KR102028645B1 - Lithium secondary battery comprising non-aqueous liquid electrolyte - Google Patents

Abstract

The present invention provides a non-aqueous electrolyte comprising lithium bisfluoro sulfonyl imide (Lithium bis (fluorosulfonyl) imid; LiFSI) and a carbodiimide compound represented by Formula 1; A positive electrode comprising a lithium-nickel-manganese-cobalt-based oxide as a positive electrode active material; cathode; And it relates to a lithium secondary battery comprising a separator.
Lithium secondary battery comprising a non-aqueous electrolyte for lithium secondary battery of the present invention, the non-aqueous electrolyte can form a solid SEI film at the negative electrode during the initial charge, and can prevent decomposition of the positive electrode surface and oxidation reaction of the electrolyte during high temperature cycle Since the elution of the positive electrode active material is suppressed by suppressing the formation of HF, which is an impurity that may be formed in the electrolyte, excellent low temperature output characteristics can be exhibited and improved high temperature storage characteristics and lifetime characteristics can be exhibited.

Description

Lithium secondary battery containing a non-aqueous electrolyte {LITHIUM SECONDARY BATTERY COMPRISING NON-AQUEOUS LIQUID ELECTROLYTE}

The present invention is a non-aqueous electrolyte containing lithium bis (fluorosulfonyl) imide (LiFSI) and a carbodiimide compound represented by Formula 1, and a lithium-nickel-manganese-cobalt-based electrode as a positive electrode active material The present invention relates to a lithium secondary battery including an anode, an anode, and a separator including an oxide.

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

Lithium metal oxide is used as a positive electrode active material of a lithium secondary battery, and lithium metal, a lithium alloy, crystalline or amorphous carbon or a carbon composite material is used as a negative electrode active material. The active material is applied to a current collector with a suitable thickness and length, or the active material itself is applied in a film shape to form an electrode group by winding or laminating together with a separator, which is an insulator, and then put it in a can or a similar container, and then injecting an electrolyte solution. A secondary battery is manufactured.

In such a lithium secondary battery, charging and discharging progress while repeating a process of intercalating and deintercalating lithium ions from a lithium metal oxide of a positive electrode to a graphite electrode of a negative electrode. At this time, lithium is highly reactive and reacts with the carbon electrode to generate Li ₂ CO ₃ , LiO, LiOH and the like to form a film on the surface of the negative electrode. Such a film is called a solid electrolyte interface (SEI) film, and the SEI film formed at the beginning of charging prevents the reaction between lithium ions and a carbon anode or other material during charging and discharging. It also acts as an ion tunnel, allowing only lithium ions to pass through. The ion tunnel serves to prevent the organic solvents of a large molecular weight electrolyte which solvates lithium ions and move together and are co-intercalated with the carbon anode to decay the structure of the carbon anode.

Therefore, in order to improve the high temperature cycle characteristics and the low temperature output of the lithium secondary battery, a solid SEI film must be formed on the negative electrode of the lithium secondary battery. Once formed, the SEI membrane prevents the reaction between lithium ions and the negative electrode or other materials during repeated charge / discharge cycles, and serves as an ion tunnel that passes only lithium ions between the electrolyte and the negative electrode. Will be performed.

Conventionally, in the case of an electrolyte solution containing no electrolyte additive or an electrolyte additive having poor properties, it is difficult to expect improvement in low temperature output characteristics due to the formation of a non-uniform SEI film. Furthermore, even when it contains an electrolyte additive, when the input amount cannot be adjusted to the required amount, the electrolyte additive decomposes the surface of the anode during the high temperature reaction or the electrolyte causes an oxidation reaction, ultimately increasing the irreversible capacity of the secondary battery and output characteristics. There was a problem of this deterioration.

On the other hand, the lithium secondary battery may cause a decrease in the performance of the battery, if moisture is included in the inside. In the lithium secondary battery, moisture may be included in the active material during the manufacturing process, or may be included in a small amount present in the electrolyte. For example, lithium titanium oxide, which is used as a negative electrode active material, has a very low structural change during charging and discharging, and thus has a zero-strain material having excellent life characteristics, forming a relatively high voltage band, and It is known as a material having excellent safety and stability because it does not occur, and also has the advantage of having a fast charging electrode that can be charged in a few minutes, but due to the property of absorbing moisture in the air. In the case of manufacturing the electrode by using, there is a problem in that the contained moisture is decomposed to generate a large amount of gas.

In addition, the moisture present in the electrolyte may react with the electrolyte by the potential energy provided in the charging process, thereby deteriorating the reliability of the battery, such as gas generation and swelling of the cell, such as LiPF ₆ lithium. The salt reacts with water to form HF, which is a strong acid, which spontaneously reacts with the electrode active material exhibiting weak basicity to elute the electrode active material component, resulting in degradation of the battery, and also lithium fluoride on the surface of the positive electrode. (LiF) is formed to increase the electrical resistance in the electrode and generate gas to cause a decrease in the life of the battery. Therefore, it is necessary to suppress formation of HF in electrolyte solution as much as possible.

The problem to be solved of the present invention is not only to improve the low temperature and room temperature output characteristics, but also to improve the room temperature and high temperature cycle characteristics, and the capacity characteristics after high temperature storage, and to suppress the generation of HF as an impurity in the electrode The present invention provides a non-aqueous electrolyte solution for a lithium secondary battery and a lithium secondary battery including the same, by which side reactions can be reduced to suppress elution of the positive electrode and can form a stable film.

In order to solve the above problems, the present invention provides a non-aqueous electrolyte solution containing lithium bis (fluorosulfonyl) imid (LiFSI) and a carbodiimide compound represented by Formula 1, and lithium- as a positive electrode active material. It provides a lithium secondary battery comprising a positive electrode, a negative electrode, and a separator comprising a nickel-manganese-cobalt-based oxide.

Lithium secondary battery comprising a non-aqueous electrolyte for lithium secondary battery of the present invention, the non-aqueous electrolyte can form a solid SEI film at the negative electrode during the initial charge, and can prevent decomposition of the positive electrode surface and oxidation reaction of the electrolyte during high temperature cycle Since the elution of the positive electrode active material is suppressed by suppressing the formation of HF, which is an impurity that may be formed in the electrolyte, excellent low temperature output characteristics can be exhibited and improved high temperature storage characteristics and lifetime characteristics can be exhibited.

Hereinafter, the present invention will be described in more detail to aid in understanding the present invention. The terms or words used in this specification and claims are not to be construed as limiting in their usual or dictionary meanings, and the inventors may appropriately define the concept of terms in order to best explain their invention in the best way possible. It should be interpreted as meaning and concept corresponding to the technical idea of the present invention based on the principle that the present invention.

The lithium secondary battery of the present invention is a lithium non-aqueous electrolyte solution containing a lithium bis (fluorosulfonyl) imide (LiFSI) and a carbodiimide compound represented by the formula (1); A positive electrode comprising a lithium-nickel-manganese-cobalt-based oxide as a positive electrode active material; cathode; And separators.

[Formula 1]

In Formula 1, R ₁ and R ₂ are each independently alkyl having 1 to 12 carbons or cycloalkyl having 3 to 12 carbons.

As used herein, the term 'alkyl' means a straight, cyclic or branched hydrocarbon moiety unless stated otherwise.

The term cycloalkyl, as used herein, unless otherwise indicated, refers to cyclic alkyl including cyclopropyl and the like.

The non-aqueous electrolyte solution includes lithium bis (fluorosulfonyl) imide (LiFSI) and a carbodiimide compound represented by Formula 1, wherein the lithium bisfluorosulfonyl imide is a lithium salt. It can be added to the non-aqueous electrolyte to form a solid, thin SEI film on the cathode to improve the low temperature output characteristics, to suppress decomposition of the surface of the anode that may occur during high temperature cycle operation, and to prevent oxidation reaction of the electrolyte, The carbodiimide-based compound represented by Formula 1 may be added to a non-aqueous electrolyte solution to improve room temperature capacity characteristics and output characteristics of a lithium secondary battery including the same, and further to provide a carbodiimide-based compound represented by Formula 1 Since the carbodiimide-based compound represented by Formula 1 acts as a scavenger for moisture in the electrode As a result, by lowering the content of HF, which is an impurity that may be formed under the influence of moisture in the electrolyte, it is possible to prevent the HF from eluting the positive electrode active material, and the surface of the positive electrode formed through the reaction between HF and the positive electrode active material. It is possible to prevent the lithium fluoride (LiF) from increasing the electrical resistance in the electrode and generating gas to cause the life of the battery to decrease. Thereby, the effect which can prevent a battery from deteriorating as a result can be exhibited.

According to one embodiment of the present invention, the lithium bisfluorosulfonylimide may have a concentration in the non-aqueous electrolyte solution of 0.01 mole / l to 2 mole / l, specifically 0.01 mole / l to 1 mole / l have. When the concentration of the lithium bisfluorosulfonylimide is less than 0.1 mole / l, the effect of improving the low temperature output and the high temperature cycle characteristics of the lithium secondary battery is insignificant, and the concentration of the lithium bisfluorosulfonylimide is When more than 2 mole / l side reactions in the electrolyte during the charge and discharge of the battery excessively swelling (swelling) may occur, it may cause corrosion of the positive electrode or negative electrode current collector made of metal in the electrolyte.

In order to prevent such side reactions, the non-aqueous electrolyte of the present invention may further include a lithium salt. The lithium salt may be used a lithium salt commonly used in the art, for example LiPF ₆ , LiAsF ₆ , LiCF ₃ SO ₃ , LiBF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiSbF ₆ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiAlO ₄ , LiAlCl ₄ , and LiClO ₄ may be any one selected from the group consisting of, or a mixture of two or more thereof.

The mixing ratio of the lithium salt and lithium bisfluoro sulfonyl imide may be 1: 0.01 to 1 as molar ratio. When the mixing ratio of the lithium salt and lithium bisfluoro sulfonyl imide is greater than or equal to the molar ratio, side reactions in the electrolyte may occur excessively during charging and discharging of the battery, and a swelling phenomenon may occur. In this case, output improvement of the generated secondary battery may be reduced. Specifically, when the mixing ratio of the lithium salt and lithium bisfluoro sulfonyl imide is less than 1: 0.01, a process of forming an SEI film in a lithium ion battery, and lithium ions solvated by a carbonate solvent In the process of being inserted between the negative electrode, a large number of irreversible reactions may occur, and by the peeling of the negative electrode surface layer (for example, the carbon surface layer) and the decomposition of the electrolyte, the low temperature output of the secondary battery may be improved, the high temperature storage may be performed, The effect of improving the dose characteristics may be insignificant. When the mixing ratio of the lithium salt and the lithium bisfluoro sulfonyl imide is a molar ratio, when the ratio is greater than 1: 1, lithium bisfluoro sulfonyl imide of excessive capacity is included in the electrolyte to prevent corrosion of the electrode current collector during charging and discharging. This may affect the stability of the secondary battery.

The positive electrode active material which is the lithium-nickel-manganese-cobalt-based oxide may include an oxide represented by Formula 2 below.

[Formula 2]

Li _{1 + x} (Ni _a Co _b Mn _c ) O ₂

In Formula 2, 0.55 ≦ a ≦ 0.65, 0.18 ≦ b ≦ 0.22, 0.18 ≦ c ≦ 0.22, −0.2 ≦ x ≦ 0.2, and x + a + b + c + = 1.

By using the positive electrode active material, which is the lithium-nickel-manganese-cobalt-based oxide, for the positive electrode, it may be combined with lithium bisfluoro sulfonyl imide to have a synergistic effect. In the lithium-nickel-manganese-cobalt-based oxide positive electrode active material, Li + 1 ions and Ni + 2 ions in the layered structure of the positive electrode active material change as the Ni content increases in the transition metal. mixing) occurs and the structure thereof collapses, and the cathode active material causes side reactions with the electrolyte, or dissolution of transition metals. This occurs because Li +1 ions and Ni +2 ions have similar sizes. As a result, the performance of the battery is easily degraded due to electrolyte depletion and structural collapse of the positive electrode active material inside the secondary battery.

Therefore, using LiFSI applied electrolyte to the positive electrode active material of Formula 2 according to an embodiment of the present invention to form a layer layer of the LiFSI-based components on the surface of the anode cation mixing of Li + 1 ions and Ni + 2 ions While suppressing the phenomenon, a range was found in which sufficient nickel transition metal amount for securing the capacity of the positive electrode active material could be secured. According to the cathode active material including the oxide according to Chemical Formula 2 of the present invention, when using a LiFSI-applied electrolyte, it is possible to effectively suppress the electrolyte, side reactions, metal dissolution and the like.

In particular, when the ratio of the Ni transition metal in the oxide represented by Formula 2 exceeds 0.65, since the excess Ni is included in the positive electrode active material, Li + 1 is also ionized by the layer layer formed of LiFSI on the electrode surface described above. And Ni +2 may not suppress cation mixing of ions.

In addition, when an excessive amount of Ni transition metal is included in the positive electrode active material, a nickel transition metal having a d-orbit should have an octahedral structure in coordination bonds at high temperature or the like due to variation in the oxidation number of Ni. The order is reversed, or the oxidation number is varied (heterogeneous reaction) to form a distorted octahedron. As a result, the crystal structure of the positive electrode active material including the nickel transition metal is deformed to increase the probability of eluting nickel metal in the positive electrode active material.

As a result, the present inventors have confirmed that while producing a high output when the positive electrode active material including the oxide according to the range of the formula (2) and LiFSI salt combination, while showing a high efficiency in high temperature stability and capacity characteristics.

When the positive electrode active material including the oxide of Formula 2 and LiFSI lithium salt combination has a high output and stability, the electrolyte may be decomposed in a high power environment, may cause the breakdown of the negative electrode. In the case where the additives are included in the nonaqueous electrolyte, the secondary battery may be stable at high temperatures.

LiPF ₆ Lithium Salt In the case of, the electrolyte lacking thermal safety easily decomposes in the cell to form LiF and PF ₅ . At this time, the LiF salt reduces the conductivity and the number of free Li ⁺ ions, thereby increasing the resistance of the cell and consequently reducing the capacity of the cell. That is, Esa and FEC act as anion receptors to stably form PF ₆ ^- to the stable decomposition of PF ₆ ^- ions at the anode surface that may occur during high temperature cycle operation. Li ⁺ and PF ₆ ^{It is possible} to increase the ion pair separation of-, thereby improving the solubility of LiF in the electrolyte, thereby lowering the interfacial resistance.

The non-aqueous electrolyte may include a non-aqueous organic solvent, and the non-aqueous organic solvent may be minimized as long as decomposition by an oxidation reaction or the like may be minimized during charging and discharging of the battery, and may exhibit desired properties with an additive. Free, for example nitrile solvents, cyclic carbonates, linear carbonates, esters, ethers or ketones. These may be used alone, or two or more thereof may be used in combination.

Carbonate-based organic solvents of the organic solvents can be easily used, the cyclic carbonate is any one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate (BC) or two of them A mixture of two or more species, the linear carbonate consists of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethylmethyl carbonate (EMC), methylpropyl carbonate (MPC) and ethylpropyl carbonate (EPC) It may be any one selected from the group or a mixture of two or more thereof.

The nitrile solvents include acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, 2-fluorobenzonitrile and 4-fluorobenzonitrile , Difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, 4-fluorophenylacetonitrile may be one or more selected from the group consisting of, one embodiment of the present invention Acetonitrile may be used as the non-aqueous solvent according to the example.

By using an acetonitrile solvent, the positive electrode active material, which is the lithium-nickel-manganese-cobalt-based oxide, is used for the positive electrode, thereby effectively preventing side effects due to deterioration in stability of the high-output battery due to the combination with lithium bisfluoro sulfonyl imide can do.

In one example of the present invention, the carbodiimide-based compound represented by Formula 1 may be specifically R ₁ and R ₂ may each independently be a cycloalkyl having 3 to 8 carbon atoms, more specifically It may be the dicyclohexyl methane diimine represented.

[Formula 3]

Carbodiimide-based compound represented by the formula (1) may be 0.001 to 3% by weight, specifically 0.005 to 1% by weight, more specifically 0.005 to 0.1% by weight based on the total weight of the non-aqueous electrolyte Can be.

When the content of the carbodiimide-based compound is 0.001% by weight or more, an appropriate effect can be expected due to the addition of the carbodiimide-based compound, when the content of the carbodiimide-based compound is 3% by weight or less, the effect to an appropriate degree While exhibiting, it is possible to prevent problems such as increasing the irreversible capacity of the battery or preventing excess of carbodiimide-based compounds from moving lithium ions in the electrolyte.

The content of the carbodiimide compound represented by Chemical Formula 1 may be adjusted according to the amount of lithium bis fluoro sulfonyl imide added, and thus the lithium bis fluoro sulfonyl imide and carbodiimide compound may be 100: 0.02. It may be used in a weight ratio of 35 to 35, specifically, it may be used in a weight ratio of 100: 0.1 to 12, and more specifically may be used in a weight ratio of 100: 0.1 to 1.

When the lithium bis fluoro sulfonyl imide and the carbodiimide compound represented by Chemical Formula 1 are used in a weight ratio of 100: 0.02 to 35, lithium may be generated by the addition of the lithium bis fluoro sulfonyl imide. While the carbodiimide-based compound can appropriately suppress side reactions in the electrolyte during battery charging and discharging at room temperature of the secondary battery, the secondary battery can exhibit an additional effect of improving durability of the negative electrode.

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

On the other hand, the negative electrode active material includes amorphous carbon or crystalline carbon, specifically, carbon such as non-graphitized carbon, graphite-based 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 , Metal complex oxides such as Si, Group 1, 2, 3 Group elements of the periodic table, halogen, 0 <x ≦ 1, 1 ≦ y ≦ 3, 1 ≦ z ≦ 8); Lithium metal; Lithium alloys; Silicon-based alloys; Tin-based alloys; 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 oxides such as Bi ₂ O ₅ ; Conductive polymers such as polyacetylene; Li-Co-Ni-based materials and the like can be used.

In addition, the separator is a porous polymer film, for example, a porous polymer film made of a polyolefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer This may be a single or two or more laminated. In addition to the above, conventional porous nonwoven fabrics such as high-melting glass fibers, polyethylene terephthalate fibers, and the like may be used, but are not limited thereto.

The secondary battery is various according to the purpose of performing the cylindrical, square, pouch type and the like, and is not limited to the configuration known in the art. Lithium secondary battery according to an embodiment of the present invention may be a pouch type secondary battery.

Although the following Examples and Experimental Examples will be further described, the present invention is not limited to these Examples and Experimental Examples.

Example

Example 1

Preparation of Electrolyte

Ethylene carbonate (EC): Non-aqueous organic solvent and lithium salt having a composition of ethyl methyl carbonate (EMC) 3: 7 (volume ratio), LiPF ₆ based on the total amount of the non-aqueous electrolyte. 0.9 mol / l was added, and 0.1 mol / l of lithium bisfluorosulfonylimide and 0.02% by weight of dicyclohexylmethanediimine were added to prepare a non-aqueous electrolyte solution.

[Manufacture of Lithium Secondary Battery]

92% by weight of Li (Ni _0.6 Co _0.2 Mn _0.2 ) O ₂ as a positive electrode active material, 4% by weight of carbon black as a conductive agent, and 4% by weight of polyvinylidene fluoride (PVdF) as a binder, N-methyl- A positive electrode mixture slurry was prepared by addition to 2-pyrrolidone (NMP). The positive electrode mixture slurry was applied to a thin film of aluminum (Al), which is a positive electrode current collector having a thickness of about 20 μm, dried to prepare a positive electrode, and then subjected to 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 at 96 wt%, 3 wt%, and 1 wt%, respectively, to NMP as a solvent. The negative electrode mixture slurry was applied to a thin film of copper (Cu), which is a negative electrode current collector having a thickness of 10 μm, and dried to prepare a negative electrode, followed by a roll press to prepare a negative electrode.

The positive electrode and the negative electrode prepared as described above were manufactured with a polymer battery by a conventional method with a separator composed of three layers of polypropylene / polyethylene / polypropylene (PP / PE / PP), followed by pouring the prepared non-aqueous electrolyte solution into a lithium secondary battery. The manufacture of the battery was completed.

Example 2

LiPF ₆ A non-aqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1 except that the amount was changed to 0.7 mol / L and 0.3 mol / L of lithium bisfluorosulfonylimide.

Example 3

LiPF ₆ A non-aqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1 except that the amount was changed to 0.5 mol / l and 0.5 mol / l of lithium bisfluorosulfonylimide.

Example 4

LiPF ₆ A non-aqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1 except that the amount was changed to 0.8 mol / l and 0.2 mol / l of lithium bisfluorosulfonylimide.

Example 5

LiPF ₆ A non-aqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1 except that the amount thereof was changed to 0.3 mol / L and 0.7 mol / L of lithium bisfluorosulfonylimide.

Example 6

A non-aqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 2, except that the dicyclohexylmethanedimine was used at 0.05% by weight.

Example 7

A non-aqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 2, except that dicyclohexylmethanedimine was used at 3% by weight.

Comparative Example 1

A non-aqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 2, except that Li (Ni _0.5 Co _0.3 Mn _0.2 ) O ₂ was used as the cathode active material.

Comparative Example 2

A non-aqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 2, except that Li (Ni _0.8 Co _0.1 Mn _0.1 ) O ₂ was used as the cathode active material.

Comparative Example 3

LiPF ₆ A non-aqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Comparative Example 1 except that the amount was changed to 0.5 mol / l and 0.5 mol / l of lithium bisfluorosulfonylimide.

Comparative Example 4

A non-aqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1 except that lithium bisfluorosulfonyl imide and dicyclohexyl methane diimine were not used.

Comparative Example 5

A non-aqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1 except that lithium bisfluorosulfonylimide was not used.

Comparative Example 6

A non-aqueous electrolyte solution and a lithium secondary battery were prepared in the same manner as in Example 1, except that dicyclohexylmethanedimine was not used.

Experimental Example 1

<High temperature life measurement>

The lithium secondary batteries prepared in Examples 1 to 7, and Comparative Examples 1 to 7 were charged at 1 C up to 4.2 V / 38 mA under constant current / constant voltage (CC / CV) conditions at 45 ° C., followed by constant current (CC) conditions. Was discharged at 2 C up to 2.5 V, and the discharge capacity thereof was measured. This was repeated 1 to 1000 cycles, and the capacity after 1000 cycles is calculated as the capacity after 100 cycles / 1 capacity after cycle # 100 and is shown in Table 1 as a% value.

Experimental Example 2

Capacity characteristics after high temperature storage

The secondary batteries prepared in Examples 1 to 7, and Comparative Examples 1 to 7 were charged at 1 C to 4.2 V / 38 mA under constant current / constant voltage (CC / CV) conditions, and then to 2.5 V under constant current (CC) conditions. It discharged at 2 C, and the discharge capacity was measured. Then, after storing the secondary batteries prepared in Examples 1 to 7 and Comparative Examples 1 to 6 for 16 weeks at 60 ° C., the secondary batteries were again 4.2 V / 38 mA under constant current / constant voltage (CC / CV) conditions at room temperature. After charging to 1 C until, and discharged at 2 C to 2.5 V under constant current (CC) conditions, the discharge capacity was measured. The results obtained by calculating the discharge capacity after 16 weeks based on the initial discharge capacity as a percentage (discharge capacity after 16 weeks / initial discharge capacity * 100 (%)) are shown in Table 1 below.

Experimental Example 3

<Output characteristics after high temperature storage>

The secondary battery prepared in Examples 1 to 7, and Comparative Examples 1 to 7 was calculated using the voltage difference generated when charging and discharging for 10 seconds at room temperature after 5 weeks at 60 ℃ stored for 16 weeks. The results obtained by calculating the output after 16 weeks as a percentage (16 weeks output (W) / initial output (W) * 100 (%)) based on the initial output amount are shown in Table 1 below. The test was performed at 50% SOC (state of charge).

Experimental Example 4

<Measurement of battery thickness increase rate>

The thicknesses of the secondary batteries prepared in Examples 1 to 7, and Comparative Examples 1 to 7 were measured, and the thickness after storage at 60 ° C. for 16 weeks was measured to determine the increase in battery thickness (thickness of thickness / week 0 after 100 weeks Ⅹ100 It is shown in Table 1 as a% value calculated as) -100.

anode
Active material LiPF ₆ : LiFSI additive
(weight%) High temperature life (%) High Temperature Storage Characteristics
(%) Volume Print thickness Example 1 NMC622 9: 1 DCC 0.02 90.6 88 81.4 6.3 Example 2 NMC622 7: 3 DCC 0.02 93 91.1 89.9 5.1 Example 3 NMC622 5: 5 DCC 0.02 87.9 82.6 80 7.1 Example 4 NMC622 8: 2 DCC 0.02 82.1 79.5 76 6.9 Example 5 NMC622 3: 7 DCC 0.02 77 72.3 81.2 8.3 Example 6 NMC622 7: 3 DCC 0.05 91.4 89.4 83.2 5.9 Example 7 NMC622 7: 3 DCC
3 76.3 79.3 63.3 10.2 Comparative Example 1 NMC532 7: 3 DCC 0.02 91.5 87.6 79.4 16.8 Comparative Example 2 NMC811 7: 3 DCC 0.02 88.1 86.3 77 17.6 Comparative Example 3 NMC532 5: 5 DCC 0.02 90.1 87.1 80.5 16.9 Comparative Example 4 NMC622 9: 0 0 75.3 77 75.1 5.5 Comparative Example 5 NMC622 9: 0 DCC 0.02 81.8 80.9 80.5 5.6 Comparative Example 6 NMC622 9: 1 0 78.7 79.8 79.3 6.2

In Table 1, NMC622 is Li (Ni _0.6 Co _0.2 Mn _0.2 ) O ₂ , NMC532 is Li (Ni _0.5 Co _0.3 Mn _0.2 ) O ₂ , and NMC811 is Li (Ni _0.8 Co _0.1 Mn _0.1 ) O ₂ And DCC represents dicyclohexylmethanediimine.

Referring to Table 1, the secondary batteries of Examples 1 to 7 including Li (Ni _0.6 Co _0.2 Mn _0.2 ) O ₂ as the cathode active material are Li (Ni _0.5 Co _0.3 Mn _0.2 ) O ₂ or Li ( Compared with the secondary batteries of Comparative Examples 1 to 3 containing Ni _0.8 Co _0.1 Mn _0.1 ) O ₂ , the increase in thickness after the high temperature storage was small, and thus it was confirmed that the high temperature storage performance was excellent.

On the other hand, from the viewpoint of the addition of lithium bisfluoro sulfonyl imide, comparing Example 1 and Comparative Example 5, Example 1 containing a non-aqueous electrolyte containing lithium bisfluoro sulfonyl imide Secondary batteries were excellent in both high temperature life and high temperature storage characteristics compared to Comparative Example 5 including a non-aqueous electrolyte containing no lithium bisfluoro sulfonyl imide.

In addition, in view of the addition of the carbodiimide compound, Example 1 and Comparative Example 7 is compared, Example 1 comprising a non-aqueous electrolyte solution containing dicyclohexyl methane diimine as a carbodiimide compound The secondary battery was superior in both high temperature life and high temperature storage characteristics compared with Comparative Example 7 including a non-aqueous electrolyte solution containing no dicyclohexyl methane diimine.

Claims (14)

Non-aqueous electrolyte solution containing at least one selected from the group consisting of lithium bisfluoro sulphonyl imide (Lithium bis (fluorosulfonyl) imid; LiFSI) and carbodiimide-based compound represented by the formula (1); A positive electrode comprising a lithium-nickel-manganese-cobalt-based oxide as a positive electrode active material; cathode; And a separator,
The lithium-nickel-manganese-cobalt oxide is a lithium secondary battery comprising an oxide represented by the following formula (2):
[Formula 1]

In Formula 1, R ₁ and R ₂ are each independently alkyl having 1 to 12 carbon atoms, or cycloalkyl having 3 to 12 carbon atoms,
[Formula 2]
Li _{1 + x} (Ni _a Co _b Mn _c ) O ₂
In Formula 2, 0.55 ≦ a ≦ 0.65, 0.18 ≦ b ≦ 0.22, 0.18 ≦ c ≦ 0.22, −0.2 ≦ x ≦ 0.2, and x + a + b + c + = 1.
The method of claim 1,
The non-aqueous electrolyte solution further comprises a lithium salt.
The method of claim 2,
A mixing ratio of the lithium salt and lithium bisfluoro sulfonyl imide is 1: 0.01 to 1: 1 in molar ratio.
The method of claim 1,
The lithium bisfluoro sulfonyl imide has a concentration of 0.01 mol / l to 2 mol / l in the non-aqueous electrolyte.
The method of claim 2,
The lithium salt is LiPF ₆ , 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 , and LiClO ₄ Lithium secondary battery comprising any one or a mixture of two or more selected from the group consisting of.
delete The method of claim 1,
The non-aqueous electrolyte solution includes a non-aqueous organic solvent,
The non-aqueous organic solvent is a lithium secondary battery comprising a nitrile-based solvent, linear carbonate, cyclic carbonate, ester, ether, ketone or a combination thereof.
The method of claim 7, wherein
The cyclic carbonate is any one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate (BC) or a mixture of two or more thereof, and the linear carbonate is dimethyl carbonate (DMC) or diethyl carbonate. (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC) and ethyl propyl carbonate (EPC) any one selected from the group consisting of or a mixture of two or more thereof.
The method of claim 7, wherein
The nitrile solvents include acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, 2-fluorobenzonitrile and 4-fluorobenzonitrile And at least one lithium secondary battery selected from the group consisting of difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile.
The method of claim 1,
The lithium secondary battery wherein R ₁ and R ₂ are each independently cycloalkyl having 3 to 8 carbon atoms.
The method of claim 1,
A lithium secondary battery, wherein the carbodiimide compound is dicyclohexyl methane diimine.
The method of claim 1,
Carbodiimide-based compound represented by the formula 1 is a lithium secondary battery is 0.001% to 3% by weight based on the total weight of the non-aqueous electrolyte.
The method of claim 1,
The lithium bis fluoro sulfonyl imide and the carbodiimide compound represented by the formula (1) is a lithium secondary battery having a weight ratio of 100: 0.02 to 35.
The secondary battery of any one of claims 1 to 5 and 7 to 13 is a pouch type lithium secondary battery.