KR100886529B1 - Anode material of 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 of the present invention is manufactured by coating a low crystalline carbon on a core carbon material and firing it, and the molding strength ratio is 0.6 or more. According to the present invention, there is an advantage that the efficiency and cycle capacity of the negative electrode material can be improved by improving the protection against electrolyte decomposition reaction on the surface of the negative electrode material.

Negative material, secondary battery, forming strength ratio, graphite, coating

Description

Anode material of secondary battery and secondary battery using the same}

The present invention relates to a negative electrode material for a secondary battery and a secondary battery using the same. More specifically, the molding strength ratio of the negative electrode agent for a secondary battery manufactured by coating and sintering low crystalline carbon on a core carbon material is more than 0.6. The present invention relates to a negative electrode material for a secondary battery and a secondary battery using the same, which may improve the efficiency and cycle capacity of the negative electrode material by improving the protection against electrolyte decomposition reaction on the surface of the negative electrode material.

As portable electronic devices such as video cameras, cordless phones, mobile phones, and notebook computers are rapidly spreading in daily life, the demand for secondary batteries used as a power source has increased greatly. Among them, lithium secondary batteries have high capacity and high energy density. Due to the high battery characteristics, active research and development has been carried out at home and abroad, and is currently the most widely used secondary battery.

A lithium secondary battery basically consists of a positive electrode, a negative electrode, and an electrolyte. Therefore, research and development of a lithium secondary battery can be largely divided into studies on a cathode, an anode material, and an electrolyte.

Among these, natural graphite, which is used as a negative electrode material for lithium secondary batteries, exhibits excellent initial capacity but poor efficiency and cycle capacity. This phenomenon is known to be due to the electrolyte decomposition reaction in the highly crystalline natural graphite edge portion.

In order to overcome this problem, the low-crystalline carbon is surface-treated (coated) on natural graphite and heat-treated at 1,000 ° C or higher to coat low-crystalline carbide on the surface of natural graphite, thereby reducing the initial capacity by a small amount, but increasing efficiency and cycle capacity. A negative electrode active material having improved characteristics can be obtained. In particular, when artificial graphite of low crystalline carbon, which is used as a cladding material, by high temperature heat treatment to reduce the initial capacity reduction, it is possible to reduce the initial capacity and to suppress the electrolyte decomposition reaction.

As an example, Japanese Laid-Open Patent Publication No. 2002-084836 discloses a characteristic of graphite in which some or all of the edge portions of the crystal of the core carbon material are coated with the carbon material for forming the coating.

However, the coated carbide is broken in the process of coating the negative electrode active material as the electrode on the copper coil and then compressing it, through which the highly crystalline natural graphite edge portion reacts with the electrolyte again. There is a problem that the carbide coating effect is actually lowered.

In addition, the patents so far include the amount of low crystalline carbon coated on natural graphite, heat treatment temperature, and X-ray diffraction and Raman analysis of low crystalline carbon coated natural graphite. However, there was no information on the effect of cracking the coated carbide during the crimping process. In addition, when used as an active material of a lithium secondary battery, the active material is broken due to a volume change in the process of repeating charging and discharging. The patent does not mention the effect caused by this phenomenon. .

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

The technical problem to be achieved by the present invention is to prevent the carbon layer on the surface of the core carbon material coated with low crystalline carbon during the pressing process for controlling the electrode density, and to protect the electrolyte solution decomposition reaction on the surface of the negative electrode material It is an object of the present invention to improve the function to improve the efficiency and cycle capacity of the negative electrode material, to provide the [name of the invention] that can achieve this technical problem.

In the negative electrode material for a secondary battery for achieving the technical problem to be achieved by the present invention, the secondary battery negative electrode material produced by coating a low crystalline carbon on a core carbon material and firing, the forming strength ratio of the negative electrode material is 0.6 or more Shall be.

A secondary battery for achieving the technical problem to be achieved by the present invention is characterized in that it comprises the negative electrode material described above as a negative electrode.

Hereinafter, preferred embodiments of the present invention will be described in detail. Prior to this, terms or words used in the present specification and claims should not be construed as being limited to the ordinary or dictionary meanings, and the inventors should properly explain the concept of terms in order to best explain their own invention. Based on the principle that can be defined, it should be interpreted as meaning and concept corresponding to the technical idea of the present invention. Therefore, the embodiments described herein are only exemplary embodiments of the present invention, and do not represent all of the technical ideas of the present invention, and various equivalents and modifications that may substitute them at the time of the present application may be used. It should be understood that there may be.

In the present invention, the degree of maintaining the electrode state of the electrode active material applied to the actual battery according to the molding strength ratio measured by measuring the ratio between the molding strength of the core carbon material and the molding strength of the core carbon material coated with low crystalline carbon It was confirmed that this affects the charge / discharge characteristics of the battery.

The negative electrode material for a secondary battery of the present invention is characterized in that the forming strength ratio of the negative electrode agent for a secondary battery manufactured by coating low crystalline carbon on a core carbon material and firing the same.

Forming strength ratio of the negative electrode material can be obtained according to the following equation 1 by measuring the molding strength of the core carbon material itself and the molding strength of the core carbon material coated with low crystalline carbon. In addition, the molding strength of the core carbon material itself and the molding strength of the core carbon material coated with low crystalline carbon can be measured using a compressive yield strength meter.

[Equation 1]

It is preferable that the forming strength ratio of the said negative electrode material is 0.6 or more. When the forming strength ratio of the negative electrode material is 0.6 or more, the initial efficiency is 93.0% or more, and the discharge capacity (holding capacity) in the 30th cycle can be maintained at 97% or more, whereas the general evaluation criteria of the negative electrode material applied to the battery can be maintained. If the forming strength ratio of the ash is less than 0.6, the initial efficiency is less than 93.0%, and the discharge capacity at the 30th cycle is less than 97%, which is not preferable.

In addition, the negative electrode material for a secondary battery of the present invention can be produced by coating a low crystalline carbon on the core carbon material and firing according to a conventional method carried out in the art. In the present invention, in order to have a molding strength ratio (0.6 or more) of the negative electrode material as described above, it can be achieved by optimally adjusting the type of low crystalline carbon and the coating process conditions of the core carbon material using the same.

The core carbon material may be natural graphite, artificial graphite, or a mixture thereof, and particularly, natural graphite may be used.

As the low crystalline carbon, pitch, tar, phenol resin, furan resin, furfuryl alcohol, etc. may be used as carbon.

The low crystalline carbon is preferably contained in 5 to 10% by weight in the core carbon material. In the lower limit of the content of the low crystalline carbon, the cycle discharge capacity decreases when the content is less than the lower limit.

The negative electrode material for the secondary battery of the present invention is mixed with the low crystalline carbon and the core carbon material as described above, wet stirred and dried at normal pressure for 2 hours or more, and then calcined for 1 to 2 hours at a temperature of 1,100 to 1,500 ° C, and classified. It can manufacture by removing fine powder. At this time, the forming strength ratio of the negative electrode material can be adjusted according to the conditions of the type of low crystalline carbon, heat treatment temperature, temperature rise rate, cooling rate. The surface-coated core carbon material may be covered by some or all of the edge portions of the core carbon material with low crystalline carbon.

A small amount of a conductive agent or a binder can be selectively added to the slurry for electrode plate production including the negative electrode material prepared as described above, if necessary.

The use amount of the conductive agent or binder can be appropriately adjusted and used to the extent commonly used in the art, the range does not affect the present invention.

The conductive agent may be used as long as it is an electron conductive material that does not cause chemical change in the battery configured. For example, there are carbon blacks such as acetylene black, Ketjen black, farnes black, thermal black, natural graphite, artificial graphite, conductive fibrous fibers, and the like, and in particular, carbon black, graphite powder or carbon fiber is preferably used.

As the binder, a thermoplastic resin, a thermosetting resin or a mixture thereof may be used, and in particular, polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE) is preferably used, and more preferably polyvinylidene fluoride Is to use

As described above, the slurry for preparing a cathode plate including the negative electrode active material and optionally at least one of a conductive agent and a binder is then coated on an electrode current collector and then dried to remove a solvent or a dispersion medium, thereby binding the active material to the current collector. It binds between active materials.

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

In addition, the present invention is characterized in that in the secondary battery comprising a separator and an electrolyte interposed between the positive electrode, the negative electrode, both electrodes, the negative electrode material prepared by the above-described manufacturing method as a negative electrode.

The secondary battery of the present invention can be prepared by inserting a porous separator between the positive electrode and the negative electrode in a conventional manner known in the art.

The electrolyte is a non-aqueous electrolyte containing a lithium salt and an electrolyte compound, wherein the lithium salt is selected from the group consisting of LiClO ₄ , LiCF ₃ SO ₃ , LiPF ₆ , LiBF ₄ , LiAsF ₆ and LiN (CF ₃ SO ₂ ) ₂ . Preference is given to compounds of species or more. In addition, the electrolyte compounds include ethylene carbonate (EC), propylene carbonate (PC), gamma butyrolactone (GBL), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethylmethyl carbonate (EMC) and methyl propyl carbonate (MPC). It is preferable that it is 1 or more types chosen from the group which consists of

In the manufacture of the battery of the present invention, it is preferable to use a porous separator as a separator, and non-limiting examples include a polypropylene-based, polyethylene-based, and polyolefin-based porous separator.

The secondary battery of the present invention is not limited in appearance, but may be cylindrical, square, pouch type, coin type, etc. using a can.

Hereinafter, in order to help the understanding of the present invention will be described in more detail through preferred examples and comparative examples.

Forming and molding strength in the examples and comparative examples described below, the molding strength ratio was measured by the following method.

First, forming and forming strength were put 2 g of natural graphite in a hole of φ 1.4 cm, and a force of 0.5 t was applied to the area of φ 1.4 cm for 2 seconds using a press. That is, it pressurized for 2 second by the pressure of 31,852 KPa, and obtained the cylindrical molded object. Then, the breaking strength of the natural graphite molded product was measured by using a compressive yield strength tester.

In addition, the molding strength ratio was calculated according to the above equation (1).

Example 1

The pitch was melted with tetrahydrofuran in spherical natural graphite having a molding strength of 873 at 5% by weight, mixed by wet stirring at normal pressure for 2 hours or more, and then dried to prepare a mixture. The mixture was calcined first and second at 1,100 ° C. and 1,500 ° C. for 1 hour, and classified to remove fine powder, thereby preparing a negative electrode material having a molding strength ratio of 0.60.

100 g of the prepared negative electrode material was placed in a 500 ml reactor, a small amount of N-methylpyrrolidone (NMP) and polyvinylidene fluoride (PVDF) were added as a binder, and kneaded using a mixer to prepare a plate. Slurry was prepared. Then, the above prepared slurry for producing a plate was pressed and dried on a foil foil, and used as an electrode. At this time, the density after compression of the electrode was uniformized to 1.65 g / cm 3.

Example 2

7 wt% of the pitch dissolved in tetrahydrofuran in spherical natural graphite having a molding strength of 873 was mixed, followed by wet stirring at normal pressure for 2 hours or more, followed by drying to prepare a mixture. The mixture was calcined for 1 hour at 1,100 ° C. and 1,500 ° C. for 1 hour, and classified to remove fine powder, thereby preparing a negative electrode material having a molding strength ratio of 0.73. Since the process was carried out in the same manner as in Example 1.

Example 3

The pitch dissolved in tetrahydrofuran was mixed with spherical natural graphite having a molding strength of 873 at 10% by weight, followed by wet stirring at normal pressure for 2 hours or more, followed by drying to prepare a mixture. The mixture was calcined first and second at 1,100 ° C. and 1,500 ° C. for 1 hour, and classified to remove fine powder, thereby preparing a negative electrode material having a molding strength ratio of 0.81. Since the process was carried out in the same manner as in Example 1.

Comparative example  One

The pitch dissolved in tetrahydrofuran in spherical natural graphite having a molding strength of 873 was mixed at 2% by weight, followed by wet stirring at normal pressure for 2 hours or more, followed by drying to prepare a mixture. The mixture was calcined first and second at 1,100 ° C. and 1,500 ° C. for 1 hour, and classified to remove fine powder, thereby preparing a negative electrode material having a molding strength ratio of 0.43. Since the process was carried out in the same manner as in Example 1.

Comparative Example 2

The pitch dissolved in tetrahydrofuran was mixed with spherical natural graphite having a molding strength of 873 at 3% by weight, followed by wet stirring at normal pressure for 2 hours or more, followed by drying to prepare a mixture. The mixture was calcined first and second at 1,100 ° C. and 1,500 ° C. for 1 hour, and classified to remove fine powder, thereby preparing a negative electrode material having a molding strength ratio of 0.52. Since the process was carried out in the same manner as in Example 1.

In order to evaluate the charge / discharge efficiency using the electrodes prepared in Examples 1 to 3 and Comparative Examples 1 or 2, a coin cell was prepared and evaluated for charge / discharge characteristics through the following test, The results are shown in Table 1 below.

First, the charge / discharge test regulates the potential in the range of 0 to 1.5 V to charge until the charging current is 0.5 V / cm 2 until it becomes 0.01 V, maintains the voltage of 0.01 V, and the charging current becomes 0.02 mA / cm 2. Charging continued until. The discharge current was discharged up to 1.5 V at 0.5 mA / cm 2. In Table 1, the charge / discharge efficiency shows the ratio of the discharged capacity to the charged capacity.

division Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Natural Graphite Forming Strength (1) (N) 873 Coated Natural Graphite Forming Strength (2) (N) 523.8 637.3 707.1 375.4 454.0 Forming Strength Ratio (2) / (1) 0.60 0.73 0.81 0.43 0.52 1 ^st cycle discharge capacity (mAh / g) 357.5 356.1 355.9 351.0 354.2 1 ^st cycle efficiency (%) 93.0 93.2 93.7 91.3 92.5 Holding capacity (30 ^st cycle discharge capacity,%) 97.4 97.9 98.8 85.3 92.6

As shown in Table 1, in Examples 1 to 3 manufactured by adjusting the molding strength ratio of the negative electrode material to 0.6 or more according to the present invention, in the initial discharge capacity or the efficiency, the molding strength ratio was less than 0.6 and Compared to the similar degree, but in the 30th cycle discharge capacity was 97.0% or more was confirmed to be very excellent compared to Comparative Example 1 or 2.

As described above, although the present invention has been described by means of a limited embodiment, the present invention is not limited thereto and will be described below by the person skilled in the art and the technical spirit of the present invention. Of course, various modifications and variations are possible within the scope of the claims.

According to the present invention, the coating strength ratio of the negative electrode agent for secondary batteries manufactured by coating and sintering low crystalline carbon on the core carbon material is made to be 0.6 or more, thereby improving the protection against electrolyte decomposition reactions on the surface of the negative electrode material. Improve ash efficiency and cycle capacity.

Claims (5)

A negative electrode material for a secondary battery produced by coating a core carbon material with low crystalline carbon and firing, wherein the forming strength ratio of the negative electrode material is 0.6 or more. The method of claim 1, The core carbon material is a negative electrode material for a secondary battery, characterized in that a single substance or a mixture of two or more selected from the group consisting of natural graphite and artificial graphite. The method of claim 1, The low crystalline carbon is a negative electrode material for a secondary battery, characterized in that a single substance or a mixture of two or more selected from the group consisting of pitch, tar (tar), phenol resin, furan resin, and furfuryl alcohol. The method of claim 1, The low crystalline carbon, the negative electrode material for a secondary battery, characterized in that contained in the core carbon material in 5 to 10% by weight. A secondary battery comprising the negative electrode material according to any one of claims 1 to 4 as a negative electrode.