KR101916569B1 - Flexible electrode and method of manufacturing the same - Google Patents

Abstract

The present invention relates to a flexible electrode and a manufacturing method thereof, and more particularly, to a flexible electrode for a flexible lithium ion battery having a problem of insufficient loading level of a cathode active material and low rigidity and mechanical strength in repetitive bending or folding process And a method for producing the flexible electrode.

Description

[0001] The present invention relates to a flexible electrode and a manufacturing method thereof,

The present invention relates to a flexible electrode and a manufacturing method thereof, and more particularly, to a free-standing flexible electrode applicable to a flexible lithium ion battery without a current collector and a manufacturing method thereof.

The anode of a lithium rechargeable battery is typically a powdered material capable of reversibly inserting and desorbing lithium. The powder is deposited as an electrode film on a metal foil serving as a current collector. The electrode film often contains more than 95% of the cathode material and a small amount of binder and conductive additive. The anode (cathode) thus produced is laminated or wound on the separator and the cathode film (anode). Generally, the cathode film contains carbon. Finally, the stacked or wound cathode-separator-anode-roll is inserted into the case, the electrolyte is added, and the case is sealed to form a complete cell.

Lithium-ion batteries have been the mainstream market for small-sized batteries, including notebook PCs and mobile phones, but the use of electric vehicles (xEVs) and electric energy storage systems (ESSs), which surpass the power supply of portable electronic devices The large-sized battery market, such as electric vehicles and electric power storage systems, is expected to become more active in the future.

In addition, there is an increasing demand for flexible lithium ion batteries for use as a power source for wearable and flexible IT devices (smart clocks, flexible displays, etc.).

However, existing flexible Li-ion batteries include several non-flexible components that offer flexibility. Therefore, extensive research has been conducted to solve these problems.

Cellulosic, carbon felt and metal mesh were used as materials that can accommodate active materials, binders, and conductive agents while maintaining the flexibility of lithium ion batteries. This new structure improves flexibility and demonstrates promising performance for flexible Li-ion batteries.

In particular, Li et al. In yes flexible lithium-ion battery consisting of Li ₄ Ti ₅ O ₁₂ with a pin foam it was demonstrated that, while maintaining 55% of the capacity to 20C-rate can increase the current density, TiO ₂ (B) and poly-acrylic Activated carbon fibers derived from ronitril (PAN) complexes have demonstrated long lifetime characteristics from 20C-rate to 2000 cycles.

However, when a flexible lithium ion battery is constructed by a complicated structure and process using nanostructure electrode material and separator, there is a high possibility that the price of the battery increases and commercialization is hindered.

In addition, a problem of high resistance of the flexible lithium ion battery, a problem of insufficient loading level of the cathode active material, and low rigidity and mechanical strength in repetitive bending or folding process remain as yet unsolved problems.

Therefore, a novel flexible electrode and a manufacturing method thereof that overcome the above-described problems will be required.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of the present invention to provide a method of manufacturing a flexible flexible electrode.

Another aspect of the present invention is to provide a stand-alone flexible battery.

According to an aspect of the present invention, there is provided a method of manufacturing a flexible electrode.

The method for manufacturing the independent flexible electrode includes the steps of: preparing a slurry containing an electrode active material, a binder, a conductive agent, and an additive; casting the slurry on a substrate and drying; and removing the dried slurry on the substrate And may be characterized in that the current collector is not required.

The electrode active material may be at least one selected from the group consisting of lithium cobalt oxide (LCO), nickel cobalt manganese oxide (NCM), and nickel cobalt aluminum oxide (NCA).

The electrode active material may be at least one selected from the group consisting of carbon-based materials including graphitic carbon and graphitizable carbon, which are cathode materials, and silicon-based materials.

The binder may be PVDF-HFP.

The conductive agent may be carbon black.

The additive may be at least one selected from the group consisting of carbon nanotubes and graphene.

The substrate may be a glass substrate.

The content ratio of the electrode active material, the conductive agent, the binder and the additive is in the range of 46 to 76: 15 to 45: 6 to 9: 2 to 5 (wt%) based on the total amount of the slurry, Lt; / RTI >

According to another aspect of the present invention, there is provided an independent flexible battery.

The independent type flexible battery may include a positive electrode manufactured by the above-described manufacturing method and a negative electrode manufactured by the above-described manufacturing method.

According to the present invention, it is possible to manufacture a flexible electrode without a current collector by manufacturing an electrode by casting slurry on a substrate and removing the slurry.

In addition, by appropriately adjusting the content of the binder contained in the slurry, it is possible to manufacture the independent flexible electrode without further applying a force or damaging the electrode when separating the electrode from the substrate.

In addition, by using PVDF-HFP as a binder, it is possible to produce an independent flexible electrode having excellent mechanical characteristics.

In addition, by appropriately adjusting the content of the additive contained in the slurry, it is possible to manufacture a flexible flexible electrode having excellent mechanical properties and excellent electrical conductivity.

Also, by including the additive in the slurry, the electrode active material can be prevented from becoming dense, and the electrolyte can easily access the electrode structure, thereby improving the electrical conductivity of the battery.

Further, by using the independent flexible electrode of the present invention, it is possible to manufacture a flexible battery having specific capacities equivalent to those of a battery manufactured using general LiCoO ₂ without a current collector.

Further, by using the independent flexible electrode of the present invention, it is possible to manufacture a flexible battery having cycling stability superior to that of a battery manufactured using general LiCoO ₂ without a current collector.

Further, by using the independent flexible electrode of the present invention, it is possible to manufacture a flexible battery having a discharge capacity ratio superior to that of a battery manufactured using general LiCoO ₂ without a current collector.

Also, by using the slurry produced in the content ratio of the present invention, it is possible to produce an electrode in which any wrinkles or damage are not observed even in the repetitive bending or folding process.

Also, by using the independent flexible electrode of the present invention, it is possible to manufacture a flexible battery capable of supplying power to a connected device even when bent.

The technical effects of the present invention are not limited to those mentioned above, and other technical effects not mentioned can be clearly understood by those skilled in the art from the following description.

FIG. 1 is a schematic view showing a preferred method of manufacturing the independent flexible electrode of the present invention.
FIG. 2 is a graph showing peel-off strengths of an electrode manufactured through a comparative example of the present invention.
3 is a graph of mechanical properties according to the additive content of the electrode prepared through the comparative example and the production example of the present invention.
4 is an SEM image of an electrode manufactured through the comparative example and the production example of the present invention.
5 is a graph of charge and discharge profiles of half cells made with the electrodes of the comparative and production examples of the present invention.
6 is a graph showing the cycle stability of a half cell made of the electrode of the comparative example and the production example of the present invention.
FIG. 7 is a graph showing a discharge capacity ratio capability of a half cell made of the electrode of the comparative example and the production example of the present invention.
Figure 8 is a graph of cyclic voltammograms of half cells made with the electrodes of the preferred comparative and manufacturing examples of the present invention.
9 is an image showing the endurance against folding of the electrode manufactured according to the comparative example and the production example of the present invention.
Figure 10 is an image of a flexible cell fabricated in accordance with another preferred embodiment of the present invention.

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

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. Rather, the intention is not to limit the invention to the particular forms disclosed, but rather, the invention includes all modifications, equivalents and substitutions that are consistent with the spirit of the invention as defined by the claims.

It will be appreciated that when an element such as a layer, region or substrate is referred to as being present on another element "on," it may be directly on the other element or there may be an intermediate element in between .

Although the terms first, second, etc. may be used to describe various elements, components, regions, layers and / or regions, such elements, components, regions, layers and / And should not be limited by these terms.

Example

FIG. 1 is a schematic view showing a preferred method of manufacturing the independent flexible electrode of the present invention.

As a method of manufacturing the independent flexible electrode, first, a step of manufacturing a slurry including an electrode active material, a binder, a conductive agent, and an additive is performed.

The electrode active material may be a commonly used cathode active material or an anode active material. The slurry contains an amount of 46 to 76 wt%, more preferably 60 to 66 wt%, based on the total amount of the slurry.

When the electrode active material is contained in the slurry in an amount of less than 46% by weight, a battery capacity of the finally produced electrode is insufficient. When the electrode active material is contained in the slurry in excess of 76% by weight, The flexibility of the electrode is deteriorated and it is impossible to produce a flexible electrode for the purpose of the present invention.

The cathode active material may include a manganese-based spinel active material, a lithium metal oxide, or a mixture thereof. Further, the lithium metal oxide may be selected from the group consisting of lithium-manganese-based oxide, lithium-nickel-manganese-based oxide, lithium-manganese-cobalt oxide, lithium-nickel-manganese-cobalt oxide and nickel-cobalt-aluminum oxide And more specifically LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li (Ni _a Co _b Mn _c ) O ₂ (Where, 0 <a <1, 0 <b <1, 0 <c <1, a + b + c = 1), LiNi 1 - Y Co Y O 2, LiCo 1 - Y Mn Y O 2, LiNi _{1 - (wherein, 0≤Y <1) Y Mn Y} O 2, Li (Ni a Co b Mn c) O 4 ( where, 0 <a <2, 0 <b <2, 0 <c <2 , a + b + c = 2), LiMn _2-z Ni _z O ₄ , and LiMn _2-z Co _z O ₄ (where 0 <Z <2).

Preferably, the cathode active material according to an embodiment of the present invention is at least one selected from the group consisting of lithium cobalt oxide (LCO), nickel cobalt manganese oxide (NCM), and nickel cobalt aluminum oxide (NCA).

The negative electrode active material may include a carbon-based material, and the carbon-based material is at least one selected from the group consisting of crystalline carbon and amorphous carbon. The crystalline carbon includes graphite carbon such as natural graphite and artificial graphite. The amorphous carbon is a mixture of non-graphitizable carbons (hard carbons) obtained by carbonizing a polymer resin, And graphitizable carbons (soft carbons) obtained by heat treatment. As the negative electrode active material, a generally used negative electrode active material may be used.

The binder may provide flexibility to the independent flexible electrode and bind the electrode active material, the conductive agent, and the additive. The binder may contain 15 to 45 wt%, more preferably 23 To 29% by weight of the slurry is included in the slurry.

When the binder is contained in the slurry in an amount of less than 15% by weight, the flexibility of the finally produced electrode deteriorates and it is impossible to produce a flexible electrode for the purpose of the present invention. If the binder contains more than 45% by weight of the binder in the slurry, the battery capacity of the finally produced electrode may be insufficient.

The binder may be selected from the group consisting of PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene), PVDF (polyvinylidene fluoride), polyacrylonitrile, polymethylmethacrylate, polyvinyl alcohol, carboxymethylcellulose (CMC) Propylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), fluorocarbon rubber, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, At least one selected from the group consisting of polyacrylic acid and a polymer in which hydrogen thereof is substituted with Li, Na, or Ca can be used.

The preferred binder of the present invention is polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP).

The conductive agent may serve to maintain conductivity and mechanical strength of the independent flexible electrode. An amount of 6 to 9 wt%, more preferably 7 to 8 wt%, based on the total amount of the slurry, .

If the conductive agent is contained in the slurry in an amount of less than 6% by weight, the mechanical properties of the finally produced electrode may be deteriorated. When the conductive agent is contained in the slurry in an amount of more than 9 wt%, the conductivity of the finally produced electrode may be lowered.

The conductive agent may be a carbon-based material, and carbon black is used as a conductive agent according to an exemplary embodiment of the present invention.

The additive may improve the conductivity of the independent flexible electrode. The slurry may contain an amount of 2 to 5 wt%, more preferably 3 to 4 wt%, based on the total amount of the slurry.

When the additive is contained in the slurry in an amount of less than 2% by weight, the conductivity of the finally produced electrode may be lowered. If the additive is contained in the slurry in an amount exceeding 5% by weight, the mechanical properties of the finally produced electrode may be deteriorated.

The additive may be selected from the group consisting of carbon nanotubes (CNTs) and graphene-based materials, and carbon nanotubes (CNTs) are preferably used as the additive according to one embodiment of the present invention .

The ratios of the electrode active material, the binder, the conductive agent and the additive contained in the slurry are summarized in Table 1 below.

Wt% (wt%, based on the total amount of slurry) Electrode active material 46 ~ 76 bookbinder 15 ~ 45 Conductive agent 6 to 9 additive 2 to 5

The free-standing flexible electrode of the present invention is a free-standing type electrode which does not require a current collector. In order to realize this, a slurry having an appropriate content ratio as shown in Table 1 should be prepared.

The slurry is prepared by dispersing an electrode active material, a binder, a conductive agent, and an additive in a solvent. The solvent may be any solvent that can be used without limitation, and NMP (N-Methylpyrrolidone) is used as a solvent according to one embodiment of the present invention.

After the slurry is prepared through the above-described method and an appropriate content ratio, the step of casting and drying the slurry on the substrate 100 is performed, and the step of removing the dried slurry 200 on the substrate is performed .

The substrate 100 can be used without limitation as long as the dried slurry 200 can be easily dropped. Specifically, at least one substrate selected from the group consisting of a metal foil such as aluminum or copper foil and a glass substrate can be used have. The substrate 100 according to an exemplary embodiment of the present invention uses a glass substrate in consideration of desorption.

The dried slurry 200 may be used as an electrode after being dropped on the substrate 100, and the independent flexible electrode according to the preferred embodiment of the present invention can be manufactured through the above-described method.

Hereinafter, preferred examples of the preparation are described for the purpose of facilitating understanding of the present invention. However, the following Production Examples are for the purpose of helping understanding of the present invention, and the present invention is not limited by the following Production Examples.

&Lt; Comparative Example 1 > Conventional electrode including an aluminum foil current collector (written as Electrode_AL)

(1) A slurry containing an electrode active material, a binder and a conductive agent was prepared. (LCO electrode active material: PVDF binder: carbon black conductive agent = 90: 5: 5 wt%)

(2) The slurry was cast on an aluminum foil collector and dried to prepare Electrode_AL.

COMPARATIVE EXAMPLE 2 Independent Flexible Electrode (manufactured by Electrode A) manufactured by casting and removing the slurry (LCO electrode active material: PVDF binder: carbon black conductive agent = 90: 5: 5 wt%

(1) A slurry containing an electrode active material, a binder and a conductive agent was prepared. (LCO electrode active material: PVDF binder: carbon black conductive agent = 90: 5: 5 wt%)

(2) The slurry was cast on a glass substrate and dried.

(3) Electrode A was prepared by removing the dried slurry on the glass substrate.

COMPARATIVE EXAMPLE 3: Stand-alone flexible electrode (designated Electrode B) manufactured through a process of casting and removing a slurry (LCO electrode active material: PVDF binder: carbon black conductive agent = 63: 26: 11 wt%

(1) A slurry containing an electrode active material, a binder and a conductive agent was prepared. (LCO electrode active material: PVDF binder: carbon black conductive agent = 63: 26: 11 wt%)

(2) The slurry was cast on a glass substrate and dried.

(3) Electrode B was prepared by removing the dried slurry on the glass substrate.

COMPARATIVE EXAMPLE 4 A free-standing flexible electrode (manufactured by Electrode C manufactured through a manufacturing process in which a slurry (LCO electrode active material: PVDF-HFP binder: carbon black conductive agent = 90: 5: 5 wt% )>

(1) A slurry containing an electrode active material, a binder and a conductive agent was prepared. (LCO electrode active material: PVDF-HFP binder: carbon black conductive agent = 90: 5: 5 wt%)

(2) The slurry was cast on a glass substrate and dried.

(3) Electrode C was prepared by removing the dried slurry on the glass substrate.

COMPARATIVE EXAMPLE 5 A free-standing flexible electrode (manufactured by Electrode D manufactured through a manufacturing process in which a slurry (LCO electrode active material: PVDF-HFP binder: carbon black conductive agent = 83: 6: 11 wt% )>

(1) A slurry containing an electrode active material, a binder and a conductive agent was prepared. (LCO electrode active material: PVDF-HFP binder: carbon black conductive agent = 83: 6: 11 wt%)

(2) The slurry was cast on a glass substrate and dried.

(3) Electrode D was prepared by removing the dried slurry on the glass substrate.

COMPARATIVE EXAMPLE 6 A free-standing flexible electrode (manufactured by Electrode E manufactured by a process of casting and removing a slurry (LCO electrode active material: PVDF-HFP binder: carbon black conductive agent = 76:13:11 wt% )>

(1) A slurry containing an electrode active material, a binder and a conductive agent was prepared. (LCO electrode active material: PVDF-HFP binder: carbon black conductive agent = 76: 13: 11 wt%)

(2) The slurry was cast on a glass substrate and dried.

(3) Electrode E was prepared by removing the dried slurry on the glass substrate.

COMPARATIVE EXAMPLE 7 A free-standing flexible electrode (manufactured by Electrode F manufactured by a manufacturing process in which a slurry (LCO electrode active material: PVDF-HFP binder: carbon black conductive agent = 63:26:11 wt% )>

(1) A slurry containing an electrode active material, a binder and a conductive agent was prepared. (LCO electrode active material: PVDF-HFP binder: carbon black conductive agent = 63: 26: 11 wt%)

(2) The slurry was cast on a glass substrate and dried.

(3) The dried slurry was removed from the glass substrate to prepare Electrode F.

COMPARATIVE EXAMPLE 8 A free-standing flexible electrode manufactured through a manufacturing process of casting and slitting a slurry (LCO electrode active material: PVDF-HFP binder: carbon black conductive agent: CNT additive = 63: 26: 4: 7 wt% (Electrode G)>

(1) A slurry containing an electrode active material, a binder, a conductive agent, and an additive was prepared. (LCO electrode active material: PVDF-HFP binder: carbon black conductive agent: CNT additive = 63: 26: 4: 7 wt%)

(2) The slurry was cast on a glass substrate and dried.

(3) Electrode G was prepared by removing the dried slurry on the glass substrate.

COMPARATIVE EXAMPLE 9 Independent Flexible Electrode (manufactured by Electrode H) manufactured through a process of casting and removing a slurry (LCO electrode active material: PVDF-HFP binder: CNT additive = 63:26:11 wt%

(1) A slurry containing an electrode active material, a binder and an additive was prepared. (LCO electrode active material: PVDF-HFP binder: CNT additive = 63:26:11 wt%)

(2) The slurry was cast on a glass substrate and dried.

(3) The dried slurry was removed from the glass substrate to prepare Electrode H.

&Lt; Comparative Example 10: PVDF film produced through a process of casting on a glass substrate and peeling off >

① PVDF polymer was dissolved in NMP solvent.

(2) The dissolved PVDF polymer was cast on a glass substrate and dried.

(3) The dried PVDF polymer was poured onto the glass substrate to prepare a PVDF film.

&Lt; Comparative Example 11: PVDF-HFP film produced through a process of casting on a glass substrate and peeling off >

① PVDF-HFP polymer was dissolved in NMP solvent.

② The dissolved PVDF-HFP polymer was cast on a glass substrate and dried.

(3) The PVDF-HFP polymer dried on the glass substrate was taken out to prepare a PVDF-HFP film.

Production Example: Production of a slurry (LCO electrode active material: PVDF-HFP binder: carbon black conductive agent: CNT additive = 63: 26: 7: 4 wt%) prepared by the content ratio of the present invention is cast on a substrate and then peeled off (Manufactured by Electrode Manufacturing Example) < RTI ID = 0.0 >

(1) A slurry containing an electrode active material, a binder, a conductive agent, and an additive was prepared. (LCO electrode active material: PVDF-HFP binder: carbon black conductive agent: CNT additive = 63: 26: 7: 4 wt%)

(2) The slurry was cast on a glass substrate and dried.

(3) The dried slurry was peeled off from the glass substrate to prepare an Electrode production example.

The electrodes and films prepared through the above production examples and comparative examples are summarized in Table 2 below.

LCO (wt%) PVdF-HFP (wt%) PVdF (wt%) Carbon black (wt%) CNT (wt%) Substrate Electrode_AL 90 5 5 Al Foil Electrodea 90 5 5 Glass Electrode B 63 26 11 Glass Electrode C 90 5 5 Glass Electrode D 83 6 11 Glass Electrode E 76 13 11 Glass Electrode F 63 26 11 Glass Electrode Manufacturing Example 63 26 7 4 Glass Electrode G 63 26 4 7 Glass Electrode H 63 26 11 Glass PVDF film 100 PVDF-HFP film 100

Referring to Table 2, it can be seen that electrodes and films were produced using various ratios of electrode active material, binder, conductive agent, and additive.

FIG. 2 is a graph showing peel-off strengths of an electrode manufactured through a comparative example of the present invention.

Electrodes A, Electrode B, and Electrode C were used to investigate the peelability of two types of substrates (aluminum foil and glass), two types of binders (PVDF and PVDF-HFP) , And the adhesive force and detachability of Electrode D, Electrode E, and Electrode F electrodes were measured using an adhesive and peel testing system (INSTRON, 5960).

2, the peel-off strengths of the electrode (Electrode_AL) cast on the aluminum foil were 1319 mN and the same slurry content conditions (LCO electrode active material: PVDF binder: carbon black conductive agent = 90: 5: 5 wt.%), the peel strength of the electrode (Electrode A) cast on the glass substrate is 579 mN. That is, it can be seen that an electrode manufactured from a glass substrate among two types of substrates (aluminum foil and glass) has a low peel strength.

Further, the kind of the binder contained in the slurry is an important factor for determining the peel strength of the electrode. The peel strength of Electrode A (electrode using slurry containing 5 wt% of PVDF binder) was 579 mN and the peel strength of Electrode C (electrode using slurry containing 5 wt% of PVDF-HFP binder) was 343 mN. That is, the peeling strength of the electrode using the PVDF-HFP binder among the two types of binders (PVDF and PVDF-HFP) is low.

This is due to the high hydrophobicity of the HFP-groups. In addition, PVDF-HFP contains an amorphous region capable of trapping a large amount of organic solvent, so that the electrode made of PVDF-HFP shrinks more during the drying process, so that PVDF-HFP has the ability to absorb more solvent than PVDF , Which makes it easier to separate from the glass substrate.

The content of the binder is also an important factor for determining the peel strength of the electrode. Comparing Electrode D (electrode with slurry containing 6 wt% of PVDF-HFP binder) and Electrode E (electrode with slurry containing 13 wt% of PVDF-HFP binder), it was confirmed that the peel strength was decreased with increasing binder content And it was confirmed that the peeling strength of Electrode F (electrode using slurry containing 26 wt% of PVDF-HFP binder) reached 0 mN. That is, when the content of the binder contained in the slurry is 15 wt% or more, it can be confirmed that a stand-alone electrode can be easily obtained without exerting additional force or damaging the electrode when separating the electrode from the glass substrate.

The inventors of the present invention measured the tensile stress and the tensile strain in order to investigate the mechanical properties of the electrode and the film manufactured through the comparative example according to the present invention and summarized in the following Table 3 .

Tensile Stress
at Max. Load [kPa] Tensile Strain
at Max. Load [%] Max. Load [N] PVDF film 17,496 3.489 5.249 PVDF-HFP film 21,739 6.617 6.522 Electrode B 2,210 0.363 0.663 Electrode F 13,206 3.075 3.962

Tensile stress is the restoring force that maintains its original shape with respect to external force, and tensile strain is the degree to which a body or object is deformed when an external force is applied.

Referring to the above Table 3, the PVDF film and the PVDF-HFP film had tensile stresses of 17,496 and 21,739 kPa, respectively, and tensile strains of 3.49 and 6.62%, respectively. That is, the PVDF-HFP film is 124% more resistant to external force and 190% more elastic than PVDF film. Hence, PVDF-HFP binders are more flexible and flexible than PVDF binders, and thus are more suitable binders for the flexible electrodes of the present invention.

It can also be seen that the tensile stress and the tensile strain decrease with the addition of the electrode active material (LCO) and the conductive agent (carbon black). That is, the tensile stress and strain of the electrode prepared in the comparative example and the production example are smaller than the tensile stress and tensile strain of the polymer film (PVDF film, PVDF-HFP film), especially Electrode B (including PVDF binder) Of tensile stress and 10.5% of tensile strain. This means that the PVDF binder is mixed with the electrode active material and the conductive agent to lose most of the resistance to external force or deformation.

In contrast, Electrode F (including PVDF-HFP binder) has a tensile stress about 6.0 times higher than electrode B and a tensile strain 8.5 times greater. Thus, the PVDF-HFP binder means that when mixed with the electrode active material and the conductive agent, little resistance to external force or deformation is lost. That is, it has been proved that the PVDF-HFP binder is an excellent binder in the production of the independent flexible electrode.

3 is a graph of mechanical properties according to the additive content of the electrode prepared through the comparative example and the production example of the present invention.

More specifically, the electrode active material and the binder are fixed, and carbon black is partially replaced with CNT while maintaining the total mass of carbon (= additive + conductive agent), thereby manufacturing electrodes (Electrode F, Electrode G and Electrode H), tensile stress and tensile strain were measured.

3, an Electrode production example (including slurry containing 7wt% of carbon black and 4wt% of CNT), Electrode G (containing slurry containing 4wt% of carbon black and 11wt% of CNT) and Electrode H (slurry containing 11wt% of CNT) Showed 52.8%, 89.3% and 91.3% reduction in tensile stress and 24.4%, 39.3% and 41.8%, respectively, in tensile strain compared with Electrode F (containing 11wt% carbon black in the slurry). That is, as the content of CNT increases, the mechanical strength of the electrode becomes weaker.

This is because the CNT intervenes between the polymer chains of the binder and destroys the connected path of the chain. However, the addition of CNT is expected to decrease the resistance of the electrode and increase the wettability of the electrode with respect to the electrolyte. Thus, the present applicant measured the electrical conductivity according to the additive content of the electrode prepared in Comparative Examples and Preparation Examples, Table 4 summarizes the results.

Electrode_AL Electrode F Electrode Manufacturing Example 3.808 x 10 ² 1.316 x 10 2.165 x 10

Referring to Table 4, it can be seen that the electron conductivity increases with the addition of CNT (Electrode Manufacturing Example). However, the stand - alone electrode containing CNT showed lower conductivity than Electrode_AL including current collector.

Considering the mechanical strength and electrical characteristics according to the content of the additive as described above, it is preferable to form the slurry including the conductive agent: additive = 6 to 9: 2 to 5 (wt%).

4 is an SEM image of an electrode manufactured through the comparative example and the production example of the present invention.

(A): surface of Electrode B, (b): surface of Electrode F, (c): surface of Electrode production example, and (d) : Cross section of Electrode B, (e) cross section of Electrode F, and (f): cross section of Electrode production example.

Referring to FIGS. 4 (a) and 4 (d), it can be seen that there is an empty space (or pore) on the surface and the cross section of Electrode B. This leads to a reduction in the mechanical properties of the electrode, and as described above, the tensile stress and tensile strain of Electrode B can not be kept at 12.7% and 10.5% of the tensile stress and tensile strain of the PVDF film.

Referring to FIGS. 4 (b), 4 (c), 4 (e) and 4 (f), it can be seen that there is no empty space in Electrode F (b, e) Similar fabrication and cross-sectional images were obtained except that the fabrication examples were less dense than Electrode F.

This density difference is a change due to the addition of CNT, and CNT clusters have the effect of preventing the dense electrode active material and making the electrolyte easily accessible to the electrode structure, thereby improving the electrical conductivity of the cell.

Hereinafter, an electrode manufactured through the production example of the present invention (Electrode preparation example) and the comparative examples (Electrode F and Electrode_AL), which are preferable for measuring the electrochemical properties of the independent flexible electrode, (coin-type half cell).

Electrodes F, and Electrode_AL were used as positive electrodes and LiPF ₆ as an electrolyte was dissolved in a 1.0 M solution of ethylene carbonate (EC) / dimethyl carbonate (DEC) (1: 1, v / v) A coin-type half cell was fabricated using a porous polyethylene film as a counter electrode and a lithium metal foil as a counter electrode. Cells were designated Cell_F, and Cell_AL, respectively.

5 is a graph of charge and discharge profiles of half cells made with the electrodes of the comparative and production examples of the present invention.

More specifically, the charging and discharging profiles of the initial two cycles of Cell_Production, Cell_F and Cell_AL were measured at a current density of 0.1C-rate.

The loading level, the thickness, the electrode density, the area capacity, and the volumetric capacity of the Cell_Production and Cell_F and Cell_AL are shown in the following [ Table 5].

Cell_AL Cell_F Cell_ Manufacturing Example Loading level (mg / cm2) 7.1 8.1 6.0 Thickness (mm) 45 64 52 Electrode density (g / cm3) 2.6 2.0 1.8 Area capacity (mAh / cm2) 1.207 1.360 1.020 Volumetric capacity (mAh / cm3) 37.9 33.0 39.7

Referring to FIG. 5 and Table 5, it can be seen that the capacity of Cell_F is less than that of Cell_AL by about 15 mAh / g. This difference in capacity is related to the area where the electrode active material particles are exposed to the electrolyte.

Since the electrode active material particles in the independent flexible electrode of the present invention are mostly surrounded by a large amount of binder, the exposed region is limited. Electrodes with such a large number of binders can be difficult to secure an efficient path for the active material to contact the electrolyte. As described above, the CNT additive has the effect of preventing the dense electrode active material and allowing the electrolyte to easily access the electrode structure, thereby improving the electrical conductivity of the battery.

In fact, in the case of the Cell_ production example containing a CNT additive, it has specific capacities of about 150 mAh / g without a current collector. This is equivalent to the capacity of cells fabricated using conventional LiCoO ₂ . Therefore, it can be confirmed that the Cell_ production example can effectively keep the space for impregnating the electrolyte with the electrodes with the help of the CNT.

6 is a graph showing the cycle stability of a half cell made of the electrode of the comparative example and the production example of the present invention.

More specifically, cycle characteristics of Cell_F, Cell_F and Cell_AL were measured, the initial two cycles were performed at a current density of 0.1 C-rate, and the next 48 cycles were performed at 1.0 C-rate current density .

Referring to FIG. 6, all electrodes showed stable cycling up to 50 cycles, while Cell_AL, Cell_F, and Cell_G maintained 96.6%, 95.9%, and 97.0% of the initial capacities, respectively. That is, the independent flexible electrode according to the present invention does not deteriorate the cycling stability compared to conventional electrodes without a current collector.

FIG. 7 is a graph showing a discharge capacity ratio capability of a half cell made of the electrode of the comparative example and the production example of the present invention.

More specifically, the discharge capacity ratio of Cell_F and Cell_AL was measured and measured at various current density conditions of 0.1C-rate to 7.0C-rate.

Referring to FIG. 7, although the cell was constructed using the Electrode production example having low conductivity as compared with Electrode_AL, the production example of Cell containing CNT was equivalent or better at 1.0 and 3.0C current density than Cell_AL Discharge capacity ratio (rate capability). This demonstrates that the inclusion of the CNT additive in the electrode effectively keeps the space for impregnating the electrolyte with the electrode.

On the other hand, only the cell_F has a clearly lowered rate capability as compared with other electrodes, which means that the active material of the electrode including many binders can not secure an efficient path for contacting the electrolyte.

Figure 8 is a graph of cyclic voltammograms of half cells made with the electrodes of the preferred comparative and manufacturing examples of the present invention.

More specifically, cyclic voltammograms of Cell_F production, Cell_F and Cell_AL were measured.

Referring to FIG. 8, all three cells exhibited similar peak patterns. In the first cycle, a cathode peak at 4.2 V and an anode peak at 3.7 V were observed. After the second cycle, the cathode peak shifted to 4.0 V and the anode peak shifted to 3.8 V. In the case of the Cell_ production example, the peak position and intensity showed little change after the second cycle and the other electrodes (Cell_F and Cell_AL) showed continuous changes in peak position and intensity. That is, it means that the Cell_ production example has better cycle stability.

In addition, the Cell_AL and Cell_ production examples exhibited a potential difference of about 240 mV between the anode and the cathode, while a cell_F showed a potential difference of about 300 mV. This means that the Cell_ production example reacts faster in the electrochemical reaction than Cell_F. This is because CNT promotes electron transfer at the electrode.

9 is an image showing the endurance against folding of the electrode manufactured according to the comparative example and the production example of the present invention.

More specifically, the Electrode Manufacturing Example, Electrode F, and Electrode_AL are repeated after 0, 1, and 5 times. (A) Electrode_AL 0, (b) Electrode_AL 1, (c) Electrode_AL 5, (d) Electrode F 0, (e) Electrode F 1, (f) Electrode F 5, Production Example No. 0, (h) Electrode Production Example No. 1 and (i) Electrode Production Example No. 5 Folded image.

9 (a), 9 (b) and 9 (c), it can be confirmed that the electrodes are clearly damaged when they are repeatedly folded one or more times in Electrode_AL, 9 (g), (h) and (i), it can be seen that a weakly folded line appears on the electrode when the electrode is repeatedly folded five or more times in Electrode F, When repeatedly folded more than 5 times, it can be confirmed that no wrinkles or damage are seen on the electrode.

From these observations, the independent flexible electrode of the present invention including CNT can prove excellent durability against bending or folding.

Figure 10 is an image of a flexible cell fabricated in accordance with another preferred embodiment of the present invention.

The graphite electrode active material: PVDF-HFP binder: carbon black conductive agent: CNT additive = 63: 26: 7: 4 wt% was used instead of LCO as a counter electrode, The electrode prepared in the same manner as in the production example was used.

Referring to FIG. 10, it can be confirmed that the flexible cell can supply power to the light emitting diode (LED) device even when bent.

As described above, the present applicant provides a self-contained flexible electrode and a method of manufacturing the same. This was accomplished by simply adjusting the formulation (amount of binder) and did not use any additional components to improve complex nanostructure or flexibility.

The optimum content of the materials contained in the slurry was determined through various comparative examples and the ratio of the electrode active material: binder: conductive agent: additive = 46 to 76: 15 to 45: 6 to 9: 2 to 5 (wt% When the slurry is constituted, the independent flexible electrode of the present invention has excellent electrical conductivity and mechanical properties without a current collector.

In addition, the peel strength reached 0 mN, and it became an electrode that could be cast and detached on a glass substrate without the need to apply additional force, and a flexible electrode which was folded more than five times and completely untouched could be obtained.

When these independent flexible electrodes were used as the anode, they had the same or superior performance as the electrochemical performance such as discharge capacity, speed performance and cycling stability as compared with general cell (Cell_AL).

In addition, when the independent flexible electrode according to the present invention is fabricated from a positive electrode and a negative electrode to form a cell, it can be confirmed that power can be supplied to a device connected to the cell even when the flexible electrode is bent.

Accordingly, there is a need for a novel flexible electrode that solves the problems of high resistance, insufficient loading level of the positive electrode active material, and the conventional electrode for a flexible lithium ion battery having low rigidity and mechanical strength in repeated bending or folding process. It can be said that it is a manufacturing method thereof.

100: substrate
200: dried slurry

Claims (8)

Preparing a slurry comprising an electrode active material, a binder, a conductive agent, and an additive;
Casting and drying the slurry on a glass substrate; And
And removing the dried slurry on the glass substrate,
And the current collector is not required. The method according to claim 1,
Wherein the electrode active material is at least one selected from the group consisting of lithium cobalt oxide (LCO), nickel cobalt manganese oxide (NCM), and nickel cobalt aluminum oxide (NCA) as cathode materials. The method according to claim 1,
Wherein the electrode active material is at least one selected from the group consisting of carbon-based materials including graphitic carbon and graphitizable carbon, which are cathode materials, and silicon-based materials. The method according to claim 1,
Wherein the binder is PVDF-HFP. The method according to claim 1,
Wherein the conductive agent is carbon black. The method according to claim 1,
Wherein the additive is at least one selected from the group consisting of carbon nanotubes and graphenes. delete The method according to claim 1,
The content ratio of the electrode active material, the conductive agent, the binder and the additive is in the range of 46 to 76: 15 to 45: 6 to 9: 2 to 5 (wt%) based on the total amount of the slurry, Wherein the flexible electrode is formed of a metal.

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