JP2010526409A - Anode material for secondary battery and secondary battery using the same - Google Patents

Abstract

The present invention relates to a negative electrode material for a secondary battery and a secondary battery using the same. The negative electrode material for a secondary battery according to the present invention is a mixture of a carbon material of the first core material having a sphericity of more than 10 and less than 100 and a carbon material of a second core material having a sphericity of more than 0 and less than 10. The mixing weight ratio of the carbon material of the first core material and the carbon material of the second core material is 1: 1 to 9: 1.
According to the present invention, it is possible to alleviate the phenomenon that the negative electrode material breaks during the crimping process during electrode manufacturing, and to improve the efficiency and cycle characteristics of the battery while maintaining the initial high capacity.
[Selection figure] None

Description

  The present invention relates to a negative electrode material for a secondary battery and a secondary battery using the same, and more specifically, the carbon material and the sphericity of the first core material having a sphericity of more than 10 and less than 100. By mixing and using a carbon material of the second core material that is greater than 0 and 10 or less, the phenomenon of the negative electrode material cracking by the crimping process during electrode production is alleviated, and the efficiency and cycle of the battery while maintaining the initial high capacity The present invention relates to a negative electrode material for a secondary battery capable of improving characteristics and a secondary battery using the same.

Various types of portable electronic devices such as video cameras, wireless telephones, cellular phones, and notebook PCs are rapidly spreading in daily life, and the demand for secondary batteries used as a power supply source is greatly increasing. Among them, lithium secondary batteries are currently used in the widest range of secondary batteries because of their excellent battery characteristics with large capacity and high energy density.
A lithium secondary battery basically includes a positive electrode, a negative electrode, and an electrolyte. Therefore, research and development on a lithium secondary battery is largely divided into research on a positive electrode, a negative electrode material, and an electrolyte.
Among these, natural graphite used as a negative electrode material for lithium secondary batteries has excellent initial capacity, but is inefficient in efficiency and cycle capacity. This is known to be due to the decomposition reaction of the electrolytic solution generated at the edge portion of highly crystalline natural graphite.

  In order to overcome such problems, Japanese Patent Laid-Open No. 2002-084836 (Patent Document 1) coats a part or all of the edge portion of the carbon material crystal of the core material with a carbon material for coating formation. Disclosed for the properties of graphite. The above patent discloses a coating forming technique for improving characteristics during the production of a negative electrode material. However, in the above patent, there is no mention of a technique for improving characteristics by mixing carbon materials having different sphericity degrees.

  Further, the natural graphite is not only the edge of the negative electrode material itself, but also the shape of the negative electrode material cannot be maintained in the pressure-bonding process at the time of electrode production, and cracks to increase the edge. Accordingly, the efficiency and cycle characteristics of the battery using natural graphite as the cathode material are further deteriorated.

  Therefore, efforts to solve the above-mentioned problems of the prior art have been sustained in related industries, and the present invention has been devised under such a technical background.

Japanese Unexamined Patent Publication No. 2002-084836

  The technical problem to be solved by the present invention is to solve the phenomenon in which the efficiency and cycle characteristics of the battery are lowered when natural graphite is used as the cathode material. It is an object of the present invention to provide a negative electrode material for a battery and a secondary battery using the same.

  The negative electrode material for a secondary battery for achieving the technical problem to be solved by the present invention includes a carbon material of the first core material having a sphericity of more than 10 and less than 100 and a sphericity of more than 0 and less than 10 It is made of a mixture of carbon materials of a second core material, and the mixing weight ratio of the carbon material of the first core material and the carbon material of the second core material is 1: 1 to 9: 1.

The carbon material of the first core material is preferably spherical natural graphite.
The carbon material of the second core material is preferably plate-like natural graphite.
Moreover, the carbon material of the said 1st core material or the carbon material of the 2nd core material can coat | cover low crystalline carbon on each surface.

  A secondary battery for achieving the technical problem to be solved by the present invention is characterized by including a negative electrode made of the negative electrode material described above.

BEST MODE FOR CARRYING OUT THE INVENTION

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

  In the present invention, in addition to the conventional process of coating low-crystalline carbon on natural graphite, the cracking phenomenon of the negative electrode material that occurs in the crimping process is mitigated by mixing the core carbon material with a different degree of spheroidization. Through the battery charge / discharge test, it was confirmed that the battery efficiency and cycle characteristics were improved.

  Hereinafter, the degree of spheroidization described in the present invention is determined according to the following formula 1 by measuring the intensities of the 110 and 004 planes of the graphite material using X-ray diffraction.

  The negative electrode material for a secondary battery according to the present invention is a mixture of a carbon material of the first core material having a sphericity of more than 10 and less than 100 and a carbon material of a second core material having a sphericity of more than 0 and less than 10. The mixing weight ratio of the carbon material of the first core material and the carbon material of the second core material is 1: 1 to 9: 1.

  The carbon material of the first core material is preferably spherical natural graphite. When the spheroidization degree of the carbon material of the first core material satisfies the above numerical range, it is desirable that the side reaction between the cathode active material and the electrolytic solution can be maintained at an appropriate level. Further, when the carbon material of the first core material is natural graphite having a spherical shape, a side reaction with the electrolytic solution occurs at an appropriate level, and the filling density of the cathode active material is appropriate, which is desirable. .

  The carbon material of the second core material is preferably plate-like natural graphite. When the sphericity of the carbon material of the second core material satisfies the above numerical range, it is desirable because the effect of improving characteristics generated when the carbon material of the core material is mixed is sufficient. Further, when the carbon material of the second core material is a plate-like natural graphite, the effect of improving the characteristics obtained by mixing the carbon material of the core material, particularly the effect of the pressure-bonding characteristics can be appropriately achieved. desirable.

  The carbon material of the first core material and the carbon material of the second core material as described above are desirably mixed and used at a weight ratio of 1: 1 to 9: 1. When the mixing ratio of the carbon material of the core material having a different degree of spheroidization satisfies the above range, the mixing effect of the carbon material of the core material can be sufficiently exerted, and unnecessary side reaction of the electrolyte does not occur. So desirable.

In addition, one or both of the carbon material of the first core material and the carbon material of the second core material can be coated with low crystalline carbon as necessary.
As the low crystalline carbon material, pitch, tar, phenol resin, furan resin, furfuryl alcohol, or the like can be used. At this time, the efficiency and cycle characteristics of the battery differ depending on the ratio of the surface energy between the low crystalline carbon and the core carbon material. Therefore, it is preferable to appropriately select the kind of low crystalline carbon.

The core carbon material can be coated by the following method.
First, the low crystalline carbon and the core carbon material are mixed and dry-stirred. Next, the mixture can be produced by baking at a temperature of 800 to 3,000 ° C. for 1 to 5 hours, and classification to remove fine powder. In the carbon material of the core material whose surface is coated in this way, part or all of the edge portion of the carbon material of the core material is coated with low crystalline carbon.

A conductive material and a binder can be selectively added in a small amount, if necessary, to the slurry for producing an electrode plate containing the negative electrode material produced as described above.
The use amount of the conductive material and the binder can be appropriately adjusted and used as much as is normally used in the art, and the range does not affect the present invention.

  As the conductive material, any electronic conductive material that does not cause a chemical change in the battery constructed can be used. For example, examples of the conductive material include carbon black such as acetylene black, ketjen black, furnace black, and thermal black; natural graphite; artificial graphite; conductive carbon fiber; and particularly carbon black, graphite powder, or carbon. It is desirable to use fibers.

  As the binder, a thermoplastic resin, a thermosetting resin, or a mixture thereof can be used. The binder is preferably polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE), and more preferably polyvinylidene fluoride.

  As described above, a slurry for producing an electrode plate containing a negative electrode material and optionally at least one of a conductive material and a binder is applied to an electrode current collector and then dried to remove a solvent, a dispersion medium, or the like. Thus, the negative electrode material is bound to the current collector and the negative electrode material is bound.

  The electrode current collector is not particularly limited as long as it is made of a conductive material. In particular, it is desirable to use a foil manufactured from copper, gold, nickel, a copper alloy, or a combination thereof.

  In addition, the present invention is a secondary battery including a positive electrode, a negative electrode, a separation membrane interposed between the two electrodes, and an electrolyte, comprising the negative electrode manufactured using the negative electrode material manufactured according to the manufacturing method described above. .

The secondary battery of the present invention can be manufactured by inserting a porous separation membrane between a positive electrode and a negative electrode and injecting an electrolyte according to a conventional method known in the art.
The electrolyte is a non-aqueous electrolyte containing a lithium salt and an electrolyte solution compound. As the lithium salt, LiClO ₄ , LiCF ₃ SO ₃ , LiPF ₆ , LiBF ₄ , LiAsF ₆ and LiN (CF ₃ SO ₂ ). One or more compounds selected from the group consisting of ₂ can be used. Examples of the electrolyte compound include ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (GBL), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and methyl propyl carbonate ( One or more compounds selected from the group consisting of MPC) can be used.

The battery separation membrane of the present invention is preferably a porous separation membrane, and examples thereof include polypropylene-based, polyethylene-based, and polyolefin-based porous separation membranes.
The secondary battery of the present invention can be manufactured in various forms without limitation on the outer shape, and examples thereof include a cylindrical shape using a can, a square shape, a pouch shape, and a coin shape.
[Example]
Hereinafter, in order to help understanding of the present invention, preferred examples and comparative examples for comparison will be described in more detail.

Hereinafter, the sphericity of Examples and Comparative Examples was measured using an X-ray diffraction analyzer. At this time, the scan range was 20 to 80 °, the step size was 0.02 °, and the scan speed was 0.4 s / step. The standard material was Si powder (-325 mesh, 99%). The peak position of data measured after mixing Si powder with each sample at about 15 to 20% by weight was corrected using data obtained by measuring only Si powder. Using the XRD data measured by such a method, the degree of spheroidization was determined by the intensity values of the peak indicating the 110 plane (77.6 °) and the peak indicating the 004 plane (53.2 to 54.7 °). .
Example 1
A spherical natural graphite was dry-mixed with a pitch of 20% by weight at high speed for about 10 minutes to produce a mixture. This mixture was subjected to primary and secondary firing for 1 hour at 1,100 ° C. and 2,200 ° C. for 1 hour, respectively, and fine powder was removed to produce a negative electrode material having a sphericity of 37.1. At this time, the sphericity was obtained through XRD analysis. 10% by weight of natural graphite having a sphericity of 5.3 was dry mixed at a low speed with 90% by weight of the negative electrode material having a sphericity of 37.1.

Thus, 100 g of the negative electrode material mixed with carbon materials having different spheroidization degrees was put into a 500 ml reactor, and a small amount of N-methylpyrrolidone (NMP) and polyvinylidene fluoride (PVDF) as a binder were added. Subsequently, the said mixture was knead | mixed using the mixer and the slurry for electrode plate manufacture was manufactured. Next, the prepared slurry for producing an electrode plate was pressure-bonded and dried on a copper foil and used as an electrode.
Example 2
In Example 1 above, natural graphite having a sphericity of 37.1 was used at 80%, and natural graphite having a sphericity of 5.3 was used at 20% by weight. 1 in the same manner.
Example 3
In Example 1 above, natural graphite having a sphericity of 37.1 was used at 70%, and natural graphite having a sphericity of 5.3 was used at 30% by weight. 1 in the same manner.
Example 4
In Example 1 above, natural graphite having a sphericity of 37.1 was used at 60%, and natural graphite having a sphericity of 5.3 was used at 40% by weight. 1 in the same manner.
Example 5
In Example 1 above, natural graphite having a sphericity of 37.1 was used at 50%, and natural graphite having a sphericity of 5.3 was used at 50% by weight. 1 in the same manner.
Example 6
A spherical natural graphite was dry-mixed with 10% by weight pitch at high speed for about 10 minutes to produce a mixture. This mixture was subjected to primary and secondary firing for 1 hour at 1,100 ° C. and 2,200 ° C. for 1 hour, respectively, and fine powder was removed to produce a negative electrode material having a sphericity of 37.1. At this time, the sphericity was determined through XRD analysis.

  Next, a plate-like natural graphite was dry-mixed at a high speed with 5 wt% pitch for about 10 minutes to produce a mixture. This mixture was primarily fired at 1,100 ° C. for 1 hour, classified to remove fine powder, and a negative electrode material having a sphericity of 8.9 was produced.

90% by weight of natural graphite having a sphericity of 37.1 and 10% by weight of natural graphite having a sphericity of 8.9 were dry mixed at a low speed.
Thus, 100 g of the negative electrode material mixed with carbon materials having different spheroidization degrees was put into a 500 ml reactor, and a small amount of N-methylpyrrolidone (NMP) and polyvinylidene fluoride (PVDF) as a binder were added. Subsequently, the said mixture was knead | mixed using the mixer and the slurry for electrode plate manufacture was manufactured. Next, the prepared slurry for producing an electrode plate was pressure-bonded and dried on a copper foil and used as an electrode.
Comparative Example 1
A spherical natural graphite was dry-mixed with a pitch of 20% by weight at high speed for about 10 minutes to produce a mixture. This mixture was subjected to primary and secondary firing for 1 hour at 1,100 ° C. and 2,200 ° C. for 1 hour, respectively, and fine powder was removed to produce a negative electrode material having a sphericity of 37.1. At this time, the sphericity was measured through XRD analysis.

100 g of the negative electrode 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. Subsequently, the said mixture was knead | mixed using the mixer and the slurry for electrode plate manufacture was manufactured. Next, the prepared slurry for producing an electrode plate was pressure-bonded and dried on a copper foil and used as an electrode.
Comparative Example 2
A spherical natural graphite was produced in the same manner as in Example 1 except that 15 wt% pitch was dry-mixed at high speed for about 10 minutes to produce a mixture.
A coin cell was manufactured using the electrodes manufactured in Examples 1 to 6 and Comparative Examples 1 and 2. Next, the charge / discharge characteristics of the battery were evaluated by the following method, and the results are shown in Table 1 below.

First, in the charge / discharge test, the electric potential is regulated in the range of 0 to 1.5 V, the charge current is charged at 0.5 mA / cm ² until it reaches 0.01 V, and the charge current is maintained while maintaining the voltage of 0.01 V. The battery was continuously charged until 0.02 mA / cm ² was obtained. A discharge current of 0.5 mA / cm ² was discharged up to 1.5 V. In the following Table 1, the charge / discharge efficiency indicates the ratio of the discharged electric capacity to the charged electric capacity.

  From Table 1 above, Examples 1 to 6 according to the present invention have improved battery efficiency and cycle characteristics while maintaining the initial high capacity, which is an advantage of natural graphite, as compared with Comparative Examples 1 and 2. I understand.

  As described above, the present invention has been described by way of a limited embodiment, but the present invention is not limited thereto, and the technical idea of the present invention can be obtained by a person having ordinary knowledge in the technical field to which the present invention belongs. Needless to say, various modifications and variations are possible within the scope of the claims.

  According to the present invention, it is possible to alleviate the phenomenon that the negative electrode material breaks during the crimping process during electrode production, and to improve the efficiency and cycle characteristics of the battery while maintaining the initial high capacity.

Claims (7)

In the negative electrode material for secondary batteries, the negative electrode material is
A carbon material of a first core material having a sphericity of more than 10 and less than or equal to 100; and a carbon material of a second core material having a sphericity of more than 0 and less than 10; A negative electrode material for a secondary battery, wherein a mixing weight ratio of the second core material to the carbon material of the second core material is 1: 1 to 9: 1.   2. The negative electrode material for a secondary battery according to claim 1, wherein the carbon material of the first core material is spherical natural graphite.   2. The negative electrode material for a secondary battery according to claim 1, wherein the carbon material of the second core material is plate-like natural graphite.   The negative electrode material for a secondary battery according to claim 1, wherein the carbon material of the first core material is coated with low crystalline carbon.   2. The negative electrode material for a secondary battery according to claim 1, wherein the carbon material of the second core material is coated with low crystalline carbon.   6. The low crystalline carbon is a single substance or a mixture of two or more selected from the group consisting of pitch, tar, phenol resin, furan resin and furfuryl alcohol. The negative electrode material for secondary batteries as described in 2.   A secondary battery comprising a negative electrode made of a negative electrode material according to any one of claims 1 to 6.