KR100855802B1 - Anode material of secondary battery and secondary battery using the same - Google Patents

Abstract

An anode material for a secondary battery is provided to prevent carbide coated on an electrode from being cleaved during the compression, and to inhibit side reactions between natural graphite and an electrolyte caused by swelling of an electrode. An anode material for a secondary battery is obtained by coating low crystalline carbon onto a core carbonaceous material, followed by baking. The anode material has a compression density ratio of at least 0.9. The core carbonaceous material is at least one selected from the group consisting of natural graphite and artificial graphite. The low crystalline carbon is at least one selected from the group consisting of pitch, tar, phenolic resins and furan resins.

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, and more particularly, by adjusting the compressive density ratio of the negative electrode material to be 0.9 or more, thereby improving the protection function against the reaction with the electrolyte on the surface of the negative electrode material. The present invention relates to a negative electrode material for a secondary battery capable of improving efficiency and cycle capacity, and a secondary battery using the same.

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, has excellent initial capacity but poor efficiency and cycle capacity. This is known to be due to the electrolyte decomposition reaction in the highly crystalline natural graphite edge portion.

In order to overcome this characteristic, the initial capacity is reduced by surface treatment (coating) of low-crystalline carbon on natural graphite and heat-treated at 1,000 ° C or higher to coat low crystalline carbide on the surface of natural graphite. An anode active material having improved characteristics could be obtained. In the process of coating and compressing an electrode current collector such as a copper coil to use the anode active material as an electrode, the coated carbide is broken, through which the highly crystalline natural graphite edge portion reacts again with the electrolyte solution. The coating effect is reduced.

Japanese Laid-Open Patent Publication No. 2002-084836 discloses a characteristic of graphite in which part or all of an edge portion of a crystal of a core carbon material is coated with a carbon material for forming a coating.

In the case of the patent, there is a description of the amount of the carbon material for forming the coating on the natural graphite, the heat treatment temperature and the analysis of the X-ray diffraction, Raman, etc. of the natural graphite coated with the coating carbon material, There was no information on the effect of cracking the coated carbide during the crimping process in actual electrode applications. In addition, when used as an active material of a lithium secondary battery, the phenomenon in which the active material is broken due to volume change occurs in a process of repeating charging and discharging. The patent does not mention the effect caused by such a 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 a natural problem due to the problem of breaking the coated carbide during the pressing process in the actual electrode application and the phenomenon that the active material is broken due to the volume change during repeated charging / discharging process when used as the active material of the lithium secondary battery In order to prevent decomposition reaction between graphite and electrolyte, it is to improve the protection against reaction of electrolyte on the surface of the negative electrode material, and to provide a negative electrode material for a secondary battery and a secondary battery using the same, which can achieve the technical problem. There is an object of the present invention.

In the negative electrode material for a secondary battery for achieving the technical problem to be achieved by the present invention is a secondary battery negative electrode material prepared by coating a low crystalline carbon on the core carbon material and firing, characterized in that the compression density ratio of the negative electrode material is 0.9 or more do.

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 specification and claims should not be construed as having a conventional or dictionary meaning, 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 configurations shown in the embodiments described herein are only one of the most preferred embodiments of the present invention and do not represent all of the technical idea of the present invention, and various equivalents may be substituted for them at the time of the present application. It should be understood that there may be variations and variations.

In the negative electrode material for secondary batteries, according to the compression density ratio (PD [coated natural graphite] / PD [natural graphite]) measured by measuring the pressed density (PD) in a specific pressurized state of the coated natural graphite. The degree to which the coating property of the electrode active material applied to the actual battery is maintained up to the electrode state is changed, and it is confirmed that this affects the charge / discharge characteristics of the battery.

The negative electrode material for a secondary battery of the present invention is a negative electrode material for a secondary battery manufactured by coating a low crystalline carbon on a core carbon material and firing, wherein the compression density ratio of the negative electrode material is 0.9 or more.

The compression density ratio of the negative electrode material may be obtained by measuring the compression density of natural graphite coated with low crystalline carbon in a specific pressurized state. At this time, the pressure is preferably in the range of 20 to 130 MPa. In the numerical range of the pressurization, when the lower limit is less than the lower limit, it is not preferable due to the electrode plate adhesion and lack of battery capacity, and when the upper limit is exceeded, it is not preferable due to the electrolyte solution and the side reaction and lack of impregnation.

The compression density is measured according to Equation 1 below, and the compression density ratio is measured according to Equation 2 below.

In Equation 1, m is the weight (g) of coated or uncoated natural graphite in a specific pressurized state, and V is the volume (cm 3) of coated or uncoated natural graphite in a specific pressurized state.

In Equation 2, PDc is the compressive density of the coated natural graphite, PDn is the compressive density of the natural graphite.

It is preferable that the compression density ratio of the negative electrode material measured as mentioned above is 0.9 or more. In the numerical range of the compression density ratio, the initial efficiency is 93.5% or more when the compression density ratio is 0.9 or more, and the discharge capacity (holding capacity) in the 30th cycle is 95% or more. Is less than 93.5%, and the discharge capacity at the 30th cycle is less than 95%, 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 a core carbon material and firing according to a conventional method performed in the art.

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 and the like can be used.

That is, in the present invention, the type and process conditions of the low crystalline carbon are selected so that the compression density ratio of the negative electrode material manufactured by coating a part or all of the edge portion of the core carbon material with the low crystalline carbon is 0.9 or more, and the coating is performed. As a result, an anode material having excellent efficiency and cycle characteristics can be produced.

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, carbon black such as acetylene black, ketjen black, farnes black, thermal black, and the like, natural graphite, artificial graphite, or conductive fibrous fibers, and the like, and in particular, carbon black, graphite powder, or carbon fiber is preferably used. Do.

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 polyvinyl fluoride. It is to use Leeden.

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 manufacturing 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 or polyolefin-based porous separator.

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

As described above, the secondary battery of the present invention has a charge / discharge efficiency of 93.5% or more, and a discharge capacity of 95% or more in the 30th cycle.

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

Example 1

A spherical natural graphite carbon material and pitch were prepared.

First, the pitch dissolved in tetrahydrofuran in spherical natural graphite was mixed by 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 to prepare a negative electrode material having a compression density ratio of 0.9.

Example 2

Except that the negative electrode material having a compressive density ratio of 0.98 was prepared by adjusting the pitch content to 3% by weight, the heat treatment temperature to 1,000 ℃, the temperature increase rate to 0.14 ℃ per minute in Example 1 was prepared It was carried out by the method.

Example 3

Except that the negative electrode material having a compressive density ratio of 1.12 was prepared by adjusting the pitch content to 1% by weight, the heat treatment temperature to 1,000 ℃, the temperature increase rate to 0.14 ℃ per minute in Example 1 was prepared It was carried out by the method.

Comparative Example 1

Except that the negative electrode material having a compression density ratio of 0.71 was prepared by adjusting the heat treatment temperature to 1,000 ℃ in Example 1, the temperature rising rate to 10 ℃ per minute was carried out in the same manner as in Example 1.

Comparative Example 2

Except that the negative electrode material with a compression density ratio of 0.82 was prepared by adjusting the heat treatment temperature to 1,000 ℃ in Example 1, the temperature increase rate to 10 ℃ per minute was carried out in the same manner as in Example 1.

Battery characteristics of the negative electrode materials prepared in Examples 1 to 3 and Comparative Examples 1 to 2 were evaluated in the following manner.

First, 2 g of natural graphite was placed in a φ 1.4 cm hole, and a force of 0.5 t was applied to the φ 1.4 cm area for 2 seconds using a press machine (that is, pressurized for 2 seconds at a pressure of 31,852 KPa). One). In the pressurized state, the height of the hole was measured by a micro gauge to obtain a compression density.

In the same manner as described above, the compressive densities of the coated natural graphite prepared in Examples 1 to 3 and Comparative Examples 1 and 2 were measured, respectively. Then, the compression density ratio of each of the negative electrode materials prepared in Examples 1 to 3 and Comparative Examples 1 and 2 was calculated according to Equation 2 above. The calculated compression density and compression density ratio are shown in Table 1 below.

division Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Compressed density of coated natural graphite (g / ㎥) 1.68 1.83 2.09 1.33 1.53 Natural Graphite Compression Density (g / ㎥) 1.87 1.87 1.87 1.87 1.87 Compression Density Ratio 0.90 0.98 1.12 0.71 0.82

100 g of the negative electrode material prepared in Examples 1 to 3 and Comparative Examples 1 and 2 were placed in a 500 ml reactor, and polyvinylidene fluoride (PVDF) was added to a small amount of N-methylpyrrolidone (NMP) and a binder. The mixture was then kneaded using a mixer, pressed and dried on a copper foil, and used as an electrode. At this time, the density after crimping of the electrodes was uniformized to 1.65 g / cm 2. The charge / discharge efficiency of this electrode was evaluated using a coin cell.

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 until the charging current reaches 0.02 mA / cm 2. Charging continued. The discharge current was discharged up to 1.5 V at 0.5 mA / cm 2. The test results are shown in Table 2 below, and the charging / discharging efficiency in Table 2 shows the ratio of the discharged capacity to the charged capacity.

division Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 1 ^st cycle discharge capacity (mAh / g) 358.5 356.0 356.7 351.7 353.2 1 ^st cycle efficiency (%) 93.6 94.2 94.7 90.8 92.1 Holding capacity (30 ^th cycle discharge capacity,%) 95.4 98.3 99.8 83.3 90.9

As shown in Table 2, according to the present invention, Examples 1 to 3 prepared with a compression density ratio of 9.0 or more according to the present invention showed an initial efficiency (1 ^st cycle efficiency) of 93.5 or more, and a storage capacity (30 ^th Cycle discharge capacity) was more than 95%. On the other hand, Comparative Examples 1 and 2, the initial efficiency was 90.8%, 92.1%, respectively, the retention capacity was found to be low as 83.3%, 90.9%.

Through Table 1 and Table 2, the compression density ratio has no correlation with the initial efficiency, but it was confirmed that the smaller the compression density ratio, the lower the efficiency and cycle performance.

As described above, it could be predicted that the smaller the compression density ratio, the more the surface area of the natural graphite, which was coated with pitch, was the result of cracking and coating and heat treatment of the carbon layer during the pressing process to match the electrode density.

Although only described in detail with respect to the described embodiments of the present invention, it will be apparent to those skilled in the art that various modifications and variations are possible within the technical spirit of the present invention, it is natural that such variations and modifications belong to the appended claims. .

According to the present invention, natural graphite and an electrolyte due to a problem of breaking the coated carbide during the crimping process in the actual electrode application and the active material being broken due to the volume change during repeated charging / discharging when used as an active material of a lithium secondary battery. It is possible to improve the efficiency and cycle capacity of the negative electrode material by preventing the decomposition reaction to improve the protection function against the reaction with the electrolyte on the surface of the negative electrode material.

Claims (5)

A negative electrode material for secondary batteries prepared by coating a core carbon material with low crystalline carbon and firing, wherein the negative electrode material has a compressive density ratio of 0.9 or more. The method of claim 1, The core material 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 single material or a mixture of two or more selected from the group consisting of pitch, tar, phenol resin and furan resin. A secondary battery comprising the negative electrode material according to any one of claims 1 to 3 as a negative electrode. The method of claim 4, wherein The secondary battery has a secondary efficiency of 93.5% or more, and a secondary battery having a discharge capacity (holding capacity) of 95% or more in the 30th cycle.