Method for preparing spherical hard carbon and spherical hard carbon manufactured thereby

Abstract

The present invention relates to a method for preparing spherical hard carbon and spherical hard carbon prepared thereby. The preparation method comprises the steps of: subjecting an aqueous solution containing sugars and a capping agent to a hydrothermal synthesis reaction to form a carbon precursor; and carbonizing the carbon precursor by heat treatment under an inert gas atmosphere.

Description

Method for manufacturing spherical hard carbon and spherical hard carbon manufactured therefrom

[0001] The present invention relates to a method for producing spherical hard carbon and spherical hard carbon produced therefrom, and more particularly, to a method for producing hard carbon having a high degree of sphericity and easy insertion and de-insertion of cations, thereby improving the initial efficiency and energy density of a battery, and to hard carbon produced therefrom.

[0002] Currently, interest in high-speed charge / discharge cathode materials is increasing as the demand for medium- to large-sized batteries, such as ESS, increases along with the growth of the electric vehicle market.

[0003] Graphite, recently used as the main negative active material in secondary batteries, has a narrow basal plane interplanar distance (d002 = 0.335 nm). Therefore, in lithium secondary batteries using graphite, lithium ions can only be inserted and deintercalated through the edge plane of the layered structure. Consequently, during high-speed charge / discharge, lithium insertion into the layered structure of graphite is delayed, leading to dendrite formation by Li-plating. This causes problems such as capacity reduction due to dead-Li formation and electrolyte depletion due to continuous SEI (Solid Electrolyte Interphase) formation. Furthermore, it not only reduces the rate and life performance of secondary batteries, but can also cause internal short circuits, thereby reducing battery stability. In addition, as mentioned above, graphite has a narrow interplanar distance between the basal planes, so volume expansion (about 10%) occurs when lithium is inserted and removed, which may cause structural changes in the battery, reducing the battery capacity. In addition, Na, which is attracting attention as a next-generation battery, is also attracting attention due to concerns about the scarcity of lithium and supply and demand instability. + , K + For cations such as Li + Because the diameter of the ion is large compared to the ion, Na+ , K + When inserting cations such as these into a graphite anode, relatively greater energy is required. Accordingly, when graphite is used as an anode active material in next-generation secondary batteries, it may reduce the capacity life and rate characteristics of the battery.

[0004] The present invention relates to a lithium ion (Li) + ) of course, Na + , K + The present invention provides a method for manufacturing hard carbon having a high degree of sphericity while facilitating insertion and de-insertion of cations such as cations, and a spherical hard carbon manufactured thereby.

[0005] In addition, the present invention seeks to provide a negative electrode and secondary battery having excellent initial efficiency and rate characteristics, including the aforementioned spherical hard carbon.

[0006] In order to achieve the above-described task, the present invention provides a method for producing spherical hard carbon, comprising the steps of forming a carbon precursor by subjecting an aqueous solution containing a sugar and a capping agent to a hydrothermal synthesis reaction; and the step of carbonizing the carbon precursor by heat treatment under an inert gas atmosphere.

[0007] According to an example of the present invention, the sugar may include at least one selected from the group consisting of glucose, sucrose, fructose, galactose, maltose, and lactose.

[0008] According to another example of the present invention, the capping agent may include at least one selected from the group consisting of a surfactant and a hydrophilic polymer. At this time, the surfactant may include an alkyltrimethyl ammonium halide-based cationic surfactant, a polyoxyethylene glycol-based nonionic surfactant, a fatty acid ester-based nonionic surfactant, a sulfate-based anionic surfactant, a sulfonate-based anionic surfactant, etc. In addition, the hydrophilic polymer may include at least one selected from the group consisting of polyacrylic acid (PAA), polyvinyl pyrrolidone (PVP), and polytetrafluoroethylene (PTFE).

[0009] According to another example of the present invention, the sugar and capping agent may be contained in a weight ratio of 13 to 14:1.

[0010] According to another example of the present invention, the aqueous solution may include 9 to 25 wt% of sugar; 0.68 to 1.84 wt% of capping agent; and 73 to 91 wt% of water, based on the total amount of the aqueous solution.

[0011] According to another example of the present invention, the hydrothermal synthesis reaction can be carried out by heating the aqueous solution at a temperature of about 100 to 200° C. under a pressure of about 1 to 15 bar for about 2 to 72 hours.

[0012] According to another example of the present invention, the heat treatment can be performed at a temperature of 900 to 1500°C for 30 to 180 minutes under an inert gas atmosphere.

[0013] According to another example of the present invention, the step of classifying the fired material may be additionally included.

[0014] In addition, the present invention provides a spherical hard carbon manufactured by the method described above.

[0015] According to another example of the present invention, the spherical hard carbon may have a circularity of 0.9 or more.

[0016] According to another example of the present invention, the spherical hard carbon may have an average particle diameter (D50) in the range of 0.7 to 15 μm.

[0017] According to another example of the present invention, the spherical hard carbon may have a powder density (apparent density) in the range of 0.85 to 1.15 g / cc under an applied pressure of 50 to 500 MPa.

[0018] According to another example of the present invention, the spherical hard carbon can be used as a negative electrode active material.

[0019] In addition, the present invention provides a cathode comprising the aforementioned spherical hard carbon.

[0020] In addition, the present invention provides a secondary battery including the above-described negative electrode.

[0021] The present invention relates to a method for producing lithium ions (Li) by hydrothermal synthesis and carbonization of an aqueous solution containing sugars and a capping agent. + ) of course, Na + , K + It is possible to manufacture spherical hard carbon having a high degree of sphericity while facilitating the insertion and de-insertion of cations such as cations. The spherical hard carbon manufactured in this way can be used as an anode active material not only for lithium-ion secondary batteries but also for sodium and potassium-ion secondary batteries, thereby improving the initial efficiency and rate characteristics of the batteries.

[0022] Figure 1 is a flowchart showing a process for manufacturing spherical hard carbon according to the present invention.

[0023] Figure 2 is a SEM (Scanning Electron Microscope) photograph of the spherical hard carbon manufactured in Example 1-1.

[0024] Figure 3 is an SEM photograph of the spherical hard carbon manufactured in Example 2-1.

[0025] Figure 4 is an SEM photograph of the spherical hard carbon manufactured in Example 3-1.

[0026] Figure 5 is an SEM photograph of amorphous hard carbon used in Comparative Example 1.

[0027] Figure 6 is an SEM photograph of amorphous artificial graphite used as comparative example 2.

[0028] Figure 7 is a graph showing the specific capacity according to the charging speed of lithium secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 2, respectively.

[0029] Figure 8 is a graph showing the capacity ratio of lithium secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 2, respectively.

[0030] Fig. 9(a) is an SEM photograph of the spherical hard carbon manufactured in Example 1, and Fig. 9(b) is an EDS (Energy Dispersive Spectrometer) photograph of the spherical hard carbon manufactured in Example 1.

[0031] Fig. 10(a) is an SEM image of the amorphous hard carbon used in Comparative Example 1, and Fig. 10(b) is an EDS image of the amorphous hard carbon used in Comparative Example 1.

[0032] Fig. 11(a) is an SEM image of the amorphous artificial graphite used in Comparative Example 2, and Fig. 11(b) is an EDS image of the amorphous artificial graphite used in Comparative Example 2.

[0033] Figure 12 is a charge / discharge graph of the sodium ion batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 2, respectively.

[0034] Figure 13 is a graph showing the powder density of the spherical hard carbon of Example 1 and the amorphous hard carbon of Comparative Example 1 according to the applied pressure.

[0035] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. These embodiments of the present invention are provided to more fully explain the present invention to those skilled in the art. The following embodiments may be modified in various ways, and the scope of the present invention is not limited to the following embodiments. Throughout this specification, the same reference numerals denote the same structures.

[0036] Unless otherwise defined, all terms (including technical and scientific terms) used herein may be used in their common sense to those of ordinary skill in the art to which the present invention pertains. Furthermore, terms defined in commonly used dictionaries are not to be interpreted ideally or excessively unless explicitly and specifically defined otherwise.

[0037] Furthermore, the sizes and thicknesses of each component shown in the drawings are arbitrarily indicated for convenience of explanation, and thus the present invention is not necessarily limited to the illustrated components. In the drawings, the thicknesses are enlarged to clearly represent various layers and regions. Furthermore, in the drawings, the thicknesses of some layers and regions are exaggerated for convenience of explanation.

[0038] Additionally, throughout the specification, whenever a part is said to "include" a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

[0039] Additionally, throughout the specification, “above” or “on” means not only when located above or below the target part, but also when there is another part in between, and does not necessarily mean located above with respect to the direction of gravity.

[0040] In addition, terms such as “first”, “second”, etc. in this specification are not used to indicate any order or importance, but are used to distinguish components from each other.

[0041]

[0042] <Method for manufacturing spherical hard carbon and spherical hard carbon manufactured therefrom>

[0043] In general, hard carbon, like graphite, is a carbon-based material. Compared to artificial graphite, which requires high-temperature heat treatment of approximately 2500℃ or higher, hard carbon is manufactured by carbonization at a lower temperature, resulting in a lower manufacturing cost. In addition, hard carbon has an interplanar distance (d002) of approximately 0.370㎚ or higher and numerous micropores within it. Due to these structural characteristics of hard carbon, unlike conventional graphite, there is almost no volume change during lithium insertion and de-insertion, resulting in excellent battery life characteristics. In addition, hard carbon has excellent rate performance due to lithium ion channels and micropores existing in all directions of the particles, and the lithium-plating phenomenon does not occur. In addition, hard carbon has a high reversible capacity of approximately 400 mAh / g or higher, compared to graphitic carbon (e.g., natural graphite, artificial graphite), which has a reversible capacity of approximately 300 mAh / g. In addition, the wide interplanar distance (d002) of hard carbon makes Na + , K + Cations such as these can be easily inserted and removed, and thus can be applied as next-generation cathode materials.

[0044] However, hard carbon has lower crystallinity than graphite and has micropores, so although it has a large specific surface area, its density is about 1.0 g / cc, which is lower than that of graphite, so the energy density per volume of the battery is low. In addition, since hard carbon is generally manufactured in a lump form, it must go through a pulverization process to be used in a battery. The particles of pulverized hard carbon are not uniform in shape and size, and the specific surface area is large. Since such hard carbon has a low charging density and a large specific surface area, not only does the initial irreversible capacity increase, but the initial efficiency is also low, and the formability of the electrode plate is also low.

[0045] Accordingly, the inventors of the present invention found that when a capping agent such as a surfactant or a hydrophilic polymer is added during hydrothermal synthesis using a sugar as a carbon source selectively, the capping agent is distributed (present) on the surface of the carbon precursor, so that aggregation between carbon precursor particles is suppressed and surface energy is minimized, thereby obtaining a spherical carbon precursor.

[0046] Therefore, in the present invention, by hydrothermally synthesizing an aqueous solution containing a sugar and a capping agent and then carbonizing it, spherical hard carbon having a high sphericity of about 0.9 or higher can be manufactured. Since the spherical hard carbon manufactured in this way has a high packing density and a small specific surface area, when used as an anode active material, the packing amount can be increased, thereby improving the energy density of the battery per volume. In addition, the initial irreversible capacity can be reduced, thereby improving the initial efficiency.

[0047] According to an example, a method for producing spherical hard carbon according to the present invention includes the step of (S100) forming a carbon precursor by subjecting an aqueous solution containing a sugar and a capping agent to a hydrothermal synthesis reaction; and the step of (S200) carbonizing the carbon precursor by heat treatment under an inert gas atmosphere.

[0048] According to another example, the method for manufacturing spherical hard carbon according to the present invention may additionally include a step of classifying the carbonized material (S300) in addition to the steps (S100) and (S200).

[0049] Hereinafter, each step of manufacturing spherical hard carbon according to the present invention will be described with reference to FIG. 1.

[0050] (a) Formation step of carbon precursor

[0051] As illustrated in Fig. 1, a carbon precursor is formed by a hydrothermal synthesis reaction of an aqueous solution containing sugars and a capping agent (hereinafter, '(S100) step').

[0052] Specifically, step (S100) may include a step of (S110) dissolving a sugar and a capping agent in water (e.g., DI water) and stirring to form an aqueous solution; and a step of (S120) hydrothermally reacting the aqueous solution, and then stirring and vacuum filtering under atmospheric pressure to form a carbon precursor. However, the stirring in step (S110) and the stirring and vacuum filtering in step (S120) may be omitted.

[0053] In the present invention, sugars serve as a carbon source. Compared to carbon sources such as phenolic resins and pitch obtained from conventional petrochemical processes, sugars can be extracted from biomass, offering cost and environmental benefits. These sugars include monosaccharides and disaccharides.

[0054] According to an example, the sugar may include at least one selected from the group consisting of glucose, sucrose, fructose, galactose, maltose, and lactose.

[0055] In the present invention, a capping agent is adsorbed and distributed on the surface of a carbon precursor formed by a hydrothermal synthesis reaction of a sugar. The capping agent present on the surface of the carbon precursor inhibits aggregation between carbon precursors and lowers surface energy, allowing the carbon precursor to form a spherical shape.

[0056] These capping agents include surfactants, hydrophilic polymers, etc., and these can be used alone or in combination of two or more.

[0057] Surfactants usable in the present invention may be cationic surfactants, nonionic surfactants, anionic surfactants, etc., and specifically, alkyltrimethyl ammonium halide-based cationic surfactants, polyoxyethylene glycol-based nonionic surfactants, fatty acid ester-based nonionic surfactants, sulfate-based anionic surfactants, sulfonate-based anionic surfactants, etc. Non-limiting examples of the cationic surfactants include cetyltrimethylammonium bromide (CTAB), cetyltrimethyl ammonium chloride (CTAC), and dodecyltrimethyl ammonium bromide (CTAB). Non-limiting examples of the above nonionic surfactants include fatty acid esters of d-sorbitol such as Span 20, Span 40, Span 60, Span 65, Span 80, and Span 85, polyoxyethylene glycol sorbitan alkyl esters such as Tween 20, Tween 21, Tween 40, Tween 60, Tween 65, Tween 80, Tween 81, and Tween 85, and polyoxyethylene glycol pt-octylphenyl ether such as TritonX-100.In addition, non-limiting examples of the anionic surfactant include Sodium Dodecyl Sulfate, Ammonium Lauryl Sulfate, Sodium Lauryl Ethylene Sulfate, Linear Alkylbenzene Sulfonate, α-Olefin Sulfonate, Alkyl Sulfate, Alkyl Ether Sulfate, Sodium Alkane Sulfonate, etc.

[0058] The hydrophilic polymer usable in the present invention is not particularly limited as long as it is a water-soluble polymer containing a hydrophilic functional group, and non-limiting examples include polyacrylic acid (PAA), polyvinyl pyrrolidone (PVP), polytetrafluoroethylene (PTFE), etc., and these may be used alone or in a mixture of two or more.

[0059] According to an example, the capping agent may include at least one selected from the group consisting of cetyltrimethylammonium bromide (CTAB), cetyltrimethyl ammonium chloride (CTAC), dodecyltrimethyl ammonium bromide (CTAB), polyacrylic acid (PAA), polyvinyl pyrrolidone (PVP), and polytetrafluoroethylene (PTFE).

[0060] The aforementioned sugars and capping agents can control the sphericity and particle size of hard carbon depending on their use (mixing) ratio. However, using too little capping agent may have minimal effects on suppressing agglomeration and achieving sphericity, while using too much capping agent can be cost-effective.

[0061] For example, the aqueous solution may contain a sugar and a capping agent in a weight ratio of 13 to 14:1. If the proportion of the capping agent used in the aqueous solution is too low, the effect of inhibiting aggregation and forming spheroids may be reduced, while if the proportion of the capping agent used in the aqueous solution is too high, it may be disadvantageous in terms of price.

[0062] According to another example, the aqueous solution may contain 9 to 25 wt% of sugar; 0.68 to 1.84 wt% of capping agent; and 73 to 91 wt% of water, based on the total amount of the aqueous solution. In this case, the particle size of the spherical hard carbon can be controlled to a constant level.

[0063] The stirring time in the above step (S110) is not particularly limited, and may be about 20 to 40 minutes, as an example.

[0064] Thereafter, the aqueous solution obtained in the above step (S110) is placed in an autoclave and subjected to a hydrothermal synthesis reaction under high temperature and high pressure. In one example, the aqueous solution may be heated at a temperature of about 100 to 200°C under a pressure of about 1 to 15 bar for about 2 to 72 hours to cause the hydrothermal synthesis reaction.

[0065] After the above-described hydrothermal synthesis reaction, the reaction product can be stirred and vacuum filtered for about 1.5 to 2.5 hours under atmospheric pressure (e.g., about 1 atm) to obtain a carbon precursor. The carbon precursor obtained at this time may be in the form of spherical particles due to the capping agent.

[0066] (b) Calcination step of carbon precursor

[0067] As illustrated in Fig. 1, the carbon precursor obtained in the step (S100) is carbonized by calcination (heat treatment) in an inert gas atmosphere (hereinafter, 'step (S200)'). Thus, the present invention can obtain spherical hard carbon.

[0068] The above-mentioned calcination (heat treatment) can be performed at a temperature of about 900 to 1500°C for about 30 to 180 minutes under an inert gas atmosphere. Specifically, by heating the carbon precursor to a temperature of about 900 to 1500°C at a heating rate of about 2 to 10°C / min under an inert gas atmosphere, and then calcining at a temperature of about 900 to 1500°C for 30 to 180 minutes, the spherical carbon precursor obtained in the step (S100) can be carbonized to obtain spherical hard carbon in a powder state.

[0069] If necessary, a classification process may be additionally performed on the material (i.e., spherical hard carbon) calcined in the above step (S200). The classification process removes powder exceeding a certain size from the spherical hard carbon produced by discharging it to the outside using a classifier (sieve) or the like. Classifiers that can be used at this time include high-speed rotary classifiers, ultrasonic classifiers, and air-flow classifiers.

[0070]

[0071] The spherical hard carbon manufactured by the above-described method may have a circularity of 0.9 or more, specifically, about 0.91 to 0.93. Here, the spherical degree may be calculated according to the mathematical formula 1 described in Experimental Example 2 below. At this time, the aspect ratio (length of the major axis / length of the minor axis) of the spherical hard carbon may be about 0.9 to 1.0. As such, the spherical hard carbon manufactured according to the present invention has a large specific surface area compared to graphite, but since it is a particle close to a spherical shape, the packing density is large and the specific surface area is small. Therefore, when the spherical hard carbon is applied as an anode active material of a secondary battery, the packing amount is improved, thereby improving the energy density of the battery per volume, and the initial irreversible capacity is also low, thereby improving the initial efficiency.

[0072] The above spherical hard carbon may have an average particle diameter (D50) in the range of about 0.7 to 15 μm. At this time, the spherical hard carbon may have a uniform particle size distribution and thus monodispersity. In one example, the spherical hard carbon may have a particle size distribution that satisfies the following relationship 1.

[0073] [Relationship 1]

[0074] 1.5 ≤ (D90 - D10) / D50 ≤ 2.5

[0075] (In the above formula,

[0076] D90, D10 and D50 are the particle sizes at which the cumulative volume is 90% by volume, the particle sizes at which the cumulative volume is 10% by volume, and the particle sizes at which the cumulative volume is 50% by volume, respectively, in the volume-based particle size distribution by laser diffraction particle size distribution measurement method.

[0077] In addition, the powder density (apparent density) of the above-mentioned spherical hard carbon may be in the range of 0.85 to 1.15 g / cc under an applied pressure of about 50 to 500 MPa. In this case, the present invention can increase the density of the electrode, thereby improving the energy density per volume.

[0078]

[0079] <Cathode>

[0080] The present invention provides a negative electrode comprising the aforementioned spherical hard carbon. In this case, the spherical hard carbon is included as a negative electrode active material.

[0081] For example, the negative electrode of the present invention includes a current collector; and a negative electrode active material layer including the aforementioned spherical hard carbon on at least one surface of the current collector.

[0082] The current collector may be any metal that has high conductivity and to which the slurry of the negative electrode active material can easily adhere, as long as it is non-reactive within the voltage range of the battery. Examples thereof include aluminum (Al), copper (Cu), gold (Au), nickel (Ni), titanium (Ti), sintered carbon, stainless steel, aluminum alloys (e.g., aluminum-cadmium alloys), copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., or a mesh or foil manufactured using a combination thereof. The thickness of the current collector is not particularly limited, and may be in the typically applied range of about 9 to 16 μm.

[0083] The above negative electrode active material layer can be manufactured by coating a negative electrode slurry containing a negative electrode active material, a binder, a solvent, and, if necessary, a conductive material, on at least one surface of a current collector, drying the same, and then rolling the same.

[0084] The above negative electrode active material includes the above-described spherical hard carbon, and may optionally additionally include a negative electrode active material known in the art.

[0085] The content of the above-mentioned spherical hard carbon is not particularly limited, and may be, for example, about 60 to 97 wt% based on the total amount of the cathode slurry.

[0086] The above binder is not particularly limited as long as it is commonly used in the art while attaching the negative electrode active material particles to each other and attaching the negative electrode active material to the current collector. For example, there are polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HEP), polyvinylidene fluoride, polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid, styrene butylene rubber (SBR), lithium-substituted polyacrylate (Li-PAA), etc., and these may be used alone or in combination of two or more.

[0087] The content of such binder is not particularly limited and may be, for example, about 3 to 20 wt% based on the total amount of the cathode slurry.

[0088] The conductive material is used to provide conductivity to the electrode, and is not particularly limited as long as it has conductivity without causing chemical changes in the battery to be formed. Examples thereof include natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon nanotubes, graphene, conductive fibers (e.g., carbon fibers or metal fibers), metal powders (e.g., fluorocarbon, copper, aluminum, nickel, silver powders), conductive whiskers (e.g., zinc oxide, potassium titanate, etc.), conductive metal oxides (e.g., titanium oxide, etc.), conductive polymers (e.g., polyphenylene derivatives, etc.), or mixtures thereof. The content of the conductive material may be about 0 to 20 wt%, and specifically, 0.001 to 20 wt%, based on the total amount of the negative electrode slurry composition.

[0089] Non-limiting examples of the above solvents include dimethyl sulfoxide (DMSO), N-methyl pyrrolidon (NMP), dimethyl formamide (DMF), etc. The content of these solvents is not particularly limited and can be used in an amount that provides a desirable viscosity of the negative electrode slurry.

[0090] The coating method of the above cathode slurry is not particularly limited as long as it is a method commonly used in the art. Examples include slot die coating, gravure coating, immersion coating, and spray coating.

[0091]

[0092] Secondary battery

[0093] Meanwhile, the present invention provides a secondary battery including the aforementioned negative electrode.

[0094] The secondary battery of the present invention comprises the aforementioned negative electrode; positive electrode, electrolyte, and separator. Such a secondary battery is any device that undergoes continuous electrochemical reactions through charging and discharging, and may be, for example, a lithium (Li) secondary battery, a sodium (Na) secondary battery, a potassium (K) secondary battery, etc. In one example, the secondary battery of the present invention may be a lithium ion secondary battery or a sodium ion secondary battery.

[0095] The above positive electrode can be manufactured by mixing a positive electrode active material, a conductive agent, a binder, and a solvent to prepare a positive electrode slurry, and then directly coating the slurry on a metal current collector, or by casting the slurry on a separate support and laminating a positive electrode active material film peeled from the support onto a metal current collector.

[0096] The cathode active material usable in the present invention is not particularly limited as long as it is a cathode active material used in secondary batteries (e.g., lithium secondary batteries, sodium secondary batteries, etc.) in the relevant industry. Non-limiting examples of the cathode active material include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, Li(Ni a Cob Mn c )O2(0 <a<1, 0<b<1, a+b+c=1), LiNi1 - Y Co Y O2, LiCo1 - Y Mn Y O2, LiNi1 - Y Mn Y O2 (where 0≤Y<1), Li(Ni a Co b Mn c )O4(0 <a<2, 0<b<2, a+b+c=2), LiMn2 - Z Ni Z O4, LiMn2 - Z Co Z O4 (where 0 <Z<2), LiCoPO4, LiFePO4및 이들의 혼합물 등과 같은 리튬 함유 전이금속 산화물; Na x CoO2 (where 0 <x≤1), Na x Co2 / 3Mn1 / 3O2 (Here, 0 <x≤1), Na x Fe1 / 2Mn1 / 2O2 (Here, 0 <x≤1), NaCrO2, NaLi0 . 2Ni0 . 25 Mn0 . 75 O2 .35 , Na0 . 44 MnO2, NaMnO2, Na0 . 7VO2, Na 0.33 V2O 5, Na3V2(PO4)3, NaFePO4, NaMn0 . 5Fe0 . 5PO4, Na3V2(PO4)3 , There are sodium-containing transition metal oxides such as Na2FePO4F, Na3V2(PO4)3, NaFeSO4F, and mixtures thereof.

[0097] Descriptions of the above-mentioned conductive agent, binder and solvent are omitted as they are the same as those described in the cathode section described above.

[0098] The above-mentioned separator is not particularly limited as long as it is used as a separator in the art, and it is preferably a porous separator, and non-limiting examples include porous polymer films made of polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer; porous non-woven fabrics made of high-melting-point glass fiber, polyethylene terephthalate fiber, etc., and these may be used alone or in a laminate of two or more types. In addition, an insulating thin film having ion permeability and mechanical strength may be used.

[0099] The above electrolyte may include a non-aqueous solvent and an electrolyte salt, and optionally may further include additives such as an overcharge prevention agent.

[0100] The non-aqueous solvent is not particularly limited as long as it is a non-aqueous solvent commonly used for non-aqueous electrolytes, and cyclic carbonates, linear carbonates, lactones, ethers, esters, or ketones can be used.

[0101] Examples of the cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BE), fluoroethylene carbonate (FEC), etc., and examples of the linear carbonates include diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), ethylmethyl carbonate (EMC), and methylpropyl carbonate (MPC), etc. An example of the lactone is gamma-butyrolactone (GBL), and examples of the ethers are dibutyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, etc. In addition, examples of the esters include n-methyl acetate, n-ethyl acetate, methyl propionate, methyl pivalate, etc., and examples of the ketones are polymethylvinyl ketone. These non-aqueous solvents can be used alone or in combination of two or more.

[0102] Electrolyte salts are not particularly limited as long as they are commonly used as electrolyte salts for non-aqueous electrolytes. Non-limiting examples of electrolyte salts include A + B - As a salt with the same structure, A + is Li + , Na + , K + Contains ions composed of alkali metal cations or combinations thereof, such as B - is PF6 - , BF4 - , Cl - , Br - , I - , ClO4 - , AsF6 - , CH3CO2 - , CF3SO3 - , N(CF3SO2)2 - , C(CF2SO2)2 -A salt containing an ion such as an anion or a combination thereof. These electrolyte salts may be used alone or in combination of two or more. In one example, the electrolyte salt may be a lithium salt or a sodium salt.

[0103] The aforementioned secondary battery can be manufactured by forming an electrode assembly by placing a separator between the positive and negative electrodes, placing the electrode assembly in a pouch, cylindrical battery case, or square battery case, and then injecting an electrolyte. Alternatively, the electrode assembly can be manufactured by stacking the electrode assembly, then impregnating it with an electrolyte, and then placing the resulting product in a battery case and sealing it.

[0104] These secondary batteries can be used not only as battery cells used as power sources for small devices, but also as unit batteries in medium- to large-sized battery modules comprising multiple battery cells. Examples of such medium- to large-sized devices include electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems, and are particularly useful in areas requiring high output, such as hybrid electric vehicles and batteries for storing renewable energy.

[0105]

[0106] Hereinafter, the present invention will be described in detail through examples, but the following examples and experimental examples are merely illustrative of one form of the present invention, and the scope of the present invention is not limited to the following examples and experimental examples.

[0107] [Example 1]

[0108] 1-1. Manufacturing of old hard carbon

[0109] About 9 wt% (28 g) of sucrose and about 0.7 wt% (2.1 g) of cetyltrimethylammonium bromide (CTAB) were dissolved in 90.3 wt% (280 g) of deionized water (DI water), and the mixture was stirred for 30 minutes to prepare an aqueous solution. The prepared aqueous solution was placed in an autoclave, and a hydrothermal synthesis reaction was performed at a temperature of about 180°C for about 12 hours. Afterwards, the mixture was stirred with distilled water for more than 2 hours under atmospheric pressure (about 1 atm), and then a spherical carbon precursor was obtained using a vacuum filter. Thereafter, the spherical carbon precursor was heated to about 1300°C at a heating rate of 5°C / min under an argon (Ar) atmosphere, and then calcined (heat-treated) at about 1300°C for 1 hour, and then subjected to a classification process to produce spherical hard carbon.

[0110] Figure 2 is a scanning electron microscope (SEM) photograph of the spherical hard carbon manufactured in Example 1-1, and it can be seen that the shape of the hard carbon is a spherical particle.

[0111] 1-2. Manufacturing of lithium ion batteries

[0112] The spherical hard carbon manufactured in Example 1-1 was mixed with super P as a conductive agent and CMC / SBR as an aqueous binder in a weight % of spherical hard carbon : conductive agent : aqueous binder = 85 : 10 : 5 to manufacture an anode. Thereafter, a lithium ion battery half-cell using lithium metal as a counter electrode was manufactured using the manufactured anode, and the electrochemical characteristics according to the rate in the voltage range of 0.005 to 2 V were evaluated. At this time, the composition of the electrolyte was 1.15 M LiPF6in EC : EMC : DEC (= 3 : 5 : 2 vol. %) + FEC 5 wt%, and the separator used was Celgard2400 of the PP series.

[0113] 1-3. Manufacturing of sodium ion batteries

[0114] The spherical hard carbon manufactured in Example 1-1 was mixed with super P as a conductive agent and CMC / SBR as an aqueous binder in a weight % of spherical hard carbon : conductive agent : aqueous binder = 85 : 10 : 5 to manufacture a negative electrode. Afterwards, a sodium ion battery half-cell using sodium metal as a counter electrode was manufactured using the manufactured negative electrode, and the electrochemical characteristics according to the rate in the voltage range of 0.005 to 2 V were evaluated. At this time, the composition of the electrolyte was 1M NaPF6in EC : PC : DMC (= 9 : 9 : 2 vol.%), and Whatman's GF / F nonwoven fabric was used as the separator.

[0115]

[0116] [Example 2]

[0117] 2-1. Manufacturing of old hard carbon

[0118] A spherical hard carbon was manufactured in the same manner as in Example 1-1, except that about 16.5 wt% (28 g) of sucrose, 1.2 wt% (2.1 g) of cetyltrimethylammonium bromide (CTAB), and 82.3 wt% (140 g) of water were used instead of about 9 wt% (28 g) of sucrose, 0.7 wt% (2.1 g) of cetyltrimethylammonium bromide (CTAB), and 90.3 wt% (280 g) of water used in Example 1-1.

[0119] Figure 3 is an SEM photograph of the spherical hard carbon manufactured above, and it can be seen that the shape of the hard carbon is a spherical particle.

[0120] 2-2. Manufacturing of lithium ion batteries

[0121] A lithium ion battery was manufactured in the same manner as in Example 1-2, except that the spherical hard carbon manufactured in Example 2-1 was used instead of the spherical hard carbon of Example 1-1.

[0122] 2-3. Manufacturing of sodium ion batteries

[0123] A sodium ion battery was manufactured in the same manner as in Example 1-3, except that the spherical hard carbon manufactured in Example 2-1 was used instead of the spherical hard carbon of Example 1-1.

[0124]

[0125] [Example 3]

[0126] 3-1. Manufacturing of old hard carbon

[0127] Spherical hard carbon was manufactured in the same manner as in Example 1, except that about 24.5 wt% (28 g) of sucrose, 1.8 wt% (2.1 g) of cetyltrimethylammonium bromide (CTAB), and 73.6 wt% (84 g) of water were used instead of about 9 wt% (28 g) of sucrose, 0.7 wt% (2.1 g) of cetyltrimethylammonium bromide (CTAB), and 90.3 wt% (280 g) of water used in Example 1.

[0128] Figure 4 is an SEM photograph of the spherical hard carbon manufactured above, and it can be seen that the shape of the hard carbon is a spherical particle.

[0129] 3-2. Manufacturing of lithium ion batteries

[0130] A lithium ion battery was manufactured in the same manner as in Example 1-2, except that the spherical hard carbon manufactured in Example 3-1 was used instead of the spherical hard carbon of Example 1-1.

[0131] 3-3. Manufacturing of sodium ion batteries

[0132] A sodium ion battery was manufactured in the same manner as in Example 1-3, except that the spherical hard carbon manufactured in Example 3-1 was used instead of the spherical hard carbon of Example 1-1.

[0133]

[0134] [Comparative Example 1]

[0135] 1-1. Amorphous hard carbon

[0136] Amorphous hard carbon with an average particle diameter (D50) of 6.32 ㎛ and a sphericity of 0.786 was used as comparative example 1.

[0137] Figure 5 is an SEM photograph of the amorphous hard carbon, and it can be seen that the shape of the hard carbon is not spherical but amorphous particles.

[0138] 2-2. Manufacturing of lithium ion batteries

[0139] A lithium ion battery was manufactured in the same manner as in Example 1-2, except that the amorphous hard carbon prepared in Comparative Example 1-1 was used instead of the spherical hard carbon of Example 1-1.

[0140] 2-3. Manufacturing of sodium ion batteries

[0141] A sodium ion battery was manufactured in the same manner as in Example 1-3, except that the amorphous hard carbon prepared in Comparative Example 1-1 was used instead of the spherical hard carbon of Example 1-1.

[0142]

[0143] [Comparative Example 2]

[0144] 2-1. Amorphous artificial graphite

[0145] Commercially available amorphous artificial graphite with an average particle diameter (D50) of 14.3 ㎛ and a sphericity of 0.723 was used as comparative example 2.

[0146] Figure 6 is an SEM photograph of the amorphous artificial graphite manufactured above, and it can be seen that the shape of the artificial graphite is an amorphous particle.

[0147] 2-2. Manufacturing of lithium ion batteries

[0148] A lithium ion battery was manufactured in the same manner as in Example 1-2, except that the amorphous artificial graphite prepared in Comparative Example 2-1 was used instead of the spherical hard carbon of Example 1-1.

[0149] 2-3. Manufacturing of sodium ion batteries

[0150] A sodium ion battery was manufactured in the same manner as in Example 1-3, except that the amorphous artificial graphite prepared in Comparative Example 2-1 was used instead of the spherical hard carbon of Example 1-1.

[0151]

[0152] [Experimental Example 1] - Rate-dependent characteristics of lithium-ion secondary batteries

[0153] The rate characteristics of the lithium ion batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 3 were evaluated as follows, and the results are shown in Table 1 and Fig. 7 below.

[0154] Rate characteristics were evaluated from 0.005 V to 2.0 V (vs. Li / Li + ) was carried out in the voltage range, and the rate was 0.1C for the first and second charge / discharge, and in the subsequent cycle evaluations, the discharge rate of each cycle was fixed at 0.5C, and the charge rate of each cycle was changed to 0.3C, 0.5C, 1C, 2C, 3C, 4C, 5C, 6C, 10C, and 12C, and the specific capacity of each cycle was measured.

[0155] C-rate test(%), xC / 0.5C(x=1~12)1C2C3C4C5C6C10C12CExample 19080767580817670Example 28978696965666461Example 39081757571726561Comparative example 19080747169686158Comparative example 2968567493523115

[0156] As a result of the measurement, in the case of the lithium ion secondary battery using the spherical hard carbon of Examples 1 to 3, the rate was about 72 to 81% at a ratio of 0.5 C to 6 C, and also 61 to 70% at a ratio of 0.5 C to 12 C. On the other hand, in the case of the lithium ion battery using the amorphous hard carbon of Comparative Example 1, the rate was 68% at 0.5 C to 6 C, and 58% at 0.5 C to 12 C. In addition, in the case of the lithium ion battery using the amorphous artificial graphite of Comparative Example 2, the rate was about 23% at 0.5 C to 6 C, and 5% at 0.5 C to 12 C.

[0157] In this way, it was confirmed that the secondary battery using the spherical hard carbon manufactured according to the present invention has excellent rate characteristics even when charged at high speed.

[0158]

[0159] [Experimental Example 2]

[0160] In order to measure the degree of sphericity of the spherical hard carbon of Examples 1 to 3, the amorphous hard carbon of Comparative Example 1, and the amorphous artificial graphite of Comparative Example 2, the particle shape was analyzed using a particle size shape analyzer, and the degree of circularity was calculated according to the following mathematical equation 1, which is shown in Table 2 below. In Table 2, the closer the degree of sphericity is to 1, the better.

[0161] [Mathematical Formula 1]

[0162]

[0163] (In the above formula,

[0164] X A means the diameter of a circle equivalent to the area (A) of the cross-sectional image of a spherical hard carbon,

[0165] X p refers to the diameter of a circle equivalent to the circumference (P) of the cross-sectional image of a spherical hard carbon).

[0166] Average particle size (D50) (㎛) Sphericity 0.5C discharge capacity (mAh / g) 6C discharge capacity (mAh / g) 6C / 0.5C capacity retention rate (%) Example 10.7 0.9 28 25 22 0 38 0.5 Example 27.8 0.9 19 22 3 15 4 69.1 Example 3 12 0.9 15 20 5 14 16 8.7 Comparative Example 16.3 20.7 8 6 23 6 16 26 8.8 Comparative Example 2 14.3 0.7 23 30 9 7 6 24.6

[0167] As a result of the analysis, it was found that the spherical hard carbons of Examples 1 to 3 had a sphericity of approximately 0.91 or higher, indicating that they were particles close to spherical. In particular, the spherical hard carbon of Example 1 had a sphericity of 0.928 and an average particle size (D50) of approximately 0.7 ㎛.

[0168] On the other hand, the amorphous hard carbon of Comparative Example 1 had a sphericity of 0.786, and the amorphous artificial graphite of Comparative Example 2 had a sphericity of 0.723, indicating that the sphericity was not high.

[0169] In this way, it was confirmed that the present invention can produce spherical hard carbon having a sphericity close to 1.

[0170]

[0171] [Experimental Example 3]

[0172] In order to confirm the capacity retention and the occurrence of Li-plating phenomenon according to fast charging using lithium ion batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 3, the following analysis was performed, and the analysis results are shown in Table 3 and Figures 8 to 11.

[0173] First, each lithium-ion battery was subjected to 300 charge-discharge cycles at a rate of 3C, the cell was disassembled, and the cathode surface was analyzed using a scanning electron microscope and EDS (Energy Dispersive Spectrometer).

[0174] Element Example 1 Comparative Example 1 Comparative Example 2 C (At%) 100 37.59 24.42 O (At%) 062.41 75.58 Total (At%) 100 100 100

[0175] As can be seen in Fig. 8, the lithium ion battery of Example 1 had a high capacity retention rate of about 80% or more after 300 cycles. On the other hand, the lithium ion battery of Comparative Example 1 had a low capacity retention rate of about 63% after 300 cycles, and the lithium ion battery of Comparative Example 2 had a very low capacity retention rate of about 37%.

[0176] In addition, as shown in Table 3, in the case of Example 1, the content of carbon (C) element on the cathode surface was 100 atomic%, and, as before the test, no oxygen (O) element was detected (see Figs. 9(a) and (b)). On the other hand, in both Comparative Examples 1 and 2, unlike before the test, oxygen element was detected on the cathode surface in addition to carbon element (see Figs. 10-11).

[0177] In this way, it was confirmed that the spherical hard carbon manufactured according to the present invention not only has excellent charge / discharge cycle characteristics, but also that no Li-plating is observed even when fast charging is performed.

[0178]

[0179] [Experimental Example 4] - Charge / Discharge Characteristics of a Sodium Ion Battery

[0180] The charge / discharge characteristics of the sodium ion batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 3 were evaluated as follows, and the evaluation results are shown in Table 4 and Figure 12 below.

[0181] Charge / discharge evaluation is 0.05 V to 2.0 V (vs. Na / Na + ) was carried out in the voltage range, and the first and second charge / discharge were carried out at a rate of 0.1C.

[0182] 1 stCycle performance Charge capacity (mAh / g) Discharge capacity (mAh / g) Initial efficiency (%) Example 133028586.4 Comparative example 135827476.5 Comparative example 21388863.8

[0183] As a result of the evaluation, the sodium ion battery of Example 1 had a high initial efficiency of 86.4%, whereas the sodium ion batteries of Comparative Examples 1 and 2 had low initial efficiencies of less than about 80%, and in particular, the initial efficiency of Comparative Example 2 was very low at about 63.8%.

[0184] In this way, it was confirmed that when the spherical hard carbon manufactured according to the present invention was applied to a sodium ion battery, the initial efficiency was high.

[0185]

[0186] [Experimental Example 5] - Powder density of spherical hard carbon

[0187] The powder density of the spherical hard carbon of Example 1 and the amorphous hard carbon of Comparative Example 1 was measured as follows, and the measurement results are shown in Fig. 13.

[0188] The spherical hard carbon powder of Example 1 was placed in a container, pressure was applied, and the density was measured according to the applied pressure, thereby analyzing the change in density according to the applied pressure. At this time, the amorphous hard carbon of Comparative Example 1 was used as a control group.

[0189] As shown in Fig. 13, the spherical hard carbon of Example 1 had a higher density than the amorphous hard carbon of Comparative Example 1.

[0190] From this, it was confirmed that the spherical hard carbon manufactured according to the present invention can further improve the energy density of the battery compared to the conventional amorphous hard carbon.

Claims

1. A step of forming a carbon precursor by subjecting an aqueous solution containing sugars and a capping agent to a hydrothermal synthesis reaction; and A step of carbonizing the above carbon precursor by heat treatment under an inert gas atmosphere. A method for manufacturing spherical hard carbon including:

2. In paragraph 1, A method for producing spherical hard carbon, wherein the above sugar comprises at least one selected from the group consisting of glucose, sucrose, fructose, galactose, maltose, and lactose.

3. In paragraph 1, A method for producing spherical hard carbon, wherein the capping agent comprises at least one selected from the group consisting of a surfactant and a hydrophilic polymer.

4. In paragraph 3, A method for producing spherical hard carbon, wherein the surfactant comprises at least one selected from the group consisting of an alkyltrimethyl ammonium halide-based cationic surfactant, a polyoxyethylene glycol-based nonionic surfactant, a fatty acid ester-based nonionic surfactant, a sulfate-based anionic surfactant, and a sulfonate-based anionic surfactant.

5. In paragraph 3, A method for producing spherical hard carbon, wherein the hydrophilic polymer comprises at least one selected from the group consisting of polyacrylic acid (PAA), polyvinyl pyrrolidone (PVP), and polytetrafluoroethylene (PTFE).

6. In paragraph 1, A method for producing spherical hard carbon, wherein the above-mentioned sugar and capping agent are contained in a weight ratio of 13 to 14:

1.

7. In paragraph 1, A method for producing spherical hard carbon, wherein the aqueous solution contains 9 to 25 wt% of sugar; 0.68 to 1.84 wt% of capping agent; and 73 to 91 wt% of water, based on the total amount of the aqueous solution.

8. In paragraph 1, A method for producing spherical hard carbon, wherein the above-mentioned hydrothermal synthesis reaction is performed by heating the aqueous solution at a temperature of 100 to 200°C under a pressure of 1 to 15 bar for 2 to 72 hours.

9. In paragraph 1, A method for producing spherical hard carbon, wherein the above heat treatment is performed at a temperature of 900 to 1500°C for 30 to 180 minutes under an inert gas atmosphere.

10. In paragraph 1, A method for producing spherical hard carbon, further comprising a step of classifying the carbonized material.

11. Spherical hard carbon manufactured by the method described in any one of claims 1 to 10.

12. In paragraph 11, Spherical hard carbon with a circularity of 0.9 or greater.

13. In paragraph 12, Spherical hard carbon with an average particle diameter (D50) in the range of 0.7 to 15 ㎛.

14. In paragraph 12, Spherical hard carbon having a powder density in the range of 0.85 to 1.15 g / cc under an applied pressure of 50 to 500 MPa.

15. In paragraph 11, Spherical hard carbon used as a negative electrode material.

16. A cathode comprising the spherical hard carbon described in Article 11.

17. A secondary battery comprising the negative electrode described in Article 16.

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