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

Abstract

The present invention relates to an electrolyte additive, an electrolyte comprising same, and a secondary battery. The present invention has the effect of providing a secondary battery in which a stable film is formed on a positive electrode and a negative electrode of a lithium secondary battery such that side reactions inside the battery are suppressed and the charge and discharge resistance are low, and thus charging efficiency and output may be improved, an increase in the resistance of the battery can be suppressed even when the battery is stored for a long time under high-temperature conditions, and gas generation due to decomposition of electrolyte components is significantly suppressed, and thus the secondary battery not only has a long lifespan and an excellent high-temperature capacity retention rate, but also has excellent low-temperature performance.

Description

Electrolyte additive, electrolyte for battery containing the same, and secondary battery containing the same

[0001] The present invention relates to an electrolyte additive, a battery electrolyte containing the same, and a secondary battery containing the same, and more particularly, to an electrolyte additive that forms a stable film on a positive and negative electrode of a lithium secondary battery to suppress side reactions inside the battery and improve charging efficiency and output by lowering charge / discharge resistance, and can suppress an increase in battery resistance and gas generation even when stored for a long time under high-temperature conditions, thereby providing a secondary battery with excellent low-temperature performance as well as a long-term lifespan and high-temperature capacity retention rate.

[0002] Lithium secondary batteries facilitate the use of electrical energy by allowing the smooth movement of lithium ions by placing an electrolyte between the positive and negative electrodes, and generating or consuming electricity through oxidation-reduction reactions resulting from insertion and deintercalation at the positive and negative electrodes.

[0003] Meanwhile, with environmental regulations strengthening globally and growing concern for the environment, interest in eco-friendly vehicles that can replace fossil fuel-powered vehicles, a major source of air pollution, is also growing. Consequently, the domestic and international battery industries are actively developing automotive batteries.

[0004] In order to use batteries in automobiles, not only must the output and capacity of the battery be significantly increased, but also the problem of improving output and increasing resistance at high and low temperatures must be solved according to the usage environment such as weather changes. In particular, in the case of electric vehicles, since output and driving range performance are important, research is being conducted to lower the internal resistance of the battery and increase the remaining capacity. In particular, it is necessary to develop a battery that suppresses internal side reactions of the battery and secures low resistance and long-life performance even when stored for a long time under high-temperature conditions.

[0005] The cathode active material used in the cathode active material layer of the above battery includes lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2, etc.), lithium nickel manganese cobalt oxide (NCM, LiNi x Mn y Co 1-x-y O2), lithium iron phosphate compound (LFP, LiFePO4), etc., and among these, lithium iron phosphate compound (LiFePO4) is increasingly being applied to large-capacity lithium secondary batteries for electric vehicles due to its low unit price and supply stability.

[0006] In the case of the above nickel manganese cobalt oxide (NCM), the high-temperature performance improvement effect required for a conventional lithium-based battery is required, whereas in the case of the above lithium iron phosphate compound (LFP), in addition to the high-temperature performance improvement effect, there is a need for technology development that improves the low-temperature performance effect to overcome the problem of rapid decrease in capacity retention rate at low temperatures in LFP EV vehicles.

[0007] [Prior Art Literature]

[0008] [Patent Document]

[0009] Korean Patent Publication No. 2019-0014711

[0010] In order to solve the problems of the prior art as described above, the present invention aims to provide a novel battery electrolyte additive, a battery electrolyte containing the same, and a secondary battery containing the same.

[0011] In addition, the present invention aims to provide a secondary battery that suppresses internal side reactions of the battery, reduces charging resistance to improve battery output, improves recovery capacity at high temperatures to enable long-term storage, and has excellent capacity retention at both high and low temperatures.

[0012] The above and other objects of the present invention can all be achieved by the present invention described below.

[0013] In order to achieve the above object, the present invention provides an electrolyte additive comprising: I) a compound in which one SX bond and two S=O bonds are directly connected to a sulfur (S) element; and at least one compound selected from the group consisting of vinylene carbonate and fluoroethylene carbonate, wherein X is a halogen element.

[0014] II) In the above I), the compound in which one SX bond and two S=O bonds are directly connected to the sulfur (S) element may have an asymmetric structure having a terminal -O-R3 (wherein R3 is an alkyl group having 1 to 3 carbon atoms).

[0015] III) In the above I) to II), the compound in which one SX bond and two S=O bonds are directly connected to the sulfur (S) element may be a compound in which one SX bond and two S=O bonds are directly connected to the sulfur (S) element.

[0016] [Chemical Formula 1]

[0017]

[0018] (In the above chemical formula 1, a line is a bond, and when a separate element is not described, the point where a bond meets a bond is carbon, and the number of hydrogens satisfying the valence of the carbon is omitted, R1 is -O-R3, R2 is alkylene having 1 to 3 carbon atoms, R3 is alkyl having 1 to 3 carbon atoms, and X is F, Cl, I, or Br.)

[0019] IV) In the above I) to III), the compound in which one SX bond and two S=O bonds are directly connected to the sulfur (S) element may be a compound represented by the following chemical formula 1a.

[0020] [Chemical Formula 1-1]

[0021]

[0022] (In the above chemical formula 1-1, a line is a bond, and when a separate element is not described, the point where a bond meets a bond is carbon, and the number of hydrogens satisfying the valence of the carbon is omitted, and X is F, Cl, I, or Br.)

[0023] V) In the above I) to IV), the compound represented by the chemical formula 1-1 may be a compound represented by the following chemical formula 1a.

[0024] [Chemical Formula 1a]

[0025]

[0026] VI) In the above I) to V), a compound in which one SX bond and two S=O bonds are directly connected to the sulfur (S) element; and at least one compound selected from the group consisting of vinylene carbonate and fluoroethylene carbonate may be included in a weight ratio of, for example, 1:1 to 1:30.

[0027] VII) In the above I) to VI), the compound in which one SX bond and two S=O bonds are directly connected to the sulfur (S) element may be included in an amount of, for example, 10 wt% or less among 100 wt% of the components constituting the electrolyte additive.

[0028] VIII) In the above I) to VII), at least one compound selected from the group consisting of vinylene carbonate and fluoroethylene carbonate may be included in an amount of, for example, 10 wt% or less among 100 wt% of the components constituting the electrolyte additive.

[0029] IX) In the above I) to VIII), the vinylene carbonate may be included in an amount of, for example, 0.1 to 5 wt% among 100 wt% of the components constituting the electrolyte additive.

[0030] X) In the above I) to IX), the fluoroethylene carbonate may be included in an amount of, for example, 10 wt% or less among 100 wt% of the components constituting the electrolyte additive.

[0031]

[0032] In addition, the present invention provides an electrolyte comprising XI) an organic solvent, a lithium salt, and an electrolyte additive, wherein the electrolyte additive comprises the electrolyte additive described above.

[0033] XII) In the above XI), the organic solvent may include at least one selected from the group consisting of ethylene carbonate (EC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate (PC), dipropyl carbonate (DPC), butylene carbonate, methylpropyl carbonate, and ethylpropyl carbonate.

[0034] XIII) In the above XI) to XII), the lithium salt is LiPF6, LiF4, LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 , LiSbF6, LiAsF6, LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiCF3SO3, LiCF3CO2, Li(CF3SO2)2N, LiN(SO3C2F5)2, Li(FSO2)2N, LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, LiN(C x F 2x +1SO2)(C y F 2y+1SO2) (wherein, x and y are natural numbers, for example, integers from 1 to 20), LiAsF6, LiSbF6, LiAlCl4, LiB(C2O4)2 (lithium bis(oxalato) borate: LiBOB), CH3SO3Li, and CF3SO3Li.

[0035] XIV) In the above XI) to XIII), the electrolyte additive may be included in an amount of 10 wt% or less based on 100 wt% of the total electrolyte.

[0036]

[0037] In addition, the present invention provides a secondary battery including XV) a negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and an electrolyte, wherein the electrolyte includes the aforementioned electrolyte, and the positive electrode active material includes a compound represented by the following chemical formula 2.

[0038] [Chemical Formula 2]

[0039] Li 1+a M1 1-x M2 x (PO 4-b )D b

[0040] In the above chemical formula 2, M1 is Fe, M2 is at least one element selected from any one of groups 2 to 15, excluding element M1, D is at least one element selected from the group consisting of F, S, and N, a is an integer from -0.5 to 0.5, x is an integer from 0 to 0.5, and b is an integer from 0 to 1.

[0041] XVI) In the above XV), the secondary battery may be a battery for an automobile or a battery for an energy storage device.

[0042] XVII) In the above XV) to XVI), the automobile battery may be a lithium iron phosphate battery such as LFP or LMFP.

[0043] A secondary battery including an electrolyte including an electrolyte additive according to the present invention can suppress side reactions inside the battery and have low charging resistance, thereby improving charging efficiency and output, and can suppress an increase in the resistance of the battery even when stored for a long time under high-temperature conditions, thereby providing a secondary battery having an excellent resistance increase rate and capacity retention rate during long-term storage and high-temperature storage, as well as a capacity retention rate at low temperatures.

[0044] The present invention will be described in detail below, but the present invention is not limited thereto.

[0045]

[0046] The present inventors, while researching a secondary battery that suppresses internal side reactions of the battery to improve output and suppresses an increase in resistance of the battery even when stored for a long time under high-temperature conditions, thereby exhibiting excellent high-temperature recovery capacity and lifespan characteristics as well as improved capacity retention even under low-temperature conditions, in order to manufacture a battery that can be used as an automobile battery or an energy storage device battery, confirmed that when an additive having a specific structure is added to the electrolyte of the secondary battery, all of the above-mentioned objectives can be achieved, and completed the present invention based on this.

[0047]

[0048] The electrolyte additive included in the electrolyte according to embodiments of the present invention includes a compound in which one SX bond and two S=O bonds are directly connected to a sulfur (S) element; and at least one compound selected from the group consisting of vinylene carbonate and fluoroethylene carbonate, wherein X is a halogen element. In this case, internal side reactions of the battery are suppressed and the charging resistance of the secondary battery is lowered, so that the charging efficiency and output can be improved, and even when stored for a long time under high-temperature conditions, an increase in the resistance of the battery can be suppressed, so that there is an effect of excellent low-temperature performance as well as a long-term lifespan and high-temperature capacity retention rate.

[0049] For example, a compound in which one SX bond and two S=O bonds are directly connected to the sulfur (S) element used in the present invention forms a sulfonyl-based film after the middle of the reaction together with the initial LiF-based inorganic film component, thereby stabilizing the interface between the electrode and the electrolyte. Specifically, it effectively generates Li2SO3, known as a low-resistance component, thereby stabilizing the electrode and reducing resistance.

[0050]

[0051] The compound in which one SX bond and two S=O bonds are directly connected to the above sulfur (S) element may have an asymmetric structure having a terminal -O-R3 (wherein R3 is an alkyl group having 1 to 3 carbon atoms), in which case the internal side reaction of the battery is suppressed, the charging resistance of the secondary battery is lowered, the charging efficiency and output can be improved, and there is an effect of excellent low-temperature performance as well as long-term life and high-temperature capacity retention.

[0052]

[0053] In the present invention, the compound in which one SX bond and two S=O bonds are directly connected to the sulfur (S) element may be at least one selected from compounds in which one SX bond and two S=O bonds are directly connected to the sulfur (S) element below, and in this case, internal side reactions of the battery are suppressed, the charging resistance of the secondary battery is lowered, so that the charging efficiency and output can be improved, and there are advantages in that it has excellent low-temperature performance capacity as well as a long-term lifespan and high-temperature capacity retention rate.

[0054] [Chemical Formula 1]

[0055]

[0056] (In the above chemical formula 1, a line is a bond, and when a separate element is not described, the point where a bond meets a bond is carbon, and the number of hydrogens satisfying the valence of the carbon is omitted, R1 is -O-R3, R2 is alkylene having 1 to 3 carbon atoms, R3 is alkyl having 1 to 3 carbon atoms, and X is F, Cl, I, or Br.)

[0057] In order to provide the aforementioned effect, it is preferable to use F or Cl, which has a large difference in electronegativity from sulfur (S), as the above X.

[0058] The aforementioned electrolyte additive, when added to the electrolyte of a battery, causes electrons to be concentrated toward the O element or the F element due to the difference in electronegativity between the O element and the X element (e.g., the O element or the F element) directly connected to the sulfur (S) element, and further, due to the overall asymmetric structure of the chemical formula, the S element becomes electron-deficient (e-poor, δ+), thereby inducing an oxidation reaction in the electrolyte containing lithium ions, thereby forming a stable film on the electrode, specifically, the cathode.

[0059] Due to the stability of the above film, decomposition of the electrolyte can be prevented, thereby improving cycle characteristics, and in particular, since it does not decompose at high temperatures, it has an excellent effect of greatly improving high-temperature storability compared to conventional electrode films that deteriorate high-temperature storability due to decomposition at high temperatures. In addition, since resistance increase is prevented, charge / discharge efficiency and output are improved, and since gas generation due to chemical reactions inside the battery is also suppressed, battery safety can be improved. In addition, since collapse of the electrode active material structure of the positive and negative electrodes is prevented at high temperatures, capacity retention is improved, thereby extending the lifespan. In addition, since lithium ion conductivity is improved due to the formation of the film, there is an effect of improving capacity retention at low temperatures.

[0060] A compound in which one SX bond and two S=O bonds are directly connected to the above sulfur (S) element may be a compound represented by the following chemical formula 1a.

[0061] [Chemical Formula 1-1]

[0062]

[0063] (In the above chemical formula 1-1, a line is a bond, and when a separate element is not described, the point where a bond meets a bond is carbon, and the number of hydrogens satisfying the valence of the carbon is omitted, and X is F, Cl, I, or Br.)

[0064] The compound represented by the above chemical formula 1-1 may be a compound represented by the following chemical formula 1a.

[0065] [Chemical Formula 1a]

[0066]

[0067] In the present invention, at least one compound selected from the group consisting of vinylene carbonate and fluoroethylene carbonate can suppress internal side reactions of a battery and lower the charging resistance of a secondary battery, thereby improving charging efficiency and output, and has the advantage of long life and excellent capacity retention at high temperatures as well as low temperatures.

[0068]

[0069] The compound in which one SX bond and two S=O bonds are directly connected to the above sulfur (S) element may be included in an amount of 10 wt% or less, specifically 0.1 to 5 wt%, preferably 0.1 to 1.0 wt%, more preferably 0.15 to 0.5 wt%, and most preferably 0.15 to 0.3 wt%, based on 100 wt% of the total electrolyte. In this case, when the electrolyte including the electrolyte additive is applied to an LFP EV vehicle, etc., the life efficiency at low temperatures as well as high temperatures can be improved.

[0070] It is preferable to introduce a compound in which one SX bond and two S=O bonds are directly connected to the sulfur (S) element together with one or more compounds selected from the group consisting of vinylene carbonate and fluoroethylene carbonate, as this can provide a predetermined synergistic effect without adversely affecting the components constituting the battery.

[0071] At least one compound selected from the group consisting of vinylene carbonate and fluoroethylene carbonate may be included in a total content of 10 wt% or less, specifically 0.1 to 5 wt%, preferably 0.5 to 4 wt%, and more preferably 0.5 to 2.5 wt%, based on 100 wt% of the total electrolyte. In this case, when the electrolyte including the electrolyte additive is applied to an LFP EV vehicle or the like, the life efficiency at low temperatures as well as high temperatures can be improved.

[0072] The above vinylene carbonate may be included in an amount of, for example, 0.1 to 5 wt%, preferably 1 to 4 wt%, and more preferably 1.5 to 2.5 wt%, based on 100 wt% of the total electrolyte. In this case, when the electrolyte including the electrolyte additive is applied to an LFP EV vehicle, the life efficiency at low temperatures as well as high temperatures can be improved.

[0073] The above fluoroethylene carbonate may be included in an amount of, for example, 10 wt% or less, specifically 0.1 to 3 wt%, preferably 0.3 to 3 wt%, and more preferably 0.5 to 1.5 wt%, based on 100 wt% of the total electrolyte. In this case, when the electrolyte including the electrolyte additive is applied to an LFP EV vehicle, etc., the lifespan efficiency at low temperatures as well as high temperatures can be improved.

[0074]

[0075] A compound in which one SX bond and two S=O bonds are directly connected to the sulfur (S) element; and at least one compound selected from the group consisting of vinylene carbonate and fluoroethylene carbonate may be used in a weight ratio of 1:1 to 1:30, specifically, a weight ratio of 1:3 to 1:22. In this case, when an electrolyte including the electrolyte additive is applied to an LFP EV vehicle, etc., the life efficiency at low temperatures as well as high temperatures can be improved.

[0076] The aforementioned additive component must be additionally included in a compound in which one SX bond and two S=O bonds are directly connected to the aforementioned sulfur (S) element. When only the other additive components are injected without a compound in which one SX bond and two S=O bonds are directly connected to the sulfur (S) element, it was confirmed through comparative examples described below that the improvement effect on long-term life and low resistance is poor.

[0077]

[0078] For example, in addition to the electrolyte additives described above, the electrolyte of the present invention may further include additives that can be generally used in electrolytes for the purposes of suppressing internal side reactions of a battery, improving the life characteristics of a battery, suppressing battery capacity reduction, and improving the discharge capacity of a battery.

[0079] Preferred specific examples of the above additive components include ethyl propionate (EP), propyl propionate (PP), succinic anhydride, tetravinyl silane, 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether, 1,2-bis((difluorophosphaenyl)oxy)ethane, 1,3,6-hexanetricarbonitrile, succinonitrile, 1-ethyl-3-methylimidazolium dicyanamide, trimethoxyboroxine, lithium bis(oxaleto)borate, lithium difluoro(oxalato)borate, tris(trimethylsilyl)borate, lithium tetrafluoroborate, triisopropyl borate, lithium tetrafluoro(oxalato)phosphate, lithium difluoro(bisoxalato)phosphate, lithium difluorophosphate, diethyl (difluoromethyl)phosphonate, tris(trimethylsilyl)phosphite, It may be at least one selected from the group consisting of tripropargyl phosphate, 2,4,8,10-tetraoxa-3,9-dithiaspiro [5.5]undecane 3,3,9,9-tetraoxide, dimethyl sulfate, ethylene dimethanesulfonate, methylenemethyldisulfonate, lithium bis(fluorosulfonyl)imide, 3-fluoro-1,3-propanesultone, 1,3-propylene sulfate, 1,4-butanesultone, sulfolene, biphenyl, cyclohexyl benzene, 4-fluorotoluene, triphenyl phosphate, fluorobenzene, and 2-fluoro-biphenyl.

[0080] Among the aforementioned types, at least one selected from the group consisting of metal phosphate compounds, specifically lithium difluoro(bisoxalato) phosphate (LiDFOP), lithium tetrafluorooxalato phosphate (LiTFOP), and lithium trioxalato phosphate, is a component added to improve the performance of lithium secondary batteries, lithium ion capacitors, etc., suppress internal side reactions of the battery, improve resistance and lifespan, etc., and may be included in the electrolyte at, for example, 0.3 to 2.5 wt%, preferably 0.5 to 1.5 wt%. When the content of the electrolyte additive satisfies the above range, it is preferable in terms of the effect of improving the high-temperature characteristics, low-temperature characteristics, and cycle characteristics of the battery.

[0081] The above electrolyte additive may be included in the above-described electrolyte in an amount of, for example, 10 wt% or less, 0.2 to 8 wt%, 0.2 to 5 wt%, 0.2 to 4.5 wt%, 1 to 4.5 wt%, or 2.2 to 4.5 wt%, including the total content of all components used. When the electrolyte additive content satisfies the above range, it is preferable in terms of improving the high-temperature characteristics, low-temperature characteristics, and cycle characteristics of the battery.

[0082]

[0083] The present invention also provides an electrolyte comprising the electrolyte additive of the present invention. The electrolyte is an electrolyte for a non-aqueous lithium secondary battery, and comprises the electrolyte additive, an organic solvent, and a lithium salt.

[0084] The organic solvent may be, for example, a carbonate-based organic solvent, and specifically, may be an organic solvent including at least one selected from the group consisting of ethylene carbonate (EC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate (PC), dipropyl carbonate (DPC), butylene carbonate, methylpropyl carbonate, and ethylpropyl carbonate.

[0085] The organic solvent may be, for example, one type or a mixed solvent of two or more types, and preferably, a high-dielectric constant organic solvent having high ionic conductivity to improve the charge / discharge performance of the battery and a low-viscosity organic solvent whose viscosity can be adjusted to have an appropriate viscosity for application to the battery may be mixed and used as a mixed solvent.

[0086] As the organic solvent having the high dielectric constant, for example, EC and PC can be used, and as the organic solvent having the low viscosity, for example, EMC, DMC, and DEC can be used, and it is preferable to mix and use the organic solvents having the high dielectric constant and low viscosity in a volume ratio of 2:8 to 8:2. More specifically, it may be a binary mixed solvent of EC and EMC, or a ternary mixed solvent of EC; EMC; and DEC and / or DMC; and the ratio of EC and EMC may be, for example, a volume ratio of 1:1 to 5, or 1:2 to 4, and the ratio of EC; EMC; and DEC and / or DMC may be, for example, a volume ratio of 1:2 to 5:0.1 to 1, or a volume ratio of 1:2 to 3:0.1 to 1.

[0087] Since lithium ions in the electrolyte may be hydrolyzed when the organic solvent contains moisture, it is preferable that the moisture in the organic solvent be controlled to 150 ppm or less, preferably 100 ppm or less.

[0088] The above lithium salt can be used without any special restrictions as long as it is a compound that can provide lithium ions used in a lithium secondary battery, and specifically, LiPF6, LiF4, LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10, LiSbF6, LiAsF6, LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiCF3SO3, LiCF3CO2, Li(CF3SO2)2N, LiN(SO3C2F5)2, Li(FSO2)2N, LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, LiN(C x F 2x +1SO2)(C y F 2y +1SO2) (wherein, x and y are natural numbers, for example, integers from 1 to 20), LiAsF6, LiSbF6, LiAlCl4, LiB(C2O4)2 (lithium bis(oxalato) borate: LiBOB), CH3SO3Li, and CF3SO3Li.

[0089] When the lithium salt is dissolved in the electrolyte, the lithium salt can function as a source of lithium ions in the lithium secondary battery and promote the movement of lithium ions between the positive and negative electrodes. Accordingly, the lithium salt is preferably included in the electrolyte at a concentration of approximately 0.6 mol% to 3 mol%. When the concentration of the lithium salt is less than 0.6 mol%, the conductivity of the electrolyte may decrease, thereby deteriorating the electrolyte performance, and when it exceeds 3 mol%, the viscosity of the electrolyte may increase, thereby reducing the mobility of lithium ions. Considering the conductivity of the electrolyte and the mobility of lithium ions, the lithium salt may be included in the electrolyte at a concentration of preferably 0.7 mol% to 3 mol%, and more preferably 0.8 mol% to 2 mol%.

[0090] The above electrolyte additive may be included in the above electrolyte in an amount of, for example, 10 wt% or less, 0.1 to 10 wt%, 0.1 to 8.0 wt%, 0.5 to 7 wt%, 1 to 7 wt%, 1.5 to 6 wt%, or 2 to 5 wt%, including the total content of all components used. When the content of the above electrolyte additive satisfies the above range, it is preferable in terms of the effect of improving the high-temperature characteristics, low-temperature characteristics, and cycle characteristics of the battery.

[0091]

[0092] The secondary battery of the present invention is characterized by including a negative electrode, a positive electrode, a separator interposed between the negative electrode and the positive electrode, and the electrolyte.

[0093] The above positive electrode can be manufactured by, for example, mixing a positive electrode active material, a binder, and optionally a conductive material to prepare a composition for forming a positive electrode active material layer, and then applying the composition to a positive electrode current collector such as aluminum foil.

[0094] As the positive electrode active material, a compound capable of reversible intercalation and deintercalation of lithium (lithiated intercalation compound) can be used.

[0095] The above positive electrode active material may be, for example, a lithium iron phosphate compound used in a lithium secondary battery.

[0096] The above lithium iron phosphate compound may include, for example, a compound represented by the following chemical formula 2.

[0097] [Chemical Formula 2]

[0098] Li 1+a M1 1-x M2 x (PO 4-b )D b

[0099] In the above chemical formula 2, M1 is Fe, M2 is at least one element selected from any one of groups 2 to 15, excluding element M1, D is at least one element selected from the group consisting of F, S, and N, a is an integer from -0.5 to 0.5, x is an integer from 0 to 0.5, and b is an integer from 0 to 1.

[0100] A compound having a coating layer on the surface of the compound may also be used, or a compound having a coating layer may be mixed and used. The coating layer may include at least one coating element compound selected from the group consisting of an oxide of the coating element, a hydroxide of the coating element, an oxyhydroxide of the coating element, an oxycarbonate of the coating element, and a hydroxycarbonate of the coating element. The compounds forming the coating layer may be amorphous or crystalline.

[0101] The coating elements included in the above coating layer may include C, Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof. The coating layer forming process may use any coating method as long as it can coat the compound with these elements using a method (e.g., spray coating, dipping, etc.) that does not adversely affect the properties of the positive electrode active material. Since this is well known in the art, a detailed description thereof will be omitted.

[0102] The content of the positive electrode active material may be, for example, 90 wt% or more, or 90 to 98 wt%, based on the total weight of the positive electrode active material layer.

[0103] In one embodiment of the present invention, the positive electrode active material layer may include a binder and a conductive material. In this case, the content of the binder and the conductive material may be 1 wt% or more, or 1 to 5 wt%, respectively, based on the total weight of the positive electrode active material layer.

[0104] The above binder serves to adhere positive electrode active material particles well to each other and also to adhere positive electrode active material well to a current collector, and examples thereof include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like.

[0105] The above conductive material is used to provide conductivity to the electrode, and in the battery to be formed, any material that does not cause a chemical change and is electronically conductive can be used. For example, a conductive material including a carbon-based material such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.; a metal-based material such as a metal powder or metal fiber such as copper, nickel, aluminum, silver, etc.; a conductive polymer such as a polyphenylene derivative; or a mixture thereof can be used.

[0106] Al can be used as a current collector, but is not limited thereto.

[0107]

[0108] The above negative electrode can be manufactured by, for example, mixing a negative electrode active material, a binder, and optionally a conductive material to prepare a composition for forming a negative electrode active material layer, and then applying the composition to a negative electrode current collector such as copper foil.

[0109] The surface of the above cathode may further include a SEI film (solid electrolyte interface).

[0110] The above negative active material includes a material capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a material capable of doping and dedoping lithium, or a transition metal oxide.

[0111] The material capable of reversibly intercalating / deintercalating the lithium ions is a carbon material, and any carbon-based negative electrode active material commonly used in lithium ion secondary batteries can be used.

[0112] Specific examples of the above-mentioned negative electrode active material may include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon. In addition to the above-mentioned carbonaceous materials, a metallic compound capable of alloying with lithium, or a composite including a metallic compound and a carbonaceous material may also be used as the negative electrode active material, and an example thereof may be graphite.

[0113] Additionally, a metallic lithium thin film may be used as the negative electrode active material. As the negative electrode active material, any one or more selected from the group consisting of crystalline carbon, amorphous carbon, carbon composites, lithium metal, and alloys containing lithium may be used in view of their high stability.

[0114] As a metal that can be alloyed with the lithium, at least one of Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy can be used, for example.

[0115] Materials capable of doping and dedoping the lithium include Si, Si-C composites, SiOx (0 < x < 2), Si-Q alloys (wherein Q is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, and is not Si), Sn, SnO2, Sn-R (wherein R is an element selected from the group consisting of alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, and is not Sn), and at least one of these may be mixed with SiO2 for use.

[0116] The above elements Q and R may be selected from the group consisting of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0117] Examples of the above transition metal oxides include vanadium oxide, lithium vanadium oxide, or lithium titanium oxide.

[0118] In the above negative electrode active material layer, the content of the negative electrode active material may be, for example, 95 wt% or more, or 95 to 99 wt%, based on the total weight of the negative electrode active material layer.

[0119] The content of the binder in the above negative electrode active material layer may be, for example, 1 wt% or more, or 1 to 5 wt%, based on the total weight of the negative electrode active material layer.

[0120] In the case of including a conductive material, the negative active material can be used in a range of 90 to 98 wt%, the binder in a range of 1 to 5 wt%, and the conductive material in a range of 1 to 5 wt%.

[0121] The above binder serves to adhere the negative electrode active material particles well to each other and also to adhere the negative electrode active material well to the current collector. The binder may be an insoluble binder, a water-soluble binder, or a combination thereof.

[0122] Examples of the above-described non-aqueous binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or combinations thereof.

[0123] Examples of the above water-soluble binder include a rubber-based binder or a polymer resin binder.

[0124] The above rubber binder may be selected from styrene-butadiene rubber, acrylated styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, acrylic rubber, butyl rubber, fluoroelastomer, and combinations thereof.

[0125] The polymer resin binder may be selected from polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene copolymer, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, polyacrylonitrile, polystyrene, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0126] When a water-soluble binder is used as the above-mentioned negative electrode binder, a cellulose-based compound capable of imparting viscosity may be further included.

[0127] The above cellulose series compound may be used by mixing one or more kinds of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof, for example.

[0128] As the alkali metal, Na, K or Li may be used. The amount of such thickener may be, for example, 0.1 to 5 parts by weight or 0.1 to 3 parts by weight per 100 parts by weight of the negative electrode active material.

[0129] The above conductive material is used to provide conductivity to the electrode, and any material that does not cause chemical changes and is electronically conductive in the battery to be constructed can be used. For example, a conductive material including a carbon-based material such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.; a metal-based material such as metal powder or metal fiber such as copper, nickel, aluminum, silver, etc.; a conductive polymer such as a polyphenylene derivative; or a mixture thereof can be used.

[0130] The above-mentioned current collector may be selected from the group consisting of copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with conductive metal, and combinations thereof.

[0131]

[0132] Depending on the type of lithium secondary battery, a separator may exist between the positive and negative electrodes. Such separators may include polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more layers thereof. Of course, mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may also be used.

[0133]

[0134] The secondary battery of the present invention has the effect of improving battery characteristics such as battery charge resistance measured by the HPPC (Hybrid Pulse Power Characterization) method, output characteristics, capacity recovery characteristics and life characteristics even when stored for a long period of time of 4 weeks or more at a high temperature of 60°C or higher, and low-temperature discharge characteristics by adding the aforementioned electrolyte additive together with the conventional compound added to the electrolyte to improve battery performance, and is further improved not only at high temperatures but also at low temperatures.

[0135] Specifically, the secondary battery of the present invention may have an initial DC-IR discharge resistance value of HPPC, for example, 64 mΩ or less, preferably 63 mΩ or less, and more preferably 62 mΩ or less, and the resistance value measured after storage at 60°C for 4 weeks does not increase by more than 51% compared to the initial resistance.

[0136] In this description, the HPPC discharge (charge) resistance value can be measured by the method specified in the document "Battery test manual for plug-in hybrid electric vehicles," (2010, Idaho National Laboratory for the US Department of Energy.), and is an important index indicating the characteristics of the battery, such as battery output. In addition, the charge (discharge) resistance is a resistance value measured when charging (discharging) the battery, and the lower the charge (discharge) resistance, the less energy loss there is, so the charging speed can be faster and the output of the battery can be improved. The secondary battery of the present invention has a low HPPC discharge resistance value as described above, and thus has excellent charging speed and output, and is suitable for use as a battery for automobiles, for example.

[0137] The above secondary battery exhibits a retention rate of 85% or more, preferably 88% or more, of the measured recovery capacity after 4 weeks of storage at 60°C.

[0138] In this paper, the recovery capacity represents the capacity retention characteristic of a battery that has been left for a long time. It is obtained by measuring the discharged electric capacity when a battery that has been left for a long time is discharged to the discharge end voltage, and the discharged electric capacity when the discharged battery is recharged and discharged again to the discharge end voltage, and comparing the two capacity values. The higher the recovery capacity, the less the amount of natural discharge due to battery preservation (storage), which means that the battery can be preserved for a long time.

[0139] The secondary battery of the present invention may have a life maintenance efficiency measured after 500 repetitions of charging and discharging of 90% or more, preferably 93% or more, and more preferably 93.9% or more.

[0140] The above secondary battery exhibits a discharge capacity retention rate of 43% or more, preferably 44% or more, at low temperatures.

[0141] In this paper, the low-temperature discharge capacity retention rate represents the capacity retention characteristic of a battery left at sub-zero temperatures. The discharged capacity when the battery is charged at room temperature and discharged to the discharge end voltage is measured, and the discharged capacity when the discharged battery is recharged and the battery left for a long time under sub-zero conditions is discharged to the discharge end voltage is measured, and the two capacity values ​​are compared. The higher the capacity retention rate, the less the amount of natural discharge due to battery preservation (storage) under sub-zero conditions, which means that the battery can be stored for a long time. Therefore, it is a very important characteristic in LFP EV vehicle batteries, which are known to have a rapid decrease in discharge capacity at low temperatures. When the electrolyte additive of the present invention is added to the electrolyte, the recovery capacity is improved by, for example, up to 18.5%, specifically, 5.6 to 18.5%, compared to when only the conventional additive is used, thereby enabling longer-term storage under sub-zero conditions with a single charge.

[0142]

[0143] Therefore, when the battery of the present invention is used as an automobile battery, it can exhibit excellent performance as an automobile battery by securing improved performance at low temperatures as well as improved performance at high temperatures, which is a problem due to the characteristics of automobiles that are mostly directly exposed to sunlight while driving or parked, as well as improved output, which becomes important depending on the size of the automobile.

[0144]

[0145] Hereinafter, preferred examples are presented to help understand the present invention, but the following examples are only illustrative of the present invention, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and technical idea of ​​the present invention, and it is also natural that such changes and modifications fall within the scope of the appended patent claims.

[0146] <Example>

[0147] Examples 1 to 5, Comparative Examples 1 to 3

[0148] A carbonate-based mixed solvent having a volume ratio of EC:EMC = 25:75 was used as the organic solvent, and a solution containing LiPF6 at a concentration of 1.2 M as the lithium salt was used, and an electrolyte for a battery was prepared using the types and contents of electrolyte additives shown in Table 1 below.

[0149] For example, in the case of Example 1, it corresponds to an experiment in which a battery electrolyte was prepared by adding 0.15 wt% of the compound represented by the above chemical formula 1a, 2.5 wt% of vinylene carbonate, and 1.5 wt% of fluoroethylene carbonate, and in the case of Example 2, it corresponds to an experiment in which a battery electrolyte was prepared by adding 0.2 wt% of the compound represented by the above chemical formula 1a, 2.5 wt% of vinylene carbonate, and 1.5 wt% of fluoroethylene carbonate.

[0150]

[0151] Examples 6 to 7, Comparative Example 4

[0152] A carbonate-based mixed solvent having a volume ratio of EC:EMC:DMC = 25:55:20 was used as the organic solvent, and a solution containing LiPF6 as the lithium salt at the concentration shown in Table 2 below was used to prepare a battery electrolyte using the types and contents of electrolyte additives shown in the table below.

[0153] For example, in the case of Example 6, it corresponds to an experiment in which a battery electrolyte was prepared by adding 0.2 wt% of the compound represented by the above chemical formula 1a, 1.5 wt% of vinylene chloride, and 0.5 wt% of fluoroethylene carbonate to a solution containing 1.2 M of LiPF6 as a lithium salt, and in the case of Example 7, it corresponds to an experiment in which a battery electrolyte was prepared by adding 0.3 wt% of the compound represented by the above chemical formula 1a, 1.5 wt% of vinylene chloride, and 1.0 wt% of fluoroethylene carbonate to a solution containing 0.9 M of LiPF6 as a lithium salt.

[0154] Furthermore, in Example 7 and Comparative Example 4 below, 0.9 M of LiPF6 was used as a lithium salt, and 0.25 M of lithium bis(fluorosulfonyl)imide was used together.

[0155]

[0156] Batteries were manufactured using the electrolytes obtained in Examples 1 to 7 and Comparative Examples 1 to 4 according to the battery manufacturing method described below, and then performance evaluations were performed, and the results are shown in the table below.

[0157]

[0158] Battery manufacturing

[0159] A positive electrode mixture slurry was prepared by adding 95 wt% of LiFePO4 as a positive electrode active material, 4.2 wt% of carbon black as a conductive material, and 0.8 wt% of a binder to N-methyl-2-pyrrolidone (NMP) as a solvent. The positive electrode mixture slurry was applied to an aluminum (Al) thin film as a positive electrode current collector with a thickness of about 20 μm, dried, and then roll pressed to prepare a positive electrode.

[0160] A negative electrode mixture slurry was prepared by adding 93 wt%, 6 wt%, and 1 wt% of carbon powder as a negative electrode active material, PVdF as a binder, and carbon black as a conductive material to NMP as a solvent. The negative electrode mixture slurry was applied to a copper (Cu) thin film as a negative electrode current collector with a thickness of 10 μm, dried, and then roll pressed to prepare a negative electrode.

[0161] After manufacturing a pouch-type battery using the manufactured positive and negative electrodes together with a separator made of a three-layer polypropylene / polyethylene / polypropylene (PP / PE / PP) using a conventional method, the respective electrolytes manufactured in Examples 1 to 7 and Comparative Examples 1 to 4 were injected to complete the manufacture of a lithium secondary battery.

[0162]

[0163] Performance Evaluation

[0164] [HPPC discharge (charge) resistance evaluation]

[0165] Measurements were made according to the method specified in the literature, "Battery test manual for plug-in hybrid electric vehicles," (2010, Idaho National Laboratory for the US Department of Energy.).

[0166] After storing at 60℃ for 4 weeks, the measured voltage value, charge / discharge current value corresponding to the C-rate, current change (△I), discharge voltage change (△V), charge voltage change (△V), charge resistance, and discharge resistance were measured, and the charge / discharge current was briefly applied for a certain period of time for each C-rate, and the resistance increase rate was calculated using the slope value obtained from the current and voltage changes.

[0167]

[0168] [High-temperature recovery capacity evaluation]

[0169] The charging conditions were a constant current of 0.5 C and a voltage of 3.65 V, charging until the charging current became 1 / 20 C. The discharging conditions were a constant current of 0.5 C, charging and discharging until 2.5 V, and then the discharge capacity was measured.

[0170] After charging under the same charge and discharge conditions, the battery was stored at 60°C for 4 weeks, and then discharged to a discharge voltage of 2.5 V under the same conditions. The change in remaining capacity was measured and presented as high-temperature recovery capacity in Table 1 below.

[0171]

[0172] [Low-temperature performance capacity retention rate evaluation]

[0173] The charging conditions were charging at a constant current of 0.5 C and a voltage of 3.65 V until the charging current became 1 / 20 C. The discharging conditions were charging and discharging by discharging to 2.5 V with a constant current of 0.5 C, and then charging under the same charge and discharge conditions as the measured discharge capacity. After storing for 2 hours under sub-zero conditions (-10°C), the measured discharge capacity was compared and shown as the low-temperature capacity retention rate in Table 1 below.

[0174]

[0175] [Life Assessment]

[0176] The secondary battery was charged at room temperature at a constant current rate of 1C until the voltage reached 3.65 V (vs. Li), and then cut off at a current rate of 0.05 C while maintaining 3.65 V in constant voltage mode. Subsequently, the battery was discharged at a constant current rate of 1C until the voltage reached 2.5 V (vs. Li) (1st cycle). After repeating the above cycle 500 times, the battery was stored for 4 weeks, and the changes in capacity and retention rate were measured, which are presented as high-temperature life capacity efficiency in Table 1 below.

[0177] Classification Additive Composition Additive Content (wt%) Initial discharge DC-IR (mΩ) Discharge DC-IR after high temperature storage (mΩ) Discharge DC-IR Increase rate (%) High temperature recovery capacity efficiency (%) Low temperature capacity retention rate (%) Life efficiency (%) Example 1 Chemical formula 1a + VC + FEC 0.15 +2.5 + 1.56 2.39 3.75 0.48 8.74 4.89 4.5 Example 2 Chemical formula 1a + VC + FEC 0.2 +2.5 + 1.56 0.28 7.34 5.08 8.84 7.99 4.6 Example 3 Chemical formula 1a + VC + FEC 0.3 +2.5 + 1.55 9.98 6.64 4.68 9.14 9.39 4.6 Example 4 Chemical formula 1a + VC + FEC 0.2 +1.5+1.558.678.534.088.950.195.4Example 5Chemical Formula 1a+VC+FEC0.2 +1.5+0.557.970.822.388.851.093.9Example 6Chemical Formula 1a+VC+FEC0.2 +1.5+0.557.669.420.588.952.095.5Example 7Chemical Formula 1a+VC+FEC0.3+1.5+1.057.969.319.788.955.296.3Comparative Example 1Chemical Formula 3a+VC+FEC0.3+2.5+1.564.3102.359.187.742.894.1Comparative Example 2Chemical Formula 3b+ VC+FEC0.3+2.5+1.565.2105.662.087.041.494.0Comparative Example 3Chemical Formula 3c+VC+FEC0.3+2.5+1.566.3105.058.487.540.293.9Comparative Example 4Chemical Formula 1a+VC+FEC0.5+1.5+1.057.575.627.188.352.195.9

[0178] (In the above table, VC refers to vinylene carbonate, FEC refers to fluoroethylene carbonate, and chemical formulae 1a, 3a, 3b, and 3c refer to compounds having the following chemical formulas, respectively.) [Chemical formula 1a]

[0179]

[0180] [Chemical Formula 3a]

[0181]

[0182] [Chemical Formula 3b]

[0183]

[0184] [Chemical formula 3c]

[0185]

[0186] As shown in Table 1 above, in the case of Examples 1 to 7 using the electrolyte additive of the present invention, it was confirmed that the resistance characteristics, high-temperature recovery capacity, low-temperature discharge capacity, and high-temperature life capacity efficiency were improved compared to Comparative Examples 1 to 4 that did not include the electrolyte additive represented by the chemical formula 1a.

[0187] For reference, it is known that the high-temperature recovery capacity is related to the reversibility of Li ions, and that if it leads to the elution of transition metals from the anode, the deposition of the eluted metal ions on the cathode surface, or if irreversible Li ions increase due to the interfacial side reaction between the anode and cathode, it leads to a decrease in capacity.

[0188] In particular, it was possible to confirm the results of simultaneously improving high-temperature characteristics and low-temperature characteristics.

[0189] Furthermore, even if the electrolyte additive of the present invention contained only about half of the amount of chemical formula 1a used in Example 3, it was possible to confirm improved results equivalent to or similar to those of Example 3, as seen in Example 1.

[0190]

[0191] As a result, it was found that the secondary batteries of Examples 1 to 7, in which the electrolyte additive of a specific composition was appropriately used in combination with the conventional electrolyte additive, had superior efficiency at both high and low temperatures in terms of output, discharge capacity, and life performance of the final finished composition compared to Comparative Examples 1 to 4, in which the electrolyte additive of a specific composition was not included at all.

[0192]

[0193] Therefore, when the electrolyte additive according to embodiments of the present invention and the electrolyte containing the same are applied to a secondary battery, it can be seen that not only does it provide the effect of reducing gas generation by suppressing internal side reactions of the battery, but also the charge resistance, discharge resistance, output, recovery capacity, and life efficiency are improved even when stored for a long time at high temperatures, and even the low-temperature performance capacity retention rate is improved even when stored at low temperatures, making it suitable for use as a secondary battery for automobiles.

Claims

1. An electrolyte additive comprising a compound in which one SX bond and two S=O bonds are directly connected to a sulfur (S) element; at least one compound selected from the group consisting of vinylene carbonate and fluoroethylene carbonate; wherein X is a halogen element.

2. In paragraph 1, An electrolyte additive characterized in that the compound in which one SX bond and two S=O bonds are directly connected to the sulfur (S) element has an asymmetric structure having a terminal -O-R3 (wherein R3 is an alkyl group having 1 to 3 carbon atoms).

3. In paragraph 1, An electrolyte additive characterized in that the compound in which one SX bond and two S=O bonds are directly connected to the sulfur (S) element is a compound in which one SX bond and two S=O bonds are directly connected to the sulfur (S) element. [Chemical Formula 1] (In the above chemical formula 1, a line is a bond, and when a separate element is not described, the point where a bond and a bond meet is carbon, and the number of hydrogens satisfying the valence of the carbon are omitted, R1 is -O-R3, R2 is alkylene having 1 to 3 carbon atoms, R3 is alkyl having 1 to 3 carbon atoms, and X is F, Cl, I, or Br.) 4. In paragraph 1, An electrolyte additive, characterized in that a compound in which one SX bond and two S=O bonds are directly connected to a sulfur (S) element is contained in an amount of 10 wt% or less based on 100 wt% of the total electrolyte.

5. In paragraph 1, An electrolyte additive, characterized in that at least one compound selected from the group consisting of vinylene carbonate and fluoroethylene carbonate is contained in a total content of 10 wt% or less based on 100 wt% of the total electrolyte.

6. In paragraph 1, An electrolyte additive characterized in that the compounds having one SX bond and two S=O bonds directly connected to the sulfur (S) element; and at least one compound selected from the group consisting of vinylene carbonate and fluoroethylene carbonate; are included in a weight ratio of 1:1 to 1:

30.

7. An electrolyte comprising an organic solvent, a lithium salt, and an electrolyte additive, An electrolyte, characterized in that the electrolyte additive comprises an electrolyte additive according to any one of claims 1 to 6.

8. In paragraph 7, An electrolyte solution characterized in that the organic solvent comprises at least one selected from the group consisting of ethylene carbonate (EC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate (PC), dipropyl carbonate (DPC), butylene carbonate, methyl propyl carbonate, and ethyl propyl carbonate.

9. In paragraph 7, The above lithium salts are LiPF6, LiF4, LiCl, LiBr, LiI, LiClO4, LiB. 10 Cl 10 An electrolyte characterized by comprising at least one selected from the group consisting of LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, and (CF3SO2)2NLi.

10. A secondary battery comprising a cathode, an anode, a separator interposed between the cathode and the anode, and an electrolyte, The above electrolyte comprises the electrolyte of claim 7, A secondary battery, characterized in that the positive electrode active material comprises a compound represented by the following chemical formula 2. [Chemical formula 2] <h2 style=";text-align:left;direction:ltr">Li<h2 style=";text-align:left;direction:ltr"> 1+a <h2 style=";text-align:left;direction:ltr"> M1<h2 style=";text-align:left;direction:ltr"> 1-x <h2 style=";text-align:left;direction:ltr"> M2<h2 style=";text-align:left;direction:ltr"> x <h2 style=";text-align:left;direction:ltr"> (PO<h2 style=";text-align:left;direction:ltr"> 4-b <h2 style=";text-align:left;direction:ltr"> D)<h2 style=";text-align:left;direction:ltr"> b In the chemical formula 2, M1 is Fe, M2 is at least one element selected from any one of groups 2 to 15, excluding element M1, D is at least one element selected from the group consisting of F, S, and N, a is an integer from -0.5 to 0.5, x is an integer from 0 to 0.5, and b is an integer from 0 to 1.

11. In paragraph 10, A secondary battery characterized in that the secondary battery is a battery for an automobile or a battery for an energy storage device.

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