KR101683534B1 - electrolyte for lithium secondary battery and lithium secondary battery containing the same - Google Patents

Abstract

The present invention relates to a secondary battery electrolyte and a secondary battery comprising the same, wherein the non-aqueous electrolyte for a secondary battery according to the present invention is decomposed earlier than the organic solvent at the time of initial charging of the battery, so that a solid electrolyte interface (SEI) By stable formation, the anode resistance in the high-frequency range and the anode resistance in the low-frequency range are reduced at the same time, and the lifetime characteristics at room temperature are improved. The decomposition of the cathode and anode surfaces at high temperatures is suppressed and the electrical resistance is reduced. Do.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary battery and a secondary battery including the same,

The present invention relates to a secondary battery electrolyte and a secondary battery comprising the same. More particularly, the present invention relates to a non-aqueous organic solvent, an alkali metal salt and a 1,3-dithiol-2-thione derivative, a phosphoric acid-based lithium salt, The anode resistance of the high-frequency region and the anode resistance of the low-frequency region can be reduced at the same time, thereby improving the performance of the battery.

[0002] Recently, portable electronic devices have been widely used, and these portable electronic devices are becoming thinner, smaller, and lighter. As a result, the secondary battery used as the power source is also small and lightweight, and can be charged and discharged for a long period of time.

 The secondary battery is classified into a lead-acid battery, a nickel-cadmium battery, a nickel-hydrogen (Ni-MH) battery and a lithium battery according to an anode material and a cathode material. The potential and the energy density are determined. Among them, lithium secondary batteries are widely used as driving power sources for portable electronic devices such as notebook computers, camcorders, and mobile phones because of their high energy density due to the low oxidation / reduction potential and molecular weight of lithium.

However, the lithium secondary battery has a serious problem of deterioration of the safety of the battery caused by continuous charging. One of the causes that may affect the stability of the battery is heat generation due to the structural collapse of the anode. Among the secondary batteries, the battery stability according to the working principle of the non-aqueous electrolyte secondary battery is as follows.

That is, the positive electrode active material of the nonaqueous electrolyte secondary battery is composed of lithium or a lithium-containing metal oxide capable of intercalating and deintercalating lithium ions or the like. Such a positive electrode active material deforms into a thermally unstable structure as a large amount of lithium is released during overcharging . When the battery temperature reaches a critical temperature due to an external physical impact such as high temperature exposure in the overcharged state, oxygen is released from the cathode active material having an unstable structure, and the released oxygen causes an exothermic decomposition reaction with the electrolyte solvent or the like. Particularly, since the combustion of the electrolytic solution is further accelerated by the oxygen released from the anode, such a series exothermic reaction causes ignition and rupture of the battery due to thermal runaway.

In addition, the positive electrode transition metal deposited on the negative electrode acts as a catalyst promoting the decomposition of the non-aqueous electrolyte, thereby generating gas inside the battery, or interfering with lithium ion migration as the SEI layer of the negative electrode progresses charge / discharge The cell performance and efficiency are significantly reduced.

Therefore, in order to solve the above problems, Japanese Unexamined Patent Application Publication No. 2013-157305 proposes an electrolyte solution containing two isocyanate group-containing compounds. However, researches on electrolytes having excellent lifetime characteristics and stability at high temperature and low temperature It is a fact that is demanded.

Japanese Patent Publication No. 2013-157305 (Aug. 15, 2013)

Disclosure of Invention Technical Problem [8] Accordingly, the present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a nonaqueous electrolyte solution for a secondary battery which can simultaneously reduce cathode resistance in a high frequency region and anode resistance in a low frequency region, There is a purpose.

Another object of the present invention is to provide a secondary battery comprising the nonaqueous electrolyte solution for the secondary battery.

The present invention relates to a secondary battery electrolyte and a secondary battery including the same.

One aspect of the present invention is a composition comprising: a) an alkali metal salt; b) non-aqueous organic solvent; c) a 1,3-dithiol-2-thione derivative represented by the following formula (1); And d) an additive that is a phosphate-based lithium salt, a carbonate compound, or a mixture thereof.

[Chemical Formula 1]

(Wherein X ₁ and X ₂ are each independently hydrogen or

ego,

Y represents an ester group (-C (= O) O-), a carbonyl group (-C (= O) -), an ether group (-O-), a thiol group (-S-) (H) -), an alkylamine group (-N (R) -) and a phosphine group (-P (H) -)

Wherein R ₁ is hydrogen or (C ₁ -C 10) alkyl, (C 6 -C 12) aryl, (C 1 -C 10) alkenyl,

X ₁ and X ₂ are both

, R < ₁ > may combine with adjacent substituents to form a ring.)

In the present invention, the 1,3-dithiol-2-thione derivative may be any one selected from the following formulas (2) to (4).

(2)

(3)

[Chemical Formula 4]

(Wherein R ₂ and R ₃ are each independently (C 1 -C 10) alkyl, (C 2 -C 10) alkenyl or (C 6 -C 12) aryl,

R ₄ and R ₅ are each independently (C 1 -C 5) alkyl, (C 2 -C 5) alkenyl,

and n is an integer of 1 to 5.)

In the present invention, the phosphoric acid-based lithium salt is preferably selected from the group consisting of lithium difluorobisoxalatophosphate, lithium difluorophosphate, lithium phosphate, lithium tetrafluorooxalate phosphate, lithium difluorobismethylmalonate phosphate, and lithium difluoro Bis-ethyl malonate phosphate, and the like.

In the present invention, the carbonate compound may be vinylene carbonate, vinylethylene carbonate or a mixture thereof.

In the present invention, the non-aqueous organic solvent may be any one or more selected from a linear carbonate solvent, a cyclic carbonate solvent, a linear ester solvent, and a cyclic ester solvent. Specifically, the linear carbonate solvent may be dimethyl carbonate , Diethyl carbonate, dipropyl carbonate, ethyl propyl carbonate, ethyl methyl carbonate and methyl propyl carbonate, and the cyclic carbonate solvent is at least one selected from the group consisting of ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, Butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate, vinylethylene carbonate and fluorethylene carbonate, and the linear ester solvent Include methyl propionate, ethyl propionate Onate, propyl acetate, and at least either one or both selected from butyl acetate and ethyl acetate, the cyclic ester solvent may be at least one or more selected from lactone lactone, caprolactone and ballet as gamma -butyrolactone.

In the present invention, the non-aqueous organic solvent may be mixed with a linear carbonate solvent: cyclic carbonate solvent in a volume ratio of 1: 9 to 9: 1.

In the present invention, the alkali metal salt may be contained in the non-aqueous organic solvent at a concentration of 0.6 to 2.0 M, and the alkali metal salt may include a lithium salt or a sodium salt as a cation and an anion such as PF ₆ ^- , ClO ₄ ^- , BF _{4 ^{-, SbF 6 -, AlO 4}} -, AlCl 4 -, CF 3 SO 3 -, C 4 F 9 SO 3 -, N (C 2 F 5 SO 3) 2 -, N (C 2 F 5 SO 2) 2 _{^{-, N (CF 3 SO 2}} ) 2 -, SCN -, LiN (C x F 2x + 1 SO 2) (C y F 2y + 1 SO 2) - ( in this example, x, y is 0 or a natural number), B ^{_{(C 2 O 4) 2 -}} , BF 2 (C 2 O 4), LiPF 4 (C 2 O 4) -, PF 2 (C 2 O 4) 2 - , and _{P (C 2 O 4) 3} - having Or a mixture of two or more thereof.

In the present invention, the secondary battery electrolyte may contain 0.05 to 10% by weight of 1,3-dithiol-2-thione derivative, 0.01 to 10% by weight of an additive, and 85 to 99% by weight of a non-aqueous organic solvent.

Another aspect of the present invention is a positive electrode comprising: a) a positive electrode comprising a positive electrode active material capable of absorbing and desorbing an alkali metal; b) a negative electrode comprising a negative electrode active material capable of absorbing and desorbing alkali metals; c) a secondary battery electrolyte according to any one of claims 1 to 8; And d) a separator.

The nonaqueous electrolytic solution for a secondary battery according to the present invention decomposes before the organic solvent at the initial charging of the battery to effectively and stably form a SEI (solid electrolyte interface) coating on the surface of the negative electrode, whereby the anode resistance in the high frequency range and the anode resistance in the low frequency range At the same time, it improves the lifetime characteristics at room temperature and improves the battery characteristics by suppressing the decomposition of the cathode and the anode surface at high temperature and reducing the electric resistance.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing an AC impedance of a secondary battery including a secondary battery electrolyte according to Examples 4, 6, 9, and Comparative Examples 1 and 2. FIG.

Hereinafter, a secondary battery electrolyte according to the present invention and a secondary battery including the same will be described in detail with reference to specific examples. It should be understood, however, that the invention is not limited thereto and that various changes and modifications may be made without departing from the spirit and scope of the invention.

Unless otherwise defined, all technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

The term "alkyl", "alkoxy", and other "alkyl" moieties as described herein includes both linear and branched forms. The 'aryl' described in the present invention is an organic radical derived from aromatic hydrocarbons by the removal of one hydrogen, and includes a single or fused ring containing 4 to 7, preferably 5 or 6 ring atoms, A ring system, and a form in which a plurality of aryls are connected by a single bond. Specific examples include, but are not limited to, phenyl, naphthyl, biphenyl, anthryl, indenyl, fluorenyl, and the like.

The term " alkenyl " as used herein refers to straight, branched or cyclic hydrocarbon radicals containing from 2 to 10 carbon atoms and at least one carbon to carbon double bond.

The term " alicyclic ring " as used in the present invention means a fully saturated and partially unsaturated hydrocarbon ring of 3 to 12 carbon atoms, including the case where the aryl or heteroaryl is fused, The ring may be more preferably a 5- to 7-membered ring.

As described above, in the overcharge of the secondary battery as described above, while the alkaline metal ions are prevented from escaping from the anode active material and the exothermic decomposition reaction due to the oxygen release is suppressed, the electrolytic solution contains a phosphoric acid lithium salt, a carbonate compound Or a mixture thereof, the additive is decomposed earlier than the organic solvent to effectively and stably form a solid electrolyte interface (SEI) coating on the surface of the anode, thereby preventing the alkali metal ion from escaping into the overcharge, The present inventors have found that the decomposition of the surface of the anode and cathode of the anode and the anode of the cathode is reduced and at the same time the anode resistance is reduced to improve the lifetime characteristics at room temperature and the battery characteristics are improved by reducing the electric resistance.

The present invention provides an electrolyte for a secondary battery and a secondary battery comprising the same, wherein the electrolyte for a secondary battery according to the present invention comprises a non-aqueous organic solvent, an alkali metal salt and a phosphate-based lithium salt, a carbonate Compounds or mixtures thereof.

In the present invention, the 1,3-dithiol-2-thione derivative may be represented by the following formula (1).

[Chemical Formula 1]

(Wherein X ₁ and X ₂ are each independently hydrogen or

ego,

Y represents an ester group (-C (= O) O-), a carbonyl group (-C (= O) -), an ether group (-O-), a thiol group (-S-) (H) -), an alkylamine group (-N (R) -) and a phosphine group (-P (H) -)

Wherein R ₁ is hydrogen or (C ₁ -C 10) alkyl, (C 6 -C 12) aryl, (C 1 -C 10) alkenyl,

X ₁ and X ₂ are both

, R < ₁ > may combine with adjacent substituents to form a ring.)

In the present invention, the 1,3-dithiol-2-thione derivative reduces the anode resistance in the high-frequency region and the anode resistance in the low-frequency region simultaneously, and the output characteristics and lifetime characteristics at high temperature and room temperature can be improved.

In the present invention, the 1,3-dithiol-2-thione derivative includes a cyclic dithiolithione, and the cyclic dithiolithione is decomposed at the cathode to form a SEI film composed of Li ₂ S, a compound of carbon and sulfur This film has a disadvantage in that it has a disadvantage in that the decomposition of the solvent is suppressed but the resistance is somewhat large, the stability at a high temperature is low, and the performance is deteriorated in a high voltage battery of 4.3V or more.

The cyclic dithiolthione used in the present invention can be controlled by introducing a substituent as described above or by introducing an alicyclic ring to thereby adjust the kind and elemental composition ratio of elements such as Li, S, C, and O constituting the SEI film A more excellent film can be formed. Therefore, decomposition of the non-aqueous organic solvent in the electrolyte can be prevented more effectively, thereby improving the room temperature and high temperature service life characteristics of the battery. That is, the electrolyte of the secondary battery of the present invention includes the 1,3-dithiol-2-thione derivative of Formula 1 to lower the resistance of the battery and more efficiently form a solid electrolyte interface (SEI) It is more electrochemically stable than the electrolyte of the secondary battery, so that the output characteristics and lifetime characteristics of the battery can be improved not only at room temperature but also at high temperature.

In the present invention, the formula (1) is preferably a compound wherein X ₁ and X ₂ are both

, And Y is preferably connected to oxygen or sulfur. More preferably, Y is any one of an ester group, an ether group and a thiol group.

Further, it is preferable that R ₁ is (C ₁ -C 10) alkyl, more preferably X ₁ and X ₂ are both

, Each R < ₁ > is preferably linked to form an alicyclic ring of 5 to 9 members.

In the present invention, the 1,3-dithiol-2-thione derivative of the formula (1) may be any one selected from the following formulas (2) to (4) to reduce the resistance and improve the battery performance.

(2)

(3)

[Chemical Formula 4]

(Wherein R ₂ and R ₃ are each independently (C 1 -C 10) alkyl, (C 2 -C 10) alkenyl or (C 6 -C 12) aryl,

R ₄ and R ₅ are each independently (C 1 -C 5) alkyl, (C 2 -C 5) alkenyl,

and n is an integer of 1 to 5.)

(C1-C10) alkyl, (C2-C10) alkyl, (C2-C10) Is (C1-C5) alkyl or (C2-C5) alkenyl, and (C6-C12) aryl is preferably (C6-C10) aryl.

In the present invention, examples of the formulas 2 to 4 include dimethyl 2-thioxo-1,3-dithiole-4,5-dicarboxylate, dicarboxylate, 1,3-dithiole-2-thione, 4,5-ethylenedithio- 1,3-dithiole-2thione), but the present invention is not limited thereto.

In the electrolyte of the secondary battery according to an embodiment of the present invention, the 1,3-dithiol-2-thione derivative of Formula 1 may be contained in an amount of 0.05 to 10% by weight based on the total weight of the electrolytic solution, more preferably 0.5 To 5% by weight. When the content of the 1,3-dithiol-2-thione derivative of the formula (1) is less than 0.05% by weight, an effective SEI film is not formed and the effect of improving the lifetime of the secondary battery is insufficient. A thick and high resistance SEI film may be formed, the effect of increasing the charging / discharging efficiency may be insignificant, and the lifetime performance may be deteriorated.

In the present invention, the additive is for supporting the 1,3-dithiol-2-thione derivative to lower the resistance of the battery and more effectively form a solid electrolyte interface (SEI) coating, A phosphate-based lithium salt, a carbonate compound, or a mixture thereof.

In the present invention, the phosphate-based lithium salt is added to the non-aqueous electrolytic solution to improve the low-temperature output characteristics by forming a solid SEI film on the anode, as well as to suppress the decomposition of the surface of the anode, Can be prevented.

In the present invention, the phosphoric acid-based lithium salt is not limited to the kind within the scope of not impairing the object of the present invention. Examples include lithium difluoro bis (oxalato) phosphate, lithium difluoro Lithium dihydrogen phosphate, lithium difluoro phosphate, lithium phosphate, lithium tetrafluoro oxalate phosphate, lithium difluorobis (methylmalonate) phosphate, and lithium difluoro And lithium difluorobis (ethylmalonate) phosphate).

In the present invention, the carbonate compound acts as an additive for forming SEI by assisting the 1,3-dithiol-2-thione derivative. Examples of the carbonate compound include vinylene carbonate and vinylethylene carbonate. In addition, fluoroethylene carbonate, cyclic sulfite, saturated sulphone, unsaturated sulphone and non-cyclic sulphone can be used alone or as a mixture of two or more kinds But is not limited thereto.

Examples of the cyclic sulfite include ethylene sulfite, methyl ethylene sulfite, ethyl ethylene sulfite, 4,5-dimethylethylene sulfite, 4,5-diethyl ethylene sulfite, propylene sulfite, Diethyl propyl sulfite, 4,6-diethyl propyl sulfite, and 1,3-butylene glycol sulfite. The saturated sulphone includes, for example, 1,3-propane sultone, and 1,4-butane sultone. Examples of the unsaturated sultone include ethene sultone, 1,3-propene sultone, 1,4-butene sultone, Phenolsaltone, and the like. Examples of the non-cyclic sulfone include divinyl sulfone, dimethyl sulfone, diethyl sulfone, methyl ethyl sulfone, and methyl vinyl sulfone.

In the present invention, the additive may be contained in an amount of 0.01 to 10% by weight based on the total electrolyte solution. If it is added in an amount less than 0.01% by weight, it may be difficult to form a SEI film. If it is added in an amount exceeding 10% by weight, performance of the secondary battery such as the life of the secondary battery may be deteriorated.

In the present invention, the non-aqueous organic solvent is not limited to any kind as long as it is included in the electrolyte solution of the secondary battery in the art, but it may be any one selected from linear carbonate solvents, cyclic carbonate solvents, linear ester solvents and cyclic ester solvents Or two or more.

Examples of the non-aqueous linear carbonate-based solvent used in the present invention include any one or two or more selected from dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylpropyl carbonate, ethylmethyl carbonate and methylpropyl carbonate. , And more preferably ethyl methyl carbonate.

Examples of the cyclic carbonate solvent include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate , Vinyl ethylene carbonate, and fluoroethylene carbonate, and more preferably, ethylene carbonate is used.

Examples of the linear ester solvents include methyl propionate, ethyl propionate, propyl acetate, butyl acetate, and ethyl acetate.

The cyclic ester-based solvent may be one or two or more selected from gamma-butyrolactone, caprolactone, and valerolactone.

In the present invention, the non-aqueous organic solvent is more preferably mixed with the linear carbonate solvent: cyclic carbonate solvent in a volume ratio of 1: 9 to 9: 1. This is because the cyclic carbonate solvent has a large polarity and can sufficiently dissociate lithium ions, but has a disadvantage in that the ionic conductivity is low due to the high viscosity. Therefore, by using a linear carbonate solvent having low polarity but low viscosity in the cyclic carbonate solvent, Can be optimized.

The volume ratio of the linear carbonate-based solvent to the cyclic carbonate-based solvent is preferably 2: 8 to 8: 2 in terms of volume ratio and storage stability.

In the present invention, the alkali metal salt is dissociated in the non-aqueous organic solvent to act as a cation, basically enabling the operation of the secondary battery and promoting ion movement between the anode and the cathode.

In the present invention, but are not limited to a type of the alkali metal salts, as the anion with a lithium salt or a sodium salt of a cation _{^{PF 6 -, ClO 4 -,}} BF 4 -, SbF 6 -, AlO 4 -, AlCl 4 -, CF _{^{3 SO 3 -, C 4 F}} 9 SO 3 -, N (C 2 F 5 SO 3) 2 -, N (C 2 F 5 SO 2) 2 -, N (CF 3 SO 2) 2 -, SCN -, _{LiN (C x F 2x + 1} SO 2) (C y F 2y + 1 SO 2) - ( in this example, x, y is 0 or a natural _{number), B (C 2 O 4} ) 2 -, BF 2 (C 2 O ₄ ), LiPF ₄ (C ₂ O ₄ ) ^- , PF ₂ (C ₂ O ₄ ) ₂ ^- and P (C ₂ O ₄ ) ₃ ^- .

The alkali metal salt is preferably dissolved in the non-aqueous organic solvent in the range of 0.6 to 2.0 M, and the use of the alkali metal salt in the range of 0.8 to 1.5 M, considering the properties related to the electric conductivity and the viscosity related to the migration of the alkali metal ion More preferable. When the concentration of the alkali metal salt is less than 0.6M, the electric conductivity of the electrolytic solution is lowered, so that the performance of the electrolytic solution which transfers ions at a high speed between the anode and the cathode of the secondary battery is lowered. When the concentration exceeds 2.0M, There is a problem that the mobility of metal ions is reduced. The alkali metal salt acts as a source of alkali metal ions in the battery, thereby enabling operation of the basic secondary battery.

The secondary battery electrolyte of the present invention is generally electrochemically stable in a temperature range of -20 ° C to 60 ° C so that the life of the secondary battery can be prolonged when applied to the secondary battery and the safety and reliability of the secondary battery can be improved. Accordingly, the secondary battery electrolyte may be applied to any secondary battery such as an alkali metal ion battery, an alkali metal polymer battery, and the like.

In the present invention, the secondary battery electrolyte may contain 0.05 to 10% by weight of 1,3-dithiol-2-thione derivative, 0.01 to 10% by weight of an additive and 85 to 99% by weight of a non-aqueous organic solvent.

The present invention also provides a positive electrode comprising: a) a positive electrode comprising a positive electrode active material capable of absorbing and desorbing alkali metals; b) a negative electrode comprising a negative electrode active material capable of absorbing and desorbing alkali metals; c) a secondary battery electrolyte according to any one of claims 1 to 8; And d) a separator.

The secondary battery is manufactured by a conventional method, and the battery manufactured using the electrolyte solution containing the electrolyte additive of the present invention is excellent in the room temperature and high temperature service life characteristics.

Non-limiting examples of the secondary battery include a lithium metal secondary battery, an alkali metal ion secondary battery, an alkali metal polymer secondary battery, and an alkali metal ion polymer secondary battery.

An anode according to an embodiment of the present invention includes a current collector and a cathode active material layer formed on the current collector. The cathode active material layer may include a cathode active material capable of occluding and releasing an alkali metal, a binder, a conductive material, and the like. The positive electrode active material is preferably a composite metal oxide of at least one selected from the group consisting of cobalt, manganese, and nickel and an alkali metal. In addition to these metals, the employment rate of the metals may be varied. In addition to these metals, Mg, Al, Co, K, Na, Ca, Si, Ti, Sn, V, Ge, Ga, B, As, Zr, Mn, Sr, V, and a rare earth element. Specific examples of the positive electrode active material may include a compound represented by any one of the following formulas:

Li _a A _{1 - b} B _b D ₂ wherein, in the formula, 0.90? A? 1.8, and 0? B? 0.5; Li _a E _{1 - b} B _b O _{2 - c} D _{c where} 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05; LiE _{2 - b} B _b O _{4 - c} D _{c where} 0? B? 0.5, 0? C? 0.05; Li _a Ni _{1 -b- c} Co _b B _c D _? Wherein, in the formula, 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <? Li _a Ni _{1 -b- c} Co _b B _c O _{2 - ?} F _? Wherein, in the formula, 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <? Li _a Ni _{1 -b- c} Co _b B _c O _{2 - ?} F ₂ wherein 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <? Li _a Ni _{1 -b- c} Mn _b B _c D _? Wherein, in the formula, 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <? Li _a Ni _{1 -b- c} Mn _b B _c O _{2 - ?} F _? Wherein, in the formula, 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <? Li _a Ni _{1 -b- c} Mn _b B _c O _{2 - ?} F ₂ wherein 0.90? A? 1.8, 0? B? 0.5, 0? C? 0.05, 0 <? Li _a Ni _b E _c G _d O ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, and 0.001 ≤ d ≤ 0.1; Li _a Ni _b Co _c Mn _d GeO ₂ wherein 0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, and 0.001 ≤ e ≤ 0.1; Li _a NiG _b O ₂ (in the above formula, 0.90? A? 1.8, and 0.001? B? 0.1); Li _a CoG _b O ₂ wherein, in the above formula, 0.90? A? 1.8, and 0.001? B? 0.1; Li _a MnG _b O ₂ (in the above formula, 0.90? A? 1.8, 0.001? B? 0.1); Li _a Mn ₂ G _b O ₄ wherein, in the above formula, 0.90? A? 1.8, and 0.001? B? 0.1; QO _2; QS ₂ ; LiQS ₂ ; V ₂ O ₅ ; LiV ₂ O ₅ ; LiIO ₂ ; LiNiVO _4; Li _(3-f) J ₂ (PO ₄ ) ₃ (0? F? 2); _{Li (3-f) Fe 2} (PO 4) 3 (0≤ f ≤ 2); And LiFePO _4.

In the above formula, A is Ni, Co, Mn or a combination thereof; B is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element or a combination thereof; D is O, F, S, P, or a combination thereof; E is Co, Mn or a combination thereof; F is F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or a combination thereof; Q is Ti, Mo, Mn or a combination thereof; I is Cr, V, Fe, Sc, Y or a combination thereof; J may be V, Cr, Mn, Co, Ni, Cu or a combination thereof.

The negative electrode according to an embodiment of the present invention includes a current collector and a negative electrode active material layer formed on the current collector. The negative electrode active material layer may include a negative electrode active material capable of absorbing and desorbing alkali metals, a binder, a conductive material, and the like. As the negative electrode active material, a carbon material such as crystalline carbon, amorphous carbon, carbon composite, or carbon fiber, a lithium metal, an alloy of lithium and other elements, and the like can be used. Examples of the amorphous carbon include hard carbon, coke, mesocarbon microbead (MCMB) calcined at 1,500 ° C or lower, and mesophase pitch-based carbon fiber (MPCF). The crystalline carbon is a graphite-based material, specifically natural graphite, graphitized coke, graphitized MCMB, and graphitized MPCF. The carbonaceous material is preferably a material having an interplanar distance of 3.35 to 3.38 Å and a crystallite size (Lc) of at least 20 nm by X-ray diffraction. Other elements constituting the alloy with lithium may be aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium or indium.

The anode and / or the cathode according to an embodiment of the present invention may be manufactured by dispersing an electrode active material, a binder and a conductive material, if necessary, a thickener in a solvent to prepare an electrode slurry composition, and applying the slurry composition to an electrode current collector have. As the positive electrode current collector, aluminum or an aluminum alloy may be commonly used, and copper or a copper alloy may be used as the negative electrode current collector. The anode current collector and the anode current collector may be in the form of a foil or a mesh.

The binder according to one embodiment of the present invention acts as a paste for the active material, mutual adhesion of the active material, adhesion to the current collector, buffering effect on expansion and contraction of the active material, and the like. Anything is possible. For example, there may be mentioned polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyethylene oxide, polyvinylpyrrolidone, polyurethane, Polyvinylidene fluoride (PVdF), copolymer of polyhexafluoropropylene-polyvinylidene fluoride (PVdF / HFP)), poly (vinyl acetate), alkylated polyethylene oxide, polyvinyl Butadiene rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene rubber, acrylonitrile-butadiene rubber, polyacrylonitrile, , Epoxy resin, nylon, and the like can be used, but the present invention is not limited thereto. The content of the binder is 0.1 to 30% by weight, preferably 1 to 10% by weight, based on the electrode active material. If the content of the binder is too small, the adhesive force between the electrode active material and the current collector is insufficient. If the content of the binder is too large, the adhesive force is improved but the content of the electrode active material is reduced accordingly.

The conductive material according to one embodiment of the present invention is used for imparting conductivity to an electrode, and any material can be used as an electron conductive material without causing any chemical change in the battery. As the conductive material, at least one selected from the group consisting of a graphite-based conductive material, a carbon black-based conductive material, and a metal or metal compound-based conductive material may be used. Examples of the black graphite conductive material include artificial graphite and natural graphite. Examples of the carbon black conductive material include acetylene black, ketjen black, denkablack, thermal black, channel black black or the like. Examples of metal or metal compound conductive agents include perovskite materials such as tin, tin oxide, tin phosphate (SnPO ₄ ), titanium oxide, potassium titanate, LaSrCoO ₃ and LaSrMnO ₃ have. However, the present invention is not limited to the above-mentioned conductive materials. The content of the conductive material is preferably 0.1 to 10% by weight based on the electrode active material. When the content of the conductive material is less than 0.1% by weight, the electrochemical characteristics are deteriorated, and when it exceeds 10% by weight, the energy density per weight is decreased.

The thickening agent according to an embodiment of the present invention is not particularly limited as long as it can control the viscosity of the active material slurry. For example, carboxymethylcellulose, hydroxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose and the like are used .

As the solvent in which the electrode active material, the binder, the conductive material and the like are dispersed, a non-aqueous solvent or an aqueous solvent is used. Examples of the non-aqueous solvent include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N, N-dimethylaminopropylamine, ethylene oxide and tetrahydrofuran.

The secondary battery of the present invention may include a separator that prevents a short circuit between the anode and the cathode and provides a path for moving the alkali metal ion. Examples of the separator include a polypropylene, a polyethylene, a polyethylene / polypropylene, a polyethylene / polypropylene / Polyolefin-based polymer membranes such as polyethylene, polypropylene / polyethylene / polypropylene, or multi-membranes thereof, microporous films, woven fabrics and nonwoven fabrics can be used. Further, a film coated with a resin having excellent stability may be used for the porous polyolefin film.

The secondary battery of the present invention may have other shapes such as a cylindrical shape, a pouch shape, and the like.

The present invention will be described in detail with reference to the following examples. However, the following examples are only illustrative of the present invention and the scope of the present invention is not limited thereby.

The physical properties of the specimens prepared through Examples and Comparative Examples were measured as follows.

(Cycle life characteristics at room temperature (25 占 폚)

The secondary batteries manufactured through Examples and Comparative Examples were charged at 1 C to 4.3 V and then discharged at 2C. This process was repeated 300 times to measure lifetime characteristics (cycle performance). Cycle performance was evaluated at room temperature (25 캜), and the discharge capacity at 300 cycles, the percentage relative to the initial capacity, and the percentage of initial capacity increased relative to Comparative Example 1 were measured.

(Output characteristics after storage at high temperature (70 ° C))

The secondary batteries prepared in Examples and Comparative Examples were charged at 1 C to 4.3 V and then stored at high temperature (70 ° C) for 7 days. After charging 1C until 4.3V, 1C discharging was performed twice, and discharge output was measured at 0.2, 1, 2, 4C charging and discharging. The output characteristics were evaluated at room temperature (25 ° C.) after storage at high temperature (70 ° C.) for 7 days, and after storage at high temperature (25 ° C.)

(Electrical resistance characteristics after storage at high temperature (70 ° C))

The secondary batteries prepared in Examples and Comparative Examples were charged at 1 C to 4.3 V and then stored at high temperature (70 ° C) for 7 days. After charging 1C until 4.3V, 1C discharging was performed twice and impedance of AC was measured using impedance analyzer. The characteristics were evaluated at room temperature (25 ℃) after storage for 7 days at high temperature (70 ℃), and resistance value was measured after storage at high temperature.

[Example 1]

Li (Ni _0.6 Co _0.2 Mn _0.2 ) O ₂ as a positive electrode active material, polyvinylidene fluoride (PVdF) as a binder and carbon black as a conductive material were mixed in a weight ratio of 92: 4: 4, And dispersed in pyrrolidone to prepare a positive electrode slurry. This slurry was coated on an aluminum foil having a thickness of 20 mu m, followed by drying and rolling to prepare a positive electrode.

Acetylene black as a conductive material and polyvinylidene fluoride (PVdF) as a binder were mixed in a weight ratio of 92: 1: 7 and dispersed in N-methyl-2-pyrrolidone as an anode active material to obtain an anode active material slurry . This slurry was coated on a copper foil having a thickness of 15 mu m, followed by drying and rolling to prepare a negative electrode.

A thickness of 20 mu m Polyethylene (PE) film A separator was stacked and wound and compressed to form a cell using a pouch having a size of 6 mm x 35 mm x 60 mm in size, and the following secondary battery electrolyte was injected to manufacture a lithium secondary battery .

To a mixed solvent of ethylene carbonate (EC): ethyl methyl carbonate (EMC) (EC: EMC = 3: 7 by volume) in which LiPF ₆ was dissolved in 1.0 M of lithium secondary battery electrolyte, dimethyl-2-thioxo-1,3-dithiol -4,5-dicarboxylate (prepared by adding 0.5% by weight of 4,5-ethylenedithio-1,3-dithiole-2-thione) to form a cell using a pouch having a size of 60 mm , The following secondary battery electrolyte was injected to prepare a lithium secondary battery.

[Example 2]

Instead of adding 1.0% by weight of lithium difluoro bis (oxalato) phosphate to the electrolyte for the secondary battery of Example 1, 1.0% by weight of lithium difluorophosphate was added The secondary battery was fabricated in the same manner as described above.

[Example 3]

Except that 1.0 wt% of vinylene carbonate was added instead of 1.0 wt% of lithium difluoro bis (oxalato) phosphate to the electrolyte for the secondary battery of Example 1 A secondary battery was manufactured in the same manner.

[Example 4]

Except that 1.0 wt% of vinylethylene carbonate was added instead of 1.0 wt% of lithium difluoro bis (oxalato) phosphate to the electrolyte for the secondary battery of Example 1 A secondary battery was manufactured in the same manner.

[Example 5]

0.5% by weight of dimethyl 2-thioxo-1,3-dithiole-4,5-dicarboxylate was added to the electrolyte for the secondary battery of Example 1, Except that 0.25% by weight of 1,3-dithiole-2-thione was added instead of 1,3-dithiole-2-thione.

[Example 6]

0.5% by weight of dimethyl 2-thioxo-1,3-dithiole-4,5-dicarboxylate was added to the electrolyte for the secondary battery of Example 2, A secondary battery was prepared in the same manner as in Example 1, except that 0.25 wt% of 1,3-dithiole-2-thione was added instead of 1,3-dithiole-2-thione.

[Example 7]

0.5% by weight of dimethyl 2-thioxo-1,3-dithiole-4,5-dicarboxylate was added to the electrolyte for the secondary battery of Example 3, A secondary battery was prepared in the same manner as in Example 1, except that 0.25 wt% of 1,3-dithiole-2-thione was added instead of 1,3-dithiole-2-thione.

[Example 8]

0.5% by weight of dimethyl 2-thioxo-1,3-dithiole-4,5-dicarboxylate was added to the electrolyte for the secondary battery of Example 4, A secondary battery was prepared in the same manner as in Example 1, except that 0.25 wt% of 1,3-dithiole-2-thione was added instead of 1,3-dithiole-2-thione.

[Example 9]

0.5% by weight of dimethyl 2-thioxo-1,3-dithiole-4,5-dicarboxylate was added to the electrolyte for the secondary battery of Example 1, Except that 0.25 wt% of 4,5-Ethylenedithio-1,3-dithiole-2-thione was added instead of 4-ethylenedithio-1,3-dithiole- A secondary battery was manufactured in the same manner.

[Example 10]

0.5% by weight of dimethyl 2-thioxo-1,3-dithiole-4,5-dicarboxylate was added to the electrolyte for the secondary battery of Example 2, Except that 0.25 wt% of 4,5-Ethylenedithio-1,3-dithiole-2-thione was added instead of 4-ethylenedithio-1,3-dithiole- A secondary battery was produced in the same manner as in Example 1.

[Example 11]

0.5% by weight of dimethyl 2-thioxo-1,3-dithiole-4,5-dicarboxylate was added to the electrolyte for the secondary battery of Example 3, Except that 0.25 wt% of 4,5-Ethylenedithio-1,3-dithiole-2-thione was added instead of 4-ethylenedithio-1,3-dithiole- A secondary battery was produced in the same manner as in Example 1.

[Example 12]

0.5% by weight of dimethyl 2-thioxo-1,3-dithiole-4,5-dicarboxylate was added to the electrolyte for the secondary battery of Example 4, Except that 0.25 wt% of 4,5-Ethylenedithio-1,3-dithiole-2-thione was added instead of 4-ethylenedithio-1,3-dithiole- A secondary battery was produced in the same manner as in Example 1.

[Comparative Example 1]

0.5% by weight of dimethyl 2-thioxo-1,3-dithiole-4,5-dicarboxylate was added to the electrolyte for the secondary battery of Example 1, And 1.0% by weight of lithium difluoro bis (oxalato) phosphate were not added to the secondary battery.

[Comparative Example 2]

0.5% by weight of dimethyl 2-thioxo-1,3-dithiole-4,5-dicarboxylate was added to the electrolyte for the secondary battery of Comparative Example 1, A secondary battery was prepared in the same manner as in Example 1. The results are shown in Table 1. &lt; tb &gt; &lt; TABLE &gt;

[Comparative Example 3]

A secondary battery was produced in the same manner as in Example 1, except that 0.25% by weight of 1,3-dithiole-2-thione was added to the electrolyte for a secondary battery of Comparative Example 1 Respectively.

[Comparative Example 4]

0.25 wt% of 4,5-ethylenedithio-1,3-dithiole-2-thione was added to the electrolyte for the secondary battery of Comparative Example 1 A secondary battery was manufactured in the same manner as in Example 1.

[Comparative Example 5]

A secondary battery was prepared in the same manner as in Example 1, except that 1.0 wt% of lithium difluoro bis (oxalato) phosphate was added to the electrolyte for the secondary battery of Comparative Example 1.

[Comparative Example 6]

A secondary battery was prepared in the same manner as in Example 1, except that 1.0 weight% of lithium difluorophosphate was added to the electrolyte for the secondary battery of Comparative Example 1.

[Comparative Example 7]

A secondary battery was prepared in the same manner as in Example 1, except that 1.0% by weight of vinylene carbonate was added to the electrolyte for the secondary battery of Comparative Example 1.

[Comparative Example 8]

A secondary battery was prepared in the same manner as in Example 1, except that 1.0 wt% of vinylethylene carbonate was added to the secondary battery electrolyte of Comparative Example 1.

[Table 1]

[Table 2]

[Table 3]

As shown in Table 1, the secondary batteries according to Examples 1 to 12 of the present invention showed life characteristics in which the cycle capacity ratio to the initial capacity was improved in comparison with Comparative Examples 1 to 8 at 300 cycles. Among them, the secondary battery of Example 3, to which 0.5% by weight of dimethyl 2-thioxo-1,3-dithiol-4,5-dicarboxylate and 0.5% by weight of vinylene carbonate was added, And 97.29% as a percentage of capacity.

As shown in Table 2, it can be seen that the secondary battery according to Examples 1 to 12 of the present invention has excellent output characteristics after being stored at high temperature for 7 days, as compared with Comparative Examples. Specifically, 0.25 wt% of 4,5-ethylenedithio-1,3-dithiole-2-thione, and lithium difluorobisoxalate phosphate ( Lithium difluoro bis (oxalato) phosphate 1.0% by weight The secondary battery of Example 9, which was stored for 7 days at high temperature (70 ° C), showed the best output characteristics with an output value of 46.22 W.

As shown in Table 3, it can be seen that the secondary batteries according to Examples 1 to 12 of the present invention had better resistance characteristics after being stored at high temperature for 7 days than the comparative example. Specifically, 0.25 wt% of 4,5-ethylenedithio-1,3-dithiole-2-thione, and lithium difluorobisoxalate phosphate ( Lithium difluoro bis (oxalato) phosphate 1.0 wt% The battery of Example 9 showed the lowest cell resistance with a resistance value of 0.029 Z / Ohm after being stored at high temperature (70 ° C) for 7 days.

Also, as shown in FIG. 1, the 2-thioxo-1,3-dithiol-4,5-dicarboxylate compound, the 1,3-dithiol-2-thione compound and the phosphoric acid type lithium salt, the vinylidene carbonate type The secondary battery including the compound as an electrolyte additive improves the performance of the battery by simultaneously reducing the resistance of the negative electrode in the high frequency range and the resistance of the positive electrode in the low frequency range.

As described above, the electrolyte for a secondary battery according to the present invention comprises a thioxo-1,3-dithiol-4,5-dicarboxylate compound which effectively and stably forms a SEI (solid electrolyte interface) When the 3-dithiol-2-thione compound is combined with at least one of a negative electrode at high temperature, a phosphate-based lithium salt and a vinylidene carbonate compound which inhibits decomposition of the surface of the positive electrode, the output characteristics and electrochemical characteristics Is further improved.

While the invention has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims. Therefore, the above description does not limit the scope of the present invention, which is defined by the limitations of the following claims.

Claims (11)

a) an alkali metal salt;
b) non-aqueous organic solvent;
c) a 1,3-dithiol-2-thione derivative represented by the following formula 3 or 4; And
d) an additive that is lithium difluorobisoxalatophosphate, lithium difluorophosphate, vinylene carbonate or vinylethylene carbonate;
Wherein the secondary battery electrolyte is a lithium secondary battery.
(3)

[Chemical Formula 4]

(In the formula 3 or 4 wherein R ₄ and R ₅ are each independently alkyl (C1-C5),
n is an integer of 2.) delete delete delete The method according to claim 1,
Wherein the non-aqueous organic solvent is any one or more selected from a linear carbonate-based solvent, a cyclic carbonate-based solvent, a linear ester-based solvent, and a cyclic ester-based solvent. 6. The method of claim 5,
Wherein the linear carbonate-based solvent is any one or two or more selected from the group consisting of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethylpropyl carbonate, ethylmethyl carbonate and methylpropyl carbonate,
The cyclic carbonate-based solvent 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, Carbonate, and fluoroethylene carbonate,
Wherein the linear ester solvent is at least one selected from methyl propionate, ethyl propionate, propyl acetate, butyl acetate and ethyl acetate,
Wherein the cyclic ester-based solvent is at least one selected from gamma-butyrolactone, caprolactone, and valerolactone. 6. The method of claim 5,
Wherein the non-aqueous organic solvent is a linear carbonate-based solvent: a cyclic carbonate-based solvent mixed in a volume ratio of 1: 9 to 9: 1. The method according to claim 1,
Wherein the alkali metal salt is contained in the non-aqueous organic solvent at a concentration of 0.6 to 2.0M. 9. The method of claim 8,
The alkali metal salt includes a lithium salt or a sodium salt as a cation and an anion such as PF ₆ ^- , ClO ₄ ^- , BF ₄ ^- , SbF ₆ ^- , AlO ₄ ^- , AlCl ₄ ^- , CF ₃ SO ₃ ^- , C ₄ F ₉ SO ^{_{3 -, N (C 2 F}} 5 SO 3) 2 -, N (C 2 F 5 SO 2) 2 -, N (CF 3 SO 2) 2 -, SCN -, LiN (C x F 2x + 1 SO 2 _{) (C y F 2y + 1} SO 2) - ( in this example, x, y is 0 or a natural _{number), B (C 2 O 4} ) 2 -, BF 2 (C 2 O 4), LiPF 4 (C 2 O 4 ) ^- , PF ₂ (C ₂ O ₄ ) ₂ ^- and P (C ₂ O ₄ ) ₃ ^- . The method according to claim 1,
Wherein the secondary battery electrolyte is 0.05 to 10 wt% of a 1,3-dithiol-2-thione derivative, 0.01 to 10 wt% of an additive, and 85 to 99 wt% of a non-aqueous organic solvent. a) a positive electrode comprising a positive electrode active material capable of occluding and releasing an alkali metal;
b) a negative electrode comprising a negative electrode active material capable of absorbing and desorbing alkali metals;
c) a secondary battery electrolyte according to any one of claims 1 and 5 to 8; And
d) a separator;
And a secondary battery.

Images