KR100576221B1 - Negative active material for large capacity rechargeable lithium battery and large capacity rechargeable lithium battery comprising thereof - Google Patents

Abstract

The present invention relates to a large-capacity lithium secondary battery negative electrode active material and a large-capacity lithium secondary battery including the same, in particular, a negative electrode active material containing a crystalline carbon compound and an amorphous carbon-based compound and the negative electrode active material in the negative electrode output density is high The present invention relates to a large capacity lithium secondary battery which is excellent in energy density and significantly improved.

Electric element, large capacity lithium secondary battery, negative electrode active material, crystalline carbon compound, amorphous carbon compound, high power density, high energy density

Description

Negative active material for high capacity lithium secondary battery and high capacity lithium secondary battery including same {NEGATIVE ACTIVE MATERIAL FOR LARGE CAPACITY RECHARGEABLE LITHIUM BATTERY AND LARGE CAPACITY RECHARGEABLE LITHIUM BATTERY COMPRISING THEREOF}

1 is a graph showing a large current and a low current discharge capacity of a battery while increasing the amount of amorphous carbon powder in a negative electrode according to an embodiment of the present invention.

Figure 2 is a graph showing the discharge power density and energy density of the battery while increasing the amount of amorphous carbon powder in the negative electrode according to an embodiment of the present invention.

Figure 3 is a graph showing the half-cell results of the artificial graphite powder and the amorphous carbon powder of the negative electrode active material used in the present invention.

The present invention relates to a negative electrode active material for a large capacity lithium secondary battery, and a large capacity lithium secondary battery including the same. More particularly, the present invention relates to a large capacity lithium secondary battery having an excellent output density and a markedly improved energy density.

Lithium secondary batteries have a high energy density advantage compared to conventional Ni / Cd batteries or Ni / MH batteries, and thus are mainly used as power sources for mobile phones and laptops.

Meanwhile, with the tightening regulations on automobile exhaust in the United States and Europe, the development of electric vehicles and the development of hybrid electric vehicles powered by internal combustion engines and batteries are accelerating, and some are in the commercialization stage. A secondary battery as an electric vehicle power source is required to obtain a high power and high energy density at the same time, a lithium secondary battery is attracting attention as a battery that can satisfy this.

Output characteristics are very important for lithium secondary batteries to be used as batteries for electric vehicles or hybrid electric vehicles. In addition, considering the mountability in the car, a high energy density is required to minimize the volume and weight of the battery.

In addition, a battery used in a conventional mobile phone or a notebook is a high energy density battery that supplies a small amount of power over a long time, while a hybrid electric vehicle requires a high power density battery that supplies a large amount of power in a short time. . Therefore, conventional lithium secondary batteries for small cellular phones cannot satisfy hybrid electric vehicles requiring high power density.

In the case of the conventional small lithium secondary battery, a battery was manufactured using a crystalline carbon-based compound such as natural graphite, artificial graphite (eg, lumps, spheres, etc.) as a negative electrode material. Such graphite compounds have a large discharge capacity of 310 to 350 mAh / g, small irreversible capacity, and flat voltage characteristics, and thus are widely used as materials for small lithium secondary batteries. However, since the charging and discharging characteristics of the large current are very bad, there is a problem that it is not suitable for use as a negative electrode material of a large capacity lithium secondary battery requiring high output.

On the other hand, the amorphous carbon-based compound has a very high discharge capacity of 280 to 450 mAh / g, but due to the large irreversible capacity, the initial efficiency is very low, such as 75 to 85%, which is not practical for small lithium secondary batteries. .

European Patent EP1052719A discloses a battery for a hybrid electric vehicle including an amorphous carbon compound, but has a problem in that energy density per unit volume of the battery is low due to the high irreversible capacity of the non-graphite carbon compound. In addition, there is a problem that the output that the battery can provide greatly changes depending on the state of charge of the battery.

Therefore, there is a need for further research on a large capacity lithium secondary battery that satisfies a high power density and a high energy density simultaneously.

In order to solve the above problems, an object of the present invention is to provide a negative electrode active material for a large capacity lithium secondary battery having a high output and a high energy density.

Another object of the present invention is to provide a large capacity lithium secondary battery having a high power and high energy density applicable to electric vehicles and hybrid electric vehicles by including the negative electrode active material in the negative electrode.

In order to achieve the above object, the present invention provides a negative electrode active material comprising a crystalline carbon-based compound and an amorphous carbon-based compound in the negative electrode active material for large capacity lithium secondary battery.

The present invention also provides an electrical device such as a large capacity lithium secondary battery including the negative electrode active material in the negative electrode.

Hereinafter, the present invention will be described in detail.

The present inventors studied a large-capacity lithium secondary battery having a high power and a high energy density, and replaced a part of the crystalline carbon compound used as an active material of the negative electrode with a certain ratio of amorphous carbon compound, resulting in high power density and high energy. It was confirmed that there is an excellent effect on the improvement of the energy density, the present invention was completed based on this.

The negative electrode active material for a large capacity lithium secondary battery of the present invention is characterized by including a crystalline carbon compound and an amorphous carbon compound. In another aspect, the present invention to provide a large capacity lithium secondary battery comprising the negative electrode active material as a negative electrode.

As the crystalline carbon compound used in the present invention, it is preferable to use a graphite crystalline carbon compound having a high crystallinity and an average particle diameter of 6 to 20 μm. Examples thereof include graphite-based crystalline carbon of natural graphite or artificial graphite having a high graphitization degree.

The amorphous carbon-based compound used in the present invention preferably has an average particle diameter of 8 to 25 ㎛, for example, amorphous carbon-based (hard carbon), cokes (cokes) or needle coke decomposed phenol resin or furan resin And carbonaceous amorphous carbon (soft carbon).

In the present invention, the crystalline carbon compound and the amorphous carbon compound are preferably mixed in a weight ratio of 80:20 to 20:80. More preferably, the content of the amorphous carbonaceous compound is 55 to 65% by weight of the negative electrode active material. If the content of the amorphous carbon-based compound is within the above range there is an advantage that can satisfy both the output density and the capacitance.

In another aspect, the present invention provides a large capacity lithium secondary battery comprising a negative electrode active material containing the crystalline carbon compound and the amorphous carbon compound.

In the large-capacity lithium secondary battery of the present invention, a positive electrode and a negative electrode in a thin film form are in close contact with each other with a separator therebetween, and a stacked electrode assembly wound in this close form is mounted inside the battery. As the battery exterior case, a laminated sheet of aluminum, which is conventionally used for a lithium polymer battery, is used.

The positive electrode may be prepared by applying and drying a slurry mixed with a positive electrode active material, a conductive material, and a binder on a current collector. The cathode active material may be a metal oxide, a metal sulfide, or a specific polymer compound, which is a material capable of reversibly charging and discharging lithium, and examples thereof include LiNiO ₂ , LiNiCoO ₂ , LiCoO ₂ , and LiMn ₂ O _4. , TiS ₂ , or MoS ₂ .

In addition, the negative electrode is a thin current collector (Cu foil, Ni foil, etc.) of a slurry mixed by adding a conductive material and a binder to a negative electrode active material for a large capacity lithium secondary battery including a crystalline carbon compound and an amorphous carbon compound. It can be prepared by applying and drying on the top.

Of course, the conductive material commonly used in secondary batteries may be used as the conductive material, and carbon black is particularly preferable. In addition, the binder may be used as a binder commonly used in secondary batteries, and preferably, polyvinylidene dechloride (PVDF) may be used.

The electrolyte of the large capacity lithium secondary battery of this invention melt | dissolves lithium salt in the organic solvent. The organic solvent may be N-methylpyrrolidone (NMP, N-methylpyrrolidone), ethylene carbonate (EC), propylene carbonate (PC), gamma-butylolactone (GBL), diethyl carbonate (DEC), or dimethyl carbonate ( A mixed solvent such as DMC) may be used, and lithium salt may be LiClO ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , CF ₃ SO ₃ Li, or the like.

In addition, the large-capacity lithium secondary battery of the present invention can be applied in a form in which a positive electrode and a negative electrode are stacked, and in a wound form.

The large-capacity lithium secondary battery according to the present invention has excellent battery characteristics satisfying both high power density and high energy density by using a mixture of the above crystalline carbon compound and amorphous carbon compound in an appropriate ratio.

Hereinafter, preferred examples are provided to help understanding of the present invention, but the following examples are merely to illustrate the present invention, and the scope of the present invention is not limited to the following examples.

EXAMPLE

Example 1

(Anode manufacturing)

Lithium manganese oxide (LiMn ₂ O ₄ ) with an average particle diameter of 20 µm capable of intercalation / deintercalation of lithium ions and carbon black and a polyvinylidene dichloride (PVDF) as a binder as an organic solvent A slurry was prepared by mixing with methylpyrrolidone (NMP). It was coated on an aluminum foil (Al foil) of 20 ㎛ thickness, dried and roll press (roll press) to a predetermined thickness to prepare a positive electrode.

(Cathode production)

The negative active material was mixed with artificial graphite powder having a high crystallization degree of spherical average particle diameter of 20 μm and pyrolyzed plate-shaped amorphous carbon powder having an average particle diameter of 10 μm in a weight ratio of 9: 1, and then added to an appropriate amount. Carbon black was added as a conductive agent. This mixed powder was mixed with polyvinylidene dichloride as a binder and N-methylpyrrolidone as an organic solvent to prepare a slurry. It was coated on a copper foil (Cu foil) of 10 ㎛ thickness, dried and roll press (roll press) to a predetermined thickness to prepare a negative electrode.

(Battery manufacturing)

Using a positive electrode and a negative electrode prepared above to produce a stacked battery of a constant size. At this time, 1M LiPF ₆ in EC / DMC (1: 1 by vol%) was used as the electrolyte.

Example 2

Except for mixing artificial graphite powder and amorphous carbon powder in a weight ratio of 8: 2 as a negative electrode active material in Example 1 was carried out in the same manner as in Example 1.

Example 3

Except for mixing artificial graphite powder and amorphous carbon powder in a weight ratio of 6: 4 as a negative electrode active material in Example 1 was carried out in the same manner as in Example 1.

Example 4

Except that the artificial graphite powder and the amorphous carbon powder as a negative electrode active material in Example 1 was mixed in a weight ratio of 4: 6 was carried out in the same manner as in Example 1.

Example 5

Except for mixing artificial graphite powder and amorphous carbon powder in a weight ratio of 2: 8 as the negative electrode active material in Example 1 was carried out in the same manner as in Example 1.

Comparative Example 1

Except for using only artificial graphite powder having an average particle diameter of 20 ㎛ as the negative electrode active material in Example 1 was carried out in the same manner as in Example 1.

Comparative Example 2

Except that in Example 1, only the thermally decomposed amorphous carbon powder having an average particle diameter of 8 ㎛ as a negative electrode active material was carried out in the same manner as in Example 1.

Experimental Example 1. Discharge Capacity

The discharge capacity of the battery was evaluated by varying the amount of current density of 0.5 C to 30 C from 4.2 V to 2.5 V using the batteries prepared in Examples 1 to 5 and Comparative Examples 1 or 2. Table 1 and FIG. 1.

division Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 Mixing ratio (weight ratio) 10: 0 9: 1 8: 2 6: 4 4: 6 2: 8 0:10 Initial Efficiency (%) 90.5 89.2 88.5 86.1 83.8 83.2 82.0 Discharge Capacity at 3A (1C) Discharge (Ah) 3.50 3.43 3.37 3.25 3.02 2.93 2.78 Discharge Capacity at 60A (20C) Discharge (Ah) 1.19 1.28 1.36 1.47 1.67 1.84 1.45

Through the above Table 1, the battery of Examples 1 to 5 including the artificial graphite powder and the amorphous carbon powder according to the present invention is increased compared to the battery of Comparative Example 1 using only the artificial graphite powder as the content of the amorphous carbon powder increases It can be seen that the capacity during discharge increases.

As shown in FIG. 1, the smaller the difference between the discharge capacity at the time of high current discharge and the discharge capacity at the time of low current discharge, the better the battery performance for the hybrid electric vehicle is, thereby greatly improving the performance of the battery through substitution of amorphous carbon. You can. In addition, it can be seen that the battery of Examples 1 to 5 according to the present invention has excellent high current discharge characteristics compared to the battery of Comparative Example 2 using only amorphous carbon powder.

Experimental Example 2. Power Density and Energy Density

In the state of charging the battery prepared in Examples 1 to 5, and Comparative Examples 1 or 2 to 50% charged by applying a discharge current pulse of 10 C for 10 seconds, the results are shown in Table 2, and Figure 2 Shown in

division Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 Mixing ratio (weight ratio) 10: 0 9: 1 8: 2 6: 4 4: 6 2: 8 0:10 Discharge output density (W / ㎏) 2,000 2,135 2,409 2,527 2,782 2,674 2,563 Charge output density (W / ㎏) 1,090 1,227 1,381 1,753 1,860 1,813 1,747 Energy Density Per Weight (Wh / ㎏) 84 83 82 80 79 74 71

Through Table 2, the battery of Examples 1 to 5 including the artificial graphite powder and the amorphous carbon powder according to the present invention improved the discharge output by more than 30% compared to Comparative Example 1 using only artificial graphite powder, Increased by more than 80%.

FIG. 2 is a diagram illustrating power density and energy density by substituting an amorphous carbon compound for an artificial graphite compound. When the amount of substitution of the amorphous carbonaceous compound was less than 20% with respect to the artificial graphite, the effect of improving the power density of the battery was insignificant. When the amount of substitution of the amorphous carbonaceous compound was 80% or more, the irreversible capacity of the battery was increased to increase the energy density Since greatly reduced, the content ratio of the artificial graphite and the amorphous carbon-based compound was found to be in the range of 80:20 ~ 20:80.

Example 6

In Example 1, artificial graphite powder having a high crystallization degree of spherical average particle diameter of 6 μm and pyrolyzed flake amorphous carbon powder having an average particle diameter of 22 μm were mixed at a weight ratio of 9: 1. Except that was carried out in the same manner as in Example 1.

Example 7

Example 6 was carried out in the same manner as in Example 6, except that artificial graphite powder and amorphous carbon powder were mixed at a weight ratio of 8: 2 as the negative electrode active material.

Example 8

Example 6 was carried out in the same manner as in Example 6, except that artificial graphite powder and amorphous carbon powder were mixed at a weight ratio of 6: 4 as the negative electrode active material.

Example 9

Example 6 was carried out in the same manner as in Example 6, except that artificial graphite powder and amorphous carbon powder were mixed at a weight ratio of 4: 6 as the negative electrode active material.

Example 10

Example 6 was carried out in the same manner as in Example 6, except that artificial graphite powder and amorphous carbon powder were mixed at a weight ratio of 2: 8 as the negative electrode active material.

Comparative Example 3

The same process as in Example 6 was carried out except that only artificial graphite powder having an average particle diameter of 6 μm was used as the anode active material in Example 6.

Comparative Example 4

Example 6 was carried out in the same manner as in Example 6, except that only the thermally decomposed amorphous carbon powder having an average particle diameter of 22 ㎛ as the negative electrode active material.

Experimental Example 3

The discharge capacity, the output density, and the energy density of the batteries prepared in Examples 6 to 10 and Comparative Examples 3 or 4 were measured in the same manner as in Experimental Example 1 or Experimental Example 2, and the results were measured. It is shown in Table 3 below.

division Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 Mixing ratio (weight ratio) 10: 0 9: 1 8: 2 6: 4 4: 6 2: 8 0:10 Discharge capacity 3.48 3.41 3.36 3.23 3.15 2.97 2.78 Discharge output density (W / ㎏) 2,181 2,267 2,379 2,450 2,395 2,313 2,250 Charge output density (W / ㎏) 1,453 1,545 1,754 1,869 2,103 2,065 1,953 Energy Density Per Weight (Wh / ㎏) 83 82 81 79 77 75 71

Through Table 3, the output density of the battery is improved up to 60% of the content of the amorphous carbon powder in the battery, but at 60% or more, the capacity of the battery is reduced due to the increase of the content of the amorphous carbon powder, and more than 80% In the battery, the capacity decrease of the battery was much greater, and it was found that the content of the amorphous carbonaceous compound in the battery was more preferably at most 80%.

In addition, through Comparative Example 1 and Comparative Example 3, it was found that when the average particle diameter of the artificial graphite used for the negative electrode is reduced from 20 μm to 6 μm, the power density of the battery is improved by 10% or more.

From the above results, the high-capacity lithium secondary battery including the artificial graphite powder and the amorphous carbon powder in a ratio of 80:20 to 20:80 according to the present invention repeats many charge and discharge cycles under high current conditions for a short time like a hybrid vehicle. It was found that a battery suitable for the system can be provided.

Experimental Example 4

Half cell experiments were performed using the artificial graphite powder and the amorphous carbon powder used in Example 1, and the results are shown in FIG. 3.

As shown in FIG. 3, the initial efficiency of the artificial graphite powder was about 91%, and the discharge capacity was 310 mAh / g. In addition, the discharge capacity of the amorphous carbon powder was about 370 mAh / g or more, higher than the artificial graphite powder, the initial efficiency was about 82% was found to be much lower than the artificial graphite powder.

According to the present invention, a large-capacity lithium secondary battery including a negative active material including a crystalline carbon compound and an amorphous carbon compound has an effect of having excellent battery characteristics satisfying both high power density and high energy density.

Claims (6)

In the negative electrode active material for large capacity lithium secondary battery, 40 to 45% by weight of a spherical crystalline carbonaceous compound selected from natural graphite or artificial graphite, having an average particle diameter of 6 to 20 μm, and From an average particle diameter of 8 to 25 ㎛, from the group consisting of amorphous carbon-based (hard carbon) and cokes (pykes) or pyrolysis of phenol resin or furan resin, or amorphous carbon (soft carbon) carbonized needle coke A negative electrode active material comprising 55 to 60% by weight of at least one flake amorphous amorphous carbon compound. delete delete delete A large capacity lithium secondary battery comprising the negative electrode active material of claim 1. The method of claim 5, The lithium secondary battery is a large capacity lithium secondary battery, characterized in that for electric vehicles.

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