JP2011070773A - Lithium ion battery electrode - Google Patents

Abstract

Provided is an electrode for a lithium ion battery in which an electrolyte solution is not easily decomposed even at a high potential with a wide potential window, and a material that extends to a positive potential region with high charge / discharge can be used as a positive electrode active material. .
An electrode for a lithium ion battery according to the present invention is an electrode in which the total of nitrogen in the form of organic nitrogen and nitrogen in the form of ammonium salt is 2 atm% or more when surface analysis is performed by XPS. Further, phosphorus is present in an amount of 1 atm% or more, and the main component of phosphorus may be in the form of PF bond, or boron is present in an amount of 1 atm% or more, and the main component of boron is in the form of BF bond. There may be.
[Selection figure] None

Description

  The present invention relates to an electrode for a lithium ion battery in which a potential window is wide and an electrolytic solution is hardly decomposed even at a high potential.

A conventional lithium ion battery uses lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), a solid solution thereof, lithium manganate (LiMn ₂ O ₄ ) or the like as a positive electrode, and consists of carbon such as graphite as a negative electrode. A negative electrode material is used. An electrolytic solution in which a liquid organic compound such as ethylene carbonate or propylene carbonate is dissolved in a solvent and a lithium salt as a solute is used.

In order to further increase the energy density of such a lithium ion battery, a search for a new positive electrode active material is underway. As such a positive electrode active material, for example, a positive electrode active material having an olivine type crystal structure such as LiNiPO ₄ , LiCoPO ₄ , Li ₂ NiPO ₄ F, and Li ₂ CoPO ₄ F has been proposed (Patent Document 1 and Patent Document). 2). If these positive electrode active materials are used in a lithium ion battery, a battery with a large electromotive force is obtained. Therefore, theoretically, a lithium ion battery having a large energy density should be obtained.

Patent No. 3624205 Patent No. 3631202

  However, in the positive electrode active material having the above olivine type crystal structure, since the charging reaction occurs at a very high potential, the electrolytic solution is decomposed and deteriorated, and the electromotive force having a high angle cannot be exhibited. It has been difficult to put high-density batteries into practical use. In addition, there has been a problem that the conductive assistant, the current collector, and the electrode case constituting the positive electrode are corroded by a high potential during charging.

  The present invention has been made in view of the above-described conventional situation, and an object to be solved is to provide an electrode for a lithium ion battery which is difficult to decompose even at a high potential and has excellent corrosion resistance.

  In order to solve the above-described conventional problems, the present inventors considered forming a corrosion-resistant film on the electrode surface as a pretreatment of the electrode for a lithium ion battery. As a result, it has been found that the potential window is remarkably widened by applying a positive voltage to the electrode in an electrolyte for a lithium ion battery using an organic solvent having a nitrile group. Furthermore, when the surface analysis of the electrode with the potential window widened by such treatment was performed, a film containing nitrogen in the form of organic nitrogen and nitrogen in the form of ammonium salt was formed. The present inventors have found that the above problems can be solved by forming the battery electrode, and have completed the present invention.

  That is, the lithium ion battery electrode according to the first aspect of the present invention forms a film in which the total of nitrogen in the form of organic nitrogen and nitrogen in the form of ammonium salt is 2 atm% or more when surface analysis is performed by XPS. It is characterized by being.

The present inventors have also found that the presence of phosphorus mainly composed of PF bonds in the film makes the electrolyte difficult to decompose even at a high potential and is excellent in corrosion resistance.
That is, the electrode for a lithium ion battery according to the second aspect of the present invention is the electrode for a lithium ion battery according to the first aspect, and when surface analysis is performed by XPS, phosphorus is present at 1 atm% or more. The main component is a form of PF bond.

Furthermore, the present inventors have found that the presence of boron mainly composed of BF bonds in the coating makes the electrolytic solution difficult to decompose even at a high potential, and is excellent in corrosion resistance.
That is, the lithium ion battery electrode according to the third aspect of the present invention is the lithium ion battery electrode according to the first aspect, and when surface analysis is performed by XPS, boron is present in an amount of 1 atm% or more. The main component is in the form of a BF bond.

The electrode for a lithium ion battery of the present invention includes not only a positive electrode for a lithium ion battery but also a negative electrode for a lithium ion battery.
The positive electrode for a lithium ion battery includes a current collector and a positive electrode active material, and a conductive assistant such as carbon and a binder such as PTFE may be mixed in the positive electrode active material. It is preferable that a film is formed on all surfaces of the current collector, the positive electrode active material, and the conductive additive, but a film is formed on one or two types of the current collector, the positive electrode active material, and the conductive auxiliary agent. Also good.
The negative electrode for a lithium ion battery may include a current collector and a negative electrode active material, and the negative electrode active material may be mixed with a conductive additive such as carbon and a binder such as PTFE. It is preferable that a film is formed on all surfaces of the current collector, the positive electrode active material, and the conductive additive, but a film is formed on one or two types of the current collector, the positive electrode active material, and the conductive auxiliary agent. Also good.

<The manufacturing method of the electrode for lithium ion batteries of this invention>
The lithium ion battery electrode of the present invention is immersed in a pretreatment electrolyte in which a lithium salt is dissolved in an organic solvent containing 1% by volume or more of a nitrile compound (immersion treatment step), and is immersed in the pretreatment electrolyte. In this state, it can be easily manufactured by applying a positive voltage to the electrode (positive voltage processing step). When the surface analysis by XPS is performed, the electrode obtained in this way is formed with a film in which the total of nitrogen in the form of organic nitrogen and nitrogen in the form of ammonium salt is 2 atm% or more. The window is large and spreads in the positive direction. For this reason, in an electrode that is not subjected to pretreatment, an electrolytic solution that decomposes at 5.2 V (vs. Li / Li ⁺ ) or lower (for example, ethylene carbonate and dimethoxy carbonate, which are often used as an electrolytic solution for lithium ion batteries) In the case of using a mixed solvent and the like, the electrolytic solution hardly decomposes at a potential of 5.2 V or higher. Therefore, a high potential redox positive electrode active material that exists in a region where the potential for charging exceeds 5.2 V (vs. Li / Li ⁺ ) can be used as the positive electrode active material. The electromotive force and energy density can be made extremely high.

In addition, it is also preferable to use the electrode for lithium ion batteries of this invention for the lithium ion battery using the electrolyte solution in which lithium salt melt | dissolved in the organic solvent containing less than 10 volume% of nitrile compounds. In this case, the effect of expanding the potential window even during charging is exhibited by the nitrile compound, and it is expected that a lithium ion battery with higher durability will be obtained.
Further, the lithium ion battery electrode of the present invention is also applicable as an electrolyte for a sodium ion battery using the NaPF _6, NaBF _4, NaTFSI like to the electrolyte.

  The organic solvent of the electrolyte used in the dipping process is 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 is bonded to at least one terminal of the chain ether compound. It is preferable that at least one nitrile compound is included among the chain ether nitrile compound and the cyanoacetate ester.

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.

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.

  Furthermore, 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.

Moreover, it is preferable that the lithium salt in the pretreatment electrolytic solution contains at least one of LiPF ₆ , LiBF ₄ , LiTFSI, and LiBETI.

  Furthermore, the concentration of the nitrile compound in the organic solvent used for the electrolytic solution in the immersion treatment step is 1% by volume or more. When the concentration of the nitrile compound is less than 1% by volume, the effect of expanding the potential window is reduced. Preferably it is 5 volume% or more, More preferably, it is 10 volume% or more, More preferably, it is 30 volume% or more, Most preferably, it is 70 volume% or more.

When the electrode for a lithium ion battery of the present invention is used as an electrolyte for a lithium ion battery, the potential window is wide, so that the potential for charging exists in a region exceeding 5 V (vs. Li / Li ⁺ ). A redox positive electrode active material can be used. For this reason, it can be set as a battery with a large electromotive force and high energy density.

The positive voltage applied to the electrode in the positive voltage application step is preferably a potential higher than the potential set at the time of charging when incorporated in the lithium ion battery. Specifically, it is preferable to exceed 6 V with respect to the (Li / Li ⁺ ) reference electrode. According to the test results of the inventors, when the positive voltage applied to the electrode exceeds 6 V with respect to the (Li / Li ⁺ ) reference electrode, the potential window dramatically increases in the electrolyte for the lithium ion battery. It becomes possible to use a high potential redox positive electrode active material. Particularly preferred is 6.2 V or more, more preferred is 6.5 V or more, and most preferred is 7 V or more.

A lithium battery electrode of the present invention as a positive electrode active material when used in the positive electrode, for _{example, Li 2 CoPO 4 F, Li} 2 NiPO 4 F, LiCoPO 4, LiNiPO 4 , and the like. 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.
These positive electrode active materials have high energy density and can be a lithium ion battery having a large capacity. For example, Li ₂ CoPO ₄ F is predicted to have a theoretical energy density that is at least twice that of LiCoO ₂ as a positive electrode active material. If the potential density can be sufficiently exhibited, a lithium-ion battery having a large capacity can be produced. be able to. In addition, since the potential at which Li ₂ CoPO ₄ F is oxidized extends to a high potential region, a battery with high electromotive force can be obtained. Furthermore, Li ₂ CoPO ₄ F is excellent in thermal stability, and it is known from the thermal analysis results that it does not show an exothermic reaction even at a high temperature of 400 ° C., and it is possible to prevent the battery temperature from rising.

  Examples in which the lithium ion battery electrode of the present invention is embodied will be described in more detail below.

(Example 1-1 to Example 1-6)
-Preparation of electrolyte for pretreatment As a solvent, a mixture of sebacononitrile, ethylene carbonate (EC), and dimethyl carbonate (DMC) in a volume ratio of 50:25:25 was used, and a lithium salt was used for this. LiPF ₆ (lithium hexafluorophosphate) was dissolved to 1 mol / L to obtain a pretreatment electrolyte.

・ Immersion treatment process and positive voltage treatment process The pretreatment electrolyte prepared in this way is put into a glass cell for electrochemical measurement, a glassy carbon electrode (hereinafter abbreviated as “GC electrode”) is immersed as an electrode, and a platinum wire as a counter electrode , And using (Li / Li ⁺ ) as a reference electrode, a natural potential to a predetermined potential (7 V in Example 1-1, 6.5 V in Example 1-2, 6.2 V in Example 1-3) The potential operation (scanning speed 5 mV / sec) was performed up to 6 V in Example 1-4, 5.5 V in Example 1-5, and 5 V in Example 1-6. Then, the GC electrode was pulled up and washed with DMC to obtain lithium ion battery electrodes of Examples 1-1 to 1-6.

(Example 2)
In Example 2, as a pretreatment electrolyte, LiPF ₆ (lithium hexafluorophosphate) as a lithium salt was dissolved in sebacononitrile to a concentration of 0.1 mol / L to obtain an electrolyte. In the positive voltage processing step, the potential operation was performed up to 8 V with respect to the reference electrode (Li / Li ⁺ ). Other processing conditions are the same as those in Example 1-1, and a description thereof will be omitted.

(Comparative Example 1)
In Comparative Example 1, the GC electrode was simply immersed in the pretreatment electrolyte used in Example 1 for 3 hours, pulled up without performing a positive voltage treatment step, washed with DMC, and dried. It is.

(Comparative Example 2)
Comparative Example 2 is a GC electrode that has not been subjected to any treatment.

-Evaluation-
(Measurement of potential-current curve)
The electrodes of Examples 1-1 to 1-6, Example 2, Comparative Example 1 and Comparative Example 2 obtained as described above were mixed with ethylene carbonate (EC): dimethoxy carbonate (DMC) = 1: 1. It was immersed in a solvent and a potential-current curve was measured. A platinum wire was used as the counter electrode, and (Li / Li ⁺ ) was used as the reference electrode.

  As a result, as shown in FIG. 1, Comparative Example 1 which is a GC electrode simply immersed in the pretreatment electrolytic solution was almost the same as Comparative Example 2 which was an untreated GC electrode, whereas 6 V It was found that the potential window of the CG electrodes of Examples 1-1 to 1-3 and Example 2 in which the positive voltage treatment process was performed up to a potential exceeding 6 V was dramatically expanded to 6 V or more.

(Measurement of cyclic voltammogram for pretreatment electrolyte)
In order to investigate the change of the electrode surface in the positive voltage treatment step, the pretreatment electrolyte solution used in Example 1 (that is, sebacononitrile: ethylene carbonate (EC): dimethyl carbonate (DMC) = 50: 25: 25 (volume ratio) , LiPF ₆ (lithium hexafluorophosphate) of 1 mol / L), a cyclic voltammogram from near natural potential to 8.1 V was measured. The scan speed is 5 mV / sec. As a result, as shown in FIG. 2, during the first sweep in the positive direction, after a slight oxidation current flows around 5.2V, a large oxidation current flows after 6V, but in the second positive direction. During the sweep, the oxidation current near 5.2V almost disappeared, and the current after 6V became smaller. From this, it was suggested that by performing the positive voltage treatment step in the pretreatment electrolyte, some kind of corrosion-resistant film was formed, which caused the potential window to be widened.

(Measurement of XPS)
In order to investigate the formation of the corrosion-resistant film suggested from the measurement result of the cyclic voltammogram of the pretreatment electrolyte, the electrode of Example 1-1 was subjected to surface analysis by X-ray photoelectron spectroscopy (XPS). XPS is a measurement method in which information on the type, valence, and bonding state of elements existing on the surface is obtained by irradiating the surface of the sample with soft X-rays and measuring the energy of photoelectrons emitted from the surface. Since the mean free path of photoelectrons is several nm, the detection region in the depth direction of the surface analysis by XPS is several nm, so that analysis on the extreme surface can be performed. The measurement conditions are as follows.
Measuring device: Quantera SXI (PHI)
Excitation X-ray: monochromatic AlKα _1,2 line
X-ray diameter: 200 μm
Photoelectron escape angle: 45 ° (inclination of detector with respect to sample surface)
Pretreatment method: Sampling and transport of the sample to the apparatus were performed in an argon atmosphere.
Data processing: Smoothing was performed by 9-point smoothing, and horizontal axis correction was performed with the C1 _S main peak at 284.6 eV.

-Result of XPS measurement of Example 1-1 From the result of the wide scan shown in the uppermost part of Fig. 3, it was found that carbon, oxygen, nitrogen, fluorine and phosphorus were present as shown in Table 1 below. Lithium was below the detection limit. Moreover, the result of the state analysis of each element by narrow scan is shown in FIGS. For carbon, C—C, CHX (hydrocarbon component), α component (see note 1 in Table 1), carbonyl group, COO component, and β component (see note 1 in Table 1) were recognized from the C1s peak split. . As for nitrogen, from the N1s peak splitting, an ammonia component or -NO component and a CN (triple bond) or CN bond component were observed. For fluorine and phosphorus, the PF component was determined to be the main component from the peak positions of F1s and P2p.

(Examples 3 to 13 and Comparative Examples 3 and 4)
The electrodes for lithium ion batteries of Examples 3 to 13 and Comparative Examples 3 and 4 were prepared under various conditions using various pretreatment electrolytic solutions shown below. These conditions are shown in Table 2.

In the electrode production of Examples 3 to 13 and Comparative Examples 3 and 4, as in Example 1-1 to Example 1-6, using a platinum wire as a counter electrode and using (Li / Li ⁺ ) as a reference electrode, A potential operation (scanning speed 5 mV / sec) was performed from a natural potential to a predetermined potential. Thereafter, the electrodes were pulled up and washed with DMC to obtain the electrodes of Examples 3 to 13 and Comparative Examples 3 and 4. In Example 9, 4 mg of diamond-like carbon powder (average particle size 0.03 μm) and 1 mg of PTFE powder were mixed to form a disk-shaped electrode of 8 mmφ, and this electrode was subjected to a positive voltage treatment step. In Example 10, a pure nickel plate, in Example 11, a pure titanium plate, in Example 12, a pure aluminum plate, and in Example 13, an electrode obtained by coating a pure titanium plate with diamond-like carbon by plasma CVD. Each was used.

-Evaluation-
The electrodes of Examples 3 to 13 and Comparative Examples 3 and 4 were subjected to surface analysis by X-ray photoelectron spectroscopy (XPS). The measurement conditions are the same as the XPS measurement in Example 1-1.

<Result>
-About the presence rate of the element which exists in the surface Table 3 and FIG. 6 show the presence rate of the element which exists on the electrode surface calculated | required from the result of XPS wide scan. From Table 3, nitrogen exists in the range of 2.7 to 12.8 atm% in Examples 1-3 and 3-13, and in Examples 1-3, 3-7, and Examples 9-13, phosphorus is 1. It was found that it was present in the range of 2 to 4.1 atm%, fluorine was present in the range of 15.6 to 29.7 atm%, and other oxygen was present. Nitrogen is attributed to the nitrile contained in the pretreatment electrolyte solution, and phosphorus is attributed to LiPF ₆ added as an electrolyte. That is, it was found that nitrile and LiPF ₆ cause an electrode reaction in the positive voltage treatment process, and a corrosion-resistant film containing nitrogen, phosphorus and fluorine as components is formed on the electrode surface. However, in Example 8, LiBF ₄ is used as the electrolyte, there is no phosphorus source, and phosphorus is not detected, but the potential window is widened (see Table 4 described later). The window was found to have a spreading effect.
On the other hand, in Comparative Example 3 and Comparative Example 4, a large amount of lithium was detected, and other fluorine, oxygen, and the like were detected, and it was found that a corrosion-resistant film containing nitrogen and phosphorus as components was hardly formed. Note that phosphorus and fluorine detected in Comparative Examples 3 and 4 are considered to be decomposition products of LiPF ₆ added as an electrolyte.

  Further, in Example 10, nickel as a substrate was hardly detected, whereas in Examples 11 and 12, Ti and Al as substrates were considerably detected. This suggests that a dense corrosion-resistant film is formed when nickel is used as the substrate.

  Further, when Comparative Example 4 is compared with Examples 1-3 and 6, Examples 1-3 and 6 have a large amount of phosphorus and nitrogen, whereas Comparative Example 4 has an amount of phosphorus and nitrogen present. There were few. Comparative Example 4 and Examples 1-3 and 6 have the same composition of the pretreatment electrolyte and differ only in the applied voltage in the positive voltage treatment step. That is, the applied voltage is 5 V in Comparative Example 4, whereas it is 6.2 V in Example 1-3 and 7 V in Example 6. From this, it was found that the corrosion-resistant film containing a large amount of phosphorus and nitrogen detected on the electrode surface of Example 4 was formed at a potential higher than 5V.

FIG. 7 shows the nitrogen surface abundance ratio and the bonding state ratio obtained from the wide scan and the nitrogen narrow scan. As shown in this figure, the presence ratio of nitrogen was large on the electrode surfaces of Examples 3 to 13, and the bonding state was CN triple bond or CN single bond and ammonium salt, -NO. In Example 11 using the Ti substrate, nitrides were also confirmed on Ti. In Example 1-3, the presence ratio of nitrogen was large on the electrode surface, and the bonding state was CN triple bond or CN single bond, ammonium salt, and -NO.

-Phosphorus surface abundance ratio and binding state FIG. 8 shows the phosphorous surface abundance ratio and binding state ratio obtained from wide scan and phosphorous narrow scan. As shown in this figure, the phosphorus which exists in the electrode surface of Examples 3-7 and 9-13 originates in the phosphorus compound which concerns on a PF coupling | bonding. On the other hand, the phosphorus of Comparative Example 3 and Comparative Example 4 has little that is attributed to the phosphorus compound related to the PF bond, and PO _X and PF that are considered to be attributed to the decomposition product of LiPF ₆ that is the electrolyte. those based on _X O _Y is large.
Note that Example 8 shows the abundance ratio and bonding state of boron instead of phosphorus. And it is thought that the boron which exists in the electrode surface of Example 8 originates in the boron compound regarding a BF bond. Also in Example 1-3, the phosphorus present on the electrode surface was attributed to the phosphorus compound related to the PF bond.

-Fluorine surface abundance ratio and bonding state Figure 9 shows the fluorine surface abundance ratio and bonding state ratio obtained from wide scan and fluorine narrow scan. As shown in this figure, the fluorine existing on the electrode surfaces of Examples 3 to 7 and Examples 10 to 12 is mostly fluorine attributed to C—F bonds or PF bonds. Only fluorine attributed to the -F bond was detected. In Example 8 in which LiBF ₄ was used as the electrolyte, a large amount of fluorine attributed to the BF bond was detected. On the other hand, the fluorine in Comparative Example 3 and Comparative Example 4 was mostly based on PF _X O _Y , and was considered to be caused by a decomposition product of LiPF _{6 as} an electrolyte. The fluorine present on the electrode surface of Example 1-3 was mainly composed of a phosphorus compound related to the PF bond.

When an EC: DMC: SB = 1: 1: 2 electrolyte was used as the organic solvent and a 1 M LiTFSI potential operation of 6.5 V and a GC electrode were used, 8.5 atm% of nitrogen element was observed on the electrode surface. The bonding state was CN triple bond or CN single bond and ammonium salt, -NO.

From the results of the surface analysis by XPS as described above, the surface film formed on the electrode of the example has the following properties.
(1) A large amount of nitrogen is present on the electrode surface, and the bonding state of nitrogen is CN triple bond or CN single bond, ammonium salt, and -NO. Further, when a titanium substrate is used, nitride is also present.
(2) A film containing nitrogen and fluorine as components is formed on the electrode surface.
(3) When LiPF ₆ is used as the electrolyte, a phosphorus compound related to the PF bond is detected in the film. When LiBF ₄ is used as the electrolyte, a boron compound related to the BF bond is detected on the electrode.
(4) Fluorine is mostly fluorine attributed to C—F bonds or PF bonds. However, in Example 14, only the fluorine attributed to the PF bond was detected. In Examples 3 to 13, the amount of fluorine attributed to the C—F bond or PF bond is larger than that based on PF _X O _Y. In addition, when LiBF ₄ is used as the electrolyte, a boron compound related to the BF bond is detected.

<Combination of nitrile compound and lithium salt>
In the lithium ion battery electrode of the present invention, various nitrile compounds and various lithium salts were combined in addition to the pretreatment electrolytes used in Examples 1-1 to 1-6 and Examples 2-13. An electrolyte for pretreatment can be used. This is proved by the fact that the potential window is greatly widened in the measurement of the potential-current curve in the pretreatment electrolytes of Examples 15 to 61 below in which various nitrile compounds and lithium salts are combined.

(Example 15)
In Example 15, 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 a pretreatment electrolytic solution.

(Comparative Example 5)
In Comparative Example 5, 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 to 1 mol / L to obtain a pretreatment electrolyte. .

(Examples 16 to 23)
In Examples 16 to 23, 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 so-dissolved electrolyte solution was used as a pretreatment electrolyte (however, in Example 18 in which the nitrile compound was oxydipropionitrile, LiPF ₆ was adjusted to 0.5 mol / L).
The types of nitriles used in each example are as follows.
Example 15 adiponitrile NC _{(CH 2)} 4 CN
Example 16 succinonitrile NC _{(CH 2) 2} CN
Example 17 sebaconitrile NC _{(CH 2)} 8 CN
Example 18 Dodecanedinitrile NC (CH ₂ ) ₁₀ CN
Example 19 2-methylglutaronitrile _{NCCH (CH 3) CH 2 CH} 2 CN
Example 20 oxy dipropionate nitrile _{NCCH 2 CH 2 -O-CH 2} CH 2 CN
Example 21 3-Methoxy-propionitrile _{CH 3 -O-CH 2 CH 2} CN
Example 22 methyl cyanoacetate NCCH ₂ COOCH ₃
Example 23 cyanoacetate butyl _{NCCH 2 COO (CH 2) 3} CH 3

-Evaluation-
(Measurement of potential-current curve)
With respect to the pretreatment electrolytes of Examples 15 to 23 and Comparative Example 5 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. The reference electrode was (Ag / Ag ⁺ ) or (Li / Li ⁺ ). 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. 10, the potential window of the electrolytic solution of Example 15 was 6.9 V with respect to (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 5 using a mixed solvent of ethylene carbonate and dimethyl carbonate is 5.2 V as shown in FIG. 12, and the potential window of the electrolytic solution of Example 15 is Comparative Example 5. Compared to the electrolyte solution of, it was found that it spreads greatly on the positive side. From this result, when the pretreatment electrolyte of Example 15 is used, a high potential redox positive electrode active material that exists in a region where the potential for charging exceeds 5.2 V is converted into a positive electrode active material of a lithium ion battery. Therefore, a lithium ion battery with high electromotive force and energy density and high capacity can be obtained.

Further, as shown in FIG. 11, in the pretreatment electrolytes of Examples 16 to 23, as in Example 15, the potential window is positive in comparison with the pretreatment electrolyte of Comparative Example 5. I understood that it spreads. From these results, the chain saturated hydrocarbon dinitrile compound (Examples 15 to 19) in which a nitrile group was bonded to both ends of the chain saturated hydrocarbon compound to ethylene carbonate and dimethyl carbonate, the terminal of the chain ether compound was obtained. By adding a chain ether nitrile compound having a nitrile group bonded to at least one (Examples 20 and 21) and at least one nitrile compound (Examples 22 and 23) of cyanoacetate, the solvent is decomposed to a high potential. It was found that it can exist stably without doing. In particular, the potential window greatly widened in Examples 15 to 19 using a branched saturated hydrocarbon dinitrile compound in which a nitrile group was bonded to both ends of the chain saturated hydrocarbon compound as a nitrile compound, which has branches. Also in Example 19, it was found that the potential window greatly spreads in the positive direction. Also, in Example 20 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.

(Examples 24-31)
In Examples 24-31, 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 Example 24 in which the nitrile compound was glutaronitrile, LiPF ₆ (lithium hexafluorophosphate) was 0.5 mol / L. ).
The types of nitriles used in each example are as follows.
Example 24 glutaronitrile NC _{(CH 2)} 3 CN
Example 25 sebaconitrile NC _{(CH 2)} 8 CN
Example 26 dodecane dinitrile _{NC (CH 2)} 10 CN
Example 27 2-methylglutaronitrile _{NCCH (CH 3) CH 2 CH} 2 CN
Example 28 oxy dipropionate nitrile _{NCCH 2 CH 2 -O-CH 2} CH 2 CN
Example 29 3-Methoxy-propionitrile _{CH 3 -O-CH 2 CH 2} CN
Example 30 methyl cyanoacetate NCCH ₂ COOCH ₃
Example 31 cyanoacetate butyl _{NCCH 2 COO (CH 2) 3} CH 3

(Comparative Example 6)
In Comparative Example 6, a mixed solvent of ethylene carbonate: diethyl carbonate = 50: 50 (capacity ratio) was used as the organic solvent, and LiPF ₆ was dissolved as a lithium salt in such a manner that the concentration was 1 mol / L. Liquid.

-Evaluation-
(Measurement of potential-current curve)
For the pretreatment electrolytes of Examples 24-31 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, it was found that in the pretreatment electrolytes of Examples 24-31, the potential window widened in the positive direction as compared with the pretreatment electrolyte of Comparative Example 6. From this result, even when ethylene carbonate and diethyl carbonate were used as solvents, both of the chain saturated hydrocarbon compounds were the same as when ethylene carbonate and dimethyl carbonate were used as solvents (that is, in the case of Examples 15 to 23). 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 24 to 27 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 Example 27, it was found that the potential window greatly expanded in the positive direction. Also, in Example 28 and Example 29 using a chain ether nitrile compound in which a 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.

(Examples 32-39)
In Examples 32-39, the solvent was various nitriles: 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 dissolved so that it might become was set as the electrolyte solution for pre-processing. In Example 33 using adiponitrile as the nitrile, LiPF ₆ was set to 0.5 mol / L.
The types of nitriles used in each example are as follows.
Example 32 glutaronitrile NC _{(CH 2)} 3 CN
Example 33 adiponitrile NC _{(CH 2)} 4 CN
Example 34 sebaconitrile NC _{(CH 2)} 8 CN
Example 35 dodecane dinitrile _{NC (CH 2)} 10 CN
Example 36 2-methylglutaronitrile _{NCCH (CH 3) CH 2 CH} 2 CN
Example 37 oxy dipropionate nitrile _{NCCH 2 CH 2 -O-CH 2} CH 2 CN
Example 38 methyl cyanoacetate NCCH ₂ COOCH ₃
Example 39 cyanoacetate butyl _{NCCH 2 COO (CH 2) 3} CH 3

(Comparative Example 7)
In Comparative Example 7, a mixed solvent of γ-butyrolactone: dimethyl carbonate = 50: 50 (volume ratio) was used as an organic solvent, and LiPF ₆ was dissolved as a lithium salt in an amount of 1 mol / L to perform pretreatment electrolysis. Liquid.

-Evaluation-
(Measurement of potential-current curve)
For the pretreatment electrolytes of Examples 32-39 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, it was found that also in the pretreatment electrolytes of Examples 32-39, the potential window greatly expanded in the positive direction as compared with the pretreatment electrolyte of Comparative Example 7. 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 turned out that a potential window spreads in the positive direction greatly not only in Examples 32 to 35 which are linear molecules among the chain saturated hydrocarbon dinitrile compounds but also in Example 36 having branches. Furthermore, also in Example 37 using a chain ether nitrile compound in which a nitrile group is bonded to both ends of the chain ether compound, and Examples 38 and 39 using cyanoacetate, the potential window greatly expands in the positive direction. I understood that.

(Examples 40 to 45)
In Examples 40 to 45, the solvent was various nitriles: dimethyl carbonate = 50: 50 (volume ratio), and the electrolyte was LiPF ₆ (lithium hexafluorophosphate) in this mixed solvent at 1 mol / L (Examples 44 and 45). In this case, the electrolyte solution for pretreatment was dissolved so as to be 0.1 mol / L). The types of nitriles used in each example are as follows.
Example 40 glutaronitrile NC _{(CH 2)} 3 CN
Example 41 sebaconitrile NC _{(CH 2)} 8 CN
Example 42 dodecane dinitrile _{NC (CH 2)} 10 CN
Example 43 2-methylglutaronitrile _{NCCH (CH 3) CH 2 CH} 2 CN
Example 44 oxy dipropionate nitrile _{NCCH 2 CH 2 -O-CH 2} CH 2 CN
Example 45 methyl cyanoacetate NCCH ₂ COOCH ₃

(Comparative Example 8)
In Comparative Example 8, a pretreatment electrolyte was prepared by dissolving LiPF ₆ as a lithium salt in dimethyl carbonate as an organic solvent so as to be 1 mol / L.

-Evaluation-
(Measurement of potential-current curve)
For the electrolytic solutions of Examples 40 to 45 and Comparative Example 8, 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 Examples 40 to 45 in which dimethyl carbonate alone was added in addition to the nitrile compound as a solvent, the potential window was compared with the pretreatment electrolytic solution of Comparative Example 8 in which dimethyl carbonate was the sole solvent. Was found to spread 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 (Examples 40 to 45). Furthermore, it was found that, among the chain-type saturated hydrocarbon dinitrile compounds, not only in Examples 40 to 42 which are linear molecules but also in Example 43 having branches, the potential window greatly spreads in the positive direction. Furthermore, in Example 44 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 45 using a cyanoacetate ester, the potential window was expanded.

(Examples 46 and 47)
In Examples 46 and 47, the solvent was various nitriles: 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 the pretreatment electrolyte. The types of nitriles used in each example are as follows.
Example 46 sebaconitrile NC _{(CH 2)} 8 CN
Example 47 dodecane dinitrile _{NC (CH 2)} 10 CN

(Comparative Example 9)
In Comparative Example 9, a pretreatment electrolyte 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 Examples 46 and 47 and Comparative Example 9, 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 Examples 46 and 47 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 9 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.

(Examples 48 to 50)
In Examples 48 to 50, 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 a pretreatment electrolyte. The types of nitriles used in each example are as follows.
Example 48 glutaronitrile NC _{(CH 2)} 3 CN
Example 49 sebaconitrile NC _{(CH 2)} 8 CN
Example 50 dodecane dinitrile _{NC (CH 2)} 10 CN

(Comparative Example 10)
In Comparative Example 10, an electrolyte solution for pretreatment 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 pretreatment electrolytes of Examples 48 to 50 and Comparative Example 10, potential-current curves were measured in the same manner as described above. The results are shown in FIG.
From this figure, the pretreatment electrolytes of Examples 48 to 50 in which γ-butyrolactone alone was added in addition to the nitrile compound as a solvent were compared with the pretreatment electrolyte of Comparative Example 10 in which γ-butyrolactone was the sole solvent. As a result, it was found that the potential window greatly expanded 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.

(Examples 51-53)
In Examples 51-53, 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 dissolved so that it might become was set as the electrolyte solution for pre-processing. The types of nitriles used in each example are as follows.
Example 51 sebaconitrile NC _{(CH 2)} 8 CN
Example 52 2-methylglutaronitrile _{NCCH (CH 3) CH 2 CH} 2 CN
Example 53 oxy dipropionate nitrile _{NCCH 2 CH 2 -O-CH 2} CH 2 CN

(Comparative Example 11)
In Comparative Example 11, an electrolyte solution for pretreatment 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 electrolyte solutions of Examples 51 to 53 and Comparative Example 11, potential-current curves were measured in the same manner as described above. The results are shown in FIG.
From this figure, in the pretreatment electrolytes of Examples 51 to 53 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, It was found that the potential window greatly expanded in the positive direction and the negative direction as compared with the pretreatment electrolyte solution of Comparative Example 11 which was not included. It was also found that the potential window was greatly expanded by adding a chain saturated hydrocarbon dinitrile compound having a nitrile group bonded to both ends of the chain saturated hydrocarbon compound. Furthermore, it was found that, among the chain-type saturated hydrocarbon dinitrile compounds, not only in Example 51 which is a linear molecule but also in Example 52 having a branch, the potential window greatly spreads in the positive direction and the negative direction. Furthermore, also in Example 53 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.

(Examples 54 to 58)
In Examples 54 to 58, the solvent was sebacononitrile (adiponitrile in Example 56): ethylene carbonate: dimethyl carbonate = 50: 25: 25 (volume ratio), and various electrolytes were dissolved in this mixed solvent so as to be 1 mol / L. This was used as an electrolyte for a lithium ion battery. The types of electrolyte used in each example are as follows.
Example 54 LiPF ₆
Example 55 LiTFSI
Example 56 LiTFSI
Example 57 LiBF ₄
Example 58 LiBETI

(Example 59)
In Example 59, a solvent obtained by mixing sebacononitrile, ethylene carbonate (EC), and dimethyl carbonate (DMC) 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 a pretreatment electrolyte.

(Example 60)
In Example 60, 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 a pretreatment electrolyte.

(Example 61)
In Example 61, 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 a pretreatment electrolyte.

(Comparative Examples 12-14)
In Comparative Examples 12 to 14, various lithium salts were added instead of LiPF ₆ which is the lithium salt in Comparative Example 5. That is, various lithium salts (LiTFSI in Comparative Example 12, LiBF ₄ in Comparative Example 13, LiBETI in Comparative Example 14) at 1 mol / L as an organic solvent with ethylene carbonate: dimethyl carbonate = 50: 50 (volume ratio). It was made to melt | dissolve and it was set as the electrolyte solution for pre-processing.

-Evaluation-
(Measurement of potential-current curve)
For the pretreatment electrolytes of Examples 54 to 58, Comparative Example 5 and Comparative Examples 12 to 14, potential-current curves were measured in the same manner as described above. The results are shown in FIG. Table 4 shows the potential values obtained from this figure when the current density is 50 μA / cm ² .
From FIG. 19 and Table 4, in addition to the nitrile compound as the solvent, ethylene carbonate as a cyclic carbonate and dimethyl carbonate as a chain carbonate were added as solvents. Regardless of the type, it was found that the potential window greatly expanded in the positive direction as compared with the pretreatment electrolytes of Comparative Example 5 and Comparative Examples 12 to 14 in which no nitrile compound was added.
Further, the potential window of the electrolytic solution of Example 59 is 6.6 V (see FIG. 20), the potential window of the pretreatment electrolytic solution of Example 60 is 5.4 V (see FIG. 21), and the electrolytic solution of Example 61 The potential window was 6.1 V (see FIG. 22), and it was found that both expanded to the positive side.

Similarly, the lithium salt and LiPF _6, the preconditioning electrolyte solution of the other Examples and Comparative Examples, the potential - was determined from current curve, shown in Table 5 electrode potential when a predetermined current density. 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 amount of nitrile added in the pretreatment electrolyte, 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. The preferred amount of sebacononitrile added as the pretreatment electrolyte is 5% by volume or more, more preferably 10% by volume or more, still more preferably 30% by volume or more, and most preferably 70% by volume or more. is there.

  As described above, it was found that by adding a nitrile compound to the organic solvent of the pretreatment electrolyte, the potential window is greatly expanded in the positive direction. In the measurement of the potential-current curve of the above example, as described above, after scanning several times on the positive side and the negative side, the potential is swept at a rate of 5 mV / sec from the natural potential in the positive direction or the negative direction. And the potential-current curve is measured. In the potential scan several times before this measurement, the potential window spreads after the second time. Therefore, by sweeping the potential in the positive direction in the electrolytic solution of the present invention, an electrode having a wide potential window is formed. It can be seen that it can be manufactured.

<Measurement of battery characteristics>
In order to evaluate the performance of the lithium ion battery electrode of the present invention, a potential-current curve was measured using a lithium battery cathode and a lithium battery cathode.
That is, the pretreatment electrolytic solution of Example 55 (that is, EC: DMC: sebaconitrile = 25: 25: 50 by volume ratio, LiTFSI (lithium bis (trifluoromethanesulfonyl) imide) as a lithium salt was 1.0 mol / L). ), And a lithium battery cathode and a lithium battery anode were used as working electrodes, and a potential-current curve of lithium occlusion / release was measured. The cathode for a lithium battery using _Li 4 _Ti 5 O1 _2, as a positive electrode for a lithium battery using LiCoO ₂ and LiCoPO _4. A potentiogalvanostat was used for the measurement. Further, (Ag / Ag ⁺ ) was used as the reference electrode. In the measurement, as the positive voltage processing step, the positive side and the negative side are scanned several times, and then the potential is swept from the natural potential to the positive direction or the negative direction at a speed of 0.5 mV / sec. Was measured.

As a result, as shown in FIG. 24, Li ₄ Ti ₅ O ₁₂ as the cathode for the lithium battery, LiCoO ₂ and LiCoPO ₄ as the cathode for the lithium battery, both of lithium (0) and lithium ions A nearly reversible current associated with redox was observed. From this result, it was found that smooth charge / discharge between lithium (0) and lithium ions was possible.

The electrode for a lithium ion battery of 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. As such an organic solvent, one kind or two or more kinds selected from cyclic carbonates, cyclic carboxylic acid esters and chain carbonates are preferable. More preferably, a cyclic carbonate and a chain carbonate are used in combination. Specifically, 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.
Furthermore, a nitrile compound can be used as an organic solvent. Here, as the nitrile compound, a chain saturated hydrocarbon dinitrile compound in which a nitrile group is bonded to both ends of a chain saturated hydrocarbon compound, a chain ether in which a nitrile group is bonded to at least one terminal of a chain ether compound. Mention may be made of at least one nitrile compound among nitrile compounds and cyanoacetic acid esters.

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

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

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

The concentration of the Li salt is 0.01 mol / L or more and is lower than the saturated state. When the concentration of the Li salt is less than 0.01 mol / L, ion conduction 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.

(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 their solid solutions (here, the solid solution is the above oxide system) In which the metal atoms are mixed in a free ratio.). Moreover, what doped the metal atom of these with the other metal atom is also contained. The dopant is not particularly limited as long as the electrochemical characteristics can be changed in the oxidation-reduction reaction. For example, one or more of Li, Mg, Al, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, and Mo can be used.

1-2 Characteristics The general discharge potential of this positive electrode active material is less than 5 V vs Li / Li ⁺ ). However, LiNi _0.5 Mn _1.5 O ₄ partially substituted with Ni in the LiMn ₂ O ₄ system has a discharge potential of 4.7 V, and takes into account overvoltage when performing rapid charging, and 5 V May require a charging voltage exceeding. Further, since LiCoMnO ₄ starts with a discharge voltage of about 5.2V, the charge voltage also exceeds 5V. In addition, oxide systems generally decompose at less than 300 ° C., and have a relatively large exothermic reaction as oxygen is generated. Therefore, a control circuit that does not cause overcharging is required.

(2) Phosphate-based 2-1 specific substance having an olivine-type crystal structure As a phosphate-based substance having an 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 (where solid solutions and Refers to a substance in which metal atoms are mixed in a free ratio in the phosphate-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 Mg, Al, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, and Mo can be used. (See JP2008-130525)
2-2 Characteristics The oxidation-reduction potential of this positive electrode active material has attracted attention because it has a low exothermic reaction at 300 ° C. or lower, and does not generate oxygen and is highly safe, unlike the oxide type. 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 Unlike the olivine system, the oxidation-reduction potential of this positive electrode active material is different from that of the 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). 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. Further, transition metal chalcogenides, vanadium oxides and lithium salts thereof, niobium oxides and lithium salts thereof, and a plurality of different positive electrode active materials can 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 positive electrode active material having an olivine-type crystal structure with a high redox potential and its olivine fluoride-based material, it is preferable to use a material excellent in corrosion resistance.
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. However, it may be selected as appropriate in consideration of the operating potential of the positive electrode active material to be used. preferable. 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. In addition, when LiTFSI is used as the electrolyte, it is preferable that LiPF6 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.

(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 is oxidized / reduced accordingly”. Examples of the negative electrode active material include artificial graphite, natural graphite, Various carbon materials such as 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 and the} like can be 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.

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 when a carbon-based or Si-based material is used as the negative electrode active material. When lithium titanate or Fe2O2 based compound is used as the negative electrode active material, all of the above materials including copper are applicable. 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 shape of the electron conducting member is not particularly limited as long as an electron conduction path can be formed between the positive electrode active material and the current collector. For example, conductive materials such as carbon black, graphite powder, diamond-like carbon, and glassy carbon are used. Conductive powder (conductive aid) can be used. Diamond-like carbon and glassy carbon have a much wider potential window than carbon black and graphite, and are excellent in corrosion resistance when a high potential is applied, and therefore can be suitably used. Moreover, it is also preferable that metal fine particles are supported on these conductive assistants. Examples of the metal fine particles include Pt, Au, Ni and the like. These may be used alone or an alloy thereof.
As the electron conductive material, a conductive film (such as a DLC film) covering the positive electrode active material or a conductive thin film (such as a gold thin film) in which the positive electrode active material is embedded can be used.
In particular, since the Li ₂ NiPO ₄ F-based positive electrode active material has low conductivity of its own and / or its surface coating, it does not function as a positive electrode of a lithium ion battery if it is simply supported on a current collector. There is a case. In order to evaluate the performance of the Li ₂ NiPO ₄ F-based positive electrode active material, it can be physically driven into a conductive thin film such as gold with a hammer or the like to form the positive electrode of the battery.
Here, the Li ₂ NiPO ₄ F-based positive electrode active material refers to Li ₂ NiPO ₄ F and a material appropriately doped with dopant.

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

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

(Case)
The case is formed of a material having corrosion resistance against the electrolytic solution. The shape can be arbitrarily designed according to the intended use of the battery.
When LiPF6 or LiBF4 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.

  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.

It is an electric potential-current curve in Example 1-1 to Example 1-6, Example 2, Comparative Example 1, and Comparative Example 2. 2 is a cyclic voltammogram of the pretreatment electrolyte used in Example 1. FIG. It is a chart which shows the result of the wide scan measurement of XPS of Example 1-1, and the narrow scan measurement (carbon and nitrogen). It is a chart which shows the result of the narrow scan measurement (oxygen, fluorine, and phosphorus) of XPS of Example 1-1. It is a chart which shows the result of having performed C1s peak division and N1s peak division of XPS of Example 1-1. It is a graph which shows the abundance ratio of the element which exists in the surface calculated | required from the XPS measurement result about the electrode of Examples 3-13, Example 1-3, and Comparative Examples 3 and 4. FIG. It is a graph which shows the surface presence rate of the nitrogen calculated | required from the XPS measurement result about the electrode of Examples 3-13, Example 1-3, and Comparative Examples 3 and 4, and the ratio of the bonding state of those elements. The surface presence ratio of phosphorus obtained from the XPS measurement results for the electrodes of Examples 3 to 13, Example 1-3 and Comparative Examples 3 and 4 and the ratio of the bonding state of these elements (however, in Example 8, boron It is a graph which shows the surface existence ratio and the ratio of those combined states). It is a graph which shows the surface presence rate of the fluorine calculated | required from the XPS measurement result about the electrode of Examples 3-13, Example 1-3, and Comparative Examples 3 and 4, and the ratio of the bonding state of those elements. It is an electric potential-current curve of Example 15 and Comparative Example 5. It is an electric potential-current curve of Examples 16-23 and Comparative Example 5. 10 is a potential-current curve of Comparative Example 4. It is an electric potential-current curve of Examples 24-31 and Comparative Example 6. It is an electric potential-current curve of Examples 32-39 and Comparative Example 7. It is an electric potential-current curve of Examples 40-45 and Comparative Example 8. It is the electric potential-current curve of Examples 46 and 47 and Comparative Example 9. It is an electric potential-current curve of Examples 48-50 and Comparative Example 10. 6 is a potential-current curve of Examples 51 to 53 and Comparative Example 11. It is an electric potential-current curve of Examples 54-58 and Comparative Examples 5, 12, 13, and 14. It is an electric potential-current curve of Example 59 and Comparative Example 12. It is an electric potential-current curve of Example 60 and Comparative Example 12. 6 is a potential-current curve of Example 61 and Comparative Example 5. FIG. It is an electric potential-current curve at the time of using the mixed solvent which set ethylene carbonate: dimethyl carbonate = 1: 1, and also added a predetermined amount of sebacononitrile. It is the electric potential-current curve of lithium occlusion discharge | release using the electrolyte solution for lithium ion batteries of Example 55. FIG.

Claims (3)

  An electrode for a lithium ion battery, characterized in that when a surface analysis is performed by XPS, a film in which a total of 2 atm% or more of nitrogen in the form of organic nitrogen and nitrogen in the form of ammonium salt is present is formed.   2. The lithium ion battery according to claim 1, wherein when surface analysis is performed by XPS, phosphorus is present in an amount of 1 atm% or more, and a film in which the main component of the phosphorus is in the form of a PF bond is formed. electrode.   2. The lithium ion battery according to claim 1, wherein when the surface analysis is performed by XPS, boron is present in an amount of 1 atm% or more, and a film in which the main component of the boron is in the form of a BF bond is formed. electrode.