JP2019175576A - Nonaqueous electrolyte solution for battery and lithium secondary battery - Google Patents

Abstract

To provide a nonaqueous electrolyte solution for a battery, which contains a cyclic sulfate ester compound different from a conventional cyclic sulfate ester compound, and which enables the decline in battery resistance.SOLUTION: A nonaqueous electrolyte solution for a battery is to be used for a battery having a negative electrode containing a negative electrode active material including natural graphite. The nonaqueous electrolyte solution comprises a nonaqueous electrolyte solution containing a compound represented by the formula (1) below. In the formula (1), Rand Rindependently represent a hydrogen atom, a halogen atom, an alkyl group with 1-3 carbon atoms, or a halogenated alkyl group with 1-3 carbon atoms.SELECTED DRAWING: None

Description

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

2. Description of the Related Art In recent years, lithium secondary batteries have been widely used as electronic devices such as mobile phones and laptop computers, electric vehicles, and power storage sources. In particular, recently, there has been a rapid increase in demand for batteries with high capacity, high output, and high energy density that can be mounted on hybrid vehicles and electric vehicles.
Conventionally, various additives have been added to non-aqueous electrolytes of batteries including the above-described lithium secondary batteries.
For example, attempts have been made to improve battery performance by incorporating various cyclic sulfate compounds into a non-aqueous electrolyte of a lithium secondary battery (see, for example, Patent Documents 1 to 7).

JP-A-10-189042 JP 2003-151623 A JP 2003-308875 A JP 2004-22523 A JP 2005-011762 A International Publication No. 2012/053644 US Patent Application Publication No. 2016/0359196

However, it may be required to reduce battery resistance by using a cyclic sulfate ester compound having a structure different from that of the conventional cyclic sulfate ester compound as an additive in the battery non-aqueous electrolyte.
For example, depending on the combination of the type of the cyclic sulfate compound and the type of the negative electrode active material, when the cyclic sulfate compound is added to the non-aqueous electrolyte, compared to the case where the cyclic sulfate compound is not added, On the contrary, the battery resistance may increase.
An object of the present disclosure is to provide a nonaqueous electrolyte for a battery that contains a cyclic sulfate ester compound different from a conventional cyclic sulfate ester compound as an additive in the nonaqueous electrolyte for a battery, and that can reduce battery resistance, and An object of the present invention is to provide a lithium secondary battery using this non-aqueous electrolyte for a battery.

Means for solving the above problems include the following aspects.
<1> A battery non-aqueous electrolyte solution for use in a battery including a negative electrode containing a negative electrode active material containing natural graphite, the battery containing a compound represented by the following formula (1).

In formula (1), R ¹ and R ² each independently represent a hydrogen atom, a halogen atom, an alkyl group having 1 to 3 carbon atoms, or a halogenated alkyl group having 1 to 3 carbon atoms. ]

<2> The battery nonaqueous electrolyte solution according to <1>, wherein the content of the compound represented by the formula (1) with respect to the total amount of the battery nonaqueous electrolyte solution is 0.001% by mass to 10% by mass. .

<3> The nonaqueous electrolytic solution for batteries according to <1> or <2>, further comprising a boron compound (X) containing a structure in which three oxygen atoms are bonded to one boron atom.
<4> The nonaqueous electrolytic solution for battery according to <3>, wherein the molecular weight of the boron compound (X) is 1000 or less.
<5> The battery according to <3> or <4>, wherein the boron compound (X) is at least one selected from the group consisting of compounds represented by the following formula (X1) to the following formula (X3). Non-aqueous electrolyte for use.

In formula (X1), R ^{X11 to} R ^X13 each independently represents an unsubstituted aryl group or an aliphatic group having 1 to 12 carbon atoms.
In formula (X2), n represents an integer of 1 to 5, and M ⁺ represents a Li ⁺ ion or an H ⁺ ion. When n is an integer of 2 to 5, a plurality of M ⁺ may be the same or different.
In formula (X3), R represents a C 1-12 alkyl group, a C 2-12 alkenyl group, or a group represented by formula (RX). In the formula (RX), R ^{X31 to} R ^X33 each independently represent a hydrogen atom, a halogen atom, an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, or an aryl group having 6 to 12 carbon atoms. * Represents a bonding position.

<6> In the formula (X1), R ^{X11 to} R ^X13 each independently represent a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group, a cyclohexyl group, Or a phenyl group,
In the formula (X2), M ⁺ represents a Li ⁺ ion,
In formula (X3), R represents a group represented by formula (RX), and the battery non-aqueous electrolyte according to <5>.

<7> a positive electrode;
A negative electrode including a negative electrode active material including natural graphite;
<1>-<6> any one of the nonaqueous electrolyte solutions for batteries,
Including lithium secondary battery.
<8> A lithium secondary battery obtained by charging and discharging the lithium secondary battery according to <7>.

  According to the present disclosure, as a additive in a non-aqueous electrolyte for a battery, a non-aqueous electrolyte for a battery containing a cyclic sulfate ester compound different from a conventional cyclic sulfate ester compound and capable of reducing battery resistance, and A lithium secondary battery using this nonaqueous electrolytic solution for a battery is provided.

It is a schematic perspective view which shows an example of the laminate type battery which is an example of the lithium secondary battery of this indication. It is a schematic sectional drawing of the thickness direction of the laminated electrode body accommodated in the laminate type battery shown in FIG. It is a schematic sectional drawing which shows an example of the coin-type battery which is another example of the lithium secondary battery of this indication.

In this specification, a numerical range expressed using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.
In this specification, the amount of each component in the composition is the total amount of the plurality of substances present in the composition unless there is a specific indication when there are a plurality of substances corresponding to each component in the composition. Means.

[Non-aqueous electrolyte for batteries]
The battery non-aqueous electrolyte of the present disclosure (hereinafter also simply referred to as “non-aqueous electrolyte”) is a battery non-aqueous electrolyte used for a battery including a negative electrode including a negative electrode active material containing natural graphite, As an additive in the non-aqueous electrolyte for batteries, a compound represented by the following formula (1) is contained as a cyclic sulfate compound different from the conventional cyclic sulfate compound.
According to the nonaqueous electrolytic solution of the present disclosure, battery resistance can be reduced.
More specifically, battery resistance is reduced by using a non-aqueous electrolyte containing a compound represented by formula (1) as a non-aqueous electrolyte of a battery including a negative electrode containing a negative electrode active material containing natural graphite. Is done.
The reason for this effect is not clear, but compared to artificial graphite, natural graphite with a small crystallite size and high amorphousness, applicable to cyclic sulfate compounds and also applicable to condensed cyclic compounds This is probably because a combination of the compound represented by the formula (1) and the compound represented by the formula (1) forms a low-resistance film on the negative electrode of the battery.
In contrast, when a non-aqueous electrolyte containing a compound represented by the formula (1) is used as a non-aqueous electrolyte of a battery including a negative electrode containing a negative electrode active material containing artificial graphite, battery resistance ( In particular, the battery resistance at a low temperature may increase instead (see Comparative Examples 102 and 103 in Table 3 described later).

The compound represented by the following formula (1) corresponds to a cyclic sulfate compound and also corresponds to a condensed cyclic compound as shown in the following structure.
The compound represented by the following formula (1) has an open-circuit voltage reduction rate as compared with a conventional cyclic sulfate compound that does not correspond to a condensed cyclic compound (for example, comparative compounds (C1) and (C2) described later). It is excellent in the effect of improving (that is, reducing) and the effect of improving the battery capacity.

<Compound represented by Formula (1)>

In formula (1), R ¹ and R ² each independently represent a hydrogen atom, a halogen atom, an alkyl group having 1 to 3 carbon atoms, or a halogenated alkyl group having 1 to 3 carbon atoms.

The halogen atom represented by R ¹ or R ² is preferably a fluorine atom, a chlorine atom, a bromine atom or an iodine atom, more preferably a fluorine atom, a chlorine atom or a bromine atom, still more preferably a fluorine atom or a chlorine atom, A fluorine atom is particularly preferred.

As a C1-C3 alkyl group represented by R < ¹ > or R < ² >, a methyl group or an ethyl group is preferable, and a methyl group is especially preferable.

As a halogen atom in a C1-C3 halogenated alkyl group represented by R < ¹ > or R < ² >, a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom are preferable, and a fluorine atom, a chlorine atom, or a bromine atom is More preferably, a fluorine atom or a chlorine atom is still more preferable, and a fluorine atom is particularly preferable.
Examples of the halogenated alkyl group having 1 to 3 carbon atoms represented by R ¹ or R ² include a fluoromethyl group, a difluoromethyl group, a trifluoromethyl group, a 2,2,2-trifluoroethyl group, or perfluoroethyl. Group is preferable, a fluoromethyl group, a difluoromethyl group, or a trifluoromethyl group is more preferable, and a trifluoromethyl group is particularly preferable.

R ¹ and R ² are each independently a hydrogen atom, a fluorine atom, a methyl group, an ethyl group, a fluoromethyl group, a difluoromethyl group, a trifluoromethyl group, a 2,2,2-trifluoroethyl group, or perfluoro An ethyl group is preferable, a hydrogen atom, a fluorine atom, a methyl group, or a trifluoromethyl group is more preferable, and a hydrogen atom is particularly preferable.

  Specific examples of the compound represented by the formula (1) include compounds represented by the following formula (1-1) to the following formula (1-11) (hereinafter referred to as the compound (1-1) to the compound (1 respectively). -11)), but the compound represented by the formula (1) is not limited to these specific examples.

  For a method for synthesizing the compound represented by the formula (1), for example, publicly known documents such as US Patent Application Publication No. 2016/0359196 can be referred to as appropriate.

The nonaqueous electrolytic solution of the present disclosure may contain only one type of compound represented by the formula (1), or may contain two or more types.
As content of the compound represented by Formula (1) with respect to the whole quantity of the non-aqueous electrolyte of this indication, 0.001 mass%-10 mass% are preferable, 0.005 mass%-5 mass% are more preferable, 0.01 mass%-2 mass% are still more preferable, and 0.1 mass%-1 mass% are especially preferable.

The nonaqueous electrolytic solution of the present disclosure may contain other additives other than the compound represented by the formula (1).
When the nonaqueous electrolytic solution of the present disclosure contains other additives, the other additives contained may be only one kind or two or more kinds.

<Boron compound (X)>
The nonaqueous electrolytic solution of the present disclosure may contain a boron compound (X) including a structure in which three oxygen atoms are bonded to one boron atom as another additive.
When the nonaqueous electrolytic solution of the present disclosure contains the boron compound (X), the nonaqueous electrolytic solution of the present disclosure does not contain the boron compound (X), and other boron compounds other than the boron compound (X) Compared with the case of containing, battery resistance (especially, initial battery resistance before storing the battery) can be further reduced.
The reason for this is not clear, but the boron compound (X) binds to B as compared with a boron compound (for example, LiBOB described later) including a structure in which four oxygen atoms are bonded to one boron atom. Since the number of O to be reduced is small, it is considered that the reactivity on the edge surface of graphite is excellent, and as a result, a more uniform film is formed on the negative electrode. More specifically, the compound represented by the formula (1) and the boron compound are hybridized by using the compound represented by the formula (1) and the boron compound in combination as an additive for the non-aqueous electrolyte. It is considered that a low resistance film is formed on the negative electrode. At this time, it is considered that by selecting the boron compound (X) as the boron compound, a more uniform low-resistance film is formed on the negative electrode, and as a result, the battery resistance is more effectively reduced.

The boron compound (X) may contain only one structure in which three oxygen atoms are bonded to one boron atom (in other words, a boron atom to which three oxygen atoms are bonded). Two or more may be included.
Further, the boron compound (X) may contain a boron atom other than the boron atom to which three oxygen atoms are bonded.

The boron compound (X) may be a low molecular compound or a high molecular compound, but is preferably a low molecular compound.
The molecular weight of the boron compound (X) is preferably 1000 or less, more preferably 500 or less, still more preferably 400 or less, and even more preferably 300 or less.

When the nonaqueous electrolytic solution of the present disclosure contains the boron compound (X), the boron compound (X) contained may be only one type or two or more types.
When the nonaqueous electrolytic solution of the present disclosure contains the boron compound (X), the content of the boron compound (X) with respect to the total amount of the nonaqueous electrolytic solution of the present disclosure is preferably 0.001% by mass to 10% by mass. 0.005 mass% to 5 mass% is more preferable, 0.01 mass% to 2 mass% is still more preferable, and 0.1 mass% to 1 mass% is particularly preferable.

  When the nonaqueous electrolytic solution of the present disclosure contains the boron compound (X), the preferred range of the content of the compound represented by the formula (1) is the above-described formula for the total amount of the nonaqueous electrolytic solution of the present disclosure. This is the same as the preferred range of the content of the compound represented by (1).

  The boron compound (X) is preferably at least one selected from the group consisting of compounds represented by the following formula (X1) to the following formula (X3).

In formula (X1), R ^{X11 to} R ^X13 each independently represents an unsubstituted aryl group or an aliphatic group having 1 to 12 carbon atoms.
In formula (X2), n represents an integer of 1 to 5, and M ⁺ represents a Li ⁺ ion or an H ⁺ ion. When n is an integer of 2 to 5, a plurality of M ⁺ may be the same or different.
In formula (X3), R represents a C 1-12 alkyl group, a C 2-12 alkenyl group, or a group represented by formula (RX). In the formula (RX), R ^{X31 to} R ^X33 each independently represent a hydrogen atom, a halogen atom, an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, or an aryl group having 6 to 12 carbon atoms. * Represents a bonding position.

In formula (X1), examples of the unsubstituted aryl group represented by R ^{X11 to} R ^X13 include a phenyl group, a naphthyl group, an anthracenyl group, a phenanthryl group, and the like, and a phenyl group is preferable.

In formula (X1), the aliphatic group having 1 to 12 carbon atoms represented by R ^{X11 to} R ^X13 may independently be a linear aliphatic group or a branched aliphatic group. It may be an aliphatic group having a cyclic structure.
In formula (X1), the aliphatic group having 1 to 12 carbon atoms represented by R ^{X11 to} R ^X13 may be each independently a saturated aliphatic group (that is, an alkyl group), or an unsaturated fat It may be a group (that is, an alkenyl group or an alkynyl group).

Specific examples of the aliphatic group having 1 to 12 carbon atoms represented by R ^{X11 to} R ^X13 include
Methyl group, ethyl group, n-propyl group, isopropyl group, 1-ethylpropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, 2-methylbutyl group, 3,3-dimethylbutyl group N-pentyl group, isopentyl group, neopentyl group, 1-methylpentyl group, n-hexyl group, isohexyl group, sec-hexyl group, tert-hexyl group, n-heptyl group, isoheptyl group, sec-heptyl group, tert A linear or branched saturated aliphatic group such as a heptyl group, an n-octyl group, an isooctyl group, a sec-octyl group, a tert-octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group (i.e., Alkyl group);
Vinyl group, 1-propenyl group, allyl group (2-propenyl group), isopropenyl group, 1-butenyl group, 2-butenyl group, 3-butenyl group, pentenyl group, hexenyl group, 2-methyl-2-propenyl group 1-methyl-2-propenyl group, 2-methyl-1-propenyl group, hexenyl group, ethynyl group, 1-propynyl group, 2-propynyl group (synonymous with propargyl group), 1-butynyl group, 2-butynyl group 3-butynyl group, 1-pentynyl group, 2-pentynyl group, 3-pentynyl group, 4-pentynyl group, 5-hexynyl group, 1-methyl-2-propynyl group, 2-methyl-3-butynyl group, 2 -Methyl-3-pentynyl group, 1-methyl-2-butynyl group, 1,1-dimethyl-2-propynyl, 1,1-dimethyl-2-butynyl group, 1-hexynyl group Which, linear or branched unsaturated aliphatic group (i.e., alkenyl or alkynyl group);
An aliphatic group having a cyclic structure such as cyclopropyl group, cyclobutyl group, cyclopentyl group, cyclohexyl group, cycloheptyl group, 1-cyclopentenyl group, 1-cyclohexenyl group;
Etc.

The aliphatic group having 1 to 12 carbon atoms represented by R ^{X11 to} R ^X13 is independently a methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, t-butyl. Group or a cyclohexyl group is preferable, a methyl group, an ethyl group, or an isopropyl group is more preferable, and a methyl group is still more preferable.

In the formula (X1), R ^{X11 to} R ^X13 each independently represent a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group, a cyclohexyl group, or a phenyl group. It is preferably a methyl group, an ethyl group, an isopropyl group, or a phenyl group, more preferably a methyl group or a phenyl group, and particularly preferably a methyl group.

In formula (X2), n represents an integer of 1 to 5, and M ⁺ represents a Li ⁺ ion or an H ⁺ ion. When n is an integer of 2 to 5, a plurality of M ⁺ may be the same or different.

In the formula (X2), n is preferably an integer of 1 to 3, and 2 is particularly preferable.
In the formula (X2), M ⁺ is particularly preferably Li ⁺ ion.

In formula (X3), R represents a C 1-12 alkyl group, a C 2-12 alkenyl group, or a group represented by formula (RX). In the formula (RX), R ^{X31 to} R ^X33 each independently represent a hydrogen atom, a halogen atom, an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, or an aryl group having 6 to 12 carbon atoms. * Represents a bonding position.

In formula (X3), the alkyl group having 1 to 12 carbon atoms represented by R is more preferably an alkyl group having 1 to 10 carbon atoms, still more preferably an alkyl group having 1 to 8 carbon atoms, and 1 to 1 carbon atoms. An alkyl group having 6 carbon atoms is more preferable, and an alkyl group having 1 to 4 carbon atoms is more preferable.
Examples of the alkyl group include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, n-pentyl group, isopentyl group, and neopentyl group. Tert-pentyl group, n-hexyl group, isohexyl group, sec-hexyl group, tert-hexyl group, n-heptyl group, isoheptyl group, sec-heptyl group, tert-heptyl group, n-octyl group, isooctyl group, A sec-octyl group, a tert-octyl group, etc. are mentioned.
The C1-C12 alkyl group represented by R may be unsubstituted or substituted with a halogen atom (for example, a fluorine atom or a chlorine atom).

In formula (X3), the alkenyl group having 2 to 12 carbon atoms represented by R is more preferably an alkenyl group having 2 to 10 carbon atoms, further preferably an alkenyl group having 2 to 8 carbon atoms, and 2 to 2 carbon atoms. An alkenyl group having 6 carbon atoms is more preferable, and an alkenyl group having 2 to 4 carbon atoms is more preferable.
Examples of the alkenyl group include ethenyl group, propenyl group, butenyl group, pentenyl group, hexenyl group, heptenyl group, octenyl group and the like.
The alkenyl group having 2 to 12 carbon atoms represented by R may be unsubstituted or substituted with a halogen atom (for example, a fluorine atom or a chlorine atom).

In the formula (X3), R is preferably a group represented by the formula (RX).
In the formula (RX), R ^{X31 to} R ^X33 each independently represent a hydrogen atom, a halogen atom, an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, or an aryl group having 6 to 12 carbon atoms. Represents.

Examples of the halogen atom represented by R ^{X31 to} R ^X33 include a fluorine atom, a chlorine atom, and a bromine atom, and a fluorine atom is preferable.

As a C1-C12 alkyl group represented by R ^{< X31>} -R ^<X33> , a C1-C10 alkyl group is more preferable, A C1-C8 alkyl group is still more preferable, C1-C6 An alkyl group is more preferable, an alkyl group having 1 to 4 carbon atoms is more preferable, and an alkyl group having 1 to 3 carbon atoms is further preferable.
Examples of the alkyl group include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, n-pentyl group, isopentyl group, and neopentyl group. Tert-pentyl group, n-hexyl group, isohexyl group, sec-hexyl group, tert-hexyl group, n-heptyl group, isoheptyl group, sec-heptyl group, tert-heptyl group, n-octyl group, isooctyl group, A sec-octyl group, a tert-octyl group, etc. are mentioned.
The alkyl group having 1 to 12 carbon atoms represented by R ^{X31 to} R ^X33 may be unsubstituted or may be substituted with a halogen atom (for example, a fluorine atom or a chlorine atom).

As a C2-C12 alkenyl group represented by R ^{< X31>} -R ^<X33> , a C2-C10 alkenyl group is more preferable, A C2-C8 alkenyl group is more preferable, A C2-C6 alkenyl group is more preferable. An alkenyl group is more preferable, and an alkenyl group having 2 to 4 carbon atoms is more preferable.
Examples of the alkenyl group include ethenyl group, propenyl group, butenyl group, pentenyl group, hexenyl group, heptenyl group, octenyl group and the like.
The alkenyl group having 2 to 12 carbon atoms represented by R ^{X31 to} R ^X33 may be unsubstituted or may be substituted with a halogen atom (for example, a fluorine atom or a chlorine atom).

The aryl group having 6 to 12 carbon atoms represented by R ^{X31 to} R ^X33 is more preferably an aryl group having 6 to 10 carbon atoms.
Examples of the aryl group include a phenyl group, a group in which one hydrogen atom is removed from an alkylbenzene (for example, a benzyl group, a tolyl group, a xylyl group, a mesityl group, etc.), a naphthyl group, and a hydrogen atom from a substituted alkyl group of naphthalene. And the like, and the like.
The aryl group having 6 to 12 carbon atoms represented by R ^{X31 to} R ^X33 may be unsubstituted or may be substituted with a halogen atom (for example, a fluorine atom or a chlorine atom).

In formula (X3), at least one of R ^{X31 to} R ^X33 is preferably an alkyl group, an alkenyl group, or an aryl group, and at least two of R ^{X31 to} R ^X33 are an alkyl group, an alkenyl group, or More preferred is an aryl group. In this case, preferred embodiments of the alkyl group, alkenyl group and aryl group are as described above, and among the alkyl group, alkenyl group and aryl group, the alkyl group is preferred.

  The boron compound represented by the formula (X3) can be synthesized, for example, by the method described in Chemische Berichte, Volume 68, Issue 6, Pages 1949-55, 1965.

Particularly preferred embodiments of formula (X1) to formula (X3) are:
In the formula (X1), R ^{X11 to} R ^X13 each independently represent a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group, a cyclohexyl group, or a phenyl group. Represents
In the formula (X2), M ⁺ represents a Li ⁺ ion,
In Formula (X3), R is an embodiment representing a group represented by Formula (RX).

  Hereinafter, although the specific example of a compound represented by a formula (X1) is shown, the compound represented by a formula (X1) is not limited to the following specific examples.

Hereinafter, although the specific example of a compound represented by Formula (X2) is shown, the compound represented by Formula (X2) is not limited to the following specific examples.
Specific examples of the compound represented by the formula (X2) include
Lithium triborate (a compound in which n is 1 and M ⁺ is a Li ⁺ ion),
Lithium tetraborate (a compound in which n is 2 and two M ⁺ are Li ⁺ ions; a compound (X2-1) described later),
Lithium pentaborate (compound where n is 3 and three M ⁺ are Li ⁺ ions),
Lithium hexaborate (a compound in which n is 4 and four M ⁺ are Li ⁺ ions),
Lithium heptaborate (compound where n is 5 and 5 M ⁺ are Li ⁺ ions),
Etc.

  Hereinafter, although the specific example of a compound represented by a formula (X3) is shown, the compound represented by a formula (X3) is not limited to the following specific examples.

  Next, other components of the nonaqueous electrolytic solution will be described. The nonaqueous electrolytic solution generally contains an electrolyte and a nonaqueous solvent.

(Non-aqueous solvent)
A non-aqueous electrolyte generally contains a non-aqueous solvent.
Various known solvents can be appropriately selected as the non-aqueous solvent, but at least one selected from a cyclic aprotic solvent and a chain aprotic solvent is preferably used.

  In order to improve the safety of the battery, when aiming to improve the flash point of the solvent, it is preferable to use a cyclic aprotic solvent as the non-aqueous solvent.

(Cyclic aprotic solvent)
As the cyclic aprotic solvent, cyclic carbonate, cyclic carboxylic acid ester, cyclic sulfone, and cyclic ether can be used.

The cyclic aprotic solvent may be used alone or in combination of two or more.
The mixing ratio of the cyclic aprotic solvent in the non-aqueous solvent is 10% by mass to 100% by mass, more preferably 20% by mass to 90% by mass, and particularly preferably 30% by mass to 80% by mass. By setting it as such a ratio, the electroconductivity of the electrolyte solution relating to the charge / discharge characteristics of the battery can be increased.

  Specific examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and the like. Of these, ethylene carbonate and propylene carbonate having a high dielectric constant are preferably used. In the case of a battery using graphite as the negative electrode active material, ethylene carbonate is more preferable. Moreover, you may use these cyclic carbonates in mixture of 2 or more types.

Specific examples of the cyclic carboxylic acid ester include γ-butyrolactone, δ-valerolactone, alkyl substitution products such as methyl γ-butyrolactone, ethyl γ-butyrolactone, and ethyl δ-valerolactone.
The cyclic carboxylic acid ester has a low vapor pressure, a low viscosity, a high dielectric constant, and can lower the viscosity of the electrolytic solution without lowering the degree of dissociation between the flash point of the electrolytic solution and the electrolyte. For this reason, since it has the feature that the conductivity of the electrolytic solution, which is an index related to the discharge characteristics of the battery, can be increased without increasing the flammability of the electrolytic solution, when aiming to improve the flash point of the solvent, It is preferable to use a cyclic carboxylic acid ester as the cyclic aprotic solvent. Most preferred is γ-butyrolactone.

  The cyclic carboxylic acid ester is preferably used by mixing with another cyclic aprotic solvent. Examples thereof include a mixture of a cyclic carboxylic acid ester and a cyclic carbonate and / or a chain carbonate.

  Specific examples of combinations of cyclic carboxylic acid esters and cyclic carbonates and / or chain carbonates include γ-butyrolactone and ethylene carbonate, γ-butyrolactone and ethylene carbonate and dimethyl carbonate, and γ-butyrolactone and ethylene carbonate and methylethyl. Carbonate, γ-butyrolactone and ethylene carbonate and diethyl carbonate, γ-butyrolactone and propylene carbonate, γ-butyrolactone and propylene carbonate and dimethyl carbonate, γ-butyrolactone and propylene carbonate and methyl ethyl carbonate, γ-butyrolactone and propylene carbonate and diethyl carbonate, γ-butyrolactone, ethylene carbonate and propylene carbonate, γ-butyrolactone Ethylene carbonate and propylene carbonate and dimethyl carbonate, γ-butyrolactone and ethylene carbonate and propylene carbonate and methyl ethyl carbonate, γ-butyrolactone and ethylene carbonate, propylene carbonate and diethyl carbonate, γ-butyrolactone, ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate, γ-butyrolactone, ethylene carbonate, dimethyl carbonate and diethyl carbonate, γ-butyrolactone, ethylene carbonate, methyl ethyl carbonate and diethyl carbonate, γ-butyrolactone, ethylene carbonate, dimethyl carbonate, methyl ethyl carbonate and diethyl carbonate, γ-butyrolactone and ethylene carbonate And Pyrene carbonate, dimethyl carbonate and methyl ethyl carbonate, γ-butyrolactone, ethylene carbonate, propylene carbonate, dimethyl carbonate and diethyl carbonate, γ-butyrolactone, ethylene carbonate, propylene carbonate, methyl ethyl carbonate and diethyl carbonate, γ-butyrolactone and ethylene carbonate Propylene carbonate, dimethyl carbonate, methyl ethyl carbonate and diethyl carbonate, γ-butyrolactone and sulfolane, γ-butyrolactone and ethylene carbonate and sulfolane, γ-butyrolactone and propylene carbonate and sulfolane, γ-butyrolactone, ethylene carbonate, propylene carbonate and sulfolane, γ -Butyrolactone and Su Such Horan and dimethyl carbonate.

Examples of the cyclic sulfone include sulfolane, 2-methylsulfolane, 3-methylsulfolane, dimethyl sulfone, diethyl sulfone, dipropyl sulfone, methylethyl sulfone, methylpropyl sulfone and the like.
An example of a cyclic ether is dioxolane.

(Chain aprotic solvent)
As the chain aprotic solvent, a chain carbonate, a chain carboxylic acid ester, a chain ether, a chain phosphate, or the like can be used.

  The mixing ratio of the chain aprotic solvent in the non-aqueous solvent is 10% by mass to 100% by mass, more preferably 20% by mass to 90% by mass, and particularly preferably 30% by mass to 80% by mass.

  Specific examples of the chain carbonate include dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl propyl carbonate, dipropyl carbonate, methyl butyl carbonate, ethyl butyl carbonate, dibutyl carbonate, methyl pentyl carbonate, Examples include ethyl pentyl carbonate, dipentyl carbonate, methyl heptyl carbonate, ethyl heptyl carbonate, diheptyl carbonate, methyl hexyl carbonate, ethyl hexyl carbonate, dihexyl carbonate, methyl octyl carbonate, ethyl octyl carbonate, dioctyl carbonate, and methyltrifluoroethyl carbonate. These chain carbonates may be used as a mixture of two or more.

Specific examples of the chain carboxylic acid ester include methyl pivalate.
Specific examples of the chain ether include dimethoxyethane.
Specific examples of the chain phosphate ester include trimethyl phosphate.

(Solvent combination)
The nonaqueous solvent contained in the nonaqueous electrolytic solution of the present disclosure may be only one type or two or more types.
Further, only one or a plurality of cyclic aprotic solvents may be used, or only one or a plurality of chain aprotic solvents may be used, or a cyclic aprotic solvent and a chain protic solvent. You may mix and use a solvent. When the load characteristics and low temperature characteristics of the battery are particularly intended to be improved, it is preferable to use a combination of a cyclic aprotic solvent and a chain aprotic solvent as the nonaqueous solvent.

  Furthermore, in view of the electrochemical stability of the electrolytic solution, it is most preferable to apply a cyclic carbonate to the cyclic aprotic solvent and a chain carbonate to the chain aprotic solvent. Moreover, the conductivity of the electrolyte solution related to the charge / discharge characteristics of the battery can be increased by a combination of the cyclic carboxylic acid ester and the cyclic carbonate and / or the chain carbonate.

  As a combination of cyclic carbonate and chain carbonate, specifically, 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 Diethyl carbonate, ethylene carbonate, dimethyl carbonate, methyl ethyl carbonate and diethyl carbonate, ethylene carbonate, propylene carbonate, dimethyl carbonate and methyl ethyl carbonate, ethylene carbonate, propylene carbonate, dimethyl carbonate and diethyl carbonate, ethylene carbonate, propylene carbonate and methyl ethyl carbonate And diethyl carbonate, ethylene carbonate, propylene carbonate, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate.

  The mixing ratio of the cyclic carbonate and the chain carbonate is expressed by mass ratio, and the cyclic carbonate: chain carbonate is 5:95 to 80:20, more preferably 10:90 to 70:30, particularly preferably 15:85. ~ 55: 45. By setting it as such a ratio, since the raise of the viscosity of electrolyte solution can be suppressed and the dissociation degree of electrolyte can be raised, the conductivity of the electrolyte solution in connection with the charge / discharge characteristic of a battery can be raised. In addition, the solubility of the electrolyte can be further increased. Therefore, since it can be set as the electrolyte solution excellent in the electrical conductivity in normal temperature or low temperature, the load characteristic of the battery from normal temperature to low temperature can be improved.

(Other solvents)
Examples of the non-aqueous solvent include other solvents other than those described above.
Specific examples of other solvents include amides such as dimethylformamide, chain carbamates such as methyl-N, N-dimethylcarbamate, cyclic amides such as N-methylpyrrolidone, N, N-dimethylimidazolidinone, and the like. Examples thereof include boron compounds such as cyclic urea, trimethyl borate, triethyl borate, tributyl borate, trioctyl borate, trimethylsilyl borate, and polyethylene glycol derivatives represented by the following general formula.
HO (CH ₂ CH ₂ O) _a H
HO [CH ₂ CH (CH ₃ ) O] _b H
CH ₃ O (CH ₂ CH ₂ O) _c H
CH ₃ O [CH ₂ CH (CH ₃ ) O] _d H
CH ₃ O (CH ₂ CH ₂ O) _e CH ₃
CH ₃ O [CH ₂ CH (CH ₃ ) O] _f CH _{3
C 9 H 19 PhO (CH 2} CH 2 O) g [CH (CH 3) O] h CH 3
(Ph is a phenyl group)
CH ₃ O [CH ₂ CH (CH ₃ ) O] _i CO [OCH (CH ₃ ) CH ₂ ] _j OCH ₃
In the above formula, a to f are integers of 5 to 250, g to j are integers of 2 to 249, 5 ≦ g + h ≦ 250, and 5 ≦ i + j ≦ 250.

(Electrolytes)
Various known electrolytes can be used for the nonaqueous electrolytic solution of the present disclosure, and any of them can be used as long as it is normally used as an electrolyte for a nonaqueous electrolytic solution.

Specific examples of the electrolyte include (C ₂ H ₅ ) ₄ NPF ₆ , (C ₂ H ₅ ) ₄ NBF ₄ , (C ₂ H ₅ ) ₄ NClO ₄ , (C ₂ H ₅ ) ₄ NAsF ₆ , (C ₂ H ₅ ) ₄ N ₂ SiF ₆ , (C ₂ H ₅ ) ₄ NOSO ₂ C _k F _{(2k + 1)} (k = 1 to 8), (C ₂ H ₅ ) ₄ NPF _n [C _k F _{(2k + 1)} ] _(6-n) Tetraalkylammonium salts such as (n = 1 to 5, k = 1 to 8), LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , Li ₂ SiF ₆ , LiOSO ₂ C _k F Lithium salts such as _{(2k + 1)} (k = 1 to 8), LiPF _n [C _k F _{(2k + 1)} ] _(6-n) (n = 1 to 5, k = 1 to 8) are included. . Moreover, the lithium salt represented by the following general formula can also be used.

LiC (SO ₂ R ⁷ ) (SO ₂ R ⁸ ) (SO ₂ R ⁹ ), LiN (SO ₂ OR ¹⁰ ) (SO ₂ OR ¹¹ ), LiN (SO ₂ R ¹² ) (SO ₂ R ¹³ ) (where R ^{7 to} R ¹³ may be the same as or different from each other, and are a fluorine atom or a C 1-8 perfluoroalkyl group). These electrolytes may be used alone or in combination of two or more.
Of these, lithium salts are particularly desirable, and LiPF ₆ , LiBF ₄ , LiOSO ₂ C _k F _{(2k + 1)} (k = 1 to 8), LiClO ₄ , LiAsF ₆ , LiNSO ₂ [C _k F _{( 2k + 1)] 2 (k} = 1~8 _{integer), LiPF n [C k F} (2k + 1)] (6-n) (n = 1~5, k = 1~8 integer) are preferred.

  The electrolyte is usually preferably contained in the nonaqueous electrolytic solution at a concentration of 0.1 mol / L to 3 mol / L, preferably 0.5 mol / L to 2 mol / L.

In the nonaqueous electrolytic solution of the present disclosure, when a cyclic carboxylic acid ester such as γ-butyrolactone is used in combination as the nonaqueous solvent, it is particularly desirable to contain LiPF ₆ . Since LiPF ₆ has a high degree of dissociation, the conductivity of the electrolytic solution can be increased, and the reductive decomposition reaction of the electrolytic solution on the negative electrode can be suppressed. LiPF ₆ may be used alone, or LiPF ₆ and other electrolytes may be used. Any other electrolyte can be used as long as it is normally used as an electrolyte for a non-aqueous electrolyte, but lithium salts other than LiPF ₆ are preferred among the specific examples of the lithium salts described above. .
Specific examples include LiPF ₆ and LiBF ₄ , LiPF ₆ and LiN [SO ₂ C _k F _{(2k + 1)} ] ₂ (k = 1 to 8), LiPF ₆ , LiBF ₄ and LiN [SO ₂ C _k F _{( 2k + 1)} ] (k = 1 to 8).

The ratio of LiPF _{6 in} the lithium salt is preferably 1% by mass to 100% by mass, more preferably 10% by mass to 100% by mass, and further preferably 50% by mass to 100% by mass. Such an electrolyte is preferably contained in the nonaqueous electrolytic solution at a concentration of 0.1 mol / L to 3 mol / L, preferably 0.5 mol / L to 2 mol / L.

  The non-aqueous electrolyte of the present disclosure is not only suitable as a non-aqueous electrolyte for a lithium secondary battery, but also a non-aqueous electrolyte for a primary battery, a non-aqueous electrolyte for an electrochemical capacitor, and an electric double layer capacitor. It can also be used as an electrolytic solution for aluminum electrolytic capacitors.

[Lithium secondary battery]
The lithium secondary battery according to the present disclosure includes a positive electrode, a negative electrode including a negative electrode active material including natural graphite, and the nonaqueous electrolytic solution according to the present disclosure.

<Negative electrode>
The negative electrode includes a negative electrode active material containing natural graphite.
The form of the negative electrode active material may be any of a fibrous form, a spherical form, a potato form, and a flake form.

  As described above, natural graphite has a smaller crystallite size and higher amorphousness than artificial graphite. The effect of reducing battery resistance by the nonaqueous electrolytic solution of the present disclosure is achieved by a combination of natural graphite having such properties and the compound represented by the above formula (1).

Here, the amorphous property can be evaluated by an R value [I (1350) / I (1850)] of Raman spectrum (hereinafter also simply referred to as “R value [I (1350) / I (1850)]”). .
The R value [I (1350) / I (1850)] is the ratio of the intensity (I (1350)) at the Raman shift of 1350 cm ^{−1 to} the intensity at the Raman shift of 1850 cm ⁻¹ (I (1850)).
I (1850) is the intensity of the G peak reflecting the graphite structure.
I (1350) is the intensity of the D peak reflecting the irregularity.
A higher R value [I (1350) / I (1850)] means higher amorphousness.

The R value [I (1350) / I (1850)] of natural graphite is preferably 0.090 or more, more preferably 0.100 or more, still more preferably 0.110 or more, and still more preferably. It is 0.120 or more.
The upper limit of the R value [I (1350) / I (1850)] of natural graphite is not particularly limited. The upper limit is, for example, 0.300, preferably 0.200, and more preferably 0.150.

The crystallite size of natural graphite can be measured by X-ray analysis.
The crystallite size of natural graphite is preferably 120 mm or less, more preferably 100 mm or less, and still more preferably 80 mm or less.
The lower limit of the crystallite size of natural graphite is, for example, 30 mm, and preferably 40 mm.

The interplanar spacing d (002) of the (002) plane of natural graphite is preferably 0.340 nm or less.
The lower limit of the interplanar spacing d (002) of the (002) plane of natural graphite is, for example, 0.334 nm.
The interplanar spacing d (002) of the (002) plane of natural graphite can be measured by X-ray analysis.

  The proportion of natural graphite in the negative electrode active material is preferably 50% by mass or more, more preferably 60% by mass or more, and still more preferably 80% by mass or more.

The negative electrode active material may contain components other than natural graphite.
Examples of components other than natural graphite include carbon materials such as carbon black, activated carbon, artificial graphite, and amorphous carbon materials; metals or alloys such as silicon, silicon alloys, tin, and tin alloys; lithium titanate;
Examples of the amorphous carbon material include hard carbon, coke, mesocarbon microbeads (MCMB) fired at 1500 ° C. or less, and mesophase pitch carbon fiber (MCF).
Further, as the negative electrode active material, natural graphite coated with an amorphous carbon material; natural graphite coated with a metal such as gold, platinum, silver, copper, tin, or the like may be used.

The negative electrode may include a negative electrode current collector.
There is no restriction | limiting in particular in the material of the negative electrode electrical power collector in a negative electrode, A well-known thing can be used arbitrarily.
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 preferable 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 <X <1], Li _{1 + α} Me _1-α O ₂ having an α-NaFeO ₂ type crystal structure (Me is a transition metal element containing Mn, Ni and Co, 1.0 ≦ (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, 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 , LiMnPO ₄ and other complex oxides composed of lithium and transition metals, Polyaniline, Li thiophene, polypyrrole, polyacetylene, polyacene, dimercaptothiadiazoles, conductive polymer materials such as polyaniline complex thereof. Among these, a composite oxide composed of lithium and a transition metal is particularly preferable. When the negative electrode is lithium metal or a lithium alloy, a carbon material can be used as the positive electrode. In addition, a mixture of a composite oxide of lithium and a transition metal and a carbon material can be used as the positive electrode.
A positive electrode active material may be used by 1 type, and may mix and use 2 or more types. When the positive electrode active material has insufficient conductivity, it can be used together with a conductive auxiliary agent to constitute a positive electrode. Examples of the conductive assistant include carbon materials such as carbon black, amorphous whiskers, and graphite.

There is no restriction | limiting in particular in the material of the positive electrode electrical power collector in a positive electrode, A well-known thing can be used arbitrarily.
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;

<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 film that electrically insulates the positive electrode and the negative electrode and transmits lithium ions, and examples thereof include a porous film and a polymer electrolyte.
A microporous polymer film is preferably used as the porous film, and examples of the material include polyolefin, polyimide, polyvinylidene fluoride, and polyester.
In particular, porous polyolefin is preferable. Specifically, a porous polyethylene film, a porous polypropylene film, or a multilayer film of a porous polyethylene film and a polypropylene film can be exemplified. On the porous polyolefin film, other resin excellent in thermal stability may be coated.
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 nonaqueous electrolytic solution of the present disclosure may be used for the purpose of obtaining a polymer electrolyte by swelling a polymer.

<Battery configuration>
The lithium secondary battery of the present disclosure can take various known shapes, and can be formed into a cylindrical shape, a coin shape, a square shape, a laminate shape, a film shape, or any other shape. However, the basic structure of the battery is the same regardless of the shape, and the design can be changed according to the purpose.

Examples of the lithium secondary battery of the present disclosure include a laminate type battery.
FIG. 1 is a schematic perspective view showing an example of a laminated battery that is an example of the lithium secondary battery of the present disclosure, and FIG. 2 shows the thickness of the laminated electrode body accommodated in the laminated battery shown in FIG. It is a schematic sectional drawing of a direction.
The laminate type 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) inside, and the periphery is sealed. The laminate outer package 1 is sealed inside. As the laminate exterior body 1, for example, an aluminum laminate exterior body is used.
As shown in FIG. 2, the laminated electrode body accommodated in the laminate outer package 1 includes a laminated body in which positive plates 5 and negative plates 6 are alternately laminated with separators 7 interposed therebetween. And a separator 8 surrounding the periphery. The positive electrode plate 5, the negative electrode plate 6, the separator 7, and the separator 8 are impregnated with the nonaqueous electrolytic solution of the present disclosure.
The plurality of positive electrode plates 5 in the laminated electrode body are all 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 part of the laminate outer package 1. It protrudes outward from the peripheral end (FIG. 1). The portion where the positive electrode terminal 2 protrudes at the peripheral end of the laminate outer package 1 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 through a negative electrode tab (not shown), and a part of the negative electrode terminal 3 is part of the laminate exterior. It protrudes outward from the peripheral edge of the body 1 (FIG. 1). The portion where the negative electrode terminal 3 protrudes at the peripheral end of the laminate outer package 1 is sealed with an insulating seal 4.
In the laminate type battery according to the above example, the number of the positive plates 5 is 5 and the number of the negative plates 6 is 6, and the positive plates 5 and the negative plates 6 are separated from each other through the separators 7. All the outer layers are laminated in an arrangement to be the negative electrode plate 6. However, it is needless to say that the number of positive plates, the number of negative plates, and the arrangement in the laminated battery are not limited to this example, and various changes may be made.

As another example of the lithium secondary battery of the present disclosure, a coin-type battery is also included.
FIG. 3 is a schematic perspective view illustrating 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 into which a non-aqueous electrolyte is injected, a disc-shaped positive electrode 11, and spacer plates 17 and 18 such as stainless steel or aluminum as necessary are arranged in this order. In a laminated state, the positive electrode can 13 (hereinafter also referred to as “battery can”) and a sealing plate 14 (hereinafter also referred to as “battery can lid”) are accommodated. The positive electrode can 13 and the sealing plate 14 are caulked and sealed via a gasket 16.
In this example, the nonaqueous electrolytic solution of the present disclosure is used as the nonaqueous electrolytic solution injected into the separator 15.

In addition, the lithium secondary battery of this indication is obtained by charging / discharging a lithium secondary battery (lithium secondary battery before charging / discharging) containing a negative electrode, a positive electrode, and the non-aqueous electrolyte of the said indication. Lithium secondary batteries may be used.
That is, a lithium secondary battery according to the present disclosure is prepared by first preparing a lithium secondary battery before charge / discharge including a negative electrode, a positive electrode, and the non-aqueous electrolyte according to the present disclosure, and then, before the charge / discharge. It may be a lithium secondary battery (charged / discharged lithium secondary battery) produced by charging / discharging the lithium secondary battery one or more times.

  The use of the lithium secondary battery of the present disclosure is not particularly limited, and 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 supply applications, motors, automobiles, electric cars, motorcycles, electric bikes, bicycles, electric motors Bicycles, lighting fixtures, game machines, watches, electric tools, cameras, etc. can be widely used regardless of small portable devices or large devices.

Examples of the present disclosure will be described below, but the present disclosure is not limited to the following examples.
In the following, “addition amount” means content with respect to the total amount of the nonaqueous electrolyte finally obtained, and “wt%” means mass%.

[Example 1]
A coin-type lithium secondary battery (hereinafter, also referred to as “coin-type battery”) having the configuration shown in FIG. 3 was manufactured by the following procedure.

<Production of negative electrode>
Amorphous coated natural graphite (97 parts by mass), carboxymethylcellulose (1 part by mass) and SBR latex (2 parts by mass) were kneaded with an aqueous solvent to prepare a paste-like negative electrode mixture slurry.
Next, this negative electrode mixture slurry was applied to a negative electrode current collector made of a strip-shaped copper foil having a thickness of 10 μm, dried, and then compressed by a roll press to form a sheet-shaped negative electrode comprising a negative electrode current collector and a negative electrode active material layer Got. The coating density of the negative electrode active material layer at this time was 10 mg / cm ² , and the packing density was 1.5 g / ml.
Here, the amorphous coated natural graphite is an example of a negative electrode active material containing natural graphite, and is natural graphite coated with amorphous (amorphous) carbon.
The proportion of natural graphite in the amorphous coated natural graphite is 99% by mass.
Hereinafter, the above amorphous coated natural graphite may be referred to as “natural graphite 1”.

The natural graphite 1 (amorphous coated natural graphite) had the following R value, interplanar spacing d (002), and crystallite size. Since the ratio of natural graphite to natural graphite 1 (amorphous coated natural graphite) is 99% by mass, these values are substantially the values of natural graphite in natural graphite 1 (amorphous coated natural graphite). is there.
R value of Raman spectrum [I (1350) / I (1850)] = 0.123
-Distance between (002) planes measured by X-ray analysis d (002) = 0.33601 nm
-Crystallite size measured by X-ray analysis = 61.61Å

<Preparation of positive electrode>
LiCoO 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 prepare a paste-like positive electrode mixture slurry.
Next, this positive electrode mixture slurry is applied to a positive electrode current collector made of a strip-shaped aluminum foil having a thickness of 20 μm, dried, and then compressed by a roll press to form a sheet-like positive electrode comprising a positive electrode current collector and a positive electrode active material layer Got. The coating density of the positive electrode active material layer at this time was 30 mg / cm ² , and the packing density was 2.5 g / ml.

<Preparation of non-aqueous electrolyte>
While mixing ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (EMC) in a ratio of 34:33:33 (mass ratio) as a non-aqueous solvent, the electrolyte LiPF ₆ was finalized. The electrolyte concentration in the obtained non-aqueous electrolyte solution was dissolved so as to be 1 mol / liter.
With respect to the obtained solution, as an additive, the following compound (1-1), which is a specific example of the compound represented by the formula (1), is 0.5% by mass based on the total amount of the non-aqueous electrolyte. It added so that the non-aqueous electrolyte solution was obtained.

<Production of coin-type battery>
The negative electrode was 14 mm in diameter and the positive electrode was 13 mm in diameter, and each was punched into a disk shape to obtain a coin-shaped negative electrode and a coin-shaped positive electrode. Further, a microporous polyethylene film having a thickness of 20 μm was punched into a disk shape having a diameter of 17 mm to obtain a separator.
The obtained coin-shaped negative electrode, separator, and coin-shaped positive electrode were laminated in this order in a stainless steel battery can (2032 size), and then 20 μl of nonaqueous electrolyte was injected into the battery can. The separator, the positive electrode and the 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 the battery was sealed by caulking the battery can lid through a polypropylene gasket.
In this way, a coin-type battery (that is, a coin-type lithium secondary battery) having the configuration shown in FIG.

<Evaluation>
The following evaluation was implemented about the obtained coin-type battery.
Hereinafter, “conditioning” refers to repeating charging and discharging three times between 2.75 V and 4.2 V at 25 ° C. in a thermostat for a coin-type battery.
Hereinafter, “high temperature storage” means an operation of storing a coin-type battery in a constant temperature bath at 60 ° C. for 120 hours.

(Battery resistance; impedance before storage at high temperature (25 ° C, -10 ° C))
The coin-type battery obtained above was conditioned.
The SOC of the coin-type battery after conditioning was adjusted to 80%, then the impedance of the coin-type battery was measured, and the result obtained was taken as the impedance before high-temperature storage. The impedance was measured under two temperature conditions of 25 ° C. and −10 ° C.
Similarly, the impedance before storage at high temperature was measured for a coin-type battery of Comparative Example 1 described later.
As a relative value when the impedance before high-temperature storage in Comparative Example 1 was 100, the impedance (relative value) before storage at high temperature in Example 1 was determined.
The results are shown in Table 1.

(Battery resistance; impedance after high temperature storage (25 ° C, -10 ° C))
An operation of CC-CV charging to 4.25V at a charging rate of 0.2C at 25 ° C in a constant temperature bath to a coin-type battery after conditioning and before adjusting the SOC to 80%, followed by high-temperature storage The impedance after high-temperature storage was measured in the same manner as the measurement of impedance before high-temperature storage described above, except that was added.
Similarly, the impedance of the coin-type battery of Comparative Example 1 described later after high temperature storage was measured.
The impedance (relative value) after high-temperature storage in Example 1 was determined as a relative value when the impedance after high-temperature storage in Comparative Example 1 was 100.
The results are shown in Table 1.

(Battery resistance; DCIR before high-temperature storage (25 ° C., −20 ° C.))
The coin-type battery obtained above was conditioned.
The SOC (State of Charge) of the coin-type battery after conditioning was adjusted to 80%, and then DCIR (Direct Current Internal Resistance) before high-temperature storage of the coin-type battery was measured by the following method. The DCIR measurement was performed under two temperature conditions of 25 ° C and -20 ° C.
Using the above-described coin-type battery adjusted to SOC 80%, CC10s discharge at a discharge rate of 0.2C, pause for 300 seconds, CC10s discharge at a discharge rate of 1C, pause for 300 seconds, CC10s discharge at a discharge rate of 2C, A pause for 300 seconds and a CC10s discharge at a discharge rate of 5 C were performed in this order.
In addition, CC10s discharge means discharging for 10 seconds by a constant current (Constant Current).
The DC resistance is obtained based on the relationship between each discharge rate and the voltage 10 seconds after the start of discharge at each discharge rate, and the obtained DC resistance (Ω) is calculated as the battery resistance ( Ω).
The results are shown in Table 1.
Similarly, for a coin-type battery of Comparative Example 1 described later, DCIR before high-temperature storage was measured.
As a relative value when the DCIR before high temperature storage in Comparative Example 1 was 100, the DCIR (relative value) before high temperature storage in Example 1 was determined.
The results are shown in Table 1.

(Battery resistance; DCIR after high-temperature storage (25 ° C., −20 ° C.))
An operation of CC-CV charging to 4.25V at a charging rate of 0.2C at 25 ° C in a constant temperature bath to a coin-type battery after conditioning and before adjusting the SOC to 80%, followed by high-temperature storage The DCIR after high-temperature storage was measured in the same manner as the above-described measurement of DCIR before high-temperature storage except that was added.
Similarly, for a coin-type battery of Comparative Example 1 described later, DCIR after high-temperature storage was measured.
As a relative value when the DCIR after high temperature storage in Comparative Example 1 was 100, the DCIR (relative value) after high temperature storage in Example 1 was determined.
The results are shown in Table 1.

(Discharge capacity after high-temperature storage (residual capacity; 0.2C))
The coin-type battery obtained above was conditioned.
The coin-type battery after conditioning was CC-CV charged to 25 ° C at a charge rate of 0.2C to 4.25V at 25 ° C, and then stored at high temperature.
The coin-type battery after high-temperature storage was subjected to CC discharge at 25 ° C. at a discharge rate of 0.2 C, and the discharge capacity (residual capacity; 0.2 C) after high-temperature storage was measured.
Similarly, for the coin-type battery of Comparative Example 1 described later, the discharge capacity (0.2 C) after high-temperature storage was measured.
The discharge capacity after high-temperature storage in Example 1 (residual capacity; 0.2 C) (relative value) as a relative value when the discharge capacity after high-temperature storage in Comparative Example 1 (residual capacity; 0.2 C) is 100. Asked.
The results are shown in Table 2.

(Discharge capacity after high-temperature storage (recovery capacity; 0.2C))
The above-described conditioning was applied to the coin-type battery obtained above.
The coin-shaped battery after conditioning was CC-CV charged to 4.25 V at a charging rate of 0.2 C at 25 ° C. in a thermostatic chamber, and then stored at a high temperature.
The coin-type battery after high-temperature storage is CC-discharged at 25 ° C. in a thermostatic chamber at a discharge rate of 0.2 C until the SOC becomes 0%, and then CC-CV charge to 4.2 V at a charge rate of 0.2 C. Then, CC discharge was performed at a discharge rate of 0.2 C, and the discharge capacity after high temperature storage (recovery capacity; 0.2 C) was measured.
Similarly, in Comparative Example 1 described later, the discharge capacity (recovery capacity; 0.2C) of the coin-type battery after high temperature storage was measured.
As a relative value when the discharge capacity after high temperature storage (recovery capacity; 0.2 C) in Comparative Example 1 is taken as 100, the discharge capacity after high temperature storage in Example 1 (recovery capacity; 0.2 C) (relative value) Asked.
The results are shown in Table 2.

(Open voltage drop rate after high temperature storage)
The above-described conditioning was applied to the coin-type battery obtained above.
The coin-shaped battery after conditioning was CC-CV charged to 4.25 V at a charging rate of 0.2 C at 25 ° C. in a thermostatic chamber, and then stored at a high temperature.
About the coin-type battery after high temperature storage, open circuit voltage (OCV) [V] was measured at 25 degreeC, and the obtained value was made into the open voltage [V] after high temperature storage. Based on the obtained open-circuit voltage [V] after high-temperature storage, the open-circuit voltage reduction rate was calculated by the following formula.
Open voltage drop rate [%]
= ((4.25−Open voltage after high temperature storage [V]) / 4.25) × 100 [%]

Similarly, Comparative Example 1 described later was used to measure the open circuit voltage drop rate after high-temperature storage.
As a relative value when the open circuit voltage decrease rate after high temperature storage in Comparative Example 1 was 100, the open circuit voltage decrease rate (relative value) after high temperature storage in Example 1 was determined.
The results are shown in Table 2.
In addition, the lower the open circuit voltage drop rate of the battery, the better.

[Comparative Example 1]
The same operation as in Example 1 was performed except that the compound represented by the formula (1) was not contained in the nonaqueous electrolytic solution.
The results are shown in Tables 1 and 2.

[Comparative Examples 2 and 3]
The same operation as in Example 1 was performed except that the compound (1-1) was changed to the following comparative compound (C1) or the following comparative compound (C2) having the same mass.
The results are shown in Tables 1 and 2.

  In Tables 1 and 2, natural graphite 1 means the above-mentioned amorphous coated natural graphite.

As shown in Table 1, in Example 1 in which the compound represented by the formula (1) was contained in the non-aqueous electrolyte, the non-aqueous electrolyte did not contain the compound represented by the formula (1) Compared to Example 1, the battery resistance (specifically, impedance and DCIR) was reduced.
As shown in Table 2, in Example 1 in which the compound represented by the formula (1) was contained in the non-aqueous electrolyte, the non-aqueous electrolyte did not contain the compound represented by the formula (1) Compared with Example 1, the open circuit voltage drop rate was improved (that is, reduced), and the battery capacity (discharge capacity) was also improved.

  Moreover, the compound represented by Formula (1) applicable to a condensed cyclic compound by comparison of Example 1 and Comparative Examples 2 and 3 in Table 2 is a conventional cyclic sulfate that does not correspond to a condensed cyclic compound. Compared with the compounds (that is, comparative compounds (C1) and (C2)), it is confirmed that the effect of improving (that is, reducing) the open-circuit voltage reduction rate and the effect of improving the battery capacity (discharge capacity) are excellent. It was done.

Example 101
A coin-type battery was produced in the same manner as in Example 1.
About the produced coin-type battery, it carried out similarly to Example 1, and measured DCIR (-20 degreeC) before high temperature preservation | save and DCIR (-20 degreeC) after high temperature preservation | save.
The results are shown in Table 3.
In Table 3 and Table 4 to be described later, the DCIR measurement results are expressed in absolute values (Ω).

[Comparative Example 101]
The same operation as in Example 101 was performed except that the non-aqueous electrolyte solution did not contain the compound represented by formula (1).
The results are shown in Table 3.

[Comparative Example 102]
The same operation as in Example 101 was performed except that natural graphite 1 was changed to artificial graphite 1 having the same mass and the following properties.
The results are shown in Table 3.

The artificial graphite 1 had the following R value, interplanar spacing d (002), and crystallite size.
R value of Raman spectrum [I (1350) / I (1850)] = 0.076
-(002) plane spacing d (002) = 0.33534 nm measured by X-ray analysis
-Crystallite size measured by X-ray analysis = 131.17Å

[Comparative Example 103]
The same operation as in Comparative Example 102 was performed except that the non-aqueous electrolyte solution did not contain the compound represented by formula (1).
The results are shown in Table 3.

In Table 3, the comparison between Example 101 and Comparative Example 101 shows that the non-aqueous electrolyte contains a compound represented by the formula (1) under the condition that the negative electrode active material is natural graphite 1 (implementation) In Example 101), it can be seen that the DCIR is reduced as compared to the case where the non-aqueous electrolyte does not contain the compound represented by the formula (1) (Comparative Example 101).
On the other hand, in Table 3, from the comparison between Comparative Example 102 and Comparative Example 103, the non-aqueous electrolyte contains a compound represented by Formula (1) under the condition that the negative electrode active material is artificial graphite 1. In this case (Comparative Example 102), it can be seen that the DCIR rises as compared with the case where the non-aqueous electrolyte does not contain the compound represented by Formula (1) (Comparative Example 103).

[Examples 201 to 204]
A coin-type battery was produced in the same manner as in Example 1 except that other additives were further added to the non-aqueous electrolyte. The amount of other additives added was 0.5% by mass.
About the produced coin-type battery, DCIR before high temperature storage was measured similarly to the measurement of DCIR before high temperature storage in Example 101.
The results are shown in Table 4.

Other additives used in Examples 201 to 204 are LiBOB, Compound (X1-1), Compound (X2-1), and Compound (X3-25) shown below.
These compounds are all boron compounds, and among these, the compound (X1-1), the compound (X2-1), and the compound (X3-25) are the boron compounds (X) (that is, 1 This is a specific example of a boron compound (X) including a structure in which three O (oxygen atoms) are bonded to one B (boron atom).
LiBOB is another boron compound other than the boron compound (X), and does not include a structure in which three Os are bonded to one B, but instead has a structure in which four Os are bonded to one B. Contains.

As shown in Table 4, a compound represented by the formula (1) and a boron compound (X) containing a structure in which three Os are bonded to one B are used in combination as an additive for a nonaqueous electrolyte. (Examples 202 to 204), as an additive for the non-aqueous electrolyte, a compound represented by the formula (1) and LiBOB including a structure in which four Os are bonded to one B, Compared with the case of using together (Example 201), the battery resistance before high temperature storage (that is, the initial battery resistance) was further reduced.
The reason for this is not clear, but since boron compound (X) has fewer O atoms bonded to B than LiBOB, it has better reactivity on the edge surface of graphite, and as a result, more on the negative electrode. This is probably because a uniform film is formed. More specifically, the compound represented by the formula (1) and the boron compound are hybridized by using the compound represented by the formula (1) and the boron compound in combination as an additive for the non-aqueous electrolyte. It is considered that a low resistance film is formed on the negative electrode. At this time, by selecting the boron compound (X) as the boron compound, a more uniform low-resistance film is formed on the negative electrode. As a result, the battery resistance before high-temperature storage (ie, the initial battery resistance) is reduced. It is thought that it is reduced more effectively.

DESCRIPTION OF SYMBOLS 1 Laminate exterior body 2 Positive electrode terminal 3 Negative electrode terminal 4 Insulation seal 5 Positive electrode plate 6 Negative electrode plates 7 and 8 Separator 11 Positive electrode 12 Negative electrode 13 Positive electrode can 14 Sealing plate 15 Separator 16 Gaskets 17 and 18 Spacer plate

Claims (8)

A non-aqueous electrolyte for a battery used in a battery comprising a negative electrode containing a negative electrode active material containing natural graphite,
A nonaqueous electrolytic solution for a battery containing a compound represented by the following formula (1).

[In Formula (1), R < ¹ > and R < ² > represents a hydrogen atom, a halogen atom, a C1-C3 alkyl group, or a C1-C3 halogenated alkyl group each independently. ]   The battery nonaqueous electrolyte solution according to claim 1, wherein the content of the compound represented by the formula (1) with respect to the total amount of the battery nonaqueous electrolyte solution is 0.001 mass% to 10 mass%.   Furthermore, the non-aqueous electrolyte for batteries of Claim 1 or 2 containing the boron compound (X) containing the structure which three oxygen atoms couple | bonded with respect to one boron atom.   The battery nonaqueous electrolyte solution according to claim 3, wherein the molecular weight of the boron compound (X) is 1000 or less. The nonaqueous battery for battery according to claim 3 or 4, wherein the boron compound (X) is at least one selected from the group consisting of compounds represented by the following formula (X1) to the following formula (X3). Electrolytic solution.

[In formula (X1), R ^{<X11 >} -R ^<X13> represents an unsubstituted aryl group or a C1-C12 aliphatic group each independently.
In formula (X2), n represents an integer of 1 to 5, and M ⁺ represents a Li ⁺ ion or an H ⁺ ion. When n is an integer of 2 to 5, a plurality of M ⁺ may be the same or different.
In formula (X3), R represents a C 1-12 alkyl group, a C 2-12 alkenyl group, or a group represented by formula (RX). In the formula (RX), R ^{X31 to} R ^X33 each independently represent a hydrogen atom, a halogen atom, an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, or an aryl group having 6 to 12 carbon atoms. * Represents a bonding position. ] In the formula (X1), R ^{X11 to} R ^X13 each independently represent a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a t-butyl group, a cyclohexyl group, or a phenyl group. Represents
In the formula (X2), M ⁺ represents a Li ⁺ ion,
In formula (X3), R represents the group represented by formula (RX), The nonaqueous electrolyte solution for batteries of Claim 5. A positive electrode;
A negative electrode including a negative electrode active material including natural graphite;
The nonaqueous electrolytic solution for a battery according to any one of claims 1 to 6,
Including lithium secondary battery.   A lithium secondary battery obtained by charging and discharging the lithium secondary battery according to claim 7.