KR100463188B1 - An electrolyte for a lithium ion battery and a lithium ion battery comprising the same - Google Patents

Abstract

The present invention relates to a lithium ion battery electrolyte and a lithium ion battery comprising the same, wherein the electrolyte comprises a non-aqueous organic solvent; Lithium salts; And linear low molecular polymer additives, the additives being polymethylmethacrylate, polyacrylonitrile, polyethylene oxide, and polyethylene glycol, polyacrylamide ([-CH ₂ CH (CONH ₂ )-] _n ), poly ( Allylamine) ([-CH ₂ CH (CH ₂ NH ₂ )-], poly (azelaic anhydride; ([-CO (CH ₂ ) ₇ CO _2- ]), poly (benzyl meta Acrylate) ([-CH ₂ C (CH ₃ ) (CO ₂ CH ₂ C ₆ H ₅ )-] _n ), poly (4-bromostyrene) ([-CH ₂ CH (C ₆ H ₄ Br)- _n ), polycaprolactone ([-O (CH ₂ ) ₅ CO-] _n ), polycaprolactone diol, polycarbomethylsilane ([-Si (CH ₃ ) HCH _2- ] _n ), polystyrene ([ -CH ₂ CH (C ₆ H ₅ )-] _n , poly (propylene glycol) (H [OCH (CH ₃ ) CH ₂ ] _n OH), polysulfone, polytetrafluoroethylene ((-CF ₂ CF _{2- n} ), poly (vinyl acetate), poly (vinyl alcohol), poly (vinyl chloride), and at least one selected from the group consisting of polyvinylpyrrolidone My linear low molecular polymer.

The lithium ion battery including the electrolyte has excellent electrochemical and swelling characteristics.

Description

TECHNICAL FIELD The electrolyte for a lithium ion battery, and a lithium ion battery including the same TECHNICAL FIELD

[Industrial use]

The present invention relates to a lithium ion battery electrolyte and a lithium ion battery including the same, and more particularly, to a lithium ion battery electrolyte and a lithium ion battery including the same capable of improving swelling characteristics of the battery.

[Prior art]

Recently, with the trend toward miniaturization and light weight of portable electronic devices, the need for high performance and high capacity of batteries used as power sources for these devices is increasing. Lithium secondary batteries, which are commercially available and currently used, correspond to the heart of the digital era, which is rapidly being applied to portable phones, notebook computers, camcorders, and the like, which have an average discharge potential of 3.7V, that is, 4C.

In addition to improving battery capacity and performance characteristics, studies are being actively conducted to improve safety such as overcharging characteristics. When the battery is overcharged, depending on the state of charge, lithium is excessively precipitated at the positive electrode, lithium is excessively inserted at the negative electrode, and the positive electrode and negative electrode are thermally unstable, causing rapid exothermic reactions such as decomposition of the organic solvent in the electrolyte and thermal runaway. Occurs, a serious problem occurs in the safety of the battery.

In order to solve this problem, a method of adding an aromatic compound as a redox shuttle additive in an electrolyte has been used. For example, U.S. Patent No. 5,709,968 adds a benzene compound such as 2,4-difluoroanisole to prevent overcharge currents and the resulting thermal runaway phenomenon. It is starting. No. 5,879,834 add a small amount of aromatic compounds such as biphenyl, 3-chlorothiophene, furan and the like to electrochemically polymerize at abnormal overvoltage conditions to increase the internal resistance to improve battery safety. A method is described. These redox shuttle additives act to suppress the overcharge reaction by prematurely raising the temperature inside the battery due to the heat generated by the oxidative heating reaction to shut down the pores of the separator quickly and uniformly. In addition, the polymerization reaction of the additive on the surface of the positive electrode during overcharge also functions to protect the battery by consuming the overcharge current.

However, it is not possible to sufficiently remove the overcharge current by the polymerization reaction of the additive, and the gas swelling phenomenon is intensified due to the decomposition of the oxidation reaction. There is a limit to improvement. The swelling phenomenon refers to a phenomenon in which a central portion of a specific surface is deformed, such as a battery swelling in a specific direction. In addition, these additives have a problem that adversely affect the electrochemical properties of the battery, such as high temperature characteristics or life characteristics of the battery.

As a method for solving the swelling phenomenon, there is a method of improving the safety of the secondary battery by installing a vent or a current breaker for ejecting the internal gas when the internal pressure of the battery rises above a certain level. However, this method has a problem of causing a risk of malfunction due to the internal pressure rise.

In addition, in order to improve the swelling characteristic of the battery, a method of heat-treating the electrode plate in the range of 100 to 200 ° C and then cooling it to room temperature is known (Patent Application 1999-10904).

The present invention has been made to solve the above problems, and an object of the present invention is to provide an electrolyte for a lithium ion battery that can improve the swelling characteristics of the battery.

Another object of the present invention is to provide a lithium ion battery having excellent swelling characteristics.

1 is a cross-sectional view of a rectangular lithium ion battery.

In order to achieve the above object, the present invention is a non-aqueous organic solvent; Lithium salts; And linear low molecular polymer additives, the additives being polymethylmethacrylate, polyacrylonitrile, polyethylene oxide, and polyethylene glycol, polyacrylamide ([-CH ₂ CH (CONH ₂ )-] _n ), poly ( Allylamine) ([-CH ₂ CH (CH ₂ NH ₂ )-], poly (azelaic anhydride; ([-CO (CH ₂ ) ₇ CO _2- ]), poly (benzyl meta Acrylate) ([-CH ₂ C (CH ₃ ) (CO ₂ CH ₂ C ₆ H ₅ )-] _n ), poly (4-bromostyrene) ([-CH ₂ CH (C ₆ H ₄ Br)- _n ), polycaprolactone ([-O (CH ₂ ) ₅ CO-] _n ), polycaprolactone diol, polycarbomethylsilane ([-Si (CH ₃ ) HCH _2- ] _n ), polystyrene ([ -CH ₂ CH (C ₆ H ₅ )-] _n , poly (propylene glycol) (H [OCH (CH ₃ ) CH ₂ ] _n OH), polysulfone, polytetrafluoroethylene ((-CF ₂ CF _2- ) _n), poly (vinyl acetate), poly (vinyl alcohol), poly (vinyl chloride), and polyvinyl at least selected from the group consisting of a pyrrolidone It provides my linear low-molecular polymer lithium ion battery electrolyte.

The present invention also provides a lithium ion battery comprising the electrolyte.

Hereinafter, the present invention will be described in more detail.

The structure of the general non-aqueous lithium secondary battery 1 is as shown in FIG. The battery uses a lithiated intercalation compound as a positive electrode (2) and a negative electrode (4), inserts a separator (6) between the positive electrode (2) and the negative electrode (4) and wound the electrode assembly (8). After forming it is put into the case 10 is manufactured. The top of the cell is sealed with a cap plate 12 and a gasket 14. The cap plate 12 may be provided with a safety vent (16) to prevent the battery from forming overpressure. The positive electrode tab 18 and the negative electrode tab 20 are respectively provided on the positive electrode 2 and the negative electrode 4, and the insulators 22 and 24 are inserted to prevent internal short circuit of the battery. The electrolyte 26 is injected before sealing the cell. The injected electrolyte 26 is impregnated into the separator 6.

In the present invention, at least one linear selected from the group consisting of polymethyl methacrylate, polyacrylonitrile, polyethylene oxide, and polyethylene glycol as an electrolyte additive to a non-aqueous organic solvent and lithium salt, which are generally used as electrolytes for lithium ion batteries. A low molecular polymer is added to prepare an electrolyte for a lithium ion battery.

The linear low molecular weight polymer used as the electrolyte additive may improve the swelling characteristics of the battery, and is particularly effective in suppressing the swelling phenomenon at a high temperature. It is preferably used in an amount of 0.001 to 5% by weight based on the total electrolyte. If the added amount is less than 0.001% by weight, the addition effect is insignificant, and if it exceeds 5% by weight, solubility and battery performance deteriorate, which is not preferable.

The molecular weight of the linear low molecular polymer is preferably about 1000 to 100,000 or less. If the molecular weight of the linear low molecular weight polymer is less than 1000, there is a problem in that the addition effect is insignificant. If it exceeds 100,000, it is not preferable because it is not dissolved in the nonaqueous electrolyte.

The electrolyte additive is added to the non-aqueous organic solvent containing the lithium salt. Lithium salt acts as a source of lithium ions in the battery to enable the operation of the basic lithium ion battery, the non-aqueous organic solvent serves as a medium to move the ions involved in the electrochemical reaction of the battery.

The lithium salt may be LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiAlO ₄ , LiAlCl ₄ , LiGaCl ₄ , ₁ or 2 selected from the group consisting of LiN (C _x F _{2x + 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ ), wherein x and y are natural numbers, LiNO ₃ , LiCl, and LiI It is possible to mix and use species.

The concentration of the lithium salt is preferably used in the range of 0.6 to 2.0M, more preferably in the range of 0.7 to 1.6M. When the concentration of the lithium salt is less than 0.6M, the conductivity of the electrolyte is lowered, and the performance of the electrolyte is lowered. When the concentration of the lithium salt is higher than 2.0M, the viscosity of the electrolyte is increased to reduce the mobility of lithium ions.

As the non-aqueous organic solvent, carbonate, ester, ether or ketone can be used. The carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC) ethylene carbonate (EC), Propylene carbonate (PC), butylene carbonate (BC) and the like may be used, and the ester may be n-methyl acetate, n-ethyl acetate, n-propyl acetate, or the like. In the case of the carbonate-based solvent in the non-aqueous organic solvent, it is preferable to use a mixture of a cyclic carbonate and a chain carbonate. In this case, it is preferable to use the cyclic carbonate and the chain carbonate by mixing in a volume ratio of 1: 1 to 1: 9. The performance of the electrolyte is preferable when mixed in the above volume ratio.

In addition, the electrolyte of the present invention may further include an aromatic hydrocarbon organic solvent in the carbonate solvent. As the aromatic hydrocarbon organic solvent, an aromatic hydrocarbon compound represented by Chemical Formula 4 may be used.

[Formula 1]

(Wherein R is a halogen or an alkyl group having 1 to 10 carbon atoms and p is an integer of 0 to 6).

Specific examples of the aromatic hydrocarbon-based organic solvent include benzene, fluorobenzene, toluene, fluorotoluene, trifluorotoluene, xylene and the like. In the electrolyte containing an aromatic hydrocarbon-based organic solvent, the volume ratio of the carbonate solvent / aromatic hydrocarbon solvent is preferably 1: 1 to 30: 1. The performance of the electrolyte is preferable when mixed in the above volume ratio.

The electrolyte of the present invention is prepared by adding the compound of Formula 1 as an electrolyte additive to an organic solvent containing a lithium salt.

The present invention provides a lithium ion battery comprising the electrolyte. The lithium ion battery of the present invention can be manufactured through the following process.

A positive electrode active material, a binder, and a conductive agent are mixed, and these are applied to a current collector made of metal foil or a metal network and molded into sheets to use as a positive electrode, a negative electrode active material, a binder, and a conductive agent are mixed as necessary. These are applied to a current collector made of a metal foil or a metal net and molded into a sheet to use as a negative electrode.

Inserting a separator made of a porous insulating resin between the positive electrode and the negative electrode prepared as described above, and winding or stacking the separator to form an electrode assembly, and then put it in a battery case to inject the electrolyte of the present invention Assemble the battery.

As a positive electrode active material of a lithium ion battery, a compound capable of reversible intercalation / deintercalation of lithium (lithiated intercalation compound), or a material capable of reversibly reacting with lithium to form a lithium-containing compound And the like can be used. Specific examples of these materials include complex metal oxides such as LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , LiFeO ₂ , V ₂ O ₅ , sulfide compounds such as TiS and MoS, organic disulfide compounds and organic polysulfide compounds.

As the negative electrode active material, lithium metal or a carbonaceous material capable of reversible intercalation / deintercalation of lithium is used. For example, artificial graphite, natural graphite, graphitized carbon fibers, amorphous carbon, etc. may be mentioned. In addition, materials that have conventionally been used as a positive electrode or a negative electrode of a lithium ion battery may be used.

As the separator, a polyethylene separator, a polypropylene separator, a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may be used.

A cross-sectional view of a prismatic lithium ion battery among lithium ion batteries manufactured through such a process is shown in FIG. 1.

The lithium ion battery including the electrolyte of the present invention not only has excellent electrochemical characteristics, but also has excellent swelling characteristics compared to a battery using a conventional non-aqueous electrolyte.

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

(Example 1)

1.3M LiPF ₆ was added to an organic solvent obtained by mixing ethylene carbonate (EC): ethylmethyl carbonate (EMC): propylene carbonate (PC): fluorobenzene (FB) in a volume ratio of 30: 55: 5: 10. An electrolyte composition was prepared by adding 0.5% by weight of polymethyl methacrylate having a molecular weight of 15000 as an electrolyte additive.

A slurry was prepared by adding LiCoO ₂ (average particle diameter: 10 μm), a conductive agent (super P), and a binder (Solef6020) as a positive electrode active material to N-methylpyrrolidone (NMP) in a weight ratio of 96: 2: 2. The slurry was applied on an aluminum foil, dried, and rolled by a roll press to prepare a positive electrode plate having a width of 5.15 cm and a thickness of 117 μm. PHS (Nippon Carbon Co., Ltd.), oxalic acid, and binder (Solef6020), which are negative electrode active materials, were dissolved in NMP at a weight ratio of 95: 0.2: 5 to prepare a slurry. A negative electrode plate having a thickness of 5.3 cm and a thickness of 124 μm was prepared. An electrode assembly prepared by inserting a separator made of a polyethylene (PE) porous film (width: 5.5 cm, thickness: 16 μm) between the positive electrode plate and the negative electrode plate was placed in a rectangular battery case, and 5.6 g of the electrolyte composition was injected. To produce a rectangular lithium ion secondary battery.

(Example 2)

A rectangular lithium ion secondary battery was prepared in the same manner as in Example 1, except that the amount of the polymethyl methacrylate added was 1 wt%.

(Example 3)

A rectangular lithium ion secondary battery was manufactured in the same manner as in Example 1, except that the amount of polymethyl methacrylate was 5% by weight.

(Comparative Example 1)

A solution obtained by adding 1.3M LiPF ₆ to an organic solvent obtained by mixing ethylene carbonate (EC): ethyl methyl carbonate (EMC): propylene carbonate (PC): fluorobenzene (FB) in a volume ratio of 30: 55: 5: 10 A rectangular lithium ion secondary battery was prepared in the same manner as in Example 1, except that the electrolyte composition was used.

In order to evaluate the swelling characteristics of the Examples and Comparative Examples, each of the three rectangular lithium ion secondary batteries of Examples 1 to 3 and Comparative Example 1 was charged and discharged at 0.2 C in a voltage range of 0 V to 4.2 V Formation was carried out. After standing for 4 hours and 48 hours in a high-temperature chamber at 90 ° C. with a standard charge of 0.5 C, the thickest part of the cell was measured and averaged. Among them, the average value of Example 1 and Comparative Example 1 is shown in Table 1 below.

Evaluation item Example 1 Comparative Example 1 Battery thickness (mm) Early 3.49 3.49 4 hours later 4.20 4.42 48 hours later 9.80 11.08

As shown in Table 1, the swelling characteristics of Example 1 according to the present invention were found to be superior to Comparative Example 1.

The lithium ion battery containing the electrolyte of the present invention has excellent electrochemical and swelling characteristics.

Claims (13)

In the electrolyte for lithium ion batteries containing a non-aqueous organic solvent and a lithium salt, An electrolyte for a lithium ion battery, comprising 0.001 to 5% by weight of a polymethyl methacrylate polymer with respect to the electrolyte. delete The electrolyte for a lithium ion battery according to claim 1, wherein the polymethyl methacrylate has a molecular weight of 1000 to 100,000. The method of claim 1, wherein the lithium salt is LiPF ₆ , LiBF ₄ , LiSbF ₆ , LiAsF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , Li (CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiAlO ₄ , LiAlCl ₄ , LiGaCl ₄ , LiN (C _x F _{2x + 1} SO ₂ ) (C _y F _{2y + 1} SO ₂ ), where x and y are natural numbers, LiNO ₃ , LiCl, and LiI 1 or 2 or more types of electrolytes for lithium ion batteries. The electrolyte for a lithium ion battery according to claim 1, wherein the lithium salt is used at a concentration of 0.7 to 2.0 M. The electrolyte of claim 1, wherein the non-aqueous organic solvent is at least one solvent selected from the group consisting of carbonates, esters, ethers, and ketones. The method of claim 6, wherein the carbonate is dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methylethyl carbonate (MEC) ethylene An electrolyte for a lithium ion battery, wherein the electrolyte is at least one solvent selected from the group consisting of carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). The electrolyte of claim 6, wherein the carbonate is a mixed solvent of a cyclic carbonate and a chain carbonate. The electrolyte for a lithium ion battery according to claim 1, wherein the nonaqueous organic solvent is a mixed solvent of a carbonate solvent and an aromatic hydrocarbon organic solvent. The electrolyte of claim 9, wherein the aromatic hydrocarbon-based organic solvent is an aromatic compound represented by Chemical Formula 1 below. [Formula 1] (Wherein R is a halogen or an alkyl group having 1 to 10 carbon atoms and p is an integer of 0 to 6). The method of claim 10, wherein the aromatic hydrocarbon-based organic solvent is at least one solvent selected from the group consisting of benzene, fluorobenzene, toluene, fluorotoluene, trifluorotoluene, xylene and mixtures thereof for a lithium ion battery Electrolyte. The electrolyte of claim 9, wherein the carbonate solvent and the aromatic hydrocarbon organic solvent are mixed in a volume ratio of 1: 1 to 30: 1. A lithium ion battery comprising the electrolyte according to any one of claims 1 to 12.