ELECTRODE FOR ELECTROCHEMCAL DEVICE, METHOD FOR MANUFACTURING THE SAME, AND ELECTROCHEMCAL DEVICE INCLUDING THE SAME

Abstract

Provided are an electrode capable of maintaining electrical conductivity during elongation and shrinkage, a method for manufacturing the same, and electrochemical device including the same.

Claims

1. An electrode for an electrochemical device, comprising a composite film including an elastic polymer matrix and a first conductive material embedded in the elastic polymer matrix; a conductive film disposed on the composite film and including a second conductive material; and an electrode active material layer disposed on the conductive film, wherein each of the first conductive material and the second conductive material are a gold nanosheet.

2. The electrode for an electrochemical device of claim 1, wherein the gold nanosheet has a diameter of about 10 μm to about 20 μm.

3. The electrode for an electrochemical device of claim 1, wherein the gold nanosheet has a thickness of about 2 nm to about 5 nm.

4. The electrode for an electrochemical device of claim 1, wherein the elastic polymer matrix includes one of block copolymers represented by Chemical Formulae 1 to 4:
A-block-B  [Chemical Formula 1]
A-block-B-block-C  [Chemical Formula 2]
A-block-B-block-C-block-D  [Chemical Formula 3] wherein, in Chemical Formulae 1 to 3, A, B, C, and D are the same or different and are independently one of polystyrene, polybutadiene, polybutylene, polyethylene, polyurethane, polyisoprene, or a derivative thereof.

5. The electrode for an electrochemical device of claim 1, wherein the first conductive material is uniformly dispersed and embedded inside the polymer matrix.

6. The electrode for an electrochemical device of claim 1, wherein a weight ratio of the first conductive material/the polymer matrix in the composite film ranges from about 10/100 to about 20/100.

7. The electrode for an electrochemical device of claim 1, wherein the conductive film is disposed on one surface or both surfaces of the composite film.

8. The electrode for an electrochemical device of claim 7, wherein the electrode active material layer is disposed on one surface of the conductive film.

9. The electrode for an electrochemical device of claim 1, wherein the electrode active material layer includes an electrode active material having a particle diameter of about 100 nm to about 200 nm.

10. The electrode for an electrochemical device of claim 1, wherein the composite film has a thickness of about 20 μm to about 40 μm.

11. The electrode for an electrochemical device of claim 1, wherein the conductive film has a thickness of about 1 μm to about 10 μm.

12. The electrode for an electrochemical device of claim 1, wherein the active material layer has a thickness of about 1 μm to about 5 μm.

13. The electrode for an electrochemical device of claim 1, wherein the first conductive material is included in an amount of about 10 wt % to about 20 wt %, the second conductive material is included in an amount of about 30 wt % to about 40 wt %, the electrode active material layer is included in an amount of about 10 wt % to about 15 wt %, and the polymer matrix is included in a balance based on a total amount, 100 wt % of the electrode.

14. A method for manufacturing an electrode for an electrochemical device, comprising transferring a first conductive material on a substrate to form a first conductive film; spin-coating an elastic polymer solution on the first conductive film to disperse the elastic polymer solution inside and outside the first conductive film; drying the dispersed elastic polymer solution to form an elastic polymer matrix and to obtain a composite film including a first conductive material embedded inside the elastic polymer matrix; transferring a second conductive material on the composite film to form a second conductive film; and forming an active material layer on the second conductive film, wherein each of the first conductive material and the second conductive material are a gold nanosheet,

15. The method of claim 14, wherein the spin-coating of an elastic polymer solution on the first conductive film to disperse the elastic polymer solution inside and outside the first conductive film is performed at a rotation speed of about 1000 rpm to about 2000 rpm.

16. The method of claim 14, wherein the drying of the dispersed elastic polymer solution to form an elastic polymer matrix and to obtain a composite film including a first conductive material embedded inside the elastic polymer matrix is performed at a temperature range of about 70° C. to about 80° C.

17. The method of claim 14, wherein the transferring of the second conductive material on the composite film to form a second conductive film is transferring the second conductive material on one surface or both surfaces of the composite film twice or more.

18. The method of claim 14, wherein the forming of the active material layer on the second conductive film is performed by spin coating, transferring, spraying, electro-spinning, a hydrothermal synthesis method, a polyol synthesis method, or a solid-phase method.

19. The method of claim 14, wherein the transferring of the first conductive material on a substrate to form a first conductive film is transferring the first conductive material on one surface of the substrate twice or more.

20. An electrochemical device, comprising a positive electrode; a negative electrode; and an electrolyte between the positive electrode and the negative electrode, wherein at least one electrode of the positive electrode and the negative electrode is the electrode of claim 1.

21. The electrochemical device of claim 20, wherein the electrolyte is a gel polymer electrolyte.

22. The electrochemical device of claim 20, wherein the electrochemical device is packed with PDMS (polydimethlysiloxane).

23. The electrochemical device of claim 20, wherein the electrochemical device is a rechargeable lithium battery, a sodium rechargeable battery, or a super capacitor.

24. The electrochemical device of claim 20, wherein the electrochemical device is applied to a driving power of a wearable apparatus or a flexible apparatus.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0068] FIG. 1 schematically shows a process of manufacturing an electrode according to an example embodiment of the present invention.

[0069] FIGS. 2 and 3 are scanning electron microscope (SEM) photographs respectively showing a first conductive film (FIG. 2) and a composite film (FIG. 3) according to the example embodiment of the present invention.

[0070] FIG. 4 is a photograph enlarging FIG. 3.

[0071] FIG. 5 is a photograph showing a cross section of FIG. 4.

[0072] FIG. 6 is a SEM photograph showing an electrode active material layer on a third conductive film according to Example 1 of the present invention.

[0073] FIG. 7 shows electrical conductivity results of electrodes according to Example of the present invention and Comparative Example while elongated.

[0074] FIG. 8 shows tensile strength results of the electrode according to Example of the present invention.

[0075] FIG. 9 shows a negative electrode voltage profile of a rechargeable lithium battery cell according to Example of the present invention.

[0076] FIG. 10 shows a positive electrode voltage profile of the rechargeable lithium battery cell according to Example of the present invention.

[0077] FIG. 11 shows negative electrode cycle characteristics of the rechargeable lithium battery cell according to Comparative Example.

[0078] FIG. 12 shows cycle characteristics of a positive electrode of the rechargeable lithium battery cell according to Comparative Example.

[0079] FIG. 13 shows cycle characteristics of the rechargeable lithium battery cell according to Example of the present invention after an elongation of 15%.

[0080] FIG. 14 shows cycle characteristics of the rechargeable lithium battery cell according to Comparative Example after an elongation of 15%.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0081] Hereinafter, Examples of the present invention, Comparative Examples, and Evaluation Examples are described. These examples, however, are not in any sense to be interpreted as limiting the scope of the invention.

Example 1

[0082] (1) Manufacture of Negative Electrode

[0083] An electrode was manufactured according to a process schematically shown in FIG. 1.

[0084] 1) Forming Composite Film on Substrate

[0085] A thin film was formed by dispersing a gold nanosheet (width: 10 μm, length: 15 μm, thickness: 5 nm) in butanol to prepare a solution (a concentration: 5 wt %)) and dropping the solution on the surface water and then, transferred into a PDMS (polydimethylsiloxane) substrate. The process was 7 to 8 times repeated on the substrate to form a 2 cm-wide, 2 cm-long, and 1 μm-thick first conductive film.

[0086] On the first conductive film, a SBS block copolymer solution (a concentration: 10 wt %, viscosity: 10 poise) was spin-coated. Herein, the spin coating was performed under a condition (a rotation speed: 2000 rpm, time: 60 seconds).

[0087] Accordingly, a 2 cm-wide, 2 cm-long, and 40 μm-thick composite film was formed on the substrate. The composite film has a structure that a gold nanosheet was embedded in an elastic polymer matrix consisting of a SBS block copolymer, wherein the gold nanosheet/the elastic polymer matrix had a weight ratio of 10/100 and with a total thickness of 40 μm.

[0088] 2) Forming Second Conductive Film on Composite Film

[0089] A second conductive film was formed by transferring a gold nanosheet on the composite film according to the same method as above.

[0090] However, the second conductive film was formed on both surfaces of the composite film by seven times transferring the second conductive material only on one surface of the composite film to form a gold nanosheet aggregate (i.e., a second conductive film) and forming another second conductive film on the other surface of the composite film.

[0091] Then, the substrate was removed and then, bonded with the second conductive film, so that the other surface of the composite film might be exposed outside. On the exposed composite film, the second conductive material was seven times transferred to form each 1 μm-thick second conductive film on both surfaces of the composite film. In other words, a structure of the second conductive film/the composite film/the second conductive composite film was obtained.

[0092] 3) Forming Negative Active Material Layer on Second Conductive Film

[0093] A negative active material was spin-coated on the second conductive film.

[0094] Specifically, as for the negative active material, L.sub.4Ti.sub.5O.sub.12 (an average particle diameter: 200 nm) was used to prepare electrode active material slurry, and the electrode active material slurry was used to form an electrode active material layer on the second conductive film.

[0095] More specifically, the negative active material slurry was prepared by mixing the negative active material: carbon black (an average particle diameter: 20 nm): CMC (carboxylmethyl cellulose) in a weight ratio of 8:1:1 and adjusting its slurry phase with a solvent (deionized water).

[0096] The negative active material slurry was spin-coated on the second conductive film at a rotation speed of 2000 rpm for 60 seconds and then, heat-treated and dried at 100° C.

[0097] Accordingly, the second conductive film having the negative active material layer (a loading amount: 0.0018 g/cm.sup.2) was obtained. In other words, a negative electrode having a structure of the conductive film/the composite film/the conductive film/the negative active material was obtained.

[0098] (2) Manufacture of Positive Electrode

[0099] A positive electrode was manufactured according to the same process as the above process of manufacturing the negative electrode except for using LiFePO.sub.4 (an average particle diameter: 150 nm) as a positive active material instead of the negative active material.

[0100] Accordingly, the positive electrode having a structure of the conductive film/the composite film/the conductive film/the positive active material was obtained.

[0101] (3) Manufacture of Rechargeable Lithium Battery (Half-Cell)

[0102] A rechargeable lithium battery coin half-cell was manufactured by using the negative electrode manufactured in (1) of Example 1 and a Li-metal as a counter electrode.

[0103] On the other hand, a rechargeable lithium battery pouch half-cell was also manufactured by using the negative electrode manufactured in (5) of Example 1 and a Li-metal as a counter electrode.

[0104] Each battery used a gel electrolyte prepared by using sebaconitrile as a solvent and LiTFSi (lithium bis-trifluoromethanesulphonimide) as a lithium salt. When the lithium salt was used in a concentration ranging from 0.1 to 2.0 M, the electrolyte had appropriate conductivity and viscosity during an elongation process and showed excellent electrolyte performance.

[0105] As for the rechargeable lithium battery pouch half-cell, PDMS (poly dimethlysiloxane) was used as a packing material in a commonly known method.

Comparative Example 1

[0106] (1) Manufacture of Electrode

[0107] An SBS block copolymer solution was spin-coated on a substrate without forming the first conductive film unlike. Accordingly, only a 2 cm-wide, 2 cm-long, and 40 μm-thick elastic polymer matrix was formed on the substrate.

[0108] (2) Manufacture of Rechargeable Lithium Battery Cell

[0109] A rechargeable lithium battery coin half-cell was manufactured according to the same method as Example 1 by using the electrode according to Comparative Example 1.

Evaluation Example 1: Examination with Scanning Electron Microscope (SEM)

[0110] 1) FIG. 2 is a SEM photograph showing the first conductive film according to Example 1.

[0111] Referring to FIG. 2, 10 μm-wide, 15 μm-long, and 2 nm-thick gold nanosheets were three dimensionally aggregated to form a film.

[0112] 2) FIG. 3 is a SEM photograph showing the composite film of Example 1, FIG. 4 is a photograph enlarging the SEM photograph of FIG. 3, and FIG. 5 is a photograph showing the cross section of FIG. 4.

[0113] Referring to FIGS. 3 to 5, a structure that the gold nanosheets were uniformly embedded inside the elastic polymer matrix with high density was found through spin coating.

[0114] 3) FIG. 6 is a SEM photograph showing the conductive film coated with the negative active material layer according to Example 1.

[0115] Referring to FIG. 6, the negative active material layer had a total thickness of 5 μm by uniformly coating a negative active material having an average particle diameter of 100 nm and a conductive material having an average particle diameter of 10 nm.

Evaluation Example 2: Electrical Conductivity and Tensile Strength of Electrode in Elongation State

[0116] Electrical conductivity and tensile strength were measured by respectively elongating the negative electrodes according to Example 1 and Comparative Example 1. The results are shown in graphs of FIGS. 7 and 8.

[0117] Referring to FIG. 7, the negative electrode of Example 1 showed almost no resistance increase when twice elongated (i.e., an x axis is 100%) relative to that of the negative electrode before the elongation (i.e., the x axis is 0). The electrode of Comparative Example 1 showed greater than or equal to 100 times increased resistance when twice elongated compared with that of the electrode before the elongation (i.e., an x axis is 0).

[0118] Referring to FIG. 8, the negative electrode of Example 1 was finally broken when greater than or equal to 900% elongated.

Evaluation Example 3: Initial Voltage Profile

[0119] An initial voltage profile of positive and negative electrodes about the rechargeable lithium battery cell of Example 1 was evaluated, and the results are shown in FIG. 9 (negative electrode) and FIG. 10 (positive electrode). The voltage profile was evaluated at a 0.1 C rate within a voltage range of 1 V to 3.0 V as for the negative electrode but within a voltage range of 2.5 V to 4 V as for the positive electrode. In FIG. 9, since a descending curved line indicates discharge capacity, while an ascending curved line indicates charge capacity, electrochemical characteristics may be evaluated referring to FIG. 9.

[0120] In FIG. 9, when the negative electrode of (1) of Example 1 was used, initial discharge capacity was 170 mAh/g, charge capacity was 165 mAh/g, and initial coulomb efficiency was 97%. In addition, in FIG. 10, when the positive electrode of (1) of Example 1 was used, initial discharge capacity was 181 mAh/g, and charge capacity was 172 mAh/g.

[0121] Accordingly, each electrode of Example 1 secured electrochemical safety at a potential where lithium ion battery cells were operated.

Evaluation Example 4: Cycle Characteristics

[0122] Cycle characteristics of the rechargeable lithium battery cells of Example 1 were evaluated, and the results are shown in FIGS. 11 and 12. In FIGS. 11 and 12, a lower graph indicates charge capacity, and an upper graph indicates coulomb efficiency. The cycle characteristics were evaluated by performing charge/discharge at a 1 C rate within the same voltage range as Evaluation Example 3.

[0123] Referring to FIG. 11, when the negative electrode of Example 1 was used, the cell exhibited capacity of 155 mAh/g after 50 cycles and maintained greater than or equal to 99.5% of the capacity. In addition, referring to FIG. 12, when the positive electrode of (1) of Example 1 was used, the cell exhibited capacity of 165 mAh/g after 15 cycles.

Evaluation Example 5: Capacity Change Depending on Elongation

[0124] A capacity change of rechargeable lithium battery cells respectively using the negative active materials of Example 1 and Comparative Example 1 depending on an elongation was evaluated, and the results are shown in FIGS. 13 and 14. Separately, a capacity change of the rechargeable lithium battery cell of Comparative Example 1 depending on an elongation was evaluated, and the results are shown in FIG. 13.

[0125] Referring to FIG. 13, the electrode showed stable cycle performance and greater than or equal to 99.5% of coulomb efficiency when 15% elongated. On the contrary, in FIG. 14, the electrode of Comparative Example 1 showed five times reduced capacity of 30 mAh/g after 5 cycles relative to the initial capacity.

[0126] While this invention has been described in connection with what is presently considered to be practical example embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.