JP2011071083A - Lithium ion battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium ion battery with an electrolyte hardly decomposed even when an overvoltage of a positive electrode gets high during charging, in the lithium ion battery using an oxide-based positive active material. <P>SOLUTION: This lithium ion battery uses, as a positive active material, at least one out of Li<SB>1-x</SB>CoO<SB>2</SB>, Li<SB>1-x</SB>NiO<SB>2</SB>, Li<SB>1-x</SB>Mn<SB>2</SB>O<SB>4</SB>, 2-1-3 system lithium manganate and a complex component thereof, and Li<SB>1-x</SB>FePO<SB>4</SB>, Li<SB>1-x</SB>MnPO<SB>4</SB>, Li<SB>2-y</SB>FePO<SB>4</SB>F, Li<SB>2-y</SB>MnPO<SB>4</SB>F (x is number of 0 or more and 1 or less, y is number of 0 or more and 2 or less, and some of Co, Ni, Mn and Fe may doped with other metal including Li) and a complex component thereof. An organic solvent of the electrolyte contains: at least one nitrile compound selected from the group of a chain saturated hydrocarbon dinitrile compound in which a chain saturated hydrocarbon compound bonds a nitride group to each of terminals thereof, a chain ether nitrile compound in which a chain ether compound bonds a nitrile group to at least one of terminals thereof, and ester cyanoacetate; and at least one selected from the group of a cyclic carbonate, a cyclic carboxylate ester, and a chain carbonate. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a lithium ion battery, and more particularly to a lithium ion battery in which the amount of electricity that can be discharged even when charged by an excessive voltage is unlikely to decrease.

A lithium ion battery has a structure in which a positive electrode including a positive electrode active material and a negative electrode including a negative electrode active material are in contact with an electrolyte solution in which a lithium salt is dissolved in an organic solvent.
Examples of the positive electrode active material used in the lithium ion battery include an oxide-based positive electrode active material (for example, lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), 2-1-3 lithium manganate (that is, Li ₂ MnO ₃ lithium manganate), spinel-based lithium manganate (LiMn ₂ O ₂ ) and the like, and solid solutions thereof, phosphate-based positive electrode active materials having an olivine type crystal structure (LiFePO ₄ , LiMnPO ₄ , Various materials such as LiCoPO ₄ and LiNiPO ₄ ) and positive electrode active materials (Li ₂ FePO ₄ F, Li ₂ MnPO ₄ F, Li ₂ CoPO ₄ F, and Li ₂ NiPO ₄ F) as fluorides have been developed. Has been.

Among these, there are substances that can obtain a large electromotive force in a single cell because they have a high oxidation-reduction potential in some of the positive electrode active materials of phosphates and fluorides having an olivine type crystal structure. . In particular, Li ₂ CoPO ₄ F and Li ₂ NiPO ₄ F have a larger oxidation-reduction potential because part of the oxygen in the phosphate polyanion PO ₄ is substituted with fluorine having a higher electronegativity than oxygen, and the oxidation-reduction potential is further increased. An electromotive force battery can be obtained (Patent Document 1).

However, a positive electrode active material having high oxidation-reduction potential as the positive electrode active substances LiCoPO _4, LiNiPO ₄ and _Li 2 CoPO ₄ F or _Li 2 NiPO ₄ F of olivine phosphates or fluorides in the lithium ion battery If it is intended to be used, it is charged at a high voltage, so that the electrolytic solution may be decomposed or altered. For this reason, even if it has a high electromotive force and theoretically has a high energy density, the charge efficiency and the amount of electricity that can be discharged are small, and its performance could not be fully exploited. .

  For this reason, the present inventors have developed an electrolytic solution that does not decompose even with these positive electrode active materials having a high oxidation-reduction potential, and has already filed an application (Japanese Patent Application No. 2009-046955). This electrolyte is an organic solvent, a chain saturated hydrocarbon dinitrile compound in which a nitrile group is bonded to both ends of a chain saturated hydrocarbon compound, a chain formula in which a nitrile group is bonded to at least one terminal of a chain ether compound. It contains at least one nitrile compound of an ether nitrile compound and a cyanoacetate ester, and at least one of a cyclic carbonate ester, a cyclic carboxylic acid ester and a chain carbonate ester.

JP 2003-229126 A

However, an oxide-based positive electrode active material such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O _4, Li ₂ MnO _3, and a composite material thereof, which has a redox potential not as high as that of an olivine-based phosphate, an olivine type crystal structure Even if it is a phosphate-based positive electrode active material (LiFePO ₄ , LiMnPO ₄ ) or a positive electrode active material (Li ₂ FePO ₄ F, Li ₂ MnPO ₄ F) as a fluoride system, The overvoltage at the time of charging becomes high and may exceed the withstand voltage of the electrolytic solution. In such a case, the electrolytic solution may be decomposed.
In addition, when charging by connecting a number of lithium ion batteries in series, if the charge voltage is controlled only by the voltage at both ends, the overvoltage of the positive electrode may increase in some cells. In some cases, the electrolyte solution may be decomposed or deteriorated.

  The present invention has been made in view of the above-described conventional situation, and in a lithium ion battery using an oxide-based positive electrode active material, the lithium ion is difficult to decompose even if the overvoltage of the positive electrode increases during charging. Providing a battery is a problem to be solved.

  The present inventors have found that an organic solvent having a nitrile group hardly decomposes even at a high positive potential and has a wide potential window, and has already filed a patent application for an electrolytic solution for a lithium ion battery using the same. (Japanese Patent Application No. 2009-046955). And when the electrolyte solution which has the wide electric potential window containing this nitrile compound was used, it discovered that the said subject could be solved and came to complete this invention.

That is, the lithium ion battery of the present invention is a lithium ion battery in which a positive electrode including a positive electrode active material and a negative electrode including a negative electrode active material are in contact with an electrolyte solution in which a lithium salt is dissolved in an organic solvent.
The positive electrode active material is Li _1-x CoO ₂ , Li _1-x NiO ₂ , Li _1-x Mn ₂ O _4, 2-1-3 lithium manganate, and a composite thereof, and Li _1-x FePO. ₄ , Li _1-x MnPO ₄ , Li _2-y FePO ₄ F, Li _2-y MnPO ₄ F (wherein x is a number from 0 to 1 and y is a number from 0 to 2; Including Co, Ni, Mn and part of Fe doped with other metal atoms including Li) and their composites,
The organic solvent of the electrolytic solution has a chain saturated hydrocarbon dinitrile compound in which a nitrile group is bonded to both ends of the chain saturated hydrocarbon compound, and a chain in which a nitrile group is bonded to at least one end of the chain ether compound. It contains at least one nitrile compound of the formula ether nitrile compound and cyanoacetate ester, and at least one of cyclic carbonate ester, cyclic carboxylic acid ester and chain carbonate ester.

  In the lithium ion battery of the present invention, a high voltage electrolytic solution containing a nitrile compound is used. That is, the organic solvent used in the electrolytic solution includes a chain saturated hydrocarbon dinitrile compound in which a nitrile group is bonded to both ends of the chain saturated hydrocarbon compound, and a nitrile group at least at one end of the chain ether compound. At least one of a chain ether nitrile compound and a cyanoacetate bonded to each other, and at least one of a cyclic carbonate, a cyclic carboxylic acid ester and a chain carbonate.

According to the test results of the present inventors, such an electrolyte has a wide potential window particularly at a high positive potential. Therefore, the positive electrode active material is Li _1-x CoO ₂ , Li _1-x NiO ₂ , Li _1-x Mn ₂ O _4, 2-1-3 lithium manganate, and a composite thereof, and Li _{1 -x FePO 4, Li 1-x} MnPO 4, Li 2-y FePO 4 F, Li 2-y MnPO 4 F ( although the x is a number of 0 or more and 1 or less, the number of the y is 0 to 2 And a lithium ion battery using a composite of these, including a part of the Co, Ni, Mn, and Fe doped with other metal atoms including Li). The withstand voltage of the electrolytic solution is not exceeded, and the electrolytic solution is difficult to decompose. In addition, when a number of lithium ion batteries are connected in series for charging, even if the overvoltage for charging the positive electrode active material increases in some cells, the electrolyte is difficult to decompose.
Note that the 2-1-3-type lithium manganate, refers to a compound formula is represented by _Li 2-y MnO _3.

The nitrile compound contained in the electrolytic solution used in the present invention 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 pass Li ion while improving reduction resistance by forming a protective film called SEI on the carbon negative electrode. 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 and a cyclic carbonate and / or a cyclic carboxylic acid ester in combination in the electrolytic solution. 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.

LiCoMnO is a graph showing the results of CV measurement ₄ (Test Example 1). LiNi is a graph showing the results of CV measurement _0.5 Mn _1.5 O ₄ (Test Example 2). 2 is a potential-current curve of Experimental Example 1 and Comparative Example 1. It is the electric potential-current curve of Experimental Examples 2-9 and Comparative Example 1. 6 is a potential-current curve of Comparative Example 1. It is an electric potential-current curve of Experimental Examples 10-17 and Comparative Example 2. 6 is a potential-current curve of Experimental Examples 18 to 25 and Comparative Example 3. 6 is a potential-current curve of Experimental Examples 26 to 31 and Comparative Example 4. 6 is a potential-current curve of Experimental Examples 32 and 33 and Comparative Example 5. 7 is a potential-current curve of Experimental Examples 34 to 36 and Comparative Example 6. 10 is a potential-current curve of Experimental Examples 37 to 39 and Comparative Example 7. It is an electric potential-current curve of Experimental example 40-44, Comparative example 1, and Comparative example 8-10. 10 is a potential-current curve of Experimental Example 45 and Comparative Example 8. 10 is a potential-current curve of Experimental Example 46 and Comparative Example 8. 10 is a potential-current curve of Experimental Example 47 and Comparative Example 9. It is a potential-current curve in a mixed solvent in which ethylene carbonate: dimethyl carbonate = 1: 1 and a predetermined amount of sebacononitrile was added. 14 is a potential-current curve of lithium occlusion / release using the lithium ion battery electrolyte solution of Experimental Example 41. FIG. It is sectional drawing of the battery case used for the lithium ion battery of the Example. It is sectional drawing of the lithium ion battery of an Example. Even if Li is desorbed from the positive electrode active material at 5 V or higher, the positive electrode material particles 1 that are not decomposed or altered by the reaction with the electrolytic solution but are altered by the high-potential positive electrode active material 2 It is a schematic cross section at the time of encapsulating. Even if Li is desorbed from the positive electrode active material at 5 V or higher, the positive electrode material powder 3 that does not decompose or change in quality but reacts with the electrolyte solution in the high-potential positive electrode active material 4 It is a schematic cross section at the time of setting it as the structure which is mixed and included. Even if Li is desorbed from the positive electrode active material at 5 V or more, the high-potential positive electrode active material fine particles are not surrounded by the positive electrode active material particles 5 around the positive electrode material particles 5 that do not decompose or change in quality but the active material surface reacts with the electrolyte and changes in quality. FIG. 6 is a schematic cross-sectional view in the case of a structure wrapped with powder 6. It is a graph which shows the relationship between charging / discharging capacity | capacitance and a voltage.

Hereinafter, embodiments of the present invention will be described.
The lithium ion battery of the embodiment 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. The organic solvent includes 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 terminal of the chain ether compound, and At least one nitrile compound among cyanoacetic acid esters and at least one of cyclic carbonic acid ester, cyclic carboxylic acid ester and chain carbonic acid ester are included.
Preferably, a cyclic carbonate and a chain carbonate are used in combination. Specifically, ethylene carbonate and dimethyl carbonate are used in combination. The blending ratio of both is not particularly limited. As the cyclic carboxylic acid ester, γ-butyrolactone can be used.

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%.

On the other hand, the lithium salt contained in the electrolyte includes LiPF ₆ (lithium hexafluorophosphate), LiBF ₄ (lithium tetrafluoroborate), LiTFSI (lithium bis (trifluoromethanesulfonyl) imide), LiTFS (trifluoromethane). Lithium sulfonate), LiBETI (lithium bis (pentafluoroethanesulfonyl) imide), and the like can be used. These lithium salts dissolve in the nitrile organic solvent used in the electrolyte for lithium ion batteries of the present invention and have a sufficient potential window that does not decompose even at high potentials. Among these, it is preferable that at least one of LiPF ₆ (lithium hexafluorophosphate), LiBF ₄ (lithium tetrafluoroborate) and LiTFSI (lithium bis (trifluoromethanesulfonyl) imide) is contained. LiPF ₆ (lithium hexafluorophosphate) and LiBF ₄ (lithium tetrafluoroborate) are less corrosive to aluminum, which is often used as a current collector for positive electrodes of lithium ion batteries. Furthermore, they are also more effective in expanding the potential window than LiTFS (lithium trifluoromethanesulfonate) and LiBETI (lithium bis (pentafluoroethanesulfonyl) imide). LiTFSI (lithium bis (trifluoromethanesulfonyl) imide) has a particularly high decomposition temperature, improved heat resistance, high solubility, and high specific conductivity.

  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 due to 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.

  Moreover, it is preferable that the density | concentration of the nitrile compound contained in electrolyte solution is 1 volume% or more and less than 100 volume%. When the concentration of the nitrile compound is less than 1% by volume, the effect of expanding the potential window is reduced. More preferably, it is 5 volume% or more and less than 90 volume%. When the concentration of the nitrile compound is 90% by volume or more, the solubility of the electrolyte is lowered and the viscosity is also increased. Therefore, the conductivity is lowered, and the internal resistance of the battery is increased. Most preferred is 30% by volume or more and less than 70% by volume.

(Positive electrode)
The positive electrode includes a positive electrode active material and a current collector.
(Positive electrode active material)
An oxide-based material is used as the positive electrode active material.
Specifically, as an oxide-based positive electrode active material,
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 (y = 0 to 2) and solid solutions thereof (here, solid solution refers to a material in which metal atoms are mixed in a free ratio in the above-described oxide-based positive electrode active material. ). 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.

The general discharge potential of this positive electrode active material is less than 5 V vs Li / Li ⁺ . However, when rapid charging is performed or the charging voltage is controlled only by the voltage at both ends, the overvoltage of the positive electrode may be increased in some cells, and LiCoMnO ₄ has a discharge voltage of 5.2 V. Start with a degree. For this reason, the charging voltage may exceed 5V.
However, in the present invention, a high voltage electrolytic solution containing a nitrile compound is used. That is, the organic solvent used in the electrolytic solution includes a chain saturated hydrocarbon dinitrile compound in which a nitrile group is bonded to both ends of the chain saturated hydrocarbon compound, and a nitrile group at least at one end of the chain ether compound. At least one of a chain ether nitrile compound and a cyanoacetate bonded to each other, and at least one of a cyclic carbonate, a cyclic carboxylate and a chain carbonate. This electrolyte has a wide potential window, especially at a high positive potential. For this reason, even if charging voltage exceeds 5V, it does not exceed the withstand voltage of electrolyte solution, and electrolyte solution is hard to decompose | disassemble.

(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 even when the overvoltage increases during charging.
For example, when LiPF ₆ or LiBF ₄ is used as the electrolyte, SUS304, SUS316, SUS316L, Ni, Al, Ti, or the like can be used, but should be appropriately selected in consideration of the operating potential of the positive electrode active material during charging. Is preferred.
When LiPF ₆ is used as the electrolyte, it can be used even at 6V with respect to the Li / Li ⁺ electrode. However, when LiBF ₄ is used as the electrolyte, SUS304 is 5.8V 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. 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.

(Current collector for negative electrode)
The current collector for the negative electrode can be formed of a general-purpose conductive metal material such as Cu, Al, Ni, Ti, SUS304, SUS316, 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, SUS304, 316, 316L, Ni, Al, and Ti 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, SUS304, SUS316, 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 SUS316, SUS316L and Cu are not preferable. In addition, when LiTFSI, LiBETI, or LiTFS is used as the electrolyte, any of Ni, Ti, Al, Cu, SUS304, 316, and 316L 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. The conductive thin film in which the positive electrode active material is embedded can be manufactured by physically driving the conductive thin film such as gold with a hammer or the like.

(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 LiPF ₆ or LiBF ₄ is used as the electrolyte, a case made of SUS304, 316, 316L, Ni, Al, Ti 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.

<Cyclic voltammograms (CV) of various oxide-based positive electrode active materials>
As oxide-based positive electrode active materials, LiCoMnO ₄ was used as a CV measurement object in Test Example 1, and LiNi _0.5 Mn _1.5 O ₄ was used as a CV measurement object in Test Example 2. In addition, as the measurement solution, the electrolyte solution used in the lithium ion battery of the present invention is LiPF _{6 in} a mixed solvent of ethylene carbonate: dimethyl carbonate: sebaconitrile = 25: 25: 50 (volume ratio) at 1 mol / L. The solution dissolved in was used.
As a method for producing the positive electrode, in Test Example 1, LiCoMnO ₄ , glassy carbon powder as a conductive additive, and polytetrafluoroethylene (PTFE) as a binder were in a ratio of 70: 25: 5 (weight ratio). Were used and mixed into a plate using a hot press.
In Test Example 2, LiNi _0.5 Mn _1.5 O ₄ powder was thinly laid on a gold plate and hammered from above with a hammer to embed LiNi _0.5 Mn _1.5 O ₄ in a gold thin film, which was used for CV measurement. Used as an electrode.

As a result, in LiCoMnO ₄ (Test Example 1), as shown in FIG. 1, a redox peak was observed in the vicinity of 4.6 V vs Li / Li ⁺ . Also in LiNi _0.5 Mn _1.5 O ₄ (Test Example 2), as shown in FIG. 2, a redox peak was observed in the vicinity of 4.7 V vs Li / Li ⁺ . Therefore, when rapid charging is performed using these oxides as the positive electrode active material, the overvoltage during charging increases and may exceed 5V. However, since the lithium ion battery of the present invention uses a high-voltage electrolytic solution containing a nitrile compound, it has a wide potential window particularly at a high positive potential. For this reason, even when rapid charging is performed, the electrolytic solution is unlikely to be decomposed or altered.
The fact that the electrolyte used in the lithium ion battery of the present invention has a wide potential window at a high positive potential has already been proved in Japanese Patent Application No. 2009-046955 filed by the present applicant. The contents are shown in Experimental Examples 1 to 47 and Comparative Examples 1 to 10.

(Experimental example 1)
In Experimental Example 1, a solvent in which adiponitrile, ethylene carbonate (EC), and dimethyl carbonate (DMC) were mixed at a volume ratio of 50:25:25 was used as the organic solvent, and LiPF ₆ ( Lithium hexafluorophosphate) was dissolved at 0.05 mol / L to obtain an electrolyte for a lithium ion battery.

(Comparative Example 1)
In Comparative Example 1, a mixed solvent of 50% by volume of ethylene carbonate and 50% by volume of dimethyl carbonate was used as the organic solvent, and LiPF ₆ was dissolved as a lithium salt at a concentration of 1 mol / L. did.

(Experimental Examples 2-9)
In Experimental Examples 2 to 9, the solvent was various nitrile: ethylene carbonate: dimethyl carbonate = 50: 25: 25 (volume ratio), and the electrolyte was LiPF ₆ (lithium hexafluorophosphate) at 1 mol / L in this mixed solvent. The electrolyte solution for the lithium ion battery was dissolved as described above (however, in Example 6 in which the nitrile compound was oxydipropionitrile, LiPF ₆ was 0.5 mol / L).
The types of nitrile used in each experimental example are as follows.
Experimental Example 1 Adiponitrile NC (CH ₂ ) ₄ CN
Experimental Example 2 Succinonitrile NC (CH ₂ ) ₂ CN
Experimental Example 3 Sevacononitrile NC (CH ₂ ) ₈ CN
Experimental Example 4 Dodecanedinitrile NC (CH ₂ ) ₁₀ CN
Experimental Example 5 2-Methylglutaronitrile NCCH (CH ₃ ) CH ₂ CH ₂ CN
Experimental Example 6 Oxydipropionitrile NCCH ₂ CH ₂ —O—CH ₂ CH ₂ CN
Experimental Example 7 3-Methoxypropionitrile CH ₃ —O—CH ₂ CH ₂ CN
Experimental Example 8 Methyl cyanoacetate NCCH ₂ COOCH ₃
Experimental Example 9 Butyl cyanoacetate NCCH ₂ COO (CH ₂ ) ₃ CH ₃

-Evaluation-
(Measurement of potential-current curve)
With respect to the electrolyte solutions for lithium ion batteries of Experimental Examples 1 to 9 and Comparative Example 1 prepared as described above, potential-current curves were measured. A potentiogalvanostat was used for measurement, glassy carbon was used for the working electrode, and a platinum wire was used for the counter electrode. As the reference electrode, (Ag / Ag +) or (Li / Li +) was used. In the measurement, after scanning several times on the positive side and the negative side, the potential was swept from the natural potential in the positive direction or in the negative direction at a speed of 5 mV / sec, and the potential-current curve was measured. The results are shown in FIGS.

As a result, as shown in FIG. 3, the potential window of the electrolytic solution of Experimental Example 1 was 6.9 V with respect to the Li potential (Li / Li ⁺ ) (the judgment criterion of the potential window was 50 μA / cm ^2, and so on). It became. On the other hand, the potential window of Comparative Example 1 using a mixed solvent of ethylene carbonate and dimethyl carbonate is 5.2 V as shown in FIG. 5, and the potential window of the electrolyte solution of Experimental Example 1 is Comparative Example 1. Compared to the electrolyte solution of, it was found that it spreads greatly on the positive side. From this result, when the electrolytic solution of Experimental Example 1 is used, a high potential redox positive electrode active material that exists in the region where the potential for charging exceeds 5.2 V can be used as the positive electrode active material of the lithium ion battery. Thus, a lithium ion battery having high electromotive force and energy density and large capacity can be obtained. For example, in the electrolytic solution of Comparative Example 1, the organic solvent undergoes electrolysis even at the oxidation-reduction potential of Li ₂ CoPO ₄ F or Li ₂ NiPO ₄ F, and these positive electrode oxidizing substances cannot be used. If the electrolytic solution of Example 1 is used, not only Li ₂ CoPO ₄ F or Li ₂ NiPO ₄ F can be used as the positive electrode active material, but also LiCoPO ₄ , LiNiPO _4, etc. can be used.

Further, as shown in FIG. 4, in the electrolytic solutions of Experimental Examples 2 to 9, as in Experimental Example 1, all of the potential windows spread in the positive direction as compared with the electrolytic solution of Comparative Example 1. . From these results, a chain saturated hydrocarbon dinitrile compound (Experimental Examples 1 to 5) in which a nitrile group is bonded to both ends of a chain saturated hydrocarbon compound to ethylene carbonate and dimethyl carbonate, the end of a chain ether compound is obtained. By adding at least one nitrile compound (Experimental Examples 8 and 9) of chain ether nitrile compounds (Experimental Examples 6 and 7) having a nitrile group bonded to at least one of them, the solvent is decomposed to a high potential. It was found that it can exist stably without doing. In particular, the potential window greatly expanded in Experimental Examples 1 to 5 using a branched saturated hydrocarbon dinitrile compound in which a nitrile group was bonded to both ends of a chain saturated hydrocarbon compound as a nitrile compound, and has a branch. Also in Experimental Example 5, it was found that the potential window greatly spreads in the positive direction. In addition, in Experimental Example 6 using oxydipropionitrile NCCH ₂ CH ₂ —O—CH ₂ CH ₂ CN, it was found that the potential window greatly expanded in the positive direction.

(Experimental Examples 10 to 17)
In Experimental Examples 10 to 17, the solvent was various nitrile: ethylene carbonate: diethyl carbonate = 50: 25: 25 (volume ratio), and the electrolyte was LiPF ₆ (lithium hexafluorophosphate) at 1 mol / L in this mixed solvent. What was dissolved in this way was used as the electrolyte solution for lithium ion batteries (however, in Experimental Example 10 in which the nitrile compound was glutaronitrile, LiPF ₆ (lithium hexafluorophosphate) was 0.5 mol / L. ).
The types of nitrile used in each experimental example are as follows.
Experimental Example 10 Glutaronitrile NC (CH ₂ ) ₃ CN
Experimental Example 11 Sevacononitrile NC (CH ₂ ) ₈ CN
Experimental Example 12 Dodecanedinitrile NC (CH ₂ ) ₁₀ CN
Experimental Example 13 2-Methylglutaronitrile NCCH (CH ₃ ) CH ₂ CH ₂ CN
Experimental Example 14 Oxydipropionitrile NCCH ₂ CH ₂ —O—CH ₂ CH ₂ CN
Experimental Example 15 3-Methoxypropionitrile CH ₃ —O—CH ₂ CH ₂ CN
Experimental Example 16 Methyl cyanoacetate NCCH ₂ COOCH ₃
Experimental Example 17 Butyl cyanoacetate NCCH ₂ COO (CH ₂ ) ₃ CH ₃

(Comparative Example 2)
In Comparative Example 2, a mixed solvent of ethylene carbonate: diethyl carbonate = 50: 50 (volume ratio) was used as the organic solvent, and LiPF ₆ was dissolved as a lithium salt in an amount of 1 mol / L to perform electrolysis for a lithium ion battery. A liquid was used.

-Evaluation-
(Measurement of potential-current curve)
For the electrolytic solutions of Experimental Examples 10 to 17 and Comparative Example 2, potential-current curves were measured in the same manner as described above. The results are shown in FIG.
From this figure, it was found that in the electrolytic solutions of Experimental Examples 10 to 17, the potential window spreads in the positive direction as compared with the electrolytic solution of Comparative Example 2. From this result, even when ethylene carbonate and diethyl carbonate are used as solvents, both of the chain saturated hydrocarbon compounds are the same as when ethylene carbonate and dimethyl carbonate are used as solvents (that is, in the case of Experimental Examples 1 to 9). Add at least one nitrile compound among a chain saturated hydrocarbon dinitrile compound having a nitrile group bonded to the terminal, a chain ether nitrile compound having a nitrile group bonded to at least one terminal of the chain ether compound, and a cyanoacetate ester. It was found that the solvent exists stably up to a high potential. In particular, the potential window greatly widened in Examples 10 to 13 using a chain saturated hydrocarbon dinitrile compound in which a nitrile group was bonded to both ends of a chain saturated hydrocarbon compound as a nitrile compound, which has branches. Also in Experimental Example 13, it was found that the potential window greatly spreads in the positive direction. Also, in Experimental Examples 14 and 15 using the chain ether nitrile compound in which the nitrile group was bonded to at least one end of the chain ether compound, it was found that the potential window greatly expanded in the positive direction.

(Experimental Examples 18-25)
In Experimental Examples 18 to 25, the solvent was various nitrile: γ-butyrolactone: dimethyl carbonate = 50: 25: 25 (volume ratio), and the electrolyte was LiPF ₆ (lithium hexafluorophosphate) at 1 mol / L in this mixed solvent. What was melt | dissolved so that it might become was used as the electrolyte solution for lithium ion batteries. Also, in the experimental examples using the adiponitrile as nitrile, the LiPF ₆ was 0.5 mol / L.
The types of nitrile used in each experimental example are as follows.
Experimental Example 18 Glutaronitrile NC (CH ₂ ) ₃ CN
Experimental Example 19 Adiponitrile NC (CH ₂ ) ₄ CN
Experimental Example 20 Sevacononitrile NC (CH ₂ ) ₈ CN
Experimental Example 21 Dodecanedinitrile NC (CH ₂ ) ₁₀ CN
Experimental Example 22 2-Methylglutaronitrile NCCH (CH ₃ ) CH ₂ CH ₂ CN
Experimental Example 23 Oxydipropionitrile NCCH ₂ CH ₂ —O—CH ₂ CH ₂ CN
Experimental Example 24 Methyl cyanoacetate NCCH ₂ COOCH ₃
Experimental Example 25 Butyl cyanoacetate NCCH ₂ COO (CH ₂ ) ₃ CH ₃

(Comparative Example 3)
In Comparative Example 3, a mixed solvent of γ-butyrolactone: dimethyl carbonate = 50: 50 (volume ratio) was used as the organic solvent, and LiPF ₆ was dissolved as a lithium salt at 1 mol / L so as to be used for a lithium ion battery. An electrolyte was used.

-Evaluation-
(Measurement of potential-current curve)
For the electrolytic solutions of Experimental Examples 18 to 25 and Comparative Example 3, potential-current curves were measured in the same manner as described above. The results are shown in FIG.
From this figure, it was found that also in the electrolyte solutions of Experimental Examples 18 to 25, the potential window greatly expanded in the positive direction as compared with the electrolyte solution of Comparative Example 3. From this result, even when dimethyl carbonate and γ-butyrolactone, which is a cyclic carboxylic acid ester, are used as solvents instead of ethylene carbonate, which is a cyclic carbonate, nitrile groups are bonded to both ends of the chain saturated hydrocarbon compound. It was found that by adding the chain saturated hydrocarbon dinitrile compound, the solvent exists stably to a high potential. Moreover, it was found that, among the chain-type saturated hydrocarbon dinitrile compounds, not only in Experimental Examples 18 to 21 which are linear molecules, but also in Experimental Example 22 having a branch, the potential window greatly expands in the positive direction. Further, in Experimental Example 23 using a chain ether nitrile compound in which a nitrile group is bonded to both ends of the chain ether compound, and in Experimental Examples 24 and 25 using cyanoacetate, the potential window is greatly widened in the positive direction. I understood that.

(Experimental examples 26 to 31)
In Experimental Examples 26 to 31, the solvent was various nitriles: dimethyl carbonate = 50: 50 (volume ratio), and the electrolyte was LiPF ₆ (lithium hexafluorophosphate) 1 mol / L in this mixed solvent (Experimental Examples 30, 31). In this case, an electrolyte solution for a lithium ion battery was dissolved so as to be 0.1 mol / L). The types of nitrile used in each experimental example are as follows.
Experimental Example 26 Glutaronitrile NC (CH ₂ ) ₃ CN
Experimental Example 27 Sebacononitrile NC (CH ₂ ) ₈ CN
Experimental Example 28 Dodecanedinitrile NC (CH ₂ ) ₁₀ CN
Experimental Example 29 2-Methylglutaronitrile NCCH (CH ₃ ) CH ₂ CH ₂ CN
Experimental Example 30 Oxydipropionitrile NCCH ₂ CH ₂ —O—CH ₂ CH ₂ CN
Experimental Example 31 Methyl cyanoacetate NCCH ₂ COOCH ₃

(Comparative Example 4)
In Comparative Example 4, LiPF ₆ as a lithium salt was dissolved in dimethyl carbonate as an organic solvent so as to be 1 mol / L to obtain an electrolytic solution for a lithium ion battery.

-Evaluation-
(Measurement of potential-current curve)
For the electrolytic solutions of Experimental Examples 26 to 31 and Comparative Example 4, potential-current curves were measured in the same manner as described above. The results are shown in FIG.
From this figure, in the electrolytic solutions of Experimental Examples 26 to 31 in which dimethyl carbonate alone was added in addition to the nitrile compound as the solvent, the potential window was positive in comparison with the electrolytic solution of Comparative Example 4 in which dimethyl carbonate was the sole solvent. I understood that it spreads. It was also found that the solvent was stably present up to a high potential by adding a chain saturated hydrocarbon dinitrile compound having a nitrile group bonded to both ends of the chain saturated hydrocarbon compound (Experimental Examples 26 to 29). Furthermore, it was found that, among the chain-type saturated hydrocarbon dinitrile compounds, not only in Experimental Examples 26 to 28 which are linear molecules, but also in Experimental Example 29 having a branch, the potential window greatly expands in the positive direction. Furthermore, in Example 30 using a chain ether nitrile compound in which a nitrile group was bonded to both ends of the chain ether compound, the potential window was greatly expanded, and in Example 31 using cyanoacetate, the potential window was expanded.

(Experimental examples 32, 33)
In Experimental Examples 32 and 33, the solvent was various nitrile: propylene carbonate = 50: 50 (volume ratio), and the electrolyte was dissolved in LiPF ₆ (lithium hexafluorophosphate) at 1 mol / L in this mixed solvent. This was used as an electrolyte for lithium ion batteries. The types of nitrile used in each experimental example are as follows.
Experimental Example 32 Sevacononitrile NC (CH ₂ ) ₈ CN
Experimental Example 33 Dodecanedinitrile NC (CH ₂ ) ₁₀ CN

(Comparative Example 5)
In Comparative Example 5, an electrolyte solution for a lithium ion battery was prepared by dissolving LiPF ₆ as a lithium salt in propylene carbonate as an organic solvent so as to be 1 mol / L.

-Evaluation-
(Measurement of potential-current curve)
For the electrolytic solutions of Experimental Examples 32 and 33 and Comparative Example 5, potential-current curves were measured in the same manner as described above. The results are shown in FIG.
From this figure, in the electrolytic solutions of Experimental Examples 32 and 33 in which propylene carbonate alone was added in addition to the nitrile compound as a solvent, the potential window was positive in comparison with the electrolytic solution of Comparative Example 5 in which propylene carbonate was the sole solvent. It was found that it spreads greatly. It was also found that the solvent was stably present up to a high potential by adding a chain saturated hydrocarbon dinitrile compound having nitrile groups bonded to both ends of the chain saturated hydrocarbon compound.

(Experimental examples 34 to 36)
In Experimental Examples 34 to 36, the solvent was various nitriles: γ-butyrolactone = 50: 50 (volume ratio), and the electrolyte was dissolved in this mixed solvent so that LiPF ₆ (lithium hexafluorophosphate) was 1 mol / L. This was used as an electrolyte for a lithium ion battery. The types of nitrile used in each experimental example are as follows.
Experimental Example 34 Glutaronitrile NC (CH ₂ ) ₃ CN
Experimental Example 35 Sevacononitrile NC (CH ₂ ) ₈ CN
Experimental Example 36 Dodecanedinitrile NC (CH ₂ ) ₁₀ CN

(Comparative Example 6)
In Comparative Example 6, an electrolyte solution for a lithium ion battery was prepared by dissolving LiPF ₆ as a lithium salt in γ-butyrolactone as an organic solvent so as to be 0.1 mol / L.

-Evaluation-
(Measurement of potential-current curve)
For the electrolytic solutions of Experimental Examples 34 to 36 and Comparative Example 6, potential-current curves were measured in the same manner as described above. The results are shown in FIG.
From this figure, in the electrolytic solutions of Experimental Examples 34 to 36 in which γ-butyrolactone alone was added in addition to the nitrile compound as a solvent, the potential window was larger than that of the electrolytic solution of Comparative Example 6 in which γ-butyrolactone was the sole solvent. It turns out that it spreads greatly in the positive direction. It was also found that the solvent was stably present up to a high potential by adding a chain saturated hydrocarbon dinitrile compound having nitrile groups bonded to both ends of the chain saturated hydrocarbon compound.

(Experimental Examples 37 to 39)
In Experimental Examples 37 to 39, the solvent was various nitrile: ethylene carbonate: γ-butyrolactone = 50: 25: 25 (volume ratio), and the electrolyte was LiPF ₆ (lithium hexafluorophosphate) at 1 mol / L in this mixed solvent. What was melt | dissolved so that it might become was used as the electrolyte solution for lithium ion batteries. The types of nitrile used in each experimental example are as follows.
Experimental Example 37 Sevacononitrile NC (CH ₂ ) ₈ CN
Experimental Example 38 2-Methylglutaronitrile NCCH (CH ₃ ) CH ₂ CH ₂ CN
Experimental Example 39 Oxydipropionitrile NCCH ₂ CH ₂ —O—CH ₂ CH ₂ CN

(Comparative Example 7)
In Comparative Example 7, an electrolyte solution for a lithium ion battery was prepared by dissolving LiPF ₆ as a lithium salt in ethylene carbonate: γ-butyrolactone = 50: 50 (volume ratio) as an organic solvent so as to be 1 mol / L.

-Evaluation-
(Measurement of potential-current curve)
For the electrolytic solutions of Experimental Examples 37 to 39 and Comparative Example 7, potential-current curves were measured in the same manner as described above. The results are shown in FIG.
From this figure, in the electrolytic solutions of Experimental Examples 37 to 39 in which ethylene carbonate, which is a cyclic carbonate, and γ-butyrolactone, which is a cyclic carboxylic acid ester, are added as solvents in addition to the nitrile compound, the nitrile compound is not added. Compared with the electrolyte solution of Example 7, it was found that the potential window greatly expanded in the positive direction and the negative direction. It was also found that the solvent was stably present up to a high potential by adding a chain saturated hydrocarbon dinitrile compound having nitrile groups bonded to both ends of the chain saturated hydrocarbon compound. Furthermore, it was found that, among the chain saturated hydrocarbon dinitrile compounds, not only in Experimental Example 37, which is a linear molecule, but also in Experimental Example 38 having branches, the potential window greatly spreads in the positive and negative directions. Furthermore, also in Experimental Example 39 using a chain ether nitrile compound in which a nitrile group was bonded to both ends of the chain ether compound, the potential window greatly increased in the positive and negative directions.

(Experimental Examples 40 to 44)
In Experimental Examples 40 to 44, the solvent was sebacononitrile (adiponitrile in Experimental Example 42): ethylene carbonate: dimethyl carbonate = 50: 25: 25 (volume ratio), and various electrolytes were dissolved in this mixed solvent to 1 mol / L. This was used as an electrolyte for a lithium ion battery. The types of electrolyte used in each experimental example are as follows.
Experimental Example 40 LiPF ₆
Experimental Example 41 LiTFSI
Experimental Example 42 LiTFSI
Experimental Example 43 LiBF ₄
Experimental Example 44 LiBETI

(Experimental example 45)
In Experimental Example 45, a solvent in which sebacononitrile, ethylene carbonate (EC), and dimethyl carbonate (DMC) were mixed at a volume ratio of 50:25:25 was used as the organic solvent, and LiPF ₆ ( Lithium hexafluorophosphate) was dissolved at 0.05 mol / L and LiTFSI (lithium bis (trifluoromethanesulfonyl) imide) was dissolved at 1.0 mol / L to obtain an electrolyte for a lithium ion battery.

(Experimental example 46)
In Experimental Example 46, a solvent in which butyl cyanoacetate, ethylene carbonate (EC), and dimethyl carbonate (DMC) were mixed at a volume ratio of 50:25:25 as an organic solvent, and LiTFSI as a lithium salt was used. (Lithium bis (trifluoromethanesulfonyl) imide) was dissolved at 1.0 mol / L to obtain an electrolytic solution for a lithium ion battery.

(Experimental example 47)
In Experimental Example 47, a solvent in which butyl cyanoacetate, ethylene carbonate (EC), and dimethyl carbonate (DMC) were mixed at a volume ratio of 50:25:25 as an organic solvent, and LiBF as a lithium salt was used. ₄ (lithium tetrafluoroborate) was dissolved at 1.0 mol / L to obtain an electrolyte for a lithium ion battery.

(Comparative Examples 8 to 10)
In Comparative Examples 8 to 10, various lithium salts were added instead of LiPF ₆ which is the lithium salt in Comparative Example 1. That is, various lithium salts (LiTFSI in Comparative Example 8, LiBF ₄ in Comparative Example 9, LiBETI in Comparative Example 10) at 1 mol / L as an organic solvent, ethylene carbonate: dimethyl carbonate = 50: 50 (volume ratio). It was made to melt | dissolve and it was set as the electrolyte solution for lithium ion batteries.

-Evaluation-
(Measurement of potential-current curve)
For the electrolytic solutions of Experimental Examples 40 to 44, Comparative Example 1 and Comparative Examples 8 to 10, potential-current curves were measured in the same manner as described above. The results are shown in FIG. In addition, Table 1 shows the value of the potential obtained from this figure when the current density is 50 μA / cm ² .
From FIG. 12 and Table 1, in addition to the nitrile compound as a solvent, in the electrolytic solutions of Experimental Examples 40 to 44 in which ethylene carbonate, which is a cyclic carbonate, and dimethyl carbonate, which is a chain carbonate, are added as solvents, Regardless, it was found that the potential window greatly expanded in the positive direction as compared with the electrolytic solutions of Comparative Example 1 and Comparative Examples 8 to 10 in which no nitrile compound was added.
Further, the potential window of the electrolytic solution of Experimental Example 45 is 6.6 V (see FIG. 13), the potential window of the electrolytic solution of Experimental Example 46 is 5.4 V (see FIG. 14), and the potential window of the electrolytic solution of Experimental Example 47 is It became 6.1V (refer FIG. 15), and it turned out that all have spread to the positive side.

Similarly, Table 2 shows the electrode potentials at the predetermined current density obtained from the potential-current curves for the electrolytes of other experimental examples and comparative examples in which the lithium salt is LiPF ₆ . From this table, 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 can be seen that the potential window widens in the positive direction when at least one nitrile compound of acetic acid ester and at least one of cyclic carbonic acid ester, cyclic carboxylic acid ester and chain carbonic acid ester are contained.

<Influence of nitrile addition amount>
In order to examine the influence of the addition amount of nitrile in the electrolytic solution of the present invention, a predetermined amount of sebacononitrile was added to a mixed solvent of ethylene carbonate: dimethyl carbonate = 1: 1 (volume ratio), and a potential-current curve was measured. Incidentally, the electrolyte was added LiPF ₆ as a 1M (However, in the case of sebaconitrile 100% by volume, it was 0.1M for dissolution of 1M was difficult). The results are shown in FIG. From this figure, it was found that the amount of sebacononitrile added had the effect of expanding the potential window even at 1% by volume, and the potential window expanded in the higher potential direction as the amount added increased. However, when 100% by volume of sebacononitrile is used, the solubility of LiPF ₆ that is an electrolyte is lowered and the viscosity is also increased. Therefore, there is a problem that the conductivity is lowered and the internal resistance of the battery is increased. For this reason, the preferable amount of sebacononitrile added as an electrolyte for a lithium battery is 1% by volume or more and less than 100% by volume, more preferably 5% by volume or more and less than 90% by volume, and most preferably 30% by volume or more and 70% by volume. %.

  As described above, in the potential-current curve for the electrolytic solution of the experimental example, it was found that the potential window greatly expanded in the positive direction by adding the nitrile compound to the organic solvent.

<Measurement of battery characteristics>
Using the electrolytic solution of the above experimental example, Li _1-x CoO ₂ , Li _1-x NiO ₂ , Li _1-x Mn ₂ O _4, 2-1-3 lithium manganate, and composites thereof as the positive electrode active material And Li _1−x FePO ₄ , Li _1−x MnPO ₄ , Li _2−y FePO ₄ F, Li _2−y MnPO ₄ F (wherein x is a number from 0 to 1 and y is 0) A lithium ion battery according to the present invention by using the above-mentioned number of 2 or less, including those in which a part of Co, Ni, Mn and Fe is doped with other metal atoms including Li) Is configured. Examples of the metal atom to be doped include one or more of Mg, Al, Ti, V, Cu, Zn, Zr, Nb, and Mo.
As a specific example, for the positive electrode on which LiCoO ₂ is supported as the positive electrode active material, the electrolyte solution for lithium ion batteries of Experimental Example 41 (that is, EC: DMC: sebacononitrile = 25: 25: 50, lithium salt in capacity ratio) LiTFSI (1.0 mol / L of lithium bis (trifluoromethanesulfonyl) imide) was used to measure the potential-current curve. The potential-current curve was also measured for the cathode for a lithium ion battery supporting Li ₄ Ti ₅ O ₁₂ and the cathode for a lithium ion battery supporting LiCoPO ₄ which is an olivine phosphate-based positive electrode active material. A potentiogalvanostat was used for the measurement. Further, (Ag / Ag ⁺ ) was used as the reference electrode. In the measurement, after scanning several times on the positive side and the negative side, the potential was swept from the natural potential in the positive direction or in the negative direction at a speed of 0.5 mV / sec, and the potential-current curve was measured.

As a result, as shown in FIG. 17, Li ₄ Ti ₅ O ₁₂ as a negative electrode for a lithium battery, and LiCoO ₂ and LiCoPO ₄ as positive electrodes for a lithium battery, both lithium (0) and lithium ions A nearly reversible current associated with redox was observed. From this result, it was found that by using the lithium ion battery electrolyte of Experimental Example 41, smooth charge / discharge between lithium (0) and lithium ions was possible.

<Production of lithium ion battery>
An example of producing a lithium ion battery using the battery container of the present invention is shown below. That is, first, as shown in FIG. 18, 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 container.

Next, as shown in FIG. 19, the positive electrode can 11 is filled with a titanium or nickel spacer 13, a positive electrode active material pellet 14 containing an oxide-based positive electrode active material, and a separator 15. The positive electrode active material pellet 14 is, for example, a LiCoO ₂ 70 by weight part, the glassy carbon powder 25 parts by weight as a conductive additive were mixed in a mortar, further polytetrafluoroethylene (PTFE) powder was added 5 parts by weight To obtain a disk-shaped pellet by press molding. 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. Then, after putting the nitrile-containing electrolyte in the positive electrode can 11, the negative electrode cap 12 is placed via an insulating gasket 19 and sealed to form a lithium ion battery. Here, as the nitrile-containing electrolytic solution, for example, a solution obtained by dissolving LiBF _{4 in} a mixed solvent of sebacononitrile: ethylene carbonate: dimethyl carbonate = 50: 25: 25 (volume%) so as to be 1 mol / L can be used. .

In the lithium ion battery configured as described above, the electrolytic solution has a wide potential window and exists stably even at 5 V with respect to the Li / Li ⁺ electrode. For this reason, even when the overvoltage becomes as high as 5 V with respect to the Li / Li ⁺ electrode during charging, the electrolytic solution is difficult to be decomposed or altered.

In the lithium ion battery of the present invention, Li _1-x CoO ₂ , Li _1-x NiO ₂ , Li _1-x Mn ₂ O _4, 2-1-3 lithium manganate, a composite thereof, and Li _{1 -x FePO 4, Li 1-x} MnPO 4, Li 2-y FePO 4 F, Li 2-y MnPO 4 F ( although the x is a number of 0 or more and 1 or less, the number of the y is 0 to 2 In which a part of the Co, Ni, Mn, and Fe is doped with other metal atoms including Li) and a composite thereof, and the potential of the positive electrode is applied to the Li / Li ⁺ electrode. On the other hand, a substance (for example, LiMnPO ₄ system or LiNi _0.5 Mn _1.5 O ₄ system) that has a high value of about 5 V and does not decompose or change even when Li is almost desorbed from the positive electrode is used. be able to. Examples of the metal atom to be doped include one or more of Mg, Al, Ti, V, Cu, Zn, Zr, Nb, and Mo.
In general, a layered oxide-based positive electrode active material has a high potential far exceeding 5 V, and when Li is almost eliminated, it often generates heat and decomposes by generating oxygen (for example, LiCoO ₂ or LiNiO _2). And a pure substance in which the metal element is not substituted at all by other elements). On the other hand, even if Li is desorbed, the active material itself is not decomposed, but the surface of the active material reacts with the electrolyte and changes in quality, and the positive electrode active material that inhibits Li ion conduction is inhibited. In the case of a substance (for example, a substance in which a metal element is not substituted with another element such as LiMnPO ₄ or LiNi _0.5 Mn _1.5 O ₄ ), there is room for improvement. As shown in FIG. 20, even when Li is desorbed from the positive electrode active material at 5 V or more, it does not decompose or change quality, but the active material surface reacts with the electrolyte and changes quality, thereby inhibiting Li ion conduction. The positive electrode material particles 1 that are generated are microencapsulated with a high potential positive electrode active material 2 and, as shown in FIG. 21, they are not decomposed or deteriorated even if Li is desorbed at 5 V or more. The positive electrode material powder 3 that reacts with the electrolyte and changes its quality and inhibits Li ion conduction is mixed in the high-potential positive electrode active material 4 and included, or as shown in FIG. As described above, even if Li is desorbed, it does not decompose or change in quality, but the active material surface reacts with the electrolytic solution and changes in quality, and around the positive electrode material particles 5 that inhibit Li ion conduction, has a high potential resistance. By wrapping with positive electrode active material fine powder 6, The positive electrode active material to a high potential to exist stably, may be a lithium ion battery that can withstand high voltage.

Examples of such a high potential positive electrode active material include a phosphate positive electrode active material having an olivine crystal structure and an olivine fluoride positive electrode active material. Specific examples of the phosphate-based positive electrode active material include Li _1-x FePO ₄ (x = 0 to 1). 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).
The oxidation-reduction potential of a phosphate-based positive electrode active material having an olivine-type crystal structure, unlike the above-mentioned oxide-based materials, is less exothermic when it is less than 300 ° C., and oxygen is not generated, and safety is high.

As olivine fluoride-based positive electrode active materials, Li _2−x NiPO ₄ F (x = 0 to 2) and Li _2−x CoPO ₄ F (x = 0 to 2) are known, and other Li _{2 -x MnPO 4 F (x = 0~2} ), Li 2-x FePO 4 F (x = 0~2), or a mixture of lithium manganese phosphate fluoride and manganese phosphate sodium fluoride _{(Na 2- x} Li _x MnPO ₄ F: x = 0 to 2).
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.

  Similar to the olivine system, the oxidation-reduction potential of the olivine fluoride-based positive electrode active material is different from that of the above oxide system. The impact 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).

Further, by using a structure using a lithium ion conductor that can withstand a high potential instead of the high-potential positive electrode active material 2 in FIG. 20, the positive electrode active material stably exists up to a higher potential, and is high. It can be set as the lithium ion battery which can endure an electric potential. Similarly, by using a lithium ion conductor that can withstand a high potential in place of the high-potential-resistant positive electrode active material 4 shown in FIG. 21, the positive electrode active material stably exists up to a higher potential, and a high potential. It can be set as the lithium ion battery which can endure. Furthermore, by using a lithium ion conductor that can withstand a high potential instead of the high-potential-resistant positive electrode active material fine powder 6 shown in FIG. 22, the positive electrode active material is stably present up to a higher potential. It can be set as the lithium ion battery which can endure an electric potential.
Examples of such a high withstand voltage lithium ion conductor include lithium titanate (Li ₄ Ti ₅ O ₁₂ ) and Li ₂ S · P ₂ S ₅ based solid electrolytes such as (100-x) Li ₂ S · xP. ₂ S ₅ (x = _10~40) can be given complex, etc., such as.

(Reference example)
As a reference example, the charging / discharging characteristics of lithium ions shown below are set to 10 C at normal charging and starting at 0.01 C, and the results measured as constant potential charging after reaching 6 V (vs Li / Li +) are shown in FIG. Show.
-Working electrode LiFePO ₄ / Conductive aid glassy carbon powder / Binder PTFE
・ Counter electrode Li metal ・ Electrolyte 1.0M LiBF ₄ / Sebacononitrile: EC: DMC = 50: 25: 25 (capacity ratio)
・ Cell Coin Cell Ni 2032 type ・ Potential sweep range 2.5-6.0V (vs Li / Li +)

  As a result, as shown in FIG. 23, it was found that the discharge capacities are almost the same in both charging methods, and even charging at 6V can sufficiently withstand practical use.

  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.

Claims (1)

In a lithium ion battery in which a positive electrode including a positive electrode active material and a negative electrode including a negative electrode active material are in contact with an electrolyte solution in which a lithium salt is dissolved in an organic solvent,
The positive electrode active material is Li _1-x CoO ₂ , Li _1-x NiO ₂ , Li _1-x Mn ₂ O _4, 2-1-3 lithium manganate, and a composite thereof, and Li _1-x FePO. ₄ , Li _1-x MnPO ₄ , Li _2-y FePO ₄ F, Li _2-y MnPO ₄ F) (wherein x is a number from 0 to 1 and y is a number from 0 to 2) , Including a part of the Co, Ni, Mn and Fe doped with other metal atoms including Li) and a composite thereof.
The organic solvent of the electrolytic solution has a chain saturated hydrocarbon dinitrile compound in which a nitrile group is bonded to both ends of the chain saturated hydrocarbon compound, and a chain in which a nitrile group is bonded to at least one end of the chain ether compound. A lithium ion battery comprising at least one nitrile compound of the formula ether nitrile compound and cyanoacetate and at least one of cyclic carbonate, cyclic carboxylic acid ester and chain carbonate.

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