JP2017079193A - Electrolyte for nonaqueous secondary battery and nonaqueous secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrolyte for a nonaqueous secondary battery, improved in cycle characteristics even when being charged at high voltages (for example, 4.7-4.8 V or the like) in order to increase energy density.SOLUTION: An electrolyte for a nonaqueous secondary battery contains an inorganic lithium salt, an organic lithium salt having a sulfonyl group, and an organic lithium salt having a boron atom, the inorganic lithium salt having a concentration of 0.3 mol/L or more. The inorganic lithium salt is preferably LiPF, the organic lithium salt having a sulfonyl group is preferably Li(CFSO)N, and the organic lithium salt having a boron atom is preferably lithium bis(oxalato)borate.SELECTED DRAWING: None

Description

  The present invention relates to an electrolyte for a non-aqueous secondary battery and a non-aqueous secondary battery using the same.

  Non-aqueous secondary batteries such as lithium ion secondary batteries have a high energy density, and are therefore widely used for power supplies for notebook computers, mobile phones and the like. In recent years, in addition to power sources for electric tools and power sources for electric vehicles, development as power sources for portable electronic devices such as mobile phones, notebook computers, tablets, and the like is also progressing.

As described above, lithium ion secondary batteries are currently used for various power sources, but the market demand is not limited, and there is a demand for further improving the energy density. Among the methods for improving the energy density, the method of increasing the charging voltage has an advantage that there are few changes in the battery design, and this method is effective. However, when the current electrolyte is the mainstream electrolyte (electrolyte salt: LiPF ₆ only, solvent: mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC)), simply charging at high voltage, An electrolyte side reaction such as gas generation occurs in a high voltage range, and the battery performance deteriorates rapidly.

  On the other hand, in order to adopt a completely new electrolyte system, in addition to charge / discharge cycle characteristics, long-term evaluations such as safety and reliability are required, and development takes time. For this reason, there is a demand for the development of an electrolytic solution that can withstand high-voltage charging based on an electrolytic solution close to the current system.

Under such circumstances, for example, Patent Document 1 describes an electrolytic solution containing LiTFSI or LiTFSA (Li ⁺ (CF ₃ SO ₂ ) ₂ N ⁻ ) as a lithium compound and LiBOB, LiPF ₆ or the like as an additive. In Example 2, an electrolyte containing LiTFSI and LiBOB, in Examples 3 to 5 LiTFSI and LiPF ₆ , and in Example 6 using LiTFSI, LiPF _6, and LiBOB is employed. According to these examples, it is shown that a non-aqueous secondary battery that can withstand a charge of 4.2 V can be obtained.

Special table 2013-546137 gazette

However, in Patent Document 1, LiTFSI or the like is used as a main electrolyte, and LiPF ₆ and LiBOB are additives. Therefore, the addition amount of LiTFSI and the like is large, and the addition amount of LiPF ₆ and LiBOB is small. For this reason, when charging at a higher voltage (for example, 4.7 to 4.8 V, etc.), the aluminum foil normally used as the positive electrode current collector is dissolved, so it cannot be endured at all. The cycle characteristics are not sufficient.

  Accordingly, the present invention provides an electrolyte for a non-aqueous secondary battery that has improved cycle characteristics even when charged at a high voltage (for example, 4.7 to 4.8 V) in order to improve energy density. The purpose is to do.

The inventors of the present invention have intensively studied to achieve the above-described object. As a result, by employing an electrolytic solution containing an inorganic lithium salt, an organic lithium salt having a sulfonyl group, and an organic lithium salt having a boron atom, and having a concentration of the inorganic lithium salt of 0.3 mol / L or more, It has been found that the cycle characteristics can be remarkably improved even when charging is performed at a high voltage (for example, 4.7 to 4.8 V). The present invention has been completed as a result of further research based on such knowledge. That is, the present invention includes the following configurations.
Item 1. An electrolyte solution for a non-aqueous secondary battery, comprising an inorganic lithium salt, an organic lithium salt having a sulfonyl group, and an organic lithium salt having a boron atom, wherein the concentration of the inorganic lithium salt is 0.3 mol / L or more.
Item 2. Wherein the inorganic lithium salt is LiPF _6, non-aqueous liquid electrolyte for a secondary battery according to claim 1.
Item 3. Item 3. The electrolyte solution for a nonaqueous secondary battery according to Item 1 or 2, wherein the organic lithium salt having a sulfonyl group is Li ⁺ (CF ₃ SO ₂ ) ₂ N ^— .
Item 4. Item 4. The electrolyte solution for a non-aqueous secondary battery according to any one of Items 1 to 3, wherein the organic lithium salt having a boron atom is lithium bis (oxalate) borate.
Item 5. Item 5. The electrolyte solution for a non-aqueous secondary battery according to any one of Items 1 to 4, wherein the content of the organic lithium salt having a boron atom is 0.2 mol / L or less.
Item 6. Item 6. The electrolyte solution for a non-aqueous secondary battery according to any one of Items 1 to 5, wherein the concentration of the organic lithium salt having a sulfonyl group is 0.1 to 2.0 mol / L.
Item 7. Item 7. The nonaqueous secondary battery according to any one of Items 1 to 6, wherein the total concentration of the inorganic lithium salt, the organic lithium salt having a sulfonyl group, and the organic lithium salt having a boron atom is 1.0 mol / L or more. Electrolytic solution.
Item 8. A non-aqueous secondary battery comprising the electrolyte solution for a non-aqueous secondary battery according to any one of Items 1 to 7.
Item 9. The nonaqueous secondary battery according to Item 8, further comprising a positive electrode in which a positive electrode mixture layer is formed on one side or both sides of the positive electrode current collector, and no conductive coating is applied on the positive electrode current collector.

  According to the present invention, the electrolyte for a non-aqueous secondary battery contains all of the inorganic lithium salt, the organic lithium salt having a sulfonyl group, and the organic lithium salt having a boron atom, and the concentration of the inorganic lithium salt is increased. Therefore, even when charging is performed at a high voltage (for example, 4.7 to 4.8 V or the like) in order to improve the energy density, the cycle characteristics can be remarkably improved.

6 is a graph showing the results of Test Example 1. 6 is a graph showing the results of Test Example 2. 10 is a graph showing the results of Test Example 3. 10 is a graph showing the results of Test Example 4. 10 is a graph showing the results of Test Example 5.

  In this specification, the concentration (mol / L) of each component means that the desired number of moles is included with respect to 1 L of the organic solvent.

1. Non -aqueous secondary battery electrolyte The non-aqueous secondary battery electrolyte of the present invention contains an inorganic lithium salt, an organic lithium salt having a sulfonyl group, and an organic lithium salt having a boron atom. The concentration is 0.3 mol / L or more.

The inorganic lithium salt is not particularly limited as long as it is conventionally used in electrolytes for non-aqueous secondary batteries. For example, lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), Examples thereof include lithium hexafluoroarsenate (LiAsF ₆ ) and lithium perchlorate (LiClO ₄ ). Among these, LiPF ₆ , LiBF _{4, and the} like are preferable, and LiPF ₆ is more preferable from the viewpoint of enduring charging at a higher voltage (for example, 4.7 to 4.8 V) and further improving cycle characteristics. These inorganic lithium salts may be used alone or in combination of two or more.

  In the electrolyte solution for a non-aqueous secondary battery of the present invention, the concentration of the inorganic lithium salt is 0.3 mol / L or more, preferably 0.35 mol / L or more, more preferably 0.4 mol / L or more. When the concentration of the inorganic lithium salt is less than 0.3 mol / L, the cycle characteristics deteriorate during charge / discharge at a high voltage (for example, 4.7 to 4.8 V, etc.), so that the energy density cannot be improved. In the electrolyte for a non-aqueous secondary battery of the present invention, the upper limit of the concentration of the inorganic lithium salt is not particularly limited, but is preferably 2.5 mol / L or less in consideration of solubility and the like, and is 2.0 mol / L L or less is more preferable.

The organic lithium salt having a sulfonyl group is not particularly limited as long as it is conventionally used in an electrolyte for a non-aqueous secondary battery. For example, LiCF ₃ SO ₃ ; an organic lithium salt having a perfluoroalkanesulfonyl group ^{_{(Li + (CF 3 SO 2}} ) 2 N - (LiTFSA), Li + (C 2 F 5 SO 2) 2 N - , ^{_{etc.), Li + (CF 3 SO}} 2) 3 C - , and the like. Among these, from the viewpoint of withstanding charging at a higher voltage (for example, 4.7 to 4.8 V, etc.) and further improving cycle characteristics, an organic lithium salt having a perfluoroalkanesulfonyl group is preferable, and Li ⁺ (CF _{3 ^{SO 2) 2 N - (LiTFSA}} ) is more preferable. These organic lithium salts having a sulfonyl group may be used alone or in combination of two or more.

  In the electrolyte solution for a non-aqueous secondary battery of the present invention, the concentration of the organic lithium salt having a sulfonyl group is preferably 0.1 to 2.0 mol / L, more preferably 0.15 to 1.5 mol / L, and 2-1.0 mol / L is more preferable. By setting the concentration of the organic lithium salt having a sulfonyl group within this range, the organic lithium salt having a sulfonyl group is dissolved more appropriately in the electrolytic solution, and at a high voltage (for example, 4.7 to 4.8 V). Cycle characteristics can be further improved during charging and discharging, and the energy density can be further improved.

The organic lithium salt having a boron atom is not particularly limited as long as it is conventionally used in an electrolyte for non-aqueous secondary batteries. For example, LiBF ₃ CF ₃ , lithium bis (oxalate) borate (LiBOB; LiB (C ₂ O ₄ ) ₂ ), lithium oxalate difluoroborate (LiBF ₂ (C ₂ O ₄ )), lithium bis (malonate) borate (LiB (C ₃ O ₄ H ₂ ) ₂ ) and the like. Among these, lithium bis (oxalate) borate (LiBOB; LiB (C ₂ O ₄ ) ₂ ) is used from the viewpoint of withstanding charging at a higher voltage (for example, 4.7 to 4.8 V, etc.) and further improving cycle characteristics. Is preferred. These organolithium salts having a boron atom may be used alone or in combination of two or more.

  In the electrolyte solution for a non-aqueous secondary battery of the present invention, the concentration of the organic lithium salt having a boron atom is preferably 0.2 mol / L or less, more preferably 0.01 to 0.18 mol / L, and 0.02 to 0 More preferably, 15 mol / L. In addition, when the density | concentration of inorganic lithium salt is high (for example, when it is 1.2 mol / L or more), 0.03-0.12 mol / L is especially preferable. By setting the content (concentration) of the organic lithium salt having a boron atom within this range, the organic lithium salt having a boron atom is more appropriately dissolved in the electrolytic solution, and a high voltage (for example, 4.7 to 4. The cycle characteristics can be further improved and the energy density can be further improved during charging / discharging at 8V or the like.

  In the electrolyte solution for a non-aqueous secondary battery of the present invention, the total concentration of the inorganic lithium salt, the organic lithium salt having a sulfonyl group, and the organic lithium salt having a boron atom is preferably 1.0 mol / L or more. 2 to 4.0 mol / L is more preferable, and 1.3 to 3.5 mol / L is more preferable. By setting the total concentration of the inorganic lithium salt, the organic lithium salt having a sulfonyl group, and the organic lithium salt having a boron atom within this range, the cycle is performed at the time of charging / discharging at a high voltage (for example, 4.5 to 5.0 V). The characteristics can be further improved and the energy density can be further improved.

  The electrolyte solution for a non-aqueous secondary battery of the present invention uses the above-described inorganic lithium salt, organic lithium salt having a sulfonyl group, and organic lithium salt having a boron atom as an electrolyte salt. It can be set as the component similar to the component conventionally employ | adopted as the electrolyte solution for non-aqueous secondary batteries. For example, the electrolyte for a non-aqueous secondary battery of the present invention contains an organic solvent in addition to the inorganic lithium salt, the organic lithium salt having a sulfonyl group, and the organic lithium salt having a boron atom, It is preferable to dissolve a lithium salt, an organic lithium salt having a sulfonyl group, and an organic lithium salt having a boron atom.

  The organic solvent that can be included in the electrolyte solution for a non-aqueous secondary battery of the present invention is an organic solvent that can dissolve the above-described inorganic lithium salt, organic lithium salt having a sulfonyl group, and organic lithium salt having a boron atom. Not particularly limited, for example, chain carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate; ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, etc. Cyclic carbonates such as γ-butyrolactone; chain carboxylic acid esters such as methyl acetate, methyl propionate and ethyl acetate; sulfones such as sulfolane and diethylsulfone; tetrahydrofuran, 2-methyltetrahydrofuran, 1, -Ethers such as dimethoxyethane and the like. From the viewpoint of solubility of the above-described inorganic lithium salt, organic lithium salt having a sulfonyl group, and organic lithium salt having a boron atom, dimethyl carbonate (DMC), diethyl carbonate (DEC), chain carbonates such as ethyl methyl carbonate (EMC), methyl propyl carbonate; cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, etc. are preferred, ethylene carbonate (EC) and ethyl methyl A mixed solvent of carbonate (EMC) is more preferable. These organic solvents may be used alone or in combination of two or more.

  The content of the organic solvent in the electrolyte solution for a non-aqueous secondary battery of the present invention may be an excess amount. Specifically, the inorganic lithium salt, the organic lithium salt having a sulfonyl group, and a boron atom may be used. It is preferable to adjust the concentration of the organic lithium salt to be within the above range.

  In the electrolyte solution for a non-aqueous secondary battery of the present invention, components other than those described above are within a range not impairing the effects of the present invention (for example, 0 to 0.2 mol / L, particularly 0 to 0.1 mol / L). For example, additives can be included. Examples of such additives include tetrabutylammonium hexafluorophosphate, tetrabutylammonium perchlorate, tetramethylammonium tetrafluoroborate, tetramethylammonium chloride, tetraethylammonium chloride, tetrabutylammonium chloride, and tetramethylammonium bromide. , Tetraethylammonium bromide, tetrabutylammonium bromide, vinylene carbonate, fluoroethylene carbonate, trifluoromethyl ethylene carbonate, vinyl ethylene carbonate, 1,3,2-dioxathiolane-2-oxide, 3-sulfolene, biphenyl, trialkylphos Examples thereof include fert (trimethyl phosphate, etc.). These additives may be used alone or in combination of two or more.

  The electrolyte solution for a non-aqueous secondary battery of the present invention is usually in a liquid state, but a gel electrolyte gelled with a gelling agent composed of a polymer or the like can also be used.

2. Non-aqueous secondary battery The non-aqueous secondary battery of the present invention includes the above-described electrolyte for a non-aqueous secondary battery. About another structure and structure, the structure and structure employ | adopted by the conventionally known non-aqueous secondary battery are applicable. In general, the non-aqueous secondary battery of the present invention can include a positive electrode, a negative electrode, and a separator in addition to the above-described electrolyte for a non-aqueous secondary battery.

<Positive electrode>
As a positive electrode, the structure which formed the positive mix layer containing a positive electrode active material, a binder, etc. in the single side | surface or both surfaces of a positive electrode electrical power collector can be employ | adopted.

  In this positive electrode mixture layer, a binder is added to the following positive electrode active material and a conductive additive added as necessary, and this is dispersed in an organic solvent to prepare a positive electrode mixture layer forming paste (this In this case, the binder may be dissolved or dispersed in an organic solvent in advance) and applied to the surface (one side or both sides) of a positive electrode current collector made of a metal foil or the like and dried to form a positive electrode mixture layer. And it can manufacture through the process processed as needed.

The positive electrode active material is not particularly limited, and a material that is charged and discharged at a high potential can be employed. For example, LiMnO ₂ , LiNiO ₂ , LiCoO ₂ , Li (Mn _x Ni _1-x ) O ₂ , Li (Mn _x Co _1-x ) O ₂ , Li (Ni _y Co _1-y ) O ₂ , Li (Mn _{x Ni y Co 1-x-} y) layered oxides such as _{O 2; Li 2 MnO 3 -LiNiO} 2, Li 2 MnO 3 -LiCoO 2, Li 2 MnO 3 -Li (Ni y Co 1-y) O 2 Li ₂ MnSiO ₄ , Li ₂ NiSiO ₄ , Li ₂ CoSiO ₄ , Li ₂ (Mn _x Ni _1-x ) SiO ₄ , Li ₂ (Mn _x Co _1-x ) SiO ₄ , Li ₂ (Ni _{y Co 1-y) SiO 4,} Li 2 (Mn x Ni y Co 1-x-y) silicates of SiO ₄ and the _{like; LiMnBO 3, LiNiBO 3, LiCoBO} 3, Li (Mn x _{i 1-x) BO 3,} Li (Mn x Co 1-x) BO 3, Li (Ni y Co 1-y) BO 3, Li (Mn x Ni y Co 1-x-y) BO 3 boric of _{salt; V 2 O 5; LiV 3} O 6; MnO and the like. In the above formula, 0 <x <1, 0 <y <1, and 0 <x + y <1. Among these materials, the layered oxide is about 2.8 to 4.5 V, the solid solution is about 2.7 to 4.5 V, the silicate is about 3.0 to 4.5 V, and the borate is 2.5. ˜4.0V, V ₂ O ₅ , LiV ₃ O ₆ and MnO are known as materials that can be charged and discharged at about 2.5 to 3.5V. By using these materials in combination with the electrolyte for non-aqueous secondary batteries of the present invention, charging / discharging at a higher potential (for example, 4.7 to 4.8 V) can be performed. In particular, it is known that the layered oxide and solid solution have a higher capacity density as the charging potential is increased (the capacity density of other materials is almost the same even when the charging potential is increased). Thus, when a layered oxide and a solid solution are used as the positive electrode active material, the energy density can be particularly improved by the synergistic effect of the effect of increasing the charging potential and the effect of improving the capacity density by increasing the charging potential. Is possible. Among these, Li ₂ MnO ₃ —Li (Ni _y Co _1-y ) O ₂ is particularly preferable from the viewpoint of the balance between the charging potential, the capacity density, and the cycle characteristics. These positive electrode active materials may be used alone or in combination of two or more.

  As a conductive auxiliary agent, as with normal non-aqueous secondary batteries, amorphous carbon materials such as graphite; carbon black (acetylene black, ketjen black, etc.); carbon materials with amorphous carbon formed on the surface Fibrous carbon (vapor-grown carbon fiber, carbon fiber obtained by carbonizing after spinning a pitch, etc.); carbon nanotubes (various multi-layer or single-wall carbon nanotubes), etc. can be used. As a conductive support agent of a positive electrode, you may use individually and may be used in combination of 2 or more type.

  Examples of the binder include polyvinylidene fluoride (PVDF), polytetrafluoroethylene, polyacrylic acid, styrene butadiene rubber, polyimide, polyvinyl alcohol, and water-soluble carboxymethyl cellulose.

  There is no restriction | limiting in particular as an organic solvent used when manufacturing a positive electrode mixture, N-methylpyrrolidone (NMP) etc. are mentioned, Make it into paste form using this, a positive electrode active material, a binder, etc. Can do.

  Regarding the composition of the positive electrode mixture layer, for example, the positive electrode active material is preferably about 70 to 95% by weight, and the binder is preferably about 1 to 30% by weight. Moreover, when using a conductive support agent, said positive electrode active material is about 50 to 90 weight%, a binder is about 1 to 20 weight%, and a conductive support agent is about 1 to 40 weight%. preferable. Furthermore, the thickness of the positive electrode mixture layer is preferably about 1 to 100 μm per one side of the current collector.

  As the positive electrode current collector, for example, a foil made of aluminum, stainless steel, nickel, titanium, or an alloy thereof, a punched metal, an expanded metal, a net, or the like can be used. Usually, aluminum having a thickness of about 10 to 30 μm. A foil is preferably used. In addition, like patent document 1, in order to prevent deterioration and performance loss of a battery by suppressing that an electrolyte solution and a positive electrode collector react and corrode at the time of charge at a high potential, the positive electrode collector A conductive coating containing conductive carbon, graphite, or the like may be applied on the substrate, but the manufacturing process increases and the manufacturing cost increases. When the electrolyte for a non-aqueous secondary battery of the present invention is adopted, since the electrolyte and the positive electrode current collector hardly react even when charged at a high potential, a conductive coating is formed on the positive electrode current collector. There is no need to form.

<Negative electrode>
As a negative electrode, the structure which formed the negative mix layer containing a negative electrode active material, a binder, etc. in the single side | surface or both surfaces of a negative electrode collector can be employ | adopted.

  This negative electrode mixture layer is formed into a sheet by mixing a negative electrode active material and a conductive additive added as necessary, into a sheet, and this is formed on the surface (one side of the negative electrode current collector made of a metal foil or the like. Or it can manufacture through the process crimped | bonded to both surfaces.

  The negative electrode active material is not particularly limited, and for example, graphite (natural graphite, artificial graphite, etc.), hardly sinterable carbon, lithium metal, tin, silicon, an alloy containing these, SiO, or the like can be used. Preferably, a lithium metal, a lithium alloy, or the like can be used in a metal lithium primary battery and a metal lithium secondary battery. In a lithium ion secondary battery, a material (graphite (natural graphite, artificial Graphite, etc.), hardly sinterable carbon, etc.) can be used as the active material. These negative electrode active materials may be used alone or in combination of two or more.

  As a conductive auxiliary agent, as with normal non-aqueous secondary batteries, amorphous carbon materials such as graphite; carbon black (acetylene black, ketjen black, etc.); carbon materials with amorphous carbon formed on the surface Fibrous carbon (vapor-grown carbon fiber, carbon fiber obtained by carbonizing after spinning a pitch, etc.); carbon nanotubes (various multi-layer or single-wall carbon nanotubes), etc. can be used. As a conductive support agent of a negative electrode, it may be used independently, may be used in combination of 2 or more type, and may not be used when the electroconductivity of a negative electrode active material is high.

  Examples of the binder include polyvinylidene fluoride (PVDF), polytetrafluoroethylene, polyacrylic acid, styrene butadiene rubber, polyimide, polyvinyl alcohol, and water-soluble carboxymethyl cellulose.

  About the composition of a negative mix layer, it is preferable that said negative electrode active material is about 70 to 95 weight% and a binder is about 1 to 30 weight%, for example. Moreover, when using a conductive support agent, it is preferable that said negative electrode active material is about 50 to 90 weight%, a binder is about 1 to 20 weight%, and a conductive support agent is about 1 to 40 weight%. preferable. Furthermore, the thickness of the negative electrode mixture layer is preferably about 1 to 100 μm per one side of the current collector.

  As the negative electrode current collector, for example, a foil made of aluminum, copper, stainless steel, nickel, titanium, or an alloy thereof, a punched metal, an expanded metal, a mesh, a net, or the like can be used. A copper foil of about 30 μm is preferably used.

<Separator>
The above-described positive electrode and negative electrode can be used, for example, in the form of a laminated electrode body laminated with a separator interposed therebetween, or a wound electrode body obtained by winding the separator in a spiral shape.

  As the separator, a separator having sufficient strength and capable of holding a large amount of electrolyte is preferable. From such a viewpoint, polyethylene, polypropylene, and ethylene-propylene copolymer having a thickness of 10 to 50 μm and an aperture ratio of 30 to 70% are used. A microporous film or a non-woven fabric containing one kind or plural kinds of coalescence is preferable.

  Moreover, as a form of the non-aqueous secondary battery of the present invention, a cylindrical shape (such as a rectangular tube shape or a cylindrical shape) using a stainless steel can, an aluminum can, or the like as an outer can can be employed. Moreover, a soft package battery having a laminate film integrated with a metal foil as an outer package may be employed.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, it cannot be overemphasized that this invention is not limited to a following example.

Example 1: 1.5 M LiPF ₆ +0.5 M LiTFSA + 0.12 M LiBOB
In a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (EC: EMC = 3: 7 (volume ratio)), lithium hexafluorophosphate (LiPF ₆ ), lithium perfluoromethanesulfonylamide (Li (CF ₃ SO ₂ ) ₂ N; LiTFSA), lithium bis (oxalate) borate (LiB (C ₂ O ₄ ) ₂ ; LiBOB), LiPF ₆ concentration of 1.5 mol / L (volume based on solvent), LiTFSA It was added so that the concentration was 0.5 mol / L and the content of LiBOB was 0.12 mol / L, and 1.5 mol / L LiPF ₆ , 0.5 mol / L LiTFSA, and 0.12 mol / L LiBOB were added. Was obtained.

Comparative Example 1: 1.5 M LiPF ₆
An electrolyte solution in which 1.5 mol / L of LiPF ₆ was dissolved was obtained in the same manner as in Example 1 except that LiTFSA and LiBOB were not used (LiTFSA: 0 mol / L, LiBOB: 0 mol / L).

Comparative Example 2: 1.5 M LiPF ₆ +0.12 M LiBOB
An electrolyte solution in which 1.5 mol / L LiPF ₆ and 0.12 mol / L LiBOB were dissolved was obtained in the same manner as in Example 1 except that LiTFSA was not used (0 mol / L).

Example 2: 1.0 M LiPF ₆ +0.5 M LiTFSA + 0.12 M LiBOB
Similar to Example 1, except that the concentration of LiPF ₆ was adjusted to 1.0 mol / L, 1.0 mol / L LiPF ₆ , 0.5 mol / L LiTFSA, and 0.12 mol / L An electrolytic solution in which LiBOB was dissolved was obtained.

Comparative Example 3: 1.0 M LiPF ₆ +0.12 M LiBOB
The concentration of LiPF ₆ was adjusted to 1.0 mol / L, and LiTFSA was not used (0 mol / L), except that 1.0 mol / L LiPF ₆ and 0. An electrolytic solution in which 12 mol / L LiBOB was dissolved was obtained.

Example 3: 1.5 M LiPF ₆ +0.5 M LiTFSA + 0.03 M LiBOB
Similar to Example 1, except that the LiBOB content was adjusted to 0.03 mol / L, 1.5 mol / L LiPF ₆ , 0.5 mol / L LiTFSA, and 0.03 mol / L An electrolytic solution in which LiBOB was dissolved was obtained.

Example 4: 1.5 M LiPF ₆ +0.5 M LiTFSA + 0.06 M LiBOB
Similar to Example 1 except that the LiBOB content was adjusted to 0.06 mol / L, 1.5 mol / L LiPF ₆ , 0.5 mol / L LiTFSA, and 0.06 mol / L An electrolytic solution in which LiBOB was dissolved was obtained.

Comparative Example 4: 1.5 M LiPF ₆ +0.5 M LiTFSA
An electrolytic solution in which 1.5 mol / L LiPF ₆ and 0.5 mol / L LiTFSA were dissolved was obtained in the same manner as in Example 1 except that LiBOB was not used (0 mol / L).

Example 5: 1.5 M LiPF ₆ +1.0 M LiTFSA + 0.06 M LiBOB
Similar to Example 1, except that the concentration of LiTFSA was 1.0 mol / L and the content of LiBOB was 0.06 mol / L, 1.5 mol / L LiPF ₆ , 1.0 mol / L An electrolytic solution in which LiTFSA and 0.06 mol / L LiBOB were dissolved was obtained.

Example 6: 1.0 M LiPF ₆ +1.0 M LiTFSA + 0.06 M LiBOB
As in Example 1, 1.0 mol except that the concentration of LiPF ₆ was adjusted to 1.0 mol / L, the concentration of LiTFSA was 1.0 mol / L, and the content of LiBOB was 0.06 mol / L. An electrolytic solution in which / L LiPF ₆ , 1.0 mol / L LiTFSA, and 0.06 mol / L LiBOB were dissolved was obtained.

Comparative Example 5: 1.0 M LiTFSA + 0.06 M LiBOB
In the same manner as in Example 1, except that the concentration of LiTFSA was adjusted to 1.0 mol / L and the content of LiBOB was adjusted to 0.06 mol / L, and LiPF ₆ was not used (0 mol / L). An electrolytic solution in which 0.0 mol / L LiTFSA and 0.06 mol / L LiBOB were dissolved was obtained.

Comparative Example 6: 0.1 M LiPF ₆ +1.0 M LiTFSA +0.06 M LiBOB
0.1 mol as in Example 1 except that the concentration of LiPF ₆ was adjusted to 0.1 mol / L, the concentration of LiTFSA was adjusted to 1.0 mol / L, and the content of LiBOB was adjusted to 0.06 mol / L. An electrolytic solution in which / L LiPF ₆ , 1.0 mol / L LiTFSA, and 0.06 mol / L LiBOB were dissolved was obtained.

Production Example 1 (graphite negative electrode)
Using the electrolyte solutions of Examples 1 to 6 and Comparative Examples 1 to 6, test tripolar lamicelles were produced. Specifically, a test tripolar lamicelle was prepared as follows.

Li ₂ MnO ₃ —Li (Ni _y Co _1-y ) O ₂ solid solution (MNC0125 manufactured by Toda Kogyo Co., Ltd.) was used as a positive electrode active material, and scaly graphite (Super manufactured by TIMCAL) was used as a conductive aid. P) and polyvinylidene fluoride (PVDF) (a KF polymer manufactured by Kureha Co., Ltd.) as a binder, and a ratio of positive electrode active material: conductive aid: binder = 90: 5: 5 (weight ratio) Thus, a positive electrode mixture was prepared by dispersing in N-methylpyrrolidone (NMP). This positive electrode mixture is applied to an aluminum foil (thickness 20 μm; no conductive coating is provided on the surface), and after drying, rolled to such an extent that no peeling of the mixture or current collector flaws occur. did.

  Next, carbon black (MAGD manufactured by Hitachi Chemical Co., Ltd.) is used as the negative electrode active material, and polyvinylidene fluoride (PVDF) (KF polymer manufactured by Kureha Co., Ltd.) is used as the binder. : Binder = 95: 5 (weight ratio) mixed to form a sheet, applied to a copper foil (thickness 15 μm), dried and rolled to prepare a negative electrode.

  The positive electrode and the negative electrode thus produced were laminated via a separator (polypropylene film; thickness 25 μm; Cellguard 2500 manufactured by Celgard), and Examples 1 to 6 and Comparative Examples 1 to 1 were incorporated into the Ramellels as battery containers. A tripolar lamicel (1) using a graphite negative electrode was prepared by accommodating together with the electrolytic solution 6 and lithium metal as a reference electrode.

Production Example 2 (silicon negative electrode)
Instead of carbon black (MAGD manufactured by Hitachi Chemical Co., Ltd.) as the negative electrode active material, silicon (30-50 nm Si nanopowder manufactured by Nanostructured & Amorphous Materials) is used, and acetylene black (DENKA (DENKA Denka Black manufactured by Co., Ltd.) and polyimide (DREAMBOND manufactured by IST) as a binder were mixed in a ratio of negative electrode active material: conductive aid: binder = 80: 5: 15 (weight ratio). Except for the above, a tripolar lamellar cell (2) using a silicon negative electrode was produced in the same manner as in Production Example 1.

Test example 1
Using the tripolar lamicelle (1) produced according to Production Example 1 using the electrolytic solutions of Example 1 and Comparative Examples 1 and 2, the following conditions:
Charging 10 mA constant current and constant voltage charging at 2 mA and 4.8 V Discharging Discharging to 2.5 V at a constant current of 2 mA Standing time between cycles (rest time) 5 minutes Before the 24th and 25th cycle tests Since another electrochemical measurement was performed, the cycle test was temporarily suspended. Charge / discharge temperature 25 ° C
The battery was charged and discharged up to 30 cycles.

The results are shown in FIG. From FIG. 1, it is understood that in Comparative Example 1 in which LiTFSA and LiBOB are not used, the electrolyte solution and the positive electrode active material are reacted under a high potential charging condition, or the deterioration is rapid and the cycle characteristics are inferior. it can. Further, in Comparative Example 2 in which LiTFSA is not used, it can be understood that the deterioration is fast and the cycle characteristics are inferior because the electrolytic solution and the positive electrode active material are reacted under the high potential charging condition. On the other hand, in Example 1, since an electrolyte containing three types of LiPF ₆ , LiTFSA, and LiBOB and having a high concentration of LiPF ₆ is employed, the electrolyte and the positive electrode active material even under charging conditions at a high potential And the cycle characteristics could be improved. Further, when Comparative Example 1 and Comparative Example 2 are compared, since the cycle characteristics are deteriorated even when the type of electrolyte salt is increased, the concentration of LiPF ₆ is high, including three types of LiPF ₆ , LiTFSA, and LiBOB. It is an unexpected result that the cycle characteristics can be particularly improved by employing the electrolytic solution.

Test example 2
Using the tripolar lamellar cell (1) produced according to the manufacture example 1 using the electrolyte solution of Example 2 and the comparative example 3, it charged / discharged to 20 cycles by the method similar to the test example 1. FIG. In other words, the following conditions:
Charging Constant current constant voltage charging for 10 minutes at 2 mA and 4.8 V Discharging Discharge to 2.5 V at a constant current of 2 mA Standing time between cycles (rest time) 5 minutes Charging / discharging temperature 25 ° C.
The battery was charged and discharged up to 20 cycles.

The results are shown in FIG. From FIG. 2, it can be understood that in Comparative Example 3 in which LiTFSA is not used, the deterioration is rapid and the cycle characteristics are inferior because the electrolytic solution and the positive electrode active material are reacted under the charge condition at a high potential. On the other hand, in Example 2, since an electrolyte containing three types of LiPF ₆ , LiTFSA, and LiBOB and having a high concentration of LiPF ₆ is employed, the electrolyte and the positive electrode active material are used even under charging conditions at a high potential. And the cycle characteristics could be improved.

Test example 3
Using the tripolar lamicel (1) produced according to Production Example 1 using the electrolytic solutions of Example 3 (4) and Comparative Example 4, the following conditions:
1-50 cycle charge 10mA constant current constant voltage charge at 2mA and 4.8V Discharge 51mA to 59cycle charge 2mA constant current to 2.5V constant current 10V constant current constant voltage charge at 1mA and 4.8V Discharge Discharge to 2.5 V at a constant current of 1 mA. Example 3 and Comparative Example 4 were performed before the 24th and 25th cycle tests and before the 50th cycle test. Before the cycle test, another electrochemical measurement was performed, so the cycle test was suspended. Charge / discharge temperature: 25 ° C
The battery was charged and discharged up to 59 cycles.

The results are shown in FIG. From FIG. 3, it can be understood that in Comparative Example 4 in which LiBOB is not used, the deterioration is rapid and the cycle characteristics are inferior because the electrolytic solution and the positive electrode active material are reacted under the charging condition at a high potential. On the other hand, in Examples 3 and 4, since an electrolyte containing three types of LiPF ₆ , LiTFSA, and LiBOB and having a high concentration of LiPF ₆ is employed, the electrolyte and the positive electrode are used even under charging conditions at a high potential. It was possible to suppress the reaction with the active material and improve the cycle characteristics.

Test example 4
Using the three-electrode lamicel (1) produced according to Production Example 1 using the electrolytic solutions of Examples 5 to 6 and Comparative Examples 5 to 6, the following conditions:
Charging Constant current and constant voltage charging at 1mA and 4.8V (cutoff current 0.2mA)
Discharge up to 2.5 V at a constant current of 1 mA Discharge charge / discharge temperature: 25 ° C.
The battery was charged and discharged up to 49 cycles. In Comparative Example 5, the cycle test was suspended because another electrochemical measurement was performed before the 21st cycle test.

The results are shown in FIG. 4, the density is low comparative example 6 of LiPF ₆ but including a three Comparative Example _5, LiPF 6, LiTFSA and LiBOB are not using LiPF _6, electrolyte and cathode active in charge condition at high potential It can be understood that the deterioration is remarkably fast and the cycle characteristics are inferior because of the reaction with the substance. From these results, compared with the electrolytic solution containing only two components of LiTFSA and LiBOB (Comparative Example 5), in Comparative Example _{6 in} which only a small amount of LiPF ₆ was added, the cycle characteristics were further deteriorated. It can be understood that the cycle characteristics are not always improved as the number of salt types is increased. In contrast, in Examples _5-6, includes three LiPF 6, LiTFSA and LiBOB, since the concentration of LiPF ₆ employs a high electrolyte, the electrolyte and the cathode even in the charge condition of a high potential It was possible to suppress the reaction with the active material and improve the cycle characteristics. This result is an unexpected result from the above disclosure that the cycle characteristics are not always improved as the types of electrolyte salts are increased.

Test Example 5
Using the three-electrode lamicel (2) produced according to Production Example 2 using the electrolytic solutions of Example 4 and Comparative Example 4, the following conditions:
Charging Constant current constant voltage charging at 4.7 mA at a constant current of 2 mA for 10 minutes Discharging / discharging temperature up to 2.5 V at a constant current of 2 mA: 25 ° C.
The battery was charged and discharged up to 49 cycles.

The results are shown in FIG. From FIG. 5, even when a silicon negative electrode is used, Comparative Example 4 in which LiBOB is not used is deteriorated because the electrolyte solution and the positive electrode active material are reacted under a high potential charging condition. It can be understood early that the cycle characteristics are inferior. On the other hand, in Example 4, since an electrolyte containing three types of LiPF ₆ , LiTFSA, and LiBOB and having a high concentration of LiPF ₆ is employed, the electrolyte and the positive electrode active material are used even under charging conditions at a high potential. And the cycle characteristics could be improved.

Claims (9)

An electrolyte solution for a non-aqueous secondary battery, comprising an inorganic lithium salt, an organic lithium salt having a sulfonyl group, and an organic lithium salt having a boron atom, wherein the concentration of the inorganic lithium salt is 0.3 mol / L or more. The electrolyte solution for non-aqueous secondary batteries according to claim 1, wherein the inorganic lithium salt is LiPF ₆ . The organic lithium salt having a sulfonyl group is ^{_{Li + (CF 3 SO 2)}} 2 N - is a non-aqueous liquid electrolyte for a secondary battery according to claim 1 or 2. The electrolyte solution for nonaqueous secondary batteries in any one of Claims 1-3 whose organic lithium salt which has the said boron atom is lithium bis (oxalate) borate. The electrolyte solution for nonaqueous secondary batteries in any one of Claims 1-4 whose content of the organic lithium salt which has the said boron atom is 0.2 mol / L or less. The electrolyte solution for nonaqueous secondary batteries in any one of Claims 1-5 whose density | concentration of the organic lithium salt which has the said sulfonyl group is 0.1-2.0 mol / L. The nonaqueous secondary battery according to any one of claims 1 to 6, wherein a total concentration of the inorganic lithium salt, the organic lithium salt having a sulfonyl group, and the organic lithium salt having a boron atom is 1.0 mol / L or more. Electrolyte. A nonaqueous secondary battery provided with the electrolyte solution for nonaqueous secondary batteries in any one of Claims 1-7. The nonaqueous secondary battery according to claim 8, further comprising a positive electrode in which a positive electrode mixture layer is formed on one side or both sides of a positive electrode current collector, wherein a conductive coating is not applied on the positive electrode current collector. .