KR100508931B1 - Lithium secondary battery - Google Patents

Abstract

The present invention provides a lithium secondary battery having high safety and low deterioration in charge and discharge capacity. The lithium secondary battery includes a positive electrode, a negative electrode, and a nonaqueous electrolyte, a nonflammable solvent is included in the nonaqueous electrolyte, and a film made of a polyacrylate compound and / or an aziridine compound is formed on a surface of the negative electrode.

Description

Lithium secondary battery {LITHIUM SECONDARY BATTERY}

[Industrial use]

The present invention relates to a lithium secondary battery, and more particularly to a lithium secondary battery excellent in safety.

[Prior art]

Conventionally, the mixture which mixed cyclic ester, such as dimethyl carbonate and a propionic acid ether, and cyclic ether, such as tetrahydrofuran, is used for cyclic esters, such as ethylene carbonate and a propylene carbonate, as a nonaqueous electrolyte for lithium secondary batteries. However, in the conventional nonaqueous electrolyte, a flammable solvent having a flash point is often used, which does not satisfy safety.

Moreover, in recent years, in order to improve the safety of a lithium secondary battery, the electrolyte solution which used the organic halogen compound with high stability for heat and oxidative decomposition as a solvent is proposed. Since an electrolyte solution containing an organic halogen compound tends to be hard to ignite, it is attracting attention as a means for improving the safety of a battery. For example, Japanese Patent Laid-Open No. 7-249432 describes an electrolytic solution using a halogenated polyether. However, such halogenated polyethers are not yet mass-produced, and there is a problem that the price is high.

An object of the present invention is to provide a lithium secondary battery having high safety and low deterioration of charge and discharge capacity.

In order to achieve the above object, the present invention provides a lithium secondary battery comprising a nonaqueous electrolyte comprising a positive electrode, a negative electrode and a nonflammable solvent.

The nonflammable solvent is preferably an organic halogen compound, and specifically, tetrachloroethylene or butane difluoropentane is preferable. There are various structural isomers as the dichloropentenated butane, but it is preferable to mix two kinds of isomers of the following Chemical Formulas 1 and 2 in a 1: 1 ratio.

[Formula 1]

CF ₃ CF ₂ CHCl ₂

[Formula 2]

CClF ₂ CF ₂ CHClF

Since the nonflammable solvent has a low flash point and a halogen element in the molecule, it has excellent self-extinguishing property and low vapor pressure. Therefore, when it is added to the nonaqueous electrolyte, the nonflammable solvent can increase the flash point of the nonaqueous electrolyte and prevent the flash. Can improve.

The lithium secondary battery of the present invention is also characterized in that a film made of a polyacrylate compound and / or an aziridine compound is formed on the surface of the negative electrode.

As such, if a film made of a polyacrylate compound and / or an aziridine compound is formed on the surface of the negative electrode, the film prevents the disadvantage of dissolving the binder in the negative electrode by a nonflammable solvent, thereby preventing the negative electrode active material from falling off the current collector. In addition, there is no fear that the components of the nonaqueous electrolyte are decomposed on the surface of the negative electrode, and the charge and discharge capacity of the lithium secondary battery can be improved.

As the polyacrylate compound, some or all of the hydroxyl groups of the (polyester) polyol having three or more hydroxyl groups (-OH) are substituted with (meth) acrylic acid esters and the remaining part is not substituted with (meth) acrylic acid esters. Unreacted hydroxyl groups are preferably poly (ester) (meth) acrylates substituted with groups that are not radically reactive.

In addition, the aziridine compound is preferably one of the following Chemical Formulas 3 to 6.

However, in the structural formula of Formula 3, R ₁ is _one of H, CH ₃ , OH, R ₂ is one of H or CH ₃ .

As the aziridine compound, a compound represented by the following formula (4) or a compound represented by the following formula (3) and a compound represented by the structural formula represented by the following formula (4) is preferable.

Moreover, the compound represented by following formula (5) or 6 can also be used as an aziridine compound. Such compounds are preferably used simultaneously with the formulas (3) and / or (4).

In addition, in the following Chemical Formula 4, R ₂ is one of H or CH ₃ , n ₁ in Formula 5 is preferably in the range of 0 to 10, and n ₂ in Formula 6 is preferably in the range of 0 to 10. Do.

[Formula 3]

[Formula 4]

[Formula 5]

[Formula 6]

In addition, the lithium secondary battery of the present invention is characterized in that the nonaqueous electrolyte further includes antimony oxide.

Since the antimony oxide has self-extinguishing ability, even if a small amount is dissolved in the nonaqueous electrolyte, the antimony oxide serves to increase the flash point of the nonaqueous electrolyte.

Therefore, when the antimony oxide is added, the flash point of the nonaqueous electrolyte (nonaqueous electrolyte) can be increased to prevent the flash, and the safety of the lithium secondary battery can be improved.

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 nonaqueous electrolyte contains a nonflammable solvent.

The nonaqueous electrolyte of the present invention is a nonaqueous electrolyte (nonaqueous electrolyte) in which lithium salt is dissolved in a mixed solvent of a nonflammable solvent and an aprotic solvent, or a gel nonaqueous electrolyte in which a nonaqueous electrolyte is contained in a polymer. Polymers include polyethylene oxide (PEO), polypropylene oxide (PPO), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polymethacrylate (PMA), polymethyl methacrylate (PMMA) or these The polymer of can be used.

This nonflammable solvent is a so-called organic halogen compound, which has a low flash point, a halogen element present in the molecule, and thus has excellent self-extinguishing property and a low vapor pressure. Therefore, when added to a nonaqueous electrolyte, the nonaqueous electrolyte is flame retardant. To be.

Therefore, since the non-aqueous electrolyte is added to the nonaqueous electrolyte, the flash point of the nonaqueous electrolyte (nonaqueous electrolyte) itself increases, so that the nonaqueous electrolyte does not ignite and the safety of the lithium secondary battery is improved.

As the separator, an essential separator such as a porous polypropylene film and a porous polyethylene film can be suitably used as an essential element when the nonaqueous electrolyte is not gelled.

The nonflammable solvent contained in the nonaqueous electrolyte is preferably an organic halogen compound, and specifically, tetrachloroethylene or difluorobutane dichloride is preferable. In addition, although there are various structural isomers in the dichloropentenyl butyrate, it is preferable to mix two kinds of isomers of the following general formulas (1) and (2) in a 1: 1 ratio.

[Formula 1]

CF ₃ CF ₂ CHCl ₂

[Formula 2]

CClF ₂ CF ₂ CHClF

As the aprotic solvent, for example, one or more of cyclic carbonates or cyclic esters such as ethylene carbonate, butylene carbonate, propylene carbonate and γ-butyrolactone is preferable, and in addition, dimethyl carbonate, methyl Ethyl carbonate or diethyl carbonate may be included.

Since the aprotic solvent is included with the nonflammable solvent in the nonaqueous electrolyte, the dissociation of lithium ions may be improved to increase the ionic conductivity of the nonaqueous electrolyte itself.

LiPF may be LiPF ₆ , LiBF ₄ , Li [N (SO ₂ C ₂ F ₆ ) ₂ ], Li [B (OCOCF ₃ ) ₄ ], Li [B (OCOC ₂ F ₅ ) ₄ ], but LiPF It is preferable to use one or at least one of ₆ or BETI (Li [N (SO ₂ C ₂ F ₅ ] ₂ ). 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. Do.

Since the lithium salt is included in the nonaqueous electrolyte, the ionic conductivity of the nonaqueous electrolyte itself may be improved.

The content of the nonflammable solvent is preferably in the range of 5% by mass or more and 40% by mass or less, more preferably in the range of 10% by mass or more and 30% by mass or less with respect to the nonaqueous electrolyte (nonaqueous electrolyte). If the content of the nonflammable solvent is less than 5% by mass, the flash point of the nonaqueous electrolyte cannot be increased, and this is not preferable. If the content is more than 30% by mass, the content of the aprotic solvent is relatively lowered and the ion conductivity is lowered, which is not preferable. .

The positive electrode can be prepared by mixing a binder such as polyvinylidene fluoride with a conductive additive such as carbon black in a positive electrode active material powder and forming a sheet, a flat disc, or the like. The thing shape | molded by the flat disk shape etc. and laminated | stacked on the metal electrical power collector can be illustrated. As the cathode active material, at least one selected from cobalt, manganese, nickel, and at least one of lithium complex oxides may be used. Specifically, LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , LiFeO ₂ , V ₂ O ₅ and the like are preferable. Moreover, you may use the thing which can occlude | release and release lithium, such as TiS, MoS, an organic disulfate compound, or an organic polysulfate compound.

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, what shape | molded the negative electrode active material etc. in the sheet form, the flat disk shape, etc., and laminated | stacked on the metal electrical power collector can be illustrated. Examples of the negative electrode active material include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, graphitized mesocarbon microbeads, and amorphous carbon. In addition, a metal material that can be alloyed with lithium alone and a composite including the metal material and carbonaceous material may also be exemplified as a negative electrode active material. Examples of the metal that can be alloyed with lithium include Al, Si, Sn, Pb, Zn, Bi, In, Mg, Ga, and Cd. Moreover, metal lithium foil can also be used as a negative electrode active material.

Furthermore, it is preferable that the film | membrane which consists of an aziridine compound containing a polyacrylate compound and / or an aziridine ring is formed in the surface of a negative electrode. When a film made of a polyacrylate compound and / or an aziridine compound is formed, the film prevents the dissolution of the binder in the negative electrode due to the incombustible solvent, thereby preventing the negative electrode active material from falling off the current collector, thereby increasing the charge and discharge capacity of the lithium secondary battery. Can be improved.

In addition, as the polyacrylate compound, a part or all of the hydroxyl groups of the (polyester) polyol having three or more hydroxyl groups (-OH) are substituted with (meth) acrylic acid esters and the remainder not substituted with (meth) acrylic acid esters. Some unreacted hydroxyl groups are preferably poly (ester) (meth) acrylates substituted with groups that are not radically reactive.

Moreover, as an aziridine compound, the thing of the structure shown in the said Formula (3)-(6) is preferable. However, in the structural formula of Formula 3, R ₁ is any one of H, CH ₃ , OH, R ₂ is any one of H or CH ₃ .

As the aziridine compound, a compound represented by the structural formula of Formula 4 or a mixture of a compound represented by the structural formula of Formula 3 and a compound represented by the structural formula of Formula 4 is also preferable.

As the aziridine compound, the compounds of the formulas (5) to (6) may also be used. Such a compound is preferably used simultaneously with the compound of Formula 3 and / or Formula 4.

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

The polyacrylate compound and the aziridine compound are added to the lithium secondary battery in the state of being added to the nonaqueous electrolyte, and are polymerized on the surface of the negative electrode during initial charging to form a film. The formed film has excellent conductivity of lithium ions and is low in solubility by a nonflammable solvent to maintain a stable film structure.

The polyacrylate compound is an anionic addition polymerizable monomer to be anionic polymerized to form a film on the surface of the negative electrode which becomes a low potential during charging. When this polyacrylate compound is not polymerized, double contention in a molecule | numerator opens, reaction which couple | bonds with a separate polyacrylate compound occurs continuously, and the film | membrane in which the polyacrylate compound was superposed | polymerized on the negative electrode surface is formed.

In addition, the film formation by a polyacrylate compound is estimated to advance as shown in FIG. First, as shown in Fig. 1 (a), before the start of super charging, a polyacrylate compound is present in the nonaqueous electrolyte (nonaqueous electrolyte), and when the charge is initiated as shown in Fig. 1 (b), the polyacrylate compound is It is pulled onto the cathode surface, anionic polymerization on the cathode surface, and finally a film is formed as shown in Fig. 1 (c).

In addition, the aziridine compound represented by Formulas 3 to 6 includes an aziridine ring having a skeleton of 2 carbons and 1 nitrogen, and the aziridine ring is coordinated with or opened with lithium to form a polymer together with another aziridine compound. A film is formed by doing it.

That is, the film formation by the aziridine compound, as shown in FIG. 2, is such that all or some of the lithium ions and the aziridine compound in the nonaqueous electrolyte (nonaqueous electrolyte) do not reach the higher order network structure before the start of supercharge. It is considered to exist as a crosslinked material (referred to as "Li-aziridine crosslinked product"). This Li-aziridine crosslinked product is thought to be formed by coordinating the aziridine ring having a negative charge of the aziridine compound to lithium ions which are cations.

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

Subsequently, lithium ions are liberated from the aziridine ring and the ionic bridge and occluded in the negative electrode. Then, the remaining aziridine ring is opened to start the polymerization reaction. As a result, a film is formed as shown in Fig. 2 (c). Since this produced film has a negative charge, it becomes a film for transporting only cations. For this reason, it can prevent that electrolyte solution contacts a negative electrode and decomposes directly.

In addition, the film in which the polyacrylate compound and the aziridine compound are mixed can have a particularly low solubility due to a nonflammable solvent, thereby maintaining a more stable film.

That is, as shown in Fig. 3, when the polyacrylate compound and the aziridine compound are added at the same time, the same reaction as the polymerization reaction described in Figs. 1 and 2 proceeds respectively (Figs. 3 (a) and (b)). ), And finally, a film in which the polyacrylate compound and the aziridine compound are mixed is formed (FIG. 3 (c)). This coating is very dense and firm and has a very high resistance to incombustible solvents.

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. 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.

If the addition amount of the polyacrylate compound and / or the aziridine compound is less than the above range, it is not preferable because a sufficient coating is not formed on the surface of the negative electrode. If the addition amount is larger than the above range, the coating becomes thick and the interface resistance increases, which is not preferable.

In addition, it is preferable to add and dissolve antimony oxide in the nonaqueous electrolyte. When the antimony oxide is dissolved, the organic halogen compound and the antimony oxide interact with each other, and the flash point of the nonaqueous electrolyte is higher than when the organic halogen compound is added alone. Since antimony oxide is self-extinguishing, even a small amount is dissolved in the nonaqueous electrolyte to increase the flash point of the nonaqueous electrolyte.

In the addition amount of antimony oxide, 0.1 mass% or more and 1 mass% or less are preferable with respect to a nonaqueous electrolyte. If the addition amount is smaller than the above range, the flash point is mostly changed, and it is not preferable.

According to the lithium secondary battery, the non-aqueous electrolyte may contain the nonflammable solvent to increase the flash point of the nonaqueous electrolyte, thereby improving the safety of the lithium secondary battery.

In addition, since a film made of a polyacrylate compound and / or an aziridine compound is formed on the surface of the negative electrode, dissolution of the binder in the negative electrode by a non-flammable solvent prevents the negative electrode active material from dropping off the current collector, and the component of the nonaqueous electrolyte. Since there is no possibility of decomposition on the negative electrode surface, the charge / discharge capacity of the lithium secondary battery can be improved.

In the lithium secondary battery of this embodiment, it is preferable to perform the process of forming the film of a polyacrylate compound and / or an aziridine compound in a negative electrode by the charge / discharge by "chemical conversion" mentioned later.

Moreover, when a polyacrylate compound and / or an aziridine compound have high content with respect to a nonaqueous electrolyte, it may gel with another solvent and lithium salt itself, and may 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 / or aziridine compound is added to the nonaqueous electrolyte to such an extent that a gel cannot be formed even if left unattended. It is appropriate to form a film only 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 compound and / or azirizine compound sufficient for gel formation is added to the nonaqueous electrolyte and before gelation is completed completely. It is appropriate to form a film on the cathode as the supercharging is carried out.

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.

(Examples 1 to 6 and Comparative Examples 1 to 5)

As shown in Table 1, trichloroethylene, butyric difluorobutane (a mixture of CF ₃ CF ₂ CHCl ₂ and CClF ₂ CF ₂ CHClF in 1: 1), C ₆ HF ₁₃ and CHF as a nonflammable solvent ₂ (CF ₂ ) ₃ CH ₂ OH was prepared. It has at least a flash point and has fluorine or chlorine in the molecule and exhibits self-extinguishing ability.

Subsequently, a nonaqueous electrolyte was prepared by dissolving LiPF ₆ at a concentration of 1.3 mol / L in a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) (EC: DEC = 3: 7 by volume ratio).

In addition, a polyacrylate compound having a structure represented by the following formula (7) was prepared as a compound for forming a film (hereinafter referred to as PAA).

[Formula 7]

In addition, as a compound to form a separate film Tetramethylolmethane-tri-β-aziridinylpropionate of the structure of Formula 8 and the compound of R ₂ of Formula 4 is H A mixed mixture (hereinafter referred to as TAZO) in a ratio of 25:75 was prepared.

[Formula 8]

The non-aqueous electrolytes of Examples 1 to 6 and Comparative Examples 1 to 5 were prepared by mixing the nonflammable solvent, the nonaqueous electrolyte solution, and the polyacrylate compound or TAZO. Table 1 shows the mixing ratio of each nonaqueous electrolyte.

Nonflammable solvent Film forming material Non-aqueous electrolyte content Kinds Content rate (mass%) Kinds Content rate (mass%) (mass%) Example 1 Tetrachloroethylene 10 TAZO One Balance Example 2 Tetrachloroethylene 10 PAA 0.2 Balance Example 3 Dichlorochloride Obuturized Butane 10 TAZO One Balance Example 4 Difluoro pentafluorobutane 10 PAA 0.2 Balance Example 5 Tetrachloroethylene 10 TAZO + PAA TAZO: 1%, PAA: 0.2% Balance Example 6 Difluoro pentafluorobutane 10 TAZO + PAA TAZO: 1%, PAA: 0.2% Balance Comparative Example 1 - - - - 100 Comparative Example 2 Trichloroethylene 10 - - Balance Comparative Example 3 Difluoro pentafluorobutane 10 - - Balance Comparative Example 4 C ₆ HF ₁₃ 10 - - Balance Comparative Example 5 CHF ₂ (CF ₂ ) ₃ CH ₂ OH 10 - - Balance

As a result of visually observing the properties of the prepared nonaqueous electrolyte, phase separation was confirmed in the nonaqueous electrolyte of Comparative Example 4 to which C ₆ HF ₁₃ was added, and thus it was not possible to use it as a nonaqueous electrolyte of a lithium secondary battery. Nonaqueous electrolytes other than Comparative Example 4 did not phase separate, and at first glance, a uniform one was obtained.

In addition, in all of the nonaqueous electrolytes except Comparative Example 4, the flash point of the open flash point measuring apparatus according to JIS-K2265 was measured. As a result, the flash point of the battery of Comparative Example 1 was found to have a flash point of 58 ° C. In Examples 2 to 3 and 5, no flash point was observed in the room temperature to 70 ° C range. Since nonflammable solvents exhibiting self-extinguishing properties at low vapor pressure are added to the nonaqueous electrolytes of Examples 1 to 6 and Comparative Examples 2 to 3 and 5, since the vapor of the nonflammable solvent is present at a high concentration in the headspace of the nonaqueous electrolyte. It is not believed that flashing occurs in the flash point measuring device.

In addition, the flash point at the time of adding and dissolving 0.5 mass% of antimony oxides to Examples 1-6 and Comparative Examples 2-3 and 5 simultaneously was measured. As a result, it was possible to confirm the ignition in the range from room temperature to 75 ℃. This is thought to be due to the interaction of organic halogen compounds with antimony oxide.

Subsequently, a coin-type lithium secondary battery was manufactured using the prepared nonaqueous electrolyte (except Comparative Example 4). The manufacture of the battery is a sheet-like positive electrode and graphite negative electrode active material, a polyvinylidene fluoride binder, a Cu foil current collector using LiCoO ₂ as a positive electrode active material, a polyvinylidene fluoride binder, a carbon black conductive assistant, and an Al foil as a current collector. The sheet-like negative electrode and the polypropylene separator were put into the battery container in a winding state, and the prepared nonaqueous electrolyte was injected, followed by sealing the battery container. A coin-type battery having a diameter of 20 mm, a height of 1.6 mm, and a design charge and discharge capacity of 5 mAh was manufactured.

The lithium secondary batteries of Examples 1 and 3 and Comparative Examples 1 to 3 and 5 were subjected to two-stage charging with constant voltage charging for 9 hours after constant current charging at 0.2 C current until the battery voltage reached 4.2V. Each battery was supercharged (chemically formed) to form a film on the surface of the negative electrode.

On the other hand, the lithium secondary batteries of Examples 2, 4, 5, and 6 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 further to the low voltage at 0.2C current. After performing constant current charging until reaching 4.2V, two-stage charging with constant voltage charging for 9 hours was performed, and supercharge (chemical conversion) was performed with respect to each battery, and the film was formed in the negative electrode surface.

Thereafter, all the batteries were discharged with a current of 0.2 C until the battery voltage became 2.75 V to measure the discharge capacity. The charge / discharge curves of the respective batteries are shown in FIGS. 4 to 6, and the discharge capacity ratio (%) of each battery when the discharge capacity of Comparative Example 1 is 100% is shown in Table 2.

Discharge capacity ratio (%) Example 1 90.3 Example 2 83.6 Example 3 90.8 Example 4 87.2 Example 5 93.2 Example 6 98.6 Comparative Example 1 100 Comparative Example 2 72.7 Comparative Example 3 55.5 Comparative Example 5 0

First, as shown in FIG. 4 and Table 2, the discharge capacity of the batteries of Comparative Examples 2 and 3 was much larger than that of Comparative Example 1. When discharging the batteries of Comparative Examples 2 and 3 after discharge, a part of the negative electrode active material was dropped from the Cu foil. As a result, in Comparative Examples 2 and 3, it is considered that the discharging does not proceed normally as the binder of the negative electrode swells or dissolves due to the incombustible solvent added to the nonaqueous electrolyte to separate the negative active material and the Cu foil.

In addition, as shown in Table 2, the battery of Comparative Example 5 was not charged or discharged. This is considered to be because the non-flammable solvent added in Comparative Example 5 is alcohol, so that lithium reacts with the hydroxyl group of the alcohol and is changed to lithium hydroxide which is inert.

Next, as shown in FIG. 5 and Table 2, the discharge capacity ratio of the batteries of Examples 1 to 4 was significantly improved as compared with Comparative Examples 2 and 3. FIG. As a result of disassembling the battery, no dropping of the negative electrode active material was found from the current collector, and a good adhesion state was maintained. This is thought to be due to the addition of PAA or TAZO to form a coating on the surface of the negative electrode, as a result of which binder dissolution of the negative electrode was prevented and also nonaqueous electrolyte decomposition on the negative electrode surface was prevented as the coating was present.

6 and Table 2, the discharge capacity ratio of the batteries of Examples 5 and 6 was also improved. This is thought to be because the addition of PAA and TAZO simultaneously resulted in the formation of a very hard film on the surface of the cathode, which effectively prevented the dissolution of the binder from the cathode and the decomposition of the nonaqueous electrolyte on the surface of the anode.

As described in detail above, according to the lithium secondary battery of the present invention, as the nonaqueous electrolyte contains a nonflammable solvent, the flash point of the nonaqueous electrolyte can be improved to prevent ignition, and the safety of the lithium secondary battery can be further improved.

In addition, a film made of a polyacrylate compound and / or an aziridine compound is formed on the surface of the negative electrode. As a result of this coating, dissolution of the binder in the negative electrode by a non-flammable solvent is prevented, so that the negative electrode active material does not fall off from the current collector and the negative electrode surface. In the non-aqueous electrolyte component is not decomposed can improve the charge and discharge capacity of the lithium secondary battery.

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 charge and discharge curves of Comparative Examples 1 to 3. FIG.

5 is a graph showing charge and discharge curves of Examples 1 to 4 and Comparative Example 1 of the present invention.

6 is a graph showing charge and discharge curves of Examples 5 and 6 and Comparative Examples 1 to 3 of the present invention.

Claims (6)

anode; cathode; And  Non-aqueous electrolyte comprising a nonflammable solvent comprising tetrachloroethylene or butane difluoropentane Lithium secondary battery comprising a. delete delete delete The lithium secondary battery according to claim 1, wherein a film made of a polyacrylate compound and / or an aziridine compound is formed on the surface of the negative electrode. The lithium secondary battery of claim 1, wherein the nonaqueous electrolyte further comprises antimony oxide.