KR20210029067A - Additive for electrolyte, nonaqueous electrolyte for lithium secondary battery comprising the same, and lithium secondary battery - Google Patents

Abstract

The present invention relates to an electrolyte additive for a lithium secondary battery, an electrolyte including the additive, and a lithium secondary battery including the electrolyte, wherein the additive includes diphosphonic acid borate or diphosphonic acid phosphorate. The electrolyte additive of the present invention has an effect of sufficiently improving the capacity retention rate and life retention rate of the secondary battery.

Description

Electrolyte additive, lithium secondary battery electrolyte and lithium secondary battery containing the same {ADDITIVE FOR ELECTROLYTE, NONAQUEOUS ELECTROLYTE FOR LITHIUM SECONDARY BATTERY COMPRISING THE SAME, AND LITHIUM SECONDARY BATTERY}

The present invention relates to an electrolyte solution additive for a lithium secondary battery, an electrolyte solution including the additive, and a lithium secondary battery including the electrolyte solution.

Recently, interest in medium and large-capacity lithium secondary batteries for application to power sources for next-generation automobiles has been increasing.

In this regard, when a layered oxide containing an excessive amount of lithium (i.e., lithium-rich) is used as the positive electrode active material, the charging driving voltage of the battery can be improved, and a silicon-based material other than a carbon-based material is used. Since it can be used as an anode active material, the capacity of the battery can be improved.

Meanwhile, in a general lithium secondary battery, a lithium salt dissolved in an organic solvent is used as an electrolyte.The overlithium positive electrode active material creates a high voltage environment while generating oxygen gas during the first charge, and the silicon-based negative electrode active material is repeatedly charged and discharged. Accordingly, severe volume expansion occurs, and cracking is formed on the surface thereof, resulting in a decomposition reaction of the electrolyte in common on the surface of the electrode to which each active material is applied.

As a result, the electrochemical performance of the battery is rapidly deteriorated due to the gradual depletion of the electrolyte, and the electrochemical reaction rate of the battery decreases as a thick film acting as resistance is formed on the surface of each electrode, resulting in a decomposition of the electrolyte solution. There is a problem in that the electrochemical stability of the battery is not guaranteed because an acidic substance (eg, HF, etc.) melts each electrode film or damages the positive electrode active material.

Unexamined Patent Publication 10-2009-0039211

The present invention aims to solve the above-noted problem by adding a special additive to the electrolyte for a lithium secondary battery.

Specifically, the present invention is to provide an oxidative decomposition additive, which is a material capable of forming a protective film on the surface of an anode by oxidative decomposition with an electrolyte additive.

In another embodiment of the present invention, it is intended to provide a secondary battery electrolyte comprising a reduction decomposition additive, which is a material that forms a protective film on the surface of a negative electrode by reducing decomposition together with the oxidative decomposition additive.

In addition, the present invention is to provide a lithium secondary battery including the electrolyte.

The present invention provides a secondary battery electrolyte additive comprising at least one selected from the group consisting of ionic compounds represented by the following Chemical Formulas 1 and 2 below.

[Formula 1] [Formula 2]

In Formulas 1 and 2 above

M is a monovalent cation of an alkali metal, ammonium, phosphonium or sulfonium,

n is an integer from 1 to 2,

m is 4-2n,

z is an integer from 1 to 3,

l is 6-2z,

X and Y are each independently hydrogen, halogen, C1-C6 alkyl, C1-C6 alkoxy group-substituted alkyl, alkenyl, alkynyl, -NR1R2, -OR3, phenyl or heteroaryl,

R1 and R2 are each independently C1-C6 alkyl, or R1 and R2 may be connected to each other to form a saturated or unsaturated ring that may contain a hetero atom,

R3 is C1-C6 alkyl or tri(C1-C6)alkylsilyl,

The X and Y may be connected to each other to form a saturated or unsaturated ring that may contain a hetero atom, or to form methylene.

The hetero atom may be nitrogen or oxygen.

The present invention preferably provides a secondary battery electrolyte additive in which the ionic compound is at least one selected from the group consisting of the following compound group A and compound group B.

<Compound group A>

<Compound group B>

The secondary battery electrolyte additive is an oxidative decomposition additive.

The present invention provides a secondary battery electrolyte comprising at least one oxidative decomposition additive selected from the group consisting of ionic compounds represented by Chemical Formulas 1 and 2 above.

The secondary battery electrolyte may further include a reduction decomposition additive.

The present invention provides a secondary battery comprising the secondary battery electrolyte.

The present invention relates to a secondary battery electrolyte containing an ionic compound represented by Formula 1 or Formula 2. By adding the additive to the secondary battery electrolyte, the electrochemical performance, reaction speed, and stability of the battery may be improved. Specifically, a protective film is formed on the surface of the anode by the oxidative decomposition additive, so that the electrochemical performance, reaction speed, and stability of the battery may be improved. In addition, the electrolyte solution additive of the present invention has the effect of sufficiently improving the capacity retention rate and the life retention rate of a secondary battery.

In addition, since it is included in the electrolyte solution together with a solvent and an electrolyte, it is possible to simultaneously apply a lithium secondary positive electrode active material and a silicon-based negative electrode active material, and as a result, a lithium secondary battery having a high voltage and a high capacity can be implemented.

In addition, the protective film is formed on the surface of the anode by the oxidative decomposition additive, the protective film is formed on the surface of the cathode by the reduction decomposition additive, and the function of removing acidic substances by the reactive additive may be performed at the same time.

Hereinafter, embodiments of the present invention will be described in detail. However, this is presented as an example, and the present invention is not limited thereby, and the present invention is only defined by the scope of the claims to be described later.

Lithium secondary batteries can be classified into lithium-ion batteries, lithium-ion polymer batteries, and lithium polymer batteries according to the type of separator and electrolyte used, and can be classified into cylindrical, rectangular, coin-type, and pouch-type according to their shape. Depending on the size, it can be divided into bulk type and thin film type. The structure and manufacturing method of these batteries are widely known in this field, and thus detailed descriptions thereof will be omitted.

A lithium secondary battery is constructed by sequentially stacking a negative electrode, a separator, and a positive electrode, and then receiving them in a battery container while being wound in a spiral shape.

The negative electrode includes a current collector and a negative active material layer formed on the current collector, and the negative active material layer includes a negative active material. As the negative active material, lithium metal, an alloy of lithium metal, a material capable of doping and undoping lithium, or a transition metal oxide is used as a material capable of reversibly intercalating and deintercalating lithium ions.

Among the negative active materials, carbon-based materials such as graphite are widely known as materials capable of reversibly intercalating and deintercalating lithium ions. Graphite has a low discharge voltage of -0.2V compared to lithium, and a battery using graphite as an anode active material exhibits a high discharge voltage of 3.6V, providing an advantage in terms of energy density of a lithium battery. In addition, secondary batteries using graphite as an anode active material are the most widely used by ensuring a long life of lithium secondary batteries with excellent reversibility.

However, the graphite active material has a problem of low capacity in terms of energy density per unit volume of the electrode plate due to the low density of graphite (theoretical density 2.2 g/cc) when manufacturing the electrode plate, and at high discharge voltage, side reactions with the used organic electrolyte are likely to occur. There is a problem of swelling of the battery and a decrease in capacity accordingly. Therefore, recently, silicon-based materials having a high capacity as a material capable of dope and undoping lithium are in the spotlight as a substitute.

Meanwhile, the positive electrode includes a current collector and a positive electrode active material layer formed on the current collector. As the positive electrode active material, a compound capable of reversible intercalation and deintercalation of lithium (lithiated intercalation compound) may be used, and generally LiCoO ₂ , LiMn ₂ O ₄ , LiNi _1-x Co _x O ₂ (0 <x <1), etc., which have a structure capable of intercalating lithium ions, are mainly used as oxides of lithium and transition metals.

Recently, a technology for improving the charging driving voltage of a battery by using a layered oxide containing an excessive amount of lithium (ie, lithium-rich) as a positive electrode active material has been studied. In this case, since a silicon-based material other than a carbon-based material can be used as the negative electrode active material, the capacity of the battery can be further improved.

Meanwhile, in a general lithium secondary battery, a lithium salt dissolved in an organic solvent is used as an electrolyte.The overlithium positive electrode active material creates a high voltage environment while generating oxygen gas during the first charge, and the silicon-based negative electrode active material is repeatedly charged and discharged. Accordingly, severe volume expansion occurs, and cracking is formed on the surface thereof, resulting in a decomposition reaction of the electrolyte in common on the surface of the electrode to which each active material is applied.

As a result, the electrochemical solution is gradually depleted and the electrochemical performance of the battery is rapidly deteriorated, and as a thick film acting as resistance is formed on the surface of each electrode, the electrochemical reaction rate of the battery is lowered. In addition, there is a problem that the electrochemical stability of the battery is not guaranteed because an acidic substance (eg, HF, etc.) generated as a result of decomposition of the electrolyte melts each electrode film or damages the positive electrode active material.

In order to solve the above problem, an electrolyte solution to which a functional additive is added has recently been developed.

Functional additives include reduction decomposition additives, oxidative decomposition additives, and reactive additives, and oxidative decomposition additives are substances that perform oxidation decomposition to form a protective film on the surface of the anode, and the electrolyte solution decomposition reaction on the anode surface You can prevent this from happening.

When the oxidative decomposition additive is added to the electrolyte, a high voltage lithium secondary battery is implemented by applying a lithium positive electrode active material, while the structure of the active materials is stably maintained while the battery is driven, so that the electrochemical performance and reaction speed of the battery And it can contribute to improve the stability.

<Oxidative decomposition additive>

However, the previously developed oxidative decomposition additives do not sufficiently satisfy the capacity retention rate and life retention rate.

Accordingly, the present inventors have tried to develop an oxidative decomposition additive that prevents the decomposition of the electrolyte and damages the active material by adding it to the electrolyte. When used as a type additive, it was confirmed that the electrochemical performance, reaction rate, and stability of the lithium secondary battery can be improved, and the capacity retention rate and the life retention rate can be sufficiently improved, and the present invention was completed.

[Formula 1] [Formula 2]

In Formulas 1 and 2 above

M is a monovalent cation of an alkali metal, ammonium, phosphonium or sulfonium,

n is an integer from 1 to 2,

m is 4-2n,

z is an integer from 1 to 3,

l is 6-2z,

X and Y are each independently hydrogen, halogen, C1-C6 alkyl, C1-C6 alkoxy group-substituted alkyl, alkenyl, alkynyl, -NR1R2, -OR3, phenyl or heteroaryl,

R1 and R2 are each independently C1-C6 alkyl, or R1 and R2 may be connected to each other to form a saturated or unsaturated ring that may contain a hetero atom,

R3 is C1-C6 alkyl or tri(C1-C6)alkylsilyl,

The X and Y may be connected to each other to form a saturated or unsaturated ring that may contain a hetero atom, or to form methylene.

The hetero atom may be nitrogen or oxygen.

The oxidative decomposition additive may be preferably at least one selected from the group consisting of the following compound group A and compound group B.

<Compound group A>

<Compound group B>

The ionic compound represented by Formula 1 or Formula 2 used as the oxidative decomposition additive of the present invention may be purchased or prepared.

In the case of manufacturing, the manufacturing method is not limited, but may preferably be the method of Reaction Scheme 1 below.

[Scheme 1]

In the above formula, M is a monovalent cation of an alkali metal, ammonium, phosphonium or sulfonium

X and Y are each independently hydrogen, halogen, C1-C6 alkyl, C1-C6 alkoxy group-substituted alkyl, alkenyl, alkynyl, -NR1R2, -OR3, phenyl or heteroaryl,

R1 and R2 are each independently C1-C6 alkyl, or R1 and R2 may be connected to each other to form a saturated or unsaturated ring that may contain a hetero atom,

R3 is C1-C6 alkyl or tri(C1-C6)alkylsilyl,

The X and Y may be connected to each other to form a saturated or unsaturated ring that may contain a hetero atom, or to form methylene.

The hetero atom may be nitrogen or oxygen.

Compounds of Formulas 1 and 2 can be prepared by reaction of tetramethylsilylphosphonic acid prepared by trimethylsilylation reaction of diphosphonic acid derivatives with MBF4 or MPF6, and adjusting the equivalent weight of tetramethylsilylphosphonic acid. Thus, the number of fluorine in the molecule can be controlled.

<Electrolyte>

The present invention is an electrolyte; solvent; At least one oxidative decomposition additive selected from the group consisting of ionic compounds represented by the following Chemical Formulas 1 and 2; And it provides a secondary battery electrolyte comprising a reduction decomposition additive.

[Formula 1] [Formula 2]

In Formulas 1 and 2 above

M is a monovalent cation of an alkali metal, ammonium, phosphonium or sulfonium,

n is an integer from 1 to 2,

m is 4-2n,

z is an integer from 1 to 3,

l is 6-2z,

X and Y are each independently hydrogen, halogen, C1-C6 alkyl, C1-C6 alkoxy group-substituted alkyl, alkenyl, alkynyl, -NR1R2, -OR3, phenyl or heteroaryl,

R1 and R2 are each independently C1-C6 alkyl, or R1 and R2 may be connected to each other to form a saturated or unsaturated ring that may contain a hetero atom,

R3 is C1-C6 alkyl or tri(C1-C6)alkylsilyl,

The X and Y may be connected to each other to form a saturated or unsaturated ring that may contain a hetero atom, or to form methylene.

The hetero atom may be nitrogen or oxygen.

The electrolyte solution of the present invention may contain 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. When the oxidative decomposition additive is included in the above content, decomposition of the electrolyte solution may be prevented and damage to the positive electrode active material may be prevented, and as a result, the capacity maintenance rate and the life maintenance rate of the battery may be improved.

The present invention may further include a conventional oxidative decomposition additive used in the art in addition to the oxidative decomposition additive of the present invention.

Examples of the conventional oxidative decomposition additive include the following LiFOB, LiBOB, WCA1, WCA2, WCA3, and the like.

The present invention is one of fluoroethylene carbonate (FEC) and vinylene carbonate (VC), propanesultone (PS), propanylsultone (PRS), or these It may contain a mixture of.

The reducing decomposition additive may include 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. When the reduction decomposition additive is included in the above amount, decomposition of the electrolyte solution may be prevented and damage to the negative electrode active material may be prevented.

The electrolyte solution of the present invention may further include a reactive additive, and the reactive additive may be a compound containing a silyl group. Specific examples include tris (trimethylsilyl) phosphite (TMSP), tris (trimethylsilyl) phosphate ( TMSPA) and the like. The reactive additive may include 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 electrolyte of the present invention contains a lithium salt as an electrolyte, preferably LiPF ₆ , LiBF ₄ , LiClO ₄ , LiCl, LiBr, LiI, LiB ₁₀ Cl ₁₀ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, LiN(SO ₂ C ₂ F ₅ ) ₂ , Li(CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiB(C ₆ H ₅ ) ₄ , Li(SO ₂ F) ₂ N (LiFSI) and (CF ₃ SO ₂ ) _{2 It} may be one or more selected from the group consisting of NLi.

The concentration of the lithium salt in the electrolyte solution of the present invention may be 0.1 to 2 M.

The solvent included in the electrolytic solution of the present invention may be a carbonate-based, ester-based, ether-based, ketone-based, alcohol-based, aprotic solvent, or a combination thereof. The solvent is preferably ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), or a combination thereof. have.

The lithium secondary battery electrolyte of the present invention is generally stable in a temperature range of -20°C and can maintain electrochemically stable characteristics even at a voltage in the 4.5V range, so it can be applied to all lithium secondary batteries such as lithium ion batteries and lithium polymer batteries. have.

<Secondary battery>

In another embodiment of the present invention, the present invention is a positive electrode; cathode; A separator interposed between the anode and the cathode; And an electrolytic solution impregnated with the anode, cathode, and separator including an electrolyte, a solvent and an additive to have ion conductivity, wherein the additive is one selected from the group consisting of ionic compounds represented by Chemical Formulas 1 and 2 It provides a lithium secondary battery comprising an oxidative decomposition additive and a reduction decomposition additive including the above.

In another embodiment of the present invention, the electrolyte solution provides a lithium secondary battery further comprising a reactive additive including a silyl group.

The description of the electrolyte solution included in the secondary battery of the present invention is the same as that of the previous electrolyte solution.

The lithium secondary battery of the present invention includes a current collector as a positive electrode and a positive active material layer formed on the current collector, and the positive active material layer includes a positive active material.

In the present invention, any positive electrode active material available in the art may be used as the positive electrode active material. For example, the positive electrode active material is a lithium-containing transition metal oxide, that is, a lithium cobalt-based oxide, a lithium manganese-based oxide, a lithium copper oxide, a lithium nickel-based oxide, a lithium manganese composite oxide, and a lithium-nickel-manganese-cobalt-based oxide. At least one selected from the group consisting of may be preferably used, for example 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 and LiFePO ₄ selected from the group consisting of Any one or a mixture of two or more of them may be used.

In addition, according to one embodiment, the lithium secondary battery of the present invention may include a lithium-rich positive electrode active material, and the positive electrode active material may include a compound represented by Formula 3 below.

[Formula 3]

Li _x Ni _y Mn _z Co _w O ₂

In Formula 3, 1<x≤2, 0<y≤1, 0<z≤1, and 0<w≤1.

The positive electrode active material layer also includes a binder and/or a conductive material.

The binder adheres well the positive electrode active material particles to each other, and also plays a role in attaching the positive electrode active material to the current collector well, and representative examples thereof include polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, and polyvinyl Chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride (PVDF), polyethylene, polypropylene , Styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc. may be used, but the present invention is not limited thereto.

The conductive material is used to impart conductivity to the electrode, and in the battery constituted, any material may be used as long as it does not cause chemical change and is an electron conductive material. Examples of such materials include natural graphite, artificial graphite, carbon black, acetylene black, and Ketjen. Metal powders such as black, carbon fiber, copper, nickel, aluminum, and silver, metal fibers, etc. may be used, and conductive materials such as polyphenylene derivatives may be used alone or in combination of one or more.

The lithium secondary battery includes a current collector as a negative electrode and a negative active material layer formed on the current collector, and the negative active material layer includes a negative active material. The present invention includes a carbon-based material, lithium metal, lithium metal alloy, silicon-based or transition metal oxide as a material capable of reversibly intercalating/deintercalating lithium ions as the negative electrode active material.

The carbon-based material includes crystalline carbon and amorphous carbon. Examples of the crystalline carbon include graphite such as amorphous, plate-shaped, flake, spherical or fibrous natural graphite or artificial graphite, and examples of the amorphous carbon include soft carbon (low-temperature calcined carbon). Alternatively, hard carbon, mesophase pitch carbide, and fired coke may be used.

As the lithium metal alloy, in 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 The alloy of the metal of choice can be used.

The silicon-based material may be a combination of graphite and silicon, a material coated with silicon on the surface of the graphite particles, or a material in which silicon and carbon are simultaneously coated on the surface of the graphite particles, and may be a SiO _x or Si carbon-based material.

Examples of the transition metal oxide include vanadium oxide and lithium vanadium oxide.

The negative active material layer may further include a binder and/or a conductive material.

The binder serves to attach the negative electrode active material particles well to each other, and also serves to attach the negative electrode active material well to the current collector, and representative examples thereof include polyvinyl alcohol, carboxylmethyl cellulose, carboxymethylcellulose ( A mixture of carboxylmethyl cellulose)/polyacrylic acid, hydroxypropyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride fluoride), polymer containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene (polyethylene), polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, styrene-butadiene rubber/carboxymethylcellulose One or more of a mixture of (carboxymethyl cellulose), epoxy resin, or nylon may be used, but the present invention is not limited thereto.

The conductive material is used to impart conductivity to the electrode, and any electronically conductive material can be used without causing a chemical change in the configured battery, such as natural graphite, artificial graphite, Carbon-based materials such as carbon black, acetylene black, ketjen black, and carbon fiber; Metal-based materials such as metal powders such as copper, nickel, aluminum, and silver, or metal fibers; Conductive polymers such as polyphenylene derivatives; Alternatively, a conductive material containing a mixture thereof may be used.

The average charging voltage of the lithium secondary battery may be 4.5 V or more. This is a high voltage range that can be expressed when the positive electrode including the perlithium positive electrode active material and the negative electrode including the silicon-based negative electrode active material are applied, and can be stably maintained by the functional additive included in the electrolyte solution of the present invention. have.

Hereinafter, examples will be described in detail in order to describe the present invention in detail. However, the embodiments according to the present invention may be modified in various other forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to more completely describe the present invention to those of ordinary skill in the art.

[Synthesis Example 1] Preparation of Compound 1-1

[Formula 1-1]

While maintaining a nitrogen atmosphere in 100 ml of a dry-prepared two-neck flask, 300 mg (3.2 mmol) of lithium tetrafluoroborate was added, and 20 ml of dimethyl carbonate was added dropwise. While stirring at room temperature, 3.2 g (3.2 mmol) of tetrakis(trimethylsilyl)(1-((trimethylsilyl)oxy)ethane-1,1-dinyl)bis(phosphonate) was slowly added dropwise. The reaction was stirred at room temperature for 12 hours, and dimethyl carbonate was removed by distillation under reduced pressure, and then the target compound lithium 6,6-difluoro-3-methyl-2,3,4-tris(trimethylsilyl)oxy) through vacuum drying. -1,5,2,4,6-dioxadiphorfavorinan-6-Uide-2,4-dioxide 1.4g (yield = 92%) was obtained.

Elemental analysis of C and H: C, 27.23; H, 6.29

Theoretical value: C, 27.74; H, 6.35; B, 2.27; F, 7.98; Li, 1.46; O, 23.51; P, 13.01; Si, 17.69

NMR/CDCl ₃ : 0.08 (s, 9H), 0.12 (s, 18), 1.42 (s, 3H)

[Synthesis Example 2] Preparation 2 of Compound 1-2

[Formula 1-2]

Tetrakis(trimethylsilyl)(1-((trimethylsilyl)oxy)ethane-1,1-dinyl)bis(phosphonate) 1 equivalent instead of tetrakis(trimethylsilyl)(1-((trimethylsilyl)oxy) Except for the use of 2 equivalents of ethane-1,1-dinyl) bis (phosphonate), it was carried out in the same manner as in Synthesis Example 1 to prepare a compound of Formula 1-2.

Elemental analysis of C and H: C, 30.11; H, 6.95

Theoretical value: C, 30.77; H, 7.04; B, 1.26; Li, 0.81; O, 26.08; P, 14.43; Si, 19.62

NMR/CDCl ₃ : 0.06 (s, 18H), 0.10 (s, 36), 1.35 (s, 6H)

[Synthesis Example 3] Preparation of Compound 2-1

[Formula 2-1]

While maintaining a nitrogen atmosphere in 100 ml of a dry-prepared two-neck flask, 486 mg (3.2 mmol) of lithium hexafluorophosphate was added, and 20 ml of dimethyl carbonate was added dropwise. While stirring at room temperature, 3.2 g (3.2 mmol) of tetrakis(trimethylsilyl)(1-((trimethylsilyl)oxy)ethane-1,1-dinyl)bis(phosphonate) was slowly added dropwise. The reaction was stirred at room temperature for 12 hours, and dimethyl carbonate was removed by distillation under reduced pressure, and then 1.5 g of the compound of Formula 2-1 (yield = 90%) was obtained through vacuum drying.

Elemental analysis of C and H: C, 24.51; H, 5.54

Theoretical value: C, 24.72; H, 5.66; F, 14.22; Li, 1.30; O, 20.95; P, 17.39; Si, 15.76

NMR/CDCl ₃ : 0.09 (s, 9H), 0.15 (s, 18), 1.48 (s, 3H)

[Synthesis Example 4] Preparation of Compound 2-2

[Formula 2-2]

Tetrakis(trimethylsilyl)(1-((trimethylsilyl)oxy)ethane-1,1-dinyl)bis(phosphonate) 1 equivalent instead of tetrakis(trimethylsilyl)(1-((trimethylsilyl)oxy) Except for the use of 2 equivalents of ethane-1,1-dinyl) bis (phosphonate), it was carried out in the same manner as in Synthesis Example 3 to prepare a compound of Formula 2-2.

Elemental analysis of C and H: C, 28.37; H, 6.51

Theoretical value: C, 28.81; H, 6.59; F, 4.14; Li, 0.76; O, 24.43; P, 16.89; S

NMR/CDCl ₃ : 0.08 (s, 18H), 0.11 (s, 36), 1.37 (s, 6H)

[Production Examples 1 to 4] Preparation of electrolyte

1M LiPF6 and FEC (fluoroethylene carbonate) in a non-aqueous organic solvent in which ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in 2:5:5 (v/v/v) 1% by weight was added, and 2% by weight of the additives of Synthesis Examples 1 to 4 were added, respectively, to prepare an electrolyte solution for a secondary battery.

[Comparative Preparation Examples 1 to 3] Preparation of electrolytic solution

Prepared in the same manner as in Preparation Examples 1 to 4, but no additives were added (Comparative Preparation Example 1), LiBOB was added instead of the Synthesis Example (Comparative Preparation Example 2), or WCA-2 was added (Comparative Preparation Example 3). Thus, an electrolyte solution was prepared.

[Examples 1 to 4 and Comparative Examples 1 to 3] Preparation of secondary battery

A positive electrode was prepared using a composition for forming a positive electrode active material layer containing 94% by weight of LiCoO2 as a positive electrode active material, 3% by weight of PVDF (polyvinylidene fluoride) as a binder, and 3% of carbon black as a conductive material. In addition, a negative electrode was prepared by including a composition for forming a negative active material layer comprising 96% by weight of graphite as a negative active material, 3% by weight of PVDF as a binder, and 1% by weight of carbon black as a conductive material.

After placing the separator on the positive electrode prepared above and placing the negative electrode thereon again, the electrolyte solutions prepared in Preparation Examples 1 to 4 and Comparative Preparation Examples 1 to 3 were respectively injected, and vacuum-packed to prepare a lithium secondary battery.

[Experimental Example] Characteristics of secondary battery

The battery characteristics of the secondary batteries prepared in Examples 1 to 4 and Comparative Examples 1 to 3 were evaluated as follows, and the results are shown in Table 1 below.

(1) DC-IR (direct current-internal resistance)

Each lithium secondary battery manufactured according to Examples 1 to 4 and Comparative Examples 1 to 3 was discharged at a constant current of 0.1C in a 50% charge state, and discharged at a constant current of 1C for 10 seconds, respectively.

The initial direct current resistance (DC-IR) was calculated by the formula ΔR=ΔV/ΔI from 10s discharge data of 1C and 5C, and the results are shown in Table 1 below.

(2) Capacity retention rate (%)

The manufactured battery was charged at room temperature (1C charge from 25℃ to 4.5V, discharged at 2.75V 1C, then charged at 0.5C to 4.2V, then left at 45℃ for 1 week, then charged to 4.2V for 1C, 2.75V 1C discharged 2 cycles) Then, the discharged capacity at the second cycle was measured and compared.

(3) Room temperature lifetime maintenance rate (%)

The manufactured battery was charged at room temperature (25℃, 1C to 4.5V, then discharged to 2.75V for 2C to measure the initial capacity, and the capacity after repeating it 500 times was measured, formula: life retention rate = (repeated 500 times) After capacity / initial capacity) * 100 to calculate the room temperature lifetime maintenance rate is shown in Table 1 below.

(4) High temperature life retention rate (%)

The manufactured battery was charged at high temperature (45℃, 1C to 4.5V, then discharged to 2.75V for 2C to measure the initial capacity, and the capacity after repeating it 500 times was measured, formula: life retention rate = (repeated 500 times) After capacity/initial capacity)*100, the high-temperature lifespan maintenance rate was calculated and shown in Table 1 below.

Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 (1) Initial DC resistance (DC-IR) (mΩ) 89.3 91.5 93.2 88.2 110.2 108.2 112.3 (2) Capacity retention rate (%) 87.6 86.7 88.2 87.5 52.2 81.6 82.3 (3) Room temperature lifetime maintenance rate (%) 95.4 94.8 94.1 95.2 67.1 92.4 91.2 (4) High temperature lifetime maintenance rate (%) 93.2 92.9 92.7 93.5 61.7 90.5 89.3

The value before and after DC-IR of a lithium secondary battery prepared using the electrolyte containing the oxidative decomposition type additive of the present invention does not contain an additive (Comparative Example 1), LiBOB is added (Comparative Example 2), or WCA-2 Compared to the case of adding (Comparative Example 3), excellent results were shown in DC-IR, capacity retention, room temperature and high-temperature life retention rate.

A lithium secondary battery manufactured using the electrolyte containing the oxidative decomposition additive of the present invention does not contain an additive (Comparative Example 1), LiBO is added (Comparative Example 2), or WCA-2 is added (Comparative Example 3) It can be seen that the capacity retention rate and life retention rate are superior compared to one case.

Claims (8)

A secondary battery electrolyte additive comprising at least one selected from the group consisting of ionic compounds represented by the following Chemical Formulas 1 and 2.
[Formula 1] [Formula 2]

In Formulas 1 and 2 above
M is a monovalent cation of an alkali metal, ammonium, phosphonium or sulfonium,
n is an integer from 1 to 2,
m is 4-2n,
z is an integer from 1 to 3,
l is 6-2z,
X and Y are each independently hydrogen, halogen, C1-C6 alkyl, C1-C6 alkoxy group-substituted alkyl, alkenyl, alkynyl, -NR1R2, -OR3, phenyl or heteroaryl,
R1 and R2 are each independently C1-C6 alkyl, or R1 and R2 may be connected to each other to form a saturated or unsaturated ring that may contain a hetero atom,
R3 is C1-C6 alkyl or tri(C1-C6)alkylsilyl,
The X and Y may be connected to each other to form a saturated or unsaturated ring that may contain a hetero atom, or to form methylene.
The hetero atom may be nitrogen or oxygen. The secondary battery electrolyte solution additive according to claim 1, wherein the ionic compound is at least one ionic compound selected from the group consisting of the following compound group A and compound group B.
<Compound group A>

<Compound group B>

Electrolytes; solvent; At least one oxidative decomposition additive selected from the group consisting of ionic compounds represented by the following Chemical Formulas 1 and 2; And a secondary battery electrolyte containing a reduction decomposition additive
[Formula 1] [Formula 2]

In Formulas 1 and 2 above
M is a monovalent cation of an alkali metal, ammonium, phosphonium or sulfonium,
n is an integer from 1 to 2,
m is 4-2n,
z is an integer from 1 to 3,
l is 6-2z,
X and Y are each independently hydrogen, halogen, C1-C6 alkyl, C1-C6 alkoxy group-substituted alkyl, alkenyl, alkynyl, -NR1R2, -OR3, phenyl or heteroaryl,
R1 and R2 are each independently C1-C6 alkyl, or R1 and R2 may be connected to each other to form a saturated or unsaturated ring that may contain a hetero atom,
R3 is C1-C6 alkyl or tri(C1-C6)alkylsilyl,
The X and Y may be connected to each other to form a saturated or unsaturated ring that may contain a hetero atom, or to form methylene.
The hetero atom may be nitrogen or oxygen. The lithium secondary battery electrolyte of claim 3, comprising 0.1 to 10% by weight of an oxidative decomposition additive The lithium secondary battery electrolyte of claim 3, further comprising a reactive additive anode; cathode; A separator interposed between the anode and the cathode; And an electrolyte having ion conductivity by impregnating the positive electrode, negative electrode, and separator containing an electrolyte, a solvent and an additive, and wherein the additive comprises the additive of claim 1 and a reduction decomposition type additive. The lithium secondary battery according to claim 6, wherein the positive electrode includes a lithium-rich positive electrode active material. The lithium secondary battery according to claim 6, wherein the negative electrode comprises a silicon-based material.