JP2015008154A - Battery case - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a battery case showing excellent corrosion resistance and hardly causing deterioration of an electrolyte even at charging and discharging, in a lithium ion battery having a charge potential of 5 V or more.SOLUTION: A battery case includes an electrolyte comprising a fluorine-containing lithium salt dissolved in a solvent containing a dinitrile compound and at least one of a chain carbonic ester, a cyclic carbonic ester and a cyclic carboxylate ester, is in contact with a positive electrode or a negative electrode, and is used for a lithium ion battery having a voltage of 5 V or more at charging. At least a part in contact with the electrolyte of the battery case is formed of a base material comprising SUS 316 or SUS 316L or a base material comprising titanium or nickel.

Description

  The present invention relates to a battery case having excellent corrosion resistance.

  In a lithium ion battery, an electrolyte solution in which a positive electrode material, a negative electrode material, and a lithium salt are dissolved is sealed in a coin-shaped or cylindrical battery case, and the battery case is exposed to a severe corrosive environment. Furthermore, since the battery case also serves as a current-carrying material in charging and discharging, there is a possibility of electrochemical corrosion. For this reason, stainless steel such as SUS304 having excellent corrosion resistance is used as a material for a battery case used in a lithium ion battery (for example, Patent Document 1).

JP 2008-84752 A

Journal of Power Sources 146 (2005) 565-569

In response to demands for higher capacity and higher output of lithium ion batteries, positive electrode active materials such as Li ₂ NiPO ₄ F, LiNiPO ₄ , LiCoPO ₄ , and Li ₂ CoPO ₄ F have been proposed as high-energy-density positive electrode active materials. ing. If these positive electrode active materials having a large energy density are used in a lithium ion battery, theoretically, a lithium ion battery having a large charge capacity should be obtained.

  However, since the charging reaction of such a positive electrode active material occurs at an extremely high potential, in conventional electrolytes for lithium ion batteries using an organic solvent such as a cyclic carbonate or a chain carbonate, the solvent is oxidatively decomposed. There was a problem that it could not be used. For this reason, there is a problem that the capacity that can be actually taken out is less than half of the theoretical capacity (Non-Patent Document 1).

The inventors of the present invention conducted intensive studies to solve the above-mentioned conventional problems, and found that an organic solvent containing a nitrile group is difficult to decompose even at a high positive potential and has a wide potential window. Patent applications have already been filed for electrolyte solutions for lithium batteries (Japanese Patent Application Nos. 2007-333829 and 2009-046955). According to this electrolyte solution for lithium ion batteries, because it has a wide potential window, particularly at high positive _{potential, Li 2 CoPO 4 F, Li} 2 NiPO 4 F, a high positive electrode material having the redox potential such LiCoPO 4, LiNiPO ₄ Can be used. For this reason, it can be set as a battery with a large electromotive force and an output.

  However, when this lithium ion battery electrolyte is used, a very high voltage is applied to the positive electrode during charging and discharging, so the battery case in contact with the positive electrode is also exposed to a harsh oxidative environment and has been used conventionally. A stainless steel battery case may not be used due to corrosion, and there is a problem that there is no container suitable for this electrolytic solution.

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 positive electrode container made of aluminum is used, 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.

  Also, in the negative electrode, since the charge / discharge reaction of the negative electrode active material of the lithium ion battery occurs at a low potential, the battery case in contact with the negative electrode is also exposed to a severe reducing environment, the battery case surface is altered, There is a possibility that the electrolyte solution may be deteriorated on the surface of the battery case, and it has not been understood what kind of current collecting material for the negative electrode is appropriate.

  This invention is made | formed in view of the said conventional situation, and makes it the problem which should be solved to provide the battery case which shows the outstanding corrosion resistance and does not change an electrolyte solution little also at the time of charging / discharging.

  The inventors diligently studied battery materials that can withstand corrosion even when the above-described new lithium ion battery electrolyte is used. As a result, an austenitic stainless steel, titanium (preferably austenitic stainless steel containing molybdenum), nickel and aluminum are imparted with a high positive potential in the electrolyte for lithium ion batteries, thereby forming an excellent corrosion-resistant film. I found out. Furthermore, even when these materials are exposed to a low potential when the negative electrode active material is charged, they are found to exhibit excellent corrosion resistance and rarely alter the electrolyte, thereby completing the present invention. It came.

  That is, the battery case of the present invention is a battery case used for a lithium ion battery provided with an electrolyte solution in which a lithium salt is dissolved, and at least a portion in contact with the electrolyte solution of the battery case is austenitic stainless steel, titanium It consists of the base material which has at least 1 sort (s) of nickel and aluminum as a main structural component.

  In the battery case of the present invention, the portion of the container that comes into contact with the electrolyte solution is made of a base material mainly composed of at least one of austenitic stainless steel, titanium, nickel, and aluminum. When a positive potential is applied, an excellent corrosion-resistant film is formed and the progress of corrosion is stopped. Furthermore, even when these materials are exposed to a low potential when charged in contact with the negative electrode, they exhibit excellent corrosion resistance and rarely alter the electrolyte.

  Since corrosion is a problem in the portion that comes into contact with the electrolytic solution, it is not necessary to make the entire battery case with these substrates, and only the portion that comes into contact with the electrolytic solution may be used. For example, using a material clad with these base materials and other metals, the base material having at least one of austenitic stainless steel, titanium, nickel and aluminum as a main constituent is exposed only inside the battery case. Or nickel plating is applied to a battery case material obtained by press-molding an iron plate or a stainless steel plate.

  Further, in the present invention, the “base material containing titanium, nickel or aluminum as a main constituent” means that a corrosion resistance film is formed by applying a high positive potential in the electrolyte for a lithium ion battery. A high content of titanium, nickel or aluminum. Preferably, the metal contains 90% by mass or more of titanium, nickel, or aluminum.

The battery case of the present invention is effective when applied to a lithium ion battery including an electrolytic solution in which LiPF ₆ (lithium hexafluorophosphate) and / or LiBF ₄ (lithium tetrafluoroborate) is dissolved. .

In addition to LiPF ₆ and / or LiBF ₄ , LiTFSI (lithium bis (trifluoromethanesulfonyl) imide) and / or LiBETI (lithium bis (pentafluoromethanesulfonyl) imide) is also preferably contained. This is because LiTFSI and LiBETI are difficult to form a corrosion-resistant film by themselves, 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 advantage that the decomposition temperature is particularly high, the heat resistance is improved, the solubility is high, and the specific conductivity can be increased.
Incidentally, when coexist and LiPF ₆ and / or LiBF ₄ and LiTFSI and / or LiBETI, amount of LiPF ₆ and / or LiBF ₄ is 0.5 in a molar ratio with respect to LiPF ₆ and / or LiBF ₄ The range is preferably 4 times, more preferably 1 to 2 times. In addition, the concentration of LiPF ₆ and / or LiBF ₄ is preferably 0.5 mol / L or more, and more preferably 1 mol / L or more.

  Moreover, it is effective to apply the battery case of the present invention to a lithium ion battery in which the electrolytic solution contains a nitrile compound. This is because the electrolytic solution containing the nitrile compound has a wide potential window, and thus the battery case is required to have excellent corrosion resistance.

  Among these, a chain saturated hydrocarbon dinitrile compound having a nitrile group bonded to both ends of the chain saturated hydrocarbon compound, a chain ether nitrile compound having a nitrile group bonded to at least one of the ends of the chain ether compound, and cyano It is effective to be applied to a lithium ion battery including an electrolytic solution containing at least one nitrile compound of acetate and at least one of cyclic carbonate, cyclic carboxylate and chain carbonate. is there. This is because such an electrolytic solution has an effect of enlarging a particularly excellent potential window, and thus the battery case is required to have particularly excellent corrosion resistance.

It is a graph which shows the electric potential-current curve about Test Example 1 (pure titanium electrode) and Test Example 3 (SUS304 electrode). It is a graph which shows the electric potential-current curve about Test Example 2 (pure nickel electrode) and Test Example 3 (SUS304 electrode). It is the electric potential current curve of various metals in Test Example 5. It is an electric potential current curve of various metals in example 6 of an examination. 10 is a graph showing a potential-current curve for Test Example 7. 10 is a graph showing a potential-current curve for Test Example 8. 10 is a graph showing a potential-current curve for Test Example 9. It is a graph which shows the electric potential current curve and oxidation-reduction potential (position of the arrow in a figure) of various electrode active materials. It is sectional drawing of a positive electrode can and a negative electrode cap. It is sectional drawing of a lithium ion battery.

  The battery case of the present invention is at least one of a base material made of austenitic stainless steel and a base material mainly containing titanium, nickel, or aluminum, except for a sealing material for insulating the positive electrode and the negative electrode. Although it can be constituted by seeds, electroless nickel plating or electrolytic nickel plating may be applied to a molded base material press-formed from an iron plate or a stainless steel plate, or a clad material combined with other metals can also be used. . However, at least one of a base material made of austenitic stainless steel and a base material mainly composed of titanium, nickel, or aluminum needs to be exposed on the surface in contact with the electrolytic solution. When using austenitic stainless steel, one containing molybdenum is preferable because it is particularly excellent in corrosion resistance.

  The battery case of the present invention is effective when applied to a battery case containing an electrolytic solution containing a nitrile compound. This is because the electrolytic solution containing the nitrile compound has a wide potential window (see Japanese Patent Application Nos. 2007-333829 and 2009-046955 filed earlier by the present inventors), and therefore, the battery case is required to have excellent corrosion resistance. .

  Among these, a chain saturated hydrocarbon dinitrile compound having a nitrile group bonded to both ends of the chain saturated hydrocarbon compound, a chain ether nitrile compound having a nitrile group bonded to at least one of the ends of the chain ether compound, and cyano It is effective to be applied to a lithium ion battery including an electrolytic solution containing at least one nitrile compound of acetate and at least one of cyclic carbonate, cyclic carboxylate and chain carbonate. is there. This is because such an electrolytic solution has an effect of enlarging a particularly excellent potential window, and thus the battery case is required to have particularly excellent corrosion resistance.

The reason why the electrolytic solution for lithium ion batteries of the present invention using such an electrolytic solution has an effect of expanding an excellent potential window is not necessarily clear, but is considered as follows. That is, of the organic solvents contained in the electrolytic solution, the nitrile compound serves to widen the potential window. In addition, the chain carbonate ester is presumed to play a role of increasing the specific conductivity in order to lower the viscosity. And cyclic carbonate ester and cyclic carboxylate ester dissolve Lithium salt, and form a protective film called SEI on the carbon anode, thereby allowing Li ions to pass through while improving reduction resistance. It is possible to impart characteristics that can be Therefore, it is considered that the effect can be exerted on the enlargement of the potential window on the negative side and the positive side.
From the above, it is preferable to use a chain carbonate ester and a cyclic carbonate ester and / or a cyclic carboxylate ester in combination. More preferably, it is a combined use of a chain carbonate ester and a cyclic carbonate ester. Specifically, dimethyl carbonate and ethylene carbonate are used in combination. The blending ratio of both is not particularly limited.

<Electrochemical behavior of titanium, nickel and aluminum in electrolyte for lithium ion battery>
When titanium, nickel, and aluminum are given a high positive potential in the electrolyte for a lithium ion battery, an excellent corrosion-resistant film is formed. This has been clarified from Test Examples 1 to 4 below.

(Test Example 1)
In Test Example 1, a pure titanium electrode was subjected to potential scanning in an electrolyte for a lithium ion battery, 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 LiBF ₄ was dissolved to 1 mol / L was used as an electrolytic solution. Placed in an electrolytic cell container.

  In the electrochemical measurement, a pure titanium electrode was used as a working electrode, a platinum net as a counter electrode, and Li metal as a reference electrode, and a potential-current curve was measured a plurality of times. The sweep speed was 5 mV / sec. Moreover, the surface analysis of the titanium electrode after potential scanning was performed by X-ray photoelectron analysis (XPS).

(Test Example 2)
In Test Example 2, the potential-current curve was measured multiple times for the pure nickel electrode under the same conditions as in Experimental Example 1. Moreover, the surface analysis of the nickel electrode after potential scanning was performed by X-ray photoelectron analysis (XPS).

(Test Example 3)
In Test Example 3, a potential-current curve was measured a plurality of times under the same conditions as in Experimental Example 1 for an electrode made of stainless steel (SUS304). SUS304 belongs to austenitic stainless steel and is an alloy containing 8 to 10.5% by weight of Ni and 18 to 20% by weight of Cr in addition to Fe as a main component.

(Test Example 4)
In Test Example 4, a potential sweep was performed on an electrode made of pure aluminum under the same conditions as in Experimental Example 1.

<Result>
(1) Potential Current Curve / Pure Titanium Electrode Results for Test Example 1 (pure titanium electrode) and Test Example 3 (SUS304 electrode) are shown in FIG. As can be seen from this figure, in Test Example 1 (pure titanium electrode), in the first sweep, an oxidation current began to flow from about 4.5 V, and a larger oxidation current flowed as the potential increased. As a result, the current value gradually decreased. In addition, in the second sweep, it was found that the oxidation current hardly flowed, and could sufficiently withstand the battery case up to 7V or more. From the above results, it was found that a passive film excellent in corrosion resistance was formed with a pure titanium electrode.
On the other hand, in Test Example 3 (SUS304 electrode), an oxidation current starts to flow from about 4.6 V in the first sweep, and a large oxidation current flows as the potential increases. It was found that a large oxidation current flowed after 8 V and the corrosion resistance was insufficient.

-Pure nickel electrode The result about Test Example 2 (pure titanium electrode) and Test Example 3 (SUS304 electrode) is shown in FIG. As can be seen from this figure, in Test Example 2 (pure nickel electrode), an oxidation current began to flow from about 4 V in the first sweep, and a larger oxidation current flowed as the potential increased. Then, although an oxidation current slightly flows from about 4.5V, it was found that the current hardly increased up to about 6.3V, and that the battery case could withstand up to 6V. From the above results, it was found that a passive film excellent in corrosion resistance was formed even with a pure nickel electrode.

(2) XPS measurement The results of XPS measurement of the electrode surface after potential scanning in Test Example 1 (pure titanium electrode), Test Example 2 (pure nickel electrode) and Test Example 4 (pure aluminum electrode) are shown in Table 1 (element composition). ) And Table 2 (peak splitting). From the elemental composition of Table 1, it was found that nitrogen and fluorine were detected on the surface of any electrode, and the amounts of titanium, nickel and aluminum were small. This suggested the formation of a film made of a nitrogen compound in addition to the film made of a fluorine compound. Further, from the results of peak splitting in Table 2, CN triple bonds and -CN bonds considered to be derived from nitriles were detected, suggesting that the addition of nitrile contributed to the formation of a corrosion-resistant film. The fluorine compound is a compound having a PF bond and a C—F bond based on the result of peak separation.

(Test Example 5)
In Test Example 5, 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. Here, SUS316 belongs to austenitic stainless steel and is an alloy containing 10 to 14% by weight of Ni, 16 to 18% by weight of Cr and 2 to 3% by weight of Mo in addition to Fe as a main component. SUS316L is an austenitic stainless steel similar to SUS316 with respect to SUS316 and Fe, Ni, Cr, and Mo, but further has a carbon content of 0.03% by weight or less.
SUS304, SUS316, SUS316L, pure nickel, pure titanium, pure aluminum, and pure copper were subjected to potential sweeping toward the negative potential side, and potential-current curves were measured.
The solvent of the electrolytic solution is ethylene carbonate: dimethyl carbonate: sebaconitrile = 25: 25: 50 (volume ratio), and a solution in which LiBF ₄ is dissolved so as to be 1 mol / L is used as the electrolytic solution. Put it 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. 3, in the potential sweep to the high potential side, the potential where the oxidation current exceeds 50 μA is in the order of SUS304 <SUS316 <nickel <SUS316L <titanium. The oxidation current was about 5 μA even at .6 V vs 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 further LiBF ₄ is dissolved at 1 mol / L, the positive electrode Titanium, aluminum, SUS304, SUS316L, nickel, and SUS316 are applicable as the material of the battery case that contacts the battery, preferably titanium, aluminum, SUS316L, and nickel, and more preferably titanium, aluminum, and SUS316L. I understood.

On the other hand, in the potential sweep to the low potential side, the potential at which the reduction current exceeds 50 μA is 1.7V for Cu, 0.8V for Al, 0.2V for SUS316, 0 for SUS304 with respect to Li / Li ⁺ . .15V, SUS316L became 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 the battery case material in contact with the battery, 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.

(Test Example 6)
In Test Example 6, 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 Test Example 5.

As a result, as shown in FIG. 4, in the potential sweep to the high potential side, the oxidation current of any metal does not exceed 50 μA up to 7.5 V vs Li / Li ⁺ , and SUS304, SUS316, SUS316L It has been found that any of pure nickel, pure titanium and pure aluminum can be sufficiently used as a battery case in contact with the positive electrode.

On the other hand, in the potential sweep to the low potential side, the potential at which the oxidation current exceeds 50 μA is such that Cu is 1.2 V, SUS316 is 1.1 V, SUS316L is 0.1 V, and Al is 0 with respect to Li / Li ⁺ . .2V and SUS304 became 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 material of the battery case in contact with each other, and nickel and titanium are particularly preferable.
However, the potential for operation of the negative electrode active material are different depending on the type, in the case of using a negative electrode active material of lithium titanate-based or Fe ₂ O ₃ system, the oxidation-reduction potential against Li / Li ⁺ 1. It is about 5 V, which is higher than the deposition potential of lithium. 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 battery case material in contact with the negative electrode.

(Test Example 7)
In Test Example 7, a nickel plate was used as the working electrode, and an electrolytic solution containing both LiPF ₆ and LITFSI as the lithium salt was used. That is, ethylene carbonate, dimethyl carbonate and sebaconitrile are mixed so that the volume 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. It was made into electrolyte solution and put into the tripolar electrolytic cell container. The electrochemical measurement was the same as in Test Example 5.

(Test Example 8)
In Test Example 8, the same electrolytic solution as in Test Example 7 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 Test Example 5.

(Test Example 9)
In Test Example 9, 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 Test Example 7 using a nickel plate, as shown in FIG. 5, 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 Test Example 8 using an aluminum plate, as shown in FIG. 6, it was found that the potential window widens dramatically by making LiPF ₆ coexist with LiTFSI. Similarly, in Experimental Example 9 using a titanium plate, as shown in FIG. 7, it was found that LiPF ₆ coexists with LiTFSI, so that the potential window is dramatically expanded.

From the measurement results of the potential current curves of Test Example 7 and Test Example 8 described above, it was found that the potential window was dramatically expanded by allowing LiPF ₆ to coexist with LiTFSI in nickel, aluminum, and titanium. That is, when the lithium salt is LITFSI alone and when the concentration of LITFSI is 1 mol / L and LiPF ₆ is as low as 0.1 mol / L of 1/10, the potential window is not so wide. It was found that when LiPF ₆ was added at 0.5 mol / L or more, the potential window was large and spread in the noble direction, and a passive film excellent in corrosion resistance was formed. 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.

<Selection of battery case material>
The material of the battery case is preferably selected in consideration of the operating potential of the electrode active material and the type of electrolyte. FIG. 7 shows potential-current curves and oxidation-reduction potentials (positions of arrows in the figure) of various electrode active materials.
The operating potential of the negative electrode active material is close to the lithium deposition potential in the carbon-based and silicon-based materials, but when a lithium titanate-based or Fe ₂ O ₃ -based negative electrode active material is used, the redox potential Is about 1.5 V with respect to Li / Li ⁺ , which is considerably higher than the deposition potential of lithium. For this reason, for example, in a lithium ion battery using a lithium titanate-based or Fe ₂ O _3- based negative electrode active material, ethylene carbonate: dimethyl carbonate: sebacononitrile = 25: 25: 50 (capacity ratio), and further LiBF ₄ is used. When the solution dissolved so as to be 1 mol / L is used as the electrolyte, the electrolyte is titanium, nickel, aluminum, SUS304, SUS316, and SUS316L as shown in FIG. It can also be used as a material for battery cases that come into contact with the battery. This is because these materials have a small reduction current at a lithium titanate-based or Fe ₂ O _3- based operating potential, so that there is little risk of alteration of the negative electrode of the battery case or the electrolyte.
On the other hand, in a lithium ion battery using a carbon-based or silicon-based negative electrode active material, it is preferable to use titanium, nickel, aluminum, SUS304, SUS316, and SUS316L. This is because these materials have a reduced reduction current at a carbon-based or silicon-based operating potential, and are less likely to be deteriorated in the negative electrode of the battery case or the electrolytic solution.

Further, in the case where ethylene carbonate: dimethyl carbonate: sebaconitrile = 25: 25: 50 (volume ratio) and a solution obtained by dissolving LiBF ₄ to 1 mol / L is used as the electrolytic solution, as shown in FIG. , SUS304, since the rapid oxidation current flows through a 5.5V vs Li / Li ^+, the operating potential is at the high electric potential LiCoMn0 _{4 system,} Li 2 NiP0 _{4 F-based,} Li 2 CoP0 ₄ F system and LiNi _0.5 Mn _1.5 0 SUS304 ₄ based positive electrode active material as a battery case of a lithium ion battery using can not be used for this, SUS316, Ni, Al, SUS316L and Ti can be used. Among these, Ni, Al, SUS316L and Ti are preferable, Al, SUS316L and Ti are more preferable, and Ti is most preferable.

On the other hand, when ethylene carbonate: dimethyl carbonate: sebaconitrile = 25: 25: 50 (volume ratio) and a solution in which LiPF ₆ is dissolved at 1 mol / L is used as the electrolyte, as shown in FIG. As a battery case of a lithium ion battery using a positive active material of LiCoMn0 ₄ system, Li ₂ NiP0 ₄ F system, Li ₂ CoP0 ₄ F system and LiNi _0.5 Mn _1.5 0 ₄ system having a high operating potential, SUS304, Any of SUS316, Ni, Al, SUS316L, and Ti can be used. Among these, SUS304, SUS316, Al, SUS316L, and Ti are preferable, and SUS304, SUS316, Al, and SUS316L are more preferable.

The operating potential of the negative electrode active material is close to the lithium deposition potential in the carbon-based and silicon-based materials, but when a lithium titanate-based or Fe ₂ O ₃ -based negative electrode active material is used, the redox potential Is about 1.5 V, which is considerably higher than the deposition potential of lithium. For this reason, for example, in a lithium ion battery using a lithium titanate-based or Fe ₂ O _3- based negative electrode active material, ethylene carbonate: dimethyl carbonate: sebacononitrile = 25: 25: 50 (capacity ratio), and further LiPF ₆ is When the solution dissolved so as to be 1 mol / L is used as the electrolytic solution, the electrolytic solution is copper, titanium, nickel, aluminum, SUS304, SUS316, and SUS316L as shown in FIG. Can also be used as a material for the battery case in contact with the negative electrode. This is because these materials have a small reduction current at a lithium titanate-based or Fe ₂ O _3- based operating potential, so that there is little risk of alteration of the negative electrode of the battery case or the electrolyte.
On the other hand, in a lithium ion battery using a carbon-based or silicon-based negative electrode active material, it is preferable to use titanium, nickel, aluminum, or SUS304. This is because these materials have a reduced reduction current at a carbon-based or silicon-based operating potential, and are less likely to be deteriorated in the negative electrode of the battery case or the electrolytic solution.

<Production of lithium ion battery>
An example of producing a lithium ion battery using the battery case of the present invention is shown below. That is, first, as shown in FIG. 8, a bottomed cylindrical titanium or nickel positive electrode can 11 and a bottomed cylindrical and flat titanium or nickel negative electrode cap 12 are prepared. The positive electrode can 11 and the negative electrode cap 12 constitute a battery case.

  Next, as shown in FIG. 9, the cathode can 11 is filled with a spacer 13 made of titanium or nickel, a cathode active material pellet 14, and a separator 15. On the other hand, the negative electrode cap 12 is filled with a wave washer 16 made of titanium or nickel, a spacer 17 made of titanium or nickel, and a lithium negative electrode active material 18. And after putting electrolyte solution in the positive electrode can 11, the negative electrode cap 12 is mounted and crimped | sealed through the insulating gasket 19, and it is set as a lithium ion battery.

  The lithium ion battery configured as described above has sufficient corrosion resistance because a corrosion-resistant passive film is formed on the inner surface of the positive electrode can 11 during charging.

The present invention is applied to a lithium ion battery.
Here, the lithium ion battery includes an electrolytic solution, a positive electrode, a negative electrode, a separator, and a case.

(Electrolyte)
The electrolytic solution 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%.

  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.

(Positive electrode)
The positive electrode includes a positive electrode active material and a current collector.
(Positive electrode active material)
The positive electrode active material refers to “a material in which lithium is inserted / extracted in the crystal structure at a higher potential than 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 (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.

(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 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 performs an immersion treatment step of immersing the positive electrode in a pretreatment electrolytic solution in which a lithium salt is dissolved in an organic solvent containing 1% by volume or more of a nitrile compound before being incorporated in the lithium ion battery, Further, a positive voltage processing step for applying a positive voltage to the electrode is 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. 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.

(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 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.

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 following matters are disclosed below.
(1) An electrolytic solution in which a lithium salt containing fluorine is dissolved in a solvent containing at least one of a chain carbonate ester, a cyclic carbonate ester and a cyclic carboxylate ester, and a dinitrile compound, and is in contact with the positive electrode and the negative electrode; A battery case used for a lithium ion battery having a voltage of 5 V or more during charging, wherein at least a portion of the battery case that comes into contact with the electrolyte is made of a base material made of SUS316 or SUS316L, or made of titanium or nickel A battery case comprising a base material.
(2) The battery case according to (1), wherein the lithium salt contains LiPF ₆ and / or LiBF ₄ .
(3) The battery case according to (2), wherein the lithium salt further contains LiTFSI and / or LiBETI.
(4) A battery case substrate made of SUS316 or SUS316L or a battery case substrate made of titanium or nickel, which is made of a cyclic carbonate and / or a chain carbonate and a dinitrile. Contacting an electrolytic solution in which a lithium salt containing fluorine is dissolved in a solvent containing a compound;
Applying a voltage of 5 V or higher to the base material in contact with the electrolytic solution to form a passive film on the surface of the base material.

11, 12 ... Battery case made of titanium or nickel (11 ... positive electrode can, 12 ... negative electrode cap)
DESCRIPTION OF SYMBOLS 13 ... Spacer 14 ... Positive electrode active material pellet 15 ... Separator 16 ... Wave washer 17 ... Spacer 18 ... Lithium negative electrode active material 19 ... Insulation gasket

Claims (1)

  It comprises an electrolyte solution in which a lithium salt containing fluorine is dissolved in a solvent containing at least one of a chain carbonate ester, a cyclic carbonate ester and a cyclic carboxylic acid ester and a dinitrile compound. A battery case used for a lithium ion battery having a voltage of 5 V or more, wherein at least a portion of the battery case that comes into contact with the electrolyte solution is a base material made of SUS316 or SUS316L, or a base material made of titanium or nickel, A battery case, wherein a passive film is formed on the surface of the substrate.

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