Method for manufacturing lithium secondary battery, and lithium secondary battery

Abstract

The present specification relates to a method for manufacturing a lithium secondary battery and a lithium secondary battery. According to one embodiment of the present invention, provided is a method for manufacturing a lithium secondary battery, the method comprising the steps of: injecting a first electrolyte solution into a battery case in which an electrode assembly including a positive electrode and a negative electrode is accommodated; performing a first activation process after injecting the first electrolyte solution; injecting a second electrolyte solution different from the first electrolyte solution into the battery case in which the first activation process has been performed; and performing a second activation process after injecting the second electrolyte solution, wherein the lithium salt concentration of the first electrolyte solution is greater than the lithium salt concentration of the second electrolyte solution, and the difference between the lithium salt concentrations of the first electrolyte solution and the second electrolyte solution satisfies a specific range.

Description

Lithium secondary battery manufacturing method and lithium secondary battery

[0001] This application claims the benefit of Korean Patent Application No. 10-2024-0098612, filed with the Korean Intellectual Property Office on July 25, 2024, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to a method for manufacturing a lithium secondary battery and a lithium secondary battery.

[0003] The recent rapid proliferation of battery-powered electronic devices, including mobile phones, laptops, electric vehicles, power tools, and vacuum cleaners, has led to a rapid increase in demand for compact, lightweight, and relatively high-capacity and / or high-output secondary batteries. In particular, lithium secondary batteries, with their lightweight design and high energy density, are attracting significant attention as power sources for electronic devices. Accordingly, active research and development efforts are underway to improve the performance of lithium secondary batteries.

[0004] Lithium secondary batteries produce electrical energy through oxidation and reduction reactions when lithium ions are inserted / deintercalated from the positive and negative electrodes, while an organic electrolyte or polymer electrolyte is charged between the positive and negative electrodes, which are made of active materials capable of intercalating and deintercalating lithium ions.

[0005] During the initial charging of a lithium secondary battery, lithium ions released from the positive electrode active material, such as lithium metal oxide, migrate to the negative electrode active material and are intercalated between the layers of the negative electrode active material. At this time, due to the strong reactivity of lithium ions, an electrolyte-derived film, such as a CEI (Cathode-Electrolyte Interface) film formed between the positive electrode and the electrolyte, or a SEI (Solid Electrolyte Interphase) film formed between the negative electrode and the electrolyte, is formed on the surface of the electrode active material.

[0006] These electrolyte-derived films act as lithium ion tunnels, preventing direct contact between the electrolyte and the electrode active material, thereby reducing side reactions during charge and discharge. However, the electrolyte-derived film may not be uniformly formed on the surface of the electrode active material, or may be unstably formed depending on the composition of the electrolyte, thereby degrading battery performance.

[0007] The problem to be solved by the present invention is to provide a method for manufacturing a lithium secondary battery and a lithium secondary battery, which improves the initial efficiency, fast charging, and life characteristics of a lithium secondary battery by forming a uniform electrolyte-derived film on the surface of a positive or negative electrode active material.

[0008] The problems to be solved by the present invention are not limited to the problems mentioned above, and other problems not mentioned will be clearly understood by those skilled in the art from the description below.

[0009] One embodiment of the present invention provides a method for manufacturing a lithium secondary battery, comprising: a step of injecting a first electrolyte into a battery case containing an electrode assembly including a positive electrode and a negative electrode; a step of performing a first activation process after injecting the first electrolyte; a step of injecting a second electrolyte different from the first electrolyte into the battery case in which the first activation process has been performed; and a step of performing a second activation process after injecting the second electrolyte, wherein the first electrolyte and the second electrolyte each independently contain a lithium salt, the lithium salt concentration of the first electrolyte is greater than the lithium salt concentration of the second electrolyte, and a difference between the lithium salt concentrations of the first electrolyte and the second electrolyte is 0.5 M to 2 M.

[0010] One embodiment of the present invention provides a lithium secondary battery manufactured by the above manufacturing method.

[0011] According to a method for manufacturing a lithium secondary battery and a lithium secondary battery according to an embodiment of the present invention, a CEI film or SEI film having a high density, a thin thickness, and a strong strength derived from the first and second electrolytes can be stably formed on the surface of an electrode active material.

[0012] A method for manufacturing a lithium secondary battery according to one embodiment of the present invention and a lithium secondary battery can have improved initial efficiency, fast charging characteristics, and lifespan characteristics.

[0013] Figure 1 is a schematic diagram showing a simplified representation of an electrode in a secondary battery.

[0014] Figure 2 is a step diagram showing the theoretical electrolyte-derived film formation process.

[0015] Figure 3 is a step diagram showing the experimental electrolyte-derived film formation process.

[0016] Figure 4 is a schematic diagram for explaining an electrolyte-derived film according to one embodiment of the present invention.

[0017] [Explanation of symbols]

[0018] 1: Whole house

[0019] 2: Electrode active material

[0020] 3: Electrolyte-derived membrane

[0021] 31: First electrolyte-derived film

[0022] 32: Second electrolyte-derived membrane

[0023] Hereinafter, the present specification will be described in more detail.

[0024] In this specification, when a part is said to "include" a certain component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

[0025] In this specification, when it is said that a member is located “on” another member, this includes not only cases where the member is in contact with the other member, but also cases where another member exists between the two members.

[0026] The terms and words used in this specification should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as meanings and concepts that conform to the technical idea of ​​the present invention based on the principle that the inventor can appropriately define the concept of the term to explain his or her own invention in the best way.

[0027] In this specification, the composition of the first electrolyte and the second electrolyte being “different” may mean that the types, concentrations or weight ratios of lithium salts, solvents and / or additives contained in the first electrolyte and the second electrolyte are different.

[0028] In this specification, “p to q” means a range of “p or more and q or less.”

[0029] In this specification, "electrolyte-derived film" means a film (layer) derived from the electrolyte and formed on the surface of an electrode active material during the charge / discharge process of a battery. For example, the electrolyte-derived film may include a SEI (Solid Electrolyte Interphase) film formed on the surface of a negative electrode active material or a CEI (Cathode Electrolyte Interphase) film formed on the surface of a positive electrode active material.

[0030] In one embodiment of the present invention, the fact that the first electrolyte and the second electrolyte are different means that the types of lithium salts contained in the first electrolyte and the second electrolyte are different. For example, but not limited to, the first electrolyte may contain lithium salt A and the second electrolyte may contain lithium salt B, or the first electrolyte may contain lithium salts A and C and the second electrolyte may contain lithium salts B and C, or the first electrolyte may contain lithium salt A and the second electrolyte may contain lithium salts B and C.

[0031] In one embodiment of the present invention, the fact that the first electrolyte and the second electrolyte are different means that the concentrations of lithium salts contained in the first electrolyte and the second electrolyte are different. For example, but not limited to, when the first electrolyte and the second electrolyte each contain lithium salt A and the concentration of the lithium salt in the first electrolyte is a M, the concentration of the lithium salt in the second electrolyte may be b M, or when the first electrolyte contains lithium salt A and the second electrolyte contains lithium salt B and the concentration of the lithium salt in the first electrolyte is a M, the concentration of the lithium salt in the second electrolyte may be b M.

[0032] As used herein, the singular expression of a term includes the plural expression unless the context clearly indicates otherwise.

[0033] Hereinafter, preferred embodiments of the present invention will be described in detail. However, the embodiments of the present invention may be modified in various ways, and the scope of the present invention is not limited to the embodiments described below.

[0034] Figure 1 is a schematic diagram showing a simplified representation of an electrode in a secondary battery.

[0035] When charging and discharging a lithium secondary battery, an electrolyte-derived film (3), such as a SEI (Solid Electrolyte Interphase) film or CEI (Cathode-Electrolyte Interphase) film, formed on the surface of the electrode active material (2) acts as a tunnel for lithium ions, thereby preventing direct contact between the electrolyte and the electrode active material (2). This plays an important role in reducing side reactions that may occur during charging and discharging.

[0036] However, if the electrolyte-derived film (3) is not uniformly formed on the surface of the electrode active material (2), is formed unstably depending on the composition of the electrolyte, such as being formed with an excessive thickness or having a weak strength, a problem may arise in that the required characteristics cannot be met at various interfaces within the battery.

[0037] Referring to Fig. 1, at the interface (point a) close to the electrode active material (2), the transfer of lithium ions must be smooth so that lithium insertion and extraction can easily occur during the charging and discharging processes, and therefore, the characteristics of lithium ion transfer from the electrolyte to the active material through the electrolyte-derived film (3) are required. On the other hand, at the interface (point b) relatively far from the electrode active material (2), the characteristics of lithium ion movement through the electrolyte itself are required more importantly. However, if the electrolyte-derived film (3) is formed unevenly, the electrolyte-derived film (3) may not be formed normally at point a, or the electrolyte-derived film (3) may be formed with an excessive thickness in a local area, such that the electrolyte-derived film (3) is formed up to point b, and the required characteristics may not be satisfied at each interface. As a result, the reaction speed between each interface in the battery may be delayed or limited, and in the worst case, the reaction may stop, resulting in a problem of reduced battery performance.

[0038] Figure 2 is a step diagram showing a theoretical electrolyte-derived film (3) formation process, and Figure 3 is a step diagram showing an experimental electrolyte-derived film (3) formation process.

[0039] Figures 2(a) and 3(a) show electrodes in an electrode assembly before electrolyte injection. The electrode includes a current collector (1) and an electrode active material (2) (positive electrode active material or negative electrode active material) provided on the current collector (1). Figures 2(b) and 3(b) show electrodes immediately after electrolyte injection. Figures 2(c) and 3(c) show that an activation process is performed in the electrolyte injection state of Figure 2(b) or Figure 3(b) to form an electrolyte-derived film (3).

[0040] To solve this problem, a method was proposed in which an electrolyte-derived film (3) is formed in advance by injecting an electrolyte once into a battery case including an electrode assembly and then performing an activation process. Theoretically, it was expected that an electrolyte-derived film (3) would be formed uniformly and stably on the surface of an electrode active material (2) as shown in Fig. 2(c), but in practice, it was confirmed that it was formed unevenly as shown in Fig. 3(c), and a uniform electrolyte-derived film (3) as shown in Fig. 2(c) could not be formed.

[0041] Accordingly, the inventor of the present invention devised a method for forming a solid and uniform electrolyte-derived film (3) that satisfies the required characteristics of each interface on an electrode active material (2) by injecting two types of electrolytes that satisfy specific conditions twice and performing an activation process after each injection process.

[0042]

[0043] Method for manufacturing secondary batteries

[0044] A method for manufacturing a lithium secondary battery according to one embodiment of the present invention comprises the steps of: injecting a first electrolyte into a battery case containing an electrode assembly including a positive electrode and a negative electrode; performing a first activation process after injecting the first electrolyte; injecting a second electrolyte different from the first electrolyte into the battery case in which the first activation process has been performed; and performing a second activation process after injecting the second electrolyte, wherein the first electrolyte and the second electrolyte each independently contain a lithium salt, the lithium salt concentration of the first electrolyte is greater than the lithium salt concentration of the second electrolyte, and the difference between the lithium salt concentrations of the first electrolyte and the second electrolyte is 0.5 M to 2 M.

[0045] According to one embodiment of the present invention, the lithium salt concentration of the first electrolyte is greater than the lithium salt concentration of the second electrolyte.

[0046] When the activation process is performed after the electrolyte is injected, an electrolyte-derived film (3) (SEI film or CEI film) is formed on the surface close to the electrode active material (2). At this time, the electrolyte-derived film derived from an electrolyte having a sufficiently high lithium salt concentration has a high viscosity, so there is an advantage in that many ion transfer channels can be secured within the electrode active material (2). However, since the electrolyte-derived film (3) with such a high concentration has a low electrolyte impregnation rate into the porous electrode layer due to the characteristics of the first electrolyte having a high viscosity, it is difficult for the electrolyte-derived film (3) to be uniformly formed on the surface of the electrode active material (2). As a result, the electrolyte-derived film (3) may not be formed in some areas of the surface of the electrode active material (2) or may be formed excessively thick.

[0047] Referring to FIG. 4, a method for manufacturing a lithium secondary battery according to an embodiment of the present invention is characterized in that, after injecting and activating a first electrolyte having a high lithium salt concentration, a second electrolyte having a lower lithium salt concentration than the first electrolyte is injected, and a second activation process is performed, thereby forming a second electrolyte-derived film (32) that complements the unevenly formed first electrolyte-derived film (31), so that the electrolyte-derived film (3) can be uniformly formed on the surface of the electrode active material (2). That is, since the concentration of the second electrolyte lithium salt is lower than the lithium salt concentration of the first electrolyte, the second electrolyte-derived film (32) can be uniformly formed on the unevenly formed first electrolyte-derived film (31) on the surface of the electrode active material (2).

[0048] In one embodiment of the present invention, the difference in the concentration of the lithium salt of the first electrolyte and the second electrolyte is 0.5 M to 2 M. For example, the difference in the concentration of the first electrolyte and the second electrolyte may be 0.5 M or more or 0.7 M or more, and may be 2 M or less, 1.5 M or less, 1.2 M or less, or 1 M or less. That is, in one embodiment of the present invention, the difference in the concentration of the lithium salt of the first electrolyte and the second electrolyte may be 0.5 M to 1 M.

[0049] When the difference in the concentration of the lithium salt of the first electrolyte and the second electrolyte satisfies the above range, since the first electrolyte and the second electrolyte have a sufficient concentration difference, a second electrolyte-derived film (32) that complements the first electrolyte-derived film (31) by the low-concentration second electrolyte can be easily formed, and ultimately, the electrolyte-derived film (3) can be uniformly formed over the entire electrode active material (2). On the other hand, when the difference in the concentration of the lithium salt of the first electrolyte and the second electrolyte exceeds the above range, the concentration of the first electrolyte lithium salt may become excessively high, which may lower the ionic conductivity of the first electrolyte and prevent the first electrolyte-derived film from being formed, or the concentration of the second electrolyte lithium salt may become excessively low, which may prevent the second electrolyte-derived film from being formed normally after the second activation process.

[0050] In one embodiment of the present invention, the concentration of the lithium salt of the first electrolyte may be 0.8 M to 2 M. For example, the concentration of the lithium salt of the first electrolyte may be 1 M or more, 1.1 M or more, or 1.2 M or more, and may be 2 M or less, 1.8 M or less, 1.6 M or less, or 1.5 M or less.

[0051] When the concentration of the first electrolyte lithium salt satisfies the above range, after the first activation process, an ion channel with improved ion transport characteristics derived from the high-viscosity first electrolyte is sufficiently secured at the closest location to the active material in the electrode, thereby forming a first electrolyte-derived film that enables lithium ions to be smoothly transported at the electrode active material interface.

[0052] In one embodiment of the present invention, the concentration of the second electrolyte lithium salt may be 0.3 M to 1 M. For example, the concentration of the second electrolyte lithium salt may be 0.3 M or more, 0.4 M or more, 0.5 M or more, or 0.7 M or more, and may be 1 M or less, 0.8 M or less, 0.75 M or less, or 0.7 M or less.

[0053] When the second electrolyte contains a lithium salt in the above concentration range, since the second electrolyte has a lower viscosity than the first electrolyte, a second electrolyte-derived film that complements the first electrolyte-derived film can be uniformly formed with a thin thickness on the unevenly formed first electrolyte-derived film. On the other hand, when the concentration of the second electrolyte lithium salt exceeds the upper limit, the difference in concentration with the first electrolyte is not sufficient, making it difficult to form a second electrolyte-derived film between the unevenly formed first electrolyte-derived films, and may further aggravate the unevenness of the electrolyte-derived film. When the concentration of the second electrolyte lithium salt is less than the lower limit, the concentration of the lithium salt may be too low, making it difficult for the second electrolyte to be sufficiently formed even after the activation process.

[0054] In one embodiment of the present invention, the first electrolyte lithium salt and the second electrolyte lithium salt are each independently the same or different, and each lithium salt can be used without any particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. For example, the first electrolyte lithium salt and the second electrolyte lithium salt are each independently the same or different, and LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, LiFSI, LiTFSI, LiBF4, LiDFOB, or a combination thereof can be used. Specifically, the first electrolyte lithium salt and the second electrolyte lithium salt are each independently the same or different, and LiPF6, LiFSI, or a combination thereof may be used.

[0055] In one embodiment of the present invention, the types of the first electrolyte lithium salt and the second electrolyte lithium salt may be the same or different.

[0056] In one embodiment of the present invention, the types of the first electrolyte lithium salt and the second electrolyte lithium salt may be the same.

[0057] In one embodiment of the present invention, the types of the first electrolyte lithium salt and the second electrolyte lithium salt may be different.

[0058] In one embodiment of the present invention, the thermal decomposition temperature of the first electrolyte lithium salt may be lower than the thermal decomposition temperature of the second electrolyte lithium salt. That is, the thermal decomposition temperature of the second electrolyte lithium salt may be higher than the thermal decomposition temperature of the first electrolyte lithium salt. When a lithium salt having a high thermal decomposition temperature is used as the second electrolyte lithium salt, a second electrolyte-derived film having high thermal stability is formed on the outer side (opposite direction from the active material) of the electrolyte-derived film, thereby preventing the electrolyte-derived film from being thermally decomposed in a battery operating environment.

[0059] In one embodiment of the present invention, the anion of the first electrolyte lithium salt may be smaller than the anion of the second electrolyte lithium salt. The anion of the second electrolyte lithium salt may be larger than the anion of the lithium salt of the first electrolyte. That is, when the size of the anion of the second electrolyte lithium salt is larger than that of the first electrolyte lithium salt, the mobility of the ions of the second electrolyte is further improved, so that a second electrolyte-derived film can be easily formed.

[0060] Specifically, when a lithium salt having a large anion size is used as the second electrolyte, the mobility characteristics of the second electrolyte lithium salt can be improved by size resistance compared to when a lithium salt having a small anion size is used as the second electrolyte, so that relatively high ionic conductivity and low viscosity can be achieved even at low concentrations. For example, when LiPF6 is used as the first electrolyte lithium salt, when LiFSI is used instead of LiPF6 as the second electrolyte lithium salt, the ionic conductivity of the second electrolyte becomes relatively high, so that improved battery characteristics are exhibited.

[0061] However, in the case of a high-concentration first electrolyte, the concentration of lithium salt in the electrolyte becomes dense, the Debye length between ions in the electrolyte becomes short, and the resulting ion relaxation effect and the electrophoretic effect that appear as the viscosity increases do not significantly improve the ion conductivity due to the size resistance by changing the type of lithium salt. Therefore, when the type of lithium salt in the relatively low-concentration second electrolyte is changed, the above-described effect can be exhibited.

[0062] In one embodiment of the present invention, the first electrolyte lithium salt may be LiPF6, and the second electrolyte lithium salt may be LiFSI. When LiPF6 is used as the first electrolyte lithium salt, a first electrolyte-derived film can be stably formed on a current collector or an active material during the first electrolyte-derived film formation process. When the second electrolyte lithium salt is LiFSI, side reactions such as corrosion between the current collector and the lithium salt can be prevented, and even when the concentration of the second electrolyte lithium salt is low, the ionic conductivity is high, and an electrolyte-derived film can be evenly formed on the surface of the active material.

[0063] In one embodiment of the present invention, the viscosity of the first electrolyte may be higher than the viscosity of the second electrolyte.

[0064] In one embodiment of the present invention, the viscosity of the first electrolyte may be 1 cP to 5 cP. For example, the viscosity of the first electrolyte may be 1 cP or more, 1.5 cP or more, 2 cP or more, 2.1 cP or more, 2.5 cP or more, 2.7 cP or more, 2.8 cP or more, and 5 cP or less, 4 cP or less, 3 cP or less, or 2 cP or less.

[0065] In one embodiment of the present invention, the viscosity of the second electrolyte may be 0.5 cP to 4 cP. For example, the viscosity of the second electrolyte may be 0.5 cP or more, 0.7 cP or more, 1 cP or more, or 1.2 cP or more, and may be 4 cP or less, 3 cP or less, 2 cP or less, 1.5 cP or less, or 1.4 cP or less.

[0066] When the first electrolyte has a higher viscosity than the second electrolyte, a number of ion channels in the first electrolyte-derived film can be secured, thereby forming a robust electrolyte-derived film. When the second electrolyte has a lower viscosity than the first electrolyte, the mobility of ions is improved, so that a second electrolyte-derived film can be formed on the surface of the active material where the first electrolyte-derived film has not been formed or on the first electrolyte-derived film formed with an uneven thickness, thereby forming a thin and uniform electrolyte-derived film.

[0067] In one embodiment of the present invention, the viscosity of the electrolyte means the viscosity of the electrolyte measured at room temperature (25°C). For example, the viscosity may be measured at 25°C using an RS150 viscometer (manufacturer: McIntosh) for an electrolyte containing an organic solvent mixed with ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 20:5:75.

[0068] In one embodiment of the present invention, the ionic conductivity of the first electrolyte may be higher than the ionic conductivity of the second electrolyte. That is, the ionic conductivity of the second electrolyte may be lower than the ionic conductivity of the first electrolyte.

[0069] In one embodiment of the present invention, the ionic conductivity of the first electrolyte may be 10 mS / cm to 15 mS / cm. For example, the ionic conductivity of the first electrolyte may be 10 mS / cm or more, 11 mS / cm or more, or 12 mS / cm or more, and may be 15 mS / cm or less, 14 mS / cm or less, or 13 mS / cm or less.

[0070] In one embodiment of the present invention, the ionic conductivity of the second electrolyte may be 7 mS / cm to 13 mS / cm. For example, the ionic conductivity of the second electrolyte may be 7 mS / cm or more, 7.5 mS / cm or more, 8 mS / cm or more, 8.5 mS / cm or more, 9 mS / cm or more, or 9.5 mS / cm or more, and may be 13 mS / cm or less, 12 mS / cm or less, 11 mS / cm or less, or 10 mS / cm or less. When the ionic conductivity of the second electrolyte is within the above range, the mobility of ions in the second electrolyte is improved, so that a second electrolyte-derived film may be formed on the surface of the active material on which the first electrolyte-derived film is not formed or on the first electrolyte-derived film formed with an uneven thickness, thereby forming a thin and uniform electrolyte-derived film.

[0071] In one embodiment of the present invention, the ionic conductivity of the electrolyte means the ionic conductivity of the electrolyte measured at room temperature (25°C). For example, the ionic conductivity may be measured using a probe-type ionic conductivity measuring device (InoLab 731. Model S470, manufacturer: Mettler Torodo) for an electrolyte containing an organic solvent in which ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) are mixed in a volume ratio of 20:5:75.

[0072] In one embodiment of the present invention, the first electrolyte may further include an additive.

[0073] In one embodiment of the present invention, the first electrolyte may include an SEI film forming agent as an additive. The SEI film forming agent is a compound that facilitates the formation of an SEI film by an electrochemical oxidation or reduction decomposition reaction, and may be at least one selected from the group consisting of a cyclic carbonate compound, a halogen-substituted carbonate compound, a sultone compound, a sulfate compound, a borate compound, a nitrile compound, a benzene compound, an amine compound, a silane compound, and a lithium salt compound different from the lithium salt contained in the first electrolyte.

[0074] The above SEI film forming agent can be selected depending on the type of lithium salt or solvent of the first electrolyte. Specifically, the SEI film forming agent is vinylene carbonate (VC), vinylethylene carbonate (VEC), fluoroethylene carbonate (FEC), succinic anhydride (SA), propylphosphonic anhydride (T3P), 1,3-propane sultone (PS), 1,4-butane sultone, ethyl sultone, 1,3-propene sultone (PRS), 1,4-butene sultone, 1-methyl-1,3-propene sultone, ethylene sulfate, trimethylene sulfate (TMS), methyl trimethylene sulfate (MTMS), tetraphenylborate, lithium oxalyldifluoroborate, succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, It may be at least one selected from the group consisting of caprylonitrile, heptanenitrile, cyclopentane carbonitrile, cyclohexane carbonitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, 4-fluoroacetonitrile, fluorobenzene, triethanolamine, ethylenediamine, tetravinylsilane, LiN(SO2F)2 (lithium bis(trifluoromethane sulfonyl)imide, LiTFSI), LiPO2F2, LiODFB, LiBOB, and LiBF4.

[0075] Alternatively, the SEI film forming agent may be vinylene carbonate (VC), vinylethylene carbonate (VEC), fluoroethylene carbonate (FEC), 1,3-propane sultone (PS), succinic anhydride (SA), propylphosphonic anhydride (T3P), 1,3-propane sultone (PS), or a combination thereof.

[0076] The above first electrolyte may contain the SEI film-forming agent in an amount of 3.0 wt% or less, 2.0 wt% or less, 1.5 wt% or less, 1.2 wt% or less, or 1.0 wt% or less. When the content of the additive satisfies the above range, the effects of improving the low-temperature output, high-temperature storage characteristics, and high-temperature lifespan characteristics of the battery are exhibited, while the amount of the SEI film-forming agent is not excessive and sufficiently decomposes at high temperatures, so that the SEI film-forming agent does not exist as an unreacted substance or precipitate at room temperature, and thus, side reactions in the electrolyte can be prevented from occurring during battery charging and discharging.

[0077] In addition to the components of the first electrolyte, the first electrolyte may further include one or more additives, such as, for example, difluoroethylene carbonate and other haloalkylene carbonate compounds, pyridine, triethylphosphite, triethanolamine, cyclic ethers, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, lithium salts for corrosion prevention, or HF scavengers, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery.

[0078] In one embodiment of the present invention, the second electrolyte may further include an additive.

[0079] In one embodiment of the present invention, the second electrolyte may include an HF scavenger as an additive.

[0080] The above HF scavenger is added to remove HF generated by the reaction between incompletely dissociated lithium salt and H2O remaining inside the battery, and is not particularly limited as long as it is a substance capable of removing HF without participating in the electrochemical reaction of the battery. Specifically, it may be a substance containing a functional group capable of removing HF, and may be a substance containing a Si-O bond, a silane compound, or a silazane compound.

[0081] According to one embodiment of the present invention, the HF scavenger may be a silane compound.

[0082] According to one embodiment of the present invention, the HF scavenger may be at least one of trimethoxysilane (TMS), triethoxysilane (TES), hexamethyldisilazane (HMDS), or bis(trimethylsilyl)amine (HMDSA).

[0083] In this specification, the term “removal” refers to a function such as elimination, adsorption or capture of a by-product (HF) by an HF scavenger.

[0084] The second electrolyte may contain 2 wt% or less of the HF scavenger, preferably 1.9 wt% or less or 1.8 wt% or less. If the content of the HF scavenger is less than 0.1 wt%, the scavenger may have a minimal effect in removing by-products, and if the content of the HF scavenger exceeds 10 wt%, the HF scavenger material itself may act as a by-product in the battery, thereby deteriorating the electrochemical performance of the battery.

[0085] When the content of the above HF scavenger satisfies the above range, by-products generated after the first activation process can be effectively removed, and thus the battery characteristics of the final product can be improved.

[0086] In addition to the components of the second electrolyte, the second electrolyte may further include one or more additives, such as, for example, a haloalkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethylphosphite, triethanolamine, a cyclic ether, ethylene diamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, aluminum trichloride, lithium salts for corrosion prevention, or SEI forming agents, for the purpose of improving the life characteristics of the battery, suppressing battery capacity decrease, and improving the discharge capacity of the battery.

[0087] In one embodiment of the present invention, the first electrolyte and the second electrolyte each independently contain the same or different solvents. Any solvent commonly used in the art may be used without limitation.

[0088] For example, the solvent may be a non-aqueous organic solvent. Specifically, the solvent may include a cyclic carbonate solvent, a linear carbonate solvent, an ester solvent, or a combination thereof.

[0089] The solvent may include a mixture comprising a cyclic carbonate solvent and a linear carbonate solvent, a mixture comprising a cyclic carbonate solvent and an ester solvent, or a cyclic carbonate solvent, a linear carbonate solvent, and an ester solvent.

[0090] The cyclic carbonate solvent may be included in an amount of 10 to 45 parts by weight based on 100 parts by weight of the total solvent. For example, the cyclic carbonate solvent may be included in an amount of 10 parts by weight or more, 15 parts by weight or more, 20 parts by weight or more, or 30 parts by weight or more, and may be included in an amount of 45 parts by weight or less, 40 parts by weight or less, 35 parts by weight or less, or 30 parts by weight or less based on 100 parts by weight of the total solvent. When the cyclic carbonate solvent is included within the above range, the electrolyte can smoothly dissociate the lithium salt, thereby ensuring sufficient ion conductivity and cation transport capacity.

[0091] The above cyclic carbonate solvent is a high viscosity organic solvent, and when it is included in the solvent, the dielectric constant of the cyclic carbonate solvent is high, so that the lithium salt can be smoothly dissociated in the electrolyte, thereby improving ion conductivity and cation transport capacity.

[0092] In one embodiment of the present invention, the cyclic carbonate solvent may be at least one selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and vinylene carbonate.

[0093] The linear carbonate-based solvent may be included in an amount of 55 to 90 parts by weight based on 100 parts by weight of the total solvent. For example, the linear carbonate-based solvent may be included in an amount of 55 parts by weight or more, 60 parts by weight or more, 65 parts by weight or more, or 70 parts by weight or more, based on 100 parts by weight of the total solvent, and may be included in an amount of 90 parts by weight or less, 80 parts by weight or less, 70 parts by weight or less, or 60 parts by weight or less. If the linear carbonate-based solvent is not included within the above range based on 100 parts by weight of the total solvent, the viscosity of the electrolyte may be excessively high, and thus the impregnation property of the electrolyte may not be sufficiently secured.

[0094] Therefore, the electrolyte can provide an electrolyte having excellent electrolyte impregnation properties while sufficiently dissociating lithium salts and having an excellent level of ion conductivity by mixing a cyclic carbonate solvent having a high dielectric constant and high viscosity and a linear carbonate solvent having a relatively low dielectric constant and relatively low viscosity in an appropriate ratio.

[0095] The linear carbonate solvent may be at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methylpropyl carbonate, and ethylpropyl carbonate.

[0096] The ester solvent may be included in an amount of 1 to 70 parts by weight based on 100 parts by weight of the total solvent. For example, the ester solvent may be included in an amount of 1 part by weight or more, 5 parts by weight or more, 10 parts by weight or more, or 20 parts by weight or more, based on 100 parts by weight of the total solvent, and may be included in an amount of 70 parts by weight or less, 60 parts by weight or less, 50 parts by weight or less, or 40 parts by weight or less. When the ester solvent is included in an amount within the above range based on 100 parts by weight of the total solvent, the impregnation property of the electrolyte may be improved and the low-temperature characteristics may be enhanced.

[0097] The above ester solvent is an organic solvent having low density, low viscosity and low melting point, and when included in the solvent, it can prevent the viscosity of the electrolyte from becoming excessively high and improve low-temperature characteristics.

[0098] The above ester solvent may be at least one selected from the group consisting of methyl acetate, ethyl acetate (EA), dimethyl acetate, methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), decanolide, valerolactone, mevalonolactone, and caprolactone.

[0099] The ester solvent may be a linear ester solvent. Specifically, the ester solvent may be at least one selected from the group consisting of methyl acetate, ethyl acetate (EA), dimethyl acetate, methyl propionate (MP), ethyl propionate (EP), and propyl propionate (PP).

[0100] The method for manufacturing a lithium secondary battery according to the present invention comprises the steps of manufacturing an electrode assembly including a positive electrode and a negative electrode and housing the electrode assembly in a battery case. The battery case housing the electrode assembly may be classified into square, coin-shaped, cylindrical, pouch-shaped, etc., depending on its shape. The method for housing the electrode assembly in the case varies slightly depending on the shape.

[0101] A method for manufacturing a lithium secondary battery according to one embodiment of the present invention includes a step of injecting a first electrolyte into a battery case. The step of injecting the first electrolyte is a step of injecting the first electrolyte into a battery case in which an electrode assembly including a positive electrode and a negative electrode is housed, and the method of injecting the electrolyte can be performed by various methods known in the art.

[0102] In one embodiment of the present invention, the first activation process includes a step of charging a battery case into which a first electrolyte is injected.

[0103] By performing the above first activation process, a first electrolyte-derived film can be formed on various interfaces within the electrode, for example, on the surface of the active material.

[0104] In one embodiment of the present invention, the first activation process includes a step of charging a battery case into which a first electrolyte is injected.

[0105] In one embodiment of the present invention, the first activation process includes the steps of aging, degassing, charging, and discharging a battery case containing a first electrolyte. The aging and degassing methods are not limited to those known in the art.

[0106] According to one embodiment of the present invention, the first activation process includes a step of sealing a battery case into which a first electrolyte is injected; and a step of charging the sealed battery case.

[0107] The first activation process may be a process of sealing an electrode assembly into which a first electrolyte is injected and then charging under constant current conditions of 0.01 C to 5 C at a charging voltage range of 1.0 V to 4.5 V. Specifically, the charging voltage may be 1.0 V or more or 1.2 V or more, and may be 4.5 V or less, 4.2 V or less, or 4.0 V or less. The constant current conditions may be 0.5 C or more, 0.2 C or more, or 0.1 C or more, and may be 1 C or less, 2 C or less, or 3 C or less.

[0108] In one embodiment of the present invention, the step of injecting the second electrolyte is a step of injecting the second electrolyte into the battery case in which the first electrolyte injection and first activation processes have been performed. That is, since it is a step of injecting the second electrolyte while the first electrolyte is present inside the battery case, mixing of the first electrolyte and the second electrolyte may occur inside the battery case in which the second electrolyte has been injected.

[0109] In one embodiment of the present invention, the second activation process includes a step of charging a battery case into which a second electrolyte is injected.

[0110] By performing the above second activation process, a second electrolyte-derived film that complements the first electrolyte-derived film can be formed at various interfaces within the electrode, such as the first electrolyte-derived film or the surface of the active material.

[0111] In one embodiment of the present invention, the second activation process includes a step of charging a battery case into which a second electrolyte is injected.

[0112] The second activation process may be the same as or different from the first activation process.

[0113] In one embodiment of the present invention, the second activation process includes a step of charging and discharging a battery case in which a second electrolyte is injected.

[0114] In one embodiment of the present invention, the first activation process includes the steps of aging, degassing, charging, and discharging a battery case into which a second electrolyte is injected. The aging and degassing methods are not limited to any method known in the art.

[0115] According to one embodiment of the present invention, the second activation process includes a step of sealing a battery case into which a second electrolyte is injected; and a step of charging the sealed battery case.

[0116] The second activation process may be performed by sealing the electrode assembly into which the second electrolyte is injected and then charging under constant current conditions of 0.01 C to 5 C under conditions of a charging voltage range of 1.0 V to 4.5 V. Specifically, the charging voltage may be 1.0 V or more or 1.2 V or more, and may be 4.5 V or less, 4.2 V or less, or 4.0 V or less. The constant current conditions may be 0.5 C or more, 0.2 C or more, or 0.1 C or more, and may be 1 C or less, 2 C or less, or 3 C or less.

[0117] According to one embodiment of the present invention, a method for manufacturing a lithium secondary battery comprises injecting a first electrolyte into an electrode assembly and then performing a first activation step, thereby stably forming a corrosion-preventive film (electrolyte-derived film) on the surface of an active material. With the corrosion-preventive film stably formed, injecting a second electrolyte and then performing a second activation step can simultaneously improve the output characteristics and lifespan characteristics of the lithium secondary battery.

[0118] That is, the method for manufacturing a lithium secondary battery according to one embodiment of the present invention is characterized in that it forms a solid and uniform electrolyte-derived film by sequentially injecting two different types of electrolytes and performing an activation process for each, thereby supplementing a portion where an electrolyte-derived film is formed unevenly according to a local electrolyte concentration gradient.

[0119] Accordingly, it is possible to improve the phenomenon of stopping due to decreased reactivity or overload of reactivity that frequently occurs when using one type of electrolyte, and to provide a smooth source of film formation that is destroyed or created as the charge / discharge cycle progresses, as well as to improve the diffusion and conductivity of ions in the electrolyte.

[0120]

[0121] secondary batteries

[0122] According to one embodiment of the present invention, a lithium secondary battery manufactured by the above-described method is provided.

[0123] A lithium secondary battery according to one embodiment of the present invention includes a positive electrode and a negative electrode.

[0124] In one embodiment of the present invention, the positive electrode may include a positive electrode current collector and a positive electrode active material laminated on the positive electrode current collector.

[0125] In one embodiment of the present invention, the positive electrode includes a current collector layer and a positive electrode active material layer provided on the current collector layer, and the positive electrode active material layer includes a positive electrode active material, a first electrolyte-derived film provided on the positive electrode active material, and a second electrolyte-derived film provided on the positive electrode active material or the first electrolyte-derived film.

[0126] The above first electrolyte-derived film and the second electrolyte-derived film are films derived from the first electrolyte and the second electrolyte, respectively, and the shape, composition, and characteristics of the first electrolyte-derived film and the second electrolyte-derived film are different depending on the composition of the first electrolyte and the second electrolyte. The first electrolyte-derived film and the second electrolyte-derived film can be distinguished through analysis of the electrolyte-derived film using residual electrolyte analysis, NMR, or XPS depth profile.

[0127] The above first electrolyte-derived film is formed in the step of performing the first activation process in the method for manufacturing a lithium secondary battery according to one embodiment of the present invention. That is, the first electrolyte-derived film is an electrolyte-derived film derived from the first electrolyte according to one embodiment of the present invention.

[0128] The above second electrolyte-derived film is formed in the step of performing the second activation process in the method for manufacturing a lithium secondary battery according to one embodiment of the present invention. That is, the second electrolyte-derived film is an electrolyte-derived film derived from the second electrolyte according to one embodiment of the present invention.

[0129] In one embodiment of the present invention, the first electrolyte-derived film and the second electrolyte-derived film are CEI films.

[0130] The above-described positive electrode collector layer includes a positive electrode collector, and the positive electrode collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode collector may typically have a thickness of 1 to 500 μm, and fine unevenness may be formed on the surface of the positive electrode collector to increase the adhesion of the positive electrode active material. For example, the positive electrode collector may be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc.

[0131] The positive electrode active material may include a lithium composite transition metal compound including nickel (Ni), cobalt (Co), and manganese (Mn). In addition, the positive electrode active material may include nickel, cobalt, and manganese, and may further include aluminum, but is not limited thereto.

[0132] In addition, the positive electrode active material may include 80 mol% or more and less than 100 mol% of nickel among metals other than lithium, and the lithium composite transition metal compound including 80 mol% or more and less than 100 mol% of nickel among metals other than lithium may include one or a mixture of two or more types represented by the following chemical formula 1.

[0133] [Chemical Formula 1]

[0134] Li a Ni 1-b-c-d Co b Mn c Q d O 2+δ

[0135] In the above formula, Q is at least one element selected from the group consisting of Na, K, Mg, Ca, Sr, Ni, Co, Ti, Al, Si, Sn, Mn, Cr, Fe, V, and Zr, and 1≤a≤1.5, 0 <b≤0.5, 0<c≤0.5, 0≤d≤0.1, 0 <b+c+d≤20, -0.1≤δ≤1.0이다.

[0136] According to one embodiment of the present invention, the positive electrode according to the above-described embodiment further includes a positive electrode binder and a conductive material.

[0137] The above-described positive electrode binder can serve to improve adhesion between positive electrode active material particles and adhesion between positive electrode active material particles and positive electrode current collector. Those known in the art can be used as the positive electrode binder, and non-limiting examples thereof include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated-EPDM, styrene butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof.

[0138] The conductive material included in the above-described positive electrode active material layer is used to provide conductivity to the electrode, and can be used without special restrictions as long as it does not cause chemical changes within the battery and has electronic conductivity. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, and carbon fiber; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskey such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like. One of these may be used alone or a mixture of two or more may be used.

[0139] In one embodiment of the present invention, the negative electrode may include a negative electrode current collector and a negative electrode active material laminated on the negative electrode current collector.

[0140] In one embodiment of the present invention, the negative electrode includes a current collector layer and a negative electrode active material layer provided on the current collector layer, and the negative electrode active material layer includes a negative electrode active material, a first electrolyte-derived film provided on the negative electrode active material, and a second electrolyte-derived film provided on the negative electrode active material or the first electrolyte-derived film.

[0141] The above first electrolyte-derived film and the second electrolyte-derived film are films derived from the first electrolyte and the second electrolyte, respectively, and the shape, composition, and characteristics of the first electrolyte-derived film and the second electrolyte-derived film are different depending on the composition of the first electrolyte and the second electrolyte. The first electrolyte-derived film and the second electrolyte-derived film can be distinguished through analysis of the electrolyte-derived film using residual electrolyte analysis, NMR, or XPS depth profile.

[0142] The above first electrolyte-derived film is formed in the step of performing the first activation process in the method for manufacturing a lithium secondary battery according to one embodiment of the present invention. That is, the first electrolyte-derived film is an electrolyte-derived film derived from the first electrolyte according to one embodiment of the present invention.

[0143] The above second electrolyte-derived film is formed in the step of performing the second activation process in the method for manufacturing a lithium secondary battery according to one embodiment of the present invention. That is, the second electrolyte-derived film is an electrolyte-derived film derived from the second electrolyte according to one embodiment of the present invention.

[0144] In one embodiment of the present invention, the first electrolyte-derived film and the second electrolyte-derived film are SEI films.

[0145] The above-described negative electrode collector layer includes a negative electrode collector, and the negative electrode collector is not particularly limited as long as it has conductivity and does not cause a chemical change in the battery. For example, the current collector may be made of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. Specifically, a transition metal that adsorbs carbon well, such as copper or nickel, may be used as the current collector. The thickness of the current collector may be 1 μm to 500 μm, but the thickness of the current collector is not limited thereto.

[0146] In one embodiment of the present invention, the negative electrode active material is a carbon-based active material or a silicon-based active material.

[0147] The above carbon-based active material may be graphite. The graphite may be natural graphite or artificial graphite, or may be a mixture of natural graphite and artificial graphite. In addition, when the graphite is a mixture of natural graphite and artificial graphite, the weight ratio of the natural graphite to the artificial graphite may be 50:50 to 90:10, and specifically 60:40 to 80:20 or 65:35 to 75:25.

[0148] In one embodiment of the present invention, the average particle diameter (D) of the graphite 50 ) may be 10 ㎛ to 20 ㎛. Specifically, it may be 15 ㎛ to 20 ㎛. When the average particle diameter of graphite satisfies the above range, the influence of particle agglomeration is reduced, and the slurry dispersibility can be improved.

[0149] In one embodiment of the present invention, the silicon-based active material is SiOx (x=0), SiOx (0 <x<2) 또는 실리콘 카본 복합체 일 수 있다.

[0150] The silicon-carbon composite may be a Si / C-based active material. The silicon-carbon composite may be composed of Si and C that are not bonded to each other, but may also include additional components as needed. For example, the silicon-carbon composite may or may not include silicon carbide, denoted as SiC. When the silicon-carbon composite includes silicon carbide, the content thereof is 3 wt% or less. The silicon-carbon composite may exist in a crystalline, amorphous, or mixed state thereof. In one example, C in the silicon-carbon composite may exist in an amorphous state.

[0151] The above silicon-carbon composite may be a composite of silicon and carbon, and may form a structure in which a core composed of silicon and carbon is surrounded by graphite, graphene, or amorphous carbon. The silicon in the silicon-carbon composite may be nano silicon.

[0152] The above silicon carbon composite may be a physical or chemical composite of the carbon and silicon materials, and is not limited to a composition in which the carbon and silicon materials form a composite.

[0153] In one embodiment of the present invention, in the lithium secondary battery according to the above-described embodiment, the negative electrode active material layer may further include a negative electrode binder in addition to the negative electrode active material.

[0154] The above negative electrode binder can play a role in improving the adhesion between negative electrode active material particles and the adhesive strength between the negative electrode active material particles and the negative electrode current collector. The above-mentioned negative electrode binder may be one known in the art, and non-limiting examples thereof include at least one selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluoroelastomer, polyacrylic acid, and a material in which hydrogens of these are substituted with Li, Na, Ca, etc., and may also include various copolymers thereof.

[0155] The above-described negative electrode active material layer may not include a conductive material, but may further include a conductive material as needed. The conductive material included in the negative electrode active material layer is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and examples thereof include graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, paneth black, lamp black, thermal black; conductive fibers such as carbon fiber or metal fiber; conductive tubes such as carbon nanotubes; metal powders such as fluorocarbon, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0156] In one embodiment of the present invention, the positive electrode further includes a positive electrode active material layer including the positive electrode active material, and the negative electrode further includes a negative electrode active material layer including the negative electrode active material, and the thicknesses of the positive electrode and negative electrode active material layers are each 10 ㎛ to 500 ㎛. The thickness of the positive electrode active material layer may be 90% to 110%, for example, 95% to 105%, of the thickness of the negative electrode active material layer, and these thicknesses may be the same. Specifically, the thicknesses of the positive electrode and negative electrode active material layers may be 15 ㎛ to 400 ㎛, 20 ㎛ to 300 ㎛, 25 ㎛ to 200 ㎛, or 30 ㎛ to 100 ㎛, respectively.

[0157] In one embodiment of the present invention, the electrode assembly includes a positive electrode and a negative electrode, and may further include a separator.

[0158] The separator above separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in secondary batteries can be used without any particular restrictions, and in particular, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture retention capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof, may be used. In addition, a conventional porous non-woven fabric, for example, a non-woven fabric made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc. may be used. In addition, a coated separator containing a ceramic component or a polymer material to secure heat resistance or mechanical strength may be used, and may optionally be used in a single-layer or multi-layer structure.

[0159] In one embodiment of the present invention, the electrode assembly is a power generation element capable of charging and discharging, and includes a positive electrode and a negative electrode. The electrode assembly is not particularly limited as long as it has a structure including the positive electrode and the negative electrode, and the electrode assembly can be manufactured by various methods known in the art.

[0160] Hereinafter, preferred embodiments are presented to help understand the present invention, but the above embodiments are only illustrative of the present disclosure, 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 disclosure, and it is natural that such changes and modifications fall within the scope of the appended patent claims.

[0161]

[0162] <Manufacturing Example>

[0163] Example 1

[0164] 1) Manufacturing of electrode assembly

[0165] LiNi as a cathode active material 0.92 Co0.06 Mn 0.02 A positive electrode active material layer composition was prepared with O2 (average particle size (D50): 15 μm), carbon black (product name: Super C65, manufactured by Timcal) as a conductive agent, and polyvinylidene fluoride (PVdF) as a binder at a weight ratio of 97:1.5:1.5. The positive electrode active material layer composition was added to N-methyl-2-pyrrolidone (NMP) as a solvent for forming a positive electrode slurry to prepare a positive electrode slurry with a solid content of 78 wt%. The positive electrode slurry was applied to both sides of an aluminum current collector (thickness: 12 μm) as a positive electrode collector at a density of 537 mg / 25 cm. 2 The positive electrode was manufactured by coating with a loading amount, rolling (roll pressing), and drying in a vacuum oven at 130°C for 10 hours to form a 65 μm thick positive electrode active material layer (porosity 26%).

[0166] SiO as a negative electrode active material x (x=0) (average particle diameter (D50): 8㎛), single-walled carbon nanotubes (SWCNTs) as a conductive agent and polyacrylamide (PAM) as a binder were prepared in a weight ratio of 89:1:19 to prepare a negative electrode active material layer composition. The negative electrode active material layer composition was added to distilled water as a solvent for forming a negative electrode slurry to prepare a negative electrode slurry having a solid content of 25 wt%. The negative electrode slurry was applied to both sides of a copper current collector (thickness: 8㎛) as a negative electrode collector at a density of 85 mg / 25 cm. 2 The negative electrode was manufactured by coating with a loading amount, rolling (roll pressing), and drying in a vacuum oven at 130°C for 10 hours to form a 33 μm thick negative electrode active material layer (porosity 55%).

[0167] An electrode assembly was prepared by interposing a polyethylene (PE) separator between the positive and negative electrodes.

[0168] 2) Preparation of electrolyte

[0169] Preparation of the first electrolyte

[0170] A first electrolyte was prepared by adding 1.5 wt% of vinylene carbonate (VC) as an SEI film forming agent based on the total weight of the electrolyte to an organic solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) mixed in a volume ratio of 20:5:75, and adding 1.2 M of LiPF6 as a lithium salt.

[0171] Preparation of the second electrolyte

[0172] A second electrolyte was prepared by adding 1.8 wt% of trimethoxysilane (TMS) as an HF scavenger based on the total weight of the electrolyte to an organic solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 20:5:75, and adding 0.5 M of LiFSI as a lithium salt.

[0173] 3) Manufacturing of secondary batteries

[0174] The electrode assembly prepared by the above-described method was placed in a battery case, and 70 volume% of the first electrolyte was injected based on 100 volume% of the total electrolyte injection amount. The battery case into which the first electrolyte was injected was left at 25°C for 40 hours, and then charged under constant current conditions of 1 C to 4.2 V to perform the first activation process.

[0175] A secondary battery was manufactured by injecting 30% by volume of the second electrolyte solution based on 100% by volume of the total electrolyte solution into a battery case in which the first activation process was performed, and then charging under constant current conditions of 1.0C up to 4.2 V to perform the second activation process.

[0176]

[0177] Examples 2 to 4

[0178] In the step 2) of preparing the electrolyte of Example 1, a secondary battery was manufactured in the same manner as in Example 1, except that the first electrolyte and the second electrolyte had the compositions described in Table 1 below.

[0179]

[0180] Comparative Example 1

[0181] In the step of preparing the electrolyte in Example 1, 2), a secondary battery was prepared in the same manner as in Example 1, except that the electrolyte was prepared by adding 1.5 wt% of vinylene carbonate (VC) as an SEI film forming agent based on the total weight of the electrolyte to an organic solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 20:5:75, and adding 1.2 M of LiPF6 as a lithium salt.

[0182]

[0183] Comparative Examples 2 to 6

[0184] In the step 2) of preparing the electrolyte of Example 1, a secondary battery was manufactured in the same manner as in Example 1, except that the first electrolyte and the second electrolyte had the compositions described in Table 1 below.

[0185]

[0186] First electrolyte lithium salt (M)Second electrolyte lithium salt (M)Lithium salt concentration difference (M)Example 1LiPF61.2MLiFSI 0.5M0.7Example 2LiPF61.5MLiPF60.5M1Example 3LiPF61.2MLiPF60.5M0.7Example 4LiPF61.2MLiPF60.7M0.5Comparative Example 1LiPF61.2M--Comparative Example 2LiPF61 MLiFSI 1 M0 Comparative Example 3LiPF61 MLiPF61 M0 Comparative Example 4LiPF61.2MLiPF60.8M0.4 Comparative Example 5LiPF60.5MLiPF60.8M0.3 Comparative Example 6LiPF60.5MLiPF61.2M0.7

[0187]

[0188] <Experimental Example>

[0189] The following items were evaluated for Examples 1 to 4 and Comparative Examples 1 to 6 manufactured above.

[0190]

[0191] Experimental Example 1: Evaluation of discharge capacity, initial efficiency, and lifespan (capacity retention) characteristics.

[0192] Charge and discharge were performed on the secondary batteries manufactured in the examples and comparative examples, and the discharge capacity, initial efficiency, and capacity retention rate were evaluated, which are listed in Table 2 or 3 below.

[0193] The 1st and 2nd cycles were charged and discharged at 0.1C, and from the 3rd to the 49th cycles, the charging and discharging was performed at 0.5C. The 50th cycle was terminated in a charged state (with lithium in the negative electrode).

[0194] Charging conditions: CC (constant current) / CV (constant voltage) (5mV / 0.005C current cut-off)

[0195] Discharge conditions: CC (constant current) condition 1.5 V

[0196] Based on the results of a single charge / discharge cycle, the discharge capacity (mAh / g) and initial efficiency (%) were derived. Specifically, the initial efficiency (%) was derived using the following calculation.

[0197] Initial efficiency (%) = (1-time discharge capacity / 1-time charge capacity) Х100

[0198] The capacity retention rate was derived by the following calculations.

[0199] Capacity retention rate (%) = (49 discharge capacity / 1 discharge capacity) Х100

[0200]

[0201] Experimental Example 2: Evaluation of Li plating time point

[0202] The secondary batteries manufactured in the examples and comparative examples were subjected to charging and discharging to evaluate the Li plating time, which is described in Table 2 or 3 below.

[0203] The 1st and 2nd cycles were charged / discharged at 0.1C, and from the 3rd cycle onwards, the cell resistance was measured while charging / discharging at a rate of 3C.

[0204] Charging conditions: CC (constant current) / CV (constant voltage) (5mV / 0.005C current cut-off)

[0205] Discharge conditions: CC (constant current) condition 1.5 V

[0206] The SOC (State of Charge) at which the cell resistance rapidly decreases and the current value changes rapidly is calculated as the point at which lithium plating occurs.

[0207]

[0208] First electrolyte lithium salt (M)Second electrolyte lithium salt (M)Lithium salt concentration difference (M)Discharge capacity (mAh / g)Initial efficiency (%)Capacity retention rate (%)Li plating point (SOC (%))Example 1LiPF61.2MLiFSI 0.5M0.7243.791.397.645.2Example 2LiPF61.5MLiPF60.5M1243.991.497.745.6Example 3LiPF61.2MLiPF60.5M0.7242.491.096.944.8Example 4LiPF61.2MLiPF60.7M0.5242.191.096.843.3Comparative Example 1LiPF61.2M--238.589.994.639.0Comparative Example 2LiPF61 MLiFSI 1 M0 2 4 1.9 9 0.8 9 6.3 4 3.0 Comparative Example 3 LiPF61 MLiPF61 M0 2 4 0.2 9 0.7 9 5.4 4 1.8 Comparative Example 4 LiPF61.2 MLiPF60.8 M0.4 2 4 0.7 9 0.8 9 5.5 4 2.5 Comparative Example 5 LiPF60.5 MLiPF60.8 M0.3 2 3 9.5 9 0.1 9 5.3 4 1.2

[0209] According to Table 2 above, it was confirmed that Examples 1 to 4 according to the embodiment of the present invention exhibited superior discharge capacity, initial efficiency, capacity retention rate, and Li plating time compared to Comparative Examples 1 to 5. On the other hand, in the case of Comparative Examples 1 to 5, where the difference in lithium salt concentration between the first and second electrolytes is not within the scope of the present invention, it was confirmed that an electrolyte-derived film was not stably formed on the electrode surface, resulting in inferior effects. In particular, in the case of Comparative Example 1, since the electrolyte was injected and activated once, degassing was insufficient during the battery manufacturing process, resulting in the most inferior battery characteristics compared to Examples 1 to 4 and Comparative Examples 2 to 5.

[0210] For Examples 1, 3 and Comparative Example 6, in which the difference in lithium salt concentration between the first and second electrolytes was the same as 0.7 M, the ionic conductivity and viscosity of each electrolyte were additionally measured in the first and second electrolytes, and these results are shown together with the experimental results in Table 3.

[0211] Ionic conductivity and viscosity were measured at 25°C for each electrolyte using a probe-type ionic conductivity measuring device (InoLab 731. Model S470, manufacturer: Mettler Torodo), and viscosity was measured at 25°C using an RS150 viscometer (manufacturer: McIntosh).

[0212]

[0213] Example 1 Example 3 Comparative Example 6 First electrolyte Lithium salt concentration (M) LiPF 6 1.2 MLiPF 6 1.2 MLiPF 6 0.5 M Lithium salt thermal decomposition temperature (℃) 80 80 200 Ionic conductivity (mS / cm) 12.8 12.8 9.55 Viscosity (cP) 2.8 2.8 2 1.34 Second electrolyte Lithium salt concentration (M) LiFSI 0.5MLiPF60.5MLiPF61.2M Lithium salt thermal decomposition temperature (℃)2008080Ionic conductivity (mS / cm)9.558.4712.8Viscosity (cP)1.341.412.82Lithium salt concentration difference (M)0.70.70.7Discharge capacity (mAh / g)243.7242.4239.6Initial efficiency (%)91.391.090.4Capacity retention (%)97.696.995.3Li plating point (SOC(%))45.244.841.6

[0214] According to Table 3 above, when comparing Examples 1, 3 and Comparative Example 6, it was confirmed that Examples 1 and 3 exhibited superior discharge capacity, initial efficiency, capacity retention rate and Li plating time compared to Comparative Example 6. This is understood to be because the lithium salt concentration of the first electrolyte of Comparative Example 6 is lower than the lithium salt concentration of the second electrolyte, so that the first electrolyte-derived film that is primarily formed on the electrode surface is not formed stably. In addition, it can be confirmed that Example 1 exhibits superior battery characteristics compared to Example 3. This is understood to be because even if the lithium salt concentrations of the second electrolytes of Examples 1 and 3 are the same, the anion size of the lithium salt included in the second electrolyte of Example 1 is larger than the anion size of the lithium salt included in the second electrolyte of Example 3, so that even when the lithium salt of the second electrolyte exhibits the same concentration, the second electrolyte exhibits higher ionic conductivity and lower viscosity.

[0215] Although the present invention has been described with reference to embodiments thereof, those skilled in the art will be able to make various applications and modifications within the scope of the present invention based on the above contents.

Claims

1. A step of injecting a first electrolyte into a battery case containing an electrode assembly including a positive electrode and a negative electrode; A step of performing a first activation process after injecting the first electrolyte; A step of injecting a second electrolyte different from the first electrolyte into the inside of the battery case in which the first activation process has been performed; and It includes a step of performing a second activation process after injecting the second electrolyte, The first electrolyte and the second electrolyte each independently contain a lithium salt, The above first electrolyte lithium salt concentration is greater than the above second electrolyte lithium salt concentration, A method for manufacturing a lithium secondary battery, wherein the difference in lithium salt concentration between the first electrolyte and the second electrolyte is 0.5 M to 2 M.

2. In paragraph 1, A method for manufacturing a lithium secondary battery, wherein the concentration of the first electrolyte lithium salt is 0.8 M to 2 M.

3. In paragraph 1, A method for manufacturing a lithium secondary battery, wherein the concentration of the second electrolyte lithium salt is 0.3 M to 1 M.

4. In paragraph 1, A method for manufacturing a lithium secondary battery, wherein the types of the first electrolyte lithium salt and the second electrolyte lithium salt are the same.

5. In paragraph 1, A method for manufacturing a lithium secondary battery, wherein the types of the first electrolyte lithium salt and the second electrolyte lithium salt are different.

6. In paragraph 5, A method for manufacturing a lithium secondary battery, wherein the thermal decomposition temperature of the first electrolyte lithium salt is lower than the thermal decomposition temperature of the second electrolyte lithium salt.

7. In paragraph 1, A method for manufacturing a lithium secondary battery, wherein the viscosity of the first electrolyte is higher than the viscosity of the second electrolyte.

8. In paragraph 1, A method for manufacturing a lithium secondary battery, wherein the ionic conductivity of the first electrolyte is higher than the ionic conductivity of the second electrolyte.

9. In paragraph 1, A method for manufacturing a lithium secondary battery, wherein the first electrolyte further includes a SEI (Solid Electrolyte Interphase) film forming agent.

10. In paragraph 1, A method for manufacturing a lithium secondary battery, wherein the second electrolyte further includes an HF scavenger.

11. In paragraph 10, A method for manufacturing a lithium secondary battery, wherein the above HF scavenger is a silane compound.

12. A lithium secondary battery manufactured by the method for manufacturing a lithium secondary battery according to any one of claims 1 to 11.

13. In claim 12, The above lithium secondary battery includes a positive electrode and a negative electrode, The above positive electrode includes a current collector layer and a positive electrode active material layer provided on the current collector layer, The above positive electrode active material layer is, positive electrode active material, A first electrolyte-derived film provided on the positive electrode active material and A lithium secondary battery comprising a second electrolyte-derived film provided on the positive electrode active material or the first electrolyte-derived film.

14. In claim 12, The above lithium secondary battery includes a positive electrode and a negative electrode, The above negative electrode includes a current collector layer and a negative electrode active material layer provided on the current collector layer, The above negative active material layer is, negative active material, A first electrolyte-derived film provided on the above negative active material and A lithium secondary battery comprising a second electrolyte-derived film provided on the negative active material or the first electrolyte-derived film.

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