JP2008047479A - Nonaqueous electrolyte, and electrochemical energy storage device equipped with it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem where, when a lithium salt is combined with DME or EME in high salt concentration, it becomes solid or discolored, or the lithium salt is not completely dissolved, and, when a nonaqueous electrolyte in high salt concentration represented by a composition of LiBF<SB>4</SB>/DME=1/1 (molar ratio) or LiBF<SB>4</SB>/EME=1/1 (molar ratio) is used, lithium ions solvated with DME or EME are inserted between graphite layers to break a graphite structure, whereby the potential of a negative electrode is prevented from becoming base. <P>SOLUTION: A nonaqueous electrolyte in which an additional mass prepared by adding DME having a molar ratio equal to that of LiClO<SB>4</SB>in an electrolyte solidified at low temperature is present is used. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrochemical energy storage device, and more particularly to an improvement of the non-aqueous electrolyte.

  In the electric double layer capacitor in which polarizable electrodes are used for the positive electrode and the negative electrode, the cation and the anion in the electrolytic solution are adsorbed on the electrode surface during the charging process, thereby accumulating electrochemical energy. There are two methods for increasing the energy density of the electric double layer capacitor. One is to reduce the amount of the electrolyte by increasing the salt concentration in the electrolyte, and to increase the polarizable material accordingly. The other is to be able to set the charging voltage high. That is, by using a non-aqueous solvent for the electrolyte solution in which the supporting salt is dissolved, it is possible to set a high charging voltage for the electric double layer capacitor, and as a result, the energy density of the capacitor is increased.

In a non-aqueous electrolyte battery using a lithium ion conductive non-aqueous electrolyte, lithium ions move in the electrolyte between the positive electrode and the negative electrode. In this non-aqueous electrolyte battery, the salt concentration in the non-aqueous electrolyte does not change during discharge in the primary battery and during charge / discharge in the secondary battery. Therefore, in order to increase the energy density of the nonaqueous electrolyte battery, it is only necessary to reduce the amount of the electrolyte and increase the amount of the positive electrode and the negative electrode material as in the case of the electric double layer capacitor. Here, while reducing the amount of the non-aqueous electrolyte, it is necessary to keep the amount of ions that can move between the positive electrode and the negative electrode, so it is necessary to increase the salt concentration in the non-aqueous electrolyte. In addition, in a non-aqueous electrolyte battery, since a non-aqueous electrolyte solution in which a lithium salt such as lithium hexafluorophosphate (LiPF ₆ ) is dissolved in a non-aqueous solvent is used, a high charging voltage can be obtained. By using a carbon material such as graphite or lithium metal, the negative electrode potential can be made lower (lower), and a high charging voltage can be set also from this point.

  Therefore, to achieve high energy density in any electrochemical energy storage device, use a non-aqueous electrolyte with a high salt concentration as the electrolyte, and on the negative electrode surface where the charging potential is low (low) It is necessary to suppress various side reactions that occur.

In electric double layer capacitors and non-aqueous electrolyte batteries, typical non-aqueous solvents used for the non-aqueous electrolyte are cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), Examples thereof include γ-butyrolactone (γ-BL) which is a cyclic ester, dimethyl carbonate (DMC) which is a chain carbonate, ethyl methyl carbonate (EMC), diethyl carbonate (DEC) and the like. Nonaqueous electrolytes dissolve lithium salts such as LiPF ₆ , lithium tetrafluoroborate (LiBF ₄ ), lithium perchlorate (LiClO ₄ ), and lithium bis [trifluoromethanesulfonyl] imide (LiTFSI) in these nonaqueous solvents. Prepared. The concentration of the lithium salt dissolved in the non-aqueous electrolyte is usually about 0.8 mol / kg (1 mol / L). As the high salt concentration non-aqueous electrolyte, for example, LiBF ₄ and EC are used. The limit is the case of mixing at a molar ratio of LiBF ₄ / EC = 1/4, that is, 2.2 mol / kg.

In order to further increase the salt concentration in the non-aqueous electrolyte, it has been proposed to use a monoglyme compound such as 1,2-dimethoxyethane (DME) as the non-aqueous solvent. Specifically, a 6 mol / L nonaqueous electrolytic solution (approximately LiBF ₄ / DME = 1/1 in molar ratio) composed of LiBF ₄ and DME is disclosed. (For example, see Patent Document 1)
6 consisting of LiBF ₄ , DME and 1-ethoxy-2-methoxyethane (EME).
A non-aqueous electrolyte (molar ratio of LiBF ₄ /(DME+EME)=1/(0.5+0.5)) is disclosed. (For example, see Patent Document 2)
Non-patent document 1 includes a phase diagram of a two-component system composed of LiClO ₄ and DME, although partially. According to this, it can be seen that in the combination of LiClO ₄ and DME, the composition of LiClO ₄ / DME = 1/2 (molar ratio) is solid at room temperature. Furthermore, Non-Patent Document 2 reports the crystal structure of a composition of LiClO ₄ / DME = 1/2 (molar ratio). Non-Patent Document 2 describes that the melting point of a composition of LiClO ₄ / DME = 1/2 (molar ratio) is 68 ° C. by differential thermal analysis. Non-patent document 2 describes that the melting point of the composition of LiClO ₄ / DME = 1/2 (molar ratio) is 62 ° C. in the phase diagram described in non-patent document 1.

Further, Non-Patent Document 3 describes that in the composition of LiClO ₄ / DME = 1/1 (molar ratio), an adduct that only dissolves 5 g in 100 g of methylene dichloride is formed.

For this reason, there was no report that the composition in the vicinity of LiClO ₄ / DME = 1/1 (molar ratio) having a high concentration was used as an electrolytic solution of an electrochemical energy storage device.

On the other hand, particularly in a non-aqueous electrolyte secondary battery using a graphite material that occludes and releases lithium ions as a negative electrode, when DME is used as a solvent for the electrolyte, lithium ions cannot be electrochemically inserted into the graphite material. (For example, see Non-Patent Document 4).
JP-A-1-107468 Japanese Patent Laid-Open No. 3-84771 G. Perron and three others, “Phase diagrams, molar volumes, heat capacities, conductivities and viscosities of some lithium salts of aprotic solvents), Journal of Electroanalytical Chemistry, Switzerland, Elsevier Sequoia SA, Lausanne (Elsevier Sequoia SA, Vol. 27, 93, 35). Wesley, A, Henderson and 3 others, “LiClO4 Electrolyte Solvate Structures”, Journal of Physical Chemistry A, USA, American Chemical American Chemical Society), 2004, 108, p225-229. Dr. John R. Long, “Perchlorates in Organic Media”, [online], GF CHEMICALS homepage, “April 17, 2006 Day search ", Internet <URL: HYPERLINK"http://www.gfschemicals.com/technicallibrary/fa#100102.asp"http: // www. gfchemicals. com / technical library / fa — 100102. asp> Supervised by Zenichiro Takehara, “High-density lithium secondary battery”, Techno System Co., Ltd., 1998, p. 184-185

The present inventors have investigated in detail, when using LiBF ₄ in a lithium salt, LiBF
The non-aqueous electrolyte with ₄ / DME = 1/1 (molar ratio) is in a supersaturated state at room temperature, and eventually a crystalline substance estimated to be LiBF4 is deposited. In addition, non-aqueous electrolytes of LiBF ₄ / DME = 1/1 (molar ratio) and LiBF ₄ /(DME+EME)=1/(0.5+0.5) (molar ratio) are unstable at room temperature and left to stand. It changes to yellow or brown by decomposition of the monoglyme compound.

In Patent Document 2, in addition LiBF ₄ as a lithium salt, LiPF _6, lithium trifluoromethanesulfonate (LiCF ₃ SO _3), lithium hexafluoroantimonate (LiSbF _6), also lithium hexafluoro Ah cell sulfonate (LiAsF ₆₎ It is disclosed. However, with these salts, even if an attempt is made to prepare a non-aqueous electrolyte having a high salt concentration such as lithium salt / monoglyme compound = 1/1 (molar ratio), the lithium salt does not dissolve or is prepared in the same manner as LiBF _4. Since the non-aqueous electrolyte changed color or became solid at room temperature, it was difficult to use as a non-aqueous electrolyte for electrochemical energy storage devices.

On the other hand, as a result of repeated studies using a non-aqueous electrolyte having a high salt concentration represented by a composition of LiBF ₄ / DME = 1/1 (molar ratio) or LiBF ₄ / EME = 1/1 (molar ratio), charging Since lithium ions solvated with DME or EME in the initial stage are inserted between graphite layers to destroy the graphite structure, the problem that the potential of the negative electrode does not become low is clarified. Here, the initial stage of charging means an initial process in which lithium ions are electrochemically inserted in a state where lithium is not present between graphite layers.

  The object of the present invention has been made in view of the above-mentioned problems, and provides a high-salt concentration non-aqueous electrolyte that is stable at room temperature, enabling the energy density of an electrochemical energy storage device to be increased. It is.

  In order to solve the above problems, the nonaqueous electrolytic solution of the present invention is characterized in that an adduct obtained by adding equimolar 1,2-dimethoxyethane to lithium perchlorate is present in a solidified state at a low temperature. And

  With the non-aqueous electrolyte of the present invention, a non-aqueous electrolyte that is liquid at room temperature and chemically stable even at a high salt concentration can be obtained.

  The electrochemical energy storage device of the present invention comprises the non-aqueous electrolyte of the present invention. Since the non-aqueous electrolyte has a high salt concentration, the amount of liquid can be reduced, and the positive electrode and negative electrode materials can be increased, resulting in a high energy density.

  As described above, according to the present invention, it is possible to prepare a non-aqueous electrolyte that is stable at a high salt concentration. In addition, an electrochemical energy storage device having a high energy density can be obtained.

  The nonaqueous electrolytic solution according to claim 1 of the present invention is characterized in that an adduct obtained by adding equimolar 1,2-dimethoxyethane to lithium perchlorate is present in a solidified state at a low temperature.

The reason why an electrolyte having a high salt concentration can be prepared by including an adduct of LiClO ₄ / DME = 1/1 (molar ratio) in a solidified state at a low temperature is presumed as follows. That is, the composition of LiClO ₄ / DME = 1/1 (molar ratio) is a solid at room temperature according to Non-Patent Document 3, and forms an adduct. Even when the inventors measured the melting point of the composition frozen at a low temperature (by differential thermal analysis under a temperature rising condition of 5 ° C./min), the melting point was about 41 ° C. However, a liquid that is viscous at room temperature can be obtained by leaving it as a uniform liquid at a temperature equal to or higher than the melting point. Due to its viscosity, the liquid state remains at room temperature even after 6 months. It is thought that it can be kept.

In the composition of LiClO ₄ / DME = 1/1 (molar ratio), the lithium salt concentration is a high concentration of 5.1 mol / kg.

In addition, by using a high salt concentration electrolytic solution containing LiClO ₄ and DME, lithium ions can be inserted between layers of carbon materials such as graphite, and the potential of the negative electrode becomes low. The energy density of can be improved. Here, when LiBF ₄ is used for the lithium salt, lithium ions cannot be inserted between the graphite layers, and when LiClO ₄ is used, the reason why lithium ions can be inserted is unknown.

The nonaqueous electrolytic solution according to claim 2 of the present invention satisfies the following formula (1) in the nonaqueous electrolytic solution according to claim 1.
0.8 ≦ B / A ≦ 1.4 (where A is the number of moles of lithium perchlorate (LiClO ₄ ) in the non-aqueous electrolyte, and B is the non-mol of 1,2-dimethoxyethane (DME)). Number of moles in water electrolyte) (1)
When the molar ratio satisfies the formula (1) in the non-aqueous electrolyte as described above, it is considered that an adduct having an equimolar ratio is suitably generated in a solidified state at a low temperature.

The nonaqueous electrolytic solution according to claim 3 of the present invention produces an adduct in which equimolar 1,2-dimethoxyethane (DME) is added to lithium perchlorate (LiClO ₄ ) in a solidified state at a low temperature. In addition to the electrolytic solution, it further contains at least one compound selected from the group consisting of cyclic carbonates, cyclic esters and chain carbonates.

  Thus, by including at least one compound selected from the group consisting of cyclic carbonates, cyclic esters, and chain carbonates, the high voltage is maintained while taking advantage of the characteristics of a high salt concentration electrolyte solution that is stable at room temperature. Thus, an electrochemical energy storage device having excellent cycle characteristics and good high temperature characteristics can be obtained.

Here, in order to maintain a high salt concentration even when cyclic carbonate or the like is included, it is necessary that an adduct of approximately LiClO ₄ / DME = 1/1 (molar ratio) be present in the electrolyte solution solidified at a low temperature. is there. Electrolysis with a low salt concentration in which LiClO ₄ is dissolved in a mixed solvent of DME and PC (DME / PC = 1/1 (volume ratio)) of 0.5 to 2 mol / L, which is commonly used in lithium batteries. In the liquid, the adduct does not exist even when solidified at a low temperature, that is, in order for the adduct to exist in a solidified state at a low temperature, the number of moles A in the non-aqueous electrolyte of LiClO ₄ and DME The ratio B / A to the number of moles B in the non-aqueous electrolyte solution needs to be close to 1, but if the adduct is present, a single LiClO ₄ or DME may be present. If 0.8 ≦ B / A ≦ 1.4, the nonaqueous electrolytic solution of the present invention can be prepared.

The presence of the adduct in the electrolyte solution solidified at a low temperature can be confirmed, for example, by differential thermal analysis. That is, after freezing the electrolyte solution at −100 ° C. and then warming it up at 5 ° C./min, an endothermic peak corresponding to the melting point of the adduct is observed in the range of about 30 ° C. to 50 ° C. Is done. The reason why the adduct has a melting point as wide as 30 ° C. to 50 ° C. is considered to be because the melting point shifts due to the interaction with the carbonate and ester coexisting with the adduct. The magnitude of the melting point shift depends on the type and amount of carbonate or ester. In further explanation, an endothermic peak corresponding to the melting point of some crystals may be observed during the temperature rise, but the melting point of the adduct corresponds to the highest endothermic peak observed. To do.

  Examples of the cyclic carbonate include fluoroethylene carbonate in addition to EC, PC, and BC. Among cyclic carbonates, those having a C = C unsaturated bond include vinylene carbonate, vinyl ethylene carbonate, divinyl ethylene carbonate, and phenyl. Examples thereof include ethylene carbonate and diphenyl ethylene carbonate.

  Examples of the cyclic ester include α-methyl-γ-butyrolactone and γ-valerolactone in addition to γ-BL. Examples of the cyclic ester having a C═C unsaturated bond include furanone, 3-methyl -2 (5H) -furanone, α-angelica lactone and the like.

  Examples of the chain carbonate include methylpropyl carbonate and methylbutyl carbonate in addition to DMC, EMC, and DEC. Examples of the chain carbonate having a C═C unsaturated bond include methyl vinyl carbonate and ethyl vinyl. Examples include carbonate, divinyl carbonate, allyl methyl carbonate, allyl ethyl carbonate, diallyl carbonate, allyl phenyl carbonate, and diphenyl carbonate.

In the non-aqueous electrolyte according to any one of claims 1 to 3 of the present invention, LiClO ₄ is used as a main lithium salt, but LiPF ₆ , LiBF ₄ , LiTFSI, lithium bis [pentafluoroethanesulfonyl] imide, lithium [Trifluoromethanesulfonyl] [nonafluorobutanesulfonyl] imide, lithium cyclohexafluoropropane-1,3-bis [sulfonyl] imide, lithium bis [oxalate (2-)] borate, lithium trifluoromethyltrifluoroborate, lithium penta A lithium salt such as fluoroethyl trifluoroborate, lithium heptafluoropropyl trifluoroborate, or lithium tris [pentafluoroethyl] trifluorophosphate may be mixed. The mixing ratio is determined so that the nonaqueous electrolytic solution exists stably.

  Furthermore, the electrochemical energy storage device according to claim 4 of the present invention comprises the positive electrode and the negative electrode, and the non-aqueous electrolyte according to any one of claims 1 to 3. As described above, the non-aqueous electrolyte of the present invention exists as a liquid at room temperature even at a high salt concentration, so that the energy density can be reduced by using it in an electrochemical energy storage device such as an electric double layer capacitor or a non-aqueous electrolyte battery. Can be increased.

  In particular, the present invention can improve energy density by using this non-aqueous electrolyte in an electrochemical energy storage device having a negative electrode using a carbon material such as graphite.

  Examples of the carbon material used for the negative electrode include activated carbon for electric double layer capacitors. Specific examples of the activated carbon include natural plant-based activated carbon such as coconut shell, synthetic resin-based activated carbon such as phenol, fossil fuel-based activated carbon such as coke, and the like, which are used alone or in combination of two or more. May be. Moreover, the ultra fine powder activated carbon obtained by activating carbon black may be used. Moreover, graphite is mentioned as a carbon material used for a nonaqueous electrolyte battery. Specific examples of the graphite include natural graphite, artificial graphite, and a highly crystalline carbon material close to graphite. Examples of the highly crystalline carbon material include mesophase pitch-based graphite fibers, graphitized mesocarbon microbeads, vapor-grown carbon fibers, and graphite whiskers. These may be used alone or in combination of two or more. Other carbon materials include non-graphitizable carbon and single-walled and multi-walled nanotubes. Among these carbon materials, graphite is preferable because the potential of the negative electrode can be made the lowest.

In addition, as the negative electrode material other than the carbon material, lithium metal, metal that can be alloyed with lithium (for example, Ag, Au, Zn, Al, Ga, In, Si, Ge, Sn, Pb, Bi), Si, Sn, etc. Alternatively, a lithium-containing transition metal oxide (for example, Li ₄ Ti ₅ O ₁₂ ) may be used.

  Examples relating to the present invention will be described below.

(Electrolytes 11-15)
Electrolytes 11 to 15 were prepared by weighing LiClO ₄ and DME so as to have a total of 10 g with the composition shown in Table 1 and putting them in a PFA container at 60 ° C. for 2 hours. The mixture became a transparent liquid visually, and became a viscous liquid when left at room temperature. These liquids remained in a liquid state even after being left at room temperature for 6 months.

(Electrolytic solutions 1a to 1f)
LiClO ₄ and DME were weighed so as to give a total of 10 g with the composition shown in Table 1, placed in a PFA container, and mixed at 60 ° C. for 2 hours to prepare electrolytes 1a to 1f. When LiClO ₄ / DME = 1 / X (molar ratio) and the value of X was less than 0.8, not all LiClO ₄ could be dissolved. On the other hand, when the value of X exceeds 1.4, the mixture becomes a jelly-like solid at room temperature, or a mixture of white crystalline powder or rough crystals and a transparent liquid. For example, a clear liquid could not be obtained.

(1 g of electrolyte)
LiClO ₄ , DME, and EME were weighed so as to have a composition of LiClO ₄ /(DME+EME)=1/(0.5+0.5) (molar ratio) and 10 g as a whole. A weighed product was put in a PFA container and stirred and mixed at 60 ° C. for 2 hours. Immediately after stirring at 60 ° C., the mixture was a transparent liquid, but became a crystalline mass at room temperature.

(Electrolytic solution 1h)
LiClO ₄ and 1,2-diethoxyethane (hereinafter abbreviated as DEE) were weighed with a composition of LiClO ₄ / DEE = 1/1 (molar ratio) so that the total was 10 g. A weighed material was put in a PFA container and stirred at 60 ° C. for 2 hours, but most of the LiClO ₄ could not be dissolved.

As shown in this example, the electrolytic solutions 11 to 15 of the present invention have a high concentration and are more stable than the comparative electrolytic solutions 1a to 1h. This is because when the electrolytic solution is heated from a low-temperature solid state to a liquid state, the addition state of the adduct of LiClO ₄ / DME = 1/1 (molar ratio) changes, and the electrolytic solution becomes viscous. By nature, it means that it can exist metastable at room temperature. In addition, since the LiClO ₄ or DME may exist if the electrolyte is metastable, the number of moles A in the nonaqueous electrolyte and the DME in the nonaqueous electrolyte can be obtained from Table 1. It can be seen that the non-aqueous electrolyte of the present invention can be prepared if the ratio B / A to the number of moles B is 0.8 ≦ B / A ≦ 1.4.

(Electrolytic solution 20-29)
Mixing cyclic carbonate, cyclic ester, and chain carbonate in a ratio as shown in Table 2 into a viscous liquid prepared by mixing LiClO ₄ and DME with a composition of LiClO ₄ / DME = 1/1 (molar ratio). The electrolytic solutions 20 to 29 were prepared by the above. After stirring at 60 ° C. for 2 hours, the solution was allowed to stand at room temperature, and the state change of the solution was observed. As a result, the liquid state was maintained even after about 1 month. In Table 2, even the electrolyte solution having the lowest salt concentration of LiClO ₄ / DME / EMC = 1/1/1 (molar ratio) has a high concentration of 3.3 mol / kg.

Further, the presence of an adduct of LiClO ₄ / DME = 1/1 (molar ratio) in the electrolyte solution solidified at a low temperature was confirmed by differential thermal analysis. The composition frozen at −100 ° C. was measured by differential thermal analysis under a temperature rising condition of 5 ° C./min. The melting point was about 42 ± 4 ° C. for all of the electrolyte solutions 20 to 29.

(Test cell 1)
In a non-aqueous electrolyte, the possibility of inserting lithium ions into the graphite material was examined. Artificial graphite powder was used as a negative electrode material that occludes and releases lithium ions by charging and discharging. And the negative electrode plate was produced as follows. First, 75 parts by weight of artificial graphite powder, 20 parts by weight of acetylene black as a conductive agent, 5 parts by weight of polyvinylidene fluoride resin as a binder, and dehydrated N-methyl-2-pyrrolidone as a dispersion solvent were mixed. . Next, this mixture was applied to one side of a copper foil current collector having a thickness of 20 μm and dried to form an active material layer having a thickness of 80 μm. Next, the copper foil current collector on which the active material layer was formed was cut into a size of 35 mm × 35 mm, and ultrasonically welded to a 0.5 mm thick copper current collector with a lead.

As the nonaqueous electrolytic solution, the electrolytic solution 13 used in Example 1, that is, a mixture of LiClO ₄ and DME so that LiClO ₄ / DME = 1/1 (molar ratio) was used.

A test cell 1 was prepared from the negative electrode plate produced as described above using a lithium metal foil as a test electrode, a counter electrode and a reference electrode, and an attempt was made to electrochemically insert lithium ions into the artificial graphite powder. The insertion conditions were a temperature of 20 ° C., a cathode current density of 0.03 mA / cm ² , and an amount of electricity of 60 mAh / g with respect to the artificial graphite powder. In addition, after the insertion of lithium ions was confirmed, the release conditions were 20 ° C. and 0.03 mA / cm ² for electrochemically attempting to release lithium ions from the artificial graphite powder.

  A solid line “a” in FIG. 1 shows a potential change when a cathode electricity amount of 60 mAh / g is applied to the artificial graphite powder. From the solid line a, the potential after the end of energization is about 0.2 V, which indicates that lithium ions have penetrated between the graphite layers to form a third stage structure.

  Moreover, the broken line b of FIG. 1 shows the potential change when an anode current is passed through the artificial graphite powder. It can be seen from the broken line b that lithium ions are released from the graphite layer.

(Test cell A)
The non-aqueous electrolyte solution used was a mixture of LiBF ₄ and DME so as to have the composition of _{LiBF 4 / DME = 1/1} ( molar ratio). In the preparation, LiBF ₄ and DME were mixed at LiBF ₄ / DME = 1/1 (molar ratio), then heated at 60 ° C. for 2 hours and cooled to room temperature. A test cell A was prepared in the same manner as in the test cell 1 except for this electrolytic solution. However, since this nonaqueous electrolytic solution is in a supersaturated state and a crystalline substance estimated to be LiBF ₄ is likely to be precipitated, the one immediately after preparation was used as the electrolytic solution. In the same manner as in the test cell 1, whether or not lithium ions can be inserted into the artificial graphite material was examined.

  The solid line c in FIG. 2 shows the potential change when a cathode electricity amount of 60 mAh / g is passed through the artificial graphite powder. From the solid line c, the electric potential after the end of energization is about 0.6 V, which indicates that lithium ion and graphite did not form a third stage structure compound. Moreover, the broken line d of FIG. 1 shows the potential change when an anode current is passed through the artificial graphite powder. Since the solid line c and the broken line d are similar to each other, it can be presumed that lithium ions solvated in DME were inserted and released into the artificial graphite powder instead of lithium ions.

From the comparison between test cell 1 and test cell A, LiCl ₄ / DME = 1/1 (the Lithium ion solvated with LiBF ₄ and DME destroys the graphite structure and does not make the negative electrode potential low. In the adduct of (molar ratio), lithium ions can enter and exit between graphite layers without destroying the graphite structure, and the negative electrode potential can be reduced.

(Nonaqueous electrolyte battery 1)
The nonaqueous electrolyte battery 1 was assembled and evaluated as follows using LiFePO ₄ as a positive electrode material that occludes and releases lithium ions by charging and discharging, and artificial graphite as a negative electrode material.

First, 93 parts by weight of LiFePO ₄ powder, 3 parts by weight of acetylene black as a conductive agent, and 4 parts by weight of polyvinylidene fluoride resin as a binder were mixed. This mixture was dispersed in dehydrated N-methyl-2-pyrrolidone to prepare a slurry-like positive electrode mixture.

  This positive electrode mixture was applied onto a positive electrode current collector made of aluminum foil having a thickness of 15 μm, and then dried and rolled to form a positive electrode active material layer having a thickness of 63 μm. Next, the positive electrode current collector on which the positive electrode active material layer was formed was cut into a size of 35 mm × 35 mm. This positive electrode current collector was ultrasonically welded to a 0.5 mm thick aluminum current collector plate with a lead to produce a positive electrode plate.

  A negative electrode plate produced in the same manner as the test cell 1 of Example 3 was used.

As the nonaqueous electrolytic solution, the electrolytic solution 29 used in Example 2, that is, a mixture of LiClO ₄ , DME and EMC with a composition of LiClO ₄ / DME / EMC = 1/1/1 (molar ratio) was used. .

  Next, the positive electrode plate and the negative electrode plate prepared above were arranged opposite to each other through a polypropylene nonwoven fabric, and then the positive electrode plate and the negative electrode plate were fixed with a tape and integrated to prepare an electrode body. This electrode body was placed in a cylindrical aluminum laminate bag having openings at both ends, and one opening portion of the bag was welded at the lead portions of both electrodes. And the non-aqueous electrolyte prepared above was dripped from the other opening part. After dripping, deaeration was performed under 10 mmHg for 5 seconds. The other opening was sealed by welding to produce a nonaqueous electrolyte battery.

The nonaqueous electrolyte battery assembled as described above was charged and discharged at an ambient temperature of 20 ° C. and a current density of 0.3 mA / cm ² . The charging upper limit voltage of the battery was 4.0V, and the discharging lower limit voltage was 2.8V. Assuming that the discharge capacity at the 10th cycle was 100, the discharge capacity after 100 cycles was 83.

(Nonaqueous electrolyte battery A)
LiBF ₄ , DME and EMC are added to the non-aqueous electrolyte, and LiBF ₄ / DME / EMC = 1/1 /
What mixed by the composition of 1 (molar ratio) was used. In the preparation, LiBF ₄ , DME and EMC were mixed at LiBF ₄ / DME / EMC = 1/1/1 (molar ratio), then heated at 60 ° C. for 2 hours and cooled to room temperature. This electrolyte solution is slightly yellowish, but no precipitation of LiBF ₄ was observed at room temperature. Otherwise, the nonaqueous electrolyte battery A was assembled in the same manner as the nonaqueous electrolyte battery 1.

The nonaqueous electrolyte battery assembled as described above was charged and discharged at an atmospheric temperature of 20 ° C. and a current density of 0.3 mA / cm ² . However, in the first charge of the battery, the battery swelled and could not be charged / discharged. The cause of the swelling of the battery was the expansion of artificial graphite, which is the negative electrode material, and the generation of a large amount of gas within the battery.

  Thus, compared with the nonaqueous electrolyte battery A of the present invention and the comparative nonaqueous electrolyte battery A, the electrolyte of the present invention is clearly useful as an electrolyte for nonaqueous electrolyte batteries and operates stably. I understand that.

(Lithium primary battery 1)
Fluorinated graphite was used as the positive electrode material, and the lithium primary battery 1 was assembled by the following procedure. The positive electrode plate was produced in the same manner as the non-aqueous electrolyte battery 1 of Example 4.

  The negative electrode plate was prepared by cutting a lithium metal foil into a size of 35 mm × 35 mm and then pressing it onto a copper current collector with a lead having a thickness of 0.5 mm.

As the non-aqueous electrolyte, a mixture of LiClO ₄ , DME, PC, and DEC so as to have a composition of LiClO ₄ / DME / PC / DEC = 1/1/1/1 (molar ratio) was used. In the preparation, LiClO ₄ , DME, PC and DEC were mixed at LiClO ₄ / DME / PC / DEC = 1/1/1/1 (molar ratio), then heated at 60 ° C. for 2 hours and cooled to room temperature. This electrolytic solution was colorless and transparent, and did not solidify at room temperature even when left for 1 month.

  The salt concentration of this electrolytic solution is 2.4 mol / kg, which is still a high salt concentration.

  The positive electrode plate and the negative electrode plate were opposed to each other with a polyethylene porous film in between, and the positive electrode plate and the negative electrode plate were fixed by tape and integrated. Next, this integrated product was placed in a cylindrical aluminum laminated bag having both ends open, and one opening portion of the bag was welded at the lead portions of both electrodes. And the non-aqueous electrolyte prepared from the other opening part was dripped.

  The battery assembled in this way was deaerated at 10 mmHg for 5 seconds, and then the injected opening was sealed by welding.

The lithium primary battery 1 assembled as described above was subjected to preliminary discharge for about 5% of the positive electrode capacity under the conditions of 20 ° C. and 0.03 mA / cm ² . After the preliminary discharge, the battery was stored at 60 ° C. for 1 month, and the change in internal impedance before and after storage was examined. When the resistance at 10 kHz was measured, it was 2.9Ω before storage, but was 3.7Ω after storage.

(Lithium primary battery A)
A non-aqueous electrolyte mixed with LiBF ₄ , DME, PC, and DEC so as to have a composition of LiBF ₄ / DME / PC / DEC = 1/1/1/1 (molar ratio) was used. In the preparation, LiBF ₄ , DME, PC, and DEC were mixed at LiBF ₄ / DME / PC / DEC = 1/1/1/1 (molar ratio), then heated at 60 ° C. for 2 hours and cooled to room temperature. This electrolyte was slightly yellowish, but it did not solidify at room temperature even when left for 1 month. Otherwise, the lithium primary battery A was assembled in the same manner as the lithium primary battery 1.

  The lithium primary battery A assembled as described above was stored at 60 ° C. for 1 month, and changes in internal impedance before and after storage were examined. When the resistance at 10 kHz was measured, it was 2.7Ω before storage, but it was 5.6Ω after storage.

The internal impedance of the lithium primary battery A is increased as compared with the lithium primary battery 1. This is because a small amount of moisture present in the battery reacts with LiBF _{4 and} is generated on the lithium metal of the negative electrode by the generated HF. This is probably because a resistive film was formed.

  Thus, it is apparent that the electrolytic solution of the present invention is useful as an electrolytic solution for a lithium primary battery and can suppress an increase in internal resistance before and after storage at a high temperature.

(Electric double layer capacitor 1)
A polarizable electrode was prepared by the following procedure.

Activated carbon powder made of phenol resin having a specific surface area of 1700 m ² / g, acetylene black as a conductive agent, ammonium salt of carboxymethyl cellulose as a binder, water and methanol as a dispersion medium, and a weight ratio of 10: 2: 1: Mixed at a ratio of 100: 40. This mixture was applied to one side of a current collector made of aluminum foil having a thickness of 20 μm, and then dried to form a power storage layer having a thickness of 80 μm. This was cut into a size of 35 mm × 35 mm, and then ultrasonically welded to a 0.5 mm thick aluminum current collector plate with leads.

  Two polarizable electrodes facing each other through a separator made of polypropylene nonwoven fabric were housed in an aluminum laminated tube to form an electric double layer capacitor.

The non-aqueous electrolyte used was a mixture of LiClO ₄ , DME, PC, and DMC so as to have a composition of LiClO ₄ / DME / PC / DMC = 1/1/1/1 (molar ratio). In the preparation, LiClO ₄ , DME, PC and DMC were mixed at LiClO ₄ / DME / PC / DMC = 1/1/1/1 (molar ratio), then heated at 60 ° C. for 2 hours and cooled to room temperature. This electrolytic solution was colorless and transparent, and did not solidify at room temperature even when left for 1 month.

Using the electric double layer capacitor 1 assembled as described above, charging / discharging was performed in the voltage range of 0 to 2.3 V at an ambient temperature of 60 ° C. and a current value of 6 mA / cm ² . The capacity of the capacitor after 500 cycles was approximately 94, assuming that the capacity at the 20th cycle was 100.

(Electric double layer capacitor A)
The non-aqueous electrolyte, a LiBF ₄ and DME, PC and _DMC, was a mixture so that the composition of LiBF 4 / DME / PC / DMC = 1/1/1/1 ( molar ratio). In the preparation, LiBF ₄ , DME, PC and DMC were mixed at LiBF ₄ / DME / PC / DMC = 1/1/1/1 (molar ratio), then heated at 60 ° C. for 2 hours and cooled to room temperature. This electrolyte was slightly yellowish, but it did not solidify at room temperature even when left for 1 month. Otherwise, the electric double layer capacitor A was assembled in the same manner as the electric double layer capacitor 1.

Using the electric double layer capacitor A produced as described above, charging / discharging was performed in the voltage range of 0 to 2.3 V at an ambient temperature of 60 ° C. and a current value of 6 mA / cm ² . The capacity of the capacitor after 500 cycles was approximately 57, assuming that the capacity at the 20th cycle was 100. It is considered that the capacitance deterioration is larger than that of the electric double layer capacitor 1 because the decomposition of DME is promoted due to the HF generated by the reaction between the moisture contained in the electrode and LiBF ₄ .

  Thus, it is apparent that the electrolytic solution of the present invention is useful as an electrolytic solution for electric double layer capacitors and operates stably.

(Hybrid capacitor 1)
A hybrid capacitor was assembled using the polarizable electrode produced in the same manner as in Example 6 as the positive electrode and the electrode that occludes and releases lithium ions produced in the same manner as in Example 3 as the negative electrode.

  The two electrodes were opposed to each other with a separator made of polypropylene non-woven fabric and housed in an aluminum laminated tube to obtain a hybrid capacitor.

The non-aqueous electrolyte used was a mixture of LiClO ₄ , DME, and DEC so as to have a composition of LiClO ₄ / DME / DEC = 1/1/1 (molar ratio). In the preparation, LiClO ₄ , DME, and DEC were mixed at LiClO ₄ / DME / DEC = 1/1/1 (molar ratio), then heated at 60 ° C. for 2 hours and cooled to room temperature. This electrolytic solution was colorless and transparent, and did not solidify at room temperature even when left for 1 month.

Using the hybrid capacitor assembled as described above, charging and discharging were performed in the voltage range of 0 to 3.8 V at an ambient temperature of 20 ° C. and a current value of 3 mA / cm ² . The capacity of the hybrid capacitor after 100 cycles was approximately 91, assuming that the capacity of the 20th cycle was 100.

(Hybrid capacitor A)
A non-aqueous electrolyte mixed with LiBF ₄ , DME, and DEC so as to have a composition of LiBF ₄ / DME / DEC = 1/1/1 (molar ratio) was used. In the preparation, LiBF ₄ , DME and DEC were mixed at LiBF ₄ / DME / DEC = 1/1/1 (molar ratio), then heated at 60 ° C. for 2 hours and cooled to room temperature. This electrolyte was slightly yellowish, and did not solidify at room temperature even after being left for 1 month. Otherwise, the hybrid capacitor A was assembled in the same manner as the hybrid capacitor 1.

Using the hybrid capacitor fabricated as described above, charging and discharging were attempted in the voltage range of 0 to 3.8 V at an atmospheric temperature of 20 ° C. and a current value of 3 mA / cm ² . However, at the first charge, the hybrid capacitor swelled and could not be charged or discharged. The reason why the hybrid capacitor swelled was due to the expansion of artificial graphite, which is a negative electrode material, and the generation of a large amount of gas in the battery.

  Thus, it is apparent that the electrolytic solution of the present invention is useful as an electrolytic solution for a hybrid capacitor and operates stably.

  As described above, according to the present invention, a high salt density non-aqueous electrolyte can be prepared, and thus an electrochemical energy storage device having a high energy density can be obtained.

  The electrochemical energy storage device of the present invention is useful as a lithium ion battery, a lithium primary battery, an electric double layer capacitor, and the like, for example, as a power source for portable electronic devices.

Charging / discharging characteristic diagram of graphite negative electrode in non-aqueous electrolyte of the present invention Charging / discharging characteristics of graphite negative electrode in non-aqueous electrolyte of comparative example

Explanation of symbols

a, c Solid line b, d Broken line

Claims (4)

  A non-aqueous electrolyte characterized in that an adduct obtained by adding equimolar 1,2-dimethoxyethane to lithium perchlorate in a solidified state at a low temperature exists. The nonaqueous electrolytic solution according to claim 1, which satisfies the following formula (1).
0.8 ≤ B / A ≤ 1.4
(Where A is the number of moles of lithium perchlorate in the non-aqueous electrolyte, and B is the number of moles of 1,2-dimethoxyethane in the non-aqueous electrolyte) (1)   A non-aqueous electrolyte solution comprising the non-aqueous electrolyte solution according to claim 1 further containing at least one compound selected from the group consisting of a cyclic carbonate, a cyclic ester, and a chain carbonate. The electrochemical energy storage device which comprises a positive electrode, a negative electrode, and the non-aqueous electrolyte of any one of Claim 1 to 3.

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