KR100884431B1 - 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 a negative electrode material for a secondary battery manufactured by coating low crystalline carbon on a core carbon and firing, wherein the specific surface area ratio of the negative electrode material is 1.4 or less. 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.

Graphite, negative electrode material, specific surface area ratio, cycle capacity, secondary battery

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 specific surface area ratio of the negative electrode material to 1.4 or less, thereby improving the protection function against the electrolyte decomposition reaction 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 used as a negative electrode material of a lithium secondary battery 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 (edge).

In order to overcome these characteristics, 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, resulting in a small reduction in initial capacity, but efficiency and cycle capacity. A method of obtaining a negative electrode active material having improved characteristics has been proposed.

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, in the process of coating the negative electrode active material obtained by the above method on an electrode current collector such as a copper coil and then compressing it for use as an electrode, the coated carbide is broken, through which the highly crystalline natural graphite edge is broken. The part was reacted with the electrolyte again, and there was a problem that the carbide coating effect was actually lowered.

In addition, in the case of the Japanese patent, the contents of the amount of carbon coating material for forming a coating on natural graphite, the heat treatment temperature, and the analysis of X-ray diffraction, Raman, etc. of natural graphite coated with coating carbon material However, there was no information on the effect of cracking the coated carbide during the crimping process in the actual electrode application. In addition, when used as an active material of a lithium secondary battery, a phenomenon in which the active material is broken due to volume change occurs in a process of repeating charging and discharging, and 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 to improve the protection function against the electrolyte decomposition reaction on the surface of the negative electrode material in order to solve the problem that the coated carbide during the pressing process in the actual electrode application to improve the efficiency and cycle capacity of the negative electrode material In addition, an object of the present invention to provide a secondary battery negative electrode material and a secondary battery using the same that can achieve the technical problem.

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 a core carbon material and firing, characterized in that the specific surface area ratio of the negative electrode material is 1.4 or less. 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 present invention, in the negative electrode material for the secondary battery, the electrode state of the electrode active material that is applied to the actual battery according to the specific surface area ratio measured by measuring the specific surface area before and after crimping during electrode production using the coated natural graphite electrode state The degree to which it is maintained varies, and it is confirmed that this affects the charge / discharge characteristics of the battery.

The specific surface area ratio of the negative electrode material is measured by measuring the specific surface area before and after pressing the core carbon coated with low crystalline carbon, respectively, it can be obtained according to the following equation (1).

It is preferable that the specific surface area ratio of the negative electrode material for secondary batteries of this invention measured as mentioned above is 1.4 or less.

  According to the present invention, when the specific surface area ratio of the negative electrode material is 1.4 or less, the initial efficiency is 94% or more, and the discharge capacity (holding capacity) in the 25th cycle can be maintained at 95% or more, whereas the specific surface area ratio of the negative electrode material is 1.4 If exceeded, the initial efficiency is less than 94%, and the discharge capacity at the 25th cycle is less than 95%, which is not preferable because there is a problem in cycle performance (characteristic of repeated charging and discharging).

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 in particular, natural graphite may be used.

As the low crystalline carbon, pitch, tar, phenol resin, furan resin, fulfuryl alcohol 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 specific surface area ratio of the negative electrode material manufactured by coating a part or all of the edge portions of the core carbon material with the low crystalline carbon is 1.4 or less. 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, 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 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. Particularly, it is 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 ( It is preferable that it is 1 or more types chosen from the group which consists of MPC).

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 94% or more and a discharge capacity of 95% or more in the 25th 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 with tetrahydrofuran in spherical natural graphite was mixed by 3% by weight relative to the weight of natural graphite, mixed by wet stirring at normal pressure for 2 hours or more, and then dried to prepare a mixture. The mixture was heated at a temperature increase rate of 1 ° C./min, calcined at 1,100 ° C. for 1 hour, and classified to remove fine powder to prepare a negative electrode active material.

100 g of the prepared negative active 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 then kneaded using a mixer to obtain a specific surface area. A negative electrode material having a ratio of 1.21 was prepared.

Example 2

In the same manner as in Example 1 except that the negative electrode material having a specific surface area ratio of 1.38 was prepared by adjusting the pitch to 5 wt% based on the weight of natural graphite and adjusting the temperature increase rate to 3 ° C./min. Was carried out.

Comparative example  One

In the same manner as in Example 1 except that the negative electrode material having a specific surface area ratio of 1.45 was prepared by adjusting the pitch to 10% by weight relative to the weight of natural graphite and adjusting the temperature increase rate to 3 ° C / min. Was carried out.

Comparative example  2

In Example 1, the pitch was adjusted to 10 wt% based on the weight of natural graphite, and the temperature increase rate was adjusted to 5 ° C./min, except that a negative electrode material having a specific surface area ratio of 1.53 was manufactured. Was carried out.

Comparative Example 3

In Example 1, except that the pitch was adjusted to 10% by weight based on the weight of natural graphite, and the temperature increase rate was adjusted to 10 ° C / min to prepare a negative electrode material having a specific surface area ratio of 1.61. Was carried out.

Comparative example  4

In Example 1, the pitch was adjusted to 10 wt% based on the weight of natural graphite, and the temperature increase rate was adjusted to 15 ° C./min in the same manner as in Example 1 except that a negative electrode material having a specific surface area ratio of 1.67 was manufactured. Was carried out.

The specific surface area ratio and charge / discharge characteristics were evaluated using the negative electrode materials for secondary batteries prepared in Examples 1 and 2 and Comparative Examples 1 to 4 in the following manner, and the results are shown in Table 1 below.

end. Measurement of specific surface area before compression-The negative electrode materials for secondary batteries prepared in Examples 1 and 2 and Comparative Examples 1 to 4 were measured using a TriStar 3000 Model (Micromeritics) as a specific surface area meter.

I. Crimping-After dipping 2 g each of the negative electrode material for secondary batteries prepared in Examples 1 and 2 and Comparative Examples 1 to 4 in a φ 1.4 cm hole, the force of 2 t using a press machine It was applied to an area of 1.4 cm for 2 seconds (that is, pressed for 2 seconds at a pressure of 1.3 t / cm 2).

All. Measurement of specific surface area after crimping-The specific surface area of the negative electrode material for secondary batteries manufactured in Examples 1 and 2 and Comparative Examples 1 to 4 pressed in the above B. was measured using a MicroStar 3000 model (TriStar 3000 Model). ) Was measured.

la. Specific Surface Area Ratio Calculation-Measured according to Equation 1 above.

hemp. Electrode Preparation-Electrodes were prepared by coating the negative electrode material for secondary batteries prepared in Examples 1 and 2 and Comparative Examples 1 to 4 on a copper foil, pressing, and drying. At this time, the density after crimping of the electrodes was uniformized to 1.65 g / cm 2.

bar. Charge / discharge characteristics-A coin cell was prepared to measure the charge / discharge efficiency of the electrode prepared in E. The charge / discharge test regulates the potential in the range of 0 to 1.5 V and charges until the charging current is 0.5 V / cm 2 until it reaches 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.

division Example 1 Example 2 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Specific surface area before pressing (㎡ / g) 3.14 2.45 1.63 1.67 1.64 1.71 Specific surface area after pressing (㎡ / g) 3.80 3.38 2.36 2.56 2.64 2.86 Specific surface area ratio 1.21 1.38 1.45 1.53 1.61 1.67 1 ^st cycle discharge capacity (mAh / g) 351 348 350 347 349 350 1 ^st cycle efficiency (%) 94.7 94.0 92.8 92.1 91 90.1 Holding capacity (25 ^th cycle discharge capacity,%) 98.3 97.5 92.4 91.0 90.3 87.2

As shown in Table 1, Examples 1 and 2 prepared by adjusting the specific surface area ratio of the negative electrode material in accordance with the present invention to 1.4 or less compared to Comparative Examples 1 to 4 with a specific surface area ratio of more than 1.4, respectively, the initial efficiency is 94.7 %, 94.0%, was 94% or more, and the discharge capacity (holding capacity) at the 25th cycle was 98.3%, 97.5%, respectively, it was confirmed that more than 95%.

In addition, it can be seen from Table 1 that the specific surface area ratio has no correlation with the initial capacitance, but the efficiency and cycle performance deteriorate as the specific surface area ratio increases. From these results, it can be predicted that the specific surface area ratio, that is, the specific surface area after the compression, is a result of the surface of the natural graphite, which was coated with pitch, cracked during the pressing process and the carbon layer coated during the compression process was exposed to the electrolyte and decomposed.

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, it is possible to improve the efficiency and cycle capacity of the negative electrode material by improving the protection against the electrolyte decomposition reaction on the surface of the negative electrode material in order to solve the problem that the coated carbide breaks during the pressing process in the actual electrode application have.

Claims (5)

In the negative electrode material for secondary batteries manufactured by coating low-crystalline carbon on a core carbon material and baking, the negative electrode material for secondary batteries, characterized in that the specific surface area after pressing the negative electrode material is 1.4 times or less the specific surface area before pressing. . 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, furan resin, and furfuryl alcohol. 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 charge / discharge efficiency of 94% or more, and a secondary battery having a discharge capacity in a 25th cycle of 95% or more.