JP4900561B2 - Lithium salt and its use - Google Patents

Description

  The present invention relates to a lithium salt useful as an electrolyte of a lithium battery and a method for producing the same. The present invention also relates to a battery using such a lithium salt (for example, a lithium battery).

Lithium salts having an aluminate structure with an oligoether group and an electron withdrawing group are known. Patent document 1 is mentioned as a prior art document regarding this lithium salt. Such lithium salts can exhibit good ionic conductivity and lithium ion transport number alone (eg, without mixing non-aqueous solvents) at room temperature. Further, it may be a salt which is liquid at normal temperature, that is, a normal temperature molten salt having lithium (Li) as a cation (hereinafter, also referred to as “lithium molten salt”).
JP 2003-146951 A

  One object of the present invention is to provide a more useful lithium salt, which is a salt of an anion having a structure in which an oligoether group is bonded to a central element and a lithium ion. For example, it is to provide a lithium salt that can achieve at least one of the effects of improving ionic conductivity, relaxing the temperature dependence of ionic conductivity, and reducing viscosity. Another object of the present invention is to provide a method for producing such a lithium salt. Moreover, it is providing a battery (for example, lithium battery) provided with the electrolyte containing the said lithium salt.

According to the present invention, a lithium salt represented by the following formula (1) is provided.
LiM (OY) _n (N (COR ^X ) ₂ ) _4-n (1)
Here, n in the formula (1) may be a number selected from 1 to 3 (typically an integer). M may be an element belonging to Group 13 of the periodic table. Y is an oligoether group, represented by ^{_{(R 1 O) m -R 2}} , Ru chain oligoether der having a hydroxyl group at at least one end. m is 1 to 20, ^{R 1} is an alkylene group having 1 to 8 carbon atoms, R ² is one selected from an alkyl group, an aryl group or alkylaryl group having 1 to 8 carbon atoms. R ^X may be a halogenated alkyl group having 1 to 3 carbon atoms. In one preferred embodiment, R ^X is a trifluoromethyl group. The lithium salt having such a structure may exhibit good ionic conductivity. Moreover, the temperature dependence of the ionic conductivity may be relatively small. It can also be of relatively low viscosity. According to the lithium salt of the present invention, one or more of these effects can be realized.

Moreover, according to this invention, the lithium salt manufacturing method suitable for manufacture of the lithium salt represented by the said Formula (1) etc. is provided. The production method includes a compound represented by the formula LiMH ₄ (M in the formula is equal to M in the formula (1)), and a formula HOY (Y in the formula is in the formula (1)). And a compound represented by the formula LiM (OY) _n H _4-n (wherein n is equal to n in the formula (1)). The process of producing is included. The compound represented by the formula LiM (OY) _n H _4-n and the formula HN (COR ^X ) ₂ (R ^X in the formula is equal to R ^X in the formula (1)). And a step of reacting the compound to form a lithium salt represented by the formula (1).

  According to the present invention, a battery (typically a lithium battery) comprising any of the lithium salts described above is provided. The electrolyte containing the lithium salt may exhibit one or more effects of good ion conductivity, relatively low temperature dependence of ionic conductivity, and low viscosity. Therefore, a battery including such an electrolyte can exhibit better battery characteristics.

  Hereinafter, preferred embodiments of the present invention will be described in detail. It should be noted that technical matters other than the contents particularly mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters for those skilled in the art based on the prior art. The present invention can be carried out based on the technical contents disclosed in the present specification and the common general technical knowledge in the field.

The lithium salt disclosed here is represented by the formula (1): LiM (OY) _n (N (COR ^X ) ₂ ) _4-n ; N in the formula may be a number selected from 1 to 3 (typically an integer). The lithium salt represented by this formula may be a mixture of a plurality of types of lithium salts having different values of n. From the viewpoint of usefulness as an ion conductive material, a lithium salt in which n in the above formula (1) is 2 is particularly preferable. M in the above formula (1) is any element selected from elements belonging to group 13 (that is, B, Al, Ga, In, and Tl) in the long-period type (in accordance with group representation of 1 to 18) element periodic table. It is. Typically, M is boron (B) or aluminum (Al).

R ^x in the above formula (1) is a halogenated alkyl group having 1 to 3 carbon atoms. From the viewpoint of obtaining a lower viscosity lithium salt, a halogenated alkyl group having 1 or 2 carbon atoms is preferable, and a halogenated alkyl group having 1 carbon atom (that is, a halogenated methyl group) is particularly preferable. Here, the “halogenated alkyl group” refers to a group in which some or all (preferably all) hydrogen atoms of the alkyl group are replaced with halogen atoms. The halogen atom replacing the hydrogen atom may be any one selected from the group consisting of a fluorine atom (F), a chlorine atom (Cl), a bromine atom (Br), and an iodine atom (I). Preferable examples of the halogenated alkyl group include alkyl groups in which some or all (preferably all) hydrogen atoms are substituted with either fluorine atoms or chlorine atoms. Alkyl groups in which some or all of the hydrogen atoms are substituted with fluorine atoms (ie, fluorinated alkyl groups) are preferred, and alkyl groups in which all of the hydrogen atoms are substituted with fluorine atoms (ie, perfluoroalkyl groups) are particularly preferred. Specific examples of suitable R ^X include a trifluoromethyl group (CF ₃ ) and a pentafluoroethyl group (CF ₂ CF ₃ ). Particularly preferred R ^{X for the} present invention is a trifluoromethyl group.

Two R ^X contained in one N (COR ^X ) ₂ may be the same or different. Usually, a lithium salt in which two R ^x contained in each N (COR ^x ) ₂ are the same is preferable because the raw materials are easily obtained and / or synthesized. The lithium salt represented by the formula (1) may have 1 to 3 N (COR ^x ) ₂ depending on the number of n. When n is greater than 1, the lithium salt may have a plurality of the same kind of N (COR ^x ) ₂ on the central element (M), and different types (two or more) of the same on the central element. N (COR ^x ) ₂ may be included. From the viewpoint of easy synthesis and the like, a lithium salt having a structure having n pieces of the same kind of N (COR ^x ) ₂ on the central element is preferable.

Y in the above formula (1) is an oligoether group. For example, it is preferably an oligoether group having a molecular weight of about 70 to 550 (more preferably 100 to 400). As a suitable example of Y, following formula (2):
(R ¹ O) _m -R ² (2);
The oligoalkylene oxide group represented by these is mentioned. Here, m in Formula (2) may be 1-20. m is preferably 2 to 14, and m is more preferably 5 to 12. R ¹ is an alkylene group having 1 to 8 carbon atoms, preferably 2 to 4 carbon atoms, more preferably 2 to 3 carbon atoms. It is particularly preferred that R ¹ is an ethylene group (that is, Y is an oligoethylene oxide group). R ² may be an alkyl group having 1 to 8 carbon atoms, an aryl group, or an alkylaryl group (for example, a benzyl group). R ² is particularly preferably an alkyl group having 1 to 3 carbon atoms (for example, a methyl group).

The lithium salt represented by the formula (1) may have 1 to 3 Ys depending on the number of n. When n in Formula (1) is larger than 1, this lithium salt may have a plurality of the same kind of Y on the central element (M), and different types (two or more) of the same kind on the central element. Y may be included. For example, it may be a lithium salt in which n in the formula (1) is 2, and at least one of m, R ^1, and R ² in the formula (2) has two types of Y on one central element.

The lithium salt having the structure represented by the above formula (1) can be suitably produced, for example, by the following method. That is, the compound represented by the formula LiMH ₄ is reacted with the compound represented by the formula HOY. This gives rise to compounds represented by the formula LiM (OY) _n H _4-n (including dissociated ones, and so on). Here, the compound represented by the formula HOY is a compound corresponding to a structure in which a hydroxyl group (OH) is bonded to Y in the formula (1), and an oligoether having at least one hydroxyl group (typically, A linear oligoether having a hydroxyl group at least at one end). For example, when it is intended to produce a lithium salt in which Y in the above formula (1) is an oligoalkylene glycol monoalkyl ether, an oligoalkylene glycol monoalkyl ether can be selected as the compound represented by the formula HOY.

This reaction can be allowed to proceed by mixing the compound represented by the formula LiMH ₄ and the compound represented by the formula HOY in a suitable solvent. Examples of solvents that can be preferably used include tetrahydrofuran (THF), diethyl ether, dimethoxyethane, diglyme (diethylene glycol dimethyl ether) and the like. Of these, the use of THF is particularly preferred. The reaction can proceed in a temperature range of −78 to 60 ° C., for example. From the viewpoint of generating a lithium salt having a target structure with high purity, the reaction is preferably performed in a temperature range of 0 to 40 ° C. Moreover, the temperature range around room temperature (for example, 20-35 degreeC) can be selected as reaction temperature. This is advantageous in that the reaction operation is easy and the reaction apparatus can be simplified.
The number of _n in the formula LiM (OY) _n H _4-n can be adjusted by, for example, the charging ratio (molar ratio) between the compound represented by the formula LiMH ₄ and the compound represented by the formula HOY. For example, when it is intended to produce a compound in which _n in LiM (OY) _n H _4-n is approximately 2, the compound represented by the formula HOY is added to 1 mol of the compound represented by the formula LiMH _4. The reaction may be carried out at a rate of 1.8 to 2.2 mol (preferably about 2 mol).

Next, the compound represented by LiM (OY) _n H _4-n is reacted with the compound represented by the formula HN (COR ^x ) ₂ . The compound represented by the formula HN (COR ^x ) ₂ is an amide corresponding to the N (COR ^x ) ₂ group of the compound represented by the formula (1). Thereby, a lithium salt having a structure represented by the formula (1) is generated.
This reaction can proceed by mixing the compound represented by LiM (OY) _n H _4-n and the compound represented by the formula HN (COR ^x ) ₂ in a suitable solvent. Examples of the solvent that can be preferably used include tetrahydrofuran (THF), dimethoxyethane, diglyme and the like. Of these, the use of THF is particularly preferred. The reaction can proceed in a temperature range of 0 to 60 ° C, for example. From the viewpoint of efficiently producing a lithium salt having a target structure, the reaction is preferably performed in a temperature range of 0 to 40 ° C. Further, from the viewpoint of ease of operation, etc., a temperature range around room temperature (for example, 20 to 35 ° C.) can be preferably selected as the reaction temperature. For example, after the above reaction that yields the compound represented by LiM (OY) _n H _4-n , the compound represented by the formula HN (COR ^x ) ₂ is added to the reaction solution to produce these two steps. The process can be carried out efficiently.

The reaction between the compound represented by LiM (OY) _n H _4-n and the compound represented by the formula HN (COR ^x ) ₂ is a reaction temperature around room temperature even when THF is selected as the reaction solvent. (For example, side reactions such as ring-opening polymerization of THF do not cause a problem). Therefore, THF, which is a general-purpose solvent, can be used without forcibly cooling the system during the reaction (for example, cooling to about −78 ° C.), and thus there is an advantage that synthesis is easy. However, this does not limit the reaction temperature at the time of carrying out the reaction to around room temperature, and it is of course possible to select a lower reaction temperature.

The amount of the compound represented by the formula HN (COR ^x ) ₂ may be about 4-nmol or more per 1 mol of the compound represented by LiM (OY) _n H _4-n. Is appropriate. For example, when a lithium salt in which n in formula (1) is approximately 2 is to be produced, 1 mol of the compound represented by LiM (OY) ₂ H ₂ is represented by formula HN (COR ^x ) ₂ The compound represented may be reacted at a ratio of 1.8 to 3 mol (preferably 1.8 to 2.5 mol, more preferably about 2 mol). Then, the target lithium salt can be obtained by performing an appropriate post-treatment (such as solvent removal) as necessary.

In one preferred embodiment of the lithium salt disclosed herein, the lithium salt is a compound that is liquid at room temperature (ie, a lithium molten salt). Here, the “room temperature range” is, for example, an upper limit of about 80 ° C. (typically about 60 ° C., and in some cases about 40 ° C.), and a lower limit of about −20 ° C. (typically about 0 ° C., In some cases, it refers to a temperature range of approximately 20 ° C. A lithium salt exhibiting a liquid state in at least a part of the temperature range is preferable. A lithium salt which is liquid at least at about 25 ° C. is preferred, and is in a liquid state over the entire temperature range of at least about 20 to 40 ° C. (more preferably about 0 to 60 ° C., more preferably about −20 to + 80 ° C.). More preferred is a lithium salt capable of maintaining the above.
Such a lithium molten salt can exhibit good ionic conductivity and / or lithium ion transport number in a normal temperature range. Therefore, the lithium salt alone (for example, without mixing a non-aqueous solvent or the like) can be used as an ion conductive material provided in various electrochemical devices (for example, power storage elements such as batteries and capacitors). For example, it can be suitably used as an electrolyte of a lithium battery (typically a lithium ion secondary battery).

  A battery (such as a lithium ion secondary battery) disclosed herein includes an electrolyte containing any of the lithium salts described above. The electrolyte may have a composition containing one or more selected from the lithium salt represented by the above formula (1) (preferably a lithium molten salt) and substantially not containing a non-aqueous solvent. An electrolyte having such a composition and showing a liquid state at least at about 25 ° C. is preferable.

  Further, the electrolyte provided in the battery disclosed herein may have a composition containing other components in addition to the lithium salt represented by the above formula (1). Examples of such “other components” include various non-aqueous solvents that can be used as electrolytes for general non-aqueous batteries. For example, one or two selected from propylene carbonate (PC), ethylene carbonate (EC), γ-butyrolactone, tetrahydrofuran, 1,3-dioxolane, dimethyl carbonate, diethyl carbonate (DEC), ethyl methyl carbonate (EMC), etc. It can be set as the electrolyte of the composition containing the above. In an electrolyte having a composition containing such a non-aqueous solvent, the mass ratio of the non-aqueous solvent to the total mass of the electrolyte is preferably about 50% or less, more preferably about 25% or less, and about 10% or less. More preferably.

Other examples of the “other components” include various lithium salts known as supporting electrolytes for general lithium batteries. For example, one or more selected from LiPF ₆ , LiBF ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiC (SO ₂ CF ₃ ) ₃ , LiClO _{4 and the} like. An electrolyte having a composition containing the lithium salt as a supporting electrolyte. The concentration of the supporting electrolyte in the electrolyte having such a composition is not particularly limited, but it is usually preferable that the concentration is such that the supporting electrolyte can be stably dissolved (no precipitation or the like is observed) at least at 25 ° C. For example, it can be set as the composition containing about 0.1-15 mol (preferably 0.5-10 mol) of supporting electrolyte per liter (L) of electrolyte.

The electrolyte provided in the battery disclosed herein may have a composition containing a salt of a cation other than lithium and an anion (for example, a room temperature molten salt having an imidazolium cation, an ammonium cation, a pyridinium cation, or the like). Further, in place of N (COR ^x ) ₂ in the above formula (1), OC ₆ F ₅ , OCOR (R is a perfluoroalkyl group having 1 to 4 carbon atoms), OB (OY) ₂ , N ( The composition may include a lithium salt (preferably a lithium molten salt) having a structure having at least one group selected from the group consisting of SO ₂ CF ₃ ) ₂ and N (SO ₂ C ₂ F ₅ ) ₂ . The total amount of these salts used is suitably less than about 100 parts by mass and less than about 50 parts by mass with respect to 100 parts by mass of the lithium salt represented by the above formula (1). The amount is preferably less than about 10 parts by mass.

  Further, the lithium salt represented by the above formula (1) includes, for example, polyethylene oxide (PEO), ethylene oxide-propylene oxide copolymer (EO-PO), polymethyl methacrylate (PMMA), polyvinylidene fluoride (PVdF), polyfluoride. It can also be used as a solid electrolyte by molding (film formation) together with a support such as vinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP).

As a positive electrode constituting a lithium battery (typically, a lithium ion secondary battery) including such an electrolyte, a positive electrode current collector attached to a positive electrode current collector can be used. As the positive electrode current collector, a rod-like body, a plate-like body, a foil-like body, a net-like body or the like mainly composed of aluminum (Al), nickel (Ni), titanium (Ti), or the like can be used. Alternatively, carbon paper or the like may be used. As the positive electrode active material, an oxide-based positive electrode active material having a layered structure used in a general lithium battery, an oxide-based positive electrode active material having a spinel structure, or the like can be used. For example, the main component is a lithium cobalt complex oxide (typically LiCoO ₂ ), a lithium nickel complex oxide (typically LiNiO ₂ ), a lithium manganese complex oxide (LiMn ₂ O ₄ ), or the like. A positive electrode active material can be used. Such a positive electrode active material can be made into a positive electrode in a form in which the positive electrode active material is attached to a positive electrode current collector as a positive electrode mixture together with a conductive material, a binder (binder) and the like as necessary. As the conductive material, a carbon material such as carbon black (acetylene black or the like), a conductive metal powder such as nickel powder, or the like can be used. As the binder, use is made of polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyvinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), styrene butadiene block copolymer (SBR), or the like. Can do. Although it does not specifically limit, the usage-amount of the electrically conductive material with respect to 100 mass parts of positive electrode active materials can be made into the range of 1-15 mass parts, for example. Moreover, the usage-amount of the binder with respect to 100 mass parts of positive electrode active materials can be made into the range of about 1-10 mass parts, for example.

As the negative electrode, a negative electrode current collector having a negative electrode active material attached thereto can be used. As the negative electrode current collector, a rod-like body, a plate-like body, a foil-like body, a net-like body or the like mainly composed of aluminum (Al), nickel (Ni), copper (Cu), or the like can be used. Alternatively, carbon paper or the like may be used. As the negative electrode active material, a carbon material having an amorphous structure and / or a graphite structure can be used. For example, natural graphite, mesocarbon microbeads (MCMB), highly oriented graphite (HOPG), hard carbon, soft carbon, etc. can be used as the negative electrode active material. Further, Si, Sn or the like may be used as the negative electrode active material. Lithium titanate (for example, Li ₄ Ti ₅ O ₁₂ ) may be used as the negative electrode active material. Such a negative electrode active material can be made into a negative electrode in a form in which the negative electrode active material is attached to a negative electrode current collector as a negative electrode mixture together with a binder (binder) or the like as necessary. As the binder, the same as the positive electrode can be used. As another structure of the negative electrode, a Li (metal) foil, a Si vapor deposition film, a Sn plating foil, or the like can be adopted.

  As the separator, for example, a porous film made of a polyolefin resin such as polyethylene (PE) or polypropylene (PP) can be used. Moreover, you may use the woven fabric or nonwoven fabric which consists of a polypropylene, a polyethylene terephthalate (PET), methylcellulose, etc.

  Hereinafter, experimental examples relating to the present invention will be described. However, the present invention is not intended to be limited to the specific examples.

<Experimental Example 1: Synthesis of Salt C>
The lithium salt (Salt C) according to this experimental example was synthesized according to the following synthesis scheme.

That is, 5 mL of tetrahydrofuran (THF) was placed in a 50 mL flask, and a THF solution containing 1.81 g (2.00 mol) of lithium aluminum hydride (THF solution having a lithium aluminum hydride concentration of 1.0 M, product of Aldrich) was added. It was. Here, 0.657 g of oligoethylene glycol monomethyl ether (CH ₃ O (CH ₂ CH ₂ O) ₃ H, product of Aldrich, molecular weight 164.20) having a polymerization degree of 3 (that is, the number of units of ether chain n = 3) A solution prepared by dissolving (4.00 mol) in 5 mL of THF was slowly added dropwise and stirred at room temperature for 4 hours to give LiAl (O (CH ₂ CH ₂ O) ₃ CH ₃ ) ₂ H ₂ . After the reaction was completed, 0.836 g (4.00 mol) of bistrifluoroacetamide (product of Tokyo Chemical Industry Co., Ltd.) was slowly added dropwise thereto and stirred at room temperature for 12 hours. The reaction solution was purified to obtain a lithium salt having the structure shown in the above synthesis scheme, that is, Salt C (n = 3). The yield was 95% (1.47 g).

The FT-IR spectrum of Salt C (n = 3) obtained in this experimental example was measured by the As ₂ Se ₃ plate method. The spectrum data is shown in Table 1. In addition, in this FT-IR measurement, the absorption which shows -OH group and NH group was not observed.

  In place of n = 3 oligoethylene glycol monomethyl ether, n = 7.2 oligoethylene glycol monomethyl ether (Aldrich product, average molecular weight 350) and n = 11.8 oligoethylene glycol monomethyl ether (Aldrich) Salt C (n = 7.2) and Salt C (n = 11.8) were synthesized in the same manner as the synthesis of Salt C (n = 3) except that the product and average molecular weight 550) were used. .

<Experimental Example 2: Synthesis of Salt D>
Except for using lithium borohydride instead of lithium aluminum hydride, the same as in Experimental Example 1 above, three types of lithium salts having different ether chain unit numbers n, that is, Salt D (n = 3), Salt D (n = 7.2) and Salt D (n = 11.8) were synthesized. The yield for Salt D (n = 3) was 94.3% (1.46 g). A synthesis scheme of these lithium salts is shown below.

The FT-IR spectrum of Salt D (n = 3) obtained in this experimental example was measured by the As ₂ Se ₃ plate method. In this FT-IR measurement, no absorption showing an —OH group and an NH group was observed. Further, this Salt D (n = 3) was dissolved in dimethyl sulfoxide-d ₆ and a ¹ H-NMR spectrum was measured. Their spectral data are shown in Table 2.

  The glass transition temperature (Tg) and melting point (Tm) of each lithium salt obtained in Experimental Examples 1 and 2 were measured by DSC. The results are shown below together with the properties of each lithium salt at 25 ° C. “-” In the table indicates that the measurement has not been performed.

<Experimental Example 3: Measurement of ion conductivity>
The ionic conductivity σ (S / cm) of each lithium salt obtained in Experimental Example 1 was measured. The measurement was performed under each temperature condition between about 25 ° C. and 80 ° C. by the AC impedance method using a stainless steel electrode. As the cell for measuring ionic conductivity, a cell heated at 90 ° C. for 1 hour in an argon atmosphere and then cooled at room temperature for 3 hours was used.

[Salt C]
Table 4 and FIG. 1 show the ionic conductivity measurement results for three types of Salt C having different ether chain unit numbers n.

  Salt C (n = 7.2) and Salt C (n = 11.8) both showed good ionic conductivity. The ionic conductivity of Salt C (n = 7.2) was even better than Salt C (n = 11.8). This is considered to be because the lithium ion concentration per volume is higher in Salt C (n = 7.2) than in Salt C (n = 11.8) having a longer ether chain. On the other hand, since Salt C (n = 3) was solid at 25 ° C., its ionic conductivity was lower than Salt C (n = 7.2) and Salt C (n = 11.8).

[Salt D]
Table 5 and FIG. 2 show the ionic conductivity measurement results for three types of Salt D having different numbers of ether chain units n.

  Salt D showed good ionic conductivity for all salts of n = 3, 7.2, 11.8. When comparing Salt C and Salt D with the same number n of ether chain units, Salt D showed higher ionic conductivity at any of n = 3, 7.2, and 11.8. This is because the electronegativity of B, which is the central element of Salt D, is higher than that of Al, which is the central element of Salt C. Therefore, it is considered that the interaction between lithium ions and anions is weakened, the dissociation of the salt is improved, and the ionic conductivity is improved. Moreover, it is thought that the low viscosity of Salt D compared with Salt C also contributed to the improvement of ionic conductivity. Unlike Salt C, Salt D showed higher ionic conductivity when n = 11.8 than n = 7.2 in the temperature range of room temperature to 60 ° C. This suggests that Salt D has a higher salt dissociation than Salt C, and therefore has a higher concentration of lithium ions as a carrier.

[Salt (TFA)]
Instead of the N (COCF ₃ ) ₂ group in Salt C, a lithium salt having a structure having a trifluoroacetate group (ie, the formula: LiAl (O (CH ₂ CH ₂ O) _n CH ₃ ) ₂ ) (OCOCF ₃ ) ₂ ; Lithium salt represented by :; hereinafter referred to as “Salt (TFA)”. ), And three types of lithium salts with different numbers of ether chain units, namely Salt (TFA) (n = 3), Salt (TFA) (n = 7.2) and Salt (TFA) (n = 11.1). 8) was synthesized. In this synthesis, trifluoroacetic acid was used in place of bistrifluoroacetamide, and the reaction between lithium aluminum hydride and oligoethylene glycol monomethyl ether and the resulting product with trifluoroacetic acid were both -78 ° C. The procedure was the same as in Experimental Example 1 except that the procedure was performed in. The obtained Salt (TFA) (n = 3, 7.2, 11.8) was a highly viscous liquid at 25 ° C.
About these Salt (TFA), it carried out similarly to Salt C, and measured the ionic conductivity. As a result, the ionic conductivity of Salt C (n = 7.2) was equal to or higher than that of Salt (TFA) (n = 7.2). In addition, the ionic conductivity (σ) of Salt C (n = 11.8) was improved by more than a half digit compared to Salt (TFA) (n = 11.8).

[Salt (TFSI)]
Instead of the N (COCF ₃ ) ₂ group in Salt C, a lithium salt having a structure having an N (SO ₂ CF ₃ ) ₂ group (that is, the formula: LiAl (O (CH ₂ CH ₂ O) _n CH ₃ ) ₂ ( Lithium salt represented by N (SO ₂ CF ₃ ) ₂ ) ₂ ; (hereinafter sometimes referred to as “Salt (TFSI)”), wherein the ether chain unit number n is 7.2 A salt, Salt (TFSI) (n = 7.2) was synthesized. In this synthesis, trifluoromethanesulfonimide (HN (SO ₂ CF ₃ ) ₂ ) was used instead of bistrifluoroacetamide, and the reaction of lithium aluminum hydride with oligoethylene glycol monomethyl ether and the resulting trifluoromethane The reaction was conducted in the same manner as in Experimental Example 1 except that the reaction with romethanesulfonimide was carried out at -78 ° C. The obtained Salt (TFSI) (n = 7.2) was a highly viscous liquid at 25 ° C.
About this Salt (TFSI), the ionic conductivity in 25-80 degreeC was measured like Salt C. As a result, Salt C (n = 7.2) has less ionic conductivity temperature dependency than Salt (TFSI) (n = 7.2) (more specifically, in a temperature range below room temperature). It was also found that there is little decrease in ionic conductivity). That is, Salt C (n = 7.2) showed stable ionic conductivity in a wider temperature range than Salt (TFSI) (n = 7.2). Also, the viscosity of Salt C (n = 7.2) was clearly lower than that of Salt (TFSI) (n = 7.2).

<Experimental Example 4: Measurement of lithium ion transport number>
The lithium ion transport number t ⁺ of Salt D (n = 7.2) and Salt D (n = 11.8) was determined using the following formula (I) by a combination of AC impedance and DC impedance. Here, t ⁺ in formula (I) is the lithium ion transport number, I ₀ is the initial current value, I _s is the steady current value, ΔV is the applied voltage, R _e ⁱ is the initial interface resistance value, and R _e ^s is the steady state. The interface resistance value, R _b ⁱ represents the initial bulk resistance value, and R _b ^f represents the final bulk resistance value. The results obtained are shown in Table 6.

As shown in this table, both Salt D (n = 7.2) and Salt D (n = 11.8) exhibited lithium ion transport number t ⁺ exceeding 0.7. This is because the lithium ion transport number of a liquid electrolyte used in a general lithium secondary battery (for example, the lithium ion transport number of an electrolyte having a composition in which LiPF ₆ is dissolved in a mixed solvent of ethylene carbonate and propylene carbonate is 0). It is clearly higher than that of. Moreover, it is understood from the comparison between Salt D (n = 7.2) and Salt D (n = 11.8) that the transport number is improved as the ether chain becomes longer. This is thought to be due to the increase in the molecular weight of the anion due to the longer ether chain (increasing the number of units n), resulting in an increase in bulk, and thus the mobility of the anion decreased.

MOPAC (general-purpose semiempirical molecular orbital package) calculation was performed by PM5 parameter using CAChe Worksystem version 5.0 manufactured by Fujitsu Limited for calculation of intramolecular local charges of Salt C, Salt D, and Salt (TFA). The results of such partial charge simulation are shown in FIGS.
As shown in FIG. 5, in Salt (TFA), the magnitude of the negative charge localized on the oxygen atom bonded to the central element (Al) in the trifluoroacetate group was 0.44. The magnitude of the negative charge localized at the carbonyl oxygen (C═O) of the trifluoroacetate group was 0.41. This value is larger than the magnitude of the negative charge (0.39) localized in the ether oxygen of the oligoether chain. In contrast, in Salt C and Salt D, as shown in FIGS. 3 and 4, the magnitude of the negative charge localized at each carbonyl oxygen (C═O) of the bistrifluoroacetamide group is 0.33 and 0, respectively. .31. All of these values are clearly smaller than the magnitude of the negative charge localized at the ether oxygen of the oligoether chain of each salt (0.40 for Salt C and 0.38 for Salt D). Thus, the relaxation of the localization of the negative charge on the carbonyl oxygen reduces the interaction between the carbonyl oxygen and the lithium ion, thereby improving the dissociation of the salt. As a result, in Salt C and Salt D, It is presumed that the ionic conductivity is improved as compared with Salt (TFA).

  Further, when Salt C and Salt D are compared, the central element is changed from aluminum (Al electronegativity: 1.5) to boron (B electronegativity: 2.0). Negative charges localized in the vicinity are smaller. For example, the magnitude of the negative charge localized in the oxygen atom connecting the oligoether chain and the central element is 0.56 in Salt C, but is as small as 0.44 in Salt D. For this reason, it is considered that in Salt D, the interaction between the anion and the lithium ion is weaker than Salt C, the dissociation property of the salt is increased, and the ionic conductivity is further improved.

Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.
In addition, the technical elements described in the present specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology illustrated in the present specification or the drawings achieves a plurality of objects at the same time, and has technical utility by achieving one of the objects.

It is a graph which shows the relationship between ionic conductivity and temperature. It is a graph which shows the relationship between ionic conductivity and temperature. It is explanatory drawing which shows the partial charge simulation result of Salt C. It is explanatory drawing which shows the partial charge simulation result of Salt D. It is explanatory drawing which shows the partial charge simulation result of Salt (TFA).

Claims (4)

Following formula (1):
LiM (OY) _n (N (COR ^X ) ₂ ) _4-n (1)
(Where, n .Y is .M is 1-3 is an element belonging to periodic table group 13 are Ri der oligoether ^group, represented by ^{_{(R 1 O) m -R 2}} , at least one end A linear oligoether having a hydroxyl group in which m is 1 to 20, R ¹ is an alkylene group having 1 to 8 carbon atoms, and R ² is an alkyl group, aryl group or alkylaryl having 1 to 8 carbon atoms. is one selected from the group R ^X is a halogenated alkyl group having 1 to 3 carbon atoms)..;
Lithium salt represented by The lithium salt according to claim 1, wherein R ^X is a trifluoromethyl group. Following formula (1):
LiM (OY) _n (N (COR ^X ) ₂ ) _4-n (1)
(Where, n .Y is .M is 1-3 is an element belonging to periodic table group 13 are Ri der oligoether ^group, represented by ^{_{(R 1 O) m -R 2}} , at least one end A linear oligoether having a hydroxyl group in which m is 1 to 20, R ¹ is an alkylene group having 1 to 8 carbon atoms, and R ² is an alkyl group, aryl group or alkylaryl having 1 to 8 carbon atoms. is one selected from the group R ^X is a halogenated alkyl group having 1 to 3 carbon atoms)..;
A method for producing a lithium salt represented by the following steps:
A compound represented by the formula LiMH ₄ (M in the formula is equal to M in the formula (1)), and a formula HOY (Y in the formula is equal to Y in the formula (1)). Reacting with a compound represented by the formula: LiM (OY) _n H _4-n (wherein n is equal to n in the formula (1)) to give a compound represented by the formula: and,
The compound represented by the formula LiM (OY) _n H _4-n and the formula HN (COR ^X ) ₂ (R ^X in the formula is equal to R ^X in the formula (1)). Reacting with a compound to produce a lithium salt represented by the formula (1);
A process for producing a lithium salt.   A battery comprising an electrolyte containing the lithium salt according to claim 1.

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