JP7351442B2 - Non-aqueous electrolytes for batteries and lithium secondary batteries - Google Patents

Description

The present disclosure relates to a non-aqueous electrolyte for batteries and a lithium secondary battery.

Conventionally, various studies have been made regarding nonaqueous electrolytes for batteries used in batteries such as lithium secondary batteries.
For example, Patent Document 1 describes an electrolytic solution for a lithium secondary battery that includes a lithium salt and a non-aqueous solvent as an electrolytic solution for a lithium secondary battery that exhibits excellent output and life characteristics. An electrolytic solution for a lithium secondary battery is disclosed, which is characterized in that 0.1 to 20% by weight is added to the electrolytic solution based on the total weight of the electrolytic solution. Patent Document 1 discloses that the silane-based material is selected from the group consisting of trimethoxysilylpropylaniline (TMSPA), tetramethylorthosilicate, tetraethylorthosilicate, tetrapropylorthosilicate, tetrabutylorthosilicate, and mixtures thereof. It is also disclosed that any one of the above is preferred.

Special table 2015-534707 publication

However, there are cases where it is required to further reduce battery resistance.
An object of one aspect of the present disclosure is to provide a non-aqueous electrolyte for batteries that can reduce battery resistance.
Another object of the present disclosure is to provide a lithium secondary battery with reduced battery resistance.

Means for solving the above problems include the following aspects.
<1> A nonaqueous electrolyte for batteries containing a compound represented by the following formula (1).

In formula (1),
R ¹ to R ⁹ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or a phenyl group,
R ¹⁰ represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, a phenyl group, or a group represented by formula (S1).
In formula (S1),
R ¹¹ to R ¹³ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or a phenyl group,
L ¹ represents a single bond or an oxygen atom,
* represents the bonding position.

<2> The non-aqueous electrolyte for batteries according to <1>, wherein the content of the compound represented by formula (1) is 0.001% by mass to 10% by mass based on the total amount of the non-aqueous electrolyte. .
<3> The nonaqueous electrolyte for a battery according to <1> or <2>, further containing a compound represented by the following formula (2).

In formula (2), R ²¹ and R ²² each independently represent a hydrogen atom, a fluorine atom, a hydrocarbon group having 1 to 6 carbon atoms, or a fluorinated hydrocarbon group having 1 to 6 carbon atoms.

<4> The non-aqueous electrolyte for batteries according to <3>, wherein the content of the compound represented by formula (2) is 0.001% by mass to 10% by mass based on the total amount of the non-aqueous electrolyte. .

<5> A positive electrode,
Metallic lithium, lithium-containing alloys, metals or alloys that can be alloyed with lithium, oxides that can be doped and dedoped with lithium ions, transition metal nitrides that can be doped and dedoped with lithium ions, and lithium. a negative electrode containing as a negative electrode active material at least one member selected from the group consisting of carbon materials capable of doping and dedoping ions;
The nonaqueous electrolyte for batteries according to any one of <1> to <4>,
Lithium secondary batteries including.
<6> A lithium secondary battery obtained by charging and discharging the lithium secondary battery according to <5>.

According to one aspect of the present disclosure, a nonaqueous electrolyte for batteries that can reduce battery resistance is provided.
According to another aspect of the present disclosure, a lithium secondary battery with reduced battery resistance is provided.

1 is a schematic perspective view showing an example of a laminate type battery, which is an example of a lithium secondary battery of the present disclosure. 2 is a schematic cross-sectional view in the thickness direction of a laminated electrode body housed in the laminated battery shown in FIG. 1. FIG. FIG. 2 is a schematic cross-sectional view showing an example of a coin-type battery, which is another example of the lithium secondary battery of the present disclosure.

In this specification, a numerical range expressed using "~" means a range that includes the numerical values written before and after "~" as lower and upper limits.
In this specification, if there are multiple substances corresponding to each component in the composition, unless otherwise specified, the amount of each component in the composition refers to the total amount of the multiple substances present in the composition. means.

[Non-aqueous electrolyte for batteries]
The non-aqueous electrolyte for batteries (hereinafter also simply referred to as "non-aqueous electrolyte") of the present disclosure contains a compound represented by the following formula (1).
According to the non-aqueous electrolyte of the present disclosure, battery resistance, particularly positive electrode resistance, can be reduced.
Although the reason for this effect is not clear, by incorporating the compound represented by the following formula (1) into the non-aqueous electrolyte, the increase in decomposed products of the non-aqueous electrolyte on the positive electrode is suppressed, This is thought to be because the increase in resistance can be suppressed.

<Compound represented by formula (1)>

In formula (1),
R ¹ to R ⁹ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or a phenyl group,
R ¹⁰ represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, a phenyl group, or a group represented by formula (S1).
In formula (S1),
R ¹¹ to R ¹³ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or a phenyl group,
L ¹ represents a single bond or an oxygen atom,
* represents the bonding position.

In formula (1), the alkyl group having 1 to 6 carbon atoms represented by R ¹ to R ¹³ is more preferably an alkyl group having 1 to 3 carbon atoms, even more preferably a methyl group or an ethyl group, and a methyl group is more preferable. More preferred.

In formula (1), the alkenyl group having 2 to 6 carbon atoms represented by R ¹ to R ¹³ is preferably an alkenyl group having 2 or 3 carbon atoms, and more preferably a vinyl group or an allyl group.

In formula (S1), L ¹ represents a single bond or an oxygen atom (in other words, an ether bond (-O-)).
In the group represented by formula (S1), an embodiment in which L ¹ is a single bond is a group represented by the following formula (S1A), and an embodiment in which L ¹ is an oxygen atom is in the following formula (S1B). is the group represented.

R ¹¹ to R ¹³ in formula (S1A) have the same meanings as R 11 to R 13 in formula (S1), respectively, and R ¹¹ to R ¹³ in formula (S1B) each have the same meaning as R ¹¹ to R ¹³ in formula (S1). It has the same meaning as R ¹¹ to R ¹³ in the above.

L ¹ in formula (S1) is preferably a single bond. That is, the group represented by formula (S1) is preferably a group represented by formula (S1A).

Specific examples of the compound represented by formula (1) will be shown below, but the compound represented by formula (1) is not limited to the following specific examples.

The content of the compound represented by formula (1) is preferably 0.001% by mass to 10% by mass, more preferably 0.01% by mass to 5% by mass, based on the total amount of the nonaqueous electrolyte. The content is preferably 0.1% by mass to 2% by mass, and even more preferably 0.1% by mass to 0.6% by mass.

<Compound represented by formula (2)>
The non-aqueous electrolyte of the present disclosure preferably contains a compound represented by the following formula (2).

In formula (2), R ²¹ and R ²² each independently represent a hydrogen atom, a fluorine atom, a hydrocarbon group having 1 to 6 carbon atoms, or a fluorinated hydrocarbon group having 1 to 6 carbon atoms.

In formula (2), the hydrocarbon group having 1 to 6 carbon atoms represented by R ²¹ or R ²² may be a straight chain hydrocarbon group, or a hydrocarbon group having a branched and/or ring structure. It may be.
The hydrocarbon group having 1 to 6 carbon atoms represented by R ²¹ or R ²² is preferably an alkyl group or an aryl group, and more preferably an alkyl group.

In formula (2), the fluorinated hydrocarbon group having 1 to 6 carbon atoms represented by R ²¹ or R ²² may be a linear fluorinated hydrocarbon group, or may have a branched and/or ring structure. It may also be a fluorinated hydrocarbon group.
The fluorinated hydrocarbon group having 1 to 6 carbon atoms represented by R ²¹ or R ²² is preferably a fluorinated alkyl group or a fluorinated aryl group, and more preferably a fluorinated alkyl group.

In formula (2), the number of carbon atoms in the fluorinated hydrocarbon group having 1 to 6 carbon atoms represented by R ²¹ or R ²² is more preferably 1 to 3, still more preferably 1 or 2, and particularly preferably 1. .

Specific examples of the compound represented by formula (2) include compounds represented by the following formulas (2-1) to (2-11) (hereinafter, compound (2-1) to compound (2), respectively). -11)), but the compound represented by formula (2) is not limited to these specific examples.
Among these, compound (2-1) (vinylene carbonate) is particularly preferred.

When the non-aqueous electrolyte of the present disclosure contains the compound represented by formula (2), the content of the compound represented by formula (2) with respect to the total amount of the non-aqueous electrolyte is 0.001% by mass to The content is preferably 10% by weight, more preferably 0.005% by weight to 5% by weight, even more preferably 0.01% to 5% by weight, and particularly preferably 0.1% to 3% by weight.

When the nonaqueous electrolyte of the present disclosure contains a compound represented by formula (2), the ratio of the mass content of the compound represented by formula (2) to the mass content of the compound represented by formula (1) ( Hereinafter, the content mass ratio [compound represented by formula (2)/compound represented by formula (1)] is preferably 0.1 to 10, more preferably 0.2 to 10. 5, more preferably 0.3 to 3, still more preferably 0.5 to 2.

<Other additives>
The non-aqueous electrolyte of the present disclosure may contain at least one other additive other than the compound represented by the above formula (1) and the compound represented by the above formula (2).
Other additives include known additives that can be contained in the non-aqueous electrolyte.
Other additives include, for example,
Oxalato compounds such as lithium difluorobis(oxalato)phosphate, lithium tetrafluoro(oxalato)phosphate, lithium tris(oxalato)phosphate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate;
1,3-propanesultone, 1,4-butanesultone, 1,3-propenesultone, 1-methyl-1,3-propenesultone, 2-methyl-1,3-propenesultone, 3-methyl-1,3- Sultone compounds such as propene sultone;
Catechol sulfate, 1,2-cyclohexyl sulfate, 2,2-dioxo-1,3,2-dioxathiolane, 4-methyl-2,2-dioxo-1,3,2-dioxathiolane, 4-ethyl-2,2- Dioxo-1,3,2-dioxathiolane, 4-propyl-2,2-dioxo-1,3,2-dioxathiolane, 4-butyl-2,2-dioxo-1,3,2-dioxathiolane, 4-pentyl- 2,2-dioxo-1,3,2-dioxathiolane, 4-hexyl-2,2-dioxo-1,3,2-dioxathiolane,
4-Methylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, 4-ethylsulfonyloxymethyl-2,2-dioxo-1,3,2-dioxathiolane, bis((2,2-dioxo Cyclic sulfate ester compounds such as -1,3,2-dioxathiolan-4-yl)methyl) sulfate and 4,4'-bis(2,2-dioxo-1,3,2-dioxathiolane);
etc.

In addition, other additives include:
Sulfur compounds such as ethylene sulfite, propylene sulfite, ethylene sulfate, propylene sulfate, butene sulfate, hexene sulfate, vinylene sulfate, 3-sulfolene, divinyl sulfone, dimethyl sulfate, diethyl sulfate; dimethyl vinyl boronate, diethyl vinyl boronate, dipropyl vinyl boronate , vinyl boronic acid compounds such as dibutyl vinyl boronate;
Amides such as dimethylformamide;
Chain carbamates such as methyl-N,N-dimethyl carbamate;
Cyclic amides such as N-methylpyrrolidone;
Cyclic ureas such as N,N-dimethylimidazolidinone;
Boric acid esters such as trimethyl borate, triethyl borate, tributyl borate, trioctyl borate, tri(trimethylsilyl) borate;
Phosphate esters such as lithium difluorophosphate, lithium monofluorophosphate, trimethyl phosphate, triethyl phosphate, tributyl phosphate, trioctyl phosphate, tri(trimethylsilyl) phosphate, triphenyl phosphate;
Ethylene glycol derivatives such as ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, polyethylene glycol dimethyl ether;
Aromatic hydrocarbons such as biphenyl, fluorobiphenyl, o-terphenyl, toluene, ethylbenzene, fluorobenzene, cyclohexylbenzene, 2-fluoroanisole, 4-fluoroanisole;
Carboxylic acid anhydrides having carbon-carbon unsaturated bonds, such as maleic anhydride and norbornenedicarboxylic anhydride;
etc. can also be mentioned.

Next, other components of the non-aqueous electrolyte will be explained. A non-aqueous electrolyte generally contains an electrolyte and a non-aqueous solvent.

<Electrolyte>
The electrolyte in the non-aqueous electrolyte of the present disclosure preferably contains a lithium salt, and more preferably contains _LiPF6 .
When the electrolyte contains LiPF ₆ , the proportion of LiPF ₆ in the electrolyte is preferably 10% by mass to 100% by mass, more preferably 50% by mass to 100% by mass, even more preferably 70% by mass to 100% by mass. be.

The concentration of electrolyte in the non-aqueous electrolyte of the present disclosure is preferably 0.1 mol/L to 3 mol/L, more preferably 0.5 mol/L to 2 mol/L.
Further, the concentration of LiPF ₆ in the non-aqueous electrolyte of the present disclosure is preferably 0.1 mol/L to 3 mol/L, more preferably 0.5 mol/L to 2 mol/L.

When the electrolyte contains LiPF ₆ , the electrolyte may contain compounds other than LiPF ₆ .
As compounds other than LiPF ₆ ;
( _{C2H5 ) 4NPF6 , ( C2H5 ) 4NBF4 , ( C2H5 ) 4NClO4 ,} (C2H5 _{) 4NAsF6 , ( C2H5} ) _{4N2SiF 6} , (C ₂ H ₅ ) ₄ NOSO ₂ C _k F _(2k+1) (k=integer from 1 to 8), (C ₂ H ₅ ) ₄ NPF _n [C _k F _(2k+1) ] _(6-n) ( tetraalkylammonium salts such as n = integer of 1 to 5, k = integer of 1 to 8);
LiBF ₄ , LiClO ₄ , LiAsF ₆ , Li ₂ SiF ₆ , LiOSO ₂ C _k F _(2k+1) (k=integer from 1 to 8), LiPF _n [C _k F _(2k+1) ] _(6-n) (n= 1 to 5, k=an integer of 1 to 8), LiC (SO ₂ R ^7X ) (SO ₂ R ^8X ) (SO ₂ R ^9X ), LiN (SO ₂ OR ^10X ) (SO ₂ OR ^11X ), LiN (SO ₂ R ^12X ) (SO ₂ R ^13X ) (where R ^7X to R ^13X may be the same or different and are a fluorine atom or a perfluoroalkyl group having 1 to 8 carbon atoms) , lithium salt other than LiPF ₆ );
etc.

<Non-aqueous solvent>
The number of nonaqueous solvents in the nonaqueous electrolyte of the present disclosure may be one, or two or more.
As the non-aqueous solvent, various known ones can be appropriately selected.
As the nonaqueous solvent, for example, the nonaqueous solvents described in paragraphs 0069 to 0087 of JP 2017-45723A can be used.

Preferably, the nonaqueous solvent contains a cyclic carbonate compound and a chain carbonate compound.
In this case, the number of cyclic carbonate compounds and chain carbonate compounds contained in the nonaqueous solvent may be one, or two or more.

Examples of the cyclic carbonate compound include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, and 2,3-pentylene carbonate.
Among these, ethylene carbonate and propylene carbonate, which have a high dielectric constant, are preferred. In the case of a battery using a negative electrode active material containing graphite, the nonaqueous solvent more preferably contains ethylene carbonate.

Examples of chain carbonate compounds include dimethyl carbonate, methylethyl carbonate, diethyl carbonate, methylpropyl carbonate, methylisopropyl carbonate, ethylpropyl carbonate, dipropyl carbonate, methylbutyl carbonate, ethylbutyl carbonate, dibutyl carbonate, methylpentyl carbonate, and ethylpentyl. carbonate, dipentyl carbonate, methylheptyl carbonate, ethylheptyl carbonate, diheptyl carbonate, methylhexyl carbonate, ethylhexyl carbonate, dihexyl carbonate, methyloctyl carbonate, ethyl octyl carbonate, dioctyl carbonate, and the like.

Examples of combinations of cyclic carbonate and linear carbonate include ethylene carbonate and dimethyl carbonate, ethylene carbonate and methyl ethyl carbonate, ethylene carbonate and diethyl carbonate, propylene carbonate and dimethyl carbonate, propylene carbonate and methyl ethyl carbonate, propylene carbonate and Diethyl carbonate, ethylene carbonate and propylene carbonate and methyl ethyl carbonate, ethylene carbonate and propylene carbonate and diethyl carbonate, ethylene carbonate and dimethyl carbonate and methyl ethyl carbonate, ethylene carbonate and dimethyl carbonate and diethyl carbonate, ethylene carbonate and methyl ethyl carbonate and diethyl carbonate , ethylene carbonate and dimethyl carbonate and methyl ethyl carbonate and diethyl carbonate, ethylene carbonate and propylene carbonate and dimethyl carbonate and methyl ethyl carbonate, ethylene carbonate and propylene carbonate and dimethyl carbonate and diethyl carbonate, ethylene carbonate and propylene carbonate and methyl ethyl carbonate and diethyl carbonate, ethylene carbonate, propylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, and the like.

The mixing ratio of the cyclic carbonate compound and the chain carbonate compound, expressed as a mass ratio, is, for example, 5:95 to 80:20, preferably 10:90 to 70:30, more preferably 10:90 to 70:30. is from 15:85 to 55:45. By setting such a ratio, it is possible to suppress the increase in viscosity of the non-aqueous electrolyte and increase the degree of dissociation of the electrolyte, thereby increasing the conductivity of the non-aqueous electrolyte, which is related to the charging and discharging characteristics of the battery. . Furthermore, the solubility of the electrolyte can be further increased. Therefore, a non-aqueous electrolyte having excellent electrical conductivity at room temperature or low temperature can be obtained, so that the load characteristics of the battery at room temperature or low temperature can be improved.

The non-aqueous solvent may contain other compounds than the cyclic carbonate compound and the chain carbonate compound.
In this case, the number of other compounds contained in the nonaqueous solvent may be one, or two or more.
Other compounds include cyclic carboxylic acid ester compounds (e.g. γ-butyrolactone), cyclic sulfone compounds, cyclic ether compounds, chain carboxylic acid ester compounds, chain ether compounds, chain phosphate ester compounds, amide compounds, and chain carbamates. compounds, cyclic amide compounds, cyclic urea compounds, boron compounds, polyethylene glycol derivatives, and the like.
Regarding these compounds, the descriptions in paragraphs 0069 to 0087 of JP 2017-45723 A can be appropriately referred to.

The proportion of the cyclic carbonate compound and the chain carbonate compound in the nonaqueous solvent is preferably 80% by mass or more, more preferably 90% by mass or more, and still more preferably 95% by mass or more.
The proportion of the cyclic carbonate compound and the chain carbonate compound in the nonaqueous solvent may be 100% by mass.

The proportion of the nonaqueous solvent in the nonaqueous electrolyte is preferably 60% by mass or more, more preferably 70% by mass or more.
The upper limit of the proportion of the nonaqueous solvent in the nonaqueous electrolyte depends on the content of other components (electrolytes, additives, etc.), but the upper limit is, for example, 99% by mass, preferably 97% by mass. The content is more preferably 90% by mass.

[Lithium secondary battery]
A lithium secondary battery of the present disclosure includes a positive electrode, a negative electrode, and a nonaqueous electrolyte of the present disclosure.

<Negative electrode>
The negative electrode may include a negative electrode active material and a negative electrode current collector.
The negative electrode active materials in the negative electrode include metallic lithium, lithium-containing alloys, metals or alloys that can be alloyed with lithium, oxides that can dope and dedope lithium ions, and oxides that can dope and dedope lithium ions. At least one member selected from the group consisting of a transition metal nitride and a carbon material capable of doping and dedoping lithium ions (it may be used alone or a mixture containing two or more of these may be used) good) can be used.
Examples of metals or alloys that can be alloyed with lithium (or lithium ions) include silicon, silicon alloys, tin, and tin alloys.
Examples of oxides that can be doped and dedoped with lithium ions include lithium titanate, silicon oxide (preferably SiOx (X represents 0.5 or more and less than 1.6), more preferably SiO), etc. I can do it.
Among these, carbon materials that can be doped and dedoped with lithium ions are preferred. Examples of such carbon materials include carbon black, activated carbon, graphite materials (artificial graphite, natural graphite), amorphous carbon materials, and the like. The carbon material may be in any of fibrous, spherical, potato-like, and flake-like forms.

Specific examples of the amorphous carbon material include hard carbon, coke, mesocarbon microbeads (MCMB) fired at 1500° C. or lower, and mesophase pitch carbon fiber (MCF).
Examples of the graphite material include natural graphite and artificial graphite. As the artificial graphite, graphitized MCMB, graphitized MCF, etc. are used. Further, as the graphite material, one containing boron can also be used. Further, as the graphite material, those coated with metals such as gold, platinum, silver, copper, and tin, those coated with amorphous carbon, and those coated with a mixture of amorphous carbon and graphite can also be used.

These carbon materials may be used alone or in combination of two or more.
The above-mentioned carbon material is particularly preferably a carbon material in which the interplanar spacing d(002) of the (002) plane measured by X-ray analysis is 0.340 nm or less. Further, as the carbon material, graphite having a true density of 1.70 g/cm ³ or more or a highly crystalline carbon material having properties similar to graphite is also preferable. By using carbon materials such as those described above, it is possible to further increase the energy density of the battery.

The material of the negative electrode current collector in the negative electrode is not particularly limited, and any known material can be used.
Specific examples of the negative electrode current collector include metal materials such as copper, nickel, stainless steel, and nickel-plated steel. Among these, copper is particularly preferred from the viewpoint of ease of processing.

<Positive electrode>
The positive electrode may include a positive electrode active material and a positive electrode current collector.
As the positive electrode active material in the positive electrode, transition metal oxides or transition metal sulfides such as MoS ₂ , TiS ₂ , MnO ₂ , V ₂ O ₅ , LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNi _X Co _{( 1 -X) O 2} [0 _< ≦(1+α)/(1-α)≦1.6), LiNi _x Co _y Mn _z O ₂ [x+y+z=1, 0<x<1, 0<y<1, 0<z<1] (for example, Composite oxides made of lithium and transition metals such as LiNi _0.33 Co _0.33 Mn _0.33 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ etc.), LiFePO ₄ and LiMnPO ₄ ; Examples include conductive polymer materials such as polyaniline, polythiophene, polypyrrole, polyacetylene, polyacene, dimercaptothiadiazole, and polyaniline composites. Among these, a composite oxide consisting of lithium and a transition metal is particularly preferred. When the negative electrode is lithium metal or lithium alloy, a carbon material can also be used as the positive electrode. Moreover, a mixture of a composite oxide of lithium and a transition metal and a carbon material can also be used as the positive electrode.
One type of positive electrode active material may be used, or two or more types may be used in combination. If the positive electrode active material has insufficient electrical conductivity, it can be used together with a conductive additive to form a positive electrode. Examples of the conductive aid include carbon materials such as carbon black, amorphous whiskers, and graphite.

The material of the positive electrode current collector in the positive electrode is not particularly limited, and any known material can be used.
Specific examples of the positive electrode current collector include metal materials such as aluminum, aluminum alloy, stainless steel, nickel, titanium, and tantalum; carbon materials such as carbon cloth and carbon paper; and the like.

<Separator>
The lithium secondary battery of the present disclosure preferably includes a separator between the negative electrode and the positive electrode.
The separator is a membrane that electrically insulates the positive electrode and the negative electrode and transmits lithium ions, and examples thereof include a porous membrane and a polymer electrolyte.
A microporous polymer film is preferably used as the porous membrane, and examples of the material include polyolefin, polyimide, polyvinylidene fluoride, and polyester.
Particularly preferred are porous polyolefins, and specific examples include porous polyethylene films, porous polypropylene films, and multilayer films of porous polyethylene films and polypropylene films. Other resins having excellent thermal stability may be coated on the porous polyolefin film.
Examples of the polymer electrolyte include a polymer in which a lithium salt is dissolved, a polymer swollen with an electrolytic solution, and the like.
The non-aqueous electrolyte of the present disclosure may be used for the purpose of swelling a polymer to obtain a polymer electrolyte.

<Battery configuration>
The lithium secondary battery of the present disclosure can take various known shapes, such as a cylindrical shape, a coin shape, a square shape, a laminate shape, a film shape, and other arbitrary shapes. However, the basic structure of a battery is the same regardless of its shape, and the design can be changed depending on the purpose.

An example of the lithium secondary battery of the present disclosure is a laminate type battery.
FIG. 1 is a schematic perspective view showing an example of a laminated battery that is an example of a lithium secondary battery of the present disclosure, and FIG. 2 is a diagram showing the thickness of a laminated electrode body accommodated in the laminated battery shown in FIG. It is a schematic cross-sectional view of the direction.
The laminated battery shown in FIG. 1 contains a non-aqueous electrolyte (not shown in FIG. 1) and a laminated electrode body (not shown in FIG. 1), and has a sealed peripheral edge. The device includes a laminate exterior body 1 whose interior is hermetically sealed. As the laminate exterior body 1, for example, a laminate exterior body made of aluminum is used.
As shown in FIG. 2, the laminated electrode body housed in the laminate exterior body 1 includes a laminated body in which positive electrode plates 5 and negative electrode plates 6 are alternately laminated with separators 7 in between, and a laminated body of this laminated body. A separator 8 surrounding the periphery is provided. The positive electrode plate 5, the negative electrode plate 6, the separator 7, and the separator 8 are impregnated with the nonaqueous electrolyte of the present disclosure.
Each of the plurality of positive electrode plates 5 in the laminated electrode body is electrically connected to the positive electrode terminal 2 via a positive electrode tab (not shown), and a part of the positive electrode terminal 2 is connected to the laminate exterior body 1. It protrudes outward from the peripheral edge (Figure 1). A portion of the peripheral end of the laminate exterior body 1 from which the positive electrode terminal 2 protrudes is sealed with an insulating seal 4.
Similarly, each of the plurality of negative electrode plates 6 in the laminated electrode body is electrically connected to the negative electrode terminal 3 via a negative electrode tab (not shown), and a part of the negative electrode terminal 3 is connected to the laminate exterior. It protrudes outward from the peripheral end of the body 1 (Fig. 1). A portion of the peripheral end of the laminate exterior body 1 from which the negative electrode terminal 3 protrudes is sealed with an insulating seal 4.
In addition, in the laminated battery according to the above example, the number of positive electrode plates 5 is five and the number of negative electrode plates 6 is six, and the positive electrode plate 5 and the negative electrode plate 6 are connected to the uppermost part of both sides with a separator 7 in between. The outer layers are laminated in such a manner that each of them becomes a negative electrode plate 6. However, it goes without saying that the number of positive electrode plates, the number of negative electrode plates, and their arrangement in the laminate type battery are not limited to this example, and various changes may be made.

Another example of the lithium secondary battery of the present disclosure is a coin-type battery.
FIG. 3 is a schematic perspective view showing an example of a coin-type battery that is another example of the lithium secondary battery of the present disclosure.
In the coin-type battery shown in FIG. 3, a disc-shaped negative electrode 12, a separator 15 injected with a non-aqueous electrolyte, a disc-shaped positive electrode 11, and spacer plates 17 and 18 made of stainless steel or aluminum, if necessary, are arranged in this order. The stacked state is stored between the positive electrode can 13 (hereinafter also referred to as "battery can") and the sealing plate 14 (hereinafter also referred to as "battery can lid"). The positive electrode can 13 and the sealing plate 14 are caulked and sealed via a gasket 16.
In this example, the nonaqueous electrolyte of the present disclosure is used as the nonaqueous electrolyte injected into the separator 15.

Note that the lithium secondary battery of the present disclosure is obtained by charging and discharging a lithium secondary battery (a lithium secondary battery before charging and discharging) that includes a negative electrode, a positive electrode, and the nonaqueous electrolyte of the present disclosure. It may also be a rechargeable lithium battery.
That is, in the lithium secondary battery of the present disclosure, a lithium secondary battery containing a negative electrode, a positive electrode, and the non-aqueous electrolyte of the present disclosure is first prepared before charging and discharging, and then the lithium secondary battery before charging and discharging is prepared. It may be a lithium secondary battery produced by charging and discharging a lithium secondary battery one or more times (charged and discharged lithium secondary battery).

The use of the lithium secondary battery of the present disclosure is not particularly limited, and it can be used for various known uses. For example, notebook computers, mobile computers, mobile phones, headphone stereos, video movies, LCD TVs, handy cleaners, electronic notebooks, calculators, radios, backup power supplies, motors, automobiles, electric vehicles, motorcycles, electric motorcycles, bicycles, electric It can be widely used in bicycles, lighting equipment, game consoles, watches, power tools, cameras, etc., regardless of whether they are small portable devices or large devices.

Examples of the present disclosure will be shown below, but the present disclosure is not limited to the following examples.
In addition, in the following examples, "addition amount" means the content with respect to the total amount of the non-aqueous electrolyte finally obtained, "wt%" means mass%, ” means a compound represented by formula (1), and “formula (2) compound” means a compound represented by formula (2).

[Example 1]
A coin-shaped lithium secondary battery (hereinafter also referred to as a "coin-shaped battery") having the configuration shown in FIG. 3 was produced using the following procedure.

<Preparation of positive electrode>
LiNi _0.5 Mn _0.3 Co _0.2 O ₂ (90 parts by mass), acetylene black (5 parts by mass) and polyvinylidene fluoride (5 parts by mass) were kneaded using N-methylpyrrolidinone as a solvent to form a paste. A positive electrode mixture slurry was prepared.
Next, this positive electrode mixture slurry is applied to a positive electrode current collector made of a strip of aluminum foil with a thickness of 20 μm, dried, and then compressed with a roll press to form a sheet-like positive electrode consisting of a positive electrode current collector and a positive electrode active material layer. I got it. The coating density of the positive electrode active material layer at this time was 22 mg/cm ² and the packing density was 2.5 g/mL.

<Preparation of negative electrode>
A paste-like negative electrode mixture slurry was prepared by kneading amorphous coated natural graphite (97 parts by mass), carboxymethyl cellulose (1 part by mass), and SBR latex (2 parts by mass) with a water solvent.
Next, this negative electrode mixture slurry is applied to a 10 μm thick strip-shaped copper foil negative electrode current collector, dried, and then compressed with a roll press to form a sheet-like negative electrode consisting of the negative electrode current collector and negative electrode active material layer. I got it. The coating density of the negative electrode active material layer at this time was 12 mg/cm ² and the packing density was 1.5 g/mL.

<Preparation of non-aqueous electrolyte>
As a nonaqueous solvent, ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (EMC) were mixed at a ratio of 30:35:35 (mass ratio), respectively, to obtain a mixed solvent.
LiPF ₆ as an electrolyte was dissolved in the obtained mixed solvent so that the electrolyte concentration in the finally prepared non-aqueous electrolyte was 1.2 mol/liter.
As an additive to the obtained solution,
The content of compound (1-5), which is a specific example of the compound represented by formula (1) (hereinafter also referred to as "formula (1) compound"), relative to the total mass of the non-aqueous electrolyte finally prepared. is added so that it is 0.5% by mass (that is, added at an amount of 0.5% by mass),
A non-aqueous electrolyte was obtained.

<Production of coin-type battery>
The above-mentioned negative electrode was punched out into a disk shape with a diameter of 14 mm, and the above-mentioned positive electrode was punched out into a disk shape with a diameter of 13 mm to obtain a coin-shaped negative electrode and a coin-shaped positive electrode, respectively. Further, a 20 μm thick microporous polyethylene film was punched out into a disc shape with a diameter of 17 mm to obtain a separator.
The obtained coin-shaped negative electrode, separator, and coin-shaped positive electrode were stacked in this order in a stainless steel battery can (2032 size), and then 20 μL of non-aqueous electrolyte was injected into the battery can. The separator, positive electrode, and negative electrode were impregnated.
Next, an aluminum plate (thickness: 1.2 mm, diameter: 16 mm) and a spring were placed on the positive electrode, and a battery can lid was caulked through a polypropylene gasket to seal the battery.
As a result, a coin-shaped battery (ie, a coin-shaped lithium secondary battery) having the configuration shown in FIG. 3 and having a diameter of 20 mm and a height of 3.2 mm was obtained.

<Evaluation>
The following evaluations were performed on the obtained coin-type battery.
The evaluation results are shown in Table 1.
In Table 1, the battery resistance (DC resistance) and positive electrode resistance (positive electrode impedance) in each example are shown as relative values when the value in Comparative Example 1, which will be described later, is set to 100.

In the following,
"Conditioning" means repeating charging and discharging of a coin-type battery three times between 2.75V and 4.25V at 25°C in a constant temperature bath,
"High-temperature storage" refers to an operation in which a coin-type battery is stored at 80° C. for 2 days in a constant temperature bath.
Hereinafter, DC resistance was measured at a temperature of -20°C, and impedance was measured at a temperature of -10°C.

(Measurement of battery resistance (DC resistance) before high temperature storage)
Conditioning was applied to the above coin-type battery.
The conditioned coin-type battery is charged to a constant voltage of 3.9V, then the charged coin-type battery is cooled to -20°C in a thermostatic oven, and discharged at -20°C with a constant current of 0.2mA. Then, the battery resistance (DC resistance (-20°C)) of the coin-type battery before high-temperature storage was measured by measuring the potential drop in 10 seconds from the start of discharge. The battery resistance (DC resistance (-20°C)) before high-temperature storage was similarly measured for the coin-shaped battery of Comparative Example 1, which will be described later.
Table 1 shows the battery resistance (DC resistance) before high temperature storage as a relative value when the value in Comparative Example 1 is taken as 100.

(Measurement of battery resistance (DC resistance) after high temperature storage)
After conditioning and before charging to a constant voltage of 3.9V, the coin-type battery was CC-CV charged to 4.25V at a charging rate of 0.2C at 25°C in a thermostatic chamber, and then stored at high temperature (i.e. Measure the battery resistance (DC resistance) after high-temperature storage in the same manner as the measurement of battery resistance (DC resistance) before high-temperature storage described above, except for adding the operation of storing the battery at 80°C for 2 days. did.
Table 1 shows the battery resistance (DC resistance) after high temperature storage as a relative value when the value in Comparative Example 1 is taken as 100.

(Measurement of positive electrode resistance (positive electrode impedance) before high temperature storage)
Conditioning was applied to the above coin-type battery.
The coin-shaped battery after conditioning was adjusted to 100% SOC (State of Charge), and then the impedance of the coin-shaped battery was measured at a frequency f in the range of 0.1 Hz to 100,000 Hz. Based on the obtained results, a graph showing the relationship between frequency f and impedance was created, and in the obtained graph, the impedance at 0.1 Hz was defined as the positive electrode impedance.
The obtained results are shown in Table 1 as relative values when the value in Comparative Example 1 is set as 100.

(Measurement of positive electrode resistance (positive electrode impedance) after high temperature storage)
After conditioning and before adjusting the SOC to 100%, the coin-type battery was CC-CV charged to 4.25V at a charging rate of 0.2C at 25°C in a thermostatic chamber, and then stored at high temperature (i.e., at 80°C). The positive electrode resistance (positive electrode impedance) after high-temperature storage was measured in the same manner as the measurement of the positive electrode resistance (positive electrode impedance) before high-temperature storage described above, except that the operation of performing 2-day storage) was added.
The obtained results are shown in Table 1 as relative values when the value in Comparative Example 1 is set as 100.

[Examples 2 to 6]
The same operation as in Example 1 was performed except that the type of compound of formula (1) in the non-aqueous electrolyte was changed as shown in Table 1.
The results are shown in Table 1.
The types of compounds of formula (1) in Table 1 correspond to the compound numbers of the specific examples described above.

[Comparative example 1]
The same operation as in Example 1 was performed except that the compound of formula (1) was not contained in the non-aqueous electrolyte.
The results are shown in Table 1.

As shown in Table 1, in Examples 1 to 6 using a battery non-aqueous electrolyte containing the compound of formula (1), Comparative Examples using a battery non-aqueous electrolyte not containing the formula (1) compound Compared to No. 1, the battery resistance and positive electrode resistance were reduced.

[Examples 101 to 107]
The same operation as in Example 1 was performed except that the additive (formula (1) compound) in the non-aqueous electrolyte was changed to the additive (formula (1) compound and formula (2) compound) shown in Table 2. Ta.
However, each of the battery resistance and the positive electrode resistance was expressed as a relative value when the value of Comparative Example 101, which will be described later, was set to 100.
The results are shown in Table 2.

[Comparative example 101]
The same operation as in Example 101 was performed except that the non-aqueous electrolyte did not contain the compound of formula (1).
The results are shown in Table 2.

As shown in Table 2, in Examples 101 to 107 using non-aqueous electrolytes for batteries containing the compound of formula (1) and the compound of formula (2), the compound of formula (2) was used, but the compound of formula (1) Compared to Comparative Example 101 using a non-aqueous battery electrolyte containing no compound, the battery resistance and positive electrode resistance were reduced.

1 Laminate exterior body 2 Positive electrode terminal 3 Negative electrode terminal 4 Insulating seal 5 Positive electrode plate 6 Negative electrode plates 7, 8 Separator 11 Positive electrode 12 Negative electrode 13 Positive electrode can 14 Sealing plate 15 Separator 16 Gasket 17, 18 Spacer plate

Claims (9)

The following formula (1-1), formula (1-2), formula (1-3), formula (1-4), formula (1-5), formula (1-6), formula (1-8), A non-aqueous electrolyte for batteries containing at least one selected from the group consisting of compounds represented by formula (1-9) and formula (1-10) .

The formula (1-1), formula (1-2), formula (1-3), formula (1-4), formula (1-5), formula (1-6), formula (1-8), The content of at least one selected from the group consisting of compounds represented by formula (1-9) and formula (1-10) is 0.001% by mass to 10% by mass based on the total amount of the non-aqueous electrolyte. %. The non-aqueous electrolyte for batteries according to claim 1. It contains a compound represented by the following formula (1-7), and the content of the compound represented by the formula (1-7) is 0.1% by mass to 0.1% by mass based on the total amount of the nonaqueous electrolyte. A non-aqueous electrolyte for batteries having a concentration of 6% by mass.

The nonaqueous electrolyte for batteries according to any one of claims 1 to 3, further comprising a compound represented by the following formula (2).


[In formula (2), R ²¹ and R ²² each independently represent a hydrogen atom, a fluorine atom, a hydrocarbon group having 1 to 6 carbon atoms, or a fluorinated hydrocarbon group having 1 to 6 carbon atoms. ]
A non-aqueous electrolyte for batteries containing a compound represented by the following formula (1) and further containing a compound represented by the following formula (2).


[In formula (1),
R ¹ to R ⁹ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or a phenyl group,
R ¹⁰ represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, a phenyl group, or a group represented by formula (S1).
In formula (S1),
R ¹¹ to R ¹³ each independently represent a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or a phenyl group,
L ¹ represents a single bond or an oxygen atom,
* represents the bonding position. ]


[In formula (2), R ²¹ and R ²² each independently represent a hydrogen atom, a fluorine atom, a hydrocarbon group having 1 to 6 carbon atoms, or a fluorinated hydrocarbon group having 1 to 6 carbon atoms. ]
The non-aqueous electrolyte for a battery according to claim 5 , wherein the content of the compound represented by formula (1) is 0.001% by mass to 10% by mass based on the total amount of the non-aqueous electrolyte. The content of the compound represented by the formula (2) is 0.001% by mass to 10% by mass with respect to the total amount of the non-aqueous electrolyte , according to any one of claims 4 to 6. Non-aqueous electrolyte for batteries. a positive electrode;
Metallic lithium, lithium-containing alloys, metals or alloys that can be alloyed with lithium, oxides that can be doped and dedoped with lithium ions, transition metal nitrides that can be doped and dedoped with lithium ions, and lithium. a negative electrode containing as a negative electrode active material at least one member selected from the group consisting of carbon materials capable of doping and dedoping ions;
The non-aqueous electrolyte for batteries according to any one of claims 1 to 7 ,
Lithium secondary batteries including. A lithium secondary battery obtained by charging and discharging the lithium secondary battery according to claim 8 .

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