JP2010003698A - Nonaqueous electrolyte for electrochemical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte useful for manufacturing an electrochemical element with superior charge and discharge load characteristics and a shape retention property. <P>SOLUTION: By using the nonaqueous electrolyte containing an acid denaturation object of polyvinyl acetal resin with specific physical properties, the electrochemical elements with superior charge and discharge load characteristics, high temperature preservability, a shape retention property and ability to respond to a large capacity requirement can be obtained without the need of special operation. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte for an electrochemical device.

  Electrochemical elements such as a battery, a capacitor, and a solar battery using an electrolyte called a Gretcher cell are devices for charging and discharging electricity using an electrochemical reaction. In particular, since batteries and capacitors have high energy density and can be easily reduced in size, they are widely used as power sources for home appliances and portable devices, backup power sources, and the like.

  Among such batteries and capacitors, the lithium battery has a very high energy density, and even if stored for a long period of time or continuously used for a long period of time, there is little change in charge / discharge characteristics and a decrease in charge / discharge capacity. Therefore, it is widely used as a power source for portable information terminal devices such as mobile phones and mobile devices, and its demand is constantly increasing with the rapid spread of portable information terminal devices. A lithium battery is an electrochemical element having the above-described excellent characteristics, but is required to have a higher capacity and a thinner thickness, and to increase its shape flexibility. This is in order to meet the demand for further improving the convenience by further increasing the usage time per charge of the portable information terminal device and further downsizing the portable information terminal device.

  A battery generally includes a separator interposed between a positive electrode, a negative electrode, and a positive and negative electrode, and the separator is impregnated with an electrolytic solution that is an electrolyte. Such a battery has high ionic conductivity, that is, battery performance because the electrolyte is in a liquid state. On the other hand, battery performance is likely to deteriorate due to leakage of the electrolyte to the outside. In order to prevent this, it is necessary to completely seal the inside of the battery, so that the shape of the battery is limited and it is difficult to reduce the thickness of the battery.

  On the other hand, an electrolyte made of a solid polymer compound (hereinafter referred to as “solid polymer electrolyte”) has almost no risk of leaking to the outside, and therefore does not require a special structure for preventing leakage. In addition, since the solid polymer electrolyte can be bonded to the electrode, separator, and the like, the strength and shape retention of the battery can be improved. Therefore, the solid polymer electrolyte is very effective in reducing the thickness of the battery and increasing the degree of freedom of shape of the battery. It is also effective for obtaining a large-area battery.

  The solid polymer electrolyte includes a gel type polymer electrolyte containing an electrolyte solution together with a solid polymer compound, and an all solid polymer electrolyte consisting only of a solid polymer compound. Since the gel type polymer electrolyte has relatively higher ionic conductivity than the all solid type polymer electrolyte, most of the batteries using the solid type polymer electrolyte employ the gel type polymer electrolyte.

  As a gel type polymer electrolyte, for example, a copolymer of vinylidene fluoride and hexafluoropropylene impregnated with an electrolytic solution is known. However, such a copolymer is limited in the composition of the electrolyte solution that can be impregnated, and it is difficult to add a large amount of a solvent having a chain molecular structure effective in improving the ionic conductivity in the electrolyte solution. A battery having excellent electrical load characteristics cannot be obtained.

  In addition, a macromonomer containing a double bond such as polyalkylene glycol acrylate is added to the electrolytic solution, and the macromonomer is polymerized and crosslinked by irradiating UV or adding a polymerization initiator thereto. A method is known in which gel is gelled to obtain a gel-type polymer electrolyte. However, such an electrolyte does not have a sufficiently satisfactory ionic conductivity. Moreover, in order to gelatinize electrolyte solution, it is necessary to add extra processes, such as UV irradiation and a heating process, to a normal battery manufacturing process. Furthermore, since macromonomers generally have a short pot life, strict quality control is required. Therefore, when the electrolyte solution is gelled using the macromonomer, there is a problem that the battery manufacturing process becomes complicated.

  Moreover, the gel type polymer electrolyte which impregnated the polyvinyl acetal resin with the electrolyte solution is also known (for example, refer patent document 1, patent document 2, patent document 3, patent document 4). In the techniques described in Patent Documents 1 to 4, a polyvinyl acetal resin, a protic salt, and an organic solvent are mixed to prepare an electrolyte solution, and most of the organic solvent is evaporated to prepare a film electrolyte. The resin is fixed at a certain position in the film electrolyte. When such a film-like electrolyte is incorporated in a battery and used, most of the film-like electrolyte stays in a fixed position in the film-like electrolyte, so that the ionic conductivity is lowered and a high-capacity battery cannot be obtained. . In addition, in order to obtain a film electrolyte using a polyvinyl acetal resin, it is necessary to contain the resin in an amount of 10% by weight or more based on the total amount of the electrolyte solution. If the polyvinyl acetal resin is contained in a large amount as described above, the resin inhibits ionic conduction. From this point of view as well, an electrolyte having an ionic conductivity sufficient to cope with an increase in battery capacity cannot be obtained.

  Furthermore, it is also known to use it as a solid polymer electrolyte without impregnating the polyvinyl acetal resin with an electrolytic solution (see, for example, Patent Document 5). However, this electrolyte also does not have ionic conductivity that can cope with the increase in capacity of the battery. Further, it is known to be used as a binder constituting the negative electrode (see, for example, Patent Document 6).

  Thus, in the conventional gel-type polymer electrolyte, the polymer compound molecules are dispersed at a high concentration in the electrolyte solution, and the polymer compound molecules inhibit ion migration. The ion conductivity will be lower than that. For this reason, an electrochemical element using a gel type polymer electrolyte has poor electrical load characteristics as compared with an electrochemical element using an electrolytic solution as an electrolyte. If the content of the polymer compound is reduced, the ion conductivity can be increased, but the advantages inherent in the solid polymer electrolyte that the gel strength is lowered and the shape retention of the electrochemical element is improved are lost. Moreover, although the high molecular compound which has ion conductivity is also performed, it has not resulted in fully raising the ionic conductivity of electrolyte solution.

  Thus, in the prior art, in order to improve the mechanical strength of the electrochemical element, there is only a technical idea of obtaining a film-like electrolyte or a solid electrolyte. When a synthetic resin such as a polyvinyl acetal resin is used It has been customary that the resin is contained in the electrolytic solution at a ratio of 10% by weight or more. Therefore, in the prior art, a gel type polymer electrolyte obtained by blending a polyvinyl acetal resin in an electrolyte solution with a content of less than 10% by weight has not been proposed. There is no description or suggestion about the use of the cross-linked product cross-linked by the method for adhesion between the positive electrode and / or the negative electrode and the separator.

JP-A-57-143355 JP-A-57-143356 JP-A-3-43909 Japanese Patent Laid-Open No. 3-43910 Japanese Patent Laid-Open No. 10-50141 Japanese Patent Laid-Open No. 6-163031

  An object of the present invention is to provide a non-aqueous electrolyte useful for producing an electrochemical device that has excellent electrical load characteristics, charge / discharge characteristics, shape retention and high-temperature storage stability, and is capable of high capacity. is there.

  As a result of intensive studies to solve the above-mentioned problems, the present inventor succeeded in obtaining a crosslinkable polymer material exhibiting higher adhesive strength than polyvinyl acetal resin. Since the mechanical strength of the electrochemical element can be improved to a practically sufficient level by the amount, even if the non-aqueous electrolyte is gelled, the ionic conductivity is hardly lowered, and in addition, the material As a result, it was found that a desired electrochemical element can be obtained in the same manner as in the conventional method for producing an electrochemical element without adding an extra step, and the present invention has been completed.

In the present invention, the proton content showing a peak at 4.25 to 4.35 ppm based on the DMSO-d ₆ peak (2.49 ppm) in ¹ H-NMR measurement is 0.25 mol / kg or less, further hydroxyl group content is non-aqueous electrolytic solution for electrochemical device which comprises a 0.1 to 2 mol / kg polyvinyl acetal resin of the acid-modified product is, the present invention is ^{the 1 H-NMR} measurement The content of protons having a peak at 4.25 to 4.35 ppm with respect to the DMSO-d ₆ peak (2.49 ppm) is 0.25 mol / kg or less, and the hydroxyl group content is 0.1 to The acid-modified product of polyvinyl acetal resin at 2 mol / kg is obtained by measuring the polystyrene-reduced number average molecular weight λ by gel permeation chromatography measurement of the acid-modified product and the non-hydroelectric of the acid-modified product. A non-aqueous electrolytic solution for electrochemical device which comprises a concentration c (wt%) Togashiki 100 ≦ λ ^1/2 × c ≦ 1000 in the liquid to Mitsurusu so.

  The non-aqueous electrolyte of the present invention is characterized in that the polyvinyl acetal resin is obtained by acetalizing, esterifying, acetalizing and esterifying polyvinyl alcohol.

  Furthermore, the non-aqueous electrolytic solution of the present invention is characterized in that the polyvinyl acetal resin is polyvinyl formal.

  Furthermore, the nonaqueous electrolytic solution of the present invention is characterized in that the concentration of the acid-modified product is 0.3 to 3.5% by weight of the total amount of the nonaqueous electrolytic solution.

  Furthermore, the nonaqueous electrolytic solution of the present invention is characterized by further containing a compound that generates an acid.

  Furthermore, in the nonaqueous electrolytic solution of the present invention, the compound that generates an acid is a Lewis acid and / or a Lewis acid salt having a fluorine atom.

  The nonaqueous electrolytic solution containing the acid-modified product of the polyvinyl acetal resin of the present invention is subjected to electrolytic oxidation by energization to become a crosslinked product, and exhibits a much higher adhesive strength than the polyvinyl acetal resin. Accordingly, the mechanical strength of the electrochemical element can be increased and its shape retention property, high temperature storage property, and the like can be improved with a much smaller content than the polyvinyl acetal resin. In addition, since the content of the acid-modified product is very small, even if the non-aqueous electrolyte is gelated at the time of crosslinking by energization, there is almost no hindrance to the movement of ions, and the non-aqueous electrolyte There is an advantage that an electrochemical element excellent in electrical load characteristics and charge / discharge characteristics can be obtained without lowering the ionic conductivity of the liquid crystal.

  Furthermore, when an electrochemical element such as a battery is manufactured using this non-aqueous electrolyte, the acid-modified product of the polyvinyl acetal resin accompanies charging in the charging process, which is the final process of manufacturing the electrochemical element. Since it crosslinks by electrolytic oxidation or the like and is insolubilized in a non-aqueous solvent, an electrochemical element having excellent characteristics as described above can be produced by a conventional method for producing an electrochemical element without adding an extra step.

[Acid modified product of polyvinyl acetal resin]
In addition, the acid-modified product of the polyvinyl acetal resin is usually dissolved or uniformly swollen in the electrolytic solution. However, in the charging step, which is the final step for manufacturing an electrochemical element, it is subjected to electrolytic oxidation during charging. Crosslink. The cross-linked product is insoluble in the electrolytic solution or coarsened in the electrolytic solution, and exhibits higher adhesive strength than the polyvinyl acetal resin that does not undergo acid modification. That is, the cross-linked product strongly adheres the negative electrode and / or positive electrode to the separator with a content smaller than that of the polyvinyl acetal resin that does not undergo acid modification (usually less than 10% by weight of the total amount of the non-aqueous electrolyte). Furthermore, since there is little content in a non-aqueous electrolyte, even if a non-aqueous electrolyte is gelatinized by bridge | crosslinking, the ionic conductivity of a non-aqueous electrolyte is hardly impaired.

  Therefore, if the non-aqueous electrolyte of the present invention is used, the high ionic conductivity of the non-aqueous electrolyte is sufficiently exhibited, so that the capacity of the electrochemical device can be increased, and a laminate of the negative electrode, separator and positive electrode can be obtained. Since bonding is performed with high mechanical strength, the degree of freedom in shape is large, and the electrochemical element can be made thinner and smaller.

  The reason why the acid-modified product of the polyvinyl acetal resin is crosslinked by energization is assumed as follows, for example. That is, the hydroxyl group of the acid-modified main chain is electrolytically oxidized by energization in the charging step to generate an aldehyde group or a ketone group, and this aldehyde group and / or ketone group is converted to 1,2-dihydroxy in the main chain. By reacting with the hydroxyl group which has escaped electrolytic oxidation in the ethylene structure or 1,3-dihydroxy-1,3-propylene structure, a new acetal ring structure is formed, and crosslinking occurs. Further, due to acid modification, the 1,2-dihydroxyethylene structure and / or 1,3-dihydroxy-1,3-propylene structure in the polyvinyl acetal resin main chain with respect to the total amount of hydroxyl groups contained in the polyvinyl acetal resin. The proportion of hydroxyl groups increases.

The present ^invention, the content of protons exhibiting a peak at 4.25~4.35ppm peak (2.49 ppm) as the reference for _{DMSO-d 6} with the 1 H-NMR measurement is not more than 0.25 mol / kg, A non-aqueous electrolyte for an electrochemical device, comprising an acid-modified product of a polyvinyl acetal resin having a hydroxyl group content of 0.1 to 2 mol / kg.

Further, in the present invention, the proton content showing a peak at 4.25 to 4.35 ppm with reference to the peak (2.49 ppm) of DMSO-d ₆ in ¹ H-NMR measurement is 0.25 mol / kg or less. An acid-modified product of a polyvinyl acetal resin having a hydroxyl group content of 0.1 to 2 mol / kg, a polystyrene-reduced number average molecular weight λ by gel permeation chromatography measurement of the acid-modified product, and the acid-modified product A nonaqueous electrolytic solution for an electrochemical device, wherein the concentration c (% by weight) in the nonaqueous electrolytic solution satisfies the formula 100 ≦ λ ^1/2 × c ≦ 1000.

  The acid-modified product of the polyvinyl acetal resin of the present invention can be obtained by bringing a polyvinyl acetal resin and an acid into contact with each other, preferably in a non-aqueous solvent.

  A well-known thing can be used as a polyvinyl acetal resin, For example, polyvinyl formal, polyvinyl ethylal, polyvinyl propylal, polyvinyl butyral etc. are mentioned. In the present invention, polyvinyl acetate, polyvinyl propionate and the like are also included in the polyvinyl acetal.

  Among these, those obtained by acetalization of polyvinyl alcohol, esterification of polyvinyl alcohol, acetalization and esterification of polyvinyl alcohol and the like are preferable.

Although it does not restrict | limit especially as polyvinyl alcohol, Although a well-known thing can be used, a thing with an average polymerization degree of 10-20000 is preferable, and the thing of 300-2000 is more preferable.
Polyvinyl alcohol includes those obtained by saponifying polyvinyl carboxylate, poly (alkyl vinyl carbonate) and the like. The saponification degree in these saponified products is not particularly limited, but is preferably 60 to 99 mol%, more preferably 80 to 99 mol%.

  Acetalization of polyvinyl alcohol can be carried out according to a known method. For example, an aldehyde may be allowed to act on polyvinyl alcohol in the presence of an acid catalyst in water. Known aldehydes can be used, and examples include formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, isobutyraldehyde and the like. Among these, formaldehyde is preferable. Although the usage-amount of an aldehyde can be suitably selected according to polyvinyl alcohol concentration etc., Preferably it is 0.1-4 mol per 1 liter of reaction solvent (water), More preferably, it is 0.2-3 mol. Examples of the acid catalyst include sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, trichloroacetic acid, organic sulfonic acid and the like, and sulfuric acid and hydrochloric acid are preferable. Although the usage-amount of an acid catalyst can be suitably selected according to the density | concentration etc. of polyvinyl alcohol resin and an aldehyde, Preferably it is 1-6 gram equivalent with respect to 1 liter of reaction solvent (water), More preferably, it is 2-5 gram equivalent. The acetalization reaction is preferably performed at a temperature of 5 to 90 ° C, more preferably 25 to 80 ° C, and is completed in about 1 to 10 hours.

  For esterification of polyvinyl alcohol, formic acid esterification, acetic acid esterification, propionic acid esterification, carbonic acid esterification, 1,2-hydroxyethylene structure and / or 1,3-hydroxy-1,3 contained in polyvinyl alcohol -Cyclic carbonate esterification of propylene structure.

  The esterification can be performed according to a known method such as a transesterification reaction. The esterification will be described by taking carbonic esterification as an example. Carbonation esterification can be carried out by transesterifying polyvinyl alcohol and dialkyl carbonate in a solvent in the presence or absence of an esterification catalyst. As the esterification catalyst, those commonly used in this field can be used. For example, an ion exchange containing an alkyl ammonium salt, a pyridinium salt, a diazabicycloalkene, a tertiary amine, an alkyl ammonium group, or a tertiary amino group. Examples thereof include resins and alkaline catalysts. An esterification catalyst can be used individually by 1 type, or can use 2 or more types together. The amount of esterification reaction catalyst used depends on the amount of polyvinyl alcohol used, the type and amount of dialkyl carbonate used, the type and amount of solvent used, the reaction temperature, the reaction pressure, the reaction time, the target value for the degree of carbonation esterification, etc. Although it can be suitably selected from a wide range, it is preferably 50% by weight or less, preferably 30% by weight or less of the total amount of polyvinyl alcohol. Examples of the dialkyl carbonate include dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, diisopropyl carbonate, di-n-butyl carbonate, diisobutyl carbonate, di-sec-butyl carbonate, di-tert-butyl carbonate, methyl carbonate / ethyl carbonate, methyl carbonate / n -Propyl, methyl isopropyl carbonate, methyl carbonate n-butyl, methyl carbonate isobutyl, methyl carbonate sec-butyl, methyl carbonate tert-butyl, ethyl carbonate n-propyl, ethyl carbonate isopropyl, ethyl carbonate n -Butyl, ethyl carbonate / isobutyl, ethyl carbonate / sec-butyl, ethyl tert-butyl carbonate, n-propyl / n-butyl carbonate, n-propyl / isobutyl carbonate, n-propyl / sec-butyl carbonate, n-carbonate Propyl tert-butyl, isopropyl carbonate n-buty , Carbonate isopropyl isobutyl, isopropyl sec-butyl carbonate and carbonate isopropyl tert-butyl. Although the usage-amount of dialkyl carbonate is not specifically limited, Preferably it is 0.1-20 times mole amount with respect to polyvinyl alcohol, More preferably, it is 0.1-10 times mole amount. As a solvent, each raw material can be dissolved or dispersed, and those inert to transesterification can be used. For example, aliphatic hydrocarbons such as n-hexane and n-octane, benzene, toluene, xylene and the like Aromatic hydrocarbons, ketones such as acetone, methyl ethyl ketone, and methyl propyl ketone, halogenated hydrocarbons such as dichloromethane and dichloroethane, ethers, dioxane, tetrahydrofuran, and the like. A solvent can be used individually by 1 type or can use 2 or more types together. The carbonic acid esterification reaction is preferably carried out at a lower temperature of the boiling point of the alcohol by-produced by this reaction to the boiling point of the reaction solvent or 200 ° C., more preferably 50 to 180 ° C., for 5 minutes to 50 minutes. It ends in time, preferably 10 minutes to 30 hours. This carbonic esterification reaction can be carried out under any pressure of reduced pressure, normal pressure or increased pressure. Other esterification reactions can be carried out in the same manner as in the conventional method, except that other corresponding raw material compounds are used instead of dialkyl carbonate.

  Acetalization and esterification of polyvinyl alcohol are carried out by subjecting polyvinyl alcohol to acetalization and esterification in the same manner as described above.

  Among the polyvinyl acetal resins thus obtained, a polyvinyl formal resin is preferable.

  The contact (reaction) between the polyvinyl acetal resin and the acid is performed, for example, in a non-aqueous solvent with stirring or without stirring. The amount of the polyvinyl acetal resin used is not particularly limited, but when considering the smooth progress of the reaction, preferably 0.5 to 20% by weight of the total amount of the reaction mixture consisting of the polyvinyl acetal resin, acid and non-aqueous solvent, Preferably it is 1 to 10% by weight. Moreover, a well-known thing can be used as an acid made to react with polyvinyl acetal resin, For example, an acetic acid, phosphoric acid, hydrochloric acid, a hydrofluoric acid, a sulfuric acid, trifluoroacetic acid, nitric acid etc. are mentioned. Of these, acetic acid, phosphoric acid, sulfuric acid, and hydrofluoric acid are desirable. An acid can be used individually by 1 type, or can use 2 or more types together. The amount of the acid used is not particularly limited, but is preferably 0.0005 to 1% by weight, more preferably 0.001 to 0.01% by weight, based on the total amount of the reaction mixture. As the non-aqueous solvent, the same solvents as those exemplified above can be used, and among them, carbonate esters, carboxylic acid esters and the like are preferable. A non-aqueous solvent can be used individually by 1 type, or can use 2 or more types together. By using a non-aqueous solvent as a reaction solvent, an acid-modified product of the polyvinyl acetal resin peculiar to the present invention is produced, and after completion of the reaction, an electrolyte is added to the reaction mixture. An electrolytic solution can be prepared. The reaction between the polyvinyl acetal resin and the acid is preferably performed at a temperature of room temperature to 100 ° C., more preferably 40 to 70 ° C., and preferably 1 to 100 hours, more preferably 5 to 48 hours.

  After completion of the reaction, as described above, the reaction mixture containing the acid-modified product of the polyvinyl acetal resin can be used as it is as a raw material for the nonaqueous electrolytic solution of the present invention. In addition, the acid-modified product can be used after being separated from the reaction mixture according to a general purification means.

  Among the acid-modified products of the polyvinyl acetal resin thus obtained, an acid-modified product of a polyvinyl formal resin is preferable.

  Since the hydroxyl group in the acid-modified product is assumed to be involved in crosslinking of the acid-modified product as described above, when the hydroxyl group content is in the range of 0.1 to 2 mol, The solubility in the electrolytic solution or uniform swellability, adhesion between the negative electrode and / or the positive electrode and the separator due to crosslinking of the acid-modified product are particularly good. Moreover, when the ratio of the hydroxyl groups of 1,2-dihydroxyethylene and / or 1,3-dihydroxy-1,3-propylene structure is increased, the crosslinkability of the polyvinyl acetal resin is improved, and the negative electrode and / or the positive electrode This is desirable because it is estimated that adhesion between the separator and the separator is improved. In addition, the content of the 1,2-dihydroxyethylene structure and the 1,3-dihydroxy-1,3-propylene structure in the acid-modified main chain is determined by appropriately selecting the reaction time in the reaction between the polyvinyl acetal resin and the acid. Can be adjusted.

  In addition, the molecular weight of the acid-modified product of the polyvinyl acetal resin is not particularly limited, but the liquid injection property (injectability) of the non-aqueous electrolyte to the electrochemical device is made as good as possible, and the laminate composed of the negative electrode, separator and positive electrode In consideration of increasing the adhesive strength as much as possible, it is preferably 10,000 to 300,000, more preferably 40,000 to 150,000, and particularly preferably 40,000 to 80,000. Here, the molecular weight means the number average molecular weight in terms of polystyrene as measured by GPC (gel permeation chromatography).

In order to determine whether or not the polyvinyl acetal resin has been subjected to acid modification, the present inventor measured ¹ H-NMR spectrum of the polyvinyl acetal resin before and after the acid modification to determine the DMSO-d ₆ peak (2. 49 ppm) as a reference, it is assumed that the determination can be made by measuring protons appearing in the region of 4 to 5 ppm. It is considered that a peak derived from the hydroxyl group of the polyvinyl acetal resin appears in this region, and a peak in which the strength decreases due to acid modification is observed. This intensity decrease peak is presumed to be a peak peculiar to an isolated hydroxyl group sandwiched between acetal rings and carboxyl groups. It is considered that the amount of the isolated hydroxyl group is reduced by acid modification.

  On the other hand, a polyvinyl acetal resin contains a hydroxyl group in the 1,2-dihydroxyethylene and / or 1,3-dihydroxy-1,3-propylene structure of the main chain together with the isolated hydroxyl group. Therefore, when the number of isolated hydroxyl groups is reduced, the ratio of hydroxyl groups in the 1,2-dihydroxyethylene and / or 1,3-dihydroxy-1,3-propylene structure to the total amount of hydroxyl groups in the polyvinyl acetal resin is increased. It will increase relatively. According to the study of the present inventor, the ratio of the hydroxyl group in the 1,2-dihydroxyethylene and / or 1,3-dihydroxy-1,3-propylene structure to the total hydroxyl group amount is 70 mol% due to acid modification. As mentioned above, it is estimated that it is more preferably increased to 80 mol% or more.

Based on this, among those obtained by contacting the polyvinyl acetal resin and acid, in the region of 4 to 5 ppm, based on the DMSO-d ₆ peak (2.49 ppm) in the ¹ H-NMR spectrum, Those having a specific peak with reduced intensity are preferred.

  Taking polyvinyl formal as an example, the peak at 4.25-4.35 ppm is reduced or eliminated by acid modification. Polyvinyl formal not in contact with acid usually has a proton corresponding to a peak of 4.25-4.35 ppm of 0.3 mol / kg or more, but those subjected to acid modification are reduced by 30% or more, preferably 50% or more. Or reduced to 0.25 mol / kg or less. Therefore, the amount of protons corresponding to the peak of 4.25-4.35 ppm in the acid-modified product of polyvinyl formal is preferably 0.25 mol / kg or less, more preferably 0.15 mol / kg or less.

  It is presumed that it is possible to determine whether or not an acid treatment has been performed by conducting the same measurement for polyvinyl acetal resins other than polyvinyl formal and examining the change in peak intensity.

[Non-aqueous electrolyte]
The nonaqueous electrolytic solution of the present invention comprises an electrolyte, a nonaqueous solvent, and an acid-modified product of the polyvinyl acetal resin obtained above, a number average molecular weight λ in terms of polystyrene by gel permeation chromatography measurement of the acid-modified product, The concentration c (% by weight) of the acid-modified product in the non-aqueous electrolyte solution satisfies the formula 100 ≦ λ ^1/2 × c ≦ 1000.

  The content of the acid-modified polyvinyl acetal resin in the non-aqueous electrolyte solution is not particularly limited, but it prevents the ionic conductivity, load characteristics, high temperature storage stability, etc. of the electrochemical element from being reduced as much as possible, and the negative electrode, separator and positive electrode From the viewpoint of increasing the mechanical strength of the laminated body as much as possible, it is preferably 0.3 to 3.5% by weight, more preferably 0.7 to 2.3% by weight of the total amount of the non-aqueous electrolyte.

Furthermore, in the present invention, from the viewpoint of further enhancing the injectability of the non-aqueous electrolyte into the electrochemical element, the adhesive strength of the laminate composed of the negative electrode, the separator and the positive electrode, the square root of the number average molecular weight λ of the acid-modified product (λ ^{1 / 2} ) and the concentration c (% by weight) of the acid-modified product in the non-aqueous electrolyte (λ ^1/2 × c) is 200 to 800 (200 ≦ λ ^1/2 × c ≦ 800). It is particularly desirable to be in range.

Here, the number average molecular weight of the acid-modified product means the number-average molecular weight in terms of polystyrene by gel permeation chromatography (GPC) measurement of the acid-modified product. The conditions of gel permeation chromatography are as follows. Using a differential refractive index detector as the detector, as a separation column
Shoudex KF-8 05L (trade name) × 2 and Shoudex KF-800P (trade name) are used as a precolumn, and tetrahydrofuran is used as a carrier solvent. A sample of polystyrene having a molecular weight standard and 20 mg of a sample polyvinyl acetal resin is dissolved in 20 ml of tetrahydrofuran to prepare a sample. A chromatogram is obtained by injecting 100 ul of sample at 30 ° C. with a carrier solvent flow rate of 1 ml / min.

[Nonaqueous solvent]
As the non-aqueous solvent, organic solvents commonly used in this field can be used, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, trifluoromethylethylene carbonate, and cyclic carboxylic acid esters such as γ-butyrolactone. Dimethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl trifluoroethyl carbonate, ditrifluoroethyl carbonate, diethyl carbonate, dibutyl carbonate, methyl octyl carbonate and other chain carbonates, methyl acetate, methyl propionate, pentafluoropropyl Chain carboxylic esters such as acetate and methyl trifluoroacetate, dimethoxyethane, tetrahydrofuran Ethers such as N-methylpyrrolidone, amides such as dimethylformamide, carbamates such as methyl-N, N-dimethylcarbamate, N-methyloxazolidinone, ureas such as N, N-dimethylimidazolidinone, boric acid Borate esters such as triethyl and tributyl borate, phosphate esters such as trimethyl phosphate and trioctyl phosphate, aromatic hydrocarbons such as benzene, toluene, xylene, fluorobenzene, fluorotoluene, chlorobenzene, biphenyl, and fluorobiphenyl And fluorinated ethers such as trifluoroethyl methyl ether. A non-aqueous solvent can be used individually by 1 type, or can use 2 or more types together.

〔Electrolytes〕
The electrolyte can be appropriately selected from those commonly used in this field according to the type of electrochemical element.

[Compound that generates acid]
The nonaqueous electrolytic solution of the present invention can further contain a compound that generates an acid in order to facilitate crosslinking by charging.

  The compound that generates an acid is mainly composed of an aldehyde group formed by electrolytic oxidation of the hydroxyl group of the acid-modified main chain by energization in the charging step, and a 1,2-dihydroxyethylene structure or 1, 1, This is preferable because it exhibits an action of catalyzing a reaction with a hydroxyl group which is free from electrolytic oxidation in a 3-dihydroxy-1,3-propylene structure. Moreover, the acid modification | denaturation of polyvinyl acetal resin can also be performed. Therefore, a non-acid-modified polyvinyl acetal resin and a compound that generates an acid are added to the non-aqueous electrolyte, and acid is generated in the non-aqueous electrolyte by adding water or charging. The polyvinyl acetal resin can be acid-modified by generating an acid in the step and the aging step. However, from the viewpoint of increasing the adhesive strength of the laminate comprising the negative electrode, the separator, and the positive electrode, it is preferable that the polyvinyl acetal resin is previously acid-modified and added to the non-aqueous electrolyte.

  As a compound which produces | generates an acid, the compound which produces | generates an acid by reaction with water, the compound electrolytically oxidized in the operating voltage range of an electrochemical element, etc. are mentioned, for example.

A compound that generates an acid by reaction with water reacts with moisture remaining in the separator or electrode of the electrochemical device to generate an acid. The generation of acid can be accelerated by heating in the aging process. In addition, with the present technique, the water | moisture content in an electrochemical element cannot be removed completely. As such a compound, a known compound that generates an acid by reaction with water can be used, and examples thereof include a Lewis acid having a halogen atom, a Lewis acid salt, a sulfate ester, and a nitrate ester. Examples of the Lewis acid having a halogen atom include PF _n R _(5-n) (n = 1 to 5, R = organic group), BF _n R _(3-n) (n = 1 to 3, R = organic). Group), AsF _n R _(5-n) (n = 1 to 5, R = organic group), SiF _n R _(4-n) (n = 1 to 4, R = organic group), AlF _n R _{(3 -N)} (n = 1 to 3, R = organic group), TiF _n R _(4-n) (n = 1 to 4, R = organic group), PCl _n R _(5-n) (n = 1 to 5, R = organic group), BCl _n R _(3-n) (n = 1-3, R = organic group), AsCl _n R _(5-n) (n = 1-5, R = organic group), SiCl _n R _(4-n) (n = 1 to 4, R = organic group), AlCl _n R _(3-n) (n = 1 to 3, R = organic group), TiCl _n R _(4-n) (N = 1-4, R = organic group) It is. Examples of the Lewis acid salt having a halogen atom include LiPF ₆ , LiBF ₄ , LiAsF ₆ , Li ₂ SiF ₆ , LiClO ₄ , LiPF _n (C _k F _{(2k + 1)} ) _(6-n) (n = 1 to 5 , K = 1 to 8), LiBF _n (C _k F _{(2k + 1)} ) _(4-n) (n = 1 to 3, k = 1 to 8), R ₄ NPF ₆ (R = organic group) ), R ₄ NBF ₄ (R = organic group), R ₄ NAsF ₆ (R = organic group), R ₄ N ₂ SiF ₆ (R = organic group), R ₄ NPF _n (C _k F _{(2k + 1)} ) _{( 6-n)} (n = 1-5, k = 1-8, R = organic group), R ₄ NBF _n (C _k F _{(2k + 1)} ) _(4-n) (n = 1-3, k = Integer of 1 to 8, R = organic group). Examples of the halogen atom include fluorine, chlorine, bromine, and the like, but considering the influence on the corrosion resistance of the electrochemical device, the fluorine atom is desirable. Examples of the sulfate ester include 1,3-propane sultone, methyl benzenesulfonate, 1,3-prop-2-ene sultone, 1,4-butane sultone, dimethyl sulfate, diethyl sulfate, and ethylene sulfate. Examples of the nitrate ester include ethyl nitrate. Among these, a Lewis acid and a Lewis acid salt having a halogen atom are preferable. In consideration of handleability and availability, LiPF ₆ , LiBF ₄ , R ₄ NPF ₆ (R = organic group), R ₄ NBF ₄ (R = Organic group), SiF _n R _(4-n) (n = 1 to 4, R = organic group) and the like are more preferable. In addition, LiPF ₆ , LiBF ₄ , R ₄ NPF ₆ (R = organic group), R ₄ NBF ₄ (R = organic group) and the like are particularly preferable because they also function as an electrolyte salt of an electrochemical element. When the crosslinkable polymer material is a polyvinyl acetal resin, SiF _n R _(4-n) (n = 1 to 4, R = organic group) is preferable. The compound which generates an acid by reaction with water can be used alone or in combination of two or more. The content of the compound that generates an acid by reaction with water in the non-aqueous electrolyte is appropriately selected from a wide range according to the type of the electrochemical element. Taking the case where the electrochemical element is a lithium battery as an example, there is a concern about the deterioration of battery characteristics due to the compound. Therefore, the content of the compound in the nonaqueous electrolytic solution is 0.2 mol / liter or less, preferably 0. .05 mol / liter or less. However, when the electrochemical element is a lithium battery, and the compound is a Lewis acid or Lewis acid salt having a fluorine atom and is a lithium salt, an adverse effect on properties is less likely to occur, so 0.2 mol / liter is used. You may make it contain exceeding.

  The compound that is electrolytically oxidized in the operating voltage range of the electrochemical element can be oxidized and oxidized in the initial charging process of the electrochemical element to contribute to the crosslinking of the acid-modified product of the polyvinyl acetal resin. Examples of such compounds include protic compounds such as water, methanol, ethanol, propanol, ethylene glycol, diethylene glycol, polyethylene glycol, propylene glycol, toluene, diphenylmethane, cyclohexylbenzene, acetone, malonic acid esters, and polyvinyl alcohol. Is mentioned. The compounds that are electrolytically oxidized within the operating voltage range of the electrochemical device can be used alone or in combination of two or more. The voltage applied at the time of initial charging may be appropriately selected from the operating voltage range of the electrochemical element so that the voltage at which the compound is electrolytically oxidized. For example, when the compound to be electrolytically oxidized is an alcohol, the voltage is 3 V or more, and in the case of an aromatic compound, the voltage is 4 V or more with respect to the lithium precipitation potential. The content of the compound to be electrolytically oxidized in the non-aqueous electrolyte varies from a wide range depending on the type of electrochemical element, the type of crosslinkable polymer material present in the laminate comprising the negative electrode, separator and positive electrode. Although it can select suitably, it is 0.002-0.1 mol / liter normally, Preferably it is 0.005-0.05 mol / liter.

  Moreover, the compound which produces | generates an acid by reaction with water, and the compound electrolytically oxidized in the operating voltage range of an electrochemical element can also be used together.

  Among these, compounds that generate an acid by reaction with water are preferable, and Lewis acids and Lewis acid salts having a halogen atom are particularly preferable.

  Among such non-aqueous electrolytes of the present invention, those obtained by adding an electrolyte, an acid-modified product of polyvinyl acetal resin and a compound that generates an acid to a non-aqueous solvent are preferable, and the electrolyte and the acid of the polyvinyl acetal resin are added to the non-aqueous solvent. What added the compound which produces | generates an acid by reaction with a modified material and water is further more preferable.

  The nonaqueous electrolytic solution of the present invention can be prepared by adding an electrolyte to a nonaqueous solvent and dissolving it, and further adding an acid-modified product of a polyvinyl acetal resin to dissolve or swell in accordance with a normal method. Further, a solution in which an electrolyte is dissolved in a non-aqueous solvent and a solution in which an acid-modified product of polyvinyl acetal resin is dissolved or swollen in a non-aqueous solvent may be mixed.

  In addition, the non-aqueous electrolyte of the present invention is prepared in advance by preparing an ordinary non-aqueous electrolyte by dissolving an electrolyte in a non-aqueous solvent, while laminating a negative electrode, a separator, and a positive electrode. Also, by manufacturing a laminate in which an acid-modified product of polyvinyl acetal resin is present between the negative electrode and / or the positive electrode and the separator, and injecting the general non-aqueous electrolyte into the laminate Can be prepared. That is, the non-aqueous electrolyte injected into the laminate contacts the acid-modified product of the polyvinyl acetal resin, and the modified product dissolves or swells in the non-aqueous electrolyte. A water electrolyte is obtained. When such a preparation method is adopted, after injecting a general nonaqueous electrolytic solution into the laminate, it is preferable to leave it for a while in order to sufficiently dissolve or swell the crosslinkable polymer material. The leaving conditions are not particularly limited, but considering that metal components are eluted from metal cans, current collectors, etc., for example, half a day to two days at room temperature, several hours to one day at 45 ° C., and at 60 ° C. 1 to several hours.

  In the thus obtained nonaqueous electrolytic solution of the present invention, the electrode and the separator are bonded to each other by a cross-linked product of an acid-modified product of polyvinyl acetal resin. As described above, the content of the cross-linked product is a very small amount of 3.5% by weight or less. Moreover, since the cross-linked product is insolubilized in the non-aqueous electrolyte, even if the non-aqueous electrolyte is gelled, the ionic conductivity is hardly lowered. If such a structure is taken, since the amount of the cross-linked product is very small, ions between the positive electrode and the negative electrode are not inhibited by the cross-linked product and can freely move in the non-aqueous electrolyte. Therefore, the cross-linked product does not need to exhibit ionic conductivity, and it is only necessary to bond the electrode and the separator. That is, the cross-linked product does not need to contain a large amount of non-aqueous electrolyte unlike conventional gel-type polymer electrolytes, so that the adhesion strength between the electrode and the separator is hardly reduced. Can be increased.

  The non-aqueous electrolyte for an electrochemical device of the present invention containing the acid-modified product of the polyvinyl acetal resin of the present invention thus obtained is, for example, an electrochemical device including at least a negative electrode, a separator, a positive electrode, and a non-aqueous electrolyte, The negative electrode and / or the positive electrode and the separator can be suitably used for an electrochemical device characterized by being bonded with a cross-linked product of an acid-modified product of polyvinyl acetal resin.

  Among such electrochemical elements, those in which an adhesive layer is formed between the negative electrode and the separator and between the positive electrode and the separator are preferable.

  The adhesive layer may be formed so as to cover the whole surface of the negative electrode and the separator or the positive electrode and the separator, or may be formed in an arbitrary pattern in part.

  In the electrochemical element, the cross-linked product of the acid-modified product of the polyvinyl acetal resin is preferably 3.5% by weight or less, more preferably 0%, based on the total amount of the nonaqueous solvent, the electrolyte, and the cross-linked product. It is contained in a proportion of from 3 to 3.5% by weight, particularly preferably from 0.7 to 2.5% by weight. This range is particularly effective in preventing the characteristics as an electrochemical element from being lowered and preventing the adhesive strength of the laminate composed of the negative electrode, the separator and the positive electrode from being lowered.

  The negative electrode used in such an electrochemical device includes a negative electrode active material and a negative electrode current collector. The negative electrode active material can be appropriately selected from those conventionally used in this field depending on the type of electrochemical element. A negative electrode active material can be used individually by 1 type, or can use 2 or more types together as needed. Examples of the negative electrode current collector include copper, nickel, stainless steel, aluminum, and titanium.

  The negative electrode is formed, for example, by molding a composition containing a negative electrode active material and a binder into a desired shape, and bonding the molded product to the negative electrode current collector, and increasing the packing density of the negative electrode active material as necessary. A method of performing pressure pressing of the above, a solvent is further added to the composition containing the negative electrode active material and the binder to form a negative electrode mixture slurry, and this negative electrode mixture slurry is applied to one side of the negative electrode current collector and dried. , A method of performing pressure pressing to increase the packing density of the negative electrode active material as necessary, a method of forming the negative electrode active material coated with the negative electrode active material or the binder into a desired shape by roll molding, compression molding or the like It can be created according to the above. In these methods, binders commonly used in this field can be used, for example, fluorine resins such as polyvinylidene fluoride and polytetrafluoroethylene, celluloses such as carboxymethylcellulose and cellulose, styrene-butadiene rubber, and the like. And latexes such as isoprene rubber, butadiene rubber, ethylene / propylene rubber, and natural rubber. As the solvent, those commonly used in this field can be used, and examples thereof include water, N-methylpyrrolidone, dimethylacetamide, dimethylformamide, propylene carbonate, γ-butyrolactone, and N-methyloxazolidinone. A solvent can be used individually by 1 type, or can use 2 or more types together as needed.

  In addition, as described in detail in the method for manufacturing an electrochemical element described later, the negative electrode includes a coating layer containing a polyvinyl acetal resin on the surface of the negative electrode active material layer after increasing the active material packing density of the negative electrode active material layer. Those provided are preferred. By using such a negative electrode, side reactions occurring on the surface of the negative electrode are suppressed, and the capacity of the resulting electrochemical element as an electrochemical element can be increased.

  The positive electrode includes a positive electrode active material and a positive electrode current collector. The positive electrode active material can be appropriately selected from those commonly used in this field depending on the type of electrochemical element. A positive electrode active material can be used individually by 1 type, or can use 2 or more types together as needed. As the positive electrode current collector, for example, a passive film is formed on the surface by anodic oxidation in a non-aqueous electrolyte such as Al, Ti, Zr, Hf, Nb, Ta, or an alloy containing two or more of these. A metal etc. are mentioned. The positive electrode may contain a conductive additive. As the conductive assistant, known ones can be used, and examples thereof include carbon black, amorphous whisker, and graphite. The positive electrode can be produced in the same manner as in the above-described method for producing a negative electrode, except that a positive electrode active material is used instead of the negative electrode active material, and a positive electrode current collector is used instead of the negative electrode current collector.

  The separator is a film that electrically insulates the positive electrode and the negative electrode and transmits ions. For example, a porous film can be suitably used as the separator. Examples of the porous film include a microporous polymer film and a nonwoven fabric made of a polymer material such as polyolefin, polyimide, polyvinylidene fluoride, and polyester. Among these, a porous polyolefin film is preferable, and a porous polyethylene film, a porous polypropylene film, a multilayer film of a porous polyethylene film and a porous polypropylene film, and the like are particularly preferable. Furthermore, the surface of the microporous polymer film may be coated with another resin having excellent thermal stability.

[Method for producing electrochemical element]
When an electrochemical element is produced using the nonaqueous electrolytic solution of the present invention, a negative electrode, a separator, and a positive electrode are laminated, and the laminated body includes a polyvinyl acetal resin component together with an electrolyte and a nonaqueous solvent. It can be produced by charging an electrochemical element impregnated with a liquid and bonding the negative electrode and / or positive electrode to a separator with a cross-linked product of an acid-modified product of polyvinyl acetal resin generated by charging.

  The greatest feature of the method for producing an electrochemical device using the nonaqueous electrolytic solution of the present invention is that the acid-modified product of the polyvinyl acetal resin is modified with a charging operation as a trigger, and the negative electrode and / or the positive electrode The separator can be bonded.

  That is, for example, the electrochemical element is formed by laminating a negative electrode, a separator and a positive electrode, impregnating the obtained laminate with the non-aqueous electrolyte of the present invention, and a polyvinyl acetal resin contained in the non-aqueous electrolyte by energization in a charging process. Can be produced by electrolytically oxidizing and crosslinking, depositing and adhering to the interface between the negative electrode and the separator and / or the positive electrode and the separator.

  The electrochemical element is formed of a negative electrode, separator, and positive electrode laminate in an arbitrary shape as necessary, and then accommodated in an electrochemical element casing of an appropriate shape, and a non-aqueous electrolyte is placed in the laminate. The casing is sealed by pouring, and a voltage is applied to the casing to perform initial charging. Further, the casing can be manufactured by a general method for manufacturing an electrochemical element that is subjected to an aging process, and contains a polyvinyl acetal resin component. Polyvinyl acetate which is a crosslinkable polymer material in the electrolytic solution using a nonaqueous electrolytic solution containing an acid-modified product of a polyvinyl acetal resin or a nonaqueous electrolytic solution containing a compound that generates an acid with the polyvinyl acetal resin as the aqueous electrolytic solution. It can be produced by crosslinking an acid-modified product of an acetal resin by energization in the initial charging step.

1) Step of Injecting Nonaqueous Electrolyte Solution into Laminate Consisting of Negative Electrode, Separator and Positive Electrode In the present invention, first, the negative electrode, separator and positive electrode are laminated. This laminated body is formed into an arbitrary shape such as a cylindrical shape, a coin shape, a square shape, or a film shape as necessary, and is applied to a casing for an electrochemical element such as a bag made of a metal can or a metal laminate film. Stored. The non-aqueous electrolyte of the present invention is injected into the laminate. For injection, a general nonaqueous electrolyte injection method can be employed.

  In addition, an acid-modified product of polyvinyl acetal resin is present in the laminate, for example, between the negative electrode and the separator, between the positive electrode and the separator, in the separator, and the like. A non-aqueous electrolytic solution containing the above components (that is, a solvent in which an electrolyte and, if necessary, a compound capable of generating an acid are added) may be injected. The crosslinkable polymer material can be used in the form of beads, powder, pellets and the like. Sheets and films containing a crosslinkable polymer material can also be used. Sheets, films, and the like are suitable for lamination between a negative electrode or a positive electrode and a separator. In this way, an electrochemical element can be manufactured more easily. That is, since it is not necessary to dissolve the crosslinkable polymer material in the non-aqueous electrolyte, the viscosity of the non-aqueous electrolyte does not increase and the injection into the laminate is facilitated. Also in this case, it is preferable that the acid content of the non-aqueous electrolyte is in the above range. However, in this method, the solubility of the acid-modified product of the polyvinyl acetal resin in the non-aqueous electrolyte solution may be reduced, and the adhesiveness after crosslinking may not be sufficiently exhibited. In order to dissolve in the liquid, it is necessary to leave it for a certain period of time, and there are the same disadvantages as described above, such that the productivity of the electrochemical device is reduced. Therefore, it is desirable to dissolve or swell the acid-modified product of the polyvinyl acetal resin in advance in a non-aqueous solvent.

  Further, a coating layer containing an acid-modified product of polyvinyl acetal resin is formed on one or more selected from the surface of the negative electrode active material layer of the negative electrode, both or one side of the separator, and the surface of the positive electrode active material layer of the positive electrode. Also good. This also makes it possible to further simplify the production of the electrochemical element. The coating layer is prepared by, for example, dissolving or dispersing an acid-modified product of polyvinyl acetal resin in an organic solvent, applying this solution or slurry to the surface on which the coating layer is to be formed, and heating the organic solvent by heating or the like. Can be formed by removing. As the organic solvent used here, a known organic solvent that does not corrode the negative electrode active material or the positive electrode active material and can uniformly dissolve or disperse the acid-modified product of the polyvinyl acetal resin can be used. Examples include carbonate, ethylene carbonate, N-methylpyrrolidinone, dimethylformamide, and γ-butyrolactone. Further, a method of spraying an acid-modified product of a polyvinyl acetal resin, a method of sputtering an acid-modified product of a polyvinyl acetal resin, a method of pressure-bonding an acid-modified product of a polyvinyl acetal resin, and the like are also included. Furthermore, an acid-modified product of polyvinyl acetal resin may be used as part or all of the binder for forming the active material layer, and an acid-modified product of polyvinyl acetal resin may be included in the negative electrode active material layer. .

  In the case where an acid-modified product of polyvinyl acetal resin is present in a laminate composed of a negative electrode, a separator and a positive electrode, the amount of acid-modified product of polyvinyl acetal resin used depends on the internal volume and porosity of the electrochemical element, non-aqueous electrolyte Depending on the amount of liquid and the like, it can be appropriately selected. If the amount of the acid modified product of the polyvinyl acetal resin is too small, the adhesive strength becomes weak, and if it is too large, the ion transfer in the non-aqueous electrolyte may be inhibited.

Among various forms in which an acid-modified product of polyvinyl acetal resin is present in a laminate composed of a negative electrode, a separator, and a positive electrode, a coating layer of an acid-modified product of polyvinyl acetal resin is formed on the surface of the negative electrode active material layer of the negative electrode In some cases, the electrochemical device can be advantageously manufactured, and other favorable effects can be exhibited. In other words, secondary electrolysis of the non-aqueous electrolyte that occurs on the surface of the negative electrode active material layer is suppressed. As a result, the charge / discharge efficiency during the first charge / discharge to the negative electrode is improved, and the capacity of the electrochemical device is increased. it can. The reason why such an excellent effect is obtained is not sufficiently clear, but diffusion of nonaqueous solvent molecules to the surface of the negative electrode active material layer is suppressed or formed on the surface of the negative electrode active material layer during initial charging. This is presumably due to the stabilization of the protective layer. This effect becomes more prominent by forming a coating layer containing an acid-modified product of polyvinyl acetal resin after increasing the packing density of the negative electrode active material layer. As a method for increasing the packing density, for example, a method of pressing and pressing the negative electrode, a method of selecting a negative electrode active material having a closest particle size distribution, a plating method or a CVD method to form a negative electrode active material layer, Examples thereof include a method of increasing the packing density by controlling the formation rate and supply rate of the negative electrode active material. For example, the porosity is used as an index of the packing density in the negative electrode active material layer. The lower the porosity, the higher the packing density. In the acid-modified product of the present invention or the nonaqueous electrolytic solution containing the same, the negative electrode active material layer has a porosity of 0.05 to 0.95, preferably 0.1 to 0.9, more preferably 0.1 to 0.9. What is necessary is just to raise a packing density so that it may be set to 0.5. In the case where priority is given to suppressing the electrolysis of non-aqueous electrolyte, the amount of the polyvinyl acetal resin is a negative electrode active material layer of the surface area of 1 m ² per 0.5-20, preferably 1~5mg It is.

  The porosity is a value obtained by (V1-V0) / V1, where V1 is the volume of the solid and V0 is the volume obtained by dividing the weight of the solid by the true density.

2) Step of cross-linking the acid-modified product of polyvinyl acetal resin by charging As described above, after injecting the non-aqueous electrolyte into the laminate composed of the negative electrode, the separator and the positive electrode, the electrochemical device is sealed, and the initial charging step In addition, it is subjected to an aging process for the purpose of stabilizing the characteristics of the electrochemical element, determining defects, and the like.

  In the initial charging step, the acid-modified product of the polyvinyl acetal resin is cross-linked by electrolytic oxidation by energization, and the negative electrode and the separator and / or the positive electrode and the separator are bonded by the cross-linked product. At this time, when the non-aqueous electrolyte of the present invention contains a compound that generates an acid, the crosslinking of the crosslinkable polymer material proceeds more smoothly. When the non-aqueous electrolyte contains a polyvinyl acetal resin and a compound that generates an acid, acid modification and crosslinking of the polyvinyl acetal resin occur, and the negative electrode and / or the positive electrode and the separator adhere to each other.

  In the state where the non-aqueous electrolyte is injected into the laminate, the polyvinyl acetal resin or the acid-modified product thereof is present in a dissolved or swollen state in the non-aqueous electrolyte, and the electrode and the separator are not bonded. By sealing the electrochemical element and receiving an electric current in the initial charging step, the acid-modified product of the polyvinyl acetal resin is cross-linked, and the electrode and the separator are bonded. In order to perform crosslinking of the acid-modified product, in the charging step, the positive electrode of the electrochemical device may be charged so that a potential of 3 V or more, preferably 3.8 V or more is applied to the lithium dissolution deposition battery. The amount of electricity in energization is not particularly limited, but may be appropriately selected so that an electrolytic oxidation reaction of 100 coulomb or more per kg occurs with respect to the acid-modified polyvinyl acetal resin.

Furthermore, when the non-aqueous electrolyte contains a compound that generates an acid, the electrochemical device may be heated in the initial charging step and the aging step. By heating the electrochemical element, generation of acid is promoted, and crosslinking of the acid-modified product of the polyvinyl acetal resin proceeds more smoothly. The heating at this time is performed within a range not deteriorating the electrochemical element. Specific heating conditions include, for example, 45 ° C. for 0.5 to 30 days (preferably 1 to 7 days), 60 ° C. for 1 hour to 7 days (preferably 5 hours to 3 days), and the like. .
In this way, an electrochemical element can be manufactured.

  The cross-linked product of acid-modified polyvinyl acetal resin is insolubilized in the non-aqueous solvent by cross-linking in the electrochemical element and exists in a state that can be separated from the non-aqueous solvent by simple separation means such as filtration or centrifugation. In some cases, it is insoluble in the non-aqueous solvent, but is dispersed almost uniformly in the non-aqueous solvent and the non-aqueous solvent is gelled. Of course, both cases may be mixed. In any case, whether or not the acid-modified product of the polyvinyl acetal resin is crosslinked in the electrochemical element can be secondarily confirmed from, for example, improvement in the adhesive strength of the laminate composed of the negative electrode, the separator and the positive electrode. .

  However, from the viewpoint of improving the adhesive strength of the laminate composed of the negative electrode, the separator, and the positive electrode, it is preferable that the cross-linked product is selectively present at the interface between the negative electrode and the separator and the interface between the positive electrode and the separator. When adopting such a structure, when the amount of the non-aqueous electrolyte including the cross-linked product is W1 (g) and the amount of the filtrate after separating and removing the cross-linked product by filtration is W2 (g), The percentage value obtained by dividing W2 by W1 (W2 / W1 × 100) is preferably 20% or more, more preferably 40% or more, and particularly preferably 60% or more. The upper limit of this percentage value is determined by the content of the acid-modified product of the polyvinyl acetal resin in the nonaqueous electrolytic solution.

  In order to make the cross-linked product of the acid-modified product of the polyvinyl acetal resin as much as possible at the interface between the negative electrode and the separator and the interface between the positive electrode and the separator, for example, immediately after charging the electrochemical element, A technique of heating at the highest possible temperature may be used as long as the characteristic is not deteriorated. By adopting such a method, since the acid-modified polyvinyl acetal resin is rapidly oxidized after electrolytic oxidation on the electrode surface, a large amount of cross-linked products are present at the interface between the electrode and the separator. The temperature at which the electrochemical element is heated for such a purpose is 40 ° C. to 90 ° C., preferably 50 ° C. to 60 ° C. The heating time may be determined in consideration of the influence on the battery characteristics.

  The reason why the acid-modified product of the polyvinyl acetal resin is cross-linked by energization is, for example, that the hydroxyl group of the acid-modified main chain is electrolytically oxidized by energization in the charging step to generate an aldehyde group or a ketone group. Aldehyde groups and / or ketone groups are renewed by reacting with hydroxyl groups in the main chain in the 1,2-dihydroxyethylene structure or 1,3-dihydroxy-1,3-propylene structure, which have escaped electrolytic oxidation. An acetal ring structure is formed and crosslinking occurs. Further, due to acid modification, the 1,2-dihydroxyethylene structure and / or 1,3-dihydroxy-1,3-propylene structure in the polyvinyl acetal resin main chain with respect to the total amount of hydroxyl groups contained in the polyvinyl acetal resin. It is presumed that the proportion of hydroxyl groups is increased.

[Lithium battery]
A lithium battery is mentioned as one form of the electrochemical element which can use the electrolyte solution of this invention. A lithium battery is a battery in which a non-aqueous electrolyte is injected into a laminate including a negative electrode, a positive electrode, and a separator, and the negative electrode and the separator and / or the positive electrode and the separator are bonded by a cross-linked product of an acid-modified polyvinyl acetal resin. The non-aqueous electrolyte is a non-aqueous electrolyte for a lithium battery containing a lithium salt as an electrolyte, and the negative electrode contains lithium metal or a negative electrode active material capable of occluding and / or releasing lithium.

  The negative electrode includes a negative electrode active material and a negative electrode current collector. As the negative electrode active material, lithium metal or a known compound capable of occluding and / or releasing lithium can be used. For example, lithium, lithium-containing alloy, silicon that can be alloyed with lithium, silicon alloy, tin, tin alloy, Examples thereof include tin oxide that can occlude and release lithium, silicon oxide, transition metal oxide that can occlude and release lithium, transition metal nitride that can occlude and release lithium, and a carbon material that can occlude and release lithium. Among these, carbon materials that can occlude and release lithium, alloy materials that can be alloyed with lithium, and the like are preferable. The carbon material includes crystalline carbon and amorphous carbon. Examples of crystalline carbon include carbon black, activated carbon, artificial graphite, natural graphite, graphitized mesocarbon microbeads (MCMB), graphitized mesophase pitch carbon fiber (MCF), and the like. Graphite-based crystalline carbon may contain boron. The shape of the crystalline carbon is not particularly limited, and examples thereof include a fibrous shape, a spherical shape, a potato shape, and a flake shape (scale shape). The graphite-based crystalline carbon is preferably scaly. Examples of the amorphous carbon include hard carbon, coke, MCMB, MCF, and the like fired at 1500 ° C. or less. Further, crystalline carbon, particularly graphite-based crystalline carbon coated with a crosslinkable polymer material, a metal such as gold, platinum, silver, copper, tin, amorphous carbon, or the like can also be used. Furthermore, a composite material of graphite-based crystalline carbon and Sn, Si, or an alloy material thereof can also be used. Among negative electrode active materials, when using materials with low mechanical strength or large volume changes due to charging and discharging, the effect of increasing the adhesive strength between the negative electrode and the separator and improving the shape retention of the battery is remarkable. Appears. From this viewpoint, the negative electrode active material is preferably a graphite material (particularly scaly graphite material), Sn, Si, an alloy material thereof, or a composite material thereof. A carbon material can be used individually by 1 type, or can use 2 or more types together. As the negative electrode current collector, those commonly used in this field can be used, and examples thereof include copper, nickel, and stainless steel.

  The negative electrode is, for example, uniformly mixed with a negative electrode active material and a binder such as polyvinylidene fluoride, carboxymethyl cellulose, latex, crosslinkable polymer material, and this mixture is applied on the negative electrode current collector and dried, preferably It can create by performing the press for raising the packing density of a negative electrode active material. Among the negative electrodes, as described above, it is preferable to provide a coating layer containing a polyvinyl acetal resin on the surface of the negative electrode active material layer after increasing the packing density of the negative electrode active material in the negative electrode active material layer.

The positive electrode includes a positive electrode active material and a positive electrode current collector. As the positive electrode active material, those commonly used in this field can be used. For example, transition metal oxides or transition metal sulfides such as FeS ₂ , MoS ₂ , TiS ₂ , MnO ₂ , V ₂ O ₅ , LiCoO ₂ , _{LiMnO 2, LiMn 2 O 4,} LiNiO 2, LiNi X Co (1-X) O 2, LiNi x Co y Mn (1-x-y) composite oxide comprising lithium such as _{O 2} and a transition metal, polyaniline , Conductive polymer materials such as polythiophene, polypyrrole, polyacetylene, polyacene, dimercaptothiadiazole / polyaniline complex, and carbon materials such as fluorinated carbon and activated carbon. Among these, an active material capable of generating an electromotive force of 3 V or more, preferably 3.8 V or more with respect to a lithium dissolution precipitation potential is preferable, and a composite oxide composed of lithium and a transition metal is particularly preferable. A positive electrode active material can be used individually by 1 type, or can use 2 or more types together. If the positive electrode active material exhibits an electromotive force of 3 V or more with respect to the dissolution and precipitation potential of lithium, the polyvinyl acetal resin is sufficiently subjected to electrolytic oxidation, and the crosslinking of the polyvinyl acetal resin is likely to proceed. As the positive electrode current collector, those commonly used in this field can be used. For example, non-aqueous electrolytes such as Al, Ti, Zr, Hf, Nb, Ta, and alloys containing one or more of these Examples thereof include metals capable of forming a passive film on the surface by anodic oxidation therein.

  For the positive electrode, for example, the positive electrode active material and a binder such as polyvinylidene fluoride, polytetrafluoroethylene, and a crosslinkable polymer material are uniformly mixed, and this mixture is applied to the positive electrode current collector and dried. Can be made by pressing to increase the packing density of the positive electrode active material. Along with the positive electrode active material, a conductive additive such as carbon black, amorphous whisker, or graphite can also be used.

  As a separator, the thing similar to the separator shown to the term of an electrochemical element can be used.

  The non-aqueous electrolyte for a lithium battery contains a lithium salt that is an electrolyte and a non-aqueous solvent for a lithium battery.

As the lithium salt, those commonly used as electrolytes for lithium batteries can be used. For example, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , Li ₂ SiF ₆ , LiOSO ₂ C _k F _{(2k + 1)} (k = 1 ₎ ˜8), LiPF _n (C _k F _{(2k + 1)} ) _(6-n) (n = 1 to 5, k = 1 to 8), LiC (SO ₂ R ⁵ ) (SO ₂ R ⁶ ) (SO ₂ R ⁷ ), LiN (SO ₂ OR ⁸ ) (SO ₂ OR ⁹ ), LiN (SO ₂ R ¹⁰ ) (SO ₂ R ¹¹ ) (R ^{7 to} R ¹³ may be the same or different and have 1 to 8 carbon atoms. A lithium salt such as a perfluoroalkyl group). Among these, LiPF ₆ , LiBF ₄ , LiN (SO ₂ R ¹⁰ ) (SO ₂ R ¹¹ ) (R ¹⁰ and R ¹¹ are the same as described above) and the like are preferable, and LiPF ₆ , LiBF _{4 and the} like are particularly preferable. A lithium salt can be used individually by 1 type, or can use 2 or more types together. The content of the lithium salt in the non-aqueous electrolyte is 0.1 to 3 mol / liter, preferably 0.5 to 2 mol / liter.

  As the non-aqueous solvent for lithium batteries, the above-mentioned non-aqueous solvents can be used, and in view of electrochemical stability (redox stability), chemical stability, aprotic organic solvents are preferable, and aprotic The esters are particularly preferred. Esters include cyclic esters and chain esters. Examples of the cyclic ester include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, and trifluoroethylene carbonate, and cyclic carboxylic acid esters such as γ-butyrolactone. Examples of the chain ester include chain carbonates such as dimethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, methyl trifluoroethyl carbonate, ditrifluoroethyl carbonate, diethyl carbonate, dibutyl carbonate, methyl octyl carbonate, methyl acetate, propionic acid Examples thereof include chain carboxylic acid esters such as methyl, pentafluoropropyl acetate and methyl trifluoroacetate. Esters can be used singly or in combination of two or more, but it is preferable to use a cyclic ester and a chain ester in consideration of improving the load characteristics, low temperature characteristics, etc. of the resulting battery. Furthermore, in view of the electrochemical stability of the nonaqueous electrolytic solution, it is preferable to use a cyclic carbonate as the cyclic ester and a chain carbonate as the chain ester. The mixing ratio of the cyclic ester and the chain ester (cyclic carbonate: chain carbonate) is 5:95 to 80:20, preferably 10:90 to 70:30, more preferably 15:85 to 55: by weight. 45. By setting such a ratio, it is possible to increase the degree of dissociation of the nonaqueous electrolyte while suppressing an increase in the viscosity of the nonaqueous electrolyte, thereby increasing the conductivity of the nonaqueous electrolyte related to the charge / discharge characteristics of the battery. And the solubility of the non-aqueous electrolyte can be maintained at a high level. As a result, since it can be set as the nonaqueous electrolyte excellent in electrical conductivity in normal temperature or low temperature, the charge / discharge load characteristic of the battery from normal temperature to low temperature can be improved. In consideration of adjusting the solvent composition to increase the flash point of the solvent and improving the safety of the battery, the cyclic ester is used alone or the mixed amount of the chain ester is 20% of the total amount of the non-aqueous solvent. % Or less is preferable. In this case, the cyclic ester is preferably ethylene carbonate, propylene carbonate, γ-butyrolactone, a mixture of two or more of these. As the chain ester, a chain carbonate is preferable.

  Moreover, you may use together cyclic carbonates which have a vinyl group with the above-mentioned ester. Thereby, the reductive decomposition reaction of the non-aqueous electrolyte on the negative electrode is further suppressed, and the high-temperature storage characteristics and cycle charge / discharge characteristics of the battery are further improved. Known cyclic carbonates having a vinyl group can be used, such as vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, propyl vinylene carbonate, phenyl vinylene carbonate, dimethyl vinylene carbonate, diethyl vinylene carbonate, dipropyl vinylene carbonate, Examples thereof include diphenyl vinylene carbonate, vinyl ethylene carbonate, 4,5-divinyl ethylene carbonate. Among these, vinyl ethylene carbonate, divinyl ethylene carbonate, vinylene carbonate and the like are preferable, and vinylene carbonate is particularly preferable. The cyclic carbonates having a vinyl group can be used alone or in combination of two or more. As a combination when using 2 or more types together, vinylene carbonate and vinyl ethylene carbonate, vinylene carbonate and divinyl ethylene carbonate, etc. are preferable. The content of the cyclic carbonate having a vinyl group is 0.1 to 10% by weight, preferably 0.5 to 5% by weight, based on the total amount of the electrolytic solution.

  The non-aqueous electrolyte for a lithium battery may contain solvents and additives other than those described above as long as the characteristics are not impaired. Specific examples thereof include ethers such as dimethoxyethane and tetrahydrofuran, amides such as N-methylpyrrolidone and dimethylformamide, carbamates such as methyl-N, N-dimethylcarbamate and N-methyloxazolidinone, N, N -Ureas such as dimethylimidazolidinone, boric acid esters such as triethyl borate and tributyl borate, phosphoric acid esters such as trimethyl phosphate and trioctyl phosphate, benzene, toluene, xylene, fluorobenzene, fluorotoluene, Examples thereof include aromatic hydrocarbons such as chlorobenzene, biphenyl, cyclohexylbenzene, and fluorobiphenyl, and fluorinated ethers such as trifluoroethyl methyl ether.

  Furthermore, as the non-aqueous electrolyte of the present invention, a halogen that is a compound that generates an acid by reacting with the above-described non-aqueous electrolyte for a lithium battery, an acid-modified polyvinyl acetal resin that is a crosslinkable polymer material, and water. What added the Lewis acid and / or Lewis acid salt which have an atom is preferable.

  As the non-aqueous solvent and the lithium salt, the same kind as the non-aqueous solvent and lithium salt for lithium battery used in the non-aqueous electrolyte for lithium battery can be used with the same content.

  As the acid-modified product of the polyvinyl acetal resin, those described above can be used, and among them, the acid-modified product of the polyvinyl formal resin is preferable. The content of the acid-modified product of the polyvinyl acetal resin in the nonaqueous electrolytic solution is 0.5 to 5% by weight, preferably 0.5 to 3% by weight, based on the total amount of the nonaqueous electrolytic solution. By setting the content in this range, it is possible to obtain a lithium battery having excellent shape retention properties while minimizing the influence on the charge / discharge load characteristics.

As the Lewis acid and Lewis acid salt having a halogen atom, those mentioned above can be used, and among them, the Lewis acid and Lewis acid salt having a fluorine atom are preferable. For example, LiPF ₆ and LiBF ₄ that also have a function as an electrolyte salt are preferable. In order to increase the crosslinking rate in the non-aqueous electrolyte, Lewis acids and Lewis acid salts having a high acid generation rate are preferred. Examples of such Lewis acids include PF _n R _(5-n) (n = 1 to 5, R represents an organic group), BF _n R _(3-n) (n = 1 to 3, R is Represents an organic group), AsF _n R _(5-n) (n = 1 to 5, R represents an organic group), SiF _n R _(4-n) (n = 1 to 4, R represents an organic group) ), AlF _n R _(3-n) (n = 1 to 3, R represents an organic group), TiF _n R _(4-n) (n = 1 to 4, R represents an organic group), and the like. It is done. Among these, considering the ease of handling, the availability of high-purity products, the stability to the electrolyte, the acid generation rate, etc., SiF _n R _(4-n) (n = 1 to 4, R is an organic group) Is more preferable. Specific examples of SiF _n R _(4-n) include trimethylsilyl fluoride, triphenylsilyl fluoride, dimethylsilyl difluoride, diphenylsilyl difluoride, methylsilyl trifluoride, phenylsilyl trifluoride, and the like. Trimethylsilyl fluoride is particularly preferred. When SiF _n R _(4-n) is used, SiF _n R _(4-n) is added directly to the non-aqueous electrolyte or changed in the non-aqueous electrolyte to change SiF _n R _{(4- What} is necessary is just to add the compound which produces | generates _n) . Examples of the compound that changes in the non-aqueous electrolyte to become SiF _n R _(4-n) include alkoxysilanes, carbonic acid silyl esters, carboxylic acid silyl esters, sulfuric acid silyl esters, phosphoric acid silyl esters, and boric acid silyl esters. And various silyl esters. Of these, silyl phosphate is preferred. The silyl phosphate ester not only generates SiF _n R _(4-n) but also has a property of gelling a liquid containing a polyvinyl acetal resin. In the portion of the non-aqueous electrolyte that protrudes from the electrode laminate in the battery, current does not occur, so crosslinking of the acid-modified product of the polyvinyl acetal resin is unlikely to occur, but when a phosphoric acid silyl ester is added to the non-aqueous electrolyte The non-aqueous electrolyte gels well and the effect of preventing liquid leakage is enhanced. In the presence of an acid, the action of generating SiF _n R _(4-n) and crosslinking the acid-modified product of the polyvinyl acetal resin is better than the action of gelling the acid-modified product of the polyvinyl acetal resin. Since it is expressed preferentially, there is no inconvenience as in the case of using a conventional gelled polymer electrolyte, and a desired battery can be obtained. A Lewis acid or Lewis acid salt containing a halogen atom can be used alone or in combination of two or more. The content of the Lewis acid having a halogen atom and the Lewis acid salt is 0.01 to 10% by weight, preferably 0.05 to 2% by weight, based on the total amount of the non-aqueous electrolyte.

  Such a lithium battery can have an arbitrary shape, and is formed in, for example, a cylindrical shape, a coin shape, a square shape, a film shape, or the like. However, the basic structure of the battery is the same regardless of the shape, and the design can be changed according to the purpose.

  For example, in a cylindrical lithium battery, a sheet-like negative electrode and a sheet-like positive electrode are wound through a separator, impregnated with a non-aqueous electrolyte, and insulating plates are placed above and below the wound body. It is configured to be stored in a battery can.

  In addition, the coin-type battery is configured to be stored in a coin-type battery can with a laminate of a disc-shaped negative electrode, a separator, and a disc-shaped positive electrode impregnated with an electrolyte, and with a spacer plate inserted as necessary. It has become.

  Furthermore, the lithium battery can be used for the same applications as conventional lithium batteries. For example, various consumer electronic devices, among others, mobile phones, mobiles, laptop personal computers, cameras, portable video recorders, portable CD players, portable MD players and the like can be mentioned.

  The present invention will be specifically described with reference to Examples, Reference Examples and Test Examples. In the following, “%” and “parts” indicate “% by weight” and “parts by weight” unless otherwise specified.

Example 1
Polyvinyl acetate was subjected to alkali saponification to obtain a polyvinyl alcohol resin (degree of saponification 89%) partially esterified.

  After mixing 25 g of this polyvinyl alcohol, 200 ml of 50% aqueous acetic acid solution and 40 ml of 10% hydrochloric acid, 100 ml of formalin (37% aqueous solution of formaldehyde) was added and reacted at 30 ° C. for 5 hours. After completion of the reaction, dilute acetic acid was added to the reaction solution to precipitate the reaction product, which was filtered, neutralized with sodium hydroxide, washed with water and dried to obtain polyvinyl formal. This solid was analyzed for composition by JIS K6729 “Testing method for polyvinyl formal”. As a result, polyvinyl formal resin consisting of 82.5% vinyl formal part, 11.6% vinyl acetate part and 5.9% vinyl alcohol part was obtained. It was confirmed that. The concentration of the hydroxyl group converted from the composition ratio of the vinyl alcohol part in the polyvinyl formal resin was 1.34 mol / kg.

  In the above, (A) is a vinyl formal part, (B) is a vinyl acetate part, and (C) is a vinyl alcohol part.

  This polyvinyl formal resin is dissolved in 100 ml of a 2: 1 volume ratio solution of ethylene carbonate and ethyl methyl carbonate at a concentration of 5%, 0.01% sulfuric acid is added, and heat treatment is performed at 45 ° C. for 144 hours (acid modification treatment). And a solution containing an acid-modified product of polyvinyl formal resin was obtained.

The polyvinyl formal resin before and after the acid modification treatment is subjected to NMR spectrometer (trade name: JNM-A500 (500 MHz), manufactured by JEOL Ltd.), and DMSO-d ₆ is used as a solvent and DMSO-d ₆ is shifted. When the standard (2.49 ppm) was used and tetrachloroethane was used as an internal standard and the concentration of protons appearing at 4.28 ppm was quantified, it was 0.3 mol per kg of resin before the acid modification treatment. Was reduced to 0.1 mole.

Example 2
An acid-modified product of a polyvinyl formal resin is obtained in the same manner as in Example 1 except that a polyvinyl formal resin having different content ratios of the vinyl formal part (A), the vinyl acetate part (B) and the vinyl alcohol part (C) is used. A solution containing was obtained. The obtained acid-modified product had the physical properties shown in Table 1. In addition, except for polyvinyl formal having a hydroxyl group content of 2.8 mol / kg, the proton concentration appearing at 4.28 ppm in all of the three acid-modified products thus obtained was reduced to 70% or less by acid treatment. It was done.

Example 3
A solution containing the acid-modified product of the polyvinyl acetal resin obtained in Examples 1 and 2 and a mixed solution of ethylene carbonate and ethyl methyl carbonate (weight ratio = 4: 6) were mixed, and LiPF ₆ (1 mol / liter) was mixed therewith. Was further dissolved so that the concentration of the acid-modified product of the polyvinyl acetal resin was the concentration (c) shown in Table 1 to obtain the nonaqueous electrolytic solution of the present invention.

  Among the non-aqueous electrolytes shown in Table 1, R4 did not dissolve the acid-modified product uniformly in the non-aqueous solvent, and a large amount of insoluble product remained. From this, it can be seen that when the content of hydroxy groups in the polyvinyl formal resin exceeds 2 mol / liter, it is not suitable as an additive to the non-aqueous electrolyte. In other non-aqueous electrolytes, acid-modified products were dissolved in non-aqueous solvents.

Example 4
Polyvinyl acetal resin (T3-1), polyvinyl propylal resin (T3-2), or polyvinyl butyral resin (T3-3) in place of the polyvinyl formal resin in the same composition as the nonaqueous electrolytic solution of T3 in Example 3. Was used to prepare acid-modified products, and a non-aqueous electrolyte was prepared using them. The solubility of each resin in a non-aqueous solvent and the stability when the non-aqueous electrolyte was stored at 25 ° C. were visually observed. The results are shown in Table 2.

  From Table 2, T3 can be uniformly dissolved in the electrolytic solution, and even when stored for 30 days or longer, it maintains a liquid state free from insolubles and precipitates, and is optimal for use in the nonaqueous electrolytic solution of the present invention. It turns out that it is. Although the resin of T3-1 to T3-3 can also be used for the non-aqueous electrolyte of the present invention, in some cases, it is necessary to remove the insoluble matter, and after preparing the non-aqueous electrolyte, without storing for a long time, It is clear that it is better to immediately inject into the electrochemical element.

Reference example 1
A coin-type lithium ion secondary battery was manufactured using 10 types of nonaqueous electrolyte solutions obtained in Example 3, and in Test Example 2 described below, the nonaqueous electrolyte solution of the present invention adheres a battery by charging. .

1) Production of negative electrode 74 parts of mesocarbon microbeads (trade name: MCMB10-28, manufactured by Osaka Gas Co., Ltd.), 20 parts of natural graphite (trade name: LF18A, manufactured by Chuetsu Graphite Co., Ltd.) and polyvinylidene fluoride (PVDF) , 6 parts of binder) was mixed and dispersed in 100 parts of N-methylpyrrolidinone to prepare a negative electrode mixture slurry. This negative electrode mixture slurry was applied to a negative electrode current collector made of a strip-shaped copper foil having a thickness of 18 μm and dried. This was compressed with a roll press to obtain a negative electrode.

2) Preparation of positive electrode LiCoO ₂ (trade name: HLC-22, manufactured by Honjo FMC Energy Systems Co., Ltd.) 82 parts, graphite (conductive agent) 7 parts, acetylene black (conductive agent) 3 parts, and polyvinylidene fluoride (PVDF, (Binder) 8 parts were mixed and dispersed in 80 parts of N-methylpyrrolidone to prepare a LiCoO ₂ mixture slurry. This LiCoO ₂ mixture slurry was applied to an aluminum foil (positive electrode current collector) having a thickness of 20 μm and dried. This was compressed by a roll press to obtain a positive electrode.

3) Production of coin-type battery For the negative electrode, the negative electrode obtained in 2) was punched into a circle having a diameter of 14 mm. The negative electrode had a negative electrode mixture thickness of 80 μm and a weight of 20 mg / 14 mmφ.

As the positive electrode, the positive electrode obtained in 3) above was punched into a circular shape having a diameter of 13.5 mm. This LiCoO ₂ electrode had a LiCoO ₂ mixture thickness of 70 μm and a weight of 42 mg / 13.5 mmφ.

  A negative electrode (diameter: 14 mm) is disposed on the negative electrode can surface of a 2032 size stainless steel battery can so that the negative electrode current collector is in contact with it, and a separator (thickness: 25 μm, diameter: 16 mm) made of a microporous polypropylene film; The positive electrode (diameter 13.5 mm) was laminated in order. Thereafter, 0.25 ml of the nonaqueous electrolyte solution of the present invention (T1 to T10) of Example 3 or the five types of nonaqueous electrolyte solutions (R1 to R5) of Comparative Example 1 was injected between the separator and the negative electrode and between the separator and the positive electrode. Then, an aluminum plate (thickness 1.2 mm, diameter 16 mm) and a spring were housed. Finally, by attaching a battery can lid through a polypropylene gasket, a coin-type lithium ion secondary battery having a diameter of 20 mm and a height of 3.2 mm was manufactured while maintaining the airtightness in the battery. The obtained coin-type lithium ion secondary battery is charged to 4.2 V at a current of 2 mA to crosslink the acid-modified product of the polyvinyl formal resin contained in the non-aqueous electrolyte, and the coin-type lithium ion secondary battery is Manufactured.

Reference example 2
Cylindrical secondary batteries were manufactured using the five types of non-aqueous electrolytes of the present invention (T1, T2, T3, T5, T6) obtained in Example 3, and in Test Example 3 to be described later, It shows that a non-aqueous electrolyte adheres a battery by charge.

Production of Negative Electrode 70 parts of mesocarbon microbeads (trade name: MCMB10-28, manufactured by Osaka Gas Co., Ltd.), 20 parts of natural graphite (trade name: LF18A, manufactured by Chuetsu Graphite Co., Ltd.) and polyfluoride as a binder A negative electrode mixture was prepared by mixing 10 parts of vinylidene and further dispersed in N-methyl-2-pyrrolidone to form a slurry. And this slurry was uniformly apply | coated to both surfaces of the 10-micrometer-thick strip | belt-shaped copper foil which is a negative electrode electrical power collector, and it was compression-molded with the roll press machine after drying, and produced the negative electrode.

2) Production of positive electrode 91 parts LiCoO ₂ (trade name: HLC-22, manufactured by Honjo FMC Energy Systems Co., Ltd.), 6 parts graphite as a conductive agent, and 3 parts polyvinylidene fluoride as a binder The mixture was mixed to prepare a positive electrode mixture, which was further dispersed in N-methyl-2-pyrrolidone to form a slurry. And this slurry was uniformly apply | coated on both surfaces of the 20-micrometer-thick aluminum foil which is a positive electrode electrical power collector, and after drying, it compression-molded with the roll press machine, and produced the positive electrode.

3) Production of Battery Next, a negative electrode and a positive electrode were sequentially laminated through a separator made of a microporous polypropylene film having a thickness of 20 μm, and a wound body was produced by winding a number of times in a spiral shape. An insulating plate was inserted into the bottom of the nickel-plated iron battery can, and the wound body was stored. And in order to take the collector of a negative electrode, one end of the negative electrode lead made from nickel was crimped | bonded to the negative electrode, and the other end was welded to the battery can. In addition, in order to collect the positive electrode, one end of an aluminum positive electrode lead was attached to the positive electrode, and the other end was electrically connected to the battery lid via a current blocking thin plate that cuts off the current according to the battery internal pressure. .

  Next, 5 kinds of the nonaqueous electrolytes of the present invention (T1, T2, T3, T5, T6) and 2 ml of the nonaqueous electrolytes (R1, R2) in Example 3 were added to each of the battery cans. The operation of reducing the pressure inside the battery can and returning it to normal pressure was repeated while injecting the electrolyte into the battery can. Finally, the battery lid was fixed by caulking the battery can through an insulating sealing gasket coated with asphalt to produce a cylindrical nonaqueous electrolyte battery having a diameter of 18 mm and a height of 65 mm.

  The obtained cylindrical lithium ion secondary battery is charged to 4.2 V at a current of 0.2 A to crosslink the acid-modified product of the polyvinyl formal resin contained in the non-aqueous electrolyte, and the cylindrical lithium ion secondary battery A battery was manufactured.

(Test Example 1)
Using the non-aqueous electrolyte T5 obtained in Example 3, coin-type lithium batteries that were produced in the same manner as in Reference Example 1 and were not subjected to only the charging treatment were 0.5 V, 3.8 V, and 4 at a current of 2 mA. The battery was charged at 0.0 V and allowed to stand at room temperature (25 ° C.) or 50 ° C. for 24 hours. This standing for 24 hours corresponds to an aging step in a general method for producing an electrochemical element.

  Next, the coin-type lithium secondary battery was disassembled, and the adhesion between the electrode and the separator was examined. The results are shown in Table 3.

  Similarly, the adhesion between the electrode and the separator was also examined for a coin-type lithium secondary battery that was left at room temperature (25 ° C.) or 50 ° C. for 24 hours without being charged. The results are shown in Table 3.

  From Table 3, by charging to 3.8 V or 4.0 V, the acid-modified product of the polyvinyl acetal resin contained in the non-aqueous electrolyte is cross-linked, and the electrode (negative electrode and positive electrode) and the separator are bonded. Is clear. Furthermore, it is clear that the adhesive strength is further increased when aging is performed at 50 ° C. after charging at around 3.8 to 4.0 V.

  On the other hand, it can be seen that, when charged or uncharged at about 0.5 V, the acid-modified product does not crosslink even when heated in the aging process, and the electrode and the separator do not adhere at all.

The difference in the instrumental analysis between the acid-modified product of the polyvinyl formal resin and the cross-linked product of the acid-modified product is presumed to be clear in the ¹³ C-solid state NMR spectra of the present invention. Specifically, it was performed as follows. Disassemble the battery, collect the gel-like material in the separator or at the interface between the separator and electrode, place the gel-like material in a commercially available Teflon (registered trademark) sealed cell, and insert the sealed cell into a 7.5 mm sample tube did. The sample tube was spun at 2000 Hz and ¹³ C-solid state NMR measurement was performed. The measuring device used was a CMX300 7.5 mm probe manufactured by Chemagnetics. The measurement conditions were a single pulse method with a resonance frequency of 75.5578 MHz, a pulse of 30 μs of 1.7 μs, and a bandwidth of 30 kHz.

In the ¹³ C-solid NMR spectrum of the cross-linked product measured by the above method, the signal around 70 ppm decreased compared with the ¹³ C-solid NMR spectrum of the acid-modified product, and the acid-modified product was converted to the acid-modified product at 90-110 ppm. No signal is observed. The signal around 70 ppm is presumed to be a signal of carbon bonded to a hydroxyl group, and the signal around 90 to 110 ppm is presumed to be a signal of carbon bound to two oxygens of the acetal ring. Therefore, the signal around 70 ppm decreases and the signal that is not found in the original acid-modified product is observed at around 90-110 ppm. This means that the hydroxyl group in the acid-modified product of polyvinyl formal resin is generated at the end of the polymer chain. It can be presumed to react with the aldehyde group thus formed to form a new acetal ring, indicating that the polymer chain has been crosslinked.

Test example 2
For the coin-type lithium ion secondary battery of Reference Example 1 and the cylindrical lithium ion secondary battery of Reference Example 2, the impedance at 10 kHz was measured, and the impedance change rate was examined according to the following formula.
Further, the electrolyte injection amount of the cylindrical lithium ion secondary battery of Reference Example 2 was examined.

As a comparative example, a comparative cylindrical or coin-type lithium ion secondary battery was carried out in the same manner as in Reference Examples 1 and 2 except that two types of comparative non-aqueous electrolytes (R1 to R2) shown in Table 1 were used. These were also evaluated and compared in the same manner as the secondary battery of the present invention.
The results are shown in Tables 4 and 5.

Impedance change rate = X / Y
X: Impedance of each battery,
Y: Impedance of the battery into which the nonaqueous electrolytic solution of Example 1 was injected

(Amount of electrolyte injected into cylindrical lithium ion secondary battery)
From Table 4, it can be seen that in the examples, there is almost no decrease in the pouring property of the nonaqueous electrolytic solution into the battery, whereas in the reference example, the property that the amount of the nonaqueous electrolytic solution injected is small is significantly lowered. In particular, in a cylindrical battery that is highly filled with an electrode active material or the like, a decrease in the liquid injection property of the non-aqueous electrolyte was remarkable.

Also, from Table 5, the impedance of the battery of the example was remarkably increased in the battery of the comparative example, while the impedance of 10 kHz was equivalent. The impedance of 10 kHz corresponds to the electrical resistance derived from the non-aqueous electrolyte in the battery. A large impedance means that the non-aqueous electrolyte is not sufficiently injected into the battery, or that there is a small amount in the active material or between active materials. It indicates that the electrolyte solution is not sufficiently penetrated into the pores. Therefore, when including the results of Test Example 2, the non-aqueous electrolyte having λ ^1/2 × c of 1000 or more has poor liquid-injectability of the non-aqueous electrolyte into the battery, and is particularly highly filled with an electrode active material and the like. In the cylindrical battery, the drop in liquid injection property was remarkable.

Test example 3
The coin-type lithium ion secondary battery obtained in Reference Example 1 was charged to 4.2 V and discharged to 3.0 V with a current of 0.5 mA. The discharge capacity at this time was defined as “initial discharge capacity”. The battery was charged to 4.0 V and left for 24 hours. The battery was evaluated for adhesiveness, initial charge / discharge characteristics, and battery characteristics after high-temperature storage.

  Further, as a comparative example, a coin type lithium ion secondary battery for comparison was manufactured in the same manner as in Reference Example 1 except that five types of nonaqueous electrolyte solutions (R1 to R5) of the comparative example of Table 1 were used. These were also evaluated and compared.

  The results are shown in Table 6. The comparative non-aqueous electrolyte R5 contains a large amount of insoluble matter derived from the polymer substance, but was used as it was except for the insoluble matter.

[Adhesion evaluation]
These batteries were disassembled, peeled off from the electrode and the separator, examined for adhesion, and evaluated according to the following criteria.
“Strong adhesion”: The active material layer of the electrode and the separator are firmly adhered to each other, and even when the peeling operation is performed, the electrode is peeled off from the interface between the current collector and the active material layer, and the separator sticks to the active material layer of the electrode It remained.
“Adhesion”: The active material layer of the electrode and the separator were sufficiently adhered, but when the peeling operation was performed, the electrode was peeled off from the interface between the active material layer and the separator.
“Weak adhesion”: The active material layer of the electrode and the separator were in close contact, but when the peeling operation was performed, the electrode was easily peeled from the interface between the active material layer and the separator.
“None”; not in close contact.

[Evaluation of initial charge / discharge characteristics]
These batteries were charged to 4.2 V and then discharged to 3.0 V at a current of 10 mA to obtain “discharge capacity at 10 mA”. Subsequently, the battery was charged to 4.2 V, and then discharged to 3.0 V at a current of 5 mA to obtain “discharge capacity at 5 mA”. The percentage of “discharge capacity at 10 mA” relative to “initial discharge capacity” is set as “high load index”, and the percentage of “discharge capacity at 5 mA” relative to “initial discharge capacity” is set as “medium load index” for comparison. did.

[Evaluation of battery characteristics after high temperature storage]
After charging these batteries to 4.2 V and storing them at 85 ° C. for 3 days, “high load index” and “medium load index” were obtained again.
The above results are summarized in the table below.

From the above, the batteries of Examples 2 to 11 lambda ^1/2 × c was used a non-aqueous electrolyte from 100 1000 of electrodes and the separator are adhered, and is also excellent battery characteristics.

On the other hand, in the batteries of Comparative Examples 2 to 4 using an electrolytic solution having λ ^1/2 × c larger than 1000, the electrode and the separator are bonded, but the battery characteristics are deteriorated. Further, Comparative Example 6 using an electrolyte solution having a hydroxyl group concentration of less than 0.1 mol / kg in an acid-modified product of polyvinyl formal resin, although λ ^1/2 × c is 100 to 1000, battery characteristics are Although it is excellent, the electrode and the separator do not adhere. λ ^1/2 × c is 100 to 1000, but Comparative Example 5 using an electrolytic solution having a hydroxyl group concentration of 2.0 mol / kg or more in the acid-modified product of the polyvinyl formal resin is an electrode and a separator. Although it adheres, the battery characteristics are degraded.

The following embodiments are possible for the present invention.
(1) A non-aqueous electrolytic solution containing an electrolyte and a non-aqueous solvent, wherein the non-aqueous electrolytic solution includes an acid-modified product of a polyvinyl acetal resin.

(2) The acid-modified product of the aforementioned polyvinyl acetal resin has a proton content that shows a peak at 4.25 to 4.35 ppm based on the peak (2.49 ppm) of DMSO-d ₆ in ¹ H-NMR measurement. A non-aqueous electrolyte characterized by being an acid-modified product of polyvinyl formal having a concentration of 0.25 mol / kg or less.

(3) The polystyrene-reduced number average molecular weight λ by gel permeation chromatography measurement of the above-mentioned acid-modified product and the concentration c (% by weight) in the non-aqueous electrolyte of the acid-modified product have the following relationship: A feature of non-aqueous electrolyte.
100 ≦ λ ^1/2 × c ≦ 1000

  (4) A non-aqueous electrolyte, wherein the acid-modified product has a hydroxyl group content of 0.1 to 2 mol / kg.

  (5) An electrochemical element including at least a negative electrode, a separator, a positive electrode, and a non-aqueous electrolyte, wherein the negative electrode and / or the positive electrode and the separator are bonded by a cross-linked product of an acid-modified product of polyvinyl acetal resin. Electrochemical element to do.

  In place of the nonaqueous electrolytic solution, an electrolyte containing a polyvinyl acetal resin and a compound that generates an acid is used together with an electrolyte and a nonaqueous solvent to generate an acid by heating in a charging step or an aging step. An acid is generated from the compound, and the acid and the polyvinyl acetal resin react with each other to cause acid modification of the polyvinyl acetal resin, and thus crosslinking, to obtain an electrochemical element. In this case, there is a compound that generates an acid in the electrolyte, but it is necessary to further include a compound that generates an acid in addition to the amount necessary for the electrolyte.

  As described above, the electrochemical element is excellent in electrical load characteristics, charge / discharge characteristics, shape retention and high-temperature storage, and exhibits high mechanical strength. Therefore, the electrochemical element can be easily reduced in thickness, can maintain sufficient electric load characteristics and charge / discharge characteristics even after long-term use, and there is no concern about liquid leakage or damage. It is not necessary to provide a special structure for preventing these.

  (6) The electrochemical element, wherein the ratio of the cross-linked product to the total amount of the cross-linked product and the non-aqueous electrolyte is 3.5% by weight or less.

  (7) The negative electrode includes an active material capable of occluding and / or releasing lithium metal and / or lithium, the positive electrode includes an active material capable of generating an electromotive force of 3 V or more with respect to a lithium dissolution precipitation potential, and non-aqueous An electrochemical element, wherein the electrolytic solution contains an electrolyte selected from lithium salts.

  (8) A negative electrode, a separator, and a positive electrode are laminated, and an electrochemical element formed by impregnating the laminated body with a non-aqueous electrolyte containing a polyvinyl acetal resin component together with an electrolyte and a non-aqueous solvent is charged to obtain a polyvinyl acetal resin. A method for producing an electrochemical element, comprising bonding a negative electrode and / or a positive electrode and a separator with a cross-linked product of the acid-modified product.

  (9) The method for producing an electrochemical element, wherein the polyvinyl acetal resin component is a) an acid-modified product of a polyvinyl acetal resin or b) a mixture of a polyvinyl acetal resin and a compound that generates an acid.

Claims (7)

Proton content showing a peak at 4.25 to 4.35 ppm based on DMSO-d ₆ peak (2.49 ppm) by ¹ H-NMR measurement is 0.25 mol / kg or less, and hydroxyl group content A non-aqueous electrolyte for an electrochemical device, comprising an acid-modified product of a polyvinyl acetal resin having a mol of 0.1 to 2 mol / kg. Proton content showing a peak at 4.25 to 4.35 ppm based on DMSO-d ₆ peak (2.49 ppm) by ¹ H-NMR measurement is 0.25 mol / kg or less, and hydroxyl group content An acid-modified product of polyvinyl acetal resin having a molecular weight of 0.1 to 2 mol / kg, a polystyrene-equivalent number average molecular weight λ by gel permeation chromatography measurement of the acid-modified product, and a non-aqueous electrolyte solution of the acid-modified product 2. The non-aqueous electrolyte for an electrochemical device according to claim 1, wherein the concentration c (weight%) of the electrochemical device includes a formula 100 ≦ λ ^1/2 × c ≦ 1000.   The non-aqueous electrolyte according to claim 2, wherein the polyvinyl acetal resin is obtained by acetalizing, esterifying, or acetalizing and esterifying polyvinyl alcohol.   The non-aqueous electrolyte according to claim 2 or 3, wherein the polyvinyl acetal resin is polyvinyl formal.   The nonaqueous electrolyte solution according to any one of claims 2 to 4, wherein the concentration of the acid-modified product is 0.3 to 3.5% by weight of the total amount of the nonaqueous electrolyte solution.   Furthermore, the compound which produces | generates an acid is contained, The nonaqueous electrolyte solution of any one of Claims 2-5 characterized by the above-mentioned.   7. The non-aqueous electrolyte according to claim 6, wherein the compound that generates an acid is a Lewis acid and / or a Lewis acid salt having a fluorine atom.