KR101641763B1 - High voltage lithium secondary battery - Google Patents

Abstract

anode; cathode; A separator; And a gel polymer electrolyte, wherein the gel polymer electrolyte comprises an acrylate polymer, and the charging voltage of the battery is in the range of 4.3 V to 5.0 V. Description: . The high-voltage lithium secondary battery of the present invention has excellent capacity characteristics at a high voltage of 4.3 V or higher.

Description

HIGH VOLTAGE LITHIUM SECONDARY BATTERY Technical Field [1] The present invention relates to a high-

The present invention relates to a high-voltage lithium secondary battery, and more particularly, to a high-voltage lithium secondary battery including a gel polymer electrolyte including monomers having 2 to 6 acrylate groups and having a charging voltage ranging from 4.3 V to 5.0 V .

Recently, the development of electronics and information and communication industry has been rapidly growing through the portability, miniaturization, light weight, and high performance of electronic devices. Therefore, a high performance lithium secondary battery is being used as a power source for these portable electronic devices, and the demand is rapidly increasing. Rechargeable batteries that are used repeatedly for charging and discharging are essential for power supply for portable electronic devices, electric bicycles, and electric vehicles for information and communication.

Particularly, since the performance of these products depends on the battery, which is a core component, the demand for high capacity batteries is increasing. As the capacity of such a battery is increased, the battery system is progressing in high voltage.

Conventional lithium secondary batteries have been charged at a charging voltage of 3.0 V to 4.2 V, but studies have been made to exhibit a higher energy capacity by applying a higher charging voltage (4.3 V to 5.0 V).

However, when a negative electrode, a positive electrode, or a non-aqueous carbonate-based solvent is used as an electrolyte solution, charging is performed at a voltage higher than 4.2 V, which is a typical charging potential, so that the oxidizing power is increased. As the charging / There is a problem that the decomposition reaction of the electrolytic solution proceeds and the lifetime characteristics are rapidly deteriorated.

On the other hand, LiCoO ₂ , which is a conventional cathode active material, is inadequate in terms of thermal characteristics and electrochemical characteristics when it is applied to a high voltage.

SUMMARY OF THE INVENTION The present invention provides a high-voltage lithium secondary battery having excellent lifetime characteristics and capacity characteristics at a high voltage of 4.3 V to 5.0 V.

According to an aspect of the present invention, cathode; A separator; And a gel polymer electrolyte, wherein the gel polymer electrolyte comprises an acrylate polymer, and the charging voltage of the battery ranges from 4.3V to 5.0V.

According to another aspect of the present invention, there is provided a method of manufacturing a battery, including: inserting an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode into a battery case; And

Injecting a composition for a gel polymer electrolyte into the battery case and polymerizing the gel polymer electrolyte to form a gel polymer electrolyte,

The composition for the gel polymer electrolyte may include an electrolyte solvent; Ionizable lithium salts; And a monomer having 2 to 6 acrylate groups. The present invention also provides a method for producing a lithium secondary battery.

The lithium secondary battery according to an embodiment of the present invention is excellent in life characteristics and capacity characteristics even when charged at a high voltage of 4.3 V or more.

FIG. 1 is a graph showing the capacity of a lithium secondary battery manufactured in Examples 1 and 2 and Comparative Examples 1 and 2 when the battery is charged at a high voltage of 4.3 V. FIG.

Hereinafter, the present invention will be described in detail in order to facilitate understanding of the present invention.

The terms and words used in the present specification and claims should not be construed as limited to ordinary or dictionary terms and the inventor may appropriately define the concept of the term in order to best describe its invention It should be construed as meaning and concept consistent with the technical idea of the present invention.

A lithium secondary battery according to an embodiment of the present invention includes: a positive electrode; cathode; A separator; And a gel polymer electrolyte, wherein the gel polymer electrolyte comprises an acrylate-based polymer, and the charging voltage of the battery is in the range of 4.3 V to 5.0 V. The lithium secondary battery according to claim 1, .

Wherein the gel polymer electrolyte comprises an electrolyte solvent; Ionizable lithium salts; And a monomer having 2 to 6 acrylate groups.

The monomer having 2 to 6 acrylate groups is preferably branched and is, for example, selected from the group consisting of ditrimethylolpropane tetraacrylate, dipentaerythritol pentaacrylate and dipentaerythritol hexaacrylate Any one or a mixture of two or more thereof may be used.

The monomer may be contained in an amount of 0.1 wt% to 10 wt%, preferably 0.5 wt% to 5 wt% based on the total weight of the composition for a gel polymer electrolyte.

According to one embodiment of the invention, the ionizable lithium salt contained in the electrolyte, for _{example, LiPF 6, LiBF 4, LiSbF} 6, LiAsF 6, LiClO 4, LiN (C 2 F 5 SO 2) 2, LiN (CF ₃ SO ₂ ) ₂ , CF ₃ SO ₃ Li, LiC (CF ₃ SO ₂ ) ₃ and LiC ₄ BO ₈ , or a mixture of two or more thereof. no.

As the electrolyte solvent used in the present invention, any of those commonly used in an electrolyte for a lithium secondary battery can be used without limitation, and examples thereof include an ether, an ester, an amide, a linear carbonate and a cyclic carbonate, Can be mixed and used.

Among them, a carbonate compound which is typically a cyclic carbonate, a linear carbonate or a mixture thereof may be included. Specific examples of the cyclic carbonate compound include ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, A carbonate, a vinylene carbonate, and a halide thereof, or a mixture of two or more thereof. Specific examples of the linear carbonate compound include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC) and ethyl propyl carbonate , Or a mixture of two or more thereof may be used. However, the present invention is not limited thereto.

In particular, propylene carbonate and ethylene carbonate, which are cyclic carbonates in the carbonate electrolyte solution, are highly viscous organic solvents having a high dielectric constant and can dissociate the lithium salt in the electrolytic solution well. Thus, cyclic carbonates such as ethylmethyl carbonate, diethyl carbonate Or a low viscosity, low dielectric constant linear carbonate such as dimethyl carbonate in an appropriate ratio can be used to more advantageously use an electrolytic solution having a high electrical conductivity.

Examples of the ester in the electrolyte solvent include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate,? -Butyrolactone,? -Valerolactone,? -Caprolactone,? -Valerolactone And? -Caprolactone, or a mixture of two or more thereof, but the present invention is not limited thereto.

According to an embodiment of the present invention, the composition for gel polymer electrolyte may further comprise a polymerization initiator, and the polymerization initiator may be a conventional polymerization initiator known in the art.

Non-limiting examples of the polymerization initiator include benzoyl peroxide, acetyl peroxide, dilauryl peroxide, di-tert-butyl peroxide, organic peroxides such as t-butyl peroxy-2-ethyl-hexanoate, cumyl hydroperoxide and hydrogen peroxide, and hydroperoxides such as hydroperoxide, Azobis (isobutyronitrile) and AMVN (2-cyanobutane), 2,2'-azobis (methylbutyronitrile), AIBN , 2'-azobisdimethyl-valeronitrile), and the like, but the present invention is not limited thereto.

The polymerization initiator can be decomposed by heat in a battery, in a non-limiting example, at 30 ° C to 100 ° C or decomposed at room temperature (5 ° C to 30 ° C) to form radicals, and the radical polymerization is carried out by free radical polymerization. Lt; RTI ID = 0.0 > polymer. ≪ / RTI >

The polymerization initiator may be used in an amount of 0.01% by weight to 2% by weight based on the total weight of the composition for a gel polymer electrolyte. When the amount of the polymerization initiator is more than 2% by weight, gelation occurs too early or the unreacted polymerization initiator remains after the liquid polymer composition is injected into the cell, which adversely affects battery performance. On the other hand, , There is a problem that the gelation is not performed well.

In addition to the components described above, the electrolyte according to one embodiment of the present invention may optionally contain other additives known in the art.

According to an embodiment of the present invention, there is also provided a method of manufacturing a battery, comprising: inserting an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode into a battery case; And injecting a composition for a gel polymer electrolyte into the battery case and polymerizing the gel polymer electrolyte to form a gel polymer electrolyte, wherein the gel polymer electrolyte composition comprises: an electrolyte solvent; Ionizable lithium salts; And a monomer having 2 to 6 acrylate groups. The present invention also provides a method for producing a lithium secondary battery.

According to one embodiment of the present invention, the gel polymer electrolyte is formed by polymerizing a composition for a gel polymer electrolyte described above according to a conventional method known in the art. For example, the electrolyte can be formed by in- situ polymerization of a composition for a gel polymer electrolyte inside a secondary battery.

(A) inserting an electrode assembly comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode into a battery case, and (b) inserting a gel polymer electrolyte And then polymerizing the gel polymer electrolyte to form a gel polymer electrolyte.

The in - situ polymerization in the lithium secondary battery can proceed through thermal polymerization. In this case, the polymerization time is about 2 minutes to 12 hours, and the thermal polymerization temperature is 30 to 100 ° C.

When the gelation by the polymerization reaction is performed, a gel polymer electrolyte is formed, and a liquid electrolyte in which the electrolyte salt is dissociated into the electrolyte solvent can be uniformly impregnated in the formed gel polymer.

The electrode of the lithium secondary battery according to an embodiment of the present invention can be manufactured by a conventional method known in the art. For example, a slurry may be prepared by mixing and stirring a solvent, if necessary, a binder, a conductive agent, and a dispersant in an electrode active material, coating the electrode active material with a collector of a metal material, have.

In one embodiment of the present invention, the positive electrode active material contained in the positive electrode may be applied to a high voltage in the range of 4.3 V to 5.0 V, and is not limited as long as it is a compound capable of reversibly intercalating / deintercalating lithium. .

Specifically, the cathode active material may be any one selected from the group consisting of V ₂ O ₅ , TiS, and MoS, a lithium transition metal oxide of spinel having a cubic system layered salt structure, olivine structure, cubic structure, Or a composite oxide of two or more of them.

More specifically, it may include, for example, a cathode active material which is any one selected from the following Chemical Formulas 1 to 3, or a mixture of two or more thereof:

≪ Formula 1 >

Li [Li _x Ni _a Co _b Mn _c ] O ₂ (0 <x? 0.3, 0.3? C? 0.7, 0 <a + b <0.5, x + a + b + c = 1);

(2)

LiMn _{2 - x} M _x O ₄ (M = at least one element selected from the group consisting of Ni, Co, Fe, P, S, Zr, Ti and Al, 0 <x? 2);

(3)

Li, Zr, Ce, In, Zn and Y are selected from the group consisting of Li _{1 + a} Co _x M _{1 - x} AX ₄ (M = Al, Mg, Ni, Co, Mn, Ti, Ga, Cu, V, Nb, X is at least one element selected from the group consisting of O, F and N, A is P, S or a mixed element thereof, and 0? A? 0.2 and 0.5? X? 1.

To the cathode active material is preferably a in the formula 1 0.4≤c≤0.7, 0.2 ≤a + b < 0.5, LiNi 0 .5 Mn 1 .5 O 4, LiCoPO 4 And LiFePO ₄ , or a mixture of two or more thereof.

In the negative electrode according to an embodiment of the present invention, a carbonaceous material, lithium metal, silicon, or tin which lithium ions can be occluded and discharged is usually used as the negative electrode active material. Preferably, carbon materials can be used, and carbon materials such as low-crystalline carbon and highly-crystalline carbon can be used. Examples of the low crystalline carbon include soft carbon and hard carbon. Examples of highly crystalline carbon include natural graphite, Kish graphite, pyrolytic carbon, liquid crystal pitch carbon fiber high temperature sintered carbon such as mesophase pitch based carbon fiber, meso-carbon microbeads, mesophase pitches and petroleum or coal tar pitch derived cokes.

The anode and / or the cathode can be prepared by preparing a slurry by mixing and stirring a binder and a solvent, a conductive agent and a dispersant, which can be conventionally used according to need, applying the slurry to a current collector, and compressing the anode to produce a cathode.

Examples of the binder include polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HEP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, Polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, ethylene-propylene-diene monomer (EPDM) Various kinds of binder polymers such as sulfonated EPDM, styrene butylene rubber (SBR), fluorine rubber, and various copolymers can be used.

As the separator, a conventional porous polymer film conventionally used as a separator, for example, a polyolefin such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer and an ethylene / methacrylate copolymer A porous polymer film made of a high molecular weight polymer may be used alone or in a laminated manner, or a nonwoven fabric made of a conventional porous nonwoven fabric such as a glass fiber having a high melting point, a polyethylene terephthalate fiber or the like may be used. It is not.

The outer shape of the lithium secondary battery according to an embodiment of the present invention is not particularly limited, but may be cylindrical, square, pouch type, coin type, or the like using a can.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to examples. However, the embodiments according to the present invention may be modified into various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to enable those skilled in the art to more fully understand the present invention.

Example

EXAMPLES The present invention will be further illustrated by the following examples and experimental examples, but the present invention is not limited by these examples and experimental examples.

Example  One

&Lt; Preparation of composition for gel polymer electrolyte &

An electrolytic solution was prepared by dissolving LiPF ₆ in a non-aqueous electrolyte solvent having a composition of ethylene carbonate (EC): ethyl methyl carbonate (EMC) = 1: 2 (volume ratio) so as to have a concentration of 1M. 5 parts by weight of ditrimethylolpropane tetraacrylate and 0.25 part by weight of t-butylperoxy-2-ethylhexanoate as a polymerization initiator were added to 100 parts by weight of the electrolytic solution to prepare a gel polymer electrolyte composition.

<Preparation of coin-shaped secondary battery>

Anode manufacturing

Li in the positive electrode active material _{[Li 0 .29 Ni 0 .14 Co} 0 .11 Mn 0 .46] O 2 94 % by weight, the conductive agent of carbon black (carbon black) 3% by weight, 3% by weight of PVdF as a binder, solvent, N -Methyl-2-pyrrolidone (NMP) to prepare a positive electrode mixture slurry. The positive electrode mixture slurry was applied to an aluminum (Al) thin film having a thickness of about 20 mu m and dried to produce a positive electrode, followed by roll pressing to produce a positive electrode.

Cathode manufacture

A negative electrode mixture slurry was prepared by adding carbon powder as a negative electrode active material, PVdF as a binder, and carbon black as a conductive material to 96 wt%, 3 wt% and 1 wt%, respectively, as a solvent. The negative electrode mixture slurry was applied to a copper (Cu) thin film as an anode current collector having a thickness of 10 mu m and dried to prepare a negative electrode, followed by roll pressing to produce a negative electrode.

Battery Manufacturing

The battery was assembled using the positive electrode, the negative electrode and a separator composed of three layers of polypropylene / polyethylene / polypropylene (PP / PE / PP). The prepared gel polymer electrolyte composition was injected into the assembled battery, At 80 DEG C for 2 to 30 minutes to prepare a secondary battery.

Example  2

A secondary battery was fabricated in the same manner as in Example 1, except that dipentaerythritol pentaacrylate was used instead of ditrimethylolpropane tetraacrylate in the preparation of the gel polymer electrolyte composition of Example 1.

Comparative Example  One

Except that ditrimethylolpropane tetraacrylate and t-butylperoxy-2-ethylhexanoate were not used in the preparation of the gel polymer electrolyte composition of Example 1, A battery was prepared.

Comparative Example  2

A secondary battery was produced in the same manner as in Example 1, except that LiCoO ₂ was used as the positive electrode active material in the production of the positive electrode of Example 1.

Experimental Example

The secondary batteries (battery capacity: 4.3 mAh) produced in Examples 1 and 2 and Comparative Examples 1 and 2 were charged at a constant current of 0.7 C at a temperature of 55 캜 until a constant current of 4.3 V was obtained and then charged at a constant voltage of 4.3 V, The charging was terminated. After that, it was left for 10 minutes and then discharged at a constant current of 0.5 C until it reached 3.0 V. [ The battery was charged and discharged for 30 cycles, and the battery capacity was measured and shown in Fig.

Specifically, referring to FIG. 1, the capacities of Examples 1 and 2 and Comparative Examples 1 and 2 were similar at less than about 5th cycle, but the capacities of Comparative Examples 1 and 2 rapidly decreased after about 5th cycle. Particularly, Comparative Example 2 using LiCoO ₂ as a cathode active material significantly decreased from the fifth cycle, and the capacity was close to 0 mAh at the 30th cycle. On the other hand, Examples 1 and 2 exhibited excellent capacity up to the 30th cycle even at a high voltage and exhibited capacity characteristics of 2 to 4 times or more as compared with Comparative Examples 1 and 2.

Therefore, it can be seen that the capacity of the battery prepared in Examples 1 and 2 after 30 cycles of charging at a high voltage of 4.3 V was greatly improved as compared with the capacity of the battery prepared in Comparative Example 1 or 2. [

Claims (16)

anode; cathode; A separator; And a gel polymer electrolyte, the lithium secondary battery comprising:
Wherein the anode is reversibly intercalated and deintercalated with lithium at a high voltage in the range of 4.3 V to 5.0 V and comprises a cathode active material comprising a compound of Formula 1,
Wherein the gel polymer electrolyte comprises an acrylate-based polymer, and the charging voltage of the battery ranges from 4.3 V to 5.0 V.
&Lt; Formula 1 >
Li [Li _x Ni _a Co _b Mn _c ] O ₂
(0 <x? 0.3, 0.4? C? 0.7, 0.2? A + b? 0.5, x + a + b + c = 1)
The method according to claim 1,
Wherein the gel polymer electrolyte comprises an electrolyte solvent; Ionizable lithium salts; And a monomer having 2 to 6 acrylate groups.
delete delete 3. The method of claim 2,
Wherein the monomer is any one selected from the group consisting of ditrimethylolpropane tetraacrylate, dipentaerythritol pentaacrylate and dipentaerythritol hexaacrylate, or a mixture of two or more thereof.
3. The method of claim 2,
Wherein the monomer is contained in an amount of 0.1% by weight to 10% by weight based on the total weight of the composition.
3. The method of claim 2,
The lithium salt is _{LiPF 6, LiBF 4, LiSbF 6} , LiAsF 6, LiClO 4, LiN (C 2 F 5 SO 2) 2, LiN (CF 3 SO 2) 2, CF 3 SO 3 Li, LiC (CF 3 SO ₂ ) ₃ and LiC ₄ BO ₈ , or a mixture of two or more thereof.
3. The method of claim 2,
Wherein the electrolyte solvent is a linear carbonate, a cyclic carbonate, or a combination thereof.
9. The method of claim 8,
Wherein the linear carbonate comprises any one selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate and ethyl propyl carbonate, or a mixture of two or more thereof. battery.
9. The method of claim 8,
The cyclic carbonate may be at least one selected from the group consisting of ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, Or a mixture of two or more thereof. The lithium secondary battery according to claim 1,
The method according to claim 1,
Wherein the negative electrode comprises a carbonaceous anode active material.
Inserting an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode into a battery case; And
Injecting a composition for a gel polymer electrolyte into the battery case and polymerizing the gel polymer electrolyte to form a gel polymer electrolyte,
The composition for the gel polymer electrolyte may include an electrolyte solvent; Ionizable lithium salts; And a monomer having 2 to 6 acrylate groups,
The positive electrode according to any one of claims 1 to 3, wherein the positive electrode is applied to a high voltage in the range of 4.3 V to 5.0 V and reversibly intercalates and deintercalates lithium, Wherein the lithium secondary battery is a lithium secondary battery.
&Lt; Formula 1 >
Li [Li _x Ni _a Co _b Mn _c ] O ₂
(0 <x? 0.3, 0.4? C? 0.7, 0.2? A + b? 0.5, x + a + b + c = 1)
13. The method of claim 12,
Wherein the composition for the gel polymer electrolyte further comprises a polymerization initiator.
13. The method of claim 12,
Wherein the polymerization is carried out at a temperature ranging from 30 ° C to 100 ° C.
13. The method of claim 12,
Wherein the monomer is any one selected from the group consisting of ditrimethylolpropane tetraacrylate, dipentaerythritol pentaacrylate and dipentaerythritol hexaacrylate, or a mixture of two or more thereof. Gt;
delete

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