WO2012091515A2 - Negative electrode active material for a lithium secondary battery, method for manufacturing same, and lithium secondary battery using same - Google Patents

Abstract

The present invention relates to a negative electrode active material for a lithium secondary battery, to a method for manufacturing same, and to a lithium secondary battery using same, in which the negative electrode active material comprises carbides obtained by heat-treating a polyurethane resin in an active-gas atmosphere, and carbonizing the heat-treated resin, thereby reducing the specific surface area and thus relieving problems of moisture adsorption, improving initial charging/discharging efficiency of a secondary battery, and thus improving the energy density of the secondary battery and improving the characteristics of the battery, such as imparting a lengthened lifespan and improved charging/discharging output properties, high-temperature storage characteristics, etc. thereto.

Description

Anode active material for lithium secondary battery, manufacturing method thereof, and lithium secondary battery using same

The present invention relates to a negative electrode active material for a lithium secondary battery, a method for manufacturing the same, and a lithium secondary battery using the same, and more particularly, by preparing a negative electrode active material including a carbonized carbide obtained by heat treatment of a polyurethane resin under an active gas atmosphere. The specific surface area reduces the problem of water adsorption, improves the initial charge and discharge efficiency of the secondary battery, improves the energy density of the battery, and improves battery characteristics such as excellent life characteristics, charge and discharge output, and high temperature storage characteristics. The present invention relates to a negative electrode active material for a lithium secondary battery, a method of manufacturing the same, and a lithium secondary battery using the same.

Recently, with the increasing interest and demand for eco-friendly green cars, the emergence of electric motor-driven cars is becoming visible. The type of vehicle driven by an electric motor may be classified into an electric vehicle (EV), a hybrid electric vehicle (HEV), a plug-in hybrid electric vehicle (PHEV), and the like. The secondary battery is responsible for a power source for driving the motor. Unlike secondary batteries applied to mobile IT devices, automotive secondary batteries require very large output characteristics and lifetime characteristics. Among secondary batteries, lithium secondary batteries have higher energy density to weight and superior output characteristics than nickel-hydrogen batteries, and thus, they are widely used as power sources for driving motors of electric vehicles.

Graphite is mostly used as a negative electrode active material of automotive lithium secondary batteries, and exhibits a high discharge voltage of 3.6 V, which is the most widely used for ensuring high energy density of lithium secondary batteries and high life characteristics of secondary batteries with excellent reversibility. . However, graphite has a problem in that energy input / output characteristics are inferior, and in particular, low temperature output characteristics are insufficient. In addition, about 10% of the volume change of graphite occurs during charging and discharging, thereby adversely affecting the bonding strength between the current collector and the mixture layer, thereby degrading the lifespan of the battery.

In order to solve this problem, non-graphitizable carbon having fine pores has been proposed and partially used. The non-graphitizable carbon is a structure in which lithium ions are stored and released in numerous pores, and there is almost no volume expansion during charging and discharging of lithium ions, so the battery has excellent life characteristics, and fine lithium pores are present in all directions of particles. It is known to be excellent in output characteristics because it can be stored and released. However, since non-graphitizable carbon has a large specific surface area, the amount of solvents and binders must be increased when manufacturing electrode slurries, and the energy density of the battery is lowered as the amount of binder increases. When the secondary battery is increased, moisture reacts with the electrolyte to form hydrofluoric acid (HF), thereby increasing irreversible capacity and lowering durability.

In order to solve the above problem, a method of carbonizing under normal pressure / pressurization to reduce specific surface area by developing closed pores rather than open pores, or reducing specific surface area by forming pyrolytic carbon on a non-graphitizable carbon surface is disclosed. There is a bar. However, when the carbonization of the raw material is recontaminated by the tar component or the like, there is a problem that the uniformity of the product of the upper and lower raw crucible is inferior.

Republic of Korea Patent No. 0450642 (Patent Document 1) relates to nano-sized spherical non-graphitizable carbon and a method for manufacturing the same and a lithium secondary battery containing the carbon as a negative electrode active material, nano-sized non-graphite including a surfactant Chemical carbon was prepared, and Korean Unexamined Patent Publication No. 2011-0042840 (Patent Document 2) discloses a negative active material for a lithium secondary battery including spherical graphite and plate-like graphite obtained by coating amorphous carbon on natural graphite and firing the same. A secondary battery was manufactured.

The conventional anode active material for lithium secondary batteries using the non-graphitizable carbon and graphite as described above has a small specific surface area and is insufficient to be used as a negative electrode active material by satisfying the requirements of a carbon material having excellent output characteristics.

The present invention is to solve the conventional problems, by producing a negative electrode active material comprising a carbonized carbide by heat-treating the polyurethane resin in an active gas atmosphere, the problem of water adsorption is reduced due to the low specific surface area, 2 The purpose of the present invention is to provide a negative electrode active material for a lithium secondary battery and a method of manufacturing the same, which improves the energy density of the battery by improving the initial charge and discharge efficiency of the secondary battery and improves battery characteristics such as excellent life characteristics, charge and discharge output, and high temperature storage characteristics. It is done.

In addition, another object of the present invention is to provide a negative electrode for a lithium secondary battery including the negative electrode active material and a lithium secondary battery comprising the same.

According to the present invention for achieving the above object,

In order to manufacture the negative electrode active material for lithium secondary battery, the polyurethane resin is heat treated and carbonized under an inert gas atmosphere to smooth out the gas so as not to contaminate the surface of the product due to the tar component, and further carbon coating after carbonization. It is possible to achieve the desired surface properties only by the carbonization process of the present invention so that no post-treatment is required.

The polyurethane resin, which is a precursor of the negative electrode active material for a lithium secondary battery according to the present invention, may be prepared by the reaction of a polyol and an isocyanate.

The polyol is a conventional one used for preparing a polyurethane resin, but is not particularly limited, but specifically, a polyether polyol, a polyester polyol, a polytetramethylene ether glycol polyol, a Polyharnstoff Dispersion (PHD) polyol, Any one or two or more selected from amine-modified polyols, Manmich polyols, and mixtures thereof are preferred, more preferably polyester polyols, amine-modified polyols, Manmich polyols Or mixtures thereof.

It is preferable that the molecular weight of the said polyol is 300-3000, More preferably, it is effective that it is 400-1500. If the molecular weight of the polyol is less than 300, there is a disadvantage in that the thermal stability of the polyurethane resin synthesized by the formation of a monool is reduced and melting occurs in the carbonization process.If the molecular weight of the polyol exceeds 3000, it is amorphous in the polyol structure. Carbon chains increase and the thermal stability of polyurethane resin falls. In addition, the number of hydroxyl groups of the polyol is preferably 1.5 to 6.0, more preferably 2.0 to 4.0, and it is effective that the hydroxyl group content present in the polyol is 3 to 15% by weight. This is to have a specific surface area and surface characteristics of the preferred range when the polyol having the optimum molecular weight is carbonized polyurethane resin containing the optimum content to prepare a negative electrode active material. When the number of hydroxyl groups and the content of hydroxyl groups exceed the above ranges, the specific surface area becomes excessively large when the polyurethane resin is carbonized, thereby increasing water adsorption, thereby reducing battery efficiency.

In addition, the isocyanate reacting with the polyol is a conventional one used for preparing a polyurethane resin, but is not particularly limited. Specifically, hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), 4,4'-dicyclo Hexylmethane diisocyanate (H12MDI), polyethylene polyphenyl isocyanate, toluene diisocyanate (TDI), 2,2'-diphenylmethane diisocyanate (2,2'-MDI), 2,4'-diphenylmethane diisocyanate ( 2,4'-MDI), 4,4'-diphenylmethane diisocyanate (4,4'-MDI, monomeric MDI), polymeric diphenylmethane diisocyanate (polymeric MDI), orthotoluidine diisocyanate (TODI), Any one or two or more selected from naphthalene diosocyanate (NDI), xylene diisocyanate (XDI), lysine diisocyanate (LDI) and triphenylmethane triisocyanate (TPTI) are preferred. It said, more preferably 4,4'-diphenylmethane diisocyanate (4,4'-MDI, monomeric MDI), polymeric diphenylmethane diisocyanate (polymeric MDI) or polyethylene polyphenyl isocyanate is effective.

The mixing ratio of the polyol and isocyanate is effective to include 150 to 240 parts by weight of the isocyanate based on 100 parts by weight of the polyol. If the content of isocyanate is less than 150 parts by weight, the formation of isocyanurate bonds that enhance thermal stability is not sufficient, resulting in a problem that the resin is melted similarly to digraphitizable carbon during the carbonization process, and the content of isocyanate is If it is more than 240 parts by weight, isocyanurate bonds are excessively generated, and the specific surface area is increased after the carbonization process, thereby increasing the water adsorption rate, and the element ratio of oxygen to the resulting polyurethane resin is increased to produce a secondary battery. When the problem occurs that the electrical characteristics are deteriorated.

A catalyst may be added to induce the reaction of the polyol and the isocyanate to prepare the polyurethane resin. The catalyst is pentamethyldiethylene triamine, dimethyl cyclohexyl amine, bis- (2-dimethyl aminoethyl) ether, triethylene diamine ( (triethylene diamine) potassium octoate (potassium octoate), tris (dimethylaminomethyl) phenol (tris (dimethylaminomethyl) phenol), potassium acetate (potassium acetate) or any one or more selected from them may be used, and The content of the catalyst is preferably added in an amount of 0.1 to 5 parts by weight based on the polyol, and more preferably in an amount of 0.5 to 3 parts by weight, and when the content of the catalyst is 0.1 parts by weight or less, the reaction between the polyol and the isocyanate is too slow. The problem occurs that the production efficiency of the negative electrode active material decreases, and when the content of the catalyst exceeds 5 parts by weight It proceeds too fast and the formed non-uniformly is a polyurethane resin, so that there arises a problem that the physical properties of the negative electrode active material decreases.

In addition, a foaming agent may be included in order to facilitate the pulverization of the polyurethane resin, and a foam stabilizer may be further added to improve the quality of the polyurethane resin.

In addition, flame retardants such as Tris (2-ChloroPropyl) Phosphate (TCPP), Tris (2-Chroroethyl) Phosphate (TCEP), Triethyl phosphate (TEP), and Trimethyl phosphate (TMP) are further added to improve the thermal stability of the polyurethane resin. More may be added.

The mixing ratio of the polyol and isocyanate may vary depending on the amount of additives such as catalysts, foam stabilizers, blowing agents, flame retardants, etc., but is not limited thereto.

Preferably, it is effective to base the content of oxygen, nitrogen and hydrogen through elemental analysis of the synthesized polyurethane resin. Since the isocyanate contains a large amount of NCO group, as the addition rate of the isocyanate increases, the content of nitrogen and oxygen increases. It is effective that the preferred nitrogen content ranges from 7 to 9% by weight of the total polyurethane resin. If the content of nitrogen is more than 9% by weight, the specific surface area of carbon after the carbonization process increases to increase the moisture adsorption in the air to reduce the efficiency of the battery, when the content of nitrogen is less than 7% by weight It is not preferable because the amount of isocyanurate bond is insufficient, so that the thermal stability of the polyurethane resin is reduced and the resin melts like carbonaceous carbon when carbonized.

In addition, the content of hydrogen is preferably 4 to 6% by weight of the total polyurethane resin, the oxygen content is preferably 15 to 22% by weight of the total polyurethane resin. When the content of hydrogen and oxygen is less than the above range, the specific surface area becomes excessively large when carbonizing the polyurethane resin due to excessive content of the isocyanurate structure, thereby increasing the amount of water adsorption in the air and reducing battery efficiency. A problem arises. When the content of hydrogen and oxygen exceeds the above range, when the carbonized polyurethane resin is carbonized, the chemical reaction for the optimum microstructure modification is not sufficient, so that the polyurethane resin is melted and hardly suitable for the negative electrode active material of the lithium secondary battery. It does not express carbon structure.

Next, the manufacturing method of the negative electrode active material for lithium secondary batteries is demonstrated in detail. The above-mentioned polyol and isocyanate are reacted to prepare a polyurethane resin, and the carbonized step of heat-treating the prepared polyurethane resin under an inert gas atmosphere.

The polyurethane resin may be obtained by exothermic reaction by uniformly mixing the polyol and isocyanate at a constant ratio. As the mixing method, a conventional polymer resin mixing method may be used. Preferably, mixing by an impeller or in-line mixing by high pressure extrusion is effective.

The obtained polyurethane resin is in the form of agglomerates, and is preferably pulverized to a suitable size to perform a carbonization step because the density is low due to foaming and the processing yield per hour is lowered. However, the process is not necessarily performed, and a process of pulverizing the bulk polyurethane resin after the carbonization process is also possible. Before the pre-carbonization process, that is, when the bulk polyurethane resin is pulverized, the cumulative volume of the particles analyzed by the particle size analyzer is 50% after the first crushing through a crusher using a mechanical crushing method. The secondary grinding process is performed such that the average particle size (D50) of the spot is about 100 to 200 μm.

In addition, the carbonization step includes a pre-carbonization step and the main carbonization step, the pre-carbonization step is heat-treated for 30 to 120 minutes at 600 to 1000 ℃ temperature, the main carbonization step is 1000 to 1400 ℃ temperature It is effective to heat treatment for 30 to 120 minutes at. In addition, the pre-carbonization step and the main carbonation step is preferably performed sequentially.

The precarbonization step is carried out under an inert gas atmosphere, the inert gas is preferably used helium, nitrogen, argon or a mixture thereof. The precarbonization step is preferably performed at 600 to 1000 ° C, more preferably at 700 to 900 ° C. If the preliminary carbonization is carried out below 600 ° C., the low molecular weight gases are less volatilized and thus remain inside the material, which may reduce the yield of the product, and due to the residual gas generated in the main carbonization step, There is a problem of contaminating the inside of the furnace and the surface of the product. In addition, when the pre-carbonization is performed in excess of 1000 ℃ causes the production cost increase by supplying more calories than necessary, there is a problem that the contamination of the product with the pyrolysis product of the tar gas discharged from the raw material due to the high temperature.

The pre-carbonization step, after the pre-carbonization step or after the main carbonization step may include a fine grinding step of adjusting the particle size to a size suitable for manufacturing as an electrode for a lithium secondary battery.

The pulverizing step may be pulverized using a conventional pulverizer using a mechanical pulverization method, and in particular, various pulverizers such as ball mills, pin mills, rotor mills, and jet mills may be used. In general, the jet mill grinding process, which is easy to pulverize, has a problem in that it is difficult to reduce the particle size to 60 µm or less since the specific gravity of the polyurethane resin is low when the pre-carbonization step is performed, thereby limiting the impact between particles. Pin mill and rotor mill processes also have a limit in the rotational force, it is difficult to reduce the particle size due to the low specific gravity of the particles. Therefore, when the fine grinding step is performed using a jet mill, a pin mill and a rotor mill, it is preferable to carry out after the precarbonization step or after the main carbonization step.

In addition, when the finely pulverized polyurethane particles are subjected to pre-pulverization and pre-carbonization, the fine-pulverization step is performed after the pre-carbonization step because the fine-pulverized particles may aggregate with each other after the pre-carbonization step. Is more effective. Jet mills are most effective when the milling step is carried out after the preliminary carbonization step. The average particle size (D50) of the particles pulverized by the jet mill is preferably 3 to 50 µm, more preferably 3 to 20 µm, and most preferably 6 to 15 µm. When the average particle size (D50) is less than 3 μm, the amount of fine particles generated less than 1 μm increases, the specific surface area of the particles increases, and the property of adsorbing moisture in the air increases, causing lithium ions and water to react in the battery reaction. There is a problem that the capacity can be increased, and the fine powder increases, the porosity between the particles increases, the filling density of the particles is lowered, and lithium ions inserted into the carbon particles are easily eluted at a high temperature of 65 ° C. or higher during the battery reaction. A problem occurs that the high temperature storage characteristics of the deteriorate. In addition, when the average particle size (D50) is greater than 50㎛, since the interface of the particles becomes small and the entrance and exit area of the lithium ions becomes narrow, there is a problem that the input and output characteristics of the lithium ions during the battery reaction is reduced.

After the preliminary carbonization step and the fine grinding step, the main carbonization step of heat treatment for 30 to 120 minutes at a temperature of 1000 to 1500 ℃. This carbonization step improves the conductivity of carbon after removing the low molecular weight gases generated in the precarbonization step, and optimizes the characteristics as a negative electrode material for secondary batteries by reducing the element ratio (H / C%) of hydrogen and carbon. It is a step for. The main carbonization step is carried out under an inert gas atmosphere, and the inert gas is preferably helium, nitrogen, argon or a mixture thereof.

The heat treatment temperature of the carbonization step is preferably 1000 to 1500 ° C, more preferably 1200 to 1400 ° C. When carbonizing at a temperature below 1000 ° C., the element ratio (H / C%) of hydrogen and carbon is increased to decrease the output characteristics of the battery, and the remaining hydrogen in carbon reacts irreversibly with lithium ions for the first 5 cycles. When the carbonization temperature is higher than 1400 ° C, the reversible capacity, which is the storage capacity of lithium ions, decreases, the energy density of the battery is greatly reduced, and the specific surface area increases. As the property of adsorbing moisture in the air increases, there arises a problem that the lithium ion reacts with moisture in the battery reaction, thereby increasing the irreversible capacity. In addition, the commercial furnace in order to withstand the heat treatment temperature of more than 1500 ℃ because the material and configuration of the electric furnace must be changed to a heat-resistant material, there arises a problem that the manufacturing cost and process cost increases.

The negative active material for a lithium secondary battery that has undergone the preliminary carbonization step, the fine grinding step and the carbonization step according to the present invention has a specific surface area of 2.0 to 5.0 m 2 / g, and as shown in FIG. 6, an average pore size of 1 It is preferable that it is-5 nm. Further, the (002) mean layer spacing (d002) obtained by the X-ray diffraction method (XRD) was 3.7 to 4.0 kPa, the crystallite diameter Lc (002) in the C-axis direction was 0.8 to 2 nm, and the R value was 1.3 to It is preferable that it is 2, and it is preferable that the peak intensity ratio (5 degree peak / 002 peak) is 2-4, The element ratio of hydrogen and carbon (H / C%) calculated | required by elemental analysis is 0.1 or less, oxygen and It is preferable that the element ratio (O / C%) of carbon is 1.0 or less.

This is because the negative electrode active material for a lithium secondary battery manufactured by the manufacturing method of the present invention has physical properties in the above range, the water adsorption rate is reduced, it is formed in a structure that is easy to charge and discharge lithium ions to improve the initial charge and discharge efficiency of the secondary battery You can. In addition, the structure of the negative electrode active material for a lithium secondary battery is formed by uniformly and appropriately combining the urethane reaction, urea reaction, and isocyanurate reaction of the polyurethane resin in the structure, and the microstructure close to amorphous is fine and uniform pores. It was confirmed that including the formed.

According to the negative electrode active material for a lithium secondary battery of the present invention, a method for manufacturing the same, and a lithium secondary battery using the same, the specific surface area of the negative electrode active material is prepared by preparing a negative electrode active material including a carbonized carbide by heat-treating a polyurethane resin under an active gas atmosphere. It is lowered, prevents the adsorption of water by forming a surface in which the mesopores are not developed, and it is easy to remove moisture in the electrode drying process, thereby improving the initial efficiency, output and life characteristics of the secondary battery. In addition, the lithium secondary battery including the negative electrode active material has an advantage that the initial charge and discharge efficiency of the battery is significantly improved.

1 is a graph showing a change in the nitrogen content according to the isocyanate content of the negative electrode active material of the lithium secondary battery according to the present invention.

2 is a graph showing the change in specific surface area according to the isocyanate content of the negative electrode active material of the lithium secondary battery according to the present invention.

3 is a graph showing a change in the initial charge and discharge efficiency according to the isocyanate content of the negative electrode active material of the lithium secondary battery according to the present invention.

4 is a graph showing a change in the initial charge and discharge efficiency according to the carbonization temperature of the negative electrode active material of the lithium secondary battery according to the present invention.

5 is a graph analyzing mesopores on the surface of the negative electrode active material of the lithium secondary battery according to the present invention.

6 is a graph analyzing micropores on the surface of the negative electrode active material of the lithium secondary battery according to the present invention.

EMBODIMENT OF THE INVENTION Hereinafter, preferred embodiment and evaluation test item are demonstrated in detail about the negative electrode active material for lithium secondary batteries of this invention, and its manufacturing method. The invention can be better understood by the following examples, which are intended for purposes of illustration of the invention and are not intended to limit the scope of protection defined by the appended claims.

<Evaluation test item>

1) Elemental Analysis of Polyurethane Resin

① From the sum of the element ratios (%) obtained by C, H, N, S, O elemental analysis equipment (C, H, N, S (EA1110-FISONS), O (FlashEA 112), multiplied by the mass of each element. The percentage of each element was determined to determine the mass ratio of the elements.

② H / C ratio measurement

The element ratio of hydrogen and carbon in the element ratio (%) obtained through elemental analysis was calculated by the formula of H / C ratio = hydrogen / carbon * 100.

③O / C ratio measurement

The element ratio of oxygen and carbon in the element ratio (%) obtained through elemental analysis was determined by the formula of O / C ratio = oxygen / carbon * 100.

2) XRD measurement

① Analysis of average interlayer distance (d ₀₀₂ ) of particles

 Obtain a graph of 2θ values measured by X-ray diffraction method, calculate the peak position of the graph by the integral method, and calculate d002 (d002 = lambda / 2sinθ) by Bragg's formula. The wavelength of the CuKa line was 0.15406 nm. At this time, the measurement range was up to 2.5 ° ~ 80 °, the measurement speed was 5 ° / min.

② Graphite lattice crystallinity comparison analysis (R value)

The R value is defined as the ratio of the intensities of (A) and (B) in 2θ representing the (002) peak.

(A) is the background established by drawing a straight line based on the baselines on both sides of the (002) peak, and (B) is the intensity at the junction where the background meets the (002) peak in parallel with the (002) peak.

R = B / A

[Revision 16.01.2012 under Rule 91]

③ crystalline size analysis of particles

: The crystallite thickness Lc (002) in the C-axis direction of the particle was calculated by the Scherrer equation.

Lc ₍₀₀₂₎ = (Scherrer's equation)

K = 0.9

λ = wavelength (0.154056 nm)

B = FWHM (Full Width at Half Maximum)

3) Specific surface area measurement

Samples were collected according to KS A 0094, KS L ISO 18757 standards, and degassed at 300 ° C for 3 hours through a pretreatment device, followed by nitrogen gas adsorption BET method through surface area and pore size analyzer devices (P / P0) The specific surface area of the sample was measured at 0.05 to 0.3.

4) Surface Pore Analysis

After degassing at 300 ° C. for 3 hours through a pretreatment apparatus, pores on the surface of the sample were analyzed by nitrogen gas adsorption through a Pore Size Analyzer (Bellsorp mini II).

The analysis shows the total volume distribution of the pores (Micropore) having a diameter of 2 nm or less by the HK method, and the total volume distribution of the pores (Mesopore) having a diameter of 2-50 nm by the BJH method. .

Micropore = ≤ 2nm

Mesopore = 2 to 50 nm

Macropore = ≥ 50nm

5) Moisture adsorption amount measurement

The prepared carbon was left at a relative humidity of 70% and a temperature of 25 ° C. for 24 hours, and then maintained at 200 ° C. for 5 minutes using Karl fischer moisture measurement equipment to measure the amount of moisture adsorbed on the sample.

6) Residual moisture content measurement

A slurry was prepared in a ratio of 97: 3 to a negative electrode active material and a binder, coated to a thickness of 100 μm, dried, perforated in the form of a circular disc of 1 cm 2, and then measured by Karl Fischer for measuring the moisture content of the electrode after 120 hours vacuum drying for 6 hours. The instrument was held at 200 ° C. for 5 minutes to measure the residual moisture content of the electrode.

7) Manufacturing method of measuring cell and evaluation of charge and discharge characteristics

 The measuring cell is a coin-type half-cell with lithium metal foil as an electrode and a counter electrode prepared with a cathode active material and a binder in a ratio of 97: 3, and EC / DEC is mixed in a 1: 1 ratio with an organic electrolyte with a separator therebetween. It was prepared in 2016 type coin cell by impregnating 1M LiPF6 dissolved electrolyte solution.

8) Charge / discharge characteristic evaluation

Charging was performed by inserting lithium ions into the carbon electrode with a constant current method up to 0.005V at 0.1 C rate, and then inserting lithium ions with a constant current method from 0.005V. When the current reached 0.01 mA, the lithium ion insertion was terminated. In the discharge, lithium ion was detached from the carbon electrode at a constant current method at a rate of 0.1 C with a final voltage of 1.5 V.

9) Output Characteristic Evaluation

The output characteristic evaluation is a measure of the output characteristics at the time of lithium ion discharge. After 5 cycles of charging and discharging to 0.1 C at the initial stage, the discharge (lithium ion desorption) C rate is increased step by step and 5 C-rate compared to 0.1 C rate reversible capacity. The retention rate of the reversible capacity was measured.

Example 1

Synthesis of Polyurethane Resin for Negative Electrode Active Material

100 g of polyol (AKP SSP-104) containing 7% by weight of hydroxyl group and 175 g of 4,4′-MDI were stirred at 4000 rpm for 10 seconds to prepare a cured polyurethane resin. The polyurethane resin was pulverized using a crusher to have a particle diameter of 0.1 to 2 mm, and then the pulverized product was heated to 700 ° C. in a nitrogen gas atmosphere, and maintained at 700 ° C. for 1 hour to carry out preliminary carbonization. A yield of 38% lithium secondary battery negative electrode active material precursor was obtained. The obtained negative electrode active material precursor was pulverized with an average particle size of about 6 ~ 12㎛ using a jet mill, the maximum particle size was not to exceed 50㎛. The pulverized negative electrode active material precursor is placed in a ceramic crucible and heated to 1200 ° C. at a temperature rising rate of 5 ° C./min. Under a nitrogen gas atmosphere, and maintained at 1200 ° C. for 1 hour to undergo a carbonization process. A carbon material usable as was prepared. Table 1 below shows the composition ratio and carbonization temperature of the polyol and isocyanate, and the <evaluation test items> of the anode active material for the lithium secondary battery prepared in Example 1 were measured, and the results are shown in Tables 2 and 3 below. And in Table 4.

Example 2

Example 2 was carried out in the same manner as in Example 1 except that the carbonization temperature was carried out at 1300 ℃.

Example 3

Example 2 was carried out in the same manner as in Example 1 except that the carbonization temperature was carried out at 1400 ℃.

Example 4

Example 4 was carried out in the same manner as in Example 1 except that the isocyanate content was performed at 194 g.

Example 5

Example 5 was carried out in the same manner as in Example 4 except that the carbonization temperature was carried out at 1300 ℃.

Example 6

Example 5 was carried out in the same manner as in Example 4 except that the carbonization temperature was carried out at 1400 ℃.

Example 7

Example 7 was carried out in the same manner as in Example 1 except that the isocyanate content was carried out at 210 g.

Example 8

Example 8 was carried out similarly to Example 7, except that the carbonization temperature was performed at 1300 ° C.

Example 9

Example 9 was carried out in the same manner as in Example 7, except that the carbonization temperature was performed at 1400 ° C.

Example 10

Example 10 was carried out in the same manner as in Example 1 except that the isocyanate content was carried out at 225 g.

Example 11

Example 11 was carried out in the same manner as in Example 10 except that the carbonization temperature was performed at 1300 ° C.

Example 12

Example 12 was carried out in the same manner as in Example 10 except that the carbonization temperature was performed at 1400 ° C.

 Comparative Example 1

Sucrose as a precursor was heated to 1200 ℃ at a temperature increase rate of 5 ℃ / min in a nitrogen atmosphere and maintained for 1 hour and carbonized, and then pulverized into particles of an average particle diameter of 12 ㎛ with a rotary blade cutter mill to prepare carbon.

Comparative Example 2

Comparative Example 2 was carried out in the same manner as in Comparative Example 1 except that the carbonization temperature was 1300 ℃.

Comparative Example 3

In Comparative Example 3, the petroleum pitch was melted at 150 ° C. using a precursor, extruded to form granules, and then maintained at 300 ° C. in air for 6 hours to insolubilize. Thereafter, the temperature was raised to 700 ° C. under a nitrogen atmosphere, and preliminary carbonization was performed for 1 hour to obtain a cathode active material precursor having a yield of 68% of carbonization. The obtained negative electrode active material precursor was pulverized with an average particle size of about 6-12 μm using a jet mill, placed in a crucible made of ceramic material, heated to 1200 ° C. at a temperature increase rate of 5 ° C./min under a nitrogen atmosphere, and maintained for 1 hour. By the carbonization process, a carbon material usable as a negative electrode active material for a lithium secondary battery was prepared.

[Comparative Example 4]

Comparative Example 4 was carried out in the same manner as in Comparative Example 3 except that the carbonization temperature was 1300 ° C.

[Comparative Example 5]

Comparative Example 5 was carried out in the same manner as in Example 1 except that the carbonization temperature was 900 ° C.

Comparative Example 6

Comparative Example 6 was carried out in the same manner as in Example 2, except that the isocyanate content was carried out at 350 g.

Manufacture of Secondary Battery

(a) Electrode Fabrication

 Add 1.5 parts by weight of SBR (Stylene Butadiene Rubber) and 1.5 parts by weight of CMC (Carboxyl Methyl Cellulose) to 97 parts by weight of the negative electrode active material prepared in Examples and Comparative Examples to add distilled water and stir evenly in the form of sludge to form a copper foil Coated uniformly. The coating was uniformly coated at 110 μm using a doctor blade, dried in an oven at 60 ° C. for 30 minutes, and pressed at a pressure of 0.6 Mpa. The electrode on the foil was punched into a circular shape having a width of 1 cm 2 and dried in a vacuum oven at 120 ° C. for 12 hours.

(b) Preparation of test cell

 The negative electrode active materials prepared in Examples and Comparative Examples were used in the negative electrode of the aqueous electrolyte secondary battery, and the charge (lithium insertion) capacity and the discharge (lithium detachment) capacity of the negative electrode active material were precisely independent without being affected by the performance of the counter electrode. In order to evaluate easily, a lithium secondary battery was constructed using lithium metal as a counter electrode, and characteristics were evaluated.

The lithium secondary battery is a 2016-sized (20 mm diameter, 16 mm thick) coin-type battery assembled in a glove box under an argon atmosphere. A 1 mm thick metal lithium is pressed onto the bottom of a coin-type battery can, and a polypropylene separator is placed thereon. Was formed and the negative electrode was faced with lithium. In this case, the electrolyte used was prepared by adding 1.2 M of LiPF6 salt to a solvent prepared by mixing EC (Ethylene Carbonate), DMC (Dimethyl Carbonate) and EMC (Ethyl Methyl Carbonate) in a volume ratio of 1: 1: 1. The lithium secondary battery was assembled by putting it in a doll battery, touching the can cover, and pressing.

(c) battery capacity measurement

Characterization of the assembled lithium secondary battery was charged and discharged at 25 ℃ by the constant current-constant voltage method (CCCV) using the TOSCAT-3100 charge and discharge test apparatus manufactured by TOYO SYSTEM. Here, 'charging' is a reaction in which the voltage of the coin-type battery decreases due to the insertion of lithium into the negative electrode, and 'discharge' is a reaction in which lithium is detached from the negative electrode and moves toward the counter electrode. . In this case, the constant current-constant voltage condition is charged at a constant current density (0.1C standard) until the voltage of the coin-type battery becomes 0.005V, and then constantly until the current value becomes 0.05mA while maintaining the voltage. Decrease to proceed with charging. The amount of electricity supplied at this time divided by the weight of the negative electrode active material of the electrode was called the charging capacity per unit weight of the negative electrode active material (mAh / g). After the end of charging, the battery was stopped for 10 minutes and discharged. The discharge was carried out at a constant current until the voltage of the coin-type battery became 1.5V. The value of the discharged electricity divided by the weight of the negative electrode active material of the electrode was the discharge capacity per unit weight of the negative electrode active material (mAh / g). It was. The reversible capacity was defined as the discharge capacity, the irreversible capacity was calculated by subtracting the discharge capacity from the charging capacity, and the efficiency was calculated as the percentage (%) of the discharge capacity. The characteristic value of a basic coin-type battery was shown by averaging the characteristic value of three or more of the same batteries made from the same sample.

(d) Measurement of high rate charge and discharge characteristics

High rate charge / discharge characteristics analysis of the assembled lithium secondary battery was performed at 25 ° C. by the constant current-constant voltage method (CCCV) as in (c). The high rate charge / discharge characteristics change the current density during charge and discharge, increase the constant current density supplied or discharged by cycle, and represent the capacity (mAh / g) measured and charged at the current density.

TABLE 1

TABLE 2

TABLE 3

TABLE 4

As shown in Table 2 to Table 4 and Figures 1 to 4, when the isocyanate containing the optimum content in the production of a negative active material for a lithium secondary battery, the specific surface area is reduced, such as reversible capacity and initial charge and discharge efficiency It was confirmed that the characteristic was remarkably improved. By optimizing the carbonization temperature, it was confirmed that unnecessary energy loss was prevented and that the cell efficiency was high. In addition, as shown in FIG. 5, the active material for a lithium secondary battery of the present invention does not develop mesopores on the carbon surface, so that the water content is low, and the adsorption amount of the water is also reduced, thereby reducing irreversible capacity and initial charging and discharging efficiency. It can be seen that the electrochemical properties such as increased significantly.

In addition, compared to the negative electrode active material prepared according to the embodiment of the present invention, as shown in Comparative Example 1 and Comparative Example 2, when the negative active material was prepared by carbonizing Sucrose, as shown in FIG. As a result, the adsorption amount of moisture increases, and the residual moisture content of the electrode is significantly increased. As a result, it can be seen that the battery characteristics such as initial charge and discharge efficiency and output characteristics are not suitable, and thus it is not suitable as a negative electrode active material for lithium secondary batteries.As shown in Comparative Examples 3 and 4, petroleum-based pitches are used to When manufactured, the initial charging and discharging efficiency is good, but the reversible capacity and the output characteristics are remarkably poor, it can be seen that it is not suitable as a negative electrode active material for lithium secondary batteries.

Although the preferred embodiment of the present invention has been described above, it is clear that the present invention can use various changes and equivalents, and can be applied in the same manner by appropriately modifying the above embodiment. Accordingly, the above description is not intended to limit the scope of the invention as defined by the following claims.

Claims (16)

1. Cathode active material for lithium secondary battery containing carbide carbonized by heat-treating polyurethane resin under inert gas atmosphere
2. The method of claim 1,

   The average particle size of the carbide is 1 to 50㎛, the specific surface area is 2.0 to 5.0㎡ / g, the average pore size is 1 to 5nm negative electrode active material for lithium secondary battery
3. The method of claim 1,

   The heat treatment includes a first heat treatment and a second heat treatment,

   The first heat treatment is performed for 30 to 120 minutes at 600 to 1400 ℃ temperature,

   The secondary heat treatment is performed for 30 to 120 minutes at a temperature of 1000 to 1,400 ℃,

   The first and second heat treatments are sequentially performed negative electrode active material for lithium secondary battery
4. The method of claim 1,

   The negative electrode active material for a lithium secondary battery has a (002) mean layer spacing (d002) of 3.7 to 4.0 kPa determined by the X-ray diffraction method, a crystallite diameter Lc (002) in the C-axis direction of 0.8 to 2 nm, and an R value of A negative active material for a lithium secondary battery having a 1.3 to 2 and a peak intensity ratio (5 ° peak / 002 peak) of 2 to 4,
5. The method of claim 1,

   The negative electrode active material for a lithium secondary battery has an element ratio (H / C%) of hydrogen and carbon of 0.1 or less and an element ratio (O / C%) of oxygen and carbon of 1.0 or less.
6. The method of claim 1,

   Lithium secondary battery negative electrode active material having a residual water content of 100 to 500 ppm in the electrode containing the negative electrode active material for lithium secondary battery
7. The method of claim 1,

   The polyurethane resin has an oxygen content of 15 to 22% by weight, a nitrogen content of 7 to 9% by weight, and a hydrogen content of 4 to 6% by weight of a negative electrode active material for a lithium secondary battery
8. The method of claim 1,

   The polyurethane resin includes polyols and isocyanates,

   The negative active material for lithium secondary battery, wherein the isocyanate is 150 to 240 parts by weight based on 100 parts by weight of the polyol.
9. The method of claim 8,

   The polyol may be selected from polyether polyol, polyester polyol, polytetramethylene ether glycol polyol, Polyharnstoff Dispersion (PHD) polyol, amine modified polyol, Manmich polyol and mixtures thereof Any one or more than two,

   The isocyanates include hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), 4,4'-dicyclohexylmethane diisocyanate (H12MDI), polyethylene polyphenyl isocyanate, toluene diisocyanate (TDI), 2,2 ' -Diphenylmethane diisocyanate (2,2'-MDI), 2,4'-diphenylmethane diisocyanate (2,4'-MDI), 4,4'-diphenylmethane diisocyanate (4,4'- MDI, monomeric MDI, polymeric diphenylmethane diisocyanate (polymeric MDI), orthotoluidine diisocyanate (TODI), naphthalene diosocyanate (NDI), xylene diisocyanate (XDI), lysine diisocyanate (LDI) and triphenyl A cathode active material for any one or two or more selected from methane triisocyanate (TPTI).
10. The method of claim 8,

    The molecular weight of the polyol is 300 to 3000, the hydroxy content present in the polyol is 3 to 15% by weight of the total polyol of the negative electrode active material for lithium secondary battery.
11. The method of claim 1,

    The polyurethane resin is a negative electrode active material for a lithium secondary battery further comprising a blowing agent, a flame retardant, a catalyst or a foam stabilizer.
12. A method for producing a negative electrode active material for a lithium secondary battery comprising a carbonization step of heat-treating the polyurethane resin in an inert gas atmosphere.
13. The method of claim 12,

    The carbonization step includes a pre-carbonization step and the main carbonization step,

    The precarbonization step is a heat treatment for 30 to 120 minutes at 600 to 1000 ℃ temperature,

    The main carbonization step is a method of manufacturing a negative electrode active material for a lithium secondary battery comprising the heat treatment for 30 to 120 minutes at a temperature of 1000 to 1400 ℃.
14. The method of claim 12,

    Method for producing a negative active material for a lithium secondary battery further comprises a fine grinding step of pulverizing so that the average particle size of the negative electrode active material for a lithium secondary battery 1 to 50㎛.
15. The method of claim 13,

    The pulverization step is a method of manufacturing a negative electrode active material for a lithium secondary battery that is carried out one or more times selected from before the pre-carbonization step, after the pre-carbonization step or after the carbonization step.
16. Lithium secondary battery comprising a negative electrode active material for any one of the lithium secondary battery selected from claim 1 to claim 11

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