JP2017139068A - Electrolyte for lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrolyte for a Li ion secondary battery, by which superior battery characteristics including cycle and rate characteristics can be achieved.SOLUTION: The above purpose is achieved by an electrolyte for a Li ion secondary battery, which comprises a solvation ionic liquid containing methyl monoglyme (G1) and methyl diglyme (G2), and a Li salt. The ratio of a total mole number of oxygen atoms that the G1 and G2 include vs. the mole number of Li in the Li salt (i.e. a total mole number of oxygen atoms included in the G1 and G2 to that of Li in the Li salt) is 3.0 or more and less than 4.0. The mixing mole ratio of the G1 and G2 (i.e. G1 mole number/G2 mole number) is more than 1/4 and less than 3/2.SELECTED DRAWING: None

Description

  The present invention relates to an electrolyte for a lithium ion secondary battery and a lithium ion secondary battery using the same.

  In recent years, in order to cope with air pollution and global warming, reduction of the amount of carbon dioxide has been strongly desired. In the automobile industry, there are high expectations for reducing carbon dioxide emissions by introducing electric vehicles (EV) and hybrid electric vehicles (HEV). Electrochemicals such as secondary batteries for motor drive that hold the key to commercialization of these vehicles. Device development is actively underway.

  As a secondary battery for driving a motor, it is required to have extremely high output characteristics and high energy as compared with a consumer lithium ion secondary battery used in a mobile phone, a notebook personal computer or the like. Therefore, lithium ion secondary batteries having the highest theoretical energy among all the batteries are attracting attention, and are currently being developed rapidly.

  Generally, a lithium ion secondary battery includes a positive electrode in which a positive electrode active material or the like is applied to both surfaces of a positive electrode current collector using a binder, and a negative electrode in which a negative electrode active material or the like is applied to both surfaces of a negative electrode current collector using a binder. However, it has the structure connected through an electrolyte layer and accommodated in a battery case.

  In the lithium ion secondary battery, it is necessary to further increase the amount of energy to be stored in order to extend the cruising distance. Therefore, in order to realize an EV that has the same merchantability as a conventional gasoline vehicle, it is necessary to maintain a high energy capacity. Therefore, the battery is required to have high performance and ensure safety at a high technical level. It has been.

  In conventional lithium ion secondary batteries, a non-aqueous electrolyte (liquid electrolyte) or a gel electrolyte containing a non-aqueous electrolyte is mainly used as an electrolyte. In general, a non-aqueous electrolyte used in an electrolyte for a lithium ion secondary battery has a high lithium ion conductivity by well dissolving a lithium salt. As the solvent, carbonate compounds such as ethylene carbonate and dimethyl carbonate have been widely used because they have a wide potential window. However, non-aqueous electrolytes containing these carbonate compounds have the drawback that their flash point is low.

  Therefore, as a measure for increasing nonflammability (flame retardancy), the use of an electrolyte having extremely low volatility has been studied. As an electrolyte having extremely low volatility, a solvated ionic liquid (solvated molten salt) has attracted attention. In this solvated ionic liquid, a lithium salt such as lithium bis (trifluoromethylsulfonyl) imide [LiTFSI] interacts strongly with an etheric oxygen atom of a glyme-based solvent such as methyltriglyme (also abbreviated as G3). And forms a stable complex. The stability of these solvated ionic liquids has been studied for complex cation structures by molecular orbital calculation.

The molecular structures (a) and (b) in FIG. 21 show schematic structural diagrams of [Li (G3) ₁ ] [TFSI] (a) and [Li (G4) ₁ ] [TFSI] (b). FIG. 21 schematically shows a state in which an unshared electron pair of ether oxygen contained in a glyme molecule acts on a Li cation and is solvated.

In order to ascertain in what form the solvation structure shown in FIG. 21 actually takes the most stable structure, the following examination was performed. Select methyltriglyme (G3) and methyltetraglyme (also abbreviated as G4) as solvent molecules, and examine them with ab initio molecular orbital calculation using Gaussian 03 program for 1: 1 mixed solution with lithium salt. went. As shown in the molecular structures (a) and (b) above, a structure in which a glyme molecule is sterically surrounded around a lithium ion by donating an unshared electron pair present in ether oxygen contained in the glyme to the lithium ion. It was confirmed that a complex cation was formed. (The structure drawing obtained from the actual calculation result is a color drawing, but when it is made into an application drawing (monochrome drawing), it is not shown because each element molecule is difficult to read). Similarly, methyl monoglyme (abbreviated as G1) and methyl diglyme (abbreviated as G2) were selected as solvent molecules, and a mixed solution with a lithium salt was similarly examined. When G1 was studied with a mixed solvent having a molar ratio of 1: 2, and G2 with a mixed solvent having a molar ratio of 1: 1.33, unshared electron pairs present in ether oxygen contained in glyme were examined. It was found that a complex cation is formed by taking a structure in which glyme molecules are surrounded by lithium ions. Similarly, in the observation of the self-diffusion coefficient of each ion species and molecular species using NMR, the result of forming complex cations has been observed. In particular, in a solvated ionic liquid using an imide type lithium salt such as LiTFSI, the self-diffusion coefficient of lithium ions and the self-diffusion coefficient of glyme molecules show the same value. This also suggests that complex cations in which glyme is coordinated to lithium ions are formed in the solvated ionic liquid.

In particular, the conditions under which equimolar amounts of glymes containing four oxygen atoms such as lithium salt and methyltriglyme in the molecule, that is, [O] / [Li] = 4 are preferable from the viewpoint of the stability of the complex. (For example, also in the Example of patent document 1 shown below, all the examples (Examples 1-12) of Table 1 are the total number of moles of oxygen atoms contained in glymes and the number of moles of lithium ions in the lithium salt. The ratio of [O] / [Li] (= N _O / N _Li ) = 4 only). It is known from the results of thermal analysis and the like that this stable complex behaves as a single ionic species and does not ignite at all by heating with a burner.

  An equimolar mixture of a lithium salt and methyltriglyme (G3) or methyltetraglyme (G4) forms a complex cation by forming a complex between glymes and lithium. Therefore, since the equimolar mixture is composed only of this complex cation and anion (anion species of lithium salt), these series of compounds are salts. However, the ionic interaction between the complex cation and the anion is weakened by the influence of the complex formation, and it looks like a liquid despite being a salt. This liquid has extremely low volatility, high ion concentration, and high ion conductivity. A liquid having such characteristics is called a solvated ionic liquid.

  However, the 1: 1 (molar ratio) complex of these lithium salts and methyltriglyme increases the ionic radius of the solvated Li cation, and further causes an interaction between the Li cation and the solvated glyme molecule. To do. As a result, these electrolytes are not suitable for practical use because of their high viscosity (more than 10 times that of organic solvent-based electrolysis) and low conductivity by an order of magnitude compared to general organic electrolytes.

  Especially at low temperatures, the behavior becomes remarkable, the lithium salt dissolution ability decreases, and the interaction between lithium ions and solvent molecules increases more and more. As a result, the viscosity of the electrolyte itself increases abruptly, resulting in a decrease in ionic conductivity, so that the electrolyte performance at low temperatures is not sufficient.

Further, application of a solvated ionic liquid composed of methyltriglyme (G3) and methyltetragram (G4) to a negative electrode using a silicon-based active material having a larger capacity than a conventional carbon-based active material such as graphite. Has also been working on. It shows almost the same power generation characteristics while having a viscosity of more than 10 times compared with existing organic electrolyte systems, and it has been found that methyltetraglyme (G4) is superior in rate characteristics among solvated ionic liquids. However, sufficient cycle characteristics could not be expressed with the silicon electrode.

  Therefore, in order to obtain excellent battery characteristics even at low temperatures while ensuring electrolyte characteristics such as high ionic conductivity in the electrolyte, hydrofluoroether, which is a fluorine-based ether solvent, is used as a glyme-based solvent. Addition has led to a solution (see, for example, Patent Document 1).

  That is, it is essential that hydrofluoroether coexists in the electrolyte shown in the patent technology disclosed in Patent Document 1.

International Publication No. 2012/086602 JP 2010-287481 A JP 2014-112526 A JP 2014-192042 A

2006 47th Battery Symposium Abstracts 1F06 Abstracts of the 75th Electrochemical Society of Japan 3D09

  However, in Patent Document 1 described above, a fluorine-based ether compound (hydrofluoroether) exhibits a very good effect on reducing the viscosity of the electrolytic solution, but it is difficult to stably maintain the properties of the electrolyte. It is. Since hydrofluoroether is rich in volatility, the composition of the electrolytic solution containing hydrofluoroether is likely to change, and it is very difficult to use it for a long time while maintaining the properties of the electrolyte. In particular, in a laminated lithium ion battery (see FIGS. 1 and 2) using a laminate film as a battery outer packaging (container), the evaporation of hydrofluoroether is completely prevented even if it is sealed in the battery container. In other words, the hydrofluoroether volatilizes during long-term battery storage and continuous battery use, resulting in a significant change in the electrolyte composition. For this reason, various physical properties of the electrolyte greatly change from the initial values, and as a result, the battery performance may be greatly impaired.

  Moreover, in a high capacity battery using a silicon-based negative electrode aiming at high capacity, the reactivity of the silicon electrode alloyed with lithium ions with the electrolyte is further increased. In particular, it can be considered that it easily reacts with a hydrofluoroether containing a fluorine atom, which has a high electron density, and this also deteriorates various physical properties of the electrolytic solution, leading to a deterioration in the function of the electrolyte.

  Then, in view of the said subject, this invention aims at providing the electrolyte for lithium ion secondary batteries with which battery characteristics, such as the outstanding cycling characteristics and rate characteristics, are acquired.

  In order to solve the above-mentioned problems, the present inventors have conducted intensive research. As a result, the [O] / [Li] of the solvated ionic liquid using Li salt and G1 and G2 is controlled between 3.0 and less than 4.0, and the G1 / G2 mixing molar ratio is ( It has been found that the above-mentioned problems can be solved by setting it to (over 1/4) to (less than 3/2), and the present invention has been completed.

  According to the present invention, an optimal solvated ionic liquid electrolyte composition maintains the function of an electrode reaction involving an electrolyte and a silicon electrode without using a fluorine-based ether compound or the like that easily causes a change in the composition of the electrolyte. can do. Thereby, the electrolyte for lithium ion secondary batteries from which battery characteristics, such as the outstanding cycling characteristics and rate characteristics, are obtained can be provided.

1 is a schematic cross-sectional view schematically showing the overall structure of a high output (low resistance) and high capacity non-bipolar lithium ion secondary battery according to an embodiment of the present invention. 1 is a schematic cross-sectional view schematically showing the entire structure of a high output (low resistance) and high capacity bipolar lithium ion secondary battery according to an embodiment of the present invention. It is a figure which shows the cycle test result of Example 1 in this invention. It is a figure which shows the cycle test result of Example 2 in this invention. It is a figure which shows the cycle test result of Example 3 in this invention. It is a figure which shows the cycle test result of Example 4 in this invention. It is a figure which shows the cycle test result of the comparative example 1 in this invention. It is a figure which shows the cycle test result of the comparative example 2 in this invention. It is a figure which shows the cycle test result of the comparative example 3 in this invention. It is a figure which shows the cycle test result of the comparative example 4 in this invention. It is a figure which shows the cycle test result of Example 5 in this invention. It is a figure which shows the cycle test result of the comparative example 5 in this invention. It is a figure which shows the cycle test result of the comparative example 6 in this invention. It is a figure which shows the cycle test result of the comparative example 7 in this invention. It is a figure which shows the cycle test result of the comparative example 8 in this invention. It is a figure which shows the rate characteristic test result of Example 6 in this invention. It is a figure which shows the rate characteristic test result of Example 7 in this invention. It is a figure which shows the rate characteristic test result of the comparative example 9 in this invention. It is a figure which shows the impedance measurement result of Example 8 and Comparative Example 10 in this invention. It is drawing which represented typically the mode of the very thin film thing (pseudo thin film) formed of the electrolyte (solvated ionic liquid) in the interface of a silicon-type negative electrode. The molecular structures (a) and (b) show schematic structural diagrams of [Li (G3) ₁ ] [TFSI] (a) and [Li (G4) ₁ ] [TFSI] (b).

  Hereinafter, an embodiment of an electrolyte for a lithium ion secondary battery of the present invention (hereinafter simply referred to as “electrolyte” or “electrolyte of the present invention”) and a lithium ion secondary battery using the same with reference to the drawings Will be explained. However, the technical scope of the present invention should be determined based on the description of the scope of claims, and is not limited to the following modes. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may be different from the actual ratios.

An electrolyte for a lithium ion secondary battery according to an embodiment of the present invention is a lithium ion using a solvated ionic liquid containing methyl monoglyme (also referred to as G1) and methyldiglyme (also referred to as G2) and a lithium salt. An electrolyte for a secondary battery, wherein a ratio between the total number of moles of oxygen atoms contained in the methyl monoglyme and methyl diglyme and the number of moles of lithium in the lithium salt (= methyl monoglyme to lithium in the lithium salt and The total number of moles of oxygen atoms contained in methyl diglyme; [O] / [Li]) is 3.0 or more and less than 4.0, and the mixed molar ratio of methyl monoglyme and methyl diglyme (= methyl monoglyme) The number of moles / number of moles of methyl diglyme is (over 1/4) to (less than 3/2).
With such a configuration, the above-described effects of the invention can be effectively expressed. That is, in a solvated ionic liquid using G1 and G2 for Li salt and glymes, [O] / [Li is reduced so that the number of oxygen atoms contained in the glyme molecule is smaller than the charge neutral condition of the complex cation. ] Is controlled between 3.0 and less than 4.0. In addition, the G1 / G2 mixing molar ratio is controlled to (over ¼) to (less than 3/2) so that the anion molecules also contribute to the stabilization of the complex cation. By adopting such a configuration, while maintaining the properties of the electrolyte stably, it has low capacity with respect to the silicon-based negative electrode, and does not deteriorate various physical properties of the electrolyte. , Rate characteristics, etc.) can be provided. A lithium ion secondary battery according to an embodiment of the present invention includes the electrolyte and uses a silicon-based active material as a negative electrode active material. By adopting such a configuration, it is possible to apply a silicon-based electrode having a large capacity, so that a battery with a higher capacity can be realized. Hereinafter, first, constituent components of the electrolyte for a lithium ion secondary battery according to the present embodiment will be described, and then an embodiment according to a lithium ion secondary battery that is an application of the electrolyte will be described.

<Electrolyte for lithium ion secondary battery>
The electrolyte of this embodiment uses a solvated ionic liquid containing methyl monoglyme and methyl diglyme and a lithium salt without using a fluorine-based ether compound or the like that easily causes a change in the composition of the electrolyte. . As described above, this solvated ionic liquid has a strong Li salt such as lithium bis (trifluoromethylsulfonyl) imide [LiTFSI] and etheric oxygen atoms of G1 and G2 which are glyme solvents (glymes). It interacts to form a stable complex. That is, the mixture of lithium salt and glymes (G1 + G2) forms a complex cation by forming a complex between glymes and lithium. Since the above mixture is composed only of this complex cation and anion (anion species of Li salt), these series of compounds are salts. However, the ionic interaction between the complex cation and the anion is weakened by the influence of the complex formation, and it looks like a liquid despite being a salt. This liquid has a very low volatility, a high ion concentration, and good ion conductivity. A liquid having such characteristics is called a solvated ionic liquid. In the present embodiment, the use of the solvated ionic liquid means that the solvated ionic liquid is converted into a liquid electrolyte (an electrolytic solution comprising a solvated ionic liquid without using a fluorinated ether compound or the like that easily causes a change in the composition of the electrolyte. ). Alternatively, it means that the gel electrolyte is used as an electrolyte component (consisting of a solvated ionic liquid).

[Glyme solvents (Glimes)]
The electrolyte of the present embodiment includes a mixture (mixed solution) of methyl monoglyme (G1) and methyldiglyme (G2).

  As described above, when methylmonoglyme and methyldiglyme are used as the glymes forming the complex cation, the solvated ionic liquid is compared with the case where methyltriglyme (G3) or methyltetraglyme (G4) is applied. The viscosity can be greatly reduced. This is considered to be due to the physical properties of glymes used as a solvent. That is, the viscosity of the solvent itself is in the order of molecular weight: methyltetraglyme (molecular weight = 222.28)> methyltriglyme (molecular weight = 178.23)> methyldiglyme (molecular weight = 134.17)> methylmonoglyme ( The molecular weight is 90.12) and the viscosity is low. Furthermore, it is considered that the low viscosity of the solvent itself contributes to the reduction of the viscosity of the solvated ionic liquid. Thereby, since the viscosity of the solvent itself is low even at a low temperature, it is possible to suppress an increase in the viscosity of the solvated ionic liquid (electrolyte). Therefore, excellent electrolyte performance can be exhibited even at low temperatures without causing deterioration of various physical properties of the electrolyte such as ion conductivity. As a result, it is thought that it can contribute to improvement of battery performance such as cycle characteristics and rate characteristics of a lithium ion battery using a high-capacity silicon-based negative electrode active material using the electrolyte.

  In the electrolyte of this embodiment, the mixing ratio of methyl monoglyme (G1) and methyl diglyme (G2) is the mixing molar ratio of methyl monoglyme and methyl diglyme (= methyl monoglyme mole number / methyl diglyme mole number). ) Is (over 1/4) to (less than 3/2). From the viewpoint of further improving the cycle characteristics, the G1 mole number / G2 mole number is more preferably (9/31) to (1/1), and (1/3) to (19/21). More preferably, it is more preferably (11/29) to (9/11), and most preferably (3/7) to (17/23). Thus, in the electrolyte of this embodiment, [O] / [Li] is controlled between 3.0 and less than 4.0, and the mixing molar ratio of G1 and G2 is (over 1/4) to ( By setting it to less than 3/2, it is possible to provide an electrolyte excellent in cycle stability for a negative electrode using a silicon-based active material.

  Here, the reason for exhibiting excellent characteristics when methylmonoglyme and methyldiglyme having different numbers of oxygen atoms are mixed and used as glymes forming solvation is considered as follows. That is, in the complex cation composed of glymes and lithium ions, the solvation / desolvation reaction rate limiting process is different. For this reason, in the mixed state, each advantage can be effectively utilized while avoiding different rate-determining processes. Therefore, it is considered that the battery characteristics exhibit particularly excellent cycle characteristics.

  Further, when the number of moles of methyl monoglyme / number of moles of methyl diglyme (number of moles of G1 / number of moles of G2) is (3/2 or more), the cycle characteristics are rapidly deteriorated (each example (FIGS. 3 to 6, And FIG. 11) and the drawings showing the cycle characteristics of Comparative Example 6 (FIG. 13). This is considered to be caused by the suppression of the spread of the network structure of glymes across a plurality of molecules. G1 has two oxygen atoms and G2 has three in its molecular structure. When forming a complex cation, an unpaired electron pair is provided from the oxygen atom of the glyme, and the glyme molecule is coordinated around the lithium ion. Since the coordination number of oxygen atoms with respect to lithium ions is stable in a state of 4, one G1 molecule is insufficient in the number of oxygen atoms to satisfy the stable state. In the case of using G1 alone, a stable complex cation is formed by coordination of two molecules of G1 with lithium ions.

  However, here, when the total number of moles of oxygen atoms contained in the glymes solvated so as to be less than [O] / [Li] = 4, the lithium ions (of which two molecules are coordinated) are reduced. The first G1 molecule can stably form a complex cation. However, the second G1 glyme molecule cannot hold [O] / [Li] = 4 for all lithium cations. That is, the glymes alone cannot exhibit a sufficient effect for the stable complex cation formation. Therefore, in order to compensate for the insufficient solvation state, complex cations are formed by utilizing oxygen atoms constituting sulfonyl groups contained in Li salts (imide-type Li salts) that are anions for forming some complexes. It is considered a thing.

  At this time, the G1 molecule coordinated with one oxygen atom to the lithium ion is in an unstable state and forms a coordination structure with the adjacent lithium cation, but lithium ions and glymes constantly vibrate. It is difficult to always maintain a stable coordination structure of the complex cation, and the complex cation is always formed while switching the coordination destination. Since some G1 molecules are accompanied by this transient behavior, the G1 molecules exposed to this transient state are decomposed by reacting with a highly active silicon electrode because they are temporarily unstable. It is thought that the film formation of the decomposition product is caused in this. In order to avoid such a situation, the mixing ratio of G1 and G2 (G1 mole number / G2 mole number should be less than 3/2) so that the number of G1 molecules is not equal to or more than the mole number of lithium ions. Is desirable.

On the other hand, when the mixing ratio of G1 and G2 is G1 mole number / G2 mole number = (1/4 or less), the cycle characteristics of the negative electrode using the silicon-based active material are deteriorated (each example (FIG. 3 To FIG. 6 and FIG. 11) and the drawings showing the cycle characteristics of Comparative Example 5 (FIG. 12). Although the clear mechanism is not clear, as the content of G2 increases, the solvation of lithium ions and G2 is further promoted, and the number of oxygen atoms that G1 contributes to complex cation formation decreases. In such a situation, G1 partially contributing to complex cation formation is exposed to a transient stable state as in the case of G1 mole number / G2 mole number = (3/2 or more), and G1 is exposed to silicon. It reacts with the system negative electrode and decomposes. As a result, the performance of the silicon-based electrode and the characteristics of the electrolyte are degraded. Further, when the number of moles of G1 / number of moles of G2 = (1/4 or less), it becomes difficult to stably express the state of the solvated ionic liquid, and solidifies. For this reason, it becomes difficult to use as an electrolyte. In order to avoid such a situation, it is desirable that the mixing ratio of G1 and G2 (number of moles of G1 / number of moles of G2) is (over 1/4) so that the content of G2 with respect to the content of G1 does not increase excessively.

[Lithium salt]
The electrolyte of the present embodiment includes a lithium salt (LiX). Preferably, it is an imide type lithium salt. This is because the imide-type lithium salt can suppress the generation of HF due to anion hydrolysis, and thus can be expected to promote the improvement of the stability of the lithium ion secondary battery. Further, as the anion species (X) of the imide type lithium salt, a sulfonated imide is desirable, and as the imide type lithium salt, LiN (FSO ₂ ) ₂ (also simply referred to as LiFSI) is desirable. This is because the molecular structure of the anion molecule contributes to the interaction between the complex cation and the anion, and the effect is remarkable with the FSI anion having a more compact molecular structure.

X (anion species) in the lithium salt (LiX) includes Cl, Br, I, BF ₄ , PF ₆ , CF ₃ SO ₃ , and ClO from the viewpoints of the melting point, viscosity, and ionic conductivity of the solvated ionic liquid. ₄ , CF ₃ CO ₂ , AsF ₆ , SbF ₆ , AlCl ₄ , N (FSO ₂ ) ₂ [bis (fluorosulfonyl) imide (also simply referred to as FSI)], N (FSO ₂ ) (CF ₃ SO ₂ ) [( Fluorosulfonyl) (trifluoromethylsulfonyl) imide (also simply referred to as FTI)], N (CF ₃ SO ₂ ) ₂ [bis (trifluoromethylsulfonyl) imide (also simply referred to as TFSI)], N (CF ₃ CF ₂ SO ₂ ) ₂ [Bis (pentafluoroethylsulfonyl) imide (also simply referred to as BETI)] and the like, but not particularly limited. These X (anionic species) may be used alone or in combination of two or more. Preferred are imide type lithium salt anion species such as FSI, FTI, TFSI, and BETI. By using anionic species such as FSI, FTI, TFSI, and BETI, the resulting solvated ionic liquid (electrolyte) has a low viscosity, and its ionic conductivity exceeds 8 mS · cm ^−1. It is particularly suitable because it can sufficiently withstand use. Among them, the effect is remarkable with the FSI anion having a more compact molecular structure. This is because FSI has a molecular structure smaller than that of TFSI, so that steric hindrance to lithium ions is further suppressed, lithium ions are more likely to be closer than TFSI, and a complex cation structure having lithium ions as a nucleus is easily formed. Therefore, it is considered that the stability of the electrolyte is further improved.

Specific examples of the lithium salt, for _{example, LiCl, LiBr, LiI, LiBF} 4, LiPF 6, LiCF 3 SO 3, LiClO 4, LiCF 3 CO 2, LiAsF 6, LiSbF 6, LiAlCl 4, LiN (FSO 2) 2 , N (FSO ₂ ) (CF ₃ SO ₂ ), LiN (CF ₃ SO ₂ ) _2, LiN (CF ₃ CF ₂ SO ₂ ) _{2 and the} like, but are not limited thereto. Preferably, LiN (FSO ₂ ) ₂ (also simply referred to as LiFSI), N (FSO ₂ ) (CF ₃ SO ₂ ) (also simply referred to as LiFTI), LiN (CF ₃ SO ₂ ) ₂ (also simply referred to as LiTFSI) and LiN An imide-type lithium salt such as (CF ₃ CF ₂ SO ₂ ) ₂ (also simply referred to as LiBETI), and more preferably LiFSI. This is because, when a solvated ionic liquid is applied as an electrolyte to a negative electrode using a silicon-based active material, an imide-type lithium salt, particularly LiFSI, can be used as a lithium salt constituting the electrolyte. This is because an electrolyte having excellent properties can be formed (used). That is, as the imide-type lithium salt, lithium sulfonated imide is preferable, and LiFSI is more preferable. This is also because the molecular structure of the anion molecule contributes to the interaction between the complex cation and the anion, and the effect is remarkable with the FSI anion having a more compact molecular structure.

Of the above lithium salts, LiPF ₆ conventionally used is very reactive, and as shown by the following reaction formula, it is hydrolyzed by water present in the system and hydrofluoric acid (HF ) Is generated. The generation of HF causes deterioration of the lithium ion secondary battery. Usually, since it is applied to an electrolyte for a secondary battery in an environment in which moisture is not mixed as much as possible, the deterioration rate is at a level that does not cause a problem in practice, but is preferably an electrolyte that does not cause the deterioration.

The above reaction formula is based on “decomposition mechanism of LiPF _{6 in} an electrolyte containing a trace amount of water” (The TRC News No. 108 (2009) P39).

  On the other hand, among the above lithium salts, the imide type lithium salt can suppress the generation of HF due to such anion hydrolysis, and thus is excellent in that the effect of promoting the stability improvement of the lithium ion secondary battery can be expected. ing.

  Note that even a lithium salt developed after the filing of the present application can be included in the technical scope of the present application as long as the claims are satisfied.

  The electrolyte of this embodiment is a ratio ([O] / [Li]) of the total number of moles of oxygen atoms contained in methylmonoglyme (G1) and methyldiglyme (G2) to the number of moles of lithium ions in the lithium salt. However, it is essential that it is 3.0 or more and less than 4.0. When the [O] / [Li] is less than 3.0, when the electrolyte is applied to a lithium ion secondary battery using a silicon-based active material, a negative electrode using the silicon-based active material is suddenly used. The cycle characteristics may deteriorate. Although the reason is not clear, it is considered as the following hypothesis because the charge transfer resistance at the electrode interface is large. That is, since the number of glymes (G1 + G2), which are solvent molecules that solvate with lithium ions, decreases, the interaction between Li ions and solvent molecules becomes stronger, and the desolvation process of Li ions is less likely to occur. . Further, when an anion is used to supplement a coordination structure that is insufficient for complex cation formation, the balance of the charge balance between the cation and the anion is lost, and the stability as an electrolyte is impaired. As a result, irreversible reactions, desolvated free solvent molecules, and anion reduction reactions are promoted, and film formation on the electrode surface (interface between the electrolyte and the negative electrode) proceeds and cycle characteristics are improved. It is thought to get worse.

On the other hand, even when [O] / [Li] is 4.0 or more, the cycle characteristics may be deteriorated. Although the reason is not clear, in a steady state, the solvated ionic liquid is stable because the solvent molecules are solvated with respect to lithium ions so that [O] / [Li] = 4. However, when it functions as an electrolyte in the battery, lithium ions are desolvated from the solvated state, and lithium ions are provided to the electrode reaction. As a result of the progress of the desolvation reaction, free solvent molecules are generated in the electrolyte, but the stability of the free solvent molecules is inferior to that of the solvated state. It is considered that a reductive decomposition reaction of solvent molecules occurs at the silicon electrode interface activated by alloying with Li. When the battery reaction is repeated and charging and discharging are performed, the free solvent molecule decomposition reaction occurs continuously, resulting in the generation of many decomposition products at the electrode interface. It is thought that the reaction decreases.

  [O] / [Li] of the electrolyte of this embodiment may be 3.0 or more and less than 4.0. In addition to suppressing the volatility of the solvents G1 and G2, the electrochemical stability of the electrolyte is improved, and battery characteristics (especially cycle characteristics and rate characteristics, etc.) when applied to a negative electrode using a silicon-based active material ) Is preferably 3.2 to 3.95, more preferably 3.3 to 3.9, still more preferably 3.4 to 3.85, and particularly preferably 3. 5 to 3.8.

  The electrolyte of this embodiment is preferably applied to a secondary battery using a high-capacity silicon-based active material as the negative electrode active material. This is because the electrolyte of this embodiment is applied to a lithium ion secondary battery including a negative electrode containing a high-capacity silicon-based active material, so that battery characteristics such as cycle characteristics and rate characteristics can be improved with high capacity. This is because it can. Specifically, the [O] / [Li] of the solvated ionic liquid of this embodiment is controlled between 3.0 and less than 4.0, and the mixing molar ratio of G1 and G2 is (over 1/4) to ( This is because it is possible to provide a battery including a silicon negative electrode having a high capacity and excellent cycle characteristics and rate characteristics.

  Specifically, a solvated ionic liquid composed of a glyme having a [O] / [Li] of 3.0 or more and less than 4.0 and a Li salt is used as a negative electrode containing a silicon-based active material (silicon (Si) -based negative electrode). ), The cycle characteristics are considered to be improved by the following mechanism. That is, when the electrolyte is applied to a battery using a Si-based negative electrode, a part of the anion species is coordinated to the complex cation in the electrolyte, and the anion in a state of being bonded to the Li ion passes through the Li cation. It is expected that a pseudo thin film will be formed by orienting to the negative electrode surface. It is considered that this thin pseudo film functions as a protective film on the surface of the silicon-based negative electrode, so that excellent cycle characteristics can be expressed in the silicon-based negative electrode. This is because the conventional electrode coating is mainly composed of a decomposition product of the electrolytic solution (for example, lithium carbonate, lithium oxide, etc. generated by decomposition of ethylene carbonate (EC)), and has a certain thickness. On the other hand, the film formed on the electrode interface with the electrolyte (solvated ionic liquid) of this embodiment is a very thin film (pseudo thin film) that can be considered according to the electric double layer as shown in FIG. It has become. Since it is a (pseudo) thin film in this way, the charge transfer resistance in the electrode reaction is reduced, so that the battery characteristics are considered excellent.

There is no restriction | limiting in particular as a preparation method of electrolyte (solvation ionic liquid), It can prepare by mixing glymes (G1 and G2) and Li salt suitably suitably. For example, (i) a method of preparing an electrolyte by adding an appropriate amount of a Li salt (particularly an imide-type lithium salt) to a glyme mixture in which G1 and G2 are previously mixed at an appropriate mixing ratio; (ii) a Li salt in G1 A mixture obtained by mixing (especially an imide salt) by an appropriate amount and a mixture obtained by mixing an appropriate amount of Li salt (especially an imide type lithium salt) with G2 by mixing at an appropriate mixing ratio. (Iii) A method of preparing an electrolyte by mixing a mixture obtained by mixing an appropriate amount of Li salt (especially an imide type lithium salt) with G1 and G2 at an appropriate mixing ratio; iv) A method of preparing an electrolyte by mixing a mixture obtained by mixing an appropriate amount of Li salt (particularly an imide-type lithium salt) with G2 and G1 at an appropriate mixing ratio, and the like. The electrolyte of this form (solvation Down liquid) can be obtained.

  The conditions for mixing are not particularly limited, but it is preferable to stir and mix as necessary at a temperature of 20 to 80 ° C. until it is homogeneous. From the viewpoint of stirring and mixing until homogeneous, the mixing time is preferably 12 hours to 7 days, more preferably 24 to 120 hours. The electrolyte is preferably prepared in an inert gas atmosphere such as argon, nitrogen or helium.

  Since the moisture in the electrolyte affects the battery reaction, it is important to keep the moisture in the inert gas as low as possible, and it is preferable to work at a dew point of −50 ° C. or lower. In particular, the dew point is more preferably −60 ° C. or lower.

[Lithium ion secondary battery]
Next, specific embodiments of the lithium ion secondary battery using the above-described electrolyte will be described. However, the present invention is not limited only to the following embodiments. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may be different from the actual ratios.

  First, in the above-described electrolyte and a lithium ion secondary battery using the electrolyte, the present electrolyte can provide energy by transmitting carrier ions between the positive electrode and the negative electrode, and the voltage of the cell (single battery layer) is large. High energy density and high power density can be achieved. In addition, when the above-described electrolyte is applied to a lithium ion secondary battery, the Li salt concentration increases, that is, the Li ion activity increases, so that the reaction rate can be increased. For this reason, even if it raises an electric current value, the function of a lithium ion secondary battery (electrochemical device) can be expressed, without impairing performance. Therefore, the lithium ion secondary battery using the electrolyte of the present embodiment is excellent as a vehicle driving power source or an auxiliary power source. As a result, it can be suitably used as a lithium ion secondary battery for a vehicle driving power source or the like. In addition to this, the present invention can be sufficiently applied to lithium ion secondary batteries for portable devices such as mobile phones.

  That is, the lithium ion secondary battery that is the subject of the present embodiment is not particularly limited as long as it uses the electrolyte of the present embodiment described above. However, it is preferable to use a silicon-based active material having a large capacity for the negative electrode. By applying a novel electrolyte composed of the solvated ionic liquid obtained in this embodiment to a lithium ion secondary battery, a battery having excellent battery characteristics can be obtained. As described above, the present electrolyte has characteristics that greatly increase cycle characteristics, particularly with respect to a negative electrode containing a silicon-based active material such as a silicon alloy. When the electrolyte of the present invention is used for a lithium ion secondary battery, a silicon-based electrode having a large capacity can be applied, so that a battery with a higher capacity can be realized.

  When the lithium ion secondary battery is distinguished by its form / structure, it can be applied to any conventionally known form / structure, such as a stacked (flat) battery or a wound (cylindrical) battery. is there. By adopting a stacked (flat) battery structure, long-term reliability can be secured by a sealing technique such as simple thermocompression bonding, which is advantageous in terms of cost and workability.

  Moreover, when viewed in terms of electrical connection form (electrode structure) in a lithium ion secondary battery, it can be applied to both non-bipolar (internal parallel connection type) batteries and bipolar (internal series connection type) batteries. Is.

The lithium ion secondary battery according to the present embodiment includes a positive electrode containing a positive electrode active material capable of inserting and removing lithium ions, a negative electrode containing a negative electrode active material capable of inserting and removing lithium ions, and the positive electrode And an electrolyte layer interposed between the negative electrodes. In the following description, a lithium ion secondary battery will be described as an example, but the present invention is not limited to this.

  FIG. 1 schematically illustrates the overall structure of a lithium ion secondary battery (hereinafter also simply referred to as “parallel stacked battery”) stacked in parallel with a high output (low resistance) and high capacity according to an embodiment of the present invention. FIG. As shown in FIG. 1, the parallel laminated battery 10a of the present embodiment has a structure in which a substantially rectangular power generation element 17 in which a charge / discharge reaction actually proceeds is sealed inside a laminate film 22 that is a battery exterior material. Have Specifically, the power generation element 17 is housed and sealed by using a polymer-metal composite laminate film as a battery exterior material and joining all of its peripheral parts by thermal fusion.

  The power generation element 17 includes a negative electrode in which the negative electrode active material layer 12 is disposed on both sides of the negative electrode current collector 11 (only one side for the lowermost layer and the uppermost layer of the power generation element), an electrolyte layer 13, and a positive electrode current collector 14. And a positive electrode in which the positive electrode active material layer 15 is disposed on both sides. Specifically, the negative electrode, the electrolyte layer 13 and the positive electrode are laminated in this order so that one negative electrode active material layer 12 and the positive electrode active material layer 15 adjacent to the negative electrode active material layer 15 face each other with the electrolyte layer 13 therebetween. Yes. It is preferable to use a high-capacity silicon-based active material for the negative electrode active material layer.

  Thus, the adjacent negative electrode, electrolyte layer 13 and positive electrode constitute one single cell layer 16. Therefore, it can be said that the parallel stacked battery 10 of the present embodiment has a configuration in which a plurality of single battery layers 16 are stacked and electrically connected in parallel. Further, a seal portion (insulating layer) (not shown) for insulating between the adjacent negative electrode current collector 11 and the positive electrode current collector 14 may be provided on the outer periphery of the unit cell layer 16. . The negative electrode active material layer 12 is disposed only on one side of the outermost layer negative electrode current collector 11 a located in both outermost layers of the power generation element 17. 1, the arrangement of the negative electrode and the positive electrode is reversed so that the outermost positive electrode current collector is positioned on both outermost layers of the power generation element 17, and the positive electrode is provided only on one side of the outermost positive electrode current collector. An active material layer may be arranged.

  The negative electrode current collector 11 and the positive electrode current collector 14 are attached with a negative electrode current collector plate 18 and a positive electrode current collector plate 19 that are electrically connected to the respective electrodes (negative electrode and positive electrode), and are sandwiched between ends of the laminate film 22. Thus, it has a structure led out of the laminate film 22. The negative electrode current collector 18 and the positive electrode current collector 19 are connected to the negative electrode current collector 11 and the positive electrode current collector 14 of each electrode by ultrasonic welding or resistance via a negative electrode terminal lead 20 and a positive electrode terminal lead 21 as necessary. It may be attached by welding or the like (this form is shown in FIG. 1). However, the negative electrode current collector 11 may be extended to form the negative electrode current collector plate 18 and may be led out from the laminate film 22. Similarly, the positive electrode current collector 14 may be extended to form a positive electrode current collector plate 19, which may be similarly derived from the battery exterior material 22.

  FIG. 2 shows an overall configuration of a bipolar lithium ion secondary battery (hereinafter also simply referred to as “series stacked battery”) having a high output (low resistance) and a high capacity stacked in series according to an embodiment of the present invention. It is the cross-sectional schematic which represented the structure typically. The series stacked battery 10b shown in FIG. 2 has a structure in which a substantially rectangular power generation element 17 in which a charge / discharge reaction actually proceeds is sealed inside a laminate film 22 that is a battery exterior material.

As shown in FIG. 2, the power generation element 17 of the series stacked battery 10 b is formed with a positive electrode active material layer 15 electrically coupled to one surface of the current collector 23, and the surface on the opposite side of the current collector 23. A plurality of bipolar electrodes 24 each having a negative electrode active material layer 12 electrically coupled thereto. It is preferable to use a high-capacity silicon-based active material for the negative electrode active material layer. Each bipolar electrode 24 is laminated via the electrolyte layer 13 to form the power generation element 17. The electrolyte layer 13 has a configuration in which an electrolyte is held at the center in the surface direction of a separator as a base material. At this time, the positive electrode active material layer 15 of one bipolar electrode 24 and the negative electrode active material layer 12 of another bipolar electrode 24 adjacent to the one bipolar electrode 24 face each other through the electrolyte layer 13. Each bipolar electrode 24 and the electrolyte layer 13 are alternately laminated. That is, the electrolyte layer 13 is sandwiched between the positive electrode active material layer 15 of one bipolar electrode 24 and the negative electrode active material layer 12 of another bipolar electrode 24 adjacent to the one bipolar electrode 24. ing.

  The adjacent positive electrode active material layer 15, electrolyte layer 13, and negative electrode active material layer 12 constitute one unit cell layer 16. Therefore, it can be said that the serially stacked battery 10b of the present embodiment has a configuration in which a plurality of single battery layers 16 are stacked and electrically connected in series. Further, for the purpose of preventing liquid junction due to leakage of the electrolyte from the electrolyte layer 13, a seal portion (insulating portion) 25 is disposed on the outer peripheral portion of the unit cell layer 16. The positive electrode active material layer 15 is formed on only one side of the positive electrode outermost layer current collector 23 a located in the outermost layer of the power generation element 17. The negative electrode active material layer 12 is formed only on one side of the negative electrode side outermost current collector 23b located in the outermost layer of the power generation element 17. However, the positive electrode active material layer 15 may be formed on both surfaces of the outermost layer current collector 23a on the positive electrode side. Similarly, the negative electrode active material layer 12 may be formed on both surfaces of the outermost current collector 23b on the negative electrode side.

  Further, in the series laminated battery 10b shown in FIG. 2, the positive electrode current collector plate 19 is disposed so as to be adjacent to the outermost layer current collector 23a on the positive electrode side, and this is extended and led out from the laminate film 22 which is a battery exterior material. doing. On the other hand, the negative electrode current collector plate 18 is disposed so as to be adjacent to the outermost layer current collector 23b on the negative electrode side, and similarly, this is extended and led out from the laminate film 22 which is an exterior of the battery.

  In the series stacked battery 10 b shown in FIG. 2, the insulating portion 25 is usually provided around each single cell layer 16. The insulating portion 25 is intended to prevent the adjacent current collectors 23 in the battery from contacting each other and the occurrence of a short circuit due to a slight irregularity of the end portions of the unit cell layer 16 in the power generation element 17. Is provided. By installing such an insulating portion 25, long-term reliability and safety can be ensured, and a high-quality series stacked battery 10b can be provided.

  Note that the number of stacks of the unit cell layers 16 is adjusted according to a desired voltage. Further, in the serially stacked battery 10b, the number of times the single battery layers 16 are stacked may be reduced if a sufficient output can be ensured even if the battery is made as thin as possible. Even in the case of the serially stacked battery 10b, it is necessary to prevent external impact and environmental degradation during use. Therefore, the power generation element 17 is preferably sealed in a laminate film 22 that is a battery exterior material, and the positive electrode current collector plate 19 and the negative electrode current collector plate 18 are taken out of the laminate film 22.

  The lithium ion secondary battery described above, particularly a lithium ion secondary battery using a high-capacity silicon-based active material as the negative electrode active material, has a feature in the electrolyte. Hereinafter, main components of the battery including the electrolyte will be described in more detail.

[Negative electrode]
The negative electrode has a function of generating electrical energy by transferring lithium ions together with the positive electrode. The negative electrode essentially includes a current collector and a negative electrode active material layer, and the negative electrode active material layer is formed on the surface of the current collector.

(Current collector)
The current collector is made of a conductive material, and a negative electrode active material layer is disposed on one side or both sides thereof. There is no particular limitation on the material constituting the current collector, and for example, a conductive resin in which a conductive filler is added to a metal or a conductive polymer material or a non-conductive polymer material may be employed.

  Examples of the metal include aluminum, nickel, iron, stainless steel (SUS), titanium, and copper. In addition to these, a clad material of nickel and aluminum, a clad material of copper and aluminum, or a plating material of a combination of these metals can be preferably used. Moreover, the foil by which aluminum is coat | covered on the metal surface may be sufficient. Of these, aluminum, stainless steel, or copper is preferably used from the viewpoint of conductivity and battery operating potential.

  Examples of the conductive polymer material include polyaniline, polypyrrole, polythiophene, polyacetylene, polyparaphenylene, polyphenylene vinylene, polyacrylonitrile, and polyoxadiazole. Since such a conductive polymer material has sufficient conductivity without adding a conductive filler, it is advantageous in terms of facilitating the manufacturing process or reducing the weight of the current collector.

  Examples of non-conductive polymer materials include polyethylene (PE; high density polyethylene (HDPE), low density polyethylene (LDPE)), polypropylene (PP), polyethylene terephthalate (PET), polyether nitrile (PEN), polyimide ( PI), polyamideimide (PAI), polyamide (PA), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), Examples include polyvinyl chloride (PVC), polyvinylidene fluoride (PVdF), and polystyrene (PS). Such a non-conductive polymer material may have excellent potential resistance or solvent resistance.

  A conductive filler may be added to the conductive polymer material or the non-conductive polymer material as necessary. In particular, when the resin used as the base material of the current collector is made of only a non-conductive polymer, a conductive filler is inevitably necessary to impart conductivity to the resin. The conductive filler can be used without particular limitation as long as it is a substance having conductivity. For example, metals, conductive carbon, etc. are mentioned as a material excellent in electroconductivity, electric potential resistance, or lithium ion barrier | blocking property. The metal is not particularly limited, but at least one metal selected from the group consisting of Ni, Ti, Al, Cu, Pt, Fe, Cr, Sn, Zn, In, Sb, and K, or these metals. It is preferable to include an alloy or metal oxide. Further, the conductive carbon is not particularly limited, but is at least one selected from the group consisting of acetylene black, vulcan, black pearl, carbon nanofiber, ketjen black, carbon nanotube, carbon nanohorn, carbon nanoballoon, and fullerene. Preferably it contains seeds. The amount of the conductive filler added is not particularly limited as long as it is an amount capable of imparting sufficient conductivity to the current collector, and is generally about 5 to 35% by mass.

  The size of the current collector is determined according to the intended use of the battery. For example, if it is used for a large battery that requires a high energy density, a current collector having a large area is used. Although there is no restriction | limiting in particular also about the thickness of a collector, Usually, it is about 1-100 micrometers.

(Negative electrode active material layer)
The negative electrode active material layer includes a negative electrode active material. The negative electrode active material layer may further include additives such as a conductive additive and a binder.

<Negative electrode active material>
The negative electrode active material has a composition that can desorb lithium ions during discharge and occlude lithium ions during charging. The negative electrode active material is not particularly limited as long as it can reversibly absorb and desorb lithium. Examples of the negative electrode active material include metals such as Si and Sn, or metal oxides such as TiO, Ti ₂ O ₃ , TiO ₂ , SiO ₂ , SiO, and SnO ₂ , L
Composite oxides of lithium and transition metals such as i ₄ Ti ₅ O ₁₂ or Li ₇ MnN, Li—Pb alloys, Li—Al alloys, Li, or carbon powder, graphite (natural graphite, artificial graphite), carbon Preferred examples include carbon materials such as black, activated carbon, carbon fiber, coke, soft carbon, and hard carbon. Among these, by using an element that forms an alloy with lithium, it becomes possible to obtain a battery having a high capacity and an excellent output characteristic having a higher energy density than that of a conventional carbon-based material. The negative electrode active material may be used alone or in the form of a mixture of two or more. The element alloying with lithium is not limited to the following, but specifically, Si, Ge, Sn, Pb, Al, In, Zn, H, Ca, Sr, Ba, Ru, Rh, Ir, Pd, Pt, Ag, Au, Cd, Hg, Ga, Tl, C, N, Sb, Bi, O, S, Se, Te, Cl, and the like.

Among the negative electrode active materials, a silicon (silicon) -based material (a material that includes silicon (silicon) and can function as a negative electrode active material by occluding and releasing lithium ions) is preferably included. This is because, as in Patent Document 1, in a high capacity battery using a silicon-based negative electrode, the reactivity of the silicon electrode alloyed with lithium ions with the electrolytic solution is further increased. In particular, it is thought that it easily reacts with hydrofluoroethers containing fluorine atoms, which have a high electron density, and in the electrolyte using the solvated ionic liquid of this embodiment, the reactivity to the silicon electrode alloyed with lithium ions is greatly increased. Can be reduced. Therefore, a high capacity battery can be provided without impairing the characteristics of the silicon-based material. Furthermore, it is because it is excellent in that the Li ⁺ concentration contained in the electrolytic solution can be maintained at a high concentration.

There is no restriction | limiting in particular as a silicon (silicon) type material used as a negative electrode active material, A conventionally well-known knowledge can be referred suitably. For example, a metal such as silicon metal (Si simple substance), aluminum alloyed with silicon, tin, zinc, nickel, copper, titanium, vanadium, magnesium, lithium, etc. (in addition, an element such as carbon may be included. ) A silicon alloy (which may be a binary alloy or more, but preferably a ternary alloy such as a Si—Sn—Ti alloy), SiO ₂ , SiO, a mixture of amorphous SiO ₂ particles and Si particles; From the group consisting of silicon (silicon) oxides such as SiO _x (where x represents the number of oxygen satisfying the valence of Si), lithium, carbon, aluminum, tin, zinc, nickel, copper, titanium, vanadium and magnesium Examples thereof include a silicon (silicon) compound and a silicon semiconductor containing at least one selected component. One type of negative electrode active material may be sufficient and 2 or more types may be used together. Note that silicon as the negative electrode active material is preferably doped with a predetermined element (doping element). Although silicon (Si) is inherently low in conductivity, silicon (Si) exhibits the properties of a semiconductor by doping silicon (Si) with the predetermined doping element and using it as a negative electrode active material (silicon semiconductor). become. That is, the low electrical conductivity of these materials is improved, and it becomes possible to function more effectively as a negative electrode active material. The doping element is preferably one or more elements selected from the group consisting of Group 13 or Group 15 elements in the Periodic Table. Specifically, elements of Group 13 in the periodic table include boron (B), aluminum (Al), gallium (Ga), indium (In), and thallium (Tl). Examples of the Group 15 element in the periodic table include nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi). Among these, from the viewpoint of providing a battery having excellent battery characteristics, B, P, Al, Ga, In, N, P, As, Sb, or Bi are preferable, and B, P, Al, Ga are more preferable. Or In, particularly preferably B, P or Al. Only one of these doping elements may be doped alone, or two or more may be doped in combination. At this time, the doping amount of the doping element into silicon (Si) is not particularly limited, but is preferably 1 × 10 ⁻²⁰ atoms / cm ³ or more from the viewpoint of improving conductivity in the negative electrode active material layer, More preferably, it is 1 × 10 ⁻¹⁸ atom / cm ³ or more, and particularly preferably 1 × 10 ⁻¹⁵ atom / cm ³ or more.

  As a silicon (Si) -based material, a silicon compound containing at least one element selected from the group consisting of lithium, carbon, aluminum, tin, zinc, nickel, copper, titanium, vanadium and magnesium, containing silicon as a main component And at least one selected from the group consisting of semiconductor silicon containing at least one dopant selected from the group consisting of boron, phosphorus and antimony.

  In a more preferred embodiment, the negative electrode active material contains a silicon (Si) -based material as a main component. The term “main component” as used herein means that the capacity of the silicon (Si) -based material in the total capacity of the negative electrode active material contained in the negative electrode active material layer is 50% or more. In other words, it means that the mass of the silicon (Si) -based material is 10% by mass or more. From the viewpoint that a larger theoretical capacity can be achieved, the mass is preferably 30% by mass or more, more preferably 50% by mass or more, further preferably 80% by mass or more, and particularly preferably. It is 90 mass% or more, Most preferably, it is 100 mass%.

  The silicon (Si) -based material contains silicon (Si) as a main component. Here, the “main component” means that the mass of silicon (Si) in the total mass of the silicon (Si) -based material is 50% by mass or more. From the viewpoint that a larger theoretical capacity can be achieved, the mass is preferably 70% by mass or more, more preferably 80% by mass or more, further preferably 90% by mass or more, and particularly preferably. It is 95 mass% or more. In order to achieve a larger theoretical capacity, the mass of Si in the silicon (Si) -based material is best 100% by mass. However, the use in the form of a silicon alloy, silicon oxide, silicon compound, silicon semiconductor, or the like may have a better balance between battery characteristics, higher capacity, and higher durability (cycle characteristics).

In some cases, carbon materials such as graphite (graphite), soft carbon, and hard carbon, lithium-transition metal composite oxides (for example, Li ₄ Ti ₅ O ₁₂ ), and metal materials other than silicon (for example, tin (Sn) ), Etc.) and other negative electrode active materials other than silicon-based materials may be used in combination.

  As the carbon material, carbonaceous particles having a low lithium relative discharge potential are preferable, for example, natural graphite, artificial graphite, blends of natural graphite and artificial graphite, materials obtained by coating natural graphite with amorphous carbon, soft carbon, Hard carbon or the like can be used. The shape of the carbonaceous particles is not particularly limited and may be any shape such as a lump shape, a sphere shape, and a fiber shape, but is preferably not a scale shape, and preferably a sphere shape and a lump shape. Those that are not scaly are preferred from the viewpoints of performance and durability.

  The carbonaceous particles are preferably those whose surfaces are coated with amorphous carbon. At that time, it is more preferable that the amorphous carbon covers the entire surface of the carbonaceous particles, but it may be a coating of only a part of the surface. By covering the surfaces of the carbonaceous particles with amorphous carbon, it is possible to prevent the graphite and the electrolytic solution from reacting during charging and discharging of the battery. The method for coating the surface of the graphite particles with amorphous carbon is not particularly limited. For example, there is a wet method in which carbonaceous particles (powder) serving as nuclei are dispersed and mixed in a mixed solution in which amorphous carbon is dissolved or dispersed in a solvent, and then the solvent is removed. Other examples include a dry method in which carbonaceous particles and amorphous carbon are mixed with each other, and mechanical energy is added to the mixture to coat the amorphous carbon, and a vapor phase method such as a CVD method. Whether the carbonaceous particles are coated with amorphous carbon can be confirmed by a method such as laser spectroscopy.

  The thickness in the stacking direction of the negative electrode active material layer is not particularly limited. However, from the viewpoint of providing a battery having excellent battery characteristics, the thickness is preferably 50 nm to 100 μm, more preferably 70 nm to 100 μm, and still more preferably 90 nm to 50 μm. Note that the negative electrode active material layer may be a thin film made of a silicon (silicon) -based material. Such a thin film can be formed by vapor-depositing a silicon (silicon) -based material (for example, silicon alone) as a negative electrode active material on a current collector by a vapor deposition process (dry method). There is no restriction | limiting in particular about the specific form of such a vapor-phase film-forming process, A conventionally well-known method can be employ | adopted suitably. As an example, a vacuum deposition method, a sputtering method (for example, RF sputtering method), a chemical vapor deposition (CVD) method, etc. can be illustrated. According to such a method, the negative electrode active material layer having a uniform thickness can be formed by a simple method.

Alternatively, the negative electrode active material layer may have the same shape as a conventional general active material layer. That is, the negative electrode active material layer is a mixture layer (active material layer) formed by mixing a negative electrode active material containing a silicon (silicon) -based material and additives such as a binder and a conductive additive added as necessary. Form may be sufficient. Thereby, it is possible to create an active material layer by a method similar to a conventional general active material layer creation process. In such a form, there is no restriction | limiting in particular about the size of the negative electrode active material particle which is a particulate active material. For example, from the viewpoint of providing a battery having excellent battery characteristics, the average particle diameter of the particulate negative electrode active material is not particularly limited. However, the negative electrode active material has a higher capacity, reactivity, and cycle durability. From this viewpoint, it is preferably 1 nm to 100 μm, more preferably 1 nm to 30 μm, still more preferably 1 nm to 10 μm, and particularly preferably 1 to 500 nm. The BET specific surface area of the particulate negative electrode active material is preferably 0.8 to 1.5 m ² / g. If the specific surface area is in the above range, the cycle characteristics of the nonaqueous electrolyte secondary battery can be improved. Moreover, it is preferable that the tap density of a negative electrode active material is 0.9-1.2 g / cm < ³ >. It is preferable from the viewpoint of energy density that the tap density is in the above range. In addition, the negative electrode active material layer of such a form can be produced by the same liquid phase process (dry method) as a negative electrode active material layer in the form of a conventionally known mixture layer. For example, first, each component (particulate active material and, if necessary, a binder and a conductive aid) constituting the negative electrode active material layer is dispersed in an appropriate amount of solvent (N-methyl-2-pyrrolidone, etc.) Adjust. Subsequently, the negative electrode active material layer can be produced by applying the slurry to a current collector and drying the slurry.

<Binder>
When the negative electrode active material layer contains a binder, it is preferable to contain an aqueous binder. In addition to the easy procurement of water as a raw material, water-based binders can be greatly reduced in capital investment on the production line and reduced environmental load because it is water vapor that occurs during drying. There is an advantage.

  The water-based binder refers to a binder using water as a solvent or a dispersion medium, and specifically includes a thermoplastic resin, a polymer having rubber elasticity, a water-soluble polymer, or a mixture thereof. Here, the binder using water as a dispersion medium refers to a polymer that includes all expressed as latex or emulsion and is emulsified or suspended in water. For example, a polymer latex that is emulsion-polymerized in a system that self-emulsifies. Kind.

Specific examples of water-based binders include styrene polymers (styrene-butadiene rubber, styrene-vinyl acetate copolymer, styrene-acrylic copolymer, etc.), acrylonitrile-butadiene rubber, methyl methacrylate-butadiene rubber, (meta ) Acrylic polymers (polyethyl acrylate, polyethyl methacrylate, polypropyl acrylate, polymethyl methacrylate (methyl methacrylate rubber), polypropyl methacrylate, polyisopropyl acrylate, polyisopropyl methacrylate, polybutyl acrylate, polybutyl methacrylate, polyhexyl acrylate , Polyhexyl methacrylate,
Polyethylhexyl acrylate, polyethylhexyl methacrylate, polylauryl acrylate, polylauryl methacrylate, etc.), polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene copolymer, polybutadiene, butyl rubber, fluororubber, polyethylene oxide, polyepichlorohydrin, polyphosphazene , Polyacrylonitrile, polystyrene, ethylene-propylene-diene copolymer, polyvinyl pyridine, chlorosulfonated polyethylene, polyester resin, phenol resin, epoxy resin; polyvinyl alcohol (average polymerization degree is preferably 200 to 4000, more preferably Is 1000 to 3000, the degree of saponification is preferably 80 mol% or more, more preferably 90 mol% or more) and its modified product ( Tylene / vinyl acetate = (2/98) to (30/70) molar ratio of vinyl acetate unit of 1-80 mol% saponified product, 1-50 mol% partially acetalized product of polyvinyl alcohol) , Starch and modified products thereof (oxidized starch, phosphated starch, cationized starch, etc.), cellulose derivatives (carboxymethylcellulose, methylcellulose, hydroxypropylcellulose, hydroxyethylcellulose, and salts thereof), polyvinylpyrrolidone, polyacrylic acid (Salt), polyethylene glycol, (meth) acrylamide and / or (meth) acrylate copolymer [(meth) acrylamide polymer, (meth) acrylamide- (meth) acrylate copolymer, (meth) Alkyl acrylate (C1-C1 ) Ester- (meth) acrylate copolymer, etc.], styrene-maleate copolymer, Mannich modified polyacrylamide, formalin condensation type resin (urea-formalin resin, melamine-formalin resin, etc.), polyamide polyamine Alternatively, water-soluble polymers such as dialkylamine-epichlorohydrin copolymer, polyethyleneimine, casein, soy protein, synthetic protein, and mannangalactan derivative are exemplified. These aqueous binders may be used alone or in combination of two or more.

  The aqueous binder may contain at least one rubber binder selected from the group consisting of styrene-butadiene rubber, acrylonitrile-butadiene rubber, methyl methacrylate-butadiene rubber, and methyl methacrylate rubber from the viewpoint of binding properties. preferable. Furthermore, it is preferable that the water-based binder contains a styrene-butadiene rubber because the binding property is good.

  When styrene-butadiene rubber is used as the water-based binder, it is preferable to use the water-soluble polymer in combination from the viewpoint of improving coatability. Water-soluble polymers suitable for use in combination with styrene-butadiene rubber include polyvinyl alcohol and modified products thereof, starch and modified products thereof, cellulose derivatives (carboxymethyl cellulose, methyl cellulose, hydroxyethyl cellulose, and salts thereof), polyvinyl Examples include pyrrolidone, polyacrylic acid (salt), or polyethylene glycol. Among them, it is preferable to combine styrene-butadiene rubber and carboxymethyl cellulose as a binder. The mass ratio of the styrene-butadiene rubber and the water-soluble polymer is not particularly limited, but is styrene-butadiene rubber: water-soluble polymer = 1: (0.3 to 0.7). Is preferred.

  When a negative electrode active material layer contains a binder, it is preferable that content of an aqueous binder is 80-100 mass% among the binders used for a negative electrode active material layer, and it is preferable that it is 90-100 mass%, 100 It is preferable that it is mass%. Examples of the binder other than the water-based binder include binders used in the following positive electrode active material layer.

The amount of the binder contained in the negative electrode active material layer is not particularly limited as long as it is an amount capable of binding the active material, but is preferably 0 with respect to 100% by mass of the total amount of the negative electrode active material layer. It is 0.5-15 mass%, More preferably, it is 1-10 mass%, More preferably, it is 2-4 mass%, Most preferably, it is 2.5-3.5 mass%. Since the water-based binder has high binding power, the active material layer can be formed with a small amount of addition as compared with the organic solvent-based binder.

  The negative electrode active material layer further includes a conductive additive, an electrolyte (polymer matrix, ion conductive polymer, electrolytic solution, etc.), and other additives such as a lithium salt for increasing ion conductivity, as necessary.

<Conductive aid>
The conductive auxiliary agent is an additive that is blended to improve the conductivity of the positive electrode active material layer or the negative electrode active material layer. Although not particularly limited, carbon black such as acetylene black, ketjen black and furnace black, carbon powder such as channel black, thermal black and graphite, various carbon fibers such as vapor grown carbon fiber (VGCF; registered trademark), Examples thereof include carbon materials such as expanded graphite. When the active material layer contains a conductive additive, an electronic network inside the active material layer is effectively formed, which can contribute to improvement of the output characteristics of the battery.

<Lithium salt>
The lithium salt is contained in the negative electrode active material layer when the electrolyte described above penetrates into the negative electrode active material layer. Therefore, the specific form of the lithium salt that can be contained in the negative electrode active material layer is the same as the lithium salt that constitutes the electrolyte described above.

<Ion conductive polymer>
Examples of the ion conductive polymer include polyethylene oxide (PEO) -based and polypropylene oxide (PPO) -based polymers.

  The compounding ratio of the components contained in the negative electrode active material layer is not particularly limited. The blending ratio can be adjusted by appropriately referring to known knowledge about lithium ion secondary batteries.

[Positive electrode]
The positive electrode has a function of generating electrical energy by transferring lithium ions together with the negative electrode. The positive electrode essentially includes a current collector and a positive electrode active material layer, and the positive electrode active material layer is formed on the surface of the current collector.

(Current collector)
Since the current collector that can be used for the positive electrode is the same as the current collector that can be used for the negative electrode, description thereof is omitted here.

(Positive electrode active material layer)
The positive electrode active material layer essentially includes an active material, and includes a conductive auxiliary agent, a binder, an electrolyte (polymer matrix, ion conductive polymer, electrolytic solution, etc.), and a lithium salt for enhancing ion conductivity, if necessary. It further contains other additives.

<Positive electrode active material>
The positive electrode active material has a composition capable of releasing lithium ions during charging and occluding lithium ions during discharging. Examples of the positive electrode active material include lithium transition such as LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , Li (Ni—Mn—Co) O _2, and a part of these transition metals substituted with other elements. Examples thereof include metal composite oxides, lithium transition metal phosphate compounds such as lithium iron phosphate, and lithium-transition metal sulfate compounds. In some cases, two or more positive electrode active materials may be used in combination. Preferably, from the viewpoint of capacity and output characteristics, a lithium transition metal composite oxide or a lithium transition metal phosphate compound is used as the positive electrode active material. Furthermore, Li (Ni—Mn—Co) O ₂ and those obtained by replacing a part of these transition metals with other elements (hereinafter also simply referred to as “NMC composite oxide”) can be used. The NMC composite oxide has a layered crystal structure in which a lithium atomic layer and a transition metal (Mn, Ni, and Co are arranged in order) are stacked alternately via an oxygen atomic layer. One Li atom is contained, and the amount of Li that can be taken out is twice that of the spinel lithium manganese oxide, that is, the supply capacity is doubled, so that a high capacity can be obtained.

  As described above, the NMC composite oxide includes a composite oxide in which a part of the transition metal element is substituted with another metal element. Other elements in that case include Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, Fe, B, Ga, In, Si, Mo, Y, Sn, V, Cu , Ag, Zn, etc., preferably Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, Cr, more preferably Ti, Zr, P, Al, Mg, From the viewpoint of improving cycle characteristics, Ti, Zr, Al, Mg, and Cr are more preferable.

Since the NMC composite oxide has a high theoretical discharge capacity, it is preferable that the general formula (1): Li _a Ni _b Mn _c Co _d M _x O ₂ (where a, b, c, d, x Satisfies 0.9 ≦ a ≦ 1.2, 0 <b <1, 0 <c ≦ 0.5, 0 <d ≦ 0.5, 0 ≦ x ≦ 0.3, and b + c + d = 1. And at least one element selected from Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, and Cr. Here, a represents the atomic ratio of Li, b represents the atomic ratio of Ni, c represents the atomic ratio of Mn, d represents the atomic ratio of Co, and x represents the atomic ratio of M. Represents. From the viewpoint of cycle characteristics, it is preferable that 0.4 ≦ b ≦ 0.6 in the general formula (1). The composition of each element can be measured by, for example, inductively coupled plasma (ICP) emission spectrometry.

  In general, nickel (Ni), cobalt (Co), and manganese (Mn) are known to contribute to capacity and output characteristics from the viewpoint of improving the purity of materials and improving electronic conductivity. Ti or the like partially replaces the transition metal in the crystal lattice. From the viewpoint of cycle characteristics, it is preferable that a part of the transition element is substituted with another metal element, and it is particularly preferable that 0 <x ≦ 0.3 in the general formula (1). Since at least one selected from the group consisting of Ti, Zr, Nb, W, P, Al, Mg, V, Ca, Sr, and Cr is dissolved, the crystal structure is stabilized. It is considered that the battery capacity can be prevented from decreasing even if the above is repeated, and that excellent cycle characteristics can be realized.

  As a more preferable embodiment, in the general formula (1), b, c and d are 0.44 ≦ b ≦ 0.51, 0.27 ≦ c ≦ 0.31, 0.19 ≦ d ≦ 0.26. It is preferable that it is excellent in balance between capacity and durability.

  Of course, positive electrode active materials other than those described above may be used.

  The average particle diameter of each active material contained in the positive electrode active material layer is not particularly limited, but is preferably 1 to 100 μm, more preferably 1 to 30 μm from the viewpoint of increasing output. More preferably, the thickness is 10 to 30 μm, which is desirable for a high output (low resistance) and high capacity battery that handles a large area electrode.

<Binder>
The binder is added for the purpose of maintaining the electrode structure by binding the constituent members in the active material layer or the active material layer and the current collector. Although it does not specifically limit as a binder used for a positive electrode active material layer, For example, the following materials are mentioned. Polyethylene, polypropylene, polyethylene terephthalate (PET), polyether nitrile, polyacrylonitrile, polyimide, polyamide, cellulose, carboxymethyl cellulose (CMC) and its salts, ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene rubber (SBR) ), Isoprene rubber, butadiene rubber, ethylene / propylene rubber, ethylene / propylene / diene copolymer, styrene / butadiene / styrene block copolymer and hydrogenated product thereof, styrene / isoprene / styrene block copolymer and hydrogenated product thereof Thermoplastic polymers such as products, polyvinylidene fluoride (PVdF), vinylidene fluoride copolymer (modified PVdF), polytetrafluoroethylene (PTFE), tetrafluoroethylene Rene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene- Fluoropolymers such as chlorotrifluoroethylene copolymer (ECTFE) and polyvinyl fluoride (PVF), vinylidene fluoride-hexafluoropropylene fluororubber (VDF-HFP fluoropolymer), vinylidene fluoride-hexafluoropropylene-tetra Fluoroethylene fluoro rubber (VDF-HFP-TFE fluoro rubber), vinylidene fluoride-pentafluoropropylene fluoro rubber (VDF-PFP fluoro rubber), vinylidene fluoride-pe Tafluoropropylene-tetrafluoroethylene fluorine rubber (VDF-PFP-TFE fluorine rubber), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene fluorine rubber (VDF-PFMVE-TFE fluorine rubber), vinylidene fluoride -Vinylidene fluoride-based fluororubber such as chlorotrifluoroethylene-based fluororubber (VDF-CTFE-based fluororubber), epoxy resin and the like. These binders may be used independently and may use 2 or more types together.

  The content of the binder contained in the positive electrode active material layer is not particularly limited as long as it is an amount capable of binding the active material, but is preferably 0 to 30 mass with respect to the positive electrode active material layer. %. More preferably, it is 0.5-15 mass%, More preferably, it is 1-10 mass%, More preferably, it is 2-8 mass%, Most preferably, it is 3-7 mass%. A binder (organic solvent-based binder) such as hydrophilic modified PVdF increases the liquid absorption speed by increasing its content, but it is disadvantageous in terms of energy density. Also, an excessive amount of binder increases the resistance of the battery. Therefore, by making the amount of the binder contained in the positive electrode active material layer within the above range, the active material can be bound efficiently, and the effect of this embodiment can be further enhanced.

<Conductive aid>
The conductive auxiliary agent is an additive blended to improve the conductivity of the active material layer. Although it does not restrict | limit especially as a conductive support agent, Carbon powder, such as acetylene black, Ketjen black, furnace black, carbon powder, such as channel black, thermal black, a graphite, vapor growth carbon fiber (VGCF; registered trademark), etc. Various carbon fibers, carbon materials such as expanded graphite. When the active material layer contains a conductive additive, an electronic network inside the active material layer is effectively formed, which can contribute to improvement of the output characteristics of the battery.

  The content of the conductive additive contained in the positive electrode active material layer is not particularly limited as long as it is an amount that can improve the conductivity of the active material, and is preferably 0 with respect to the positive electrode active material layer. It is the range of 5-15 mass%. More preferably, it is 1-10 mass%, More preferably, it is 2-8 mass%, Most preferably, it is the range of 3-7 mass%.

  The positive electrode active material layer further includes other additives such as a conductive additive, an electrolyte (polymer matrix, ion conductive polymer, electrolytic solution, etc.), and a lithium salt for enhancing ion conductivity, as necessary. Among these, the binder and the conductive assistant are as described above.

<Lithium salt>
The lithium salt is contained in the negative electrode active material layer when the electrolyte described above penetrates into the negative electrode active material layer. Therefore, the specific form of the lithium salt that can be contained in the negative electrode active material layer is the same as the lithium salt that constitutes the electrolyte described above.

<Ion conductive polymer>
Examples of the ion conductive polymer include polyethylene oxide (PEO) -based and polypropylene oxide (PPO) -based polymers.

  The compounding ratio of the components contained in the positive electrode active material layer is not particularly limited if not specified, and these compounding amounts (compounding ratios) are known knowledge about lithium ion secondary batteries. Can be adjusted by appropriately referring to.

  There is no restriction | limiting in particular about the thickness of a positive electrode active material layer, The conventionally well-known knowledge about a battery can be referred suitably. For example, the thickness of the positive electrode active material layer is about 2 to 100 μm.

  The positive electrode (positive electrode active material layer) can be applied by any one of a kneading method, a sputtering method, a vapor deposition method, a CVD method, a PVD method, an ion plating method, and a thermal spraying method in addition to a method of applying (coating) a normal slurry. Can be formed.

[Electrolyte layer]
The electrolyte layer is composed of a separator that holds (impregnates) the electrolyte. As the electrolyte, the above-described electrolyte of the present embodiment (solvated ionic liquid) is applied.

(Separator)
The separator has a function of holding the electrolyte of this embodiment as described above to ensure the conductivity of lithium ions (carrier ions) between the positive electrode and the negative electrode, and a function as a partition between the positive electrode and the negative electrode.

  Examples of the separator include a porous sheet separator or a nonwoven fabric separator made of a polymer or fiber that absorbs and holds the electrolyte (solvated ionic liquid).

  As a separator for a porous sheet made of a polymer or fiber, for example, a microporous (microporous film) can be used. Specific examples of the porous sheet made of the polymer or fiber include polyolefins such as polyethylene (PE) and polypropylene (PP); a laminate in which a plurality of these are laminated (for example, three layers of PP / PE / PP) And a microporous (microporous membrane) separator made of a hydrocarbon resin such as polyimide, aramid, polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), glass fiber, and the like.

  The thickness of the microporous (microporous membrane) separator cannot be uniquely defined because it varies depending on the intended use. For example, in applications such as secondary batteries for driving motors such as electric vehicles (EV), hybrid electric vehicles (HEV), and fuel cell vehicles (FCV), it may be 4 to 60 μm in a single layer or multiple layers. desirable. The fine pore diameter of the microporous (microporous membrane) separator is desirably 1 μm or less (usually a pore diameter of about several tens of nm).

As the nonwoven fabric separator, cotton, rayon, acetate, nylon, polyester; polyolefins such as PP and PE; conventionally known ones such as polyimide and aramid are used alone or in combination. The bulk density of the nonwoven fabric is not particularly limited as long as sufficient battery characteristics can be obtained by the impregnated electrolyte. Furthermore, the thickness of the nonwoven fabric separator may be the same as that of the electrolyte layer, preferably 5 to 200 μm, particularly preferably 10 to 100 μm.

  Here, the separator may be a separator in which a heat-resistant insulating layer is laminated on at least one surface of the resin porous substrate. The heat-resistant insulating layer is a ceramic layer containing inorganic particles and a binder. By having the heat-resistant insulating layer, the internal stress of the separator that increases when the temperature rises is relieved, so that the effect of suppressing thermal shrinkage can be obtained. Moreover, by having a heat-resistant insulating layer, the mechanical strength of the separator with a heat-resistant insulating layer is improved, and it is difficult for the separator to break. Furthermore, the separator is less likely to curl in the electrical device manufacturing process due to the effect of suppressing thermal shrinkage and high mechanical strength.

  As described above, in a separator having a structure in which ceramic layers as heat-resistant insulating layers are laminated, the ceramic layer serves as a gas release means for releasing the gas generated inside the power generation element to the outside of the power generation element. Also works.

  In this embodiment, the above-described electrolyte (solvated ionic liquid) is held in the separator. The above-described electrolyte held in the separator may be in the form of a liquid electrolyte (electrolytic solution made of a solvated ionic liquid). Alternatively, it may be in the form of a gel polymer electrolyte. Here, the gel polymer electrolyte has a configuration in which the above liquid electrolyte (electrolyte component composed of solvated ionic liquid) is injected into a matrix polymer (host polymer) composed of an ion conductive polymer. Use of the gel polymer electrolyte is superior in that the fluidity of the electrolyte is lost, and it becomes easy to block the ion conductivity between the layers. Examples of the ion conductive polymer used as the matrix polymer (host polymer) include polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof. Lithium salts (electrolyte salts) can be well dissolved in such polyalkylene oxide polymers.

  The matrix polymer of gel electrolyte can express excellent mechanical strength by forming a crosslinked structure. In order to form a crosslinked structure, thermal polymerization, ultraviolet polymerization, radiation polymerization, electron beam polymerization, etc. are performed on a polymerizable polymer (for example, PEO or PPO) for forming a polymer electrolyte using an appropriate polymerization initiator. A polymerization treatment may be performed.

[Current collector (tab)]
In a lithium ion secondary battery, a current collector plate (tab) electrically connected to a current collector is taken out of a laminate film as an exterior material for the purpose of taking out current outside the battery.

  The material which comprises a current collector plate (18, 19) is not restrict | limited in particular, The well-known highly electroconductive material conventionally used as a current collector plate for lithium ion secondary batteries can be used. As a constituent material of the current collector plate, for example, metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferable. From the viewpoint of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferable, and aluminum is particularly preferable. Note that the positive electrode current collector plate 19 and the negative electrode current collector plate 18 may be made of the same material or different materials.

[Seal part]
The seal portion is a member unique to the serially stacked battery and has a function of preventing leakage of the electrolyte layer. In addition to this, it is possible to prevent current collectors adjacent in the battery from coming into contact with each other and a short circuit due to a slight unevenness at the end of the laminated electrode.

  The constituent material of the seal portion is not particularly limited, but polyolefin resin such as polyethylene and polypropylene, epoxy resin, rubber, polyimide and the like can be used. Among these, it is preferable to use a polyolefin resin from the viewpoints of corrosion resistance, chemical resistance, film-forming property, economy, and the like.

[Positive lead and negative lead]
Moreover, although illustration is abbreviate | omitted, you may electrically connect between the electrical power collector 23 and a collector plate (18, 19) via a positive electrode lead or a negative electrode lead. As a constituent material of the positive electrode and the negative electrode lead, materials used in known lithium ion secondary batteries can be similarly employed. In addition, heat-shrinkable heat-shrinkable parts are removed from the exterior so that they do not affect products (for example, automobile parts, especially electronic devices) by touching peripheral devices or wiring and causing leakage. It is preferable to coat with a tube or the like.

[Battery exterior]
The battery outer body 22 is a member that encloses the power generation element therein, and a bag-like case using a laminate film containing aluminum that can cover the power generation element may be used. As the laminate film, for example, a laminate film having a three-layer structure in which polypropylene (PP), aluminum, and nylon are laminated in this order can be used, but the laminate film is not limited thereto. A laminate film is desirable from the viewpoint that it is excellent in high output and cooling performance, and can be suitably used for a battery for large equipment for EV and HEV. Moreover, since the group pressure to the power generation element applied from the outside can be easily adjusted and the battery can be enlarged, the power generation element has a laminated structure, and the exterior body is more preferably a laminate film containing aluminum.

  The internal volume of the battery outer body 22 is configured to be larger than the volume of the power generation element 17 so that the power generation element 17 can be enclosed. Here, the internal volume of the exterior body refers to the volume in the exterior body before evacuation after sealing with the exterior body. The volume of the power generation element is the volume of the space occupied by the power generation element, and includes a hole in the power generation element. Since the inner volume of the exterior body is larger than the volume of the power generation element, there is a space in which gas can be stored when gas is generated. Thereby, the gas release property from the power generation element is improved, the generated gas is less likely to affect the battery behavior, and the battery characteristics are improved.

  The lithium ion secondary battery described above can exhibit excellent cycle characteristics by using the electrolyte of this embodiment. Therefore, the secondary battery to which the electrolyte of the present embodiment is applied is assembled as necessary and is suitably used as a power supply device for an electric vehicle.

[Battery]
The assembled battery is configured by connecting a plurality of lithium ion secondary batteries of this embodiment. In detail, at least two or more of the secondary batteries are used to be serialized or parallelized or both. Capacitance and voltage can be freely adjusted by paralleling in series. In addition, a battery pack (electric vehicle power supply) with higher capacity can be realized by forming a battery pack by connecting a plurality of lithium ion secondary batteries of this embodiment with large capacity and excellent cycle characteristics. be able to.

A plurality of secondary batteries can be connected in series or in parallel to form a small assembled battery that can be attached and detached. Then, a plurality of small assembled batteries that can be attached and detached are connected in series or in parallel to provide a large capacity and large capacity suitable for vehicle drive power supplies and auxiliary power supplies that require high volume energy density and high volume output density. An assembled battery having an output can also be formed. How many secondary batteries are connected to make an assembled battery, and how many small assembled batteries are stacked to make a large-capacity assembled battery depends on the vehicle (electric vehicle) battery It may be determined according to the capacity and output.

[vehicle]
The high-output (low resistance) and high-capacity lithium ion secondary battery for automobiles of this embodiment has excellent output characteristics, maintains discharge capacity even after long-term use, and has good cycle characteristics. Vehicle applications such as electric vehicles, hybrid electric vehicles, fuel cell vehicles, and hybrid fuel cell vehicles require higher capacity, larger size, and longer life than electric and portable electronic devices. . Therefore, the high output (low resistance) and high capacity lithium ion secondary battery for automobiles of this embodiment can be suitably used as a power source for vehicles, for example, as a power source for driving vehicles or an auxiliary power source.

  Specifically, the lithium ion secondary battery of this embodiment or an assembled battery formed by combining a plurality of these can be mounted on a vehicle. In this embodiment, since a long-life lithium ion secondary battery excellent in long-term reliability and output characteristics can be configured, a plug-in hybrid electric vehicle having a long EV mileage when mounted with such a secondary battery, or a single charge mileage A long electric vehicle can be constructed. The lithium ion secondary battery of the present embodiment or an assembled battery obtained by combining a plurality of these batteries may be a hybrid vehicle, a fuel cell vehicle, an electric vehicle (for example, a four-wheel vehicle (passenger car, truck, bus, etc. (In addition to cars, light vehicles, etc.), motorcycles (including motorcycles) and tricycles) can be used to provide a long-life and highly reliable vehicle. However, the application is not limited to automobiles. For example, it can be applied to various power sources for moving vehicles such as other vehicles, for example, trains, and power sources for mounting such as uninterruptible power supplies. It is also possible to use as.

  Hereinafter, the present invention will be described in more detail with reference to examples. In addition, the following room temperature shows 20-25 degreeC.

Example 1
[Evaluation of Solvated Ionic Liquid [Li (G1) _0.6 (G2) _0.6 ] [FSI]]
[Electrolyte synthesis]
As a Li salt, a purchased lithium bisfluorosulfonylimide (hereinafter referred to as LiFSI) (manufactured by Kishida Chemical Co., Ltd.) was weighed into a sample container. Weigh methylmonoglyme (hereinafter referred to as G1) and methyldiglyme (hereinafter referred to as G2) (both G1 and G2 are manufactured by Nippon Emulsifier Co., Ltd.) so as to be 0.6 mol with respect to the weight of LiFSI. The mixture was stirred for 5 days in a container kept at 60 ° C. Thus, a predetermined solvated ionic liquid electrolyte ([Li (G1) _0.6 (G2) _0.6 ] [FSI]) was obtained. A series of operations were all performed in a glove box under an argon atmosphere with a dew point of −60 ° C. or lower. The number of moles of Li salt, G1, and G2, and [O] / [Li] of the solvated ionic liquid are shown in Table 1 below.

[Production of silicon electrode]
A nickel foil (thickness 20 μm) was prepared as an electrode current collector. Next, an amorphous silicon (silicon) thin film (thickness: 100 nm), which is a negative electrode active material layer, is formed on the surface of the nickel foil by an RF sputtering film forming method to produce a target amorphous silicon electrode sheet (negative electrode sheet). did. The size of the silicon electrode sheet was 100 mm long × 100 mm wide.

[Production of battery]
An electrode is punched out from the negative electrode sheet obtained above to a diameter (φ) of 15 mm, and a porous glass film (thickness: 200 μm) impregnated with the electrolyte obtained above is sandwiched as a separator, and a Li foil is provided as a counter electrode. Was assembled into a commercially available assembled cell (battery). A series of operations were all performed in a glove box under an argon atmosphere with a dew point of −60 ° C. or lower.

[Cycle test]
Take out the assembled battery from the glove box and place it in a thermostatic chamber at a constant temperature of 30 ° C, then charge and discharge in a constant current mode at a current value of 0.5 C and a potential range of 5 mV to 2.0 V. It was. This charge / discharge operation was defined as one cycle, and the cycle test was performed by repeating the charge / discharge up to the 100th cycle. As a cycle test result, a graph (cycle characteristic graph) showing the relationship between the number of cycles and the capacity retention rate is shown in FIG.

  From FIG. 3, it was confirmed that after 100 cycles, the discharge capacity of the battery using the silicon electrode showed a capacity retention rate of 90% or more of the initial maximum capacity (maximum discharge capacity up to the 1st to 10th cycles).

  Here, the capacity maintenance rate for each cycle was calculated by the following formula (where n is an integer of 1 to 100).

(Example 2)
[Evaluation of Solvated Ionic Liquid [Li (G1) _0.7 (G2) _0.7 ] [FSI]]
The composition of the solvated ionic liquid used as the electrolyte is [Li (G1) _0.7 (G2) _0.7 ] [FSI]. Weighed to be. Except this, it carried out similarly to Example 1, and performed electrolyte synthesis, preparation of a silicon electrode, preparation of a battery, and a cycle test. The number of moles of Li salt, G1, and G2, and [O] / [Li] of the solvated ionic liquid are shown in Table 1 below. Further, as a cycle test result, a graph (cycle characteristic graph) showing the relationship between the number of cycles and the capacity retention rate is shown in FIG.

  From FIG. 4, it was confirmed that after 100 cycles, the discharge capacity of the battery using the silicon electrode showed a capacity retention rate of 95% or more of the initial capacity.

(Example 3)
[Evaluation of Solvated Ionic Liquid [Li (G1) _0.76 (G2) _0.76 ] [FSI]]
The composition of the solvated ionic liquid used as the electrolyte is [Li (G1) _0.76 (G2) _0.76 ] [FSI]. Weighed to be. Except this, it carried out similarly to Example 1, and performed electrolyte synthesis, preparation of a silicon electrode, preparation of a battery, and a cycle test. The number of moles of Li salt, G1, and G2, and [O] / [Li] of the solvated ionic liquid are shown in Table 1 below. In addition, as a cycle test result, a graph (cycle characteristic graph) showing the relationship between the number of cycles and the capacity retention rate is shown in FIG.

  From FIG. 5, it was confirmed that after 100 cycles, the discharge capacity of the battery using the silicon electrode showed a capacity retention rate of 92% or more of the initial capacity.

Example 4
[Evaluation of Solvated Ionic Liquid [Li (G1) _0.7 (G2) _0.7 ] [TFSI]]
LiFSI used in Example 2 was replaced with lithium bistrifluoromethanesulfonylimide (
Hereinafter, electrolyte synthesis, production of a silicon electrode, production of a battery, and a cycle test were performed in accordance with Example 2 except that it was replaced with LiTFSI. The number of moles of Li salt, G1, and G2, and [O] / [Li] of the solvated ionic liquid are shown in Table 1 below. Further, as a cycle test result, a graph (cycle characteristic graph) showing the relationship between the number of cycles and the capacity retention rate is shown in FIG.

  From FIG. 6, it was confirmed that after 100 cycles, the discharge capacity of the battery using the silicon electrode showed a capacity retention rate of 88% or more of the initial capacity.

(Comparative Example 1)
[Evaluation of Solvated Ionic Liquid [Li (G1) _0.58 (G2) _0.58 ] [FSI]]
Except that the amount of G1 and G2 used in Example 1 was changed to 0.58 mol with respect to LiFSI, according to Example 1, electrolyte synthesis, silicon electrode production, battery production and cycle A test was conducted. The number of moles of Li salt, G1, and G2, and [O] / [Li] of the solvated ionic liquid are shown in Table 1 below. Further, as a cycle test result, a graph (cycle characteristic graph) showing the relationship between the number of cycles and the capacity retention rate is shown in FIG.

  From FIG. 7, it was confirmed that after 100 cycles, the discharge capacity of the battery using the silicon electrode can only obtain a capacity maintenance rate of 83% or less of the initial capacity.

(Comparative Example 2)
[Evaluation of Solvated Ionic Liquid [Li (G1) _0.8 (G2) _0.8 ] [FSI]]
Except that the amount of G1 and G2 used in Example 1 was changed to 0.8 mol with respect to LiFSI, respectively, according to Example 1, electrolyte synthesis, silicon electrode production, battery production, and cycle A test was conducted. The number of moles of Li salt, G1, and G2, and [O] / [Li] of the solvated ionic liquid are shown in Table 1 below. Further, as a cycle test result, a graph (cycle characteristic graph) showing the relationship between the number of cycles and the capacity retention rate is shown in FIG.

  From FIG. 8, it was confirmed that after 100 cycles, the discharge capacity of the battery using the silicon electrode can only obtain a capacity retention rate of 80% or less of the initial capacity.

(Comparative Example 3)
[Evaluation of Solvated Ionic Liquid [Li (G1) _0.58 (G2) _0.58 ] [TFSI]]
Except that LiFSI used in Comparative Example 1 was replaced with LiTFSI, electrolyte synthesis, silicon electrode production, battery production, and cycle test were performed according to Comparative Example 1. The number of moles of Li salt, G1, and G2, and [O] / [Li] of the solvated ionic liquid are shown in Table 1 below. Further, as a cycle test result, a graph (cycle characteristic graph) showing the relationship between the number of cycles and the capacity retention rate is shown in FIG.

  From FIG. 9, it was confirmed that after 100 cycles, the discharge capacity of the battery using the silicon electrode can only obtain a capacity retention rate of 25% or less of the initial capacity.

(Comparative Example 4)
[Evaluation of Solvated Ionic Liquid [Li (G1) _0.8 (G2) _0.8 ] [TFSI]]
Except for changing the addition amount of G1 and G2 used in Comparative Example 3 to 0.8 mol with respect to LiTFSI, according to Comparative Example 3, electrolyte synthesis, silicon electrode production, battery production and cycle A test was conducted. The number of moles of Li salt, G1, and G2, and [O] / [Li] of the solvated ionic liquid are shown in Table 1 below. Further, as a cycle test result, a graph (cycle characteristic graph) showing the relationship between the number of cycles and the capacity retention rate is shown in FIG.

  From FIG. 10, it was confirmed that after 100 cycles, the discharge capacity of the battery using the silicon electrode can only obtain a capacity retention rate of 52% or less of the initial capacity.

(Example 5)
[Evaluation of Solvated Ionic Liquid [Li (G1) _0.32 (G2) _0.95 ] [FSI]]
Except for changing the addition amount so that G1 used in Example 1 is 0.32 mol with respect to LiFSI and G2 is 0.95 mol with respect to LiFSI, electrolyte synthesis and silicon electrode Fabrication, battery fabrication and cycle testing were performed. The number of moles of Li salt, G1, and G2, and [O] / [Li] of the solvated ionic liquid are shown in Table 1 below. Further, as a cycle test result, a graph (cycle characteristic graph) showing the relationship between the number of cycles and the capacity retention rate is shown in FIG. The solvated ionic liquid of this example is precisely [Li (G1) _0.318 (G2) _0.954 ] [FSI], G1 is 0.318 mol, and G2 is 0.954 mol. However, in the above, the third decimal place is rounded off.

  From FIG. 11, it was confirmed that after 100 cycles, the discharge capacity of the battery using the silicon electrode showed a capacity retention rate of 93% or more of the initial capacity.

(Comparative Example 5)
[Evaluation of Solvated Ionic Liquid [Li (G1) _0.25 (G2) _1.00 ] [FSI]]
Except for changing the addition amount so that G1 used in Example 1 is 0.25 mol with respect to LiFSI and G2 is 1.00 mol with respect to LiFSI, electrolyte synthesis and silicon electrode Fabrication, battery fabrication and cycle testing were performed. The number of moles of Li salt, G1, and G2, and [O] / [Li] of the solvated ionic liquid are shown in Table 1 below. In addition, as a cycle test result, a graph (cycle characteristic graph) showing the relationship between the number of cycles and the capacity retention rate is shown in FIG.

  From FIG. 12, it was confirmed that after 100 cycles, the discharge capacity of the battery using the silicon electrode can only obtain a capacity retention rate of 51% or less of the initial capacity.

(Comparative Example 6)
[Evaluation of Solvated Ionic Liquid [Li (G1) _0.88 (G2) _0.58 ] [FSI]]
Except for changing the addition amount so that G1 used in Example 1 is 0.88 mol with respect to LiFSI and G2 is 0.58 mol with respect to LiFSI, electrolyte synthesis and silicon electrode Fabrication, battery fabrication and cycle testing were performed. The number of moles of Li salt, G1, and G2, and [O] / [Li] of the solvated ionic liquid are shown in Table 1 below. As a cycle test result, a graph (cycle characteristic graph) showing the relationship between the number of cycles and the capacity retention rate is shown in FIG. It should be noted that the solvated ionic liquid of this example is precisely [Li (G1) _0.875 (G2) _0.583 ] [FSI], G1 is 0.875 mol, and G2 is 0.583 mol. However, in the above, the third decimal place is rounded off.

  From FIG. 13, it was confirmed that after 100 cycles, the discharge capacity of the battery using the silicon electrode can only obtain a capacity retention rate of 70% or less of the initial capacity.

(Comparative Example 7)
[Evaluation of Solvated Ionic Liquid [Li (G1) _1.75 (G2) _0.00 ] [FSI]]
Except for changing the addition amount so that G1 used in Example 1 is 1.75 mol with respect to LiFSI and G2 is 0 mol with respect to LiFSI, electrolyte synthesis, production of a silicon electrode according to Example 1, A battery was prepared and a cycle test was performed. The number of moles of Li salt, G1, and G2, and [O] / [Li] of the solvated ionic liquid are shown in Table 1 below. As a cycle test result, a graph (cycle characteristic graph) showing the relationship between the number of cycles and the capacity retention rate is shown in FIG.

  From FIG. 14, it was confirmed that after 100 cycles, the discharge capacity of the battery using the silicon electrode can only obtain a capacity retention rate of 56% or less of the initial capacity.

(Comparative Example 8)
[Evaluation of Solvated Ionic Liquid [Li (G1) _0.00 (G2) _1.17 ] [TFSI]]
LiFSI used in Example 1 was replaced with LiTFSI, and the addition amount was changed so that G1 was 0 mole relative to LiTFSI and G2 was 1.17 mole relative to LiTFSI. Other than that, according to Example 1, electrolyte synthesis, production of a silicon electrode, production of a battery, and a cycle test were performed. The number of moles of Li salt, G1, and G2, and [O] / [Li] of the solvated ionic liquid are shown in Table 1 below. As a cycle test result, a graph (cycle characteristic graph) showing the relationship between the number of cycles and the capacity retention rate is shown in FIG. The solvated ionic liquid of this example is precisely [Li (G1) _0.000 (G2) _1.167 ] [TFSI], where G1 is 0.000 mol and G2 is 1.167 mol. However, in the above, the third decimal place is rounded off.

  From FIG. 15, it was confirmed that after 100 cycles, the discharge capacity of the battery using the silicon electrode was only 44% or less of the initial capacity.

(Example 6)
[Rate characteristics of solvated ionic liquid [Li (G1) _0.6 (G2) _0.6 ] [FSI]]
A cell (battery) was assembled by performing electrolyte synthesis, production of a silicon electrode, and production of a battery in the same manner as in Example 1. Using the assembled battery, a rate test was performed according to the following procedure. First, after charging and discharging at 0.5 C for 10 cycles, the charge process was changed from 0.2 C to 5 C, and the rate test was performed by repeating charging and discharging under the condition that the discharge rate was constant at 0.5 C. Carried out. The discharge capacity normalized with respect to the discharge capacity at 0.2 C was plotted as the charge rate value. The results are shown in FIG. 16 as a rate characteristic graph (a semi-logarithmic graph showing the relationship between the discharge rate and the normalized discharge capacity). From FIG. 16, it was confirmed that the discharge capacity at 5C was 87% or more with respect to the discharge capacity at 0.2C. In addition, the discharge capacity normalized with reference to the discharge capacity at 0.2 C is obtained by the following formula.

  What is being evaluated here is the discharge capacity (the amount of Li released from Si).

(Example 7)
[Rate characteristics of solvated ionic liquid [Li (G1) _0.7 (G2) _0.7 ] [FSI]]
In the same manner as in Example 2, electrolyte synthesis, silicon electrode production, and battery production were performed to assemble a cell (battery). Using the assembled battery, a rate test was performed according to the procedure shown in Example 6. The results are shown in FIG. 17 as a rate characteristic graph (a semi-logarithmic graph showing the relationship between the discharge rate and the capacity retention rate). From FIG. 17, it was confirmed that the discharge capacity at 5C was 88% or more with respect to the discharge capacity at 0.2C.

(Comparative Example 9)
[Rate characteristics of solvated ionic liquid [Li (G1) _0.00 (G2) _1.17 ] [FSI]]
Except that the addition amount was changed so that G1 used in Example 1 was 0 mol with respect to LiFSI and G2 was 1.17 mol with respect to LiFSI, electrolyte synthesis, production of a silicon electrode, and A battery was fabricated to assemble a cell (battery). The number of moles of Li salt, G1, and G2, and [O] / [Li] of the solvated ionic liquid are shown in Table 1 below. Using the assembled battery, a rate test was performed according to the procedure shown in Example 6. The results are shown in FIG. 18 as a rate characteristic graph (a semi-logarithmic graph showing the relationship between the discharge rate and the capacity retention rate). The solvated ionic liquid of this example is precisely [Li (G1) _0.000 (G2) _1.167 ] [FSI], G1 is 0.000 mol, and G2 is 1.167 mol. However, in the above, the third decimal place is rounded off. From FIG. 18, it was confirmed that the discharge capacity at 5C was only 31% or less with respect to the discharge capacity at 0.2C.

(Example 8)
[Impedance measurement of solvated ionic liquid [Li (G1) _0.7 (G2) _0.7 ] [FSI]]
In the same manner as in Example 2, electrolyte synthesis, silicon electrode production, and battery production were performed to assemble a cell (battery). The impedance of the assembled cell (battery) was measured by the following procedure.

  After charging and discharging for 9 cycles in a constant current mode of 0.5 C, charging and discharging were terminated in a fully charged state at the 10th cycle. The response frequency was measured for this cell (battery) using EG8 / G PAR, VMP2 Multi Potentiostat manufactured by Princeton Applied Research, with a frequency range of 1 MHz to 50 MHz and an applied voltage of 10 mV. The cell (battery) was set in a constant temperature bath at 30 ° C. and a series of measurements were performed. The obtained result is shown in FIG. The charge transfer resistance of the electrode reaction in Example 8 (= the size of the arc of the Cole-Cole plot) was about 77Ω.

(Comparative Example 10)
[Measurement of Impedance of Solvated Ionic Liquid [Li (G1) _0.00 (G2) _1.33 ] [FSI]]
Except that the addition amount was changed so that G1 used in Example 1 was 0 mol with respect to LiFSI and G2 was 1.33 mol with respect to LiFSI, electrolyte synthesis, production of a silicon electrode, and A battery was fabricated to assemble a cell (battery). The number of moles of Li salt, G1, and G2, and [O] / [Li] of the solvated ionic liquid are shown in Table 1 below. Impedance measurement was performed according to Example 8 using the assembled cell (battery). The results are shown side by side with Example 8 in FIG. Note that the solvated ionic liquid of this example is precisely [Li (G1) _0.000 (G2) _1.333 ] [FSI], where G1 is 0.000 mol, and G2 is 1.333 mol. However, in the above, the third decimal place is rounded off.

  The charge transfer resistance of the electrode reaction in Comparative Example 10 (= the size of the Cole-Cole plot arc) was about 115Ω.

  From the results of Table 1 and FIGS. 3 to 18, the electrolyte (solvated ionic liquid) of this example is a cycle for a negative electrode using a silicon-based active material as compared with the electrolyte (solvated ionic liquid) of the comparative example. It was confirmed that the stability (cycle characteristics) and the rate characteristics were excellent. Further, from FIG. 19, the electrolyte (solvated ionic liquid) used in this example has extremely high charge transfer resistance at the electrolyte / electrode interface as compared with the electrolyte (solvated ionic liquid) used in the comparative example. It turns out that it becomes low.

  Moreover, when compared between Examples, both G1 and G2 are 0.7 mol, and in Examples 2 and 4, which are examples of [O] / [Li] = 3.5, LiFSI was used as the Li salt. It was confirmed that Example 2 was superior in cycle stability (cycle characteristics) to Example 4 in which LiTFSI was used as the Li salt.

  In Examples 1 to 3, which are examples of the same Li salt, Example 1 in which [O] / [Li] is 3.0, Example 3 in which [O] / [Li] is 3.8, [ It was found that the cycle stability (cycle characteristics) was improved in the order of Example 2 where O] / [Li] was 3.5.

  In Examples 6 to 7, which are examples of the same Li salt, [O] / [Li] is 3.0, and [O] / [Li] is 3.5. It was found that the rate characteristics were also improved.

10a Lithium ion secondary battery (parallel stacked battery),
10b Lithium ion secondary battery (series stacked battery),
11 negative electrode current collector,
12 negative electrode active material layer,
13 electrolyte layer,
14 positive electrode current collector,
15 positive electrode active material layer,
16 cell layer,
17 Power generation elements,
18 negative electrode current collector plate,
19 positive current collector,
20 Negative terminal lead,
21 positive terminal lead,
22 Laminate film (battery casing),
23 current collector,
23a outermost layer current collector on the positive electrode side,
23b The outermost layer current collector on the negative electrode side,
24 bipolar electrodes,
25 Sealing part (insulating part).

Claims (5)

An electrolyte for a lithium ion secondary battery using a solvated ionic liquid containing methyl monoglyme and methyl diglyme and a lithium salt,
Ratio of the total number of moles of oxygen atoms contained in methyl monoglyme and methyl diglyme to the number of moles of lithium in the lithium salt (= total oxygen atoms contained in methyl monoglyme and methyl diglyme with respect to lithium in the lithium salt) Number of moles) is 3.0 or more and less than 4.0,
The mixing ratio of methyl monoglyme and methyl diglyme (= methyl monoglyme mole number / methyl diglyme mole number) is (over 1/4) to (less than 3/2). Secondary battery electrolyte.   The electrolyte for a lithium ion secondary battery according to claim 1, wherein the lithium salt is an imide type lithium salt.   The electrolyte for a lithium ion secondary battery according to claim 1 or 2, which is applied to a secondary battery using a silicon-based active material as a negative electrode active material.   A lithium ion secondary battery comprising the electrolyte according to claim 1 and using a silicon-based active material as a negative electrode active material.   5. The lithium ion according to claim 4, wherein the silicon-based active material is one or more selected from the group consisting of silicon metal, silicon alloy, silicon oxide, silicon compound, and silicon semiconductor. Secondary battery.