KR100804979B1 - Lithium ion secondary battery - Google Patents

Abstract

The present invention provides a non-aqueous electrolyte solution containing (i) a lithium salt, (ii) an electrolyte solution compound, (i) a compound represented by the following formula (1), and (v) a compound represented by the following formula (2), and a lithium ion comprising the non-aqueous electrolyte solution: Provide a secondary battery. The cell has good high temperature life performance.

Graphitized carbon, electrolyte compound, lithium-containing transition metal oxide, non-aqueous electrolyte, lithium ion secondary battery

Description

Lithium Ion Secondary Battery {LITHIUM ION SECONDARY BATTERY}

The present invention relates to a lithium ion secondary battery and a nonaqueous electrolyte used therein, and more particularly to a lithium ion secondary battery using a negative electrode containing graphitized carbon and a positive electrode containing a lithium-containing transition metal oxide.

Among many electrochemical cells, lithium ion liquid secondary batteries have been replaced by other secondary batteries due to their high energy density since they were first commercialized by Sony, and their use range has increased in portable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

In general, a 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, inserts a polyolefin-based porous separator between the negative electrode and the positive electrode, and has a lithium salt such as LiPF ₆ . It is prepared by injecting an aqueous electrolyte solution.

During charging, lithium ions of the positive electrode active material are released and inserted into the carbon layer of the negative electrode. On discharge, lithium ions of the carbon layer are released and inserted into the positive electrode active material. In this case, the non-aqueous electrolyte serves as a medium for transferring lithium ions between the negative electrode and the positive electrode, wherein the electrolyte should be stable in the operating voltage range of the battery, and should have a performance capable of transferring ions at a sufficiently fast rate.

U.S. Pat.Nos. 5,521,027 and 5,525,443 have a small polarity but a low viscosity to reduce the viscosity, since the viscosity increases and the ion conductivity decreases when only a highly polar cyclic carbonate capable of sufficiently dissociating lithium ions as a non-aqueous electrolyte is used. The use of a mixed electrolyte solution containing phosphorus linear carbonate is described.

Examples of linear carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). Among them, EMC, which has the lowest freezing point of -55 ° C, has excellent low temperature and long service life. Indicates.

Examples of the cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Among them, PC has a low freezing point of -49 ° C, so that low-temperature performance is good, but when graphitized carbon having a large capacity is used as a negative electrode, it reacts rapidly with the negative electrode during charging, so it is difficult to use a large amount, and thus a stable protective film at the negative electrode EC is mainly used. However, even if EC is not completely reactive, decomposition of the electrolyte generated at 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.

In order to solve this problem and improve the normal temperature and high temperature life of the battery, Japanese Patent JP2000-123867 proposes adding a small amount of an additive to the electrolyte. These additives are thought to decompose at the negative electrode or the positive electrode to form a film on the electrode surface to suppress decomposition of the electrolyte solution. However, these additives also do not completely prevent the decomposition of the electrolyte, and as the performance at high temperatures becomes more important, the need for more effective additive development is gradually increasing.

SUMMARY OF THE INVENTION In view of the problems of the prior art, the present invention uses a lithium salt-containing electrolyte solution containing a high capacity negative electrode containing graphitized carbon, a positive electrode containing a lithium-containing transition metal oxide, a porous separator, and the compounds of the present invention as an additive. It is an object of the present invention to provide a lithium ion secondary battery having a high capacity and suppressing gas generation in a battery at a high temperature, thereby improving a high temperature life.

The present invention provides a non-aqueous electrolyte solution containing (i) a lithium salt, (ii) an electrolyte solution compound, (i) a compound represented by the following formula (1), and (v) a compound represented by the following formula (2), and a lithium ion comprising the non-aqueous electrolyte solution: Provide a secondary battery.

Wherein R1 and R2 are CF _3- , C ₂ F _5- , C ₃ F _7- , or C ₄ F ₉ -groups, and R 3 is a (C1-C5) alkyl group.

Hereinafter, the present invention will be described in detail.

The additive of the present invention decomposes in the negative electrode and the positive electrode to form a protective film, thereby improving the high temperature life performance of the battery. At this time, it is presumed that the film mainly formed on the positive electrode side prevents direct contact between the electrolyte molecules and the electrode and lowers the reaction activity of the electrode.

In addition, the additive of the present invention is a combination of the compound of formula (1) and the compound of formula (2), but one shows a good effect compared to the case of using alone, it suppresses the generation of gas in the battery at high temperature (Table 1).

As an additive of the present invention having such a function, the compound of formula 1 is a bis (trifluoromethanesulfonyl) imide lithium salt, bis (pentafluoroethanesulfonyl) imide lithium salt (Lithium bis (pentafluoroethanesulfonyl) imide).

Compounds of Formula 2 include N-methyl-2-oxazolidinone, N-ethyl-2-oxazolidinone, N-propyl-2- Oxazolidinone (N-propyl-2-oxazolidinone) is mentioned.

It is preferable that content of the compound of Formula 1 is 0.01 to 10 weight% in electrolyte solution, and it is preferable that content of the compound of Formula 2 is 0.01 to 5 weight% in electrolyte solution.

If the amount of the additive of Formula 1 or 2 is too small does not have an effect, if the amount is too large, the resistance of the battery at a high temperature, or a side reaction occurs, the performance of the battery is bad.

The lithium ion secondary battery used in the present invention

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

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

(c) a porous separator; And

(d) A non-aqueous electrolyte solution containing (i) a lithium salt, (ii) an electrolytic solution compound and (iii) a compound represented by the following formula (1) and (iii) a compound represented by the following formula (2)

It is preferable to include.

The graphitized carbon of (a) is a negative electrode active material and has a crystal surface distance constant d002 of 0.338 nanometer or less measured by X-ray diffraction to provide a high capacity battery, and the specific surface area measured by the BET method. It is preferable that it is 10 m <2> / g or less.

In addition, the lithium-containing transition metal oxide of (b) is preferably selected from the group consisting of the metal oxides represented by the formulas (3) and (4).

LiCo _a Mn _b Ni _c M _d O ₂

Wherein a is 0 ≦ a ≦ 1, b is 0 ≦ b ≦ 1, c is 0 ≦ c ≦ 1, d is 0 ≦ d ≦ 1, and 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, Nb.

Li _X Mn _2-Y M ' _Y O ₄

Wherein X is 0.9 ≦ X ≦ 2 and 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, Ge.

In addition, the lithium salt of (d) (iii) is selected from the group consisting of LiClO ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiC (CF ₃ SO ₂ ) ₃ It is desirable to be.

In addition, the electrolyte solution of (d) (ii) is ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), diethyl carbonate (DEC), dimethyl carbonate (DMC ), Ethylmethyl carbonate (EMC), gamma butyrolactone (GBL), sulfolane, methyl acetate (MA), ethyl acetate (EA), methyl propionate (MP) and ethyl propionate (EP) It is preferable to select at least one from the group consisting of.

According to the present invention, when 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 solution simultaneously containing two kinds of compounds of the present invention as additives, It is possible to provide a lithium ion secondary battery having a large and improved high temperature life performance.                     

As the electrode, it is preferable to use a negative electrode composed of a carbon active material and polyvinylidene difluoride as a binder, and a positive electrode composed of a lithium transition metal oxide active material, conductive carbon and polyvinylidene difluoride as a binder.

The present invention will be described in more detail with reference to the following examples. However, the examples are only for illustrating the present invention and not for limiting the present invention.

EXAMPLE

Example 1

(Preparation of Electrolyte A)

Bis (trifluoromethanesulfonyl) imide lithium salt (3M company) and N-methyl-2-oxazolidinone (Aldrich Company, 99.5%) were used as an additive. EC: bis (trifluoromethanesulfonyl) imide lithium salt in weight ratio using F-EC and F-EMC of Mitsubishi Chem. In a glove box: N-methyl-2-oxa 30 mL of a 1M LiPF ₆ solution having a composition of zolidinone: EMC = 32: 2: 1: 65 was prepared. This electrolyte is referred to as electrolyte A.

Example 2

(Electrolyte B production)

Bis (pentafluoroethanesulfonyl) imide lithium salt (3M company) and N-methyl-2-oxazolidinone (Aldrich Company, 99.5%) were used as an additive. EC: Bis (trifluoroethanesulfonyl) imide lithium salt in weight ratio using F-EC and F-EMC of Mitsubishi Chem. In a glove box: N-methyl-2- 30 ml of a 1M LiPF ₆ solution having a composition of oxazolidinone: EMC = 31: 4: 1: 64 was prepared. This electrolyte is referred to as electrolyte B.

Comparative Example 1

(Electrolyte C Preparation)

Bis (trifluoromethanesulfonyl) imide lithium salt (3M) was used as an additive. EC: bis (trifluoromethanesulfonyl) imide lithium salt by weight ratio using F-EC, F-EMC of Mitsubishi Chem. In glove box: EMC = 33: 2: 65 30 ml of a 1M LiPF ₆ solution having a composition of was prepared. This electrolyte is referred to as electrolyte C.

Comparative Example 2

(Preparation of Electrolyte D)

Bis (trifluoromethanesulfonyl) imide lithium salt (3M) was used as an additive. EC: bis (trifluoromethanesulfonyl) imide lithium salt in weight ratio using F-EC, F-EMC of Mitsubishi Chem. In glove box: EMC = 32: 4: 64 30 ml of a 1M LiPF ₆ solution having a composition of was prepared. This electrolyte is referred to as electrolyte D.

Comparative Example 3

(Electrolyte Solution E)                     

N-methyl-2-oxazolidinone (Aldrich, 99.5%) was used as an additive. 1M having a composition of EC: N-methyl-2-oxazolidinone: EMC = 34: 1: 65 by weight ratio using F-EC and F-EMC of Mitsubishi Chem. In a glove box. 30 ml of a LiPF ₆ solution was prepared. This electrolyte is referred to as electrolyte E.

Comparative Example 4

(Electrolyte F production)

N-methyl-2-oxazolidinone (Aldrich, 99.5%) was used as an additive. 1M having a composition of EC: N-methyl-2-oxazolidinone: EMC = 33: 2: 65 by weight ratio using F-EC, F-EMC of Mitsubishi Chem. In a glove box 30 ml of a LiPF ₆ solution was prepared. This electrolyte is referred to as electrolyte F.

Comparative Example 5

(Electrolyte G production)

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

<Experiment>

(Lithium ion secondary battery production)

The negative electrode is a solvent of N-methyl-2-pyrrolidone with a composition of 93% by weight of a carbon active material (MCMB-10-28 from Osaka Gas) and 7% by weight of polyvinylidene difluoride (PVDF, Kynar 761 from Elf Atochem). After mixing for 2 hours in a mixer (Mixer of Ika) using (NMP) was coated on a copper foil current collector, it was prepared by drying at 130 ℃. The positive electrode was mixed with a solvent of N-methyl-2-pyrrolidone (NMP) in a composition of 91 wt% LiCoO ₂ , 3 wt% PVDF (Kynar 761) and 6 wt% conductive carbon (KS-6 from Lonza). (Ika Mixer) was mixed for 2 hours and then coated on an aluminum foil current collector, and dried at 130 ℃ was prepared.

Using a negative electrode, a positive electrode, and a separator (celgard 2400 manufactured by Hoechst Celanese), the separator was disposed between the negative electrode and the positive electrode, wound into a cylindrical shape, and assembled into a battery of 18650 standard. Examples 1 and 2 and Comparative Examples Electrolyte solutions A, B, C, D, E, F and G prepared in 1 to 5 were injected to prepare a lithium ion secondary battery. At this time, the battery of the 18650 standard is configured to automatically cut off the current when the internal pressure of the battery to a certain degree by embedding a current interrupt device (CID) in the battery for improving the safety of the battery.

(High temperature life performance experiment)

The above prepared batteries were charged in a 60 ° C. constant temperature oven to 4.2V at a rate of 0.5 C, and charged at 4.2V until the current became 50 mA or less, and discharged at a rate of 0.5 C to 3V to perform charge and discharge experiments. The results of this charge and discharge experiment are summarized in Table 1.                     

As can be seen from Table 1, in the case of the battery using the electrolyte solution A, B containing the additive represented by the formula (1) and the additive represented by the formula (2), the electrolyte solution C, D, E, F containing only one type of additive was added. Higher temperature lifespan performance is better than that of used batteries and batteries without electrolyte G, and especially at high temperatures, the amount of gas generated inside the battery is reduced to slow the occurrence of CID short-circuit and maintain capacity even after 700 cycles. It can be seen that the discharge. In other words, when charging and discharging hundreds of times or more at a high temperature of about 60 ° C., a battery using electrolyte C, D, E, and F with only one type of additive and a battery using electrolyte G without additives are generated by a large amount of gas. While the CID operates to stop the charging and discharging of the battery during the life performance test, the battery using the electrolytes A and B containing the additive represented by the formula (1) and the additive represented by the formula (2) according to the present invention has such a gas. The occurrence phenomenon was suppressed, allowing the battery to be charged and discharged for a longer time.

The present invention provides a lithium ion secondary battery having high capacity performance by using graphitized carbon as a negative electrode active material in a non-aqueous electrolyte containing the compound of Formula 1 and the compound of Formula 2 as an additive, and at the same time having an excellent high temperature charge and discharge life. can do.

Claims (8)

As a non-aqueous electrolyte solution containing (iii) lithium salt, (ii) electrolyte solution, (iv) the compound represented by following General formula (1), and the compound represented by General formula (2), The content of the compound of Formula 1 is 0.01 to 10% by weight in the electrolyte, the content of the compound of formula 2 is 0.01 to 5% by weight in the electrolyte solution. [Formula 1]

[Formula 2]

Wherein R 1 and R 2 are a CF _3- , C ₂ F _5- , C ₃ F ₇ -or C ₄ F ₉ -group, and R 3 is a (C1-C5) alkyl group. delete The lithium salt according to claim 1, wherein the lithium salt of (iii) is composed of LiClO ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , and LiC (CF ₃ SO ₂ ) ₃ . A non-aqueous electrolyte solution is selected from. The method of claim 1, wherein the electrolyte compound of (ii) is ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinylene carbonate (VC), diethyl carbonate (DEC), dimethyl carbonate (DMC ), Ethylmethyl carbonate (EMC), gamma butyrolactone (GBL), sulfolane, methyl acetate (MA), ethyl acetate (EA), methyl propionate (MP) and ethyl propionate (EP) A non-aqueous electrolyte solution selected from the group consisting of. The lithium ion secondary battery containing the non-aqueous electrolyte solution of any one of Claims 1, 3, and 4. The method of claim 5, (a) graphitized carbon capable of reversible storage and release of lithium as a negative electrode active material; (b) a lithium-containing transition metal oxide capable of reversible storage and release of lithium as a positive electrode active material; And (c) porous membrane Lithium ion secondary battery comprising a. The graphitized carbon of (a) has a crystal surface distance constant d002 of 0.338 nanometer or less measured by X-ray diffraction, and a specific surface area of 10 m 2 / g measured by BET method. The lithium ion secondary battery which is the following. The lithium ion secondary battery according to claim 6, wherein the lithium-containing transition metal oxide of (b) is selected from the group consisting of metal oxides represented by Formula 3 and Formula 4. [Formula 3] LiCo _a Mn _b Ni _c M _d O ₂ Wherein a is 0 ≦ a ≦ 1, b is 0 ≦ b ≦ 1, c is 0 ≦ c ≦ 1, d is 0 ≦ d ≦ 1, 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, Nb. [Formula 4] Li _X Mn _2-Y M ' _Y O ₄ Wherein X is 0.9 ≦ X ≦ 2, Y is 0 ≦ Y ≦ 0.5, and M ′ is Fe, Co, Ni, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B , Ga, In, Si, Ge.