KR20180001521A - System for manufacturing lithium secondary battery anode - Google Patents

Abstract

The present invention relates to a negative electrode for a lithium secondary battery. More specifically, a negative electrode for a lithium secondary battery is manufactured by comprising a first negative electrode thin film formed on a substrate through complex application of an electrospray (e-spraying) method and a slot-die coating method, and a second negative electrode thin film formed on the first negative electrode thin film, thereby improving thickness uniformity and deposition efficiency.

Description

SYSTEM FOR MANUFACTURING LITHIUM SECONDARY BATTERY ANODE [0002]

The present invention relates to a lithium secondary battery anode, and more particularly, to a lithium secondary battery anode, which comprises a first cathode thin film formed on a substrate by applying an e-spraying method and a slot die coating method; And a second cathode thin film formed on the first cathode thin film; To a lithium secondary battery anode having a novel structure with improved thickness uniformity and deposition efficiency.

Recently, interest in energy storage technology is increasing. As the application fields of cell phones, camcorders, notebook PCs and even electric vehicles are expanding, efforts for research and development of electrochemical devices are becoming more and more specified.

Electrochemical devices have attracted the greatest attention in this respect, among which the development of rechargeable secondary batteries has become a focus of attention. In recent years, in order to improve the capacity density and specific energy in developing such batteries, And research and development on the design of the battery.

Lithium secondary batteries are not only a secondary battery using lithium metal but also a lithium ion, a lithium polymer, and a lithium ion polymer secondary battery, and have high voltage and high energy density.

The negative electrode of such a lithium secondary battery has been developed mainly with a carbon-based material. The carbonaceous anode active material can structurally reversibly insert and desorb lithium ions between carbon layers. The carbonaceous anode active material has an advantage of high capacity and has a high potential when a carbon-based cathode is used because of its low oxidation-reduction potential.

Conventionally, such a carbon-based material is usually applied by a method using a coater. However, the uniformity of the coating is considerably lowered in the negative electrode formation method using the existing coater, and it is difficult to obtain a uniform coated surface without moving the substrate or the nozzle.

Since the improvement of the performance of the lithium secondary battery is possible by improving the performance of the anode, the cathode and the electrolyte, there is a need for further studies for improving the performance of the lithium secondary battery such as a method for securing the thickness uniformity of the cathode.

Korean Patent Laid-Open No. 10-2010-0042345 Korean Patent Laid-Open No. 10-2008-0020283

The present invention relates to a novel lithium secondary battery anode which is manufactured by applying an e-spraying method and a slot-die coating method in order to solve the problem of the conventional method for manufacturing a negative electrode for a lithium secondary battery, The purpose is to provide.

In order to solve the above problems,

A substrate 230 on which current collector is coated;

A first cathode thin film (240) formed on the substrate; And

A second cathode thin film formed on the first cathode thin film; / RTI >

A cathode for a lithium secondary battery having an electrode energy density of 600 mAh / cc or more.

In the negative electrode for a lithium secondary battery according to the present invention, the first negative electrode thin film is formed by an electrospray method.

In the negative electrode for a lithium secondary battery according to the present invention, the first negative electrode thin film has a thickness of 0.5 占 퐉 to 40 占 퐉.

In the cathode for a lithium secondary battery according to the present invention, the second cathode thin film is formed by a slot die coating method.

In the negative electrode for a lithium secondary battery according to the present invention, the thickness of the second negative electrode thin film is 10 mu m to 100 mu m.

In the negative electrode for a lithium secondary battery according to the present invention, the first negative electrode thin film and the second negative electrode thin film are the same material. In the cathode for a lithium secondary battery according to the present invention, when the first cathode thin film and the second cathode thin film are formed of the same material, it is possible to manufacture an electrode having improved structural stability between the constituent materials by forming the same type of cathode thin film .

In the negative electrode for a lithium secondary battery according to the present invention, the first negative electrode thin film and the second negative electrode thin film are different from each other. In the cathode for a lithium secondary battery according to the present invention, when the first cathode thin film and the second cathode thin film are formed of materials different from each other, by forming a different cathode thin film, excellent characteristics of the material are added to the structural stability, Improvement is easy.

In the cathode for a lithium secondary battery according to the present invention, the first anode thin film may include nanosilicon having a D50 of less than 20 to 250 nm or graphene of 0.2 to 20 wt%.

The negative electrode for a lithium secondary battery according to the present invention has a total thickness of 40 탆 to 100 탆.

In the negative electrode for a lithium secondary battery according to the present invention, the negative electrode for a lithium secondary battery has a thickness uniformity of ± 5% or less of the total thickness.

In the negative electrode for a lithium secondary battery according to the present invention, the maximum height of the negative electrode for a lithium secondary battery is 1 占 퐉 or less in the region of 10 占 10 占 퐉 ² when AFM is measured.

The cathode for a lithium secondary battery according to an embodiment of the present invention is improved in thickness uniformity and deposition efficiency through the combined application of an electrospray method and a slot die coating method, and the lithium secondary battery including the negative electrode for a lithium secondary battery according to an embodiment of the present invention The cycle characteristics of the secondary battery are improved.

1 is a flowchart showing a method of manufacturing a negative electrode for a lithium secondary battery according to an embodiment of the present invention.
2 is a schematic view schematically showing a method of manufacturing a negative electrode for a lithium secondary battery using an e-spraying apparatus according to an embodiment of the present invention.
3 is a schematic view schematically illustrating a method of manufacturing a negative electrode for a lithium secondary battery using a slot-die coater according to an embodiment of the present invention.
FIGS. 4 to 5 are cross-sectional views illustrating a cathode manufactured by a combination of the electrospray method and the slot die coating method according to the embodiment of the present invention, and a cathode manufactured by applying the electrospray method and the slot die coating method, The results of evaluation of the electrochemical characteristics of the lithium secondary battery employing the lithium secondary battery are shown in FIG. Fig. 4 shows the discharge capacity and capacity retention characteristic of the lithium secondary battery, and Fig. 5 is a graph showing the volume capacity of the electrode of the lithium secondary battery.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. The present embodiments are provided so that the disclosure of the present invention is complete and that those skilled in the art will fully understand the scope of the present invention. Like reference numerals refer to like elements throughout the specification.

Hereinafter, a method of manufacturing a negative electrode for a lithium secondary battery according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 is a flowchart showing a method of manufacturing a negative electrode for a lithium secondary battery according to an embodiment of the present invention.

Referring to FIG. 1, a method for manufacturing a negative electrode for a lithium secondary battery according to an embodiment of the present invention may include a step (S110) of manufacturing a lithium secondary battery negative electrode active material dispersion, a negative electrode forming step (S120), and a heat treatment step (S130).

In the method for manufacturing a negative electrode for a lithium secondary battery according to an exemplary embodiment of the present invention, a negative electrode active material for a lithium secondary battery, a binder, and optionally a conductive material are mixed with a lithium secondary battery negative electrode To prepare an active material dispersion.

The negative electrode active material is preferably a material exhibiting a higher capacity than graphite, Silicon (Si) composite nano-particles, graphene-based materials, and the like, and may include any one or two or more of them.

Silicon (Si) has a significantly higher theoretical cost of 4200 mAh / g and a density of 2.33 g / ml. In addition, silicon (Si) exhibits lithium intercalation potential and characteristics similar to graphite. However, silicon (Si) is cracked due to rapid volume change (300%, Li ₂₁ Si ₅ ) due to lithium intercalation and deintercalation, and continuous cracking due to breakage of the electrode and destruction of the SEI layer Cycle characteristics are very poor due to side reactions with electrolytes, and metal silicon itself is not suitable for use as a cathode material.

Accordingly, it is more preferable that the silicon-based composite nano-particles contained in the negative electrode active material are contained in the form of a silicon composite rather than silicon itself.

For example, the silicon-based composite nanoparticles may be Si-C nanoparticles, Si-CNF nanoparticles, Si graphene nanoparticles, SiOx (1???? 2) nanoparticles, SiOx (1? 2) -graffin nanoparticles, Si-M nanoparticles, and the like, and may include any one or two or more of them.

Examples of the graphene material include graphene oxide, reduced graphene oxide, graphene, and the like, and any one or a mixture of two or more thereof may be used.

Graphene has a sheet-like structure in which carbon atoms are arranged in a hexagonal mesh shape and has high electrical conductivity. In addition, graphene is sp ² It is composed of hybrid carbon structure and has excellent physical properties such as electrical, thermal and mechanical properties. Furthermore, graphene has a large surface area of more than 2600 m ² / g. As such, graphene has a higher electrical conductivity than graphite, has a large surface area, and is chemically stable.

The binder may be a water-based binder such as carboxymethylcellulose (CMC), styrene-butadiene rubber (SBR), or the like. And the like.

The conductive material is used for imparting conductivity to the electrode, and any material can be used as long as it is an electron conductive material that does not cause a chemical change in a battery constituted. For example, the conductive material may be a carbon material or the like. The carbon material preferably has a porous structure, and more preferably has a large specific surface area to provide a wider reaction area. Specific examples of the carbon material having the porous structure include mesoporous carbon, and more specifically, graphite, acetylene black, carbon nanotubes, carbon fibers, and carbon nanotubes.

In the anode active material dispersion of lithium secondary battery according to the present invention, the conductive material may be at least one selected from the group consisting of artificial graphite, natural graphite, carbon black, acetylene black, ketjen black, denka black, thermal black, channel black, carbon fiber, , Bismuth, silicon, antimony, nickel, copper, titanium, vanadium, chromium, manganese, iron, cobalt, zinc, molybdenum, tungsten, silver, gold, lanthanum, ruthenium, platinum, iridium, titanium oxide, polyaniline, Is selected from the group consisting of polyacetylene, polypyrrole, and combinations thereof.

The lithium secondary battery negative electrode active material dispersion may further include a conventional dispersant to improve the dispersibility of the negative electrode active material.

The lithium secondary battery negative electrode active material dispersion can be prepared in consideration of the viscosity, polarity, surface tension, electric conductivity, and the like suitable for electrospray.

In the method of manufacturing a negative electrode for a lithium secondary battery according to an embodiment of the present invention, the applied voltage, the distance between the nozzle and the substrate, the jetting speed of the dispersion liquid and the jetting amount are not particularly limited in the electrospray process, The thickness and area of the thin film, the viscosity of the dispersion, and the like.

In one example, the applied voltage is preferably a high voltage, specifically in the range of 0.1 to 10 kV, and preferably about 5 kV. If the applied voltage is less than 0.1 kV, it is difficult to obtain a uniform film because dispersion of the dispersion particles is difficult. On the other hand, if the applied voltage is more than 10 kV, the angle of the dispersed liquid becomes large, .

For example, the spray amount of the dispersion liquid is preferably 2 to 5 ml, and the spraying speed thereof is preferably 10 to 25 μl / min. If the spray amount of the dispersion is less than 2 ml, the sprayed amount may not be sufficient and a uniform cathode thin film may not be obtained. On the other hand, if the spray amount is more than 5 ml, unnecessary dispersion may be used.

In addition, for example, the distance D between the nozzle 210 and the substrate 230 is preferably 10 to 50 cm, which can be determined in consideration of the applied voltage. If the distance D between the nozzle 210 and the substrate 230 is less than 10 cm, the process variation with respect to the concavity and convexity of the substrate 230 is large. On the other hand, when the distance D is more than 50 cm,

In the method for manufacturing a negative electrode for a lithium secondary battery according to an embodiment of the present invention, the first negative electrode thin film 240 using the electrospray principle may be performed under a vacuum and an atmospheric pressure.

2 is a schematic view schematically showing a method of manufacturing a negative electrode for a lithium secondary battery using an e-spraying apparatus according to an embodiment of the present invention.

Referring to FIG. 2, in the method of manufacturing a negative electrode for a lithium secondary battery according to an embodiment of the present invention, an electrospray apparatus can be used according to the principle of the electrospray method.

A method of manufacturing an anode using an electrospray method is a method of manufacturing a cathode having a thickness of about 40 to 100 占 퐉 by suppressing aggregation of a thin film due to a potential difference between a dispersion of an anode active material and a substrate 230 coated with an electric current collector, The first cathode thin film 240 for a lithium secondary battery having a uniformity of ± 5% or less, that is, high uniformity in thickness can be formed.

The cathode formation method using the electrospray method is an excellent coating method in terms of improving the uniformity of the thickness of the thin film, but there is a limit in raising the thickness of the thin film.

In order to overcome the deposition limit according to the thickness of the cathode thin film, a slot die coating method was adopted in the present embodiment in the cathode formation, followed by the electrospray method. That is, the method for manufacturing a negative electrode for a lithium secondary battery according to an embodiment of the present invention is proposed to combine the electrospray method and the slot die coating method.

In the method for manufacturing a negative electrode for a lithium secondary battery according to an embodiment of the present invention, the electrospray method and the slot die coating method may be performed only one time, or may be performed a plurality of times as needed.

3 is a schematic view schematically showing a method of manufacturing a negative electrode for a lithium secondary battery using a slot die coating apparatus according to an embodiment of the present invention.

Referring to FIG. 3, a method of manufacturing a cathode for a lithium secondary battery according to an embodiment of the present invention may use a slot die coater apparatus to introduce a slot die coating method subsequent to the electrospray method described above.

The negative electrode forming step S120 may be followed by pumping the lithium secondary battery negative electrode active material dispersion liquid 320 into the slot die 310 of the slot die coater 300 shown in FIG. The second cathode thin film is coated on the first anode 330. Thus, the negative electrode for a lithium secondary battery including the first negative electrode thin film and the second negative electrode thin film is completed.

In the method of manufacturing a cathode for a lithium secondary battery using the slot die coating method according to an embodiment of the present invention, since the slot die coating method is used subsequent to the electrospray method, the thickness of the deposition is appropriately controlled . Such a slot die coating method can be used without any limitations in common known techniques.

Meanwhile, although not shown in the drawing, the current collector preprocessing step may be further included between the step of preparing the anode active material dispersion (S110) and the step of forming the cathode (S120).

The current collector pre-treatment step heats the substrate on which the negative electrode active material dispersion is to be sprayed, that is, the substrate on which the current collector is formed. The heating process in the current collector pre-treatment step can be performed at a temperature of 25 to 150 DEG C, thereby improving the affinity between the thin film and the substrate after manufacturing the negative electrode. At this time, if the heating temperature is less than 25 ° C, the adhesion between the current collector and the negative-electrode thin film can be weakened, and if the heating temperature exceeds 150 ° C, the uniformity of the film may be lowered.

In the method for manufacturing a negative electrode for a lithium secondary battery having such a constitution, by applying the electrospray method and the slot die coating method in combination, it is possible to manufacture a negative electrode for a lithium secondary battery having improved thickness uniformity as well as deposition efficiency, Thereby contributing to the improvement of the cycle characteristics of the battery.

< Example > Lithium secondary battery  Formation of cathode thin film

In the embodiments of the present invention, a lithium secondary battery anode active material dispersion based on a silicon-grafine mixed composition is produced by electrospinning and slot die coating combined application method.

The dispersion of the negative electrode active material was prepared in the same manner as the dispersion of the negative active material in Examples and Comparative Examples except that the composition ratio of the silicon active material was different.

At this time, the respective composition ratios were 8 wt% (Example 1, Comparative Examples 1 and 4), 11 wt% (Example 2, Comparative Examples 2 and 5), 15 wt% % (Example 3, Comparative Examples 3 and 6).

The prepared anode active material dispersion was pre-coated at a level of 30 μm on the copper current collector by electrospinning, followed by slot-die coating to adjust the thickness of the cathode thin film to finally achieve a uniform thickness of 60 μm Was prepared.

Thus, the cathode having the final thin film formed was compressed through a heating roll press to control the electrode density to be 1.6 g / cc.

< Experimental Example > Evaluation of battery characteristics

In the above examples, a lithium secondary battery employing a negative electrode prepared by a combination of an electrospray method and a slot die coating method, and a negative electrode prepared by applying only an electrospray method or a slot die coating method as a comparative example was fabricated.

The properties of each of the lithium secondary batteries prepared above were evaluated, and the results are shown in Table 1 and Figs. 4 to 5.

division charge
Volume
(mAh / g) Discharge
Volume
( mAh / g) Early
efficiency
(%) Volume
Retention rate
( % @ 50cyc .) volume
Expansion ratio
( % @ 50cyc .) electrode
density
(g / cc) electrode
Per volume
Volume
( mAh / cc) Example 1 Complex method 551 501 92 96 44 1.5 752 Example 2 Complex method 605 549 91 95 46 1.6 878 Example 3 Complex method 701 653 91 95 48 1.6 1045 Comparative Example 1 E-spray method 555 465 90 97 34 1.4 651 Comparative Example 2 E-spray method 602 510 91 96 38 1.3 663 Comparative Example 3 E-spray method 701 585 91 96 40 1.3 761 Comparative Example 4 Slot-die
Method 552 491 89 92 98 1.6 786 Comparative Example 5 Slot-die
Method 601 532 89 91 101 1.6 851 Comparative Example 6 Slot-die
Method 705 617 88 88 110 1.6 987

As shown in Table 1, when the thin film of the negative electrode is manufactured by applying the electrospray method of Comparative Examples 1 to 3 alone, the electrode density of the battery is lowered, and the capacity per electrode volume is reduced.

In addition, the initial efficiency and the capacity retention rate of the battery employing the slot die coating method of Comparative Examples 4 to 6 alone, when manufacturing a thin film of a negative electrode, have a problem of drastically deteriorating characteristics due to an increase in volume expansion rate Able to know.

On the other hand, it can be seen that the discharge capacity, the capacity retention rate, and the capacity per electrode volume of the battery employing the electrospray method and the slot die coating method are sequentially improved.

Accordingly, the method for manufacturing a negative electrode of a lithium secondary battery according to the present invention can improve the uniformity of the thickness of the negative electrode and the deposition efficiency, thereby making it possible to manufacture a battery having excellent characteristics.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, and that various changes, substitutions and alterations can be made therein without departing from the spirit and scope of the invention. However, it should be understood that such substitutions, changes, and the like fall within the scope of the following claims.

200: Electrospray device
210: Nozzle
220: Wires
230: substrate coated with current collector
240: first negative electrode thin film
300: Slot die coater
310: slot die
320: Negative electrode active material dispersion
330: substrate coated with the first negative electrode thin film

Claims (9)

A substrate on which a current collector is coated;
A first cathode thin film formed on the substrate; And
A second cathode thin film formed on the first cathode thin film; And
When the electrode energy density is 600 mAh / cc or more
Cathode for lithium secondary battery
A substrate on which a current collector is coated;
A first cathode thin film formed on the substrate by an electrospinning method; And
A second cathode thin film formed on the first cathode thin film by a slot die coating method; Containing
Cathode for lithium secondary battery
3. The method according to claim 1 or 2,
Wherein the first negative electrode thin film has a thickness of 0.5 to 40 m
Cathode for lithium secondary battery
3. The method according to claim 1 or 2,
And the second negative electrode thin film has a thickness of 10 mu m to 100 mu m
Cathode for lithium secondary battery
3. The method according to claim 1 or 2,
Wherein the first cathode thin film and the second cathode thin film are the same material or different materials
Cathode for lithium secondary battery
3. The method according to claim 1 or 2,
Wherein the first negative electrode thin film has a D50 of less than 20 to 250 nm nanosilicon or 0.2 to 20 wt%
Cathode for lithium secondary battery
3. The method according to claim 1 or 2,
Wherein the negative electrode for a lithium secondary battery has a total thickness of 40 to 100 mu m
Cathode for lithium secondary battery
3. The method according to claim 1 or 2,
The negative electrode for a lithium secondary battery has a thickness uniformity of 5% or less of the total thickness
Cathode for lithium secondary battery
3. The method according to claim 1 or 2,
The maximum height of the negative electrode for a lithium secondary battery is 1 m or less in the region of 10 x 10 mu m ² when AFM is measured
Cathode for lithium secondary battery

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