KR19990030823A - Anode active material for lithium ion secondary battery, negative electrode plate and lithium ion secondary battery manufactured using same - Google Patents

Abstract

The present invention is to provide a negative electrode active material, a negative electrode plate and a lithium ion secondary battery prepared using the carbon material for the lithium ion secondary battery with increased packing density, conductivity and capacity of the negative electrode plate, 90 to 50% by weight of the radial graphite carbon It provides a negative electrode active material comprising a fiber and 10 to 50% by weight of graphite-based carbon particles, which is prepared by mixing the negative electrode active material with a binder in a solvent to prepare a negative electrode active material slurry, which is applied to a negative electrode current collector and dried Provided is a negative electrode plate, and a lithium ion secondary battery assembled by using the negative electrode plate, a known positive electrode plate, a non-aqueous electrolyte, a separator, and the like.

Description

Anode active material for lithium ion secondary battery, negative electrode plate and lithium ion secondary battery manufactured using same

Industrial use field

The present invention relates to a negative electrode active material for a lithium ion secondary battery, a negative electrode plate and a lithium ion secondary battery prepared using the same, and more particularly radial type graphite carbon fibers and graphite carbon particles. It relates to a negative electrode active material, a negative electrode plate and a lithium ion secondary battery prepared using the composite.

Prior art

As the negative electrode active material for a lithium ion secondary battery, crystalline carbon or amorphous carbon is mainly used. Crystalline carbon such as graphite has a disadvantage of excellent dislocation flatness but low discharge capacity, and amorphous carbon such as cokes shows high discharge capacity but has a disadvantage of poor dislocation flatness. Recently, in the technical field, crystalline carbon having a small irreversible capacity is preferred to amorphous carbon.

The crystalline carbon anode active material represented by graphite may be classified into a fiber type, a spherical type, a particle type, and the like according to its shape. The graphite carbon fibers include isotropic pitch-based carbon fibers and anisotropic pitch-based carbon fibers. As the anisotropic pitch-based carbon fiber, as shown in Figure 6, isotropic type (radial type), radial (radial type), onion type (onion type), random 1 type (random 1 type) and random 2 type ( random 2 type).

In the case of manufacturing the negative electrode plate using the crystalline carbon negative electrode active material, generally, only one type has been selected to manufacture the negative electrode plate. However, in this case, since the negative electrode active material having the same shape is used, there is a limit in improving the packing density and increasing the capacity of the electrode plate. In order to solve this problem, US Pat. No. 5,273,842 classifies the particle size distribution of the negative electrode active material to be a grading distribution and applies it to the preparation of the negative electrode plate. However, in this case, there are many problems such as a large amount of consumption of the negative electrode active material and a long production time of the negative electrode active material.

Japanese Patent Laid-Open No. 5-283061 discloses a negative electrode prepared by mixing a small amount of isotropic pitch-based carbon fibers with carbon particles having an average particle diameter of about 20 μm. However, in this case, the structure of the negative electrode is bulky, so the diffusion of the electrolyte is easy and the charge and discharge reaction is easy. However, since the packing density of the electrode cannot be increased, the capacity of the electrode is reduced, and Since the contact area is reduced, the contact resistance is increased, resulting in a problem in that the current collector and the negative electrode active material are detached during continuous charge / discharge of the battery. In addition, when the negative electrode is applied to a battery, since the negative electrode uses isotropic pitch-based carbon fibers, intercalation and deintercalation of lithium ions is inefficient. Therefore, the capacity of the battery is also limited.

In order to solve the above problems, an object of the present invention is to increase the packing density and capacity of the negative electrode and to increase the contact area with the current collector, the negative electrode plate and lithium prepared using the negative electrode active material This is to provide an ion secondary battery.

1 is a SEM photograph of a negative electrode plate manufactured according to an embodiment of the present invention and a schematic view thereof.

Figure 2 is a SEM photograph of a negative electrode plate prepared according to a comparative example of the present invention and a schematic view thereof.

Figure 3 is a graph showing the specific resistance according to the graphite-based carbon fiber content in the negative electrode plate according to an embodiment and a comparative example of the present invention.

Figure 4 is a graph showing the discharge characteristics of the coin-type lithium ion secondary battery prepared according to an embodiment and a comparative example of the present invention.

5 is a cross-sectional view schematically showing a coin-type lithium ion secondary battery prepared according to an embodiment of the present invention.

6 is a cross-sectional view of the anisotropic pitch-based carbon fibers.

* Explanation of symbols for the main parts of the drawings *

1: Current collector for positive electrode 1 ': Current collector for negative electrode 5: Can

10: positive electrode active material or lithium metal 15: electrolyte 20: gasket

25 separator 30 negative electrode active material 35 cap

Means to solve the problem

In order to achieve the above object of the present invention, the present invention provides a negative electrode active material for a lithium ion secondary battery comprising 90 to 50% by weight graphite carbon fiber and 10 to 50% by weight graphite carbon particles. In addition, the present invention is a negative electrode plate prepared using the negative electrode active material, a lithium active material comprising a negative electrode active material and a binder containing 90 to 50% by weight of graphite-based carbon fibers and 10 to 50% by weight of graphite-based carbon particles Provided is a negative electrode plate for an ion secondary battery and a lithium ion secondary battery produced using the negative electrode active material of the present invention described above.

Referring to the present invention in more detail as follows.

The negative electrode active material of the present invention described above comprises 90 to 50% by weight graphite carbon fiber and 10 to 50% by weight graphite carbon particles.

It is preferable that the graphite carbon fiber of the negative electrode active material of the present invention is a radial type graphite carbon fiber. The radial graphite carbon fiber has an edge surface of the graphite plate facing outward, so that the intercalation and deintercalation of lithium ions during charge and discharge are easy, thereby achieving a high capacity battery. .

The graphite carbon fiber preferably has a diameter of 5 to 30 µm and an aspect ratio of 5 to 100. Carbon fibers having a value smaller than the above diameter range or aspect ratio have a large specific surface area and thus have a disadvantage of high self discharge rate. Carbon fibers having a value larger than the above range have a low filling density and thus have a low capacity. In addition, when the battery is manufactured, there is a risk of short circuiting because carbon fibers pass through the separator. More preferred graphite carbon fibers used in the present invention are those having a diameter of 10 to 20 µm and a aspect ratio of 10 to 50.

The graphite carbon particles preferably have a particle diameter of 3 to 10 µm. Carbon particles having a value larger than the particle size range cannot fill the voids generated by the toughness of the carbon fiber, so that the packing density cannot be increased. Carbon particles having a particle size smaller than the above range have a large specific surface area, which causes side reaction with the electrolyte. Big. In the present invention, more preferably graphite-based carbon particles having a particle diameter of 3 to 7 µm are used. It is preferable that the said graphite carbon particle has a specific resistance of 0.1-2 Pa.cm. More preferably, graphite-based carbon particles having a specific resistance of 0.2 to 1 Pa · cm are used. Since the graphite carbon particles have a small specific resistance and are fine, the electrical conductivity is high and the charge and discharge efficiency of the battery can be improved.

The negative electrode plate of the present invention is prepared as follows.

The negative electrode active material of the present invention is mixed with a binder such as polyvinylidene fluoride in an organic solvent such as N-methyl-2-pyrrolidone to prepare a slurry for the negative electrode, and the slurry is used for negative electrode collection such as a copper substrate. A negative electrode plate is manufactured by apply | coating to all and drying. As shown in FIG. 1, the negative electrode plate increases the filling density and the negative electrode plate capacity by filling the space between the graphite carbon fibers with the graphite carbon particles. In addition, as the contact surface of the negative electrode active material and the current collector increases, the contact resistance decreases, thereby solving the problem of detachment of the current collector and the negative electrode active material frequently generated during continuous charge and discharge.

A person skilled in the art can easily manufacture a lithium ion secondary battery using a negative electrode plate prepared by using the negative electrode active material of the present invention and a known positive electrode plate, a separator, an electrolyte, and the like according to a known method of manufacturing a lithium ion secondary battery. You can do it. Preferred positive electrode active material of the lithium ion secondary battery is a lithium transition metal oxide having a chemical formula of LiNi _x CO _1-x O ₂ (x is 0.1 to 0.9), more preferably LiNi _x CO _1-x O ₂ (x Is 0.5 to 0.8). Lithium electrolyte of the ion secondary battery of the present invention the non-aqueous electrolytic solution obtained by dissolving lithium salts such as LiPF _6, LiBF ₄ to the ethylene carbonate is preferred. In addition, ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, gamma-butyrolactone, sulfolane, 1,3-dioxalane, 2-methylfuran, tetrahydrofuran, 1 A non-aqueous electrolyte solution in which a lithium salt such as LiPF ₆ or LiBF ₄ is mixed with a solution in which one or two or more substances selected from the group consisting of, 2-dimethoxyethane and diethoxyethane are mixed is used.

The following presents a preferred embodiment to aid the understanding of the present invention. However, the following examples are merely provided to more easily understand the present invention, and the present invention is not limited to the following examples.

Example 1

1. Preparation of Radial Graphite Carbon Fiber

Primary quinoline insoluble (QI) was removed from the coal tar pitch. Since the raw pitch is mixed with a large variety of compounds, it does not remove very large molecular weights called primary QIs, and because the melting point is high, it cannot be spun into fibers and later mesophase content of the pitch. And organization is out of control. The pitch from which the primary QI was removed was heat-treated at a temperature of 430 ° C. under a nitrogen atmosphere to form anisotropic bulk mesophase, which was then spun in the form of carbon fiber. Thereafter, the spun fiber was heat-treated at 350 ° C. under a general atmospheric atmosphere to remove the molten component to maintain an oxidative stabilization process. In other words, oxygen is introduced into the pitch-based carbon fiber through an oxidation stabilization process to combine with hydrogen and desorption, resulting in condensation polycyclic reaction to remove molten components, thereby maintaining the shape of the fiber during carbonization. After pulverization, the mixture was left to carbonize at 900 to 1400 ° C. for 1 hour and then graphitized by being left at 2500 to 3000 ° C. for 30 minutes.

2. Preparation of Graphite Carbon Particles

After removing the first QI (quinoline insoluble) from the coal tar pitch, the pitch was heat-treated at a temperature of 430 ° C. under a nitrogen atmosphere to make anisotropic bulk mesophase, and then oxidized at 350 ° C. After stabilization, the mixture was ground and carbonized by standing at 900 to 1300 ° C. for 1 hour, and graphitized by being left at 2500 to 3000 ° C. for 30 minutes.

3. Preparation of composite negative electrode active material and negative electrode plate

Roll-mixing was performed for 1 hour at a mixing weight ratio of the prepared radial graphite carbon fiber and graphite carbon particles of 90:10. The roll-mixing process refers to mixing the carbon particles and the carbon fibers in a polyethylene bag and then mixing them with metal rolls for better mixing because they are not mixed well due to the difference in the apparent density of the carbon fibers and the carbon particles. The roll-mixed mixture was vacuum dried at 200 ° C. for 24 hours. The vacuum drying step is a step for removing moisture that may be adsorbed on the surface of these active materials. In fact, the roll-mixing step and the vacuum drying step may not be performed. This is because the negative electrode active material is mixed with N-methyl-2-pyrrolidone in the form of a slurry during the production of the electrode plate, and dried and cured after the production of the electrode plate to remove naturally adsorbed moisture.

Following the vacuum drying process, the vacuum was dissolved in a solution in which 10 g of poly vinylidene fluoride, a binder, was dissolved per 90 g of an organic solvent, N-methyl-2-pyrollidone. A slurry was prepared by mixing the mixed negative electrode active material of the dried carbon fiber and carbon particles. The slurry was applied to an 18 μm thick copper substrate current collector, followed by vacuum drying at 100 ° C. for 30 minutes. The vacuum dried negative electrode plate was roll-pressed at a linear pressure of 30 kg _f / cm and then cut into a 16 mm diameter disc.

4. 2016 type coin battery assembly

The assembly of a lithium ion battery according to the present invention will be described with reference to FIG. 5. The prepared negative electrode plates 1 'and 30 were welded to a can 5 made of stainless steel, and welded perforated nickel 1 as a current collector of lithium metal as a positive electrode. . Since the battery was assembled in the dry box maintained in the argon atmosphere as follows. The anode lithium metal 10 was rolled to a thickness of 160 μm and pressed to a nickel welded cap, and then an insulating gasket 20 was inserted. As the electrolyte solution 15, a mixture in which 1 M LiPF ₆ was added to ethylene carbonate / dimethylene carbonate (1 vol / 1 vol) was used. As the separator 25, a polypropylene-based porous polymer was used.

Example 2

In the negative electrode plate production of Example 1 was carried out in the same manner as in Example 1, except that the weight ratio of the radial graphite carbon fiber and the graphite-based carbon particles to 50:50.

Example 3

Example 1 was carried out in the same manner as in Example 1 except that aluminum foil was used as the positive electrode current collector and LiNi _x CO _1-x O ₂ (x is 0.1 to 0.9) as the positive electrode.

Example 4

Example 2 was carried out in the same manner as in Example 2 except that aluminum foil was used as the positive electrode current collector and LiNi _x CO _1-x O ₂ (x is 0.5 to 0.8) was used as the positive electrode.

Example 5

Except for using LiNi _x CO _1-x O ₂ (x is 0.5 to 0.8) as the positive electrode in Example 3 was carried out in the same manner as in Example 3.

Comparative Example 1

1. Preparation of Radial Graphite Carbon Fiber

After removal of the first QI (quinoline insoluble) from the coal tar pitch, the pitch was heat-treated at a temperature of 430 ° C. under a nitrogen atmosphere to make anisotropic bulk mesophase and spun in carbon fiber form. I was. Thereafter, oxidation was stabilized at 350 ° C., followed by pulverization, and left at 900 to 1400 ° C. for 1 hour for carbonization, followed by graphitization by leaving at 2500 to 3000 ° C. for 30 minutes.

2. Negative plate manufacturing

The prepared carbon fiber was mixed with a slurry in which 10 g of polyvinylidene fluoride, a binder, per 90 g of N-methyl-2-pyrollidone, which is an organic solvent, was dissolved in a slurry. Was prepared. The slurry was applied to an 18 μm thick copper substrate current collector, followed by vacuum drying at 100 ° C. for 30 minutes. The vacuum dried negative electrode plate was roll-pressed at a linear pressure of 30 kg _f / cm and then cut into a 16 mm diameter disc.

3. 2016 type coin battery assembly

The prepared negative electrode plate was welded to a stainless steel can and welded perforated nickel as a current collector of lithium metal as a positive electrode. Since the battery was assembled in the dry box maintained in the argon atmosphere as follows. A lithium metal as a positive electrode was rolled to a thickness of 160 μm, pressed into a nickel-welded cap, and then sandwiched an insulating gasket. As the electrolyte, a mixture of 1 M LiPF ₆ added to ethylene carbonate / dimethylene carbonate (1 vol / 1 vol) was used, and a polypropylene-based porous polymer was used as the separator.

Comparative Example 2

1. Preparation of Radial Graphite Carbon Fiber

After removal of the first QI (quinoline insoluble) from the coal tar pitch, the pitch was heat-treated at a temperature of 430 ° C. under a nitrogen atmosphere to make anisotropic bulk mesophase and spun in carbon fiber form. I was. Thereafter, oxidation was stabilized at 350 ° C., followed by pulverization, and left at 900 to 1400 ° C. for 1 hour for carbonization, followed by graphitization by leaving at 2500 to 3000 ° C. for 30 minutes.

2. Preparation of Graphite Carbon Particles

After removing the first QI (quinoline insoluble) from the coal tar pitch, the pitch was heat-treated at a temperature of 430 ° C. under a nitrogen atmosphere to make anisotropic bulk mesophase, and then oxidized at 350 ° C. After stabilization, the mixture was ground and carbonized by standing at 900 to 1300 ° C. for 1 hour, and graphitized by being left at 2500 to 3000 ° C. for 30 minutes.

3. Preparation of composite negative electrode active material and negative electrode plate

After the roll-mixing for 1 hour at a mixture weight ratio of the prepared radial graphite carbon fiber and the graphite carbon particles at 10:90, vacuum drying was performed at 200 ° C. for 24 hours. The vacuum-dried carbon fiber and carbon particles in a solution in which 10 g of poly vinylidene fluoride, a binder, was dissolved per 90 g of N-methyl-2-pyrollidone, an organic solvent. The negative electrode active material was mixed to prepare a slurry. The slurry was applied to an 18 μm thick copper substrate current collector, followed by vacuum drying at 100 ° C. for 30 minutes. The vacuum dried negative electrode plate was roll-pressed at a linear pressure of 30 kg _f / cm and then cut into a 16 mm diameter disc.

4. 2016 type coin battery assembly

The prepared negative electrode plate was welded to a stainless steel can and welded perforated nickel as a current collector of lithium metal as a positive electrode. Since the battery was assembled in the dry box maintained in the argon atmosphere as follows. A lithium metal as a positive electrode was rolled to a thickness of 160 μm, pressed into a nickel-welded cap, and then sandwiched an insulating gasket. As the electrolyte, a mixture of 1 M LiPF ₆ added to ethylene carbonate / dimethylene carbonate (1 vol / 1 vol) was used, and a polypropylene-based porous polymer was used as the separator.

Comparative Example 3

1. Preparation of Graphite Carbon Particles

After removing the first QI (quinoline insoluble) from the coal tar pitch, the pitch was heat-treated at a temperature of 430 ° C. under a nitrogen atmosphere to make anisotropic bulk mesophase, and then oxidized at 350 ° C. After stabilization, the mixture was ground and carbonized by standing at 900 to 1300 ° C. for 1 hour, and graphitized by being left at 2500 to 3000 ° C. for 30 minutes.

2. Negative plate manufacturing

The prepared carbon particles were mixed in a slurry in which 10 g of polyvinylidene fluoride, a binder, per 90 g of N-methyl-2-pyrollidone, which is an organic solvent, was dissolved. Was prepared. The slurry was applied to an 18 μm thick copper substrate current collector, followed by vacuum drying at 100 ° C. for 30 minutes. The vacuum dried negative electrode plate was roll-pressed at a linear pressure of 30 kg _f / cm and then cut into a 16 mm diameter disc.

3. 2016 type coin battery assembly

The prepared negative electrode plate was welded to a stainless steel can and welded perforated nickel as a current collector of lithium metal as a positive electrode. Since the battery was assembled in the dry box maintained in the argon atmosphere as follows. A lithium metal as a positive electrode was rolled to a thickness of 160 μm, pressed into a nickel-welded cap, and then sandwiched an insulating gasket. As the electrolyte, a mixture of 1 M LiPF ₆ added to ethylene carbonate / dimethylene carbonate (1 vol / 1 vol) was used, and a polypropylene-based porous polymer was used as the separator.

SEM pictures of the negative electrode plates prepared in Example 1 and Comparative Example 1 and a schematic view thereof are shown in FIGS. 1 and 2, respectively. It can be seen that Example 1 (FIG. 1) is superior in packing density of the electrode plate compared to Comparative Example 1 (FIG. 2). Therefore, in Example 1, since the contact area between the current collector and the negative electrode active material is large and the resistivity value is small, the problem of detachment of the current collector and the negative electrode active material during charge and discharge is solved.

The resistivity of the negative electrode plates prepared in Examples and Comparative Examples was measured and shown in FIG. 3. As shown in FIG. 3, the higher the content of carbon fiber and the smaller the content of carbon particles, the greater the specific resistance. Since Examples 1 and 2 have a smaller resistivity compared with Comparative Example 1, the electrical conductivity and the charge and discharge efficiency are excellent. In the case of Comparative Example 3, only the carbon particles are used, whereby the specific resistance value is small and the electrical conductivity is excellent, but the occurrence of side reactions causes the charge and discharge efficiency of the battery to be lowered.

Using the battery of Example 1 and Comparative Example 1 described above, 3 cycles at 0.2C, 1 cycle at 0.5C, 1 cycle at 1C, 2 cycles at 1.5C, 3 cycles at 2C, 2 cycles at 0.5C, The results are shown in FIG. As shown in FIG. 4, the battery of Example 1 has a larger initial discharge capacity and excellent high rate charge / discharge characteristics and cycle characteristics than the battery of Comparative Example 1.

The characteristics of the negative electrode plate and the battery prepared in Example 1 and Comparative Example 1 are shown in Table 1 below. The capacity of the battery was measured by charging and discharging at 0.2 C, and the initial efficiency was calculated as a percentage of the initial discharge capacity with respect to the initial charge capacity. In addition, initial discharge capacity was described as reversible capacity.

Negative plate density Initial efficiency Reversible capacity Resistivity Example 1 1.65 g / cm 3 93.5% 320㎃h / g 1.291 Ωcm Comparative Example 1 1.44 g / cm 3 92.4% 297㎃h / g 2.007Ω · cm

As shown in Table 1, Example 1 has a high density of the negative electrode plate and a small specific resistance value. In addition, Example 1 has a larger reversible capacity and initial efficiency, that is, charge and discharge efficiency than Comparative Example 1.

As described above, the present invention provides a negative electrode plate prepared by using a negative electrode active material in which 90 to 50% by weight of graphite-based carbon fibers and 10 to 50% by weight of graphite-based carbon particles are composited. Silver filling density and capacity are increased, and the lithium ion secondary battery manufactured using the negative electrode active material has high capacity, excellent charge and discharge efficiency, and cycle life characteristics.

Claims (7)

90 to 50 wt% graphite carbon fiber; And A negative electrode active material for lithium ion secondary batteries containing 10 to 50% by weight of graphite-based carbon particles. The negative active material of claim 1, wherein the carbon fiber is a radial type graphite carbon fiber. The negative active material of claim 1, wherein the graphite carbon fiber has a diameter of 5 to 30 μm and an aspect ratio of 5 to 100. The negative active material of claim 1, wherein the graphite carbon particles have a particle diameter of 3 to 10 μm. The negative electrode active material of claim 1, wherein the graphite carbon particles have a specific resistance of 0.1 to 2 Pa · cm. A current collector; A negative electrode active material including 90 to 50 wt% graphite carbon fiber and 10 to 50 wt% graphite carbon particles; And A negative electrode plate for a lithium ion secondary battery comprising a binder. The lithium ion secondary battery manufactured using the negative electrode active material in any one of Claims 1-5.