Negative electrode and secondary battery including the same

Abstract

The present invention relates to a negative electrode and a secondary battery including the negative electrode, the negative electrode including a negative electrode active material layer containing a negative electrode active material and a conductive material. The negative electrode active material includes a first active material and a second active material, the first active material including SiO x particles (0 < x < 2), the second active material including SiO y particles (0 < y < 2), wherein the D x of the SiO 50 particles is 0.1 - 0.6 μm, the D y of the SiO 50 particles is 3 - 8 μm, and the weight ratio of the SiO x particles to the SiO y particles is 1:2 to 1:100. The conductive material includes single-walled carbon nanotubes.

Description

Technical Field

[0001] Cross - Reference to Related Applications

[0002] This application claims priority to Korean Patent Application No. 10 - 2020 - 0109527, filed on August 28, 2020, the disclosure of which is incorporated herein by reference. Technical Field

[0004] The present invention relates to a negative electrode including different types of silicon - based particles and carbon nanotubes, and a secondary battery including the negative electrode. Background Art

[0005] Due to the rapid increase in the use of fossil fuels, the demand for using alternative energy or clean energy has increased. As part of this trend, power generation and power storage using electrochemical reactions are the most active research fields.

[0006] Currently, a typical example of an electrochemical device using electrochemical energy can be a secondary battery, and its use fields have a tendency to expand more and more. In recent years, with the increase in the development of and demand for portable devices such as portable computers, mobile phones, and cameras, the demand for secondary batteries as an energy source has increased significantly. Moreover, among these secondary batteries, a large amount of research has been conducted on lithium secondary batteries having a high energy density, that is, a high capacity, and they have been commercialized and widely used.

[0007] Generally, a secondary battery is composed of a positive electrode, a negative electrode, an electrolyte, and a separator. The negative electrode contains a negative electrode active material in which lithium ions from the positive electrode are intercalated and deintercalated, and silicon - based particles having a high discharge capacity can be used as the negative electrode active material. However, the initial efficiency of silicon - based particles is low, and their volume changes excessively during the charge and discharge processes. Therefore, there is a limitation in reducing the battery life. In particular, since cracks occur in the silicon - based particles as the charge and discharge cycles are repeated, the mechanical stability is reduced and the life is also reduced.

[0008] Generally, to solve this limitation, a technique of forming a carbon coating on the surface of silicon - based particles has been used. However, even when the carbon coating is formed, the reduction in the initial efficiency and life of the battery has not been significantly improved, and the effect of reducing the battery resistance is not significant. A method of controlling the physical properties of an adhesive or a thickener so that silicon - based particles do not detach from the negative electrode has also been used, but its effect is not great.

[0009] Therefore, there is a need for a negative electrode that uses silicon - based active material particles but can improve the life characteristics. Summary of the Invention

[0010] Technical Problem

[0011] One aspect of the present invention provides a negative electrode that can improve the life characteristics of a battery.

[0012] Another aspect of the present invention provides a secondary battery including the negative electrode.

[0013] Technical solution

[0014] According to one aspect of the present invention, there is provided a negative electrode including a negative electrode active material layer containing a negative electrode active material and a conductive agent, wherein the negative electrode active material includes a first active material and a second active material, and the first active material includes SiO x particles (0 < x < 2), the second active material includes SiO y particles (0 < y < 2), wherein the D x of the SiO 50 particles is 0.1 μm to 0.6 μm, the D y of the SiO 50 particles is 3 μm to 8 μm, the weight ratio of the SiO x particles to the SiO y particles is in the range of 1:2 to 1:100, and the conductive agent includes single-walled carbon nanotubes.

[0015] According to another aspect of the present invention, there is provided a secondary battery including the negative electrode.

[0016] Beneficial effects

[0017] According to one embodiment of the present invention, since the negative electrode includes an appropriate amount of different types of silicon-based particles (SiO x particles, SiO y particles) having specific sizes, the contact area between the silicon-based particles is increased to promote the movement of electrons in the negative electrode, thereby improving the life characteristics of the battery. Moreover, since the single-walled carbon nanotubes electrically connect and physically connect the silicon-based particles to each other, the life characteristics of the battery can be further improved. Detailed embodiments

[0018] Hereinafter, the present invention will be described in more detail so that the present invention can be understood more clearly.

[0019] It should be understood that the words or terms used in the specification and claims should not be construed as having the meanings defined in a common dictionary, and it should be further understood that the words or terms should be construed as having meanings consistent with their meanings in the context of the related art and the technical concept of the present invention based on the principle that the inventor can appropriately define the words or terms to best explain the invention.

[0020] The terms used in this specification are for the purpose of describing particular exemplary embodiments only and are not intended to limit the present invention. In this specification, the singular forms of the terms may include the plural forms unless otherwise stated to the contrary.

[0021] It will be further understood that when used in this specification, the terms "comprising", "including" or "having" specify the presence of the stated features, quantities, steps, elements or combinations thereof, but do not preclude the presence or addition of one or more other features, quantities, steps, elements or combinations thereof.

[0022] The expression "D 50 " in this specification may be defined as the particle diameter at which the cumulative volume is 50% in the particle size distribution curve of the particles. For example, D 50 can be measured by using the laser diffraction method. The laser diffraction method can generally measure the particle diameter in the range from sub-micron level to several millimeters and can obtain highly reproducible and high-resolution results.

[0023] In this specification, the specific surface area is measured by degassing at 200 °C for 8 hours and performing N2 adsorption / desorption at 77 K using a Brunauer-Emmett-Teller (BET) measuring instrument (BEL-SORP-MAX, Bell Co., Japan).

[0024] The negative electrode according to an embodiment of the present invention includes a negative electrode active material layer, the negative electrode active material layer includes a negative electrode active material and a conductive agent, wherein the negative electrode active material includes a first active material and a second active material, wherein the first active material includes SiO x particles (0 < x < 2), the second active material includes SiO y particles (0 < y < 2), wherein the D x of the SiO 50 particles is 0.1 μm to 0.6 μm, the D y of the SiO 50 particles is 3 μm to 8 μm, the weight ratio of the SiO x particles to the SiO y particles is in the range of 1:2 to 1:100, and the conductive agent includes single-walled carbon nanotubes.

[0025] The negative electrode includes a negative electrode active material layer.

[0026] The negative electrode active material layer may be provided on a current collector, or the negative electrode active material layer itself may be the negative electrode.

[0027] The current collector is not particularly limited as long as it has conductivity and does not cause adverse chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc. can be used as the current collector. Specifically, transition metals such as copper and nickel that can well adsorb carbon can be used as the current collector. The current collector can have a thickness of 6 μm to 20 μm, but the thickness of the current collector is not limited thereto.

[0028] The negative electrode active material layer can be provided on one surface or both surfaces of the current collector.

[0029] The negative electrode active material layer contains a negative electrode active material and a conductive agent.

[0030] The negative electrode active material contains a first active material and a second active material.

[0031] The first active material contains SiO x particles (0 < x < 2), and can specifically be composed of SiO x particles (0 < x < 2). The second active material contains SiO y particles (0 < y < 2) and can specifically be composed of SiO y particles (0 < y < 2). x and y respectively correspond to the ratio of the number of oxygen (O) atoms to silicon (Si) atoms contained in SiO x particles (0 < x < 2) and SiO y particles (0 < y < 2). By using SiO x particles (0 < x < 2) and SiO y particles (0 < y < 2), the capacity of the battery can be improved.

[0032] The D x of the SiO 50 particles (0 < x < 2) is 0.1 μm to 0.6 μm, for example, 0.2 μm to 0.4 μm. When the D x of the SiO 50 particles (0 < x < 2) is less than 0.1 μm, due to its too large specific surface area, a serious side reaction occurs with the electrolyte, thus reducing the life characteristics of the battery. On the contrary, when the D x of the SiO 50 particles (0 < x < 2) is greater than 0.6 μm, since the effect of increasing the contact area between particles may not be expected when the SiO x particles are mixed with the SiO y particles (0 < y < 2), the life characteristics of the battery will be reduced.

[0033] The SiOy The D of the particles (0 < y < 2) 50 is from 3 μm to 8 μm, for example, from 5.2 μm to 7 μm. In the SiO y When the D of the particles (0 < y < 2) 50 is less than 3 μm, since it may not be possible to expect the effect of increasing the contact area between the particles when the SiO y particles are mixed with the SiO x (0 < x < 2) particles, the life characteristics of the battery will be reduced. On the contrary, when the D of the SiO y particles (0 < y < 2) 50 is greater than 8 μm, due to the excessive volume change during battery charging and discharging, the life characteristics of the battery will be reduced.

[0034] SiO x The D of the particles 50 The ratio of SiO y to the D of the particles 50 can be in the range of 1:5 to 1:40, particularly 1:7 to 1:37, and more particularly 1:15 to 1:35. When this ratio satisfies the above range, since the contact area between the SiO x particles and the SiO y particles can meet the most ideal level, the life characteristics of the battery can be improved more effectively.

[0035] The SiO x The weight ratio of the particles to the SiO y particles is in the range of 1:2 to 1:100, particularly 1:10 to 1:50, and more particularly 1:10 to 1:20. When the weight ratio of the SiO x particles to the SiO y particles is outside the range of 1:2 to 1:100, since the contact area between the SiO x particles and the SiO y particles is insufficient, the life characteristics of the battery will be reduced.

[0036] The SiO x The specific surface area of the particles can be in the range of 1 m 2 / g to 10 m 2 / g, for example, 2 m 2 / g to 7 m 2 / g. The specific surface area of the SiO y particles can be in the range of 4 m 2 / g to 20 m 2 / g, for example, 9 m 2 / g to 18 m 2within the range of / g. When the above range is satisfied, due to the x contact area between the SiO y particles and the SiO

[0037] The conductive agent includes single-walled carbon nanotubes, and specifically, the conductive agent can be composed of single-walled carbon nanotubes.

[0038] The average diameter of the single-walled carbon nanotubes can be 1 nm to 30 nm, for example, 5 nm to 12 nm. When the average diameter satisfies the above range, due to the high flexibility of the single-walled carbon nanotubes, SiO x particles and SiO y A conductive network between the particles can be formed more effectively, thereby more effectively improving the life characteristics of the battery. The average diameter can be obtained by averaging the diameters of 100 single-walled carbon nanotubes in the negative electrode measured by a scanning electron microscope (SEM).

[0039] The average length of the single-walled carbon nanotubes can be 2 μm to 100 μm, for example, 3 μm to 20 μm or 3 μm to 12 μm. When the average length satisfies the above range, even if the volume of the SiO x particles and the SiO y particles changes, it is easy to maintain the conductive network connecting the SiO x particles and the SiO y particles, so the life characteristics of the battery can be improved. The average length can be obtained by averaging the lengths of 100 single-walled carbon nanotubes in the negative electrode measured by SEM.

[0040] The specific surface area of the single-walled carbon nanotubes can be 500 m 2 / g to 1,500 m 2 / g, for example, 600 m 2 / g to 1,000 m 2 / g. When the specific surface area satisfies the above range, since the single-walled carbon nanotubes can minimize the side reaction with the electrolyte while having high flexibility, the life characteristics of the battery can be further improved.

[0041] In the negative electrode active material layer, the content of the single-walled carbon nanotubes can be 0.001 wt% to 0.5 wt%, specifically, the content can be 0.02 wt% to 0.1 wt%. When the above range is satisfied, a conductive network connecting the SiO x particles and the SiO y particles can be effectively formed, and the side reaction with the electrolyte can be minimized.

[0042] The negative electrode active material layer may further include a binder.

[0043] The binder may include at least one selected from the group consisting of poly(vinylidene fluoride - hexafluoropropylene) copolymer (PVDF - co - HFP), poly(vinylidene fluoride), polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene - propylene - diene monomer (EPDM), sulfonated EPDM, styrene - butadiene rubber (SBR), fluororubber, polyacrylic acid, and materials in which hydrogen thereof is substituted with lithium (Li), sodium (Na), or calcium (Ca), or may include various copolymers thereof.

[0044] A secondary battery according to another embodiment of the present invention may include the negative electrode of the above - described embodiment. Specifically, the secondary battery may include the negative electrode of the above - described embodiment, a positive electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte, wherein the negative electrode is the same as the above - described negative electrode. Since the negative electrode has been described above, its detailed description will be omitted.

[0045] The positive electrode may include a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector and including a positive electrode active material.

[0046] In the positive electrode, there is no particular limitation on the positive electrode current collector as long as it has conductivity and does not cause an adverse chemical change in the battery. For example, stainless steel, aluminum, nickel, titanium, fired carbon, or aluminum or stainless steel surface - treated with one of carbon, nickel, titanium, or silver, etc. may be used. In addition, the positive electrode current collector generally may have a thickness of 3 μm to 500 μm and may include a surface having fine irregularities to improve the adhesion to the positive electrode active material. The positive electrode current collector may be used in various shapes, such as a film, sheet, foil, net, porous body, foam body, non - woven fabric body, etc.

[0047] The positive electrode active material may be a commonly used positive electrode active material. Specifically, the positive electrode active material may include layered compounds, such as lithium cobalt oxide (LiCoO2) or lithium nickel oxide (LiNiO2), or compounds substituted with one or more transition metals; lithium iron oxides, such as LiFe3O4; lithium manganese oxides, such as Li 1+c1 Mn 2-c1 O4(0≤c1≤0.33), LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides, such as LiV3O8, V2O5, and Cu2V2O7; compounds represented by the chemical formula LiNi 1-c2 M c2Nickel (Ni) site-type lithium nickel oxide represented by O2 (where M is at least one selected from the group consisting of cobalt (Co), manganese (Mn), aluminum (Al), copper (Cu), iron (Fe), magnesium (Mg), boron (B), and gallium (Ga), and c2 satisfies 0.01 ≤ c2 ≤ 0.3); lithium manganese composite oxide represented by the chemical formula LiMn 2-c3 M c3 O2 (where M is at least one selected from the group consisting of Co, Ni, Fe, chromium (Cr), zinc (Zn), and tantalum (Ta), and c3 satisfies 0.01 ≤ c3 ≤ 0.1) or Li2Mn3MO8 (where M is at least one selected from the group consisting of Fe, Co, Ni, Cu, and Zn); LiMn2O4 in which a part of Li is replaced by an alkaline earth metal ion, but the positive electrode active material is not limited thereto. The positive electrode may be lithium metal.

[0048] The positive electrode active material layer may contain a positive electrode conductive agent and a positive electrode binder together with the above positive electrode active material.

[0049] In this case, the positive electrode conductive agent is used to provide conductivity to the electrode. Any conductive agent can be used without particular limitation as long as it has electron conductivity and does not cause adverse chemical changes in the battery. Specific examples of the positive electrode conductive agent may be: graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal cracking carbon black, and carbon fiber; metals such as metal powders or metal fibers of copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides such as titanium oxides; or conductive polymers such as polyphenylene derivatives. One of them alone or a mixture of two or more thereof can be used.

[0050] In addition, the positive electrode binder serves to improve the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the positive electrode current collector. Specific examples of the positive electrode binder may be polyvinylidene fluoride (PVDF), polyvinylidene fluoride - hexafluoropropylene copolymer (PVDF - co - HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene - propylene - diene monomer (EPDM), sulfonated EPDM, styrene - butadiene rubber (SBR), fluororubber, or various copolymers thereof. One of them alone or a mixture of two or more thereof can be used.

[0051] The separator separates the negative electrode and the positive electrode and provides a path for the movement of lithium ions. Any separator can be used as the separator without particular limitation as long as it is commonly used in secondary batteries. In particular, a separator having a high moisture retention capacity for the electrolyte and a low resistance to the transfer of electrolyte ions can be used. Specifically, a porous polymer membrane can be used, such as a porous polymer membrane prepared from an olefin-based polymer such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof. In addition, typical porous non-woven fabrics can be used, such as non-woven fabrics formed from high-melting-point glass fibers or polyethylene terephthalate fibers. In addition, in order to ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymer component can be used, and a separator having a single-layer or multi-layer structure can be optionally used.

[0052] The electrolyte may include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, or a molten-type inorganic electrolyte that can be used to prepare a lithium secondary battery, but the present invention is not limited thereto.

[0053] Specifically, the electrolyte may include a non-aqueous organic solvent and a metal salt.

[0054] Examples of the non-aqueous organic solvent may be aprotic organic solvents such as N-methyl-2-pyrrolidone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, triphosphate ester, trimethoxymethane, dioxolane derivative, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, ether, methyl propionate, and ethyl propionate.

[0055] In particular, since ethylene carbonate and propylene carbonate (cyclic carbonates among carbonate-based organic solvents) are high-viscosity organic solvents and can dissociate lithium salts well due to their high dielectric constants, cyclic carbonates can be preferably used. Since an electrolytic solution having a high conductivity can be prepared when cyclic carbonates are mixed with linear carbonates such as dimethyl carbonate and diethyl carbonate having low viscosity and low dielectric constant in an appropriate ratio, cyclic carbonates can be more preferably used.

[0056] A lithium salt can be used as the metal salt, and the lithium salt is a material that is easily soluble in a non-aqueous electrolyte. Among them, for example, a material selected from F - , Cl - , I - , NO3- , N(CN)2 - , BF4 - , ClO4 - , PF6 - , (CF3)2PF4 - , (CF3)3PF3 - , (CF3)4PF2 - , (CF3)5PF - , (CF3)6P - , CF3SO3 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - Any one of the group consisting of is used as the anion of the lithium salt.

[0057] In addition to the above electrolyte components, at least one additive can be included in the electrolyte, for example, a halogenated alkylene carbonate compound such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ether, ethylenediamine, n-glycol dimethyl ether, hexamethylphosphoric triamide, nitrobenzene derivative, sulfur, quinone imine dye, N-substituted oxazolidone, N,N-substituted imidazoline, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxyethanol or aluminum trichloride, for the purpose of improving the life characteristics of the battery, preventing the battery capacity from decreasing, and improving the discharge capacity of the battery.

[0058] According to another embodiment of the present invention, the first active material can be the same as the negative electrode in the above embodiment, except that it includes a carbon coating provided on SiO x particles.

[0059] The carbon coating may include a carbon-based material. The carbon-based material may include at least one of amorphous carbon and crystalline carbon.

[0060] The crystalline carbon can further improve the conductivity of the negative electrode active material. The crystalline carbon may include at least one selected from the group consisting of fullerene, carbon nanotube, and graphene.

[0061] The amorphous carbon can inhibit the expansion of nuclei by appropriately maintaining the strength of the carbon coating. The amorphous carbon can be a carbide of at least one selected from the group consisting of tar, pitch, and other organic materials, or can be a carbon-based material formed by using a hydrocarbon as a chemical vapor deposition source.

[0062] The carbide of the other organic materials can be a carbide of sucrose, glucose, galactose, fructose, lactose, mannose, ribose, aldohexose, or ketohexose, and a carbide of an organic material selected from a combination thereof.

[0063] The hydrocarbon can be a substituted or unsubstituted aliphatic or alicyclic hydrocarbon, or a substituted or unsubstituted aromatic hydrocarbon. The substituted or unsubstituted aliphatic or alicyclic hydrocarbon can include methane, ethane, ethylene, acetylene, propane, butane, butene, pentane, isobutane, or hexane. The substituted or unsubstituted aromatic hydrocarbon can include benzene, toluene, xylene, styrene, ethylbenzene, diphenylmethane, naphthalene, phenol, cresol, nitrobenzene, chlorobenzene, indene, coumarone, pyridine, anthracene, or phenanthrene.

[0064] The thickness of the carbon coating can be from 1 nm to 1,000 nm, particularly from 50 nm to 800 nm, and more particularly from 100 nm to 500 nm. When the above range is satisfied, the life characteristics and output characteristics of the battery can be further improved. Although not limited thereto, the thickness of the carbon coating can be measured by SEM or transmission electron microscope (TEM).

[0065] According to another embodiment of the present invention, the second active material can be the same as the negative electrode of the above embodiment, except that it includes a carbon coating provided on SiO y particles. The carbon coating can be the same as the carbon coating of the above embodiment.

[0066] According to another embodiment of the present invention, the first active material and the second active material can be the same as the negative electrode of the above embodiment, except that the first active material includes a carbon coating provided on SiO x particles and the second active material includes a carbon coating provided on SiO y particles. The carbon coating can be the same as the carbon coating of the above embodiment.

[0067] According to another embodiment of the present invention, the first active material can further include a metal provided or distributed on the surface, inside, or both the surface and inside of the SiO x particles. Specifically, the first active material can further include a metal doped inside the SiO x particles.

[0068] Since the metal can control the volume expansion / contraction of the SiO x particles to an appropriate level by being distributed on the surface and / or inside of the SiO x particles, the metal can play a role in preventing damage to the first active material. In addition, in terms of improving the efficiency of the first active material by reducing the proportion of the irreversible phase (such as SiO2) of the SiO x particles, a metal can be included in the first active material.

[0069] The metal may include at least one selected from the group consisting of lithium (Li), magnesium (Mg), calcium (Ca), and aluminum (Al). Considering the fact that the volume expansion control, damage prevention, and initial efficiency improvement effects of the SiO x particles can be achieved at an excellent level, the metal may specifically include at least one selected from the group consisting of Li and Mg, and more specifically may include Mg.

[0070] In the first active material, the content of the metal may be 0.1 wt% to 30 wt%, for example, 2 wt% to 6 wt%. When the amount of the metal is within the above range, the effect of improving the initial efficiency of the first active material can be achieved at an excellent level.

[0071] When the first active material contains the metal, the first active material can be prepared by a method including the following steps: generating a first vapor by evaporating a compound represented by SiO a (0 < a < 2); generating a second vapor by vaporizing a metal including at least one selected from the group consisting of Li, Mg, Ca, and Al; mixing the first vapor and the second vapor to carry out a gas-phase reaction; obtaining a powder by cooling after the gas-phase reaction; adjusting the D 50 of the powder to 0.1 μm to 0.6 μm, but the present invention is not limited thereto. For example, the D 50 of the powder can be adjusted by using a jet milling method, but it is not limited thereto.

[0072] According to another embodiment of the present invention, the second active material may further include a metal disposed or distributed on the surface, inside, or both the surface and inside of the SiO y particles. Specifically, the second active material may further include a metal doped inside the SiO y particles.

[0073] Since the metal can control the volume expansion / contraction of the SiO y particles to an appropriate level by being distributed on the surface and / or inside of the SiO yThe volume expansion / contraction of the particles is controlled to an appropriate level, so that the metal can play a role in preventing damage to the second active material. In addition, in terms of improving the efficiency of the second active material by reducing the proportion of the irreversible phase (such as SiO2) of the SiO y particles, a metal can be included in the second active material.

[0074] The metal may include at least one selected from the group consisting of Li, Mg, Ca, and Al. Considering the fact that volume expansion control, damage prevention, and initial efficiency improvement effects of SiO y particles can be achieved at an excellent level, the metal may specifically include at least one selected from the group consisting of Li and Mg, and more specifically may include Mg.

[0075] In the second active material, the content of the metal may be 0.1% by weight to 30% by weight, for example, 2% by weight to 15% by weight. When the amount of the metal is within the above range, the effect of improving the initial efficiency of the second active material can be achieved at an excellent level.

[0076] When the second active material includes the metal, the second active material can be prepared by a method including the following steps: generating a first vapor by evaporating a compound represented by SiO b (0 < b < 2); generating a second vapor by vaporizing a metal including at least one selected from the group consisting of Li, Mg, Ca, and Al; mixing the first vapor and the second vapor to carry out a gas-phase reaction; obtaining a powder by cooling after the gas-phase reaction; adjusting the D 50 of the powder to 0.3 μm to 8 μm, but the present invention is not limited thereto.

[0077] According to another embodiment of the present invention, the negative electrode active material may be the same as the negative electrode of the above embodiment, except that it further includes a carbon-based active material.

[0078] The carbon-based active material may be at least one selected from the group consisting of artificial graphite, natural graphite, graphitized carbon fiber, and graphitized mesophase carbon microbeads.

[0079] The weight ratio of the total amount of the first active material particles and the second active material particles to the amount of the carbon-based active material in the negative electrode active material may be, for example, 1:99 to 70:30, for example, 5:95 to 30:70. When the above range is satisfied, the charge and discharge characteristics of the battery will be further improved, and due to the excellent conductivity of the carbon-based active material, the life characteristics of the battery can be further improved.

[0080] According to another embodiment of the present invention, there is provided a battery module including the secondary battery as a unit cell and a battery pack including the battery module. Since the battery module and the battery pack include the secondary battery having high capacity, high rate capability, and high cycle characteristics, the battery module and the battery pack can be used as a power source for medium- and large-sized devices selected from the group consisting of electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0081] Hereinafter, preferred embodiments will be provided to better understand the present invention. It will be apparent to those skilled in the art that these embodiments are provided only for illustrating the present invention, and various modifications and changes can be made within the scope and technical spirit of the present invention. Such modifications and changes fall within the scope of the claims included herein.

[0082] Examples

[0083] Example 1: Preparation of Battery

[0084] (1) Formation of the negative electrode

[0085] D 50 A mixture (weight ratio of 1:19) of first SiO (first active material) with a diameter of 0.2 μm and second SiO (second active material) with a diameter of 7 μm is used as the negative electrode active material. Carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) are used as binders. Single-walled carbon nanotubes with an average diameter of 5 nm and an average length of 8 μm are used as conductive agents. 50 A carbon nanotube dispersion is prepared in which the single-walled carbon nanotubes are dispersed in CMC as a solvent. The negative electrode active material, binder, and carbon nanotube dispersion are added to water as a solvent, and then mixed to prepare a negative electrode slurry.

[0086] The negative electrode slurry is coated on a 20-μm-thick copper (Cu) metal thin film as the negative electrode current collector, and then dried. In this case, the temperature of the circulating air is 60°C. Subsequently, the negative electrode current collector coated with the negative electrode slurry is roll-pressed, dried in a vacuum oven at 130°C for 12 hours, and then punched into a circular shape with an area of 1.4875 cm

[0087] to prepare a negative electrode. 2

[0088] The total amount of first SiO and second SiO in the negative electrode is 95.4% by weight.

[0089] (2) Preparation of the battery

[0090] Cut into 1.7671 cm 2A lithium (Li) metal thin film of a circular object is used as the positive electrode. A porous polyethylene separator is arranged between the positive electrode and the negative electrode, and an electrolyte is injected (in this electrolyte, 0.5 wt% of vinylene carbonate is dissolved in a mixed solution of ethyl methyl carbonate (EMC) and ethylene carbonate (EC) with a mixing volume ratio of 7:3, and 1 M LiPF6 is dissolved) to prepare a lithium coin half-cell.

[0091] Examples 2 to 8 and Comparative Examples 1 to 11: Preparation of Battery

[0092] The battery is prepared in the same manner as in Example 1, except that the conditions are modified as shown in Tables 1 and 2 below.

[0093] Example 9: Preparation of Battery

[0094] The negative electrode and the battery of Example 9 are prepared in the same manner as in Example 1, except that the following first active material and second active material are used instead of the first SiO and the second SiO used in Example 1.

[0095] As the first active material, SiO in which Mg is distributed or doped on its surface and / or inside is prepared (average particle size (D 50 )): 0.2 μm). 6 wt% of Mg is contained in the first active material.

[0096] In addition, as the second active material, SiO in which Mg is distributed or doped on its surface and / or inside is prepared (average particle size (D 50 )): 7 μm). 6 wt% of Mg is contained in the second active material.

[0097] [Table 1]

[0098]

[0099] [Table 2]

[0100]

[0101] Experimental Examples

[0102] Experimental Example 1: Evaluation of Life Characteristics (Capacity Retention Rate)

[0103] The batteries of the examples and comparative examples are charged and discharged to evaluate the life characteristics (capacity retention rate), and the results are presented in Table 3 below.

[0104] Charging and discharging are performed at 0.1 C in the first and second cycles, and charging and discharging are performed at 0.5 C from the third cycle to the 100th cycle.

[0105] Charging conditions: CC (constant current) / CV (constant voltage), 5 mV / 0.005C current cut-off

[0106] Discharging conditions: CC (constant current) condition, 1.5V cut-off

[0107] The capacity retention rate is calculated as follows.

[0108] Capacity retention rate (%) = (discharge capacity of the 100th cycle / discharge capacity of the 1st cycle) × 100

[0109] Experimental Example 2: Evaluation of Initial Efficiency

[0110] One charge and discharge cycle of the batteries of the examples and comparative examples was carried out under the following conditions to evaluate the initial efficiency, and the results are shown in Table 3 below.

[0111] Charging conditions: 0.1C, CC (constant current) / CV (constant voltage), 5 mV / 0.005C current cut-off Discharging conditions: 0.1C, CC (constant current) condition, 1.5V cut-off

[0112] The initial efficiency is calculated as follows.

[0113] Initial efficiency (%) = (discharge capacity of the 1st cycle / charge capacity of the 1st cycle) × 100

[0114] [Table 3]

[0115] Capacity Retention Rate (%) Initial Efficiency (%) Example 1 98 76 Example 2 97 75 Example 3 98 76 Example 4 97 75 Example 5 95 76 Example 6 95 76 Example 7 94 75 Example 8 93.5 76 Example 9 98 82 Comparative Example 1 87 76 Comparative Example 2 85 75 Comparative Example 3 92 74 Comparative Example 4 90 76 Comparative Example 5 78 76 Comparative Example 6 79 72 Comparative Example 7 81 75 Comparative Example 8 83 74 Comparative Example 9 85 74 Comparative Example 10 69 68 Comparative Example 11 87 75

[0116] *SWCNT: single-walled carbon nanotube

[0117] *MWCNT: multi-walled carbon nanotube

[0118] D is measured by the laser diffraction method 50 , and the specific surface area is measured according to the BET method. The average diameter and average length each refer to the average value of the values of 100 carbon nanotubes obtained by SEM observation of the negative electrode.

[0119] According to Table 3, it can be confirmed that the batteries of the examples exhibit better life performance compared to the batteries of the comparative examples.

[0120] Regarding Example 9, since the metal is provided on the surface and / or inside of the first SiO and the second SiO, it can be confirmed that both the life performance and the initial efficiency are improved.

Claims

1. A negative electrode comprising a negative electrode active material layer, the negative electrode active material layer comprising a negative electrode active material and a conductive agent, wherein the negative electrode active material comprises a first active material and a second active material, wherein the first active material comprises SiO x particles, where 0 < x < 2, and The second active material contains SiO y particles, where 0 < y < 2, Among them, the SiO x particle has a D 50 ranging from 0.1 μm to 0.6 μm, The SiO y particle has a D 50 ranging from 3 μm to 8 μm, The SiO x particles have a weight ratio to the SiO y particles in the range of 1:2 to 1:100, wherein the SiO x particle has a D 50 to the SiO y particle has a D 50 ratio in the range of 1:5 to 1:40, and the conductive agent comprises single-walled carbon nanotubes.

2. The negative electrode according to claim 1, wherein the weight ratio of the SiO x particles to the SiO y particles is in the range of 1:10 to 1:

20.

3. The negative electrode according to claim 1, wherein the SiO x specific surface area of the particles is in the range of 1 m 2 / g to 10 m 2 / g, and The SiO y particle has a specific surface area in the range of 4 m 2 / g to 20 m 2 / g.

4. The negative electrode according to claim 1, wherein the first active material further comprises a metal disposed on, inside, or both on and inside the surface of the SiO x particles, and The metal comprises at least one selected from the group consisting of lithium, magnesium, calcium, and aluminum.

5. The negative electrode according to claim 4, wherein the content of the metal in the first active material is 0.1 wt% to 30 wt%.

6. The negative electrode according to claim 1, wherein the second active material further comprises a metal disposed on, inside, or both on and inside the surface of the SiO y particles, and The metal comprises at least one selected from the group consisting of Li, Mg, Ca, and Al.

7. The negative electrode according to claim 6, wherein the content of the metal in the second active material is 0.1 wt% to 30 wt%.

8. The negative electrode according to claim 1, wherein the single-walled carbon nanotubes have an average length of 2 μm to 100 μm.

9. The negative electrode according to claim 1, wherein the single-walled carbon nanotubes have an average length of 3 μm to 20 μm.

10. The negative electrode according to claim 1, wherein the single-walled carbon nanotubes have a specific surface area of 500 m 2 / g to 1,500 m 2 / g.

11. The negative electrode according to claim 1, wherein the content of the single-walled carbon nanotubes in the negative electrode active material layer is 0.001 wt% to 0.5 wt%.

12. The negative electrode according to claim 1, wherein the negative electrode active material further comprises a carbon-based active material.

13. A secondary battery comprising the negative electrode according to claim 1.

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