Negative electrode active material for lithium secondary battery, negative electrode for lithium secondary battery, and lithium secondary battery

Abstract

A negative electrode active material for a lithium secondary battery according to an exemplary embodiment includes: a first negative electrode active material including a carbon-based active material; and a second negative electrode active material including a silicon-based active material having a carbon content of 1 wt% or less, in which the content of the second negative electrode active material is 0.1 wt% to 9 wt% based on the total weight of the negative electrode active material, and the peak intensity ratio of the Raman spectrum of the second negative electrode active material defined by a predetermined equation is 0.5 to 2.3. Accordingly, the resistance and expansion rate of the negative electrode are reduced and the output characteristics of the lithium secondary battery are improved.

Description

Technical Field

[0001] This invention relates to a negative electrode active material for lithium secondary batteries, a negative electrode for lithium secondary batteries, and lithium secondary batteries. Background Technology

[0002] Rechargeable batteries are batteries that can be repeatedly charged and discharged. With the rapid development of the information and communication and display industries, rechargeable batteries have been widely used as a power source for various portable electronic telecommunications devices (such as cameras, mobile phones, and laptops). Recently, battery packs that include rechargeable batteries have also been developed and are being used as a power source in environmentally friendly vehicles such as hybrid vehicles and electric vehicles.

[0003] Examples of rechargeable batteries include lithium-ion batteries, nickel-cadmium batteries, and nickel-metal hydride batteries. Among them, lithium-ion batteries have advantages in terms of high operating voltage and high energy density per unit weight, as well as fast charging speed and light weight, which has led to progress in their development.

[0004] Lithium-ion secondary batteries may include, for example, electrode assemblies comprising a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrodes; and an electrolyte impregnating the electrode assemblies therein. Lithium-ion secondary batteries may also include a pouch-shaped outer case housing the electrode assemblies and the electrolyte.

[0005] Recently, with the expansion of applications for lithium-ion batteries, progress has been made in the development of lithium-ion batteries with higher capacity and output. For example, high-capacity silicon and carbon can be prepared and used as anode active materials. However, silicon undergoes volume expansion during repeated charging and discharging, which may lead to a degradation in battery capacity and lifespan. Summary of the Invention

[0006] One object of the present invention is to provide a negative electrode active material for lithium secondary batteries, which have improved mechanical stability and output characteristics.

[0007] Another object of the present invention is to provide a negative electrode for a lithium secondary battery, which has improved mechanical stability and output characteristics.

[0008] Furthermore, another object of the present invention is to provide a lithium secondary battery having improved mechanical stability and output characteristics.

[0009] To achieve the above object, according to one aspect of the present invention, there is provided a negative electrode active material for a lithium secondary battery, comprising: a first negative electrode active material including a carbon-based active material; and a second negative electrode active material including a silicon-based active material having a carbon content of 1 wt% or less, wherein based on the total weight of the negative electrode active material, the content of the second negative electrode active material is 0.1 wt% to 9 wt%, and the peak intensity ratio of the Raman spectrum of the second negative electrode active material defined by the following Equation 1 is 0.5 to 2.3:

[0010] [Equation 1]

[0011] Peak intensity ratio of Raman spectrum = I(520) / I(470)

[0012] In Equation 1, I(520) is the peak intensity of the second negative electrode active material at a Raman shift of 520 cm -1 in the Raman spectrum, and I(470) is the peak intensity of the second negative electrode active material at a Raman shift of 470 cm -1 in the Raman spectrum.

[0013] In some embodiments, the silicon-based active material may include silicon oxide (SiO x , 0 < x < 2) particles.

[0014] In some embodiments, the silicon oxide particles may have no carbon coating on their surfaces.

[0015] In some embodiments, the carbon content of the silicon-based active material may be 0.5 wt% or less.

[0016] In some embodiments, the carbon content of the silicon-based active material may be 0 wt%.

[0017] In some embodiments, the peak intensity ratio of the Raman spectrum of the second negative electrode active material may be 0.6 to 2.

[0018] In some embodiments, based on the total weight of the negative electrode active material, the content of the second negative electrode active material may be 0.5 wt% to 8 wt%.

[0019] In some embodiments, based on the total weight of the negative electrode active material, the content of the first negative electrode active material may be 90 wt% to 98 wt%.

[0020] In some embodiments, the carbon-based active material may include at least one selected from the group consisting of artificial graphite and natural graphite.

[0021] According to another aspect of the present invention, a negative electrode for a lithium secondary battery is provided, comprising: a negative electrode current collector; and a negative electrode active material layer formed on at least one surface of the negative electrode current collector and comprising the negative electrode active material for a lithium secondary battery according to the above embodiment.

[0022] In some implementations, the pore volume of the negative electrode active material layer can be from 0.20 mL / g to 0.25 mL / g.

[0023] In some implementations, the pore volume of the negative electrode active material layer can be from 0.22 mL / g to 0.24 mL / g.

[0024] In some implementations, the expansion rate, as defined by Equation 2 below, can be from 1% to 10.5%:

[0025] [Equation 2]

[0026] Expansion rate (%) = (T) B -T A ) / (T A )×100

[0027] In equation 2, T A The thickness of the negative electrode, T, can be defined as follows: when the state of charge of the lithium secondary battery, including the negative electrode, can be 0%. B The thickness of the negative electrode can be defined as the state of charge of the lithium secondary battery, including the negative electrode, when it is 100%.

[0028] In some implementations, the expansion rate can be between 2% and 10%.

[0029] Furthermore, according to another aspect of the present invention, a lithium secondary battery is provided, comprising: a negative electrode for a lithium secondary battery according to the above embodiment; and a positive electrode configured to face the negative electrode.

[0030] According to an exemplary embodiment, the negative electrode active material for a lithium secondary battery may include a silicon-based active material and a carbon-based active material of a predetermined composition, wherein the ratio of crystalline silicon to amorphous silicon is controllable.

[0031] Therefore, the volume expansion of silicon can be suppressed, thereby preventing cracks in the negative electrode active material during repeated charging and discharging, and improving the mechanical stability and output characteristics of lithium secondary batteries.

[0032] Negative electrode active materials can be widely used in applications such as battery-powered electric vehicles, battery charging stations, and other green technologies related to solar and wind power generation. Furthermore, lithium-ion batteries can be used in environmentally friendly electric vehicles and hybrid vehicles, aiming to prevent climate change by reducing air pollution and greenhouse gas emissions. Attached Figure Description

[0033] The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, wherein:

[0034] Figure 1 and Figure 2 These are schematic plan views and cross-sectional views illustrating a rechargeable lithium battery according to an exemplary embodiment. Detailed Implementation

[0035] An embodiment of the present invention provides a negative electrode active material comprising a silicon-based active material and a carbon-based active material of a predetermined composition, wherein the ratio of crystalline silicon to amorphous silicon is controllable. Furthermore, a negative electrode comprising the negative electrode active material and a lithium secondary battery comprising the negative electrode are also provided.

[0036] As used herein, the terms “first” and “second” do not restrict the numbering or order of the subjects modified by “first” and “second”, but can be used to distinguish between subjects that are modified differently from each other.

[0037] As used in this article, "carbon-based active material" can refer to a substance that includes carbon but does not include silicon.

[0038] As used in this article, “silicon-based active material” can refer to a substance that includes silicon.

[0039] The embodiments of the present invention will be described in detail below. However, these embodiments are merely examples, and the present invention is not limited to the specific embodiments described in the examples.

[0040] The negative electrode active material (hereinafter referred to as "negative electrode active material") for a lithium secondary battery according to an exemplary embodiment may include a first negative electrode active material, which includes a carbon-based active material, and a second negative electrode active material, which includes a silicon-based active material with a carbon content of less than 1% by weight.

[0041] In some implementations, the negative electrode active material can be essentially composed of a first negative electrode active material and a second negative electrode active material.

[0042] In some implementations, the carbon-based active material includes at least one selected from the group consisting of artificial graphite and natural graphite. For example, artificial graphite can improve the mechanical stability of lithium secondary batteries, while natural graphite can increase the capacity and output of lithium secondary batteries.

[0043] In some implementations, the carbon-based active material may include artificial graphite. For example, the carbon-based active material may be composed of artificial graphite, thereby improving the output and lifespan characteristics of the lithium secondary battery.

[0044] In one embodiment, the first negative electrode active material may be composed of a carbon-based active material. In another embodiment, the first negative electrode active material may include a carbon-based active material and may not include carbon-silicon (Si / C) composite particles.

[0045] For example, when the carbon content of the silicon-based active material is greater than 1% by weight, during the heat treatment process for preparing the silicon-based active material, crystalline silicon may grow, resulting in excessive volume expansion of the electrode during repeated charging and discharging. Therefore, cracks may occur in the negative electrode active material, and the intercalation and deintercalation of lithium ions may be hindered.

[0046] In some embodiments, the silicon-based active material may have a carbon content of 0.5% by weight or less, such as 0.1% by weight or less, 0.01% by weight or less, or 0% by weight. Within the above carbon content range, the resistance and expansion rate of the negative electrode can be reduced, and the mechanical stability and output of the lithium secondary battery can be improved.

[0047] For example, a thermogravimetric analyzer (TGA) can be used to measure the carbon content in the silicon-based active material.

[0048] In some embodiments, the silicon-based active material may include silicon oxide (SiO x , 0 < x < 2) particles.

[0049] In one embodiment, the second negative electrode active material may be composed of a silicon-based active material. In another embodiment, the second negative electrode active material may be composed of silicon oxide (SiO x , 0 < x < 2) particles.

[0050] For example, the silicon oxide (SiO x , 0 < x < 2) particles may not include carbon but may include carbon as an impurity. For example, trace amounts of carbon contained in the dioxides or monoxides of metals such as iron, chromium, nickel, zinc, or copper may be included as impurities. Therefore, the silicon-based active material may have a carbon content within the above range.

[0051] In some embodiments, the silicon oxide particles may not have a carbon coating on their surface.

[0052] For example, when the silicon oxide particles are mixed with a carbon source gas and calcined by chemical vapor deposition (CVD) to form a carbon coating on the particle surface, the proportion of crystalline silicon may increase due to heating during the calcination process.

[0053] Therefore, the second negative electrode active material may have a lattice structure in which lithium ions are difficult to intercalate and deintercalate, which may not suppress volume expansion during repeated charging and discharging, thus leading to the formation of cracks in the negative electrode active material.

[0054] According to an exemplary embodiment, the peak intensity ratio of the Raman spectrum of the second negative electrode active material, as defined by the following Equation 1, can be from 0.5 to 2.3.

[0055] [Equation 1]

[0056] The peak intensity ratio of the Raman spectrum = I(520) / I(470)

[0057] In Equation 1, I(520) can be the Raman shift of 520 cm⁻¹ in the Raman spectrum. -1 The peak intensity of the second negative electrode active material, I(470), can be the Raman shift of 470 cm⁻¹ in the Raman spectrum. -1 The peak intensity of the second negative electrode active material.

[0058] For example, in Equation 1, I(520) can represent the specific gravity of silicon (crystalline Si) with a crystalline structure, and in Equation 1, I(470) can represent the specific gravity of silicon (amorphous Si) with an amorphous structure.

[0059] For example, when the peak intensity ratio of the Raman spectrum of the second negative electrode active material is greater than 2.3, the second negative electrode active material may have a lattice structure in which lithium ions are difficult to insert and deintercalate, which may not suppress volume expansion during repeated charging and discharging. Therefore, the mechanical stability and output characteristics of the lithium secondary battery may deteriorate.

[0060] For example, when the peak intensity ratio of the Raman spectrum of the second negative electrode active material is less than 0.5, the specific gravity of amorphous silicon may be too high. Therefore, the initial irreversible capacity may increase, leading to a decrease in battery capacity and efficiency, as well as an increase in electrode resistance.

[0061] In some embodiments, the peak intensity ratio of the Raman spectrum of the second negative electrode active material can be 0.6 to 2, for example 0.65 to 1.9, 0.7 to 1.8, or 0.8 to 1.7. Within these ranges, crack formation in the negative electrode active material can be suppressed, and the resistance of the negative electrode during repeated charging and discharging can be reduced.

[0062] Raman spectroscopy can be performed using Raman spectrometers of a type known in the art. For example, the laser wavelength of the Raman spectrometer can be from about 532 nm to about 785 nm, the laser power can be from about 5 mW to about 90 mW, the laser exposure time can be from about 3 seconds to about 20 seconds, and the number of scans can be from 1 to 10.

[0063] The characteristics (e.g., Raman characterization) of the second negative electrode active material according to embodiments of the present invention do not necessarily depend on the carbon content and the presence or absence of the aforementioned carbon coating. For example, the peak intensity ratio of the aforementioned Raman spectrum may also vary due to other factors (including the type of silicon oxide, individual physical properties (e.g., particle diameter, heat treatment temperature, etc.)).

[0064] According to an exemplary embodiment, the content of the second negative electrode active material can be from 0.1% by weight to 9% by weight, based on the total weight of the negative electrode active material.

[0065] For example, based on the total weight of the negative electrode active material, when the content of the second negative electrode active material is less than 0.1% by weight, the resistance of the lithium secondary battery may increase and the output characteristics may deteriorate.

[0066] For example, based on the total weight of the negative electrode active material, when the content of the second negative electrode active material is greater than 9% by weight, the volume of the electrode may excessively expand during repeated charging and discharging. Therefore, the surface structure of the negative electrode active material may collapse, and side reactions between the electrode and the electrolyte may increase, thereby degrading the battery's lifespan characteristics.

[0067] In some embodiments, the content of the second negative electrode active material can be from 0.5% to 8% by weight, for example, from 1% to 7% by weight, from 2% to 6.5% by weight, or from 3% to 6% by weight, based on the total weight of the negative electrode active material. Within the above range, crack formation in the negative electrode active material can be suppressed, and the resistance of the negative electrode can be reduced.

[0068] In some implementations, the content of the first negative electrode active material can be from 90% to 98% by weight, for example, 91% to 97% by weight, 92% to 96% by weight, or 93% to 95.5% by weight, based on the total weight of the negative electrode active material. Within the above range, the capacity and lifespan characteristics of the lithium secondary battery can be improved.

[0069] Figure 1 and Figure 2 These are schematic plan views and cross-sectional views illustrating a lithium secondary battery according to an exemplary embodiment. Specifically, Figure 2 It is along Figure 1 The cross-sectional view taken by line I-I' in the diagram.

[0070] Reference Figure 1 and Figure 2 The lithium secondary battery may include an electrode assembly 150, which includes a positive electrode 100 and a negative electrode 130. The electrode assembly 150 may also include a separator 140 disposed between the positive electrode 100 and the negative electrode 130. The electrode assembly 150 may be housed in a casing 160 together with an electrolyte comprising an electrolyte, and the electrode assembly 150 may be impregnated with the electrolyte.

[0071] The negative electrode 130 may include a negative electrode current collector 125 and a negative electrode active material layer 120, the negative electrode active material layer 120 being formed on at least one surface of the negative electrode current collector 125 and including a negative electrode active material for a lithium secondary battery according to the above embodiments.

[0072] In some embodiments, the pore volume of the negative electrode active material layer 120 can be from 0.20 mL / g to 0.25 mL / g. For example, the pore volume of the negative electrode active material layer 120 can refer to the channels for lithium ion movement per unit area and can be measured by mercury porosimetry.

[0073] The mercury porosity method can be a technique where a vacuum is applied to the negative electrode, and then pressures are applied sequentially from low to high while the entire sample is surrounded by mercury. The volume of mercury entering the pores within the sample is then measured. For example, the void volume can be measured by applying pressures ranging from 0.2 psia to 33,000 psia and forcing mercury into the pores within the sample.

[0074] For example, the pore volume of the negative electrode active material layer 120 can be calculated by measuring the total pore volume of the negative electrode active material layer 120 using a mercury porosimeter and dividing the total pore volume by the total weight of the negative electrode active material layer 120.

[0075] For example, the pore volume of the negative electrode active material layer 120 can be from 0.22 mL / g to 0.24 mL / g, from 0.225 mL / g to 0.235 mL / g, or from 0.230 mL / g to 0.235 mL / g.

[0076] Within the aforementioned range, lithium-ion diffusion from the negative electrode surface to the interior of the negative electrode can be promoted, and the volume expansion of the negative electrode active material can be accommodated. Therefore, the resistance of the negative electrode can be reduced, and the output characteristics and mechanical stability of the lithium secondary battery can be improved.

[0077] In some implementations, the peak intensity ratio of the Raman spectrum of the second negative electrode active material and the pore volume range of the negative electrode active material layer 120 can be simultaneously satisfied. Therefore, crack formation in the negative electrode active material can be suppressed, conductivity can be increased, and the capacity and efficiency of the lithium secondary battery can be improved.

[0078] In some implementations, the expansion rate of the negative electrode 130, as defined by the following Equation 2, can be from 1% to 10.5%.

[0079] [Equation 2]

[0080] Expansion rate (%) = (T) B -T A ) / (T A )x100

[0081] In equation 2, T A It can be the thickness of the negative electrode 130 when the state of charge of the lithium secondary battery, including the negative electrode 130, is 0%, T B It can be the thickness of the negative electrode 130 when the state of charge of the lithium secondary battery including the negative electrode 130 is 100%.

[0082] For example, the expansion rate of the negative electrode 130 can be 2% to 10%, 3% to 9.5%, 4% to 9%, or less than 10%. An expansion rate of the negative electrode 130 within these ranges can improve the mechanical stability and lifespan characteristics of the lithium-ion secondary battery.

[0083] For example, the negative electrode current collector 125 may include a highly conductive metal that improves adhesion to the negative electrode slurry and is non-reactive within the voltage range of the secondary battery. For example, the thickness of the negative electrode current collector 125 may be, for example, from 10 μm to 50 μm, but is not limited thereto.

[0084] For example, the negative electrode current collector 125 may include gold, copper, stainless steel, nickel, aluminum, titanium, or alloys thereof. The negative electrode current collector 125 may include copper or stainless steel that has been surface-treated with carbon, nickel, titanium, or silver.

[0085] For example, according to the above embodiments, the negative electrode active material layer 120 includes a negative electrode active material and a negative electrode binder for lithium secondary batteries, and may also include a conductive material.

[0086] For example, the negative electrode 130 can be prepared by mixing and stirring the first negative electrode active material, the second negative electrode active material, the negative electrode binder and the conductive material in the solvent, then coating the negative electrode slurry onto the negative electrode current collector 125, and then drying and calendering it.

[0087] The coating process can be carried out by methods such as gravure coating, slot die coating, multi-layer die coating, embossing, doctor blade coating, dip coating, bar coating, and casting.

[0088] Non-limiting examples of solvents used for negative electrode slurries may include water, pure water, deionized water, distilled water, ethanol, isopropanol, methanol, acetone, n-propanol, tert-butanol, etc.

[0089] In some implementations, styrene-butadiene rubber (SBR) based adhesives, carboxymethyl cellulose (CMC), polyacrylic acid based adhesives, poly(3,4-ethylenedioxythiophene) (PEDOT) based adhesives, etc., can be used as negative electrode adhesives.

[0090] Conductive materials can be added to the negative electrode active material layer to improve its conductivity and / or the mobility of lithium ions or electrons. For example, conductive materials may include carbon-based conductive materials (such as graphite, carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes (CNTs), vapor-grown carbon fibers (VGCFs), carbon fibers) and / or metal-based conductive materials including tin, tin oxide, titanium oxide, or perovskite minerals such as LaSrCoO3 and LaSrMnO3.

[0091] For example, the negative electrode active material layer 120 may also include a thickener and / or a dispersant, with carboxymethyl cellulose (CMC) used as the thickener.

[0092] The positive electrode 100 may include a positive electrode current collector 105 and a positive electrode active material layer 110 disposed on at least one surface of the positive electrode current collector 105.

[0093] For example, the positive current collector 105 may include stainless steel, nickel, aluminum, titanium, or alloys thereof. The positive current collector may also include aluminum or stainless steel that has been surface-treated with carbon, nickel, titanium, or silver, but is not limited thereto.

[0094] For example, the positive electrode active material layer 110 may include a positive electrode active material, which may include a compound that enables reversible insertion and deintercalation of lithium ions.

[0095] According to an exemplary embodiment, the positive electrode active material may include a lithium nickel metal oxide. The lithium nickel metal oxide may also include at least one of cobalt (Co), manganese (Mn), and aluminum (Al).

[0096] In some implementations, the positive electrode active material or lithium nickel metal oxide may include a layered structure or a crystal structure represented by Formula 1 below.

[0097] [Formula 1]

[0098] Li x Ni a M b O 2+z

[0099] In Equation 1, x, a, b, and z can satisfy 0.9 ≤ x ≤ 1.2, 0.6 ≤ a ≤ 0.99, 0.01 ≤ b ≤ 0.4, and -0.5 ≤ z ≤ 0.1. As mentioned above, M can include Co, Mn, and / or Al.

[0100] The chemical structure represented by Formula 1 indicates a bonding relationship between the elements contained in the layered or crystal structure of the positive electrode active material, and does not exclude other additional elements. For example, M includes Co and / or Mn, which, together with Ni, can provide Co and Mn as the main active elements of the positive electrode active material. Here, it should be understood that Formula 1 is provided to represent the bonding relationship between the main active elements, and Formula 1 is a formula that includes the introduction and substitution of additional elements.

[0101] In one embodiment, the positive electrode active material may further include auxiliary elements added to the main active element to enhance its chemical stability or layered / crystal structure. The auxiliary elements may be incorporated into the layered / crystal structure to form bonds, and it should be understood that this also applies to chemical structures represented by Formula 1.

[0102] Auxiliary elements may include at least one of, for example, Na, Mg, Ca, Y, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Cu, Ag, Zn, B, Al, Ga, C, Si, Sn, Sr, Ba, Ra, P, or Zr. For example, auxiliary elements such as Al can be used as auxiliary active elements, which, together with Co or Mn, contribute to the capacity / output activity of the positive electrode active material.

[0103] For example, the positive electrode active material or lithium nickel metal oxide may include a layered structure or a crystal structure represented by Formula 1-1 below.

[0104] [Equation 1-1]

[0105] Li x Ni a M1 b1 M2 b2 O 2+z

[0106] In Equation 1-1, M1 may include Co, Mn and / or Al. M2 may include the aforementioned auxiliary elements. In Equation 1-1, x, a, b and z may satisfy 0.9≤x≤1.2, 0.6≤a≤0.99, 0.01≤b1+b2≤0.4, and -0.5≤z≤0.1.

[0107] The positive electrode active material may also include coating elements or doping elements. For example, elements that are substantially the same as or similar to the auxiliary elements described above can be used as coating elements or doping elements. For example, the elements described above can be used alone as coating elements or doping elements, or two or more of the elements described above can be used in combination as coating elements or doping elements.

[0108] The coating element or doping element may be present on the surface of the lithium nickel metal oxide particles or may penetrate the surface of the lithium nickel metal composite oxide particles to be included in the bonding structure represented by Formula 1 or Formula 1-1 above.

[0109] The positive electrode active material can include nickel-cobalt-manganese (NCM)-based lithium oxide. In this case, NCM-based lithium oxide with increased nickel content can be used.

[0110] Ni can be provided as a transition metal related to the output and capacity of lithium secondary batteries. Therefore, as described above, by using a high-content (high-Ni) composition in the positive electrode active material, a high-capacity positive electrode and a high-capacity lithium secondary battery can be provided.

[0111] However, with increasing Ni content, the long-term storage stability and lifetime stability of the cathode or lithium secondary battery may relatively decrease, and side reactions with the electrolyte may also increase. However, according to an exemplary embodiment, lifetime stability and capacity retention characteristics can be improved by including Mn, while conductivity is maintained by including Co.

[0112] The Ni content (e.g., the mole fraction of nickel based on the total moles of nickel, cobalt, and manganese) in NCM-based lithium oxide can be 0.6 or more, 0.7 or more, or 0.8 or more. In some embodiments, the Ni content can be 0.8 to 0.95, 0.82 to 0.95, 0.83 to 0.95, 0.84 to 0.95, 0.85 to 0.95, or 0.88 to 0.95.

[0113] In some implementations, the positive electrode active material may include lithium cobalt oxide-based active material, lithium manganese oxide-based active material, lithium nickel oxide-based active material, or lithium iron phosphate (LFP)-based active material (e.g., LiFePO4).

[0114] In some embodiments, the positive electrode active material may include a manganese (Mn)-rich oxide, a lithium rich layered oxide (LLO), an over lithiated oxide (OLO)-based active material, or a cobalt (Co)-less active material, which has a chemical structure or crystal structure represented by Formula 2 below.

[0115] [Formula 2]

[0116] p[Li2MnO3]·(1-p)[Li q JO2]

[0117] In Formula 2, p and q may satisfy 0 < p < 1, 0.9 ≤ q ≤ 1.2, and J may include at least one element selected from Mn, Ni, Co, Fe, Cr, V, Cu, Zn, Ti, Al, Mg, and B.

[0118] For example, the positive electrode active material may be dispersed in a solvent to prepare a positive electrode slurry. The positive electrode current collector 105 may be coated with the positive electrode slurry, and then dried and pressed to prepare the positive electrode 100. The coating process may be performed by methods such as, but not limited to, gravure coating, slot die coating, simultaneous multi-layer die coating, imprinting, knife coating, dip coating, bar coating, or casting. The positive electrode slurry may further include a binder, and optionally also a conductive material, a thickener, etc.

[0119] Non-limiting examples of the solvent for preparing the positive electrode slurry may include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, N,N-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc.

[0120] The binder may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-co-hexafluoropropylene copolymer, polyacrylonitrile, polymethyl methacrylate, nitrile rubber (NBR), polybutadiene rubber (BR), styrene-butadiene rubber (SBR), etc. In one embodiment, a PVDF-based binder may be used as the positive electrode binder.

[0121] The above substances that can be used as the conductive material and the thickener in the preparation of the negative electrode may be used.

[0122] In one embodiment, a separator 140 may be placed between the positive electrode 100 and the negative electrode 130. The separator prevents electrical short circuits between the positive and negative electrodes and maintains ion flow. According to one embodiment, the thickness of the separator may be from 10 μm to 20 μm, but it is not limited thereto in this invention.

[0123] The diaphragm may comprise a porous polymer membrane or a porous nonwoven fabric. Porous polymer membranes may comprise polyolefin polymers, such as ethylene polymers, propylene polymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers.

[0124] The membrane can also include ceramic-based materials. For example, inorganic particles can be coated onto or dispersed within a polymer membrane to improve heat resistance.

[0125] The diaphragm can have a single-layer or multi-layer structure, including the aforementioned polymer membrane and / or nonwoven fabric.

[0126] According to an exemplary embodiment, the positive electrode 100, the negative electrode 130, and the separator 140 may be repeatedly arranged to form the electrode assembly 150. In some embodiments, the electrode assembly 150 may have a jelly roll shape formed by winding, stacking, z-folding, or stacking-folding the separator 140.

[0127] In one embodiment, the electrode assembly 150 may have a jelly roll shape formed by winding the positive electrode 100, the negative electrode 130, and the separator 140 together. In another embodiment, the electrode assembly 150 may have a jelly roll shape in which the notched positive and negative electrodes are placed in a space formed by repeatedly z-folding the separator 140.

[0128] In one implementation, an electrode assembly can be formed by repeatedly stacking a positive electrode, a negative electrode, and a separator (where the individual layers are cut or separated from each other).

[0129] For example, tabs (positive and negative tabs) may protrude from the positive current collector 105 and the negative current collector 125, respectively. The tabs belong to the respective electrode cells and may extend to one side of the housing 160. The tabs may be fused together with one side of the housing 160 to form electrode leads (positive and negative leads) extending to or exposed outside the housing 160.

[0130] For example, soft-pack shells, prismatic shells, cylindrical shells, or coin-shaped shells can be used.

[0131] The electrode assembly 150 may be housed together with the electrolyte in a casing 160 to define a lithium secondary battery. According to an exemplary embodiment, a non-aqueous electrolyte may be used as the electrolyte.

[0132] Non-aqueous electrolytes consist of a lithium salt of the electrolyte and an organic solvent, the lithium salt being, for example, Li. + X - This indicates that the anion (X) of the lithium salt... - For example, F - Cl - ,Br - 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 - wait.

[0133] Organic solvents can include organic compounds that are sufficiently soluble for lithium salts and additives and are non-reactive in the battery. For example, organic solvents can include at least one of carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, and aprotic solvents.

[0134] The following can be used as organic solvents: propylene carbonate (PC), ethylene carbonate (EC), butenyl carbonate, diethyl carbonate (DEC), dimethyl carbonate (DMC), methyl ethyl carbonate (EMC), methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, vinylene carbonate, methyl acetate (MA), ethyl acetate (EA), n-propyl acetate (n-PA), 1,1-dimethyl ethyl acetate (DMEA), methyl propionate (MP), ethyl propionate (EP), ethyl fluoroacetate (FEA), ethyl difluoroacetate (DFEA), ethyl trifluoroacetate (TFEA), dibutyl ether, tetraethylene glycol dimethyl ether (TEGDME), diethylene glycol dimethyl ether (DEGDDME), dimethoxyethane, tetrahydrofuran (THF), 2-methyltetrahydrofuran, ethanol, isopropanol, dimethyl sulfide, acetonitrile, dimethoxyethane, diethoxyethane, sulfolane, γ-butyrolactone, and propylene sulfite, etc. These solvents can be used alone or in combination of two or more of them.

[0135] Non-aqueous electrolytes may also include additives. Additives may include, for example, cyclic carbonate compounds, fluorinated carbonate compounds, sulcolepsy compounds, cyclic sulfate compounds, cyclic sulfite compounds, phosphate compounds, borate compounds, etc.

[0136] Cyclic carbonate compounds can include vinylene carbonate (VC), ethylene ethylene carbonate (VEC), etc.

[0137] Fluorine-substituted carbonate compounds can include fluoroethylene carbonate (FEC), etc.

[0138] Sulfolactone compounds may include 1,3-propanesulfonyl lactone, 1,3-propenesulfonyl lactone, 1,4-butanesulfonyl lactone, etc.

[0139] Cyclic sulfate compounds can include vinyl sulfate, propylene sulfate, etc.

[0140] Cyclic sulfite compounds can include vinyl sulfite, butene sulfite, etc.

[0141] Phosphate compounds can include lithium difluorobis(oxalato) phosphate, lithium difluorophosphate, etc.

[0142] Borate compounds can include lithium bis(oxalate)borate, etc.

[0143] The present invention will be described in detail below with reference to specific experimental examples. However, the following examples and comparative examples included in the experimental examples are only for illustrating the present invention, and those skilled in the art should understand that various changes and modifications can be made within the scope and spirit of the present invention. These changes and modifications are appropriately included in the appended claims.

[0144] Example 1

[0145] (1) Preparation of silicon-based active material

[0146] Silicon oxide (SiO x , 0 < x < 2) particles with a median particle size (D50) of 5 μm were obtained by a pulverization process using a jet mill, and the silicon oxide particles were heat-treated at 950 °C for 1 hour in the presence of an inert gas (N2) to prepare a silicon-based active material, which is a second negative electrode active material.

[0147] (2) Preparation of negative electrode

[0148] 92.3% by weight of artificial graphite (median particle size (D50): 13 μm) as the first negative electrode active material, 5.0% by weight of silicon oxide (SiO x , 0 < x < 2) particles (median particle size (D50): 5 μm) prepared in (1) as the second negative electrode active material, 1.1% by weight of CMC binder, 1.5% by weight of SBR binder, and 0.1% by weight of SWCNT conductive material were added to prepare a composition of negative electrode active material in the form of a slurry.

[0149] The prepared composition of negative electrode active material was coated on both surfaces of a copper current collector (copper foil with a thickness of 8 μm), and then dried and calendered to prepare a negative electrode.

[0150] (3) Manufacture of lithium secondary battery

[0151] A slurry was prepared by mixing Li[Ni 0.88 Co 0.1 Mn 0.02 O2 as the positive electrode active material, carbon black as the conductive material, and polyvinylidene fluoride (PVDF) as the binder in a weight ratio of 98.08:0.72:1.2. The slurry was uniformly coated on an aluminum foil with a thickness of 12 μm, and then vacuum dried to prepare a positive electrode.

[0152] The positive electrode and the negative electrode are each cut (notched) to a predetermined size and stacked, and then an electrode cell is manufactured by inserting a separator (polyethylene, thickness: 13 μm) between the positive electrode and the negative electrode. Thereafter, the tab portions of the positive electrode and the negative electrode are welded respectively. The welded combination of the positive electrode / separator / negative electrode is placed in a pouch, and then three sides of the pouch except for the side where the electrolyte is to be injected are sealed. At this time, the sealed portion includes the portion having the tab.

[0153] The electrolyte is injected through the remaining side except for the sealed portion, the remaining side is sealed, and then impregnated for more than 12 hours to manufacture a lithium secondary battery.

[0154] The following prepared solution is used as the electrolyte: LiPF6 is dissolved in a mixed solvent of EC / EMC / DEC (20 / 70 / 10; volume ratio) at 1.2 M, and then 2 wt% of fluoroethylene carbonate (FEC), 0.3 wt% of 1,3 - propylene sultone (PRS), 0.5 wt% of -1,3 - propane sultone (PS), and 0.5 wt% of 1,2 - ethylene sulfate are added.

[0155] Thereafter, the lithium secondary battery is subjected to heatpress pre - charging for 60 minutes at a current corresponding to an average of 0.5 C. After stabilizing for more than 12 hours, degassing is performed, and after aging for more than 24 hours, formation charging / discharging is performed (charging conditions: CC - CV 0.25 C 4.2 V 0.05 C cut - off, discharging conditions: CC 0.25 C 2.5 V cut - off).

[0156] Thereafter, standard charging / discharging is performed (charging conditions: CC - CV 0.33 C 4.2 V 0.05 C cut - off, discharging conditions: CC 0.33 C 2.5 V cut - off).

[0157] Example 2

[0158] Except for using silicon oxide (SiO 50 with a median particle size D x of 5 μm, but not heat - treated) particles as the second negative electrode active material, the negative electrode and the lithium secondary battery are manufactured according to the same process as described in Example 1.

[0159] Example 3

[0160] Except for using silicon oxide (SiO 50 with a median particle size D x, in addition to using silicon oxide (SiO

[0161] Example 4

[0162] , where 0 < x < 2) particles as the second negative electrode active material, the negative electrode and the lithium secondary battery are manufactured according to the same process as described in Example 1. x , in addition to using silicon oxide (SiO

[0163] Example 5

[0164] , where 0 < x < 2) particles as the second negative electrode active material, the negative electrode and the lithium secondary battery are manufactured according to the same process as described in Example 1. x , where 0 < x < 2) particles as the second negative electrode active material, the negative electrode and the lithium secondary battery are manufactured according to the same process as described in Example 1.

[0165] Comparative Example 1

[0166] (1) Preparation of carbon-coated silicon oxide particles

[0167] Place silicon oxide (SiO x , where 0 < x < 2) particles in a CVD coater and inject a mixed gas of acetylene and nitrogen at a flow rate of 50 mL / min. At this time, heat the CVD coater at a heating rate of 5 °C / min to 900 °C and hold it at 900 °C for 1 hour to prepare silicon oxide particles with a carbon coating on their surface.

[0168] Adjust the carbon content of the silicon oxide particles including the carbon coating to 3.2 wt%.

[0169] (2) Except for using the carbon-coated silicon oxide particles prepared in (1) in the same amount to replace silicon oxide (SiO x , where 0 < x < 2) particles as the second negative electrode active material, the negative electrode and the lithium secondary battery are manufactured according to the same process as described in Example 1.

[0170] Comparative Example 2

[0171] Except for using the carbon-coated silicon oxide particles (carbon content: 3.9 wt%) prepared as follows as the second negative electrode active material: using a mixed gas of methane and nitrogen to replace the mixed gas of acetylene and nitrogen and changing the heat treatment temperature to 1000 °C to replace 900 °C, the negative electrode and the lithium secondary battery are manufactured according to the same process as described in Comparative Example 1.

[0172] Comparative Example 3

[0173] Except for using silicon oxide particles including a carbon coating (carbon content: 1.9% by weight), prepared as follows, as the second negative electrode active material: changing the injection flow rate of the mixed gas of acetylene and nitrogen to a flow rate of 30 mL / minute, the negative electrode and the lithium secondary battery were manufactured according to the same process as described in Comparative Example 1.

[0174] Comparative Example 4

[0175] Except for using silicon oxide particles including a carbon coating (carbon content: 2.1% by weight), prepared from silicon oxide (SiO 最小 ), with a minimum particle size (D x ) of 1 μm (0 < x < 2), as the second negative electrode active material, the negative electrode and the lithium secondary battery were manufactured according to the same process as described in Comparative Example 1. [[ID=1这是一个关于专利文本翻译的任务,要求将给定的中文文本准确地翻译成英文。文本内容涉及锂二次电池负极活性物质的制备及相关实验分析,包括不同比较例中活性物质的成分差异,以及对活性物质进行热重分析和拉曼光谱峰强度比评价的实验方法和计算等式等。

[0176] Comparative Example 5

[0177] Except for preparing the second negative electrode active material by including crystalline silicon oxide (SiO x ), with 0 < x < 2, in the silicon-based active material at a content of 30% by weight, the negative electrode and the lithium secondary battery were manufactured according to the same process as described in Example 1.

[0178] Experimental Example

[0179] (1) Thermogravimetric Analysis

[0180] Thermogravimetric analysis was performed on the second negative electrode active materials of the examples and comparative examples to measure the carbon content in the second negative electrode active materials.

[0181] 30 mg of the dried second negative electrode active material was placed in a thermogravimetric analyzer (TGA, TA Instruments) and heated from 25°C to 900°C at a heating rate of 5°C / minute in an air atmosphere for thermal decomposition, and the carbon content in the second negative electrode active material was calculated according to the following Equation 3. The results are shown in Table 1 below.

[0182] [Equation 3]

[0183] Carbon content (weight%) in the second negative electrode active material = (weight of the second negative electrode active material at 25°C - weight of the second negative electrode active material at 600°C) / (weight of the second negative electrode active material at 25°C) × 100

[0184] (2) Evaluation of the Peak Intensity Ratio of Raman Spectroscopy

[0185] The Raman spectra of the second negative electrode active materials of the examples and comparative examples were measured using a 532 nm laser Raman analyzer.

[0186] In the obtained Raman spectra, the Raman shift at 520 cm -1(e.g., peak intensity at I(520)) and Raman shift at 470 cm⁻¹ -1 (For example, the peak intensity at I(470)). Then, the measured peak intensity was applied to Equation 1 to calculate the peak intensity ratio of the Raman spectrum, and the results are shown in Table 1 below.

[0187] [Equation 1]

[0188] The peak intensity ratio of the Raman spectrum = I(520) / I(470)

[0189] The specific measurement conditions for Raman spectroscopy are as follows.

[0190] i) Equipment: Renishaw inVia Raman Spectrometer

[0191] ii) Wavelength: 532nm

[0192] iii) Raster: 1800 lines / mm

[0193] iv) Detector: CCD

[0194] v) Objective lens: ×20

[0195] (3) Evaluation of the pore volume of the negative electrode active material layer

[0196] The pore volume of the negative electrode active material layer included in the negative electrode of the examples and comparative examples was measured using the mercury porosimetry method.

[0197] The pore volume (mL) of the entire negative electrode active material layer was measured using a mercury porosimeter at a SOC of 0%. The pore volume (mL / g) of the negative electrode active material layer was then calculated by dividing the total pore volume by the total weight (g) of the negative electrode active material layer. The obtained values ​​are used as the pore volume, as shown in Table 1 below.

[0198] (4) Evaluation of negative electrode expansion rate

[0199] After forming, charging, and discharging the lithium secondary batteries of the examples and comparative examples, batteries with a state of charge (SOC) of 0% and a SOC of 100% were disassembled, and the thickness of the negative electrode was measured to calculate the expansion rate of the negative electrode using Equation 2 below. The results are shown in Table 1 below.

[0200] [Equation 2]

[0201] Expansion rate (%) = (T) B -T A ) / (T A )×100

[0202] (In equation 2, T) A T refers to the thickness of the negative electrode when the state of charge of the lithium secondary battery, including the negative electrode, is 0%.B This refers to the thickness of the negative electrode when the state of charge of the lithium secondary battery, including the negative electrode, is 100%.

[0203] (5) Evaluation of electrode resistance

[0204] The electrode resistance (Ω*cm) of the negative electrode of the examples and comparative examples was measured using a current collector at 10mA with a SOC of 0%. The results are shown in Table 1 below.

[0205] (6) Evaluation of formation capacity and formation efficiency

[0206] The lithium secondary batteries of the examples and comparative examples were charged (CC / CV, 0.5C, 4.2V, 0.05C cutoff) and discharged (CC, 0.5C, 2.7V cutoff) at 25°C, and the charging capacity and discharging capacity were measured.

[0207] The discharge capacity was used as the formation capacity, and the formation efficiency was calculated as the percentage (%) of the discharge capacity relative to the charge capacity. The results are shown in Table 2 below.

[0208] (7) Measurement of DC-IR and power

[0209] The charge and discharge output characteristics of the lithium secondary batteries of the examples and comparative examples were measured using the hybrid pulse power characterization (HPPC) method. Discharge at a 1C rate and charge at a 0.75C rate were applied, and the DC-IR (mΩ*s) and power (W / kg) were measured at a state of charge (SOC) of 50%. The results are shown in Table 2 below.

[0210] [Table 1]

[0211]

[0212] [Table 2]

[0213]

[0214] Referring to Tables 1 and 2, the negative electrodes of Examples 1 to 5 exhibit low resistance and low expansion rate, and the batteries of Examples 1 to 5 have improved capacity and output characteristics.

[0215] The negative electrodes of Comparative Examples 1 to 4 (which include a second negative electrode active material containing silicon oxide particles with a carbon content greater than 1% by weight) exhibit high resistance and high expansion rate, and the batteries of Comparative Examples 1 to 4 have high resistance and low output.

[0216] The negative electrode of Comparative Example 5 (due to the mixed crystalline silicon oxide particles, which include a second negative electrode active material with a high proportion of silicon having a crystalline structure) exhibited high resistance and high expansion rate, and the battery of Comparative Example 5 exhibited low capacity, low efficiency and low output.

Claims

1. A negative electrode active material for lithium secondary batteries, comprising: The first negative electrode active material includes carbon-based active materials; as well as The second negative electrode active material includes silicon-based active materials with a carbon content of less than 1% by weight. The content of the second negative electrode active material is 0.1% to 9% by weight, based on the total weight of the negative electrode active material. The peak intensity ratio of the Raman spectrum of the second negative electrode active material, as defined by Equation 1 below, is 0.5 to 2.3: [Equation 1] The peak intensity ratio of the Raman spectrum = I(520) / I(470) In Equation 1, I(520) is the Raman shift of 520 cm⁻¹ in the Raman spectrum. -1 The peak intensity of the second negative electrode active material at the position, I(470), is the Raman shift of 470 cm⁻¹ in the Raman spectrum. -1 The peak intensity of the second negative electrode active material.

2. The negative electrode active material for lithium secondary batteries according to claim 1, wherein the silicon-based active material comprises silicon oxide (SiO2). x Particles, of which 0 <x<2。 3. The negative electrode active material for lithium secondary batteries according to claim 2, wherein the silicon oxide particles have no carbon coating on their surface.

4. The negative electrode active material for lithium secondary batteries according to claim 1, wherein the carbon content of the silicon-based active material is less than 0.5% by weight.

5. The negative electrode active material for lithium secondary batteries according to claim 1, wherein the carbon content of the silicon-based active material is 0 by weight.

6. The negative electrode active material for a lithium secondary battery according to claim 1, wherein the peak intensity ratio of the Raman spectrum of the second negative electrode active material is 0.6 to 2.

7. The negative electrode active material for a lithium secondary battery according to claim 1, wherein the content of the second negative electrode active material is from 0.5% to 8% by weight based on the total weight of the negative electrode active material.

8. The negative electrode active material for a lithium secondary battery according to claim 1, wherein the content of the first negative electrode active material is 90% to 98% by weight based on the total weight of the negative electrode active material.

9. The negative electrode active material for a lithium secondary battery according to claim 1, wherein the carbon-based active material comprises at least one selected from the group consisting of artificial graphite and natural graphite.

10. A negative electrode for a lithium secondary battery, comprising: Negative electrode current collector; as well as A negative electrode active material layer is formed on at least one surface of the negative electrode current collector and includes the negative electrode active material for a lithium secondary battery according to claim 1.

11. The negative electrode for a lithium secondary battery according to claim 10, wherein the pore volume of the negative electrode active material layer is from 0.20 mL / g to 0.25 mL / g.

12. The negative electrode for a lithium secondary battery according to claim 10, wherein the pore volume of the negative electrode active material layer is from 0.22 mL / g to 0.24 mL / g.

13. The negative electrode for a lithium secondary battery according to claim 10, wherein the expansion rate, as defined by Equation 2 below, is from 1% to 10.5%: [Equation 2] Expansion rate (%) = (T) B -T A ) / (T A )×100 In equation 2, T A The thickness of the negative electrode, T, is the value of the lithium secondary battery including the negative electrode when its state of charge is 0%. B It is the thickness of the negative electrode when the state of charge of the lithium secondary battery including the negative electrode is 100%.

14. The negative electrode for a lithium secondary battery according to claim 13, wherein the expansion rate is 2% to 10%.

15. A lithium secondary battery, comprising: The negative electrode for a lithium secondary battery according to claim 10; as well as The positive electrode is configured to face the negative electrode.

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