Negative electrode for lithium secondary battery, and lithium secondary battery including same

Abstract

The present disclosure relates to a negative electrode for a lithium secondary battery and a lithium secondary battery including same. According to an embodiment of the present disclosure for solving technical problems, the negative electrode for a lithium secondary battery includes a negative electrode current collector and a composite layer disposed directly on the negative electrode current collector, and the composite layer may include a polymer, carbon nanoparticles, and insulating particles.

Description

Negative electrode for a lithium secondary battery and a lithium secondary battery including the same

[0001] The present disclosure relates to a negative electrode for a lithium secondary battery and a lithium secondary battery including the same.

[0002] Lithium-ion batteries are high-performance rechargeable batteries with the highest energy density among currently commercialized rechargeable batteries, and are used in various fields such as electric vehicles.

[0003] To date, various efforts have been made to reduce the size of the anode to increase the energy density of lithium-ion batteries. While thick lithium metal was used as the anode active material layer in lithium-ion batteries, carbon-based anode active materials such as graphite are now primarily used due to safety concerns, and new anode active materials such as silicon-carbon composites and thin lithium metal films are being developed. Recently, anode-free lithium-ion batteries, which do not have an anode active material layer, are also being developed.

[0004] In lithium secondary batteries where lithium metal is used as the negative electrode active material layer or where the negative electrode active material layer is absent, the energy density and long life characteristics do not reach a satisfactory level due to the formation and growth of lithium dendrites on the negative electrode, leaving much room for improvement.

[0005] 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.

[0006] The problem that the present invention aims to solve is to provide a negative electrode for a lithium secondary battery and a lithium secondary battery including the same to solve the above-mentioned problems.

[0007] However, the technical problems that the present invention aims to solve are not limited to those described above, and other unmentioned problems can be clearly understood by those skilled in the art from the description of the invention below.

[0008] According to one embodiment of the present disclosure for solving the above technical problem, a negative electrode for a lithium secondary battery comprises a negative electrode current collector and a composite layer directly disposed on the negative electrode current collector, and the composite layer may comprise a polymer, carbon nanoparticles, and insulating particles.

[0009] According to one embodiment of the present disclosure for solving the above technical problem, a negative electrode for a lithium secondary battery comprises a negative electrode current collector, a lithium metal layer disposed on the negative electrode current collector, and a composite layer disposed on the lithium metal layer, and the composite layer may comprise a polymer, carbon nanoparticles, and insulating particles.

[0010] According to one embodiment of the present disclosure for solving the above technical problem, a lithium secondary battery may include a positive electrode, a negative electrode as described above, and an electrolyte disposed between the positive electrode and the negative electrode.

[0011] According to some embodiments of the present invention, lithium is uniformly electrodeposited at the cathode, so the density of the electrodeposited layer can be increased.

[0012] According to some embodiments of the present invention, the phenomenon of lithium being electrodeposited on the upper surface of the cathode can be prevented.

[0013] According to some embodiments of the present invention, the formation and growth of lithium dendrites on the surface of the negative electrode current collector of a lithium secondary battery can be prevented.

[0014] According to some embodiments of the present invention, the formation and growth of lithium dendrites on the lithium metal layer of a lithium secondary battery can be prevented.

[0015] According to some embodiments of the present invention, the lifespan characteristics of a lithium secondary battery are improved, and the safety of the battery can be improved by preventing short circuits between the positive and negative electrodes caused by dendrites.

[0016] According to some embodiments of the present invention, lithium loss due to the formation of lithium dead volume in a lithium secondary battery can be prevented, thereby improving the energy density of the battery.

[0017] 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.

[0018] 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.

[0019] FIG. 1 is a cross-sectional view of a cathode according to one embodiment before charging.

[0020] FIG. 2 is a cross-sectional view of a cathode according to one embodiment after charging.

[0021] FIG. 3 is a cross-sectional view of a cathode according to one embodiment before charging.

[0022] Figure 4 is a cross-sectional view of the cathode explaining the function of the composite layer.

[0023] FIG. 5 is a perspective view illustrating a lithium secondary battery according to one embodiment.

[0024] FIG. 6 is a perspective view illustrating a lithium secondary battery according to one embodiment.

[0025] FIG. 7 is a perspective view illustrating a lithium secondary battery according to one embodiment.

[0026] FIG. 8 is a cross-sectional view of a lithium secondary battery according to one embodiment before charging.

[0027] FIG. 9 is a cross-sectional view of a lithium secondary battery according to one embodiment after charging.

[0028] FIG. 10 is a cross-sectional view of a lithium secondary battery according to one embodiment before charging.

[0029] Figure 11 is a graph evaluating the lifespan and capacity characteristics of a lithium secondary battery according to Figure 8.

[0030] Figures 12a and 12b are SEM images showing cross-sections of the lithium metal layer in the comparative example and the example.

[0031] 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.

[0032] 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.

[0033] 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."

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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”.

[0040] Thicknesses have been enlarged or reduced in the drawings to clearly represent various layers and regions. Throughout the specification, the same reference numerals have been used for similar parts.

[0041] 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.

[0042] 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.

[0043] In this specification, “metal” includes both metals and metalloids such as silicon and germanium in an elemental or ionic state. In this specification, “alloy” means a mixture of two or more metals.

[0044] In this specification, "anode active material" refers to an anode material capable of undergoing lithiation and delithiation. In this specification, "anode active material" refers to an anode material capable of undergoing lithiation and delithiation.

[0045] In this specification, "lithiation" and "to lithiate" refer to the process of adding lithium to a specific substance or compound. In this specification, "delithiation" and "to delithiate" refer to the process of removing lithium from a specific substance or compound.

[0046] In this specification, "charge" and "to charge" refer to the process of providing electrochemical energy to a battery. In this specification, "discharge" and "to discharge" refer to the process of removing electrochemical energy from a battery.

[0047] In this specification, "anode" and "cathode" refer to electrodes where electrochemical reduction and lithiation occur during the discharge process. In this specification, "negative electrode" and "anode" refer to electrodes where electrochemical oxidation and delithiation occur during the discharge process.

[0048] Exemplary embodiments will be described in more detail below.

[0049] cathode

[0050] FIG. 1 is a cross-sectional view of a cathode according to one embodiment before charging. FIG. 2 is a cross-sectional view of a cathode according to one embodiment after charging.

[0051] Referring to FIG. 1, in one embodiment, the negative electrode (100) of a lithium secondary battery may not have a lithium metal layer, which is described later in FIG. 3, disposed on the negative electrode current collector (110). Therefore, lithium derived from the positive electrode active material layer and / or electrolyte may be initially electrodeposited on the negative electrode current collector (110) during the initial charging. When the battery is discharged, the electrodeposited lithium metal may be leached out and move to the positive electrode. Unlike cases where the negative electrode active material layer is a carbon-based material such as graphite, allowing lithium ions to be inserted and extracted, lithium ions may not be reversibly electrodeposited or leached out. That is, the shape or thickness electrodeposited during the initial charging cannot be naturally reproduced during the charging process of the next cycle. Therefore, a composite layer (120) capable of physically controlling this may be required.

[0052] The electrodeposited layer contains impurities remaining within the electrode and decomposition products of the electrolyte. Due to these impurities, the surface of the lithium electrodeposited layer becomes rough and hard. Lithium dendrites are electrodeposited on the lithium electrodeposited layer having a rough surface. Lithium dendrites continuously grow during the charging and discharging process and can cause a short circuit between the anode and the cathode. During battery operation, lithium metal precipitated 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 cathode, thereby degrading the battery's capacity and lifespan characteristics.

[0053] In a lithium secondary battery that uses a lithium metal thin film as the negative electrode (100), lithium dendrites are formed and grown on the upper surface of the lithium metal thin film after charging and discharging, resulting in the formation of a dead volume of lithium and lithium loss. Consequently, the lifespan and capacity characteristics of the lithium secondary battery may be degraded. Also, since the lithium metal thin film has a plate-like shape, it may only expand upwards during charging. As a result, a composite layer (120) capable of controlling the volume expansion of the lithium secondary battery after charging and discharging to a desired level may be required.

[0054] According to one embodiment, a negative electrode (100) for a lithium secondary battery may include a negative electrode current collector (110) and a composite layer (120) directly disposed on the negative electrode current collector (110), and the composite layer (120) may include a polymer, carbon nanoparticles, and insulating particles.

[0055] In one embodiment, the insulating particles included in the composite layer (120) may include at least one of hexagonal boron nitride (h-BN), rhombohedral boron nitride (r-BN), cubic boron nitride (c-BN), or wurtzite boron nitride (w-BN). Additionally, the insulating particles may be in an amount of 0.01 wt% or more and 10 wt% or less based on the total weight of the composite layer. With such an amount, they can be manufactured to be evenly dispersed within the composite layer as described below. Furthermore, even when the content of the insulating particles is low, for example, about 0.01 wt%, they may exhibit a localized insulating effect within the composite layer. When the insulating particles exceed about 10 wt%, the composite layer may act as a resistor to lithium ion movement due to the insulating particles.

[0056] In one embodiment, the polymer included in the composite layer (120) may include at least one of PVDF-HFP, PVDF, polyacrylic acid (PAA), polyacrylonitrile (PAN), and polyethylene oxide (PEO).

[0057] In one embodiment, the carbon nanoparticles included in the composite layer (120) may include at least one of carbon black, CNT (Carbon Nanotube), CNF (Carbon Nanofiber), and graphene.

[0058] According to one embodiment, the thickness of the composite layer (120) can be designed to a level capable of controlling the growth of lithium dendrites. For example, the thickness of the composite layer (120) may be 0.1 μm or more and 30 μm or less, or 1 μm or more and 5 μm or less. If the thickness of the composite layer is thinner than 0.1 μm, the effect of the lithium metal being electrodeposited on the bottom due to the composite layer may be negligible, and if the thickness of the composite layer is thicker than 30 μm, it may be difficult for lithium ions to pass through the composite layer and be electrodeposited on the bottom. That is, the composite layer may act as a resistor to the movement of lithium ions.

[0059] Referring to FIG. 2, as charging and discharging proceed, lithium ions originating from the positive active material and / or electrolyte may be electrodeposited between the negative electrode current collector (110) and the composite layer (120) due to the composite layer (120) according to one embodiment, thereby forming a lithium metal layer (210). Specifically, during the charging process of the battery, lithium ions may be electrodeposited on the negative electrode current collector. Accordingly, after charging, the negative electrode (200) may include a structure of a negative electrode current collector (110), a lithium metal layer (210), and a composite layer (120).

[0060] FIG. 3 is a cross-sectional view of a negative electrode according to one embodiment before charging. FIG. 3 shows a battery in which a lithium metal layer is placed on a negative electrode current collector from the manufacturing stage, unlike the battery of FIG. 2. Therefore, although the thickness of the lithium metal layer is shown as the same in FIG. 2 and FIG. 3, the thickness of the lithium metal layer (330) in FIG. 3 may be thicker than the thickness of the lithium metal layer (210) in FIG. 2.

[0061] A negative electrode (300) for a lithium secondary battery according to one embodiment may include a negative electrode current collector (310), a lithium metal layer (330) disposed on the negative electrode current collector (310), and a composite layer (320) disposed on the lithium metal layer. Here, the composite layer (320) may include a polymer, carbon nanoparticles, and insulating particles. In one embodiment, a lithium metal thin film may be used as the lithium metal layer (330). Such a lithium metal thin film may be manufactured by rolling into a plate-like shape.

[0062] The composition and manufacturing method of the composite layer (320) may be the same as the composition and manufacturing method of the composite layer (120) described above in FIG. 2. However, while the negative electrode (200) for a lithium secondary battery in FIG. 2 is manufactured by coating and drying a composite layer (120) forming composition on a negative electrode current collector (110), such as copper foil, the negative electrode (300) in FIG. 3 may be manufactured by coating and drying a composite layer (320) forming composition on a lithium metal layer (330).

[0063] The thickness of the composite layer (320) can be designed differently from the thickness of the composite layer (120) shown in FIG. 2. The thickness of the composite layer (320) can be changed depending on the degree of dendrite formation and growth.

[0064] The lithium metal layer (330) may include lithium metal or an alloy of lithium metal. As the lithium metal alloy, an alloy of metals selected from Li, Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn may be used.

[0065] FIG. 4 is a cross-sectional view of a cathode explaining the function of the composite layer. FIG. 4 is a drawing for specifically explaining the composite layer (120) of the cathode (200) in FIG. 2.

[0066] The composite layer (120) may include a polymer (122), carbon nanoparticles (124), and insulating particles (126). Here, the insulating particles (126) may be nanoparticles. As illustrated in FIG. 4, in one embodiment, the insulating particles (126) and carbon nanoparticles (124) may be evenly dispersed within the polymer (122). The composite layer (120) is a state in which insulating particles (126) with high electrical insulation and carbon nanoparticles (124) with high electrical conductivity are mixed. Thus, an even dispersion state within the composite layer (120) can be maintained so that the function of the carbon nanoparticles (124), which induce lithium ions to move smoothly to the bottom or top of the composite layer (120) depending on the charging and discharging of the battery, is exerted. Here, dispersion may mean, for example, that there are no aggregated parts within the polymer.

[0067] According to one embodiment, the particle size of the carbon nanoparticles (124) dispersed in the composite layer (120) of the negative electrode (200) for a lithium secondary battery can be designed to allow lithium ions to move within the polymer layer. For example, the particle size of the carbon nanoparticles (124) may be 5 nm or more and 2 μm or less, or 10 nm or more and 100 nm or less, or 10 nm or more and 40 nm or less. If the particle size of the carbon nanoparticles (124) is larger or smaller than the said particle size, the movement of lithium ions originating from the positive active material layer and / or electrolyte within the polymer layer may not be smooth. Additionally, if the particle size of the carbon nanoparticles (124) is larger than the said particle size, the dispersion of the carbon nanoparticles (124) within the polymer (122) may not be even.

[0068] The insulating particle (126) can be, for example, h-BN. Hexagonal boron nitride (h-BN) consists of boron and nitrogen located at the ends of carbon atoms in Group 4 of the periodic table. Graphite is a representative crystal structure composed of carbon atoms, and its allotropes include graphene, nanotubes, and diamond. Boron nitride is a III-V compound, and its crystal structure diversity is very similar to that of carbon. h-BN, which has a crystal structure similar to graphite, can have a layered structure. The thickness of one layer of h-BN is about 0.44 nm. h-BN has a band gap energy of about 6 eV, whereas graphite has no band gap.

[0069] h-BN can form three crystalline phases along with c-BN and w-BN, and is the most stable among them. The BN covalent bonds in h-BN can be polar due to the difference in electronegativity between boron and nitrogen. This can cause a significant difference in physical properties compared to graphite, in which all atoms are carbon. Since the bonds within a single layer of h-BN are strong, electrical insulation, thermal conductivity, chemical stability, and mechanical strength can be excellent. Therefore, together with the carbon nanoparticles (124) described later, it can contribute to improving the mechanical strength of the composite layer (120).

[0070] The insulating particle (126) may be, for example, c-BN. The band gap of c-BN is about 5 to 6 eV, and it may be electrically insulating along with h-BN. h-BN is converted into cubic boron nitride (c-BN: cubic boron nitride), a high-density phase with a diamond-like crystal structure, at high temperature and high pressure.

[0071] In one embodiment, carbon nanoparticles (124) are introduced into the polymer (122) to increase the mechanical strength of the composite layer. Nanomaterials such as carbon nanoparticles are composed of nanoparticles, so when the particles are nano-sized, the strength, hardness, and other mechanical properties of the material can increase as the particle size decreases.

[0072] Due to the characteristics of the carbon nanoparticles (124) and insulating particles (126) as described above, lithium ions can be stably electrodeposited within the composite layer (120) up to the bottom of the composite layer (120). Additionally, the electrodeposited lithium is released during battery discharge, allowing the movement of lithium ions along highly conductive channels within the composite layer (120) to proceed smoothly. These highly conductive channels can be formed by the carbon nanoparticles (124). For example, as shown in FIG. 4, lithium ions originating from the positive electrode active material can be guided in the direction where the carbon nanoparticles (124) are dispersed by high interaction with the carbon nanoparticles (124). However, since the insulating particles (126) are evenly dispersed to block the movement of electrons between the carbon nanoparticles (124), the formation of dead volume by electrodepositing within the polymer (122) surrounding the carbon nanoparticles (124) can be prevented. To this end, insulating particles can be introduced as nanomaterials, just like carbon nanoparticles.

[0073] lithium secondary battery

[0074] FIGS. 5 to 7 are perspective views illustrating a lithium secondary battery according to one embodiment. FIG. 4 may show a cylindrical type, FIG. 5 a prismatic type, and FIGS. 6 and 7 pouch-type batteries.

[0075] Referring to FIG. 5, a lithium secondary battery (500) according to one embodiment may include a positive electrode (540), a negative electrode (550) including the aforementioned composite layer, and a separator (560). The positive electrode (540), the aforementioned negative electrode (550), and the separator (560) may be wound or folded to form an electrode assembly (530). The formed electrode assembly (530) may be accommodated in a case (520). An electrolyte may be injected into the case (520) and sealed with a cap assembly (510) to manufacture a lithium secondary battery (500). The case (520) is shown as cylindrical, but is not limited thereto and may be coin-shaped, pin-shaped, prismatic, thin-film-shaped, etc.

[0076] Referring to FIG. 6, in one embodiment, a lithium secondary battery (600) may have a first electrode (622), a second electrode (624), and a separator (626) wound, stacked, or folded to form an electrode assembly (620). The formed electrode assembly (620) may be accommodated in a case (610). After an electrolyte is injected into the case (610), the lithium secondary battery (600) may be manufactured by sealing it with a cap assembly. The case (610) is shown as prismatic, but may not be limited thereto. A first lead tab (640) and a first electrode terminal (630) may be electrically connected to the first electrode (622). A second lead tab (660) and a second electrode terminal (650) may be electrically connected to the second electrode (624). Here, the first electrode (622) may be a negative electrode and the second electrode (624) may be a positive electrode, but the opposite may also be true. In this case, the negative electrode may be a negative electrode containing a composite layer as described above.

[0077] Referring to FIG. 7, a lithium secondary battery (700) according to one embodiment may include a positive electrode (740), a negative electrode (730) including the aforementioned composite layer, and a separator (750). A separator (750) may be disposed between the positive electrode (740) and the aforementioned negative electrode (730), and the positive electrode (740), the negative electrode (730), and the separator (750) may be wound or stacked to form an electrode assembly (720). The formed electrode assembly (720) may be housed in a case (710). Additionally, it may include an electrode tab (760) or a lead tab (770) that serves as an electrical path for inducing the current formed in the electrode assembly (720) to the outside. An electrolyte may be injected into the electrode assembly (720) and sealed to manufacture the lithium secondary battery (700). The case (710) may be prismatic, but may not be limited thereto.

[0078] Lithium secondary batteries have excellent lifespan and high-rate characteristics, so they can be used, for example, in electric vehicles (EVs). For example, they can be used in hybrid vehicles such as plug-in hybrid electric vehicles (PHEVs). In addition, they can be used in fields requiring large amounts of power storage. For example, they can be used in electric bicycles, power tools, etc.

[0079] Multiple lithium-ion batteries can be stacked to form a battery module, and multiple battery modules can 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 may include, for example, multiple batteries and a frame that holds them.

[0080] A battery pack may include, for example, a plurality of battery modules and a bus bar connecting them. The battery modules and / or the battery pack may further include a cooling device. A plurality of battery packs may be controlled by a battery management system. The battery management system may include a battery pack and a battery control device connected to the battery pack.

[0081] FIG. 8 is a cross-sectional view of a lithium secondary battery according to one embodiment before charging. FIG. 9 is a cross-sectional view of a lithium secondary battery according to one embodiment after charging. FIG. 9 is a drawing for explaining the case where the lithium secondary battery of FIG. 8 is charged.

[0082] Referring to FIG. 8, a lithium secondary battery according to one embodiment may include a positive electrode (140), a negative electrode (100) as described above, and an electrolyte disposed between the positive electrode (140) and the negative electrode (100). The negative electrode (100) may be composed of a negative electrode current collector (110) and a composite layer (120) disposed on the negative electrode current collector (110).

[0083] The electrolyte may be a liquid electrolyte, a solid electrolyte, or a gel electrolyte. In the case of a liquid electrolyte, an electrode assembly may be impregnated and placed between the positive and negative electrodes to form an electrolyte layer (130). In the case of a polymer electrolyte or a gel electrolyte, a lithium secondary battery may be manufactured through a process of forming an electrolyte layer (130) on the negative electrode. For example, an electrolyte-forming composition may be applied to a composite layer (120) and then dried to form an electrolyte layer. Additionally, a liquid electrolyte may be further injected into the battery to impregnate the electrode assembly.

[0084] As charging and discharging proceed, lithium ions originating from the positive active material and / or electrolyte may be electrodeposited between the negative electrode current collector (110) and the composite layer (120) due to the composite layer (120) according to one embodiment, thereby forming a lithium metal layer (210). During the charging process of the battery, lithium ions may be electrodeposited on the negative electrode current collector.

[0085] FIG. 10 is a cross-sectional view of a lithium secondary battery according to one embodiment before charging. FIG. 10 shows a lithium secondary battery including a negative electrode according to FIG. 3. The description regarding the positive active material layer (160), positive current collector (150), separator (not shown), and negative current collector (310) is the same as described in FIG. 8. The lithium metal layer (330) is the same as described in FIG. 3.

[0086] An electrolyte layer (130) may be disposed on a cathode (300) according to FIG. 3, and an anode (140) may be disposed on the electrolyte layer (130). The anode (140) may include an anode current collector (150) and an anode active material layer (160) disposed on the anode current collector (150). Accordingly, the anode active material layer (160) may be disposed on the electrolyte layer (130).

[0087] cathode current collector

[0088] Referring to FIG. 8, a negative electrode current collector (110) of a lithium secondary battery according to one embodiment may not include a negative electrode active material layer. A negative electrode current collector (110) that does not include a negative electrode active material layer may have lithium metal plated on it upon charging. The plated lithium metal layer (e.g., 210 in FIG. 9) may include plated lithium, lithium metal foil, lithium metal powder, lithium alloy foil, lithium alloy powder, an organic compound containing lithium, or a combination thereof. The lithium metal layer (210) may include 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.

[0089] The material constituting the negative electrode current collector (110) may include a conductive metal substrate, which is a material that does not react with lithium, that is, a material that does not form an alloy or compound with lithium. The metal substrate may be, for example, a metal or an alloy. The metal substrate may be made 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 an alloy thereof. The negative electrode current collector (140, 340) may have a shape 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 shapes, and any shape used in the relevant technical field is possible.

[0090] The negative current collector (110) may include, for example, a first metal substrate. The first metal substrate may include the first metal as a main component or be made of the first metal. The content of the first metal included in the first metal substrate may be, 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.

[0091] 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.

[0092] The negative current collector (110) may further include, for example, a first metal substrate and a coating layer (not shown) disposed on the first metal substrate and containing a second metal. The second metal may have a higher Mohs hardness than the first metal. That is, since the coating layer containing the second metal is harder than the substrate containing 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 may, for example, contain the second metal as a main component or be made of the second metal. The content of the second metal included in the coating layer may be, 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.

[0093] The Mohs hardness of the material constituting the coating layer is, for example, 6.0 or higher. For example, the Mohs hardness of the second metal may be 6.0 or higher, 6.5 or higher, 7.0 or higher, 7.5 or higher, 8.0 or higher, 8.5 or higher, or 9.0 or higher. 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 current collector (140, 340). If the Mohs hardness of the second metal is excessively high, processing may not be easy. The second metal is, for example, one or more selected from 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, for example, composed of one of the metals described above or composed of 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, 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 (140, 340) can be suppressed more effectively. The coating layer may have a single-layer structure or a multi-layer structure of two or more layers. The coating layer may have a two-layer structure, for example, comprising a first coating layer and a second coating layer. The coating layer may have a three-layer structure, for example, comprising 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 disposed on a 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.

[0094] For example, the negative current collector (110) may have a reduced thickness compared to a conventional negative current collector. Accordingly, the negative according to the present disclosure may be distinguished from a conventional electrode comprising a thick film current collector by including, for example, a thin film current collector.

[0095] As a result, the energy density of a lithium secondary battery employing such electrodes can be increased. The thickness of the negative electrode current collector (110) 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 (140, 340) may be, for example, 0.1 μm to less than 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.

[0096] In one embodiment, the negative current collector (110) may include, for example, a base film and a metal layer disposed on one or both sides of the base film. The negative current collector includes a substrate, and the substrate may have a structure including, for example, a base film and a metal layer disposed on one or both sides of the base film. An intermediate layer may be additionally disposed on the metal layer.

[0097] In one embodiment, the base film may include 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 rapid increase in current. The base film may be, for example, an insulator.

[0098] The metal layer may include, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), or alloys thereof. The metal layer may act as an electrochemical fuse and cut off in the event of an overcurrent to perform a short-circuit prevention function. The limit current and maximum current can be controlled by adjusting the thickness of the metal layer. The metal layer may be plated or deposited on a base film. As the thickness of the metal layer decreases, the limit current and / or maximum current of the negative electrode current collector (140, 340) decreases, thereby improving the stability of the lithium secondary battery in the event of a short circuit.

[0099] Lead tabs may be added to the metal layer for external connection. Lead tabs may be welded to the metal layer or the metal layer / base film laminate by means of ultrasonic welding, laser welding, spot welding, etc. During welding, the base film and / or metal layer melt, allowing the metal layer to be electrically connected to the lead tab. To make the weld between the metal layer and the lead tab more robust, a metal chip may be added between the metal layer and the lead tab. The metal chip may be a thin sheet of the same material as the metal in the metal 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 layer laminate or the metal chip / metal layer / base film laminate by placing the metal chip on the metal layer and then welding it to the lead tab. During welding, as the base film, metal layer, and / or metal piece melts, the metal layer or the metal layer / metal piece laminate can be electrically connected to the lead tab.

[0100] A metal chip and / or lead tab may be added to a portion of the metal layer. The thickness of the base film may be, for example, 1 to 50 μm, 1.5 to 50 μm, 1.5 to 40 μm, or 1 to 30 μm. By having the base film within this thickness range, the weight of the cathode can be reduced more effectively. The melting point of the base film may be, for example, 100 to 300 °C, 100 to 250 °C, or 100 to 200 °C. By having the base film within this melting point range, the base film can melt during the lead tab welding process and be easily bonded to the lead tab. Surface treatments, such as corona treatment, may be performed on the base film to improve the adhesion between the base film and the metal layer. The thickness of the metal layer may be, for example, 0.01 to 3 μm, 0.1 to 3 μm, 0.1 to 2 μm, or 0.1 to 1 μm. By having a thickness within this range, the stability of the cathode can be ensured while maintaining conductivity.

[0101] The thickness of the metal plate may be, for example, 2 to 10 μm, 2 to 7 μm, or 4 to 6 μm. By having the metal plate have a thickness within this range, the connection between the metal layer and the lead tab can be performed more easily. By having the negative current collector (140, 340) have this structure, the weight of the electrode can be reduced and, consequently, the energy density can be improved.

[0102] In a lithium secondary battery according to one embodiment, the positive electrode (140) may include a positive electrode current collector (150) and a positive electrode active material layer (160) disposed on the positive electrode current collector (150). Additionally, the positive electrode active material layer (160) may be disposed on an electrolyte layer (130).

[0103] Cathode: Lithium metal layer

[0104] A lithium secondary battery may further include a lithium 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.

[0105] For example, a lithium metal layer can be formed as lithium ions contained in the electrolyte are electrodeposited onto the negative current collector as the lithium secondary battery is charged. For example, the lithium metal layer may include a lithium alloy and lithium metal.

[0106] 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).

[0107] 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.

[0108] 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.

[0109] 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 battery. If the thickness of the lithium metal layer increases excessively, the structural stability of the lithium 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 battery may decrease.

[0110] 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, or 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 battery can be further improved.

[0111] 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 battery can be further improved.

[0112] positive current collector

[0113] The positive electrode (140) includes a positive electrode current collector (150). For example, the positive electrode (140) can be prepared by forming a positive electrode active material layer (160) on the positive electrode current collector (150).

[0114] For example, the positive current collector (150) 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.

[0115] According to one embodiment, the positive current collector (150) may include aluminum (Al). According to another embodiment, the positive current collector (150) may include a base film and a metal layer disposed on one or both sides of the base film, in the same manner as the negative current collector (110) described above.

[0116] positive active material layer

[0117] The positive active material layer (160) may include a positive active material, a conductive material, and a binder.

[0118] 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. Examples include lithium nickel-based oxides, lithium cobalt-based oxides, lithium manganese-based oxides, lithium iron phosphate-based compounds, cobalt-free nickel-manganese-based oxides, or combinations thereof.

[0119] As an example, a compound represented by any one of the following chemical formulas may be used. Li a A 1-b X b O 2-c D c (0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05), Li a Mn 2-b X b O 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 O 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 cO 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 Mn2G b O4(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).

[0120] 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.

[0121] 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.

[0122] For example, the lithium transition metal oxide may be a compound represented by the following chemical formula 1.

[0123] <Chemical Formula 1>

[0124] Li a Ni x Co y M z O 2-b A b

[0125] 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=1이고, 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.

[0126] In Chemical Formula 1, for example, 0.7≤x<1, 0 <y≤0.3, 0<z≤0.3, 0.8≤x<1, 0<y≤0.3, 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.

[0127] For example, the lithium transition metal oxide may be at least one of the compounds represented by the following chemical formulas 1-1 and 1-2.

[0128] <Chemical Formula 1-1>

[0129] LiNi x Co y Mn z O2

[0130] In Chemical Formula 1-1, 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.

[0131] <Chemical Formula 1-2>

[0132] LiNi x Co y Al z O2

[0133] In Chemical Formula 1-2, 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. 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.

[0134] For example, lithium transition metal oxides are LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.88 Co 0.08 Mn 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.

[0135] 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.

[0136] For example, the coating layer may include a coating element compound of an oxide, hydroxide, oxyhydroxide, oxycarbonate, or hydroxycarbonate of a coating element.

[0137] 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.).

[0138] For example, the anode may additionally include an additive that can serve as a sacrificial anode.

[0139] 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 (160), 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 (160).

[0140] A binder can serve to effectively bond the positive active material particles to each other and also to effectively bond the positive active material 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.

[0141] 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.

[0142] In one embodiment, the lithium secondary battery may further include a separator disposed between the positive electrode (140) and the negative electrode (100). The separator may be disposed on the composite layer (120) described above. The separator may be disposed between the composite layer and the positive active material layer.

[0143] separator

[0144] A lithium secondary battery according to one embodiment may further comprise a separator (not shown). As the separator, polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more layers thereof may be used, and of course, a mixed multilayer film such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may be used.

[0145] 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.

[0146] 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.

[0147] The organic material may include a polyvinylidene fluoride-based polymer or a (meth)acrylic-based polymer.

[0148] 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.

[0149] 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.

[0150] In the case where the electrolyte layer (130) of a lithium secondary battery according to one embodiment is a solid electrolyte, the electrolyte layer (130) may be at least one of a sulfide, an oxide, or a polymer. Such a lithium secondary battery may be, for example, an all-solid-state battery.

[0151] electrolytes

[0152] The electrolyte may be, for example, a liquid electrolyte, a solid electrolyte, a gel electrolyte, or a combination thereof.

[0153] The electrolyte is, for example, an organic electrolyte. The organic electrolyte is prepared, for example, by dissolving a lithium salt in an organic solvent. Any organic solvent used as an organic solvent in the relevant technical field may be used. Organic solvents are, for example, 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, dioxolane, 4-methyldioxolane, N,N-dimethylformamide, dimethylacetamide, dimethyl sulfoxide, dioxane, 1,2-dimethoxyethane, sulfolane, dichloroethane, chlorobenzene, nitrobenzene, diethylene glycol, dimethyl ether, or mixtures thereof.

[0154] Any lithium salt used as a lithium salt in the relevant technical field is also acceptable. Examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, LiAlO2, LiAlCl4, and LiN(C x F 2x+1SO2)(C y F 2y+1 The lithium salts are SO2)(1≤x≤20, 1≤y≤20), LiCl, LiI, or mixtures thereof. The concentration of the lithium salt is, for example, 0.1 M to 5.0 M.

[0155] Solid electrolytes are, for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, polymeric solid electrolytes, or combinations thereof.

[0156] Solid electrolytes are, for example, oxide-based solid electrolytes. Oxide-based solid electrolytes are Li 1+x+y Al x Ti 2-x Si y P 3-y O 12 (0 <x<2, O≤y<3), BaTiO3, Pb(Zr,Ti)O3(PZT), Pb 1-x La x Zr 1-y Ti y O3(PLZT)(O≤x<1, O≤y<1), PB(Mg3Nb 2 / 3 )O3-PbTiO3(PMN-PT), HfO2, SrTiO3, SnO2, CeO2, Na2O, MgO, NiO, CaO, BaO, ZnO, ZrO2, Y2O3, Al2O3, TiO2, SiO2, Li3PO4, Li x Ti y (PO4)3(0 <x<2, 0<y<3), Li x Al y Ti z (PO4)3(0 <x<2, 0<y<1, 0<z<3), Li 1+x+y (Al, Ga) x (Ti, Ge) 2-x Si y P 3-y O 12 (O≤x≤1 0≤y≤1), Li x La y TiO3(0 <x<2, 0<y<3), Li2O, LiOH, Li2CO3, LiAlO2, Li2O-Al2O3-SiO2-P2O5-TiO2-GeO2, Li 3+x La3M2O 12It is one or more selected from (M = Te, Nb, or Zr, where x is an integer from 1 to 10). Solid electrolytes are produced by sintering methods, etc. For example, oxide-based solid electrolytes include Li7La3Zr2O 12 (LLZO) and Li 3+x La3Zr 2-a MaO 12 It is a garnet-type solid electrolyte selected from (M doped LLZO, M=Ga, W, Nb, Ta, or Al, x is an integer from 1 to 10).

[0157] Sulfide-based solid electrolytes may comprise, for example, lithium sulfide, silicon sulfide, phosphorus sulfide, boron sulfide, or combinations thereof. Sulfide-based solid electrolyte particles may comprise Li2S, P2S5, SiS2, GeS2, B2S3, or combinations thereof. Sulfide-based solid electrolyte particles may be Li2S or P2S5. Sulfide-based solid electrolyte particles are known to have high lithium ion conductivity compared to other inorganic compounds. For example, sulfide-based solid electrolytes comprise Li2S and P2S5. When the sulfide solid electrolyte material constituting the sulfide-based solid electrolyte comprises Li2S-P2S5, the mixed molar ratio of Li2S to P2S5 may be, for example, in the range of about 50:50 to about 90:10. Additionally, Li3PO4, halogens, halogen compounds, Li 2+2x Zn 1-x GeO4("LISICON", 0≤x<1), Li 3+y PO 4-x N x ("LIPON", 0 <x<4, 0<y<3), Li 3.25 Ge 0.25 P 0.75An inorganic solid electrolyte prepared by adding S4 ("ThioLISICON"), Li2O-Al2O3-TiO2-P2O5 ("LATP"), etc., to an inorganic solid electrolyte of Li2S-P2S5, SiS2, GeS2, B2S3, or a combination thereof can be used as a sulfide solid electrolyte. Non-limiting examples of sulfide solid electrolyte materials include Li2S-P2S5, Li2S-P2S5-LiX (X = halogen element), Li2S-P2S5-Li2O, Li2S-P2S5-Li2O-LiI, Li2S-SiS2, Li2S-SiS2-LiI, Li2S-SiS2-LiBr, Li2S-SiS2-LiCl, Li2S-SiS2-B2S3-LiI, Li2S-SiS2-P2S5-LiI, Li2S-B2S3, Li2S-P2S5-ZmSn (0 <m<10, 0<n<10, Z=Ge, Zn 또는 Ga), Li2S-GeS2, Li2S-SiS2-Li3PO4, 및 Li2S-SiS2-Li p MO q (0 <p<10, 0<q<10, M=P, Si, Ge, B, Al, Ga 또는 In)을 포함한다. 이와 관련하여, 황화물계 고체전해질 재료는 황화물계 고체전해질 물질의 원료 시작 물질(예를 들면, Li2S, P2S5, 등)을 용융 담금질법(melt quenching method), 기계적 밀링법 등에 의해 처리함으로써 제조될 수 있다.

[0158] In addition, a calcination process may be performed after the above treatment. The sulfide-based solid electrolyte may be amorphous, crystalline, or a mixture thereof.

[0159] Polymer solid electrolytes are electrolytes that, for example, contain a mixture of a lithium salt and a polymer, or contain a polymer having ion-conducting functional groups. Polymer solid electrolytes are, for example, polymer electrolytes that do not contain a liquid electrolyte. The polymers included in the polymeric solid electrolyte are, for example, polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyethylene oxide (PEO), poly(styrene-b-ethylene oxide) block copolymer (PS-PEO), poly(styrene-butadiene), poly(styrene-isoprene-styrene), poly(styrene-b-divinylbenzene) block copolymer, poly(styrene-ethylene oxide-styrene) block copolymer, polystyrene sulfonate (PSS), polyvinyl fluoride (PVF), poly(methylmethacrylate) (PMMA), polyethylene glycol (PEG), polyacrylonitrile (PAN), polytetrafluoroethylene (PTFE), polyethylenedioxythiophene (PEDOT), polypyrrole (PPY), polyacrylonitrile (PAN), Polyaniline, Polyacetylene, Nafion, Aquivion, Flemion, Gore, Aciplex, Morgane ADP, Sulfonated poly, (ether ether ketone)(sulfonated poly(ether ether ketone), SPEEK), Sulfonated poly(arylene ether ketone sulfone)(sulfonated poly(aryl ether ketone, SPAEK), Poly[bis(benzimidazobenzisoquinolinones)](poly[bis(benzimidazobenzisoquinolinones)], SPBIBI), Poly(styrene sulfonate)(Poly(styrene sulfonate), PSS), Lithium 9,It may be 10-diphenylanthracene-2-sulfonate (lithium 9,10-diphenylanthracene-2-sulfonate, DPASLi+) or a combination thereof, but is not limited thereto; any that is used as a polymer electrolyte in the relevant technical field is acceptable. Any lithium salt that can be used as a lithium salt in the relevant technical field is acceptable. Examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, LiAlO2, LiAlCl4, LiN(C, x F 2x+1 SO2)(C y F 2y+1 SO2)(x and y are each 1 to 20), LiCl, LiI, or mixtures thereof, etc.

[0160] A gel electrolyte is, for example, a gel polymer electrolyte. A gel polymer electrolyte is an electrolyte that includes, for example, a liquid electrolyte and a polymer, or includes an organic solvent and a polymer having ion-conducting functional groups. The liquid electrolyte may be, for example, an ionic liquid, a mixture of a lithium salt and an organic solvent, a mixture of an ionic liquid and an organic solvent, or a mixture of a lithium salt, an ionic liquid, and an organic solvent. The polymer may be selected from among the polymers used in solid polymer electrolytes. The organic solvent may be selected from among the organic solvents used in liquid electrolytes. The lithium salt may be selected from among the lithium salts used in solid polymer electrolytes. An ionic liquid refers to a salt in a liquid state at room temperature or a room temperature molten salt that has a melting point below room temperature and consists solely of ions. The ionic liquid comprises, for example, a) one or more cations selected from ammonium, pyrrolidinium, pyridinium, pyrimidinium, imidazolium, piperidinium, pyrazolium, oxazolium, pyridazinium, phosphonium, sulfonium, triazolium, and mixtures thereof, and b) BF4 - , PF6 - , AsF6 -, SbF6 - , AlCl4 - , HSO4 - , ClO4 - , CH3SO3 - , CF3CO2 - , Cl - , Br - , I - , BF4 - , SO4 - , CF3SO3 - , (FSO2)2N - , (C2F5SO2)2N - , (C2F5SO2)(CF3SO2)N - , and (CF3SO2)2N - It may include one or more compounds selected from those containing one or more anions selected from among. A gel polymer electrolyte may be formed by impregnating the polymer solid electrolyte into the electrolyte within a lithium battery. The gel electrolyte may further include inorganic particles.

[0161] Examples

[0162] A composition for forming a composite layer was prepared by ultrasonically dispersing h-BN particles and Denka black particles in an NMP solvent, and then adding the resulting mixture to an NMP (N-Methyl-2-Pyrrolidinone) solution in which a copolymer of PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene) was dissolved. The composition was mixed using a roller to prepare a dispersion in which the h-BN particles and Denka black particles were evenly dispersed in PVDF-HFP.

[0163] Based on 100 wt% of the composition for forming a composite layer excluding the solvent, Denka black nanoparticles (particle size 40 nm) were prepared at 5 wt%, h-BN nanoparticles at 5 wt%, and PVDF-HFP at 90 wt%. The total weight of the NMP solvent used in the preparation as above was approximately 5 times the weight of the composition for forming a composite layer excluding the solvent.

[0164] The above-described dispersion was coated onto a copper thin film, which is a cathode current collector, using a doctor blade method, and then dried at 130°C (vacuum oven) to produce a cathode.

[0165] An anode composition was obtained by mixing LiCoO2, a conductive material (Super-P; Timcal Ltd.), polyvinylidene fluoride (PVDF), and N-methylpyrrolidone. The weight ratio of LiCoO2, the conductive material, and PVDF in the anode composition was 97:1.5:1.5. The anode composition was coated onto an aluminum foil (thickness: about 15 μm) and dried at 25 °C, and then the dried product was dried under vacuum at about 110 °C to produce an anode.

[0166] A liquid electrolyte was prepared by mixing 0.4M LiTFSI, 0.6M LiBOB, ethylene carbonate, and ethylmethyl carbonate in a 3:7 volume ratio. A negative electrode-free lithium secondary battery was manufactured by placing a positive electrode on top of a negative electrode and then impregnating it with the liquid electrolyte.

[0167] Comparative example

[0168] A cathode-free lithium secondary battery was manufactured by following the same method as in Example 1, except that the h-BN particles were excluded when manufacturing the composite layer of the cathode in the example.

[0169] Evaluation Example 1: Charge / Discharge Characteristics

[0170] For the anode-free lithium secondary battery prepared according to the examples and comparative examples, constant current charging was performed at 25°C at a current rate of 0.2C until the voltage reached 4.30V (vs. Li), and then cut-off was performed at a current rate of 0.05C while maintaining 4.30V in constant voltage mode. Subsequently, during discharge, the battery was discharged at a constant current rate of 0.5C until the voltage reached 2.8V (vs. Li) (formation stage, 1st cycle). This charge-discharge process was performed two more times to complete the formation process.

[0171] A lithium secondary battery that has undergone the formation stage was charged at a constant current of 0.2C at room temperature (25℃) in a voltage range of 3.0 to 4.4 V relative to lithium metal, and then discharged at a constant current of 0.72mA at 0.2C until a cut-off voltage of 4.4V was reached.

[0172] The charge and discharge process described above was repeated a total of 100 times. The results of measuring the capacity retention rate during 100 charge and discharge cycles are shown in Fig. 11.

[0173] Figure 11 is a graph evaluating the lifespan and capacity characteristics of a lithium secondary battery according to Figure 8.

[0174] Figure 11 shows the change in capacity according to the number of cycles of a negative electrode lithium secondary battery manufactured according to the examples and comparative examples.

[0175] Referring to Fig. 11, it can be seen that the capacity retention rate of the example is higher than that of the comparative example starting from about 30 cycles. Specifically, the capacity retention rate of the lithium secondary battery at 100 cycles was about 0.5% for the comparative example, while it was about 31.7% for the example.

[0176] Through this, it was confirmed that when a composite layer according to one embodiment of the present disclosure is included in the negative electrode, the capacity characteristics and charge / discharge life characteristics are excellent. This is understood to be because electron transfer between carbon nanoparticles is significantly blocked due to the h-BN nanoparticles dispersed in the composite layer, thereby preventing the phenomenon where lithium is electrodeposited on the upper part of the composite layer or on the carbon layer inside the composite layer during charging, and lithium is uniformly electrodeposited on the lower part of the composite layer, that is, on the negative electrode current collector, thereby increasing the life characteristics of the battery. In addition, due to the composite layer in which h-BN is dispersed, the dead volume of lithium formed as lithium dendrites grow on the lithium metal thin film is reduced, and it can be confirmed that the battery capacity of the example is higher than that of the comparative example.

[0177] FIGS. 12a and 12b are SEM images showing cross-sections of lithium metal layers in the comparative example and the example. Referring to FIGS. 12a and 12b, in each SEM image, the lower layer (indicated as 10.0 μm in the comparative example and 8.0 μm in the example) represents a negative electrode current collector, and a lithium metal layer is placed on the negative electrode current collector, and a composite layer is placed on the lithium metal layer.

[0178] Referring to Fig. 12a, in the comparative example, lithium was electrodeposited loosely. It can be seen that the lithium metal was electrodeposited to a maximum thickness of about 23.5 μm, and numerous lithium dendrites were formed. On the other hand, referring to Fig. 12b, in the example, lithium was electrodeposited densely. It can be seen that the lithium metal layer was electrodeposited densely to a minimum thickness of about 19.5 μm.

[0179] As in the example of FIG. 12b, when the lithium metal layer is densely electrodeposited on the lower part of the composite layer, it means that the proportion of lithium metal electrodeposited on the upper part of the composite layer or the proportion of lithium metal electrodeposited inside the composite layer was small. On the other hand, as in the comparative example of FIG. 12a, when the lithium metal layer is not densely electrodeposited, it means that the proportion of lithium metal electrodeposited on the upper part of the composite layer or the proportion of lithium metal electrodeposited inside the composite layer was large.

[0180] Although the present invention has been described above by limited embodiments and drawings, the present invention is not limited thereto, and it is obvious that various modifications and variations are possible within the scope of the technical spirit of the present invention and the equivalent scope of the claims described below by those skilled in the art to which the present invention belongs.

Claims

1. Cathode current collector; and A composite layer directly disposed on the above-mentioned cathode current collector A negative electrode for a lithium secondary battery, comprising, wherein the composite layer comprises a polymer, carbon nanoparticles, and insulating particles.

2. In Paragraph 1, The above insulating particle comprises at least one of hexagonal boron nitride (h-BN), rhombohedral boron nitride (r-BN), cubic boron nitride (c-BN), or wurtzite boron nitride (w-BN), a negative electrode for a lithium secondary battery.

3. In Paragraph 1, The above polymer is a negative electrode for a lithium secondary battery comprising at least one of PVDF-HFP, PVDF, polyacrylic acid (PAA), polyacrylonitrile (PAN), and polyethylene oxide (PEO).

4. In Paragraph 1, The above carbon nanoparticles comprise at least one of carbon black, CNT (Carbon Nanotube), CNF (Carbon Nanofiber), and graphene, for a negative electrode for a lithium secondary battery.

5. In Paragraph 1, A negative electrode for a lithium secondary battery, wherein the particle size of the carbon nanoparticles is 5 nm or more and 2 μm or less.

6. In Paragraph 5, A negative electrode for a lithium secondary battery, wherein the particle size of the carbon nanoparticles is 10 nm or more and 100 nm or less.

7. In Paragraph 1, The above insulating particles and the above carbon nanoparticles are dispersed within the polymer, forming a negative electrode for a lithium secondary battery.

8. In Paragraph 1, A negative electrode for a lithium secondary battery, wherein the thickness of the above composite layer is 0.1 μm or more and 30 μm or less.

9. In Paragraph 1, A negative electrode for a lithium secondary battery, wherein the thickness of the above composite layer is 1 μm or more and 5 μm or less.

10. In Paragraph 1, The above insulating particles are in an amount of 0.01 wt% or more and 10 wt% or less based on the total weight of the composite layer, for a negative electrode for a lithium secondary battery.

11. Cathode current collector; A lithium metal layer disposed on the above-mentioned negative current collector; and A composite layer disposed on the above lithium metal layer A negative electrode for a lithium secondary battery, comprising, wherein the composite layer comprises a polymer, carbon nanoparticles, and insulating particles.

12. In Paragraph 11, The above insulating particles comprise at least one of hexagonal boron nitride (HBN), rhombohedral boron nitride (RBN), cubic boron nitride (CBN), or wurtzite boron nitride (WBN), a negative electrode for a lithium secondary battery.

13. In Paragraph 11, The above polymer is a negative electrode for a lithium secondary battery comprising at least one of PVDF-HFP, PVDF, polyacrylic acid (PAA), polyacrylonitrile (PAN), and polyethylene oxide (PEO).

14. In Paragraph 11, The above carbon nanoparticles comprise at least one of carbon black, CNT (Carbon Nanotube), CNF (Carbon Nanofiber), and graphene, for a negative electrode for a lithium secondary battery.

15. In Paragraph 11, The above insulating particles and the above carbon nanoparticles are dispersed within the polymer, forming a negative electrode for a lithium secondary battery.

16. Anode; The cathode according to claim 1; and Electrolyte disposed between the anode and the cathode A lithium secondary battery including 17. In Paragraph 16, A lithium secondary battery comprising at least one of the insulating particles, which are hexagonal boron nitride (h-BN), rhombohedral boron nitride (r-BN), cubic boron nitride (c-BN), or wurtzite boron nitride (w-BN).

18. In Paragraph 16, The above polymer comprises at least one of PVDF-HFP, PVDF, polyacrylic acid (PAA), polyacrylonitrile (PAN), and polyethylene oxide (PEO), forming a lithium secondary battery.

19. In Paragraph 16, The above carbon nanoparticles comprise at least one of carbon black, CNT (Carbon Nanotube), CNF (Carbon Nanofiber), and graphene, forming a lithium secondary battery.

20. In Paragraph 16, A lithium secondary battery in which the insulating particles and carbon nanoparticles are dispersed within the polymer.

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