Composite anode for lithium secondary battery and lithium secondary battery comprising same

Abstract

The present invention relates to a composite anode comprising a composite anode material composed of graphite, silicon, carbon particles, and silver nanowires, and a lithium secondary battery comprising same, wherein a solid network is formed using silver nanowires, and the network fixes graphite, silicon, and carbon particles to prevent structural changes due to the expansion of silicon while maintaining pores, thereby enhancing discharge capacity, lifespan, and capacity retention rate of the lithium secondary battery through a large diameter.

Description

Composite cathode for lithium secondary battery and lithium secondary battery containing the same

[0001] The present invention relates to a composite negative electrode for a lithium secondary battery comprising graphite, silicon, carbon particles and silver nanowires, and a lithium secondary battery comprising the same.

[0002] Automakers are focusing on developing fuel cell and electric vehicles (FCEVs) in response to stricter carbon dioxide emission regulations and mandatory annual sales mandates for zero-emission vehicles. For electric vehicles, they aim to use high-energy-density lithium-ion batteries to achieve a driving range of approximately 500 km on a single charge, comparable to that of conventional internal combustion engines.

[0003] The main technical goal of the next-generation lithium-ion battery development is 300-350 Wh kg, also known as the theoretical limit capacity. -1 The goal is to secure this capacity, and the development of new electrode materials is urgently needed. Silicon-based materials are gaining attention as a potential replacement for the existing graphite materials used as cathode materials.

[0004] Silicon has a theoretical specific capacity of 372 mAh g -1 Compared to graphite, it can secure a high capacity of about 10 times more, and has the advantage of improved charging and discharging speed because lithium ion insertion is faster.

[0005] However, after lithiation, silicon undergoes a volume expansion of approximately 300% of its initial size in the {110} plane of silicon, which destroys silicon particles and causes the electrode structure to collapse more rapidly due to internal stress.

[0006] To address these issues, various particle structures are being studied, including hollow silicon, core / shell silicon applied simultaneously, and a yoke / shell structure in which silicon can expand between a carbon shell and a silicon core.

[0007] Ultimately, to commercialize 100% pure silicon anodes or graphite / silicon composite electrodes containing more than 5% silicon, the volume expansion characteristics described above must be controlled. Alternatively, if lithium ion and electron conduction are maintained during charge and discharge cycles, thereby preserving the performance and lifespan of the silicon anode, then the expansion of the silicon anode can be considered a characteristic of the silicon anode active material.

[0008] Therefore, the present invention aims to develop and provide an electrode structure capable of maintaining electrical conductivity within the electrode even when silicon expands.

[0009] In order to solve the above problems, the present invention aims to provide a composite negative electrode for a lithium secondary battery including graphite, silicon, carbon particles and silver nanowires, and a lithium secondary battery including the same.

[0010] In order to solve the above problems, the present invention provides a composite negative electrode for a lithium secondary battery and a lithium secondary battery including the same.

[0011] Specifically, the composite negative electrode for a lithium secondary battery provided in the present invention may include a composite negative electrode material composed of graphite particles, silicon particles, carbon particles, and silver nanowires.

[0012] The above silicon particles are composed of at least one selected from pure silicon, SiOx, MgxSiyOz (1≤x≤2, 1≤y≤2, 1≤z≤4), and LixSiyOz (2≤x≤4, 1≤y≤2, 3≤z≤5), and the median particle size (D50) may be 1 nm to 50 μm.

[0013] In the above composite cathode, electron transfer may occur through the graphite particles, silicon particles, carbon particles, and silver nanowires.

[0014] The above silver nanowires may form a structure surrounding the graphite particles, silicon particles, and carbon particles.

[0015] The above silver nanowires may intersect at three or more different points to form a mesh or network.

[0016] The above composite negative electrode material for a lithium secondary battery may contain 1 to 95 wt% of the graphite.

[0017] The above silicon particles may have an average particle diameter of 1 nm to 50 μm, and the silicon particles may be at least one selected from pure silicon particles without a surface oxide layer or SiOx having an oxide layer, and may be provided in combination with a composite material that suppresses silicon expansion. The silicon particles referred to in the text below mean a material composed of the above contents unless otherwise specifically stated.

[0018] The above composite negative electrode material for a lithium secondary battery may contain 1 to 100 wt% of the silicon.

[0019] The above composite negative electrode material for a lithium secondary battery may contain 0.1 to 20 wt% of the carbon particles.

[0020] The above silver nanowires may be capped with PVP (polyvinyl pyrrolidone).

[0021] The above silver nanowires may have a diameter of 40 to 60 nm.

[0022] The above silver nanowires may have a length of 20 to 50 μm.

[0023] The above composite negative electrode material for a lithium secondary battery may contain 0.1 to 2 wt% of the silver nanowires.

[0024] The above composite negative electrode material for a lithium secondary battery may have a density of 0.85 to 2.0 g cm-3.

[0025] The present invention provides a method for manufacturing the composite anode for a lithium secondary battery. The method may include the steps of: manufacturing silver nanowires; mixing silver nanowires, graphite, silicon, and carbon powder to manufacture a composite anode material; manufacturing a dispersion using the composite anode material and a binder solution; stirring the dispersion to manufacture an electrode slurry; applying the electrode slurry to a copper foil to manufacture an electrode; and drying the electrode.

[0026] In addition, the present invention provides a lithium secondary battery including the composite negative electrode for a lithium secondary battery.

[0027] The above lithium secondary battery may be one in which a LixAgy alloy is formed on the composite negative electrode for the lithium secondary battery during charging and discharging.

[0028] The composite negative electrode material for lithium secondary batteries in the above lithium secondary batteries may be a composite with a solid electrolyte.

[0029] The above is only an example, and the present invention is not necessarily limited to the above.

[0030] The composite anode for a lithium secondary battery comprising graphite, silicon, carbon particles, and silver nanowires according to the present invention forms a network with silver nanowires, thereby reducing charge and capacity resistance and thus significantly accelerating electron transfer (transfer). In addition, it provides an additional buffer space capable of accommodating volume changes in silicon, thereby having a microstructure with high electrical conductivity even when silicon expands. Furthermore, it forms a thermodynamically stable phase during lithiation and delithiation processes, and has the effect of uniformly causing lithium deposition and exfoliation and suppressing dendrite formation.

[0031] Figure 1 is a schematic diagram of a composite cathode provided in the present invention.

[0032] Figure 2 is a TEM (Transmission Electron Microscope) image of a silver nanowire.

[0033] Figure 3 is a SEM (Scanning Electron Microscope) photograph of the composite cathode.

[0034] Figure 4 is an SEM photograph of the surface and cross-section of a graphite electrode that was not calendered.

[0035] Figure 5 is a photograph confirming the breakage of silver nanowires during high-shear centrifugal mixing of electrode slurry.

[0036] Figure 6 shows surface photographs of artificial graphite and natural graphite and charge / discharge curves of a half-cell containing them, respectively.

[0037] Figure 7 shows the charge / discharge curves and CV (Cyclic Voltammetry) results of Manufacturing Examples 5 and 6.

[0038] Figure 8 shows the charge / discharge curves and CV results of Manufacturing Examples 7 and 8.

[0039] Figure 9 shows the CV results of Manufacturing Examples 7 and 8.

[0040] Figure 10 shows the results of calculating the thermodynamic formation energy of a binary system.

[0041] Figure 11 shows the results of calculating the thermodynamic production energy of a ternary system.

[0042] Figure 12 is a photograph of the surface of a composite cathode taken using SEM as charging and discharging progressed.

[0043] Figure 13 shows the results of measuring the electrochemical performance of a half-cell using the composite cathode of the present invention.

[0044] Hereinafter, a composite anode for a lithium secondary battery including graphite, silicon, carbon particles, and silver nanowires according to the present invention and a lithium secondary battery including the same will be described in detail. The drawings introduced below are provided as examples so that the spirit of the present invention can be sufficiently conveyed to those skilled in the art. Therefore, the present invention is not limited to the drawings presented below and may be embodied in other forms, and the drawings presented below may be illustrated in an exaggerated manner to clarify the spirit of the present invention. At this time, unless there is a different definition for the technical and scientific terms used in the present invention, they have the meaning commonly understood by a person of ordinary skill in the art to which this invention belongs, and a description of well-known functions and configurations that may unnecessarily obscure the gist of the present invention in the following description and the accompanying drawings will be omitted.

[0045]

[0046] The present invention aims to provide a composite negative electrode for a lithium secondary battery and a lithium secondary battery including the same.

[0047] The composite anode for the lithium secondary battery includes graphite particles, silicon particles, carbon particles, and silver nanowires, wherein the silicon particles include pure silicon particles without a surface oxide layer and SiO having an oxide layer. x It may be one or more of the selected ones, and may be provided in combination with a composite material that suppresses silicone expansion. The silicon particles mentioned in the text mean a material composed of the above contents unless otherwise specified.

[0048] At this time, the composite material that suppresses the expansion of silicon as described above is specifically Mg x Si y O z (1≤x≤2, 1≤y≤2, 1≤z≤4), Li x Si y O z(1≤x≤8, 1≤y≤3, 0≤z≤5) may be composed of at least one selected from the group consisting of: (1≤x≤8, 1≤y≤3, 0≤z≤5). In the composite anode for a lithium secondary battery provided in the present invention, the silicon directly combines with lithium to form an amorphous lithium silicate (c-Si+xLi→a-Li) from crystalline silicon (c-Si). x After delithiation, the crystalline silicon is transformed into amorphous silicon (a-Si). Here, as the volume of the crystalline silicon is greatly expanded as it transforms into the amorphous lithium silicate, the average particle diameter of the silicon may preferably be 5 to 100 nm or 1 to 10 μm.

[0049] The above silicon particles may have a medium particle size (D50) of 1 nm to 50 μm.

[0050] The above graphite particles have a median particle size (D50) of 10 to 15 μm, and the above carbon particles have a median particle size of 15 to 30 nm and a specific surface area of ​​100 to 1600 m 2 g -1 It may be composed of human particles.

[0051] In addition, electron transfer may occur through the graphite particles, silicon particles, carbon particles, and silver nanowires. The electron transfer described above means that when the composite anode is applied to a lithium secondary battery, the graphite particles, silicon particles, carbon particles, and silver nanowires become direct conductors. This characteristic is because the silver nanowires surround the graphite, silicon, and carbon particles, thereby acting as electrical passages.

[0052] In addition, the silver nanowires intersect each other at three or four or more different points to form a mesh or network, thereby preventing physical detachment of the graphite particles, silicon particles, and carbon particles.

[0053] In order to achieve the above-described shape, the diameter of the silver nanowires can be adjusted in consideration of the size of the silicon particles. Specifically, it is preferable to adjust the diameter to 5 nm or more per 1 μm of the silicon particle diameter, and this ratio can be adjusted in consideration of the medium particle size of the silicon or the size of the primary particles. If the diameter of the silver nanowires is smaller than the medium particle size of the silicon, the silver nanowires may be embedded in the silicon particles and may not form a solid network.

[0054] The above graphite particles may be composed of artificial graphite or natural graphite in the form of flakes or spheres. In this case, the artificial graphite particles in the form of flakes can be uniformly and thinly coated on a copper foil during the manufacture of a composite anode, and have a very high orientation, such that the basal plane of the graphite is exposed in the direction in which the current flows, and the edge planes are exposed in the vertical direction. In this case, considering that lithium ions are inserted into the graphene layer through the edge planes of the graphite, the initial charge / discharge efficiency may be poor because it has an elongated and irregular morphology and the electrode cross-sections are randomly stacked.

[0055] However, this morphology allows for efficient electron transfer at high speeds by aligning specific parts of the particles in a way that exposes the surface of the edge face in the direction of current flow. Therefore, although the artificial graphite as described above may have a large difference in initial charge / discharge efficiency and discharge capacity from natural graphite, in the present invention, since silicon and silver nanowires store lithium together with graphite, the lithium storage ability of graphite is not very important. In other words, artificial graphite is superior in terms of the efficiency of electron transfer as described above, and since the orientation is high and controllable during the material production stage is easy, it is preferable to use artificial graphite in the present invention.

[0056] The composite anode material for the lithium secondary battery may contain 1 to 95 wt% of the graphite particles. At this time, the ratio of the graphite particles and the silicon particles in the composite anode material may be determined by considering at least one of the degree of expansion of silicon, lithium storage capacity, discharge capacity, or charge speed. At this time, if the ratio of the graphite particles is too high and the silicon content is low, the charge / discharge capacity may be low, and the effect of improving the charge speed may be minimal. In addition, if the silicon particle content is too high, it may be difficult to control the volume change of silicon that occurs during charge / discharge.

[0057] If the median particle size of the above-mentioned silicon particles is larger than the above-mentioned range, the crystalline silicon may expand as it is lithiated, filling the pores within the composite anode and further changing the volume of the composite anode. In this case, if the volume of the silicon decreases as the composite anode is subsequently delithiated, contact between graphite, silicon, carbon, and silver nanowires within the composite anode may be lost, which is undesirable.

[0058] In addition, if the median particle size of the silicon particles is smaller than the above range, they may come into contact with graphite and block the pores of the graphite, which may significantly reduce the charge and discharge capacities of the composite anode, and the fixing effect of the mesh or network structure formed by the silver nanowires may be minimal. In this case, as described above, the ratio of the size of the silicon and the diameter of the silver nanowires must be additionally adjusted.

[0059] The above composite anode material for a lithium secondary battery may contain 1 to 100 wt% of the silicon particles. At this time, if the content of the silicon particles is very high, for example, 80 wt% or more, the silicon particles may expand excessively during lithiation, which may shorten the lifespan of the composite anode material. Therefore, it is preferable that the silicon content is 1 to 10 wt%, and if the content is lower than the above range, the charge / discharge capacity of the composite anode material may be significantly reduced. However, an anode active material composed of 100% silicon may be used by using silicon particles complexed with a composite material that suppresses the expansion of silicon.

[0060] At this time, since the complex material is as described above, redundant description is omitted.

[0061] The composite anode material for the lithium secondary battery may contain 0.1 to 20 wt% of the carbon particles. The carbon particles function as a conductive material or as an active material for storing and releasing lithium, and any known material that can be used as a conductive material, such as carbon black, channel black, furnace black, Denka black, or super p, may be used without limitation.

[0062] The above silver nanowires may be capped with PVP (Polyvinyl Pyrrolidone). The reason for capping the silver nanowires with PVP is to prevent oxidation of silver, thereby preventing additional irreversible capacity that may occur during the charging process, and to prevent entanglement and aggregation between nanowires. The method for capping silver nanowires with PVP will be described later in the method for manufacturing a composite anode. Here, PVP may be capped in an amount of 1 to 5 wt% relative to the weight of the silver nanowires.

[0063] The above silver nanowires may have a diameter of 40 to 60 nm and a length of 20 to 50 μm. The present invention forms a network with the silver nanowires to secure graphite, silicon, and carbon particles. Since a large shear stress is generated in the composite anode material during the manufacturing process of the composite anode, it is preferable to adhere to the diameter and length as described above in order to prevent breakage of the silver nanowires. If the diameter of the silver nanowires is smaller than the above range, breakage may occur during mixing of the composite anode material, and if it is larger than the above range, the effect of securing silicon particles with a smaller average particle diameter to the network may be reduced. In addition, if the length of the silver nanowires is shorter than the above range, there is a problem that the length becomes shorter than the internal pore length of the electrode, making it impossible to connect the pores inside the graphite, and if it is longer than the above range, there is a problem that there is a high possibility of breakage due to the generation of the above shear stress.

[0064] The above composite anode material for a lithium secondary battery may contain 0.1 to 2 wt% of the silver nanowires. By including the silver nanowires within this range, a solid network can be formed within the composite anode material, and the network can withstand expansion of silicon due to lithiation without collapsing, and the network can remain solid even when delithiated.

[0065] The above composite anode material for lithium secondary batteries has a density of 0.85 to 2.0 g cm -3 It can be. At this time, preferably 0.85 to 1.0 g cm -3 , more preferably 0.85 to 0.90 g cm -3It may be. The composite anode of the present invention may not perform a separate calendering process to increase the electrode density. Conventional electrodes increase the electrode density through this process to promote contact between electrode materials and increase power density. However, in the present invention, silicon particles may be detached during the calendering process, and the silicon particles may expand when the battery is later charged, so maintaining the voids is very important. Therefore, in order to secure sufficient voids while maintaining electrical contact between the graphite and silicon particles, it is preferable not to perform calendering.

[0066] The present invention provides a method for manufacturing the composite anode for a lithium secondary battery. The method may include the steps of: manufacturing silver nanowires; mixing silver nanowires, graphite, silicon, and carbon powder to manufacture a composite anode material; dispersing the composite anode material in a binder solution; stirring the dispersion to manufacture an electrode slurry; applying the electrode slurry to a copper foil to manufacture an electrode; and drying the electrode.

[0067] The step of manufacturing the above silver nanowires may include dissolving PVP (Polyvinyl pyrrolidone) in a mixture of ethylene glycol and polyethylene glycol, adding potassium bromide, ammonium chloride, and silver nitrate to the mixture, and performing heat treatment. At this time, the heat treatment is preferably performed at 150 to 180°C for 2 to 4 hours. Here, as described above, PVP may be capped to the silver nanowires.

[0068] In the step of preparing an electrode slurry by stirring the above dispersion, this may be performed by centrifugal mixing, and the RPM (round per minute) may be 1500 to 2000. More specifically, the RPM may be controlled within a range of 400 to 500 in which the centrifugal force (Centrifugal G-Force) calculated by the following formula is calculated.

[0069] [Calculation formula]

[0070] G=g×RPM×r

[0071] Here, G is the centrifugal force, g is the acceleration due to gravity, and r is the diameter of the rotating plate.

[0072] In addition, the present invention provides a lithium secondary battery including the composite negative electrode for a lithium secondary battery.

[0073] The above lithium secondary battery has Li in the composite negative electrode for the lithium secondary battery during charge and discharge. x Ag y An alloy may be formed. Conventional lithium secondary batteries only use carbon-based materials such as graphite or silicon-based materials as negative electrode active materials, but in the present invention, electronic conduction occurs through silver nanowires, and lithium ions are reduced on the surface of the silver nanowires to form Li x Ag y Lithium can be stored by forming an alloy. At this time, the Li x Ag y Alloy is 0 <x≤10, 0<y≤5, x와 y의 비율이 1:0.2 내지 3.0일 수 있고, 바람직하게는 x와 y의 비율이 1:0.625 내지 1.000일 수 있다.

[0074] The above lithium secondary battery may further include a positive electrode; an electrolyte; and a separator.

[0075] The above positive electrode may be composed of a positive electrode material; a binder; a conductive material; and a current collector.

[0076] The above cathode material can be used without limitation as long as it is a material commonly used as a cathode material for lithium secondary batteries. For example, the above cathode material may be LiCoO2, LiMnO2, LiNiO2LiMn2O4, LiNi 1-x Co x O2, LiNi x Co y Mn z O2(x+y+z=1), LiNi x Co yAl z O2(x+y+z=1), LiNi x Mn y M z O2(x+y+z=1, M is a divalent or trivalent metal or transition metal), LiFePO4, LiMnPO4, and Materials such as LiCoPO4 can be cited, but this is only an example and is not necessarily limited to them.

[0077] The above binder provides adhesion between the positive electrode material, the conductive material, and the current collector, and specific examples thereof include polyvinylidene fluoride (PVdF), polyimide (PI), fluoropolyimide (FPI), polyacrylic acid (PAA), polyvinyl alcohol (PVA), carboxymethylcellulose (CMC), polyvinylpyrrolidone (PVP), tetrafluoroethylene (PTFE), polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated ethylene-propylene-diene polymer (S-EPDM), styrene-butadiene rubber (SBR), or copolymers thereof, and any one or more selected from these may be used, but this is merely an example and is not necessarily limited thereto.

[0078] The above conductive material is used to provide conductivity to the electrode, and is chemically stable and electronically conductive. Specific examples thereof include carbon-based materials such as graphite, carbon black, super py, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, carbon fibers, carbon nanotubes, carbon nanowires, graphene, graphitized mesocarbon microbeads, fullerenes, and amorphous carbon; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives. One or a mixture of two or more of these may be used, but this is merely an example and is not necessarily limited thereto.

[0079] The above-mentioned positive electrode current collector provides an electrical path between the positive electrode active material and the power source, and may be made of aluminum processed into a shape such as aluminum foil or aluminum mesh.

[0080] The above electrolyte may be composed of a lithium salt and a mixed organic solvent containing the same, a polymer matrix, or an all-solid electrolyte.

[0081] The above lithium salt may be one or a mixture of two or more selected from the group consisting of LiPF6, LiClO4, LiAsF6, LiBF4, and LiSbF6, which are known in the art, but this is only an example and is not necessarily limited thereto.

[0082] The above mixed organic solvent may be any one or a mixture of two or more selected from the group consisting of cyclic carbonates such as ethylene carbonate, propylene carbonate, and vinylene carbonate; the group consisting of fluorinated cyclic carbonates such as fluoroethylene carbonate, difluoroethylene carbonate, and fluoropropylene carbonate; and the group consisting of linear carbonates such as dimethyl carbonate, methylethyl carbonate, and diethyl carbonate, but is not necessarily limited thereto.

[0083] The concentration of the electrolyte composed of a mixed organic solvent including the lithium salt can be adjusted to a level commonly used in the art, and specifically, for example, the concentration of the lithium salt can be 0.1 to 60 M, more preferably 0.5 to 2 M.

[0084] The above mixed organic solvent may further include additives as known in the art.

[0085] In addition, the polymer matrix may be any one selected from the group consisting of polymers or copolymers thereof, such as polyacrylate, polymethacrylate, polyethylene oxide, polypropylene oxide, etc., which are well known and widely used in the art, but are not necessarily limited thereto.

[0086] The above polymer matrix may include crosslinking units for crosslinking with each other.

[0087] The above-mentioned all-solid-state electrolyte is a composite of the polymer matrix and the lithium salt, and is in the form of a mixture thereof. The components constituting the composite are the same as those of the polymer matrix and lithium salt described above, so a duplicate description is omitted.

[0088] The above-mentioned separation membrane can be used without any particular limitation as is commonly used in the art. Specific examples thereof include porous polyolefin films such as polyethylene and polypropylene; nonwoven fabrics made of polymer fibers such as polyacrylate and polyacrylonitrile; and porous polyolefin films coated with ceramic.

[0089] However, if the electrolyte described above contains a polymer and thus has a film form and has properties that can separate the positive and negative electrodes, the separator may not be included.

[0090] The composite negative electrode material for lithium secondary batteries in the above lithium secondary batteries may specifically mean a composite material with a solid electrolyte. Here, the composite material means that the solid electrolyte is distributed between the primary or secondary particles of the composite negative electrode material.

[0091] In the case of lithium secondary batteries using a conventional solid electrolyte, the solid electrolyte is located between the positive and negative electrodes, making it difficult to transfer lithium ions, and there were limitations such as high interfacial resistance between the electrodes and the electrolyte. However, by composited as described above, contact with the electrodes is improved, and battery performance can be greatly improved.

[0092]

[0093] Hereinafter, the composite anode for a lithium secondary battery according to the present invention and the lithium secondary battery including the same will be described in more detail through examples. However, the following examples are merely references for explaining the present invention in detail, and the present invention is not limited thereto, and may be implemented in various forms.

[0094] Additionally, unless otherwise defined, all technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein is solely for the purpose of effectively describing specific embodiments and is not intended to limit the invention. Furthermore, the unit of additives not specifically described in the specification may be weight percent.

[0095]

[0096] 1. Manufacturing and analysis of composite cathode materials

[0097] [Manufacturing Example 1]-Synthesis of silver nanowires

[0098] 1.3 g of PVP (Polyvinyl pyrrolidone, K30, average molecular weight 40,000, Samchun Chemical, Korea) was dissolved in a solution of 400 mL of ethylene glycol (EG) and 300 mL of polyethylene glycol (PG). Then, potassium bromide (KBr, ACS reagent, Aldrich, USA) and ammonium chloride (NH4Cl, ACS reagent, Aldrich, USA) were added at concentrations of 300 μm and 600 μm, respectively, and 7.5 g of silver nitrate (AgNO3, ACS reagent, Aldrich, USA) was added and heat-treated at 160°C for 3 h. Next, the amount of residual PVP, except for the PVP covering the {110} plane of the silver nanowires, was adjusted by washing with acetone. Finally, 10 mg mL of silver nanowires were added. -1 A silver nanowire dispersion was synthesized by dispersing it in ultrapure water at a concentration of .

[0099]

[0100] [Manufacturing Examples 2-4]- Silver Nanowire Synthesis

[0101] Silver nanowires were synthesized in the same manner as in Manufacturing Example 1, but the concentrations of potassium bromide and ammonium chloride and the heat treatment time were adjusted as shown in Table 1 below.

[0102]

[0103] Typically, silver nanowires, which are used as transparent electrodes in optoelectronic devices such as touch displays, are synthesized to be thinner (< 20 nm) and longer (> 20 μm) to exhibit invisible properties (transmittance > 88%) along with excellent electrical conductivity (40 μsq-1).

[0104] However, in order to form the structure of the composite anode for a lithium secondary battery of the present invention as shown in Fig. 1, the diameter and length of the silver nanowires were adjusted as shown in Table 1. Afterwards, 100 samples were collected for each synthetic design through TEM analysis, and the diameter and length were measured using Digital Micrograph software (Gatan, Ametek, USA).

[0105] Design valueMeasured valueDiameter (nm)Length (㎛)Diameter (nm)Length (㎛)Manufacturing example 1301031±313±3Manufacturing example 2202025±321±3Manufacturing example 3402045±321±3Manufacturing example 4503050±326±3

[0106] To characterize the effects of the diameter and length of silver nanowires on the microstructure and morphology of composite cathodes using Manufacturing Examples 1 to 4, composite cathodes with a robust conductive network structure were fabricated using spherical conductive carbon particles (0D nanostructure), silver nanowires (1D nanostructure), and irregularly shaped artificial graphite (3D nanostructure). As shown in Figs. 2 and 3, considering the size of the pores formed inside the electrode, the length of the silver nanowires was used to be 25 μm or longer. This is because if the length of the silver nanowires is shorter than 25 μm, it becomes shorter than the size of the internal pores of the electrode, and thus cannot connect the pores inside the graphite.

[0107] When the diameter of the silver nanowires is smaller than the size of the silicon particles used in the manufacture of the cathode material, the silver nanowires may be embedded in the silicon particles and fail to form a solid network due to the length effect of the conductive carbon particles and the silver nanowires.

[0108] As a result of performing high-shear centrifugal mixing to prepare an electrode slurry using the silver nanowires manufactured as described above, it can be confirmed that some of the silver nanowires are broken, as shown in Fig. 5. Therefore, it was concluded that in order to prevent breakage of silver nanowires, it is advisable to synthesize nanowires with a diameter of 40 nm or more and a length of 25 μm or more.

[0109] Therefore, it was confirmed that Manufacturing Example 4, in which the diameter was 50 nm or more to prevent breakage of the silver nanowire and the length was 25 μm or more to electrically connect the graphite pores, was the optimal condition for forming a robust network, and all subsequent measurements were evaluated using Manufacturing Example 4.

[0110]

[0111] [Manufacturing Example 5] - Synthesis of composite cathode (micron-sized silicon)

[0112] 1.76 mg of artificial graphite (LKB-G, D50=13 μm, ShanShan Technology, China), 0.1 mg of silicon powder (crystalline, average particle size 5 μm, Thermo Scientific, USA), 0.04 mg of carbon particles (Li435, Denka, Japan), and 2 g of the silver nanowire dispersion (solid content 1 wt%) of Preparation Example 4 were dispersed in an SBR / CMC binder. The mixture was then mixed for 20 minutes using a centrifugal mixer (ARE-310, THinky Mixer, Japan) to form an electrode slurry. The electrode slurry was coated on a copper foil using a doctor blade coating method to a thickness of 150 μm and dried under vacuum at 110°C for 12 hours.

[0113]

[0114] [Manufacturing Example 6] - Synthesis of composite cathode (nano-sized silicon)

[0115] All processes were performed in the same manner as in Manufacturing Example 5, but the average particle size of the silicon powder was adjusted to 50 nm to manufacture the electrode.

[0116]

[0117] [Manufacturing Example 7] - Synthesis of composite cathode (micron-sized silicon, excluding silver nanowires)

[0118] All processes were performed in the same manner as in Manufacturing Example 5, but silver nanowires were not included.

[0119]

[0120] [Manufacturing Example 8] - Synthesis of a composite cathode (excluding nano-sized silicon and silver nanowires)

[0121] All processes were performed in the same manner as in Manufacturing Example 5, but the average particle diameter of the silicon powder was adjusted to 50 nm and silver nanowires were not included.

[0122]

[0123] Referring to FIG. 3, the microstructures of Manufacturing Example 5 (micron-sized silicon particles (average particle diameter: 5 ㎛)) and Manufacturing Example 6 (nano-sized silicon particles (average particle diameter: 50 nm)) can be confirmed.

[0124] In the case of Manufacturing Example 5 (a, b in Fig. 3), it can be confirmed that silicon particles are attached around the graphite particles, and carbon particles are formed on the graphite and silicon surfaces. This phenomenon occurs due to the size of each particle used, regardless of the order in which the particles are mixed.

[0125] In addition, silver nanowires have a microstructure that surrounds graphite, silicon, and carbon surfaces in a mesh form, and this network structure is greatly affected by the concentration of silver nanowires in the slurry, and when the concentration of silver nanowires is much higher than the critical concentration at which silver nanowires penetrate, a randomly arranged network structure with high density and high electrical conductivity can be exhibited.

[0126] On the other hand, when the concentration of silver nanowires is lower than the above-mentioned critical concentration, the silver nanowires are not connected to each other and thus cannot form an electrically conductive network structure.

[0127] In addition, although the length of the silver nanowires may be shorter than the size of the largest graphite in the electrode material, they should be formed to a size that can wrap around the graphite (25 μm or more) in order to form a randomly arranged network structure as described above.

[0128] In addition, in the case of Manufacturing Example 6 (c, d in Fig. 3), silver nanowires were able to cover the surfaces of graphite, carbon, and silicon, and when nano-sized silicon was used, a microstructure was exhibited in which silver nanowires were partially covered by silicon and carbon.

[0129]

[0130] 2. Electrochemical performance evaluation and analysis

[0131] After analyzing the electrode structure as above, each electrode was cut into a circle with a diameter of 14 mm in a glove box maintained in an argon atmosphere to serve as a working electrode, and lithium foil was cut into a circle of the same size to serve as a counter electrode.

[0132] CR2032 cells were assembled using graphite (372 mAh g) and the charge / discharge performance was evaluated after 12 hours of chemical stabilization. -1 ) and silicon (3,580mAh g -1 ) from the theoretical capacity of 507mAh g to the maximum theoretical capacity -1 It was calculated as follows.

[0133] The electrochemical performance of coin cells including manufacturing examples 5 to 8 was measured in a voltage range of 0.01 to 1.2 V using WBCS3000 (WonAtech, Korea).

[0134] At this time, the charge and discharge are 0.05C (25.35mA g) based on the theoretical capacity mentioned above. -1 ), was performed using the galvanostatic method.

[0135]

[0136] Referring to Fig. 7, Manufacturing Example 7 produced 748.5 mAh g in the first cycle. -1 Charging capacity, 387.2 mAh g -1 The discharge capacity was , the initial charge / discharge efficiency was about 51.7%, and Manufacturing Example 8 was 765.2 mAh g -1 Charging capacity, 391.0mAh g -1 The discharge capacity was shown, and the initial charge / discharge efficiency was approximately 51.1%.

[0137] After that, in the second cycle evaluation, Manufacturing Example 7 had a charging capacity of 393.7 mAh g -1 , discharge capacity is 348.5mAh g -1 , the charge / discharge efficiency was 88.5%, and Manufacturing Example 8 had a charge capacity of 412.9 mAh g -1 , discharge capacity is 385.0mAh g -1, the charge / discharge efficiency was found to be 93.4%.

[0138] In general, when performing electrode coating after manufacturing a slurry, graphite particles in the form of flakes can be uniformly and thinly coated on a copper foil, but have high orientation, with the basal surface of the graphite exposed in the direction in which the current flows and the edge surface exposed in the vertical direction.

[0139] In this case, considering that lithium ions are inserted into the graphene layer through the edges of the graphite, the initial charge / discharge efficiency is poor due to the elongated and irregular morphology and the random stacking of electrode cross-sections. This morphology aligns specific portions of the particles in a way that exposes the surface of the graphite edges in the direction of current flow, enabling efficient electron transfer at high rates.

[0140] Therefore, artificial graphite of irregular shape (density 0.83 g cm -3 ) shows a very large difference in initial charge / discharge efficiency compared to natural graphite with a similar tap density (Fig. 6, a, c) and charge / discharge results (Fig. 6, b, d). In the case of artificial graphite with exposed edge surfaces, the initial charge capacity is approximately 17.6% higher than that of natural graphite.

[0141] However, even if there is no exfoliation of graphite, a thicker SEI (Solid Electrolyte Interface) layer is formed on the edge surface using an ethylene carbonate-based electrolyte, and the SEI layer is formed until the entire graphite is covered. Therefore, since the area of ​​the basal surface is larger in the artificial graphite electrode, more lithium ions are consumed, and the low initial charge / discharge efficiency and high irreversible capacity may be attributed to this.

[0142] More specifically, the irreversible capacity increases as described above because the edges of the graphite are more reactive than the basal planes, and electrolyte decomposition occurs actively between the planes formed by the two graphene layers. This electrolyte decomposition process is Li / Li + This occurs at potentials below 0.2 V. At this potential, lithium insertion into the graphene layer through the edge surface begins, generating a concentration gradient due to lithium consumption, and causing reactants such as solvents and salts to migrate to the edge surface. If the edge surface is not completely covered by the SEI layer, this phenomenon continues to repeat.

[0143] To observe the characteristics of Manufacturing Examples 7 and 8 in more detail, CV (Cyclic Voltammetry) was performed. The initial potential of CV was Li / Li + Start at 2.0 V for the initial measurement, and scan at a rate of 0.1 mV s between 0.01 and 1.2 V, starting at 0.01 V. -1 The current density was measured using .

[0144] The formation of a significant SEI layer is generally Li / Li + It starts at 0.8 V vs. the reference voltage, and the irreversible process occurring here originates from the initiation of the reaction forming the Si / C complex and the reaction forming the SEI layer from the electrolyte.

[0145] During the first scan, Li / Li + The plateau potential occurring at 0.43 V in comparison is the formation of SEI in silicon, and the lithiation peak of graphite occurred at 0.2 V. As lithiation progresses, lithiation of silicon occurs at potentials of 0.17 V or lower, and crystalline silicon (c-Si) is converted to amorphous lithium silicate (c-Si+). x Li→a-Li xIt changes into silicon (Si), and after delithiation, it changes into amorphous silicon (a-Si).

[0146] Looking at the cathodic scan of the second cycle, as lithium ions are inserted continuously, each a-Li x1+x2 Si(Li / Li + 0.1 V vs. a-Li x1 Si(Li / Li + A peak appears at 0.25 V.

[0147] Afterwards, when lithium ions are continuously lithiated to below 0.05 V, the final phase of silicon is crystalline Li 15 Si4(c-Li 15 It changes to Si4).

[0148] When the electrode containing silicon is exposed to a voltage of less than 0.05 V, the amorphous form of lithium silicate changes back to a crystalline phase, and finally c-Li at room temperature. 15 Si4 appears as the final phase. Lithium insertion into graphite is less than 0.1 V (Li+yC→LiC y ) occurs, and these characteristics can be confirmed in b and d of Fig. 7.

[0149] Afterwards, as can be seen in the anodic scan, delithiation of graphite occurs around 0.2 V, and c-Li 15 Delithiation of Si4 and a-Li2Si was confirmed to occur at 0.3 V and 0.4 V, respectively, through their respective peaks.

[0150] Afterwards, the electrochemical performance of manufacturing examples 5 and 6 with added silver nanowires was evaluated.

[0151] Referring to a and c of Fig. 8, in the case of manufacturing example 5, the initial charge capacity is 887.9 mAh g -1 , discharge capacity is 374.7 mAh g -1 , the initial charge / discharge efficiency was 42.2%, and in the case of manufacturing example 6, the initial charge capacity was 885.8 mAh g-1 , discharge capacity is 463.9mAh g -1 , the initial charge / discharge efficiency was 51.7%.

[0152] Examining the discharge performance after the second cycle, the discharge capacity of Manufacturing Example 5 increased by 5% compared to Manufacturing Example 7, and uniform performance was maintained up to the third cycle. In addition, the charge / discharge efficiency increased to 93% in the second cycle and remained at the same level in the third cycle.

[0153] In particular, in the case of manufacturing example 6, 500 mAh g from the second cycle -1 It showed the capacity above, and the charge / discharge efficiency was maintained at over 90%.

[0154] Typically, silver (Ag) is one of the most common candidates for Li-M alloys, possessing the characteristic of forming a solid solution phase. Therefore, it can be used with or instead of carbon to enhance the conductivity within the electrode. Furthermore, when used with graphene, it can enhance the aggregation stability of graphene. It can be used as an additive or as an element forming an intermetallic compound with other metals that improve the microstructure of the electrode.

[0155] However, as described above in the present invention, the fact that the charge / discharge efficiency is maintained at the same level is largely due to the fact that the calendaring process of the composite cathode is not performed.

[0156] The calendering process compresses the active and conductive materials within the electrode, increasing the contact area between the materials and reducing contact resistance, thereby forming a better conductive path. Furthermore, because calendering can increase energy density per unit volume, it is generally used to secure high-capacity electrodes and is considered an essential process in the battery industry.

[0157] However, when designing the microstructure of silicon-based electrodes, it is necessary to consider securing space to cushion silicon expansion. When a calendaring process is performed on the composition of the composite anode material provided in the present invention, the theoretical porosity can be reduced by up to 50%. Furthermore, the pore size distribution becomes narrower and smaller, and nano-sized silicon particles, in particular, can block graphite pores and lose contact with the graphite.

[0158] In other words, in silicon-based electrodes like the present invention, it is crucial to strike a balance between securing electrical conduction paths and pores capable of buffering silicon expansion. Therefore, the present invention did not perform a calendaring process to investigate the silver nanowire effect.

[0159] The above manufacturing examples 5 and 6 have a longer, more irregular surface and a higher specific surface area by adding silver nanowires, which, combined with the morphological characteristics of the artificial graphite described above, allows more lithium ions to be consumed to form an initial SEI film.

[0160] Referring to the CV results of the above Manufacturing Examples 5 and 6 (Fig. 8, b, d), no oxidation peak was observed within the 0.7 to 0.9 V range in the first lithiation scan. This is because the silver nanowires are capped with PVP and thus there is no oxide layer.

[0161] Afterwards, if lithiation scans are performed continuously, Li / Li + A peak of silver nanowires can be observed at approximately 0.6 V. Furthermore, plateau potentials can be observed at 0.2–0.3 V and 0.1–0.2 V, respectively, indicating phase changes occurring as lithium ions are inserted into silver nanowires, namely, the Li-Ag phase and the β phase, respectively.

[0162] Comparing the CV results of Figures 7 and 8, it can be confirmed that the lithiation reaction rate and delithiation reaction rate of Manufacturing Examples 5 and 10 significantly increased. Looking at it in more detail, it can be confirmed that the oxidation current below 0.4 V significantly increased as silver nanowires were added. When lithium was inserted into the composite electrode composed of graphite, silicon, and silver nanowires, the lithiation of silicon occurred first, and c-Si was followed by a-Li. x By adding silver nanowires to Li-Si alloys and Li-C intercalation systems, lithiation to graphite or silicon occurs more efficiently and at a lower overpotential. This is because silver can act as a catalyst or mediator for electrochemical reactions occurring at the electrode surface, and the effect of adding Ag can shift the peak potential of the CV curves for both lithium and silicon.

[0163] This is because Ag can promote electrochemical reactions involving lithium and silicon, leading to more efficient charge transfer and a reduced overpotential required for the reaction to occur. The peak that can appear below 0.1 V when lithium is inserted into silver to form Li-Ag was not observed.

[0164] In the delithiation scan, LiC was compared to the fabrication examples 7 and 8 without silver nanowires. y and Li 15 There was no difference in the onset potentials of lithium desorption and dealloying from Si4, and no dealloying peak from the Li-Ag alloy was observed.

[0165] Looking at the characteristics of the subsequent CV cycles, in Manufacturing Example 5, a Li-Ag dealloy peak was observed in the 7th scan. Referring to Fig. 9a, the Li-C dealloy peak and the Li-Si dealloy corrosion peak, which were previously separated into two, were combined into one, became broader, and moved to the right. In addition, the peak changing from a-Li2Si to a-Si was narrow and sharp. Thereafter, in the 8th scan, the peak related to Ag disappeared, and typical Li-C dealloy peaks and Li-Si dealloy corrosion peaks appeared, but the peak changing from a-Li2Si to a-Si was not observed.

[0166] Referring to Figure 9, the difference in CV curves between Manufacturing Examples 5 and 6 can be confirmed.

[0167] Referring to Figure 10, the results of calculating the phases that can appear from the thermodynamic activation energy of each binary system (Li-Si, Li-Ag, Li-C, and Si-C) can be confirmed. First, if we check a in Figure 9, the most thermodynamically stable phase is Li 22 It can be seen that it is Si5. However, the final phase confirmed experimentally is Li 15 Since the remaining non-destructive Si-Si pairs limit the maximum number of lithium atoms that can bond to silicon, lithiation stops at a range less than the theoretical stoichiometry of 4.2–4.4 Li atoms bonding per Si atom.

[0168] If we check b in Fig. 10, Li in the Li-Ag binary system x Ag y The calculation results of the phase change are Li9Ag4(γ3), Li when complete lithiation is performed up to 0 V. 10 It was expressed as Ag3(γ4), which was consistent with the results of previous research in the field.

[0169] Next, if we check c in Fig. 10, similar to Li-Si above, the most thermodynamically stable phase is LiC 12However, the final prize appears to be LiC6.

[0170] Referring to Figure 11, the diagrams of the Li-Si-Ag, Li-Si-C, and Li-Ag-C ternary systems can be confirmed, respectively. By analyzing the formation energy of each ternary phase in these ternary systems, the following phases can be confirmed to exist.

[0171] Li-Si-AgLi-Si-CLi-Ag-C sequential three-component, phase-sequence three-component, phase-sequence three-component, phase-1Li 12 Si7-Si-LiAg1Li 12 Si7-SiC-Si1LiAg3-C-LiAg2Li 12 Si7-Li7Si3-LiAg2Li 12 Si7-SiC-Li7Si32Li8Ag5-LiAg-LiC 12 3Li 13 Si4-Li7Si3-LiAg3Li 13 Si4-SiC-Li7Si33Li8Ag5-Li3Ag-LiC 12 4Li 15 Si7-Li 13 Si4-Li8Ag54Li 15 Si4-Li 13 Si4-LiC 12 5Li 12 Si7-Li7Si3-LiAg5Li 12 Si7-C-SiC

[0172] Referring to Table 2, the difference between Manufacturing Examples 5 and 6 and Manufacturing Examples 7 and 8 can be said to be the presence or absence of LiAg alloy.

[0173] Referring to Fig. 12, the morphological changes of Manufacturing Examples 7 and 8 according to the progress of charge and discharge cycles can be confirmed. Referring to Fig. 12 b and e, there is an area where silicon is exposed, and accordingly, typical silicon peaks are observed as in the CV results confirmed above, but referring to Fig. 12 c and f, as the cycle is repeated, the Li-Ag alloy layer becomes thicker, and the Li-Ag alloy layer forms a dense electrode layer.

[0174] The above Li-Ag alloy has a higher lithium atomic diffusion coefficient than the lithium-plated surface and is accompanied by a reversible alloying-dealloying reaction. Therefore, by including silver nanowires, the silicon-containing electrode can perform a more reversible and rapid reaction during charge-discharge cycling.

[0175] However, referring to c of Fig. 13, an impedance graph measured in a frequency range of 0.01 Hz to 100 KHz can be confirmed, and it can be confirmed that the electronic transition resistance (Rct) and electric double layer capacitance of Manufacturing Example 8 are low.

[0176] In addition, when a 180° peeling test was performed on the composite cathodes of Manufacturing Examples 6 and 8 using commercial 3M tape, the composite cathode of Manufacturing Example 6 had a peeling resistance of about 0.56 N cm -1 , about 0.30 N cm of Manufacturing Example 8 -1 It can be seen that the adhesion between the composite cathode material and the copper foil is superior. This result is due to the improved mechanical stability of the interconnected silver nanowire network, which stably attaches to other electrode materials, and the PVP capping the surface of the silver nanowires additionally functions as a binder.

[0177] Referring to Fig. 13e, the results of measuring the long-term performance stability of Manufacturing Examples 6, 7, and 8 can be confirmed. In the case of Manufacturing Example 8, the capacity was maintained relatively stably in the beginning, but it showed a sharp fluctuation starting from the 20th to 30th cycle, and showed a tendency for the specific capacity to continuously decrease. On the other hand, in the case of Manufacturing Example 7, the capacity tended to decrease rapidly from the beginning, and although the diameter of the decrease in the specific capacity between the initial and final cycles was small, it showed a continuously unstable specific capacity. Lastly, in the case of Manufacturing Example 6, it showed a stable and high specific capacity from the beginning to the end.

[0178]

[0179] Although the present invention has been described through specific matters and limited examples as described above, these are provided only to help with the overall understanding of the present invention, and the present invention is not limited to the above examples, and those skilled in the art to which the present invention pertains can make various modifications and variations based on this description.

[0180] Therefore, the idea of ​​the present invention should not be limited to the described embodiments, and all things that are equivalent or equivalent to the claims described below as well as the claims are considered to fall within the scope of the idea of ​​the present invention.

Claims

1. A composite anode for a lithium secondary battery comprising a composite anode material composed of graphite particles, silicon particles, carbon particles, and silver nanowires. The above silicon particles are pure silicon, SiO x , Mg x Si y O z (1≤x≤2, 1≤y≤2, 1≤z≤4), Li x Si y O z It consists of at least one selected from (2≤x≤4, 1≤y≤2, 3≤z≤5), A composite anode for a lithium secondary battery in which electron transfer occurs through the graphite particles, silicon particles, carbon particles, and silver nanowires.

2. In paragraph 1, A composite anode for a lithium secondary battery, wherein the silver nanowires form a structure surrounding the graphite particles, silicon particles, and carbon particles.

3. In paragraph 1, A composite anode for a lithium secondary battery, wherein the above silver nanowires intersect each other at three or more different points to form a mesh or network.

4. In paragraph 1, The above composite negative electrode material for a lithium secondary battery is a composite negative electrode for a lithium secondary battery containing 1 to 95 wt% of the graphite.

5. In paragraph 1, The composite negative electrode material for a lithium secondary battery is a composite negative electrode for a lithium secondary battery containing 0.1 to 20 wt% of the carbon particles.

6. In paragraph 1, The above silver nanowire is a composite anode for a lithium secondary battery capped with PVP (polyvinyl pyrrolidone).

7. In paragraph 1 The composite anode for a lithium secondary battery is characterized in that it further comprises at least one selected from among PVP (polyvinyl pyrrolidone), PI (polyimide), PVDF (polyvinyledene fluoride), SBR (styrene-butadiene rubber), CMC (carboxymethyl cellulose), NBR (nitrile butadiene rubber), HNBR (hydrogenated nitrile butadiene rubber), and PAA (polyacrylic acid) as a binder.

8. In paragraph 1, The above silver nanowire is a composite negative electrode for a lithium secondary battery having a diameter of 40 to 60 nm.

9. In paragraph 1, The above silver nanowire is a composite negative electrode for a lithium secondary battery having a length of 20 to 50 μm.

10. In paragraph 1, The above composite negative electrode material for a lithium secondary battery is a composite negative electrode for a lithium secondary battery containing 0.1 to 2 wt% of the silver nanowires.

11. In paragraph 1, The above composite anode for lithium secondary batteries has a density of 0.85 to 2.0 g cm -3 Composite cathode for lithium secondary batteries.

12. Step of manufacturing silver nanowires; A step of manufacturing a composite cathode material by mixing silver nanowires, graphite, silicon and carbon powder; A step of preparing a dispersion using the above composite negative electrode material and binder solution; A step of preparing an electrode slurry by stirring the above dispersion; A step of manufacturing an electrode by applying the above electrode slurry to copper foil; and A step of drying the above electrode; A method for manufacturing a composite negative electrode for a lithium secondary battery comprising:

13. A lithium secondary battery comprising a composite negative electrode for a lithium secondary battery according to any one of claims 1 to 12.

14. In paragraph 13, Li is added to the composite negative electrode for the lithium secondary battery during charge and discharge of the lithium secondary battery. x Ag y A composite anode for a lithium secondary battery characterized by the formation of an alloy.

15. In paragraph 13, A composite anode for a lithium secondary battery, wherein the composite anode material for a lithium secondary battery in the above lithium secondary battery is composited with a solid electrolyte.

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