JP6922637B2 - Electrolytes for secondary batteries and secondary batteries - Google Patents

Description

The present invention relates to an electrolyte for a secondary battery and a secondary battery.

Conventionally known electrolytes for lithium-ion batteries mainly use flammable organic solvents, and therefore, for example, there is a risk of ignition or ignition during over-discharging or over-charging. As a highly safe electrolyte, an electrolyte using a grime-lithium salt complex system has been proposed. The grime-lithium salt complex is a complex in which a compound having an oligo ether called grime is coordinated 1: 1 with respect to lithium ions. The grime-lithium salt complex is thermochemically very stable because it forms a complex structure with a very strong interaction. However, in a glyme-lithium salt complex formed of a single glyme molecule and a lithium salt, oxidative decomposition occurs on the electrode surface of the glyme molecule in the glyme-lithium salt complex, and a lithium secondary battery using the glyme-lithium salt complex system as an electrolyte. Has a problem that the cycle characteristic of repeating charging and discharging is deteriorated. Therefore, a method for improving the oxidation resistance of grime molecules has been proposed. Specifically, an electron-withdrawing group is introduced in the vicinity of an oxygen atom in a single glyme molecule, and a glyme compound having an electron-withdrawing group is used to reduce the electron density of the oxygen atom in the glyme structure and to withstand oxidation. This is a method for improving the property (Patent Document 1).

Japanese Unexamined Patent Publication No. 2011-40311

However, the electrolyte described in Patent Document 1 has a problem in cycle characteristics under 4.4 V. This is thought to be due to the low ionic conductivity of the electrolyte. The introduced electron-withdrawing effect strongly acts, greatly reducing the electron density of the oxygen atom of the glyme molecule, and as a result, the coordination ability of the glyme molecule with respect to lithium ions is reduced, and the ionic conductivity is lowered. Conceivable. Therefore, an electrolyte for a secondary battery having good cycle characteristics at 4.4 V or higher is desired.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an electrolyte for a secondary battery using a grime-lithium salt complex system having good cycle characteristics at 4.4 V or higher.

In the glyme-lithium salt complex system, the present inventors use the obtained electrolyte for a secondary battery when the bond chain between the phosphonate diester structure, which is an electron-withdrawing group, and the glyme structure has an appropriate length. It has been found that the secondary battery can realize good cycle characteristics at 4.4 V or higher.
That is, in order to solve the above problems, the following means are provided.

[1] An electrolyte for a secondary battery, which contains a lithium salt and a compound (A) represented by the chemical formula (1).

(In the formula, n is an integer of 2 to 10, m is an integer of 1 to 10, and R ₁ and R ₂ are independently substituted or unsubstituted alkoxy groups having 1 to 6 carbon atoms. , R ₃ is a hydrogen atom or a substituted or unsubstituted alkyl group having 1 to 2 carbon atoms.)

[2] The electrolyte for a secondary battery according to [1], wherein the content of the lithium salt is 0.5 to 3 times the molar amount of the compound (A).
[3] A lithium ion secondary battery having the electrolyte for the secondary battery according to [1] or [2].

A secondary using a glyme-lithium salt complex system with excellent cycle characteristics under a high voltage of 4.4 V or higher due to both the oxidation resistance of the glyme compound due to the electron attraction effect and the coordination ability of the lithium ion of the glyme compound. Provide an electrolyte for a battery.

It is sectional drawing of the lithium secondary battery which concerns on this embodiment.

Hereinafter, the present embodiment will be described in detail with reference to the drawings as appropriate. The drawings used in the following description may be enlarged for convenience in order to make the features of the present invention easy to understand, and the dimensional ratios of the respective components may differ from the actual ones. be. The materials, dimensions, etc. exemplified in the following description are examples, and the present invention is not limited thereto, and the present invention can be appropriately modified without changing the gist thereof.

The "grime molecule" according to the present invention is a general term for linear symmetric glycol diethers, and may be represented by _{, for example, "RO (CH 2} CH ₂ O) _m-R". Here, R is any one of an alkyl group having 1 to 9 carbon atoms which may be substituted with fluorine, a phenyl group which may be substituted with a halogen atom, and a cyclohexyl group which may be substituted with a halogen atom. be. m is 1-10. In order to distinguish it from the grime compound described later, it may also be referred to as "elemental grime molecule".

The "grime structure" according to the present invention is a structure of "-O (CH ₂ CH ₂ O) _m- " contained in the grime molecule.

The "glyme compound" according to the present invention is a compound having an electron-withdrawing group and a glyme structure by introducing an electron-withdrawing group in the vicinity of an oxygen atom in a single glyme molecule.

[Secondary battery]
FIG. 1 is a schematic cross-sectional view of the lithium secondary battery according to the present embodiment. The lithium secondary battery 100 shown in FIG. 1 mainly includes a laminate 40, a case 50 that houses the laminate 40 in a sealed state, and a pair of leads 60 and 62 connected to the laminate 40. Although not shown, the electrolyte is housed in the case 50 together with the laminate 40.

In the laminated body 40, the positive electrode 20 and the negative electrode 30 are arranged so as to face each other with the separator 10 interposed therebetween. The positive electrode 20 has a positive electrode active material layer 24 provided on a plate-shaped (film-shaped) positive electrode current collector 22. The negative electrode 30 has a negative electrode active material layer 34 provided on a plate-shaped (film-shaped) negative electrode current collector 32.

The positive electrode active material layer 24 and the negative electrode active material layer 34 are in contact with both sides of the separator 10, respectively. Leads 62 and 60 are connected to the ends of the positive electrode current collector 22 and the negative electrode current collector 32, respectively, and the ends of the leads 60 and 62 extend to the outside of the case 50. In FIG. 1, a case where one laminated body 40 is provided in the case 50 is illustrated, but a plurality of laminated bodies 40 may be laminated.

"Electrolyte for secondary battery"
The electrolyte for a secondary battery (hereinafter, simply referred to as “electrolyte”) according to the present embodiment is characterized by containing a lithium salt and a compound (A) represented by the chemical formula (1).

（式中、ｎは２〜１０の整数であり、ｍは１〜１０の整数であり、Ｒ_１、Ｒ_２は、それぞれ独立して置換又は無置換の炭素数１〜６のアルコキシ基であり、Ｒ_３は水素原子又は置換もしくは無置換の炭素数１〜２のアルキル基である。）

(In the formula, n is an integer of 2 to 10, m is an integer of 1 to 10, and R ₁ and R ₂ are independently substituted or unsubstituted alkoxy groups having 1 to 6 carbon atoms. , R ₃ is a hydrogen atom or a substituted or unsubstituted alkyl group having 1 to 2 carbon atoms.)

(Lithium salt)
The lithium salt in this embodiment is an electrolyte that dissociates in the electrolyte and supplies lithium ions.
Lithium salts include LiPF ₆ , LiBF ₄ , LiClO ₄ , Li (C ₂ O ₄ ) ₂ , Li (C ₂ O ₄ ) F ₂ , LiN (SO ₂ (CF ₂ ) _p F) ₂ (however, p is Integers 1 to 5 are shown), FSO ₂ N (Li) SO ₂ F, FSO ₂ N (Li) SO ₂ CF ₃ , CF ₃ SO ₃ Li and the following compounds (2) (where q is 1 to 5). One or more selected from the group consisting of (indicating an integer of). These lithium salts are compounds known as lithium salts for lithium ion secondary batteries.
Lithium salts include LiN (SO ₂ CF ₃ ) ₂ (compound with p of 1), LiN (SO ₂ C ₂ F ₅ ) ₂ (compound with p of 2), FSO ₂ N (Li) SO ₂ F, At _{least one selected from the group consisting of FSO 2} N (Li) SO ₂ CF ₃ , CF ₃ SO ₃ Li, LiPF ₆ and compound (2) (where q indicates an integer of 1 to 5). Is preferable.

Examples of the compound (2) include the following compounds (2-1) to (2-5).

As the compound (2), the compound (2-2) having q of 2 is preferable from the viewpoint that an electrolyte having a high conductivity can be easily obtained.

The content of the lithium salt is preferably 0.5 to 3 times mol, more preferably 0.5 to 2.0 times mol, and 0.8 to 1 times the molar amount of the compound (A). It is more preferably 5.5 times the molar amount. According to such a configuration, the dissociability is improved and the cycle characteristics are improved depending on the selected concentration.

(Compound (A))
The compound (A) of this embodiment is a compound represented by the following chemical formula (1).

n is an integer of 2 to 10. n is preferably an integer of 2 to 6, more preferably an integer of 2 to 5, and particularly preferably an integer of 2 to 4.
m is an integer of 1-10. Compound (A) has a phosphonate diester structure that is an electron-withdrawing group, and the electrolyte of the present invention is used by setting the bond chain between the electron-withdrawing group and the glyme structure to an appropriate length. It is a compound that can improve the cycle characteristics of a secondary battery at 4.4 V or higher. In the electrolyte of the present invention, it is considered that a part or all of the compound (A) forms a complex with the lithium salt and exhibits the action of the present invention. , M is more preferably an integer of 1 to 7, and even more preferably an integer of 2 to 4.

R ₁ and R ₂ are independently substituted or unsubstituted alkoxy groups having 1 to 6 carbon atoms.
Examples of the unsubstituted alkoxy group having 1 to 6 carbon atoms include a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, an isobutoxy group, a sec-butoxy group, a tert-butoxy group, a pentyloxy group and an iso. Examples thereof include a pentyloxy group, a hexyloxy group, a cyclopropyloxy group, a cyclobutyloxy group, a cyclopentyloxy group, a cyclohexyloxy group and the like.
The alkoxy group having 1 to 6 substituted carbon atoms is an alkoxy group having 1 to 6 carbon atoms having a substituent. This substituent is not particularly limited as long as it does not impair the effects of the present invention, and is, for example, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, and 2 to 4 carbon atoms. Examples thereof include an alkylamino group and an aryl group having 6 to 10 carbon atoms. Specific examples thereof include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a tert-butyl group and a methoxy group. Group, ethoxy group, propoxy group, butoxy group, N, N-dimethylamino group, N, N-diethylamino group, phenyl group, 4-tolyl group, 4-ethylphenyl group, 4-propylphenyl group, 4-butylphenyl Groups, naphthyl groups and the like can be mentioned. Of these, alkyl groups having 1 to 4 carbon atoms are particularly preferable.

R ₁ and R ₂ are preferably unsubstituted alkoxy groups having 1 to 4 carbon atoms. For example, a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, an isobutoxy group, a sec-butoxy group, and a tert-butoxy group. Of these, a methoxy group and an ethoxy group are particularly preferable.

R ₃ is a hydrogen atom or a substituted or unsubstituted alkyl group having 1 to 2 carbon atoms. Examples of the unsubstituted alkyl group having 1 to 2 carbon atoms include a methyl group and an ethyl group. The alkyl group having 1 to 2 substituted carbon atoms is an alkyl group having 1 to 2 carbon atoms having a substituent. This substituent is not particularly limited as long as it does not impair the effects of the present invention, and examples thereof include an alkyl group having 1 to 3 carbon atoms and an alkoxy group having 1 to 3 carbon atoms. Examples include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, a methoxy group, an ethoxy group, a propoxy group and the like. Of these, a methyl group, an ethyl group, a methoxy group, and an ethoxy group are preferable.
R ₃ is preferably a hydrogen atom, a methyl group, or an ethyl group, and more preferably a hydrogen atom or a methyl group.

The compound (A) of the present embodiment is a compound represented by the above chemical formula (1), in which n is an integer of 2 to 10; m is an integer of 3 to 7; R ₁ , R ₂ are independent methoxy groups, ethoxy groups, propoxy groups, or isopropoxy groups, respectively; R ₃ is more preferably a compound having a hydrogen atom methyl group or an ethyl group.
The compound (A) of the present embodiment is a compound represented by the above chemical formula (1), in which n is an integer of 2 to 6; m is an integer of 3 or 4; R ₁ , R ₂ are independently methoxy groups or ethoxy groups; R ₃ is particularly preferably a compound which is a hydrogen atom or a methyl group.

As the compound (A), one type may be used alone, or two or more types may be used in combination.
The content of the lithium salt is preferably 0.5 to 3 times mol, more preferably 0.5 to 2.0 times mol, and 0.8 to 1 times the molar amount of the compound (A). It is more preferably 5.5 times the molar amount. According to such a configuration, the dissociability is improved and the cycle characteristics are improved depending on the selected concentration.

(Effect of compound (A))
Conventionally, in a lithium ion secondary battery (hereinafter, simply referred to as "secondary battery") using a grime-based solvent (solvent containing a grime molecule) as an electrolyte, the cycle characteristics may deteriorate when charging and discharging are repeated. rice field. Therefore, as shown in the chemical formula (3), the cause of the deterioration of the cycle characteristics is that in the grime-lithium salt complex formed of a single grime molecule and a lithium salt, the grime-based solvent is electrically oxidized on the electrode surface and deteriorates. It is considered to be. In the formula "X ^-" represents an anion derived from lithium salt (LiX).

Further, in order to suppress the electrical oxidation, it has been proposed to use a compound having an electron-withdrawing group. For example, when a glyme compound as shown in the chemical formula (4) is used, electrons are attracted from the oxygen atom in the skeleton of the glyme structure by the phosphonate ester structure which is an electron-withdrawing group, so that the HOMO (HOMO) of the oxygen atom is used. Since the highest occupied level) is lowered, the oxidation potential is raised and the oxidation resistance is improved to some extent.
However, due to the strong electron attraction, the coordination ability is lowered due to the decrease in electron density, the dissociation ability of the lithium salt is lowered, and the ionic conductivity is lowered. As a result, the impedance of the battery increases and the overvoltage increases. As a result, the cycle characteristics of the battery deteriorate.

Further, as in the glyme compound represented by the chemical formula (5), the electron-withdrawing effect of the phosphonic acid ester is weak because the bond chain between the phosphonate diester structure which is an electron-withdrawing group and the glyme structure is too long. As a result, the oxidation resistance is inferior and the cycle characteristics are deteriorated.

On the other hand, the compound (A) represented by the above formula (1) according to the present invention (in the formula, n is an integer of 2 to 10, m is an integer of 1 to 10, and R ₁ and R ₂ are independent of each other. It is an alkoxy group having 1 to 6 carbon atoms substituted or unsubstituted, and R ₃ is a hydrogen atom or an alkyl group having 1 to 2 carbon atoms substituted or unsubstituted.) Is represented by, for example, the chemical formula (6). As in the example of the compound (A) shown, by setting the bond chain between the phosphonic acid diester structure, which is an electron-withdrawing group, and the glyme structure to an appropriate length, the electron-withdrawing effect of the phosphonic acid ester can be obtained by the carbon chain. It can be relaxed, prevent deterioration of coordination ability, and achieve both ionic conductivity and oxidation resistance. As a result, a secondary battery using an electrolyte containing such a compound (A) can realize good cycle characteristics at 4.4 V or higher.

(Other solvents)
The electrolyte of the present invention may contain other solvents in addition to the lithium salt and the compound (A) as long as the electrolyte does not undergo phase separation.
Other solvents include, for example, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, di-n-propyl carbonate, methyl-n-propyl carbonate, ethyl-n-propyl carbonate, methyl isopropyl carbonate, ethyl-n-propyl carbonate, and the like. Ethylisopropyl carbonate, di-n-propyl carbonate, diisopropyl carbonate, 3-fluoropropylmethyl carbonate, propylene carbonate, ethylene carbonate, butylene carbonate, 4-chloro-1,3-dioxolan-2-one, 4-fluoro-1, Carbonated esters such as 3-dioxolan-2-one, 4-trifluoromethyl-1,3-dioxolan-2-one, vinylene carbonate, dimethylvinylene carbonate, vinylene carbonate, fluoroethylene carbonate, propionic acid alkyl ester, dialkyl malonate Examples thereof include esters, carboxylic acid esters such as alkyl acetate, cyclic esters such as γ-butyrolactone, cyclic sulfonic acid esters such as propanesarton, sulfonic acid alkyl esters, phosphoric acid alkyl esters, and hydrofluoro ethers.
The content of the other solvent is preferably 10% by volume or less, and more preferably 5% by volume or less, assuming that the total amount of the solvent used for the electrolyte is 100% by volume.

(Other ingredients)
In addition, the electrolyte of the present invention may contain other components as necessary in order to improve its function. Other components include, for example, conventionally known overcharge inhibitors, dehydrating agents, deoxidizers, and property improving aids for improving capacity retention and cycle properties after high temperature storage.

Examples of the overcharge inhibitor include aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, and partially hydrides of terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran; 2-fluoro. Partially fluorinated compounds of the aromatic compounds such as biphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene; fluorine-containing anisole such as 2,4-difluoroanisole, 2,5-difluoroanisole and 2,6-difluoroaniol. Examples include compounds. One type of overcharge inhibitor may be used alone, or two or more types may be used in combination.
When the electrolyte contains an overcharge inhibitor, the content of the overcharge inhibitor in the electrolyte is preferably 0.1 to 5% by mass. By containing 0.1% by mass or more of the overcharge inhibitor in the electrolyte, it becomes easier to suppress the explosion and ignition of the secondary battery due to overcharge, and the secondary battery can be used more stably.

Examples of the dehydrating agent include molecular sieves, glazed glass, magnesium sulfate, calcium hydride, potassium hydride, sodium hydride, lithium aluminum hydride, calcium chloride, sodium metal and the like. As the solvent used for the electrolyte of the present invention, it is preferable to use a solvent that has been dehydrated with the dehydrating agent and then rectified. Further, a solvent obtained by only dehydrating with the dehydrating agent without rectification may be used.

Examples of the property improving aid include carbonate compounds such as fluoroethylene carbonate, trifluoropropylene carbonate, phenylethylene carbonate, erythritan carbonate, and spiro-bis-dimethylene carbonate; succinic anhydride, glutaric anhydride, maleic anhydride, and the like. Caroxyan anhydrides such as citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic acid anhydride, cyclohexanedicarboxylic acid anhydride, cyclopentanetetracarboxylic acid dianhydride, phenylsuccinic anhydride; ethylene sulfite, 1, 3-Propane sulton, 1,4-butane sulton, methyl methanesulfonate, busulfane, sulfolane, sulfone, dimethyl sulfone, diphenyl sulfone, methyl phenyl sulfone, dibutyl disulfide, dicyclohexyl disulfide, tetramethylthium monosulfide, N, N-dimethylmethane Sulfur-containing compounds such as sulfonamide, N, N-diethylmethane sulfonamide; 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxazolidinone, 1,3-dimethyl-2-imidazole Nitrogen-containing compounds such as lydinone and N-methylsucciimide; hydrocarbon compounds such as heptane, octane and cycloheptane, and fluorine-containing aromatic compounds such as fluorobenzene, difluorobenzene, hexafluorobenzene and benzotrifluoride can be mentioned. .. These property improving aids may be used alone or in combination of two or more.
When the electrolyte contains a property improving aid, the content of the property improving aid in the electrolyte is preferably 0.1 to 5% by mass.

^{Further, the electrolyte of the present invention preferably has a conductivity of 0.25 Sm-1} or more from the viewpoint of obtaining a practically sufficient conductivity. The viscosity (20 ° C.) measured by a rotary viscometer is preferably 0.1 to 200 cP.

"Positive electrode"
(Cathode active material layer)
The positive electrode active material layer 24 is mainly composed of a positive electrode active material, a positive electrode binder, and a necessary amount of a positive electrode conductive auxiliary agent.

(Positive electrode active material)
The positive electrode active material 26 used for the positive electrode active material layer 24, occlusion of lithium ions and release, desorption and insertion of lithium ions (intercalation), or counter anions of the lithium ions and the lithium ions (e.g., PF ₆ ^-) An electrode active material capable of reversibly advancing doping and dedoping with the electrode can be used.

For example, lithium cobalt oxide (LiCoO _2), lithium nickel oxide (LiNiO _2), lithium manganese spinel (LiMn ₂ O _4), and the general _{formula: LiNi x Co y Mn z M} a O 2 (x + y + z + a = 1,0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1, 0 ≦ a ≦ 1, M is represented by one or more elements selected from Al, Mg, Nb, Ti, Cu, Zn, and Cr). Composite metal oxide, lithium vanadium compound (LiV ₂ O ₅ ), olivine type LiMPO ₄ (where M is one or more elements selected from Co, Ni, Mn, Fe, Mg, Nb, Ti, Al and Zr). or an VO), lithium titanate _{(Li 4 Ti 5 O 12)} , LiNi x Co y Al z O 2 ( composite metal oxide such as 0.9 <x + y + z < 1.1) can be mentioned.

The composition ratio of the positive electrode active material 26 in the positive electrode active material layer 24 is preferably 80% or more and 90% or less in terms of mass ratio. The composition ratio of the conductive material 28 in the positive electrode active material layer 24 is preferably 0.5% or more and 10% or less in terms of mass ratio, and the composition ratio of the binder in the positive electrode active material layer 24 is 0.5 in terms of mass ratio. It is preferably% or more and 10% or less.

(Positive binder)
The binder binds the active materials to each other and also binds the active material to the positive electrode current collector 22. The binder may be any as long as it is capable of the above-mentioned bonds, for example, polyvinylidene fluoride (PVDF), polyether sulfone (PESU), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (). FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), ethylene-tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), ethylene-chlorotrifluoroethylene copolymer (ECTFE) ), Fluororesin such as polyvinylidene fluoride (PVF).

In addition to the above, as binders, for example, vinylidene fluoride-hexafluoropropylene-based fluororubber (VDF-HFP-based fluororubber), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene-based fluororubber (VDF-HFPTFE-based) Fluororubber), vinylidene fluoride-pentafluoropropylene-based fluorine rubber (VDF-PFP-based fluorine rubber), vinylidene fluoride-pentafluoropropylene-tetrafluoroethylene-based fluorine rubber (VDF-PFP-TFE-based fluorine rubber), vinylidene fluo Vinylidene fluoride-based fluorine such as ride-perfluoromethyl vinyl ether-tetrafluoroethylene-based fluorine rubber (VDF-PFMVE-TFE-based fluorine rubber), vinylidene fluoride-chlorotrifluoroethylene-based fluorine rubber (VDF-CTFE-based fluorine rubber) Rubber may be used.

Further, an electron conductive conductive polymer or an ionic conductive polymer may be used as the binder. Examples of the electron-conducting conductive polymer include polyacetylene and the like. In this case, since the binder also functions as a conductive material, it is not necessary to add the conductive material. Examples of the ionic conductive polymer include those obtained by combining a polymer compound such as polyethylene oxide and polypropylene oxide with a lithium salt or an alkali metal salt mainly composed of lithium.

(Positive current collector)
The positive electrode current collector 22 may be any conductive plate material, and for example, a thin metal plate of aluminum, copper, or nickel foil can be used.

(Conductive aid for positive electrode)
The conductive auxiliary agent for the positive electrode is not particularly limited as long as it improves the conductivity of the positive electrode active material layer 24, and a known conductive auxiliary agent can be used. Examples thereof include carbon-based materials such as graphite and carbon black, metal fine powders such as copper, nickel, stainless steel and iron, and conductive oxides such as ITO.

"Negative electrode"
(Negative electrode active material layer)
The negative electrode has a negative electrode active material layer. The negative electrode active material layer has a negative electrode active material, and further has a negative electrode binder and a conductive auxiliary agent for the negative electrode, if necessary.

(Negative electrode active material)
The negative electrode active material may be any compound that can occlude and release lithium ions, and a known negative electrode active material for a lithium secondary battery can be used. Examples of the negative electrode active material include carbon materials such as metallic lithium, graphite capable of storing and releasing lithium ions (natural graphite, artificial graphite), carbon nanotubes, non-graphitizable carbon, easily graphitized carbon, and low-temperature calcined carbon. Metals that can be combined with lithium such as aluminum, silicon, and tin, SiO _x (0 <x <2), amorphous compounds mainly composed of oxides such as tin dioxide, lithium titanate (Li ₄ Ti ₅₎ Examples _{include particles containing O 12} ) and the like.

(Negative electrode current collector)
The negative electrode current collector 32 may be any conductive plate material, and for example, a thin metal plate of aluminum, copper, or nickel foil can be used.

(Conductive auxiliary agent for negative electrode)
Examples of the conductive auxiliary agent for the negative electrode include carbon powder such as carbon black, carbon nanotubes, carbon material, metal fine powder such as copper, nickel, stainless steel and iron, a mixture of carbon material and metal fine powder, and conductive oxidation of ITO and the like. Things can be mentioned.

(Negative electrode binder)
The binder used for the negative electrode can be the same as that used for the positive electrode. In addition to this, for example, cellulose, styrene / butadiene rubber, ethylene / propylene rubber, polyimide resin, polyamide-imide resin, acrylic resin or the like may be used as the binder.

The contents of the negative electrode active material, the conductive material and the binder in the negative electrode active material layer 34 are not particularly limited. The composition ratio of the negative electrode active material 26 in the negative electrode active material layer 34 is preferably 70% or more and 98% or less in terms of mass ratio. The composition ratio of the conductive material in the negative electrode active material layer 34 is preferably 1% or more and 20% or less in terms of mass ratio, and the composition ratio of the binder in the negative electrode active material layer 34 is 1% or more and 10% or less in terms of mass ratio. Is preferable.

By setting the contents of the negative electrode active material and the binder within the above range, it is possible to suppress the tendency that the amount of the binder in the obtained negative electrode active material layer 34 is too small to form a strong negative electrode active material layer. In addition, the amount of binder that does not contribute to the electric capacity increases, and the tendency that it becomes difficult to obtain a sufficient volumetric energy density can be suppressed.

"Separator"
The separator 10 may be formed of an electrically insulating porous structure, for example, a monolayer of a film made of polyethylene, polypropylene or polyolefin, a laminate or a stretched film of a mixture of the above resins, or cellulose, polyester and Examples thereof include fibrous nonwoven fabrics made of at least one constituent material selected from the group consisting of polypropylene.

"Case"
The case 50 seals the laminate 40 and the electrolyte inside. The case 50 is not particularly limited as long as it can suppress leakage of the electrolyte to the outside and invasion of moisture or the like into the inside of the lithium secondary battery 100 from the outside.

For example, as the case 50, as shown in FIG. 1, a metal laminate film in which a metal foil 52 is coated with a polymer film 54 from both sides can be used. For example, an aluminum foil can be used as the metal foil 52, and a film such as polypropylene can be used as the polymer film 54. For example, the material of the outer polymer film 54 is preferably a polymer having a high melting point, for example, polyethylene terephthalate (PET) or polyamide, and the material of the inner polymer film 54 is polyethylene (PE) or polypropylene (PP). Etc. are preferable.

"Lead"
The leads 60 and 62 are formed of a conductive material such as aluminum. Leads 60 and 62 are welded to the positive electrode current collector 22 and the negative electrode current collector 32, respectively, and the separator 10 is sandwiched between the positive electrode active material layer 24 of the positive electrode 20 and the negative electrode active material layer 34 of the negative electrode 30. It is inserted into the case 50 together with the electrolyte to seal the entrance of the case 50.

[Manufacturing method of secondary battery]
A method for manufacturing the lithium secondary battery 100 according to the present embodiment will be described.

First, the positive electrode active material 26, the binder and the solvent are mixed. If necessary, the conductive material 28 may be further added. As the solvent, for example, water, N-methyl-2-pyrrolidone and the like can be used. The composition ratio of the positive electrode active material 26, the conductive material 28, and the binder is preferably 80 wt% to 98 wt%: 0.1 wt% to 10 wt%: 0.1 wt% to 10 wt% in terms of mass ratio. These mass ratios are adjusted so as to be 100 wt% as a whole.

The method of mixing the components constituting the coating material is not particularly limited, and the mixing order is also not particularly limited. The above paint is applied to the positive electrode current collector 22. The coating method is not particularly limited, and a method usually adopted when producing an electrode can be used. For example, the slit die coat method and the doctor blade method can be mentioned. Similarly, for the negative electrode, a paint is applied on the negative electrode current collector 32.

Subsequently, the solvent in the paint applied on the positive electrode current collector 22 and the negative electrode current collector 32 is removed. The removal method is not particularly limited. For example, the positive electrode current collector 22 and the negative electrode current collector 32 coated with the paint may be dried in an atmosphere of 80 ° C. to 150 ° C.

Then, the electrodes on which the positive electrode active material layer 24 and the negative electrode active material layer 34 are formed in this way are pressed by a roll press device or the like, if necessary. The linear pressure of the roll press varies depending on the material used, but is adjusted so that the density of the positive electrode active material layer 24 becomes a predetermined value. The relationship between the density of the positive electrode active material layer 24 and the linear pressure can be obtained by a preliminary study based on the relationship with the material ratio constituting the positive electrode active material layer 24.

Next, the positive electrode 20 having the positive electrode active material layer 24, the negative electrode 30 having the negative electrode active material layer 34, the separator 10 interposed between the positive electrode and the negative electrode, and the electrolyte are sealed in the case 50.

For example, the positive electrode 20, the negative electrode 30, and the separator 10 are laminated, and the laminated body 40 is placed in a bag-shaped case 50 prepared in advance.

Finally, the electrolyte of the present embodiment is injected into the case 50, and the case 50 is vacuum-sealed to produce a lithium secondary battery. Instead of injecting the electrolyte into the case, the laminate 40 may be impregnated with the electrolyte. Since the positive electrode active material layer 24 is adjusted to a predetermined density, the electrolyte is sufficiently impregnated into the voids K formed in the positive electrode active material layer 24.

Although the embodiments of the present invention have been described in detail with reference to the drawings, the configurations and combinations thereof in the respective embodiments are examples, and the configurations are added or omitted within the range not deviating from the gist of the present invention. , Replacement, and other changes are possible.

According to the procedure shown below, the electrolytes for the secondary batteries of Examples 1 to 60 and Comparative Examples 1 to 6 were prepared, and the secondary batteries using the electrolytes were prepared. The charging cycle was evaluated.
The compounds used in Examples 1 to 60 are shown in Tables 1 to 3 and 5. Specifically, as the compound (A) represented by the chemical formula (1), the compound No. And, the structural formulas corresponding to _{n, m, R 1} , R ₂ and R ₃ of the chemical formula (1) are described.

(In the formula, n is an integer of 2 to 10, m is an integer of 1 to 10, R ₁ and R ₂ are independently alkoxy groups having 1 to 4 carbon atoms, and R ₃ is hydrogen. Atom, methyl group, ethyl group.)

The compounds used in Comparative Examples 1 to 3 are shown in Table 4. Specifically, as the compound (A') represented by the chemical formula (1), the compound No. And, the structural formulas corresponding to _{n, m, R 1} , R ₂ and R ₃ of the chemical formula (1) are described.

（式中、ｎは１、１５の整数であり、ｍは３の整数であり、Ｒ_１、Ｒ_２は、それぞれ独立してメトキシ基、エトキシ基であり、Ｒ_３はメチル基である。）

(In the formula, n is an integer of 1 and 15, m is an integer of 3, R ₁ and R ₂ are independently methoxy groups and ethoxy groups, and R ₃ is a methyl group.)

"Synthesis of compound (A)"
(Synthesis Example 1)
Compound No. The synthesis method of 1 is shown below.

(Synthesis Examples 2-30, 32-45)
Compound No. Compound No. 1 was used in the same manner as in 1. 2 to 30, 32 to 45 were synthesized. The respective structures are shown in Tables 1 to 4.

(Synthesis Example 31)
Compound No. The synthesis method of 31 is shown below.

"Evaluation method of cycle characteristics of secondary battery"
The cycle characteristics of the secondary battery are evaluated by the method shown below.
A _{single-pole cell sheet-shaped secondary battery made of LiCoO 2} positive electrode-lithium metal foil is sandwiched between glass plates to improve the adhesion between the electrodes, and at 25 ° C., at a constant current equivalent to 0.1C. The secondary battery is stabilized by performing 5 cycles of charging to 4.4 V and discharging to 3 V with a constant current corresponding to 0.1 C. After the 5th cycle, it is charged to 4.4V with a constant current of 0.2C, further charged with a constant voltage of 4.4V until the current value reaches 0.02C, and up to 3V with a constant current of 0.2C. The discharge cycle is repeated, and the maintenance rate of the discharge capacity in the 80th cycle with respect to the first discharge capacity is used as the evaluation result.
However, 1C represents a current value for discharging the reference capacity of the battery in 1 hour, and 0.2C represents a current value of 1/5 of that.
Further, the same cycle characteristics as described above are evaluated under the condition that the charging voltage is changed from 4.4V to 4.5V.

"Preparation and evaluation of secondary battery electrolytes and secondary batteries for evaluation"
(Example 1)
<Preparation of electrolyte>
Compound No. _{1 and LiN (SO 2} CF ₃ ) ₂ which is a lithium salt were mixed at a molar ratio of 1: 1 to prepare an electrolyte.

<Preparation of electrodes>
_{LiCoO 2} (manufactured by AGC Seimi Chemical Co., Ltd., trade name "Selion C") as the positive electrode active material, carbon black (manufactured by Denki Kagaku Kogyo Co., Ltd., trade name "Denka Black") as the positive electrode conductive auxiliary material, and polyvinylidene fluoride as the binder. Got ready. These were mixed, and N-methyl-2-pyrrolidone as a solvent was added to form a slurry, and the slurry was uniformly applied onto a positive electrode current collector made of an aluminum foil having a thickness of 20 μm. The mass ratio of the positive electrode active material, the conductive material, and the binder was 95: 2: 3. After coating, the solvent was removed. Then, a positive electrode sheet was prepared by pressing so that the density of the positive electrode active material layer was 3.0 g / cm ^3.
Metallic lithium was used as the negative electrode active material, and a metal lithium foil having a thickness of 100 μm was attached onto a negative electrode current collector made of copper foil to prepare a negative electrode sheet.

<Manufacturing of lithium-ion secondary battery for evaluation>
A separator made of a polyethylene microporous film is sandwiched between the positive electrode and the negative electrode prepared above, and a separator made of a polyethylene microporous film is sandwiched between them, and the case is filled with the electrolyte prepared above, vacuum-sealed, and lithium ions for evaluation. A secondary battery was manufactured.
<Evaluation of cycle characteristics of secondary batteries>
Using the above-mentioned evaluation method, the cycle characteristics were evaluated under the conditions where the charging voltages were 4.4V and 4.5V. The results of each evaluation are shown in Table 1.

(Examples 2-42)
Compound No. obtained in Synthesis Examples 2-42. The electrolytes of Examples 2 to 42 were prepared in the same manner as in Example 1 except that 2 to 42 were used, respectively, and a lithium ion secondary battery for evaluation was prepared.
The obtained lithium ion secondary battery was evaluated in the same manner as in Example 1. The results of each are shown in Tables 1 to 3.

(Example 43)
Compound No. obtained in Synthesis Example 1 No. 1 was used, and compound No. 1 was used. The mixing molar ratio of _{1 and LiN (SO 2} CF ₃ ) ₂ , which is a lithium salt, is the compound No. An electrolyte was prepared in the same manner as in Example 1 except that the amount of the lithium salt was 0.45 mol times that of 1, and a lithium ion secondary battery for evaluation was prepared.
The obtained lithium ion secondary battery was evaluated in the same manner as in Example 1. The results of each are shown in Table 3.

(Example 44)
Compound No. obtained in Synthesis Example 1 No. 1 was used, and compound No. 1 was used. The mixing molar ratio of _{1 and LiN (SO 2} CF ₃ ) ₂ , which is a lithium salt, is the compound No. An electrolyte was prepared in the same manner as in Example 1 except that the amount of the lithium salt was 0.50 mol times that of 1, and a lithium ion secondary battery for evaluation was prepared.
The obtained lithium ion secondary battery was evaluated in the same manner as in Example 1. The results of each are shown in Table 3.

(Example 45)
Compound No. obtained in Synthesis Example 1 No. 1 was used, and compound No. 1 was used. The mixing molar ratio of _{1 and LiN (SO 2} CF ₃ ) ₂ , which is a lithium salt, is the compound No. An electrolyte was prepared in the same manner as in Example 1 except that the lithium salt was 2.00 mol times with respect to 1, and a lithium ion secondary battery for evaluation was prepared.
The obtained lithium ion secondary battery was evaluated in the same manner as in Example 1. The results of each are shown in Table 3.

(Example 46)
Compound No. obtained in Synthesis Example 1 No. 1 was used, and compound No. 1 was used. The mixing molar ratio of _{1 and LiN (SO 2} CF ₃ ) ₂ , which is a lithium salt, is the compound No. An electrolyte was prepared in the same manner as in Example 1 except that the amount of the lithium salt was 3.00 mol times relative to 1, and a lithium ion secondary battery for evaluation was prepared.
The obtained lithium ion secondary battery was evaluated in the same manner as in Example 1. The results of each are shown in Table 3.

(Example 47)
Compound No. obtained in Synthesis Example 1 No. 1 was used, and compound No. 1 was used. The mixing molar ratio of _{1 and LiN (SO 2} CF ₃ ) ₂ , which is a lithium salt, is the compound No. An electrolyte was prepared in the same manner as in Example 1 except that the amount of the lithium salt was 3.50 mol times relative to 1, and a lithium ion secondary battery for evaluation was prepared.
The obtained lithium ion secondary battery was evaluated in the same manner as in Example 1. The results of each are shown in Table 3.

(Comparative Examples 1 to 3)
Compound No. An electrolyte was prepared and a lithium ion secondary battery for evaluation was prepared in the same manner as in Example 1 except that 43 to 45 were used respectively.
The obtained lithium ion secondary battery was evaluated in the same manner as in Example 1. The results of each are shown in Table 4.

(Comparative Examples 4 to 6)
Compound Nos. Represented by the following chemical formulas (9) to (11), respectively. An electrolyte was prepared and a lithium ion secondary battery for evaluation was prepared in the same manner as in Example 1 except that 46 to 48 were used respectively.
The obtained lithium ion secondary battery was evaluated in the same manner as in Example 1. The results of each are shown in Table 4.

(Examples 48 to 55)
Compound No. obtained in Synthesis Example 1 An electrolyte was prepared in the same manner as in Example 1 except that the lithium salt shown in Table 5 was used as the lithium salt to be mixed with 1, and a lithium ion secondary battery for evaluation was prepared.
The obtained lithium ion secondary battery was evaluated in the same manner as in Example 1. The results of each are shown in Table 5.

(Examples 56 to 60)
A lithium ion secondary battery for evaluation was produced in the same manner as in Example 1 except that the positive electrode active material shown in Table 5 was used.
The obtained lithium ion secondary battery was evaluated in the same manner as in Example 1. The results of each are shown in Table 5.

Tables 1 to 5 summarize the evaluation results of the cycle characteristics of the secondary batteries of Examples 1 to 60 and Comparative Examples 1 to 6.
As shown in Tables 1 to 5, the secondary batteries of Examples 1 to 60 provided with the electrolyte containing the compound (A) of the present invention were compared with Comparative Example 1 under all conditions of charging voltages of 4.4 V and 4.5 V. It has better cycle characteristics than the secondary batteries of ~ 6.

Note 1: Compound No. represented by the above chemical formula (9). 46
Note 2: Compound No. represented by the above chemical formula (10). 47
Note 3: Compound No. represented by the above chemical formula (11). 48

10 ... Separator, 20 ... Positive electrode, 22 ... Positive electrode current collector, 24 ... Positive electrode active material layer, 30 ... Negative electrode, 32 ... Negative electrode current collector, 34 ... Negative electrode active material layer, 40 ... Laminated body, 50 ... Case, 60 , 62 ... Reed, 100 ... Lithium secondary battery

Claims (3)

An electrolyte for a secondary battery, which contains a lithium salt and a compound (A) represented by the chemical formula (1).

(In the formula, n is an integer of 2 to 10, m is an integer of 1 to 10, and R ₁ and R ₂ are independently substituted or unsubstituted alkoxy groups having 1 to 6 carbon atoms. , R ₃ is a hydrogen atom or a substituted or unsubstituted alkyl group having 1 to 2 carbon atoms.) The electrolyte for a secondary battery according to claim 1, wherein the content of the lithium salt is 0.5 to 3 times the molar amount of the compound (A). A secondary battery having the electrolyte for a secondary battery according to claim 1 or 2.

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