KR100649914B1 - Lithium ion secondary battery - Google Patents

Abstract

The present invention relates to a secondary battery comprising a compound of the following formula in a non-aqueous electrolyte in a lithium ion secondary battery using a negative electrode containing graphitized carbon and a positive electrode containing a lithium-containing transition metal oxide. By the addition of such a compound, the capacity of the battery is large and the high temperature life is particularly excellent.

In the above formula, R1 and R2 are each independently a substituted or unsubstituted C ₁ -C ₁₅ alkyl group, or a substituted or unsubstituted C ₆ -C ₁₀ aryl group, or R1 and R2 may be connected to each other to form a ring structure. .

Description

Lithium Ion Secondary Battery {LITHIUM ION SECONDARY BATTERY}

The present invention relates to a lithium ion secondary battery, and more particularly to a non-aqueous electrolyte solution in a lithium ion secondary battery using a negative electrode containing graphitized carbon and a positive electrode containing a lithium-containing transition metal oxide. It relates to a technique for producing a battery having a large capacity and a long life of the battery by adding a compound of formula (1).

Among the electrochemical cells, liquid lithium ion secondary batteries have been replaced by other secondary batteries due to their high energy density since they were first commercialized by Sony, and their use in portable computers, mobile phones, etc. have.

Lithium ion liquid secondary battery uses a carbon material as a negative electrode active material and a metal oxide such as LiCoO ₂ as a positive electrode active material, a polyolefin-based porous separator is inserted between the negative electrode and the positive electrode, and a non-aqueous electrolyte solution having a lithium salt such as LiPF ₆ is used. It will be manufactured. During charging, lithium ions of the positive electrode active material are released and inserted into the carbon layer of the negative electrode, and during discharge, lithium ions of the carbon layer are released and inserted into the positive electrode active material. The non-aqueous electrolyte serves as a medium for transferring lithium ions between the negative electrode and the positive electrode, must be stable over the operating voltage range of the cell, and have the ability to transfer ions at a sufficiently fast rate.

In the case of using only a highly polar cyclic carbonate capable of sufficiently dissociating lithium ions as such a non-aqueous electrolyte, there is a problem that the viscosity becomes large and the ion conductivity becomes small.

Thus, U. S. Patent Nos. 5,521, 027 and 5,525, 443 disclose mixed electrolytes in which linear carbonates of low polarity but low viscosity are mixed to reduce the viscosity. The linear carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), and the like. Among them, the freezing point is the lowest at -55 ° C. EMC exhibits excellent low temperature and longevity performance in use. Examples of the cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and among these, PC has a low freezing point at -49 ° C and thus low temperature performance. In the case of using graphitized carbon having a large capacity as a cathode, EC is rapidly reacted with the cathode during charging, so that it is difficult to use a large amount, and EC, which forms a stable protective film at the cathode, is mainly used. However, since EC is not completely inactive, decomposition of the electrolyte generated from the negative electrode and the positive electrode during charging and discharging of the battery is one of the causes of deteriorating the life of the battery. do.

In order to improve the room temperature and high temperature life of the battery by solving this problem, JP 2000-123867 discloses ester compounds (eg, vinylene carbonate) having a cyclic molecular structure and C = C unsaturated bonds in the ring. Disclosed is a battery for adding a small amount to an electrolyte solution. It is believed that these additives are decomposed at the cathode or the anode to form a film on the electrode surface to suppress decomposition of the electrolyte. However, these additives also do not completely prevent the decomposition of the electrolyte. In particular, as the performance at high temperatures becomes more important, the need for more effective additive development is increasing.

Accordingly, an object of the present invention is to solve the problems of the prior art and the technical problem that has been requested from the past.

After in-depth study and various experiments, the inventors of the present invention provide a lithium ion secondary battery including a negative electrode containing graphitized carbon, a positive electrode containing a lithium-containing transition metal oxide, a porous separator, and a lithium salt-containing electrolyte. When the compound of formula (1) described later is added to the electrolyte solution, it was surprisingly found that a lithium ion secondary battery having a high capacity and an improved high temperature life can be produced, and thus, the present invention has been completed.

Therefore, the lithium ion secondary battery according to the present invention,

(a) a negative electrode active material containing graphitized carbon capable of reversible storage and release of lithium;

(b) a positive electrode active material containing a lithium-containing transition metal oxide capable of reversible storage and release of lithium;

(c) a porous separator; And

(d) an electrolyte containing (i) a lithium salt, (ii) an electrolyte solution compound and (iii) a mixture of one or more selected from compounds represented by the following formula (1);

It is configured to include.

Where

R 1 and R 2 are each independently a substituted or unsubstituted C ₁ -C ₁₅ alkyl group, or a substituted or unsubstituted C ₆ -C ₁₀ aryl group, or R 1 and R 2 may be linked to each other to form a ring structure.

Preferably, when R1 and R2 are a substituted C ₁ -C ₁₅ alkyl group or a substituted C ₆ -C ₁₀ aryl group, it is a halogen atom, a nitro group, a cyano group, a C ₆ -C ₁₀ aryl group, or C It may be substituted by a ₁ -C ₅ acyl group. Especially, a halogen atom is especially preferable.

R1 and R2 are preferably CF ₃ , C ₂ F ₅ , C ₃ F ₇ , C ₄ F ₉ , C ₅ F ₁₁ , C ₆ F ₁₃ , C ₇ F ₁₅ , C ₈ F ₁₇ , a phenyl group and a benzyl group Selected from the group consisting of, among others, a perfluoro alkyl group, for example, CF ₃ , C ₂ F ₅ , C ₃ F ₇ , C ₄ F ₉ , C ₅ F ₁₁ , C ₆ F ₁₃ , C ₇ F ₁₅ And C ₈ F ₁₇ are particularly preferred.

When the compound of Formula 1 is added as an additive to the electrolyte solution, it was confirmed in the experiments of the present inventors described later that a lithium ion secondary battery having a large capacity and particularly improved high temperature life can be produced. The additive according to the present invention is considered to inhibit the decomposition reaction of the PC by decomposing at the cathode at a voltage higher than 0.8 V, the decomposition voltage of the PC, to form a protective film. Therefore, in the case of using a large number of cyclic carbonates in order to solve the problem of swelling at high temperature, when the additive is added to the electrolyte containing EC and PC and used together with the graphitized carbon anode, a battery having a high capacity and a long lifespan is used. It can manufacture. In addition, since the negative electrode film formed by decomposing the additive is stable, even in the case of the electrolyte containing no PC, the life of the battery is improved.

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

As described above, the lithium ion secondary battery of the present invention is a negative electrode active material containing graphitized carbon, a positive electrode active material containing a lithium-containing transition metal oxide, a porous separator, and a lithium salt, an electrolyte compound, and the formula It is comprised by including the electrolyte solution containing the compound of 1.

Here, as the graphitized carbon, preferably the crystal surface distance constant d ₀₀₂ of the carbonaceous material measured by X-ray diffraction method as a negative electrode active material is 0.338 nanometer or less, and the specific surface area measured by the BET method is 10 m 2 / g. The following may be used.

As the lithium-containing transition metal oxide, one or two or more metal oxides selected from the group consisting of Chemical Formulas 2 and 3 may be used.

LiCo _a Mn _b Ni _c M _d O ₂

Where

a is 0 ≦ a ≦ 1;

b is 0 ≦ b ≦ 1;

c is 0 ≦ c ≦ 1;

d is 0 ≦ d ≦ 1, provided that a + b + c + d = 1;

M is selected from the group consisting of Al, B, Ga, Mg, Si, Ca, Ti, Zn, Ge, Y, Zr, Sn, Sr, Ba and Nb.

Li _X Mn _2-Y M ' _Y O ₄

Where

X is 0.9 ≦ X ≦ 2;

Y is 0 ≦ Y ≦ 0.5;

M 'is selected from the group consisting of Fe, Co, Ni, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si and Ge.

Preferred examples thereof include LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiNi _1-X Co _X O ₂ , and the like.

The lithium salt in the electrolyte solution is preferably LiClO ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiN (C ₂ F ₅ SO ₂ ) ₂ and LiN (CF ₃ One or two or more selected from the group consisting of SO ₂ ) ₂ may be used.

As said electrolyte compound in electrolyte solution, Preferably, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC), gammabutyrolactone (GBL), sulfolane, methyl acetate (MA), ethyl acetate (EA), methyl propio One or more than one selected from the group consisting of nate (MP) and ethyl propionate (EP) can be used. Preferably, the electrolyte can be constituted by a combination of cyclic carbonate and linear carbonate.

Representative examples of the compound of the formula (1) contained in the electrolyte as an additive include N -fluoro-bis (trifluoromethylsulfonyl) imide, N -fluoro-bis (pentafluoroethylsulfonyl) imide, N Although -fluoro-bis (methanesulfonyl) imide, N -fluoro-bis (ethanesulfonyl) imide, N -fluorobenzenesulfonimide, etc. are mentioned, It is not limited only to this.

The content of the additive is preferably 0.01 to 10% by weight based on the total weight of the electrolyte. If the amount of the additive is too small, the effect of the addition does not appear, on the contrary, if the content is too large, the viscosity of the electrolyte is increased and the resistance of the battery is increased, which is not preferable because the performance of the battery is bad.

The lithium ion secondary battery according to the present invention can be produced by conventional methods known in the art. That is, it may be prepared by inserting a porous separator between the anode and the cathode and injecting an electrolyte therein.

The positive electrode may be manufactured by, for example, applying a slurry containing the lithium transition metal oxide active material, the conductive material, and the binder described above onto a current collector and then drying. Similarly, the negative electrode can be prepared by, for example, applying a slurry containing the above-described carbon active material, a conductive material and a binder onto a thin current collector and then drying it.

In the lithium ion secondary battery according to the present invention, the structure of the positive electrode, the negative electrode, and the separator is not particularly limited. For example, each of these sheets may be wound or stacked in a cylindrical or rectangular shape. Or it may be a form inserted into the case of the pouch type.

In the following Examples, the present invention will be described in more detail, but the scope of the present invention is not limited thereto.

Example 1: Additive N Synthesis of -fluoro-bis (trifluoromethylsulfonyl) imide

10 g of bis (trifluoromethylsulfonyl) imide (Aldrich, 95%) was placed in a 500 ml stainless steel container, which was cooled to -20 ° C to remove impurities by a vacuum pump for 30 minutes. Then, the mixture was cooled to −196 ° C., fluorine gas (Air Products) was added thereto, and then sealed and left at room temperature for 24 hours. The vessel was cooled to −196 ° C. again, the unreacted product was extracted with a vacuum pump, the reaction was transferred to another stainless steel vessel, and sodium fluoride (NaF) was added thereto and left at room temperature for 2 hours. The title product was obtained in the form of a colorless liquid when the contents were extracted using a glass pump at −55 ° C. with a vacuum pump.

Example 2: Additives N Synthesis of -fluoro-bis (methanesulfonyl) imide

2.79 g of ammonium chloride was dissolved in a 100 ml 2-necked round bottom flask containing 30 ml of distilled water, and then stirred with ice water in a mixed solution of 10 ml of methanesulfonylchloride and 12 ml of acetone. . 5 ml of 10 M aqueous sodium hydroxide solution was slowly added to the reaction flask and stirred until the reaction solution became acidic. Then, 5 ml of sodium hydroxide aqueous solution was added again, and the mixture was stirred until it became acidic. The reaction solution was raised to room temperature and stirred until the reaction became acidic while adding a small amount of aqueous sodium hydroxide solution. When additional sodium hydroxide was added, a small amount of concentrated hydrochloric acid was added at the point where the solution did not become acidic. When the solution became strongly acidic, the mixed solution was extracted twice with 60 ml of ethyl acetate and twice with 60 ml of methylene chloride to remove the solvent. , 7 g of bis (methanesulfon) imide (Bismethanesulfonimide) compound was obtained.

7 g of the bis (methanesulfon) imide thus obtained were placed in a 500 ml stainless steel vessel together with 100 ml acetonitrile and 7.3 g sodium fluoride, and the vessel was cooled to -40 ° C and 10% fluorine. Lean nitrogen mixed gas (Air Products) was stirred for 3 hours while flowing into the container. Then, after flowing nitrogen gas to remove the remaining gas in the container, the solvent was removed by vacuum pump for 30 minutes, extracted with 100 ml of ethyl acetate to remove the solvent, and then recrystallized with ethyl acetate and hexane to give the title compound 5.4 g was obtained.

Example 3: Preparation of Electrolyte A

As the additive, N -fluoro-bis (trifluoromethylsulfonyl) imide synthesized in Example 1 was used. EC: N -fluoro-bis (trifluoro methylsulfonyl) imide: EMC = 34 by Mitsubishi Chem. F-EC and F-EMC in a glove box 30 ml of a 1M LiPF ₆ solution having a composition of 1:65 was prepared. This electrolyte is referred to as "electrolyte A".

Example 4: Preparation of Electrolyte B

N -fluoro-bis (methanesulfonyl) imide synthesized in Example 2 was used as the additive. 1M LiPF ₆ solution with composition of EC: N -fluoro-bis (methanesulfonyl) imide: EMC = 34: 1: 1: 65 using Mitsubishi Chem's F-EC and F-EMC in a glove box Ml was prepared. This electrolyte is referred to as "electrolyte B".

Example 5: Preparation of Electrolyte C

N-fluorobenzenesulfonimide (N-Fluorobenzenesulfonimide, ACROS, 97%) was used as an additive. Using a Mitsubishi Chem F-EC and F-EMC in a glove box, 30 ml of a 1 M LiPF ₆ solution having a composition of EC: N-fluorobenzenesulfonimide: EMC = 34: 1: 65 by weight ratio was prepared. . This electrolyte is referred to as "electrolyte C".

Comparative Example 1: Preparation of Electrolyte D

30 ml of a 1 M LiPF ₆ solution having a composition of EC: EMC = 33: 67 by weight was prepared using Mitsubishi Chem's F-EC and F-EMC in a glove box. This electrolyte is referred to as "electrolyte D".

Example 6: Lithium Ion Secondary Battery Preparation

The negative electrode was composed of 93% of a carbon active material (MCMB10-28 from Osaka Gas) and 7% of polyvinylidene difluoride (PVDF, Kynar 761 from Elf Atochem), a solvent of N-methyl-2-pyrrolidone (NMP) After mixing for 2 hours in a mixer (Mixer of Ika) using, and coated on a copper foil current collector, it was prepared by drying at 130 ℃.

The positive electrode was a mixture of 91% LiCoO ₂ , 3% PVDF (Kynar 761) and 6% conductive carbon (KS-6 from Lonza) using a solvent N-methyl-2-pyrrolidone (NMP) After mixing for 2 hours in a mixer, it was coated on an aluminum foil current collector, and dried at 130 ℃.

A separator (Celgard 2400, manufactured by Hoechst Celanese) was placed between the negative electrode and the positive electrode thus prepared and wound in a cylindrical shape to assemble a battery of 18650 standard, and then the electrolytes A, B, prepared in Examples 3 to 5 and Comparative Example 1, respectively. Each of C and D was injected to prepare a lithium ion secondary battery. The battery was charged at 25 ° C. to 4.2 V at a rate of 0.5 C until the current became 50 mA or less, discharged at a rate of 0.5 C to 3 V, and the charge and discharge experiments were conducted. Charge and discharge experiments were also conducted under the same conditions. Table 1 shows the results of this charge and discharge experiment.

division Composition of the electrolyte of the battery (% by weight) Performance EC EMC additive Initial capacity (mAh) Capacity after 300 times at 25 ℃ (mAh) Capacity after 300 times at 60 ℃ (mAh) Electrolyte A 34% 65% 1% N -fluoro-bis (trifluoromethylsulfonyl) imide 1820 1510 1450 Electrolyte B 34% 65% 1% N -fluoro-bis (methanesulfonyl) imide 1805 1480 1438 Electrolyte C 34% 65% 1% N -fluorobenzenesulfonimide 1803 1476 1432 Electrolyte D 33% 67% 0 % 1812 1497 1368

As can be seen from Table 1, the battery using the electrolyte solution A, B and C containing the additive according to the present invention can be seen that the high temperature life performance is superior to the battery using the electrolyte solution D without the additive.

In the lithium ion secondary battery according to the present invention, the compound of the formula (1) is added to the electrolyte, thereby exhibiting high capacity performance and excellent high temperature charge / discharge life.

Claims (7)

(a) a negative electrode active material containing graphitized carbon capable of reversible storage and release of lithium; (b) a positive electrode active material containing a lithium-containing transition metal oxide capable of reversible storage and release of lithium; (c) a porous separator; And (d) an electrolyte solution containing one or more mixtures selected from (i) a lithium salt, (ii) an electrolyte solution, and (iii) a compound represented by the following formula (1),

(One) Where R 1 and R 2 are each independently a substituted or unsubstituted C ₁ -C ₁₅ alkyl group, or a substituted or unsubstituted C ₆ -C ₁₀ aryl group, or R 1 and R 2 may be linked to each other to form a ring structure; Lithium ion secondary battery comprising a. The method of claim 1, wherein when said R1 and R2 is a substituted C ₁ -C ₁₅ alkyl or substituted C ₆ -C ₁₀ aryl group, a halogen atom, a nitro group, a cyano group, C ₆ -C ₁₀ aryl group or C A lithium ion secondary battery, which is substituted by a ₁ -C ₅ acyl group. The lithium ion secondary battery according to claim 2, wherein the substituent is a halogen atom. The lithium ion secondary battery of claim 1, wherein R 1 and R 2 are perfluoro C ₁ -C ₁₅ alkyl groups. According to claim 1, wherein R1 and R2 are each independently CF ₃ , C ₂ F ₅ , C ₃ F ₇ , C ₄ F ₉ , C ₅ F ₁₁ , C ₆ F ₁₃ , C ₇ F ₁₅ , C ₈ F ₁₇ , a phenyl group and a benzyl group, the lithium ion secondary battery, characterized in that selected from the group consisting of. According to claim 3, wherein R1 and R2 are each independently CF ₃ , C ₂ F ₅ , C ₃ F ₇ , C ₄ F ₉ , C ₅ F ₁₁ , C ₆ F ₁₃ , C ₇ F ₁₅ and C ₈ F Lithium ion secondary battery, characterized in that selected from the group consisting of ₁₇ . The lithium ion secondary battery according to claim 1, wherein the content of the compound of Formula 1 is 0.01-10 wt% based on the electrolyte.