JP2009266816A - Negative electrode active material for secondary battery, electrode for secondary battery containing the same, secondary battery and method of manufacturing them - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carbon material based negative electrode active material having a physical property parameter value in which electrochemical characteristics of a secondary battery are not deteriorated even if a crimping process is conducted in order to manufacture an electrode for the secondary battery, and to provide a method of manufacturing the same or the like. <P>SOLUTION: A negative electrode active material for the secondary battery, the electrode for the secondary battery containing the same, the secondary battery and the method of manufacturing the same is provided. The negative electrode active material for the secondary battery is characterized in that a part or the whole of edge contains a core carbon material covered with a carbide layer, and in that the gradient of the tangent to the parabola of a diffraction angle 2θ in a section of 25.5 to 26.3 degrees, before the peak of (002) surface starts, is 30 to 43 degrees in the XRD measurement data in which a CuK α ray serves as an X-ray source. In physical property of the carbon material based negative electrode active material, a crystalline condition and a condition of the specific surface area which are closely related to decomposition reaction of an electrolyte solution are optimized, and then a condition of tap density which is related to processability of an electrode crimping process is optimized, so that discharge capacity of the secondary battery, efficiency thereof, and a capacity maintaining ratio in a long period cycle can be improved. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a negative electrode active material for a secondary battery. More specifically, the present invention relates to a secondary battery negative electrode active material made of a core carbon material in which a part or all of edges are covered with a carbide layer, a secondary battery electrode including the secondary battery, a secondary battery, and a method for manufacturing the same.

  Recently, with the rapid spread of electronic devices using batteries such as mobile phones, notebook PCs, and electric vehicles, the demand for secondary batteries that are small and light but have a relatively high capacity is rapidly increasing. . In particular, lithium secondary batteries are light and have a high energy density, and thus are attracting attention as driving sources for portable devices. Therefore, research and development for improving the performance of the lithium secondary battery is being actively conducted.

  In the lithium secondary battery, the lithium ion is filled with an organic electrolyte or a polymer electrolyte between a negative electrode and a positive electrode made of an active material capable of intercalation and deintercalation of lithium ions. Electric energy is produced by oxidation / reduction reactions when inserted / desorbed at the negative electrode.

Transition metal compounds such as lithium cobalt oxide (LiCoO ₂ ), lithium nickel oxide (LiNiO ₂ ), and lithium manganese oxide (LiMnO ₂ ) are mainly used as the positive electrode active material of the lithium secondary battery.

  And, as the negative electrode active material, generally, a crystalline carbon material such as natural graphite or artificial graphite with a large degree of softening, or pseudo graphite obtained by carbonizing a hydrocarbon or a polymer at a low temperature of 1000 to 1500 ° C. ( A low crystalline carbon material having a pseudo-graphite structure or a turbostructural structure is used.

  A crystalline carbon material is advantageous in packing an active material because of its high true density, and has advantages such as excellent potential flatness, initial capacity, and charge / discharge reversibility. As the battery containing the carbonaceous material is used, the charge / discharge efficiency and cycle capacity of the battery are reduced. It is analyzed that such a problem is caused by the decomposition reaction of the electrolytic solution being induced at the edge portion of the crystalline carbon material as the charge / discharge cycle of the battery increases.

  Japanese Patent Application Laid-Open No. 2002-348109 (Patent Document 1) discloses a carbon material-based negative electrode active coated with a carbide layer in order to prevent an electrolyte decomposition reaction from being induced at an edge portion of a crystalline carbon material. The substance is disclosed. In the carbon material-based negative electrode active material, the carbide layer is formed by coating the surface of the carbon material with pitch and then performing a heat treatment at 1000 ° C. or higher. If the carbide layer is coated on the carbon material, the initial capacity of the secondary battery is slightly reduced, but the effect of improving the charge / discharge efficiency and the long-term capacity characteristics is achieved. In particular, when the coating material coating layer is artificially graphitized by high-temperature heat treatment, the decomposition reaction of the electrolytic solution can be efficiently suppressed while reducing the amount of decrease in the initial capacity.

  On the other hand, when manufacturing an electrode for a secondary battery using the above-mentioned carbon material-based negative electrode active material, it is common to apply pressure bonding after coating the negative electrode active material on a metal current collector. However, at this time, the negative electrode active materials collide with each other and the carbide layer is crushed, thereby causing a problem that the edge of the carbon material that reacts with the electrolytic solution is exposed. Such exposure of the edge of the carbon material causes a reduction in efficiency and long-term cycle characteristics of the secondary battery. Therefore, when manufacturing a carbon material-based negative electrode active material, the physical property conditions of the negative electrode active material capable of minimizing the influence of the crushing of the carbide layer due to the electrode crimping process must be sought.

  Therefore, the present inventor has clarified the physical property parameters of the negative electrode active material having a correlation with the performance of the battery during the production of the secondary battery using the carbon material-based negative electrode active material, and at the same time, the secondary battery by crushing the carbide layer. The present invention was devised under the technical background of attempting to present physical property conditions of a negative electrode active material that can prevent the performance degradation of the negative electrode.

JP 2002-348109 A

  The present invention has been devised to solve the above-described problems of the prior art, and newly defines physical property parameters of a negative electrode active material for a secondary battery. A carbon material with physical property parameter values that does not deteriorate the electrochemical characteristics of the secondary battery even if the crimping process is performed for the production of the secondary battery electrode by grasping the correlation between the electrochemical characteristics An object of the present invention is to provide a negative electrode active material and a method for producing the same.

  Another object of the present invention is to provide an electrode for a secondary battery manufactured using a carbon material-based negative electrode active material in which newly defined physical property parameter values are optimized, and a secondary battery including the same. .

The negative electrode active material for a secondary battery according to the present invention for solving the above technical problem is
Including a core carbon material in which part or all of the edge is covered with a carbide layer;
XRD measurement data using CuKα ray as an X-ray source. Before the peak of the (002) plane starts, the inclination of the tangent of the parabola in the section where the diffraction angle 2θ is 25.5 to 26.3 degrees is 30 to 43 degrees. It is characterized by being.

Here, the slope of the tangent of the parabola is the function of the parabola y = It is the slope of the tangent at the point closest to the focal point of the parabola function when mapped with ax ² + bx + c.

Desirably, the negative electrode active material has a tap density of 1.0 g / cm ³ or more and a specific surface area of 5 m ² / g or less.
Desirably, the core carbon material is highly crystalline natural graphite, and more desirably spherical highly crystalline natural graphite.

  Alternatively, the core carbon material may be oval, crushed, scaled or whisker-shaped natural graphite, artificial graphite, mesocarbon microbead (MCMB), mesophase pitch fine powder, etc. Any one selected from the group consisting of fine powder of isotropic pitch, resin charcoal, and amorphous powder having pseudo-graphite structure or turbostratic structure (low crystalline line). Or a mixture thereof.

  Preferably, the carbide layer is a low crystalline carbide layer formed by coating the core carbon material with a coal-based or petroleum-based pitch, tar, or a mixture thereof and then carbonizing and firing.

The technical problem of the present invention can also be solved by a secondary battery electrode comprising a metal current collector coated with the above-described negative electrode active material and a secondary battery including the same.
The secondary battery includes a negative electrode current collector coated with a negative electrode active material, a positive electrode current collector coated with a positive electrode active material, and a separator interposed between the negative electrode current collector and the positive electrode current collector. And an electrolyte for a secondary battery impregnated in the separator.

A method for producing a carbon material-based negative electrode active material for a secondary battery according to the present invention for solving the above technical problem,
A highly crystalline core carbon material, preferably a high crystalline core carbon material having a tap density of 1.0 g / cm ³ or more, and a coal-based or petroleum-based coated carbon material having a softening point of 100 ° C. or more. Mixing to obtain a mixture; and firing the mixture to carbonize the coated carbon material to form a carbide layer, particularly a low crystalline carbide layer, on part or all of the edge of the core carbon material. Including.

Here, XRD measurement data using a CuKα ray as an X-ray source for a negative electrode active material manufactured according to the present invention, that is, a negative electrode active material composed of a core carbon material on which the carbide layer is formed, is a (002) plane peak. Before the start of the parabola, the slope of the tangent of the parabola for the section with the diffraction angle 2θ of 25.5 to 26.3 degrees is 30 to 43 degrees. The slope of the parabola tangent is similar to the slope of the parabola tangent in the negative electrode active material for a secondary battery, and the parabola function when the above section is mapped by a parabolic function y = ax ² + bx + c according to a polynomial approximation method. Is the slope of the tangent at the point closest to the focal point.

In this invention, the calcination temperature of the said mixture can be 1000-2500 degreeC.
Desirably, the mixture is fired twice or more under different temperature conditions. In such a case, the firing temperature in the subsequent firing step is higher than the firing temperature in the preceding firing step.

  According to the present invention, among the physical properties of the carbon material-based negative electrode active material for a secondary battery, the crystallinity condition and the specific surface area condition closely related to the decomposition reaction of the electrolytic solution, and the processability of the electrode pressing process By optimizing the related tap density conditions, the discharge capacity and efficiency of the secondary battery and the capacity maintenance rate in the long-term cycle can be improved.

FIG. 1 is an enlarged graph showing a section where the diffraction angle 2θ is 24.5 to 26.5 degrees in the XRD measurement data of the negative electrode active material for a secondary battery manufactured according to Example 1 and Comparative Example 1. It is.

  Hereinafter, preferred embodiments of the present invention will be described in detail. Prior to this, the terms and words used in this specification and claims should not be construed to be limited to ordinary or lexicographic meanings, and the inventor shall make his invention the best way. In accordance with the principle that the concept of terms can be appropriately defined for the purpose of explanation, the meaning and concept consistent with the technical idea of the present invention should be interpreted. Therefore, the embodiment described in the present specification is only the most preferred embodiment of the present invention, and does not represent all of the technical idea of the present invention. It should be understood that there can be equivalents and variations.

  FIG. 1 shows that the diffraction angle 2θ (θ represents the Bragg angle) is 24.5 to 26. XRD measurement data of the negative electrode active material for a secondary battery manufactured according to Example 1 and Comparative Example 1 described later. It is the graph which expanded and showed the area of 5 degree | times.

  Referring to the drawings, a negative electrode active material for a secondary battery (Example 1) according to the present invention includes a core carbon material in which part or all of the edge is covered with a carbide layer, and uses CuKα rays as an X-ray source. In the XRD measurement data, before the (002) plane peak starts, the parabolic tangent slope for the section where the diffraction angle 2θ is 25.5 to 26.3 degrees is 30 to 43 degrees. Compared with Example 1, the inclination of the tangent of the parabola of Comparative Example 1 is close to about 45 degrees.

Here, the gradient of the tangent of the parabola is mapped by the parabolic function y = ax ² + bx + c according to the polynomial approximation method in the interval, that is, the interval where the diffraction angle 2θ is 25.5 to 26.3 degrees in the XRD measurement data. Is the slope of the tangent at the point closest to the focal point of the parabolic function.

  Desirably, the core carbon material is spherical highly crystalline natural graphite. Alternatively, the core carbon material is natural graphite having an elliptical shape, crushed shape, scale shape or whisker shape, artificial graphite, mesocarbon microbeads, fine powder of mesophase pitch, fine powder of isotropic pitch, resin charcoal, And any one selected from the group consisting of fine powders of amorphous carbon having a pseudo graphite structure or a turbulent layer structure, or a mixture thereof.

  Preferably, the carbide layer is a low crystalline carbide layer formed by coating a core carbon material with a coal-based or petroleum-based pitch, tar, or a mixture thereof and then carbonizing and firing. Here, low crystallinity means that the crystallinity of the carbide layer is lower than that of the core carbon material. In other words, even when carbon having low crystallinity such as amorphous carbon is used as the core carbon material, the carbide layer has a lower crystallinity than the core carbon material. means.

  The carbide layer exhibits the function of filling the pores of the core carbon material, reducing the specific surface area, and reducing the decomposition reaction sites of the electrolytic solution. Further, the carbide layer prevents deformation in the form of the negative electrode active material particles and increases the pressure bonding density by buffering collision between the negative electrode active material particles when the negative electrode active material is pressure bonded in the electrode pressure bonding process. Contribute to.

  The XRD measurement data is obtained using an X-ray diffraction analyzer (“X'pert Pro MPD” from Philips) using CuKα rays as an X-ray source. At this time, the generator of the X-Ray diffraction analyzer is set to 40 KV and 30 mA, the scan range is set to 20 to 80 degrees, the step size is set to 0.02 degrees, the scan speed is set to 0.1 s / step, and the standard substance In this case, 99% pure silicon powder classified by 325 mesh is used.

In the present invention, the inclination of the tangent of the parabola is a function of a parabola according to a polynomial approximation method in an XRD measurement data in which a diffraction angle 2θ is 25.5 to 26.3 degrees (hereinafter referred to as “crystallinity evaluation interval”). When mapping with y = ax ² + bx + c, it means the slope of the tangent at the point closest to the focal point of the parabolic function. The mapping of the crystallinity evaluation section using the above polynomial approximation method can be performed using “Microcal Origin 6.0” of “Microcal (USA)” which is a known program in the technical field to which the present invention belongs. However, the present invention is not limited by the type of program. Here, the angle representing the inclination of the tangent of the parabola is specifically calculated based on the diffraction angle and the peak height (intensity) of 0.1 degree / cm and 250 intensity / cm, respectively, in the XRD chart. Can be obtained. At this time, when the tangent has an inclination that increases Gintensity per 1 degree of diffraction angle and the angle representing the inclination of the tangent is A degree, A and G are tan (A × π / 180 ) = G / 2500.

  The inclination of the tangent of the parabola can be used as a scale for evaluating the crystallinity of the negative electrode active material. That is, it can be interpreted that the crystallization degree of the negative electrode active material is higher as the inclination of the tangent of the parabola is closer to 45 degrees as in Comparative Example 1. By the way, when the degree of crystallinity of the negative electrode active material increases, a crystal surface (in particular, an edge) on which a decomposition reaction of the electrolytic solution is induced develops. And since the hardness of the negative electrode active material is increased, the carbide layer covering the core carbon material is crushed when the negative electrode active material is crimped in the electrode crimping step, and the decomposition of the electrolyte is induced on the surface of the edge Increases the possibility of new exposure. As a result, as the usage period of the secondary battery increases, the degree of occurrence of the decomposition reaction of the electrolytic solution increases, and the stability, charge / discharge efficiency, and long-term cycle characteristics of the secondary battery deteriorate. However, as in Example 1, if the slope of the tangential line in the crystallinity evaluation section of the negative electrode active material is controlled within a range of 30 to 43 degrees, the exposure of the crystal surface that induces the decomposition reaction of the electrolyte is maximized. By suppressing to the above, the stability, charge / discharge efficiency and long-term cycle characteristics of the secondary battery can be improved.

More preferably, the negative electrode active material according to the present invention has a tap density of 1.0 g / cm ³ or more and a specific surface area of 5 m ² / g or less.
Here, the tap density conforms to JIS-K5101 and is measured using “Powder Tester PT-R” manufactured by Hosokawa Micron. That is, the negative electrode active material powder according to the present invention is dropped into a tapping cell having a capacity of 20 cc through a sieve having a graduation interval of 200 μm, and after the tapping cell is completely filled, tapping with a stroke length of 18 mm is performed once per second to 3000 After tapping, the tap density is measured by measuring the density of the tapped negative electrode active material.

The tap density is affected by the diameter, cross-sectional shape, surface shape, etc. of the negative electrode active material powder. That is, the tap density varies depending on the particle size distribution even if the average particle diameter of the negative electrode active material particles is the same. For example, if the negative electrode active material contains a large amount of fine powder, the tap density decreases due to an agglomeration phenomenon between the fine powders. Moreover, if there are many non-spherical particles in the negative electrode active material, the compression efficiency is reduced when the negative electrode active material is bonded, and the tap density is decreased. On the other hand, the tap density increases due to the coating of the core carbon material. In particular, the negative electrode active material according to a preferred embodiment of the present invention is coated with a low crystalline carbide layer. Therefore, when the negative electrode active material is pressure-bonded, the carbide layer serves as a buffer as described above, which contributes to improving the pressure-bonding density. The negative electrode active material according to the present invention has a relatively high tap density of 1.0 g / cm ³ or more because the spherical core carbon material is covered with the low crystalline carbide layer. If the tap density of the negative electrode active material satisfies the above conditions, the pressure density when the negative electrode active material is pressure bonded to the current collector metal can be increased without hindering the electrolyte from penetrating into the negative electrode active material. it can.

The specific surface area of the negative electrode active material according to the present invention is measured using a “nitrogen adsorption BET specific surface area measuring apparatus ASAP2400” manufactured by Micromeritics. The negative electrode active material according to the present invention has a specific surface area as low as 5 m ² / g or less because the pores of the core carbon material are filled with carbon adhering or coating derived from coal-based or petroleum heavy oil. When the specific surface area is small as described above, the number of sites where the decomposition reaction of the electrolytic solution can occur is reduced, so that the performance degradation of the secondary battery due to the decomposition reaction of the electrolytic solution can be prevented.

The manufacturing method of the negative electrode active material for secondary batteries according to the present invention described above will be described.
First, a core material carbon material having a particle form and a coal-based or petroleum-based carbon material are mixed in a wet or dry manner to form a carbon material coating layer on the surface of the core material carbon material.

Here, coal-based or petroleum-based carbon material is mixed with the core carbon material at 0.1 to 25% by weight with respect to the weight of the core carbon material.
Desirably, the core carbon material is highly crystalline natural graphite, and more desirably spherical highly crystalline natural graphite having a tap density of 1.0 g / cm ³ or more.

  Or natural graphite, artificial graphite, mesocarbon microbeads, fine particles of mesophase pitch, fine powder of isotropic pitch, resin charcoal, and pseudo-graphite structure or turbulent layer having an elliptical shape, crushed shape, scale shape or whisker shape Any one selected from the group consisting of fine powders of amorphous carbon having a structure or a mixture thereof can be used as the core carbon material.

Desirably, pitch, tar or a mixture thereof having a softening point of 100 ° C. or higher is used as the coal-based or petroleum-based carbon material.
Next, the core carbon material on which the carbon material coating layer is formed is baked to carbonize the coated carbon material, thereby forming a carbide layer on part or all of the edge of the core carbon material.

  Here, the firing temperature for forming the carbide layer can be set to 1000 to 2500 ° C., and the firing temperature increase rate can be set to 0.01 to 20 ° C./min. Desirably, the firing step is performed twice or more at different firing temperatures, and the firing temperature of the subsequent firing step is controlled to be higher than the firing temperature of the preceding firing step. As an example, the firing process can be performed twice, the primary firing process can be performed at 1100 ° C. for 1 hour, and the secondary firing process can be performed at 2200 ° C. for 1 hour.

The negative electrode active material manufactured through the above-described steps is XRD measurement data using CuKα rays as an X-ray source. Before the (002) plane peak starts, the diffraction angle 2θ is about 25.5 to 26.3 degrees. The parabola has a tangential slope of 30 to 43 degrees, a tap density of 1.0 g / cm ³ or more and a specific surface area of 5 m ² / g or less.

  The active material paste can be manufactured by mixing the negative electrode active material for a secondary battery manufactured according to the above-described method with a conductive material, a binder, and an organic solvent. Then, the active material paste is applied to a metal current collector such as a copper foil, followed by drying, heat treatment and pressure bonding to produce a secondary battery electrode (negative electrode).

  Moreover, the electrode for secondary batteries manufactured in this way can be used in order to manufacture a lithium secondary battery. That is, after the metal current collector obtained by binding the negative electrode active material according to the present invention at a predetermined thickness and the metal current collector obtained by binding the Li-based transition metal compound at a predetermined thickness are opposed to each other with the separator interposed therebetween. If a separator is impregnated with an electrolytic solution for a lithium secondary battery, it is possible to produce a lithium secondary battery that can be repeatedly charged and discharged. Such an electrode for a secondary battery and a method for manufacturing the secondary battery are widely known to those having ordinary knowledge in the technical field to which the present invention belongs, and thus detailed description thereof is omitted.

  In addition, this invention has the characteristics in the physical property of the negative electrode active material for secondary batteries. Therefore, when manufacturing a secondary battery electrode and a secondary battery including the same using the negative electrode active material according to the present invention, various methods known in the technical field to which the present invention belongs can be applied. Further, it is obvious that the types of secondary batteries that can utilize the negative electrode active material according to the present invention are not limited to lithium secondary batteries.

<Examples and Comparative Examples>
[Example 1]
Pitch, which is a low crystalline carbon material, was mixed with high crystalline spherical natural graphite at a ratio of 20% by weight with respect to the weight of natural graphite, and dry mixed at high speed for 10 minutes to obtain a mixture. Then, the mixture was drawn into the firing chamber, heated to 1,100 ° C. at a temperature rising rate of 17 ° C./min, fired at 1,100 ° C. for 1 hour, and 2,200 ° C. at a heating rate of 17 ° C./min. Then, the mixture was baked for 1 hour and subjected to a classification and fine powder removal step to produce a negative electrode active material. As a result of measuring the inclination, specific surface area and tap density of the parabola in the crystallinity evaluation section on the XRD data for the negative electrode active material thus produced, the values were 39 degrees, 0.65 m ² / g and 1 respectively. It was .12 g / cm ³ .

[Example 2]
A negative electrode active material was produced in the same manner as in Example 1 except that the mixing ratio of pitch to natural graphite was adjusted to 10% by weight with respect to the weight of natural graphite. As a result of measuring the tangential slope, specific surface area, and tap density of the parabola in the crystallinity evaluation section on the XRD data for the negative electrode active material thus produced, the values were 40.2 degrees and 1.28 m ² / g, respectively. And 1.1 g / cm ³ .

[Example 3]
A negative electrode active material was produced in the same manner as in Example 1 except that the mixing ratio of pitch to natural graphite was adjusted to 5% by weight with respect to the weight of natural graphite. As a result of measuring the inclination, specific surface area and tap density of the parabola in the crystallinity evaluation section on the XRD data for the negative electrode active material thus produced, the values were 40.9 degrees and 1.5 m ² / g, respectively. And 1.09 g / cm ³ .

[Example 4]
A negative electrode active material was produced in the same manner as in Example 1 except that the mixing ratio of pitch to natural graphite was adjusted to 1% by weight with respect to the weight of natural graphite. As a result of measuring the inclination, specific surface area and tap density of the parabola in the crystallinity evaluation section on the XRD data for the negative electrode active material thus produced, the values were 41.2 degrees and 2.1 m ² / g, respectively. And 1.06 g / cm ³ .

[Example 5]
A negative electrode active material was produced in the same manner as in Example 3 except that the heating rate during firing was adjusted to 10 ° C./min. As a result of measuring the inclination, specific surface area and tap density of the parabola in the crystallinity evaluation section on the XRD data for the negative electrode active material thus produced, the values were 41.4 degrees and 1.94 m ² / g, respectively. And 1.09 g / cm ³ .

[Example 6]
A negative electrode active material was produced in the same manner as in Example 3 except that the heating rate during firing was adjusted to 3 ° C./min. As a result of measuring the slope of the tangent of the parabola, the specific surface area and the tap density in the crystallinity evaluation section on the XRD data for the negative electrode active material thus produced, the values were 41.9 degrees and 1.87 m ² / g, respectively. And 1.11 g / cm ³ .

[Comparative Example 1]
As a result of measuring the tangential slope, specific surface area, and tap density of the parabola in the crystallinity evaluation section on the XRD data for the negative electrode active material composed only of highly crystalline spherical natural graphite, the values were 44.1 degrees and 6. 24 m ² / g and 0.93 g / cm ³ .

<Production of secondary battery negative electrode and coin cell>
Secondary battery electrodes were manufactured using the secondary battery negative electrode active materials produced in Examples 1 to 6 and Comparative Example 1 as raw materials. First, 100 g of the negative electrode active material was placed in a 500 ml reactor, and a small amount of N-methylpyrrolidone (NMP) and polyvinylidene fluoride (PVDF) as a binder were added and mixed. Next, the mixture was kneaded using a mixer, then coated on an 8 μm thick copper foil as a negative electrode current collector, dried at 120 ° C., and pressed at a density of 1.65 g / cm ³ to produce a negative electrode for a secondary battery. did. Then, in order to evaluate the charge / discharge characteristics of the negative electrode active material, a 2016 standard coin cell using Li as a relative electrode was manufactured for each example and comparative example.

<Evaluation of charge / discharge characteristics of coin cell>
The charge / discharge test was conducted from the first cycle to the 35th cycle. In each cycle charge / discharge test, the potential is regulated in the range of 0.01 to 1.5V while charging to 0.01V at a charging current of 0.5 mA / cm ² while maintaining the voltage of 0.01V. The charging was continued until the charging current reached 0.02 mA / cm ² . A discharge current of 0.5 mA / cm ² was discharged up to 1.5 V.

  Table 1 below shows the gradient of the parabola tangent, the specific surface area and the tap density, and the charge / discharge characteristics of the coin cell in the crystallinity evaluation section on the XRD data for each negative electrode active material manufactured according to Examples 1 to 6 and Comparative Example 1. Results are shown. In Table 1 below, the discharge capacity maintenance rate in the 35th cycle is based on the discharge capacity in the second cycle. Here, “SSA” and “TD” refer to specific surface area and tap density, respectively.

  Referring to Table 1 above, it can be confirmed that the gradient of the tangent of the parabola, the tap density, and the specific surface area of the crystallinity evaluation section on the XRD data with respect to the negative electrode active material are correlated with the performance of the secondary battery.

  That is, in Examples 1 to 6 in which the inclination of the parabola tangent to the crystallinity evaluation section is included in the range of 30 to 43 degrees, the discharge capacity and efficiency in the first cycle compared to Comparative Example 1, and the 35th cycle It has excellent discharge capacity maintenance rate.

Further, in Examples 1 to 6 in which the tap density and specific surface area are 1.0 g / cm ³ or more and 5 m ² / g or less, respectively, the discharge capacity and efficiency in the first cycle as compared with Comparative Example 1, and the 35th Excellent discharge capacity maintenance rate in cycle.

From the above results, in order to manufacture a secondary battery with excellent performance, it is desirable that the inclination of the tangent of the parabola in at least the crystallinity evaluation section of the negative electrode active material is in the range of 30 to 43 degrees. It can be confirmed that the tap density and the specific surface area are more preferably 1.0 g / cm ³ or more and 5 m ² / g or less, respectively.

  As described above, the present invention has been described with reference to the embodiments and the drawings. However, even if the embodiments and the drawings are limited, the present invention is not limited thereto, and the present invention is not limited thereto. It goes without saying that various modifications and variations can be made by persons having ordinary knowledge in the technical field to which the present invention pertains within the scope equivalent to the technical idea of the present invention and claims.

  The following drawings attached to the present specification illustrate preferred embodiments of the present invention and serve to further understand the technical idea of the present invention together with the detailed description of the invention. The invention should not be construed as limited to the matter set forth in such drawings.

Claims (15)

Including a core carbon material in which part or all of the edge is covered with a carbide layer;
In XRD measurement data using CuKα ray as an X-ray source, before the peak of the (002) plane starts, the inclination of the tangent of the parabola in the section where the diffraction angle 2θ is 25.5 to 26.3 degrees is 30 to 43 degrees. The negative electrode active material for a secondary battery characterized in that the slope of the tangent of the parabola is obtained by mapping the above section with a parabolic function y = ax ² + bx + c according to a polynomial approximation technique (Polynomial approximation technique) , The slope of the tangent at the point closest to the focal point of the parabolic function). 2. The negative electrode active material for a secondary battery according to claim 1, wherein the tap density is 1.0 g / cm ³ or more. The negative electrode active material for a secondary battery according to claim 1, wherein the specific surface area is 5 m ² / g or less.   The negative electrode active material for a secondary battery according to claim 1, wherein the core carbon material is highly crystalline natural graphite.   The negative electrode active material for a secondary battery according to claim 4, wherein the highly crystalline natural graphite is spherical highly crystalline natural graphite.   Natural carbon, artificial graphite, mesocarbon microbead (MCMB), mesophase pitch fine powder, isotropic, in which the core carbon material has an elliptical shape, crushed shape, scale shape or whisker shape Any one selected from the group consisting of fine powders of pitch, resin charcoal, and amorphous powders having pseudo-graphite structure or turbostructural structure, or The negative electrode active material for a secondary battery according to claim 1, which is a mixture thereof.   The carbide layer is a low crystalline carbide layer formed by coating the core carbon material with coal-based or petroleum-based pitch, tar, or a mixture thereof and then carbonizing and firing. The negative electrode active material for secondary batteries as described in 2.   The electrode for secondary batteries which consists of a metal collector coated with the negative electrode active material by any one of Claims 1-7.   A negative electrode current collector coated with a negative electrode active material according to any one of claims 1 to 7, a positive electrode current collector coated with a positive electrode active material, and between the negative electrode current collector and the positive electrode current collector A secondary battery comprising: a separator interposed in the separator; and an electrolytic solution impregnated in the separator. (A) mixing a core carbon material having a tap density of 1.0 g / cm ³ or more and a coal-based or petroleum-based carbon material having a softening point of 100 ° C. or more to obtain a mixture; and (b) Firing the mixture to carbonize the coated carbon material to form a carbide layer on part or all of the edge of the core carbon material;
Including, and
XRD measurement data using a CuKα ray as an X-ray source for a negative electrode active material made of a core carbon material on which the carbide layer is formed. Before the peak of the (002) plane starts, the diffraction angle 2θ is 25.5 to 26. A method of manufacturing a negative electrode active material for a secondary battery, wherein a slope of a tangent of a parabola for a section of 3 degrees is 30 to 43 degrees (where the slope of a tangent of a parabola is a polynomial This is the slope of the tangent line at the point closest to the focal point of the parabola function when mapped with the parabola function y = ax ² + bx + c according to an approximation method (Polynomial application technique).   The method for producing a negative electrode active material for a secondary battery according to claim 10, wherein the core carbon material is spherical highly crystalline natural graphite.   The method for producing a negative electrode active material for a secondary battery according to claim 10, wherein the coated carbon material is a coal-based or petroleum-based pitch, tar, or a mixture thereof.   The method for producing a negative electrode active material for a secondary battery according to claim 10, wherein the firing temperature of the mixture is 1000 to 2500 ° C. The method for producing a negative electrode active material for a secondary battery according to claim 10, wherein in the step (b), the mixture is fired twice or more under different temperature conditions.   The method for producing a negative electrode active material for a secondary battery according to claim 14, wherein the firing temperature of the subsequent firing step is higher than the firing temperature of the preceding firing step.