JP2018120761A - Additive agent for electrochemical device, method for manufacturing the same, and electrolyte solution for electrochemical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide: an additive agent for an electrochemical device, which enables the materialization of an electrochemical device having a high initial capacity and good cycle characteristics; a method for manufacturing the additive agent; and an electrolyte solution for an electrochemical device.SOLUTION: An additive agent for an electrochemical device and an electrolyte solution for an electrochemical device each comprise a reaction product of a boroxine compound represented by the general formula, (BO)(OR)[where Rs independently represent an organic group with 1-6 carbon atoms], and a lithium hexafluorophosphate; the quantity of fluorine atoms is less than 6 times that of lithium atoms. A method for manufacturing an additive agent for an electrochemical device comprises the steps of: causing a reaction of a boroxine compound and a lithium hexafluorophosphate in a nonaqueous solvent to prepare a liquid solution containing a reaction product thereof; and performing degasification of a volatile fluorine compound to obtain a solution containing an alkyl difluorophosphate, of which the quantity of fluorine atoms is less than 6 times that of lithium atoms.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an additive for electrochemical devices, a method for producing an additive for electrochemical devices, and an electrolytic solution for electrochemical devices.

  In recent years, there has been a demand for further miniaturization and higher energy density of mobile communication power supplies used for mobile phones and portable personal computers. In addition, development of drive power sources used for electric vehicles, hybrid vehicles, hybrid airway vehicles, and the like, and stationary power sources for power storage used in combination with natural energy power generation using sunlight, wind power, and the like are also progressing. Under such circumstances, lithium secondary batteries have attracted attention. However, lithium secondary batteries have low charge-discharge efficiency due to repeated charge and discharge, and therefore, lithium secondary batteries with little deterioration over time are required. .

  In recent years, the capacity of lithium ion capacitors has been increased, and the application has been expanded to stationary power sources for power storage. In many cases, an electrolytic solution having lithium ion conductivity is used between electrodes of an electrochemical device in which lithium ions are responsible for charge transfer, such as lithium secondary batteries and lithium ion capacitors. The initial characteristics and cycle characteristics of electrochemical devices are greatly affected by the ionic conductivity of the electrolyte and the stability to redox reactions, so the addition of additives to the electrolyte improves the characteristics of the electrochemical device. Is planned.

Conventionally, attempts have been made to improve various characteristics of electrochemical devices by adding boroxine to the electrolytic solution. For example, Patent Document 1 discloses an electrolyte solution for a lithium secondary battery in which at least one solvent selected from a carbonate ester and a borate ester, LiBF _4, and a boroxine compound are mixed. Patent Document 2 discloses an electrolytic solution for a lithium secondary battery, which contains a compound having trivalent and higher valence boron produced by containing a boroxine compound and LiPF ₆ and a non-aqueous solvent. It is disclosed.

International Publication No. 2012/133556 Japanese Patent Laying-Open No. 2015-041531

According to Patent Document 1, when an electrolytic solution obtained by adding LiBF ₄ as a supporting salt to a carbonate ester solvent or borate ester solvent and adding a specific boroxine compound is used, even at a high voltage of 4.4 V or higher. It is said that a rechargeable lithium secondary battery can be obtained. On the other hand, lithium hexafluorophosphate (LiPF ₆ ), which is a kind of supporting salt, loses its effect by reacting with triisopropoxyboroxine (TiPBx), so that good charge / discharge characteristics cannot be obtained. (See paragraph 0021).

However, electrochemical devices such as lithium secondary batteries are still not sufficiently equipped with initial characteristics such as initial capacity and cycle characteristics, and further improvements in various characteristics are required. From the viewpoint of improving the various characteristics of the electrochemical device and ensuring the initial capacity as well as the cycle characteristics, a technique capable of applying other supporting salts with good ion conductivity and dissociation degree such as LiPF ₆ is desired. It is. In addition, according to the technique disclosed in Patent Document 2, the initial capacity of the lithium secondary battery is increased, the decrease in battery capacity over time is suppressed, and the life characteristics of the battery are improved, but a high initial capacity is ensured. From this point of view, there is still room for improvement.

  The present invention has been made in view of the above problems, and includes an additive for an electrochemical device capable of realizing an electrochemical device having a high initial capacity and good cycle characteristics, a production method thereof, and an electrolytic solution for an electrochemical device. The purpose is to provide.

In order to solve the above problems, the additive for an electrochemical device according to the present invention has the following general formulas (I), (BO) ₃ (OR) ₃ (I) [wherein R is independently And an organic group having 1 to 6 carbon atoms. ], And the amount of fluorine atoms is less than 6 times the amount of lithium atoms.

Moreover, the manufacturing method of the additive for electrochemical devices which concerns on this invention is the following general formula (I), (BO) ₃ (OR) ₃ ... (I) [In formula, R is each independently, It is an organic group having 1 to 6 carbon atoms. A solution containing the reaction product by reacting the boroxine compound represented by formula (I) and lithium hexafluorophosphate in a non-aqueous solvent, degassing the volatile fluorine compound contained in the solution, The solution is characterized in that it contains an alkyl difluorophosphate and the amount of fluorine atoms is less than 6 times the amount of lithium atoms.

Moreover, the electrolyte solution for electrochemical devices according to the present invention has the following general formulas (I), (BO) ₃ (OR) ₃ (I) [wherein R is independently a carbon number. 1 to 6 organic groups. ], And the amount of fluorine atoms is less than 6 times the amount of lithium atoms.

  ADVANTAGE OF THE INVENTION According to this invention, the additive for electrochemical devices which can implement | achieve the electrochemical device with a high initial capacity | capacitance and favorable cycling characteristics, its manufacturing method, and the electrolyte solution for electrochemical devices can be provided.

It is a figure which shows the ¹⁹ F-NMR absorption spectrum of the solution which added the boroxine compound. It is sectional drawing which shows an example of a lithium secondary battery typically.

  Hereinafter, the additive for electrochemical devices, the production method thereof, and the electrolytic solution for electrochemical devices according to embodiments of the present invention will be specifically described. The following description shows specific examples of the contents of the present invention, and the present invention is not limited to these descriptions. Various modifications by those skilled in the art are within the scope of the technical idea disclosed in this specification. Changes and modifications are possible.

As a result of intensive research, the inventors of the present invention prepared a solution containing a reaction product by reacting a boroxine compound having a boroxine ring with LiPF ₆ and adding the solution to the electrolytic solution of the electrochemical device. It has been found that the initial characteristics and cycle characteristics of electrochemical devices are effectively improved.

In the conventional method of using a boroxine compound, the boroxine compound is directly added to an electrolytic solution in which LiPF ₆ is dissolved. Therefore, the boroxine compound and LiPF ₆ react in the electrolytic solution to reduce the effect. On the other hand, when a solution containing the reaction product is separately prepared and added to the electrolytic solution, it is difficult for a deterioration factor that is generated as a result of the reaction between the boroxine compound and LiPF ₆ to be mixed into the electrolytic solution. The following embodiments utilize a reaction product of a boroxine compound and LiPF ₆ as an additive based on such knowledge.

<Additives for electrochemical devices>
The additive for electrochemical devices according to the present embodiment has the following general formula (I),
(BO) ₃ (OR) ₃ (I)
[In formula, R is a C1-C6 organic group each independently. ]
In represented by the boroxine compound and the lithium hexafluorophosphate comprising the reaction product of (LiPF _6). This additive for electrochemical devices is a liquid additive that can be used by adding to the electrolyte of the electrochemical device.

The additive for electrochemical devices contains at least a reaction product of a boroxine compound and LiPF ₆ and a non-aqueous solvent. The additive for electrochemical devices contains a reaction product of a boroxine compound and LiPF ₆ as a main component, but the concentration of the reaction product in a non-aqueous solvent is not particularly limited.

  The boroxine compound represented by the general formula (I) has a boroxine ring structure. In the general formula (I), the organic group represented by R is any one of a linear organic group, a branched organic group, and a cyclic organic group as long as it has 1 to 6 carbon atoms. May be. The organic groups (R) may be the same as or different from each other. The organic group (R) may have a halogen atom such as a fluorine atom, a chlorine atom or a bromine atom, a nitrogen atom or a sulfur atom.

  Specific examples of the linear organic group include linear saturated hydrocarbon groups such as a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an n-pentyl group, and an n-hexyl group. . The linear saturated hydrocarbon group preferably has 3 or more carbon atoms.

  Specific examples of the branched organic group include 1-methyl-ethyl group (isopropyl group), 1-methyl-propyl group, 1-ethyl-propyl group, 2-methyl-propyl group, 1-methyl-butyl group. 1-ethyl-butyl group, 2-methyl-butyl group, 2-ethyl-butyl group, 3-methyl-butyl group, 1-methyl-pentyl group, 1-ethyl-pentyl group, 1-propyl-pentyl group, 2-methyl-pentyl group, 2-ethyl-pentyl group, 2-propyl-pentyl group, 3-methyl-pentyl group, 3-ethyl-pentyl group, 4-methyl-pentyl group, 1-methyl-hexyl group, 1 -Ethyl-hexyl group, 1-propyl-hexyl group, 1-butyl-hexyl group, 1-pentyl-hexyl group, 2-methyl-hexyl group, 2-ethyl-hexyl group, 2-propyl-hexyl group Group, 2-butyl-hexyl group, 3-methyl-hexyl group, 3-ethyl-hexyl group, 3-propyl-hexyl group, 4-methyl-hexyl group, 4-ethyl-hexyl group, 5-methyl-hexyl group And branched saturated hydrocarbon groups. The branched saturated hydrocarbon group preferably has 3 or more carbon atoms.

  Specific examples of the cyclic organic group include cyclic saturated hydrocarbon groups such as a cyclohexyl group.

  In the general formula (I), R is particularly preferably an isopropyl group. That is, the boroxine compound represented by the general formula (I) is particularly preferably triisopropoxyboroxine (TiPBx). TiPBx has a relatively stable structure and good solubility. TiPBx is advantageous because it has a high effect of improving various characteristics of the electrochemical device.

  Dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, or the like can be used as the non-aqueous solvent constituting the additive for electrochemical devices. Moreover, the appropriate organic solvent used for the electrolyte solution of a general electrochemical device can be used. Specifically, the following solvent species can be used as the electrolyte solution solvent of the electrochemical device. As the non-aqueous solvent, one of these may be used, or a plurality of types may be used in combination. The non-aqueous solvent is preferably the same type as the electrolytic solution solvent of the electrochemical device using the electrochemical device additive.

  The additive for electrochemical devices may contain an additive that forms a film on the electrode surface, such as vinylene carbonate. Specifically, the compound species described later may be contained as an additive for the electrochemical device. As an additive for forming a film on the electrode surface, one of these may be used, or a plurality of may be used in combination.

When the boroxine compound represented by the general formula (I) reacts with LiPF ₆ , a boroxine derivative in which a fluorine atom is bonded to a boron atom constituting the boroxine ring and an alkyl difluorophosphate are generated. One type of alkyl difluorophosphate is represented by the following general formula (II):
F ₂ (RO) P = O (II)
[Wherein, R represents an organic group having 1 to 6 carbon atoms. ].

FIG. 1 is a diagram showing a ¹⁹ F-NMR absorption spectrum of a solution to which a boroxine compound is added.
The lower spectrum of FIG. 1 is a spectrum of a solution obtained by reacting TiPBx and LiPF ₆ in dimethyl carbonate at a molar ratio of 1: 0.33, and corresponds to the spectrum of the additive for electrochemical devices. 1 is a spectrum of an electrolytic solution for an electrochemical device to which a solution obtained by reacting TiPBx and LiPF ₆ in dimethyl carbonate at a molar ratio of 1: 0.33 is added. This corresponds to the spectrum of the electrolytic solution to which the additive is added.

On the other hand, the upper spectrum of FIG. 1 is a spectrum of an electrolytic solution for an electrochemical device to which only TiPBx is added at a concentration of 1 mass%. In addition, as an electrolytic solution for an electrochemical device, LiPF ₆ was dissolved in advance in an electrolytic solvent obtained by mixing ethylene carbonate and ethyl methyl carbonate at a volume ratio of 1: 2 so as to have a concentration of 1 mol / L. You are using a solution. These spectra are quantitatively shown by an external standard method using tetrafluoroboric acid having a peak around 140 ppm.

In the lower spectrum of FIG. 1, a peak of alkyl difluorophosphate produced by reaction of TiPBx and LiPF ₆ can be confirmed around 85 ppm. In the middle spectrum of FIG. 1, a peak corresponding to LiPF ₆ previously dissolved in the electrolytic solution appears near 73 ppm, but difluoro produced by reaction of TiPBx and LiPF ₆ near 84 ppm. The peak of alkyl phosphate can also be confirmed.

On the other hand, in the upper spectrum of FIG. 1, in addition to the peak of alkyl difluorophosphate produced by the reaction of TiPBx and LiPF ₆ , a number of peaks whose attribution is unknown appear. Since LiPF ₆ produces phosphorus pentafluoride (PF ₅ ) having high activity as a Lewis acid, these peaks are presumed to be signals due to the fluorine compound produced by the reaction of PF ₅ .

The lower spectrum and the middle spectrum in FIG. 1 are prepared by reacting a boroxine compound and LiPF ₆ in advance to prepare a solution containing a reaction product, and when the solution is added to the electrolyte of an electrochemical device, PF ₅ reacts. As a result, the amount of the fluorine compound produced as a secondary agent is reduced. This result means that even if the production of PF ₅ is promoted by the addition of the boroxine compound, PF ₅ is volatilized before being added to the electrolytic solution, and the concentration thereof is reduced. That is, it means that a deterioration factor generated by the reaction of PF ₅ , for example, a fluorine compound such as hydrogen fluoride is difficult to be mixed into the electrolyte solution of the electrochemical device.

In the additive for electrochemical devices according to this embodiment, since the amount of the fluorine compound is thus reduced, the amount of fluorine atoms contained in the solution is less than 6 times the amount of lithium atoms. When LiPF ₆ is added to the non-aqueous solvent for the electrochemical device additive, a part of the fluorine atoms added to the reaction system as LiPF ₆ becomes PF ₅ along with the reaction with the boroxine compound, It volatilizes as PF _{5 and} is lost from the solution. On the other hand, the remainder of the added fluorine atom produces alkyl difluorophosphate and remains in the solution. Therefore, the number of moles of fluorine atoms contained in the additive for electrochemical devices is initially reduced to a range of 2 to 6 times the number of moles of lithium atoms added as LiPF ₆ .

The amount of fluorine atoms contained in the solution of the additive for electrochemical devices is more preferably 2 times or more and less than 6 times the amount of lithium atoms, and further preferably 2 or more times the amount of lithium atoms. Less than 8 times. The smaller the amount of fluorine atoms contained in the solution, the less PF ₅ that produces degradation factors such as hydrogen fluoride. Therefore, the initial characteristics and cycle characteristics of the electrochemical device can be improved by obtaining the effect of using the boroxine compound while suppressing the deterioration of the electrolytic solution. The amount of fluorine atoms contained in the additive for electrochemical devices can be confirmed by a quantitative NMR method using an internal standard method. The amount of lithium atoms can be confirmed by high frequency inductively coupled plasma (ICP) emission spectroscopic analysis or the like.

The effects of using the boroxine compound include improved ion conductivity and improved electrolyte stability. Specifically, a boroxin compound or a boroxine derivative produced by reaction with LiPF ₆ is expected to show an effect of promoting the dissociation of lithium ions by trapping anions by the boroxine ring. In addition, boroxin compounds and boroxin derivatives produced by reaction with LiPF ₆ are expected to capture lithium ions by fluorine atoms bonded to alkoxy groups or boron atoms, thereby improving the transport number. Further, alkyl difluorophosphate is expected to show the effect of improving the oxidative degradation resistance of the electrolytic solution and the like, as in the case of phosphate esters generally used in the electrolytic solution of electrochemical devices.

  The alkyl difluorophosphate represented by the general formula (II) is not limited in the structure of the organic group. In general formula (II), the organic group represented by R may be any of a linear organic group, a branched organic group, and a cyclic organic group. The organic group (R) may have a halogen atom, a nitrogen atom, a sulfur atom, or the like. The organic group (R) of the alkyl difluorophosphate is likely to be the same as the organic group (R) of the boroxine compound represented by the general formula (I). The organic group (R) of the alkyl difluorophosphate may be different from each other.

<Method for producing additive for electrochemical device>
The additive for electrochemical devices according to this embodiment prepares a solution containing a reaction product by reacting a boroxine compound represented by the general formula (I) with LiPF ₆ in a non-aqueous solvent, The volatile fluorine compound contained can be produced by deaeration. By degassing and removing fluorine compounds other than alkyl difluorophosphate, a solution of an additive for an electrochemical device containing alkyl difluorophosphate and having an amount of fluorine atoms less than 6 times the amount of lithium atoms is obtained. Can be obtained.

The boroxine compound represented by the general formula (I) and LiPF ₆ can be reacted under normal temperature and pressure by mixing in a non-aqueous solvent. As a mixing device, any stirrer can be used as long as it can uniformly mix a boroxine compound, LiPF ₆ or the like in a non-aqueous solvent.

The mixing ratio of the boroxine compound represented by the general formula (I) and LiPF ₆ is preferably 1 or less in terms of the molar ratio of LiPF _{6 to} the boroxine compound (number of moles of boroxine compound / number of moles of LiPF ₆ ), It is more preferably 0.15 or more and 1 or less, and particularly preferably about 1/3. Since the boroxine compound and LiPF ₆ react at a molar ratio of about 3: 1, the smaller the molar ratio of LiPF ₆ to the boroxine compound is about 1/3, the more difficult it is to produce PF ₅ . Therefore, it can be avoided that a large amount of PF ₅ remains in the additive for electrochemical devices and the electrolytic solution deteriorates. On the other hand, when the molar ratio of LiPF _{6 to} the boroxine compound exceeds 1, PF ₅ is generated and remains from excess LiPF _6, and thus there is a high possibility that treatment for degassing PF ₅ is required.

  The volatile fluorine compound contained in the solution containing the reaction product can be degassed by depressurizing the solution to degas the fluorine compound or leaving the solution for a predetermined time to remove the fluorine compound. And a method of degassing the fluorine compound by replacing the gas with an inert gas. The deaeration treatment is performed under a temperature condition at which hydrogen fluoride is at least degassed, for example, at room temperature or higher and below the boiling point of the boroxine compound and the non-aqueous solvent. Further, an appropriate treatment time is set according to the concentration of the solution, the ambient temperature, and the like. Argon gas or the like can be used as an inert gas for replacing the gas in the solution.

The additive for electrochemical devices according to the above-described embodiment can be used by being added to an electrolytic solution used in the electrochemical device. Examples of the electrochemical device include devices that can charge and discharge for the purpose of power storage, such as lithium secondary batteries, lithium ion capacitors, and electric double layer capacitors, in which lithium ions are responsible for charge transfer. In addition, the electrolyte solution used in an electrochemical device is not restricted to being a liquid, A gel form etc. may be sufficient. In the electrolytic solution to which the additive for electrochemical devices is added, it is preferable that a boroxine compound is not added separately from the viewpoint of preventing excessive generation of PF ₅ that generates deterioration factors in the electrolytic solution.

The amount of additive for the electrochemical device added to the electrolytic solution is such that the amount of the boroxine derivative produced by the reaction of the boroxine compound and LiPF ₆ is relative to the total amount of the electrolyte and the electrolytic solution solvent constituting the electrolytic solution of the electrochemical device. Thus, the amount is preferably 0.1% by mass or more and 1.0% by mass or less. With such an added amount, the effect of the boroxine derivative can be obtained effectively, and the amount of the boroxine derivative becomes excessive and the ion conduction resistance does not have to be excessive.

<Electrochemical device>
Next, a lithium secondary battery will be described as an example of an electrochemical device to which the electrochemical device additive according to the present embodiment is applied.

FIG. 2 is a cross-sectional view schematically showing an example of a lithium secondary battery.
As shown in FIG. 2, the lithium secondary battery 1 includes a positive electrode 10, a separator 11, a negative electrode 12, a battery container 13, a positive electrode current collector tab 14, a negative electrode current collector tab 15, an inner lid 16, an internal pressure release valve 17, and a gasket 18. , A positive temperature coefficient (PTC) resistance element 19, a battery lid 20, and an axis 21. The battery lid 20 is an integrated part composed of the inner lid 16, the internal pressure release valve 17, the gasket 18 and the resistance element 19.

  The positive electrode 10 and the negative electrode 12 are provided in a sheet shape, and are overlapped with each other with the separator 11 interposed therebetween. The positive electrode 10, the separator 11, and the negative electrode 12 are wound around the axis 21 to form a cylindrical electrode group. The battery container 13 has a cylindrical shape, and an electrode group is accommodated in the battery container 13. As a material of the shaft center 21, for example, polypropylene, polyphenylene sulfide or the like is used.

  The battery container 13 can be formed of a material having corrosion resistance to the electrolytic solution, for example, aluminum, stainless steel, nickel-plated steel, or the like. When the battery container 13 is electrically connected to the positive electrode 10 or the negative electrode 12, the battery container 13 is selected so as not to cause deterioration due to corrosion or alloying with lithium in a portion in contact with the electrolytic solution.

  The positive electrode current collecting tab 14 and the negative electrode current collecting tab 15 for drawing current are connected to the positive electrode 10 and the negative electrode 12 by spot welding, ultrasonic welding, or the like. An electrode group provided with the positive electrode current collecting tab 14 and the negative electrode current collecting tab 15 is accommodated in the battery container 13. The positive electrode current collecting tab 14 is electrically connected to the bottom surface of the battery lid 20. Further, the negative electrode current collecting tab 15 is electrically connected to the inner wall of the battery container 13.

  An electrolyte is injected into the battery container 13. The method of injecting the electrolyte may be a method of directly injecting with the battery lid 20 open, or a method of injecting from an inlet provided in the battery lid 20 with the battery lid 20 closed. Also good. The opening of the battery container 13 is sealed by joining the battery lid 20 by welding, caulking, or the like. The battery lid 20 is provided with an internal pressure release valve 17 that is opened when the internal pressure of the battery container 13 rises excessively.

(Positive electrode)
The positive electrode 10 includes a positive electrode active material capable of reversibly occluding and releasing lithium ions. The positive electrode 10 includes, for example, a positive electrode mixture layer composed of a positive electrode active material, a conductive agent, and a binder, and a positive electrode current collector in which the positive electrode mixture layer is coated on one side or both sides. Composed. As a positive electrode active material, the appropriate | suitable kind used in a general lithium ion secondary battery can be used. However, the positive electrode active material preferably contains at least one transition metal selected from the group consisting of manganese (Mn), cobalt (Co), and nickel (Ni).

Specific examples of the positive electrode active material include LiCoO ₂ , LiNiO ₂ , LiMn ₂ O _{4 and the} like. LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ , Li ₄ Mn ₅ O ₁₂ , LiMn _2−x M1 _x O ₂ (where M1 is selected from the group consisting of Co, Ni, Fe, Cr, Zn, and Ti) at least one metal element selected satisfies x = 0.01 to 0.2.) and, Li ₂ Mn ₃ M2O ₈ (where, M2 consists of Fe, Co, Ni, Cu and Zn At least one metal element selected from the group), Li _1-y A _y Mn ₂ O ₄ (where A is Mg, B, Al, Fe, Co, Ni, Cr, Zn and Ca). And at least one selected from the group consisting of y = 0.01 to 0.1) and LiNi _1-z M2 _z O ₂ (where M2 is Mn, Fe, Co, Al, At least one selected from the group consisting of Ga, Ca and Mg, and z = 0. Meet to 0.2.) _{And, LiCo 1-v M3 v O} 2 ( where, M3 is at least one Ni, selected from the group consisting of Fe and Mn, z = 0.01 to 0 .2), LiFeO ₂ , Fe ₂ (SO ₄ ) ₃ , Fe (MoO ₄ ) ₃ , FeF ₃ , LiFePO ₄ , LiMnPO _4, or the like can be used.

  As the conductive agent, for example, carbon particles such as graphite, carbon black, acetylene black, ketjen black, and channel black, carbon fibers, and the like can be used. These electrically conductive agents may be used individually by 1 type, and may use multiple types together. The amount of the conductive agent is preferably 5% by mass or more and 20% by mass or less with respect to the positive electrode active material. When the amount of the conductive agent is within such a range, good conductivity can be obtained and a high capacity can be secured.

  As the binder in the positive electrode, for example, an appropriate material such as polyvinylidene fluoride, polytetrafluoroethylene, polychlorotrifluoroethylene, polypropylene, polyethylene, an acrylic polymer, a polymer having an imide or amide group, or a copolymer thereof is used. Can be used. These binders may be used individually by 1 type, and may use multiple types together. Further, a thickening material such as carboxymethylcellulose may be used in combination. The amount of the binder is preferably 1% by mass to 7% by mass with respect to the total amount of the positive electrode active material, the conductive agent, and the binder. When the amount of the binder is in such a range, the capacity is small and the internal resistance is rarely excessive. Moreover, the applicability | paintability and moldability of a positive mix layer, and the intensity | strength of a positive mix layer are hard to be impaired.

  As the positive electrode current collector, for example, an appropriate material such as a metal foil made of aluminum, stainless steel, titanium, or the like, a metal plate, a metal foam plate, an expanded metal, or a punching metal can be used. About metal foil, it is good also as perforated foil perforated by the hole diameter of about 0.1 mm or more and 10 mm or less, for example. The thickness of the metal foil is preferably 10 μm or more and 100 μm or less.

  For example, the positive electrode 10 is obtained by mixing a positive electrode active material, a conductive agent, and a binder together with an appropriate solvent to form a positive electrode mixture, and applying the positive electrode mixture to the positive electrode current collector, followed by drying and compression molding. Can be produced. As a method for applying the positive electrode mixture, for example, a doctor blade method, a dipping method, a spray method, or the like can be used. Moreover, as a method of compression molding the positive electrode mixture, for example, a roll press or the like can be used.

  The thickness of the positive electrode mixture layer can be set to an appropriate thickness in consideration of the specifications of the lithium secondary battery to be manufactured and the balance with the negative electrode, but when applied to both surfaces of the positive electrode current collector 50 μm or more and 200 μm or less is preferable. The thickness of the positive electrode mixture layer can be set according to the specifications of the capacity, resistance value, etc. of the lithium secondary battery, but if this amount of coating, the distance between the electrodes becomes excessive, There is little distribution of lithium ion storage and release reactions.

  The particle size of the positive electrode active material is usually not more than the thickness of the positive electrode mixture layer. In the case where coarse particles are present in the synthesized positive electrode active material powder, it is preferable that the average particle size of the positive electrode active material is made smaller than the thickness of the positive electrode mixture layer by performing sieving classification, wind classification, and the like in advance.

  The density of the positive electrode mixture layer can be set to an appropriate density in consideration of the specifications of the lithium secondary battery to be manufactured and the balance with the negative electrode, but the viewpoint of securing the capacity of the lithium secondary battery Is preferably 60% or more of the true density.

(Separator)
The separator 11 is provided in order to prevent a short circuit caused by direct contact between the positive electrode 10 and the negative electrode 12. As the separator 11, a microporous film such as polyethylene, polypropylene, and aramid resin, a film in which the surface of such a microporous film is coated with a heat resistant material such as alumina particles, and the like can be used. In addition, you may provide the function of the separator 11 in the positive electrode 10 and the negative electrode 12 itself to such an extent that battery performance is not impaired.

(Negative electrode)
The negative electrode 12 includes a negative electrode active material capable of reversibly occluding and releasing lithium ions. The negative electrode 12 includes, for example, a negative electrode mixture layer composed of a negative electrode active material and a binder, and a negative electrode current collector in which the negative electrode mixture layer is coated on one side or both sides. As a negative electrode active material, the appropriate | suitable kind used in a general lithium ion secondary battery can be used.

  Specific examples of the negative electrode active material include those obtained by treating a graphitizable active material obtained from natural graphite, petroleum coke, pitch coke, and the like at a high temperature of 2500 ° C. or higher, mesophase carbon, amorphous carbon, and non-graphite surface. Carbon material coated with crystalline carbon, carbon material whose surface crystallinity has been lowered by mechanically treating the surface of natural graphite or artificial graphite, material in which organic substances such as polymers are coated and adsorbed on the carbon surface, carbon Fibers, lithium metals, alloys of lithium and aluminum, tin, silicon, indium, gallium, magnesium, etc., active materials carrying metal on the surface of silicon particles or carbon particles, oxidation of metals such as tin, silicon, iron, titanium Thing etc. are mentioned. Examples of the metal to be supported include lithium, aluminum, tin, silicon, indium, gallium, magnesium, and alloys thereof.

  As the binder in the negative electrode, any of an aqueous binder that dissolves, swells or disperses in water and an organic binder that does not dissolve, swell, or disperse in water can be used. Specific examples of the water-based binder include a styrene-butadiene copolymer, an acrylic polymer, a polymer having a cyano group, and a copolymer thereof. Specific examples of the organic binder include polyvinylidene fluoride, polytetrafluoroethylene, and copolymers thereof. These binders may be used individually by 1 type, and may use multiple types together. Further, a thickening material such as carboxymethylcellulose may be used in combination. The amount of the binder is preferably 0.8% by mass to 1.5% by mass with respect to the total amount of the negative electrode active material and the binder for the aqueous binder. On the other hand, the organic binder is preferably 3% by mass or more and 6% by mass or less with respect to the total amount of the negative electrode active material and the binder. When the amount of the binder is in such a range, the capacity is small and the internal resistance is rarely excessive. Moreover, the applicability | paintability and moldability of a negative mix layer, and the intensity | strength of a negative mix layer are hard to be impaired.

  As the negative electrode current collector, for example, an appropriate material such as a metal foil, a metal plate, a metal foam plate, an expanded metal, or a punching metal made of copper, a copper alloy containing copper as a main component, or the like can be used. About metal foil, it is good also as perforated foil perforated by the hole diameter of about 0.1 mm or more and 10 mm or less, for example. The thickness of the metal foil is preferably 7 μm or more and 25 μm or less.

  The negative electrode 12 is prepared by, for example, mixing a negative electrode active material and a binder together with an appropriate solvent to form a negative electrode mixture, applying the negative electrode mixture to the negative electrode current collector, and then drying and compression molding. Can do. As a method for applying the negative electrode mixture, for example, a doctor blade method, a dipping method, a spray method, or the like can be used. Moreover, as a method of compression-molding the negative electrode mixture, for example, a roll press or the like can be used.

  The thickness of the negative electrode mixture layer can be set to an appropriate thickness in consideration of the specifications of the lithium secondary battery to be manufactured and the balance with the positive electrode, but when applied to both sides of the negative electrode current collector 50 μm or more and 200 μm or less is preferable. The thickness of the negative electrode mixture layer can be set according to the specifications of the lithium secondary battery capacity, resistance value, etc., but if this amount of coating, the distance between the electrodes becomes excessive, There is little distribution of lithium ion storage and release reactions.

(Electrolyte)
The electrolytic solution sealed in the battery container 13 is composed of an electrolyte and an electrolytic solution solvent. As an electrolytic solution, it is common to use an electrolyte having a low content of free acid such as moisture and hydrofluoric acid. The boroxine compound represented by the general formula (I) and hexafluorophosphoric acid are added by adding the additive for an electrochemical device according to the present embodiment to an electrolytic solution containing the following electrolyte and electrolytic solvent. An electrolytic solution for a lithium secondary battery (electrolytic solution for an electrochemical device) comprising a reaction product with lithium is prepared.

In the electrolyte solution for a lithium secondary battery, some of the fluorine atoms added to the reaction system as LiPF ₆ are excluded from the solution as the volatile fluorine compound is degassed. Unless an additive or nonaqueous solvent is used, the amount of fluorine atoms is less than 6 times the amount of lithium atoms. According to such an electrolyte for a lithium secondary battery, deterioration factors such as hydrogen fluoride are eliminated, and since the effect of the boroxine compound is obtained, the lithium secondary battery has a high initial capacity and good cycle characteristics. A battery can be realized.

As the electrolyte, a lithium salt is usually used. Specific examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₂ , Li (CF ₃ SO ₂ ) ₂ N, Li (C ₂ F ₅ SO ₂ ) ₂ N, Li (F _{2 SO 2) 2 N, LiF} , Li 2 CO 3, LiPF 4 (CF 3) 2, LiPF 4 (CF 3 SO 2) 2, LiBF 3 (CF 3), LiBF 2 (CF 3 SO 2) 2 and the like Can be mentioned. These electrolytes may be used individually by 1 type, and may use multiple types together.

  The concentration of the electrolyte is preferably in the range of 0.6 mol / L or more and 1.5 mol / L or less. When the concentration is 0.6 mol / L or more, the ionic conductivity is improved, so that a high initial capacity can be realized. Further, when the concentration is 1.5 mol / L or less, the resistance of ionic conduction is suppressed to a small value, and the reaction rate of lithium ions is increased, so that deterioration of battery characteristics due to excessive electrolyte can be avoided.

  As the electrolyte solution solvent, for example, a chain carbonate, a cyclic carbonate, a chain carboxylic acid ester, a cyclic carboxylic acid ester, a chain ether, a cyclic ether, an organic phosphorus compound, an organic sulfur compound, or the like can be used. These compounds may be used individually by 1 type, and may use multiple types together.

  Examples of the chain carbonate include dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate. Examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, vinylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, and the like.

  Examples of the chain carboxylic acid ester include methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, and propyl propionate. Examples of the cyclic carboxylic acid ester include γ-butyrolactone, γ-valerolactone, and δ-valerolactone.

  Examples of the chain ether include dimethoxymethane, diethoxymethane, 1,2-dimethoxyethane, 1-ethoxy-2-methoxyethane, 1,3-dimethoxypropane and the like. Examples of the cyclic ether include tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran and the like.

  Examples of the organic phosphorus compound include phosphoric acid esters such as trimethyl phosphate, triethyl phosphate, and triphenyl phosphate, phosphorous acid esters such as trimethyl phosphite, triethyl phosphite, and triphenyl phosphite, And trimethylphosphine oxide. Examples of the organic sulfur compound include 1,3-propane sultone, 1,4-butane sultone, methyl methanesulfonate, sulfolane, sulfolene, dimethyl sulfone, ethyl methyl sulfone, methyl phenyl sulfone, and ethyl phenyl sulfone. .

  These compounds used as the electrolyte solution solvent may have a substituent, or may be a compound in which an oxygen atom is substituted with a sulfur atom. As a substituent, halogen atoms, such as a fluorine atom, a chlorine atom, a bromine atom, are mentioned, for example. When two or more compounds are used in combination as the electrolyte solvent, a compound having a high relative dielectric constant and a relatively high viscosity such as a cyclic carbonate or a cyclic lactone and a viscosity such as a chain carbonate are relatively It is preferable to combine with a low compound. For example, a composition containing ethylene carbonate and either ethyl methyl carbonate or diethyl carbonate is preferable.

  The electrolytic solution may contain various additives. Specific additives include additives that form a film on the electrode surface, additives that suppress overcharge, additives that make the electrolyte flame-retardant, and wettability of electrodes, separators, etc. An additive for improving, an additive for collecting metal ions in the electrolytic solution, an additive for improving the ionic conductivity of the electrolytic solution, and the like.

  Additives that form a film on the electrode surface include carbonates such as vinylene carbonate (VC) and monofluorinated ethylene carbonate, carboxylic acid anhydrides, sulfur compounds such as 1,3-propane sultone, lithium bisoxa Examples thereof include boron compounds such as rate borate (LiBOB) and trimethyl borate. On the surface of the negative electrode active material, functional groups such as C═O, C—H, and COO are present, and these functional groups react irreversibly with the electrolyte solvent along with the battery reaction, and SEI ( Forms a surface coating called Solid Electrolyte Interphase coating. The SEI film has an action of suppressing the decomposition of the electrolyte solvent, but it is generated by consuming electric charge in the battery reaction, which causes a decrease in the capacity of the battery. Therefore, the amount of the additive that forms a film on the electrode surface is preferably 0.1% by mass or more and 10% by mass or less based on the electrolytic solution from the viewpoint of suppressing battery capacity and output reduction.

  Examples of additives for suppressing overcharge include biphenyl, biphenyl ether, terphenyl, methyl terphenyl, dimethyl terphenyl, cyclohexylbenzene, dicyclohexylbenzene, triphenylbenzene, hexaphenylbenzene, adiponitrile, and dioxane. Can be mentioned.

  Examples of the additive for making the electrolytic solution flame-retardant include organic phosphorus compounds such as trimethyl phosphate and triethyl phosphate, fluorides of electrolytic solution including boric acid ester, and the like. Examples of the additive for improving wettability include chain ethers such as 1,2-dimethoxyethane.

  As an additive for collecting the metal ions in the electrolytic solution, a substance having a complex forming ability to form a complex with the metal ions eluted in the electrolytic solution can be used. In addition, as an additive for improving the ionic conductivity of the electrolytic solution, a substance that forms an electrostatic interaction with lithium ions can be used.

  The lithium secondary battery having the above configuration uses the battery lid as the positive electrode external terminal and the bottom of the battery can as the negative electrode external terminal, and accumulates power supplied from the outside in the wound electrode group and also in the wound electrode group. Can be supplied to an external device or the like. The lithium secondary battery of this embodiment is, for example, a small power source such as a portable electronic device or a household electric device, a stationary power source such as an uninterruptible power source or a power leveling device, a ship, a railway, a hybrid vehicle, an electric vehicle, etc. It can be used as a drive power supply.

  In the lithium secondary battery shown in FIG. 2, the electrode group and the battery container 13 are formed in a cylindrical shape. However, the form of the electrode group is an appropriate form such as a form wound in a flat circular shape, a form in which strip-shaped electrodes are laminated, and a form in which a bag-like separator containing electrodes is laminated to form a multilayer structure. can do. In addition, the battery case 13 can have an appropriate shape such as a cylindrical shape, a flat elliptical shape, a flat elliptical shape, a square shape, a coin shape, or a button shape according to the form of the electrode group. Further, it is possible to adopt a form in which the axis 21 is not provided.

  Further, in place of the lithium secondary battery having the above configuration, the additive for electrochemical devices according to the present embodiment is added to the electrolytic solution of the capacitor, whereby the boroxine compound represented by the general formula (I) and An electrolytic solution for a capacitor (electrolytic solution for an electrochemical device) comprising a reaction product with lithium hexafluorophosphate is prepared.

  The electrolytic solution for a capacitor is composed of an electrolyte and an electrolytic solution solvent. As the electrolyte and the electrolyte solution solvent, the same compound species as in the lithium secondary battery can be used. The capacitor includes, for example, a positive electrode that generates polarization, a negative electrode, and an electrolytic solution.

  As an electrode material that generates polarization, for example, activated carbon or the like can be used. Activated carbon is made from waste wood, coconut husk, pulp waste liquid, coal, heavy petroleum oil, coal-based pitch, petroleum-based pitch, various resins, etc., and these materials are carbonized and activated as necessary. can get. Using activated carbon as a positive electrode active material, a positive electrode is formed using the binder, a porous positive electrode current collector, and the like. The activation treatment applied to the activated carbon may be a gas treatment with carbon dioxide gas, air, water vapor, or the like, or a chemical treatment with zinc chloride, sodium hydroxide, phosphoric acid, or the like.

  The negative electrode is formed of the negative electrode active material such as amorphous carbon, a conductive agent, a binder, a porous negative electrode current collector, and the like. Examples of amorphous carbon include hard carbon and soft carbon. The positive electrode and the negative electrode may be stacked and accommodated in a container with a separator interposed therebetween, and lithium may be doped by pre-doping a metal foil or a negative electrode active material.

In the electrolytic solution for capacitors, since some of the fluorine atoms added to the reaction system as LiPF ₆ are excluded from the solution as the volatile fluorine compound is degassed, other additives containing fluorine atoms, Unless a non-aqueous solvent is used, the amount of fluorine atoms is less than 6 times the amount of lithium atoms. According to such an electrolytic solution for capacitors, deterioration factors such as hydrogen fluoride are eliminated, and since the effect of the boroxine compound can be obtained, a lithium ion capacitor having improved initial characteristics and cycle characteristics can be realized. It is possible.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated further more concretely, this invention is not limited to these.

Example 1
<Negative electrode>
As the negative electrode active material, natural graphite having an interplanar spacing of 0.368 nm, an average particle diameter of 20 μm, and a specific surface area of 5 m ² / g obtained by X-ray diffraction measurement was used. Natural graphite and an aqueous dispersion containing a water-swelled carboxymethyl cellulose and a styrene-butadiene copolymer were sufficiently kneaded using a mixer equipped with a stirring blade to prepare a negative electrode mixture slurry. The mixing ratio of the negative electrode active material, carboxymethyl cellulose, and styrene butadiene copolymer was 97: 1.5: 1.5 by weight.

The prepared negative electrode mixture slurry was uniformly applied to both surfaces of a rolled copper foil having a thickness of 10 μm. And after drying, it is compression-molded by a roll press machine so that the electrode density is about 1.5 g / cm ³ , the total length of the applied length 55 cm of the negative electrode mixture layer and the uncoated portion 5 cm is 60 cm, and the coated width is 5.6 cm. It cut so that it might become. Thereafter, a Ni lead piece was welded to the uncoated portion, and a negative electrode provided with a current extraction portion was produced.

<Positive electrode>
As the positive electrode active material, LiNiCoMnO ₂ having an average particle diameter of 10 μm and a specific surface area of 1.5 m ² / g was used. A positive electrode mixture slurry was prepared by dispersing a positive electrode active material and a conductive agent in which massive graphite and acetylene black were mixed at a weight ratio of 9: 2 in an NMP solution in which 5% by weight of PVDF was dissolved. As in the case of the negative electrode, the positive electrode mixture slurry was sufficiently kneaded using a mixer equipped with a stirring blade. The mixing ratio of the positive electrode active material, the conductive agent, and PVDF was 85: 10: 5 by weight.

The prepared positive electrode mixture slurry was uniformly applied on both surfaces of an aluminum foil having a thickness of 20 μm. Then, it compression-molded so that the electrode density might be 2.6 g / cm < ³ > with a roll press machine, and it cut | disconnected so that it might become a total of 55 cm of 50 cm of application | coating length of a positive mix layer, and 5 cm of non-application parts. Thereafter, a lead piece made of aluminum foil was welded to the uncoated part, and a positive electrode equipped with a current extraction part was produced.

<Electrolyte>
In 8 g of dimethyl carbonate having a water content of 20 ppm or less, 0.2 g of triisopropoxyboroxine (TiPBx) was dissolved. To this solution, 0.018 g of LiPF ₆ was weighed and added to obtain an additive for electrochemical devices. The mixing ratio of TiPBx and LiPF ₆ is (1 molar ratio of TiPBx and LiPF _6: 0.15) 0.15 at a molar ratio of LiPF ₆ with respect to boroxine compound was. This additive for electrochemical devices is added to an electrolytic solution in which LiPF ₆ is dissolved in advance to a concentration of 1 mol / L in an electrolytic solution solvent in which ethylene carbonate and ethyl methyl carbonate are mixed at a volume ratio of 1: 2. Thus, an electrolyte for a lithium secondary battery was obtained. In addition, the amount of fluorine contained in the electrolyte solution to which such an additive for electrochemical devices or the additive for electrochemical devices was added was measured by ¹⁹ F-NMR such as trifluorobenzene as an internal standard substance. In some cases, a substance that shows a signal that can be separated from the chemical shift of the measurement sample is used, and the integrated intensity of the internal standard substance can be quantified by comparing it with the result at a known concentration. The amount of lithium can be quantified by ICP emission spectroscopic analysis or the like.

<Lithium secondary battery>
A cylindrical lithium secondary battery as shown in FIG. 2 was produced using the produced positive electrode and negative electrode. A positive electrode current collecting tab and a negative electrode current collecting tab for current drawing were ultrasonically welded to the positive electrode and the negative electrode, respectively. Each of the positive electrode current collecting tab and the negative electrode current collecting tab is made of a metal foil made of the same material as the rectangular current collector. A separator, which is a polyethylene single layer film, was sandwiched between the positive electrode and the negative electrode, and this was wound spirally to form an electrode group, which was stored in a cylindrical battery container. After the electrode group is stored in the battery container, an electrolyte solution is injected into the battery container, and the battery cover for sealing with the positive electrode current collecting tab attached thereto is brought into close contact with the battery container through a gasket and sealed by caulking. A cylindrical lithium secondary battery having a length of 18 mm and a length of 650 mm was produced.

  The manufactured lithium secondary battery was charged in a constant temperature bath at 25 ° C. with a charging current of 1500 mA, a voltage of 4.2 V, a constant current and a constant voltage for 3 hours, and after a rest of 5 hours, the battery voltage was 3 at a discharge current of 1500 mA. The battery was discharged at a constant current until the voltage reached 0.0 V, and charging and discharging for a total of 3 cycles were performed with this charging and discharging process as one cycle. The discharge capacity at the third cycle was set as the initial capacity of the lithium secondary battery. Next, a cycle load characteristic test was performed. In the cycle load characteristic test, charging current 1500 mA, voltage 4.2 V, constant current constant voltage charging for 5 hours, after resting for 5 hours, discharging at a constant current of 1500 mA until the battery voltage reaches 3.0 V, This charging and discharging process was taken as one cycle, and a load characteristic test was conducted for a total of 500 cycles. After the 500 cycle test, the ratio (capacity maintenance ratio) of the discharge capacity at the 500th cycle to the discharge capacity (initial capacity) at the 3rd cycle was determined. A larger value of this ratio means better cycle characteristics.

(Example 2)
A lithium secondary battery was produced in the same manner as in Example 1 except that triisopropoxyboroxine (TiPBx) and LiPF ₆ were reacted at a molar ratio of 1: 0.3. The capacity maintenance rate was obtained.

(Example 3)
A lithium secondary battery was produced in the same manner as in Example 1 except that triisopropoxyboroxine (TiPBx) and LiPF ₆ were reacted in a molar ratio of 1: 1, and the initial capacity and capacity maintained at the 500th cycle were maintained. We asked for rate.

Example 4
A lithium secondary battery was produced in the same manner as in Example 1 except that triisopropoxyboroxine (TiPBx) and LiPF ₆ were reacted at a molar ratio of 1: 3, and the initial capacity and capacity maintained at the 500th cycle were maintained. We asked for rate.

(Example 5)
An additive for electrochemical devices obtained by reacting triisopropoxyboroxine (TiPBx) and LiPF ₆ at a molar ratio of 1: 0.15 is dissolved in advance so that LiPF ₆ has a concentration of 1M, Further, a lithium secondary battery was produced in the same manner as in Example 1 except that vinylene carbonate (VC) was added to the electrolytic solution that had been added so as to have a concentration of 1% by mass. The capacity maintenance rate was obtained.

(Example 6)
An additive for electrochemical devices obtained by reacting triisopropoxyboroxine (TiPBx) and LiPF ₆ at a molar ratio of 1: 0.3 is dissolved in advance so that LiPF ₆ has a concentration of 1M, Further, a lithium secondary battery was produced in the same manner as in Example 1 except that vinylene carbonate (VC) was added to the electrolytic solution that had been added so as to have a concentration of 1% by mass. The capacity maintenance rate was obtained.

(Example 7)
An additive for electrochemical devices obtained by reacting triisopropoxyboroxine (TiPBx) and LiPF ₆ at a molar ratio of 1: 1 is dissolved in advance so that LiPF ₆ has a concentration of 1M, and further vinylene. A lithium secondary battery was produced in the same manner as in Example 1 except that carbonate (VC) was added to the electrolytic solution that had been added to a concentration of 1% by mass. The maintenance rate was calculated.

(Comparative Example 1)
Example 1 except that an electrolytic solution to which no additive for electrochemical devices was added, that is, an electrolytic solution in which LiPF ₆ was dissolved at 1 M in an electrolytic solvent obtained by mixing ethylene carbonate and ethyl methyl carbonate was used. A lithium secondary battery was prepared in the same manner as described above, and the initial capacity and the capacity retention rate at the 500th cycle were determined.

(Comparative Example 2)
For an electrolytic solution to which no additive for electrochemical devices is added, that is, an electrolytic solution in which LiPF ₆ is dissolved at 1 M in an electrolytic solvent obtained by mixing ethylene carbonate and ethyl methyl carbonate at a volume ratio of 1: 2. A lithium secondary battery was produced in the same manner as in Example 1 except that an electrolytic solution to which mass% of triisopropoxyboroxine (TiPBx) was added was used. The initial capacity and the capacity retention rate at the 500th cycle were determined. Asked.

(Comparative Example 3)
For an electrolytic solution to which no additive for electrochemical devices is added, that is, an electrolytic solution in which LiPF ₆ is dissolved at 1 M in an electrolytic solvent obtained by mixing ethylene carbonate and ethyl methyl carbonate at a volume ratio of 1: 2. A lithium secondary battery was produced in the same manner as in Example 1 except that an electrolytic solution to which 1% by mass of triisopropoxyboroxine (TiPBx) and 1% by mass of vinylene carbonate (VC) were used was used. The initial capacity and the capacity maintenance rate at the 500th cycle were determined.

  Table 1 shows the results of the composition of the additive for electrochemical devices, the composition of the electrolytic solution, the initial capacity, and the capacity retention rate at the 500th cycle for the lithium secondary batteries according to Examples and Comparative Examples.

  As shown in Table 1, in Comparative Example 1, the additive for electrochemical devices was not added, and TiPBx was not added in advance to the electrolytic solution, so the discharge capacity after 500 cycles decreased to 66%. did.

  Further, in Comparative Example 2, 1% by mass of TiPBx was previously added to the electrolytic solution, so that the discharge capacity after 500 cycles was improved by 2 points compared to Comparative Example 1. However, since the additive for electrochemical devices is not added, it is not sufficiently improved.

On the other hand, in Example 1, since the additive for an electrochemical device in which TiPBx and LiPF ₆ were reacted at a molar ratio of 1: 1 was added, the initial capacity was improved as compared with Comparative Example 1. Further, the discharge capacity after 500 cycles was improved by 7 points with respect to Comparative Example 1 and by 5 points with respect to Comparative Example 2.

In Example 2, since the additive for electrochemical devices in which TiPBx and LiPF ₆ were reacted at a molar ratio of 1: 0.3 was added, the initial capacity was improved compared to Comparative Example 1. Further, the discharge capacity after 500 cycles was improved by 16 points with respect to Comparative Example 1 and 14 points with respect to Comparative Example 2.

In Example 3, since an additive for electrochemical devices in which TiPBx and LiPF ₆ were reacted at a molar ratio of 1: 1 was added, the initial capacity was improved as compared with Comparative Example 1. Further, the discharge capacity after 500 cycles was improved by 13 points with respect to Comparative Example 1 and 11 points with respect to Comparative Example 2.

In Example 4, since an additive for electrochemical devices in which TiPBx and LiPF ₆ were reacted at a molar ratio of 1: 3 was added, the discharge capacity after 500 cycles was 8 points compared to Comparative Example 1, Comparative Example 2 10 points. Thus, reaction of the boroxine compound and the LiPF _6, the molar ratio of LiPF ₆ (number of moles / LiPF ₆ of boroxine compound) is preferably carried out in a mixing ratio of 3 or less for the boroxine compound is 1 or less It can be said that it is more preferable to carry out at a mixing ratio.

  On the other hand, in Comparative Example 3, 1% by mass of TiPBx and 1% by mass of VC were previously added to the electrolytic solution. Therefore, the discharge capacity after 500 cycles was improved by 5 points compared to Comparative Example 1. However, since the additive for electrochemical devices is not added, it is not sufficiently improved.

On the other hand, in Example 5, since the additive for electrochemical devices in which TiPBx and LiPF ₆ were reacted at a molar ratio of 1: 0.15 was added to the electrolyte solution in which VC was previously added by 1 mass%, The initial capacity was improved with respect to Example 1, and the discharge capacity after 500 cycles was improved by 2 points with respect to Example 1.

In Example 6, since the additive for an electrochemical device obtained by reacting TiPBx and LiPF ₆ at a molar ratio of 1: 0.3 was added to the electrolytic solution to which 1 mass% of VC was previously added, the initial capacity was As compared with Example 2, the discharge capacity after 500 cycles was improved by 4 points over Example 2.

Further, in Example 7, the additive for electrochemical devices in which TiPBx and LiPF ₆ were reacted at a molar ratio of 1: 1 was added to the electrolytic solution to which VC was added in advance by 1% by mass. Compared to Example 3, the discharge capacity after 500 cycles was improved by 3 points over Example 3.

As shown in Table 1, in Comparative Example 2, the discharge capacity after 500 cycles was not sufficiently improved despite the addition of TiPBx to the electrolytic solution. As shown in the upper part of FIG. 1, it is considered that PF ₅ produced by reaction of LiPF ₆ produced a fluorine compound such as hydrogen fluoride and deteriorated the electrolytic solution. On the other hand, in Examples 1 to 3 and 5 to _{7, in} which a reaction product of TiPBx and LiPF ₆ was separately prepared and added, PF ₅ generated by adding TiPBx was volatilized and removed. It is considered that the cycle characteristics are improved.

Therefore, by using a reaction product obtained by separately reacting a boroxine compound and LiPF _{6 in} the form of an additive, and preventing fluorine compounds such as hydrogen fluoride from being mixed into the electrolyte as a deterioration factor, electrochemical It is considered that the cycle characteristics of the device can be improved. In addition, by using the reaction product in the form of an additive, the effect of using the boroxine compound can be used with little deterioration of the electrolyte solution, so that the initial characteristics such as the initial capacity of the electrochemical device can also be obtained. It can be improved.

DESCRIPTION OF SYMBOLS 1 Lithium secondary battery 10 Positive electrode 11 Separator 12 Negative electrode 13 Battery container 14 Positive electrode current collection tab 15 Negative electrode current collection tab 16 Inner cover 17 Internal pressure release valve 18 Gasket 19 Positive temperature coefficient resistance element 20 Battery cover 21 Axis center

Claims (9)

The following general formula (I),
(BO) ₃ (OR) ₃ (I)
[In formula, R is a C1-C6 organic group each independently. ]
Comprising a reaction product of a boroxine compound represented by: and lithium hexafluorophosphate,
An additive for electrochemical devices, wherein the amount of fluorine atoms is less than 6 times the amount of lithium atoms.   The additive for electrochemical devices according to claim 1, wherein R in the general formula (I) is an isopropyl group.   The additive for electrochemical devices according to claim 1, wherein the reaction product contains an alkyl difluorophosphate.   The additive for electrochemical devices according to claim 3, wherein the alkyl difluorophosphate has an isopropyl group. The following general formula (I),
(BO) ₃ (OR) ₃ (I)
[In formula, R is a C1-C6 organic group each independently. ]
A solution containing the reaction product is prepared by reacting the boroxine compound represented by the following formula with lithium hexafluorophosphate in a non-aqueous solvent,
Degassing volatile fluorine compounds contained in the solution;
A method for producing an additive for an electrochemical device, comprising an alkyl difluorophosphate, wherein the solution contains an amount of fluorine atoms that is less than 6 times the amount of lithium atoms. The following general formula (I),
(BO) ₃ (OR) ₃ (I)
[In formula, R is a C1-C6 organic group each independently. ]
Comprising a reaction product of a boroxine compound represented by: and lithium hexafluorophosphate,
An electrolytic solution for electrochemical devices, wherein the amount of fluorine atoms is less than 6 times the amount of lithium atoms.   The electrolyte solution for electrochemical devices according to claim 6, wherein R in the general formula (I) is an isopropyl group.   The electrolytic solution for an electrochemical device according to claim 6, wherein the reaction product contains an alkyl difluorophosphate.   The electrolyte solution for electrochemical devices according to claim 8, wherein the alkyl difluorophosphate has an isopropyl group.

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