KR20230125708A - Additive for secondary battery, electrolyte for lithium secondary battery and lithium secondary batter including the same - Google Patents

Abstract

Additives for secondary batteries according to embodiments of the present invention may include a borate salt-based compound having a “-BF ₃ ” structure in its molecular structure. In addition, the electrolyte solution for a lithium secondary battery according to embodiments of the present invention may include a lithium salt, an organic solvent, and an additive for a secondary battery. Accordingly, a lithium secondary battery having improved lifespan characteristics at room temperature, high-temperature storage characteristics, and high-temperature lifespan characteristics may be provided.

Description

Additives for secondary batteries, electrolytes for lithium secondary batteries, and lithium secondary batteries containing the same

The present invention relates to an additive for a secondary battery, an electrolyte solution for a lithium secondary battery, and a lithium secondary battery including the same. More specifically, it relates to a secondary battery additive containing boron, an electrolyte solution for a lithium secondary battery and a lithium secondary battery including the same.

A secondary battery is a battery capable of repeating charging and discharging, and is widely used as a power source for portable electronic communication devices such as camcorders, mobile phones, and notebook PCs with the development of information communication and display industries. In addition, recently, a battery pack including a secondary battery has been developed and applied as a power source for eco-friendly vehicles such as hybrid vehicles.

Secondary batteries include, for example, lithium secondary batteries, nickel-cadmium batteries, nickel-hydrogen batteries, etc. Among them, lithium secondary batteries have high operating voltage and energy density per unit weight, and are advantageous in charging speed and weight reduction. It is being actively developed and applied in this regard.

A lithium secondary battery may include an electrode assembly including a positive electrode, a negative electrode, and a separator (separator), and an electrolyte solution impregnating the electrode assembly. The lithium secondary battery may further include, for example, a pouch-shaped exterior material for accommodating the electrode assembly and the electrolyte solution.

Recently, as the range of use of lithium secondary batteries has expanded from conventional small electronic devices to large electronic devices, automobiles, smart grids, etc., there is a need for lithium secondary batteries that can maintain excellent performance not only at room temperature but also in harsher external environments such as high or low temperature environments. Demand is gradually increasing.

Considering electrochemical stability and flame retardancy, a non-aqueous electrolyte may be used as the electrolyte. For example, the non-aqueous electrolyte may be prepared by using a carbonate-based organic solvent such as ethylene carbonate or dimethyl carbonate as an electrolyte solvent and using a lithium salt such as LiPF ₆ or LiBF ₄ as an electrolyte salt.

However, the carbonate-based organic solvent used in the non-aqueous electrolyte may be decomposed on the surface of the electrode during charging and discharging, causing side reactions in the battery. In addition, the carbonate-based solvent has a high molecular weight and, for example, may be intercalated between graphite layers included in the negative electrode, thereby disrupting the structure of the negative electrode. Accordingly, the performance of the lithium secondary battery may deteriorate as charging and discharging are repeated.

In addition, during repetitive charging and discharging of the lithium secondary battery, side reactions between the electrolyte and lithium metal oxide and consequent structural deformation of the positive electrode may occur. In this case, lifespan characteristics (eg, capacity retention rate) of the lithium secondary battery may deteriorate. In addition, the lithium secondary battery is placed in a high-temperature environment during repeated charging and discharging and overcharging. In this case, gas may be generated due to decomposition of the electrolyte, and the battery may ignite or explode due to swelling and internal short circuit.

Therefore, there is a continuous demand for development of non-aqueous electrolytes containing additives capable of improving battery performance. For example, Korean Patent Registration No. 10-1999615 discloses an electrolyte solution for a lithium secondary battery.

Korean Registered Patent Publication No. 10-1999615

One object of the present invention is to provide an additive for a secondary battery that improves the electrochemical properties and stability of the secondary battery.

One object of the present invention is to provide an electrolyte solution for a lithium secondary battery that improves the electrochemical characteristics and stability of the secondary battery.

One object of the present invention is to provide a lithium secondary battery with improved electrochemical properties and stability.

Additives for secondary batteries according to exemplary embodiments may include at least one of compounds represented by Chemical Formulas 1 to 3 below.

[Formula 1]

[Formula 2]

[Formula 3]

In Chemical Formulas 1 to 3, M ⁺ may be a monovalent cation.

In Chemical Formulas 2 and 3, Rf ₁ and Rf ₂ may each independently be fluorine or a fluorinated alkyl group having 1 to 4 carbon atoms.

In some embodiments, in Chemical Formulas 2 and 3, Rf ₁ and Rf ₂ may each independently be fluorine or a trifluoromethyl group (—CF ₃ ).

In some embodiments, in Chemical Formulas 1 to 3, M ⁺ may be a lithium cation (Li ⁺ ).

In some embodiments, the secondary battery additive may include at least one of compounds represented by Chemical Formulas 4 to 8 below.

[Formula 4]

[Formula 5]

[Formula 6]

[Formula 7]

[Formula 8]

An electrolyte solution for a lithium secondary battery according to exemplary embodiments may include an additive including at least one of a lithium salt, an organic solvent, and compounds represented by Formulas 1 to 3 above.

In some embodiments, the content of the additive may be 0.01% to 10% by weight based on the total weight of the electrolyte for a lithium secondary battery.

In one embodiment, the content of the additive may be 0.1% to 5% by weight of the total weight of the electrolyte for a lithium secondary battery.

In some embodiments, the organic solvent may include at least one of a carbonate-based solvent, an ester-based solvent, an ether-based solvent, a ketone-based solvent, an alcohol-based solvent, and an aprotic solvent.

In one embodiment, the organic solvent may include a linear carbonate-based solvent and a cyclic carbonate-based solvent.

In one embodiment, the ratio of the volume of the cyclic carbonate-based solvent to the volume of the linear carbonate-based solvent may be 0.1 to 1.

In some embodiments, the electrolyte solution for a lithium secondary battery may further include an auxiliary additive.

In one embodiment, the auxiliary additive is a fluorine-containing cyclic carbonate-based compound, a fluorine-containing phosphate-based compound, a cyclic carbonate-based compound having a double bond, a sultone-based compound, a borate-based compound, a cyclic sulfate-based compound, and a silyl group. It may include at least one of the phosphorus-based compounds having.

In one embodiment, the content of the auxiliary additive may be 0.1% to 10% by weight of the total weight of the electrolyte for the lithium secondary battery.

In some embodiments, the concentration of the lithium salt in the organic solvent may be 0.1M to 2M.

A lithium secondary battery according to exemplary embodiments may include a positive electrode, a negative electrode facing the positive electrode, and the above-described electrolyte solution for a lithium secondary battery.

An additive for a secondary battery according to exemplary embodiments includes a compound represented by a specific chemical formula. The aforementioned additive for a secondary battery may be applied to an electrolyte solution for a lithium secondary battery. The additive may form an oxide film on a defect point or an activation point of the electrode surface of the lithium secondary battery to suppress the oxidative decomposition reaction of the electrolyte solution.

In addition, the additive can form a stable protective film on the surface of the positive electrode, thereby preventing aging and deterioration of performance of the lithium secondary battery. Therefore, it is possible to prevent the exhaustion of the electrolyte solution due to repetitive charging and discharging of the lithium secondary battery, and side reactions at the interface between the electrode and the electrolyte solution can be suppressed.

Also, the lithium secondary battery according to exemplary embodiments may include the above-described electrolyte solution for a lithium secondary battery. Accordingly, high-temperature stability and chemical stability of the lithium secondary battery may be improved, and output characteristics, room-temperature and high-temperature lifespan characteristics may be improved.

1 is a schematic plan perspective view of a lithium secondary battery according to example embodiments.
2 is a schematic cross-sectional view of a lithium secondary battery according to example embodiments.

Additives for secondary batteries according to embodiments of the present invention may include a trifluoroborate-based compound having a “-BF ₃ ” structure in its molecular structure. For example, the aforementioned additives may include trifluoroborate salts.

In addition, the electrolyte solution for a lithium secondary battery according to embodiments of the present invention may include the above-described additive for a secondary battery. In addition, the lithium secondary battery according to embodiments of the present invention may include the above-described electrolyte solution for a lithium secondary battery.

As used herein, the term “X compound” may refer to a compound containing an X unit as a parent, side group or substituent.

Hereinafter, the present invention will be described in detail.

<Electrolyte for Lithium Secondary Battery>

An electrolyte solution for a lithium secondary battery (hereinafter, may be abbreviated as an electrolyte solution) according to exemplary embodiments may include an organic solvent, a lithium salt, and an additive for a secondary battery.

The secondary battery additive (hereinafter, it may be abbreviated as an additive) may include at least one of compounds represented by Chemical Formulas 1 to 3 below.

[Formula 1]

[Formula 2]

[Formula 3]

In Chemical Formulas 1 to 3, M ⁺ may be a monovalent cation. For example, M ⁺ may be a monovalent metal cation, and may be Li ⁺ , K ⁺ , Na ⁺ , Rb ⁺ , Cs ⁺ or Fr ⁺ . Preferably, M ⁺ may be Li ⁺ , K ⁺ or Na ⁺ .

In one embodiment, in Chemical Formulas 1 to 3, M ⁺ may be Li ⁺ . For example, the additive may be applied to an electrolyte solution for a lithium secondary battery to improve output characteristics, charge/discharge capacity, and thermal stability of the lithium secondary battery.

In Chemical Formulas 2 and 3, Rf ₁ and Rf ₂ may each independently be fluorine or a fluorinated alkyl group having 1 to 4 carbon atoms. For example, Rf ₁ and Rf ₂ may be a fluorine atom or an alkyl group having 1 to 4 carbon atoms in which at least one hydrogen atom is replaced with a fluorine atom.

The additive for a secondary battery may form a protective film on a defect or activation point on the surface of an electrode for a lithium secondary battery. For example, the additive for a secondary battery may form an oxide film on the surface of an anode or a cathode during operation of a lithium secondary battery or form a complex compound with an electrode active material. For example, the secondary battery additive is an oxidative decomposition type additive and may be oxidatively decomposed on the surface of an electrode to form a protective film.

Therefore, direct contact between the electrode active material and the electrolyte may be reduced or suppressed by the additive for secondary batteries. Accordingly, a side reaction between the electrolyte and the electrode active material and generation of gas may be prevented, and life characteristics of the lithium secondary battery may be improved.

In addition, the additive for a secondary battery may prevent or prevent metal ions eluted/released from cations from being electrodeposited on the negative electrode. Accordingly, lithium ions can be smoothly absorbed/released from the surface of the negative electrode, and the lifespan and output characteristics of the lithium secondary battery can be improved.

The secondary battery additive has a trifluoroborate (-BF ₃ ) functional group in its molecular structure, so that a film having high ionic conductivity can be formed on the surface of the electrode and thermal decomposition of the electrolyte can be suppressed. Accordingly, interfacial resistance of the secondary battery may be reduced, and low-temperature life characteristics and high-temperature stability may be improved.

In addition, as an oxygen double bond (=O) and a fluorine (F) atom or a fluorinated alkyl group (Rf ₁ , Rf ₂ ) are directly bonded to a phosphorus (P) atom or a sulfur (S) atom, the reactivity of the electrolyte may be lowered. and thermal/chemical stability can be further improved. Therefore, irreversible decomposition of the electrolyte can be prevented, and high power characteristics and high temperature stability can be improved even when charging/discharging at a high C-rate or driving at a high voltage.

In addition, the stable protective film formed by the additive can suppress the generation of acidic substances, such as HF, generated by decomposition of the electrolyte. Accordingly, decomposition of the protective film and damage to the active material may be prevented, and electrochemical stability of the lithium secondary battery may be improved.

In some embodiments, Rf ₁ and Rf ₂ in Chemical Formulas 2 and 3 may each independently be fluorine or a fluorinated alkyl group having 1 to 4 carbon atoms in which all hydrogen atoms are substituted with fluorine atoms, preferably fluorine (- F) or a trifluoromethyl group (-CF ₃ ).

In this case, flame retardancy and chemical stability of the additive for a lithium secondary battery may be improved, and a stable film may be formed on the surface of the positive electrode. Accordingly, the lifespan of the lithium secondary battery at room temperature and high temperature may be improved, and decomposition and depletion of the electrolyte solution may be prevented.

According to exemplary embodiments, the additive may include at least one of compounds represented by Chemical Formulas 4 to 8 below.

[Formula 4]

[Formula 5]

[Formula 6]

[Formula 7]

[Formula 8]

As the electrolyte solution for a secondary battery includes the compounds represented by Chemical Formulas 4 to 8, output characteristics, lifespan characteristics at room temperature and lifespan at high temperatures of the lithium secondary battery may be improved.

For example, in the case of using an over-lithium cathode active material to implement a high-voltage secondary battery, oxygen gas may be generated during charging and discharging. In addition, when a silicon-based negative active material having a high capacity is used, the volume of the active material may expand due to repeated charge/discharge, and cracks may occur on the surface.

In addition, when the electrolyte is decomposed on the surface of the electrode, an unstable film may be formed on the surface of the electrode. In this case, the film may be repeatedly destroyed/regenerated due to repeated charging and discharging, and thus, the thickness of the film may increase. Accordingly, the resistance of the electrode surface may increase, and capacity characteristics and cycle characteristics may be deteriorated due to the depletion of the electrolyte solution.

Additives for secondary batteries according to exemplary embodiments may form a thermally and chemically stable protective film on the surface of an electrode. Accordingly, the thickness of the secondary battery may be maintained uniformly, and leakage and consumption of the electrolyte solution may be prevented. Accordingly, resistance of the secondary battery may be reduced, and an increase in irreversible capacity may be prevented.

In addition, the structure of the active material may be stably maintained even when a lithium-plus positive electrode active material and a silicon-based negative electrode active material are used as active materials or the secondary battery is driven at a high voltage. Accordingly, the electrochemical performance, reaction rate, and stability of the secondary battery may be improved.

In some embodiments, the content of the secondary battery additive may be 0.01 wt % to 10 wt % based on the total weight of the electrolyte solution. Preferably, the content of the additive may be 0.1% to 5% by weight, more preferably 0.3% to 3% by weight, based on the total weight of the electrolyte.

Within the above range, cycle characteristics of the lithium secondary battery may be improved, and decrease in capacity and ionic conductivity and increase in viscosity due to repeated charging and discharging may be suppressed.

According to example embodiments, the organic solvent may include an organic compound that provides sufficient solubility for a lithium salt, an additive, and/or auxiliary additives and has no reactivity in a lithium secondary battery.

For example, the organic solvent may have a degree of salt dissociation of about 0.1 M or more with respect to a lithium salt. When the solubility of the lithium salt in the organic solvent is low, the viscosity of the electrolyte may increase, and thus the performance of the lithium secondary battery may deteriorate. Also, since the lithium salt is not uniformly dissolved in the organic solvent and remains in the form of a salt, the internal resistance of the electrolyte solution may increase. In this case, a side reaction may occur due to the remaining lithium salt, and desorption or polarization of the electrode may occur.

According to example embodiments, the organic solvent may include a carbonate-based solvent, an ester-based solvent, an ether-based solvent, a ketone-based solvent, an alcohol-based solvent, or an aprotic solvent. These may be used alone or in combination of two or more.

The carbonate-based solvent may include a linear carbonate-based solvent and/or a cyclic carbonate-based solvent.

The linear carbonate-based solvent is dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl propyl carbonate, ethyl propyl carbonate, diethyl carbonate , DEC), dipropyl carbonate, and the like.

The cyclic carbonate-based compound is propylene carbonate (PC), ethylene carbonate (EC), fluoroethylene carbonate (FEC), butylenes carbonate, pentylene carbonate, vinylene It may include carbonate (vinylene carbonate, VC), vinyl ethylene carbonate, and the like.

Examples of the ester-based solvent include methyl acetate (MA), ethyl acetate (EA), n-propyl acetate (n-PA), 1,1-dimethylethyl acetate (1, 1-dimethylethyl acetate (DMEA), methyl propionate (MP), ethyl propionate (EP), γ-butyrolacton (GBL), decanolide, and valerolactone, mevalonolactone, caprolactone, and the like.

Examples of the ether-based organic solvent include dibutyl ether, tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether (DEGDME), and dimethoxy ethane. ), 2-methyltetrahydrofuran, tetrahydrofuran, and the like.

An example of the ketone solvent is cyclohexanone. Examples of the alcohol-based solvent include ethyl alcohol and isopropyl alcohol.

The aprotic solvent includes a nitrile solvent, an amide solvent such as dimethyl formamide (DMF), a dioxolane solvent such as 1,3-dioxolane, a sulfolane solvent, and the like can do.

Preferably, a carbonate-based solvent may be used as the organic solvent. In this case, the solubility of the additive in the organic solvent may be improved due to the structural affinity, and the internal resistance of the electrolyte solution for a lithium secondary battery may be reduced.

For example, the organic solvent may include a mixed solvent of a linear carbonate-based solvent and a cyclic carbonate-based solvent. The cyclic carbonate-based solvent may have excellent ionic conductivity due to low viscosity, and the linear carbonate-based solvent may have excellent solubility in lithium salt due to high permittivity.

In some embodiments, when the organic solvent includes a mixed solvent of a linear carbonate-based solvent and a cyclic carbonate-based solvent, the ratio of the volume of the cyclic carbonate-based solvent to the volume of the linear carbonate-based solvent is 0.1 to 1 can be Preferably, the ratio of the volume of the cyclic carbonate-based solvent to the volume of the linear carbonate-based solvent may be 0.1 to 0.5, more preferably 0.1 to 0.4.

Within the above range, the viscosity of the electrolyte may be maintained low, and the degree of dissociation of the lithium salt and the additive may be high. Accordingly, room temperature and high temperature life characteristics of the lithium secondary battery may be improved, and high-temperature output may be obtained.

According to exemplary embodiments, the lithium salt may include a compound represented by Li ⁺ X ^- .

Examples of the anion (X ^- ) of the lithium salt include F ^- , Cl ^- , Br ^- , I ^- , NO ₃ ^- , N(CN) ₂ ^- , BF ₄ ^- , ClO ₄ ^- , PF ₆ ^- , SbF ₆ ^- , AsF ₆ ^- , (CF ₃ ) ₂ PF ₄ ^- , (CF ₃ ) ₃ PF ₃ ^- , (CF ₃ ) ₄ PF ₂ ^- , (CF ₃ ) ₅ PF ^- , (CF ₃ ) ₆ P ^- , CF ₃ SO ₃ ^- , CF ₃ CF ₂ SO ₃ ^- , (CF ₃ SO ₂ ) ₂ N ^- , (FSO ₂ ) ₂ N ^- _, CF ₃ CF ₂ (CF ₃ ) ₂ CO ^- , (CF ₃ SO ₂ ) ₂ CH ^- , (SF ₅ ) ₃ C ^- , (CF ₃ SO ₂ ) ₃ C ^- , CF ₃ (CF ₂ ) ₇ SO ₃ ^- , CF ₃ CO ₂ ^- , CH ₃ CO ₂ ^- , SCN ^- , (CF ₃ CF ₂ SO ₂ ) ₂ N ^- or PO ₂ F ₂ ^- . These anions may be single or a combination of two or more.

In some embodiments, the lithium salt may be included in a concentration of 0.1 M to 2.0 M, preferably 0.5 M to 1.5 M with respect to the organic solvent.

When the concentration of the lithium salt is less than 0.1 M, the ionic conductivity of the electrolyte solution is reduced, and thus the electrochemical performance of the lithium secondary battery may be deteriorated. When the concentration of the lithium salt exceeds 2.0 M, the viscosity of the electrolyte solution increases and the mobility of lithium ions decreases, and thus the initial efficiency and charging speed of the lithium secondary battery may decrease. Within the above range, the transfer of lithium ions and/or electrons in the electrolyte may be promoted during charge/discharge, and rapid charge performance and charge/discharge capacity may be improved.

According to exemplary embodiments, the electrolyte solution for a lithium secondary battery may further include an auxiliary additive. The auxiliary additive may be oxidized and decomposed to form a protective film on the surface of the anode, and may prevent a decomposition reaction of the electrolyte on the surface of the anode.

For example, the auxiliary additive may include a fluorine-containing cyclic carbonate-based compound, a fluorine-containing phosphate-based compound, a cyclic carbonate-based compound having a double bond, a sultone-based compound, a borate-based compound, a sulfate-based compound, a phosphorus-based compound having a silyl group, and the like. can include

In some embodiments, the auxiliary additive may include the fluorine-containing cyclic carbonate-based compound and the borate-based compound. In this case, lifespan characteristics of the lithium secondary battery may be further improved.

The fluorine-containing cyclic carbonate-based compound may have a 5- to 7-membered cyclic structure. For example, the fluorine-containing cyclic carbonate-based compound may include fluoroethylene carbonate (FEC) and the like.

For example, the fluorine-containing cyclic carbonate-based compound may be included in an amount of 0.1 to 10 wt%, preferably 0.5 to 5 wt%, and more preferably 1 to 3 wt%, based on the total weight of the electrolyte solution.

The fluorine-containing phosphate-based compound is a compound represented by Formula 9-1 (WCA-1), a compound represented by Formula 9-2 (WCA-2), and a compound represented by Formula 9-3 (WCA-3) ) and the like.

[Formula 9-1]

[Formula 9-2]

[Formula 9-3]

For example, the fluorine-containing phosphate-based compound may be included in an amount of 0.1 to 10% by weight, preferably 0.5 to 5% by weight, and more preferably 1 to 3% by weight, based on the total weight of the electrolyte solution.

The cyclic carbonate-based compound having a double bond may include a double bond in a ring structure. For example, the cyclic carbonate-based compound having a double bond may include vinylene carbonate (VC) and the like.

For example, the cyclic carbonate-based compound having a double bond may be included in an amount of 0.1 to 10 wt%, preferably 0.5 to 5 wt%, and more preferably 1 to 3 wt%, based on the total weight of the electrolyte solution.

The sultone-based compound may include propane sultone (PS), propene sultone (PRS), and the like.

For example, the sultone-based compound may be included in an amount of 0.1 to 10% by weight, preferably 0.5 to 5% by weight, and more preferably 1 to 3% by weight, based on the total weight of the electrolyte.

The borate-based compound may include a compound represented by Chemical Formula 10-1 (LiFOB), a compound represented by Chemical Formula 10-2 (LiBOB), and the like.

[Formula 10-1]

[Formula 10-2]

For example, the borate-based compound may be included in an amount of 0.1 to 10% by weight, preferably 0.5 to 5% by weight, and more preferably 1 to 3% by weight, based on the total weight of the electrolyte.

The cyclic sulfate-based compound may have a 5- to 7-membered cyclic structure. For example, the cyclic sulfate-based compound may include ethylene sulfate (ESA) and the like.

For example, the cyclic sulfate-based compound may be included in an amount of 0.1 to 10 wt%, preferably 0.5 to 5 wt%, and more preferably 1 to 3 wt%, based on the total weight of the electrolyte solution.

The phosphorus-based compound having the silyl group may include tris(trimethylsilyl) phosphite, tris(trimethylsilyl) phosphate, and the like.

For example, the phosphorus-based compound having a silyl group may be included in an amount of 0.1 to 10% by weight, preferably 0.5 to 5% by weight, and more preferably 1 to 3% by weight, based on the total weight of the electrolyte solution.

In some embodiments, the total content of the auxiliary additive may be 0.1 to 10% by weight of the total weight of the electrolyte solution. Structural stability of the electrode active material may be improved while preventing decomposition of the electrolyte within the above range. Accordingly, electrochemical performance, reaction rate, and stability of the lithium secondary battery may be improved.

In some embodiments, the ratio of the weight of the auxiliary additive to the weight of the secondary battery additive may be 0.1 to 5, for example, 0.2 to 2. Within the above range, the ion conductivity and thermal/chemical stability of the electrolyte for a lithium secondary battery may be improved, and the output characteristics, room temperature and high temperature life characteristics of the lithium secondary battery may be improved.

<Lithium secondary battery>

A lithium secondary battery according to example embodiments may include a positive electrode, a negative electrode disposed to face the positive electrode, and an electrolyte solution impregnating the positive electrode and the negative electrode. The electrolyte solution may be an electrolyte solution for a lithium secondary battery according to the above-described embodiments.

For example, the electrolyte solution may include a lithium salt, an organic solvent, and an additive for a secondary battery including at least one of the compounds represented by Chemical Formulas 1 to 3 above.

Hereinafter, embodiments of the present invention will be described in more detail with reference to the drawings. However, the following drawings attached to this specification illustrate preferred embodiments of the present invention, and serve to further understand the technical idea of the present invention together with the contents of the above-described invention, so the present invention is described in such drawings should not be construed as limited to

1 and 2 are schematic plan perspective views and cross-sectional views illustrating a lithium secondary battery according to exemplary embodiments, respectively.

Referring to FIG. 2 , the lithium secondary battery may include a positive electrode 100 and a negative electrode 130 facing the positive electrode 100 .

The cathode 100 may include a cathode current collector 105 and a cathode active material layer 110 formed on the cathode current collector 105 .

The cathode active material layer 110 may include a cathode active material, a cathode binder, and a conductive material, if necessary.

For example, the cathode current collector 105 may include stainless steel, nickel, aluminum, titanium, copper, or the like.

The cathode active material may include a lithium metal oxide capable of reversibly intercalating and deintercalating lithium ions. For example, the cathode active material includes at least one element of nickel (Ni), aluminum (Al), iron (Fe), cobalt (Co), manganese (Mn), copper (Cu), and phosphorus (P). It may contain lithium metal oxide.

In some embodiments, the lithium metal oxide is lithium cobalt-based oxide, lithium nickel-based oxide, lithium manganese-based oxide, lithium copper oxide, lithium nickel-manganese-cobalt-based oxide, lithium nickel-cobalt-aluminum-based oxide, lithium cobalt phosphate or lithium iron phosphate; and the like.

For example, the lithium metal oxide is LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li(Ni _a Co _b Mn _c ) O ₂ (0<a<1, 0<b<1, 0<c <1, a+b+c=1), LiNi _1-y Co _y O ₂ (O<y<1), LiCo _1-y Mn _y O ₂ (O<y<1), LiNi _1-y Mn _y O ₂ (O≤y<1), Li(Ni _a Co _b Mn _c )O ₄ (0<a<2, 0<b<2, 0<c<2, a+b+c=2), LiMn _2-z Ni _z O ₄ (0<z<2), LiMn _2-z Co _z O ₄ (0<z<2), LiCoPO ₄ , LiFePO _{4 ,} and the like.

In one embodiment, the lithium metal oxide may include excess lithium (Lithium-rich) metal oxide. For example, the excess lithium metal oxide may be represented by Chemical Formula 12 below.

[Formula 12]

Li _x Ni _y Mn _z Co _w O ₂

In Chemical Formula 12, 1<x≤2, 0<y≤1, 0<z≤1, and 0<w≤1.

In Chemical Formula 12, x/y+z+w may be greater than 1.1, greater than 1.2, or 1.2 to 1.5.

In some embodiments, the average charging voltage of the lithium secondary battery may be 4.5V or more. For example, by including excess lithium metal oxide as a cathode active material, a high voltage range can be implemented.

In addition, since the electrolyte for a lithium secondary battery includes the aforementioned additive for a secondary battery, the electrochemical stability of the lithium secondary battery can be maintained even at a high voltage of 4.5 V or more.

For example, the binder may serve to attach the cathode active materials to each other or to attach the cathode active material to the cathode current collector 110 . For example, the binder is polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polymers including ethylene oxide, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like.

For example, the conductive material may be used to impart conductivity to the cathode active material layer 110 . For example, the conductive material may include natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, metal powder such as copper, nickel, aluminum, or silver, or metal fiber. In addition, the conductive material may include a conductive polymer such as a polyphenylene derivative.

The negative electrode 130 may include a negative electrode current collector 125 and a negative electrode active material layer 120 on the negative electrode current collector 125 .

The anode active material layer 120 may include an anode active material, and, if necessary, an anode binder and an anode conductive material.

For example, the anode current collector 125 may include gold, stainless steel, nickel, aluminum, titanium, copper, or the like.

For example, the anode active material may be a material capable of intercalating and deintercalating lithium ions. For example, the anode active material may include a carbon-based material, lithium metal, a lithium metal alloy, a silicon-based material, a transition metal oxide, and the like.

The carbon-based material may include crystalline carbon, amorphous carbon, and the like. For example, the crystalline carbon may include graphite such as amorphous, plate, flake, spherical or fibrous natural graphite or artificial graphite. In addition, the amorphous carbon may include soft carbon, hard carbon, mesophase pitch carbide, calcined coke, and the like.

The alloy of lithium metal is from the group consisting of lithium and Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al and Sn. Alloys of selected metals may be used.

The silicon-based material may include Si, SiOx (0<x<2), a combination of graphite and Si, a material coated with Si on the surface of graphite particles, a material coated with Si and carbon on the surface of graphite particles, and the like.

The transition metal oxide may include vanadium oxide, lithium vanadium oxide, and the like.

The anode binder and the anode conductive material may be materials substantially the same as or similar to the above-described cathode binder and the anode conductive material.

For example, the anode binder is polyvinylidene fluoride, polyvinyl alcohol, carboxymethylcellulose, a mixture of carboxymethylcellulose and polyacrylic acid, hydroxypropylcellulose, diacetylcellulose, a polymer including ethylene oxide, polyvinylchloride , carboxylated polyvinylchloride, polyvinylfluoride, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon etc. may be included.

For example, the negative electrode binder may be an aqueous binder such as styrene-butadiene rubber (SBR). Also, for example, the negative electrode binder may be used together with a thickener such as carboxymethyl cellulose (CMC).

A separator 140 may be interposed between the anode 100 and the cathode 130 .

For example, the separator 140 may include ethylene homopolymer or propylene homopolymer.

An electrode cell may be formed including the anode 100 , the cathode 130 and the separator 140 . A plurality of electrode cells may be stacked to form the electrode assembly 150 (however, one electrode cell is shown in FIG. 2 for convenience).

The electrode assembly 150 may be formed by winding or lamination of the separator 140 .

A lithium secondary battery according to example embodiments includes a cathode lead 107 connected to the cathode 100 and protruding out of the case 160; and a cathode lead 127 connected to the cathode 130 and protruding out of the case 160 .

The anode 100 and the cathode lead 107 may be electrically connected. Similarly, the cathode 130 and the cathode lead 127 may be electrically connected.

The cathode lead 107 may be electrically connected to the cathode current collector 105 . Also, the anode lead 130 may be electrically connected to the anode current collector 125 .

The cathode current collector 105 may include a protrusion (anode tab) 106 on one side. The positive electrode active material layer 110 may not be formed on the positive electrode tab 106 . The positive electrode tab 106 may be integral with the positive electrode current collector 105 or may be connected by welding or the like. The positive current collector 105 and the positive electrode lead 107 may be electrically connected through the positive electrode tab 106 .

The negative current collector 125 may include a protrusion (negative electrode tab) 126 on one side. The negative electrode active material layer 120 may not be formed on the negative electrode tab. The negative electrode tab 126 may be integral with the negative electrode current collector 125 or may be connected by welding or the like. The negative current collector 125 and the negative electrode lead 127 may be electrically connected through the negative electrode tab 126 .

For example, the electrode assembly 150 and the electrolyte solution for a secondary lithium battery according to exemplary embodiments of the present invention may be accommodated in the case 160 to form a secondary lithium battery.

For example, the lithium secondary battery may be a cylindrical shape, a prismatic shape, a pouch shape, or a coin shape.

Hereinafter, preferred embodiments are presented to aid understanding of the present invention, but these embodiments are only illustrative of the present invention and do not limit the scope of the appended claims, and embodiments within the scope and spirit of the present invention It is obvious to those skilled in the art that various changes and modifications to the are possible, and it is natural that these variations and modifications fall within the scope of the appended claims.

Examples and Comparative Examples

(1) Preparation of electrolyte solution

A 1 M LiPF ₆ solution was prepared using an organic solvent in which ethylene carbonate (EC), ethylmethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 2:5:5.

In the LiPF ₆ solution, based on the total weight (100wt%) of the electrolyte, the additives according to Table 1 are mixed, and 1wt% of fluoroethylene carbonate (FEC) and 1wt% of vinylidene carbonate (VC) are added as auxiliary additives and mixed to prepare electrolyte solutions of Examples and Comparative Examples.

(2) Manufacture of lithium secondary battery

A positive electrode slurry was prepared by dispersing LiCoO ₂ , PVDF, and carbon black in NMP at a weight ratio of 94:3:3. An anode was prepared by coating the cathode slurry on an aluminum foil.

An anode slurry was prepared by dispersing graphite, PVDF, and carbon black in water at a weight ratio of 96:3:1. A negative electrode was prepared by coating the negative electrode slurry on a copper foil.

In the above, an electrode assembly was formed by interposing a separator (polyethylene) between the positive electrode and the negative electrode. The electrode assembly and the electrolyte solution according to the above were put into a pouch and vacuum-packed to prepare a lithium secondary battery.

Classification (% by weight) additive auxiliary additives FEC VC Example 1 A-1 (1wt%) 1wt% 1wt% Example 2 A-2 (1wt%) 1wt% 1wt% Example 3 A-3 (1wt%) 1wt% 1wt% Example 4 A-4 (1wt%) 1wt% 1wt% Example 5 A-5 (1wt%) 1wt% 1wt% Example 6 A-2 (0.1wt%) 1wt% 1wt% Example 7 A-2 (5wt%) 1wt% 1wt% Comparative Example 1 - - - Comparative Example 2 - 1wt% 1wt% Comparative Example 3 A-6 (1wt%) 1wt% 1wt% Comparative Example 4 A-7 (1wt%) 1wt% 1wt%

The specific component names listed in Table 1 are as follows.

Additive (A)

1) A-1: A compound represented by the following formula (4)

[Formula 4]

2) A-2: A compound represented by the following formula (5)

[Formula 5]

3) A-3: A compound represented by the following formula (6)

[Formula 6]

4) A-4: A compound represented by the following formula (7)

[Formula 7]

5) A-5: A compound represented by the following formula (8)

[Formula 8]

6) A-6: LiFOB represented by Formula 10-1

[Formula 10-1]

7) A-7: LiPO of Formula 13 ₂ F ₂

[Formula 13]

Experimental example

(1) Capacity retention rate

Lithium secondary batteries of Examples and Comparative Examples were charged with a constant current at room temperature (25° C.) to 4.5V at 1.0C, and discharged at 1.0C to 2.75V to measure the discharge capacity A1.

Thereafter, it was charged with a constant current at 0.5C to 4.2V and left at a high temperature (45° C.) for 1 week. The lithium secondary battery left for one week was charged with a constant current at 1.0C to 4.2V and discharged at 1.0C to 2.75V to measure the discharge capacity A2.

The capacity retention ratio (%) was calculated according to Equation 1 below. The evaluation results are shown in Table 2.

[Equation 1]

Capacity retention rate (%) = A2/A1 × 100

(2) Room temperature life characteristics

Lithium secondary batteries of Examples and Comparative Examples were charged with a constant current at room temperature (25° C.) to 4.5V at 1.0C, and discharged at 2.0C to 2.75V to measure initial discharge capacity B1.

The charge and discharge were repeatedly performed 500 times, and the discharge capacity B2 at the 500th time was measured. Room temperature life characteristics (%) were calculated according to Equation 2 below. The evaluation results are shown in Table 2.

[Equation 2]

Room temperature life characteristics (%) = B2/B1 × 100

(3) High temperature life characteristics

Lithium secondary batteries of Examples and Comparative Examples were charged with a constant current at 1.0C to 4.5V at a high temperature (45°C), and discharged at 2.0C to 2.75V to measure initial discharge capacity C1.

The charge and discharge were repeatedly performed 500 times, and the discharge capacity C2 at the 500th time was measured. High temperature life characteristics (%) were calculated according to Equation 1 below. The evaluation results are shown in Table 2.

[Equation 3]

High temperature life characteristics (%) = C2/C1 × 100

division capacity retention rate
(%) Room temperature life characteristics
(%) High temperature life characteristics
(%) Example 1 84.2 94.5 92.2 Example 2 86.5 92.7 92.5 Example 3 86.4 93.5 93.2 Example 4 86.1 93.3 93.3 Example 5 86.7 93.6 93.5 Example 6 83.8 92.1 91.7 Example 7 84.0 92.3 91.4 Comparative Example 1 80.1 90.8 83.9 Comparative Example 2 80.8 92.6 85.2 Comparative Example 3 83.1 92.0 90.1 Comparative Example 4 82.2 91.2 89.6

Referring to Tables 1 and 2, it can be seen that the room temperature lifespan and high temperature stability are improved in the examples by including the compounds represented by Formulas 1 to 3 as additives.

In the case of Example 6 and Example 7, in which the contents of the additives represented by Formulas 1 to 3 were relatively small, it could be seen that the high-temperature capacity retention rate and the room temperature and high-temperature lifespan characteristics were relatively reduced.

On the other hand, since Comparative Examples do not include the additives represented by Chemical Formulas 1 to 3 as additives of the electrolyte solution for a lithium secondary battery, it can be confirmed that the lifespan at room temperature and the stability at high temperature are deteriorated.

Specifically, in Comparative Example 1 and Comparative Example 2 not including the additive, it can be confirmed that the discharge capacity of the secondary battery is rapidly lowered by repeated cycles. Comparative Example 3 and Comparative Example 4 including LiFOB and LiLiPO ₂ F ₂ as additives, respectively, also showed a significant decrease in lifespan characteristics at room temperature and a slight decrease in high-temperature stability.

100: positive electrode 105: positive electrode current collector
106: positive tab 107: positive lead
110: positive active material layer 120: negative active material layer
125: negative current collector 126: negative electrode tab
127: negative lead 130: negative electrode
140: separator 150: electrode assembly
160: case

Claims (13)

An additive for a secondary battery comprising at least one of the compounds represented by Formulas 1 to 3 below:
[Formula 1]

[Formula 2]

[Formula 3]

(In Formulas 1 to 3, M ⁺ is a monovalent cation,
Rf ₁ and Rf ₂ are each independently fluorine or a fluorinated alkyl group having 1 to 4 carbon atoms).
The additive for a secondary battery of claim 1, wherein Rf ₁ and Rf ₂ in Formula 2 and Formula 3 are each independently fluorine or a trifluoromethyl group.
The method according to claim 1, wherein in Formulas 1 to 3, M ⁺ is a lithium cation, the secondary battery additive.
The additive for a secondary battery according to claim 1, comprising at least one of the compounds represented by the following Chemical Formulas 4 to 8:
[Formula 4]

[Formula 5]

[Formula 6]

[Formula 7]

[Formula 8]
.
lithium salt;
organic solvents; and
An electrolyte solution for a lithium secondary battery comprising an additive containing at least one of the compounds represented by Formulas 1 to 3 below:
[Formula 1]

[Formula 2]

[Formula 3]

(In Formulas 1 to 3, M ⁺ is a monovalent cation,
Rf ₁ and Rf ₂ are each independently fluorine or a fluorinated alkyl group having 1 to 4 carbon atoms).
The method according to claim 5, The content of the additive is 0.01% to 10% by weight of the total weight of the electrolyte, the electrolyte solution for a lithium secondary battery.
The electrolyte solution for a lithium secondary battery according to claim 5, wherein the organic solvent includes at least one of a carbonate-based solvent, an ester-based solvent, an ether-based solvent, a ketone-based solvent, an alcohol-based solvent, and an aprotic solvent.
The electrolyte solution for a lithium secondary battery according to claim 7, wherein the organic solvent includes a linear carbonate-based solvent and a cyclic carbonate-based solvent.
The method according to claim 8, wherein the ratio of the volume of the cyclic carbonate-based solvent to the volume of the linear carbonate-based solvent is 0.1 to 1, the electrolyte solution for a lithium secondary battery.
The method according to claim 5, wherein at least one of a fluorine-containing cyclic carbonate-based compound, a fluorine-containing phosphate-based compound, a cyclic carbonate-based compound having a double bond, a sultone-based compound, a borate-based compound, a cyclic sulfate-based compound, and a phosphorus-based compound having a silyl group Further comprising an auxiliary additive containing one, the electrolyte solution for a lithium secondary battery.
The method according to claim 10, The content of the auxiliary additive is 0.1% to 10% by weight of the total weight of the electrolyte, the electrolyte solution for a lithium secondary battery.
The method according to claim 5, wherein the concentration of the lithium salt with respect to the organic solvent is 0.1M to 2M, the electrolyte solution for a lithium secondary battery.
anode;
a cathode facing the anode; and
A lithium secondary battery comprising the electrolyte for a lithium secondary battery according to claim 5 .