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

Abstract

This invention relates to an electrolyte additive, an electrolyte containing the additive, and a secondary battery. According to the invention, it provides the following effects for a secondary battery: a stable coating is formed on the positive and negative electrodes of a lithium secondary battery, thereby suppressing side reactions inside the battery and providing low charge and discharge resistance, thus improving charging efficiency and power; even when stored for a long time under high temperature conditions, it can suppress the increase in battery resistance; and it can also significantly suppress gas generation caused by the decomposition of electrolyte components, thereby exhibiting excellent long-term lifespan and high-temperature capacity retention.

Description

Technical Field

[0001] This invention relates to an electrolyte additive, a battery electrolyte containing the additive, and a secondary battery containing the electrolyte. More specifically, it relates to an electrolyte additive that provides a secondary battery in which a stable coating is formed on the positive and negative electrodes of a lithium secondary battery, thereby suppressing side reactions inside the battery, reducing charge and discharge resistance, and thus improving charging efficiency and power. Even when stored at high temperatures for a long time, it can suppress the increase in battery resistance and the generation of gas, thereby exhibiting excellent long-term lifespan and high-temperature capacity retention. Background Technology

[0002] Lithium-ion batteries facilitate the use of electrical energy by adding an electrolyte between the positive and negative electrodes to allow lithium ions to migrate smoothly and by generating or consuming electricity through redox reactions caused by insertion and detachment between the positive and negative electrodes.

[0003] On the other hand, in recent years, with increasingly stringent global environmental regulations and growing public awareness of the environment, there has been a growing focus on environmentally friendly vehicles that can replace fossil fuel vehicles, a major cause of air pollution. Consequently, the battery industry both domestically and internationally is actively developing batteries for automobiles.

[0004] To use batteries in automobiles, it is necessary not only to significantly increase battery power and capacity, but also to solve problems such as power improvement and increased resistance under high and low temperature conditions to adapt to the usage environment such as weather changes. In particular, for electric vehicles, which are associated with power and driving range performance, research is needed to reduce the internal resistance of batteries and increase the remaining capacity. In view of this, it is especially necessary to develop a battery that can suppress internal side reactions and ensure low resistance and long life even when stored for a long time under high temperature conditions.

[0005] Existing technical documents Patent documents Korean Patent Publication No. 2019-0014711 Summary of the Invention The problem the invention aims to solve In order to solve the problems of the prior art as described above, the object of the present invention is to provide a novel electrolyte additive for batteries, an electrolyte for batteries containing the additive, and a secondary battery containing the electrolyte.

[0006] In addition, the present invention aims to provide a secondary battery that can suppress side reactions inside the battery and reduce charging resistance, thereby increasing the battery power and improving the recovery capacity under high temperature conditions, thus enabling long-term storage and exhibiting excellent life retention rate under high temperature conditions.

[0007] The objectives and other objectives of this invention can be achieved by the invention as described below.

[0008] means for solving problems To achieve the above objectives, the present invention provides an electrolyte additive, characterized in that it comprises: a compound having one S=X bond and two S=O bonds directly attached to a sulfur (S) element; and one or more compounds selected from the group consisting of 1-propene-1,3-sulfonolactone and vinyl sulfate, wherein X is a halogen element.

[0009] The compound having one SX bond and two S=O bonds directly attached to the sulfur (S) element can have an asymmetric structure with a terminal -O-R3 (where R3 is an alkyl group having 1 to 3 carbon atoms).

[0010] The compound in which one S-X bond and two S=O bonds are directly attached to the sulfur (S) element can be the following compound in which one S-X bond and two S=O bonds are directly attached to the sulfur (S) element.

[0011] [Chemical Formula 1]

[0012] (In the above chemical formula 1, lines represent bonds. When no individual element is specified, the point where bonds intersect represents carbon atoms. Hydrogen atoms that satisfy the required number of valences of carbon atoms are omitted. R1 is -O-R3, R2 is an alkylene group with 1 to 3 carbon atoms, R3 is an alkyl group with 1 to 3 carbon atoms, and X is F, Cl, I, or Br.)

[0013] The compound in which one S=S bond and two S=O bonds are directly attached to the sulfur (S) element can be represented by the following chemical formula 1-1.

[0014] [Chemical Formula 1-1]

[0015] (In the chemical formula 1-1, the lines represent bonds. When no individual element is specified, the point where a bond intersects another bond represents carbon. The number of hydrogen atoms that satisfy the valence of carbon atoms is omitted. X is F, Cl, I, or Br.)

[0016] The compound represented by the chemical formula 1-1 can be a compound represented by the chemical formula 1a below.

[0017] [Chemical Formula 1a]

[0018] The compound having one SX bond and two S=O bonds directly attached to the sulfur (S) element, and one or more compounds selected from the group consisting of 1-propene-1,3-sulfonolactone and vinyl sulfate, can be used in a weight ratio of 1:0.5 to 1:3.

[0019] As an example, in 100% by weight of the components constituting the electrolyte additive, the compound having one S X bond and two S=O bonds directly attached to the sulfur (S) element may be contained in less than 10% by weight. As a specific example, it may be contained in 0.2% by weight to 5% by weight, and as a preferred example, it may be contained in 0.2% by weight to 1.0% by weight.

[0020] As an example, in 100% by weight of the components constituting the electrolyte additive, one or more compounds selected from the group consisting of 1-propylene-1,3-sulfonyl lactone and vinyl sulfate may be contained at less than 10% by weight. As a specific example, it may contain 0.2% by weight to 5% by weight, and as a preferred example, it may contain 0.2% by weight to 1.8% by weight.

[0021] In addition, the present invention provides an electrolyte comprising an organic solvent, a lithium salt, and an electrolyte additive, wherein the electrolyte additive comprises the electrolyte additives described above.

[0022] The organic solvent may include one or more selected from the group consisting of ethylene carbonate (EC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate (PC), dipropyl carbonate (DPC), butene carbonate, methyl propyl carbonate, and ethyl propyl carbonate.

[0023] The lithium salt may include, selected from, LiPF6, LiF4, LiCl, LiBr, LiI, LiClO4, LiBF4, and 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) (where x and y are natural numbers, such as integers from 1 to 20), LiAsF6, LiSbF6, LiAlCl4, LiB(C2O4)2 (one or more of the group consisting of lithium bis(oxalato) borate (LiBOB), CH3SO3Li and CF3SO3Li).

[0024] Based on a total electrolyte volume of 100% by weight, the electrolyte additive may contain less than 10% by weight.

[0025] In addition, the present invention provides a secondary battery, the secondary battery comprising a negative electrode, a positive electrode, a separator between the negative electrode and the positive electrode, and an electrolyte, wherein the electrolyte is the electrolyte as described above.

[0026] The secondary battery can be a car battery.

[0027] The automotive batteries can be high-nickel NCA, NCM, medium-nickel NCM, lithium iron phosphate (LFP, LMFP), lithium-rich manganese (LMR, LMX, OLO, HLM), or lithium-rich (DRX) full batteries, etc.

[0028] Invention Effects The secondary battery containing the electrolyte additive according to the present invention has the following effects: it can suppress side reactions inside the battery and has low charging resistance, thus improving charging efficiency and power. Even when stored for a long time under high temperature conditions, it can suppress the increase of battery resistance, thereby having excellent long life and high temperature capacity retention. Detailed Implementation

[0029] The present invention will now be described in detail, but it is not limited thereto.

[0030] In order to manufacture a battery that can be used as an automobile battery, the inventors, while researching a secondary battery that can improve power by suppressing side reactions inside the battery and suppress the increase of battery resistance even when stored for a long time under high temperature conditions, thereby exhibiting excellent high-temperature recovery capacity and lifespan characteristics, discovered that adding additives with specific structures to the electrolyte of the secondary battery could achieve the above-mentioned objectives, and based on this, completed the present invention.

[0031] The electrolyte additive included in the electrolyte of the embodiments of the present invention is characterized in that the electrolyte additive comprises: a compound having one S=X bond and two S=O bonds directly attached to a sulfur (S) element; and one or more compounds selected from the group consisting of 1-propenyl-1,3-sulfonyl lactone and vinyl sulfate, wherein X is a halogen element. In this case, the following effects are achieved: side reactions inside the battery are suppressed, and due to the low charging resistance of the secondary battery, charging efficiency and power are improved; even when stored for a long time under high temperature conditions, the increase in battery resistance is suppressed, thereby exhibiting excellent long-term lifespan and high-temperature capacity retention.

[0032] As an example, density functional theory (DFT) calculations for this compound show that, compared to ethylene carbonate (EC) with a HOMO of -10.92 eV and a LUMO of 1.41 eV, the HOMO of this compound is -10.18 eV and the LUMO is 1.42 eV. Judging from the HOMO value, which shows almost similar reduction reactivity but a higher oxidation reactivity of 0.74 eV, it is predicted that this compound can also act on the positive electrode. In fact, it reacts with the initial LiF series inorganic coating components and forms a sulfonyl-based coating after the mid-reaction stage, thereby stabilizing the interface between the electrode and the electrolyte. Specifically, it effectively generates Li₂SO₃, a known low-resistivity component, thus exhibiting electrode stabilization and resistance reduction effects.

[0033] The compound having one SX bond and two S=O bonds directly attached to the sulfur (S) element can have an asymmetric structure with terminal -O-R3 (R3 being an alkyl group with 1 to 3 carbon atoms). In this case, it has the following effects: suppressing side reactions inside the battery, and improving charging efficiency and power due to the low charging resistance of the secondary battery, thus exhibiting excellent long-term life and high-temperature capacity retention.

[0034] In this specification, the compound in which one S X bond and two S=O bonds are directly attached to the sulfur (S) element can be selected from one or more compounds in which one S X bond and two S=O bonds are directly attached to the sulfur (S) element. In this case, it has the following advantages: it suppresses side reactions inside the battery, and because the charging resistance of the secondary battery is low, it can improve charging efficiency and power, thereby having excellent long-term life and high-temperature capacity retention.

[0035] [Chemical Formula 1]

[0036] (In the above chemical formula 1, lines represent bonds. When no individual element is specified, the point where bonds intersect represents carbon atoms. Hydrogen atoms that satisfy the required number of valences of carbon atoms are omitted. R1 is -O-R3, R2 is an alkylene group with 1 to 3 carbon atoms, R3 is an alkyl group with 1 to 3 carbon atoms, and X is F, Cl, I, or Br.)

[0037] The X is preferably F or Cl, which has a large difference in electronegativity from sulfur (S), in order to provide the aforementioned effects.

[0038] When the aforementioned electrolyte additive is added to the battery electrolyte, due to the electronegativity difference between the O element and the X element (e.g., O or F element) directly connected to the sulfur (S) element, electrons are biased towards the O or F element side. Furthermore, due to the asymmetric structure of the overall chemical formula, the S element is in an electron-deficient (e-poor, δ+) state, thus inducing an oxidation reaction in the electrolyte containing lithium ions, thereby forming a stable coating on the electrode (specifically, the positive electrode (Cathode)).

[0039] Due to the stability of the coating, electrolyte decomposition is prevented, thereby improving cycle characteristics. In particular, since it does not decompose at high temperatures, it offers significantly improved high-temperature storage performance compared to existing electrode coatings that decompose at high temperatures, resulting in reduced high-temperature storage. Furthermore, by preventing increased resistance, it improves charge / discharge efficiency and power, and suppresses gases generated by internal chemical reactions, thus enhancing battery stability. Additionally, it improves capacity retention by preventing the collapse of the active electrode material structure at high temperatures, thereby extending battery life.

[0040] The compound in which one S=S bond and two S=O bonds are directly attached to the sulfur (S) element can be a compound represented by the following chemical formula 1-1.

[0041] [Chemical Formula 1-1]

[0042] (In the chemical formula 1-1, the lines represent bonds. When no individual element is specified, the point where a bond intersects another bond represents carbon. The number of hydrogen atoms that satisfy the valence of carbon atoms is omitted. X is F, Cl, I, or Br.)

[0043] The compound represented by the chemical formula 1-1 can be a compound represented by the chemical formula 1a below.

[0044] [Chemical Formula 1a]

[0045] As described in this specification, one or more compounds selected from the group consisting of 1-propen-1,3-sulfonolactone and vinyl sulfate have the following advantages: they suppress side reactions inside the battery, and due to the low charging resistance of the secondary battery, they can improve charging efficiency and power, thereby having excellent long-term life and high-temperature capacity retention.

[0046] Based on a total electrolyte volume of 100% by weight, the compound containing one S=S bond and two S=O bonds directly bonded to the sulfur (S) element may be less than 10% by weight, preferably 0.1% to 5% by weight, and more preferably 0.2% to 1.0% by weight. Within this range, the battery exhibits the best improvement in charging efficiency and high-temperature lifespan.

[0047] The addition of a compound with one S X bond and two S=O bonds directly attached to the sulfur (S) element, together with one or more compounds selected from the group consisting of 1-propen-1,3-sulfonolactone and vinyl sulfate, can not adversely affect the components constituting the battery and can provide the intended improvement effect.

[0048] Based on a total electrolyte volume of 100% by weight, the total content of one or more compounds selected from the group consisting of 1-propen-1,3-sulfonyl lactone and vinyl sulfate may be less than 10% by weight, preferably from 0.2% by weight to 5% by weight, and more preferably from 0.2% by weight to 1.8% by weight. When the content of the compound meets the above range, it is preferred in terms of improving the high-temperature characteristics and cycle characteristics of the battery.

[0049] Based on a total electrolyte volume of 100% by weight, the 1-propylene-1,3-sulfonolactone may contain 0.2% by weight to 5% by weight, preferably 0.2% by weight to 2.5% by weight, and more preferably 0.2% by weight to 0.9% by weight. When the content of the compound meets the above range, it is preferred in terms of improving the high-temperature characteristics and cycle characteristics of the battery.

[0050] Based on a total electrolyte volume of 100% by weight, the ethylene sulfate may contain 0.2% by weight to 5% by weight, preferably 0.2% by weight to 2.5% by weight, and more preferably 0.2% by weight to 0.9% by weight. When the content of the compound meets the above range, it is preferred in terms of improving the high-temperature characteristics and cycle characteristics of the battery.

[0051] The compound having one SX bond and two S=O bonds directly attached to the sulfur (S) element, and one or more compounds selected from the group consisting of 1-propenyl-1,3-sulfonyl lactone and vinyl sulfate, can be used in a weight ratio of 1:0.1 to 1:3, 1:0.7 to 2, or 1:0.7 to 1:1.7. In this case, the following advantages are achieved: suppression of internal side reactions in the battery, and improved charging efficiency and power due to the low charging resistance of the secondary battery, resulting in excellent long-term lifespan and high-temperature capacity retention.

[0052] The aforementioned additive components need to be additionally included in a compound in which one SX bond and two S=O bonds are directly attached to the aforementioned sulfur (S) element. As can be confirmed by the comparative examples described later, when other additive components are injected alone without including the compound in which one SX bond and two S=O bonds are directly attached to the aforementioned sulfur (S) element, the improvement effect on long-term life and low resistance is not good.

[0053] As an example, in addition to the electrolyte additives mentioned above, the electrolyte of the present invention may also contain additives that are commonly used in electrolytes to suppress side reactions inside the battery, improve battery life characteristics, suppress battery capacity reduction, and improve battery discharge capacity, etc.

[0054] As a preferred specific example, the additive component may be selected from ethyl propionate (EP), propyl propionate (PP), succinic anhydride, tetravinylsilane, 1,1,2,2-tetrafluoroethyl 2,2,2-trifluoroethyl ether, 1,2-bis((difluorophosphanyl)oxy)ethane, 1,3,6-hexanetrionitrile, butadionitrile, 1-ethyl-3-methylimidazolium diaminonitrile, trimethoxycycloboroxane, etc. The group consisting of one or more of the following: lithium bis(oxalato)borate, lithium difluorooxalato)borate, tri(trimethylsilyl)borate, lithium tetrafluoroborate, triisopropyl borate, lithium tetrafluorooxalatophosphate, lithium difluoro(bis(oxalato))phosphate, lithium difluorophosphate, diethyl (difluoromethyl)phosphonate, tri(trimethylsilyl)phosphite, triargyl phosphate, 2,4,8,10-tetraoxa-3,9-dithiospiro[5.5]undecane 3,3,9,9-tetraoxide, dimethyl sulfate, ethane dimethylsulfonate, methylene methanedisulfonate, lithium bis(fluorosulfonyl)imide, 3-fluoro-1,3-propanesulfonyl lactone, 1,3-propene sulfate, 1,4-butanesulfonyl lactone, cyclobutene sulfone, biphenyl, cyclohexylbenzene, 4-fluorotoluene, triphenyl phosphate, fluorobenzene, and 2-fluorobiphenyl.

[0055] Among the aforementioned types, as specific examples, the metal phosphate compound is selected from one or more of the group consisting of lithium difluoro(bis(oxalato)phosphate) (LiDFOP), lithium tetrafluoro(oxalato)phosphate (LiTFOP), and lithium tris(oxalato)phosphate. This compound is added to improve the performance of lithium secondary batteries, lithium-ion capacitors, etc., to suppress internal side reactions, and to improve resistance and lifespan. As an example, it may be contained in the electrolyte at a concentration of 0.3% to 2.5% by weight, preferably 0.5% to 1.5% by weight. When the content of the aforementioned electrolyte additive meets the above range, it is preferred to improve the high-temperature characteristics and cycle characteristics of the battery.

[0056] As an example, the electrolyte additive (including the total content of the components used) may be included in the aforementioned electrolyte in amounts of less than 10% by weight, 0.2% to 8% by weight, 0.2% to 5% by weight, 0.2% to 3.5% by weight, 0.2% to 3.0% by weight, or 0.2% to 2.7% by weight. When the content of the electrolyte additive meets the above ranges, it is preferred in terms of improving the high-temperature characteristics and cycle characteristics of the battery.

[0057] Furthermore, the present invention provides an electrolyte comprising the electrolyte additive of the present invention. The electrolyte is a non-aqueous lithium secondary battery electrolyte, comprising the electrolyte additive, an organic solvent, and a lithium salt.

[0058] As an example, the organic solvent may be a carbonate organic solvent. Specifically, the organic solvent may be one or more organic solvents selected from the group consisting of ethylene carbonate (EC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate (PC), dipropyl carbonate (DPC), butenyl carbonate, methyl propyl carbonate, and ethyl propyl carbonate.

[0059] As an example, the organic solvent can be one or more mixed solvents. Preferably, in order to improve the charge and discharge performance of the battery, an organic solvent with high dielectric constant and high ionic conductivity can be mixed with a low viscosity organic solvent whose viscosity can be adjusted to suit its application in the battery, and this mixture can be used as a mixed solvent.

[0060] As an example, the high dielectric constant organic solvent can be EC and PC, etc.; as an example, the low viscosity organic solvent can be EMC, DMC, and DEC, etc. Preferably, the high dielectric constant organic solvent and the low viscosity organic solvent are mixed in a volume ratio of 2:8 to 8:2. More specifically, it can be a ternary mixed solvent of one of EC and PC, EMC, and DEC. As an example, the ratio of EC or PC, EMC, and DEC can be 1:0.1 to 1:2 to 5, or 1:0.2 to 0.5:3 to 5, or 1:0.2 to 0.3:3 to 4.

[0061] When the organic solvent contains water, the water content in the organic solvent is preferably controlled to be below 150 ppm, and more preferably below 100 ppm, since lithium ions in the electrolyte can be hydrolyzed.

[0062] The lithium salt can be used without particular restriction as long as it is a compound that can provide lithium ions used in lithium secondary batteries. Specifically, the lithium salt may include compounds selected from LiPF6, LiF4, LiCl, LiBr, LiI, LiClO4, LiBF4, and 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) (where x and y are natural numbers, such as integers from 1 to 20), LiAsF6, LiSbF6, LiAlCl4, LiB(C2O4)2 (one or more of the group consisting of lithium bis(oxalato) borate (LiBOB), CH3SO3Li and CF3SO3Li).

[0063] When the lithium salt is dissolved in the electrolyte, the lithium salt can be used as a source of lithium ions in a lithium secondary battery and can promote the migration of lithium ions between the positive electrode and the negative electrode. Thus, preferably, in the electrolyte, the concentration of the lithium salt is about 0.6 mol% to 3 mol%. When the concentration of the lithium salt is less than 0.6 mol%, the conductivity of the electrolyte decreases, which may lead to a reduction in electrolyte performance. When it exceeds 3 mol%, the viscosity of the electrolyte increases, which may lead to a reduction in the migration performance of lithium ions. Considering the conductivity of the electrolyte and the migration performance of lithium ions as described above, preferably, in the electrolyte, the content of the lithium salt can be 0.7 mol% to 3 mol%, and more preferably, 0.8 mol% to 3 mol%.

[0064] As an example, the electrolyte additive can be included in the electrolyte at 0.1 wt% to 10 wt%, 0.1 wt% to 8.0 wt%, 0.1 wt% to 7 wt%, 0.3 wt% to 7 wt%, 0.5 wt% to 6 wt%, or 0.� wt% to 5 wt%. When the content of the aforementioned electrolyte additive satisfies the above range, it is preferable in terms of the improvement effect of the high-temperature characteristics and cycle characteristics of the battery.

[0065] 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.

[0066] As an example, the positive electrode is prepared by mixing a positive electrode active material, a binder, and an optional conductive agent to form a composition for forming a positive electrode active material layer, and then the composition can be coated on a positive electrode current collector (such as aluminum foil) for preparation.

[0067] The positive electrode active material can use a compound (lithiated insertion compound) capable of reversibly inserting and extracting lithium.

[0068] As an example, the positive electrode active material can use a conventional NCM (lithium nickel manganese cobalt oxide, LiNiMnCoO2) positive electrode active material used in a lithium secondary battery. Specifically, the positive electrode active material can be a lithium composite metal oxide in the form of the chemical formula Li[Ni x Co y Mn z O2 (where 0 < x < 95, 0 < y < 35, 0 < z < 35, however, x + y + z = 100), but not limited thereto. For example, conventional LFP (lithium iron phosphate compound, LiFe2O4), NCA, lithium-rich manganese (LMR, LMX, OLO, HLM), and lithium-rich (DRX) positive electrode active materials can also be used.

[0069] As an example, the chemical formula of the lithium composite metal oxide Li[Ni x Coy Mn z For the parameters x, y, and z of ]O2, 0.0001 < x < 95, 0.0001 < y < 35, 0.0001 < z < 35. Preferably, 1 ≤ x ≤ 93, 1 ≤ y ≤ 30, 1 ≤ z ≤ 30. More preferably, 5 ≤ x ≤ 91, 3 ≤ y ≤ 25, 3 ≤ z ≤ 25. At this time, x + y + z satisfies 100.

[0070] As another example, the lithium composite metal oxide may be selected from the group consisting of LiCoO2, LiMnO2, LiMn2O4, LiNiO2, LiNi x Mn (1-x) O2 (however, 0 < x < 1) and LiM1 x M2 y O2 (however, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ x + y ≤ 1, and M1 and M2 are each independently selected from any one of the group consisting of Al, Sr, Mg, and La), in this case, the capacity characteristics and stability of the battery can be improved.

[0071] It is also possible to use a compound having a coating layer on the surface of the compound, or a compound and a compound having a coating layer can also be used in combination. The coating layer may include at least one coating element compound selected from the group consisting of oxides of coating elements, hydroxides of coating elements, hydroxyoxides of coating elements, oxycarbonates of coating elements, and hydroxycarbonates of coating elements. The compounds forming these coating layers can be amorphous or crystalline.

[0072] The coating elements contained in the coating layer can use Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or a mixture thereof. As long as the physical properties of the positive electrode active material are not adversely affected by using these elements in the compound (for example, spraying, dipping method, etc.) for coating, any coating method can be used for the coating layer formation process. Since it is well-known in the art, its detailed description is omitted.

[0073] As an example, the content of the positive electrode active material can be 90% by weight or more, or 90% to 98% by weight, based on the total weight of the positive electrode active material layer.

[0074] In one implementation example of the present invention, the positive electrode active material layer may include a binder and a conductive material. At this time, the contents of the binder and the conductive material can be 1% by weight or more, or 1% to 5% by weight, respectively, based on the total weight of the positive electrode active material layer.

[0075] The adhesive is used to ensure that the positive electrode active material particles adhere well to each other and to ensure that the positive electrode active material adheres well to the current collector. For example, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, cellulose diacetate, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, and nylon can be used.

[0076] The conductive material is used to provide conductivity to the electrodes. In the battery, any electronically conductive material that does not cause chemical changes can be used. As an example, conductive materials can include: carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fiber; metal-based substances such as copper, nickel, aluminum, silver, metal powders or metal fibers; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0077] The current collector can be Al, but is not limited to this.

[0078] As an example, the negative electrode is prepared by mixing a negative electrode active material, a binder, and an optional conductive agent to form a composition for forming a negative electrode active material layer, and then the composition can be coated onto a negative electrode current collector (copper foil, etc.) for preparation.

[0079] The surface of the negative electrode may also include a solid electrolyte interface (SEI) membrane.

[0080] The negative electrode active material includes materials capable of reversibly inserting / deintercalating lithium ions, lithium metal, lithium metal alloys, materials capable of doping or dedoping lithium, or transition metal oxides.

[0081] The material capable of reversibly inserting / deintercalating the lithium ions is a carbon material, and any material can be used for the carbon-based negative electrode active material commonly used in lithium-ion secondary batteries.

[0082] As a specific example, the negative electrode active material can be carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon. In addition to the aforementioned carbonaceous materials, metal compounds capable of alloying with lithium, or composites containing metal compounds and carbonaceous materials, can also be used as negative electrode active materials; for example, graphite.

[0083] Alternatively, a thin film of lithium metal can also be used as the negative electrode active material. Because the negative electrode active material has high stability, one or more materials selected from the group consisting of crystalline carbon, amorphous carbon, carbon complexes, lithium metal, and lithium-containing alloys can be used.

[0084] As an example, the metal capable of alloying with lithium may be at least one selected from Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy or Al alloy.

[0085] The material capable of doping or dedoping lithium may include Si, Si-C composite, SiOx (0 < x < 2), Si-Q alloy (where 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, but not Si), Sn, SnO2 and Sn-R (where 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 not Sn), etc. Additionally, it may also be used by mixing at least one of them and SiO2.

[0086] The elements Q and R may be elements 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.

[0087] The transition metal oxide may include vanadium oxide, lithium vanadium oxide or lithium titanium oxide, etc.

[0088] In the negative electrode active material layer, as an example, relative to the total weight of the negative electrode active material layer, the content of the negative electrode active material may be 95% by weight or more, or 95% to 99% by weight.

[0089] In the negative electrode active material layer, as an example, relative to the total weight of the negative electrode active material layer, the content of the binder may be 1% by weight or more, or 1% to 5% by weight.

[0090] When a conductive material is included, 90% to 98% by weight of the negative electrode active material, 1% to 5% by weight of the binder, and 1% to 5% by weight of the conductive material may be used.

[0091] The function of the binder is to make the negative electrode active material particles adhere well to each other, and in addition, to adhere the negative electrode active material well to the current collector. The binder may be a water-insoluble binder, a water-soluble binder or a combination thereof.

[0092] Examples of the non-water-soluble adhesives include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, or combinations thereof.

[0093] The water-soluble adhesive may include a rubber-based adhesive or a polymer resin adhesive.

[0094] The rubber-based adhesive may be selected from styrene-butadiene rubber, acrylated styrene-butadiene rubber (SBR), nitrile rubber, acrylic rubber, butyl rubber, fluororubber, and combinations thereof.

[0095] The polymer resin adhesive may be selected from polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene copolymer, polyethylene oxide, polyvinylpyrrolidone, polyepoxychloropropane, polyphosphazene, polyacrylonitrile, polystyrene, ethylene propylene diene terpolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0096] When a water-soluble adhesive is used as the negative electrode adhesive, it may also contain a cellulose compound that imparts viscosity.

[0097] As an example, the cellulose compound can be used by mixing one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or their alkali metal salts.

[0098] The alkali metal may be Na, K, or Li. As an example, the amount of this thickener used may be 0.1 to 5 parts by weight or 0.1 to 3 parts by weight relative to 100 parts by weight of the negative electrode active material.

[0099] The conductive material is used to provide conductivity to the electrodes. In the battery, any electronically conductive material that does not cause chemical changes can be used. As an example, conductive materials can include: carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fiber; metal-based substances such as copper, nickel, aluminum, silver, metal powders or metal fibers; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0100] The current collector may be a material 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.

[0101] Depending on the type of lithium-ion secondary battery, a separator may be present between the positive and negative electrodes. This separator can be made of polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more layers thereof. Of course, mixed multilayer films can also be used, such as two-layer separators of polyethylene / polypropylene, three-layer separators of polyethylene / polypropylene / polyethylene, and three-layer separators of polypropylene / polyethylene / polypropylene, etc.

[0102] In the secondary battery of the present invention, in addition to the conventional compounds added to the electrolyte to improve the performance of existing batteries, the aforementioned electrolyte additives are also added together. Compared with adding only existing electrolyte additives, the following effects are achieved: the battery charging resistance, power characteristics, and battery characteristics (capacity recovery characteristics and lifespan characteristics, etc.) measured by the Hybrid Pulse Power Characterization (HPPC) method are further improved.

[0103] Specifically, the initial DC internal resistance (DC-IR) discharge of the secondary battery of the present invention can be the HPPC discharge resistance value. For example, it can be 75mΩ or less, preferably 70mΩ or less, more preferably 69mΩ or less, and the increase rate of the resistance value measured after storage at 60°C for 60 days compared with the initial resistance does not exceed 15%.

[0104] As described in this specification, the HPPC discharge (charge) resistance value can be measured using the methods specified in the "Battery test manual for plug-in hybrid electric vehicles" (2010, Idaho National Laboratory for the US Department of Energy). It is an important indicator of battery characteristics (such as battery power). Furthermore, charge (discharge) resistance refers to the resistance value measured during battery charging (discharging). Lower charge (discharge) resistance indicates lower energy loss, thus accelerating charging and increasing battery power. As described above, the secondary battery of the present invention has a low HPPC discharge resistance value and excellent charging speed and power, making it suitable for use, for example, as an automotive battery.

[0105] The secondary battery, after being stored at 60°C for 60 days, retains a recovery capacity of 85% or more, preferably 88% or more.

[0106] In this specification, recovery capacity refers to the capacity retention characteristic of a battery after prolonged storage. It is determined by measuring the discharge amount when a battery is discharged to its discharge termination voltage after prolonged storage, and the discharge amount when the discharged battery is recharged and discharged again to its discharge termination voltage, and comparing these two capacity values. A higher recovery capacity indicates less natural discharge during battery storage, thus meaning the battery can be stored for a longer period. In particular, the higher the storage temperature, the faster the natural discharge rate; therefore, recovery capacity under high-temperature conditions is a very important characteristic in automotive batteries. When the electrolyte additive of this invention is added to the electrolyte, the recovery capacity is increased by up to 11% compared to using existing additives alone, for example, by 2% to 11%, thus achieving the effect of longer storage with a single charge.

[0107] The secondary battery of the present invention has a life retention efficiency of 80% or more, preferably 85% or more, and more preferably 88% or more, after being stored at a temperature of 60°C for 60 days.

[0108] Therefore, when the battery of the present invention is used as an automotive battery, it not only achieves improved power (which becomes important depending on the size of the vehicle) and improved performance at low and high temperatures (problems arising from climate change and the fact that vehicles are mostly directly exposed to sunlight while driving or parked), but also ensures stability even when using high-content nickel cathode materials suitable for high-capacity expression, thus exhibiting excellent performance as an automotive battery.

[0109] Preferred embodiments are provided below to aid in understanding the present invention. However, these embodiments are merely illustrative of the invention. Various changes and modifications can be made within the scope and technical concept of the present invention, which will be obvious to those skilled in the art. Of course, such variations and modifications fall within the scope of the appended claims.

[0110] Example Examples 1 to 8, Comparative Examples 1 to 5 An organic solvent of carbonate mixed solvent with a volume ratio of EC:EMC:DEC=20:5:75 was used as lithium salt. In a solution containing LiPF6 at a concentration of 1.15M, electrolytes for batteries were prepared using the types and amounts of electrolyte additives shown in Table 1 below.

[0111] For example, Example 1 corresponds to the following experiment: 0.5% by weight of the compound represented by the chemical formula 1a and 0.5% by weight of ethylene sulfate (ESA) are added to prepare an electrolyte for batteries. Example 2 corresponds to the following experiment: 0.5% by weight of the compound represented by the chemical formula 1a and 0.5% by weight of 1-propylene-1,3-sulfonolactone (PRS) are added to prepare an electrolyte for batteries.

[0112] The electrolytes obtained in Examples 1 to 8 and Comparative Examples 1 to 5 were used to manufacture batteries according to the battery manufacturing method described later. The performance of the batteries was evaluated, and the results are shown in Table 1 below.

[0113] Battery manufacturing 92% by weight of Li(Ni) will be used as the positive electrode active material. 0.8 Co 0.1 Mn 0.1 O2, 4% by weight carbon black as a conductive agent, and 4% by weight polyvinylidene fluoride (PVdF) as a binder were added to N-methyl-2-pyrrolidone (NMP) as a solvent to prepare a positive electrode mixture slurry. The positive electrode mixture slurry was coated onto an aluminum (Al) thin film (approximately 20 μm thick) as the positive electrode current collector, and the positive electrode was prepared by drying and then by roll pressing.

[0114] A negative electrode mixture slurry was prepared by adding 96% by weight of carbon powder as the negative electrode active material, 3% by weight of PVdF as the binder, and 1% by weight of carbon black as the conductive agent to NMP as the solvent. The negative electrode mixture slurry was coated onto a copper (Cu) thin film (10 μm thick) as the negative electrode current collector, and the negative electrode was prepared by drying and then by roll pressing.

[0115] The prepared positive and negative electrodes, together with the separator formed by three layers of polypropylene / polyethylene / polypropylene (PP / PE / PP), were prepared into a pouch cell by conventional methods. Then, the electrolytes prepared in Examples 1 to 8 and Comparative Examples 1 to 5 were injected to complete the preparation of the lithium secondary battery.

[0116] Performance Evaluation [HPPC Discharge (Charge) Resistance Evaluation] The measurements were performed according to the methods specified in the "Battery test manual for plug-in hybrid electric vehicles" (2010, Idaho National Laboratory for the US Department of Energy).

[0117] After being stored at 60℃ for 60 days, the voltage value, the charge / discharge current value corresponding to the charge / discharge rate (C-rate), the change in current (ΔI), the change in discharge voltage (ΔV), the change in charging voltage (ΔV), the charging resistance, and the discharge resistance were measured. The charge / discharge current was allowed to flow briefly for a specified time according to each charge / discharge rate (C-rate), and the rate of increase in resistance was calculated by using the slope values ​​obtained from the changes in current and voltage.

[0118] [Evaluation of High-Temperature Recovery Capacity] The charging conditions were a constant current of 0.5C and a voltage of 4.2V, charging until the charging current reached 1 / 10C. The discharging conditions were a constant current of 0.5C to 3.0V. After charging and discharging in this manner, the discharge capacity was measured.

[0119] After being charged under the same charge and discharge conditions, the cells were stored at 60°C for 60 days. Then, under the same conditions, they were discharged until the discharge voltage reached 3V. The change in remaining capacity was measured and is shown in Table 1 below as the capacity recovered at high temperature.

[0120] [High-Temperature Lifetime Evaluation] The secondary battery was charged at a constant current at a charge-discharge rate (C rate) of 1 at 60°C until the voltage reached 4.20V (vs. Li). Then, in constant voltage mode, the voltage was maintained at 4.20V and cut-off was performed at a charge-discharge rate (C rate) of 0.1. Next, it was discharged at a constant current at a charge-discharge rate (C rate) of 1 until the voltage reached 3.0V (vs. Li) (first cycle). After repeating the above cycle 300 times and storing for 60 days, the capacity and retention changes were measured and are shown in Table 1 below as high-temperature lifetime capacity efficiency.

[0121] Table 1

[0122] (In the table, ESA refers to vinyl sulfate, and PRS refers to 1-propylene-1,3-sulfonolactone.)

[0123] As shown in Table 1, in Examples 1 to 8 using the electrolyte additive of the present invention, compared with Comparative Example 1, which did not contain the electrolyte additive represented by Chemical Formula 1a and the combined additive, and Comparative Examples 3 to 5, which contained the combined additive with Chemical Formula 1a alone or in combination, it can be confirmed that the resistance characteristics, high temperature recovery capacity and high temperature lifetime capacity efficiency are improved.

[0124] In particular, the high-temperature recovery capacity showed significant differences. For reference, the recovery capacity is related to the reversibility of Li ions. It is known that if the positive electrode transition metal dissolves, the dissolved metal ions are deposited on the negative electrode surface, or an interfacial side reaction occurs between the positive and negative electrodes, an irreversible increase in Li ions will occur, leading to a decrease in capacity.

[0125] Furthermore, the evaluation results of the compounds represented by chemical formula 1a as electrolyte additives of the present invention confirm that, compared with Comparative Example 2, which did not add any other additional ingredients and used only the compounds represented by chemical formula 1a as electrolyte additives of the present invention, the high-temperature recovery capacity and high-temperature lifetime capacity efficiency of Examples 1 to 8 were improved.

[0126] Additional Comparative Examples 1 to 10 An organic solvent of carbonates with a volume ratio of EC:EMC:DMC=20:5:75 was used as the lithium salt. Electrolytes for batteries were prepared by using the types and amounts of electrolyte additives shown in Table 2 below in a solution containing LiPF6 at a concentration of 1.15M.

[0127] The electrolytes obtained in Additional Comparative Examples 1 to 10 were used to manufacture batteries according to the aforementioned battery manufacturing method. The performance of the batteries was evaluated, and the results are shown in Table 2 below.

[0128] Table 2

[0129] (In the table, ESA refers to vinyl sulfate, and PRS refers to 1-propylene-1,3-sulfonolactone.)

[0130] As shown in Table 2, the evaluation results of the electrolyte additive of the present invention, which includes the compound represented by chemical formula 1a, confirmed that, compared with the additional comparative examples 1 to 10 which used additives that exceeded the appropriate range, at least one of the DC-IR resistance characteristics, high-temperature recovery capacity characteristics and high-temperature lifetime characteristics of Examples 1 to 8 after high-temperature storage were significantly improved.

[0131] Furthermore, the results of measuring the change in battery thickness before and after high-temperature storage confirm that the electrolyte additive of the present invention significantly inhibits the oxidation / reduction decomposition of the electrolyte, thereby also having the effect of reducing the amount of gas generated.

[0132] Ultimately, it can be seen that, in the case of the secondary batteries of Examples 1 to 8, which appropriately combine electrolyte additives of a specific composition with existing electrolyte additives, the discharge efficiency of the final composition is superior in terms of power and lifespan performance compared to Comparative Example 1, which does not contain electrolyte additives, Comparative Example 2, which only contains electrolyte additives with a specific structure, or Comparative Examples 3 to 5, which only use existing electrolyte additives (multiple), and Additional Comparative Examples 1 to 10, which contain these but exceed the appropriate content range.

[0133] Therefore, it can be confirmed that when the electrolyte additive of the present invention and the electrolyte containing the additive are used in secondary batteries, not only does it reduce gas production by suppressing side reactions inside the battery, but it also improves charging resistance, discharging resistance, power, recovery capacity and life efficiency even when stored for a long time under high temperature conditions. Therefore, it is suitable for use in automotive secondary batteries.

Claims

1. An electrolyte additive, characterized in that, Include: Compounds in which sulfur is directly bonded by one S=X bond and two S=O bonds; and One or more compounds selected from the group consisting of 1-propen-1,3-sulfonolactone and vinyl sulfate. X is a halogen element.

2. The electrolyte additive according to claim 1, characterized in that, The compound having one SX bond and two S=O bonds directly attached to the sulfur element has an asymmetric structure with terminal -O-R3, wherein R3 is an alkyl group having 1 to 3 carbon atoms.

3. The electrolyte additive according to claim 1, characterized in that, The compound in which one Sx bond and two S=O bonds are directly attached to the sulfur element is as follows: [Chemical Formula 1] In the chemical formula 1, lines represent bonds. When no individual element is specified, the point where bonds intersect is carbon. Hydrogen atoms that satisfy the required number of valences of carbon atoms are omitted. R1 is -O-R3, R2 is an alkylene group with 1 to 3 carbon atoms, R3 is an alkyl group with 1 to 3 carbon atoms, and X is F, Cl, I, or Br.

4. The electrolyte additive according to claim 1, characterized in that, Based on a total electrolyte volume of 100% by weight, the compound contains less than 10% by weight of sulfur element directly connected to one SX bond and two S=O bonds.

5. The electrolyte additive according to claim 1, characterized in that, Based on a total electrolyte volume of 100% by weight, the total content of one or more compounds selected from the group consisting of 1-propylene-1,3-sulfonolactone and vinyl sulfate is less than 10% by weight.

6. The electrolyte additive according to claim 1, characterized in that, The compound having one SX bond and two S=O bonds directly attached to the sulfur element is present in a weight ratio of 1:0.5 to 1:3 with one or more compounds selected from the group consisting of 1-propene-1,3-sulfonolactone and vinyl sulfate.

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

8. The electrolyte according to claim 7, characterized in that, The organic solvent includes one or more selected from the group consisting of ethylene carbonate, diethyl carbonate, methyl ethyl carbonate, dimethyl carbonate, propylene carbonate, dipropyl carbonate, butene carbonate, methyl propyl carbonate, and ethyl propyl carbonate.

9. The electrolyte according to claim 7, characterized in that, The lithium salt includes those selected from LiPF6, LiF4, LiCl, LiBr, LiI, LiClO4, and LiB. 10 Cl 10 One or more of the group consisting of LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li and (CF3SO2)2NLi.

10. A secondary battery, comprising a negative electrode, a positive electrode, a separator between the negative electrode and the positive electrode, and an electrolyte, characterized in that, The electrolyte is the electrolyte according to claim 7.

11. The secondary battery according to claim 10, characterized in that, The secondary battery is a car battery.

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