KR20180027996A - Electrolyte agent and lithium secondary battery comprising the same - Google Patents

Abstract

The present invention is to provide an electrolyte additive which comprises a nitrogen atom-containing compound-derived anion, and a salt with Cs^+ or Rb^+, and to provide an electrolyte additive which further comprises lithium difluoro bisoxalato phosphate. Also, according to the present invention, provided are a non-aqueous electrolyte containing a lithium salt, a non-aqueous organic solvent, and the electrolyte additive, and a lithium secondary battery containing a positive electrode including a positive active material, a negative electrode including a negative active material, a separator interposed between the positive electrode and the negative electrode, and the non-aqueous electrolyte. According to the present invention, the secondary battery formed by containing the electrolyte additive has excellent high- and low-temperature lifespan characteristics, high-temperature storage characteristics, and thickness change rate. According to another embodiment of the present invention, the secondary battery, formed by containing an electrolyte additive including a compound containing a nitrogen atom-containing compound-derived anion and a salt with Cs^+ or Rb^+, and lithium difluoro bisoxalato phosphate, has excellent high temperature output characteristics.

Description

ELECTROLYTE AGENT AND LITHIUM SECONDARY BATTERY COMPRISING THE SAME Technical Field [1] The present invention relates to an electrolyte additive,

The present invention relates to an electrolyte additive and a lithium secondary battery including the same in a non-aqueous electrolyte.

BACKGROUND ART [0002] With the development of the information communication industry in recent years, electronic devices are becoming smaller, lighter, thinner, and portable. As a result, there is a growing demand for higher energy density of batteries used as power sources for such electronic devices. Lithium secondary batteries are the ones that can best meet this demand, and researches thereon are actively being carried out.

The lithium secondary battery includes a positive electrode, a negative electrode, and an electrolyte solution for providing a pathway for lithium ions between the positive electrode and the negative electrode, and a separator. The lithium secondary battery is characterized in that the lithium ions are oxidized and reduced when lithium ions are intercalated and deintercalated in the positive and negative electrodes To generate electrical energy.

The average discharge voltage of the lithium secondary battery is about 3.6 to 3.7 V, which is one of merits that the discharge voltage is higher than other alkaline batteries and nickel-cadmium batteries. In order to achieve such a high driving voltage, an electrochemically stable electrolyte composition is required at a charge / discharge voltage range of 0 to 4.2V.

During the initial charging of the lithium secondary battery, lithium ions from the cathode active material such as lithium metal oxide migrate to the anode active material such as a graphite system and are inserted between the layers of the anode active material. At this time, since lithium is highly reactive, the electrolyte constituting the anode active material on the surface of the anode active material such as a graphite system reacts with carbon constituting the anode active material to produce compounds such as Li ₂ CO ₃ , Li ₂ O or LiOH. These compounds form a SEI (Solid Electrolyte Interface) film on the surface of a negative active material such as a graphite system.

The SEI membrane acts as an ion tunnel, allowing only lithium ions to pass through. The SEI membrane is an effect of this ion tunnel, which prevents organic solvent molecules moving together with lithium ions in the electrolyte from being intercalated between the layers of the negative electrode active material and destroying the negative electrode structure. Therefore, the electrolytic solution is not decomposed by preventing the contact between the electrolytic solution and the negative electrode active material, and the amount of lithium ions in the electrolytic solution is reversibly maintained, so that stable charge / discharge is maintained.

It has been difficult to expect an improvement in lifetime characteristics due to the formation of an uneven SEI film in the case of an electrolyte 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 a required amount, the surface of the anode may be decomposed or the oxidation reaction may occur during high temperature or high voltage reaction due to the electrolyte additive, thereby ultimately increasing the irreversible capacity of the secondary battery There is a problem that the lifetime characteristics are deteriorated.

A problem to be solved by the present invention is to provide a novel electrolyte additive.

In addition, another object of the present invention is to provide a lithium secondary battery including a cathode including a cathode active material, a cathode including a cathode active material, a separator interposed between the cathode and the anode, and a nonaqueous electrolyte containing the electrolyte additive of the present invention .

In order to solve the above problems, the present invention provides an electrolyte additive comprising a salt of Cs ⁺ or Rb ⁺ with an anion derived from a nitrogen atom-containing compound.

The present invention also provides an electrolyte additive wherein the electrolyte additive further comprises lithium difluorobisoxalatephosphate.

The present invention provides a non-aqueous electrolytic solution comprising a lithium salt, a non-aqueous organic solvent, and the electrolyte additive.

The present invention also provides a positive electrode comprising a positive electrode active material, a negative electrode including a negative electrode active material, a separator interposed between the positive electrode and the negative electrode, and a lithium secondary battery comprising the nonaqueous electrolyte.

The secondary battery formed with the electrolyte additive according to an embodiment of the present invention is excellent in high temperature and low temperature lifetime characteristics, high temperature storage characteristics, and rate of change in thickness.

Further, a secondary battery formed by including a compound including a salt of Cs ⁺ or Rb ⁺ with an anion derived from a nitrogen atom-containing compound and an electrolyte additive comprising lithium difluorobisoxalatephosphate according to another embodiment of the present invention High temperature output characteristics are excellent.

1 is a graph showing high-temperature output characteristics of 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.

The novel electrolyte additive according to one embodiment of the present invention may contain a salt of Cs ⁺ or Rb ⁺ with an anion derived from a nitrogen atom-containing compound.

Here, the anion derived from the nitrogen atom-containing compound may be one or more selected from the group consisting of amide anion, imide anion, nitrile anion, nitrite anion, and nitrate anion.

Specifically, the amide-based anion is selected from the group consisting of dimethylformamide anion, dimethylacetamide anion, diethylformamide anion, diethylacetamide anion, methylethylformamide anion, and methylethylacetamide anion Or more.

The imide anion may be represented by the following formula (1).

[Chemical Formula 1]

Here, R ₁ and R ₂ are each fluorine or fluoroalkyl having 1 to 4 carbon atoms, or R ₁ and R ₂ may be connected to each other to form a ring having a fluoroalkylene group having 1 to 4 carbon atoms.

The nitrile anion may be selected from the group consisting of an acetonitrile anion, a propionitrile anion, a butyronitrile anion, a valeronitrile anion, a caprylonitrile anion, a heptanenitrile anion, a cyclopentanecarbonitrile anion, a cyclohexanecarbonyl anion, Which is composed of a nitrile anion, a 4-fluorobenzonitrile anion, a difluorobenzonitrile anion, a trifluorobenzonitrile anion, a phenylacetonitrile anion, a 2-fluorophenylacetonitrile anion, and a 4-fluorophenylacetonitrile anion It may be one or more kinds selected from the group.

Further, the compound represented by the formula (1) may be one or more selected from the group consisting of the following formulas (2) to (6).

(2)

(3)

[Chemical Formula 4]

[Chemical Formula 5]

[Chemical Formula 6]

According to one embodiment of the present invention, the electrolyte additive is selected from the group consisting of cesium bis (trifluoromethanesulfonyl) imide, cesium nitrate, rubidium bis (trifluoromethanesulfonyl) imide, and rubidium nitrate Or at least one selected from the group.

In addition, the present invention can provide a non-aqueous electrolytic solution comprising a lithium salt, a non-aqueous organic solvent, and the electrolyte additive.

The additive may form a coating on the surfaces of the positive electrode and the negative electrode in the electrolyte solution. Generally, in an environment in which the secondary battery is repeatedly charged and discharged, the oxidation reaction proceeds on the surface of the anode, and the reduction reaction proceeds on the surface of the cathode. The additive according to an embodiment of the present invention can effectively prevent the dissolution of lithium ions generated from the anode by forming a film on the surface of the anode and the cathode, and prevent the anode from being decomposed. More specifically, the film formed by the additive on the surface of the negative electrode is partially decomposed by a reduction reaction during charging and discharging, but the decomposed additive moves to the surface of the positive electrode again to form a film on the surface of the positive electrode through the oxidation reaction have. Therefore, even when charging and discharging are repeated several times, the additive can keep the coating on the surface of the positive electrode and effectively prevent the excessive elution of lithium ions from the positive electrode. The reason for this is not clarified, but Cs ⁺ or Rb ⁺ possessed by the additive according to an embodiment of the present invention is an ion of an alkaline group element and is attributed to chemical properties close to Li ⁺ present in the anode and the cathode I guess. Therefore, the secondary battery according to an embodiment of the present invention can maintain the high temperature and low temperature lifetime characteristics of the secondary battery without deteriorating its structure even when the anode is repeatedly charged and discharged.

Conventionally, when a conventional electrolyte or additive is used in a lithium secondary battery, the additive causes degradation of the surface of the anode and oxidation of the electrolyte due to an increase in reactivity between the anode and the electrolyte, . This phenomenon is particularly troublesome in that, when stored at a low temperature or a high temperature, the conventional additives are decomposed too much to form a very thick insulator on the anode, thereby preventing the lithium ion from migrating and causing no recovery capacity at all Respectively.

However, the additive according to one embodiment of the present invention can improve the safety of the battery by reducing the negative reactivity between the positive electrode and the electrolyte and the generated contact surface. It is possible to prevent deterioration of the battery performance due to the decomposition of the conventional additives and the rapid change of the reaction potential due to the high reaction potential and almost no change in the reaction potential with the progress of the cycle. Further, the additive forms a stable film through an oxidation reaction at the anode, thereby preventing decomposition of the anode and suppressing elution, so that the anode can be more stably protected under a high voltage environment.

According to another embodiment of the present invention, the additive may further include a different kind of additive for improving the stability and output of the lithium secondary battery. This may further include lithium difluorobisoxalatephosphate in an additive containing a salt of Cs ⁺ or Rb ⁺ with an anion derived from the above nitrogen atom-containing compound, and more specifically, cesium bis (trifluoromethane (Trifluoromethanesulfonyl) imide, and rubidium nitrate, and lithium difluorobisoxalatephosphate as the cesium compound, and at least one compound selected from the group consisting of sodium bisulfate, .

Lithium difluorobisoxalate phosphate can form a stable SEI film on the surface of the positive electrode and the negative electrode. The additive containing a salt of a nitrogen atom-containing compound and a salt of Cs ⁺ or Rb ⁺ is lithium difluorobisoxalatephosphate And SEI coatings of the positive electrode and the positive electrode formed from lithium difluorobisoxalatephosphate can be more uniformly formed and the movement of lithium ions is facilitated in accordance with the formation of a uniform coating film It is possible to secure more improved output characteristics.

In order to achieve the above-mentioned effects, it is preferable that the additive including the salt with Cs ⁺ or Rb ⁺ and lithium difluorobisoxalate phosphate are contained in the electrolytic solution in a weight ratio of 1: 1 to 4.

According to an embodiment of the present invention, the content of the additive may be 0.05 to 10% by weight based on the total amount of the non-aqueous electrolytic solution. Preferably, the content of the additive may be 0.1 to 3% by weight based on the total weight of the non-aqueous electrolytic solution.

If the content of the additive is less than 0.05% by weight, the effects of improving the low-temperature and high-temperature storage characteristics and high-temperature lifetime characteristics of the lithium secondary battery are insignificant. If the content of the additive exceeds 10% by weight, This may cause an increase in the problem.

Particularly, when the additive is applied to a lithium secondary battery, the stability of the secondary battery formed by minimizing the rate of change in thickness and improving the low temperature and high temperature storage characteristics and high temperature lifetime characteristics of the additive including Cs ⁺ or Rb ⁺ In addition to the effect of improving secondary battery life and resistance characteristics particularly at high temperatures, high temperature output characteristics of the secondary battery formed due to uniform film formation can be secured.

Examples of the lithium salt include lithium salts such as LiPF ₆ , LiFSI, LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiBF ₆ , LiSbF ₆ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiAlO ₄ , LiAlCl ₄ , LiSO ₃ CF ₃ , LiTFSI, LiDFOB and LiClO ₄ , or a mixture of two or more thereof. The concentration of the lithium salt in the non-aqueous electrolytic solution is preferably 0.01 mole / liter to 2 mole / liter, more preferably 0.01 mole / liter to 1 mole / liter.

Examples of the non-aqueous organic solvent used in the present invention include, but are not limited to, ethers, esters, amides, linear carbonates, cyclic carbonates, phosphoric acid-based compounds, Nitrile-based compounds, fluorinated ether-based compounds, and fluorinated aromatic compounds may be used alone or in combination of two or more.

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.

Particularly, the cyclic carbonate in the carbonate electrolyte solution preferably contains propylene carbonate, ethylene carbonate, and a mixture thereof. The organic solvent is preferably a high-viscosity organic solvent because it has a high dielectric constant and dissociates the lithium salt in the electrolyte solution.

The cyclic carbonate is preferably a mixture of diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate, and a linear carbonate, which is a mixture thereof. These materials can be used more preferably because they can produce an electrolytic solution having a high electric conductivity when mixed with a low viscosity, low dielectric constant linear carbonate in an appropriate ratio.

Examples of the esters in the electrolyte solvent include esters such as methyl acetate, ethyl acetate, propyl acetate, ethyl propionate (EP), propyl propionate, methyl propionate (MP),? -Butyrolactone,? -Valerolactone ,? -caprolactone,? -valerolactone and? -caprolactone, or a mixture of two or more thereof. Of these, ethyl propionate (EP) having a particularly low viscosity, Propyl propionate, methyl propionate (MP), and mixtures thereof.

The phosphoric acid-based solvent and the mononitrile-based solvent may be substituted with fluorine atoms (F). When the solvent is substituted with a halogen element, the flame retardancy is further increased. However, when the solvent is substituted with Cl, Br or I, the reactivity of the solvent increases to become undesirable as an electrolyte solution.

In the nonaqueous electrolyte solution of the present invention, non-limiting examples of the phosphate compound include trimethylphosphine oxide, triethylphosphine oxide, tripropylphosphine oxide, triphenylphosphine oxide, diethylmethylphosphonate, di Diphenylmethylphosphonate, bis (2,2,2-trifluoroethyl) methylphosphonate, trimethylphosphate, triethylphosphate, tripropylphosphate, ethylmethylphenylphosphate, and the like. These phosphoric acid-based solvents may be used alone or in combination of two or more.

Nonlimiting examples of the nitrile compound include acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, 2-fluorobenzyl Nitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, 4-fluorophenylacetonitrile, and the like. These nitrile-based solvents may be used alone or in combination of two or more.

Non-limiting examples of the fluorinated ether compound include bis-, 2,2-trifluoroethyl ether, n-butyl 1,1,2,2-tetrafluoroethyl ether, 2,2,3,3- 3,3-pentafluoropropyl methyl ether, 2,2,3,3,3-pentafluoropropyl 1,1,2,2-tetrafluoroethyl ether, 1,1,2,2-tetrafluoroethyl Methyl ether, 1,1,2,2-tetrafluoroethyl ethyl ether, and trifluoroethyl dodecafluorohexyl ether. These fluorinated ether-series solvents may be used alone or in combination of two or more.

Examples of the aromatic compound solvent include, but are not limited to, halogenated benzene compounds such as chlorobenzene, chlorotoluene and fluorobenzene, tert-butylbenzene, tert-pentylbenzene, cyclohexylbenzene, hydrogen biphenyl, And the like. The alkyl group of the alkylated aromatic compound may be halogenated, and examples thereof include fluorinated ones. Examples of such a fluorinated compound include trifluoromethoxybenzene and the like.

Meanwhile, the lithium secondary battery according to an embodiment of the present invention may include a cathode including a cathode active material, a cathode including a cathode active material, a separator interposed between the cathode and the cathode, and the non-aqueous electrolyte.

In the positive electrode, the positive electrode active material can be used without limitation as long as it is a compound capable of reversibly intercalating / deintercalating lithium.

In the lithium secondary battery according to the embodiment of the present invention, the cathode active material may be a lithium-transition metal oxide of spinel having a multilayered salt-bed structure having a high bulk characteristic, an olivine structure, a cubic structure, V ₂ O ₅ , TiS , MoS, or a composite oxide of two or more of them. More specifically, it may include, for example, any one selected from the group consisting of oxides of the following general formulas (7) to (9), or a mixture of two or more thereof:

(7)

Li [Ni _a Co _b Mn _c ] O ₂ (0.1?? C?? 0.5, 0 <a + b <0.9, a + b + c = 1);

[Chemical Formula 8]

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);

[Chemical Formula 9]

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, 0? A?? 0.2, 0.5? 1).

The positive electrode active material is preferably _{Li [Ni 0.6 Co 0.2 Mn 0.2} ] O 2, Li (Ni 0.5 Co 0.2 Mn 0.3) O 2, Li [Ni 1/3 Co 1/3 Mn 1/3] O 2, and LiCoO ₂ , or a mixture of two or more thereof.

According to a particularly preferred embodiment, by using Li [Ni _a Co _b Mn _c ] O ₂ for the anode, it can have a synergistic action in combination with the compound of the formula (1) of the present invention. The positive electrode active material of the lithium-nickel-manganese-cobalt-based oxide has such a structure that the Li +1 + and Ni +2 ions in the layered structure of the positive electrode active material in the charge / the cationic mixing may occur and the structure may become unstable. Thus, the cathode active material may cause a side reaction with the electrolyte or elution of the transition metal. Therefore, when the electrolyte additive of Formula 1 according to an embodiment of the present invention is used, it is assumed that cation mixing of the ions can be minimized.

On the other hand, examples of the negative electrode active material include amorphous carbon or regular carbon, specifically carbon such as non-graphitized carbon or graphite carbon; _{LixFe 2 O 3 (0≤≤x≤≤1),} LixWO 2 (0≤≤x≤≤1), SnxMe 1 - x Me 'y O z (Me: Mn, Fe, Pb, Ge; Me': Al , B, P, Si, Group 1, Group 2, and Group 3 elements of the periodic table, halogen, and 0 <x <1; 1 <= y <= 3; 1 <= z <8); Lithium metal; Lithium alloy; Silicon-based alloys; Tin alloy; _{SnO, SnO 2, PbO, PbO} 2, Pb 2 O 3, Pb 3 O 4, Sb 2 O 3, Sb 2 O 4, Sb 2 O 5, GeO, GeO 2, Bi 2 O 3, Bi 2 O 4, And Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

The separation membrane 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, and 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 positive electrode and / or negative electrode may be prepared by preparing a slurry by mixing and stirring a binder and a solvent, a conductive agent and a dispersant, which may be conventionally used, if necessary, and then applying the slurry to a current collector and compressing the slurry.

Examples of the binder include polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HEP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, Polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, 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.

According to an embodiment of the present invention, the lithium secondary battery including the additive may undergo a formation and aging process to secure the performance of the secondary battery.

The formation process activates the battery by repeating charging and discharging after assembling the battery. Lithium ions from the lithium metal oxide used as an anode during charging are transferred to and inserted into a carbon electrode used as a cathode. At this time, Because of its strong reactivity, it reacts with the carbon anode to produce compounds such as Li ₂ CO ₃ , LiO, and LiOH, which form a solid electrolyte interface (SEI) coating on the surface of the cathode. In addition, the aging process stabilizes the activated battery by leaving it for a certain period of time.

The SEI film is formed on the surface of the negative electrode through the above forming process. The SEI film is generally stabilized by a room temperature aging step, that is, by allowing to stand at a room temperature for a certain period of time. The lithium secondary battery using the non-aqueous liquid containing the additive according to the embodiment of the present invention can be used not only in the room temperature aging step but also in the high temperature aging step, by the lithium and the cobalt elements Cs and Rb, It can be confirmed that the problems such as reduction of stability or decomposition thereof do not occur.

The formation step is not particularly limited, and can be semi-charged at 1.0 to 3.8V or fully charged at 3.8 to 4.3V. The C-RATE may be charged at a current density of 0.1 C to 2 C for 5 minutes to 1 hour.

The aging step may be performed at room temperature or at a temperature in the range of 60 to 100 DEG C (high temperature). If the temperature exceeds 100 ° C, there is a possibility that the casing is ruptured due to evaporation of the electrolytic solution or the battery is ignited. The remaining capacity SOC of the battery may be in any range from 100%, which is the fully charged state, to 0%, due to the discharge. The storage time is not particularly limited, but is preferably about 1 hour to 1 week.

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 can 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.

Examples and Comparative Examples

Example 1

[Preparation of electrolytic solution]

Aqueous organic solvent having a composition of ethylene carbonate (EC): ethylmethyl carbonate (EMC): diethyl carbonate (DEC) = 30: 50: 20 (volume ratio), LiPF ₆ as a lithium salt in an amount of 1.15 and 0.5 wt% of cesium bis (trifluoromethanesulfonyl) imide was added as an additive based on the total amount of the non-aqueous electrolytic solution to prepare a non-aqueous electrolytic solution.

[Production of lithium secondary battery]

As the cathode active material, Li (Ni _0.5 Co _0.2 Mn _0.3 ) O ₂ (NMP) as a solvent, 4 wt% of carbon black as a conductive agent and 4 wt% of polyvinylidene fluoride (PVdF) as a binder were added to the positive electrode mixture slurry . The positive electrode mixture slurry was applied to an aluminum (Al) thin film having a thickness of about 20 탆 and dried to produce a positive electrode, followed by a roll press to prepare a positive electrode.

Further, 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 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.

A pouch-type battery was fabricated by a conventional method together with a separator composed of three layers of a polypropylene / polyethylene / polypropylene (PP / PE / PP) anode and cathode thus prepared, and the non-aqueous electrolyte thus prepared was injected into lithium The preparation of the secondary battery was completed.

Example 2

A nonaqueous electrolytic solution and a lithium secondary battery were produced in the same manner as in Example 1 except that the content of cesium bis (trifluoromethanesulfonyl) imide as the additive was 0.7% by weight based on the total amount of the nonaqueous electrolytic solution Respectively.

Example 3

A nonaqueous electrolytic solution and a lithium secondary battery were produced in the same manner as in Example 1 except that the content of cesium bis (trifluoromethanesulfonyl) imide as the additive was 1 wt% based on the total amount of the nonaqueous electrolytic solution Respectively.

Example 4

A nonaqueous electrolytic solution and a lithium secondary battery were produced in the same manner as in Example 1, except that the content of cesium bis (trifluoromethanesulfonyl) imide as the additive was 3 wt% based on the total amount of the nonaqueous electrolytic solution Respectively.

Example 5

A non-aqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that cesium nitrate was used in an amount of 0.5 wt% instead of cesium bis (trifluoromethanesulfonyl) imide as the additive.

Example 6

A nonaqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that cesium nitrate was used in an amount of 0.7 wt% instead of cesium bis (trifluoromethanesulfonyl) imide as the additive.

Example 7

A non-aqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that cesium nitrate was used in an amount of 1.0 wt% instead of the additive cesium bis (trifluoromethanesulfonyl) imide.

Example 8

A non-aqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 1 except that cesium nitrate was used in an amount of 3.0 wt% instead of the additive cesium bis (trifluoromethanesulfonyl) imide.

Example 9

Except that 0.5 wt% of rubidium bis (trifluoromethanesulfonyl) imide was used in place of cesium bis (trifluoromethanesulfonyl) imide as the additive, a nonaqueous electrolytic solution and a lithium secondary A battery was prepared.

Example 10

A non-aqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that 0.5 wt% of rubidium nitrate was used instead of cesium bis (trifluoromethanesulfonyl) imide as the additive.

Example 11

Except that the content of cesium bis (trifluoromethanesulfonyl) imide as the additive was 0.5% by weight based on the total amount of the non-aqueous electrolytic solution and 0.5% by weight of lithium difluorobisoxalatephosphate was added A non-aqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 1.

Example 12

The content of cesium nitrate in place of cesium bis (trifluoromethanesulfonyl) imide as the additive was 0.5% by weight based on the total amount of the non-aqueous electrolytic solution and 0.5% by weight of lithium difluorobisoxalatephosphate A nonaqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 1.

Example 13

A non-aqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that Li [Ni _1/3 Co _1/3 Mn _1/3 ] O ₂ was used as the cathode active material.

Example 14

A nonaqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that the cathode active material was used as LiCoO ₂ .

Example 15

A non-aqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 1 except that 0.03 wt% of cesium bis (trifluoromethanesulfonyl) imide additive was added to the non-aqueous electrolytic solution.

Example 16

To the non-aqueous electrolytic solution was added cesium bis (trifluoromethanesulfonyl) imide A nonaqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that the additive was added in an amount of 11 wt%.

Example 17

In place of cesium bis (trifluoromethanesulfonyl) imide, cesium nitrate A nonaqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that the additive was added in an amount of 0.03 wt%.

Example 18

In place of cesium bis (trifluoromethanesulfonyl) imide, cesium nitrate A nonaqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that the additive was added in an amount of 11 wt%.

Experiment and evaluation

High Temperature Life Evaluation

The lithium secondary battery was charged at a constant current of 1.5 C rate at a high temperature (45 DEG C) until the voltage reached 4.20 V (vs. Li), then maintained at 4.20 V in a constant voltage mode, (cut-off). Subsequently, discharge was performed at a constant current of 1.5 C rate until the voltage reached 3.0 V (vs. Li) (1st cycle). The above cycle was repeated up to 300 cycles. The experimental results are shown in Tables 1 and 2.

Remarks High temperature life characteristics Initial cycle capacity (mAh) 300th cycle capacity (mAh) Capacity retention rate (%)
300th capacity / initial capacity * 100 (%) Example 1 911.2 644.31 70.71 Example 2 910.74 638.70 70.13 Example 3 910.09 632.60 69.51 Example 4 898.21 612.04 68.14 Example 5 908.49 634.94 69.89 Example 6 907.89 628.35 69.21 Example 7 907.18 619.97 68.34 Example 8 905.63 608.22 67.16 Example 9 902.15 624.38 69.21 Example 10 901.24 615.01 68.24 Example 11 912.13 644.69 70.68 Example 12 908.29 635.62 69.98 Example 13 912.13 636.76 69.81 Example 14 908.29 623.81 68.68

Remarks High temperature life characteristics Initial cycle capacity (mAh) 300th cycle capacity (mAh) Capacity retention rate (%)
300th capacity / initial capacity * 100 (%) Example 15 907.97 546.42 60.18 Example 16 889.23 501.08 56.35 Example 17 908.31 544.35 59.93 Example 18 884.23 480.58 54.35

Low temperature service life evaluation

Until the lithium secondary battery reaches a voltage of 4.20 V (vs. Li) at a current of 0.5 C rate at room temperature (25 ° C.) - low temperature (-10 ° C.) - low temperature (-20 ° C.) - room temperature (25 ° C.) Charged at constant current, and then cut off at a current of 0.05 C rate while maintaining 4.20 V in constant voltage mode. Then, at the time of discharging, the battery was discharged at a constant current of 0.5 C rate until the voltage reached 3.0 V (vs. Li) (1st cycle). The above-mentioned cycle was repeated 10 times in sequence according to each temperature. The capacity at the last cycle after repeating 10 times was measured and the capacity of the last cycle after the completion of all of the above cycles (room temperature (25 ° C) - low temperature (-10 ° C) - low temperature (-20 ° C) - room temperature The cycle capacity was measured to calculate the capacity retention rate. The results of the charge-discharge experiments are shown in Tables 3 and 4.

Remarks Low temperature service life characteristics Room temperature cycle capacity (mAh) -10 캜 Cycle capacity (mAh) -20 캜 Cycle capacity (mAh) After the low temperature evaluation, the room temperature cycle capacity (mAh) Capacity retention rate (%)
After the low temperature evaluation, the room temperature capacity / the initial room temperature capacity * 100 (%) Example 1 899.25 536.72 218.85 415.82 46.24 Example 2 898.16 534.12 217.5 413.17 46.00 Example 3 897.84 532.48 216.82 411.15 45.79 Example 4 896.68 529.28 214.96 405.29 45.20 Example 5 896.81 533.18 215.18 412.3 45.97 Example 6 895.18 531.84 214.79 407.17 45.48 Example 7 893.37 529.76 213.14 402.23 45.02 Example 8 890.19 526.27 211.41 399.41 44.87 Example 9 890.84 527.18 208.24 405.74 45.55 Example 10 887.21 526.87 206.74 401.84 45.29 Example 11 900.84 537.86 219.72 416.62 46.25 Example 12 897.75 534.74 216.71 413.21 46.03 Example 13 898.54 532.18 216.48 413.96 46.07 Example 14 896.43 530.26 214.86 411.52 45.91

Remarks Low temperature service life characteristics Room temperature cycle capacity (mAh) -10 캜 Cycle capacity (mAh) -20 캜 Cycle capacity (mAh) After the low temperature evaluation, the room temperature cycle capacity (mAh) Capacity retention rate (%)
After the low temperature evaluation, the room temperature capacity / the initial room temperature capacity * 100 (%) Example 15 896.96 363.06 111.68 285.82 31.87 Example 16 889.19 353.45 104.18 272.14 30.61 Example 17 895.86 361.06 110.2 283.13 31.60 Example 18 887.52 352.13 102.23 270.17 30.44

60 ℃ storage characteristics

The secondary batteries of Examples and Comparative Examples were placed in a chamber maintained at 25 占 폚, and a charging / discharging test was carried out as follows using a charging / discharging device. First, the battery was charged to 60% of the SOC (state of charge) at 1 C, and discharged / charged at 0.2 C for 10 seconds. Then, it was discharged / charged at 0.5 C for 10 seconds. Thereafter, the batteries were discharged and charged in the same manner as 1C, 2C and 3C for 10 seconds. Finally, it was charged to 4.2V at 0.5C. The initial impedance (DC-IR) was obtained by calculating the slope of the voltage-to-current graph by using the voltage value after 0.2C, 0.5C, 1C, 2C, and 3C discharge. The battery measuring the initial impedance was placed in a chamber maintained at 60 캜 and measured for 4 weeks (measured every week until 4th week), and the impedance (DC-IR) was calculated. The results are shown in Table 5 and Table 6.

Remarks Storage characteristics Initial Impedance (mΩ) Impedance after storage at 60 ℃ (mΩ) (after 4 W) Rate of change (%)
(M?) / Initial (m?) * 100 (%) after 60 占 폚 Example 1 47.5 79 166.32 Example 2 47.8 80.6 168.62 Example 3 48.4 81.9 169.21 Example 4 50.1 85.6 170.86 Example 5 48.4 84 173.55 Example 6 48.9 85.1 174.03 Example 7 49.8 87.4 175.50 Example 8 51.4 91.7 178.40 Example 9 48.1 81.1 168.61 Example 10 50.1 87.5 174.65 Example 11 47.2 78.8 166.95 Example 12 48.1 83.4 173.39 Example 13 47.9 80.8 168.68 Example 14 48.2 82.1 170.33

Remarks Storage characteristics Initial Impedance (mΩ) Impedance after storage at 60 ℃ (mΩ) (after 4 W) Rate of change (%)
(M?) / Initial (m?) * 100 (%) after 60 占 폚 Example 15 43.1 82.2 190.72 Example 16 45.5 90.6 199.12 Example 17 42.9 82.4 192.07 Example 18 46.1 92.5 200.65

Measurement of thickness change rate

The following experiments were conducted to examine the rate of change of the thickness of the secondary battery manufactured in the examples and the comparative examples.

The life characteristics of the lithium secondary battery were charged and discharged at 0.1 C for the first cycle, and then charged and discharged at 0.5 C for the subsequent cycle. The thickness change rate was measured by disassembling each lithium secondary battery in the 300th cycle charging state and comparing the electrode thickness with the electrode thickness before the first cycle. The results are shown in Tables 7 and 8.

-Thickness change ratio: electrode thickness in the 300th cycle in the charged state-electrode thickness before the first cycle) / electrode thickness before the first cycle 占 100

Remarks Thickness change ratio (%) Example 1 107.24 Example 2 107.66 Example 3 108.18 Example 4 109.14 Example 5 108.53 Example 6 108.75 Example 7 109.09 Example 8 110.24 Example 9 108.19 Example 10 109.23 Example 11 108.36 Example 12 109.98 Example 13 108.96 Example 14 108.78

Remarks Thickness change ratio (%) Example 15 113.21 Example 16 117.25 Example 17 114.12 Example 18 118.29

As can be seen from the above table, it can be confirmed that the secondary batteries of the embodiments of the present invention are significantly superior to the secondary batteries in terms of high temperature, low temperature lifetime characteristics, high temperature storage characteristics, and thickness variation rate.

Example 19

[Preparation of electrolytic solution]

Aqueous organic solvent having a composition of ethylene carbonate (EC): ethylmethyl carbonate (EMC): diethyl carbonate (DEC) = 30: 50: 20 (volume ratio), LiPF ₆ as a lithium salt in an amount of 1.15 and 0.5% by weight of cesium bis (trifluoromethanesulfonyl) imide and 1% by weight of lithium difluorobisoxalatephosphate (weight ratio 1: 2) were added as additives based on the total amount of the non-aqueous electrolytic solution To prepare a non-aqueous electrolytic solution.

[Production of lithium secondary battery]

As the cathode active material, Li (Ni _0.5 Co _0.2 Mn _0.3 ) O ₂ (NMP) as a solvent, 4 wt% of carbon black as a conductive agent and 4 wt% of polyvinylidene fluoride (PVdF) as a binder were added to the positive electrode mixture slurry . The positive electrode mixture slurry was applied to an aluminum (Al) thin film having a thickness of about 20 탆 and dried to produce a positive electrode, followed by a roll press to prepare a positive electrode.

Further, 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 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.

A pouch-type battery was fabricated by a conventional method together with a separator composed of three layers of a polypropylene / polyethylene / polypropylene (PP / PE / PP) anode and cathode thus prepared, and the non-aqueous electrolyte thus prepared was injected into lithium The preparation of the secondary battery was completed.

Example 20

As in the case of Example 19 except that 0.5% by weight of cesium bis (trifluoromethanesulfonyl) imide and 0.5% by weight of lithium difluorobisoxalatephosphate (weight ratio 1: 1) were used as the electrolyte additive To prepare a nonaqueous electrolytic solution and a lithium secondary battery.

Example 21

As in the case of Example 19 except that 0.5% by weight of cesium bis (trifluoromethanesulfonyl) imide and 2% by weight of lithium difluorobisoxalatephosphate (weight ratio 1: 4) were used as the electrolyte additive To prepare a nonaqueous electrolytic solution and a lithium secondary battery.

Example 22

As in the case of Example 19 except that 0.5% by weight of rubidium bis (trifluoromethanesulfonyl) imide and 1% by weight of lithium difluorobisoxalatephosphate (weight ratio 1: 2) were used as the electrolyte additive To prepare a nonaqueous electrolytic solution and a lithium secondary battery.

Example 23

As in the case of Example 19, except that 0.5% by weight of cesium bis (trifluoromethanesulfonyl) imide and 0.25% by weight of lithium difluorobisoxalatephosphate (weight ratio 1: 0.5) were used as the electrolyte additive To prepare a nonaqueous electrolytic solution and a lithium secondary battery.

Example 24

As in the case of Example 19 except that 0.5% by weight of cesium bis (trifluoromethanesulfonyl) imide and 2.25% by weight of lithium difluorobisoxalatephosphate (weight ratio 1: 4.5) were used as the electrolyte additive To prepare a nonaqueous electrolytic solution and a lithium secondary battery.

Comparative Example 1

Except that 0.5 wt% of cesium bis (trifluoromethanesulfonyl) imide and 0.5 wt% of gamma butylo lactone (GBL) (weight ratio 1: 1) were used as the electrolyte additive A non-aqueous electrolytic solution and a lithium secondary battery were prepared in the same manner as in Example 15.

Evaluation of high-temperature output characteristics

The voltage difference output generated by storing the lithium secondary batteries of Example 1, Examples 19 to 24, and Comparative Example 1 at 60 占 폚 and discharging the battery from SOC 50% to 5C for 10 seconds was calculated. The results are shown in Fig.

Referring to FIG. 1, it is assumed that cesium bis (trifluoromethanesulfonyl) imide (or rubidium bis (trifluoromethanesulfonyl) imide) and lithium difluorobisoxalate phosphate The high-temperature output of the lithium secondary batteries of Examples 19 to 24 is superior to the high-temperature output of Example 1 and Comparative Example 1 which are not. In particular, it can be seen that the difference in the high-temperature output characteristics becomes more significant after the storage period of 7 weeks.

Claims (17)

An electrolyte additive comprising a salt of an anion derived from a nitrogen atom-containing compound and Cs ⁺ or Rb ⁺ . The method according to claim 1,
Wherein the anion derived from the nitrogen atom-containing compound is at least one selected from the group consisting of an amide anion, an imide anion, a nitrile anion, a nitrite anion, and a nitrate anion. The method of claim 2,
The amide-based anion is at least one selected from the group consisting of dimethylformamide anion, dimethylacetamide anion, diethylformamide anion, diethylacetamide anion, methylethylformamide anion, and methylethylacetamide anion Electrolyte additive. The method of claim 2,
Wherein the imide anion is represented by the following formula (1).
[Chemical Formula 1]

Wherein R ₁ and R ₂ are each fluorine or fluoroalkyl having 1 to 4 carbon atoms or R ₁ and R ₂ are connected to each other to form a ring having a fluoroalkylene group having 1 to 4 carbon atoms. The method of claim 2,
The nitrile anion may be selected from the group consisting of an acetonitrile anion, a propionitrile anion, a butyronitrile anion, a valeronitrile anion, a caprylonitrile anion, a heptanenitrile anion, a cyclopentanecarbonitrile anion, a cyclohexanecarbonyl anion, Which is composed of a nitrile anion, a 4-fluorobenzonitrile anion, a difluorobenzonitrile anion, a trifluorobenzonitrile anion, a phenylacetonitrile anion, a 2-fluorophenylacetonitrile anion, and a 4-fluorophenylacetonitrile anion Lt; RTI ID = 0.0 &gt; 1, &lt; / RTI &gt; The method of claim 4,
Wherein the compound represented by the formula (1) is at least one selected from the group consisting of the following formulas (2) to (6).
(2)

(3)

[Chemical Formula 4]

[Chemical Formula 5]

[Chemical Formula 6]

The method according to claim 1,
The electrolyte additive includes at least one selected from the group consisting of cesium bis (trifluoromethanesulfonyl) imide, cesium nitrate, rubidium bis (trifluoromethanesulfonyl) imide, and rubidium nitrate The electrolyte additive. The method according to any one of claims 1 to 7,
&Lt; / RTI &gt; wherein the electrolytic solution further comprises lithium difluorobisoxalate phosphate. The method of claim 8,
Wherein the electrolyte additive comprises a salt of Cs ⁺ or Rb ⁺ with an anion derived from a nitrogen atom-containing compound, and lithium difluorobisoxalate phosphate in a weight ratio of 1: 1 to 4. Lithium salts;
Non-aqueous organic solvent; And
A non-aqueous electrolytic solution comprising the electrolyte additive of claim 8. The method of claim 10,
Wherein the content of the electrolyte additive is 0.05 to 10% by weight based on the total amount of the non-aqueous electrolytic solution. The method of claim 10,
The lithium salt is selected from the group consisting of LiPF ₆ , LiFSI, LiAsF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiBF ₆ , LiSbF ₆ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiAlO ₄ , LiAlCl ₄ , LiSO ₃ CF ₃ , LiTFSI, LiDFOB, and LiClO ₄ , or a mixture of two or more thereof. The method of claim 10,
Wherein the lithium salt comprises LiPF ₆ . The method of claim 10,
The non-aqueous organic solvent may be selected from the group consisting of ether, ester, amide, linear carbonate, cyclic carbonate, phosphoric acid compound, nitrile compound, fluorinated ether compound, fluorinated aromatic compound, Electrolytic solution. A cathode comprising a cathode active material;
A negative electrode comprising a negative electrode active material;
A separator interposed between the anode and the cathode; And
A lithium secondary battery comprising the non-aqueous electrolyte according to claim 8. 16. The method of claim 15,
Wherein the cathode active material is any one selected from the group consisting of oxides of the following general formulas (7) to (9), or a mixture of two or more thereof:
(7)
Li [Ni _a Co _b Mn _c ] O ₂ (0.1?? C?? 0.5, 0 <a + b <0.9, a + b + c = 1);
[Chemical Formula 8]
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);
[Chemical Formula 9]
_{Li 1 + a Co x M 1} - x BX 4 (M = Al, Mg, Ni, selected from the group consisting of Co, Mn, Ti, Ga, Cu, V, Nb, Zr, Ce, In, Zn , and Y X is at least one element selected from the group consisting of O, F and N, B is P, S or a mixed element thereof, and 0? A?? 0.2, 0.5? X? 1). 16. The method of claim 15,
The cathode active material may be Li [Ni _0.6 Co _0.2 Mn _0.2 ] O ₂ , Li Ni _0.5 Co _0.2 Mn _0.3 O _{2 ,} Li [Ni _1/3 Co _1/3 Mn _1/3 ] O ₂ , and LiCoO ₂ And a mixture of two or more thereof.

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