the second cycle, the current was smaller than in the first cycle. .
From the above results, when a current collector made of titanium, nickel, aluminum, or SUS316L is used for a sodium ion battery, a passive film having excellent corrosion resistance is formed by being charged to a high potential. I understood.

<Production of lithium ion battery>
Using the current collector of the present invention, the lithium ion battery of the present invention can be produced as follows.
First, a positive electrode active material powder is prepared, and a conductive auxiliary agent such as carbon and a fluororesin powder such as polytetraethylene (PTFE) and polyvinylidene fluoride (PVdF) as a binder are added to the hot press. To form a desired shape to obtain positive electrode material pellets. 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.

Also, a negative electrode active material powder is prepared, and in the same manner as the production of the positive electrode, a conductive auxiliary agent such as carbon and a fluororesin powder such as polytetraethylene (PTFE) or polyvinylidene fluoride (PVdF) as a binder. And is molded into a desired shape by hot pressing to obtain negative electrode material pellets. Examples of the negative electrode active material 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 , H ₂ Ti ₆ O ₁₃ , Fe ₂ O ₃ etc. are mentioned. Moreover, the composite material which mixed these suitably can also be mentioned. Further, there are 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, and the like. Further, SiO oxide, Si-SiO ₂ composite, Si-SiO ₂ - can be given complex, etc., such as carbon.

  As shown in FIG. 17, a separator 1 into which an electrolytic solution can permeate is sandwiched between a positive electrode material pellet 2 and a negative electrode material pellet 3 and accommodated in a polypropylene-coated laminate bag 5 containing an electrolytic solution 4. Further, the negative electrode current collector 6 and the positive electrode current collector 7 are disposed from both sides and sealed. Thus, the lithium ion battery 8 of the embodiment can be manufactured.

The material of the negative electrode current collector 6 and the material of the positive electrode current collector 7 are appropriately selected according to the composition of the electrolytic solution and the positive electrode active material. For example, when LiBF ₄ is used for the lithium salt, titanium, aluminum, SUS304, SUS316L, nickel, and SUS316 are applicable as the material for the positive electrode current collector, and titanium, aluminum, SUS316L, and nickel are preferable. More preferred are titanium, aluminum and SUS316L.
Moreover, as a material of the collector for negative electrodes, nickel, titanium, SUS316L, SUS304, SUS316, and aluminum can be used, and nickel, titanium, and SUS316L are particularly preferable.

On the other hand, when LiPF ₆ is used for the lithium salt, any of SUS304, SUS316, SUS316L, pure nickel, pure titanium, and pure aluminum can be used as the positive electrode current collector. Is possible.
Moreover, nickel, titanium, aluminum, and SUS304 can be used as a material for the negative electrode current collector, and nickel and titanium are particularly preferable. However, SUS316, 316L, and Cu can also be used depending on the potential of the negative electrode active material.
When the current collector for the positive electrode of the lithium ion battery is made of nickel and / or aluminum and / or titanium, the electrolyte contains LiTFSI and / or LiBETI in addition to LiPF ₆ and / or LiBF _4. Preferably it is. This is because LiTFSI and LiBETI alone are unlikely to form a corrosion-resistant film on nickel or aluminum, but an excellent corrosion-resistant film is formed by coexisting with LiPF ₆ and / or LiBF ₄ . In addition, LiTFSI (lithium bis (trifluoromethanesulfonyl) imide) has an effect that the decomposition temperature is particularly high and the heat resistance is improved, the solubility is high, and the specific conductivity can be increased.

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 the cyanoacetate 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%.

  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, diethyl carbonate and ethyl methyl carbonate can be used in addition to dimethyl carbonate.
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 the cyanoacetate 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 solid solutions thereof (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 (v..s. 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 (v..s. 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 (v..s. Li / Li ⁺ ), and an electrolytic solution having a withstand voltage of 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 a positive electrode active material 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} JP2009-129741A. 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 composite 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.

(Pretreatment of positive electrode)
Before the lithium ion battery positive electrode or sodium ion battery positive electrode is incorporated in the battery, the positive electrode is immersed in a pretreatment electrolyte in which a lithium salt or sodium salt is dissolved in an organic solvent containing 1% by volume or more of a nitrile compound. An immersion treatment step 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.
(Negative electrode active material)
The negative electrode active material refers to “a material in which lithium is inserted / extracted in the crystal structure at a lower potential than the positive electrode, and oxidation / reduction is performed accordingly”.
Examples of the negative electrode active material 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 , H ₂ Ti ₆ O ₁₃ , Fe ₂ O ₃ etc. are mentioned. Moreover, the composite material which mixed these suitably can also be mentioned. Further, there are 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, and the like. Further, SiO oxide, Si-SiO ₂ composite, Si-SiO ₂ - can be given complex, etc., such as carbon.

(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 the electron conductive material, a conductive film (such as a DLC film) covering the positive electrode active material or a conductive thin film (such as a gold thin film) in which the positive electrode active material is embedded can be used.
In particular, since the Li ₂ NiPO ₄ F-based positive electrode active material has low conductivity of its own and / or its surface coating, it does not function as a positive electrode of a lithium ion battery if it is simply supported on a current collector. There is a case. In order to evaluate the performance of the Li ₂ NiPO ₄ F-based positive electrode active material, it can be physically driven into a conductive thin film such as gold with a hammer or the like to form the positive electrode of the battery.
Here, the Li ₂ NiPO ₄ F-based positive electrode active material refers to Li ₂ NiPO ₄ F and a material appropriately doped with dopant.

(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.

DESCRIPTION OF SYMBOLS 1 ... Separator 2 ... Positive electrode material pellet 3 ... Negative electrode material pellet 4 ... Electrolyte 6 ... Current collector for negative electrodes 7 ... Current collector for positive electrodes 8 ... Lithium ion battery

Claims (11)

  A current collector for a positive electrode used in a lithium (or sodium) ion battery comprising an electrolytic solution in which a lithium salt is dissolved in a solvent containing a cyclic carbonate and / or a chain carbonate and a nitrile. A current collector for a secondary battery positive electrode comprising at least one of stainless steel, titanium, nickel, and aluminum.   The current collector for a secondary battery positive electrode according to claim 1, wherein the austenitic stainless steel is either SUS316 or SUS316L.   The surface according to claim 1 or 2, wherein the surface is covered with a passive film composed of one or more of fluorine compounds, oxygen compounds, nitrogen compounds, carbon compounds, phosphorus compounds and boron compounds. Current collector for secondary battery positive electrode.   A current collector for a negative electrode used in a lithium (or sodium) ion battery comprising an electrolytic solution in which a lithium salt is dissolved in a solvent containing a cyclic carbonate and / or a chain carbonate and a nitrile. A current collector for a secondary battery negative electrode comprising at least one of nickel, aluminum, copper, and austenitic stainless steel.   The current collector for a secondary battery negative electrode according to claim 4, wherein the austenitic stainless steel is any one of SUS304, SUS316, and SUS316L.   The surface according to claim 4 or 5, wherein the surface is covered with a passive film composed of one or more of fluorine compounds, oxygen compounds, nitrogen compounds, carbon compounds, phosphorus compounds and boron compounds. Current collector for secondary battery negative electrode.   A positive electrode for a secondary battery, wherein a positive electrode active material is supported on the positive electrode current collector according to any one of claims 1 to 3.   A negative electrode for a secondary battery, wherein a negative electrode active material is supported on the negative electrode current collector according to any one of claims 4 to 6.   A secondary battery comprising the positive electrode according to claim 7. The current collector for a positive electrode is made of at least one of nickel, aluminum, and titanium, and the electrolyte contains LiPF ₆ and / or LiBF ₄ and LiTFSI and / or LiBETI. The secondary battery as described.   A secondary battery comprising the negative electrode according to claim 8.

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