Patent Application
20210313624
The present invention relates to a nonaqueous electrolyte solution and a nonaqueous electrolyte secondary battery.
The optimization of various battery elements including positive electrode and negative electrode active materials has been investigated as a means for improving the durability of nonaqueous electrolyte secondary batteries until now. Nonaqueous electrolyte solutions are not also exceptions, and it has been proposed to suppress deterioration due to the decomposition of an electrolyte solution on the surfaces of the active positive and negative electrodes, by using various kinds of durability improvers.
Patent Literature 1, for example, discloses that a sulfonate compound in which a cyclic sulfone group is bound to a sulfonate group (a sulfonic acid ester group) is included in an electrolyte solution as an additive to improve a high temperature characteristic and a lifetime characteristic (cycle characteristic) of lithium batteries. It furthermore discloses that the second lithium salt including N(SO2F)2− may be included in the electrolyte solution, and bis(fluorosulfonyl)imide lithium (hereinafter, may be referred to as “LiFSI”) is provided as an example of the second lithium salt. In addition, Patent Literatures 2 and 3, for example, disclose that durability such as a high temperature shelf life (high temperature storage characteristic) is improved using an electrolyte solution containing a dicarboxylic acid such as oxalic acid and an imide salt having a phosphoryl group as additives. It is however neither disclosed nor suggested that these additives are used in combination with e.g., a cyclic sulfonate compound at all.
Patent Literature 1: U.S. Patent Application No. 2017/0271715
Patent Literature 2: WO2011/024251 Pamphlet
Patent Literature 3: Japanese Unexamined Patent Application Publication No. (hereinafter referred to as “JP-A-”) 2013-051122
As described in Patent Literature 1, an electrolyte solution containing a sulfonate compound in which a cyclic sulfone group is bound to a sulfonate group, and moreover LiFSI as an additive tends to improve the high temperature characteristic and lifetime characteristic (cycle characteristic) of lithium batteries. However, it has been desired that the high temperature storage characteristic and the internal resistance characteristic after storage as demanded for car batteries and large fixed batteries be further improved.
Therefore, the subject of the present invention is to provide a nonaqueous electrolyte solution which is capable of improving the high temperature storage characteristic and the internal resistance characteristic after storage in a more balanced manner as well as a nonaqueous electrolyte secondary battery comprising the nonaqueous electrolyte solution.
As a result of diligent investigations in view of such subject, the present inventors found that the high temperature storage characteristic and the internal resistance characteristic after storage can be improved in a more balanced manner, by adding a salt having an imide anion having a specific structure, to a nonaqueous electrolyte solution including a nonaqueous solvent, a solute and a sulfonate compound when the electrolyte solution is used for nonaqueous electrolyte secondary batteries, thereby completing the present invention.
Specifically, the present invention relates to a nonaqueous electrolyte solution comprising the following components:
(I) at least one selected from the salts having an imide anion represented by the following general formulae [1] and [2],
(II) a sulfonate compound represented by the following general formula [3],
(III) a nonaqueous organic solvent or an ionic liquid, and
(IV) a solute:
wherein,
in the general formula [1],
R1 to R4 are each independently a fluorine atom or an organic group selected from a C1-10 linear alkyl group, a C3-10 branched alkyl group, a C1-10 linear alkoxy group, a C3-10 branched alkoxy group, a C2-10 alkenyl group, a C2-10 alkenyloxy group, a C2-10 alkynyl group, a C2-10 alkynyloxy group, a C3-10 cycloalkyl group, a C3-10 cycloalkoxy group, a C3-10 cycloalkenyl group, a C3-10 cycloalkenyloxy group, a C6-10 aryl group and a C6-10 aryloxy group, wherein a fluorine atom, an oxygen atom or an unsaturated bond may exist in the organic group, with the proviso that at least one of R1 to R4 is a fluorine atom,
Mm+ is an alkali metal cation, an alkaline earth metal cation or an onium cation, and
m is an integer which is the same as the valence of the corresponding cation;
in the general formula [2],
R5 to R7 are each independently a fluorine atom or an organic group selected from a C1-10 linear alkyl group, a C3-10 branched alkyl group, a C1-10 linear alkoxy group, a C3-10 branched alkoxy group, a C2-10 alkenyl group, a C2-10 alkenyloxy group, a C2-10 alkynyl group, a C2-10 alkynyloxy group, a C3-10 cycloalkyl group, a C3-10 cycloalkoxy group, a C3-10 cycloalkenyl group, a C3-10 cycloalkenyloxy group, a C6-10 aryl group and a C6-10 aryloxy group, wherein a fluorine atom, an oxygen atom or an unsaturated bond may exist in the organic group, with the proviso that at least one of R5 to R7 is a fluorine atom,
Mm+ is an alkali metal cation, an alkaline earth metal cation or an onium cation, and
m is an integer which is the same as the valence of the corresponding cation; and
in the formula [3],
Ra is a halogen atom, a C1-20 alkyl group which may be substituted with a halogen atom, a C5-20 cycloalkyl group which may be substituted with a halogen atom, a C2-20 alkenyl group which may be substituted with a halogen atom, a C2-20 alkynyl group which may be substituted with a halogen atom, a C6-40 aryl group which may be substituted with a halogen atom, a C2-40 heteroaryl group which may be substituted with a halogen atom, a C1-20 alkoxy group which may be substituted with a halogen atom, a C5-20 cycloalkoxy group which may be substituted with a halogen atom, a C2-20 alkenyloxy group which may be substituted with a halogen atom, a C2-20 alkynyloxy group which may be substituted with a halogen atom, a C6-40 aryloxy group which may be substituted with a halogen atom, or a C2-40 heteroaryloxy group which may be substituted with a halogen atom,
Rb to Rh are each independently a hydrogen atom, a halogen atom, a C1-20 alkyl group which may be substituted with a halogen atom, a C2-20 alkenyl group which may be substituted with a halogen atom, a C2-20 alkynyl group which may be substituted with a halogen atom, a C1-20 alkoxy group which may be substituted with a halogen atom, a C5-20 cycloalkyl group which may be substituted with a halogen atom, a C6-40 aryl group which may be substituted with a halogen atom, or a C2-40 heteroaryl group which may be substituted with a halogen atom, and
Y is an oxygen atom or a carbon atom, and, when Y is an oxygen atom, Rf and Rg do not exist.
An action mechanism for improving battery characteristics by the present invention is not clear; however, it is important to use at least one selected from salts having an imide anion represented by the general formulae [1] and [2] (Component(I)) described above, and a sulfonate compound represented by the general formula [3] (Component(II)) described above in combination.
It is thought that a part of the above (I) and (II) is decomposed on the interface between a positive electrode and an electrolyte solution and the interface between a negative electrode and an electrolyte solution so as to form a film. This film suppresses a direct contact between the nonaqueous organic solvent and solute, and active materials to prevent the decomposition of the nonaqueous organic solvent and solute during storage at high temperatures, and to suppress the deterioration of battery performance (a capacity reduction and a resistance increase). In addition, while the mechanism is unknown, it is important that an imide anion have a phosphoryl moiety (—P(═O)RR), and it is thought that because both a phosphoryl moiety derived from the above Component (I) and a sulfone moiety derived from the above Component (II) are incorporated into the above composite film, the resultant film is stronger and has higher lithium conductivity, i.e. a film with a low resistance (a film with a good output characteristic). Furthermore, it is thought that the above effect is obtained due to that a moiety having a high electron withdrawing property (e.g. a fluorine atom and a fluorine-containing alkoxy group) is included in an imide anion, thereby further increasing a charge bias, and forming a film having a lower resistance (a film with a better output characteristic). Furthermore, it is presumed that when a hexafluorophosphoric acid anion or a tetrafluoroboric acid anion is included, a composite film including a fluoride thereof is formed, thereby forming a film which is more stable at high temperatures. From the reasons described above, it is assumed that the high temperature storage characteristic and the effect of suppressing an increase in internal resistance at storage are obtained in a balanced manner, by using the nonaqueous electrolyte solution of the present invention.
When the salt having an imide anion has a P—F bond and an S—F bond, an excellent “internal resistance characteristic after storage” is obtained. It is preferred that the number of P—F bonds and S—F bonds in the above salt having an imide anion is higher, because “internal resistance characteristic after storage” can be further improved, and it is further preferred that all of R1 to R7 of the above general formulae [1] and [2] are a fluorine atom.
Further, in the above general formula [1], it is preferred that:
at least one of R1 to R4 be a fluorine atom, and
at least one of remaining R1 to R4 be a group selected from an alkyl group, an alkenyl group, an alkynyl group, an aryl group, an alkoxy group, an alkenyloxy group, an alkynyloxy group and an aryloxy group, which have 6 or less carbon atoms and may include a fluorine atom.
In addition, in the above general formula [1], it is preferred that:
at least one of R1 to R4 be a fluorine atom, and
at least one of remaining R1 to R4 be a group selected from a methyl group, a methoxy group, an ethyl group, an ethoxy group, an n-propyl group, an isopropyl group, an n-propoxy group, an isopropoxy group, a vinyl group, an allyl group, an allyloxy group, an ethynyl group, a 2-propynyl group, a 2-propynyloxy group, a phenyl group, a phenoxy group, a trifluoromethyl group, a trifluoromethoxy group, a 2,2-difluoroethyl group, a 2,2-difluoroethoxy group, a 2,2,2-trifluoroethyl group, a 2,2,2-trifluoroethoxy group, a 2,2,3,3-tetrafluoropropyl group, a 2,2,3,3-tetrafluoropropoxy group, a 1,1,1,3,3,3-hexafluoroisopropyl group and a 1,1,1,3,3,3-hexafluoroisopropoxy group.
Further, in the above general formula [2], it is preferred that:
at least one of R5 to R7 be a fluorine atom, and
at least one of remaining R5 to R7 be a group selected from an alkyl group, an alkenyl group, an alkynyl group, an aryl group, an alkoxy group, an alkenyloxy group, an alkynyloxy group and an aryloxy group, which have 6 or less carbon atoms and may include a fluorine atom.
In addition, in the above general formula [2], it is preferred that:
at least one of R5 to R7 be a fluorine atom, and
at least one of remaining R5 to R7 be a group selected from a methyl group, a methoxy group, an ethyl group, an ethoxy group, an n-propyl group, an isopropyl group, an n-propoxy group, an isopropoxy group, a vinyl group, an allyl group, an allyloxy group, an ethynyl group, a 2-propynyl group, a 2-propynyloxy group, a phenyl group, a phenoxy group, a trifluoromethyl group, a trifluoromethoxy group, a 2,2-difluoroethyl group, a 2,2-difluoroethoxy group, a 2,2,2-trifluoroethyl group, a 2,2,2-trifluoroethoxy group, a 2,2,3,3-tetrafluoropropyl group, a 2,2,3,3-tetrafluoropropoxy group, a 1,1,1,3,3,3-hexafluoroisopropyl group and a 1,1,1,3,3,3-hexafluoroisopropoxy group.
The counter cations of the above salts having an imide anion represented by the general formulae [1] and [2] are preferably selected from the group consisting of a lithium ion, a sodium ion, a potassium ion and a tetraalkylammonium ion.
It is preferred that Ra of the above general formula [3] be an F atom, a Cl atom, a Br atom, an I atom, a methyl group, a methoxy group, an ethyl group, an ethoxy group, an n-propyl group, an n-propoxy group, an isopropyl group, an isopropoxy group, a 2-propenyl group, a 2-propenyloxy group, a 2-propynyl group, an n-butyl group, a tert-butyl group, a trifluoromethyl group, a trifluoroethyl group, a trifluoroethoxy group, a phenyl group, a phenoxy group, a naphthyl group, a perfluorophenyl group, a perfluorophenoxy group, a pyrrolyl group or a pyridinyl group, and the above Rb to Rh be each independently a hydrogen atom, an F atom, a Cl atom, a Br atom, an I atom, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a tert-butyl group, a trifluoromethyl group, a trifluoroethyl group, a phenyl group, a naphthyl group, a trifluorophenyl group, a pyrrolyl group or a pyridinyl group.
The above sulfonate compound represented by the general formula [3] is preferably a sulfonate compound represented by the following general formula [4] or [5]:
wherein, in the formula [4], Rj is a halogen atom, a C1-20 alkyl group which may be substituted with a halogen atom, a C5-20 cycloalkyl group which may be substituted with a halogen atom, a C2-20 alkenyl group which may be substituted with a halogen atom, a C2-20 alkynyl group which may be substituted with a halogen atom, a C6-40 aryl group which may be substituted with a halogen atom, a C2-40 heteroaryl group which may be substituted with a halogen atom, a C1-20 alkoxy group which may be substituted with a halogen atom, a C5-20 cycloalkoxy group which may be substituted with a halogen atom, a C2-20 alkenyloxy group which may be substituted with a halogen atom, a C2-20 alkynyloxy group which may be substituted with a halogen atom, a C6-40 aryloxy group which may be substituted with a halogen atom, or a C2-40 heteroaryloxy group which may be substituted with a halogen atom, and
Rk and Rl are each independently a hydrogen atom, a halogen atom, a C1-20 alkyl group which may be substituted with a halogen atom, a C2-20 alkenyl group which may be substituted with a halogen atom, a C2-20 alkynyl group which may be substituted with a halogen atom, a C1-20 alkoxy group which may be substituted with a halogen atom, a C5-20 cycloalkyl group which may be substituted with a halogen atom, a C6-40 aryl group which may be substituted with a halogen atom, or a C2-40 heteroaryl group which may be substituted with a halogen atom; and
in the formula [5], Rr is a halogen atom, a C1-20 alkyl group which may be substituted with a halogen atom, a C5-20 cycloalkyl group which may be substituted with a halogen atom, a C2-20 alkenyl group which may be substituted with a halogen atom, a C2-20 alkynyl group which may be substituted with a halogen atom, a C6-40 aryl group which may be substituted with a halogen atom, a C2-40 heteroaryl group which may be substituted with a halogen atom, a C1-20 alkoxy group which may be substituted with a halogen atom, a C5-20 cycloalkoxy group which may be substituted with a halogen atom, a C2-20 alkenyloxy group which may be substituted with a halogen atom, a C2-20 alkynyloxy group which may be substituted with a halogen atom, a C6-40 aryloxy group which may be substituted with a halogen atom, or a C2-40 heteroaryloxy group which may be substituted with a halogen atom, and
Rp and Rq are each independently a hydrogen atom, a halogen atom, a C1-20 alkyl group which may be substituted with a halogen atom, a C2-20 alkenyl group which may be substituted with a halogen atom, a C2-20 alkynyl group which may be substituted with a halogen atom, a C1-20 alkoxy group which may be substituted with a halogen atom, a C5-20 cycloalkyl group which may be substituted with a halogen atom, a C6-40 aryl group which may be substituted with a halogen atom, or a C2-40 heteroaryl group which may be substituted with a halogen atom.
Both Rk and Rl of the above formula [4] are preferably a hydrogen atom from the viewpoint that internal resistance tends to reduce. Similarly, both Rp and Rq of the above formula [5] are also preferably a hydrogen atom.
It is preferred that Rj of the above general formula [4] be an F atom, a Cl atom, a Br atom, an I atom, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a tert-butyl group, a trifluoromethyl group, a trifluoroethyl group, a methoxy group, a 2-propynyl group, a phenyl group, a naphthyl group, a trifluorophenyl group, a pyrrolyl group or a pyridinyl group, and the above Rk and Rl be each independently a hydrogen atom, an F atom, a Cl atom, a Br atom, an I atom, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a tert-butyl group, a trifluoromethyl group, a trifluoroethyl group, a phenyl group, a naphthyl group, a trifluorophenyl group, a pyrrolyl group or a pyridinyl group.
It is preferred that Rr of the above general formula [5] be an F atom, a Cl atom, a Br atom, an I atom, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a tert-butyl group, a trifluoromethyl group, a trifluoroethyl group, a methoxy group, a 2-propynyl group, a phenyl group, a naphthyl group, a trifluorophenyl group, a pyrrolyl group or a pyridinyl group, and the above Rp and Rq be each independently a hydrogen atom, an F atom, a Cl atom, a Br atom, an I atom, a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, a tert-butyl group, a trifluoromethyl group, a trifluoroethyl group, a phenyl group, a naphthyl group, a trifluorophenyl group, a pyrrolyl group or a pyridinyl group.
The sulfonate compound represented by the above general formula [3] is preferably at least one selected from compounds represented by the following formulae [6] to [23].
It is preferred that all of Rb and Ra of the above formula [3], Rk and Rl of the above formula [4], and Rp and Rq of the above formula [5] be a hydrogen atom from the viewpoint that internal resistance tends to reduce. In a case where the compound of the above-described formula [6] is used, for example, internal resistance is excellent compared to a case where the compound of the above-described formula [11] is used. Therefore, the above-described formulae [6] and [13] to [23] wherein all of Rb and Rh of the above formula [3], Rk and Rl of the above formula [4], and Rp and Rq of the above formula [5] are a hydrogen atom are more preferred. Among them, more preferred are the above-described formulae [6], [13], [14], [16], [17], [19], [20] and [23], and particularly preferred are the formula [6], [13], [14], [17] and [23] from the viewpoint that both the high temperature storage characteristic and internal resistance characteristic after storage are improved.
The sulfonate compound of the component (II) can be manufactured by various methods. The compound of the above formula [6], for example, can be obtained by a manufacturing method described in paragraph [0107] to [0116] of Patent Literature 1. Other sulfonate compounds can be also obtained by changing corresponding materials in the same manufacturing method.
The amount of the component (I) to be included is preferably 0.005 to 12.0 mass % with respect to the total amount of the components (I) to (IV). When the amount is above 12.0 mass %, there is a risk that the viscosity of the resultant electrolyte solution increases and characteristics are reduced at low temperatures, and when the amount is less than 0.005 mass %, there is a risk that the formation of a film is insufficient and the effect of improving characteristics is difficult to obtain.
The amount of the component (II) to be included is preferably 0.01 to 10.0 mass %, more preferably 0.1 to 5.0 mass %, and particularly preferably 0.2 to 1.5 mass % with respect to the total amount of the components (I) to (IV).
The component (III) is preferably at least one selected from the group consisting of cyclic carbonates, chain carbonates, cyclic esters, chain esters, cyclic ethers, chain ethers, sulfone compounds, sulfoxide compounds and ionic liquids. It is further preferred to include a cyclic carbonate, and it is particularly preferred to contain one or more selected from ethylene carbonate, propylene carbonate, fluoroethylene carbonate, vinylene carbonate, vinylethylene carbonate.
The component (IV) is preferably at least one selected from the group consisting of LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, LiC4F9SO3, LiAlO2, LiAlCl4, LiN(CxF2x+1SO2)(CyF2y+1SO2) (wherein 2≤x≤20 and 2≤y≤20), LiCl, LiI, LiPF2(C2O4)2, LiPF4(C2O4), LiP(C2O4)3, LiBF2(C2O4), LiB(C2O4)2, LiPO2F2, LiN(CF3SO2)2, LiN(CF3SO2) (FSO2), LiSO3F, NaPF6, NaBF4, NaSbF6, NaAsF6, NaClO4, NaCF3SO3, NaC4F9SO3, NaAlO2, NaAlCl4, NaN(CxF2x+1SO2)(CyF2y+1SO2) (wherein 2≤x≤20 and 2≤y≤20), NaCl, NaI, NaPF2(C2O4)2, NaPF4(C2O4), NaP(C2O4)3, NaBF2(C2O4), NaB(C2O4)2, NaPO2F2, NaN(CF3SO2)2, NaN(CF3SO2)(FSO2) and NaSO3F.
In addition, lithium batteries and lithium ion batteries preferably contain at least LiPF6 as the component (IV). When LiPF6 and another component (IV) are used in combination, it is preferred to use at least one selected from the group consisting of LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, LiC4F9SO3, LiAlO2, LiAlCl4, LiCl, LiI, LiPF2 (C2O4)2, LiPF4(C2O4), LiP(C2O4)3, LiBF2(C2O4), LiB(C2O4)2, LiPO2F2 and LiSO3F as such another component (IV).
Further, sodium ion batteries preferably contain at least NaPF6 as the component (IV). When NaPF6 and another component (IV) are used in combination, it is preferred to use at least one selected from the group consisting of NaBF4, NaSbF6, NaAsF6, NaClO4, NaCF3SO3, NaC4F9SO3, NaAlO2, NaAlCl4, NaCl, NaI, NaPF2(C2O4)2, NaPF4 (C404), NaP(C2O4) 3, NaBF2 (C2O4), NaB(C2O4)2, NaPO2F2, and NaSO3F as such another component (IV).
Furthermore, at least one additive selected from the group consisting of vinylene carbonate, vinylethylene carbonate, fluoroethylene carbonate, 1,6-diisocyanatohexane, ethynylethylene carbonate, trans-difluoroethylene carbonate, propane sultone, propene sultone, 1,3,2-dioxathiolane-2,2-dioxide, 4-propyl-1,3,2-dioxathiolane-2,2-dioxide, methanesulfonyl fluoride, methylene methanedisulfonate, 1,2-ethanedisulfonic anhydride, tris(trimethylsilyl)borate, succinonitrile, (ethoxy)pentafluorocyclotriphosphazene, methanesulfonyl fluoride, t-butylbenzene, t-amylbenzene, fluorobenzene and cyclohexylbenzene may be contained in the above nonaqueous electrolyte solution.
The present invention relates to a nonaqueous electrolyte secondary battery comprising at least a positive electrode, a negative electrode and the above nonaqueous electrolyte solution.
According to the present invention, it is possible to provide a nonaqueous electrolyte solution which is capable of improving a high temperature storage characteristic and a internal resistance characteristic after storage in a more balanced manner, as well as a nonaqueous electrolyte secondary battery comprising the nonaqueous electrolyte solution.
The present invention will now be described in detail. In this case, the description of constituent features below is an example of the embodiments of the present invention, and the present invention is not limited to these specific contents. The present invention can be carried out with various modifications within the scope of its gist.
The nonaqueous electrolyte solution of the present invention comprises at least one selected from salts having an imide anion represented by the above general formulae [1] and [2] (Component (I)), a sulfonate compound represented by the above general formula [3] (Component (II)), a nonaqueous organic solvent or an ionic liquid (Component (III)), and a solute (Component (IV)).
(I) Salt having an imide anion represented by above general formula [1]:
It is important that at least one of R1 to R4 of the above general formula [1] is a fluorine atom. While the reason is not clear, the effect of suppressing the internal resistance increase of batteries using the electrolyte solution is not sufficient when at least one fluorine atom is not included.
In addition, examples of the alkyl group and alkoxyl group represented by R1 to R4 of the above general formula [1] include C1-10 alkyl groups and fluorine-containing alkyl groups such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a secondary butyl group, a tertiary butyl group, a pentyl group, a 2,2-difluoroethyl group, a 2,2,2-trifluoroethyl group, a 2,2,3,3-tetrafluoropropyl group, and 1,1,1,3,3,3-hexafluoroisopropyl group, and alkoxy groups derived from these groups.
Examples of the alkenyl group and alkenyloxy group include C2-10 alkenyl groups and fluorine-containing alkenyl groups such as a vinyl group, an allyl group, a 1-propenyl group, an isopropenyl group, a 2-butenyl group, and a 1,3-butadienyl group, and alkenyloxy groups derived from these groups.
Examples of the alkynyl group and alkynyloxy group include C2-10 alkynyl groups and fluorine-containing alkynyl groups such as an ethynyl group, a 2-propynyl group, and a 1,1-dimethyl-2-propynyl group, and alkynyloxy groups derived from these groups.
Examples of the cycloalkyl group and cycloalkoxy group include C3-10 cycloalkyl groups and fluorine-containing cycloalkyl groups such as a cyclopentyl group and a cyclohexyl group, and cycloalkoxy groups derived from these groups.
Examples of the cycloalkenyl group and cycloalkenyloxy group include C3-10 cycloalkenyl groups and fluorine-containing cycloalkenyl groups such as a cyclopentenyl group and a cyclohexenyl group, and cycloalkenyloxy groups derived from these groups.
Examples of the aryl group and aryloxy group include C6-10 aryl groups and fluorine-containing aryl groups such as a phenyl group, a tolyl group and a xylyl group, and aryloxy groups derived from these groups.
More specific examples of negative ions of salts having an imide anion represented by the above general formula [1] include Compounds No. 1 to No. 9 below, etc. However, the salts having an imide anion used in the present invention are not restricted in any way by examples below.
In the above general formula [1], it is preferred that at least one of R1 to R4 be a fluorine atom and at least one of R1 to R4 be a group selected from an alkyl group, an alkenyl group, an alkynyl group, an aryl group, an alkoxy group, an alkenyloxy group, an alkynyloxy group and an aryloxy group which have 6 or less carbon atoms and may include a fluorine atom. When the above number of carbon atoms is above 6, internal resistance of a film formed on an electrode tends to be relatively high. It is preferred that the above number of carbon atoms be 6 or less because the above internal resistance tends to be lower, and it is particularly preferred that R1 to R4 be at least one group selected from a methyl group, an ethyl group, a propyl group, a vinyl group, an allyl group, an ethynyl group, a 2-propynyl group, a phenyl group, a trifluoromethyl group, a 2,2-difluoroethyl group, a 2,2,2-trifluoroethyl group, a 2,2,3,3-tetrafluoropropyl group, a 1,1,1,3,3,3-hexafluoroisopropyl group, and alkoxy groups, alkenyloxy groups, and alkynyloxy groups derived from these groups because a nonaqueous electrolyte secondary battery which is capable of providing a cycle characteristic and an internal resistance characteristic in a balanced manner is obtained. Among them, the above Compounds No. 1, No. 2, No. 3 and No. 5 are particularly preferred from the viewpoint that both the high temperature storage characteristic and internal resistance characteristic after storage are improved.
The salt having an imide anion represented by the above general formula [1] preferably has a high purity, and in particular the amount of Cl (chlorine) included in the salt having an imide anion as a material before being dissolved in an electrolyte solution is preferably 5000 ppm by mass or less, more preferably 1000 ppm by mass or less, and further preferably 100 ppm by mass or less. The use of a salt having an imide anion in which Cl (chlorine) remains at a high concentration is not preferred because battery members tend to corrode.
The salt having an imide anion represented by the above general formula [1] can be manufactured by various methods. The manufacturing method is not limited, and the salt can be obtained, for example, by the following method:
allowing a corresponding phosphoric amide (H2NP(═O)R1R2) and a corresponding phosphoryl halide (P(═O)R3R4X; X is a halogen atom) to react in the presence of an organic base or inorganic base.
As described in JP-A-2010-254554, a method for obtaining an imide anion by allowing a corresponding phosphoryl halide and ammonia to react in the presence of an organic base or inorganic base can be also used. Furthermore, a corresponding substituent (alkoxide, etc.) can be also introduced after obtaining an imide anion by the method.
It is important that at least one of R5 to R7 of the above general formula [2] be a fluorine atom. The reason is not clear; however, the effect of suppressing the internal resistance increase of batteries using the electrolyte solution is not sufficient when at least one fluorine atom is not included.
In addition, examples of the alkyl group and alkoxyl group represented by B5 to R7 of the above general formula [2] include C1-10 alkyl groups and fluorine-containing alkyl groups such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a secondary butyl group, a tertiary butyl group, a pentyl group, a 2,2-difluoroethyl group, a 2,2,2-trifluoroethyl group, a 2,2,3,3-tetrafluoropropyl group, and 1,1,1,3,3,3-hexafluoroisopropyl group, and alkoxy groups derived from these groups.
Examples of the alkenyl group and alkenyloxy group include C2-10 alkenyl groups and fluorine-containing alkenyl groups such as a vinyl group, an allyl group, a 1-propenyl group, an isopropenyl group, a 2-butenyl group, and a 1,3-butadienyl group, and alkenyloxy groups derived from these groups.
Examples of the alkynyl group and alkynyloxy group include C2-10 alkynyl groups and fluorine-containing alkynyl groups such as an ethynyl group, a 2-propynyl group, and a 1,1-dimethyl-2-propynyl group, and alkynyloxy groups derived from these groups.
Examples of the cycloalkyl group and cycloalkoxy group include C3-10 cycloalkyl groups and fluorine-containing cycloalkyl groups such as a cyclopentyl group and a cyclohexyl group, and cycloalkoxy groups derived from these groups.
Examples of the cycloalkenyl group and cycloalkenyloxy group include C3-10 cycloalkenyl groups and fluorine-containing cycloalkenyl groups such as a cyclopentenyl group and a cyclohexenyl group, and cycloalkenyloxy groups derived from these groups.
Examples of the aryl group and aryloxy group include C6-10 aryl groups and fluorine-containing aryl groups such as a phenyl group, a tolyl group and a xylyl group, and aryloxy groups derived from these groups.
More specific examples of negative ions of the salts having an imide anion represented by the above general formula [2] include Compounds No. 10 to No. 27 below, and the like. However, the salts having an imide anion used in the present invention are not restricted in any way by these examples.
In the above general formula [2], it is preferred that at least one of R5 to R7 be a fluorine atom and at least one of R5 to R7 be a group selected from an alkyl group, an alkenyl group, an alkynyl group, an aryl group, an alkoxy group, an alkenyloxy group, an alkynyloxy group and an aryloxy group, which have 6 or less carbon atoms and may include a fluorine atom. When the above number of carbon atoms is above 6, the internal resistance of a film formed on an electrode tends to be relatively high. It is preferred that the above number of carbon atoms be 6 or less because the above internal resistance tends to be lower, and it is particularly preferred that R5 to R7 be at least one group selected from a methyl group, an ethyl group, a propyl group, a vinyl group, an allyl group, an ethynyl group, a 2-propynyl group, a phenyl group, a trifluoromethyl group, a 2,2-difluoroethyl group, a 2,2,2-trifluoroethyl group, a 2,2,3,3-tetrafluoropropyl group, a 1,1,1,3,3,3-hexafluoroisopropyl group, and alkoxy groups, alkenyloxy groups, and alkynyloxy groups derived from these groups, because a nonaqueous electrolyte secondary battery which is capable of providing a cycle characteristic and an internal resistance characteristic in a balanced manner is obtained. Among them, the above Compounds No. 10, No. 11, No. 14 and No. 15 are particularly preferred from the viewpoint that both the high temperature storage characteristic and internal resistance characteristic after storage are improved.
The salt having an imide anion represented by the above general formula [2] preferably has a high purity, and in particular the amount of Cl (chlorine) included in the salt having an imide anion as a material before being dissolved in an electrolyte solution is preferably 5000 ppm by mass or less, more preferably 1000 ppm by mass or less, and further preferably 100 ppm by mass or less. The use of the salt having an imide anion in which Cl (chlorine) remains at a high concentration is not preferred because battery members tend to corrode.
The salt having an imide anion represented by the above general formula [2] can be manufactured by various methods. The manufacturing method is not limited, and the salt can be obtained, for example, by the following methods:
allowing a corresponding phosphoric amide (H2NP(═O)R5R6) and a corresponding sulfonyl halide (R7SO2X; X is a halogen atom) to react in the presence of an organic base or inorganic base, and
allowing a corresponding sulfonyl amide (H2NSO2R7) and a corresponding phosphoryl halide (R5R6P(═O)X; X is a halogen atom) to react in the presence of an organic base or inorganic base.
As described in, for example, CN101654229A and CN102617414A, a salt having an imide anion, in which a halogen atom other than a fluorine atom exists in the fluorine moiety of a corresponding salt having an imide anion, is obtained by the above method, and the salt having an imide anion represented by the above general formula [2] can be then obtained by the fluorination of the resultant salt.
The amount of the salt having an imide anion (I) used in the present invention is, as a suitable lower limit, 0.005 mass % or more with respect to the total amount of the above components (I) to (IV), preferably 0.05 mass % or more, further preferably 0.1 mass % or more, and, as a suitable upper limit, 12.0 mass %, or less, preferably 6.0 mass % or less, and further preferably 3.0 mass % or less.
When the above amount added is less than 0.005 mass %, it is difficult to sufficiently obtain the effect of improving battery characteristics and accordingly such amount is not preferred. On the other hand, when the above amount to be added is larger than 12.0 mass %, there is a risk that the viscosity of the electrolyte solution increases and characteristics are reduced at low temperatures. So long as the amount of the salt having an imide anion is not larger than 12.0 mass %, the salt can be used individually or two or more of the salts can be used in any combination at any ratio depending on usage.
The sulfonate compound represented by the above general formula [3] is preferably a sulfonate compound represented by the general formula [4] or general formula [5] in which the number of carbons bound to the carbon atom at the α position of the sulfone group is smaller from the viewpoint that internal resistance tends to reduce. Furthermore, it is more preferred that all of Rk and Rl of the general formula [4] and Rp and Rq of the general formula [5] be a hydrogen atom.
From the same viewpoint above, Rj of the general formula [4] and Rr of the general formula [5] are preferably a group selected from an alkyl group, an alkenyl group, an alkynyl group, an aryl group, an alkoxy group, an alkenyloxy group, an alkynyloxy group and an aryloxy group, which have 6 or less carbon atoms and may include a fluorine atom. When the above number of carbons is above 6, internal resistance of a film formed on an electrode tends to be relatively high. It is preferred that the above number of carbon atoms be 6 or less because the above internal resistance tends to be lower, and it is particularly preferred that Rj and Rk be at least one group selected from a methyl group, an ethyl group, a propyl group, a vinyl group, an allyl group, an ethynyl group, a 2-propynyl group, a phenyl group, a trifluoromethyl group, a 2,2-difluoroethyl group, a 2,2,2-trifluoroethyl group, a 2,2,3,3-tetrafluoropropyl group, a 1,1,1,3,3,3-hexafluoroisopropyl group, and alkoxy groups, alkenyloxy groups, and alkynyloxy groups derived from these groups because the resultant nonaqueous electrolyte secondary battery which is capable of providing a storage characteristic and an internal resistance characteristic in a balanced manner is obtained.
The sulfonate compound represented by the above general formula [3] preferably has a high purity, and in particular the amount of Cl (chlorine) included in the sulfonate compound as a material before being dissolved in an electrolyte solution is preferably 5000 ppm by mass or less, more preferably 1000 ppm by mass or less, and further preferably 100 ppm by mass or less. The use of a sulfonate compound in which Cl (chlorine) remains at a high concentration is not preferred because battery members tend to corrode.
The amount of the sulfonate compound (II) to be used in the present invention is, as a suitable lower limit, 0.01 mass % or more with respect to the total amount of the above components (I) to (IV), preferably 0.1 mass % or more, further preferably 0.2 mass % or more, and, as a suitable upper limit, 10.0 mass % or less, preferably 5.0 mass % or less, and further preferably 1.5 mass % or less.
When the above amount to be added is less than 0.01 mass %, it is difficult to sufficiently obtain the effect of improving battery characteristics and accordingly such amount is not preferred. On the other hand, when the above amount to be added is above 10.0 mass %, not only any further effect is not obtained and the above component (II) is wasted, but also resistance increases due to excess formation of a film to easily cause the deterioration of battery performance and accordingly such amount is not preferred. So long as the amount of the sulfonate compound is not larger than 10.0 mass %, the compound can be used individually or two or more of the compounds can be used in any combination at any ratio depending on usage.
The type of the nonaqueous organic solvent (III) is not particularly limited, and any nonaqueous organic solvent can be used. Specific examples thereof include cyclic carbonates such as propylene carbonate (hereinafter, may be referred to as “PC”), ethylene carbonate (hereinafter, may be referred to as “EC”) and butylene carbonate; chain carbonates such as diethyl carbonate (hereinafter, may be referred to as “DEC”), dimethyl carbonate (hereinafter, may be referred to as “DMC”) and ethyl methyl carbonate (hereinafter, may be referred to as “EMC”); cyclic esters such as γ-butyrolactone and γ-valerolactone; chain esters such as methyl acetate, methyl propionate and ethyl propionate (hereinafter, may be referred to as “EP”); cyclic ethers such as tetrahydrofuran, 2-methyltetrahydrofuran and dioxane; chain ethers such as dimethoxyethane and diethylether; sulfone compounds and sulfoxide compounds such as dimethylsulfoxide and sulfolane, and the like. In addition, e.g., an ionic liquid, which is in a category different from that of the nonaqueous organic solvent, can be also included. In addition, the nonaqueous organic solvent to be used in the present invention can be used singly or two or more of the nonaqueous organic solvents can be used in any combination at any ratio depending on usage. Among them, particularly preferred are propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl propionate and ethyl propionate from the viewpoint of the electrochemical stability to oxidation-reduction and chemical stability relating to heat and reaction with the above solute.
For example, a nonaqueous organic solvent containing one or more cyclic carbonates having a high permittivity and one or more chain carbonates or chain esters having a low liquid viscosity is preferred because the ion conductivity of an electrolyte solution increases. Specifically, those including the following combinations are more preferred:
(1) a combination of EC and EMC,
(2) a combination of EC and DEC,
(3) a combination of EC, DMC and EMC,
(4) a combination of EC, DEC and EMC,
(5) a combination of EC, EMC and EP,
(6) a combination of PC and DEC,
(7) a combination of PC and EMC,
(8) a combination of PC and EP,
(9) a combination of PC, DMC and EMC,
(10) a combination of PC, DEC and EMC,
(11) a combination of PC, DEC and EP,
(12) a combination of PC, EC and EMC,
(13) a combination of PC, EC, DNC and EMC,
(14) a combination of PC, EC, DEC and EMC, and
(15) a combination of PC, EC, EMC and EP.
Specific examples of the solute to be used in the nonaqueous electrolyte solution of the present invention include, in the case of lithium batteries and lithium ion batteries, electrolyte salts exemplified by LiPF6, LiBF4, LiSbF4, LiAsF6, LiClO4, LiCF3SO3, LiC4F9SO3, LiAlO2, LiAlCl4, LiN(CxF2x+1SO2)(CyF2y+1SO2) (wherein 2≤x≤20 and 2≤y≤20), LiCl, LiI, LiPF2(C2O4)2, LiPF4(C2O4), LiP(C2O4)3, LiBF2(C2O4), LiB(C2O4)2, LiPO2F2, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(CF3SO2) (FSO2), LiSO3F, LiC(CF3SO2)3, LiPF3(C3F7)3, LiB(CF3)4, LiBF3(C2F5) and the like, and include, in the case of sodium ion batteries, electrolyte salts exemplified by NaPF6, NaBF4, NaSbF6, NaAsF6, NaClO4, NaCF3SO3, NaC4F9SO3, NaAlO2, NaAlCl4, NaN(CxF2x+1SO2)(CyF2y+1SO2) (wherein 2≤x≤20 and 2≤y≤20), NaCl, NaI, NaPF2 (C2O4)2, NaPF4 (C2O4), NaP(C2O4)3, NaBF2(C2O4), NaB(C2O4)2, NaPO2F2, NaN(CF3SO2)2, NaN(C2F5SO2)2, NaN(CF3SO2) (FSO2), NaSO3F, NaC(CF3SO2)3, NaPF3(C3F7)3, NaB(CF3)4, NaBF3(C2F5) and the like. These solutes can be used individually or two or more of these solutes can be used in any combination at any ratio depending on usage. Among them, it is preferred to contain at least LiPF4 as the above component (IV) in the case of lithium batteries and lithium ion batteries in terms of the energy density, output characteristics, life, etc. of batteries. In addition, when LiPF4 is used in combination with another component (IV), it is preferred to use at least one selected from the group consisting of LiBF4, LiSbPF6, LiAsF6, LiClO4, LiCF3SO3, LiC4F9SO3, LiAlO2, LiAlCl4, LiCl, LiI, LiPF2(C2O4)2, LiPF4(C2O4), LiP(C2O4)3, LiBF2(C2O4), LiB(C2O4)2, LiPO2F2, and LiSO3F as such another component (IV).
In addition, it is preferred to contain at least NaPF6 as the above component (IV) in the case of sodium ion batteries. When NaPF6 is used in combination with another component (IV), it is preferred to use at least one selected from the group consisting of NaBF4, NaSbF6, NaAsF6, NaClO4, NaCF3SO3, NaC4F9SO3, NaAlO2, NaAlCl4, NaCl, NaI, NaPF2 (C2O4)2, NaPF4(C2O4), NaP(C2O4)3, NaBF2 (C2O4), NaB(C2O4)2, NaPO2F2, and NaSO3F as such another component (IV).
The concentration of the solute (IV) is not particularly restricted, and the suitable lower limit is 0.5 mol/L or more, preferably 0.7 mol/L or more, and further preferably 0.9 mol/L or more, and the suitable upper limit is 2.5 mol/L or less, preferably 2.0 mol/L or less, and further preferably 1.5 mol/L or less. When the concentration is lower than 0.5 mol/L, the cycle characteristics and output characteristic of the resultant nonaqueous electrolyte secondary battery tend to reduce due to reduction in ion conductivity. On the other hand, when the concentration exceeds 2.5 mol/L, ion conductivity still tends to reduce due to increase in viscosity of the resultant nonaqueous electrolyte solution, and there is a risk that the cycle characteristics and output characteristics of a nonaqueous electrolyte secondary battery are reduced.
When a large amount of the solute described above is dissolved in a nonaqueous solvent at one time, the temperature of the nonaqueous electrolyte solution can increase due to the heat of dissolution of the solute. When the temperature of the liquid significantly increases, there is a risk that the decomposition of a lithium salt containing a fluorine atom is promoted to form hydrogen fluoride. Hydrogen fluoride is not preferred because it deteriorates battery performance. Therefore, while the temperature of the liquid when the solute is dissolved in the nonaqueous solvent is not particularly limited, it is preferably −20 to 80° C. and more preferably 0 to 60° C.
The basic constitution of the nonaqueous electrolyte solution of the present invention is described above. In this case, any additives generally used can be also added to the nonaqueous electrolyte solution of the present invention at any ratio, without departing from the gist of the present invention. Specific examples thereof include cyclohexylbenzene, biphenyl, t-butylbenzene, t-amylbenzene, fluorobenzene, vinylene carbonate (hereinafter may be referred to as “VC”), vinylethylene carbonate, difluoroanisole, fluoroethylene carbonate (hereinafter may be referred to as “FEC”), 1,6-diisocyanatohexane, ethynylethylene carbonate, trans-difluoroethylene carbonate, propane sultone, propene sultone, dimethylvinylene carbonate, 1,3,2-dioxathiolane-2,2-dioxide, 4-propyl-1,3,2-dioxathiolane-2,2-dioxide, methylene methanedisulfonate, 1,2-ethanedisulfonic anhydride, tris(trimethylsilyl)borate, succinonitrile, (ethoxy)pentafluorocyclotriphosphazene, methanesulfonyl fluoride and the like. Alkali metal salts other than the above solutes (lithium salt, sodium salt) and salts having an imide anion represented by the above general formulae [1] and [2] (lithium salt, sodium salt) may be also used as additives. Specific examples thereof include carboxylic acid salts such as lithium acrylate, sodium acrylate, lithium methacrylate and sodium methacrylate; sulfuric acid ester salts such as lithium methyl sulfate, sodium methyl sulfate, lithium ethyl sulfate and sodium methyl sulfate, and the like.
In addition, the nonaqueous electrolyte solution can be made into a quasi-solid by a gelling agent and a cross-linking polymer as in the case of a nonaqueous electrolyte solution used for a nonaqueous electrolyte secondary battery called a lithium polymer battery.
In the nonaqueous electrolyte solution of the present invention, the total of alkali metal salts may be 4 types or more by using plural types of the above solutes (lithium salt, sodium salt) and salts having an imide anion represented by the above general formulae [1] and [2] (lithium salt, sodium salt) in combination depending on demand characteristics.
For example, as the case where 4 types of lithium salts are contained, it is thought:
to use LiPF6 as a first solute, and two of the above second solutes, and further one of the above lithium salts having an imide anion.
Specifically, it is preferred to contain 4 types of lithium salts as follows:
(1) a combination of LiPF6, the lithium salt of Compound No. 1, the lithium salt of Compound No. 2 and LiPF2(C2O4)2,
(2) a combination of LiPF6, the lithium salt of Compound No. 1, the lithium salt of Compound No. 5 and LiPO2F2,
(3) a combination of LiPF6, the lithium salt of Compound No. 1, the lithium salt of Compound No. 10, and LiPO2F2, and
(4) a combination of LiPF6, the lithium salt of Compound No. 10, LiPF2(C2O4)2 and LiPO2F2.
By the combinations above, the effect of suppressing an increase in an internal resistance at a low temperature is larger.
In addition, the above additives other than those compounds may be further added as required.
Furthermore, the total of the above alkali metal salts may be 5 types or more. For example, when 5 types of lithium salts are contained, it is thought:
to use LiPF6 as a first solute, and one of the above second solutes, and further three of lithium salts of e.g., the above Compound Nos. 1 to 27;
to use LiPF6 as a first solute, and two of the above second solutes, and further two of lithium salts of e.g., the above Compound Nos. 1 to 27; and
to use LiPF6 as a first solute, and three of the above second solutes, and further one of lithium salts of e.g. the above Compound Nos. 1 to 27.
Specifically, it is preferred to contain five types of lithium salts as follows:
(1) a combination of LiPF6, the lithium salt of Compound No. 1, the lithium salt of Compound No. 4, LiPF4(C2O4) and LiPF2 (C2O4)2;
(2) a combination of LiPF6, the lithium salt of Compound No. 10, LiBF2(C2O4), LiPO2F2 and LiSO3F;
(3) a combination of LiPF6, the lithium salt of Compound No. 1, the lithium salt of Compound No. 2, the lithium salt of Compound No. 15 and LiPO2F2;
(4) a combination of LiPF6, the lithium salt of Compound No. 14, LiPF4 (C2O4), LiPF2(C2O4)2 and LiPO2F2; and
(5) a combination of LiPF6, the lithium salt of Compound No. 15, LiBF2(C2O4), LiPO2F2, and LiSO3F.
By the combinations above, the effect of suppressing an increase in an internal resistance at a low temperature is larger. In addition, lithium salts other than those compounds above (the above additives) may be further added, if necessary.
The structure of the nonaqueous electrolyte secondary battery of the present invention will now be described. The nonaqueous electrolyte secondary battery of the present invention is characterized by using the above nonaqueous electrolyte solution of the present invention. As the other constituent members, those members which had been used for general nonaqueous electrolyte secondary batteries are used. That is, the battery may comprise positive and negative electrodes which are capable of absorbing and releasing lithium, a current collector, a separator, a container, etc.
Negative electrode materials are not particularly limited, and, in the case of lithium batteries and lithium ion batteries, lithium metal, an alloy of lithium metal and another metal, or intermetallic compounds and various carbon materials (artificial graphite, natural graphite, etc.), metal oxides, metal nitrides, tin (simple substance), tin compounds, silicon (simple substance), silicon compounds, activated carbons, conductive polymers and the like are used.
Examples of carbon materials are easily graphitizable carbon, hardly-graphitizable carbon (hard carbon) having a plane spacing of the (002) plane of 0.37 nm or more, and graphite having a plane spacing of the (002) plane of 0.34 nm or less, and the like. More specific examples thereof are pyrolytic carbons, cokes, glassy carbon fibers, fired products of high molecular organic compounds, activated carbons or carbon blacks and the like. Among them, for example, pitch coke, needle coke or petroleum coke are included as coke. The fired products of high molecular organic compounds indicate those obtained by firing phenol resin, furan resin and the like at a suitable temperature for carbonization. The carbon materials are preferred because changes in crystal structure associated with the absorption and release of lithium are very few, thereby obtaining high energy density and also obtaining an excellent cycle characteristic. In this case, the carbon materials may be in any form of fiber, ball, grain or flake. In addition, amorphous carbon and graphite materials whose surface is coated with amorphous carbon are more preferred because the reactivity between the surface of the materials and an electrolyte solution is low.
Positive electrode materials are not particularly limited, and in the case of lithium batteries and lithium ion batteries, for example, lithium-containing transition metal composite oxides such as LiCoO2, LiNiO2, LiMnO2 and LiMn2O4, those lithium-containing transition metal composite oxides wherein a plurality of transition metals such as Co, Mn and Ni are mixed, those lithium-containing transition metal composite oxides wherein a part of the transition metals is replaced with a metal other than the transition metals, phosphoric acid compounds of transition metals (referred to as olivine) such as LiFePO4, LiCoPO4 and LiMnPO4, oxides such as TiO2, V2O5 and MoO3, sulfides such as TiS2 and FeS, or conductive polymers such as polyacetylene, polyparaphenylene, polyaniline and polypyrrole, activated carbons, radical generating polymers, carbon materials and the like are used.
To the positive and negative electrode materials, acetylene black, Ketjen Black, carbon fiber, graphite as a conductive material, and polytetrafluoroethylene, polyvinylidene difluoride, SBR resin, polyimide and the like as a binder are added, and the resultant mixture can be formed into a sheet to obtain an electrode sheet.
As a separator to prevent a contact between the positive electrode and negative electrode, a nonwoven fabric and a porous sheet made from e.g., polypropylene, polyethylene, paper and glass fibers are used.
Nonaqueous electrolyte secondary batteries in the shape of coin, cylinder, prismatic cell, aluminum laminated sheet and the like are assembled from the elements described above.
In addition, the nonaqueous electrolyte secondary batteries may be nonaqueous electrolyte secondary batteries comprising (a) the above nonaqueous electrolyte solution, as well as (b) a positive electrode, (c) a negative electrode, and (d) a separator which will be described below.
The positive electrode (b) preferably includes at least one oxide and/or polyanion compound as a positive electrode active material.
In the case of lithium ion secondary batteries wherein the cation in the nonaqueous electrolyte solution is lithium as a main cation, the positive electrode active material forming the positive electrode (b) is not particularly limited and various kinds of materials can be used as the positive electrode active material, so long as they can be charged and discharged. The examples thereof include those containing at least one of: lithium transition metal composite oxides containing at least one or more metals of nickel, manganese and cobalt and having a layered structure (A), lithium manganese composite oxides having a spinel structure (B), lithium-containing olivine phosphates (C), and lithium-excess layered transition metal oxides having a layered rock salt structure (D).
Examples of (A) the lithium transition metal composite oxides containing at least one or more metals of nickel, manganese and cobalt and having a layered structure include lithium cobalt composite oxides, lithium nickel composite oxides, lithium nickel cobalt composite oxides, lithium nickel cobalt aluminum composite oxides, lithium cobalt manganese composite oxides, lithium nickel manganese composite oxides, lithium nickel manganese cobalt composite oxides and the like. In addition, those in which a part of transition metal atoms mainly constituting these lithium transition metal composite oxides is replaced with other elements such as Al, Ti, V, Cr, Fe, Cu, Zn, Mg, Ga, Zr, Si, B, Ba, Y and Sn may be used.
As specific examples of the lithium cobalt composite oxides and lithium nickel composite oxides, LiCoO2, LiNiO2 and lithium cobaltate to which different elements such as Mg, Zr, Al and Ti are added (LiCo0.98Mg0.01Zr0.01O2, LiCo0.98Mg0.01Al0.01O2, LiCo0.975Mg0.01Zr0.005Al0.01O2, etc.), lithium cobaltate having rare earth compounds fixed onto the surface thereof described in WO2014/034043 and the like may be used. As described in e.g., JP-A-2002-151077, those in which a part of the surface of particles of LiCoO2 particle powder is covered with an aluminum oxide may be also used.
Lithium nickel cobalt composite oxides and lithium nickel cobalt aluminum composite oxides are represented by the general formula (1-1):
LiaNi1-b-cCobM1cO2 (1-1).
In the formula (1-1), the conditions that M1 be at least one element selected from the group consisting of Al, Fe, Mg, Zr, Ti and B, a be 0.9≤a≤1.2, and b and c be 0.01≤b≤0.3 and 0≤c≤0.1 are satisfied.
These composite oxides can be prepared in accordance with e.g., a manufacturing method described in, for example, JP-A-2009-137834. Specific examples thereof include LiNi0.8Co0.2O2, LiNi0.85Co0.10Al0.05O2, LiNi0.87Co0.10Al0.03O2, LiNi0.90Co0.07Al0.03O2, LiNi0.6Co0.3Al0.1O2 and the like.
Specific examples of lithium cobalt manganese composite oxides and lithium nickel manganese composite oxides include LiNi0.5Mn0.5O2, LiCo0.5Mn0.5O2 and the like.
Examples of lithium nickel manganese cobalt composite oxides include lithium-containing composite oxides represented by the general formula (1-2):
LidNieMnfCogM2hO2 (1-2).
In the formula (1-2), the conditions that M2 be at least one element selected from the group consisting of Al, Fe, Mg, Zr, Ti, B and Sn, d be 0.9≤d≤1.2, and e, f, g and h be e+f+g+h=1, 0≤e≤0.9, 0≤f≤0.5, 0≤g≤0.5, and h≥0 are satisfied.
Preferred lithium nickel manganese cobalt composite oxides are those which contain manganese within the range shown in the general formula (1-2) to increase structural stability and to improve stability of lithium secondary batteries at high temperatures, and particularly more preferred are those which further contain cobalt within the range shown in the general formula (1-2) to increase a high rate characteristic of lithium ion secondary batteries.
Specific examples thereof include Li[Ni1/3Mn1/3Co1/3]O2, Li[Ni0.45Mn0.35Co0.2]O2, Li[Ni0.5Mn0.3Co0.2]2, Li[Ni0.6Mn0.2Co0.2]O2, Li[Ni0.8Mn0.1Co0.1]O2, Li[Ni0.49Mn0.3Co0.2Zr0.01]O2, Li[Ni0.49 Mn0.3Co0.2Mg0.01]O2 having charge and discharge areas in 4.3 V or more and the like.
Examples of (B) the lithium manganese composite oxides having a spinel structure include spinel type lithium manganese composite oxides represented by the general formula (1-3):
Lij(Mn2-kM3k)O4 (1-3).
In the formula (1-3), M3 is at least one metal element selected from the group consisting of Ni, Co, Fe, Mg, Cr, Cu, Al and Ti, and j is 1.05≤j≤1.15, and k is 0≤k≤0.20.
Specific examples thereof include LiMn2O4, LiMn1.95Al0.05O4, LiMn1.9Al0.1O4, LiMn1.9Ni0.1O4, LiMn1.5Ni0.5O4 and the like.
Examples of (C) the lithium-containing olivine phosphates include those represented by the general formula (1-4):
LiFe1-nM4nPO4 (1-4).
In the formula (1-4), M4 is at least one selected from Co, Ni, Mn, Cu, Zn, Nb, Mg, Al, Ti, W, Zr and Cd, and n is 0≤n≤1.
Specific examples thereof include LiFePO4, LiCoPO4, LiNiPO4, LiMnPO4 and the like, and among these, preferred are LiFePO4 and/or LiMnPO4.
Examples of (D) the lithium-rich layered transition metal oxides having a layered rock salt structure include those represented by the general formula (1-5):
xLiM5O2.(1-x)Li2M6O3 (1-5).
In the formula (1-5), x is a number satisfying 0<x<1, M5 is at least one metal element having an average oxidation number of 3+, and M6 is at least one metal element having an average oxidation number of 4+. In the formula (1-5), while M5 is preferably one metal element selected from trivalent Mn, Ni, Co, Fe, V and Cr, an average trivalent oxidation number may be used by using equal amounts of divalent and tetravalent metals.
In the formula (1-5), M6 is preferably one or more metal elements selected from Mn, Zr and Ti. Specific examples thereof include 0.5[LiNi0.5Mn0.5O2].0.5[Li2MnO3], 0.5[LiNi1/3Co1/3Mn1/3O2].0.5[Li2MnO3], 0.5[LiNi0.375Co0.25Mn0.375O2].0.5 [Li2MnO3], 0.5[LiNi0.375 Co0.125Fe0.125Mn0.375O2].0.5[Li2MnO3], 0.45[LiNi0.375Co0.25Mn0.375O2].0.10[Li2TiO3].0.45[Li2MnO3] and the like.
It is known that the positive electrode active material (D) represented by the general formula (1-5) shows a high capacity at a high voltage charging of 4.4 V or more (in terms of Li) (e.g., U.S. Pat. No. 7,135,252).
These positive electrode active materials can be prepared in accordance with e.g., manufacturing methods described in, for example, JP-A-2008-270201, WO2013/118661, and JP-A-2013-030284.
It is sufficient that the positive electrode active material contains at least one selected from the above positive electrode active materials (A) to (D) as a main component, and the examples of positive electrode active materials to be included other than the above include transition element chalcogenides such as FeS2, TiS2, V2O5, MoO3 and MoS2, or conductive polymers such as polyacetylene, polyparaphenylene, polyaniline and polypyrrole, activated carbons, radical generating polymers, carbon materials and the like.
The positive electrode (b) has a positive electrode current collector. As the positive electrode current collector, for example, aluminum, stainless steel, nickel, titanium or alloys thereof or the like can be used.
In the positive electrode (b), for example, a positive electrode active material layer is formed on at least one surface of the positive electrode current collector. The positive electrode active material layer is constituted of, for example, the above-described positive electrode active material, a binder and, as required, a conducting agent.
Examples of binders include polytetrafluoroethylene, polyvinylidene fluoride or styrene-butadiene rubber (SBR) resin and the like.
As the conducting agent, for example, a carbon material such as acetylene black, Ketjen Black, carbon fiber or graphite (granular graphite or flake graphite) can be used. In the positive electrode, acetylene black and Ketjen Black, which have low crystallizability, are preferably used.
[(c) Negative Electrode]
The negative electrode (c) preferably includes at least one negative electrode active material.
In the case of lithium ion secondary batteries in which the cation in the nonaqueous electrolyte solution is lithium as a main cation, the negative electrode active materials constituting the negative electrode (c) are those in which lithium ion can be doped and de-doped, and the examples thereof include carbon materials having a d value of the lattice plane (002 plane) of 0.340 nm or less according to X-ray diffraction (E), carbon materials having a d value of the lattice plane (002 plane) exceeding 0.340 nm according to X-ray diffraction (F), oxides of one or more metals selected from Si, Sn and Al (G), one or more metals selected from Si, Sn and Al or alloys including these metals, or alloys of these metals or alloys with lithium (H), and those containing at least one selected from lithium titanium oxides (I). These negative electrode active materials can be used individually or two or more of the materials can be used in combination.
Examples of carbon materials having a d value of the lattice plane (002 plane) of 0.340 nm or less according to X-ray diffraction (E) as a negative electrode active material include pyrolytic carbons, cokes (e.g., pitch coke, needle coke, petroleum coke, etc.), graphite, fired products of high molecular organic compounds (e.g., those obtained by firing phenol resin, furan resin, or the like at a suitable temperature for carbonization), carbon fibers, activated carbons and the like, and these materials may be also graphited. The carbon materials are those materials having a plane spacing (d002) of (002) plane of 0.340 nm or less measured according to X-ray diffraction, and among them, graphite having a true density of 1.70 g/cm3 or more or high crystallinity carbon materials having properties close to that of the graphite are preferred.
Examples of the carbon materials having a d value of the lattice plane (002 plane) exceeding 0.340 nm according to X-ray diffraction (F) as a negative electrode active material include amorphous carbon, and this is a carbon material in which the lamination system is not almost changed even when heat treated at a high temperature of 2000° C. or higher. Examples thereof include hardly-graphitizable carbon (hard carbon), mesocarbon microbeads (MCMB) and mesophase pitch carbon fibers (MCF) fired at 1500′C or lower, and the like. Typical examples thereof are CARBOTRON (registered trademark) P manufactured by KUREHA CORPORATION and the like.
((G) Oxide of One or More Metals Selected from Si, Sn and Al)
Examples of the oxides of one or more metals selected from Si, Sn and Al (G) as a negative electrode active material include silicon oxide, tin oxide and the like in which lithium ion can be doped and de-doped.
There are e.g. Siox having a structure in which Si ultrafine particles are dispersed in SiO2. When this material is used as a negative electrode active material, charging and discharging are smoothly carried out because Si reacting with Li is in the form of ultrafine particles. On the other hand, since SiOx particles having the above structure themselves have a small surface area, paintability when they are made into a composition (paste) to form a negative electrode active material layer and adhesiveness of a negative electrode mixture layer to a current collector are good.
In this case, because SiOx has large volume changes associated with charging and discharging, both a high capacity and good charging and discharging cycle characteristics can be obtained by using SiOx and graphite as the above-described negative electrode active material (E) in combination at a specific ratio for the negative electrode active material.
((H) One or More Metals Selected from Si, Sn and Al or Alloys Including these Metals, or Alloys of these Metals or Alloys with Lithium)
Examples of one or more metals selected from Si, Sn and Al or alloys including these metals or alloys of these metals or alloys with lithium (H) as a negative electrode active material include metals such as silicon, tin and aluminum, silicon alloy, tin alloy, aluminum alloy and the like, and materials in which these metals and alloys are alloyed with lithium associated with charging and discharging can be also used.
Specific preferred examples thereof include simple metals such as silicon (Si) and tin (Sn) (e.g. powder metal), alloys of the metals, compounds containing the metals, alloys including the metals with tin (Sn) and cobalt (Co), and the like described in e.g., WO2004/100293, and JP-A-2008-016424. These metals are preferably used for electrodes because a high charging capacity can be provided and the expansion and contraction of the volume associated with charging and discharging are relatively less. In addition, it is known that when used for the negative electrode of lithium ion secondary batteries, these metals are alloyed with Li at the time of charging and thus shows a high charging capacity. These metals are preferred also in this respect.
Furthermore, for example, a negative electrode active material formed from silicon pillar with a submicron diameter, a negative electrode active material including fiber formed from silicon and the like described in WO2004/042851, WO2007/083155, etc. may be used.
Examples of the lithium titanium oxides (I) as a negative electrode active material can include lithium titanate having a spinel structure, lithium titanate having a ramsdellite structure and the like.
Examples of lithium titanate having a spinel structure can include Li4+αTi5O12 (α varies within 0≤α≤3 due to the charging and discharging reaction). Examples of lithium titanate having a ramsdellite structure can include Li2+βTi3O7 (β varies within 0≤β≤3 due to the charging and discharging reaction). These negative electrode active materials can be prepared in accordance with e.g., manufacturing methods described in, for example, JP-A-2007-018883, and JP-A-2009-176752.
In the case of sodium ion secondary batteries in which cations in a nonaqueous electrolyte solution are mainly sodium, for example, hard carbon and oxides such as TiO2, V2O5 and MoO3 and the like are used as the negative electrode active material. In the case of sodium ion secondary batteries in which cations in a nonaqueous electrolyte solution are mainly sodium, for example, sodium-containing transition metal composite oxides such as NaFeO2, NaCrO2, NaNiO2, NaMnO2 and NaCoO2, those oxides in which a plurality of transition metals such as Fe, Cr, Ni, Mn and Co are mixed in the sodium-containing transition metal composite oxides, those oxides in which a part of the transition metals contained in the sodium-containing transition metal composite oxides is replaced with a metal other than the transition metals, phosphoric acid compounds of transition metals such as Na2FeP2O7 and NaCo3(PO4)2P2O7, sulfides such as TiS2 and FeS2, or conductive polymers such as polyacetylene, polyparaphenylene, polyaniline and polypyrrole, activated carbons, radical generating polymers, carbon materials and the like are used as a positive electrode active material.
[Negative Electrode Current collector]
The negative electrode (c) has a negative electrode current collector. As the negative electrode current collector, for example, copper, aluminum, stainless steel, nickel, titanium or alloys thereof or the like can be used.
In the negative electrode (c), for example, a negative electrode active material layer is formed on at least one surface of the negative electrode current collector. The negative electrode active material layer is constituted of, for example, the above-described negative electrode active material, a binder and, as needed, a conducting agent.
Examples of the binders include polytetrafluoroethylene, polyvinylidene fluoride or styrene-butadiene rubber (SBR) resin, and the like.
As the conducting agent, for example, a carbon material such as acetylene black, Ketjen Black, carbon fiber or graphite (granular graphite or flake graphite) can be used.
Electrodes can be obtained, for example, by dispersing an active material, a binder and, as needed, a conducting agent in a solvent such as N-methyl-2-pyrrolidone (NMP) or water in predetermined amounts, kneading the resultant mixture, and applying the resultant paste to a current collector and drying it to form an active material layer. It is preferred that the resultant electrode be compressed by a method such as roll pressing and adjusted to a suitable density.
The above nonaqueous electrolyte secondary battery comprises a separator (d). As a separator to prevent a contact between the positive electrode (b) and the negative electrode (c), a nonwoven fabric or porous sheet made from e.g., a polyolefin such as polypropylene or polyethylene, cellulose, paper or glass fiber is used. These films are preferably microporous films into which the electrolyte solution soaks and ions easily penetrate.
Examples of polyolefin separators include films which electrically insulate the positive electrode and negative electrode and into which lithium ion can penetrate, such as microporous polymer films e.g., porous polyolefin films. As specific examples of porous polyolefin films, for example, a porous polyethylene film can be used singly or a multilayered film having a porous polyethylene film and a porous polypropylene film laminated can be used. In addition, e.g., a composite film of a porous polyethylene film and a polypropylene film can be also used.
When forming a nonaqueous electrolyte secondary battery, a metal can in the shape of coin, cylinder, square or the like and a laminate exterior body, for example, can be used as the exterior body for the nonaqueous electrolyte secondary battery. Examples of metal can materials include a nickel plated iron and steel plate, a stainless steel plate, a nickel-plated stainless steel plate, aluminum or an alloy thereof, nickel, titanium and the like.
Laminate films such as an aluminum laminated film, an SUS laminated film, silica-coated polypropylene, and polyethylene, and the like, for example, can be used as the laminate exterior body.
The structure of the nonaqueous electrolyte secondary battery according to the present embodiment is not particularly restricted, and the structure in which electrode elements having the positive electrode and negative electrode facing each other and the nonaqueous electrolyte solution are included in an exterior body, for example, can be used. The shape of the nonaqueous electrolyte secondary battery is not particularly limited, and an electrochemical device in the shape of e.g., coin, cylinder, square or aluminum laminated sheet is assembled from the elements described above.
The present invention will now be described in detail by way of examples thereof. In this case, the scope of the present invention is not limited by the examples.
A mixed solvent of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate at a volume ratio of 2.5:4:3.5 was used as a nonaqueous organic solvent (III), and LiPF6 as a solute (IV), the lithium salt of Compound No. 1 as a salt having an imide anion (I) (the amount of Cl included in the salt having an imide anion as a material before being dissolved in an electrolyte solution is 40 ppm by mass), and the compound of the formula [6] as a sulfonate compound (II) were dissolved in the solvent so that each had the concentration shown in Table 1 to prepare the electrolyte solution No. 1Li1-[6]1. The above preparation was carried out, while maintaining a liquid temperature at 20 to 30° C. In this case, the concentration of a free acid in the electrolyte solution was 35 ppm by mass.
(Production of Electrolyte Solution Nos. 1Li1-[7]1 to 1Li1-[23]1, electrolyte solution Nos. 10Li1-[6]1 to 10Li1-[23]1, electrolyte solution Nos. 11Li1-[6]1 to 11Li1-[23]1, and electrolyte solution Nos. 15Li1-[6]1 to 15Li1-[23]1)
As shown in Table 1, various kinds of electrolyte solutions were prepared in the same manner as for the electrolyte solution No. 1Li1-[6]1 except that:
Electrolyte solutions No. 0-[6]1-LiFSI1 to 0-[23]1-LiFSI1 were prepared in the same manner as for the electrolyte solution Nos. 1Li1-[6]1 to 1Li1-[23]1 except that LiFSI was dissolved to a concentration shown in Table 1 without using the salt having an imide anion (I), as shown in Table 1. In this case, the concentration of a free acid in each of the electrolyte solutions was about 45 ppm by mass.
Electrolyte solution Nos. 2Li1-[6]1 to 27Li1-[6]1 were prepared in the same manner as for the electrolyte solution No. 1Li1-[6]1 except that the lithium salts of Compound Nos. 2, 3, 5, 8, 9, 12 to 14 and 16 to 27 were used as the salt having an imide anion (I) instead of the lithium salt of Compound No. 1 as shown in Table 2 (the amount of Cl included in the salt having an imide anion as a material before being dissolved in an electrolyte solution is about 40 ppm by mass in each case). In this case, the concentration of a free acid in each of the electrolyte solutions was about 40 ppm by mass.
(Production of Electrolyte Solutions in which Concentration of Component (I) or Concentration of Component (II) is Changed)
Electrolyte solutions were prepared in the same manner as for the electrolyte solution No. 1Li1-[6]1 except that the concentration of the component (I) or the concentration of component (II) was changed as shown in Table 3. In this case, the concentration of a free acid in each of the electrolyte solutions was about 40 ppm by mass.
A cell was produced using an electrolyte solution shown in Table 1, and LiNi0.8Co0.1Mn0.1O2 as the positive electrode material and graphite (containing silicon) as the negative electrode material, and the discharge capacity retention rate and internal resistance characteristic after storage were evaluated. The evaluation results are shown in Table 4. In this case, a test cell was produced as described below.
Five mass % of polyvinylidene fluoride (hereinafter referred to as “PVDF”) as a binder and 5 mass % of acetylene black as a conductive material were mixed with 90 mass % of LiNi0.8Co0.1Mn0.1O2 powder, and N-methylpyrrolidone was further added to the resultant mixture to obtain a paste. This paste was applied onto aluminum foil and dried to obtain a test positive electrode body.
In addition, 5 mass % of silicon powder and 10 mass % of PVDF as a binder were mixed with 85 mass % of graphite powder, and N-methylpyrrolidone was further added to the resultant mixture to obtain a slurry. This slurry was applied onto copper foil and dried at 120° C. for 12 hours to obtain a test negative electrode body.
An electrolyte solution was allowed to soak into a polyethylene separator and a 50 mAh cell with an aluminum laminate exterior body was assembled.
A battery was charged to 4.3 V at a constant current of 0.2 mA/cm2 at 25° C. and then discharged to 3.0 V at a constant current of 0.2 mA/cm2. Charging and discharging were repeated 10 cycles in the same manner as stated above. The discharge capacity at the 10th cycle is defined as the initial discharge capacity. After this, the battery was charged to 4.3 V at a constant current of 0.2 mA/cm2 and then charged at a constant voltage of 4.3 V until a current value reached 0.1 mA/cm2. This was stored at 65° C. for 4 weeks, the battery was cooled to room temperature and then discharged to 3.0 V at a constant current of 0.2 mA/cm2 at 25° C. It was charged to 4.3 V at a constant current of 0.2 mA/cm2 and then charged at a constant voltage of 4.3 V until a current value reached 0.1 mA/cm2, and then discharged to 3.0 V at a constant current of 0.2 mA/cm2. The discharge capacity at this time is defined as the recovery capacity. The capacity retention rate at storage was determined by the following formula.
Capacity retention rate at storage (%)=(recovery capacity/initial discharge capacity)×100
[Evaluation of Internal Resistance Characteristics after Storage]
The cell after the determination of the above recovery capacity was charged to 4.3 V at a constant current of 0.2 mA/cm2, and then charged at constant voltage of 4.3 V until a current value reached 0.1 mA/cWm2. The internal resistance of the battery was then measured at an environmental temperature of −20° C.
Evaluation results of the Examples are relative values when evaluation results of the Comparative Example using corresponding components (II) are designated as 100. It is desired that the “capacity retention rate at storage” have a higher value, and it is desired that the “internal resistance characteristic after storage” have a lower value.
From the evaluation results in Table 4, it was confirmed that in the case where the component (I) and the component (II) of the present invention were used in combination, the high temperature storage characteristic (capacity retention rate at storage) and the internal resistance characteristic after storage can be improved in a balanced manner compared to cases where LiFSI and the component (II) were used in combination. It was confirmed that in the Examples in which the compounds of the formulae [6], [13], [16], [17], [19], [20] and [23] were used as the component (II), both the high temperature storage characteristic and internal resistance characteristic after storage can be improved. It was confirmed that particularly in the Examples in which the compounds of the formulae [6], [13], [17] and [23] were used, the improvement effect described above was large. It is confirmed that also in the case where the compound of the formula [14] was used, the improvement effect described above was large, although this case is not described as an Example.
Cells were produced in the same manner as in Example 1-1 except that the electrolyte solutions shown in Table 2 were used, and the capacity retention rate at storage and internal resistance characteristic after storage were evaluated. The evaluation results are shown in Table 5.
Evaluation results of the Examples are relative values when evaluation results of Comparative Example 1-1 are designated as 100. It is desired that the “capacity retention rate at storage” have a higher value, and it is desired that the “internal resistance characteristic after storage” have a lower value.
From the evaluation results in Table 5, it was confirmed that in the case where the component (I) and the component (II) of the present invention were used in combination, the high temperature storage characteristic (capacity retention rate at storage) and the internal resistance characteristic after storage can be improved in a balanced manner compared to the case where LiFSI and the component (II) were used in combination. In this case, it is seen that when the component (I) having more P—F bonds and S—F bonds is used, “internal resistance characteristic after storage” tends to be better.
Cells were produced in the same manner as in Example 1-1 except that the electrolyte solutions shown in Table 3 were used, and the capacity retention rate at storage and internal resistance characteristic after storage were evaluated. The evaluation results are shown in Table 6.
Evaluation results of the Examples are relative values when evaluation results of Comparative Example 3-1 are designated as 100. It is desired that the “capacity retention rate at storage” have a higher value, and it is desired that the “internal resistance characteristic after storage” have a lower value.
From the evaluation results in Table 6, it was confirmed that in the case where the component (I) and the component (II) of the present invention were used in combination, the high temperature storage characteristic (capacity retention rate at storage) and the internal resistance characteristic after storage can be improved in a balanced manner compared to Comparative Example 3-1 to which the component (I) was not added. It was confirmed that in the Examples in which the amount of the component (I) added is in a suitable range of “0.005 to 12.0 mass %” with respect to the total amount of the components (I) to (IV), both the capacity retention rate at storage and internal resistance characteristic after storage can be well improved. It was also confirmed that in the Examples in which the amount of the component (I) added is in a more suitable range of 0.05 to 6.0 mass %, the effect of addition of the above component (I) was larger, and in the Examples in which the amount of the component (I) added is in a particularly suitable range of 0.1 to 3.0 mass %, the effect of addition of the above component (I) was particularly larger.
Cells were produced in the same manner as in Example 1-1 except that the electrolyte solutions shown in Table 3 were used, and the capacity retention rate at storage and internal resistance characteristic after storage were evaluated. The evaluation results are shown in Table 7.
Evaluation results of the Examples are relative values when evaluation results of the Comparative Examples using the corresponding component (I) are designated as 100. It is desired that the “capacity retention rate at storage” have a higher value, and it is desired that the “internal resistance characteristic after storage” have a lower value.
From the evaluation results in Table 7, it was confirmed that in the case where the component (I) and the component (II) of the present invention were used in combination, the high temperature storage characteristic (capacity retention rate at storage) and the internal resistance characteristic after storage can be improved in a balanced manner compared to Comparative Examples to which the component (II) was not added. It was confirmed that in the Examples in which the amount of the component (II) added is in a suitable range of “0.01 to 10.0 mass %” with respect to the total amount of the components (I) to (IV), both the capacity retention rate at storage and internal resistance characteristic after storage can be well improved. It was also confirmed that in the Examples in which the amount of the component (II) added is in a more suitable range of 0.1 to 5.0 mass %, the effect of addition of the above component (II) was larger, and in the Examples in which the amount of the component (II) added is in a particularly suitable range of 0.2 to 1.5 mass %, the effect of addition of the above component (II) was particularly larger.
A mixed solvent of propylene carbonate, ethylene carbonate and diethyl carbonate at a volume ratio of 1:2:7 was used as the nonaqueous organic solvent (III), and NaPF6 as the solute (IV), the sodium salt of Compound No. 1 as the salt having an imide anion (I) (the amount of Cl included in the salt having an imide anion as a material before being dissolved in an electrolyte solution was 30 ppm by mass), and the compound of the formula [6] as the sulfonate compound (II) were dissolved in the solvent so that they had the concentrations shown in Table 8 so as to prepare the electrolyte solution No. 1Na1-[6]1. The above preparation was carried out while maintaining a liquid temperature at 20 to 30° C. In this case, the concentration of a free acid in the electrolyte solution was 10 ppm by mass.
(Production of Electrolyte Solutions No. 1Na1-[7]1 to 1Na1-[23]1, Electrolyte Solutions No. 10Na1-[6]1 to 10Na1-[23]1, Electrolyte Solutions No. 11Na1-[6]1 to 11Na1-[23]1, and Electrolyte Solutions No. 15Na1-[6]1 to 15Na1-[23]1)
As shown in Table 8, various kinds of electrolyte solutions were prepared in the same manner as for the electrolyte solution No. 1Na1-[6]1 except that the sodium salts of Compound Nos. 10, 11 and 15 were used as the salt having an imide anion (I) instead of the sodium salt of Compound No. 1 (the amount of Cl included in the salt having an imide anion as a material before being dissolved in an electrolyte solution was about 30 ppm by mass in each case), and that the compounds of the formulae [7], [13], [16], [18], [20], [21] and [23] were used as the sulfonate compound (II) instead of the compound of the formula [6]. In this case, the concentration of a free acid in each of the electrolyte solutions was about 10 ppm by mass.
Electrolyte solutions Nos. 0-[6]1-NaFSI1 to 0-[23]1-NaFSI1 were prepared in the same manner as for the electrolyte solution Nos. 1Na1-[6]1 to 1Na1-[23]1 except that sodium bis(fluorosulfonyl)imide (hereinafter may be referred to as “NaFSI”) was dissolved to the concentration shown in Table 8 instead of the salt having an imide anion (I) as shown in Table 8. In this case, the concentration of a free acid in each of the electrolyte solutions was about 20 ppm by mass.
Electrolyte solution Nos. 2Na1-[6]1 to 27Na1-[6]1 were prepared in the same manner as for the electrolyte solution No. 1Na1-[6]1 except that the sodium salts of Compound Nos. 2, 3, 5, 8, 14, 18, 20, 21, 25 and 27 were used as the salt having an imide anion (I) instead of the sodium salt of Compound No. 1 as shown in Table 9 (the amount of Cl included in the salt having an imide anion as a material before being dissolved in an electrolyte solution was about 30 ppm by mass in each case). In this case, the concentration of a free acid in each of the electrolyte solutions was about 20 ppm by mass.
(Production of Electrolyte Solutions in which Concentration of Component (I) and Concentration of Component (II) are Changed)
Electrolyte solutions were prepared in the same manner as for the electrolyte solution No. 1 Na1-[6]1 except that the concentration of the component (I) and the concentration of the component (II) were changed as shown in Table 10. In this case, the concentration of a free acid in each of the electrolyte solutions was about 20 ppm by mass.
Cells were produced in the same manner as in Example 1-1 except that the electrolyte solutions shown in Table 8 were used and O3-type NaNi0.5Ti0.3Mn0.2O2 as the positive electrode material and hard carbon as the negative electrode material were used. The resultant batteries were evaluated in the same manner as in Example 1-1. In this case, the positive electrode body having NaNi0.5Ti0.3Mn0.2O2 as the positive electrode active material was produced by mixing 5 mass % of PVDF as a binder and 5 mass % of acetylene black as a conductive material with 90 mass % of NaNi0.5Ti0.3Mn0.2O2 powder and further adding NMP to the resultant mixture and applying the resultant paste onto aluminum foil and drying it. The negative electrode body having hard carbon as the negative electrode active material was produced by mixing 8 mass % of PVDF as a binder and 2 mass % of acetylene black as a conductive material with 90 mass % of hard carbon powder and further adding NMP to the resultant mixture and applying the resultant paste onto aluminum foil and drying it. The final charge voltage when evaluating the batteries was 4.25 V and the final discharge voltage was 1.7 V. The evaluation results are shown in Table 11.
Evaluation results of the Examples are relative values when evaluation results of the Comparative Examples using the corresponding component (II) are designated as 100. It is desired that the “capacity retention rate at storage” have a higher value, and it is desired that the “internal resistance characteristic after storage” have a lower value.
From the evaluation results in Table 11, it was confirmed that in the case where the component (I) and the component (II) of the present invention were used in combination, the high temperature storage characteristic (capacity retention rate at storage) and the internal resistance characteristic after storage can be improved in a balanced manner compared to the case where NaFSI and the component (II) were used in combination. It was confirmed that in the Examples in which the compounds of the formulae [6], [13], [20] and [23] were used as the component (II), both the high temperature storage characteristic and internal resistance characteristic after storage can be improved. It was confirmed that particularly in the Examples in which the compounds of the formulae [6], [13] and [23] were used, the improvement effect described above was large. It was confirmed that in the case where the compound of the formula [14] was used, the improvement effect was also large, although this case is not described as an Example.
Cells were produced in the same manner as in Example 4-1 except that the electrolyte solutions shown in Table 9 were used, and the capacity retention rate at storage and the internal resistance characteristic after storage were evaluated. The evaluation results are shown in Table 12.
Evaluation results of each Example are relative values when evaluation results of Comparative Example 4-1 are considered 100. It is desired that the “capacity retention rate at storage” have a higher value, and it is desired that the “internal resistance characteristics after storage” have a lower value.
From the evaluation results in Table 12, it was verified that in cases where the component (I) and the component (II) of the present invention were used in combination, the high temperature storage characteristic (capacity retention rate at storage) and the internal resistance characteristic after storage can be improved in a balanced manner compared to the case where NaFSI and the component (II) were used in combination. In this case, when the component (I) having more P—F bonds and S—F bonds was used, “internal resistance characteristic after storage” tends to be better.
Cells were produced in the same manner as in Example 4-1 except that the electrolyte solutions shown in Table 10 were used, and the capacity retention rate at storage and internal resistance characteristic after storage were evaluated. The evaluation results are shown in Table 13.
Evaluation results of the Examples are relative values when evaluation results of Comparative Example 6-1 are designated as 100. It is desired that the “capacity retention rate at storage” have a higher value, and it is desired that the “internal resistance characteristic after storage” have a lower value.
From the evaluation results in Table 13, it was confirmed that in the case where the component (I) and the component (II) of the present invention were used in combination, the high temperature storage characteristic (capacity retention rate at storage) and the internal resistance characteristic after storage can be improved in a balanced manner compared to Comparative Example 6-1 to which the component (I) was not added. It was confirmed that in the Examples in which the amount of the component (I) added is in a suitable range of “0.005 to 12.0 mass %” with respect to the total amount of the components (I) to (IV), both the capacity retention rate at storage and internal resistance characteristic after storage can be well improved. It was also confirmed that in the Examples in which the amount of the component (I) added is in a more suitable range of 0.05 to 6.0 mass %, the effect of addition of the above component (I) was larger, and in the Examples in which the amount of the component (I) added is in a particularly suitable range of 0.1 to 3.0 mass %, the effect of addition of the above component (I) was particularly larger.
Cells were produced in the same manner as in Example 4-1 except that the electrolyte solutions shown in Table 10 were used, and the capacity retention rate at storage and the internal resistance characteristic after storage were evaluated. The evaluation results are shown in Table 14.
Evaluation results of the Examples are relative values when evaluation results of the Comparative Examples using the corresponding component (I) are designated as 100. It is desired that the “capacity retention rate at storage” have a higher value, and it is desired that the “internal resistance characteristic after storage” have a lower value.
From the evaluation results in Table 14, it was confirmed that in the case where the component (I) and the component (II) of the present invention were used in combination, the high temperature storage characteristic (capacity retention rate at storage) and the internal resistance characteristic after storage can be improved in a balanced manner compared to the Comparative Examples to which the component (II) was not added. It was confirmed that in the Examples in which the amount of the component (II) added is in a suitable range of “0.01 to 10.0 mass %” with respect to the total amount of the components (I) to (IV), both the capacity retention rate at storage and internal resistance characteristic after storage can be well improved. It was also confirmed that in the Examples in which the amount of the component (II) added is in a more suitable range of 0.1 to 5.0 mass %, the effect of addition of the above was larger, and in Examples in which the amount of the component (II) added is in a particularly suitable range of 0.2 to 1.5 mass %, the effect of addition of the above component (II) was particularly larger.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-153181 | Aug 2018 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2019/032140 | 8/16/2019 | WO | 00 |
