Electrolyte additive for lithium secondary battery, electrolyte for lithium secondary battery comprising same, and lithium secondary battery

Abstract

The present invention aims to provide an electrolyte additive for lithium secondary batteries represented by the following Chemical Formula 1, an electrolyte for lithium secondary batteries containing the same, and a lithium secondary battery. In Chemical Formula 1, R1 to R4 each independently represent hydrogen, deuterium, C1-C6 alkyl, or C3-C6 cycloalkyl, and n represents an integer of 0 to 2. The electrolyte additive for lithium secondary batteries according to the present invention can improve the high-temperature life of a lithium secondary battery, and can improve the capacity recovery rate, thickness increase rate, and resistance increase rate upon high-temperature storage.[Chemical Formula 1]

Description

Technical Field

[0001] The present invention aims to provide an electrolyte additive for lithium secondary batteries represented by the following chemical formula 1, an electrolyte for lithium secondary batteries containing the additive, and a lithium secondary battery.

[0002] [Chemical Formula 1]

[0003] (In the above chemical formula 1, R1 to R4 each independently represent hydrogen, deuterium, C1-C6 alkyl or C3-C6 cycloalkyl, and n represents an integer from 0 to 2.)

[0004] The electrolyte additive for lithium secondary batteries according to the present invention can improve the high-temperature life of lithium secondary batteries and improve the capacity recovery rate, thickness increase rate and resistance increase rate during high-temperature storage. Background Technology

[0005] Batteries are used as power sources for portable electronic devices such as cameras, mobile phones, and laptops. Rechargeable lithium-ion batteries have more than three times the energy density per unit weight compared to existing lead-acid, nickel-cadmium, nickel-metal hydride, and nickel-zinc batteries, and can be charged at high speeds.

[0006] The demand for such lithium secondary batteries is increasing dramatically, so a lot of research has been conducted on lithium secondary batteries with high energy density and discharge voltage, and they have been commercialized and widely used.

[0007] Compared with other batteries, lithium-ion batteries have advantages such as light weight, small size, high operating voltage, high energy density, high output power, high charging efficiency, no memory effect, and long lifespan. Therefore, they are widely used in digital products such as mobile phones and laptops, and are particularly considered one of the best choices for electric vehicles and large-scale energy storage devices.

[0008] Recently, with the continuous advancement of the development of medium and large-sized lithium secondary batteries such as those for electric vehicles, various studies are being conducted to achieve high-voltage and high-capacity lithium secondary batteries. In particular, there is a need for suitable additives that can improve high-temperature lifespan and have excellent properties during high-temperature storage.

[0009] On the other hand, regarding electrolyte additives for lithium secondary batteries, the following prior art literature exists.

[0010] Prior art document 1. Korean Patent Publication No. 10-2179846

[0011] Prior art document 2. Korean Patent Publication No. 10-2440653

[0012] Prior art document 3. Korean Patent Publication No. 10-2440657

[0013] Prior art document 4. Korean Patent Publication No. 10-2440658 Summary of the Invention

[0014] Technical issues

[0015] The inventors have conducted intensive research to improve the high-temperature lifespan characteristics of lithium secondary batteries, as well as the capacity recovery rate, thickness increase rate, and resistance increase rate during high-temperature storage. The results show that when using the electrolyte additive of the present invention, it can exhibit a capacity retention rate of more than 80% after 300 cycles at 45°C, a capacity recovery rate of more than 90% after 4 weeks at 60°C, a thickness increase rate of less than 5%, and / or a resistance increase rate of less than 30% (refer to Examples 1 to 6), thereby completing the present invention.

[0016] Therefore, the object of the present invention is to provide an electrolyte additive for lithium secondary batteries represented by the following chemical formula 1, and more preferably, to provide an electrolyte additive represented by the following chemical formula 2.

[0017] [Chemical Formula 1]

[0018] (In the above chemical formula 1, R1 to R4 each independently represent hydrogen, deuterium, C1-C6 alkyl or C3-C6 cycloalkyl, and n represents an integer from 0 to 2.)

[0019] [Chemical Formula 2]

[0020] Furthermore, the object of the present invention is to provide an electrolyte for lithium secondary batteries comprising an electrolyte additive represented by the above-described chemical formula 1, and more preferably comprising an electrolyte additive represented by the above-described chemical formula 2.

[0021] Furthermore, the object of the present invention is to provide a lithium secondary battery comprising an electrolyte additive for a lithium secondary battery represented by the above chemical formula 1, and more preferably comprising an electrolyte additive represented by the above chemical formula 2.

[0022] The purpose of this invention is not limited to the purposes mentioned above. Other purposes and advantages of this invention not mentioned can be understood through the following description and can be more clearly understood through the practice of this invention.

[0023] Furthermore, it is readily apparent that the objectives and advantages of the present invention can be achieved by means and combinations thereof shown in the claims.

[0024] Solution to the problem

[0025] This invention discloses an electrolyte additive for lithium secondary batteries, an electrolyte for lithium secondary batteries, and a lithium secondary battery.

[0026] According to the first embodiment, an electrolyte additive for lithium secondary batteries represented by the following chemical formula 1 is disclosed.

[0027] [Chemical Formula 1]

[0028] (In the above chemical formula 1, R1 to R4 each independently represent hydrogen, deuterium, C1-C6 alkyl or C3-C6 cycloalkyl, and n represents an integer from 0 to 2.)

[0029] In this invention, the above-mentioned electrolyte additive for lithium secondary batteries can be represented by the following chemical formula 2.

[0030] [Chemical Formula 2]

[0031] According to the second embodiment, an electrolyte for lithium secondary batteries is disclosed, which includes an organic solvent, a lithium salt, and an additive according to the above-described chemical formula 1 or chemical formula 2.

[0032] In this invention, the above-mentioned additives may be included in 0.005 to 10% by weight based on the weight of the electrolyte.

[0033] In this invention, the organic solvent may include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), or combinations thereof.

[0034] In this invention, the lithium salt may comprise LiPF6, LiFSI, LiDFOB, LiBF4, LiAsF6, LiCF3SO3, LiC(CF3SO2)3, LiN(SO2C2F5)2, LiN(SO2C2F3)2, LiN(SO2F3)2, LiSbF6, LiPF3(CF2CF3)3, LiPF3(CF3)3, or combinations thereof.

[0035] In this invention, the above-mentioned additive may further contain 0.5 to 3% by weight of vinylene carbonate (VC) based on the weight of the electrolyte.

[0036] In this invention, the additive may further comprise, based on the weight of the electrolyte, 0.5 to 3% by weight of vinylene carbonate (VC), 0.5 to 3% by weight of propane sulfonate lactone (PS), and 0.1 to 1.5% by weight of vinyl sulfate (ESA). Furthermore, the additive may further comprise, based on the weight of the electrolyte, 100 to 10,000 ppm of triphenyl phosphite (TPPI).

[0037] According to the third embodiment, a lithium secondary battery is disclosed, comprising: an electrolyte containing an additive according to the above-described chemical formula 1 or chemical formula 2; a positive electrode; and a negative electrode.

[0038] The effects of the invention

[0039] The electrolyte additive for lithium secondary batteries according to the present invention can improve the high-temperature life of lithium secondary batteries and improve the capacity recovery rate, thickness increase rate and resistance increase rate during high-temperature storage. Detailed Implementation

[0040] Unless otherwise defined, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Generally, the nomenclature used in this specification is well-known and commonly used in the art.

[0041] Furthermore, when a part of this specification states that it "includes" a certain constituent element, this does not mean that other constituent elements are excluded, but rather that other constituent elements may be further included unless otherwise stated otherwise.

[0042] 1. Electrolyte additives for lithium secondary batteries

[0043] The present invention provides an electrolyte additive for lithium secondary batteries represented by the following chemical formula 1.

[0044] [Chemical Formula 1]

[0045] (In the above chemical formula 1, R1 to R4 each independently represent hydrogen, deuterium, C1-C6 alkyl or C3-C6 cycloalkyl, and n represents an integer from 0 to 2.)

[0046] In the electrolyte additive for lithium secondary batteries according to the present invention, the additive can be represented by the following chemical formula 2.

[0047] [Chemical Formula 2]

[0048] 2. Electrolyte for lithium secondary batteries

[0049] This invention provides an electrolyte for lithium secondary batteries, comprising:

[0050] Organic solvents, lithium salts, and An electrolyte additive for lithium secondary batteries represented by the following chemical formula 1.

[0051] [Chemical Formula 1]

[0052] (In the above chemical formula 1, R1 to R4 each independently represent hydrogen, deuterium, C1-C6 alkyl or C3-C6 cycloalkyl, and n represents an integer from 0 to 2.)

[0053] As a non-limiting example of the present invention, more preferably, the above-mentioned organic solvent may include carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, aprotic solvents, or combinations thereof.

[0054] For example, the aforementioned carbonate solvents may include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, ethyl propyl carbonate, diethyl carbonate (DEC), dipropyl carbonate, propylene carbonate (PC), ethylene carbonate (EC), fluoroethylene carbonate (FEC), or butylene carbonate. The aforementioned ester solvents may include methyl acetate (MA), ethyl acetate (EA), n-propyl acetate (n-PA), 1,1-dimethylethyl acetate (DMEA), methyl propionate (MP), ethyl propionate (EP), γ-butyrolactone (γGBL), decanolide, valerolactone, mevalonolactone, or caprolactone.

[0055] For example, the aforementioned ether organic solvents may include dibutyl ether, tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether (DEGDME), dimethoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The aforementioned ketone solvents may include cyclohexanone.

[0056] For example, the alcohol solvents mentioned above may include ethanol (ethyl alcohol) and isopropyl alcohol (isopropyl alcohol).

[0057] For example, the aforementioned aprotic solvents may include nitrile solvents, amide solvents, dioxolane solvents such as 1,3-dioxolane, or sulfolane solvents.

[0058] As a non-limiting example of the present invention, more preferably, the lithium salt may comprise LiPF6, LiFSI, LiDFOB, LiBF4, LiAsF6, LiCF3SO3, LiC(CF3SO2)3, LiN(SO2C2F5)2, LiN(SO2C2F3)2, LiN(SO2F3)2, LiSbF6, LiPF3(CF2CF3)3, LiPF3(CF3)3, or combinations thereof.

[0059] As a non-limiting example of the invention, more preferably, the lithium salt may be contained in the solvent at a concentration of 0.01 to 5 M, preferably 0.1 to 2 M. Within the above range, the transfer of lithium ions and / or electrons during the charging and discharging of the lithium secondary battery is promoted, thereby ensuring increased capacity.

[0060] In the electrolyte for lithium secondary batteries according to the present invention, the above-mentioned additive can be represented by the following chemical formula 2.

[0061] [Chemical Formula 2]

[0062] In the lithium secondary battery electrolyte according to the present invention, the above-mentioned additive may be contained in amounts of 0.005% by weight or more, 0.01% by weight or more, 0.05% by weight or more, 0.1% by weight or more, 0.2% by weight or more, 0.3% by weight or more, 0.5% by weight or more, 0.8% by weight or more, 1.0% by weight or more, 10% by weight or less, 5% by weight or less, 3% by weight or less, or 2% by weight or less, based on the weight of the electrolyte. Within the above ranges, improved capacity retention can be observed when repeated 300 times at 45°C, and improved capacity recovery rate, thickness increase rate, and resistance increase rate after 4 weeks at 60°C.

[0063] In the electrolyte for lithium secondary batteries according to the present invention, the above-mentioned additives may further comprise, as additional additives, vinylene carbonate (VC), propanesultone (PS), ethylene sulfate (ESA), triphenyl phosphite (TPPI), or combinations thereof. In this case, the total content of the additional additives or combinations thereof, excluding the additives represented by the above-described chemical formula 1, may be 0.5% by weight or more, 1.0% by weight or more, 5% by weight or less, 3% by weight or less, or 2% by weight or less, based on the weight of the electrolyte.

[0064] In one exemplary embodiment, the electrolyte for lithium secondary batteries according to the present invention may further contain vinylene carbonate (VC) in addition to the additives represented by the above-described chemical formula 1. In this case, the vinylene carbonate (VC) may be contained at 0.5 to 3% by weight, preferably 1.0 to 1.5% by weight, based on the weight of the electrolyte. Furthermore, in this case, the weight ratio of the additives represented by the above-described chemical formula 1 to vinylene carbonate (VC) may be 0.1:1 to 10:1, preferably 0.5:1 to 5:1.

[0065] In one exemplary embodiment, the electrolyte for lithium secondary batteries according to the present invention may also contain, in addition to the additives represented by the above-described chemical formula 1, vinylene carbonate (VC), propane sulfonate lactone (PS), and vinyl sulfate (ESA). In this case, the vinylene carbonate (VC) may be contained at 0.5 to 3% by weight, preferably 1.0 to 1.5% by weight, based on the weight of the electrolyte; the propane sulfonate lactone (PS) may be contained at 0.5 to 3% by weight, preferably 1.0 to 1.5% by weight, based on the weight of the electrolyte; and the vinyl sulfate (ESA) may be contained at 0.1 to 1.5% by weight, preferably 0.5 to 1.0% by weight, based on the weight of the electrolyte. Furthermore, in this case, the weight ratio of the additive represented by Formula 1 to vinylene carbonate (VC) can be from 0.1:1 to 10:1, preferably from 0.5:1 to 5:1; the weight ratio of the additive represented by Formula 1 to propane sulfonate lactone (PS) can be from 0.1:1 to 5:1, preferably from 0.5:1 to 5:1; and the weight ratio of the additive represented by Formula 1 to vinyl sulfate (ESA) can be from 0.1:0.5 to 15:1, preferably from 0.5:1 to 10:1.

[0066] In one exemplary embodiment, the electrolyte for lithium secondary batteries according to the present invention, in addition to the additives represented by the above-described chemical formula 1, may also contain vinylene carbonate (VC), propane sulfonate lactone (PS), vinyl sulfate (ESA), and triphenyl phosphite (TPPI). In this case, the vinylene carbonate (VC) may be contained at 0.5 to 3% by weight, preferably 1.0 to 1.5% by weight, based on the weight of the electrolyte; the propane sulfonate lactone (PS) may be contained at 0.5 to 3% by weight, preferably 1.0 to 1.5% by weight, based on the weight of the electrolyte; the vinyl sulfate (ESA) may be contained at 0.1 to 1.5% by weight, preferably 0.5 to 1.0% by weight, based on the weight of the electrolyte; and the triphenyl phosphite (TPPI) may be contained at 100 to 10,000 ppm, preferably 300 to 1,000 ppm, based on the weight of the electrolyte. Furthermore, in this case, the weight ratio of the additive represented by Formula 1 to vinylene carbonate (VC) can be from 0.1:1 to 10:1, preferably from 0.5:1 to 5:1; the weight ratio of the additive represented by Formula 1 to propane sulfonate lactone (PS) can be from 0.1:1 to 5:1, preferably from 0.5:1 to 5:1; the weight ratio of the additive represented by Formula 1 to vinyl sulfate (ESA) can be from 0.1:0.5 to 15:1, preferably from 0.5:1 to 10:1; and the weight ratio of the additive represented by Formula 1 to triphenyl phosphite (TPPI) can be from 1:0.01 to 1:0.5.

[0067] 3. Lithium secondary batteries

[0068] The present invention aims to provide a lithium secondary battery comprising...

[0069] The electrolyte used in the above-mentioned lithium secondary batteries; Positive electrode; and negative electrode.

[0070] In the lithium secondary battery according to the present invention, the positive electrode may include a current collector and a positive electrode active material layer formed on the current collector. Aluminum can be used as the current collector, but it is not limited thereto. The positive electrode active material layer may include a positive electrode active material, a binder, and optionally a conductive agent. The binder may be selected, for example, from polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, cellulose diacetate, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, or combinations thereof. The conductive agent is used to impart conductivity to the electrode; any material can be used as long as it is an electronically conductive material that does not cause chemical changes in the battery. Examples of the conductive agent may be selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, metal powders such as copper, nickel, aluminum, and silver, metal fibers, polyphenylene derivatives, or combinations thereof. In one exemplary embodiment, the above-mentioned positive electrode active material can be represented by the following chemical formula 1.

[0071] [Chemical Formula 3]

[0072] LiNi a Co b Mn c M d O2

[0073] Given 0.1≤a≤0.98, 0.01≤b≤0.9, 0.01≤c≤0.9, 0.0≤d≤0.05, and a+b+c+d=1, The M mentioned above can be selected from Al, Mg, Fe, Cu, Zn, Cr, Ag, Ca, Na, K, In, Ga, Ge, V, Mo, Nb, Si, Ti, or combinations thereof. In the above chemical formula 1, a is preferably 0.5 to 0.98, most preferably 0.6 to 0.98; b is preferably 0.01 to 0.3, most preferably 0.05 to 0.1; c is preferably 0.01 to 0.3, most preferably 0.05 to 0.1; and d is preferably 0 to 0.1 or less. In the lithium secondary battery according to the present invention, the negative electrode may include a current collector and a negative electrode active material layer formed on the current collector. As the current collector, copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or a combination thereof may be used. The negative electrode active material layer may include a negative electrode active material, a binder composition, and / or a conductive agent. The negative electrode active material may include a material capable of reversibly inserting / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0074] In the lithium secondary battery according to the present invention, the lithium secondary battery may further include a separator that prevents short circuits between the positive and negative electrodes and provides a channel for the movement of lithium ions. The separator may be a polyolefin polymer film such as polypropylene, polyethylene, polyethylene / polypropylene, polyethylene / polypropylene / polyethylene, polypropylene / polyethylene / polypropylene, or a multilayer film, microporous film, woven fabric, or nonwoven fabric thereof. Furthermore, a film coated with a resin of excellent stability on a porous polyolefin film may also be used, but the invention is not limited thereto.

[0075] In the lithium secondary battery according to the present invention, the shape of the lithium secondary battery may include square, cylindrical or pouch type.

[0076] In the lithium secondary battery according to the present invention, the lithium secondary battery can exhibit a capacity retention rate of more than 80% after 300 cycles at 45°C, a capacity recovery rate of more than 90% after 4 weeks at 60°C, a thickness increase rate of less than 5%, and / or a resistance increase rate of less than 30%.

[0077] The present invention will be specifically described below through embodiments. However, the embodiments and experimental examples described below are only illustrative of one form of the present invention, and the scope of the present invention is not limited to the embodiments and experimental examples described below.

[0078] Preparation of the electrolyte additive of chemical formula 2 of the present invention

[0079] [Reaction Formula 1]

[0080] An electrolyte additive of chemical formula 2 according to the present invention was prepared according to the above reaction formula 1.

[0081] 1 st Step: In a 250 mL three-necked jacketed reactor, 16.04 g of catechol and 80.18 g (5 vol) of isopropyl ether (IPE) were added and the mixture was cooled and stirred (below -10 °C). While maintaining the internal temperature, phosphorus trichloride was added dropwise (non-exothermic, approximately every 10 minutes). The mixture was then heated to room temperature and reacted for 48 hours (GC analysis confirmed the completion of the reaction). The reactants were filtered through a membrane filter and transferred to a 250 mL single-necked flask (to remove unreacted substances and byproducts). The solids were removed using a nitrogen filter and the mixture was dried. The solvent and HCl gas (a reaction byproduct) were removed under reduced pressure to obtain a pale yellow liquid (yield approximately 40%).

[0082] 2 nd Step: In a 500 ml three-necked flask, add 50 g of 1,3,2-benzodioxaphosphole (2-chloro) and 100 g (5 vol.) of isopropyl ether and mix. Then, add 10.41 g (0.4 eq) of antimony trifluoride at room temperature. React the mixture at room temperature for 2 hours, filter through a membrane filter, and transfer to a 250 ml flask. Add 50 ml of 5% NaHCO3 and 50 ml of deionized water (DIW) to the mixture, perform one workup for each, and separate the organic layer. Treat the organic layer with MgSO4 to remove trace amounts of water, and concentrate the filtrate under reduced pressure to remove the solvent, yielding a white solid with a yield of 90% (GC purity 98.5%).

[0083] Preparation of electrolyte

[0084] [Preparation Example 1]

[0085] A basic electrolyte was prepared by dissolving LiPF6 in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (EC:EMC=25:75v / v%) to achieve a concentration of 1M.

[0086] [Preparation Example 2]

[0087] An electrolyte was prepared by adding 1.0% by weight of vinylene carbonate (VC) to the basic electrolyte of Preparation Example 1 above.

[0088] [Preparation Example 3]

[0089] An electrolyte was prepared by adding 0.01% by weight of the electrolyte additive of chemical formula 2 of the present invention to the electrolyte of Preparation Example 2 above.

[0090] [Preparation Example 4]

[0091] An electrolyte was prepared by adding 0.05% by weight of the electrolyte additive of chemical formula 2 of the present invention to the electrolyte of Preparation Example 2 above.

[0092] [Preparation Example 5]

[0093] An electrolyte was prepared by adding 0.1% by weight of the electrolyte additive of chemical formula 2 of the present invention to the electrolyte of preparation example 2 above.

[0094] [Preparation Example 6]

[0095] An electrolyte was prepared by adding 0.2% by weight of the electrolyte additive of chemical formula 2 of the present invention to the electrolyte of preparation example 2 above.

[0096] [Preparation Example 7]

[0097] An electrolyte was prepared by adding 0.3% by weight of the electrolyte additive of chemical formula 2 of the present invention to the electrolyte of preparation example 2 above.

[0098] [Preparation Example 8]

[0099] An electrolyte was prepared by adding 0.5% by weight of the electrolyte additive of chemical formula 2 of the present invention to the electrolyte of the above preparation example 2.

[0100] [Preparation Example 9]

[0101] An electrolyte was prepared by adding 1.0% by weight of the electrolyte additive of chemical formula 2 of the present invention to the electrolyte of Preparation Example 2 above.

[0102] [Preparation Example 10]

[0103] An electrolyte was prepared by adding 2.0% by weight of the electrolyte additive of chemical formula 2 of the present invention to the electrolyte of preparation example 2 above.

[0104] [Preparation Example 11]

[0105] An electrolyte was prepared by adding 5.0% by weight of the electrolyte additive of chemical formula 2 of the present invention to the electrolyte of the above preparation example 2.

[0106] [Preparation Example 12]

[0107] An electrolyte was prepared by adding 1.0 wt% of the electrolyte additive of chemical formula 2 of the present invention, 1.0 wt% of PS and 0.5 wt% of ESA to the electrolyte of Preparation Example 2 above.

[0108] [Preparation Example 13]

[0109] An electrolyte was prepared by adding 1.0 wt% of the electrolyte additive of chemical formula 2 of the present invention, 1.0 wt% of PS, 0.5 wt% of ESA and 500 ppm of TPPI to the electrolyte of Preparation Example 2 above.

[0110] Preparation of lithium secondary batteries

[0111] Will contain Li[Ni 0.9 Co 0.05 Mn 0.05A positive electrode active material slurry was prepared by adding 96 wt% of NCM-based positive electrode active material (O2), 2 wt% of carbon black as a conductive agent, and 2 wt% of polyvinylidene fluoride (PVdF) as a binder to an N-methyl-2-pyrrolidinone (NMP) solvent. The above positive electrode active material slurry was coated onto an aluminum film used as a current collector and dried to prepare the positive electrode, which was then rolled using a roller press to prepare the positive electrode.

[0112] Graphite was used as the negative electrode active material, CMC and SBR were used as binders, and carbon black was used as a conductive agent. These were added to the solvent H2O at 97.1 wt%, 1 wt%, 1 wt%, and 0.9 wt%, respectively, to prepare a negative electrode active material slurry. The above negative electrode mixture was coated onto a copper thin film, which served as the negative electrode current collector, and dried to prepare the negative electrode.

[0113] Furthermore, positive and negative electrodes prepared as described above were prepared, and a PE separator was placed between them. Batteries were fabricated with a base capacity of 730 mAh, and the initial capacity deviation of each battery could exhibit a difference of ±20 mAh. Electrolytes prepared according to the above example were then injected into each battery to prepare aluminum-pouch type lithium secondary batteries.

[0114] Feature Evaluation

[0115] 1. Capacity retention at 45℃: The capacitor was charged to 4.2V at 1C rate at 45℃ and allowed to stand for 10 minutes. Then it was discharged to 2.7V at 1C rate and allowed to stand for another 10 minutes. This process was counted as one cycle and repeated 300 times. The capacity retention rate (%) was then measured.

[0116] 2. Capacity recovery rate after 4 weeks at 60°C: After charging at 4.2V and 0.33C CC-CV 0.05C for 3 hours at room temperature, the cells were placed at 60°C for 4 weeks and then discharged to 2.8V at 0.33C. The usable capacity (%) relative to the initial capacity was measured.

[0117] 3. Thickness increase rate after 4 weeks at 60℃: After charging at 4.2V, 0.33C CC-CV 0.05C for 3 hours at room temperature, the thickness of the battery is set as A. The thickness of the battery placed in a constant temperature device at atmospheric pressure 60℃ for 4 weeks is set as B. The thickness increase rate is calculated as (BA) / A. Calculate using the formula for 100.

[0118] 4. Resistance increase rate after 4 weeks at 60℃: After charging at 4.2V, 0.33C CC-CV 0.05C for 3 hours at room temperature, and then discharging at 0.33C to 50% SOC, the resistance value at the point of discharge at 2C-rate for 30 seconds is set as C. Then, after being placed in a constant temperature device at atmospheric pressure and 60℃ for 4 weeks, and then discharged at 0.33C to 50% SOC, the resistance value at the point of discharge at 2C-rate for 30 seconds is set as D. The resistance increase rate is calculated as (CD) / C. Calculate using the formula for 100.

[0119] [Table 1]

[0120] With the addition of the electrolyte additive of the above chemical formula 2, compared with the case without the additive, the capacity retention rate after 300 cycles at 45°C increased, the capacity recovery rate after 4 weeks at 60°C also increased, and the thickness increase rate and resistance increase rate were significantly reduced.

[0121] The foregoing has described specific aspects of the present invention in detail. It will be apparent to those skilled in the art that this specific description is merely a preferred embodiment, and the scope of the invention is not limited thereto. Therefore, the essential scope of the invention should be defined by the appended claims and their equivalents.

Claims

1. An electrolyte additive for lithium secondary batteries, characterized in that, The electrolyte additive for lithium secondary batteries is represented by the following chemical formula 1: [Chemical Formula 1] In the chemical formula 1, R1 to R4 each independently represent hydrogen, deuterium, C1-C6 alkyl or C3-C6 cycloalkyl, and n represents an integer from 0 to 2.

2. The electrolyte additive for lithium secondary batteries according to claim 1, characterized in that, The electrolyte additive for lithium secondary batteries is represented by the following chemical formula 2: [Chemical Formula 2] 。 3. An electrolyte for lithium secondary batteries, characterized in that, Include: Organic solvents; Lithium salts; and The additive according to claim 1.

4. The electrolyte for lithium secondary batteries according to claim 3, characterized in that, The additive is contained in 0.005 to 10% by weight of the electrolyte.

5. The electrolyte for lithium secondary batteries according to claim 3, characterized in that, The organic solvent comprises ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), or combinations thereof.

6. The electrolyte for lithium secondary batteries according to claim 3, characterized in that, The lithium salt comprises LiPF6, LiFSI, LiDFOB, LiBF4, LiAsF6, LiCF3SO3, LiC(CF3SO2)3, LiN(SO2C2F5)2, LiN(SO2C2F3)2, LiN(SO2F3)2, LiSbF6, LiPF3(CF2CF3)3, LiPF3(CF3)3, or combinations thereof.

7. The electrolyte for lithium secondary batteries according to claim 3, characterized in that, The additive, as an additional additive, further comprises vinylene carbonate (VC), propanesultone (PS), ethylene sulfate (ESA), triphenyl phosphite (TPPI), or combinations thereof.

8. The electrolyte for lithium secondary batteries according to claim 3, characterized in that, The additive further comprises 0.5 to 3% by weight of vinylene carbonate (VC) based on the weight of the electrolyte.

9. The electrolyte for lithium secondary batteries according to claim 3, characterized in that, The additive further comprises, based on the weight of the electrolyte, 0.5 to 3% by weight of vinylene carbonate (VC), 0.5 to 3% by weight of propane sulfonate lactone (PS), and 0.1 to 1.5% by weight of vinyl sulfate (ESA).

10. The electrolyte for lithium secondary batteries according to claim 9, characterized in that, The additive further comprises 100 to 10,000 ppm of triphenyl phosphite (TPPI) based on the weight of the electrolyte.

11. A lithium secondary battery, characterized in that, Include: The electrolyte for lithium secondary batteries according to claim 3; Positive electrode; and negative electrode.

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