Electrolyte additive, method for preparing it, electrolyte composition and secondary battery containing the additive

Abstract

Electrolyte additive, represented by the chemical formula as follows: where M is an alkali metal, and R is hydrogen, a substituted or unsubstituted C1 to C5 alkyl group, a substituted or unsubstituted C1 to C5 perfluoroalkyl group, a substituted or unsubstituted C6 to C30 aryl group, a substituted or unsubstituted C6 to C30 perfluoroaryl group or CF3.

Description

[Technical application area]

[0001] The present invention relates to an electrolyte, and in particular to an electrolyte additive for a secondary battery and a secondary battery comprising the same. [Previous state of the art]

[0002] A secondary battery refers to a battery that can be used repeatedly because it can be charged and discharged in the same way. A lithium secondary battery, which is a representative example, works on the principle that lithium ions contained in an active cathode material move through an electrolyte towards an anode, are then introduced into a layered structure of active anode material (charging), and subsequently return the lithium ions introduced into the layered structure of the active anode material to a cathode (discharging).

[0003] Interest in secondary batteries has recently increased due to the rising demand for an energy source for next-generation automobiles and the growing demand for environmentally friendly energy. In particular, there is a strong interest in increasing the energy density and extending the lifespan of the secondary battery. With this in mind, to produce a medium- or large-capacity secondary battery, a high-voltage, high-capacity secondary battery can be implemented using a lithium-rich, layered oxide as the known active cathode material. Additionally, a silicon-based material, as well as a carbon-based material, can be used as the active anode material to further improve the battery's capacity.

[0004] Meanwhile, a typical lithium secondary battery uses a lithium salt dissolved in an organic solvent as the electrolyte. The lithium-rich active cathode material can generate oxygen gas and create a high-voltage environment during the initial charge. Significant volume expansion occurs in the silicon-based anode material during repeated charging and discharging cycles, leading to cracks on the anode surface and potentially causing electrolyte decomposition on the electrode surfaces. This progressively depletes the electrolyte, rapidly deteriorates the battery's electrochemical performance, and can result in the formation of a thick, resistive film on each electrode surface. Consequently, the battery's electrochemical reaction rate decreases, and the acidic material (e.g., RF, etc.) becomes more susceptible to corrosion.), which is produced by decomposition of the electrolyte, melts any electrode film or damages the active cathode material, so that the electrochemical stability of the battery cannot be guaranteed. [Disclosure][Technical Problem]

[0005] To solve the above technical problem, the present invention provides an electrolyte additive for a secondary battery which exhibits low reductive decomposition while protecting a uniform protective film formed on an electrode, a manufacturing method for this additive, and an electrolyte containing the additive.

[0006] The technical problems of the present invention are not limited to the technical problems mentioned above, and further technical problems not mentioned will become clear to the person skilled in the art from the description below. [Technical solution]

[0007] One embodiment of the present invention provides an electrolyte additive. The electrolyte additive is a compound represented by chemical formula 1 or chemical formula 2 as follows:

[0008] M is an alkali metal, and R is hydrogen, a substituted or unsubstituted C1 to C5 alkyl group, a substituted or unsubstituted C1 to C5 perfluoroalkyl group, a substituted or unsubstituted C6 to C30 aryl group, a substituted or unsubstituted C6 to C30 perfluoroaryl group, or CF3.

[0009] The electrolyte additive according to chemical formula 1 can be a compound represented by the following chemical formula 3:

[0010] The electrolyte additive according to chemical formula 2 can be a compound represented by the following chemical formula 4:

[0011] Another embodiment of the present invention provides a method for producing an electrolyte additive, comprising a step of reacting hexafluorophosphate and 2-monofluoromalonic acid, a step of adding an HF scavenger to a mixed solution produced by the reaction; and a step of concentrating and drying the solution obtained from the above steps to prepare a compound represented by Chemical Formula 1 or Chemical Formula 2.

[0012] Hexafluorophosphate can include lithium hexafluorophosphate (LiPF6). 2-Monofluoromalonic acid can include 2-fluoromalonic acid.

[0013] The process may further include a step of preparing the 2-monofluoromalonic acid by reacting the 2-monofluoromalonic acid ester with an acidic solution prior to reacting the compounds. The step of preparing the 2-monofluoromalonic acid may further include drying the solution completed by the reaction using a dehydrogenating agent. The dehydrogenating agent may be an orthoester of R. 1 C(OR 2 )3 include, where R 1 It can be hydrogen or a C1 to C5 alkyl group, R 2 a C1 to C5 alkyl group and R 1 and R 2 They can be chosen independently.

[0014] The reaction of hexafluorophosphate and 2-monofluoromalonic acid can be carried out in a non-aqueous organic solvent. This reaction can be performed at a temperature of 5 to 60 °C.

[0015] The RF scavenger can include a halide, a silane compound, or a combination thereof. The halide can include an alkali metal halide, a silicon halide, a phosphorus halide, or a combination thereof. The halide can include lithium chloride, silicon tetrachloride, dichlorodimethylsilane, chlorotrimethylsilane, phosphorus trichloride, or a combination thereof. The silane compound can include an acrylicsilane compound, a cyclic silane compound, or a combination thereof.

[0016] The step of concentrating and drying the reaction solution obtained from the above steps can be carried out under reduced pressure.

[0017] Another embodiment of the present invention provides an electrolyte composition. The electrolyte composition can comprise an electrolyte additive, represented by Chemical Formula 1 or Chemical Formula 2, a non-aqueous organic solvent, and an alkali salt.

[0018] The electrolyte additive can be included in an amount of 0.1 to 10 percent by weight, based on the total amount of the electrolyte composition.

[0019] The electrolyte additive can be a mixture of the electrolyte additive according to chemical formula 1 and a coating agent. The coating agent can include fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinylethylene carbonate (VEC), or a combination thereof.

[0020] The non-aqueous organic solvent can be a cyclic carbonate, a linear carbonate, or a combination thereof.

[0021] The alkali salt can be MPF6, MAsF6, MCF3SO3, MN(CF3SO2)2, MBF4, MBF6, MSbF6, MN(C2F s SO2)2, MAlO4, MAlCl4, MSO3CF3, MClO4 or a combination thereof, where M can be an alkali metal. The concentration of the alkali salt can range from 0.1 to 3 M.

[0022] Another embodiment of the present invention provides a secondary battery. The secondary battery can comprise a cathode containing an active cathode material, an anode containing an active anode material, an electrolyte containing an electrolyte additive represented by Chemical Formula 1 or Chemical Formula 2, and a separator between the cathode and the anode.

[0023] The active cathode material can be LiNi 0.6 Co 0.2 Mn 0.2 Include O2. The active cathode material can include a lithium-rich active cathode material.

[0024] The active anode material can include graphite or a silicon-graphite composite. [Beneficial effects]

[0025] As described above, according to the embodiments of the present invention, the stability of a secondary battery can be improved by the addition of an electrolyte. Furthermore, a high-voltage, high-capacity battery can be produced by simultaneously using a lithium-rich active cathode material and an active anode material made of a graphite / silicon-graphite composite, and even in this case, the performance of the secondary battery can be further enhanced by the use of the electrolyte addition.

[0026] The technical effects of the present invention are not limited to those mentioned above, and further technical effects not mentioned will be clearly apparent to the person skilled in the art from the description below. List of characters Fig. Figure 1 is a flowchart showing a process for producing an electrolyte additive according to an embodiment of the present invention. Fig. Figure 2 is a schematic diagram illustrating a secondary battery according to an embodiment of the present invention. Fig. Figure 3 is a graph showing a voltage-current curve measured by linear loop voltametry of electrolytes according to electrolyte example 1 and electrolyte comparison examples 1-1 and 2-2. Fig. Figure 4 is a graph showing the dQ / dV distributions of secondary batteries according to secondary battery example 1 and secondary battery comparison examples 1-1 and 1-2. Fig. Figure 5 is a graph showing high-temperature lifetime characteristics of secondary batteries according to Secondary Battery Example 1 and Secondary Battery Comparison Examples 1-1 and 1-2. Fig.5a is a graph showing a specific capacity according to the number of cycles, and Fig. Figure 5b is a graph showing the Coulomb efficiency as a function of the number of cycles. Additionally, Fig. 5c a graph showing the change in open circuit voltage during high temperature storage. Fig. Figure 6 is a graph showing a specific discharge capacity according to the number of cycles at room temperature for secondary batteries according to secondary battery example 1 and secondary battery comparison examples 1-1 and 1-2. Fig. Figure 7 is a graph illustrating room temperature lifetime characteristics of secondary batteries according to Secondary Battery Example 2 and Secondary Battery Comparison Examples 2-1 and 2-2. Fig. Figure 7a is a graph showing a specific capacity according to the number of cycles, and Fig.Figure 7b is a graph showing a coulomb efficiency as a function of the number of cycles. Fig. Figure 8 is a graph showing high-rate discharge characteristics of secondary batteries according to Secondary Battery Example 2 and Secondary Battery Comparison Examples 2-1 and 2-2. Fig. Figure 9 is a graph showing the impedance of the interface between an electrode and an electrolyte with respect to the secondary batteries according to Secondary Battery Example 2 and Secondary Battery Comparison Examples 2-1 and 2-2. [Types of embodiments of the invention]

[0027] Since the present invention can have numerous modifications and take on numerous embodiments, specific embodiments are illustrated in the drawings and described in detail. However, it is not intended to limit the present invention to specific embodiments, and it is understood that modifications, equivalents, and substitutes of all kinds, which are within the spirit and scope of the present invention, are included.

[0028] The terms used in the present invention are used solely to describe specific embodiments and are not intended to limit the present invention. A singular expression includes the plural expression unless the context clearly indicates otherwise. In the present invention, terms such as "comprise" or "have" are intended to denote the fact that a feature, number, step, operation, component, part, or combination thereof described in the specification exists, but it is understood that this does not exclude the existence or addition of one or more features or numbers, steps, operations, components, parts, or combinations thereof.

[0029] Unless otherwise defined, all technical or scientific terms used herein have the same meaning as generally understood by an average person of expertise. It is further understood that terms such as those defined in commonly used dictionaries are to be interpreted in a manner consistent with their meaning in the context of the relevant technology and not in an idealized or overly formal manner, unless expressly defined as such herein.

[0030] Preferred embodiments of the present invention are described in more detail below with reference to the accompanying drawings. To facilitate general understanding, the same reference numerals are used in the description of the present invention for the same components in the drawings, and repeated descriptions of the same components are omitted.

[0031] When something is described as “Cx to Cy” in this specification, it is to be interpreted as having a number of carbon atoms which corresponds to all integers between the number of carbon x and the number of carbon y.

[0032] As used herein, the term "alkyl group" refers to an aliphatic hydrocarbon group unless otherwise defined. The alkyl group may be a "saturated alkyl group" that contains no double or triple bonds. The alkyl group may be branched, straight-chain, or cyclic.

[0033] In this specification, unless otherwise defined, the term "aryl group" may refer to a monocyclic aromatic compound or a polycyclic aromatic compound composed of fused aromatic rings.

[0034] As used herein, “substitution” can mean a substitution in which one or more or all of the hydrogens are substituted with a halogen group, and specifically with a fluorine group.

[0035] An electrolyte additive according to an embodiment of the present invention can be an additive represented by chemical formula 1, an additive represented by chemical formula 2, or a mixture thereof.

[0036] In Chemical Formula 1 and Chemical Formula 2, M can be an alkali metal or ammonium. The alkali metal can be, for example, Li (lithium), Na (sodium), or K (potassium). R can be hydrogen, a substituted or unsubstituted C1 to C5 alkyl group, a substituted or unsubstituted C1 to C5 perfluoroalkyl group, a substituted or unsubstituted C6 to C30 aryl group, a substituted or unsubstituted C6 to C30 perfluoroaryl group, or CF3.

[0037] The electrolyte additive of chemical formula 1 can be represented by the following chemical formula 3, and the electrolyte additive of chemical formula 3 can be lithium tetrafluoro-(2-fluoromalonate)phosphate (LiFMTFP).

[0038] The electrolyte additive of chemical formula 2 can be represented by the following chemical formula 4, and the electrolyte additive of chemical formula 4 can be lithium difluorobis(2-fluoromalonate)phosphate.

[0039] Fig. Figure 1 is a flowchart showing a process for producing an electrolyte additive according to an embodiment of the present invention.

[0040] The procedure for preparing the electrolyte additive may include the step of preparing 2-monofluoromalonic acid (S10).

[0041] In Scheme 1, R' can be a substituted or unsubstituted C1 to C10 alkyl group or a substituted or unsubstituted C6 to C30 aryl group. R is hydrogen, a substituted or unsubstituted C1 to C5 alkyl group, a substituted or unsubstituted C1 to C5 perfluoroalkyl group, a substituted or unsubstituted C6 to C30 aryl group, a substituted or unsubstituted C6 to C30 perfluoroaryl group, or CF3.

[0042] As shown in Scheme 1, the step of preparing 2-monofluoromalonic acid can include reacting 2-monofluoromalonic acid esters with an acid (HA). Specifically, the acid can be provided as an acidic solution, which is a solution containing the acid. The acidic solution can be an aqueous solution containing the acid.

[0043] The 2-monofluoromalonic acid can be, for example, 2-fluoromalonic acid. The 2-monofluoromalonic acid can be dried, either by heating or vacuum drying. The water concentration in the 2-monofluoromalonic acid can be 150 ppm by weight or less, and preferably 120 ppm by weight or less. If the water concentration meets the aforementioned range, hydrolysis of the phosphate obtained by the following reaction and of the electrolyte additive of the present invention, obtained according to the present reaction, can be omitted.

[0044] The preparation of 2-monofluoromalonic acid can be carried out at a reaction temperature of 25 to 60 °C, preferably 30 to 50 °C, and the reaction itself can be performed at room temperature. Any acidic solution can be used, provided it reacts with 2-monofluoromalonic acid ester to generate 2-monofluoromalonic acid. In the case of reacting 2-monofluoromalonic acid ester with a basic solution, the reaction must be carried out in two steps, whereas using an acidic solution allows the reaction to be carried out in one step, thus simplifying the reaction and consequently reducing the synthesis time. Furthermore, using an acidic solution, compared to using a basic solution, reduces the types of reaction byproducts and offers the advantage of a high reaction yield.

[0045] The preparation of 2-monofluoromalonic acid may further include drying the reaction solution using a dehydrating agent. Since the reaction in the preparation step of 2-monofluoromalonic acid is carried out in the presence of an acidic solution, particularly water, the water content of the product can be high. Consequently, 2-monofluoromalonic acid can be obtained by drying the reaction solution. Here, to remove moisture contained in the product, provided it can be dried without affecting the structure or the 2-monofluoromalonic acid content, any method other than the one using a dehydrating agent may be used without restriction.

[0046] The dehydrating agent can be used without restriction as long as it does not interfere with the reaction while removing moisture from the product, 2-monofluoromalonic acid. For example, orthoesters of R can be used. 1 C(OR2 )3 can be used as the dehydrating agent, and in this case, water can be removed as shown in Scheme 2 below. Here, R 1 be hydrogen or a C1 to C5 alkyl group, R 2 can be a C1 to C5 alkyl group and R 1 and R 2 They can be chosen independently. For example, orthoesters can be trimethyl orthoformate and triethyl orthoformate, but this is not the only option. [Schema 2] H2O + R 1 C(OR 2 )3 → 2R 2 OH + R 1 CO2R 2

[0047] In addition, an organic dehydrating agent such as silicates can be used, or an inorganic dehydrating agent can be used. Examples of silicates that can be used include tetraethyl silicate, etc.

[0048] The method for preparing the electrolyte additive according to the present invention may include reacting hexafluorophosphate and 2-monofluoromalonic acid (S20) as shown in Scheme 3 or 4 below.

[0049] In schemes 3 and 4, M is an alkali metal or ammonium.

[0050] The hexafluorophosphate can be alkali hexafluorophosphate or ammonium hexafluorophosphate, but is not limited to either. For example, the alkali hexafluorophosphate can be lithium hexafluorophosphate (LiPF6), sodium hexafluorophosphate (NaPF6), or potassium hexafluorophosphate (KPF6). The ammonium hexafluorophosphate can be a tetraalkylammonium hexafluorophosphate. Preferably, the hexafluorophosphate can be lithium hexafluorophosphate (LiPF6).

[0051] The molar ratio between hexafluorophosphate and 2-monofluoromalonic acid can satisfy the equivalent ratio of Scheme 3 or 4 above. Specifically, in the case of Scheme 3, the molar ratio between hexafluorophosphate and 2-monofluoromalonic acid can be 1:0.9 to 1:1.1, preferably 1:0.95 to 1:1.05. Additionally, in the case of Scheme 4, the molar ratio between hexafluorophosphate and 2-monofluoromalonic acid can be 1:1.8 to 1:2.2, preferably 1:1.9 to 1:2.1.

[0052] The above reaction can be carried out in a reaction solvent. The reaction solvent can be an organic solvent, specifically a non-aqueous organic solvent. The non-aqueous organic solvent can be carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based, or a combination thereof.

[0053] Specifically, the carbonate-based organic solvent can be a cyclic carbonate or a linear carbonate. The cyclic carbonate can be ethylene carbonate (EC), fluoroethylene carbonate, propylene carbonate (PC), or butylene carbonate (BC), and the linear carbonate can be dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), or ethyl propyl carbonate (EPC).

[0054] The ester-based organic solvent can be, but is not limited to, methyl formate, methyl acetate, ethyl acetate, isopropyl acetate, isoamyl acetate, methyl propionate, ethyl propionate, methyl butylate or ethyl butylate, etc.

[0055] The ether-based organic solvent can be dibutyl ether, tetraglyme (tetraethylene glycol dimethyl ether, TEGDME), diglyme (diethylene glycol dimethyl ether, DEGDME), dimethoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran, etc., but is not limited to these.

[0056] The ketone-based organic solvent can be cyclohexanone or the like, and the alcohol-based solvent can be ethyl alcohol, isopropyl alcohol or the like, but is not limited to these.

[0057] Specifically, a carbonate-based organic solvent or an ester-based organic solvent can be used as the reaction solvent, and preferably the carbonate-based organic solvent can be ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), or diethyl carbonate (DEC). These non-aqueous organic solvents can be dehydrated solvents, and they can be used alone or in combination with two or more of them.

[0058] The moisture concentration in the non-aqueous organic solvent can be 30 ppm by weight or less, preferably 15 ppm by weight or less. If the moisture concentration meets the above range, the hydrolysis of the phosphate and the electrolyte additive of the present invention can be omitted.

[0059] The reaction temperature can be in the range of 5 to 60 °C, preferably in the range of 10 to 45 °C. If this temperature range is maintained, the formation of byproducts and solvent decomposition can be suppressed, and due to excellent reactivity, there is no need to extend the reaction time, resulting in advantages. Likewise, the yield of electrolyte additive according to the present invention can be excellent.

[0060] It may include a step of further adding an RF scavenger to a mixed solution generated by the reaction (S30).

[0061] The HF scavenger serves to remove the HF gas produced by the reaction of hexafluorophosphate and 2-monofluoromalonic acid, and when the HF scavenger is added to the mixture of hexafluorophosphate and 2-monofluoromalonic acid, the forward reaction of the synthesis reaction can proceed favorably.

[0062] Any suitable HF scavenger can be used, provided it serves to remove HF gas and does not participate in the electrolyte addition reaction according to the present invention. For example, it can include a halide other than fluoride, a silane compound, or a combination thereof. Additionally, the HF scavenger can be, but is not limited to, lithium carbonate, sodium carbonate, calcium hydroxide, sodium hydroxide, activated carbon, or the like.

[0063] The halide can be converted into a high-vapor-pressure acid such as hydrogen chloride (HCl), hydrogen bromide (HBr), or hydrogen iodide (HI) by reaction with HF, and subsequently purified and removed by distillation or similar methods. The halide can be a chloride, a bromide, or an iodide, and an inorganic halide, an organic halide, or a combination thereof can be used as the halide.

[0064] The inorganic halide can be an alkali metal halide, an alkaline earth metal halide, a metalloid halide, a post-transition metal halide, or the like. Specifically, the alkaline earth metal halide can be lithium chloride, lithium bromide, lithium iodide, sodium chloride, sodium bromide, sodium iodide, potassium chloride, potassium bromide, potassium iodide, cesium chloride, cesium bromide, cesium iodide, or the like. The alkaline earth metal halide can be magnesium chloride, magnesium bromide, magnesium iodide, calcium chloride, calcium bromide, calcium iodide, barium chloride, barium bromide, barium iodide, or the like. The post-transition metal halide can be aluminum trichloride, aluminum tribromide, aluminum triiodide, or the like. The metalloid halide can be a silicon halide, and the silicon halide can be silicon tetrachloride, silicon tetrabromide, silicon tetraiodide, dichlorodimethylsilane, chlorotrimethylsilane, or the like.

[0065] The organic halide can be an ammonium halide, a phosphorus halide, or the like. Specifically, the ammonium halide can be tetramethylammonium chloride, tetramethylammonium bromide, tetramethylammonium iodide, or the like. The phosphorus halide can be phosphorus trichloride, phosphorus tribromide, phosphorus triiodide, or the like. Additionally, the organic halide can be acetyl chloride, acetyl bromide, acetylated iodide, propionyl chloride, propionyl bromide, propionyl iodide, oxalyl chloride, oxalyl bromide, oxalyl iodide, or the like.

[0066] In particular, the halide can be an alkali metal halide, a silicon halide, a phosphorus halide, or a combination thereof. Preferably, the halogen contained in the halide can be chlorine (Cl), and accordingly, lithium chloride, silicon tetrachloride, dichlorodimethylsilane, chlorotrimethylsilane, phosphorus trichloride, or a combination thereof can be used as the halide. Since these exhibit a fast reaction rate, productivity can be improved, and cations that are not relevant for the lithium-ion battery cannot remain in the electrolyte.

[0067] The HF formed according to the present reaction can be removed in proportion to the number of halogens contained in the halide. Consequently, if the number of halogens contained in one molecule of the halide is n, the lower limit of the amount of halide used in relation to 1 mol of HF can be 1 / n mol, preferably 1.2 / n mol, and the upper limit is 5 / n mol, preferably 3 / n mol. If the above range is met, no acids or unreacted halides, which would adversely affect the battery's performance, can remain.

[0068] The term silane refers to a compound containing a silyl group and can be an acyclic silane, a cyclic silane, or a combination thereof. Examples of acyclic silanes include tris(trimethylsilyl)phosphite (TMSP) or hexamethyldisiloxane (HMDSO), while examples of cyclic silanes include octamethylcyclotetrasiloxane or decamethylcyclopentasiloxane, but are not limited to these.

[0069] Simultaneously, since the product can be hydrolyzed by moisture after the electrolyte additive has been prepared, the reaction can be carried out in an inert gas atmosphere, which is an atmosphere that does not contain moisture. It can be performed, for example, in an inert gas atmosphere such as nitrogen or argon.

[0070] The reaction solution obtained from the above steps (S40) can be concentrated and dried. Concentration and drying are carried out by a process that utilizes a vapor pressure differential. More specifically, byproducts can be removed by introducing an inert gas into the solution at reduced pressure and simultaneously releasing the solution along with the inert gas. A vacuum pump, suction device, etc., can be used to reduce the pressure, and this can be achieved by maintaining the pressure in the system below atmospheric pressure after the reactor has been brought into a tightly sealed state. The introduction of an inert gas into the solution can be accomplished by bubbling the solution with nitrogen, helium, neon, argon, krypton, or xenon gas. Depressurization of the reaction system and the introduction of an inert gas into the solution can be carried out simultaneously.Similarly, the solution can be heated to 20 to 50 °C under reduced pressure and / or by introducing an inert gas. Accordingly, it is possible to obtain the electrolyte additive according to the present invention in solid form.

[0071] According to another embodiment of the present invention, an electrolyte composition comprising an electrolyte additive, an alkali salt and a non-aqueous organic solvent can be provided.

[0072] The electrolyte additive according to the present invention can be one of the electrolyte additives represented by Chemical Formulas 1 to 4 above.

[0073] The electrolyte additive according to the present invention can be included in an amount of 0.1 to 10 percent by weight, based on the total amount of the electrolyte composition. Preferably, the electrolyte additive according to the present invention can be included in an amount of 0.5 to 5 percent by weight, based on the total amount of the electrolyte composition. If the content falls within the above range, the stability-enhancing effect of the electrode can be sufficiently noticeable. In more detail, it is possible to suppress an increase in the internal resistance of the secondary battery due to the occurrence of a side reaction.

[0074] The electrolyte additives of chemical formulas 1 to 4 can be used alone as an electrolyte additive in the electrolyte composition, or they can be used in combination with a coating agent that forms a stable and uniform protective film on the electrode of the secondary battery. The coating agent can be, but is not limited to, fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinylethylene carbonate (VEC), or a combination thereof.

[0075] As an example, lithium tetrafluoro(2-fluoromalonate)phosphate (LiFMTFP) can be used as an electrolyte additive of the present invention, and fluoroethylene carbonate can be used as a coating agent. When fluoroethylene carbonate is added to the electrolyte composition containing lithium tetrafluoro(2-fluoromalonate)phosphate (LiFMTFP), the lithium tetrafluoro(2-fluoromalonate)phosphate (LiFMTFP) and fluoroethylene carbonate can have a weight ratio of 1:10 to 2:5, specifically 1:10 to 3:10, preferably 1:5.

[0076] The alkali salt can be any alkali salt commonly used in secondary battery electrolytes. Examples of alkali salts include, but are not limited to, MPF6, MAsF6, MCF3SO3, MN(CF3SO2)2, MBF4, MBF6, MSbF6, MN(C2F5SO2)2, MAlO4, MAlCl4, MSO3CF3, or MClO4. These can be used individually, or two or more can be used in combination. Here, M is an alkali metal and can be Li (lithium), Na (sodium), or K (potassium).

[0077] The concentration of the alkali salt in the electrolyte composition can be 0.1 to 3 M, for example 0.1 to 2 M. If this concentration range is met, since the electrolyte can have a suitable conductivity and viscosity, it can be advantageous for the introduction or release of alkali ions during charging and discharging, and the decomposition of the solvent due to side reactions can be suppressed.

[0078] The non-aqueous organic solvent is an organic solvent commonly used in secondary batteries, which can minimize decomposition due to oxidation reactions during charging and discharging, and which, together with additives, can exhibit the desired properties of the present invention. Examples of the non-aqueous organic solvent can be carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based. These can be used alone, or two or more of them can be combined.

[0079] Preferably, a carbonate-based organic solvent may be used. Examples of carbonate-based organic solvents include cyclic and linear carbonates. Cyclic carbonates may include ethylene carbonate (EC), fluoroethylene carbonate, propylene carbonate (PC), butylene carbonate (BC), or the like. Linear carbonates may include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), or ethyl propyl carbonate (EPC). Preferably, the non-aqueous organic solvent may be ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), or a combination thereof. In this case, the volume ratio of the organic solvent may be as follows: EC:EMC:DMC = 3:4:3.

[0080] The organic solvent can be an ester-based solvent, and in particular methyl formate, methyl acetate, ethyl acetate, isopropyl acetate, isoamyl acetate, methyl propionate, ethyl propionate, methyl butylate or ethyl butylate.

[0081] The organic solvent can be an ether-based solvent, and examples of ester-based solvents may include dibutyl ether, tetraglym (tetraethylene glycol dimethyl ether, TEGDME), diglym (diethylene glycol dimethyl ether, DEGDME), dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or the like.

[0082] A ketone-based solvent can be used as the organic solvent, and the ketone-based solvent can be cyclohexanone, etc., and the alcohol-based solvent can be ethyl alcohol, isopropyl alcohol, etc.

[0083] Another embodiment of the present invention can provide a secondary battery which includes the electrolyte additive.

[0084] Fig. Figure 2 is a schematic diagram illustrating a secondary battery according to an embodiment of the present invention.

[0085] With reference to Fig. 2 The secondary battery 100 includes an active anode material layer 120, which contains an active anode material, an active cathode material layer 140, which contains an active cathode material, and a separator 130 interposed between them. An electrolyte 160 can be arranged or charged between the active anode material layer 120 and the separator 130 and between the active cathode material layer 140 and the separator 130. The active anode material layer 120 can be arranged at the anode current collector 110, and the active cathode material layer 140 can be arranged at the cathode current collector 150. <kathode>

[0086] The cathode 140 can be formed by applying a slurry containing a mixture of an active cathode material, a binder, and a solvent to the cathode current collector 150. The cathode can also be produced using a cathode material obtained by mixing an active material for a secondary battery, a conductive material, and a binder.

[0087] The active cathode material can be a well-known, layered alkali metal compound. For example, the active cathode material can contain at least one compound phosphorus oxide, a compound oxide of cobalt, nickel, manganese, chromium, or a combination thereof, and lithium. In particular, the active cathode material can be M x (Ni a Co b Mn c Al d )O2 (here, 0.5≤x≤1.5, 0≤a≤1, 0≤b≤1, 0≤c≤1, 0≤d<1, a+b+c+d=1), M(Ni a Co b Mn c )O4 (0 <a≤2, 0<b≤2, 0<c≤2, a+b+c=2) oder MTmPO4 (wobei Tm Fe, Mn, Co, Ni oder eine Kombination davon ist) sein. Hier ist M ein Alkalimetall und kann Li (Lithium), Na (Natrium) oder K (Kalium) sein. Das aktive Kathodenmaterial kann insbesondere MCoO2, MCoPO4, MNiO2, MMPO4, NMnO2, NMn2O4, MMnPO4, MCrO2, MNi 0.6 Co 0.2 Mn 0.2 O2, MNiMnCoO2, M(Co x Ni 1-x )O2 (0.5≤x<1), etc., but is not limited to this. The active cathode material LiNi can serve as an example. 0.6 Co 0.2 Mn 0.2 Include O2.

[0088] Additionally, the active cathode material can be a lithium-rich active cathode material. The lithium-rich active cathode material can be a compound containing an excess of lithium and can exhibit high capacity and high energy density for a battery. The lithium-rich active cathode material can be a material represented by the following formula 3. [Formula 3] Li x Ni y Mn z Co w O2 1 <x≤2, 0<y≤1, 0<z≤1, und 0<w≤1.

[0089] Furthermore, a coating layer can be enclosed on the surface of the active cathode material. The coating layer is a compound consisting of a coating element and can include oxide, hydroxide, oxyhydroxide, oxycarbonate, or hydroxycarbonate of the coating element. The compound forming the coating layer can be amorphous or crystalline. The coating element enclosed in the coating layer can be Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof. Any coating process can be used for the coating layer formation process, provided it does not adversely affect the physical properties of the active cathode material (e.g., spray coating, dipping, etc.).

[0090] The conductive material can be a carbon-based material such as natural graphite, synthetic graphite, coal, carbon black, carbon nanotubes, or graphene. The binder can be a thermoplastic resin, for example, a fluorinated resin such as polyvinylidene fluoride, polytetrafluoroethylene, ethylene tetrafluoride, or vinylidene fluoride-based copolymer, propylene hexafluoride, and / or a polyolefin resin such as polyethylene or polypropylene.

[0091] The cathode current collector 150 can be a heat-resistant metal, such as iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, or the like. In one embodiment, the cathode current collector can be aluminum or stainless steel. The upper surface of the cathode current collector 150 can also be roughened to improve adhesion with the active cathode material layer 140. <anode>

[0092] The active anode material can intercalate and deintercalate lithium ions or cause a conversion reaction and can be a metal, a metal alloy, a metal oxide, a metal fluoride, a metal sulfide, a carbon material such as graphite (natural graphite, synthetic graphite), coal, carbon black, carbon nanotubes, graphene, or silicon. Preferably, graphite or a silicon-graphite composite can be used as the active anode material.

[0093] An anode material can be obtained by mixing the active anode material, a conductive material, and a binder. In this case, the conductive material can be a carbon material such as natural graphite, synthetic graphite, coal, carbon black, carbon nanotubes, or graphene. The binder can be a thermoplastic resin, for example, a fluorinated resin such as polyvinylidene fluoride, polytetrafluoroethylene, ethylene tetrafluoride, or vinylidene fluoride-based copolymer, propylene hexafluoride, and / or a polyolefin resin such as polyethylene or polypropylene.

[0094] The anode material can be applied to an anode current collector to form an anode. The anode current collector can be a conductor such as aluminum (Al), nickel (Ni), stainless steel (SUS), or molybdenum (Mo). The application of the anode material to the anode current collector can be achieved by compression molding or by a process of preparing a paste using an organic solvent or the like, followed by application of the paste to the current collector and pressing to fix it in place. The organic solvent can be an amine-based solvent such as N,N-dimethylaminopropylamine or diethyltriamine; ethers such as ethylene oxide and tetrahydrofuran; ketones such as methyl ethyl ketone; esters such as methyl acetate; or an aprotic polar solvent such as dimethylacetamide or N-methyl-2-pyrrolidone.The paste can be applied to the anode current collector, for example, using an engraving coating process, a slot nozzle coating process, a knife coating process, or a spray coating process. <elektrolyt>

[0095] As described above, the present invention can provide an electrolyte which includes the electrolyte additive of chemical formulas 1 to 4, a lithium salt and a non-aqueous organic solvent.

[0096] In chemical formulas 1 and 2, M can be an alkali metal or ammonium. The alkali metal can be, for example, Li (lithium), Na (sodium), or K (potassium). R can be hydrogen, a substituted or unsubstituted C1 to C5 alkyl group, a C1 to C5 perfluoroalkyl group, a substituted or unsubstituted C6 to C30 aryl group, a C6 to C30 perfluoroaryl group, or CF3.

[0097] In particular, in the case of electrolyte addition according to chemical formulas 3 and 4, the electrochemical properties of the secondary battery containing it can be more excellent compared to the compound in which two hydrogens are bonded to the alpha carbon of the malonate group.

[0098] In the case of the compounds according to chemical formulas 3 and 4, in which fluorine is bonded to the alpha carbon of the malonate group, LiF can be formed. As an example of the reaction to form LiF, referring to Scheme 5 above, fluorine bonded to the alpha carbon of the malonate group can react with lithium ions (Li₂). + ) and electrons react to form LiF. When LiF is generated as described above, it forms a film surrounding the electrode to inhibit the elution of the electrode's transition metal, and consequently, the electrochemical performance of the secondary battery, including the electrolyte additive, can be improved in terms of longevity, etc.

[0099] On the other hand, referring to Scheme 6, the fluorine group, in the case of a compound in which two hydrogens are bonded to the alpha carbon of the malonate group, is not bonded to the alpha carbon, thus forming an acidic atmosphere in the electrolyte. This means that, unlike the compounds of chemical formulas 3 and 4, the LiF, which serves as a protective layer for the electrode, cannot be formed, and furthermore, that the acid formed can promote a side reaction of the electrolyte.

[0100] The electrolyte additives of chemical formulas 1 to 4 according to the present invention can be used by mixing them with a coating agent. The coating agent can form a stable and uniform protective film on the electrode of the secondary battery. For example, the coating agent can be fluoroethylene carbonate (FEC). Additionally, the coating agent can be vinylene carbonate (VC) or vinylethylene carbonate (VEC).

[0101] The coating agent has a lower reduction potential than the electrolyte additive of chemical formulas 1 to 4, and when used in combination with the electrolyte additive according to the present invention, the coating agent can be reduced and decomposed earlier than the electrolyte additive according to chemical formulas 1 to 4. This means that the electrolyte additives of chemical formulas 1 to 4 may exhibit lower reductive decomposition.

[0102] Therefore, when the electrolyte additive according to the present invention and the coating agent are mixed, a uniform and stable protective film can be formed on the electrode of the secondary battery, which incorporates the electrolyte additive, by the coating agent. Subsequently, the pre-formed protective layer and the electrode can be protected by the electrolyte additive of chemical formulas 1 to 4. Consequently, since the interface between the electrode material and the electrolyte is stabilized by the electrolyte additive, the lithium secondary battery incorporating the electrolyte additive according to the present invention can exhibit improved life cycle characteristics at room temperature, and its electrochemical performance can be enhanced.

[0103] Furthermore, the electrolyte additives of chemical formulas 1 to 4 according to the present invention can be used alone as an electrolyte additive in the electrolyte composition. By adding the electrolyte additive according to chemical formulas 1 to 4 alone as an electrolyte additive in the electrolyte composition, even if no further electrolyte additive such as the coating agent is added, the stability of the electrode interface can be improved, and a secondary battery incorporating the same can exhibit excellent electrochemical properties.

[0104] In particular, since the secondary battery exhibits excellent cycle capacity retention, lifetime characteristics, and coulombic efficiency at high temperatures, as well as excellent storage performance at high temperatures, it can be operated with excellent stability even at high temperatures. Additionally, even without an additional electrolyte additive such as a coating agent, the secondary battery incorporating the electrolyte additive according to the present invention can exhibit excellent room-temperature lifetime performance.

[0105] Accordingly, the secondary battery, which includes the electrolyte additive according to the present invention, can exhibit excellent high-temperature lifetime characteristics. Furthermore, even when using a cathode comprising a lithium-rich active material and an anode comprising a silicon-graphite composite active material, the secondary battery can operate stably while simultaneously exhibiting high capacity and high voltage. This makes it possible to increase the energy density of the secondary battery and improve its capacity retention characteristics. <separator>

[0106] A separator 130 can be arranged between the anode and the cathode. The separator can be a material in the form of a porous film, a nonwoven fabric, or a woven fabric, consisting of a material such as a polyolefin resin like polyethylene or polypropylene, a fluorinated resin, or a nitrogen-containing aromatic polymer. The thickness of the separator is preferably thinner, provided that the mechanical strength is maintained from the standpoint of increasing the volume energy density of the battery and reducing the internal resistance. The thickness of the separator can generally be approximately 5 to 200 µm, and particularly 5 to 40 µm. <Herstellungsverfahren einer Sekundärbatterie>

[0107] After the cathode, separator, and anode have been stacked sequentially to form an electrode assembly, the assembly is coiled and stored in a battery canister when needed, and the secondary battery can be produced by impregnating the electrode assembly with the non-aqueous electrolyte. Alternatively, after forming an electrode assembly by laminating the cathode, a solid electrolyte, and the anode, the assembly can be coiled and stored in a battery canister when needed to produce a secondary battery.

[0108] Examples of the present invention are provided below to aid understanding. However, these examples are provided solely to facilitate understanding of the present invention, and the present invention is not limited to the examples below. [Examples] Preparation example of 2-fluoromalonic acid

[0109] At room temperature, 1000 g of a 35% aqueous hydrogen chloride (HCl) solution was added to a 2000 mL three-necked flask and stirred. Subsequently, 200 g of diethyl 2-fluoromalonate was added dropwise to the flask containing the 35% aqueous hydrogen chloride solution over 1 hour using a dropping funnel. The reaction was then carried out at 10°C for 16 hours. During this time, hydrogen chloride dissolved in water was produced as a gas by simultaneously increasing the temperature. This gas was absorbed by a canister filled with sodium lime. After the reaction was complete, trimethyl orthoformate was added, and the mixture was dried under vacuum at 50°C to yield 2-fluoromalonic acid.

[0110] The obtained 2-fluoromalonic acid was dissolved in dimethyl sulfoxide-d6 and an NMR analysis was performed to show that the yield of 2-fluoromalonic acid was 92.5%, based on diethyl 2-fluoromalonate. Electrolyte additive preparation example 1

[0111] In a glovebox with a dew point of -50 °C, 100 g of dehydrated ethyl methyl carbonate (EMC), containing 10 ppm water by weight, were placed in a 250 ml three-necked round-bottom flask, and 16.23 g (0.107 mol) of lithium hexafluorophosphate (LiPF6) were added and dissolved. Subsequently, after drying 2-fluoromalonic acid, prepared according to the preparation example for 2-fluoromalonic acid, to a moisture content of 100 ppm by weight, 13.04 g (0.107 mol) of the dried 2-fluoromalonic acid were added. The three-necked round-bottom flask was removed from the glovebox, immersed in an oil bath at 30 °C, and stirred thoroughly using a magnetic stirrer to obtain a mixed solution.

[0112] Subsequently, 13.79 g (0.107 mol) of dichlorodimethylsilane (Me₂SiCl₂) was added to the mixture over 1 hour using a dropping funnel as an HF scavenger. Simultaneously with the addition, difluorodimethylsilane and hydrogen chloride were generated, and the reaction was complete after sufficient reaction time of 3 hours following the cessation of gas production.

[0113] After the reaction, the resulting reaction solution was concentrated and dried under reduced pressure of 5 Torr at 40 °C to obtain 23.75 g of lithium tetrafluoro(2-fluoromalonate)phosphate (LiFMTFP) in a solid state with a reaction yield of 95%. The resulting electrolyte additive was dissolved in dimethyl sulfoxide-d6 and a 19 F-NMR analysis was performed to show that the lithium tetrafluoro(2-fluoromalonate)phosphate (LiFMTFP) was 99% by weight. Electrical additive preparation example 2

[0114] An electrolyte additive was prepared in the same manner as in Electrolyte Additive Preparation Example 1, except that 9.06 g (0.214 mol) of lithium chloride (LiCl) were used as the HF scavenger. The result was 22.5 g of lithium tetrafluoro(2-fluoromalonate)phosphate (LiFMTFP) in a solid state with a reaction yield of 90%, as shown by a 19 F-NMR analysis revealed a value of 97% by weight. Electrolyte additive preparation example 3

[0115] An electrolyte additive was prepared in the same manner as in Electrolyte Additive Preparation Example 1, except that 9.83 g (0.072 mol) of phosphorus trichloride (PCl3) was used as the HF scavenger. The result was 21.25 g of lithium tetrafluoro(2-fluoromalonate)phosphate (LiFMTFP) in a solid state with a reaction yield of 85%, as a result of a 19 F-NMR analysis revealed a concentration of 45 percent by weight. Electrical additive preparation example 4

[0116] An electrolyte additive was prepared in the same manner as in Electrolyte Additive Preparation Example 1, except that the reaction was carried out at a reaction temperature of 60 °C. The result was 24.5 g of lithium tetrafluoro(2-fluoromalonate)phosphate (LiFMTFP) in a solid state with a reaction yield of 98%, as shown by a 19 F-NMR analysis revealed a weight of 91 percent. Electrolyte additive preparation example 5

[0117] An electrolyte additive was prepared in the same manner as in Electrolyte Additive Preparation Example 1, except that 7.78 g (0.072 mol) of chlorotrimethylsilane (Me3SiCl) was used as the HF scavenger and the reaction was carried out at a reaction temperature of 10 °C. The result was 11.25 g of lithium tetrafluoro(2-fluoromalonate)phosphate (LiFMTFP) in a solid state with a reaction yield of 45%, which resulted from a 19 F-NMR analysis revealed a concentration of 65% by weight. Electrical additive preparation example 6

[0118] An electrolyte additive was prepared in the same manner as in Electrolyte Additive Preparation Example 1, except that 9.83 g (0.072 mol) of phosphorus trichloride (PCl3) was used as the HF scavenger and the reaction was carried out at a reaction temperature of 45 °C. The result was 15 g of lithium tetrafluoro(2-fluoromalonate)phosphate (LiFMTFP) in a solid state with a reaction yield of 60%, as evidenced by a 19 F-NMR analysis revealed it to be 57 percent by weight. Electrical additive preparation example 7

[0119] An electrolyte additive was prepared in the same manner as in Electrolyte Additive Preparation Example 1, except that 9.08 g (0.053 mol) of silicon tetrachloride (SiCl4) was used as the HF scavenger, diethyl carbonate (DEC) was used as the organic solvent, and the reaction was carried out at a reaction temperature of 10 °C. The result was 19.5 g of lithium tetrafluoro(2-fluoromalonate)phosphate (LiFMTFP) in a solid state with a reaction yield of 78%, as evidenced by a 19 F-NMR analysis revealed it to be 85 percent by weight. Electrolyte additive preparation example 8

[0120] An electrolyte additive was prepared in the same manner as in Electrolyte Additive Preparation Example 1, except that ethyl acetate (AcOEt) was used as the organic solvent. The result was 24 g of lithium tetrafluoro(2-fluoromalonate)phosphate (LiFMTFP) in a solid state with a reaction yield of 96%, as shown by a 19 F-NMR analysis revealed it to be 90 percent by weight.

[0121] Table 1 below summarizes the electrolyte additive preparation examples. [Table 1] Electrolyte additive preparation examples reaction condition reaction result organic solvent Reaction temperature phosphate RF detector LiFMTFP weight Reaction yield LiFMTFP content (°C) (g) (%) (%) Preparation example 1 EMC 30 LiPF6 Me2SiCl2 23,75 95 99 Preparation example 2 EMC 30 LiPF6 LiCl 22,5 90 97 Preparation example 3 EMC 30 LiPF6 PCL3 21,25 85 45 Preparation example 4 EMC 60 LiPF6 Me2SiCl2 24,5 98 91 Preparation example 5 DEC 10 LiPF6 Me3SiCl 11,25 45 65 Preparation example 6 DEC 45 LiPF6 PCL3 15 60 57 Preparation example 7 DEC 10 LiPF6 SiCl4 19,5 78 85 Preparation example 8 AcOEt 30 LiPF6 Me2SiCl2 24 96 90 Electrolyte additive preparation example 9

[0122] In a glovebox with a dew point of -50 °C, 100 g of dehydrated ethyl methyl carbonate (EMC), containing 10 ppm water by weight, were placed in a 250 ml three-necked round-bottom flask, and 16.23 g (0.107 mol) of lithium hexafluorophosphate (LiPF6) were added and dissolved. Subsequently, after drying 2-fluoromalonic acid, obtained according to the preparation example for 2-fluoromalonic acid, to a moisture content of 100 ppm by weight, 26.08 g (0.214 mol) of the dried 2-fluoromalonic acid were added. The three-necked round-bottom flask was removed from the glovebox, immersed in an oil bath at 40 °C, and stirred thoroughly using a magnetic stirrer to obtain a mixed solution.

[0123] Subsequently, 27.58 g (0.214 mol) of dichlorodimethylsilane (Me₂SiCl₂) was added to the mixture as an HF scavenger over 1 hour using a dropping funnel. Simultaneously with the addition, difluorodimethylsilane and hydrogen chloride were generated, and the reaction was complete after sufficient reaction over 3 hours following the cessation of gas production. The result was lithium difluorobis(2-fluoromalonate)phosphate, represented by chemical formula 4. Electrolyte example 1

[0124] Lithium tetrafluoro(2-fluoromalonate)phosphate (LiFMTFP) was added to an electrolyte comprising ethylene carbonate (EC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC) in a volume ratio of 3:4:3 as an organic solvent and 1.15 M LiPF6 as a lithium salt, in accordance with Electrolyte Additive Preparation Example 1, in an amount of 1 wt% as an electrolyte additive, based on the total amount of electrolyte. Electrolyte comparison example 1-1

[0125] A non-aqueous electrolyte was prepared in the same manner as in Electrolyte Example 1, except that 5 wt% fluoroethylene carbonate (FEC) was added instead of 1 wt% lithium tetrafluoro(2-fluoromalonate)phosphate (LiFMTFP) as the electrolyte additive. Electrolyte comparison example 1-2

[0126] A non-aqueous electrolyte was prepared in the same manner as in Electrolyte Example 1, except that 1 wt% lithium tetrafluoro(oxalate)phosphate (LiTFOP) was added instead of 1 wt% lithium tetrafluoro(2-fluoromalonate)phosphate (LiFMTFP) as the electrolyte additive. Electrolyte Example 2

[0127] In an electrolyte comprising ethylene carbonate (EC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC) in a volume ratio of 3:4:3 as an organic solvent and 1.3 M LiPF6 as a lithium salt, based on the total amount of electrolyte, 5 wt% fluoroethylene carbonate (FEC) and 1 wt% lithium tetrafluoro(2-fluoromalonate)phosphate (LiFMTFP) were added as electrolyte additives to prepare an electrolyte according to Electrolyte Additive Preparation Example 1. Electrolyte comparison example 2-1

[0128] An electrolyte was prepared in the same way as in electrolyte example 2, except that only fluoroethylene carbonate (FEC) was added from the electrolyte additives in an amount of 5 percent by weight. Electrolyte comparison example 2-2

[0129] A non-aqueous electrolyte was prepared in the same manner as in Electrolyte Example 2, except that 1 wt% lithium tetrafluoro(oxalate)phosphate (LiPF4(C2O4), LiTFOP) was added instead of 1 wt% lithium tetrafluoro(2-fluoromalonate)phosphate (LiFMTFP) as the electrolyte additive.

[0130] Table 2 below summarizes the electrolyte examples and comparisons. [Table 2] Electrolyte examples and comparisons EC:EMC:DMC volume ratio LiPF6 concentration Additional information Secondary battery examples and comparisons Example 1 3:4:3 1,15 M 1 wt.% LiFMTFP Example 1 Comparison example 1-1 3:4:3 1,15 M 5 wt.% FEC Comparison example 1-1 Comparison example 1-2 3:4:3 1,15 M 1 wt.% LiTFOP Comparison example 1-2 Example 2 3:4:3 1,3 M 5 wt% FEC + 1 wt% LiFMTFP Example 2 Comparative example 2-1 3:4:3 1,3 M 5 wt.% FEC Comparative example 2-1 Comparative example 2-2 3:4:3 1,3 M 5 wt.% FEC + 1 wt.% LiTFOP Vergleichsbeispiel 2-2

[0131] Fig. Figure 3 is a graph showing a voltage-current curve measured by linear loop voltammetry of electrolytes according to electrolyte example 2 and electrolyte comparison examples 2-1 and 2-2. Sampling was performed at a sampling rate of 1 mV / s in a voltage range of 3 V to 6 V at 25 °C.

[0132] With reference to Fig. 3. According to electrolyte examples and comparison examples, the electrolytes showed similar oxidation stability up to approximately 4.3 V. However, from that point onward, it is evident that a peak potential increases according to the oxidative decomposition reaction in the sequence electrolyte comparison example 2-2, electrolyte comparison example 2-1, and electrolyte example 2. Accordingly, it is evident that the oxidative decomposition stability of electrolyte example 2 is better than that of electrolyte comparison example 2-2 and electrolyte comparison example 2-1, and that in the case of electrolyte example 2, the oxidative decomposition stability of the electrolyte is significantly improved.

[0133] Therefore, when lithium tetrafluoro(2-fluoromalonate)phosphate (LiFMTFP) is used as an additive, compared to the use of lithium tetrafluoro(oxalate)phosphate (LiPF4(C2O4), LiTFOP), the oxidative stability is excellent. Consequently, the electrochemical stability of the electrolyte containing lithium tetrafluoro(2-fluoromalonate)phosphate (LiFMTFP) is better than that of the electrolyte containing tetrafluoro(oxalate)phosphate (LiPF4(C2O4), LiTFOP), and therefore the electrolyte additive according to the present invention may be better suited for application to a secondary battery operating at high voltage. Secondary battery example 1

[0134] An active cathode material layer was created using LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622) was formed as an active cathode material, and an active anode material layer was formed using graphite as the active anode material. Additionally, the electrolyte prepared according to Electrolyte Example 1 was placed between the active cathode material layer and the active anode material layer to create a lithium secondary battery. Secondary battery comparison example 1-1

[0135] A lithium secondary battery was prepared in the same way as in Battery Example 1, except that the electrolyte prepared according to Electrolyte Comparison Example 1-1 was used instead of the electrolyte prepared according to Electrolyte Example 1. Secondary battery comparison example 1-2

[0136] A lithium secondary battery was prepared in the same way as in Battery Example 1, except that the electrolyte prepared according to Electrolyte Comparison Example 1-2 was used instead of the electrolyte prepared according to Electrolyte Example 1.

[0137] Fig. Figure 4 is a graph showing the dQ / dV distributions of secondary batteries according to secondary battery example 1 and secondary battery comparison examples 1-1 and 1-2.

[0138] After a secondary battery has been assembled, its performance as a battery is only complete after a predetermined charging / discharging process, i.e., a generation process. Fig. 4 corresponds to the cycle during the formation process. Specifically, during a formation charge / discharge cycle, the secondary battery was charged to 4.3 V, and a constant voltage (CV) condition was applied at 4.3 V after charging, with a stop condition of 0.02 C. The secondary battery was then discharged to 2.7 V under a constant current condition. The C-rate during the lifetime evaluation was 0.1 C.

[0139] With reference to Fig. 4. When checking the main peaks, the reduction potential of the secondary battery according to Secondary Battery Example 1 appears to be 3.0 V or higher. On the other hand, it is evident that the reduction potential of the secondary battery according to Secondary Battery Comparison Example 1-1 is approximately 2.5 V, and the reduction potential of the secondary battery according to Secondary Battery Comparison Example 1-2 is 3.0 V or less. From this, it is evident that the FEC and the LiTFOP from Secondary Battery Comparison Examples 1-1 and 1-2 will be reduced and decomposed earlier than the LiFMTFP contained in the secondary battery according to Secondary Battery Example 1. This means it can be confirmed that the LiFMTFP contained in the secondary battery according to Secondary Battery Example 1 exhibits the lowest reductive decomposition tendency.

[0140] Fig. Figure 5 is a graph showing high-temperature lifetime characteristics of secondary batteries according to Secondary Battery Example 1 and Secondary Battery Comparison Examples 1-1 and 1-2. Fig. 5a is a graph showing a specific capacity according to the number of cycles, and Fig. Figure 5b is a graph showing the Coulomb efficiency as a function of the number of cycles.

[0141] In the Fig. 5a and Fig. 5b. The high-temperature lifetime characteristics were evaluated for each secondary battery after an initial charge / discharge cycle. Specifically, during an initial charge / discharge cycle, each secondary battery was charged to 4.3 V, and a constant voltage (CV) condition was applied at 4.3 V after charging, with a stop condition of 0.05 C. The secondary battery was then discharged to 2.7 V under a constant current condition. The C-rate during the initial charge / discharge cycle was 0.1 C.

[0142] In the high-temperature lifetime assessment, each secondary battery was charged to 4.3 V at 45 °C, and a constant voltage (CV) condition was applied at 4.3 V after charging, with a stop condition of 0.05 C. The secondary battery was then discharged to 2.7 V under a constant current condition. The C-rate during the incipient charge / discharge phase of the lifetime assessment was 0.1 C.

[0143] With reference to Fig. 5a. Although there is no difference in the initial capacity depending on the electrolyte, it is evident that there is a difference in the degree of capacity degradation with increasing cycle count and in the specific discharge capacity in the last cycle. Compared to the secondary batteries according to the secondary battery comparison examples, the secondary battery according to Secondary Battery Example 1 exhibited a better specific discharge capacity, even after 250 cycles had been performed. Accordingly, it can be confirmed that the secondary battery incorporating the electrolyte additive according to the present invention exhibits excellent capacity retention and lifetime characteristics at high temperatures.

[0144] With reference to Fig. 5b, over 160 cycles, compared to the secondary batteries according to the secondary battery comparison examples, the secondary battery according to secondary battery example 1 exhibits a constant coulombic efficiency value from the initial cycle, and the coulombic efficiency reaches approximately 99.9%, thus demonstrating that a more stable operation of the secondary battery is achieved.

[0145] Additionally, Fig. 5c a graph showing the change in open circuit voltage during high temperature storage.

[0146] In Fig. In section 5c, the high-temperature storage performance was confirmed by evaluating the self-discharge characteristics of each secondary battery stored at 45°C for approximately 20 days following an initial charge / discharge and subsequent charge. Specifically, during a single initial charge / discharge, each secondary battery was charged to 4.3 V, and a constant voltage (CV) condition was applied at 4.3 V post-charge with a stop condition of 0.05 C. The secondary battery was then discharged to 2.7 V under a constant current condition. The C-rate during the initial charge / discharge was 0.1 C. To evaluate self-discharge, an additional charge was performed at room temperature. The charge condition was the same as that of the initial charge, and the open-circuit voltage (OCV) of the cell was measured.

[0147] With reference to Fig. 5c shows that the reduction in open-circuit voltage of the secondary battery according to Example 1 is less than that of the secondary battery according to Comparative Example 1-2, and it is consequently evident that the high-temperature lifetime storage performance is excellent.

[0148] In light of this, the secondary battery containing lithium tetrafluoro(2-fluoromalonate)phosphate (LiFMTFP) exhibits excellent discharge capacity, excellent coulombic efficiency, and excellent high-temperature lifetime storage performance compared to tetrafluoro(oxalate)phosphate (LiPF4(C2O4), LiTFOP) and fluoroethylene carbonate (FEC), thus offering improved high-temperature lifetime characteristics. Consequently, when the electrolyte additive according to the present invention is included, the lifetime can be excellent, even in a secondary battery that generates a significant amount of heat, making it suitable for use in medium-sized or large-sized batteries.

[0149] Fig. Figure 6 is a graph showing a specific discharge capacity according to the number of cycles at room temperature for secondary batteries according to secondary battery example 1 and secondary battery comparison examples 1-1 and 1-2.

[0150] Room temperature lifetime characteristics were evaluated for each secondary battery after a single inception charge and discharge. Specifically, during this single inception charge / discharge cycle, each secondary battery was charged to 4.3 V, and a constant voltage (CV) condition was applied at 4.3 V post-charge with a stop condition of 0.02 C. The secondary battery was then discharged to 2.7 V under a constant current condition. The C-rate during the inception charge and discharge cycle was 0.1 C.

[0151] After the initial charge / discharge cycle, three additional charge and discharge cycles were performed to ensure lifetime stability before evaluating room temperature lifetime characteristics. Specifically, each secondary battery was charged to 4.3 V, a constant voltage (CV) condition was applied at 4.3 V after charging, with a stop condition of 0.05 C, and the secondary battery was discharged to 2.7 V under a constant current condition. At this point, the C-rate was 0.2 C.

[0152] In the room-temperature lifetime assessment, each secondary battery was charged to 4.3 V at 25 °C, and a constant voltage (CV) condition was applied at 4.3 V after charging, with a stop condition of 0.05 C. The secondary battery was then discharged to 2.7 V under a constant current condition. The C-rate during the lifetime assessment was 1.0 C. Charge and discharge experiments were performed up to approximately 200 cycles.

[0153] With reference to Fig. 6. Although there is no difference in initial capacity depending on the electrolyte, the secondary battery according to Secondary Battery Example 1 exhibits an improved specific discharge capacity value compared to the secondary batteries according to Secondary Battery Comparison Examples 1-1 and 1-2 at the last cycle. Similarly, a secondary battery containing lithium tetrafluoro(2-fluoromalonate)phosphate (LiFMTFP) may exhibit better room-temperature lifetime performance compared to tetrafluoro(oxalate)phosphate (LiPF4(C2O4), LiTFOP) and fluoroethylene carbonate (FEC).

[0154] As described above, by adding the electrolyte additive according to the present invention alone as an electrolyte additive in the electrolyte composition, even if no further electrolyte additive such as a coating agent is added, the stability of the electrode interface is improved, and the secondary battery incorporating it can exhibit excellent electrochemical properties. Secondary battery example 2

[0155] Li 1.17 Ni 0.17 Mn 0.5 Co 0.17 O2, a lithium-rich active cathode material, a binder (PVDF), and a conductive material (Super P) were uniformly mixed in n-methyl-2-pyrrolidone (NMP) solvent at a weight ratio of 8:1:1 (active cathode material:conductive material:binder). A cathode was prepared by uniformly applying the mixture containing the lithium-rich active cathode material to an aluminum (Al) current collector, pressing it in a roller press, and vacuum drying it in a vacuum oven at 110 °C for 2 hours. The target electrode density was 1.9 g / cc.

[0156] An active anode material layer was formed using a silicon-graphite composite as the active anode material. Additionally, a polyethylene separator was placed between the prepared cathode and the prepared anode in a battery container, and the electrolyte prepared according to Electrolyte Example 2 was placed between the active cathode material layer and the active anode material layer to fabricate a lithium secondary battery in the form of a 2032 full cell according to a conventional manufacturing process. Secondary battery comparison example 2-1

[0157] A lithium secondary battery was prepared in the same manner as in Secondary Battery Example 2, except that the electrolyte prepared according to Electrolyte Comparison Example 2-1 was used instead of the electrolyte prepared according to Electrolyte Example 2. Secondary battery comparison example 2-2

[0158] A lithium secondary battery was prepared in the same manner as in Secondary Battery Example 2, except that the electrolyte prepared according to Electrolyte Comparison Example 2-2 was used instead of the electrolyte prepared according to Electrolyte Example 2.

[0159] Fig. Figure 7 is a graph illustrating room temperature lifetime characteristics of secondary batteries according to Secondary Battery Example 2 and Secondary Battery Comparison Examples 2-1 and 2-2. Fig. Figure 7a is a graph showing a specific capacity according to the number of cycles, and Fig. Figure 7b is a graph showing the Coulomb efficiency as a function of the number of cycles.

[0160] Room temperature lifetime characteristics were evaluated for each secondary battery after an initial charge / discharge cycle. Specifically, during this initial charge / discharge cycle, each secondary battery was charged to 4.55 V, and a constant voltage (CV) condition was applied at 4.55 V post-charge with a stop condition of 0.02 C. The secondary battery was then discharged to 2.0 V under a constant current condition. The C-rate during the initial charge / discharge cycle was 0.1 C.

[0161] After the initial charge / discharge cycle, three additional charge and discharge cycles were performed to ensure lifetime stability before evaluating room temperature lifetime characteristics. Specifically, each secondary battery was charged to 4.55 V, a constant voltage (CV) condition was applied at 4.55 V after charging, with a stop condition of 0.05 C, and the secondary battery was discharged to 2.0 V under a constant current condition. At this point, the C-rate was 0.2 C.

[0162] In the room-temperature lifetime assessment, each secondary battery was charged to 4.55 V at 25 °C, and a constant voltage (CV) condition was applied at 4.55 V after charging, with a stop condition of 0.05 C. The secondary battery was then discharged to 2.0 V under a constant current condition. The C-rate during the lifetime assessment was 0.5 C, and the charge and discharge experiments were performed for up to approximately 100 cycles.

[0163] With reference to Fig. 7a, although there is no difference in the initial capacity depending on the electrolyte, it is evident that there is a difference in the degree of capacity degradation according to the increase in cycle count and in the specific discharge capacity in the last cycle. In other words, compared to other secondary batteries, the secondary battery according to Secondary Battery Comparison Example 2-1 exhibits a high degree of capacity degradation and a low specific discharge capacity at the 100th cycle. Compared to the secondary battery according to Secondary Battery Comparison Example 2-2, the secondary battery according to Secondary Battery Example 2 showed similar specific discharge capacity values ​​at the 100th cycle, but exhibited a higher specific discharge capacity value at approximately the 20th cycle.It is therefore evident that the secondary battery including the electrolyte additive according to the present invention exhibits excellent cycle capacity retention and excellent initial lifetime characteristics.

[0164] Likewise, with reference to Fig. As can be seen in section 7b, the secondary battery has no problem completing 100 cycles; however, the average coulombic efficiency varies depending on the electrolyte used in the secondary battery. It is evident that the coulombic efficiency of the secondary battery according to the example is more stable than that of the secondary battery according to the comparison examples.

[0165] Consequently, as described above, a secondary battery containing lithium tetrafluoro(2-fluoromalonate)phosphate (LiFMTFP) exhibits superior discharge capacity and coulombic efficiency at room temperature compared to tetrafluoro(oxalate)phosphate (LiPF4(C2O4), LiTFOP), thus exhibiting improved lifetime characteristics at room temperature.

[0166] Fig. Figure 8 is a graph showing high-rate discharge characteristics of secondary batteries according to Secondary Battery Example 2 and Secondary Battery Comparison Examples 2-1 and 2-2.

[0167] For each secondary battery, the charge rate after an initial charge / discharge cycle at 25°C was set to 0.5C, and the discharge rate was varied to 0.5C, 1C, 2C, 3C, 4C, 5C, and 0.5C, thereby evaluating high-rate discharge characteristics. The evaluation was performed over three cycles for each discharge rate.

[0168] With reference to Fig. 8. It can be confirmed that the secondary battery exhibits operability despite the current density in the range from a C-rate of 0.5 to a C-rate of 5, and it is evident that the reduction in specific discharge capacity of the other secondary batteries is smaller than that of the secondary battery according to secondary battery comparison example 2-1, despite the high current density. Furthermore, the secondary battery according to the secondary battery example shows no significant difference in the C-rate from 0.5 to C-rate 3 compared to the secondary battery according to secondary battery comparison example 2-2; however, it is evident that there is a small difference between the specific discharge capacity at the current densities of C-rate 4 and C-rate 5.

[0169] Consequently, the high-rate charge and discharge characteristics of the electrolyte containing lithium tetrafluoro(2-fluoromalonate)phosphate (LiFMTFP) were improved compared to tetrafluoro(oxalate)phosphate (LiPF4(C2O4), LiTFOP). It is therefore evident that the secondary battery according to one embodiment of the present invention can exhibit excellent high-rate discharge characteristics at room temperature and excellent lifetime stability with respect to C-rate changes.

[0170] Fig. Figure 9 is a graph showing the impedance of the interface between an electrode and an electrolyte with respect to the secondary batteries according to Secondary Battery Example 2 and Secondary Battery Comparison Examples 2-1 and 2-2.

[0171] The interface resistance was measured after the formation process of each secondary battery. Specifically, during a single formation charge / discharge cycle, each secondary battery was charged to 4.55 V, and a constant voltage (CV) condition was applied at 4.55 V after charging, with a stop condition of 0.02 C. The secondary battery was then discharged to 2.0 V under a constant current condition, with a C-rate of 0.1 C.

[0172] With reference to Fig. 9. It can be predicted that the internal resistance of the secondary battery also increases, while the interface resistance between the electrode and the electrolyte in the secondary battery according to the secondary battery example increases slightly, compared to the secondary battery comparison examples 2-1 and 2-2. This is assumed to be due to the formation of a film in the initial stage of the electrode.

[0173] As described above, when the electrolyte additive according to the present invention is mixed with the coating agent, a uniform and stable protective film can be generated by the coating agent on the electrode of the secondary battery, which encloses it, and subsequently the already formed protective film and the electrode are protected by the electrolyte additive according to the present invention in such a way that the interface between the electrode and the electrolyte can be stabilized.

[0174] In the above statements, the present invention has been described in detail with reference to preferred embodiments, but the present invention is not limited to the above embodiments and numerous modifications and changes by persons skilled in the art are possible within the spirit and scope of the present invention.< / separator> < / elektrolyt> < / anode> < / kathode>

Claims

[1] Electrolyte additive, represented by chemical formula 1 or chemical formula 2 as follows: where M is an alkali metal, and R is hydrogen, a substituted or unsubstituted C1 to C5 alkyl group, a substituted or unsubstituted C1 to C5 perfluoroalkyl group, a substituted or unsubstituted C6 to C30 aryl group, a substituted or unsubstituted C6 to C30 perfluoroaryl group, or CF3. [2] Electrolyte additive according to claim 1, wherein the electrolyte additive of chemical formula 1 is represented by the following chemical formula 3: [3] Electrolyte additive according to claim 1, wherein the electrolyte additive of chemical formula 2 is represented by the following chemical formula 4: [4] Method for producing an electrolyte additive, comprising the following: a step in the reaction of hexafluorophosphate and 2-monofluoromalonic acid; a step of adding an RF scavenger to a mixed solution produced by the reaction; and a step of concentrating and drying the solution obtained from the above steps to prepare a compound represented by Chemical Formula 1 or Chemical Formula 2 as follows: where M is an alkali metal, and R is hydrogen, a substituted or unsubstituted C1 to C5 alkyl group, a substituted or unsubstituted C1 to C5 perfluoroalkyl group, a substituted or unsubstituted C6 to C30 aryl group, a substituted or unsubstituted C6 to C30 perfluoroaryl group, or CF3. [5] Method according to claim 4, wherein the hexafluorophosphate includes lithium hexafluorophosphate (LiPF6). [6] The method of claim 4, further comprising: a step of preparing the 2-monofluoromalonic acid by reacting 2-monofluoromalonic acid ester with an acidic solution prior to reacting the hexafluorophosphate and the 2-monofluoromalonic acid. [7] The method of claim 6, further comprising: a step of drying the solution completed by reaction using a dehydrating agent in the step of preparing the 2-monofluoromalonic acid. [8] Method according to claim 7, wherein the dehydrating agent is orthoester of R 1 C(OR 2 )3 includes, where R 1 hydrogen or a C1 to C5 alkyl group, R 2 a C1 to C5 alkyl group and R 1 and R 2 are chosen independently. [9] Method according to claim 4, wherein the step of reacting the hexafluorophosphate and the 2-monofluoromalonic acid is carried out in a non-aqueous organic solvent. [10] Method according to claim 4, wherein the step of reacting the hexafluorophosphate and the 2-monofluoromalonic acid is carried out at a reaction temperature of 5 to 60 °C. [11] Method according to claim 4, wherein the HF scavenger includes a halide, a silane compound or a combination thereof. [12] Method according to claim 11, wherein the halide includes an alkali metal halide, a silicon halide, a phosphorus halide or a combination thereof. [13] Method according to claim 11, wherein the halide includes lithium chloride, silicon tetrachloride, dichlorodimethylsilane, phosphorus trichloride or a combination thereof. [14] Method according to claim 11, wherein the silane compound includes an acyclic silane compound, a cyclic silane compound or a combination thereof. [15] Method according to claim 4, wherein the step of concentrating and drying the reaction solution obtained from the above steps is carried out under reduced pressure. [16] Electrolyte composition, comprising the following: an electrolyte additive, a non-aqueous organic solvent; and an alkali salt wherein the electrolyte additive includes a compound represented by Chemical Formula 1 or Chemical Formula 2 as follows: where M is an alkali metal, and R is hydrogen, a substituted or unsubstituted C1 to C5 alkyl group, a substituted or unsubstituted C1 to C5 perfluoroalkyl group, a substituted or unsubstituted C6 to C30 aryl group, a substituted or unsubstituted C6 to C30 perfluoroaryl group, or CF3. [17] Electrolyte composition according to claim 16, wherein the electrolyte additive is included in an amount of 0.1 to 10 percent by weight, based on the total amount of the electrolyte composition. [18] Electrolyte composition according to claim 16, wherein the electrolyte additive is a mixture of the electrolyte additive according to chemical formula 1 and a coating agent. [19] Electrolyte composition according to claim 18, wherein the coating agent includes fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinylethylene carbonate (VEC) or a combination thereof. [20] Electrolyte composition according to claim 16, wherein the non-aqueous organic solvent includes a cyclic carbonate, a linear carbonate or a combination thereof. [21] Electrolyte composition according to claim 20, wherein the non-aqueous organic solvent includes ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) or a combination thereof. [22] Electrolyte composition according to claim 16, wherein the alkali salt is MPF6, MAsF6, MCF3SO3, MN(CF3SO2)2, MBF4, MBF6, MSbF6, MN(C2F5SO2)2, MAlO4, MAlCl4, MSO3CF3, MClO4 or a combination thereof, wherein M is an alkali metal. [23] Electrolyte composition according to claim 16, wherein the concentration of the alkali salt is 0.1 to 3 M. [24] Secondary battery, comprising the following: a cathode which contains an active cathode material; an anode containing an active anode material; and an electrolyte containing an electrolyte additive, represented by chemical formula 1 or chemical formula 2 as follows: where M is an alkali metal, and R is hydrogen, a substituted or unsubstituted C1 to C5 alkyl group, a substituted or unsubstituted C1 to C5 perfluoroalkyl group, a substituted or unsubstituted C6 to C30 aryl group, a substituted or unsubstituted C6 to C30 perfluoroaryl group, or CF3. [25] Secondary battery according to claim 24, wherein the active cathode material is LiNi 0.6 Co 0.2 Mn 0.2 O2 is included. [26] Secondary battery according to claim 24, wherein the active cathode material includes a lithium-rich active cathode material. [27] Secondary battery according to claim 24, wherein the active anode material includes graphite or a silicon-graphite composite.