KR20040065152A - Non aqueous electrolyte and rechargeable lithium battery - Google Patents

Abstract

PURPOSE: Provided are a nonaqueous electrolyte having excellent thermal stability and lithium ion conductivity, and a lithium secondary battery having excellent stability at high temperature and high charge/discharge rates. CONSTITUTION: The nonaqueous electrolyte comprises a polyether-modified silicon oil having a structure represented by formula 1 or 2, a cyclic carbonate, and a solute, wherein the structure of the polyether-modified silicon oil has a polyether chain connected to end of linear polysiloxane chain. In the formulas, k is 0-10, m is a natural number of 2-4, n is a natural number of 1-4, each of R1 to R7 is hydrogen or C1-C5 alkyl group, Z is CH3 or C2H5. The polyether-modified silicon oil has a viscosity of less than 10 cSt at 25 deg.C.

Description

Non-aqueous electrolyte and lithium secondary battery {NON AQUEOUS ELECTROLYTE AND RECHARGEABLE LITHIUM BATTERY}

[Industrial use]

The present invention relates to a nonaqueous electrolyte and a lithium secondary battery, and more particularly, to a nonaqueous electrolyte and a lithium secondary battery having excellent thermal stability and excellent lithium ion conductivity.

[Prior art]

Conventionally, the mixture which mixed cyclic ether, such as cyclic ester, such as ethylene carbonate and propylene carbonate, dimethyl carbonate, and propionic acid, and cyclic ether, such as tetrahydrofuran, is used as a non-aqueous electrolyte solution for lithium secondary batteries. However, the linear non-aqueous electrolyte containing a linear ester and a cyclic ether having a low flash point at a ratio of several tens of volume% has a problem in terms of thermal stability. Therefore, recently, as described in Japanese Patent Application Laid-Open Nos. 8-78053, 11-213042 and 2000-581123, an electrolyte solution having excellent thermal stability and excellent environmental friendliness has been proposed for an electrolyte solution using silicone oils as a solvent. .

However, the silicone oils described in the above document have excellent thermal stability, but there is a problem that the ion conductivity is insufficient when used as an electrolyte solution of a lithium secondary battery.

The present invention has been made to solve the above-described problems, and an object thereof is to provide a nonaqueous electrolyte and a lithium secondary battery having excellent thermal stability and excellent lithium ion conductivity.

1 is an explanatory diagram of a mechanism for forming a polyacrylate compound film on a negative electrode;

2 is an explanatory diagram of a mechanism for forming an aziridine compound film on a cathode;

3 is an explanatory diagram of a mechanism for forming a polyacrylate compound and an aziridine compound film on a negative electrode;

4 is a graph showing discharge curves of the lithium secondary batteries of Test Examples 1 to 5;

5 is a graph showing discharge curves of the lithium secondary batteries of Test Examples 2, 4, and 6 to 9;

6 is a graph showing the relationship between discharge current and discharge capacity of the lithium secondary batteries of Examples 1 to 4 and Comparative Example 1. FIG.

7 is a graph showing a relationship between discharge current and discharge capacity of the lithium secondary batteries of Comparative Examples 1 to 3. FIG.

8 is a graph showing the relationship between the cycle number and discharge capacity of the lithium secondary batteries of Examples 3 to 4 and Comparative Examples 1 and 3. FIG.

9 is a graph showing the relationship between the discharge current and the discharge capacity of the lithium secondary batteries of Examples 1 and 4 and Comparative Example 1. FIG.

10 is a schematic diagram illustrating a reaction mechanism during initial charging when the nonaqueous electrolyte solution of Example 1 is used.

11 is a schematic diagram illustrating a reaction mechanism during initial charging when a nonaqueous electrolyte solution of Example 5 is used.

12 is a graph showing a relationship between discharge current and discharge capacity of the lithium secondary batteries of Examples 6 to 11 of the present invention.

13 is a graph showing the relationship between the cycle number and discharge capacity of the lithium secondary batteries of Examples 6 to 11 of the present invention.

14 is a graph showing a profile of the coulombic efficiency with respect to the charging voltage during supercharge of the lithium secondary battery of Example 6 of the present invention.

FIG. 15 is a graph showing a profile of coulombic efficiency with respect to charging voltage during supercharging of the lithium secondary battery of Example 7 of the present invention; FIG.

FIG. 16 is a graph showing a profile of coulombic efficiency with respect to charging voltage during supercharge of the lithium secondary battery of Example 8 of the present invention. FIG.

FIG. 17 is a graph showing a profile of coulombic efficiency with respect to charging voltage during supercharging of the lithium secondary battery of Example 9 of the present invention; FIG.

18 is a graph showing a profile of coulombic efficiency with respect to charging voltage during supercharge of the lithium secondary batteries of Examples 10 and 11 of the present invention.

In order to achieve the above object, the present invention adopts the following configuration.

The nonaqueous electrolyte of the present invention has a structure represented by the following Chemical Formula 1 (for example, Oil 1 in the Examples) or the following Chemical Formula 2 (for example, Oil 2 in the Examples) in which a polyether chain is bonded to a straight polysiloxane chain terminal. It is characterized by containing a polyether modified silicone oil, cyclic carbonate, and a solute (for example, the nonaqueous electrolyte solution of Test Examples 1-4, 7-9, and Examples 1-4 in an Example).

[Formula 1]

[Formula 2]

(In Formula 1 or Formula 2, k is in the range of 0 to 10, m is a natural number in the range of 2 to 4, n is a natural number in the range of 1 to 4, R ₁ to R ₇ are each hydrogen or C ₁ to Alkyl group of C ₅ , preferably CH ₃ or C ₂ H ₅ , and Z is CH ₃ or C ₂ H ₅ .

When the polyether modified silicone oil having the structure of Formula 1 or Formula 2 is included, a nonaqueous electrolyte having excellent thermal stability and high ion conductivity of lithium ions may be provided.

In the nonaqueous electrolytic solution of the present invention, the polyether-modified silicone oil has a viscosity of less than 10 cSt (for example, oils 1 and 2 in Examples) at 25 ° C.

As described above, since the viscosity of the polyether-modified silicone oil is less than 10 cSt, lithium ion migration occurs smoothly, so that lithium ion conductivity does not decrease.

In the nonaqueous electrolyte of the present invention, the flash point of the polyether-modified silicone oil is preferably 120 ° C. or more (eg, oils 5, 6, and 7 in the examples), and 160 ° C. or more (eg, oil 1 in the examples). , 2) is more preferable.

Since the flash point of the polyether-modified silicone oil is 120 ° C. or more, the possibility of ignition at high temperatures is low, and the thermal stability of the nonaqueous electrolyte may be increased.

Moreover, in the nonaqueous electrolyte solution of this invention, cyclic carbonate may be added (for example, the nonaqueous electrolyte solution of Examples 1-4 in an Example).

In the nonaqueous electrolyte of the present invention, fluorinated cyclic carbonate may be added (for example, the nonaqueous electrolyte of Examples 10 and 11 in Examples).

In addition, the lithium secondary battery of the present invention includes a positive electrode, a negative electrode and a nonaqueous electrolyte, wherein the non-aqueous electrolyte has a polyether chain bonded to a straight chain polysiloxane chain terminal of Formula 1 (for example, Oil 1 in Examples) or the following Formula Polyether modified silicone oil, cyclic carbonate and solute represented by 2 (for example, oil 2 in the examples) (for example, in Examples 1 to 4, 7 to 9 and Lithium secondary batteries of Examples 1 to 4).

[Formula 1]

[Formula 2]

(In Formula 1 or Formula 2, k is in the range of 0 to 10, m is a natural number in the range of 2 to 4, n is a natural number in the range of 1 to 4, R ₁ to R ₇ are each hydrogen or C ₁ to Alkyl group of C ₅ , preferably CH ₃ or C ₂ H ₅ , respectively, and Z is CH ₃ or C ₂ H ₅ .

Since the non-aqueous electrolyte in the lithium secondary battery includes a polyether modified silicone oil having a structure represented by Formula 1 or Formula 2, thermal stability and ion conductivity of the non-aqueous electrolyte are improved, and stability at high temperature and high rate charge / discharge are possible. A lithium secondary battery can be achieved.

In addition, the lithium secondary battery of the present invention is characterized in that a film containing one or more polyacrylate compounds, aziridine compounds, fluorinated cyclic carbonates, or the like is formed on the surface of the negative electrode (for example, in the test example) Lithium secondary batteries of Examples 7 to 9 and Examples 3 and 4).

Since the coating is formed on the negative electrode surface, there is no fear that the nonaqueous electrolyte containing polyether-modified silicone oil may be decomposed on the negative electrode surface and the charge and discharge capacity of the lithium secondary battery can be improved.

In the lithium secondary battery of the present invention, it is also preferable to further add a chain carbonate to the nonaqueous electrolyte (for example, the electrolyte solutions of Examples 1 to 4 in Examples).

In the lithium secondary battery of the present invention, it is also preferable to further add fluorinated cyclic carbonate to the nonaqueous electrolyte (for example, electrolyte solutions of Examples 10 and 11 in Examples).

Moreover, as said polyacrylate compound, polyfunctional acrylate is preferable. The polyfunctional acrylate is a hydroxyl group of the (polyester) polyol having three or more hydroxyl groups (-OH), some or all of which is substituted with a (meth) acrylic acid ester, and some remaining unsubstituted with a (meth) acrylic acid ester Reactive hydroxyl groups refer to poly (ester) (meth) acrylates substituted with groups that are not radically reactive.

As said aziridine compound, what has a structure represented by following formula (3-6) can be illustrated.

In addition, the aziridine compound represented by the structural formula represented by the following formula (4), or the compound represented by the following formula (3) and the compound represented by the following formula (4) (for example, Examples 7 to 9 and Example 3 in Examples And a mixture of lithium secondary batteries of 4 to 4 may be used.

In addition, the aziridine compound may include those represented by the following formulas (5) to (6). Such compounds are preferably used simultaneously with the formulas (3) and / or (4).

[Formula 3]

(In Formula 3, R ₁ is H, CH ₃ or OH, R ₂ is H or CH ₃ )

[Formula 4]

(In Formula 4, R ₂ is H or CH ₃ )

[Formula 5]

(In Formula 5, n ₁ is preferably in the range of 0 to 10.)

[Formula 6]

(In Formula 6, n ₁ is preferably in the range of 0 to 10.)

Embodiments of the present invention will be described below with reference to the drawings.

The lithium secondary battery of the present invention includes a positive electrode, a negative electrode, and a nonaqueous electrolyte, and the polyether modified silicone oil represented by the formula (1) or the formula (2) in which the polyether chain is bonded to a straight polysiloxane chain terminal is connected to the nonaqueous electrolyte. It includes carbonate and solute. In Chemical Formula 1 or Chemical Formula 2, k is in the range of 0 to 10, m is a natural number in the range of 2 to 4, n is a natural number in the range of 1 to 4, and R ₁ to R ₇ are each hydrogen or C ₁ to C ₅ is an alkyl group, preferably CH ₃ or C ₂ H ₅ , and Z is CH ₃ or C ₂ H ₅ .

In the present invention, the nonaqueous electrolyte is a nonaqueous electrolyte in which a lithium salt (solute) is dissolved in a mixed solvent of polyether modified silicone oil and cyclic carbonate. Moreover, you may further add chain carbonate to this nonaqueous electrolyte.

It is also possible to use a gel electrolyte in which the nonaqueous electrolyte solution is impregnated with a polymer. As the polymer, a polymer such as PEO, PPO, PAN, PVDF, PMA, PMMA, or a polymer thereof may be used.

The polyether-modified silicone oil contains two polyether chains (-(CH ₂ ) _m -O- () at both ends of the linear polysiloxane chain (SiR ₂ -O- (SiR ₂ O-) _k -SiR ₂ ) represented by Chemical Formula 1 above. C ₂ H ₄ O) _n -Z) is bonded or one polyether chain at one end of the linear polysiloxane chain (SiR ₃ -O- (SiR ₂ O-) _k -SiR ₂ ) represented by the formula ( ₂ ) (-(CH ₂ ) _m -O- (C ₂ H ₄ O) _n -Z) is bonded. These polyether-modified silicone oils exhibit high ionic conductivity because they have polysiloxane chains, and thus have high thermal stability and solvate oxygen and lithium ions constituting ether bonds in the polyether chains.

In addition, since the polyether chain is bonded to one or both of the ends of the linear polysiloxane chain, the entire structure of the polyether-modified siloxane oil is linear, thereby improving the flexibility of the polyether chain and lowering the viscosity. Thereby, the ion conductivity of a nonaqueous electrolyte solution can be improved. In addition, since the polyether chain is bonded to one or both of the linear polysiloxane chains, the viscosity of the polyether-modified siloxane oil can be further lowered and the ionic conductivity of the nonaqueous electrolyte can be further improved.

By adding such polyether-modified siloxane oil to the nonaqueous electrolyte, the flash point of the nonaqueous electrolyte can be increased to improve thermal stability, and the ion conductivity of lithium ions can be increased. In addition, since the nonaqueous electrolyte containing polyether-modified siloxane oil is used as the electrolyte of the lithium secondary battery, it is possible to construct a lithium secondary battery having excellent safety at high temperature and capable of high rate charge / discharge.

Moreover, it is preferable that the polyether modified silicone oil of this embodiment has a viscosity of less than 10 cSt at 25 degreeC. If the viscosity is less than 10 cSt, the change in viscosity of the nonaqueous electrolyte solution is not greatly influenced, so that the resistance to movement of lithium ions is not large.

Moreover, as for the polyether modified silicone oil of this embodiment, a flash point of 120 degreeC or more is preferable and 160 degreeC or more is more preferable. If flash point is 120 degreeC or more, the flash point of a nonaqueous electrolyte can be made high, and the thermal stability of a nonaqueous electrolyte can be improved.

In addition, in Chemical Formulas 1 and 2, k is in the range of 0 to 10, m is a natural number in the range of 2 to 4, n is a natural number in the range of 1 to 4, and R ₁ to R ₇ are each hydrogen or C ₁ to An alkyl group of C ₅ , preferably CH ₃ or C ₂ H ₅ , and Z is CH ₃ or C ₂ H ₅ .

When k exceeds 10, the thermal stability is improved, but the viscosity may be increased, and the ability to solvate lithium ions is lowered, which is not preferable because the ionic conductivity is lowered.

Moreover, when m is less than 2, the synthesis | combination of the polyether modified silicone oil mentioned later is difficult, and when m exceeds 4, a viscosity will become high and as a result, ion conductivity will fall and it is unpreferable.

If n is less than 1 (i.e., 0 is 0), there is almost no polyether chain bonded to the polysiloxane chain, and since the compatibility with cyclic carbonate is lowered, it is not preferable. If n exceeds 4, the polyether chain is long. It is unfavorable because it loses viscosity and the ion conductivity falls.

Further, when R ₁ to R ₇ are each hydrogen or an alkyl group of C ₁ to C ₅ , preferably CH ₃ or C ₂ H ₅ , respectively, and Z is CH ₃ or C ₂ H ₅ , the synthesis of polyether-modified silicone oil This becomes easy.

Subsequently, it is preferable that cyclic carbonate contains 1 or more types of ethylene carbonate, butylene carbonate, propylene carbonate, (gamma) -butyrolactone, for example. Since cyclic carbonates are easily solvated with lithium ions, the ionic conductivity of the nonaqueous electrolyte itself can be increased.

Moreover, as chain carbonate, it is preferable to contain 1 or more types of dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate, for example. Since the chain carbonate has a low viscosity, the ionic conductivity may be increased by lowering the viscosity of the nonaqueous electrolyte itself. However, since such a chain carbonate has a low flash point, excessive addition of the chain carbonate may lower the flash point of the nonaqueous electrolyte, so care should be taken not to overload it.

In addition, examples of the fluorinated cyclic carbonate include ethylene fluoro carbonate, and monofluoroethylene carbonate is particularly preferable. As the fluorinated cyclic carbonate is added, the nonflammability of the nonaqueous electrolyte is further improved, and thus the safety of the lithium secondary battery can be improved. Moreover, the film | membrane by fluorinated cyclic carbonate is formed in the surface of a negative electrode, and this film | membrane suppresses decomposition | disassembly of a nonaqueous electrolyte solution, and can improve cycling characteristics of a lithium secondary battery. In addition, since decomposition of the nonaqueous electrolyte is suppressed, the amount of decomposition gas generated is also reduced.

LiPF ₆ , LiBF ₄ , Li [N (SO ₂ C ₂ F ₆ ) ₂ ], Li [B (OCOCF ₃ ) ₄ ], LiB (OCOC ₂ F ₅ ) ₄ ] can be used as the lithium salt (solute). However, it is preferable to use one or a mixture of LiPF ₆ or BETI salt (Li [N (SO ₂ C ₂ F ₅ ) ₂ ). In the present invention, since the Si-O bond of polyether-modified silicone oil may be cleaved with the decomposition of LiPF ₆ , it is more preferable to use BETI salt (Li [N (SO ₂ C ₂ F ₅ ) ₂ ]) as a lithium salt. desirable. The concentration of the lithium salt in the nonaqueous electrolyte is preferably 0.5 mol / L or more and 2.0 mol / L or less. Since the lithium salt is contained in the nonaqueous electrolyte, the ionic conductivity of the nonaqueous electrolyte itself may be increased.

The content of polyether modified siloxane oil in the nonaqueous electrolyte is preferably in the range of 5% by volume or more and 70% by volume or less, and more preferably in the range of 10% by volume or more and 50% by volume or less. If the content of the polyether-modified siloxane oil is less than 5% by volume, the flash point of the nonaqueous electrolyte cannot be increased, which is not preferable. If the content is more than 70% by volume, the viscosity of the non-aqueous electrolyte is high and the ion conductivity is not preferable.

In the nonaqueous electrolyte, the content of the cyclic carbonate is preferably 30% by volume or more and 95% by volume or less, and more preferably 50% by volume or more and 90% by volume or less. If the content of the cyclic carbonate is less than 30% by volume, the ion conductivity is lowered, which is not preferable. If the content is more than 95% by volume, the viscosity of the nonaqueous electrolyte is increased and the ion conductivity is lowered, which is not preferable.

Moreover, when adding a linear carbonate to a nonaqueous electrolyte solution, it is preferable to make content rate of a linear carbonate into the range of 5 volume% or more and 70 volume% or less, and it is more preferable to set it as the range of 10 volume% or more and 65 volume% or less. . If the content of the linear carbonate is less than 5% by volume, the addition efficiency does not appear, and if the content is more than 70% by volume, the content of the cyclic carbonate and the polyether-modified silicone oil is relatively lowered and the flash point of the non-aqueous electrolyte is lowered, which is not preferable. .

The polyether modified silicone oil is produced by, for example, reacting a polysiloxane having a part of the R group replaced with hydrogen, for example, a polyether compound having a double bond of (CH ₂ -CH-).

For example, the polyether-modified silicone oil of Chemical Formula 1 may be, for example, CH ₂ = CH (CH ₂ ) _m-2 O in SiHR ₂ O (SiR ₂ O) _k SiHR ₂ (polysiloxane) in the presence of a platinum chloride catalyst. (C ₂ H ₅ O) _n Z can be obtained by the hydration reaction (polyether-polyolefin-substituted).

In addition, the polyether-modified silicone oil of Chemical Formula 2 is, for example, in the presence of a platinum catalyst, in a SiR ₃ O (SiR ₂ O) _k SiHR ₂ (polysiloxane) CH ₂ = CH (CH ₂ ) _m-2 O (C ₂ a H ₅ O) _n Z (polyolefin-polyether substituted) are obtained by reacting hydroxyl illustration.

The polyether-modified silicone oil obtained by the above process contains Pt (platinum), which is a catalyst component, and BHT (dibutyl hydroxytoluene), which is a polymerization inhibitor, of several to several tens of ppm. These Pt and BHT may adversely affect the cycle characteristics, so it is better to remove them if possible. As a method of removing, means such as vacuum distillation can be used. Although the number of distillation may be one or more times, it is better to carry out two or more times safely. As distillation is carried out, the content of Pt and BHT falls below the detection limit.

The polyether-modified silicone oil before vacuum distillation contains about 5 ppm of Pt and about 60 ppm of BHT. However, in the present invention, it is preferable that the Pt contained in the polyether-modified silicone oil is at least less than 5 ppm and BHT is less than 60 ppm, and Pt and BHT It is more preferable that is each below the detection limit.

Subsequently, the positive electrode can be exemplified by mixing a binder such as polyvinylidene fluoride and a conductive additive such as carbon black in the positive electrode active material powder to form a sheet, a flat disc, or the like. The thing laminated | stacked on the metal electrical power collector by forming in disk shape etc. can be illustrated. As said positive electrode active material, 1 or more types of at least 1 sort (s) chosen from cobalt, manganese, and nickel, and a composite oxide of lithium are preferable. Specifically, LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , LiFeO ₂ , V ₂ O _5, and the like are preferable. Moreover, it is also possible to use what can occlude and discharge | release lithium, such as TiS, MoS, an organic disulfide compound, or an organic polysulfide compound.

Moreover, as a separator, it is essential when a nonaqueous electrolyte solution does not gelatinize, and well-known separators, such as a porous polypropylene film and a porous polyethylene film, can be used suitably.

The negative electrode may be formed by mixing a binder such as polyvinylidene fluoride and a conductive additive such as carbon black in some cases with a negative active material powder capable of occluding and releasing lithium, and forming a sheet, a flat disc, or the like. Moreover, carbonaceous materials, such as artificial graphite, natural graphite, graphitized carbon fiber, graphitized mesocarbon microbead, and amorphous carbon, can be illustrated as a negative electrode active material. In addition, a metal material alloyable with lithium alone or a composite material including the metal material and the carbonaceous material may be exemplified as a negative electrode active material. Examples of metals alloyable with lithium include Al, Sl, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd and the like. Moreover, metal lithium foil can be used as a negative electrode active material.

Moreover, it is preferable that the film containing one or more of a polyacrylate compound and the aziridine compound which has an aziridine ring is formed in the negative electrode surface. If such a film is formed, the decomposition capacity of the polyether modified silicone oil is prevented by the presence of this film, so that the discharge capacity of the lithium secondary battery can be increased.

That is, as a polyacrylate compound, polyfunctional acrylate is preferable. The polyfunctional acrylate is a hydroxyl group of the (polyester) polyol having three or more hydroxyl groups (-OH), some or all of which is substituted with a (meth) acrylic acid ester, and some remaining unsubstituted with a (meth) acrylic acid ester Reactive hydroxyl groups refer to poly (ester) (meth) acrylates substituted with groups that are not radically reactive.

As an aziridine compound, what has a structure represented by following Chemical formulas 3-6 can be illustrated.

In addition, the aziridine compound may be a compound represented by the structural formula represented by the following formula (4), or a mixture of the compound represented by the following formula (3) and the compound represented by the following formula (4).

In addition, the aziridine compound may include those represented by the following formulas (5) to (6). Such compounds are preferably used simultaneously with the formulas (3) and / or (4).

In the structural formula of Formula 3, R ₁ is H, CH ₃ or OH, R ₂ is H or CH ₃ . In addition, in the structural formula of Formula 4, R ₂ is H or CH ₃ , in the formula 5, n ₁ is preferably in the range of 0 to 10, and in the formula 6, n ₁ is preferably in the range of 0 to 10.

The polyacrylate compound and the aziridine compound are assembled into a lithium secondary battery in the state of being added to the nonaqueous electrolyte, and polymerized on the surface of the negative electrode during initial charge and discharge to form a film. The formed film is excellent in lithium ion conductivity and lower in solubility than polyether modified silicone oil to maintain a stable film structure.

A polyacrylate compound is an anion addition polymerizable monomer which performs anion polymerization, and forms a film on the negative electrode surface which showed low electric potential at the time of charge. When the polyacrylate compound is anionic polymerized, a double bond is opened in the molecule to cause a reaction to bond with each other polyacrylate compound continuously, thereby forming a film in which the polyacrylate compound is polymerized on the surface of the negative electrode.

That is, the film formation by a polyacrylate compound is estimated to advance as shown in FIG. As shown in Fig. 1 (a), the polyacrylate compound is present in the nonaqueous electrolyte prior to the start of the initial charge, and then the charge is initiated as shown in Fig. 1 (b) to induce the polyacrylate compound to the negative electrode surface. Anionic polymerization is carried out on the surface of the negative electrode to finally form a film as shown in Fig. 1 (c).

In addition, the aziridine compound represented by Formula 3 to Formula 6 includes an aziridine ring having a skeleton of 2 carbons and 1 nitrogen, wherein the aziridine ring is coordinated with or opened with lithium to form a polymer with another aziridine compound. As a result, a film is formed.

That is, the film formation by the aziridine compound is estimated to proceed as shown in FIG. That is, as shown in FIG. E2 (a), before the initial charge start, the ion crosslinked material ("Li-aziridine crosslinked product) is such that all or part of lithium ions and aziridine compounds do not become a higher network structure in the nonaqueous electrolyte. It is considered to exist ". This Li-aziridine crosslinked product is considered to be formed by coordinating aziridine rings having a negative charge of the aziridine compound to lithium ions which are cations.

Subsequently, when charging is started as shown in Fig. 2 (b), lithium ions, which are cations, are attracted to the negative electrode so that the Li-aziridine crosslinked product adheres to the negative electrode surface. This causes an increase in the density of the aziridine compound on the surface of the negative electrode.

Subsequently, lithium ions are decomposed and released from the aziridine ring and the ion crosslink, and stored in the negative electrode. That is, when the remaining aziridine ring is opened, the polymerization reaction is started, and as a result, a film is formed as shown in Fig. 2 (c). The resulting film is negatively charged and can only transport cations. For this reason, it is possible to prevent the electrolyte from directly decomposing by contacting the cathode.

In addition, the film in which the polyacrylate compound and the aziridine compound are mixed has a particularly low solubility due to polyether modified silicone oil, thereby maintaining a more stable film.

That is, when the polyacrylate compound and the aziridine compound are added at the same time as shown in FIG. 3, the reaction proceeds in the same manner as in the polymerization reaction described in FIGS. 1 and 2 (FIGS. 3A and 3B). ), And finally, a film in which the polyacrylate compound and the aziridine compound are mixed is formed (FIG. 3 (c)). These coatings are very dense, rigid and very resistant to polyether modified silicone oils.

It is preferable to add a polyacrylate compound in 0.1 mass% or more and 1.0 mass% or less with respect to a nonaqueous electrolyte solution. Moreover, it is preferable to add an aziridine compound in 0.5 mass% or more and 1.5 mass% or less with respect to a nonaqueous electrolyte solution.

If the addition amount of the polyacrylate compound and the aziridine compound is smaller than the above range, it is not preferable because a sufficient film cannot be formed on the surface of the negative electrode.

According to the lithium secondary battery, since the polyether-modified silicone oil is included in the nonaqueous electrolyte, thermal stability of the nonaqueous electrolyte may be improved, thereby improving the high temperature characteristics of the lithium secondary battery and increasing heat resistance. In addition, since the polyether-modified silicone oil is contained in the nonaqueous electrolyte, ionic conductivity is lowered, thereby improving high rate charging characteristics of the lithium secondary battery.

In addition, since a film made of a polyacrylate compound and an aziridine compound is formed on the surface of the negative electrode, decomposition of the polyether-modified silicone oil is prevented, thereby improving high rate charge / discharge characteristics of the lithium secondary battery.

In the lithium secondary battery of this embodiment, what forms the film | membrane which consists of a polyacrylate compound and an aziridine compound in a negative electrode may be supercharged like "chemical formation" mentioned later.

When a polyacrylate compound and an aziridine compound have high content with respect to a nonaqueous electrolyte, it may absorb another solvent and lithium salt itself, and may gelatinize to form a solid electrolyte.

Therefore, when the lithium secondary battery of the present embodiment is manufactured as a nonaqueous electrolyte secondary battery, for example, a small amount of polyacrylate compound and aziridine compound are added to one or more nonaqueous electrolytes to a degree that does not form a gel even when discharged. The film only needs to be formed on the surface of the cathode.

When the lithium secondary battery of the present embodiment is prepared as a gel electrolyte secondary battery, a relatively large amount of polyacrylate and aziridine compound sufficient for gel formation is added to the nonaqueous electrolyte and supercharged before gelation is completely completed. What is necessary is just to form a film in a cathode.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only preferred embodiments of the present invention and the present invention is not limited to the following examples.

(Experiment 1: Characteristics of nonaqueous electrolyte solution)

SiH (CH ₃ ) ₂ OSiH (CH ₃ ) ₂ and CH ₂ = CHCH ₂ CH ₂ O (C ₂ H ₅ O) ₃ CH ₃ by hydration reaction in the presence of a platinum chloride catalyst, Polyether modified silicone oil was prepared. Hereinafter referred to as oil 1. Oil 1 is in the formula 1, R ₁ to R ₆ is CH ₃ , Z is CH ₃ , k is O, m is 4, n is 3.

In addition, Si (CH ₃ ) ₃ OSiH (CH ₃ ) ₂ and CH ₂ = CHCH ₂ CH ₂ O (C ₂ H ₅ O) ₃ CH ₃ are hydrated in the presence of a platinum chloride catalyst, and are represented by the following Chemical Formula 8 A polyether modified silicone oil of structure was prepared. Hereinafter referred to as oil 2. In Formula 2, R ₁ to R ₇ are CH ₃ , Z is CH ₃ , k is O, m is 4, and n is 3.

Furthermore, Si (CH ₃ ) ₂ OSiH (CH ₃ ) OSi (CH ₃ ) ₃ and CH ₂ = CHCH ₂ CH ₂ O (C ₂ H ₅ O) ₃ CH ₃ were hydrated in the presence of a platinum chloride catalyst, A polyether modified silicone oil having a structure represented by Formula 9 was prepared. Hereinafter referred to as oil 3.

[Formula 7]

[Formula 8]

[Formula 9]

The viscosity of oil 1 was 9.7 cSt at 25 ° C., the viscosity of oil 2 was 4.9 cSt at 25 ° C., and the viscosity of oil 3 was 9.4 cSt at 25 ° C. Oils 1 and 2 were also liquid at -40 ° C and oil 3 was solid at -40 ° C.

In addition, when the flash point was measured about the oil 1 and the oil 2 in the range of room temperature to 160 degreeC according to the open flash point measuring apparatus of JIS-K2265, the flash point was not detected. The flash points of oils 1 and 2 are therefore above at least 160 ° C.

The obtained oils 1-3 and ethylene carbonate were mixed to make a mixed solvent, and LiPF ₆ was added to this mixed solvent so as to have a concentration of 1 mol / l to prepare the nonaqueous electrolyte solutions of Test Examples 1-9. Table 1 shows the composition of the nonaqueous electrolyte. In Table 1, the mixing ratio of the oils 1-3 and EC is a volume ratio.

LiPF ₆ (mol / L) EC mixing ratio Mixing ratio of oil 1 Mixing ratio of oil 2 Mixing ratio of oil 3 Film forming compounds Ionic Conductivity (mS / cm: 20 ℃) Ionic Conductivity (mS / cm: 0 ℃) Viscosity (cSt) Test Example 1 One 5 5 - - none 4.2 1.73 19.0 Test Example 2 11 8 2 - - none 6.5 freezing 10.0 Test Example 3 One 5 - 5 - none 4.3 freezing 12.0 Test Example 4 One 8 - 2 - none 6.8 3.7 9.0 Test Example 5 One 5 - - 5 none 3.8 freezing 22.5 Test Example 6 One 8 - - 2 none 6.0 freezing 14.0 Test Example 7 One 8 - - - none - - - Test Example 8 One 8 2 2 - none - - - Test Example 9 One 8 - - 2 none - - -

Table 1 also shows the nonaqueous electrolyte ion conductivity and viscosity of each test example. Ionic conductivity was measured at 20 ° C and 0 ° C and viscosity was measured at 25 ° C. The nonaqueous electrolyte solutions of Test Examples 1 to 4 contained polyether modified silicone oils (oils 1 and 2) in which polyether groups were bonded to the ends of the polysiloxane chains, while the nonaqueous electrolyte solutions of Test Examples 5 to 6 had approximately the polyether groups of the polysiloxane chains. It contains a polyether modified silicone oil (oil 3) bonded at the center.

First, when comparing the viscosity of the non-aqueous electrolyte of Test Examples 1, 3, and 5 whose ratio of EC and the oils 1-3 are 5: 5, as shown in Table 1, the viscosity of the non-aqueous electrolyte of Test Example 5 was the same as that of Test Example 1 It appeared higher than the nonaqueous electrolyte of 3. It is thought that the ionic conductivity is lower than Test Example 1 or 3 at 20 ° C of Test Example 5 depending on the tendency of this viscosity. In Test Examples 1, 3, and 5, ionic conductivity at 0 ° C. was Test Example 1 including oil 1 having two polyether chains, and was found to have excellent ion conductivity at low temperature.

Subsequently, when comparing the viscosity of the nonaqueous electrolyte of Test Examples 2, 4, and 6 whose ratio of EC and the oils 1-3 are 8: 2, as shown in Table 1, the viscosity of the nonaqueous electrolyte of Test Example 6 was set to Test Example 2 or It was higher than the nonaqueous electrolyte solution of 4. It is thought that ionic viscosity is lower than Test example 2 or 4 at 20 degreeC of Test Example 6 according to this viscosity tendency. In addition, among Experiments 2, 4 and 6, the ionic conductivity at 0 ° C. was Experimental Example 4 including the oil 2 having one polyether chain, and it was found that the ionic conductivity was excellent at low temperatures.

From these results, the non-aqueous electrolyte (Test Examples 1 to 4) containing the oil 1 or 2 of the linear structure has a higher ion conductivity than the non-aqueous electrolyte (Test Examples 5 and 6) containing the oil 3 of the branch structure (test examples 5 and 6). It is judged to be suitable as an electrolyte solution of a battery.

(Experiment 2: Performance of Lithium Secondary Battery)

The coin-type lithium secondary battery was produced using the nonaqueous electrolyte solution of the test examples 1-6 obtained according to the experiment 1, and discharge capacity was measured.

The battery preparation includes LiCoO ₂ as a positive electrode active material, a polyvinylidene fluoride binder, carbon black as a conductive aid, a sheet positive electrode using Al foil as a current collector, graphite as a negative electrode active material, a polyvinylidene fluoride binder, and Cu. The sheet-like negative electrode used as the current collector and the polypropylene separator were placed in the battery container, and the nonaqueous electrolyte solutions of Test Examples 1 to 6 were injected, and then sealed in the battery container, having a diameter of 20 mm, a height of 1.6 mm, and a design charge / discharge capacity. A coin battery (Test Examples 1 to 6) of 5 mAh was manufactured.

Subsequently, each battery was charged under the condition of constant voltage charging for 9 hours after constant current charging until the battery voltage reached 4.2V at 0.2C current. Subsequently, the battery was discharged at a current of 0.2 C until the battery voltage reached 2.75 V, and the discharge capacity of each battery was measured. The results are shown in FIGS. 4 and 5.

Moreover, the coin type lithium secondary battery was produced using what added the film formation compound to the nonaqueous electrolyte solution of Test Examples 2, 4, and 6, and discharge capacity was measured.

As the added film forming compound, a polyacrylate compound represented by the following formula (10) (hereinafter referred to as PAA), tetramethyrolmethane-tri-β-aziridinylpropionate having the structure represented by the following formula (11) and the above formula A mixture (hereinafter described as TAZO) in which a compound in which R ₂ of 4 is H in a ratio of 25:75 was used.

[Formula 10]

[Formula 11]

To the nonaqueous electrolyte of Test Examples 2, 4 and 5, PAA was added at a ratio of 0.2% by mass and 1% by mass of TAZO to prepare the nonaqueous electrolyte of Test Examples 7, 8 and 9. Their specific composition is shown together in Table 1.

Subsequently, the lithium secondary batteries of Test Examples 7a, 8a and 9a were prepared in the same manner as above except that the nonaqueous electrolyte solutions of Test Examples 7, 8 and 9 were used.

In addition, for each of the batteries of Test Examples 7a, 8a, and 9a, constant current charging was performed at 0.2C current until the battery voltage reached 3V, followed by constant voltage charging for 4 hours, and again at 0.2C current. After performing constant current charging until reaching V, two-stage charging with constant voltage charging for 9 hours was performed to perform supercharge (chemical conversion) for each battery and to form a film on the surface of the negative electrode.

Thereafter, discharge was performed at a current of 0.2C for all the batteries until the battery voltage reached 2.75V to measure the discharge capacity. The results are shown in FIG.

As shown in FIG. 4, the discharge capacities of the test examples 2a, 4a, and 6a batteries were higher than those of the test examples 1, 3, and 5. This is considered to be because the content of EC in the nonaqueous electrolyte solution for Test Examples 2, 4, and 6 is relatively high, and the viscosity is low, so that the ionic conductivity is high.

On the other hand, as shown in FIG. 5, the battery (Test Examples 7a, 8a) to which the film-forming compound was added has significantly improved the discharge capacity with respect to the batteries of Test Examples 2a, 4a and 6a to which the film forming compound was not added. It can be seen that. The batteries of Test Examples 7a and 8a contain a polyether modified silicone oil (oils 1 and 2) having a straight chain structure, and the batteries of Test Example 9a (including a polyether modified silicone (oil 3) having a branched structure). It can be seen that it shows an excellent discharge capacity in comparison.

In addition, as a result of measuring the flash point of the nonaqueous electrolytes of the test examples 1 to 9 and the flash point of the conventional nonaqueous electrolyte, the flash point of 58 ° C. was confirmed in the conventional nonaqueous electrolyte, and the flash point was confirmed in the range of 160 ° C. at room temperature in the test examples 1 to 9. It became. This includes all the substances which ignite below 160 degreeC in the nonaqueous electrolyte of Test Examples 1-9, and it is thought that it flashes also as this flash point measuring apparatus.

In the conventional nonaqueous electrolyte, LiPF ₆ is dissolved in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) at a concentration of 1.3 mol / L in a volume ratio of EC: DEC = 3: 7. In addition, the measurement of a flash point measured the flash point in the range from room temperature to 160 degreeC by the open flash point measuring apparatus prescribed | regulated to JIS-K2265.

(Experiment 3: performance of lithium secondary battery)

LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (vol ratio EC: DEC = 3: 7) at a concentration of 1.3 mol / L to prepare a nonaqueous electrolyte solution of Comparative Example 1.

Subsequently, oil 1 having a structure shown in Chemical Formula 7 was added to the nonaqueous electrolyte solution of Comparative Example 1 to have a content ratio of 10% by volume to prepare a nonaqueous electrolyte solution of Example 1.

In addition, the nonaqueous electrolyte solution of Example 2 was prepared by adding oil 2 having a structure shown in Chemical Formula 8 to a content ratio of 10% by volume to the nonaqueous electrolyte solution of Comparative Example 1.

Furthermore, PAA was added to the nonaqueous electrolyte solution of Example 1 in the ratio of 0.2 mass% and TAZO 1 mass%, and the nonaqueous electrolyte solution of Example 3 was prepared.

PAA was added to the nonaqueous electrolyte solution of Example 2 in the ratio of 0.2 mass% and TAZO 1 mass%, and the nonaqueous electrolyte solution of Example 4 was prepared.

Subsequently, oil 3 of the structure represented by Formula 9 was added to the nonaqueous electrolyte solution of Comparative Example 1 to have a 10% by volume content to prepare a nonaqueous electrolyte solution of Comparative Example 2.

In addition, PAA was added to the nonaqueous electrolyte solution of Comparative Example 2 at a ratio of 0.2% by mass and 1% by mass of TAZO to prepare a nonaqueous electrolyte solution of Comparative Example 3.

Therefore, the lithium secondary batteries of Examples 1 to 4 and Comparative Examples 1 to 3 were prepared in the same manner as Experimental Example 2, except that the nonaqueous electrolyte solutions of Examples 1 to 4 and Comparative Examples 1 to 3 were used.

Subsequently, each of the batteries of Examples 1 and 2 and Comparative Examples 1 and 2 was charged under constant voltage charging for 9 hours after constant current charging until the battery voltage reached 4.2V at a current of 0.5C. Subsequently, discharge was performed at a current of 0.2C, 0.5C, 1.0C, and 2.0C until the battery voltage became 2.75V, and the discharge capacity of each battery was measured for each discharge current. The results are shown in FIGS. 6 and 7.

In addition, the batteries of Examples 3 and 4 and Comparative Example 3 were subjected to constant current charging until the battery voltage reached 3V at a current of 0.2C, followed by constant voltage charging for 4 hours, and the battery at a current of 0.2C. After performing constant current charging until the voltage reached 4.2V, two-stage charging with constant voltage charging for 9 hours was performed to perform supercharge (chemical conversion) in each battery to form a film on the surface of the negative electrode.

Thereafter, charging was performed at a current of 0.2C, 0.5C, 1.0C, and 2.0C until the battery voltage reached 2.75V, and the discharge capacity of each battery was measured for each discharge current. The results are shown in FIGS. 6 and 7.

As shown in FIG. 6, it can be seen that the discharge capacity of the batteries of Examples 3 and 4 is higher than that of Examples 1 and 2 in the discharge current range of 0.2 to 1.0C. In the batteries of Examples 3 and 4, it is thought that a film is formed on the surface of the negative electrode by adding a film forming compound, so that decomposition of oils 1 and 2 is suppressed and discharge capacity is improved.

6 and 7, Comparative Example 2 shows substantially the same discharge capacity as Example 3 even in the discharge current, but Comparative Example 3 has a discharge capacity higher than Examples 1 to 4 in the range of 1.0 to 2.0C. It was shown to degrade.

Next, FIG. 8 shows the cycle characteristic which made charge-discharge current 1C. As shown in FIG. 8, the battery of Example 3 was found to have better cycle characteristics than Comparative Example 1a.

In addition, in Example 4, although the discharge capacity is lower than that of Comparative Example 1a, the cycle curve is smaller than that of Comparative Example 1, and as the cycle progresses, it can be seen that the degradation of the discharge capacity is smaller than that of Comparative Example 1.

Subsequently, the battery of Comparative Example 3 had a smaller discharge capacity than Example 4a, the inclination of the cycle curve was larger than that of Example 4, and the deterioration of power generation capacity accompanying the progress of the cycle was greater than that of Example 4.

Therefore, it can be seen that the lithium secondary batteries (Examples 3 and 4) including the nonaqueous electrolyte solution to which the film-forming mixture was added have excellent cycle characteristics.

Next, the polyether modified silicone oil of the structure shown by following formula (12) was synthesize | combined. Hereinafter referred to as oil 4. However, this oil 4 in Formula 1, R is CH ₃ , Z is CH ₃ , k is 0, m is 4, n is 2.

Subsequently, oil 4 having a structure represented by the following Chemical Formula 12 was added to the nonaqueous electrolyte solution of Comparative Example 1 to obtain a content ratio of 10% by volume to prepare a nonaqueous electrolyte solution of Example 5.

Next, it carried out similarly to Example 2 except having used the nonaqueous electrolyte solution of Example 5, and manufactured the lithium secondary battery of Example 5.

`` Formula 12 ''

Subsequently, the battery of Example 5 was charged under the condition of constant voltage charging for 9 hours after constant current charging was performed at a current of 0.5C until the battery voltage reached 4.2V. Subsequently, the battery was charged with currents of 0.2C, 0.5C, 1.0C, and 2.0C until the battery voltage reached 2.75V, and the discharge capacity of the battery was measured for each discharge current. The results are shown in FIG. In addition, Fig. 9 also shows the results of Example 1 and Comparative Example 1.

As shown in FIG. 9, it can be seen that the discharge capacity of the battery of Example 5 is improved compared to Example 1 when the discharge current is 0.2C and 0.5C.

It is thought that the battery discharge capacity of this Example 5 improved from Example 1 for the following reason.

That is, the oil 1 contained in the nonaqueous electrolyte of Example 1 is n is 3 in the structural formula shown in Formula 1, but this oil 1 is coordinated with lithium ions (Li +) alone as shown in FIG. 10. Can be. In the electrolyte, lithium ions (Li +) coordinated by EC also coexist. In the case of using the electrolyte solution of Example 1, as shown in FIG. 10 in the super charging, the film 10 formed from EC and the film 20 formed from decomposition of silicon oil are produced in a competition reaction on the surface of the cathode. In this way, it is considered that the film 20 formed from decomposition of the silicon oil in which lithium ions are not permeated on the surface of the negative electrode is produced.

In contrast, the oil 4 contained in the nonaqueous electrolyte of Example 5 has n of 2 with respect to the structural formula shown in the above formula (1), but since the oil 4 alone has a small number of n as shown in FIG. It cannot be coordinated with ions (Li +). That is, as shown in FIG. 11, lithium ion coordinates only to EC in electrolyte solution.

For this reason, as shown in FIG. 11, the film 10 derived from EC is formed larger than the case of FIG. As a result, the electrolyte solution of Example 5 can form a better film than the electrolyte solution of Example 1, and it is thought that discharge capacity increases at 0.2C and 0.5C by this.

(Experiment 4: Characteristics of nonaqueous electrolyte and lithium secondary battery)

Si (CH ₃ ) ₃ OSiH (CH ₃ ) ₂ and CH ₂ = CHCH ₂ O (C ₂ H ₅ O) ₃ CH ₃ by hydration reaction in the presence of a platinum chloride catalyst, a polyether having a structure represented by the following formula (13) A modified silicone oil was prepared. Hereinafter referred to as oil 5. Oil 5 is in the above formula 2, R ₁ to R ₇ is CH ₃ , Z is CH ₃ , k is O, m is 3, n is 2.

[Formula 13]

In addition, vacuum distillation was performed on the oil 5 to remove Pt, BHT, and the like contained in the oil. The oil 6 which distilled twice and the thing which distilled once are called oil 7.

The viscosity of oil 5 was 2.6 cP (3.7 cSt) at 25 ° C. Moreover, about the oil 5, when the flash point was measured in the range from room temperature to 120 degreeC by the open-type flash point measuring apparatus prescribed | regulated by JIS-K2265, a flash point was not detected. The flash point of oil 5 is therefore above at least 120 ° C.

In addition, the amount of Pt and BHT contained in oils 5 to 7 was measured, respectively. The Pt amount was measured by ICP emission spectrometry, and the BHT was measured by gas chromatography. As a result, the oil 5 contained 5 ppm of Pt and 60 ppm of BHT. On the other hand, in oils 6 and 7 subjected to vacuum distillation, both Pt and BHT were below the detection limit.

Subsequently, LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio EC: DEC = 3: 7) at a concentration of 1.3 mol / L to prepare a first electrolyte solution. The nonaqueous electrolyte solution of Example 6 was prepared by adding 15% by volume of oil 5 to the first electrolyte solution.

In addition, 15% by volume of oil 6 was added to the first electrolyte to prepare a nonaqueous electrolyte of Example 7.

In addition, 15% by volume of oil 7 was added to the first electrolyte solution to prepare a nonaqueous electrolyte solution of Example 8.

Further, LiBETI was dissolved in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (volume ratio EC; DEC = 3: 7) at a concentration of 1.3 mol / L to prepare a second electrolyte solution. 15 vol% of oil 6 was added to the second electrolyte to prepare a nonaqueous electrolyte of Example 9.

The nonaqueous electrolyte of Example 10 was prepared by adding 15% by volume of oil 5 and 5% by volume of monofluoroethylene carbonate (FEC) to the first electrolyte.

The nonaqueous electrolyte of Example 11 was prepared by adding 15% by volume of oil 6 and 5% by volume of monofluoroethylene carbonate (FEC) to the first electrolyte.

In the nonaqueous electrolyte of Example 6, the viscosity and the conductivity were measured, and the viscosity was 5.66 cP and the conductivity was 6.1 mS / cm. Also in the nonaqueous electrolyte solution of Examples 7-11, the same result as Example 6 was shown. Accordingly, it can be seen that the nonaqueous electrolyte solutions of Examples 6 to 11 have physical properties applicable to electrolyte solutions for lithium secondary batteries in terms of viscosity and conductivity.

Next, the pouch type lithium secondary battery was produced using the nonaqueous electrolyte solution of Examples 6-11, and discharge capacity was measured.

The battery production includes LiCoO ₂ as a positive electrode active material, a polyvinylidene fluoride binder, carbon black as a conductive assistant, an Al foil as a current collector, graphite as a negative electrode active material, a polyvinylidene fluoride binder, and Cu foil. The negative electrode used as the current collector and the polypropylene separator were superimposed, and the nonaqueous electrolyte solution of Examples 6 to 11 was injected thereinto, and then the battery container was sealed to manufacture a battery having a design charge / discharge capacity of 820 mAh.

Subsequently, for the batteries of Examples 6 to 11, supercharge, which is a step of carrying out constant current charging until the battery voltage reaches 4.2 V at a current of 0.2 C, followed by two-stage charging for 9 hours. (Chemical formation) was performed about each battery, and the film was formed in the negative electrode surface.

Thereafter, the batteries were discharged at currents of 0.2C, 0.5C, 0.1C, and 2.0C until the battery voltage reached 2.75V, and the discharge capacity of each battery was measured for each discharge current. The results are shown in FIG.

As shown in FIG. 12, there were no significant differences in the batteries of Examples 6 to 9, and significant differences were found depending on the presence or absence of the distillation process and the type of lithium salt. On the other hand, in Examples 10 and 11 to which FEC was added, the discharge capacity was higher than that of Examples 6 to 9, and appeared closer to the design capacity of 820 mAh. This is because a favorable film by FEC is formed on the surface of the cathode during chemical formation, and the film prevents decomposition of the nonaqueous electrolyte.

Next, FIG. 13 shows cycle characteristics when the charge / discharge current is 1C. As shown in Fig. 13, the cycle characteristics of the batteries of Examples 10 and 11 to which FEC was added were improved compared to Examples 6, 7, and 9. However, in Example 10 without distillation, it turns out that cycling characteristics deteriorate as 40 cycles pass. Moreover, when Example 6 is compared with Example 7, it turns out that the cycle characteristic of Example 7 which distilled was improved. The cycle characteristics differ by the distillation as described above because Pt and BHT are removed by distillation.

In addition, it can be seen that Example 9 using LiBETI as a lithium salt exhibits the same cycle characteristics as Example 7. In addition, although not shown any more, the cycle was superior to LiPF ₆ when the charge and discharge cycle was repeated more. Accordingly, it can be seen that LiBETI shows better cycle characteristics than LiPF ₆ .

14 to 18 show the coulombic efficiency profile with respect to the charging voltage when the lithium secondary batteries of Examples 6 to 11 are formed. 14 is a profile of Coulomb efficiency of Example 6, FIG. 15, Example 7, FIG. 16, Example 8, FIG. 17, Example 9, and FIG.

As shown in Figs. 14 to 18, in Examples 6 to 8 where FEC was not added, a peak was observed near 3.3V. This peak is thought to be caused by the reaction when LiPF ₆ is inserted into the cathode surface. On the other hand, in the batteries of Examples 10 and 11, the current value of the peak near 3.3 V shown in Examples 6 to 8 decreased. In addition, the amount of gas generated on Mars was also reduced. This is considered to be because favorable film formation was promoted on the surface of the cathode by the addition of FEC.

In addition, in Example 9, since LiBETI is added, it is considered that the current value of the peak near 3.3 V is small, and favorable film formation is promoted on the surface of the cathode.

In addition, in Formula 2, R ₁ to R ₇ is CH ₃ , m is 4, k is 0, and n is 2, which is the same as Experimental Example 4 as a result of the same experiment as Experimental Example 4 The results were shown.

As described above in detail, according to the nonaqueous electrolyte of the present invention, since the polyether-modified silicone oil having the structure of Formula 1 or Formula 2 is included, the nonaqueous electrolyte having excellent thermal stability and high ion conductivity of lithium ions is used. Can provide.

In addition, according to the lithium secondary battery of the present invention, since the nonaqueous electrolyte includes a polyether modified silicone oil having the structure of Formula 1 or Formula 2, the thermal stability and the ion conductivity of the nonaqueous electrolyte are improved, and the stability at high temperature is high, and the high rate. A lithium secondary battery capable of charging and discharging can be provided.

Claims (17)

A non-aqueous electrolyte solution comprising a polyether-modified silicone oil, a cyclic carbonate, and a solute having a structure represented by the following formula (1) or (2) in which a polyether chain is bonded to a terminal of a straight chain polysiloxane chain. `` Formula 1 '' `` Formula 2 '' (In Formula 1 or Formula 2, k ranges from 0 to 10; m is a natural number ranging from 2 to 4; n is a natural number ranging from 1 to 4; R ₁ to R ₇ are each hydrogen or an alkyl group of C ₁ to C ₅ , Z is CH ₃ or C ₂ H ₅ ). The nonaqueous electrolyte of Claim 1 whose viscosity of the said polyether modified silicone oil at 25 degreeC is less than 10 cSt. The nonaqueous electrolyte of Claim 1 whose flash point of the said polyether modified silicone oil is 120 degreeC or more. The nonaqueous electrolyte of claim 1, wherein the nonaqueous electrolyte further comprises a linear carbonate. The nonaqueous electrolyte of claim 1, wherein the nonaqueous electrolyte further comprises a fluorinated cyclic carbonate. anode; cathode; And Non-aqueous electrolyte solution containing polyether modified silicone oil, cyclic carbonate, and solute represented by the following general formula (1) or (2), in which a polyether chain is bonded to the terminal of the linear polysilicon chain. Lithium secondary battery comprising a. `` Formula 1 '' `` Formula 2 '' (In Formula 1 or Formula 2, k ranges from 0 to 10; m is a natural number ranging from 2 to 4; n is a natural number ranging from 1 to 4; R ₁ to R ₇ are each hydrogen or an alkyl group of C ₁ to C ₅ , Z is CH ₃ or C ₂ H ₅ ). The lithium secondary battery according to claim 6, wherein a film including one or more of a polyacrylate compound, an aziridine compound, and a fluorinated cyclic carbonate is formed on the surface of the negative electrode. The lithium secondary battery according to claim 6, wherein a chain carbonate is further added to the nonaqueous electrolyte. The lithium secondary battery of claim 6, wherein the nonaqueous electrolyte further comprises a fluorinated cyclic carbonate. A non-aqueous electrolyte comprising polyether modified silicone oil, cyclic carbonate and solute having a viscosity of less than 10 cst at 25 ° C. The nonaqueous electrolyte of Claim 10 whose flash point of the said polyether modified silicone oil is 120 degreeC or more. The nonaqueous electrolyte of claim 10, wherein the nonaqueous electrolyte further comprises a linear carbonate. The nonaqueous electrolyte of claim 10, wherein the nonaqueous electrolyte further comprises a fluorinated cyclic carbonate. anode; cathode; And Non-aqueous electrolyte solution containing polyether modified silicone oil, cyclic carbonate and solute having a viscosity of less than 10 cst at 25 ℃ Lithium secondary battery comprising a. The lithium secondary battery according to claim 14, wherein a film containing one or more of a polyacrylate compound, an aziridine compound, and a fluorinated cyclic carbonate is formed on the surface of the negative electrode. The lithium secondary battery according to claim 14, wherein a chain carbonate is further added to the nonaqueous electrolyte. 15. The nonaqueous electrolyte of claim 14, wherein the nonaqueous electrolyte further comprises a fluorinated cyclic carbonate.