Electrolyte for lithium secondary battery and lithium secondary battery comprising electrolyte

Abstract

The present disclosure provides an electrolyte for a lithium secondary battery and a lithium secondary battery comprising the electrolyte. The lithium secondary battery according to the present disclosure comprises a positive electrode for a lithium secondary battery, a negative electrode including a negative electrode current collector, a separator interposed between the positive electrode and the negative electrode, and an electrolyte disposed between the positive electrode and the negative electrode, wherein the positive electrode may include a positive electrode active material and a sacrificial positive electrode active material, and the electrolyte may include lecithin.

Description

Electrolyte for lithium secondary batteries and lithium secondary batteries containing the electrolyte

[0001] The present disclosure relates to an electrolyte for a lithium secondary battery and a lithium secondary battery comprising the electrolyte.

[0002] Recently, accompanied by the rapid proliferation of battery-powered electronic devices such as mobile phones, laptop computers, and electric vehicles, the demand for high-energy-density, high-capacity rechargeable batteries is rapidly increasing. Accordingly, research and development to improve the performance of lithium-ion batteries is actively underway.

[0003] A lithium secondary battery is a battery comprising a positive electrode and a negative electrode containing an active material capable of lithium ion intercalation and deintercalation, and an electrolyte, and produces electrical energy through oxidation and reduction reactions when lithium ions are intercalated / deintercalated from the positive electrode and the negative electrode.

[0004] Currently commercially available lithium secondary batteries mainly use carbon-based negative electrode active materials such as graphite. Carbon-based negative electrode active materials do not change in volume during charging and discharging, so the stability of lithium secondary batteries is high. The theoretical electric capacity of graphite is small, about 372 mAh / g.

[0005] In contrast, recently, numerous studies have been conducted on lithium metal batteries using lithium metal instead of carbon-based negative electrode active material on the negative electrode current collector to increase energy density. Lithium metal has a very large theoretical electric capacity of approximately 3,860 mAh / g. Therefore, lithium metal batteries without a negative electrode active material layer have the advantage of having a significantly higher energy density per unit weight compared to conventional lithium-ion batteries coated with a thick layer of carbon-based negative electrode active material on the negative electrode current collector.

[0006] However, since such lithium metal batteries lack a source of extra lithium, their lifespan characteristics may be degraded due to the continuous consumption of lithium during charging and discharging and the progression of irreversible reactions. Therefore, in order to dramatically improve lifespan characteristics while maintaining the structure of a lithium metal battery without a negative electrode active material layer, methods have been pursued to introduce a sacrificial cathode to supply additional lithium within the cell.

[0007] However, when an over-lithiated oxide such as LFO (Li5FeO4) is introduced as a sacrificial cathode, oxygen gas may be released through irreversible side reactions. The generated oxygen gas can increase the internal resistance of the secondary battery cell, promote lithium dendrite growth, and cause non-uniform current distribution, thereby weakening the cell's performance. Therefore, a means to remove oxygen gas is required to improve the lifespan characteristics and performance of lithium metal secondary batteries.

[0008] The information described above disclosed in the background technology of this invention is intended only to enhance understanding of the background of the present invention and may therefore include information that does not constitute prior art.

[0009] One embodiment provides an electrolyte for a lithium secondary battery to solve the above technical problem.

[0010] Another embodiment provides a lithium secondary battery comprising an electrolyte to solve the above technical problem.

[0011] An electrolyte for a lithium secondary battery according to one embodiment of the present invention for solving the above technical problem may include an organic solvent, a lithium salt, and an oxygen capture additive comprising lecithin.

[0012] A lithium secondary battery according to one embodiment of the present invention for solving the above technical problem comprises a positive electrode for a lithium secondary battery, a negative electrode including a negative electrode current collector, a separator interposed between the positive electrode and the negative electrode, and an electrolyte disposed between the positive electrode and the negative electrode, wherein the positive electrode comprises a positive active material and a sacrificial positive active material, and the electrolyte may comprise lecithin.

[0013] An electrolyte for a lithium secondary battery according to some embodiments of the present disclosure can capture oxygen gas generated at a sacrificial cathode by introducing lecithin as an additive. By doing so, the cell stability of the secondary battery can be enhanced and the lifespan characteristics of the cell can be improved.

[0014] An electrolyte for a lithium secondary battery according to some embodiments of the present disclosure can provide a lithium metal battery with improved capacity retention rate, lifespan characteristics, and thermal stability by suppressing dendrite formation during the charging and discharging process through the introduction of phosphoric acid functional groups.

[0015] However, the effects obtainable through the present invention are not limited to those described above, and other unmentioned technical effects will be clearly understood by those skilled in the art from the description of the invention below.

[0016] The following drawings attached to this specification illustrate preferred embodiments of the present invention and serve to further enhance understanding of the technical concept of the present invention together with the detailed description of the invention provided below; therefore, the present invention should not be interpreted as being limited only to the matters described in such drawings.

[0017] FIG. 1 is a diagram showing a stacked structure of a lithium secondary battery according to one embodiment.

[0018] Figure 2 is a diagram showing the stacked structure of the lithium secondary battery of Figure 1 after charging.

[0019] FIG. 3 is a diagram showing a stacked structure of a lithium secondary battery according to another embodiment.

[0020] FIG. 4 is a perspective view illustrating a lithium secondary battery according to one embodiment.

[0021] FIG. 5 is a perspective view illustrating a lithium secondary battery according to one embodiment.

[0022] FIG. 6 is a perspective view illustrating a lithium secondary battery according to one embodiment.

[0023] FIG. 7 is a perspective view illustrating a lithium secondary battery according to one embodiment.

[0024] Hereinafter, embodiments of the present invention will be described in detail. However, these are presented as examples and are not intended to limit the present invention, and the present invention is defined only by the scope of the claims set forth below.

[0025] Unless otherwise specifically stated in this specification, when a part such as a layer, film, region, plate, etc. is described as being "on" another part, this includes not only cases where it is "immediately on" another part, but also cases where there is another part in between.

[0026] Unless otherwise specified in this specification, a singular form may also include a plural form. Additionally, unless otherwise specified, "A or B" may mean "including A, including B, or including A and B."

[0027] In this specification, "combination of these" may mean a mixture of components, a laminate, a composite, a copolymer, an alloy, a blend, and a reaction product, etc.

[0028] Unless otherwise defined in this specification, the particle size may be the average particle size. Additionally, the particle size refers to the average particle size (D50), which means the diameter of the particle whose cumulative volume in the particle size distribution is 50% by volume. The average particle size (D50) may be measured by methods widely known to those skilled in the art, for example, by measuring with a particle size analyzer, or by measuring with a transmission electron microscope (TEM) image or a scanning electron microscope (SEM) image. Alternatively, the average particle size (D50) value may be obtained by measuring using a measuring device utilizing dynamic light scattering, performing data analysis to count the number of particles for each particle size range, and then calculating from this. Alternatively, it may be measured using a laser diffraction method. When measuring by laser diffraction, more specifically, after dispersing the particles to be measured in a dispersion medium, they are introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000) and irradiated with ultrasound of about 28 kHz at an output of 60 W, and then the average particle size (D50) at 50% of the particle size distribution in the measuring device can be calculated.

[0029] Methods and materials similar or equivalent to those described herein may be used in the practice or testing of the present invention, but suitable methods and materials are described herein. The singular expression includes the plural expression unless the context clearly indicates otherwise.

[0030] In this specification, terms such as “comprising” or “having” are intended to indicate the existence of the features, numbers, steps, actions, components, parts, components, materials, or combinations thereof described in the specification, and should be understood as not excluding in advance the existence or addition of one or more other features, numbers, steps, actions, components, parts, components, materials, or combinations thereof.

[0031] In this specification, the term “combination of these” means a mixture or combination with one or more of the described components, and may mean a mixture of components, a laminate, a composite, a copolymer, an alloy, a blend, and a reaction product, etc.

[0032] In this specification, the term “and / or” means any combination of one or more items described in relation and all combinations thereof. In this specification, the term “or” means “and / or”.

[0033] In this specification, when a part such as a layer, film, region, plate, etc. is described as being "on" another part, this includes not only cases where it is directly above the other part, but also cases where there is another part in between.

[0034] In this specification, terms such as "first," "second," etc., may be used to describe various components, but the components should not be limited by these terms. The terms are used solely for the purpose of distinguishing one component from another.

[0035] In this specification, “metal” includes both metals and metalloids such as silicon and germanium in an elemental or ionic state.

[0036] In this specification, "alloy" means a mixture of two or more metals.

[0037] In this specification, "anode active material" refers to an anode material capable of undergoing lithiation and delithiation.

[0038] In this specification, "anode active material" refers to an anode material capable of undergoing lithiation and delithiation.

[0039] In this specification, "lithiation" and "to lithiate" refer to the process of adding lithium to a positive electrode active material or a negative electrode active material.

[0040] In this specification, "delithiation" and "to delithiate" refer to the process of removing lithium from a positive electrode active material or a negative electrode active material.

[0041] In this specification, "charge" and "to charge" refer to the process of providing electrochemical energy to a battery.

[0042] In this specification, "discharge" and "discharge" refer to the process of removing electrochemical energy from a battery.

[0043] In this specification, "anode" and "cathode" refer to electrodes where electrochemical reduction and lithiation occur during the discharge process.

[0044] In this specification, "cathode" and "anode" refer to electrodes where electrochemical oxidation and delithiation occur during the discharge process.

[0045] Exemplary embodiments will be described in more detail below with reference to the attached drawings.

[0046] A negative electrode-free lithium secondary battery is a battery that uses only a negative electrode current collector without a negative electrode active material layer, and the battery can be operated through a process in which lithium ions transferred from the positive electrode are deposited on the surface of the negative electrode current collector during charging, and the lithium deposited on the negative electrode current collector is leached out and inserted into the positive electrode during discharging.

[0047] Anode-free lithium secondary batteries can have the advantage of maximizing energy density per unit volume and weight of the battery by omitting the anode active material. However, lithium metal precipitated during operation causes lithium dendrites to grow due to non-uniform current concentration during oxidation and reduction processes, and these lithium dendrites can cause losses in the lithium anode, thereby degrading the battery's capacity and lifespan characteristics. Additionally, the growth of lithium dendrites can cause a short circuit between the anode and the cathode.

[0048] Secondary batteries have primarily utilized ion-conducting electrolytes in which salts are dissolved in organic solvents. However, these electrolytes degrade electrode materials and are highly susceptible to the volatilization of organic solvents, resulting in low battery safety due to combustion caused by rising ambient and / or internal battery temperatures. Furthermore, during charging and discharging, the decomposition of organic solvents and / or adverse reactions between the solvents and the electrodes can generate gas inside the battery, potentially causing the battery thickness to expand.

[0049]

[0050] electrolytes

[0051] An electrolyte for a lithium secondary battery according to one embodiment of the present invention may include an organic solvent, a lithium salt, and an oxygen capture additive. The oxygen capture additive may include lecithin.

[0052] In one embodiment, lecithin may be composed as shown in the following structural formula 1. For example, lecithin may refer to a compound in which R and R' in the following structural formula 1 are substituted with various fatty acids or aliphatic functional groups.

[0053]

[0054] <Structural Formula 1>

[0055]

[0056]

[0057] In one embodiment, lecithin may comprise phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylinositol (PI), phosphatidylserine, phosphatidic acid, or a combination thereof. For example, lecithin may comprise L-α-lecithin (soybean lecithin or soy lecithin).

[0058] Lecithin may contain fatty acids with varying chain lengths (number of carbons in R and R' in structural formula 1). For example, lecithin may be phosphatidylcholine containing fatty acids with a chain length of less than 22. As another example, lecithin may be phosphatidylcholine containing fatty acids with a chain length of 22 or more.

[0059] In one embodiment, an electrolyte containing an oxygen capture additive including lecithin can capture oxygen gas released during the electrochemical reaction of a sacrificial anode. Additionally, since lecithin contains phosphate-based functional groups, the electrolyte containing the oxygen capture additive can be flame-retardant. However, because lecithin has a large molecular weight, excessive addition may increase the viscosity of the electrolyte and tend to lower its ionic conductivity. Therefore, a limited amount is required.

[0060] An oxygen capture additive containing lecithin may be included in a specific range of proportions in an electrolyte for a lithium secondary battery. For example, the proportion of lecithin in the electrolyte may be 0.1 wt% to 3.0 wt%, 0.1 wt% to 0.5 wt%, 0.5 wt% to 3.0 wt%, 0.5 wt% to 2.0 wt%, or 0.5 wt% to 1.0 wt% based on the weight of the electrolyte excluding lecithin (100 wt%).

[0061] In one embodiment, the electrolyte for a lithium secondary battery may be a liquid electrolyte. The liquid electrolyte may be prepared, for example, by dissolving a lithium salt in an organic solvent and then mixing in an oxygen capture additive. For example, the organic solvent may include fluoroethylene carbonate (FEC), diethyl carbonate (DEC), butyronitrile (BN), or a combination thereof.

[0062] For example, the organic solvent may be propylene carbonate, ethylene carbonate, fluoroethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, dibutyl carbonate, benzonitrile, acetonitrile, tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, dioxolan, 4-methyldioxolan, N,N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, diethylene glycol, dimethyl ether, or a combination thereof.

[0063] For example, the lithium salt may include lithium hexafluorophosphate (LiPF6), lithium difluoro(oxalato)borate (LiDFOB), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), or a combination thereof. The concentration of the lithium salt may be, for example, 0.1 M to 5.0 M, 0.1 M to 3.0 M, or 0.5 M to 1.0 M.

[0064] In one embodiment, the electrolyte for a lithium secondary battery may be a gel polymer electrolyte. Specifically, to improve upon the liquid electrolyte described above, a gel polymer electrolyte (GPE) may be applied. The gel polymer electrolyte has high electrochemical safety and can maintain a constant thickness of the battery. In addition, due to the adhesive strength characteristic of the gel phase, the contact between the electrode and the electrolyte can be excellent.

[0065] In addition, in one embodiment, in a lithium secondary battery utilizing lithium metal as a negative electrode active material layer, a gel polymer electrolyte can be applied that stably forms an SEI film to suppress side reactions of lithium metal and control lithium dendrites, while simultaneously improving high-temperature safety.

[0066] In the present disclosure, the gel polymer electrolyte may comprise a cross-linked polymer and a fluorinated linear alkyl phosphate. By doing so, a gel polymer electrolyte with high ionic conductivity and self-extinguishing properties is provided, and a lithium secondary battery with high safety, lifespan, and efficiency characteristics can be provided by including the same.

[0067] A gel polymer electrolyte according to one embodiment of the present disclosure is an anode-free lithium secondary battery or a positive electrode having a negative electrode capacity per unit area (mAh / cm²) for a positive electrode in which a negative electrode active material layer is absent on a negative electrode current collector. 2 It can be applied to lithium metal batteries with a ratio of less than 1.

[0068] A gel polymer electrolyte for a lithium secondary battery according to one embodiment may further include a crosslinking agent for forming a polymer matrix in the above-described organic solvent, lithium salt, and oxygen capture additive. Here, the crosslinking agent may have two or more reactive functional groups.

[0069] In one embodiment, the crosslinking agent may include two or more carbon-carbon double bonds (C=C) capable of crosslinking reactions within one molecule. For example, the crosslinking agent may include PETTA (pentaerythritol tetraacrylate), TMPTMA (trimethylolpropane trimethacrylate), DPHA (dipentaerythritol hexacrylate), EGDMA (Eth-ylene Glycol Dimethacrylate), DVB (Divinylbenzene), or any combination thereof.

[0070] In one embodiment, the crosslinking agent may include two or more carbon-oxygen double bonds (C=O) capable of crosslinking reactions within one molecule. For example, the crosslinking agent may include a diester of acrylic acid, urethane acrylate, a diester of maleic acid, bisphenol A diacrylate, or any combination thereof.

[0071] A liquid electrolyte containing an organic solvent and a lithium salt can be impregnated into a polymer matrix formed by a crosslinking agent to form a gel polymer electrolyte. The proportion of the crosslinking agent in the gel polymer electrolyte may be 2 wt% to 20 wt%, 3 wt% to 10 wt%, or 4 wt% to 5 wt%.

[0072] An electrolyte for a lithium secondary battery according to some embodiments of the present disclosure can capture oxygen gas generated at a sacrificial cathode by introducing lecithin as an additive. By doing so, the cell stability of the secondary battery can be enhanced and the lifespan characteristics improved.

[0073]

[0074] lithium secondary battery

[0075] FIG. 1 is a diagram showing a stacked structure of a lithium secondary battery according to one embodiment. FIG. 2 is a diagram showing the stacked structure of the lithium secondary battery of FIG. 1 after charging. FIG. 3 is a diagram showing a stacked structure of a lithium secondary battery according to another embodiment.

[0076] Referring to FIGS. 1 and 2, a lithium secondary battery (100) according to one embodiment of the present invention comprises a positive electrode (130) for a lithium secondary battery, a negative electrode including a negative electrode current collector (140), a separator (not shown) interposed between the positive electrode (130) and the negative electrode, and an electrolyte (160) disposed between the positive electrode (130) and the negative electrode. The positive electrode (130) may include a positive active material layer (120) including a positive active material and a sacrificial positive active material, and a positive current collector (110). Here, the electrolyte (160) may include the electrolyte described above. For example, the electrolyte (160) may include lecithin.

[0077] In one embodiment, the sacrificial cathode active material may include Li2MoO3, Li2CuO2, Li2NiO2, Li6CoO4, Li5FeO4, Li8ZrO6, Li2O, Li3N, Li3P, or a combination thereof. In the cathode (130) of the secondary battery according to one embodiment, the ratio of the sacrificial cathode active material may be 0.5 wt% to 20 wt%, 3.0 wt% to 15 wt%, 3.0 wt% to 20 wt%, 5 wt% to 10 wt%, 5 wt% to 15 wt%, or 5 wt% to 20 wt%.

[0078] A lithium secondary battery according to one embodiment comprises a positive electrode, a negative electrode, and an electrolyte disposed between the positive electrode and the negative electrode. The electrolyte may have a solid, liquid, or gel form. Although the present disclosure describes lithium metal secondary batteries primarily, it is not limited thereto and may be, for example, a lithium primary battery, and may also be applied to lithium-sulfur batteries, lithium-air batteries, etc.

[0079] A lithium secondary battery according to one embodiment of the present invention may be a negative electrode-free lithium secondary battery. Specifically, the negative electrode of the lithium secondary battery (100) includes a negative electrode current collector (140) in which a negative electrode active material layer is free, and an electrolyte (160) may be disposed on top of the negative electrode current collector (140).

[0080] FIG. 1 is a drawing showing a stacked structure of a non-anode lithium secondary battery (100), and FIG. 2 may correspond to a drawing showing lithium metal precipitated on a negative current collector as the non-anode lithium secondary battery (100) is charged. FIG. 3 may correspond to a drawing showing a lithium metal secondary battery (300) in which lithium metal is used as a negative active material layer. The thickness of each layer shown in FIG. 1 to FIG. 3 is shown as an arbitrary size and is not necessarily limited thereto.

[0081] Referring to FIG. 2, a lithium secondary battery (100) according to one embodiment may have a lithium metal layer (150) formed on a negative electrode current collector (140) after charging. Specifically, the lithium metal layer (150) may be disposed between the negative electrode current collector (140) and the electrolyte (160). For example, the lithium metal layer (150) may be a lithium electrodeposited layer. For example, the lithium metal layer (150) may include a lithium alloy and a lithium metal. For example, the lithium alloy included in the lithium metal layer (150) may weaken the reactivity of the lithium metal, thereby effectively preventing side reactions between the lithium metal layer (150) and the polymer electrolyte. In addition, the lithium metal layer (150) has excellent electrical conductivity, which can reduce the internal resistance of the lithium secondary battery containing it. Accordingly, the lithium secondary battery (100) containing the lithium metal layer (150) may have improved lifespan characteristics as well as charge / discharge efficiency.

[0082] Here, the lithium constituting the lithium metal layer (150) may originate from the sacrificial positive active material contained in the positive active material layer (120). For example, the lithium metal layer (150) may be formed as lithium ions contained in the electrolyte (160), originating from the sacrificial positive active material, are electrodeposited onto the negative current collector (140) as the lithium secondary battery is charged and discharged.

[0083] In a lithium-ion secondary battery, only the irreversible reaction at the beginning of the charge / discharge is compensated for, so a small proportion of sacrificial cathode active material is sufficient; however, in a lithium metal secondary battery according to one embodiment, since lithium derived from the sacrificial cathode is continuously utilized during the charge / discharge process, a large amount of sacrificial cathode active material may be required compared to a lithium-ion battery of the same capacity. In a secondary battery (100) according to one embodiment, the electrical capacity of the negative electrode relative to the electrical capacity of the positive electrode (130) may be less than 100%.

[0084] Referring to FIG. 3, a lithium secondary battery (300) according to one embodiment may further include a lithium metal layer (350) disposed between a negative electrode current collector (340) and an electrolyte (360). In this case, the negative electrode may include a lithium metal layer (350) disposed between the negative electrode current collector (340) and the electrolyte (360). For example, the lithium secondary battery (300) may include a negative electrode current collector (340), a lithium metal layer (350) disposed on top of the negative electrode current collector (340), an electrolyte (360) disposed on top of the lithium metal layer (350), and a positive electrode (330) disposed on top of the electrolyte (360). The positive electrode (330) may include a positive electrode current collector (310) and a positive electrode active material layer (320) disposed on the positive electrode current collector (310). Accordingly, the electrolyte (360) can be placed between the positive active material layer (320) and the lithium metal layer (350).

[0085] For example, the lithium metal layer (350) may include lithium metal or a lithium alloy. For example, the lithium metal layer (350) may be reduced in thickness by dissociating into lithium ions and metal cations during the discharge process. Conversely, the lithium metal layer (350) may be increased in thickness by electrodepositing lithium ions during the charging process.

[0086] According to one embodiment, a lithium secondary battery (100, 300) comprising an electrolyte (160, 360) may further include a protective layer (not shown) disposed between a negative electrode and the electrolyte. For example, the protective layer may be formed between a negative electrode current collector (140) and the electrolyte (160). Alternatively, the protective layer may be formed between a lithium metal layer (350) and the electrolyte (360). According to one embodiment, the protective layer of the lithium secondary battery (100, 300) comprises an inorganic oxide, and the electrolyte (160, 360) may be disposed between the protective layer and the positive electrode (130, 330).

[0087] According to one embodiment, one or more stacked structures of the lithium secondary battery (100, 300) as described above may be stacked or wound and accommodated in a case, and the case may be classified into cylindrical, prismatic, thin film, coin, pin type, etc.

[0088] FIGS. 4 to 7 are schematic diagrams illustrating a lithium secondary battery according to one embodiment, where FIG. 4 is cylindrical, FIG. 5 is prismatic, and FIGS. 6 and 7 are pouch-type batteries. Referring to FIGS. 4 to 7, the lithium secondary battery (1) includes a battery structure (7, electrode assembly) having a separator (4, separator) interposed between a positive electrode (3) and a negative electrode (2), and a case (5) in which the battery structure (7) is housed. The positive electrode (3), the negative electrode (2), and the separator (4) may be impregnated with an electrolyte (not shown). The lithium secondary battery (1) may include an assembly (6, sealing member) that seals the case (5) as in FIG. 4. Additionally, in FIG. 5, the lithium secondary battery (1) may include a positive lead tab (3') and a positive terminal (3"), a negative lead tab (2') and a negative terminal (2"). As shown in FIGS. 6 and 7, the lithium secondary battery (1) may include electrode tabs (70), namely a positive electrode tab (71) and a negative electrode tab (72), which serve as electrical passages for inducing current formed in the battery structure (7) to the outside.

[0089] Referring to FIG. 4, a lithium secondary battery (1) according to one embodiment includes the anode (3), the cathode (2), and the separator (4) described above. The anode (3), the cathode (2), and the separator (4) are wound or folded to form a battery structure (7). The formed battery structure (7) is housed in a case (5). An electrolyte is injected into the case (5) and sealed with a cap assembly (6) to complete the lithium secondary battery (1). The case (5) is cylindrical but is not necessarily limited to this shape and may be, for example, prismatic, thin film, etc.

[0090] Referring to FIG. 5, a lithium secondary battery (1) according to one embodiment includes a positive electrode (3), the aforementioned negative electrode (2), and a separator (4). The positive electrode (3), the negative electrode (2), and the separator (4) are wound, folded, or stacked to form a battery structure (7). The formed battery structure (7) is housed in a case (5). An electrolyte is injected into the case (5), cross-linked, and sealed to complete the lithium secondary battery (1). The case (5) is prismatic, but is not necessarily limited to this shape and may be, for example, cylindrical, thin film, etc. A positive lead tab (3') and a positive terminal (3") are electrically connected to the positive electrode (3). A negative lead tab (2') and a negative terminal (2") are electrically connected to the negative electrode (2).

[0091] Referring to FIG. 6, a lithium secondary battery (1) according to one embodiment includes a positive electrode (3), the aforementioned negative electrode (2), and a separator (4). A separator (4) is disposed between the positive electrode (3) and the negative electrode (2), and the positive electrode (3), the negative electrode (2), and the separator (4) are wound or folded to form a battery structure (7). The formed battery structure (7) is housed in a case (5). It may include an electrode tab (70) that serves as an electrical path for inducing the current formed in the battery structure (7) to the outside. An electrolyte is injected into the case (5) and sealed to complete the lithium secondary battery (1). The case (5) is prismatic, but is not necessarily limited to this shape and may be, for example, cylindrical, thin film, etc.

[0092] Referring to FIG. 7, a lithium secondary battery (1) according to one embodiment includes a positive electrode (3), a negative electrode (2) and a separator (4) as described above. An electrolyte as described above, including a separator (4), is disposed between the positive electrode (3) and the negative electrode (2) to form a battery structure. For example, the battery structure (7) is stacked in a bicell structure and then housed in a case (5). It may include a positive electrode tab (71) and a negative electrode tab (72) that serve as electrical pathways for inducing current formed in the battery structure (7) to the outside. The electrolyte is injected into the case (5) and sealed to complete the lithium secondary battery (1). The case (5) is prismatic but is not necessarily limited to this shape and may be, for example, cylindrical, thin film, etc.

[0093] However, the present invention is not limited to this, and the case (5) may be configured in various shapes such as circular or pouch type. For example, the pouch-type lithium secondary battery corresponds to the lithium secondary battery (1) of FIGS. 4 to 7 in which a pouch is used as the case (5). The pouch-type lithium secondary battery includes one or more battery structures (7). A separator (4) is disposed between the positive electrode (3) and the negative electrode (2) to form the battery structure (7). The battery structure (7) is stacked in a bicell structure, then impregnated with an electrolyte, and then housed and sealed in a pouch to complete the pouch-type lithium secondary battery.

[0094] Specifically, the battery structure (7) including the aforementioned positive electrode (3), negative electrode (2), and separator (4) is simply stacked and contained in a pouch, or wound into a jelly roll shape or folded and contained in a pouch. Subsequently, an electrolyte is injected into the pouch and sealed to complete the lithium secondary battery (1).

[0095] The case (5) may be made of metal such as aluminum, aluminum alloy, nickel-plated steel, or a laminate film or plastic that constitutes the pouch.

[0096] Lithium secondary battery (1) has excellent lifespan characteristics and high rate characteristics, so it is used in, for example, electric vehicles (EV). For example, it is used in hybrid vehicles such as plug-in hybrid electric vehicles (PHEV). In addition, it is used in fields where a large amount of power storage is required. For example, it is used in electric bicycles, power tools, etc.

[0097] A plurality of lithium secondary batteries (1) are stacked to form a battery module, and a plurality of battery modules form a battery pack. Such a battery pack can be used in any device requiring high capacity and high output. For example, it can be used in laptops, smartphones, electric vehicles, etc. A battery module includes, for example, a plurality of batteries and a frame that holds them.

[0098] A battery pack includes, for example, a plurality of battery modules and a bus bar connecting them. The battery modules and / or battery pack may further include a cooling device. A plurality of battery packs are controlled by a battery management system. The battery management system includes a battery pack and a battery control device connected to the battery pack.

[0099]

[0100] anode

[0101] A positive active material layer is disposed on a positive current collector to form a positive electrode. A positive active material layer is disposed on an electrolyte, and a positive current collector may be disposed on the positive active material layer.

[0102]

[0103] Positive: Positive current collector

[0104] The positive electrode includes a positive electrode current collector. For example, a positive electrode can be prepared by forming a layer of positive electrode active material on the positive electrode current collector.

[0105] For example, the positive current collector may include indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof.

[0106] According to one embodiment, the anode current collector may include aluminum (Al).

[0107] For example, the positive current collector may include a base film and a metal substrate layer disposed on one or both sides of the base film, just like the negative current collector.

[0108]

[0109] Anode: Anode active material

[0110] Referring to FIGS. 1 to 3, the positive active material layer (120, 320) included in the positive electrode (130, 330) of the present invention may include a positive active material to be described later. For example, the positive active material may include LiMO2 (M is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements or a combination thereof), LFP, LiM2O4 (M is Ti, V, Mn), or a combination thereof.

[0111] As a positive electrode active material, a compound capable of reversible intercalation and deintercalation of lithium (a lithated intercalation compound) may be used. Specifically, one or more composite oxides of lithium and a metal selected from cobalt, manganese, nickel, and combinations thereof may be used. The composite oxide may be a lithium transition metal composite oxide, and specific examples include a lithium nickel-based oxide, a lithium cobalt-based oxide, a lithium manganese-based oxide, a lithium iron phosphate-based compound, a cobalt-free nickel-manganese-based oxide, or a combination thereof.

[0112] As an example, a compound represented by any one of the following chemical formulas may be used. Li a A 1-b Xb About 2-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05), Li a Mn 2-b X b About 4-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05), Li a Ni 1-b-c Co b X c About 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2), Li a Ni 1-b-c Mn b X c About 2-α D α (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.5, 0<α<2), Li a Ni b Co c L 1 d G e O2(0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, 0≤e≤0.1), Li a NiG b O2(0.90≤a≤1.8, 0.001≤b≤0.1), Li a CoG b O2(0.90≤a≤1.8, 0.001≤b≤0.1), Li a Mn 1-b G b O2(0.90≤a≤1.8, 0.001≤b≤0.1), Li a Mn2GbO4(0.90≤a≤1.8, 0.001≤b≤0.1), Li a Mn 1-g G g PO4(0.90≤a≤1.8, 0≤g≤0.5), Li (3-f) Fe2(PO4)3(0≤f≤2), Li a FePO4(0.90≤a≤1.8).

[0113] In the chemical formula, A is Ni, Co, Mn, or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, or a combination thereof; D is O, F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; and L 1 is Mn, Al, or a combination thereof.

[0114] For example, the cathode active material may be a high-nickel cathode active material in which the nickel content relative to 100 mol% of the metal excluding lithium in a lithium transition metal composite oxide is 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more and 99 mol% or less. The high-nickel cathode active material can achieve high capacity and can be applied to high-capacity, high-density lithium secondary batteries.

[0115] For example, the lithium transition metal oxide may be a compound represented by the following chemical formula 1:

[0116]

[0117] <Chemical Formula 1>

[0118] Li a Ni x Co y M z O 2-b A b

[0119]

[0120] In Chemical Formula 1, 1.0≤a≤1.2, 0≤b≤0.2, 0.6≤x<1, 0≤y≤0.3, 0 <z≤0.3, x+y+z=1, M은 망간(Mn), 바나듐(V), 마그네슘(Mg), 갈륨(Ga), 실리콘(Si), 텅스텐(W), 몰리브덴(Mo), 철(Fe), 크롬(Cr), 구리(Cu), 아연(Zn), 티타늄(Ti), 알루미늄(Al) 및 보론(B)으로 이루어진 군으로부터 선택된 하나 이상이고, A는 F, S, Cl, Br 또는 이들의 조합이다.

[0121] In Chemical Formula 1, for example, 0.7≤x<1, 0 <y≤0.3, 0<z≤0.3, 0.8≤x<1, 0<y≤0.2, 0<z≤0.2, 0.83≤x<0.97, 0<y≤0.15, 0<z≤0.15, 또는 0.85≤x<0.95, 0<y≤0.1, 0<z≤0.1일 수 있다.

[0122] For example, the lithium transition metal oxide may be at least one of the compounds represented by the following chemical formulas 2 and 3:

[0123]

[0124] <Chemical Formula 2>

[0125] LiNi x Co y Mn z O2

[0126]

[0127] In Chemical Formula 2, 0.6≤x≤0.95, 0 <y≤0.2, 0<z≤0.1이다. 예를 들어, 0.7≤x≤0.95, 0<y≤0.3, 0<z≤0.3이다.

[0128]

[0129] <Chemical Formula 3>

[0130] LiNi x Co y Al z O2

[0131]

[0132] In Chemical Formula 3, 0.6≤x≤0.95, 0 <y≤0.2, 0<z≤0.1이다. 예를 들어, 0.7≤x≤0.95, 0<y≤0.3, 0<z≤0.3이다. 예를 들어, 0.8≤x≤0.95, 0<y≤0.3, 0<z≤0.3이다. 예를 들어, 0.82≤x≤0.95, 0<y≤0.15, 0<z≤0.15이다. 예를 들어, 0.85≤x≤0.95, 0<y≤0.1, 0<z≤0.1이다.

[0133] For example, lithium transition metal oxides are LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.88 Co 0.08Mn 0.04O2 , LiNi 0.8 Co 0.15 Mn 0.05O2 , LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.88 Co 0.1 Mn 0.02O2 , LiNi 0.8 Co 0.15 Al 0.05O2 , LiNi 0.8 Co 0.1 Mn 0.2O2 or LiNi 0.88 Co 0.1 Al 0.02O2 It could be.

[0134] For example, the positive electrode active material may be one having a coating layer on the surface of a lithium transition metal oxide, or a mixture of a lithium transition metal oxide and a lithium transition metal oxide having a coating layer may be used.

[0135] For example, the coating layer may include a coating element compound of an oxide, hydroxide, oxyhydroxide, oxycarbonate, or hydroxycarbonate of a coating element.

[0136] For example, the compound forming the coating layer may be amorphous or crystalline. The coating elements included in the coating layer may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof. For the coating layer formation process, any coating method may be used as long as the coating can be applied to the lithium transition metal oxide using the coating elements in a manner that does not adversely affect the physical properties of the cathode active material (e.g., spray coating, immersion method, etc.).

[0137] For example, the anode may additionally include an additive that can serve as a sacrificial anode.

[0138] The content of the positive active material is 90% to 99.5% by weight with respect to 100% by weight of the positive active material layer, and the content of the binder and the conductive material may each be 0.5% to 5% by weight with respect to 100% by weight of the positive active material layer.

[0139] The binder serves to adhere the positive active material particles well to each other and also to adhere the positive active material well to the current collector. Representative examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride (PVDF), polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc.

[0140] A conductive material is used to impart conductivity to an electrode, and any electronically conductive material that does not cause chemical changes can be used in the battery being constructed. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fibers containing copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0141]

[0142] Cathode: Cathode current collector

[0143] The negative current collector may not include a negative active material layer. In a negative current collector that does not include a negative active material layer, lithium metal may be plated onto the negative current collector by charging. The plated metal layer may comprise plated lithium, lithium metal foil, lithium metal powder, lithium alloy foil, lithium alloy powder, an organic compound containing lithium, or a combination thereof. The metal layer may comprise non-fibrous lithium, non-needle lithium, plate lithium, or any combination thereof. The lithium alloy contains lithium and a first metal, and the first metal may include indium (In), silicon (Si), gallium (Ga), tin (Sn), aluminum (Al), titanium (Ti), zirconium (Zr), niobium (Nb), germanium (Ge), antimony (Sb), bismuth (Bi), gold (Au), platinum (Pt), palladium (Pd), magnesium (Mg), silver (Ag), zinc (Zn), nickel, iron, cobalt, chromium, cesium, sodium, potassium, calcium, yttrium, bismuth, tantalum, hafnium, barium, vanadium, strontium, lanthanum, or a combination thereof.

[0144] The material constituting the negative electrode current collector can be any material that does not react with lithium, that is, a material that does not form an alloy or compound with lithium and possesses conductivity. The metal substrate is, for example, a metal or an alloy. The metal substrate may be composed of, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or alloys thereof. The electrode current collector may have a form selected from, for example, a sheet, foil, film, plate, porous body, mesoporous body, through-hole containing body, polygonal ring body, mesh body, foam, and nonwoven body, but is not necessarily limited to these forms and any form used in the relevant technical field is possible.

[0145] The negative current collector comprises, for example, a first metal substrate. The first metal substrate comprises the first metal as a main component or is composed of the first metal. The first metal substrate comprises the first metal as a main component or is composed of the first metal. The content of the first metal included in the first metal substrate is, for example, 90 weight% or more, 95 weight% or more, 99 weight% or more, or 99.9 weight% or more with respect to the total weight of the first metal substrate. The first metal substrate may be composed of, for example, a material that does not react with lithium, that is, does not form an alloy and / or compound with lithium.

[0146] The first metal may be, for example, copper (Cu), nickel (Ni), stainless steel (SUS), iron (Fe), and cobalt (Co), but is not necessarily limited to these; any metal used as a current collector in the relevant technical field may be used. The first metal substrate may be composed of, for example, one of the metals described above, or may be composed of an alloy of two or more metals. The first metal substrate is, for example, in the form of a sheet or foil.

[0147] The negative current collector may further include a coating layer (not shown) containing a second metal on a first metal substrate.

[0148] The cathode current collector may include, for example, a first metal substrate and a coating layer disposed on the first metal substrate and comprising a second metal. The second metal has a higher Mohs hardness than the first metal. That is, since the coating layer comprising the second metal is harder than the substrate comprising the first metal, deterioration of the first metal substrate can be prevented. The Mohs hardness of the material constituting the first metal substrate is, for example, 5.5 or less. The Mohs hardness of the first metal is, for example, 5.5 or less, 5.0 or less, 4.5 or less, 4.0 or less, 3.5 or less, or 3.0 or less. The Mohs hardness of the first metal may be, for example, 2.0 to 6.0. The coating layer comprises the second metal. The coating layer may, for example, comprise the second metal as a main component or be composed of the second metal. The content of the second metal included in the coating layer is, for example, 90% by weight or more, 95% by weight or more, 99% by weight or more, or 99.9% by weight or more with respect to the total weight of the coating layer. The coating layer may be composed of, for example, a material that does not react with lithium, that is, does not form an alloy and / or compound with lithium. The Mohs hardness of the material constituting the coating layer is, for example, 6.0 or more. For example, the Mohs hardness of the second metal is 6.0 or more, 6.5 or more, 7.0 or more, 7.5 or more, 8.0 or more, 8.5 or more, or 9.0 or more. The Mohs hardness of the second metal may be, for example, 6.0 to 12. If the Mohs hardness of the second metal is excessively low, it may be difficult to suppress the deterioration of the negative electrode current collector. If the Mohs hardness of the second metal is excessively high, processing may not be easy. The second metal is one or more selected from, for example, titanium (Ti), manganese (Mn), niobium (Nb), tantalum (Ta), iridium (Ir), vanadium (V), rhenium (Re), osmium (Os), tungsten (W), chromium (Cr), boron (B), ruthenium (Ru), and rhodium (Rh).The coating layer may be composed of, for example, one of the metals described above, or an alloy of two or more metals. The difference in Mohs hardness between the first metal included in the first metal substrate and the second metal included in the coating layer may be, for example, 2 or more, 2.5 or more, 3 or more, 3.5 or more, or 4 or more. By having such a difference in Mohs hardness between the first metal and the second metal, the deterioration of the negative current collector can be suppressed more effectively. The coating layer may have a single-layer structure or a multilayer structure of two or more layers. The coating layer may have a two-layer structure including, for example, a first coating layer and a second coating layer. The coating layer may have a three-layer structure including, for example, a first coating layer, a second coating layer, and a third coating layer. The thickness of the coating layer may be, for example, 10 nm to 1 μm, 50 nm to 500 nm, 50 nm to 200 nm, or 50 nm to 150 nm. The coating layer may be deposited on the first metal substrate by, for example, vacuum deposition, sputtering, plating, etc., but is not necessarily limited to these methods; any method capable of forming a coating layer in the relevant technical field is possible.

[0149] For example, the cathode current collector may have a reduced thickness compared to a conventional cathode current collector. Accordingly, the cathode according to the present disclosure is distinguished from a conventional electrode comprising a thick film current collector by including, for example, a thin film current collector.

[0150] As a result, the energy density of a lithium metal secondary battery employing such an electrode is increased. The thickness of the negative electrode current collector may be, for example, less than 15 μm, 14.5 μm or less, or 14 μm or less. The thickness of the negative electrode current collector may be, for example, 0.1 μm to 15 μm, 1 μm to 14.5 μm, 2 μm to 14 μm, 3 μm to 14 μm, 5 μm to 14 μm, or 10 μm to 14 μm.

[0151] The cathode current collector may have a form selected from, for example, a sheet, foil, film, plate, porous body, mesoporous body, through-hole containing body, polygonal ring body, mesh body, foam, and nonwoven body, but is not necessarily limited to these forms, and any form used in the relevant technical field is possible.

[0152] The negative current collector may include, for example, a base film and a metal substrate layer disposed on one or both sides of the base film. The negative current collector may have a structure comprising a substrate, wherein the substrate may include, for example, a base film and a metal substrate layer disposed on one or both sides of the base film. An intermediate layer may be additionally disposed on the metal substrate layer.

[0153] For example, the base film may include, for example, a polymer. The polymer may be, for example, a thermoplastic polymer. The polymer may include, for example, polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), polybutylene terephthalate (PBT), polyimide (PI), or a combination thereof. By including a thermoplastic polymer in the base film, the base film may melt upon the occurrence of a short circuit, thereby suppressing a sudden increase in current. The base film may be, for example, an insulator.

[0154] The metal substrate layer may include, for example, copper (Cu), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), or alloys thereof. The metal substrate layer can act as an electrochemical fuse and cut off upon overcurrent to perform a short-circuit prevention function. The limit current and maximum current can be controlled by adjusting the thickness of the metal substrate layer. The metal substrate layer may be plated or deposited on a base film. As the thickness of the metal substrate layer decreases, the limit current and / or maximum current of the negative electrode current collector decreases, thereby improving the stability of the lithium metal secondary battery during a short circuit.

[0155] A lead tab may be added to the metal substrate layer for external connection. The lead tab may be welded to the metal substrate layer or the metal substrate layer / base film laminate by means of ultrasonic welding, laser welding, spot welding, etc. During welding, the base film and / or the metal substrate layer may melt, thereby electrically connecting the metal substrate layer to the lead tab. To make the weld between the metal substrate layer and the lead tab more robust, a metal chip may be added between the metal substrate layer and the lead tab. The metal chip may be a thin sheet of the same material as the metal of the metal substrate layer. The metal chip may be, for example, metal foil, metal mesh, etc. The metal chip may be, for example, aluminum foil, copper foil, SUS foil, etc. The lead tab may be welded to the metal chip / metal substrate layer laminate or the metal chip / metal substrate layer / base film laminate by placing the metal chip on the metal substrate layer and then welding it to the lead tab. During welding, the base film, metal layer, and / or metal chip may melt, allowing the metal layer or the metal layer / metal chip laminate to be electrically connected to the lead tab. A metal chip and / or lead tab may be added to a portion of the metal substrate layer. The thickness of the base film may be, for example, 1 μm to 50 μm, 1.5 μm to 50 μm, 1.5 μm to 40 μm, or 1 μm to 30 μm. By having the base film within this thickness range, the weight of the cathode assembly can be reduced more effectively. The melting point of the base film may be, for example, 100° to 300° (Celsius), 100° to 250° (Celsius) or lower, or 100° to 200° (Celsius). By having the base film within this melting point range, the base film can melt during the welding process of the lead tab and be easily bonded to the lead tab. To improve the adhesion between the base film and the metal substrate layer, a surface treatment such as corona treatment may be performed on the base film.The thickness of the metal substrate layer may be, for example, 0.01 μm to 3 μm, 0.1 μm to 3 μm, 0.1 μm to 2 μm, or 0.1 μm to 1 μm. By having the metal substrate layer within this thickness range, the stability of the cathode can be ensured while maintaining conductivity. The thickness of the metal piece may be, for example, 2 μm to 10 μm, 2 μm to 7 μm, or 4 μm to 6 μm. By having the metal piece within this thickness range, the connection between the metal layer and the lead tab can be performed more easily. By having the cathode current collector with this structure, the weight of the electrode can be reduced and, consequently, the energy density can be improved.

[0156] According to one embodiment, a negative electrode active material layer may be free on the negative electrode current collector before charging and discharging. For example, a lithium metal layer may be free on the negative electrode current collector before charging and discharging.

[0157] According to one embodiment, a lithium metal layer including a plate-shaped lithium metal thin film may be disposed on a negative electrode current collector before performing charging and discharging.

[0158] According to one embodiment, the cathode may further include an interlayer disposed between the cathode current collector and the lithium metal layer.

[0159] According to one embodiment, the interlayer may be placed directly on, for example, one or both sides of the negative electrode current collector. Therefore, no other layer may be placed between the negative electrode current collector and the interlayer. By placing the interlayer directly on one or both sides of the negative electrode current collector, the bonding strength between the negative electrode current collector and the lithium metal layer may be further improved.

[0160] The thickness of the intermediate layer (not shown) may be, for example, 30% or less of the thickness of the cathode current collector. The thickness of the intermediate layer (not shown) is, for example, 0.01% to 30%, 0.1% to 30%, 0.5% to 30%, 1% to 25%, 1% to 20%, 1% to 15%, 1% to 10%, 1% to 5%, or 1% to 3% of the thickness of the cathode current collector. The thickness of the intermediate layer is, for example, 10 nm to 5 µm, 50 nm to 5 µm, 200 nm to 4 µm, 500 nm to 3 µm, 500 nm to 2 µm, 500 nm to 1.5 µm, or 700 nm to 1.3 µm.

[0161] By having the intermediate layer have a thickness within this range, the bonding strength between the cathode current collector and the metal layer is further improved, and the increase in interfacial resistance can be suppressed.

[0162] For example, the intermediate layer may include a binder. By including a binder in the intermediate layer, the bonding strength between the negative current collector and the lithium metal layer can be further improved. The binder included in the intermediate layer is, for example, a conductive binder or a non-conductive binder.

[0163] Conductive binders are, for example, ion-conducting binders and / or electronic-conducting binders. Binders that possess both ion conductivity and electronic conductivity may belong to both ion-conducting binders and electronic-conducting binders.

[0164] Ion-conducting binders are, for example, polystyrene sulfonate (PSS), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyvinyl fluoride (PVF), polyvinylidene fluoride (PVDF), poly(methylmethacrylate) (PMMA), polyethylene oxide (PEO), polyethylene glycol (PEG), polyacrylonitrile (PAN), polytetrafluoroethylene (PTFE), polyethylenedioxythiophene (PEDOT), polypyrrole (PPY), polyacrylonitrile (PAN), polyaniline, and polyacetylene. Ion-conducting binders may include polar functional groups. Ion-conducting binders containing polar functional groups are, for example, Nafion, Aquivion, Flemion, Gore, Aciplex, Morgane ADP, sulfonated poly(ether ether ketone) (SPEEK), sulfonated poly(arylene ether ketone ketone sulfone) (SPAEKKS), sulfonated poly(aryl ether ketone) (SPAEK), poly[bis(benzimidazobenzisoquinolinones)] (SPBIBI), poly(styrene sulfonate) (PSS), lithium 9,10-diphenylanthracene-2-sulfonate, DPASLi+ etc.The electronically conductive binder is, for example, polyacetylene, polythiophene, polypyrrole, poly(p-phenylene), poly(phenylenevinylene), poly(phenylenesulfide), polyaniline, etc. The intermediate layer may be, for example, a conductive layer containing a conductive polymer.

[0165] The binder included in the intermediate layer may be, for example, a fluorine-based binder. The fluorine-based binder included in the intermediate layer may be, for example, polyvinylidene fluoride (PVDF). The intermediate layer may be disposed on the cathode current collector, for example, dry or wet. The intermediate layer may be, for example, a binding layer containing a binder.

[0166] The intermediate layer may additionally include, for example, a carbon-based conductive material. By including the carbon-based conductive material, the intermediate layer may be, for example, a conductive layer. The intermediate layer may be, for example, a conductive layer including a binder and a carbon-based conductive material.

[0167] The intermediate layer can be disposed on the cathode current collector in a dry manner by deposition, for example, CVD, PVD, etc. The intermediate layer can be disposed on the cathode current collector in a wet manner by, for example, spin coating, dip coating, etc. The intermediate layer can be disposed on the cathode current collector by, for example, depositing a carbon-based conductive material on the cathode current collector by deposition. The dry-coated intermediate layer consists of a carbon-based conductive material and may not contain a binder. Alternatively, the intermediate layer can be disposed on the cathode current collector by, for example, coating a composition comprising a carbon-based conductive material, a binder, and a solvent onto the surface of the cathode current collector and drying it. The intermediate layer may have a single-layer structure or a multilayer structure comprising multiple layers.

[0168]

[0169] Cathode: Lithium metal layer

[0170] A lithium secondary battery may further include a metal layer disposed between a negative electrode current collector and an electrolyte. For example, the lithium metal layer may include lithium metal or a lithium alloy. For example, the lithium metal layer may be a negative electrode active material layer. For example, the lithium metal layer may be a lithium electrodeposited layer.

[0171] For example, a lithium metal layer can be formed as lithium ions contained in the electrolyte are electrodeposited onto the negative current collector while the lithium secondary battery is being charged. For example, the lithium metal layer may include a lithium alloy and lithium metal. For instance, the lithium alloy included in the lithium metal layer weakens the reactivity of the lithium metal, thereby effectively preventing adverse reactions between the lithium metal layer and the electrolyte. Additionally, the lithium metal layer has excellent electrical conductivity, which can reduce the internal resistance of the lithium secondary battery containing it. Accordingly, the lithium secondary battery containing the lithium metal layer can improve not only its lifespan characteristics but also its charge / discharge efficiency.

[0172] According to one embodiment, the lithium metal layer may comprise, for example, lithium foil, lithium powder, plated lithium, a carbon-based material, or a combination thereof. For example, the lithium metal layer may comprise lithium foil. In this case, the lithium metal layer may be a negative electrode active material layer. For example, the lithium metal layer may be introduced by coating a slurry containing lithium powder and a binder, etc., onto a negative electrode current collector. For example, the binder may be a fluorine-based binder such as polyvinylidene fluoride (PVDF).

[0173] According to one embodiment, it may comprise only lithium metal or lithium alloy electrodeposited with a lithium metal layer. In this case, the lithium metal layer may be a lithium electrodeposited layer.

[0174] According to one embodiment, the lithium metal layer may not include a carbon-based negative electrode active material. Accordingly, the lithium metal layer may be composed of a metal-based negative electrode active material.

[0175] For example, the thickness of the lithium metal layer may be, for example, 0.1 μm to 100 μm, 0.1 μm to 80 μm, 1 μm to 80 μm, or 10 μm to 80 μm, but is not necessarily limited to these ranges and can be adjusted according to the required shape, capacity, etc. of the lithium secondary battery. If the thickness of the lithium metal layer increases excessively, the structural stability of the lithium secondary battery may decrease and side reactions may increase. If the thickness of the lithium metal layer is excessively small, the energy density of the lithium metal secondary battery may decrease.

[0176] According to one embodiment, the thickness of the lithium foil included in the lithium metal layer may be, for example, 1 μm to 50 μm, 1 μm to 30 μm, 10 μm to 30 μm, or 10 μm to 80 μm. By having the lithium foil within this range of thickness, the lifespan characteristics of the lithium metal secondary battery can be further improved.

[0177] According to one embodiment, the particle size of the lithium powder included in the lithium metal layer may be, for example, 0.1 μm to 3 μm, 0.1 μm to 2 μm, or 0.1 μm to 1 μm. By having the lithium powder have a thickness within this range, the lifespan characteristics of the lithium secondary battery can be further improved.

[0178]

[0179] separator

[0180] A lithium battery according to one embodiment may further include a separator (not shown).

[0181] As a separator, polyethylene, polypropylene, polyvinylidene fluoride, or multilayer films of two or more layers thereof may be used, and of course, mixed multilayer films such as polyethylene / polypropylene two-layer separator, polyethylene / polypropylene / polyethylene three-layer separator, polypropylene / polyethylene / polypropylene three-layer separator may be used.

[0182] The separator may include a porous substrate and a coating layer comprising an organic material, an inorganic material, or a combination thereof located on one or both sides of the porous substrate.

[0183] The porous substrate may be a polymer membrane formed from any one of the following: polyolefins such as polyethylene and polypropylene; polyesters such as polyethylene terephthalate and polybutylene terephthalate; polyacetal; polyamide; polyimide; polycarbonate; polyetherketone; polyaryletherketone; polyetherimide; polyamideimide; polybenzimidazole; polyethersulfone; polyphenylene oxide; cyclic olefin copolymer; polyphenylene sulfide; polyethylene naphthalate; glass fiber; Teflon; and polytetrafluoroethylene, or a copolymer or mixture of two or more of these.

[0184] The organic material may include a polyvinylidene fluoride-based polymer or a (meth)acrylic-based polymer.

[0185] The inorganic material may include, but is not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof.

[0186] Organic and inorganic materials may exist mixed in a single coating layer, or may exist in a stacked form with a coating layer containing organic materials and a coating layer containing inorganic materials.

[0187]

[0188] This will be explained in more detail through the following examples and comparative examples. However, the examples are for illustrative purposes only and are not limited thereto.

[0189]

[0190] Example 1

[0191] Copper foil was prepared as a cathode current collector. Based on 100% of the total weight of the gel polymer electrolyte excluding the oxygen capture additive, 96 wt% of the liquid electrolyte and 4 wt% of the crosslinking agent were mixed, and 0.5 wt% of phosphatidylcholine (PC), a lecithin-based oxygen capture additive, was added to this mixture. The fatty acid chain length of the phosphatidylcholine was set to less than C22.

[0192] For the liquid electrolyte to make the gel polymer electrolyte, 0.6M LiDFOB (lithium difluorooxalatoborate) and 0.6M LiBF4 (lithium tetrafluoroborate) were used as lithium salts, and FEC (fluoroethylene carbonate), DEC (diethyl carbonate), and BN (butyronitrile) were uniformly mixed in a volume ratio of 42:48:10 as organic solvents. DPHA (dipentaerythritol hexaacrylate) was used as the crosslinking agent to make the gel polymer electrolyte.

[0193] The cathode was prepared by mixing LFO (lithium iron oxide) as a sacrificial cathode active material and LCO (lithium cobalt oxide) as a cathode active material.

[0194] An electrode assembly was prepared by sequentially stacking a negative electrode current collector, a separator, and a positive electrode, and a gel polymer electrolyte precursor containing phosphatidylcholine was injected into the electrode assembly. Then, a lithium secondary battery was prepared by thermal crosslinking.

[0195]

[0196] Example 2

[0197] As indicated in Table 1, a lithium secondary battery was prepared in the same manner as in Example 1, except for the oxygen capture additive content.

[0198]

[0199] Example 3

[0200] As indicated in Table 1, a lithium secondary battery was prepared in the same manner as in Example 1, except for the oxygen capture additive content.

[0201]

[0202] Example 4

[0203] A lithium secondary battery was prepared by carrying out the same procedure as in Example 1, except for the chain length of the fatty acid as indicated in Table 1.

[0204]

[0205] Example 5

[0206] A lithium secondary battery was prepared in the same manner as Example 4, except for the content of the oxygen capture additive as indicated in Table 1.

[0207]

[0208] Example 6

[0209] A lithium secondary battery was prepared in the same manner as Example 4, except for the content of the oxygen capture additive as indicated in Table 1.

[0210]

[0211] Example 7

[0212] A lithium secondary battery was prepared in the same manner as in Example 1, except that the type of lecithin was changed to phosphatidylinositol (PI) as indicated in Table 1.

[0213]

[0214] Comparative Example 1

[0215] A lithium secondary battery was prepared in the same manner as in Example 1, except that the type of oxygen capture additive was different, as indicated in Table 1, which was carbohydrazide.

[0216]

[0217] Comparative Example 2

[0218] A lithium secondary battery was prepared in the same manner as Comparative Example 1, except for the difference in the content of carbohydrazide as indicated in Table 1.

[0219]

[0220] Comparative Example 3

[0221] A lithium secondary battery was prepared in the same manner as Comparative Example 1, except for the difference in the content of carbohydrazide as indicated in Table 1.

[0222]

[0223] Comparative Example 4

[0224] A lithium secondary battery was prepared in the same manner as Comparative Example 1, except that an oxygen capture additive was not added as indicated in Table 1.

[0225]

[0226] Classification Type of Lecithin Fatty Acid Chain Length Lecithin Content (wt%) Carbohydrazide Content (wt%) Example 1 PC (Phosphatidylcholine) C 22 Less than 0.5 - Example 2 ↑↑ 1.0 - Example 3 ↑↑ 2.0 - Example 4 ↑C 22 0.5-Example 5↑↑1.0-Example 6↑↑2.0-Example 7 PI(phosphatidylinositol)C 22 Less than 0.5 - Comparative Example 1 - 0.5 Comparative Example 2 - 1.0 Comparative Example 3 - 2.0 Comparative Example 4

[0227] In the table, the "↑" symbol is used to indicate that the same components as in the preceding example are used for the related components.

[0228] Evaluation Example 1: Measurement of expansion rate (%, @50cy)

[0229] For the lithium secondary batteries prepared according to the examples and comparative examples, a formation process is carried out by charging at a current rate of 0.1C. Subsequently, during the charging process, the secondary battery cell is charged at a constant current rate of 0.33C until the voltage reaches 4.5V (vs. Li), and then cut-off is performed at a current rate of 0.05C while maintaining a constant voltage of 4.5V in constant voltage mode. Subsequently, during discharge, a constant current discharge at a rate of 1.0C is performed until the voltage reaches 2.8V (vs. Li). The above-described charge-discharge process was repeated, and the charge-discharge process was repeated a total of 50 times. In all charge-discharge cycles, a 5-minute pause was allowed after each charge / discharge cycle. Here, the capacity retention rate in the Nth cycle is defined by the following formula.

[0230]

[0231] [ceremony]

[0232] Expansion Rate (%) = {(Charge thickness of the secondary battery cell at the Nth cycle - Charge thickness of the secondary battery cell after the formation process) / (Charge thickness of the secondary battery cell after the formation process)} × 100

[0233] The expansion rate at the 50th cycle for each is listed in Table 2 below.

[0234]

[0235] Evaluation Example 2: Measurement of self-extinguishing time

[0236] The self-extinguishing time (SET) was measured by pouring 0.3g of gel polymer electrolyte into the lid of a lithium secondary battery (coin cell) prepared according to the examples and comparative examples and contacting it with a torch flame for about 1 second to determine whether it ignites (refer to international standards ASTM D93-11, JIS K 2265:1996), and is shown in Table 2. The numerical values ​​in Table 2 below represent the time from when the fire ignites until it goes out.

[0237]

[0238] Evaluation Example 3: Measurement of Lithium Secondary Battery Capacity Retention Rate (%, @80cy)

[0239] For the lithium secondary batteries prepared according to the examples and comparative examples, a formation process is carried out by charging at a current rate of 0.1C. Subsequently, during the charging process, the secondary battery cell is charged at a constant current rate of 0.33C until the voltage reaches 4.5V (vs. Li), and then cut-off is performed at a current rate of 0.05C while maintaining a constant voltage of 4.5V in constant voltage mode. Subsequently, during discharge, a constant current discharge at a rate of 1.0C is performed until the voltage reaches 3.0V (vs. Li). The above-described charge-discharge process was repeated, and the charge-discharge process was repeated a total of 80 times. In all charge-discharge cycles, a 5-minute pause was provided after each charge / discharge cycle. Here, the capacity retention rate in the Nth cycle is defined by the following formula.

[0240]

[0241] [ceremony]

[0242] Capacity Retention Rate (%) = (Discharge Capacity at Nth Cycle / Discharge Capacity at 1st Cycle) × 100

[0243] The capacity retention rate at the 80th cycle for each is listed in Table 2 below.

[0244]

[0245] Classification Expansion Rate (%) (@ 50 cycles) Self-extinguish time (sec / g) Lifespan (Cycle @ SOH 80%) Example 1 9.4 117 135 Example 2 8.5 103 142 Example 3 7.189 139 Example 4 12.7 107 124 Example 5 10.398 134 Example 6 9.994 132 Example 7 18.7 125 101 Comparative Example 1 19.6 148 98 Comparative Example 2 22.9 146 99 Comparative Example 3 27.2 149 101 Comparative Example 4 18.4 147 84

[0246] Referring to Table 2, it was confirmed that the examples mixed with lecithin as an oxygen capture additive each had a lower expansion rate, a shorter self-digestion time, and superior lifespan characteristics of the lithium secondary battery compared to the comparative examples. Although preferred embodiments of the present invention have been described above, the present invention is not limited thereto and can be implemented with various modifications within the scope of the claims, the detailed description of the invention, and the attached drawings, and it is obvious that such modifications also fall within the scope of the present invention.

Claims

1. Cathode for lithium secondary batteries; A cathode including a cathode current collector; A separator interposed between the anode and the cathode; and Electrolyte placed between the anode and the cathode Includes, The above-mentioned anode includes an anode active material and a sacrificial anode active material, and The above electrolyte is a lithium secondary battery containing lecithin.

2. In Paragraph 1, A lithium secondary battery comprising the above lecithin, phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, phosphatidylserine, phosphatidic acid, or a combination thereof.

3. In Paragraph 1, The proportion of the lecithin in the electrolyte is 0.1 wt% to 3.0 wt% based on the weight of the electrolyte excluding the lecithin. Lithium secondary battery.

4. In Paragraph 1, The above electrolyte comprises an organic solvent and a lithium salt, Lithium secondary battery.

5. In Paragraph 4, The above electrolyte further comprises a crosslinking agent for forming a polymer matrix, Lithium secondary battery.

6. In Paragraph 5, The above-mentioned crosslinking agent comprises PETTA (pentaerythritol tetraacrylate), TMPTMA (trimethylolpropane trimethacrylate), DPHA (dipentaerythritol hexacrylate), EGDMA (Ethylene Glycol Dimethacrylate), DVB (Divinylbenzene), diester of acrylic acid, urethane acrylate, diester of maleic acid, bisphenol A diacrylate, or any combination thereof. Lithium secondary battery.

7. In Paragraph 5, The ratio of the crosslinking agent in the above electrolyte is 2 wt% to 20 wt%, Lithium secondary battery.

8. In Paragraph 4, A lithium secondary battery comprising the above lithium salt, lithium hexafluorophosphate (LiPF6), lithium difluoro(oxalato)borate (LiDFOB), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), or a combination thereof.

9. In Paragraph 1, The above sacrificial cathode active material comprises Li2MoO3, Li2CuO2, Li2NiO2, Li6CoO4, Li5FeO4, Li8ZrO6, Li2O, Li3N, Li3P, or a combination thereof. Lithium secondary battery.

10. In Paragraph 1, The ratio of the sacrificial cathode active material in the above anode is 0.5 wt% to 20 wt%, Lithium secondary battery.

11. In Paragraph 1, The electrical capacitance of the cathode relative to the electrical capacitance of the anode is less than 100%, Lithium secondary battery.

12. In Paragraph 1, A lithium metal layer further comprising a lithium metal layer disposed between the above-mentioned negative current collector and the above-mentioned electrolyte, Lithium secondary battery.

13. Organic solvent; Lithium salt; A crosslinking agent for forming a polymer matrix; and Electrolyte for lithium secondary batteries containing lecithin.

14. In Paragraph 13, The above lecithin comprises phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, phosphatidylserine, phosphatidic acid, or a combination thereof. Electrolyte for lithium secondary batteries.

15. In Paragraph 13, The proportion of the lecithin in the electrolyte is 0.1 wt% to 3.0 wt% based on the weight of the electrolyte excluding the lecithin. Electrolyte for lithium secondary batteries.

16. In Paragraph 13, The above crosslinking agent has two or more reactive functional groups, Electrolyte for lithium secondary batteries.

17. In Paragraph 13, The above-mentioned crosslinking agent comprises PETTA (pentaerythritol tetraacrylate), TMPTMA (trimethylolpropane trimethacrylate), DPHA (dipentaerythritol hexacrylate), EGDMA (Ethylene Glycol Dimethacrylate), DVB (Divinylbenzene), diester of acrylic acid, urethane acrylate, diester of maleic acid, bisphenol A diacrylate, or any combination thereof. Electrolyte for lithium secondary batteries.

18. In Paragraph 13, The ratio of the crosslinking agent in the above electrolyte is 2 wt% to 20 wt%, Electrolyte for lithium secondary batteries.

19. In Paragraph 13, The above lithium salt is an electrolyte for a lithium secondary battery comprising lithium hexafluorophosphate (LiPF6), lithium difluoro(oxalato)borate (LiDFOB), lithium tetrafluoroborate (LiBF4), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), or a combination thereof.

20. In Paragraph 13, The above organic solvent is an electrolyte for a lithium secondary battery comprising fluoroethylene carbonate (FEC), diethyl carbonate (DEC), butyronitrile (BN), or a combination thereof.

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