KR101649014B1 - Additive for non-aqueous liquid electrolyte, non-aqueous liquid electrolyte, and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention provides a non-aqueous electrolytic solution containing a glycidyl compound as an additive and a lithium secondary battery comprising the same. The non-aqueous electrolytic solution of the present invention is characterized in that the above-mentioned glycidyl compound additive forms a stable film on the surface of the negative electrode, suppresses gas formation which can be generated by decomposition of the electrolyte at a high temperature, And the cycle characteristics of the battery can be improved.

Description

[0001] The present invention relates to an electrolyte additive for a lithium secondary battery, a non-aqueous electrolytic solution containing the electrolyte additive, and a lithium secondary battery comprising the lithium secondary battery as an additive for a non-aqueous liquid electrolyte,

The present invention relates to an electrolyte additive for a lithium secondary battery comprising a glycidyl compound, a non-aqueous electrolyte containing the electrolyte additive, and a lithium secondary battery comprising the same.

As technology development and demand for mobile devices are increasing, the demand for secondary batteries as energy sources is rapidly increasing. Among these secondary batteries, lithium secondary batteries having high energy density and voltage have been commercialized and widely used.

Lithium metal oxide is used as the positive electrode active material of the lithium secondary battery, and lithium metal, lithium alloy, crystalline or amorphous carbon or carbon composite material is used as the negative electrode active material. The active material is coated on the current collector with an appropriate thickness and length, or the active material itself is coated in a film form and wrapped or laminated with a separator as an insulator to form an electrode group. The electrode group is then placed in a can or similar container, Thereby manufacturing a secondary battery.

This lithium secondary battery is charged and discharged while repeating the process of intercalating lithium ions from the lithium metal oxide of the anode into the graphite electrode of the cathode and deintercalating the lithium ions. At this time, since lithium is highly reactive, it reacts with the carbon electrode to form Li ₂ CO ₃ , LiO, LiOH and the like to form a film on the surface of the cathode. This film is called a solid electrolyte interface (SEI) film.

The SEI film formed at the beginning of charging prevents the reaction between lithium ion and carbon anode or other materials during charging and discharging. It also acts as an ion tunnel, allowing only lithium ions to pass through. This ion tunnel serves to prevent the collapse of the structure of the carbon anode by co-intercalating the organic solvent of the electrolyte having a large molecular weight moving together by solvation of the lithium ion together with the carbon anode.

Therefore, in order to improve the high-temperature cycle characteristics and the low-temperature output of the lithium secondary battery, a solid SEI film must always be formed on the cathode of the lithium secondary battery. Once the SEI membrane is formed at the time of initial charging, it is used as an ion tunnel to prevent the reaction between the lithium ion and the negative electrode or other materials during repetition of charging and discharging by using the battery and passing only lithium ions between the electrolyte and the negative electrode .

It has been difficult to expect an improvement in battery life due to the formation of an uneven SEI film in the case of an electrolyte solution containing no electrolyte additive or poor electrolyte characteristics. Further, even when the electrolyte additive is included, if the amount of the electrolyte additive can not be adjusted to the required amount, gas may be generated during the high temperature reaction due to the electrolyte additive, or a uniform SEI film may not be formed on the carbon surface of the anode, The cycle performance of the secondary battery is reduced.

The present invention aims at solving the technical problems requested from the past as described above.

The inventors of the present application have confirmed that the cycle performance of a battery is improved when an electrolyte for a lithium secondary battery includes an additive which is a glycidyl compound, and completed the present invention.

In order to solve the above problems, the present invention provides an electrolyte additive comprising a glycidyl compound; Non-aqueous organic solvent; And a non-aqueous electrolytic solution containing a lithium salt.

The present invention also provides a lithium secondary battery comprising a positive electrode, a negative electrode, and the non-aqueous electrolyte solution.

INDUSTRIAL APPLICABILITY The electrolyte additive for a lithium secondary battery of the present invention can form a stable coating (SEI) on the surface of a carbon anode during initial charging and discharging of the lithium secondary battery, thereby improving the cycle characteristics of the battery.

1 is a graph showing a capacity (mA) according to the number of times of charging and discharging at room temperature (23 ° C) in Examples and Comparative Examples of the present invention.
2 is a graph showing the charge / discharge ratio (%) according to the number of charge / discharge cycles at room temperature (23 ° C) of the examples and comparative examples of the present invention.
3 is a graph showing the capacity (mA) according to the number of times of charging and discharging at a high temperature (45 ° C) in Examples and Comparative Examples of the present invention.
4 is a chart showing the charge / discharge ratio (%) according to the number of times of charging and discharging at a high temperature (45 ° C) in Examples and Comparative Examples of the present invention.

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.

One embodiment of the present invention may include a non-aqueous electrolyte solution, a lithium salt, and a glycidyl-based compound as an additive in a lithium secondary battery.

The glycidyl compound is specifically exemplified by allyl glycidyl ether, diglycidyl 1,2-cyclohexanedicarboxylate, trimethylolpropane triglycidyl ether, butyl glycidyl ether, (3-glycidyloxy Propyl) trimethoxysilane, N, N, N, N'-tetraglycidyl-m-xylylenediamine and 1,3-bis (3-glycidyloxypropyl) tetramethyldisiloxane Or more.

Each of the glycidyl compounds may be represented by the following formulas (1) to (7).

Formula 1

Allyl glycidyl ether

(2)

Butyl glycidyl ether

(3)

Diglycidyl 1,2-cyclohexanedicarboxylate

Formula 4

(3-Glycidyloxypropyl) trimethoxysilane

Formula 5

Trimethylolpropane triglycidyl ether

6

N, N, N, N'-tetraglycidyl-m-xylenediamine

Formula 7

1,3-Bis (3-glycidyloxypropyl) tetramethyldisiloxane

)가 가교반응을 통하여 저분자량의 올리고머를 형성하여 음극 표면에 안정한 SEI 피막을 형성하고, Li 이온이 음극과의 상호작용 channel을 SEI 피막내에 용이하게 형성할 수 있어서 싸이클 성능을 개선시킬 수 있다. 본 발명의 일 실시예에 이용될 수 있는 상기 글리시딜계 화합물 중 알릴 글리시딜 에테르의 경우에는 관능기 중의 하나인 알릴(Allyl)기의 이중결합이 가교 반응에 참가하여 안정한 피막형성을 보다 효과적으로 할 수 있다. 그렇기 때문에, 초기 충방전시 음극 활물질 표면에 안정한 피막을 형성하여 전지의 수명 성능을 향상시킬 수 있다.The additive of the glycidyl compound may be an epoxide of a glycidyl group (

) Forms a stable SEI film on the surface of the anode by forming a low molecular weight oligomer through a crosslinking reaction, and an interaction channel between Li ions and the cathode can be easily formed in the SEI film, thereby improving the cycle performance. In the case of allyl glycidyl ether among the glycidyl compounds that can be used in one embodiment of the present invention, the double bond of the allyl group, which is one of the functional groups, participates in the crosslinking reaction to more effectively form a stable film . Therefore, it is possible to improve the lifetime performance of the battery by forming a stable film on the surface of the negative electrode active material during the initial charging and discharging.

Here, the glycidyl type compound additive may be contained in an amount of 0.1 wt% to 5.0 wt%, preferably 0.1 wt% to 1.0 wt%, based on the total amount of the electrolytic solution. When the content of the glycidyl compound is less than 0.1 wt%, it is impossible to form a sufficient film on the surface of the negative electrode. When the content of the glycidyl compound additive is more than 1.0 wt%, the lithium ion permeability of the protective coating is lowered, And may not obtain the characteristics of lifetime improvement.

The non-aqueous electrolyte according to one embodiment of the present invention may further include a compound containing a vinylene group or a vinyl group capable of forming an SEI film on the surface of the negative electrode at the time of initial charging as described above. The vinylene or vinyl group-containing compound may be any one selected from the group consisting of a vinylene carbonate-based compound, an acrylate-based compound containing a vinyl group, a sulfonate-based compound containing a vinyl group, and an ethylene carbonate- Or a mixture of two or more thereof. Here, the vinylene carbonate-based compound may be vinylene carbonate.

On the other hand, the compound containing the vinylene group or the vinyl group may be added to the non-aqueous electrolyte at 2 to 5% by weight based on the total weight of the non-aqueous electrolyte.

In order to form a stable SEI film on the surface of the electrode, the non-aqueous electrolyte according to one embodiment of the present invention may further include 1,3-propane sultone or ethylene sulfate additive in a total amount of electrolyte 0.5 to 1.5% by weight relative to the total weight of the composition.

Further, the non-aqueous electrolyte according to one embodiment of the present invention may further include a cyclic carbonate substituted with a halogen. The halogen-substituted cyclic carbonate may be fluoroethylene carbonate (FEC). Furthermore, when the fluoroethylene carbonate is added to the non-aqueous electrolyte, the content thereof may be 1 to 10% by weight based on the total weight of the non-aqueous electrolyte.

If the content of the fluoroethylene carbonate is less than 1% by weight, the amount of the fluoroethylene carbonate to be added is too small to achieve a desired effect. If the fluoroethylene carbonate content is more than 10% by weight, the lithium ion permeability of the protective coating is lowered to increase the impedance, So that characteristics of improvement in cycle performance may not be obtained.

Specifically, when the fluoroethylene carbonate is used together with the compound containing a vinylene group or a sulfonic acid group, an SEI film having a high dielectric constant and an excellent ion conductivity can be formed on the surface of the anode, This is effective for improving the cycle performance of the battery. Further, the fluoroethylene carbonate compound can prevent or retard the ignition of the battery by an exothermic reaction. This is because the fluoroethylene compound is composed of fluorine which is a halogen compound having a high flame retardant effect. In particular, when the compound is charged, an SEI protective layer is formed on the surface of the negative electrode to delay a micro- or macro- I can do it. In addition, the FEC forms a dense and dense passivation film on the anode during initial charging (formation), thereby preventing the carbonate-based solvent from co-intercalating and decomposing in the layered active material layer, thereby reducing the irreversible capacity of the battery, And plays an important role in enhancing the cycle performance of the battery by interposing and releasing only Li ^{< +} >.

However, fluoroethylene carbonate compounds are thermally very fragile and easily decompose at high temperatures. A large amount of gas (CO ₂ , CO) generated at this time accelerates the combustion of electrolyte by venting the pouch type or can type case At the same time, the internal short-circuiting can be caused to significantly deteriorate the battery performance.

The non-aqueous electrolyte according to an embodiment of the present invention includes a glycidyl additive, thereby effectively preventing the high temperature instability and gas generation of the FEC. Specifically, a glycidyl group, which is a functional group of the glycidyl compound, forms an oligomer through a cross-linking reaction on the surface of the anode to form a stable (SEI) coating, thereby suppressing the decomposition of the electrolyte due to the reaction between the electrolyte and the cathode. It is possible to suppress the generation of gas due to the side reaction of the gas.

Meanwhile, the non-aqueous electrolytic solution according to an embodiment of the present invention may include the electrolyte additive, a non-aqueous organic solvent, and a lithium salt.

On the other hand, as the lithium salt that may be included in the non-aqueous electrolyte solution according to an embodiment of the present invention is _{LiPF 6, LiAsF 6, LiCF 3} SO 3, LiN (CF 3 SO 2) 2, LiBF 4, LiBF 6, LiSbF 6 _{, LiN (C 2 F 5 SO} 2) 2, LiAlO 4, LiAlCl 4, LiSO 3 CF 3, LiClO 4, Li (CF 3 SO 2) (C 2 F 5 SO 2) N , and Li (SO ₂ F) ₂ N , Or a mixture of two or more of them may be used. In one embodiment of the present invention, LiPF ₆ may be used.

The non-aqueous organic solvent that can be included in the non-aqueous electrolyte solution is not limited as long as it can minimize decomposition due to oxidation reaction during charging and discharging of the battery, For example, a carbonate compound, a propionate compound, and the like. These may be used alone, or two or more of them may be used in combination.

Examples of the organic solvent of the carbonate compound in the non-aqueous organic solvents include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate May be any one selected from the group consisting of ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate (BC), or a mixture of two or more thereof. (EP), propyl propionate (PP), n-propyl propionate, iso-propyl propionate, n-butyl propionate, isobutyl propionate and isobutyl propionate And mixtures of two or more of these.

Meanwhile, the non-aqueous organic solvent according to an embodiment of the present invention may be a combination of a carbonate compound and a propionate compound. It is possible to increase the initial capacity of the battery by improving the movement of lithium ions in the electrolyte by preparing a non-aqueous electrolytic solution by combining the solvent of the propionate compound rather than using only the solvent of the carbonate-based compound.

As a preferable combination of the organic solvent according to an embodiment of the present invention, ethylene carbonate, propyl carbonate and ethyl propionate may be mixed at a weight ratio of 3: 1: 6.

Meanwhile, the lithium secondary battery according to an embodiment of the present invention may include a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and the non-aqueous electrolyte. The positive electrode and the negative electrode may include a positive electrode active material and a negative electrode active material, respectively.

Here, the cathode active material may include a manganese-based spinel active material, a lithium metal oxide, or a mixture thereof. Further, the lithium metal oxide may be selected from the group consisting of lithium-cobalt oxide, lithium-manganese oxide, lithium-nickel-manganese oxide, lithium-manganese-cobalt oxide and lithium-nickel-manganese-cobalt oxide And more specifically LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li (Ni _a Co _b Mn _c ) O ₂ (where 0 <a <1, 0 <b < (where 0 &lt; _Y &lt; 1), LiNi _{1 - Y} Co _Y O ₂ , LiCo _{1 - Y} Mn _Y O ₂ , LiNi _{1 - Y} Mn _Y O ₂ , _{Li (Ni a Co b Mn c} ) O 4 (0 <a <2, 0 <b <2, 0 <c <2, a + b + c = 2), LiMn 2 - z Ni z O 4, LiMn 2 _-z Co _z O ₄ (where 0 <Z <2).

As the negative electrode active material, graphite based anode active materials such as carbonaceous, natural graphite and artificial graphite such as crystalline carbon, amorphous carbon or carbon composite may be used alone or in combination of two or more.

In addition, a silicon based material may be used as a negative electrode active material, or a silicon based alone or a mixture of carbon and silicon may be used. Examples of usable silicon based materials include Si, SiOx (0 <x <2), Si-Q alloy (Q is an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element, a Group 15 element, Rare earth elements and combinations thereof, but not Si), Sn, SnO ₂ , Sn-R (wherein R is at least one element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, An element selected from the group consisting of a Group 16 element, a transition metal, a rare earth element, and combinations thereof, and is not Sn), and at least one of them may be mixed with SiO ₂ . The element Q and the element R may be at least one element selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Pb, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Ti, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

By using the silicone compound, the capacity of the secondary battery can be increased, but the phenomenon of swelling of the negative electrode can be increased through the charge / discharge cycle. Therefore, when a silicon compound is used as the negative electrode active material, the content of the fluoroethylene carbonate may be increased to 10 wt% to 15 wt% to reduce the swelling phenomenon.

The separator may be a porous polymer film such as a porous polymer film made of a polyolefin-based polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, or an ethylene / methacrylate copolymer Or may be a laminate of two or more kinds. In addition, nonwoven fabrics made of conventional porous nonwoven fabrics, for example, glass fibers having a high melting point, polyethylene terephthalate fibers, or the like can be used, but the present invention is not limited thereto.

The lithium secondary battery may be manufactured by a conventional method according to the present invention, and may be preferably a pouch type secondary battery.

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 1

[Preparation of electrolytic solution]

Aqueous organic solvent having a composition of ethylene carbonate (EC): propyl carbonate (PC): ethyl propionate (EP) = 3: 1: 6 (weight ratio) and 1.0 M of LiPF ₆ were mixed, An electrolytic solution containing 3 wt% of vinylene carbonate (VC), 1 wt% of 1,3 propane sultone (PS), and 0.5 wt% of allyl glycidyl ester as a glycidyl compound was prepared.

[Production of lithium secondary battery]

(NMP) as a solvent, 96 wt% of LiCoO ₂ as a positive electrode active material, ₂ wt% of carbon black as a conductive agent, and 2 wt% of polyvinylidene fluoride (PVdF) 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.

The negative electrode mixture slurry was prepared by adding artificial graphite as a negative electrode active material, PVdF as a binder, and carbon black as a conductive agent 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.

The thus prepared positive electrode and negative electrode were fabricated by polymerizing a polymer type cell with a separator composed of three layers of polypropylene / polyethylene / polypropylene (PP / PE / PP), and then the prepared non-aqueous electrolyte was injected, The preparation of the battery was completed.

Example 2

A lithium secondary battery was prepared in the same manner as in Example 1 except that 0.5% by weight of butyl glycidyl ester was added as the glycidyl compound.

Example 3

A lithium secondary battery was prepared in the same manner as in Example 1, except that 0.5% by weight of diglycidyl 1,2-cyclohexanedicarboxylate was added as the glycidyl compound.

Example 4

A lithium secondary battery was prepared in the same manner as in Example 1, except that 0.5% by weight of (3-glycidyloxypropyl) trimethoxysilane was added as the glycidyl compound.

Example 5

A lithium secondary battery was prepared in the same manner as in Example 1 except that 0.5% by weight of trimethylolpropane triglycidyl ester was added as the glycidyl compound.

Example 6

A lithium secondary battery was prepared in the same manner as in Example 1 except that 0.5% by weight of N, N, N, N'-tetraglycidyl-m-xylylenediamine was added as the glycidyl compound.

Example 7

A lithium secondary battery was produced in the same manner as in Example 1, except that 0.5% by weight of 1,3-bis (3-glycidyloxypropyl) tetramethyldisiloxane was added as the glycidyl compound.

Comparative Example 1

A lithium secondary battery was produced in the same manner as in Example 1 except that the glycidyl compound was not added.

<Battery life test>

The secondary batteries of Examples 1 to 5 and Comparative Example 1 were repeatedly charged and discharged at 23 占 폚 and 45 占 폚 at 1 C / 1C to confirm the capacity retention ratio relative to the initial capacity. The results are shown in Figs. 1 to 4 and Table 1 below.

150th capacity retention ratio (%) = (discharge capacity of the 150th cycle / discharge capacity of the first cycle) * 100

After charging / discharging
Capacity retention rate (%) 23 ℃ 45 ° C Example 1 92.9 92.2 Example 2 93.3 92.2 Example 3 92.6 92.1 Example 4 92.7 90.8 Example 5 93.1 90.1 Comparative Example 1 90.1 82.0

As can be seen from the above, as compared with Comparative Example 1, in the secondary batteries of Examples 1 to 5, when the glycidyl compound was used as an additive, the number of times of charge and discharge of the battery was increased, It is possible to increase the cycle performance of the battery particularly at a high temperature as a result of forming a stable film on the surface of the negative electrode so as to effectively suppress a large amount of gas that can be produced.

Claims (16)

An electrolyte additive including a glycidyl compound;
Non-aqueous organic solvent; And
Lithium salts,
Wherein the glycidyl-based compound is allyl glycidyl ether.
The method according to claim 1,
Wherein the lithium salt is selected from the group consisting of LiPF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiBF ₄ , LiBF ₆ , LiSbF ₆ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiAlO ₄ , LiAlCl ₄ , _{LiSO 3 CF 3, LiClO 4,} Li (CF 3 SO 2) (C 2 F 5 SO 2) N , and Li (SO ₂ F) include any one or a mixture of two or more of those selected from the group consisting of a ₂ N A non-aqueous electrolytic solution.
The method according to claim 1,
Wherein the content of the glycidyl compound is 0.1 to 1.0 wt% based on the total weight of the electrolytic solution.
delete The method according to claim 1,
Wherein the additive further comprises fluoroethylene carbonate (FEC).
6. The method of claim 5,
Wherein the fluoroethylene carbonate is 2 to 10% by weight based on the total amount of the electrolytic solution.
The method according to claim 1,
Wherein the additive further comprises vinylene carbonate (VC) and propane sultone (PS).
8. The method of claim 7,
Wherein the vinylene carbonate (VC) is 2 to 5 wt% based on the total amount of the electrolytic solution, and the propanetetone (PS) is 0.5 to 1.5 wt% based on the total amount of the electrolytic solution.
The method according to claim 1,
Wherein the non-aqueous organic solvent comprises a carbonate-based compound and a propionate-based compound.
10. The method of claim 9,
The carbonate compound may be selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC) ), Propylene carbonate (PC), and butylene carbonate (BC), or a mixture of two or more thereof.
10. The method of claim 9,
The propionate compound may be at least one selected from the group consisting of ethyl propionate (EP), propyl propionate (PP), n-propyl propionate, isopropyl propionate, n-butyl propionate, And tert-butyl propionate, or a mixture of two or more thereof.
10. The method of claim 9,
Wherein the propionate compound is ethyl propionate (EP) or propyl propionate (PP).
anode; cathode; Separator and
A lithium secondary battery comprising the non-aqueous electrolyte according to any one of claims 1 to 3 and 5 to 12.
14. The method of claim 13,
Wherein the negative electrode is a carbon-based negative active material selected from the group consisting of crystalline carbon, amorphous carbon, artificial graphite, and natural graphite.
14. The method of claim 13,
Wherein the positive electrode is a manganese spinel-based active material or a lithium metal oxide.
14. The method of claim 13,
Wherein the lithium secondary battery is a lithium ion secondary battery or a lithium polymer secondary battery.

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