Negative electrode for lithium secondary battery and lithium secondary battery containing the same

Abstract

The present invention relates to a negative electrode for a lithium secondary battery and a lithium secondary battery comprising the negative electrode, wherein the negative electrode of the present invention comprises silicon oxide (SiO2) containing magnesium (Mg) in the negative electrode active material. x , 0

Description

Technical Field

[0001] Cross - Reference to Related Applications

[0002] This application claims the benefit of Korean Patent Application No. 10 - 2018 - 0159388, filed with the Korean Intellectual Property Office on Dec. 11, 2018, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0004] The present invention relates to a negative electrode for a lithium secondary battery and a lithium secondary battery including the negative electrode. In particular, the present invention relates to a negative electrode for a lithium secondary battery and a lithium secondary battery including the negative electrode, in which the negative electrode for a lithium secondary battery can improve the decrease in early cycle capacity and high - temperature storage performance by including a magnesium (Mg) - containing silicon oxide (SiO x , 0 < x < 2) composite material in a negative electrode active material and optimizing the type and amount of a conductive material. Background Art

[0005] With the technological development and increasing demand of mobile devices, the demand for secondary batteries as an energy source has greatly increased. Among these secondary batteries, lithium secondary batteries having high energy density, high working potential, long cycle life, and low self - discharge rate have been commercialized and widely used.

[0006] Metal oxides (such as LiCoO2, LiMnO2, LiMn2O4, or LiCrO2) are being used as the positive electrode active material constituting the positive electrode of a lithium secondary battery, and metallic lithium, carbon - based materials (such as graphite or activated carbon), or materials such as silicon oxide (SiO x ) are being used as the negative electrode active material constituting the negative electrode. Among these negative electrode active materials, metallic lithium was mainly used initially, but recently, carbon - based materials have been mainly used because the following phenomenon occurs: as the charge and discharge cycles proceed, the diaphragm is damaged due to the growth of lithium atoms on the surface of metallic lithium, thus damaging the battery. However, for carbon - based materials, their disadvantage is that their capacity is small because their theoretical capacity is only about 400 mAh / g. Therefore, various studies have been conducted on replacing carbon - based materials with silicon (Si) - based materials having a high theoretical capacity (4200 mAh / g) as the negative electrode active material.

[0007] In order to increase the energy density of a lithium secondary battery, positive electrode active materials with an increased nickel (Ni) content and silicon - based negative electrode active materials are being used. However, among silicon - based materials, SiO has the advantage of a long life due to low expansion, but since there is a problem of a decrease in early cycle capacity, improvement is required.

[0008] Prior Art Documents

[0009] [Patent Document]

[0010] (Patent Document 1) KR1586816 B Summary of the Invention

[0011] Technical Problem

[0012] One aspect of the present invention provides a negative electrode for a lithium secondary battery and a lithium secondary battery including the negative electrode, and the negative electrode for a lithium secondary battery can improve the decrease in early cycle capacity and high-temperature storage performance.

[0013] Technical Solution

[0014] According to one aspect of the present invention, there is provided a negative electrode for a lithium secondary battery, the negative electrode for a lithium secondary battery including:

[0015] a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector, wherein the negative electrode active material layer includes:

[0016] a negative electrode active material including a magnesium (Mg)-containing silicon oxide (SiO x , 0 < x < 2) composite material;

[0017] a linear conductive material as a first conductive material; and

[0018] at least one conductive material selected from a point-type conductive material and a flaky graphite-based conductive material as a second conductive material,

[0019] wherein, based on the total weight of the negative electrode active material layer, the amount of the first conductive material is in the range of 0.5 wt% to 1.7 wt%, and

[0020] the product of the amount (wt%) of the second conductive material and the Brunauer-Emmett-Teller (BET) specific surface area (m 2 / g) has a value of 100 or less.

[0021] According to another aspect of the present invention, there is provided a lithium secondary battery including the negative electrode.

[0022] Advantageous Effects

[0023] Since the negative electrode of the present invention includes a magnesium (Mg)-containing silicon oxide (SiO x , 0 < x < 2) composite material in the negative electrode active material and optimizes the type and amount of the conductive material, the life characteristics (especially the improvement of the decrease in early cycle capacity) and high-temperature storage performance of the lithium secondary battery including the negative electrode of the present invention are excellent. Detailed Description

[0024] In the following, the present invention will be described in more detail.

[0025] It will 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. It will be further understood that, based on the principle that the inventor can appropriately define the meanings of the words or terms to best explain the present invention, the words or terms should be construed as having meanings consistent with their meanings in the relevant technical background and the technical concept of the present invention.

[0026] The expression "specific surface area" in this specification is measured by the Brunauer-Emmett-Teller (BET) method. Specifically, the specific surface area can be calculated using the BELSORP-mini II of Bell Japan based on the nitrogen adsorption amount at liquid nitrogen temperature (77K).

[0027] Negative electrode

[0028] The negative electrode of the present invention is a negative electrode for a lithium secondary battery, which comprises:

[0029] A negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector, wherein the negative electrode active material layer comprises:

[0030] A negative electrode active material, which comprises a magnesium (Mg)-containing silicon oxide (SiO x , 0 < x < 2) composite material;

[0031] A linear conductive material as a first conductive material; and

[0032] At least one conductive material selected from a point-type conductive material and a flaky graphite-based conductive material as a second conductive material,

[0033] wherein, based on the total weight of the negative electrode active material layer, the amount of the first conductive material is in the range of 0.5% by weight to 1.7% by weight, and

[0034] The product of the amount (% by weight) of the second conductive material and the BET specific surface area (m 2 / g) has a value of 100 or less.

[0035] The negative electrode active material further comprises graphite and may be a magnesium (Mg)-containing silicon oxide (SiO x, a mixture of (0 < x < 2) composite material and graphite. In this case, the weight ratio of the Mg-containing silicon oxide composite material to graphite can be in the range of 1:99 to 50:50, for example, in the range of 3:95 to 20:80. If the silicon oxide composite material is included in an amount less than the above range, it may be difficult to achieve a high-capacity battery because of the difficulty in increasing the energy density, and if the silicon oxide composite material is included in an amount greater than the above range, the degree of volume expansion of the negative electrode may increase.

[0036] The Mg-containing silicon oxide composite material is a silicon oxide composite material containing at least one silicate phase selected from the following: Mg2SiO4 and MgSiO3, and the Mg-containing silicon oxide composite material may include a carbon coating on its surface.

[0037] Specifically, the Mg-containing silicon oxide composite material is formed by doping silicon oxide with Mg, and at least one silicate phase selected from Mg2SiO4 and MgSiO3 may exist in the form of domains in the silicon oxide composite material through the doped Mg.

[0038] The linear conductive material as the first conductive material may be a carbon nanotube (CNT) or a carbon nanofiber, and the dot-shaped conductive material as the second conductive material may be at least one carbon black selected from the following: acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking carbon black.

[0039] Based on the total weight of the negative electrode active material, the linear conductive material as the first conductive material may be included in an amount of 0.5 wt% to 1.7 wt%, for example, 0.5 wt% to 1.5 wt%.

[0040] When the linear conductive material is included in an amount less than 0.5 wt%, since during the charging and discharging of lithium, while the silicon oxide composite material in the electrode undergoes repeated expansion / contraction, the circuit may be easily disconnected, so the amount of the linear conductive material may be insufficient to prevent this situation, and when the linear conductive material is included in an amount greater than 1.7 wt%, since the electrode coating may become difficult due to the increase in the viscosity of the slurry or the linear conductive material cannot be well dispersed, the condition of the electrode may deteriorate.

[0041] The product of the amount of the second conductive material and the BET specific surface area may be less than or equal to 100, and specifically may have a value of 30 to 100.

[0042] When the above value is greater than 100, since the side reaction with the electrolyte increases when the battery is stored at a high temperature, the film increases, and the consumption of the electrolyte may be accelerated.

[0043] The point-type conductive material as the second conductive material may have a thickness of 30 m 2 / g to 1300m 2 / g BET specific surface area, and the flaky graphite conductive material may have a BET specific surface area of ​​3m 2 / g to 40m 2 / g BET specific surface area.

[0044] Specifically, the point-type conductive material can be Super C65 (BET = 62m 2 / g), and the flaky graphite conductive material may be SFG6L (BET = 17m 2 / g).

[0045] When the second conductive material is a point-type conductive material, its amount can be less than 3.3 weight %, for example, less than 1.6 weight %, and when the second conductive material is a flaky graphite-based conductive material, its amount can be less than 33.3 weight %, for example, less than 5.8 weight %.

[0046] Specifically, in the case where the second conductive material is Super C65 as a dot-type conductive material, the amount of Super C65 may be 1.6 wt % or less, for example, 0.5 wt % to 1.6 wt %, and in the case where the second conductive material is SFG6L as a flaky graphite-based conductive material, the amount of SFG6L may be 5.8 wt % or less, for example, 1.8 wt % to 5.8 wt %, wherein the amount (wt %) of the second conductive material and the BET specific surface area (m 2 The product of 100 g / m2 (g) and 100 g / m2 (g) may have a value of 100 or less, for example, 30 to 100.

[0047] In addition, the negative electrode active material layer generally also contains a thickener and a binder.

[0048] As in the case of preparing a common negative electrode for a lithium secondary battery, a negative electrode slurry is prepared by dissolving or dispersing a negative electrode active material, a conductive material and / or a binder in a solvent, and the negative electrode of the present invention can be prepared in the following manner: at least one surface of a negative electrode collector is coated with the negative electrode slurry, dried, and then pressed.

[0049] The negative electrode current collector is not particularly limited as long as it has high conductivity and does not cause adverse chemical changes in the battery, and for example: copper; stainless steel; aluminum; nickel; titanium; calcined carbon; copper or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc.; and aluminum-cadmium alloy. In addition, fine concavoconvexity can be formed on the surface of the negative electrode current collector to improve the adhesion of the negative electrode active material. For example, the negative electrode current collector can be used in various shapes such as a film, a sheet, a foil, a net, a porous body, a foamed body, a non-woven fabric body, etc.

[0050] The negative electrode active material may be included in an amount of 80 to 99 wt %, for example, 85 to 98 wt %, based on the total weight of the negative electrode active material layer. When the negative electrode active material is included within the above amount range, excellent capacity characteristics may be exhibited.

[0051] The binder improves the adhesion between the negative electrode active material particles and the adhesion between the negative electrode active material and the current collector. Specific examples of the binder can be polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene rubber (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluororubber or its various copolymers, and any one of the above materials or a mixture of two or more thereof can be used. Based on the gross weight of the negative electrode active material layer, the binder can be included in an amount of 1 wt % to 30 wt %.

[0052] The thickener may include methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, benzyl cellulose, trityl cellulose, cyanoethyl cellulose, carboxymethyl cellulose (CMC), carboxyethyl cellulose, aminoethyl cellulose, nitrocellulose, cellulose ether or carboxymethyl cellulose sodium salt (CMCNa). The thickener may be included in an amount of 1 wt % to 30 wt % based on the total weight of the negative electrode active material layer.

[0053] The solvent used in preparing the negative electrode slurry can be a commonly used solvent in the art, for example, dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone or water can be used alone, or a mixture of the above materials can be used. Considering the coating thickness, manufacturing yield and viscosity of the slurry, the amount of the solvent can be appropriately adjusted.

[0054] The negative electrode for a lithium secondary battery of the present invention comprises the following as basic elements: a negative electrode active material comprises a silicon oxide composite material containing magnesium (configuration 1); the negative electrode active material comprises a linear conductive material as a first conductive material in an amount of 0.5 wt % to 1.7 wt % based on the total weight of the negative electrode active material layer (configuration 2); and the negative electrode active material comprises at least one conductive material of a point-type conductive material and a flaky graphite-based conductive material as a second conductive material, wherein the amount (wt %) of the second conductive material is proportional to the BET specific surface area (m 2 The product of 100 and 100 (Structure 3) has a value of 100 or less.

[0055] That is, when all three elements are substantially combined, the desired effects of the present invention can be obtained.

[0056] For example, in the case where the conductive material contained in the negative electrode does not contain the first conductive material and the second conductive material at the same time, but contains only one of them; and even if the conductive material contains the first conductive material and the second conductive material at the same time, in the case where the amount of the first additive is not within the range of Configuration 2 or in the case where the amount of the second additive does not satisfy the value of Configuration 3, these cases may also be difficult to satisfy the desired life characteristics and high temperature storage performance (see Table 1 below).

[0057] When all three constructs are combined, the numerical ranges also have the best effect in addition to their individual meanings.

[0058] Lithium secondary battery

[0059] Next, a lithium secondary battery according to the present invention will be described.

[0060] The negative electrode according to the present invention may be suitable for preparing a lithium secondary battery.

[0061] Specifically, the lithium secondary battery according to the present invention includes a negative electrode, a positive electrode disposed facing the negative electrode, a separator disposed between the negative electrode and the positive electrode, and an electrolyte, wherein the negative electrode is the above-mentioned negative electrode according to the present invention.

[0062] The secondary battery may further selectively include a battery case accommodating an electrode assembly of a positive electrode, a negative electrode, and a separator, and a sealing member sealing the battery case.

[0063] A lithium secondary battery may be prepared according to a conventional secondary battery preparation method except for using the negative electrode according to the present invention.

[0064] In the secondary battery, the positive electrode includes a positive electrode current collector and a positive electrode active material layer provided on at least one surface of the positive electrode current collector.

[0065] The positive electrode can be prepared according to a conventional positive electrode preparation method generally known in the art. For example, the positive electrode can be prepared by dissolving or dispersing the components constituting the positive electrode active material layer (i.e., positive electrode active material, conductive material and / or binder) in a solvent to prepare a positive electrode slurry, and coating at least one surface of a positive electrode collector with the positive electrode slurry, drying it, and then pressing it; or the positive electrode slurry can be cast on a separate support, and then the film layer separated from the support is pressed on the positive electrode collector to prepare the positive electrode.

[0066] The positive electrode current collector is not particularly limited as long as it has conductivity and does not cause adverse chemical changes in the battery, and for example: stainless steel; aluminum; nickel; titanium; calcined carbon; or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc. can be used. In addition, the positive electrode current collector can generally have a thickness of 3 μm to 500 μm, and fine concavoconvexity can be formed on the surface of the current collector to improve the adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various shapes such as a film, a sheet, a foil, a net, a porous body, a foam body, a non-woven fabric body, etc.

[0067] As the positive electrode active material, for example, layered compounds such as lithium cobalt oxide (LiCoO2) and lithium nickel oxide (LiNiO2), or compounds substituted with at least one transition metal; lithium manganese oxides such as Li 1+y Mn 2-y O4 (where y is 0 to 0.33), LiMnO3, LiMn2O3 and LiMnO2; lithium copper oxide (Li2CuO2); vanadium oxides such as LiV3O8, Li3VO4, V2O5 and Cu2V2O7; 1-y M y Ni-site lithium nickel oxide represented by O2 (wherein M = cobalt (Co), manganese (Mn), aluminum (Al), copper (Cu), iron (Fe), magnesium (Mg), boron (B) or gallium (Ga), and y is 0.01 to 0.3); represented by the chemical formula LiMn 2-y M y Lithium manganese composite oxide represented by Li2Mn3MO8 (wherein M = Co, nickel (Ni), Fe, chromium (Cr), zinc (Zn) or tantalum (Ta), and y is 0.01 to 0.1); LiMn2O4 in which a portion of Li is replaced by alkaline earth metal ions; disulfide compounds; or Fe2(MoO4)3, but the positive electrode active material is not limited thereto.

[0068] In addition, the binder may be the same as the binder previously described in the negative electrode, and the conductive material is used to provide conductivity to the electrode, wherein any conductive material may be used without particular limitation, as long as it has suitable electronic conductivity and does not cause adverse chemical changes in the battery. Specific examples of the conductive material may be: graphite, such as natural graphite or artificial graphite; carbon-based materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; metals such as copper, nickel, aluminum, and silver powder or fiber; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, and any one of the above materials or a mixture of two or more thereof may be used. The conductive material may be included in an amount of 1 wt % to 30 wt % based on the total weight of the positive electrode active material layer.

[0069] In a secondary battery, the separator separates the negative electrode from the positive electrode and provides a path for the movement of lithium ions, wherein any separator can be used as a separator without particular restriction, as long as it is commonly used in a secondary battery, in particular, a separator having a high ability to retain moisture to the electrolyte and a low resistance to electrolyte ion transfer can be used. Specifically, a porous polymer film, such as a porous polymer film prepared from a polyolefin polymer (such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer) can be used; or a laminated structure having more than two layers in the above porous polymer film. In addition, a typical porous non-woven fabric can be used, such as a non-woven fabric formed of a high melting point glass fiber or a polyethylene terephthalate fiber. In addition, a coated separator containing a ceramic component or a polymer material can be used to ensure heat resistance or mechanical strength, and a separator having a single-layer or multilayer structure can be selectively used.

[0070] As the electrolyte, 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 in the preparation of a lithium secondary battery may be used, but the present invention is not limited thereto.

[0071] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0072] Any organic solvent can be used as the organic solvent without particular limitation, as long as it can act as a medium through which ions participating in the electrochemical reaction of the battery can move. Specifically, the following substances can be used as organic solvents: ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; or carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC) and propylene carbonate (PC); alcohol solvents such as ethanol and isopropanol; nitrile, such as Ra-CN (wherein Ra is a straight chain, branched or cyclic hydrocarbon group having 2 to 20 carbon atoms and may contain a double bond, an aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolanes; or cyclopentane sulfone. Among these solvents, carbonate solvents can be used, for example, a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ion conductivity and high dielectric constant and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) that can improve the charge / discharge performance of the battery can be used. In this case, when the cyclic carbonate and the chain carbonate are mixed in a volume ratio of about 1:1 to about 1:9, the performance of the electrolyte can be excellent.

[0073] Lithium salts can be used without particular limitation, as long as they are compounds that can provide lithium ions used in lithium secondary batteries. Specifically, as lithium salts, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI or LiB(C2O4)2 can be used. Lithium salts can be used in a concentration range of 0.1M to 2.0M. In the case where the concentration of the lithium salt is included in the above range, since the electrolyte can have appropriate conductivity and viscosity, the excellent performance of the electrolyte can be obtained, and the lithium ions can be efficiently moved.

[0074] In addition to the above-mentioned electrolyte components, in order to improve the life characteristics of the battery, suppress the decrease in battery capacity, and improve the discharge capacity of the battery, etc., the electrolyte may further contain at least one additive, such as: halogenated alkylene carbonate compounds (such as ethyl difluorocarbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, (poly)ethylene glycol dimethyl ethers, hexamethylphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinones, N,N-substituted imidazolines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride. In this case, based on the total weight of the electrolyte, the additive may be contained in an amount of 0.1% by weight to 5% by weight.

[0075] Examples

[0076] Hereinafter, the present invention will be described in detail according to examples. However, the following examples are provided only to illustrate the present invention and not to limit the scope of the present invention.

[0077] The BET specific surface area of Super C65, which is used as the conductive material in the following examples and comparative examples, is 62 m 2 / g, and the BET specific surface area of SFG6L is 17 m 2 / g. The specific surface area is measured by the BET method. Specifically, the specific surface area can be calculated using BELSORP-mini II of Bell Japan Co., Ltd. based on the nitrogen adsorption amount at liquid nitrogen temperature (77K).

[0078] Example 1

[0079] Mix "SiO x (0 < x < 2) formed by doping Mg into SiO and containing at least one silicate phase selected from Mg2SiO4 and MgSiO3 (Mg-containing silicon oxide composite material)" and spherical natural graphite in a weight ratio of 15:85 to be used as the negative electrode active material, and mix the negative electrode active material, CNT, Super C65 (point-type conductive material), CMC, and SBR in a weight ratio of 96:1:1:1:1 to prepare a negative electrode slurry. Coat the copper current collector with the negative electrode slurry, dry it, and roll it to prepare a negative electrode.

[0080] Example 2

[0081] Mix "SiO x (0 < x < 2) formed by doping Mg into SiO and containing at least one silicate phase selected from Mg2SiO4 and MgSiO3 x ​​(0 < x < 2) (Silicon oxide composite containing Mg) and spherical natural graphite are mixed at a weight ratio of 15:85 to be used as the negative electrode active material, and the negative electrode active material, CNT, SFG6L (flake graphite-based conductive material), CMC, and SBR are mixed at a weight ratio of 92:1:5:1:1 to prepare a negative electrode paste. The copper current collector is coated with the negative electrode paste, dried, and roll-pressed to prepare a negative electrode.

[0082] Example 3

[0083] Except for using 0.75 wt% of CNT in Example 1 to mix the negative electrode active material, CNT, Super C65 (dot-type conductive material), CMC, and SBR at a weight ratio of 96.25:0.75:1:1:1, the negative electrode is prepared in the same manner as in Example 1.

[0084] Example 4

[0085] Except for using 0.75 wt% of CNT in Example 2 to mix the negative electrode active material, CNT, SFG6L (flake graphite-based conductive material), CMC, and SBR at a weight ratio of 92.25:0.75:5:1:1, the negative electrode is prepared in the same manner as in Example 2.

[0086] Example 5

[0087] Except for using 1.5 wt% of CNT in Example 1 to mix the negative electrode active material, CNT, Super C65 (dot-type conductive material), CMC, and SBR at a weight ratio of 95.5:1.5:1:1:1, the negative electrode is prepared in the same manner as in Example 1.

[0088] Example 6

[0089] Except for using 1.5 wt% of CNT in Example 2 to mix the negative electrode active material, CNT, SFG6L (flake graphite-based conductive material), CMC, and SBR at a weight ratio of 91.5:1.5:5:1:1, the negative electrode is prepared in the same manner as in Example 2.

[0090] Comparative Example 1

[0091] Except for not using CNT as the conductive material in Example 1 and only using Super C65 to mix the negative electrode active material, Super C65, CMC, and SBR at a weight ratio of 96:2:1:1, the negative electrode is prepared in the same manner as in Example 1.

[0092] Comparative Example 2

[0093] A negative electrode was prepared in the same manner as in Example 2, except that CNT was not used as a conductive material in Example 2 and only SFG6L was used to mix the negative electrode active material, SFG6L, CMC, and SBR in a weight ratio of 88:10:1:1.

[0094] Comparative Example 3

[0095] A negative electrode was prepared in the same manner as in Example 1, except that only 1 wt % of CNT was used as a conductive material to mix the negative electrode active material, CNT, CMC, and SBR in a weight ratio of 97:1:1:1.

[0096] Comparative Example 4

[0097] A negative electrode was prepared in the same manner as in Example 1, except that 0.4 wt % of CNT was used in Example 1 to mix the negative electrode active material, CNT, Super C65, CMC, and SBR in a weight ratio of 96.6:0.4:1:1:1.

[0098] Comparative Example 5

[0099] A negative electrode was prepared in the same manner as in Example 1, except that only 2 wt % of CNT was used as a conductive material to mix the negative electrode active material, CNT, CMC, and SBR in a weight ratio of 96:2:1:1.

[0100] Comparative Example 6

[0101] A negative electrode was prepared in the same manner as in Example 1, except that 2 wt % of Super C65 was used in Example 1 to mix the negative electrode active material, CNT, Super C65, CMC, and SBR in a weight ratio of 95:1:2:1:1.

[0102] Comparative Example 7

[0103] A negative electrode was prepared in the same manner as in Example 2, except that 10 wt % of SFG6L was used in Example 2 to mix the negative active material, CNT, SFG6L, CMC, and SBR in a weight ratio of 87:1:10:1:1.

[0104] Comparative Example 8

[0105] A negative electrode was prepared in the same manner as in Example 1, except that 2 wt % of CNTs were used in Example 1 to mix the negative active material, CNTs, Super C65, CMC, and SBR in a weight ratio of 95:2:1:1:1.

[0106] Comparative Example 9

[0107] A negative electrode was prepared in the same manner as in Example 2, except that 2 wt % of CNT was used in Example 2 to mix the negative active material, CNT, SFG6L, CMC, and SBR in a weight ratio of 91:2:5:1:1.

[0108] Comparative Example 10

[0109] A negative electrode was prepared in the same manner as in Example 2, except that 0.4 wt % of CNT was used in Example 2 to mix the negative active material, CNT, SFG6L, CMC, and SBR in a weight ratio of 92.6:0.4:5:1:1.

[0110] Experimental Example 1. Capacity retention after 100 cycles at 25°C

[0111] Single cells were prepared using the NCM 811 positive electrode and the negative electrodes prepared in the examples and comparative examples.

[0112] Each of the single cells prepared using the negative electrodes prepared in the examples and comparative examples was charged and discharged at 1C / 1C at 25° C. to confirm the capacity retention ratio after 100 cycles.

[0113] The capacity retention ratio was measured according to the following equation (1).

[0114] Equation (1): Capacity retention rate (%) = {discharge capacity after 100 cycles / discharge capacity after one cycle} × 100

[0115] The measured discharge capacities are shown in Table 1 below.

[0116] Experimental Example 2. Capacity retention after storage at 60°C for 2 weeks

[0117] Single cells were prepared using the NCM 811 positive electrode and the negative electrodes prepared in the examples and comparative examples.

[0118] Each single cell prepared using the negative electrode prepared in the embodiment and the comparative example was charged to a state of charge (SOC) of 100 under constant current / constant voltage (CC / CV) conditions at 25°C (specifically, charged to 4.2V in CC mode and then charged to 0.05C in CV mode), and then stored at a high temperature of 60°C for 2 weeks. After that, the capacity retention rate was measured again at room temperature, and the results are shown in Table 1 below.

[0119] [Table 1]

[0120]

[0121] The results in Table 1 show that the battery using the negative electrode of the example is superior to the battery using the negative electrode of the comparative example in terms of life characteristics (particularly improvement in early cycle capacity reduction) and high-temperature storage performance.

[0122] For example, in the case where the conductive material contained in the negative electrode does not contain the first conductive material and the second conductive material at the same time, but contains only one of the first conductive material and the second conductive material (Comparative Examples 1, 2, 3 and 5); and even if the conductive material contains the first conductive material and the second conductive material at the same time, in the case where the amount of the first conductive material is outside the range of Configuration 2 (Comparative Examples 4, 8, 9 and 10) or in the case where the amount of the second conductive material does not satisfy the value of Configuration 3 (Comparative Examples 6 and 7), all of these cases are difficult to satisfy the desired life characteristics and high temperature storage performance (see Table 1).

[0123] Specifically, when the first conductive material is not included as the conductive material and only the second conductive material (Super C65 or SFG6L) is included (Comparative Examples 1 and 2), it can be confirmed that the capacity retention rate after 100 cycles and the capacity retention rate after high temperature storage are significantly reduced compared with the embodiment.

[0124] In addition, in the case where the second conductive material is not included and only CNTs are included as the first conductive material (Comparative Examples 3 and 5), it can be confirmed that even if the amount is within the range of the present invention (1 weight %) (Comparative Example 3), the capacity retention rate after 100 cycles and the capacity retention rate after high-temperature storage are significantly reduced compared with the embodiment; and, in the case where only CNTs are included and an excessive amount (2 weight %) is included (Comparative Example 5), it is difficult to assemble the battery because the CNTs are not well dispersed and the surface state of the electrode is poor.

[0125] In addition, when the amount of the first conductive material (CNT) is 0.4 wt % (which is less than the scope of the present invention), even if the first conductive material (CNT) and the second conductive material (Super C65 or SFG6L) are simultaneously contained (Comparative Examples 4 and 10), it can be confirmed that the capacity retention rate after 100 cycles and the capacity retention rate after high-temperature storage are significantly reduced compared with the embodiment; and, when the amount of the first conductive material (CNT) is 2 wt % (which is greater than the scope of the present invention), even if the first conductive material (CNT) and the second conductive material (Super C65 or SFG6L) are simultaneously contained (Comparative Examples 8 and 9), it is difficult to assemble the battery because the CNT is not well dispersed and the surface state of the electrode is poor.

[0126] In addition, when the product of the amount of the second conductive material and the BET specific surface area is greater than 100, even if the first conductive material (CNT) and the second conductive material (Super C65 or SFG6L) are simultaneously contained (Comparative Examples 6 and 7), it can be confirmed that the capacity retention rate after 100 cycles is similar to that of the embodiment, but the capacity retention rate after high temperature storage is significantly reduced.

Claims

1. A negative electrode for a lithium secondary battery, the negative electrode comprising: a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector, wherein the negative electrode active material layer comprises: A negative electrode active material, the negative electrode active material comprising silicon oxide SiO containing magnesium (Mg) x Composite materials, of which 0 <x<2; A linear conductive material as a first conductive material; and At least one conductive material selected from a point-type conductive material and a flaky graphite-based conductive material as the second conductive material, wherein the amount of the first conductive material is in the range of 0.5 wt % to 1.7 wt % based on the total weight of the negative electrode active material layer, and The amount of the second conductive material expressed in weight % is equal to the amount of the second conductive material expressed in m % based on the total weight of the negative electrode active material layer. 2 The product of the Brunauer-Emmett-Teller (BET) specific surface area expressed in Å / g has a value of 100 or less. 2 . The negative electrode for a lithium secondary battery according to claim 1 , wherein a content of the linear conductive material as the first conductive material is 0.5 wt % to 1.5 wt % based on the total weight of the negative electrode active material layer. 3 . The negative electrode for a lithium secondary battery according to claim 1 , wherein the negative electrode active material further comprises graphite. 4 . The negative electrode for a lithium secondary battery according to claim 3 , wherein a weight ratio of the magnesium-containing silicon oxide composite material:graphite is in the range of 1:99 to 50:

50. 5 . The negative electrode for a lithium secondary battery according to claim 1 , wherein the silicon oxide composite material containing magnesium is a silicon oxide composite material containing at least one silicate phase selected from the group consisting of Mg 2 SiO 4 and MgSiO 3 .

6. The negative electrode for lithium secondary battery according to claim 1, wherein the amount of the second conductive material expressed in weight % is equal to the amount of the second conductive material expressed in m 2 The product of the BET specific surface area expressed as 100 μm / g has a value of 30 to 100. 7 . The negative electrode for a lithium secondary battery according to claim 1 , wherein the linear conductive material comprises at least one selected from the group consisting of carbon nanotubes (CNTs) and carbon nanofibers. 8 . The negative electrode for a lithium secondary battery according to claim 1 , wherein the dot-type conductive material comprises at least one carbon black selected from the group consisting of acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black.

9. The negative electrode for a lithium secondary battery according to claim 1, wherein the point-type conductive material has a 2 / g to 1300m 2 / g BET specific surface area.

10. The negative electrode for lithium secondary battery according to claim 1, wherein the flaky graphite conductive material has a 3m 2 / g to 40m 2 / g BET specific surface area. 11 . The negative electrode for a lithium secondary battery according to claim 9 , wherein an amount of the dot-type conductive material is 1.6 wt % or less based on the total weight of the negative electrode active material layer. 12 . The negative electrode for a lithium secondary battery according to claim 10 , wherein an amount of the flaky graphite-based conductive material is 5.8 wt % or less based on the total weight of the negative electrode active material layer. 13 . The negative electrode for a lithium secondary battery according to claim 1 , wherein the negative electrode active material layer further comprises a thickener and a binder. 14 . The negative electrode for a lithium secondary battery according to claim 1 , wherein the Mg-containing silicon oxide composite material comprises a carbon coating layer on a surface thereof. 15 . A lithium secondary battery, comprising the negative electrode for a lithium secondary battery according to claim 1 .

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