KR102169929B1 - Composite material for anode active material of lithium secondary battery, and manufacturing method of the composite material - Google Patents

Abstract

It is an object of the present invention to prepare a negative electrode material for a lithium ion battery having excellent capacity and stability by coating petroleum pitches having various softening points on the surface of artificial graphite. The composite material prepared as described above can be manufactured as an excellent anode material for secondary batteries through various heat treatment processes.

Description

Composite material for anode active material of lithium secondary battery, and manufacturing method of the composite material}

The present invention relates to a secondary battery negative electrode active material composite material, and a method of manufacturing the same.

Lithium ion batteries (LIBs) are widely used in energy-intensive portable devices such as smart phones, laptops, and other electronic devices, and as people's living standards increase, the invention of energy storage devices is also actively progressing. . High energy density and stability of cycle life are important factors in lithium-ion batteries. High energy density indicates that it can provide more capacity per unit mass or volume, and long cycle life means structural stability such as cathode/anode active material and solid-fluid interface, and these properties are Can be improved by

Because of its excellent performance such as low operating potential, structural stability, reasonable cost, and good cycle life, Graphite has been the most widely used in small rechargeable batteries as a standard anode material in lithium-ion cells over the past 20 years. However, when charging at a high rate, stability problems due to volume expansion occur, and significant irreversible capacity loss occurs due to the non-uniform SEI (Solid Electrolyte Interface) layer generated after the initial cycle, resulting in collapse of the electrode and cycle instability. do. These problems cause a loss of capacity of the graphite negative electrode material due to prolonged charging and discharging, and a wide range of inventions to solve this problem are in progress.

Among the types of graphite, natural graphite is limitedly buried all over the world and exhibits a high capacity, but its lifespan is deteriorated during the charging and discharging process, so its practical use is limited. On the other hand, in the case of synthetic graphite, it is mainly produced from petroleum coke as an electrode for petroleum refining and electric discharge processing. In addition, the capacity is somewhat lower than that of natural graphite, but it has excellent life characteristics. In the secondary battery anode market, where natural graphite was recently used, artificial graphite has improved its high power and life characteristics as well as high capacity characteristics, thereby increasing its utility. Accordingly, in order to improve the performance of artificial graphite as a negative electrode material, an invention of modifying the surface by introducing a carbon composite, an ionic functional group, and a metal oxide is in progress.

It is an object of the present invention to prepare a negative electrode material for a lithium ion battery having excellent capacity and stability by coating petroleum pitches having various softening points on the surface of artificial graphite. The composite material prepared as described above can be manufactured as an excellent anode material for secondary batteries through various heat treatment processes.

In order to achieve the object of the present invention as described above,

A secondary battery negative active material composite material according to various embodiments of the present invention includes graphite; And the graphite may be coated with a coating material including any one of a petrolysis fuel oil pitch, a coal tar pitch, and coke.

The graphite is characterized in that any one selected from the group consisting of natural graphite, artificial graphite, soft carbon, and hard carbon.

The particle diameter of the graphite is characterized in that 10 ㎛ to 25 ㎛.

The softening point of the coal-based pitch is characterized in that 150 ℃ to 250 ℃.

The coating material is characterized in that it has two DTA exothermic peaks in the temperature range of 400 ℃ to 700 ℃.

A method of manufacturing a composite material for a negative electrode active material for a secondary battery according to various embodiments of the present invention includes: preparing a petroleum pitch by heat treating a petroleum-based residual oil; Mixing the petroleum pitch and the artificial graphite to prepare artificial graphite coated with the petroleum pitch; And heat-treating the coated artificial graphite.

The petroleum-based residual oil includes at least one of PFO (Pyrolysis Fuel Oil), which is a naphtha cracking process residual oil, and FCC-DO (Fluidized Catalytic Cracking Decant Oil), which is a fluidized bed catalytic cracking process residual oil,

In the step of preparing the petroleum pitch,

It characterized in that it comprises the step of preparing a carbon precursor by heat-treating the petroleum-based residual oil at 300 °C or higher for 1 hour to 5 hours.

The artificial graphite has a particle diameter of 10 to 25 ㎛, and the thickness of the artificial graphite coated with the petroleum pitch is 50 ㎚ to 1000 ㎚.

In the step of preparing the artificial graphite coated with the petroleum pitch,

After dispersing 5 to 15 weight ratio of petroleum pitch using at least one organic solvent selected from the group consisting of hexane, toluene, tetrahydrofuran, and quinoline, artificial graphite in an 85 to 95 weight ratio was added to 12 It is characterized by stirring for hours to 24 hours.

In the step of heat treating the coated artificial graphite,

It is characterized by firing for 1 to 2 hours at a temperature of 800 ℃ to 1000 ℃ in an inert atmosphere.

In the step of heat treating the coated artificial graphite,

Performing a first heat treatment for 30 minutes to 1 hour at a temperature of 400° C. to 800° C. in an inert atmosphere, depending on the softening point of the petroleum pitch; And

It characterized in that it comprises a second heat treatment step of heat treatment at a temperature of 800 ℃ to 1000 ℃ after the step of the first heat treatment.

A method of manufacturing a negative electrode for a secondary battery according to various embodiments of the present disclosure includes the steps of applying a slurry for manufacturing a negative electrode in which a composite material for a negative electrode active material for a secondary battery, a binder, and a conductive material are mixed, on a current collector; And rolling.

The negative electrode composite material manufactured using pitch obtained through low-cost petroleum residue heat treatment has excellent cycle stability and battery capacity compared to the negative electrode material made of artificial graphite not coated with petroleum pitch. By using an inexpensive pitch carbon material with high stability, it is possible to mitigate volume expansion, a disadvantage of graphite.

1 is a schematic diagram of manufacturing a composite material of graphite coated with a pitch prepared in Examples.
2 is a TGA analysis result of the pitch used in the examples.
3 is a SEM analysis result of graphite coated with pitches of various softening points in Examples.
4 is an SEM analysis result of pitch-coated graphite according to carbonization temperature in Examples.
5 is a result of analyzing charging and discharging of graphite coated with a pitch according to carbonization temperature in Examples.

Hereinafter, various embodiments of the present document will be described with reference to the accompanying drawings. The examples and terms used therein are not intended to limit the technology described in this document to a specific embodiment, and should be understood to include various modifications, equivalents, and/or substitutes of the corresponding embodiments.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Hereinafter, the present invention will be described in more detail.

The present invention relates to a secondary battery negative electrode active material composite material having increased capacity and stability as a negative electrode material for a lithium ion battery.

A secondary battery negative active material composite material according to various embodiments of the present invention includes graphite; And it may include a coating material coated on the graphite.

The coating material may include any one of Pyrolysis Fuel Oil Pitch, Coal Tar Pitch, and Cokes. When the coating material is coke, a higher capacity than the theoretical capacity of graphite can be obtained, and Li ions are rapidly diffused by a small crystal size and a wide layer distance of coke, enabling rapid charging and discharging. In addition, in the case of coating using a pitch such as coal-based pitch or petroleum-based pitch, the surface area decreases, so graphite coated with carbon extracted with the pitch exhibits less irreversible capacity and relatively large Coulomb efficiency.

Therefore, preferably, the coating material may be a petroleum pitch. In this case, the petroleum pitch may have a softening point of 150° C. to 250° C. For example, petroleum pitch may have softening points of 150°C, 200°C and 250°C. In the present invention, a composite material for negative active material for lithium ion batteries having excellent capacity and stability can be prepared by coating the surface of artificial graphite with petroleum pitches of various softening points. In addition, such a composite material can be manufactured to an excellent secondary battery negative electrode material through various heat treatment processes.

In addition, the coating material is characterized in that it has two DTA exothermic peaks in the temperature range of 400 ℃ to 700 ℃.

Graphite may be any one selected from the group consisting of natural graphite, artificial graphite, soft carbon, and hard carbon. Preferably, the graphite may be artificial graphite. The particle diameter of graphite may be 10 μm to 25 μm.

At this time, the thickness of the artificial graphite coated with petroleum pitch may be 50 ㎚ to 1000 ㎚.

Referring to FIG. 1, a method of manufacturing a composite material for a negative electrode active material for a secondary battery according to various embodiments of the present disclosure includes: preparing a petroleum pitch by heat treating a petroleum-based residual oil (S100); Manufacturing artificial graphite coated with petroleum pitch (S200); And heat-treating the coated artificial graphite (S300).

The petroleum-based residual oil may include at least one of PFO (Pyrolysis Fuel Oil), which is a naphtha cracking process residual oil, and FCC-DO (Fluidized Catalytic Cracking Decant Oil), which is a fluidized bed catalytic cracking process residual oil.

In this case, the step of preparing the petroleum pitch may include preparing a carbon precursor by heat-treating the petroleum-based residual oil at 300° C. or higher for 1 hour to 5 hours. In the step of preparing the petroleum pitch, it can be manufactured by varying the softening point of the petroleum pitch. For example, it is possible to prepare a petroleum pitch having a softening point of 150 ℃ to 250 ℃.

In the step of manufacturing artificial graphite coated with petroleum pitch, it may be coated by mixing petroleum pitch and artificial graphite. The surface of artificial graphite may be coated with a petroleum pitch of 150° C., 200° C., and 250° C. At this time, the petroleum pitch may be dispersed using an ultrasonic cleaner using at least one organic solvent selected from the group consisting of hexane, toluene, tetrahydrofuran, and quinoline. Preferably, the pitch may be dispersed and dissolved using tetrahydrofuran.

Thereafter, after adding the artificial graphite, it may be uniformly dispersed for about 30 minutes using an ultrasonic cleanr again and then stirred at about 150 rpm for about 24 hours using a Hotplate Stirrer. Specifically, after dispersing a petroleum pitch of 5 to 15 weight ratio in an organic solvent, artificial graphite of 85 to 95 weight ratio may be added and stirred for 12 to 24 hours.

In the step of heat treating the coated artificial graphite, the carbonization step may be variously set according to the peaks shown in the TGA, DTG, and DTA graphs of the petroleum pitch according to the softening point. For example, it can be fired in one step for 1 to 2 hours at a temperature of 800 ℃ to 1000 ℃ in an inert atmosphere. Or, depending on the softening point of the petroleum pitch, performing a first heat treatment for 30 minutes to 1 hour at a temperature of 400 ℃ to 800 ℃ in an inert atmosphere; And after the first heat treatment step, it may include a second heat treatment step of heat treatment at a temperature of 800 ℃ to 1000 ℃.

The petroleum pitch used as the coating material of the negative electrode material has two DTA exothermic peaks in the temperature range of 400°C to 800°C in thermal analysis under an air atmosphere. A lithium ion secondary battery electrode material having energy density, input/output characteristics, life characteristics, and thermal stability cannot be obtained with only one peak in the temperature range of 400°C or more and 800°C or less. Accordingly, a negative electrode composite material was manufactured through a first carbonization step at 400°C to 800°C and a second carbonization step at 800°C to 1000°C.

By analyzing the physical properties of the coated artificial graphite, it is possible to improve the performance of the anode material coated with petroleum pitch while variously controlling the heat treatment temperature according to the thermal properties of the anode material.

A method of manufacturing a negative electrode for a secondary battery according to various embodiments of the present invention includes applying a slurry for manufacturing a negative electrode in which a composite material for a negative electrode active material for a secondary battery prepared by the above method, a binder, and a conductive material are mixed on a current collector, and rolling can do. In this case, the binder may be an organic binder or an aqueous binder. For example, the binder for manufacturing the electrode may be PVdF. The conductive material may be Super P. In addition, the viscosity of the slurry may be adjusted using a solvent. As a solvent, NMP (1-methyl-2-pyrrodidinone, Sigma Aldrich) may be used. The electrolyte can be used by dissolving LiPF ₆ salt in an EC: DEC (1: 1 vol%) solvent.

For example, as an electrode, a slurry was prepared by adjusting the viscosity with NMP using an active material, a conductive material (Super P), and a binder (PVdF) in a weight ratio of 85:10:5, and then coated on copper foil to prepare an electrode. Then, it can be dried in an oven at 80° C. for 12 hours. The coated electrode may be vacuum dried for 24 hours after passing through 80% rolling. Coin cells can be manufactured using Li metal as a counter electrode in a glove box in an argon atmosphere.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement the present invention. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

Example 1

In the present invention, the electrochemical performance of artificial graphite coated with petroleum pitch as a negative electrode material was tested, and properties were investigated according to the solvent and composition used. Spherical artificial graphite (MTI KOREA, 19~23 ㎛) was coated with petroleum pitch, and hexane (OCI Company, 95%), toluene (SAMCHUN, 99.5%), quinoline (SAMCHUN, 96%), tetrahydrofuran (OCI Company, 99.5%) was used as a solvent. In order to disperse, an ultrasonic cleaner (60 Hz, 100W, JEIO TECH, Korea) was used, and stirred using a Hotplate Stirrer (DAIHAN Scientific Company). PVdF (Polyvinylidene fluoride) was used as a binder for manufacturing the electrode, and NMP (1-methyl-2-pyrrodidinone, Sigma Aldrich) was used as a solvent.

The prepared petroleum pitch (SP 250° C., 0.1 g) was dispersed and dissolved in a tetrahydrofuran solvent for 10 minutes using an ultrasonic cleaner. After adding artificial graphite (0.9 g), it was uniformly dispersed for 30 minutes again using an ultrasonic cleaner. After stirring at 150 rpm for 24 hours using a hotplate stirrer, a solid mixture precursor was prepared by evaporation at 80°C. The prepared material was subjected to two sintering steps at 500° C. for 30 minutes and 1000° C. for 1 hour in an argon gas atmosphere to make coated artificial graphite.

Example 2

The prepared petroleum pitch (SP 200° C., 0.1 g) was dispersed and dissolved in a tetrahydrofuran solvent for 10 minutes using an ultrasonic cleaner. After adding artificial graphite (0.9 g), it was uniformly dispersed for 30 minutes again using an ultrasonic cleaner. After stirring at 150 rpm for 24 hours using a hotplate stirrer, a solid mixture precursor was prepared by evaporation at 80°C. The prepared material was subjected to two sintering steps at 500° C. for 30 minutes and 1000° C. for 1 hour in an argon gas atmosphere to make coated artificial graphite.

Example 3

The prepared petroleum pitch (SP 150° C., 0.1 g) was dispersed and dissolved in a tetrahydrofuran solvent for 10 minutes using an ultrasonic cleaner. After adding artificial graphite (0.9 g), it was uniformly dispersed for 30 minutes again using an ultrasonic cleaner. After stirring at 150 rpm for 24 hours using a hotplate stirrer, a solid mixture precursor was prepared by evaporation at 80°C. The prepared material was subjected to two sintering steps at 500° C. for 30 minutes and 1000° C. for 1 hour in an argon gas atmosphere to make coated artificial graphite.

Example 4

The prepared petroleum pitch (SP 150° C., 0.1 g) was dispersed and dissolved in a tetrahydrofuran solvent for 10 minutes using an ultrasonic cleaner. After adding artificial graphite (0.9 g), it was uniformly dispersed for 30 minutes again using an ultrasonic cleaner. After stirring at 150 rpm for 24 hours using a hotplate stirrer, a solid mixture precursor was prepared by evaporation at 80°C. The prepared material was subjected to two sintering steps at 500° C. for 30 minutes and 900° C. for 1 hour in an argon gas atmosphere to make coated artificial graphite.

Example 5

The prepared petroleum pitch (SP 150° C., 0.1 g) was dispersed and dissolved in a tetrahydrofuran solvent for 10 minutes using an ultrasonic cleaner. After adding artificial graphite (0.9 g), it was uniformly dispersed for 30 minutes again using an ultrasonic cleaner. After stirring at 150 rpm for 24 hours using a hotplate stirrer, a solid mixture precursor was prepared by evaporation at 80°C. The prepared material was subjected to two sintering steps at 500° C. for 30 minutes and 800° C. for 1 hour in an argon gas atmosphere to make coated artificial graphite.

Comparative Example 1

Artificial graphite not coated with pitch was prepared as a negative electrode material sample.

Comparative Example 2

It was coated on the surface of artificial graphite using petroleum pitch (SP 150°C, 0.1 g), and heat-treated in two steps at 600°C for 30 minutes and 800°C for 1 hour in an argon atmosphere using the peaks of DTG and DTA graphs. . Except for this, a negative electrode material sample was prepared in the same manner as in Example 1.

Comparative Example 3

It was coated on the surface of artificial graphite using petroleum pitch (SP 150° C., 0.1 g), and heat-treated in one step at 800° C. for 1 hour in an argon atmosphere at 5° C./min. Except for this, a negative electrode material sample was prepared in the same manner as in Example 1.

The softening points and heat treatment steps of the petroleum pitch used in Examples 1 to 5 and Comparative Examples 1 to 3 are shown in Table 1 below.

Softening point of used petroleum pitch Heat treatment step Heat treatment temperature and time Example 1 250 ℃ Two steps 30 minutes at 500 ℃, 1 hour at 1000 ℃ Example 2 200 ℃ Two steps 30 minutes at 500 ℃, 1 hour at 1000 ℃ Example 3 150 ℃ Two steps 30 minutes at 500 ℃, 1 hour at 1000 ℃ Example 4 150 ℃ Two steps 30 minutes at 500 ℃, 1 hour at 900 ℃ Example 5 150 ℃ Two steps 30 minutes at 500 ℃, 1 hour at 800 ℃ Comparative Example 1 No use of petroleum pitch - Comparative Example 2 150 ℃ Two steps 30 minutes at 600 ℃, 1 hour at 800 ℃ Comparative Example 3 150 ℃ One step 1 hour at 800 ℃

In order to investigate the electrochemical properties of artificial graphite coated with petroleum pitch, the active material, conductive material (Super P) and binder (PVdF) according to each of Examples 1 to 5 and Comparative Examples 1 to 3 were 85:10: After preparing a slurry by adjusting the viscosity with NMP at a weight ratio of 5, an electrode was prepared by coating on a copper foil, and then dried in an oven at 80° C. for 12 hours. The coated electrode was vacuum-dried for 24 hours after passing through an 80% rolling process. A coin cell was manufactured using Li metal as a counter electrode in a glove box in an argon atmosphere.

Experimental Example 1 TGA, DTG, and DTA graphs according to softening point of petroleum pitch

The characteristics of coating on artificial graphite were investigated according to the softening point of the used petroleum pitch. In order to find out the characteristics in the carbonization process, the TGA of the coating pitch of Examples 1, 2 and 3 was measured in an air atmosphere. As a result, referring to FIG. 2, in Examples 1, 2 and 3, two peaks were observed between 450° C. and 600° C.

Experimental Example 2-SEM analysis

SEM analysis was performed to confirm the surface coating characteristics of artificial graphite according to the pitch of various softening points. As a result, referring to FIG. 3, it was found that the coating layer maintained the spherical shape of the artificial graphite particles in Example 1, Example 2, and Example 3, while the particle surface was not significantly changed.

SEM analysis was performed to confirm the surface coating characteristics of the artificial graphite according to the carbonization temperature. As a result, referring to FIG. 4, it was found that even in the SEM analysis results of pitch-coated artificial graphite according to various carbonization temperatures, the coating layer maintained the spherical shape of the artificial graphite particles and did not significantly change the surface of the particles. In addition, compared to the surface of the uncoated graphite (Comparative Example), it was confirmed that the surface of the coated negative electrode material reduced cracks and became smoother to reduce the specific surface area. In addition, it was shown that it was coated in a spherical shape, and compared with the surface of the uncoated artificial graphite (Comparative Example), the artificial graphite coated with a pitch had a more spherical shape and showed a relatively smooth surface.

Experimental Example 3-Cycle test

In order to evaluate the battery performance of the artificial graphite negative electrode material coated with petroleum pitch according to the carbonization temperature, the cycle tests of Examples 3, 4, 5 and Comparative Examples 1, 2 and 3 having a softening point of 150°C were performed. The results are shown in Table 2 below.

Capacity (mAh/g) Initial efficiency (%) Example 3 351 86 Example 4 363 85 Example 5 384 81 Comparative Example 1 315 73 Comparative example 2 375 78 Comparative Example 3 371 76

Comparative Example 1, an uncoated artificial graphite, showed an initial efficiency of 73%, and Example 3, a negative electrode composite material heat-treated at a carbonization temperature of 500°C and 1000°C in two stages, showed an initial efficiency of 86%.

In addition, Example 4, a negative electrode composite material heat-treated at a carbonization temperature of 500°C and 900°C in two stages, showed an initial efficiency of 85%, and Example 4, which was heat-treated at a carbonization temperature of 500°C and 800°C in two stages 5 showed an initial efficiency of 81%.

Since the formation of the SEI layer after the first cycle has a stable charge/discharge capacity from the second cycle, in the second cycle, the uncoated artificial graphite in Comparative Example 1 is 315 mAh/g, and in Example 3 is 351 mAh/g. In Example 4, 363 mAh/g and in Example 5 were 384 mAh/g, and retention rates of 99% or more were confirmed until after 30 cycles.

In addition, Comparative Example 3, which was carbonized at 800°C in one step without an intermediate firing step, showed a discharge capacity of 371 mAh/g and an initial efficiency of 76%. Comparative Example 2, which is graphite, showed a discharge capacity of 375 mAh/g and an initial efficiency of 78%.

So far, the present invention has been looked at around its preferred embodiments. Those of ordinary skill in the art to which the present invention pertains will be able to understand that the present invention can be implemented in a modified form without departing from the essential characteristics of the present invention. Therefore, the disclosed embodiments should be considered from an illustrative point of view rather than a limiting point of view. The scope of the present invention is shown in the claims rather than the foregoing description, and all differences within the scope equivalent thereto should be construed as being included in the present invention.

Claims (9)

black smoke; And
It is coated with a petrolysis fuel oil pitch having a softening point of 150 ℃ to 250 ℃ on the graphite,
Performing a first heat treatment for 30 minutes to 1 hour at a temperature of 400° C. to 800° C. in an inert atmosphere, depending on the softening point of the petroleum pitch; And
After the first heat treatment step, a secondary battery negative electrode active material composite material coated through a second heat treatment step of heat treatment at a temperature of 800 to 1000 °C. The method of claim 1,
The graphite is a secondary battery anode active material composite material, characterized in that any one selected from the group consisting of natural graphite, artificial graphite, soft carbon and hard carbon. The method of claim 1,
The negative electrode active material composite material of a secondary battery, characterized in that the particle diameter of the graphite is 10 ㎛ to 25 ㎛. delete The method of claim 1,
The coating material, a secondary battery negative electrode active material composite material, characterized in that it has two DTA exothermic peaks in the temperature range of 400 ℃ to 700 ℃. Preparing a petroleum pitch having a softening point of 150 ℃ to 250 ℃ by heat treatment of the petroleum-based residual oil;
Mixing the petroleum pitch and the artificial graphite to prepare artificial graphite coated with the petroleum pitch; And
Including; heat treating the coated artificial graphite
In the step of heat treating the coated artificial graphite,
Performing a first heat treatment for 30 minutes to 1 hour at a temperature of 400° C. to 800° C. in an inert atmosphere, depending on the softening point of the petroleum pitch; And
A method of manufacturing a secondary battery negative electrode active material composite material comprising the step of performing a second heat treatment of performing heat treatment at a temperature of 800° C. to 1000° C. after the step of performing the first heat treatment. The method of claim 6,
The petroleum-based residual oil includes at least one of PFO (Pyrolysis Fuel Oil), which is a naphtha cracking process residual oil, and FCC-DO (Fluidized Catalytic Cracking Decant Oil), which is a fluidized bed catalytic cracking process residual oil,
In the step of preparing the petroleum pitch,
The method of manufacturing a secondary battery negative active material composite material comprising the step of preparing a carbon precursor by heat-treating the petroleum-based residual oil at 300° C. or higher for 1 hour to 5 hours. The method of claim 6,
In the step of preparing the artificial graphite coated with the petroleum pitch,
After dispersing 5 to 15 weight ratio of petroleum pitch using at least one organic solvent selected from the group consisting of hexane, toluene, tetrahydrofuran, and quinoline, artificial graphite of 85 to 95 weight ratio was added to 12 Method for producing a secondary battery negative active material composite material, characterized in that stirring for 24 hours. delete

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