Quantitative analysis method for carbon-based hybrid negative electrode

Abstract

A quantitative analysis method for carbon-based hybrid anodes is disclosed, comprising: preparing a secondary battery including a carbon-based hybrid anode containing carbon-based anode active materials and non-carbon-based anode active materials; measuring the lattice d-spacing of the carbon-based anode active materials in the carbon-based hybrid anode during charging / discharging of the secondary battery using an X-ray diffractometer, and plotting a curve showing the change in lattice d-spacing values ​​as a function of charging / discharging capacity (X-axis); and quantifying the capacity contribution of the carbon-based anode active materials and non-carbon-based anode active materials to the total discharge capacity of the secondary battery by detecting the inflection point of the slope of the curve during discharge in the plotted curve.

Description

Technical Field

[0001] This disclosure relates to a quantitative analysis method for a carbon-based hybrid anode.

[0002] This application claims the benefit of Korean Patent Application No. 10-2019-0139764, filed on November 4, 2019, with the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. Background Technology

[0003] Recently, with the rapid growth of the markets for electric vehicles, robots, and energy storage systems, there is a demand for secondary batteries with high energy density, stability, compactness, light weight, and long lifespan. For large-scale applications, it is important to improve the performance of secondary batteries in terms of energy density per unit weight or volume, which is higher than current levels.

[0004] Graphite is currently the most available anode active material for lithium-ion batteries, but it has a limited theoretical capacity of 372 mAh / g (approximately 160 Wh / kg). Attention is focused on silicon (Si), which has a capacity at least 10 times higher than graphite (4200 mAh / g), as a next-generation anode material for non-aqueous electrolyte secondary batteries. Furthermore, various silicon-containing non-carbon-based materials that exhibit high theoretical capacity when alloyed with lithium have been proposed as novel alternatives to carbon-based materials such as graphite for anode active materials.

[0005] However, due to the high volume expansion rate during alloying with lithium, Si-based materials can cause cracks in the electrode neutralization and electrode surface, as well as failures in the active material, resulting in reduced electrical contact and a sharp decrease in the cycle capacity of the secondary battery. To address the problems of Si-based materials, many attempts have been made to apply hybrid anodes, including mixtures of non-carbon-based materials such as Si and carbon-based materials.

[0006] In order to improve battery performance by increasing the energy density of secondary batteries including hybrid anodes, it is necessary to analyze and diagnose the degradation of both carbon-based and non-carbon-based materials in the hybrid anode during the charging / discharging of secondary batteries, specifically the lithiation and delithiation behavior of lithium ions. Summary of the Invention

[0007] Technical issues

[0008] This disclosure relates to a quantitative analysis method for a carbon-based hybrid anode.

[0009] These and other objects and advantages of this disclosure will become apparent from the following description. It will also be readily understood that these objects and advantages of this disclosure can be achieved by the means and methods, and combinations thereof, set forth in the appended claims.

[0010] Technical solution

[0011] In order to solve the above-mentioned problems of this disclosure, according to one aspect of this disclosure, a quantitative analysis method for a carbon-based hybrid negative electrode according to the following embodiments is provided.

[0012] According to the first embodiment,

[0013] A quantitative analysis method for carbon-based hybrid anodes is provided, comprising: preparing a secondary battery including a carbon-based hybrid anode containing carbon-based anode active materials and non-carbon-based anode active materials;

[0014] The lattice d-spacing of the carbon-based anode active material in the carbon-based hybrid anode during the charge / discharge of the secondary battery was measured using an X-ray diffractometer, and a graph showing the change in lattice d-spacing values ​​as a function of charge / discharge capacity (X-axis) was plotted; and,

[0015] The capacity contribution of carbon-based and non-carbon-based anode active materials to the total discharge capacity of a secondary battery is quantified by detecting the inflection point of the slope of the curve during discharge in the plotted curve.

[0016] According to the second embodiment, in the first embodiment...

[0017] The discharge capacity after the inflection point corresponds to the capacity contribution of the non-carbon-based anode active material, while the discharge capacity before the inflection point corresponds to the capacity contribution of the carbon-based anode active material.

[0018] According to the third embodiment, in the first or second embodiment...

[0019] The capacity contribution of non-carbon-based anode active materials in carbon-based hybrid anodes can be quantified by calculating the ratio of the discharge capacity after the inflection point to the maximum capacity of the curve.

[0020] According to the fourth embodiment, in any one of the first to third embodiments,

[0021] When the capacity characteristics deteriorate with repeated charging / discharging of the secondary battery,

[0022] By observing the change in the inflection point of the slope of the curve during the charging / discharging period relative to the inflection point of the slope of the curve during the initial charging / discharging period after degradation caused by multiple charging / discharging cycles, it can be determined whether the degradation of the secondary battery is caused by the carbon-based negative electrode active material or the non-carbon-based negative electrode active material.

[0023] According to the fifth embodiment, in any one of the first to fourth embodiments,

[0024] As a result of determining the change in the inflection point position of the slope of the curve during the deteriorated charge / discharge period relative to the inflection point position of the slope of the curve during the initial charge / discharge period, the capacity reduction from the inflection point to the maximum capacity can be determined as the deterioration of the carbon-based anode active material, and the capacity reduction from the inflection point to capacity 0 can be determined as the deterioration of the non-carbon-based anode active material.

[0025] According to the sixth embodiment, in any one of the first to fifth embodiments,

[0026] The carbon-based anode active material may include natural graphite, artificial graphite, soft carbon, hard carbon, pitch carbide, sintered coke, graphene, carbon nanotubes, or at least two of them.

[0027] According to the seventh embodiment, in any one of the first to sixth embodiments,

[0028] The non-carbon-based anode active material may include a metal or quasi-metal that can form an alloy with lithium.

[0029] According to the eighth embodiment, in any one of the first to seventh embodiments,

[0030] The non-carbon-based anode active material may include a metal or metalloid selected from Si, Sn, In, Pb, Ga, Ge, Al, Bi, Sb, Ag, Mg, Zn, Pt, or Ti; an oxide of the metal or metalloid; a carbon composite of the metal or metalloid; a carbon composite of the oxide of the metal or metalloid; or a mixture thereof.

[0031] According to the ninth embodiment, in any one of the first to eighth embodiments,

[0032] The non-carbon-based anode active material may include Si, SiO2, etc. x (0 < x < 2), or a mixture thereof.

[0033] Beneficial effects

[0034] According to embodiments of this disclosure, by observing the lattice d-spacing changes of carbon-based materials during the charging and discharging of a full-cell secondary battery comprising a carbon-based hybrid negative electrode including both carbon-based and non-carbon-based materials using non-destructive analysis methods, the major reaction range and capacity contribution of non-carbon-based materials in the individual behavior of non-carbon-based materials, separate from the combined behavior of carbon-based and non-carbon-based materials, can be quantified.

[0035] Furthermore, when a secondary battery containing a carbon-based hybrid negative electrode deteriorates, unlike conventional techniques where it is difficult to find the cause of the deterioration, according to the embodiments of this disclosure, it is possible to analyze separately which of the carbon-based or non-carbon-based materials is the cause of the negative electrode deterioration. Attached Figure Description

[0036] The accompanying drawings illustrate preferred embodiments of the present disclosure and, together with the detailed disclosure below, are used to aid in understanding the technical aspects of the present disclosure; therefore, the present disclosure should not be construed as limited thereto. Furthermore, the shape, size, scale, or proportion of the elements in the drawings may be exaggerated for clearer description.

[0037] Figure 1 It is a graph showing how the lattice d-spacing of the carbon-based anode active material included in the carbon-based hybrid anode changes with the capacity of the secondary battery including the anode during charging and discharging.

[0038] Figure 2a This is a graph showing the capacity vs. voltage changes of the three-electrode secondary cell (full cell) prepared in Preparation Example 7 during 0.1C charging / discharging.

[0039] Figure 2b and Figure 2c They are shown separately. Figure 2a The curves showing the distribution of the negative and positive electrodes.

[0040] Figure 3a This is a graph showing the change in capacity vs. voltage of the three-electrode secondary cell (full cell) prepared in Preparation Example 7 during 0.33C charging / discharging.

[0041] Figure 3b and Figure 3c They are shown separately. Figure 3a The curves showing the distribution of the negative and positive electrodes.

[0042] Figure 4 It is a graph showing the distribution of each negative electrode of the coin-type half-cell secondary battery prepared in Examples 4 to 6 as a function of normalized capacity (%) and voltage.

[0043] Figure 5It is a photographic image showing a transmission X-ray diffractometer.

[0044] Figure 6 The graph shows the scan of the (002) lattice interface peak (2θ = 7.5 ~ 11 (Agλ = 0.56)) of the artificial graphite in the negative electrode of the secondary battery of Preparation Example 2 and the curve of the lattice d-spacing calculated therefrom.

[0045] Figures 7a to 7c This is a graph showing the variation of the lattice d-spacing of the artificial graphite included in each negative electrode as a function of capacity during the charging / discharging of the secondary batteries prepared in Examples 1 to 3.

[0046] Figure 8 This is a graph showing how the lattice d-spacing of the artificial graphite included in each negative electrode changes with the normalized capacity during the charging / discharging of the secondary batteries prepared in Examples 1 to 3. Detailed Implementation

[0047] It should be understood that the terms or words used in the specification and appended claims should not be construed as limited to their common or dictionary meanings, but should be interpreted based on their meaning and concepts corresponding to the technical aspects of this disclosure, on the basis of the principle that allows the inventor to appropriately define the terms for the best interpretation. Therefore, the configurations shown in the embodiments described herein are merely the most preferred embodiments of this disclosure and are not intended to fully describe the technical aspects of this disclosure; thus, it should be understood that various other equivalents or modifications may be made thereto at the time of filing this application.

[0048] This disclosure aims to address the conventional problem that, in the charge / discharge environment of secondary batteries including carbon-based hybrid anodes, it is difficult to analyze and diagnose the degradation of the lithiation and delithiation behavior of both carbon-based and non-carbon-based materials during charge / discharge.

[0049] This disclosure utilizes a non-destructive analytical method for full-cell secondary batteries to directly observe the behavior of a hybrid electrode of carbon-based and non-carbon-based materials through in-situ (operando) analysis during the charging / discharging of a secondary battery including a carbon-based hybrid negative electrode.

[0050] Secondary batteries using only carbon-based anode active materials do not exhibit competitive lithiation and delithiation of lithium ions within the anode active material. However, under mixed anode conditions involving both carbon-based and non-carbon-based anode active materials, the carbon-based and non-carbon-based anode active materials compete for lithium ion lithiation and delithiation based on reaction voltage, thus allowing for the observation of decelerated / accelerated lithium ion lithiation and delithiation.

[0051] The increase or decrease in the d-spacing of the carbon layers in carbon-based anode active materials reflects this change. This allows for the quantification of the dominant reaction range and capacity of non-carbon-based anode active materials in the behavior of both carbon-based and non-carbon-based anode active materials in hybrid anodes.

[0052] The quantitative analysis method for carbon-based hybrid anodes according to one aspect of this disclosure includes:

[0053] Prepare a secondary battery comprising a carbon-based hybrid negative electrode containing carbon-based and non-carbon-based negative electrode active materials;

[0054] The lattice d-spacing of the carbon-based anode active material in the carbon-based hybrid anode was measured using an X-ray diffractometer during the charge / discharge period of the secondary battery, and a curve was plotted showing the change in lattice d-spacing values ​​as a function of charge / discharge capacity (X-axis); and

[0055] By detecting the inflection point of the slope of the curve during discharge (the inflection point where the slope changes from a large value to a small value) in the plotted curve, the capacity contribution of carbon-based anode active materials and non-carbon-based anode active materials to the total discharge capacity of the secondary battery is quantified.

[0056] First, a secondary battery is prepared, comprising a carbon-based hybrid negative electrode containing carbon-based and non-carbon-based negative electrode active materials.

[0057] Carbon-based hybrid anodes refer to anodes that include not only carbon-based anode active materials but also non-carbon-based anode active materials.

[0058] Carbon-based anode active materials include any type of carbon-based material that allows lithiation and delithiation during battery charging / discharging, and are not limited to any particular type. Carbon-based anode active materials may include amorphous carbon, crystalline carbon, or mixtures thereof. Specifically, carbon-based anode active materials may include natural graphite, artificial graphite, soft carbon, hard carbon, pitch carbide, sintered coke, graphene, carbon nanotubes, or at least two of these. In particular, graphite is a common anode material in lithium-ion secondary batteries, and when mixed with silicon to manufacture electrodes, graphite stably ensures its capacity, has good initial efficiency, and compensates for the low initial efficiency of silicon-based anode materials. Because these advantages contribute to increasing the initial efficiency of the electrode, graphite-based materials such as artificial or natural graphite are ideal.

[0059] Non-carbon-based anode active materials include any material capable of forming alloys with lithium, and are not limited to any particular type. Specifically, non-carbon-based anode active materials may include metals or metalloids selected from Si, Sn, In, Pb, Ga, Ge, Al, Bi, Sb, Ag, Mg, Zn, Pt, Ti, or combinations thereof; such as SiO2. x (0 < x < 2), oxides of the metal or metalloid such as SnO, SnO2, TiO2; carbon complexes of the metal or metalloid; carbon complexes of oxides of the metal or metalloid; or mixtures thereof.

[0060] According to embodiments of this disclosure, non-carbon-based anode active materials may include Si, SiO2, etc. x (0 < x < 2), or a mixture thereof.

[0061] The carbon-based hybrid negative electrode according to embodiments of this disclosure can be prepared by coating a mixture of a negative electrode active material, including carbon-based negative electrode active material and non-carbon-based negative electrode active material, conductive material, and binder onto a negative electrode current collector and drying it, and if necessary, the mixture may further include filler.

[0062] In embodiments of this disclosure, the thickness of the current collector is typically from 3 μm to 500 μm. The current collector may, without limitation, include any type having high conductivity without causing chemical changes to the corresponding battery, and for example, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, and silver. They may be appropriately selected and used depending on the polarity of the positive or negative electrode.

[0063] Adhesives facilitate bonding between active and conductive materials, as well as bonding to current collectors, and are typically added in amounts ranging from 1% to 50% by weight based on the total weight of the electrode materials. Adhesives may include, but are not limited to, high molecular weight polyacrylonitrile-acrylic acid copolymers. In another example, adhesives may include polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), polyacrylates (salts), alkali-cationically or ammonium-ion-substituted polyacrylates (salts), alkali-cationically or ammonium-ion-substituted poly(alkylene-co-maleic anhydride), alkali-cationically or ammonium-ion-substituted poly(alkylene-co-maleic acid), polyethylene oxide, fluororubber, or mixtures thereof. More specifically, alkali-cationically substituted polyacrylates (salts) may include lithium-polyacrylates (salts) (Li-PAA), and alkali-cationically substituted poly(alkylene-co-maleic anhydride) may include lithium-substituted polyisobutylene-maleic anhydride.

[0064] Conductive materials may include any type of material that does not cause chemical changes to the battery, and for example, graphite such as natural or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black (trademark name), carbon nanotubes, carbon nanofibers, channel black, furnace black, lamp black, thermal black; conductive fibers such as carbon fibers or metal fibers; metal powders such as fluorinated carbon, aluminum powder, nickel powder; conductive whiskers such as zinc oxide, potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives.

[0065] According to embodiments of this disclosure, when preparing a negative electrode by coating a mixture of a negative electrode active material (including carbon-based and non-carbon-based negative electrode active materials), conductive material, and binder onto a negative electrode current collector, the negative electrode can be prepared by a dry method of directly coating a solid mixture including the negative electrode active material, conductive material, and binder, or by a wet method of adding the negative electrode active material, conductive material, and binder to a dispersion medium, stirring, coating in slurry form, and drying to remove the dispersion medium. In this case, the dispersion medium used in the wet method may include an aqueous medium such as water (deionized water) or an organic medium such as N-methyl-2-pyrrolidone (NMP).

[0066] According to one embodiment of the present disclosure, the structure of the negative electrode may be: a single-layer structure comprising a carbon-based negative electrode active material and a non-carbon-based negative electrode active material; a double-layer structure wherein a layer comprising only a carbon-based negative electrode active material as an active material and a layer comprising only a non-carbon-based negative electrode active material as an active material are respectively formed and stacked; or a multi-layer structure wherein at least one of a layer comprising only a carbon-based negative electrode active material as an active material or a layer comprising only a non-carbon-based negative electrode active material as an active material is stacked alternately.

[0067] A secondary battery according to an embodiment of the present disclosure includes a carbon-based hybrid negative electrode, a positive electrode, and a separator inserted between the positive electrode and the negative electrode.

[0068] The positive electrode can be prepared by coating a mixture of positive electrode active material, conductive material, and binder onto a positive electrode current collector and then drying it, and if necessary, the mixture may further include filler. The positive electrode active material may include layered compounds such as lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), or compounds substituted with one or more transition metals; Li 1+x Mn 2-x Lithium manganese oxides such as O4 (x = 0–0.33), LiMnO3, LiMn2O3, and LiMnO2; lithium copper oxides (Li2CuO2); vanadium oxides such as LiV3O8, LiFe3O4, V2O5, and Cu2V2O7; and LiNi... 1-x Ni-site type lithium nickel oxide represented by MxO2 (M = Co, Mn, Al, Cu, Fe, Mg, B, or Ga, x = 0.01–0.3); LiMn 2-x M x Lithium-manganese composite oxides represented by O2 (M = Co, Ni, Fe, Cr, Zn or Ta, x = 0.01 to 0.1) or Li2Mn3MO8 (M = Fe, Co, Ni, Cu or Zn); LiMn2O4 in which alkaline earth metal ions partially replace Li; disulfide compounds; and Fe2(MoO4)3, but not limited thereto.

[0069] For the conductive materials, current collectors, and adhesives of the positive electrode, refer to the above description of the negative electrode.

[0070] A separator is inserted between the positive and negative electrodes, and the separator comprises an insulating film with high dielectric constant and mechanical strength. The separator typically has a pore size of 0.01 μm to 10 μm and a thickness typically of 5 μm to 300 μm. For example, the separator comprises a film, sheet, or nonwoven fabric made of an olefin-based polymer with chemical resistance and hydrophobic properties, such as polypropylene; glass fiber; or polyethylene. The separator may further comprise a porous layer on its outermost surface containing a mixture of inorganic particles and an adhesive resin.

[0071] In embodiments of this disclosure, the electrolyte solution comprises an organic solvent and a predetermined amount of lithium salt, and the organic solvent includes, for example, propylene carbonate (PC), ethylene carbonate (EC), butenyl carbonate (BC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propionate (MP), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), vinylene carbonate (VC), galamine lactone (GBL), fluoroethylene carbonate (FEC), methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, pentyl acetate, ethyl propionate, butyl propionate, or mixtures thereof. Halogenated derivatives of the organic solvent may be used, and straight-chain esters may be used. The lithium salt may comprise materials that are well soluble in non-aqueous electrolytes, and for example, LiCl, LiBr, LiI, LiClO4, LiBF4, LiB 10 Cl 10 LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, (CF3SO2)2NLi, lithium chloroborane, lithium lower aliphatic carboxylic acids, lithium tetraphenylborate, and imides.

[0072] A secondary battery according to an embodiment of this disclosure can be manufactured by housing an electrode assembly, including positive and negative electrodes stacked alternately together with a separator, along with an electrolyte solution in a package such as a battery casing, and then sealing it. The method of manufacturing the secondary battery may include any conventional method without limitation.

[0073] According to embodiments of this disclosure, a battery module including the secondary battery as a unit cell and a battery pack including the battery module are provided. Since the battery module and the battery pack include a secondary battery exhibiting fast-charging characteristics under high load, they can be used as a power source for electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and energy storage systems.

[0074] Additionally, for battery components not described herein, such as conductive materials, refer to descriptions of components commonly used in the field of batteries, particularly lithium secondary batteries.

[0075] Subsequently, the lattice d-spacing of the carbon-based anode active material of the carbon-based hybrid anode was measured using an X-ray diffractometer during the charging / discharging of the secondary battery, and a curve was plotted showing the change of the lattice d-spacing value as a function of the charging / discharging capacity (X-axis).

[0076] According to embodiments of this disclosure, during the charging / discharging of a secondary battery, a scan can be performed to simultaneously track the (002) lattice interface peaks (2θ = 7.5–11 (Agλ = 0.56) of the carbon-based anode active material (e.g., graphite) included in the carbon-based hybrid anode of the secondary battery. The lattice d-spacing of the carbon-based anode active material can be calculated by fitting the (002) lattice interface peaks of the carbon-based anode active material included in the anode obtained by the scan (see [link to example of application] for details). Figure 5 ).

[0077] Subsequently, the capacity contribution of carbon-based and non-carbon-based anode active materials to the total discharge capacity of the secondary battery was quantified by detecting the inflection point of the slope of the curve during discharge (the inflection point where the slope changes from a large value to a small value).

[0078] The discharge capacity after the inflection point (medium slope) corresponds to the capacity contribution of the non-carbon-based anode active material, and the discharge capacity before the inflection point (large slope) corresponds to the capacity contribution of the carbon-based anode active material.

[0079] Reference Figure 1 The discharge capacity after the inflection point (medium slope), that is, the capacity contribution of non-carbon-based anode active material can be a (mAh), and the discharge capacity before the inflection point (large slope), that is, the capacity contribution of carbon-based anode active material can be ba (mAh).

[0080] Therefore, the capacity contribution of non-carbon-based anode active materials in carbon-based hybrid anodes can be quantified by calculating the ratio (a / c) of the discharge capacity (a) after the inflection point in the curve.

[0081] When the capacity characteristics deteriorate with the increase of charge / discharge cycles of the secondary battery, the cause of the deterioration of the secondary battery can be determined by the change in the inflection point of the slope of the curve during the charge / discharge period after the deterioration with the increase of charge / discharge cycles relative to the inflection point of the slope of the curve during the initial charge / discharge period. This can be used to determine whether the deterioration of the secondary battery is caused by carbon-based anode active material or non-carbon-based anode active material.

[0082] As a result of determining the change in the inflection point position of the slope of the curve during the degraded charge / discharge period relative to the inflection point position of the slope of the curve during the initial charge / discharge period, when compared with the curve during the initial charge / discharge period, the capacity reduction from the inflection point to the maximum capacity ( Figure 1 In the equation B+C=(B: large slope)+(C: plateau)), the decrease in ca[=(ba)+(cb)] can be identified as the degradation of the carbon-based anode active material, and the capacity decreases from the inflection point to capacity 0. Figure 1 The decrease in A (medium slope) in the equation, i.e., a, can be identified as the degradation of non-carbon-based anode active materials.

[0083] That is, the range from the inflection point to the maximum capacity corresponds to the capacity contribution of the carbon-based anode active material, and the range from the inflection point to zero capacity corresponds to the capacity contribution of the non-carbon-based anode active material. Therefore, the decrease from the inflection point to the maximum capacity indicates a decrease in the capacity contribution of the carbon-based anode active material, and can be identified as a degradation of the carbon-based anode active material. Similarly, the decrease from the inflection point to zero capacity indicates a decrease in the capacity contribution of the non-carbon-based anode active material, and can be identified as a degradation of the non-carbon-based anode active material.

[0084] In the following description, to aid in understanding this disclosure, the preparation and experimental examples will be presented in detail. However, the preparation and experimental examples according to embodiments of this disclosure can be modified in many different ways, and the scope of this disclosure should not be construed as limited to the preparation and experimental examples described below. The preparation and experimental examples of this disclosure are provided to help those skilled in the art to fully and completely understand this disclosure.

[0085] Preparation Example 1

[0086] <Preparation of the negative electrode: artificial graphite monolayer structure>

[0087] An active material slurry is prepared by mixing a mixture of artificial graphite (as a carbon-based active material), a binder polymer (styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC)), and carbon black (as a conductive material) in a weight ratio of 95:3.5:1.5 with water (as a dispersion medium) in a weight ratio of 1:2. In this case, the weight ratio of SBR to CMC is 2.3:1.2.

[0088] Using a slit die, an active material layer slurry is coated onto one surface of a copper (Cu) film serving as a 10 μm thick negative electrode current collector, and then dried under vacuum at 130 °C for 1 hour to form an active material layer on the copper film.

[0089] The active material layer was rolled to prepare an 80 μm thick anode with a monolayer structure. In this case, the loading was 17 mg / cm³ based on the dry weight of the anode active material layer. 2 .

[0090] <Preparation of the positive electrode>

[0091] Li(Ni) as the positive electrode active material 0.8 Mn 0.1 Co 0.1 O2 (NCM-811), carbon black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were added to N-methylpyrrolidone (NMP) as a solvent in a weight ratio of 96:2:2 to prepare a positive electrode active material slurry. This slurry was coated onto one surface of a 15 μm thick aluminum current collector and dried and pressed under the same conditions as the negative electrode to prepare the positive electrode. In this case, the loading was 20 mg / cm³ based on the dry weight of the positive electrode active material layer. 2 .

[0092] <Preparation of Lithium Secondary Batteries>

[0093] A non-aqueous electrolyte solution was prepared by dissolving LiPF6 in an organic solvent containing ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC) in a volume ratio of 3:1:6 to achieve a concentration of 1.0 M.

[0094] A polyolefin separator is inserted between the positive and negative electrodes prepared above, and an electrolyte solution is injected to prepare a lithium secondary battery.

[0095] Preparation Example 2

[0096] <Preparation of the negative electrode: a bilayer structure of artificial graphite layer / SiO layer (including 5% by weight of SiO based on the total amount of active materials)>

[0097] A first active material layer slurry is prepared by mixing a mixture of artificial graphite (as a carbon-based active material), a binder polymer (styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC)), and carbon black (as a conductive material) in a weight ratio of 95:3.5:1.5 with water (as a dispersion medium) in a weight ratio of 1:2. In this case, the weight ratio of SBR to CMC is 2.3:1.2.

[0098] The second active material layer slurry is prepared by the same method as the first active material layer slurry, except that a non-carbon-based active material, namely SiO (silicon oxide) with a coulombic efficiency of 80% or greater at 0.1C charge / discharge, is used instead of artificial graphite, and the SiO content is 5% by weight based on the total weight of artificial graphite and SiO.

[0099] Using a slit die, a first active material layer slurry is applied to a surface of a copper (Cu) film serving as a 10 μm thick negative electrode current collector. Then, a second active material layer slurry is applied to the first active material layer slurry, and the film is dried under vacuum at 130°C for 1 hour to form the first and second active material layers on the copper film.

[0100] A negative electrode with an 80 μm thick bilayer active material layer was prepared by simultaneously rolling the first and second active material layers. The loading was 17 mg / cm³ based on the dry weight of the negative electrode active material layer. 2 .

[0101] <Preparation of the positive electrode>

[0102] The positive electrode was prepared using the same method as in Preparation Example 1.

[0103] <Preparation of Lithium Secondary Batteries>

[0104] The non-aqueous electrolyte solution was prepared using the same method as in Preparation Example 1.

[0105] A polyolefin separator is inserted between the positive and negative electrodes prepared above, and an electrolyte solution is injected to prepare a lithium secondary battery.

[0106] Preparation Example 3

[0107] <Preparation of the negative electrode: a bilayer structure of artificial graphite layer / SiO layer (including 15% by weight of SiO based on the total amount of active materials)>

[0108] A first active material layer slurry is prepared by mixing a mixture of artificial graphite (as a carbon-based active material), a binder polymer (styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC)), and carbon black (as a conductive material) in a weight ratio of 95:3.5:1.5 with water (as a dispersion medium) in a weight ratio of 1:2. In this case, the weight ratio of SBR to CMC is 2.3:1.2.

[0109] The second active material layer slurry is prepared by the same method as the first active material layer slurry, except that a non-carbon-based active material, namely SiO (silicon oxide) with a coulombic efficiency of 80% or greater at 0.1C charge / discharge, is used instead of artificial graphite, and the SiO content is 15% by weight based on the total weight of artificial graphite and SiO.

[0110] Using a slit die, a first active material layer slurry is applied to a surface of a copper (Cu) film serving as a 10 μm thick negative electrode current collector. Subsequently, a second active material layer slurry is applied to the first active material layer slurry, and the film is dried under vacuum at 130°C for 1 hour to form the first and second active material layers on the copper film.

[0111] A negative electrode with an 80 μm thick bilayer active material layer was prepared by simultaneously rolling the first and second active material layers. The loading was 17 mg / cm³ based on the dry weight of the negative electrode active material layer. 2 .

[0112] <Preparation of the positive electrode>

[0113] The positive electrode was prepared using the same method as in Preparation Example 1.

[0114] <Preparation of Lithium Secondary Batteries>

[0115] The non-aqueous electrolyte solution was prepared using the same method as in Preparation Example 1.

[0116] A polyolefin separator is inserted between the positive and negative electrodes prepared above, and an electrolyte solution is injected to prepare a lithium secondary battery.

[0117] Preparation Example 4

[0118] <Preparation of the negative electrode: SiO monolayer structure negative electrode>

[0119] An active material layer slurry is prepared by mixing a mixture of SiO (silicon oxide) with a coulombic efficiency of 80% or greater at 0.1C charge / discharge, a binder polymer (styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC)), and carbon black as a conductive material in a weight ratio of 95:3.5:1.5, with water as a dispersion medium in a weight ratio of 1:2. In this case, the weight ratio of SBR to CMC is 2.3:1.2.

[0120] Using a slit die, an active material layer slurry is coated onto one surface of a copper (Cu) film serving as a 10 μm thick negative electrode current collector, and then dried under vacuum at 130 °C for 1 hour to form an active material layer on the copper film.

[0121] Simultaneously, the active material layer was rolled to prepare a SiO monolayer structure with an 80 μm thick active material layer. The loading was 17 mg / cm³ based on the dry weight of the active material layer. 2 .

[0122] <Preparation of Coin-Shaped Half-Cell Secondary Cells>

[0123] A coin-shaped half-cell secondary battery was prepared using the same method as in Preparation Example 4, except that the prepared negative electrode was used.

[0124] Preparation Example 5

[0125] <Preparation of the negative electrode>

[0126] The negative electrode with a single layer of artificial graphite was prepared by the same method as in Preparation Example 1.

[0127] <Preparation of Coin-Shaped Half-Cell Secondary Cells>

[0128] A 0.3 mm thick lithium film was used as the counter electrode, and a 30 μm porous polypropylene membrane (Celgard) was used as the separator. An electrolyte solution was prepared by dissolving LiPF6 in an organic solvent containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a 3:7 volume ratio to a concentration of 1.0 M, and dissolving fluoroethylene carbonate (FEC) to a concentration of 2 wt%. The separator was inserted between the pre-prepared negative and counter electrodes, and the electrolyte solution was injected to prepare a 2032 coin-shaped half-cell secondary battery with a thickness of 2 mm and a diameter of 32 mm.

[0129] Preparation Example 6

[0130] <Preparation of the negative electrode>

[0131] A negative electrode with a bilayer structure of artificial graphite layer / SiO layer (including 5% by weight of SiO based on the total amount of active material) was prepared by the same method as in Preparation Example 2.

[0132] <Preparation of Coin-Shaped Half-Cell Secondary Cells>

[0133] A coin-shaped half-cell secondary battery was prepared using the same method as in Preparation Example 4, except that the prepared negative electrode was used.

[0134] Preparation Example 7

[0135] <Preparation of the negative electrode>

[0136] A negative electrode with a bilayer structure of artificial graphite layer / SiO layer (including 5% by weight of SiO based on the total amount of active material) was prepared by the same method as in Preparation Example 2.

[0137] <Preparation of the positive electrode>

[0138] Li(Ni) as the positive electrode active material 0.8 Mn 0.1 Co 0.1 O2 (NCM-811), carbon black as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were added to N-methylpyrrolidone (NMP) as a solvent in a weight ratio of 96:2:2 to prepare a positive electrode active material slurry. This slurry was coated onto one surface of a 15 μm thick aluminum current collector and dried and rolled under the same conditions as the negative electrode to prepare the positive electrode. In this case, the loading was 20 mg / cm³ based on the dry weight of the positive electrode active material layer. 2 .

[0139] <Preparation of a Three-Electrode Secondary Cell>

[0140] A non-aqueous electrolyte solution was prepared by dissolving LiPF6 in an organic solvent containing ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC) in a volume ratio of 3:1:6 to achieve a concentration of 1.0 M.

[0141] Subsequently, a reference electrode probe is inserted between the positive electrode and the separator in the bag to prepare a three-electrode secondary cell, allowing for the measurement of the desired electrode potential while maintaining the cell configuration. In this case, the reference electrode probe is prepared by coating the lower end of the reference electrode probe with a lithium titanium compound (LTO) as the reference electrode material.

[0142] (For reference, the needle element material for the reference electrode probe is not limited to any type of material that is non-reactive to the electrolyte solution or has very low conductivity. The needle element itself can be made of a material that can be used for the reference electrode, and in some cases, the needle element can be prepared by coating the lower end of the reference electrode probe with a material that can be used for the reference electrode.)

[0143] Test case

[0144] Experimental Example 1

[0145] Figure 2a The changes in capacity vs. voltage of the three-electrode secondary cell (full cell) prepared in Preparation Example 7 after charging / discharging at 0.1C are shown. Figure 2b and Figure 2c The reading is obtained by using the reference potential (1.53V) of the LTO, which is a needle-shaped element used as a reference electrode. Figure 2a The relative potentials of the negative and positive electrodes are shown in the diagram relative to the full cell potential.

[0146] Experimental Example 2

[0147] Figure 3a The capacity vs. voltage changes of the three-electrode secondary cell (full cell) prepared in Preparation Example 7 after charging / discharging at 0.33C are shown. Figure 3b and Figure 3c The reading is obtained by using the reference potential (1.53V) of the LTO, which is a needle-shaped element used as a reference electrode. Figure 3a The relative potentials of the negative and positive electrodes are shown in the diagram relative to the full cell potential.

[0148] Reference Figure 2b and Figure 3b In the negative electrode with a bilayer structure of artificial graphite / SiO layer (including 5% by weight of SiO based on the total amount of active material), it is difficult to analyze the behavior of artificial graphite and SiO separately. In particular, when... Figure 3b As shown, when a high C-rate is applied, it becomes more difficult to analyze independently.

[0149] That is, in Figures 2a to 2c and Figures 3a to 3c In the traditional charge / discharge voltage distribution curves shown, even if the negative and positive electrodes are analyzed separately, it is impossible to determine how much SiO and graphite in the mixed negative electrode contribute to the total capacity of the battery.

[0150] Experimental Example 3

[0151] In the coin-type half-cell secondary cell with a SiO monolayer negative electrode prepared in Preparation Example 4, the coin-type half-cell secondary cell with an artificial graphite monolayer negative electrode prepared in Preparation Example 5, and the coin-type half-cell secondary cell with a bilayer structure of artificial graphite layer / SiO layer (including 5% by weight of SiO based on the total amount of active material) negative electrode prepared in Preparation Example 6, the distribution of each negative electrode with normalized capacity (%) and voltage is as follows: Figure 4 As shown.

[0152] Reference Figure 4 As can be seen, in the distribution of the mixed negative electrode in Example 6, it is difficult to clearly separate and analyze the distribution of SiO and graphite.

[0153] Test Example 4

[0154] During the charge / discharge period of the secondary batteries prepared in Examples 1 to 3 under the same conditions as the cycle test (0.33 CC / CV charge, 0.33 CC discharge), the following parameters were used: Figure 5 The transmission x-ray diffractometer (manufacturer: Bruker, trade name: D8 Advance) shown performed the scans while tracking the (002) lattice interface peaks (2θ = 7.5–11 (Agλ = 0.56)) of the artificial graphite included in the negative electrode of each secondary cell. The lattice d-spacing of the artificial graphite was calculated by fitting the (002) lattice interface peaks of the artificial graphite included in the negative electrodes of Preparation Examples 1 to 3 obtained by scanning, based on Bragg's Law.

[0155] Figure 6 Typical examples are shown by X-ray diffraction of the (002) lattice interface peaks (2θ = 7.5–11 (Agλ = 0.56)) of artificial graphite in the negative electrode (containing 5 wt% SiO based on the total amount of active material) of the secondary battery prepared in Example 2, and the curves of the lattice d-spacing calculated therefrom.

[0156] Figures 7a to 7c This is a graph showing the variation of the lattice d-spacing of the artificial graphite included in each negative electrode as a function of capacity during the charging / discharging of the secondary batteries prepared in Examples 1 to 3.

[0157] Reference Figure 7aWhen the negative electrode active material contains only graphite, as in Preparation Example 1, it can be seen that the d-spacing of the graphite lattice increases uniformly during charging and decreases along the same path during discharging. Since the lithiation and delithiation of lithium ions in the graphite lattice are uninterrupted, the d-spacing increases uniformly and then decreases uniformly with increasing capacity.

[0158] according to Figure 7b As can be seen, in the case of the preparation example 2 where the total amount of negative electrode active material based on artificial graphite and SiO includes 5% by weight of SiO, the curve of increasing lattice d-spacing during charging and the curve of decreasing lattice d-spacing during discharging do not match, and there is a path difference.

[0159] Figure 7b The discharge curve shows an inflection point at approximately 25 mAh discharge capacity. Above this inflection point, the graphite lattice structure changes significantly with increasing capacity, and the discharge capacity at that point is attributed to the delithiation of lithium ions within the graphite.

[0160] Meanwhile, it can be seen that in the capacity range lower than the inflection point, i.e., in the discharge capacity range of approximately 25 mAh to 0 mAh, the lattice d-spacing of graphite decreases relatively little with capacity changes. This discharge capacity range corresponds to the range reflecting lithium-ion lithiation in SiO, rather than the range reflecting lithium-ion delithiation in graphite. Therefore, based on a total discharge capacity of 160 mAh, the capacity contribution of SiO in the rechargeable / dischargeable battery is 25 mAh, or 15.6% (=25 / 160×100). It can be seen that when the total amount of negative electrode active material based on graphite and SiO includes SiO at a weight of 5%, this almost matches the theoretical value of approximately 15% contribution to the total capacity.

[0161] After lithium ionization in both graphite and SiO during charging, during discharge, lithium ion delithiation in graphite occurs in a capacity range higher than the inflection point, while lithium ion delithiation in SiO occurs in a capacity range lower than the inflection point. Therefore, even if the capacity changes, the trend of decreasing d-interval in graphite lattice is significantly reduced.

[0162] Figure 7c This is a graph showing the variation of the lattice d-spacing of graphite as a function of charging capacity in the secondary battery of Preparation Example 3, which uses a negative electrode comprising 15% by weight of SiO as the total amount of the negative electrode active material based on artificial graphite and SiO.

[0163] Figure 7cThe discharge curve shows an inflection point at approximately 24 mAh. In the capacity range above this inflection point, the lattice d-interval of graphite changes, and the capacity also changes. The discharge capacity at that point is attributed to the delithiation of lithium ions in the graphite.

[0164] Meanwhile, within a capacity range lower than the inflection point, i.e., from approximately 24 mAh to 0 mAh, the d-spacing of the graphite lattice shows little or no change, yet the capacity still varies. During discharge, lithium-ion delithiation does not occur in graphite, but rather in SiO. Therefore, the discharge capacity is caused by lithium-ion delithiation in SiO. Based on this, with a total discharge capacity of 55 mAh, the capacity contribution of SiO to the rechargeable / discharged battery is 24 mAh, or 43.6% (=24 / 55×100). It can be seen that when the total amount of negative electrode active material based on graphite and SiO includes SiO at 15% by weight, this almost matches the theoretical value of approximately 45% contribution to the total capacity.

[0165] Figure 8 This is a graph showing how the lattice d-spacing of the artificial graphite included in each negative electrode changes with the normalized capacity during the charging / discharging of the secondary batteries prepared in Examples 1 to 3.

[0166] In the secondary battery prepared in Example 3, which included a carbon-based hybrid negative electrode containing 85% by weight graphite and 15% by weight SiO, the later plateau range of 57-100%, i.e., 43%, is the capacity value exhibited by SiO. It can be seen that this is consistent with... Figure 7c The calculated value matches.

[0167] In the secondary battery prepared in Example 2, which included a carbon-based hybrid negative electrode containing 85% by weight graphite and 5% by weight SiO, the later plateau range of 85-100%, i.e., 15%, is the capacity value exhibited by SiO. It can be seen that this is consistent with... Figure 7b The calculated value matches.

Claims

1. A method of quantitative analysis of a carbon-based hybrid negative electrode, comprising: preparing a secondary battery including a carbon-based hybrid negative electrode containing a carbon-based negative electrode active material and a non-carbon-based negative electrode active material; measuring a lattice d-spacing of the carbon-based negative electrode active material in the carbon-based hybrid negative electrode during charge / discharge of the secondary battery using an X-ray diffractometer, and plotting a graph of a change in the lattice d-spacing value as a function of charge / discharge capacity, wherein the charge / discharge capacity is an X-axis; and quantifying a capacity contribution of the carbon-based negative electrode active material and the non-carbon-based negative electrode active material in a total discharge capacity of the secondary battery by detecting an inflection point of a slope of the plotted graph during discharge, wherein a discharge capacity after the inflection point corresponds to a capacity contribution of the non-carbon-based negative electrode active material, and a discharge capacity before the inflection point corresponds to a capacity contribution of the carbon-based negative electrode active material.

2. The method of quantitative analysis of a carbon-based hybrid negative electrode according to claim 1, wherein the capacity contribution of the non-carbon-based negative electrode active material in the carbon-based hybrid negative electrode is quantified by calculating a ratio of the discharge capacity after the inflection point to a maximum capacity of the graph.

3. The method of quantitative analysis of a carbon-based hybrid negative electrode according to claim 1, wherein when a capacity characteristic is deteriorated with a plurality of charge / discharge of the secondary battery, a cause of deterioration of the secondary battery is determined to be the carbon-based negative electrode active material or the non-carbon-based negative electrode active material by a change in an inflection point position of the slope of the graph during charge / discharge after the deterioration from an inflection point position of the slope of the graph during initial charge / discharge.

4. The method of quantitative analysis of a carbon-based hybrid negative electrode according to claim 3, wherein as a result of determining the change in the inflection point position of the slope of the graph during charge / discharge after the deterioration from the inflection point position of the slope of the graph during initial charge / discharge, a capacity decrease from the inflection point to a maximum capacity is determined as a deterioration of the carbon-based negative electrode active material, and a capacity decrease from the inflection point to capacity 0 is determined as a deterioration of the non-carbon-based negative electrode active material.

5. The method of quantitative analysis of a carbon-based hybrid negative electrode according to claim 1, wherein the carbon-based negative electrode active material includes natural graphite, artificial graphite, soft carbon, hard carbon, pitch carbonizate, sintered coke, graphene, carbon nanotube, or at least two thereof.

6. The method of quantitative analysis of a carbon-based hybrid negative electrode according to claim 1, wherein the non-carbon-based negative electrode active material includes a metal or a metalloid capable of forming an alloy with lithium.

7. The method of claim 1, wherein the non-carbon-based negative electrode active material comprises a metal or a metalloid selected from Si, Sn, In, Pb, Ga, Ge, Al, Bi, Sb, Ag, Mg, Zn, Pt, or Ti; an oxide of the metal or the metalloid; a carbon composite of the metal or the metalloid; a carbon composite of an oxide of the metal or the metalloid; or a mixture thereof.

8. The method of claim 1, wherein the non-carbon-based negative electrode active material comprises Si, SiO x , or a mixture thereof, wherein 0 < x < 2.

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